Terephthalic acid is how to make?

Terephthalic acid (Phthalic Acid), as an important chemical raw material, is widely used in many fields such as plastics, coatings, dyes and pharmaceuticals. Terephthalic acid is how to make it? This article will be from its production process, raw material selection, reaction conditions and other aspects of a detailed analysis to help readers in-depth understanding of the preparation of this chemical products.

1. Terephthalic acid basic concept

Terephthalic acid, chemical formula C8H6O4, is a derivative of the two carboxyl (-COOH) groups on the benzene ring. It is a colorless crystal, commonly used in synthetic plastics, plasticizers and dyes. Its importance is not only reflected in the chemical industry, but also the key raw material for the production of plastic products (such as polyester).

2. Terephthalic acid production raw materials

Before you understand how terephthalic acid is made, you must first understand the basic raw materials required for its production. The synthesis of terephthalic acid mainly depends on benzene and oxygen, and the source of benzene is mostly from petrochemical products. Oxygen is used in the oxidation reaction and plays an important role.

3. Terephthalic acid production process

3.1 Oxidation Preparation of Terephthalic Acid

The main production method of terephthalic acid is oxidation, that is, through the oxidation of benzene in the presence of oxygen. In this process, benzene reacts with oxygen to form terephthalic acid. Specific reaction is as follows:

[ \text {benzene} \text {oxygen} \rightarrow \text {terephthalic acid} ]

this reaction is usually carried out under high temperature and high pressure conditions and requires a catalyst to accelerate the reaction. Common catalysts include metal compounds such as molybdenum and vanadium.

3.2 wet oxidation and dry oxidation

Wet oxidation and dry oxidation are the two main oxidation processes for the production of terephthalic acid.

• Wet oxidation: This method uses liquid oxygen as an oxidant. The terephthalic acid produced during the reaction is dissolved in water and finally separated by crystallization. The advantage of this process is that the by-products can be effectively removed and the reaction process is relatively mild.

• Dry oxidation: Dry oxidation is the direct introduction of oxygen into the reaction gas, the reaction temperature is higher, usually requires more complex equipment and fine control. The product of the dry oxidation is usually a solid and the terephthalic acid requires further processing to obtain the final product.

4. Terephthalic acid production in the key factors

4.1 temperature and pressure control

In the production of terephthalic acid, temperature and pressure are the key factors affecting the reaction rate and product quality. The oxidation reaction requires high temperature (usually between 200-300 degrees Celsius) and a certain pressure to proceed smoothly. Controlling the temperature and pressure can improve the yield and reduce the formation of by-products.

4.2 Catalyst Selection

The catalyst plays a crucial role in the efficiency and selectivity of the reaction. Commonly used catalysts include vanadium-based catalysts, molybdenum-based catalysts and the like, which can accelerate the reaction at a relatively low temperature and increase the yield of terephthalic acid.

4.3 reaction time

The length of the reaction time will directly affect the completion of the reaction. In industrial production, it is necessary to ensure the completeness of the reaction by adjusting the reaction time, and at the same time avoid the formation of by-products caused by the reaction for a long time.

5. Terephthalic acid post-treatment and purification

After production of terephthalic acid, purification and separation are usually required. For terephthalic acid produced by wet oxidation, a common method is crystallization separation. After terephthalic acid is crystallized, it is usually washed, dried and other steps to obtain a finished product with higher purity. The dry oxidation method requires the removal of impurities through solvent extraction and other methods to ensure the quality of the product.

6. Terephthalic acid application

As an important chemical intermediate, terephthalic acid is widely used in the fields of plastics, dyes, medicine and agricultural chemicals. Its main uses include:

• Polyester production: terephthalic acid is polyethylene terephthalate (PET) of the key raw materials, widely used in the production of plastic bottles, fibers, etc.
• Plasticizer: Terephthalic acid is a synthetic plasticizer (such as phthalate dioctyl ester) of the basic raw materials, used in the plastics industry.
• Dye intermediates: Terephthalic acid can also be used as dye synthesis intermediates for the production of various pigments and dyes.

7. Summary

The synthesis of terephthalic acid from benzene and oxygen by oxidation is currently the most common industrial production method. The production process requires precise control of temperature, pressure and catalyst selection to ensure product quality and reaction efficiency. Understanding how terephthalic acid is made is undoubtedly an important basic knowledge for those engaged in the chemical and related industries.