Comparison of base-catalyzed depolymerization of lignin-enriched residues from multiple biochemical conversion processes, feedstock processing processes and biomass sources

To realize the promise of industrial-scale lignocellulosic biorefineries, effective strategies for lignin valorization are required. Lignin quantity and quality can vary significantly across feedstocks and the type of process applied to biomass, most often to extract polysaccharides. In this work, two corn stover-switchgrass 50:50 blends (pelleted and non-pelleted) were subjected to two bioconversion deconstruction processes, dilute acid pretreatment (DAP) and deacetylation and mechanical refining (DMR). The two feedstock blends from DMR and DAP were then enzymatically hydrolyzed (EH). To assess lignin susceptibility to BCD, we determined the carbohydrate yields resulting from deconstruction steps and the yields of solid, aqueous, and gas fraction from base-catalyzed depolymerization (BCD) of the post-EH solid residues, and chemical analyses were subjected to each BCD fraction.
DMR xylose yields improved upon pelletization, but the same trend was not observed in DAP. DMR-EH feedstock blends from the low severity deacetylation condition resulted in the greatest aqueous fraction yields at approximately 81%, which was higher than the non-pelleted corn stover only DMR-EH sample, even though the blend feedstock has higher sugar and lower lignin contents than CS/DMR-EH. This suggests that sugar content effects more on the yield of aqueous fraction than lignin content. There was no significant difference between the pelleted and non-pelleted samples. Based on GPC analysis, BCD solid residues from non-pelleted/pelleted DAP-EHs have higher molecular weight than those from DMR-EHs. In this work, detail effects of biochemical conversion processes, biomass sources, and feedstock processing processes on BCD results are discussed.