Method for producing ammonium persulfate

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

Technical Field

[0001] The present invention relates to a method for producing ammonium persulfate.

Background Art

[0002] Ammonium sulfate is also called ammonium sulphate and was once synthesized as a target product. Currently, most of the ammonium sulfate in circulation is a by-product in the organic chemical industry such as caprolactam, laurolactam, acrylonitrile, methyl methacrylate, and the coke production process by coal carbonization. Since ammonium sulfate contains about 20% of ammonia nitrogen, it can be used as a fertilizer, and most of the ammonium sulfate by-produced in the above-mentioned processes is used for fertilizers. Conventionally, methods for producing caprolactam, acrylonitrile, and methyl methacrylate that do not by-produce ammonium sulfate have been developed. However, these production methods have problems such as a complex process and difficulty in conversion from existing production methods. Therefore, a large amount of ammonium sulfate is still by-produced.

[0003] On the other hand, ammonium persulfate is widely used industrially mainly as a polymerization initiator for emulsion polymerization, an oxidative bleaching agent, a copper etching agent, etc. As a known method for producing ammonium persulfate, as described in Patent Document 1, using a cation exchange membrane as a diaphragm in an electrolytic cell, using an aqueous ammonium sulfate solution as a raw material on the anode side, and controlling the amount of acid-dissociable hydrogen ions in the raw material on the cathode side, in the range where hydrogen ions derived from sulfuric acid are present in the cathode solution (hereinafter, may be referred to as the cathode electrolyte), the following reaction formula (1) is prioritized, and hydrogen is generated as a cathode-side product. However, after the lack of hydrogen ions derived from the acid, the following reaction formula (2) is prioritized to generate ammonia, or as described in Patent Document 2, a diaphragm-free electrolysis method that does not use a separator such as a diaphragm between the anode and the cathode, and as described in Patent Document 3, a method that uses a mixed solution of sulfuric acid and ammonium sulfate as a raw material on the cathode side. A method is known in which all the electrolytic reactions on the cathode side are carried out only by the reaction in which hydrogen ions derived from sulfuric acid in the following reaction formula (1) become hydrogen molecules. 2H+ + 2e - → H 2 (1) 2NH 4 + + 2e - → 2NH 3 + H 2 (2)

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the production of ammonium persulfate, usually ammonium persulfate is obtained by electrolyzing a mixed solution of ammonium sulfate and ammonium persulfate obtained in the electrolysis step, and in the crystallization step, only ammonium persulfate is precipitated by dehydration and concentration, and the obtained slurry is subjected to solid - liquid separation and drying to produce ammonium persulfate crystals. However, in order to efficiently precipitate only ammonium persulfate in the crystallization step, for the product solution of the previous electrolysis step, it is more advantageous that the concentration of ammonium sulfate as the electrolysis raw material is lower than that of the target product ammonium persulfate and the concentration difference is larger. However, in the region where the concentration of ammonium sulfate as the reaction raw material is low in the electrolysis step, there is a problem that the current efficiency significantly decreases, resulting in a deterioration of the power cost.

[0006] Patent Document 1 describes that an ammonium sulfate aqueous solution of 30 to 45% by weight 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 depolarizer to produce ammonium persulfate with high current efficiency and co-produce ammonia. However, this method only describes the region where the ammonium sulfate as a reaction raw material is concentrated at 30% by weight or more, and does not describe the current efficiency in the low-concentration region of ammonium sulfate where the current efficiency decreases.

[0007] Patent Document 2 describes that an ammonium sulfate aqueous solution added with hexavalent chromium ions or a mixed solution of ammonium sulfate and ammonium persulfate is supplied to a diaphragm-free electrolytic cell that does not use a diaphragm (separator) separating the anode and the cathode, and electrolyzed, so that the ammonium persulfate generated at the anode is suppressed from being reductively decomposed at the cathode, and ammonium persulfate can be produced with high current efficiency even in diaphragm-free electrolysis. However, this also only describes the region where the ammonium sulfate concentration in the electrolysis raw material is as high as 30% by weight or more, and does not describe the region where the ammonium sulfate concentration is low. In addition, since an expensive diamond electrode is used at the anode, it is difficult to industrialize.

