Analysis of process integration and intensification of enzymatic cellulose hydrolysis in a membrane bioreactor

Enzymatic cellulose hydrolysis has been studied for many years, generating rich literatures and knowledge in respect to the underlying reaction mechanism, reaction kinetics, and bioreactor systems. This paper attempts to offer some additional information and new understanding of how reaction kinetics and reactor productivity can be improved in a process involving simultaneous reaction and product separation using a purpose-built membrane reactor with a single combined reaction zone and separation zone. Different operating strategies of batch, fed batch and continuous cellulose hydrolysis were investigated with intermittent or simultaneous removal of products (reducing sugars) to reduce enzyme inhibition and improve reactor productivity. The effect of continuous and selective product removal, reduced enzyme inhibition and higher enzyme concentration in retention were examined for the potential benefit in process integration and intensification in order to lower the high process cost of the enzymatic hydrolysis process, mainly due to slow reaction kinetics and expensive enzymes. A mathematical model was offered to account for the effect of selective product (reducing sugars) separation, permeate flux, reduced cellulase inhibition, dynamic structural change of the solid substrate and possible shear deactivation of the enzyme. Computer analysis was also carried out to analyse the quasi-steady state of the reaction intermediates in order to gain an insight into the reaction mechanism in simultaneous reaction and separation systems. Some original analysis and simulation of the effect of membrane separation parameters on the overall reactor performance is offered, including the effect of membrane selectivity (rejection coefficient) and flux. (c) 2005 Society of Chemical Industry.