JP2809666B2 - Manufacturing method of sodium borohydride - Google Patents

Description

The present invention relates to a method for producing sodium borohydride, which is a useful reducing agent.

(Prior art)

As a method for producing sodium borohydride (NaBH ₄ ), a wet method in which the reaction temperature and pressure are low and the reaction yield is good is preferable.

First, the inventors of the present invention have performed a wet process using a known trialkyl borate as a boron raw material, but using sodium aluminum hydride (NaAlH ₄ ), which is a novel compound, as an active hydrogen supply reagent. A method was proposed.

[Problems to be solved by the invention]

However, in the method using NaAlH ₄ as the active hydrogen supply reagent, in order to improve the productivity of NaBH ₄ , the raw material N
aAlH ₄ must be charged as much as possible.
Solvent that most dissolves ₄ is tetrahydrofuran (THF)
It is. However, when a large amount of NaAlH ₄ is dissolved in THF and reacted with trialkyl borate, the productivity is improved, but the generated NaBH ₄ particles are very fine and the bulk density is low. If the NaBH ₄ particles are fine and the bulk density is low, the filtration, washing, and drying steps become extremely difficult.Also, when the produced NaBH ₄ is dried and shipped as it is, the bulk density is low, so the unit weight is low. Requires a larger container to transport. Further, problems such as difficulty in charging due to the formation of a bridge at a loading port of a hopper or the like are likely to occur.

Conversely, decreasing the concentration of NaAlH ₄ in THF revealed that the particles became larger, but this time the productivity per batch decreased and the amount of THF used increased, thus increasing the recovery time and calorie. Required, and the economics declined. So TH
There has been a demand for a method in which a large amount of NaAlH ₄ is dissolved and reacted in F to increase the size of the generated NaBH ₄ particles.

In the method proposed by the present inventors,
As a method for increasing the size of NaBH ₄ particles, one of diols is used.
A method is disclosed in which a trialkyl borate synthesized using ether alcohols obtained by alkylating individual hydroxyl groups is reacted with NaAlH ₄ . Although this method can synthesize large particles of NaBH ₄ , the synthesis of the raw material trialkyl borate is rather complicated and time-consuming.
Therefore, a method for producing large particles of NaBH ₄ by a simpler method has been desired.

[Means for solving the problem]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and have completed the present invention.

That is, the method for producing sodium borohydride of the present invention is a method for producing sodium borohydride by reacting a trialkyl borate with sodium aluminum hydride. It is characterized by using a mixed solvent of certain tetrahydrofuran and ethers.

Hereinafter, the present invention will be described in more detail. The reaction of the present invention is represented by the following reaction formula.

BZ ₃ + NaAlH ₄ → NaBH ₄ + AlZ _{3 In the} above formula, BZ ₃ represents a trialkyl borate, and Z represents the following compounds: (1) alcohols or phenols (2) tetrahydrofurfuryl alcohols (3) Ether alcohols obtained by alkylating one hydroxyl group of diols (4) Organic residues obtained by removing active hydrogen atoms from a compound selected from polyether alcohols.

The production method of the trialkyl borate used in the present invention is not limited, and may be one synthesized by a known method. For example, it can be easily synthesized from boric acid and alcohol by a dehydration reaction. Preferred examples of the compound used include trimethyl borate B (—O—CH ₃ ) ₃ and tri-n-butyl borate B
_{(-O-n-Bu) 3} , boric acid tri-2-methoxy - ethyl _{B (-O-C 2 H 4} -O-CH 3) 3, boric acid tri-2-ethoxy - ethyl B (-O-C ₂ H ₄ —O—C ₂ H ₅ ) ₃ , and the like.

Also, the production method of sodium aluminum hydride is not limited, and may be synthesized by a known method. For example, it can be synthesized from metallic sodium, metallic aluminum powder and hydrogen. However, it is preferable to completely remove the metal fine powder of the reaction residue.

Next, the solvent used during the reaction, which is a feature of the present invention, will be described. As one of the components of the solvent, THF which is the best solvent of NaAlH ₄ is used, and ethers used as another component to be mixed with this are preferably aliphatic ethers, for example, diethyl ether, dibutyl ether and the like. Monoethers, diethers such as ethylene glycol dimethyl ether and ethylene glycol diethyl ether, and triethers such as diethylene glycol dimethyl ether and diethylene glycol diisopropyl ether. Mixing ratio with respect to THF, to eliminate the effect of ethers to increase the greatly bulk density particles of NaBH ₄ produced as a too small amount, since too large, the solubility of NaAlH ₄ decreases undesirably. Therefore TH
The mixing ratio of ethers to F is preferably in the range of 10 to 100%. Further, in order to control the reaction, a small amount of an aliphatic or aromatic hydrocarbon may be mixed.

When the solvent in the method of the present invention is used, NaBH ₄ having large bulk density of particles is precipitated as a solid in the solvent, but aluminum alkoxide as a by-product dissolves in the solvent. Therefore, if the reaction conditions are set so that unreacted solid NaAlH ₄ does not remain, the aluminum alkoxide by-produced can be easily separated and removed together with the solvent by filtering NaBH ₄ with a simple filtration device. And the purity of the obtained solid NaBH ₄ is very high.

