334 / 2018-07-30 16:30:08

Structural Evolution and Pyrolysis Characteristics of Lignin under Acid Pretreatment

全体主题 > 生物质多联产

Lignin, which accounts 20-30% of lignocellulosic biomass, is the hardest component for thermal conversion due to its complex and tough structure. Many studieds have shown that the acid pretreatment can change the lignin’s pyrolysis characteristics. However, few studies were focused on the structure evolution of lignin with acid pretreatment and its relationship with pyrolysis characteristics. In this paper, the lignin was pretreated with different acids, the pretreated lignins were pyrolysed in fixed bed and Thermogravimetry (TG) to obtain their pyrolysis characteristics. The relationship between lignin structure and pyrolysis products was characterized by Fourier transform infrared (FTIR) spectroscopy and two-dimensional heteronuclear single-quantum coherence nuclear magnetic resonance (2D HSQC NMR). The results of pyrolysis experiments in the fixed bed showed that hydrochloric acid pretreatment increased the light products by 2.4 times, which can be attributed to the looseness of lignin structure and then make it easy to transform. Besides, the liquid yield increased significantly, as well as phenols fraction compared with that of the original lignin. TG revealed that the decomposed temperature of pretreated lignin with hydrochloric acid was lower than that of original lignin, which is consistent with the fixed bed experiments. FTIR and 2D HSQC NMR showed that many functional groups changed a lot. For example, C-O-C linkages was destroyed after acid pretreatment, C-H linkages in -CH3 and -CH2- increased significantly, and skeleton vibration of aromatic ring strengthened largely at the same time.