Chemical Structure of Bioethanol Lignin by Low-Temperature Alkaline Catalytic Hydrothermal Treatment
LIU Xiao-huan1, ZHANG Ming-ming1, WANG Ji-fu1, XU Yu-zhi1*, WANG Chun-peng1, 2, CHU Fu-xiang1, 2*
1.Institute of Chemical Industry of Forestry Products, Chinese Academy of Forestry; Key Lab of Biomass Energy and Material, Jiangsu Province; National Engineering Lab for Biomass Chemical Utilization; Key and Lab on Forest Chemical Engineering, State Forestry Administration, Nanjing 210042, China 2.Institute of Forest New Technology, Chinese Academy of Forestry, Beijing 100091, China
Abstract：In order to improve the reaction activity of bioethanol lignin, we investigated the activation of bioethanol lignin by a hydrothermal treatment method. Catalytic hydrothermal treatment of bioethanol lignin was performed at 180 ℃ for 3 h in the presence of alkaline solutions (NaOH, Na2CO3, KOH and K2CO3), the change in bioethanol lignin structures was studied comparatively by FTIR, 1H NMR，GPC and elemental analysis. FTIR spectra showed that after alkali hydrothermal treatment, the band at 1 375 cm-1 attributed to the phenolic hydroxyl groups increased, and the band intensity at 1 116 cm-1 attributed to the ether bond decreased. On the other hand, the band at 1 597 and 1 511 cm-1 attributed to aromatic skeletal vibration remained almost unchanged. 1H NMR spectra showed that after alkali hydrothermal treatment, the number of aromatic methoxyl is increased, and based on the increment of the content of phenolic hydroxyl, the catalytic activity can be ranked as follows: KOH>NaOH>K2CO3>Na2CO3. Especially for KOH, the increment of the content of phenolic hydroxyl was 170%, because the ion radius of potassium cation is bigger than sodium cation, so the potassium cations more easily formed cation adducts with lignin. GPC results showed that the molecular weight of alkali hydrothermal treatment lignin decreased and the molecular distribution got wider. Elemental analysis showed that hydrothermal treatment could break the interlinkage between lignin and protein, which can reduce the protein content and increase the purity of lignin, meanwhile, the content of O and H both decreased，while C fell, indicating that the bioethanol lignin had suffered a decarbonylation reaction. This is the most benefit of the lignin as a substitute for phenol.
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