[0008] Patent Document 3 describes that an ammonium sulfate aqueous solution of 30 to 44% by weight is supplied to an electrolytic cell partitioned by a porous neutral alumina diaphragm plate, and electrolyzed by adding thiocyanate, cyanide, cyanate, fluoride, etc. as a depolarizer to produce ammonium persulfate with high current efficiency. However, this also only describes the region where the ammonium sulfate concentration in the electrolysis raw material is as high as 30% by weight or more, and does not describe the region where the ammonium sulfate concentration is low.

[0009] Therefore, an object of the present invention is to provide a method for producing ammonium persulfate with high current efficiency even in a low-concentration region of ammonium sulfate where the current efficiency significantly decreases in the electrolysis reaction of ammonium sulfate.

Means for Solving the Problems

[0010] The present invention relates to a method for producing ammonium persulfate with high current efficiency even in a low concentration range of ammonium sulfate where the current efficiency is significantly reduced, and has the following configuration. That is, the present invention electrolyzes ammonium sulfate to produce ammonium persulfate In fact, the cathode electrolyte is an aqueous solution of ammonium sulfate, in an anolyte (hereinafter sometimes referred to as anodic electrolyte) containing an aqueous ammonium sulfate solution with a sulfate ion concentration of 20% by weight or less a compound containing calcium is added the anodic electrolyte to 2 is characterized in that electrolysis is carried out in the presence of calcium ions of ~15 ppm, and is a method for producing ammonium persulfate.

Effect of the Invention

[0011] According to the present invention, in the electrolysis reaction of ammonium sulfate, it is possible to produce ammonium persulfate with high current efficiency even in a low concentration range of ammonium sulfate where the current efficiency is significantly reduced.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in more detail together with embodiments.

[0014] 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 electrolysis is carried out in the presence of calcium ions in the anolyte.

[0015] In the electrolysis reaction of ammonium sulfate, in order to be able to produce ammonium persulfate with high current efficiency even in the low concentration range of ammonium sulfate where the current efficiency significantly decreases, it is essential in the present invention to perform electrolysis with calcium ions present in the anolyte.

[0016] The calcium ion concentration in the anolyte of the present invention is preferably 2 to 15 ppm, more preferably 5 to 9 ppm. When added outside this concentration range, the effect of suppressing the decrease in current efficiency may be weak and it may not be possible to obtain high current efficiency. As the ion source of the calcium ions to be added, as compounds containing calcium, for example, there are calcium carbonate, calcium nitrate, calcium chloride, etc., and at least one compound selected from these may be used.

[0017] Ammonium sulfate can be used as the anodic raw material of the present invention, and 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. Further, it may contain raw materials other than ammonium sulfate, for example, acids such as sulfuric acid, bases such as ammonium hydroxide, and water-soluble solids such as depolarizers may be added. The depolarizer 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 preferable, and at least one compound selected from guanidine, guanidine salts and thiocyanates is more preferable. Examples of guanidine salts include guanidine sulfamate, guanidine nitrate, guanidine sulfate, guanidine phosphate or guanidine carbonate. The concentration of the depolarizer is preferably 0.01 to 1% by weight, more preferably 0.01 to 0.05% by weight in the anode chamber. When the depolarizer concentration is less than 0.01% by weight, almost no effect of enhancing the superiority of the main reaction for generating persulfate ions can be obtained, and when it exceeds 1% by weight, an effect commensurate with the concentration cannot be obtained.

[0018] The cathode-side raw material of the present invention is not particularly limited, but 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 can be used. It is preferable to use an ammonium sulfate aqueous solution or an ammonium hydroxide aqueous solution as the cathode-side raw material. More preferably, from the viewpoint of voltage, an ammonium sulfate aqueous solution is used.

[0019] Since such an aqueous solution contains an electrolyte, it can reduce the electrical resistance. It is composed of ions having the same composition as the anode-side raw material separated by a diaphragm, and since there are no hydrogen ions derived from sulfuric acid used in the cathode reaction, it is possible to increase the by-production amount of ammonia. In addition, it is more advantageous than using an acid also from the aspect of material selection on the cathode side.

[0020] 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 the cathode-side raw material, ammonium persulfate can be industrially advantageously produced. For both the anode side and the cathode side, the raw material supply and product discharge methods may be batch methods, but industrially, the continuous method is more advantageous.

