Screening ionic liquids for dissolving hemicellulose by COSMO-RS based on the selective model

Abstract

The utilization of biomass resources has attracted more and more attention due to the consumption of non-renewable resources. Compared with cellulose and lignin, hemicellulose has been less studied. Some ionic liquids (ILs) have been proved to be excellent solvents for lignocellulosic pretreatment. However, screening of more efficient ILs is difficult due to numerous possible ILs. Computational chemistry has been proved effective in solvent screening, but a precise model is indispensable. In this work, we focused on building several appropriate models and selected the most suitable one. According to the structure of hemicellulose, six hemicellulose models were constructed and the mid-dimer of the xylan chain hemicellulose (MDXC) model was proved to be the best compared with the reported experimental results. Based on the MDXC model, 1368 ILs were screened to evaluate their ability to dissolve hemicellulose by Conductor-like Screening Model for Real Solvents (COSMO-RS). The activity coefficient (γ), excess enthalpy (H^E), and σ-profile indicated that the hydrogen-bond (H-bond) played a vital role in the dissolution of hemicellulose. Anions played a more critical role than cations, where small anions with H-bond acceptor groups could enhance the molecular interactions with hemicellulose. This work provided a thermodynamic understanding of hemicellulose and IL solvent systems. It highlights the importance of building appropriate solute models, which may be necessary to predict of the other thermodynamic properties in the future.