Different enzyme requirements for the synthesis of biodiesel: Novozym® 435 and Lipozyme® TL IM

Enzymatic syntheses of biodiesel via alcoholysis of different vegetable oils (sunflower, borage, olive and soybean) have been studied. Loss of lipase activity induced by the nucleophile is greater with methanol than with ethanol, and is greater for Lipozyme® TL IM than for Novozym® 435. The optimum volume of ethanol depends on the loading of solid biocatalyst and is higher for preparations of Novozym® 435 than for Lipozyme® TL IM. Maximum rates were obtained with Lipozyme® TL IM, for a molar ratio of alcohol to FA residues of 0.33. By contrast, Novozym® 435 requires at least a 2:1 ratio. Alcoholysis of the vegetable oils is faster with Lipozyme® TL IM than with Novozym® 435. Use of a high loading of Novozym® 435 (50% w/w) and a large molar excess of ethanol are required to obtain an initial rate similar to that obtained with Lipozyme® TL IM at a lower enzyme loading (10% w/w) and an equimolar ratio of ethanol and FA residues. Novozym® 435 produces quantitative conversions in only 7 h at 25 °C, but complete conversions are not obtained with Lipozyme® TL IM. Three stage stepwise addition of ethanol yields 84% conversion to ethyl esters for Lipozyme® TL IM. Hence use of Novozym® 435 is preferred. After nine cycles in a batch reactor Novozym® 435 retained 85% of its initial activity.