Method for producing magnesium hydride

Abstract

To provide a method for producing magnesium hydride which improves the reactivity of magnesium and can carry out hydrogenation treatment even in a state where the pressure of hydrogen gas is kept low.SOLUTION: There is provided a method for producing magnesium hydride which comprises: a pulverization step of pulverizing magnesium by adding a fatty acid; and a hydrogenation step of hydrogenating the pulverized magnesium by heating the magnesium to a temperature of 140°C or more and less than the decomposition temperature of magnesium hydride in a reaction vessel to which hydrogen gas is supplied so as to keep the pressure 5 atmospheres or less, wherein the pulverization step is performed under an atmosphere of nitrogen gas and the pulverized magnesium is not allowed to contact with oxygen until the hydrogenation step has been completed.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for producing magnesium hydride.

Background Art

[0002] In recent years, hydrogen has attracted attention as an energy source, and magnesium hydride is one of the methods for storing hydrogen.

[0003] In Patent Document 1, a raw material powder mainly composed of magnesium is held in a hydrogen gas atmosphere sealed in a container, the pressure of the hydrogen gas atmosphere in the container is maintained at a predetermined pressure, the temperature of the hydrogen gas atmosphere in the container is raised from room temperature, and the temperature of the hydrogen gas atmosphere in the container is higher than the temperature corresponding to the predetermined pressure on the equilibrium curve of the reaction in which elemental magnesium and hydrogen molecules combine to form magnesium hydride and the reverse reaction, and the temperature difference from the temperature corresponding to the predetermined pressure on the equilibrium curve is within 100 ° C. By maintaining at a temperature within, the film on the surface of the raw material powder is removed. Next, the temperature of the hydrogen gas atmosphere in the container is not returned to room temperature, but is lower than the temperature corresponding to the predetermined pressure on the equilibrium curve, and the temperature difference from the temperature corresponding to the predetermined pressure on the equilibrium curve is within 100 ° C. A method for producing a magnesium-based hydride for producing a magnesium-based hydride from a raw material powder by maintaining at a temperature within is disclosed.

[0004] That is, Patent Document 1 is characterized in that, in a first step, the temperature is maintained for a predetermined first period at a temperature higher than the temperature corresponding to the predetermined pressure on the equilibrium curve of the reaction in which elemental magnesium and hydrogen molecules combine to form magnesium hydride and the reverse reaction, and the temperature difference from the temperature corresponding to the predetermined pressure on the equilibrium curve is within 100 ° C.

[0005] This first characteristic leads to the thermal decomposition of magnesium hydroxide (Mg(OH)2) formed on the surface of magnesium (Mg), and the reduction of magnesium oxide (MgO) formed by this thermal decomposition by hydrogen molecules, thereby removing the film on the magnesium (Mg) surface and enabling rapid reaction with hydrogen (H2).

[0006] Furthermore, Patent Document 1 has a second feature in that it maintains the temperature of the hydrogen gas atmosphere for a predetermined second period at a temperature lower than the temperature corresponding to a predetermined pressure on the equilibrium curve, and at a temperature within 100°C of the temperature corresponding to the predetermined pressure on the equilibrium curve, without returning the atmosphere to room temperature.

[0007] This second characteristic makes it possible to obtain high-purity magnesium hydride (MgH2) with less energy input compared to conventional techniques that require an activation process involving repeated heating and cooling to absorb and release hydrogen. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2008-44832 [Overview of the project] [Problems that the invention aims to solve]

[0009] By the way, in Patent Document 1, the examples show that the hydrogen gas pressure during the hydrogenation treatment is set to a pressure atmosphere of 10 atmospheres (approximately 1 MPa) or higher.

[0010] Furthermore, Patent Document 1 explains that in order to produce magnesium hydride within a realistic time range, the pressure should be at least 6 atmospheres or higher.

[0011] However, equipment that processes materials under a high-pressure hydrogen gas atmosphere has stricter specifications required of it (for example, pressure resistance).

[0012] Therefore, there is a need to develop a technology that improves the reactivity of magnesium and enables hydrogenation even when the hydrogen gas pressure is kept low.

[0013] This invention has been made in view of these circumstances, and aims to provide a method for producing magnesium hydride that improves the reactivity of magnesium and allows hydrogenation treatment even when the hydrogen gas pressure is kept low. [Means for solving the problem]

[0014] To achieve the above objective, the present invention is understood by the following configuration. (1) The present invention provides a method for producing magnesium hydride, comprising: a grinding step of grinding magnesium by adding a fatty acid; and a hydrogenation step of heating the ground magnesium to a temperature of 140°C or higher and below the decomposition temperature of magnesium hydride in a reaction vessel supplied with hydrogen gas to maintain a pressure of 5 atmospheres or less, thereby hydrogenating it, wherein the grinding step is carried out under a nitrogen gas atmosphere, and the ground magnesium is not exposed to oxygen until the end of the hydrogenation step.

[0015] (2) In the configuration of (1) above, the nitrogen gas is supplied from a nitrogen generator that produces nitrogen gas with a purity of 99.9% or higher from the atmosphere.

[0016] (3) In the configuration of (1) or (2) above, the amount of fatty acid added in the grinding step is 3% by mass or more of the total mass of the magnesium and the fatty acid combined. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a method for producing magnesium hydride that improves the reactivity of magnesium and allows for hydrogenation treatment even when the hydrogen gas pressure is kept low.

Brief Description of the Drawings

[0018] [Figure 1] It is a perspective view of a crusher used in the crushing process of the first embodiment according to the present invention. [Figure 2] It is a perspective view showing the state where the hood of the crusher of the first embodiment according to the present invention is opened. [Figure 3] It is a perspective view of a crushing container of the first embodiment according to the present invention. [Figure 4] It is an exploded perspective view of a crushing container of the first embodiment according to the present invention. [Figure 5] It is a side view showing a hydrogenation furnace of the first embodiment according to the present invention. [Figure 6] It is a flowchart showing the procedure of the hydrogenation process of the first embodiment according to the present invention. [Figure 7] It is a graph showing the decomposition generation boundary line of magnesium hydride obtained by thermodynamic calculation.

