Solubility of Organosolv Lignin in [gamma]-Valerolactone/Water Binary Mixtures

The solubility of lignin in a mixture of [gamma]-valerolactone (GVL) and water at different weight ratios was measured using the Hildebrand solubility parameters. Based on the molecular structure of lignin, its solubility parameter ([delta]-value) was calculated as 25.5MPa1/2. The [delta]-value for aqueous GVL solvent increased from 23.1MPa1/2 for pure GVL to 45.6MPa1/2 for pure water. Therefore, the lignin solubility was predicted to increase with increasing GVL concentration in the aqueous mixture up to approximately 92-96wt% of GVL. A ternary diagram describing the phase behavior of water-GVL-lignin mixtures at room temperature was constructed based on the experimental results. The three-component system exhibited a complex behavior with a liquid-liquid and solid-liquid-liquid phase split. The efficiency of the selected fractionation trials in a previous work was validated using the ternary solubility diagram. A promising recovery pathway and lignin isolation method were deduced from the results of this work.