36 - hydrocracking of used cooking oil for biofuels production

8/12/2019 36 - Hydrocracking of Used Cooking Oil for Biofuels Production

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Hydrocracking of used cooking oil for biofuels production

Stella Bezergianni *, Aggeliki Kalogianni

Chemical Process Engineering Research Institute CPERI, Center for Research and Technology Hellas CERTH, 6th km Harilaou-Thermi Rd, 57001 Thermi, Thessaloniki, Greece

a r t i c l e i n f o

Article history:

Received 28 January 2009

Received in revised form 11 March 2009

Accepted 12 March 2009Available online 14 April 2009

Keywords:

Hydrocracking

Used cooking oil

Biofuels

a b s t r a c t

Hydrocracking of used cooking oil is studied as a potential process for biofuels production. In this work

several parameters are considered for evaluating the effectiveness of this technology, including hydro-

cracking temperature, liquid hourly space velocity (LHSV) and days on stream (DOS). Conversion and

total biofuels production is favored by increasing temperature and decreasing LHSV. However moderate

reaction temperatures and LHSVs are more attractive for diesel production, whereas higher temperatures

and smaller LHSVs are more suitable for gasoline production. Furthermore heteroatom (S, N and O)

removal increases as hydrocracking temperature increases, with de-oxygenation being particularly favor-

able. Saturation, however, is not favored with temperature indicating the necessity of a pre-treatment

step prior to hydrocracking to enable saturation of the double bonds and heteroatom removal. Finally

the impact of extended operation (catalyst life) on product yields and qualities indicates that all reactions

are affected yet at different rates.

2009 Elsevier Ltd. All rights reserved.

1. Introduction

The use of biofuels as an alternative source of transportation en-

ergy is promoted via national and international legislation and pro-

tective measures, as their production enhances sustainability and

economic growth. Biodiesel is the most common biofuel employed

in Europe and its production (mostly via transesterification) is

mainly based on raw vegetable oil (Panorama of Energy, 2007).

Vegetable oil is produced from oil based crops (rapeseed, soy-bean,

palm, sunflower etc.) which gives moderate yields per hectare.

Besides the importance of producing and using biofuels, there

are several considerations associated with the existing production

processes. The price and availability of the main byproduct glyc-

erin is both an economic but also environmental consideration.

Furthermore, existing technologies demand large biodiesel pro-

duction units which require large investments (Knothe et al.,

2005). However the most important consideration is the price

and availability of vegetable oil, the cost of which might reach up

to 75% of the total production cost (Phan and Phan, 2008). The lat-

ter can be compensated by employing used cooking oil collected

from restaurants and/or homes, the price of which is at least 23

times cheaper than virgin vegetable oils (Zhang et al., 2003).

Used cooking oil has been explored as a feedstock for biodiesel

production only via transesterification techniques. Alkali-catalyzed

transesterification of a single step (Phan and Phan, 2008; Meng

et al., 2008) or of a two step process ( Wang et al., 2007; Sharma

et al., 2008) gives high yields at moderate methanol/oil ratios

and mild temperatures. Another interesting technology is based

on heterogeneous solid catalyst-based transesterification (Cao

et al., 2008; Jacobson et al., 2008; Lou et al., 2008 ) which employs

more environmentally benign catalysts and is effective for used

cooking oil feedstocks, but requires higher temperatures. Enzy-

matic-catalysis-based transesterification exhibits significant yields

at moderate operating conditions (Yagiz et al., 2007; Halim et al.,

2009; Chen et al., 2009; Dizge et al., 2009) and shows significant

potential.

Catalytic hydroprocessing is an alternative technology for biofu-

els production technology which employs the existing infrastruc-

ture of petroleum refineries (Huber and Corma, 2007; Stumborg

et al., 1996), and has already several industrial applications (Neste

oil corporation, 2007; HPInnovations, 2006; Hayashi, 2008). The

technology has significant potential as the produced hydrotreated

vegetable oils have better fuel properties than the biodiesel pro-

duced via transesterification, and their use improves engine fuel

economy (Huber and Corma, 2007). Hydroprocessing of raw vege-

table oil heavy vacuum gas oil mixtures have been explored by

employing hydrotreating (Huber et al., 2007) and hydrocracking

(Bezergianni et al., 2009) catalysts at nominal operating conditions.

Nevertheless, this technology has only been applied to raw vegeta-

ble oil feedstocks.

