Application of Mixed Acid-Modified Hollow TS-1 Zeolite to Vapor-Phase Beckman Rearrangement Reaction

ε-Caprolactam (CPL) is an important organic chemical raw material used as a monomer in the production of nylon 6. The traditional production process employs fuming sulfuric acid as a catalyst, leading to serious equipment corrosion and environmental pollution. While vapor-phase Beckman rearrangement reaction offers a solution to these issues. Unfortunately, the catalyst used is susceptible to carbon deposition and deactivation during the vapor-phase Beckman rearrangement process. Herein, a kind of mixed acid-modified hollow TS-1 zeolite was prepared in this study. It is a hollow structure of TS-1 zeolite formed by secondary crystallization, which is conducive to the shortening of the reaction path and the improvement of the anti-carbon accumulation performance. Further investigation revealed that modification of the hollow TS-1 zeolite with mixed acids facilitates the removal of non-skeletal titanium, and reduces the amount of Lewis acid in the catalyst, thereby improving its catalytic performance. Under optimal conditions, the cyclohexanone oxime (CHO) conversion rate reached 100%, with a caprolactam selectivity exceeding 98%. Notably, the catalytic activity of the catalyst remained stable after 500 h of continuous operation. Graphical Abstract: (Figure presented.)