JP2015167941A - Gas adsorbent and method for producing the same - Google Patents

Abstract

Disclosed is a gas adsorbent comprising a carbon fiber aggregate having a high density and a high gas adsorbing ability. The gas adsorbent of the present invention includes a spherical carbon fiber aggregate formed by agglomerating carbon fibers, the average density of the carbon fiber aggregate is 0.2 g / cm3 to 1 g / cm3, and The gas adsorption amount per unit volume at a gas pressure of 1 MPa is at least 50 mL / cm 3. [Selection] Figure 1

Description

  The present invention relates to a gas adsorbent and a method for producing the same.

  Methane, ethane and other hydrocarbon gases are expected to be widely used as energy sources for power generation and fuel for automobiles. As a method for storing hydrocarbon gas, a method for compressing and storing hydrocarbon gas is generally known. However, since it is necessary to set the hydrocarbon gas to a high pressure of 20 MPa or more, it is difficult to handle and the cost is low. There is a problem that becomes expensive. Thus, it has been studied to adsorb hydrocarbon gas on an adsorbent and store the hydrocarbon gas at a relatively low pressure (for example, 1 MPa or less). For example, Patent Document 1 describes the use of carbon fiber as an adsorbent for storing fuel methane such as methane-fueled automobiles.

JP 2003-144917 A

  However, carbon fiber has a larger specific surface area than activated carbon and is excellent in gas adsorption capacity, but is bulky. Therefore, the carbon fiber has a gas adsorption capacity per unit mass that is superior to activated carbon, but has a problem that the gas adsorption capacity per unit volume is inferior to activated carbon. In order to deal with such a problem, for example, it is conceivable to compress the carbon fiber to increase the density, but according to the study by the present inventors, when the carbon fiber is pressurized and densified, the hydrocarbon gas is adsorbed. It has been found that the pores serving as the adsorption sites are broken and the original gas adsorption ability is not exhibited.

  This invention is made | formed in view of this point, The main objective is to provide the method of manufacturing the gas adsorbent containing the carbon fiber aggregate of a high density and high gas adsorption ability. Another object is to provide a gas adsorbent containing a carbon fiber aggregate having a high density and a high gas adsorbability obtained by such a production method.

  As a result of intensive studies to solve the above problems, the present inventor has found that a carbon fiber aggregate can be densified without applying excessive pressure by adding a polar solvent to the carbon fiber aggregate and shaking. The headline and the present invention were completed.

  That is, the production method provided by the present invention is a method for producing a gas adsorbent containing a spherical carbon fiber aggregate formed by agglomerating carbon fibers. This manufacturing method includes preparing carbon fibers (carbon fiber preparation step). Further, the method includes aggregating the carbon fibers prepared in the carbon fiber preparation step to obtain a carbon fiber aggregate (typically spherical) (carbon fiber aggregation step). Furthermore, it includes densifying the carbon fiber aggregate by adding a polar solvent to the carbon fiber aggregate obtained in the carbon fiber aggregating step and shaking it (density increasing step).

  In the production method of the present invention, rather than compressing the carbon fibers, the carbon fiber aggregates are densified by adding a polar solvent to the carbon fiber aggregates and shaking. According to such a configuration, since the carbon fiber aggregate can be densified in a state close to no pressure, the collapse of the adsorption sites (pores) when compressed by applying excessive pressure to the carbon fiber is prevented, A high density and high gas adsorption capacity carbon fiber aggregate is obtained. Such a high density and high gas adsorption capacity carbon fiber aggregate can be suitably used as a gas adsorbent in a gas storage tank of hydrocarbon gas (for example, methane).

  In a preferred embodiment of the production method disclosed herein, carbon fibers having an average length of 1 cm to 5 cm are prepared in the carbon fiber preparation step. By using carbon fibers having such an average length, the subsequent carbon fiber agglomeration treatment can be suitably performed, and the productivity of the gas adsorbent can be increased.

  In a preferable aspect of the production method disclosed herein, the carbon fiber aggregation step includes a process of stirring the carbon fiber. Thereby, a carbon fiber aggregate in which a large number of carbon fibers are aggregated (typically in a spherical shape) can be suitably obtained.

  In a preferred embodiment of the production method disclosed herein, a diameter R1 of the carbon fiber aggregate after the carbon fiber aggregation step and before the densification step, and a diameter R2 of the carbon fiber aggregate after the densification step. (R2 / R1) is 0.4 ≦ (R2 / R1) ≦ 0.7. Within the range of such a diameter reduction ratio (R2 / R1), the density of the carbon fiber aggregates can be effectively increased, which can effectively contribute to the improvement of the gas adsorption capacity. In the present specification, the diameter of the carbon fiber aggregate refers to the longest diameter, that is, the maximum diameter of the carbon fiber aggregate.

Moreover, this invention provides the gas adsorbent which adsorb | sucks gas as another side surface. The gas adsorbent disclosed here includes a carbon fiber aggregate formed by agglomerating carbon fibers. The average density of the carbon fiber aggregate is ^{0.2g / cm 3 ~0.5g / cm 3} , and a gas adsorption amount per unit volume in the gas pressure 1MPa is at least 50 mL / cm ^3.

