METHOD FOR SEPARATING, ENRICHING AND RECOVERING OF HE-3 FROM HE-4 AND USE OF THE SEPARATED, ENRICHED AND RECOVERED HE-3

Abstract

The invention relates to a method for removing, enriching, and acquiring the isotope .sup.3He relative to the isotope .sup.4He, comprising steps as follows: a) performing adsorption of a .sup.3He/.sup.4He-containing gas onto an adsorbent, and b) performing selective desorption, so that .sup.3He is released from the adsorbent.

The invention further relates to use of the removed, enriched, and acquired isotope .sup.3He obtained by means of the method for generating a temperature in the range from 0.01 to 0.05 K, preferably of 0.02 K, or as a contrast agent for nuclear spin tomography images.

Claims

1. A method for removing, enriching, and acquiring the isotope .sup.3He relative to the isotope .sup.4He, comprising steps as follows: a) performing adsorption of a .sup.3He/.sup.4He-containing gas onto an adsorbent, and b) performing selective desorption, so that .sup.3He is released from the adsorbent.

2. The method as claimed in claim 1, wherein step a) comprises performing the adsorption with activated carbon as the adsorbent at a temperature in the range from 5 K to 12 K, preferably in the range from 7 K to 11 K, more preferably at a temperature of 11 K.

3. The method as claimed in claim 1, wherein step a) is performed in such a way that no gaseous phase is left.

4. The method as claimed in claim 1, wherein step b) comprises gradually heating the adsorbent from a temperature in the range from 5 K to 12 K, preferably 7 K to 11 K, more preferably 11 K, to a temperature in the range from 13 K to 40 K, preferably 15 K to 25 K, more preferably 18 K to 21 K.

5. The method as claimed in claim 1, wherein step a) comprises ionizing and injecting the .sup.3He/.sup.4He-containing gas into an ion getter as the adsorbent at a temperature in the range of 280 K to 315 K, preferably 285 K to 305 K, more preferably 290 K to 295 K.

6. The method as claimed in claim 5, wherein the ion getter comprises a metal, preferably barium, more preferably titanium.

7. The method as claimed in claim 5, wherein step b) comprises gradually heating the adsorbent from a temperature up to a range from 500 K to 700 K, preferably 550 K to 650 K, more preferably 575 K to 625 K.

8. The method as claimed in claim 1, comprising a step c) of transferring the .sup.3He released in step b) into an isolated reservoir.

9. The method as claimed in claim 1, wherein steps a) and b) and, if dependent from claim 8, step c) are multiply repeated.

10. The method as claimed in claim 1, wherein the .sup.3He/.sup.4He-containing gas mixture obtained according to step b) comprises an at least 1.2-fold, preferably at least 1.5-fold, enrichment of .sup.3He relative to the .sup.3He/.sup.4He-containing gas mixture used in step a).

11. The method as claimed in claim 1, wherein the .sup.3He/.sup.4He ratio in the gas phase in step b) is measured continuously by means of a mass spectrometer (10).

12. The use of the removed, enriched, and acquired isotope .sup.3He obtained by means of the method as claimed in claim 1 for generating a temperature in the range from 0.01 to 0.05 K, preferably of 0.02 K, or as a contrast agent for nuclear spin tomography images.

Description

[0027] The invention is additionally elucidated in more detail below in relation to figures and an example. Schematically and not to scale,

[0028] FIG. 1 shows an outline representation of a plant in which a method according to a first embodiment is carried out; and

[0029] FIG. 2 shows an outline representation of a further plant, in which a method according to a second embodiment is carried out.

[0030] FIG. 1 shows an outline representation of a plant in which a method according to a first embodiment is carried out. The method is practiced on a .sup.3He/.sup.4He-containing gas, which is a naturally occurring gas in the form of a gas mixture. The natural gas is supplied to the plant via a gas inlet 1, which comprises multiple valves 2 for shutting off or controlling a flow of the naturally occurring gas through the plant. The plant optionally comprises a Pirani measurement branch 8 for the pressure measurement of coarse and/or fine vacuum. In addition, optionally, the plant comprises facilities for removing extraneous gases from the .sup.3He/.sup.4He-containing gas, so that the method of the invention is practiced on a mixture of .sup.3He/.sup.4He in high purity, in which Ne (neon) is the only extraneous gas. For the removal of the extraneous gases with the exception of Ne, there are activated carbon traps 9, a cold trap 7, getters 3 (e.g., Ti getters), SAES getters and/or SAES pumps 4 and further SAES getters and/or SAES pumps 5, which are available commercially from SAES (Societa Apparecchi Elettrici e Scientifici (Lainate, Italy); the extraneous gases may be, for example, water vapor, N.sub.2 (nitrogen), O.sub.2 (oxygen), H.sub.z(hydrogen), CO.sub.2 (carbon dioxide), hydrocarbons, Ar (argon), Kr (krypton) and/or Xe (xenon). The method of the invention comprises performing adsorption of a .sup.3He/.sup.4He-containing gas on an adsorbent and is performed in a cooling head 6 charged with activated carbon.