Modes for Carrying Out the Invention

[0019] Hereinafter, with reference to the accompanying drawings, modes for carrying out the present invention (hereinafter, embodiments) will be described in detail. Throughout the description of the embodiments, the same elements are denoted by the same reference numerals.

[0020] (First Embodiment) The method for producing magnesium hydride according to the first embodiment of the present invention includes a crushing step of adding a fatty acid and crushing magnesium before crushing (hereinafter, may be simply referred to as magnesium), and in a reaction vessel to which hydrogen gas is supplied so as to maintain a pressure of 5 atm or less, heating the crushed magnesium to a temperature of 140°C or higher and lower than the decomposition temperature of magnesium hydride to hydrogenate it.

[0021] Therefore, the apparatus used consists of a pulverizer 1 (see Figure 1) for the pulverization process and a hydrogenation furnace 8 (see Figure 5) for the hydrogenation process. After explaining the pulverizer 1 and the hydrogenation furnace 8 (including the operating procedure in the hydrogenation furnace 8), we will then explain specific examples.

[0022] (Crusher) Figure 1 is a perspective view of the pulverizer 1 used in the pulverization process of the first embodiment according to the present invention; Figure 2 is a perspective view of the pulverizer 1 of the first embodiment according to the present invention with the hood 3 open; Figure 3 is a perspective view of the pulverization container 4 of the first embodiment according to the present invention; and Figure 4 is an exploded perspective view of the pulverization container 4 of the first embodiment according to the present invention. The pulverizer 1 used in the first embodiment described below is a planetary ball mill device manufactured by Fritsch.

[0023] As shown in Figures 1 and 2, the pulverizer 1 used in the first embodiment includes a pulverizer body 2 that controls the rotation of a detachably fixed pulverizing container 4 (see Figure 2), and a hood 3 that is connected to the pulverizer body 2 by a hinge structure so as to be openable and closable, and which can cover and conceal the pulverizing container 4.

[0024] As shown in Figure 1, the main body of the crusher 2 includes a condition input unit 21 for inputting conditions for controlling the rotation of the crushing container 4, and an emergency stop button 22.

[0025] As shown in Figures 3 and 4, the grinding container 4 comprises a bottomed grinding container body 41 with an upper opening, which constitutes a storage section for the material to be ground (not shown) and spherical grinding media (not shown) that promotes grinding, and a lid portion 42 that closes the upper opening of the grinding container body 41.

[0026] Furthermore, as shown in Figure 4, the grinding container body 41 is provided with a groove 411 on the upper opening side edge for positioning the O-ring 5, and a screw thread hole 412 formed radially outward from the groove 411 for screwing in. Furthermore, there are a total of four screw holes 412, spaced at 90° intervals in the circumferential direction.

[0027] On the other hand, the lid portion 42 has a through hole 421 on its outer surface (see Figure 3) which has a counterbore for accommodating the head of a screw. Furthermore, since these through holes 421 are for passing the threaded portion of the screw through to the grinding container body 41 when screwing the lid 42 to the grinding container body 41, the positions of the through holes 421 (distance from the center, etc.) correspond to the screw threaded holes 412 of the grinding container body S41, and like the screw threaded holes 412, a total of four through holes are provided at 90° intervals in the circumferential direction.

[0028] Then, the material to be crushed (not shown) and spherical crushing media (not shown) that promotes crushing are placed in the crushing container body 41, and a screw (not shown) is screwed into the screw threading hole 412 of the crushing container body 41 through the through hole 421 from the lid 42 side so that the lid 42 presses the O-ring 5 toward the crushing container body 41 side, thereby placing the material to be crushed (not shown) and spherical crushing media (not shown) that promotes crushing in a completely sealed state inside the crushing container 4.

[0029] After placing the material to be crushed (not shown) and spherical crushing media (not shown) to promote crushing inside the crushing container 4, the crushing container 4 is fixed to the crusher body 2 as shown in Figure 2, the hood 3 of the crusher body 2 is closed as shown in Figure 1, the condition input unit 21 is operated to input conditions for controlling the rotation of the crushing container 4, and the crushing start button is pressed to start the crushing process.

[0030] Specifically, when the grinding start button is pressed, the grinding container 4 itself starts to rotate, and within the sealed grinding container 4, the grinding media, specifically rigid balls (for example, 5mmφ high-hardness balls (such as SUS440C or chromium steel)) and the magnesium to be ground are vigorously agitated by the rotational force, and the grinding process proceeds.

[0031] Furthermore, as mentioned above, the grinding container 4 is designed to be completely airtight, so no outside air enters during grinding.

[0032] Therefore, if the work of placing the material to be crushed (not shown) and spherical crushing media (not shown) to promote crushing into the crushing container body 41, and then fixing the lid 42 to the crushing container body 41 with screws (not shown) is performed in a glove box under an argon gas atmosphere, the inside of the crushing container 4 will be under an argon gas atmosphere, and crushing can be performed under an argon gas atmosphere.

[0033] Furthermore, if the work of placing the material to be crushed (not shown) and spherical crushing media (not shown) to promote crushing into the crushing container body 41, and then fixing the lid 42 to the crushing container body 41 with screws (not shown) is performed in a glove box under a nitrogen gas atmosphere, the inside of the crushing container 4 will be under a nitrogen gas atmosphere, and crushing can be performed under a nitrogen gas atmosphere.

[0034] Then, once the crushing process is complete, the crushing container 4 is removed from the main body 2 of the crusher, the crushing container 4 is moved into the glove box, and the crushed material is transferred to an airtight bottle inside the glove box that prevents outside air from entering, and the crushed material is collected.

[0035] Furthermore, if this recovery operation is carried out in a glove box with an argon gas atmosphere, the crushed material will be stored in an airtight bottle filled with argon gas. If the operation is carried out in a glove box with a nitrogen gas atmosphere, the crushed material will be stored in an airtight bottle filled with nitrogen gas.

