corrosion in biodiesel production process using

CORROSION IN BIODIESEL PRODUCTION PROCESS USING

HIGH FREE FATTY ACID FEEDSTOCKS

A Thesis

Submitted to the Faculty of Graduate Studies and Research

In Partial Fulfillment of the Requirements

for the Degree of

Master of Applied Science

in Industrial Systems Engineering

University of Regina

by

Rangakrishnan Krishnaiyer Sankaranarayanan

Regina, Saskatchewan

October 2011

Copyright 2011: R.Krishnaiyer

CORROSION IN BIODIESEL PRODUCTION PROCESS USING

HIGH FREE FATTY ACID FEEDSTOCKS

A Thesis

Submitted to the Faculty of Graduate Studies and Research

In Partial Fulfillment of the Requirements

for the Degree of

Master of Applied Science

in Industrial Systems Engineering

University of Regina

by

Rangakrishnan Krishnaiyer Sankaranarayanan

Regina, Saskatchewan

October 2011

Copyright 2011: R.Krishnaiyer

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Published Heritage Branch

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Direction du Patrimoine de I'edition

395 Wellington Street Ottawa ON K1A0N4 Canada

395, rue Wellington Ottawa ON K1A 0N4 Canada

Your file Votre reference

ISBN: 978-0-494-88517-8

Our file Notre reference

ISBN: 978-0-494-88517-8

NOTICE:

The author has granted a nonexclusive license allowing Library and Archives Canada to reproduce, publish, archive, preserve, conserve, communicate to the public by telecommunication or on the Internet, loan, distrbute and sell theses worldwide, for commercial or noncommercial purposes, in microform, paper, electronic and/or any other formats.

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The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission.

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Canada

LIST OF TABLES

Table 1.1 Canadian biodiesel production plant details 4

Table 1.2 Range of free fatty acids in various feedstock oils and fats 7

Table 2.1 Range of process parameters 21

Table 2.2 Classification of Organic solvents 24

Table 2.3 Previous works and their findings on corrosion in methanol and

sulphuric acid and fatty acid components 28

Table 3.1 Composition of specimens 31

Table 3.2 Summary of chemical reagents used in experiments 35

Table 4.1 Process compositions and operating conditions of tested locations 51

Table 4.2 Summary of electrochemical corrosion data of CS 1018 (unless 53

specified)

viii

LIST OF TABLES

Table 1.1 Canadian biodiesel production plant details 4

Table 1.2 Range of free fatty acids in various feedstock oils and fats 7

Table 2.1 Range of process parameters 21

Table 2.2 Classification of Organic solvents 24

Table 2.3 Previous works and their findings on corrosion in methanol and

sulphuric acid and fatty acid components 28

Table 3.1 Composition of specimens 31

Table 3.2 Summary of chemical reagents used in experiments 35

Table 4.1 Process compositions and operating conditions of tested locations 51

Table 4.2 Summary of electrochemical corrosion data of CS 1018 (unless 53

specified)

viii

forward polarization curve exhibits an active state and overlaps with the reverse curve,

suggesting pitting tendency. However, due to higher temperature (compared to Location

10), the polarization curve shifts to a greater corrosion current, resulting in a higher

corrosion rate in the range of 900 mpy. Though Location 11 has a residual amount of

methanol and water, due to the presence of considerable amount of sulphuric acid, the pH

of this environment is in the acidic range. Hence, SS304 was evaluated as an alternative

material of construction to CS1018 as it could resist the acidic environment due to the

presence of chromium content (Banas and Banas, 2009). The results in Figures 4.19-4.20

show SS304 passivates, shifts Eco, towards a more noble value (compared to CS 1018),

reduces the corrosion rate from 911 to 10.5 mpy, and yields a negative reverse scan

suggesting the absence of pitting corrosion. By this result, it could be ascertained that

SS316 can also be used for this location to prevent the corrosion. But as it is expensive

than SS304, it was not tested.

4.2 Weight loss test

The previous section contains the results obtained from a series of

electrochemical corrosion tests done under various conditions representing the various

process locations within the acid-catalyzed esterification process. According to those

results, it can clearly be concluded that the corrosion rate of CS1018 in the acid-catalyzed

esterification reactor is insignificant. However, these short-term test results might or

might not reflect the actual corrosion process during continuous plant operation. It was,

therefore, decided to conduct a long-term corrosion test for esterification reaction

conditions using a weight loss static immersion technique.

84

forward polarization curve exhibits an active state and overlaps with the reverse curve,

suggesting pitting tendency. However, due to higher temperature (compared to Location

10), the polarization curve shifts to a greater corrosion current, resulting in a higher

corrosion rate in the range of 900 mpy. Though Location 11 has a residual amount of

methanol and water, due to the presence of considerable amount of sulphuric acid, the pH

of this environment is in the acidic range. Hence, SS304 was evaluated as an alternative

material of construction to CS1018 as it could resist the acidic environment due to the

presence of chromium content (Banas and Banas, 2009). The results in Figures 4.19-4.20

show SS304 passivates, shifts Ecorr towards a more noble value (compared to CS1018),

reduces the corrosion rate from 911 to 10.5 mpy, and yields a negative reverse scan

suggesting the absence of pitting corrosion. By this result, it could be ascertained that

SS316 can also be used for this location to prevent the corrosion. But as it is expensive

than SS304, it was not tested.

4.2 Weight loss test

The previous section contains the results obtained from a series of

electrochemical corrosion tests done under various conditions representing the various

process locations within the acid-catalyzed esterification process. According to those

results, it can clearly be concluded that the corrosion rate of CS1018 in the acid-catalyzed

esterification reactor is insignificant. However, these short-term test results might or

might not reflect the actual corrosion process during continuous plant operation. It was,

therefore, decided to conduct a long-term corrosion test for esterification reaction

conditions using a weight loss static immersion technique.

84

In this test, CS1018 specimens were immersed in a mixture of methanol, canola

oil, and sulphuric acid at 65°C and 1 atm. The corrosion test was carried out for 7 weeks

duration. Pre-weighed specimens were removed from the solution mixture and weighed

for weight loss due to uniform corrosion for the duration of 12 hours, 1 day, 3 days, and

each week starting from 1 to 7. Figure 4.21 shows the corrosion rate by weight loss test

done under various conditions. Though the initial corrosion rate was higher, the corrosion

rate obtained after 1 week was low, acceptable, and under the corrosion limit (10 — 20

mpy). Only uniform corrosion and no pitting or any other types of localized corrosion

were detected. Corrosion products were oily, loose, and black as shown in Figure 4.22.

The negligible corrosion rate found in the reactor can be explained by considering the

reactions in biodiesel production. During this long-term weight loss test, two main reactions

simultaneously took place, namely, acid esterification and acid transesterification. Acid

esterification converts oleic acid to biodiesel in a short period of time (within 12 hours),

whereas acid transesterification converts oil to biodiesel at a much slower rate than acid

esterification (in days).

Acid esterification:

C 57 H 98 0 6 + C 18 H 34 0 2 + CH 30H H2SO4 r C 19 H 36 O 2 Ll I")

Canola oil Oleic acid (FFA) Methanol Methyl Oleate (Biodiesel) (4.16)

Acid transesterification:

C 57 H 98 0 6 + Cuih r 34 0 2 + CH 30H "°°-+ C,,H 36 0 2 + C,,H 34 0 2 + Co ll 3,0 2 +C31 5 (OH )3 (4.17)

Canola oil Oleic acid Methanol Methyl Oleate Methyl Methyl Glycerol linoleate linolenate

Biodiesel

85

In this test, CS1018 specimens were immersed in a mixture of methanol, canola

oil, and sulphuric acid at 65°C and 1 atm. The corrosion test was carried out for 7 weeks

duration. Pre-weighed specimens were removed from the solution mixture and weighed

for weight loss due to uniform corrosion for the duration of 12 hours, 1 day, 3 days, and

each week starting from 1 to 7. Figure 4.21 shows the corrosion rate by weight loss test

done under various conditions. Though the initial corrosion rate was higher, the corrosion

rate obtained after 1 week was low, acceptable, and under the corrosion limit (10 ~ 20

mpy). Only uniform corrosion and no pitting or any other types of localized corrosion

were detected. Corrosion products were oily, loose, and black as shown in Figure 4.22.

The negligible corrosion rate found in the reactor can be explained by considering the

reactions in biodiesel production. During this long-term weight loss test, two main reactions

simultaneously took place, namely, acid esterification and acid transesterification. Acid

esterification converts oleic acid to biodiesel in a short period of time (within 12 hours),

whereas acid transesterification converts oil to biodiesel at a much slower rate than acid

esterification (in days).

Acid esterification:

C 5 1 H 9 S 0 6 + C l t H M 0 2 + C H z O H C { 9 H J 6 0 2 + H 2 0

Canola oil Oleic acid (FFA) Methanol Methyl Oleate (Biodiesel) < r\

Acid transesterification:

C „ H n 0 6 + C n H } i 0 2 + C H y O H — C19//3602 + C,9//3402 + C19//3202 + C } H s ( O H )3 (4.17)

Canola oil Oleic acid Methanol Methyl Oleate Methyl Methyl Glycerol linoleate linolenate

Biodiesel

85

350 -

Cor

rosi

on R

ate

(mpy

)

%Sulphuric acid (MeOH:Oil)

-*-1%(25:1)

-0-1% (18:1)

-0-1% (10:1)

-10-3% (18:1)

12H 1 Day 3 Days 1 Week 2 Weeks 3 Weeks 4 Weeks 5 Weeks 6 Weeks 7 Weeks

Duration

Figure 4.21: Corrosion rate of CS1018 in an esterification reactor measured by weight

loss method

86

400

%Sulphuric acid (MeOH:Oil) 350

-*-1% (25:1 300

1% (18:1) a. 250

1% (10:1)

<*• 200 3% (18:1)

150

100

50

0 1 Day 3 Days 1 Week 2 Weeks 3 Weeks 4 Weeks 5 Weeks 6 Weeks 7 Weeks 12H

Duration

Figure 4.21: Corrosion rate of CS 1018 in an esterification reactor measured by weight

loss method

86

Figure 4.22: Weight loss coupons with oily layer with respect to methanol:oil molar ratio

(Original in colour)

87

MeOH:Oil 10:1 18:1 25:1

Figure 4.22: Weight loss coupons with oily layer with respect to methanol:oil molar ratio


87

Figure 4.23: Biodiesel solution colour change — Fresh solution (Pale Yellow), After 1

week (Orange), After 2 weeks (Permanent dark brown) (Original in colour)

88

Fresh Solution After 1 Week After 2 Weeks

Figure 4.23: Biodiesel solution colour change - Fresh solution (Pale Yellow), After 1

week (Orange), After 2 weeks (Permanent dark brown; (Original in colour)

88

From the above reactions, it can clearly be confirmed that the esterification reactor

always contains fatty acid components, which have low conductivity, long carbon chain

length, high steric hindrance, and high viscosity. Such properties of the fatty acid bring

about insignificant corrosion on carbon steel as discussed in section 4.1.2.6.

It should be noted that over the period of 7 weeks, the compositions of the

synthesized solution appeared to be altered. This was evidenced by a colour change of the

solution from pale yellowish to orange after a week and then to dark brown after 2 weeks

as shown in Figure 4.23. Such colour change was speculated to be a result of the reaction

of sulphuric acid with the double bonds of unsaturated fatty acids as suggested by Paolo

Bondioli (2004).

89

From the above reactions, it can clearly be confirmed that the esterification reactor

always contains fatty acid components, which have low conductivity, long carbon chain

length, high steric hindrance, and high viscosity. Such properties of the fatty acid bring

about insignificant corrosion on carbon steel as discussed in section 4.1.2.6.

It should be noted that over the period of 7 weeks, the compositions of the

synthesized solution appeared to be altered. This was evidenced by a colour change of the

solution from pale yellowish to orange after a week and then to dark brown after 2 weeks

as shown in Figure 4.23. Such colour change was speculated to be a result of the reaction

of sulphuric acid with the double bonds of unsaturated fatty acids as suggested by Paolo

Bondioli (2004).

89

5. CONCLUSIONS AND FUTURE WORK

5.1 Conclusions

This work successfully investigated corrosion of carbon steel in the acid-catalyzed

esterification process for biodiesel production from low quality feedstock and provided a

recommendation for suitable corrosion control methods. It was found that five of the

eleven process locations are not susceptible to corrosion and carbon steel is a suitable

material for construction. The non-corrosion susceptible locations are the methanol

recovery flow line, storage tank of oil feedstock containing free fatty acid (FFA),

esterification reactor, glycerol feed to the stripping column, and end-product recovery

flow line. The rest of six process locations are susceptible to corrosion and require

effective strategies for corrosion control. The susceptible locations are the methanol

storage tank, sulphuric storage tank, methanol and sulphuric acid storage tank, fresh &

recovery methanol and acid mixing tank, inlet flow line to the vacuum distillation

column, and vacuum distillation. Of these locations, the vacuum distillation column is the

most susceptible, followed by the inlet flow line to the vacuum distillation column. The

use of stainless steel is recommended for these corrosion locations. The following are

important findings that relate to the corrosion mechanism and are recommendations for

suitable corrosion control methods.

✓ The methanol storage made of CS1018 is susceptible to corrosion with no pitting

corrosion. The corrosiveness is due to the instability of the oxide passive layer in the

presence of dissolved oxygen (02). Nitrogen (N2) blanketing to remove dissolved 02

90

5. CONCLUSIONS AND FUTURE WORK

5.1 Conclusions

This work successfully investigated corrosion of carbon steel in the acid-catalyzed

esterification process for biodiesel production from low quality feedstock and provided a

recommendation for suitable corrosion control methods. It was found that five of the

eleven process locations are not susceptible to corrosion and carbon steel is a suitable

material for construction. The non-corrosion susceptible locations are the methanol

recovery flow line, storage tank of oil feedstock containing free fatty acid (FFA),

esterification reactor, glycerol feed to the stripping column, and end-product recovery

flow line. The rest of six process locations are susceptible to corrosion and require

effective strategies for corrosion control. The susceptible locations are the methanol

storage tank, sulphuric storage tank, methanol and sulphuric acid storage tank, fresh &

recovery methanol and acid mixing tank, inlet flow line to the vacuum distillation

column, and vacuum distillation. Of these locations, the vacuum distillation column is the

most susceptible, followed by the inlet flow line to the vacuum distillation column. The

use of stainless steel is recommended for these corrosion locations. The following are

important findings that relate to the corrosion mechanism and are recommendations for

suitable corrosion control methods.

S The methanol storage made of CS1018 is susceptible to corrosion with no pitting

corrosion. The corrosiveness is due to the instability of the oxide passive layer in the

presence of dissolved oxygen (O2). Nitrogen (N2) blanketing to remove dissolved O2

90

from the methanol is an effective corrosion control method as it suppresses both the

formation of methoxy ions and the subsequent formation of unstable ferrous oxide

reactions. Use of SS304 is not a wise choice for corrosion control despite the fact that

it can reduce the corrosion rate to an acceptable level. This is because it induces

pitting corrosion. High-density polyethylene (HDPE)/Vulcanized natural rubber

materials are also preferred for methanol storage.

✓ The sulphuric acid storage tank made of CS1018 is susceptible to corrosion with no

pitting corrosion. The corrosion can be controlled with a proper anodic protection

system or use of fibreglass reinforced plastic (FRP) material.

✓ For the methanol and sulphuric acid mixing tank, iron cannot form a passive oxide

film in a methanolic acid environment. Hence, CS1018 is susceptible to corrosion and

not suitable for this purpose. As a normal industrial practice, high-density

polyethylene (HDPE)/fibreglass reinforced plastic (FRP) is a better choice.

✓ For the methanol recovery flow line where methanol contains a small amount of

water, CS1018 is a suitable material since a stable passive film is developed to hinder

the corrosion.

✓ For the process locations that contain FFAs (i.e., the storage tanks of oil feedstock

containing FFA, the esterification reactor, glycerol feed to stripping column, and end

product recovery line), CS1018 is a suitable material. FFAs act as corrosion inhibitors

that function by chemisorption.

✓ For the glycerol feed to the stripping column, CS1018 is susceptible to pitting

corrosion even though its corrosion rate is very low. The presence of fatty acid

components eliminates this pitting problem.

91

from the methanol is an effective corrosion control method as it suppresses both the

formation of methoxy ions and the subsequent formation of unstable ferrous oxide

reactions. Use of SS304 is not a wise choice for corrosion control despite the fact that

it can reduce the corrosion rate to an acceptable level. This is because it induces

pitting corrosion. High-density polyethylene (HDPE)/Vulcanized natural rubber

materials are also preferred for methanol storage.

^ The sulphuric acid storage tank made of CS1018 is susceptible to corrosion with no

pitting corrosion. The corrosion can be controlled with a proper anodic protection

system or use of fibreglass reinforced plastic (FRP) material.

S For the methanol and sulphuric acid mixing tank, iron cannot form a passive oxide

film in a methanolic acid environment. Hence, CS1018 is susceptible to corrosion and

not suitable for this purpose. As a normal industrial practice, high-density

polyethylene (HDPE)/fibreglass reinforced plastic (FRP) is a better choice.

S For the methanol recovery flow line where methanol contains a small amount of

water, CS1018 is a suitable material since a stable passive film is developed to hinder

the corrosion.

•S For the process locations that contain FFAs (i.e., the storage tanks of oil feedstock

containing FFA, the esterification reactor, glycerol feed to stripping column, and end

product recovery line), CS 1018 is a suitable material. FFAs act as corrosion inhibitors

that function by chemisorption.

S For the glycerol feed to the stripping column, CS1018 is susceptible to pitting

corrosion even though its corrosion rate is very low. The presence of fatty acid

components eliminates this pitting problem.

91

✓ The phase separation stage is the most corrosive area in the acid esterification process

due to the elevated temperature and the presence of methanol, sulphuric acid,

glycerol, and water. SS316 is suitable for the inlet flow rate to the vacuum distillation

column (not SS304) while SS304 is suitable for the vacuum distillation column.

5.2 Recommendations for future work

This work focuses on the acid esterification process only. This can further be

extended to the acid transesterification biodiesel production process. As far as the

transesterification reactor is concerned, the presence of fatty acid components, such as

canola oil, oleic acid, and biodiesel ester products, impede the corrosion of material.

However, this process consumes a large quantity of methanol to oil ratio and sulphuric

acid as well. This will lead to the severe corrosion of process equipment, especially in

post processing stages, which operate at high temperatures and vacuum conditions.

92

S The phase separation stage is the most corrosive area in the acid esterification process

due to the elevated temperature and the presence of methanol, sulphuric acid,

glycerol, and water. SS316 is suitable for the inlet flow rate to the vacuum distillation

column (not SS304) while SS304 is suitable for the vacuum distillation column.

5.2 Recommendations for future work

This work focuses on the acid esterification process only. This can further be

extended to the acid transesterification biodiesel production process. As far as the

transesterification reactor is concerned, the presence of fatty acid components, such as

canola oil, oleic acid, and biodiesel ester products, impede the corrosion of material.

However, this process consumes a large quantity of methanol to oil ratio and sulphuric

acid as well. This will lead to the severe corrosion of process equipment, especially in

post processing stages, which operate at high temperatures and vacuum conditions.

92

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compression ignition engines. J. Eng. Gas Turbines Power. 2001, 123, 440-447.

Alex H. West.; Dusko Posarac.; Naoko Ellis. Assessment of four biodiesel production

processes using HYSYS.Plant. Bioresour. Technol. 2008, 99, 6587-6601.

Al-Widyan, M.I.; G.Tashtoush.; M.Abu-Qudais. Utilization of ethyl ester of waste

vegetable oils as fuel in diesel engines. Fuel Process. Technol. 2002, 76, 91-103.

Anastopoulos, G.E.; Lois,A.; Serdari,F.; Zanikos,S.; Stournas.; S.Kalligerous.

Lubricating properties of Low-sulphur diesel fuels in the presence of specific types of

fatty acid derivatives. Energy Fuels. 2001, 15, 106-112.

Antolin, G.; Tinaut, FV.; Briceno, Y.; Castano, V.; Perez, C.; Ramirez, AI. Optimization

of biodiesel production by sunflower oil transesterification. Bioresour. Technol. 2002,

83, 111 — 114.

Azam, M.M.; Amtul, Waris.; N.M.Nahar. Prospects and potential of fatty acid methyl

esters of some non-traditional seed oils for use as biodiesl in India. Biomass

Bioenergy. 2005, 29, 293-302.

Banas, J. Passivity of Iron and Nickel in a CH3OH — H2O — H2SO4 System. Electrochim.

Acta. 1987, 32, 871-875.

Banas,K.; Banas,J. Corrosion Behavior of Low Chromium Fe-Cr alloys in Anhydrous

Methanol Solutions of Sulfuric acid. Arch. Metall. Mater. 2009, 54, 267-279.

Banas,J.; Lelek-Borkowska, U.; Starowicz,M. Electrochemical behaviour of p-Si in

methanol solutions of chlorides. J. Solid State Electrochem. 2004, 8, 422-429.

93

REFERENCES

Agarwal, A.K.; Das, L.M. Biodiesel development and characterization for use as a fuel in

compression ignition engines. J. Eng. Gas Turbines Power. 2001, 123, 440-447.

Alex H. West.; Dusko Posarac.; Naoko Ellis. Assessment of four biodiesel production

processes using HYSYS.Plant. Bioresour. Technol. 2008, 99, 6587—6601.

Al-Widyan, M.I.; G.Tashtoush.; M.Abu-Qudais. Utilization of ethyl ester of waste

vegetable oils as fuel in diesel engines. Fuel Process. Technol. 2002, 76, 91-103.

Anastopoulos, G.E.; Lois,A.; Serdari,F.; Zanikos,S.; Stournas.; S.Kalligerous.

Lubricating properties of Low-sulphur diesel fuels in the presence of specific types of

fatty acid derivatives. Energy Fuels. 2001, 15, 106-112.

Antolin, G.; Tinaut, FV.; Briceno, Y.; Castano, V.; Perez, C.; Ramirez, AI. Optimization

of biodiesel production by sunflower oil transesterification. Bioresour. Technol. 2002,

83, 111-114.

Azam, M.M.; Amtul, Waris.; N.M.Nahar. Prospects and potential of fatty acid methyl

esters of some non-traditional seed oils for use as biodiesl in India. Biomass

Bioenergy. 2005, 29, 293-302.

Banas, J. Passivity of Iron and Nickel in a CH3OH - H2O - H2SO4 System. Electrochim.

Acta. 1987, 32, 871-875.

Banas,K.; Banas,J. Corrosion Behavior of Low Chromium Fe-Cr alloys in Anhydrous

Methanol Solutions of Sulfuric acid. Arch. Metall. Mater. 2009, 54, 267-279.

Banas,J.; Lelek-Borkowska, U.; Starowicz,M. Electrochemical behaviour of p-Si in

methanol solutions of chlorides. J. Solid State Electrochem. 2004, 8, 422-429.

93

LIST OF FIGURES

Figure 2.1

Figure 2.2

Figure 3.1

Figure 3.2

Figure 3.3

Figure 3.4

Figure 3.5

Figure 3.6

Figure 3.7

Figure 3.8

Figure 3.9

Figure 3.10

Figure 4.1

Figure 4.2

Process flow diagram of alkali-based transesterification process

for biodiesel production

Process flow diagram of acid-based esterification pre-treatment

process for biodiesel production using high free-fatty acid

feedstocks

Shape and dimension of the specimen; (a) Electrochemical

specimen, (b) Weight loss specimen

Schematic diagram of acid esterification reactor setup

Schematic diagram of the experimental setup for electrochemical

corrosion test

A photograph of the experimental setup for electrochemical

corrosion tests

A typical Tafel plot

A typical potentiodynamic polarization curve

A typical cyclic polarization curve

A schematic diagram of the weight loss experimental setup

A photograph of the weight loss experimental setup

Mass loss of corroded specimens resulting from repetitive

cleaning cycles

Process flow diagram of an acid-catalyzed esterification process

Reproducibility of the obtained electrochemical data

15

17

32

33

36

37

39

41

42

44

45

47

50

54

ix

LIST OF FIGURES

Figure 2.1 Process flow diagram of alkali-based transesterification process

for biodiesel production 15

Figure 2.2 Process flow diagram of acid-based esterification pre-treatment

process for biodiesel production using high free-fatty acid

feedstocks 17

Figure 3.1 Shape and dimension of the specimen; (a) Electrochemical

specimen, (b) Weight loss specimen 32

Figure 3.2 Schematic diagram of acid esterification reactor setup 33

Figure 3.3 Schematic diagram of the experimental setup for electrochemical

corrosion test 36

Figure 3.4 A photograph of the experimental setup for electrochemical

corrosion tests 37

Figure 3.5 A typical Tafel plot 39

Figure 3.6 A typical potentiodynamic polarization curve 41

Figure 3.7 A typical cyclic polarization curve 42

Figure 3.8 A schematic diagram of the weight loss experimental setup 44

Figure 3.9 A photograph of the weight loss experimental setup 45

Figure 3.10 Mass loss of corroded specimens resulting from repetitive

cleaning cycles 47

Figure 4.1 Process flow diagram of an acid-catalyzed esterification process 50

Figure 4.2 Reproducibility of the obtained electrochemical data 54

ix

Banag,J.; Stypula,B K.; Bana,K.; wiatowska-Mrowiecka,J.; Starowicz,M.; Lelek-

Borkowska,U.; Corrosion and passivity of metals in methanol solutions of

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Bellucci,F.; Faita,G.; Farina,C.A.; Olivani,F. The Passivity of Ferritic (Fe-18% Cr)

Stainless Steel in Methanolic Solutions. J. Appl. Electrochem. 1981, 11, 781 — 785.

Bo, Xu.; Xiao Guomin.; Cui Kingfeng.; Wei Ruiping.; Gao Lijing. Transesterification of

Palm Oil Using KF/A1203 as a Heterogeneous Base Catalyst. Energy Fuels. 2007, 21,

3109-3112.

Boocock, DGB.; Konar, SK.; Mao, V.; Sidi, H. Fast one-phase oil-rich process for the

preparation of vegetable oil methyl esters. Biomass Bioenergy. 1996, 11, 43 — 50.

