JP2018035397A - Hydrogen storage alloy and hydrogen purification device - Google Patents

Abstract

A hydrogen storage alloy that suppresses poisoning by CO2 gas and exhibits excellent hydrogen storage characteristics even when CO2 gas is contained in a hydrogen production raw gas for purifying hydrogen gas, and such A hydrogen refining apparatus that uses pure hydrogen storage alloy and can extract pure hydrogen with high efficiency is provided. The hydrogen storage alloy of the present invention is a hydrogen storage alloy represented by the following formula (1), wherein the atomic ratio X of Cr is a value in the range of 0.8 to 0.5. In addition, by filling such a hydrogen storage alloy in a hydrogen storage tower, a hydrogen purifier capable of taking out pure hydrogen with high efficiency can be realized. ZrFe2-XCrX (1) [Selection] FIG.

Description

  The present invention relates to a hydrogen storage alloy and a hydrogen purification apparatus using the hydrogen storage alloy.

In recent years, efficient use of energy has been demanded in order to solve the problems of global warming and fossil fuel depletion. Hydrogen energy is attracting attention as an important energy in the future because of its diverse energy sources and the ability to reduce environmental impact without emitting CO ₂ gas during power generation using fuel cells or internal combustion engines. .

  Among generators using hydrogen as a fuel, fuel cells are characterized by high power generation efficiency because they can directly extract electrical energy from a chemical reaction between hydrogen and oxygen. Among the fuel cells, the polymer polymer fuel cell (PEFC), in particular, has excellent load followability and high overall efficiency due to the use of exhaust heat during power generation. The system (Fuel Cell Co-Generation System: FC-CGS) is spreading.

In order to operate a stationary device that uses hydrogen, such as FC-CGS, it is necessary to perform on-site hydrogen production using a reformer or the like. However, PEFC uses a reformed gas obtained by reforming a hydrocarbon-based fuel as a raw material for hydrogen production. In addition to hydrogen, impurity gases such as CO and CO ₂ are included in this reformed gas. Many are included. For this reason, the reformed gas cannot be used as it is as a raw material gas for hydrogen production, and it is necessary to extract high-purity hydrogen for PEFC.

  On-site pure hydrogen production is performed by separating the impurity gas from the reformed gas by a pressure swing adsorption (PSA) method. Gas separation purification by the PSA method enables high-efficiency operation by rated operation of the reformer, but it is difficult to follow fluctuating household power demand. In addition, gas separation purification by the PSA method has a problem that it takes some time until hydrogen supply becomes possible at start-up, and it is difficult to respond to sudden hydrogen demand (for example, Non-Patent Document 1).

  As a technology for purifying hydrogen, COA-MIB (CO-Adsorption Metal) is a process for purifying and storing hydrogen in a reformed gas containing CO using a CO adsorbent and a hydrogen storage alloy (Metal Hydride: MH). (Hydride Intermediate Buffer) method is known (for example, Patent Document 1 and Non-Patent Document 2).

  The hydrogen storage alloy used in the above method is an alloy capable of selectively and reversibly storing and releasing hydrogen. In the above method using such a hydrogen storage alloy, a CO adsorption / removal device filled with an adsorbent for adsorbing CO is installed in the preceding stage of the hydrogen storage alloy to thereby poison the hydrogen storage alloy or the fuel cell. Has been removed. By introducing the gas to be treated after removing CO into a plurality of tanks filled with a hydrogen storage alloy, it is possible to supply and supply hydrogen while purifying and storing hydrogen on the one hand. By carrying out such a process, it is possible to supply pure hydrogen flexibly in response to changing hydrogen demand.

  One of the problems in putting the above process into practical use is cost reduction. Considering the required auxiliary equipment, purification efficiency, thermal efficiency, etc., piping and container design are determined to some extent, and it is difficult to reduce costs by reducing these.

MmNi ₅ system AB ₅ type alloys currently used in the above process: hydrogen-absorbing alloy (Mm misch metal) is a relatively expensive. Therefore, if a hydrogen storage alloy whose raw material is cheaper can be applied, cost reduction can be expected. Accordingly, a hydrogen storage alloy (hereinafter referred to as “a hydrogen storage alloy”) made of a Zr-based AB ₂ type alloy that has a higher theoretical hydrogen storage amount per mass than that of the MmNi ₅ -based hydrogen storage alloy and can use inexpensive metals such as Zr, Mn, and Fe. ”AB ₂ type MH” may be abbreviated).

