JPS5939361B2 - Method for producing anhydrous sodium dithionite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing anhydrous sodium dithionite.

Specifically, when producing anhydrous sodium dithionite from sodium formate, anhydrous sulfite, and sodium salt that reacts with sodium hydroxide or sulfite anhydride to produce acidic sodium sulfite in an organic solvent-water mixed solvent system,
By adding sodium borohydride at the end of the reaction, unreacted sodium acid sulfite dissolved in the reaction end solution is substantially completely converted to anhydrous sodium dithionite, resulting in anhydrous sodium dithionite in high yield and high yield. This is a method for producing anhydrous sodium dithionite, which is characterized in that it is obtained at a high conversion rate and that pretreatment for recycling a solvent containing unreacted sodium formate is simple and advantageous.

Anhydrous sodium dithionite is produced by reacting with sodium formate, sulfite anhydride, and sodium hydroxide or sulfite anhydride in an organic solvent-water mixed solvent system, generally methanol or/and ethanol-water mixed solvent. A method for producing sodium salts that produce sodium sulfite, such as sodium sulfite or sodium carbonate (hereinafter referred to as the "sodium formate method"), or sodium borohydride and acidic sulfite), or sodium hydroxide and sulfite anhydride. A method of producing sodium dithionite as an aqueous solution at low temperatures (hereinafter referred to as "sodium borohydride method") is known.

In the sodium formate method, anhydrous sodium dithionite is said to be produced according to the following reaction formula.

This method is carried out in an organic solvent-water mixed solvent system, so
At the end of the reaction, almost all of the anhydrous sodium dithionite produced crystallizes out.

Therefore, once the reaction is complete, it is possible to obtain highly pure and stable crystalline anhydrous sodium dithionite by simply filtering, washing, and drying.However, the sodium borohydride method is characterized by the following reaction formula: This method allows sodium dithionite to be obtained only as an aqueous solution, but unlike anhydrous crystalline sodium dithionite, an aqueous solution cannot be stored stably for a long period of time.

In order to obtain a crystalline anhydrous sodium dithionate layer from this aqueous solution that can be stored for a long period of time, it is necessary to use salting out, dehydration, etc., such as the zinc method, which was used to produce anhydrous sodium dithionite even before the sodium formate method. Requires complex post-processing.

In the sodium borohydride method, unlike the sodium formate method, there is no known method for directly obtaining crystalline anhydrous sodium dithionite without post-treatment such as salting out.

Furthermore, when comparing the two in terms of the reaction mechanism for producing sodium dithionite, it is clear from the above reaction formula that in the sodium formate method, sodium formate reacts with sulfite anhydride, resulting in acidic sodium sulfite. In addition, formic acid is produced, and this formic acid is then reduced together with acidic sodium sulfite produced from anhydrous sulfurous acid and sodium hydroxide, etc., to produce sodium dithionite.

That is, it can be said that in the sodium formate method, sodium formate serves as a part of the sodium source for sodium dithionite and also serves as a reducing agent.

On the other hand, in the sodium borohydride method,
Sodium borohydride only serves as a reducing agent for converting sodium acid sulfite produced from anhydrous sulfite, sodium hydroxide, etc. into sodium dithionite through another reaction, and does not serve as a sodium source.

Comparing this from an industrial perspective, sodium formate is cheaper than sodium borohydride, and sodium formate is less expensive than sodium formate in the industrial manufacturing process of polyhydric alcohols such as pentaerythritol and trimethylolpropane. It is stably obtained in large quantities as a living organism.

Furthermore, the sodium ion, which is a constituent element of sodium formate, is utilized as it is in the composition of sodium dithionite, and at the same time becomes formic acid, which is a reducing agent.

From the above points, the sodium formate method is extremely advantageous as an industrial manufacturing method, as it directly produces crystalline anhydrous sodium dithionate that can be stored stably for a long period of time, rather than an unstable aqueous solution, and is currently the main manufacturing method. This is why.

However, this sodium formate method requires that the pH be maintained within an appropriate range during the reaction, and therefore it is a common method to carry out the reaction using an excess of sodium formate, which also serves as a pH buffer.

