Reactors for Soluble Enzymes

If soluble enzymes exhibit sufficient operational stability, their use is advantageous, as the effort of immobilization and resulting mass transfer limitations can be avoided. Different techniques have been developed to retain soluble enzymes. 

For small-scale synthesis enclosure of enzymes in dialysis tubes has been described for several systems (membrane-enclosed enzyme catalysis or the MEEC technique 127 ). In this case mass transport of the low-molecular-weight substrates and products across the membrane becomes rate limiting because mass transport only occurs by diffusion and not by convection as described below. 

For synthesis on a preparative scale, repetitive batch processing has proved to be an effective and easy-to-handle method1128. The repeated use of the enzyme is possible after concentration of the solution by means of commercially available ultrafiltration equipment and adding fresh substrate solution. Some of the advantages given for the Enzyme Membrane Reactor (see below) are also valid for the repetitive batch technique. 

Compared to batch processes, continuous processes often show a higher space-time yield. Reaction conditions may be kept within certain limits more easily. For easier scale-up of some enzyme-catalyzed reactions, the Enzyme Membrane Reactor (EMR) has been developed. The principle is shown in Fig. 7-26 A. The difference in size between a biocatalyst and the reactants enables continuous homogeneous catalysis to be achieved while retaining the catalyst in the vessel. For this purpose, commercially available ultrafiltration membranes are used. When continuously operated, the EMR behaves as a continuous stirred tank reactor (CSTR) with complete backmixing. For large-scale membrane reactors, hollow-fiber membranes or stacked flat membranes are used 129. To prevent concentration polarization on the membrane, the reaction mixture is circulated along the membrane surface by a low-shear recirculation pump (Fig. 7-26 B). 

Simple addition of fresh ensyme to coinpeasate for eosyine deactivation  

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