Sequential fractionation and polyoxometalate‐catalyzed oxidation of lignocellulosic biomass improves cellulose purity and formic acid yield

Abstract Lignocellulosic biomass is an important source of renewable chemicals and materials but its full valorization is necessary in order to achieve economic and sustainability goals. This study proposes a two‐step approach for the valorization of lignocellulosic biomass combining solvent‐assisted fractionation and catalytic oxidation with molecular oxygen to generate cellulose and formic acid. An industrially relevant lignocellulosic substrate, beech wood, was fractionated under a nitrogen atmosphere using either an organosolv (methanol or ethanol) or ionosolv (ionic liquid) aqueous solvent to produce dissolved hemicellulose and lignin as well as a cellulose‐rich solid. The dissolved components were oxidized catalytically to formic acid and its derivatives in a second step using the fivefold vanadium substituted Keggin‐type polyoxometalate H 8 [PV 5 Mo 7 O 40 ]. Enzymatic hydrolysis of the cellulose‐enriched solid generated purified glucose higher in yields than the single‐step comparison method. The organosolv‐fractionation increased enzymatic saccharification to 78% whereas the ionosolv‐fractionation increased the saccharification yield to 68%, in comparison with 18% for the one‐step conversion and only 8% for the untreated beech wood. In the oxidation step, a 28% formic acid yield was achieved under 125 °C, 1200 rpm, 30 bar oxygen, and 6.5 h reaction conditions. The improvements observed for the two‐step approach are attributed to the influence of the solvent on the catalyst preventing the latter from interacting with the cellulose‐enriched solid, which improved the quality of the pulp and increased the overall formic acid yield.