Terephthalic acid (PTA) is an important organic chemical raw material, widely used in the production of polyester fiber, polyester resin, film and other products. In the field of raw materials for chemical production, there are two main manufacturing methods for terephthalic acid: oxidation method and esterification method. This article will introduce these two manufacturing methods in detail.
1. Oxidation method
Oxidation method is the main production method of terephthalic acid, including liquid-phase oxidation method and gas-phase oxidation method.
1. Liquid-phase oxidation method
Liquid-phase oxidation method is to mix p-xylene with acetic acid at high temperature and high pressure, and pass air for oxidation reaction to produce terephthalic acid and acetic acid. Catalysts and stabilizers need to be added during the reaction to promote the reaction and control the generation of by-products. After the reaction, pure terephthalic acid is obtained by crystallization, filtration, drying and other processes. The advantages of the
liquid phase oxidation method are that the process is mature, the operation is stable, and high quality terephthalic acid can be produced. However, this method needs to use a large amount of acetic acid as solvent, the production cost is high, and the corrosion of equipment is serious.
2. Gas-phase oxidation
Gas-phase oxidation is a gas-phase oxidation reaction of p-xylene with oxygen at high temperature and high pressure to produce terephthalic acid and carbon dioxide. The method requires the use of a catalyst, and metal oxides such as vanadium and titanium are usually employed as catalysts. At the end of the reaction, pure terephthalic acid is obtained through processes such as condensation and separation. The advantages of the
vapor phase oxidation method are that the reaction conditions are milder, it does not require the use of large amounts of solvents, and the production costs are lower. However, the catalyst activity of this method is high, which needs to be replaced periodically, and the requirement of equipment is high.
II. Esterification
Esterification is another production method for terephthalic acid, which mainly involves the transesterification reaction of dimethyl terephthalate with methanol to produce terephthalic acid and methanol. The method requires the use of a catalyst, usually an acidic catalyst such as sulfuric acid and hydrochloric acid. At the end of the reaction, pure terephthalic acid is obtained by distillation and crystallization. The advantages of the
esterification method are that it is a simple process, easy to operate, and capable of producing high quality terephthalic acid. However, the method requires the use of a large amount of methanol as a solvent, which has a high production cost, and produces a large amount of by-product methanol, which needs to be recycled and treated.
In summary, oxidation and esterification are both common manufacturing methods for terephthalic acid, each with its own advantages and disadvantages. In actual production, the suitable manufacturing method should be selected according to the specific situation in order to obtain high quality terephthalic acid and reduce the production cost.
