JPS59443B2 - Purification method of anhydrous sodium dithionite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying anhydrous t-IJium dithionate.

More specifically, in an organic solvent and an aqueous solvent, sodium formate, sodium hydroxide or sodium sulfite, and anhydrous sulfite are used as raw materials, and anhydrous sodium dithionate suspension is added to the anhydrous sodium dithionate suspension. This is a method for purifying anhydrous sodium dithionate, which is characterized by adding crystallization to obtain anhydrous sodium dithionate having a large particle size.

Anhydrous sodium dithionate is a relatively unstable substance, so if left in the air or in an atmosphere of high temperature and humidity,
It is well known that the quality deteriorates due to partial decomposition.

In addition, during the industrial production of anhydrous sodium dithionate, some of the crystals are crushed and pulverized during the filtration, drying, etc. processes, increasing the specific surface area, making it more susceptible to the atmosphere and lowering the quality. Some of the items that have fallen may be regenerated.

Such materials tend to be dispersed into the air during industrial use, and even if they are chemically pure enough to be used, they must be said to have degraded in terms of their commercial value. .

If these low-grade products can be made into high-quality products with high purity and large particle size through simple operations, the industrial value will be extremely large.

Conventionally, the purification method for anhydrous sodium dithionate is as follows:
The following recrystallization method is known.

That is, sodium dithionite dihydrate is heated in the presence of a salt-saturated solution of water or dilute alcohol and the salt necessary to substantially saturate the free water to crystallize and separate the anhydrous sodium dithionite layer. Method of refining (% Kosho 46-18
No. 374) and a method of obtaining an anhydrous layer of sodium dithionite by adding methanol or ethanol to an aqueous solution of sodium dithionite kept at a temperature higher than the dehydration temperature of trihydrate (Japanese Patent Publication No. 16326/1983). be.

In the former case, an aqueous solution or a dilute alcohol aqueous solution of sodium dithionite is separated at 0°C as a dihydrate salt of phthalate, dithionic acid I-IJ, and then this is further diluted with a salt solution of water or a dilute alcohol solution. It takes extremely complicated operations and steps, such as dispersing it in a slurry form in a saturated solution, adding salt necessary to substantially saturate the free water, heating it, crystallizing it with anhydrous salt, and then separating and drying it. However, it is not advantageous as an industrial purification method because it requires a large amount of salt and steam.

The latter is a method in which alcohol is added to an aqueous solution of sodium dithionite at a dehydration temperature of 52° C. or higher for sodium dithionite dihydrate to gradually lower the solubility and crystallize.

In this case, if the addition method is reversed and an aqueous sodium dithionite solution is added to the alcohol, the degree of supersaturation will increase rapidly, the rate of partial nucleation will slow down, and fine crystals will crystallize almost immediately upon addition. .

Since it is undesirable to obtain only low-grade anhydrous sodium dithionate crystals, the general method is not to add a crude aqueous solution of sodium dithionate to alcohol.

Therefore, this latter method was also carried out simply by the general operation of adding alcohol to an aqueous sodium dithionite solution as described above.

However, when this method is examined in detail from an industrial standpoint, a large number of disadvantageous problems are found in its implementation.

That is, raising the temperature of the sodium dithionite aqueous solution to the dihydrate dehydration temperature of 52°C or higher and adding alcohol while maintaining this temperature to crystallize is as described in the specification of the above-mentioned patent. It is clear that this cannot be done in a short period of time.

Because sodium dithionite is highly susceptible to decomposition during ripening in the coexistence of water, it is desirable to complete crystallization in as short a time as possible in order to purify it with a high yield. It is extremely difficult to implement this in Japan.

Furthermore, all three of the above methods require a large amount of dedicated equipment for purification.

Therefore, the inventors conducted extensive research on a purification method that is most suitable for the properties of this easily decomposable anhydrous sodium dithionate, is extremely advantageous from an industrial perspective, and is even simpler, and as a result, they have arrived at the method of the present invention. did.

That is, at the end of the reaction, anhydrous sodium dithionate was produced from sodium formate, sodium hydroxide or sodium sulfite, and anhydrous sulfite in an aqueous solution of low-grade sodium dithionite in an organic solvent such as alcohol and an aqueous solvent. By simultaneously adding an organic solvent used in the reaction, such as alcohol, if necessary, to the suspension at a temperature higher than the dehydration temperature of sodium dithionite dihydrate, a high-grade anhydrous layer of dithionite with large particle size can be obtained. ) IJum has good yield,
It has been found that the anhydrous layer produced by the synthesis can be obtained together with sodium dithionate.

Contrary to the conventionally known recrystallization method in which an organic solvent is added to an aqueous solution of sodium dithionite, this addition method, which normally yields only a fine, low-grade anhydrous layer of sodium dithionite, can produce large-sized particles of sodium dithionite. It was discovered that high quality anhydrous sodium dithionate can be obtained in high yield, and this invention was completed.

In order to carry out the conventionally known recrystallization method, it is necessary to install a complete set of equipment for this purpose, but according to the method of the present invention, it is necessary to install a complete set of equipment for this purpose. It can be easily carried out as long as you have the equipment,
Its industrial effects are extremely significant.

