Production of biodiesel from groundnut (Arachis hypogea, L.) oil

Abstract

Biodiesel is an environmental-friendly substitute for fossil fuel.  Research on the production of biodiesel from vegetable oils has concentrated on Jatropha, soybean, palm kernel, sunflower and rapeseed oils with scarce information on groundnut oils.  This study focussed on the production of biodiesel from groundnut oil.  Oil was mechanically extracted from groundnut seeds that were bought from Sabo market in Ogbomoso, Nigeria.  The extracted oil was trans-esterized with ethanol using potassium hydroxide as catalyst in a two-step trans-esterification process to yield ethyl esters and glycerol.  The fuel properties of groundnut oil and its ethyl ester were determined according to American Society for Testing Materials (ASTM) standard methods and compared with that of Automotive Gas Oil (AGO).  The results showed that groundnut seeds gave oil yield of 45.3%, while trans-esterification yielded 86.8% groundnut oil ethyl ester on a volume basis.  At 40ºC, higher viscosity of 39.2 mm²/s was obtained for raw groundnut oil than 7.60 mm²/s obtained for groundnut oil ethyl ester.  At 15ºC, specific gravity of raw groundnut oil and its ethyl ester were 0.9 (1.047 times that of AGO) and 0.85 (1.012 times that of AGO) respectively and are within limit specified by international standards.  The biofuels contained lower amounts of sulphur (9.73% for groundnut oil ethyl ester and 12.8% for raw groundnut oil) than the reference AGO which was 61.8%.  Higher pour (4ºC and 3ºC) points, cloud (7ºC and 8ºC) points and flash (200ºC and >280ºC) points were obtained for groundnut oil ethyl ester and the raw groundnut oil respectively compared to -16ºC, -12ºC and 74ºC respectively obtained for AGO.  The fatty acid profile of the groundnut oil reveals 75.03% unsaturated fatty acids in the oil composition.  Groundnut oil ethyl ester was found to have better fuel quality than raw groundnut oil and it has potentials to fuel a diesel engine.

Keywords: groundnut oil, automotive gas oil, transesterification, ethyl esters, biodiesel, fuel, diesel engine, Nigeria