METHOD FOR THE PREPARATION OF ISOTOPE-ENRICHED GERMANIUM-HYDROGEN COMPOUNDS

Description

[0001] The invention relates to a process which enables the conversion of an isotopically pure germanium fluoride compound into a germanium hydrogen compound. Technological background

[0002] Fluorides play a major role in technical isotope enrichment. Fluorine has only one naturally occurring isotope, fluorine-19, which means that in centrifuges, the mass enrichment of fluorine compounds depends solely on the atomic mass of other components. During enrichment in centrifuges, molecules of different masses are separated. Since the mass of fluorine is always the same, individual isotopes of the second molecular component can be enriched, as is the case with germanium in the present disclosure. When enriching from other gases, such as hydrogen compounds, the different hydrogen isotopes interfere and limit the maximum possible enrichment.

[0003] Isotope enrichment has been established for decades for the utilization of radioactive material for energy production, military purposes, or specialized medical applications. More recent are applications for mega-experiments in physics, such as the silicon-28 prototype kilogram in the Avogadro project, neutrino detectors for the Gerda project made of germanium without germanium-73, or as high-performance low-temperature thermal conductors for the Einstein telescope made of silicon-28.

[0004] For the new application in semiconducting quantum computers, highly purified germanium-72 could become relevant. These quantum computers utilize energy level splitting of quantum objects such as electrons and electron vacancies to construct quantum logic circuits. The spin neutrality of the even-numbered isotopes is used in this process. Only when impurities from sources of odd spins are minimal can the quantum states be maintained for 1000 ms, the likely necessary timeframe for stable quantum computers.

[0005] Isotope enrichment is very complex and expensive. An atom-efficient reduction of germanium tetrafluoride is therefore desirable. Currently, methods for processing fluorides to hydrides are primarily derived from the adaptation of conventional industrial processes. These methods, adapted or currently being adapted for handling silicon fluoride, have several disadvantages. For example, they offer limited scalability beyond the laboratory scale and exhibit limited yield (atom efficiency). No established technology exists for their application to germanium tetrafluoride.

[0006] WO 2013 / 066033 A1 discloses a process for the production of Germane (GeH 4). GeF 4 is dissolved in an aqueous solution and reacted with a reducing agent, such as NaAlH 4. This produces Germane.

[0007] Since no methods for processing germanium tetrafluoride are currently in use, germanium is typically enriched directly in germanium. However, this process is disrupted by naturally occurring hydrogen isotopes, and the maximum enrichment rate of germanium isotopes is physically limited. Germanium possesses significantly more natural isotopes than silicon, which further complicates enrichment. As a result, in current industrial applications, a clean isotope separation is not performed, and only the single isotope with an odd mass number, germanium-73, is removed. This leaves behind, for example, the radioactive isotope germanium-76, which can interfere with applications. Therefore, there is a continuing need for an alternative synthesis method that enables the economical enrichment of germanium isotopes. Summary of the invention

[0008] One or more of the described disadvantages of the prior art are eliminated or at least reduced by means of the inventive process for the production of isotopically enriched germanium hydrogen compounds according to claim 1. The process comprises the following steps: a) Providing a gas of chemically highly purified, isotopically enriched germanium tetrafluoride; and providing a reduction solution in an inert reaction vessel, wherein the reduction solution contains an organic solvent and an alkali aluminum hydride as a reducing agent; c) introducing the gas into the reduction solution; and d) condensing the gaseous germanium hydrogen compounds produced by reduction.

[0009] Further preferred embodiments of the invention can be found in the dependent claims and the following description. Brief description of the characters

[0010] The invention is explained in more detail below with reference to an exemplary embodiment and accompanying drawings. The figures show: Figs. 1 to 3 Schematic illustrations of different measures used to optimize the mixing of the reducing solution and gaseous germanium tetrafluoride; Fig. 4 A schematic representation illustrating the rise path of germanium tetrafluoride bubbles during simple injection into the reaction vessel; and Figs. 5 to 7 Schematic illustrations of further measures used to optimize the reaction of the reducing solution and gaseous germanium tetrafluoride. Detailed description of the invention

[0011] The invention will now be explained in more detail in general terms and with reference to exemplary embodiments.

[0012] The present process for the production of isotopically enriched germanium hydrogen compounds comprises the following process steps: a) Providing a gas of chemically highly purified, isotopically enriched germanium tetrafluoride; and providing a reduction solution in an inert reaction vessel, wherein the reduction solution contains an organic solvent and an alkali aluminum hydride as a reducing agent; c) introducing the gas into the reduction solution; and d) condensing the gaseous germanium hydrogen compounds produced by reduction.