[0036] Furthermore, as will be described later, by adding fatty acids when placing the magnesium to be crushed into the crushing container 4, the crushing process can be carried out in which fatty acids are added to crush the magnesium, resulting in highly reactive crushed magnesium with good hydrogenation efficiency.

[0037] The reason for the increased reactivity is that fatty acids contain carboxyl groups, and these carboxyl groups react with the oxygen in metal oxides (for example, the oxygen in the oxide film formed on the surface of magnesium) to form metal soaps, which have significantly lower melting points, boiling points, and hardness than metal oxides. It is therefore presumed that this reaction contributes to the formation of highly reactive pulverized magnesium with good hydrogenation efficiency. Furthermore, fatty acids are thought to react with metals themselves, forming metal soaps.

[0038] For example, suitable fatty acids to be added include butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, eicosanoic acid, henicosanoic acid, docosanoic acid, tetracosanoic acid, hexacosanoic acid, octacosanoic acid, triacontanoic acid, and others.

[0039] However, shorter alkyl chains result in weaker hydrophobicity and increased water absorption, requiring careful handling to prevent water absorption. Conversely, longer alkyl chains increase the melting point, making it difficult to melt fatty acids during the pulverization process due to temperature increases, thus hindering their addition to magnesium.

[0040] Therefore, it is considered that fatty acids with a total number of carbon atoms of approximately 7 to 30 are more preferable, namely heptanoic acid (7 carbon atoms), octanoic acid (8 carbon atoms), nonanoic acid (9 carbon atoms), decanoic acid (10 carbon atoms), dodecanoic acid (12 carbon atoms), tetradecanoic acid (14 carbon atoms), pentadecanoic acid (15 carbon atoms), hexadecanoic acid (16 carbon atoms), heptadecanoic acid (17 carbon atoms), octadecanoic acid (18 carbon atoms), eicosanoic acid (20 carbon atoms), henicosanoic acid (21 carbon atoms), docosanoic acid (22 carbon atoms), tetracosanoic acid (24 carbon atoms), hexacosanoic acid (26 carbon atoms), octacosanoic acid (28 carbon atoms), and triacontanoic acid (30 carbon atoms).

[0041] (Hydrogenator) Figure 5 is a side view showing a hydrogenation furnace 8 of the first embodiment according to the present invention. Figure 5 shows the heating furnace 81 as a cross-sectional view for easier understanding of the explanation. Furthermore, in Figure 5, for the sake of clarity, the mounting position of clamp 824 is only indicated by a dotted line; the clamp actually used is a commercially available clamp that clamps NW standard flanges.

[0042] As shown in Figure 5, the hydrogenation furnace 8 comprises a reaction vessel 82 for carrying out the hydrogenation reaction of pulverized magnesium, a heating furnace 81 that can detachably receive the reaction vessel 82 and heat the temperature inside the reaction vessel 82 to a temperature suitable for hydrogenation, and a pressure regulating tank 83 that controls the hydrogen gas pressure to be maintained at a predetermined pressure and is connected to the reaction vessel 82 via a flexible gas piping FGP so that the hydrogen gas can be supplied to it.

[0043] The reaction vessel 82 has a flange portion 8211 supported by the heating furnace 81 on its outer circumference at an intermediate position in the vertical direction, and comprises a reaction vessel body 821 with an opening at the top to accommodate crushed magnesium, a lid portion 822 for closing the upper opening, an O-ring 823 positioned on the edge of the opening side of the reaction vessel body 821 and sandwiched between the reaction vessel body 821 and the lid portion 822 to create an airtight seal, and a clamp 824 for fixing the O-ring 823 so as to be pressed by the reaction vessel body 821 and the lid portion 822.

[0044] Furthermore, the lid portion 822 is equipped with an intake / exhaust port 8221 that can be opened and closed by operating the needle valve N1, which is attached to the flexible gas piping FGP.

[0045] The heating furnace 81 comprises an insulated housing 811 having an opening for receiving the reaction vessel body 821, a heater section 812 provided inside the insulated housing 811, and a temperature controller (not shown) that controls the heater section 812 to maintain a set temperature. The opening for receiving the reaction vessel body 821 is set to have an inner diameter slightly smaller than the outer diameter of the flange section 8211 so as to support the flange section 8211 of the reaction vessel body 821.

[0046] However, the opening for receiving the reaction vessel body 821 is set to have an inner diameter larger than the outer diameter of the body of the reaction vessel body 821 so that the reaction vessel body 821 can be received.

[0047] The temperature controller includes a temperature measuring unit (for example, a thermocouple) that measures the temperature of the heater unit 812, and a power control unit that controls the power supplied to the heater unit 812 based on the results of the temperature measurement to maintain the set temperature.

[0048] The pressure regulating tank 83 is a stainless steel tank with a sealed structure for containing gas, and includes a mounting port PT1 for mounting a digital pressure gauge DP for measuring the pressure inside the tank, a hydrogen gas receiving port PT2 for receiving hydrogen gas and equipped with an on / off valve OCB2, an argon gas receiving port PT3 for receiving argon gas and equipped with an on / off valve OCB3, a gas supply port PT4 for which a needle valve N2 is installed and to which a flexible gas pipe FGP is connected for sending the gas inside the tank to the reaction vessel 82, and an exhaust port PT5 for which an on / off valve OCB5 is installed and connected to a vacuum pump P2 used when replacing the gas inside the tank.

[0049] Furthermore, the hydrogen gas supply to the pressure adjustment tank 83 is configured such that the hydrogen gas, which has been reduced to a pressure of 0.2 to 0.3 MPa (the operating pressure of the mass flow controller) by the pressure reducing valve of the high-pressure hydrogen gas cylinder B2, is supplied via the hydrogen gas mass flow controller MFC-H, which is connected by piping to the hydrogen gas receiving port PT2.

