Chemical Engineering Department, Universiti Teknologi PETRONAS

Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia

nunung1468@yahoo.com

Chemical Engineering Department, Universiti Teknologi PETRONAS

Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia

duvvuri_subbarao@petronas.com.my

Chemical Engineering Department, Universiti Teknologi PETRONAS

Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia

lukmis@petronas.com.my

Abstract - The solubility and extractability of alcohol to triglyceride is an important factor in biodiesel production to enhance the reaction rate and to obtain a better purification. Methanol and isopropanol have an opposite properties of solubility and extractability to Jatropha curcas oil. Therefore, the mixture of methanol and isopropanol was used for conducting in situ transesterification of Jatropha curcas seeds with sodium methoxide as alkaline catalyst. The reaction was carried out by varying the ratio of solvent volume to seed weight from 6.25 to 8.75 (ml/g), various volume ratio of methanol to mixture from 0.33 to 0.66 (ml MeOH/ml mixture), and various catalyst concentration from 1.0 to 2.0 wt% at 60 0C and reaction time 120 minutes. The highest conversion to biodiesel 74.28% was achieved with ratio of methanol and isopropanol volume to seed weight of 7.39, volume ratio of methanol to mixture of 0.655 and NaOMe concentration 1.58 wt% at 60 0C and reaction time 120 minutes.

I. INTRODUCTION

Increasing air pollution and diminishing petroleum reserves led to the attention of biodiesel as an alternative to substitute petrodiesel fuel. Biodiesel is a renewable fuel that is biodegradable, non toxic and has a net zero greenhouse gasses. Carbon dioxide from biodiesel can be recycled by photosynthesis and can minimize greenhouse gas emission [1,2,3].

Three main processes to produce biodiesel are pyrolysis, micro-emulsification, and transesterification. These processes reduce viscosity and density of the vegetable oil and animal fats and make it possible to use the fatty esters in regular combustion engines. Transesterification of vegetable oils and animal fats is the most method selected for preparing fatty esters [3,4].

Transesterification or alcoholysis is the reaction between short-chain alcohol and triglyceride (triacylglycerol) in the presence of an appropriate catalyst. Short-chain alcohols include methanol, ethanol, propanol, and butanol. Methanol and ethanol are most frequently used, especially methanol because of its low cost and its physical and chemical advanages (polar and shortest chain alcohol). Methanol is

slightly soluble in oil. However, methanol allows simultaneous separation of glycerol. Ethanol is more complicated as it requires a water-free alcohol in order to obtain glycerol separation [5].

A catalyst is used to enhance the reaction rate and yield. According to the reaction in Fig. 1, every 1 mol of triacylglyceride required 3 moles of alcohol to produce 3 moles of alkyl ester and a glycerol. However, more than 3 moles of alcohol is required to accomplish the reaction at faster rate, because the reaction is reversible, commonly at least 6 moles of alcohol is used. [1-5].

Figure. 1. Transesterification of triglycerides with alcohol

The challenge of biodiesel production are the cost of raw

material, the cost of processing, cheap & easily available oil resources. Biodiesel is produced mainly from edible oil, such as: soybean, rapeseed, sunflower, coconut and palm oils [1-4]. The cost of raw materials and the processing is around 60 to 70% of the total biodiesel fuel cost [4]. Use of non-edible oil/seed is recommended, such as Jathropha curcas oilseed to reduce the cost of raw materials.

In situ transesterification can reduce the cost of processing, because in this method the oil-bearing seeds contact with alcohol and catalyst. Thus extraction and transesterification take place in one step and the alcohol is used for extracting oil from the seeds and esterifying it [6].

