Control of High-Solids Saccharification using a Model-Based Methodology for Fed-Batch Operation

This work utilizes both insights obtained from experimental work and kinetic modeling to develop an optimization strategy for high-solids cellulose saccharification, which presents a problem for the operation of stirred tank reactors (STRs) at insoluble solids levels greater than ~15%. In this work, a previously developed model for enyzmatic hydrolysis of cellulose was modified to consider the effects of feeding a stream of pretreated corn stover (PCS) solids and cellulase for a fed-batch process. By solving the set of model differential equations while controlling for a feed stream, it was possible to develop an open-loop control feeding profile that controls the insoluble solids at a constant or manageable level throughout the course of the reaction. This prevents any difficulties that would otherwise be encountered in mixing high-solids slurries. Experimental application of two fed-batch feeding policies in bench-scale STRs resulted in similar cellulose conversion profiles to batch shake flasks, with final cellulose conversions reaching ~80% for fed-batch STRs fed at the equivalent of 25% initial insoluble solids.