Process for improving the stability of potassium sulfate production

Abstract

The application relates to the technical field of potassium sulfate and discloses a process for improving the production stability of potassium sulfate, which comprises the following steps: introducing potassium chloride and concentrated sulfuric acid into a reaction furnace, segmentally regulating the furnace temperature of the reaction furnace, reacting, cooling, scraping, screening and crushing to obtain potassium sulfate finished products. Through systematic research, the optimal process parameters of the preparation of potassium sulfate by the Mannheim method are successfully determined, the optimal temperature at the top of the furnace is 730 DEG C, the optimal reaction temperature in the furnace is 530 DEG C, the potassium oxide K2O content is stably kept at about 52%, the chloride ion Cl ‑ content is reduced to 1.36% and 2.38% respectively, meanwhile, the feeding flow of the concentrated sulfuric acid is 70.5%, the potassium oxide content can be up to 52.4% at most, and the impurity content is low, which is a key operation point for realizing complete reaction and obtaining high-purity products.

Description

Technical Field

[0001] This invention relates to the field of potassium sulfate technology, specifically a process for improving the stability of potassium sulfate production. Background Technology

[0002] Potassium sulfate, an important basic chemical raw material and high-quality chlorine-free potassium fertilizer, is a colorless orthorhombic or hexagonal crystal or powder with a bitter and salty taste. It has low hygroscopicity, is easily soluble in water, but insoluble in solvents such as ethanol, acetone, and carbon disulfide. In recent years, demand from industrial, pharmaceutical, and high-end agricultural sectors (such as tobacco and fruit trees, which are sensitive to chlorine) has continued to grow. Currently, the mainstream method for preparing potassium sulfate internationally is the Mannheim process, which holds a dominant position in China. The economic benefits of its byproduct hydrochloric acid make it the preferred choice for many enterprises. However, this process has long faced some technical bottlenecks that urgently need to be addressed in practice.

[0003] Many companies using the Mannheim process are facing the core challenge of unstable product quality. Specifically, the potassium oxide content in the finished product is frequently below 52%, and key intermediate control indicators such as free acid and chloride content are too high, leading to fluctuations in product qualification rates and an inability to consistently meet premium-grade standards. Furthermore, the finished product sometimes exhibits yellowing or blackening, severely impacting its appearance and market value. These problems not only reduce the premium-grade product rate and potassium yield, affecting the company's economic benefits, but also pose environmental pollution risks due to potential issues such as acid leakage from the furnace bottom during the preparation process. Therefore, systematically researching and overcoming these technical challenges to improve the stability and product quality of potassium sulfate preparation using the Mannheim process has become an urgent practical need within the industry, and this is the direct motivation behind this project.

[0004] Based on a comprehensive techno-economic analysis of mainstream potassium sulfate production methods both domestically and internationally, although other processes such as the brine process and sulfate mine process exist, these processes are generally limited by inherent drawbacks such as low potassium yield, strong regionality of resources, difficulty in treating by-product pollution, or unstable product quality. In contrast, the Mannheim process is mature, has a dominant production capacity in China, and its unique economic advantage of producing low-cost hydrochloric acid as a by-product constitutes a key link in the enterprise's circular economy. This makes in-depth exploration and improvement of the potential of this process the most feasible and economical strategic choice. Summary of the Invention

[0005] (a) Technical problems to be solved: To address the shortcomings of existing technologies, this invention provides a process for improving the stability of potassium sulfate production. This process avoids incomplete potassium sulfate reaction due to insufficient furnace temperature, reduces material refeeding, and results in a more stable product.

[0006] (II) Technical solution: A process to improve the stability of potassium sulfate production: potassium chloride and concentrated sulfuric acid are introduced into a Mannheim reactor, and the furnace temperature is controlled in stages to carry out the reaction, followed by cooling, scraping, sieving, and crushing to obtain the finished potassium sulfate product; the hydrogen chloride gas generated during the reaction is discharged to make a dilute hydrochloric acid solution, which is then introduced into a fermenter containing yellow short bacteria and culture medium for fermentation and acid production.

[0007] Preferably, the flow rate of potassium chloride in the reactor is set to a percentage (opening / load percentage) of 12-14%.

[0008] Preferably, the flow rate setting percentage (opening / load percentage) of concentrated sulfuric acid is 54.5-71.5%.

[0009] Preferably, the furnace top temperature is 670-770℃.

[0010] Preferably, the furnace temperature is 490-550℃.

[0011] Preferably, the potassium element in the finished potassium sulfate product is converted to potassium oxide, the potassium oxide content is ≥52%, the chloride ion content in the finished potassium sulfate product is ≤2.0%, and the free acid content is ≤3.0%.

[0012] Preferably, a dilute hydrochloric acid solution is introduced into the fermenter to control the pH of the fermentation system to 6.5-6.8.

[0013] Preferably, the mass fraction of the dilute hydrochloric acid solution is 2-6%.

[0014] Preferably, the culture medium includes glucose, corn steep liquor, urea, ammonium sulfate, calcium carbonate, potassium dihydrogen phosphate, and magnesium sulfate.

[0015] Preferably, the fermentation temperature is 30-32℃.

[0016] Preferably, the acid production rate of fermentation is ≥226g / L and the conversion rate is ≥69.8%.

