JPS6131048B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing dithionite, and more specifically, a method for effectively reusing a liquid from which dithionite crystals are separated or a crystal washing solution for the production of dithionite. Regarding. In order to effectively utilize unreacted raw materials in the so-called formate method, which produces dithionite from a formic acid compound, an alkali compound, and anhydrous sulfite in a water-organic solvent, dithionite crystals are separated after the reaction. Attempts were made to reuse the dithionite, but the yield and purity of the resulting dithionite were significantly reduced, making it impractical. Therefore, a method was proposed to recover the formate remaining in the liquid as methyl formate.
In this case, since distillation is carried out while heating under acid treatment, the material of the equipment needs to be of a high quality, and a large amount of solid matter remains in the equipment after recovering methyl formate, making it difficult to handle, and the equipment cost is extremely high. It is unsuitable for practical use because of its large size. On the other hand, the reason why it is difficult to reuse the solution mentioned above is that thiosulfate, which is a by-product from the decomposition of dithionite, is dissolved in the solution, which inhibits the production of dithionite and decomposes it. A method of removing thiosulfate from the liquid has been proposed because the purpose is to promote the For example, there is a method of oxidatively decomposing thiosulfate, but in this case there are many unit operations such as making the liquid acidic and evaporating it to dryness, which increases equipment costs and consumes a lot of heating energy, making it impractical. The present invention was completed as a result of research to overcome these drawbacks, and its structure is based on a reaction process for producing dithionite from a formic acid compound, an alkali compound, and anhydrous sulfite in a water-organic solvent. In the final step, an epoxy compound, a halogenated hydrocarbon represented by the formula R-X, or a mixture of two or more thereof is added to the reaction solution, and then the dithionite crystals are separated in a solution or an organic solvent. It is characterized in that the washing solution for the washed crystals or a mixed solution thereof is recycled and reused in the production of the dithionite salt. The method for producing dithionite according to the present invention will be explained in detail. First, in the formate method, water is usually
Dithionite is synthesized by reacting formate, an alkali compound, and anhydrous sulfite in an organic solvent, and in the final stage of the reaction (for example, just before or during cooling of the reaction solution), an epoxy compound or a halogenated hydrocarbon or A mixture of two or more of these is added to the reaction solution, and the dithionite crystals are separated. Examples of the formic acid compound used in the present invention include formate salts, formic acid, and formic acid esters; examples of the alkali compounds include sodium hydroxide, sodium carbonate, and sodium sulfite;
Examples of organic solvents include alcohols such as methanol, ethanol, and isopropanol, ethers such as dioxane, and acid amides such as dimethylformamide. Among these, alcohols, particularly methanol, are preferred. Unreacted formate and hydrogen sulfite remain in the liquid from which the crystals are separated or in the crystal washing solution, but thiosulfate, which is a by-product from the decomposition of dithionite, is present in the final stage of the reaction. By adding a compound that selectively reacts with thiosulfate in the reaction solution, it is converted into a so-called harmless substance that does not participate in any way in inhibiting the production or decomposition of dithionite. As the compound added to the reaction solution in the final stage of the reaction, an epoxy compound or a halogenated hydrocarbon represented by the formula RX is used. Examples of the epoxy compound include ethylene oxide, propylene oxide, butylene oxide, isobutylene oxide, styrene oxide, cyclohexene oxide, epichlorohydrin, and epibromohydrin, but of course compounds other than these may also be used. Further, as the halogenated hydrocarbon represented by the formula R-X, R is a primary or secondary alkyl group having 1 to 8 carbon atoms, an allyl group, a 2-methyl group, or a 2-ethylallyl group. One, X
is a compound in which halogen is used. All of the above compounds selectively react with thiosulfate in the reaction solution, and can almost completely remove thiosulfate from the solution. In addition, the above treatment is carried out near the reaction temperature, usually above 60°C, so
The processing speed is increased compared to the case where the processing is carried out at room temperature, and the processing time can be extremely shortened. The addition amount is usually 1 to 3 times the molar amount, preferably 1 to 2 times the amount of thiosulfate contained in the reaction solution.
This is twice the molar amount. The liquid obtained by adding the above compound to convert thiosulfate into a harmless substance contains almost no substance that inhibits the production or decomposition of dithionite. It can be recycled and reused in salt production, in which case a product with high purity can be obtained in high yield. In addition, in the production of dithionite by the formate method, conditions such as raw material molar ratio, solvent composition, and amount of solvent have a large influence, so when the liquid or cleaning liquid is recycled, the formate and sulfite in the circulating liquid are It is necessary to measure the contents of hydrogen salts, organic solvents, water, etc., determine the amount 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 dithionite according to the present invention, not only can the thiosulfate dissolved in the liquid in the reactor be almost completely treated in a short time, but also the thiosulfate dissolved in the solution in the reactor can be completely treated. Because the reactor is under an atmosphere of carbon dioxide gas, which is a by-product from the production of dithionite, it is possible to suppress the dangers caused by compounds added to the liquid. Since it can be processed, it is very easy to handle in industrial applications, such as not requiring a new container for processing thiosulfate. Furthermore, since thiosulfate in the liquid can be almost completely removed, even if these liquids are recycled, highly pure products can be obtained at a high yield, and raw materials can be recycled, making effective use of resources. . Furthermore, in the past, methanol was recovered by distilling the entire amount of 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 formate and hydrogen sulfite are not disposed of, the burden of waste liquid treatment is significantly reduced. Next, the method for producing dithionite according to the present invention will be explained in more detail with reference to Examples. Example 1 (1) First reaction A slurry of 81 parts of sodium formate dissolved in 74 parts of hot water and 105 parts of methanol was added using a stirrer, thermometer, reflux condenser, and deep cooling for collecting low-boiling substances. The mixture is placed in a jacketed reactor equipped with a condenser and a tank for dropping raw materials, and the liquid in the reactor is heated to 82°C under a pressure of 1.0 Kg/cm ² gauge while stirring. Furthermore, 276 parts of methanol and methyl formate
A solution prepared by dissolving 105 parts of anhydrous sulfurous acid and 69 parts of 50% caustic soda solution were added dropwise in parallel over 90 minutes to the 16 parts of the solution, and stirring was continued for an additional 150 minutes while maintaining the temperature and pressure. Next, add the reaction solution to 20
Start cooling to 73°C over a period of minutes, and at the same time start adding the compounds listed in Table 1 to the reaction solution via the inlet tube reaching the bottom of the reaction solution so that the compounds listed in Table 1 are supplied into the reaction solution. ,5
Finish adding within minutes. After cooling the reaction solution,
The dithionite crystals were filtered under pressure with carbon dioxide gas to separate the crystals and the liquid, and then the crystals were washed with 120 parts of methanol. After washing the crystals were dried under reduced pressure for 75 minutes.
Dry by holding at ~90°C for 90 minutes. The yield of each product reacting with each compound added in the final stage of the reaction and the purity of sodium dithionite are also listed in Table 1. (2) Second reaction The methanol composition in the liquid recovered in the first reaction was 68%. The circulating liquid was 154 parts, which is the same amount of methanol as the methanol at the start of the first reaction.This circulating liquid was used instead of methanol at the start of the first reaction. The same reaction was repeated. Equimolar amounts of caustic soda and sulfurous anhydride as sodium formate and sodium hydrogen sulfite dissolved in the circulating fluid were supplied to the reactor by subtracting their dissolved amounts in the circulating fluid from the first reaction charge amount. Furthermore, the amount of water for dissolving sodium formate was determined by subtracting the amount of water present in the circulating fluid. At the final stage of the reaction, the compounds listed in Table 1 are added to the reaction solution in the same manner as in the first reaction,
The crystals of sodium dithionite and the liquid were separated according to a conventional method, and then the crystals were washed with methanol, and the crystals were dried at 75 to 90°C under reduced pressure. The product yield and purity of sodium dithionite are listed in Table 1.

