Lignin extraction and valorization using heterogeneous transition metal catalysts

Abstract

Lignocellulosic biomass is the most abundant renewable carbon source on our planet. It offers an alternative as well as a complementary source to petrochemical refining for energy and chemical production. The market of renewable energy and chemicals has been rapidly growing over the past two decades. However, utilization of biomass is still underdeveloped. Energy production from biomass has seen only moderate increases. Today's second generation biorefinery only uses the carbohydrate components (cellulose and hemicellulose) from the biomass and lignin is generated as a waste byproduct to be used for its low value heat. In contrast, the concept of lignin valorization can improve the economics of biorefining by producing value-added products from lignin. This can be accomplished by changing the pretreatment of biomass to provide fractionation and upgrading of lignin first into valuable products, “lignin-first” biorefinery concept. Alternatively, if the pretreatment can provide a protected technical lignin byproduct which can be valorized to chemicals and/or hydrocarbon biofuels. Monomeric phenols are the major products of lignin valorization through heterogeneous catalysis. The complex structure of lignin, impurities from its preparation, and catalyst selection are among the key factors restricting yield of products. This chapter presents and contrasts preparation techniques of technical lignin, reviews the use of inorganic transition metal heterogeneous catalysts for lignin valorization into chemicals and fuels, and lastly demonstrated examples of subsequent applications of lignin derived monomers.