JP7683238B2 - How Ammonium Persulfate is Produced - Google Patents

Description

The present invention relates to a method for producing ammonium persulfate.

Ammonium sulfate, also known as ammonium sulfate, was once synthesized as a desired product, but is now mainly distributed as a by-product in the organic chemical industry, such as caprolactam, laurolactam, acrylonitrile, and methyl methacrylate, and in the coke manufacturing process by coal dry distillation. Ammonium sulfate contains about 20% ammonia nitrogen, so it can be used as a fertilizer, and most of the ammonium sulfate by-produced in the above-mentioned process is used for fertilizer. Previously, methods for producing caprolactam, acrylonitrile, and methyl methacrylate that do not produce ammonium sulfate as a by-product have been developed. However, these methods have issues such as complex processes and the inability to easily switch from existing methods. For this reason, a large amount of ammonium sulfate is still produced as a by-product.

On the other hand, ammonium persulfate is widely used industrially mainly as a polymerization initiator for emulsion polymerization, an oxidation bleach, a copper etching agent, etc. As a method for producing ammonium persulfate that has been known so far, as described in Patent Document 1, a cation exchange membrane is used as a diaphragm in an electrolytic cell, an ammonium sulfate aqueous solution is used as an anode-side feedstock, and the amount of acid-dissociable hydrogen ions in the cathode-side feedstock is controlled, so that within the range in which hydrogen ions derived from sulfuric acid are present in the catholyte (hereinafter, sometimes referred to as the catholyte), the following reaction formula (1) is prioritized to generate hydrogen as a cathode-side product, but after a shortage of hydrogen ions derived from acid, the following reaction formula (2) is prioritized to generate ammonia; as described in Patent Document 2, a diaphragmless electrolysis method that does not use a separator such as a diaphragm between the anode and cathode; and as described in Patent Document 3, a method in which a mixed solution of sulfuric acid and ammonium sulfate is used as a cathode-side feedstock, in which only the reaction of the following reaction formula (1) in which hydrogen ions derived from sulfuric acid become hydrogen molecules is carried out as the electrolytic reaction on the cathode side, are known.
2H ⁺ + 2e ^- → H ₂ (1)
2NH ₄ ⁺ + 2e ^- → 2NH ₃ + H ₂ (2)

International Publication No. 2018/131493 JP 2004-99914 A Patent No. 2000-38691

In the production of ammonium persulfate, ammonium persulfate is usually produced by dehydrating and concentrating a mixed solution of ammonium sulfate and ammonium persulfate obtained in the electrolysis process in a crystallization process to precipitate only ammonium persulfate, and then separating the resulting slurry into solid-liquid form and drying it to produce ammonium persulfate crystals. However, in order to efficiently precipitate only ammonium persulfate in the crystallization process, it is more advantageous for the solution produced in the previous electrolysis process to have a lower concentration of ammonium sulfate, the electrolysis raw material, than the target product, ammonium persulfate, and the greater the concentration difference is. However, in areas where the concentration of ammonium sulfate, the reaction raw material in the electrolysis process, is low, there is a problem of a significant decrease in current efficiency, which increases power costs.

Patent Document 1 describes how ammonium persulfate can be produced with high current efficiency and ammonia can be co-produced by supplying a 30-45% by weight aqueous ammonium sulfate solution to both sides of an electrolytic cell in which the anode and cathode are separated by a cation exchange membrane and using guanidine sulfamate as a polarizing agent. However, this method is only described for the region where the ammonium sulfate raw material is concentrated at 30% by weight or more, and does not describe the current efficiency in the low ammonium sulfate concentration region where the current efficiency decreases.

