JPS5891004A - Production of dithionite - Google Patents

Abstract

PURPOSE:To permit the reuse of the washing liquid of a titled salt obtd. by allowing formic acid compds., alkali compds. and SO2 to react in a water-org. solvent by adding specific epoxy compds. to said liquid. CONSTITUTION:Formic acid compds., alkali compds., and SO2 are allowed to react in a water-org. solvent to form dithionic anhydride. The reacting liquid is cooled to separate the crystals of said salt and the mother liquor stuck on the crystals is washed with an org. solvent. The crystals are dried. >=1 kinds of ethylene oxide and propylene oxide are added to the washing liquid. Since these compds. react selectively with good reaction percentage with the thiosulfate in the washing liquid, these compds. are converted to harmless materials which make no contribution at all to the interference of formation and the decomposition of dithionite. Thus, this liquid is reusable for production of dithionite and the product having high purity is obtained in high yields.

Description

[Detailed description of the invention] The present invention relates to a method for producing dithionite.

In the method of producing anhydrous dithionite from a formic acid compound, an alkali compound, and anhydrous sulfite in a water-organic solvent, dithionite precipitates in the reaction solution during the reaction, so in the p-filtration step upon completion of the reaction. Crystals of dithionite can be obtained by separation from the reaction mother liquor. If these crystals are dried as they are, the product purity will decrease due to the influence of the mother liquor adhering to the crystals, and the moisture contained in the mother liquor will significantly slow down the drying process and accelerate the decomposition of the dithionite.9 Nithionite If the rate of decomposition is high, it is extremely dangerous and can cause ignition in the drying equipment. Therefore, usually the mother liquor is extracted from the crystals.
After separation, it is essential to thoroughly wash the dithionite crystals with an organic solvent (e.g. methanol or ethanol) to remove the water adhering to the crystals or the mother liquor containing impurity salts. The crystals must be dried.

There have been very few reports on washing operations for dithionite salts, and there are usually only reports on washing the crystals with an organic solvent after filtration.

Generally, the cleaning liquid is purified by distillation or the like, either independently or combined with the mother liquor, to recover the organic solvent. For example, in the specification of Japanese Patent Publication No. 48-68556, it is stated that the alcohol used in the reaction can be recovered by distillation and reused. However, distillation recovery has the disadvantage that distillation requires a large amount of energy.

On the other hand, if a solution containing thiosulfate is recycled as it is for the reaction, thiosulfate will have a significant negative effect on the synthesis reaction of dithionite, and the reaction to produce dithionite will be inhibited. At the same time, there was a drawback that the decomposition of dithionite was accelerated.

In order to overcome these drawbacks, the present invention conducted research on additives that selectively react with thiosulfates in cleaning solutions, and as a result, it was discovered that thiosulfates can be rendered harmless and reused as they are in the reaction. The present invention is based on this knowledge.

That is, the present invention provides a method for producing anhydrous dithionite by reacting a formic acid compound, an alkali compound, and anhydrous sulfite in a water-organic solvent. After the reaction, crystals of anhydrous dithionite are separated from the mother liquor, and The mother liquor adhering to the water is washed with an organic solvent, one or more of ethylene oxide or propylene oxide is added to the discharged washing liquid, and this liquid is then recycled and reused in the production of the dithionite salt. This is a characteristic method for producing dinition salts.

The method for producing sodium dithionite according to the present invention will be explained in detail. First, in the sodium formate method, sodium formate, an alkali compound, and anhydrous sulfite are usually reacted in a water-organic solvent to synthesize sodium dithionite, and the reaction solution is cooled to separate crystals of sodium dithionite. , the mother liquor adhering to the crystals is washed with an organic solvent, and the crystals are dried. Examples of the alkaline compounds used here include hydroxide, sodium carbonate, sodium sulfite, etc., and organic solvents include alcohols such as methanol, ethanol, and impropatol, and dioxane. Examples include ethers and acid amides such as dimethylpolamide, among which alcohols, particularly methanol, are preferred. Unreacted sodium formate and hydrogen sulfite remain in the washing solution for the crystals, and sodium thiosulfate, a by-product of the decomposition of sodium dithionite, is dissolved. In the present invention, a compound that selectively reacts with sodium thiosulfate is added to the crystal washing solution to inhibit the formation of sodium 5-nithionite and decompose the sodium thiosulfate into a harmless substance that does not participate in any way. Transform.

As the compound added to the crystal washing solution, one or more of ethylene oxide and propylene oxide is used.

