Method for preparing potassium sulfate from potassium chloride and ammonium sulfate
By optimizing the two-stage metathesis-crystallization separation process for producing potassium sulfate from potassium chloride and ammonium sulfate, the problems of low potassium conversion rate and low product purity were solved, achieving efficient and low-energy-consumption potassium sulfate production and meeting the standards for superior products.
Patent Information
- Application Number
- CN202511710994.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-20
- Publication Date
- 2026-01-09
AI Technical Summary
The existing process for producing potassium sulfate from potassium chloride and ammonium sulfate has problems such as low potassium conversion rate, low product purity, and high chloride ion content. In addition, the traditional process has high energy consumption and serious equipment corrosion.
A two-stage metathesis-crystallization separation process is adopted. By controlling the reaction temperature, concentration and crystallization conditions, and combining the recycling of mother liquor, the reaction conditions and crystallization parameters are optimized to achieve efficient separation and purification of potassium sulfate, reduce chloride ion content and improve potassium recovery rate.
It has increased the potassium conversion rate to over 90%, the K2O content of the product to over 50%, the chloride ion content to less than 0.3%, and the moisture content to less than 0.5%, meeting the standards for superior grade potassium sulfate for agricultural use, and reducing energy consumption by more than 20%.
Smart Images
Figure CN121292472A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of chemical preparation technology, specifically to a method for producing potassium sulfate from potassium chloride and ammonium sulfate. Background Technology
[0002] Potassium sulfate, as an important chlorine-free potassium fertilizer, plays an irreplaceable role in agricultural production. It is suitable not only for chlorine-sensitive cash crops such as tobacco, citrus, tea, grapes, sugar beets, and sugarcane, but also widely used in industries such as pharmaceuticals, glass, and dyes. With the global agricultural development towards precision and efficiency, the demand for high-quality potassium sulfate is increasing. Global potash fertilizer consumption grew by 7% (approximately 3 million tons) in 2024, and demand is projected to reach 71-74 million tons in 2025, with potassium sulfate demand showing a recovery.
[0003] Traditional potassium sulfate production methods mainly include the Mannheim process, associative process, and metathesis process. The Mannheim process accounts for 40%-50% of the global potassium sulfate supply, but it suffers from high investment costs, high energy consumption (requiring reactions at 600-700℃), severe equipment corrosion, and poor sales of the byproduct hydrochloric acid. While the associative process offers advantages such as milder operating conditions and less equipment corrosion, it is complex, requires careful selection and recovery of associative agents, and most of its organic solvents are toxic.
[0004] In contrast, the potassium sulfate production process via the metathesis reaction of potassium chloride and ammonium sulfate is considered the most economical and environmentally friendly route due to its wide availability of raw materials, mild reaction conditions, and environmental friendliness. This process uses industrial byproducts ammonium sulfate and potassium chloride as raw materials, producing potassium sulfate and nitrogen-potassium fertilizer through a metathesis reaction. It not only achieves waste resource utilization but also boasts advantages such as low investment, simple process, low cost, and low energy consumption. However, this process currently still faces technical bottlenecks such as low potassium conversion rate (generally around 70%), low product purity (K₂O content 43%-45%), and relatively high chloride ion content (3.4%-5.1%).
[0005] Therefore, our in-depth study of the process of producing potassium sulfate from potassium chloride and ammonium sulfate, optimization of reaction conditions, and improvement of potassium conversion rate and product quality have important theoretical significance and practical value for promoting the technological progress of potassium sulfate production, reducing production costs, and reducing environmental pollution. Summary of the Invention
[0006] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a method for producing potassium sulfate from potassium chloride and ammonium sulfate. This method features efficient separation of potassium sulfate, reduces the chloride ion content in the product, achieves high potassium recovery rate and long-term stable operation of the system, and meets the superior grade standard for agricultural potassium sulfate.
