EFFECT OF EXCHANGE PROCEDURE AND CRYSTAL SIZE ON HIGH SILICA MFI ZEOLITE AS CATALYST FOR VAPOR PHASE BECKMANN REARRANGEMENT

摘要

Caprolactam is the starting monomer for the production of Nylon-6 fibers and resins. The current caprolactam manufacturing process is energy intensive and generates considerable wastes (ammonium sulphate). For this reason, alternative paths for the production of caprolactam providing few-step cost effective production and environmentally friendly process are required. In year 2000 Sumitomo Inc. announced the build-up of a demonstration plant for the production of caprolactam.. This process allows an ammonium sulphate-free caprolactam manufacture and will result in an industrial plant by the end of year 2003. In a recent paper Ichihashi et al. claimed long-time catalytic tests with a high silica MFI zeolite which is rather active and selective towards caprolactam production. In this paper we report a study on the effect of catalyst activation method and acid sites distribution on caprolactam selectivity of high silica MFI zeolites of different crystal size. We found that catalysts activation by a NH_4NO_3 alkaline solution and calcinations at 450℃ promotes structural rearrangement of silicalite-1 unit cell and catalytic performances remarkably higher than other silicalite-1 activated by other methods. In addition we show the direct correlation between caprolactam selectivity and H-bonded (nests of silanols and vicinal silanols) distribution.