JP7116397B2 - Dry water electrolysis hydrogen gas production method and absorption liquid - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing dry water electrolyzed hydrogen gas and an absorbent.

Demand for hydrogen gas is increasing for applications such as fuel for hydrogen vehicles and fuel for fuel cell vehicles. For example, in a hydrogen station for a fuel cell vehicle, there is a portion that becomes low temperature due to adiabatic expansion when high pressure hydrogen gas is filled into the fuel cell vehicle. problems such as clogging of pipes may occur. Therefore, it is desirable that the dew point of hydrogen gas to be used is as low as possible. As standards for the purity and dew point of hydrogen gas, the G1 grade specifies that the purity is more than 99.99999% by volume, the nitrogen content is less than 0.05 volume ppm, and the dew point is less than -80 ° C., and the G2 grade specifies that the purity is greater than 99.999% by volume, the nitrogen content is less than 5 ppm by volume, and the dew point is −70° C. or lower.

On the other hand, as a method for producing hydrogen, there are methods for producing hydrogen by electrolyzing water, such as alkaline water electrolysis and solid polymer water electrolysis. Production of hydrogen by water electrolysis is beneficial because it can use power generated by renewable energy sources such as sunlight and wind power. However, since the hydrogen obtained by water electrolysis contains moisture derived from the raw material water, it is necessary to remove this moisture, and dehumidification processes have been studied.

For example, in Patent Literature 1, the present inventors describe a water electrolysis gas generation step for electrolyzing water to obtain a water electrolysis gas, and water containing water vapor derived from raw material water obtained in the water electrolysis gas generation step. An absorption step of bringing an electrolytic gas into contact with an absorption liquid containing an ionic liquid to selectively absorb water vapor into the absorption liquid; and a separation step of gas-liquid separation of the rich absorbent.

JP 2018-51543 A

General gas dehumidification processes include a process of cooling a mixed gas containing water vapor with a chiller to lower the dew point, a process of contacting a mixed gas containing water vapor with an adsorbent or an absorbent, and the like.

However, if the former dehumidification process is applied to the water-electrolyzed hydrogen gas, not only the water to be removed but also the water-electrolyzed hydrogen gas itself must be cooled, requiring extra energy. In addition, the hydrogen gas of the water electrolysis hydrogen gas is often compressed after dehumidification and stored or transported. disadvantageous.

The latter dehumidification process includes a method using a solid adsorbent and a liquid absorption liquid. When dehumidification is performed using a solid adsorbent such as zeolite, heat treatment at a high temperature (up to 200° C.) is required to regenerate the solid adsorbent that has absorbed moisture. Therefore, if this dehumidification process is applied to water-electrolyzed hydrogen gas with a large amount of water, a large amount of energy is required. In general, dehumidification using a solid adsorbent is performed in a batch process (two-cylinder or multi-cylinder system). This batch processing requires heating of the entire apparatus of the batch processing section each time, followed by cooling. Since heat exchange is difficult in this treatment, it is necessary to heat and cool not only the adsorbent but also the apparatus itself, which consumes a large amount of energy.

When a liquid absorption liquid is used, it is possible to feed the water-rich absorption liquid into the regeneration tower, remove the absorbed water, and return the regenerated lean absorption liquid to the absorption tower for reuse. . In this case, the regeneration tower may be kept at a predetermined temperature, and there is no need to repeat heating and cooling. In addition, heat exchange is facilitated, such as between a cold, water-rich absorbent and a hot, lean absorbent. As the absorbing liquid, triethylene glycol (hereinafter sometimes abbreviated as "TEG") is known as a gas absorbing liquid or an air humidity conditioning liquid. However, if an attempt is made to use TEG as an absorbent for the dehumidification process of water electrolysis hydrogen gas, the absorbent itself has a vapor pressure, which hinders the purification of hydrogen. TEG also has other problems, such as being flammable and unsuitable for use with hydrogen gas.

Accordingly, an object of the present invention is to provide a method for efficiently producing dry water-electrolyzed hydrogen gas from high-humidity water-electrolyzed hydrogen gas produced by water electrolysis.

The inventors of the present invention conducted intensive studies to achieve the above object, and found that an absorption liquid obtained by adding an inorganic salt to an ionic liquid is useful for dehumidifying high-humidity water-electrolyzed hydrogen gas produced by water electrolysis. I found something. The present inventors have completed the present invention based on these findings.

In order to solve the above problems, the method for producing dry water electrolysis hydrogen gas of the present invention comprises:
a hydrogen generation step of electrolyzing water to obtain wet water electrolysis hydrogen gas containing hydrogen and water vapor derived from raw water;
The wet water electrolyzed hydrogen gas is brought into contact with an absorption liquid containing an ionic liquid and an inorganic salt to selectively absorb the water vapor into the absorption liquid, thereby absorbing the dry water electrolyzed hydrogen gas with reduced humidity and the water vapor. an absorption step for obtaining a rich absorbent solution;
a separation step of gas-liquid separation of the dry water electrolysis hydrogen gas and the rich absorbent;
including
The inorganic salt is a salt (excluding the ionic liquid) composed of an anion of a carbon-free acid, carbonic acid, acetic acid, formic acid, cyanic acid, or hydrocyanic acid and a cation of an inorganic compound .

Preferably, the inorganic salt is an inorganic salt that can be uniformly dissolved in the ionic liquid, and the content of the inorganic salt in the ionic liquid is equal to or less than the solubility of the ionic liquid at room temperature.

Preferably, the inorganic salt is lithium acetate, calcium acetate, lithium chloride, calcium chloride, lithium nitrate or calcium nitrate.

Preferably, the ionic liquid is a salt composed of phosphoniums and phosphate ester ions.

Preferably, the ionic liquid is represented by Formula (1).

further comprising a regeneration step of removing water from the rich absorbent to regenerate the absorbent;
The regeneration step is preferably a method of contacting the rich absorbent with a dry gas, a method of heating the rich absorbent, and/or a method of reducing the pressure of the rich absorbent.

Preferably, the regeneration step is a method of contacting the rich absorbent with a dry gas, and the dry gas is a part of the dry water-electrolyzed hydrogen gas separated from gas and liquid in the separation step.

It is preferable that the regeneration step is performed at 100° C. or lower.

Further, the absorption liquid of the present invention contains an ionic liquid represented by formula (1) and an inorganic salt ,
The inorganic salt is a salt (excluding the ionic liquid) composed of an anion of a carbon-free acid, carbonic acid, acetic acid, formic acid, cyanic acid, or hydrocyanic acid and a cation of an inorganic compound .

Preferably, the inorganic salt is lithium acetate, calcium acetate, lithium chloride, calcium chloride, lithium nitrate or calcium nitrate.

The present invention provides a method for efficiently producing dry water-electrolyzed hydrogen gas from high-humidity water-electrolyzed hydrogen gas produced by water electrolysis.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing one aspect of a dry water electrolysis hydrogen gas production apparatus according to the present invention (when only depressurization is performed to regenerate an absorbent); BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing one aspect of a dry water electrolysis hydrogen gas production apparatus according to the present invention (when only nitrogen is used for absorbent regeneration); BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing one aspect of a dry water electrolysis hydrogen gas production apparatus according to the present invention (when nitrogen is used to regenerate an absorbent and the pressure is reduced). BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing one aspect of a dry water electrolysis hydrogen gas production apparatus according to the present invention (when only hydrogen is used to regenerate an absorbent); BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows one aspect|mode of the manufacturing apparatus of the dry water electrolysis hydrogen gas which concerns on this invention (when hydrogen is used for absorption liquid reproduction|regeneration and it pressure-reduces). BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing one aspect of a dry water electrolysis hydrogen gas production apparatus according to the present invention (when hydrogen is circulated to regenerate an absorbent); 2 is a photograph (25° C.) showing the phase state of water vapor-absorbing absorbents of Examples 2 to 7 and Comparative Examples 1 and 2. FIG. 4 is a photograph (80° C.) showing the phase state of the water vapor-absorbing absorbents of Examples 2 to 7 and Comparative Examples 1 and 2. FIG. 1 is a graph showing the humidity dependence (25° C.) of the amount of water vapor absorbed by the absorbents of Examples 1 to 7 and Comparative Examples 1 to 3. FIG. Graph showing the humidity dependence (80° C.) of the water vapor absorption amount of the absorbents of Examples 1 to 7 and Comparative Examples 1 to 3. FIG. Photographs (25° C., 80° C.) showing the phase states of absorption liquids that have absorbed water vapor in Examples 8 to 11. FIG. 4 is a graph showing the humidity dependence (25° C.) of the water vapor absorption amount of the absorbents of Examples 3, 4, 7 to 11 and Comparative Example 3. FIG. 5 is a graph showing the humidity dependence (80° C.) of water vapor absorption in Examples 3, 4, 7 to 11 and Comparative Example 3. FIG. A photograph of the device used for the dehumidification test.