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APPENDIX A

EXPERIMENTAL DATA OF WEIGHT LOSS TEST

101

APPENDIX A

EXPERIMENTAL DATA OF WEIGHT LOSS TEST

101

10:1 MeOH: Oil - 1% Acid

12H 1 Day 3 Days 1 Week 2

Weeks- 1

2 Weeks-

2

3 Weeks

4 Weeks

5 Weeks

6 Weeks

7 Weeks

Density (glcc) 7.86

Duration in hours

12 24 72 168 168 336 504 672 840 1008 1176 Surface area(cm2) 14.93

Specimen No 91 B2 B3 B4 B5 Al A2 A3 A4 A5 A6

Initial Wt(g) 11.5484 10.8108 10.8169 10.7658 10.7577 10.7878 10.7895 10.7840 10.7904 10.7960 10.7796

Specimen No B1 82 B3 B4 B5 Al A2 A3 A4 A5 A6


Weeks- 1

2 Weeks-

2

3 Weeks

4 Weeks 5

Weeks 6

Weeks 7

Weeks

Duration in hours

12 24 72 168 336 336 504 672 840 1008 1176

Chemical Cleaning Cyde

Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss WI Loss Wt Loss Wt Loss Wt Loss

Before Cleaning

10.6042 0.2066 10.4282 0.3887 10.3593 0.4065 10.3578 0.3999 10.4124 0.3754 10.4133 0.3762 10.2177 0.5663 10.1278 0.6626 10.2298 0.5662 10.2807 0.4989

1 11.4638 0.0846 10.6036 0.2072 10.4277 0.3892 10.3582 0.4076 10.3572 0.4005 10.4116 0.3762 10.4123 0.3772 10.2170 0.5670 10.1274 0.6630 10.2292 0.5668 10.2803 0.4993

2 11.4636 0,0848 10.6034 0.2074 10.4276 0.3893 10.3580 0.4078 10.3571 0.4006 10.4115 0.3763 10.4121 0.3774 10.2168 0.5672 10.1273 0.6631 10.2291 0.5669 10.2798 0.4998

3 11.4634 0.0850 10.6033 0.2075 10.4275 0.3894 10.3579 0.4079 10.3571 0.4006 10.4115 0.3763 10.4119 0.3776 10.2168 0.5672 10.1271 0.6633 10.2291 0.5669 10.2798 0.4998

4 11.4634 0.0850 10.6031 0.2077 10.4274 0.3895 10.3579 0.4079 10.3571 0.4006 10.4115 0.3763 10.4118 0.3777 10.2168 0.5672 10.1271 0.6633 10.2291 0.5669 10.2798 0,4998

5 11.4634 0.0850 10.6029 0.2079 10.4274 0.3895 10.3579 0.4079 10.3571 0.4006 10.4115 0.3763 10.4118 0.3777 10.2168 0.5672 10.1269 0.6635 10.2291 0.5669 10.2798 0.4998

6 11.4634 0.0850 10.6026 0.2082 10.4274 0.3895 10.3579 0.4079 10.4118 0.3777 10.1269 0.6635 10.2291 0.5669

7 10.6024 0.2084 10.4274 0.3895 10.4118 0.3777 10.1269 0.6635

8 10.6021 0.2087 10.1269 0.6635

9 10.6021 0.2087

10 10.6021 0.2087

11 10.6021 0.2087

0.0850 0.2087 0.3895 0.4079 0.4006 0.3763 0.3777 0.5672 0.6635 0.5669 0.4998

(8.76 x 104 x weight loss in g)/ (Area in cm2x Time of exposure in h x Density in g/cc)

Corrosion Rate 12H 1D 3D 1W 2W-1 2W-2 3W 4W 5W 6W 7W

mmpy 5.2868 6.4903 4.0376 1.8122 0.8899 0.8359 0.5593 0.6300 0.5895 0.4198 0.3172

mpy 208.2119 255.6108 159.0168 71.3695 35.0461 32.9202 22.0285 24.8105 23.2183 16.5316 12.4927

102

10:1 MeOH: Oil -1% Acid


Weeks-1

2 Weeks-

2

3 Weeks

4 Weeks

5 Weeks

6 Weeks

7 Weeks

Density (g/cc) 7.86

Duration in hours

12 24 72 168 168 336 504 672 840 1008 1176 Surface area(cm2) 14.93

Specimen No B1 B2 B3 B4 B5 A1 A2 A3 A4 A5 A6

Initial Wt(g) 11.5484 10.8108 10.8169 10.7658 10.7577 10.7878 10.7895 10.7840 10.7904 10.7960 10.7796

Specimen No B1 B2 B3 B4 B5 A1 A2 A3 A4 A5 A6


Weeks-2

Weeks-2

3 Weeks

4 Weeks 5

Weeks 6

Weeks 7

Weeks

Duration in hours

12 24 72 168 336 336 504 672 840 1008 1176

Chemical Cleaning Cycle

Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss

Before Cleaning

10.6042 0.2066 10.4282 0.3887 10.3593 0.4065 10.3578 0.3999 10.4124 0.3754 10.4133 0.3762 10.2177 0.5663 10.1278 0.6626 10.2298 0.5662 10.2807 0.4989

1 11.4638 0.0846 10.6036 0.2072 10.4277 0.3892 10.3582 0.4076 10.3572 0.4005 10.4116 0.3762 10.4123 0.3772 10.2170 0.5670 10.1274 0.6630 10.2292 0.5668 10.2803 0.4993

2 11.4636 0.0848 10.6034 0.2074 10.4276 0.3893 10.3580 0.4078 10.3571 0.4006 10.4115 0.3763 10.4121 0.3774 10.2168 0.5672 10.1273 0.6631 10.2291 0.5669 10.2798 0.4998

3 11.4634 0.0850 10.6033 0.2075 10.4275 0.3894 10.3579 0.4079 10.3571 0.4006 10.4115 0.3763 10.4119 0.3776 10.2168 0.5672 10.1271 0.6633 10.2291 0.5669 10.2798 0.4998

4 11.4634 0.0850 10.6031 0.2077 10.4274 0.3895 10.3579 0.4079 10.3571 0.4006 10.4115 0.3763 10.4118 0.3777 10.2168 0.5672 10.1271 0.6633 10.2291 0.5669 10.2798 0.4998

5 11.4634 0.0850 10.6029 0.2079 10.4274 0.3895 10.3579 0.4079 10.3571 0.4006 10.4115 0.3763 10.4118 0.3777 10.2168 0.5672 10.1269 0.6635 10.2291 0.5669 10.2798 0.4998

6 11.4634 0.0850 10.6026 0.2082 10.4274 0.3895 10.3579 0.4079 10.4118 0.3777 10.1269 0.6635 10.2291 0.5669

7 10.6024 0.2084 10.4274 0.3895 10.4118 0.3777 10.1269 0.6635

8 10.6021 0.2087 10.1269 0.6635

9 10.6021 0.2087

10 10.6021 0.2087

11 10.6021 0.2087

0.0850 0.2087 0.3895 0.4079 0.4006 0.3763 0.3777 0.5672 0.6635 0.5669 0.4998

(8.76 x 10* x weight loss in gy (Area in cm2x Time of exposure in h x Density in g/cc)

Corrosion Rale 12H 1D 3D 1W 2W-1 2W-2 3W 4W 5W 6W 7W

mmpy 5.2868 6.4903 4.0376 1.8122 0.8899 0.8359 0.5593 0.6300 0.5895 0.4198 0.3172

mpy 208.2119 255.6108 159.0168 71.3695 35.0461 32.9202 22.0285 24.8105 23.2183 16.5316 12.4927

102

18:1 MeOH: Oil - 1% Acid 121-1 1 Day 3 Days 1 Week Weeks

3 Weeks

4 Weeks

5 Weeks

6 Weeks

7 Weeks

Density (g/cc) 7.86

Duration in hours

12 24 72 168 336 504 672 840 1008 1176 Surface area(cm2) 14.93

Specimen No B1 B2 B3 B4 Al A2 A3 A4 A5 A6

Initial Wt(g) 10.8050 10.7723 10.7556 10.7475 10.7811 10.7891 10.7681 10.7795 10.7418 10.8216

Specimen No 81 82 B3 B4 Al A2 A3 A4 A5 A6


Weeks 3

Weeks 4

Weeks 5

Weeks 6

Weeks 7

Weeks Duration in

hours 12 24 72 168 336 504 672 840 1008 1176

Chemical Cleaning

Cycle Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss

Before Cleaning 10.6817 0.1233 10.4448 0.3275 10.1094 0.6462 9.9959 0.7516 10.3664 0.4147 10.2895 0.4996 10.2080 0.5601 10.3584 0.4211 10.3464 0.3954 10.3366 0.4850

1 10.6805 0.1245 10.4439 0.3284 10.1085 0.6471 9.9947 0.7528 10.3649 0.4162 10.2884 0.5007 10.2071 0.5610 10.3576 0.4219 10.3453 0.3965 10.3361 0.4855

2 10.6804 0.1246 10.4437 0.3286 10.1084 0.6472 9.9946 0.7529 10.3647 0.4164 10.2883 0.5008 10.2069 0.5612 10.3575 0.4220 10.3452 0.3966 10.3360 0.4856

3 10.6801 0.1249 10.4437 0.3286 10.1083 0.6473 9.9945 0.7530 10.3646 0.4165 10.2882 0.5009 10.2068 0.5613 10.3575 0.4220 10.3450 0.3968 10.3358 0.4858

4 10.6800 0.1250 10.4437 0.3286 10.1081 0.6475 9.9943 0.7532 10.3645 0.4166 10.2880 0.5011 10.2068 0.5613 10.3573 0.4222 10.3449 0.3969 10.3357 0.4859

5 10.6800 0.1250 10.4436 0.3287 10.1081 0.6475 9.9940 0.7535 10.3645 0.4166 10.2880 0.5011 10.2067 0.5614 10.3572 0.4223 10.3445 0.3973 10.3356 0.4860

6 10.6800 0.1250 10.4434 0.3289 10.1081 0.6475 9.9939 0.7536 10.3645 0.4166 10.2880 0.5011 10.2067 0.5614 10.3572 0.4223 10.3445 0.3973 10.3354 0.4862

7 10.6800 0.1250 10.4434 0.3289 10.1081 0.6475 9.9938 0.7537 10.3645 0.4166 10.2880 0.5011 10.2067 0.5614 10.3572 0.4223 10.3445 0.3973 10.3348 0.4868

8 10.4433 0.3290 9.9938 0.7537 10.2067 0.5614 10.3572 0.4223 10.3445 0.3973 10.3344 0.4872

9 10.4431 0.3292 9.9938 0.7537 10.3341 0.4875

10 10.4431 0.3292 9.9938 0.7537 10.3341 0.4875

11 10.4431 0.3292 9.9938 0.7537 10.3341 0.4875

12 10.4431 0.3292 10.3341 0.4875

0.1250 0.3125 0.6475 0.7537 0.4166 0.5011 0.5614 0.4223 0.3973 0.4875

(8.76 x 104 x weight loss in g)/ (Area in cm2x Time of exposure in h x Density in g/cc)

Corrosion Rate

12H 1D 3D 1W 2W 3W 4W 5W 6W 7W

mmpy 7.7747 9.7183 6.7121 3.3484 0.9254 0.7421 0.6235 0.3752 0.2942 0.3094

mpy 306.1940 382.7426 264.3475 131.8734 36.4458 29.2255 24.5568 14.7778 11.5858 12.1853

103

18:1 MeOH: Oil -1% Acid


Weeks 3

Weeks 4

Weeks 5

Weeks 6

Weeks 7

Weeks Density (g/cc) 7.86

Duration iri hours

12 24 72 168 336 504 672 840 1008 1176 Surface area(cm2) 14.93

Specimen No B1 B2 B3 B4 A1 A2 A3 A4 A5 A6

Initial Wt(g) 10.8050 10.7723 10.7556 10.7475 10.7811 10.7891 10.7681 10.7795 10.7418 10.8216



Weeks 3

Weeks 4

Weeks 5

Weeks 6

Weeks 7

Weeks

Duration in hours

12 24 72 168 336 504 672 840 1008 1176

Chemical Cleaning


Before Cleaning

10.6817 0.1233 10.4448 0.3275 10.1094 0.6462 9.9959 0.7516 10.3664 0.4147 10.2895 0.4996 10.2080 0.5601 10.3584 0.4211 10.3464 0.3954 10.3366 0.4850

1 10.6805 0.1245 10.4439 0.3284 10.1085 0.6471 9.9947 0.7528 10.3649 0.4162 10.2884 0.5007 10.2071 0.5610 10.3576 0.4219 10.3453 0.3965 10.3361 0.4855

2 10.6804 0.1246 10.4437 0.3286 10.1084 0.6472 9.9946 0.7529 10.3647 0.4164 10.2883 0.5008 10.2069 0.5612 10.3575 0.4220 10.3452 0.3966 10.3360 0.4856

3 10.6801 0.1249 10.4437 0.3286 10.1083 0.6473 9.9945 0.7530 10.3646 0.4165 10.2882 0.5009 10.2068 0.5613 10.3575 0.4220 10.3450 0.3968 10.3358 0.4858

4 10.6800 0.1250 10,4437 0.3286 10.1081 0.6475 9.9943 0.7532 10.3645 0.4166 10.2880 0.5011 10.2068 0.5613 10.3573 0.4222 10.3449 0.3969 10.3357 0.4859

5 10.6800 0.1250 10.4436 0.3287 10.1081 0.6475 9.9940 0.7535 10.3645 0.4166 10.2880 0.5011 10.2067 0.5614 10.3572 0.4223 10.3445 0.3973 10.3356 0.4860

6 10.6800 0.1250 10.4434 0.3289 10.1081 0.6475 9.9939 0.7536 10.3645 0.4166 10.2880 0.5011 10.2067 0.5614 10.3572 0.4223 10.3445 0.3973 10.3354 0.4862

7 10.6800 0.1250 10.4434 0.3289 10.1081 0.6475 9.9938 0.7537 10.3645 0.4166 10.2880 0.5011 10.2067 0.5614 10.3572 0.4223 10.3445 0.3973 10.3348 0.4868

8 10.4433 0.3290 9.9938 0.7537 10.2067 0.5614 10.3572 0.4223 10.3445 0.3973 10.3344 0.4872

9 10.4431 0.3292 9.9938 0.7537 10.3341 0.4875

10 10.4431 0.3292 9.9938 0.7537 10.3341 0.4875

11 10.4431 0.3292 9.9938 0.7537 10.3341 0.4875

12 10.4431 0.3292 10.3341 0.4875

0.1250 0.3125 0.6475 0.7537 0.4166 0.5011 0.5614 0.4223 0.3973 0.4875

(8.76 x 104 x weight loss in gV (/vea in cm2x Time of exposure in h x Density in g/cc)

Corrosion Rate

12H 1D 3D 1W 2W 3W 4W 5W 6W 7W

mmpy 7.7747 9.7183 6.7121 3.3484 0.9254 0.7421 0.6235 0.3752 0.2942 0.3094

mpy 306.1940 382.7426 264.3475 131.8734 36.4458 29.2255 24.5568 14.7778 11.5858 12.1853

103

Figure 4.3 Potentiodynamic polarization curve of CS1018 in methanol at

25°C and 1 atm 55

Figure 4.4 Potentiodynamic polarization curves produced from the

applications of N2 blanketing and SS304 as corrosion control

methods for methanol storage at 25°C and 1 atm 58

Figure 4.5 Potentiodynamic polarization curve of CS1018 in sulphuric acid

at 25°C and 1 atm 60

Figure 4.6 Potentiodynamic polarization curve of CS1018 in a mixture of

methanol (67%) and sulphuric acid (33%) at 25°C and 1 atm 61


methanol (99.6%) and water (0.4%) at 35°C and 0.2 atm 63


methanol (95.8%), sulphuric acid (3.8%), and water (0.4%) at

25°C and 1 atm 65

Figure 4.9 Free fatty acid conversion over time (Final FFA: 0.10% ± 0.05) 69


oil, methyl oleate, methanol, sulphuric acid, and water (prepared

from 7a in Table 4.1) at 65°C and 1 atm 70

Figure 4.11 Effect of methanol concentration on polarization behaviour of

CS1018 in an esterification reactor at 65°C and 1 atm (Solution

prepared from [7b] and [7c] in Table 4.1) 71

Figure 4.12 Effect of sulphuric acid concentration on polarization behaviour

of CS1018 in an esterification reactor at 65°C and 1 atm 72

Figure 4.3 Potentiodynamic polarization curve of CS1018 in methanol at

25°C and 1 atm 55

Figure 4.4 Potentiodynamic polarization curves produced from the

applications of N2 blanketing and SS304 as corrosion control

methods for methanol storage at 25°C and 1 atm 58

Figure 4.5 Potentiodynamic polarization curve of CS1018 in sulphuric acid

at 25°C and 1 atm 60


methanol (67%) and sulphuric acid (33%) at 25°C and 1 atm 61


methanol (99.6%) and water (0.4%) at 35°C and 0.2 atm 63


methanol (95.8%), sulphuric acid (3.8%), and water (0.4%) at

25°C and 1 atm 65

Figure 4.9 Free fatty acid conversion over time (Final FFA: 0.10% ± 0.05) 69


oil, methyl oleate, methanol, sulphuric acid, and water (prepared

from 7a in Table 4.1) at 65°C and 1 atm 70

Figure 4.11 Effect of methanol concentration on polarization behaviour of

CS1018 in an esterification reactor at 65°C and 1 atm (Solution

prepared from [7b] and [7c] in Table 4.1) 71

Figure 4.12 Effect of sulphuric acid concentration on polarization behaviour

of CS1018 in an esterification reactor at 65°C and 1 atm 72

25:1 MeOH: Oil - 1% Acid 12H 1 Day 3 Days 1 Week

2 Weeks

3 Weeks

4 Weeks

5 Weeks

6 Weeks

7 Weeks

Density (g/m1 7.86

Duration in hours

12 24 72 168 336 504 672 840 1008 1176 Surface area(cm2) 14.93

Specimen No B1 82 B3 84 Al A2 A3 A4 A5 A6

Initial Wt(g) 13.9529 13.9801 13.9733 13.8750 13.9399 13.9759 13.9775 13.9716 13.9294 13.9472

Specimen No B1 82 B3 B4 Al A2 A3 A4 A5 A6


Weeks 3

Weeks 4 Weeks 5 Weeks

6 Weeks

7 Weeks

Duration in hours

12 24 72 168 336 504 672 840 1008 1176

Chemical Cleaning


Before Cleaning

13.8774 0.0755 13.7717 0.2084 13.5640 0.4093 13.4839 0.3911 13.8699 0.0700 13.7980 0.1779 13.3223 0.6552 13.2891 0.6825 13.7790 0.1504 13.8281 0.1191

1 13.8757 0.0772 13.7705 0.2096 13.5614 0.4119 13.4788 0.3962 13.8689 0.0710 13.7970 0.1789 13.3134 0.6641 13.2763 0.6953 13.7781 0.1513 13.8273 0.1199

2 13.8756 0.0773 13.7698 0.2103 13.5603 0.4130 13.4772 0.3978 13.8685 0.0714 13.7969 0.1790 13.3062 0.6713 13.2704 0.7012 13.7781 0.1513 13.8272 0.1200

3 13.8752 0.0777 13.7693 0.2108 13.5579 0.4154 13.4761 0.3989 13.8685 0.0714 13.7966 0.1793 13.3015 0.6760 13.2665 0.7051 13.7779 0.1515 13.8269 0.1203

4 13.8751 0.0778 13.7686 0.2115 13.5579 0.4154 13.4757 0.3993 13.8685 0.0714 13.7965 0.1794 13.3015 0.6760 13.2660 0.7056 13.7775 0.1519 13.8266 0.1206

5 13.8748 0.0781 13.7683 0.2118 13.5579 0.4154 13.4757 0.3993 13.8685 0.0714 13.7964 0.1795 13.3015 0.6760 13.2660 0.7056 13.7775 0.1519 13.8266 0.1206

6 13.8747 0.0782 13.7680 0.2121 13.5579 0.4154 13.4757 0.3993 13.7961 0.1798 13.3015 0.6760 13.2660 0.7056 13.7773 0.1521 13.8266 0.1206

7 13.8744 0.0785 13.7678 0.2123 13.4757 0.3993 13.7961 0.1798 13.2660 0.7056 13.7771 0.1523 13.8266 0.1206

8 13.8742 0.0787 13.7678 0.2123 13.7961 0.1798 13.7771 0.1523

9 13.8742 0.0787 13.7678 0.2123 13.7961 0.1798 13.7771 0.1523

10 13.8742 0.0787 13.7678 0.2123 13.7771 0.1523

11 13.8742 0.0787

0.0787 0.2123 0.4154 0.3993 0.0714 0.1798 0.6760 0.7056 0.1523 0.1206

(8.76 x 10' x weight loss n g)/ (Area in cm2x Time of exposure in h x Density in g/cc)

Corrosion Rate

12H 1D 3D 1W 2W 3W 4W 5W 6W 7W

mmpy 4.6764 6.3076 4.1139 1.6948 0.1515 0.2544 0.7173 0.5990 0.1077 0.0731

mpy 184.1752 248.4141 162.0211 66.7464 5.9676 10.0184 28.2498 23.5894 4.2430 2.8799

104

25:1 MeOH: Oil-1% Acid 12H 1 Day 3 Days 1 Week

2 Weeks

3 Weeks

4 Weeks

5 Weeks

6 Weeks

7 Weeks

Density (g/cc) 7.86

Duration in hours

12 24 72 168 336 504 672 840 1008 1176 Surface area(cm2) 14.93


Initial Wt(g) 13.9529 13.9801 13.9733 13.8750 13.9399 13.9759 13.9775 13.9716 13.9294 13.9472



Weeks 3

Weeks 4 Weeks

5 Weeks

6 Weeks

7 Weeks

Duration in hours

12 24 72 168 336 504 672 840 1008 1176

Chemical Cleaning


Before Cleaning

13.8774 0.0755 13.7717 0.2084 13.5640 0.4093 13.4839 0.3911 13.8699 0.0700 13.7980 0.1779 13.3223 0.6552 13.2891 0.6825 13.7790 0.1504 13.8281 0.1191

1 13.8757 0.0772 13.7705 0.2096 13.5614 0.4119 13.4788 0.3962 13.8689 0.0710 13.7970 0.1789 13.3134 0.6641 13.2763 0.6953 13.7781 0.1513 13.8273 0.1199

2 13.8756 0.0773 13.7698 0.2103 13.5603 0.4130 13.4772 0.3978 13.8685 0.0714 13.7969 0.1790 13.3062 0.6713 13.2704 0.7012 13.7781 0.1513 13.8272 0,1200

3 13.8752 0.0777 13.7693 0.2108 13.5579 0.4154 13.4761 0.3989 13.8685 0.0714 13.7966 0.1793 13.3015 0.6760 13.2665 0.7051 13.7779 0.1515 13.8269 0.1203

4 13.8751 0.0778 13.7686 0.2115 13.5579 0.4154 13,4757 0.3993 13.8685 0.0714 13.7965 0.1794 13.3015 0.6760 13.2660 0.7056 13.7775 0.1519 13.8266 0.1206

5 13.8748 0.0781 13.7683 0.2118 13.5579 0.4154 13.4757 0.3993 13.8685 0.0714 13.7964 0.1795 13.3015 0.6760 13.2660 0.7056 13,7775 0.1519 13.8266 0.1206

6 13.8747 0.0782 13.7680 0.2121 13.5579 0.4154 13.4757 0.3993 13.7961 0.1798 13.3015 0.6760 13.2660 0.7056 13.7773 0.1521 13.8266 0.1206

7 13.8744 0.0785 13.7678 0.2123 13.4757 0.3993 13.7961 0.1798 13.2660 0.7056 13.7771 0.1523 13.8266 0.1206

8 13.8742 0.0787 13.7678 0.2123 13.7961 0.1798 13.7771 0.1523

9 13.8742 0.0787 13.7678 0.2123 13.7961 0.1798 13.7771 0.1523

10 13.8742 0.0787 13.7678 0.2123 13.7771 0.1523

11 13.8742 0.0787

0.0787 0.2123 0.4154 0.3993 0,0714 0.1798 0.6760 0.7056 0.1523 0.1206

(8.76 x 104 x weigh! loss in gy (Area in cm2x Time of exposure in h x Density in g/cc)

Corrosion Rate

12H 1D 3D 1W 2W 3W 4W 5W 6W 7W

mmpy 4.6764 6.3076 4.1139 1.6948 0.1515 0.2544 0.7173 0.5990 0.1077 0.0731

mpy 184.1752 248.4141 162.0211 66.7464 5.9676 10.0184 28.2498 23.5894 4.2430 2.8799

104

18:1 ratio - 3% H2SO41 Day 1 Week 2 Weeks 3 Weeks 4 Weeks 5 Weeks 6 Weeks 7 Weeks Density (g/cc) 7.86

Duration in hours

24 168 336 504 672 840 1008 1176 Surface area(cm2) 14.93

Specimen No 56 52 53 54 58 57 59 60

Initial Wt(g) 13.9591 13.9933 13.9377 13.9630 13.9539 13.9382 13.9359 13.9862

Specimen No

56 52 53 54 57 59 60

1 Day 1 Week 2 Weeks 3 Weeks 4 Weeks 5 Weeks 6 Weeks 7 Weeks

Duration in hours 24 168 336 504 672 840 1008 1176

Chemical Cleaning

Cycle Wt Loss WI Loss Wt Loss Wt Loss Wt Loss WI Loss Wt Loss Wt Loss

Before Cleaning

13.9214 0.0377 13.3051 0.6882 12.2388 1.6989 12.2918 1.6712 13.6718 0.2821 13.7378 0.2004 13.6282 0.3077 13.6494 0.3368

1 13.9208 0.0383 13.2818 0.7115 12.2362 1.7015 12.2754 1.6876 13.6611 0.2928 13.6460 0.2922 13.6229 0.3130 13.6438 0.3424

2 13.9207 0.0384 13.2806 0.7127 12.2245 1.7132 12.2719 1.6911 13.6595 0.2944 13,6285 0.3097 13.6218 0.3141 13.6423 0.3439

3 13.9206 0.0385 13.2731 0.7202 12.2241 1.7136 12.2694 1.6936 13.6594 0.2945 13.6260 0.3122 13.6212 0.3147 13.6415 0.3447

4 13.9209 0.0382 13.2701 0.7232 12.2240 1.7137 12.2550 1.7080 13.6573 0.2966 13.6254 0.3128 13.6194 0.3165 13.6406 0.3456

5 13.9204 0.0387 13.2692 0.7241 12.2055 1.7322 12.2523 1.7107 13.6552 0.2987 13.6253 0.3129 13.6193 0.3166 13.6405 0.3457

6 13.9203 0.0388 13.2690 0.7243 12.2042 1.7335 12.2522 1.7108 13.6545 0.2994 13.6213 0.3169 13.6165 0.3194 13.6358 0.3504

7 13.9198 0.0393 13.2597 0.7336 12.1972 1.7405 12.2321 1.7309 13.6544 0.2995 13.6195 0.3187 13.6161 0.3198 13.6349 0.3513

8 13.9195 0.0396 13.2568 0.7365 12.1934 1.7443 12.2239 1.7391 13.6542 0.2997 13.6190 0.3192 13.6147 0.3212 13.6339 0.3523

9 13.9191 0.0400 13.2543 0.7390 12.1918 1.7459 12.2222 1.7408 13.6541 0.2998 13.6185 0.3197 13.6147 0.3212 13.6340 0.3522

10 13.9192 0.0399 13.2434 0.7499 12.1908 1.7469 12.2220 1.7410 13.6533 0.3006 13.6181 0.3201 13.6143 0.3216 13.6339 0.3523

11 13.9187 0.0404 13.2418 0.7515 12.1894 1.7483 12.2217 1.7413 13.6534 0.3005 13.6179 0.3203 13.6138 0.3221 13.6336 0.3526

0.0434 0.7879 1.7483 1.7391 0.3047 0.3187 0.3260 0.3527

(8.76 x 10`x weight loss in g)/ (Area in cm25 Time of exposure in h x Density in g/cc)

Corrosion Rate

1D 1W 2W 3W 4W 5W 6W 7W

mmpy 1.3066 3.3885 3.7595 2.4931 0.3276 0.2741 0.2337 0.2167

mpy 51.4569 133.4527 148.0615 98.1882 12.9023 10.7961 9.2029 8.5342

105

18:1 ratio - 3% H2S04

1 Day 1 Week 2 Weeks 3 Weeks 4 Weeks 5 Weeks 6 Weeks 7 Weeks Density (g/cc) 7.86

Duration in hours

24 168 336 504 672 840 1008 1176 Surface area(cm2) 14.93

Specimen No

56 52 53 54 58 57 59 60

Initial Wt(g) 13.9591 13.9933 13.9377 13.9630 13.9539 13.9382 13.9359 13.9862

Specimen No

56 52 53 54 57 59 60

1 Day 1 Week 2 Weeks 3 Weeks 4 Weeks 5 Weeks 6 Weeks 7 Weeks

Duration in hours

24 168 336 504 672 840 1008 1176

Chemical Cleaning

Cycle Wt Loss Wl Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt Loss Wt LOSS

Before Cleaning

13.9214 0.0377 13.3051 0.6882 12.2388 1.6989 12.2918 1.6712 13.6718 0.2821 13.7378 0.2004 13.6282 0.3077 13.6494 0.3368

1 13.9208 0.0383 13.2818 0.7115 12.2362 1.7015 12.2754 1.6876 13.6611 0.2928 13.6460 0.2922 13.6229 0.3130 13.6438 0.3424

2 13.9207 0.0384 13.2806 0.7127 12.2245 1.7132 12.2719 1.6911 13.6595 0.2944 13.6285 0.3097 13.6218 0.3141 13.6423 0.3439

3 13.9206 0.0385 13.2731 0,7202 12.2241 1.7136 12.2694 1.6936 13.6594 0.2945 13.6260 0.3122 13.6212 0.3147 13.6415 0.3447

4 13.9209 0.0382 13.2701 0.7232 12.2240 1.7137 12.2550 1.7080 13.6573 0.2966 13.6254 0.3128 13.6194 0.3165 13.6406 0.3456

5 13.9204 0.0387 13.2692 0.7241 12.2055 1.7322 12.2523 1.7107 13.6552 0.2987 13.6253 0.3129 13.6193 0.3166 13.6405 0.3457

6 13.9203 0.0388 13.2690 0.7243 12.2042 1.7335 12.2522 1.7108 13.6545 0.2994 13.6213 0.3169 13.6165 0.3194 13.6358 0.3504

7 13,9198 0.0393 13.2597 0.7336 12.1972 1.7405 12.2321 1.7309 13.6544 0.2995 13.6195 0.3187 13.6161 0.3198 13.6349 0.3513

8 13.9195 0.0396 13.2568 0.7365 12.1934 1.7443 12.2239 1.7391 13.6542 0.2997 13.6190 0.3192 13.6147 0.3212 13.6339 0.3523

9 13.9191 0.0400 13.2543 0.7390 12.1918 1.7459 12.2222 1.7408 13.6541 0.2998 13.6185 0.3197 13.6147 0.3212 13.6340 0.3522

10 13.9192 0.0399 13.2434 0.7499 12.1908 1.7469 12.2220 1.7410 13.6533 0.3006 13.6181 0.3201 13.6143 0.3216 13.6339 0.3523

11 13.9187 0.0404 13.2418 0.7515 12.1894 1.7483 12.2217 1.7413 13.6534 0.3005 13.6179 0.3203 13.6138 0.3221 13.6336 0.3526

0.0434 0.7879 1.7483 1.7391 0.3047 0.3187 0.3260 0.3527

{8.76 x 10* x weight loss in g)/ (Area in cm2x Time of exposure in h x Density in g/cc)

Corrosion Rate

1D 1W 2W 3W 4W 5W 6W 7W

mmpy 1.3066 3.3885 3.7595 2.4931 0.3276 0.2741 0.2337 0.2167

mpy 51.4569 133.4527 148.0615 98.1882 12.9023 10.7961 9.2029 8.5342

105

(Solution prepared from [7b] and [7d] in Table 4.1)

Figure 4.13 Potentiodynamic polarization curve of CS1018 in glycerol at

35°C and 1 atm 73


methanol (55%), glycerol (40%), sulphuric acid (3.5%), and

water (1.5%) at 60°C and 1 atm 75

Figure 4.15 Potentiodynamic polarization curve of SS304 in a mixture of



Figure 4.16 Comparison of polarization behaviour of various materials of

construction for Location 10 78





methanol (10.5%), glycerol (79.5%), sulphuric acid (7.1%), and

water (2.9%) at 72°C and 0.3 atm 81



water (2.9%) at 72°C and 0.3atm 82

Figure 4.20 Comparison of polarization behaviour of CS1018 and SS304 for

Location 11 83

Figure 4.21 Corrosion rate of CS1018 in an esterification reactor measured 86

xi

(Solution prepared from [7b] and [7d] in Table 4.1)

Figure 4.13 Potentiodynamic polarization curve of CS1018 in glycerol at

35°C and 1 atm 73







Figure 4.16 Comparison of polarization behaviour of various materials of

construction for Location 10 78






water (2.9%) at 72°C and 0.3 atm 81



water (2.9%) at 72°C and 0.3atm 82

Figure 4.20 Comparison of polarization behaviour of CS1018 and SS304 for

Location 11 83

Figure 4.21 Corrosion rate of CS1018 in an esterification reactor measured 86

xi

by weight loss method

Figure 4.22 Weight loss coupons with oily layer with respect to methanol: oil

molar ratio

Figure 4.23 Biodiesel solution colour change — Fresh solution (Pale Yellow),

After 1 week (Orange), After 2 weeks (Permanent dark brown)

xii

by weight loss method

Figure 4.22 Weight loss coupons with oily layer with respect to methanol: oil

molar ratio 87

Figure 4.23 Biodiesel solution colour change - Fresh solution (Pale Yellow),

After 1 week (Orange), After 2 weeks (Permanent dark brown) 88

Xll

NOMENCLATURE

A Area of working electrode in cm2

CR Corrosion rate

CS1018 Carbon steel 1018

D Density of the specimen in g/cm3

E Electrode potential

EW Equivalent weight of specimen

Ecorr Corrosion electrode potential

Ecp Completion of film formation

Epp Primary passivation potential

Ere Reversible electrode potential

Erp Repassivation potential

Etrans Transpassive potential

icorr Corrosion current density

io Equilibrium current density

mpy Mils per year

Degree centigrade

SS 304 Stainless steel 304


T Temperature

W Mass loss in g

NOMENCLATURE

A Area of working electrode in cm

CR Corrosion rate

CS1018 Carbon steel 1018

D Density of the specimen in g/cm"

E Electrode potential

EW Equivalent weight of specimen

Ecorr Corrosion electrode potential

ECp Completion of film formation

Epp Primary passivation potential

F ^rev Reversible electrode potential

F ^rp Repassivation potential

Eirans Transpassive potential

Icorr Corrosion current density

io Equilibrium current density

mpy Mils per year

°C Degree centigrade


SS316 Stainless steel 316

T Temperature

W Mass loss in g

xiii

Greek letters:

/3a

fic

Tafel slope for anodic polarization (mV/decade of current density)

Tafel slope for cathodic polarization (mV/decade of current density)

xiv

Greek letters:

Pa Tafel slope for anodic polarization (mV/decade of current density)

[$c Tafel slope for cathodic polarization (mV/decade of current density)

xiv

1. INTRODUCTION

The present scenario of fluctuating petroleum prices and climate change is forcing

us to look for an alternative fuel that could lessen the world's dependence on non-

renewable fossil fuels and stabilize fuel prices. Biofuel has the potential to become a

major alternative fuel source to address the challenges of both climate change and energy

stability. There are a number of types of biofuel, including biogas, bioethanol,

biobutanol, and biodiesel, each with advantages and disadvantages. The focus of this

thesis is on achieving a better understanding of one of the disadvantages of biodiesel

production. A thorough understanding of corrosion associated with the acid-catalyzed

esterification process for biodiesel production does not exist in the literature. This thesis

presents a comprehensive set of relevant corrosion studies.