However, in the above process, the hydrogen storage alloy is exposed to CO ₂ during hydrogen purification. Therefore, in order to use AB ₂ type MH as an alternative to the MmNi ₅ type hydrogen storage alloy, this AB ₂ type MH is covered by CO ₂ . It is necessary to have excellent resistance to poison (hereinafter, this characteristic may be referred to as “CO ₂ poisoning resistance”). If the AB ₂ type MH has poor resistance to CO ₂ poisoning, the characteristics of the hydrogen storage alloy, such as a decrease in the hydrogen storage rate and the hydrogen storage capacity, will be significantly deteriorated.

If an AB ₂ type MH with excellent resistance to CO ₂ poisoning can be realized, cost reduction can be expected, and even if CO ₂ is contained in the source gas for hydrogen production, the characteristics of the hydrogen storage alloy deteriorate due to CO ₂ poisoning. Can be prevented. In addition, if such a hydrogen storage alloy can be realized, a hydrogen refining apparatus that can efficiently extract pure hydrogen can be expected by providing a hydrogen storage tower filled with the hydrogen storage alloy.

As a technique related to AB ₂ type MH, it has been studied from various angles so far. As such a technique, for example, Non-Patent Document 3 reports that CO ₂ poisoning resistance in AB ₂ type MH is improved by partial substitution with a specific metal such as Fe or Ti. On the other hand, there is a problem that the hydrogen storage characteristics are deteriorated, for example, the hydrogen equilibrium pressure increases or the hydrogen storage amount decreases due to metal substitution (for example, Non-Patent Document 4).

"Development of load-capable hydrogen recovery, purification, and utilization system using hydrogen storage alloy" Kobe Steel, Ltd. 2013 Masayoshi Ishida: “Fuel cell load fluctuation countermeasures by purifying pure hydrogen from reformed gas using hydrogen storage alloy”, IEEJ Transactions B, Vol. 121, no. 8, pp. 1036-1043, 2001 Daiki Asada: “Compositional design for improving CO2 poisoning resistance of AB2 type hydrogen storage alloy for hydrogen purification”, University of Tsukuba, Master thesis, 2015 Yasuaki Osaku: "New edition of hydrogen storage alloy-its physical properties and applications-" issued by Agne Technology Center, 2008

JP 2010-241657 A

This type of AB ₂ type MH having a proposed CO ₂ poisoning resistance until less, AB ₂ type MH what component composition is excellent in CO ₂ poisoning resistance, excellent hydrogen storage characteristics exhibited It is not clear what will be done.

The present invention has been made in view of the above-described situation, and the object thereof is poisoning by CO ₂ gas even if CO ₂ gas is contained in the raw material gas for hydrogen production for purifying hydrogen gas. An object of the present invention is to provide a hydrogen storage alloy that exhibits excellent hydrogen storage characteristics by suppressing the above, and a hydrogen refining apparatus that can extract pure hydrogen with high efficiency using such a hydrogen storage alloy.

  The hydrogen storage alloy of the present invention that has achieved the above object is a hydrogen storage alloy represented by the following formula (1), wherein the atomic ratio X of Cr is in the range of 0.8 to 0.5: It is characterized by that.

_{ZrFe 2-X Cr X ... (} 1)
In the hydrogen storage alloy of the present invention, the atomic ratio X is preferably in the range of 0.8 to 0.7.

  A preferred embodiment of the present invention is a hydrogen storage alloy in which a part of Zr in the formula (1) is substituted with Ti, and the substitution atomic ratio Y of Ti represented by the following formula (2) is 0.1 to 0.1. A hydrogen storage alloy having a value in the range of 0.4 may be mentioned.

_{Zr 1-Y Ti Y Fe 2} -X Cr X ... (2)
If a hydrogen storage tower filled with the hydrogen storage alloy of the present invention is arranged, a hydrogen purifier capable of extracting pure hydrogen with high efficiency without being poisoned by CO ₂ gas can be realized.

The present invention is configured as described above, and can realize a hydrogen storage alloy that exhibits excellent hydrogen storage characteristics by reducing poisoning by CO ₂ gas, and a hydrogen refining apparatus using such a hydrogen storage alloy. It was.