After completion of the reaction, the crystallized anhydrous sodium dithionate layer is separated in a furnace, and the resulting mother liquor contains 34 to 45% of the sodium formate used, and 0.0% to 1 mole of anhydrous sulfite used.
15 to 0.2 moles of unreacted sodium acid sulfite, a small amount of sodium thiosulfate produced by side reactions,
and formic acid esters.

Therefore, recycling the mother liquor is advantageous from the standpoint of reducing product costs and preventing pollution.
This is very important for industrially producing anhydrous sodium dithionite.

However, since sodium thiosulfate is dissolved as a by-product in the mother liquor, it is disadvantageous to recycle it as it is.

This is because when sodium thiosulfate is present in advance, the sodium thiosulfate by-product reaction proceeds even more rapidly, which significantly inhibits the production of anhydrous sodium dithionite (Japanese Patent Publication No. 47-16413). .

Therefore, in order to recycle the mother liquor, a pretreatment method such as removing sodium thiosulfate or chemically changing it is required, and various methods have been proposed in this regard.

For example, (4) a method in which the mother liquor is treated with sulfuric acid and acidic to decompose acidic sodium sulfite, sodium thiosulfate, and sodium formate, and a mixed solution of sulfite anhydride, formic acid ester, and alcohol is recovered and recycled. 48-3
8558).

(6) A method of oxidizing the mother liquor through air or oxygen at a temperature of 45°C or less and a pH of 3 to 5 and then circulating it (Special Publication No. 47-
16413).

(Q: A method in which the mother liquor is neutralized with sodium hydroxide, acidic sodium sulfite is crystallized as sodium sulfite, separated in a furnace, and the tear fluid containing sodium thiosulfate and sodium formate is treated with hydrogen peroxide and reused. -15299
6).

However, when considering these from an industrial perspective, method (5) requires equipment made of special and expensive materials to treat the mother liquor with acidity, and it is difficult to reduce corrosion of the equipment. requires complex processes and precise operations.

In this method, sodium thiosulfate must be oxidized with air or oxygen in the coexistence of acidic sodium sulfite.
Since it has to be carried out under mild conditions, the process requires a very long time.

(Method Q requires a complicated process because hydrogen peroxide treatment cannot be performed until the filtrate has been neutralized and sodium acid sulfite has been separated.

It has many disadvantages.

Furthermore, the acidic sodium sulfite in the upper vessel liquid is only used as a part of the next raw material, and in the case of a batch reaction, it is based on the anhydrous sulfite or sodium ion added per reactor. The conversion rate does not increase at all even if the mother liquor is recycled. Therefore, in the sodium formate method, the acidic sulfite dissolved in the reaction solution at the end of the reaction is converted into anhydrous sodium dithionite for thermal spraying. If it is possible to increase the production amount per reactor to 15 to 20
%increase.

This increase in production not only contributes to lower production costs, but also because the salts dissolved in the mother liquor are mainly sodium formate and sodium thiosulfate, so the various treatment methods mentioned above are applied when circulating the mother liquor. It also becomes extremely simple and easy.

The present inventors focused on these points and completed the present invention after repeated research.

Specifically, sodium formate, sulfite anhydride, and sodium hydroxide, or a sodium salt that reacts with sulfur anhydride to produce sodium acid sulfite, are reacted in an organic solvent-water mixed solvent system by the sodium formate method, and at the end of the reaction, (Acidic sulfite dissolved as unreacted in the reaction completed solution)
Crystalline anhydrous sodium dithionate is obtained at a high conversion rate by an extremely simple operation of adding and reacting a small amount of sodium borohydride necessary to reduce IJium to anhydrous sodium dithionite.

Further, the content of unreacted acidic sodium sulfite in the slurry obtained by individually collecting anhydrous sodium dithionite after the above-mentioned sodium borohydride treatment can be reduced to 0.05% or less, which is substantially zero.

Therefore, when recycling the furnace liquid, the various pretreatments described above can be simplified and advantageously carried out.

As the sodium formate method in the method of the present invention, any method known up to now can be applied.

In the present invention, the reaction completion solution refers to a suspension containing crystallized anhydrous sodium dithionite at the end of the reaction in the sodium formate method, and as a matter of course, anhydrous sodium dithionite is removed from the suspension. Also refers to the mother liquor obtained separately.

