Analysis and parameter estimation of immobilized enzyme
摘要
Determining the intrinsic rate constants of the immobilized enzyme is very important toward scaling up large-scale biochemical engineering processes. But the existence of inter-phase mass transfer and intra-particle diffusion effects make it difficult to estimate. A new approach for estimating the kinetics parameters of the immobilized enzyme reactor is proposed. Intrinsic rate constants can be determined by decoupling those two mass transport effects. When catalyst particles are suddenly introduced into a CSTR, two types of dynamic responses can be obtained. For a first-order reaction system, the critical condition which distinguishes the two types of responses is related to the inlet flow rate and the other system parameters, but not the mass transfer and diffusion coefficients. This enables us to calculate the intrinsic rate constant directly once the flow rate at the critical condition is determined. The method is also extended to the immobilized enzyme system with Michaelis-Menten kinetics. But in this case the inlet substrate concentration is also a parameter in determining the intrinsic rate constants. Dynamic experiments need to be performed in a CSTR in order to determine the critical flow rate. Four different types of CSTR have been considered for purposes of the dynamic experiment. The pros and cons of each type of reactor will be discussed based on the experimental results. Mixing tests and the tanks-in-series model are used to determine the non-ideality of the reactor performance. Three sugar reactions were chosen as the model systems to verify the proposed method. Two types of dynamic responses are clearly shown in all three systems. The rate constants estimated by our method are comparable to those listed in literature or estimated by the stirred-batch method. After the rate constants were determined, the mass transfer and diffusion coefficients of each model system were obtained by curve fitting the original dynamic experiment data; they are also in