Enzymatic reactions in dense gases

The developments on applications of supercritical fluids as alternative solvents for biocatalytic processes that have taken place over the past two decades have been reviewed. An overview of process parameters influencing enzyme activity and stability, the influence of process parameters on reaction rates and productivity are presented. Applications of various types of reactors for enzymatic reaction in dense fluids, limitations of using enzymes as biocatalyst in supercritical fluids as well as future trends are presented. Main advantages of using dense gases as solvents for biocatalyzed reactions are the tunability of solvent properties and simple down stream processing features that can be readily combined with other unit operations. Although many enzymes are stable in supercritical fluids (SCFs) one should pay considerable attention to finding the correct reaction conditions for each substrate/enzyme/SCF system. One of the persistent problems is the instability and deactivation of enzymes under pressure and temperature. At present the most stable enzymes are hydrolases (lipases and esterases) for which pressure effect is lower than temperature deactivation.