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Correlation between physicochemical properties and enzymatic digestibility of rice straw pretreated with cholinium ionic liquids Jie Xu, Min-Hua Zong, Shiyu Fu, and Ning Li ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00860 • Publication Date (Web): 22 Jun 2016 Downloaded from http://pubs.acs.org on June 23, 2016

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ACS Sustainable Chemistry & Engineering

Correlation between physicochemical properties and enzymatic digestibility of rice straw pretreated with cholinium ionic liquids

Jie Xu, Min-Hua Zong*, Shi-Yu Fu, Ning Li* State Key Laboratory of Pulp and Paper Engineering, School of Food Science and Engineering, South China University of Technology, 381 Wushan Road, Guangzhou 510640, China *

Corresponding authors.

Dr. N. Li, Tel/Fax: +86 20 2223 6669; Email: [email protected]. Prof. M. H. Zong, Tel: +86 20 8711 1452; Fax: +86 20 2223 6669; Email: [email protected]

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ABSTRACT: Ionic liquid (IL)-based lignocellulosic biomass pretreatment has attracted growing interest recently. In this work, cholinium ILs, a type of bio ILs composed totally of renewable biomaterials, were used to pretreat rice straw, and various physicochemical properties of the pretreated biomass including the morphological structure, biomass composition, biomass crystallinity, surface area and pore volume were studied. These physicochemical properties were correlated with the polysaccharide enzymatic digestibility (21-99% for cellulose and 9-83% for xylan). All the physicochemical properties examined exerted significant effects on the enzymatic hydrolysis of rice straw. Among these physicochemical features, surface area and pore volume were the principal factors affecting the polysaccharide digestibility. These physicochemical properties appeared to be inter-correlated, which could be converted into a linearly uncorrelated variable (the first principal component, PC1) by principal component analysis (PCA). PC1 proved to be a good predictor of the enzymatic digestibility of the pretreated rice straw, because there existed a closely positive linear correlation between the cellulose digestibility and PC1 score. KEYWORDS: Cholinium ionic liquids; enzymatic hydrolysis; lignocellulosic biomass; physicochemical properties; pretreatment; principal component analysis

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INTRODUCTION Lignocellulosic biomass, which is mainly composed of cellulose, xylan and lignin, has been recognized as a promising feedstock for the production of biofuels and platform chemicals.1 However, valorization of lignocellulosic biomass remains a challenge because of its complicated, cross-linked and recalcitrant structure. Therefore, pretreatment is usually used to deconstruct and fractionate lignocellulosic materials, which will significantly improve the polysaccharide accessibility to (bio)catalysts and thus facilitate the subsequent degradation. Over the last three decades, a lot of efforts have been made to develop various pretreatment methods including physical, physicochemical, chemical, and biological routes for improving efficiency, lowering costs and environmental impact, etc.2 Ionic liquids (ILs) are a kind of salts with melting points of