A kinetic study of the hydrogenation of ethyne and ethene on a commercial Pd/Al₂O₃ catalyst

The kinetics of the hydrogenation of gas mixtures of ethyne and ethene on a commercial Pd catalyst was studied experimentally using a Berty reactor. The experimental conditions corresponded with typical industrial tail-end conditions, 0.3–1.3% C₂H₂, 0.4–4% H₂, the balance being ethene. The influence of small amounts of carbon monoxide added to the feed gas was also investigated. The pressure was varied between 0.3 and 2.1 MPa and the temperature between 299 and 330 K. The maximum temperature was limited due to mechanical problems of the Berty reactor. Eight different sets of rate expressions, partially adapted from expressions previously proposed in the literature, have been tested. No ‘best” model was chosen, because many models were found to describe the data equally well. The prediction of the rate of ethane formation was less accurate than the prediction of the rate of ethyne hydrogenation. This was not only due to the higher experimental error involved, but also because ethane could be formed by alternative routes. In deriving adequate rate expressions for the rather complex system, a compromise has to be sought between the relative inaccuracy of the simpler expressions and the inability of determining the large number of parameters in more complex expressions.