[0007] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: a method for preparing potassium sulfate from potassium chloride and ammonium sulfate, comprising utilizing K + NH4 + / / Cl - SO4 2- The solubility difference of the -H2O quaternary system at different temperatures is investigated. By controlling the reaction temperature, concentration, and crystallization conditions, potassium sulfate can be efficiently separated. The specific process is as follows: The first stage of the reaction involves reacting ammonium sulfate solution with potassium chloride at 60-80℃ to produce a mixture of potassium ammonium sulfate and nitrogen-potassium fertilizer. After the reaction is completed, the mixture is cooled and crystallized and then separated into solid and liquid components to obtain crude potassium ammonium sulfate and a mother liquor containing nitrogen-potassium fertilizer. The second stage of the reaction involves a secondary conversion of crude potassium ammonium sulfate with potassium chloride solution at 60-100℃, which converts the ammonium sulfate in the potassium ammonium sulfate into potassium sulfate. After cooling and crystallization and separation, crude potassium sulfate and mother liquor are obtained. The third stage reaction: The unreacted potassium chloride and ammonium sulfate in the mother liquor separated after the second stage reaction are reacted again at 40-60℃. After the reaction is completed, the crude potassium ammonium sulfate is obtained by cooling crystallization and solid-liquid separation and returned to the second stage and the mother liquor enters the first stage.
[0008] Preferably, the crude potassium ammonium sulfate needs to be washed and refined. The crude potassium sulfate is washed with hot water at 20-90℃ in three stages: coarse, medium, and fine washing to remove impurities attached to the surface, and then dried to obtain the potassium sulfate product.
[0009] Preferably, the mother liquor obtained in the reaction is recycled. Most of the separated mother liquor is returned to the reaction system for recycling, and a small portion is evaporated and concentrated to generate solid by-product nitrogen and potassium fertilizer. The mother liquor is then returned to the heating tank for further evaporation and concentration.
[0010] Preferably, the potassium chloride is pretreated before the reaction. The pretreatment includes crushing the potassium chloride to a particle size of 0.1-1 mm, controlling the ball mill speed at 300-500 r / min, the ball-to-material ratio at 2-5:1, and the grinding time at 3-8 minutes.
[0011] Preferably, in the first stage of the reaction, the molar ratio of ammonium sulfate to potassium chloride is controlled within the range of 1:1.4-1:2.2 to obtain a high potassium conversion rate. In the second stage of the reaction, the molar ratio is increased to 1:1.8-1:2.8. When the mass ratio of KCl to (NH4)2SO4 is 1:1.2, potassium chloride can be almost completely reacted.
[0012] Preferably, the crystallization temperature is controlled at 10-30℃ and the crystallization time is 1-3 hours.
[0013] Compared with the prior art, the present invention provides a method for producing potassium sulfate from potassium chloride and ammonium sulfate, which has the following beneficial effects: 1. This method for producing potassium sulfate from potassium chloride and ammonium sulfate proposes a novel two-stage metathesis-crystallization separation process. By controlling reaction conditions and crystallization parameters, high-purity potassium sulfate is produced. Compared with the traditional single-stage process, the potassium conversion rate is increased by 10-15 percentage points. A temperature gradient controlled crystallization technology was developed, utilizing the differences in solubility of components at different temperatures to achieve efficient separation of potassium sulfate. pH control technology effectively reduces the chloride ion content in the product. A multi-stage mother liquor circulation system was designed, and by optimizing the circulation ratio and controlling impurity content, a high potassium recovery rate and long-term stable system operation were achieved. The total potassium recovery rate reaches over 90%, far exceeding the 70% of the traditional process. The unit operations of reaction, crystallization, separation, and washing are optimized and integrated, shortening the process flow and improving production efficiency. Through waste heat recovery and energy optimization, energy consumption is reduced by more than 20%. Through process optimization and purification technology improvements, the product's K2O content reaches over 50%, chloride ion content is below 0.3%, and moisture content is below 0.5%, meeting the standards for superior grade agricultural potassium sulfate. Attached Figure Description
