JP7164882B2 - Method for producing water or aqueous solution enriched with hydrogen isotope, method and apparatus for producing hydrogen gas with reduced hydrogen isotope concentration - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing water or an aqueous solution enriched with hydrogen isotopes, and a method and apparatus for producing hydrogen gas with reduced hydrogen isotope concentration. More specifically, the present invention relates to a method for producing hydrogen isotope-enriched water or an aqueous solution from water or an aqueous solution containing hydrogen isotope-containing water, and a method and apparatus for producing hydrogen gas with a reduced hydrogen isotope concentration. The method and apparatus for producing water or an aqueous solution enriched with hydrogen isotopes can co-produce hydrogen gas with reduced hydrogen isotope concentration.
Cross-Reference to Related Applications This application claims priority from Japanese Patent Application No. 2017-084386 filed on April 21, 2017, the entire description of which is specifically incorporated herein by reference.

Hydrogen isotopes of deuterium and tritium are important as raw materials for nuclear fusion reactor fuel and medical materials. Furthermore, the contaminated water related to the Fukushima nuclear power plant accident has not found an effective separation method for tritium, which is still the biggest concern for contaminated water treatment.

Technologies for separating and concentrating hydrogen isotopes such as deuterium and tritium include a distillation method that utilizes differences in boiling points, a water-hydrogen sulfide exchange method (GS method) that uses light hydrogen atoms and exchange substitution, a water electrolysis method, and platinum catalysts. (CECE method) in which the chemical exchange method is combined (see Non-Patent Document 1 (provided by TEPCO)).

Non-Patent Document 1: http://www.tepco.co.jp/nu/fukushima-np/roadmap/images/c130426_06-j

Among them, the water electrolysis method was started in 1933 by G.N. Lewis et al. by continuously electrolyzing water in an old electrolytic cell to obtain a small amount of heavy water, and this method is still used industrially today. However, at the Fukushima nuclear power plant, it is necessary to treat a large amount of contaminated water every day, which consumes a huge amount of electricity, making it unsuitable for large-scale production.

Therefore, proposing an innovative electrolysis method with low power consumption is required for the nuclear industry, which requires large-scale hydrogen isotopes, and for solving the problem of contaminated water in Fukushima. An object of the present invention is to provide a new technique for concentrating water containing hydrogen isotopes.

The present invention is as follows.
[1]
A fuel cell connected in series with at least one water electrolyser and at least two hydrogen gas streams (FCn, where n is an integer greater than or equal to 2 and firstly connected to the water electrolyser) is FC1.), and each fuel cell generates power independently, and water electrolysis is performed in a water electrolysis device to obtain water or an aqueous solution containing hydrogen isotopes (hereinafter, aqueous solution AS ₀ ) A method for producing a water or aqueous solution (AS _e ) having a higher hydrogen isotope content than the aqueous solution AS ₀ from
(we1) water electrolysis of the aqueous solution AS ₀ in a water electrolyzer to obtain hydrogen gas and oxygen gas;
(fc1) The hydrogen gas obtained by the electrolysis is supplied to the negative electrode side of the fuel cell 1 (FC1), part of the hydrogen gas (HG ₀ ) is reacted at the negative electrode, and the remaining hydrogen gas (HG ₁ ) and recovering the hydrogen isotope-containing water (W ₁ ) produced on the positive electrode side;
(fc2) The recovered hydrogen gas (HG ₁ ) is supplied to the negative electrode side of the fuel cell 2 (FC2), part of the hydrogen gas (HG ₁ ) is reacted at the negative electrode, and the remaining hydrogen gas (HG ₂ ) and recovering hydrogen isotope-containing water (W ₂ ) produced on the positive electrode side;
(fc3) If fuel cells are connected next to fuel cell 2 (FC2), this operation is sequentially repeated up to fuel cell n (FCn), and the remaining hydrogen gas (HG _n ) and recovering hydrogen isotope-containing water (W _n ) generated on the positive electrode side (n is an integer of 3 or more);
(we2) recovering water or an aqueous solution AS _e having a higher hydrogen isotope content than the aqueous solution AS ₀ after electrolysis from the water electrolyzer.
[2]
Oxygen gas or an oxygen-containing gas is supplied to the positive electrode sides of FC1 to _FCn , and at least part of the recovered hydrogen isotope-containing water W1 to Wn is supplied to the water electrolysis device, [ ₁ ] described method.
[3]
The method according to [1] or [2], wherein at least part of the recovered hydrogen isotope _- containing water W1 to _Wn is supplied to the water electrolyzer together with the aqueous solution _AS0 .
[4]
Any one of [1] to [3], wherein the recovery of the hydrogen isotope _- containing water W1 to _Wn from the fuel cell is carried out by entraining it with the oxygen gas or oxygen-containing gas discharged from the positive electrode side of the fuel cell. The method described in .
[5]
The method according to any one of [1] to [4], comprising supplying at least part of the oxygen gas obtained by the water electrolysis to the positive electrode side of at least part of the fuel cells.
[6]
At least part of the oxygen gas obtained by the water electrolysis is supplied to the positive electrode side of FCn, and the oxygen gas or oxygen-containing gas discharged from the positive electrode side of FCn is the positive electrode of fuel cell n-1 (FCn-1). The method according to [5], in which the supply of discharged oxygen gas or oxygen-containing gas to the next fuel cell is repeated, in sequence, up to FC1.
[7]
Co-producing hydrogen gas by recovering hydrogen gas _HG2 or HGn having a _lower hydrogen isotope content than hydrogen gas HG0 from FC2 in step (fc2) or _FCn in step (fc3) (however, , n is an integer of 2 or more), and the method according to any one of [1] to [6].
[8]
A fuel cell connected in series with at least one water electrolyser and at least two hydrogen gas streams (FCn, where n is an integer greater than or equal to 2 and firstly connected to the water electrolyser) shall be referred to as FC1.), generating power independently in each fuel cell, and performing water electrolysis in a water electrolyzer, producing hydrogen gas with a reduced hydrogen isotope concentration and
(we1) obtaining hydrogen gas (HG ₀ ) and oxygen gas by water electrolysis of water or an aqueous solution containing hydrogen isotopes in a water electrolyzer;
(fc1h) The hydrogen gas HG ₀ obtained by the electrolysis is supplied to the negative electrode side of the fuel cell 1 (FC1), a part of the hydrogen gas HG ₀ is reacted at the negative electrode, and the remaining hydrogen gas (HG ₁ ),
(fc2h) The recovered hydrogen gas HG ₁ is supplied to the negative electrode side of the fuel cell 2 (FC2), part of the hydrogen gas HG ₁ is reacted at the negative electrode, and the remaining hydrogen gas (HG ₂ ) is recovered at the negative electrode side. thing,
(fc3h) If fuel cells are connected next to fuel cell 2 (FC2), this operation is sequentially repeated up to fuel cell n (FCn), and the remaining hydrogen gas (HG _n ) is released on the negative electrode side. Collect (n is an integer of 3 or more),
obtaining a hydrogen gas HG ₂ or HG _n having a lower hydrogen isotope concentration than hydrogen gas HG ₀ ;
The above method, comprising
[9]
The ratio of the amount of hydrogen gas supplied to the negative electrode side of FC1 in the step (fc1) to the amount of hydrogen gas recovered from FC2 in the step (fc2) or FCn in the step (fc3) is 100:0. The method according to any one of [1] to [8], wherein the range is ∼50.
[10]
The method according to any one of [1] to [9], wherein at least part of the electric power for water electrolysis in the water electrolysis device is covered by electric power generated in the fuel cell.
[11]
The method of any one of [1] to [10], wherein the at least two series-connected fuel cells are 3 to 10 fuel cells connected in series.
[12]
The method according to any one of [1] to [11], wherein the aqueous solution AS ₀ is pure water, alkaline aqueous solution or seawater.
[13]
at least one water electrolyser and at least two fuel cells connected in series with a stream of hydrogen gas, said water electrolyzer having a cathode compartment and an anode compartment, said fuel cell having an anode compartment and a cathode compartment, respectively. has
a means for flowing hydrogen gas from the cathode chamber of the water electrolyzer to the anode chamber of the fuel cell adjacent to the water electrolyzer of the fuel cells connected in series;
The fuel cells connected in series have hydrogen gas flow means between the negative electrode chambers of the fuel cells connected in order from the fuel cell adjacent to the water electrolysis device,
The fuel cells connected in series have an oxygen gas or oxygen-containing gas distribution means between the positive electrode chambers of the fuel cells sequentially connected from the fuel cell adjacent to the water electrolysis device, and
Having a distribution means for recovering the water generated by the fuel cell to the water electrolysis device,
Equipment for producing water or aqueous solutions enriched with hydrogen isotopes.
[14]
The production apparatus according to [13], for co-producing hydrogen gas with a reduced isotope concentration.
[15]
at least one water electrolyser and at least two fuel cells connected in series with a stream of hydrogen gas, said water electrolyzer having a cathode compartment and an anode compartment, said fuel cell having an anode compartment and a cathode compartment, respectively. has
a means for flowing hydrogen gas from the cathode chamber of the water electrolyzer to the anode chamber of the fuel cell adjacent to the water electrolyzer of the fuel cells connected in series;
The fuel cells connected in series have hydrogen gas flow means between the negative electrode chambers of the fuel cells connected in order from the fuel cell adjacent to the water electrolysis device.
An apparatus for producing hydrogen gas in which hydrogen isotopes are reduced from the hydrogen gas obtained by a water electrolyzer.
[16]
The manufacturing apparatus according to any one of [13] to [15], wherein the at least two series-connected fuel cells are 3 to 10 fuel cells connected in series.
[17]
The manufacturing apparatus according to any one of [13] to [16], wherein the fuel cell is a polymer electrolyte fuel cell.
[18]
The production apparatus according to any one of [13] to [17], wherein the water electrolysis device has an oxygen gas or oxygen-containing gas distribution means connected to an adjacent fuel cell.

