Treatment method and system for xylene oxidation reaction liquid

Abstract

The invention relates to the technical field of fine chemical engineering, and in particular, relates to a treatment method for a xylene oxidation reaction liquid, wherein a treatment system used by the method comprises a light component removal system (A) and a heavy component removal system (B). The method comprises the steps: carrying out light component removal operation on the oxidation reaction liquid, and separating light components to form light component removal mother liquid; and carrying out heavy component removal operation on the light component removal mother liquid by introducing a high-boiling-point solvent, and separating heavy components containing the high-boiling-point solvent, phthalic acid and carboxybenzaldehyde and a byproduct impurity benzoic acid to obtain the target product methyl benzoic acid. According to the method, the product loss in the oxidation reaction liquid treatment process can be remarkably reduced, the content of single impurity benzoic acid can be reduced, and the purity of methyl benzoic acid is improved.

Description

technical field [0001] The invention relates to the technical field of fine chemicals, in particular to a method and a system for treating xylene oxidation reaction liquid. The method of the invention can not only reduce the product loss in the process of treating the oxidation reaction solution, but also can significantly reduce the content of single impurity benzoic acid and improve the purity of toluic acid. Background technique [0002] According to the oxidation principle of xylene, in the oxidation process of xylene, methyl benzyl alcohol, methyl benzaldehyde, methyl benzoic acid, hydroxymethyl benzoic acid, carboxybenzaldehyde, phthalic acid, etc. Product, in order to control the selectivity of product toluic acid in actual production, the conversion rate of xylene is generally 20-40%. Therefore, in the oxidation reaction liquid of xylene, the above-mentioned products with different oxidation degrees will exist at the same time. [0003] In order to obtain the main ...

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Problems solved by technology

According to the common sense of those skilled in the art, in the process of rectification, the tower still must keep completely dissolving all the time, and in the process of rectifying, along with the component that boiling point is lower than toluic acid successively steams out, in the tower still liquid The only solvent that can dissolve high-boiling point peroxidation impurities and high-boiling point impurities produced by deep side reactions is the product methylbenzoic acid. When separating methylbenzoic acid and high-boiling point impurities by rectification, part of the methylbenzoic acid remains as a solvent It cannot be recovered in the rectification raffinate at the bottom of the tower, causing the loss of part of the product methyl benzoic acid, making the product yield low, the effective utilization rate of xylene is low, and due to the impurity benzoic acid directly produced in the oxidation process of xylene The proportion of benzoic acid is relatively low, ignoring that side reactions such as decarboxylation in the process of rectification and separation will cause the cumulative increase of benzoic acid content, it is believed that benzoic acid has little impact on the quality of downstream products, and it is believed that the boiling points of methyl benzyl alcohol and benzoic acid are different It is not suitable to increase energy consumption for the separation of a small amount of benzoic acid and many other reasons. During the rectification process, there is no export of impurity benzoic acid, resulting in too high content of impurity benzoic acid in the product, and the purity of the product methyl benzoic acid cannot directly meet the requirements of high-quality products. Requirements for the purity of raw materials for products such as DEET

[0005] On the basis of CN106831393A, CN105061187A replaces intermittent operation with continuous operation, greatly shortens the heating time of the mixture to be separated, and significantly suppresses various deep by-products generated by the chemical reaction of the material during the rectification process, so that the single-pass yield can be reduced. Increase to about 90%. According to the common sense of those skilled in the art, to achieve a product yield of 90%, on the one hand, it is necessary to strictly control the selectivity of the xylene oxidation reaction, and on the other hand, it is necessary to reduce the solvent used as a solvent to the greatest extent in the rectifying separation stage. The amount of methyl benzoic acid used to reduce the loss of methyl benzoic acid is not only complicated to operate but also has potential safety hazards, and does not effectively solve the loss of product methyl benzoic acid caused by using methyl benzoic acid as a solvent when separating high-boiling impurities problem, and did not solve the problem of high content of impurity benzoic acid in the product

[0006] CN107903165A uses a continuous production method to oxidize xylene, and adopts multi-stage series rectification towers for separation and purification. The yield can reach 60-90%, and the highest purity can reach 99%, but it will stop the reaction by exploring conditions. One step in m-toluic acid, although the loss of m-toluic acid has been reduced to a certain extent, according to the common sense of those skilled in the art, in order to make the oxidation of m-xylene stay in the process of m-toluic acid, The per-pass conversion rate of m-xylene will be very low, generally not higher than 10%, which will increase the treatment capacity of the oxidation process and post-treatment process, causing the overall investment cost to be too high, and although the conversion rate of control xylene is low The generation of peroxidation impurities cannot be completely avoided, and the oxidation reaction still needs to be rectified in the post-treatment process. After gradually accumulating, the loss of methyl benzoic acid due to the need to dissolve high-boiling point peroxide impurities is still relatively high

In addition, in the process of multi-stage rectification, impurity benzoic acid will inevitably be produced. With the continuous improvement of the quality requirements of downstream products of p-toluic acid, not only the purity of raw material toluic acid is required, but also the content of single impurity benzoic acid There are also restrictions, 99% of raw material purity can no longer meet the raw material requirements of high-quality DEET products

[0007] In summary, the common technology of the existing xylene oxidation reaction liquid treatment method is direct rectification, and the common disadvantages are that the loss of toluic acid is more in the process of oxidation reaction liquid treatment, the yield of product is low, and the product The content of key impurity benzoic acid is high, and the product purity is low

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