水热环境下的核桃壳木质素提取及结构表征

为研究核桃壳木质素分子结构特征及其在高压水热环境下木质素的溶出效率,本研究依次用二氧六环和碱性水溶液在不同环境条件下对脱脂后的核桃壳原料进行抽提处理,并采用FTIR、13C-NMR和二维HSQC-NMK等手段对抽提所得的核桃壳木质素组分进行结构表征。研究结果表明,二氧六环和碱性水溶液多步抽提一共可以从核桃壳原料中分离得到75.9%的核桃壳木质素,水热处理能够较好地促进原料中木质素组分的溶出; 核桃壳木质素大分子主要由愈创木基和紫丁香基结构单元构成,同时含有少量的对羟基苯丙烷结构单元; 核桃壳木质素大分子的主要联接键为β-O-4'醚键,其次是β-β'和β-5'联接; 在核桃壳木质素大分子中,紫丁香基结构单元侧链中有部分的β-O-4'芳基醚键结构的γ位发生了酰化。
Hydrothermal pretreatments, including steam explosion, autohydrolysis, and hot water extraction, are considered to be economically and environmentally attractive technologies aiming to fractionate and utilize the individual component of lignocellulosic material. This study investigated the structure of lignin extracted from hydrothermal pretreated walnut shell, and the extraction efficiency hydrothermal pretreatment was also evaluated. Six lignin fractions were isolated successively from both original and hydrothermal pretreated walnut shell with dioxane and sodium hydroxide aqueous solutions. The extracted lignin was characterized by Fourier trans form infrared spectroscopy, 1D 13C and 2D heteronuclear single quantum coherence nuclear magnetic resonance(HSQC-NMR)spectroscopy. The results indicated that 75.9% walnut shell lignin was isolated from walnut shell after six successive extractions. The walnut shell lignin was mainly consisted of guaiacyl and syringyl units with trace amount of p-hydroxyphenyl unit. The major interunit linkages presented in the obtained walnut shell lignin were β-O-4' aryl ether linkages. A few amount of β-β' and β-5' linkages were also found in the resulting walnut shell lignin. In addition, part of the β-O-4' aryl ether of syringyl unit in the walnut shell lignin molecule was esterified at γ position