A comparison of conventional and in situ methods of transesterification of seed oil from a series of sunflower cultivars had been conducted by Harington et al., 1985. In this research, the method of in situ transesterification with acidified methanol had been shown to produce fatty acid methyl esters in yield significantly greater than those obtained

978-1-4577-1884-7/11/$26.00 ©2011 IEEE

In-Situ Transesterification of Jatropha curcas seeds using The mixture of Methanol and IsopropanolNunung Prabaningrum* Duvvuri Subbarao Lukman Ismail

Keywords: in-situ transesterification, isopropanol, methanol, sodium methoxide, solubility, extractability, Jatropha curcas

from conventional reaction with pre-extracted seed oil. Yield improvements of over 20% were achieved and could be related to moisture content of the seed [7].

Ozgul et al., 1993 investigated in situ esterification of high-acidity rice bran oil with methanol and ethanol and with sulfuric acid as catalyst. In the esterification with methanol, all free fatty acid dissolved in methanol were interesterified within 15 min. The amount of methyl esters obtained was dependent on the free fatty acid content. In the esterification with ethanol, pure esters as in methanol esterification had not been obtained, because the solubility of oil components in ethanol were much higher than those in methanol [8].

In-situ alcoholysis of soybean oil with methanol, ethanol, n-propanol, and n-butanol had been investigated by Kildiran et.al., 1996. Because methanol is a poor solvent for soybean oil, the amount of oil dissolved in methanol and converted to methyl esters was low after in-situ alcoholysis. Ethyl, propyl, and butyl esters of soybean fatty acids could be obtained directly in high yields by this method. The purity product could be increased by decreasing the particle size of the soybeans and water content of ethanol, and by increasing reaction temperature and time [9].

Ginting, et al., 2009, conducted synthesis of biodiesel through in situ transesterification of Jatropha curcas. The experiment was carried out in a batch reactor equipped with a reflux condenser, a magnetic stirrer and a thermometer. The highest yield of the alkyl ester (99.97%) was obtained at 30 0C, with 2.00 wt.% sodium methoxide concentration and stirrer speed of 600 rpm for 2 hours of reaction time [10].

Rapid in-situ transesterification of sunflower oil with methanol assisted by diethoxymethane (DEM) had been done by Zeng, et al., 2009. The biodiesel yield 97.7% had been achieved within 13 minutes when in-situ transesterification had carried out at the molar ratio of catalyst/oil of 0.5:1, the molar ratio of methanol/oil of 101.39:1, the molar ratio of DEM/oil of 57.85:1, the agitation speed of 150 rpm, and reaction temperature of 200C [11].

Kaul, et al., 2010 had conducted reactive extraction (in-situ transesterification) of Jatropha seeds with methanol and sodium hydroxide. The experiment had been carried out by varying the reaction parameter, that was seed size (0.85 mm to >2.46 mm), seed/solvent ratio (w/w) (1:2.6 – 1:7.8) and catalyst concentration (0.05-0.1 M). The conversion to methyl ester 98% had been obtained under optimum condition, seed size (>2.46 mm), seed/solvent ratio (w/w) (1:7.8), catalyst concentration (0.1 M) and reaction time 1 hour at 650C [12].

Shuit, S.H., et al., 2010 had studied about reactive extraction and in situ esterification of Jatropha curcas L. seed. They used n-hexane as co-solvent and sulphuric acid as a catalyst. The seeds with size less than 0.355 mm had been esterified during 24 h at 600C and biodiesel yield had been achieved 99.8% [13].

The solubility between alcohol and triglyceride is an important factor to enhance the reaction rate, to obtain a better purification of biodiesel production. Based on the previous experiment about solubility of methanol, ethanol, and

isopropanol in palm oil, sunflower seed oil, canola oil, corn oil and Jatropha curcas oil at temperatures 25, 40, 600C. It was determined that methanol had a low solubility and extractability to Jatropha curcas oil. Isopropanol could be dissolved totally in Jatropha curcas oil at all temperatures and had a high extractability of oil from Jatropha curcas seeds. However, methanol is a good solvent for transesterifying oil to produce fatty acid alkyl ester (biodiesel) with a low density and kinematic viscosity, because methanol is the shortest-chain alcohol.

