JPS6018603B2 - Method for producing dithionite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing dithionite, and more specifically, the present invention relates to a method for producing dithionite, and more specifically, a method in which a furnace liquid from which dithionite crystals are separated or a crystal washing solution is recycled for the production of dithionite. and how to reuse it effectively.

In order to effectively utilize unreacted raw materials in the so-called sodium formate process, which produces sodium stothionite from sodium formate, an alkaline agent, and anhydrous sulfurite in a water-organic solvent, the crystals of sodium dithionite are separated after the reaction. Although it was attempted to reuse the solution, the yield and purity of the resulting sodium dithionite were significantly reduced, making it impractical.

Therefore, a method was proposed to recover the sodium formate remaining in the furnace liquid as methyl formate, but in this case, the equipment was distilled while heating under acid treatment, which required a high quality equipment, and the recovery of methyl formate was also proposed. Afterwards, a large amount of solid matter remains in the device, making it difficult to handle, and the equipment cost is extremely high, making it unsuitable for practical use. On the other hand, the reason why it is difficult to reuse the furnace fluid mentioned above is that sodium thiosulfate, which is created by the decomposition of sodium dithionite, is dissolved in the furnace fluid, which inhibits the production of sodium dithionite and decomposes it. A method for removing sodium thiosulfate from the furnace fluid has been proposed to promote this.

For example, there is a method of oxidizing and decomposing sodium thiosulfate, but this requires many unit operations such as making the furnace liquid acidic and evaporating it to dryness, which increases equipment costs and consumes a lot of heating energy, making it impractical. . In addition, sodium thiosulfate can be rendered harmless by adding ethylene oxide or propylene oxide to the furnace fluid, or by adding butylene oxide, epichlorohydrin, etc. to the furnace fluid or crystal cleaning solution. A method has been proposed.

However, in these methods, when the above-mentioned compound is added to the furnace solution, alkali is gradually generated in response to the reaction rate between the epoxy compound and sodium thiosulfate, and a part of the sodium bisulfite in the solution is mixed with alkali. The reaction produces sodium sulfite, and crystals gradually precipitate. Therefore,
When reusing the detoxified sodium thiosulfate liquid as it is in the production of sodium dithionite, the amount of circulation and composition of the circulating liquid must be controlled because crystals are unevenly present in the circulating liquid. This makes it extremely difficult to recycle the liquid in industrial equipment. The present invention aims to obtain a liquid in which sodium thiosulfate is rendered harmless and has extremely few crystals by preventing the precipitation of crystals or dissolving the precipitated crystals after adding an epoxy compound to the furnace solution or crystal cleaning solution. It was completed as a result of research.

Its composition is that when dithionite is produced from sodium formate or formic acid, an alkaline agent, and anhydrous sulfurite in a water-organic solvent, the precipitated dithionite crystals are separated from the furnace liquid or crystal washing liquid. While adding the epoxy compound, an acidic substance is added so that the - of the liquid after the addition of the epoxy compound does not increase from before the addition, and then this liquid is recycled to the production of the dithionite salt for reuse. Features.
The method for producing sodium dithionite according to the present invention will be explained in detail.

First, in the sodium formate method, sodium dithionite is usually synthesized by reacting sodium formate, sodium hydroxide, and sulfite anhydride in a water-organic solvent, and the reaction solution is cooled to form crystals of sodium dithionite. To separate. Examples of alkaline agents used here include sodium hydroxide, sodium carbonate, and sodium sulfite, and examples of organic solvents include alcohols such as methanol, ethanol, and isopropanol, ethers such as dioxane, and dimethylformamide. Among them, alcohols, particularly methanol, are preferred. Unreacted sodium formate and sodium bisulfite remain in the furnace liquid from which the crystals were separated or in the crystal washing solution, and sodium thiosulfate, which is a by-product from the decomposition of sodium dithionite, is dissolved. In the present invention, an epoxy compound that selectively reacts with sodium thiosulfate is added to the furnace solution or crystal cleaning solution, so that the sodium thiosulfate in the solution is rendered harmless because it does not interfere with the formation or decomposition of sodium dithionite. A liquid with extremely few crystals can be obtained by converting it into a substance and adding an acidic substance to prevent the precipitation of crystals that occur at that time, or by dissolving the precipitated crystals. Examples of epoxy compounds added to the furnace solution or after cleaning include ethylene oxide, propylene oxide, butylene oxide, isobutylene oxide, styrene oxide, cyclohexene oxide, epichlorohydrin, and epipromohydrin, but of course compounds other than these may also be used.

All of the above compounds react selectively with sodium thiosulfate in the furnace solution, and can almost completely remove sodium thiosulfate from the solution.

