Pretreatment of the corncob enzymatic residue with p-toluenesulfonic acid and valorization

In order to develop a green method for the purification and valorization of lignin, pretreatment of the corncob enzymatic residue with p-toluenesulfonic acid was investigated. The effects of p-toluenesulfonic acid concentration, pretreatment temperature and time on the purity and structure of the purified lignin were studied by phenolic hydroxyl content test, FT-IR, UV, H-1-NMR, sulfonation degree test and molecular weight test. Compared with alkali dissolution-acidic precipitation, the purified lignin had high purity (up to 99.38%), greater phenolic hydroxyl content (up to 4.28 mmol/g), less syringyl units and higher sulfonation degree (up to 2.16 mmol/g). It also had better dispersibility, because the plastic viscosity of the EHL-T slurry was only about 75% of EHL-A when they were at 1% addition. The p-toluenesulfonic acid could be recycled easily. This study helps to promote the value of lignin.