In the present specification, the density of the carbon fiber aggregate refers to a density when the volume of the outer periphery of the carbon fiber aggregate (typically spherical) is used, for example, the volume of the carbon fiber aggregate itself, It may include the volume of voids within the carbon fiber aggregate and the volume of irregularities on the surface of the carbon fiber aggregate. The density of the carbon fiber aggregate may be obtained, for example, by dividing the mass of the carbon fiber aggregate by the volume. Here, the volume of the carbon fiber aggregate is an equation for measuring the maximum diameter of the carbon fiber aggregate, setting 1/2 of the maximum diameter as the radius r of the carbon fiber aggregate, and determining the volume of the sphere using the radius r. It shall be calculated from (4πr ^3/3). The average density may be evaluated in, for example, at least 10 (preferably 10 to 20, more preferably 10 to 50) carbon fiber aggregates extracted at random, and an approximate average value (arithmetic average value) thereof. ) To evaluate. Further, the gas adsorption amount per unit volume at a gas pressure of 1 MPa referred to in this specification indicates the value of the gas adsorption amount measured at room temperature. Here, “normal temperature” refers to a temperature range of 15 to 40 ° C., and typically refers to a temperature range of 20 to 35 ° C. (for example, 25 ° C.).

In one preferred embodiment of the gas adsorbing material described herein, for example, the average density of the carbon fiber aggregate was high at ^{0.2g / cm 3 ~1g / cm 3} , per unit volume in the gas pressure 1MPa gas The amount of adsorption is at least 50 mL / cm ³ , which is larger than in the past. Such a carbon fiber aggregate having a high density and a high gas storage capacity can adsorb a large amount of a gas such as a hydrocarbon gas, and therefore can be preferably used as a gas adsorbent for a gas storage tank or the like.

  In a preferred embodiment of the gas adsorbent disclosed herein, an average length of carbon fibers constituting the carbon fiber aggregate is 0.1 mm to 0.5 mm. When the carbon fiber is within such an average length, the shape of the carbon fiber aggregate can be appropriately maintained. Therefore, a gas adsorbent with higher performance (for example, better durability) can be realized.

In one preferred embodiment of the gas adsorbing material described herein, the specific surface area of the carbon fibers constituting the carbon fiber aggregate is 1500m ² / g~2200m ² / g. When the carbon fiber is within the range of the specific surface area, the gas adsorption capacity can be further increased. In a preferred embodiment, the carbon fiber constituting the carbon fiber aggregate has a pore diameter of 1.8 nm to 2.5 nm. If it does in this way, gas adsorption capacity can be raised further.

Moreover, this invention provides the gas storage tank for storing gas as another side surface. The gas storage tank disclosed here includes a gas adsorbent and a container filled with the gas adsorbent. The gas adsorbent comprises a carbon fiber aggregate carbon fibers are aggregated, the mean density of the carbon fiber aggregate is ^{0.2g / cm 3 ~1g / cm 3} , and the unit in the gas pressure 1MPa The amount of gas adsorption per volume is at least 50 mL / cm ³ . According to such a gas storage tank, a large amount of gas can be stored as compared with the conventional case.

  In a preferred aspect of the gas storage tank disclosed herein, a partition plate that divides the inside of the container into a plurality of (for example, 2 to 6, typically 3 or 4) filling chambers is provided. The gas adsorbent is arranged in the plurality of filling chambers. According to such a configuration, heat of adsorption generated by gas adsorption of the gas adsorbent is efficiently discharged outside the tank through the partition plate. Therefore, it is possible to suppress a decrease in adsorption efficiency (and consequently a decrease in gas storage amount and storage speed) accompanying a temperature increase of the gas adsorbent.

  In a preferred aspect of the gas storage tank disclosed herein, the partition plate is formed with a hole communicating between the plurality of filling chambers. In this way, gas flows between the plurality of filling chambers through the holes in the partition plate, so that the opportunity for contact between the gas adsorbent and the gas increases, and the adsorption efficiency of the gas adsorbent can be increased.

  In a preferred aspect of the gas storage tank disclosed herein, the container is a cylindrical container. And the said partition plate is provided so that the space in alignment with the circumferential direction of the said container may be divided into several fan-shaped filling chambers while extending in the cylinder axial direction of the said container. In this way, the gas introduced into the container diffuses not only in the cylinder axis direction of the container but also in the circumferential direction of the container, so that the gas can be efficiently stored in the tank. Moreover, according to the said structure, a carbon fiber aggregate can be filled into a filling chamber, without applying excessive pressure other than dead weight. Therefore, the original gas adsorption ability of the carbon fiber aggregate that is weak against compression can be sufficiently exhibited.

FIG. 1 is a diagram showing a manufacturing flow of a gas adsorbent according to an embodiment. FIG. 2 is a perspective view schematically showing a gas storage tank according to an embodiment. FIG. 3 is a map of the carbon fiber after cutting. FIG. 4 is a mapping of the carbon fiber aggregate after the carbon fiber aggregation step. FIG. 5 is a mapping of the carbon fiber aggregate before and after the densification step. FIG. 6 is a map of the untreated carbon fiber. FIG. 7 is a map of pelletized carbon fiber. FIG. 8 is a map of untreated activated carbon. FIG. 9 is a map of the activated carbon after pulverization. FIG. 10 is a mapping of untreated carbon nanotubes. FIG. 11 is a map of pelletized carbon nanotubes. FIG. 12 is a map showing a cross-shaped partition plate. FIG. 13 is a map showing a disk-shaped partition plate. FIG. 14 is a graph showing the relationship between time and temperature.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention (for example, a method for producing a carbon fiber as a raw material) are those skilled in the art based on conventional techniques in the field. It can be grasped as a design item. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  A method for producing the gas adsorbent disclosed herein (hereinafter, referred to as “manufacturing method” as appropriate) will be described. The gas adsorbent produced by the production method disclosed herein includes a carbon fiber aggregate (typically spherical) formed by agglomerating carbon fibers. In the present specification, “carbon fiber” refers to fibrous activated carbon, which is typically a fiber obtained by carbonizing and activating various fibers as raw materials at a high temperature (for example, activation treatment in a steam atmosphere). Say. For example, carbon fibers are pitch (by-products such as petroleum, coal, coal tar) carbon fiber, polyacrylonitrile carbon fiber (PAN carbon fiber), cellulosic carbon fiber, phenol resin carbon fiber, rayon carbon. It can be a fiber or the like. Of these, pitch-based carbon fibers are preferred.