1.1 Advantages and disadvantages of biodiesel

Biodiesel is renewable, biodegradable, and non-toxic to the environment and

ecology. Although biodiesel cannot be a substitute for conventional fossil fuels due to the

limited availability of raw materials (i.e., oil) for its production, it is an additional source

of fuel that can have a notable global impact on aspects of sustainability and reduction of

fossil fuel dependence. For instance, in the United States, the combined vegetable oil and

animal fat production is 36.0 billion pounds per year (Jacobsen Publishing Company,

2004-05), which can be used to produce 4.74 billion gallons of biodiesel (Gerpen et al.,

2006). However, this would fulfil only approximately 13% of the current demand for on-

1

1. INTRODUCTION

The present scenario of fluctuating petroleum prices and climate change is forcing

us to look for an alternative fuel that could lessen the world's dependence on non

renewable fossil fuels and stabilize fuel prices. Biofuel has the potential to become a

major alternative fuel source to address the challenges of both climate change and energy

stability. There are a number of types of biofuel, including biogas, bioethanol,

biobutanol, and biodiesel, each with advantages and disadvantages. The focus of this

thesis is on achieving a better understanding of one of the disadvantages of biodiesel

production. A thorough understanding of corrosion associated with the acid-catalyzed

esterification process for biodiesel production does not exist in the literature. This thesis

presents a comprehensive set of relevant corrosion studies.

1.1 Advantages and disadvantages of biodiesel

Biodiesel is renewable, biodegradable, and non-toxic to the environment and

ecology. Although biodiesel cannot be a substitute for conventional fossil fuels due to the

limited availability of raw materials (i.e., oil) for its production, it is an additional source

of fuel that can have a notable global impact on aspects of sustainability and reduction of

fossil fuel dependence. For instance, in the United States, the combined vegetable oil and

animal fat production is 36.0 billion pounds per year (Jacobsen Publishing Company,

2004-05), which can be used to produce 4.74 billion gallons of biodiesel (Gerpen et al.,

2006). However, this would fulfil only approximately 13% of the current demand for on-

1

highway diesel fuel (i.e., 39.12 billion gallons per year consumption in 2006)

(http:/itonto.eia.doe.gov).

As compared to petro-diesel, biodiesel has a number of advantages and

disadvantages. Since biodiesel has a high flash point (? 120°C), it is less volatile than

petro-diesel, making it safer to handle, store, and transport (Krawczyk, 1996). Biodiesel

can be directly used in present conventional diesel engines without any engine

modification. Biodiesel tends to promote complete combustion due to the presence of an

oxygen molecule in the biodiesel compound, resulting in lower emissions of carbon

monoxide (CO), particulate matters (PMs), and unburned hydrocarbons. Due to its closed

carbon cycle, the carbon dioxide (CO2) released from the combustion of biodiesel can be

recycled through the photosynthesis process involved in the growth of the plant materials

from which the biodiesel is derived, thereby reducing its impact on the environment by

virtually eliminating its contribution to the greenhouse gas effect (Agarwal and Das,

2001; Korbitz, 1999). As per the report published on http://www.bfuelcanada.com, (as of

November, 2010), 91% less greenhouse gas (GHG) is emitted from biodiesel compared

to sulphur-free petro-diesel. Its good lubricative nature also reduces engine wear and

enhances smooth engine performance and extends the engine's life span (Anastopoulos et

al., 2001; Mittelbach and Claudia, 2004). In addition, the facts that it has a higher cetane

number than petro-diesel and is sulphur free in nature counts as significant advantages.

Since biodiesel is non-toxic and biodegradable, it leaves no negative impact on human

health and the environment.

Conversely, a Life Cycle Assessment (LCA) study (Knothe et al., 2004) reveals

some disadvantages of biodiesel that stem from its production from biomass. For

2

highway diesel fuel (i.e., 39.12 billion gallons per year consumption in 2006)

fhttp: //ton to .eia.doe.»ov).

As compared to petro-diesel, biodiesel has a number of advantages and

disadvantages. Since biodiesel has a high flash point (> 120°C), it is less volatile than

petro-diesel, making it safer to handle, store, and transport (Krawczyk, 1996). Biodiesel

can be directly used in present conventional diesel engines without any engine

modification. Biodiesel tends to promote complete combustion due to the presence of an

oxygen molecule in the biodiesel compound, resulting in lower emissions of carbon

monoxide (CO), particulate matters (PMs), and unburned hydrocarbons. Due to its closed

carbon cycle, the carbon dioxide (CO2) released from the combustion of biodiesel can be

recycled through the photosynthesis process involved in the growth of the plant materials

from which the biodiesel is derived, thereby reducing its impact on the environment by

virtually eliminating its contribution to the greenhouse gas effect (Agarwal and Das,

2001; Korbitz, 1999). As per the report published on http://www.bfue 1 canada.com, (as of

November, 2010), 91% less greenhouse gas (GHG) is emitted from biodiesel compared

to sulphur-free petro-diesel. Its good lubricative nature also reduces engine wear and

enhances smooth engine performance and extends the engine's life span (Anastopoulos et

al., 2001; Mittelbach and Claudia, 2004). In addition, the facts that it has a higher cetane

number than petro-diesel and is sulphur free in nature counts as significant advantages.

Since biodiesel is non-toxic and biodegradable, it leaves no negative impact on human

health and the environment.

Conversely, a Life Cycle Assessment (LCA) study (Knothe et al., 2004) reveals

some disadvantages of biodiesel that stem from its production from biomass. For

2

instance, in agricultural production of oil seeds, the primary feedstock for biodiesel,

consumes fertilizers, biocides, and a significant amount of tractor fuel. This leads to

environmental problems, such as increased GHG emissions and the leaching of

pesticides, nitrogen, and phosphorous from fertilizers into surface, ground, and coastal

waters, causing major negative impacts on ecology such as acidification, eutrophication,

etc.

1.2 Biodiesel production across the globe

In the past decades, biodiesel commercial production commenced at a rapid rate

across the globe. Europe and the United States are the forerunners of this industry.

According to Sims (2007), the growth of the global biodiesel market, considering the

average annual rate by 2016, will be 42 percent, which equals 37 billion gallons, as

mentioned in the report published by global information service company Fuji Keizai

USA in early October 2007. Europe dominates the market with its estimated annual

capacity of 2.5 billion gallons, followed by the US with 1.85 billion gallons (Fuji Keizai

2007). Canada, in its embryonic stage of biodiesel development, has seven plants in

operation and five under construction (http://www.greenfuels.ora) (as on November,

2010) as tabulated in Table 1.1.

Because of its major key resources, including inexpensive land, cheap labour,

high volume production of soybeans and sunflowers, and efficient oil production

industries, Argentina has attracted worldwide attention for the production of biofuels. Its

biodiesel production forecast for 2008 exceeds 800 million gallons as per the report

mentioned by the USDA Foreign Agricultural Services (Sims, 2007).

3

instance, in agricultural production of oil seeds, the primary feedstock for biodiesel,

consumes fertilizers, biocides, and a significant amount of tractor fuel. This leads to

environmental problems, such as increased GHG emissions and the leaching of

pesticides, nitrogen, and phosphorous from fertilizers into surface, ground, and coastal

waters, causing major negative impacts on ecology such as acidification, eutrophication,

etc.

1.2 Biodiesel production across the globe

In the past decades, biodiesel commercial production commenced at a rapid rate

across the globe. Europe and the United States are the forerunners of this industry.

According to Sims (2007), the growth of the global biodiesel market, considering the

average annual rate by 2016, will be 42 percent, which equals 37 billion gallons, as

mentioned in the report published by global information service company Fuji Keizai

USA in early October 2007. Europe dominates the market with its estimated annual

capacity of 2.5 billion gallons, followed by the US with 1.85 billion gallons (Fuji Keizai

2007). Canada, in its embryonic stage of biodiesel development, has seven plants in

operation and five under construction (http://www.grcenfuels.org) (as on November,

2010) as tabulated in Table 1.1.

Because of its major key resources, including inexpensive land, cheap labour,

high volume production of soybeans and sunflowers, and efficient oil production

industries, Argentina has attracted worldwide attention for the production of biofuels. Its

biodiesel production forecast for 2008 exceeds 800 million gallons as per the report

mentioned by the USDA Foreign Agricultural Services (Sims, 2007).

3

http://www.grcenfuels.org

UNIVERSITY OF REGINA

FACULTY OF GRADUATE STUDIES AND RESEARCH

SUPERVISORY AND EXAMINING COMMITTEE

Rangakrishnan Krishnaiyer Sankaranarayanan, candidate for the degree of Master of Applied Science in Industrial Systems Engineering, has presented a thesis titled, Corrosion in Biodiesel Production Process Using High Free Fatty Acid Feedstocks, in an oral examination held on August 8, 2011. The following committee members have found the thesis acceptable in form and content, and that the candidate demonstrated satisfactory knowledge of the subject material.

External Examiner:

Supervisor:

Committee Member:

Committee Member:

Chair of Defense:

*Not present at defense

Dr. Farshid Torabi, Petroleum Systems Engineering

Dr. Amornvadee Veawab, Environmental Systems Engineering

Dr. David deMontigny, Industrial Systems Engineering

Dr. Adisorn Aroonwilas, lndusctrial Systems Engineering

Dr. Nader Mobed, Department of Physics

UNIVERSITY OF REGINA

FACULTY OF GRADUATE STUDIES AND RESEARCH

SUPERVISORY AND EXAMINING COMMITTEE

Rangakrishnan Krishnaiyer Sankaranarayanan, candidate for the degree of Master of Applied Science in Industrial Systems Engineering, has presented a thesis titled,

Corrosion in Biodiesel Production Process Using High Free Fatty Acid Feedstocks, in an oral examination held on August 8, 2011. The following committee members have

found the thesis acceptable in form and content, and that the candidate demonstrated satisfactory knowledge of the subject material.

External Examiner:

Supervisor:

Dr. Farshid Torabi, Petroleum Systems Engineering

Dr. Amornvadee Veawab, Environmental Systems Engineering

Committee Member: Dr. David deMontigny, Industrial Systems Engineering

Committee Member: Dr. Adisorn Aroonwilas, Indusctrial Systems Engineering

Chair of Defense: Dr. Nader Mobed, Department of Physics

*Not present at defense

Table 1.1 Canadian biodiesel production plant details

(http:Ilgreenfuels.org/en/industry-inforniationiplants.aspx accessed on November, 2010)

Plant Name Location Feedstock Capacity*

Bifrost Bio-Blends Ltd. Arborg, MB Canola 3

Bio-Diesel Quebec Inc. St-Alexis-des-

Monts, PQ Yellow Grease 10

BIOX Corporation Hamilton, ON Multi-Feedstock 66

City-Farm Biofuel Ltd. Delta, BC Recycled Oil/Tallow 10

Canadian Bioenergy

Corporation **

Sturgeon County,

AB Canola 225

Eastman Bio-Fuels Ltd.** Beausejour, MB Canola 11

Greenway Biodiesel** Winnipeg, MB Canola 20

Kyoto Fuels** Lethbridge, AB Multi-Feedstock 66

Methes Energies Canada

Inc.** Mississauga, ON Multi-Feedstock 5

Milligan Bio-Tech Inc. Foam Lake, SK Canola 1

Rothsay Biodiesel Montreal, PQ Tallow/Yellow

Grease 35

Western Biodiesel Inc. Calgary, AB Multi-Feedstock 19

* Capacity noted in million litres per year (Mmly), ** plant currently under construction

4

Table 1.1 Canadian biodiesel production plant details

nittp://greenfuels.org/en/industry-information/plants.aspx accessed on November, 2010)

Plant Name Location Feedstock Capacity*

Bifrost Bio-Blends Ltd. Arborg, MB Canola 3

Bio-Diesel Quebec Inc. St-Alexis-des-

Monts, PQ Yellow Grease 10

BIOX Corporation Hamilton, ON Multi-Feedstock 66

City-Farm Biofuel Ltd. Delta, BC Recycled Oil/Tallow 10

Canadian Bioenergy

Corporation **

Sturgeon County,

AB Canola 225

Eastman Bio-Fuels Ltd.** Beausejour, MB Canola 11

Greenway Biodiesel** Winnipeg, MB Canola 20

Kyoto Fuels** Lethbridge, AB Multi-Feedstock 66

Methes Energies Canada

Inc.** Mississauga, ON Multi-Feedstock 5

Milligan Bio-Tech Inc. Foam Lake, SK Canola 1

Rothsay Biodiesel Montreal, PQ Tallow/Yellow

Grease 35

Western Biodiesel Inc. Calgary, AB Multi-Feedstock 19

* Capacity noted in million litres per year (Mmly), ** plant currently under construction

4

In Asia, the use of non-edible oil seeds, such as jatropa and pongamia pinnata, for

biodiesel production are of great importance, especially in India (Azam et al., 2005).

1.3 Oil feedstocks for biodiesel production

The primary feedstocks for biodiesel production are: 1) virgin vegetable oils such

as rapeseed oil, canola (rapeseed—low erucic acid oil), sunflower oil, soybean oil, and

palm oil; 2) animal fats such as grease from grease traps and tallow; and 3) waste

vegetable oil. Out of these, rapeseed occupies an 85% share as the primary feedstock for

biodiesel production across the globe (Mittelbach and Claudia, 2004). In the United

States, soybean is the most popular feedstock. In eastern countries, including Indonesia

and Malaysia, palm oil, which is the largest volume triglyceride resource in the world

(Gerpen et al., 2006), is used for biodiesel production. Apart from the abovementioned

edible oils, a number of alternative edible oils such as Ethiopian mustard, gold of

pleasure (camelina sativa), and linseed in Central Europe, tigernut in Africa, and palm

kernel oil and coconut oil in Southern Asian countries have successfully been used for

biodiesel production (Mittelbach and Claudia, 2004). The non-edible oils such as castor

(Ricinus communis), physic nut (Jatropha curcas), sal oil, mahua oil, neem oil, and

karanja oil have also been used successfully in biodiesel the production, and their cost is

cheaper than edible oils (Azam et al., 2005; Srivastava and Ram Prasad, 2000).

In addition to vegetable oil, the by-products of meat packing and fishery

industries such as beef tallow (Fogila et al., 1997; Hanna and Ali, 1997; Zheng and

Hanna, 1996), lard (Lee et al., 2002), and fish oils (Mittelbach and Claudia, 2004) have

been tested for their suitability for biodiesel production. Animal fats are used as feedstock

5

In Asia, the use of non-edible oil seeds, such as jatropa and pongamia pinnata, for

biodiesel production are of great importance, especially in India (Azam et al., 2005).

1.3 Oil feedstocks for biodiesel production

The primary feedstocks for biodiesel production are: 1) virgin vegetable oils such

as rapeseed oil, canola (rapeseed-low erucic acid oil), sunflower oil, soybean oil, and

palm oil; 2) animal fats such as grease from grease traps and tallow; and 3) waste

vegetable oil. Out of these, rapeseed occupies an 85% share as the primary feedstock for

biodiesel production across the globe (Mittelbach and Claudia, 2004). In the United

States, soybean is the most popular feedstock. In eastern countries, including Indonesia

and Malaysia, palm oil, which is the largest volume triglyceride resource in the world

(Gerpen et al., 2006), is used for biodiesel production. Apart from the abovementioned

edible oils, a number of alternative edible oils such as Ethiopian mustard, gold of

pleasure (camelina sativa), and linseed in Central Europe, tigernut in Africa, and palm

kernel oil and coconut oil in Southern Asian countries have successfully been used for

biodiesel production (Mittelbach and Claudia, 2004). The non-edible oils such as castor

(Ricinus communis), physic nut (Jatropha curcas), sal oil, mahua oil, neem oil, and

karanja oil have also been used successfully in biodiesel the production, and their cost is

cheaper than edible oils (Azam et al., 2005; Srivastava and Ram Prasad, 2000).

In addition to vegetable oil, the by-products of meat packing and fishery

industries such as beef tallow (Fogila et al., 1997; Hanna and Ali, 1997; Zheng and

Hanna, 1996), lard (Lee et al., 2002), and fish oils (Mittelbach and Claudia, 2004) have

been tested for their suitability for biodiesel production. Animal fats are used as feedstock

5

due to their high degree of saturation, whereas fish oils, due to high amounts of poly

unsaturated fatty acids, are found not suitable for the biodiesel production. Because of

their higher amount of free fatty acid compositions, such feedstock has disadvantages

including poor properties like high iodine values and poor oxidation stability, which

causes problems in cold conditions (Mittelbach and Claudia, 2004).

Finally, recycled and waste vegetable oils have become a popular feedstock for

biodiesel production, as they are inexpensive and have added the benefits economically

and environmentally. A large number of references are found on biodiesel production

using waste oil worldwide (Al-Widyan et al., 2002; Lee et al., 2002; Nye et al., 1983;

Supple et al., 2002; Watanbe et al., 2001). As the waste oils naturally contain high

amounts of free fatty acids (FFA) and water, the level of FFA content has to be reduced

before biodiesel production. Table 1.2 shows FFA content of various feedstocks.

1.4 Biodiesel production and its bottlenecks

Biodiesel production using feedstock with high free fatty acid (FFAs) contents

has a number of short comings including methanol loss, catalyst loss, long reaction

duration, and potential corrosion problem. In principle, conversion of FFAs by

esterification reaction requires a high amount of methanol (methanol: oil ratio 30-50:1

molar basis) compared to biodiesel production from high quality feedstock with low

FFAs (methanol: oil ratio 6:1 molar basis). As such, it requires an energy intensive

process (i.e. distillation) to recover methanol or to minimize the methanol loss. The

conversion of FFAs by esterification reaction using acid catalyst also requires a longer

6

due to their high degree of saturation, whereas fish oils, due to high amounts of poly

unsaturated fatty acids, are found not suitable for the biodiesel production. Because of

their higher amount of free fatty acid compositions, such feedstock has disadvantages

including poor properties like high iodine values and poor oxidation stability, which

causes problems in cold conditions (Mittelbach and Claudia, 2004).

Finally, recycled and waste vegetable oils have become a popular feedstock for

biodiesel production, as they are inexpensive and have added the benefits economically

and environmentally. A large number of references are found on biodiesel production

using waste oil worldwide (Al-Widyan et al., 2002; Lee et al., 2002; Nye et al., 1983;

Supple et al., 2002; Watanbe et al., 2001). As the waste oils naturally contain high

amounts of free fatty acids (FFA) and water, the level of FFA content has to be reduced

before biodiesel production. Table 1.2 shows FFA content of various feedstocks.

1.4 Biodiesel production and its bottlenecks

Biodiesel production using feedstock with high free fatty acid (FFAs) contents

has a number of short comings including methanol loss, catalyst loss, long reaction

duration, and potential corrosion problem. In principle, conversion of FFAs by

esterification reaction requires a high amount of methanol (methanol: oil ratio 30~50:1

molar basis) compared to biodiesel production from high quality feedstock with low

FFAs (methanol: oil ratio 6:1 molar basis). As such, it requires an energy intensive

process (i.e. distillation) to recover methanol or to minimize the methanol loss. The

conversion of FFAs by esterification reaction using acid catalyst also requires a longer

6

Table 1.2: Range of free fatty acids in various feedstock oils and fats (Kemp, 2006)

Feedstock Free fatty acid content (%)

Refined vegetable oil (Canola, Soybean) 0-1

Waste fryer oil and fat 2-7

Animal Fats (beef tallow, lard) 5-30

Yellow grease 7-30

Brown grease >30

7

Table 1.2: Range of free fatty acids in various feedstock oils and fats (Kemp, 2006)

Feedstock Free fatty acid content (%)

Refined vegetable oil (Canola, Soybean) 0-1

Waste fryer oil and fat 2-7

Animal Fats (beef tallow, lard) 5-30

Yellow grease 7-30

Brown grease >30

7

reaction time. Therefore, to expedite the reaction time, the process is often operated at

higher temperature, which leads to greater process cost.

In addition, corrosion of process equipment can be expected in an acid-catalyzed

esterification process due to the presence of sulphuric acid. Furthermore, if the feedstock

with high FFA content is processed using an alkali - catalyzed transesterification process,

a side reaction called saponification (reaction between a base catalyst and FFA) will take

place and result in soap formation, which in turn causes loss of FFAs, raw material, and

catalyst, thereby increasing the production cost.

1.5 Research motivation, objectives and scope

As previously mentioned, the use of sulphuric acid in biodiesel production

processes to pre-treat oil feedstock or to neutralize residual base catalyst in esterification

and transesterification processes poses the possibility of corrosion of process equipment.

This has been addressed in several publications (Gaupp., 1937; Matthys and Damalist,

2003; Kaul et al., 2007; Vargas, 2007). In 1937, Gaupp carried out corrosion experiments

to study the effects of vegetable oils such as soy bean oil, sesame oil, and palm oil, etc.,

on corrosion of various metals such as copper, brass, aluminium, and steel. This was done

by immersing these metals in oils for a period of 5 months. No severe corrosion and in

some cases, no corrosion was found. No detailed results with testing conditions or the

analysis of corrosion samples were provided. In 2003, Matthys and Damalist reported

corrosion problems in ester washing and methanol recovery processes and suggested the

use of carbon steel coated with sulphates as the best material of construction. Later, in

2007, Kaul et al. evaluated corrosion of biodiesel made from non-edible oils on diesel

8

reaction time. Therefore, to expedite the reaction time, the process is often operated at

higher temperature, which leads to greater process cost.

In addition, corrosion of process equipment can be expected in an acid catalyzed

esterification process due to the presence of sulphuric acid. Furthermore, if the feedstock

with high FFA content is processed using an alkali - catalyzed transesterification process,

a side reaction called saponification (reaction between a base catalyst and FFA) will take

place and result in soap formation, which in turn causes loss of FFAs, raw material, and

catalyst, thereby increasing the production cost.

1.5 Research motivation, objectives and scope

As previously mentioned, the use of sulphuric acid in biodiesel production

processes to pre-treat oil feedstock or to neutralize residual base catalyst in esterification

and transesterification processes poses the possibility of corrosion of process equipment.

This has been addressed in several publications (Gaupp., 1937; Matthys and Damalist,

2003; Kaul et al., 2007; Vargas, 2007). In 1937, Gaupp carried out corrosion experiments

to study the effects of vegetable oils such as soy bean oil, sesame oil, and palm oil, etc.,

on corrosion of various metals such as copper, brass, aluminium, and steel. This was done

by immersing these metals in oils for a period of 5 months. No severe corrosion and in

some cases, no corrosion was found. No detailed results with testing conditions or the

analysis of corrosion samples were provided. In 2003, Matthys and Damalist reported

corrosion problems in ester washing and methanol recovery processes and suggested the

use of carbon steel coated with sulphates as the best material of construction. Later, in

2007, Kaul et al. evaluated corrosion of biodiesel made from non-edible oils on diesel

8

engine parts by conducting the static immersion tests for 300 days. They reported no

corrosion from the biodiesel made from mahua and karanja on diesel engine parts (piston

metal) and severe corrosion from the biodiesel made from Salvadora seed oil due to the

presence of sulphur content in the oil. Vargas (2007) also reported no corrosion was

found in biodiesel made from vegetable oils.

To date, no further corrosion studies in the biodiesel production process have

been published in the literature, even though it is necessary for the development of cost

effective biodiesel production processes, especially processes that uses low quality

feedstock. This work, therefore, aimed to provide detailed studies on corrosion in acid-

catalyzed esterification biodiesel production processes. Specific objectives were: 1) to

investigate corrosion (type and degree) of process equipment in the acid-catalyzed

esterification process, 2) to understand corrosion mechanism in such processes, and 3) to

recommend effective corrosion prevention and control strategies (where corrosion was

found to be a serious problem). The outcome of this work is detailed information on

corrosion of carbon steel at eleven locations of the acid-catalyzed esterification process,

which is at present not available in the literature. This will be helpful in identifying

suitable material for designing the process equipment, which could minimize unplanned

shutdowns from corrosion problems and, at the same time, increase productivity and

profits.

In order to achieve the objectives, two tasks were carried out as briefly explained

below:

1. Electrochemical test for short term exposure

9

engine parts by conducting the static immersion tests for 300 days. They reported no

corrosion from the biodiesel made from mahua and karanja on diesel engine parts (piston

metal) and severe corrosion from the biodiesel made from Salvadora seed oil due to the

presence of sulphur content in the oil. Vargas (2007) also reported no corrosion was

found in biodiesel made from vegetable oils.

To date, no further corrosion studies in the biodiesel production process have

been published in the literature, even though it is necessary for the development of cost

effective biodiesel production processes, especially processes that uses low quality

feedstock. This work, therefore, aimed to provide detailed studies on corrosion in acid-

catalyzed esterification biodiesel production processes. Specific objectives were: 1) to

investigate corrosion (type and degree) of process equipment in the acid-catalyzed

esterification process, 2) to understand corrosion mechanism in such processes, and 3) to

recommend effective corrosion prevention and control strategies (where corrosion was

found to be a serious problem). The outcome of this work is detailed information on

corrosion of carbon steel at eleven locations of the acid-catalyzed esterification process,

which is at present not available in the literature. This will be helpful in identifying

suitable material for designing the process equipment, which could minimize unplanned

shutdowns from corrosion problems and, at the same time, increase productivity and

profits.

In order to achieve the objectives, two tasks were carried out as briefly explained

below:

1. Electrochemical test for short term exposure

9

The objectives of this task were to investigate corrosion of carbon steel 1018 (the

common material of construction) and recommend effective corrosion prevention and

control methods (if required) in the simulated environment of various esterification

process locations starting from raw materials storage to final product separation. A

number of corrosion experiments were carried out in a 100 ml three-electrode corrosion

cell using electrochemical techniques (i.e. Tafel plot and cyclic polarization) for

corrosion measurement and analysis.

2. Weight loss test for long term exposure

The objective of this task was to investigate corrosion of carbon steel specifically

in the environment of an esterification reactor over a long-term duration (up to 7 weeks).

This was to validate the results obtained from the short-term electrochemical tests. The

experiments were carried out in 2 litre corrosion immersion cells containing synthetic

esterification products using a weight loss technique for corrosion measurement and

analysis. During the tests, careful visual observations of specimens and solutions were

made.

