- Email: [email protected]
Optimization of alkali-catalyzed transesterification of Pongamia pinnata oil for production of biodiesel
Bioresource Technology 97 (2006) 1392–1397
Optimization of alkali-catalyzed transesteriWcation of Pongamia pinnata oil for production of biodiesel L.C. Meher a, Vidya S.S. Dharmagadda b, S.N. Naik
a,¤
a
b
Centre for Rural Development and Technology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110 016, India Department of Biosystems and Agricultural Engineering, University of Kentucky, 128 CE Barnhart Bldg., Lexington, KY 40546, USA Received 19 October 2004; received in revised form 30 June 2005; accepted 4 July 2005 Available online 15 December 2005
Abstract Studies were carried out on transesteriWcation of Karanja oil with methanol for the production of biodiesel. The reaction parameters such as catalyst concentration, alcohol/oil molar ratio, temperature, and rate of mixing were optimized for production of Karanja oil methyl ester (KOME). The fatty acid methyl esters content in the reaction mixture were quantiWed by HPLC and 1H NMR method. The yield of methyl esters from Karanja oil under the optimal condition was 97–98%. © 2005 Elsevier Ltd. All rights reserved. Keywords: Biodiesel; Methyl esters; Karanja oil; Methanolysis; TransesteriWcation
1. Introduction Presently the world’s energy needs are met through non-renewable resources such as petrochemicals, natural gas and coal. Since the demand and cost of petroleum based fuel is growing rapidly, and if the present pattern of consumption continues, these resources will be depleted in few years. Hence, eVorts are being made to explore for alternative source of energy. An alternative fuel must be technically feasible, economically competitive, environmentally acceptable and readily available (Srivastava and Prasad, 2000). Fatty acid methyl esters derived from renewable sources such as vegetable oils has gained importance as an alternative fuel for diesel engines. The edible oils such as soybean oil in USA, rapeseed oil in Europe and palm oil in countries with tropical climate such as Malaysia * Corresponding author. Tel.: +91 11 2659 1162; fax: +91 11 2659 1121. E-mail addresses: [email protected], [email protected] (S.N. Naik).
0960-8524/$ - see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2005.07.003
are being used for the production of biodiesel to fuel their compression ignition engines (Knothe, 2002). In Indian context, the use of edible oils for engine fuel is not feasible; however, there are several non-edible oilseed species such as Karanja (Pongamia pinnata), Jatropha (Jatropha curcas), Neem (Azadirachta indica), Mahua (Madhuca indica), Simarouba (Simarouba indica) etc., which could be utilized as a source for production of oil. Among these, Karanja is an oil seed bearing tree, which is non-edible and does not Wnd any suitable application with only 6% being utilized out of 200 million tons per annum (Biswas, 2002). Karanja is a native to humid and subtropical environments having annual rainfall ranging from 500 to 2500 mm in its natural habitat. The maximum temperature ranges from 27 to 38 °C and the minimum 1 to 16 °C. It can grow on most soil types ranging from stony to sandy to clay, including verticals. It does not do well in dry sands. It is highly tolerant to salinity. It can be propagated either by seeds or by root suckers (Duke, 1983). The yield of kernels per tree is between 8 and 24 kg (Bringi and Mukerjee, 1987).
L.C. Meher et al. / Bioresource Technology 97 (2006) 1392–1397
The freshly extracted Karanja oil is yellowish orange to brown and rapidly darkens on storage. It has a disagreeable odor and bitter taste. The oil contains several furanoXavones such as karanjin, pongapin, and pongaglabrin. The presence of toxic Xavonoids makes the oil non-edible. At present the oil is being used as a raw material for soap, and after sulphonating and sulphation in the leather tanning industries, the main constraints for its more usage are the color and odor (Bringi and Mukerjee, 1987). Vegetable oils and animal fats are chemically triglyceride molecules, in which three fatty acid groups are ester bound to one glycerol molecule. The triglyceride molecules diVer by the nature of the alkyl chain bound to glycerol. TransesteriWcation is the process of reacting a triglyceride such as one of the vegetable oils with alcohol in presence of a catalyst to produce fatty acid esters and glycerol. In this process, there is the displacement of alcohol part by a monohydric alcohol that yields three alkyl esters from one triglyceride molecule. The molecular weight of a typical ester molecule is roughly one-third that of a straight vegetable oil molecule and has viscosity approximately twice that of diesel fuel instead of 10–20 times as in the case of neat vegetable oils (Peterson, 1986). There is decrease in viscosity and improvement of fuel properties of product fatty acid alkyl esters in the process of transesteriWcation. Attempts have been made for the conversion of Karanja oil to fatty acid methyl esters (De and Bhattacharyya, 1999; Karmee et al., 2004). The latest studies by Vivek and Gupta (2004) revealed the maximum yield of methyl esters up to 89% with molar ratio of MeOH/oil 8–10, KOH 1.5% w/w of oil as catalyst when the reaction was conducted for 40 min at 68–70 °C. In the present study, the optimal reaction conditions were investigated to increase the yield of methyl esters from Karanja oil. The inXuence of the variables such as catalyst concentration, alcohol to oil molar ratio, reaction temperature, mixing intensity on transesteriWcation was studied.