The method for producing dry water electrolyzed hydrogen gas of the present invention includes a hydrogen generation step of electrolyzing water to obtain wet water electrolyzed hydrogen gas containing hydrogen and water vapor derived from raw water, the wet water electrolyzed hydrogen gas, The ionic liquid of the organic salt and the absorbing liquid containing the inorganic salt are brought into contact with each other to selectively absorb the water vapor into the absorbing liquid, resulting in a dry water electrolyzed hydrogen gas with reduced humidity and a rich absorbing liquid with the water vapor absorbed. and a separation step of separating gas and liquid from the dry water electrolysis hydrogen gas and the rich absorbent.

(Hydrogen generation step)
In the hydrogen generation step according to the present invention, water is electrolyzed to obtain electrolyzed wet water hydrogen gas containing hydrogen and water vapor derived from raw water. The method of electrolyzing water is not particularly limited as long as it generates hydrogen, and examples thereof include alkaline water electrolysis, solid polymer water electrolysis, and high-temperature steam electrolysis.

Alkaline water electrolysis usually uses an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution as an electrolyte. In alkaline water electrolysis, hydrogen and hydroxide ions are obtained from water on the cathode side, and water and oxygen are obtained from the hydroxide ions on the anode side. Since oxygen is obtained on the anode side and hydrogen is obtained on the cathode side, the hydrogen can be obtained separately from the oxygen, but contains water at a high humidity corresponding to the vapor pressure. The electrolysis temperature for alkaline water electrolysis is usually room temperature to 200°C, preferably 70°C to 90°C. If the temperature is high, the electrode reaction rate tends to improve.

Proton-type cation membranes such as fluororesin-based cation membranes are usually used as electrolyte membranes in solid polymer type water electrolysis. In solid polymer type water electrolysis, when water is supplied to the anode side, oxygen and hydrogen ions are generated. These hydrogen ions pass through the film and move to the cathode side, acquire electrons, and become hydrogen. As the hydrogen ions move through the membrane, water also moves to the cathode side as affinity water. Hydrogen gas is obtained by gas-liquid separation of the generated gas and the transferred water on the cathode side. Hydrogen, which can be obtained separately from oxygen, contains water at a high humidity relative to its vapor pressure. The electrolysis temperature of solid polymer type water electrolysis is usually 60°C to 100°C.

High-temperature steam electrolysis is an improvement of alkaline water electrolysis, and uses a solid electrolyte such as zirconium oxide as an electrolyte. In high-temperature steam electrolysis, part of the steam supplied to the cathode side becomes hydrogen and oxide ions, and a mixed gas of hydrogen and steam is obtained. Oxide ions migrate through the electrolyte membrane and become oxygen on the anode side. Hydrogen can thus be obtained separately from oxygen, but as a mixed gas with unreacted water vapor, containing water at high humidity. The electrolysis temperature of high-temperature steam electrolysis is, for example, 500° C. or higher, 700° C. or higher, or 1000° C. or lower.

Thus, in the hydrogen generation step according to the present invention, hydrogen gas is obtained as wet water electrolysis hydrogen gas containing hydrogen and water vapor derived from raw water.

(Absorption process)
In the absorption step according to the present invention, the wet water electrolysis hydrogen gas obtained in the hydrogen generation step is brought into contact with the absorption liquid. The absorption liquid used in the present invention contains an ionic liquid of an organic salt and an inorganic salt. The water vapor in the wet water electrolyzed hydrogen gas is selectively absorbed by the absorbent to obtain the dry water electrolyzed hydrogen gas with reduced humidity and the rich absorbent with the water vapor absorbed. In this specification, the absorbing liquid that has absorbed water vapor is sometimes referred to as a "rich absorbing liquid" or a "water-rich absorbing liquid" to distinguish it from the absorbing liquid before absorption.

(ionic liquid)
The ionic liquid used in the present invention is a salt that consists of a cation and an anion and is liquid at 100° C. under atmospheric pressure. The ionic liquid according to the present invention is preferably liquid especially at room temperature (25° C.). That is, the melting point of the ionic liquid according to the present invention is not particularly limited as long as it is 100°C or lower, but it is preferably less than 50°C, more preferably less than 25°C, and particularly preferably less than 10°C. The ionic liquid may also contain a liquid having a melting point of 100° C. or less by containing a trace amount of water. Moreover, the lower limit of the melting point of the ionic liquid according to the present invention is not particularly limited. Note that the ionic liquid is often supercooled and takes a liquid state even below the melting point, and the melting point is not limited even if the melting point is high as long as such a liquid state can be maintained.

Both or one of the cations and anions constituting the ionic liquid used in the present invention is preferably an organic compound.

The anion that constitutes the ionic liquid used in the present invention is not particularly limited, but is preferably an oxoacid ion. As used herein, an oxoacid is an inorganic or organic acid containing oxygen.

Oxoacids include, for example, carboxylic acids, nitric acids, sulfuric acids, sulfonic acids, phosphoric acid esters, phosphoric acid, phosphonic acid esters, and phosphonic acids.

ここで、式１中Ｒ^１は、水素原子又は無置換若しくは置換基を有していてもよい炭化水素基である。炭化水素基は、特に限定されないが、例えば、アルキル基、アルケニル基、アルキニル基、芳香族炭化水素基が挙げられ、環状であっても非環状であってもよく、骨格にヘテロ原子を有していてもよい。具体的には、メチル基、エチル基、ｎ－プロピル基、ｎ－ブチル基、ｎ－ペンチル基、ｎ－ヘキシル基、ｎ－ヘプチル基、ｎ－オクチル基などのアルキル基；これらのアルケニル基、アルキニル基；メトキシ基、エトキシ基などアルコキシ基、アリル基、アリール基などが挙げられる。炭化水素基としては、脂肪族炭化水素基が好ましく、アルキル基がより好ましい。置換基としては、フッ素、塩素、臭素、ヨウ素などのハロゲン基；水酸基；シアノ基などが挙げられる。 A carboxylate ion is an anion represented by Formula 1.

Here, R ¹ in Formula 1 is a hydrogen atom or an unsubstituted or optionally substituted hydrocarbon group. The hydrocarbon group is not particularly limited, and examples thereof include alkyl groups, alkenyl groups, alkynyl groups and aromatic hydrocarbon groups, which may be cyclic or acyclic and have a heteroatom in the skeleton. may be Specifically, alkyl groups such as methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group and n-octyl group; these alkenyl groups, alkynyl group; alkoxy group such as methoxy group and ethoxy group, allyl group, aryl group and the like. As the hydrocarbon group, an aliphatic hydrocarbon group is preferable, and an alkyl group is more preferable. Examples of substituents include halogen groups such as fluorine, chlorine, bromine and iodine; hydroxyl groups; and cyano groups.

More specific examples of carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, oleic acid, benzoic acid, lactic acid, trifluoroacetic acid and heptafluorobutyric acid. Among them, acetic acid and trifluoroacetic acid are preferred.

ここで、式２中Ｒ^２は、水素原子又は無置換若しくは置換基を有していてもよい炭化水素基である。置換基及び炭化水素基としては、カルボン酸イオンの置換基及び炭化水素基として挙げたものが挙げられる。スルホン酸の具体例としては、メチルスルホン酸、エタンスルホン酸などのアルキルスルホン酸；トリフルオロメタンスルホン酸、ノナフルオロブタンスルホン酸などのパーフルオロアルキルスルホン酸；ラウリル硫酸、ポリオキシエチレンアルキル硫酸などのアルキル硫酸が挙げられる。中でもメチルスルホン酸が好ましい。 A sulfonate ion is an anion represented by Formula 2.

Here, R ² in Formula 2 is a hydrogen atom or an unsubstituted or optionally substituted hydrocarbon group. Substituents and hydrocarbon groups include those exemplified as substituents and hydrocarbon groups for carboxylate ions. Specific examples of sulfonic acids include alkylsulfonic acids such as methylsulfonic acid and ethanesulfonic acid; perfluoroalkylsulfonic acids such as trifluoromethanesulfonic acid and nonafluorobutanesulfonic acid; sulfuric acid. Among them, methylsulfonic acid is preferred.

