Catalyst deactivation in the Beckmann rearrangement of cyclohexanone oxime over HSZM-5 zeolite and silica-alumina catalysts

The vapor-solid phase Beckmann rearrangement over HZSM-5 zeolite and silica-alumina was carried out to elucidate the effects of reaction temperature and diluent solvent on the selectivity to F-caprolactam (CL) and the catalyst deactivation. When the HZSM-5 was regenerated with oxygen atmosphere after the rearrangement using methanol as the solvent, the cyclohexanone oxime (CHO) conversion decreased with the regeneration number, whereas the caprolactam selectivity was almost constant. The catalyst deactivation at the fresh zeolite was largest among the regenerated zeolites. Although the crystalline structure did not change with the regeneration, the acid strength of the zeolite decreased with the regeneration number. These results suggest that the acid sites in the extra-lattice of the zeolite were responsible for the catalyst deactivation. It was found that the yield of the oligomers of epsilon-caprolactam, such as dimers, trimers and tetramers, changed with the catalyst deactivation constant. The rearrangement was carried out over silica alumina to obtain a significant amount of oligomers. As a result, the catalyst deactivation was related to the selectivity of the tetramer. The tetramer yield significantly changed with the solvent. These results indicate that the oligomer as a coke precursor was easily removed by vapor of a polar solvent, such as alcohol or acetonitrile. (C) 2004 Elsevier B.V. All rights reserved.