(782b) Hydrothermal Processing of Un-Hydrolyzed Biomass for Biocrude and Biochar Production

Un-hydrolyzed biomass (UHS) resulting from enzymatic hydrolysis during cellulosic ethanol production is a wet and carbon-rich residue. It mainly contains lignin and unconverted sugars depending upon the types of biomass pretreatment used in the earlier stages. Energy Independence and Security Act, 2007 of the USA mandates 21 billion gallons of advanced biofuels production by 2022 from cellulosic biomass e.g. energy crops, agricultural residues, and forest residues. Majority of the biofuels productions are focused on cellulosic ethanol. Several tons of UHS will be generated during cellulosic ethanol/butanol production. The efficient utilization of this residue will have a positive impact in making the biofuels cost-competitive.

Hydrothermal processing of biomass under subcritical water conditions is considered as an environmentally benign method for producing biocrude and biochar together. The process is particularly suitable for a feedstock with very high water/moisture content. Hydrothermal processes capitalize on the extraordinary solvent properties of water at elevated temperature for converting biomass to high energy density liquid and solid products. Here, biocrude is defined as a mixture of oxygenated hydrocarbons produced from the liquefaction of biomass which can be upgraded to liquid fuels and chemicals. Biochar is carbon rich, high energy density solid product resulting from the carbonization of biomass components during hydrothermal processing. Corn stovers pretreated by Packed Bed Ammonia Fiber Expansion pretreatment (PB-AFEX^TM) and Extractive AFEX^TM (E-AFEX^TM) methods were hydrolyzed using commercial enzymes. The UHS generated after enzymatic saccharification was used as a feedstock for producing biocrude and biochar in a 500 ml batch reactor under subcritical water conditions. The effect of temperature in the range of 250-350°C, homogeneous catalyst, and reaction time on biocrude and biochar yields and their heating values were studied. The complete mass and energy balance in the conversion of UHS to products were developed.