Hydrogen isotope enrichment device

Abstract

To inexpensively obtain gaseous deuterium from mixed gas of hydrogen and deuterium.SOLUTION: A first electrode 11 is an electrode composed of metal (hydrogen permeable metal) permeating hydrogen (H component and D component), and the hydrogen permeable metal is, for example, Pd. H ions and D ions having permeated the first electrode 11 flow to the side of a second electrode 12 in a proton conductive layer 20. When the first electrode 11 is used as an anode and the second electrode 12 is used as a cathode, the H ions and the D ions flow to the right side from the left side in the figure in the proton conductive layer 20. At this time, a hydrogen component in input gas more easily flows into atmosphere on a cathode side than a deuterium component, and an H / D composition ratio in production gas becomes higher than an H / D composition ratio in the input gas. In discharge gas discharged after the H component and the D component in the input gas have been consumed, the D component is concentrated.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to hydrogen ( 1 This paper deals with a hydrogen isotope enrichment device that selectively enriches deuterium in a mixture of hydrogen (H) and deuterium. [Background technology]

[0002] A stable isotope of hydrogen that is a component of naturally occurring water and hydrogen gas has a mass number of 1 (the nucleus consists of only one proton). 1 H (hereafter referred to as H) and deuterium, which has a mass number of 2 (the nucleus consists of one proton and one neutron). 2 There is H (hereafter referred to as D), and the abundance ratio of D is overwhelmingly smaller than that of H. H and D have almost the same chemical properties, but D is known to be particularly effective in applications in the nuclear power and semiconductor manufacturing fields. For this reason, there is a demand for technology to selectively extract (separate) D from water or hydrogen gas, which contains a mixture of H and D. However, since it is practically impossible to completely separate H and D instantly, in reality, materials containing a mixture of these (water, hydrogen gas, etc.) are treated to increase the concentration of one of them (especially D) in order to separate them.

[0003] Because the chemical properties of H and D are nearly identical, they are generally not easily separated by chemical methods. Techniques for separating them using differences in their properties, such as boiling point or vapor pressure, are known. However, these techniques require high or extremely low temperatures, complex processes, and expensive chemicals, making it difficult to obtain D inexpensively. Techniques for separating H and D using differences in their zero-point vibrational energy or atomic size are also known, but these techniques also require an extremely low-temperature environment, making it similarly difficult to obtain D inexpensively.

[0004] Furthermore, as described in Non-Patent Document 1, a technique for separating H and D by utilizing the difference in diffusion coefficients of H and D in a hydrogen-permeable metal (e.g., Pd). This method can be easily implemented with a simpler configuration than the aforementioned chemical techniques, but it suffers from the problem of the metal being embrittled by hydrogen. To reduce the effects of embrittlement, for example, it is effective to thicken the metal (e.g., Pd), with a thickness of, for example, several hundred nanometers to several tens of micrometers. It is also effective to use this metal as an alloy with another metal (e.g., Ag). However, these methods have problems such as the high cost of the metal material and a decrease in separation efficiency. It is also effective to perform this process at a high temperature, but this complicates the device configuration. Furthermore, in order to allow hydrogen to permeate the metal, it is necessary to create a pressure difference between the upstream and downstream sides of the metal, which requires a complex device configuration.

[0005] In response to this, Patent Document 1 describes a technology for separating H and D using a membrane electrode assembly (MEA) that functions as a fuel cell. In this MEA, a proton conductor is sandwiched between electrodes (anode and cathode), with hydrogen gas containing H and D supplied to the anode side and oxygen gas (air) supplied to the cathode side. In this case, positive H ions or D ions supplied from the anode side and passing through the proton conductor react with oxygen on the cathode side to produce water, and an electromotive force is generated between the anode and cathode, resulting in a reaction opposite to that of water electrolysis. Nafion (registered trademark) or the like is used as a proton conductor. Here, the hydrogen gas supplied to the anode side contains H, HD, and D, to be precise, while the water produced on the cathode side is a mixture of HO, HDO, and the like. In this case, due to differences in the conduction conditions and reaction rates of H ions and D ions in the proton conductor, HDO, which contains more D than HO, is more likely to be produced on the cathode side, so the D component increases more on the cathode side than on the anode side.

[0006] Here, an oxidation reaction occurs on the anode side, and a reduction reaction occurs on the cathode side. The materials constituting the anode and cathode are made of materials that function as catalysts to promote these reactions. Examples of such materials include precious metals such as platinum (Pt) and ruthenium (Ru). However, in fuel cells, dispersing Pt microparticles rather than constructing the entire electrode from dense Pt increases the surface area of Pt available for the catalytic reaction and facilitates the transport of H ions and D ions into the proton conductor, resulting in higher efficiency. For this reason, as described in Non-Patent Document 2 and elsewhere, Pt / C electrodes, in which Pt microparticles are dispersed on a carbon (C) sheet, are particularly preferred for the anode and cathode. This device allows deuterium to be enriched more cheaply than the device described in Non-Patent Document 1. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Yasuo Suzuki and Takashi Kimura, "Study on Separation of Hydrogen Isotopes Including Tritium Using Palladium Alloy Membranes," Production Research, Vol. 36, No. 6, p. 293 (June 1983) [Non-patent document 2] Hiroshi Fukazawa, Takeshi Ume, and Naotoshi Suzuki, "Platinum-saving technology for catalyst layers in fuel cells," Toshiba Review, Vol. 68, No. 4, p. 54 (2013) [Patent documents]

[0008] [Patent Document 1] International Publication No. 2018 / 049343 Summary of the Invention [Problem to be solved by the invention]

[0009] In the techniques described in Patent Document 1 and Non-Patent Document 2, what is obtained by concentration (separation) is a liquid such as HDO, and it is difficult to obtain gaseous D (HD, D2, etc.). Furthermore, in the techniques described in Non-Patent Document 1 and Patent Document 1, the separation efficiency of H and D is low, so a technique that can obtain D at even lower cost has been desired.

