Design of Organosolv Lignin Fractionation: Influence of Temperature, Antisolvent, and Source on Molecular Weight, Structure, and Functionality of Lignin Fragments

Lignin offers a sustainable alternative to fossil raw materials for chemical and material synthesis. Improving its utilization requires the production of lignin fragments with a controlled dispersity and reactivity. In this study, a sustainable protocol for direct organosolv lignin fractionation from black liquor using water as an antisolvent is developed. The approach utilizes the complementarity of the process temperature and solubility parameters to generate lignin streams with tailored properties. In particular, the protocol allows control of the structural characteristics of the lignin fractions, including OH group content, interunit bonds, and degree of ethoxylation, as demonstrated for spruce and beech lignins. The ability to adjust the ratio of aliphatic to aromatic OH groups emphasizes the potential to significantly influence the reactivity and functionality of the lignin. This water-driven fractional precipitation approach offers a sustainable way to produce well-defined lignin streams suitable for various applications, depending on the desired properties. In addition, a techno-economic assessment highlights solvent recovery and lignin value as key parameters for scaling up the process and highlights both opportunities and challenges in implementing this process on an industrial scale.