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

A well-known polyoxometalate, [PV2Mo10O40](5-), in both acidic (acidic POM, H-5[PV2Mo10O40]) and ionic liquid-compatible form ([C(2)mim]POM, [1-ethyl-3-methylimidazolium](4)H[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. [C(2)mim]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 [C(2)mim]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.