Sustainable approaches to lignin recovery from kraft black liquor and its application in environmental remediation

Abstract

Black liquor, the alkaline effluent of kraft pulping, is one of the largest underutilized sources of technical lignin globally. This chemically valuable aromatic biopolymer is predominantly incinerated for energy recovery, foregoing the considerable chemical value embedded in lignin’s aromatic backbone and reactive functional groups. Conventional lignin isolation via acid precipitation is constrained by high energy demands, equipment corrosion, and acidic waste generation. These limitations collectively undermine the large-scale valorization of lignin. This review examines conventional and emerging approaches for lignin recovery from kraft black liquor, with particular emphasis on ionic liquids and deep eutectic solvents. Beyond extraction, the potential of lignin-derived materials for environmental applications is discussed, highlighting their role in promoting a circular economy. This review discusses lignin precipitation mechanisms and evaluates key barriers, including solvent recovery, scalability, and techno-economic feasibility. Addressing these challenges positions the pulp and paper industry at the forefront of sustainable chemical manufacturing.