Use of Polyoxometalate Catalysts in Ionic Liquids to Enhance the Dissolution and Delignification of Woody Biomass

Abstract

A well-known polyoxometalate, [PV₂Mo₁₀O₄₀]⁵⁻, in both acidic (acidic POM, H₅[PV₂Mo₁₀O₄₀]) and ionic liquid-compatible form ([C₂mim]POM, [1-ethyl-3-methylimidazolium]₄H[PV₂Mo₁₀O₄₀]), has been studied as a catalyst for the dissolution and delignification of wood in the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C(2) mim]OAc). Differences were observed with variables such as the form of POM, POM loading, and reaction conditions. Generally, the addition of POM leads to a faster dissolution, a lower lignin content in the recovered cellulose-rich materials (isolated pulp), and a lower isolated yield of lignin due to its oxidation. Acidic POM decreases the lignin content of the pulp without compromising the yield of the pulp. [C₂mim]POM in the IL facilitates greater delignification (lower lignin content in pulp) than the IL with acidic POM; however, the overall pulp yield is also lower indicating some degradation of the carbohydrates. The POM can be recovered with [C₂mim]OAc after evaporation of the reconstitution solvent (e.g., acetone/water) and can be reused, albeit with some loss of POM and loss of POM activity under the current conditions.