Optimization of process parameters for biodiesel extraction from tamanu oil usingdesign of experimentsG. Antony Miraculas, N. Bose, and R. Edwin Raj

Citation: Journal of Renewable and Sustainable Energy 6, 033120 (2014); doi: 10.1063/1.4880216 View online: http://dx.doi.org/10.1063/1.4880216 View Table of Contents: http://scitation.aip.org/content/aip/journal/jrse/6/3?ver=pdfcov Published by the AIP Publishing Articles you may be interested in The use of oil shale ash in the production of biodiesel from waste vegetable oil J. Renewable Sustainable Energy 4, 063123 (2012); 10.1063/1.4768544 Improvement of the oxidative stability of used-oil biodiesel by epoxidation reaction J. Renewable Sustainable Energy 4, 053108 (2012); 10.1063/1.4754441 Microwave irradiation biodiesel processing of waste cooking oil AIP Conf. Proc. 1440, 842 (2012); 10.1063/1.4704295 Production of bio-oil from mahua de-oiled cake by thermal pyrolysis J. Renewable Sustainable Energy 4, 013101 (2012); 10.1063/1.3676074 Biogas potential on Long Island, New York: A quantification study J. Renewable Sustainable Energy 3, 043118 (2011); 10.1063/1.3614443

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Optimization of process parameters for biodiesel extractionfrom tamanu oil using design of experiments

G. Antony Miraculas,1 N. Bose,2 and R. Edwin Raj11St. Xavier’s Catholic College of Engineering, Nagercoil 629003, India2Mepco Schlenk Engineering College, Sivakasi 626005, India

(Received 18 February 2014; accepted 16 May 2014; published online 28 May 2014)

Petroleum reserves are diminishing at a faster rate and the world is facing twin crisis

in fossil fuel depletion and environmental degradation owing to extensive use of

fossil fuel. Finding viable and sustainable alternative fuel is crucial for the world at

large and especially for oil importing countries like India. In the present work,

biodiesel is produced from tamanu oil, which is non-edible, plentiful, and cost

effective. However, the viscosity is high which demands a two stage esterification to

reduce its fatty acid content within the limits for automotive applications. Due to

interactive effects among the process parameters, design of experiments is employed

for optimization. It was observed that methanol and catalyst concentration are the

major influencing process parameters, whereas time and temperature have

insignificant role on acid value reduction and percentage of oil yield. The extracted

biodiesel was tested for fuel properties with standard test procedures and found to be

in compliance with ASTM standards. VC 2014 AIP Publishing LLC.

[http://dx.doi.org/10.1063/1.4880216]

I. INTRODUCTION

The conventional fuel resources are declining day by day and the world is challenged by

the environmental degradation caused by them. The dearth of petroleum based fuels makes it

necessary for the search of new possible sources of renewable energy. To date, biodiesel

research is carried out in more than 28 countries of which Germany and France are the pio-

neers. The United States department of energy has assessed that up to 50% of the total conven-

tional diesel fuel could be possibly replaced by biodiesel (Reyes and Sepulveda, 2006). One

such possible source for biodiesel is the Calophyllum inophyllum oil extracted from “tamanu”

or “punnai” seed (Raj et al., 2012). Biodiesel is renewable and has a lesser health risk due to

reduced emission (Xuea et al., 2011; Ravikumar and Senthilkumar, 2013). The alternative

energy resources, such as biomass, biogas, primary alcohols, vegetable oils, and biodiesel, are

mostly eco-friendly but they need to be assessed on case-to-case basis for their advantages, dis-

advantages, and exact applications (Cao, 2003). Some of the vegetable oils can be used directly

while others must be formulated to get the appropriate properties closer to that of conventional

fuels. Petroleum driven automobiles are on the increase, and they are the most important sour-

ces of greenhouse gas emission (Kessel, 2000). Biodiesel derived from renewable resources,

especially from non-edible sources can provide a feasible solution to this worldwide twin crisis

of pollution and depletion of conventional fuel sources (Kannan and Anand, 2012).

Biodiesel are being produced from edible vegetable oil such as coconut (Jiang and Tan,

2012), palm nut (Chongkhong et al., 2007), radish (Ravikumar and Senthilkumar, 2013), lin-

seed (Jindal and Salvi, 2012), soybean (€Ozener et al., 2014), and groundnut, and also from non-

edible crops, such as jatropha curcas (Kumar et al., 2007), pongamia pinnata (Kumar and Anju,

2005), polanga (Sahoo et al., 2007), eruca sativa gars (Li et al., 2009), rapeseed (Nwafor and

Rice, 1995), neem (Awolu et al., 2013), cotton seed (Nabi et al., 2009), and rubber seed

(Melvin Jose et al., 2011). Extraction of edible vegetable oil for biodiesel production is not a

viable solution for countries like India, where there is a dare need for edible vegetable oil of

cooking purpose itself.