[0021] By setting the cathode-side raw material of the present invention to the above composition, the following reaction formula (1) is prioritized in the range where hydrogen ions derived from sulfuric acid are present in the anolyte, and hydrogen is generated as a cathode-side product. However, after the lack of hydrogen ions derived from the acid, reactions such as the following reaction formula (2) and the following reaction formula (3) are prioritized. Since there is an equilibrium reaction of the following reaction formula (4) in the system, hydrogen and ammonia can be generated 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 2O + 2e - → H 2 + 2OH - (3) NH 4 + + OH - ⇔ NH 3 + H 2 O (4)

[0022] The electrolytic cell used in the present invention is not particularly limited. For example, an electrolytic cell partitioned 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, as the diaphragm separating the anode chamber and the cathode chamber, a diaphragm capable of inhibiting the migration of anions generated in the anode chamber to the cathode chamber is used. Examples of the diaphragm include a cation exchange membrane and a neutral alumina diaphragm, and a cation exchange membrane is preferably used.

[0023] As the anode of the present invention, it is preferable to use a conductive diamond electrode or an electrode of a platinum group, and it is more preferable to use an electrode with platinum exposed on the electrode surface (hereinafter referred to as "platinum electrode"). As the platinum electrode, it is preferable to use a non-scaling platinum electrode and a clad steel obtained by crimping platinum and a metal such as titanium, and it is possible to significantly improve the current efficiency as compared with 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. Neither the anode nor the cathode is particularly limited in the shape of the electrode, but it is more preferable to use a metal processed into a mesh or net shape as the electrode.

[0024] The current density of the anode of the present invention is preferably in the range of 20 to 500 A / dm 2 and more preferably in the range of 40 to 80 A / dm 2It is more preferable that it is within the range. When the current density becomes lower than the lower limit value, the electrolysis efficiency deteriorates, and the production efficiency may also deteriorate. Therefore, it is preferable to increase the size of the electrolysis apparatus. When the current density exceeds the upper limit value and becomes too large, the applied voltage during the electrolysis reaction becomes too high, which is economically disadvantageous. The temperature inside the electrolytic cell is preferably maintained at 40°C or lower. When the temperature inside the electrolytic cell exceeds 40°C and becomes too high, it becomes difficult to suppress the reaction in which the salts inside the electrolytic cell decompose.

[0025] By adopting the production method of the present invention, ammonium persulfate can be produced with high current efficiency. Under preferable 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. The upper limit of the current efficiency is theoretically 100%. Here, the current efficiency (%) is a value represented by (mol of generated persulfate ions × 2) / charge quantity (F) × 100, and it can be calculated by measuring the amount of persulfate ions generated per unit charge quantity.

[0026] By carrying out the electrolysis reaction with the anolyte filled in the anode chamber of the present invention, persulfate ions are generated in the anolyte. Therefore, this anodic product solution can be supplied to, for example, a crystallization tank in the same manner as in the prior art, and ammonium persulfate can be precipitated by evaporating the water until it becomes less than the solubility. The ammonium persulfate slurry after crystallization can be separated into ammonium persulfate crystals and crystallization mother liquor by a solid-liquid separator such as a centrifuge. The obtained ammonium persulfate crystals can be dried and made into products using a powder dryer. Further, the mother liquor after crystallization can be resupplied to the process as an anode-side raw material.

[0027] Regarding the cathode chamber of the present invention, as the electrolysis reaction proceeds, cations corresponding to the amount of charge transfer and water molecules hydrated to the cations move from the anode to the cathode side, increasing the liquid volume. Therefore, during continuous operation, this increased amount is dehydrated from the cathode-side generated liquid and then supplied back to the cathode side again, enabling continuous operation. The method for dehydrating the water that has moved to the cathode side is not particularly limited, but dehydration by evaporation concentration or membrane separation is preferred. Regarding the amount of dehydration, it is preferably more than a certain amount relative to the amount of charge transfer, and when the cathode generated liquid contains salts or the like, it is preferably less than the amount of crystals precipitated by dehydration. The amount of dehydration 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, and for example, it can be mixed (neutralized) with caprolactam sulfate as aqueous ammonia and used in the process for producing caprolactam and ammonium sulfate.