1393
mechanical expeller, Soxhlet extraction and cold percolation. In the process of mechanical expression, a screw press oil expeller was used. For cold percolation and Soxhlet extraction, the kernels were crushed using a mechanical blender. In cold percolation method, 200 ml of n-hexane was added to 100 g of the crushed kernel in a Xask and kept overnight. In Soxhlet extraction procedure, 50 g of crushed kernel was packed in a thimble and the oil was extracted with n-hexane for 2 h. In both, cold percolation and Soxhlet extraction methods, the oil was isolated from n-hexane by rotary evaporator (Laborata 4000-EYcient, Heidolph Instruments). The oil after mechanical extraction was subjected to Wltration and neutralization. The acid value of the mechanically extracted oil was 5.06 mg KOH/g and neutralized by using appropriate amount of potassium hydroxide to reduce the acid value to 0.6 mg KOH/g. Karanja oil extracted by screw press expeller was Wltered by using muslin cloth with 10–15 m pore size. The apparatus used for transesteriWcation consisted of oil bath, reaction Xask with condenser and digital rpm controlled mechanical stirrer. The volume of the glass reactor capacity was 1 l and consisted of three necks, one for stirrer, and the others for condenser and inlet for the reactants. A digital temperature indicator was used to measure the reaction temperature. The batch reactor had a valve at the bottom for collection of the Wnal product. Karanja oil (200 ml) was preheated to the desired temperature before starting the reaction. The potassium hydroxide–methanol solution was prepared freshly in order to maintain the catalytic activity and to prevent moisture absorbance. The methanolic solution was added to Karanja oil in the reaction Xask and the measurement of time was started at this point. At proper spaced interval of time, 50 l of the reaction mixture were withdrawn from the reaction vessel and diluted up to 20 times with HPLC grade methanol, which was analyzed by high performance liquid chromatography. 2.3. Analysis
2. Materials 2.1. Chemicals Methanol (99.8%) and potassium hydroxide were purchased from Merck. Reference standards, such as methyl esters of palmitic, stearic, oleic, linoleic acids were purchased from Sigma-Aldrich (New Delhi) for chromatographic analysis. All the chemicals used were analytical reagent grade. 2.2. Extraction of oil Karanja seeds were obtained from Maharashtra, India and the oil was extracted from the kernel by
The amounts of methyl esters in the product of transesteriWcation of Karanja oil were analyzed using high performance liquid chromatography (HPLC) (Perkin–Elmer Series 200) equipped with refractive index detector (Shodex RI 71). A Spheri-5 C-18 column (Perkin–Elmer Brownlee Column) (220 £ 4.6 mm with 5 m particle size) at temperature 40 °C was used for separation with 1 ml/min Xow rate of methanol as a carrier solvent. The sample injection was 20 l and each constituent was quantiWed by comparing the peak areas with their respective standards. The percentage of methyl esters was also quantiWed by 1H NMR Bruker DPX 300 spectrometer (Bruker, Rheinstetten, Germany) with 300 MHz (solvent CDCl3) spectroscopic method.
