Enzyme Reactor Engineering

Abstract

Design procedures for enzyme reactors do not differ fundamentally from those of conventional catalytic reactors. Initially, the decision must be made whether continuous operation has economic advantages over batchwise processing. Generally, a continuous flow reactor can be expected to yield a more uniform product and lend itself to scale-up. Control of the reaction environment in a continuous system is possible by holding the reactor at its steady-state conditions.

The type of continuous reactor chosen will depend primarily on the sensitivity of the reaction to substrate and product concentrations. Knowing the exact form of the reaction rate expression enables the chemical engineer to perform mass balance calculations which will provide quantitative comparison of the performance of different reactor designs. Special attention is necessary when evaluating laboratory kinetic data and making design calculations if the enzyme is immobilized on a solid support. Such two-phase catalytic systems are often influenced by mass diffusion rates. Chemical engineering principles can be applied to understand and quantitatively estimate the influence of process variables on diffusion rates.

Membrane enzyme reactors provide the possibility of retaining a mobile and soluble enzyme within a flow reactor. This design calls for a tank-type reactor equipped with a semipermeable membrane on the reactor outlet. The membrane permeability characteristics are selected to hold the larger enzyme molecules within the reactor while at the same time allowing the smaller product molecules to leave the reactor.

Evaluation studies and reaction rate data with immobilized enzymes under controlled mass transfer conditions can be conveniently performed using a differential-bed recirculation-loop reactor. In this laboratory reactor a large volume of fluid is continuously pumped around a tubular loop and through a small bed of supported enzyme catalyst. The pumping rate will determine the mass diffusion rates the catalyst surface. The sensitivity of the apparent reaction rate to changing flow conditions can be easily and reproducibly investigated.