ここで、式３中Ｒ^３とＲ^４は、水素原子又は無置換若しくは置換基を有していてもよい炭化水素基である。置換基及び炭化水素基としては、カルボン酸イオンの置換基及び炭化水素基として挙げたものが挙げられる。式３で表されるアニオンは、Ｒ^３とＲ^４が水素原子である場合がリン酸イオンであり、一方が水素原子で他方が炭化水素基である場合がリン酸モノエステルイオンであり、両方が炭化水素基である場合がリン酸ジエステルイオンである。リン酸エステルの具体例としては、ブチルホスフェート、フェニルホスフェートなどのリン酸エステル；ジメチルホスフェート、ジブチルホスフェート、ビス（２－エチルヘキシル）ホスフェートなどのリン酸ジエステルが挙げられる。炭化水素基の中でも、脂肪族炭化水素基が好ましく、アルキル基がより好ましく、炭素数２以下のアルキル基が特に好ましく、メチル基が最も好ましい。 A phosphate ester ion and a phosphate ion are anions represented by Formula 3.

Here, R ³ and R ⁴ in Formula 3 are a hydrogen atom or a hydrocarbon group that is unsubstituted or may have a substituent. Substituents and hydrocarbon groups include those exemplified as substituents and hydrocarbon groups for carboxylate ions. The anion represented by Formula 3 is a phosphate ion when R ³ and R ⁴ are hydrogen atoms, a phosphate monoester ion when one is a hydrogen atom and the other is a hydrocarbon group, and both is a hydrocarbon group, it is a phosphate diester ion. Specific examples of phosphate esters include phosphate esters such as butyl phosphate and phenyl phosphate; and phosphate diesters such as dimethyl phosphate, dibutyl phosphate and bis(2-ethylhexyl) phosphate. Among the hydrocarbon groups, an aliphatic hydrocarbon group is preferred, an alkyl group is more preferred, an alkyl group having 2 or less carbon atoms is particularly preferred, and a methyl group is most preferred.

ここで、式４中Ｒ^５は、水素原子又は無置換若しくは置換基を有していてもよい炭化水素基である。置換基及び炭化水素基としては、カルボン酸イオンの置換基及び炭化水素基として挙げたものが挙げられる。式４で表されるアニオンは、Ｒ^５が水素原子である場合がホスホン酸イオンであり、Ｒ^５が炭化水素基である場合がホスホン酸エステルイオンである。炭化水素基の中でも、脂肪族炭化水素基が好ましく、アルキル基がより好ましく、炭素数２以下のアルキル基が特に好ましく、メチル基が最も好ましい。ホスホン酸エステルの具体例としては、メチルホスファイト（（ＭｅＯ）ＨＰＯＯ^－）が挙げられる。 Phosphonate ions and phosphonate ions are anions represented by Formula 4.

Here, R ⁵ in Formula 4 is a hydrogen atom or an unsubstituted or optionally substituted hydrocarbon group. Substituents and hydrocarbon groups include those exemplified as substituents and hydrocarbon groups for carboxylate ions. The anion represented by Formula 4 is a phosphonate ion when R ⁵ is a hydrogen atom, and a phosphonate ester ion when R ⁵ is a hydrocarbon group. Among the hydrocarbon groups, an aliphatic hydrocarbon group is preferred, an alkyl group is more preferred, an alkyl group having 2 or less carbon atoms is particularly preferred, and a methyl group is most preferred. Specific examples of phosphonates include methyl phosphite ((MeO)HPOO ⁻ ).

Among these anions, phosphate ions are preferred, phosphate is more preferred, and dimethyl phosphate is particularly preferred.

Cations constituting the ionic liquid according to the present invention are not particularly limited, but examples include imidazoliums, pyrrolidiniums, piperidiniums, pyridiniums, morpholiniums, ammoniums, phosphoniums, and sulfoniums.

Among these cations, phosphoniums are preferred, and methyltributylphosphonium is more preferred.

In the ionic liquid according to the present invention, the combination of the aforementioned cation and anion is not particularly limited as long as the salt becomes an ionic liquid. More specifically, a combination of methyltributylphosphonium and dimethylphosphate is preferred. When the absorbing liquid contains methyltributylphosphonium dimethyl phosphate as the ionic liquid, the amount of dehumidification is doubled or more compared to the absorbing liquid using triethylene glycol alone, which is preferable.

The ionic liquid according to the present invention is commercially available or can be produced by a known method. For example, the aforementioned methyltributylphosphonium dimethylphosphate is available under the trade name of "Hishicolin PX-4MP" (manufactured by Nippon Kagaku Kogyo Co., Ltd.).

(Inorganic salt)
The inorganic salt according to the present invention is a salt composed of an anion of an inorganic compound and a cation of an inorganic compound, and is a compound other than the aforementioned ionic liquid. Specifically, it is a salt composed of an anion of a carbon-free acid such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and chromic acid, an inorganic acid such as carbonic acid, acetic acid, cyanic acid, and hydrocyanic acid, and a cation of a metal ion. There are compounds that are non-liquid at 100° C. and atmospheric pressure.

The cation of the inorganic salt is not particularly limited as long as it is an inorganic cation, but is preferably a metal cation, preferably an alkali metal cation or an alkaline earth metal cation, and more preferably a lithium ion or a calcium ion.

The anion of the inorganic salt is not particularly limited as long as it is an anion of an inorganic acid. Examples thereof include anions of halogen, acetic acid, formic acid, carbonic acid, nitric acid, sulfuric acid, nitric acid, phosphoric acid, chromic acid, cyanic acid, and hydrocyanic acid. . Halogen, nitric acid, and acetic acid anions are preferred, and hydrochloric acid, nitric acid, and acetic acid anions are preferred.

Specific examples of the inorganic salt according to the present invention include a combination of the inorganic cation described above and the anion of the inorganic acid described above. More specifically, lithium acetate, potassium acetate, potassium acetate, magnesium acetate , acetate salts such as calcium acetate; chloride salts such as lithium chloride, potassium chloride, sodium chloride, potassium chloride, magnesium chloride, calcium chloride, magnesium chloride; lithium bromide, potassium bromide, sodium bromide, potassium bromide, bromide salts such as magnesium bromide, calcium bromide and magnesium bromide; and nitrates such as lithium nitrate, potassium nitrate, sodium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate and magnesium nitrate. Among them, lithium salts and calcium salts, as well as acetates, chloride salts, bromide salts and nitrates are preferred, lithium acetate, calcium acetate, calcium chloride, lithium chloride, calcium nitrate and lithium bromide are more preferred, lithium acetate and calcium chloride , lithium chloride, lithium nitrate and calcium nitrate are particularly preferred.

(Absorbing liquid)
The combination of the ionic liquid and the inorganic salt in the absorption liquid according to the present invention is not particularly limited, but it is preferable that the inorganic salt is an inorganic salt that can be uniformly dissolved in the ionic liquid. It is more preferable that it can be uniformly dissolved or dispersed. Specifically, a combination of methyltributylphosphonium dimethyl phosphate as the ionic liquid and lithium acetate, calcium acetate, calcium chloride, lithium chloride, calcium nitrate, lithium nitrate or lithium bromide as the inorganic salt is preferable. A combination of methyltributylphosphonium dimethylphosphate and lithium acetate, calcium chloride or lithium chloride as inorganic salts is more preferred.

The content ratio of the ionic liquid and the inorganic salt in the absorbing liquid according to the present invention is not particularly limited, but the ratio at which the inorganic salt can be uniformly dissolved or dispersed in the ionic liquid at the operating temperature so that the absorbing liquid has fluidity. It is more preferable that it is equal to or less than the solubility of the ionic liquid at room temperature, and it is particularly preferable that the inorganic salt is uniformly dissolved in the ionic liquid at the temperature of use. Here, normal temperature means, for example, 20° C.±15° C. (JIS Z8703). When the content ratio is within this range, the absorbing liquid is excellent in circulating properties and is preferable in that the speed of absorption and release is high.

Some of the inorganic salts used in the absorption liquid according to the present invention are used alone as desiccants for air and organic solvents. When it becomes a solution and is dried for regeneration, the shape may become unsuitable for a desiccant, or the drying itself may be difficult. On the other hand, the absorption liquid according to the present invention using both an inorganic salt and an ionic liquid can be circulated because it is in a liquid state, has a high rate of absorption and release, and is easy to regenerate.