The crude sodium dithionate of this invention refers to the anhydrous sodium dithionate (IJium) partially decomposed to a low purity, and the anhydrous sodium dithionate (IJium) crystals partially decomposed during the process of product production. Particularly fine powders are available.

The crude sodium dithionate aqueous solution to be added here is adjusted to a pH above neutral using sodium hydroxide in an inert gas.
Prepare to.

The preferred pH range is 9 to 13, but this is done in order to minimize the decomposition of thorium dithionite during industrial implementation. When added to the suspension, this pH range may be exceeded as long as substantial decomposition is not expected.

The temperature for preparing the crude sodium dithionate may be at room temperature or below room temperature.

Of course, the aqueous solution may be heated within a stable range.

Alternatively, the slurry may be maintained at a low temperature and dissolved while continuously heating or adding water immediately before addition.

The concentration of the crude sodium dithionate aqueous solution is not particularly limited, but it is preferably close to a saturated solution.

When adding the crude sodium dithionate aqueous solution to the suspension at the end of the IJium production reaction, it is preferable to add the solvent such as alcohol used in the reaction at the same time. Addition is not necessarily necessary as long as the solvent composition of the liquid is within a range where addition of the crude sodium dithionate aqueous solution does not substantially affect the solvent composition.

In addition, although this article mainly describes the case where the reaction is carried out with a suspension of anhydrous sodium dithionate in an alcohol and water solvent, other solvents such as dioxane, formamide, dimethyl sulfoxide, acetonitrile, dimethyl The same concept can be applied even when formamide etc. are used or when these are used together.

The amount of roughened sodium dithionate to be added is suitably not more than % parts by weight, preferably not more than % parts by weight, based on the sodium dithionite produced in the synthesis reaction.

In addition, the addition rate of the crude sodium dithionate aqueous solution is
Crystalline anhydrous t-IJium dithionite in the reaction completed solution 1
00 parts at a rate of 8 parts or less per minute).

The anhydrous sodium dithionite aqueous solution to be added does not necessarily need to be heated, but should be heated to approximately 50'C immediately before addition.
It is preferable to raise the temperature to the above appropriate temperature.

The temperature of the suspension to which this is added at the end of the anhydrous sodium dithionite synthesis reaction may be 52°C or higher, the dehydration temperature of sodium dithionite trihydrate, and may be 60 to 70°C.
It is preferable to keep it at

Next, the method of the present invention will be specifically explained using examples.

Example Methanol (100%) was placed in a stainless steel reactor (capacity 11) equipped with a stirrer, reflux condenser, pressure regulator, raw material supply pipe, metering pump, gas outlet pipe, thermometer and heating device.
69g and water'17g and sodium formate (97%)2
Charge 4 g, pressurize to 1 kg/i by drilling, and raise the temperature to 80°C.

While maintaining this temperature and pressure, sodium formate aqueous solution (5
Section 3, 8) 173g and caustic soda aqueous solution (48.5%)
A solution prepared by dissolving 41 g in methanol (100%) 86.9 and an anhydrous sulfite methanol solution (anhydrous sulfite concentration 34
．． 2%) and 281 g from separate supply pipes, 60
Drop at a constant rate for minutes.

Next, a solution prepared by dissolving 20 g of a caustic soda aqueous solution (48.5 parts) in 37 g of methanol (100%) and 94 g of an anhydrous sulfite methanol solution (anhydrous sulfite concentration 34.2 parts) are supplied over 90 minutes.

After supplying the raw materials, stirring was continued for 3 hours while maintaining the temperature and pressure, and the mixture was cooled to 60°C.

Micronized anhydrous sodium dithionite (purity factor 82, particle size 10 μ or less) is added to a solution prepared in advance by adding 1 g of caustic soda aqueous solution (48.5%) to 57.9 g of water prepared in advance.
A crude aqueous solution of sodium dithionate (pH = 12) in which 14 g of sodium dithionate was dissolved at room temperature and 162 g of methanol (100%) were added dropwise to the reaction-completed suspension kept at 60°C at a constant rate for 20 minutes from the injection port. After that, it was cooled to 45°C, anhydrous sodium dithionite was filtered off, and methanol (100
%) and dried to obtain 152 g of anhydrous sodium dithionite with a purity of 90.8%.

In addition, when the sodium dithionite aqueous solution is not added, anhydrous sodium dithionite 14 with a purity of 90.8% is used.
Obtained 0g.

The particle size distribution of each is as shown in Table 1.

As shown in the above examples, when a crude sodium dithionate aqueous solution is added, anhydrous sodium dithionite having a large particle size can be obtained at a high yield.

Claims (1)

[Claims] 1. When producing anhydrous sodium dithionate using sodium formate, sodium hydroxide or sodium sulfite, and anhydrous sulfite as raw materials in an organic solvent and an aqueous solvent during purification of crude sodium dithionate, the suspension at the end of the reaction. 1. A method for purifying anhydrous sodium dithionate, which comprises adding crude sodium dithionate as an aqueous solution to a turbid liquid and crystallizing it to obtain an anhydrous sodium dithionate having a large particle size.