Recent advances in generation of bioproducts from lignin: a comprehensive review

Lignin, the most abundant renewable aromatic biopolymer on earth, offers vast potential as a sustainable feedstock for the production of high-value chemicals, fuels, and advanced materials. Once regarded largely as a low-value byproduct of the pulp and paper sector, recent breakthroughs in catalysis, process engineering, and biorefinery design have enabled more selective and efficient lignin valorization. This review critically examines the major lignin conversion pathways—including reduction, oxidation, and lignin modification reactions such as alkylation, hydroxylation, and amination—highlighting their mechanisms, catalytic systems, and process conditions. Despite encouraging progress, lignin valorization faces several persistent challenges. Chief among these are the structural heterogeneity of lignin, limited product selectivity, and rapid catalyst deactivation, each of which hinders reproducibility and scalability. Additionally, effective integration of feedstock standardization, process modeling, and catalyst discovery remains essential to address these bottlenecks. Regulatory and safety barriers, particularly for lignin-derived nanomaterials and bioproducts intended for pharmaceutical or food applications, require increased attention and validation. While most lignin valorization processes remain at laboratory or pilot scale, several industrial case studies—such as commercial vanillin production and emerging lignin-based carbon fibers—demonstrate growing momentum toward commercialization. The convergence of artificial intelligence, advanced catalysis, and digital process control, along with evolving regulatory frameworks, is expected to accelerate market adoption. Ultimately, overcoming the core challenges of lignin heterogeneity and scalable depolymerization will be critical to establishing lignin as a cornerstone of the circular bioeconomy and low-carbon manufacturing.