Isopropanol had been tested to produce biodiesel by in situ transesterification of Jatropha curcas seeds with sodium hydroxide as an alkaline catalyst. The reaction was carried out by varying the ratio of isopropanol volume to seed weight (v/w), catalyst concentration, reaction temperature, and reaction time which was affected the biodiesel yield. The highest conversion to biodiesel 91.34% was achieved with the ratio of isopropanol volume to seed weight 7.5 (v/w), NaOH concentration 1.0 wt%, at 700C and reaction time 120 minutes. The reaction order 1.62 and reaction rate constant 0.0032 (ml0.62/ml0.62.s) had been obtained by conducting in situ transesterification of Jatropha curcas seeds with the ratio of isopropanol to seeds 7.5 (v/w) and 1 wt% NaOH at 600 C.

Because of the opposite properties of solubility and extractability to Jatropha curcas oil between methanol and isopropanol, in situ transesterification of Jatropha curcas seeds using the mixture of methanol and isopropanol as a solvent and sodium methoxide as alkaline catalyst was conducted. The reaction was carried out by varying the ratio of methanol and isopropanol volume to seed weight (ml/gram), volume ratio of methanol to mixture (ml MeOH/ml mixture), and catalyst concentration (wt%). Response surface methodology (RSM) was used for modelling the biodiesel yield.

II. MATERIALS AND METHOD

A. ANOVA and regression analysis The experimental tests were conducted according to a full 23 factorial design where factors were ratio of solvent to seed (6.25; 8.75 ml/g), volume ratio (0.33; 0.66 ml MeOH/ml iPrOH), and NaOMe concentration (1.0; 2.0 wt%). Each test was replicated twice. Response surface methodology, a mathemathical-statistical tool, was used for modelling the biodiesel yield. Second-order polynomials were used to describe the response surface for biodiesel yield,

∑∑∑<==

+++=n

jijiij

n

iiii

n

iii xxxxY ββββ

1

2

10 (1)

where Y is predicted response, β0 is constant coefficient, βi

is linear coefficient, βiiis quadratic coefficient, βij is interaction coefficient, xi and xj are independent factors. The experimental design for fitting the second-order models was rotatable. Orthogonality is optimal design property as it minimizes the variance of the regression coefficients.

Rotatability describes the variance of a response at a certain point is only a function of the distance of the point from the design centre and independ on direction. The central composite design can be rotatable by calculating a ,

4 na = (2) where n is the number of points used in the design. In this case there was eight points and a is equal to 1.68. Table 1 shows the conditions of the full factorial design, both in terms of coded and non-coded variables. The central point test was replicated four times (test 9–12, Table 1) to produce a good estimation of experimental error. Six axial tests (tests 13-18, Table 1) were conducted to obtain better shape of response surfaces. Statgraphics Centurion XV software was used to design and analyze the experiment. B. Materials

Jatropha curcas seeds were obtained from Yogyakarta and Medan, Indonesia. The chemicals used in this research included methanol (>99%), n-hexane (99%), 2-propanol/isopropanol (>99%), sodium hydroxide, potassium hydroxide, sodium sulphate anhydrous, TLC silica gel, diethyl ether, n-heptane, acetic acid was purchased from Merck.

The standards, mono-, di-, tri-olein and tricaprin used for gas chromatography analysis and pyridine, glycerin, N-Methyl-N-trimethyl-silyltriflouroacetamide (MSTFA) was purchased from Sigma Aldrich, Malaysia. C. Experimental Approach

Jatropha curcas seeds were dehulled and milled using an electric grinder to the particle size of around 500 μm. Sieve tray was used for homogeneous and accurate particle size of

this seeds. After that process, the seeds were placed in the oven to remove excess moisture at 700C for 24 hours.

