(43d) Defeating Biomass Recalcitrance with a Novel Co-Solvent Pretreatment Technology

Biomass recalcitrance is a major obstacle to economic conversion of lignocellulosic biomass to fuels and renewable chemicals that could sustain current and future energy demands. Recalcitrance is a multi-layered phenomenon influenced by physical and chemical characteristics of biomass that prevent enzymes from accessing and hydrolyzing its sugar polymers into fermentable monomers. We recently developed a highly-effective pretreatment strategy that uses tetrahydrofuran (THF) as a renewable co-solvent to enhance both biomass deconstruction and delignification and achieve unprecedented sugar yields from raw agricultural and forestry feedstocks. By optimizing THF co-solvent pretreatment of corn stover, we achieved nearly theoretical yields of glucose with as little as about 4 FPU of enzyme/gram of glucan in the corn stover. We report here physiochemical changes in biomass that result from THF pretreatment to understand factors that could be responsible for its unprecedented digestibility. We compared results from THF co-solvent pretreatment for three different biomass feedstocks (corn stover, maple wood, and poplar wood) to those from application of leading ethanol-organosolv and dilute-acid options. The pretreated solids were first characterized by SEM and NMR to follow differences in micro- and macro- level structures and crystallinity. Simons’ Staining as well as long-term enzyme activity studies were also employed to better understand substrate-enzyme interactions. These results showed that THF co-solvent was highly effective in solubilizing both hemicellulose and lignin fractions to produce solids highly enriched in glucan that were more amorphous than from other pretreatments.  In addition to being highly accessible to enzymes, less enzyme deactivation was observed over long hydrolysis times, suggesting the loss of enzyme activity was not a major factor limiting yields from biomass. Overall, these findings further support the potential value of THF co-solvent pretreatment as a promising strategy for overcoming biomass recalcitrance.