Reactor Systems for Immobilized Enzymes

The choice of an appropriate reactor for applications of immobilized enzymes as well as for soluble enzymes depends on the kinetics of the reaction. Kinetics of immobilized enzymes are not only a function of enzyme activity but also of substrate transport to the enzyme, which is affected by the matrix used for immobilization. For a description of immobilized enzyme kinetics the reader is referred to the comprehensive literature in this field[35 40, 138 14H. Additionally, the use of immobilized enzymes is treated in Chap. 6 of this book. 

A brief overview of enzyme reactors used for application of immobilized biocatalysts in the laboratory and on the industrial scale is given in Fig. 7-35. Examples of industrial processes are given in [2] and [20]. 

To study the kinetics of immobilized enzymes a recirculation reactor may be used. This reactor allows one to perform kinetic measurements with defined external mass transfer effects, reached by establishing a high flow rate near the catalyst, minimizing mass transfer resistance. The reactor behaves as a differential gradientless reactor allowing initial-rate kinetic measurements to be made. 

The fixed bed reactor, behaving as a plug flow reactor, is most often used for immobilized enzyme reactions. Typically, the reactor is used with an upward direction of the flow to avoid compression of the bed and to release gas bubbles generated during the reaction. Reactor design may be done readily without knowing the detailed enzyme kinetics. Kinetic measurements are performed with a recirculation reactor and the data are plotted in the form 1/v = f(%) (see above). From this plot, the residence time necessary to reach a desired conversion x can be calculated as described. The different enzyme concentrations in the recirculation reactor and in the plug flow reactor have to be considered. 

Fluidized bed reactors are advantageous if small particles which would give high flow resistance in a fixed bed reactor are used to minimize external mass transfer resistances. Often it is useful to install nets at different heights of the reactor to approach plug flow characteristics. 

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