Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Utility Patent
1999-03-30
2001-01-02
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C095S045000, C096S010000, C096S011000
Utility Patent
active
06168650
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an apparatus for the purification of a constituent gas and also to the generation and the subsequent separation and purification of a constituent gas from a mixed gas flow. More specifically, the present invention relates to the generation of hydrogen or purification of hydrogen from a mixture containing hydrogen. The apparatus utilizes one or more gas extraction membrane for removing hydrogen or other extractable gas from a mixed gas flow.
BACKGROUND OF THE INVENTION
The common technology for extracting gases such as hydrogen from industrial streams, for use in the electronics industry for hydrogenation or for changing the balance of hydrogen in those streams is to use membranes. The membranes are disposed in a housing. A mixed gas flow is conducted to the housing wherein the extraction occurs. Extracted gas (such as hydrogen) is preferentially extracted through the membranes and exits through an outlet port. A second outlet allows for the exhaust of raffinate out of the chamber, Examples of such chambers are shown in U.S. Pat. Nos. 5,205,841, and 4,468,235.
Many protocols require the mixed gas to be at elevated temperatures. In such cases, heat is lost from the housing, through the housing walls or carried away with the extracted gas, thereby resulting in the loss of thermal efficiency of this system. Furthermore, heating methods currently in use tend to produce large thermal gradients, with the gas extraction membrane often being heated excessively in some areas and being under heated in other areas. The result of this is decreased flow rates and/or damage to the membranes. Johnson Matthey, Ltd., as used a system of multiple heaters and temperature controllers, but this approach is energy inefficient and does not control the temperature much better than the single heater as the multiple controllers often fight one another.
Raffinate flow control and safety are also problems with the currently available purification and generation systems. The inventor has observed an input gas explosion during hot start up. Similarly, explosive conditions can result from a cool down in air when the module, full of combustible gas, sucks air in through the raffinate port. In either case, an explosive mixture of air and gas mixture suddenly contacts a hot membrane and thus creates a serious danger. This danger is all the more severe if the present invention is used as a hydrogen generator to fuel a fuel cell, e.g., to run a car, because of the demanding operating environment and the variety of mechanical talent, and the desire for a unit than can be turned on or off instantly.
Pure gas suck-back can also ruin a membrane if the sucked-back gas has already been mixed with a component, like arsine, that can poison the membrane. Purified hydrogen is mixed with arsine in the manufacture of semiconductors.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a high temperature gas purification system including a housing, a gas heating means for heating a mixed gas flow within the housing and a gas extraction means for selectively passing therethrough a constituent gas from the mixed gas flow. An annulus surrounds the housing for insulating the housing by circulating the incoming mixed gas flow about the housing and then injecting the mixed gas flow into the housing for extraction by the gas extraction means. A second annulus is optionally provided to enhance the transfer of heat from the extracted gas to the incoming mixture.
The heating means includes a heating chamber disposed within the housing and in thermal contact with the gas extraction means. Alternatively, the heat is applied from outside of the annulus. The heat can be electrical, or steam, and includes the possibility of providing a fluid conduit for conducting raffinate from the gas extraction means to the heating chamber. In this case, the heating chamber contains a catalyst for reacting the raffinate (e.g., with air) to generate heat within the heating chamber. This set-up is particularly useful if the invention is used as a hydrogen generator, e.g., as a methanol or ethanol reformer, when combined with a suitable catalyst within the housing.
The housing includes an outlet for releasing raffinate mixed gas flow therethrough and flow restricting means of controlling raffinate movement out of the housing.
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Buxbaum, R.E. et al., “Hydrogen Transport Through Tubular Membranes of Palladium-Coated Tantalum and Niobium”, Industrial & Engineering Chemistry Research, vol. 35, No. 2, pp. 530-537, 1996.*
Gifford, Krass, Groh Sprinkle, Anderson & Citkowski, P.C.
Spitzer Robert H.
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