This thesis consists of five chapters. Chapter 1 gives the introduction about

biodiesel, present scenarios of the global production, the research motivation, research

objectives and scope of the work. Chapter 2 provides in depth details on biodiesel

production processes and the literature review on corrosion in the related environment.

Chapter 3 explains the experimental setup, procedure, and data analysis. Chapter 4

provides the results and discussion of Tasks 1 and 2. Finally, chapter 5 draws the

conclusions of this work with recommendations for future work.

10

The objectives of this task were to investigate corrosion of carbon steel 1018 (the

common material of construction) and recommend effective corrosion prevention and

control methods (if required) in the simulated environment of various esterification

process locations starting from raw materials storage to final product separation. A

number of corrosion experiments were carried out in a 100 ml three-electrode corrosion

cell using electrochemical techniques (i.e. Tafel plot and cyclic polarization) for

corrosion measurement and analysis.

2. Weight loss test for long term exposure

The objective of this task was to investigate corrosion of carbon steel specifically

in the environment of an esterification reactor over a long-term duration (up to 7 weeks).

This was to validate the results obtained from the short-term electrochemical tests. The

experiments were carried out in 2 litre corrosion immersion cells containing synthetic

esterification products using a weight loss technique for corrosion measurement and

analysis. During the tests, careful visual observations of specimens and solutions were

made.

This thesis consists of five chapters. Chapter 1 gives the introduction about

biodiesel, present scenarios of the global production, the research motivation, research

objectives and scope of the work. Chapter 2 provides in depth details on biodiesel

production processes and the literature review on corrosion in the related environment.

Chapter 3 explains the experimental setup, procedure, and data analysis. Chapter 4

provides the results and discussion of Tasks 1 and 2. Finally, chapter 5 draws the

conclusions of this work with recommendations for future work.

10

2. FUNDAMENTALS AND LITERATURE REVIEW

This chapter covers the fundamental principles behind the biodiesel production

processes and explains the chemistry of the biodiesel reaction, various methods to

produce biodiesel, steps involved in the biodiesel production process, and its operating

parameters.

2.1 Biodiesel production

Biodiesel, in technical terms, is defined as mono-alkyl esters of fatty acids derived

from vegetable oils and animal fats. Various methods have been employed to produce

biodiesel from vegetable oils and fats since 1980 (Fangrui and Milford, 1999), i.e. direct

use and blending, micro emulsions, pyrolysis (thermal cracking), and transesterification

including acid-based, alkali-based, and enzyme-based transesterification. Of these,

transesterification is the most commonly used.

Transesterification is the current method of choice for biodiesel production. The

process is also known as alcoholysis-displacement, as it involves removal of an alcohol

from an ester by using another alcohol. It is the reaction of a vegetable oil or animal fat

with an alcohol in the presence of catalyst (acid or base) to produce fatty acid (mono)

alkyl esters or biodiesel as a product and glycerol as a by-product. It involves reaction

between triglycerides with lower alcohols, yielding free glycerol and fatty acid esters of

the respective alcohols. As shown in Reaction (2.1), one mole of triglycerides reacts with

three moles of methanol in the presence of catalyst and produces 3 moles of fatty acid

methyl esters and one molecule of glycerol. Although this reaction can also be carried out

11

2. FUNDAMENTALS AND LITERATURE REVIEW

This chapter covers the fundamental principles behind the biodiesel production

processes and explains the chemistry of the biodiesel reaction, various methods to

produce biodiesel, steps involved in the biodiesel production process, and its operating

parameters.

2.1 Biodiesel production

Biodiesel, in technical terms, is defined as mono-alkyl esters of fatty acids derived

from vegetable oils and animal fats. Various methods have been employed to produce

biodiesel from vegetable oils and fats since 1980 (Fangrui and Milford, 1999), i.e. direct

use and blending, micro emulsions, pyrolysis (thermal cracking), and transesterification

including acid-based, alkali-based, and enzyme-based transesterification. Of these,

transesterification is the most commonly used.

Transesterification is the current method of choice for biodiesel production. The

process is also known as alcoholysis-displacement, as it involves removal of an alcohol

from an ester by using another alcohol. It is the reaction of a vegetable oil or animal fat

with an alcohol in the presence of catalyst (acid or base) to produce fatty acid (mono)

alkyl esters or biodiesel as a product and glycerol as a by-product. It involves reaction

between triglycerides with lower alcohols, yielding free glycerol and fatty acid esters of

the respective alcohols. As shown in Reaction (2.1), one mole of triglycerides reacts with

three moles of methanol in the presence of catalyst and produces 3 moles of fatty acid

methyl esters and one molecule of glycerol. Although this reaction can also be carried out

11

with higher alcohols, methanol or ethanol is usually used due to their lower cost. The

higher alcohols are also sensitive to water, as discussed in many patents (Gerpen et al.,

2006), which causes problems with separation of esters, and to glycerol when an excess

amount is used to shift the equilibrium to product side. Reaction (2.1) can also be broken

down into three reactions (Reactions 2.2-2.4), i.e. production of fatty acid methyl ester

(biodiesel) and diglyceride, monoglyceride, and glycerol (Freedman et al., 1986;

Noureddini and Zhu, 1997). As the density of glycerol is higher than biodiesel, it settles

at the bottom and biodiesel remains in the upper phase.

0 0

I I I I CH2-0—C—R CH3 — 0 — C — R

0 0

I I I I CH — 0 — C — R' +3 CH3 — OH <

0

[Catalyst] > CH3 — 0 — C — R' + 0

I I I I

CH2 — OH

CH — OH

CH2 — 0 — C — R" CH3 — 0 — C R" CH2 — OH

(2.1)

Triacylglycerol Fatty acid methyl esters Glycerol (Triglyceride) Methanol (FAME)

[Catalyst] Triglyceride + ROH Diglyceride + R'COOR (2.2) < >

Diglyceride + ROH Monoglyceride + R"COOR (2.3) < >

Monoglyceride + ROH [catalyst] Glycerol + R' "COOR (2.4) < >

12

with higher alcohols, methanol or ethanol is usually used due to their lower cost. The

higher alcohols are also sensitive to water, as discussed in many patents (Gerpen et al.,

2006), which causes problems with separation of esters, and to glycerol when an excess

amount is used to shift the equilibrium to product side. Reaction (2.1) can also be broken

down into three reactions (Reactions 2.2-2.4), i.e. production of fatty acid methyl ester

(biodiesel) and diglyceride, monoglyceride, and glycerol (Freedman et al., 1986;

Noureddini and Zhu, 1997). As the density of glycerol is higher than biodiesel, it settles

at the bottom and biodiesel remains in the upper phase.

O O

CH2- O - C - R

O

CH3- O - C - R CH2- O H

O

C H - O - C - R ' + 3 C H 3 - O H < > C H 3 - 0 - C - R ' + C H - O H O O

CH2- O - C - R " CH3- O - C —R " CH2- O H

Triacylglycerol (Triglyceride) Methanol

Fatty acid methyl esters Glycerol (FAME)

Triglyceride + ROH < tCa,alys,] ) Diglyceride + R'COOR (2.2)

Diglyceride + ROH < 1Ca,alys'^ > Monoglyceride + R' 'COOR (2.3)

Monoglyceride + ROH < tCa,aly"1 > Glycerol + R"'COOR (2.4)

12

where, ROH is alcohol and R'COOR, R"COOR, and R"'COOR are ester products

(biodiesel compounds).

Transesterification can be categorized into three types depending on the type of

catalyst used, i.e. 1) alkali-based transesterification, 2) acid-based transesterification, and

3) enzyme-based transesterification. The first two types have attracted the greatest

attention worldwide and remain the focus of this dissertation. As for enzyme-catalyzed

transesterification, this reaction involves a much longer reaction time compared to the

other two methods. Due to the high cost of lipase enzymes, the commercial production of

biodiesel using this method is not viable (Knothe et al., 2004).

2.1.1 Alkali-based transesterification

Alkali-based transesterification is the mostly preferred method for biodiesel

production as it gives better yield under low temperature and pressure with a faster

reaction rate (Freedman et al., 1986). The corrosive nature of basic catalysts on industrial

equipment is also less so that carbon steel, the least expensive material, can be used for

construction of process equipment. On the other hand, the major disadvantage of this

method is sensitivity of basic catalysts to free fatty acids (FFAs) in feedstock material,

which induces soap formation instead of esters. The implication is that this method is

suitable for high quality, low FFA feedstocks such as virgin vegetable oil, which are

more expensive. In the case of low cost, lower-qualtiy feedstocks such as waste vegetable

oils and fats containing high levels of FFAs, oil pre-treatment, i.e. pre-esterification,

using acid catalyst is required before alkali-based transesterification can proceed. Sodium

hydroxide (NaOH), potassium hydroxide (KOH), or their alkoxides (RONa and ROK) is

13

where, ROH is alcohol and R'COOR, R"COOR, and R'"COOR are ester products

(biodiesel compounds).

Transesterification can be categorized into three types depending on the type of

catalyst used, i.e. 1) alkali-based transesterification, 2) acid-based transesterification, and

3) enzyme-based transesterification. The first two types have attracted the greatest

attention worldwide and remain the focus of this dissertation. As for enzyme-catalyzed

transesterification, this reaction involves a much longer reaction time compared to the

other two methods. Due to the high cost of lipase enzymes, the commercial production of

biodiesel using this method is not viable (Knothe et al., 2004).

2.1.1 Alkali-based transesterification

Alkali-based transesterification is the mostly preferred method for biodiesel

production as it gives better yield under low temperature and pressure with a faster

reaction rate (Freedman et al., 1986). The corrosive nature of basic catalysts on industrial

equipment is also less so that carbon steel, the least expensive material, can be used for

construction of process equipment. On the other hand, the major disadvantage of this

method is sensitivity of basic catalysts to free fatty acids (FFAs) in feedstock material,

which induces soap formation instead of esters. The implication is that this method is

suitable for high quality, low FFA feedstocks such as virgin vegetable oil, which are

more expensive. In the case of low cost, lower-qualtiy feedstocks such as waste vegetable

oils and fats containing high levels of FFAs, oil pre-treatment, i.e. pre-esterification,

using acid catalyst is required before alkali-based transesterification can proceed. Sodium

hydroxide (NaOH), potassium hydroxide (KOH), or their alkoxides (RONa and ROK) is

13

ABSTRACT

Recently, biodiesel has received worldwide attention due to its renewable,

biodegradable, and non-toxic nature. It can be produced from vegetable oils and animal

fats through a `transesterification reaction' using alcohol and a catalyst. The use of virgin

vegetable oil as a raw material to produce biodiesel could divert agriculture from food to

fuel production, which in turn raises food prices and leaves some parts of world

vulnerable to famine. The use of cheap raw materials, such as waste/used vegetable oils,

animal fats, and non-edible oils, could help avoid imbalance in food chains and enhance

the utilization of waste oils. The production process using these high free fatty acid

feedstocks involves sulphuric acid as a catalyst to convert oil and fatty acid to biodiesel,

typically methyl esters. This can be achieved through an acid transesterification process

or two step process wherein acid esterification is followed by an alkali transesterification

process. However, the use of acid in the processes may lead to the corrosion of process

equipment, as has been addressed in a number of publications. However, to date, no

detailed study on corrosion in this process has been carried out.

This work investigates the corrosion of carbon steel in the acid catalyzed

esterification process by carrying out electrochemical corrosion experiments using cyclic

polarization and Tafel plot techniques and weight loss immersion experiments. Eleven

process locations in the esterification process were simulated for corrosion testing, and

their susceptibility to corrosion was reported in terms of corrosion rate and pitting

tendency. Canola oil and oleic acid were used as oil feedstock and free fatty acid,

respectively. Results show that carbon steel is suitable for five of the eleven process

Recently, biodiesel has received worldwide attention due to its renewable,

biodegradable, and non-toxic nature. It can be produced from vegetable oils and animal

fats through a 'transesterification reaction' using alcohol and a catalyst. The use of virgin

vegetable oil as a raw material to produce biodiesel could divert agriculture from food to

fuel production, which in turn raises food prices and leaves some parts of world

vulnerable to famine. The use of cheap raw materials, such as waste/used vegetable oils,

animal fats, and non-edible oils, could help avoid imbalance in food chains and enhance

the utilization of waste oils. The production process using these high free fatty acid

feedstocks involves sulphuric acid as a catalyst to convert oil and fatty acid to biodiesel,

typically methyl esters. This can be achieved through an acid transesterification process

or two step process wherein acid esterification is followed by an alkali transesterification

process. However, the use of acid in the processes may lead to the corrosion of process

equipment, as has been addressed in a number of publications. However, to date, no

detailed study on corrosion in this process has been carried out.

This work investigates the corrosion of carbon steel in the acid catalyzed

esterification process by carrying out electrochemical corrosion experiments using cyclic

polarization and Tafel plot techniques and weight loss immersion experiments. Eleven

process locations in the esterification process were simulated for corrosion testing, and

their susceptibility to corrosion was reported in terms of corrosion rate and pitting

tendency. Canola oil and oleic acid were used as oil feedstock and free fatty acid,

respectively. Results show that carbon steel is suitable for five of the eleven process

used as the catalyst in the range of 0.5 - 1% by weight of oil. NaOH is less expensive and

offers a faster reaction rate than KOH (Vicente et al., 2004). The use of such catalysts can

have impacts on the process performance. For instance, when KOH is used, it makes

easier phase separation by increasing the density of the glycerol and also reduces the

amount of methyl ester dissolved in the glycerol phase. In the case of reactions involving

higher alcohols, the above-mentioned basic catalysts cannot be used, as their reactivity

with the alcohols decreases with increase in carbon chain length. Pure sodium or

potassium is recommended instead (Lang et al., 2001). A simplified process flow

diagram is shown in Figure 2.1.

2.1.2 Acid-based process

In acid-based process, sulphuric acid (H2SO4) is commonly used as catalyst due to

its cheaper cost than other acids like H3PO4 and HC1, and also because of its hygroscopic

nature for esterification of FFAs. This method is preferred only for oil feedstocks

containing high FFA content, which is very difficult to be converted by alkali catalysis

due to saponification — soap formation — by alkali with FFAs. In acid catalysis, the FFAs

are converted into esters by H2SO4 through esterification mechanisms and simultaneous

transesterification reaction is carried out. This reaction, however, takes place at a very

slow rate. In order to increase the reaction rate and reaction yield, a great amount of

alcohol is required, i.e. typically 10 to 40 times of triglyceride on a molar basis, and also

the reaction has to be carried out at higher temperature and pressure. As H2SO4 is

corrosive in nature, special care has to be taken in terms of material of construction for

industrial equipment. Stainless steel is preferred (Zhang et al.", 2003).

14

used as the catalyst in the range of 0.5 - 1% by weight of oil. NaOH is less expensive and

offers a faster reaction rate than KOH (Vicente et al., 2004). The use of such catalysts can

have impacts on the process performance. For instance, when KOH is used, it makes

easier phase separation by increasing the density of the glycerol and also reduces the

amount of methyl ester dissolved in the glycerol phase. In the case of reactions involving

higher alcohols, the above-mentioned basic catalysts cannot be used, as their reactivity

with the alcohols decreases with increase in carbon chain length. Pure sodium or

potassium is recommended instead (Lang et al., 2001). A simplified process flow

diagram is shown in Figure 2.1.

2.1.2 Acid-based process

In acid-based process, sulphuric acid (H2SO4) is commonly used as catalyst due to

its cheaper cost than other acids like H3PO4 and HC1, and also because of its hygroscopic

nature for esterification of FFAs. This method is preferred only for oil feedstocks

containing high FFA content, which is very difficult to be converted by alkali catalysis

due to saponification - soap formation - by alkali with FFAs. In acid catalysis, the FFAs

are converted into esters by H2SO4 through esterification mechanisms and simultaneous

transesterification reaction is carried out. This reaction, however, takes place at a very

slow rate. In order to increase the reaction rate and reaction yield, a great amount of

alcohol is required, i.e. typically 10 to 40 times of triglyceride on a molar basis, and also

the reaction has to be carried out at higher temperature and pressure. As H2SO4 is

corrosive in nature, special care has to be taken in terms of material of construction for

industrial equipment. Stainless steel is preferred (Zhang et al.a'b, 2003).

14

Biodiesel

Oil Acid

Jr Alcohol

Reactor Ester

Neutraliza ion & Separator (Transesterification) -► -► Alcohol Recovery

Catalyst

Glycerol Recovery

SaltAlcorol

1 Dryer

Water Wash

Wash Water

Figure 2.1: Process flow diagram of alkali-based transesterification process for biodiesel

production. (Redrawn from Gerpen et al., 2004)

15

Biodiesel

Acid Oil

Alcohol Ester

Catalyst

Salt Alcohol

Wash Water

Dryer

Water Wash

Separator

Glycerol Recovery

Neutralization & Alcohol Recovery

Reactor (T ransesteri fication)

Figure 2.1: Process flow diagram of alkali-based transesterification process for biodiesel

production. (Redrawn from Gerpen et al., 2004)

15

as such, this may be another disadvantage for commercialization of this method of

biodiesel production (Mittelbach and Claudia, 2004).

At present, the acid-based process is employed as a pre-treatment for the alkaline-

based transesterification process handling feedstocks with more than 5% FFAs (Knothe

et al., 2004). It converts FFAs into esters, which are then processed through alkali-based

transesterification, to produce biodiesel and glycerol. A simplified process flow diagram

of the acid-based esterification pre-treatment process is shown in Figure 2.2.

2.1.3 Post production processes

In addition to the transesterification in Section (2.1.1) and esterification in Section

(2.1.2) taking place in a reactor, post production processes play a vital role in product

quality and recovery aspects. The post production processes comprise phase separation of

ester (or biodiesel) and glycerol, methanol recovery, and ester washing and drying.

2.1.3.1 Phase separation

Phase separation of ester and glycerol is the first step of the product recovery in

biodiesel production processes. After completion of the transesterification reaction, the

resultant product is a mixture of esters (biodiesel), glycerol, alcohol (typically methanol),

catalyst, and a small amount of water. As a denser material than ester, glycerol can be

separated from the system by gravity. However, gravity separation is a time-consuming

process taking anywhere from one hour to a full day. The separation time also depends on

initial mixing and catalyst concentration. If vigorous mixing is applied until the end of

16

as such, this may be another disadvantage for commercialization of this method of

biodiesel production (Mittelbach and Claudia, 2004).

At present, the acid-based process is employed as a pre-treatment for the alkaline-

based transesterification process handling feedstocks with more than 5% FFAs (Knothe

et al., 2004). It converts FFAs into esters, which are then processed through alkali-based

transesterification, to produce biodiesel and glycerol. A simplified process flow diagram

of the acid-based esterification pre-treatment process is shown in Figure 2.2.

2.1.3 Post production processes

In addition to the transesterification in Section (2.1.1) and esterification in Section

(2.1.2) taking place in a reactor, post production processes play a vital role in product

quality and recovery aspects. The post production processes comprise phase separation of

ester (or biodiesel) and glycerol, methanol recovery, and ester washing and drying.

2.1.3.1 Phase separation

Phase separation of ester and glycerol is the first step of the product recovery in

biodiesel production processes. After completion of the transesterification reaction, the

resultant product is a mixture of esters (biodiesel), glycerol, alcohol (typically methanol),

catalyst, and a small amount of water. As a denser material than ester, glycerol can be

separated from the system by gravity. However, gravity separation is a time-consuming

process taking anywhere from one hour to a full day. The separation time also depends on

initial mixing and catalyst concentration. If vigorous mixing is applied until the end of

16

Oil + High FFA

Alcohol

Acid (H2SO4)

Reactor (Esterification)

Base

Neutralization & Separation

Water

Salt Alcohol

Dryer

Oil

—410. Ester

Figure 2.2: Process flow diagram of acid-based esterification pre-treatment process for

biodiesel production using high free-fatty acid feedstocks. (Redrawn from Gerpen et al.,

2004)

17

Base Oil + High FFA Water

Alcohol

Alcohol Salt

Dryer Neutralization &

Separation

Reactor (Esterification)

Figure 2.2: Process flow diagram of acid-based esterification pre-treatment process for

biodiesel production using high free-fatty acid feedstocks. (Redrawn from Gerpen et al.,

2004)

17

the reaction, glycerol will disperse as fine droplets into the mixture, making separation of

ester and glycerol difficult. To achieve effective separation, centrifuge and hydro—

cyclone are recommended (Gerpen et al., 2006).

2.1.3.2 Methanol recovery

As the transesterification reaction is reversible in nature, high amounts of

methanol are used to shift the reaction towards ester formation. This excess methanol can

be recovered via distillation processes such as conventional distillation, vacuum

distillation, and single stage flash processes. The residual methanol can then be recovered

in an ester water washing process. This saves raw material costs and avoids methanol

emission to the environment.

2.1.3.3 Ester Washing & Drying

The objective of this process is to remove any soap formed during the

transesterification reaction and to remove residual methanol. In the process, the mixture

of ester, water, and methanol is washed with warm water and then dried by vacuum driers

for large-scale purposes or otherwise by single-stage isothermal flash vaporization for

small-scale applications.

2.2 Mode of production operation

Biodiesel production based on either alkaline- or acid-based transesterification

can be operated in one of two modes: batch or continuous.

18

the reaction, glycerol will disperse as fine droplets into the mixture, making separation of

ester and glycerol difficult. To achieve effective separation, centrifuge and hydro-

cyclone are recommended (Gerpen et al., 2006).

2.1.3.2 Methanol recovery

As the transesterification reaction is reversible in nature, high amounts of

methanol are used to shift the reaction towards ester formation. This excess methanol can

be recovered via distillation processes such as conventional distillation, vacuum

distillation, and single stage flash processes. The residual methanol can then be recovered

in an ester water washing process. This saves raw material costs and avoids methanol

emission to the environment.

2.1.3.3 Ester Washing & Drying

The objective of this process is to remove any soap formed during the

transesterification reaction and to remove residual methanol. In the process, the mixture

of ester, water, and methanol is washed with warm water and then dried by vacuum driers

for large-scale purposes or otherwise by single-stage isothermal flash vaporization for

small-scale applications.

2.2 Mode of production operation

Biodiesel production based on either alkaline- or acid-based transesterification

can be operated in one of two modes: batch or continuous.

18

2.2.1 Batch Process

The batch process is the simplest mode of operation for biodiesel production on a

small scale using a batch stirred reactor. In many cases, this reactor is sealed or equipped

with a reflux condenser to avoid methanol wastage by vapourization. The range of

process parameters is listed in Table 2.1. Alcohol and oils are both sparingly soluble. In

order to promote a homogenous mixture of alcohol, oil, and catalyst for better yield and

fast reaction, thorough mixing is required. The expected yield ranges from 85 to 95%

with the reaction time ranging from 20 minutes to more than an hour. Higher reaction

temperature and higher alcohol-to-oil ratio can expedite the reaction rate.

In the batch process, oil is loaded into the reactor first, followed by catalyst and

alcohol, all of which are thoroughly mixed during the reaction time. After the completion

of reaction, the alcohol is removed from the system using an evaporator or flash unit and

glycerol is separated using centrifuge. The resulting esters — biodiesel — are washed with

warm water to remove residual methanol and are neutralized (by acid in the case of alkali

processes or by base in case of acid catalysis) and dried.

2.2.2 Continuous process

A continuous process is employed to produce biodiesel in large volumes using

continuous stirred tank reactors (CSTR). The expected yield is more than 98% with a

shorter reaction time (as low as 6-10 minutes). In this system, the reaction mixture moves

through the reactor in a continuous plug fashion and mixing is carried out in the radial

rather than axial direction, which reduces the reaction time. In this system, glycerol is

separated between the stages using decanters.

19

2.2.1 Batch Process

The batch process is the simplest mode of operation for biodiesel production on a

small scale using a batch stirred reactor. In many cases, this reactor is sealed or equipped

with a reflux condenser to avoid methanol wastage by vapourization. The range of

process parameters is listed in Table 2.1. Alcohol and oils are both sparingly soluble. In

order to promote a homogenous mixture of alcohol, oil, and catalyst for better yield and

fast reaction, thorough mixing is required. The expected yield ranges from 85 to 95%

with the reaction time ranging from 20 minutes to more than an hour. Higher reaction

temperature and higher alcohol-to-oil ratio can expedite the reaction rate.

In the batch process, oil is loaded into the reactor first, followed by catalyst and

alcohol, all of which are thoroughly mixed during the reaction time. After the completion

of reaction, the alcohol is removed from the system using an evaporator or flash unit and

glycerol is separated using centrifuge. The resulting esters - biodiesel - are washed with

warm water to remove residual methanol and are neutralized (by acid in the case of alkali

processes or by base in case of acid catalysis) and dried.

2.2.2 Continuous process

A continuous process is employed to produce biodiesel in large volumes using

continuous stirred tank reactors (CSTR). The expected yield is more than 98% with a

shorter reaction time (as low as 6-10 minutes). In this system, the reaction mixture moves

through the reactor in a continuous plug fashion and mixing is carried out in the radial

rather than axial direction, which reduces the reaction time. In this system, glycerol is

separated between the stages using decanters.

19

2.3 Process parameters

A number operating parameters significantly influence the biodiesel production

process in many aspects, including process design, material of construction, reaction rate,

product quality and yield, and production cost. These parameters are temperature,

pressure, alcohol-to-oil (triglyceride — TG) ratio, alcohol and oil purity level, catalyst

type and concentration, and mixing intensity. A summary of parameter ranges is given in

Table 2.1.

2.3.1 Temperature and pressure

Reaction conditions such as temperature and pressure have a strong influence on

the reaction rate as well as yield of the product. Freedman et al., (1986) carried out the

reaction at various temperatures ranging from 77-117°C and reported significant rate

change for every 10°C temperature rise. This reaction is normally carried out at a

temperature of 60-70°C, close to boiling point of methanol at atmospheric pressure. If

temperature is increased above the boiling point of methanol, the pressure has to be

increased in order to keep the alcohol in liquid form. The advantage of high pressure

reaction is the elimination of the need for pre-treatment processes for feedstocks having

high amounts of FFAs and for glycerol purification processes, as it yields high purity

glycerol. However, due to high process costs and safety considerations in dealing with

high pressure vessels, it is not viable

20

2.3 Process parameters

A number operating parameters significantly influence the biodiesel production

process in many aspects, including process design, material of construction, reaction rate,

product quality and yield, and production cost. These parameters are temperature,

pressure, alcohol-to-oil (triglyceride - TG) ratio, alcohol and oil purity level, catalyst

type and concentration, and mixing intensity. A summary of parameter ranges is given in

Table 2.1.

2.3.1 Temperature and pressure

Reaction conditions such as temperature and pressure have a strong influence on

the reaction rate as well as yield of the product. Freedman et al., (1986) carried out the

reaction at various temperatures ranging from 77-117°C and reported significant rate

change for every 10°C temperature rise. This reaction is normally carried out at a

temperature of 60-70°C, close to boiling point of methanol at atmospheric pressure. If

temperature is increased above the boiling point of methanol, the pressure has to be

increased in order to keep the alcohol in liquid form. The advantage of high pressure

reaction is the elimination of the need for pre-treatment processes for feedstocks having

high amounts of FFAs and for glycerol purification processes, as it yields high purity

glycerol. However, due to high process costs and safety considerations in dealing with

high pressure vessels, it is not viable

20

Table 2.1: Range of process parameters (Boocock et al., 1996; Karaosmanoglu et al.,

1996; Vicente et al., 1998; Lang et al., 2001; Antolin et al.,2002; Zhanga et al., 2003;

Vicente et al.,2004; Harding et al., 2007; Sharma et al., 2008; Junhua and Lifeng, 2008)

Parameters Range

Temperature 20-110°C

Pressure 1 — 4 atm

Methanol: Oil ratio

• Acid Process

• Alkali Process

10:1 to 30:1

4:1 to 20:1

Catalyst

• Sulphuric acid (Acid Catalysis

esterification)

• Sodium hydroxide or Potassium

hydroxide (Alkali Catalysis)

• Sodium Methoxide or Potassium

Methoxide (Alkali Catalysis)

0.3 — 1.5% by wt of oil

0.3 — 1.5% by wt of oil

0.3-0.5 % by wt of oil

Reaction time

• Alkali Process

• Acid esterification

10min — 8h (Low temp--> longer time)

30 -- 120 min

21

Table 2.1: Range of process parameters (Boocock et al., 1996; Karaosmanoglu et al.,

1996; Vicente et al., 1998; Lang et al., 2001; Antolin et al.,2002; Zhanga et al., 2003;

Vicente et al.,2004; Harding et al., 2007; Sharma et al., 2008; Junhua and Lifeng, 2008)

Parameters Range

Temperature 20—110°C

Pressure 1 ~ 4 atm

Methanol: Oil ratio

• Acid Process

• Alkali Process

10:1 to 30:1

4:1 to 20:1

Catalyst

• Sulphuric acid (Acid Catalysis

esterification)

• Sodium hydroxide or Potassium

hydroxide (Alkali Catalysis)

• Sodium Methoxide or Potassium

Methoxide (Alkali Catalysis)

0.3 ~ 1.5% by wt of oil

0.3 ~ 1.5% by wt of oil

0.3-0.5 % by wt of oil

Reaction time

• Alkali Process

• Acid esterification

lOmin ~ 8h (Low temp-> longer time)

30 ~ 120 min

21

for commercial production. The reaction can even be achieved at room temperature

provided enough time is available to complete the reaction, which may take 7-8 hours.

Through supercritical properties of methanol, Saka and Kusdiana (2001) achieved

a reaction time as low as 240 seconds by increasing temperature and pressure to 350-

400°C and 45-65 MPa, respectively, eliminating the need for catalyst.