[0028] Also, by dehydrating the cathode-side generated liquid and continuously supplying it back to the cathode side while continuing electrolysis, hydrogen ions and ammonium ions corresponding to the amount of charge transfer move from the anode to the cathode side. Therefore, a mixed gas of hydrogen and ammonia and / or ammonium hydroxide (ammonia-containing water) is generated in the cathode generated gas in the cathode chamber and / or in the generated liquid. The hydrogen-ammonia mixed gas generated on the cathode side can be separated by generally used ammonia gas separation methods, such as cryogenic separation or compression separation.

[0029] The separated hydrogen gas is purified and compressed using a pressure swing adsorption method or the like and can be used in the hydrogenation process of the organic chemical industry or as fuel for fuel cells.

[0030] The method for producing ammonium persulfate according to the present invention can use ammonium sulfate by-produced in the production processes of lactam, acrylonitrile, methyl methacrylate, etc., and the coke production process by coal carbonization, which were described above, as raw materials. At this time, by-products containing ammonium sulfate in various processes may contain impurities other than ammonium sulfate, and depending on their components and contents, the current efficiency in the production process of ammonium persulfate may decrease due to side reactions. In such cases, it is preferable to purify the impurities in ammonium sulfate in advance, reduce the metal ions that lower the current efficiency, and then supply it to the ammonium persulfate production process. As a method for removing impurities in ammonium sulfate, for example, a chelating treatment method is preferable for inorganic substances.

[0031] As a specific example of the method for producing ammonium persulfate according to the present invention, FIG. 1 illustrates the 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. On the anode side 2 of the electrolytic cell 1, ammonium sulfate ((NH4)2SO4) by-produced in the lactam production process 4 as a specific other production process is supplied as the anode side raw material. As the anodic reaction, as in the prior art, as follows, sulfate ions react (are consumed) to generate persulfate ions. 2SO 4 2- → S 2 O 8 2- + 2e - As the dissolved ions, Before electrolysis: NH 4 + , SO 4 2- = Aqueous ammonium sulfate solution After electrolysis: NH 4 + , S 2 O 8 2- = Aqueous ammonium persulfate solution As a result, ammonium ions migrate to the cathode side, and an aqueous solution of ammonium persulfate is formed. The solution generated on the anode side is concentrated and crystallized, separated into a crystallization mother liquor and crystals, and the crystals can be commercialized as a salt of ammonium persulfate, for example, by a powder dryer. The crystallization mother liquor can be recycled to the process as an anode-side raw material.

[0032] On the other hand, in the cathode side 3, the cathode reaction will be described for the case where an aqueous solution of ammonium sulfate is used as a raw material. An aqueous solution containing ammonium sulfate is circulated and supplied. Since there is little or no hydrogen ion as a reaction source, the ammonium ions migrated from the anode react as shown in the following reaction formula, and ammonia and hydrogen are generated. Also, when there is an acid on the cathode side, hydrogen ions derived from the acid react (are consumed) as shown in the following reaction formula, and hydrogen gas is generated. 2NH 4 + + 2e - → 2NH 3 + H 2 2H + + 2e - → H 2 (when there is a small amount of acid)

[0033] By electrolysis, hydrogen ions, ammonium ions, and water molecules corresponding to the amount of charge transferred from the anode to the cathode side and hydrated to these ions move.

[0034] Also, FIG. 2 illustrates the case of electrolysis while circulating the liquid between the external tanks 14 and 15 and the electrolytic cell. In FIG. 2, 11 indicates the electrolytic cell. On the anode side 12 of the electrolytic cell 11, ammonium sulfate ((NH 4 ) 2 SO 4 ) is circulated and supplied as an anode-side raw material. As the anode reaction, as in the prior art, sulfate ions react (are consumed) to generate persulfate ions. The solution generated on the anode side is concentrated and crystallized, separated into a crystallization mother liquor and crystals, and the crystals can be commercialized as a salt of ammonium persulfate, for example, by a powder dryer. The crystallization mother liquor can be recycled to the process as an anode-side raw material.