[0013] The invention therefore relates to a scale-up process that enables the time-efficient and highly atom-efficient conversion of isotopically enriched germanium tetrafluoride (e.g., germanium-72) to the corresponding germanium. The synthesis of germanium from germanium tetrafluoride presents a particular challenge. While established methods exist for obtaining, for example, silane from silicon fluoride, these cannot be readily applied to germanium compounds. This is due to the chemistry of group 14, where metallic character increases with increasing atomic number. While silicon tends to exhibit electron-accepting chemistry, germanium preferentially donates its electrons. For this reason, nucleophilic substitution of silicon halides is generally easier than that of germanium halides.

[0014] Isotopically enriched germanium tetrafluoride is provided for the process. This must already meet the desired isotopic enrichment, as it is not further enhanced by the process. Furthermore, the germanium tetrafluoride must be of high chemical purity. Isotopically enriched germanium tetrafluoride (e.g., germanium-72 tetrafluoride) is preferably stored in a tightly sealed gas container conforming to industry standards. Temperature fluctuations should be severely limited (e.g., to + / - 1 K) using a climate control system or a storage cabinet. These measures ensure that the container pressure remains constant and prevent condensation inside or on the container, both of which can lead to loss or contamination of the starting material. Quality control can be performed on a gas sample representative of the entire volume.

[0015] The reduction solution contains an organic solvent and an alkali aluminum hydride as a reducing agent and is placed in the reaction vessel. The reduction solution can consist of the organic reducing agent, preferably tetrahydrofuran or diglycol dimethyl ether, and an alkali aluminum hydride as the reducing agent. The reduction solution can be prepared directly on-site. Sodium aluminum hydride is preferably used as the reducing agent, since stable reduction solutions with tetrahydrofuran or diglycol dimethyl ether are readily available or can be obtained commercially.

[0016] In step c), the reduction solution preferably has a temperature in the range of -40°C to 40°C, particularly -10°C to 10°C, to control the rate of the exothermic reaction and prevent the formation of byproducts. During the exothermic reaction, the reaction vessel and reaction mixture should therefore preferably be cooled. This controls the synthesis rate and ensures increased atom efficiency. Furthermore, cooling prevents damage to the reactor vessel. The target temperature is regulated, for example, by liquid cooling applied to the reaction vessel, where the desired target temperature is set using a cooling fluid. The required heat removal rate can be determined in the usual manner. The target temperature can also be achieved by pressure changes within the reactor.For example, the gas is first compressed and then cools down to the target temperature during the subsequent expansion into the system (Joule-Thompson effect).

[0017] The provided reaction vessel should have sufficient volume for both the reduction solution and the reaction gas. In particular, the reaction vessel should be designed to withstand a moderate overpressure of 1000 to 2500 mbar, as the process typically takes place at normal pressure to slight overpressure.

[0018] The reaction vessel, at least in the areas that come into contact with the reduction solution, germanium tetrafluoride, and the resulting products, is made of an inert material. Neither the starting materials nor the products generated during the process should be able to react with the material from which the reaction vessel is made. Furthermore, no traces of elements that exhibit a high reactivity with the starting material or the target compound should be present. This prevents product contamination, the removal of which typically results in a reduction in yield.

[0019] In this process, gaseous germanium tetrafluoride is reduced to germanium in a reaction vessel using, for example, a sodium aluminum hydride solution in THF or diglycol dimethyl ether. From a process engineering perspective, it is important to use germanium fluoride with high isotopic purity so that the resulting end product (isotopically pure germanium) can be used for applications such as quantum technology. To maintain isotopic purity during the process, no germanium-containing material, such as germanium-free steel, should be used for the reaction vessel. Therefore, it is preferable for the reaction vessel to be germanium-free. All other system components that come into contact with the starting materials used in the process and the resulting process products should also consist of an inert, germanium-free material, at least at the contact surface.

[0020] For example, the carbon content in alloys should be as low as possible, as otherwise hydrocarbon compounds could form, which would then have to be removed in subsequent process and purification steps. Metallic materials and plastics are particularly suitable as materials for the reaction vessel. Especially suitable materials include: Chemical-resistant and stainless steels with a low carbon content. Examples include titanium-stabilized austenitic steels, such as X6CrNiMoTi17-12-2. Low-carbon nickel-based alloys, especially nickel-copper, nickel-iron, nickel-iron-chromium, nickel-chromium, nickel-molybdenum-chromium, nickel-chromium-cobalt alloys, and other multi-component alloys. Examples include NiCr19NbMo, NiCr15Fe, and NiCr21Mo14W (Hastelloy C-22). Unalloyed tantalum. Fluoropolymers, such as FEP or PTFE.