  Hereinafter, the procedure for producing a gas adsorbent using carbon fiber as a raw material will be described with reference to FIG. FIG. 1 is a flowchart showing the manufacturing process. The manufacturing method of this embodiment has a carbon fiber preparation process (step S10), a carbon fiber aggregation process (step S20), and a densification process (step S30). The outline of these steps is as follows.

<Carbon fiber preparation process>
In the carbon fiber preparation step of Step S10, carbon fibers used as a raw material for the gas adsorbent are prepared. The size of the carbon fiber used as the raw material is not particularly limited. However, if the carbon fiber is too long, the processing time may become longer or the carbon fiber may not easily aggregate in the carbon fiber preparation step described later. Therefore, it is preferable to cut the carbon fiber to a certain length in advance. For example, the average length (average fiber length) of the carbon fibers used as the raw material is approximately 1 cm to 5 cm, preferably 2 cm to 5 cm, more preferably 2 cm to 3 cm. Moreover, the average value (typically measured value based on observation with an electron microscope) of the carbon fiber is approximately 0.5 μm to 30 μm, preferably 5 μm to 25 μm, more preferably 10 μm to 15 μm. . In addition, the said carbon fiber may contain the impurity originating in a raw material, a manufacturing method, etc. Moreover, you may use what performed the arbitrary process for removing the said impurity as said carbon fiber.

<Carbon fiber aggregation process>
In the carbon fiber aggregation step of step S20, the carbon fibers prepared in the carbon fiber preparation step are aggregated to obtain a spherical carbon fiber aggregate. Such a carbon fiber aggregating step may include, for example, a process of stirring the carbon fiber. As a stirrer for stirring, a mechanical stirrer such as a food processor, a homomixer, a Henschel mixer, a super mixer, a propeller stirrer, or a high-speed mixer can be preferably used. Here, the carbon fiber has a fibrous shape unlike the granular activated carbon. Therefore, when it is cut into a certain range of fiber length by the shearing force of the stirrer and stirred, it is entangled and spheroidized during rotation. Thereby, a spherical carbon fiber aggregate is obtained.

  In the carbon fiber aggregating step, it is preferable that the carbon fiber is sufficiently stirred until the carbon fiber is spheroidized to a certain size. For example, it is preferable to set the stirring conditions so that the average diameter of the carbon fiber aggregate after the carbon fiber aggregation step is 1 mm to 20 mm (preferably 5 mm to 15 mm, more preferably 8 mm to 12 mm). If the carbon fiber aggregate having such an average diameter is used, the subsequent densification step can be suitably performed, and the productivity of the gas adsorbent can be increased. As a preferred example, carbon fibers having an average length of 1 cm to 5 cm are put into a food processor and stirred for 5 minutes to 15 minutes under conditions of a rotational speed of 3000 rpm to 15000 rpm (for example, 5000 rpm to 15000 rpm). Thus, carbon fiber aggregates having an average diameter of 1 mm to 20 mm in which the carbon fibers are cut into an average length of 0.1 mm to 0.5 mm and the carbon fibers are intertwined in a spherical shape can be obtained. Such stirring conditions can be appropriately changed according to the size and design of the carbon fiber used.

  In addition, the manufacturing method disclosed here can form a carbon fiber aggregate easily even if it does not use the binder for aggregation. However, from the viewpoint of stably forming the carbon fiber aggregate, an aggregating binder may be used. The aggregating binder can be used without particular limitation as long as it has a function of binding carbon fibers to each other, but the thermal decomposition temperature is 200 ° C. or lower (eg, 120 ° C. to 160 ° C., typical Is preferably 130 ° C. to 150 ° C.). As such a binder for aggregation, an aqueous dextrin solution (for example, an aqueous solution containing 1% by mass to 20% by mass (preferably 3% by mass to 10% by mass) of dextrin) is exemplified.

<Densification process>
In the densification step of step S30, the carbon fiber aggregate is densified by adding a polar solvent to the carbon fiber aggregate obtained in the carbon fiber aggregation step and shaking. That is, the density of the carbon fiber aggregate is increased by swinging the container containing the carbon fiber aggregate in the vertical direction, the horizontal direction, the diagonal direction, the random direction, and the like. As the shaking device used in the densification step, a conventionally known device used for this kind of shaking can be used without any particular limitation. For example, swirlers such as a swivel type, a reciprocating type, a vibration type, a figure-eight type, a seesaw type, and a vertical movement type can be appropriately employed.

  Examples of the polar solvent used in the densification step include water or a mixed solvent mainly composed of water. As a solvent component other than water constituting such a mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use an aqueous solvent in which 80% by mass or more (more preferably 90% by mass or more, more preferably 95% by mass or more) of the polar solvent is water. A particularly preferred example is a polar solvent consisting essentially of water. Alternatively, a polar solvent mainly composed of an organic solvent may be used. For example, alcohol, ketone, ester, pyridine, ether or the like may be used. As a preferred example, lower alcohols such as methanol, ethanol and propanol having a small number of carbon atoms (for example, having 4 or less carbon atoms) can be mentioned. Although it does not specifically limit as addition amount of a polar solvent, It is appropriate to set it as about 30 mass parts-200 mass parts with respect to 100 mass parts of carbon fibers, Preferably it is 50 mass parts-200 mass parts, More preferably Is 50 parts by mass to 100 parts by mass. The method for adding the polar solvent to the carbon fiber aggregate is not particularly limited, but from the viewpoint of uniform dispersibility, for example, supply means such as spraying can be suitably employed.