1394
L.C. Meher et al. / Bioresource Technology 97 (2006) 1392–1397
2.4. Separation and puriWcation of biodiesel After the completion of the reaction, the product was kept overnight for separation of biodiesel and glycerol layer. These were also separated in short time period in centrifuge. The catalysts and unused methanol were in the lower glycerol layer whereas fewer amounts of catalysts, methanol and glycerol were in the upper biodiesel layer. The upper layer was collected for further puriWcation. To obtain pure biodiesel, methods of washing with hot distilled water, dissolving in petroleum ether and then washing with hot distilled water, and neutralization with H2SO4 (1:1) were performed in the reWning process (Karaosmanoglu et al., 1996). The biodiesel after separation was washed using same amount of hot water (60 °C) for three times to remove catalysts, KOH and glycerol if any present in it. The moisture from washed biodiesel was removed by using anhydrous sodium sulphate.
3. Results and discussion 3.1. Characterization of oil The quality of oil is expressed in terms of the physicochemical properties such as acid value, iodine value, saponiWcation value, unsaponiWable matter. These properties of crude Karanja oil (without further treatment) were determined as per Bureau of Indian Standard. The fatty acid composition of Karanja oil was determined by gas chromatographic method.
Fig. 1. InXuence of KOH concentration on methanolysis of Karanja oil (MeOH/oil molar ratio 6:1, temperature 65 °C, rate of stirring 600 rpm).
presence of high amount of catalysts, which increased the viscosity of the reactants and lowered the yield.
3.2. TransesteriWcation
3.4. InXuence of methanol/oil molar ratio
The variables aVecting transesteriWcation such as catalyst concentration (0.25–1.5% wt. of oil), alcohol/oil molar ratio (6:1 to 24:1), temperature (37–65 °C), rate of stirring (180–600 rev. per min) and reaction time were studied to get higher conversion under optimal reaction condition.
The alcohol to oil molar ratio is one of the important factors that aVect the reaction. In the present work, the average molecular weight of oil from its composition was calculated as 887.5 g and accordingly the amount of methanol was taken in the reaction so that the alcohol to oil molar ratio varied from 6:1 to 24:1. The yield of methyl esters versus time at diVerent molar ratio of methanol/oil, such as, 6:1, 9:1, 12:1, 18:1, 24:1 are shown in Fig. 2. The yield of methyl esters for methanol/oil molar ratio of 6:1 after 3 h was 97% whereas the same yield was obtained with molar ratio of 24:1 in 30 min. It was found that the reaction was faster with higher molar ratio of methanol to oil whereas longer time was required for lower molar ratio (6:1) to get the same conversion.
3.3. InXuence of catalyst concentration Methanolysis of Karanja oil was carried out with KOH as a catalyst at a concentration of 0.25–1.5% wt. of oil at 65 °C with MeOH/oil molar ratio of 6:1, and stirring speed 600 rpm. Fig. 1 shows the yield of methyl esters versus time at diVerent catalytic concentrations. The lower catalytic concentration i.e. 0.25% of KOH was insigniWcant to catalyze the reaction to completion. However, 1% KOH was optimal in the reaction with a yield of 96% in 3 h and the reaction was completed 86.4% in 10 min. With the increase in the concentration of catalyst, there was decrease in the yield of methyl esters. This was in accordance with the result obtained by Dorado et al. (2004) and was due to the formation of soap in
3.5. InXuence of reaction temperature Studies were carried out at diVerent temperature such as 37, 50 and 65 °C with 1% KOH as catalyst and methanol/oil molar ratio of 6:1 at a stirring speed of 600 rpm. The yield of KOME versus time was plotted at diVerent
L.C. Meher et al. / Bioresource Technology 97 (2006) 1392–1397
1395
Encinar et al. (1999); the reaction temperature is linked to the reaction time. Same yields could be obtained at room temperature by simply extending the reaction time (Freedman et al., 1984). The reaction temperature above boiling point of alcohol is avoided since at high temperature it tends to accelerate the saponiWcation of glycerides by the alkaline catalyst before completion of the alcoholysis (Dorado et al., 2004). 3.6. InXuence of mixing intensity
Fig. 2. InXuence of molar ratio on methanolysis of Karanja oil (KOH 1%, temperature 65 °C, rate of mixing 600 rpm).
