Vinyl caprolactam preparation method

Abstract

The invention discloses a vinyl caprolactam preparation method, and belongs to the technical field of chemical industry production. According to the present invention, based on the nucleophilic addition reaction principle, vinyl caprolactam is subjected to low temperature synthesis through a one-pot method by using an alkali metal salt or alkali metal hydroxide as a catalyst and using acetylene and caprolactam as raw materials, and then the vinyl caprolactam having different purities is obtained through polar solvent recrystallization and vacuum distillation; and the preparation method has characteristics of simple process, simple operation, mild and controlled reaction condition, reaction conversion rate improving, product yield improving and production cost reducing, effectively solves the problem of catalyst decomposition deactivation caused by the presence of the water in the system, avoids the occurrence of the side reaction, and avoids the pollution of the organic solvent on the environment, and the obtained two products such as the crystal and the liquid have different appearance forms and different purities so as to conveniently package and use.

Description

technical field [0001] The invention belongs to the technical field of chemical production, and relates to a preparation method of vinyl caprolactam, in particular to a preparation method of vinyl caprolactam and obtained crystal products of different forms. Background technique [0002] Vinyl caprolactam (N-Vinyl Caprolactam), CAS: 2235-00-9, the Chinese name is also called N-vinyl caprolactam, 1-vinyl hexahydro-2H-Y heptin-2-one, etc. The English name is also called vinyl caprolactam, 1-ethenylhexahydro-2H-Azrpin-2-one, vinyl-epsilon-caprolactam, etc. Its structural formula is as follows: [0003] [0004] Vinyl caprolactam is an important intermediate for the synthesis of poly-N-vinyl caprolactam. Poly N-vinylcaprolactam (PNVCL) is a temperature-sensitive high polymer with a low critical phase transition temperature (LCST). Its series of high polymers have extremely wide application prospects in biomedicine, daily chemicals, and petrochemicals. Therefore, the devel...

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Problems solved by technology

There are following problems in this synthesis process route: (1) prepare catalyst caprolactam potassium salt with caprolactam and alkali metal hydroxide, then potassium salt is added in the reaction system and react, because catalyst potassium salt encounters water or air will quickly Hydrolysis has only a short lifespan, and the presence of water will also lead to the ring opening of the raw material caprolactam, and the preparation of the catalyst caprolactam potassium salt in stages cannot solve the problem of easy deactivation of the catalyst

(2) It is reported in the literature that potassium tert-butoxide or cocatalyst crown ether is used to solve the problem in (1), but because of the high price, it only stays in the experimental stage and cannot realize large-scale industrial production

(3) According to literature reports, conventional stirred reactors are used, and the reaction conditions are either high pressure 4-12MPa, or high temperature 170-300°C, which is dangerous to operate and technically difficult.

Under high pressure and high temperature conditions, the reactor transmission and shaft rotation seals are prone to leakage, especially the leakage of acetylene gas will cause serious consequences and affect the surrounding environment

(4) Special reactors such as loop jet reactors are only in the experimental stage and cannot be industrialized yet.

(5) The process conditions for the preparation of vinyl caprolactam by the acetylene liquid phase addition method reported in the literature are still in the small-scale test stage, the reaction conditions are extreme, the reaction system is viscous and easy to solidify, and the product yield is generally low

[0006] At the same time, the vinyl caprolactam products reported in the literature are mainly purified by rectification tower purification, and the purification process has the following problems: (1) high equipment investment cost

(2) It is difficult to obtain high-purity vinyl caprolactam in one rectification

(4) There are catalysts and unreacted raw material caprolactam in the reaction solution at the same time. Under high temperature and alkaline conditions, caprolactam is easy to ring-open and polymerize, resulting in many side reactions in the rectification process, which are prone to correlative reactions and affect product yield.

(5) The product obtained after rectification is easy to form large massive crystals when stored at room temperature, and needs to be heated at a high temperature above 200°C to be melted and used. The melting process is likely to cause polymerization and discoloration of the product, which is not conducive to large drum packaging and storage

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