Depolymerization of Lignin with Nanoporous Catalysts

Lignin is a renewable and natural polymer resource that is rich in aromatic rings. At present, the lignin depolymerization level is relatively low due to its complicated three-dimensional structure and insolubility in common solvents. However, abundant waste lignin exists from the pulping and paper industry, as well as from bioethanol technology. Effective depolymerization techniques, especially for waste lignin, should be urgently developed. The current main techniques for lignin conversion include hydrogenolysis, oxidation, hydrolysis, catalytic cracking, and others, and the main products formed comprise phenols, alcohols, aldehydes, acids, and alkanes. In this chapter, attention will be focused on reduction (in the presence and absence of hydrogen) and oxidation, as well as hydrolysis processes in the liquid phases. The selected catalysts, reaction conditions, and reaction mechanisms are compared and analyzed in specific catalytic systems. Other techniques such as photocatalysis, electrocatalysis, and biocatalysis for lignin depolymerization are also discussed.