JPH069205A - Production of alkali metal azide powder - Google Patents

Abstract

PURPOSE:To obtain powder of an alkali metal azide having a preferable specific surface area, excellent powder fluidity and low compression degree of powder by dissolving an alkali metal azide in an aqueous solvent and precipitating under a specific pH condition. CONSTITUTION:An alkali metal azide (e.g. sodium azide) having >=97wt.% purity is dissolved in an aqueous solvent (e.g. solvent having >=50wt.% water content) to give 5-30wt.% solution. The solution of the alkali metal azide in the aqueous solvent is adjusted to 7-13, preferably 7.5-11, more preferably 8-10. The solution is cooled as it is or concentrated to a proper concentration and then cooled to precipitate the alkali metal azide. Then the precipitate is separated by filtration and dried. The prepared alkali metal azide has >=97wt.%, preferably >=98wt.% purity and has about 50-400mum average particle diameter (volume average diameter). The powder is optionally classified or ground and classified to give the objective powder having a desired particle diameter.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is used as a main starting material for tetrazole, which is a raw material for medicines, photographic agents, and the like.
The present invention relates to a method for producing an alkali metal azide powder, which is a compound extremely useful as a gas generating agent for an airbag, which is a safety device for automobiles, and has a mild self-degrading property. And sodium azide powder.

[0002]

2. Description of the Related Art Conventionally, several methods for producing sodium azide have been known, for example, US Pat. No. 1,628,380.
In the publication, the reaction of hydrazine and alkyl nitrite is described as a non-anhydrous reaction medium.
s) and a substantially non-aqueous reaction medium (anhydro)
us reaction mediums). Also, West German Patent No. 1,144,243 describes a method of carrying out the reaction of sodium amide and nitrous oxide in liquid ammonia.

However, sodium azide, which is a typical alkali metal azide by these conventional methods, is generally a powder having an average particle size of about 50 to 400 μ and having poor fluidity, and all of them have excellent self-decomposition characteristics. Therefore, the handling is subject to extremely strict regulations as Class 5 Class 1 hazardous materials under the Fire Service Act. Therefore, handling a large amount of sodium azide requires a large amount of investment in equipment, and there are problems such as strict restrictions on the quantity of transportation and the form of packaging during transportation.

Particularly in recent years, sodium azide has come to be used in large amounts as a gas generating agent for air bags, which is a safety device for automobiles. In this case, generally, the average particle size is about 30 μm, Alternatively, fine particles of 10 μm or less are required, and treatment such as pulverization is required.However, when pulverizing sodium azide, not only the self-degrading property is severe but also the poor powder fluidity is a problem. It was

[0005]

DISCLOSURE OF THE INVENTION The present inventors have studied in order to obtain a stabilized alkali metal azide having a mild self-decomposition property as described above and excellent flow properties as a powder. I went. As a result, an aqueous solvent solution obtained by dissolving a commercially available alkali metal azide produced by a usual production method in an aqueous solvent is concentrated under certain pH conditions, for example, to crystallize the alkali metal azide. Let
The alkali metal azide obtained by filtering this has extremely slow self-decomposition property and is classified as Class 5 Second Class Hazardous Materials under the Fire Service Act.

Among these alkali metal azides, sodium azide powder having a specific particle shape, that is, the value of the microtrack type specific surface area measured after performing ultrasonic dispersion treatment by a specific method is 0.0
The inventors have found that a sodium azide powder having a particle size of 8 m ² / cc or less has excellent powder fluidity and is extremely suitable for pulverization processing and various other handlings, and thus completed the present invention.

[0007]

According to the present invention, an alkali metal azide is dissolved in an aqueous solvent, and then the alkali metal azide is precipitated from an aqueous solution of the obtained alkali metal azide under conditions of pH 7 to 13. In order to provide a method for producing an alkali metal azide powder such as sodium azide, the microtrack specific surface area after ultrasonic dispersion treatment is 0.08 m ² The purpose of the present invention is to provide a sodium azide powder characterized by being less than / cc.

The present invention will be described in detail below.

Examples of the alkali metal azide in the present invention include lithium azide, sodium azide, potassium azide, etc. Among them, sodium azide is the most common.

