Production method of ammonium persulfate

Abstract

To provide a method of efficiently producing an ammonium persulfate while suppressing deterioration of current efficiency.SOLUTION: A method includes producing an ammonium persulfate on the anode side by electrolysis in a state that a polarizing agent exists in the anode side in an electrolytic tank, in which an ammonium sulfate solution is supplied in the anode side and at least one solution selected from an ammonium sulfate solution, an ammonium hydroxide solution, and a sulfuric acid aqueous solution is supplied in the cathode side. The production method of the ammonium persulfate is performed so that the concentration of the polarizing agent in an anode-side electrolyte is between 0.003 weight% and 0.020 weight%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing ammonium persulfate using ammonium sulfate as a raw material, and more particularly to a method for efficiently producing ammonium persulfate. [Background technology]

[0002] Ammonium sulfate, also known as ammonium sulfate, was once synthesized as a target product, but currently, it is mainly distributed as a by-product in the organic chemical industry and coke production processes using coal carbonization, along with caprolactam, laurolactam, acrylonitrile, and methyl methacrylate. Ammonium sulfate contains about 20% ammoniacal nitrogen, so it can be used as fertilizer, and the majority of ammonium sulfate produced as a by-product in the aforementioned processes is used for fertilizer. Conventionally, methods for producing caprolactam, acrylonitrile, and methyl methacrylate without producing ammonium sulfate as a by-product have been developed. However, these methods have challenges such as complex processes and difficulty in switching from existing methods. As a result, a large amount of ammonium sulfate is still produced as a by-product.

[0003] On the other hand, ammonium persulfate is widely used industrially, mainly as a polymerization initiator in emulsion polymerization, an oxidizing bleaching agent, and a copper etching agent. Known methods for producing ammonium persulfate include, as described in Patent Document 1, a method using a porous neutral alumina diaphragm as a diaphragm in an electrolytic cell, containing 0.03% by weight of ammonium thiocyanate as a polarizer in the anode-side raw material, and using only ammonium sulfate as the sulfate ions in the anode-side raw material; as described in Patent Document 2, a method using a cation exchange membrane as a diaphragm in an electrolytic cell, using an aqueous solution of ammonium sulfate containing 0.03% by weight of guanidine sulfamate as a polarizer in the anode-side raw material, and controlling the amount of acid-dissociable hydrogen ions in the cathode-side raw material to produce ammonia as a co-product; and as described in Patent Document 3, a method using a porous neutral alumina diaphragm in an electrolytic cell, adding 0.03% by weight of guanidine sulfamate as a polarizer to the anode-side raw material to suppress the formation of cyanide compounds. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-293484 [Patent Document 2] International Publication No. 2018 / 131493 [Patent Document 3] Japanese Patent Publication No. 2000-38691 [Overview of the project] [Problems that the invention aims to solve]

[0005] The inventors' investigations revealed that using a high concentration of polarizer during recycling operation could gradually decrease the current efficiency. Therefore, the methods disclosed in Patent Documents 1, 2, and 3 had the problem of decreased current efficiency during recycling operation due to the use of a high concentration of polarizer.

[0006] Therefore, in view of the above-mentioned prior art, the object of the present invention is to provide a method that can suppress the decrease in current efficiency when producing ammonium persulfate and efficiently produce ammonium persulfate. [Means for solving the problem]