Patent Document 2 describes how, by supplying an aqueous solution of ammonium sulfate to which hexavalent chromium ions have been added or a mixed solution of ammonium sulfate and ammonium persulfate to a diaphragm-less electrolytic cell that does not use a diaphragm (separator) separating the anode and cathode, and performing electrolysis, the ammonium persulfate produced at the anode is prevented from being reduced and decomposed at the cathode, and ammonium persulfate is produced with high current efficiency even with diaphragm-less electrolysis. However, this also describes only the range in which the ammonium sulfate concentration in the electrolysis raw material is high, at 30% by weight or more, and does not describe the range in which ammonium sulfate is low in concentration. In addition, an expensive diamond electrode is used for the anode, making it difficult to put into practical industrial use.

Patent Document 3 describes how ammonium persulfate can be produced with high current efficiency by supplying a 30-44% by weight aqueous solution of ammonium sulfate to an electrolytic cell separated by a porous neutral alumina diaphragm plate, and then adding thiocyanate, cyanide, cyanate, fluoride, etc. as a polarizing agent and electrolyzing the solution. However, this also describes only the high ammonium sulfate concentration range of 30% by weight or more in the electrolysis raw material, and does not describe the low ammonium sulfate concentration range.

The present invention aims to provide a method for producing ammonium persulfate with high current efficiency, even in the low ammonium sulfate concentration range where the current efficiency drops significantly in the electrolytic reaction of ammonium sulfate.

The present invention relates to a method for producing ammonium persulfate with high current efficiency even in a low ammonium sulfate concentration range where the current efficiency drops significantly, and has the following configuration. That is, the present invention is a method for producing ammonium persulfate, characterized in that, when producing ammonium persulfate by electrolyzing ammonium sulfate, the catholyte is an aqueous ammonium sulfate solution, a compound containing calcium is added to an anolyte (hereinafter sometimes referred to as an anolyte) containing an ammonium sulfate aqueous solution having a sulfate ion concentration of 20% by weight or less, and electrolysis is performed in a state in which 2 to 15 ppm of calcium ions are present in the anolyte.

According to the present invention, it is possible to produce ammonium persulfate with high current efficiency even in the low ammonium sulfate concentration range where the current efficiency drops significantly in the electrolytic reaction of ammonium sulfate.

FIG. 1 is a schematic diagram showing a method for producing ammonium persulfate by directly supplying electrolysis raw materials to the anode and cathode of an electrolytic cell that does not have an external tank. FIG. 1 is a schematic diagram showing a method for producing ammonium persulfate by providing external tanks on both the anode and cathode sides and circulating an electrolyte.

The present invention will be described in more detail below with examples.

The method for producing ammonium persulfate according to the present invention is a method for producing ammonium persulfate by electrolyzing ammonium sulfate, characterized in that the electrolysis is carried out in the presence of calcium ions in the anolyte.

In the electrolysis reaction of ammonium sulfate, in order to make it possible to produce ammonium persulfate with high current efficiency even in the low concentration region of ammonium sulfate where the current efficiency drops significantly, it is essential in the present invention to perform electrolysis in the presence of calcium ions in the anolyte.

The calcium ion concentration in the anolyte of the present invention is preferably 2 to 15 ppm, and more preferably 5 to 9 ppm. If added outside this concentration range, the effect of suppressing the decrease in current efficiency may be weak, and high current efficiency may not be obtained. The ion source of the calcium ions to be added may be at least one compound selected from calcium-containing compounds such as calcium carbonate, calcium nitrate, and calcium chloride.

Ammonium sulfate can be used as the anode side raw material of the present invention. The concentration of ammonium sulfate is not particularly limited, but in order to maintain high current efficiency, a concentration of 20% by weight or less is preferable. Raw materials other than ammonium sulfate may also be included, and for example, water-soluble solids such as acids such as sulfuric acid, bases such as ammonium hydroxide, and polarizing agents may be added. The polarizing agent is not particularly limited as long as it is advantageous for the production of known persulfates, but guanidine, guanidine salts, thiocyanates, cyanides, cyanates, fluorides, etc. are preferred, and at least one compound selected from guanidine, guanidine salts, and thiocyanates is more preferred. Examples of guanidine salts include guanidine sulfamate, guanidine nitrate, guanidine sulfate, guanidine phosphate, and guanidine carbonate. The concentration of the polarizing agent in the anode chamber is preferably 0.01 to 1% by weight, more preferably 0.01 to 0.05% by weight. If the polarizing agent concentration is less than 0.01% by weight, there is little effect in increasing the dominance of the main reaction that produces persulfate ions, and if it exceeds 1% by weight, no effect commensurate with the concentration is obtained.

