A method for preparing low-ammonia nitrogen sodium persulfate

Abstract

The present invention relates to the field of chemical industry, and discloses a method for preparing low-ammonia nitrogen sodium persulfate, and specifically discloses a method for reducing ammonia nitrogen impurities in the sodium persulfate production process. The traditional electrolysis process uses ammonia nitrogen-containing compounds such as ammonium sulfate to improve the electrolysis efficiency, resulting in ammonia nitrogen impurities in the product, so that the quality of the prepared sodium persulfate product is not high. This process does not require the use of ammonium sulfate materials, has low cost, uses less materials, and has high electrolysis efficiency. The ammonia nitrogen content is further reduced by adding disodium hydrogen phosphate and magnesium sulfate, and recrystallization and purification are performed, so that high-quality sodium persulfate products with low ammonia nitrogen impurity content can be produced, and the ammonia nitrogen impurity content is far less than 0.0010%.

Description

Technical Field

[0001] The invention relates to the field of chemical industry, and more specifically discloses a method for preparing low-ammonia nitrogen sodium persulfate. Background Art

[0002] Sodium persulfate, also known as sodium persulfate, has a molecular formula of Na2S2O8. It is a white crystalline powder, soluble in water but insoluble in ethanol. It is mainly used as a bleach, oxidant, and emulsion polymerization accelerator. In the chemical industry, sodium persulfate is mainly used to generate free radicals as an initiator for polymerization reactions; in the oil extraction industry, it is used as an additive for downhole fracturing and for decolorizing oil; in the food industry, it is a regulator for starch production; it is also one of the basic ingredients of hair dyes, which plays a decolorizing role; in the electronics industry, persulfate is widely used for cleaning copper plates of printed circuits in the electronics industry, acting as an etchant for printed circuit boards, etc.; it is also used in electroplating, battery and metal oxidation surface treatment, photography, storage batteries, sugar making and other industrial sectors.

[0003] The industrial preparation methods of sodium persulfate mainly include chemical synthesis and electrolysis. The chemical synthesis method uses ammonium persulfate and sodium hydroxide as raw materials, and the reaction generates sodium persulfate while releasing a large amount of ammonia. The generated ammonia is removed by an absorption tower or decompression. However, the residual ammonia nitrogen impurities are difficult to completely remove, and the energy consumption is high and the yield is low. In addition, ammonium persulfate is prepared by electrolysis in industry, so the materials of the chemical synthesis method are essentially derived from the electrolysis method. Therefore, the electrolysis method has become the main method for industrial production of sodium persulfate. The electrolysis method adopts an H-type electrolytic cell system. The anode of the electrolytic cell generally uses sodium sulfate, ammonium sulfate, and a depolarizer solution, and the cathode contains a sulfuric acid solution. The anode and cathode of the electrolytic cell are separated by a conductive partition or a filter membrane. The sodium persulfate generation reaction occurs in the anode electrolytic cell. After the reaction is completed, the anode electrolytic cell reaction liquid removes part of the solvent, cools and crystallizes, and is dried to obtain sodium persulfate. Disadvantage 1: In order to improve the yield, the mother liquor generally needs to be concentrated several times and then cooled and crystallized, which greatly increases energy consumption and labor costs, and ultimately leads to high production costs; Disadvantage 2: Since sodium sulfate has low solubility and high resistance, the electrolysis efficiency of direct electrolysis of sodium sulfate solution is extremely low, only about 5%. The currently reported process solution is to add ammonium sulfate and depolarizers to the anode electrolytic cell to improve the current efficiency. However, the addition of a large amount of ammonium sulfate will inevitably introduce ammonia nitrogen impurities that will remain in the finished sodium persulfate product. The addition of ammonium sulfate not only greatly increases the material cost, but also the impurities introduced by it lead to low product quality and even unqualified products. Summary of the invention

[0004] The present invention mainly provides a method for preparing low-ammonia nitrogen sodium persulfate, so as to solve the problems in the background technology that the production cost of the sodium persulfate electrolysis process is high and the addition of ammonium sulfate leads to high ammonia nitrogen impurities in the product or even unqualified products.

