Advances in depolymerization and hydrodeoxygenation of lignin

Abstract

Lignin is a renewable and available resource rich in aromatic rings. Abundant waste lignin can be produced from the pulp and paper industry as well as bioethanol technology derived from enzymatic hydrolysis of lignocellulose. However, the lignin conversion is as low as 2%. From the viewpoint of resource utilization and environmental conservation, the importance of efficient use of lignin, especially of waste lignin, should be addressed. The research progress on converting of lignin is relatively slow in the last decades, and the main techniques include catalytic cracking, hydrolysis, (sulfur-containing or sulfur-free) metals catalyzed reduction and oxidation. After depolymerization, the further upgrading of derived phenolic fragments uses (sulfur-containing or sulfur-free) metals to remove the oxygens to form the final alkanes and aromatics. The purpose of this review is to summary the progress of depolymerization and hydrodeoxygenation of lignin such as catalysts, reaction conditions, reaction mechanisms, deactivation of catalysts. We also present the suggestions and outlooks concerning on the current techniques and further directions towards key researches.