4-04: High consistency enzymatic hydrolysis with split addition of enzymes to increase sugar concentration

One challenge for making the biomass to ethanol process economically feasible is to increase hydrolysis solids loading while not decreasing sugar conversion. Enzymatic hydrolysis at 2-5% solids ensures proper mixing and gives the best sugar conversion. However, removal of excess water from hydrolysate requires enormous amount of heat, large volume and CAPEX of equipment, long operating time, and high operating cost.  Limited work discussed high consistency enzymatic hydrolysis process capable for real industry application on pretreated biomass. When increase solid loading from 5% to 20%, sugar conversion decreased markedly from 64% to 44% when enzymes were added altogether with no mixing strategies. A novel approach will be presented in this research to increase the sugar concentration without decreasing enzymatic hydrolysis efficiency. In this approach, cellulase is mixed with pulp at 5% solids and then pressed to 20% solids after 10minutes resident time. Even though a significant volume of the liquid was removed, preliminary results showed that 80% of the cellulase still retained in the mixture due to the preferential absorption of cellulase on the biomass. The retained cellulase decreases the viscosity of the biomass matrix in 2-6 hours, which enables for additional cellulose, xylanase and β-glucosidase to be added and intimately mixed into the slurry.  This two-stage enzymatic hydrolysis with split enzyme addition significantly improved sugar concentration from 26g/L to 121g/L, while kept sugar conversion at 63%. A patent has been granted to N.C. State for this concept and licenses have been granted to various companies.