The oil of Jatropha curcas must be extracted from the seeds to determine the oil properties. Soxhlet extractor with n-hexane as the solvent was used for this purpose. The dry seeds of 20 grams was placed in the thimble and 150 ml hexane was poured into the round bottom flask. The extraction was carried out for 2 hours. The oil was separated from n-hexane using rotary evaporator and the oil content could be determined, that is the weight of oil divided by weight of seeds.

For in situ transesterification, twenty grams of ground seeds was transferred into a 250 ml three-neck round-bottom flask. Sodium methoxide as alkaline catalysts was added to the mixture of methanol and isopropanol. After the mixture was heated at 60 0C, the catalyst and solvent were poured into the flask. The reaction was kept at constant temperature 60 0C, stirring speed of 400 rpm during 120 minutes.

At the end of reaction, the mixture was separated by vacuum-filter. The filtrate obtained was transferred into separator funnel, added water, and extracted with n-hexane. The solution was left in separator funnel for 24 hours. After that, two layers was formed, the upper layer which contained biodiesel, n-hexane and a few of impurities was separated from lower layer which contained methanol and isopropanol, glycerol, and NaOMe. The upper layer was washed with water and evaporated using rotary evaporator. The transesterification product was examined qualitatively by TLC. The FFA content was determined by titration with standard KOH solution and phenolphthalein as indicator [14]. The ester, mono-, di-, and triglyceride content of the transesterification product was determined by gas chromatography (GC) [15].

The GC was equipped with an on-column injection, HT-5, with a diameter of 0.32 mm, a film thickness of 0.1 μm,

Table 1. Test condition of the full factorial design

Test Treatment combination

Coded factors A B C A B C [NaOMe]

(wt%) Solvent:seed

(ml/g) Vol ratio

(ml MeOH/ml mix) 1 (1) -1 -1 -1 1.0 6.25 0.33 2 a 1 -1 -1 1.0 8.75 0.33 3 b -1 1 -1 1.0 6.25 0.66 4 ab 1 1 -1 1.0 8.75 0.66 5 c -1 -1 1 2.0 6.25 0.33 6 ac 1 -1 1 2.0 8.75 0.33 7 bc -1 1 1 2.0 6.25 0.66 8 abc 1 1 1 2.0 8.75 0.66 9 0 0 0 0 1.5 7.50 0.50

10 0 0 0 0 1.5 7.50 0.50 11 0 0 0 0 1.5 7.50 0.50 12 0 0 0 0 1.5 7.50 0.50 13 - -1.68 0 0 1.5 5.40 0.50 14 - 1.68 0 0 1.5 9.60 0.50 15 - 0 -1.68 0 1.5 7.50 0.22 16 - 0 1.68 0 1.5 7.50 0.77 17 - 0 0 -1.68 0.66 7.50 0.50 18 - 0 0 1.68 2.34 7.50 0.50

a length of 30 m and flame ionization detector (FID). The temperature of column was set at initial temperature of 500C for 1 minute. Then, it was increased to 1800C with the rate of 150C/min, followed by 70C/min up to 2300C. The rate was increased to 300C/min until the temperature of 3800C and it was held for 10 minutes. The FID was set at 3800C and helium was used as carrier gas with the flow rate of 3 ml/min.

Biodiesel yield was calculated as follows,

%100(%) ×=ltheoritica

actual

BD

BDBD W

WY (3)

)100

1(exp

TotalBDBD

GWWactual

−= (4)

GTotal is mass percentage of total glycerin (free gycerin and bound glycerin, which consist of mono-, di-, triglyceride) obtained from GC.

III. RESULT AND DISCUSSION A. ANOVA and regression analysis

The response of factorial design is presented in Table 2. Each result is expressed as arithmetic mean of duplicate.

