JP2003278997A - Gas storage device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas storage device having superior characteristics in comparison with a conventional one. <P>SOLUTION: In this gas storage device, adsorption-desorption isotherm relating to a stored gas, includes a compound having hysteresis loop. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas storage device such as a gas tank, and more specifically, by using a material whose adsorption / desorption isotherm exhibits a hysteresis loop, various properties such as storage performance, safety and freedom of shape can be obtained. The present invention relates to a gas storage device having improved characteristics.

[0002]

2. Description of the Related Art As a technique for storing gas, a method of compressing the volume by simply pressurizing and filling a cylinder with high pressure, a method of liquefying by cooling and filling an insulating container,
There is known a method of dissolving in a solvent and filling a cylinder, which is used in the case of acetylene.

However, these methods have the following problems.

The above-mentioned method requires a special pressurizing device for increasing the pressure, resulting in a high equipment cost. Further, since the pressure of the stored gas is extremely high, it is necessary to give due consideration to safety. In addition, the shape of the container is restricted to ensure the ability to withstand high pressure, and
The mass of the gas storage device must be increased in order to increase the pressure resistance. For example, in the fuel storage tank of a natural gas vehicle, 200
It is necessary to pressurize the tank structure to a high pressure state, and it is necessary to adjust the shape of the tank so that the pressure is uniformly applied to the tank structure. In addition, it is necessary to form the tank with a material that can withstand a high pressure of 200 atm. The above method requires a special compression device and a cooling device for liquefaction, which leads to a high equipment cost. Also,
The container for storing the liquefied gas also needs to have a special structure in order to ensure the heat retention performance. The above method
When the gas is taken out, contamination of the solvent container occurs, and the transport mass increases due to the presence of the solvent. It also has the drawback that it can only be used for special gases. In recent years, hydrogen storage alloys have been actively developed for storing hydrogen, but expensive materials are required and the storage capacity is not sufficient.

In view of such circumstances, a gas storage device using a compound having adsorption and desorption characteristics of gas components has been developed. Japanese Patent Laid-Open No. 9-227571 discloses [C
There is disclosed a gas storage device containing a metal complex having a composition formula such as o (4,4′-bpy) _1.5 (NO ₃ ) ₂ ] _n . It has been elucidated that such a metal complex has a space in the crystal structure and can adsorb and store various gas components depending on the size of the space and the characteristics of the constituents. Allows gas storage at low pressures. However, the gas storage device has not yet been fully satisfactory, and there is a strong demand for the development of a gas storage device having more excellent characteristics.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a gas storage device having significantly superior characteristics as compared with the conventional gas storage device. Specifically, it is an object of the present invention to provide a gas storage device that can store a large amount of gas without requiring high-pressure equipment and is excellent in safety and shape flexibility. Another object of the present invention is to provide a vehicle equipped with the gas storage device.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the inventors of the present invention can fundamentally solve the above problems by using a compound having completely different adsorption / desorption characteristics from the conventional one. I found that. The compound used in the conventional gas storage device is basically Lan.
Those exhibiting behavior according to the gmuir isotherm θ = Kp _A / (1 + Kp _A ) have been used. We have La
By using a compound that does not behave according to the ngmuir isotherm and the gas pressure-gas adsorption amount curve shows a hysteresis loop, it is possible to obtain a gas adsorption device having fundamentally different characteristics from the conventional type. Heading The present invention has been completed.

The effect of the present invention can be obtained by using a compound whose adsorption / desorption isotherm related to gas exhibits a hysteresis loop (hereinafter, also referred to as "hysteresis compound" for convenience). In order to obtain the effect of the present invention, The principle is not particularly limited as long as it shows a hysteresis loop. As one of the principles of showing the hysteresis loop, it is considered that the adsorbent has many valve structures at the molecular level. This is called a nano-molecular valve type adsorbent to distinguish it from conventional adsorbents. Many pores exist in the conventional adsorption / desorption material, and gas molecules are adsorbed in the pores. The nano-molecular valve type adsorbent also has many pores in which gas molecules are adsorbed, but it is considered that a valve structure at the molecular level exists when the nano-molecular valve adsorbent enters and leaves the pores. Therefore, the gas molecules cannot pass through the valve structure at the molecular level unless they have a predetermined kinetic energy.
As a valve structure at the molecular level, there is a valve consisting of hydrogen bonds with a weak binding force, which can stick or separate like a small magnet, so only gas molecules with a certain kinetic energy pass through. can do.
By changing the nano-molecular valve in terms of the molecular structure, it becomes possible to control the passage of gas molecules. The presence of this nanomolecular valve structure
Gas molecules adsorbed at a certain pressure are retained in the pores by the nanomolecular valve structure and cannot be desorbed from the pores even when the pressure is reduced. Therefore, it can be inferred that a hysteresis loop regarding the gas pressure-gas adsorption amount curve appears. Therefore, it is possible to prepare a special adsorbent having a desired hysteresis loop by variously changing the nano-molecular valve structure from weak to strong.

