JP7121578B2 - Hydrogen generator and hydrogen production method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a hydrogen generator and a hydrogen production method, and more particularly, a hydrogen generator using a TTF-based compound having a tetrathiafulvalene (TTF) skeleton as a catalyst, and hydrogen production using such a hydrogen generator. Regarding the method.

As a method for producing hydrogen, for example,
(a) a method of electrolyzing water;
(b) a method of obtaining hydrogen from hydrocarbons such as methane using a steam reforming method, a partial oxidation method, etc.;
(c) A method of obtaining hydrogen from water using a photocatalyst is known.
However, conventional hydrogen production methods
(A) There is little room for cost reduction,
(B) the resulting hydrogen may contain harmful impurities;
(C) Reactions at high temperatures and pressures, and may require large-scale equipment.
There are problems such as

In order to solve this problem, various proposals have been conventionally made.
For example, Patent Document 1 discloses a method of adding an aqueous hydrochloric acid solution or water to a hydrogen generating agent containing a compound having a tetrathiafulvalene (TTF) skeleton.
In the same document,
(a) the hydrogen generating agent containing a compound having a TTF skeleton can generate hydrogen from water within a certain pH range;
(b) the hydrogen generating agent becomes a different substance through the hydrogen generating reaction, but can be regenerated as the original hydrogen generating material by changing the pH of the solution;
(c) It is stated that, in principle, no oxygen is generated in the hydrogen generation reaction, so there is no need to perform a process for separating oxygen.

Patent Document 1 describes that hydrogen is generated by dispersing a compound having a TTF skeleton in water. However, in the method described in Patent Document 1, the reaction rate of hydrogen generation is slow, and the amount of hydrogen generated is less than the amount of the hydrogen generating agent.

WO2017/141692

The problem to be solved by the present invention is to provide a hydrogen generator capable of easily generating a relatively large amount of hydrogen, and a hydrogen production method using the same.

In order to solve the above problems, the hydrogen generator according to the present invention includes:
a reaction vessel for containing a dispersion liquid in which a hydrogen generating agent is dispersed in water;
and an ultrasonic irradiation device for applying ultrasonic waves to the dispersion.
The hydrogen generating agent preferably contains a TTF-based compound having a tetrathiafulvalene (TTF) skeleton.

The gist of the hydrogen production method according to the present invention is to generate hydrogen using the hydrogen generator and the dispersion liquid according to the present invention.

In the case of dispersing a hydrogen generating agent such as a TTF-based compound in water to generate hydrogen, irradiating the dispersion with ultrasonic waves remarkably increases the amount of hydrogen generated. Also, if the hydrogen generation conditions are optimized, the hydrogen generation rate will be 1000 times or more that of the conventional method. This is probably because the irradiation of the dispersion liquid with ultrasonic waves suppressed aggregation of the hydrogen generating agent in the dispersion liquid and increased the contact area between the water and the hydrogen generating agent.

FIG. 1(A) is a schematic diagram of a hydrogen generator. FIG. 1B is a schematic diagram showing how the reaction vessel is held in a constant temperature bath. FIG. 4 is a diagram showing the relationship between the presence or absence of ultrasonic irradiation and the rate of hydrogen generation. FIG. 3 is a diagram showing the relationship between the number of times of ultrasonic irradiation and the amount of hydrogen generated. FIG. 3 is a graph showing the relationship between the concentration of hydrogen generating agent and the hydrogen amount (N _cat )/hydrogen generating agent ratio. FIG. 4 is a diagram showing the relationship between the concentration of a hydrogen generating agent and the amount of hydrogen (N _cat );

An embodiment of the present invention will be described in detail below.
[1. Hydrogen generating agent]
[1.1. definition]
In the present invention, the "hydrogen generating agent" refers to a substance that acts as a catalyst for decomposing water using external energy (eg, ultrasonic waves, heat, etc.). For this purpose, the hydrogen generating agent must be a substance capable of taking two states of reductant (R) and oxidant (O). The reductant (R) has an electromotive force of −0.4 V or less (below the electrolytic potential of water) with respect to the reversible hydrogen electrode at neutral (pH = 7), and when it comes into contact with water, it reduces water and generates hydrogen. and itself becomes an oxidant (O). Then, the oxidant (O) is reduced by external energy to return to the reductant (R), and it becomes possible to reduce water again.
Such hydrogen generating agents include, for example,
(a) a compound having a tetrathiafulvalene (TTF) skeleton (hereinafter also referred to as "TTF-based compound"),
(b) a photocatalyst such as _TiO2 ;
(c) metals/metal oxides for thermochemical cycling;
and so on.

