JP2004010446A - Method for producing alkali metal boron hydride - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing alkali metal boron hydride with high yield by effectively utilizing byproducts at the time of producing the alkali metal boron hydride by using meta-boric acid alkali metal salt as a raw material. <P>SOLUTION: The alkali metal boron hydride is produced by following four processes : (1) a process in which hydrogen halide is made to react with an alkaline earth metal oxide to obtain an alkaline earth metal halide, (2) a process in which the alkaline earth metal halide obtained by the process (1) is electrolyzed to an alkaline earth metal and a halogen, (3) a process in which the alkaline earth metal obtained by the process (2) is hydrogenated by hydrogen to obtain an alkaline earth metal hydride, and (4) a process in which the alkaline earth metal hydride obtained by the process (3) is made to react with meta-boric acid alkali metal salt to obtain the alkali metal boron hydride. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a novel method for producing an alkali metal boron hydride, particularly, an alkaline earth metal oxide produced as a by-product when producing an alkali metal boron hydride using an alkali metal metaborate as a raw material. It is intended to provide a method for improving the efficiency of an alkali metal borohydride by converting it into a derivable compound.
[0002]
[Prior art]
Alkali metal borohydrides, such as sodium borohydride, have been widely used as reducing or hydrogenating agents, but recently attempts have been made to use them as hydrogen generating agents or fuels for fuel cells.
[0003]
Heretofore, as a method for producing alkali metal boron hydride, for example, a method in which two molecules of alkali metal hydride and one molecule of borax are heated and reacted under substantially anhydrous conditions (Japanese Patent Publication No. 42-27256). A method in which hydrogen and sodium or sodium hydride or aluminum or an alloy thereof are reacted with anhydrous borax at a temperature of 200 to 600 ° C. and a hydrogen pressure of 1 × 10 ² to 50 × 10 ² kPa (Japanese Patent Publication No. 43-2221). ), An alkali metal or alkaline earth metal borate and an alkali metal hydride or a mixture of alkali metal and hydrogen at a ratio different from the molar ratio of metal oxide and boron oxide in the metaborate. A dry method such as a method of reacting at -1000 ° C (JP-B-47-48117) is known.
[0004]
However, in these dry methods, it is necessary to use a raw material that must be prepared by complicated operations, a raw material that is dangerous to handle such as metallic sodium, and it is necessary to react under a hydrogen pressure or a high temperature. It was unsuitable as a method.
[0005]
By the way, the present inventor has proposed a method of improving the disadvantages of the conventional method by reacting an alkali metal metaborate, which is easily available, with an alkaline earth metal hydride, which is easy to handle, using mechanochemical technology. (Japanese Patent Application No. 2000-372093) was proposed.
However, in this method, since the by-produced alkaline earth metal oxide, particularly the oxide after releasing hydrogen from MgH ₂ , is chemically stabilized, it is hydrogenated to regenerate MgH _2. The problem remains that it cannot be reused as a raw material, and the alkali metal borohydride cannot be industrially efficiently produced.
[0006]
[Problems to be solved by the invention]
Under such circumstances, the present invention uses easily available and easy-to-handle raw materials, can be reacted under mild conditions, and uses alkali metal borohydride as a raw material of alkali metal metaborate. The purpose of the present invention is to provide a method for producing an alkali metal borohydride in high yield by effectively utilizing a by-product at the time of producing the compound.
[0007]
[Means for Solving the Problems]
The present inventors have conducted various studies on a method for efficiently producing an alkali metal borohydride by a simple operation using easily available raw materials, and as a result, after halogenating an alkaline earth metal oxide, electrolyzing the alkaline earth metal oxide. By converting to a class of metals and halogens, it is possible to obtain an alkaline earth metal hydride that can easily lead to the production of an alkali metal boron hydride by using the hydrogen halide generated in this process. It has been found that it is effective to use an alkaline earth metal oxide by-produced in the production of an alkali metal boron hydride by hydrogenating an acid alkali metal salt with an alkaline earth metal hydride or an alkaline earth metal and hydrogen. The present invention has been accomplished based on this finding.
[0008]
That is, the present invention provides (1) a step of reacting an alkaline earth metal oxide with hydrogen halide to produce an alkaline earth metal halide;
(2) electrolyzing the alkaline earth metal halide obtained in step (1) into an alkaline earth metal and a halogen,
(3) a step of hydrogenating the alkaline earth metal obtained in the step (2) with hydrogen to produce an alkaline earth metal hydride, and (4) an alkaline earth metal hydride obtained in the step (3) And a method of producing an alkali metal borohydride by reacting the compound with an alkali metal metaborate, and an alkali metal borate as the alkaline earth metal oxide as the raw material, comprising: An object of the present invention is to provide a method for using a by-product in producing an alkali metal boron hydride by hydrogenating a metal salt with an alkaline earth metal hydride or an alkaline earth metal and hydrogen.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
The method of the present invention includes the steps (1) to (4) as described above.
