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

Abstract

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.

Overcoming Softwood Recalcitrance by Improved 2-Naphthol Addition to Steam Explosion Pretreatment

“…67 Up to 192% higher saccharification yields have been reported, compared to a pretreatment without additive. 50,51 2-Naphthol proved, in particular, to be effective for overcoming the high softwood recalcitrance to bioconversion. Even at moderate enzyme concentrations of 15 and 20 FPU g −1 cellulose, high digestibilities of 81% 68 and 100%, 34 respectively, have been reported.…”

“…54,61,63,65 In addition, the integration of 2-naphthol into the lignin backbone can add aromatic functionality, which was proposed to be beneficial for certain polymer applications. 40 As of today, 2-naphthol has been included in more than twothirds of the pretreatment studies which use carbocation scavengers, 50 showing its effectiveness and importance as a model compound. Traditional industrial routes for 2-naphthol production use fossil-based naphthalene as starting material.…”

“…The use of carbocation scavengers for enhancing cellulose bioconversion and lignin quality has gained increasing attention in recent years. To date, about 40 corresponding research studies have been published, and several effective pretreatment additives have been identified . 2-Naphthol has been found to be a very efficient compound for suppressing lignin repolymerization and for improving cellulose bioconversion. , The compound has been used in several studies to enhance the pretreatment of softwood, ,,− hardwood, ,− mixed wood, and bamboo .…”

“…2-Naphthol has been found to be a very efficient compound for suppressing lignin repolymerization and for improving cellulose bioconversion. , The compound has been used in several studies to enhance the pretreatment of softwood, ,,− hardwood, ,− mixed wood, and bamboo . Up to 192% higher saccharification yields have been reported, compared to a pretreatment without additive. , 2-Naphthol proved, in particular, to be effective for overcoming the high softwood recalcitrance to bioconversion. Even at moderate enzyme concentrations of 15 and 20 FPU g –1 cellulose, high digestibilities of 81% and 100%, respectively, have been reported.…”

“…As of today, 2-naphthol has been included in more than two-thirds of the pretreatment studies which use carbocation scavengers, showing its effectiveness and importance as a model compound. Traditional industrial routes for 2-naphthol production use fossil-based naphthalene as starting material .…”