JP4711644B2 - Metal amide compound and method for producing the same - Google Patents

Description

  The present invention relates to a metal amide compound used as a raw material for producing a hydrogen storage material that generates hydrogen used as a fuel for a fuel cell or the like, and a method for producing the metal amide compound.

NO _X and development of fuel cells have been actively as a clean energy source that does not emit greenhouse gases such as toxic substances and CO ₂ in the SO _X or the like, and is already practiced in several areas. As an important technology that supports this fuel cell technology, there is a technology for storing hydrogen as fuel for the fuel cell. As storage forms of hydrogen, compression storage by high-pressure cylinders, cooling storage by liquid hydrogenation, and storage by hydrogen storage materials are known. Among these forms, storage by hydrogen storage materials is used for distributed storage and transportation. This is advantageous. Hydrogen storage materials include materials with high hydrogen storage efficiency, that is, materials with a high hydrogen storage amount per unit weight or volume of the hydrogen storage material, materials that absorb and release hydrogen at a low temperature, and good durability. A material having is desired.

Conventionally, as a hydrogen storage material, various materials such as metal materials such as rare earth, titanium, vanadium, and magnesium, lightweight inorganic compounds such as metal alanate (for example, NaAlH ₄ and LiAlH ₄ ), and carbon, etc. It has been known. In addition, for example, a hydrogen storage method using lithium nitride represented by the following formula (1) has also been reported (see, for example, Non-Patent Document 1).
Li ₃ N + 2H ₂ ⇔Li ₂ NH + LiH + H ₂ ⇔LiNH ₂ + 2LiH (1)

Here, absorption of hydrogen by Li ₃ N started from about 100 ° C., and 9.3 mass% hydrogen absorption was confirmed at 255 ° C. for 30 minutes. In addition, it has been reported that the absorption characteristics of absorbed hydrogen pass through two steps: 6.3% by mass at less than 200 ° C. and 3.0% by mass at 320 ° C. or higher by slowly heating. . That is, the reaction of the following formula (2) corresponding to the right side portion of the above formula (1) starts to proceed at a little less than 200 ° C., and the reaction of the following formula (3) corresponding to the left side portion of the above formula (1) is about 320 It has been shown to begin to progress at ° C.
LiNH ₂ + 2LiH → Li ₂ NH + LiH + H ₂ ↑ (2)
Li ₂ NH + LiH → Li ₃ N + H ₂ ↑ (3)

However, the lithium nitride represented by the above formula (1) has a problem that the hydrogen release rate is slow. There is also a problem that the hydrogen release start temperature is high.
Ping Chen et al., Interaction ofhydrogen with metalnitrides and imides, NATURE Vol.420, 21 NOVEMBER 2002, p302〜304

In view of such circumstances, the inventors previously made a nanostructure of lithium amide (LiNH ₂ ) and lithium hydride (LiH) in Japanese Patent Application No. 2003-291672 to shift the hydrogen generation reaction temperature to the low temperature side. A hydrogen storage material has been disclosed. Here, as a method for producing lithium amide, there is a method of reacting lithium nitride with hydrogen gas as shown in the above formula (1).

  However, in such a method, since a metal hydride is formed simultaneously with the metal amide compound, it is difficult to isolate the metal amide compound. For this reason, it is difficult to increase the purity in the production of hydrogen storage materials having different metal amide compounds, or in the production of hydrogen storage materials having different metal species of the metal amide compound and the metal hydride. Further, in the reaction using hydrogen gas, safety measures for the manufacturing apparatus are indispensable, and there are problems that the manufacturing apparatus becomes expensive and that mass production is difficult. Furthermore, with metals other than lithium, there are many obstacles in synthesizing a metal amide compound, such as not causing such a reaction, or requiring a special apparatus for causing the reaction.

  In view of such circumstances, an object of the present invention is to provide a method for producing a metal amide compound capable of efficiently producing a metal amide compound alone, and a metal amide compound obtained by this production method. .

According to this invention, the manufacturing method of the metal amide compound characterized by making calcium hydride or magnesium hydride and ammonia react.

In the method for producing the metal amide compound, it is also preferable to add metal lithium to the calcium hydride or the magnesium hydride and react them with ammonia. Liquid ammonia is preferably used as the ammonia. In addition, this reaction is not preferable to carry out while pulverizing said metallic lithium and the calcium hydride or the magnesium hydride.

Moreover, according to this invention, the metal amide compound manufactured by adding metal lithium to the said calcium hydride or the said magnesium hydride, and making it react with the said ammonia is provided.

  According to the present invention, a highly pure metal amide compound can be easily produced by itself. Accordingly, for example, even when the metal constituting the metal hydride and the metal constituting the metal amide compound are different, the hydrogen storage material can be produced with high purity. Furthermore, a mixture of a plurality of types of metal amide compounds can be easily obtained.