All of the above compounds are thiosulfuric acid in the cleaning solution) I
Since it selectively reacts with Jium and has a high reaction rate, it is possible to almost completely remove the thiosulfuric acid in the liquid. Furthermore, since the crystal washing solution has a high organic solvent composition, especially when the organic solvent is methanol, the above-mentioned epoxy compound dissolves and diffuses easily and quickly, so the reaction temperature can be raised, usually 30°C or higher, preferably 1. -< is 40
Processed at temperatures above °C. In this case, the reaction rate is further increased compared to the case where the reaction is carried out at room temperature, and the processing time can be significantly shortened.

In addition, the amount added is usually 1 to 3 times the molar amount per 11 um of sodium thiosulfate contained in the liquid, preferably 1 to 3 times the molar amount.
~2 times the molar amount. In the present invention, the organic solvent composition of the liquid after addition is usually 81] heavy 6-! B% or more, preferably 85% by weight or more, particularly preferably 90% by weight or more, and this liquid is circulated and reused.

The solution obtained by converting +1um into a harmless substance contains almost no substances that inhibit the production or decompose sodium dithionite. It can be recycled and reused in the spinning of 1-lium dicarboxylic acid, and in this case, it can be produced with a high yield of a product of high purity. 8. In the production of thorium dithionite by the sodium formate method, conditions such as raw material cell ratio, solvent M1 composition, and amount of solvent have a large effect. Su1
- It is necessary to measure the content of sodium chloride, sodium hydrogen sulfite, 4fiI solvent, water, etc., determine the amount of each raw material to be used in the next reaction, and always add 79 liters in the same column 1'1. ○ As mentioned above, the crucible according to the invention is sodium dithionate.
In the manufacturing method of , monolithium thiosulfate present in the crystal washing solution can be almost completely removed,
Moreover, since the cleaning solution has a high organic solvent composition, the compounds to be added can be quickly dissolved and diffused, which not only increases the reaction temperature and shortens the processing time, but also reduces the amount of water that is recycled during the reaction. In the case of a conventional method in which IJum or an alkali compound is used as an aqueous solution, there is no need to increase the concentration of the aqueous solution to an extreme degree, and even when used industrially, it is very easy to handle. Furthermore, since sulfur and lithium thiosulfate can be almost completely removed from the liquid, even if these liquids are recycled, products with high purity can be obtained at a high yield, and the recycling of raw materials saves resources. It can be used effectively. In addition, conventionally, methanol was recovered by distilling the entire amount of the cleaning solution.
In the present invention, since these liquids are used in circulation, recovery and distillation of methanol is not necessary for the circulating liquid, and energy can be saved.

Furthermore, since unreacted formic acid, sodium bisulfite and sodium bisulfite are not disposed of, the burden of waste liquid treatment is reduced.

Next, the method for producing sodium dithionite according to the present invention will be explained in more detail with reference to Examples.

Example 1 1000 ffi parts of a crystal washing solution (methanol composition 92%) containing 2.9 parts of sodium thiosulfate, 18.6 parts of sodium bisulfite, and 6.6 parts of sodium formate were placed in a flask equipped with a stirrer and a reflux device, and the temperature was adjusted. Leave it undisturbed in the thermostatic oven. After the temperature of the cleaning solution reaches equilibrium, the compounds listed in Table 11 in an amount of 1.5 times the molar amount of thiosulfate (II) in the cleaning solution are taken off the ship at a predetermined temperature and dissolved. After a period of time, the sodium thiosulfate concentration in the solution was measured and the reduction rate of sodium thiosulfate was determined. The results are shown in Table 1.

=9- Table 1 Example 2 81 parts of sodium formate paste was dissolved in 74 parts of hot water, 105 parts of methanol was added, and the slurry was stirred with a stirrer.
The liquid in the reactor was placed in a jacketed reactor equipped with a thermometer, a reflux condenser, a deep-cooled condenser for collecting low boiling points, and a tank for storing the raw materials, and was heated under pressure using a 1-o K9A zeguage without stirring. Warm to 82°C. Furthermore, 105 parts of an anhydrous solution and 69 parts of a 50% caustic soda solution were added dropwise in parallel over a period of 91 parts to a solution consisting of 276 parts of methanol and 16 parts of methyl formate, and the temperature was increased. The pressure was then maintained and stirring continued for a further 15,111 minutes.

Next, the reaction solution was cooled to 76°C, and after 10 minutes, the dithionite crystals were filtered under pressure through carbonic acid scum to separate them from the reaction mother liquor. Next, the crystals are mixed with methanol 120
Washed at room temperature. The crystals were soaked in methanol, and the filter was pressurized with carbon dioxide gas to collect 120 parts of the washing liquid. After washing, the crystals were dried by holding at 75-90°C for 90 minutes under reduced pressure.