[0005] To solve the above technical problems, according to the present invention, more specifically, a method for preparing low-ammonia nitrogen sodium persulfate comprises the following contents:

[0006] S1. Weigh sodium sulfate, add water to dissolve it, and prepare a solution with a mass concentration of 13-20%. After circulating through a precision filter to remove impurities, circulate it to the electrolytic cell;

[0007] S2, weigh sulfuric acid, add water to dilute to a mass concentration of 20-30%, remove impurities through a precision filter and then circulate to the electrolytic cell;

[0008] S3, circulating a sodium persulfate solution having a mass concentration of 5-20% to the electrolytic cell through a precision filter;

[0009] S4, electrolysis reaction for 2-5h, during which the electrolyte microcirculation is maintained and the reaction temperature is maintained at 20-25 degrees Celsius;

[0010] S5, real-time monitoring of the reaction rate of sodium sulfate in the electrolyte, when the reaction rate drops to 50-70% of the initial rate, adding a depolarizing catalyst to the electrolytic cell, and continuing the electrolysis reaction until completion;

[0011] S6, transferring the mother liquid of the electrolytic reaction in step S5 to a crystallization kettle, evaporating part of the solvent under reduced pressure, cooling the reaction liquid for crystallization, and filtering after the crystallization to obtain a crude sodium persulfate;

[0012] S7, adding the crude sodium persulfate product of step S6 into purified water, heating and stirring to dissolve, adding disodium hydrogen phosphate and magnesium sulfate after dissolving, stirring for 10-30 minutes, keeping warm and filtering to remove solids formed by ammonia nitrogen impurities, cooling the filtrate for crystallization, filtering to obtain wet sodium persulfate, and recycling the mother liquor to enter step S3 of the next batch production;

[0013] S8. Dry the wet sodium persulfate product from step S7 to obtain a low-ammonia nitrogen sodium persulfate finished product.

[0014] Furthermore, in step S1, the electrolytic cell is cylindrical, there is no conductive partition or filter membrane between the positive and negative electrodes, the anode of the electrolytic cell is platinum or platinum-titanium alloy, more preferably platinum-titanium alloy, and the cathode is lead; the current density is 0.5-0.8A / cm 2 , more preferably 0.6A / cm 2 .

[0015] Furthermore, in step S5, the depolarization catalyst is one or a combination of sodium pyrophosphate, sodium pyrophosphate hydrate, and manganese thiocyanate, and the feed amount is catalyst: sodium sulfate = 1:1500-2000 molar ratio.

[0016] Furthermore, in step S6, the temperature when part of the solvent is evaporated under reduced pressure is 30-50 degrees Celsius, the pressure is 5-15 kPa, and the crystallization temperature is 20-25 degrees Celsius.

[0017] Furthermore, in step S7, the dissolution temperature is 40-55 degrees Celsius, more preferably 50 degrees Celsius; the crystallization temperature is 20-25 degrees Celsius; the ammonia nitrogen impurity solid is MgNH4PO4·6H2O; and the feed amount is disodium hydrogen phosphate: magnesium sulfate: sodium sulfate = 1:1:1000-2000 molar ratio.

[0018] Furthermore, in step S8, the drying temperature is 30-50 degrees Celsius; the drying method is one of air drying, vacuum drying, and fluidized bed drying.