Embodiments of the present invention will be described below.
In the present invention, a metal amide compound is produced by reacting a metal hydride with ammonia. Examples of metal hydrides include lithium hydride (LiH), sodium hydride (NaH), potassium hydride (KH), rubidium hydride (RbH), cesium hydride (CsH), magnesium hydride (MgH ₂ ), hydrogen Calcium hydride (CaH ₂ ), beryllium hydride (BeH ₂ ), strontium hydride (SrH ₂ ), barium hydride (BaH ₂ ), scandium hydride (ScH ₂ ), lanthanum hydride (LaH ₂ , LaH ₃ ), Examples thereof include titanium hydride (TiH ₂ ), vanadium hydride (VH _X ), yttrium hydride (YH ₃ , YH ₂ ), zirconium hydride (ZrH ₂ ), and neodymium hydride (NdH ₃ , NdH ₂ ). A mixture of two or more metal hydrides selected from these metal hydrides is also preferably used.

  The metal hydride preferably contains an alkali metal or alkaline earth metal hydride. This is because the metal amide compound obtained by the reaction has good hydrogen release characteristics.

  It is also preferable that the metal hydride is refined by a predetermined mechanical pulverization, and a metal amide compound having good hydrogen release characteristics can be obtained by reaction with ammonia. In the pulverization treatment of a single metal hydride or the mixing and pulverization treatment of a plurality of types of metal hydrides, it is possible to efficiently add an inorganic carrier, a synthetic carrier, a plant carrier, an organic solvent, etc. as a grinding aid. This is effective in reducing the size of the screen.

For example, the reaction between lithium hydride and ammonia (NH ₃ ) is represented by the following formula (4). The reaction between magnesium hydride and ammonia is represented by the following formula (5), and the reaction between calcium hydride and ammonia is represented by the following formula (6).
LiH + NH ₃ → LiNH ₂ + H ₂ ↑ (4)
MgH ₂ + 2NH ₃ → Mg (NH ₂ ) ₂ + 2H ₂ ↑ (5)
CaH ₂ + 2NH ₃ → Ca (NH ₂ ) ₂ + 2H ₂ ↑ (6)

  Liquid ammonia is preferably used as the ammonia. In this case, of course, the reaction temperature is kept below the boiling point of ammonia (about −33 ° C.). In order to increase the reaction efficiency, it is preferable to sufficiently stir the liquid ammonia.

  On the other hand, when gaseous ammonia is used, various organic solvents such as saturated aliphatic hydrocarbons such as pentane, hexane and cyclohexane, aromatic hydrocarbons such as benzene and toluene, alkyl halides such as chloroform, ethers and the like. The reaction is preferably carried out by dispersing the metal hydride in the active solvent and stirring the solvent in gaseous ammonia. This allows the metal hydride to react evenly. In addition, these solvents may be used independently and may mix and use 2 or more types. After the reaction, the product can be isolated by evaporating the solvent.

  As shown in the above formulas (4) to (6), the ammonia may be in the number of moles corresponding to the chemical equivalent with respect to 1 mole of the metal hydride. However, in order to accelerate the reaction, excess ammonia is used. It is preferable to do.

It is also preferable to mix a metal simple substance or alloy that reacts with ammonia and a metal hydride. Examples of such a simple metal or alloy include Li, Na, K, Be, Mg, and Ca. For example, the reaction between metallic lithium and ammonia is represented by the following formula (7).
2Li + 2NH ₃ → 2LiNH ₂ + H ₂ ↑ (7)

  By mixing the metal hydride and the metal simple substance or alloy, the synthesized metal amide compound is destabilized and the decomposition temperature of the synthesized metal amide compound is lowered. In addition, reacting these metals alone or metal alloys with ammonia without the presence of a metal hydride may require high temperature and high pressure (for example, in the case of magnesium metal), making it difficult to put it to practical use in operation. In addition, it is not preferable because it is not preferable in terms of energy efficiency.

  Any of a batch system, a semi-batch system, and a continuous system may be employed for the reaction of the metal amide compound described above.

In a high-purity argon glove box, 400 g ³ of a stainless steel microreactor was charged with 10 g (0.24 mol) of calcium hydride (Aldrich, purity: 95%), sealed, and then dried. The mixture was cooled to below the boiling point of ammonia with ice-methanol cryogen, and about 10 g (about 0.60 mol) of liquid ammonia was supplied from the cylinder to the microreactor and continuously stirred for 5 hours.

  Thereafter, the microreactor is returned to room temperature, the pressure of the gas after the reaction including the gasified ammonia is measured, a certain amount is sampled, and the composition analysis is performed by a gas chromatograph apparatus (manufactured by Shimadzu Corporation, GC9A, TCD detector, Column: Analyzed using Molecular Sieve 5A). As a result, the amount of hydrogen in the sampled gas was measured, and as a result, the yield of calcium amide was 82%. The resulting reaction product, calcium amide (solid), was easily collected from the microreactor in a high purity argon glove box.