In this step (1), after the target alkali metal borohydride is separated from the product of the hydrogenation reaction of the alkali metal metaborate, the alkaline earth metal oxide remaining as a by-product is reacted with hydrogen halide. In this way, an alkaline earth metal halide is produced, and if necessary, the alkaline earth metal halide is crystallized, separated and dried. The by-product alkaline earth metal oxide obtained when the alkali metal metaborate salt subjected to the step (1) is subjected to a hydrogenation reaction is in the form of finely divided particles, particularly MgH ₂ or the like. When a magnesium-based hydride is used, hydrogen is released from the particle surface to cause a hydrogenation reaction, and at the same time, an oxide is formed only in the vicinity of the particle surface. By using hydrogen halide, oxides on the particle surface are easily removed, and magnesium halide MgX ₂ (where X is a halogen atom) is quickly formed.
Examples of the hydrogen halide used in this step (1) include hydrogen fluoride, hydrogen chloride, hydrogen bromide, and hydrogen iodide, and a fluoride, chloride or bromide of an alkaline earth metal is obtained according to each. .
[0010]
Next, in the step (2), using the alkaline earth metal halide obtained in the step (1), the alkaline earth metal halide which has been made anhydrous while removing impurities is electrolyzed by a molten salt electrolysis method. As a result, an alkaline earth metal is deposited on the cathode, and halogen is generated on the anode. For example, when obtaining metal Mg and chlorine Cl ₂ using anhydrous magnesium chloride MgCl ₂ , an electrolytic bath having a predetermined concentration prepared by adding an appropriate salt (NaCl or the like) for lowering the melting point as needed is used. When electrolysis is performed at a temperature of 700 ° C. and a cell voltage of 6 to 8 V, a current efficiency of 75 to 85% is obtained. When metal Ca and chlorine Cl ₂ are obtained using CaCl ₂ , a temperature of 780 ° C. and a cell voltage of Electrolysis at 25V gives a current efficiency of 65-80%.
[0011]
As described in Japanese Patent Publication No. 32-9052, when metal Mg and chlorine Cl ₂ are obtained using hydrous magnesium chloride MgCl ₂ , the following steps (4) are carried out in a molten electrolytic bath. By supplying the hydrous magnesium chloride while blowing the dry hydrogen chloride (HCl) gas obtained in the above), it is possible to dehydrate and electrolyze while preventing its decomposition and generation of magnesium oxide.
[0012]
The alkaline earth metal obtained in this step (2) can be supplied together with hydrogen as a raw material in the production of alkali metal boron hydride as it is, or the following step of producing an alkaline earth metal chloride ( It can also be supplied as a raw material of 3).
[0013]
In the step (3), the alkaline earth metal obtained in the step (2) is reacted with hydrogen to generate an alkaline earth metal hydride. Alkaline earth metals usually provide stable hydrides when contacted with hydrogen under heating. For example, when calcium metal, metal barium, and metal strontium are heated to 350 ° C. or more in a hydrogen stream, they react quickly to form calcium hydride, and metal magnesium is pulverized to 100 μm or less and hydrogenated at 24 to 400 atm. When heated to 300 to 400 ° C. under pressure, it becomes magnesium hydride.
[0014]
In the case of metallic magnesium, since its surface is usually oxidized and the initial rate in the hydrogenation reaction is low, it is advantageous to carry out fluorination treatment with an aqueous alkali fluoride solution before hydrogenation. The fluorination treatment increases the reaction rate, and a high yield of 80% or more can be obtained even at a low temperature and low pressure of 100 ° C. or less. In this case, the aqueous solution containing alkali fluoride such as sodium fluoride, potassium fluoride and ammonium fluoride at a concentration of 0.2 to 10.0% by weight is adjusted to pH 2.0 with hydrogen fluoride. To 6.5, preferably 4.5 to 6.0.
[0015]
In the step (4) of the method of the present invention, the desired alkali metal borohydride is produced by reacting the alkaline earth metal hydride obtained in the step (3) with the alkali metal metaborate.