FIG. 1 is a graph showing measurement results of PCT characteristics of a ZFC-based alloy. FIG. 2 is a graph showing the measurement results of PCT characteristics of a ZTFC alloy. FIG. 3 is a graph showing changes over time in the hydrogen storage amount, hydrogen storage rate, and cell pressure in a ZFC-based alloy. FIG. 4 is a graph showing temporal changes in hydrogen storage amount, hydrogen storage rate, and cell pressure in a ZTFC-based alloy. FIG. 5 is a graph showing changes over time in the hydrogen storage amount, hydrogen storage rate, and cell pressure in an H ₂ —CO ₂ mixed gas atmosphere in a ZFC-based alloy. FIG. 6 is a graph showing changes over time in the hydrogen storage amount, hydrogen storage rate, and cell pressure in a mixed gas atmosphere of H ₂ —CO ₂ in a ZTFC-based alloy. 7, in the ZFC alloy is a bar graph showing a comparison of the constant k _r about CO ₂ resistance. 8, in ZTFC alloy is a bar graph showing a comparison of the constant k _r about CO ₂ resistance. FIG. 9 is a graph showing temporal changes in the hydrogen storage amount, hydrogen storage rate, and cell pressure in a H ₂ —CO ₂ mixed gas atmosphere in a conventional hydrogen storage alloy. 10, in a conventional hydrogen storage alloy is a bar graph showing a comparison of the constant k _r about CO ₂ resistance. FIG. 11 is a schematic explanatory diagram showing a configuration example of the hydrogen purifier of the present invention.

The inventors of the present invention have made extensive studies on the component composition, particularly for realizing a hydrogen storage alloy that has excellent poisoning resistance to CO ₂ gas and exhibits excellent hydrogen storage characteristics. As a result, AB ₂ type MH represented by the following formula (1), in which the atomic ratio X of Cr is set to a value in the range of 0.8 to 0.5, the above object can be achieved brilliantly. The headline and the present invention were completed. Hereinafter, the configuration and operational effects of the present invention will be described.

_{ZrFe 2-X Cr X ... (} 1)
The amount of hydrogen stored in the hydrogen storage alloy (Content) changes depending on the pressure (pressure) and temperature (temperature) of the hydrogen. A pressure-composition isothermal curve shows the relationship between the logarithm of the pressure of hydrogen at a constant temperature (that is, the hydrogen equilibrium pressure) and the hydrogen storage amount. This pressure-composition isothermal curve is hereinafter referred to as “PCT curve”, and the characteristics of the hydrogen storage alloy evaluated based on the PCT curve are referred to as “PCT characteristics”.

  It is known that when the amount of occluded hydrogen is small in the solid solution region, the amount of occluded hydrogen increases in proportion to the ½ power of the pressure, and hydride is formed when the amount of occluded hydrogen further increases. When the solid solution and the hydride coexist, the amount of occlusion of hydrogen increases, but a plateau region where the hydrogen pressure does not increase appears. In the hydrogen storage alloy, hydrogen is stored and released mainly in the plateau region. Therefore, it is useful to grasp the PCT characteristics as described above in evaluating the hydrogen storage characteristics of each hydrogen storage alloy.

The basic characteristics of the hydrogen storage alloy can be evaluated by the PCT characteristics. To evaluate the resistance of the hydrogen storage alloy to CO ₂ poisoning, the hydrogen storage amount and hydrogen storage rate of the hydrogen storage alloy in a CO ₂ -containing atmosphere can be used. Need to figure out.

  In particular, it can be easily imagined that the hydrogen occlusion speed of the hydrogen occlusion alloy depends on the supplied hydrogen flow rate and plateau pressure, and it is difficult to directly evaluate the magnitude of the hydrogen occlusion speed only from the data of the measurement results. Therefore, the present inventors use the relationship between the hydrogen pressure and the hydrogen storage rate at a certain storage amount during dynamic characteristic measurement considering various conditions, and the relationship between the hydrogen equilibrium pressure and the hydrogen storage amount obtained from the PCT characteristics, By estimating the reaction rate constant, the hydrogen storage rate of the hydrogen storage alloy was evaluated.

In the AB ₂ type MH represented by the above formula (1), the present inventors have repeatedly examined the influence of the atomic ratio X of Cr on the hydrogen storage rate. As a result, the atomic ratio X of Cr is 0.8 to 0.8. It was found that a value in the range of 0.5 can maintain a good hydrogen storage rate, that is, good resistance to CO ₂ poisoning. The atomic ratio X of Cr is preferably a value in the range of 0.8 to 0.7.

  The hydrogen storage alloy of the present invention includes a hydrogen storage alloy in which a part of Zr in the formula (1) is substituted with Ti. This hydrogen storage alloy has the following formula (2) as shown in the examples described later. It is preferable that the substitutional atomic ratio Y of Ti represented by () is a value in the range of 0.1 to 0.4.

_{Zr 1-Y Ti Y Fe 2} -X Cr X ... (2)
In order to produce the hydrogen storage alloy of the present invention, the necessary mass is calculated from the atomic weight of each metal, each raw metal is weighed and mixed so as to have the atomic ratio shown in the above formula (1), and the arc It is melted by a melting method to make an ingot. Thereafter, in order to homogenize the composition, for example, heat treatment is performed in an Ar atmosphere.

