Indigenous oil crops as a source for production of biodiesel in Kenya

Abstract

In this study, oils extracted from four crops, 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 as a catalyst. Methyl esters obtained were characterized by GC-MS and further tested for fuel properties relative to convectional diesel fuels (automotive and kerosene). Methyl esters of commercial oils: sunflower and soybean were also tested for fuel properties for comparison. Some of parameters tested included kinematic viscosity, flash point, distillation temperatures, copper corrosion, cetane number, ash content, and gross heating value. 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 %, Jatropha and C. capense esters had unsaturation of 65.2 % and 61.2 %, respectively, while coconut ester recorded only 2.8 %. The ester viscosities at 40 °C were with range of 4.16-4.63 mm2/s except coconut ester with viscosity 2.71 mm2/s, which is close to that of kerosene 2.35 mm2/s. The esters were found to be less volatile that diesel fuels with coconut esters registering as most volatile among the esters. Esters of sunflower and soybean have their volatility very close to that of Jatropha ester. The flash points of the esters were typically much higher (> 100 °C) than petroleum diesels, automotives and kerosene (74 and 45.5 °C, respectively). 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 density of the esters was found to be 2-4 % higher than that of petroleum automotive diesel and 10-12 % more than that of kerosene. The heating values of the esters were however 12 % lower than diesel fuels on average. In general, coconut esters were found to compare well with kerosene while the rest of the esters showed properties very close to that of automotive diesel and can thus be used as neat or blended fuels in diesel engines without any modifications.