The specific constitution of the present invention completed based on the above findings is as follows.

The present invention is a gas storage device in which a compound whose adsorption / desorption isotherm for a stored gas exhibits a hysteresis loop is housed inside a pressure resistant container.

The stored gas is preferably one or more gases selected from the group consisting of hydrocarbon gas, oxygen, nitrogen, carbon dioxide, carbon monoxide, argon and hydrogen.

Further, the compound is preferably a metal complex.

The metal complex preferably contains copper, cobalt, nickel or zinc as metal ions.

The metal complex is pyrazine, 4,4 '.
-Bipyridine, trans-1,2-bis (4-pyridyl) ethylene, 1,4-dicyanobenzene, 4,4-dicyanobiphenyl, 1,2-dicyanoethylene, 1,4
It is preferable to include at least one of -bis (4-pyridyl) benzene as a ligand.

The metal complex is [Cu (bpy)]
It is preferably represented by (BF ₄ ) ₂ (H ₂ O) ₂ · (bpy)] _n (in the formula, bpy represents 4,4′-bipyridine).

The present invention is also a vehicle equipped with the above-described gas storage device.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The gas storage device of the present invention will be described in detail below. First, the superiority of the gas storage device using the hysteresis compound will be described with reference to the drawings. FIG. 1 is a graph showing a pressure-adsorption amount relationship of a compound stored in a gas storage device according to the present invention. Figure 2
Is the pressure of the compound stored in the conventional gas storage device −
It is a graph which shows the relationship of adsorption amount. In the figure, the horizontal axis represents the gas pressure and the vertical axis represents the gas adsorption amount per 1 g of the compound.

In the conventional gas storage device, the gas adsorption amount also increases as the gas pressure increases, and the pressure-adsorption amount curve during adsorption and the pressure-adsorption amount curve during desorption coincide with each other (Fig. 2). For example, when the adsorption amount to be adsorbed in the gas storage device is A ₁ , it is necessary to increase the gas pressure to p ₁ . Since the gas pressure and the gas storage amount have the relationship shown in FIG. 2, it is necessary to increase the gas pressure in order to increase the gas storage amount.

On the other hand, in the gas storage device according to the present invention, the pressure-adsorption amount curve during gas adsorption shows a hysteresis loop (FIG. 1). With such characteristics, it is possible to dramatically reduce the pressure during transportation and storage. For convenience of description, the gas adsorption amount at a pressure p ₁ will be described assuming a compound which is A _1, to the gas adsorption amount A ₁ increases the pressure applied to the gas storage device up to p ₁ There is a need. However,
In the gas storage device according to the present invention, since the pressure-adsorption amount curve draws a hysteresis loop, even when the pressure is reduced from p ₁ , unlike the conventional technique shown in FIG. Does not decrease. For example, assuming that 95% of the gas adsorption amount A ₁ is maintained, in the gas storage device of the present invention equipped with the compound showing the pressure-adsorption amount curve shown in FIG. 1, the gas pressure is changed from P ₁ to P ₃ . It is possible to greatly reduce. On the other hand, in the conventional gas storage device provided with the adsorbent, the gas pressure can be slightly decreased from P ₁ to P ₅ as shown in FIG. Thus, in the gas storage device of the present invention, it is possible to reduce the gas pressure during transportation and storage.

In order to lower the gas pressure during gas storage, it is effective to lower the gas adsorption temperature from T ₁ to T ₂ . As a result, the gas pressure for obtaining the gas adsorption amount A ₁ can be reduced from P ₁ to P ₂ . Low temperature T
_{Even if} a large amount of gas is held in ₂ and then the temperature is raised to a higher temperature T ₁ , it is possible to hold the gas in the storage tank without releasing gas molecules. In this case, the entire storage tank may be cooled to cool the adsorbed gas.
This effect is advantageous when storing a gas having a low melting point. For example, when storing LNG or the like having a melting point of −162 ° C. or lower, it is effective to cool the storage tank to reduce the adsorption pressure.