[0007] To solve the above problems, the method for producing ammonium persulfate according to the present invention is as follows. (1) A method for producing ammonium persulfate, comprising supplying an aqueous ammonium sulfate solution as the anode-side raw material to the anode side of an electrolytic cell separated by a diaphragm, and supplying at least one selected from aqueous ammonium sulfate solution, aqueous ammonium hydroxide solution, and aqueous sulfuric acid solution as the cathode-side raw material to the cathode side, and generating ammonium persulfate on the anode side by electrolysis while a polarizer is present on the anode side, wherein the electrolytic cell is operated so that the polarizer concentration in the anode-side electrolyte is 0.003% by weight or more and 0.020% by weight or less. (2) The method for producing ammonium persulfate according to (1), wherein the concentration of the aqueous solution of ammonium sulfate as the anode raw material is in the range of 30-45% by weight. (3) The method for producing ammonium persulfate according to (1) or (2), wherein the polarizer is at least one selected from guanidine, guanidine salt, thiocyanate, and thiocyanate. (4) The method for producing ammonium persulfate according to (3), wherein the polarizer is guanidine sulfamate. (5) A method for producing ammonium persulfate according to any one of (1) to (4), wherein the cathode-side raw material is an aqueous solution of ammonium sulfate. (6) The method for producing ammonium persulfate according to (5), wherein the concentration of the aqueous solution of ammonium sulfate as the cathode raw material is in the range of 30-45% by weight. (7) A method for producing ammonium persulfate according to any one of (1) to (6), wherein the anode-side product is crystallized, and the slurry after crystallization is separated into solid and liquid components to obtain a mother liquor which is recycled as an anode-side raw material. (8) The method for producing ammonium persulfate as described in (7), wherein a portion of the mother liquor is recycled as an anode-side raw material. (9) The method for producing ammonium persulfate according to any one of (1) to (8), wherein the production of ammonium persulfate is carried out in a continuous manner. (10) The method for producing ammonium persulfate according to any one of (1) to (9), wherein the anode electrode is a platinum group or conductive diamond. (11) The method for producing ammonium persulfate according to any one of (1) to (10), wherein the ammonium sulfate contained in the anode-side raw material and the cathode-side raw material includes that by-produced in the lactam production process. (12) The method for producing ammonium persulfate according to any one of (1) to (11), wherein the ammonia generated on the cathode side is utilized in the lactam production process.

Advantages of the Invention

[0008] Thus, according to the method for producing ammonium persulfate according to the present invention, it is possible to suppress a decrease in current efficiency during long-time production of ammonium persulfate and enable efficient production.

Brief Description of the Drawings

[0009] [Figure 1] It is a schematic diagram showing the ammonium persulfate production process carried out in Example 1. [Figure 2] It is a schematic diagram showing the ammonium persulfate production process carried out in Example 2.

Modes for Carrying Out the Invention

[0010] Hereinafter, the present invention will be described in more detail together with embodiments. The method for producing ammonium persulfate according to the present invention is a method for producing ammonium persulfate by electrolyzing ammonium sulfate. When ammonium persulfate is precipitated from the anode-side product solution and the mother liquor obtained by solid-liquid separation of the slurry after crystallization is recycled as the anode-side raw material (hereinafter referred to as recycle operation), the concentration of the depolarizer in the anode-side electrolyte is controlled within a certain range.

[0011] The electrolytic cell used in the present invention is not particularly limited and may be any electrolytic cell divided into an anode chamber and a cathode chamber separated by a diaphragm. A box-type electrolytic cell or a filter-press type electrolytic cell can be used. In addition, a buffer tank may be provided separately from the electrolytic cell during electrolysis, and the electrolyte may be circulated between the buffer tank and the electrolytic cell. Here, the diaphragm separating the anode chamber and the cathode chamber can be a diaphragm that can inhibit the electrophoresis of anions generated in the anode chamber into the cathode chamber. A cation exchange membrane or a neutral alumina diaphragm is preferred as the diaphragm, and a cation exchange membrane is more preferred.

[0012] While there are no restrictions on the raw material supply method or the liquid output method for both the anode and cathode sides, a continuous process is industrially more advantageous than a batch process.

[0013] As the anode-side raw material, ammonium sulfate must be used. While the concentration of the ammonium sulfate aqueous solution is not particularly limited, from the viewpoint of improving productivity in the electrolytic reaction, 30% by weight or more is more preferable, and 35% by weight or more is even more preferable. Furthermore, from the viewpoint of suppressing the precipitation of ammonium sulfate crystals into the system, the concentration of ammonium sulfate is preferably 45% by weight or less.

[0014] In this specification, current efficiency is expressed as (number of persulfate ions generated (mol) × 2) / charge transfer amount (mol) × 100%, and refers to the ratio of persulfate ions generated per unit of charge transfer. Charge transfer amount (mol) is a value obtained by current (A) × energizing time (s) / Faraday constant (A·s / mol), and refers to the number of electrons supplied from the negative electrode to the cathode of the power supply during electrolysis, and transferred from the anode to the positive electrode of the power supply through the electrolytic reaction.