The absorbent according to the present invention may further contain additives within a range that does not impair the effects of the present invention.

The method of contacting the water-electrolyzed hydrogen gas with the absorbent in the absorption step is not particularly limited as long as water vapor in the water-electrolyzed hydrogen gas is absorbed by the absorbent. For example, a method of spraying the absorbent onto the water-electrolyzed hydrogen gas, a method of allowing the water-electrolyzed hydrogen gas to flow down the wall of the tower from above, and a method of allowing the absorbent to flow down from above a packed tower filled with packing. , a method of circulating the water-electrolyzed hydrogen gas, and a method of bubbling the water-electrolyzed hydrogen gas into the absorbent.

As described above, the hydrogen obtained in the water electrolysis hydrogen gas generation process is accompanied by gaseous or liquid water. If liquid water is present, it can be removed by gas-liquid separation prior to the absorption step. The gas obtained by gas-liquid separation as necessary becomes a mixed gas of hydrogen and water vapor, but contains a large amount of water, and usually contains a saturated amount of water vapor. For example, at 25° C. and normal pressure, 1 m ³ contains 23 g of saturated water vapor.

The ionic liquid and inorganic salt in the absorption liquid absorb water while hardly absorbing hydrogen. Therefore, when the water-electrolyzed hydrogen gas is brought into contact with the absorption liquid in the absorption step, water vapor in the gas phase can be moved to the absorption liquid side of the liquid phase, and the water content in the gas phase can be reduced.

(Separation process)
In the separation step according to the present invention, the dry water-electrolyzed hydrogen gas, the humidity of which has been reduced in the absorption step, and the rich absorption liquid, which has absorbed water vapor, are gas-liquid separated. Since the ionic liquid and inorganic salt contained in the absorbing liquid absorb water vapor and have a low vapor pressure, dry water electrolysis hydrogen gas can be obtained simply by removing the rich absorbing liquid by gas-liquid separation.

The separation step according to the present invention is not particularly limited as long as it is a method capable of gas-liquid separation of the dry water electrolyzed hydrogen gas whose humidity has been reduced in the absorption step and the rich absorption liquid that has absorbed water vapor in the absorption step, but it can be carried out at the same time as the absorption step. is preferred. For example, in the absorption step, when a method of spraying an absorption solution onto the water-electrolyzed hydrogen gas is used, the water-electrolyzed hydrogen gas is circulated from one end of the pipe to the other, and the water-electrolyzed hydrogen gas is sprayed with the absorption solution, A method of extracting the rich absorbent that has absorbed water vapor from below can be mentioned. Water vapor in the water-electrolyzed hydrogen gas is absorbed by the absorbent and extracted, and dry water-electrolyzed hydrogen gas is discharged from the other end of the pipe.

In addition, as an absorption process, a method in which an absorbent is flowed down from above on the wall surface of a tower and water-electrolyzed hydrogen gas is circulated, or a packed tower filled with packing is flowed down from above in an absorbent and water-electrolyzed hydrogen gas is circulated. In the case of using the method of allowing the water-electrolyzed hydrogen gas to be blown in from below, the dry water-electrolyzed hydrogen gas can be extracted from above, and the rich absorbent that has absorbed water vapor can be extracted from below.

The water electrolysis hydrogen gas generation process described above has high energy efficiency when the temperature is high. On the other hand, the absorption liquid in the absorption step absorbs more water as the temperature is lower. Therefore, it is preferable to cool the electrolyzed high-humidity water hydrogen gas before the absorption step. Therefore, it is preferable in terms of energy efficiency to perform a heat exchange step in which heat is exchanged between the water-electrolyzed hydrogen gas and the rich absorbent prior to the absorption step.

(regeneration process)
The method for producing hydrogen gas by dry water electrolysis according to the present invention can include a regeneration step of regenerating the rich absorbent obtained in the separation step described above.

A method for regenerating the rich absorbent into an absorbent is not particularly limited. Examples include contacting the rich absorbent with a dry gas, heating the rich absorbent, and/or reducing the pressure of the rich absorbent.

When the dry gas is brought into contact with the rich absorbent, moisture is transferred from the rich absorbent to the dry gas, and the rich absorbent can be regenerated into an absorbent. As the dry gas, dry nitrogen gas or part of the dry water-electrolyzed hydrogen gas obtained in the absorption step can be used.

Also, the amount of water absorbed by the absorbent of the present invention tends to decrease as the temperature increases. Therefore, by raising the temperature of the rich absorbent higher than the temperature at which the water-electrolyzed hydrogen gas and the absorbent are brought into contact with each other, water vapor can be released and the absorbent can be regenerated.

In addition, using the difference between the vapor pressure of the ionic liquid and the vapor pressure of water in the absorbing liquid, and the fact that the amount of water absorbed by the ionic liquid and inorganic salt decreases as the water vapor partial pressure decreases, the rich absorbing liquid is decompressed. By doing so, water vapor can be released and the absorbent can be regenerated. Heating and pressure reduction can also be performed simultaneously. The released steam can be reused as a raw material for water electrolysis.

When the rich absorbent is heated in the regeneration step, it is preferable in terms of energy efficiency to heat the rich absorbent by exchanging heat with the water-electrolyzed hydrogen gas before the absorption step.

On the other hand, when the absorbent regenerated in the regeneration step is used in the absorption step, it is preferable to lower the temperature in order to increase the amount of water absorbed. The rich absorbent prior to the regeneration step can be used for cooling the regenerated absorbent. That is, it is preferable in terms of energy efficiency to perform a second heat exchange step in which heat is exchanged between the absorbent regenerated in the regeneration step and the rich absorbent.

The absorption step using the absorption liquid containing the above-described ionic liquid can also reduce the water-electrolyzed hydrogen gas with a very high water vapor content to a moderate humidity continuously at a low cost. Therefore, even when the dry water electrolyzed hydrogen gas with reduced water content obtained in the subsequent separation process is further reduced in water content with a solid desiccant such as calcium chloride or zeolite, the amount of solid desiccant used can be reduced. You can reduce it or extend its life.

(Production device for dry water electrolysis hydrogen gas)
The method for producing hydrogen gas from dry water electrolysis according to the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

FIG. 1 is a diagram showing one aspect of a dry water electrolysis hydrogen gas production apparatus, in which the absorbent is regenerated under reduced pressure. The water electrolysis device 1 electrolyzes water to generate hydrogen and oxygen. Examples of electrolysis include alkaline water electrolysis, solid polymer type water electrolysis, and high-temperature steam electrolysis. For example, in the case of alkaline water electrolysis, hydrogen is generated on the cathode side (cathode side). The amount of hydrogen generated can be controlled by the amount of electric power of the water electrolysis device 1, and the water electrolysis device 1 is put into a pressurized state. This hydrogen is wet hydrogen 2 containing water vapor. A mass flow controller (MFC) 3 is provided at the outlet of the water electrolysis device 1 to control the flow rate of wet hydrogen 2 . Wet hydrogen 2 is introduced into absorption tower 5 via three-way valve 4 . In the absorption tower 5, the absorption liquid 6 and the wet hydrogen 2 are brought into contact. For example, the inside of the absorption tower 5 is packed with packing, the absorption liquid 6 is introduced from the upper part of the absorption tower 5, and the wet hydrogen 2 is introduced from the lower part of the absorption tower 5 to bring them into contact. The temperature of the absorbent 6 in the absorption tower 5 can be controlled to a constant temperature such as 25°C. The pressure in the absorption tower 5 can also be controlled by providing a pressure regulating valve. The moisture in the wet hydrogen 2 is absorbed by the absorption liquid 6 and reduced. Hydrogen with reduced water content is introduced into the trap 8 from the upper part of the absorption tower 5 through the three-way valve 7 . A trap 8 can remove the absorbing liquid entrained in the hydrogen. Hydrogen passing through the trap 8 has its dew point measured through a capacitance dew point meter 9 and a specular dew point meter 10, and dry hydrogen 11 is obtained.

