A production process for preparing an electroplating grade potassium pyrophosphate

Abstract

The application discloses a production process of electroplating grade potassium pyrophosphate, which uses potassium carbonate and diaphosphorus pentoxide as raw materials, and adds a catalyst to react in a high-pressure reaction kettle. After the reaction is completed, water is added for dissolution, and the pH value of the slurry is controlled to be 9.0-10.0. After being filtered through a precision filter, the slurry is punched into a slurry storage tank, and the slurry storage tank is maintained at 75-95 DEG C. The slurry in the storage tank is punched into an evaporation and concentration device for concentration, and then the concentrated liquid is punched into a continuous crystallization device for continuous crystallization operation. After centrifugal treatment, the filtrate is recycled into the evaporation and concentration device. The potassium pyrophosphate crystals are subjected to vacuum drying treatment in a vacuum drying equipment, and then are packaged into finished products after being crushed and sieved. The potassium pyrophosphate crystals obtained by the application have high purity, less caking phenomenon, and stable and controllable product quality.

Description

Technical Field

[0001] This invention relates to a production process and apparatus for preparing electroplating grade potassium pyrophosphate, belonging to the field of inorganic salt technology. Background Technology

[0002] Potassium pyrophosphate, with the chemical formula K4P2O7 and a relative molecular weight of 330.334, is a white solid powder at room temperature. It is highly hygroscopic, readily soluble in water, but insoluble in organic solvents such as ethanol and glycerol. In industry, it is primarily used in cyanide-free electroplating as a substitute for cyanide complexing agents, significantly reducing environmental pollution and toxicity to humans, while also significantly improving coating quality. It can also be used as a descaling agent, significantly reducing water hardness and preventing scaling by binding with calcium and magnesium ions. Furthermore, it can be used as a dispersant for ceramic clays and pigments / dyes, improving the stability of production processes and enhancing product quality. In the food industry, it serves as an emulsifier and quality improver, preventing the formation of struvite in canned seafood, discoloration of fruits, improving the water retention of meat products, and increasing the expansion of ice cream. Additionally, it is often compounded with phosphates such as sodium pyrophosphate as a binder for meat products such as ham and sausages.

[0003] Traditional methods for synthesizing potassium pyrophosphate typically involve evaporating and concentrating a potassium dihydrogen phosphate solution, cooling and crystallizing it to obtain solid potassium dihydrogen phosphate, and then calcining it at high temperatures. This method involves numerous steps, and especially in large calcination equipment, it often results in uneven heating of the solid potassium dihydrogen phosphate, easy agglomeration during calcination, high energy consumption, unstable product quality, and low reaction conversion rates. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned problems by providing a method for preparing potassium pyrophosphate using phosphorus pentoxide and potassium carbonate in a high-pressure reactor.

[0005] This invention provides a method for preparing potassium pyrophosphate using potassium carbonate and phosphorus pentoxide as raw materials, comprising the following steps: (1) mixing potassium carbonate and phosphorus pentoxide in the presence of a co-catalyst, and then carrying out a high-temperature solid-phase reaction in a closed reactor to obtain a reaction product containing potassium pyrophosphate. Then, the reaction vessel is vented to discharge the tail gas.

[0006] (2) Add water to the reactor to completely dissolve the solid powder into a solution, and control the pH of the solution to 9.0~10.0. Then filter it in the fine filter tank, and the filtrate enters the slurry storage tank, maintaining the slurry storage tank at 75~95℃. Then enter the evaporation and concentration device to start concentration, and then put the concentrated liquid into the continuous crystallization device for continuous crystallization. After centrifugation, the filtrate is returned to the evaporation and concentration device, and the potassium pyrophosphate crystals enter the vacuum drying equipment for vacuum drying, and then crush, screen and package into finished products.

[0007] In step (1), the co-catalyst is anhydrous potassium citrate, calcium aspartate, or lithium cobalt oxide.

[0008] Based on the total mass of potassium carbonate and phosphorus pentoxide, the amount of the co-catalyst added is from 0.01 wt% to 1.5 wt%.

[0009] The purity of the potassium carbonate is ≥99%, and the purity of the phosphorus pentoxide is ≥99%.

[0010] The high-temperature solid-phase reaction has a reaction temperature of 350°C to 420°C and a reaction time of 1 hour to 6 hours.