The cathode side feedstock of the present invention is not particularly limited, but may be an aqueous solution containing an acid such as sulfuric acid, a base such as ammonium hydroxide, or a water-soluble salt such as ammonium sulfate, and it is preferable to use an aqueous solution of ammonium sulfate or ammonium hydroxide as the cathode side feedstock. More preferably, from the viewpoint of voltage, an aqueous solution of ammonium sulfate is used.

Since this aqueous solution contains electrolytes, it is possible to reduce electrical resistance, and since it is composed of ions with the same composition as the anode side feedstock separated by the diaphragm, and since it does not contain hydrogen ions derived from sulfuric acid that are used in the cathode reaction, it is possible to increase the amount of ammonia by-product, and in addition, it is more advantageous than using an acid in terms of the selection of materials on the cathode side.

The concentration of the cathode side feedstock in the present invention is not particularly limited, but for example, in the case of an ammonium sulfate aqueous solution, a concentration range of 30 to 45% by weight is more preferable. By using such a high-concentration ammonium sulfate aqueous solution as the cathode side feedstock, ammonium persulfate can be produced industrially advantageously. For both the anode and cathode sides, the feedstock supply and product discharge methods may be batch methods, but from an industrial perspective, a continuous method is more advantageous.

By making the cathode feedstock of the present invention have the above composition, the following reaction formula (1) takes precedence in the range where hydrogen ions derived from sulfuric acid are present in the anolyte, and hydrogen is generated as the cathode product, but after the hydrogen ions derived from the acid are deficient, reactions such as the following reaction formula (2) and reaction formula (3) take precedence. Since the equilibrium reaction of the following reaction formula (4) exists in the system, hydrogen and ammonia can be generated as the cathode product in both cases of reaction formula (2) and reaction formula (3).
2H ⁺ + 2e ^- → H ₂ (1)
2NH ₄ ⁺ + 2e ^- → 2NH ₃ + H ₂ (2)
2H ₂ O + 2e ^- → H ₂ + 2OH ^- (3)
NH ₄ ⁺ + OH ^- ⇔ NH ₃ + H ₂ O (4)

The electrolytic cell used in the present invention is not particularly limited, and for example, an electrolytic cell divided into an anode chamber and a cathode chamber separated by a diaphragm can be used. A box-shaped electrolytic cell or a filter press type electrolytic cell can be used. Here, the diaphragm separating the anode chamber and the cathode chamber is a diaphragm that can inhibit the migration of anions generated in the anode chamber to the cathode chamber. Examples of the diaphragm include a cation exchange membrane and a neutral alumina diaphragm, but a cation exchange membrane is preferably used.

As the anode of the present invention, it is preferable to use a conductive diamond electrode or a platinum group electrode, and it is more preferable to use an electrode with platinum exposed on the electrode surface (hereinafter referred to as a "platinum electrode"). As the platinum electrode, it is preferable to use a solid platinum electrode or a clad steel electrode in which platinum and a metal such as titanium are pressed together, which makes it possible to significantly improve the current efficiency compared to a platinum-plated electrode. As the cathode, it is preferable to use lead, zirconium, platinum, nickel, or stainless steel, and it is more preferable to use nickel or SUS316. There are no particular restrictions on the shape of the electrode for either the anode or the cathode, but it is more preferable to use a metal processed into a foil or wire mesh as the electrode.