[0019] From the above, it can be seen that the technical solution provided by the present invention adopts a cylindrical electrolytic cell, and there is no conductive partition or filter membrane between the cathode and anode electrolytic cells, which enables various ions to be distributed quickly, thereby reducing the ion concentration near the electrode, protecting the electrode and preventing the electrolysis rate from decreasing too quickly; on the other hand, the technical solution provided by the present invention greatly reduces the content of ammonia nitrogen impurities in sodium persulfate by adding impurity removal and recrystallization processes, and produces high-quality sodium persulfate products. Among them, the impurity removal process uses disodium hydrogen phosphate, magnesium sulfate and ammonia nitrogen impurities to form MgNH4PO4·6H2O precipitation to remove trace ammonia nitrogen impurities in the product, and then filters to remove the impurity precipitate, crystallizes to obtain sodium persulfate with low ammonia nitrogen, and adds the crystallization mother liquor to the electrolytic cell for the next batch of production. We are surprised to find that it can greatly increase the electrolysis efficiency, and can solve the problem of extremely low electrolysis efficiency without the need to add additional ammonium sulfate, greatly reducing material costs, and the crystallization waste mother liquor in the production and purification process does not need to be crystallized and recovered sodium persulfate multiple times, which greatly reduces time and energy consumption costs. More importantly, since there is no need to use amine compounds such as ammonium sulfate, the purification pressure of sodium persulfate will be greatly reduced, and ultimately a sodium persulfate product with cost and quality advantages will be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0021] Figure 1 This is the sample test report diagram of Example 2;

[0022] Figure 2 A schematic diagram of the method flow chart. DETAILED DESCRIPTION

[0023] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict. Example 1

[0024] Weigh 100 kg of sodium sulfate, add water to dissolve it, and prepare a solution with a mass concentration of 20%. After circulating it through a precision filter for 1 hour to remove impurities, it is circulated to a cylindrical electrolytic cell; weigh 30 kg of concentrated sulfuric acid, dilute it with water to a mass concentration of 30%, remove impurities through a precision filter, and then circulate it to a cylindrical electrolytic cell; circulate a 5% sodium persulfate solution through a precision filter to a cylindrical electrolytic cell, the temperature control system is 25 degrees Celsius, the anode of the electrolytic cell is platinum-titanium alloy, and the cathode is lead; connect the voltage across the electrolytic cell, and the current is 0.8A / cm 2 , monitor the reaction rate of sodium sulfate in the electrolyte in real time. When the reaction rate drops to 50% of the initial rate, add 0.1 kg of depolarizing catalyst sodium pyrophosphate to the electrolytic cell. The feeding amount is sodium pyrophosphate: sodium sulfate = 1:2000 molar ratio. Continue electrolysis. Keep the electrolyte microcirculation during the electrolysis process. Keep the temperature at 25 degrees Celsius. The reaction is completed in about 3 hours. The mother liquor of the electrolysis reaction is transferred to the crystallization kettle, evacuated to 10 kPa, and part of the solvent is evaporated under reduced pressure at 50 degrees Celsius. The remaining reaction liquid is cooled to 20-25 degrees Celsius for crystallization for 1 hour. After the crystallization is completed, filter it. The crude sodium persulfate is obtained; the crude sodium persulfate is added into purified water with a weight ratio of 1.6 times the crude sodium persulfate, heated to 55 degrees Celsius, stirred and dissolved, after the crude sodium persulfate is dissolved, 0.1 kg of disodium hydrogen phosphate and 0.084 kg of magnesium sulfate are added, the temperature is kept at 55 degrees Celsius and stirred for 20 minutes, filtered, and the MgNH4PO4·6H2O solid formed by ammonia nitrogen impurities is removed; the filtrate is cooled to 20-25 degrees Celsius for crystallization for 1 hour, filtered, and a wet sodium persulfate product is obtained, and the filtered mother liquor is recycled and reused for the next batch of production; the wet product is dried at 50 degrees Celsius in a vacuum double cone to obtain sodium persulfate. Example 2