  In such a densification step, it is preferable to gently shake the carbon fiber aggregate until the carbon fiber aggregate is reduced to a desired size while maintaining a spherical shape. For example, the ratio (R2 / R1) between the average diameter R1 of the carbon fiber aggregate after the carbon fiber aggregation step and before the densification step and the average diameter R2 of the carbon fiber aggregate after the densification step is (R2 / R1) It is preferable to set the shaking conditions so as to satisfy 0.7. More preferably, (R2 / R1) ≦ 0.65, and further preferably (R2 / R1) ≦ 0.6. If the diameter ratio (R2 / R1) is too large, densification of the carbon fiber aggregates may be insufficient, and a desired gas adsorption capacity may not be obtained. On the other hand, if the diameter ratio (R2 / R1) is too small, the shape of the carbon fiber aggregate may tend to collapse. From the viewpoint of shape maintainability, 0.4 ≦ (R2 / R1) is appropriate, and preferably 0.5 ≦ (R2 / R1). As a preferred example, the carbon fiber aggregate obtained in the carbon fiber agglomeration step is put into a swirl type shaker and shaken at a frequency of 100 to 1000 rpm (for example, 5 to 10 minutes). ) Shake. As a result, a high-density carbon fiber aggregate in which the diameter ratio (R2 / R1) satisfies 0.4 ≦ (R2 / R1) ≦ 0.7 can be obtained. Such shaking conditions can be appropriately changed according to the size and design of the carbon fiber used.

  In this way, a gas adsorbent composed of a high-density carbon fiber aggregate formed by agglomerating carbon fibers can be produced. When the carbon fiber aggregate includes the aggregation binder, the aggregation binder in the carbon fiber aggregate may be burned out by performing an appropriate heat treatment as necessary. In this case, the heat treatment temperature may be set higher than the thermal decomposition temperature of the aggregating binder (for example, 200 ° C. or more) and lower than the thermal decomposition temperature of the carbon fiber.

<High-density carbon fiber aggregate>
The carbon fiber aggregate (gas adsorbent) disclosed herein is a carbon fiber aggregation step in which carbon fibers are aggregated to obtain spherical carbon fiber aggregates, and a polar solvent is added to the carbon fiber aggregates and shaken. The carbon fiber aggregate is manufactured through a densification step for densifying the carbon fiber aggregate. Therefore, the obtained carbon fiber aggregate can be one in which carbon fibers are aggregated at a high density without applying excessive pressure. Typically, the average density of the carbon fiber aggregate is 0.2 g / cm ³ or more (for example, 0.2 g / cm ^{3 to} 1 g / cm ³ ), preferably 0.22 g / cm ³ or more, and more Preferably it is 0.25 g / cm ³ or more, more preferably 0.27 g / cm ³ or more, and particularly preferably 0.29 g / cm ³ or more. Moreover, since the carbon fiber aggregate is densified in a state close to no pressure, the adsorption sites (pores) are prevented from collapsing when the carbon fiber is compressed by applying excessive pressure. , May exhibit high gas adsorption capacity. For example, the gas adsorption capacity is such that the gas adsorption amount per unit volume at a gas pressure of 1 MPa is 50 mL / cm ³ or more (for example, 50 mL / cm ^{3 to} 150 mL / cm ³ ), preferably 60 mL / cm ³ or more, more preferably 65 mL / cm ³ or more, still more preferably 70 mL / cm ³ or more, and particularly preferably 75 mL / cm ³ or more.

As a suitable example of the carbon fiber aggregate (gas adsorbent) disclosed here, the average density of the carbon fiber aggregate is 0.2 g / cm ³ or more, and the amount of gas adsorption per unit volume at a gas pressure of 1 MPa. what is the average density of the carbon fiber aggregate 0.23 g / cm ³ or more, and is gas adsorption amount per unit volume in the gas pressure 1MPa is 60 mL / cm ³ or more; but not more 50 mL / cm ³ or more The average density of the carbon fiber aggregates is 0.25 g / cm ³ or more and the gas adsorption amount per unit volume at a gas pressure of 1 MPa is 65 mL / cm ³ or more; the average density of the carbon fiber aggregates is and at 0.28 g / cm ³ or more, and those gas adsorption amount per unit volume in the gas pressure 1MPa is 75 mL / cm ³ or more; and the like. By having both the average density and the gas adsorption capacity of the carbon fiber aggregates within such a predetermined range, it is possible to construct a gas storage tank capable of mass storage that could not be obtained conventionally.

Further, the gas adsorption amount per unit mass at a gas pressure of 1 MPa of the carbon fiber aggregate is suitably about 220 mL / g or more (for example, 220 mL / g to 300 mL / g), preferably 250 mL / g or more. (For example, 250 mL / g to 300 mL / g), particularly preferably 260 mL / g or more (for example, 260 mL / g to 280 mL / g). As a preferred example of the carbon fiber aggregate disclosed herein, the gas adsorption amount per unit mass at a gas pressure of 1 MPa is approximately 220 mL / g or more, and the gas adsorption amount per unit volume is 50 mL / cm ³ or more. A gas adsorption amount per unit mass at a gas pressure of 1 MPa is approximately 250 mL / g or more, and a gas adsorption amount per unit volume is 55 mL / cm ³ or more.