The absorbent 6 that has absorbed moisture in the absorption tower 5 is discharged as a rich absorbent 12 from the bottom of the absorption tower 5 and introduced from the top into the regeneration tower 14 through the flow meter 13 . The regeneration tower 14 can be adjusted to a constant temperature such as 80°C. In FIG. 1, a vacuum pump 17 is arranged above the regeneration tower 14 via a trap 16 to reduce the pressure. When the inside of the regeneration tower 14 is depressurized, the moisture in the rich absorbent 12 is released from the rich absorbent 12 and the absorbent 6 is regenerated. Moisture is discharged from the top of regeneration tower 14 and collected in trap 16 or exhausted from outlet 18 . The regenerated absorbent 6 is discharged from the bottom of the regeneration tower 14 and circulated to the absorption tower 5 by the liquid feed pump 15 .

FIG. 2 is a diagram showing one aspect of the dry water electrolysis hydrogen gas production apparatus, in which dry nitrogen is used to regenerate the absorbent. In the apparatus for producing hydrogen gas by dry water electrolysis shown in FIG. It is brought into contact with the rich absorbent 12 introduced from above. The regeneration tower 14 can be adjusted to a constant temperature such as 100°C, 80°C, and 60°C. In the regeneration tower 14, the dry nitrogen 21 and the rich absorbent 12 are brought into contact with each other, whereby the moisture in the rich absorbent 12 moves from the rich absorbent 12 to the dry nitrogen 21, and is released as wet nitrogen 22 from the exhaust port 23. It is released and the absorption liquid 6 is regenerated. The regenerated absorbent 6 is discharged from the bottom of the regeneration tower 14 and circulated to the absorption tower 5 by the liquid feed pump 15 .

The flow rate of the dry nitrogen 21 in the regeneration tower 14 is not particularly limited. 1:1 is more preferred. The smaller the amount of dry nitrogen, the more energy required for regeneration can be reduced, which is preferable.

FIG. 3 is a diagram showing one embodiment of a dry water electrolysis hydrogen gas production apparatus, in which dry nitrogen is used to regenerate the absorbing liquid and the pressure is reduced. In the apparatus for producing hydrogen gas by dry water electrolysis shown in FIG. It is brought into contact with the rich absorbent 12 introduced from above. The regeneration tower 14 can be adjusted to a constant temperature such as 100°C, 80°C, and 60°C. Further, in FIG. 3, a vacuum pump 17 is arranged above the regeneration tower 14 via a trap 16 to reduce the pressure. The reduced pressure can be, for example, −50 kPaG (gauge pressure). In the regeneration tower 14, the dry nitrogen 21 and the rich absorbent 12 come into contact with each other under reduced pressure, so that the moisture in the rich absorbent 12 moves from the rich absorbent 12 to the dry nitrogen 21 and is exhausted as wet nitrogen 22. It is discharged from the port 18 and the absorbent 6 is regenerated. The regenerated absorbent 6 is discharged from the bottom of the regeneration tower 14 and circulated to the absorption tower 5 by the liquid feed pump 15 .

FIG. 4 is a diagram showing one embodiment of a dry water electrolytic hydrogen gas production apparatus, in which part of the produced dry hydrogen is used to regenerate the absorption liquid. In the apparatus for producing hydrogen gas by dry water electrolysis shown in FIG. 4, part of the hydrogen with reduced moisture extracted from the upper part of the absorption tower 5 is extracted through a T-shaped connector 24 and the flow rate is controlled by a mass flow controller (MFC) 25. , a certain amount is introduced into the regeneration tower 14 from the bottom and brought into contact with the rich absorbent 12 introduced into the regeneration tower 14 from the top. The regeneration tower 14 can be adjusted to a constant temperature such as 100°C, 80°C, and 60°C. In the regeneration tower 14, the hydrogen with reduced water content and the rich absorbent 12 come into contact with each other, whereby the water in the rich absorbent 12 moves from the rich absorbent 12 to the hydrogen with reduced water content, and the water content increases. The absorbent 6 is regenerated by being discharged as hydrogen from the exhaust port 23 . The regenerated absorbent 6 is discharged from the bottom of the regeneration tower 14 and circulated to the absorption tower 5 by the liquid feed pump 15 .

FIG. 5 is a diagram showing one embodiment of a dry water electrolysis hydrogen gas production apparatus, in which part of the produced dry hydrogen is used to regenerate the absorption liquid and the pressure is reduced. In the apparatus for producing hydrogen gas by dry water electrolysis shown in FIG. 5, part of the hydrogen with reduced moisture extracted from the upper part of the absorption tower 5 is extracted by a T-shaped connector 24 and the flow rate is controlled by a mass flow controller (MFC) 25. , a certain amount is introduced into the regeneration tower 14 from the bottom and brought into contact with the rich absorbent 12 introduced into the regeneration tower 14 from the top. The regeneration tower 14 can be adjusted to a constant temperature such as 100°C, 80°C, and 60°C. Furthermore, in FIG. 5, a vacuum pump 17 is arranged above the regeneration tower 14 via a trap 16 to reduce the pressure. The reduced pressure can be, for example, −50 kPaG (gauge pressure). In the regeneration tower 14, the hydrogen with reduced water content and the rich absorbent 12 come into contact with each other under reduced pressure, whereby the water in the rich absorbent 12 is transferred from the rich absorbent 12 to hydrogen, and is exhausted as wet hydrogen. It is discharged from the port 18 and the absorbent 6 is regenerated. The regenerated absorbent 6 is discharged from the bottom of the regeneration tower 14 and circulated to the absorption tower 5 by the liquid feed pump 15 .

FIG. 6 is a diagram showing one embodiment of the apparatus for producing hydrogen gas by electrolysis of dry water, in which part of the dry hydrogen produced is used to regenerate the absorbent and the hydrogen is circulated to the water electrolysis apparatus. In the apparatus for producing hydrogen gas by dry water electrolysis shown in FIG. 6, part of the hydrogen with reduced moisture extracted from the upper part of the absorption tower 5 is extracted through a T-shaped connector 24 and the flow rate is controlled by a mass flow controller (MFC) 25. , a certain amount is introduced into the regeneration tower 14 from the bottom and brought into contact with the rich absorbent 12 introduced into the regeneration tower 14 from the top. The regeneration tower 14 can be adjusted to a constant temperature such as 100°C, 80°C, and 60°C. In the regeneration tower 14, the hydrogen with reduced water content and the rich absorbent 12 come into contact with each other, whereby the water in the rich absorbent 12 moves from the rich absorbent 12 to the hydrogen with reduced water content, and the water content of the hydrogen is reduced. As it increases, the absorbent 6 is regenerated. Hydrogen with increased water content is obtained from the upper portion of the regeneration tower 14 , and regenerated absorbent 6 is obtained from the lower portion of the regeneration tower 14 . The regenerated absorbent 6 is discharged from the lower part of the regeneration tower 14 and circulated to the absorption tower 5 by the liquid feed pump 15 . The hydrogen with increased water content is pressurized by the compressor 26 and returned to the water electrolysis device 1 .

(Example)
EXAMPLES The present invention will be described below based on examples, but the present invention is not limited to these examples. Pressures are absolute unless otherwise specified.

(Measurement of dew point)
Under atmospheric pressure, using a dew point meter (manufactured by Rotronic; industrial temperature/humidity converter HF533-WAA3D14X, pressure-resistant probe HC2-IE102-M, manufactured by Tokyo Optoelectronics Industry Co., Ltd.; mirror dew point meter DPH-703A) , the dew point was measured.

(Measurement of water vapor absorption amount)
Using various absorption liquids, their water vapor absorption amounts were measured. For the measurement, a predetermined mass of absorption liquid (ionic liquid and inorganic salt) is placed in a sample bottle in a thermo-hygrostat filled with dry air. After that, while stirring the absorbent with a stirrer, air of a predetermined temperature and humidity was passed through the thermo-hygrostat to bring it into contact with the absorbent, and the change in mass of the absorbed amount was measured at predetermined time intervals. A saturated state was assumed when the mass of the absorbing liquid stopped changing, and the water vapor absorption amount w _H2O (g/g-absorbing liquid) was obtained. Here, "g-absorbing liquid" is the mass of the absorbing liquid unless otherwise specified. The temperature and relative humidity conditions are about 25°C (about 50%, about 70%, about 90% relative humidity) and about 80°C (about 30%, about 50%, about 70%, about 90% relative humidity). gone. The amount of hydrogen absorbed by the ionic liquid and the inorganic salt and the amount of air absorbed are all negligible compared to the amount of water absorbed. Also, there is no difference in water vapor absorption between moist hydrogen and moist air. Therefore, the dehumidifying effect of wet hydrogen can be confirmed by measuring the water vapor absorption amount of moist air.