The current density of the anode of the present invention is preferably in the range of 20 to 500 A/ ^dm2 , more preferably in the range of 40 to 80 A/ ^dm2 . If the current density is lower than the lower limit, the electrolysis efficiency may deteriorate and the production efficiency may also deteriorate, so it is preferable to increase the size of the electrolysis device. If the current density is higher than the upper limit, the voltage applied during the electrolysis reaction becomes too high, which is economically disadvantageous. The temperature in the electrolytic cell is preferably maintained at 40°C or lower. If the temperature in the electrolytic cell is higher than 40°C, it becomes difficult to suppress the reaction in which the salts in the electrolytic cell decompose.

By adopting the manufacturing method of the present invention, ammonium persulfate can be produced with high current efficiency. Under preferred conditions, it is possible to produce ammonium persulfate with a current efficiency of 80% or more, and more preferably with a current efficiency of 85% or more. Theoretically, the upper limit of current efficiency is 100%. Here, current efficiency (%) is a value expressed as (persulfate ions generated (mol) x 2) / current flow rate (F) x 100, and can be calculated by measuring the amount of persulfate ions generated per unit current flow rate.

In the present invention, by carrying out an electrolytic reaction with the anode chamber filled with anolyte, persulfate ions are generated in the anolyte, and this anolyte-produced solution can be supplied to a crystallization tank, for example, as in the conventional technology, and ammonium persulfate can be precipitated by evaporating the water until it is below the solubility. The ammonium persulfate slurry after crystallization can be separated into ammonium persulfate crystals and crystallization mother liquor using a solid-liquid separator such as a centrifuge. The obtained ammonium persulfate crystals can be dried and commercialized using a powder dryer. In addition, the mother liquor after crystallization can be resupplied to the process as an anode-side feedstock.

In the cathode chamber of the present invention, as the electrolysis reaction proceeds, cations and water molecules hydrated with the cations move from the anode to the cathode side in an amount equivalent to the charge transfer amount, and the amount of liquid increases. During continuous operation, this increase is dehydrated and then resupplied to the cathode side from the cathode side product liquid, enabling continuous operation. There are no particular limitations on the method for dehydrating the water that has moved to the cathode side, but dehydration by evaporation and concentration or membrane separation is preferred. It is preferable to dehydrate a certain amount of water relative to the charge transfer amount, and if the cathode product liquid contains salts, it is preferable to dehydrate the amount of water below the amount at which crystals precipitate due to dehydration. The amount of water dehydrated per mol of charge transfer amount is preferably 20 to 90 g, and more preferably 30 to 80 g. The water obtained by dehydration contains ammonia, and can be mixed (neutralized) with caprolactam sulfate as ammonia water, for example, and used in the process of producing caprolactam and ammonium sulfate.

In addition, by dehydrating the cathode side product liquid and continuing the electrolysis while supplying it again to the cathode side, hydrogen ions and ammonium ions move from the anode to the cathode side in an amount equal to the amount of charge transfer, producing a mixed gas of hydrogen and ammonia in the cathode product gas in the cathode chamber and/or ammonium hydroxide (ammonia-containing water) in the product liquid. The hydrogen/ammonia mixed gas produced on the cathode side can be separated by commonly used ammonia gas separation methods, such as cryogenic separation or compression separation.

The separated hydrogen gas can be refined and compressed using methods such as pressure swing adsorption, and used in hydrogenation processes in the organic chemical industry or as fuel for fuel cells.

The method for producing ammonium persulfate of the present invention can use ammonium sulfate, which is a by-product of the above-mentioned production processes for lactams, acrylonitrile, methyl methacrylate, etc., and the coke production process by coal dry distillation, as a raw material. At this time, by-products containing ammonium sulfate in various processes may contain impurities other than ammonium sulfate, and depending on the components and contents of these impurities, side reactions may occur, causing a decrease in the current efficiency in the ammonium persulfate production process. In such cases, it is preferable to purify the impurities in the ammonium sulfate in advance and reduce the metal ions that reduce the current efficiency before supplying it to the ammonium persulfate production process. As a method for removing impurities from ammonium sulfate, for example, if it is an inorganic substance, a chelate treatment method is preferable.

