Preparation and characterization of palladium composite membranes for hydrogen removal in hydrocarbon dehydrogenation membrane reactors

Palladium composite membranes were prepared by high velocity oxy-fuel flame spraying (HVOF) and electroless plating, respectively. Palladium was deposited onto porous stainless steel and alumina tubes. High-temperature permeation tests (350-650 degreesC) were carried out to determine the permeation properties as well as the thermal and mechanical stability of the prepared membranes. The membrane morphology was characterized by scanning electron microscopy. Thicknesses of the Pd-layers greater than or equal to3 (electroless plating) and > 50 mum (HVOF) were necessary to get defect-free films. The membranes showed a good hydrogen permeability and selectivity for both preparation methods. However, the experimental results indicate that the separation behaviour - for membranes prepared by electroless plating - depends on the thickness of the Pd-layer. The Nz-permeation of membranes with Pd-layers less than or equal to about 7 mum thickness increased significantly in presence of hydrogen at temperatures above 400 degreesC. In contrast membranes having a Pd-layer well above 7 mum thickness proved to be stable at high temperatures, which is one of the prerequisites for employment of these membranes in industrially relevant dehydrogenation reactions. This was evident from a comparison of the data of permeation runs with H-2/N-2-mixtures and single gases. (C) 2001 Elsevier Science B.V. All rights reserved.