Solubility of Organosolv Lignin in γ‐Valerolactone/Water Binary Mixtures

The solubility of lignin in a mixture of γ‐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 (δ‐value) was calculated as 25.5 MPa(1/2). The δ‐value for aqueous GVL solvent increased from 23.1 MPa(1/2) for pure GVL to 45.6 MPa(1/2) for pure water. Therefore, the lignin solubility was predicted to increase with increasing GVL concentration in the aqueous mixture up to approximately 92–96 wt % 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.