Heating Treatment as a Simple Approach to Improve Lignin Filtration Efficiency in the LignoBoost Process

Journal article, 2026

The LignoBoost process enables efficient isolation of high-purity lignin from black liquor; however, lignin colloidal behavior during the acidic washing step strongly influences the filtration performance, and the impacts of temperature remain insufficiently understood. In this study, Kraft lignin suspensions were thermally treated at 75 degrees C, 85 degrees C, and 95 degrees C to evaluate their effects on volumetric flow rate during filtration and on lignin physicochemical properties. Thermal treatment at 85 degrees C yields the optimal filtration efficiency, with the volumetric flow rate increasing by 11-fold (lignin A) and 19-fold (Lignin B) compared to the control group. Particle size analysis revealed clear lignin particle growth after heating treatment, which was accompanied by a decrease in smaller particles. Beyond physical noncovalent interactions, chemical contributions to particle growth were elucidated by analyzing radical concentration, molar mass, and structural features. Radical concentrations decreased significantly, accompanied by increased condensation and reduced ester linkages in the recovered lignin. The molar mass changed slightly. Despite these changes, the overall functional group content (methoxy, aliphatic hydroxyl groups, and aromatic hydroxyl groups) and glass transition temperature remained largely unchanged. This work elucidates the interactive effects of heating treatment on lignin structure and recovery performance, providing a mechanistic understanding to optimize kraft lignin separation and thereby promote its subsequent valorization.