Method for separating, enriching and obtaining the isotope 3He from the isotope 4He and using the separated, enriched and obtained 3He

Abstract

The invention relates to a method for separating, enriching and obtaining the isotope 3 He compared to the isotope 4 He, exhibiting the following steps: a) Performing an adsorption of a 3 He / 4 He-containing gas to an adsorbent, and b) Performing selective desorption, such that 3 He from the Adsorbent is released. Furthermore, the invention relates to a use of the separated, enriched and obtained isotope by means of the process. 3 He for generating a temperature in the range of 0.01 to 0.05 K, preferably 0.02 K, or as a contrast agent for magnetic resonance imaging.

Description

[0001] The invention relates to a process for the separation, enrichment and extraction of the isotope 3 He compared to the isotope 4 He and a use of the separated, enriched and recovered 3 Hey.

[0002] Helium is a colorless, odorless, and non-toxic noble gas that remains gaseous even at low temperatures and only becomes liquid near absolute zero. Helium does not become solid at absolute zero (0 K) at normal pressure. Furthermore, helium is very unreactive, so it essentially only exists in atomic form. Helium has several isotopes, two of which are stable. The most common stable isotope is 4 He. Another stable isotope is 3 Hey, that occurs relatively rarely naturally. 3 He and 4 He exhibits different physical properties. Therefore, the two isotopes have different uses.

[0003] Next to 4Here comes the lighter stable 3 It occurs primordial on Earth, is enriched in the Earth's mantle, and comes to the Earth's surface particularly through hot-spot volcanism. 3 He comes from the decay of tritium, primarily from nuclear reactors and nuclear weapons. Currently, only about 15 kilograms are produced annually. 3 He is extracted mainly as a by-product of nuclear weapons reprocessing. Furthermore, interplanetary dust and lunar regolith are exposed to solar wind and spallation reactions of cosmic rays with non-volatile particles. 3 He-enriched.

[0004] There are more 4 He atoms as 3He atoms. However, the ratio of the two isotopes varies depending on their place of origin. S. Niedermann et al. describe in Geochimica et Cosmochimica Acta. Vol. 61. No. 13, pp. 2697-2715., 1997, a method for determining the isotopic compositions of noble gases, among others, in basalt glasses, in which the isotopic compositions of the noble gases are determined using a mass spectrometer.

[0005] Dmitriev, VV et al. “Separation of 3He from 3He-4He Mixture by Means of Adsorption.” from Journal of low temperature physics 138.3-4 (2005): 877-880. Web. discloses a method for the separation of 3 He from 4 He. This is done by adsorption on activated carbon, which has a selective affinity to 4 He. In a controlled experiment, a mixture of 4 He and 3 He is passed through the activated carbon, on the surface of which 4 He is adsorbed, while 3He remains in the gas phase. A subsequent desorption process can 4 He is released again from the activated carbon, thereby achieving an effective separation of the two isotopes.

[0006] The consumption of 3 He is increasing, so there is still a need, 3 He from 4 To separate, enrich and extract.

[0007] It is an object of the invention to provide a process for the separation, enrichment and recovery of the isotope 3 He and the separated, enriched and recovered 3 He to use.

[0008] This object is achieved by a method having the features of patent claim 1 and a use having the features of patent claim 6. Advantageous further developments and modifications are mentioned in the subclaims.

[0009] The invention relates to a process for the separation, enrichment and extraction of the isotope 3 He compared to the isotope 4 Hey, comprising the following steps: a) Carrying out an adsorption of a 3 He / 4 He-containing gas to an adsorbent, and b) Carrying out a selective desorption so that 3 He is released from the adsorbent.

[0010] The process for separation, enrichment and recovery according to the invention includes a process for isotope separation of the isotopes 3 He and 4 He. Under the expression “ 3 He / 4 He-containing gas” is a gas that 3 He and 4 He contains. Preferably, the 3 He / 4 He-containing gas next to 3 He and 4 He does not contain any other foreign gases except Ne (neon).

[0011] Preferably, in step a) a naturally occurring gas is used which 3 He and 4 He contains, as the 3 He / 4 He-containing gas is used. Since naturally occurring, 3 He / 4 Since He-containing gases always contain foreign gases, the natural gas is preferably freed of these gases before step a). From an undocumented prior art, it is known to remove interfering foreign gases from the natural gas, which is present as a gas mixture, so that He is present in high purity. The natural gas mixture can be any natural gas that contains helium. For example, the natural gas can be natural gas or air. Preferably, the natural gas already has an elevated helium content initially. This can be volcanic gas, more preferably a hot-spot volcanic gas, or even natural gas in some regions. A volcanic gas usually has a higher helium content than air.