[0021] The reaction vessel is typically evacuated by applying a vacuum before commissioning. The quality of this cleaning can be improved by attaching heating elements to the reactor or plant housing, as impurities on the reactor's inner wall evaporate rapidly in conjunction with the vacuum and are thus removed from the vessel. During this bake-out process, the pressure could rise rapidly and significantly due to the evaporating molecules, potentially exceeding the load limit of the pumps used. This can be avoided by increasing the temperature manually only in increments or by using a digital temperature controller.

[0022] The process should be as time- and atom-efficient as possible (i.e., with the most complete conversion and yield possible). To ensure this, the mixing of the two fluids (gas + reduction solution) can be optimized by one or more of the following measures.

[0023] In a preferred embodiment of the process, the gas is introduced in step c) under constant stirring using a stirrer and / or under constant stirring in a rotating reaction vessel. This method, in particular, prevents local concentration variations of the reducing agent from leading to incomplete conversion of germanium tetrafluoride. Stirring, for example with a magnetic stirrer, can also extend the residence time of the gas introduced into the reduction solution, thus increasing the time window available for the reduction.

[0024] The Figures 1 and 2 Schematic diagrams illustrating the aforementioned measures, which serve to optimize the mixing of reduction solution and gaseous germanium tetrafluoride, can be found below. Figure 1Figure 1 shows a rotating, cylindrical reaction vessel 10, which is approximately half-filled with a reduction solution 20. Above a liquid boundary 30, a gas space 40 extends, in which the reaction gas collects after passing through the reduction solution 20. Gaseous germanium tetrafluoride is introduced at the bottom of the reaction vessel 10. The rotation improves the mixing of the reduction solution 20 and the injected gas. In the embodiment according to Figure 2 The stirring is carried out using a magnetic stirrer, which sets a magnetic fish 50 in motion.

[0025] Other preferred variants of the method for ensuring complete conversion of the germanium fluorine compound used provide that i) the path of the gas in the reduction solution is lengthened by arranging gas guidance structures in the reaction vessel; and / or ii) the phase interface between the gas and the reduction solution is increased by generating bubbles; and / or iii) the gas is passed through the reduction solution several times before condensation in step d).

[0026] According to variant i), the reaction vessel contains structures that deflect rising gas bubbles on their upward path, thus increasing the distance traveled in the reduction solution. For example, plates with a predetermined angle are installed inside the reaction vessel, on the underside of which the rising bubbles must travel at an angle to the liquid surface of the reduction solution. By lengthening the ascent path, the yield of the process can be improved.

[0027] Another process optimization option, according to variant ii), involves increasing the phase interface between the incoming gaseous germanium tetrafluoride and the liquid reduction solution. This is achieved through active bubble formation during gas introduction without foaming. Accordingly, such a system, adapted for this process, includes means for bubble generation. One example of a particularly robust and cost-effective means is a Venturi nozzle, which, in the configuration of a so-called Venturi injector, is suitable for introducing gases into liquids. In other words, the elements for bubble generation include, but are not limited to, a Venturi nozzle. Other bubble generation techniques, especially microbubbles (bubbles with a mean diameter in the range of 1 µm to 100 µm), can also be used.

[0028] According to variant iii), the gas is passed through the reduction solution several times before condensation in step d). This measure is also intended to ensure the most complete possible conversion of germanium tetrafluoride in the reduction solution. A system adapted for carrying out this process variant therefore includes means that capture the gas escaping above the reduction solution and reintroduce it into the reduction solution at the same or a different point.

[0029] All of the aforementioned variants i) to iii) can be combined (at will). Likewise, the reduction solution can be stirred simultaneously, as described above.