2.3.2 Alcohol-to-oil ratio and alcohol and oil purity

This is one of the most important parameters affecting the yield of the reaction.

The stoichiometric requirement of alcohol concentration is 3 moles for the reaction. In

order to avoid reversible reaction and to increase reaction rate, a higher molar ratio is

used. The study by Freedman et al. (1986) concluded that alcohol-to-oil ratios of 6:1 and

30:1 are required for alkali- and acid-based reactions, respectively, to achieve higher ester

conversions (i.e. 93-98%). Despite its greater yields, using a high ratio of alcohol-to-oil

(>15:1) makes post-production processes, such as phase separation (ester/glycerol) and

ester washing, difficult and costly due to the large amounts of methanol used. The purity

of feedstocks is also of importance to the efficiency of biodiesel production. FFA levels

of less than 2% for alkali-based processes and the water content of less than 0.5% are

required to ensure the quality of the biodiesel.

2.3.3 Catalyst type and concentration

In terms of catalysts, generally, 1% wt. sulphuric acid (H2SO4) is used for acid-

based processes while 1% wt. sodium or potassium hydroxide (NaOH or KOH) or 0.3-

0.5% wt. alkoxides are used for alkali-based processes. Though hydrochloric acid (HCl),

22

for commercial production. The reaction can even be achieved at room temperature

provided enough time is available to complete the reaction, which may take 7-8 hours.

Through supercritical properties of methanol, Saka and Kusdiana (2001) achieved

a reaction time as low as 240 seconds by increasing temperature and pressure to 350-

400°C and 45-65 MPa, respectively, eliminating the need for catalyst.

2.3.2 Alcohol-to-oil ratio and alcohol and oil purity

This is one of the most important parameters affecting the yield of the reaction.

The stoichiometric requirement of alcohol concentration is 3 moles for the reaction. In

order to avoid reversible reaction and to increase reaction rate, a higher molar ratio is

used. The study by Freedman et al. (1986) concluded that alcohol-to-oil ratios of 6:1 and

30:1 are required for alkali- and acid-based reactions, respectively, to achieve higher ester

conversions (i.e. 93-98%). Despite its greater yields, using a high ratio of alcohol-to-oil

(>15:1) makes post-production processes, such as phase separation (ester/glycerol) and

ester washing, difficult and costly due to the large amounts of methanol used. The purity

of feedstocks is also of importance to the efficiency of biodiesel production. FFA levels

of less than 2% for alkali-based processes and the water content of less than 0.5% are

required to ensure the quality of the biodiesel.

2.3.3 Catalyst type and concentration

In terms of catalysts, generally, 1% wt. sulphuric acid (H2SO4) is used for acid-

based processes while 1% wt. sodium or potassium hydroxide (NaOH or KOH) or 0.3-

0.5% wt. alkoxides are used for alkali-based processes. Though hydrochloric acid (HC1),

22

phosphoric acid, and organo-sulphonic acid are used for acid-based reactions, H2SO4 is

preferred because of its hygroscopic nature and cost effectiveness. In general, alkali-

catalyzed reaction is favoured worldwide, as it has shorter reaction time and higher yield

with better quality. Apart from these conventional catalysts, studies on the use of

heterogeneous catalysts such as KF/Eu2O3 (Sun et al., 2008), KF/A120 3 (Bo et al., 2007),

Zeolite Y (Brito et al., 2007) have been undertaken in order to avoid the problems caused

at the product separation stage due to water formation by conventional catalysts.

2.3.4 Reaction time and mixing intensity

In the transesterification reaction, the reactants initially form a two-phase liquid

system. To generate homogeneous mixture of reactants, thorough mixing is required. As

this reaction is diffusion-controlled and poor diffusion between these phases results in a

slow rate, vigorous mixing must be provided until the formation of esters. By increasing

the reaction time, the ester conversion can be increased. This reaction usually happens

faster in the initial period (1-5 min) with approximately 80% conversion, and by

increasing the reaction time to 1 hour, 93-98% conversion can be achieved under the

conditions of 6:1 methanol:oil ratio, 0.5% sodium methoxide catalyst, and 60°C, as

reported by Freedman et al. (1984).

2.4. Corrosion in organic solvent and sulphuric acid systems

Corrosion of metals from organic solvents has gained greater attention in the

chemical and petrochemical industries. The failure of materials due in aggressive organic

solvent environments, deterioration of mechanical properties of metals and unwanted

23

phosphoric acid, and organo-sulphonic acid are used for acid-based reactions, H2SO4 is

preferred because of its hygroscopic nature and cost effectiveness. In general, alkali-

catalyzed reaction is favoured worldwide, as it has shorter reaction time and higher yield

with better quality. Apart from these conventional catalysts, studies on the use of

heterogeneous catalysts such as KF/EU2O3 (Sun et al., 2008), KF/AI2O3 (Bo et al., 2007),

Zeolite Y (Brito et al., 2007) have been undertaken in order to avoid the problems caused

at the product separation stage due to water formation by conventional catalysts.

2.3.4 Reaction time and mixing intensity

In the transesterification reaction, the reactants initially form a two-phase liquid

system. To generate homogeneous mixture of reactants, thorough mixing is required. As

this reaction is diffusion-controlled and poor diffusion between these phases results in a

slow rate, vigorous mixing must be provided until the formation of esters. By increasing

the reaction time, the ester conversion can be increased. This reaction usually happens

faster in the initial period (1-5 min) with approximately 80% conversion, and by

increasing the reaction time to 1 hour, 93-98% conversion can be achieved under the

conditions of 6:1 methanokoil ratio, 0.5% sodium methoxide catalyst, and 60°C, as

reported by Freedman et al. (1984).

2.4. Corrosion in organic solvent and sulphuric acid systems

Corrosion of metals from organic solvents has gained greater attention in the

chemical and petrochemical industries. The failure of materials due in aggressive organic

solvent environments, deterioration of mechanical properties of metals and unwanted

23

locations. The presence of a small amount of water in methanolic solution contributes to

non- or low-corrosion rates in the methanol recovery flow line, while the presence of free

fatty acid contributes to non- or low-corrosion rates in the storage tanks of oil feedstock,

the esterification reactor, the glycerol feed to the stripping column, and the end-product

recovery flow line. The other six process locations made of carbon steel are corrodible

and require the application of effective corrosion control methods. These locations are the

methanol storage tank, sulphuric storage tank, methanol and sulphuric acid storage tank,

fresh and recovery methanol and acid mixing tank, inlet flow line to the vacuum

distillation column, and vacuum distillation column. The vacuum distillation column and

its inlet flow line are the most susceptible to corrosion due to the elevated temperature

and the presence of methanol, sulphuric acid, glycerol, and water. The application of

nitrogen blanketing to remove dissolved oxygen is effective for corrosion control in the

methanol storage tank, and the use of corrosion resistant materials, i.e., stainless steel and

fibreglass reinforced plastic, is effective for the rest of the corrosive process locations.

ii

locations. The presence of a small amount of water in methanolic solution contributes to

non- or low-corrosion rates in the methanol recovery flow line, while the presence of free

fatty acid contributes to non- or low-corrosion rates in the storage tanks of oil feedstock,

the esterification reactor, the glycerol feed to the stripping column, and the end-product

recovery flow line. The other six process locations made of carbon steel are corrodible

and require the application of effective corrosion control methods. These locations are the

methanol storage tank, sulphuric storage tank, methanol and sulphuric acid storage tank,

fresh and recovery methanol and acid mixing tank, inlet flow line to the vacuum

distillation column, and vacuum distillation column. The vacuum distillation column and

its inlet flow line are the most susceptible to corrosion due to the elevated temperature

and the presence of methanol, sulphuric acid, glycerol, and water. The application of

nitrogen blanketing to remove dissolved oxygen is effective for corrosion control in the

methanol storage tank, and the use of corrosion resistant materials, i.e., stainless steel and

fibreglass reinforced plastic, is effective for the rest of the corrosive process locations.

ii

Table 2.2 Classification of Organic solvents (Heitz and Kyriazls, 1978)

Protic — Aprotic systems Alcohols (ROH), Carboxylic acids (RCOOH), and

amines (R-NH2) are protic solvents

Hydrocarbons(R-H), Esters(RCOOR) and

halogenated hydrocarbons (R-X) are aprotic

solvents

One-Component/Multi-

Component Systems

ROH, RCOOH, R-X are one component systems.

With the presence of H2O, 0 2, inorganic acids and

halogenides form multi-component systems

One Phase/ Multi-Phase Systems One phase can be a vapour (RH, RX), a liquid, or a

solid (coatings, polymer). Multi-phase could mean

the presence of more than 2 phases.

24

Table 2.2 Classification of Organic solvents (Heitz and Kyriazls, 1978)

Protic - Aprotic systems Alcohols (ROH), Carboxylic acids (RCOOH), and

amines (R-NH2) are protic solvents

Hydrocarbons(R-H), Esters(RCOOR) and

halogenated hydrocarbons (R-X) are aprotic

solvents

One-Component/Multi-

Component Systems

ROH, RCOOH, R-X are one component systems.

With the presence of H2O, O2, inorganic acids and

halogenides form multi-component systems

One Phase/ Multi-Phase Systems One phase can be a vapour (RH, RX), a liquid, or a

solid (coatings, polymer). Multi-phase could mean

the presence of more than 2 phases.

24

changes and discoloration of solvents require detailed study. However, the complete

corrosion mechanism of metals in organic solvents is yet to be understood. As tabulated

in Table. 2.2, Heitz and Kyriazls (1978) classified the types of organic solvents in order

to study their corrosive nature. They concluded that the protic type of organic solvents

such as alcohols, carboxylic acids, and amines, in either one component or multi-

component systems, accelerate the corrosion of metals. As far as this work is concerned,

it falls in the category of multi-component protic systems, i.e, the mixture of methanol

and sulphuric acid. The following sections discuss previous works and their findings on

the corrosion of metals in methanol and mixed methanol and acid systems. Additionally,

it also provides a review of the corrosion studies done with fatty acid components as

listed in Table. 2.3.

2.4J Corrosion in mixed methanol and sulphuric acid systems

The study of corrosion mechanisms in methanol and methanol—acid environments

is scarce, and they are not completely understood. Farina et al. (1978) studied the

electrochemical behaviour of iron in methanol solutions with different amounts of water

content in order to identify the effect of water on passivation. They concluded that water

content is the deciding factor for passivation and stability of the passive state. They

observed easier passivation states occur with higher water content. In 1981, Belucci et al.,

carried out the same study for Ni and Mo electrodes in neutral methanol and methanol

water environments and observed the passivation state in a methanol water system. They

observed that Ni is vulnerable to high corrosion and dense pitting at the end of anodic

polarization. In the case of Mo, they observed no significant effect due to water or

25

changes and discoloration of solvents require detailed study. However, the complete

corrosion mechanism of metals in organic solvents is yet to be understood. As tabulated

in Table. 2.2, Heitz and Kyriazls (1978) classified the types of organic solvents in order

to study their corrosive nature. They concluded that the protic type of organic solvents

such as alcohols, carboxylic acids, and amines, in either one component or multi-

component systems, accelerate the corrosion of metals. As far as this work is concerned,

it falls in the category of multi-component protic systems, i.e, the mixture of methanol

and sulphuric acid. The following sections discuss previous works and their findings on

the corrosion of metals in methanol and mixed methanol and acid systems. Additionally,

it also provides a review of the corrosion studies done with fatty acid components as

listed in Table. 2.3.

2.4.1 Corrosion in mixed methanol and sulphuric acid systems

The study of corrosion mechanisms in methanol and methanol-acid environments

is scarce, and they are not completely understood. Farina et al. (1978) studied the

electrochemical behaviour of iron in methanol solutions with different amounts of water

content in order to identify the effect of water on passivation. They concluded that water

content is the deciding factor for passivation and stability of the passive state. They

observed easier passivation states occur with higher water content. In 1981, Belucci et al.,

carried out the same study for Ni and Mo electrodes in neutral methanol and methanol

water environments and observed the passivation state in a methanol water system. They

observed that Ni is vulnerable to high corrosion and dense pitting at the end of anodic

polarization. In the case of Mo, they observed no significant effect due to water or

25

chloride or acid concentrations in methanolic environments. Later, in 1995, Brossia et al

studied the corrosion behaviour of iron in methanol and varied the concentrations of

water and sulphuric acid. They postulated an acid corrosion inhibition mechanism based

on the proton hopping mechanism due to preferential protonation of water and methanol.

The polarization measurements of iron in anhydrous methanol solution with various

concentrations of FeC13 studied by Kawai et al. (1995) show that the corrosion rate of

iron increases with increase in FeC13 concentration, and they also observed a decrease in

anodic current density due to formation of Fe3O4 by decomposition of ferrous methoxide.

Recent studies by Banas et al.(2004) and Banas and Banas, 2009 on various metals such

as Cu, Zn, Al, Fe, Si, and Ti show that at low anodic over voltage, a relatively stable

passive layer is formed on the metal surface, which decomposes at higher anodic over

voltage, leading to higher corrosion in anhydrous methanol solutions. A similar effect

was reported by the authors in methanol and acid systems, as well.

2.4.2 Corrosion in the presence of fatty acid components

In spite of limited corrosion study done on fatty acid components, the inhibition

performance of fatty acid components is quite interesting due to their inherent properties

such as high viscosity, steric hindrance, low conductivity, and long carbon chain length

as reported by Heitz and Kyriazls, (1978). Later, in 1998, Luo et al. (1998) carried out

inhibition studies of oleate component in mild steel systems in sulphuric acid medium.

They observed good inhibition efficiency at pH levels varying from 1 to 3. They

concluded that the molecules of soluble oleic acid chemisorbed on mild steel, which

increased the hydrophobicity of the steel-solution interface and significantly inhibited

26

chloride or acid concentrations in methanolic environments. Later, in 1995, Brossia et al

studied the corrosion behaviour of iron in methanol and varied the concentrations of

water and sulphuric acid. They postulated an acid corrosion inhibition mechanism based

on the proton hopping mechanism due to preferential protonation of water and methanol.

The polarization measurements of iron in anhydrous methanol solution with various

concentrations of FeCh studied by Kawai et al. (1995) show that the corrosion rate of

iron increases with increase in FeCl3 concentration, and they also observed a decrease in

anodic current density due to formation of Fe3C>4 by decomposition of ferrous methoxide.

Recent studies by Banas et al.(2004) and Banas and Banas, 2009 on various metals such

as Cu, Zn, Al, Fe, Si, and Ti show that at low anodic over voltage, a relatively stable

passive layer is formed on the metal surface, which decomposes at higher anodic over

voltage, leading to higher corrosion in anhydrous methanol solutions. A similar effect

was reported by the authors in methanol and acid systems, as well.

2.4.2 Corrosion in the presence of fatty acid components

In spite of limited corrosion study done on fatty acid components, the inhibition

performance of fatty acid components is quite interesting due to their inherent properties

such as high viscosity, steric hindrance, low conductivity, and long carbon chain length

as reported by Heitz and Kyriazls, (1978). Later, in 1998, Luo et al. (1998) carried out

inhibition studies of oleate component in mild steel systems in sulphuric acid medium.

They observed good inhibition efficiency at pH levels varying from 1 to 3. They

concluded that the molecules of soluble oleic acid chemisorbed on mild steel, which

increased the hydrophobicity of the steel-solution interface and significantly inhibited

26

corrosion as a blocking barrier. They also observed that the increase in pH value

increased the inhibition efficiency, as the dissociation of organic acid due to the rise in

pH increased the activity of organic anions. Later, in 2002, a study by Quraishi et al.

(2002) on the inhibition of various fatty acids of C11 to C18 components on cold rolled

mild steel strips revealed the excellent corrosion inhibition performance of the fatty acid

thiosemicarbazide in acidic medium. Corrosion mechanisms were explained based on

adsorption mechanisms. Furthermore, the inhibition study of fatty acid components of

oleate and linoleate on carbon steel in HC1 medium by Martinez-Palou et al. (2004)

observed good inhibition efficiency and concluded that the long chain fatty acid

components offer excellent corrosion inhibition particularly in acid corrosive media.

27

corrosion as a blocking barrier. They also observed that the increase in pH value

increased the inhibition efficiency, as the dissociation of organic acid due to the rise in

pH increased the activity of organic anions. Later, in 2002, a study by Quraishi et al.

(2002) on the inhibition of various fatty acids of Cn to Cis components on cold rolled

mild steel strips revealed the excellent corrosion inhibition performance of the fatty acid

thiosemicarbazide in acidic medium. Corrosion mechanisms were explained based on

adsorption mechanisms. Furthermore, the inhibition study of fatty acid components of

oleate and linoleate on carbon steel in HC1 medium by Martinez-Palou et al. (2004)

observed good inhibition efficiency and concluded that the long chain fatty acid

components offer excellent corrosion inhibition particularly in acid corrosive media.

27

Table: 2.3: Previous works and their findings on corrosion in methanol and sulphuric

acid and fatty acid components

Reference System Material Findings

Farina et al. (1978)

1M OH + 0. CH3

LiC1004 + 0.5 to 1%

H2

Armco iron

Water content is the main factor for passivation and stability of passive state

Bellucci et al. (1980)

CH3OH + 0.1 M LiC104CH3OH + 0.1 M LiC104 + H2O (0.05%, 0.5%, 1.0%) CH3OH + 0.1 M LiC104 + 1 0(3 M H2SO4 +1% H2O

Ni Mo ,

Ni — Vulnerable to high corrosion in methanolic environment Mo — Effect of acidity, water content, and chloride concentrations is negligible.

Brossia et al. (1995)

CH3OH, H2SO4(0 to 1 mM), H2O (0.05 and 0.5 wt% )

99.985% Pure iron

Increase in corrosion by addition of 1mM of H2SO4, Inhibition by Water addition due to decrease in mobility of fr ions (proton hopping mechanism)

Kawai et al. (1995)

CH3OH, FeCl3(10"4 to 0.1M)

99.99% Iron

Increase in corrosion with increase in FeCl3, Decrease in anodic current density due to Fe3O4formed by decomposition of ferrous methoxide

Banas et al. (2004)

CH3OH + LiC1 CH3OH + 0.1M HCl + LiC1

Boron doped p-Si single crystals wafers

. Higher anodic over voltage accelerates the anodic dissolution process

Banas and Banas (2009)

CH3OH + 0.1M LiC104 + LiC1 (0.1M, 0.01M, 0.001M)

Cu, Zn, Fe, Al, and Ti

At low anodic over voltage, a relatively stable passive layer forms on the surface. At higher anodic over voltage, protective film decomposes and accelerates the corrosion

Luo et al. (1998)

Sodium Dodecyl Benzene Sulfonate and Sodium Oleate

Mild steel

Good corrosion inhibition efficiency in acidic medium Inhibition mechanism follows the adsorption mechanism

Quraishi et al. (2002)

Fatty acids of C11— C18 components

Cold rolled mild steel strips

Fatty acid thiosemicarbazide offers excellent corrosion inhibition in both HCl and H2SO4system Corrosion inhibition mechanism is explained based on the adsorption mechanism

Martinez- Palou et al. (2004)

Tall oil (Oleic acid— 51%, Linoleic acid— 45%, Other fatty acids— 4%

Carbon steel 1018

Excellent corrosion protection in 1M HC1 solution Long chain fatty acid components act as corrosion inhibitors especially for acid corrosion

28

Table: 2.3: Previous works and their findings on corrosion in methanol and sulphuric

acid and fatty acid components

Reference System Material Findings

Farina et al. (1978)

CH3OH + O.IM LiC104 + 0.5 to 1% H2O

Armco iron

Water content is the main factor for passivation and stability of passive state

Bellucci et al. (1980)

CH3OH + O.I M LiC104

CH3OH + O.I M UCIO4 + H2O (0.05%, 0.5%, 1.0%) CHJOH + O.l M UCIO4+ 10"3M H2SO4 +1% H20

Ni, Mo

Ni - Vulnerable to high corrosion in methanolic environment Mo - Effect of acidity, water content, and chloride concentrations is negligible.

Brossia et al. (1995)

CH3OH, H2SO4

(0 to 1 mM), H20 (0.05 and 0.5 wt% )

99.985% Pure iron

Increase in corrosion by addition of ImM of H2S04, Inhibition by Water addition due to decrease in mobility of H+ ions (proton hopping mechanism)

Kawai et al. (1995)

CH3OH, FeCl3

(10"4 to 0.1M) 99.99% Iron

Increase in corrosion with increase in FeCl3, Decrease in anodic current density due to Fe304

formed by decomposition of ferrous methoxide

Banas et al. (2004)

CH3OH + LiCl CH3OH + O.IMHCI + LiCl

Boron doped p-Si single crystals wafers

Higher anodic over voltage accelerates the anodic dissolution process

Banas and Banas (2009)

CH3OH + O.IM LiC104 + LiCl (0.1M, 0.01M, 0.001M)

Cu, Zn, Fe, Al, and Ti

At low anodic over voltage, a relatively stable passive layer forms on the surface. At higher anodic over voltage, protective film decomposes and accelerates the corrosion

Luo et al. (1998)

Sodium Dodecyl Benzene Sulfonate and Sodium Oleate

Mild steel

Good corrosion inhibition efficiency in acidic medium Inhibition mechanism follows the adsorption mechanism

Quraishi et al. (2002)

Fatty acids of CU-C)8 components

Cold rolled mild steel strips

Fatty acid thiosemicarbazide offers excellent corrosion inhibition in both HC1 and H2S04

system Corrosion inhibition mechanism is explained based on the adsorption mechanism

Martinez-Palou et al. (2004)

Tall oil (Oleic acid-51%, Linoleic acid-45%, Other fatty acids- 4%

Carbon steel 1018

Excellent corrosion protection in 1M HC1 solution Long chain fatty acid components act as corrosion inhibitors especially for acid corrosion

28

3. CORROSION EXPERIMENTS

This chapter describes in detail the corrosion experiments undertaken in this

study, including descriptions of the specimen preparation, synthesis of tested solutions,

experimental setup, experimental procedures, and methods of data analysis. A series of

corrosion experiments was carried out in two phases: short-term exposure experiments

using electrochemical analysis technique and long-term exposure experiments using

weight loss immersion analysis technique. The electrochemical experiments utilize an

external power source to apply a range of voltages to force an imbalance between the

numbers of the anodic and cathodic sites, causing the electrons to flow in an attempt to

re-establish charge neutrality. The electrons flowing to or from the electrode are

electronically counted at each applied voltage level, yielding a data set consisting of the

voltage and its corresponding electric current and ultimately corrosion rate (Tait, 1994).

The weight loss experiments are commonly referred to as immersion tests of

material. They were used for determining corrosion rates and revealing corrosion

behaviour under long-term exposure of material to the tested environment. A pre-

weighed specimen was placed in the tested solution under given operating conditions.

After a certain interval of time, the specimen was removed, cleaned, and weighed to

calculate the weight loss, which can be translated into the corrosion rate.

3.1 Specimen preparation

Three types of specimens, carbon steel (CS1018), stainless steel 304 (SS304), and

stainless steel 316 (S5316) were used in this work. CS1018 was used for all

29

3. CORROSION EXPERIMENTS

This chapter describes in detail the corrosion experiments undertaken in this

study, including descriptions of the specimen preparation, synthesis of tested solutions,

experimental setup, experimental procedures, and methods of data analysis. A series of

corrosion experiments was carried out in two phases: short-term exposure experiments

using electrochemical analysis technique and long-term exposure experiments using

weight loss immersion analysis technique. The electrochemical experiments utilize an

external power source to apply a range of voltages to force an imbalance between the

numbers of the anodic and cathodic sites, causing the electrons to flow in an attempt to

re-establish charge neutrality. The electrons flowing to or from the electrode are

electronically counted at each applied voltage level, yielding a data set consisting of the

voltage and its corresponding electric current and ultimately corrosion rate (Tait, 1994).

The weight loss experiments are commonly referred to as immersion tests of

material. They were used for determining corrosion rates and revealing corrosion

behaviour under long-term exposure of material to the tested environment. A pre-

weighed specimen was placed in the tested solution under given operating conditions.

After a certain interval of time, the specimen was removed, cleaned, and weighed to

calculate the weight loss, which can be translated into the corrosion rate.

3.1 Specimen preparation

Three types of specimens, carbon steel (CS1018), stainless steel 304 (SS304), and

stainless steel 316 (SS316) were used in this work. CS1018 was used for all

29

electrochemical and weight loss tests, while SS304 and 316 were used as corrosion

resistant materials where CS1018 was susceptible to high corrosion. The compositions of

these materials are given in Table. 3.1 and the sketches of specimens are shown in Figure

3.1.

The specimens used in the electrochemical tests were cylindrical in shape with

height, outside diameter, and center hole diameter of 0.80, 1.20 and 0.60 cm,

respectively, while those used in the weight loss tests were flat and rectangular in shape

with dimensions of 2.50 cm high, 2.50 cm wide, and 0.30 cm thick. Prior to tests, all

specimens were prepared by wet grinding with up to 600 grit silicon carbide papers and

deionized water, then degreasing with high purity methanol, and drying with hot air in

accordance with the ASTM standard G1-90 (1999). The specimens were kept in a

desiccator until used.

3.2. Solution preparation

To simulate the environment of process locations, the tested solutions were

prepared as per the compositions found during process operation. The tested solutions for

most process locations, except for the esterification reactor, were synthesized by simply

mixing all the chemical ingredients with pre-determined amounts to achieve service

compositions. The solutions in the esterification reactor were synthesized by carrying out

esterification reactions in a stirred reactor. A schematic diagram of the bench-scale

esterification reactor setup is shown in Figure 3.2. Reactants (i.e. canola oil as the virgin

oil, oleic acid as the free-fatty acid, methanol as the alcohol, and sulphuric acid as the

catalyst) with given concentrations were added to the reactor and well mixed at 65°C.

30

electrochemical and weight loss tests, while SS304 and 316 were used as corrosion

resistant materials where CS1018 was susceptible to high corrosion. The compositions of

these materials are given in Table. 3.1 and the sketches of specimens are shown in Figure

3.1.

The specimens used in the electrochemical tests were cylindrical in shape with

height, outside diameter, and center hole diameter of 0.80, 1.20 and 0.60 cm,

respectively, while those used in the weight loss tests were flat and rectangular in shape

with dimensions of 2.50 cm high, 2.50 cm wide, and 0.30 cm thick. Prior to tests, all

specimens were prepared by wet grinding with up to 600 grit silicon carbide papers and

deionized water, then degreasing with high purity methanol, and drying with hot air in

accordance with the ASTM standard Gl-90 (1999). The specimens were kept in a

desiccator until used.

3.2. Solution preparation

To simulate the environment of process locations, the tested solutions were

prepared as per the compositions found during process operation. The tested solutions for

most process locations, except for the esterification reactor, were synthesized by simply

mixing all the chemical ingredients with pre-determined amounts to achieve service

compositions. The solutions in the esterification reactor were synthesized by carrying out

esterification reactions in a stirred reactor. A schematic diagram of the bench-scale

esterification reactor setup is shown in Figure 3.2. Reactants (i.e. canola oil as the virgin

oil, oleic acid as the free-fatty acid, methanol as the alcohol, and sulphuric acid as the

catalyst) with given concentrations were added to the reactor and well mixed at 65°C.

30

Table 3.1: Composition of specimens

Types of specimen Chemical composition (%)

CS 1018 C — 0.175

Mn — 0.750

Fe — Balance

SS 304 C — 0.08

Mn — 2.00

P — 0.045

S — 0.030

Si — 0.75

Cr — 18.00 — 20.00

Ni — 8.00 — 12.00

N — 0.10

Fe — Balance

SS 316 C — 0.022

Mn — 1.42

Si — 0.40

S — 0.022

P — 0.038

Ni — 10.05

Cr — 16.35

Mo — 2.02

Cu — 0.41

N — 0.062

Co — 0.18

Fe — Balance

31

Table 3.1: Composition of specimens

Types of specimen Chemical composition (%)

CS 1018 C - 0.175

Mn-0.750

Fe - Balance

SS 304 C - 0.08

Mn - 2.00

P- 0.045

S-0.030

Si-0.75

Cr- 18.00 ~ 20.00

Ni-8.00- 12.00

N - 0.10

Fe - Balance

SS 316 C- 0.022

Mn - 1.42

Si-0.40

S - 0.022

P- 0.038

Ni - 10.05

Cr- 16.35

Mo-2.02

Cu - 0.41

N- 0.062

Co - 0.18

Fe - Balance

31

1.2 cm

:4 0.6 CM I

(a)

2.5cm —A04

0

(b)

./

k

0.30cm

Figure 3.1: Shape and dimension of the specimen; (a) Electrochemical specimen, (b)

Weight loss specimen.

32

i

(»)

2.5cm

(b)

A

0.30cm

Figure 3.1: Shape and dimension of the specimen; (a) Electrochemical specimen, (b)

Weight loss specimen.

32

1'ent

4 —Thermometer

(CW = Cooling water)

4 —

Glass beaker

Water

0

Magnetic Stirrer with temperature controller

Figure 3.2: Schematic diagram of the esterification reactor setup.

33

Vent

Tliemionieter

<; vv (CW = Cooling water)

Glass beaker

* Water

Magnetic Stirrer with temperature controller

Figure 3.2: Schematic diagram of the esterification reactor setup.

33

ACKNOWLEDGEMENTS

I would like to thank my supervisor, Dr. Amornvadee Veawab, for her constant

support and technical guidance, which enabled me to complete my research work

successfully. I would also like to thank Dr. Adisom Aroonwilas for his help and guidance

in my experimental setup.

