Kinetics and reactor modeling of a Pd-Ag/Al2O3 catalyst during selective hydrogenation of ethyne

The selective hydrogenation of ethyne is one process to remove traces of ethyne from steam cracker cuts during the production of ethene. Even though Pd-Ag/Al2O3 catalysts are predominantly used in industrial C-2-tail end-selective hydrogenation reactors, a detailed kinetic study with this catalyst type has not yet been published in the open literature. For this reason, kinetic measurements were carried out on a Pd-Ag/Al2O3 catalyst in an integral fixed bed reactor at different process conditions for the selective hydrogenation of ethyne. The results of these measurements were fitted on different kinetic models ranging from a classical Hougen-Watson, Langmuir-Hinshelwood and Rideal-Eley approach up to simple power law equations. The kinetic model with the best fit was found by statistical and thermodynamical evaluations of all models and their respective kinetic parameters. This model is based on a Langmuir-Hinshelwood reaction mechanism involving two different active sites for the hydrogenation of ethyne and ethene. The kinetic measurements were not dependent on mass and heat transfer as demonstrated by using the criteria from Mears and the Weisz-Prater as well as for the Damkoehler numbers in 3rd and 4th order. Finally the performance of a bypass reactor, running in parallel to an industrial C2-tail end-selective hydrogenation reactor, was successfully calculated with a reactor model. (C) 2012 Elsevier B.V. All rights reserved.