(48c) Non-Reductive Fast Lignin Solvolysis in Flow-through Reactors for the Sustainable Production of BTEX Aromatics from Corn Stover

The efficient separation and conversion of lignin to form valuable commodity products remains the primary challenge in economically utilizing low-cost renewable carbon resources. Typical solvolytic lignin extraction methods are hindered by the low stability of the resulting lignin oligomers at extraction conditions, thus requiring immediate reductive stabilization with a noble metal catalyst and high-pressure H₂ to prevent recondensation and the formation of refractory C-C bonds. Here, we show that carefully controlling the solvent space-time in a flow-through reactor can eliminate the need for this costly reductive step. Notably, increased solvent flow rates limit the exposure of the extracted lignin oligomers in the heated zone help to prevent solvent-induced decomposition of β-O-4 linkages and subsequently minimize the formation of reactive intermediates. For corn stover, the preservation of these linkages was found to be optimally balanced with delignification (~70 wt%) and carbohydrate retention (~80 wt%) by using methanol with a space-time of 60 s at 225° C and 30 s at 250° C. Critically, the recovery of these “native-like” lignin oligomers allows for subsequent depolymerization through pyrolysis, which is less capital intensive than reductive processes and promotes the partial decomposition of the propyl side chains of the monolignol building blocks to lower, more valuable ranges. As such, coupling pyrolysis with immediate hydrodeoxygenation (HDO) using MoO₃ allows for the conversion of the obtained lignin oligomers to monoaromatic and C₂-C₄ aliphatic platform chemicals at yields of ~40 C% and 6-12 C%, respectively. This overall recovery of aromatic rings (1.6–1.7 mmol/g initial lignin) compares similarly to that of reductive catalytic fractionation (1.9) of corn stover while producing higher value products, namely with benzene, toluene, xylene, and ethylbenzene accounting for 75-90 mol% of the produced monoaromatics.