This paper involves the investigation of used cooking oil as a

hydrocracking feedstock as well as the key parameters affecting

product yield and quality of such process. In particular the effect

of reactor temperature and liquid hourly space velocity (LHSV)

on product yields and quality are studied. Furthermore the depen-

dence of the hydrocracking effectiveness on the catalyst life (days

0960-8524/$ - see front matter 2009 Elsevier Ltd. All rights reserved.doi:10.1016/j.biortech.2009.03.039

* Corresponding author. Tel.: +30 2310 498315; fax: +30 2310 498380.

E-mail address:[email protected](S. Bezergianni).

Bioresource Technology 100 (2009) 39273932

Contents lists available at ScienceDirect

Bioresource Technology

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / b i o r t e c h
mailto:[email protected]://www.sciencedirect.com/science/journal/09608524http://www.elsevier.com/locate/biortechhttp://www.elsevier.com/locate/biortechhttp://www.sciencedirect.com/science/journal/09608524mailto:[email protected]


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on stream) is also explored. It should be mentioned that it is the

first application of catalytic hydroprocessing on used cooking oil.

2. Methodology

The CPERI hydroprocessing unit is a small-scale pilot plant unit

which is employed for hydrotreating (HDS, HDN) and hydrocrack-

ing of various feedstocks, varying from light gas oil to heavy vac-

uum gas oil. This small-scale pilot plant consists of a feed

system, a reactor system and a product separation system, as sche-

matically depicted inFig. 1(Bezergianni et al., 2009).

The total liquid product is collected and several analyses can

take place in the analytical laboratory of CPERI. The simulated dis-

tillation curve is determined via an Agilent 6890 N-GC according to

the ASTM D-7213 procedure. The density of the total liquid prod-

uct is measured via an Anton-Paar density/concentration meter

DMA 4500 according to ASTM D-1052. The concentration of sulfur

and nitrogen is measured via an Antek 5000 system, according to

ASTM D5453-93 and ASTM D4629 procedures, respectively. Total

carbon concentration is measured via a CHN LECO 800 analyzer. Fi-

nally, hydrogen is measured via an Oxford Instruments NMR MQA

7020. Once total carbon, hydrogen, sulfur and nitrogen wt% are

determined, the oxygen concentration is indirectly determinedassuming its the only significant element contained in the product.

The aforementioned analyses are also performed for the feed-

stocks. The reaction gases are analyzed offline via a Hewlett-Pack-

ard 5890 Series II-GC equipped with two detectors, a Thermal

Conductivity Detector (TCD) and a Flame Ionization Detector

(FID). The TCD is used for the analysis of H2, CO, CO2, O2, N2 and

H2S while the FID is used for CH4 and C2C6, hydrocarbons.

For all experiments the same commercial hydrocracking cata-

lyst and feedstock were employed. The catalyst was pre-sulphided

according to the catalyst providers recommended procedure. Fur-

thermore, in order to maintain constant catalyst activity, DMDS

(Di-Methyl-Di-Sulfide) and TBA (Tetra-Butyl-Amine) were added

to achieve a specific sulfur and nitrogen concentration in each

feedstock. An experiment was considered complete when the reac-tions reached steady state, usually after 56 days on stream. This

was examined by monitoring the product density on a daily basis.

Once the product density was stabilized, the individual effects of

each experiment were considered stable and the study complete.

The product collected during the last day of each study was ana-

lyzed in detail, as it represented that particular condition.

In order to analyze the effectiveness of hydrocracking reactions,

hydrocracking conversion can be employed. Hydrocracking con-

version (%) is defined as the percentage of the heavy fraction of

feed which has been converted to lighter products during

hydrocracking:

Conversion % Feed360 Product360

Feed360100 1

where Feed360and Product360are the wt% of the feed and product,

respectively, which have a boiling point higher than 360 C.

Furthermore, in order to measure the hydrocracking effective-

ness towards the production of a particular product instead of

other products, the measure of selectivity is employed. Selectivity

can be defined for different products (ex diesel, gasoline etc.) based

on the boiling point range which defines these products. For exam-

ple, for a product with initial and final boiling points A and B,

respectively, selectivity is defined as:

Product selectivity% ProductAB FeedAB

Feed360 Product360 100 2

where Feed360and Product360are the wt% of the feed and product,

respectively, which have a boiling point higher than 360C (i.e. hea-

vy molecules of feed and product) and FeedAB and ProductAB are

the wt% of the feed and product, respectively, which have a boiling

point range betweenA and B degrees Celsius. From Eq.(2)selectiv-

ity can be defined for diesel (180360C), kerosene/jet (170

270C) and naphtha (40200 C).