Table 2. The difference between observed and fitted value (Δobs-fitted) of biodiesel yield (%)

Test A [NaOMe]

(wt%)

B solvent:seed

(ml/g)

C Vol ratio (ml/ml)

Observed value (%)

Fitted value (%)

Δobs-fitted (%)

1 1.0 6.25 0.33 54.94 54.93 0.02 2 1.0 8.75 0.33 39.89 38.80 2.73 3 1.0 6.25 0.66 67.15 67.85 -1.04 4 1.0 8.75 0.66 59.27 59.29 -0.03 5 2.0 6.25 0.33 50.96 51.17 -0.41 6 2.0 8.75 0.33 49.17 50.59 -2.89 7 2.0 6.25 0.66 62.44 62.76 -0.51 8 2.0 8.75 0.66 68.75 68.15 0.87 9 1.5 7.50 0.50 70.16 69.36 1.14

10 1.5 7.50 0.50 69.77 69.36 0.59 11 1.5 7.50 0.50 69.2 69.36 -0.23 12 1.5 7.50 0.50 69.2 69.36 -0.23 13 1.5 5.40 0.50 59.62 59.94 -0.54 14 1.5 9.60 0.50 52.71 52.25 0.87 15 1.5 7.50 0.22 45.78 43.24 5.55 16 1.5 7.50 0.77 73.68 70.22 4.70 17 0.66 7.50 0.50 56.37 56.04 0.59 18 2.34 7.50 0.50 61.89 61.67 0.36

Figure 2 presents the main effect and interaction among

factors. Three factors, catalyst concentration (factor A), ratio of solvent volume to seed (factor B), and volume ratio of methanol to mixture (factor C), had a significant effect to biodiesel yield. Volume ratio (factor C) had the strongest positive effect on crude BD yield. Increasing volume of methanol in the mixture of methanol and isopropanol the amount of biodiesel increased. The ratio of solvent volume to seed weight (factor B) shown a negative effect on crude BD yield.

Figure 2 The main effect and interaction among factors

Interactions AA, BB, and CC had a strong negative effect on the amount of biodiesel. Interaction between the ratio of solvent to seed and catalyst concentration (interaction AB) had a positive influence on the biodiesel yield. Increasing ratio of solvent to seed and catalyst concentration enhanced the amount of biodiesel. Interaction between the ratio of solvent to seed and volume ratio (BC) had a negative effect on the biodiesel yield, the increase in the volume ratio and catalyst concentration reduced the number of biodiesel. Interaction between volume ratio and the catalyst concentration (AC) was very small effect on the increase in biodiesel yield

Experimental results were fitted by empirical models according to RSM for predicting biodiesel yield as a function of ratio of solvent volume to seed weight, volume ratio of methanol to the mixture of methanol and isopropanol, and catalyst concentration:

(5) 73.1265.1457.1742.86X

0.35X38.395.2443.23992.4327.1762332

2231

2121321

XXXXX

XXXXXY

−−−+

+−+++−=

where Y is predicted biodiesel yield (%), X1 is ratio of MeOH+iPrOH to seed weight (ml/g), X2 is volume ratio of MeOH to iPrOH (ml/ml), X3 is NaOMe concentration (wt % based on oil weight). Equation (5) was used to determine the optimum value of biodiesel yield.

B. Effect of the ratio of methanol and isopropanol volume to

seed weight

The effect of different ratio of methanol and isopropanol volume to seed weight from 6.25 to 8.75 ml/g and volume ratio from 0.33 to 0.66 at 1.58 wt% NaOMe for 2 hours is presented in Figure 3.

