The fatty acid analysis of microalgae for biodiesel production

Abstract

Current biodiesel feedstocks are food crops, which are an added strain to the food market. However, algae are not a primary food source for humans, and can accumulate a high lipid yield. The suitability of Acutodesmus obliquus and Chlamydomonas CC125 as lipid feedstock was investigated by studying their fatty methyl ester content in the esterified oil (i.e. biodiesel) extracted from algae grown under different conditions of light and stirring regime. Algae cells were grown in pure CO2 for 12 days, harvested and dried. Lipid extraction followed the Bligh and Dyer method, while fatty esters were derived via transesterification. A 5% phenyl polysilphenylene-siloxane GC column was used to identify the fatty esters. Their quantities were used to predict biodiesel quality from equations in literature. The condition with the light intensity of I = 80 µmol.m-2.s-1 and an agitation speed of S = 100 rpm was the most suitable of all tested. Under this condition, A. obliquus was 0.17 g.L-1.d-1 more productive in biomass than Chlamydomonas. Both algae yielded lipid extracts above 80% dwt., under all conditions. This confirms literature reports, that green microalgae are able to accumulate high amounts of storage lipids (e.g. triacylglycerides). Both algae species contained more methyl linolelaidate (C18:2) than any other fatty ester: 94.0% in A. obliquus and 66.6% in Chlamydomonas. For comparison, waste cooking oil fatty ester content contained 71.4% methyl linolelaidate. Algae fuel resembled a good cold-filter plugging point (CFPP = -17ºC). That is, it can be used in cold climates. A. obliquus produced the most suitable combustion quality (CN = 0.54) than Chlamydomonas (CN = 0.013). Therefore, it is the most suitable candidate than Chlamydomonas, for further improvements to the algae biodiesel process.