Method for capturing and purifying pyromellitic dianhydride

Abstract

The invention discloses a method for capturing and purifying pyromellitic dianhydride. The method comprises the following steps of: directly performing heat exchange on a gas-phase product prepared from durene through gas-phase catalytic oxidation twice, introducing into a capture device, exchanging heat between air and the reaction product, making the gas-phase reaction product pass through the inside of the capture device and cooling air pass through a jacket layer of the capture device, separating out the pyromellitic dianhydride and byproducts from the gas-phase reaction product through heat exchange and cooling, and finally obtaining high-purity pyromellitic dianhydride. By the method, the pyromellitic dianhydride and the byproducts in the gas-phase reaction product prepared from the durene through a fixed bed gas-phase catalytic oxidation process are effectively separated, the high-purity pyromellitic dianhydride can be continuously and efficiently captured directly, and the method has the advantages that the technological process is simple, the cost is low, the energy consumption in the process can be reduced, the operating environment is improved and the floor area is reduced.

Description

technical field [0001] The invention relates to the technical field of preparation of pyromellitic dianhydride, in particular to a method for trapping and purifying pyromellitic dianhydride in a gas-phase reaction product obtained by gas-phase catalytic oxidation of a fixed bed of durene. Background technique [0002] Pyromellitic dianhydride (PMDA) is an important chemical intermediate material, mainly used for the production of polyimide resins and films, monomers of heat-resistant resins such as polyimidazole, high-temperature-resistant electrical insulating paints, Raw materials for solid lubricants, epoxy resin curing agents, coating additives, etc., are widely used, among which engineering plastics and plastic additives produced with pyromellitic dianhydride as raw materials have excellent electrical insulation properties, high and low temperature resistance , high mechanical properties, etc., are widely used in aviation, electronics, electromechanical and other high-t...

AI Technical Summary

Problems solved by technology

This process has poor trapping and separation effects on reaction products, and the obtained PMDA has low purity

Chinese patent CN1388127A proposes the trapping method that adopts the vertical cylindrical trapping device of series connection, and carries out hanging net (such as figure 1 ), the trapping temperature of this method still relies on natural cooling, and the reaction product gas enters the 1# trap and enters through the baffle plate from the bottom of the 2# trap. As the airflow rises and meets the wire mesh, the PMDA content is relatively high The gaseous phase product of the gaseous phase first desublimates and crystallizes at the bottom of the trap, while the gaseous phase product with a relatively low concentration gradually crystallizes at the upper part of the trapper, and the desublimated product condensed on the metal mesh falls to the bottom of the trapper during discharge, then The desublimation product with higher PMDA content at the bottom of the trap will mix with the desublimation product with lower content at the upper part of the trap, which is not conducive to obtaining crude PMDA with higher purity; When there is a lot of crude anhydride, it will form a large resistance to the airflow, which will make the airflow easy to short circuit, and will make the capture and separation of the reaction product less effective; and the capture method uses 6 vertical cylinder traps on the ground Arranged in series above, occupying a large area; although many improvements have been made to the trapping equipment during the production process, such as adding baffles inside the trap, adding cooling coils, etc., the overall effect is not ideal. Therefore, the trapping and separation effect of this type of trapping device is not ideal, and the crude product PMDA with higher purity cannot be trapped.

[0007] There is also a collection method in China that uses a tubular trap. The reaction mixture gas goes to the tube side of the trap, and the cooling air goes to the shell side of the trap. Several traps are connected in series, and the reaction product gas is sent from the first The lower part of the first trap enters the trap and is discharged from the upper part of the third trap, and the cooling air enters the reactor for oxidation reaction after countercurrent heat exchange with the reaction product; a vertical hanging net is used at the bottom of each trap to trap The collection effect is significantly improved, which increases the resistance of the reaction product airflow. After the reaction product enters the trap, the desublimated crystals fall to the bottom of the equipment and are collected. However, the crystallization products on the tube wall need to be cleaned by manual special tools.

When the local tubes are easily blocked by product crystallization, it is very difficult to discharge the material, especially after some tubes are blocked, the heat transfer will be uneven, which will cause the local temperature to be too high, and the product will be easily carbonized, which will seriously affect the product quality. PMDA content is about 70-80% in the device crystallization product, if needing to separate the useful component wherein, will increase production cost greatly, be difficult to meet the needs of technological production, if handle directly as waste, then will cause serious waste of useful resources waste, causing serious environmental pollution

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