JP2022129759A - Method for producing ammonium persulfate - Google Patents

Abstract

To make it possible to produce ammonium persulfate with high current efficiency even in a low concentration region of ammonium sulfate in which the current efficiency significantly decreases in the electrolytic reaction of the ammonium sulfate.SOLUTION: A production method for ammonium persulfate is performed by electrolyzing ammonium sulfate in a state in which calcium ions exist in an anolyte.SELECTED DRAWING: None

Description

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

Ammonium sulfate, also known as ammonium sulfate, was once synthesized as a target product, but today it is mainly produced 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 distillation. in circulation. Since ammonium sulfate contains about 20% ammonia nitrogen, it can be used as a fertilizer, and most of the ammonium sulfate produced as a by-product in the above-described process is used as a fertilizer. Conventionally, methods for producing caprolactam, acrylonitrile, and methyl methacrylate that do not produce ammonium sulfate as a by-product have been developed. However, these production methods have problems such as complicated processes and difficulty in conversion from existing production methods. Therefore, a large amount of ammonium sulfate is still by-produced.

On the other hand, ammonium persulfate is widely industrially used mainly as a polymerization initiator for emulsion polymerization, an oxidation bleaching agent, a copper etching agent, and the like. As a known method for producing ammonium persulfate, as described in Patent Document 1, a cation exchange membrane is used as a diaphragm in an electrolytic cell, an aqueous solution of ammonium sulfate is used as a raw material on the anode side, and a raw material on the cathode side is used. By controlling the amount of acid-dissociable hydrogen ions in the catholyte (hereinafter sometimes referred to as the catholyte), the following reaction formula (1) is given priority in the range where hydrogen ions derived from sulfuric acid are present, Hydrogen is generated as a product on the cathode side, but after depletion of hydrogen ions derived from the acid, the following reaction formula (2) is given priority, so that the method of generating ammonia or the anode as described in Patent Document 2 Electrolytic reaction on the cathode side, such as a non-diaphragm electrolysis method that does not use a separator such as a diaphragm between and the cathode, and a method using a mixed solution of sulfuric acid and ammonium sulfate as a cathode side raw material as described in Patent Document 3 are all known methods in which only the reaction in which hydrogen ions derived from sulfuric acid in the following reaction formula (1) become hydrogen molecules is carried out.
2H ⁺ + 2e ⁻ → H ₂ (1)
2NH ₄ ⁺ + 2e ⁻ → 2NH ₃ + H ₂ (2)

WO2018/131493 Japanese Unexamined Patent Publication No. 2004-99914 Patent No. 2000-38691

In the production of ammonium persulfate, the mixed solution of ammonium sulfate and ammonium persulfate obtained in the electrolysis process is usually dehydrated and concentrated in the crystallization process to precipitate only ammonium persulfate, and the resulting slurry is solid-liquid separated and dried. However, in order to efficiently deposit only ammonium persulfate in the crystallization process, the concentration of ammonium sulfate, which is the raw material for electrolysis, is lower than that of the target product, ammonium persulfate, in the solution produced in the preceding electrolysis process. Moreover, the greater the density difference, the more advantageous. However, in the region where the concentration of ammonium sulfate, which is a reaction raw material in the electrolysis step, is low, the current efficiency is significantly lowered, resulting in a problem of worsening power costs.

In Patent Document 1, 30 to 45% by weight of ammonium sulfate aqueous solution is supplied to both sides of an electrolytic cell in which an anode and a cathode are separated by a cation exchange membrane, and guanidine sulfamate is used as a polarizing agent to achieve high current efficiency. However, this method is described only for the region where the ammonium sulfate concentration of the reaction raw material is 30% by weight or more. Current efficiency with respect to area is not stated.

In Patent Document 2, an ammonium sulfate aqueous solution containing hexavalent chromium ions or a mixed solution of ammonium sulfate and ammonium persulfate is supplied to a non-diaphragm electrolytic cell that does not use a diaphragm (separator) to separate the anode and the cathode, and electrolysis is performed. It is described that the reductive decomposition of ammonium persulfate produced at the anode is suppressed at the cathode, and ammonium persulfate is produced with high current efficiency even in non-diaphragm electrolysis. However, even in this case, the ammonium sulfate concentration in the electrolytic raw material is described only in the high concentration range of 30% by weight or more, and the low concentration range of ammonium sulfate is not described. In addition, an expensive diamond electrode is used for the anode. Therefore, it is difficult to put it into practical use industrially.