The alkali metal azide, which is the starting material of the method of the present invention, may have any crystal form,
In addition, any manufacturing method may be used, and commercially available products may be used as they are, but the dangerous materials evaluation method of the Fire Service Act, which will be described later, uses a 9 mmφ orifice plate to test a dangerous vessel The ones classified into are used.
The purity of the alkali metal azide is generally 97% by weight or more, preferably 99% by weight or more.

The concentration of the alkali metal azide in the aqueous solution of the alkali metal azide obtained by dissolving the above alkali metal azide in the aqueous solvent is an appropriate concentration up to the saturated concentration of the alkali metal azide in the aqueous solvent. 5 to 30% by weight, preferably 10 to 25%
It is preferable to be about% by weight.

The above-mentioned aqueous solvent means that the content of water is 50% by weight.
Above, preferably 90% by weight or more of solvent. The aqueous solvent may be mixed with an appropriate hydrophilic organic solvent other than water as long as it does not hinder the stabilization of the alkali metal azide, but from the viewpoint of eliminating the risk of fire or explosion. ,
Further, from the viewpoint of improving the precipitation efficiency of the alkali metal azide by using the high-concentration alkali metal azide aqueous solvent solution, it is desirable that the amount of the organic solvent is as small as possible.

It is necessary that the pH of the resulting aqueous solution of alkali metal azide in the solvent is adjusted to the range of 7 to 13, preferably 7.5 to 11, and more preferably 8 to 10. The
If the pH value is too low below the lower limit value, it is not preferable since highly dangerous hydrogen azide may be generated, and if the pH value is too high above the upper limit value, the obtained alkali metal azide may flow. It is not preferable because the properties may become insufficient and the self-degrading property may be intensified.

In the method using sodium amide as a starting material described in the above-mentioned West German Patent No. 1,144,243, etc.,
When sodium azide is used as an alkali metal azide as a starting material of the method of the present invention, an aqueous solvent of sodium azide obtained is obtained because sodium hydroxide is by-produced together with sodium hydroxide in an equimolar amount. In some cases, the solution becomes strongly alkaline, and in this case, it is preferable that the aqueous solvent solution is treated with a cation exchange resin or the like so as to have the above pH range.

In addition, when used as a gas generating agent for an air bag, it is sometimes required to mix a small amount of an alkaline component, and at that time, a desired amount of the alkaline component, such as sodium hydroxide, is mixed with an alkaline metal. It can also be adjusted to pH 8-11, especially 8.5-10 by adding it to an aqueous solution of azide. (The amount of the alkali component in the aqueous solvent solution is usually about 1 to 5 mmol relative to 1 mol of the alkali metal azide.)

If desired, the aqueous solution of the alkali metal azide may contain a surfactant or the like. The content thereof is generally 0 to 1% by weight, preferably 0 to 0.5% by weight.

In order to dissolve the alkali metal azide in the aqueous solvent, for example, the aqueous solvent is placed in a suitable container, and a commercially available powder of the alkali metal azide is added to the aqueous solvent. A method of suitably adding a surfactant or the like and stirring and dissolving at a temperature of, for example, 4 to 100 ° C., preferably 4 to 40 ° C. can be suitably used.

According to the method of the present invention, the aqueous solution of the alkali metal azide thus obtained is used as it is,
Alternatively, it is concentrated to an appropriate concentration and then cooled to precipitate an alkali metal azide, and then the precipitate is separated by filtration and dried to obtain a stabilized alkali metal azide having a self-degrading property. You can

When the alkali metal azide is deposited, the ratio of the azide and the aqueous solvent in the aqueous solution or the aqueous solvent slurry liquid in which a part of the azide is deposited by concentration or the like is The amount of the aqueous solvent is generally 190 to 400 parts by weight, preferably 250 to 300 parts by weight, based on 100 parts by weight of the total amount of the azide or the dissolved azide and the precipitated azide.

The filtrate may be diluted with water, if necessary, and then adjusted by adding the commercially available alkali metal azide, and may be recycled.

The process according to the invention can be carried out in the usual batch form or in the form of circulating the filtrate as described above. Which one to choose may be decided considering the production scale and equipment requirements.

