Effect of ionic liquid pretreatment on the physicochemical properties of hemicellulose from bamboo

Abstract Ionic liquid (IL) pretreatment of lignocellulosic biomass has been the focus of attention due to its numerous advantages compared with conventional methods. The change in the physicochemical properties of the three main components of this biomass during IL pretreatment is the key factor for their further utilization and conversion. In this study, hemicellulose extracted from bamboo was dissolved in three ILs with different imidazolium cations and the same anion of acetate, including 1-ethyl-3-methylimidazolium acetate (EmimAc), 1-butyl-3-methylimidazolium acetate (BmimAc), and 1-allyl-3-methylimidazolium acetate (AmimAc). The solubility of hemicellulose in the ILs was measured as a function of temperature from 120 °C to 150 °C. Hemicelluloses regenerated from the saturated IL solutions were characterized by using Fourier transform infrared spectroscopy, gel permeation chromatography, gas chromatography–mass spectrometry, 13C–1H heteronuclear single-quantum correlation nuclear magnetic resonance, and thermogravimetry. The solubility of hemicellulose in the three ILs was greatly affected by temperature, and the solubility increased with increasing temperature. The highest solubilities per 100 g of IL were 15.56, 15.09, and 6.73 g in BmimAc, EmimAc, and AmimAc, respectively. Hemicelluloses regenerated from saturated IL solutions showed similar physicochemical features with that of the original hemicellulose before being pretreated with ILs. These features included molecular weight, relative neutral sugar composition, structural feature, and thermal stability. Hence, hemicellulose was litter degraded during IL solving. In addition, the recovered EmimAc was analyzed after dissolving hemicellulose to a saturated state at 150 °C by using 13C and 1H NMR. The recovered IL contained minimal amounts of ethanol and other impurities.