The impacts of biopolymer-ionic liquid interactions on the utilization of lignocellulosic biomass

In the bioenergy field, the recalcitrance of lignocellulosic biomass has been mainly attributed to lignin. Many ionic liquid (IL) pretreatments were performed to maximize the removal of lignin. However, those methods seriously degraded lignin and hemicellulose, and could generate lignin or hemicellulose for developing an integrated biorefinery that utilizes efficiently the whole biomass. To fulfill the requirements of the integrated biorefineries, this dissertation explored the interactions between biopolymers and IL for a better utilization of lignocellulosic biomass as feedstock. By removing a large portion of hemicellulose, through an autohydrolysis, this physical and chemical barrier for IL diffusion was dismantled and the interactions of the remaining biopolymers with 1-ethyl-3-methylimidazolium acetate were distinctly improved, which significantly enhanced the dissolution ability of biomass in this IL. The percentage of dissolution of biomass increased by a factor of 8 with the highest severity autohydrolysis (160 °C for 60 min) at 100 °C. Furthermore, rheological data showed that autohydrolyzed biomass-IL solution had adequate viscosity for film casting. Therefore, biomass films were directly cast from the solution, coagulated with a solvent and generated materials free of any cracks or wrinkles. The properties of the films highly depended on the coagulant. The film coagulated in methanol showed the most homogeneous texture, and the best thermal and mechanical properties. These characteristics could mainly be explained by the impacts of low polarity of methanol on the morphology and chemical composition of biomass films. Finally, an efficient fractionation process was investigated. Autohydrolyzed biomass was activated under mild IL conditions (60 °C for 3 h) and was then subjected to an enzymatic saccharification. The superior carbohydrates conversion kinetics resulted from a combination of both treatments. The process isolated 87 wt% of cellulose and 81 wt% of hemicellulose in the carbohydrates fractions, and 70 wt% of the lignin with a purity of 90.1%. The main linkages present in the biomass were preserved during the fractionation process. Overall, the successful production of biomass films and the complete fractionation of lignocellulosic biomass demonstrated that the improved interactions of biopolymers with IL by hemicellulose extraction paved the way for a better utilization of lignocellulosic biomass.