In the production method and apparatus of the present invention, water electrolysis and power generation by a fuel cell can be combined to enrich the hydrogen isotope concentration of water containing hydrogen isotopes, the concentration efficiency is high, and power is generated by the fuel cell. Since the generated electricity can be used for water electrolysis, the power consumption of the system as a whole can be suppressed. In the present invention, it is also possible to co-produce hydrogen gas with a reduced hydrogen isotope concentration. Furthermore, in another aspect of the present invention, it is also possible to provide a method and apparatus capable of producing hydrogen gas with reduced hydrogen isotope concentration.

1 is a schematic illustration of one embodiment of the apparatus of the present invention; FIG. It is explanatory drawing of the method of this invention. 1 shows an outline of an experimental apparatus used in Example 1. FIG. 1 shows experimental results of Example 1. FIG. 2 shows experimental results of Example 2. FIG. The outline of the experimental apparatus used in Example 3 is shown. 3 shows experimental results of Example 3. FIG. FIG. 10 is a schematic illustration of the oxygen downflow type apparatus of the present invention used in Example 5. FIG. FIG. 10 is a schematic explanatory view of the oxygen backflow type apparatus of the present invention used in Example 5. FIG. 1 shows experimental results of Example 5. FIG. 1 shows experimental results of Example 5. FIG.

<Method for producing hydrogen isotope-enriched water/aqueous solution>
The present invention employs fuel cells connected in series with at least one water electrolyser and at least two hydrogen gas streams, and independently generating electricity in each fuel cell and electrolyzing water in the water electrolyzer. to produce water or an aqueous solution (AS _e ) having a hydrogen isotope content higher than that of the aqueous solution AS ₀ from water or an aqueous solution containing a hydrogen isotope (hereinafter referred to as an aqueous solution AS ₀ ).

<Production equipment for hydrogen isotope enriched water/water solution>
Further, the present invention relates to an apparatus for producing hydrogen isotopically enriched water or aqueous solution (hydrogen isotopically enriched water/aqueous solution) comprising at least one water electrolysis device and at least two series connected fuel cells. The water electrolyzer has a cathode compartment and an anode compartment, and the fuel cells each have an anode compartment and a cathode compartment.

