Production method of o-toluic acid or m-toluic acid

Abstract

The invention relates to the technical field of fine chemical engineering, in particular to a production method of o-toluic acid or m-toluic acid, and a production system used by the method comprises an oxidation device 100; a light component removal device 200; a weight removal device 300; a rectification device 400; and a purification device 500. The production method comprises the following steps: performing oxidation reaction on xylene to form oxidation reaction liquid; performing light component removal operation on the oxidation reaction liquid, and separating light components to form light component removal mother liquid; carrying out heavy component removal operation on the light component removal mother liquor, and separating heavy components to form heavy component removal light components; rectifying the heavy-component-removed light component, and separating a middle component to form a rectified mother solution; and refining the rectification mother liquor, and separating benzoic acid and refined raffinate to obtain the target product methyl benzoic acid. According to the production system and the method, high-purity methyl benzoic acid can be prepared, the waste amount is obviously reduced, the production cost is reduced, and the remarkable environmental protection effect is achieved.

Description

technical field [0001] The invention relates to the technical field of fine chemicals, in particular to a production method of high-purity o-toluic acid or m-toluic acid. The production method of the invention can not only reduce the content of single impurity benzoic acid and produce high-purity toluic acid, but also significantly reduce the amount of waste in the entire reaction system, which not only reduces production costs, but also has a significant environmental protection effect. Background technique [0002] It is known that the production process of toluic acid (including m-toluic acid and o-toluic acid) is basically the same, and can be obtained by air oxidation of xylene. According to the principle of xylene oxidation, during the oxidation process, methyl benzyl alcohol, methyl benzaldehyde, methyl benzoic acid, hydroxymethyl benzoic acid, carboxybenzaldehyde, phthalic acid, etc. will be produced in order of oxidation. In order to control the selectivity of the ...

AI Technical Summary

Problems solved by technology

This method does not control the content of single impurity benzoic acid, and cannot directly obtain high-purity m-toluic acid, and has a large amount of waste, cumbersome operation, and poor economy

[0006] CN1373117A proposes that the o-toluic acid obtained by the conventional method of air oxidation and rectification has problems such as low purity and instability, and discloses a method of adding alkali to the crude product of o-toluic acid to form a salt, extract, activate carbon, etc. The method of improving the purity of the product by means of decolorization and heating recrystallization, although a product with higher purity can be obtained, does not control the content of a single impurity, benzoic acid, and the refining process is long and complicated, which greatly increases the production cost and low economic benefit

[0009] CN108863757B discloses a method for co-producing methylbenzoic acid, methylbenzonitrile and phthalonitrile, which solves the problems of low target product yield and large solid waste in the prior art, and the product structure is single

This patent first distills xylene, methylbenzaldehyde, and methylbenzyl alcohol from the oxidation reaction liquid, and then distills the product toluic acid from the initial distillation column liquid. When heated for a long time, this will lead to a series of deep side reactions such as alkyd esterification, aldol condensation, simple dimerization of aldehydes, carboxyl decarboxylation coupling, and carboxyl decarboxylation of alcohols, aldehydes, and acids at high temperatures, forming high-boiling point esters, colored Deep by-product impurities such as impurities, biphenyl compounds and benzoic acid

Therefore, although the technique described in CN108863757B has improved the total product yield of methylbenzoic acid, methylbenzonitrile and dicyanophthalonitrile on the whole, because there is most of methylbenzoic acid, it is not obtained from the initial distillation tower still liquid. Distilled out from the medium, resulting in a low yield of the final single product toluic acid, and because the process of refining the product in the preparation process of p-toluic acid was abandoned, resulting in high content of impurity benzoic acid in the product toluic acid , low product purity

[0010] CN107903165A utilizes the continuous production mode to carry out the oxidation of xylene, and this patent intends to stop the reaction in the step of m-toluic acid to achieve higher yield and product purity, but according to the common sense of those skilled in the art, if you want to Making the oxidation of m-xylene stay in the process of m-toluic acid can only reduce the single-pass conversion rate of m-xylene, which is generally not higher than 10%. This operation will greatly increase the treatment capacity of the oxidation process and post-treatment process , the overall investment cost is too high, and the control of the low conversion rate of xylene cannot completely avoid the generation of peroxidation impurities. In the post-treatment process, the oxidation reaction still needs to be rectified. This patent uses multi-stage series rectification Tower for separation and purification, there is still the loss of toluic acid due to the need to dissolve high-boiling point peroxidation impurities, and impurity benzoic acid will inevitably be produced. Although the amount of single-pass waste is apparently reduced, the overall waste amount after accumulation is not the same. Neither reduced nor controlled the content of impurity benzoic acid in the product

But even so, the yield and purity of the single product methyl benzoic acid are low, although it has additionally obtained two products of methyl benzoic acid ester and phthalic acid diester

[0012] In addition, in the prior art, the light components with a boiling point lower than toluic acid can be distilled out successively according to the boiling point order of each component in the xylene oxidation reaction liquid, and finally the product toluic acid is collected at the top of the rectifying tower, and The bottom of the rectification tower removes the high-boiling rectification raffinate, but whether this treatment method is batch operation or continuous operation, the peroxidized impurities with a boiling point higher than toluic acid will always be heated in the separation system

On the one hand, because the boiling point of impurity benzoic acid is lower than the boiling point of product methylbenzoic acid, if there is no outlet of benzoic acid in the production system, when separating product methylbenzoic acid, impurity benzoic acid will be produced together with methylbenzoic acid The top of the tower is collected into the product collection tank, resulting in low purity of toluic acid and limited application fields

On the other hand, the amount of toluic acid used to dissolve these high-boiling impurities increases due to the increase in the depth of side reactions that are difficult to recover, which means that the amount of toluic acid that is difficult to evaporate increases, resulting in Increased loss of product methyl benzoic acid and increased waste

[0013] In order to further increase the profit margin of the enterprise, the existing technology has been improved before separating toluic acid by adding a tolualdehyde recovery tower to separate and recover tolualdehyde, and in the process of rectification and separation, the oxidation reaction liquid The relatively large proportion of methyl benzyl alcohol and benzoic acid and other by-product impurities are collected into the low-boiler waste tank as waste treatment, which increases the amount of waste and reduces the utilization rate of m-xylene

[0014] In summary, the common disadvantages of the existing production methods of methyl benzoic acid are that the key impurity benzoic acid content in the product is high, the application field of the product is limited, and a large amount of rectification residue is produced in the production process, which makes the environmental protection pressure huge. The economic benefit is not significant

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