Deacetylation and Mechanical Refining (DMR) and Deacetylation and Dilute Acid (DDA) Pretreatment of Corn Stover, Switchgrass, and a 50/50 Corn Stover/Switchgrass Blend

The most economical feedstock available to future lignocellulosic biorefineries may be a feedstock blend. Corn stover, switchgrass, and a 50:50 blend of corn stover and switchgrass were subjected to three different dilute alkali deacetylation conditions in a 90 L reactor prior to either mechanical refining (DMR) in a disc refiner followed by a Szego mill or dilute acid pretreatment (DDA) at five different conditions in a 4 L batch steam explosion reactor. The forty-five DDA and nine DMR slurries were subjected to high solids enzymatic hydrolysis at an enzyme loading of 15 mg protein per gram cellulose using Novozymes Cellic CTec3 (DDA) or a 4:1 mix of Novozymes Cellic CTec3:HTec 3 (DMR). The highest glucose yield was achieved using DMR processed corn stover from the high severity deacetylation condition (92 °C and 100 kg NaOH/ODMT) at 95.9% ± 0.8%, while the greatest monomeric glucose yields for switchgrass were between 75% to 80%. The glucose yields from saccharification of the 50:50 corn stover/switchgrass blend was approximately the average of the two individual feedstocks for both DDA and DMR processes. Statistical analysis showed that for a given feedstock type dilute alkali deacetylation severity had a significant impact (p < 0.05) on enzymatic hydrolysis yields, and for a given deacetylation severity the feedstock type had a significant effect on glucose conversion with the addition of switchgrass resulting in lower glucose yields. A blending strategy to maximize enzymatic hydrolysis sugar yields while reducing carbohydrate solubilization during the alkaline treatment step was proposed that allows deacetylation of feedstocks with different recalcitrance at optimal conditions for that feedstock, then blending prior to enzymatic hydrolysis.