A schematic diagram of one embodiment of the manufacturing apparatus of the present invention is shown in FIG.
The apparatus shown in FIG. 1 includes one water electrolyzer (water electrolyzer) 10 and fuel cells FC1, FC2, . . . FCn connected in series. n is an integer of 3 or more. There is no upper limit to n, and it can be an integer of 10 or less, for example. Although FCn is shown in FIG. 1, there may be two fuel cells, FC1 and FC2. When the fuel cells are connected in series, it means that a plurality of fuel cells are connected along the flow of hydrogen gas flowing between the fuel cells. It does not mean that multiple fuel cells are connected in series with respect to the flow of electricity between them. A plurality of fuel cells are operated under independent conditions and are not electrically connected in series.

Although not shown, the water electrolytic bath 10 has an anode, a negative electrode, and a diaphragm (for example, an ion exchange membrane) installed between the anode and the negative electrode in the electrolytic bath. There are no particular restrictions on the type, structure, shape, size, etc. of the anode, anode and diaphragm (eg, ion exchange membrane) that constitute the water electrolytic cell. An external power source (not shown) is connected to the anode and the negative electrode.

Solid polymer water electrolyzers, alkaline water electrolyzers, and the like are known as water electrolyzers, but alkaline water electrolyzers are suitable because they can generate a large amount of hydrogen gas. A suitable temperature range for operating the water electrolyzer is, for example, 20°C to 70°C. However, it is not intended to be limited to this range. In electrolysis, the amount of hydrogen generated can be controlled by adjusting the amount of current. A preferred current can range, for example, from 0.1 to 100A. However, it is not intended to be limited to this range. A plurality of water electrolyzers may be used in combination.

The anode chamber has flow means for supplying water/aqueous solution and oxygen gas flow means for discharging oxygen gas generated at the anode by electrolysis. The cathode chamber may have hydrogen gas circulation means for discharging hydrogen gas, and the cathode chamber may have circulation means for supplying water/aqueous solution. However, in the apparatus shown in FIG. 1, the flow means for supplying water/aqueous solution is connected to the anode chamber side.

Fuel cells FC1, FC2, . . . FCn have a positive electrode catalyst layer and a negative electrode catalyst layer on both sides of an electrolyte. has a negative electrode chamber on the outside of the There are no particular restrictions on the types, structures, shapes, and dimensions of the electrolyte, positive electrode, and negative electrode. However, the catalyst used in the catalyst layer serving as the positive electrode is preferably a material capable of preferentially causing the water-producing reaction between hydrogen isotope ions and oxygen over the water-producing reaction between hydrogen ions and oxygen. Examples of such materials include noble metals such as platinum and ruthenium, transition metals such as nickel and cobalt, and their alloys and oxides. The catalyst used in the catalyst layer that serves as the negative electrode is preferably a material that can preferentially cause the oxidation reaction of hydrogen gas containing hydrogen isotopes as compared with the oxidation reaction of hydrogen gas. Examples of such materials include noble metals such as platinum and ruthenium, transition metals such as nickel and cobalt, and their alloys and oxides.

The electrolyte is preferably a material that readily permits the diffusion of not only hydrogen ions, but also hydrogen isotope ions, within the electrolyte. Examples of such materials include proton conductive solid polymer membranes and anion conductive solid polymer membranes.

Oxygen gas circulation means (supply side and discharge side) are connected to the positive electrode chamber, and hydrogen gas circulation means (supply side and discharge side) are connected to the negative electrode chamber. However, in this specification, the oxygen gas circulating means is means for circulating oxygen gas or oxygen-containing gas. Although not shown, the positive electrode chamber can be further provided with flow means (supply side and discharge side) for supplying water/aqueous solution. Incidentally, the water/aqueous solution can be discharged together with the oxygen-containing gas discharged from the positive electrode chamber. Circulation means for supplying water/aqueous solution (supply side and discharge side), oxygen gas circulation means (supply side and discharge side), and hydrogen gas circulation means (supply side and discharge side) provided in the fuel cell are adjacent to each other. It can be connected to a fuel cell, a water electrolyser, or externally. In FIG. 1, FC1 is adjacent to the water electrolyzer, the oxygen gas circulation means (supply side) of FC1 adjacent to the water electrolysis vessel is connected to the anode chamber of the water electrolysis vessel, and the hydrogen gas circulation means of FC1 ( supply side) connects with the cathode chamber of the water electrolyser. The flow means (discharge side) for supplying the water/aqueous solution of FC1 can also be a water electrolytic bath.

On the other hand, the flow means for supplying the water/aqueous solution of FCn (supply side), the oxygen gas flow means (discharge side), and the hydrogen gas flow means (discharge side) are connected to the outside of the apparatus. However, the oxygen gas distribution means (supply side) to each fuel cell is not connected to the oxygen gas distribution means (discharge side) of the adjacent water electrolyzer or the adjacent fuel cell, and oxygen gas (for example, air ) can also be connected to a source.

A hydrogen gas flow means connecting between the fuel cells connected in series communicates between the anode chambers of the adjacent fuel cells. The oxygen gas flow means connecting the fuel cells connected in series communicates between the positive electrode chambers of the adjacent fuel cells. Alternatively, a water or aqueous solution flow means may connect between the positive electrode chambers of adjacent fuel cells in series-connected fuel cells.

The method for producing hydrogen isotope-enriched water/aqueous solution of the present invention can be carried out using, for example, the apparatus of the present invention. The method of the invention will now be described with reference to FIG.

(we1) Hydrogen gas and oxygen gas are obtained by water electrolysis of the aqueous solution AS ₀ in a water electrolyzer.
(fc1) The hydrogen gas obtained by the electrolysis is supplied to the negative electrode side of the fuel cell 1 (FC1), part of the hydrogen gas (HG ₀ ) is reacted at the negative electrode, and the remaining hydrogen gas (HG ₁ ) and hydrogen isotope-containing water (W ₁ ) produced on the positive electrode side are recovered.
(fc2) The recovered hydrogen gas (HG ₁ ) is supplied to the negative electrode side of the fuel cell 2 (FC2), part of the hydrogen gas (HG ₁ ) is reacted at the negative electrode, and the remaining hydrogen gas (HG ₂ ) and hydrogen isotope-containing water (W ₂ ) produced on the positive electrode side are recovered.
(fc3) If fuel cells are connected next to fuel cell 2, this operation is repeated until fuel cell n (FCn), and the remaining hydrogen gas (HG n ) on the negative electrode side and the remaining hydrogen gas (HG _n ) on the positive electrode side The produced hydrogen isotope-containing water (W _n ) is recovered (n is an integer of 3 or more).
(we2) Recover water or aqueous solution _ASe having a hydrogen isotope content higher than that of aqueous solution _AS0 after electrolysis from the water electrolyzer.