I gratefully acknowledge the financial support from Natural Sciences and

Engineering Research Council (NSERC) and the City of Regina. I would also like to

thank the Faculty of Engineering and Applied Science and the Faculty of Graduate

Studies and Research for providing me the opportunity to carry out my research work.

Finally, I wish to thank my parents for their profound understanding and strong

encouragement.

iii

ACKNOWLEDGEMENTS

I would like to thank my supervisor, Dr. Amornvadee Veawab, for her constant

support and technical guidance, which enabled me to complete my research work

successfully. I would also like to thank Dr. Adisorn Aroonwilas for his help and guidance

in my experimental setup.

I gratefully acknowledge the financial support from Natural Sciences and

Engineering Research Council (NSERC) and the City of Regina. I would also like to

thank the Faculty of Engineering and Applied Science and the Faculty of Graduate

Studies and Research for providing me the opportunity to carry out my research work.

Finally, I wish to thank my parents for their profound understanding and strong

encouragement.

iii

Samples of solutions were taken for acid number measurements as per ASTM D974 to

ensure the completion of esterification reaction. The purities of all chemicals used for

solution synthesis are tabulated in Table. 3.2.

3.3. Electrochemical experiment

3.3.1. Setup

As shown in Figure 3.3, the electrochemical corrosion testing system consists of a

100 ml jacketed corrosion cell (Model 636, Princeton Applied Research, USA), a water

bath with a temperature controller with accuracy of ± 0.1°C, a condenser, a rotator with a

speed controller, a potentiostat (Model 273A, Princeton Applied Research, USA), and a

data-acquisition system. The corrosion cell was a three-electrode assembly with a

cylindrical working electrode with a surface area of 3.0 cm2, a silver/silver chloride

(Ag/AgC1) reference electrode, and a platinum (Pt) counter electrode. A computer-

controlled potentiostat was used for potentiodynamic cyclic polarization scanning with a

scan rate of 1 mV/s. The results were recorded and analyzed using SOFTCORR III

corrosion software (Princeton Applied Research, USA). Figure 3.4 shows a photograph

of the electrochemical experimental setup.

3.3.2. Experimental procedure

For each experiment, the synthesized solution was transferred into a corrosion cell

that was connected to a water bath equipped with a temperature controller for

maintaining the solution at the desired temperature. A working electrode (corrosion

specimen) was degreased using 99.9% methanol and mounted on the specimen holder.

34

Samples of solutions were taken for acid number measurements as per ASTM D974 to

ensure the completion of esterification reaction. The purities of all chemicals used for

solution synthesis are tabulated in Table. 3.2.

3.3. Electrochemical experiment

3.3.1. Setup

As shown in Figure 3.3, the electrochemical corrosion testing system consists of a

100 ml jacketed corrosion cell (Model 636, Princeton Applied Research, USA), a water

bath with a temperature controller with accuracy of ± 0.1°C, a condenser, a rotator with a

speed controller, a potentiostat (Model 273A, Princeton Applied Research, USA), and a

data-acquisition system. The corrosion cell was a three-electrode assembly with a

cylindrical working electrode with a surface area of 3.0 cm2, a silver/silver chloride

(Ag/AgCl) reference electrode, and a platinum (Pt) counter electrode. A computer-

controlled potentiostat was used for potentiodynamic cyclic polarization scanning with a

scan rate of 1 mV/s. The results were recorded and analyzed using SOFTCORR III

corrosion software (Princeton Applied Research, USA). Figure 3.4 shows a photograph

of the electrochemical experimental setup.

3.3.2. Experimental procedure

For each experiment, the synthesized solution was transferred into a corrosion cell

that was connected to a water bath equipped with a temperature controller for

maintaining the solution at the desired temperature. A working electrode (corrosion

specimen) was degreased using 99.9% methanol and mounted on the specimen holder.

34

Table 3.2: Summary of chemical reagents used in experiments

Chemicals Supplier Purity (%)

2 — Propanol Fisher Scientific HPLC grade

Antimony Trioxide Fisher Scientific 99

Canola Oil No Name - Product of Canada 100

Glycerol GE Healthcare 84.5 — 85.5

Hydrochloric acid J.T.Baker 36.5 — 38.0

Methanol Sigma Aldrich 99

Methyl Oleate Acros Organics >99

Naptholbenzein Fisher Scientific 99%

Oleic acid Sigma Aldrich 90

Potassium hydroxide Fisher Scientific 0.1N

Stannous Chloride Fisher Scientific 99

Sulphuric acid BDH, Fisher Scientific 95 — 98

Toluene Fisher Scientific HPLC grade

35

Table 3.2: Summary of chemical reagents used in experiments

Chemicals Supplier Purity (%)

2 - Propanol Fisher Scientific HPLC grade

Antimony Trioxide Fisher Scientific 99

Canola Oil No Name - Product of Canada 100

Glycerol GE Healthcare 84.5 -85.5

Hydrochloric acid J.T.Baker 36.5 -38.0

Methanol Sigma Aldrich 99

Methyl Oleate Acros Organics >99

Naptholbenzein Fisher Scientific 99%

Oleic acid Sigma Aldrich 90

Potassium hydroxide Fisher Scientific 0.1N

Stannous Chloride Fisher Scientific 99

Sulphuric acid BDH, Fisher Scientific 9 5 - 9 8

Toluene Fisher Scientific HPLC grade

35

Rotator

C.W Cooling water H.W Hot water NV.IE = W'orking electrode C.E Counter electrode R.E = Reference electrode T = Thermometer

Figure 3.3: Schematic diagram of the experimental setup for electrochemical corrosion

tests. (Modified from Soosaiprakasam, 2007)

36

Rotator

Vent

C.W i

r.w,

W.F.

R.F.

C.E

H.W -P>— Microccll

C.W = Cooling water H.W -- Hot water W.E - Working tied rode C.K — Counter ekctrodc R.E » Rcfercncc dcctrodc T = Thermometer

Figure 3.3: Schematic diagram of the experimental setup for electrochemical corrosion

tests. (Modified from Soosaiprakasam, 2007)

36

Figure 3.4: A photograph of the experimental setup for electrochemical corrosion tests


37

Figure 3.4: A photograph of the experimental setup for electrochemical corrosion tests


37

The other two electrodes, i.e. a Pt counter electrode and a Ag/AgCI reference electrode,

were then assembled. The reference electrode vycor frit was completely wet and free of

air bubbles, which was ensured by visual observation. The assembled corrosion cell was

subsequently connected to a potentiostat equipped with a data acquisition system.

Experimental parameters, as well as the type of corrosion measuring technique, were

specified on the data acquisition software. A polarization scan was conducted after the

potential of the specimen reached equilibrium, or was constant with time. The experiment

was reproduced to ensure reliability of the data.

3.3.3 Corrosion measuring technique

(a) Tafel plot

A Tafel plot is a commonly used and accepted method for corrosion rate

determination. It generally depicts the anodic/cathodic polarization curve of a working

electrode — the corrosion specimen — in the potential gamut of ± 200 mV from the

equilibrium potential (Econ.). Figure 3.5 shows a typical Tafel plot, with anodic (Pa) and

cathodic (PO Tafel slopes and corrosion current density (icon) generated from the plot;

corrosion rate is calculated using the following equation:

CR = (K x iCOrr x EW )

D (3.1)

where CR is corrosion rate, K is constant (0.129 for CR in mpy, 3.272 x 10-3 for CR in

mmpy), icorr in p.A/cm2, EW is the equivalent weight of the specimen, and D is the density

of the specimen in g/cm3.

38

The other two electrodes, i.e. a Pt counter electrode and a Ag/AgCl reference electrode,

were then assembled. The reference electrode vycor frit was completely wet and free of

air bubbles, which was ensured by visual observation. The assembled corrosion cell was

subsequently connected to a potentiostat equipped with a data acquisition system.

Experimental parameters, as well as the type of corrosion measuring technique, were

specified on the data acquisition software. A polarization scan was conducted after the

potential of the specimen reached equilibrium, or was constant with time. The experiment

was reproduced to ensure reliability of the data.

3.3.3 Corrosion measuring technique

(a) Tafel plot

A Tafel plot is a commonly used and accepted method for corrosion rate

determination. It generally depicts the anodic/cathodic polarization curve of a working

electrode - the corrosion specimen - in the potential gamut of ± 200 mV from the

equilibrium potential (EC0IT). Figure 3.5 shows a typical Tafel plot, with anodic ((3a) and

cathodic (pb) Tafel slopes and corrosion current density (iCOrr) generated from the plot;

corrosion rate is calculated using the following equation:

™ (K x icorr X EW ) CR = 25 (3.1)

"1

where CR is corrosion rate, K is constant (0.129 for CR in mpy, 3.272 x 10" for CR in

mmpy), icorr in ^A/cm2, EW is the equivalent weight of the specimen, and D is the density

of the specimen in g/cm3.

38

.............. ..

Anodic Slope = j3.

9athodic Slope = .........................

icon

Log current density

Figure 3.5: A typical Tafel plot. (Srinivasan, 2006)

39

re C r-d) E. o

CL

\ Anodic Slope = Pa

Cathodic Slope = (3C

...aC,

Log current density

Figure 3.5: A typical Tafel plot. (Srinivasan, 2006)

39

(b) Potentiodynamic polarization

The typical potentiodynamic polarization curve of a specimen under a given

environment is shown in Figure 3.6. The curve consists of two profiles, cathodic and

anodic, representing reduction of oxidizing agent and oxidation of specimen,

respectively. The cathodic polarization scan is below the corrosion potential (Ecorr),

whereas the anodic is above. The anodic profile can further be subdivided into three

phases, namely active, passive, and transpassive. In the active phase, the current density

increases rapidly with increasing potential from Econ in the positive direction. The current

density starts decreasing after reaching a particular potential, which indicates the

initiation of passive film formation. The potential at which the film begins to form on the

electrode surface is known as primary passivation potential (Epp). The current density

becomes constant at a particular potential, which indicates the completion of film

formation (Ecp). Then the current density increases rapidly at a specific potential, which

is noted as transpassive potential (Evans). The zone between the primary passivation

potential and transpassive potential is denoted as the passivation zone, as the passive film

formed on the surface generally impedes the corrosion of the electrode. The zone after

the transpassive potential is called the transpassivation zone, which in turn indicates the

passive layer is broken and uninhibited corrosion of the electrode is induced.

(c) Cyclic polarization

Cyclic polarization (CP) is an extension of potentiodynamic polarization, and it

indicates the behaviour of pitting corrosion and the ability of the metal to repair after the

pits occur. The cyclic polarization curve is typically a combination of a forward scan of

40

(b) Potentiodynamic polarization

The typical potentiodynamic polarization curve of a specimen under a given

environment is shown in Figure 3.6. The curve consists of two profiles, cathodic and

anodic, representing reduction of oxidizing agent and oxidation of specimen,

respectively. The cathodic polarization scan is below the corrosion potential (Ecorr),

whereas the anodic is above. The anodic profile can further be subdivided into three

phases, namely active, passive, and transpassive. In the active phase, the current density

increases rapidly with increasing potential from EC01T in the positive direction. The current

density starts decreasing after reaching a particular potential, which indicates the

initiation of passive film formation. The potential at which the film begins to form on the

electrode surface is known as primary passivation potential (EPP). The current density

becomes constant at a particular potential, which indicates the completion of film

formation (Ecp). Then the current density increases rapidly at a specific potential, which

is noted as transpassive potential (Etrans)- The zone between the primary passivation

potential and transpassive potential is denoted as the passivation zone, as the passive film

formed on the surface generally impedes the corrosion of the electrode. The zone after

the transpassive potential is called the transpassivation zone, which in turn indicates the

passive layer is broken and uninhibited corrosion of the electrode is induced.

(c) Cyclic polarization

Cyclic polarization (CP) is an extension of potentiodynamic polarization, and it

indicates the behaviour of pitting corrosion and the ability of the metal to repair after the

pits occur. The cyclic polarization curve is typically a combination of a forward scan of

40

A

co

a)

0.

Log current density

Figure 3.6: A typical potentiodynamic polarization curve. (Srinivasan, 2006)

41

E

C M o

QL

E.

Log current density

Figure 3.6: A typical potentiodynamic polarization curve. (Srinivasan, 2006)

41

Reverse Scan Negative hysteresis

Forward Scan

Log current density

(a) Negative hysteresis — No pitting corrosion

0. E,s

Forward Scan Reverse Scan: Positive hysteresis

Log current density

(b) Positive hysteresis —Pitting corrosion

Figure 3.7: A typical cyclic polarization curve. (Srinivasan, 2006)

42

Forward Scan

E,

Log current density

(a) Negative hysteresis - No pitting corrosion

Forward Scan

Erp

Log current density

(b) Positive hysteresis -Pitting corrosion

Figure 3.7: A typical cyclic polarization curve. (Srinivasan, 2006)

42

potentiodynamic polarization and a reverse scan towards the corrosion potential (Ecorr)

added to the forward scan, as shown in Figure 3.7. The CP scan can be found in either

negative or positive hysteresis. Pitting corrosion is likely to happen in that pits tend to

initiate and any damage to the passive film cannot be self repaired if the reverse scan

shows positive hysteresis. In addition, pits will tend to grow continuously when the

repassivation potential (Em) is greater than Econ. On the other hand, the negative reverse

scan affirms pitting free corrosion behaviour.

3.4 Weight Loss Experiment

3.4.1 Setup

Figure 3.8 shows the weight loss experimental setup consisting of 3 cylindrical

glass cells of 2 litre capacity. Each cell had an outer jacket for hot water circulation, a

thermometer, a sample holder, and a condenser. The outer jackets were connected to a

water bath equipped with a temperature controller. These cells were kept on the magnetic

stirrer for mixing of the solution. Figure 3.9 shows a photograph of the weight loss

experimental setup.

3.4.2 Procedure

The weight loss experiments were designed for estimating corrosion rates of

carbon steel 1018 in the environment of an acid-catalyzed esterification reactor. Prior to

each experiment, specimens were weighed using a microbalance with 0.01 mg accuracy.

To maintain the temperature of the esterification reaction at 65°C, hot water from the

43

potentiodynamic polarization and a reverse scan towards the corrosion potential (Ecorr)

added to the forward scan, as shown in Figure 3.7. The CP scan can be found in either

negative or positive hysteresis. Pitting corrosion is likely to happen in that pits tend to

initiate and any damage to the passive film cannot be self repaired if the reverse scan

shows positive hysteresis. In addition, pits will tend to grow continuously when the

repassivation potential (Erp) is greater than ECOrr- On the other hand, the negative reverse

scan affirms pitting free corrosion behaviour.

3.4 Weight Loss Experiment

3.4.1 Setup

Figure 3.8 shows the weight loss experimental setup consisting of 3 cylindrical

glass cells of 2 litre capacity. Each cell had an outer jacket for hot water circulation, a

thermometer, a sample holder, and a condenser. The outer jackets were connected to a

water bath equipped with a temperature controller. These cells were kept on the magnetic

stirrer for mixing of the solution. Figure 3.9 shows a photograph of the weight loss

experimental setup.

3.4.2 Procedure

The weight loss experiments were designed for estimating corrosion rates of

carbon steel 1018 in the environment of an acid-catalyzed esterification reactor. Prior to

each experiment, specimens were weighed using a microbalance with 0.01 mg accuracy.

To maintain the temperature of the esterification reaction at 65°C, hot water from the

43

TABLE OF CONTENTS

Abstract

Acknowledgements iii

Table of Contents iv

List of Tables vii

List of Figures viii

Nomenclature xiii

1. INTRODUCTION 1

1.1 Advantages and disadvantages of biodiesel 1

1.2 Biodiesel production across the globe 3

1.3 Oil feedstocks for biodiesel production 5

1.4 Biodiesel production and its bottlenecks 6

1.5 Research motivation, objectives and scope 8

2. FUNDAMENTALS AND LITERATURE REVIEW 11

2.1 Biodiesel production 11

2.1.1 Alkali-based transesterification 13

2.1.2 Acid-based process 14

2.1.3 Post production processes 16

2.1.3.1 Phase separation 16

2.1.3.2 Methanol recovery 18

2.1.3.3 Ester Washing & Drying 18

2.2 Mode of production operation 18

iv

TABLE OF CONTENTS

Abstract i

Acknowledgements iii

Table of Contents iv

List of Tables vii

List of Figures viii

Nomenclature xiii

1. INTRODUCTION 1

1.1 Advantages and disadvantages of biodiesel 1

1.2 Biodiesel production across the globe 3

1.3 Oil feedstocks for biodiesel production 5

1.4 Biodiesel production and its bottlenecks 6

1.5 Research motivation, objectives and scope 8

2. FUNDAMENTALS AND LITERATURE REVIEW 11

2.1 Biodiesel production 11

2.1.1 Alkali-based transesterification 13

2.1.2 Acid-based process 14

2.1.3 Post production processes 16

2.1.3.1 Phase separation 16

2.1.3.2 Methanol recovery 18

2.1.3.3 Ester Washing & Drying 18

2.2 Mode of production operation 18

iv

TO VENT

civ OUT h•—""

Condenser-4o

Thermometer—ol

Gas disperse

Specimen

iN

Magnetic stirrer—.

W OUT

C W tN O.W. IN

.g0 OUT

O

H.W = hot water C.W = cooling water

Figure 3.8: A schematic diagram of the weight loss experimental setup. (Modified from

Srinivasan, 2006)

44

TO VENT

3 C|v. CUT H cyw. OUT

:w w O W i N

OUT

c.w. at

"4*

Thermometer

Gas disperses

Specimen

HW IN

Magnetic stirrer

H.W - hot water C.W = cooling water

Figure 3.8: A schematic diagram of the weight loss experimental setup. (Modified from

Srinivasan, 2006)

44

Figure 3.9: A photograph of the weight loss experimental setup (Original in colour)

45

Figure 3.9: A photograph of the weight loss experimental setup (Original in colour)

45

water bath was circulated to the outer jackets of the corrosion cells. A mixture of canola

oil, oleic acid, methanol, and sulphuric acid with given quantities was preheated to -55-

60°C and transferred to the corrosion cells. The solution was thoroughly mixed using

magnetic stirrers with a fixed paddle speed throughout the experiment to ensure proper

mixing of the solution. The reaction temperature was continuously monitored, and

condensers were used to prevent methanol loss by vaporization. After the corrosion cell

was prepared for use, the specimens were immersed in the corrosion cells. The specimens

were removed from the corrosion cells at specific time intervals, cleaned, and eventually

weighed to measure the weight loss, which was in turn translated into the corrosion rate.

3.4.3 Cleaning procedure

After the tested specimens were removed from the corrosion cells, they were

cleaned using a procedure as per ASTM standard G1 — 90 (Reapproved 1999). This

procedure included both mechanical and chemical cleaning. In mechanical cleaning, the

specimen was washed under running water and brushed lightly using a non-metallic

bristle, dried with air, and weighed. After the mechanical cleaning, chemical cleaning

was carried out by immersing the specimen in a cleaning solution that was a mixture of

1000 ml of hydrochloric acid (HCl, sp.gr 1.19), 20g antimony trioxide (Sb20 3), and 50g

stannous chloride (SnC12). The immersion time was 1 minute for each cycle. The

cleaning cycles were repeated a number of times, and weight loss measured in each cycle

was calculated. The mass loss was plotted against the number of cleaning cycles as

shown in Figure 3.10. The mass loss due to corrosion approximately corresponded to

point B.

46

water bath was circulated to the outer jackets of the corrosion cells. A mixture of canola

oil, oleic acid, methanol, and sulphuric acid with given quantities was preheated to ~55-

60°C and transferred to the corrosion cells. The solution was thoroughly mixed using

magnetic stirrers with a fixed paddle speed throughout the experiment to ensure proper

mixing of the solution. The reaction temperature was continuously monitored, and

condensers were used to prevent methanol loss by vaporization. After the corrosion cell

was prepared for use, the specimens were immersed in the corrosion cells. The specimens

were removed from the corrosion cells at specific time intervals, cleaned, and eventually

weighed to measure the weight loss, which was in turn translated into the corrosion rate.

3.4.3 Cleaning procedure

After the tested specimens were removed from the corrosion cells, they were

cleaned using a procedure as per ASTM standard G1 - 90 (Reapproved 1999). This

procedure included both mechanical and chemical cleaning. In mechanical cleaning, the

specimen was washed under running water and brushed lightly using a non-metallic

bristle, dried with air, and weighed. After the mechanical cleaning, chemical cleaning

was carried out by immersing the specimen in a cleaning solution that was a mixture of

1000 ml of hydrochloric acid (HC1, sp.gr 1.19), 20g antimony trioxide (Sb203), and 50g

stannous chloride (SnCh). The immersion time was 1 minute for each cycle. The

cleaning cycles were repeated a number of times, and weight loss measured in each cycle

was calculated. The mass loss was plotted against the number of cleaning cycles as

shown in Figure 3.10. The mass loss due to corrosion approximately corresponded to

point B.

46

Number of Cleaning Cycles

Figure 3.10: Mass loss of corroded specimens resulting from repetitive cleaning cycles.

47

Number of Cleaning Cycles

Figure 3.10: Mass loss of corroded specimens resulting from repetitive cleaning cycles.

47

3.4.4 Corrosion rate determination

The corrosion rates estimated in this study were based on the following

assumptions (as defined by ASTM standard G31 — 72: Reapproved 1999):

• All mass loss is due to general corrosion and not to localized corrosion such as

pitting or intergranular corrosion.

• Material is not internally attacked as by dezincification or intergranular corrosion.

The average corrosion rate was calculated using the following equation:

where:

(K x W) CR=

(AxT xD) (3.2)

K = a constant (8.76 x 104 for corrosion rate in mmpy and 3.45 x 106 for corrosion

rate in mpy)

W = mass loss in g

A = area in cm2

T = time of exposure in hours

D = density in g/cm3

48

3.4.4 Corrosion rate determination

The corrosion rates estimated in this study were based on the following

assumptions (as defined by ASTM standard G31 - 72: Reapproved 1999):

• All mass loss is due to general corrosion and not to localized corrosion such as

pitting or intergranular corrosion.

• Material is not internally attacked as by dezincification or intergranular corrosion.

The average corrosion rate was calculated using the following equation:

C S = J ( A x T x D )

where:

K = a constant (8.76x 104 for corrosion rate in mmpy and 3.45x 106 for corrosion

rate in mpy)

W = mass loss in g

A = area in cm2

T = time of exposure in hours

D = density in g/cm

48

4. RESULTS AND DISCUSSION

4.1 Electrochemical tests

4.1.1 Acid-catalyzed esterification process and tested locations

This work is the result of an investigation of corrosion in an acid-catalyzed

esterification process used to pre-treat feedstock or convert free fatty acid (FFA) in the

feedstock to biodiesel prior to the transesterification process where the treated feedstock

is converted into a biodiesel product. The corrosion investigation was carried out using

the process flow diagram (Figure 4.1) and process conditions (Table 4.1) found in Alex et

al. (2008). As shown in Figure 4.1, raw materials (i.e., methanol and sulphuric acid) with

required quantities from Locations 1 and 2 are premixed at Location 3. The mixture of

methanol and sulphuric acid is then pumped to Location 5, where the mixture is further

mixed with the recovered methanol from Location 4 to adjust for the required ratio of oil

to methanol for the esterification reaction. The mixture of methanol and sulphuric acid is

then fed to an esterification reactor (Location 7) where oil containing FFA from Location

6 is also introduced. In Location 7, the esterification reaction between FFA (represented

by oleic acid in this work) and methanol takes place in the presence of sulphuric acid,

which serves as a catalyst at 65°C and 1 atm. As a result, methyl oleate (or biodiesel) and

water are produced as shown in the following esterification reaction:

Oleic acid + Methanol Sulphuric acid Methyl oleate + Water (4.1)

The product stream containing unreacted oil, methyl oleate, water, sulphuric acid, and

methanol is then introduced to a stripping column where glycerol (from Location 8) is

used as a stripping agent to separate the unreacted oil and methyl oleate for use as

49

4. RESULTS AND DISCUSSION

4.1 Electrochemical tests

4.1.1 Acid-catalyzed esterification process and tested locations

This work is the result of an investigation of corrosion in an acid-catalyzed

esterification process used to pre-treat feedstock or convert free fatty acid (FFA) in the

feedstock to biodiesel prior to the transesterification process where the treated feedstock

is converted into a biodiesel product. The corrosion investigation was carried out using

the process flow diagram (Figure 4.1) and process conditions (Table 4.1) found in Alex et

al. (2008). As shown in Figure 4.1, raw materials (i.e., methanol and sulphuric acid) with

required quantities from Locations 1 and 2 are premixed at Location 3. The mixture of

methanol and sulphuric acid is then pumped to Location 5, where the mixture is further

mixed with the recovered methanol from Location 4 to adjust for the required ratio of oil

to methanol for the esterification reaction. The mixture of methanol and sulphuric acid is

then fed to an esterification reactor (Location 7) where oil containing FFA from Location

6 is also introduced. In Location 7, the esterification reaction between FFA (represented

by oleic acid in this work) and methanol takes place in the presence of sulphuric acid,

which serves as a catalyst at 65°C and 1 atm. As a result, methyl oleate (or biodiesel) and

water are produced as shown in the following esterification reaction:

Oleic acid + Methanol Sulphuric acid Methyl oleate + Water (4.1) •

The product stream containing unreacted oil, methyl oleate, water, sulphuric acid, and

methanol is then introduced to a stripping column where glycerol (from Location 8) is

used as a stripping agent to separate the unreacted oil and methyl oleate for use as

49

0 0

0

1. Methanol storage tank 2. Sulphuric acid storage tank 3. Methanol + Sulphuric acid mixing tank 4. Methanol recovery flow line 5. Fresh and recovered Methanol + Sulphuric acid mixing tank 6. Oil + FFA storage tank

7. Esterification reactor 8. Glycerol feed to stripping column 9. Oil + biodiesel flow line 10. Inlet to vacuum distillation column 11. Vacuum distillation column

Figure 4.1: Process flow diagram of an acid-catalyzed esterification process

(Modified from Alex et al., 2008)

50

1. Methanol storage tank 7. Esterification reactor 2. Sulphuric acid storage tank 8. Glycerol feed to stripping column 3. Methanol + Sulphuric acid mixing tank 9. Oil + biodiesel flow line 4. Methanol recovery flow line 10. Inlet to vacuum distillation column 5. Fresh and recovered Methanol + 11. Vacuum distillation column Sulphuric acid mixing tank 6. Oil + FFA storage tank

Figure 4.1: Process flow diagram of an acid-catalyzed esterification process

(Modified from Alex et al., 2008)

50

Table 4.1: Process compositions and operating conditions of tested locations

Location number

Process Operating conditions

Composition (% by wt)

1 Methanol storage tank 25°C latm

Methanol (100%)

2 Sulphuric acid storage tank

25°C latm

Sulphuric acid (100%)

3 Methanol & acid mixing tank

25°C latm

Methanol (67%) + Sulphuric acid (33%)

4 Methanol recovery flow line

35°C 0.2 atm

Methanol (99.6%) + Water (0.4%)

5 Fresh & Recovered Methanol & acid mixing tank

25°C latm

Methanol (95.8%) + Sulphuric acid (3.8%) + Water (0.4%)

6 Canola Oil & FFA storage tank

25°C latm

Canola Oil (95%) + FFA (Oleic acid) (5%)

7 Esterification reactor 65°C latm

Oil+ Methyl Oleate + Methanol + Sulphuric acid + Water

This composition was prepared from the followings.. [7a] Oil + 5% FFA + Methanol (6:1 molar basis) + 1% Sulphuric acid [7b] Oil + 10% FFA + Methanol (10:1 molar basis) + I% Sulphuric acid [7c] Oil + 10% FFA + Methanol (18:1 molar basis) + I% Sulphuric acid [7d] Oil + 10% FFA + Methanol (18:1 molar basis) + 5% Sulphuric acid

8 Glycerol feed to stripping column

35°C latm

Glycerol (100%)

9 Oil + biodiesel flow line to transesterification Process

60 °C latm

Oil (93.7%) + Methyl Oleate (6.3%)

10 Inlet to vacuum distillation column

60 °C latm

Methanol (55%) + Glycerol (40%) + Sulphuric acid (3.5%) + Water (1.5%)

11 Vacuum distillation column

72°C 0.3 atm

Methanol (10.5%) + Glycerol (79.5%) +Sulphuric acid (7.1%) + Water (2.9%)

Note: All operating conditions and process compositions were taken from Alex et al. (2008), except [7b], [7c] and [7d].