[Table] Example 2 In the first reaction of Example 1, the washing liquid was
120 copies were collected. The methanol composition in this cleaning solution was 92%. Methanol in the cleaning solution is the first
114 parts of the washing liquid was used as a circulating liquid so that the amount was the same as that of methanol at the start of the reaction. Equimolar amounts of caustic soda and sulfurous anhydride as sodium formate and sodium hydrogen sulfite dissolved in this circulating fluid are supplied to the reactor by subtracting their dissolved amounts in the circulating fluid from the amount charged in the first reaction. The amount of water that dissolves sodium was determined by subtracting the amount of water present in the circulating fluid. In the final stage of the reaction, the compounds listed in Table 2 were added to the reaction solution in the same manner as in the first reaction, and the crystals of sodium dithionite and the liquid were separated according to a conventional method, and then the crystals were washed with methanol. The crystals were dried at 75-90°C under reduced pressure. The product yield and purity of sodium dithionite are listed in Table 2.

[Table] Example 3 The first reaction described in Example 1 was carried out, and the crystals of sodium dithionite produced in the reaction were separated from the reaction solution, and then the crystals were washed with 120 parts of methanol. The crystals were soaked in methanol, and the liquid in the filter was pressurized with carbon dioxide gas to recover 120 parts of the cleaning liquid. The methanol composition in this cleaning solution was 92%. Next, in place of the 276 parts of methanol used to dissolve sulfurous anhydride in the first reaction, the entire amount of the above washing liquid, 165.6 parts of methanol, and methyl formate were used to dissolve sulfurous anhydride, and the sulfurous anhydride was dissolved in the washing liquid. Caustic soda and anhydrous sulfurous acid in equimolar amounts as sodium formate and sodium hydrogen sulfite are supplied to the reactor by subtracting their dissolved amount in the washing liquid from the first reaction charge, and the water that dissolves the caustic soda is present in the washing liquid. The same reaction as in the first reaction was carried out by subtracting the amount of water used in the reaction, and in the final stage of the reaction, the compounds listed in Table 3 were added to the reaction solution, and sodium dithionite crystals were prepared according to a conventional method. The liquid was separated and the crystals were subsequently washed with methanol and dried at 75-90°C under reduced pressure. The product yield and purity of sodium dithionite are listed in Table 3.

【table】

Claims (1)

[Claims] 1. When producing a dithionite salt by reacting a formic acid compound, an alkali compound, and anhydrous sulfite in a water-organic solvent, an epoxy compound or a formula R- A halogenated hydrocarbon represented by A method for producing dithionite, characterized by recycling and reusing it in the production of dithionite. 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 or epibromohydrin. 3 R of the halogenated hydrocarbon represented by the formula RX is one of a primary or secondary alkyl group having 1 to 8 carbon atoms, an allyl group, 2-methyl or 2-ethylallyl group, 2. The method of claim 1, wherein X is halogen.