In Patent Document 3, 30 to 44% by weight of ammonium sulfate aqueous solution is supplied to an electrolytic cell partitioned by a porous neutral alumina diaphragm plate, and thiocyanate, cyanide, cyanate, fluoride, etc. are added as a polarizing agent. It is described that ammonium persulfate is produced with high current efficiency by adding and electrolyzing. No regions of low concentration are mentioned.

Accordingly, it is an object of the present invention to provide a method for producing ammonium persulfate with high current efficiency in the electrolysis reaction of ammonium sulfate even in a low concentration region of ammonium sulfate where the current efficiency is significantly reduced.

The present invention relates to the provision of a method for producing ammonium persulfate with high current efficiency even in a low ammonium sulfate concentration region where the current efficiency is remarkably lowered, and has the following configuration. That is, the present invention is characterized in that in the method of producing ammonium persulfate by electrolyzing ammonium sulfate, electrolysis is performed in the presence of calcium ions in the anolyte (hereinafter sometimes referred to as anolyte). , a method for the production of ammonium persulfate.

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

FIG. 2 is a schematic configuration diagram showing a method of producing ammonium persulfate by directly supplying raw materials for electrolysis to the anode and cathode of an electrolytic cell having no external tank. 1 is a schematic configuration diagram showing a method of producing ammonium persulfate while providing external tanks on both sides of an anode and a cathode and circulating an electrolytic solution. FIG.

The present invention will be described in further detail below 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, wherein the electrolysis is performed in the presence of calcium ions in the anolyte.

In the electrolytic reaction of ammonium sulfate, even in a low concentration region of ammonium sulfate where the current efficiency is significantly reduced, in order to make it possible to produce ammonium persulfate with high current efficiency, in the present invention, calcium ions are present in the anolyte. It is essential to carry out electrolysis in this state.

The calcium ion concentration in the anode electrolyte of the present invention is desirably 2-15 ppm, more desirably 5-9 ppm. If the concentration is outside this range, the effect of suppressing a decrease in current efficiency may be small, and high current efficiency may not be obtained. As an ion source of calcium ions to be added, compounds containing calcium include, for example, calcium carbonate, calcium nitrate, and calcium chloride, and at least one compound selected from these may be used.

Ammonium sulfate can be used as the anode-side raw material in the present invention, and although the concentration of ammonium sulfate is not particularly limited, a concentration of 20% by weight or less is preferable in order to maintain high current efficiency. Moreover, raw materials other than ammonium sulfate may be included, and for example, an acid such as sulfuric acid, a base such as ammonium hydroxide, or a water-soluble solid such as a polarizing agent may be added. The polarizing agent is not particularly limited as long as it is advantageous for the production of known persulfates. and at least one compound selected from thiocyanate. Guanidine salts include guanidine sulfamate, guanidine nitrate, guanidine sulfate, guanidine phosphate and guanidine carbonate. The concentration of the polarizing agent is preferably 0.01 to 1% by weight, more preferably 0.01 to 0.05% by weight, in the anode chamber. If the concentration of the polarizing agent is less than 0.01% by weight, the effect of increasing the dominance of the main reaction that produces persulfate ions is hardly obtained, and if it exceeds 1% by weight, the effect corresponding to the concentration cannot be obtained.

The cathode-side raw material of the present invention is not particularly limited, but it is possible to use 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. It is preferable to use an aqueous ammonium sulfate solution or an aqueous ammonium hydroxide solution as the solvent. From the viewpoint of voltage, it is more preferable to use an ammonium sulfate aqueous solution.