[0015] Furthermore, the anode-side raw materials may contain raw materials other than ammonium sulfate. Examples of raw materials other than ammonium sulfate include acids such as sulfuric acid, bases such as ammonium hydroxide, and polarizers. The polarizer is not particularly limited as long as it is advantageous for the production of known persulfates, but guanidine, guanidine salts, thiocyanates, cyanides, cyanates, and fluorides are preferred. From the viewpoint of improving current efficiency, the polarizer is more preferably guanidine or a guanidine salt. Examples of guanidine salts include guanidine sulfamate, guanidine nitrate, guanidine sulfate, guanidine phosphate, or guanidine carbonate, with guanidine sulfamate being even more preferred.

[0016] The concentration of the polarizer in the anode electrolyte must be 0.003% by weight or more, more preferably 0.005% by weight or more, and even more preferably 0.010% by weight or more, from the viewpoint of improving current efficiency. Furthermore, if a high concentration of polarizer is used when performing recycling operation, the current efficiency may gradually decrease, so the concentration of the polarizer must be 0.020% by weight or less, more preferably 0.018% by weight or less, and even more preferably 0.016% by weight or less.

[0017] The method for controlling the polarizer concentration in the anode electrolyte is not particularly limited. For example, in a continuous process, the polarizer is contained in the extracted anode-generated solution, so any deficiency can be added to the anode electrolyte. The method of adding the polarizer is not particularly limited; it may be mixed with the anode raw materials, or the polarizer may be added to the anode electrolyte.

[0018] As the cathode-side raw material, it is necessary to use at least one selected from aqueous ammonium sulfate solution, aqueous ammonium hydroxide solution, and aqueous sulfuric acid solution, with the use of aqueous ammonium sulfate solution or aqueous ammonium hydroxide solution being preferable. These aqueous solutions contain electrolytes, which can reduce electrical resistance, and are composed of ions with the same composition as the anode-side raw material separated by a diaphragm. Since there are no hydrogen ions derived from sulfuric acid that are subjected to the cathode reaction, it is possible to increase the amount of ammonia produced as a by-product. In addition, it is more advantageous than using an acid in terms of selecting the material for the cathode side. The concentration of the cathode-side raw material is not particularly limited, but for example, if it is aqueous ammonium sulfate solution, 30% by weight or more is preferable, and 35% by weight or more is more preferable. Also, 45% by weight or less is preferable.

[0019] In the range where hydrogen ions derived from sulfuric acid are present in the cathode electrolyte, reaction equation (1) below takes precedence, generating hydrogen as a cathode product. However, after the deficiency of hydrogen ions derived from the acid, reactions such as reaction equation (2) and reaction equation (3) below take precedence. Since the equilibrium reaction shown in reaction equation (4) below exists in the system, hydrogen and ammonia can be produced as cathode products in both reaction equation (2) and reaction equation (3). 2H + + 2e - → H2(1) 2NH4 + + 2e - → 2NH3 + H2(2) 2H2O + 2e - → H2 + 2OH - (3) NH4 + + OH - ⇔ NH3 + H2O (4)

[0020] As the anode, it is preferable to use an electrode containing a platinum group metal or a conductive diamond electrode. Among the above electrodes, an electrode containing a platinum group metal is more preferable, an electrode containing platinum is further preferable, and it is even more preferable to use an electrode in which platinum is exposed on the electrode surface (hereinafter referred to as "platinum electrode"). Examples of the platinum electrode include a pure platinum electrode in which pure platinum and a metal substrate are joined, a platinum clad electrode using clad steel in which platinum and a metal substrate are pressure-bonded, and a platinum plated electrode in which platinum is plated on a metal substrate. The metal constituting the metal substrate is not particularly limited, but from the viewpoint of the corrosion resistance of the electrolytic solution, a metal that forms a passive film on the surface is preferable, and titanium is more preferable. The metal substrate is used to ensure the electrical conductivity required for the electrode and to provide rigidity.

[0021] As the cathode, it is preferable to use stainless steel, nickel, platinum, lead, or zirconium, and it is more preferable to use SUS316 (stainless steel) or nickel.

[0022] The current density of the anode is preferably 20 A / d m 2 or more. If it is lower than this, the current efficiency may be low. Preferably it is 40 A / dm 2 or more. Also, the current density of the anode is preferably 500 A / dm 2 or less, more preferably 200 A / dm 2 or less, and particularly preferably 80 A / dm 2 or less. Industrially, operation at a high current density is more preferable because the size of the device can be reduced.