  The ingot after heat treatment is cut into an appropriate size and then pulverized to an appropriate size. The particle size after pulverization is preferably about 3 to 500 μm. If the particle size is smaller than 3 μm, activation for hydrogen storage may become difficult. The particle size of the hydrogen storage alloy is more preferably 50 μm or more, and still more preferably 100 μm or more. In addition, an iron powder can also be mixed with a powdery hydrogen storage alloy as needed, and durability of a hydrogen storage alloy improves by mixing an iron powder.

  The hydrogen storage alloy obtained as described above is activated in an atmosphere of a predetermined temperature, hydrogen pressure, and hydrogen flow rate in order to make hydrogen storage and release possible.

If the hydrogen storage alloy of the present invention that exhibits the above characteristics is used, pure hydrogen can be efficiently extracted from the H ₂ —CO ₂ mixed gas by providing a hydrogen storage tower filled with the hydrogen storage alloy. A hydrogen purifier can be realized.

FIG. 11 is a schematic explanatory diagram showing a configuration example of the hydrogen purifier of the present invention. In the figure, 1 is a reformer, 2 is a CO adsorption remover, 3 is a hydrogen storage tower filled with the hydrogen storage alloy of the present invention, and 4 is a PEFC stack. For example, the hydrocarbon-based fuel G is sent to the reformer 1 to be reformed to generate hydrogen, and includes CO, CO ₂ , water (H ₂ O), and the like as impurities. The to-be-processed gas reformed by the reformer 1 is sent to the CO adsorption / removal device 2, and CO in the to-be-processed gas is adsorbed and removed. At the same time, water is also removed by adsorption. The gas to be treated from which CO has been adsorbed and removed is then sent to the hydrogen storage tower 3 where the hydrogen is stored by the hydrogen storage alloy filled in the hydrogen storage tower 3. The impurity gas in the gas to be treated after the hydrogen is occluded is discharged from the hydrogen adsorption tower 3.

  The configuration of the hydrogen purification apparatus shown in FIG. 11 assumes a case where the COA-MIB method is applied. For this purpose, a plurality of hydrogen storage towers 3 are installed. As described above, a plurality of hydrogen storage towers 3 are provided, and by alternately storing and releasing hydrogen, it is configured to stably supply pure hydrogen to the PEFC stack in response to changing hydrogen demand. . However, the hydrogen purification apparatus of the present invention is not limited to the case where the COA-MIB method is applied. For example, when the raw material gas does not contain CO, the CO adsorption / removal device 2 may not be disposed.

By adopting the configuration of the hydrogen purification apparatus of the present invention, pure hydrogen can be efficiently extracted from the H ₂ —CO ₂ mixed gas without being poisoned by CO ₂ .

  Hereinafter, the working effects of the present invention will be described more specifically by way of examples. However, the following examples are not intended to limit the present invention, and any change in design in accordance with the gist of the invention described above and below will be described. Included in the technical scope.

Example 1
Hydrogen storage alloys having the component compositions shown in Table 1 below were produced. Table 1 also shows the abbreviated sample names for each sample, and this sample name may be used in the following description. Sample No. When referring to the samples 1 to 6 collectively, they are referred to as “ZFC-based alloys”. When summing up 7 to 10 samples, they are called “ZTFC-based alloys”.

  From the component composition shown in Table 1 and the atomic weight of each metal, the required mass was calculated to the fourth decimal place, and each raw metal was weighed. When weighing, it was matched to the third decimal place. An arc melting furnace was used for melting the raw metal. At the time of arc melting, melting was performed three times per sample in order to make the component composition uniform. After the arc melting was completed, the sample was taken out in the air. The ingot obtained by arc melting was heat-treated at 900 ° C. for 24 hours in an Ar atmosphere in order to homogenize the composition. The ingot after heat treatment was cut into an appropriate size, and those other than those used for cross-sectional observation were pulverized in the atmosphere, and samples having a particle diameter of 150 to 500 μm were used as samples.

  PCT characteristics were measured for each sample shown in Table 1. The configuration of the apparatus for measuring the PCT characteristics and the PCT measurement method are referred to “JIS H 7201:“ Measurement Method of Pressure-Composition Isothermal Curve (PCT Curve) of Hydrogen Storage Alloy ””, 2007 of the Japan Industrial Standards Committee. did. Control of the sample temperature during the PCT characteristic measurement was performed in a constant temperature water bath. The purity of the hydrogen gas used was G1 grade (7N), and the sample weight was 1 g.

