Kinetic Study of the Hydrogenation and Hydroisomerization of the n-Butenes on a Commercial Palladium/Alumina Catalyst

Abstract

A kinetic investigation of the vapor-phase hydrogenation and hydroisomerization of 1-butene and cis-and trans-2-butene is presented. This investigation is aimed at validating a practical set of rate equations. The experiments were performed at approximately atmospheric pressure using a commercial Pd/Al 2 O 3 catalyst of the eggshell type in an integral fixed-bed isothermal reactor. The outlet composition was measured under 120 sets of operating conditions at six levels of temperature between -8 and 30 °C. The mole fractions of 1-butene and hydrogen in the feed were varied between 0.5 and 3% and between 0.5 and 50%, respectively. Space-time covered the range of (5-55) × 10 -3 s. Internal diffusion limitations affected the effective reaction rates and product distribution. Hence, the mass conservation equations inside the catalyst had to be solved to estimate the intrinsic values of the kinetic parameters. Two rival kinetic models of the Langmuir-Hinshelwood-Hougen-Watson type were proposed, one of which could be confidently discriminated as the better of the two models considered. An essential feature of the chosen model is that hydrogen concentration exhibits distinct effects on the hydrogenation and hydroisomerization reactions of n-butenes. The selected model predicts the experimental results with an average deviation of 8.8%. The estimates of the kinetic parameters show inference intervals in the range of (10-30%.

Kinetic study of the selective catalytic hydrogenation of 1,3-butadiene in a mixture of n-butenes

“…The behavior of the system can be explained by recognizing the effect of strong diffusional resistances inside the active shell of the catalyst particles, a fact that was verified previously [12,[22][23][24]. Thus, if BD is present in the reacting mixture, the magnitude of the mass transport resistance is such that the limiting reactant, either H 2 or BD, is depleted before the end of the active shell.…”

“…This hypothesis assumes that when hydrocarbon species are adsorbed, even at the extent of saturation, free interstitial sites remain accessible for the very small H 2 molecules (but not for additional molecules of the bulkier hydrocarbons). This noncompetitive adsorption hypothesis is widely accepted in literature ( [3,23] and references therein). In this regard, it is important to mention the results and analysis of Silvestre-Albero et al [26], who studied the effect of Pd particle size on the behavior of BD hydrogenation catalyzed by model catalysts of Pd nanoparticles supported on alumina films.…”

“…The remaining steps in Table 3 were first proposed from the analysis of experiments carried out in vapor phase [23].…”

“…The value t = 1.5 was previously estimated by Bressa et al [23]. The molecular diffusion coefficients Dm j were estimated as those of the species j in n-hexane as solvent.…”

Kinetic study of the liquid-phase selective hydrogenation of 1-butyne in presence of 1-butene over a commercial palladium-based catalyst

“…This hypothesis assumes that there is no direct competition between hydrogen and the unsaturated hydrocarbons for the same sites because hydrogen molecules are so small that they can find free sites even though the catalytic surface is almost completely covered by the strongly adsorbed 1-butyne and 1-butene. This noncompetitive adsorption hypothesis is widely accepted in literature not only for 1-butyne and 1-butene but for other unsaturated compounds too (Bressa et al, 2003;Boitiaux et al, 1987; and references therein).…”