Hydrogen gas and oxygen gas are obtained by water electrolysis of the aqueous solution AS ₀ in the water electrolyzer, and water or aqueous solution AS _e having a higher hydrogen isotope content than the aqueous solution AS ₀ after electrolysis is recovered.

The aqueous solution AS ₀ can be water (aqueous solution) containing water containing the hydrogen isotopes deuterium (D) or tritium (T). Water containing the hydrogen isotope deuterium ₍ D) contains _H2O , HDO and/or D2O. Water containing the hydrogen isotope tritium (T) contains _H2O , HTO and/or _T2O . The concentration of water containing hydrogen isotopes (such as HDO and/or D ₂ O, HTO and/or T ₂ O) contained in the aqueous solution AS ₀ is not particularly limited. For example, hydrogen isotope elements can range from 0.1 to 100 atomic percent. However, it is not intended to be limited to this range.

As for the operation of the fuel cell, in the case of a polymer electrolyte water electrolyzer, the aqueous solution is preferably pure water containing no electrolyte.

In the case of an alkaline water electrolyzer, the presence of alkaline ions is required, and the water may contain electrolytes. Rather, in consideration of electrical resistance, it is preferable that the aqueous solution AS ₀ or the electrolytic solution for water electrolysis to which the aqueous solution AS ₀ is supplied contain an electrolyte. If the aqueous solution AS ₀ is pure water, electrolytes can be added to the aqueous solution AS _n . The electrolyte can be, for example, an alkaline substance from the viewpoint of not having adverse reactivity such as corrosiveness, and the alkaline substance is preferably, for example, sodium hydroxide, potassium hydroxide, or the like. The aqueous solution containing the electrolyte can also be seawater. It can also be pond water. The concentration of the electrolyte can be appropriately determined in consideration of the electrolysis conditions and the like.

The conditions for water electrolysis in the water electrolyzer are not particularly limited, and may be any conditions as long as oxygen molecules are produced at the anode and hydrogen molecules are produced at the cathode in the water electrolyzer. In water electrolysis, water containing hydrogen isotopes contained in an aqueous solution is less likely to be electrolyzed than water (H ₂ O) not containing hydrogen isotopes. However, this does not mean that water containing hydrogen isotopes contained in the aqueous solution is not electrolyzed at all. The ratio of light hydrogen and hydrogen isotope elements (expressed as H/X (X is D or T), which is decomposed into oxygen molecules and hydrogen molecules in water electrolysis) depends on the type of hydrogen isotope element and electrolysis. Although it varies depending on the equipment and operating conditions, it exceeds 1, for example, in the range of 1.5 to 5. The greater the H/X, the higher the hydrogen isotope enrichment effect in electrolysis.H/X is 2. It is preferable to perform electrolysis at the above, preferably at least 3. The aqueous solution after electrolysis contains hydrogen isotopes at a higher concentration than the aqueous solution AS ₀ , that is, the hydrogen isotopes are enriched. The hydrogen isotope concentration in the hydrogen gas produced by electrolysis is lower than that of the aqueous solution AS _0. However, the hydrogen gas also contains hydrogen isotopes, and water containing deuterium (D), which is a hydrogen isotope element, contains HD and/or D ₂ in addition to H _2. In the electrolysis of water containing tritium (T), which is a hydrogen isotope, HT and/or T ₂ are contained in addition to H ₂ . contains.

In step (fc1), hydrogen gas HG ₀ produced by water electrolysis is supplied to the negative electrode side of FC1. This hydrogen gas contains hydrogen isotopes as described above. Hydrogen gas containing hydrogen isotopes reacts with oxygen on the positive electrode side in the fuel cell to produce water. Reaction formulas at the positive and negative electrodes of the fuel cell are illustrated in FIG. The reactivity of the fuel cell with oxygen varies depending on the type of hydrogen isotope element, the type of fuel cell (electrode, electrolyte, etc.) and operating conditions. higher. For example, denoting reactivity as X/H, where X is D or T, X/H is greater than 1, eg, in the range of 1.5-5. As a result, when hydrogen gas remains on the negative electrode side, the concentration of hydrogen isotope elements in the _remaining hydrogen gas _HG1 is lower than the concentration of hydrogen isotope elements in HG0. On the other hand, the concentration of hydrogen isotope contained in the water produced on the positive electrode side of the fuel cell is higher than the concentration of hydrogen isotope in _HG0 . That is, the hydrogen isotopes are concentrated on the water side and depleted in the hydrogen gas.

In step (fc2) following step (fc1), the operation in FC1 is the same as in step (fc1) except that hydrogen gas _HG1 is supplied to FC2. When hydrogen gas remains on the negative electrode side of FC2, the concentration of hydrogen isotope elements in the remaining hydrogen gas _HG2 is lower than the concentration of hydrogen isotope elements in _HG1 . On the other hand, the concentration of hydrogen isotope contained in water generated on the positive electrode side of FC2 is higher than the concentration of hydrogen isotope in _HG1 . That is, the hydrogen isotopes are concentrated on the water side and depleted in the hydrogen gas. This relationship continues until FCn in step (fc3).

_The ratio _{( HG 0} :HG ₂ or HG _n ) can range, for example, from 100:0 to 50. 100:0 means that all hydrogen gas is consumed in FCn, and greater than 100:0 means that some hydrogen gas is recovered in FCn. The consumption of hydrogen gas in each FC can be adjusted by adjusting the power generation amount in each FC. Adjustment of the power generation is by control of the set electrical external load. When the ratio exceeds 100: ₀ , the concentration of hydrogen isotope elements contained in _HGn varies depending on the concentration of hydrogen isotope elements contained in HG0, the number of fuel cells to be connected, the operating conditions of the fuel cells, and the like. For example, it can be 50% or less, preferably 10% or less, of the hydrogen isotope concentration contained in _HG0 . For example, hydrogen gas _HG2 or HGn having a lower hydrogen isotope content than hydrogen gas HG0 can be recovered from FC2 of (fc2) or _FCn of ( _fc3 ) to co-produce hydrogen gas.

