Stepwise separation of poplar wood in oxalic acid/ water and g-valerolactone/water systems Liuming Song, a Ruizhen Wang, b Jianchun Jiang, b Junming Xu * b and Jinsheng Gou * a 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 g- valerolactone/H 2 O 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. Introduction Increasing economic and social development has resulted in increased consumption of petroleum fossil resources, leading to the depletion of these resources and the gradual deteriora- tion of the environment. 1–3 Lignocellulose biomass is an abun- dant renewable starting material that is a possible replacement for nonrenewable petroleum resources used in the sustainable production of chemicals and fuels. 4,5 This material is mainly composed of cellulose, hemicellulose, and lignin. Biomass is characterized by a cellulose content of 35–50%. Cellulose is a D-glucose baseline type polymer homopolysaccharide, which is formed by linking b-1,4-glycosidic bonds. 6–8 Cellulose can be converted to glucose by means of hydrolysis or biotransforma- tion, or via further chemical or biological processing that yields ethanol or other products. 9 Biomass is characterized by a hemicellulose content of 20–30%. Hemicellulose is a heterogeneous oligosaccharide that is composed of two or more types of monosaccharides, such as xylose, arabinose, mannose, and glucose. 6,10 Lignin is a complex hydrophobic cross-linked aromatic polymer composed of phenylpropane structural units linked by ether bonds and carbon–carbon bonds. 11,12 This substance is the second-most abundant component in plants and accounts for 20–35% of biomass. 13,14 Therefore, lignin is considered an important renewable resource for the production of chemicals or materials, such as additives for concrete admixtures, dust control, feed and food additives, dispersants, resin, and binder compositions. 15,16 However, complete separation of these three biomass compo- nents is difficult, owing to the high crystallinity of cellulose, complex chemical cross-linking between components, and sheathing of cellulose by hemicellulose and lignin. 17–19 Many studies have focused on improving the utilization efficiency of lignocellulosic biomass. However, the composition varies among lignocelluloses and therefore, a suitable pretreatment method for improving the utilization efficiency of this material and reducing the cost is needed. 20 Pretreatment methods employing chemical, physical, biological approaches, ionic liquids, and combinations of these approaches have achieved some improvement. 21,22 For example, a dilute acid hydrothermal pretreatment process has been used for hemi- cellulose removal and degradation into C5 sugars (e.g., xylose and arabinose) and a small amount of intermediates (e.g., furfural and acetic acid). Unlike inorganic acids such as H 2 SO 4 and HNO 3 , OA is a weak acid with a dicarboxylic acid structure. This acid can be used for highly selective hydrolysis of hemicellulose and can be obtained from natural resources of biomass. 23–25 Compared with traditional chemical pretreatment methods, the dilute acid hydrothermal pretreatment method, which results in only mild corrosion on equipment and mild reaction conditions, has received increasing attention. 25,26 a College Materials Science & Technology, Beijing Forestry University, Key Laboratory of Wooden Material Science and Application, Ministry of Education, Beijing 100083, China. E-mail: jinsheng@bjfu.edu.cn; Tel: +86 10 62336711 b Institute of Chemical Industry of Forest Products, Chinese Academy of Forestry, National Engineering Lab. for Biomass Chemical Utilization, Key and Open Lab. on Forest Chemical Engineering, SFA, Key Lab. of Biomass Energy and Material, Nanjing 210042, China. E-mail: xujunming@icifp.cn; Tel: +86 25 85482478 Cite this: RSC Adv. , 2020, 10, 11188 Received 6th February 2020 Accepted 8th March 2020 DOI: 10.1039/d0ra01163k rsc.li/rsc-advances 11188 | RSC Adv. , 2020, 10, 11188–11199 This journal is © The Royal Society of Chemistry 2020 RSC Advances PAPER Open Access Article. Published on 17 March 2020. Downloaded on 4/15/2020 6:08:51 AM. This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. View Article Online View Journal | View Issue