51

Table 4.1: Process compositions and operating conditions of tested locations

Location number

Process Operating conditions

Composition (% by wt)

1 Methanol storage tank 25°C

latm Methanol (100%)

2 Sulphuric acid storage tank

25°C latm

Sulphuric acid (100%)

3 Methanol & acid mixing tank

25°C latm

Methanol (67%) + Sulphuric acid (33%)

4 Methanol recovery flow line

35°C 0.2 atm

Methanol (99.6%) + Water (0.4%)

5 Fresh & Recovered Methanol & acid mixing tank

25°C latm

Methanol (95.8%) + Sulphuric acid (3.8%) + Water (0.4%)

6 Canola Oil & FFA storage tank

25°C latm

Canola Oil (95%) + FFA (Oleic acid) (5%)

7 Esterification reactor 65°C latm

Oil+ Methyl Oleate + Methanol + Sulphuric acid + Water

This composition was prepared from the fallowings.. [7a] Oil + 5% FFA + Methanol (6:1 molar basis) + 1% Sulphuric acid [7 b] Oil + 10% FFA + Methanol (10:1 molar basis) + 1% Sulphuric acid [7c] Oil + 10% FFA + Methanol (18:1 molar basis) + 1% Sulphuric acid [7d] Oil + 10% FFA + Methanol (18:1 molar basis) + 5% Sulphuric acid

8 Glycerol feed to stripping column

35°C latm

Glycerol (100%)

9 Oil + biodiesel flow line to transesterification process

60 °C latm

Oil (93.7%) + Methyl Oleate (6.3%)

10 Inlet to vacuum distillation column

60 °C latm

Methanol (55%) + Glycerol (40%) + Sulphuric acid (3.5%) + Water (1.5%)

11 Vacuum distillation column

72°C 0.3 atm

Methanol (10.5%) + Glycerol (79.5%) +Sulphuric acid (7.1%) + Water (2.9%)

Note: All operating conditions and process compositions were taken from Alex et al. (2008), except [7b], [7c] and [7d].

51

reactants in the downstream base-catalyzed transesterification process where the final

biodiesel product is generated. The remaining product stream containing methanol,

sulphuric acid, glycerol, and water (Location 10) is fed to a vacuum distillation column

(Location 11) where methanol is recovered. The recovered methanol (Location 4) is sent

back to the esterification reactor for further esterification reaction while the remaining

stream, containing sulphuric acid, glycerol, and water, is sent to be used in treatment

processes to neutralize the sulphuric acid with a base agent for safe disposal and to purify

the glycerol for use as the end product.

4.1.2 Corrosion in tested process locations

Electrochemical corrosion results, including electrochemical kinetic data,

corrosion rate, and pitting tendency for the eleven tested process locations, are

summarized in Table 4.2. Each datum represents an average value from replicated tests.

Examples of the duplicated runs to ensure the reliability of the obtained data are given in

Figure 4.2.

4.1.2.1 Location 1: Methanol storage tank

Figure 4.3 shows the cyclic polarization curve of CS1018 in methanol at 25°C

under atmospheric pressure, representing the environment of methanol storage. The curve

shows CS 1018 passivates in the methanol environment, induces a corrosion rate of 29

mpy, and yields negative hysteresis, suggesting no pitting tendency.

52

reactants in the downstream base-catalyzed transesterification process where the final

biodiesel product is generated. The remaining product stream containing methanol,

sulphuric acid, glycerol, and water (Location 10) is fed to a vacuum distillation column

(Location 11) where methanol is recovered. The recovered methanol (Location 4) is sent

back to the esterifxcation reactor for further esterification reaction while the remaining

stream, containing sulphuric acid, glycerol, and water, is sent to be used in treatment

processes to neutralize the sulphuric acid with a base agent for safe disposal and to purify

the glycerol for use as the end product.

4.1.2 Corrosion in tested process locations

Electrochemical corrosion results, including electrochemical kinetic data,

corrosion rate, and pitting tendency for the eleven tested process locations, are

summarized in Table 4.2. Each datum represents an average value from replicated tests.

Examples of the duplicated runs to ensure the reliability of the obtained data are given in

Figure 4.2.

4.1.2.1 Location 1: Methanol storage tank

Figure 4.3 shows the cyclic polarization curve of CS1018 in methanol at 25°C

under atmospheric pressure, representing the environment of methanol storage. The curve

shows CS 1018 passivates in the methanol environment, induces a corrosion rate of 29

mpy, and yields negative hysteresis, suggesting no pitting tendency.

52

Table 4.2: Summary of electrochemical corrosion data of CS 1018 (unless specified)

Location Ecorr (mV) icorr (PVC M2) II. (mV/decade) it, (mV/decade) Corrosion rate

(mPY)

Pitting

1 -31.8 ± 7.6 63.30 + 10.80 2.8E+03 ± 330.0 3.53E+04 ± 1.70E+04 29.30 + 5.00 No

1 (With N2

blanketing)

-315.7 ± -6.1 0.11 + 0.03 545.0 ± 19.6 123.0 ± 12.8 0.05 + 0.02 No

1 SS304 91.1+ 46.4 0.09 ± 0.07 275.0 + 4.1 118.0 ± 16.3 0.04 ± 0.03 Yes

2 -275.5 ± -17.5 66.10 ± 3.04 - - 30.61+ 1.41 Yes

3 -290.6 ± 13.6 85.60 + 16.30 94.4 ± 1.8 146.0 ± 5.3 39.50 ± 7.50 Yes

4 44.1 ± 5.6 4.21 ± 0.15 366.0 ± 1.9 3.96E+06 ± 1.98E+06 1.90 ± 0.20 No

5 -300.3+2.5 218 + 25.7 126.0 ± 4.6 235.0 ± 20.1 100.50 ± 11.80 Yes

6* - - - -

7a -432.4 ± 6.4 0.008 ± 0.004 8330.0 ± 1660.0 2290.0 ± 684 0.004 + 0.002 No

7b -371.1+-6.8 0.004 + 0.002 3.9 ± 1.0 1.32 ± 0.1 0.002 ± 0.001 No

7c -363.3 ± 2.1 0.003 + 0.001 1.3+ 0.1 0.6 ± 0.3 0.001 + 0.000 No

7d -333.7 ± 4.8 0.007 ± 0.001 3.3 ± 1.9 1.0 + 0.09 0.003 + 0.000 No

8 -461.2 5.13 913.0 959.3 2.37 Yes

9* - - - - - -

10 -365.2 ± 0.1 1550.00 ± 124 350.0 ± 13.3 322.0 ± 3.28 717.90 ± 57.20 Yes

10 (SS304)

-206.1 ±4.0 54.10 ± 3.27 73.7+ 1.8 147.0+ 11.1 25.00+ 1.50 Yes

10 (SS316)

38.5 ± 8.5 8.82 ± 0.75 64.4 ± 1.0 127.0 ± 1.7 3.60 + 0.30 No

11 -363.0 ± 1.5 1970.00 ± 581.00 465.0 ± 0.5 342.0 ± 51.3 910.80 ± 268.30 Yes

11 (SS304)

-240.7+2.2 25.60 ± 0.59 119 ± 8.7 112.0 ± 32.0 10.50 ± 2.30 No

Eco, = corrosion potential; icor, = corrosion current density; pa = anodic slope; pc = cathodic slope * Out of detectable range of PAR 273A

53

Table 4.2: Summary of electrochemical corrosion data of CS 1018 (unless specified)

Location ^corr ( V) icorr (flA/cm2) P, (mV/decade) pc (mV/decade) Corrosion rate (mpy)

Pitting

1 -31.8 ±7.6 63.30 ± 10.80 2.8E+03 ± 330.0 3.53E+04± 1.70E+04 29.30 ± 5.00 No

1 (With N2

blanketing)

-315.7 ±-6.1 0.11 ±0.03 545.0 ± 19.6 123.0 ± 12.8 0.05 ± 0.02 No

1 SS304 91.1± 46.4 0.09 ±0.07 275.0 ±4.1 118.0 ± 16.3 0.04 ± 0.03 Yes

2 -275.5 ±-17.5 66.10 ±3.04 - - 30.61± 1.41 Yes

3 -290.6 ± 13.6 85.60 ± 16.30 94.4 ± 1.8 146.0 ±5.3 39.50 ±7.50 Yes

4 44.1 ±5.6 4.21 ±0.15 366.0 ± 1.9 3.96E+06 ± 1.98E+06 1.90 ±0.20 No

5 -300.3 ±2.5 218 ± 25.7 126.0 ±4.6 235.0 ±20.1 100.50 ± 11.80 Yes

6* - - - - - -

7a -432.4 ± 6.4 0.008 ± 0.004 8330.0 ± 1660.0 2290.0 ± 684 0.004 ± 0.002 No

7b -371.1 ±-6.8 0.004 ± 0.002 3.9 ± 1.0 1.32 ± 0.1 0.002 ±0.001 No

7c -363.3 ±2.1 0.003 ±0.001 1.3± 0.1 0.6 ±0.3 0.001 ±0.000 No

7d -333.7 ±4.8 0.007 ±0.001 3.3 ± 1.9 1.0 ±0.09 0.003 ± 0.000 No

8 -461.2 5.13 913.0 959.3 2.37 Yes

9* - - - - - -

10 -365.2 ±0.1 1550.00 ± 124 350.0 ± 13.3 322.0 ±3.28 717.90 ±57.20 Yes

10 (SS304)

-206.1 ±4.0 54.10 ±3.27 73.7 ± 1.8 147.0 ±11.1 25.00 ± 1.50 Yes

10 (SS316)

38.5 ±8.5 8.82 ± 0.75 64.4 ± 1.0 127.0 ± 1.7 3.60 ±0.30 No

11 -363.0 ± 1.5 1970.00 ±581.00 465.0 ±0.5 342.0 ±51.3 910.80 ±268.30 Yes

11 (SS304)

-240.7 ± 2.2 25.60 ±0.59 119 ± 8.7 112.0 ±32.0 10.50 ±2.30 No

ECorr = corrosion potential; icorr = corrosion current density; pa = anodic slope; pc = cathodic slope * Out of detectable range of PAR 273A

53

2.2.1 Batch Process 19

2.2.2 Continuous process 19

2.3 Process parameters 20

2.3.1 Temperature and pressure 20

2.3.2 Alcohol-to-oil ratio and alcohol and oil purity 22

2.3.3 Catalyst type and concentration 22

2.3.4 Reaction time and mixing intensity 23

2.4 Corrosion in organic solvent and sulphuric acid systems 23

2.4.1 Corrosion in mixed methanol and sulphuric acid

systems 25

2.4.2 Corrosion in the presence of fatty acid components 26

3. CORROSION EXPERIMENTS 29

3.1 Specimen preparation 29

3.2. Solution preparation 30

3.3. Electrochemical experiment 34

3.3.1. Setup 34

3.3.2. Experimental procedure 34

3.3.3 Corrosion measuring technique 38

3.4 Weight loss Experiment 43

3.4.1 Setup 43

3.4.2 Procedure 43

3.4.3 Cleaning procedure 46

3.4.4 Corrosion rate determination 48

2.2.1 Batch Process 19

2.2.2 Continuous process 19

2.3 Process parameters 20

2.3.1 Temperature and pressure 20

2.3.2 Alcohol-to-oil ratio and alcohol and oil purity 22

2.3.3 Catalyst type and concentration 22

2.3.4 Reaction time and mixing intensity 23

2.4 Corrosion in organic solvent and sulphuric acid systems 23

2.4.1 Corrosion in mixed methanol and sulphuric acid

systems 25

2.4.2 Corrosion in the presence of fatty acid components 26

3. CORROSION EXPERIMENTS 29

3.1 Specimen preparation 29

3.2. Solution preparation 30

3.3. Electrochemical experiment 34

3.3.1. Setup 34

3.3.2. Experimental procedure 34

3.3.3 Corrosion measuring technique 38

3.4 Weight loss Experiment 43

3.4.1 Setup 43

3.4.2 Procedure 43

3.4.3 Cleaning procedure 46

3.4.4 Corrosion rate determination 48

v

Pot

entia

l (m

V v

s. A

g/A

gCI)

P

oten

tial (

mV

vs.

Ag/

AgC

I)

1500

1000

500

-500 Run1 — Run 2

-10 -8 -6 -4 -2

500

0

-500

-1000

Log current density (A/cm2)

(a)

Run 1 —Run 2

-a -6 -4 -2


(c)

0

C.) 1000

a)

Cl) 500

E

0 CL -500

Pot

entia

l (m

V v

s. A

g/A

gCI)

-1000

500

0

-500

-1000

--- Run 1 —Run 2

-7 -5 -3


(b)

- - Run 1 —Run 2

-a -6 -4 -2


(d)

Figure 4.2: Reproducibility of the obtained electrochemical data from: (a) Location 1, (b)

Location 2, (c) Location 3, and (d) Location 5

54

Log current density (A/cm2) Log current density (A/cm2)

Log current density (A/cm2) Log current density (A/cm2)

Figure 4.2: Reproducibility of the obtained electrochemical data from: (a) Location 1, (b)

Location 2, (c) Location 3, and (d) Location 5

54

Pot

entia

l (m

V v

s. A

g/A

gCI)

1400

1200

1000

800

600

400

200

0

-200

-400

-Forward Scan

Reverse Scan

-8 -7 -6 -5 -4 -3 -2


Figure 4.3: Potentiodynamic polarization curve of CS1018 in methanol at 25°C and 1

atm

55

• Forward Scan

Reverse Scan

-7 -6 -5 -4 -3 -2

Log current density (A/cm )

Figure 4.3: Potentiodynamic polarization curve of CS1018 in methanol at 25°C and 1

atm

55

The obtained corrosion behaviour can be explained by considering a typical

corrosion mechanism in organic solvents. According to Heitz and Kyriazls (1978),

methanol is classified as a protic solvent that induces corrosion of metal (Me) even if it is

present in low concentrations. The anodic dissolution reaction of metal is:

Me --> Me n+ + n e (4.2)

and the cathodic reaction, i.e., the reduction of acidic hydrogen (HA) of a proton donor

is:

HA + e 'A H2 + A- (4.3)

In our tests, the methanol was not degassed to remove dissolved oxygen (02). Thus, in

addition to the acidic hydrogen (in Reaction 4.3), the dissolved 0 2 was a primary

contributor to the corrosion. According to Kawai et al. (1995) and Banas and Banas,

(2009), the anodic reaction involves the dissolution of iron (Fe) and the cathodic reaction

involves the reduction of methanol (CH3OH) in the presence of dissolved 0 2, promoting

the formation of methoxy ions (CH30 - ) as shown below.

Fe -› Fe2+ + 2e (4.4)

0 2 + 2CH3OH + 4e -› 2CI-130 - + 20H- (4.5)

The methoxy ion reacts with Fe2+ to form ferrous methoxide (Fe(OCH3)2) on the surface

and decomposes into ferrous oxide (FeO) as a passive layer on the surface. The formation

of such a passive layer can be written as:

Fe2+ + 2CH30" --> Fe(OCH3)2 (4.6)

Fe(OCH3)2 -FeO + CH3OCH3 (4.7)

It is apparent from our results that, although the cyclic polarization scan (Figure 4.3)

shows a long passive region, the corrosion rate is still high. This might be due to the

56

The obtained corrosion behaviour can be explained by considering a typical

corrosion mechanism in organic solvents. According to Heitz and Kyriazls (1978),

methanol is classified as a protic solvent that induces corrosion of metal (Me) even if it is

present in low concentrations. The anodic dissolution reaction of metal is:

Me Me "+ + n e " (4.2)

and the cathodic reaction, i.e., the reduction of acidic hydrogen (HA) of a proton donor

is:

HA + e " '/2 H2 + A" (4.3)

In our tests, the methanol was not degassed to remove dissolved oxygen (O2). Thus, in

addition to the acidic hydrogen (in Reaction 4.3), the dissolved O2 was a primary

contributor to the corrosion. According to Kawai et al. (1995) and Banas and Banas,

(2009), the anodic reaction involves the dissolution of iron (Fe) and the cathodic reaction

involves the reduction of methanol (CH3OH) in the presence of dissolved O2, promoting

the formation of methoxy ions (CH3O") as shown below.

Fe -> Fe2+ + 2e" (4.4)

02 + 2CH3OH + 4e" -» 2CH30" + 20H" (4.5)

The methoxy ion reacts with Fe to form ferrous methoxide (Fe(OCH3)2) on the surface

and decomposes into ferrous oxide (FeO) as a passive layer on the surface. The formation

of such a passive layer can be written as:

Fe2+ + 2CH30' -» Fe(OCH3)2 (4.6)

Fe(OCH3)2 ->FeO + CH3OCH3 (4.7)

It is apparent from our results that, although the cyclic polarization scan (Figure 4.3)

shows a long passive region, the corrosion rate is still high. This might be due to the

56

nature of the unstable FeO layer. Similar results were also reported in Banas and Banas,

(2009).

To reduce the corrosion rate in the methanol storage tank, two corrosion control

methods were evaluated in this work. The first is the application of nitrogen (N2)

blanketing to remove dissolved 0 2 from the methanol and prevent 0 2 from further

dissolution. The second is the use of stainless steel SS304 instead of CS1018. The results

in Table 4.2 and Figure 4.4 show that both control methods are effective in suppressing

corrosion.

N2 blanketing induces passivation of Fe(OCH3)2 on the metal surface (Reaction

4.6) to a level that is similar to the aerated methanol environment. However, it shifts the

polarization curve of CS1018 to the left and lowers corrosion potential (Ec.,-,), thus

making Fe(OCH3)2 stable and preventing Fe(OCH3)2 from decomposing into the

unstable FeO (Banas and Banas, 2009). As a result, the corrosion current (Lo„) is reduced,

which in turn significantly reduces the corrosion rate of CS1018 from 29 to 0.05 mpy.

SS304 induces passivation in the aerated methanolic environment and causes a

positive shift in Ecorr and a decrease in Iron compared to CS1018 in the aerated methanolic

environment. This results in a significant reduction in corrosion rate to 0.04 mpy. Note

that SS304 may not be preferred in spite of its high corrosion-resistant property. This is

due to two reasons. Firstly, SS304 could be susceptible to pitting and localized corrosion

in a methanolic environment over long-term exposure due to the oxidation products of

methanol, especially in presence of water (Smialowska and Mankowski, 1982). Secondly,

SS304 is more costly than carbon steel. Due to the cost, high-density polyethylene and

vulcanized rubber

57

nature of the unstable FeO layer. Similar results were also reported in Banas and Banas,

(2009).

To reduce the corrosion rate in the methanol storage tank, two corrosion control

methods were evaluated in this work. The first is the application of nitrogen (N2)

blanketing to remove dissolved O2 from the methanol and prevent O2 from further

dissolution. The second is the use of stainless steel SS304 instead of CS 1018. The results

in Table 4.2 and Figure 4.4 show that both control methods are effective in suppressing

corrosion.

N2 blanketing induces passivation of Fe(OCH3)2 on the metal surface (Reaction

4.6) to a level that is similar to the aerated methanol environment. However, it shifts the

polarization curve of CS1018 to the left and lowers corrosion potential (Ecorr), thus

making Fe(OCH3)2 stable and preventing Fe(OCH3)2 from decomposing into the

unstable FeO (Banas and Banas, 2009). As a result, the corrosion current (ICOrr) is reduced,

which in turn significantly reduces the corrosion rate of CS1018 from 29 to 0.05 mpy.

SS304 induces passivation in the aerated methanolic environment and causes a

positive shift in Ecorr and a decrease in Icon- compared to CS1018 in the aerated methanolic

environment. This results in a significant reduction in corrosion rate to 0.04 mpy. Note

that SS304 may not be preferred in spite of its high corrosion-resistant property. This is

due to two reasons. Firstly, SS304 could be susceptible to pitting and localized corrosion

in a methanolic environment over long-term exposure due to the oxidation products of

methanol, especially in presence of water (Smialowska and Mankowski, 1982). Secondly,

SS304 is more costly than carbon steel. Due to the cost, high-density polyethylene and

vulcanized rubber

57

Pot

entia

l (m

V v

s. A

g/A

gCI)

250

150

50

-50

-150

-250

-350

-450

-550

o CS 1018 Without N2 blanketing

CS 1018 With N2 blanketing

SS 304 without N2 blanketing

-10 -9 -8 -7 -6 -5 -4 -3 -2


Figure 4.4: Potentiodynamic polarization curves produced from the applications of N2

blanketing and SS304 as corrosion control methods for methanol storage at 25°C and 1

atm

58

250

150

5" 50 O) < J -50 wi > -150 E

1 -250 c OJ £ -350

-450

-550

-10 -9 -8 -7 -6 -5 -4 -3 -2


o/«

o CS 1018 Without N2 blanketing

CS 1018 With N2 blanketing

SS 304 without N2 blanketing

Figure 4.4: Potentiodynamic polarization curves produced from the applications of N2

blanketing and SS304 as corrosion control methods for methanol storage at 25°C and 1

atm

58

materials are preferred for methanol storage

(http://www.inchem.ogr ldocuments/hsg/hsg/v 1 05 hsg.htm#SectionN umber4.5 as of Sept.

2010 — Published by the World Health Organization for the International Program on

Chemical Safety).

4.1.2.2 Location 2: Sulphuric acid storage tank

As seen from Figure 4.5, CS1018 in sulfuric acid at 25°C and atmospheric

pressure exhibits a long passive zone with a transpassive region with a corrosion rate of

30 mpy. The reverse scan crosses the forward scan, indicating no pitting tendency. The

corrosion in this acidic environment occurs due to the anodic dissolution reaction

(Reaction 4.4) and cathodic reduction of hydrogen ions (H+) (Reaction 4.8).

2H+ + 2e -3 112 (4.8)

The passive film found on the metal surface is iron sulphate (FeSO4) (Crolet, 1993) and is

formed as per the following reaction:

Fe2+ + S042- 4—* FeSO4 (4.9)

To reduce the corrosion rate in the sulfuric acid storage, due to the long

passivation zone, proper anodic protection can be used (Jones, D.A, 1992). Otherwise,

fibre reinforced plastic (FRP), which is cheaper than CS1018 and maintenance free

(Fontana, 3rd Ed, 1986) is an alternative.

4.1.2.3 Location 3: Methanol and acid mixing tank

Figure 4.6 shows the cyclic polarization curve of Location 3 where methanol

(67%) and sulphuric acid (33%) are premixed. The curve exhibits an active state of

59

materials are preferred for methanol storage

(http://www.inchem.Org/documents/hsa/hsg/vl05hsg.htm#SectionNumber:4.5 as of Sept.

2010 - Published by the World Health Organization for the International Program on

Chemical Safety).

4.1.2.2 Location 2: Sulphuric acid storage tank

As seen from Figure 4.5, CS1018 in sulfuric acid at 25°C and atmospheric

pressure exhibits a long passive zone with a transpassive region with a corrosion rate of

30 mpy. The reverse scan crosses the forward scan, indicating no pitting tendency. The

corrosion in this acidic environment occurs due to the anodic dissolution reaction

(Reaction 4.4) and cathodic reduction of hydrogen ions (H+) (Reaction 4.8).

2H+ + 2e" -» H2 (4.8)

The passive film found on the metal surface is iron sulphate (FeS04) (Crolet, 1993) and is

formed as per the following reaction:

Fe2+ + S042"~FeS04 (4.9)

To reduce the corrosion rate in the sulfuric acid storage, due to the long

passivation zone, proper anodic protection can be used (Jones, D.A, 1992). Otherwise,

fibre reinforced plastic (FRP), which is cheaper than CS1018 and maintenance free

(Fontana, 3rd Ed, 1986) is an alternative.

4.1.2.3 Location 3: Methanol and acid mixing tank

Figure 4.6 shows the cyclic polarization curve of Location 3 where methanol

(67%) and sulphuric acid (33%) are premixed. The curve exhibits an active state of

59

Pot

entia

l (m

V v

s. A

g/A

gCI)

800

600

400

200

0

-200

-400

-600

.• ow gm . mn• .11:".... ... m a es

• m . m m. mil. mod' i 11. : ..

—Forward scan

- - - Reverse scan

-8 -7 -6 -5 -4 -3 -2 -1

Log Current density (A/cm2)

Figure 4.5: Potentiodynamic polarization curve of CS1018 in sulphuric acid at 25°C and

1 atm

60

800

600

O 400 O) $ O)

> E rr o ro

o -200

-400

-600

-8 -7 -6 -5 -4 -3 -2 -1

Log Current density (A/cm2)

Figure 4.5: Potentiodynamic polarization curve of CS 1018 in sulphuric acid at 25°C and

1 atm

Forward scan

- - Reverse scan

60

200

Pot

entia

l (m

V v

s. A

g/A

gCI)

100

0

-100

-200

-300

-400

-500

-600

-700

—Forward Scan

- - - Reverse Scan

-7 -6 -5 -4 -3 -2 -1 0


Figure 4.6: Potentiodynamic polarization curve of CS1018 in a mixture of

methanol (67%) and sulphuric acid (33%) at 25°C and 1 atm

61

— Forward Scan

- Reverse Scan

-6 -5 -4 -3 -2


-1

Figure 4.6: Potentiodynamic polarization curve of CS 1018 in a mixture of

methanol (67%) and sulphuric acid (33%) at 25°C and 1 atm

61

CS1018 with a corrosion rate of 40 mpy. The reverse scan occurs before passivation

begins and somewhat overlaps with the forward scan, suggesting the possibility of

pitting. The reason that CS1018 does not passivate was given by Banas (1987) and Banas

and Banas (2009): iron forms a methoxy compound Fe(OCH3)2 as per Reaction (4.6).

However, the presence of H+ in the methanolic acid solution activates the metal surface,

thereby hindering the inhibiting nature of the methoxide film. Use of HDPE or fibreglass

reinforced plastic with epoxy vinyl ester resin (FRP) could be an effective corrosion

control method for this location.

4.1.2.4 Location 4: Methanol recovery flow line

As seen in Figure 4.7, CS1018 is in the passive state when exposed to the mixture

of methanol (99.6%) and water (0.4%) at 35°C and 0.2 atm, resulting in a very low

corrosion rate of 1.9 mpy. Compared to Location 1 (methanol storage), the methanol

recovery flow line is much less susceptible to corrosion despite the methanolic solution

composition. This is due to the presence of a small amount of water as is explained

below.

According to Heitz and Kyriazls (1978), Banas (1987), the presence of the small

amount of water in methanol inhibits the corrosion of metal by forming a stable passive

layer. Farina et al. (1978) suggested the following mechanism based on the inherent

acidity of protic solvent:

2 CH3OH H CH3OH2+ + CH30" (4.10)

Fe2+ + H20 ---+ Fe0H+ + H+ (4.11)

Fe2+ + CH3OH FeOCH3+ + H+ (4.12)

62

CS1018 with a corrosion rate of 40 mpy. The reverse scan occurs before passivation

begins and somewhat overlaps with the forward scan, suggesting the possibility of

pitting. The reason that CS1018 does not passivate was given by Banas (1987) and Banas

and Banas (2009): iron forms a methoxy compound Fe(OCH3)2 as per Reaction (4.6).

However, the presence of H+ in the methanolic acid solution activates the metal surface,

thereby hindering the inhibiting nature of the methoxide film. Use of HDPE or fibreglass

reinforced plastic with epoxy vinyl ester resin (FRP) could be an effective corrosion

control method for this location.

4.1.2.4 Location 4: Methanol recovery flow line

As seen in Figure 4.7, CS1018 is in the passive state when exposed to the mixture

of methanol (99.6%) and water (0.4%) at 35°C and 0.2 atm, resulting in a very low

corrosion rate of 1.9 mpy. Compared to Location 1 (methanol storage), the methanol

recovery flow line is much less susceptible to corrosion despite the methanolic solution

composition. This is due to the presence of a small amount of water as is explained

below.

According to Heitz and Kyriazls (1978), Banas (1987), the presence of the small

amount of water in methanol inhibits the corrosion of metal by forming a stable passive

layer. Farina et al. (1978) suggested the following mechanism based on the inherent

acidity of protic solvent:

2 CH3OH <-• CH3OH2++ CH3O"

Fe2+ + H20 -• FeOH+ + H+

Fe2+ + CH3OH — FeOCH3+ + H+

(4.10)

(4.11)

(4.12)

62

Pot

entia

l (m

V v

s. A

g/A

gCI)

500

400

300

200

100

0

-100

-200

-300

-400

-9 -8 -7 -6 -5 -4


Figure 4.7: Potentiodynamic polarization curve of CS1018 in a mixture of methanol

(99.6%) and water (0.4%) at 35°C and 0.2 atm

63

500

400

300 o

<. 200 o> < c/j 100 >

100

> E 0 —

"-4—• c -100 0) o

CL -200

-300

-400

-9 -7


Figure 4.7: Potentiodynamic polarization curve of CS 1018 in a mixture of methanol

(99.6%) and water (0.4%) at 35°C and 0.2 atm

63

4. RESULTS AND DISCUSSION 49

4.1 Electrochemical tests 49

4.1.1 Acid esterification process and tested locations 49

4.1.2 Corrosion in tested process locations 52

4.1.2.1 Location 1: Methanol Storage tank 52

4.1.2.2 Location 2: Sulphuric acid storage tank 59

4.1.2.3 Location 3: Methanol and acid mixing tank 59

4.1.2.4 Location 4: Methanol recovery flow line 62

4.1.2.5 Location 5: Mixing tank of fresh and

recovered methanol and sulphuric acid 64

4.1.2.6 Location 6: Oil and free-fatty acid (FFA)

storage tank 66

4.1.2.7 Location 7: Esterification reactor 68

4.1.2.8 Location 8: Glycerol feed to stripping column 74

4.1.2.9 Location 9: End product recovery flow line 74

4.1.2.10 Location 10: Inlet to vacuum distillation

column 74

4.1.2.11 Location 11: Vacuum distillation column 80

4.2 Weight loss test 84

5. CONCLUSIONS AND FUTURE WORK 90

5.1 Conclusions 90

5.2 Recommendations for future work 92

vi

4. RESULTS AND DISCUSSION 49

4.1 Electrochemical tests 49

4.1.1 Acid esterification process and tested locations 49

4.1.2 Corrosion in tested process locations 52

4.1.2.1 Location 1: Methanol Storage tank 52

4.1.2.2 Location 2: Sulphuric acid storage tank 59

4.1.2.3 Location 3: Methanol and acid mixing tank 59

4.1.2.4 Location 4: Methanol recovery flow line 62

4.1.2.5 Location 5: Mixing tank of fresh and

recovered methanol and sulphuric acid 64

4.1.2.6 Location 6: Oil and free-fatty acid (FFA)

storage tank 66

4.1.2.7 Location 7: Esterification reactor 68

4.1.2.8 Location 8: Glycerol feed to stripping column 74

4.1.2.9 Location 9: End product recovery flow line 74

4.1.2.10 Location 10: Inlet to vacuum distillation

column 74

4.1.2.11 Location 11: Vacuum distillation column 80

4.2 Weight loss test 84

5. CONCLUSIONS AND FUTURE WORK 90

5.1 Conclusions 90

5.2 Recommendations for future work 92

vi

In addition, Brossia et al. (1995) reported that the corrosion inhibition of iron in a

methanol system by water is based on the proton hopping mechanism. The water

molecules decrease the mobility of 1-1+ ions and decrease the corrosion rate of iron.

