Review on Catalytic Cleavage of C–C Inter-unit Linkages in Lignin Model Compounds: Towards Lignin Depolymerisation

• Published in: Topics in catalysis Vol. 61; no. 3-4; pp. 183 - 198
• Main Authors: Guadix-Montero, Susana, Sankar, Meenakshisundaram
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.04.2018; Springer Nature B.V
• Subjects: Alternative fuels; Bonding strength; Breaking; Catalysis; Characterization and Evaluation of Materials; Chemical bonds; Chemistry; Chemistry and Materials Science; Cleavage; Depolymerization; Fossil fuels; Hydrogenolysis; Industrial Chemistry/Chemical Engineering; Lignin; Linkages; Original Paper; Pharmacy; Physical Chemistry; Technical lignins; Lignin valorisation; Lignin model compounds; Catalytic depolymerisation; C–C bond cleavage
• DOI: 10.1007/s11244-018-0909-2
• ISSN: 1022-5528

Lignin depolymerisation has received considerable attention recently due to the pressing need to find sustainable alternatives to fossil fuel feedstock to produce chemicals and fuels. Two types of interunit linkages (C–C and C–O linkages) link several aromatic units in the structure of lignin. Between these two inter-unit linkages, the bond energies of C–C linkages are higher than that of C–O linkages, making them harder to break. However, for an efficient lignin depolymerisation, both types of inter-unit linkages have to be broken. This is more relevant because of the fact that many delignification processes tend to result in the formation of additional C–C inter-unit bonds. Here we review the strategies reported for the cleavage of C–C inter-unit linkages in lignin model compounds and lignin. Although a number of articles are available on the cleavage of C–O inter-unit linkages, reports on the selective cleavage of C–C inter-unit linkages are relatively less. Oxidative cleavage, hydrogenolysis, two-step redox-neutral process, microwave assisted cleavage, biocatalytic and photocatalytic methods have been reported for the breaking of C–C inter-unit linkages in lignin. Here we review all these methods in detail, focused only on the breaking of C–C linkages. The objective of this review is to motivate researchers to design new strategies to break this strong C–C inter-unit bonds to valorise lignins, technical lignins in particular.