[0025] Weigh 100 kg of sodium sulfate, add water to dissolve, and prepare a solution with a mass concentration of 20%. After circulating for 1 hour to remove impurities through a precision filter, circulate to a cylindrical electrolytic cell; weigh 30 kg of concentrated sulfuric acid, dilute it with water to a mass concentration of 30%, remove impurities through a precision filter, and circulate to a cylindrical electrolytic cell; the sodium persulfate solution with a mass concentration of 6.3% recovered in Example 1 is circulated to a cylindrical electrolytic cell through a precision filter, the temperature control system is 25 degrees Celsius, the anode of the electrolytic cell is a platinum-titanium alloy, and the cathode is lead; connect the voltage across the electrolytic cell, and the current is 0.8A / cm 2, monitor the reaction rate of sodium sulfate in the electrolyte in real time. When the reaction rate drops to 53% of the initial rate, add 0.1kg of depolarizing catalyst sodium pyrophosphate to the electrolytic cell. The feeding amount is sodium pyrophosphate: sodium sulfate = 1:2000 molar ratio. Continue electrolysis. Keep the electrolyte microcirculation during the electrolysis process. Keep the temperature at 25 degrees Celsius. The reaction is completed in about 3 hours. The mother liquor of the electrolysis reaction is transferred to the crystallization kettle, evacuated to 10kPa, and part of the solvent is evaporated under reduced pressure at 50 degrees Celsius. The remaining reaction liquid is cooled to 20-25 degrees Celsius for crystallization for 1 hour. After the crystallization is completed, filter it. The crude sodium persulfate is obtained; the crude sodium persulfate is added into purified water with a weight ratio of 1.6 times the crude sodium persulfate, heated to 55 degrees Celsius, stirred and dissolved, after the crude sodium persulfate is dissolved, 0.1 kg of disodium hydrogen phosphate and 0.084 kg of magnesium sulfate are added, the temperature is kept at 55 degrees Celsius and stirred for 20 minutes, filtered, and the MgNH4PO4·6H2O solid formed by ammonia nitrogen impurities is removed; the filtrate is cooled to 20-25 degrees Celsius for crystallization for 1 hour, filtered, and a wet sodium persulfate product is obtained, and the filtered mother liquor is recycled and reused for the next batch of production; the wet product is dried at 50 degrees Celsius in a vacuum double cone to obtain sodium persulfate. Example 3

[0026] Weigh 100 kg of sodium sulfate, add water to dissolve it, and prepare a solution with a mass concentration of 13%. After circulating it through a precision filter for 1 hour to remove impurities, it is circulated to a cylindrical electrolytic cell; weigh 30 kg of concentrated sulfuric acid, dilute it with water to a mass concentration of 20%, remove impurities through a precision filter, and then circulate it to a cylindrical electrolytic cell; circulate the 20% mass concentration of sodium persulfate solution to the cylindrical electrolytic cell through a precision filter, the temperature control system is 25 degrees Celsius, the anode of the electrolytic cell is platinum-titanium alloy, and the cathode is lead; connect the voltage across the electrolytic cell, and the current is 0.5A / cm 2 , monitor the reaction rate of sodium sulfate in the electrolyte in real time. When the reaction rate drops to 70% of the initial rate, add 0.13kg of depolarizing catalyst sodium pyrophosphate to the electrolytic cell. The feeding amount is sodium pyrophosphate: sodium sulfate = 1:1500 molar ratio. Continue electrolysis. Keep the electrolyte microcirculation during the electrolysis process. Keep the temperature at 25 degrees Celsius. The reaction is completed in about 3 hours. The mother liquor of the electrolysis reaction is transferred to the crystallization kettle, evacuated to 10kPa, and part of the solvent is evaporated under reduced pressure at 30 degrees Celsius. The remaining reaction liquid is cooled to 20-25 degrees Celsius for crystallization for 1 hour. After the crystallization is completed, filter it. The crude sodium persulfate is obtained; the crude sodium persulfate is added into purified water with a weight ratio of 1.6 times the crude sodium persulfate, the temperature is raised to 55 degrees Celsius, and the mixture is stirred to dissolve; after the crude sodium persulfate is dissolved, 0.05 kg of disodium hydrogen phosphate and 0.042 kg of magnesium sulfate are added, the mixture is kept at 40 degrees Celsius and stirred for 20 minutes, and the mixture is filtered to remove the MgNH4PO4·6H2O solid formed by ammonia nitrogen impurities; the filtrate is cooled to 20-25 degrees Celsius to crystallize for 1 hour, and the mixture is filtered to obtain a wet sodium persulfate product, and the filtered mother liquor is recycled and reused to enter the next batch of production; the wet product is dried at 30 degrees Celsius under vacuum with double cones to obtain sodium persulfate.

