Submitted to: Institute of Biological Engineering Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 1/15/2005
Publication Date: 3/1/2005
Citation: Haas, M.J., Foglia, T.A. 2005. Enzymes as catalysts in the synthesis of biodiesel [abstract]. International Meeting of the Institute of Biological Engineering Program. p. 6. Interpretive Summary:
Technical Abstract: 'Biodiesel' is the name given to the simple alcohol esters of fatty acids when they are intended for use as a fuel for diesel engines. Compared with petroleum-based fuel, biodiesel reduces the production of undesirable exhaust emissions, profoundly reduces greenhouse gas production, reduces reliance on imported petroleum, and enhances rural community income. For these reasons, a fledgling industry is emerging and growing, with approximately 30 million gallons produced annually in the U.S. Biodiesel is being adopted worldwide, and its use in Europe exceeds that in the U.S. by about 10-fold. Biodiesel is produced from lipids, such as vegetable oils and animal fats, by an ester exchange process known as transesterification. This converts the triglycerides of the feedstock into simple fatty acid alkyl esters. Alkaline earth metal hydroxides, especially sodium hydroxide, are the predominant catalysts for the reaction. In cases where the feedstock also contains free fatty acids, an acid-catalyzed step is also required, sulfuric acid being most commonly employed. These inorganic catalysts offer the advantages of affordability and high degrees of substrate conversion. Lipases are enzymes that, in the high-water systems of the living world, hydrolyze the ester bonds of triglycerides, releasing free fatty acids. However, they are also active in low water systems, where they catalyze ester exchange reactions. Lipases are potentially attractive catalysts for biodiesel production because they produce a cleaner product than do inorganic catalysts, decrease downstream processing costs, and can both esterify free fatty acids and transesterify triglycerides. Nonetheless, due to such matters as cost, stability, and rate and extent of reaction, lipase catalysis has yet to be applied in commercial biodiesel production. An overview will be presented, using data from this and other laboratories to highlight the achievements to date and the challenges remaining in the development and application of lipases as catalysts in biodiesel production.