JP2000342961A - Methane adsorbent - Google Patents

Abstract

(57) [Summary] [Problem] To provide a methane adsorbent capable of increasing the pore volume ratio and greatly improving the amount of adsorbed and stored methane. SOLUTION: As a methane adsorbent, a graphite or silica-based intercalation compound is used, a predetermined guest material is intercalated between each layer, and only one skeletal molecular layer exists between each pore. State. As a result, the pore volume ratio is increased, and the amount of stored methane can be significantly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in a methane adsorbent for storing methane or natural gas containing methane as a main component.

[0002]

2. Description of the Related Art Conventionally, in order to store a large amount of natural gas or methane at a relatively low pressure, a method has been proposed in which a container is filled with an adsorbent such as activated carbon and methane is adsorbed and stored. ing.

[0003] For example, Japanese Patent Application Laid-Open No. 6-55067 also discloses a method for adsorbing and storing methane using activated carbon.
A technique for increasing the adsorption capacity of activated carbon has been disclosed.

[0004]

However, in the above-mentioned conventional methane adsorbent, there is a certain limit in reducing the thickness of the partition wall between the pores for adsorbing methane. The pore volume ratio in the adsorbent could not be increased. For this reason, when the above-mentioned conventional adsorbent is used, there is a problem that it is difficult to dramatically improve the amount of adsorbed and stored methane.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a methane adsorbent capable of increasing the pore volume ratio and greatly improving the amount of adsorbed and stored methane. .

[0006]

According to the present invention, there is provided a methane adsorbent comprising a graphite or silica-based intercalation compound.

[0007]

Embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

The present inventors have studied a methane adsorbent capable of greatly improving the amount of methane adsorbed and stored.
It has been found that when an intercalation compound is used as the adsorbent, the amount of adsorption can be greatly improved.

FIG. 1 shows a schematic diagram of the structure of the above-mentioned intercalation compound. Examples of the interlayer compound include a layer compound such as a clay compound, graphite, and silica. These interlayer compounds have a structure in which skeleton planes formed by skeleton molecules are laminated in layers. If such a layered compound is used as a host material and a substance serving as a pillar between the layers is intercalated as a guest material, a predetermined interval can be provided between the skeleton planes. The space between the skeleton planes is hereinafter referred to as the pore diameter.

The most significant feature of the intercalation compound is that the condition of intercalation of the guest material into the host material can be adjusted to control the number of layers in the skeleton plane where intercalation occurs. For example, it is possible to control the first stage where intercalation occurs for each layer and the second stage where intercalation occurs for every two layers. Therefore, each layer constituting the pores can be composed of one skeleton plane, and the volume ratio of the pores can be increased. As a method of controlling such intercalation, for example, a heat treatment method (Two-bulb method) or a method of immersing a host material in a solution of a guest material to perform intercalation can be considered.

As the above-mentioned host material, carbonaceous materials such as graphite, carbon nanofiber, and carbon nanotube can be considered. In addition, for silica-based materials, aialite, magadiite, Kenyaite,
Layered polyacid salts such as macatite are conceivable.

The following can be considered as a guest material to be intercalated into the host material. First, for the above carbon-based host material, FeCL ₃ , WCl ₆
Metal halides such as AlBr ₃ , GaBr ₃ , TiBr
₃ , metal halides such as CdBr ₂ and FeBr ₃ , Al
_{NO 3, GaNO 3, FeNO 3} , Ti (NO 3) 4, Ge
(NO ₃ ) ₄ , VO (NO ₃ ) ₃ , MoO ₂ (NO ₃ ) ₂ , W
Oxides such as O (NO ₃ ) ₂ can be considered. When these guest materials are intercalated into the carbon-based host material, the interlayer distance is 7 to 20 ° when the first stage state is reached in which the guest material is intercalated for each layer.

For a carbon-based host material, 3
A metal (NH ₃ ) ₂ system can also be considered as the original guest material.
As the metal in this case, for example, Li, Na, K, R
b, Cs, Ca, Sr, Ba and the like. Furthermore, YCl
_3- FeCl ₃ , CoCl ₂ —FeCl _{3 and the} like are also conceivable.
In these cases, when the first stage state is reached as described above, the interlayer distance is about 20 to 50 °.

