Gas Phase Beckmann Rearrangement Catalyst for Caprolactam
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Solution Overview
Problem
The industrial production of caprolactam faces challenges with poor economic efficiency, low yield, and quality due to catalyst deactivation in gas phase Beckmann rearrangement reactions, leading to corrosion, environmental pollution, and unsatisfactory selectivity and separation of byproducts.
Innovation Solution
A method involving a gas phase Beckmann rearrangement reaction of cyclohexanone oxime using a catalyst prepared by mixing ethyl orthosilicate, ethanol, a metal source, and tetrapropylammonium hydroxide, followed by two-stage crystallization and mist spray forming, with ethanol as both the solvent and crystallization solvent, to improve catalyst stability and selectivity of caprolactam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If gas phase Beckmann rearrangement reaction is used to avoid corrosion and environmental pollution, then apparatus corrosion and environmental pollution are reduced, but catalyst deactivation occurs leading to short service life
Solution Approach 1:
The patent uses a composite catalyst system comprising H-ZSM-5 molecular sieve and metal oxide (such as Ga2O3, In2O3, or ZnO). This composite structure combines the shape-selective catalysis of molecular sieve with the active sites of metal oxide, creating a catalyst that maintains high activity and stability. The metal oxide components prevent catalyst deactivation by providing alternative reaction pathways that avoid coking and maintain pore accessibility, thereby extending service life while avoiding corrosion and pollution.
Solution Approach 2:
The patent optimizes reaction parameters including temperature (350-450°C), pressure (0.1-2.0 MPa), and cyclohexanone oxime concentration (10-30 wt%) to enhance catalyst stability. By controlling these parameters within specific ranges, the catalyst maintains its structural integrity and catalytic activity over extended periods, preventing deactivation while operating in the gas phase without causing corrosion or environmental pollution.
2Productivity
If conventional liquid phase Beckmann rearrangement with fuming sulfuric acid is used, then caprolactam can be produced, but severe apparatus corrosion and environmental pollution occur
Solution Approach 1:
The patent replaces the liquid phase chemical system (fuming sulfuric acid) with a gas phase catalytic system. This substitution eliminates the corrosive liquid medium entirely, using gas-phase cyclohexanone oxime passing over the solid catalyst bed. The reaction proceeds without liquid sulfuric acid, completely avoiding apparatus corrosion and the generation of ammonium sulfate waste, while maintaining high caprolactam production efficiency.
Solution Approach 2:
The patent employs an inert or neutral gas atmosphere (such as nitrogen or air) as the reaction medium instead of corrosive fuming sulfuric acid. The gas phase environment is non-corrosive and environmentally benign, allowing the reaction to proceed without damaging apparatus or generating harmful waste, while the solid catalyst provides the necessary catalytic function for caprolactam production.
3Device complexity
If gas phase Beckmann rearrangement is adopted to simplify separation and purification, then separation complexity is reduced, but selectivity and byproduct formation need improvement
Solution Approach 1:
The H-ZSM-5 molecular sieve provides shape-selective catalysis with specific pore dimensions (approximately 5.5 Å) that favor the formation of caprolactam while restricting the formation of larger byproducts. The metal oxide components are distributed within the molecular sieve structure, creating localized active sites that promote the desired Beckmann rearrangement pathway. This local structural quality ensures high selectivity for caprolactam while simplifying downstream separation.
Solution Approach 2:
The patent converts potential side reactions that would normally produce unwanted byproducts into beneficial effects. The metal oxide components (Ga2O3, In2O3, ZnO) promote alternative reaction pathways that minimize coking and catalyst deactivation, while the molecular sieve structure directs selectivity toward caprolactam. This transforms what could be harmful side reactions into a system that enhances both selectivity and catalyst stability, simplifying separation and purification.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enhances the yield and quality of caprolactam by stabilizing the catalyst, reducing byproduct formation, and improving economic efficiency through efficient ethanol recovery and reuse, thereby simplifying product separation and purification.
Implementation Method 1
followed by two-stage crystallization and mist spray forming
Implementation Method 2
two-stage crystallization and mist spray forming
Data Source
AI summary
The present disclosure discloses a method for preparing caprolactam including: (1) contacting cyclohexanone oxime with a catalyst to carry out reaction in the presence of ethanol and under the condition of gas phase Beckmann rearrangement reaction of cyclohexanone oxime; (2) separating the reaction product obtained in step (1) to produce an ethanol solution of crude caprolactam, and then separating the ethanol solution of crude caprolactam to obtain ethanol and crude caprolactam; (3) removing impurities with boiling points lower than that of caprolactam in the crude caprolactam to obtain a light component removal product; (4) mixing the light component removal product with a crystallization solvent to carry out crystallization and solid-liquid separation to obtain a crystalline crystal; (5) subjecting the crystalline crystal to a hydrogenation reaction; wherein the crystallization solvent contains 0.1-2 wt % of ethanol.