Palladium/ceramic membrane

E. Kikuchi, Palladium/Ceramic Membranes for Selective Hydrogen Permeation and Their Application to Membrane Reactor , Catal. Today, 25 333-37 (1995). 

Collins JP, Way JD. Preparation and characterization of a composite palladium-ceramic membrane. Ind Eng Chem Res. 1993 32 3006. 

Kikuchi E (1995) Palladium/ceramic membranes for selective hydrogen permeation and their application to membrane reactor. Catal Today 25 333-337... 

Tosti S, Bettinali L, Castelli S, Sarto F, Scaglione S, Violante V (2002) Sputtered, electroless and rolled palladium-ceramic membranes. J Membr Sci 196 241-249... 

S. Tosti, L. Bettinali, S. Castelli, F. Sarto, S. Scaglione and V. Violante, Sputtered, electroless, and rolled palladium-ceramic membranes, J. Membr. Sci., 2002, 196, 241-249. 

Catalytic decomposition of ammonia into nitrogen and hydrogen (palladium ceramic membrane)... 

FIGURE 13.7 Shear stress at the interface Pd-Ag/ceramic support versus the temperature for different thicknesses of the metal layer. (Reprinted from Journal of Membrane Science, 196, S. Tosti et ah, Sputtered, electroless, and rolled palladium-ceramic membranes, 241-249, Copyright 2002, with permission from Elsevier.)... 

Ceramic, Metal, and Liquid Membranes. The discussion so far implies that membrane materials are organic polymers and, in fact, the vast majority of membranes used commercially are polymer based. However, interest in membranes formed from less conventional materials has increased. Ceramic membranes, a special class of microporous membranes, are being used in ultrafHtration and microfiltration appHcations, for which solvent resistance and thermal stabHity are required. Dense metal membranes, particularly palladium membranes, are being considered for the separation of hydrogen from gas mixtures, and supported or emulsified Hquid films are being developed for coupled and facHitated transport processes. 

Recently, attempts have been made to reduce the cost of palladium metal membranes by preparing composite membranes. In these membranes a thin selective palladium layer is deposited onto a microporous ceramic, polymer or base metal layer [19-21], The palladium layer is applied by electrolysis coating, vacuum sputtering or chemical vapor deposition. This work is still at the bench scale. 

Electroplating. Basically in electroplating, a substrate is coated with a metal or its alloy in a plating bath where the substrate is the cathode and the temperature is maintained constant Membranes from a few microns to a few millimeters thick can be deposited by carefully controlling the plating time, temperature, current density and the bath composition. Dense membranes made of palladium and its various alloys such as Pd-Cu have been prepared. Porous palladium-based membranes have also been made by deposition on porous support materials such as glass, ceramics, etc. 

Although some inorganic membranes such as porous glass and dense palladium membranes have been commercially available for some time, the recent escalated commercial activities of inorganic membranes can be attributed to the availability of large-scale ceramic membranes of consistent quality. As indicated in Chapter 2, commercialization of alumina and zirconia membranes mostly has been the technical and marketing extensions of the development activities in gas diffusion membranes for the nuclear industry. 

Thermal stability. Thermal stability of several common ceramic and metallic membrane materials has been briefly reviewed in Chapter 4. The materials include alumina, glass, silica, zirconia, titania and palladium. As the reactor temperature increases, phase transition of the membrane material may occur. Even if the temperature has not reached but is approaching the phase transition temperature, the membrane may still undergo some structural change which could result in corresponding permeability and permselectivity changes. These issues for the more common ceramic membranes will be further discussed here. 

The key problem of the cross-flow reactor is not how to construct an effective separation of the two flowing phases. It is instead connected with how to design the porosity and location of the catalytic active zones of the separating walls so that the transport resistance across the wall does not limit the conversion and the selectivity of the chemical reactions. Palladium-alloy membranes, or thin films of these alloys on porous ceramic tubs, seem to have the potential to be good solutions of the separating-wall problem for cross-flow reactors used for hydrogenation reactions. 

---