Revealing the mechanisms of lignin modification by phenolic additives during pre-hydrolysis treatment and its effects on enzymatic hydrolysis

Abstract

Condensed lignin formed during eucalyptus woodchip pre-hydrolysis adversely affects subsequent enzymatic saccharification, and phenolic additives are popular lignin condensation inhibitors. The goal of this project was to reveal the mechanisms of lignin modification by phenolic additives during woodchip pre-hydrolysis and its effects on subsequent enzymatic saccharification. The HSQC and 31P NMR analyses confirmed that resorcinol with three electrophilic substitution of active sites could act as a cross-linking agent to promote the formation of condensed lignin, whereas 2-naphthol and sodium 2-naphthol-7-sulfonate could block benzyl carbocations and reduce the formation of condensed lignin. Interestingly, the introduction of sulfonic acid groups increased the electrostatic repulsion between enzyme and lignin as well as increased the hydrophilicity of lignin, thereby greatly reducing non-productive adsorption and physical obstacle effects. Sodium 2-naphthol-7-sulfonate as an efficient benzyl carbocations scavenger reduced the non-productive adsorption and physical obstacle effects of lignin by 82.4% and 13.3%, respectively.