[0031] The activated carbon is the adsorbent. The adsorption with activated carbon as the adsorbent in the cooling head 6 charged with activated carbon is performed at a temperature of 11 K, for example. The adsorption is performed in such a way that no gaseous phase is left. Following the adsorption, a selective desorption is carried out, so that .sup.3He is released from the adsorbent. As a result, the .sup.3He is removed from the .sup.4He, enriched, and acquired. The selective desorption is accomplished by gradual heating of the adsorbent, i.e., the activated carbon, from the temperature of 11 K to a temperature of 20 K, for example. Under these conditions, Ne remains adsorbed on the adsorbent.

[0032] The .sup.3He/.sup.4He ratio may be measured continuously by means of a mass spectrometer 10. The .sup.3He-enriched gas fraction released is transferred into an isolated reservoir. The adsorption and selective desorption with the gas fraction removed in the preceding step with preferably high .sup.3He/.sup.4He ratio and preferably large gas quantity may be performed with multiple repetition, so that .sup.3He is further enriched relative to .sup.4He and acquired.

[0033] FIG. 2 shows an outline representation of a further plant, in which a method according to a second embodiment is carried out. The further plant shown in FIG. 2 corresponds to the plant shown in FIG. 1, with the difference that it comprises an ion getter pump 11 instead of the cooling head charged with activated carbon. The ion getter comprises a metal such as titanium. The method according to the second embodiment comprises the adsorption of a .sup.3He/.sup.4He-containing gas on an adsorbent and the selective desorption, so that .sup.3He is released from the adsorbent; the adsorption is performed by means of ionizing and injecting the .sup.3He/.sup.4He-containing gas into an ion getter as the adsorbent at a temperature which is, for example, room temperature. The selective desorption is realized by gradual heating of the adsorbent, i.e., the ion getter, to a temperature of, for example, 600 K. The .sup.3He-enriched gas fraction released by means of the desorption is transferred into an isolated reservoir. The adsorption and selective desorption with the gas fraction removed in the preceding step with the highest .sup.3He/.sup.4He ratio may be performed with multiple repetition, so that .sup.3He is further removed and enriched relative to .sup.4He and acquired.

EXAMPLE

[0034] A single-stage test series was performed using a naturally occurring gas freed from extraneous gases, in the form of a gas having a .sup.3He/.sup.4He ratio of (21.660.24)10.sup.6, which corresponds to a typical value for a gas resulting from hot-spot volcanism.

[0035] First, adsorption of the .sup.3He/.sup.4He-containing gas on an adsorbent in the form of activated carbon was performed. The adsorption with activated carbon as the adsorbent may be performed, for example, in the cooling head charged with activated carbon that is shown in FIG. 1, at a temperature of 11 K, so that no gaseous phase is left. Following the adsorption, a selective desorption is carried out, so that .sup.3He is released from the adsorbent. The selective desorption is realized by gradual heating of the adsorbent, i.e., the activated carbon, from the temperature of 11 K to a temperature of, for example, 20 K. The gradual heating may be carried out in 5 K steps, for example. Under these conditions, Ne remains adsorbed on the adsorbent. A .sup.3He/.sup.4He ratio may be measured continuously by means of the mass spectrometer shown in FIG. 1.

[0036] The helium isotopes were measured in a VG5400 90-sector mass spectrometer from Vacuum Generators Instruments, now Thermo Fisher Scientific (Waltham, USA). Table 1 shows .sup.4He signals and measured .sup.3He/.sup.4He ratios with 2sigma error of the desorbed gas phase at different temperatures:

TABLE-US-00001 Temperature (K) He (volts) .sup.3He/.sup.4He (10.sup.6) 15 0.001278 34 14 20 0.076970 34.5 1.3 25 0.97230 24.82 0.52 30 0.86159 17.71 0.40 35 0.115312 15.98 0.67 40 0.008314 16.6 3.2

[0037] At a temperature of 20 K, in particular, .sup.3He was enriched 1.5-fold relative to .sup.4He. In particular, the gas fraction enriched in .sup.3He at 20 K was transferred into an isolated reservoir. A further enrichment in .sup.3He can be achieved by optimizing the step increment and by multistage isotopic separation, i.e., repetition of the absorption and selective desorption of the gas fraction removed in the preceding step, with preferably high .sup.3He/.sup.4He ratio and preferably large gas quantity.

LIST OF REFERENCE SIGNS

[0038] 1 gas inlet [0039] 2 valve [0040] 3 getter [0041] 4 SAES pump [0042] 5 further SAES pump [0043] 6 cooling head charged with activated carbon [0044] 7 cold trap [0045] 8 Pirani measurement branch [0046] 9 activated carbon trap [0047] 10 mass spectrometer [0048] 11 ion getter pump