Coating processes – Vacuum utilized prior to or during coating
Patent
1996-02-26
1999-11-09
Langel, Wayne
Coating processes
Vacuum utilized prior to or during coating
96 11, 96 12, 4274431, B01D 6700, B01D 6900
Patent
active
059809892
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a gas separator for separating a specific gas from a mixed gas by diffusion, and a method for preparing the same.
BACKGROUND ART
Heretofore, as a technique for obtaining a specific gas from a mixed gas, there is known a separation method by the use of an organic or an inorganic gas separating film. Among the separating films, examples of a hydrogen separating film for use in a film separation method include organic polymeric films of polyimide, polysulfone and the like, and inorganic compound films of palladium, palladium alloys and the like, and examples of an oxygen separating film include films of silver and silver alloys. The palladium film and the palladium alloy films have heat resistance and can obtain extremely high-purity hydrogen.
Palladium and the palladium alloys have characteristics which allow hydrogen to be dissolved therein and which allow hydrogen to permeate therethrough, and by the utilization of the characteristics, a thin film comprising palladium or the palladium alloy has been widely used as a gas separator for separating hydrogen from a mixed gas containing hydrogen. However, the thin film comprising palladium itself is weak in mechanical strength, and so, in Japanese Patent Application Laid-open No. 273030/1987, palladium or the palladium alloy is deposited on the surface of an inorganic porous support of a porous glass, porous ceramics, a porous aluminum oxide or the like to increase the mechanical strength of the thin film comprising palladium or the palladium alloy.
Japanese Patent Application Laid-open No. 146122/1991 discloses a method for preparing a hydrogen separator which comprises first forming a palladium thin film on the surface of a heat-resistant porous substrate by a chemical plating process, and further forming a silver thin film on the palladium thin film by the chemical plating process, followed by a heat treatment. According to this disclosed method, the hydrogen separator having the porous substrate and the palladium alloy thin film covering it can be obtained. In this palladium alloy thin film, palladium and silver are uniformly distributed by the above-mentioned heat treatment.
In addition, U.S. Pat. No. 3,359,705 discloses a silver thin film for separating oxygen.
However, these gas separators have a drawback that a material gas to be subjected to the gas separation leaks into a purified gas through holes (hereinafter referred to as "throughhole-defects") which extend through the gas separating film comprising the metal for separating the gas. Therefore, the concentration of hydrogen in the purified gas deteriorates as much as the leaked material gas. For example, Japanese Patent Application Laid-open No. 273030/1987 discloses a method for preparing a hydrogen separating film using palladium or the palladium alloy in which the surface of an inorganic porous material is chemically activated, and the palladium thin film is then deposited thereon by the chemical plating process. However, the palladium film formed by the chemical plating process has the holes extending through the palladium film, and the material gas inconveniently flows into the purified gas through these holes. In the method disclosed in this publication, the palladium film is formed on the surface of the porous material, but this palladium film is not formed in the pores.
Furthermore, in Japanese Patent Application Laid-open No. 171617/1988, there is disclosed a method for preparing a hydrogen separating film in which palladium is supported on an inorganic porous film, and this method comprises vapor-depositing palladium or the palladium alloy on the inorganic porous film by sputtering or the like, immersing it in an aqueous [Pd(NH.sub.3).sub.4 ]Cl.sub.2 solution, and then carrying out a vacuum deaeration treatment via the inorganic porous film to vaporize a solvent, thereby supporting palladium on the inorganic porous film. However, according to an example, this hydrogen separating film allows not only hydrogen but also nitrogen to permeate
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Industrial and Engineering Chemistry Research, "Thin palladium membrane formed in support pores by metal organic chemical vapor deposition . . . " vol. 33, No. 3, 1994, Mar. 1994.
Uemiya, S., et al. "A Palladium/Porous-Glass Composite Membrane . . . ", Chemistry Letters, 1988, pp. 1687-1690, Mar. 1988.
Patent Abstracts of Japan, vol. 012, No. 159 (C-495), May 14, 1988, & JP 62 273029 A (ISE Kagaku Kogyo KK), Nov. 27, 1987.
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Kosaka Shinichi
Takahashi Tomonori
DiMauro Peter
Langel Wayne
NGK Insulators Ltd.
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