Polar aprotic solvent properties influence pulp characteristics and delignification kinetics of CO2/Organic base organosolv pretreatments of lignocellulosic biomass

In the present study, polar aprotic solvents (e.g., dimethylimidazolidinone (DMI), sulfolane (SUL), dimethylsulfoxide (DMSO)) and organic bases with low vapor pressures are evaluated for the organosolv processing of lodgepole pine. Carbon dioxide (CO2) is also evaluated as a pulping additive. Under mild conditions (150-200 degrees C, 2-10 bar), appreciable delignification (80-85 wt%) is observed within 60 min for all solvent candidates. Amongst the solvent candidates, DMSO promotes the highest delignification (similar to 85 wt%), albeit at the cost of low pulp yields (similar to 0.3 g/g). SUL organosolv facilitates comparable delignification (similar to 80 wt%) while maintaining high yields of pulp (similar to 0.6 g/g). Solvent speciation impacts morphological characteristics of the residual pulps as DMI and SUL pulps consist of bundled fibrous structures whereas DMSO pulps comprise randomly oriented strains. A first-order, kinetic model is applied to quantify delignification kinetics and demonstrates that solvents with high dielectric constants and low molar volumes readily facilitate delignification.