[0050] Furthermore, the supply of argon gas to the pressure adjustment tank 83 is configured such that argon gas, which has been reduced to a pressure of 0.2 to 0.3 MPa (the operating pressure of the mass flow controller) by the pressure reducing valve of the high-pressure argon gas cylinder B3, is supplied via the argon gas mass flow controller MFC-A, which is connected by piping to the argon gas receiving port PT3.

[0051] Furthermore, the hydrogenation reactor 8 is equipped with a control device for controlling the gas supply, and specifically, it uses a sequencer PLC, which is a controller capable of building control programs for this device. In Figure 5, the dashed lines connecting the sequencer PLC, the digital pressure gauge DP, the hydrogen gas mass flow controller MFC-H, and the argon gas mass flow controller MFC-A indicate that they are connected by signal lines that transmit input and output signals.

[0052] The control program for the sequencer PLC includes a direct input mode in which the sequencer PLC's LCD screen displays the mass flow controller and flow rate to be operated, and controls the specified mass flow controller (hydrogen gas mass flow controller MFC-H, argon gas mass flow controller MFC-A) to flow at that flow rate; and a pressure control mode in which the sequencer's LCD screen displays the mass flow controller and upper and lower pressure limits to be operated, and when the output value of the digital pressure gauge DP falls below the lower pressure limit, the specified mass flow controller is operated to supply gas at a preset flow rate.

[0053] In pressure control mode, when the output value of the digital pressure gauge DP reaches the upper limit of the pressure due to the gas supply, the mass flow controller stops operating and the gas supply is cut off.

[0054] Furthermore, although the above explanation describes a configuration in which argon gas can be supplied to the hydrogenation reactor 8, there is no problem in changing the argon gas to nitrogen gas. In this case, the high-pressure argon gas cylinder B3 should be replaced with a high-pressure nitrogen gas cylinder, or a nitrogen generator that produces nitrogen gas with a purity of 99.9% or higher from the atmosphere, and the argon gas mass flow controller MFC-A should be replaced with a nitrogen gas mass flow controller.

[0055] (Operating procedures in a hydrogenation reactor) Next, we will explain the work procedure (hydrogenation process procedure) using the hydrogenation furnace 8 as described above. Figure 6 is a flowchart showing the procedure of the hydrogenation process according to the first embodiment of the present invention. The following explanation assumes that argon gas is supplied to the hydrogenation reactor 8. However, as explained earlier, there is no problem in substituting nitrogen gas for argon gas. In that case, simply read the descriptions regarding argon gas as referring to nitrogen gas.

[0056] Prior to explaining the hydrogenation process procedure, it should be assumed that the reaction vessel 82 is filled with argon gas at atmospheric pressure from the pressure adjustment tank 83, and that the on / off valves OCB2, OCB3, and OCB5 attached to the hydrogen gas receiving port PT2, the argon gas receiving port PT3, and the exhaust port PT5 are in the closed position. Furthermore, the needle valves N1 and N2 attached to the intake / exhaust port 8221 of the lid 822 and the gas supply port PT4 are assumed to be in a closed state.

[0057] (Step 1) First, the reaction vessel 82 is removed from the hydrogenation furnace 8 (S1). Specifically, the needle valve N1 attached to the intake / exhaust port 8221 of the lid 822 and the flexible gas piping FGP are disconnected, and the reaction vessel 82 is removed from the hydrogenation furnace 8.

[0058] Although disconnecting the connection would allow outside air (atmosphere) to enter the flexible gas piping FGP, the reaction vessel 82 is in a closed state because the needle valve N1 attached to the intake / exhaust port 8221 of the lid 822 is closed. Similarly, since the needle valve N2 is also closed, no outside air enters the pressure regulating tank 83.

[0059] (Step 2) Next, the removed reaction vessel 82 is placed inside the glove box, and the material to be crushed in the crushing process (specifically, crushed magnesium) is placed inside the reaction vessel 82 (S2).

[0060] Specifically, the clamp 824 of the reaction vessel 82 is removed inside the glove box, the lid 822 is removed from the reaction vessel body 821, and the crushed magnesium is placed into the reaction vessel body 821 through the opening on the top of the reaction vessel body 821. Next, the lid 822 is installed to close the upper opening of the reaction vessel body 821, and the clamp 824 is attached to create a sealed state so that outside air (atmosphere) cannot enter the reaction vessel 82.

[0061] Furthermore, if the glove box is kept in an argon gas atmosphere during the process of placing the crushed magnesium into the reaction vessel 82, the reaction vessel 82 containing the crushed magnesium will be filled with argon gas.

[0062] Similarly, when the process of placing the crushed magnesium into the reaction vessel 82 is carried out inside the glove box, if the inside of the glove box is kept under a nitrogen gas atmosphere, the reaction vessel 82 containing the crushed magnesium will be filled with nitrogen gas.

[0063] (Step 3) Next, the reaction vessel 82 containing the crushed magnesium is reattached to the heating furnace 8 (S3). Specifically, as shown in Figure 5, the reaction vessel 82, which is filled with atmospheric gas inside the glove box, is installed such that the flange portion 8211 of the reaction vessel body 821 is supported by the insulated housing 811, and the needle valve N1 attached to the intake / exhaust port 8221 of the lid portion 822 is connected to the flexible gas piping FGP.

[0064] (Step 4) Next, the outside air (atmosphere) mixed in the flexible gas piping FGP, the argon gas in the pressure adjustment tank 83, and the gas in the reaction vessel 82 are evacuated, and a vacuum is created to make it possible to fill with hydrogen gas (S4).

[0065] First, the vacuum pump P2 is activated, and the on / off valve OCB5 attached to the exhaust port PT5 is opened to begin evacuating the argon gas from the pressure regulating tank 83.

[0066] Next, the needle valve N2 attached to the gas supply port PT4 is opened to exhaust the outside air (atmosphere) mixed in the flexible gas piping FGP.

[0067] Then, wait in this state for a while until all the outside air (atmosphere) mixed in with the flexible gas piping (FGP) is completely expelled.

[0068] After sufficiently evacuating the system (for example, to a few Pa), the needle valve N1 attached to the intake / exhaust port 8221 of the lid 822 is slowly turned to the open position.