[0030] In Figure 3The principle of variant iii) is shown – in a highly schematic form. The reaction vessel 10 is approximately half-filled with the reduction solution 20, and gas is introduced at the bottom of the reaction vessel 10 via an inlet opening 12. The reaction gas exiting the reduction solution – consisting of germanium, possibly unreacted germanium tetrafluoride, and gaseous byproducts – is collected in the gas space 40. A pipe system 60 with a pump 62 connects to an outlet opening 14 at the top of the reaction vessel 10. The pipe system 60 allows for the continuous recirculation of the reaction gas to complete the conversion of any remaining germanium tetrafluoride. In other words, the embodiment features a gas circuit that enables a continuous supply of reaction gas.For the sake of clarity, the illustration of a valve system that controls the feed-in of germanium tetrafluoride from the storage tank and the removal of the fully converted reaction gas has been omitted.

[0031] Figure 4 The structure is similar to that of the one in Figure 3 The embodiment shown. Also shown are bubbles 42 of the reaction gas rising in the reduction solution 20. As can be seen, the rising bubbles 42 have an almost vertical path starting from the inlet opening 12. The embodiment of Figure 4 combines the above-mentioned variants ii) and iii), and therefore also has a gas cycle.

[0032] To further improve mixing, the reaction gas can also be injected at several points. In the bottom area of ​​the in Figure 5In the illustrated embodiment, a component 70 is provided for generating bubbles 42, enabling the bubbles 42 to escape throughout the entire bottom area. This component 70 is also commonly referred to as a bubbler. This measure typically also leads to a reduction in the average diameter of the bubbles 42, thus increasing the overall interface between the liquid and gas.

[0033] A further increase in the phase boundary area between liquid and gas is achieved with the in Figure 6 The illustrated embodiment is possible. The reaction gas is fed into the bottom region of the reaction vessel 10 via a Venturi nozzle 80. The average diameter of the bubbles 42 can be significantly reduced in this way. For example, microbubbles with an average diameter of 1 µm to 100 µm can be produced.

[0034] Finally, it shows Figure 7Stak schematically illustrates an embodiment according to variant i), in which the rising path of the reactant gas is increased by gas guiding structures 90. The gas guiding structures 90 are exemplified here by plates arranged horizontally in the reduction solution 20.

[0035] In step d), the gaseous germanium hydrogen compound produced by reduction is collected by condensation and can then be further processed. A cold trap is typically used for condensation, in which the liquefied germanium collects. In a preferred embodiment of the process, the condensation in step d) takes place in a two-stage process. The reaction gas first passes through a first cold trap at a temperature in the range of -80°C to -50°C, and the isotopically enriched germanium hydrogen compound is then condensed in a second cold trap at a temperature in the range of -110°C to -90°C. In the first cold trap, the product is purified by removing unreacted germanium tetrafluoride and byproducts. In the second cold trap, the product (germanium) condenses and is collected in liquid form. The purified germanium can be stored in gas tanks.

Claims

1. A method for the producing of isotope-enriched germanium-hydrogen compounds, comprising the following method steps: a) providing a gas of chemically ultra-pure, isotope-enriched germanium tetrafluoride; and b) providing a reducing solution (20) in an inert reaction vessel (10), wherein the reducing solution (20) contains an organic solvent and an alkali-aluminium hydride as reducing agent; c) introducing the gas into the reducing solution (20); and d) condensing the gaseous germanium-hydrogen compounds produced by reduction.

2. The method of claim 1, characterised in that sodium aluminium hydride is used as the reducing agent.

3. The method of claim 1 or 2, characterised in that tetrahydrofuran or diglycol dimethyl ether is used as the solvent.

4. The method of any one of the preceding claims, characterised in that the reducing solution (20) in step c) has a temperature in the range from -40°C to 40°C.

5. The method of any one of the preceding claims, characterised in that the reaction vessel (10) is free of germanium.

6. The method of any one of the preceding claims, characterised in that said introducing the gas in step c) takes place with constant stirring by means of a stirring body and / or with constant stirring in a rotating reaction vessel (10).

7. The method of any one of the preceding claims, characterised in that i) a rising path of the gas in the reducing solution (20) is extended by arranging gas guiding structures (90) in the reaction vessel (10); and / or ii) a phase interface between the gas and the reducing solution (20) is increased by generating bubbles (42); and / or iii) the gas is passed through the reducing solution (20) several times prior to said condensing in step d).

8. The method of claim 7, characterised in that the means for increasing the phase interface comprise elements for generating bubbles (42) or a Venturi nozzle (80).

9. The method of any one of the preceding claims, characterised in that said condensing in step d) takes place in a two-stage process, wherein the reaction gas first passes through a first cold trap at a temperature in the range from -80°C to -50°C and then the isotope-enriched germanium-hydrogen compound is condensed out in a second cold trap at a temperature in the range from -110°C to -90°C.