  Further, the average length (average fiber length) of the carbon fibers constituting the carbon fiber aggregate is suitably within a range of about 0.1 mm to 1 mm, preferably 0.2 mm to 0.8 mm. More preferably, it is 0.2 mm-0.5 mm, Most preferably, it is 0.2 mm-0.3 mm. Since the carbon fibers constituting the carbon fiber aggregates are suitably intertwined within the range of the average length of such carbon fibers, the shape of the carbon fiber aggregates can be appropriately maintained, and higher performance ( For example, a carbon fiber aggregate excellent in durability) can be obtained.

As the specific surface area based on a gas adsorption method of carbon fibers constituting the carbon fiber aggregate, it is generally 1500 m ² / g or more (e.g., 1500m ² / g~2200m ² / g) and appropriate to, preferably 1650m and ² / g or more, more preferably 1800 m ² / g or more, particularly preferably 2000 m ² / g or more. Within the range of the specific surface area of such a carbon fiber, the gas adsorption ability of the carbon fiber aggregate can be further enhanced. In addition, the pore diameter based on the gas adsorption method of the carbon fibers constituting the carbon fiber aggregate is suitably in the range of approximately 1.8 nm to 2.5 nm, preferably 1.9 nm to 2.2 nm. is there. Within the range of the pore diameter of such carbon fibers, the gas adsorption ability of the carbon fiber aggregate can be further enhanced.

<Application>
The carbon fiber aggregate disclosed herein can be preferably used as a gas adsorbent for a gas storage tank for storing various gases. The type of gas that can be stored in the gas storage tank may be any gas species that can be adsorbed on the carbon fiber aggregate. For example, hydrocarbon gas such as methane, ethane, and propane, carbon dioxide, hydrogen, nitrogen, nitrogen oxidation A gas such as an object (NOx) is exemplified. Particularly preferred gas species include hydrocarbon gases having 4 or less carbon atoms such as methane, ethane, propane, and butane, and hydrocarbon gases having 3 or less carbon atoms are particularly preferable. The carbon fiber aggregate disclosed herein is a product that requires storage of a large amount of hydrocarbon gas at a relatively low pressure (eg, 5 MPa or less, preferably 3 MPa or less, more preferably 1 MPa or less), such as methane fermentation. It can be preferably used as a gas adsorbing material such as a low-pressure ANG methane storage tank in a system, a fuel tank of an ANG methane automobile using methane as a fuel, and a domestic cylinder for storing propane.

<Methane storage tank>
Hereinafter, a preferred embodiment in the case of constructing a methane storage tank using the carbon fiber aggregate disclosed herein will be described. FIG. 2 is an exploded perspective view showing an example of a methane storage tank constructed using the carbon fiber aggregate disclosed herein. Here, for convenience, the state in which the lid 16 is removed from the container main body 12 is illustrated.

  As shown in FIG. 2, the methane storage tank 100 includes a container 10 and a partition plate 20. The container 10 includes a substantially cylindrical container main body 12 having an open upper end, and a lid body 14 that closes the opening. An annular seal member (not shown) is disposed between the lid body 14 and the container body 12, thereby ensuring airtightness in the container 10. A gas supply / discharge port 18 for supplying or discharging methane to / from the container 10 is provided on the upper surface of the container 10 (that is, the lid body 14). In addition, a measurement unit 15 for measuring the temperature and pressure in the container 10 is provided on the upper surface (lid 14) of the container 10. Inside the container 10, a partition plate 20 is accommodated together with a carbon fiber aggregate (gas adsorbent) (not shown).

The partition plate 20 is a member that partitions the inside of the container 10 into a plurality of (for example, 2 to 6, typically 3 or 4) filling chambers 30. As a material constituting the partition plate 20, a material having high thermal conductivity is preferably used. For example, the material constituting the partition plate 20 has a thermal conductivity of 1 × 10 ⁻⁶ m ² / s or more (for example, 1 × 10 ⁻⁶ m ² / s to 200 × 10 ⁻⁶ m ² / s). Is preferred. Examples of such materials include metal materials such as aluminum (thermal conductivity 96.8 × 10 ⁻⁶ m ² / s), stainless steel (thermal conductivity 4.1 × 10 ⁻⁶ m ² / s), and copper. The

  The partition plate 20 extends in the cylinder axis direction of the container 10 and is provided so as to partition a space along the circumferential direction of the container 10 into a plurality of fan-shaped filling chambers 30. In this embodiment, the partition plate 20 is formed in a substantially cross shape when viewed from above, and divides a space along the circumferential direction of the container 10 into four fan-shaped filling chambers 30. The partition plate 20 is formed with a plurality of holes 22 communicating with the plurality of filling chambers 30. In this embodiment, the plurality of holes 22 are punching holes 22 formed at predetermined intervals on the entire surface of the partition plate 20. A carbon fiber aggregate (gas adsorbent) (not shown) is divided into a plurality of filling chambers 30 partitioned by the partition plate 20.

  When storing methane in the methane storage tank 100, methane is introduced into the container 10 through the gas supply / discharge port 18. The methane introduced into the container 10 is guided to the plurality of filling chambers 30 partitioned by the partition plate 20 and travels between the plurality of filling chambers 30 through the holes 22 of the partition plate 20. Thereby, the methane introduced into the container 10 diffuses not only in the cylinder axis direction of the container 10 but also in the circumferential direction of the container 10 and is adsorbed by the gas adsorbent. When the gas adsorbent adsorbs methane, heat of adsorption is generated. In this embodiment, the heat of adsorption diffuses in the radial direction of the container 10 via the partition plate 20 and can be quickly discharged to the outside of the tank.