Although the above reaction proceeds at room temperature, it is usually treated at 30°C. In this case, the reaction rate increases and the reaction time can be significantly shortened compared to when the reaction is carried out at room temperature. The addition amount is usually 1 to 3 times the molar amount of sodium thiosulfate contained in the liquid, preferably 1 to 2 times the molar amount. On the other hand, the acidic substances added to the furnace solution or after cleaning include anhydrous sulfurous acid, sulfurous acid, formic acid, hydrochloric acid, acetic acid, butyric acid, hydrobromic acid, nitric acid, etc., or a mixture of two or more thereof.

Among these, sulfuric anhydride, formic acid, or a mixture thereof, which are raw materials for producing dithionite, are particularly preferred. The pH of the liquid is controlled so as not to increase due to the addition of the acidic substance.

The acidic substance may be added either gradually while observing the pH of the liquid or by adding a predetermined amount of the acidic substance all at once.
Usually, the amount of acidic substance added is 1 to 3 times the molar amount of sodium thiosulfate contained in the liquid. The liquid obtained by adding the above epoxy compound and acidic substance to convert sodium thiosulfate into a harmless substance contains almost no substances that inhibit the production or cause decomposition of sodium dithionite. Therefore, this liquid can be recycled and reused in the production of sodium dithionite, and in this case, a product with high purity can be obtained in an even higher yield.

In addition, in the production of sodium dithionite by the sodium formate method, conditions such as the raw material molar ratio, solvent composition, and amount of solvent have a large effect. It is necessary to measure the contents of sodium bisulfite, organic solvent, water, etc., determine the base of each raw material to be used in the next reaction, and always perform the reaction under the same conditions. As mentioned above, in the method for producing sodium dithionite according to the present invention, sodium thiosulfate dissolved in the reactor liquid or crystal washing liquid can be almost completely removed in a short time, and Since the liquid contains very few crystals, it is very easy to handle when used industrially.

Furthermore, since sodium thiosulfate in the liquid can be almost completely removed, even if these liquids are recycled, high-purity products can be obtained at high yields, and raw materials can be recycled, making effective use of resources. . Furthermore, in the past, methanol was recovered by distilling the entire amount of the furnace liquid and cleaning liquid, but in the present invention, these liquids are recycled and used, so there is no need to recover and distill methanol from the circulating liquid, which saves energy. Furthermore, since unreacted sodium formate and sodium hydrogen sulfite are not disposed of, the burden of waste liquid treatment is significantly reduced. Next, the method for producing sodium dithionite according to the present invention will be described in more detail with reference to Examples.

Note that in the following examples, 0/0 and parts are expressed as weight basis **thin. Example 1 Sodium thiosulfate Shigezasa, sodium bisulfite 1
3,000 g of a furnace liquid containing 121 g of sodium formate was placed in a reactor equipped with a reflux device, and the furnace liquid was maintained at a predetermined temperature while being lit.

Next, in order to convert the sodium thiosulfate in the furnace solution into a harmless substance, the epoxy compounds listed in Table 1 were added to the furnace solution for 2 minutes and dissolved. At the same time, while measuring the pH of the treatment liquid, anhydrous sulfurous acid (methanol solution, concentration 27%) was gradually added to control the pH of the treatment liquid to be 6 or less. The solution was controlled at predetermined times and the sodium thiosulfate concentration was measured. In addition, the amount of crystals was measured by passing the above treatment solution through a furnace. Table 1 shows the reduction rate of sodium thiosulfate and the amount of crystals after filtration. Anhydrous sulfite (as 100%)
The amount of addition is No. 1 thigh, 17g, 1 each for 1 to 7
It was 6g, 17g, 17g, 16g'16g. For comparison, Table 1 also shows the amount of crystals in the treated solution when the epoxy compound was added to the furnace solution and the pH was not controlled by adding sulfite anhydride.

Table 1 Example 2 A slurry made by dissolving 81 parts of sodium formate in 74 parts of hot water and further adding 105 parts of methanol was added to a slurry, a thermometer, a reflux condenser, a cryogenic condenser for collecting low-boiling substances, and a raw material dripping. into a jacketed reactor with a tank for
The liquid in the reactor is flooded to 8.0 k/m under pressure of 1.0 k9/swift gauge while stirring.

Furthermore, a solution in which 105 parts of sulfite anhydride was dissolved in 276 parts of methanol and 16 parts of methyl formate and 50 parts of methyl formate were added.
% caustic soda solution was added dropwise in parallel over 90 minutes, and the addition was continued for an additional 150 minutes while maintaining the temperature and pressure. Next, the reaction solution was cooled to 7,300 ℃, and the dithionite crystals were separated from the reaction solution by passing through a pressurized furnace with carbon dioxide gas. This was followed by washing with 12 drops of crystalline methanol. After washing, the crystals were dried by keeping them at 75-90° C. for 90 minutes under reduced pressure. The product yield was 116.5 parts and the purity of sodium dithionite was 92.3%. Next, during pressure furnace filtration,
510 parts of furnace liquid were recovered.

