Kinetics and Rheological Behavior of Higher Solid (Solids >20%) Enzymatic Hydrolysis Reactions Using Dilute Acid Pretreated, Deacetylation and Disk Refined, and Deacetylation and Mechanical Refined (DMR) Corn Stover Slurries

Many potential biochemical pathways producing advanced hydrocarbon fuels from renewable lignocellulosic biomass require hydrolysates with high sugar concentrations and low toxicity, enabling flexible fermentation strategies, such as fed-batch fermentations capable of producing high product titers and production rates during fermentation. High sugar concentrations also increase the osmotic pressure in the hydrolysates, thus helping to decrease contamination issues. We have shown the production of high sugar concentrations directly from biomass without the need for energy/capital intensive concentration, conditioning, and/or purification steps. In our previous work, we successfully demonstrated high biomass derived sugar concentrations (over 230 g/L fermentable sugars) in enzymatic hydrolysis from high solid (>20 wt % insoluble solids) digestions of dilute alkali deacetylated and mechanically refined (DMR) corn stover slurries. The goal of this work was to understand the effects of initial solid loadings on differently pretreated corn stover substrates on the rheological property changes of enzymatic-hydrolyzed slurries as well as the rates and yields of the enzymatic hydrolysis reactions. We performed high-solid enzymatic hydrolysis using deacetylated and disk refined (DDR), DMR, and dilute acid pretreated (DAP) corn stover substrates at four different initial total solid loadings, 17, 22, 27, and 32%. Slurry samples were collected at regular intervals for measurements of monomeric and oligomeric sugar concentrations (glucose and xylose), particle size distributions, viscosities, and yield stresses. We produced over 270 g/L of fermentable, monomeric sugars (157 g/L of glucose and 114 g/L of xylose) at 32 wt % total insoluble solid during enzymatic hydrolysis of the DMR substrates. The pumpabilities of the digested, high-solid enzymatic hydrolysates were shown to be comparable to other commercially relevant slurry streams, such as honey, peanut butter, and ketchup from the food industry. The conversion and rheological results indicate that high-solid enzymatic hydrolysis (similar to 33 wt %) of DMR substrates is a promising and scalable technology for producing high sugar concentration slurries from lignocellulosic biomass.