In (fc1) to (fc3), the ratio of the amount of hydrogen gas supplied to the negative electrode side of any fuel cell FCn-1 to the amount of hydrogen gas recovered from the negative electrode side of FCn-1 (i.e., hydrogen gas consumption ratio) is not particularly limited, but is, for example, in the range of 100:10 to 90 (where n is 3 or more, and when n is 2, the ratio is in the range of 100:0 to 50). be). The consumption ratio of hydrogen gas in each FC can be set independently between FCs.

Oxygen gas or an oxygen-containing gas is supplied to the positive electrode sides of FC1 to FCn. On the other hand, water electrolysis also produces oxygen gas as described above. At least part of this oxygen gas can be supplied to the positive electrode side of at least part of the fuel cells. The oxygen gas supplied to the positive electrode side of the fuel cell can be not only oxygen gas obtained by water electrolysis, but also oxygen gas in the air or a mixture of both. In the explanatory diagram of FIG. 2, a plurality of options are described for the method of supplying oxygen gas in each fuel cell, and at least one of these options can be adopted. For example, oxygen gas generated by water electrolysis can be sequentially circulated from FC1 to FCn, or air can be added to this oxygen gas. Alternatively, the oxygen gas produced by water electrolysis can be temporarily stored in an oxygen gas pool (not shown), and supplied from there to each of the fuel cells FC1 to FCn independently.

For example, at least part of the oxygen gas obtained by water electrolysis is supplied to the positive electrode side of FCn, and the oxygen gas or oxygen-containing gas discharged from the positive electrode side of FCn is the fuel cell n-1 (FCn-1). The oxygen gas or oxygen-containing gas is supplied to the positive electrode side, and the discharged oxygen gas or oxygen-containing gas is sequentially supplied to the next fuel cell up to FC1.

On the positive electrode side of each fuel cell, water containing hydrogen isotopes is produced as described above. This water is recovered. The recovery method is not particularly limited, but, for example, when the unconsumed oxygen gas supplied to the positive electrode chamber is discharged from the positive electrode chamber, it can be discharged and collected together with the gas. At least part of the recovered hydrogen isotope _- containing water W1 to _Wn depends on the concentration of the contained hydrogen isotope, but when the hydrogen isotope concentration is relatively high (for example, recovered water from FC1 or FC2), hydrogen It can be combined with AS _e as an isotopically enriched aqueous solution. Alternatively, if the hydrogen isotope concentration is relatively low (eg recovered water from FCn), it can be subjected to water electrolysis together with AS ₀ .

At least part of the power for water electrolysis in the water electrolyzer can be covered by power generated in the fuel cell. However, the power for water electrolysis can be power other than the power generated by the fuel cell.

The at least two series-connected fuel cells can be, for example, 3 to 10 fuel cells connected in series, and the number of series-connected fuel cells can be 2, 3, 4, 5, Any of 6, 7, 8, 9 and 10 may be used. Also, each fuel cell may be one or more fuel cells connected in parallel. Also, each fuel cell may be the same type of fuel cell or a different type of fuel cell.

The present invention is characterized in that the fuel cell can generate power independently. In each fuel cell, the hydrogen gas generated from the water electrolyzer is consumed under independent operating conditions to generate power, and at the same time, the generated water is enriched with hydrogen isotopes. Here, the effect of concentrating the hydrogen isotope element is synergistically expressed by the multi-stage fuel cell. On the other hand, in the apparatus of the present invention, the amount of hydrogen gas generated in the water electrolyzer (corresponding to the amount of energy consumed) and the amount of hydrogen gas consumed in each fuel cell (corresponding to the amount of energy generated) It becomes an important factor for designing the overall energy balance. In the present invention, the amount of energy generated in each fuel cell can be controlled independently, and it is possible to achieve both the maximum effect of concentrating hydrogen isotopes and the maximum energy efficiency, which is the object of the present invention. It will be possible. The amount of energy generated in each fuel cell can be adjusted, for example, by the degree of electrical resistance load.

Examples of fuel cells include phosphoric acid fuel cells, solid oxide fuel cells, polymer electrolyte fuel cells, alkaline membrane fuel cells, and alkaline fuel cells. For example, when using a solid polymer fuel cell, it is preferable because it can generate power at a temperature in the range of 20 to 90°C. When using polymer electrolyte fuel cells, the temperature is preferably in the range of 60 to 80°C.

The production apparatus of the present invention can also be used to co-produce hydrogen gas with reduced isotope concentration. For example, when three fuel cells are connected in series, the isotope concentration is reduced, for example, to about 1/100 times, and the hydrogen gas with the reduced isotope concentration can be used for other purposes as high-purity hydrogen. can be done.

<Method for producing hydrogen gas with reduced hydrogen isotope concentration>
The present invention provides a fuel cell (FCn) connected in series with at least one water electrolyser and at least two hydrogen gas streams, where n is an integer greater than or equal to 2, and the water electrolyzer The connected fuel cells are referred to as FC1.), generating power independently in each fuel cell, and performing water electrolysis in a water electrolyzer. Hydrogen gas with reduced hydrogen isotope concentration including a method of making a This manufacturing method
(we1) obtaining hydrogen gas (HG ₀ ) and oxygen gas by water electrolysis of water or an aqueous solution containing hydrogen isotopes in a water electrolyzer;
(fc1h) The hydrogen gas HG ₀ obtained by the electrolysis is supplied to the negative electrode side of the fuel cell 1 (FC1), a part of the hydrogen gas HG ₀ is reacted at the negative electrode, and the remaining hydrogen gas (HG ₁ ),
(fc2h) The recovered hydrogen gas HG ₁ is supplied to the negative electrode side of the fuel cell 2 (FC2), part of the hydrogen gas HG ₁ is reacted at the negative electrode, and the remaining hydrogen gas (HG ₂ ) is recovered at the negative electrode side. thing,
(fc3h) If fuel cells are connected next to fuel cell 2 (FC2), this operation is sequentially repeated up to fuel cell n (FCn), and the remaining hydrogen gas (HG _n ) is released on the negative electrode side. Collect (n is an integer of 3 or more),
Obtaining a hydrogen gas HG ₂ or HG _n having a lower hydrogen isotope concentration than the hydrogen gas HG ₀ .