[0023] The temperature in the electrolytic cell is preferably 15 to 40 °C. By setting it within this range, the dissolution of salts in the electrolytic cell can be maintained within an appropriate range, and undesirable side reactions can be suppressed, which is preferable.

[0024] The anode-side product containing ammonium persulfate obtained by electrolysis can be purified in the same manner as in conventional techniques to obtain a product. This purification process is not particularly limited; for example, the step of precipitating ammonium persulfate can be carried out by supplying it to a commonly used crystallization tank and using methods such as evaporation crystallization or cooling crystallization. The step of separating the ammonium persulfate slurry after crystallization into ammonium persulfate crystals and mother liquor can be carried out using a commonly used solid-liquid separator such as a centrifuge. The step of drying and processing the obtained ammonium persulfate crystals into a product can be carried out using a powder dryer.

[0025] The mother liquor obtained above can be resupplied to the process as a raw material for the anode side. Here, the mother liquor may be resupplied in its entirety, partially, or mixed with other raw materials to form a new raw material. The supply method may be continuous or intermittent.

[0026] In the cathode chamber, as electrolysis progresses, cations and water molecules hydrated with cations move from the anode to the cathode, increasing the liquid volume. Therefore, during continuous electrolysis, the increased volume from the cathode-side product may be dehydrated and then supplied back to the cathode. Alternatively, during batch operation, the cathode-side product may be dehydrated until it returns to the same weight as before electrolysis and then supplied again as the cathode-side raw material. The dehydration method is not particularly limited; any method that can dehydrate the increased volume on the cathode side is acceptable, but dehydration by evaporation and concentration or membrane separation is preferred. Furthermore, it is not a problem if the water obtained by dehydration contains ammonia, and it can be used in processes that utilize ammonia or water, such as the neutralization salt conversion process in the lactam manufacturing process. Dehydration of the cathode-side product is preferably performed to a certain extent relative to the charge transfer amount in order to prevent the cathode liquid from continuously increasing. Furthermore, if the cathode-side product contains salts or the like, it is preferable to dehydrate it to an amount less than or equal to the amount that causes crystal precipitation. Specifically, the amount of dehydration per 1 mol of charge transfer is preferably 20 to 90 g, and more preferably 30 to 80 g.

[0027] Furthermore, by dehydrating the cathode-side product solution and continuing electrolysis while supplying it back to the cathode side, hydrogen ions and ammonium ions equivalent to the charge transfer amount move from the anode to the cathode side. As a result, a mixture of hydrogen and ammonia gas is produced in the cathode-side product gas of the cathode chamber, and / or ammonium hydroxide (ammonia-containing water) is produced in the product solution. The hydrogen-ammonia mixture gas produced on the cathode side can be separated by widely used ammonia gas separation methods, such as cryogenic separation or compression separation. Also, if the produced ammonia is supplied to a process that provides it as ammonia water, such as the neutralization salt conversion process in the lactam manufacturing process, it can be separated from the hydrogen gas using a widely used gas absorption tower and recovered as ammonia water. The separated hydrogen gas can be purified and compressed using methods such as pressure fluctuation adsorption and used in the hydrogenation process of the organic chemical industry or as fuel for fuel cells.

[0028] The present invention's method for producing ammonium persulfate can utilize ammonium sulfate produced as a by-product in the manufacturing processes of lactam, acrylonitrile, methyl methacrylate, etc., as well as in the coke production process by coal carbonization, as described above. In this case, by-products containing ammonium sulfate in various processes may contain impurities other than ammonium sulfate, and depending on the components and their content, side reactions may occur, reducing the current efficiency in the ammonium persulfate production process. In such cases, it is preferable to purify the by-products containing ammonium sulfate beforehand to reduce the components that reduce current efficiency before supplying them to the ammonium persulfate production process. As a method for purifying impurities in ammonium sulfate, for example, chelation treatment is preferred if the impurities are inorganic.

[0029] As an example of a method for producing ammonium persulfate according to the present invention, the ammonium persulfate production process performed in Example 1 described below is shown. In the production process shown in Figure 1, an example is given in which ammonium sulfate is supplied from the anode-side raw material tank 8 and the cathode-side raw material tank 9, and electrolysis is performed by supplying power to the anode 5 and cathode 6 from the power supply 10.

