Integrated separation process of C5 sugars and phenolics from poplar wood using CO 2 -assisted hydrolysis followed by hydrogenolysis
This study presents an efficient methodology to remove hemicellulose and lignin from lignocellulosic biomass by a three-step process to obtain C5 sugars, phenolics and high purity cellulose. The first step, a CO2-assisted hydrolysis pretreatment was conducted for the selective extraction of the hemicellulose fraction. The process effectively extracted hemicellulose at 180 °C with CO2 at 20 bar initial pressure for 10 min, during which a variety of monosaccharides and other intermediates were obtained. The second step, the catalytic hydrogenolysis of the pretreated feedstock, was performed in a cosolvent isopropyl alcohol− water system with Raney Ni as the catalyst, which can catalyze the depolymerization of lignin components for phenolic products. A variety of phenolic components with lower molecular weights were detected via GC−MS and HSQC. Further treatment with alkaline hydrogen peroxide was used to extract the remaining small amount of lignin and hemicellulose fractions in biomass and to obtain high purity cellulose (>96%). Characterization results indicated that 96% of the lignin and 99% of the hemicellulose could be fractionated by the three-step treatment. This method can be used for the efficient fractionation of hemicellulose, cellulose and lignin, thus achieving high valorization of the entire biomass.