Removal,Enrichment And Determination Of The Impurities Which Influence The UV Absorption Value At 290nm In Caprolactam

Caprolactam is an important raw material for the versatile polyamide fiber production with a wide application in the artificial fiber industry as well as a structural material in the electronics and motorization industry. As the monomer of polyamide, caprolactam must have a high level of purity (>99.9%) for certain trace level impurities in caprolactam directly influence the polymerization and the property of the fiber. The UV absorption value at 290nm is one of quality indexs of caprolactam. If the index of the product could not achieve the international level, the economic benefits of the enterprise would be affected. As these colored impurities which have UV absorbance at 290nm have significant influenced the quality of caprolactam produced from toluene in Shijiazhuang Chemical Fiber Company, therefore, it is important to develop a method to analyze and determine these impurities and thereby to discuss their possible origination. This could be of great importance to the industrial purity control of caprolactam.This article studied the analytical methods of caprolactam and the impurities by HPLC. The chromatographic conditions including the detection wavelength, composition of mobile phase etc. were optimized. The optimal separating condition of chromatography analysis of the impurities and caprolactam was: Shimadzu VP-ODS (150mm×4.6mm, 5μm) as chromatographic column; ultraviolet (UV) detectorλat 290nm and 230nm; acetonitrile/water, 12/88 (V/V, contained 1.25mmol/L phosphoric acid) as mobile phase with flow rate of 1.0ml/min. The RSD of this method for CPL was 1.06%, while the average recovery was 93.8% and the liner range was 10mg/ml-100mg/ml. The impurities were separated well with high repeatability and the RSD was 0.41%-2.35%.Because of the great variety and low concentration of impurities in caprolactam, the existence of large amount of caprolactam matrix usually interferes the determination of these impurities. So it is necessary to pre-concentrate the impurities for analysis. In this work, we studied the enrichment methods of the impurities from crude caprolactam product solution by different types macroporous ion-exchange resins and activated carbon. The suitable conditions of enrichment were established. In this experimental dynamic installation, the results showed that: when using 5% P720 solution with flow speed of 1.5ml/min, the adsorption rate of the impurities on anion exchange resin and activated carbon can be more than 80%, and also can reach 73% for strong acid cation exchange resin. After the impurities were desorpted by eluent with flow rate of 1.0ml/min, the recovery of the impurities on D072 and D201 were separately 62% and 66%, and the content of caprolactam decreased to 38% and 16%.The enriched impurities were determined by LC-MS and GC-MS. The five main impurities influencing the absorption value at 290nm were Benzonitrile, 4-Methyl -2-hydroxyquinoline, 2,6-Pyridinediamine, O-ethyloxime Cyclohexanone and a compound with 220 molecular weight.