Catalytic combustion of propane in a membrane reactor with separate feed of reactants. III: Role of catalyst load on reactor performance

This paper deals with a pilot plant study on the catalytic combustion of propane in a membrane reactor with separate feed of reactants. The importance of the amount of catalyst (1% b.w. Pt on γ-Al2O3), deposited on the pore walls of the membrane, is investigated. Two membranes were prepared by the so called urea method, intruding different amounts of the above catalyst (2% and 4% b.w., respectively) in anα-Al2O3 basic porous tubular structure (pore diameter: 0.7 μm; length: 100 mm; internal radius 7 mm; thickness: 3 mm). The performance of the two membranes was tested in a pilot plant, feeding air at one membrane side and a propane/N2 mixture at the other side. Either the kinetics- or the transport-controlled operating regimes were investigated, and, in this last case, operation was considered both in presence and in absence of trans-membrane pressure gradients. From this study the catalyst load of the membrane seems to affect seriously the reactor performance. The more the catalyst deposited in the membrane pores, the higher the conversion attainable in the kinetics controlled regime (low temperature operation), and the easier to reach the transport-controlling condition at higher temperatures. However, this last feature is achieved at the price of relatively low overall propane conversions due to the entailed lowering of membrane permeability. Therefore, provided the propane feed concentration and the eventual trans-membrane pressure gradient are not too high, a limited catalyst amount should be employed thus allowing higher membrane permeability and propane conversions, with minor slip of reactants through the membrane.