Production of biodiesel using rubber
[
He
6
ea brasiliensis
(Kunth. Muell.)] seed oil
O.E. Ikwuagwu *, I.C. Ononogbu, O.U. Njoku
Lipid and Lipoprotein Research Unit,Department of Biochemistry,Uni6ersity of Nigeria,Nsukka,Enugu State,Nigeria
Accepted 10 December 1999
Abstract
Rubber (He6ea brasiliensis) seed oil was extracted, and its physical and chemical characteristics determined. The
crude oil was bleached and the ester-fuel (methyl-ester) was prepared bytrans-esterification with 6-molar excess of methanol using sodium hydroxide as a catalyst. Methyl ester yield and fuel properties of the oil (crude and bleached) and its methyl ester were determined and compared to that of commercial diesel fuel. The analysis of the properties in comparison to commercial diesel fuel showed thattrans-methylation improved the fuel properties of the oil. The viscosity was substantially reduced from 37.85 to 6.29 cSt. Calculated cetane index (increased from 34.00 to 44.81), other fuel properties were also found to improved. The results supports the choice of monosters, in place of straight rubber seed oil, as having better potential for use as alternative diesel fuel. However, oxidative stability was reduced bytrans-methylation. © 2000 Published by Elsevier Science B.V. All rights reserved.
Keywords:Rubber seed oil; Biodiesel; Methylester
www.elsevier.com/locate/indcrop
1. Introduction
Ever since it was known that fossil fuels are finite and indeed will only suffice for a few gener-ations, scientists have been looking for alterna-tives (Klopfenstein and Walker, 1983; Krause, 1998). Recently, there has been growing interest in biodiesel, alternative diesel fuels made from natu-ral, renewable sources such as vegetable fats and oils (Ratledge and Boulton, 1985; Lee et al., 1995). These biodiesels are either in the form of
triacylglycerols or trans-esterified with various
monohydric alcohols (Klopfenstein and Walker, 1983). Methyl esters based on sunflower and soy oil are already on the market in the US (Krause, 1998). Currently, only 10% of the vegetable oils produced are used in the non-food applications and the use of vegetable oils for biodiesel will put pressure on the food use of the commodity. This challenge can best be alleviated by the exploration of new crops and unexploited oil crops capable of producing fats and oils for the industry (Gray, 1993).
The rubber plant which is widely used as a natural source of rubber have been reported to have oil rich seeds (Njoku et al., 1996). Although there are variations in the oil content of the seed * Corresponding author.
E-mail address:[email protected] (O.E. Ikwuagwu)
O.E.Ikwuagwu et al./Industrial Crops and Products12 (2000) 57 – 62
58
from different countries, the average oil yield have been reported to be 40% (Hilditch et al., 1951; Njoku et al., 1996). The oil has found little or no economic importance except for scanty reports on its possible uses in soap, alkyd resin, and lubricat-ing oil industries (Sthapitanonda et al., 1981; Njoku et al., 1996). The industrial value of a vegetable oil generally depends on its specified fatty acids and the ease with which it can be modified or combined with other chemicals (Pryde and Rothfus, 1989). Rubber Seed Oil (RSO) contains 17 – 20% saturated fatty acids (myristic, palmitic, stearic, arachidic, and behenic) and 77 – 82% unsaturated fatty acids (palmitoleic,
oleic, linoleic, linolenic and arachidoleic) (Hardjo-suwito and Hoesnan, 1978; Njoku et al., 1996). This study was undertaken to determine whether rubber seed oil and its methyl ester are desirable as alternative diesel fuel. Also investigated was the oxidative stability of the methyl ester in compari-son with the oil.
2. Materials and methods
Fresh rubber (He6ea brasiliensis) seeds were
collected from the Faculty of Agriculture, Univer-sity of Nigeria, Nsukka Rubber Plantation. The seeds were dried in the oven at 45°C for 72 h and shelled. The kernels were milled using attrition mill and the proximate analysis carried out ac-cording to the method of the Association of Offi-cial Analytical Chemists (AOAC, 1980). The oil was extracted from the milled kernels with petroleum-ether (40 – 60°C) using Soxlet extractor. The diesel fuel used as reference oil was obtained from the Nigerian National Petroleum Corpora-tion Depot, Aba, Abia State, Nigeria.