The alkali metal azide thus obtained has a purity of 97% by weight or more, preferably 98% by weight or more,
The average particle size (volume average particle size) is about 50 to 400 µ, preferably about 150 to 350 µ. The azide is
It is also possible to obtain an alkali metal azide powder having a desired particle size by performing classification as required, or classifying after pulverization.

The alkali metal azide stabilized by the method of the present invention as described above has a very mild self-decomposition property. The self-decomposition property is measured according to the Hazardous Materials Evaluation Method of the Fire Service Law, and is performed by a pressure vessel test using a 9 mmφ orifice plate as described below.

Measurement of self -degrading property The self-degrading property is measured by "manual of conducting dangerous goods confirmation test" of the Fire Service Law [Supervised by the Dangerous Goods Regulation Division of the Fire Service Agency, published by New Japan Law Regulations]
Issued by Co., Ltd.], pages 66 to 82, "Test method of Class 5", "3. Pressure vessel test". A 9 mmφ orifice plate was used as the orifice plate.

5 g of the test sample was placed in a predetermined container, which was then placed in the above pressure container and heated at 200 ° C. at a temperature rising rate of 40 ± 5 ° C./min.
Up to 400 ° C and continue heating to 400 ° C. When the self-decomposition characteristic is mild, the decomposed gas flows out from the orifice at the time of temperature rise, but when the self-decomposition characteristic is severe, the internal pressure rapidly rises and the rupture plate bursts.

The self-degrading property is evaluated by repeating the test 10 times for the same test sample and observing the number of times the rupture plate ruptures. According to the Fire Service Act, those with 5 or more bursts out of 10 are classified as dangerous goods class 5 class 1 and those with less than 5 bursts are classified as hazardous material class 5 class 2 To be done. As a reference, with respect to the test sample in which no burst occurred, the decomposition time, that is, the outflow duration of the decomposed gas from the orifice was measured.

According to the above-mentioned test method, as an example of sodium azide, a conventional commercially available powdery sodium azide is compared with the sodium azide stabilized by the method of the present invention. In the decomposition characteristic test, the rupture disc ruptures every time and is classified as a dangerous substance class 5 class 1 whereas the one according to the method of the present invention is 1 for decomposition.
It took about 2 seconds to be fairly gentle, and it was found that the number of ruptures in the self-degrading property test was 4 or less and it was classified as a dangerous substance class 5 type 2.

[0028] Therefore, the conventional commercial products are subject to strict restrictions on the transportation quantity, the packaging form, etc., especially in the case of transportation thereof, whereas the sodium azide stabilized by the method of the present invention is far more than that. The regulations are fairly lenient, such as the fact that it can be transported in a much larger amount in a simple packaging form, and it can be handled much more easily.

The most preferred product is sodium azide powder in the process of the present invention, the micro-track specific surface area after ultrasonic dispersion treatment is 0.1 m ² / cc or less, preferably 0.09 m ² / cc, Particularly preferably 0.02-0.08 m ² / cc
belongs to. When the specific surface area is not more than the upper limit value, the powder flow characteristics are excellent, and the workability in further pulverization of the sodium azide powder is not deteriorated, which is preferable.

The above-mentioned Microtrac type specific surface area and the volume average particle size and particle size distribution are measured by Catalog No. 3060 “Nikki Sogyo Co., Ltd.” “Measuring principle of particle size analyzer applying microtrack light and laser”. Vol. 16th-23
It is based on the principle described on page and page 28, and specifically, is a value obtained by measuring by the method of "microtrack type particle size distribution, volume average particle size and specific surface area measurement" described later. .

Microtrac type particle size distribution, volume average particles
Measurement of diameter and specific surface area A laser diffraction type particle size distribution measuring device “MICROTRAC FRA” (trade name) (manufactured by LEEDS & NORTHRUP) is used and the particle size measuring range is 0.12 to 704.00 μ.
Use n-heptane as the dispersion solvent for measurement, and use SVR (small sample specification) as the sample circulation device. The measurement sample has an average particle size of 50μ or less, 0.1 to 0.35g, about 100μ, 0.15 to 0.25g, and 200μ, 0.25 to 0.35g.
Take an appropriate amount into a 50 ml beaker as a guide and disperse the high molecular polyester amine salt "Disparlon KS-873N".
(Trade name) [manufactured by Kusumoto Kasei Co., Ltd.] is added with 4 to 5 drops with a dropper, and well mixed with a micro spatula to form a paste. Add about 20 ml of n-heptane to this and disperse well to make a slurry sample.