[0011] In some preferred embodiments, the high-temperature solid-state reaction includes a first reaction stage and a second reaction stage; wherein the reaction temperature of the first reaction stage is 260°C to 320°C and the reaction time is 3 hours to 5 hours; and the reaction temperature of the second reaction stage is 380°C to 400°C and the reaction time is 0.5 hours to 2 hours.

[0012] In step S2, after dissolving in water, the pH value of the slurry is adjusted using an alkaline solution or carbon dioxide gas. After obtaining the refined slurry in step S2 and before evaporation and concentration in step S3, the refined slurry is kept at a temperature of 75°C to 95°C.

[0013] In step S3, the endpoint of evaporation and concentration is controlled as follows: the mass concentration of potassium pyrophosphate in the resulting concentrate is 70% to 85%.

[0014] The crystallization process is a continuous cooling crystallization, with the temperature controlled within the range of 30°C to 50°C.

[0015] The drying process is vacuum drying, with the following conditions: vacuum degree -0.06 MPa to -0.15 MPa, temperature 60℃ to 120℃, and the moisture content of the dried material controlled at 2% to 4%.

[0016] This invention also provides a production apparatus for electroplating-grade potassium pyrophosphate. A high-pressure reactor is connected to a fine filter, which is then connected to a slurry storage tank. The slurry storage tank is connected to an evaporator / concentrator, which is connected to a continuous crystallizer, which is then connected to a centrifuge. The centrifuge is connected to a vacuum dryer, which is then connected to a crushing and screening unit, thus forming the production apparatus for electroplating-grade potassium pyrophosphate. The centrifuge is also connected to the evaporator / concentrator.

[0017] The technical solution of this invention has the following beneficial effects: the process flow is simple and easy to operate, significantly reducing production costs. The added co-catalyst generates bubbles during heating, ensuring thorough and uniform mixing of materials, thereby promoting the reaction and making it suitable for industrial production. This invention solves the problems of agglomeration and powder dispersion associated with traditional spray drying and calcination processes, making it clean and environmentally friendly. Furthermore, this invention improves product purity and bulk density through crystallization, thereby enhancing product quality. Detailed Implementation

[0018] The present invention will be further explained and described below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0019] Example 1

[0020] First, 2.5 tons of 99% potassium carbonate solid and 1.29 tons of 99% phosphorus pentoxide solid were added separately to a high-pressure reactor. Then, 0.050 tons of anhydrous potassium citrate were added, and the reactor was purged with nitrogen three times. The temperature was slowly raised to 200°C, stirring was started, and then the temperature was raised to 280°C. Stirring was continued to ensure uniform mixing of the materials, and the reaction was allowed to proceed for 4 hours. After the reaction was completed, the temperature was raised to 380°C, and the reaction was allowed to proceed for 1 hour. Then, the reactor was vented to release the exhaust gas. After the temperature dropped to 90°C, 2 tons of water were added to the reactor to completely dissolve the solid powder into a solution, and the pH of the solution was controlled at 9.2. After fine filtration, the slurry temperature was maintained at 80°C. The slurry was then pumped into an evaporation and concentration device for concentration to 74 wt%. The concentrated liquid was then pumped into a continuous crystallization device for continuous crystallization. The feed temperature for continuous crystallization was controlled at 75°C, and the temperature of the crystallization zone was controlled at 35°C. After centrifugation... The filtrate was returned to the evaporation and concentration unit, while the potassium pyrophosphate crystals were subjected to vacuum drying at a vacuum level of -0.08 MPa and a temperature of 110°C. After vacuum drying, the moisture content of the material was controlled at 4%. After crushing and sieving, the product was packaged into the finished product. Testing revealed that the product contained 98.1% potassium pyrophosphate, had a bulk density of 0.78 ± 0.1 g / mL, and a complexation index of 3.2. The obtained product was dissolved in water to prepare a saturated solution, which had a pH of 11.0 at 25°C. After three months of storage, the pH was measured again using the same method, showing a change to 10.2.

