Kinetic study of vapor-phase Beckmann rearrangement of cyclohexanone oxime over silicalite-1

Abstract

The intrinsic kinetics for vapor-phase Beckmann rearrangement of cyclohexanone oxime (CHO) to caprolactam (CPL) over fresh silicalite-1 was studied at atmospheric pressure by an improved approach that combines the differential and the integral methods. To keep the reaction zone temperature constant at high flow rate and obtain homogeneous mixture of CHO and methanol largely different in boiling point, a special fixed-bed tubular reactor was designed. The relationship of deactivation rate with weight hourly space velocity (WHSV) was investigated in a wide range of CHO concentrations under high gas superficial velocity. The rate equation was directly deduced by the differential method on the basis of the dependence of CHO disappearance rate on CHO and CPL partial pressures. The reaction mechanism and rate-limiting step were determined by in situ infrared spectroscopy and comparison of the catalytic results of fresh and partially poisoned silicalite-1. The kinetic parameters were estimated and statistically tested by the integral method. It is shown that the vapor-phase Beckmann rearrangement of CHO to CPL occurs via a single-site surface reaction route with activation energy of 94.69kJ/mol, and desorption of CPL is the rate-limiting step.