[0010] For this reason, a technology was needed to inexpensively obtain gaseous deuterium from a mixture of hydrogen (H) and deuterium.

[0011] The present invention has been made in view of the above problems, and an object of the present invention is to provide an invention that solves the above problems. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention has the following configurations. The hydrogen isotope enrichment device of the present invention is a hydrogen ( 1 1. A hydrogen isotope enrichment device for outputting an output gas in which the concentration of hydrogen isotopes relative to the hydrogen in an input gas containing a mixture of hydrogen isotopes (H) and hydrogen isotopes that are isotopes of hydrogen is increased, the device comprising: a proton conducting layer made of a proton conductor that conducts hydrogen positive ions and having two opposing main surfaces; a first electrode made of a thin film of a hydrogen-permeable metal selected from palladium (Pd), vanadium (V), tantalum (Ta), and titanium (Ti) and formed on one main surface of the proton conducting layer; and a second electrode formed by a first electrode and a second electrode formed by a second electrode, wherein a DC voltage is applied between the first electrode and the second electrode in the membrane electrode assembly, with the first electrode acting as a positive side and the second electrode acting as a negative side, the hydrogen and the hydrogen isotopes in the input gas in contact with the first electrode flow between the first electrode and the second electrode, a product gas is produced on the side of the second electrode, and an exhaust gas, which is the input gas after the hydrogen and the hydrogen isotopes have been consumed to produce the product gas, is extracted as the output gas. The present invention relates to hydrogen ( 1A hydrogen isotope enrichment device that outputs an output gas in which the concentration of the hydrogen isotopes relative to the hydrogen in an input gas containing a mixture of hydrogen (H) and hydrogen isotopes that are isotopes of the hydrogen is increased, the device comprising: a proton conducting layer made of a proton conductor that conducts positive hydrogen ions and having two opposing main surfaces; a first electrode made of a thin film of a hydrogen-permeable metal selected from palladium (Pd), vanadium (V), tantalum (Ta), and titanium (Ti) and formed on one main surface of the proton conducting layer; and a second electrode formed on the other main surface of the proton conducting layer. a DC voltage is applied between the first electrode and the second electrode in the membrane electrode assembly, with the first electrode acting as a negative side and the second electrode acting as a positive side; the hydrogen and the hydrogen isotopes in the input gas in contact with the second electrode flow between the first electrode and the second electrode; a product gas is produced on the first electrode side; and an exhaust gas, which is the input gas after the hydrogen and the hydrogen isotopes have been consumed to produce the product gas, is produced on the second electrode side; and the product gas is extracted as the output gas. 。 In the hydrogen isotope enrichment device of the present invention, the second electrode is made of a thin film of the hydrogen-permeable metal. In the hydrogen isotope enrichment device of the present invention, the first electrode is a vapor-deposited film of the hydrogen-permeable metal. The hydrogen isotope enrichment device of the present invention is characterized in that the first electrode and the proton conducting layer are in contact with each other via monolayer graphene. In the hydrogen isotope enrichment apparatus of the present invention, a plurality of the membrane electrode assemblies are used in stages from the time the input gas is input until the time the output gas is output, and the output gas from the membrane electrode assembly in the preceding stage is used as the input gas for the membrane electrode assembly in the adjacent subsequent stage. In the hydrogen isotope enrichment device of the present invention, one of the exhaust gas and the generated gas that is not used as the output gas in one of the membrane electrode assemblies is used as the input gas for the membrane electrode assembly in a stage upstream of the one membrane electrode assembly. The hydrogen isotope enrichment device of the present invention is characterized in that a membrane electrode assembly base material is used that includes the first electrode, the second electrode, and the proton conducting layer, and each of the plurality of membrane electrode assemblies is formed as a different region within the surface of the single membrane electrode assembly base material. In the hydrogen isotope enrichment device of the present invention, the hydrogen isotope is deuterium ( 2 H or D), or tritium ( 3 H or T). [Effects of the Invention]

