Insights into delignification behavior using aqueous p-toluenesulfonic acid treatment: comparison with different biomass species

Exploring an efficient delignification technique is imperative for further advance on biorefinery, together with elucidation on affecting factors and mechanism of delignification. Biomass fractionation using the aqueous p-toluenesulfonic acid (p-TsOH) changed tremendously with biomass species. Herein, effect of biomass species on delignification using the aqueous p-TsOH treatment was investigated. Compared to cellulose and hemicelluloses removal, delignification was greatly affected by biomass species, and delignification of softwood was the toughest. The dissolved lignin and residual lignin in the pretreated biomass, together with the original lignin without pretreatment were determined, analyzed and compared using various techniques. Essentially, the active linkages and groups in the dissolved lignin decreased compared to the original lignin from TGA and GPC analysis. However, the primary structure of lignin was not drastically altered after treatment from FTIR results. The high content of phenolic hydroxyl and the hydrophilic carboxyl in the original lignin of hardwood and grass were detected, which mainly accounted for their super solubility during the aqueous p-TsOH treatment. Moreover, the active aryl ether linkages reduced and C–C linkages increased for softwood after treatment. Compared with the guaiacyl unit, dissolution of the syringyl and p-hydroxyphenyl units were readily achieved. Therefore, the ideal feedstocks for the aqueous p-TsOH treatment are hardwood and grass species.