Co-solvent enhanced lignocellulosic fractionation (CELF): a novel and versatile pretreatment to increase yields from biological or catalytic biorefining

Our team recently invented a novel pretreatment called Co-solvent Enhanced Lignocellulosic Fractionation (CELF) that applies renewable, water-miscible tetrahydrofuran (THF) with dilute sulfuric acid to fractionate cellulosic biomass and achieve high yields of sugars or furfural, 5-hydroxymethylfurfural, and levulinic acid for biological or catalytic conversion, respectively, into fuels and chemicals.  Recovering highly volatile THF for recycle from post CELF liquid precipitates nearly pure lignin.  For biological conversion, 150°C CELF for 25 minutes with 0.5% sulfuric acid recovered over 90% of available sugars from hemicellulose while removing similar fractions of lignin.  Of note, hydrolysis of CELF solids with just 2 mg enzyme/g glucan achieved nearly theoretical glucan yields, and simultaneous saccharification and fermentation (SSF) hydrolyzed and fermented about 90% at 5 mg-enzyme g-glucan^-1. Consolidated bioprocessing (CBP) with Clostridium thermocellum solubilized most CELF glucan in 1 day without enzyme supplementation.  Alternatively, operating CELF at more severe conditions converted about 87% of pentose sugars to furfural for catalytic conversion, and glucan-rich solids were further reacted with dilute acid to levulinic acid at about 75% of theoretical or digested to glucose with high yields at very low enzyme loadings.  Adding metal halide acids, e.g., FeCl₃, increased theoretical yields to about 95% and 51% for furfural and 5-HMF, respectively, in one vessel.  Additionally, CELF realized similar results with agricultural residues and recalcitrant hardwoods.  The remarkable features of CELF can also be invaluable for gaining new insights into biomass deconstruction that suggest advanced approaches to overcoming recalcitrance, the key economic obstacle to fuels and chemicals from biomass.