  According to the gas storage tank 100 configured as described above, the partition plate 20 that divides the inside of the container 10 into a plurality of filling chambers 30 is provided, and the gas adsorbent is divided into the plurality of filling chambers 30. In this case, adsorption heat generated by gas adsorption of the gas adsorbent is efficiently discharged to the outside of the tank 100 through the partition plate 20. Therefore, it is possible to suppress a decrease in adsorption efficiency (and consequently a decrease in gas storage amount and storage speed) accompanying a temperature increase of the gas adsorbent.

  In the present embodiment, the partition plate 20 is formed with holes 22 that communicate between the plurality of filling chambers 30. In this way, since gas flows between the plurality of filling chambers 30 through the holes 22 of the partition plate 20, the opportunity for contact between the gas adsorbent and the gas increases, and the adsorption efficiency of the gas adsorbent can be increased.

  Furthermore, according to the gas storage tank 100, the container 10 is a cylindrical container 10, and the partition plate 20 extends in the cylinder axis direction of the container 10, and the circumferential space of the container 10 is divided into a plurality of fan-shaped filling chambers 30. It is provided to partition. In this way, the gas introduced into the container 10 diffuses not only in the cylinder axis direction of the container 10 but also in the circumferential direction of the container 10, so that the gas can be efficiently stored in the tank. Moreover, according to the said structure, a carbon fiber aggregate can be filled into a filling chamber, without applying excessive pressure other than dead weight. Therefore, the original gas adsorption ability of the carbon fiber aggregate that is weak against compression can be sufficiently exhibited. In this respect, the technical value is high.

  In the embodiment described above, the partition plate 20 is formed in a substantially cross shape when viewed from above. The shape of the partition plate 20 is not limited to this. For example, as shown in FIG. 13, the partition plate 20 may be a disc-shaped partition plate. For example, a plurality (for example, 2 to 6, typically 2 or 3) of disk-shaped partition plates are arranged in parallel in the cylinder axis direction of the container 10, and a space along the cylinder axis direction of the container is formed into a plurality of cylindrical shapes. You may partition into a filling chamber. In this case, a hole that communicates between the plurality of cylindrical filling chambers may be formed in the disc-shaped partition plate so that the gas diffuses between the plurality of cylindrical filling chambers. Even if it is such a structure, the heat dissipation improvement effect mentioned above can be acquired. However, as in the above-described embodiment, the cross-shaped partition plate 20 is preferable in that a higher heat dissipation improvement effect can be obtained.

  Next, some examples relating to the present invention will be described, but the present invention is not intended to be limited to those shown in the examples.

(Test Example 1)
<Examples 1-4>
A gas adsorbent made of carbon fiber aggregates was produced using carbon fibers (ACF). Specifically, commercially available activated carbon fibers (manufactured by Unitika Ltd., product number A-20, specific surface area 2070 m ² / g, pore diameter 2.2 nm) are prepared and cut to have an average length of 1 to 3 cm. (Carbon fiber preparation step; see FIG. 3). Next, the cut activated carbon fiber was put into a food processor and stirred for 10 minutes under the condition of a rotational speed of 5000 rpm to obtain a spherical carbon fiber aggregate (carbon fiber aggregation step; see FIG. 4). Next, 50 parts by mass of water is sprayed on 100 parts by mass of the carbon fiber aggregate, and the carbon fiber aggregate is shaken for 10 minutes under the condition of a shaking frequency (number of rotations) of 500 rpm using a swirl type shaker. Densification was performed (densification step; see FIG. 5). Thus, the gas adsorbent which consists of a carbon fiber aggregate which concerns on Examples 1-4 was obtained.

About the carbon fiber aggregate obtained above, the diameter R1 of the carbon fiber aggregate after the carbon fiber aggregation step and before the densification step and the diameter R2 of the carbon fiber aggregate after the densification step are measured, The ratio (R2 / R1) was determined. Also, calculate the volume of the carbon fiber aggregate than half the diameter R2 of the carbon fiber aggregate after densification step a radius r of the carbon fiber aggregate, by using the radius r (4πr ^3/3) did. And what divided the mass of the carbon fiber aggregate by the volume was made into the density of the carbon fiber aggregate. Properties of the carbon fiber aggregates according to Examples 1 to 4 are shown in the corresponding columns of Table 1.

In Example 1, R1 is 9.3 mm, R2 is 5.75 mm, (R2 / R1) is 0.62, and the density is 0.255 g / cm ³ . In Example 2, R1 is 8.7 mm, R2 is 5.5 mm, (R2 / R1) is 0.63, and the density is 0.237 g / cm ³ . In Example 3, R1 is 9.15 mm, R2 is 5.9 mm, (R2 / R1) is 0.64, and the density is 0.223 g / cm ³ . In Example 4, R1 is 10.05 mm, R2 is 5.95 mm, (R2 / R1) is 0.6, and the density is 0.29 g / cm ³ .

<Comparative Example 1>
Commercially available activated carbon fibers (ACF: manufactured by Unitika Ltd., product number A-20, specific surface area 2070 m ² / g, pore diameter 2.2 nm) were used as they were (see FIG. 6). The properties of the activated carbon fiber of this example are shown in the corresponding column of Table 1.

<Comparative Example 2>
Commercially available activated carbon fibers (ACF: manufactured by Unitika Ltd., product number A-16, specific surface area 1680 m ² / g, pore diameter 1.9 nm) were used as they were. The properties of the activated carbon fiber of this example are shown in the corresponding column of Table 1.

