CASCADING REACTOR-SEPARATOR SETS REDUCES TOTAL PROCESSING TIME FOR LOW-YIELD MICHAELIS-MENTEN REACTIONS - MODEL PREDICTIONS

Integration of reaction with separation has often been claimed to prov ide enhanced processing due to alleviation of processing constraints w hich, like equilibrium limitation or product inhibition, are common in enzyme-catalyzed reactions. In this paper, a mathematical model is de veloped to assess the effect of cascading sets of enzyme reactors and physical separators (which, when the number of sets tends to infinity, is equivalent to full integration of reaction and separation), when c ompared with the classical unit operation approach, in terms of total time required to effect reaction and separation for a given overall co nversion. The analysis is laid out using several relevant reactional p arameters [final conversion of substrate (chi(f)), equilibrium constan t (K-eq) and dimensionless dissociation constants of substrate and pro duct (K-m,K-S and K-m,K-P*)] and separational parameters [extent of s eparation in a single step (zeta) and ratio of time scales for molecul ar transport and chemical reaction (Xi)]. Cascading provides a gain in processing time, up to an optimum at a finite degree of cascading, on ly for reaction-controlled processes (typified by low zeta, low Xi, lo w K-eq, low K-m,K-P, high chi(f) and high K-m,K-S*); hence, full inte gration is not necessarily the best processing solution. Lengthening o f the cascade leads to a decrease in the maximum substrate conversion while permitting higher degrees of product recovery.