[0030] In the electrolytic cell 1, ammonium sulfate is supplied from the anode-side raw material tank 8 and the cathode-side raw material tank 9 to the anode chamber 3, which is equipped with an anode 5, and the cathode chamber 4, which is equipped with a cathode 6, which are separated by a diaphragm 2. In the anodic reaction, as in the conventional technology, sulfate ions are consumed and persulfate ions are generated as described below. 2SO4 2- → S2O8 2- + 2e - The dissolved ions in anode chamber 3 are: Before electrolysis: NH4 + SO4 2- = Ammonium sulfate aqueous solution After electrolysis: NH4 + S2O8 2- = Ammonium persulfate solution As a result, ammonium ions migrate towards the cathode chamber 4, and an aqueous solution of ammonium persulfate is generated in the anode chamber 3. This anode-side generated liquid is sent to the purification process 7 through the anode-side generated liquid extraction line 11, where it is crystallized and separated into mother liquor and ammonium persulfate crystals. The crystals are dried, for example, by a powder dryer and extracted through the crystal extraction line 15, where they can be commercialized as ammonium persulfate salts. The mother liquor is extracted through the mother liquor extraction line 14, and for example, a portion of it is resupplied to the process as an anode-side raw material via the mother liquor circulation line 13, where any insufficient ammonium sulfate can be added and used as an anode-side raw material.

[0031] On the other hand, in cathode chamber 4, since there are few or no hydrogen ions as a reaction source, ammonium ions that have migrated from the anode side react as shown below in the cathode reaction, producing ammonia and hydrogen. Also, if there is a small amount of acid on the cathode side, hydrogen ions from the acid react (are consumed) as shown in the reaction equation below, and hydrogen gas is generated. 2NH4 + + 2e - → 2NH3+ H2 2H + + 2e - → H2 (if there is a small amount of acid)

[0032] During electrolysis, hydrogen ions, ammonium ions, and water molecules hydrated by these ions move from the anode to the cathode, corresponding to the amount of charge transferred. As a result, the volume of liquid on the cathode side increases. Therefore, the cathode-side generated liquid can be either supplied as a new cathode-side raw material without recycling, a portion of the cathode-side generated liquid extracted in the cathode-side generated liquid extraction line 12 can be recycled as a cathode-side raw material via the cathode-side generated liquid circulation line 20, or an amount equivalent to the increase can be dehydrated from the cathode-side generated liquid and recycled as a cathode-side raw material.

[0033] Furthermore, the ammonium persulfate production process performed in Example 2, described later, is shown. In the production process shown in Figure 2, ammonium sulfate is supplied from the anode-side raw material tank 8 and the cathode-side raw material tank 9, and the anode-side product and cathode-side product are extracted from the anode buffer tank 16 and the cathode buffer tank 17 through the anode-side product extraction line 18 and the cathode-side product extraction line 19, respectively. Ammonium sulfate is circulated and supplied to the anode chamber 3 of the electrolytic cell 1 from the anode buffer tank 16, and in the anodic reaction, sulfate ions are consumed and persulfate ions are generated, similar to the conventional technology. This anode-side product is crystallized and separated into mother liquor and ammonium persulfate crystals, and the crystals can be commercialized as ammonium persulfate salts, for example, by drying in a powder dryer. A portion of the mother liquor is resupplied to the process, and any insufficient ammonium sulfate can be added and used as an anode-side raw material.

[0034] Meanwhile, in the cathode chamber 4, ammonium sulfate is circulated and supplied from the cathode buffer tank 17. In the cathode reaction, since there are few or no hydrogen ions as a reaction source, ammonium ions that have migrated from the anode side react, producing ammonia and hydrogen. Also, if there is a small amount of acid on the cathode side, hydrogen ions from the acid react (are consumed), generating hydrogen gas. Due to electrolysis, hydrogen ions, ammonium ions, and water molecules that hydrate these ions move from the anode side to the cathode side in proportion to the amount of charge transfer, increasing the amount of liquid on the cathode side. Therefore, the cathode-side generated liquid can be either supplied as a new cathode-side raw material without recycling it, or a portion of the cathode-side generated liquid extracted in the cathode-side generated liquid extraction line 19 can be recycled as a cathode-side raw material via the cathode-side generated liquid circulation line 20, or the increased amount can be dehydrated from the cathode-side generated liquid and recycled as a cathode-side raw material. [Examples]

[0035] The present invention will be specifically described below with reference to examples, but the present invention is not limited in any way by these examples. In the examples, the current efficiency is expressed as (number of persulfate ions generated (mol) × 2) / charge transfer amount (mol) × 100%, and refers to the ratio of persulfate ions generated per unit of charge transfer.