Among these, TTF compounds are
(A) not substantially depleted even when used in a hydrogen generation reaction;
(B) In principle, hydrogen can be generated repeatedly without limit,
(C) Since no oxygen is generated during the hydrogen generation reaction, there is no need for a process to separate oxygen, unlike normal water decomposition reactions.
(D) the oxidant (O) can be converted back to the reductant (R) by ultrasonic irradiation;
There are advantages such as Therefore, the TTF-based compound is particularly suitable as a hydrogen generating agent.

[1.2. TTF-based compound]
A "TTF _- based compound" refers to a compound having a tetrathiafulvalene _{( H2C2S2C = CS2C2H2} ) skeleton ₍ TTF skeleton) in its structure.
The TTF-based compound is
(a) may be a compound having one TTF skeleton in the structure, or
(b) A compound having a condensed tetrathiafulvalene skeleton (TTF _n -TTF) in which two or more TTF skeletons are condensed via two carbon atoms of a five-membered ring.
When the TTF-based compound has a condensed TTF skeleton, the number of condensed TTF skeletons is not particularly limited. However, if the number of TTF skeletons is too large, synthesis becomes difficult. Therefore, the number of TTF skeletons contained in the condensed TTF skeleton is preferably 6 or less. The number of TTF skeletons is particularly preferably two.

Further, the TTF-based compound is a compound in which a carboxylic acid group (-COOH) or an alkali metal salt of a carboxylic acid group (-COOM, where M is an alkali metal) is bound to the five-membered ring carbon atoms contained in the TTF skeleton. But it's okay. The alkali metal is preferably Li or Na. In particular, since Li has a smaller ionic radius than Na, it has the advantage of increasing the stability of the TTF-based compound.
In addition, the TTF-based compound is
(a) may be a compound consisting only of a TTF skeleton, or
(b) A complex in which MOH (M is an alkali metal) is coordinated to the TTF skeleton.
Furthermore, the TTF-based compound may have at least part of the sulfur atoms in the TTF skeleton substituted with selenium.

In particular, the TTF-based compound is
the TTF skeleton consisting of a condensed tetrathiafulvalene skeleton;
an alkali metal salt of a carboxylic acid group bonded to a carbon atom of the TTF skeleton;
and an alkali metal hydroxide coordinated to the TTF skeleton. This is considered to be due to the following reasons.
That is, the TTF skeleton is electron-rich and easily emits electrons. Therefore, electrons are transferred from the TTF skeleton to water (that is, the TTF skeleton is reduced) to generate hydrogen. At this time, the TTF skeleton loses one electron and becomes electrically positive. The charge compensation ionizes the alkali metal from the carboxylate to form a negatively charged carboxylate group ( ^--COO.sup.- ). Therefore, the compound as a whole becomes neutral and stabilizes. Such a phenomenon also occurs when all or part of the sulfur contained in the TTF skeleton is replaced with selenium.

In order to efficiently generate hydrogen, the hydrogen generating agent is
(a) a first compound comprising a (TTF _n -TTF)(COOM) ₂ (MOH) complex (n is an integer of 1 or more and M is Li or Na);
(b) a second compound comprising a (COOM) ₂ (TTF-TTF _m -TTF) (COOM) ₂ (MOH) ₂ complex (m is an integer of 0 or more and M is Li or Na), or
(c) A third compound in which at least part of the sulfur contained in the TTF skeleton of the first compound or the second compound is substituted with selenium is preferred. Any one of these compounds may be used as the hydrogen generating agent, or two or more of them may be used in combination.

