Process for stirring type multi-kettle continuous oxidation preparation of trimellitic anhydride

Abstract

The invention relates to a process for stirring type multi-kettle continuous oxidation preparation of trimellitic anhydride with 1,2,3-trimethylbenzene as raw materials, acetic acid as solvent, tetrabromoethane as promoter, and cobalt acetate and manganese acetate as catalyst. Three and four stage cascade oxidation reaction kettles with stirring device are employed, the temperature of kettle is 160C.í½250C. with step type temperature rise among kettles, and pressure is 1.8í½3.2MPa (absolute pressure); Two and three stage cascade anhydride-forming reaction kettles with stirring device are employed with the temperature of kettle of 160C.í½250C. and pressure of 0.08MPaí½0.12Mpa (absolute pressure). Said materials are added separately in proportion in oxidation reaction kettle, and fed into multi-stage cascade reaction kettle with stirring device through pipeline connection by pump power, liquid phase continuous oxidation, anhydride-forming, purification are carried out with stirring to produce trimellitic anhydride. Miulti-kettle continuous production can prevent frequent operation of temperature and pressure control.

Description

technical field [0001] The invention relates to a method for producing trimellitic anhydride by continuous oxidation into anhydride, in particular to a method for producing trimellitic anhydride by continuous oxidation into anhydride in agitated multi-pots. Background technique [0002] Trimellitic anhydride is an important chemical raw material for modern new materials. It has high reactivity and can produce a series of valuable fine chemicals. It is mainly used in engineering plastics, high-quality plasticizers, heat-resistant insulating varnishes, advanced coatings and other industries. For example, it can be used in the production of PVC plasticizer trioctyl trimellitate, etc. [0003] At present, the domestic production methods of trimellitic anhydride are all produced by batch oxidation process, that is, trimellitic anhydride is produced in acetic acid solvent, with cobalt acetate, manganese acetate, tetrabromoethane or hydrogen bromide as catalyst, and compressed air ...

AI Technical Summary

Problems solved by technology

The reactor for batch production of trimellitic anhydride needs to repeatedly increase and decrease the pressure and temperature, the equipment is prone to fatigue, the service life is shortened, and the production safety is reduced. At the same time, the output and yield are low, the quality is unstable, and it is difficult to form large-scale production

Chinese patent application CN 1401642 A discloses a "Method for Producing Trimellitic Anhydride by Continuous Oxidation Process". Although the production method involved in this application proposes to solve the problem of continuity of oxidation reaction, it must carry out innovative specific step design in the implementation process , such as the requirements for the number of oxidation and anhydride reaction devices, the requirements for the temperature and pressure parameters of the step-by-step reaction, and the connection between the various process steps, etc., it is possible to truly solve the problem of the continuity of trimellitic anhydride production

In the initial stage of the reaction, that is, during the generation of trimellitic acid and trimphthalic acid, the exothermic heat is very large, and the requirements for the reaction temperature can be carried out at a lower temperature, so cooling is used to remove the heat of reaction; The heat is less, in order to ensure the completion of the reaction process, the reaction temperature should be maintained, so a certain amount of heat must be added, and the single-pot continuous production is difficult to achieve this optimized reaction condition, so it has to be operated at a higher temperature, resulting in excessive oxidation , burning acetic acid and side reactions, the same goes for the two kettles

Facts show that the production of trimellitic acid by continuous oxidation in one or two kettles is not ideal enough, difficult to operate, low conversion rate, total acid value of oxides decreases by 15% to 30%, and yield of finished products decreases by 8% to 15%. Especially in the single-pot continuous reaction, the operation of the raw materials is very easy to short-circuit, and the unreacted trimethylene and the intermediate product, that is, the mixture of trimellitic acid and trimphthalic acid are output to the oxidation reactor under the action of stirring. Therefore, the trimethylene Insolubles tend to remain in the triacids and increase consumption, especially the single-pot continuous production method, whose yield and quality are not as good as the single-pot continuous production method with stirring

From the perspective of one-time addition of the catalyst, because trimellitic acid has two carboxyl groups in its ortho position, it is easy to form a complex with the heavy metal ion in the catalyst, thereby reducing the activity of the catalyst and making the oxidation reaction insufficient.

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