Studies on the structural characterization of lignin, hemicelluloses and cellulose fractionated by ionic liquid followed by alkaline extraction from bamboo.

摘要

In order to explore the potential application of green solvent ionic liquids (ILs) in lignocellulosic biomass refinery, 1-allyl-3-methylimidazolium chloride ([Amim]Cl) was used as solvent to dissolve and fractionate bamboo Phyllostachys sulphurea (Carr.) A. et C. Riv in this study. The ball milled bamboo was firstly dissolved in [Amim]Cl and regenerated with distilled water, followed by consecutively extraction with 0.5 M NaOH aqueous and 70% ethanol containing 1.0 M NaOH to obtain lignin, hemicelluloses and cellulose-rich fractions. A set of comparison experiment, which was carried out in a similar process aforementioned but excluding the [Amim]Cl dissolution, was firstly introduced to further investigate the fractionation process. The comparative study on chemical and physicochemical properties of the extracted fractions from two different processes was conducted by means of HPAEC, GPC, UV, XRD, quantitative 13C NMR and HSQC spectra. It was shown that lignin (containing 2.19-3.83% polysaccharides, wt.%), hemicelluloses, and cellulose (containing 92.02-93.88% glucose, wt.%) fractions were effectively isolated, and alkaline extraction was confirmed to have the main contribution. The obtained lignin fractions were S-G-H type, and isolated hemicelluloses mainly consisted of 4-O-methyl- alpha -D-glucurono- alpha -L-arabino- beta -D-xylan. [Amim]Cl dissolution and regeneration was confirmed to decrease the total yield of fractionation. Moreover, the results illustrated that during [Amim]Cl treatment lignin and hemicelluloses were slightly degraded and the side-chains of hemicelluloses were partially cleaved; besides, no significant impact of [Amim]Cl treatment on fractionation process could be observed.