An investigation an the role of a Pt/Al2O3 catalyst in the oxidative dehydrogenation of propane in annular reactor

Oxidative dehydrogenation of propane was studied over a commercial Pt/gamma-Al2O3 catalyst using an annular reactor, wherein high space velocities (referred to the catalyst load) and controlled temperature conditions can be realized. The reaction was studied in a wide temperature range. Tests in the presence of the catalyst showed that up to 500 degrees C, only products of combustion were produced; above this temperature olefins were also formed in large amounts. Comparison with additional experiments which were carried out in the absence of the catalyst showed that: (1) the oxidation of propane at low to medium temperatures was purely catalytic; the reaction rate was so fast that in the present annular reactor the catalytic combustion underwent interphase mass transfer control already at 200 degrees C oven T; (2) above 500 degrees C gas-phase oxidative pyrolysis of propane was active and could explain the formation of olefins observed in the catalytic tests. Tests of sensitivity of the product yields upon variation of the catalyst load were performed; while the yields of CO2, CO, H2O, and H-2 increased with increasing amount of catalyst, the yields of propylene, ethylene, and methane decreased progressively: No positive evidence of heterogeneous formation of olefins was thus provided by the various experiments. The data were coherent with a homogeneous formation of propylene and ethylene. (C) 1999 Academic Press.