Chemical and Biological Delignification of Biomass: A Review

Lignin is a highly abundant biopolymer with a complex polyphenolic structure, making it a potential source of aromatic precursors, polymers, and energy. However, its thermal stability limits its economic potential, with less than 3 wt % of waste lignin transformed into commodity products. This review focuses on the chemical and biological extraction methods for lignin to promote its valorization, which involves extraction, depolymerization, and fermentation or derivatization. As there is no universal method for extraction due to the heterogeneity of lignin, a range of methods each with their advantages and disadvantages are discussed, including sulfite pulping, Kraft, Organosolv, ozonolysis, steam-explosion, ionic-liquids and supercritical CO2 extraction, and microwave- and ultrasound-assisted extraction. Biological methods, such as bacterial, fungal, and enzymatic delignification, are also explored. The review aims to provide insights to tailor extraction methods to individual needs and promote the sustainable utilization of lignocellulosic biomass.