Study On The Analysis And Control Method Of PTA Purity

As a main raw material of polyethylene terephthalate (PET) manufacture, purefied terephthalic acid (PTA) has a rapid development in recent two decades in China, and its quality has important effect on fibers and other plastic products. Development and optimization of analysis method, improving on the quality control means, stabilizing and improving the quality of PTA are the aim of our work. In this study, we build three novel methods for the determination of PTA purity including spectral analysis, the determination of the benzaldehyde (BA), 4-carboxy benzaldehyde (4-CBA) and para to luic acid (P-TL) content in PTA, and the improvement way of quality control in oxidation system of PTA.The way of spectral analysis was employed to test the purity determination of PTA, in which spectrophotometer was being used to determine the transmission (T400) of PTA products. Compared with the traditional method of acid value determination, this way is faster, more accurate, and easier to control the purity of PTA on line. We have studied and optimize the experiment conditions, which include wavelength, solution concentration, colorimetric cell and the others, in orde to enhance the precise of the analysis results.The advanced testing technique of high performance capillary electrophoresis have been adopted to determine the amount of BA, 4-CBA and P-TL in PTA. In this way we could determine BA, 4-CBA and P-TL in PTA simultaneously, so it has more advantages than tradational ways in which only one or two components could be determined at one time. In orde to achieve satisfied separation efficiency, we also analyzed the effect of the species, concentration and pH value of solution. Running voltage, detection wavelength, sample volume and other aspects of eletrophoresis were also studied in the experiment.The traditional way of control the quality in oxidation system is to analyze the 4CBA content in CTA slurry, it should spend long time. So the improvement quality control means was obtained through setting the relation curve of combustion value and 4CBA content. The relation curve of combustion value and 4CBA content was depicted by analyzing and converting the content of O₂, CO, CO₂ into combustion value timely. In addition, contents of 4CBA in CTA within proper level was realized by control impurity content of the main mass parameter of 4CBA, regulating O₂ concentration in exhaust, adjusting reaction temperature, catalyst ratio, water content and other factors in reactor. The productive excellence rate of PTA increases to more than 99% from 98% through the optimization of quality analysis and control means. By our work, the quality fluctuation of PTA is decreasing, and the purity, stability of quality, quality benefit is improving significantly.