Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Sequential extraction of hemicelluloses and lignin for wood fractionation using acid hydrotrope at mild conditions Xuehai Wu a,b , Tongtong Zhang b , Na Liu b , Yingjie Zhao c , Guoyu Tian a, *, Zhaojiang Wang b, * a Key Laboratory of Green Printing & Packaging Materials and Technology in Universities of Shandong, School of Light Industry Science and Engineering, Qilu University of Technology, Shandong Academy of Sciences, Jinan, 250353, China b State Key Laboratory of Biobased Material and Green Papermaking, Qilu University of Technology, Shandong Academy of Sciences, Jinan, 250353, China c Department of Rheumatology, Qilu Hospital, Shandong University, Jinan, Shandong, China ARTICLE INFO Keywords: Hemicelluloses Hydrotrope Lignin Fractionation Biomass ABSTRACT Sequential fractionation (SF) of woody biomass using acid hydrotrope p-toluenesulfonic acid (p-TsOH) as re- action medium was investigated. Hemicellulosic sugars, lignin, and cellulose-rich solid were harvested as the main products from the stepwise deconstruction of biomass as results of hemicelluloses hydrolysis and sub- sequent lignin dissolution. The first step of SF employed 2wt% p-TsOH, far below the minimum hydrotrope concentration (MHC) of 11.5wt%, and reached 23.5 % of biomass dissolution with 55.1 % removal of xylan from wood at 120 °C for 2 h. The second step of SF was characterized with mild conditions of 100 °C, 40wt% p-TsOH, and one hour, and achieved 83 % lignin dissolution with well-preserved structure. The obtained cellulose-rich solid from SF showed a high crystallinity index of 73.3 % and a complete recovery of glucan. This means excellent performance of SF for sustainable bio-refining. 1. Introduction Lignocellulose is a renewable natural resource from photosynthesis of plant, and primarily consists of cellulose, hemicelluloses and lignin in plant cell wall. Cellulose is a polysaccharide containing many glucose units in parallel chains. Hemicelluloses are a heterogeneous group of polysaccharides including xyloglucans, xylans, mannans and gluco- mannans (Scheller and Ulvskov, 2010). Lignin is an irregular poly- phenolic polymer containing guaiacyl (G), syringyl (S) and p-hydro- xyphenyl (H) structures (Sannigrahi et al., 2010). The biorefinery process offers good answers to the approaching oil crisis by producing biofuels, functional materials and chemical using renewable lig- nocellulose (Esposito and Antonietti, 2015; Ragauskas et al., 2006; Sheldon, 2014; Tuck et al., 2012). However, different from petroleum, lignocellulose is a solid, heterogeneous, and recalcitrant material for direct chemical transformation (Himmel et al., 2007; Zhao et al., 2012). To overcome these inherent obstacles, fractionation of structural con- stituents of lignocellulose into processable cellulose, hemicelluloses and lignin is necessary for subsequent product upgrading. The fractionation technologies that have been developed so far in- clude dilute acid (Tian et al., 2011), alkaline (Zhao et al., 2008), or- ganosolv (Pan et al., 2005), ionic liquid (Brandt et al., 2011), and sulfite (Zhu et al., 2015). For an effective fractionation of structural constituents, delignification is a critical step since lignin acts as glue holding cellulose and hemicellulose together in plant cell wall (Ferrer et al., 2012). Fractionation of lignocellulose by dilute acid and alkali has a long history, and achieves commercial successes for bio-ethanol and chemical pulp production, respectively. However, these fractiona- tion methods focus only on cellulose, and ignore the valorization of hemicellulose and lignin. Further, the separation of soluble sugar from spent liquor, the feasible valorization of structurally modified of lignin, and the recovery of solvent have remained as substantial obstacles (Zhang et al., 2007). In the term of structural transformation of lignin during fractionation process, Sun et al. (2015) studied the lignin chemistry during dilute acid pretreatment of switch grass. The study demonstrated the depolymerization reactions within the first 2 min and the subsequent repolymerization reactions beyond 5 min of treatment. To avoid lignin degradation, namely, depolymerization and re- polymerization, Mild fractionation methods were developed with re- ported advantages in preserving lignin structure (Renders et al., 2017). However, the rate of delignification of mild fractionation processes is too low to be practically employed. To enhance lignin dissolution at mild conditions, hydrotrope was chosen as solvent for biomass fractionation due to the unparalleled performance in dissolving lignin at temperatures below the boiling point of water (Amarasekara and Wiredu, 2012; Chen et al., 2017; https://doi.org/10.1016/j.indcrop.2020.112086 Received 15 November 2019; Received in revised form 31 December 2019; Accepted 2 January 2020 ⁎ Corresponding authors at: Qilu University of Technology, 3501 University Rd, Changqing District, Jinan, 250353, China. E-mail addresses: tianguoyutgy@163.com (G. Tian), wzj820415@qlu.edu.cn (Z. Wang). Industrial Crops & Products 145 (2020) 112086 0926-6690/ © 2020 Elsevier B.V. All rights reserved. T