In the description of the TTF-based compound, for example, "(TTF _n -TTF)..." indicates that a total of (n+1) TTF skeletons are condensed.
Moreover, "...TTF)(COOM) ₂ ..." indicates that a -COOM group is bonded to each of the two carbon atoms of the five-membered ring located at the ends of the TTF skeleton.
Furthermore, "...(MOH) ₂ " represents that two MOH are coordinated to the TTF skeleton.

[2. Dispersion]
The dispersion consists of water in which the hydrogen generating agent is dispersed. The hydrogen generating agent serves as a catalyst for the reaction that generates hydrogen from water. As will be described later, in the present invention, hydrogen is generated by irradiating the dispersion liquid with ultrasonic waves. In this case, the concentration of the hydrogen generating agent in the dispersion is not particularly limited, and an optimum concentration can be selected according to the purpose.

Generally, the higher the concentration of the hydrogen generating agent in the dispersion, the faster the rate of hydrogen generation. In order to obtain such effects, the concentration of the hydrogen generating agent is preferably 0.3 μmol/L or more. The concentration of the hydrogen generating agent is preferably 1.0 μmol/L or more.
On the other hand, if the concentration of the hydrogen generating agent becomes too high, the amount of hydrogen generated decreases. Also, the ratio of the amount of hydrogen to the amount of hydrogen generating agent is reduced. Therefore, the concentration of the hydrogen generating agent is preferably 30 μmol/L or less. The concentration of the hydrogen generating agent is preferably 15 μmol/L or less, more preferably 5 μmol/L or less.

[3. Hydrogen generator]
The hydrogen generator according to the present invention is
a reaction vessel for containing a dispersion liquid in which a hydrogen generating agent is dispersed in water;
and an ultrasonic irradiation device for irradiating the dispersion liquid with ultrasonic waves.

The hydrogen generator is
(a) a heat retaining device for keeping the reaction container warm;
(b) a hydrogen generation amount measuring device for measuring the hydrogen generation amount in the reaction vessel, and/or
(c) Calculate the hydrogen generation rate (v _H2 ) from the time change of the hydrogen generation amount, and when the hydrogen generation rate (v _H2 ) becomes equal to or less than the threshold value (v _cri ), turn on the ultrasonic irradiation device. A feedback means may be further provided to operate for a predetermined time (t).

[3.1. Hydrogen generating agent, dispersion liquid]
A dispersion liquid in which a hydrogen generating agent is dispersed in water is used for hydrogen generation. Since the details of the hydrogen generating agent and the dispersion are as described above, the description is omitted.

[3.2. reaction container]
The reaction vessel is for containing a dispersion liquid in which the hydrogen generating agent is dispersed in water. The material, shape, size, etc. of the reaction vessel are not particularly limited, and an optimum one can be selected according to the purpose.

[3.3. Ultrasonic irradiation device]
A hydrogen generator according to the present invention includes an ultrasonic irradiation device for applying ultrasonic waves to a dispersion liquid. This point is different from the conventional one. The ultrasonic irradiation device is not particularly limited as long as it can irradiate the dispersion liquid with ultrasonic waves for a predetermined time.
In the case of generating hydrogen from a dispersion containing a hydrogen generating agent, the rate of hydrogen generation is remarkably increased by irradiating the dispersion with ultrasonic waves. In this case, even if the irradiation of ultrasonic waves is stopped, hydrogen continues to be generated for a while. However, after a predetermined period of time has passed since the ultrasonic irradiation was stopped, the generation rate of hydrogen decreases significantly. Therefore, it is preferable that the ultrasonic irradiation device can continuously or intermittently irradiate the dispersion liquid with ultrasonic waves having a predetermined energy.

[3.4. Thermal insulation device]
The hydrogen generator may further include a heat retaining device for keeping the reaction container warm. The hydrogen generation rate depends not only on the ultrasonic irradiation conditions but also on the temperature of the dispersion. The heat retaining device is not particularly limited as long as it can maintain the dispersion at a predetermined temperature.