<Comparative Example 3>
A commercial activated carbon fiber (manufactured by Unitika Ltd., product number A-20, specific surface area 2070 m ² / g, pore diameter 2.2 nm) was compressed by applying a load of 10 kg / cm ^{2 with} a press. The properties of the activated carbon fiber of this example are shown in the corresponding column of Table 1.

<Comparative Example 4>
A commercial activated carbon fiber (ACF: manufactured by Unitika Ltd., product number A-20, specific surface area 2070 m ² / g, pore diameter 2.2 nm) was compressed by applying a load of 480 kg / cm ^{2 with} a press. The properties of the activated carbon fiber of this example are shown in the corresponding column of Table 1.

<Comparative Example 5>
A commercially available activated carbon fiber (ACF: manufactured by Unitika Co., Ltd., product number A-20, specific surface area 2070 m ² / g, pore diameter 2.2 nm) was cut to an average length of 2 to 3 cm, and as a binder 5% dextrin aqueous solution was added, and a load of 10 kg / cm ² was applied with a press machine and compressed into a pellet having a diameter of 40 mm (see FIG. 7). The properties of the activated carbon fiber of this example are shown in the corresponding column of Table 1.

<Comparative Example 6>
A commercially available activated carbon fiber (ACF: manufactured by Unitika Co., Ltd., product number A-20, specific surface area 2070 m ² / g, pore diameter 2.2 nm) was cut to an average length of 2 to 3 cm, and as a binder A 5% dextrin aqueous solution was added, and a load of 480 kg / cm ² was applied with a press to compress the pellets into a 40 mm diameter pellet. The properties of the activated carbon fiber of this example are shown in the corresponding column of Table 1.

<Comparative Example 7>
A cut activated carbon fiber (ACF: manufactured by Unitika Ltd., product number A-20, specific surface area 2070 m ² / g, pore diameter 2.2 nm) was cut to an average length of 2 to 3 cm. Carbon fibers were put into a food processor and stirred to obtain spherical carbon fiber aggregates. Properties of the activated carbon fiber aggregate of this example are shown in the corresponding column of Table 1.

<Comparative Example 8>
Commercially available activated carbon (AC: manufactured by Kuraray Co., Ltd., specific surface area 840 m ² / g, pore diameter 3.2 nm to 6.4 nm) was used as it was (see FIG. 8). The properties of the activated carbon of this example are shown in the corresponding column of Table 1.

<Comparative Example 9>
Commercially available activated carbon (AC: manufactured by Kuraray Co., Ltd., specific surface area 840 m ² / g, pore diameter 3.2 nm to 6.4 nm) pulverized with a food processor was used (see FIG. 9). The properties of the activated carbon of this example are shown in the corresponding column of Table 1.

<Comparative Example 10>
Commercially available carbon nanotubes (CNT: manufactured by Showa Denko KK, product number VGCF-X, pore diameter 15 nm) were used as they were (see FIG. 10). Properties of the carbon nanotubes of this example are shown in the corresponding columns of Table 1.

<Comparative Example 11>
A 5% dextrin aqueous solution was added to commercially available carbon nanotubes (CNT: Showa Denko Co., Ltd., product number VGCF-X, pore diameter 15 nm), and a load was applied with a press to compress the pellets into a 40 mm diameter pellet (FIG. 11). reference). Properties of the carbon nanotubes of this example are shown in the corresponding columns of Table 1.

About the sample of each example, the gas adsorption amount per unit volume in 25 degreeC and methane gas pressure 1MPa was measured. The gas adsorption amount was measured according to the following procedure.
(1) The sample of each example was accommodated in a measurement container and vacuum deaerated at 25 ° C. for 1 hour.
(2) Methane gas was introduced into the measurement container at 25 ° C. until the pressure reached 1 MPa.
(3) The change in pressure in the measurement container was measured until the equilibrium pressure was reached.
(4) The mass of the methane gas introduced into the measurement container was measured, and the gas adsorption amount at the equilibrium pressure was calculated.
(5) The above procedures (1) to (4) were repeated until the equilibrium pressure reached 1 MPa.
Here, the state where the pressure did not change for more than 10 minutes was defined as the equilibrium pressure. The results are shown in the corresponding column of Table 1. Here, the methane adsorption amount per unit mass and the methane adsorption amount per unit volume are shown based on the density of each example.

As shown in Table 1, although the carbon fibers of Comparative Examples 1 and 2 using commercially available carbon fibers as they were, the methane adsorption amount per unit mass was larger than those of Comparative Examples 8 and 9 using activated carbon. The amount of methane adsorbed per unit volume was small, making it unsuitable as a gas adsorbent. On the other hand, the carbon fiber aggregates of Examples 1 to 4 that were subjected to aggregation and densification treatment on the carbon fiber had a larger amount of methane adsorption per unit volume than Comparative Examples 1 to 11, It was suitable as a gas adsorbent. In the case of the carbon fiber aggregates used here, a high methane adsorption amount (volume basis) of 59 mL / cm ³ or more could be achieved by setting the density to 0.22 or more. In particular, by setting the density to 0.29 or more, an extremely high methane adsorption amount (volume basis) of 77 mL / cm ³ or more could be achieved.

  In addition, in Comparative Examples 3 to 6 in which the carbon fibers were densified by the compression treatment, the methane adsorption amount per unit mass tended to be lower than that in Comparative Example 1 in which the carbon fibers were used as they were. In Comparative Examples 3 to 6, since the adsorption site (pores) collapsed when the carbon fiber was compressed, it is presumed that the original gas adsorption ability was not exhibited. In contrast, in Examples 1 to 4, in which the carbon fibers were densified by aggregation and shaking treatment, the amount of methane adsorbed per unit mass was maintained at the same level as in Comparative Example 1 despite the densification. It was. From this result, according to the present Example, it was confirmed that a carbon fiber aggregate having a high density and a high gas adsorption ability can be obtained by performing the aggregation and shaking treatment.

