Increased Dissolution of Lignocellulosic Biomass in Ionic Liquid 1-Butyl-3-Methylimidazolium Chloride at High Temperature

Abstract

The increased dissolution of ball-milled lignocellulosic biomass including sugarcane bagasse, Eucalyptus, and Masson pine was investigated in ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) at relatively high temperature. The dissolution time of bagasse in [C4mim]Cl decreased from 13.5 h at 90oC to 2.0 h at 140oC, and further decreased to 0.5 h at 170oC, 0.33 h at 180oC, and 0.28 h at 190oC. Similarly, the dissolution of ball-milled Eucalyptus and Masson pine in [C4mim]Cl was achieved under same conditions within 0.75 h and 0.25 h, respectively. The order of the dissolution efficiency of the ball-milled lignocellulosics in [C4mim]Cl at 170oC was Masson pine > bagasse > Eucalyptus, which was probably related to the more compact and complicated cell wall structure of Eucalyptus than bagasse and Masson pine. The physicochemical properties of the regenerated lignocellulosics were characterized with FT-IR, CP/MAS 13C-NMR and wide-angle X-ray diffraction as well as thermal analysis. The results indicated that no derivatization occurred in dissolution in ionic liquid even at high dissolution temperature. The crystalline structure in native bagasse was destroyed and converted from cellulose I to amorphous structure at low dissolution temperature and to cellulose II at high dissolution temperature after regeneration. Thermal stability of lignocellulosics was slightly decreased after dissolution and regeneration in [C4mim]Cl.