Biodiesel derived from vegetable oils has drawn considerable attention with increasing environmental consciousness. We attempted continuous methanolysis of vegetable oil by an enzymatic process. Immobilized Candida antarctica lipase was found to be the most effective for the methanolysis among lipases tested. The enzyme was inactivated by shaking in a mixture containing more than 1.5 molar equivalents of methanol against the oil. To fully convert the oil to its corresponding methyl esters, at least 3 molar equivalents of methanol are needed. Thus, the reaction was conducted by adding methanol stepwise to avoid lipase inactivation. The first step of the reaction was conducted at 30°C for 10 h in a mixture of oil/methanol (1:1, mol/mol) and 4% immobilized lipase with shaking at 130 oscillations/min. After more than 95% methanol was consumed in ester formation, a second molar equivalent of methanol was added and the reaction continued for 14 h. The third molar equivalent of methanol was finally added and the reaction continued for 24 h (total reaction time, 48 h). This three-step process converted 98.4% of the oil to its corresponding methyl esters. To investigate the stability of the lipase, the three-step methanolysis process was repeated by transferring the immobilized lipase to a fresh substrate mixture. As a result, more than 95% of the ester conversion was maintained even after 50 cycles of the reaction (100 d).Paper no. J9045 in JAOCS 76, 789-793 (July 1999).
KEY WORDS:Biodiesel, Candida antarctica lipase, immobilized enzyme, methanolysis, vegetable oil.Biodiesel (fatty acid methyl esters) is produced by alcoholysis of vegetable oils and animal fats. The main advantages of biodiesel are its biodegradability, renewability, and improved exhaust emissions. Because of these environmental advantages, biodiesel has drawn considerable attention. Currently, biodiesel is produced from vegetable oils in Europe and North America (1,2), and from waste edible oil in Japan. At present, chemical methods are used for biodiesel production, but these methods have drawbacks, such as, difficulties in the recovery of glycerol, the need for removal of catalyst, and the energyintensive nature of the processes. Furthermore, oils containing free fatty acids and/or water are incompletely transesterified using chemical methods. A biochemical approach can overcome these problems, but has not been adopted industrially because of the high cost of the enzyme catalyst. The establishment of a continuous production process using an immobilized enzyme is strongly needed to decrease the production cost of biodiesel using this approach. Several studies report alcoholyses of vegetable oils and animal fats with primary and secondary alcohols and straightand branched-chain alcohols using lipases as catalysts (3-6). However, these reports do not contain the continuous methanolysis of oils and fats in an organic solvent-free environment. A continuous reaction system without organic solvent is necessary for the industrial production of biodiesel. Our ...