[0021] Example 2

[0022] First, 2.5 tons of 99% potassium carbonate solid and 1.29 tons of phosphorus pentoxide were added separately to a high-pressure reactor, followed by 0.023 tons of lithium cobalt oxide. The reactor was then purged with nitrogen three times. The temperature was slowly raised to 210°C, stirring was started, and then the temperature was further raised to 290°C while continuing to stir to ensure uniform mixing of the materials. The reaction was allowed to proceed for 4 hours, and after the reaction was complete, the temperature was raised to 390°C and the reaction was allowed to continue for 1 hour. Then, the reactor was vented to release the exhaust gas. After the temperature dropped to 90°C, 2 tons of water were added to the reactor to completely dissolve the solid powder into a solution, and the pH of the solution was controlled at 9.4. After fine filtration, the slurry temperature was maintained at 85°C. The slurry from the storage tank was then pumped into an evaporation and concentration unit for concentration to 76 wt%. The concentrated liquid was then pumped into a continuous crystallization unit for continuous crystallization, with the feed temperature controlled at 80°C and the crystallization zone temperature controlled at 40°C. After centrifugation... The filtrate was returned to the evaporation and concentration unit, while the potassium pyrophosphate crystals were subjected to vacuum drying at a vacuum level of -0.10 MPa and a temperature of 105°C. After vacuum drying, the moisture content of the material was controlled at 3%. After crushing and sieving, the product was packaged into the finished product. Testing revealed that the product contained 99.5% potassium pyrophosphate, had a bulk density of 0.77 g ± 0.03 g / mL, and a complexation index of 3.3. The obtained product was dissolved in water to prepare a saturated solution, which had a pH of 11.3 at 25°C. After three months of storage, the pH was measured again using the same method, showing a change to 10.5.

[0023] Example 3

[0024] First, 2.5 tons of 99% potassium carbonate solid and 1.29 tons of phosphorus pentoxide were added separately to a high-pressure reactor. Then, 0.031 tons of calcium aspartate were added, and the reactor was purged with nitrogen three times. The temperature was slowly raised to 220°C, and stirring was started. The temperature was then raised to 300°C, and stirring continued to ensure uniform mixing of the materials. The reaction was allowed to proceed for 4 hours, after which the temperature was raised to 400°C, and the reaction was allowed to continue for 1 hour. The reactor was then vented to release the exhaust gas. After the temperature dropped to 90°C, 2 tons of water were added to the reactor to completely dissolve the solid powder into a solution, and the pH of the solution was controlled at 9.8. After fine filtration, the slurry temperature is maintained at 95℃. The slurry from the storage tank is then pumped into an evaporation and concentration unit for concentration to 78 wt%. The concentrated liquid is then pumped into a continuous crystallization unit for continuous crystallization, with the feed temperature controlled at 95℃ and the crystallization zone temperature controlled at 45℃. After centrifugation, the filtrate is returned to the evaporation and concentration unit, while the potassium pyrophosphate crystals undergo vacuum drying at -0.12 MPa and 100℃, with the moisture content controlled at 2%. After crushing and screening, the product is packaged into the finished product. Testing revealed a potassium pyrophosphate content of 99.6%, a bulk density of 0.76 ± 0.01 g / mL, and a complexation index of 3.2. The obtained product was dissolved in water to prepare a saturated solution, which had a pH of 11.1 at 25℃. After three months of storage, the pH was tested again using the same method, showing a change to 10.6.

[0025] Comparative Example 1

[0026] Follow the steps of Example 1, but without adding anhydrous potassium citrate. All other ingredient ratios, reaction temperatures, and times are exactly the same.

[0027] Results: After the reaction, the material in the reactor severely agglomerated, with some parts remaining molten, making stirring difficult. After dissolving in water, the solution became turbid and difficult to filter. The final product, upon testing, showed a potassium pyrophosphate content of only 94.3%, high impurity content, a bulk density of only 0.69 g / mL, and was prone to absorbing moisture and agglomerating.

[0028] Comparative Example 2

[0029] The traditional process involves neutralizing phosphoric acid with potassium hydroxide to obtain a potassium dihydrogen phosphate solution, which is then evaporated, concentrated, and cooled to crystallize, yielding potassium dihydrogen phosphate crystals. The crystals are then placed in a muffle furnace and calcined at 420°C for 2 hours.

[0030] Results: The calcined product exhibited severe agglomeration, requiring vigorous crushing. The product contained 97.5% potassium pyrophosphate, but had a low bulk density (0.65 g / mL), poor flowability, and significantly higher energy consumption than the example.

