Conventional and Advanced Lignin Extraction Technologies from Lignocellulosic Biomass: A Review

The chemical engineering field has shown growing interest in the valorization of lignocellulosic biomass, driven by its abundance, renewability, and potential as an alternative to petroleum-based feedstocks. Despite this, the selective and efficient extraction of structurally intact, high-purity lignin continues to pose significant technical challenges. This review synthesized secondary data from peer-reviewed journal articles, conference papers, and authoritative texts to examine conventional, environmentally benign, and emerging lignin extraction techniques. Emphasis was placed on subcritical and supercritical fluid technologies, with detailed analysis of how operational parameters—such as temperature, pressure, residence time, and solvent selection—influence lignin yield and structural integrity. Findings suggested that sub- and supercritical fluid extraction methods present a promising alternative to traditional approaches, offering tunable solvent properties that enable selective lignin isolation and the potential for enhanced purity. These advancements could play a pivotal role in enabling the commercial-scale production of lignin-derived biomaterials and accelerating the transition toward a more sustainable, bio-economy and bio-based chemical industry.