[0069] The needle valve N1 attached to the intake / exhaust port 8221 is slowly turned to open in order to gently exhaust the gas from the reaction vessel 82 so as not to draw in the crushed magnesium inside the reaction vessel 82.

[0070] (Step 5) Once the reaction vessel 82 is under vacuum, a hydrogenation treatment is carried out by heating the pulverized magnesium to a temperature at which hydrogenation can proceed under a hydrogen gas atmosphere (S5).

[0071] First, before actually supplying hydrogen gas and performing the hydrogenation process, the heater section 812 of the heating furnace 81 is turned ON while the vacuum is still being maintained, and the heating of the crushed magnesium is started. The set temperature of the heater section 812 may be any temperature that is suitable for heating the crushed magnesium to a temperature suitable for hydrogenation.

[0072] Specifically, when the hydrogen gas pressure is around 90 kPa (approximately 0.9 atmospheres), the hydrogenation reaction slows down rapidly below 140°C, so it is desirable to keep the heating temperature above 140°C. A range of approximately 220°C ± 40°C provides relatively good hydrogenation efficiency. Therefore, in the first embodiment, the set temperature of the heater section 812 is set to the temperature at which the pulverized magnesium is heated to 220°C.

[0073] In this way, by starting the heating process under vacuum, excess fatty acids added during the grinding process that adhere to the surface of the ground magnesium can be removed, preventing a decrease in hydrogenation efficiency due to the influence of these fatty acids.

[0074] However, if the amount of fatty acid added is not large, the heat treatment of heating the crushed magnesium while vacuuming may be omitted. In other words, it is also possible to supply hydrogen gas first and then start heating.

[0075] Next, the on / off valve OCB5 attached to the exhaust port PT5 is closed to stop the operation of the vacuum pump P2, and then the on / off valve OCB2 attached to the hydrogen gas receiving port PT2 is opened to start the pressure control mode of the sequencer PLC.

[0076] In the first embodiment, the hydrogen gas pressure is controlled to approximately 90 kPa (approximately 0.9 atmospheres). The upper and lower limits of the controlled pressure are set to 89 kPa and 91 kPa, respectively. When the output value of the digital pressure gauge DP reaches 91 kPa, the hydrogen gas mass flow controller MFC-H stops operating, and the hydrogen gas supply is halted.

[0077] As hydrogenation progresses, hydrogen gas is incorporated into the pulverized magnesium, causing the pressure in the pressure adjustment tank 83 to decrease, and the output value of the digital pressure gauge DP becomes 89 kPa.

[0078] Then, the hydrogen gas mass flow controller MFC-H is activated again, and hydrogen gas is supplied until the output value of the digital pressure gauge DP reaches 91 kPa.

[0079] In this way, while maintaining the hydrogen gas atmosphere pressure at approximately 90 kPa, the pulverized magnesium is heated to approximately 220°C for a predetermined time during the hydrogenation process. Then, the heater unit 812 of the heating furnace 81 is turned OFF, and the pressure control mode of the sequencer PLC is terminated, ending the hydrogenation process.

[0080] (Step 6) After the hydrogenation process is complete, the hydrogenated material (magnesium hydride) is removed. However, since the pressure adjustment tank 83 and the reaction vessel 82 are filled with hydrogen gas, the gas is first replaced with argon gas (S6).

[0081] Specifically, after closing the on / off valve OCB2 attached to the hydrogen gas receiving port PT2, the vacuum pump P2 is started, and the on / off valve OCB5 attached to the exhaust port PT5 is opened.

[0082] After sufficient vacuuming is performed, the on / off valve OCB5 attached to the exhaust port PT5 is closed to stop the operation of the vacuum pump P2, and the on / off valve OCB3 attached to the argon gas receiving port PT3 is opened to supply argon gas until atmospheric pressure is reached.

[0083] Once the pressure in the pressure adjustment tank 83 and the reaction vessel 82 has been filled with argon gas until the pressure reaches atmospheric pressure, the supply of argon gas is stopped and the on / off valve OCB3 attached to the argon gas receiving port PT3 is closed.

[0084] At this time, the needle valve N1 attached to the intake / exhaust port 8221 of the lid 822 of the reaction vessel 82, and the needle valve N2 attached to the gas supply port PT4 of the pressure adjustment tank 83 are closed, and the gas replacement operation is completed.

[0085] (Step 7) After the gas exchange is complete, the final step is to remove the magnesium hydride, which is the material after hydrogenation (S7). Since magnesium hydride is relatively stable in the atmosphere as long as it is not exposed to moisture, it is not necessary to do so in the glove box used when placing the crushed magnesium into the reaction vessel 82.

[0086] However, if the work is performed inside a glove box, the magnesium hydride can be extracted in an extremely low-humidity environment. Therefore, the magnesium hydride may be recovered and stored in airtight containers inside a glove box under a nitrogen or argon gas atmosphere.

[0087] Thus, once the magnesium hydride, the material after hydrogenation, has been removed from the reaction vessel 82, the hydrogenation process is complete.

[0088] Here, we will briefly explain the hydrogen gas atmosphere and heating conditions for the hydrogenation treatment. Figure 7 is a graph showing the decomposition boundary of magnesium hydride, as determined by thermodynamic calculations. The temperature at this decomposition boundary is sometimes referred to as the decomposition boundary temperature. The graph shown in Figure 7 has the pressure of the hydrogen gas atmosphere (in Pa) on the vertical axis and the temperature (in °C) on the horizontal axis. It graphs the lowest temperature at which magnesium hydride decomposition begins at each pressure.

[0089] In other words, on the right side (high temperature side) of the magnesium hydride decomposition and formation boundary line BL, magnesium hydride decomposes into magnesium and hydrogen gas, while on the left side (low temperature side), decomposition of magnesium hydride does not occur, and if magnesium and hydrogen gas are present, the formation reaction to produce magnesium hydride proceeds.

