Boosting POM-Ionosolv Biorefining of Lignocellulosic Biomass by Using Redox-Balanced Polyoxometalate Catalysts in Methanolic Ionic Liquid Reaction Media

This article presents an advanced iteration of the polyoxometalate (POM)-Ionosolv concept to generate biobased methyl formate in high yield and a bleached cellulose pulp from lignocellulosic biomass in a single-step operation by using redox-balanced POM catalysts and molecular oxygen in alcoholic ionic liquid (IL) mixtures. The performance of the three Ionosolv-ILs triethylammonium hydrogen sulfate ([TEA][HSO₄]), N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4]), and tributylmethylphosphonium methyl sulfate ([TBMP][MeSO₄]), mixed with methanol (MeOH) (30/70 wt%), is evaluated by methyl formate yield from extracted hemicellulose and lignin as well as purity of the bleached cellulose pulp in the presence of various Keggin-type POMs. The redox-balanced H₈PVMnMo₁₀O₄₀ POM catalyst in [TBMP][MeSO₄]/MeOH emerge as the most effective combination, achieving 20% methyl formate yield from commercial beech wood. The glucan content in the bleached cellulose-enriched solid consisted is over 90%, demonstrating that the use of MeOH drastically improved lignin extraction in parallel with full hemicellulose extraction. The cellulose is highly susceptible to enzymatic hydrolysis, generating a pure and concentrated cellulosic glucose stream. The formed solid catalyst complex is examined in detail to reveal its chemical nature as POM-IL-complex. The approach is applicable to disparate types of lignocellulosic biomass, including hardwood, softwood, and grass.