Advancement in technologies for the depolymerization of lignin

Lignin is one of the largest sources of naturally occurring aromatic building blocks that possess immense potential to be employed as starting material for the production of value-added chemicals involving biofuels. Despite various challenges associated with lignin valorization, several strategies have emerged that could deliver value-added products in good yields. The present contribution aims to critically review recent advancements in biological, thermochemical and electrochemical strategies for lignin depolymerization mainly focusing on enzymatic, acid/base/metal-catalyzed, and microwave-assisted degradation approaches. All lignin degradation strategies result in the production of an arsenal of several monomeric, oligomeric and polymeric compounds, with no single molecule being produced in significant amount. For large-scale production of biofuels and other value-added chemicals via lignin depolymerization, the combination of two or more technologies with low cost and recyclable catalysts operating at mild reaction conditions needs to be explored.