10-03: Pretreatment of Miscanthus with a switchable solvent

Pretreatment is a crucial step of breaking recalcitrant lignocellulosic biomass prior to enzymatic hydrolysis and fermentation for the production of fuels and value-added chemicals. A new pretreatment approach using butadiene sulfone (BS) was investigated for the deconstruction of Miscanthus x giganteus, a C4 perennial grass and energy crop, under batch conditions at 90°C-110°C for 6-30 h in a one-step approach.  A unique feature of the process is the ability of BS to “switch” in equilibrium from solvent to 1,3-butadiene and sulfur dioxide, forming sulfurous acid in the presence of water.  The sulfurous acid hydrolyzed and removed up to 91% of xylan in Miscanthus via Brønsted acid catalysis, and the process followed irreversible first-order kinetics with the activation energy determined to be 89 kJ/mol.  The BS was mainly attributed to the solubilization of 50-58% 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 when the treatment conditions were less than 110°C and 18 h, which also allowed for the preservation of 90-99% of glucan.  It was demonstrated that all of the BS after pretreatment can be decomposed with the potential of solvent reformation and the benefit of isolating the solubilized xylan derivatives and lignin. The new process thus can separate xylan and lignin from glucan, key substrates in bio-based processing, while warranting facile solvent recovery.