Evaluation of the dissolving selectivity of ionic liquids for the three main components of bamboo powder under microwave irradiation

Abstract

Understanding the dissolving selectivity of ionic liquids (ILs) for cellulose, hemicellulose, and lignin in plant cell wall is critical to explore new ILs for efficient pretreatment of lignocellulosic biomass. Here, the bamboo powder was treated at 150 ℃ under microwave irradiation by 1-butyl-3-methylimidazolium chloride (BmimCl) and 1-butyl-3-methylimidazolium acetate (BmimAc) which had the different anions. The recovered bamboo powder and lignin samples were characterized. It indicated that the solubilities of bamboo powder in BmimCl and BmimAc were 27.04 and 7.00 g/100 g IL, respectively. A large amount of polysaccharides, especially hemicellulose, were possibly degraded by BmimCl, resulting in a low recovery rate (24.17 %) of bamboo powder with high content of lignin (41.81 %). The dissolving selectivity of BmimCl for the three main components was in the order: hemicellulose>cellulose>lignin, while that of BmimAc was in a different order: lignin>cellulose>hemicellulose. The dissolving selectivity of BmimAc was less obvious than that of BmimCl. The pretreatment of bamboo powder with BmimCl and BmimAc could greatly improve the yield of reducing sugar. BmimAc performed stronger ability than BmimCl to destroy the crystal structure of cellulose. Both the bamboo lignins extracted by BmimCl and BmimAc were syringyl (S)/guaiacyl (G)/p-hydroxyphenyl (H) type with different S/G/H ratios of 10.11/5.32/1.00 and 7.61/2.47/1.00, respectively. The lignin extracted by BmimAc was rich in hemicellulose and side alkyl chains. While the β-O-4 bonds in the lignin extracted by BmimCl were seriously broken, leading to the high contents of aliphatic OH, syringyl phenolic OH, and guaiacyl phenolic OH. BmimAc performed weaker ability than BmimCl to damage the lignin structure.