Vapor phase Beckmann rearrangement of cyclohexanone oxime over MCM-22

A comprehensive study has been made on the Beckmann rearrangement of cyclohexanone oxime (CHO oxime) to E-caprolactam, catalyzed by MCM-22 under various operating conditions. The distinct identities of MCM-22 were characterized by XRD, SEM, and NH3-temperature programming desorption (NH3-TPD). The acidic strength of MCM-22 is much weaker than those of ZSM-5 and beta zeolites with similar SiO2/Al2O3 ratio. It was found that catalytic active sites with moderate acidic strengths are more favorable for the rearrangement reaction. The carbonaceous residues, which contain mainly functional groups with CdropN bonds, can be effectively removed by purging the H-MCM-22 catalyst with nitrogen gas at higher temperatures in the absence of oxygen. A reaction pathway was proposed which invokes the main rearrangement reaction of CHO oxime accompanied by two side reactions, namely ring opening reaction of E-caprolactam to form 5-hexenenitrile (5-HEN) (coke precursor) and hydrolysis reaction to form cyclohexanone. The effects of the Pt incorporation and operating conditions, viz temperature, carrier gas, space velocity, feed concentration, solvent etc., on related reaction equilibriums of the reactions involved and ultimately on catalyst stability and product selectivity were discussed. (C) 2004 Elsevier B.V. All rights reserved.