Mixing is very important in the transesteriWcation reaction, as oils or fats are immiscible with sodium hydroxide–methanol solution. Methanolysis was conducted with diVerent rate of stirring such as 180, 360 and 600 revolutions per minute (rpm). The yield of methyl esters versus time at diVerent rate of mixing is shown in Fig. 4. It was observed that the reaction was incomplete with 180 rpm and rate of mixing was insigniWcant for methanolysis. The yield of methyl esters at 360 rpm and 600 rpm was same i.e. 97% after three hours of reaction. These results are in accordance with Ma et al. (1999). 3.7. QuantiWcation of methyl esters The methyl esters in the product were quantiWed by reverse phase HPLC. Fig. 5 shows the chromatogram of
Fig. 3. InXuence of temperature on methanolysis of Karanja oil (KOH 1%, MeOH/oil molar ratio 6:1, rate of mixing 600 rpm).
reaction temperature (Fig. 3). It was observed that temperature had positive inXuence on methanolysis of Karanja oil. This is in accordance with the result of
Fig. 4. InXuence of mixing on methanolysis of Karanja oil (KOH 1%, temperature 65 °C, MeOH/oil 6:1).
1396
L.C. Meher et al. / Bioresource Technology 97 (2006) 1392–1397
Fig. 5. HPLC chromatogram of Karanja oil methyl esters (where MGs: monoglyceride, DGs: diglycerides, TGs: triglycerides, MeLn: methyl linoleate, MeO: methyl oleate, MeP: methyl palmitate, MeS: methyl stearate).
180 rpm, whereas stirring at high rpm was a time eYcient process. Acknowledgements The authors express their gratitude to Council of ScientiWc and Industrial Research (CSIR), New Delhi, India, for providing Wnancial support to Mr. Lekha Charan Meher in the form of Junior Research Fellowship. References
Fig. 6. 1H NMR spectroscopy of Karanja oil methyl esters.
Karanja oil methyl ester. The 1H NMR spectrum of reaction mixture is shown in Fig. 6. The yield of methyl esters was calculated by comparing the peak area of methoxy and methylene protons as described by Gelbard et al. (1995).
4. Conclusions The experimental study revealed that the optimum reaction conditions for methanolysis of Karanja oil was 1% KOH as catalyst, MeOH/oil molar ratio 6:1, reaction temperature 65 °C, rate of mixing 360 rpm for a period of 3 h. The yield of methyl esters was >85% in 15 min and reaction was almost complete in two hours with an yield of 97–98%. With 12:1 molar ratio of MeOH/oil or higher, the reaction was completed within 1 h. The reaction was incomplete with a low rate of stirring i.e. at
Biswas, D., 2002. Parivesh, Biodiesel as Automobile Fuel. Central Pollution Control Board, Ministry of Environment and Forests. Available from:. Bringi, N.V., Mukerjee, S.K., 1987. In: Bringi, N.V. (Ed.), Non-traditional Oilseeds and Oils of India. Oxford IBH Publishing Co. Pvt. Ltd., New Delhi, pp. 143–166. De, B.K., Bhattacharyya, D.K., 1999. Biodiesel from minor vegetable oils like karanja oil and nahor oil. Fett Lipid 101 (10), 404–406. Dorado, M.P., Ballesteros, E., Lopez, F.J., Mittelbach, M., 2004. Optimization of alkali-catalyzed transesteriWcation of Brassica carinata oil for biodiesel production. Energ. Fuel 18 (1), 77–83. Duke, J.A., 1983. Handbook of energy crops. Unpublished. Available from: . Encinar, J.M., Gonzalez, J.F., Sabio, E., Ramiro, M.J., 1999. Preparation and properties of biodiesel from Cynara cardunculus L. oil. Ind. Eng. Chem. Res. 38, 2927–2931. Freedman, B., Pryde, E.H., Mounts, T.L., 1984. Variables aVecting the yields of fatty acid esters from transesteriWed vegetable oils. J. Am. Oil Chem. Soc. 61 (10), 1638–1643. Gelbard, G., Bres, O., Vargas, R.M., Vielfaure, F., Schuchardt, U.F., 1995. 1H nuclear magnetic resonance determination of the yield of the transesteriWcation of rapeseed oil with methanol. J. Am. Oil Chem. Soc. 72 (10), 1239–1241. Karaosmanoglu, F., Cigizoglu, K.B., Tuter, M., Ertekin, S., 1996. Investigation of reWning steps of biodiesel production. Energ. Fuel 10, 890–895. Karmee, S.K., Mahesh, P., Ravi, R., Chadha, A., 2004. Kinetic study of the base-catalyzed transesteriWcation of monoglycerides from Pongamia oil. J. Am. Oil Chem. Soc. 81 (5), 425–430.