  In order to make hydrogen occlusion and release possible, the activation process was performed by passing the hydrogen flow rate at about 500 cc / min for 1 hour at a sample temperature of 150 ° C. and a hydrogen pressure of 0.9 MPa. Thereafter, the sample temperature was lowered to 20 ° C. and evacuation was performed, and the evacuation was terminated when the value of the vacuum gauge reached about 1 Pa which is the ultimate pressure of the vacuum pump. A “vacuum origin method” was adopted in which the hydrogen storage amount at this time was zero. The details of this vacuum origin method can be referred to “JIS H 7003:“ Hydrogen Storage Alloy Terms ”, 2007, from the Japan Industrial Standards Committee. From this state, measurement of the PCT curve was started, and hydrogen storage up to a hydrogen pressure of 1 MPa was performed.

  The measurement result of the PCT characteristic of the ZFC alloy is shown in FIG. The hydrogen equilibrium pressure tended to increase as the amount of Fe increased.

  FIG. 2 shows the measurement results of PCT characteristics of the ZTFC alloy. In the ZTFC alloy, the hydrogen storage amount decreased as the Ti amount increased, and the hydrogen equilibrium pressure tended to increase. It was also found that the hydrogen equilibrium pressure was abruptly increased as the amount of Ti increased. This is considered to be because Ti-rich portions increased and the crystal uniformity deteriorated by increasing Ti.

  The “hydrogen storage amount” shown in FIGS. 1 and 2 is a value indicating how many hydrogen atoms are stored per total number of atoms of the hydrogen storage alloy (this value is expressed as “H / M”). It was evaluated in.

  FIG. 3 shows changes with time in the hydrogen storage amount, hydrogen storage rate, and cell pressure in the ZFC-based alloy. Here, the “hydrogen storage amount” is evaluated by the mass ratio (mass%) of the amount of hydrogen stored in the hydrogen storage alloy to the hydrogen storage alloy (the same applies to FIGS. 4 and 9 described later). The “cell pressure” means a hydrogen pressure in pure hydrogen and a total pressure in a mixed gas.

  The maximum hydrogen storage amount within the measurement time (hereinafter sometimes referred to as “maximum hydrogen storage amount”) is 1.65% by mass (H / M = 1.08) for ZFC and 1.68 for ZFC1. % By mass (H / M = 1.11), 1.67% by mass (H / M = 1.11) for ZFC2, 1.53% by mass (H / M = 1.01) for ZFC3, 1. It became 48 mass% (H / M = 0.98) and 1.45 mass% (H / M = 0.97) in ZFC5, and there was a tendency to decrease slightly as the amount of Fe increased.

  The hydrogen storage rate tends to decrease as Fe increases. In ZFC, ZFC1, and ZFC2, the storage rate is maintained while maintaining a hydrogen storage rate of approximately 5 cc / min (volume at 20 ° C. and 0.1013 MPa). Advances. However, two peaks were observed in the hydrogen storage rate from ZFC3. In particular, in ZFC4 and ZFC5, a peak appears remarkably.

  This suggests that ZFC3, ZFC4, and ZFC5 have two plateau regions. Two plateau regions can also be seen from the pressure change. Therefore, in ZFC3, ZFC4, and ZFC5 where two plateau regions were observed, a mixed region of α phase and β phase was formed as hydrogen storage progressed, and a further mixing of β phase and newly formed γ phase was performed as hydrogen storage progressed. An area is considered to be created.

  FIG. 4 shows changes with time in the hydrogen storage amount, hydrogen storage rate, and cell pressure in the ZTFC alloy. Regarding the maximum hydrogen storage amount, ZTFC1 is 1.73 mass% (H / M = 1.11), ZTFC2 is 1.69 mass% (H / M = 1.06), ZTFC3 is 1.51 mass% (H /M=0.93) and ZTFC4 was 1.48% by mass (H / M = 0.91), and a tendency to decrease as the Ti content increased was observed.

  The hydrogen storage rate tended to decrease slightly as Ti increased. In ZFC2, ZFC3 and ZFC4, the hydrogen storage rate tended to decrease gradually during the hydrogen storage. This is thought to be due to the inclination of the hydrogen equilibrium pressure as Ti increases.

Based on these basic experiments, further investigations were made on the CO ₂ poisoning resistance of each hydrogen storage alloy. In order to evaluate the CO ₂ poisoning resistance, it is important to grasp the storage speed of each hydrogen storage alloy in a CO ₂ -containing atmosphere.