3. Results

A series of experiments were conducted to study the effect of

reactor temperature and liquid hourly space velocity (LHSV) on

hydrocracking of used cooking oil. Moreover the effects of catalyst

deactivation are also explored. The feedstock employed was 100%

used cooking oil. The used cooking oil was mainly collected from

local restaurants, while smaller amounts (


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(with boiling point > 360 C) compose the unconverted part of the

feed that cannot be utilized as liquid biofuels. The product yields in

thisFig. 2indicate that as reactor temperature increases, the pro-

duced liquid biofuels (gasoline and diesel) increase. This is ex-

pected as hydrocracking activity rises with increasing

temperature. As it is evident from this figure, diesel yield is more

than seven times higher than the gasoline yield at all temperatures,

indicating that this technology is more suitable for diesel produc-tion rather than gasoline production. Furthermore gasoline yield

increases monotonically with temperature, while diesel yield is

smaller at the middle temperature (370 C). The minimum diesel

yield observed at 370 C is attributed to the fact that increasing

temperature causes not only heavy molecules but also diesel ones

are cracked into lighter molecules.

The conversion as well as the diesel, kerosene/jet and naphtha

selectivities for the three different hydrocracking temperatures is

depicted inFig. 3. The conversion and selectivities are calculated

from the simulated distillation data of the total liquid product of

each hydrocracking temperature (Table 2), using Eqs.(1) and (2)

respectively. As temperature increases, the conversion increases

from 73% (at 350 C) to 82% (at 390 C). This is an expected out-

come as hydrocracking activity is favoured with temperature.When comparing the product selectivities however, the results

are more interesting. Diesel selectivity has the most significant val-

ues (>90%), as diesel production is most favorable. In the mean

time kerosene/jet and naphtha selectivities are below 20%. Dieselselectivity however, is not favoured with temperature, while the

other two selectivities are clearly favoured. This is expected as

increasing temperature causes more intensive cracking thus not

only heavier molecules but also some diesel molecules are further

cracked into lighter molecules. Therefore milder hydrocracking

temperatures (350 and 370 C) promote diesel rather than kero-

sene/jet or naphtha production.

The hydrogenation effect on the hydrocracked product at the

three reactor temperatures is given inTable 3. Bromine index indi-

cates the presence of olefins or double bonds. According to this ta-

ble, the feed bromine index is significantly reduced for all products.

However the bromine index increases for increasing hydrocracking

temperature, signifying that the saturation of double bonds de-

creases as reactor temperature increases. Therefore catalyst activ-ity is primarily driven towards cracking or other reactions rather

than saturation, which indicates that a hydrotreatment step might

be necessary prior to hydrocracking. The same conclusion is drawn

from the C/H ratio also given in Table 3. The C/H ratio is signifi-

cantly dropped from feed to products. However the C/H ratio in-

creases as hydrocracking temperature increases, indicating that

saturation is not favored with temperature, compared to the other

hydrocracking reactions.

Besides cracking and saturation, heteroatom removal (mainly

sulfur, nitrogen and oxygen) is another group of reactions that take

place during hydrocracking. The concentration of S, N and O for the

hydrocracking feed and products (at the three reactor tempera-

tures) are given inTable 2. The heteroatom removal as percent of

its concentration in the feed for the three different temperaturesis compared inFig. 4. Clearly the efficiency of heteroatom removal

71 69 73

2 6

10

0

10

20

30

40

50

60

70

80

90

100

093073053

Reactor Temperature (deg C)

%o

ftotal

liquidproduct

Gasoline

Diesel

Fig. 2. Temperature effect on diesel and gasoline yield (as vol% of total liquid

product). All experiments were performed at P= 2000 psig (13789.5 kPa),

LHSV = 1.5 h1 and H2/oil = 6000 scfb (1068 nm3/m3).

Table 2

Effect of reactor temperature on product quality. All experiments were performed at

P= 2000 psig (13789.5 kPa), LHSV = 1.5 h1 and H2/oil = 6000 scfb (1068 nm3/m3).

