Mild continuous-flow methanol extraction coupled with formic acid assisted catalytic hydrogenolysis of corn stover

Abstract

Fractionation of lignocellulosic biomass is important for efficient utilization of both lignin and carbohydrates. Conventional one-pot reductive catalytic fractionation (RCF) can effectively depolymerize lignin, but challenges remain in balancing lignin monomer yield, carbohydrate retention, and external H 2 demand, as well as in separating the heterogeneous catalyst from carbohydrate-rich solids. Herein, a decoupled route for corn stover valorization was developed. Mild continuous-flow methanol extraction was first used to obtain lignin fragments while preserving the carbohydrate-rich solids. The extracted lignin fragments were subsequently subjected to formic-acid-assisted catalytic hydrogenolysis to produce lignin monomers. The extraction conditions were optimized to balance lignin-fragment recovery and carbohydrate preservation. Subsequently, the extracted lignin fragments were hydrogenolyzed under H 2 and H 2 -free atmosphere. Under optimal extraction conditions, yield of lignin fragments reaches 17.3 ± 0.5 wt%, while the carbohydrate retention remains above 95%. The lignin fragments can preserve a part of chemical structures in raw lignin, while carbohydrate-rich solids retain cellulose I. In the subsequent hydrogenolysis step, the addition of 10% formic acid gives a lignin monomer yield of 21.0 wt% without external H 2 . Compared with one-pot RCF, the decoupled route reduces the monomer yield by 8.1 percentage points, but makes carbohydrate retention increase from 24.1% to over 95%. The work could provide a competitive process-design option for high-efficiency utilization of lignocellulosic biomass.