ENZYMATIC TRANSESTERIFICATION OF WASTE ANIMAL FATS FOR PRODUCTION OF BIODIESEL
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The process of transesterification is the exchange of the organic group R” of an ester with the organic group R’of an alcohol, often catalyzed by acid, base or enzyme. Biodiesel, a mixture of monoalkyl esters of long chain fatty acids, is produced from vegetable oils, animal fats and fish oils by transesterification in presence of alcohol. Biodiesel is a fuel which can be used in a mixture of other fuels or alone. The base catalyzed transesterification method of biodiesel production is not suitable for waste animal fat as it contains 10–15% free fatty acids which result in higher soap formation and cause extensive downstream processing. Enzyme catalyzed transesterification can overcome the problem of soap formation and multi-step purification of end products and results in a higher purity biodiesel. Lipase is the enzyme widely used in the process of enzymatic transesterification. Various lipases have been used to transesterify triglycerides with short chain alcohols to alkyl esters. The objectives of this study were to screen lipase enzymes for the transesterification process and to use the best lipase for biodiesel production from waste animal fat. Enzymatic transesterification by individual and combined enzyme catalysts (Novozyme 435 and NS88001) was first carried out to investigate the effects of reaction time (4, 8, 12 and 16 hour), oil : alcohol molar ratios (1:1, 1:2, 1:3, 1:4 and 1:5), the effects of alcohol type (methanol and 2-butanol) and reaction temperature (35, 40, 45 and 50°C) on biodiesel yield in solvent and solvent-free systems. The highest conversion yield of biodiesel (96.67%) was obtained from a combination of Novozyme and NS88001 lipase with the optimal reaction condition of oil : 2-butanol molar ratio of 1:4, enzyme concentration of 25% (12.5% w/w of each enzyme), hexane as solvent, a 45°C reaction temperature, a reaction time of 16 h and a mixing speed of 200 rpm. The reusability of lipase enzymes by individual and combination of enzyme catalysts (Novozyme 435 and NS88001) with solvent and solvent-free systems was also investigated in order to reduce the cost of the process. The lipase enzymes lost their activity after being reused for 30 cycles in solvent-free systems and after 10 cycles in solvent system.