(Test Example 2)
In order to confirm the heat dissipation effect of the partition plate, the following test was performed as a reference example. That is, activated carbon heated to 60 ° C. in a methane storage tank was filled with 400 cm ³ , and the subsequent temperature change was measured. Under the same conditions, sample 1 has no partition plate, sample 2 has a cross-like partition plate (see FIG. 12, height 6 cm, width 10 cm, thickness 1.2 mm, copper), and sample 3 has a disk-like partition plate (see FIG. The experiment was conducted with three types (see Fig. 13, 2 sheets, diameter 10 cm, thickness 1.2 mm, copper). The methane storage tank had a capacity of 500 mL, an internal diameter of 10 cm, an internal height of 6.37 cm, and stainless steel. As the activated carbon, one having a specific surface area of 977.5 m ² / g, a density of 0.59 g / cm ³ , and a particle size of 0.36 to 3.18 mm was used. The results are shown in FIG. FIG. 14 is a graph showing changes in temperature change from 60 ° C. for each sample.

  As shown in FIG. 14, samples 2 and 3 in which a partition plate is arranged in the methane storage tank have a faster temperature drop in the tank and heat dissipation than sample 1 in which no partition plate is arranged in the methane storage tank. Was good. From this result, it was confirmed that the heat dissipation can be improved by arranging the partition plate in the methane storage tank.

  Note that Sample 2 using a cross-shaped partition plate had a faster temperature drop in the tank and better heat dissipation than Sample 3 using a disk-shaped partition plate. Sample 3 (disc shape) has the effect of promoting heat transfer only in the radial direction of the tank, whereas sample 2 (cross shape) promotes heat transfer in the radial direction of the tank and the cylinder axis direction simultaneously. Since there is an effect, it is presumed that a greater effect of improving heat dissipation was obtained. From the viewpoint of heat dissipation, it is more preferable to use a cross-shaped partition plate than a disc shape.

  As mentioned above, although this invention was demonstrated by suitable embodiment, such description is not a limitation matter and of course various modifications are possible.

DESCRIPTION OF SYMBOLS 10 Container 12 Container main body 14 Cover 15 Measurement part 18 Gas supply / exhaust port 20 Partition plate 22 Hole 30 Filling chamber 100 Methane storage tank

Claims (13)

A gas adsorbent that adsorbs gas,
A carbon fiber aggregate formed by agglomerating carbon fibers,
The carbon average density of the fiber aggregate is ^{0.2g / cm 3 ~1g / cm 3} , and the gas adsorption amount per unit volume in the gas pressure 1MPa is at least 50 mL / cm ^3, the gas adsorbent. The average density of the carbon fiber aggregate is ^{0.2g / cm 3 ~0.3g / cm 3} , the gas adsorbent according to claim 1.   The gas adsorbent according to claim 1 or 2, wherein an average length of carbon fibers constituting the carbon fiber aggregate is 0.1 mm to 0.5 mm. The specific surface area of the carbon fibers constituting the carbon fiber aggregate is 1500m ² / g~2200m ² / g, the gas adsorbent according to any one of claims 1 to 3.   The gas adsorbent according to any one of claims 1 to 4, wherein the carbon fiber constituting the carbon fiber aggregate has a pore diameter of 1.8 nm to 2.5 nm. Includes a carbon fiber aggregate carbon fibers are aggregated, the mean density of the carbon fiber aggregate is ^{0.2g / cm 3 ~1g / cm 3} , and the gas adsorption amount per unit volume of gas pressure 1MPa Is a method for producing a gas adsorbent having at least 50 mL / cm ³ ,
A carbon fiber preparation process for preparing carbon fiber;
A carbon fiber aggregation step of aggregating the carbon fibers prepared in the carbon fiber preparation step to obtain a carbon fiber aggregate; and
A method for producing a gas adsorbent comprising a densification step of densifying the carbon fiber aggregate by adding a polar solvent to the carbon fiber aggregate obtained in the carbon fiber aggregation step and shaking.   The manufacturing method according to claim 6, wherein in the carbon fiber preparation step, carbon fibers having an average length of 1 cm to 5 cm are prepared.   The said carbon fiber aggregation process is a manufacturing method of Claim 6 or 7 including the process which stirs the said carbon fiber.   The ratio (R2 / R1) of the diameter R1 of the carbon fiber aggregate after the carbon fiber aggregation step and before the densification step to the diameter R2 of the carbon fiber aggregate after the densification step is 0.4. The manufacturing method according to claim 6, wherein ≦ (R2 / R1) ≦ 0.7. A gas storage tank for storing gas,
A gas adsorbent,
A container filled with the gas adsorbent,
The gas adsorbent comprises a carbon fiber aggregate carbon fibers are aggregated, the mean density of the carbon fiber aggregate is ^{0.2g / cm 3 ~1g / cm 3} , and the unit in the gas pressure 1MPa A gas storage tank, wherein the gas adsorption amount per volume is at least 50 mL / cm ³ . A partition plate for partitioning the inside of the container into a plurality of filling chambers;
The gas storage tank according to claim 10, wherein the gas adsorbent is divided into the plurality of filling chambers.   The gas storage tank according to claim 11, wherein a hole communicating with the plurality of filling chambers is formed in the partition plate. The container is a cylindrical container,
The partition plate is provided so as to extend in a cylinder axis direction of the container and partition a space along the circumferential direction of the container into a plurality of fan-shaped filling chambers. The gas storage tank described.