Computational prediction of cellulose solubilities in ionic liquids based on COSMO-RS Yunhan Chu a , Xiangping Zhang b , Magne Hillestad a , Xuezhong He a, * a Department of Chemical Engineering, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway b Beijing Key Laboratory of Ionic Liquids Clean Process, Institute of Process Engineering, Chinese Academy of Sciences, P.O. Box 353, Beijing,100190, China article info Article history: Received 15 June 2018 Received in revised form 18 July 2018 Accepted 26 July 2018 Available online 27 July 2018 Keywords: Ionic liquids Cellulose solubility COSMO-RS Activity coefficient Excess enthalpy abstract A computational approach is presented for prediction of cellulose solubilities in ionic liquids (ILs) based on COSMO-RS (Conductor-like Screening Model for Real Solvents). Thermodynamically stable molecular structures were optimized from 2D structures of cellulose and ILs following specific force-field based search of conformation lowest in energy and quantum chemical optimizations of molecular geometry. The thermodynamic property of logarithmic activity coefficient (lng) and excess enthalpy (H E ) were calculated by COSMO-RS based on the COSMO molecular surfaces of cellulose and ILs to qualitatively predict the ability of ILs for cellulose dissolution. To evaluate the method, four sets of ILs were used to calculate lng and H E based on four different cellulose models. The goodness-of-fit of linear regressions between the experimental cellulose solubilities and the calculated lng and H E shows that lng is more reliable than H E for prediction of the dissolving power of ILs to dissolve cellulose. However, H E is more suitable for prediction of the dissolution ability of halogen-based ILs. Moreover, all the cellulose models gave comparably good prediction results regarding of the dissolving power of ILs based on the calculated lng, but the cellobiose model was identified as the optimal model due to the relatively higher prediction ability (R 2 ) across different IL datasets. The approach is time efficient and robust, which provides a novel method for large-scale screening of ILs for cellulose dissolution. © 2018 Elsevier B.V. All rights reserved. 1. Introduction Biomass is an abundant renewable resource on the earth [1]. Growing concerns about sustainability and environmental protec- tion brings large amount of attention to efficient conversion of biomass into valuable products such as biofuels, chemicals and biomaterials, as the concept of biorefinery suggests [2e4]. Plants and plant-based biomass (lignocellulose) contains three major components: cellulose, hemicellulose and lignin [5]. Cellulose, as the largest component of lignocellulose and a sustainable raw material, is widely used in producing paper, fiber, membrane, and other commodity materials and chemicals, meanwhile, it has a high global quantity (~700,000 billion tons) and only a small amount (~0.1 billion tons) is currently used for production, which leaves a large space for wide employment [6,7]. For the full utilization of cellulose, a prime step is to dissolve cellulose. Cellulose is a type of linear-chain biopolymer consisting of several hundred to over ten thousand b-(1e>4)-linked glucose repeating units [6,8]. The linear structure enables numerous cellulose strands to be packed into crystalline fibrils through enormous number of intramolecular and intermolecular hydrogen bonds [9], which makes cellulose highly resistant to chemical modification and difficult to dissolve. Ionic liquids (ILs) as a new type of green solvents, provides the possibility to dissolve cellulose [8, 10] and lignocellulosic biomass [5, 11] in a clean process, which has attracted a great deal of academic and industrial interest. These solvents are salts generally composed of a large, low-symmetry and non-reactive organic cation and an organic or inorganic anion that can largely tune their physical and chemical properties [12, 13]. Compared to conventional solvents [14e19], ILs show remarkable properties such as low vapor pres- sure, high thermal stability, non-flammability, non-volatility and low toxicity. Moreover, by proper selection of cation e anion combinations, ILs can be tailored with desired properties (e.g. vis- cosity, density and solubility) [20,21]. Appropriate ILs can be selected as cellulose solvents. In the recent years, more than 60 ILs have been experimentally examined for their solubilities of cellulose [8]. However, there is a vast * Corresponding author. E-mail address: xuezhong.he@ntnu.no (X. He). Contents lists available at ScienceDirect Fluid Phase Equilibria journal homepage: www.elsevier.com/locate/fluid https://doi.org/10.1016/j.fluid.2018.07.026 0378-3812/© 2018 Elsevier B.V. All rights reserved. Fluid Phase Equilibria 475 (2018) 25e36