Such an aqueous solution contains an electrolyte, so that the electric resistance can be reduced, and the aqueous solution is composed of ions of the same composition as the anode-side raw material separated by a diaphragm, and does not contain hydrogen ions derived from sulfuric acid that are subjected to the cathode reaction. It is possible to increase the amount of by-products, and in addition, it is more advantageous than using acid in terms of material selection on the cathode side.

Although the concentration of the cathode-side raw material of the present invention is not particularly limited, 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 a cathode-side raw material, ammonium persulfate can be produced industrially advantageously. Both the anode side and the cathode side may be of a batch system for supplying raw materials and discharging a product, but a continuous system is more advantageous from an industrial point of view.

By making the cathode side raw material of the present invention have the above composition, the following reaction formula (1) is given priority in the range where hydrogen ions derived from sulfuric acid are present in the anolyte, and hydrogen is generated as a cathode side product. After acid-derived hydrogen ion deficiency, reactions such as the following reaction formula (2) and the following reaction formula (3) are given priority. Since the equilibrium reaction of the following reaction formula (4) exists in the system, hydrogen and ammonia can be produced as cathode-side products 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 type electrolytic cell or a filter press type electrolytic cell can be used. Here, as the diaphragm separating the anode chamber and the cathode chamber, a diaphragm capable of inhibiting migration of anions generated in the anode chamber to the cathode chamber is used. Examples of the diaphragm include a cation exchange membrane, a neutral alumina diaphragm and the like, and 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 in which platinum is exposed on the electrode surface (hereinafter referred to as "platinum electrode"). As the platinum electrode, it is preferable to use a pure platinum electrode or a clad steel in which platinum and a metal such as titanium are pressure-bonded, and it is possible to greatly improve the current efficiency compared to a platinum-plated electrode. As the cathode, lead, zirconium, platinum, nickel, and stainless steel are preferably used, and nickel or SUS316 is more preferably used. There are no particular restrictions on the shape of the electrodes for both the anode and the cathode, but it is more preferable to use a metal processed into the shape of a foil or a wire net as the electrode.

The current density of the anode of the present invention is preferably in the range of 20-500 A/dm ² , more preferably in the range of 40-80 A/dm ² . If the current density falls below the lower limit, the electrolysis efficiency and production efficiency may deteriorate, so it is preferable to increase the size of the electrolysis apparatus. If the current density exceeds the upper limit, the voltage applied during the electrolytic reaction becomes too high, which is economically disadvantageous. It is preferable to keep the temperature in the electrolytic cell at 40° C. or lower. When the temperature in the electrolytic cell exceeds 40° C., it becomes difficult to suppress the decomposition reaction of the salts in the electrolytic cell.

By adopting the production method of the present invention, ammonium persulfate can be produced with high current efficiency. Under preferable conditions, ammonium persulfate can be produced with a current efficiency of 80% or higher, and more preferably a current efficiency of 85% or higher. The upper limit of current efficiency is theoretically 100%. Here, the current efficiency (%) is a value represented by (generated persulfate ions (mol) x 2)/energization amount (F) x 100, which is the amount of persulfate ions generated per unit amount of electricity. can be calculated by measuring

By carrying out the electrolytic reaction with the anode chamber filled with the anolyte according to the present invention, persulfate ions are generated in the anolyte. Then, the ammonium persulfate can be precipitated by evaporating water until it becomes less than the solubility. The ammonium persulfate slurry after crystallization can be separated into ammonium persulfate crystals and a crystallization mother liquor by a solid-liquid separator such as a centrifuge. The obtained ammonium persulfate crystals can be dried and commercialized using a powder dryer. Also, the mother liquor after crystallization can be re-supplied to the process as an anode-side raw material.

In the cathode chamber of the present invention, as the electrolytic reaction progresses, cations corresponding to the charge transfer amount and water molecules hydrated by the cations move from the anode to the cathode side, and the liquid volume increases. Continuous operation becomes possible by resupplying the increased amount from the produced liquid to the cathode side after dehydration. The method of dehydrating the water that has moved to the cathode side is not particularly limited, but dehydration by evaporative concentration or membrane separation is preferred. As for the amount of dehydration, it is preferable to dehydrate more than a certain amount with respect to the amount of charge transfer, and when salt or the like is contained in the catholyte generated liquid, it is preferable to set the amount of dehydration to an amount equal to or less than the amount of crystals precipitated by dehydration. The dehydration amount per 1 mol of charge transfer is preferably 20 to 90 g, more preferably 30 to 80 g. The water obtained by dehydration contains ammonia. For example, it can be mixed (neutralized) with caprolactam sulfate as ammonia water and used in the step of producing caprolactam and ammonium sulfate.