Next, the beaker was placed in an ultrasonic water tank "W-103T".
(Trade name) [manufactured by Honda Electronics Co., Ltd.], and subjected to ultrasonic dispersion treatment for 1 minute. At this time, the water level in the water tank should be lower than the n-heptane level in the beaker. After ultrasonic dispersion treatment, the total amount of this slurry is put into a sample circulation device, and measurement is performed according to the support of the display screen of the device below.

The most preferred product of the method of the present invention, sodium azide powder, has a loose apparent specific gravity of 0.6.
It is preferably 5 or more, more preferably 0.7 or more, still more preferably 0.75 or more, and most preferably 0.8 or more. When the value of the apparent specific gravity is not less than the lower limit value, the powder fluidity of the sodium azide powder is excellent, which is preferable. The true specific gravity of sodium azide is
It is 1.84, and the apparent specific gravity does not exceed this value, but it is desirable to be as close as possible to that value. In order to meet such an apparent specific gravity condition, the particle shape of the sodium azide powder is preferably a lump or agglomerate of lumps rather than a plate-like shape, and further, it should be close to a cube or a sphere. Is advantageous. Further, it is advantageous to make the distribution of particle diameters as sharp as possible.

Further, the compressibility of the sodium azide powder is preferably 35% or less, more preferably 30% or less, further preferably 0.5 to 25%, and 1 to 20%. Is particularly preferable. When the compression degree is not more than the upper limit value, the powder fluidity of the sodium azide powder is particularly excellent, which is preferable. The values of the apparent specific gravity and the compression degree are values obtained by measuring by the following method.

Measurement of compression degree 1) Measurement of loose apparent specific gravity (A) Using a JIS standard sieve with a diameter of 10 cm and a diameter of 710 μ and a “Powder Tester” (trade name) [manufactured by Hosokawa Micron Co., Ltd.] , 150g of sample is oscillated in a 100cc powder receiving cup of known weight with a strength that makes it pile up in 20 to 30 seconds, and then a flat spatula is erected vertically and rubbed to scrape the sample weight with the cup. Measure and calculate the value of the loose apparent specific gravity A.

2) Measurement of tap specific gravity (P) Using the "powder tester" described above, add a cap attached to the powder receiving cup, attach a cap cover, and put in the tapping holder. While adding samples with a scoop, tap for 180 seconds at a tapping frequency of 180 times / minute. After the tapping is completed, the cap and the jack cover are removed, and the value of the tap specific gravity P is calculated in the same manner as above.

3) Calculation of Compressibility Using the apparent specific gravity A and tap specific gravity P described above, the powder compressibility is calculated according to the following equation.

[0038]

[Equation 1]

Furthermore, the most preferred product of the method of the present invention, sodium azide powder, has an angle of repose of 52 or less, and particularly 50 or less, because of the powder flow characteristics of the sodium azide powder. It is preferable from the viewpoint of excellence. The value of the angle of repose is a value obtained by measuring by the following method.

Measurement of angle of repose Using the "powder tester" described above, a funnel having an opening of 65 mmφ and a lower pipe portion of 5 mmφ was placed on the table for measuring the angle of repose and the height of the lower end of the lower pipe portion from the table was 75 mm. And a sieve with an opening of 710 μm is mounted on the funnel. About 150 g of the sample powder is put into the sieve and vibrated with an amplitude of 2 mm or less so that the sample flows down through the funnel onto the table. A protractor is applied to the ridge of the accumulated sample powder to measure its angle of repose.

[0041]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

Example 1 A 500 ml three-neck separable flask equipped with a stirrer equipped with a pressure reducing seal, a distillation tube and a thermometer was used.
The distillation tube was connected to a cooling tube, a flask and a decompression adapter, and the decompression adapter was connected to a vacuum pump.