After extraction with petroleum ether, the oil was dried over anhydrous sodium sulphate, filtered and the solvent removed by rotary evapo-ration. The oil was partially refined (bleaching) according to the method used by POS Pilot Plant, Saskatoon, Canada. The oils were characterized using suitable physical and chemical techniques according to the method of AOCS (1980).
Methyl esters of rubber seed oil were prepared according to the method adapted from Nye et al. (1983) and Freedman et al. (1984) by refluxing the oil at 60°C with 6-molar excess of methanol con-taining 1% NaOH as catalyst for 1 h.
Petroleum-ether (3×volume) was added to the reaction to
produce two phases. The bottom glycerol layer
was separated using separation funnel and
weighed. The top ester layer was separated and
washed with water and 5% NaHCO3, dried over
anhydrous Na2SO4 and the ether removed under
vacuum on a rotary evaporator in a 50°C water bath. After evaporation of the petroleum ether, the crude fuel was allowed to stand at room temperature for 48 h followed by gravity filtra-tion. The weights of the separated fractions were Table 1
Physicochemical properties of crude and refined (bleached) rubber seed oil
Analysis Crude RSO Refined RSO
Physical state at Liquid Liquid 30°C
Colour Golden yellow Golden yellow Specific gravity at 0.922 0.918
30°C
1.4654 1.4650 Refractive index at
40°C
Viscosity (cSt) at 41.24 37.85 30°C
245 244
Smoke point (°C) 294
Flash point (°C) 290
345
Fire point (°C) 345
4.0
Yields of ester-fuel (weight per cent)
% Yield of ester % Yield of glycerol at 30°C
Crude oil 76.64 13.98
8.79 Refined 84.46
Fig. 1. Effect of catalyst (NaOH) concentration on ester-fuel yield.
measured and the percentage ester-yield
determined.
Fuel properties of the oil (crude and partially refined), its methyl ester and commercial diesel fuel were determined. The AOCS, (1980) proce-dures were used for the following properties: re-fractive index, specific gravity, viscosity, cloud point, fire point, ash content, iodine value, perox-ide value and acid value. The refractive index and specific gravity were measured at 30°C and 40°C, respectively. The kinematic viscosity was deter-mined using a Ferrantic portable viscometer at 30°. Heats of combustion were measured using bomb calorimetry. Cetane index was calculated according to Klopfenstein (1982).
Oxidative stability of the oils were determined using the Active Oxygen Method: modified swift
test. Fifty grams of samples were placed in a round bottom flask (500 ml capacity) provided with two tubes. The flask was connected via a suction pump and air was allowed through the inlet into the sample. The contents were heated at
97.890.20C on a water bath and constantly
aer-ated. At intervals, the peroxide value of the sam-ple was determined by taking 1.0 g of the samsam-ple. The time (nearest in h) required to reach a
perox-ide value of 100 meg/kg was taken as AOM
(swift) induction time.
3. Results and discussion
O.E.Ikwuagwu et al./Industrial Crops and Products12 (2000) 57 – 62
60
2.71% ash, 3.71% moisture, 22.17% protein, and 24.21% carbohydrate. The result shows that rub-ber seed is a potential source of oil and hence justifies the study on possible industrial uses. However the moisture content is moderately high and may cause a serious degradation of the fatty materials by hydrolysis, thereby rendering the ma-terial poor in stability. Drying the kernel at 60°C for 24 h and storing in almost air-tight container have been found to improve storage (Njoku, 1993).
The physical and chemical properties of the crude and bleached oils are shown in Table 1. From the result, bleaching of the oil decreased the acid value, peroxide value, unsaponifiable matter, and viscosity. This could be explained by the fact that bleaching removes impurities and contami-nants present in the oil which include pigments, soaps, non-hydratable lecithins, oxidized fats and many other non-lipid materials (Hoffmann, 1986). Table 2 shows the yields by weight of liquid ester-fuel (methyl ester) after crystallization at room temperature for 48 h. The result shows that refined oil formed ester-fuel in greater yield than
the crude oil (84% and 74.64%, respectively). This higher ester-fuel yield could be attributed to the reduction in impurities and acid value which would have interfered in the reaction, suggesting that insufficient alkali would have been available for catalysis (Markley, 1961). However, the ester-yield is relatively low compared to 91.9% reported for cafeteria oil (Nye et al., 1983) and 99.0% reported for sunflower oil (Freedman et al., 1984; Hamilton et al., 1992). Ester yield would have been greater if centrifugation had been used rather than gravity filtration. The relative lower ester-yield could also be due to the properties of the rubber seed oil since methylation depends on the triacylglycerol present. It has been verified
that unsaturation and congugated bonds
markedly inhibit the speed of esterification
(Markley, 1961) and rubber seed oil from results of fatty acid analysis is high in unsaturation (Njoku et al., 1996).