In the method of the present invention, a hydrogen halide is produced by a direct reaction with hydrogen using the halogen produced in the above step (2) and, if necessary, absorbed in water to produce a hydrogen halide of up to about 35% by mass. An acid is produced, and the thus obtained hydrogen halide or hydrohalic acid is stored in, for example, a storage tank, and after adjusting the concentration and the supply amount as necessary, it is circulated to the above step (1), It is preferably used as a raw material for producing an alkaline earth metal halide from an earth metal oxide.
[0016]
In addition, the hydrogen source supplied to the step (3) and used for hydrogenation of the alkaline earth metal and the hydrogen source used for producing the hydrogen halide from the halogen obtained in the step (2) are both particularly There is no limitation, and commercial products can be used.
[0017]
Examples of the alkaline earth metal oxide as a raw material of the method of the present invention include an alkali metal borohydride or an alkaline earth metal hydride that is hydrogenated with an alkaline earth metal and hydrogen to produce an alkali metal boron hydride. It is advantageous to use the resulting alkali metal metaborate to form a series of alkali metal borohydride production cycles. Examples of the alkali metal metaborate used at this time include sodium metaborate (NaBO ₂ ), potassium metaborate (KBO ₂ ), and lithium metaborate (LiBO ₂ ). Of these, sodium metaborate, which is obtained in a simple and large amount by reacting sodium hydroxide with natural borax, followed by dehydration and heat drying, is particularly preferable.
[0018]
In addition, the residue after using alkali metal boron hydride as a hydrogen generator, a fuel or a reducing agent for a fuel cell that directly converts its chemical energy into electric energy is dehydrated, and metaboric acid contained therein is dehydrated. The alkali metal salt can be recovered and used.
The thus recovered alkali metal metaborate is preferably heated and dried in advance to reduce the water of crystallization to 1 or less, preferably 0, and then hydrogenated.
[0019]
Next, examples of the alkaline earth metal hydride used for hydrogenating the alkali metal metaborate include calcium hydride (CaH ₂ ), barium hydride (BaH ₂ ), and strontium hydride (SrH ₂ ). However, magnesium hydride (MgH ₂ ) is particularly preferred. Alkaline earth metals used with hydrogen include magnesium (Mg), calcium (Ca), barium (Ba), strontium (Sr), and the like.
[0020]
This hydrogenation with an alkali metal metaborate and an alkaline earth metal hydride or an alkaline earth metal and hydrogen can be carried out under high-temperature and high-pressure conditions, each of which has a fine powder of 500 μm or less, preferably 100 μm or less. It is advantageous to mix and contact the raw materials, and to react them at room temperature and atmospheric pressure while applying mechanical energy such as grinding energy, grinding energy, impact energy, and ultrasonic grinding energy. Alkali metal borohydride can be obtained in a yield.
[0021]
The mechanical energy at this time is applied by a ball mill, a tube mill, a rod mill, an attrition mill, a vibration mill, a jet mill, a micronizer, or the like, and it is particularly preferable to use a ball mill. The energy applied at this time is generally at least 4 kJ / g or more, preferably at least 10 kJ / g. For example, the energy efficiency can be increased in a shorter time as ball milling is performed at a higher rotation speed. The reaction product is obtained by dissolving an alkali metal borohydride in an aqueous alkali solution, or extracting and separating the alkali metal borohydride with anhydrous ethylenediamine and drying.
[0022]
FIG. 1 is a process diagram showing a production cycle in which the method of the present invention is incorporated by taking, as an example, a method for producing sodium borohydride (NaBH ₄ ) from sodium metaborate (NaBO ₂ ) and magnesium hydride (MgH ₂ ). , and the by reacting HCl to MgO by-produced during the production of NaBH ₄ is reacted with NaBO ₂ and MgH ₂ to generate MgCl ₂ [step (1)], the MgCl ₂ by electrolyzing Mg and Cl ₂ are generated [Step (2)], and the Mg is reacted with H ₂ to be converted into MgH ₂ [Step (3)]. Then, the MgH ₂ obtained in the above step (3) is reacted with NaBO ₂ to produce NaBH ₄ . The Cl ₂ obtained in the step (2) is reacted with H ₂ to form HCl, and the HCl is circulated to the step (1) and used for the reaction with MgO. The Mg obtained in the step (2) is mixed with H ₂ and supplied to a raw material for producing NaBH _{4 in} the same manner as the above-mentioned MgH ₂ .
[0023]
In this manner, by constructing a series of production cycles of NaBH ₄ including the method of the present invention, by-products can be completely and effectively used, so that NaBH _4, that is, alkali metal boron hydride can be produced in high yield. Can be.
The method of the present invention is particularly suitable for producing sodium borohydride or potassium borohydride.
[0024]
【Example】
Next, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.