[0027] Comparative Example 1

[0028] Weigh 100 kg of sodium sulfate, add water to dissolve it, and prepare a solution with a mass concentration of 20%. After circulating it through a precision filter for 1 hour to remove impurities, it is circulated to a cylindrical electrolytic cell; weigh 30 kg of concentrated sulfuric acid, dilute it with water to a mass concentration of 30%, remove impurities through a precision filter, and then circulate it to a cylindrical electrolytic cell; the temperature control system is 25 degrees Celsius, the anode of the electrolytic cell is platinum-titanium alloy, and the cathode is lead; connect the voltage across the electrolytic cell, and the current is 0.6A / cm 2 , monitor the reaction rate of sodium sulfate in the electrolyte in real time. When the reaction rate drops to 53% of the initial rate, add 0.1 kg of depolarizing catalyst sodium pyrophosphate to the electrolytic cell. The feeding amount is sodium pyrophosphate: sodium sulfate = 1:2000 molar ratio. Continue electrolysis. Keep the electrolyte microcirculation during the electrolysis process. Keep the temperature at 25 degrees Celsius. The reaction is completed in about 3 hours. The mother liquor of the electrolysis reaction is transferred to the crystallization kettle, evacuated to 10 kPa, and part of the solvent is evaporated under reduced pressure at 45 degrees Celsius. The remaining reaction liquid is cooled to 20-25 degrees Celsius for crystallization for 1 hour. After the crystallization is completed, filter it. The crude sodium persulfate is obtained; the crude sodium persulfate is added into purified water with a weight ratio of 1.6 times the crude sodium persulfate, heated to 48 degrees Celsius, stirred and dissolved, and after the crude sodium persulfate is dissolved, 0.1 kg of disodium hydrogen phosphate and 0.084 kg of magnesium sulfate are added, and the mixture is kept at 48 degrees Celsius and stirred for 20 minutes, and filtered to remove the MgNH4PO4·6H2O solid formed by ammonia nitrogen impurities; the filtrate is cooled to 20-23 degrees Celsius to crystallize for 1 hour, filtered to obtain a wet sodium persulfate product, and the filtered mother liquor is recycled and reused for the next batch of production; the wet product is dried at 40 degrees Celsius under vacuum with double cones to obtain sodium persulfate.