1941-7012/2014/6(3)/033120/10/$30.00 VC 2014 AIP Publishing LLC6, 033120-1

JOURNAL OF RENEWABLE AND SUSTAINABLE ENERGY 6, 033120 (2014)

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Tamanu oil is highly viscous which cannot be used directly and needs further processing to

reduce its viscosity. Biodiesel are extracted by chemical reaction of the vegetable oil with an

alcohol such as methanol or ethanol. Since the viscosity is too high, it has to be done in two

steps by using an acid catalyst, H2SO4 in the first stage and an alkaline catalyst, potassium hy-

droxide in the second stage. The reaction produces a new chemical compound called methyl or

ethyl esters known as biodiesel.

The present work infers the findings of the research in extracting biodiesel from Calophylluminophyllum seed oil, which is a non-edible oil seed available in plenty in India. Design of experi-

ment (DOE) is employed in the present work for designing the process parameters to statistically

analyze and to derive authenticated inferences. The primary process parameters for biodiesel

extraction were designed by doing pilot experiments, and the process parameters for acid and

alkaline esterification were optimized. Optimization of the process parameters using robust opti-

mization tools with empirical values is crucial to maximize the biodiesel yield. The quantity of

monoester (biodiesel) yield was measured to estimate the percentage yield.

II. EXPERIMENTAL PROCEDURE

A. Potential and extraction of tamanu oil

Calophyllum inophyllum plant is available in Africa, Asia, and Pacific regions (Dweck and

Meadowsy, 2002). It is a member of the mangosteen family. It is also named as Alexandrian

FIG. 1. Extraction process of biodiesel from tamanu seed oil.

033120-2 Miraculas, Bose, and Raj J. Renewable Sustainable Energy 6, 033120 (2014)

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Laurel, Tamanu, Pannay Tree, Sweet Scented Calophyllum, Punnai, etc. In India, these trees

are found mostly in coastal areas, which are planted to prevent soil erosion. Each seed is

around 50 mm in diameter having smooth epidermis layer followed by hard cover which enclo-

ses a rather pale yellow kernel of around 25 mm in diameter weighing approximately 7 g.

The seeds are collected and sun dried to separate the kernels by breaking the outer shell.

They are then dried and crushed to extract oil by allowing it to pass through a screw press. The

extracted oil is then filtered and the seed cake, which is rich in protein is used as cattle and

poultry feed. The procedure is shown in the block diagram (Fig. 1). The tamanu oil extracted

had an acid value of 48 mg KOH/g, which is equivalent to 24% free fatty acid (FFA) content.

High FFA content demands two stage esterification processes with acid and base catalyst.

B. Extraction of biodiesel

The high FFA content along with higher viscosity deters its direct usage in internal com-

bustion engines (Jain and Sharma, 2010). Different approaches, such as dilution, micro-

emulsification, pyrolysis, and esterification, are being established to reduce the viscosity of oil.

Of these methods, esterification is proven to be robust and comprehensive for conditioning the

fuel property for IC engine applications. Studies conducted on esterification of heavy vegetable

oil indicates, process parameters such as alcohol/oil ratio, catalyst, reaction time, reaction tem-

perature, and stirring speed are the major influencing parameters (Kumar and Anju, 2005; Li

et al., 2009; Wang et al., 2013).

Since many process parameters are involved, it is quite complex to assess the reason for

the observed changes in the outcome. Therefore, the DOE is implemented to conduct designed

set of experiment to observe and identify the influential process parameter to derive objective

conclusions. Pilot experiment isolates certain parameters and the following parameters are con-

sidered for the acid esterification stage: oil/methanol ratio, H2SO4, temperature, and time.

100 ml of extracted raw tamanu oil is taken in a round bottom conical flask and heated to the

designed temperature. The corresponding amount of sulphuric acid and methanol as per the

design shown in Table I were then added and stirred at a constant speed of 1000 rpm using

magnetic stirrer for the intended time period. The reactants are then allowed to separate in a

separating funnel, where the impurities and excess alcohol separates at the top and the oil at

the bottom are collected. The acid values of the oil are determined separately by titrating it

against KOH for every experiment, where the objective of this stage is to minimize the acid

value.

