Analysis Of Impurities In EPTA Residue And Evaluation Of TA Recovery Methods

Purified terephthalic acid (PTA) is an important raw material for the synthesis of polyester fibers, which is mainly produced by p-xylene (PX) liquid-phase oxidation. A lot of oxidation residue, a kind of solid waste material, would be produced during the process of EPTA manufacture (exploited by Eastman Chemical Company, USA). However, this residue contains a large amount of TA. Therefore, the recovery of TA from oxidation residue would be of great significance to reduce environment pollution and to make full use of resource. This thesis analyzed the components of EPTA oxidation residue, theoretically explained the impurity formation mechanism according to the characteristic of free-radical reactions, then, proposed two kinds of TA recovery methods, and did a lot of experimental study to provide an evidence for residue recovery technology industrialization.The concrete research contents of this thesis are as follows. First, gas chromatograph-mass spectrometer (GC-MS), liquid chromatograph-mass spectrometer (LC-MS) and high performance liquid chromatograph(HPLC) were used to qualitatively analyze the impurities of residue, UV-spectrophotometer was used to quantitatively analyze the total amount of impurities which would deeply affect the color property of oxidation residue. According to the free-radical reaction rule of aromatic oxidation, a formation path of impurities during the oxidation of PX was put forward. Moreover, two practicable technologies of recovering TA from oxidation residue were studied. One method of removing impurities from residue is to use dimethyl sulfoxide (DMSO) as solvent to solve residue and to add activated carbon (AC) as adsorbent to adsorb impurities. Another method is to use NaOH solution to solve oxidation residue and also to adopt AC as adsorbent. These two methods can both achieve the aim of recovering TA from oxidation residue effectively. Factors that may affect adsorption process like temperature, water content, acetic acid content and AC concentration were carefully investigated when using DMSO as solvent, and factors like PH value of adsorption process, PH value of acid eduction process ,temperature and AC concentration were investigated in detail as well when using NaOH solution as solvent. Further studies were did on these two methods, adsorption isotherms of colored impurities removal were obtained, Langmuir model and Freundlich model were used to regress, and gained relevant model parameters. These achievement above lays a foundation for the future industrial application of TA recovery from oxidation residue by AC adsorption.