Catalytic Oxidation of Biorefinery Lignin to Value‐added Chemicals to Support Sustainable Biofuel Production

Abstract

Transforming plant biomass to biofuel is one of the few solutions that can truly sustain mankind's long-term needs for liquid transportation fuel with minimized environmental impact. However, despite decades of effort, commercial development of biomass-to-biofuel conversion processes is still not an economically viable proposition. Identifying value-added co-products along with the production of biofuel provides a key solution to overcoming this economic barrier. Lignin is the second most abundant component next to cellulose in almost all plant biomass; the emerging biomass refinery industry will inevitably generate an enormous amount of lignin. Development of selective biorefinery lignin-to-bioproducts conversion processes will play a pivotal role in significantly improving the economic feasibility and sustainability of biofuel production from renewable biomass. The urgency and importance of this endeavor has been increasingly recognized in the last few years. This paper reviews state-of-the-art oxidative lignin depolymerization chemistries employed in the papermaking process and oxidative catalysts that can be applied to biorefinery lignin to produce platform chemicals including phenolic compounds, dicarboxylic acids, and quinones in high selectivity and yield. The potential synergies of integrating new catalysts with commercial delignification chemistries are discussed. We hope the information will build on the existing body of knowledge to provide new insights towards developing practical and commercially viable lignin conversion technologies, enabling sustainable biofuel production from lignocellulosic biomass to be competitive with fossil fuel.

Paving the Way for Lignin Valorisation: Recent Advances in Bioengineering, Biorefining and Catalysis

“…Mild Oxidative Depolymerisation Pathways Several oxidative routes targeting different end-products from lignin have been reported, and are discussed in detail in ar ecent review article. [334] Indeed, al arge number of these oxidation methods target the cleavage of the b-ethers,o f which an umber are discussed in this section. Ac hemoselective and organocatalytic method for the selective oxidation of the secondary (benzylic) alcohol of lignin model compounds and Aspen lignin was demonstrated.…”

The influence of interunit carbon–carbon linkages during lignin upgrading

“…However, mixing and subsequently separating these two solids may have several technical limitations at industrial scales, including those associated with mass transfer, catalyst recovery or catalyst deactivation. In parallel, the catalytic oxidation of lignin has been extensively investigated to break CeO and CeC linkages but most of these processes were non-selective and led to high carbon loss [22]. Recent work has shown that selective oxidation of a hydroxyl group could weaken b-O-4 linkages…”

Heterogeneously catalyzed lignin depolymerization

“…Homogeneous catalysts have been rarely utilised due to their inherent disadvantages in respect of their difficult separation from the reaction mixture, corrosiveness (in the case of soluble acid catalysts), and, hence, are more favoured for selective bond cleavage within model compounds, but have been implemented in oxidative depolymerisation [21,22]. The present review focuses on reductive catalytic solutions which favour phenolic compounds suitable for subsequent upgrading by HDO routes [23] to yield fuels and fuel additives.…”