Since the methanol composition in this furnace liquid was 69%, 15 Moribe of the furnace liquid, in which the methanol in the furnace liquid corresponded to the same amount of methanol at the start of the reaction, was used as the circulating liquid. In order to convert the sodium thiosulfate (2.1 parts) dissolved in this circulating fluid into a harmless substance, the compounds listed in Table 2 are added at once, and sulfuric anhydride is added until the pH of the circulating fluid is 6 or less. The mixture was gradually added to the circulating fluid while controlling the amount of water, and the treatment was carried out under the conditions listed in Table 2. 6.7 parts of sodium formate*IJum and sodium bisulfite dissolved in this treatment solution 6.
2.6 parts of caustic soda equivalent to 7 parts, 4 parts of anhydrous sulfite
．． One part was the amount subtracted from the initial reaction charge. In addition, water in the processing solution is 29. Because $ parts were present, sodium formate was dissolved in 44.7 parts of hot water. Sodium dithionite was produced in the same manner as in the first case, using the above treatment liquid instead of methanol at the start of the reaction. Since the solid matter in the treatment liquid was extremely low, the treatment liquid could be easily charged into the reactor. After the reaction was completed, sodium dithionite crystals were separated from the reaction solution according to a conventional method, and then the crystals were washed with methanol.

After washing, the crystals were dried by holding at 75 to 90 qo under reduced pressure for a period of time. The product yield and purity of sodium dithionite are shown in Table 2. Table 2 Example 3 In order to detoxify sodium thiosulfate in the furnace fluid in the same manner as in Example 1, the epoxy compounds listed in Table 3 were added to the monkey fluid and dissolved, and at the same time 20 g of formic acid (85% concentration) was added to each of the epoxy compounds listed in Table 3. By adding it all at once to the solution, the pH of the solution was controlled to be 6 or less.

The pH of the solution was controlled for a predetermined period of time, and the concentration of sodium thiosulfate and the amount of crystals in the solution were measured. Table 3 shows the reduction rate of sodium thiosulfate and the amount of crystals after filtration. Table 3 Example 4 The initial reaction described in Example 2 was carried out in the same manner, and the crystals of dithionite produced in the reaction were separated from the reaction solution in a pressurized oven with carbon dioxide gas, and then the crystals were dissolved in methanol. After washing with water, the crystals were dried under reduced pressure.

Next, since the methanol composition in the furnace liquid recovered during the pressurized furnace filtration was 69%, 152 parts of the furnace liquid, which corresponds to the amount of methanol at the start of the first reaction, was used as the circulating liquid. .

Sodium thiosulfate (2.
1 part) into a harmless substance, the compounds listed in Table 4 and formic acid (concentration 85%) were added to the circulating fluid at once while controlling the circulating fluid pH to be 6 or less, and the compounds listed in Table 4 were added *
It was processed under the following conditions. Next, in the same machine as in Example 2, the amounts of caustic soda, anhydrous sulfite, and water corresponding to sodium formate and sodium hydrogen sulfite present in the above treatment liquid were subtracted from the initial reaction charge amount, and the treatment liquid was replaced with methanol. Sodium dithionite was produced in the same manner as in the first case described above.

Since the solid matter in the treated liquid was extremely low, it could be easily charged into the reactor. After the reaction was completed, the sodium dithionite crystals were separated from the reaction solution according to a conventional method, and then the crystals were washed with methanol and dried under reduced pressure.

The product yield and purity of sodium dithionite are shown in Table 4. Table 4 Example 5 In the same manner as in Example 1, three bases of epichlorohydrin were added to 3,000 ml of furnace liquid over 2 minutes.

At the same time, the acidic substances listed in Table 5 were gradually added while monitoring the pH to control the pH of the solution to 6 or less.
The pH of the solution was controlled at 45 qo for 2 hours, the rate of decrease was determined from the measurement of the sodium thiosulfate concentration, and the amount of crystals was measured by passing the treated solution through a furnace. The results are shown in Table 5. The amount of acidic substance added is M. 1 is 35% hydrochloric acid 3 females,
M. 2 is up to acetic acid technology, M. 3 was nitric acid 2 difficulty. Table 5

Claims (1)

[Claims] 1. A filtrate or crystals obtained by separating precipitated dithionite crystals during the production of dithionite from sodium formate or formic acid, an alkaline agent, and anhydrous sulfurite in a water-organic solvent. An epoxy compound is added to the cleaning solution, and an acidic substance is added so that the pH of the solution after the addition of the epoxy compound does not increase from before the addition, and then this solution is recycled and reused in the production of the dithionite salt. A method for producing a dithionite salt. 2. The method according to claim 1, wherein the epoxy compound is ethylene oxide, propylene oxide, butylene oxide, isobutylene oxide, styrene oxide, cyclohexene oxide, epichlorohydrin, epibromohydrin, or a mixture of two or more thereof. 3. The method according to claim 1, wherein the acidic substance is anhydrous sulfite, sulfurous acid, formic acid, hydrochloric acid, acetic acid, nitric acid, or a mixture of two or more thereof.