A highly efficient dilute alkali deacetylation and mechanical (disc) refining process for the conversion of renewable biomass to lower cost sugars

Abstract

The deconstruction of renewable biomass feedstocks into soluble sugars at low cost is a critical component of the biochemical conversion of biomass to fuels and chemicals. Providing low cost high concentration sugar syrups with low levels of chemicals and toxic inhibitors, at high process yields is essential for biochemical platform processes using pretreatment and enzymatic hydrolysis. In this work, we utilize a process consisting of deacetylation, followed by mechanical refining in a disc refiner (DDR) for the conversion of renewable biomass to low cost sugars at high yields and at high concentrations without a conventional chemical pretreatment step. The new process features a low temperature dilute alkaline deacetylation step followed by disc refining under modest levels of energy consumption. The proposed process was demonstrated using a commercial scale Andritz double disc refiner. Disc refined and deacetylated corn stover result in monomeric glucose yields of 78 to 84% and monomeric xylose yields of 71 to 77% after enzymatic hydrolysis at process-relevant solids and enzyme loadings. The glucose and xylose yields of the disc refined substrates in enzymatic hydrolysis are enhanced by 13% and 19%, respectively. Fermentation of the DDR substrates at 20% total solids with Z.mobilis utilized almost all sugars in 20hrs indicating the sugar hydrolyzate produced from the DDR process is highly fermentable due to low levels of chemical contaminants. The ethanol titer and ethanol process yield are approximately 70 g/L and 90% respectively. The proposed new process has been demonstrated using pilot scale deacetylation and disc refiners. The deacetylated and disc refined corn stover was rapidly deconstructed to monomeric sugars at 20% wt solids with enzymatic hydrolysis. High process sugar conversions were achieved, with high concentrations of monomeric sugars that exceeded 150 g/L. The sugar syrups produced were found to have low concentrations of known major fermentation inhibitors: acetic acid, furfural and HMF. The low levels of these fermentation inhibitors lead to high fermentation yields. The results suggest that this process is a very promising development for the nascent cellulosic biofuels industry.