It can be easily imagined that the storage speed of the hydrogen storage alloy depends on the supplied hydrogen flow rate and the plateau pressure, and it is difficult to directly evaluate the magnitude of the hydrogen storage speed only from the data of the PCT characteristic measurement results. Therefore, the reaction rate constant is calculated using the relationship between the hydrogen partial pressure and the hydrogen storage rate at the time of the storage amount during dynamic characteristics measurement considering various conditions, and the relationship between the hydrogen equilibrium pressure and the hydrogen storage amount obtained from the PCT characteristics. By estimating, the magnitude of the storage speed of each hydrogen storage alloy in the CO ₂ -containing atmosphere was quantified. The following formula (3) is a simplified formula of a reaction rate formula used in numerical calculation or the like.

In formula (3), v is the hydrogen storage rate [H / M / s] of the hydrogen storage alloy, F is the hydrogen storage amount [H / M], and k _T is the reaction rate constant [s ⁻¹ depending on the temperature. ], P (F) is a hydrogen pressure _{[MPa], P eq (F} , T) hydrogen storage capacity in the hydrogen equilibrium pressure at the temperature [MPa], _{P 0} is atmospheric pressure [MPa], f (F) is occluded The function [H / M] depending on the quantity is represented respectively. dF / dt and P (F) are values obtained by measuring dynamic characteristics during pure hydrogen storage, and P _eq (F, T) is a value obtained from a PCT curve, and the influence of hydrogen pressure during pure hydrogen storage. The hydrogen occlusion speed v ′ _bef excluding the above can be obtained as in the following formula (4).

By calculating v ′ _bef using values at the same time when the temperature and the hydrogen storage amount are the same for each sample, the magnitude of the hydrogen storage rate can be grasped. If the hydrogen occlusion rate excluding the influence of the hydrogen pressure in the CO ₂ -containing atmosphere is v ′ _aft , it can be obtained as in equation (5).

To quantify the degree of CO ₂ poisoning resistance regarding storage rate, to the formula (4) was inserted constants k _r about CO ₂ resistance. Here, k _T and f (F) are values inherent to each hydrogen storage alloy, and therefore, it is considered that there is no change in pure hydrogen and in a CO ₂ -containing atmosphere. Then, v ′ _bef represented by the above equation (4) and v ′ _aft represented by the above equation (5) are calculated under the same occlusion amount / temperature conditions, as in equation (6) by taking the ratio, it is possible to extract only the constant k _r about CO ₂ resistance.

The CO ₂ resistance related constant k _r is hydrogen absorbing speed v _'bef, v' excluding the effect of the hydrogen pressure in the pure hydrogen and CO ₂ containing atmosphere is the value of the ratio of the _aft, the value of the constant k _r larger, CO ₂ shows to have excellent poisoning resistance.

In order to obtain “k _r in the plateau region” which is most important in using the hydrogen storage alloy, the present inventors have a region where the value of (H / M) is 0.2 to 0.6. Then, the “constant k _r regarding CO ₂ resistance” was obtained. To determine this constant k _r is from a plot obtained by PCT characteristic measurement, a hydrogen equilibrium pressure in the region to be the H / M = 0.2 to 0.6, the relationship of the value of the (H / M) Need to be formulated. In the present invention, Expression (7) is used as an expression for formulating the relationship between the hydrogen equilibrium pressure and the value of (H / M).

Here, P ₁ is the hydrogen equilibrium pressure, F is the hydrogen concentration corresponding to the value of (H / M), and A ₀ , B ₀ , ψ, ψ ₀ , F ₀ and β are parameters specific to the hydrogen storage alloy. It is. These parameters are determined by fitting to match the experimental values.

The above “constant k _r regarding CO ₂ resistance” was determined for each hydrogen storage alloy. The manufacturing method of each sample and the subsequent processing are the same as described above. With respect to the alloy after the hydrogen releasing operation, a hydrogen storage operation was performed with a state where CO ₂ was introduced to 0.1 MPa in the sample system as a starting state. The measurement end condition was when the flow rate display of the mass flow meter was remarkably lowered and became constant, or after 300 minutes had passed.

At this time, the same evaluation as described above was performed for each sample (sample Nos. 11 to 13) shown in Table 2 below for comparison. However, these alloys were subjected to an exposure test in a CO ₂ atmosphere before performing the test in a CO ₂ -containing atmosphere, and the value of the “constant k _r regarding CO ₂ resistance” was evaluated above. It becomes smaller than the value. In addition, the sample No. shown in Table 2 was used. Nos. 11 and 13 have been proposed as hydrogen storage alloys with improved CO ₂ poisoning resistance (Non-Patent Document 3). Sample No. No. 12 is a sample No. shown in Table 1 in order to judge the difference in “constant k _r regarding CO ₂ resistance” due to the difference in test conditions. The same composition as 7 was shown.