As an effect resulting from the fact that the gas pressure during transportation and storage can be reduced, improvement of the degree of freedom in shape can be mentioned first. In the conventional storage tank, the gas adsorption amount cannot be maintained high without maintaining the pressure during storage. However, in the storage tank of the present invention, a sufficient gas adsorption amount can be maintained even if the pressure is reduced. For this reason,
The pressure resistance of the container can be reduced, and the shape of the gas storage device can be freely designed to some extent. This effect is great in a gas storage device for an automobile, for example. In a conventional gas storage device, the shape of the gas storage device is determined independently of the shape of the vehicle. This inevitably causes a considerable amount of dead space. In addition, a special device is required to maintain the high pressure. In this respect, since the gas storage device of the present invention has less restrictions on pressure resistance as described above, the shape can be freely designed to some extent. Specifically, it becomes possible to adjust the shape of the gas storage device so as to fit the shape of the wheels, seats, etc. of the vehicle. As a result, various advantages such as reduction in size of the vehicle, securing of luggage space, and improvement of fuel efficiency due to weight reduction of the vehicle can be obtained.

The hysteresis loop of adsorption and desorption isotherms is
Sufficient amount of gas adsorbed even if the pressure is reduced during sending and storage
In order to maintain the
It is preferable that the pressure axis moves substantially horizontally within a certain range.
Good That is, the holding pressure of the storage tank (in FIG.
P₃It can be said that the lower the pressure, the more preferable. Specifically
Is the pressure p at gas adsorption₀Adsorption amount in₀When
Adsorption amount is 0.95A ₀Pressure is 0.7p₀Below
Preferably, 0.6P₀Is less than
Preferably 0.5P₀Even more preferred to be
Correctly, 0.3P₀The following is particularly preferable. Na
In the above rules, "pressure during adsorption" means gas storage
The pressure actually used when using the device. Sucking
Wearing pressure P₀Is not particularly limited, but
The higher the pressure, the better in terms of equipment cost and safety.
Yes.

The hysteresis compound contained in the gas storage device of the present invention is not particularly limited as long as it has such characteristics. Two or more compounds may be used in combination. When selecting the compound to be actually used, it may be selected according to the gas to be stored and the pressure required for adsorption. Although not particularly limited, a metal complex can be given as a preferable example in consideration of absorbing a sufficient amount of gas. Examples of metal ions contained in the metal complex include copper, cobalt, nickel and zinc. The gas storage device may house more than one complex.

The ligand contained in the metal complex is not particularly limited, and examples thereof include pyrazine and 4,4'-.
Bipyridine, trans-1,2-bis (4-pyridyl)
Ethylene, 1,4-dicyanobenzene, 4,4-dicyanobiphenyl, 1,2-dicyanoethylene, 1,4-bis (4-pyridyl) benzene or the like can be used.

By storing the above-mentioned hysteresis compound in a container such as a tank, a gas storage device can be obtained. The configuration and material of the container such as the tank can be selected from those known in the art and are not particularly limited. For example, it is possible to use a metal container or the like that can control the flow of gas through the valve control. For example, it is possible to use a thin metal container in which a carbon fiber reinforced plastic material having excellent strength per unit density is wound around the outer surface. If the container is provided with a regulating valve for controlling the internal pressure of the gas storage device, the regulating valve can be utilized when releasing gas from the gas storage device.

Specific examples of the hysteresis compound include
[Cu (bpy) (BF_Four)₂(H₂O) ₂・ (Bpy)]_n
(In the formula, bpy represents 4,4'-bipyridine.
Same. ) And a metal complex represented by other
As a specific example, [Cu (bpy) (BF_Four)₂(H₂O)
_Four・ (Bpy)]_nAnd so on.

Even if the same component is used, 20
It is also possible to change the structure of the nanomolecular valve by hydrogen bonding and change the shape of the hysteresis loop by preheating to 0 to 600 ° C.

The gas stored in the gas storage device of the present invention is not particularly limited, but examples thereof include hydrocarbon gas, oxygen, nitrogen, carbon dioxide, carbon monoxide, argon and hydrogen. Examples of the hydrocarbon gas include methane, ethane, propane, isopropane, methylpropane, propene, butane, isobutane, butene and the like. L
It may be a mixture of a plurality of hydrocarbon gases such as NG. In order to reduce the pressure during storage by storing the gas at a low temperature, a gas having a low melting point such as LNG is preferable.

Next, a method of manufacturing the gas storage device of the present invention will be described.