[0014] Figure 1 This is a schematic diagram of the steps in the method for preparing potassium sulfate according to the present invention. Detailed Implementation
[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0016] A method for preparing potassium sulfate from potassium chloride and ammonium sulfate, comprising utilizing K + NH4 + / / Cl - SO4 2- The solubility difference of the -H2O quaternary system at different temperatures is investigated. By controlling the reaction temperature, concentration, and crystallization conditions, potassium sulfate can be efficiently separated. The specific process is as follows: The first stage of the reaction involves reacting ammonium sulfate solution with potassium chloride at 60-80℃ to produce a mixture of potassium ammonium sulfate and nitrogen-potassium fertilizer. After the reaction is completed, the mixture is cooled and crystallized and then separated into solid and liquid components to obtain crude potassium ammonium sulfate and a mother liquor containing nitrogen-potassium fertilizer. The second stage of the reaction involves a secondary conversion of crude potassium ammonium sulfate with potassium chloride solution at 60-100℃, which converts the ammonium sulfate in the potassium ammonium sulfate into potassium sulfate. After cooling and crystallization and separation, crude potassium sulfate and mother liquor are obtained. The third stage reaction: The unreacted potassium chloride and ammonium sulfate in the mother liquor separated after the second stage reaction are reacted again at 40-60℃. After the reaction is completed, the crude potassium ammonium sulfate is obtained by cooling crystallization and solid-liquid separation and returned to the second stage and the mother liquor enters the first stage.
[0017] Furthermore, the crude potassium ammonium sulfate needs to be washed and refined. The crude potassium sulfate is washed with hot water at 20-90℃ in three stages: coarse, medium, and fine washing to remove impurities attached to the surface, and then dried to obtain the potassium sulfate product.
[0018] Furthermore, the mother liquor obtained in the reaction is recycled. Most of the separated mother liquor is returned to the reaction system for recycling, while a small portion is evaporated and concentrated to generate solid by-product nitrogen and potassium fertilizer. The mother liquor is then returned to the heating tank for further evaporation and concentration.
[0019] Furthermore, the potassium chloride is pretreated before the reaction. The pretreatment includes crushing the potassium chloride to a particle size of 0.1-1 mm, controlling the ball mill speed at 300-500 r / min, the ball-to-material ratio at 2-5:1, and the grinding time at 3-8 minutes.
[0020] Furthermore, in the first stage of the reaction, the molar ratio of ammonium sulfate to potassium chloride is controlled within the range of 1:1.4-1:2.2 to obtain a high potassium conversion rate. In the second stage of the reaction, the molar ratio is increased to 1:1.8-1:2.8. When the mass ratio of KCl to (NH4)2SO4 is 1:1.2, potassium chloride can be almost completely reacted.
[0021] Furthermore, the crystallization temperature is controlled at 10-30℃, and the crystallization time is 1-3 hours.
[0022] Example 1: Reaction temperature is a key factor affecting conversion rate and product quality. Studies have shown that a reaction temperature controlled within the range of 60-80℃ is most suitable. Reacting at 60℃ for 1 hour yields approximately 78% potassium sulfate. Excessively high temperatures increase energy consumption and equipment corrosion, while excessively low temperatures result in slow reaction rates and low conversion rates. Optimization studies of reaction time show that extending the reaction time from 30 minutes to 60 minutes increases the potassium sulfate yield by approximately 10%; further extending it to 120 minutes only increases the yield by about 13%. Therefore, considering both production efficiency and energy consumption, a reaction time of 60-90 minutes is preferable. Stirring intensity has a significant impact on the reaction effect. The stirring intensity used in the reactor is related to material concentration and temperature, and the rapid changes in the internal environment make it difficult to determine the optimal stirring intensity. Therefore, we have independently developed a dedicated reaction device for double displacement reactions, which ensures stable operation and high reaction efficiency. The mother liquor circulation device in the crystallizer adopts frequency conversion control, and multiple observation mirrors are installed on the side wall of the crystallizer to directly observe the operating status inside the crystallizer for timely adjustment. This ensures that the reactants are fully mixed and is conducive to crystal growth. Excessive stirring speed will cause crystal breakage and affect the particle size distribution of the product.
