Catalytic valorization of lignin: From conventional to advanced catalytic technologies

To achieve greener biorefineries with minimal waste, the valorization of lignin is crucial for valuable chemicals rather than burning it for energy. Instead of burning lignin for energy, it can be converted into valuable chemicals through advanced refining processes. This chapter provides a detailed overview of how lignin can be extracted, broken down into smaller units, and transformed into fine chemicals using a method called catalytic funneling. It explores both conventional lignin valorization techniques, such as thermal processing, solvolysis, and acid or base catalysis, and modern strategies like reductive catalytic fractionation (RCF) and oxidative catalytic fractionation (OCF). These modern methods aim to utilize lignin more efficiently within integrated green biorefinery systems. This chapter further emphasizes solid catalysts that are applicable during the redox catalytic fractionation process, and these solid catalysts assist in enhancing lignin breakdown and conversion under different conditions. Additionally, the issues of the catalytic lignin processing are also addressed, which include the need to enhance efficiency and product selectivity. Most importantly, this chapter points out that these superior lignin valorization technologies would need to show a clean environmental utility, e.g., a considerable decrease in greenhouse gases, notably carbon dioxide (CO₂), in comparison to the traditional petroleum-based refining approaches, to qualify as a sustainable solution for the future.