[0036] (Example 1) Using the electrolytic cell 1 shown in Figure 1, the diaphragm 2 is a cation exchange membrane (Nafion® 114, manufactured by Chemours), and the anode 5 has an effective area of ​​0.1 dm². 2 The electrode is made of 80-mesh platinum mesh and titanium, and the cathode 6 has an effective area of ​​0.1 dm². 2 An electrode made of 80-mesh SUS316 wire mesh was used. 500g of a 43 wt% aqueous solution of ammonium sulfate containing 0.015 wt% guanidine sulfamate was supplied to anode chamber 3. 400g of a 43 wt% aqueous solution of ammonium sulfate was supplied to cathode chamber 4.

[0037] After supply, the anode current density is 45 A / dm 2Batch electrolysis was performed by applying current. The charge transfer amount in this electrolysis was 1.34 mol. The concentration of ammonium persulfate in the solution was measured by redox titration, and the concentration of ammonium sulfate was determined by measuring sulfate ions. The current efficiency of the batch electrolysis was calculated by determining the amount of persulfate ions generated by measuring the total amount of persulfate ions in the anode chamber before and after electrolysis. The amount of product solution on the anode side at this time was 422 g, with ammonium sulfate at 16.9 wt% and ammonium persulfate at 29.3 wt%. 0.54 mol of ammonium persulfate was generated on the anode side, and the current efficiency was 81.0%.

[0038] The anode-produced solution was supplied to a double-walled glass container and crystallized while stirring to precipitate ammonium persulfate. Crystallization was carried out at a glass container pressure of 20 Torr and a liquid temperature of 30°C, resulting in a dehydration rate of 23.2%. 245 g of mother liquor was obtained by filtering the slurry obtained from the crystallization.

[0039] A portion of the mother liquor was recycled as anode-side raw material, and ammonium sulfate was added to create a new anode-side raw material that contained an amount equivalent to the ammonium sulfate consumed during electrolysis. In addition, the deficit was supplied so that the guanidine sulfamate concentration in the anode-side raw material was 0.015% by weight. At this time, the anode-side raw material amounted to 566g, with ammonium sulfate at 37.1% by weight, ammonium persulfate at 8.1% by weight, and guanidine sulfamate at 0.015% by weight.

[0040] Using 400 g of a newly prepared 43 wt% aqueous solution of ammonium sulfate as the anode and cathode raw materials, current was applied under the same conditions as the previous electrolysis. The charge transfer in this electrolysis was 1.34 mol. The anode-side product at this time was 489 g, with 13.7 wt% ammonium sulfate and 34.6 wt% ammonium persulfate. 0.54 mol of ammonium persulfate was produced on the anode side, and the current efficiency was 80.5%. The obtained anode-side product was crystallized using the same apparatus and conditions as the previous crystallization. The dehydration rate at this time was 26.8%. Furthermore, 225 g of mother liquor was obtained using the same procedure as the previous filtration. A portion of the mother liquor was reused as the anode-side raw material, and ammonium sulfate was added to create a new anode-side raw material that contained an amount equivalent to the ammonium sulfate consumed in the electrolysis. In addition, the deficiency was supplied so that the guanidine sulfamate concentration of the anode-side raw material was 0.015 wt%. The anode raw material at this time was 570g, consisting of 37.5% by weight of ammonium sulfate, 7.5% by weight of ammonium persulfate, and 0.015% by weight of guanidine sulfamate. This batch electrolysis and crystallization process was repeated 20 times each.

[0041] (Comparative Example 1) Ammonium persulfate was produced under the same conditions as in Example 1, except that the guanidine sulfamate concentration in the anode chamber was 0.030% by weight. Table 1 summarizes the changes in current efficiency in Example 1 and Comparative Example 1.

