气相色谱-质谱法测定组合工艺己内酰胺产品中的微量关键杂质

Determination of the key impurity in caprolactam produced from a combined process by gas chromatography-mass spectroscopy

己内酰胺(CPL)是重要的化工原料,CPL中即使存在微量的杂质都会对聚合产物的性能产生一定的影响,因此对聚合级CPL的纯度有很高的要求。该文对光密度值严重超标的组合工艺工业试验产品采用气相色谱-火焰离子化检测技术(GC/FID)、气相色谱-质谱(GC-MS)等手段进行了定性分析,确定该杂质的相对分子质量为188,分子式为C_(12)H_(16)N_2,环加双键数为6,为八氢吩嗪。结合组合工艺生产CPL所涉及化学反应的特点对八氢吩嗪的来源进行了理论推测,认为该杂质来源于Beckmann重排反应的副反应Neber重排,结构中含有较强的生色基团,对产品的光密度指标影响严重。因此,CPL生产过程中必须对八氢吩嗪的产生过程和生成浓度严格控制。

Caprolactam (CPL) is an important chemical raw material. Because even trace level contaminations in CPL can directly influence the polymerization and the resulting properties of fibers, the CPL monomer must be very pure. In this study, gas chromatography with a flame ionization detector (GC/FID) and gas chromatography mass spectroscopy (GC-MS) techniques were developed to determinate the key impurities in CPL using a novel process which characterized the ultraviolet (UV) absorption rates of the samples. The GC-MS results indicated that the major impurity had a relative molecular mass of 188 and was qualitatively characterized as 1,2,3,4,6,7,8,9-octahydrophenazine. Considering the reaction conditions and properties of the substances in the reactor, we speculated that the octahydrophenazine may have originated from a Neber rearrangement, which is a side-reaction of the Beckmann rearrangement. The impurity contains strong chromophores and severely impacted the UV absorption rate of the CPL product. Therefore, during CPL production, the concentration of octahydrophenazine must be strictly controlled.