Suppression of Lignin Repolymerisation to Enhance Cellulose Bioconversion and Lignin Valorisation - A Review

The recent discovery that the prevention of lignin repolymerisation/condensation in lignocellulosic biomass pretreatment can both enhance the bioconversion of cellulose and the quality of the obtained lignin, has brought a lignocellulose biorefinery closer to reality. In this work, the development of this approach and the last advancements are reviewed. The review reveals the successful implementation for a wide range of lignocellulosic substrates including softwood, hardwood, and agricultural residues. As well, it is shown that the approach can enhance various pretreatment technologies, including steam, acid and organosolv processes. Recent developments involve the discovery of new and greener additives which prevent lignin repolymerisation, the implementation of cellulose saccharification at industrially realistic conditions and high-yield fermentation. In addition, first applications of the lignin obtained in these processes are reviewed, showcasing its enhanced quality for functionalisation and use in polymers, as well as for its depolymerisation to aromatic monomers. The recent progresses bring closer the prospect of a biorefinery that can valorise all fractions of lignocellulosic biomass.