Oil Plants As Sources For Production Of Fatty Acid Methyl Esters (Biodiesel) In Kenya

ABSTRACT

The increased environmental awareness, the world’s petroleum supply constraints and high petroleum fuel prices have spurred efforts in many countries to search for suitable alternatives to diesel fuels. Diesel fuels derived from triglycerides (vegetable oils or animal fats) present a promising alternative. In this study, oils extracted from four plants, Jatropha curcas L., Croton megalocarpus Hutch., Calodendrum capense (L.f.) Thunb. (cape chestnut) and Cocos nucifera L. (coconut) were transesterified in methanol using sodium hydroxide catalyst. Methyl esters obtained were characterized by GC–MS and further tested for fuel properties relative to convectional diesel fuels (automotive diesel and kerosene). Methyl esters of commercial oils; sunflower and soybean were also prepared and tested for fuel properties for comparison. The results showed hexadecanoate and octadecanoate were common fatty acids esters identified in the four analyzed methyl esters. Total unsaturation was highest for Croton ester with 86.6% and lowest for coconut ester, 2.8%. The esters viscosities at 40 °C were in the range of 4.16-4.63 mm2/s except coconut ester whose viscosity (2.71 mm2/s) was close to that of kerosene, 2.35 mm2/s. All esters were found to be less volatile than diesel fuels. The flash points of the esters were much higher (>100 °C) than referenced diesel fuels. Jatropha, sunflower and soybean esters passed the ASTM Standard D6751 for flash point, 130 °C minimum. All the esters however, were within the European Standard EN-14214 for biodiesel of above 101 °C. The densities of the esters were 2-4% higher than that of automotive diesel and 10-12% more than that of kerosene. The heating values of the esters were 12% lower than diesel fuels on average. The esters of Jatropha curcas and croton megalocurpus were further blended with automotive diesel in ranges of 5-70% on volume to volume ratio. Blend of 20% biodiesel in 80% diesel demonstrated the most ideal properties with viscosity, density same as that of diesel, distillation temperature in the range ±5% relative to diesel fuel and heating value 3-13% higher than the pure ester fuels. Al the esters were further tested in a multi-wick stove following standard water boiling test (WBT) and their performance in terms of time to boil, heat transfer efficiency, power output and specific fuel consumption. The esters burnt with odorless and non-pungent smell unlike kerosene fuel taking 50-100% more time while consuming 67-89%, by weight, more fuel than kerosene to boil a liter of water. Heat transfer efficiency for esters was 4-13% lower than for kerosene during boiling phase while specific consumption for the esters was 16-33% higher than kerosene. Ideally it was found that methyl esters (biodiesel) of non-coconut origin showed fuel properties very close to automotive diesel while blended or neat and thus could be used in diesel appliances without any modifications. Coconut ester on the other hand showed properties very close to kerosene and gave stove performance characteristics almost similar to kerosene, making it most favorable as biokerosene.