[0013] Since the present invention is configured as described above, gaseous deuterium can be obtained inexpensively from a mixed gas of hydrogen (H) and deuterium. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram showing a configuration of a membrane electrode assembly and its surroundings used in a hydrogen isotope enrichment device according to an embodiment of the present invention. [Figure 2] FIG. 1 is a diagram showing the configuration when measurements were carried out for Example 1 of the present invention, in which the first electrode was an anode and the second electrode was a cathode. [Figure 3] 1 shows the results of measuring the time change in ion current corresponding to H, D, and HD in the generated gas in Example 1(a) and Comparative Example 1(b). [Figure 4] 1 shows the results of measuring the composition ratio of the generated gas in Example 1 and Comparative Examples 1 and 2. [Figure 5] 1 shows the results of calculating the D concentration ratios in the exhaust gases of Example 1 and Comparative Examples 1 and 2. [Figure 6] The graph shows the results of measuring the D concentration ratio for Example 1, Comparative Example 1, and Comparative Example 2 while changing the applied voltage. [Figure 7] 1 shows the results of measuring the composition of exhaust gas in Example 1 and Comparative Example 2. [Figure 8] FIG. 10 is a diagram showing the configuration when measurements were carried out for Example 2 of the present invention, in which the first electrode was a cathode and the second electrode was an anode. [Figure 9]1 shows the results of calculating the D enrichment ratio in the product gas in Examples 2 to 5. [Figure 10] FIG. 10 is a diagram showing the configuration of a first modified example of a hydrogen isotope enrichment device using a plurality of membrane electrode assemblies corresponding to the first embodiment. [Figure 11] FIG. 10 is a diagram showing the configuration of a second modified example obtained by further modifying the first modified example. [Figure 12] FIG. 10 is a diagram showing the configuration of a third modified example of a hydrogen isotope enrichment device using a plurality of membrane electrode assemblies corresponding to the second embodiment. [Figure 13] FIG. 10 is a diagram showing the configuration of a fourth modified example obtained by further modifying the third modified example. DETAILED DESCRIPTION OF THE INVENTION

[0015] An isotope separation device according to an embodiment of the present invention will be described below. This isotope separation device, like the device described in Patent Document 1, uses a membrane electrode assembly (MEA) as a basic component. FIG. 1 shows the configuration of this MEA M and its surroundings. This configuration uses two electrodes (a first electrode 11 and a second electrode 12) to which a DC voltage is applied, and a proton-conducting layer 20 sandwiched between them. Here, a DC voltage is applied between the first electrode 11 (terminal A) and the second electrode 12 (terminal B). While the first electrode 11 side may be positive or the second electrode 12 side may be positive, the first description will focus on the case where the first electrode 11 side is positive. The atmosphere on the first electrode 11 side (the left side of the first electrode 11 in FIG. 1) and the atmosphere on the second electrode 12 side (the right side of the second electrode 12 in FIG. 1) are both gaseous.

[0016] In FIG. 1, a gas containing hydrogen (H) and deuterium (D) (a mixed gas of H2 and D2) enters the space (the space on the left side of the figure: anode-side gas chamber 31) where the surface of the first electrode 11, which serves as the anode, is located from the upper side of the figure, and this gas is referred to as the input gas. H2 and D2 in this input gas dissociate on the surface of the first electrode 11 (anode), and the H and D components react and are consumed as described below. Meanwhile, the H components (H ions) and D components (D ions) migrate through the proton-conducting layer 20 to the right side of the figure and combine on the surface of the second electrode 12 (cathode), thereby forming H2 and D2 again in the space (the space on the right side of the figure: cathode-side gas chamber 32) where the surface of the second electrode 12 is located. The gas thus generated on the cathode side is referred to as the generated gas.

[0017] The first electrode 11 is an electrode made of a metal (hydrogen-permeable metal) that allows hydrogen (H component, D component) to permeate, and as will be described later, this hydrogen-permeable metal is, for example, Pd. The H (positive) ions and D (positive) ions that permeate the first electrode 11 flow through the proton conducting layer 20 toward the second electrode 12. A portion of the H2 and D2 in the input gas flows from the anode to the cathode in this way, where they are consumed and become exhaust gas. When the first electrode 11 contains Pd in this way, Pd causes the catalytic reactions of the following formulas (1) and (2) to convert H + , D + are generated and flow through the proton conducting layer 20 to the right in the figure.

[0018]

number

[0019] The proton conducting layer 20 may be made of a conductor of H ions and D ions (proton conductor), such as Nafion (registered trademark) as described in Patent Document 1. These ions flow through the proton conducting layer 20 from the left to the right in the drawing, and an oxidation reaction occurs again at the second electrode 12, whereby H2, D2, etc., which are the same as the input gas, are produced as product gases on the second electrode 12 side.

[0020] 1, when the first electrode 11 is used as the anode and the second electrode 12 is used as the cathode, H ions and D ions flow from left to right in the proton conducting layer 20. In this case, if the hydrogen (H) component in the input gas flows more easily into the atmosphere on the cathode side (right side in the figure) than the deuterium (D) component, the H / D composition ratio in the generated gas will be higher than the H / D composition ratio in the input gas. As a result, more H2 is consumed in the input gas than D2, and the D component is concentrated in the exhaust gas discharged after the H and D components of the input gas have been consumed in this way. This exhaust gas can be used as an output gas with an increased concentration of the D component.

[0021] 1, if the D component in the input gas flows more easily into the atmosphere on the cathode side (right side in the figure) than the H component, the D / H composition ratio in the generated gas will be higher than the D / H composition ratio in the input gas, and this generated gas can be used as an output gas with an increased concentration of the D component.

[0022] In the fuel cell described in Patent Document 1, the anode and cathode are made of the same material (e.g., platinum (Pt)). In particular, a Pt / C catalyst, in which catalytic Pt is combined with carbon particles in the form of fine particles, is often used as the electrode material. In this case, the use of Pt in the form of fine particles increases the surface area, strengthening the catalytic activity and allowing hydrogen to easily permeate through the electrode. Meanwhile, the first electrode 11 in this MEA M is made of a thin film of a hydrogen-permeable metal, such as palladium (Pd), vanadium (V), tantalum (Ta), or titanium (Ti). This thin film has a denser structure than the Pt in the Pt / C catalyst and is formed, for example, by vacuum deposition. Despite the dense structure of the hydrogen-permeable metal used here, hydrogen can still permeate through the thin film.