Sufficient quantities of oil are prepared with the optimized process condition from the acid

esterification stage where the FFA of the extracted oil is kept less than 3 mg KOH/g. It is

TABLE I. Process parameter range for the acid esterification process.

Process parameters Axial (�a) Axial (þa) Center Low (�) High (þ)

Oil/Methanol (v/v) 2.75 4.25 3.5 2 5

H2SO4 (%v/v) 1.25 1.75 1.5 1 2

Temperature (�C) 45 55 50 40 60

Time (min) 75 105 90 60 120

TABLE II. Process parameter range for the alkaline esterification process.

Process parameters Axial (�a) Axial (þa) Center Low (�) High (þ)

Methanol/oil (v/v) 0.3125 0.4375 0.375 0.25 0.5

KOH (%W/v) 0.9375 1.3125 1.125 0.75 1.5

Temperature ( �C) 45 55 50 40 60

Time (min) 67.5 102.5 85 50 120

033120-3 Miraculas, Bose, and Raj J. Renewable Sustainable Energy 6, 033120 (2014)

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further processed through alkaline esterification stage, where maximizing the yield percentage

is considered as the primary objective. Pilot experiments were carried out in the same reactor

which was used for acid esterification process. The parameter ranges were sensibly selected in

reference with literature and are shown in Table II. 50 ml of oil extracted from the acid esterifi-

cation process is taken in a reactor and heated to the required temperature. The desired quantity

of methanol and KOH is then added into the reactor, and the reactants were stirred at constant

TABLE III. Experimental plan with process data and the FFA response for acid esterification process.

Run Oil/methanol (v/v) H2SO4 (%v/v) Temperature ( �C) Time (min) FFA (mgKOH/g)

1 2.75 1.75 45 75 14.5

2 3.5 1.5 50 90 15.95

3 4.25 1.25 55 75 31.34

4 2.75 1.25 55 75 13.8

5 2.75 1.25 45 105 8.76

6 3.5 1 50 90 31.98

7 4.25 1.25 55 105 32.83

8 3.5 1.5 50 90 12.34

9 4.25 1.75 55 105 23.6

10 4.25 1.75 45 75 26.98

11 2 1.5 50 90 3.8

12 2.75 1.75 55 105 2.7

13 3.5 1.5 40 90 26.9

14 3.5 1.5 60 90 22.65

15 5 1.5 50 90 36

16 2.75 1.75 55 75 4.8

17 3.5 1.5 50 120 17.8

18 4.25 1.75 45 105 20.31

19 2.75 1.75 45 105 13.6

20 3.5 1.5 45 90 21.76

21 3.5 2 50 90 13.78

22 4.25 1.25 45 75 25.6

23 3.5 1.5 50 90 13.2

24 2.75 1.25 55 105 6.8

25 3.5 1.5 50 75 20.86

26 2.75 1.25 45 75 15.87

27 4.25 1.75 55 75 25.86

28 3.5 1.5 50 90 16.41

29 3.5 1.5 50 60 18.56

30 4.25 1.25 45 105 18.9

TABLE IV. ANOVA result for response surface linear model by acid esterification method.

Source Sum of squares df Mean square F value P-value prob > F

Model 1683.7 4 420.9 19.6 < 0.0001

A-Oil/methanol 1488.2 1 1488.2 69.2 < 0.0001

B-H2SO4 139.9 1 139.9 6.5 0.0173

C-temperature 10.8 1 10.8 0.5 0.4849

D-time 44.7 1 44.7 2.1 0.1617

Residual 537.9 25 21.5

Total 2221.6 29

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speed using a magnetic stirrer, for a predefined time period. The products are then allowed to

separate under the influence of gravity in a separating funnel. Methyl esters settle at the top

and heavy glycerol at the bottom. The biodiesel was collected and the percentage yield was cal-

culated after each trial.

III. RESULT AND DISCUSSION

A. Optimization of process parameters for acid-esterification

A series of pilot esterification trials were conducted to evaluate the relevance of various

process parameters in reducing the acid value. After finalizing the influential parameters,

experiments were conducted as per the design by varying the input parameters to record the

outcome, the acid value (Table III). The analysis of variance was done for the acid esterifica-

tion model, and the results are shown in Table IV. Before drawing any inference, the model

has to be validated satisfactorily. The model p-value was less than 0.0001 which indicates that

the model terms considered are significant, and especially the most significant model term is

the ratio of oil to methanol (factor A) with a F-value of 69.2. The amount of acid catalyst

H2SO4 is also significant variable having F-value of 6.5, whereas the other factors such as reac-

tion time and temperature have less influence on the acid value. The "Pred. R-Squared" value

of 0.6516 is in reasonable agreement with the "Adj. R-Squared" of 0.7191. "Adeq Precision"

measures the signal to noise ratio and a value greater than 4 is desirable and for this model it

was 16.633, which indicates that the signals are adequate enough. The analysis of variance sig-

nifies that the model can be used to navigate the design space.

