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[Chemical Knowledge]：The production and manufacturing method and process of purified terephthalic acid.

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Purified terephthalic acid (PTA) is an important organic chemical raw material, which is widely used in polyester fiber, polyester film, polyester bottle and other fields. There are two main manufacturing methods: oxidation method and esterification method, in which oxidation method is the main method used in industrial production. In this paper, the process flow, reaction principle, production control, advantages and disadvantages of the oxidation method for the preparation of purified terephthalic acid will be introduced in detail.

1. Process
The process of preparing purified terephthalic acid by
oxidation method mainly includes oxidation reaction, crystallization, filtration, drying and other steps. The specific process is as follows:

1. Paraxylene (PX) is mixed with acetic acid, a catalyst is added, and the mixture enters an oxidation reactor after preheating.
2. In the oxidation reactor, oxygen is introduced to control a certain temperature and pressure to oxidize p-xylene to produce crude terephthalic acid (CTA).
3. The crude terephthalic acid is separated from the mother liquor, washed with hot water, and crystallized by adding a crystallizing agent.
4. The crystallized material was filtered to give a filter cake and a filtrate. The filter cake is dried to obtain purified terephthalic acid product.

2. reaction principle
the reaction principle of
oxidation method for the preparation of purified terephthalic acid is mainly the oxidation reaction of p-xylene with oxygen in acetic acid solvent to produce terephthalic acid. The specific reaction equation is as follows:

C8H10 O2 → C6H4(COOH)2 H2O

3. production control

In the production process of preparing purified terephthalic acid by oxidation method, the following key factors need to be controlled:

1. Temperature: The temperature of oxidation reaction is generally 180-200 ℃, and the temperature range needs to be strictly controlled to ensure the reaction and the quality of products.
2. Pressure: The pressure of the oxidation reaction is generally 0.8-1.2MPa, and it is necessary to maintain a stable pressure to avoid equipment damage and product quality problems.
3. Catalyst: The type and dosage of catalyst have a great influence on the reaction speed and product quality, and need to be selected and controlled according to the actual situation.
4. Crystallization conditions: The type and dosage of crystallization agent, crystallization temperature and time have a great influence on the purity and yield of the product, and need to be optimized.

4. advantages and disadvantages

oxidation method for the preparation of purified terephthalic acid has the following advantages and disadvantages:

advantages:

1. mature process, high production efficiency, can achieve large-scale production.
2. The product has high purity and good quality, which can meet the needs of different fields.
3. Raw materials are easy to obtain, low cost, and have good economic benefits.

disadvantages:

1. The production process requires a large amount of acetic acid and catalyst, and the cost is high.
2. Oxidation reaction process will produce a large amount of waste gas and waste water, need to be environmentally friendly treatment.
3, equipment investment is large, requires a higher level of technology and maintenance costs.

In summary, the oxidation method for the preparation of purified terephthalic acid is a relatively mature and commonly used production method with high production efficiency and product purity. In the actual production process, it is necessary to optimize and control according to different raw materials and process conditions to improve product quality and yield. At the same time, it is also necessary to strengthen the work of environmental protection treatment and equipment maintenance to ensure the safety and stability of production.

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