[3.5. Hydrogen generation amount measuring device]
The hydrogen generator may further include a hydrogen generation amount measuring device for measuring the hydrogen generation amount in the reaction vessel. The measured amount of hydrogen generation can be used for calculation of hydrogen generation rate, calculation of cumulative hydrogen generation amount, control of ultrasonic irradiation time, and the like.
The hydrogen generation amount measuring device is not particularly limited as long as it can measure the hydrogen generation amount. As a hydrogen generation amount measuring device, for example,
(a) Gas Chromatograph-Thermal Conductivity Detector Device (GC-TCD),
(b) a mass spectrometer (MS);
(c) Infrared spectrophotometer (FT-IR)
and so on.

[3.6. Feedback Means]
The hydrogen generator calculates the hydrogen generation rate (v _H2 ) from the change in the amount of hydrogen generation over time, and when the hydrogen generation rate (v _H2 ) becomes equal to or less than the threshold value (v _cri ), the ultrasonic irradiation device is turned on. A further feedback means may be provided to activate for a time (t).
As described above, when the dispersion is irradiated with ultrasonic waves, the rate of hydrogen generation is remarkably increased, but the effect of ultrasonic irradiation soon disappears. Therefore, by intermittently irradiating ultrasonic waves while monitoring the hydrogen generation rate, a relatively large amount of hydrogen can be generated with a small input energy.

[4. Hydrogen production method]
The gist of the hydrogen production method according to the present invention is to generate hydrogen using the hydrogen generator and the dispersion liquid according to the present invention. Hydrogen generating conditions that affect the amount of hydrogen generated include, for example, the concentration of the hydrogen generating agent in the dispersion, the temperature of the dispersion, and the ultrasonic irradiation time. Hydrogen generation conditions are not particularly limited, and it is preferable to select optimum conditions according to the purpose.

[5. action]
In the case of dispersing a hydrogen generating agent such as a TTF-based compound in water to generate hydrogen, irradiating the dispersion with ultrasonic waves remarkably increases the amount of hydrogen generated. In addition, by optimizing the hydrogen generation conditions, the hydrogen generation rate is 1000 times or more that of the conventional method. This is probably because the ultrasonic irradiation of the dispersion inhibited aggregation of the hydrogen generating agent in the dispersion and increased the contact area between the water and the hydrogen generating agent.

(Example 1, Comparative Example 1)
[1. Hydrogen generator]
FIG. 1A shows a schematic diagram of the hydrogen generator used in the experiment. In FIG. 1(A), the hydrogen generator 10 includes a reaction vessel 20, an ultrasonic irradiation tank 30 having an ultrasonic irradiation device 30a, and a GC-TCD (not shown).

The reaction vessel 20 is for containing a dispersion liquid 26 in which a hydrogen generating agent is dispersed in water, and includes a main body 22 and a cap 24 . A predetermined amount of dispersion liquid 26 is accommodated in the main body 22, and the gap is filled with argon gas. A stirrer 28 for stirring the dispersion liquid 26 is inserted in the main body 22 .
An upper opening of the main body 22 is sealed with a cap 24 . A gas sampling port 24a is provided at the tip of the cap 24 . The gas sampling port 24a is connected to a GC-TCD (not shown) so that the type and amount of gas generated within the reaction vessel 20 can be analyzed.

The reaction vessel 20 is installed in an ultrasonic irradiation bath 30 . Water 32 at room temperature is placed in the ultrasonic irradiation tank 30, and ultrasonic waves are irradiated from the ultrasonic irradiation device 30a at the bottom of the ultrasonic irradiation tank 30 toward the reaction vessel 20. there is

[2. Test method]
A TTF-based compound having a structure represented by the following formula (1) was used as the hydrogen generating agent. This hydrogen generating agent was dispersed in water to obtain a dispersion.

A predetermined amount of the dispersion liquid 26 was placed in the reaction vessel 20 of the hydrogen generator 10 shown in FIG. 1(A). Room temperature water 32 was put into an ultrasonic irradiation bath 30 and the reaction vessel 20 was placed in the water 32 .
The dispersion liquid 26 in the reaction vessel 20 was irradiated with ultrasonic waves at room temperature (18 to 25° C.) for 10 minutes at 135 W and 40 kHz. After stopping the irradiation of the ultrasonic waves, the reaction vessel 20 was moved to a constant temperature bath 34 containing hot water 36 as shown in FIG. 1(B). Next, while stirring the dispersion 26 with a stirrer 28, it was heated at 50° C. for 1 hour, and the amount of hydrogen generated was measured by GC-TCD (Example 1).
Further, the dispersion liquid was held at 50° C. for 72 hours without irradiating ultrasonic waves, and the amount of hydrogen generated was measured with a gas chromatograph (Comparative Example 1).

