Continuous enzymatic hydrolysis of biomass in a membrane reactor

Development of efficient separation and purification operations are essential for production of cost-competitive drop in biofuels. Membrane based separations processes are attractive as they could lead to significant process intensification. Today enzymatic hydrolysis of biomass is usually conducted in batch mode. However, continuous operation is desirable for a number of reasons. Higher overall investment costs due to larger reactor volumes, higher running costs due to frequent startup/shut down, one-time use of enzymes as well as enzyme separation costs are disadvantages of batch operation. Though there has been significant research focusing on reducing enzyme cost, recovery and reuse of the enzymes is attractive. In addition, high sugar concentrations are desirable for subsequent fermentation steps, but obtaining high sugar concentrations directly from batch hydrolysis is limited by product inhibition of the enzymes. A continuous saccharification process with integrated membrane separations overcomes the limitations of batch operation.

In this work we have designed and tested an integrated continuous membrane reactor. The integrated membrane reactor includes a microfiltration/ultrafiltration membrane for recovery and recycle of the enzyme and a nanofiltration membrane for concentration of the sugars.  Results show that the membrane reactor is capable of retaining enzymes using ultrafiltration and microfiltration membranes. It also alleviates enzyme inhibition, notably inhibition by glucose. We obtain faster hydrolysis rates than in batch operation. Results are also presented for a continuous integrated membrane reactor and compared to a batch reactor.  We show that higher glucose production rates and product sugar concentrations are achieved for the integrated continuous membrane reactor.