Feed 350 C 370 C 390 C

Density (kgr/m3) 0.9011 0.7734 0.7758 0.7719

S (wppm) 27070 278.6 156.8 109.2

N (wppm) 551.70 1.95 1.31 0.10

H (wt%) 11.29 14.62 14.63 14.62

C (wt%) 73.37 83.49 84.78 84.90

O (wt%) 12.58 1.86 0.57 0.47

IBP (C) 298.2 147.0 101.2 124.0

5% (C) 526.6 268.8 195.8 171.6

10% (C) 565.0 284.2 270.6 201.0

20% (C) 600.6 300.0 289.0 268.0

30% (C) 605.2 303.2 302.8 287.6

40% (C) 608.4 304.6 305.2 299.0

50% (C) 610.2 306.4 306.6 304.6

60% (C) 611.8 316.4 318.2 309.8

70% (C) 613.0 328.4 331.4 318.6

80% (C) 614.0 434.0 397.6 346.8

90% (C) 617.8 461.8 459.6 409.0

95% (C) 641.2 474.0 474.8 457.8

FBP (C) 733.4 590.0 571.0 571.2

0

10

20

30

40

50

60

70

80

90

100

350 355 360 365 370 375 380 385 390


Convers

ion

/S

elec

tiv

ities

(%)

Conversion

Diesel SelectivityKero/Jet Selectivity

Naphtha Selectivity

Fig. 3. Conversion and selectivities at different hydrocracking temperatures. All

experiments were performed atP= 2000 psig (13789.5 kPa), LHSV = 1.5 h1 and H2/

oil = 6000 scfb (1068 nm 3/m3).

Table 3

Bromine index and carbon-to-hydrogen (C/H) ratio of hydrocracking feed and

products at three different reactor temperatures. All experiments were performed

at P= 2000 psig (13789.5 kPa), LHSV = 1.5 h1 and H2/oil = 6000 scfb (1068 nm3/m3).

Feed Product

350 C 370 C 390 C

Br index 49,100 158.2 224.4 425

C/H 6.499 5.711 5.795 5.806

S. Bezergianni, A. Kalogianni/ Bioresource Technology 100 (2009) 39273932 3929


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for all three species (S, N and O) is high and is increasing with

hydrocracking temperature. Deoxygenation is particularly favor-

able to hydrocracking temperature, as the oxygen removal percent

of oxygen contained in feed increases from 85.2% to 96.3% between

350 and 390 C.

3.2. Effect of LHSV

The Liquid Hourly Space Velocity (LHSV) is an important oper-

ating parameter for regulating catalyst effectiveness and also cata-

lyst life expectancy. The effect of LHSV on cracking is the main

premise of this analysis. This study on product quality and yields

was performed on hydrocracking of used cooking oil at five differ-

ent LHSVs, i.e. 0.5, 1, 1.5, 2 and 2.5 h1. For this study three differ-

ent experimental runs were employed using the same

hydrocracking catalyst (used also for the study described in Section

3.1) and the same operating parameters i.e. T= 370 C,

P= 2000 psig (13789.5 kPa), and H2/oil = 6000 scfb (1068 nm3/m3).

The product yields at the five different LHSVs are given inFig. 5.

The product yields in this figure are not as variable with LHSV as

they were in the case of reactor temperature (Fig. 2). However an

overall decreasing trend is observed with increasing LHSV, which

is expected, as increasing LHSV implies smaller residence time of

the feed in the catalyst section (reactor) and therefore smaller

reaction time. FromFig. 5it is evident that diesel yield is signifi-

cantly higher than gasoline yield at all LHSVs.

The conversion as well as the diesel, kerosene/jet and naphtha

selectivities for the five different LHSVs are presented in Fig. 6.

As temperature increases the conversion decreases from 80% (at

LHSV = 0.5 h1) to 74% (at LHSV = 2.5 h1). This conversion de-

crease for increasing LHSV is anticipated since high LHSVs result

in smaller reaction time. Regarding individual product selectivities,

on one hand the diesel selectivity exhibits once again the most sig-

nificant values (>93%). On the other hand the kerosene/jet and

naphtha selectivities are below 20% for all LHSVs. Furthermore die-

sel selectivity is favoured with LHSV while kerosene/jet and naph-

tha selectivities are not. This is also expected as increasing LHSV(therefore decreasing reaction time) causes less cracking and

therefore a smaller production of the lighter products (kerosene/

jet and naphtha). Therefore higher LHSVs (P1.5 h1) promote die-

sel than kerosene/jet or naphtha production.

