| Abstract:Lignin exiting in the black liquor of aspen ethanol-organosolv pulping was purified by the methods of mild acid hydrolysis and liquid-liquid extraction. The properties of purified lignin, including chemical structure and thermal stability, were analyzed by ion chromatography, FT-IR, 13C-NMR and thermogravimetric analysis. Results showed that the method of liquid-liquid extraction was better than mild acid hydrolysis in terms of removing carbohydrates. The content of total sugar in crude lignin was 0.99% and the purity of lignin was 98.67%. After purification, the content of total sugar in lignin was decreased to 0.36% and the purity of lignin was increased to 99.64%. It was found that the thermal stability of purified lignin was better than crude lignin indicated by the fact that the maximum weight loss peak of lignin shifted from 320℃ to 350℃. However, the structure of lignin had little change after purification. The purified aspen ethanol-organosolv lignin was rich in functional groups such as hydroxyl groups, methoxy groups, which was more benefite to its utilization. The higher purity of lignin was beneficial for analyzing the structure of the ethanol-organosolv lignin. |