(Example 1)
In a dry air atmosphere, put 0.5084 g of lithium acetate as an inorganic salt into a sample bottle with a lid (capacity 9 ml) containing a stirrer, and methyltributylphosphonium dimethyl phosphate ( 0.5080 g of Hishikorin PX-4MP, chemical formula [(n-C ₄ H ₉ ) ₃ P ⁺ (CH ₃ )] [(MeO) ₂ PO ₂ ⁻ ]) manufactured by Nippon Kagaku Kogyo Co., Ltd. was added to obtain lithium acetate. The mixture was stirred until it was completely dissolved to prepare a homogeneous absorption liquid E1 (mass ratio; ionic liquid:inorganic salt=1:1).

About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid E1 We measured the amount of water vapor absorption. Table 1 shows the measurement results. Lithium acetate before preparing the absorption liquid E1 was a white solid. In the case of the absorption liquid E1, when the temperature was about 25° C. and the humidity was 50% RH, a solid remained. When the humidity was 70% RH and 90% RH, the absorbent became a transparent uniform solution. Further, in the absorption liquid E1, when the temperature was about 80° C., a solid remained when the humidity was 30% RH, and became a transparent uniform solution when the humidity was 50% RH and 90% RH.

Thus, when the absorbent has fluidity, the wet water electrolyzed hydrogen gas is brought into contact with the absorbent in the absorption tower to selectively remove the water vapor in the wet water electrolyzed hydrogen gas. to obtain a dry water-electrolyzed hydrogen gas with reduced humidity and a rich absorbent that has absorbed water vapor, and the dry water-electrolyzed hydrogen gas and the rich absorbent are separated from gas and liquid to obtain a dry water-electrolyzed hydrogen gas. can be manufactured. In addition, by transferring the rich absorbent from the absorption tower to the regeneration tower and bringing it into contact with the low-humidity gas, the moisture in the rich absorbent moves to the low-humidity gas. The liquid can be regenerated. The regenerated absorbent can be transferred to the absorption tower and used again.

(Example 2)
Absorption liquid E2 was prepared in the same manner as in Example 1, except that the mass of lithium acetate as the inorganic salt was changed to 0.5042 g and the mass of PX-4MP as the ionic liquid was changed to 0.2523 g (mass ratio ionic liquid: inorganic salt=1:2). About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid E2 We measured the amount of water vapor absorption. Table 1 shows the measurement results. Also, FIGS. 7 and 8 show visual appearances of lithium acetate before preparation of the absorbing liquid E2 in a saturated state at each temperature and humidity. Lithium acetate before preparing the absorption liquid E2 was a white solid. In the case of the absorption liquid E2, when the temperature was about 25° C. and the humidity was 50% RH, a solid remained. When the humidity was 70% RH and 90% RH, the absorbent became a transparent uniform solution. Further, at about 80° C., the absorbent E1 becomes a transparent uniform solution at a humidity of 30% RH, a gel at a humidity of 50% RH, and a solid at a humidity of 90% RH. rice field. In the case of such a composition ratio that becomes solid under specific conditions, the absorbing liquid can be transferred under conditions that do not become solid.

(Example 3)
Absorption liquid E3 was prepared in the same manner as in Example 1 except that the mass of the inorganic salt lithium acetate was changed to 0.6203 g and the ionic liquid PX-4MP was changed to 0.2063 g (mass ratio: ionic liquid : inorganic salt = 1:3). About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid E3 We measured the amount of water vapor absorption. Table 1 shows the measurement results. Also, FIGS. 7 and 8 show visual appearances of lithium acetate before preparation of the absorbing liquid E3 in a saturated state at each temperature and humidity. Lithium acetate before preparation of absorption liquid E3 was a white solid. Further, in the case of the absorption liquid E3, when the temperature was about 25° C. and the humidity was 50% RH and 70% RH, solid remained. When the humidity was 90% RH, a transparent homogeneous solution was obtained. Furthermore, when the temperature was about 80° C., the absorption liquid E3 became a transparent uniform solution at a humidity of 30% RH, a solid remained at a humidity of 50% RH, and a solid at a humidity of 90% RH.

(Example 4)
Absorption liquid E4 was prepared in the same manner as in Example 1 except that lithium acetate as an inorganic salt was changed to 0.4181 g of calcium chloride and PX-4MP of the ionic liquid was changed to 0.4180 g of PX-4MP (mass ratio ionic liquid: inorganic salt=1:1). About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid E4 We measured the amount of water vapor absorption. Table 1 shows the measurement results. 7 and 8 show the visual appearance of calcium chloride before preparation of the absorption liquid E4 in a saturated state at each temperature and humidity. Calcium chloride before preparation of absorption liquid E4 was a white solid. Further, in the case of about 25° C., the absorption liquid E4 remained solid at a humidity of 50% RH, and became a transparent uniform solution at a humidity of 70% RH and a humidity of 90% RH. Moreover, when the temperature was about 80° C., the absorption liquid E4 became a cloudy solution at a humidity of 30% RH, and became a solid at a humidity of 70% RH and a humidity of 90% RH.

(Example 5)
Absorption liquid E5 was prepared in the same manner as in Example 1, except that lithium acetate as an inorganic salt was changed to 0.4141 g of calcium nitrate and PX-4MP of the ionic liquid was changed to 0.4148 g (mass ratio; ionic liquid: inorganic salt=1:1). About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid E5 We measured the amount of water vapor absorption. Table 1 shows the measurement results. 7 and 8 show the visual appearance of calcium nitrate before preparation of the absorption liquid E5 in a saturated state at each temperature and humidity. Calcium nitrate before preparation of absorption liquid E5 was a white solid. Further, in the absorption liquid E5, when the temperature was about 25° C., a solid remained when the humidity was 50% RH and 70% RH, and became a transparent two-layer solution when the humidity was 90% RH. Moreover, when the temperature was about 80° C., the absorption liquid E5 became a yellow two-layer solution at a humidity of 30% RH, and became a solid at a humidity of 70% RH and a humidity of 90% RH.

(Example 6)
Absorption liquid E6 was prepared in the same manner as in Example 1, except that lithium acetate as an inorganic salt was changed to 0.4141 g of calcium acetate and PX-4MP of the ionic liquid was changed to 0.4148 g (mass ratio; ionic liquid: inorganic salt=1:1). About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid E6 We measured the amount of water vapor absorption. Table 1 shows the measurement results. 7 and 8 show the visual appearance of calcium acetate before preparation of the absorption liquid E6, in a saturated state at each temperature and humidity. Calcium nitrate before preparation of absorption liquid E6 was a white solid. Moreover, the absorption liquid E6 was solid at about 25° C., at a humidity of 50% RH, at a humidity of 70% RH, and at a humidity of 90% RH. Moreover, when the temperature was about 80° C., the absorbing liquid E6 became a yellow two-layer solution at a humidity of 30% RH, and became a solid at a humidity of 70% RH and a humidity of 90% RH.

(Example 7)
Absorption liquid E7 was prepared in the same manner as in Example 1, except that lithium acetate as the inorganic salt was changed to 0.402 g of lithium chloride and PX-4MP of the ionic liquid was changed to 0.4013 g (mass ratio; ionic liquid: inorganic salt=1:1). About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid E7 We measured the amount of water vapor absorption. Table 1 shows the measurement results. 7 and 8 show visual appearances of lithium chloride before preparation of the absorbing liquid E7 and in a saturated state at each temperature and humidity. Lithium chloride before preparation of absorption liquid E7 was a white solid. Moreover, the absorption liquid E7 was a uniform solution at about 25° C. and at all of the humidity of 50% RH, 70% RH and 90% RH. Moreover, when the temperature was about 80° C., the absorption liquid E7 was a uniform and transparent solution at a humidity of 30% RH, and was a solid-liquid mixture at a humidity of 70% RH and a humidity of 90% RH.

(Comparative example 1)
Triethylene glycol (hereinafter sometimes abbreviated as "TEG") is used as the absorption liquid R1, and is heated at about 25°C (relative humidity about 50%, about 70%, about 90%) and about 80°C (relative humidity about 30%). , about 50%, about 70%, and about 90%). Table 1 shows the measurement results. The absorption amount in Table 1 indicates the water vapor absorption amount per unit mass of TEG. Under the condition of 80° C., the absorption liquid volatilized and the absorption amount could not be measured. 7 and 8 show the visual appearance of the absorption liquid R1 in a saturated state at each temperature and humidity. Absorption liquid R1 before absorbing water vapor was a colorless liquid. Moreover, in the case of about 25° C., it was a transparent and colorless liquid when the humidity was 50% RH, 70% RH, and 90% RH.

