CATALYST DEACTIVATION OF HIGH-SILICA HZSM-5 IN THE BECKMANN REARRANGEMENT REACTION OF CYCLOHEXANONE OXIME

The Beckmann rearrangement of cyclohexanone oxime was carried out over high-silica HZSM-5 zeolites and boron-modified HZSM-5 to elucidate the effects of silica/alumina ratio and boron modification on the catalyst deactivation rate. The relationship between cyclohexanone oxime conversion and time on stream could be represented by the equation x(t)=x(0). exp(-b . t) where x(t) and x(0) are conversions at a time on stream t and at the initial stage t= 0, respectively, and b is the deactivation coefficient. The deactivation coefficient increased with increasing concentration of strong acid sites. When the deactivated zeolites were evacuated under a pressure of 1 Torr at 573 K for 5 h, the catalytic activity was recovered up to 50% of the initial activity. The deactivation of the ZSM-5-type zeolite was mainly due to the adsorption of volatile material on the acid sites.