Rapid and Complete Dissolution of Softwood Biomass in Tetra-n-butylphosphonium Hydroxide with Hydrogen Peroxide

The wood dissolution properties of tetra-n-butylphosphonium hydroxide ([P-4,P-4,P-4,P-4]OH) were investigated. Cedar wood meal was treated with several concentrations of aqueous (aq.) [P-4,P-4,P-4,P-4]OH with hydrogen peroxide (H2O2) in a glass tube at 121 degrees C. The solution of 60% aq. [P-4,P-4,P-4,P-4]OH with H2O2 at 121 degrees C showed the best dissolution capability for woody biomass with a high dissolution rate of 0.152 g min(-1). Under this condition, 98.5% of the woody biomass, including both lignin and holocellulose, was dissolved after 3 h of treatment. The molecular weight distribution of lignin in the soluble fraction of the [P-4,P-4,P-4,P-4]OH mixtures was determined via size exclusion chromatography, and its weight-average molecular weight decreased from approximately 7500 g/mole after 0.5 h to 2 h of treatment to 5700 g/mole after 3 h and 2500 g/mole after 5 h of treatment. Lower molecular weight components were determined by high-performance liquid chromatography, and vanillin and vanillic acid were identified. The dissolved cellulose was precipitated, and its polymerization degree decreased significantly after 0.5 h of treatment compared to that of the original cellulose.