GERANYL ACETATE SYNTHESIS BY LIPASE-CATALYZED TRANSESTERIFICATION IN SUPERCRITICAL CARBON-DIOXIDE

The synthesis of geranyl acetate by transesterification catalyzed by immobilized lipase from Mucor miehei was studied in supercritical carbon dioxide (SCCO2) and compared with n-hexane. The influence of water content on the thermostability of the enzyme was investigated in SCCO2. The increase of water content and increase of temperature diminished enzyme stability. The half-life of the dry enzyme in SCCO2 at 100-degrees-C was about 24 h. The effect of ester chain length on the rate of reaction was investigated. Propyl acetate was found to be the best substrate for geranyl acetate synthesis in both media. In order to define the optimal conditions of the reaction, optimization of water content was carried out. The water content of the solid phase seemed to be the most important factor for the activity of the enzyme. The same optimum, 8-10% (w/w) water content, was determined in both media. The kinetics of the reaction are suggested to fit a Ping-Pong Bi Bi mechanism in which inhibition by excess of geraniol has been identified. The values of all apparent kinetic parameters which were not affected by the external diffusional limitations were calculated. The differences between the kinetic constants in both media were discussed. Considering the reaction rates and the maximum velocity of the reaction, the SCCO2 is not better than the conventional organic solvents, such as hexane, for the reaction of transesterification between geraniol and propyl acetate.