Deionized water (280 g) was charged into the above flask, and then commercially available sodium azide (100 g) (purity 99.7% by weight, water content 0.1% by weight) was charged with stirring to completely dissolve it at 40 ° C. The pH of the aqueous solution was about 9.5. After the dissolution was completed, the degree of pressure reduction was adjusted so that the temperature of the flask contents was kept at 40 ° C., and the concentration was started while stirring. When the amount of distilled water reached 190 ml, the pressure in the flask was returned to atmospheric pressure to stop the concentration, and the mixture was cooled to room temperature. The content of the flask after concentration was an aqueous solvent slurry solution, and the weight thereof was
180.2g, pH was about 9.5.

The obtained slurry liquid was filtered with a centrifugal filter to obtain 60.4 g of wet crystals, which was dried in a drying oven at 103 ° C. to obtain 59.1 g of dry powder (purity 99.8% by weight, water content: 0.
08% by weight). Table 1 shows the measurement results of the powder properties such as specific surface area, particle size distribution, volume average particle size, loose apparent specific gravity, compressibility and angle of repose of the obtained powder, and self-decomposition property.

Example 2 The same procedure as in Example 1 was carried out except that 0.12 g of the nonionic surfactant "Emulgen 950" (trade name; manufactured by Kao Corporation) was added in Example 1, and an aqueous solvent slurry solution of 181.5 was added. g, 60.0 g of wet crystals by centrifugal filtration and 58.7 g of dry crystals (purity 9
9.8% by weight, water content 0.06% by weight) was obtained. The pH of the obtained aqueous solvent solution and the aqueous solvent slurry solution is about 9.
Was 5. Table 1 shows various powder characteristics of the obtained powder and measurement results of self-decomposition characteristics.

Example 3 Aqueous solvent slurry 1 was prepared in the same manner as in Example 1 except that 5 g of sodium hydroxide was added.
80.0g, 62.4g wet crystals by centrifugal filtration and 61.0 dry crystals
g (purity 99.5% by weight, water content 0.10% by weight) was obtained. The pH of the resulting aqueous solvent solution and the aqueous solvent slurry solution,
All were about 10. Various powder characteristics of the obtained powder,
In addition, Table 1 shows the measurement results of the self-decomposition characteristics.

Comparative Example 1 A pressure vessel test was conducted using the commercially available sodium azide used in Examples 1 to 3 as it was. As a result, decomposition of the sodium azide occurred explosively and the rupturable plate burst every time. It was extremely dangerous. Table 1 shows the measurement results of various powder characteristics and self-decomposition characteristics of the sodium azide used.

[0048]

[Table 1]

[0049]

Among the alkali metal azides produced by the method of the present invention, sodium azide powder having the most preferable specific surface area has the following remarkable advantages.

(1) Its self-degrading property is fairly mild, and it is classified as a dangerous substance class 5 class 2. Therefore, the regulation is comparatively lenient, such as a much simpler packaging form compared to conventional commercial products, and a much larger quantity can be transported.
It can be handled more easily than commercial products.

(2) The powder flow characteristics are excellent, the powder cross-linking phenomenon does not easily occur at the time of taking out even if the powder cross-linking phenomenon occurs even if it is put in a storage facility such as a hopper, and even if a slight cross-linking phenomenon occurs, use of a vibrator or the like. Therefore, it can be easily taken out.

(3) The powder can be automatically metered, which contributes to the automation of the production line for gas generating agents for air bags.

(4) The compaction degree of the powder is small and the bulk density is large, so that the packaging can be made compact and the transportation cost can be reduced.

[0054]

[Brief description of drawings]

FIG. 1 is a chart of particle size distribution measurement results of sodium azide powder, which is the most preferable product according to the method of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasushi Imai 1-6-27 Inokashira, Mitaka City, Tokyo Inokashira Dormitory (72) Inventor Takehiko Yoshie 1-9-11 Shinkanaya, Uozu, Toyama Prefecture Nippon Carbide Industry Co., Ltd. Seiwa Dormitory

Claims (3)

[Claims] 1. An alkali metal which comprises dissolving an alkali metal azide in an aqueous solvent and then precipitating the alkali metal azide from the resulting aqueous solution of the alkali metal azide under pH 7 to 13 conditions. Method for producing azide powder. 2. The method according to claim 1, wherein the alkali metal azide powder is sodium azide powder. 3. The sodium azide powder according to claim 2, which has a Microtrac type specific surface area of 0.08 m ² / cc or less after the ultrasonic dispersion treatment.