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

The separated hydrogen gas is refined and compressed by using a pressure swing adsorption method or the like, and can be used in the hydrogenation process in the organic chemical industry or as a fuel for fuel cells.

In the method for producing ammonium persulfate of the present invention, ammonium sulfate, which is a by-product in the above-described process for producing lactam, acrylonitrile, methyl methacrylate, etc., and the process for producing coke by coal dry distillation, can be used as a raw material. At this time, by-products containing ammonium sulfate in various processes may contain impurities other than ammonium sulfate. Current efficiency may decrease. In such a case, it is preferable to purify the impurities in the ammonium sulfate in advance to reduce metal ions that lower the current efficiency, and then supply the ammonium persulfate to the ammonium persulfate production step. As a method for removing impurities in ammonium sulfate, for example, a method of chelating an inorganic substance is preferable.

As a specific example of the method for producing ammonium persulfate according to the present invention, FIG. 1 illustrates a case where an ammonium sulfate (ammonium sulfate) solution is used as the anode and cathode side raw material solutions. In FIG. 1, 1 indicates an electrolytic cell, and on the anode side 2 of the electrolytic cell 1, ammonium sulfate ((NH4)2SO4) produced as a by-product in the lactam manufacturing process 4, which is another manufacturing process, is used as the raw material for the anode side. ) is supplied, and in the anode reaction, sulfate ions react (consume) to generate persulfate ions, as in the prior art, as described below.
2SO ₄ ^2- → S ₂ O ₈ ^2- + 2e ^-
As dissolved ions,
Before electrolysis: NH ₄ ⁺ , SO ₄ ^2- = aqueous solution of ammonium sulfate After electrolysis: NH ₄ ⁺ , S ₂ O ₈ ^2- = aqueous solution of ammonium persulfate, ammonium ions migrate to the cathode side, and an aqueous solution of ammonium persulfate is produced. go. This anode-side produced liquid is concentrated and crystallized, separated into a crystallization mother liquor and crystals, and the crystals can be manufactured as an ammonium persulfate salt by, for example, a powder dryer. The crystallization mother liquor can be re-supplied to the process as an anode feedstock.

On the other hand, on the cathode side 3, to explain the case where an ammonium sulfate aqueous solution is used as a raw material for the cathode reaction, an aqueous solution containing ammonium sulfate is circulated and supplied, and hydrogen ions as a reaction source are absent or scarce. Ammonium ions migrating from the anode react like this to produce ammonia and hydrogen. Further, when 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 ⁻ → H ₂ (if there is a small amount of acid)

Hydrogen ions and ammonium ions corresponding to the amount of charge transfer and water molecules hydrated by these ions are transferred from the anode to the cathode side by electrolysis.

In addition, FIG. 2 illustrates the case where electrolysis is performed while the liquid is circulated between the external tanks 14 and 15 and the electrolytic cell. In FIG. 2, reference numeral 11 denotes an electrolytic cell, and ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) is circulated and supplied as an anode-side raw material to the anode side 12 of the electrolytic cell 11. Similarly, sulfate ions react (consume) to generate persulfate ions. This anode-side produced liquid is concentrated and crystallized, separated into a crystallization mother liquor and crystals, and the crystals can be manufactured as an ammonium persulfate salt by, for example, a powder dryer. The crystallization mother liquor can be re-supplied to the process as an anode feedstock.

On the other hand, on the cathode side 13, an aqueous solution containing ammonium sulfate is supplied as a cathodic reaction, and since hydrogen ions as a reaction source are absent or scarce, the ammonium ions migrated from the anode react to produce ammonia and hydrogen. Moreover, when there is acid on the cathode side, hydrogen ions derived from the acid react (consume) to generate hydrogen gas. Hydrogen ions and ammonium ions corresponding to the amount of charge transfer and water molecules hydrated by these ions are transferred from the anode to the cathode side by electrolysis.