As a specific example of the method for producing ammonium persulfate according to the present invention, a case where an ammonium sulfate solution is used as the anode and cathode side feed solution is illustrated in Fig. 1. In Fig. 1, 1 indicates an electrolytic cell, and ammonium sulfate ((NH4)2SO4), which is specifically a by-product of a lactam production process 4 as another production process, is supplied to the anode side 2 of the electrolytic cell 1 as the anode side feed, and as the anode reaction, sulfate ions react (consume) as follows to generate persulfate ions, as in the conventional technology.
2SO ₄ ^2- → S ₂ O ₈ ^2- + 2e ^-
The dissolved ions are:
Before electrolysis: _NH4 ⁺ , _SO42- = ammonium sulfate aqueous solution After electrolysis: _NH4 ⁺ , _S2O82- ⁼ ammonium _persulfate aqueous solution, and as ammonium ions migrate to the cathode side, ^an ammonium persulfate aqueous solution is produced. This anode-side product liquid is concentrated and crystallized, and separated into crystallization mother liquor and crystals, and the crystals can be commercialized as ammonium persulfate salt using, for example, a powder dryer. The crystallization mother liquor can be resupplied to the process as the anode-side feedstock.

On the other hand, in the cathode side 3, in the case where an ammonium sulfate aqueous solution is used as a raw material, an aqueous solution containing ammonium sulfate is circulated and supplied, and since there is no or a scarcity of hydrogen ions as a reaction source, ammonium ions that have migrated from the anode react as shown in the following reaction formula to generate ammonia and hydrogen. Also, if there is an acid on the cathode side, hydrogen ions derived from the acid react (consume) as shown in the following reaction formula to generate hydrogen gas.
2NH ₄ ⁺ + 2e ^- → 2NH ₃ + H ₂
2H ^{++ 2e-} → _H2 (if a small amount of acid is present)

Electrolysis causes hydrogen ions, ammonium ions, and the amount of water molecules hydrated by these ions to move from the anode to the cathode in amounts equivalent to the amount of charge transferred.

2 illustrates an example of electrolysis in which the solution is circulated between external tanks 14, 15 and the electrolytic cell. In FIG. 2, reference numeral 11 denotes the electrolytic cell, and ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) is circulated and supplied to the anode side 12 of the electrolytic cell 11 as an anode-side feedstock, and as an anode reaction, sulfate ions react (consume) to generate persulfate ions, as in the prior art. This anode-side product solution is concentrated and crystallized, and separated into a crystallization mother liquor and crystals, and the crystals can be commercialized as an ammonium persulfate salt using, for example, a powder dryer. The crystallization mother liquor can be resupplied to the process as an anode-side feedstock.

On the other hand, an aqueous solution containing ammonium sulfate is supplied to the cathode side 13 as a cathode reaction, and since there are few or no hydrogen ions as a reaction source, the ammonium ions that migrate from the anode react to produce ammonia and hydrogen. Also, if there is an acid on the cathode side, the hydrogen ions derived from the acid react (consume) and hydrogen gas is generated. Hydrogen ions, ammonium ions, and water molecules hydrated by these ions, in an amount equivalent to the amount of charge transferred, move from the anode to the cathode side due to electrolysis.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The current efficiency in the examples is expressed as (peroxysulfate ions generated (mol) x 2) / current flow (F) x 100%, and represents the ratio of peroxysulfate ions generated per unit current flow.

