Lignin solvation by ionic liquids: The role of cation

Abstract

The use of ionic liquids as solvents for the processing of lignocellulosic material has received considerable attention in the last years, since it presents remarkable advantages over previous solvent-based procedures. In particular, their ability to dissolve and treat the lignin has become of major interest lately. Liquid salts at room temperature, ionic liquids have unique physicochemical properties as compared to conventional solvents, due to the interactions they can establish among ions and with other solutes. From the theoretical chemistry point of view, the correct description of these interactions in a dynamic environment requires computationally demanding methodologies, and therefore settling for a certain theoretical level requires invariably a compromise between accuracy and computational cost. In this article, we present a detailed analysis of the interactions established by commonly used ionic liquids with the lignin, with special focus on the role of the cation, motivated by the discrepancies arising from literature. A multiscale simulation strategy, including static and dynamic density functional theory and molecular dynamics calculations, has permitted to provide a reliable, multifaceted description of the solvation pattern of lignin, reporting for the first time the dual role of imidazolium-based cations stabilizing both the hydroxyl groups and aromatic rings of the lignin.