Pure Terephthalic Acid (PTA) of New Manufacturing Process

Pure terephthalic acid (PTA) is white crystal or powder, low toxicity, flammable. If it is mixed with air, it will burn or even explode when it meets fire within a certain limit. Its spontaneous combustion point is 680℃, the ignition point is 384~421℃, the heating heat is 98.4kJ/mol, the combustion heat is 3225.9kJ/mol, and the density is 1.55g/cm3. Soluble in alkaline solution, slightly soluble in hot ethanol, insoluble in water, ether, glacial acetic acid and chloroform.

Pure erephthalic acid (PTA) Uses

Pure terephthalic acid (PTA) is one of the important bulk organic raw materials, its main use is the production of polyester fiber (polyester), polyester film and polyester bottles, widely used in chemical fiber, light industry, electronics, construction and other aspects of the national economy, closely related to the level of people’s living standards. The application of PTA is relatively concentrated, more than 90% of the world’s PTA is used for the production of polyethylene glycol terephthalate (PET), and the other parts are used as polytrimethylene terephthalate (PTT) and Polybutylene terephthalate.

Old production methods Pure terephthalic acid (PTA)

The old production methods are mainly divided into low temperature oxidation method and high temperature oxidation method.

Low temperature oxidation of p-xylene

The raw material paraxylene (PX) was oxidized to terephthalic acid in acetic acid solution with cobalt acetate (or manganese acetate) and bromide as catalyst and trimaldehyde as oxidation accelerator at 130-140℃ and 1.5-4.0 mpa. The product terephthalic acid was washed with acetic acid at 160℃ and 0.55MPa pressure, then washed with acetic acid at 100℃ and atmospheric pressure, and then dried to obtain the product refined terephthalic acid.

High temperature oxidation of p-xylene:

Terephthalic acid was oxidized by p-xylene with acetic acid as solvent, cobalt acetate and manganese acetate as catalyst in the presence of tetrabromoethane at 221-225℃ and pressure of 0.255 mpa. The reaction product is dissolved in water at 280-290℃ and 6.5-7.0 mpa pressure to form an aqueous solution of terephthalic acid. After hydrotreating with palladium/activated carbon catalyst, the trace amount of p-carbonyl benzaldehyde was removed, and the finished refined terephthalic acid was obtained by crystallization, washing and drying.

New production methods Pure terephthalic acid (PTA)

In recent years, various patent vendors have continuously improved and improved the PTA process flow, process parameters and equipment, and made great progress in terms of reducing raw and auxiliary materials and public engineering consumption, saving investment, and improving the operating rate of the device.

Optimized reaction condition

PX oxidation is the core of PTA plant. Choosing suitable oxidation reaction conditions is the decisive factor to reduce raw and auxiliary material consumption, reduce by-product generation and improve product quality. Optimizing reaction conditions has become the commanding point of technology development. The general trend of optimization of reaction conditions is to reduce reaction pressure and temperature, increase catalyst concentration and improve the ratio of catalyst and accelerator, as shown in the following tabble 1.

ItemReaction pressure/MPaReaction temperature/℃Br: (Co+Mn) / molCo: Mn/ mol
Eastman0.56160  
Dupont1.472010.51:2
Amoco1.261910.51:2
Interquisa1.451950.5-0.81:(2-3)
INCA1.602001.01:2
Mitsui oil1.061851.02:1
Table 1 The main technological parameter of oxidation reaction

Increase mother liquor circulation, reduce raw material and energy consumption:

Increased the mother liquor circulation from 50% to more than 90%, significantly reducingthe amount of oxidation residue, reducing raw materials, catalysts and utility consumption, while also saving energy. The content of 4-CBA and PT acid in MTA is low, the impurity content in the solvent (water) of the refined part is low, and the circulating rate of the mother liquor is high.

Enhanced hydrofining reaction:

The concentration of CTA in the original hydrogenation reaction was less than 28% and the reaction temperature was about 280℃. Then the concentration of CTA was increased to 30%, the reaction temperature was increased to 286℃, the hydrogenation reaction was greatly strengthened, and the salt water removal and energy consumption were reduced.

Solid recovery and utilization of PTA mother liquor:

After further separation, terephthalic acid, p-methylbenzoic acid and p-methylbenzaldehyde in the mother liquor of PTA crystallization centrifuge are recovered and sent to the oxidation system for recycling, which improves the yield of products and reduces the discharge of three wastes.

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