[0029] Comparative Example 2

[0030] Weigh 100 kg of sodium sulfate, add water to dissolve it, and prepare a solution with a mass concentration of 20%. After circulating it through a precision filter for 1 hour to remove impurities, it is circulated to a cylindrical electrolytic cell; weigh 30 kg of concentrated sulfuric acid, dilute it with water to a mass concentration of 30%, remove impurities through a precision filter, and then circulate it to a cylindrical electrolytic cell; circulate a sodium persulfate solution with a mass concentration of 6% to a cylindrical electrolytic cell through a precision filter, the temperature control system is 25 degrees Celsius, the anode of the electrolytic cell is platinum-titanium alloy, and the cathode is lead; connect the voltage across the electrolytic cell, and the current is 0.6A / cm 2, monitor the reaction rate of sodium sulfate in the electrolyte in real time, when the reaction rate drops to 33% of the initial rate, add 0.1kg of depolarizing catalyst sodium pyrophosphate to the electrolytic cell, the feeding amount is sodium pyrophosphate: sodium sulfate = 1:2000 molar ratio, continue electrolysis, keep the electrolyte microcirculation during the electrolysis process, keep it warm at 25 degrees Celsius, and complete the reaction in about 3 hours; transfer the mother liquor of the electrolysis reaction to a crystallization kettle, evacuate to 10kPa, evaporate part of the solvent under reduced pressure at 45 degrees Celsius, cool the remaining reaction liquid to 20-25 degrees Celsius for crystallization for 1 hour, after the crystallization is completed, filter to obtain crude sodium persulfate; add the crude sodium persulfate to purified water with a weight ratio of 1.6 times the weight of the crude sodium persulfate, heat it to 48 degrees Celsius, stir and dissolve, after dissolving, cool it to 20-25 degrees Celsius for crystallization for 1 hour, filter to obtain wet sodium persulfate; the wet product is dried at 40 degrees Celsius under vacuum double cone to obtain sodium persulfate.

[0031] Comparative Example 3

[0032] Weigh 100 kg of sodium sulfate, add water to dissolve it, and prepare a solution with a mass concentration of 20%. After circulating it through a precision filter for 1 hour to remove impurities, it is circulated to a cylindrical electrolytic cell; weigh 30 kg of concentrated sulfuric acid, dilute it with water to a mass concentration of 30%, remove impurities through a precision filter, and circulate it to a cylindrical electrolytic cell; weigh 5 kg of ammonium sulfate, add water to dissolve it, and prepare a solution with a mass concentration of 10%. After circulating it through a precision filter to a cylindrical electrolytic cell; the anode of the electrolytic cell is platinum-titanium alloy, and the cathode is lead; connect the voltage across the electrolytic cell, and the current is 0.6A / cm 2 , monitor the reaction rate of sodium sulfate in the electrolyte in real time, when the reaction rate drops to 53% of the initial rate, add 0.1kg of depolarizing catalyst sodium pyrophosphate to the electrolytic cell, the feeding amount is sodium pyrophosphate: sodium sulfate = 1:2000 molar ratio, continue electrolysis, keep the electrolyte microcirculation during the electrolysis process, keep the temperature at 25 degrees Celsius, and complete the reaction in about 3 hours; transfer the mother liquor of the electrolysis reaction to a crystallization kettle, evacuate to 10kPa, and evaporate part of the solvent under reduced pressure at 45 degrees Celsius, and cool the remaining reaction liquid to 20-25 degrees Celsius for crystallization for 1 hour. After the crystallization is completed, filter to obtain crude sodium persulfate; the crude sodium persulfate The product is added to purified water with a weight ratio of 1.6 times its weight, heated to 48 degrees Celsius, stirred and dissolved, and after the solution is clear, 0.1kg disodium hydrogen phosphate and 0.084kg magnesium sulfate are added, and the mixture is kept at 48 degrees Celsius and stirred for 20 minutes, filtered, and the MgNH4PO4·6H2O solid formed by ammonia nitrogen impurities is removed, and the MgNH4PO4·6H2O solid formed by ammonia nitrogen impurities is removed; the filtrate is cooled to 20-25 degrees Celsius for crystallization for 1 hour, filtered, and the wet product of sodium persulfate is obtained, and the mother liquor is recycled and reused for the next batch of production; the wet product is dried at 40 degrees Celsius by double cone vacuum to obtain sodium persulfate. The filtrate is cooled to 20-25 degrees Celsius for crystallization for 1 hour, filtered, and the wet product of sodium persulfate is obtained. The filtrate is repeated 2-3 times, and the product is combined to calculate the yield; the wet product is dried at 40 degrees Celsius by double cone vacuum to obtain sodium persulfate.

