Switchable butadiene sulfone pretreatment of Miscanthus in the presence of water

Abstract

Pretreatment breaks the recalcitrant structure of lignocellulosic biomass prior to enzymatic hydrolysis and fermentation for the production of biofuels and chemicals. In this study, Miscanthus × giganteus, a C₄ perennial grass and energy crop, was pretreated effectively with a new one-step chemical approach at 90 °C–110 °C for 6–30 h using switchable butadiene sulfone. The solvent has the ability to “switch” in equilibrium to 1,3-butadiene and sulfur dioxide, forming sulfurous acid in the presence of water. Sulfurous acid hydrolyzed xylan in Miscanthus, removing up to 91% of xylan into the liquid phase, via Brønsted acid catalysis following irreversible first-order kinetics with the activation energy determined to be 89 kJ mol⁻¹. Butadiene sulfone was mainly responsible for the solubilization of up to 58% of lignin during or after the hydrolysis of xylan. X-ray diffractograms showed that unwanted diene polymers from solvent decomposition can be minimized in the pretreated solids below 110 °C and 18 h, conditions that also allowed for the preservation of 90–99% of glucan. It was demonstrated that all of the butadiene sulfone after pretreatment can be decomposed into 1,3-butadiene and sulfur dioxide, which enables potential solvent reformation and separation from the solubilized xylan derivatives and lignin.