Kinetics of the vapor phase hydrogenation of cyclohexene

Abstract

The kinetics of the vapor phase hydrogenation of cyclohexene over a Pt/$SiO_2$ (containing 2\% Pt) was investigated in the temperature range 20 - 70$^\circ$C. The experiments were performed in a flow recycle reactor at atmospheric pressure. The use of the recycle reactor helped in the elimination of external diffusion resistance. In order to eliminate pore diffusional resistance, small size catalyst particles (80 - 120 mesh) were used. Analysis of the kinetic data was done using both the power law and Langmuir-Hinshelwood type models. In power law model, the rate of the reaction was found to be zero order with respect to cyclohexene; the order with respect to hydrogen was 0.53 at temperatures above 40$^\circ$C and increased toward unity at low temperatures. The activation energy was 6.8Kcal/gmole in the temperature range 40 - 70$^\circ$C. Determination of the most plausible mechanism of reaction was based on discrimination among various proposed Langmuir-Hinshelwood type models for the reaction. In order to discriminate models, the parameters of these models were estimated by nonlinear least squares analysis. Horiuti-Polanyi model fitted kinetic data adequately and hence might be accepted as the most plausible model. The shift in reaction order was ezplained by this Horiuti-Polanyi mechanism.