Dynamic membranes with immobilized Candida antarctica lipase B (CALB) were successfully applied for butyl propionate synthesis in a recirculating bioreactor in supercritical carbon dioxide medium and in room temperature ionic liquid/supercritical carbon dioxide biphasic systems at 50 degrees C and 80 bar. In room temperature ionic liquid/supercritical carbon dioxide biphasic systems, the immobilized enzyme coated with three different ionic liquids based on dialkylimidazolium cations, showed an increase in the selectivity of the process (up to 99.5%) compared with supercrifical carbon dioxide assayed in the absence of room temperature ionic liquid. For the RTILs assayed, it was observed that the increase in activity was in agreement with an increase in the partition coefficients of the substrates between RTIL and hexane. Additionally, a model based on the Ping Pong Bi-Bi mechanism with competitive alcohol inhibition is proposed to describe the kinetics of the transesterification reaction in supercrifical carbon dioxide. (c) 2006 Elsevier B.V. All rights reserved.