(631c) Aqueous Processing of Cellulosic Biomass to Reactive Intermediates for Biological and Catalytic Conversion to Liquid Fuels and Other Products

Hot water and dilute acid pretreatments are industrially scalable processes that can break the lignin matrix of cellulosic biomass and release hemicellulose sugars with good yields. High severity treatments facilitate deconstruction of crystalline cellulosic structure but also lead to the dehydration of hemicellulose sugars to furfural and formation of other degradation products. As a result, moderate severity conditions are typically applied to ensure high recovery of xylose and dissolved xylooligomers. However, xylan along with furfural can be catalytically converted to alkanes that can be used to synthesize jet and other hydrocarbon fuels. Thus, higher severity pretreatment conditions than typically considered to feed fermentation pathways can improve yields of dissolved carbon (xylan, furfural, glucan, levulinic acid, formic acid, and HMF) and prove to be a more economical for catalytic routes to making biofuels. In the present study, release of dissolved compounds was followed for treatment of sorghum biomass with just hot water and with dilute sulfuric acid at temperatures ranging between 160 and 260°C and reaction times between 5 and 50 minutes. In addition, some of the volatile compounds were captured and analyzed with gas chromatography. Optimal severities were identified for (i) maximum recovery of dissolved xylose and (ii) maximum production of dissolved organic carbon. When using just hot water, 6.9g/l of xylose was extracted into the liquid phase when biomass was held at 180°C for 30 minutes, and a total organic carbon concentration of 14g/l was obtained from reaction at 200°C for 5 minutes. It was interesting to find that while the solid residue progressively lost organic carbon with increasing severity, the highest severity did not provide the highest extraction of organic carbon into the liquid phase. The energy yields at both the optimal conditions were calculated and compared along with the mass yields of the products, and a higher energy yield from single unit process was found to be more economical than higher mass yield from several processes.