Study On Tubular Bag Filtration Technology Of PTA Mother Liquor

Purified Terephthalic Acid (PTA) is an important petrochemical product, and the main raw material of Polyethylene Terephthalate (PET). The refining process PTA will produce a great number of PTA mother liquor, and the PTA particles in the liquor will be a waste of resources on the one hand, on the other hand increase the COD content, which will strengthen the water pollution and increase the water processing burden. Therefore, dealing with the mother liquor to recover the PTA particles and reduce the COD content is necessary not only for economy but also for environmental protection. Utilizing the tubular bag filtration to deal with the PTA mother liquor, the PTA particles are trapped on the outer surface of the bag to form a cake to be recovered. After the filtration, the filter cake is dewatered to obtain PTA cake with satisfied water content. Following that will be a backwashing operation of the tubular bag to restore its filtration performance. This paper has researched the PTA mother liquor filtering mechanism, cake dewatering mechanism and the filter media backwashing mechanism, researched influences different filter operation parameters on liquor's filtration characteristics, influences different dewatering operation parameters on cake's water content, different backwashing parameters on the regeneration of the bag's performance. According to Darcy filtration theory and experimental data, gotten the filtering mathematical model of two filter elements and the model can be used to predict the PTA mother liquor's filtration process. And the different performances of the two kind of filter element have been compared. The research found that 95% solid particles in PTA mother liquor can be recovered with tubular bag filtration, during filtering process, the greater the filtration rate and slurry concentration, the greater the growth rate of filtration pressure drop, higher temperature and viscosity of the slurry are beneficial to the conduct of filtration, the filter cake's water content can be limited to less than 30% only by the dewatering of compressed air in the process of discharging mother liquor, the dewatering pressure should be better 0.08MPa to 0.15MPa to get a lower water content, the total time should be better about 5 minutes, dewatering with steam or compressed gas with an high temperature can get a better effect, the higher the backwashing pressure and the more times the backwashing can get a better backwashing effect, the gas backwashing pressure should be better 0.2MPa to 0.4MPa and the backwashing time is not less than 3, the liquid backwashing pressure is better between 0.25MPa to 0.4MPa, and the backwashing time is better not less than 2.