The field of the invention is gas separation by a barrier for selective diffusion of gases. The state of the art of dissociation of water vapor by thermal energy into hydrogen and oxygen followed by the separation of the hydrogen with a hydrogen permeable membrane is disclosed in U.S. Pat. Nos. 4,003,725; 4,019,868; and 4,053,576, the disclosures of which are incorporated herein and Technical Support Package TSP 75-10314 for NASA TECH BRIEF 75-10314 (MSC-12600) entitled "Using Permeable Membranes to Produce Hydrogen and Oxygen from Water," the disclosure of which is incorporated herein.
Solar heat is one of the ways used to thermally dissociate water vapor and this is disclosed in previously mentioned U.S. Pat. Nos. 4,019,868 and 4,053,576 and U.S. Pat. No. 4,030,890, the disclosure of which is incorporated herein. Other heat sources such as nuclear energy and electrical resistance furnaces are suitable for bringing water vapor to a dissociation temperature. TSP 75-10314 and U.S. Pat. No. 4,003,725 show resistance furnances suitable for the present invention.
That platinum, palladium and palladium alloy metal films are permeable to hydrogen and have been used as barriers for selective diffusion of hydrogen has been known, as disclosed by Kirk-Othmer "Encyclopedia of Chemical Technology", 2nd edition, vol. 15 (1968) under the section Platinum Group Metals, pages 832-860, particularly page 832 where the melting point of palladium is given as 1552.degree. C., pages 853 and 854 where the use of palladium and a 75% Pd-25% Ag alloy is disclosed for the separation of pure hydrogen from mixed gases by diffussion at a temperature of 350.degree. C. in tubes of the alloy with a wall thickness of about 0.003 inches and page 855 where electrodeposition of palladium is disclosed.
TSP 75-10314 discloses, among other things, the separation of hydrogen from oxygen and water vapor at temperatures of about 600.degree. C. to 950.degree. C. and pressures from about 5 mm Hg (0.1 psia) to 760 mm Hg (14.7 psia) using tubes of about 0.1 mm (0.004 inches) wall thickness as the diffusion membrane. This diffusion membrane was made from pure platinum, pure palladium, 75% palladium- 25% silver and 90% palladium-10% silver with 90% palladium-10% silver giving preferred results.
One of the many problems experienced by the prior art was to increase the surface area of contact at elevated temperatures between the platinum and palladium diffusion membranes and the dissociating water vapor or other hydrogen containing mixtures.
All prior art methods of producing hydrogen by dissociation of water vapor or from gaseous mixtures containing hydrogen have been limited by inability to separate large quantities of hydrogen from a mixture of hydrogen containing gas mixtures in a small space at elevated temperatures and at elevated pressures.