Method for producing terephthalic acid through oxidation of p-xylene by using air based on gas-liquid-solid heterogeneous reaction separation synchronizing reactor

Abstract

The invention discloses a method for producing a terephthalic acid through the oxidation of p-xylene by using air based on a gas-liquid-solid heterogeneous reaction separation synchronizing reactor, which comprises the following steps that: p-xylene is added into the gas-liquid-solid heterogeneous reaction separation synchronizing reactor, wherein the reactor comprises a reaction tower and at least two constant-temperature subsidence towers communicated with the bottom of the reaction tower, a gaseous phase area, an oxidation area and a gas outlet are arranged in the reaction tower; in the process of reaction, the oxidation area and the constant-temperature subsidence tower are filled with p-xylene, air is continuously fed from bottom of the oxidation area so as to contact and react with the p-xylene, and generated terephthalic acid solids enter the constant-temperature subsidence tower by settling, and meanwhile, the p-xylene in the constant-temperature subsidence tower enters the oxidation area through an outer circulatory system, so that the reaction is running continuously, the p-xylene continues to be settled in the constant-temperature subsidence tower until the constant-temperature subsidence tower is filled, then the reaction tower is switched to be communicated with the other constant-temperature subsidence tower filled with p-xylene, in such an alternate way, continuous production is achieved. According to the method, a terephthalic acid can be continuously produced at high conversion rate and high yield, so that the production efficiency is improved, and the production cost is reduced.

Description

technical field [0001] The invention relates to a process for producing terephthalic acid by oxidizing p-xylene with air. Background technique [0002] Terephthalic acid is the main raw material for the polyester industry. Using cobalt acetate and manganese acetate as catalysts and bromide as promoters, oxidizing PX (p-xylene) with air at 180-200°C and 14-16MPa can produce terephthalic acid. However, both the catalyst metal salt and the reaction product terephthalic acid are solid substances insoluble in the reactant PX, so the above scheme cannot be directly applied industrially. In order to solve the mutual solubility problem of metal salts, terephthalic acid, and PX, US6,175,038 discloses a technical scheme that uses 70% acetic acid and 10% water as a mixed solvent to dissolve metal salts, terephthalic acid, and PX , and has become the current industrial technology for preparing terephthalic acid. But there are following problems in this scheme: one, bromide and acetic...

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Problems solved by technology

But there are following problems in this scheme: one, bromide and acetic acid seriously pollute the environment and corrode equipment; the other is that the reactant PX only accounts for 20% of the system total amount, resulting in huge production and separation equipment, complicated product refining and separation, and difficult operation technology. Difficulty is big, and production efficiency is low; The 3rd, solvent acetic acid is also oxidized in the reaction process, every ton of terephthalic acid is produced in industry at present, the loss of solvent acetic acid is 60~80 kilograms; The 4th, product terephthalic acid in the production process Formic acid exists in the solvent in the form of suspension for a long time. Under the conditions of high temperature and high pressure, some products are further decarboxylated to form by-products, which makes the purification of terephthalic acid more difficult.

However, the process still has the following problems: one is that a large number of pipelines are connected between the oxidation reactor or the crystallization separation tank and the solid pump, and the solid oxidation product terephthalic acid is insoluble in the reactant PX and appears at the bottom of the oxidation reactor and crystallization in the flow pipeline; the second is that the primary oxidation product of PX is a mixture of p-toluic acid, p-toluene alcohol and terephthalic acid, and the product terephthalic acid needs to be separated in the crystallizer, and this The realization of the process needs to consume a lot of energy; the third is that the product terephthalic acid in this technology still stays in the reaction system for a long time, and there is a problem of further decarboxylation of some products to form by-products under high temperature and high pressure conditions

The continuous process of insoluble products can be realized by adding solvents; however, the addition of solvents makes the chemical production process complicated, and also increases the corresponding equipment investment and energy consumption, material consumption and environmental pollution by solvents; another One option is to use interstitial operations to produce

In the above two schemes, the residence time of the reaction product in the reaction system will be increased, and under the reaction operating conditions, the reaction product will be decomposed or deeply reacted, resulting in a decrease in the yield and yield of the reaction product

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