Advances in mild degradation and directional upgrading of lignites: From feature identification to value-added utilization

Lignites are important raw materials for obtaining clean liquid fuels and value-added organic chemicals. On the basis of conforming to the global concept of green and sustainable development, the focus should be on the current low feedstock-to-product conversionand added value. Therefore, directional conversion from lignite to downstream products is promising for coping with these challenges. Starting from the identification of lignite structural characteristics, chemical degradation methods, compositional analysis of organic matter, and comprehensive utilization of lignite-based derivatives are mainly discussed in this review. Special attention is also paid to the application and related catalysis in lignite conversion. Combined with future research directions, several points for the efficient conversion of lignites were proposed. Key breakthroughs could also be achieved by using several feasible pathways introduced in this review. This review also aims at increasing the ongoing discussions on new technologies for efficient conversion of lignites to downstream value-added products. [Display omitted] •Feature identification of OCBDs and aromatic units in lignite needs to be focused.•For obtaining various SPs, the directional cleavage of OCBDs is a breakthrough.•Rapid enrichment is a promising direction for efficient classification of SPs.•The system construction of group classification is a prerequisite for upgrading.