Factors to decrease the cellulose conversion of enzymatic hydrolysis of lignocellulose at high solid concentrations

The enzymatic hydrolysis of lignocelluloses is a key step in the production of ethanol. Economic considerations for large-scale implementation of the process require operation at high solid concentrations. However, the decrease in cellulose conversion offsets the advantages of working at high solid concentrations. The conversion showed a linear decrease in the reaction of pretreated corn stover (PCS) from 2 to 20 % (w/w) and filter paper from 1 to 10 % (w/w) initial total solid content. Hydrolysis experiments with PCS at various mixing speeds showed that the mass transfer limitation could not restrict the cellulose conversion except the solid concentrations over 5 % DM(w/w). The lignin, if added separately, does not correspond directly to the decrease. At increased concentrations, furfural and 5-hydroxymethylfurfural played a part in the effect, and 5-hydroxymethylfurfural only affected exoglucanase. Product inhibition caused by glucose accumulation at increased solid concentrations was found to be a significant and perhaps principal factor. The decrease in yield was caused by the synergetic inhibition, which was more serious with increased solid concentrations.