[0090] In the first embodiment, the pressure of the hydrogen gas atmosphere is set to approximately 90 kPa, which is slightly lower than 100,000 Pa, and the temperature on the magnesium hydride decomposition boundary line BL is around 280°C.

[0091] However, since the actual heating temperature is around 220°C, it is sufficient to use a temperature approximately 60°C lower than the temperature at the magnesium hydride decomposition boundary line BL.

[0092] From this, for example, in the case of processing in a hydrogen gas atmosphere of 5 atm (5 atmospheres) as shown by the dotted line on the graph, the temperature on the magnesium hydride decomposition and formation boundary line BL is approximately 350°C, so it can be considered that the actual heating temperature can be 300°C or lower.

[0093] On the other hand, as shown in prior art literature, if we attempt to perform processing at a temperature about 50°C higher than the temperature on the magnesium hydride decomposition boundary line BL, the temperature will be heated to over 400°C in a hydrogen gas atmosphere of 5 atm (5 atmospheres), in which case radiant heat will be dominant.

[0094] Furthermore, while metal materials such as stainless steel are generally used for the reaction vessel 82, using stainless steel or similar materials is thought to reduce heat transfer efficiency and increase energy loss because radiation is reflected.

[0095] However, by implementing a grinding process in which fatty acids are added and magnesium is ground, it is possible to produce magnesium hydride of sufficiently high purity without requiring processing at a temperature approximately 50°C higher than the temperature on the magnesium hydride decomposition boundary line BL as shown in prior art literature.

[0096] Therefore, by keeping the hydrogen gas atmosphere pressure in the hydrogenation process below 5 atm (5 atmospheres), hydrogenation can be performed in the low-temperature range of 100°C or higher, from approximately 400°C where radiant heat is dominant, resulting in an energy-efficient hydrogenation process.

[0097] Furthermore, because processing is possible at relatively low pressures of 5 atm (5 atmospheres) or less, there is no need to increase the thickness of the reaction vessel 82 for pressure resistance, which allows for good heat transfer and efficient heating of the pulverized magnesium. In this respect as well, it is considered to be energy efficient.

[0098] On the other hand, thermodynamic calculations suggest that magnesium hydride can exist stably even at low temperatures. However, thermodynamic calculations lack a reaction rate factor, and when the heating temperature of magnesium falls below 140°C, the pressure decrease observed in the hydrogenation process due to the absorption of hydrogen gas into the magnesium slows down considerably.

[0099] Therefore, in the hydrogenation process, it is preferable to heat the magnesium to a temperature of 140°C or higher.

[0100] Specifically, the dashed line in the graph of Figure 7 represents 500 Pa. In this case, the temperature on the magnesium hydride decomposition boundary line BL is approximately 150°C. Therefore, if the pressure of the hydrogen gas atmosphere is increased to 500 Pa or higher, magnesium hydride will not decompose at a temperature of 140°C.

[0101] Therefore, the hydrogenation process is preferably carried out by heating the pulverized magnesium to a temperature of 140°C or higher and below the decomposition temperature of magnesium hydride under a hydrogen gas pressure of 500 Pa or higher and 5 atmospheres or lower. This allows the process to be carried out at a temperature range 100°C or higher below 400°C, where the effect of radiant heat becomes strong, and also eliminates the need to increase the thickness of the reaction vessel 82, resulting in good heat transfer and an energy-efficient process.

[0102] For example, if the hydrogen gas pressure in the hydrogenation process is less than 0.2 MPa, there is no legal requirement for periodic inspections. Furthermore, since higher pressures, such as 30 kPa (approximately 0.3 atmospheres) or more, are preferable for promoting hydrogenation, it is more preferable to perform the hydrogenation treatment in the hydrogenation process by heating pulverized magnesium under a hydrogen gas pressure of 30 kPa or more and less than 0.2 MPa.

[0103] Next, Example 1 and Comparative Example 1 will be described. In the grinding process of Example 1 and Comparative Example 1, in both cases, the grinding conditions involved adding rigid balls made of high-hardness stainless steel (SUS440C) with a diameter of 5 mm in diameter to occupy 1 / 3 of the internal volume of the grinding container 4, and similarly adding 70 g of magnesium with an average particle size of 180 μm to occupy 1 / 3 of the internal volume.

[0104] Furthermore, when adding magnesium to the grinding container 4, octadecanoic acid is added as a fatty acid, so that the grinding process involves adding a fatty acid to grind the magnesium.

[0105] Specifically, in both Example 1 and Comparative Example 1, magnesium (70g) and octadecanoic acid (3.684g) were placed in the grinding container 4, and 5% by mass (wt%) of octadecanoic acid (fatty acid) was added to the total mass of magnesium and octadecanoic acid (73.684g), resulting in a grinding process in which 5% by mass (wt%) of octadecanoic acid was added to grind the magnesium.

[0106] In both Example 1 and Comparative Example 1, the operation of the pulverizer 1 involved running it at a rotational speed of 330 rpm for 1 hour, followed by a 1-hour stop, and repeating this cycle 24 times, so that the pulverizing container 4 was rotating for 24 hours in total.

[0107] The reason for the one-hour shutdown after one hour of operation is to suppress the temperature rise of the grinding container 4 used for grinding, and the manufacturer recommends using it so that the temperature does not exceed 100°C.

[0108] In Example 1, the process of placing magnesium, fatty acids, and rigid balls into the grinding container 4 was carried out in a glove box with a nitrogen gas atmosphere, thereby creating a nitrogen gas atmosphere inside the grinding container 4 and performing the grinding process under a nitrogen gas atmosphere.

[0109] In order to create a nitrogen gas atmosphere inside the glove box, nitrogen gas generated by a nitrogen generator (manufactured by Hitachi Industrial Systems Co., Ltd.) that produces 99.9% pure nitrogen gas from the atmosphere was supplied to the gas receiving port of the glove box. The oxygen concentration meter installed inside the glove box was set to display 0%, and under these conditions, magnesium, fatty acids, and rigid balls were placed into the grinding container 4.

