Scaling Up an Immobilized Enzyme System
HOWARD H. WEETALL 1 and
WAYNE H. PITCHER JR. 2
1 Ciba Corning Diagnostics Corporation, Cambridge, MA 02139.
2 Genencor, Incorporated, South San Francisco, CA 94080.
The development of an immobilized enzyme system for commercial application involves a series of decisions and compromises beginning with the choice of enzyme support and ending with the decision on operational mode. Each step is dependent on the other steps, and all the steps influence the overall economics of the final process. Compromises need to be made about the support, method of enzyme attachment, reactor type, kinetic behavior, and operating strategy. Selection of the enzyme carrier and its composition will have a major effect on the pH optimum, metal requirements, and overall performance of the immobilized enzyme system. The reactor type and its behavior will also affect performance. For commercial applications the fixed-bed reactor is generally the reactor type of choice. Knowledge of the appropriate kinetics is necessary to achieve the desired product quality and to reduce cost. One important kinetic parameter is reaction velocity under real world conditions. Rate expressions must take into consideration back-mixing and mass transfer limitations, both internal and external to the immobilized enzyme particles. In addition to understanding kinetic behavior, one must devise a proper operating strategy for producing the greatest amount of product at the least cost, while maintaining constant productivity over time. The success of any scale-up will be determined by the final processing cost as compared to that of the alternatives.