The step (we1) is synonymous with the step (we1) in the method for producing hydrogen isotope-enriched water/aqueous solution.
Except that the step (fc1h) may not include the step (fc1) in the method for producing a hydrogen isotope-enriched water/aqueous solution and recovering the hydrogen isotope-containing water (W ₁ ) produced on the positive electrode side. , are synonymous.
Except that the step (fc2h) may not include the step (fc2) in the method for producing a hydrogen isotope-enriched water/aqueous solution and recovering the hydrogen isotope-containing water (W ₂ ) produced on the positive electrode side. , are synonymous.
Except that the step (fc3h) may not include the step (fc3) in the method for producing a hydrogen isotope-enriched water/aqueous solution and recovering the hydrogen isotope-containing water (W _n ) produced on the positive electrode side. , are synonymous.

The hydrogen gas _HG2 recovered in the step ( _fc2h ) and the hydrogen gas HGn recovered in the step ( _fc3h ) have lower hydrogen isotope concentrations than the hydrogen gas HG0. This is the same for hydrogen gas _HG2 recovered in step (fc2) and hydrogen gas HGn recovered in step ( _fc3 ) in the method for producing hydrogen isotope-enriched water/aqueous solution.

The degree of reduction of the hydrogen isotope concentrations in the hydrogen gases _HG2 and _HGn varies depending on the hydrogen isotope concentration of the hydrogen gas HG0 and the configuration and operating conditions of the fuel cell _FCn , and can be appropriately controlled.

<Hydrogen isotope concentration reduction hydrogen gas production equipment>
The present invention includes an apparatus for producing hydrogen gas with reduced hydrogen isotope concentration including at least one water electrolyzer and at least two series connected fuel cells.

The water electrolyzer, the hydrogen gas distribution means between the water electrolyzer and the fuel cell, and the hydrogen gas distribution means between the fuel cells in this production apparatus are , hydrogen gas distribution means between the water electrolyzer and the fuel cell, and hydrogen gas distribution means between the fuel cells.

Using the hydrogen isotope concentration-reduced hydrogen gas production apparatus of the present invention, hydrogen gas with hydrogen isotopes reduced from the hydrogen gas obtained by the water electrolysis apparatus is produced. With this apparatus, the above method for producing hydrogen gas with reduced hydrogen isotope concentration can be carried out.

Hereinafter, the present invention will be described in more detail based on examples. However, the examples are illustrative of the present invention, and the present invention is not intended to be limited to the examples.

Example 1
Experimental method: One-stage fuel cell In this experiment, alkaline water electrolysis (AWE) and polymer electrolyte fuel cell (PEFC) were used. Fig. 3 shows an outline of the experimental setup.

In AWE, circular nickel mesh electrodes (actual area: 35 cm ² ) were used for the anode and cathode, and ultrasonically cleaned with acetone and ethanol before electrolysis. A diaphragm was used between the anode and cathode to keep the gases generated at the individual electrodes from mixing. An aqueous solution of potassium hydroxide (pH 15) was used as the electrolyte, and heavy water (D ₂ O) was added so that the ratio of deuterium/hydrogen (D/H) was 1:9. filled with L. During the electrolysis, the water was circulated in the water electrolyzer with a pump. For water electrolysis, the current was varied from 1 to 5 A using a DC power supply, and the equipment was operated under the conditions of constant current and room temperature.

In the PEFC, an electrode junction membrane (50×50 mm) using a platinum catalyst (Pt loading: 0.52 mg/cm ² ) was used for both the positive and negative electrodes, and Nafion (NRE211) was used for the electrolyte membrane. Hydrogen gas generated from AWE was directly supplied to the negative electrode of PEFC, and pure oxygen gas was supplied to the positive electrode from an oxygen cylinder. Electricity was generated at room temperature. The PEFC was connected to a variable resistor (PLZ164W manufactured by Kikusui Denshi Kogyo Co., Ltd.) and adjusted so that the generated current was constant.

A quadrupole mass spectrometer (ULVAC, Qulee HGM202, Q-Mass) was used to measure the separation factor. The sample gas was supplied to the detector after having a constant pressure (10 ^-5 Pa) with a needle valve. The temperature of the detector is maintained at 60°C, and the detection sensitivity is designed so that it does not depend on the external environment. The hydrogen isotope separation factor α was obtained by analyzing the hydrogen gas emitted from the PEFC before and after power generation with Q-Mass, and calculating the ratio between the two using the formula (1). The results are shown in the figure.

Example 2
Experimental method: Concentration dependence
The relationship between the separation factor and hydrogen isotope concentration (deuterium) in PEFC alone was investigated. An electrode junction membrane (50×50 mm) using a platinum catalyst (Pt loading: 0.52 mg/cm ² ) was used for both the positive and negative electrodes, and Nafion (NRE211) was used for the electrolyte membrane. A mixed gas of hydrogen gas and deuterium gas was supplied to the negative electrode, and pure oxygen gas (80 ml min ^-1 ) was supplied to the positive electrode. At this time, the flow rate of hydrogen gas (H ₂ ) was fixed at 20 ml min ^-1 and the flow rate of deuterium gas (D ₂ ) was adjusted with a mass flow controller to achieve a D/H ratio of 10 ^-5 to 10 ^-3 . did. The PEFC was connected to a variable resistor (PLZ164W manufactured by Kikusui Denshi Kogyo Co., Ltd.) and generated power at room temperature so that the generated current was constant.

Separation factor measurement was performed using Q-Mass. The sample gas was supplied to the detector under a constant pressure (10 ^-5 Pa) with a needle valve. The temperature of the detector is maintained at 60°C, and the detection sensitivity is designed so that it does not depend on the external environment. The hydrogen isotope separation factor α was obtained by analyzing the hydrogen gas discharged from the PEFC before and after power generation using Q-Mass, and calculating the ratio between the two using the formula (2). The results are shown in FIG.

