Oxidation of isobutane over supported noble metal catalysts in a palladium membrane reactor

Pd membranes are often used to remove the H-2 produced in dehydrogenation reactions, thereby relieving the equilibrium limitations on the: product yield. These processes, however, can still be limited by the slow kinetics of the dehydrogenation reaction. If O-2 is added to the system, the reaction proceeds through both the very fast oxidative dehydrogenation route as well as the dehydrogenation route. Thus, the addition of O-2 can suppress a kinetic limitation, while the removal of H-2 through the Pd membrane can alleviate the equilibrium limitation imposed on the system by the dehydrogenation route, in this study, we have examined the oxidative dehydrogenation of isobutane in a Pd membrane reactor over Pt/alpha-Al2O3 and Rh/alpha-Al2O3 monoliths and Pt/gamma-Al2O3 pellets. We have examined iC(4)H(10):O-2 ratios of 1.0 to 2.0, resulting in operating temperatures ranging from 400 to 700 degrees C. While most of this heat is generated by the exothermicity of the reaction, some additional heating was used to boost conversions. Typical contact times ranged from 0.04 to 0.25 s. By continuously removing the H-2 produced, isobutylene yields increased. Yield improvements depended strongly on the balance of reaction time with H-2 removal time and the importance of the dehydrogenation in the overall reaction scheme. (C) 2000 Elsevier Science B.V. All rights reserved.