GC-TCD quantified the amount of gaseous hydrogen (N _gas ) in the space above the dispersion liquid 26 . Since hydrogen is slightly soluble in water, the amount of dissolved hydrogen (N _soln ) in the dispersion was calculated based on Henry's law. Further, it is known that the irradiation of ultrasonic waves to a dispersion induces a radical reaction to generate hydrogen. Therefore, blank measurement was performed, and the amount of hydrogen (N _sonic ) generated by ultrasonic irradiation for 10 minutes was calculated. The amount of hydrogen (N _cat ) generated by the reaction between water and the hydrogen generating agent is represented by the following formula (2).
N _cat = N _gas + N _soln - N _sonic (2)

[3. result]
FIG. 2 shows the relationship between the presence or absence of ultrasonic irradiation and the rate of hydrogen generation. From FIG. 2, the following can be understood.
(1) The hydrogen generation rate of Example 1 was 1000 times or more that of Comparative Example 1. This is probably because the ultrasonic irradiation improved the dispersibility of the hydrogen generating agent.
(2) Ncat/hydrogen generating agent molar ratio of Comparative Example 1 was 1.4×10 ⁻³ . That is, the amount of hydrogen generated in Example 1 is significantly less than the amount of the hydrogen generating agent. On the other hand, the N _cat /hydrogen generating agent ratio (molar ratio) of Example 1 was 2.3, and more hydrogen was generated than the amount of the hydrogen generating agent.

(Example 2)
[1. Test method]
A TTF-based compound represented by formula (1) was used as the hydrogen generating agent. Ultrapure water and a hydrogen generating agent were added to the reaction vessel 20 of the hydrogen generator 10 used in Example 1. After heating at 50° C. for 1 hour without ultrasonic irradiation, the amount of hydrogen was measured (A).
Next, the dispersion liquid 26 in the reaction vessel 20 was irradiated with ultrasonic waves at room temperature (18 to 25° C.) for 10 minutes. Then, after heating the dispersion at 50° C. for 1 hour, the amount of hydrogen was measured (B).
Thereafter, after confirming that hydrogen generation was completed, ultrasonic irradiation for 10 minutes at room temperature (18 to 25° C.), heating at 50° C. for 1 hour, and measurement of the amount of hydrogen were repeated (C, D). .

[2. result]
FIG. 3 shows the relationship between the frequency of ultrasonic irradiation and the amount of hydrogen generated. From FIG. 3, the following can be understood.
(1) When ultrasonic waves were applied, the amount of hydrogen generated increased temporarily, but hydrogen generation almost stopped after a certain period of time. Further, when the ultrasonic wave was applied again after hydrogen generation stopped, the amount of hydrogen generated increased again. The reason why the amount of hydrogen generation stops after ultrasonic irradiation is considered to be that the hydrogen generating agent aggregates in the dispersion liquid. Further, the reason why the amount of hydrogen generated increases again when ultrasonic irradiation is resumed is considered to be that the hydrogen generating agent is re-dispersed.
(2) The catalyst represented by formula (1) is stable in water and is not decomposed by ultrasonic irradiation.

(Example 3)
[1. Test method]
A TTF-based compound represented by formula (1) was used as the hydrogen generating agent. Ultrapure water and a hydrogen generating agent were added to the reaction vessel 20 of the hydrogen generator 10 used in Example 1. The concentration of the hydrogen generating agent was 0.3, 14, 29, or 288 μmol/L.
The dispersion liquid 26 in the reaction vessel 20 was irradiated with ultrasonic waves at room temperature (18 to 25° C.). Then, after heating the dispersion liquid at 50° C. for 24 hours, the amount of hydrogen was measured.