Example 3
Experimental method: multi-stage fuel cell As a model of multi-stage fuel cell, we made a device consisting of one stage AWE and three stages PEFC and conducted verification experiments. An outline of the experimental setup is shown in FIG.
In AWE, circular nickel mesh electrodes (actual area: 35 cm ² ) were used for the anode and cathode, and ultrasonically cleaned with acetone and ethanol before electrolysis. A diaphragm was used between the anode and cathode to keep the gases generated at the individual electrodes from mixing. An aqueous solution of potassium hydroxide (pH 15) was used as the electrolyte, and heavy water was added so that the ratio of deuterium/hydrogen (D/H) was 1:9. During the electrolysis, the water was circulated in the water electrolyzer with a pump. Water electrolysis was carried out at room temperature with a constant current of 5 A using a DC power supply.

In both PEFCs, electrode junction membranes (50 x 50 mm) using platinum catalyst (Pt loading: 0.52 mg/cm ² ) are used for both the positive and negative electrodes, and Nafion (NRE211) is used for the electrolyte membrane. It was used. The hydrogen gas generated from the AWE was supplied to the negative electrode of the PEFC in the first stage, and the hydrogen gas discharged from the first stage was sequentially supplied to the negative electrode of the PEFC in the next stage. Pure oxygen gas was supplied from an oxygen cylinder to the positive electrode in the first stage, and the oxygen gas discharged from the first stage was successively supplied to the positive electrode of the PEFC in the next stage. Each stage of PEFC was connected to three independent variable resistors, and the generated current was adjusted to a constant value. The following three conditions were examined so that the total generated current would be 4.5A, with PEFCs set to FC1, FC2, and FC3 from the side closest to AWE. The operating temperature was room temperature.

(i) FC1 = 1.2A, FC2 = 0.6A, FC3 = 1.7A
(maximum hydrogen utilization rate of the last PEFC)
(ii) FC1 = 2.7A, FC2 = 1.2A, FC3 = 0.6A
(maximum hydrogen utilization of first PEFC)
(iii) FC1 = 1.5A, FC2 = 1.5A, FC3 = 1.5A
(The hydrogen utilization rate of both PEFCs is equal)

A quadrupole mass spectrometer (ULVAC, Qulee HGM202, Q-Mass) was used to measure the separation factor. The sample gas was supplied to the detector after having a constant pressure (10 ^-5 Pa) with a needle valve. The temperature of the detector is maintained at 60°C, and the detection sensitivity is designed so that it does not depend on the external environment. The hydrogen isotope separation factor α was obtained by analyzing the hydrogen gas discharged from the third-stage PEFC by Q-Mass, and calculating the ratio between the two using the formula (3). The results are shown in Table 1 and FIG.

The theoretical separation factor α of the multistage fuel cell is defined as follows, with the separation factor of water electrolysis as α _AWE , FC1, FC2, and the separation factor of FC3 as α _FC1 , α _FC2 , α _FC3 .
α=α _AWE × α _FC1 × α _FC2 × α _FC3
The following conditions were used in the calculation of α.
・α _AFE was set to 6.0 based on the result of another experiment.
・Fuel cell separation factors α _FC1 , α _FC2 , α _FC3 :

From the results of the single-stage fuel cell, α is proportional to the hydrogen utilization rate U, and the approximation formula α = 3.1 × U + 0.93 is used. (Corresponds to the dotted line in the graph of Fig. 4.)
Furthermore, in order to consider the concentration dependence, let X be the D/H ratio in the inflow gas, and use the approximation formula α=20.075×X ^0.188 (corresponding to the dotted line in the graph of FIG. 5).

From the concentration-dependent results, it is assumed that the rate of decrease of α with decreasing concentration is the same, and the correction term is (20.075×X ^0.188 )/(20.075×(1/540) ^0.188 for α _FC1 , α _FC2 , and α _FC3 ). However, 1/540 is the D/H ratio in the gas after water electrolysis, and X is the D/H ratio before flowing into the fuel cell calculated backward from α obtained from the approximation formula of the fuel utilization rate.
The separation factor _αFC1 of the fuel cell under the condition (ii) obtained under these conditions was 2.16, _αFC2 was 1.78, and _αFC3 was 1.53. Table 1 shows the values obtained by multiplying these by _αAWE 6.0 The theoretical separation factor α = 35.30 = 6.0 x 2.16 x 1.78 x 1.53.

Example 4
The following experiments were carried out to demonstrate that when the same amount of hydrogen is used for power generation, the greater the number of FCs, the higher the separation factor and generated power.

A KOH electrolytic solution (5 M, 10 at% D ₂ O) was electrolyzed at 3.0 A, and using hydrogen gas generated, the following three experiments were performed. The fuel cell FC is the same as that used in Example 1. Table 2 shows the results. From the results shown in Table 2, it can be seen that when the same amount of hydrogen is used for power generation, the greater the number of FCs, the higher the separation factor and generated power.

(1) Power generation by setting the current amount to 1.8 A using one fuel cell FC
(2) Using two fuel cells FC in parallel, generating 0.9 A each (total 1.8 A)
(3) Using three fuel cells FC in parallel, generating 0.6 A each (total 1.8 A)

Example 5
Investigation of the Direction of Oxygen Gas Introduction to Fuel Cell Using two fuel cell FCs, the difference in separation factor due to the difference in the direction of introduction of oxygen gas was measured. As for the introduction direction of the oxygen gas, the direction shown in FIG. 8 is the oxygen forward flow type, and the hydrogen gas and the oxygen gas are sequentially supplied to the fuel cell in the same direction. In the oxygen forward flow type shown in FIG. 8, oxygen gas reacts in the fuel cell in order from hydrogen gas with a high D concentration. The direction shown in FIG. 9 is the oxygen reverse flow type, in which hydrogen gas and oxygen gas are sequentially supplied to the fuel cell in opposite directions. In the oxygen backflow type shown in FIG. 9, oxygen gas reacts in order from hydrogen gas with low D concentration. Separation to the oxygen electrode side can also be expected. In order to confirm this point, the following experiment was conducted.