The Perturbation plot compares the influence of various factors at a specific point in the

design space (Fig. 2). The acid value (response) was plotted by varying a single factor over its

range while holding the other factors at constant midpoint value. A sharp positive slope for the

factor A, the oil/methanol ratio indicates that the acid value decreases with decrease in oil/me-

thanol ratio. The negative slope for H2SO4 implies that the acid value decreases with increase

in acid concentration and the fairly flat lines for time and temperature show its insensitivity in

deciding the acid value. Since the quantity of alcohol and catalyst are the two most influencing

parameter in the reaction, the three dimensional response plot was drawn with oil/methanol ra-

tio and volume percentage of H2SO4 as axis in relation to acid value. The temperature and time

FIG. 2. Perturbation chart of acid esterification process.

033120-5 Miraculas, Bose, and Raj J. Renewable Sustainable Energy 6, 033120 (2014)

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of reaction are kept at the center point of the design and are shown in Fig. 3. It can be observed

that the lower acid value can be achieved by reducing the oil/methanol ratio and by increasing

the H2SO4 catalyst. Adequate quantity of oil was esterified for further processing at the opti-

mized condition (Table V) and further processed in the second stage using alkaline catalyst.

B. Optimization of process parameters for alkaline-esterification

Acid esterified methyl ester having less than 2% FFA were subjected to alkaline esterifica-

tion process to reduce its viscosity within the allowable limit for automotive applications.

Planned set of experiments with significant input process parameters are done to maximize the

bio-diesel yield in the second stage (Table VI). The analysis of variance was done to validate

the model for deriving inference and the results are shown in Table VII. Since the response is

nonlinear, the quadratic model was selected. The model F-value of 8.59 and the p-value of

<0.001 signify the significance of the model for deriving inference.

In this stage also, the methanol to oil ratio is the most influencing factor (F-value of 69.09)

for maximizing the methyl ester yield and the acid catalyst has some influence to be considered

for biodiesel yield. However, temperature and time are insignificant influencing parameter to

decide the quantity of biodiesel yield. There were significant interactive effects (p-value of AB

is <0.05) between methanol/oil ratio (A) and the amount of KOH (B) in the process which can-

not be inferred by simple experiments and were taken care by the surface response model

(Fig. 4). The “Predicted R-Squared” value of 0.740 is close to the “Adjusted R-Squared” value

of 0.7857 as one might normally expect. Adequate precision measures the signal to noise ratio

of 11.026 indicates adequate signal, which allows the model to be navigated in the designed

space. The perturbation chart depicts the response of one factor over its range while holding

the other factors constant at midpoint (Fig. 5). The steep positive slope for the factor A, metha-

nol/oil ratio indicates that it is the most significant factor in comparison with other process pa-

rameters influencing the percentage of yield. The influence of KOH (factor B) on yield percent-

age is significant in the lower range. However, after the midpoint, the slope of the curve

reduces showing saturation level for the catalytic influence on the process. The surface response

FIG. 3. Surface response model for the acid value.

TABLE V. The optimum projected parameters for minimising FFA content by acid esterification method.

Oil/methanol (v/v) H2SO4 (%v/v) Temperature ( �C) Time (min)

2.75 1.75 54.94 105

033120-6 Miraculas, Bose, and Raj J. Renewable Sustainable Energy 6, 033120 (2014)

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model (Fig. 4) plotted with these two significant process parameter indicates higher biodiesel

yield at higher methanol/oil ratio. Increase in KOH concentration gives better yield to a certain

extent and beyond that it has a negative effect on the yield of biodiesel. The optimum condition

for getting higher yield is shown in Table VIII, and it was validated by conducting experiments

with these optimized process parameters.

TABLE VII. ANOVA results for methyl ester yield model by alkali esterification method.

