Transesterification of waste oil to biodiesel in solvent free system catalyzed by immobilized lipase

The transesterification of waste oil to biodiesel in a solvent free system catalyzed by an immobilized lipase Novozym 435 was explored. The byproduct glycerol was found to be adsorbed on the support and the stability of the immobilized lipase was enhanced by rinsing the enzyme with acetone. The optimal reaction conditions such as molar ratio of methanol to oil, enzyme amount, temperature and shaking rate were 1, 6.6 U/g, 35similar to40 degreesC and 150 r/min, respectively. Water addition was not favorable for the reaction. A three-step methanolysis protocol was used to protect the immobilized lipase from inactivation by methanol. One molar equivalent of methanol was successively added at reaction time of 0, 6 and 14 h, by which a methyl ester content of 88.6% in the reaction mixture could be achieved after total reaction time of 30 h. Acetone was used to remove glycerol from the enzyme surface at each step. The enzyme showed no appreciable loss in activity after being continuously operated for 300 h.