(Comparative example 2)
Tetrabutylphosphonium o,o-diethylphosphorodithioate represented by the following formula (manufactured by Nippon Kagaku Kogyo Co., Ltd., Hishikorin PX-4ET, chemical formula [( _n- C ₄ H ₉ ) ₄ P ⁺ ][ (C ₂ H ₅ O) ₂ PSS ⁻ ]) was used as the absorption liquid R2, and the temperature was about 25° C. (relative humidity about 50%, about 70%, about 90%) and about 80° C. (relative humidity about 30%, about 50%). %, about 70%, and about 90%). Table 1 shows the measurement results. The absorption amount in Table 1 indicates the water vapor absorption amount per unit mass of PX-4ET.

FIGS. 7 and 8 show the visual appearance of the absorption liquid R2 in a saturated state at each temperature and humidity. Absorption liquid R2 before absorbing water vapor was a colorless liquid. In the case of about 25° C., it was a transparent and colorless liquid at all of the humidity of 50% RH, 70% RH and 90% RH. Also, the absorbing liquid R2 was a transparent and colorless liquid at a temperature of about 80° C. and at all of the humidity of 30% RH, 70% RH and 90% RH.

(Comparative Example 3)
Absorbing liquid R3 (ionic liquid only) was prepared in the same manner as in Example 1, except that the inorganic salt was not used. About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid R3 We measured the amount of water vapor absorption. Table 1 shows the measurement results. Absorption liquid R3 before absorbing water vapor was a colorless liquid. In the case of about 25° C., it was a transparent and colorless liquid at all of the humidity of 50% RH, 70% RH and 90% RH. Also, the absorbing liquid R3 was a transparent and colorless liquid at a temperature of about 80° C. and at all of the humidity of 30% RH, 70% RH and 90% RH.

For Examples 1 to 7 and Comparative Examples 1 to 3, the humidity dependence of water vapor absorption at 25° C. is shown in FIG. 9, and the humidity dependence of water vapor absorption at 80° C. is shown in FIG.
From the above results, it was found that the addition of inorganic salts such as calcium salts and lithium salts increased the amount of water vapor absorption. Regarding water absorption, Example 4 (PX-4MP+CaCl ₂ =1:1) has the highest water vapor absorption, followed by Example 7 (PX-4MP+LiCl=1:1), Example 2 (PX-4MP+CH ₃ COOLi=1:2), Example 3 (PX-4MP+CH ₃ COOLi=1:3), Example 1 (PX-4MP+CH ₃ COOLi=1:1), Example 5 (PX-4MP+Ca(NO ₃ ) ₂ = It can be seen that the water vapor absorption amount increased in the order of 1:1). When comparing the ionic liquid and TEG, Comparative Example 3 (PX-4MP) has a higher water absorption amount than Comparative Example 1 (TEG), and Comparative Example 2 (PX-4ET) hardly absorbs water vapor. I understand. When lithium acetate is added to the ionic liquid, the mixing ratio is PX-4MP:CH3COOLi, which is 1:2 (Example 2) and 1:3 (Example 3) from 1:1 (Example 1). The amount of water vapor absorbed was higher than that of the sintered body, and the dependence on humidity was also higher. 1:2 (Example 2) was slightly more absorbed than 1:3 (Example 3).
Next, the amount of water vapor absorption relative to the ratio of inorganic salts was examined.

(Example 8)
Absorption liquid E8 was prepared in the same manner as in Example 1, except that lithium acetate as the inorganic salt was changed to 0.4524 g of lithium chloride and PX-4MP of the ionic liquid was changed to 0.2272 g (mass ratio; ionic liquid: inorganic salt=1:2). About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid E8 We measured the amount of water vapor absorption. Table 2 shows the measurement results. FIG. 11 shows the visual appearance of saturated lithium chloride at each temperature and humidity before preparing the absorbing liquid E8. Lithium chloride before preparation of absorption liquid E8 was a white solid. In addition, the absorption liquid E8 became a transparent uniform solution at about 25° C., 50% RH, 70% RH, and 90% RH. At about 80° C., the absorption liquid E8 became a cloudy solution at a humidity of 30% RH and a humidity of 70% RH, and became a transparent uniform solution at a humidity of 90% RH.

(Example 9)
Absorption liquid E9 was prepared in the same manner as in Example 1, except that lithium acetate as an inorganic salt was changed to 0.7991 g of lithium chloride and PX-4MP of the ionic liquid was changed to 0.2655 g (mass ratio; ionic liquid: inorganic salt=1:3). About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid E9 We measured the amount of water vapor absorption. Table 2 shows the measurement results. Also, FIG. 11 shows the visual appearance of lithium chloride before preparation of the absorbing liquid E9 in a saturated state at each temperature and humidity. Lithium chloride before preparing absorption liquid E9 was a white solid. Moreover, the absorption liquid E9 became a transparent uniform solution at about 25° C., 50% RH, 70% RH and 90% RH humidity. At about 80° C., the absorption liquid E9 became a cloudy solution at a humidity of 30% RH and a humidity of 70% RH, and became a transparent uniform solution at a humidity of 90% RH.

(Example 10)
Absorption liquid E10 was prepared in the same manner as in Example 1, except that lithium acetate as the inorganic salt was changed to 0.6018 g of calcium chloride and PX-4MP of the ionic liquid was changed to 0.3007 g (mass ratio; ionic liquid: inorganic salt=1:2). About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid E10 We measured the amount of water vapor absorption. Table 2 shows the measurement results. FIG. 11 shows the visual appearance of calcium chloride before preparation of the absorption liquid E10 in a saturated state at each temperature and humidity. Calcium chloride before preparation of absorption liquid E10 was a white solid. In addition, the absorption liquid E10 became a transparent uniform solution at about 25° C., 50% RH, 70% RH, and 90% RH. At about 80° C., the absorbent E10 became a solid at a humidity of 30% RH, a two-layered solution at a humidity of 70% RH, and a transparent uniform solution at a humidity of 90% RH.

(Example 11)
Absorption liquid E11 was prepared in the same manner as in Example 1, except that lithium acetate as an inorganic salt was changed to 0.6375 g of calcium chloride and PX-4MP of the ionic liquid was changed to 0.2078 g (mass ratio; ionic liquid: inorganic salt=1:3). About 25 ° C. (relative humidity about 50%, about 70%, about 90%) and about 80 ° C. (relative humidity about 30%, about 50%, about 70%, about 90%) for the prepared absorption liquid E11 We measured the amount of water vapor absorption. Table 2 shows the measurement results. Also, FIG. 11 shows the visual appearance of calcium chloride before preparation of the absorption liquid E11 in a saturated state at each temperature and humidity. Lithium chloride before preparation of absorption liquid E11 was a white solid. In addition, the absorption liquid E10 became a transparent uniform solution at about 25° C., 50% RH, 70% RH, and 90% RH. At about 80° C., the absorbing liquid E11 became solid at a humidity of 30% RH, formed two layers at a humidity of 70% RH, and became a transparent uniform solution at a humidity of 90% RH.

(Dehumidification test)
Using the dehumidifier shown in FIG. 14, dehumidification of water-electrolyzed hydrogen gas was performed under various conditions. The dehumidifier shown in FIG. 14 includes a water electrolysis device (not shown), a water electrolysis hydrogen line 27, a humidification tower 28, a flow meter 30 for a rich absorbent 33, a regeneration tower 31, and a liquid feed for a regenerated absorbent 34. A pump 32 is provided. After confirming the dew point, the water-electrolyzed hydrogen gas generated by the water electrolyzer (not shown) is supplied to the humidification tower 28 through the water-electrolyzed hydrogen line 27 . In the humidification tower 28, humidification is performed at a temperature of 10° C. to saturated humidity in order to evaluate the dehumidification performance. In the absorption tower 29, humidified wet hydrogen and the absorption liquid 34 are brought into contact at a predetermined temperature. The rich absorbent 33 having absorbed moisture in the absorption tower 29 is transferred to the regeneration tower 31 after being adjusted in flow rate by the flow meter 30 . In the regeneration tower 31, the absorbent 34 is regenerated by bringing the rich absorbent 33 into contact with dry nitrogen. The regenerated absorbent 34 is circulated to the absorption tower 29 with the flow rate adjusted by the liquid feed pump 32 .
In the following experiment, the absorbing solution of ionic liquid alone and ethylene glycol alone were used, but by performing the same using the absorbing solution of the present invention, the water electrolysis hydrogen gas can be more efficiently dehumidified. can be done.

