In operando monitoring of wood transformation during pretreatment with ionic liquids

The conversion of lignocellulosic biomass or wood into chemicals still poses a challenge due to the recalcitrance of this composite-like material consisting of lignin, hemicellulose and cellulose. A very high accessibility of cellulose is reported by a pretreatment with ionic liquids that enables high conversion rates by enzymatic hydrolysis. However, the underlying mechanisms have not yet been monitored in operando nor are they fully understood. We monitored the transformation of wood in ionic liquids using small-angle neutron scattering to observe changes in the material in operando and to elucidate the intrinsic effects. The data analysis shows three different stages that is (1) impregnation, (2) the formation of voids and (3) increasing structure size within cellulose fibrils. This consecutive mechanism coincides with macroscopic disintegration of the tissue. The analysis further reveals that the reduction of order in longitudinal direction along the fiber axis is a prerequisite for disintegration of cells along the radial direction. This understanding supports further research and development of pretreatment processes starting from lignocellulosic raw material. Graphic abstract