3.3. Effect of catalyst life (days on stream)

The industrial hydrocracking unit run length is one of the most

crucial parameters of catalyst selection and is mainly limited by

Catalyst Life. Catalyst Life or Catalyst Aging is mostly attributedto extended operation or by blockage of active sites attributed to

80

82

84

86

88

90

92

94

96

98

100

350 355 360 365 370 375 380 385 390


He

teroa

tom

Remova

l(%o

ffee

d)

Sulphur

Nitrogen

Oxygen

Fig. 4. Heteroatom (sulfur, nitrogen and oxygen) removal at different hydrocrack-

ing temperatures. All experiments were performed at P= 2000 psig (13789.5 kPa),LHSV = 1.5 h1 and H2/oil = 6000 scfb (1068 nm

3/m3).

71 70 69 70 71

9 86 7 5

0

10

20

30

40

50

60

70

80

90

100

0.5 1 1.5 2 2.5

LHSV (1/hr)

%o

ftotal

liqu

idpro

duc

t

Gasoline

Diesel

Fig. 5. LHSV effect on diesel and gasoline yield (as vol% of total liquid product). All

experiments were performed at P= 2000 psig (13789.5 kPa), LHSV = 1.5 h1 and H2/

oil = 6000 scfb (1068 nm3/m3).

0

10

20

30

40

50

60

70

80

90

100

0.5 1 1.5 2 2.5

LHSV (1/hr)

Convers

ion

(%)

Conversion

Diesel Selectivity

Kero/Jet Selectivity

Naphtha Selectivity

Fig. 6. Conversion and Selectivities at different LHSVs. All experiments were

performed at T= 370 C, P= 2000 psig (13789.5 kPa) and H2/oil = 6000 scfb

(1068 nm3/m3).

72.62 73.97

81.88

73.6570.8072.72

0

10

20

30

40

50

60

70

80

90

100

390370350


%C

onvers

ion

RUN-A

RUN-B

9 DOS 26 DOS 16 DOS 34 DOS

23 DOS

37 DOS

Fig. 7. Effect of DOS on hydrocracking conversion at different hydrocracking

temperatures. All experiments were performed at P= 2000 psig (13789.5 kPa),

LHSV = 1.5 h1 and H2/oil = 6000 scfb (1068 nm3/m3).

3930 S. Bezergianni, A. Kalogianni/ Bioresource Technology 100 (2009) 39273932


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the feedstock components. As it is extremely important to antici-

pate typical reasons for deactivation, this study aims to assess this

technology during an early stage and a latter stage of the experi-

ment. For this analysis two experimental runs were employed

using the same hydrocracking catalyst (used also for the previous

studies described in Sections3.1 and 3.2) and the same operating

parameters i.e. T= 350, 370 and 390 C, P= 2000 psig

(13789.5 kPa), LHSV = 1.5 h1 and H2/oil = 6000 scfb (1068 nm3/

m3). The only difference between the two runs was that data from

RUN-A were collected at an early stage of the experimental run

while data from RUN-B were collected at a latter stage of the

experimental run.

Conversion is a key assessment measure of catalyst activity and

its stability on increasing operation time indicates good catalyst

life expectancy. Increasing operation time in pilot plant experi-

mental protocols is expressed as increasing number of days that

feedstock is flowing over the catalyst, i.e. days on stream or DOS.

InFig. 7conversion at three hydrocracking temperatures is com-

pared for the two experimental runs. For RUN-A conversion grad-

ually increases with temperature as expected, since increasing

temperature favors cracking. However, conversion exhibits a dif-

ferent behaviour at higher DOS. For RUN-B conversion at 370 C

is smaller than the one of RUN-A, while it is even smaller than con-

version of RUN-B at 350

C. Therefore after at least 34 DOS the cat-alyst activity is decreased and increasing temperature is not able to

compensate for this activity loss, possibly due to catalyst blockage

by the large feed molecules. For RUN-B, conversion at the highest

hydrocracking temperature (390C) is higher than the one at the

middle temperature, but still significantly smaller than the conver-

sion calculated as smaller DOS (RUN-A).

The hydrogenation effectiveness at increasing DOS is examined

inFig. 8. In particular for both runs the decrease of C/H ratio % of C/

H of feed is monotonically decreasing with increasing temperature

as it was discussed in Section 3.1, since saturation is not favored

with temperature. However in the case of higher DOS (RUN-B) this

C/H ratio decrease is dramatic at the DOS = 37, indicating that after

at least 37 DOS the ability of the catalyst to allow saturation is hy-

drant significantly. Therefore, the extended DOS cause an increas-

ing inhibition of saturation activity.

