铝氧单钠固体超强碱催化降解木质素的研究

Catalytic Degradation of Lignin by Aluminum Oxide Monosodium Solid Superbase

为提高木质素的活性、促进木质素的高效利用,以玉米秸秆发酵制乙醇剩余物经碱溶酸沉获得的精制木质素(PL)为原料,在以异丙醇/水的混合溶剂为反应介质、液固比为10∶1(mL∶g)、铝氧单钠固体超强碱作为催化剂条件下降解PL,得到降解木质素(DL),采用正交试验优化降解条件,并对降解前后木质素进行了分析与表征。研究结果表明:优化降解条件为催化剂用量为木质素质量的20%、反应温度200℃、反应时间150min,此时降解木质素的产率和甲醛值分别为77.5%和0.365。傅里叶红外光谱(FT-IR)、二维核磁共振(2DHSQC)、凝胶渗透色谱(GPC)和热重(TG)等分析表明:固体超强碱对木质素的催化降解很好地保留了木质素的芳香性结构;降解后DL侧链区连接键β-O-4、β-β和β-5/α-O-4含量明显降低,降解使木质素的部分Ar—O—C醚键断裂、酚羟基和醇羟基含量增加、相对分子质量和多分散性明显下降;与PL相比,DL的主热解发生温度范围变窄、最大热解速率降低。

In order to improve the activity of lignin and promote the efficient utilization of lignin, the refined lignin (PL) obtained by fermenting corn stover to produce ethanol residue and alkali-soluble acid precipitation is used as the raw material, and reacted with isopropanol-water cosolvent. The degradation of lignin (DL) was obtained by catalytic degradation under the condition of medium, liquid-solid ratio of 10 ∶ 1 (mL ∶ g) and aluminum-oxygen monosodium solid superbase as catalyst. The orthogonal conditions were used to optimize the degradation conditions before and after degradation, followed by the analyzed and characterized of lignin. The results showed that the optimized degradation condition was 20% lignin mass, 200 ℃ reaction temperature and 150 min reaction time. The yield and formaldehyde value of lignin degradation were 77. 5% and 0. 365, respectively. The aromatic structure of lignin was well retained in the process of the solid superbase catalyzed degradation of lignin, which was confirmed by Fourier transform infrared spectroscopy (FT-IR), two-dimensional nuclear magnetic resonance (2D HSQC), gel permeation chromatography (GPC), thermogravimetric (TG) analysis. The content of β-O-4,β-β and β-5/α-O-4 in the DL side chain region was significantly reduced after degradation, and Ar-O-C ether bond was partially cleavage through the degradation of lignin. The content of phenolichydroxyl group and alcohol hydroxyl group increased, whereas the molecular mass and polydispersity decreased significantly. Compared with PL, the main pyrolysis temperature range of DL became narrower and the maximum pyrolysis rate decreased.