Abstract
Crude Rhizopus oryzae lipase was immobilized on different supports. The CaCO 3 was selected as the most suitable adsorbent preserving the catalytic activity almost intact and offering maximum adsorption capacity. Immobilization enhanced the thermo-stability of lipase. Enzymatic esterification between oleic acid and butanol at 37 °C with shaking (200 rpm) was realized in two systems: n-hexane and solvent-free system. The product of this reaction, 1-butyl oleate, is useful as a diesel additive, a polyvinyl chloride plastisizer, a water-resisting agent and in hydraulic fluids. The influence of reaction conditions such as the amount of lipase used, the presence of water and the substrate concentrations on 1-butyl oleate synthesis were investigated. The optimal conditions for the esterification reaction in a solvent-free system were 60 IU of immobilized lipase and a molar ratio of oleic acid to butanol of 1:1. The reaction could be performed in presence of hexane and the highest conversion percentage (73%) was obtained with 60 IU of immobilized lipase and substrate concentrations of 0.1 M each. Immobilized lipase could be repeatedly used for six cycles without a decrease of synthesis activity. The immobilized R. oryzae lipase exhibited long-chain fatty acids specificity similar to that shown for the free lipase. Besides, the former lipase synthesizes more efficiently the short-chain alcohols than the longer-chain.
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