Palladium film membrane

Metallic Palladium films pass H9 readily, especially above 300°C. Ot for this separation is extremely high, and H9 produced by purification through certain Pd alloy membranes is uniquely pure. Pd alloys are used to overcome the ciystalline instability of pure Pd during heat-ing-coohng cycles. Economics limit this membrane to high-purity apphcations. 

The separation factors are relatively low and consequently the MR is not able to approach full conversion. With a molecular sieve silica (MSS) or a supported palladium film membrane, an (almost) absolute separation can be obtained (Table 10.1). The MSS membranes however, suffer from a flux/selectivity trade-off meaning that a high separation factor is combined with a relative low flux. Pd membranes do not suffer from this trade-off and can combine an absolute separation factor with very high fluxes. A favorable aspect for zeoHte membranes is their thermal and chemical stability. Pd membranes can become unstable due to impurities like CO, H2S, and carbonaceous deposits, and for the MSS membrane, hydrothermal stability is a major concern [62]. But the performance of the currently used zeolite membranes is insufficient to compete with other inorganic membranes, as was also concluded by Caro et al. [63] for the use of zeolite membranes for hydrogen purification. 

Palladium catalysts, 10 42 14 49 16 250 Palladium-catalyzed carbonylation, 13 656 Palladium chloride/copper chloride, supported catalyst, 5 329 Palladium compounds, 19 650-654 synthesis of, 19 652 uses for, 19 653-654 Palladium films, 19 654 Palladium membranes, 15 813 Palladium monoxide, 19 651 Palladium oxide, 19 601... 

The term composite membrane, as defined in membrane technology, refers to membranes with two or more distinct layers. A layer within a composite membrane could itself be a composite material possessing two or more distinct components, as in membranes employing a layer of palladium cermet (ceramic-metal) supported by a layer of porous ceramic. The layers need not be composite, as in membranes using films of palladium on both sides of foils of niobium, tantalum, vanadium or zirconium. 

Thorough cleaning and the avoidance of any extraneous debris are essential in any membrane fabrication scheme. After EP, a composite membrane can be soaked in hot water or dilute ammonia to help remove any impurities trapped in the porous support that may be detrimental to the palladium film during high temperature operation [72, 73]. However, traces of impurities from the EP bath such as chlorine, sodium, and carbon, inevitably become incorporated into the metal film. Membrane defects can be a consequence of preparation conditions. Fabrication in a dean-room environment has resulted in increased permselectivity [140]. Porous stainless steel (PSS) must be cleaned and pickled before electrodeposition or else activated for electroless plating. 

C. Su, T. Jin, K. Kuraoka, Y. Matsumura, T. Yazawa, Thin palladium film supported on Si02-modified porous stainless steel for a high-hydrogen-flux membrane, Ind. Eng. Chem. Res. 2005, 44(9), 3053-3058. 

BasUe et aL [116] studied the WGS reaction using a MR consisting of a composite palladium-based membrane realized with an ultrathin palladium film ( 0.1 pm) coated on the inner surface of a porous ceramic support (y-Al203) by the co-condensation technique. The authors pointed out the benefit of applying a palladium MR, taking into account that, at 320°C and 1.1 bar, the thermodynamic equilibrium of CO conversion is around 70%, while the authors obtained with the MR CO conversion of around 100%. Moreover, the same authors illustrated that a complete CO conversion could be reached by using a composite membrane with a thinner palladium layer (10 pm Pd film coated on a ceramic support) [117]. 

In the MOC concept, the porous support itself has the function of reforming catalyst in addition to the role of membrane-support. The integrated structure of support and catalyst makes the membrane reformer more compact since separate catalysts placed around the membrane modules in the conventional membrane reformers can be eliminated. With relative ease, a thinner palladium film on the porous support can be made and the manufacturing process is appropriate to a mass production system, which will lead to significant reduction of module production cost. 

Kirchner, A., Brown, I.W.M., Bowden, M.E., Kemmitt, T. (2007b). Hydrogen Purification using Ultra-thin Palladium Films supported on Porous Anodic Alumina Membranes, in Functional Nanoscale Ceramics for Energy Systems, ed. E. Ivers-Tiffee and S. Barnett (Mater. Res. Soc. Symp. Proc. 1023E, Warrendale, PA, 2007), Paper 1023-JJ09-02. 

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