Oxidation of isobutane over supported noble metal catalysts in a palladiummembrane reactor

Pd membranes are often used to remove the H-2 produced in dehydrogenation r eactions, thereby relieving the equilibrium limitations on the: product yie ld. 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 p roceeds through both the very fast oxidative dehydrogenation route as well as the dehydrogenation route. Thus, the addition of O-2 can suppress a kine tic limitation, while the removal of H-2 through the Pd membrane can allevi ate the equilibrium limitation imposed on the system by the dehydrogenation route, in this study, we have examined the oxidative dehydrogenation of is obutane in a Pd membrane reactor over Pt/alpha-Al2O3 and Rh/alpha-Al2O3 mon oliths and Pt/gamma-Al2O3 pellets. We have examined iC(4)H(10):O-2 ratios o f 1.0 to 2.0, resulting in operating temperatures ranging from 400 to 700 d egrees C. While most of this heat is generated by the exothermicity of the reaction, some additional heating was used to boost conversions. Typical co ntact times ranged from 0.04 to 0.25 s. By continuously removing the H-2 pr oduced, 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 Scie nce B.V. All rights reserved.