[0110] Furthermore, in Example 1, the process of collecting the crushed magnesium into an airtight bottle after crushing was also carried out in a glove box with a nitrogen gas atmosphere created by nitrogen gas from a nitrogen generator.

[0111] On the other hand, in Comparative Example 1, the process of placing magnesium, fatty acids, and rigid balls into the grinding container 4 was carried out in a glove box with an argon gas atmosphere, thereby creating an argon gas atmosphere inside the grinding container 4, and the grinding process was carried out under an argon gas atmosphere.

[0112] In order to create an argon gas atmosphere inside the glove box, argon gas from a high-purity argon cylinder was supplied to the gas receiving port of the glove box, and the oxygen concentration meter installed inside the glove box was set to display 0%. Under these conditions, magnesium, fatty acids, and rigid balls were placed into the grinding container 4.

[0113] In Comparative Example 1, the process of collecting the crushed magnesium into an airtight bottle after crushing was also carried out in a glove box with an argon gas atmosphere created by argon gas from a high-purity argon cylinder.

[0114] Next, the hydrogenation process of the pulverized magnesium from Example 1 and Comparative Example 1 was carried out according to the procedure described earlier.

[0115] However, in Example 1, the process of transferring the pulverized magnesium from the airtight bottle to the reaction vessel 82 of the hydrogenation furnace 8, that is, the process of placing the pulverized magnesium in the airtight bottle into the reaction vessel 82 of the hydrogenation furnace 8, was carried out in a glove box under a nitrogen gas atmosphere, and the process of placing the magnesium was carried out under a nitrogen gas atmosphere.

[0116] On the other hand, in Comparative Example 1, the process of transferring the pulverized magnesium from the airtight bottle to the reaction vessel 82 of the hydrogenation furnace 8, that is, the process of placing the pulverized magnesium in the airtight bottle into the reaction vessel 82 of the hydrogenation furnace 8, was carried out in a glove box under an argon gas atmosphere, and the process of placing the magnesium was carried out under an argon gas atmosphere.

[0117] The specific conditions for the hydrogenation treatment were the same in both Example 1 and Comparative Example 1. Specifically, the heater unit 812 was turned ON while the system was under vacuum, and the vacuum state was maintained until the set temperature was reached. Once the set temperature was reached, hydrogen gas was supplied, and the hydrogen gas atmosphere pressure was maintained at approximately 90 kPa (approximately 0.9 atmospheres) for 4 hours of heating (hydrogenation treatment). After turning OFF the heater unit 812, the system was cooled to room temperature, and the hydrogenated magnesium was removed.

[0118] As can be seen from the above explanation, in Example 1, the pulverized magnesium was only exposed to nitrogen gas and hydrogen gas from the pulverization process to the end of the hydrogenation process, while in Comparative Example 1, the pulverized magnesium was only exposed to argon gas and hydrogen gas from the pulverization process to the end of the hydrogenation process.

[0119] Therefore, in both Example 1 and Comparative Example 1, the magnesium was handled in such a way that it did not come into contact with the atmosphere from the grinding process to the end of the hydrogenation process, and the ground magnesium was kept from coming into contact with oxygen until the end of the hydrogenation process, so that the reactivity of the magnesium, which was enhanced by the grinding process, would not deteriorate due to the influence of the atmosphere (mainly oxygen).

[0120] Next, the hydrogenated and pulverized magnesium from Example 1 and Comparative Example 1 were subjected to an X-ray diffractometer (XRD apparatus) to determine the hydrogenation rate, that is, the magnesium hydride content in the hydrogenated and pulverized magnesium. The results showed that the average hydrogenation rate for Example 1 was 22.8% by mass (wt%), and the average hydrogenation rate for Comparative Example 1 was 7.6% by mass (wt%).

[0121] The average hydrogenation rate refers to the average hydrogenation rate that includes the variation in particle size within the crushed magnesium, even though hydrogenation efficiency is thought to be particle size-dependent, meaning that hydrogenation progresses more rapidly with smaller particles. This average hydrogenation rate is calculated without any sieving or other filtering processes.

[0122] Furthermore, since the hydrogenation reaction is thought to proceed from the surface of the pulverized magnesium towards the center, the results of Example 1 suggest that, when considering the entire pulverized magnesium, hydrogenation progressed to a depth where a hydrogenation rate of 22.8% by mass (wt%) could be achieved from the surface.

[0123] Therefore, if the magnesium is pulverized to particles with a diameter approximately twice the depth to which the pulverization progressed, specifically by reducing the particle size (average particle size) of the magnesium to about 1 / 13 of that of the pulverized magnesium in Example 1, it is expected that magnesium hydride close to 100% by mass (wt%) can be obtained under the same hydrogenation conditions as in Example 1.

[0124] For example, in a planetary ball mill, a larger diameter of the rigid balls used to promote grinding results in a faster grinding speed, but also a larger limit particle size achievable through grinding. Conversely, a smaller diameter of the rigid balls results in a slower grinding speed, but also a smaller limit particle size achievable through grinding. Therefore, it is thought that an even higher hydrogenation rate can be obtained by performing additional grinding using rigid balls with a smaller diameter.

[0125] Generally, it is said that the presence of nitride and oxide films on the surface of magnesium makes hydrogenation difficult. However, the above results show that even when the grinding process for magnesium is carried out in an atmosphere of nitrogen gas generated by a nitrogen generator, the hydrogenation efficiency does not deteriorate. On the contrary, surprisingly, better hydrogenation efficiency was obtained than when the grinding process was carried out in argon gas.

[0126] Furthermore, generating nitrogen gas using a nitrogen generator is cheaper than purchasing and using nitrogen gas in gas cylinders. Therefore, when nitrogen gas usage increases due to the enlargement of crushers and other equipment, it is preferable to use nitrogen gas generated by a nitrogen generator, as this can significantly reduce running costs.

[0127] Furthermore, in Example 1, the containment process of placing the pulverized magnesium into the reaction vessel 82 of the hydrogenation furnace 8 was also carried out under a nitrogen gas atmosphere, and even when such work is performed under a nitrogen gas atmosphere, the hydrogenation efficiency does not deteriorate.

