Review on catalytic cleavage of C-C inter-unit linkages in lignin model compounds: Towards lignin depolymerisation

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

Heterogeneously catalyzed lignin depolymerization

Biomass offers a unique resource for the sustainable production of bio-derived chemical and fuels as drop-in replacements for the current fossil fuel products. Lignin represents a major component of lignocellulosic biomass, but is particularly recalcitrant for valorization by existing chemical technologies due to its complex cross-linking polymeric network. Here, we highlight a range of catalytic approaches to lignin depolymerisation for the production of aromatic bio-oil and monomeric oxygenates

Valorization of Kraft Lignin of Different Molecular Weights as Surfactant Agent for the Oil Industry

After cellulose, lignin is the second most abundant biopolymer in the vegetable world. Since lignin is a natural phenolic polymer, there are a variety of potential products obtainable by its chemical modification, including surfactants. In this regard, lignin is of great interest because represent a byproduct of pulp industries for papermaking; however, this byproduct can be harnessed for obtaining aromatic derivatives of industrial interest. In this work, alkali lignin derivatives of different molecular weights were synthesized from lignin fractions from Pinus caribaea obtained by ultrafiltration. Lignin and ligninfractions were modified with succinic anhydride (SA), and dodecyl-succinic anhydride (DSA) under microwave heating. The reaction was monitored by Fourier Transform Infrared Spectroscopy. The surface activity of lignin, and lignin-derivatives was evaluated through surface tension measurements, while the stability of suspensions and emulsions was evaluated by the volumetric separation method. The lignin fractions, and the esterified derivatives were obtained in very short reaction times (90–110 s) using a mixture of acetonitrile/ethanol. The lignin-derivatives showed higher surface activity in comparison to the neat lignin. Derivatives prepared from the lower molecular weight fraction by using DSA showed the best emulsifying properties. Lignin-derivatives also showed significant dispersing properties in comparison to a commercial dispersant (lignosulfonate). The best dispersant properties were obtained from the higher molecular weight ultrafiltered lignin fraction esterified with SA.Facultad de Ciencia