FIG. 5 shows changes over time in the hydrogen storage amount, hydrogen storage rate, and hydrogen pressure in a ZFC-based alloy in an H ₂ —CO ₂ mixed gas atmosphere up to 300 minutes. The hydrogen storage amount shown in FIG. 5 is normalized by dividing the hydrogen storage amount (mass%) in the H ₂ —CO ₂ mixed gas atmosphere by the hydrogen storage amount (mass%) in a pure hydrogen atmosphere. (The same applies to FIG. 6 described later).

From this result, it can be considered as follows. As for ZFC1, the normalized hydrogen storage amount at the end of storage is as small as about 0.60. However, in other alloys, the normalized hydrogen storage amount at the end of storage is 0.9 or more. It is clear that the CO ₂ poisoning tolerance in terms of quantity is improved.

  The maximum hydrogen storage rate is ZFC3 ≧ ZFC2> ZFC4 ≧ ZFC> ZFC5 ≧ ZFC1, but the reason is that the hydrogen storage rate increases and decreases as the hydrogen storage progresses and is further affected by the hydrogen equilibrium pressure. So it is difficult to judge which alloy is superior. There was no significant difference in pressure change between alloys, but the time to reach the maximum value (0.9 MPa) slightly changed due to the difference in hydrogen storage rate.

  In addition, since the time when the peak of the hydrogen storage rate coincides with the time when the cell pressure reaches the maximum value, the pressure difference between the inside of the container and the supply side is also involved in the reaction rate in this alloy system and this experimental condition. I think that.

FIG. 6 shows changes with time in the hydrogen storage amount, hydrogen storage rate, and cell pressure in the Z 2 -FC 2 alloy in an H ₂ —CO ₂ mixed gas atmosphere up to 300 minutes. It can be seen that in the ZTFC-based alloy, the normalized hydrogen storage amount is as high as 0.9 or more in all alloys. Regarding the hydrogen storage rate, ZTFC1 containing Ti is significantly improved compared with ZFC not containing Ti, although there is no significant difference in hydrogen equilibrium pressure. From this, it is understood that the hydrogen occlusion speed in the H ₂ —CO ₂ mixed gas atmosphere is improved by including Ti.

  However, even if the Ti substitution atom ratio is increased as compared with ZFC1, the hydrogen storage rate is not improved. This is considered to be due to the influence of the hydrogen equilibrium pressure, as in the ZFC system.

As described above, in evaluating a CO ₂ poisoning resistance must be considered in isolation and the influence of hydrogen equilibrium pressure, the influence of CO ₂ poisoning. Were determined constant k _r about CO ₂ resistance in the procedure shown in the equation (3) to (7). At this time, sample no. The values of A ₀ , B ₀ , ψ, ψ ₀ , F ₀ and β in each of the hydrogen storage alloys 1 to 11 are as shown in Table 3 below.

The measurement results of the constant k _r about CO ₂ tolerance for ZFC alloy, shown in the bar graph of FIG. Further the CO ₂ resistance measurements constants k _r about about ZTFC alloy, shown in the bar graph of Figure 8.

From Figure 7, the constant k _r is about CO ₂ resistance, although increased by increasing the Fe, increasing the atomic ratio of Fe than ZFC3, it becomes constant after the coefficient k _r is smaller regarding CO ₂ poisoning I understand that.

From this, there is a certain effect in improving the CO ₂ poisoning resistance by the Fe substitution, but the CO ₂ poisoning resistance does not increase as the atomic ratio of Fe increases. That is, in the hydrogen storage alloy represented by the above formula (1), the Cr atomic ratio X having a value in the range of 0.8 to 0.5 is excellent in CO ₂ poisoning resistance. I understand. In particular, the atomic ratio X of Cr is preferably in the range of 0.8 to 0.7.

From Figure 8, compared with ZFC not containing Ti, towards ZTFC based alloy containing Ti is, since the constant k _r is large concerning CO ₂ resistance, that the hydrogen storage rate increases by increasing the Ti I understand. That is, with regard to substitution with Ti, the substitutional atomic ratio Y of Ti represented by the above formula (2) is set to a value in the range of 0.1 to 0.4, which is effective in improving CO ₂ poisoning resistance. .

In addition, FIG. 9 shows changes over time in the hydrogen storage amount, hydrogen storage rate, and cell pressure in the H ₂ —CO ₂ mixed gas atmosphere up to 300 minutes in the hydrogen storage alloys shown in Table 2. Of these, sample no. The measurement results of the constant k _r about CO ₂ resistance in 11 hydrogen storage alloy shown in the bar graph of Figure 10. In addition, in FIG. 9, 10, the result of ZFC (sample No. 1 shown in Table 1) was also shown for reference. Further, the results shown in FIGS. 9 and 10 are obtained by performing an exposure test in a CO ₂ atmosphere before performing a test in a CO ₂ -containing atmosphere, such as a value of “constant k _r regarding CO ₂ resistance”. Is smaller than the values shown in FIGS. By using 1 and 12 data as a reference, an objective evaluation can be performed.

