Evaluation of Two-Step Reaction and Enzyme Catalysis Approaches for Biodiesel Production from Spent Coffee Grounds

Currently, the biodiesel industry is investigating non-food crops with high oil content. The industry is also evaluating oil sources from deeper into the industrial or commercial waste streams. Spent coffee grounds could be a feedstock that qualifies for both as a non-food crop and a waste product. The purpose of this study is to evaluate the feasibility of using coffee oil extracted from spent coffee grounds as raw material to produce ASTM standard biodiesel. The two biodiesel production methods that were used are acid-catalyzed esterification followed by alkali-catalyzed transesterification and lipase catalyzed transesterification. It was found that the high level of free fatty acids (FFA) in the coffee oil was reduced from 16.3% to 2.64% by acid-catalyzed esterification with 40/1 molar ratio of methanol to FFA in the presence of 5% (v/v, based on FFA) hydrochloric acid. However, poor conversion was obtained for the further alkali-catalyzed transesterification. In comparison, 98.5% conversion was achieved by using enzymatic catalysis, demonstrating the feasibility of using this approach to process low quality coffee oil from spent coffee grounds for biodiesel production.