L.C. Meher et al. / Bioresource Technology 97 (2006) 1392–1397 Knothe, G., 2002. Curr. Perspect. Biodiesel Inform. 13, 900–903. Ma, F., Clements, L.D., Hanna, M.A., 1999. The eVect of mixing on transesteriWcation of beef tallow. Bioresource Technol. 69, 289–293. Peterson, C.L., 1986. Vegetable oil as a diesel fuel: Status and research priorities. Trans. ASAE 29 (5), 1412–1422.
1397
Srivastava, A., Prasad, R., 2000. Triglycerides-based diesel fuels. Renew. Sust. Energ. Rev. 4 (2), 111–133. Vivek, Gupta, A.K., 2004. Biodiesel production from Karanja oil. J. Sci. Ind. Res. 63, 39–47.
Optimization of alkali-catalyzed transesteriWcation of Pongamia pinnata oil for production of biodiesel L.C. Meher a, Vidya S.S. Dharmagadda b, S.N. Naik
a,¤
a
b
Centre for Rural Development and Technology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110 016, India Department of Biosystems and Agricultural Engineering, University of Kentucky, 128 CE Barnhart Bldg., Lexington, KY 40546, USA Received 19 October 2004; received in revised form 30 June 2005; accepted 4 July 2005 Available online 15 December 2005
Abstract Studies were carried out on transesteriWcation of Karanja oil with methanol for the production of biodiesel. The reaction parameters such as catalyst concentration, alcohol/oil molar ratio, temperature, and rate of mixing were optimized for production of Karanja oil methyl ester (KOME). The fatty acid methyl esters content in the reaction mixture were quantiWed by HPLC and 1H NMR method. The yield of methyl esters from Karanja oil under the optimal condition was 97–98%. © 2005 Elsevier Ltd. All rights reserved. Keywords: Biodiesel; Methyl esters; Karanja oil; Methanolysis; TransesteriWcation
1. Introduction Presently the world’s energy needs are met through non-renewable resources such as petrochemicals, natural gas and coal. Since the demand and cost of petroleum based fuel is growing rapidly, and if the present pattern of consumption continues, these resources will be depleted in few years. Hence, eVorts are being made to explore for alternative source of energy. An alternative fuel must be technically feasible, economically competitive, environmentally acceptable and readily available (Srivastava and Prasad, 2000). Fatty acid methyl esters derived from renewable sources such as vegetable oils has gained importance as an alternative fuel for diesel engines. The edible oils such as soybean oil in USA, rapeseed oil in Europe and palm oil in countries with tropical climate such as Malaysia * Corresponding author. Tel.: +91 11 2659 1162; fax: +91 11 2659 1121. E-mail addresses: [email protected], [email protected] (S.N. Naik).
0960-8524/$ - see front matter © 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2005.07.003
are being used for the production of biodiesel to fuel their compression ignition engines (Knothe, 2002). In Indian context, the use of edible oils for engine fuel is not feasible; however, there are several non-edible oilseed species such as Karanja (Pongamia pinnata), Jatropha (Jatropha curcas), Neem (Azadirachta indica), Mahua (Madhuca indica), Simarouba (Simarouba indica) etc., which could be utilized as a source for production of oil. Among these, Karanja is an oil seed bearing tree, which is non-edible and does not Wnd any suitable application with only 6% being utilized out of 200 million tons per annum (Biswas, 2002). Karanja is a native to humid and subtropical environments having annual rainfall ranging from 500 to 2500 mm in its natural habitat. The maximum temperature ranges from 27 to 38 °C and the minimum 1 to 16 °C. It can grow on most soil types ranging from stony to sandy to clay, including verticals. It does not do well in dry sands. It is highly tolerant to salinity. It can be propagated either by seeds or by root suckers (Duke, 1983). The yield of kernels per tree is between 8 and 24 kg (Bringi and Mukerjee, 1987).
