A cost-efficient methodology was developed for a two-step removal of hemicellulose from lignocellulosic biomass, thereby yielding C5 sugars, further separated residue, and high purity cellulose as well as lignin. In the first step of the process, an oxalic acid (OA)-assisted hydrolysis pretreatment was conducted for the selective decomposition of hemicellulose to C5 sugars. The optimized process conditions were as follows: temperature: 160 °C, OA concentration: 1%, holding time: 10 min. Under these conditions, various monosaccharides and other intermediates were obtained and more than 98.32% of the hemicellulose was removed from the original poplar. In the second step of the process, to extract lignin, a low concentration of sulfuric acid was used as a catalyst during the treatment of samples in a γ-valerolactone/H2O system; more than 91.57% lignin was removed, 82.99% cellulose was retained in the solid cellulose-rich substrates, and 94.45% (i.e., high-purity) cellulose was obtained. This method can be used for efficient fractionation of hemicellulose, cellulose, and lignin with the aim of achieving high value utilization of the entire biomass.
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