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

Abstract

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% HZ, 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 cthyne 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.

Monodispersed Pd-nanoparticles on carbon fiber fabrics as structured catalyst for selective hydrogenation

“…This is in agreement with the reaction thermodynamics if high selectivity to 1-alkene is due to the stronger adsorption of alkyne compared to alkene and not to the higher hydrogenation rate constant (Molnar et al, 2001). The ratio K Y /K H 2 was found to be 511 being close to the reported value of 400 for acetylene hydrogenation over Pd/Al 2 O 3 (Bos et al, 1993). This confirms weak hydrogen adsorption assumed.…”

Cu/Al 2 O 3 catalysts modified with Pd for selective acetylene hydrogenation

“…Furthermore, a 5-point Arrhenius plot (323-373 K) used to calculate apparent activation energy for acetylene conversion up to 99.5% (R 2 = 0.986) give a value of 47.3 kJ mol À1 (for 50-CuPd) similar to the value (46.8 kJ mol À1 ) reported by McGowan et al [58]. Values of 40 kJ mol À1 [59] and between 40 and 50 kJ mol À1 [60] have been reported for acetylene hydrogenation to ethylene under conditions which have been tested and confirmed to be representative of reaction in the absence of transfer resistances. This is not the case for data obtained at acetylene conversion levels closer to 100% where reaction rates become limited by reagent availability and consequently rates (and TOF values) will not be reported.…”

“…6) compared to monometallic Cu but also display selectivity that suggest the reaction takes place on a Cu surface. These two catalysts demonstrate that the concept of H 2 activation on Pd and spillover onto Cu can be transferred from single crystal studies to powdered catalysts [59]. However, it should be noted that any modification to the metal composition and its electronic properties might also influence the relative rates of ethylene desorption relative to further hydrogenation.…”

Oxidation of ethene in a wall-cooled packed-bed reactor

“…A different reaction system could be chosen with better known kinetics, e.g. the hydrogenation of ethyne and ethene [see Bos et al (1993)], the total combustion of propene [see Daszkowski and Eigenberger (1992)] or the combustion of carbon monoxide. In a future article the authors will demonstrate whether changing the heat transport parameters results in better agreement between experiments and calculations_ Also heat transfer parameters will be measured separately.…”