Palladium-based membranes Technologies

Examples of Up-scaled State-of-the-Art Palladium-based Membrane Technology... 

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. 

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. 

Arstad et al. [141] used a self-supported, Pd/(23 wt%) Ag-based MR (with a thickness of 1.6 pm) achieving 100.0% the production of pure hydrogen. Hence, the authors concluded that the low-thickness of the paUadium-based membrane can represent a fundamental step for reducing the palladium-cost and making competitive the hydrogen separation technologies by palladium-based membrane. 

Membrane Reactor Technologies Ltd (MRT) has experimentally verified the permeative-stage membrane reactor concept. With the membranes outside the reaetor, operation at more favorable conditions for both reaction (750 °C) and membrane separation (450 °C or lower) is possible. A decrease in the metal cost of palladium-based membranes by 86.5% and membrane area by >70% to aehieve equal hydrogen production capacity was reported. The volume of reformer decreases accordingly, thus, the costs of both the reactor and membrane module are reduced. 

Tong H D (2004), Microfabricated palladium-based membranes for hydrogen separation , PhD thesis. Transducers Science and Technology of the MESA+ Research Institute at the University of Twente, Enschede, Netherlands. 

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. 

An essential element of the Hysep technology is the use of thin film palladium composite membranes to enable low cost and reliable hydrogen separation. The supported palladium layer in the Hysep module has a thickness as low as 3-9 pm, a substantial improvement over current commercial available palladium membranes, which are based on self supporting metal foils with a thickness of 20-100 pm. 

Basic principles of hydrogen sorption in, and permeation through, palladium-based metallic membranes are then presented in Sections 18.3 and 18.4. Membrane characterization and performance are discussed in Section 18.5, and some applications are presented in Section 18.6. Finally, advantages and limitations of existing technologies are discussed in Section 18.7, and some prospective issues are considered. 

Barbieri et al. [146] developed a MR for the WGS reaction. A palladium/silver fihn containing 23 wL% silver, which had a thickness between 1 and 1.5 pm, v is prepared by sputtering and coated onto a porous stainless steel support. This preparation method generated a much higher ratio of pore size to fihn thickness compared to conventional methods. Tubular membranes of 13 mm outer diameter, 10 to 20 mm length, were fabricated. Commercial Cu-based catalyst from Haldor-Topsoe was introduced into the fixed bed. At reaction temperatures between 260 and 300 C, and a GHSV of 2085 h, the thermodynamic equilibrium conversion could be exceeded by 5-10% by the membrane technology. 

Ionic liquids have already been demonstrated to be effective membrane materials for gas separation when supported within a porous polymer support. However, supported ionic liquid membranes offer another versatile approach by which to perform two-phase catalysis. This technology combines some of the advantages of the ionic liquid as a catalyst solvent with the ruggedness of the ionic liquid-polymer gels. Transition metal complexes based on palladium or rhodium have been incorporated into gas-permeable polymer gels composed of [BMIM][PFg] and poly(vinyli-dene fluoride)-hexafluoropropylene copolymer and have been used to investigate the hydrogenation of propene [21]. 

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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