Operation of Enzyme Reactors Under Inactivation and Thermal Optimization

4 Operation of Enzyme Reactors Under Inactivation and Thermal Optimization 

The main objective of reactor operation is to deliver a product of uniform quahty at the required level of production. To do so, final substrate conversion must be kept constant from batch to batch. In the case of continuous operation, outlet substrate conversion must be kept constant throughout. This means that a strategy is required to compensate for enzyme inactivation. 

As an example of the first strategy outlined above, the simulation of sequential batch operation with immobilized penicillin acylase is presented. Penicillin acylase is inhibited by both products, being phenylacetic acid a competitive inhibitor and 6-aminopenicillanic acid a non-competitive inhibitor (lllanes et al. 1994). Simulation was done by solving differential Eq. 5.6, which represents the material balance with the corresponding kinetic expression (Eq. 3.43), and Eq. 5.76, which represents the two-phase series type enzyme inactivation kinetics. The scheme for this situation is presented in Fig. 5.20. 

Results ofthe simulation ofreactor operation are presented in Fig. 5.21 (Illanes etal. 1996). The curvatures in line b (non-modulated) and line c (modulated inactivation) in Fig. 5.21 show that reaction time for each batch increases from batch to batch to compensate for enzyme inactivation. In practice, the use of very stable immobilized enzymes makes the adjustment of reaction time batch after batch unnecessary and sparse corrections are made after a number of batches when a significant reduction in substrate conversion (i.e. 1%) has occurred. 

Usually, Nr -h 1 reactors will be required to absorb non-productive time (discharge, cleaning and filling of reactor). Solving the equation that represents enzyme inactivation under operation conditions (i.e. Eq. 5.76) and the equation that model conversion profiles within the biocatalyst bed in CPBR (Eq. 5.79), residual enzyme activity in each bioreactor after each time interval can be determined and feed flow-rate to each bioreactor during each interval calculated as  

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