[0042] [Table 1]

[0043] (Example 2) Using the electrolytic cell 1 shown in Figure 2, the diaphragm 2 is a cation exchange membrane (Nafion® 551, manufactured by Chemours), and the anode 5 has an effective area of ​​1 dm². 2 The electrode consists of an 80-mesh platinum wire mesh welded to a titanium metal substrate, and the cathode 6 has an effective area of ​​1 dm². 2Electrodes made of 80-mesh SUS316 wire mesh were used. Each chamber was equipped with a buffer tank, and liquid was pumped from the buffer tank to the electrolytic cell. Liquid was returned from the electrolytic cell to the buffer tank by overflow. When performing continuous electrolysis, the anode and cathode raw materials were pumped to the buffer tank, and the anode and cathode generated liquids were pumped out of the buffer tank.

[0044] As preparation for continuous electrolysis, 5200g of a 43 wt% aqueous solution of ammonium sulfate containing 0.015 wt% guanidine sulfamate was supplied to the anode buffer tank 16 as the anode raw material, and 4000g of a 43 wt% aqueous solution of ammonium sulfate was supplied to the cathode buffer tank 17 as the cathode raw material, and batch electrolysis was performed. The anode current density was 45 A / dm². 2 The system was then energized. The charge transfer during this electrolysis was 15.1 mol. The anode-side product at this time was 4270 g, with 32.7% by weight of ammonium persulfate and 14.5% by weight of ammonium sulfate. The entire amount of the anode-side product obtained in the previous batch electrolysis was supplied to the anode buffer tank 16, and 4000 g of newly prepared 43% by weight aqueous solution of ammonium sulfate was supplied to the cathode buffer tank 17.

[0045] For continuous electrolysis, 5200g of a 43% by weight aqueous solution of ammonium sulfate containing guanidine sulfamate was used as the anode raw material, and 4000g of a 43% by weight aqueous solution of ammonium sulfate was used as the cathode raw material. These solutions were then pumped into each buffer tank over 10 hours. Continuous electrolysis was then performed by pumping the anode and cathode products from the buffer tanks to maintain a constant liquid level. The anode current density at this time was 45 A / dm². 2The system was energized and continuous electrolysis was performed. The charge transfer during this electrolysis was 16.8 mol. During continuous electrolysis, guanidine sulfamate was added to the anode-side raw material and anode-side electrolyte to control the concentration of guanidine sulfamate in the anode-side electrolyte to 0.015% by weight. The current efficiency of the continuous electrolysis was calculated every 10 hours by measuring the total amount of persulfate ions in the anode-side raw material and anode buffer tank before electrolysis and the total amount of persulfate ions in the anode-side product solution and anode buffer tank after electrolysis to determine the amount of persulfate ions generated. At this time, the anode-side product solution was 4286 g, with 16.2% by weight of ammonium sulfate and 31.0% by weight of ammonium persulfate. The anode electrolyte solution in the buffer tank was 4297 g, with 16.2% by weight of ammonium sulfate and 31.1% by weight of ammonium persulfate. 5.54 mol of ammonium persulfate was generated on the anode side, and the current efficiency was 66.0%.

[0046] The anode-produced solution was supplied to a double-walled glass container and crystallized while stirring to precipitate ammonium persulfate. Crystallization was carried out at a glass container pressure of 20 Torr and a liquid temperature of 30°C, resulting in a dehydration rate of 23.4%. The slurry obtained from crystallization was filtered to obtain 2377 g of mother liquor.

[0047] A portion of the mother liquor was reused as the anode-side raw material. Ammonium sulfate was added to compensate for the ammonium sulfate consumed during electrolysis, and guanidine sulfamate was added to create a new anode-side raw material. In this new anode-side raw material, 5660g contained 37.2% by weight of ammonium sulfate, 7.9% by weight of ammonium persulfate, and 0.015% by weight of guanidine sulfamate.

