Analysis Of Acid Cluster In Industrial Caprolactam

The technique of caprolactam(CPL) produced from toluene in Shijiazhuang Chemical and Chemical Fiber Company is developed by SINA company in Italy. Systematic analysis methods have been done on the raw materials of CPL production and control of intermediate technique, few reports were focused on the acid cluster in industrial CPL. The acid cluster in industrial CPL is a product of amidation.There are CPL, cyclohexane-carboxylic acid(CCA), a-carboxyl cyclohexane sulphonic acid(SCCA), massive sulphuric acidand small amount of hexane. in the acid cluster. The analysis methods for the determination of various composition in acid cluster of caprolactam was developed in this paper. A reversed phase ion-pair liquid chromatographic method has been adopted to analysis CPL, CCA and SCCA simultaneously. Indirect photomeric-liquid chromatography detection method for the determination of hexane and ion-chromatography for sulphuric acid was applied for analysis of acid cluster respectively. The method is accurate for the quantitative analysis of various composition in acid cluster of caprolactam. The aim of this paper is to provide analysis datas for optimizing process parameter.First,a reversed phase ion-pair high performance liquid chromatographic(HPLC) method has been adopted to analysis CPL, CCA and SCCA by Agilent 1200 chromatographic system. The chromatographic separation of CPL, CCA and SCCA was achieved on a 4.6mmx250mm Agilent HC-C18(5μm) column. The mobile phase was a mixture solution of methanol-water(30:70,v/v) containing tetrabutylammonium bromide as ion-pairing reagents 4mmol/L and potassium dihydrogen phosphate as buffering reagents 10mmol/L (pH=3.5) at a flow rate of 1.0mL/min and column temperature was set at 35℃. The UV-detection wavelength was set at 230nm.The method can separate three different materials, have great peak shape and lead to accurate and reliable results.Secondly, an indirect photometric detection method for determination of hexane in acid cluster of caprolactam by HPLC was developed. Strong UV absorbable background reagents were added to the mobile phase, and the hexane was directly determined by UV detector. The effects of species and concentration of the background reagents, mobile phase composition and gradient of wavelength on the analyzed results were discussed. The optimization of separation was performed on aAgilentHC-C18 column (250mm×4.6mm,5μum) by Agilent 1200 chromatographic system. A methanol-water (85:15, v/v) solution containing 1.17mmol/L 1, 5-naphthalene disulfonic acid was used as mobile phase at a flow rate of 1.0mL/min and column temperature was set at 35 ℃. The gradient of wavelength was adopted to adjust relative size of system peak and target peak. The method developed is simple, and have good selectivity, high sensitivity and strong anti-interference ability for accurate determination of hexane quickly.Thirdly, ion-chromatography was applied to detect sulphuric acid with electric conductivity detector. Sulphuric acid was performed on an IC-A1 hydrophilic anion exchange column (5μm×4.6mm×10cm). The solution containing 1.14 mmol/L phthalic acid and 1.08 mmol/L trishydroxymethl aminomethane was used as eluent at a flow rate of 1.5 mL/min and column temperature was set at 45 ℃. The method is time-saving, simple and good selectivity for accurate determination of sulfate ion.According to the calculation of external standard method, the value was 23.61% for CPL,0.316% for CCA and 0.314% for SCCA in acid cluster in industrial CPL. The contents of hexane and sulphuric acid were 0.112% and 74.53% respectively.