The sorption of the product was 116-5 parts and the purity of sodium dithionite was 92.3%.

On the other hand, since the methanol composition in the recovered cleaning liquid was 92%, 114 parts of the cleaning liquid was used as a circulating liquid so that the methanol in the cleaning liquid was the same amount as the methanol at the start of the reaction. Sodium sulfate dissolved in this circulating fluid
A compound listed in Table 2 was added in an amount of 1.5 times the molar amount based on dam (0.40 parts), and the mixture was kept at 45° C. for 4 hours, and then used for the next reaction. In addition, in this second reaction, the amounts of sodium formate, caustic soda, and anhydrous sulfite were 0.9 parts of sodium formate dissolved in the circulating fluid;
and 1.0 part of caustic soda, which corresponds to 2.5 parts of sodium bisulfite, and 1.5 parts of anhydrous sulfite were subtracted from the initial charge amount. Also, water in the circulating fluid is 4.3
Sodium formate was dissolved in 69.7 parts of hot water. Nithionite was produced in the same manner as in the first case using the above circulating fluid.

After the reaction is completed, crystals of 11 um of sodium dithionite are separated from the reaction solution according to a conventional method, and then the crystals are mixed with methanol 1
The crystals were washed with 20 parts and dried under reduced pressure. The product yield and purity of sodium dithionite are shown in Table 2.

Table 2 Example 3 The initial reaction described in Example 2 was carried out, and the crystals of sodium dithionite produced in the reaction were separated from the reaction solution and subsequently washed with 120 parts of crystalline methanol. The crystals were soaked in methanol, and the filter was pressurized with carbon dioxide gas to collect 120 parts of the washing liquid.

120 parts of the recovered cleaning solution is sodium thiosulfate 0
．． 42 parts, sodium bisulfite 266 parts, and sodium formate 0.9 parts, and the methanol composition was 92%. A compound listed in Table 6 was added in an amount of 1.5 times the molar value per 1 piece of sodium thiosulfate contained in this washing solution, and 4
After being maintained at 5° C. for 4 hours, it was used as part of the solution in which sulfite anhydride was dissolved in the next reaction.

Next, instead of the 276 parts of methanol used to dissolve the anhydrous sulfite in the first reaction, the entire amount of the washing solution in which the sodium thiosulfate was rendered harmless and 1 part of methanol were added.
10 in a solution consisting of 65.6 parts and 15 parts of methyl formate.
3.4 parts of anhydrous sulfite dissolved therein, 16-63.5 parts of 56% caustic soda instead of 69 parts of 50% caustic soda solution, and 80.1 parts of sodium formate instead of 81 parts of sodium formate. The reaction was carried out in the same manner as the first time, and the crystals of sodium dithionite were separated from the reaction solution according to a conventional method, the crystals were washed with methanol, and the crystals were dried under reduced pressure. The yield of the product and the purity of 11 um of dithionite are shown in Table 6.

Table 6 Patent Applicant Mitsubishi Gas Chemical Co., Ltd. Representative Kazuyoshi Nagano 14- Procedural Amendment April 1980 (Japanese Patent Office Commissioner) 1 Indication of Case 1989 Patent Application No. 189710 2 Name of Invention A2 Process for producing thiono acid salts 6 Relationship with the case of the person making the amendment Special applicant 4, “Detailed explanation of the invention” column 5 of the specification subject to amendment Q14 Correct as shown below.

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Claims (4)

[Claims] (1) In a method for producing anhydrous dithionite by reacting a formic acid compound, an alkali compound, and anhydrous sulfite in a water-organic solvent, after the reaction, the crystals of anhydrous dithionite are separated from the mother liquor in a furnace, and the crystals are The mother liquor adhering to the water is washed with an organic solvent, one or more of ethylene oxide or propylene oxide is added to the discharged washing liquid, and this liquid is then recycled and reused in the production of the dithionite salt. Characteristic manufacturing method of dithionite (2) The manufacturing method according to claim 1, wherein the organic solvent composition of the liquid after addition is 80% by weight or more and is recycled and reused. (3) The manufacturing method according to claim 1, wherein one or more of ethylene oxide or propylene oxide is added to the cleaning liquid at a temperature of 60°C or higher. (4) The manufacturing method according to claim 1, wherein one or more of ethylene oxide and abioxide is added in an amount of 1 to 3 times the molar amount of thiosulfuric acid salt contained in the cleaning solution.