[0033] The statistics of the test results of different material sources and ammonia nitrogen removal reagents are shown in Table 1 below:

[0034] Table 1 Comparison of test results of different materials

[0035]

[0036] Test results: No ammonia nitrogen impurities were detected in the sodium persulfate products prepared in Examples 1, 2, 3 and Comparative Example 1, while the ammonia nitrogen impurities in the product of Comparative Example 2 exceeded the standard (the limit requirement was less than 0.0010%), indicating that the process did not use disodium hydrogen phosphate and magnesium sulfate to further remove the residual ammonia nitrogen impurities, resulting in unqualified products. The raw material of Comparative Example 3 used ammonium sulfate, resulting in serious excess of ammonia nitrogen impurities in the product, and the product was unqualified; using the recycled sodium persulfate mother liquor, the product yield, current efficiency, and product quality were equivalent to those using the newly configured sodium persulfate; adding sodium persulfate solution can greatly improve the current efficiency.

[0037] Conclusion of the experiment: By using the sodium persulfate solution recycled from the process, avoiding the use of ammonium sulfate, and further using disodium hydrogen phosphate and magnesium sulfate to remove the residual trace ammonia nitrogen impurities, high-quality sodium persulfate without residual ammonia nitrogen impurities can be produced.

[0038] Comparative Example 4

[0039] Weigh 100 kg of sodium sulfate, add water to dissolve it, and prepare a solution with a mass concentration of 20%. After circulating it through a precision filter for 1 hour to remove impurities, it is circulated to the H-type electrolytic cell; weigh 30 kg of concentrated sulfuric acid, dilute it with water to a mass concentration of 30%, remove impurities through a precision filter, and circulate it to the H-type electrolytic cell; weigh 5 kg of ammonium sulfate, add water to dissolve it, and prepare a solution with a mass concentration of 10%. After circulating it through a precision filter to the H-type electrolytic cell; the temperature control system is 25 degrees Celsius, the anode of the electrolytic cell is platinum-titanium alloy, the cathode is lead, and a conductive ceramic partition is used in the middle; connect the voltage at both ends of the electrolytic cell, and the current is 0.6A / cm 2 During the electrolysis process, the anolyte is kept in microcirculation and kept at 25 degrees Celsius. The reaction end point is when the reaction rate remains unchanged for about 6 hours; the mother liquor of the anodic electrolysis reaction is transferred to a crystallization kettle, evacuated to -0.08MPa, and part of the solvent is evaporated under reduced pressure at 45 degrees Celsius. The remaining reaction solution is cooled to 20-23 degrees Celsius for crystallization for 1 hour. After the crystallization is completed, it is filtered to obtain crude sodium persulfate. The filtrate is crystallized 2-3 times, and the products are combined to calculate the yield; the crude sodium persulfate is added to purified water with a weight ratio of 1.6 times the weight of the crude sodium persulfate, heated to 48 degrees Celsius, stirred and dissolved, and after the filtrate is dissolved, the filtrate is cooled to 20-23 degrees Celsius for crystallization for 1 hour, filtered to obtain wet sodium persulfate; the wet product is dried at 40 degrees Celsius under vacuum with double cones to obtain sodium persulfate.

[0040] The corresponding test results of different electrolytic cells, material sources, and ammonia nitrogen removal reagents are shown in Table 2 below:

[0041] Table 2 Comparison of test results

[0042]

[0043] Test results: In comparative example 4, the conventional process used ammonium sulfate as the material, and no ammonia nitrogen impurity removal reagent was further used, resulting in serious excess of ammonia nitrogen impurities in the product and unqualified products; and the addition of ammonium sulfate to the material increased the material cost, and the post-processing purification process required multiple recrystallizations to recover the product in the mother liquor to increase the yield, which increased energy consumption and labor costs.