(Examples 1 to 5)
A transparent acrylic electrolytic cell separated by a cation exchange membrane (Chemours, Nafion (registered trademark) 117) was used as the diaphragm, an electrode made of 80 mesh platinum wire mesh and titanium was used as the anode, and an electrode made of 80 mesh SUS316 wire mesh was used as the cathode. In the anode chamber, 0.03 wt% guanidine sulfamate as a polarizing agent was added to a mixed solution of 14.6 wt% ammonium sulfate (SA) and 30.0 wt% ammonium persulfate (APS), and calcium (Ca) standard solution (Kanto Chemical Co., Ltd., calcium (Ca): 1000 mg/L) was added so that the calcium concentration was 2.8 to 11 ppm, and 450 g was supplied as the anode raw material. 400 g of 30 wt% ammonium sulfate aqueous solution was supplied to the cathode chamber. After supply, the anode current density was set to 45 A/dm2 and current was applied. The charge transfer amount was 0.13 mol. The amount of charge transfer is calculated by multiplying the amount of current by the time of current application. After current application, the amount of ammonium persulfate (mol) was calculated by measuring the ammonium persulfate concentration (wt%) in the resulting anode product solution by titration, and the current efficiency was calculated from the amount of ammonium persulfate produced (mol) obtained by subtracting the amount of ammonium persulfate contained in the anode raw material before current application. The current efficiency and the composition of the anode product solution obtained by changing the amount of calcium (Ca) added are shown in Table 1.

(Comparative Example 1)
Except for not adding calcium (Ca) standard solution to the anode feedstock, the same procedure as in Example 1 was carried out. The current efficiency and the composition of the anode product solution obtained at this time are shown in Table 2.

According to the present invention, in the production of ammonium persulfate by the electrolytic reaction of ammonium sulfate, it is possible to produce ammonium persulfate with high current efficiency even in the low concentration region of ammonium sulfate where the current efficiency drops significantly. In addition, since ammonium persulfate can be efficiently purified in the subsequent crystallization process, it is possible to produce ammonium persulfate in an extremely industrially advantageous manner.

Reference Signs List 1 Electrolytic cell 2 Anode side 3 Cathode side 4 Lactam production process 11 Electrolytic cell 12 Anode side 13 Cathode side 14 External tank 15 External tank

Claims (10)

A method for producing ammonium persulfate, in which ammonium sulfate is electrolyzed to produce ammonium persulfate, a cation exchange membrane is used as a diaphragm separating an anode and a cathode, the catholyte is an aqueous ammonium sulfate solution , a compound containing calcium is added to an anolyte containing an aqueous ammonium sulfate solution having a sulfate ion concentration of 20% by weight or less, and electrolysis is performed in a state in which 2 to 15 ppm of calcium ions are present in the anolyte . 2. The method for producing ammonium persulfate according to claim 1 , wherein the calcium-containing compound is a compound selected from at least one of calcium carbonate, calcium nitrate, and calcium chloride. The method for producing ammonium persulfate according to any one of claims 1 to 2 , wherein the concentration of the ammonium sulfate aqueous solution as the catholyte is 30 to 45% by weight. The method for producing ammonium persulfate according to any one of claims 1 to 3 , wherein a polarizing agent is added to the anolyte. The method for producing ammonium persulfate according to claim 4, wherein the polarizing agent is at least one compound selected from guanidine, a guanidine salt, and a thiocyanate salt. The method for producing ammonium persulfate according to any one of claims 1 to 5 , wherein the anode electrode is made of platinum or a platinum group metal. The method for producing ammonium persulfate according to any one of claims 1 to 6 , wherein the current density of the anode is in the range of 20 to 500 A/ ^dm2 . The method for producing ammonium persulfate according to any one of claims 1 to 7 , wherein ammonium persulfate is produced at a current efficiency of 80% or more. The method for producing ammonium persulfate according to any one of claims 1 to 8 , wherein the ammonium sulfate in the anolyte electrolyte includes ammonium sulfate by-produced in a lactam production process. The method for producing ammonium persulfate according to any one of claims 1 to 9 , wherein the ammonia produced on the cathode side is utilized in a lactam production process.

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