Method for producing caprolactam by methylbenzene

Abstract

The invention relates to a method for producing caprolactam by methylbenzene, which comprises the following processes of oxidation, esterification, hydrogenation, distillation, amidation, hydrolyzing and refining, wherein in the oxidation process, the methylbenzene is completely converted into benzoic acid by adopting an ester solvent; in the esterification process, the benzoic acid dissolved in ester reacts with alcohol to form corresponding benzoate; in the hydrogenation reaction, a benzene ring of the benzoate is hydrogenated till saturation to form cyclohexanecarboxylate in a fixed bed reactor, and the cyclohexanecarboxylate enters the amidation process; and in the amidation process, the cyclohexanecarboxylate reacts with nitrosyl sulfuric acid, the reaction product is subjected to hydrolyzing rearrangement in the sulfuric acid to form the caprolactam by refining. In the method, the conventional rectification of the benzoic acid is changed into the rectification of the benzoate, agranular catalyst replaces the original powder palladium-carbon catalyst, the processes of catalyst sedimentation, centrifugal separation and the like are reduced, the generation of ammonium sulfate is reduced, and dimethyl sulfate serving as a by-product is produced simultaneously.

Description

technical field [0001] The present invention relates to a process for the production of caprolactam. The provided method includes processes such as toluene oxidation, esterification, hydrogenation, distillation, amidation, hydrolysis and refining. Background technique [0002] At present, the production method of caprolactam mainly adopts cyclohexane method (DSM method, Toray method), toluene method (SNIA method), phenol method and butadiene method according to raw material classification. Among them, the phenol method has been eliminated, and the butadiene method still has some bottlenecks in industrialization. At present, the DSM cyclohexane method and the SNIA toluene method are mainly used in China. The SNIA method using toluene as a raw material was developed by the Italian SNIA company in the 1950s. Because every mole of caprolactam produced will lose 1 mole of carbon atoms, the technical route has poor atom economy, but the price of toluene is lower than that of benz...

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Problems solved by technology

[0011] The disadvantage of the toluene method is that there are many by-products of ammonium sulfate, and the by-product of 3.8 tons of ammonium sulfate per ton of caprolactam

At the same time, this method also has disadvantages such as large corrosion and difficulty in catalyst recovery, mainly in three main units. During the preparation of benzoic acid by oxidation of toluene in unit 01 and the hydrogenation of benzoic acid in unit 02, the intermediate benzoic acid has a melting point of 122 ° C and a boiling point of 248°C, resulting in two major disadvantages:

[0012] (1) In order to prevent the high-temperature corrosion of benzoic acid, all pipelines use high-standard stainless steel, and the equipment investment is huge;

[0013] (2) Low-temperature benzoic acid coagulates and blocks pipelines, and all pipelines are insulated with steam sleeves, so the investment and operation costs are huge

[0014] In addition, the existing 02 unit uses four series-connected stirring hydrogenation reactors for the hydrogenation of benzoic acid, and the catalyst uses palladium supported on powdered activated carbon. The separation of the product and the catalyst is troublesome, resulting in an alarming consumption of expensive catalysts

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