[0012] Foreign gases such as water vapor, N2 (nitrogen), O2 (oxygen), H2 (hydrogen), CO2 (carbon dioxide), hydrocarbons, Ar (argon), Kr (krypton) and Xe (xenon) can be removed from the natural gas in the following ways: Water vapor can be removed by freezing it out on a component such as a pipe loop, which is cooled to a predetermined temperature with a suitable coolant such as liquid nitrogen or dry ice. N2 and O2 can each be absorbed for removal at 400°C on a getter equipped with titanium, e.g. in the form of sponges or chips. H2 can be absorbed for removal from the natural gas at room temperature on a getter equipped with a Zr-Al alloy. CO2 and hydrocarbons can be absorbed for removal at 400°C on a getter equipped with a Zr-Al alloy. To remove Ar, Kr, Xe from the natural gas, these can be absorbed, for example, in an adsorption cryostat on a getter equipped with e.g.50 K cooled steel frit or on an adsorption trap cooled with a suitable refrigerant such as liquid N2 and filled with activated carbon.

[0013] According to the invention, step a) comprises carrying out the adsorption with activated carbon as the adsorbent at a temperature in the range of 5 K to 12 K, preferably in the range of 7 K to 11 K, more preferably at a temperature of 11 K. Step a) is carried out, for example, in a cryostat coated with activated carbon.

[0014] According to the invention, step a) is carried out in such a way that no gaseous phase remains. This avoids losses in this step.

[0015] According to the invention, step b) comprises a stepwise heating of the adsorbent from a temperature in the range of 5 K to 12 K, more preferably 7 K to 11 K, more preferably 11 K, to a further temperature in the range of 13 K to 40 K. Preferably, the further temperature is in the range of 15 K to 25 K, more preferably 18 K to 21 K. In step b), the isotope separation and enrichment of 3 He opposite 4 He instead. The isotopes 3 He and 4 He are released according to specific desorption temperatures. Since the Van der Waals forces responsible for adsorption are 3 He are comparatively weaker than 4 He, it desorbs at lower temperatures, whereas 4 He is only released at higher temperatures. This physicochemical difference allows 3 He opposite 4He in the first released gas phase. Preferably, the stepwise heating comprises heating in 2 K to 8 K steps, more preferably 3 K to 7 K steps, even more preferably 4 K to 6 K steps. By continuously measuring the He isotope ratios, optimal helium fractionation conditions and temperatures can be determined depending on the used 3 He / 4 He-containing gas can be determined. 3 He-enriched gas fraction is preferably transferred according to step c) into a separate reservoir and thus separated from the rest of the system, so that subsequent, upon further temperature increase, it does not lead to renewed mixing with gas with lower 3 He concentration comes.

[0016] Alternatively, in a further variant, step a) comprises ionizing and injecting the 3 He / 4He-containing gas into an ion getter as the adsorbent at a temperature in the range 280 K to 315 K, preferably 285 K to 305 K, more preferably 290 K to 295 K. For the sake of simplicity, step a) is preferably carried out at room temperature in the further variant.

[0017] According to the invention, the ion getter comprises a metal. The metal is preferably barium, more preferably titanium.

[0018] According to the invention, step b) in the further variant comprises a stepwise heating of the adsorbent from a temperature up to a range of 500 K to 700 K, preferably 550 K to 650 K, more preferably 575 K to 625 K. During the stepwise or stepwise heating to the above-mentioned temperatures, the two helium isotopes 3 He and 4 He is released from the ion getter according to the specific desorption temperatures. Without wishing to be bound to any theory, it is assumed that 3He is comparatively less strongly adsorbed in the ion getter and it desorbs at lower temperatures, whereas 4 He is only released in greater quantities at higher temperatures. By continuously measuring the He isotope ratios, optimal helium fractionation conditions and temperatures can be determined depending on the used 3 He / 4 He-containing gas can be determined. Preferably, the stepwise heating comprises heating in 2 K to 8 K steps, more preferably 3 K to 7 K steps, even more preferably 4 K to 6 K steps. The gas fraction with preferably high 3 He / 4 The ratio and preferably a large amount of gas is preferably transferred according to step c) into a separate reservoir and thus separated from the rest of the system, so that there is no subsequent mixing with gas with a lower 3 He concentration occurs.

[0019] In a preferred embodiment, the method further comprises the step c) transferring the substance released in step b) 3 He into a separate reservoir. 3 He enriched gas fraction is transferred to the separated reservoir, which also continues 4 He contains. Step c) can be carried out during and / or after step b). Preferably, step c) is carried out during step b) in order to 3 He enriched gas fraction, which has a high and / or the highest 3 He / 4 He ratio and these are separated from gas fractions with lower 3 He / 4 He ratio. The separated reservoir represents a reservoir that is physically separated from a device in which step b) is performed.

