MFI Zeolites For The Vapor Phase Beckmann Rearrangement Of Cyclohexanone Oxime

Beckmann rearrangement of cyclohexanone oxime (CHO) toε-caprolactam (CPL) is an important industrial process. In order to solve the problems caused by sulfuric acid as the catalyst in the conventional processes, such as corrosion, pollution and by-product production, many solid catalysts have been investigated. Among these, MFI zeolites have been considered as active and selective catalysts for the vapor phase Beckmann rearrangement.In the present work, MFI zeolites, TS-1, Silicalite-1 (S-1) and B-MFI, were first synthesized by a hydrothermal method. The as-synthesized zeolites were treated by acids and bases. All the catalysts obtained were characterized by XRD, BET, IR, SEM and TG etc., and studied in the vapor phase Beckmann rearrangement of cyclohexanone oxime. The effects of reaction temperature, WHSV, CHO concen- trations in ethanol, crystal sizes of MFI zeolites and solvents on the Beckmann rearrangement were also investigated. The hydrothermally synthesized samples were compared with TS-1, prepared by a sol-gel method.The results showed that hydrothermal method had the advantages over the sol-gel method in preparation of TS-1, in terms of the crystal properties or Beckmann rearrangement performance. The hydrothermally synthesized TS-1 with inorganic titanium was active than the traditional TS-1 synthesized with organic titanium in the Beckmann rearrangement.For the as-synthesized S-1 catalysts, since the presence of silanol nests, the orthorhombic sample was more effective than the monoclinic sample in terms of both CHO conversion and CPL selectivity. However, the catalytic property of the modified S-1 could not be correlated with the structure phases.When the monoclinic S-1 was treated by inorganic base of ammonia solution or the mixture solution of ammonia and NH4NO3 at 383 K to 443 K, the structure of S-1 could change into orthorhombic phase and its Beckmann rearrangement performance was also improved. Lower temperature and shorter treatment time was preferred. However, when the as-synthesized orthorhombic S-1 was treated under the same conditions, there was little effect on the Beckmann rearrangement performance.