[0023] The experimental results on this point are explained below. Here, Nafion with a film thickness of 52 μm was used as the proton conductive layer 20, and in FIG. 1, the first electrode 11 was the anode and the second electrode 12 was the cathode. Furthermore, Pt / C was used as the second electrode 12, and various materials were used as the first electrode 11. Here, Pt / C refers to an electrode in which a Pt / C catalyst is supported on a carbon sheet, similar to that used in fuel cells. A Pt / C catalyst is a large number of Pt microparticles with an average particle size of several nanometers supported on carbon microparticles with an average particle size of approximately 10 to 50 nm. This Pt / C electrode is generally used as an electrode in fuel cells, and in this case, the carbon sheet mainly functions as the electrode, and the Pt microparticles mainly function as the catalyst.

[0024] Three types of materials were used for the first electrode 11: Pt / C, the same as that for the second electrode 12 (Comparative Example 1); Pd / C, in which the Pt fine particles in Pt / C were replaced with Pd fine particles (Comparative Example 2); and a Pd thin film formed by vapor deposition (Example 1). Comparative Example 1 uses the same material for the first electrode 11 and the second electrode 12, and corresponds to a structure similar to that of the fuel cell described in Patent Document 1, etc. Both Example 1 and Comparative Example 2 use Pd, but in different ways. The thickness of the Pd thin film (Example 1) was 6 nm. The Pd in the Pd thin film in Example 1 has a denser structure than the Pd in the Pd / C in Comparative Example 2 or the Pt in the Pt / C in Comparative Example 1. That is, the Pd in Example 1 and Comparative Example 2 differ greatly in their denseness.

[0025] The D enrichment ratio was measured using these three types of gases. Figure 2 shows a schematic diagram of the apparatus used for this measurement. The area enclosed by the dashed-dotted line in the figure corresponds to the hydrogen isotope enrichment apparatus 1. The actual input gas to the first electrode 11 was a mixed gas of Ar, H2, and D2, with the flow rates controlled by mass flow controllers (MFCs) 101, 102, and 103. Ar was used as the carrier gas. Furthermore, since water (HO) is required for conduction in the proton-conducting layer 20 (Nafion), Ar was also introduced to the second electrode 12 (product gas) after its flow rate was adjusted by mass flow controller 104 and bubbled with HO in bubbler 105. In Figure 2, the atmospheres on both the first electrode 11 and second electrode 12 sides were atmospheric pressure, and the proton-conducting layer 20 and other components were at room temperature. The H and D composition analysis of the generated gas on the second electrode 12 side was performed by evacuating the generated gas using a vacuum exhaust system 110 (a combination of a turbo molecular pump and a dry pump) and then using a Q-mass (quadrupole mass spectrometer) 120. The H and D composition of the input gas was set by MFCs 102 and 103.

[0026] In this case, since the H / D composition ratio in the generated gas in Example 1 is increased as described later, the exhaust gas in Figures 1 and 2 can be used as the output gas as described above. In this case, the D / H composition ratio (molar ratio) in the input gas initially introduced is in and D / H, which is the D / H composition ratio in the exhaust gas in which H and D are consumed and emitted as described above. out (D / H in ) / (D / H out ) can be used as the D enrichment ratio. When this D enrichment ratio is 1, there is no selectivity between H and D in the configuration of Figure 1, and when this D enrichment ratio exceeds 1, it means that there is an effect of selectively removing H in the input gas as described above. However, the composition ratio of H and D was actually measured here because the input gas (composition D / H in ) and the product gas generated on the cathode side. outcan be calculated assuming that the H and D in the input gas multiplied by the reaction efficiency undergo the above reaction to achieve the composition of the product gas. Here, the D enrichment rate was calculated assuming this reaction efficiency is 50%.

[0027] 3 shows the results of measurements of Example 1(a) and Comparative Example 1(b) of the time change in ion current corresponding to the H2, HD, and D2 compositions separated and recognized according to mass by Q-mass 120 when a voltage was applied between first electrode 11 and second electrode 12 so that the current flowed was 0.025 A (in this case, the voltage was approximately 0.01 to 0.1 V). In both cases, the above reaction proceeds, and as H ions and D ions flow toward the cathode, H2 and D2 are gradually produced on the cathode side, and HD is also produced, and after approximately 45 minutes, the respective compositions become constant (saturate).

[0028] Figure 4 shows the composition ratios for each of the three materials for the first electrode 11 (anode) when the saturated value of the composition of the produced gas is set to each composition of the produced gas. Figure 5 also shows the D concentration ratio in the output gas (exhaust gas) for each material when the reaction efficiency on the anode side is set to 50% as described above. These results show that, particularly in Example 1, in which a Pd thin film was used for the anode, a large amount of H component can be selectively generated in the produced gas as shown in Figure 4, thereby consuming more H component in the input gas, and the D composition in the output gas (exhaust gas) can be increased (the D concentration ratio can be made greater than 1) as shown in Figure 5.