L.C. Meher et al. / Bioresource Technology 97 (2006) 1392–1397
The freshly extracted Karanja oil is yellowish orange to brown and rapidly darkens on storage. It has a disagreeable odor and bitter taste. The oil contains several furanoXavones such as karanjin, pongapin, and pongaglabrin. The presence of toxic Xavonoids makes the oil non-edible. At present the oil is being used as a raw material for soap, and after sulphonating and sulphation in the leather tanning industries, the main constraints for its more usage are the color and odor (Bringi and Mukerjee, 1987). Vegetable oils and animal fats are chemically triglyceride molecules, in which three fatty acid groups are ester bound to one glycerol molecule. The triglyceride molecules diVer by the nature of the alkyl chain bound to glycerol. TransesteriWcation is the process of reacting a triglyceride such as one of the vegetable oils with alcohol in presence of a catalyst to produce fatty acid esters and glycerol. In this process, there is the displacement of alcohol part by a monohydric alcohol that yields three alkyl esters from one triglyceride molecule. The molecular weight of a typical ester molecule is roughly one-third that of a straight vegetable oil molecule and has viscosity approximately twice that of diesel fuel instead of 10–20 times as in the case of neat vegetable oils (Peterson, 1986). There is decrease in viscosity and improvement of fuel properties of product fatty acid alkyl esters in the process of transesteriWcation. Attempts have been made for the conversion of Karanja oil to fatty acid methyl esters (De and Bhattacharyya, 1999; Karmee et al., 2004). The latest studies by Vivek and Gupta (2004) revealed the maximum yield of methyl esters up to 89% with molar ratio of MeOH/oil 8–10, KOH 1.5% w/w of oil as catalyst when the reaction was conducted for 40 min at 68–70 °C. In the present study, the optimal reaction conditions were investigated to increase the yield of methyl esters from Karanja oil. The inXuence of the variables such as catalyst concentration, alcohol to oil molar ratio, reaction temperature, mixing intensity on transesteriWcation was studied.
1393
mechanical expeller, Soxhlet extraction and cold percolation. In the process of mechanical expression, a screw press oil expeller was used. For cold percolation and Soxhlet extraction, the kernels were crushed using a mechanical blender. In cold percolation method, 200 ml of n-hexane was added to 100 g of the crushed kernel in a Xask and kept overnight. In Soxhlet extraction procedure, 50 g of crushed kernel was packed in a thimble and the oil was extracted with n-hexane for 2 h. In both, cold percolation and Soxhlet extraction methods, the oil was isolated from n-hexane by rotary evaporator (Laborata 4000-EYcient, Heidolph Instruments). The oil after mechanical extraction was subjected to Wltration and neutralization. The acid value of the mechanically extracted oil was 5.06 mg KOH/g and neutralized by using appropriate amount of potassium hydroxide to reduce the acid value to 0.6 mg KOH/g. Karanja oil extracted by screw press expeller was Wltered by using muslin cloth with 10–15 m pore size. The apparatus used for transesteriWcation consisted of oil bath, reaction Xask with condenser and digital rpm controlled mechanical stirrer. The volume of the glass reactor capacity was 1 l and consisted of three necks, one for stirrer, and the others for condenser and inlet for the reactants. A digital temperature indicator was used to measure the reaction temperature. The batch reactor had a valve at the bottom for collection of the Wnal product. Karanja oil (200 ml) was preheated to the desired temperature before starting the reaction. The potassium hydroxide–methanol solution was prepared freshly in order to maintain the catalytic activity and to prevent moisture absorbance. The methanolic solution was added to Karanja oil in the reaction Xask and the measurement of time was started at this point. At proper spaced interval of time, 50 l of the reaction mixture were withdrawn from the reaction vessel and diluted up to 20 times with HPLC grade methanol, which was analyzed by high performance liquid chromatography. 2.3. Analysis
2. Materials 2.1. Chemicals Methanol (99.8%) and potassium hydroxide were purchased from Merck. Reference standards, such as methyl esters of palmitic, stearic, oleic, linoleic acids were purchased from Sigma-Aldrich (New Delhi) for chromatographic analysis. All the chemicals used were analytical reagent grade. 2.2. Extraction of oil Karanja seeds were obtained from Maharashtra, India and the oil was extracted from the kernel by
The amounts of methyl esters in the product of transesteriWcation of Karanja oil were analyzed using high performance liquid chromatography (HPLC) (Perkin–Elmer Series 200) equipped with refractive index detector (Shodex RI 71). A Spheri-5 C-18 column (Perkin–Elmer Brownlee Column) (220 £ 4.6 mm with 5 m particle size) at temperature 40 °C was used for separation with 1 ml/min Xow rate of methanol as a carrier solvent. The sample injection was 20 l and each constituent was quantiWed by comparing the peak areas with their respective standards. The percentage of methyl esters was also quantiWed by 1H NMR Bruker DPX 300 spectrometer (Bruker, Rheinstetten, Germany) with 300 MHz (solvent CDCl3) spectroscopic method.