  In a high purity argon glove box, 6 g (0.24 mol) of magnesium hydride was weighed and reacted with liquid ammonia under the same conditions as in Example 1 above. As a result of quantification of the amount of hydrogen in the sampling gas, the yield of magnesium amide was 72%.

In a high-purity argon glove box, a 400 cm ³ stainless steel microreactor was charged with 5 g (0.12 mol) of calcium hydride (Aldrich, purity: 95%) and 1.6 g (0.24 mol) of metallic lithium. After being sealed and sealed, the microreactor was cooled with dry ice-methanol cryogen, and about 10 g (about 0.60 mol) of liquid ammonia was supplied from the bomb to the microreactor and continuously stirred for 5 hours.

The microreactor was returned to room temperature, the pressure of the generated gas was measured, and sampling was performed. As a result of analyzing the amount of hydrogen in the sampled reaction gas by gas chromatography, the yield of a mixture of calcium amide and lithium amide (solid corresponding to Ca _0.5 Li (NH ₂ ) ₂ ) was 83%.

In a high purity argon glove box, 3.1 g (0.12 mol) of magnesium hydride and 1.6 g (0.24 mol) of lithium metal were weighed and reacted with liquid ammonia under the same conditions as in Example 3. As a result of analyzing the amount of hydrogen in the sampled reaction gas, the yield of the obtained mixture of magnesium amide and lithium amide (solid corresponding to Mg _0.5 Li (NH ₂ ) ₂ ) was 75%.

2 g of calcium hydride (manufactured by Aldrich, purity: 95%) was weighed in a high-purity argon glove box and put into a mill vessel with a valve (internal volume: 250 cm ³ ) made of high-chromium steel. Subsequently, after the inside of the mill container was evacuated, 1 MPa of argon gas was introduced, and a planetary ball mill apparatus (manufactured by Fritsch, P-5) was used at room temperature with a revolution number of 250 r. p. Milling was performed for 30 minutes at m to refine the raw material powder. Subsequently, after the inside of the mill was evacuated, an argon-10 vol% ammonia mixed gas was introduced at 1 MPa, and the same planetary ball mill apparatus was used at room temperature with a revolution number of 250 r. p. After milling for 2 hours at m and sampling the gas in the mill vessel after milling, the inside of the mill was evacuated. The reaction operation with this ammonia mixed gas was repeated 5 times.

  As a result of calculating the yield by measuring the amount of hydrogen in the reaction gas collected from inside the mill after each milling, the final yield of calcium amide was 83%.

  In a high-purity argon glove box, 2 g of magnesium hydride (manufactured by Aldrich, purity 95%) was weighed and pulverized in 1 MPa argon gas in the same manner as in Example 5, and then argon-10 vol% ammonia. The mixture was reacted with the mixed gas for 10 hours (2 hours × 5 times). As a result of sampling the reaction gas and quantifying the amount of hydrogen in the gas, the final yield of magnesium amide was 75%.

In a high-purity argon glove box, 1.5 g (0.036 mol) of calcium hydride (manufactured by Aldrich, purity: 95%) and 0.48 g (0.072 mol) of metallic lithium were weighed and used as examples. After pulverizing in 1 MPa argon gas in the same manner as in No. 5, the mixture was reacted with an argon-10 vol% ammonia mixed gas for 10 hours (2 hours × 5 times). As a result of sampling the reaction gas and quantifying the amount of hydrogen in the gas, the final yield of a mixture of calcium amide and lithium amide (a solid corresponding to Ca _0.5 Li (NH ₂ ) ₂ ) as a reaction product was 84%. Met.

In a high-purity argon glove box, 1.32 g (0.051 mol) of magnesium hydride and 0.68 g (0.102 mol) of lithium metal were weighed and these were subjected to 1 MPa argon gas in the same manner as in Example 5. After being pulverized in the reactor, it was reacted with an argon-10 vol% ammonia mixed gas for 10 hours (2 hours × 5 times). The reaction gas was sampled and the amount of hydrogen in the gas was quantified. As a result, the final yield of the mixture of magnesium amide and lithium amide (equivalent to Mg _0.5 Li (NH ₂ ) ₂ ) was 77%. It was.

  The metal amide compound of the present invention is suitable for a hydrogen storage material used in a fuel cell or the like that generates power using hydrogen and oxygen as fuel.

Claims (4)

A process for producing a metal amide compound comprising reacting calcium hydride or magnesium hydride with ammonia. The method for producing a metal amide compound according to claim 1, wherein metal lithium is further added to the calcium hydride or the magnesium hydride and reacted with the ammonia.   The method for producing a metal amide compound according to claim 1 or 2, wherein liquid ammonia is used as the ammonia.   A metal amide compound produced by adding metallic lithium to the calcium hydride or the magnesium hydride and reacting with the ammonia.