Reducing Solvent\nConsumption in Reductive Catalytic\nFractionation through Lignin Oil Recycling

Reductive catalytic\nfractionation (RCF) enables the simultaneous\nvalorization of lignin and carbohydrates in lignocellulosic biomass\nthrough solvent-based lignin extraction, followed by depolymerization\nand catalytic stabilization of the extracted lignin. Process modeling\nhas shown that the use of exogenous organic solvent in RCF is a challenge\nfor economic and environmental feasibility, and previous works proposed\nthat lignin oil, a mixture of lignin-derived monomers and oligomers\nproduced by RCF, can be used as a cosolvent in RCF. Here, we further\nexplore the potential of RCF solvent recycling with lignin oil, extending\nthe feasible lignin oil concentration in the solvent to 100 wt %,\nrelative to the previously demonstrated 0–19 wt % range. Solvents\ncontaining up to 80 wt % lignin oil exhibited 83–93% delignification,\ncomparable to 83% delignification with a methanol–water mixture,\nand notably, using lignin oil solely as a solvent achieved 67% delignification\nin the absence of water. In additional experiments, applying the RCF\nsolvent recycling approach to ten consecutive RCF reactions resulted\nin a final lignin oil concentration of 11 wt %, without detrimental\nimpacts on lignin extraction, lignin oil molar mass distribution,\naromatic monomer selectivity, and cellulose retention. Overall, this\nwork further demonstrates the potential for using lignin oil as an\neffective cosolvent in RCF, which can reduce the burden on downstream\nsolvent recovery.