[0031] Comparative Example 3

[0032] Follow the steps of Example 1, but adjust the pH of the slurry to 8.0 after dissolving in water.

[0033] Results: During the subsequent evaporation and concentration process, the viscosity of the material increased, and a small amount of hydrolysis occurred. The purity of the crystallized product decreased (96.8%), and the bulk density was low (0.70 g / mL).

[0034] Comparative Example 4

[0035] The steps of Example 1 are followed, but vacuum drying is replaced with atmospheric pressure hot air drying at a drying temperature of 110°C.

[0036] Results: The dried product surface showed slight signs of melting, some particles clumped together, and its flowability decreased. The product moisture content was difficult to reduce to below 4%, and it showed a clear tendency to clump after long-term storage.

[0037] Comparative Example 5

[0038] Following the steps of Example 1, the co-catalyst was replaced with potassium oxalate. All other raw material ratios, reaction temperatures, and times remained identical.

[0039] Results: After the reaction, the potassium pyrophosphate content of the calcium product was found to be 97.5%, the bulk density was 0.79 ± 0.04 g / mL, and the complexation index was 3.0. The hygroscopicity of the product was significantly improved, the product was less prone to clumping, and the particle dispersibility was better. The obtained product was dissolved in water to prepare a saturated solution, and the pH was 11.2 at 25°C. After three months of storage, the pH was measured again using the same method, and the change was 9.6. This pH change was more significant than that in Example 1.

Claims

1. A method for preparing electroplating grade potassium pyrophosphate, characterized in that, Includes the following steps: S1. Potassium carbonate and phosphorus pentoxide are mixed in the presence of a co-catalyst, and then subjected to a high-temperature solid-phase reaction in a closed reactor to obtain a reaction product containing potassium pyrophosphate; the co-catalyst is anhydrous potassium citrate, calcium aspartate, or lithium cobalt oxide, and the amount of the co-catalyst added is 0.01 wt% to 1.5 wt% based on the total mass of potassium carbonate and phosphorus pentoxide. S2. Dissolve the reaction product obtained in step S1 in water and adjust the pH value of the resulting slurry to the range of 9.0 to 10.0 to obtain a refined slurry; S3. The refined slurry obtained in step S2 is evaporated and concentrated to obtain potassium pyrophosphate concentrate. S4. The potassium pyrophosphate concentrate obtained in step S3 is subjected to crystallization treatment to obtain potassium pyrophosphate slurry. S5. The potassium pyrophosphate slurry obtained in step S4 is subjected to solid-liquid separation to obtain wet potassium pyrophosphate crystals and mother liquor. S6. The potassium pyrophosphate wet crystals obtained in step S5 are dried. The drying process is vacuum drying. The drying conditions are: vacuum degree -0.06 MPa to -0.15 MPa, temperature 60℃ to 120℃. The moisture content of the material after drying is controlled at 2% to 4%, and electroplating grade potassium pyrophosphate product is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the reaction temperature of the high-temperature solid-phase reaction is 350°C to 420°C, and the reaction time is 1 hour to 6 hours.

3. The preparation method according to claim 2, characterized in that, The high-temperature solid-state reaction includes a first reaction stage and a second reaction stage; wherein, the reaction temperature of the first reaction stage is 260°C to 320°C and the reaction time is 3 hours to 5 hours; the reaction temperature of the second reaction stage is 380°C to 400°C and the reaction time is 0.5 hours to 2 hours.

4. The preparation method according to claim 1, characterized in that, In step S2, after dissolving in water, the pH value of the slurry is adjusted using an alkaline solution or carbon dioxide gas. After obtaining the refined slurry in step S2 and before evaporation and concentration in step S3, the refined slurry is kept at a temperature of 75°C to 95°C.

5. The preparation method according to claim 1, characterized in that, In step S3, the endpoint of evaporation and concentration is controlled as follows: the mass concentration of potassium pyrophosphate in the resulting concentrate is 70% to 85%.

6. The preparation method according to claim 1, characterized in that, In step S4, the crystallization process is a continuous cooling crystallization, and the temperature of the crystallization process is controlled within the range of 30°C to 50°C.

7. The preparation method according to any one of claims 1-6, characterized in that, In step S1, the purity of the potassium carbonate is ≥99%, and the purity of the phosphorus pentoxide is ≥99%.