[0023] pH control has a significant impact on product quality. Studies have found that adjusting the pH to 7.0-8.5 by adding potassium hydroxide solution can effectively reduce the chloride ion content in the product. The mass concentration of the alkaline regulator should be controlled within the range of 15-20%.
[0024] Example 2: Solid-liquid separation is a crucial step in product purification. Commonly used separation methods include vacuum filtration and centrifugation. Centrifugation is more effective than vacuum filtration, especially suitable for separating crystals with small particle sizes. Controlling the separation temperature between 10-40℃ improves separation efficiency and product purity. To guarantee 100% separation effectiveness, we collaborated with a well-known domestic equipment manufacturer to develop a multi-cone centrifugal dehydrator, further increasing the solid yield by 28%. The washing process is critical to product quality. Research shows that washing crude potassium sulfate with hot water at 20-90℃ is effective. To save costs, we collect the condensate after heating and use it as washing water, which is clean, energy-efficient, and avoids waste. The weight ratio of washing water to crude potassium sulfate is 1:1-2, effectively removing surface-adhered impurities. Excessively high washing temperatures lead to product dissolution and loss, while excessively low temperatures result in poor washing effects. Optimizing crystallization conditions directly affects the particle size and purity of the product. Controlling the crystallization temperature between 10-30℃ and the crystallization time between 1-3 hours yields potassium sulfate crystals with uniform particle size and high purity. Studies have found that lowering the crystallization temperature from 28℃ to 10℃ can increase the potassium sulfate yield by 20%. Re-introducing the concentrated slurry into the reaction system also significantly improves potassium yield; drying conditions have a crucial impact on product quality. Drying at 105-110℃ for 1-3 hours yields potassium sulfate with a moisture content below 0.5%. Excessive drying temperature leads to discoloration of the crystal surface, while insufficient drying results in incomplete drying.
[0025] Example 3: Mother liquor recycling is a key technology for improving raw material utilization and reducing production costs. Studies show that most of mother liquor II is returned to the reaction step, reacting with fresh ammonium sulfate solution and potassium chloride. A small portion of mother liquor II is evaporated and concentrated to obtain solid nitrogen and potassium fertilizer, achieving full resource utilization. The closed-loop recycling process can achieve a total potassium recovery rate of 96.5%-97.5%. The specific recycling scheme is as follows: Mother liquor I after separating crude potassium sulfate reacts with ammonium sulfate and ammonia-precipitated ammonium sulfate at high temperature. The mother liquor from which the thermally precipitated ammonium sulfate is separated is cooled after evaporating a certain amount of water to produce crude nitrogen and potassium fertilizer. After dissolving the crude nitrogen and potassium fertilizer in the ammonia-poor mother liquor, the mother liquor separated by ammonia-precipitated ammonium sulfate is subjected to ammonia stripping and then cooled to precipitate nitrogen and potassium fertilizer. During the mother liquor recycling process, attention must be paid to the accumulation of impurities. Due to the presence of calcium... 2+ and Mg 2+ Accumulation of impurities during the mother liquor recycling process can affect product quality. Therefore, it is necessary to regularly remove impurities from the mother liquor, or control the concentration of impurities by partially discharging the mother liquor. By optimizing the recycling ratio and controlling the impurity content, long-term stable recycling of the mother liquor can be achieved. It is recommended to control the mother liquor recycling rate at 80-90%, with the remaining 10-20% of the mother liquor being treated to recover nitrogen and potassium fertilizers. This ensures high raw material utilization.
