Process for preparing caprolactam by cyclohexanone-oxime gas phase rearrangement

Abstract

The process of preparing caprolactam with cyclohexanone oxime includes the vapor Beckmann rearrangement reaction of cyclohexanone oxime inside one first fixed bed reactor in the presence of MFI structure molecular sieve catalyst; the decomposition and conversion of the reaction side product O-alkyl-epsilon-caprolactim into caprolactam inside one second fixed bed reactor in the presence of MFI structure molecular sieve catalyst and water; and the separation and purification of the reaction effluent. Compared with single vapor Beckmann rearrangement reaction process of cyclohexanone oxime, the present invention has 1-3 % raised caprolactam yield.

Description

technical field [0001] The invention relates to a method for producing caprolactam by gas-phase Beckmann rearrangement of cyclohexanone oxime. More specifically, it relates to a method for preparing caprolactam in a fixed-bed reactor using MFI structural molecular sieves as a catalyst for gas-phase Beckmann rearrangement of cyclohexanone oxime. Background technique [0002] Caprolactam, the product of the Beckmann rearrangement reaction of cyclohexanone oxime, is the main raw material for the production of three series of products: nylon, industrial cord, and nylon engineering plastics. 10 4 Ton. The domestic caprolactam gap has been relatively large, and the annual import volume is generally 30×10 4 More than tons, with the increase of consumption in the future, the gap of caprolactam will be bigger. [0003] In industry, the cyclohexanone oxime liquid-phase Beckmann rearrangement process using concentrated sulfuric acid or oleum as a catalyst is often used to produce ε...

AI Technical Summary

Problems solved by technology

[0008] Although the fluidized bed process can continuously complete the production of caprolactam, and can better solve the problem of taking heat from the reaction, it has the following disadvantages: 1, because the conversion rate of cyclohexanone oxime is only about 95%, the remaining reaction product Unreacted cyclohexanone oxime is difficult to separate from caprolactam due to its own thermal instability and the boiling point of the product caprolactam, which brings trouble to the follow-up purification process; 2, MFI structure molecular sieve catalyst has better In the stable activity period, frequent regeneration in the fluidized bed cannot fully utilize the reactivity of the catalyst; 3. There is an initial stage of reaction in the regenerated catalyst, at which the conversion rate of cyclohexanone oxime is relatively high, but caprolactam The selectivity of the caprolactam is low, and the catalyst is frequently regenerated, which will inevitably affect the selectivity of caprolactam; 4. Caused by the reasons of the fluidized bed itself, such as: the tumbling phenomenon of the gas in the fluidized bed affects the fluidization gas and the catalyst particles. The contact efficiency of the unreacted material is diluted by the reacted material, which leads to the decrease of the conversion rate of cyclohexanone oxime, etc.; 5. The violent agitation and circular movement of the material cause the wear of the catalyst particles, which has higher requirements on the wear resistance of the catalyst

[0009] On the other hand, as far as the molecular sieve with MFI structure is used as the catalyst for gas-phase rearrangement, although a higher conversion rate of cyclohexanone oxime and caprolactam selectivity can be obtained, and the catalyst has better regeneration performance, the fly in the ointment is: 1. The catalyst needs to use a fatty alcohol with a carbon number less than 6 as a solvent. During the rearrangement reaction, the fatty alcohol is easy to dehydrate with the product caprolactam to generate a by-product o-alkyl-ε-caprolactam. Its selectivity accounts for 60% of all by-products, and this by-product has increased free alkalinity, has reduced caprolactam product quality; 2, the selectivity of this vapor phase rearrangement process to caprolactam generally only has about 96.5%, has influenced its industrialization economy feasibility

[0010] So far, there have been no reports of industrialized construction devices using reactors other than fluidized beds alone, such as fixed-bed reactors, directly performing Beckmann rearrangement reactions to produce caprolactam

Images