Generally extraction purification procedures have been used to improve the purity of NaBH _4, practically sufficient purity can be obtained even without extraction purification for example by liquid ammonia or amines.
Of course, there is no problem in performing extraction and purification to further increase the purity.

If the reaction temperature is too low, there is no reaction, but there is no need to raise the temperature too high. In general, the temperature may be in the range of 50 ° C to 100 ° C, and the reaction is sufficiently performed at the boiling point of tetrahydrofuran.

The order of mixing may be such that a solution of boron trialkyl is mixed with a solution of NaAlH _{4 or} vice versa. The mixing ratio of the reagents is generally, NaAlH ₄ 1 mol, although 0.8 to 1.5 moles of boric acid trialkyl, the amount of boric acid trialkyl thinking economy is preferably from 1.0 to 1.2 mol.

After the reaction, solid NaBH ₄ can be separated by a simple filtration operation by setting the reaction conditions so that solid NaAlH ₄ does not remain as described above. Thereafter, washing, drying operation and can be obtained NaBH ₄ large bulk dense and high purity of the particles in the course of treatment.

For some reason, such as when using NaAlH ₄ containing a large amount of insoluble impurities, a purification operation is required,
In this case, known extraction and purification using liquid NH ₃ , isopropylamine, or the like is performed. Even in this case, since the NaBH ₄ particles are large and have a high bulk density, the advantage that operations such as filtration, washing and drying in the production process are easy is not lost.

Aluminum alkoxide, a by-product, can be widely used as a raw material for chemicals.

〔Example〕

 Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 A 500 ml glass four-necked flask was stirred with a stirrer, a dropping funnel,
After installing a reflux condenser and replacing the inside with nitrogen, sodium aluminum hydride NaAlH ₄ 21.6 was added to the four-necked flask.
A solution in which g (0.4 mol) was dissolved in a mixed solvent of 227 g of tetrahydrolane and 35 g of di-n-butyl ether was charged. The ratio of di-n-butyl ether to tetrahydrofuran was 15.4%.

While maintaining the temperature of the solution at 70 ° C., 97 g (0.42 mol) of tri-n-butyl borate was dropped from the dropping funnel over 4 hours, followed by a post-reaction for 1 hour, followed by filtration through a G-4 glass filter. The obtained solid was further washed with 200 g of tetrahydrofuran, filtered, and dried under reduced pressure at 100 ° C. As a result, 14.6 g of white crystals of NaBH ₄ were obtained, and the yield was 96%.

The purity measured by iodometry was 99.3%. The average particle size of NaBH ₄ was 40 μm, and the bulk density was 0.48 g / cm ³ .

Comparative Example 1 The procedure of Example 1 was repeated except for di-n-butyl ether.

The yield of the obtained NaBH ₄ was 95%, the purity was 99.4%, the average particle size of the particles was 10μ, and the bulk density was 0.23 g / cm ³ .

Comparative Example 2 An experiment was performed in the same manner as in Example 1 except that the same amount of n-hexane was used instead of di-n-butyl ether.

The yield of the obtained NaBH ₄ was 96%, the purity was 99.5%, the average particle size of the particles was 10μ, and the bulk density was 0.25 g / cm ³ .

Comparative Example 3 An experiment was performed in the same manner as in Example 1, except that the same amount of toluene was used instead of di-n-butyl ether.

The yield of the obtained NaBH ₄ was 95%, the purity was 99.3%, the average particle size of the particles was 10μ, and the bulk density was 0.24 g / cm ³ .

Examples 2, 3, 4 and Comparative Examples 4, 5 The total amount of the mixed solvent used was kept constant, and the mixing ratio of di-n-butyl ether to tetrahydrofuran was changed.
The same experiment as in Example 1 was performed. The results are shown in Table 1. It can be seen that the mixing ratio is preferably between 10% by weight and 100% by weight.

Example 5 An experiment was performed in the same manner as in Example 1 except that 23 g of ethylene glycol dimethyl ether was used instead of di-n-butyl ether.

In this case, the ratio of ethylene glycol dimethyl ether to tetrahydrofuran was 10%. 14.4 g of white crystals of NaBH ₄ were obtained, the yield was 92%, the purity was 99.3%,
The average particle size of the particles was 45μ.

According to the method of [Effect of the Invention The present invention, purity quite easily and can be economical, obtained crystals high NaBH ₄ particles of large bulk density, not particularly require manipulation of the extraction purification such as It is a great advantage for industry because it can be a product with high quality.

Claims (1)

(57) [Claims] A method for producing sodium borohydride by reacting a trialkyl borate with sodium aluminum hydride, wherein a mixture of tetrahydrofuran and ether having a mixing ratio of ether to tetrahydrofuran of 10 to 100 wt% during the reaction. A method for producing sodium borohydride, comprising using a solvent.