Source Sum of squares df Mean square F value p-value prob > F

Model 983.08 14 70.22 8.59 < 0.0001

A-methanol/Oil 564.54 1 564.54 69.09 < 0.0001

B-KOH 180.40 1 180.40 22.08 0.0003

C-time 1667 1 0.0016 0.0002 0.9888

D-temperature 43.20 1 43.20 5.29 0.0363

Residual 122.57 15 8.17

Total 1105.65 29

TABLE VI. Experimental design with process data and the percentage yield for alkaline-esterification process model.

Run Methanol/oil (v/v) KOH (%w/v) Temperature (�C) Time (min) Yield (%)

1 0.31 0.94 67.5 45 76.2

2 0.44 1.31 102.5 45 92.3

3 0.31 0.94 102.5 55 79.0

4 0.38 0.75 85.0 50 79.2

5 0.38 1.13 85.0 40 91.3

6 0.38 1.13 120.0 50 92.5

7 0.25 1.13 85.0 50 78.9

8 0.31 1.31 67.5 55 88.5

9 0.38 1.13 50.0 50 93.4

10 0.44 0.94 67.5 55 88.9

11 0.50 1.13 85.0 50 93.4

12 0.44 0.94 102.5 55 93.1

13 0.31 0.94 102.5 45 79.0

14 0.44 1.31 67.5 45 93.5

15 0.31 0.94 67.5 55 78.9

16 0.44 0.94 102.5 45 87.4

17 0.38 1.13 85.0 60 93.0

18 0.38 1.13 85.0 50 92.1

19 0.38 1.13 85.0 50 91.8

20 0.38 1.13 85.0 50 90.9

21 0.31 1.31 102.5 55 84.6

22 0.38 1.13 85.0 50 91.6

23 0.38 1.50 85.0 50 93.3

24 0.31 1.31 67.5 45 80.1

25 0.31 1.31 102.5 45 78.4

26 0.38 1.13 85.0 50 92.6

27 0.44 0.94 67.5 45 87.1

28 0.44 1.31 67.5 55 94.2

29 0.44 1.31 102.5 55 95.6

30 0.38 1.13 85.0 50 90.4

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C. Fuel properties

Enough quantity of biodiesel was extracted with the optimized process condition and then

purified further for fuel testing. The entrained glycerol and catalysts were removed by gently

washing them with warm water and finally dried using silica gel. Standard test procedures were

followed to determine the properties of extracted tamanu oil methyl esters. The viscosity was

measured using BROOKFIELD LV-DV-IIþ Pro viscometer, Middleboro, USA at 40 �C and

atmospheric pressure. The viscosity of the raw tamanu seed oil was reduced from 45.8 mm2/s

to 4.2 mm2/s after two stage esterification process, which is within the ASTM D6751-02 stand-

ard of biodiesel.

FIG. 4. Surface response model for alkaline esterification method.

FIG. 5. Perturbation chart for alkaline-esterification process.

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The flash point and fire point of biodiesel were determined by using the Pensky Martins

closed cup apparatus. The energy content of the fuel was measured using standard 6772 calori-

metric thermometer as 40 800 kJ/kg, which is very close to that of diesel which will ensure sat-

isfactory performance with the existing engine. The properties of tested tamanu seed biodiesel

are listed in Table IX.

IV. CONCLUSION

Highly viscous, abundantly available, non-edible tamanu oil was extracted from the seeds

of Calophyllum inophyllum plant. High FFA content (24%) of raw tamanu oil demands acid

and alkaline catalyst induced esterification (two stages) to convert it into biodiesel. Since inter-

active effect of process parameters is involved, design of experiments is implemented to opti-

mize the process parameters. Methanol concentration was the most significant influencing pro-

cess parameters followed by catalyst percentage in reducing the acid value and increasing the

biodiesel yield in two stages, respectively. The process parameters such as time and temperature

have little influence on the outcome. The properties of extracted tamanu oil based biodiesel

were tested under standard test procedure and found to be closer to that of diesel which needs

no engine modification for automotive applications.

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0.42 1.3 83.17 53.8 95.94

TABLE IX. Properties of tamanu oil biodiesel in comparison with diesel.

Properties Diesel Biodiesel standard ASTM D6751-02 Tamanu oil methyl ester

Kinematic viscosity @ 40 �C (mm2/s) 3.18 1.9–6.0 4.2

Flash point ( �C) 68 130 110

Specific gravity 0.839 0.87–0.90 0.885

Calorific value(KJ/kg) 42 000 … 40 800

Pour point ( �C) �20 �1.5–10 10.8

033120-9 Miraculas, Bose, and Raj J. Renewable Sustainable Energy 6, 033120 (2014)

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