Gamma-valerolactone and ionic liquid-based separation processes of cellulose and hemicelluloses, and its associated green/sustainable biorefinery processes
University of New Brunswick
Biomass is one of the abundant renewable resources on earth, and a promising feedstock for the production of energy, chemicals, and materials. Paper-grade bleached pulp consisting of cellulose and hemicelluloses is very suitable to use to produce high-purity cellulose and other hemicellulose-based products. gamma-valerolactone (GVL) and ionic liquid (IL)-based separation processes were developed to separate hemicelluloses from cellulose in this work. Three separation processes including GVL/water/dilute acid, IL/water, and IL/GVL (also IL/GVL/water) were investigated. In the GVL/water process, the CHM (cellulose/hemicelluloses matrix) was treated with binary mixtures having a sufuric acid concentration of 0.007N at 135-150°C for 30 to 120 min. The purified cellulose produced was characterized by a cellulose content of 96-98 wt% at yields of 41-55 wt% and a CrI (crystalline index) of around 72%, under optimized conditions. The acid concentration was proved to be critical, and temperature also very important, as the two dictated the hydrolysis rate of the carbohydrates. IL/water, IL/GVL, and IL/GVL/water systems demonstrated as effective separation mediums for the production of high-purity cellulose. CHM were treated with these mixtures at 60°C for 2h, the purified cellulose products were characterized by cellulose contents of 92 wt%, 95 wt%, and 95 wt%, with yields of 78 wt%, 76 wt%, and 77 wt% respectively, under their optimized mixture ingredient and operational conditions. The ionic liquid involved processes had advantages in gaining high purity at higher yields but tended to disturb the original cellulose crystalline structures (CrIs were around 62%) when compared with the GVL/water/dilute acid process. Extraction liquor recovery strategies were also proposed, including the recovery of hemicellulose, ionic liquid, GVL, and soluble sugars in sequence.