Pure Terephthalic Acid (PTA) is an important raw material for the production of polyester fiber and resin. In PTA production plant, because the process involves a variety of corrosive media and complex working conditions, the corrosion resistance and high temperature resistance of equipment materials are very high. Hastelloy C-276 has been widely used in PTA plants for its excellent properties.

1. PTA device process and corrosion environment

The production of PTA mainly includes two processes: oxidation and refining. In the oxidation process, with p-xylene as raw material, in acetic acid solvent, under the action of catalysts (such as cobalt acetate, manganese acetate), crude terephthalic acid is oxidized by air. There are many corrosive substances in this process, such as acetic acid, bromine ion (added as a cocatalyst) and so on. The refining process is the further purification of crude terephthalic acid, and the mother liquor also contains acidic and corrosive components in the process.

2. Performance advantages of Hastelloy C-276

Hastelloy C-276 is a nickel-molybdenum-chromium-tungsten alloy with the following properties that make it suitable for PTA plants:

2.  1 Excellent corrosion resistance: It can resist a variety of acidic media, including organic acids such as acetic acid. It also has good tolerance to bromine ion corrosion during oxidation. In the environment containing chloride ions, its high content of molybdenum and chromium elements enable it to effectively prevent pitting and crevice corrosion, which is crucial in the complex chemical media environment of PTA devices.

2.2 Good high temperature resistance: Under the high temperature conditions of PTA oxidation reaction (the general reaction temperature is about 180-200 ℃), the alloy C-276 can maintain stable performance, and will not cause a significant decrease in material strength or deformation due to high temperature, so as to ensure the normal operation of the equipment.

2.3 Excellent resistance to stress corrosion cracking: In PTA devices, equipment and pipelines are subjected to internal medium pressure but also to corrosion, C-276 can effectively resist this stress corrosion cracking, extend the service life of the equipment.

3. The concrete application in PTA device

3.1 Oxidation reactor: Oxidation reactor is the core equipment of PTA production. Hastelloy C-276 is often used for stirrer, cooling coil, baffle and other components inside the reactor. The agitator is in full contact with the corrosive medium during the rotation process, and the corrosion resistance of C-276 can ensure its long-term stable operation, maintain a good mixing effect, and promote the uniform reaction. Cooling coils need to effectively carry away the reaction heat in high temperature corrosive environments, and C-276's high temperature and corrosion resistance make it an ideal material.

3.2 Pipeline system: In the PTA unit, the pipelines transporting acetic acid, oxidized mother liquor, refined mother liquor and other corrosive media are made of Hastelloy C-276. These pipelines can withstand long-term corrosion of the medium, avoid pipeline leakage, and ensure the continuity of the production process. For example, the use of C-276 can greatly reduce the frequency of maintenance and replacement of pipes connecting oxidation reactors and subsequent separation and refining equipment.

3.3 Heat exchanger: The heat exchanger is used in the PTA device to heat or cool the process medium. Hastelloy C-276 is used for tube bundles and housings of heat exchangers. In the heat exchange process, it can resist the corrosive components that may exist in the heat medium and refrigerant, while maintaining good heat conduction performance at high temperatures, improving the heat exchange efficiency, and ensuring the stability and reliability of the entire heat exchange process.

3.4 Filtration equipment: In the refining process of filtration equipment, some of the key components in contact with the corrosive mother liquid, such as filter element, filter screen, etc., use Hastelloy C-276. It can effectively filter impurities in a corrosive environment to ensure the purity of PTA products, while itself will not be damaged by corrosion, reducing the maintenance cost of filtration equipment.

The application of Hastelloy C-276 in PTA plant is of great significance to ensure the stable and efficient operation of the plant. Its excellent corrosion resistance, high temperature resistance and resistance to stress corrosion cracking ability, so that it can be long-term service under the harsh conditions of PTA equipment, although its cost is high, but in the long run, reduce the frequent replacement and maintenance of equipment caused by production stagnation and other problems, improve the economic efficiency and safety of PTA production.