The effect of catalyst (NaOH) concentration on the ester-fuel yield is shown in Fig. 1. From the results of esterificationexperiments at different concentration of alkali (catalyst), it can been seen
Table 3
Fuel properties of rubber seed methyl ester in comparison with the oil and diesel fuel
Refined RSO
Crude RSO Linseed oil
Analysis RSO methyl ester Sunflower oil Diesel
methyl estera methyl estera
Specific gravity at 0.922 0.918 0.885 0.880 0.8962 0.840
30°C
4.22b
6.29 37.85
41.24
Viscosity (cSt) at 8.4c 3.12
30°C
Cloud point (°C) 0 −1.0 0.4 1.0 NA B−1
235
Flash point (°C) 294 290 183 NA 79
276
Heat of combus- 39.25 38.76 tion (KJ/g)
0.01
NA NA
0.01 Ash content (%) 0.2 0.02
34.00 44.81
Calculated cetane 34.00 47–51 NA 46.00
index
142.6 142.6
Iodine value 144.0 NA NA 84
0.8
Peroxide value 2.5 1.0 NA NA 0.2
(meq/kg)
Acid value 4.0 1.0 0.9 NA NA 0.02
Fig. 2. Oxidative stability of oils and methyl ester.
that concentartion of 1% alkali brought about the highest yield of 84%. This confirms that catalyst concentration has a variable affect on the ester-yield (Freedman et al., 1984). This result confirms that when excess alkali is used, the resulting soap formed by saponification produces emulsification of the ester and glycerol thereby making separa-tion difficult (Markley, 1961).
The fuel properties of crude rubber seed oil, refined oil and its methyl ester in comparison with commercial diesel fuel are shown in Table 3. The fuel properties of rubber seed oil methyl ester compared favourably to those of other oil seeds which include soyabean, linseed, sunflower oils
(Quick, 1989). The result shows thattrans
-methy-lation improved the following fuel properties of the oil: specific gravity; viscosity; flash point; fire point; ash content; cetane index; and petroxide value. The comparison of these properties with
that of diesel fuel shows that the methyl ester has a relatively closer fuel properties to diesel fuel than that of oil. The viscosity was substantially reduced from 37.85 to 6.29 cSt. The calculated cetane index as well as other fuel properties were found to be improved.
O.E.Ikwuagwu et al./Industrial Crops and Products12 (2000) 57 – 62
62
fact that the refined oil and methyl ester are significantly less viscous than the parent rubber seed oil. This lower viscosity allows a higher oxygen diffusion rate which increases contact be-tween oxygen and the refined oil and ester molecules, respectively. These results show that the oxidative stability of the methyl ester was retrogressive compared to that of the parent rub-ber seed oil and diesel fuel. However, commercial diesel fuel contains anti-oxidants and dispersants as additives for oxidative stability.
These observations suggest thattrans
-esterifica-tion of vegetable oil with monohydric alcohols to produce their esters, has a high potential to be used in alternative diesel fuel production. The oxidative instability calls for the search for a vegetable oil based antioxidant additive as well as other additives. However, work on production of vegetable oil based anti-oxidants and dispersants is being pursued in many laboratories. Thus, it is only through further research and development and through additional measures, and given the political will, that biofuels will in the medium term find their rightful place in the energy supply in countries with agricultural over-production or with sufficient resources of land.
Acknowledgements
The authors are grateful to Professor O. Obidoa of Deptartment of Biochemistry, Science and Technology Centre (STC) and Department of Animal Science of University of Nigeria for equipment/facility assistance.