[0029] 5, when Pd / C (Comparative Example 2) or Pt / C (Comparative Example 1) was used as the anode, the D enrichment ratio was close to 1.0, which means that in these cases, no significant selectivity between H and D was observed. On the other hand, only when the Pd thin film (Example 1) was used, the D enrichment ratio was 3.0, which means that the D concentration in the exhaust gas could be increased.

[0030] FIG. 6 shows the results of measuring the D enrichment ratios for Example 1, Comparative Example 1, and Comparative Example 2 while varying the applied voltage. Because there is a one-to-one correspondence between the current flowing between the electrodes and the reaction efficiency, the horizontal axis represents the reaction efficiency converted from the current corresponding to the applied voltage. From these results, regardless of the voltage between the first electrode 11 and the second electrode 12, enrichment of the D composition was not possible in Comparative Example 1, in which Pt / C was used, whereas enrichment of the D composition was achieved in Example 1 and Comparative Example 2, in which Pd was used. However, this effect was particularly pronounced in Example 1, in which a Pd thin film was used, and was small in Comparative Example 2, in which Pd / C was used. Note that the absolute values of the D enrichment ratios here differ slightly from those in FIG. 5 due to differences in the measurement method used compared to FIG. 5.

[0031] Because the surface area of Pd in Comparative Example 2 is larger than that in Example 1, the efficiency of the reaction (oxidation reaction) in which hydrogen molecules (H2, D2) dissociate on the anode 11 is higher in Comparative Example 2. Therefore, the above results indicate that the high D concentration rate is not due to this oxidation reaction, but rather to other reactions, such as the subsequent absorption and diffusion of H ions and D ions into the anode. Furthermore, as mentioned above, in Example 1, the Pd film thickness is 6 nm, which is thinner than when used as an independent hydrogen-permeable membrane as described in Non-Patent Document 1, making this anode inexpensive. Even with such a thin Pd, the main component of the structure in Figure 1 is the thick proton-conducting layer 20, making it less likely to cause problems due to Pd embrittlement by hydrogen. Furthermore, because thin Pd is used, it is clear that the above configuration can be obtained inexpensively.

[0032] The results of a detailed composition analysis of the output gas (exhaust gas in Figures 1 and 2) in Example 1 (where the anode was Pd) were compared with those of Comparative Example 2, in which Pd was also used. Here, the compositions of H2, D2, and HD in the output gas were measured when the same input gas was used. Figure 7 shows the measurement results for Example 1 and Comparative Example 2. From these results, it is clear that the presence of HD in the output gas is significant in Comparative Example 2, whereas the HD component in Example 1 is extremely low.

[0033] In the configuration shown in Figure 2, HD is not originally present in the input gas, but is generated by the bonding of H and D dissociated by the catalytic action of Pd. Therefore, as with the generated gas shown in Figure 4, it is believed that a particularly large amount of HD was generated on the anode side in Comparative Example 2, in which Pd / C, which has a large Pd surface area and strong catalytic action, was used as the anode. What is particularly desired as gaseous deuterium is not HD, in which D is bonded with H, but D2, which consists only of D and does not contain H. From this perspective, Example 1, in which a Pd thin film (evaporated film) was used as the deuterium concentrator, is preferable.

[0034] Next, we will explain the results when the first electrode 11 is used as the cathode and the second electrode 12 as the anode, in contrast to the above example, and when a material other than Pd is used for the first electrode 11. The device configuration used for this measurement is shown in FIG. 8, corresponding to FIG. 2. The area enclosed by the dashed-dotted line in the figure corresponds to the hydrogen isotope enrichment device 2. In the configuration of FIG. 2, the input gas is input to the space where the first electrode 11 is located, whereas in this case, the input gas is input to the space where the second electrode 12 is located. Therefore, in the configuration of FIG. 8, the positions of the first electrode 11 and the second electrode 12 are reversed compared to the case of FIG. 2, but the positions and functions of the anode-side gas chamber 31 and the cathode-side gas chamber 32 remain unchanged. In this case, since the D / H ratio in the generated gas in the example is higher than that of the input gas, the generated gas is used as the output gas, as described above. In this case, the composition of the output gas (generated gas) is measured by the Q-mass 120 in the configuration of FIG. 8.

[0035] Here, the first electrode 11 is used as the cathode (right side in the figure), and the second electrode 12 is used as the anode (left side in the figure). The second electrode 12 is made of Pt / C, as described above, but Pd is used for the first electrode 11. Similarly, the cathode 12 is made of vanadium (V), tantalum (Ta), or titanium (Ti), which is a hydrogen-permeable metal like Pd, as shown in Examples 2 to 5. The same measurements were performed to measure the D concentration ratio. In these cases, the input gas was also configured to contact the surface on the anode (second electrode 12) side, and H ions and D ions flow through the proton-conducting layer 20 from the anode side toward the cathode (first electrode 11) side. The measurement results for the D concentration ratio in these cases are shown in FIG. 9 . The results for Comparative Example 1, in which both the anode and cathode were Pt / C, are also shown. For ease of handling the MEA, metal foils of Pd, V, Ta, or Ti with a thickness of 50 μm were used as the first electrode 11 in Examples 2 to 5. However, even when the evaporated film that became the first electrode in Example 1 was made as thick as 20 nm, no significant difference was obtained from Example 1. Therefore, there is no essential difference between this metal foil and the evaporated film, and it is thought that there is no difference due to the film thickness, at least within these film thickness ranges.