(Dehumidification test 1)
Water-electrolyzed hydrogen gas is supplied to the water-electrolyzed hydrogen line 27 at a flow rate of 2 L/min and a pressure of 0.30 MPaG. The volume is 500 mL, the regeneration tower liquid volume is 500 mL, the absorbent is fixed to the ionic liquid PX-4MP, the temperature of the regeneration tower is about 60 ° C. to 100 ° C., the pressure of the regeneration tower is -50 kPaG to 0 kPaG, the dry nitrogen flow rate is A dehumidification test was conducted under the conditions shown in Table 3 in the range of 100 to 500 mL/min and the circulation rate of the absorbent in the range of 2 to 5 mL/min. More specifically, 1) flow the dried water-electrolyzed hydrogen gas to the dew point meter to measure the dew point of the dry hydrogen, and then 2) switch the line from the humidification tower 28 to the dew point meter to measure the dew point of the humidified hydrogen. After confirming that the dew point is about 10 ° C., then 3) switch the line from the absorption tower 29 to the dew point meter (that is, introduce the water electrolysis hydrogen gas into the humidification tower 28 through the water electrolysis hydrogen line 27 and humidify and then introduced into the absorption tower 29), dehumidification was performed with the absorbent, the dew point of the dehumidified hydrogen was measured over time, and the dew point when the dew point became constant was taken as the dew point of the dehumidified hydrogen. Table 3 shows the results. Also, the water content in the absorbent was measured. Table 3 shows the results.

The above results reveal the following. 1) As the nitrogen flow rate was decreased to 500 mL/min, 300 mL/min, and 100 mL/min, the dew point of dehumidified hydrogen gradually increased. 2) As the regeneration tower temperature was lowered to 100°C, 80°C and 60°C, the dew point of the dehumidified hydrogen gradually increased. 3) When the pressure in the regeneration tower was increased from -50 kPa to 0 kPa, the dew point of the dehumidified hydrogen increased, and this tendency was more pronounced at the regeneration tower temperature of 60°C than at 100°C. 4) When the circulation rate of the absorbing liquid was decreased from 5 mL/min to 2 mL/min, the dew point of the dehumidified hydrogen increased, and this tendency was more pronounced at the regeneration tower temperature of 60°C than at 100°C. In particular, at nitrogen flow rates of 300 mL/min and 100 mL/min, regeneration tower temperatures of 80° C. and 60° C., and regeneration tower pressures of −50 kPa and 0 kPa, the difference in the dew point of the dehumidified hydrogen is large and is a more important factor.

(Dehumidification test 2)
Next, comparison was made using ionic liquids PX-4MP and TEG as absorption liquids.
(Fixed conditions) Hydrogen flow rate was fixed at 2 L/min, humidification tower temperature at 10°C, absorption tower temperature at 25°C, absorption tower pressure at 0.30 MPaG, absorption tower liquid volume at 500 mL, regeneration tower liquid volume at 500 mL, A dehumidification test was performed in the same manner as dehumidification test 1 under the conditions shown in Table 4. Table 4 shows the results.

The above results reveal the following. When the ionic liquid PX-4MP was used as the absorption liquid, the dew point of the dehumidified hydrogen was lowered by about 6 to 11°C rather than the TEG. Specifically, 1) when the nitrogen flow rate is reduced to 500 mL/min, 300 mL/min, and 100 mL/min, the difference in the dew point of dehumidified hydrogen increases to 7.13°C, 8.85°C, and 11.18°C. became. 2) When the regeneration tower temperature was lowered from 100°C to 80°C, the dew point difference of dehumidified hydrogen increased from 7.13°C to 11.18°C. 3) When the pressure of the regeneration tower was increased from -50 kPaG to 0 kPaG, the dew point difference of dehumidified hydrogen decreased from 7.13°C to 6.18°C. 4) Even when the circulation rate of the absorbing liquid was decreased from 5 mL/min to 2 mL/min, the difference in the dew points of the dehumidified hydrogen was 7.13 and 6.98°C, which remained substantially constant. Thus, when the nitrogen flow rate is low, the regeneration tower temperature is low, and the regeneration tower pressure is low, the performance of the absorbent containing the ionic liquid tends to be higher than that of TEG.

In the above dehumidification test, the ionic liquid PX-4MP alone was used as the absorbent. When used, it becomes a method for producing dry hydrogen with better performance.

DESCRIPTION OF SYMBOLS 1... Water electrolysis apparatus 2... Wet hydrogen 3... Mass flow controller (MFC)
4 ... Three-way valve 5 ... Absorption tower 6 ... Absorption liquid 7 ... Three-way valve 8 ... Trap 9 ... Capacitance dew point meter 10 ... Mirror surface type dew point meter 11 ... Dry hydrogen 12 Rich absorbent 13 Flow meter 14 Regeneration tower 15 Liquid feed pump 16 Trap 17 Vacuum pump 18 Exhaust port 19 Dry nitrogen cylinder 20 Flow meter 21 Dry nitrogen 22 Wet nitrogen 23 Exhaust port 24 T-shaped connector 25 Mass flow controller (MFC)
26 Compressor 27 Water electrolysis hydrogen line 28 Humidification tower 29 Absorption tower 30 Flow meter 31 Regeneration tower 32 Liquid feed pump 33 Rich absorption Liquid 34... Absorption liquid

Claims (10)

a hydrogen generation step of electrolyzing water to obtain wet water electrolysis hydrogen gas containing hydrogen and water vapor derived from raw water;
The wet water electrolyzed hydrogen gas is brought into contact with an absorption liquid containing an ionic liquid and an inorganic salt to selectively absorb the water vapor into the absorption liquid, thereby absorbing the dry water electrolyzed hydrogen gas with reduced humidity and the water vapor. an absorption step for obtaining a rich absorbent solution;
a separation step of gas-liquid separation of the dry water electrolysis hydrogen gas and the rich absorbent;
including
The inorganic salt is a salt (excluding the ionic liquid) composed of an anion of a carbon-free acid, carbonic acid, acetic acid, formic acid, cyanic acid, or hydrocyanic acid and a cation of an inorganic compound. manufacturing method. The drying according to claim 1, wherein the inorganic salt is an inorganic salt that can be uniformly dissolved in the ionic liquid, and the content of the inorganic salt in the ionic liquid is the solubility of the ionic liquid at room temperature or less. A method for producing water electrolysis hydrogen gas. 3. The method for producing hydrogen gas by dry water electrolysis according to claim 1, wherein said inorganic salt is lithium acetate, calcium acetate, lithium chloride, calcium chloride, lithium nitrate or calcium nitrate. The method for producing hydrogen gas by dry water electrolysis according to any one of claims 1 to 3, wherein the ionic liquid is a salt composed of phosphoniums and phosphate ester ions. The method for producing hydrogen gas by dry water electrolysis according to any one of claims 1 to 4, wherein the ionic liquid is represented by formula (1).

further comprising a regeneration step of removing water from the rich absorbent to regenerate the absorbent;
6. Any one of claims 1 to 5, wherein the regeneration step is a method of contacting the rich absorbent with a dry gas, a method of heating the rich absorbent, and/or a method of depressurizing the rich absorbent. 2. The method for producing dry water electrolytic hydrogen gas according to item 1. 7. The method according to claim 6, wherein the regeneration step is a method of contacting the rich absorbent with dry gas, and the dry gas is a part of the dry water electrolyzed hydrogen gas separated from gas and liquid in the separation step. A method for producing dry water electrolysis hydrogen gas as described. The method for producing dry water electrolyzed hydrogen gas according to claim 6 or 7, wherein the regeneration step is performed at 100°C or lower. Containing an ionic liquid represented by formula (1) and an inorganic salt ,
The inorganic salt is a salt (excluding the ionic liquid) composed of an anion of a carbon-free acid, carbonic acid, acetic acid, formic acid, cyanic acid, or hydrocyanic acid and a cation of an inorganic compound .

The absorption liquid according to claim 9, wherein the inorganic salt is lithium acetate, calcium acetate, lithium chloride, calcium chloride, lithium nitrate or calcium nitrate.

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