First, a hysteresis compound contained in the gas storage device of the present invention is prepared. Although the method for preparing a compound varies depending on the compound and cannot be uniquely determined, here, [Cu (bpy) (BF ₄ ) ₂
A case of synthesizing (H ₂ O) ₂ · (bpy)] _n will be described as an example.

First, 4,4'-bipyridine
While refluxing the aniline solution (hereinafter abbreviated as bpy),
An aqueous solution containing copper (II) tetrafluoroborate hydrate is added. The precipitate formed is filtered off, vapors of diethyl ether are diffused into the mother liquor with a stream of nitrogen and the mother liquor is stored at room temperature for several days. Then, a precipitate is obtained by filtration,
Dry under vacuum for several hours. By such an operation, the target product can be obtained. However, it is needless to say that the method is not limited to the above method, and the synthesis may be performed using various methods.

The obtained hysteresis compound is housed in a pressure resistant container which constitutes a gas storage device. As a method for accommodating the hysteresis compound, a known method such as filling in a pressure resistant container can be used and is not particularly limited. The storage amount of the hysteresis compound may be determined according to the adsorption capacity required for the gas storage device. The shape and material of the pressure resistant container are not particularly limited. The gas storage device of the present invention does not need to be provided with a special pressure resistant structure since it may be at a lower pressure in order to secure the same storage amount as compared with the conventional type. In this respect, it can be said that there is a cost advantage.

If the hysteresis compound is in the form of powder, there is a risk that it will not be able to be filled successfully if it is to be stored in a container constituting the gas storage device. This problem may become more noticeable when a tank having a high degree of freedom in shape is used. In this case, the powder may be stored in the form of a tablet, or a tablet-shaped product in which a porous material such as activated carbon or zeolite is filled with the powder may be stored. If a porous material is used, it may also have the advantages of improved breathability and accelerated gas storage. In addition, when a tablet-shaped product is used as described above, it is easy to handle and very convenient when replacing aged compounds.

In order to adsorb and desorb the gas in the gas storage device according to the present invention, it is effective to control the temperature and / or the pressure. In order to adsorb the gas, the desired gas is injected into the gas storage device in consideration of the adsorption / desorption isotherm peculiar to the contained compound. The gas injection can be performed using a known technique such as a compressor. At this time, temperature control may be performed together with pressure control. In order to take out the gas from the gas storage device, the internal pressure of the gas storage device is reduced by using a pressure control means such as a regulating valve provided in the gas storage device. It is necessary to control the temperature of the compound acting as the adsorbent so as to prevent physical destruction of the gas storage device due to heating or cooling and the chemical reaction of the compound acting as the adsorbent. The temperature range to be changed is not particularly limited as long as these phenomena do not occur.

The above-described gas storage device has various applications such as, but not limited to, a commercial gas tank, a consumer gas tank, and a vehicle fuel tank. Among them, the fuel tank is preferably mounted on the vehicle. Since the gas storage device of the present invention has excellent shape flexibility, the tank shape can be simplified and reduced in weight by manufacturing the tank shape so as to match the shape of the vehicle.

Further, in the past, in order to store the fuel in the gas storage device, high pressure equipment was required. However, the gas storage device of the present invention can store gas at a relatively low pressure, and in some cases, it is possible to store gas using a commercial gas facility. These advantages do not require the construction of new infrastructure,
It is considered to make a great contribution to the generalization of natural gas vehicles and the like.

[0037]

EXAMPLES <Synthesis Example 1: [Cu (bpy) ( BF 4) 2 (H 2 O) 2 (bpy)] n
Synthesis of 0.08M 4,4'-bipyridine in acetonitrile solution (50 ml) under reflux, 0.4
M copper (II) tetrafluoroborate hydrate aqueous solution (5
0 ml) was added. This gave a solution containing a slightly grayish precipitate. This precipitate was shown to have no pore structure due to N ₂ adsorption at 77K. After filtering this aqueous solution, a vapor of diethyl ether was diffused into the mother liquor using a nitrogen stream until the volume was 150 ml. Subsequently, this mother liquor was stored at room temperature for several days to obtain a precipitate. This is filtered and dried under reduced pressure of 10 ⁻³ Pa or less for 4 hours to obtain the target product [Cu (bpy) (BF ₄ ) ₂ (H ₂ O) ₂ (bpy)] _n.
Got

<Example 1> [Cu obtained in Synthesis Example 1]
(Bpy) (BF ₄ ) ₂ (H ₂ O) ₂ (bpy)] _n is a rectangular parallelepiped pressure tank (1 m × 1.4 m × 10 cm × 2).
Base; 0.28 m ³ ; SUS304 wall thickness 2 mm). The gas storage tank 1 was installed in the natural gas vehicle shown in FIG.