[0036] From these results, in Examples 2 to 5, a D concentration ratio sufficiently larger than 1 was obtained. That is, by using these metals with a dense structure as the cathode (first electrode 11), it is possible to obtain an output gas (product gas) in which D in the input gas is concentrated. In this case, V, Ta, and Ti can be used in addition to Pd. As described above, these hydrogen-permeable metals are metals that allow H ions and D ions to permeate, and it is preferable to use such hydrogen-permeable metals formed into a dense structure as the first electrode 11. Note that, as in Example 2 above, when the materials in Comparative Example 2 above (anode: Pd / C, cathode: Pt / C) were reversed between the anode and cathode (anode: Pt / C, cathode: Comparative Example 3), the D concentration ratio was 1.

[0037] Furthermore, when similar measurements were performed on the case where both the first electrode 11 and the second electrode 12 were Pd thin films (Example 6), the D concentration ratio was also large, at approximately 2.9. From these results, it is presumed that the D concentration effect described above is brought about particularly by the characteristics of the first electrode 11 or the interface between the first electrode 11 and the proton conducting layer 20, and is basically independent of the polarity or the second electrode 12. Regardless of the polarity, the input gas is input so as to contact the anode side, and the output gas with an increased D concentration is extracted from the first electrode 11 side (the anode side in FIG. 2 and the cathode side in FIG. 8). In this case, a Pd thin film was used in Examples 1, 2, and 6, but it can be presumed from the results of Examples 3 to 5 that similar results would be obtained when a V, Ta, or Ti thin film was used.

[0038] Next, we will explain the results when a thin layer composed of a material other than a hydrogen-permeable metal is added to the first electrode 11. Here, we used graphene, which allows hydrogen to permeate like Pd, as described in S. Hu, M. Lozada-Hidalgo, F.C. Wang, A. Mishchenko, F. Schedin, R.R.N. Air, E.W. Hill, D.W. Boukhvalov, M.I. Katsnelson, R.A.R. Dryfe, I.V. Grigorieva, H.A.W.u, and A.K. Geim, "Proton Transport Through One-Atom-Thick Crystals," Nature, Vol. 516, pp. 227-230 (2014). H ions and D ions permeate the hexagonal crystal structure of graphene.

[0039] Here, in such an example (Example 7), before Pd with a thickness of 6 nm was formed as the anode by vapor deposition as in Example 1, monolayer graphene was formed on the surface of the proton conducting layer 20 (the electrode material of the anode in this case will be referred to as Pd / Gr hereinafter). As in Example 1, Pt / C, which is the second electrode 12, was used as the cathode. The D enrichment factor in this case was 6.7, which was higher than that in Example 1. In other words, by interposing monolayer graphene between Pd (first electrode 11) and the proton conducting layer 20, the D enrichment factor was further improved.

[0040] This is thought to be because the difference in zero-point vibrational energy between H ions and D ions in the proton conducting layer 20 on the first electrode 11 side is larger when graphene is present than when graphene is not present. That is, by interposing a substance that can increase the difference in zero-point vibrational energy between H ions and D ions and that allows hydrogen (H ions, D ions) to permeate between the hydrogen-permeable metal and the proton conducting layer 20, the D concentration can be particularly increased. Even when the polarity of Example 7 was reversed (Example 8, where the first electrode 11 and graphene were on the cathode side), a D concentration greater than 1 was obtained. However, the D concentration in this case was approximately 2.1, which was smaller than that of Example 7. That is, the configuration in which graphene is combined with the first electrode 11 is particularly effective when these are on the anode side.

[0041] The D enrichment rates measured in the above examples and comparative examples are shown in Table 1. The results show that a particularly high D enrichment rate can be obtained when the above hydrogen-permeable metal thin film is used as an electrode.

[0042] [Table 1]

[0043] Next, we will explain a configuration in which multiple MEAs M are used to enrich the D component in multiple stages, thereby improving the enrichment efficiency. Figure 10 shows the configuration of a hydrogen isotope enrichment device 3 (first modified example) in which a configuration using the first electrode 11 as an anode and the second electrode 12 as a cathode, as in Figure 2 or Example 1, is provided in three stages. Here, MEAs M1, M2, and M3 are used in order from the upstream side (top side in the figure). The input gas before enrichment is input as the input gas (first input gas) to M1 in the first stage, and the output gas with the highest D concentration is the exhaust gas (third exhaust gas) from M3 in the final stage (third stage). As mentioned above, in this case, the exhaust gas on the first electrode 11 (anode) side of M1, M2, and M3 is the gas with the enriched D concentration. For convenience, Figure 10 shows a voltage applied only to M1, but in reality, voltage is applied in parallel to all of M1, M2, and M3. In addition, in FIG. 10, the configurations of M1, M2, and M3 on the second electrode 12 side are omitted because they are independent of each other and are not related to the operation.

[0044] Here, the anode-side gas chambers 31 of adjacent MEAs are connected so that the exhaust gas (first exhaust gas) in M1 becomes the input gas (second input gas) for the next stage M2, and the exhaust gas (second exhaust gas) in M2 becomes the input gas (third input gas) for the next stage M3. With this configuration, the D concentration of the input gas (first input gas) for M1 can be increased sequentially through M1, M2, and M3, and output as the exhaust gas (third exhaust gas) for M3.