As is clear from comparison between this result and the results shown in FIGS. 5 to 8, when a part of Fe at the B site is substituted with Mn for the ZrFe ₂ alloy which is an AB ₂ type alloy, Fe It can be seen that the CO ₂ poisoning resistance is not so improved as compared with the alloy in which a predetermined amount of Cr is replaced with Cr.

  Further, it can be seen that when a part of Zr is substituted with Ti for the ZrFeMn alloy, the substitution effect of Ti is not significantly exhibited as compared with the hydrogen storage alloy of the present invention (FIG. 9).

(Example 2)
Using the hydrogen purification apparatus shown in FIG. 11, the hydrogen purification characteristics of a ZrFe _1.3 Cr _0.7 alloy having a hydrogen equilibrium pressure of about 0.1 MPa and a flat plateau region were evaluated. At this time, a cylindrical container having a length of 70 mm and a diameter of 22.4 mm was used for the hydrogen storage tower 3. A container of 42 g of ZrFe _1.3 Cr _0.7 alloy was filled as it was without being consolidated. The hydrogen using G1 grade a (7N), the CO ₂ was used liquefied carbon dioxide (more than 99.97%). A rotary pump (manufactured by ULVAC, small oil rotary vacuum pump, “G-25S” (trade name)) was used for evacuation of the piping.

The flow rate control of CO ₂ and hydrogen is performed by a mass flow controller (MFC: Mass Flow Controller, manufactured by KOFLOK, “MODEL 3760” (trade name)), and the hydrogen storage amount is a mass flow meter for CO ₂ (MFM: Mass Flow). Measure the flow rate with a Meter, measure the hydrogen concentration with a thermal conductivity detector (TCD: Thermal Conductivity Gas Analyzer, Panametrics, "TM02-TC" (trade name)), calculate the hydrogen flow rate and calculate did.

  The amount of hydrogen released was measured with a hydrogen MFM. The pressure at the inlet and outlet of the MH container was measured by using a digital pressure gauge (manufactured by Keyence Corporation, “AP-C33”, “AP-C34” (trade name)).

  The hydrogen storage tower 3 was covered with a jacket so that water could flow. Hot water and cold water are allowed to flow through the jacket in order to control the temperature of the sample. A cooling pump (manufactured by TAITEC Co., Ltd., “CH-601AF” (trade name)) was used as a chiller used for flowing cold water. In addition, a heat insulating material is wound around the container for heat insulation. The inlet and outlet can be blocked by a valve so that the sample in the hydrogen storage tower 3 can be taken out. A data logger (manufactured by Keyence Corporation, “NR-250” (trade name)) was used for data collection of each device.

As conditions for storing hydrogen, the cooling water temperature was 20 ° C. and the storage time was 30 minutes. At the time of release, the hot water temperature was 80 ° C., the release time was 20 minutes, the cooling time was 10 minutes, and occlusion-release-cooling was one cycle, and the measurement was performed up to 10 cycles. The value of the back pressure valve was 0.9 MPa. The pressure of the mixed gas is 0.9 MPa, the flow rate is H ₂ : 71.3 cc / min, CO ₂ : 23.8 cc / min, and the flow rate is adjusted so that the space velocity (Space Velocity: SV) is 415 h ^−1. Went.

  The hydrogen recovery rate up to 10 cycles was 97.6% in the first cycle, but it was confirmed that a high hydrogen recovery rate of 87.3% could be maintained even after 10 cycles.

1 reformer 2 CO adsorption remover 3 hydrogen storage tower 4 PEFC stack

Claims (4)

A hydrogen storage alloy represented by the following formula (1):
A hydrogen storage alloy, wherein the atomic ratio X of Cr is a value in the range of 0.8 to 0.5.
_{ZrFe 2-X Cr X ... (} 1)   The hydrogen storage alloy according to claim 1, wherein the atomic ratio X is a value in a range of 0.8 to 0.7. A hydrogen storage alloy in which a part of Zr in the formula (1) is substituted with Ti, and the substitution atomic ratio Y of Ti represented by the following formula (2) is in a range of 0.1 to 0.4. The hydrogen storage alloy according to claim 1 or 2.
_{Zr 1-Y Ti Y Fe 2} -X Cr X ... (2)   A hydrogen purification apparatus comprising a hydrogen storage tower filled with the hydrogen storage alloy according to claim 1.

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