Palladium-based membranes development

The unusual interaction of hydrogen with palladium-based membrane materials opens up the possibility of oxidative hydrogen pump for tritium recovery from breeder blankets. The feasibility for this potential commercial application hinges on the hot-fusion and cold-fusion technology under development [Saracco and Specchia, 1994]. At first, Yoshida et al. [1983] suggested membrane separation of this radioactive isotope of hydrogen followed by its oxidation to form water. Subsequently, Hsu and Bauxbaum [1986] and Drioli et al. [1990] successfully tested the concept of combining the separation and reaction steps into a membrane reactor operation. 

Both theoretical and experimental studies have been performed on palladium-based membrane reactors for the water-gas shift reaction. Ma and Lund simulated the performance achievable in a high temperature water-gas shift membrane reactor using both ideal membranes and catalysts [18]. By comparing the results obtained with those related to the existing palladium membrane reactors, they concluded that better membrane materials are not needed, and that higher performances mainly depend on the development of a water-gas shift catalyst not inhibited by CO2. Marigliano et al. pointed out how the equilibrium shift conversion in membrane reactors is an increasing function of the sweep factor (defined as the ratio between the flow rate of the sweep at the permeate side and the flow rate of CO at the reaction side) [19]. The ratio is an index of the extractive capacity of the system. 

Development of Palladium-based Membranes and Stability Issues in Hydrogen Production... 

Another research field under development is based on MR technology. In particular, in recent years, palladium-based membrane technology has been widely studied both as a permeator and as in MRs. The latter allows combining hydrogen production and its separation in only one device with many benefits in terms of process intensification with respect to the conventional process. However, before addressing this topic, brief overviews on MSR kinetic and reforming catalyst are given. 

Klette, H., T. Peters, A. Mejdell, and R. Bredesen, Development of Palladium-Based Hydrogen Membranes for Water Gas Shift Conditions, Proceedings of Eight International Conference on Greenhouse Gas Control Technologies (GHGT-8), Trondheim, June 2006. 

R. Bredesen, Development of palladium-based hydrogen membranes for water gas shift conditions, Proceedings of the 8th International Conference on Greenhouse Gas Technologies (www.GHGT8.no), 20-23 June 2006, Trondheim, Norway. 

Because Pd-based metal membranes, commonly used for hydrogen separation [11] are not resistant towards sulphur, not much research has been performed on the use of such membranes in H2S dehydrogenation reactors. Some success has, however, been reported by Edlund and Pledger [12], They developed a platinum-based layered metal membrane that could resist irreversible attack by H2S at 700°C. At this temperature a conversion of 99.4% was achieved in the membrane reactor. Without hydrogen removal the conversion was only 13%. No permeance data is provided, but platinum-based metal membranes are known for their low hydrogen permeance [14], Johnson-Matthey developed palladium composite membranes with a hydrogen permeance of about 1 10 mol/m sPa [14], but these are most probably not resis-... 

Phair, J.W. and R. Donelson, Developments and design of novel (non-palladium-based) metal membranes for hydrogen separation. Industrial and Engineering Chemistry Research, 2006.45(16) 5657-5674. 

Non-palladium-based metal alloy materials are under development for reducing the cost, increasing the flux, and improving the durability of H2 separation membranes. 

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. 

Franz et al. [93] developed a palladium membrane micro reactor for hydrogen separation based on MEMS technology, which incorporated integrated devices for heating and temperature measurement. The reactor consisted of two channels separated by the membrane, which was composed of three layers. Two of them, which were made of silicon nitride introduced by low-pressure chemical vapor deposition (0.3 pm thick) and silicon oxide by temperature treatment (0.2 pm thick), served as perforated supports for the palladium membrane. Both layers were deposited on a silicon wafer and subsequently removed from one side completely... 

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