Although organic solvents are generally alcohols, the same concept can be applied when other solvents such as dioxane, formamide, dimethyl sulfoxide, dimethyl formamide, acetonitrile, etc. are used, or when these are used in combination. The amount of sodium borohydride added is 1.0 to 2.0 parts by weight, preferably 1.1 to 1.7 parts by weight, based on 100 parts by weight of anhydrous sulfite used in the reaction.

Sodium borohydride may be added in the form of crystals, but it is preferably added after being dissolved in a 0.1 to 2 N hydroxide aqueous solution.

In addition, the dissolution temperature when making an alkaline aqueous solution may be heated within a range where sodium borohydride does not decompose.
Usually, room temperature or below room temperature is preferable.

The temperature of the reaction solution at the end of the sodium dithionite reaction when adding sodium borohydride is the usual formic acid reaction temperature (75 to 95°C) of the IJum method.
It may be below, but preferably 40 to 50°C,
After addition, the dehydration humidity of sodium dithionite dihydrate should be at least 52°C or higher, preferably 60 to 70°C, and maintained at this temperature for 10 minutes or more.

All of the above-mentioned methods can be improved and applied to pretreatment of lachrymal fluid for circulating use, but method 0 is preferred.

The method of the present invention will be specifically explained below with reference to Examples, but the method of the present invention is not limited thereto.

Example 1 2 methanol was added with stirring into a stainless steel reactor (capacity 17) equipped with a stirrer, a reflux condenser, a pressure regulator, a raw material supply pipe, a metering pump, a gas outlet pipe, a hygrometer and a heating device.
65g and 120g of water and 1 part of 90% pure sodium formate
82 g and 93.5 g of a 48% aqueous sodium hydroxide solution were added, the pressure was increased to 1 kg/d with nitrogen, and the temperature was raised to 80°C.

While maintaining this temperature and pressure, 394 g of an anhydrous sulfite methanol solution (anhydrous sulfite concentration 34%) was added dropwise at a constant rate for 30 minutes.

Next, an anhydrous sulfite methanol solution (anhydrous sulfite concentration 34%)
) 132 g are added dropwise at a constant rate for 90 minutes.

After supplying the raw materials, the mixture was stirred for 2 hours and 30 minutes while maintaining the temperature and pressure, and then cooled to 40°C.

2.5 g of sodium borohydride was dissolved in 16 g of a 1.6% aqueous sodium hydroxide solution and added dropwise over 5 minutes.
Raise the temperature to 0°C and stir for 10 minutes.

This completes the reaction.

The crystalline anhydrous sodium dithionitite is separated in a furnace under an inert gas, washed with 300 I of methanol, and dried under reduced pressure at 75°C.

Anhydrous sodium dithionate 240J with purity 90.9%
get.

The content of acidic sodium sulfite in the offshore washing liquid thus obtained was 0.03%.

While stirring, 6.7 g of 48% sodium hydroxide and 13.7 g of 30% hydrogen peroxide were added to 360 g of this washing liquid and heated under reflux for 30 minutes.

No acidic sodium sulfite or sodium thiosulfate remained in this circulating fluid.

Since it contains 20.6g of sodium formate, this is subtracted from the initial amount.

The method of circulating the offshore washing liquid after the second time is carried out in the same manner as the first time.

The table below shows the results of recycling and reusing the Oki washing liquid four times in this way.
Shown in 1.

Comparative Example 182 g of sodium formate with a purity of 90%, 93.5 g of a 48% aqueous sodium hydroxide solution, and 526 g of an anhydrous sulfite methanol solution (anhydrous sulfite concentration 34%) were mixed in a mixed solvent consisting of 269 g of methanol and 120 g of water.
The reaction was carried out in the same manner as in 1, and the reaction suspension was filtered without treatment with sodium borohydride, and the separated anhydrous sodium dithionite was dissolved in methanol 300. After washing with p.
Drying under reduced pressure at 75° C. yields 195 g of anhydrous sodium dithionite with a purity of 90.8%.

Claims (1)

[Claims] 1 In an organic solvent-water mixed solvent system, for producing anhydrous sodium dithionite from a sodium salt that reacts with formic acid, anhydrous sulfite, and sodium hydroxide or anhydrous sulfite to produce acidic sodium sulfite. Hit,
1. A method for producing anhydrous sodium dithionite, which comprises adding sodium borohydride to a reaction-finished liquid to convert acidic sodium sulfite dissolved in the reaction-finished liquid into anhydrous sodium dithionite.