[2. result]
FIG. 4 shows the relationship between the concentration of the hydrogen generating agent and the hydrogen content (N _cat )/hydrogen generating agent ratio. FIG. 5 shows the relationship between the concentration of the hydrogen generating agent and the amount of hydrogen (N _cat ). 4 and 5 show the following.
(1) A large amount of hydrogen was generated even when the concentration of the hydrogen generating agent was 0.3 μmol/L. The amount of hydrogen (N _cat ) reached a maximum when the concentration of the hydrogen generating agent was approximately 15 μmol/L.
(2) The higher the hydrogen generating agent concentration, the smaller the N _cat /hydrogen generating agent ratio (molar ratio). Moreover, it was found that when the concentration of the hydrogen generating agent is set to 15 μmol/L or less, the amount of hydrogen (N _cat ) equal to or greater than that of the hydrogen generating agent can be obtained.
(3) After ultrasonic irradiation, it is considered that the hydrogen generation reaction and the agglomeration reaction between the catalysts proceed in parallel. At low concentrations, aggregation is less likely to occur, so the hydrogen generation reaction occurs preferentially, but at high concentrations, the aggregation reaction rate is presumed to exceed the hydrogen generation reaction rate. For this reason, it is considered that the amount of hydrogen generated was large at low concentrations, and that the amount of hydrogen generated decreased after reaching a maximum (Fig. 5).
(4) The utilization efficiency of the catalyst monotonously decreased (Fig. 4), and at 15 µmol/L or more, the reaction stopped before the generation of hydrogen equivalent to that of the catalyst. In order to avoid useless catalyst input and use the catalyst effectively, it is desirable to generate hydrogen at a concentration below a certain level.

Although the embodiments of the present invention have been described in detail above, the present invention is by no means limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present invention.

INDUSTRIAL APPLICABILITY The hydrogen generator according to the present invention can be used as a fuel production device for fuel cells, a hydrogen production device as a raw material for chemical products, and the like.

Claims (9)

Used to generate hydrogen from a dispersion in which a hydrogen generating agent is dispersed in water,
a reaction vessel for containing the dispersion ;
An ultrasonic irradiation device for irradiating the dispersion liquid with ultrasonic waves ,
The hydrogen generating agent contains a TTF-based compound having a tetrathiafulvalene (TTF) skeleton
Hydrogen generator. 2. The hydrogen generator according to claim 1, further comprising a heat retaining device for keeping said reaction container warm. 3. The hydrogen generator according to claim 1, further comprising a hydrogen generation amount measuring device for measuring the hydrogen generation amount in said reaction vessel. A hydrogen generation rate (v _H2 ) is calculated from the change in the hydrogen generation amount over time, and when the hydrogen generation rate (v _H2 ) becomes equal to or less than a threshold value (v _cri ), the ultrasonic irradiation device is operated for a predetermined time ( 4. The hydrogen generator of claim 3, further comprising feedback means for operating only t). The hydrogen generator according to any one of claims 1 to 4, wherein the concentration of the hydrogen generating agent in the dispersion liquid is 0.3 µmol/L or more and 30 µmol/L or less. The TTF-based compound is
the TTF skeleton consisting of a condensed tetrathiafulvalene skeleton;
an alkali metal salt of a carboxylic acid group bonded to a carbon atom of the TTF skeleton;
The hydrogen generator according to any one of claims 1 to 5, further comprising an alkali metal hydroxide coordinated to the TTF skeleton. 7. The hydrogen generator according to any one of claims 1 to 6 , wherein at least part of sulfur in the TTF skeleton of the TTF-based compound is replaced with selenium. The hydrogen generating agent is
(a) a first compound comprising a (TTF _n -TTF)(COOM) ₂ (MOH) complex (n is an integer of 1 or more and M is Li or Na);
(b) a second compound comprising a (COOM) ₂ (TTF-TTF _m -TTF) (COOM) ₂ (MOH) ₂ complex (m is an integer of 0 or more and M is Li or Na);
(c) any one or more compounds selected from the group consisting of a third compound in which at least part of the sulfur contained in the TTF skeleton of the first compound or the second compound is substituted with selenium; 8. The hydrogen generator according to any one of items 1 to 7 . A hydrogen production method for generating hydrogen using the hydrogen generator and the dispersion liquid according to any one of claims 1 to 8 .

Images