[0044] Test conclusion: Using sodium sulfate and sulfuric acid as starting materials, adding sodium persulfate recrystallization mother liquor recovered from the process instead of ammonium sulfate greatly reduces the source of ammonia nitrogen impurities, and using a small amount of disodium hydrogen phosphate and magnesium sulfate to further reduce the content of trace ammonia nitrogen impurities in the product. This process not only reduces production costs, but also can greatly reduce the content of ammonia nitrogen impurities in the product, and obtain high-quality sodium persulfate.

[0045] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention also fall within the protection scope of the present invention.

Claims

1. A method for preparing low-ammonia nitrogen sodium persulfate, characterized in that: The following steps are involved: S1. Weigh sodium sulfate, add water to dissolve it, and prepare a solution with a mass concentration of 13-20%. After circulating through a precision filter to remove impurities, circulate it to the electrolytic cell; S2, weigh sulfuric acid, add water to dilute to a mass concentration of 20-30%, remove impurities through a precision filter and then circulate to the electrolytic cell; S3, circulating a 5-20% sodium persulfate aqueous solution through a precision filter to the electrolytic cell; S4, electrolysis reaction for 2-5h, during which the electrolyte microcirculation is maintained and the reaction temperature is maintained at 20-25 degrees Celsius; S5, real-time monitoring of the reaction rate of sodium sulfate in the electrolyte, when the reaction rate drops to 50-70% of the initial rate, adding a depolarizing catalyst to the electrolytic cell, and continuing the electrolysis reaction until completion; S6, transferring the mother liquid of the electrolytic reaction in step S5 to a crystallization kettle, evaporating part of the solvent under reduced pressure, cooling the reaction liquid for crystallization, and filtering after the crystallization to obtain a crude sodium persulfate; S7, adding the crude sodium persulfate product of step S6 into purified water, heating and stirring to dissolve, adding disodium hydrogen phosphate and magnesium sulfate after dissolving, stirring for 10-30 minutes, keeping warm and filtering to remove solids formed by ammonia nitrogen impurities, cooling the filtrate for crystallization, filtering to obtain wet sodium persulfate, and recycling the mother liquor to enter step S3 of the next batch production; S8. Dry the wet sodium persulfate product from step S7 to obtain a low-ammonia nitrogen sodium persulfate finished product.

2. The method for preparing low-ammonia nitrogen sodium persulfate according to claim 1, characterized in that: In step S1, the electrolytic cell is cylindrical, and there is no conductive partition or filter membrane between the positive and negative electrodes.

3. The method for preparing low-ammonia nitrogen sodium persulfate according to claim 1, characterized in that: In step S1, the anode of the electrolytic reaction tank is platinum or platinum-titanium alloy, the cathode is lead, and the current density is 0.5-0.8A / cm 2 .

4. The method for preparing low-ammonia nitrogen sodium persulfate according to claim 1, characterized in that: In the step S5, the depolarization catalyst is one or a combination of sodium pyrophosphate, sodium pyrophosphate hydrate, and manganese thiocyanate, and the feed amount is catalyst: sodium sulfate = 1:1500-2000 molar ratio.

5. The method for preparing low-ammonia nitrogen sodium persulfate according to claim 1, characterized in that: In the step S6, the temperature when part of the solvent is evaporated under reduced pressure is 30-50 degrees Celsius, the pressure is 5-15 kPa, and the crystallization temperature is 20-25 degrees Celsius.

6. The method for preparing low-ammonia nitrogen sodium persulfate according to claim 1, characterized in that: In the step S7, the dissolution temperature is 40-55 degrees Celsius, the crystallization temperature is 20-25 degrees Celsius, the ammonia nitrogen impurity solid is MgNH4PO4·6H2O, and the feed amount is disodium hydrogen phosphate: magnesium sulfate: sodium sulfate = 1:1:1000-2000 molar ratio.

7. The method for preparing low-ammonia nitrogen sodium persulfate according to claim 1, characterized in that: In step S8, the drying temperature is 30-50 degrees Celsius, and the drying method is one of air drying, vacuum drying, and fluidized bed drying.

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