Further, with respect to the above-mentioned silica host material, an alkylammonium ion such as I-octylamine and I-dodecylamine is considered as a guest material. In these cases, when the first stage is reached,
The interlayer distance is about 7 to 30 °.

In contrast to the above-mentioned intercalation compound, in the case of activated carbon conventionally used as a methane adsorbent, as shown in FIG.
It is in a state of three layers or three layers. Therefore, unlike the above-mentioned intercalation compounds, adsorption of methane does not occur for each layer of the skeletal plane, so that the pore volume ratio cannot be improved.

Further, in the case of this activated carbon, the laminated structure of the skeleton plane exists randomly. Therefore, the activated carbon is in a state in which slit-shaped pores are randomly present on the surface and inside.

FIG. 3 shows that the intercalation compound and the activated carbon are
The critical pore volume ratio for each pore diameter, that is, the pore volume ratio when the voids between the particles are excluded is shown. In FIG. 3, one layer of the skeletal molecule corresponds to the intercalation compound, and two layers and three layers correspond to the activated carbon. As can be seen from FIG. 3, in activated carbon, the skeleton plane has two skeleton molecules or three skeleton molecules.
In contrast to the layer structure, the interlayer compound can be formed as a single layer, so that the pore volume ratio of the interlayer compound is greatly improved as compared with activated carbon.

FIG. 4 shows the state of the pores of the zeolite. As shown in FIG. 4, the zeolite has cylindrical pores. It is estimated that three skeletal molecular layers exist around these pores. FIG. 5 shows the critical pore volume ratio with respect to the pore diameter of this zeolite. It can be seen from the values shown in FIG. 5 that the pore volume ratio is significantly lower than the case of the intercalation compound shown in FIG.
This is presumably because the pores are surrounded by three skeletal molecular layers.

As an example of the methane adsorbent using the above-mentioned intercalation compound, graphite is used as a host material,
Aluminum bromide (AlBr ₃ ) as a guest material
Was intercalated by a heat treatment method.
In addition, a material in which polysilicate (macatite) was used as a silica-based host material and octylamine was intercalated as a guest material was also manufactured. As a result of performing a characterization evaluation for adsorbing N ₂ at a low temperature, it was found that the pore diameter was 7.6 ° when graphite was used as the host material, and that the state was the first stage. This diameter was equivalent to two methane molecules, and it was found that the methane storage capacity was good at low pressure. It was also found that even when polysilicate was used, it was still in the first stage and the pore size was 8 mm.

In addition to these intercalation compounds, Table 1 shows a comparison between the case of using a multicomponent clay mineral-based material such as kaolinite, muscovite, TiS ₂ and WS ₂ and the case of using activated carbon and zeolite. Is shown.

[0021]

[Table 1] As can be seen from Table 1, when the graphite-based or silica-based intercalation compound was used, both the pore volume ratio and the methane storage amount were significantly improved for all the comparative examples. The methane storage amount is 3.5MP.
This is a value when methane is adsorbed at room temperature under the pressure of a, and the amount of methane existing in the void portion is removed. As shown in Table 1, the values of activated carbon and zeolite are low because, as described above, the skeletal molecular layer surrounding the pores cannot be made one layer, so that the pore volume ratio cannot be increased. Also, when a multi-component clay mineral is used as the intercalation compound, since the thickness of these molecular layers themselves is large,
Again, the pore volume ratio could not be sufficiently increased, and as a result, the methane storage amount could not be increased.

[0022]

As described above, according to the present invention,
Since the skeletal molecular layer between the pores can be made into one layer, the pore volume ratio can be greatly improved, and the methane storage amount can be increased.

[Brief description of the drawings]

FIG. 1 is a schematic view of an intercalation compound used for a methane adsorbent according to the present invention.

FIG. 2 is a schematic view showing the structure of a conventional activated carbon.

FIG. 3 is a diagram showing a critical pore volume ratio between an intercalation compound and activated carbon.

FIG. 4 is a schematic view of the structure of a conventional zeolite.

FIG. 5 is a view showing a limit pore volume ratio of zeolite.

Claims (1)

[Claims] 1. A methane adsorbent comprising a graphite or silica-based intercalation compound.