The effect of water concentration on the activity and stability of CLECs in supercritical CO2 in continuous operation

In this study the effect of the water concentration on a crystallized enzyme of Candida antarctica lipase B (ChiroCLEC™-CAB) in supercritical carbon dioxide (scCO₂) is studied. The model reaction used is the enantioselective esterification of racemic 1-phenyl ethanol with vinyl acetate; the reaction is performed in scCO₂ at 40 °C and 90 bar in batch and in continuous operation. Kinetic parameters have been derived from continuous experiments, leading to a catalytic turnover number of 0.95 s⁻¹. The optimum activity is reached at low water concentrations (0.05 g L⁻¹). At lower concentrations, CO₂ is stripping water from the enzyme leading to deactivation. However, adding a small amount of water to the substrates can reverse this deactivation and the enzyme activity is restored.