[0045] Fig. 11 shows the configuration of a hydrogen isotope enrichment apparatus 4 (second modification), which is a modification of the configuration in Fig. 10. Here, MEAs M1 to M4 are used in order from top to bottom, and the anode-side gas chambers 31 of the MEAs M1 to M4 are connected so that the exhaust gas from the previous stage becomes the input gas for the next stage, as in the above. However, here, the difference is that the generated gas in Fig. 1 is also fed back and used.

[0046] In Figure 11, the D concentration of the exhaust gas from each stage and the input gas to each stage increases toward the lower stage. Therefore, the D concentration of the exhaust gas also inevitably increases toward the lower stage. In this case, as described above, although the D concentration of the product gas in one MEA is lower than the D concentration of the input gas and exhaust gas, the D concentration of the product gas in a later stage may be higher than the D concentration of the exhaust gas in an earlier stage. In the configuration of Figure 11, if the D concentration of the product gas (third product gas) from M3 is higher than the D concentration of the exhaust gas (first exhaust gas) from M1, the product gas (third product gas) can be extracted from the cathode-side gas chamber 32 of M3 and combined with the exhaust gas (first exhaust gas) from M1 to form the input gas (second input gas) for M2. This can further increase the D concentration of the second input gas, thereby further increasing the D concentration of the exhaust gas (second exhaust gas) from M2. Similarly, the product gas of M4 (fourth product gas) and the exhaust gas of M2 (second exhaust gas) can be combined to form the input gas of M3 (third input gas), which can particularly increase the D enrichment rate by the entire hydrogen isotope enrichment device 4.

[0047] As in the case of FIG. 8 or Example 2, the above-described MEA M can be configured in multiple stages, with the first electrode 11 used as the cathode and the second electrode 12 used as the anode. FIG. 12 shows the configuration of a hydrogen isotope enrichment device 5 (third modified example) using this MEA in three stages, corresponding to FIG. 10. Here, MEAs M1, M2, and M3 are used in order from the left (upstream side). The input gas before enrichment is input as the input gas (first input gas) of M1 in the first stage, and the output gas with the highest D concentration is the product gas (third product gas) of M3 in the final stage (third stage). As described above, in this case, for all of M1, M2, and M3, the product gas in the cathode-side gas chamber 32 on the first electrode 11 (cathode) side is a gas with an increased D concentration.

[0048] Here, the cathode-side gas chamber 32 of each MEA is connected to the anode-side gas chamber 31 of the next stage so that the product gas (first product gas) in M1 becomes the input gas (second input gas) for M2 in the next stage, and the product gas (second product gas) in M2 becomes the input gas (third input gas) for M3 in the next stage. With this configuration, the D concentration of the input gas (first input gas) for M1 can be increased sequentially by M1, M2, and M3, and output as the product gas (third product gas) for M3.

[0049] Fig. 13 shows the configuration of a hydrogen isotope enrichment apparatus 6 (fourth modification) corresponding to Fig. 11, which is a modification of the configuration of Fig. 12. Here, MEAs M1 to M4 are used in order from the upstream side (left side in the figure), and similarly to the above, the cathode-side gas chambers 32A of the MEAs M1 to M4 are connected to the anode-side gas chamber 31 of the next stage so that the product gas of the previous stage becomes the input gas of the next stage. However, here, similar to the configuration of Fig. 11, the difference is that exhaust gas is also fed back and used.

[0050] In Figure 13, the D concentration of the product gas at each stage and the input gas to each stage increases toward the downstream (right side in the figure). Therefore, the D concentration of the product gas also inevitably increases toward the downstream. In this case, as described above, although the D concentration of the exhaust gas for one MEA is lower than the D concentrations of the input gas and product gas, the D concentration of the exhaust gas from a downstream stage may be higher than the D concentration of the product gas from the previous stage. In the configuration of Figure 13, if the D concentration of the exhaust gas (third exhaust gas) discharged from the anode-side gas chamber 31 of M3 is higher than the D concentration of the product gas (first product gas) of M1, the D concentration of the exhaust gas (third exhaust gas) from M3 can be further increased by combining the product gas (first product gas) of M1 with the product gas (first product gas) of M1 to form the input gas (second input gas) for M2. This further increases the D concentration of the second input gas, thereby further increasing the D concentration of the product gas (second product gas) of M2. Similarly, the exhaust gas (fourth exhaust gas) of M4 and the product gas (second product gas) of M2 can be combined to form the input gas (third input gas) of M3.

[0051] The configurations shown in Figures 10 to 13 can be particularly easily realized when the above-mentioned MEA is used, because not only the substance used as input (input gas), but also the exhaust gas discharged from the anode side gas chamber 31 and the generated gas discharged from the cathode side gas chamber 32 are all gases.

[0052] In the example of FIG. 11, the product gases of M3 and M4 (third product gas and fourth product gas) were used as part of the input gases (second input gas and third input gas) of M2 and M3 one stage before them, and in the example of FIG. 13, the exhaust gases of M3 and M4 (third exhaust gas and fourth exhaust gas) were used as part of the input gases (second input gas and third input gas) of M2 and M3 one stage before them. However, when more MEAs are used, the product gas (in the case of FIG. 11) or exhaust gas (in the case of FIG. 13) may be used as part of the input gas two or more stages before the MEA that generated the product gas or exhaust gas. This setting can be made depending on the D concentration of the input gas, exhaust gas, and product gas in each MEA.

