A review on the overall process of lignin to phenolic compounds for chemicals and fuels: From separation and extraction of lignin to transformation

The transition to a renewable energy future requires the development of sustainable chemicals and fuel refining technologies. Lignin, as the only renewable aromatic resource in nature, possesses tremendous potential for substituting environmentally detrimental and non-renewable fossil resources. Due to the complex structure and interaction of lignin components, the production of phenolic compounds from the thermochemical depolymerization of lignin were reviewed from the whole refining process. The findings highlighted that limitations and challenges with both individual lignin extraction methods and the extraction of phenolic compounds from biooil, such as low lignin purity, significant structural damage, poor conversion rate, etc. Importantly, research on lignin conversion methods has gone hand in hand, but none has yet achieved large-scale industrial application. Despite the significant role of catalysts in enhancing phenolic compound enrichment, current catalysts fall short of meeting the requirements for high catalytic activity and directional conversion. Meanwhile, the economic, technological, and environmental impact assessment of the industrial chain is also imperative. An optimized design of the whole chain from source extraction to intermediate conversion, targeted preparation and subsequent product application and emission helps to achieve efficient, targeted and industrialized application of lignin. Therefore, future endeavors should focus on integrating multiple technologies and methods to optimize the overall industrial chain design from source extraction to intermediate conversion, targeted preparation, subsequent product application, and emission. In addition, the focus should be on targeted conversion and extraction technologies for single phenolic platform compounds, with a view to achieving large-scale commercialization of the lignin-to-phenolic chemicals industry chain.