Lignin extraction and recovery in hydrothermal pretreatment of bamboo

A significant amount of lignin and hemicellulose are dissolved in the hydrothermal treatment of biomass. The hemicellulose can be recovered and utilized for value-added products. The dissolved lignin can undergo depolymerization and condensation reactions, and interferes with the separation and purification process for hemicellulose recovery. This paper investigated the behavior of the lignin extracted from the hydrothermal pretreatment of bamboo and its contributions to the physical characteristics of the hydrolysate. It was found that the turbidity of the hydrolysate was strongly associated with the lignin fragments and suspended long chain hemicelluloses. As the lignin depolymerization and condensation reactions occurred simultaneously, the dissolved lignin fractions in the hydrolysate increased first and then decreased. The molecular weight (MW) of the dissolved lignin fragments ranged from 3342~5611 g/mol, with mainly guaiacyl (G) and syringyl (S) unit in the structure.