[0048] Using 4000g of a newly prepared 43% by weight aqueous solution of ammonium sulfate as the anode and cathode raw materials, continuous electrolysis was performed in the same manner as before. The charge transfer amount in this electrolysis was 16.8 mol. At this time, the anode product was 4530g, with 14.9% by weight of ammonium sulfate and 33.5% by weight of ammonium persulfate, while the anode electrolyte in the buffer tank was 4542g, with 14.9% by weight of ammonium sulfate and 33.6% by weight of ammonium persulfate. 5.50 mol of ammonium persulfate was produced on the anode side, and the current efficiency was 65.5%. The obtained anode product was crystallized using the same apparatus and conditions as before. The dehydration rate at this time was 24.6%. Furthermore, a portion of the mother liquor was reused as the anode raw material, and ammonium sulfate was added to create a new anode raw material containing an amount equivalent to the ammonium sulfate consumed in the electrolysis. The anode raw materials at this time were 5677g, consisting of 37.5% by weight of ammonium sulfate, 7.6% by weight of ammonium persulfate, and 0.015% by weight of guanidine sulfamate. This continuous electrolysis and crystallization process was repeated, and a total of 150 hours of electrolysis was performed.

[0049] (Comparative Example 2) Continuous production of ammonium persulfate was carried out under the same conditions as in Example 2, except that the concentration of guanidine sulfamate in the anode electrolyte during continuous electrolysis was controlled to 0.030% by weight. Table 2 summarizes the changes in current efficiency in Example 2 and Comparative Example 2.

[0050] [Table 2]

[0051] As is clear from Tables 1 and 2, the present invention, which controls the concentration of guanidine sulfamate within a certain range, can suppress the decrease in current efficiency and efficiently produce ammonium persulfate. [Industrial applicability]

[0052] The method according to the present invention is extremely suitable for the production of ammonium persulfate, where it is required to suppress a decrease in current efficiency and produce ammonium persulfate efficiently. [Explanation of Symbols]

[0053] 1 electrolytic cell 2 Diaphragm 3 Anode chamber 4. Cathode chamber 5 Anode 6 cathode 7 Purification process 8. Anode-side raw material tank 9. Cathode side raw material tank 10 Power supply 11. Anode-side product extraction line 12. Cathode-side product extraction line 13. Mother liquor circulation line 14. Mother liquor extraction line 15. Crystal extraction line 16 Anode buffer tank 17 Cathode buffer tank 18. Anode-side product extraction line 19. Cathode-side product extraction line 20 Cathode-side generated fluid circulation line

Claims

1. A method for producing ammonium persulfate, comprising: supplying an ammonium sulfate aqueous solution as an anode-side feedstock to an anode side of an electrolytic cell separated by a diaphragm; supplying at least one selected from an ammonium sulfate aqueous solution, an ammonium hydroxide aqueous solution, and a sulfuric acid aqueous solution as a cathode-side feedstock to the cathode side; and producing ammonium persulfate on the anode side by electrolysis in the presence of a polarizing agent on the anode side, wherein the method is operated so that the concentration of the polarizing agent in the anode-side electrolyte is 0.003% by weight or more and 0.020% by weight or less.

2. The method for producing ammonium persulfate according to claim 1, wherein the concentration of the ammonium sulfate aqueous solution as the anode side feedstock is in the range of 30 to 45% by weight.

3. The method for producing ammonium persulfate according to claim 1 or 2, wherein the polarizing agent is at least one selected from the group consisting of guanidine, a guanidine salt, thiocyan, and a thiocyanate salt.

4. 4. The method of claim 3, wherein the polarizing agent is guanidine sulfamate.

5. The method for producing ammonium persulfate according to claim 1, wherein the cathode side feedstock is an aqueous ammonium sulfate solution.

6. The method for producing ammonium persulfate according to claim 5, wherein the concentration of the ammonium sulfate aqueous solution as the cathode side feedstock is in the range of 30 to 45% by weight.

7. The method for producing ammonium persulfate according to claim 1, wherein the anode-side product liquid is crystallized, and the mother liquor obtained by solid-liquid separation of the slurry after the crystallization is recycled as the anode-side feedstock.

8. The method for producing ammonium persulfate according to claim 7, wherein a part of the mother liquor is recycled as an anode-side feedstock.

9. 2. The method of claim 1, wherein the production of ammonium persulfate is carried out in a continuous manner.

10. 2. The method for producing ammonium persulfate according to claim 1, wherein the anode electrode is a platinum group metal or a conductive diamond.

11. The method for producing ammonium persulfate according to claim 1, wherein the ammonium sulfate contained in the anode-side feedstock and the cathode-side feedstock includes ammonium sulfate by-produced in a lactam production process.

12. The method for producing ammonium persulfate according to claim 1, wherein the ammonia produced on the cathode side is utilized in the lactam production process.

Images