Design strategy and process optimization for reactors with continuous transport of an immobilized enzyme

In order to operate a process which uses immobilized enzymes at constant conversion and constant capacity, the refreshment of the enzyme must be continuous. In this paper, two reactor types with continuous refreshment of the biocatalyst are discussed: the stirred tank and the multistage fluidized bed. A method is presented for dimensioning a reactor in such a way that the costs for the conversion of substrate to product are minimized. These costs are calculated as the sum of the biocatalyst consumption and overall reactor costs. In contrast with the stirred-tank reactor, the multistage fluidized bed can be operated at a non-uniform temperature. For the glucose isomerase process, an optimal temperature gradient results in a small reduction in the biocatalyst consumption (+ 5%). It is concluded that, in general, a temperature gradient will only favour the economy of processes with relatively expensive biocatalysta. Compared with conventional reactor types, such as the continuous stirred-tank reactor and the fixedbed reactor, the multistage fluidized-bed reactor can improve the economy of an enzyme-catalysed reaction signitkantly.