Improving Enzymatic Transformation of Waste Edible Oil to Biodiesel by Adding Organic Base

Abstract

The transesterification of waste edible oil and methyl acetate to biodiesel catalyzed by the immobilized lipase Novozym 435 was explored. Novozym 435 could catalyze the transesterification of waste oil with high free fatty acid (FFA) content (up to 27.8%) and methyl acetate, and methyl ester (ME) yield reached 77.5% after a reaction time of 24 h, which was much lower than that with refined corn oil being the raw material (86.2%). FFA was demonstrated to be the major influential factor on the reaction, ME yield dropped sharply with increasing FFA concentration. Acetic acid, the by-product formed in the transesterification of FFA with methyl acetate, was found to be responsible for the decrease of ME yield. Addition of organic base trihydroxymethyl aminomethane and triethylamine at the concentration of 5% based on oil weight to the reaction system could not only speed up the reaction, but improve ME yield.