Finally the heteroatom removal effectiveness for extended DOS

is explored in Fig. 9. The removal of all atoms (S, N and O) is

decreasing for increasing DOS but the effect of DOS is different

for all atoms. In the case of sulfur and nitrogen removal it is clear

that after at least 26 days the ability of the catalyst to remove these

atoms is decreased as the results between RUN-A and RUN-B are

different even at the smallest temperature. Specifically in the case

of nitrogen removal the difference is significant, indicating that the

effectiveness of nitrogen removal is hindered earlier than the one

of sulfur removal. However the effect of catalyst life on the removal

390370350

12.13

10.6710.84

3.35

11.1212.10

0

2

4

6

8

10

12

14


C/Hra

tio

(%o

ffee

d)

RUN-A

RUN-B

9 DOS 26 DOS

16 DOS 34 DOS 23 DOS

37 DOS

Fig. 8. Effect of DOS on carbon-to-hydrogen ratio.

9 DOS 16 DOS 23 DOS


60

65

70

75

80

85

90

95

100

390370350


Su

lfur

Remova

l(%

offee

d)

23 DOS16 DOS SOD73SOD9 34 DOS

26 DOS

60

65

70

75

80

85

90

95

100


Nitrogen

Remova

l(%

offee

d)

9 DOS

16 DOS 23 DOS

26 DOS

34 DOS37 DOS

60

65

70

75

80

85

90

95

100


Oxygen

Remova

l(%

offee

d)

RUN-A

RUN-B

9 DOS 16 DOS 23 DOS


60

65

70

75

80

85

90

95

10023 DOS16 DOS SOD73SOD9 34 DOS

26 DOS

60

65

70

75

80

85

90

95

100

9 DOS

16 DOS 23 DOS

26 DOS

34 DOS37 DOS

60

65

70

75

80

85

90

95

100

390370350

390370350

Fig. 9. Effect of DOS on heteroatom removal (S, N and O) at different hydrocracking temperatures. All experiments were performed at P= 2000 psig (13789.5 kPa),LHSV = 1.5 h1 and H2/oil = 6000 scfb (1068 nm

3/m3).

S. Bezergianni, A. Kalogianni/ Bioresource Technology 100 (2009) 39273932 3931


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of these atoms is constant as the difference between the RUN-A

and RUN-B results are relatively constant. Finally the effect of

DOS on de-oxygenation is observed a little later, i.e. after 34 DOS.

However the effect of catalyst life is stronger for oxygen removal

as a significant increase of the difference between RUN-A and

RUN-B is observed for increasing DOS.

4. Conclusions

Hydrocracking of used cooking oil is a prominent process for the

production of biofuels. This work considers several parameters for

evaluating the effectiveness of this technology, mainly hydrocrack-

ing temperature, liquid hourly space velocity (LHSV) and days on

stream (DOS).

Conversion and overall biofuels yield is favored with increasing

temperature and decreasing LHSV, as cracking activity is increased.

However, moderate reaction temperatures and LHSVs are more

attractive if diesel production is targeted, whereas higher temper-

atures and smaller LHSVs should be employed if gasoline produc-

tion is also important. Heteroatom (sulfur, nitrogen and oxygen)

removal is also increasing as hydrocracking temperature increases,

with de-oxygenation particularly favorable. Saturation however is

not favored with temperature indicating a necessity of a pre-treat-

ment step prior to hydrocracking, to enable saturation of the dou-

ble bonds prior to cracking and heteroatom removal.

Finally, catalyst deactivation was observed by monitoring con-

version, heteroatom removal and saturation effectiveness with

increasing DOS. In all cases catalyst effectiveness was decreased

with increasing DOS but at different rates. Sulfur and nitrogen re-

moval are affected earlier than all other reactions. Saturation

reactions are affected only after the maximum DOS studied. Con-

version and oxygen removal are also significantly affected and

their loss of effectiveness appears more rapid than the other reac-

tion mechanisms.

Acknowledgements

The assistance of Mr Athanasios Demetriades in conducting the

experiments presented in this paper is gratefully acknowledged.

The authors also wish to express their appreciation for the financial

support provided by the program MOHLOS, funded partially from

the European Regional Development Fund by 75% and from the

Greek General Government by 25%, in conjunction with the Mea-

sure 1.3, Action 1.3.1.

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36 - hydrocracking of used cooking oil for biofuels production

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