Purified terephthalic acid (PTA) is an important organic chemical raw material, widely used in polyester fiber, polyester film, polyester bottle and other fields. Its manufacturing methods are mainly oxidation and esterification, of which oxidation is the main method used in the current industrial production. In this paper, the process flow, reaction principle, production control and advantages and disadvantages of the oxidation method for the preparation of fine terephthalic acid will be introduced in detail.
I. Process flow
The process flow of the oxidation method for the preparation of fine terephthalic acid mainly includes oxidation reaction, crystallization, filtration, drying and other steps. The specific process is as follows:
1. Mix paraxylene (PX) with acetic acid, add catalyst, preheat and enter into the oxidation reactor.
2. In the oxidation reactor, pass oxygen, control a certain temperature and pressure, make p-xylene oxidized to produce crude terephthalic acid (CTA).
3. Separate the crude terephthalic acid from the mother liquor, wash it with hot water, and then add crystallizing agent for crystallization.
4. The crystallized material is filtered to obtain filter cake and filtrate. The filter cake is dried to obtain the refined terephthalic acid product.
II. Reaction principle
The reaction principle of preparing fine terephthalic acid by oxidation method is mainly that p-xylene undergoes oxidation reaction with oxygen in acetic acid solvent to produce terephthalic acid. The specific reaction equation is as follows:
C8H10 + O2 → C6H4(COOH)2 + H2O
Three, production control
In the production process of fine terephthalic acid prepared by oxidation method, it is necessary to control the following key factors:
1. Temperature: the temperature of the oxidation reaction is generally in the range of 180-200 ℃, and it is necessary to strictly control the temperature range in order to ensure that the reaction is carried out and the quality of the product.
2. Pressure: The pressure of the oxidation reaction is generally in the range of 0.8-1.2MPa, which needs to be maintained at a stable pressure to avoid equipment damage and product quality problems.
3. Catalyst: The type and dosage of catalyst have great influence on the reaction speed and product quality, which need to be selected and controlled according to the actual situation.
4. Crystallization conditions: the type and dosage of crystallizing agent, crystallization temperature and time and other conditions have a great influence on the purity and yield of the product, and need to be optimized and controlled.
4. Advantages and disadvantages
The oxidation method for the preparation of fine terephthalic acid has the following advantages and disadvantages:
Advantages:
1. The process is mature, the production efficiency is high, and large-scale production can be achieved.
2. The products are of high purity and good quality, which can meet the demands of different fields.
3. The raw materials are easy to obtain, the cost is low, and it has good economic benefits.
Disadvantages:
1. The production process needs to consume a large amount of acetic acid and catalyst, the cost is high.
2. The oxidizing reaction process will produce a large amount of waste gas and waste water, which needs environmental protection treatment.
3. Equipment investment is large, requiring high technical level and maintenance cost.
In summary, the oxidation method for the preparation of purified terephthalic acid is a more mature and commonly used production method, with high production efficiency and product purity. In the actual production process, it needs to be optimized and controlled according to different raw materials and process conditions to improve the quality and yield of the product. At the same time, it is also necessary to strengthen the environmental protection treatment and equipment maintenance and other aspects of the work, in order to ensure the safety and stability of production.