References
Association of Official Analytical Chemists (AOAC), 1980. Official methods of analysis, 13th ed. Association of Offi-cial Analytical Chemists, Washington, DC, pp. 176 – 201. American Oil Chemists’ Society (AOCS), 1980. Official and
Tentative Methods of the American Oil Chemists’ Society, third ed. American Oil Chemists’ Society, Champion, IL. Freedman, B., Pryde, E.H., Mounts, T.L., 1984. Variables
affecting the yields of fatty esters from transesterified veg-etable oils. J. Am. Oil Chem. Soc. 61 (10), 1638 – 1643.
Gray, S.C., 1993. Oils and fats: an industrialist’s view. In: Anthony, K.R.M., Meadly, J., Robbelen, G. (Eds.), New Crops for Temperate Regions. Chapman and Hall, Lon-don, pp. 179 – 186.
Hamilton, S., Hamilton, R.J., Sewell, P.A., 1992. Extraction of lipids and derivative formation. In: Hamilton, R.J., Hamil-ton, S. (Eds.), Lipid analysis: A Practical Approach. Ox-ford University press, New York, pp. 47 – 63.
Hardjosuwito, B., Hoesnan, A., 1978. Rubber Seed Oil Abstr. 3 (7), 17.
Hilditch, T.P., Achaya, K.T., Seavell, A.J., 1951. Variations in composition of some linolenic-rich seed oil. J. Sci. Food Agric. 2, 543 – 547.
Hoffmann, C., 1986. Edible oils and fats. In: Hershchdoerfer, S.M. (Ed.), Quality control in food industry, vol. 2, second ed. Academic Press, London, pp. 407 – 501.
Klopfenstein, W.E., 1982. Estimation of cetane index for esters of fatty acids. J. Am.Oil Chem. Soc. 59 (12), 531 – 533. Klopfenstein, W.E., Walker, H.S., 1983. Efficiencies of various
esters of fatty acids as diesel fuel. J. Am. Oil Chem. Soc. 60 (8), 1596 – 1599.
Krause, R., 1998. Plant oil: local small-scale extraction and use in engine. Nat. Res. Dev. 47, 71 – 82.
Lee, I., Johnson, L.A., Hammond, E.G., 1995. Use of branched-chain esters to reduce the crystallization temper-ature of biodiesel. J. Am. Oil Chem. Soc. 72, 1155 – 1160. Markley, K.S., 1961. Fatty acids: Their chemistry, properties, production and uses. Interscience Publishers, New York, pp. 757 – 984 part 2.
Njoku, O.U., 1993. The cell wall structures and the industrial utilization of the oil ofpara-rubber seed in paint manufac-ture, unpublished Ph.D. Thesis, Department of Biochem-istry, University of Nigeria, Nsukka, pp. 1 – 80.
Njoku, O.U., Ononogbu, I.C., Owusu, J.Y., 1996. An investi-gation of oil of rubber (He6ea bransiliensis). J. of Rubber
Res. Inst. Sri-Lanka 78, 52 – 59.
Nye, M.J., Williamson, T.W., Deshpande, S., Schrades, J.H., Snively, W.H., Yurkewich, T.P., French, C.L., 1983. Con-version of used frying oil to diesel fuel by transesterifica-tion: preliminary tests. J. Am. Oil Chem. Soc. 60, 1599 – 1601.
Pryde, E.H., Rothfus, J.A., 1989. Industrial and Non-food uses of vegetable oils. In: Robbelen, G., Downey, R.K., Ashri, A. (Eds.), Oil crops of the world. McGraw – Hill, New York, pp. 87 – 117.
Quick, G.R., 1989. Oil seed as energy crops. In: Robbelen, G., Downey, R.K., Ashri, A. (Eds.), Oil crops of the world. McGraw – Hill, New York, pp. 118 – 131.
Ratledge, C., Boulton, C.A., 1985. Fats and oils. In: Moo-Young, M., Blanch, H.N., Drew, S., Wang, D.I.C. (Eds.), Comparative Biotechnology: The principles, applications and regulations of Biotechnology in Industry, agriculture and medicine, vol. 3. Pergamon Press, New York, pp. 983 – 1003.
Sthapitanonda, K., Vimolchalao, C., Mansakul, S., Undu-maakdhi, B., 1981. Rubber seed oil for paints. J. Nat. Res. Counc. Thailand 31 (2), 27 – 42.
