Gas separation: processes – Selective diffusion of gases – Selective diffusion of gases through substantially solid...
Reexamination Certificate
2000-11-30
2002-08-27
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Selective diffusion of gases
Selective diffusion of gases through substantially solid...
C095S047000, C095S051000, C095S052000, C095S054000, C095S090000, C095S114000, C095S127000, C096S004000, C096S122000, C096S126000, C096S130000, C096S143000
Reexamination Certificate
active
06440196
ABSTRACT:
DESCRIPTION
The present invention relates to a method for purifying and concentrating a gas mixture into a minority constituent, to a method for detecting this constituent and to an installation for the application of this method.
More precisely, the invention concerns a method for purifying a first minority constituent and concentrating the latter into the majority constituent of a gas mixture containing, in addition to said first minority constituent and said majority constituent, one or more other minority constituents, in order to obtain an end gas mixture highly enriched in said first minority constituent relative to the initial gas mixture.
The treated gas mixture is in particular atmospheric air of which it is desired to concentrate some of the rare gases, in particular Xenon and especially the natural and radioactive species of Xenon.
The invention associated with nuclear spectrometry therefore finds application in the detection of these species, little abundant in the atmosphere, and in monitoring the environment of nuclear installations.
The literature cites different in situ methods for extracting minority constituents from a gas mixture, for example rare gases and especially Xenon from air, for the purposes of detection in particular.
The first method envisaged was the distillation of liquefied air, as described in the document by Y. V. Bubasov, Y. S. Popov, “Technical means of radioactive inert gas monitoring for detection of underground nuclear explosions”, Khiopin Radium Institute, St. Petersburg, Russia.
Said method requires large-scale installations and considerable energy consumption to bring the air to its point of liquefaction.
A method was subsequently put forward which uses physical adsorption on solid substrates at very low temperature, as described in the document by I. Vintersved, L. E. De Geer, “Swedish experience of radionuclide monitoring”, IAEA meeting in Helsinki Dec. 10-12, 1996 on Long Range Wide Area Environmental Monitoring, and in the document by T. W. Bowyer, K. H. Abel, “Automatic Radioxenon Analyzer for CTBT Monitoring”, report PNNL-11 424, UC-713, November 1996, prepared for the U.S. DOE.
This method consists of fixing, one by one, the different minority constituents of air, at low and very low temperature, on specific solid substrates such as zeolite, activated carbon, silica gel. In this manner successive removal is made of water vapour, carbon dioxide then Radon and finally the Xenon is trapped.
This method has the disadvantage of operating at temperatures generally in the vicinity of −110° C. requiring the application-of cryogenic techniques which go hand in hand with complex installations and high energy consumption.
Also, the functioning of the system is frequently disturbed by the formation of blockages due to freezing of the water in one of the adsorbents.
This method operates using a series of adsorbents of which each one is dedicated to the adsorption of one of the initial air constituents.
It is therefore necessary to have recourse to a considerable number of substrates or adsorbents, and moreover, since each adsorption stage is applied to all or almost all of the initial volume of air, and since the volumes of minority gases removed such as carbon dioxide and water are very high, the volume of the adsorption substrates is also high.
The considerable volume of the adsorption substrates requires an installation of proportional volume and leads to difficulties during the regeneration of these voluminous substrates by heating and passing an elution gas, which require long time periods, considerable energy consumption and substantial quantities of eluting agent.
A need therefore exists for a method of separating the constituents of a gas mixture which uses a limited number of steps, adsorption steps in particular, which may be applied under a reduced volume, which operates at a temperature close to ambient temperature without having recourse to a large-scale, energy-consuming cryogenic system, which is simple to implement and which allows substantial volumes of gas to be treated.
The purpose of the invention is to provide a method which, among others, meets these needs and which does not have the disadvantages, limitations, defects and drawbacks of the methods of the prior art and which solves the problems raised by the methods of the prior art.
This purpose, and others, are achieved according to the invention by a method for purifying a first minority constituent and concentrating the latter in the majority constituent of a gas mixture which, in addition to this first minority constituent and said majority constituent, contains one or more other minority constituents, said method comprising the succession of following steps:
Selective permeation of said initial gas mixture through a selective permeation membrane specific to the treated gas mixture, after which a gas mixture is obtained which is enriched in said first minority constituent and much depleted or scarcely enriched in said other minority constituent(s),
Purifying said gas mixture enriched in said first minority constituent, derived from the first step, by adsorption at ambient temperature on a solid absorbent, followed by elution, after which a gas mixture is obtained that is essentially made up of said majority constituent and said first minority constituent and from which the other minority constituent(s) have been removed,
Concentrating said first minority constituent in the majority constituent derived from step two by successive adsorption(s) and elution(s) on a solid adsorbent until an end gas mixture is obtained essentially made up of said majority constituent and said first minority constituent, highly enriched in said first minority constituent relative to the initial gas mixture, and having the desired concentration of said first minority constituent.
The invention therefore consists of the association, combination, or coupling of two gas separating techniques, firstly selective permeation through the wall, especially polymer wall, of a membrane specific to the treated gas mixture, and secondly adsorption of the gases on a solid substrate.
The coupling, according to the invention, is neither described, nor suggested in the prior art, or else for similar purposes the described methods use only a single separation technique, namely either distillation, of liquefied air for example, or adsorption, on several specific adsorbents.
Through the method of the invention, and through the coupling of the two techniques used by the method, it is no longer necessary to have recourse to liquefaction of the gas mixture such as air, and the cost of a large-scale cryogenic system is therefore avoided.
The selective permeation membrane continuously and without regeneration produces a gas mixture enriched in the desired minority constituent and much depleted in other minority constituent(s).
On this account, the number of solid adsorbents used in the following steps, purification and concentration according to the invention, is much reduced compared with the considerable number of adsorbents required in the second method of the prior art in which each of the different minority constituents of the gas mixture is fixed one by one, each time on a specific substrate.
In other words, with the membrane it is possible to overcome the need for the series of adsorbents used in the methods of the prior art which are intended to trap all the gases whose freezing points are higher than that of the desired gas such as Xenon in the case of air.
The volume of the substrates used for adsorption in the purification and concentration steps also comes to be considerably reduced, which facilitates their regeneration and reduces energy consumption during desorption, generally conducted by heating, as well as the volumes of gas used for elution.
Moreover, the volume of constituents to be fixed by adsorption, due to the prior membrane step, is greatly reduced compared with the prior art.
Subsequently, the adsorption operations are, according to the invention, generally conducted at ambient temp
Chiappini Remo
Fontaine Jean-Pierre
Hamonet Michel
Thouard Michel
Burns Doane , Swecker, Mathis LLP
Commissariat a l'Energie Atomique
Spitzer Robert H.
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