Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
1999-09-08
2001-07-31
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C096S010000, C096S011000, C055SDIG005
Reexamination Certificate
active
06267801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing a hydrogen permeation membrane, the hydrogen permeation membrane so produced, and the use of such a hydrogen permeation membrane.
2. Background Information
The peculiarity of palladium, as well as platinum to a considerably lesser extent, of enabling the rapid permeation of hydrogen, but of no other gas, although a membrane of this metal has long been known. In this way, hydrogen can be separated from other gases.
Hydrogen permeation cells that are used to produce hydrogen of the highest purity, have already been known for several decades. In these cells, a palladium alloy is typically used as the membrane. A construction made of tubules which are fixed on one end on a perforated plate (for instance by soldering) and are welded closed, but not fixed on the other has proved to be especially advantageous. The reason why this construction has proved itself especially advantageous in industry is that the palladium material, on absorbing hydrogen, expands, and thus if the tubules were fixed at both ends or if a plane foil were fastened in a rigid frame, would lead to a hydrogen-dictated expansion and thus to the occurrence of stresses and deformation in the palladium membrane, which would quickly cause tearing and porosity.
U.S. Pat. No. 5,215,729 discloses among other subjects a membrane for extracting hydrogen from hydrogen-containing fluid streams; it substantially comprises a first non-porous layer of a refractory metal and a second non-porous layer which is located directly on the first layer; the second layer substantially comprises palladium, palladium alloys, platinum, or platinum alloys. Tubes of small diameter are coated on the inside and outside with a suitable second layer by means of a special sputtering technique.
U.S. Pat. No. 3,350,846 discloses among other subjects a method of sputtering and vapor deposition of palladium onto niobium, vanadium and tantalum surfaces.
These methods known from the prior art can be employed, however, only for relatively large tubes (with an inside tube diameter of at least 25 mm).
It is also known that platinum can be precipitated out of a plurality of different baths either galvanically or currentlessly. Most often, baths on the basis of a palladium complex, palladium diaminodichloride (Pd(NH
3
)
2
Cl
2
) are used. With such baths, however, it is virtually impossible to coat the inside surface of tubes, especially tubes with a small inside diameter (maximum inside tube diameter of approximately 25 mm) of easily electroplatable materials. The problems reside both in the delivery of material from the electrolyte within the limited internal space in the tube and also the establishment of uniform electrical fields for the metal deposition in the tube. Furthermore, even under optimal conditions, the refractory metals are very difficult to coat using electroplating methods, since both in air and in contact with aqueous solutions, a thin, firmly adhering and nonconductive surface oxide film forms, which hinders the direct metal-to-metal contact between substrate and coating.
In physical deposition from the vapor phase by vapor deposition or sputtering, two problems arise. First, the vapor deposition material or the sputtering target must be positioned centrally in the tube, and from there must be applied to the inside of the tube by heating or by being bombarded with noble gas ions. Such methods are known for large tubes (inside tube diameter of approximately 100 mm), but not for smaller tubes. Second, the oxide barrier layer on the surface of the refractory metal (refractory metals or metals of the fourth and fifth secondary groups of the Periodic System of Elements) must be removed before the coating process. Normally, such layers are removed by “sputtering off”, in which the oxide film is removed by being bombarded with noble gas ions. This process is not possible in the interior of a small tube (inside tube diameter less than 25 mm).
For the above reasons, it is not possible with methods known from the prior art to satisfactorily coat the inside of tubes of refractory metals having a small inside diameter (inside diameter of less that 25 mm) with palladium, a palladium alloy, platinum, or a platinum alloy.
SUMMARY OF THE INVENTION
Based on the above discussion, it is an object of the present invention to overcome the above disadvantages, at least in part, with the aid of a novel method, a novel membrane, and the use thereof. The resultant object is particularly to furnish tubes, which comprise at least one metal of the fourth and fifth secondary groups of the Periodic System of Elements (“PSE”) and have small inside diameters (less than 25 mm) that are coated with palladium, a palladium alloy, platinum, or a platinum alloy, at least on the inside of the tube as well, with satisfactory quality.
According to the invention, this object is attained by a method of producing a membrane, a membrane itself and a method of use of the membrane as described hereinbelow.
In the method of producing a tubular hydrogen permeation member according to the present invention, first a one- or two-sided coating (layering) of a plate-like base metal or base metal alloy body is performed. This body contains at least one metal from the fourth or fifth secondary groups of the Periodic System of Elements (“PSE”). The coating (layer) contains at least palladium, at least one palladium alloy, platinum, or at least one platinum alloy, or preferably consists of at least one of these materials.
After the coating (layering), the plate-like coated molded part (layered plate) is reshaped (shaped) into a tubular hydrogen permeation membrane.
More particularly, the present invention concerns a method for producing a tubular hydrogen permeation membrane comprising:
(a) adhering at least one layer containing palladium, at least one palladium alloy, platinum, or at least one platinum alloy to a first surface of a plate (or blank) having such first surface and a second surface disposed opposite to the first surface, the plate being of a metal or a metal alloy containing at least one metal from a group of the Periodic System of Elements selected from the group consisting of the fourth secondary group and the fifth secondary group, to form a layered plate; and
(b) reshaping the layered plate into a tubular hydrogen permeation membrane having an inside wall, so that the layer adhered to the first surface is disposed on the inside wall of the tubular hydrogen permeation membrane.
The at least one layer can also be adhered to the second surface of the plate.
DETAILED DESCRIPTION OF THE INVENTION
The plate is made of a metal or metal alloy, wherein the metal is at least one metal selected from the group consisting of the fourth secondary group of the Periodic System of Elements (such as titanium, zirconium and hafnium) and the fifth secondary group of the Periodic System of Elements (such as vanadium, niobium and tantalum).
An essential feature in the method of producing a tubular hydrogen permeation member according to the present invention is that first a coating (layer) of the above composition is applied to an as yet not tubular, but rather plate-like body of the above metal composition, and only after that is a corresponding tubular reshaping (shaping) of the molded part done. This sequence assures that there are no weld seams in the tubes. The otherwise conventional making of round shapes from coated strips and the ensuing welding, in which the coating is lost in the welded zone, is thus dispensed with.
It is thus possible in this elegant way to produce seamless tubes of appropriate composition, which are coated with palladium, a palladium alloy, platinum, or a platinum alloy, in which the inside diameter of the tubes can be only a few millimeters. As a rule, the wall thickness of the tubes is approximately 0.1 to 10.0 mm.
In the method of producing a tubular hydrogen permeation member according to the present invention, it is advantageous if the coating (layering) is
Baake Reinhard
Lupton David Francis
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Spitzer Robert H.
W. C. Heraeus GmbH & Co. KG
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