Hence, based on the insignificant corrosion rate found, it is concluded that CS1018 can

be used as a construction material for Location 4.

4.1.2.5 Location 5: Mixing tank of fresh and recovered methanol and sulphuric acid

Figure 4.8 shows the cyclic polarization curve of Location 5 where fresh and

recovered methanol with a minor amount of water is mixed with sulphuric acid in order

to achieve a proper ratio of methanol and acid for the esterification reaction with respect

to the amount of oil. The curve shows that CS1018 is subject to a high corrosion rate of

100 mpy since it exhibits an active state and does not reach passivation prior to the

reverse polarization scan. The reverse polarization scan shows positive hysteresis,

suggesting pitting tendency.

The severe corrosion of CS1018 in Location 5 is due to the presence and the

proportion of sulphuric acid and water. Brossia et al. (1995) reveals that the addition of a

small amount of acid into methanolic solutions increases the corrosion rate of iron, and

the increase in corrosion rate could be controlled by the presence of water content.

As reported by Banas (1987), water content is an important factor for corrosion

and passivation on the metals, especially in organic solvents. This is because the water

molecules act as oxygen donors in the passivation process to form a passive oxide layer

on the metal surface. In order to have a stable passivation layer, the required water

content with respect to acid content to form the passive layer has to be 4:1 (water:acid on

64

In addition, Brossia et al. (1995) reported that the corrosion inhibition of iron in a

methanol system by water is based on the proton hopping mechanism. The water

molecules decrease the mobility of H+ ions and decrease the corrosion rate of iron.

Hence, based on the insignificant corrosion rate found, it is concluded that CS1018 can

be used as a construction material for Location 4.

4.1.2.5 Location 5: Mixing tank of fresh and recovered methanol and sulphuric acid

Figure 4.8 shows the cyclic polarization curve of Location 5 where fresh and

recovered methanol with a minor amount of water is mixed with sulphuric acid in order

to achieve a proper ratio of methanol and acid for the esterification reaction with respect

to the amount of oil. The curve shows that CS1018 is subject to a high corrosion rate of

100 mpy since it exhibits an active state and does not reach passivation prior to the

reverse polarization scan. The reverse polarization scan shows positive hysteresis,

suggesting pitting tendency.

The severe corrosion of CS1018 in Location 5 is due to the presence and the

proportion of sulphuric acid and water. Brossia et al. (1995) reveals that the addition of a

small amount of acid into methanolic solutions increases the corrosion rate of iron, and

the increase in corrosion rate could be controlled by the presence of water content.

As reported by Banas (1987), water content is an important factor for corrosion

and passivation on the metals, especially in organic solvents. This is because the water

molecules act as oxygen donors in the passivation process to form a passive oxide layer

on the metal surface. In order to have a stable passivation layer, the required water

content with respect to acid content to form the passive layer has to be 4:1 (water:acid on

64

200

— Forward Scan 100

Reverse Scan

Pot

entia

l (m

V v

s. A

g/A

gCI)

-100

-200

-300

-400

-500

-600 -7 -6 -5 -4 -3 -2


-1 0


methanol (95.8%), sulphuric acid (3.8%), and water (0.4%) at 25°C and 1 atm

65

- Forward Scan

Reverse Scan

-6 -5 -4 -3 -2



methanol (95.8%), sulphuric acid (3.8%), and water (0.4%) at 25°C and 1 atm

65

water content (i.e., water to acid ratio = 0.5:1 mol:mol) like in Location 5, such passive

molar basis). This ratio has to be increased with the increase in acid content since 1-1+ ions

accelerate the dissolution of the protective oxide film. However, in the presence of minor

oxide film cannot be present on the metal surface as a result of the oxide film dissolution

by H±, thus resulting in severe corrosion.

To reduce the corrosion rate of CS1018 in Location 5, two possible methods can

be considered. The first is to use HDPE or fibreglass reinforced plastic with epoxy vinyl

ester resin (FRP) instead of carbon steel. The second is to induce the passivation of a

stable oxide layer on the metal surface by allowing a sufficient amount of water in the

recovered methanol. This, however, leads to a shortcoming in the process, i.e., a

reduction in the esterification reaction yield.

4.1.2.6 Location 6: Oil and free-fatty acid (FFA) storage tank

CS1018 in Location 6, where oil feedstock containing FFA is stored, is not

susceptible to corrosion. As observed from the polarization curve, corrosion current

values 0,00 are in the range of pA, which is below the detection limit of our potentiostat.

Therefore, CS1018 can be used for oil and FFA storage.

The corrosion resistance of CS1018 is due to physical properties of the oil

containing FFA, i.e., low conductivity in the range of ps/cm and high kinematic viscosity

(e.g., 78.2mm2/s at 20°C) (http://www.canolacouncil.org/oil tech.aspx as of October

2010). The corrosion resistance is also due to the presence of FFA. As reported by Heitz

and Kyriazls (1978), the corrosion rate decreases exponentially as the chain length of

carboxylic acids (C5 — C8) increases. In the esterification process, all FFA components

66

water content (i.e., water to acid ratio = 0.5:1 mol:mol) like in Location 5, such passive

molar basis). This ratio has to be increased with the increase in acid content since H+ ions

accelerate the dissolution of the protective oxide film. However, in the presence of minor

oxide film cannot be present on the metal surface as a result of the oxide film dissolution

by H+, thus resulting in severe corrosion.

To reduce the corrosion rate of CS1018 in Location 5, two possible methods can

be considered. The first is to use HDPE or fibreglass reinforced plastic with epoxy vinyl

ester resin (FRP) instead of carbon steel. The second is to induce the passivation of a

stable oxide layer on the metal surface by allowing a sufficient amount of water in the

recovered methanol. This, however, leads to a shortcoming in the process, i.e., a

reduction in the esterification reaction yield.

4.1.2.6 Location 6: Oil and free-fatty acid (FFA) storage tank

CS1018 in Location 6, where oil feedstock containing FFA is stored, is not

susceptible to corrosion. As observed from the polarization curve, corrosion current

values (ICorr) are in the range of pA, which is below the detection limit of our potentiostat.

Therefore, CS1018 can be used for oil and FFA storage.

The corrosion resistance of CS1018 is due to physical properties of the oil

containing FFA, i.e., low conductivity in the range of (Js/cm and high kinematic viscosity

(e.g., 78.2mm2/s at 20°C) (http://www.canolacouncil.org/oil tech.aspx as of October

2010). The corrosion resistance is also due to the presence of FFA. As reported by Heitz

and Kyriazls (1978), the corrosion rate decreases exponentially as the chain length of

carboxylic acids (C5 - C8) increases. In the esterification process, all FFA components

66

are C18 atoms with long carbon chain length, causing steric hindrance. A similar result

reported by Gaupp in 1937 for the corrosion of steel in various vegetable oils also shows

no corrosion effects due to FFAs.

Mechanistically, FFAs are known to passivate on the metal surface through

chemisorption. As reported by Luo et al. (1998), the inhibitive property of the oleate fatty

acid components in acidic medium is due to the electrostatic adsorption on the metal

surface and formation of electrostatic or covalent bonding between the metal surface

atoms and adsorbates. This electrostatic adsorption enhances the chemisorption and

thereby increases the inhibition with a significantly low value of Icon.. Luo et al. (1998)

also found that the inhibitive performance of oleate fatty acid increases as the

concentration of the fatty acid component increases.

Similarly, the passivation of FFAs on the metal surface by chemisorption was also

reported to provide high inhibitive performance by other researchers. Omanovic and

Roscoe (2000) classified linoleate fatty acid as a mixed-type inhibitor and explained that

linoleate induces chemisorption or a self-assembled blocking mechanism in which

linoleate molecules bind strongly on the metal surface to block the oxidation reaction and

act as a barrier to diffuse ions and electrons.

This can be further substantiated by the study done by Quraishi et al. (2002). They

observed that the fatty acid components of C11 — C18 were adsorbed on the metal surface

in an acidic medium and blocked the corrosion reactions, which led to a very low Icor,

value similar to what was observed in this study.

67

are C18 atoms with long carbon chain length, causing steric hindrance. A similar result

reported by Gaupp in 1937 for the corrosion of steel in various vegetable oils also shows

no corrosion effects due to FFAs.

Mechanistically, FFAs are known to passivate on the metal surface through

chemisorption. As reported by Luo et al. (1998), the inhibitive property of the oleate fatty

acid components in acidic medium is due to the electrostatic adsorption on the metal

surface and formation of electrostatic or covalent bonding between the metal surface

atoms and adsorbates. This electrostatic adsorption enhances the chemisorption and

thereby increases the inhibition with a significantly low value of Icorr- Luo et al. (1998)

also found that the inhibitive performance of oleate fatty acid increases as the

concentration of the fatty acid component increases.

Similarly, the passivation of FFAs on the metal surface by chemisorption was also

reported to provide high inhibitive performance by other researchers. Omanovic and

Roscoe (2000) classified linoleate fatty acid as a mixed-type inhibitor and explained that

linoleate induces chemisorption or a self-assembled blocking mechanism in which

linoleate molecules bind strongly on the metal surface to block the oxidation reaction and

act as a barrier to diffuse ions and electrons.

This can be further substantiated by the study done by Quraishi et al. (2002). They

observed that the fatty acid components of Cn - Cis were adsorbed on the metal surface

in an acidic medium and blocked the corrosion reactions, which led to a very low Icon-

value similar to what was observed in this study.

67

4.1.2.7 Location 7: Esterification reactor

Location 7 (the esterification reactor) is where FFAs are converted into biodiesel.

To simulate the environment of the esterification reactor, the esterification reaction was

carried out separately prior to electrochemical experiments to ascertain the completion of

the esterification reaction. The completion of the esterification reaction was confirmed by

conducting acid number measurements using a titration method approved by ASTM

D974-04. The amount of FFA is essentially equal to half of the obtained acid number

value. As seen in Figure 4.9, %FFA decreases significantly in the first 10 minutes and

then gradually decreases to a %FFA of 0.10 ± 0.05 in 60-90 minutes, depending on the

ratio of methanol to oil used. The stabilization of %FFA indicates the completion of the

esterification reaction, which was achieved in all experiment repetitions.

After the completion of the esterification reaction, the solution from the

esterification reactor was used for cyclic polarization experiments. Figure 4.10 shows that

CS1018 passivates in the esterification reactor, and its corrosion rate is 0.0037 mpy,

which is insignificant in spite of the presence of all corrosive agents such as methanol,

sulphuric acid, and water. The reverse scan exhibits negative hysteresis, suggesting no

pitting tendency. Similar results showing the corrosion resistance of CS1018 were also

found in the esterification environment with different compositions of methanol, oil, and

sulphuric acid (see Tables 4.1-4.2 and Figures 4.11-4.12). The inhibitive property of FFA

components (e.g., oleic acid) is the reason behind the low corrosion rates as previously

discussed regarding Location 6. Therefore, CS 1018 can be used for the esterification

reactor.

68

4.1.2.7 Location 7: Esterification reactor

Location 7 (the esterification reactor) is where FFAs are converted into biodiesel.

To simulate the environment of the esterification reactor, the esterification reaction was

carried out separately prior to electrochemical experiments to ascertain the completion of

the esterification reaction. The completion of the esterification reaction was confirmed by

conducting acid number measurements using a titration method approved by ASTM

D974-04. The amount of FFA is essentially equal to half of the obtained acid number

value. As seen in Figure 4.9, %FFA decreases significantly in the first 10 minutes and

then gradually decreases to a %FFA of 0.10 ± 0.05 in 60-90 minutes, depending on the

ratio of methanol to oil used. The stabilization of %FFA indicates the completion of the

esterification reaction, which was achieved in all experiment repetitions.

After the completion of the esterification reaction, the solution from the

esterification reactor was used for cyclic polarization experiments. Figure 4.10 shows that

CS1018 passivates in the esterification reactor, and its corrosion rate is 0.0037 mpy,

which is insignificant in spite of the presence of all corrosive agents such as methanol,

sulphuric acid, and water. The reverse scan exhibits negative hysteresis, suggesting no

pitting tendency. Similar results showing the corrosion resistance of CS1018 were also

found in the esterification environment with different compositions of methanol, oil, and

sulphuric acid (see Tables 4.1-4.2 and Figures 4.11-4.12). The inhibitive property of FFA

components (e.g., oleic acid) is the reason behind the low corrosion rates as previously

discussed regarding Location 6. Therefore, CS 1018 can be used for the esterification

reactor.

68

3.00

2.50

2.00

LLu- 1.50 '85-)

1.00

0.50

0.00 5 10 15 20 25 30 40 50 60 75 90 105 120

Duration (min)

Figure 4.9: Free fatty acid conversion over time (Final FFA = 0.10% ± 0.05)

69

3.00

2.50

2.00

< Li. L-vP

1.50

1.00

0.50

0.00

10 15 20 25 30 40 50 60 75 90 105 120 5

Duration (min)

Figure 4.9: Free fatty acid conversion over time (Final FFA = 0.10% ± 0.05)

69

Pot

entia

l (m

V v

s. A

g/A

gCI)

1400

1050

700

350

-350

-700

Forward Scan

Reverse Scan

, - -- - -- -

-14 -13 -12 -11 -10 -9 -8 -7

Log current density (Ncm2)

Figure 4.10: Potentiodynamic polarization curve of CS1018 in a mixture of oil, methyl

oleate, methanol, sulphuric acid, and water (prepared from 7a in Table 4.1) at 65°C and 1

atm

70

1400

Forward Scan

1050 Reverse Scan

700

350

0

-350

-700 -12 -14 -13 -10


Figure 4.10: Potentiodynamic polarization curve of CS1018 in a mixture of oil, methyl

oleate, methanol, sulphuric acid, and water (prepared from 7a in Table 4.1) at 65°C and 1

atm

70

Pot

entia

l (m

V v

s. A

g/A

gCI)

1500

1250

1000

750

500

250

0

-250

-500

-750 -14 -13

- 10:1 Methanol:Oil

18:1 Methanol:Oil

-12 -11 -10 -9

Log current density(A/cm2)

i -8 -7 -6

Figure 4.11: Effect of methanol concentration on polarization behaviour of CS1018 in an

esterification reactor at 65°C and 1 atm (Solution prepared from [7b] and [7c] in Table

4.1)

71

1500

1250

1000

750

500

250

-250

-500

-750

10:1 MethanohOil

18:1 Methanol:Oil

-14 -13 -12 -11 -10

Log current derisity(A/cm )

Figure 4.11: Effect of methanol concentration on polarization behaviour of CS 1018 in an

esterification reactor at 65°C and 1 atm (Solution prepared from [7b] and [7c] in Table

4.1)

71

Pot

entia

l (m

V v

s. A

g/A

gCI)

1500

1250

1000

750

500

250

0

-250

-500

— 1% Sulphuric acid

5% Sulphuric acid

-750 -14 -13 -12 -11 -10 -9 -8 -7 -6


Figure 4.12: Effect of sulphuric acid concentration on polarization behaviour of CS1018

in an esterification reactor at 65°C and 1 atm (Solution prepared from [7b] and [7d] in

Table 4.1)

72

1500

1250 1% Sulphuric acid

1000 5% Sulphuric acid

750

500

250

0

-250

-500

-750 -14 -13 -12 11 -10 •9 8 •7 •6


Figure 4.12: Effect of sulphuric acid concentration on polarization behaviour of CS1018

in an esterification reactor at 65°C and 1 atm (Solution prepared from [7b] and [7d] in

Table 4.1)

72

Pot

entia

l (m

V v

s. A

g/A

gCI)

2000

1500

1000

500

-500

-1000 -10

—Forward Scan

Reverse Scan

-9 -8 -7 -6

Log current density(Alcm2)

-5 -4

Figure 4.13: Potentiodynamic polarization curve of CS1018 in glycerol at 35°C and 1

atm

73

2000

1500

1000

500

•Forward Scan

Reverse Scan

-500

-1000

-10 -9 -8 -6 -5 -4

Log current density(A/cm )

Figure 4.13: Potentiodynamic polarization curve of CS1018 in glycerol at 35°C and 1

atm

73

REFERENCES 93

APPENDIX A - EXPERIMENTAL DATA OF WEIGHT LOSS TEST 101

vii

REFERENCES

APPENDIX A - EXPERIMENTAL DATA OF WEIGHT LOSS TEST

vii

4.1.2.8 Location 8: Glycerol feed to stripping column

After the esterification reactor, the product stream with unreacted oil was passed

through a stripping column where glycerol was used as a stripping agent. In order to

evaluate the corrosiveness of glycerol on CS1018, a potentiodynamic polarization scan

was carried out in the glycerol environment at 35°C and 1 atm. As shown in Table 4.2

and Figure 4.13, the corrosion rate of CS1018 is low at 2.37 mpy; however, CS1018 is

prone to the pitting type of corrosion as evidenced by the positive hysteresis of reverse

polarization scan. The presence of a large quantity of fatty acid components and its

inhibition performance according to the chemisorption mechanism as previously

described could easily eliminate the corrosion threat by glycerol. Hence, CS1018 is a

suitable material for the glycerol feed to the stripping column.

4.1.2.9 Location 9: End product recovery flow line

The end product recovery flow line containing oil (93.7%) and methyl oleate

(6.3%) is not susceptible to corrosion. Due to the low conductivity and high viscosity of

oil, the value is significantly low in terms of pA and cannot be measured by our

potentiostat. Therefore, carbon steel is compatible with this environment.

4.1.2.10 Location 10: Inlet to vacuum distillation column

The inlet to the vacuum distillation column is found to be highly corrodible when

made of CS1018. As shown in Figure 4.14, CS1018 is in the active state with a corrosion

rate of approximately 720 mpy, and the reverse polarization scan overlaps with the

74

4.1.2.8 Location 8: Glycerol feed to stripping column

After the esterification reactor, the product stream with unreacted oil was passed

through a stripping column where glycerol was used as a stripping agent. In order to

evaluate the corrosiveness of glycerol on CS1018, a potentiodynamic polarization scan

was carried out in the glycerol environment at 35°C and 1 atm. As shown in Table 4.2

and Figure 4.13, the corrosion rate of CS1018 is low at 2.37 mpy; however, CS1018 is

prone to the pitting type of corrosion as evidenced by the positive hysteresis of reverse

polarization scan. The presence of a large quantity of fatty acid components and its

inhibition performance according to the chemisorption mechanism as previously

described could easily eliminate the corrosion threat by glycerol. Hence, CS1018 is a

suitable material for the glycerol feed to the stripping column.

4.1.2.9 Location 9: End product recovery flow line

The end product recovery flow line containing oil (93.7%) and methyl oleate

(6.3%) is not susceptible to corrosion. Due to the low conductivity and high viscosity of

oil, the Icorr value is significantly low in terms of pA and cannot be measured by our

potentiostat. Therefore, carbon steel is compatible with this environment.

4.1.2.10 Location 10: Inlet to vacuum distillation column

The inlet to the vacuum distillation column is found to be highly corrodible when

made of CS1018. As shown in Figure 4.14, CS1018 is in the active state with a corrosion

rate of approximately 720 mpy, and the reverse polarization scan overlaps with the

74

Pot

entia

l (m

V v

s. A

g/A

gCI)

200

100

0

-100

-200

-300

-400

-500

-600

-700 -6 -5 -4 -3


-2 -1


(55%), glycerol (40%), sulphuric acid (3.5%), and water (1.5%) at 60°C and 1 atm

75

200

100

0

-100

-200

-300

-400

-500

-600

-700

•Forward Scan

Reverse Scan

-4 -3 -2 -1




75

forward scan indicating pitting tendency. Such severe corrosion is due to the absence of a

passive oxide layer on the surface. As previously discussed in Section 4.1.2.5 (Location

5), the presence of water generally causes a passive oxide layer to form on the metal

surface. However, the presence of sulphuric acid (or H+) induces the dissolution of the

oxide layer at Location 10 since the ratio of water to acid is much lower than 4:1

(mol:mol) (Banas 1987). Note that the corrosion rate at this location is higher than that in

Location 5. This is because this location is operated at a higher temperature, thereby

increasing the solubility of the oxide layer in the methanolic solution.

It is apparent that Location 10 requires an application of a corrosion control

measure to reduce the corrosion rate to an acceptable level. In this work, the use of a

corrosion resistant material of construction, i.e., stainless steel, was investigated. Results

in Figures 4.15-4.16 show that SS304 shifts the polarization curve to a higher corrosion

potential (Ecorr) and much less current (compared to CS1018), yielding a much lower

corrosion rate of 25 mpy. Although SS304 induces a passive film to protect the metal

surface, this film is not stable as evidenced by the breakage and re-passivation of the

passive film.

Figure 4.15 also shows the positive hysteresis of the reverse polarization scan,

suggesting pitting tendency in Location 10. Similar findings were also reported in

Mansfeld (1973), Smialowska and Mankowski (1982) and, Singh and Singh (1988).

According to Smialowska and Mankowski (1982), the pitting of SS304 occurs due to the

solution acidification by methanol oxidation, as shown below.

CH3OH CH2O + 2H+ + 2e (4.13)

CH2O + H2O HCOOH + 2H+ + 2C (4.14)

76

forward scan indicating pitting tendency. Such severe corrosion is due to the absence of a

passive oxide layer on the surface. As previously discussed in Section 4.1.2.5 (Location

5), the presence of water generally causes a passive oxide layer to form on the metal

surface. However, the presence of sulphuric acid (or H+) induces the dissolution of the

oxide layer at Location 10 since the ratio of water to acid is much lower than 4:1

(mol:mol) (Banas 1987). Note that the corrosion rate at this location is higher than that in

Location 5. This is because this location is operated at a higher temperature, thereby

increasing the solubility of the oxide layer in the methanolic solution.

It is apparent that Location 10 requires an application of a corrosion control

measure to reduce the corrosion rate to an acceptable level. In this work, the use of a

corrosion resistant material of construction, i.e., stainless steel, was investigated. Results

in Figures 4.15-4.16 show that SS304 shifts the polarization curve to a higher corrosion

potential (Ecorr) and much less current (compared to CS1018), yielding a much lower

corrosion rate of 25 mpy. Although SS304 induces a passive film to protect the metal

surface, this film is not stable as evidenced by the breakage and re-passivation of the

passive film.

Figure 4.15 also shows the positive hysteresis of the reverse polarization scan,

suggesting pitting tendency in Location 10. Similar findings were also reported in

Mansfeld (1973), Smialowska and Mankowski (1982) and, Singh and Singh (1988).

According to Smialowska and Mankowski (1982), the pitting of SS304 occurs due to the

solution acidification by methanol oxidation, as shown below.

CH3OH -» CH20 + 2H+ + 2e" (4.13)

CH20 + H20 -» HCOOH + 2H+ + 2e" (4.14)

76

Pot

entia

l (m

V v

s. A

g/A

gCI)

200

100

0

-100

-200

-300

-400

-500 -7 -6 -5 -4


-3 -2

Figure 4.15: Potentiodynamic polarization curve of SS304 in a mixture of methanol


77

.2 c o •5 -300 CL

-400

-500

-7 -6 -5 -4 -3 -2


Forward Scan



77

1400

Pot

entia

l (m

V v

s. A

g/A

gCI)

1200

1000

800

600

400

200

0

-200

-400 0 0 0 00

-600

-800 -8 -7 -6 -5

0 CS 1018

SS 304

SS 316

-4


-3 -2 -1

Figure 4.16: Comparison of polarization behaviour of various materials of construction

for Location 10

78

O CS 1018

SS 304

SS 316


Figure 4.16: Comparison of polarization behaviour of various materials of construction

for Location 10

78

Pot

entia

l (m

V v

s. A

g/A

gCI)

1200

1000

800

600

400

200

0

-200 -8 -7 -6 -5 -4


-3 -2



79

1200

1000

o> 800 <: O) < co 600 > >

400 ro

•*-»

I 200

0

-200

-8 -7 -6 -5 -4 -3 -2




Forward Scan

Reverse Scan

79

HCOOH -CO2 + 2H+ + 2e- (4.15)

Since SS304 tends to pit and still yields a considerable corrosion rate of 25 mpy,

another grade of stainless steel, SS3 1 6, was evaluated. Figures 4.16-4.17 show that

SS316 induces a long passive zone and shifts the polarization curve to a higher Econ and

fewer currents (compared to SS304), thereby reducing the corrosion rate to 3.6 mpy.

SS316 also exhibits no pitting tendency as seen from the negative reverse polarization

scan. The high corrosion resistance of SS316 was explained by Ogawa et al. (1978) based

on the dissolution of molybdenum (Mo) in SS316 from the passive oxide film followed

by the adsorption of molybdate species on to the metal surface. It was also suggested by

Singh and Singh (1990) that the Mo content slows down or inhibits the reaction of

aggressive ions with the passive films.

Despite the presence of chromium (Cr) in SS304, which normally provides good

corrosion resistance in most corrosive environments, SS304 is not suitable for a

methanolic environment, especially in this location where the methanol is present in a

large quantity. However, the presence of Mo along with Cr in SS316 renders good

corrosion resistance. This was also confirmed by the study done by Bellucci et al. (1981)

and Singh and Singh (1990). Hence, SS316 is the most suitable material of construction

for Location 10.

4.1.2.11 Location 11: Vacuum distillation column

The vacuum distillation column made of CS1018 is the most corrodible area in

the acid-catalyzed esterification process. As seen in Figure 4.18, its polarization curve is

similar to the curve of Location 10 (the inlet to vacuum distillation column), i.e., the

80

HCOOH ->C02 + 2H+ + 2e" (4.15)

Since SS304 tends to pit and still yields a considerable corrosion rate of 25 mpy,

another grade of stainless steel, SS316, was evaluated. Figures 4.16-4,17 show that

SS316 induces a long passive zone and shifts the polarization curve to a higher Ecorr and

fewer currents (compared to SS304), thereby reducing the corrosion rate to 3.6 mpy.

SS316 also exhibits no pitting tendency as seen from the negative reverse polarization

scan. The high corrosion resistance of SS316 was explained by Ogawa et al. (1978) based

on the dissolution of molybdenum (Mo) in SS316 from the passive oxide film followed

by the adsorption of molybdate species on to the metal surface. It was also suggested by

Singh and Singh (1990) that the Mo content slows down or inhibits the reaction of

aggressive ions with the passive films.

Despite the presence of chromium (Cr) in SS304, which normally provides good

corrosion resistance in most corrosive environments, SS304 is not suitable for a

methanolic environment, especially in this location where the methanol is present in a

large quantity. However, the presence of Mo along with Cr in SS316 renders good

corrosion resistance. This was also confirmed by the study done by Bellucci et al. (1981)

and Singh and Singh (1990). Hence, SS316 is the most suitable material of construction

for Location 10.

4.1.2.11 Location 11: Vacuum distillation column

The vacuum distillation column made of CS1018 is the most corrodible area in

the acid-catalyzed esterification process. As seen in Figure 4.18, its polarization curve is

similar to the curve of Location 10 (the inlet to vacuum distillation column), i.e., the

80

200

100

0

cy) < -100 rn

cri -200 >

E -300 Co

-400 0

-500

-600

-700 -6 -5 -4 -3


-2 -1


(10.5%), glycerol (79.5%), sulphuric acid (7.1%), and water (2.9%) at 72°C and 0.3 atm

81

200

100

_ 0 O CO

< -100 en <

</i -200 > > H -300

In c -400 <D

2,00

-600

-700

-6 -5 -4 -3 -2 -1


- - Forward Scan

Reverse Scan O


(10.5%), glycerol (79.5%), sulphuric acid (7.1%), and water (2.9%) at 72°C and 0.3 atm

81

Pot

entia

l (m

V v

s. A

g/A

gCI)

200

100

0

-100

-200

-300

-400

-500

-600

—Forward Scan

Reverse Scan

-9 -8 -7 -6 -5 -4 -3 -2


Figure 4.19: Potentiodynamic polarization curve of SS 304 in a mixture of methanol

(10.5%), glycerol (79.5%), sulphuric acid (7.1%), and water (2.9%) at 72°C and 0.3atm

82

Forward Scan


Figure 4.19: Potentiodynamic polarization curve of SS 304 in a mixture of methanol

(10.5%), glycerol (79.5%), sulphuric acid (7.1%), and water (2.9%) at 72°C and 0.3atm

82

200

100

Pot

entia

l (m

V v

s. A

g/A

gCI)

0

-100

-200

-300

-400

-500

-600

-700

—SS 304

CS1018

-7 -6 -5 -4 -3 -2 -1 0


Figure 4.20: Comparison of polarization behaviour of CS1018 and SS304 for Location

11

83

CS1018


Figure 4.20: Comparison of polarization behaviour of CS 1018 and SS304 for Location

11

83

corrosion in biodiesel production process using

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