1394
L.C. Meher et al. / Bioresource Technology 97 (2006) 1392–1397
2.4. Separation and puriWcation of biodiesel After the completion of the reaction, the product was kept overnight for separation of biodiesel and glycerol layer. These were also separated in short time period in centrifuge. The catalysts and unused methanol were in the lower glycerol layer whereas fewer amounts of catalysts, methanol and glycerol were in the upper biodiesel layer. The upper layer was collected for further puriWcation. To obtain pure biodiesel, methods of washing with hot distilled water, dissolving in petroleum ether and then washing with hot distilled water, and neutralization with H2SO4 (1:1) were performed in the reWning process (Karaosmanoglu et al., 1996). The biodiesel after separation was washed using same amount of hot water (60 °C) for three times to remove catalysts, KOH and glycerol if any present in it. The moisture from washed biodiesel was removed by using anhydrous sodium sulphate.
3. Results and discussion 3.1. Characterization of oil The quality of oil is expressed in terms of the physicochemical properties such as acid value, iodine value, saponiWcation value, unsaponiWable matter. These properties of crude Karanja oil (without further treatment) were determined as per Bureau of Indian Standard. The fatty acid composition of Karanja oil was determined by gas chromatographic method.
Fig. 1. InXuence of KOH concentration on methanolysis of Karanja oil (MeOH/oil molar ratio 6:1, temperature 65 °C, rate of stirring 600 rpm).
presence of high amount of catalysts, which increased the viscosity of the reactants and lowered the yield.
3.2. TransesteriWcation
3.4. InXuence of methanol/oil molar ratio
The variables aVecting transesteriWcation such as catalyst concentration (0.25–1.5% wt. of oil), alcohol/oil molar ratio (6:1 to 24:1), temperature (37–65 °C), rate of stirring (180–600 rev. per min) and reaction time were studied to get higher conversion under optimal reaction condition.
The alcohol to oil molar ratio is one of the important factors that aVect the reaction. In the present work, the average molecular weight of oil from its composition was calculated as 887.5 g and accordingly the amount of methanol was taken in the reaction so that the alcohol to oil molar ratio varied from 6:1 to 24:1. The yield of methyl esters versus time at diVerent molar ratio of methanol/oil, such as, 6:1, 9:1, 12:1, 18:1, 24:1 are shown in Fig. 2. The yield of methyl esters for methanol/oil molar ratio of 6:1 after 3 h was 97% whereas the same yield was obtained with molar ratio of 24:1 in 30 min. It was found that the reaction was faster with higher molar ratio of methanol to oil whereas longer time was required for lower molar ratio (6:1) to get the same conversion.
3.3. InXuence of catalyst concentration Methanolysis of Karanja oil was carried out with KOH as a catalyst at a concentration of 0.25–1.5% wt. of oil at 65 °C with MeOH/oil molar ratio of 6:1, and stirring speed 600 rpm. Fig. 1 shows the yield of methyl esters versus time at diVerent catalytic concentrations. The lower catalytic concentration i.e. 0.25% of KOH was insigniWcant to catalyze the reaction to completion. However, 1% KOH was optimal in the reaction with a yield of 96% in 3 h and the reaction was completed 86.4% in 10 min. With the increase in the concentration of catalyst, there was decrease in the yield of methyl esters. This was in accordance with the result obtained by Dorado et al. (2004) and was due to the formation of soap in
3.5. InXuence of reaction temperature Studies were carried out at diVerent temperature such as 37, 50 and 65 °C with 1% KOH as catalyst and methanol/oil molar ratio of 6:1 at a stirring speed of 600 rpm. The yield of KOME versus time was plotted at diVerent
L.C. Meher et al. / Bioresource Technology 97 (2006) 1392–1397
1395
Encinar et al. (1999); the reaction temperature is linked to the reaction time. Same yields could be obtained at room temperature by simply extending the reaction time (Freedman et al., 1984). The reaction temperature above boiling point of alcohol is avoided since at high temperature it tends to accelerate the saponiWcation of glycerides by the alkaline catalyst before completion of the alcoholysis (Dorado et al., 2004). 3.6. InXuence of mixing intensity
Fig. 2. InXuence of molar ratio on methanolysis of Karanja oil (KOH 1%, temperature 65 °C, rate of mixing 600 rpm).
