Biomass Pretreatment Using Dilute Aqueous Ionic Liquid (IL) Solutions with Dynamically Varying IL Concentration and Its Impact on IL Recycling

A distillation apparatus was used in the pretreatment of white poplar samples with aqueous 1-ethyl-3-methylimidazolium acetate ([C 2 C 1 Im][OAc]) solutions. During biomass pretreatment, the concentration of [C 2 C 1 Im][OAc] was increasing due to removal of water via distillation. This allowed utilization of aqueous IL solutions with initially low IL concentrations that were not considered as effective pretreatment media previously. Aqueous [C 2 C 1 Im][OAc] solutions with initial concentrations of 7 and 15 wt % were tested to pretreat white poplar samples at 130 °C for 3 h. The biomass loading in [C 2 C 1 Im][OAc] was 20 wt %. After pretreatment, sugar conversion was found to account for 72–77% of the sample pretreated in neat [C 2 C 1 Im][OAc]. The encouraging results of this operation prompted a new approach to recycle and reuse [C 2 C 1 Im][OAc]: use the liquor collected after biomass pretreatment in neat [C 2 C 1 Im][OAc] without first separating water from it. In a similar fashion, biomass pretreated with the recycled liquor was exposed to dynamically increasing [C 2 C 1 Im][OAc] concentration, combining biomass pretreatment and water evaporation into one step. Three cycles of recycling and reuse were performed in this work, and the sugar conversion was found to decrease with the number of recycling cycles. It was believed that process optimization could improve sugar conversion further. The potential of this approach of biomass pretreatment, IL recycling, and reuse may stimulate the design of new IL pretreatment technologies.