Recent progress in microwave-assisted lignin conversion

Lignin, a complex natural phenolic macromolecule, offers considerable potential in the production of high-value phenolic platform chemicals. Despite its abundance, lignin remains one of the most underutilized renewable resources due to challenges associated with its depolymerization and product separation. Therefore, developing efficient and straightforward depolymerization methods to degrade and convert lignin into value-added products is imperative for promoting resource utilization and the sustainable development of biomass materials. In this review, the technical gaps between microwave-assisted and conventional heating methods for lignin conversion are highlighted and compared. Furthermore, the most recent advances in microwave-assisted lignin degradation and conversion to value-added products are summarized. The lignin-degrading mechanisms of thermochemical treatments, solvent effects, catalyst effects, and external fields are comparatively analyzed. In addition, recent trends in the development of microwave-assisted lignin conversion are discussed. This review also provides new insights for future work to address ongoing challenges such as low efficiency, low selectivity, and the scalability of microwave-assisted lignin conversion for industrial applications.