[0020] Preferably, steps a) and b) and optionally c) are repeated several times. By repeating the process steps several times, 3 He opposite 4 He continues to enrich and win. The 3 He-enriched gas fraction preferably has a high and / or highest 3 He / 4 He ratio and steps a), b) and optionally c) are preferably repeated until a predetermined 3 He concentration is reached.

[0021] In a preferred embodiment, the product obtained after step b) 3 He / 4 He-containing gas mixture at least 1.2 times, preferably at least 1.5 times enrichment in 3 He compared to the one used in step a) 3 He / 4 He-containing gas mixture.

[0022] Preferably, in step b) the 3 He / 4He ratio in the gas phase is continuously measured using a mass spectrometer. By continuously measuring the He isotope ratios, optimal helium fractionation conditions and temperatures can be determined depending on the used 3 He / 4 He-containing gas can be determined.

[0023] Furthermore, the invention relates to a use of the separated, enriched and recovered isotope obtained by means of the method according to one or more of the previously described embodiments 3 He to generate a temperature in the range of 0.01 to 0.05 K, preferably 0.02 K, or as a contrast agent for magnetic resonance imaging. This improves the 3 He supply for research laboratories and especially medical technology.

[0024] The 3He is preferred in scientific laboratories to produce extremely low millikelvin temperatures such as 0.02 K by dissolving liquid 3 He in liquid 4 He is used. Among other things, it is primarily used to cool superconducting magnets.

[0025] Hyperpolarized 3 It is primarily used in diagnostics as a contrast agent for magnetic resonance imaging. In medical imaging procedures, hyperpolarized 3 For example, it enhances images in brain and lung imaging.

[0026] The invention is further explained in more detail below with reference to figures and an example. They show schematically and not to scale: Fig. 1 is a sketched representation of a plant in which a method according to a first embodiment is carried out; and Fig. 2 a sketched representation of another plant in which a method according to a second embodiment is carried out.

[0027] Fig. Figure 1 shows a schematic representation of a plant in which a method according to a first embodiment is carried out. The method is assigned a 3 He / 4 He-containing gas, which is a natural gas in the form of a gas mixture. The natural gas is fed to the system via a gas inlet 1, which has several valves 2 for shutting off or controlling the flow of the natural gas through the system. Optionally, the system has a Pirani measuring branch 8 for measuring the pressure of rough and / or fine vacuum. Furthermore, the system optionally has devices for removing foreign gases from the 3 He / 4 He-containing gas, so that a mixture of 3 He / 4He in high purity is subjected to the process according to the invention, which contains only Ne (neon) as foreign gas. To remove the foreign gases with the exception of Ne, activated carbon traps 9, a cold trap 7, getters 3 (e.g. Ti getters), SAES getters or SAES pumps 4 and further SAES getters or SAES pumps 5 are provided, which are commercially available from SAES (Societä Apparecchi Elettrici e Scientifici, (Lainate, Italy), wherein the foreign gases can be, for example, water vapor, N2 (nitrogen), O2 (oxygen), H2 (hydrogen), CO2 (carbon dioxide), hydrocarbons, Ar (argon), Kr (krypton) and / or Xe (xenon). The process according to the invention comprises carrying out an adsorption of a 3 He / 4 He-containing gas on an adsorbent and is carried out in a cooling head 6 equipped with activated carbon.

[0028] The activated carbon is the adsorbent. The adsorption with activated carbon as the adsorbent in the cooling head 6 equipped with activated carbon is carried out, for example, at a temperature of 11 K. The adsorption is carried out in such a way that no gaseous phase remains. Following the adsorption, a selective desorption is carried out so that 3 He is released from the adsorbent. This causes the 3 Hey from the 4 He is separated, enriched and recovered. The selective desorption is carried out by gradually heating the adsorbent, ie the activated carbon, from a temperature of 11 K to a temperature of 20 K. Under these conditions, Ne remains adsorbed on the adsorbent. Using a mass spectrometer 10, the 3 He / 4 He ratio can be measured continuously. The released 3He-enriched gas fraction is transferred to a separated reservoir. Adsorption and selective desorption with the gas fraction separated in the previous step with preferably high 3 He / 4 The ratio and preferably large amount of gas can be repeated several times, so that 3 He opposite 4 He is further enriched and extracted.