[0053] In the above configuration, M1 to M3 (M4) can be independent MEAs, or MEAs with layers made of the same material and having the same thickness can be used. In this case, M1 to M3 (M4) can be actually provided as different regions within the surface of a single large MEA (membrane electrode assembly base material). That is, by separating the first electrode 11 and the second electrode 12 into separate regions and forming the first electrode side gas chamber 11A and the second electrode side gas chamber 12A in three (four) separate regions, the configurations shown in Figures 10 to 13 can be easily realized. This configuration is particularly easy to realize because the D concentration action described above occurs in a gaseous state at room temperature. It is also easy to connect and use more MEAs in the same way.

[0054] In the above example, deuterium ( 2 H, D) is hydrogen ( 1 It has been shown that deuterium can be selectively enriched from a gas mixture containing tritium (H, H). 3It is clear that hydrogen (H, T) can be enriched in a similar manner, as can other hydrogen isotopes. [Explanation of symbols]

[0055] 1~6 Hydrogen isotope enrichment equipment 11 1st electrode 12 Second electrode 20 Proton Conducting Layer 31 Anode side gas chamber 32 Cathode gas chamber 101~104 Mass flow controller (MFC) 105 Bubbler 110 Vacuum exhaust system 120 Q-mass (quadrupole mass spectrometer) M, M1~M4 Membrane Electrode Assembly (MEA)

Claims

1. hydrogen( １ 1. A hydrogen isotope enrichment apparatus for outputting an output gas in which an input gas containing a mixture of hydrogen isotopes (H) and hydrogen isotopes that are isotopes of the hydrogen is mixed, and the output gas has an increased concentration of the hydrogen isotopes relative to the hydrogen, a proton conducting layer made of a proton conductor that conducts positive hydrogen ions and having two opposing main surfaces; a first electrode formed on one main surface of the proton conducting layer, the first electrode being made of a thin film of a hydrogen-permeable metal selected from palladium (Pd), vanadium (V), tantalum (Ta), and titanium (Ti); a second electrode formed on the other main surface of the proton conducting layer; a membrane electrode assembly having In the membrane electrode assembly, a DC voltage is applied between the first electrode and the second electrode, with the first electrode acting as a positive side and the second electrode acting as a negative side, the hydrogen and the hydrogen isotopes in the input gas in contact with the first electrode flow between the first electrode and the second electrode, and a product gas is generated on the side of the second electrode; a hydrogen isotope enrichment apparatus, characterized in that an exhaust gas, which is the input gas after the hydrogen and the hydrogen isotopes have been consumed to produce the product gas, is extracted as the output gas.

2. hydrogen( １ 1. A hydrogen isotope enrichment apparatus for outputting an output gas in which an input gas containing a mixture of hydrogen isotopes (H) and hydrogen isotopes that are isotopes of the hydrogen is mixed, and the output gas has an increased concentration of the hydrogen isotopes relative to the hydrogen, a proton conducting layer made of a proton conductor that conducts positive hydrogen ions and having two opposing main surfaces; a first electrode formed on one main surface of the proton conducting layer, the first electrode being made of a thin film of a hydrogen-permeable metal selected from palladium (Pd), vanadium (V), tantalum (Ta), and titanium (Ti); a second electrode formed on the other main surface of the proton conducting layer; a membrane electrode assembly having In the membrane electrode assembly, a DC voltage is applied between the first electrode and the second electrode, with the first electrode being negative and the second electrode being positive, the hydrogen and the hydrogen isotopes in the input gas in contact with the second electrode flow between the first electrode and the second electrode, a product gas is generated on the first electrode side, and an exhaust gas, which is the input gas after the hydrogen and the hydrogen isotopes have been consumed to generate the product gas, is generated on the second electrode side; A hydrogen isotope enrichment apparatus, wherein the product gas is extracted as the output gas.

3. 3. The hydrogen isotope enrichment device according to claim 1, wherein the second electrode is made of a thin film of the hydrogen-permeable metal.

4. 4. The hydrogen isotope enrichment device according to claim 1, wherein the first electrode is a vapor-deposited film of the hydrogen-permeable metal.

5. 5. The hydrogen isotope enrichment device according to claim 1, wherein the first electrode and the proton conducting layer are in contact with each other via a monolayer graphene.

6. a plurality of the membrane electrode assemblies are used in stages from the time when the input gas is input until the time when the output gas is output, 6. The hydrogen isotope enrichment device according to claim 1, wherein the output gas from the membrane electrode assembly in a preceding stage is used as the input gas for the membrane electrode assembly in an adjacent subsequent stage.

7. 7. The hydrogen isotope enrichment device according to claim 6, wherein one of the exhaust gas and the generated gas that is not used as the output gas in one of the membrane electrode assemblies is used as the input gas for the membrane electrode assembly in a stage upstream of the one of the membrane electrode assemblies.

8. 8. The hydrogen isotope enrichment device according to claim 6, wherein a membrane electrode assembly base material is used, the base material including the first electrode, the second electrode, and the proton conductive layer, and each of the plurality of membrane electrode assemblies is formed as a different region within a plane of the single membrane electrode assembly base material.

9. The hydrogen isotope is deuterium ( ２ H or D), or tritium ( ３ 9. The hydrogen isotope enrichment device according to claim 1, wherein the hydrogen isotope enrichment element is a hydrogen isotope enrichment element.

Images