Nonreductive Fast Lignin Solvolysis in Flow-Through Reactors for the Sustainable Production of BTEX Aromatics from Corn Stover

The efficient recovery of lignin from its parent biomass and subsequent conversion to chemicals remains a significant roadblock to the economical utilization of low-cost renewable carbon feedstocks. Lignin-first deconstruction strategies, for example through reductive catalytic fractionation (RCF), offer the best results to date but require a metal catalyst and high-pressure hydrogen gas to stabilize the most reactive fragments and prevent their recondensation. Here, we demonstrate that similar degrees of delignification, along with excellent retention of cellulose and hemicellulose, can be achieved in the absence of catalyst and H2 by carefully controlling the space time of the solvent in a flow-through reactor. In the case of corn stover, optimal fractionations were achieved using methanol at 225 °C and a space time of 60 s, or methanol at 250 °C and a space time of 30 s. Both sets of conditions afforded ∼70 wt % delignification and ∼80 wt % carbohydrate retention. Significantly, this strategy eliminates the need for immediate stabilization through catalytic reduction, as short residence times minimize the solvent-induced cleavage of intralignin linkages (i.e., β-O-4) that lead to refractory C–C bonds and recondensation. Subsequent upgrading of the recovered lignin oil through pyrolysis and hydrodeoxygenation (HDO) using MoO3 produces valuable platform hydrocarbons, with ∼40 C% of monoaromatics and an additional 6–12 C% of C2 to C4 alkanes and alkenes. Importantly, the production of platform aromatics from corn stover (1.6–1.7 mmol/g initial lignin) is comparable to RCF-HDO despite the elimination of the high-pressure hydrogenation step. Further, the presented method gives higher value products, as benzene, toluene, ethylbenzene, and xylenes (BTEX) account for 75–90 mol % of the produced monoaromatics.