[0029] Fig. Figure 2 shows a sketched representation of another system in which a method according to a second embodiment is carried out. Fig. 2 shown further system corresponds to the one in Fig. 1, with the difference that, instead of the cooling head equipped with activated carbon, it has an ion getter pump 11. The ion getter comprises a metal such as titanium. The process according to the second embodiment comprises the adsorption of a 3 He / 4He-containing gas to an adsorbent and selective desorption, so that 3 He is released from the adsorbent, wherein the adsorption is carried out by means of ionizing and injecting the 3 He / 4 He-containing gas into an ion getter as adsorbent at a temperature which is, for example, room temperature. The selective desorption is carried out by a stepwise heating of the adsorbent, ie the ion getter, to a temperature of, for example, 600 K. The released by the desorption 3 He-enriched gas fraction is transferred to a separated reservoir. Performing adsorption and selective desorption with the gas fraction with the highest 3 He / 4 He ratio can be repeated several times so that 3 He further separated and opposite 4 He is enriched and extracted. Example

[0030] A single-stage test series using a natural gas freed from foreign gases in the form of a gas with a 3 He / 4 He ratio of (21.66 ± 0.24) x 10 -6 , which corresponds to a typical value for gas resulting from hot-spot volcanism, was carried out.

[0031] First, an adsorption of the 3 He / 4 He-containing gas is carried out on an adsorbent in the form of activated carbon. The adsorption with activated carbon as the adsorbent can be carried out, for example, in the Fig. 1 shown cooling head equipped with activated carbon at a temperature of 11 K, so that no gaseous phase remains. Following adsorption, a selective desorption is carried out so that 3He is released from the adsorbent. Selective desorption is achieved by gradually heating the adsorbent, ie the activated carbon, from a temperature of 11 K to a temperature of, for example, 20 K. The stepwise heating can be carried out in 5 K steps, for example. Under these conditions, Ne remains adsorbed on the adsorbent. By means of the Fig. 1 shown mass spectrometer, a 3 He / 4 He ratio was measured continuously. The helium isotopes were measured in a 90° sector field mass spectrometer VG5400 from Vacuum Generators Instruments, now Thermo Fisher Scientific (Waltham, USA). Table 1 shows 4 He signals and measured 3 He / 4 He ratios with 2sigma error of the desorbed gas phase at different temperatures: Temperatur (K) He (Volt) 3 He / 4 He (10 -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

[0032] Especially at a temperature of 20 K, 3 He opposite4 He has been enriched by 1.5 times. In particular, the 20 K 3 He-enriched gas fraction was transferred to a separated reservoir. By optimizing the step size and multi-stage isotope separation, i.e. repeating the adsorption and selective desorption of the gas fraction separated in the previous step with preferentially high 3 He / 4 He ratio and preferably large amount of gas, can further enrichment of 3 He can be achieved. List of reference symbols: 1 gas inlet 2 valve 3 getters 4 SAES pump 5 additional SAES pumps 6 cooling head equipped with activated carbon 7 cold trap 8 Pirani measuring branch 9 Activated carbon trap 10 mass spectrometers 11 Ion getter pump

Claims

[1] Process for separation, enrichment and extraction of the isotope 3 He compared to the isotope 4 Hey, comprising the following steps: a) Carrying out an adsorption of a 3 He / 4 He-containing gas to an adsorbent, and b) Carrying out a selective desorption so that 3 He is released from the adsorbent, wherein step a) comprises carrying out the adsorption with activated carbon as the adsorbent at a temperature in the range of 5 K to 12 K, preferably in the range of 7 K to 11 K, more preferably at a temperature of 11 K, step a) is carried out such that no gaseous phase remains, and step b) comprises gradually heating the adsorbent from a temperature in the range of 5 K to 12 K, preferably 7 to 11 K, more preferably 11 K, to a temperature in the range of 13 K to 40 K, preferably 15 K to 25 K, more preferably 18 K to 21 K or wherein step a) comprises ionizing and injecting the 3 He / 4He-containing gas into an ion getter as the adsorbent at a temperature in the range 280 K to 315 K, preferably 285 K to 305 K, more preferably 290 K to 295 K, the ion getter comprises a metal, preferably barium, more preferably titanium, and step b) comprises a stepwise heating of the adsorbent from a temperature up to a range of 500 K to 700 K, preferably 550 K to 650 K, more preferably 575 K to 625 K. [2] Method according to one of the preceding claims, characterized by a step c) transferring the substance released in step b) 3 He into a separate reservoir. [3] Method according to one of the preceding claims, characterized by that steps a) and b) and, if referred back to claim 2, step c) are repeated several times. [4] Method according to one of the preceding claims, characterized by that the result obtained after step b) 3 He / 4He-containing gas mixture at least 1.2 times, preferably at least 1.5 times enrichment in 3 He compared to the one used in step a) 3 He / 4 He-containing gas mixture. [5] Method according to one of the preceding claims, characterized by that in step b) the 3 He / 4 He ratio in the gas phase is continuously measured by means of a mass spectrometer (10). [6] Use of the separated, enriched and recovered isotope obtained by the process according to any one of the preceding claims 3 He for generating a temperature in the range of 0.01 to 0.05 K, preferably 0.02 K, or as a contrast agent for magnetic resonance imaging.

Images