Mixing is very important in the transesteriWcation reaction, as oils or fats are immiscible with sodium hydroxide–methanol solution. Methanolysis was conducted with diVerent rate of stirring such as 180, 360 and 600 revolutions per minute (rpm). The yield of methyl esters versus time at diVerent rate of mixing is shown in Fig. 4. It was observed that the reaction was incomplete with 180 rpm and rate of mixing was insigniWcant for methanolysis. The yield of methyl esters at 360 rpm and 600 rpm was same i.e. 97% after three hours of reaction. These results are in accordance with Ma et al. (1999). 3.7. QuantiWcation of methyl esters The methyl esters in the product were quantiWed by reverse phase HPLC. Fig. 5 shows the chromatogram of
Fig. 3. InXuence of temperature on methanolysis of Karanja oil (KOH 1%, MeOH/oil molar ratio 6:1, rate of mixing 600 rpm).
reaction temperature (Fig. 3). It was observed that temperature had positive inXuence on methanolysis of Karanja oil. This is in accordance with the result of
Fig. 4. InXuence of mixing on methanolysis of Karanja oil (KOH 1%, temperature 65 °C, MeOH/oil 6:1).
1396
L.C. Meher et al. / Bioresource Technology 97 (2006) 1392–1397
Fig. 5. HPLC chromatogram of Karanja oil methyl esters (where MGs: monoglyceride, DGs: diglycerides, TGs: triglycerides, MeLn: methyl linoleate, MeO: methyl oleate, MeP: methyl palmitate, MeS: methyl stearate).
180 rpm, whereas stirring at high rpm was a time eYcient process. Acknowledgements The authors express their gratitude to Council of ScientiWc and Industrial Research (CSIR), New Delhi, India, for providing Wnancial support to Mr. Lekha Charan Meher in the form of Junior Research Fellowship. References
Fig. 6. 1H NMR spectroscopy of Karanja oil methyl esters.
Karanja oil methyl ester. The 1H NMR spectrum of reaction mixture is shown in Fig. 6. The yield of methyl esters was calculated by comparing the peak area of methoxy and methylene protons as described by Gelbard et al. (1995).
4. Conclusions The experimental study revealed that the optimum reaction conditions for methanolysis of Karanja oil was 1% KOH as catalyst, MeOH/oil molar ratio 6:1, reaction temperature 65 °C, rate of mixing 360 rpm for a period of 3 h. The yield of methyl esters was >85% in 15 min and reaction was almost complete in two hours with an yield of 97–98%. With 12:1 molar ratio of MeOH/oil or higher, the reaction was completed within 1 h. The reaction was incomplete with a low rate of stirring i.e. at
Biswas, D., 2002. Parivesh, Biodiesel as Automobile Fuel. Central Pollution Control Board, Ministry of Environment and Forests. Available from:
L.C. Meher et al. / Bioresource Technology 97 (2006) 1392–1397 Knothe, G., 2002. Curr. Perspect. Biodiesel Inform. 13, 900–903. Ma, F., Clements, L.D., Hanna, M.A., 1999. The eVect of mixing on transesteriWcation of beef tallow. Bioresource Technol. 69, 289–293. Peterson, C.L., 1986. Vegetable oil as a diesel fuel: Status and research priorities. Trans. ASAE 29 (5), 1412–1422.
1397
Srivastava, A., Prasad, R., 2000. Triglycerides-based diesel fuels. Renew. Sust. Energ. Rev. 4 (2), 111–133. Vivek, Gupta, A.K., 2004. Biodiesel production from Karanja oil. J. Sci. Ind. Res. 63, 39–47.