Nickel alloy membranes

J. N. Keuler, L. Lorenzen, R. D. Sanderson, V. Prozesky, W. J. Przybylowicz, Characterising palladium-silver and palladium-nickel alloy membranes using SEM, XRD and PIXE, Nucl. Instrum. Methods Phys. Res. B 1999, 158, 678-682. 

Concurrently in the U.S., membrane development efforts were sponsored and initiated by the Atomic Energy Commission for gaseous diffusion. Large scale plants were built at Oak Ridge (Tennessee) and subsequently at Paducah (Kentucky) and Portsmouth (Ohio) in the early 1950s with a total capacity of approximately 150 t/d processed. The confidential membranes are believed to be made of nickel and high-nickel alloys but other membrane materials possibly have also been considered. 

In a previous paper (2), the author described a method to dissolve the sulfonyl fluoride precursor form of a perfluorinated sulfonate ionomer. Commercially available forms of Nafion are supplied as activated membranes (i.e., saponified from the precursor to the ionic form), and near-quantitative reconstitution of the precursor functionality (such as RSOjF) must first be performed using a chemical reagent such as SF. f4) before dissolution in perhalogenated solvents is possible. Besides adding to the cost of membrane manufacture, SF. is extremely toxic and corrosive and must be handled in nickel alloy pressure equipment. Therefore, a method for dissolving perfluorinated ionomers directly would be more desirable. 

For a well designed membrane module of reasonably large scale, the initial cost should be dominated by the cost of the palladium content of the thin metal membrane (assuming a palladium alloy comprises the permselective layer). The module itself will be made of steel, most likely a nickel alloy, with or without significant chromium addition. The cost of the steel and the assembly labor should not exceed the cost of the palladium alloy membrane. 

The current collector is made of a material that resists the corrosive action of sulfuric acid, which may contact the collector in the event of a discontinuity in the membrane, such as a pinhole or crack, formed during fabrication, handling, or operation. Suitable materials capable of operating at 60 - 70 °C are nickel alloys. With optimized assemblies (DAP, De Nora Permelec, Milan, Italy), overall anodic overvoltages of 0.1-0.2 V at 3000 A/m are obtained. 

Conventional production of vitamin K consists of four steps hydrogenation of 2-methylnaphthoquinone-l,4 to 2-methylnaphthohydroquinone-l,4 in a solvent in the presence of Raney nickel separation of the product from the catalyst by filtration evaporation of the solvent and boiling with acetic anhydride. Because the anhydride is highly corrosive, it tends to attack the nickel, and hence complete separation of the catalyst is necessary. On the other hand, use of a palladium alloy membrane reactor eliminates corrosion and makes it possible to complete the whole process in a single step (Gryaznov et al., 1986). The overall reaction is... 

The cathode in diaphragm and membrane cells has been steel where the hydrogen overpotential is about 400 mV. Coatings of nickel alloys are now available which decrease this overpotential to 150—200 mV and there are expectations that improvements in the catalytic coating will reduce it further to 20—50 mV. Such cathode coatings will again substantially improve the energy consumption of the industry. 

INEOS chlor offers both precious metal and nickel alloy coatings [192]. The precious metal coatings are deposited on a nickel substrate, and the electrocatalytically active layers are applied to the smface by thermal deposition or electroplating. Thermal spraying or vacuum deposition techniques form the nickel-alloy coating. These materials have been used in the FM 21 electrolyzers for over four membrane cycles. 

Corrosion of steels and nickel alloys in NaOH and KOH solutions is promoted by OQ . Even one ppm of OCl in NaOH will promote the corrosion process, which leads to dendritic growth of oxides of Fe, especially in stressed areas. Such a process in membrane cells fitted with steel cathodes can lead to the puncturing of the membranes. TTie only way to prevent such an event is to add a reducing agent (e.g., H2O2 or Na2S03> to remove the OQ during shutdowns. 

More recently the problem of overpotential for H2 evolution on the cathodes of membrane (and diaphragm cells has been attacked. Traditionally the cathode is made of steel (overpotential 400 mV) but coatings based on high area nickel alloys have been developed which reduce the overpotential to 80-120 mV. 

Guryanova, O. S., Y. M. Serov, S. G. Gul yanova and V. M. Gryaznov. 1988. Conversion of carbon monoxide on membrane catalysts of palladium alloys Reaction between CO and H2 on binary palladium alloys with ruthenium and nickel. Kinet. and Catal. 29(4) 728-731. 

The MCFC membrane electrode assembly (MEA) comprises three layers a porous lithiated NiO cathode structure and a porous Ni/NiCr alloy anode structure, sandwiching an electrolyte matrix (see detail below). To a first approximation, the porous, p-type semiconductor, nickel oxide cathode structure is compatible with the air oxidant, and a good enough electrical conductor. The nickel anode structure, coated with a granular proprietary reform reaction catalyst, is compatible with natural gas fuel and reforming steam, and is an excellent electrical conductor. As usual, the oxygen is the actual cathode and the fuel the anode. Hence the phrase porous electrode structure . 

As mentioned earlier, two compatible reactions may be coupled or conjugated properly by a shared membrane through which the species (as a product on one side of the membrane and a reactant on the other) common to both reactions selectively passes. Summarized in Table 8.5 are some documented studies of reaction coupling using dense palladium-based membranes with the alloying component ranging from nickel, ruthenium, rhodium to silver. 

Fumeaux et al. [1987] used porous alumina membrane reactors to hydrogenate ethene to form ethane at 200X with Ft or Os as the catalyst impregnated in the alumina membranes. Conversion to ethane was detected but no data was provided. Suzuki [1987] tested porous stainless steel and nickel-aluminum alloys as membrane reactors for hydrogenation reactions. Hydrogenation of 2-butenc with stainless steel as the membrane... 

On the metallic membrane side, a well known type of material with this characteristic is Pd and certain Pd alloys. Palladium is known to be catalytic to many reactions including oxidation, hydrogenation and hydrocracking. It has been found that the catalytic activity of selected binary Pd alloys is higher than that of pure Pd. Silver catalyzes a number of oxidation reactions such as oxidation of ethylene and methanol. In addition, nickel is catalytic to many industrially important reactions. 

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