[0025]
Example Production of NaBH ₄ was performed according to the process shown in FIG.
That is, 3.0 g of a mixture of anhydrous sodium metaborate fine powder (average particle diameter of 75 nm) and magnesium hydride fine powder (average particle diameter of 100 nm) at a molar ratio of 1: 2 was mixed with a planetary ball mill fine grinder [Fritsch] Company, product symbol "P-5"], and ground at 20 ° C. under atmospheric pressure at a ball acceleration of 86.5 m / s ² for 60 minutes to react. 8 g (yield 45% based on anhydrous sodium metaborate) and 1.65 g of magnesium oxide were obtained.
Next, 15 ml of 35% strength hydrochloric acid was added to 1.65 g of the magnesium oxide, and reacted at 50 ° C. for 30 minutes to obtain 3.75 g of magnesium chloride.
Then, 0.1 g of sodium chloride was added to the magnesium chloride, heated and melted at 700 ° C., and electrolyzed at a cell voltage of 7 V to obtain 0.95 g of metallic magnesium and 2.70 g of chlorine gas.
This metallic magnesium is put into 10 ml of a 5% by mass aqueous solution of potassium fluoride adjusted to pH 5.5 with hydrogen fluoride, treated at 50 ° C. for 30 minutes, dried, and then dried at 80 ° C. in a hydrogen stream for 10 hours. By the treatment, 0.6 g of magnesium hydride was obtained.
This magnesium hydride is pulverized to an average particle diameter of 100 nm, and then mixed with anhydrous magnesium metaborate fine powder in the same ratio as described above, together with a newly supplied magnesium hydride fine powder, to produce sodium borohydride. When used, it could be processed without any hindrance.
[0026]
【The invention's effect】
According to the method of the present invention, easily available, using a raw material that is easy to handle, in addition to being able to produce an alkali metal borohydride in high yield, in addition to hydrogenating an alkali metal metaborate to form an alkali metal borohydride By incorporating into the production method, all the components of the alkaline earth metal oxide, which is a by-product, can be circulated and used for the hydrogenation reaction. By separately supplying only hydrogen required for hydrogenation of the alkali metal salt, the target alkali metal boron hydride can be efficiently produced.
[Brief description of the drawings]
FIG. 1 is a process diagram showing one example of a production cycle of an alkali metal borohydride incorporating the method of the present invention.

Claims (10)

(1) a step of reacting an alkaline earth metal oxide with hydrogen halide to produce an alkaline earth metal halide;
(2) electrolyzing the alkaline earth metal halide obtained in step (1) into an alkaline earth metal and a halogen,
(3) a step of hydrogenating the alkaline earth metal obtained in the step (2) with hydrogen to produce an alkaline earth metal hydride, and (4) an alkaline earth metal hydride obtained in the step (3) And producing an alkali metal borohydride by reacting the compound with an alkali metal metaborate. Alkaline earth metal oxide as an alkaline earth metal oxide in step (1), alkaline earth metal hydride or alkaline earth metal by hydrogenation with alkaline earth metal and hydrogen to produce alkali metal boron hydride; The method for producing an alkali metal borohydride according to claim 1, wherein a metal oxide is used. The method for producing an alkali metal boron hydride according to claim 1, wherein the halogen obtained in the step (2) is reacted with hydrogen to generate a hydrogen halide, and the hydrogen halide is circulated to the step (1). The method for producing an alkali metal boron hydride according to claim 2 or 3, wherein the hydrogenation of the alkali metal metaborate with an alkaline earth metal hydride or an alkaline earth metal with hydrogen is carried out while applying mechanical energy. The method for producing an alkali metal borohydride according to claim 2, 3 or 4, wherein the alkali metal metaborate is sodium metaborate. 6. The method for producing an alkali metal borohydride according to claim 5, wherein the sodium metaborate is sodium metaborate obtained by reacting borax with an aqueous solution of sodium hydroxide, dehydrating and heating and drying. 5. The alkali metal borohydride according to claim 2, wherein the residue obtained after the alkali metal metaborate hydrolyzes the alkali metal boron hydride to generate hydrogen is dehydrated and heated and dried. Manufacturing method. The method for producing an alkali metal borohydride according to claim 2, 3 or 4, wherein the alkali metal metaborate is recovered from spent effluent as fuel for a fuel cell. The method for producing an alkali metal borohydride according to any one of claims 1 to 8, wherein the alkali metal borohydride is sodium borohydride or potassium borohydride. The method for producing an alkali metal borohydride according to any one of claims 1 to 9, wherein the alkaline earth metal is magnesium or calcium.

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