The present invention will be specifically described below with reference to Examples, but the present invention is not limited by these Examples. The current efficiency in the examples is expressed by (generated persulfate ions (mol)×2)/energization amount (F)×100%, and represents the ratio of persulfate ions generated per unit amount of electricity.

(Examples 1 to 5)
A transparent acrylic electrolytic cell separated by a cation exchange membrane (Nafion (registered trademark) 117, Chemours Co., Ltd.) was used as the diaphragm, an electrode made of 80-mesh platinum wire mesh and titanium was used as the anode, and 80-mesh was used as the cathode. of SUS316 wire mesh was used. In the anode chamber, a mixed solution of 14.6% by weight of ammonium sulfate (SA) and 30.0% by weight of ammonium persulfate (APS) was added with 0.03% by weight of guanidine sulfamate as a polarizing agent and a calcium (Ca) standard. A liquid (Kanto Kagaku 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 an anode raw material. 400 g of a 30% by weight aqueous solution of ammonium sulfate was supplied to the cathode chamber. After the supply, electricity was applied at an anode current density of 45 A/dm2. The charge transfer amount was 0.13 mol. The amount of charge transfer is obtained by the value of the amount of energized current times the energized time. After energization, the ammonium persulfate concentration (wt%) in the resulting anode product solution was measured by titration to calculate the amount of ammonium persulfate (mol), and the amount of ammonium persulfate contained in the anode raw material before energization was subtracted. The current efficiency was obtained from the amount (mol) of ammonium persulfate produced. Table 1 shows the current efficiency and the composition of the anode-generating solution obtained by changing the amount of calcium (Ca) added.

(Comparative example 1)
The procedure was carried out in the same manner as in Example 1, except that the calcium (Ca) standard solution was not added to the anode raw material. Table 2 shows the current efficiency and the composition of the anode generated solution obtained at this time.

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

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 (15)

A method for producing ammonium persulfate by electrolyzing ammonium sulfate, wherein the electrolysis is carried out in the presence of calcium ions in the anode electrolyte. 2. The method for producing ammonium persulfate according to claim 1, wherein the anolyte has a calcium ion concentration of 2 to 15 ppm. 3. The method for producing ammonium persulfate according to claim 1, wherein a compound containing calcium is added to the anolyte. 4. The method for producing ammonium persulfate according to claim 3, wherein the compound containing calcium is a compound selected from at least one of calcium carbonate, calcium nitrate and calcium chloride. 5. The method for producing ammonium persulfate according to any one of claims 1 to 4, wherein the anode electrolyte is an ammonium sulfate aqueous solution having a sulfate ion concentration of 20% by weight or less. The method for producing ammonium persulfate according to any one of claims 1 to 5, wherein the catholyte is an aqueous solution of ammonium sulfate. The method for producing ammonium persulfate according to any one of claims 1 to 6, 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 7, wherein a cation exchange membrane is used as a diaphragm separating the anode and the cathode. The method for producing ammonium persulfate according to any one of claims 1 to 8, wherein a polarizing agent is added to the anolyte. 10. The method for producing ammonium persulfate according to claim 9, wherein the polarizing agent is at least one compound selected from guanidine, guanidine salts and thiocyanates. The method for producing ammonium persulfate according to any one of claims 1 to 10, wherein the anode electrode is platinum, platinum group or conductive diamond. The method for producing ammonium persulfate according to any one of claims 1 to 11, wherein the anode current density is in the range of 20 to 500 A/dm2. The method for producing ammonium persulfate according to any one of claims 1 to 12, wherein ammonium persulfate is produced with a current efficiency of 80% or higher. 14. The method for producing ammonium persulfate according to any one of claims 1 to 13, wherein the ammonium sulfate in the anolyte contains by-products in the lactam production process. 15. The method for producing ammonium persulfate according to any one of claims 1 to 14, wherein the ammonia produced on the cathode side is utilized in the lactam production process.

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