Lipase-catalyzed esterification of stearic acid with ethanol, and hydrolysis of ethyl stearate, near the critical point in supercritical carbon dioxide

摘要

The effect of pressure on the lipase-catalyzed reaction in supercritical carbon dioxide (SCCO2) was investigated for the esterification of steric acid (SA) with ethanol and the hydrolysis of ethyl stearate (ES) near the critical point, ranging from 6 to 20 MPa in pressure and 35 to 60°C in temperature. The esterification rate of SA began to increase near the critical point and kept increasing steadily with an increase in pressure, reflecting the increase in SA solubility in SCCO2. The hydrolysis rate of ES showed a maximum at a pressure near the critical point. When the reaction was carried out with an initial overall ES concentration below its solubility limit in SCCO2, the maximum pressure shifted along the extended line of the gas-liquid equilibrium in the supercritical region in the pressure-temperature phase plane. This seems to be related to the singular behavior of some properties in SCCO2 along this line reported in the literature. These results show the importance of pressure, as well as temperature, as a parameter to control enzyme reactions in SCCO2.