[0026] Example 4: Particle size optimization studies on potassium chloride show that pulverizing potassium chloride to a particle size of 0.1–1 mm can significantly improve the reaction rate. Overly coarse particles result in incomplete reaction, while overly fine particles increase dust pollution and energy consumption. A suitable particle size distribution can be obtained by controlling the ball mill speed at 300–500 r / min, the ball-to-material ratio at 2–5:1, and the grinding time at 3–8 minutes. The preparation parameters of the ammonium sulfate solution have a significant impact on the reaction effect. Studies have found that the optimal reaction effect is achieved when the concentration of ammonium sulfate in hot water at 45–80℃ is 1–5 mol / L. Too high a concentration leads to increased solution viscosity, affecting mass transfer; too low a concentration reduces equipment utilization efficiency. The dissolution temperature is controlled at 60-90℃ to ensure complete dissolution and avoid decomposition of ammonium sulfate. Optimization of the raw material ratio is the key to improving the conversion rate. In the first stage of the reaction, the molar ratio of ammonium sulfate to potassium chloride is controlled in the range of 1:1.4-1:2.2 to obtain a high potassium conversion rate. In the second stage of the reaction, the molar ratio is increased to 1:1.8-1:2.8, which is conducive to further improving the purity of the product. When the mass ratio of KCl to (NH4)2SO4 is 1:1.2, potassium chloride can be almost completely reacted.
[0027] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for preparing potassium sulfate from potassium chloride and ammonium sulfate, comprising utilizing K + NH4 + / / Cl - SO4 2- The solubility difference of the -H2O quaternary system at different temperatures allows for the efficient separation of potassium sulfate by controlling the reaction temperature, concentration, and crystallization conditions. The key feature is: The specific process is as follows: The first stage of the reaction involves reacting ammonium sulfate solution with potassium chloride at 60-80℃ to produce a mixture of potassium ammonium sulfate and nitrogen-potassium fertilizer. After the reaction is completed, the mixture is cooled and crystallized and then separated into solid and liquid components to obtain crude potassium ammonium sulfate and a mother liquor containing nitrogen-potassium fertilizer. The second stage of the reaction involves a secondary conversion of crude potassium ammonium sulfate with potassium chloride solution at 60-100℃, which converts the ammonium sulfate in the potassium ammonium sulfate into potassium sulfate. After cooling and crystallization and separation, crude potassium sulfate and mother liquor are obtained. The third stage reaction: The unreacted potassium chloride and ammonium sulfate in the mother liquor separated after the second stage reaction are reacted again at 40-60℃. After the reaction is completed, the crude potassium ammonium sulfate is obtained by cooling crystallization and solid-liquid separation and returned to the second stage and the mother liquor enters the first stage.
2. The method for preparing potassium sulfate from potassium chloride and ammonium sulfate according to claim 1, characterized in that: The crude potassium ammonium sulfate needs to be washed and refined. The crude potassium sulfate is washed with hot water at 20-90℃ in three stages: coarse, medium, and fine washing to remove impurities attached to the surface, and then dried to obtain the potassium sulfate product.
3. The method for preparing potassium sulfate from potassium chloride and ammonium sulfate according to claim 1, characterized in that: The mother liquor obtained in the reaction is recycled. Most of the separated mother liquor is returned to the reaction system for recycling, while a small portion is evaporated, concentrated, and separated to generate solid by-product nitrogen and potassium fertilizer. The mother liquor is then returned to the heating tank for further evaporation and concentration.
4. The method for preparing potassium sulfate from potassium chloride and ammonium sulfate according to claim 1, characterized in that: The potassium chloride is pretreated before the reaction. The pretreatment includes crushing the potassium chloride to a particle size of 0.1-1 mm, controlling the ball mill speed at 300-500 r / min, the ball-to-material ratio at 2-5:1, and the grinding time at 3-8 minutes.
5. The method for preparing potassium sulfate from potassium chloride and ammonium sulfate according to claim 1, characterized in that: In the first stage of the reaction, the molar ratio of ammonium sulfate to potassium chloride is controlled within the range of 1:1.4-1:2.2 to obtain a high potassium conversion rate. In the second stage of the reaction, the molar ratio is increased to 1:1.8-1:2.
8. When the mass ratio of KCl to (NH4)2SO4 is 1:1.2, potassium chloride can be almost completely reacted.
6. The method for preparing potassium sulfate from potassium chloride and ammonium sulfate according to claim 1, characterized in that: The crystallization temperature is controlled at 10-30℃, and the crystallization time is 1-3 hours.