Increasing ratio of methanol and isopropanol volume to seed weight from 6.25 to 7.39 and volume ratio from 0.33 to 0.655 enhanced the conversion of oil to biodiesel from 55.20% to 74.28%. At ratio 6.25 the mixture volume was 125 ml. These volume were not sufficient to extract an oil in the seeds

and to break the linkage of glycerine and fatty acid. Therefore the biodiesel yields were not high. Excess mixture volume 175 ml reduced the biodiesel yield to 58.29% because biodiesel could be dissolved in excess isopropanol, settled down to the lower layer and separated out from biodiesel layer

Figure 3. Estimated response surface of biodiesel yield at [NaOMe] = 1.42 wt%

C. Effect of volume ratio of methanol to mixture

Figure 3 also shows biodiesel yield (%) for various volume ratio of methanol to mixture (methanol and isopropanol) from 0.33 and 0.66 ml MeOH/ml mixture. Increasing volume ratio of methanol to mixture from 0.33 to 0.655 enhanced the conversion to biodiesel from 55.20% to 74.28%. However, volume ratio of methanol to mixture more than 0.655 could reduce the conversion to biodiesel because the volume of methanol is much more than the volume of isopropanol in the mixture, so that only a small amount of oil that could be extracted from the seeds by isopropanol. D. Effect of catalyst concentration (NaOMe)

Figure 4 indicates biodiesel yield (%) for various catalyst concentration (NaOMe) from 1.0 to 2.0 wt% with ratio of solvent to seed (v/w) from 6.25 to mixture. 8.75 (ml/gr) at volume ratio of 0.655 ml/ml.

The catalyst percentage was based on the weight of the oil used for in-situ transesterification. It was observed that addition of NaOMe concentration from 1.0 wt% to 1.58 wt% increased the conversion to biodiesel. The concentration of NaOMe less than 1.58 wt% was not sufficient to convert Jatropha curcas oil into fatty acid alkyl ester . However, addition of NaOMe more than 1.58 wt% decreased the conversion to biodiesel because of saponification. Addition NaOMe concentration exceeded 2.0 wt% caused more soap formed, disturbed the separation of biodiesel from glycerol, and lowered the conversion to biodiesel. The highest

conversion to biodiesel 74.28% was achieved with NaOMe concentration 1.58 wt% at 600 C.

Figure 4. Estimated response surface of biodiesel yield for volume ratio 0.655 ml MeOH/ml mixture

E. Optimization analysis

The Statgraph Centurion XV was used for optimization analysis of experimental design. Table 3 explains the high, low limit experimental region and the optimum factors.

Table 3. The combination of factor levels which maximizes biodiesel yield for methanol

Factor Low High Optimum [NaOMe] (wt%) 0.66 2.34 1.58 solvent:seed (ml/g) 5.40 9.60 7.39 VMeOH : Vmix (ml/ml) 0.22 0.77 0.66

The predictions of biodiesel yield obtained from numerical optimization of the experimental design was 74.28%. This value was compared with the biodiesel yield obtained from experiment as shown in Table 4.

Table 7: Optimum condition for methanol Test Factors Response (%) Error

[NaOMe] (wt%)

solvent:seed (ml/g)

VMeOH : Vmix

(ml/ml)

Obsv. Predct

1 1.58 7.39 0.66 72.86 74.28 -1.42 2 1.58 7.39 0.66 72.93 74.28 -1.35 3 1.58 7.39 0.66 73.57 74.28 -0.71

The optimum biodiesel yield obtained from experiment was (73.12 ± 0.39)%. This yield was less 1.59% than its predicted.

IV. CONCLUSIONS In-situ transesterification of Jatropha curcas seeds using

the mixture of methanol and isopropanol and sodium methoxide as alkaline catalyst had been done. The reaction was carried out for 20 grams dry seeds in various solvent volume from 125 ml to 175 ml, various volume ratio of methanol to mixture from 0.33 to 0.66, and various catalyst concentration from 1.0 to 2.0 wt% at 60 0C and reaction time 120 minutes. Response surface methodology based on central

composite design was used for modelling and predicted the optimum condition.

The biodiesel yield of (73.12 ± 0.39)% lower 1.59% than the predicted value was obtained with the optimum conditions as follows: 1.58 wt% sodium methoxide concentration, the ratio of the mixture volume to seed weight of 7.39 (ml/g), 0.66 (ml MeOH/ml mixture) the volume ratio of methanol to the mixture at 600C for two hours.

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