[0128] Next, we will describe Example 2, in which the amount of fatty acids added during the grinding process was increased. In Example 2, octadecanoic acid was used as the fatty acid, and the magnesium used was the same as in Example 1.

[0129] In Example 2, magnesium (70g) and octadecanoic acid (6.923g) were placed in the grinding container 4, and the grinding process involved adding 9% by mass (wt%) of octadecanoic acid to the total combined mass of magnesium and octadecanoic acid (76.923g) to grind the magnesium.

[0130] Note that Example 2 is the same as Example 1 except for the amount of fatty acid added.

[0131] In other words, Example 2 is identical to Example 1 in every way, except for the amount of fatty acid added from the grinding process to the hydrogenation process.

[0132] Then, the hydrogenation rate, or the magnesium hydride content in the hydrogenated and pulverized magnesium of Example 2, was determined by using an X-ray diffractometer (XRD apparatus). The average hydrogenation rate was 54.2% by mass (wt%), and by increasing the amount of fatty acid added, an even higher hydrogenation rate was obtained than in Example 1.

[0133] Thus, increasing the amount of fatty acids added during the grinding process significantly improves the reactivity of the ground magnesium. However, it is presumed that adding too much fatty acid will increase the time required to remove the organic compound film during vacuum heating in the hydrogenation process.

[0134] Furthermore, while fatty acids liquefy at the temperature during grinding, adding them in excess may cause the liquefied fatty acids to act as a lubricant, reducing frictional resistance during grinding and potentially decreasing the grinding speed.

[0135] Therefore, the amount of fatty acids added should be limited to 15% by mass or less of the total mass of magnesium and fatty acids combined, and even more preferably to 14% by mass or less.

[0136] On the other hand, fatty acids also have the effect of suppressing the aggregation of magnesium particles during the grinding process. Therefore, it is best to add at least 3% by mass of fatty acids to the total mass of magnesium and fatty acids combined during the grinding process.

[0137] Furthermore, as can be seen in Examples 1 and 2, increasing the amount of fatty acids added in the grinding process improves the hydrogenation rate. Therefore, in the grinding process, it is preferable to add fatty acids in an amount of 4% by mass or more of the total mass of magnesium and fatty acids combined. Moreover, it is preferable to add 5% by mass or more, 6% by mass or more, 7% by mass or more, 8% by mass or more, 9% by mass or more, and 10% by mass or more, in that order of increasing amount.

[0138] Although specific embodiments have been described above, the present invention is not limited to these specific embodiments. The above description assumes the use of a ball mill device in the pulverizer 1. However, for example, a bead mill device capable of continuous processing for large-scale pulverization, such as those provided by Ashizawa Fine Tech Co., Ltd. or Nippon Coke Industries Co., Ltd., may also be used in the pulverizer 1.

[0139] Furthermore, while continuous processing bead mill equipment naturally has an airtight structure to prevent the pulverized powder from scattering to the outside, it is not a completely sealed structure. Therefore, in addition to using nitrogen gas to increase hydrogenation efficiency, it is also necessary to supply a large amount of nitrogen gas to suppress the decrease in reactivity of the highly reactive pulverized magnesium by preventing outside air (mainly oxygen from the atmosphere) from entering the pulverizing section and the pulverized powder recovery section. In such cases, using nitrogen gas generated by a nitrogen generator can significantly reduce running costs.

[0140] Thus, the present invention is not limited to specific embodiments, and modifications and improvements made as appropriate are also included within the technical scope of the present invention, which will be clear to those skilled in the art from the description of the claims. [Explanation of symbols]

[0141] 1. Crusher 2. Crusher body 21 Condition Input Section 22 Emergency Stop Button 3 Food 4. Grinding container 41 Grinding container body 411 Groove 412 Screw thread holes 42 Lid 421 Through hole 5 O-rings 8 Hydrogen reactor 81 Heating furnace 811 Insulated enclosure 812 Heater section 82 Reaction vessel 821 Reaction vessel body 8211 Flange section 822 Lid 8221 Intake and Exhaust Ports 823 O-ring 824 Clamp 83 Pressure regulating tank B1 High-pressure gas cylinder B2 Hydrogen gas cylinder B3 Argon gas cylinder BL decomposition production boundary line DP Digital Pressure Gauge FGP gas piping MFC-A Argon Gas Mass Flow Controller MFC-H Mass Flow Controller for Hydrogen Gas N, N1, N2 Needle Valves OCB2, OCB3, OCB5 Shut-off valves P1, P2 Vacuum Pumps PLC (Programmable Logic Controller) PT1 mounting port PT2 receiving port PT3 receiving port PT4 gas supply port PT5 Exhaust Port

Claims

1. A method for producing magnesium hydride, comprising the steps of: a grinding step of grinding the magnesium by adding a fatty acid; A hydrogenation step of heating the pulverized magnesium to a temperature of 140° C. or higher and lower than the decomposition temperature of magnesium hydride in a reaction vessel to which hydrogen gas is supplied so as to maintain a pressure of 5 atmospheres or lower, The grinding step is carried out under a nitrogen gas atmosphere, A method for producing magnesium hydride, wherein the ground magnesium is not exposed to oxygen until the end of the hydrogenation step.

2. The method for producing magnesium hydride according to claim 1, wherein the nitrogen gas is supplied from a nitrogen generator that produces nitrogen gas with a purity of 99.9% or higher from the atmosphere.

3. The method for producing magnesium hydride according to claim 1 or 2, wherein the amount of the fatty acid added in the grinding step is 3 mass% or more of the total mass of the magnesium and the fatty acid.

4. The number of carbon atoms of the fatty acid is 7 or more and 30 or less. The method for producing magnesium hydride according to any one of claims 1 to 3.

5. In the grinding step, the oxide film of the magnesium is scraped off to expose the magnesium surface. The method for producing magnesium hydride according to any one of claims 1 to 4.

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