A KOH electrolytic solution (5 M, 10 at% D ₂ O) was electrolyzed at 3.0 A in the same manner as in Example 4, and hydrogen gas generated was used. The fuel cell FC is the same as that used in Example 1. The results are shown in Figures 10-1 and 10-2. The measurement of Ion Current in Fig. 10-1 was carried out by examining the exhaust gas discharged from the fuel cell. Therefore, a decrease in Ion Current means a decrease in the amount of hydrogen isotope D in the exhaust gas (an increase in D consumption in the fuel cell). From the results in Fig. 10-1, it can be seen that the D consumption in the fuel cell reaction increased by changing from the oxygen forward flow to the oxygen reverse flow. It can be seen that hydrogen gas (HD) and hydrogen gas (D ₂ ) containing hydrogen isotopes with a mass number of 4 (m=4) were consumed more in the fuel cell than in the oxygen up-flow type. Furthermore, from the results in Fig. 10-2, it can be seen that the oxygen backflow type has a separation factor about 15% better.

INDUSTRIAL APPLICABILITY The present invention is useful in the field of treatment of water containing hydrogen isotopes.

Claims (17)

A fuel cell connected in series with at least one water electrolyser and at least two hydrogen gas streams (FCn, where n is an integer greater than or equal to 2 and firstly connected to the water electrolyser) is FC1.), and each fuel cell independently generates power, and water electrolysis is performed in a water electrolyzer to obtain water or an aqueous solution containing hydrogen isotopes (hereinafter, aqueous solution AS ₀ ) A method for producing water or an aqueous solution (AS _e ) having a higher hydrogen isotope content than the aqueous solution AS ₀ from
(we1) water electrolysis of the aqueous solution AS ₀ in a water electrolyzer to obtain hydrogen gas and oxygen gas;
(fc1) The hydrogen gas obtained by the electrolysis is supplied to the negative electrode side of the fuel cell 1 (FC1), part of the hydrogen gas (HG ₀ ) is reacted at the negative electrode, and the remaining hydrogen gas (HG ₁ ) and recovering hydrogen isotope-containing water (W ₁ ) produced on the positive electrode side;
(fc2) The recovered hydrogen gas (HG ₁ ) is supplied to the negative electrode side of the fuel cell 2 (FC2), part of the hydrogen gas (HG ₁ ) is reacted at the negative electrode, and the remaining hydrogen gas (HG ₂ ) and recovering hydrogen isotope-containing water (W ₂ ) produced on the positive electrode side;
(fc3) If fuel cells are connected next to fuel cell 2 (FC2), this operation is sequentially repeated up to fuel cell n (FCn), and the remaining hydrogen gas (HG _n ) and recovering hydrogen isotope-containing water (W _n ) generated on the positive electrode side (n is an integer of 3 or more);
(we2) recovering water or an aqueous solution AS _e having a higher hydrogen isotope content than the aqueous solution AS ₀ after electrolysis from the water electrolyzer. Oxygen gas or oxygen-containing gas is supplied to the positive electrode sides of FC1 to _FCn , and at _least part of the recovered hydrogen isotope-containing water W1 to Wn is supplied to the water electrolysis device. described method. 3. The method according to claim 1 or 2, wherein at least part of the recovered hydrogen isotope _- containing water W1 to _Wn is supplied to the water electrolyzer together with the aqueous solution _AS0 . 4. The method according to any one of claims 1 to 3, wherein the hydrogen isotope-containing water W ₁ to W _n is recovered from the fuel cell by making it accompany the oxygen gas or oxygen-containing gas discharged from the positive electrode side of the fuel cell. the method of. 5. The method according to any one of claims 1 to 4, comprising supplying at least part of the oxygen gas obtained by said water electrolysis to the positive electrode side of at least part of the fuel cells. At least part of the oxygen gas obtained by the water electrolysis is supplied to the positive electrode side of FCn, and the oxygen gas or oxygen-containing gas discharged from the positive electrode side of FCn is the positive electrode of fuel cell n-1 (FCn-1). 6. A method according to claim 5, wherein the supply of discharged oxygen gas or oxygen-containing gas to the next fuel cell is repeated, in sequence, until FC1. 7. Any one of claims 1 to 6, comprising recovering hydrogen gas HG ₂ having a lower hydrogen isotope content than hydrogen gas HG ₀ from FC 2 in step (fc2) to co-produce hydrogen gas. described method. Next to the fuel cell 2 (FC2), in the case where the fuel cell is connected, hydrogen gas HG _n having a lower hydrogen isotope content than hydrogen gas HG ₀ is recovered from FCn in step (fc3), and hydrogen The method according to any one of claims 1 to 6, comprising co-producing gas (where n is an integer of 3 or more). The ratio of the amount of hydrogen gas supplied to the anode side of FC1 in step (fc1) to the amount of hydrogen gas recovered from FC2 in step (fc2) or FCn in step (fc3) is 100:0. The method of any one of claims 1-8, wherein the range is ∼50. The method according to any one of claims 1 to 9, wherein at least part of the power for water electrolysis in said water electrolyzer is provided by power generated in said fuel cell. A method according to any preceding claim, wherein the at least two series-connected fuel cells are 3-10 fuel cells connected in series. A method according to any of claims 1 to 11, wherein said aqueous solution AS ₀ is pure water, alkaline aqueous solution or seawater. at least one water electrolyser and at least two fuel cells connected in series with a stream of hydrogen gas, said water electrolyzer having a cathode compartment and an anode compartment, said fuel cell having an anode compartment and a cathode compartment, respectively. has
a means for flowing hydrogen gas from the cathode chamber of the water electrolyzer to the anode chamber of the fuel cell adjacent to the water electrolyzer of the fuel cells connected in series;
The fuel cells connected in series have hydrogen gas flow means between the negative electrode chambers of the fuel cells connected in order from the fuel cell adjacent to the water electrolysis device,
The fuel cells connected in series have an oxygen gas or oxygen-containing gas distribution means between the positive electrode chambers of the fuel cells sequentially connected from the fuel cell adjacent to the water electrolysis device, and
Having a distribution means for recovering the water generated by the fuel cell to the water electrolysis device,
Equipment for producing water or aqueous solutions enriched with hydrogen isotopes. 14. The production apparatus of claim 13 for co-producing isotope-reduced hydrogen gas. The manufacturing apparatus according to any one of claims 13 to 14 , wherein the at least two series-connected fuel cells are 3 to 10 fuel cells connected in series. The manufacturing apparatus according to any one of claims 13 to 15 , wherein said fuel cell is a polymer electrolyte fuel cell. The production apparatus according to any one of claims 13 to 16 , wherein said water electrolyzer has an oxygen gas or oxygen-containing gas communication means connected to an adjacent fuel cell.

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