[0035] On the cathode side 13, as the cathode reaction, an aqueous solution containing ammonium sulfate is supplied. Since there are no or few hydrogen ions as the reaction source, the ammonium ions migrated from the anode react to generate ammonia and hydrogen. Also, when there is an acid on the cathode side, the hydrogen ions derived from the acid react (are consumed) to generate hydrogen gas. By electrolysis, hydrogen ions, ammonium ions, and water molecules corresponding to the amount of charge transferred from the anode to the cathode side move.

Example

[0036] Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited in any way by these examples. The current efficiency in the examples is represented by (mol of generated persulfate ions × 2) / charge amount (F) × 100%, and represents the ratio of persulfate ions generated per unit charge amount.

[0037] (Examples 1 to 5) An electrolytic cell made of transparent acrylic, separated by a cation exchange membrane (Kemars Co., Ltd., Nafion® 117), was used. An electrode composed of an 80-mesh platinum wire mesh and titanium was used as the anode, and an electrode composed of an 80-mesh SUS316 wire mesh was used as the cathode. In the anode chamber, a mixed solution of 14.6 wt% ammonium sulfate (SA) and 30.0 wt% ammonium persulfate (APS) was prepared. 0.03 wt% of guanidine sulfamate was added as a depolarizer, and a calcium (Ca) standard solution (Kanto Chemical Co., Inc., calcium (Ca): 1000 mg / L) was added so that the calcium concentration became 2.8 - 11 ppm. 450 g of the anode raw material was supplied. 400 g of a 30 wt% aqueous ammonium sulfate solution was supplied to the cathode chamber. After the supply, an electric current was passed with an anode current density of 45 A / dm2. The amount of charge transfer was 0.13 mol. The amount of charge transfer was determined by the value of the current passed × the time of current passage. After the current passage, the amount of ammonium persulfate (mol) was calculated by measuring the concentration (wt%) of ammonium persulfate in the obtained anode product solution by titration, and the current efficiency was determined by subtracting the amount of ammonium persulfate contained in the anode raw material before the current passage. Table 1 shows the current efficiency and the anode product solution composition obtained by changing the amount of calcium (Ca) added.

[0038]

Table 1

[0039] (Comparative Example 1) The procedure was the same 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 anode product solution composition obtained at this time.

[0040]

Table 2

Industrial Applicability

[0041] 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 is significantly reduced. In addition, since efficient purification of ammonium persulfate can be achieved in the subsequent crystallization step, it is possible to produce ammonium persulfate, which is extremely industrially advantageous.

Explanation of Signs

[0042] 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

1. When producing ammonium persulfate by electrolyzing ammonium sulfate, a cation exchange membrane is used as a diaphragm separating the anode and the cathode, the cathode electrolyte is an aqueous ammonium sulfate solution, and a compound containing calcium is added to the anode electrolyte containing an aqueous ammonium sulfate solution with a sulfate ion concentration of 20% by weight or less, and electrolysis is carried out in a state where 2 to 15 ppm of calcium ions are present in the anode electrolyte. A method for producing ammonium persulfate, characterized in that.

2. The method for producing ammonium persulfate according to claim 1, wherein the compound containing calcium is a compound selected from at least one of calcium carbonate, calcium nitrate, and calcium chloride.

3. The method for producing ammonium persulfate according to any one of claims 1 to 2, wherein the concentration of the aqueous ammonium sulfate solution as the cathode electrolyte is 30 to 45% by weight.

4. The method for producing ammonium persulfate according to any one of claims 1 to 3, wherein a depolarizer is added to the anode electrolyte.

5. The method for producing ammonium persulfate according to claim 4, wherein the depolarizer is at least one compound selected from guanidine, guanidine salts, and thiocyanates.

6. The method for producing ammonium persulfate according to any one of claims 1 to 5, wherein the anode electrode is platinum or a platinum group.

7. The current density of the anode is in the range of 20 to 500 A / dm ２ 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 / dm

8. The method for producing ammonium persulfate according to any one of claims 1 to 7, wherein ammonium persulfate is produced with a current efficiency of 80% or more.

9. The method for producing ammonium persulfate according to any one of claims 1 to 8, wherein the ammonium sulfate in the anode electrolyte includes that by-produced in the lactam production process.

10. The method for producing ammonium persulfate according to any one of claims 1 to 9, wherein the ammonia generated on the cathode side is utilized in the lactam production process.

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