乙二醇醇解松木屑反应特征及机理分析

利用酸化的乙二醇作溶剂对松木屑进行醇解,探讨了温度和时间对醇解转化率的影响。利用热重分析、红外光谱分析、扫描电镜及X射线衍射考察了醇解残渣的性质。分别利用傅里叶变换红外光谱及色质联用分析了正己烷不溶物和可溶物中组分的分布及特征。结果表明,松木屑转化率在90 min、160℃达到最大值95.3%。松木屑中纤维素无定形区的组分和木质素发生了解离,醇解残渣的表面结构被破坏;正己烷不溶物是含有羟基、甲氧基及醚键等含氧官能团的化合物;正己烷可溶物主要由苯二甲酸酯、硬脂酸甲酯、2-甲基己酸丙酯、2-甲基丙酸、聚乙二醇及未反应的乙二醇组成。乙二醇与松木屑解离的羧酸发生酯化反应,对液相产物具有稳定作用,促进了松木屑的醇解反应;醇解过程中乙二醇自缩聚生成聚乙二醇,增大了乙二醇的消耗。

Study on alcoholysis of pine sawdust in ethylene glycol and alcoholysis mechanism

The alcoholysis of pine sawdust with acidified ethylene glycol (EG) as solvent was investigated; the influence of reaction temperature and time on the conversion of pine sawdust was examined. The alcoholysis residual was characterized by thermogravimetry (TG), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) and X-ray diffraction (XRD), whereas the composition and properties of hexane insoluble components (HIS) and hexane soluble ones (HS) were determined by FT-IR and gas chromatography-mass spectrometry (GC-MS). The results showed that the conversion of pine sawdust reaches a maximum of 95.3% at 160 ℃ after reaction for 90 min. By the alcoholysis, the amorphous components of cellulose and lignin were decomposed and the surface structure of alcoholysis residual is destructed. The hexane insoluble components are composed of compounds with oxygen-bearing functional groups such as hydroxyl, methoxyl and ether, whereas the hexane soluble components consist of mainly phthalic acid esters, methyl stearate, 2-methyl propyl caproate, 2-methyl propionic acid, polyethylene glycol and unreacted EG. The esterification of EG with carboxylic acid, derived from pine sawdust, can improve the stability of liquid product and promote the alcoholysis of pine sawdust, whereas the self-condensation of EG, forming polyethylene glycol, may increase the consumption of EG.