Continuous Saccharification of Pretreated Lignocellulose in Simulated Moving Bed Reactor

Conversion of cellulose to glucose is a complex process and its kinetics is governed by a number of substrate and enzyme related factors. In theory, continuous removal of the glucose minimizes the product inhibition on the enzymes which in turn leads to higher conversion at the expense of less enzyme which can be achieved using Packed Bed Reactors (PBR). PBRs are also demonstrated to have higher productivity in terms glucose release and offer the flexibility for enzyme recycling.

Thorough understanding of the hydrolysis pattern in single column PBR is the key in developing a viable process strategy for continuous hydrolysis of lignocellulosic biomass - employing multiple up-flow PBRs, with periodic switching of enzyme/buffer feed, akin to a Simulated Moving Bed (SMB) process. In this study we employed a four column - four zone, SMB reactor (SMBR) with each column in a specific and separate stage of hydrolysis. A fresh column of biomass entering first zone will pass through each zone during each switching interval and at the end of fourth switching interval will get unpacked and subsequently packed with new biomass. At steady state operation, one fresh column of biomass will be added to the loop during every switching.

In SMBR, with switching intervals of 10 hours and enzyme loading of 20 FPU/g_biomass, we achieved ~38% conversion and glucose concentration of ~29 g/l. The cellulose conversion in SMB process was comparable to that of batch slurry experiments at similar conditions and 80% of that achieved in a single column PBR at the expense of 40 FPU/g_biomass. Moreover, the SMBR system led to more than two fold increase in throughput in comparison to batch processes. We intend to further improve the efficiency of SMBR by a model based process optimization and couple it to fermentation for production of value added metabolites.