A city gas pipeline was introduced into the first-stage compressor 3, the pressure was increased to 5 MPa, and the city gas was stored in the pressure tank 1 through the buffer tank 2. 180 with a tank volume of 0.28 m ³ with a filling time of 5 minutes
50 m ³ of city gas, which is double, was adsorbed. Subsequently, the compressor 3 was stopped and the pressure was reduced to 2 MPa. Since a hysteresis compound is used as an adsorbent, even if the pressure is reduced to 2 MPa, the tank will have 45 m ³
The city gas was still occluded.

Comparative Example 1 Carbon fiber / epoxy resin composite high-pressure tank (diameter 0.6 m × length 1 mm;
The gas storage tank 6 was 0.28 m ³ ) and was installed in a natural gas vehicle as shown in FIG.

As in Example 1, the city gas pipeline was tried to be stored, but in order to store a sufficient amount of city gas, 160 atm (= 162MP) was stored.
Since the pressure of a) is required, the compressor 4 has 4
Needed a large compressor to compress in stages. Also,
The buffer tank 5 required a high-pressure iron cylinder. Furthermore, as compared with the case of FIG. 3, the gas storage tank 6
Since it is a high pressure, it occupies most of the trunk room, and it was necessary for all equipment such as valves and piping to be of high pressure specifications.

[0042]

As described above, since the gas storage device according to the present invention contains the hysteresis compound as an adsorbent, it is possible to store a large amount of gas without requiring high pressure equipment. Further, since a large amount of gas can be stored at a relatively low pressure, it is excellent in safety and freedom of shape. In the gas storage device having such characteristics, the tank shape can be manufactured so as to match the shape of the vehicle, so that the vehicle body can be simplified and reduced in weight. Therefore, by storing hydrogen gas, natural gas, or the like and using it as a fuel source, it is possible to promote the improvement of fuel efficiency and miniaturization of fuel cell vehicles and natural gas vehicles, and to promote the generalization of these vehicles. it can.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a relationship between a gas adsorption amount of a hysteresis compound stored in a gas storage device of the present invention and a gas pressure.

FIG. 2 is a schematic diagram showing the relationship between the gas adsorption amount of a compound housed in a conventional gas storage device and the gas pressure.

FIG. 3 is a schematic diagram showing an automobile equipped with the gas storage device of the present invention and a gas supply system.

FIG. 4 is a schematic view showing an automobile equipped with a conventional gas storage device and a gas supply system.

[Explanation of symbols]

Gas storage tank as 1 gas storage device 2 buffer tank 3 compressors (1 stage) 4 compressors (4 stages) 5 buffer tank (equipped with high-pressure cylinder) 6 Gas storage tank as gas storage device

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsumi Kaneko             6-25-1 Aobadai, Ichihara City, Chiba Prefecture F-term (reference) 3E072 EA01                 4H048 AA01 AB83 VA56 VB10

Claims (7)

[Claims] 1. A gas storage device in which a compound whose adsorption / desorption isotherm for a stored gas exhibits a hysteresis loop is housed inside a pressure vessel. 2. The stored gas is a hydrocarbon gas,
The gas storage device according to claim 1, wherein the gas storage device is one or more gases selected from the group consisting of oxygen, nitrogen, carbon dioxide, carbon monoxide, argon and hydrogen. 3. The gas storage device according to claim 1, wherein the compound is a metal complex. 4. The gas storage device according to claim 3, wherein the metal complex contains copper, cobalt, nickel, or zinc as metal ions. 5. The metal complex is pyrazine, 4,4′-
Bipyridine, trans-1,2-bis (4-pyridyl)
It is characterized by containing at least one kind of ethylene, 1,4-dicyanobenzene, 4,4-dicyanobiphenyl, 1,2-dicyanoethylene, 1,4-bis (4-pyridyl) benzene as a ligand. Item 5. The gas storage device according to item 3 or 4. 6. The metal complex is [Cu (bpy) (B
F ₄ ) ₂ (H ₂ O) ₂ · (bpy)] _n (where bpy is 4,
The gas storage device according to claim 3, wherein the gas storage device is represented by 4′-bipyridine). 7. A vehicle equipped with the gas storage device according to any one of claims 1 to 6.