Ionic liquid as a green solvent for lignin

This study examined the application of select ionic liquids (ILs) as aprotic green solvents for lignin. Dissolution experiments were carried out employing lignin isolated from pine kraft pulp. Up to 20 wt% lignin could be dissolved in [hmim][CF3SO3], [mmim][MeSO4] and [bmim][MeSO4]. For the [bmim](+)-containing ionic liquids, the order of lignin solubility for varying anions was: [MeSO4](-) > Cl- similar to Br- >>> [PF6](-), indicating that the solubility of lignin was principally influenced by the nature of the anions. Ionic liquids containing large, non-coordinating anions [PF4](-) and [PF6](-) were unsuitable as a solvent for lignin. C-13 nuclear magnetic resonance (NMR) analyses of lignin and model compounds showed that C-13 signals using ionic liquid as a solvent were shifted up-field by delta 0.1 to 1.9 ppm in comparison to C-13 NMR data acquired using dimethyl sulfoxide (DMSO) as the solvent.