[0017] (III) Beneficial technical effects: This invention proposes a method to regulate the furnace temperature and top temperature of the reactor, which can avoid incomplete potassium sulfate reaction due to insufficient furnace temperature, reduce material refeeding, and make the product more stable. Regulating the feed flow rates of concentrated sulfuric acid and potassium chloride reduces the phenomenon of excessive free acid or chloride ions in the finished product caused by material or acid interruptions, thereby improving the qualification rate and stability of the finished product. The invention also explores the possibility of using hydrochloric acid, a byproduct, for pH control in amino acid fermentation, reducing the cost of amino acid preparation and minimizing air pollution caused by direct gas emissions.

[0018] The experimental content of this invention focuses on improving the quality of potassium sulfate as the main product and the value utilization of by-products. First, the influence of the Mannheim furnace reaction temperature on the yield of the finished potassium sulfate product is systematically investigated. This is achieved by precisely controlling the furnace temperature and top temperature, and using the potassium oxide content, chloride ion content, and free acid content in the finished product as core indicators for comprehensive evaluation. Second, the optimization scheme of raw material feed flow rate is studied in depth. By precisely controlling the feed flow rates of concentrated sulfuric acid and potassium chloride, real-time tracking and calculation are performed to stabilize their ratio within the optimal stoichiometric range, thus examining its key role in the product yield. Furthermore, the project will expand the high-value application pathways of the by-product hydrochloric acid, focusing on exploring its feasibility and applicability for pH control during amino acid fermentation.

[0019] The core objective of this invention is to completely solve the problems of unstable product quality and low yield of superior grade products in the current Mannheim process for potassium sulfate production through systematic technical research and process optimization. The project aims to establish a strict raw material control system by deeply analyzing the intrinsic relationship between raw material quality, process parameters, and final product quality, and to develop refining technologies to improve product stability and yield. Ultimately, the goal is to significantly improve the quality of finished potassium sulfate, increase product added value, and enhance the company's core competitiveness.

[0020] At the microscopic level, this project's research stems directly from an in-depth analysis of the core chemical reaction of the Mannheim process (KCl + H₂SO₄ → K₂SO₄ + HCl). All technical bottlenecks can be traced back to chemical thermodynamics, kinetics, and process control theories: insufficient potassium oxide content and high free acid content in the finished product essentially indicate incomplete reaction. This points to two key control parameters: reaction temperature and the molar ratio of raw materials. Insufficient furnace temperature fails to meet the activation energy requirements, while imprecise manual proportioning directly disrupts the reaction equilibrium. Simultaneously, the abnormal yellowing or blackening of the finished product is theoretically attributed to the thermal decomposition or catalytic coking of organic impurities (such as flotation agents) in the potassium chloride raw material at high temperatures, generating coloring substances (such as carbon particles). Therefore, it is crucial to establish strict standards for controlling the raw material impurity profile to prevent side reactions from occurring at the source.

[0021] This invention successfully determined the optimal process parameters for potassium sulfate preparation via the Mannheim process through systematic research. Experiments showed that the furnace top and furnace interior temperatures have a decisive impact on reaction efficiency. The optimal furnace top temperature was ultimately determined to be 730℃, and the optimal furnace interior reaction temperature to be 530℃. Under these temperature conditions, the core product indicators reach optimal levels, with the potassium oxide (K₂O) content (converted from potassium element in the finished potassium sulfate product) remaining stable at approximately 52%, and the chloride ion (Cl₂) content... -The free acid content was reduced to 1.36% and 2.38% respectively, effectively ensuring a complete reaction and significantly reducing impurity content. Meanwhile, the concentrated sulfuric acid feed ratio was 70.5%, at which the potassium oxide content could reach a maximum of 52.4% with low impurity content, a key operational point for achieving complete reaction and obtaining high-purity products.

[0022] This invention successfully opens up a high-value application path for by-product hydrochloric acid. Experiments have confirmed that this hydrochloric acid has high purity and can effectively control the pH value in lysine fermentation processes, achieving an acid production rate of 235.5 g / L and a conversion rate of 72.7%. The results are excellent and stable, indicating that the by-product hydrochloric acid can fully meet the needs of high-end bio-fermentation, realizing resource recycling and value extension of the industrial chain, meeting the experimental requirements, and achieving the expected results.

[0023] The successful implementation of this invention can significantly improve the stability and controllability of the preparation process, ultimately leading to a substantial increase in the qualification rate of potassium sulfate products. This not only directly enhances the market competitiveness and profitability of the company's core products, but also successfully opens up new revenue channels by developing by-product hydrochloric acid for high-value applications such as amino acid fermentation, turning "waste" into treasure and forming a circular economy model driven by the dual products of "potassium sulfate-hydrochloric acid".

[0024] At the technical level, this invention will result in a widely applicable optimized solution for the Mannheim process of potassium sulfate production, providing practical evidence for technological advancement across the industry. At the economic level, improved product quality and stability will directly translate into higher market prices and profits, while also better protecting the benefits of the byproduct hydrochloric acid. At the environmental level, by optimizing the process and enhancing equipment sealing, the uncontrolled emission of pollutants such as sulfuric acid leaks will be effectively reduced, promoting the green and sustainable development of enterprises.

[0025] At the industry technology promotion level, the complete set of solutions developed by this project regarding raw material control, process optimization, and by-product utilization has strong demonstrative and universal applicability for potassium sulfate enterprises in China that widely adopt the Mannheim process. This technology requires no disruptive equipment investment, effectively solves common industry problems, and has the potential to become an industry standard operating procedure, with broad application prospects.

[0026] From the perspective of downstream industries and social benefits, this invention provides high-quality and highly stable potassium sulfate products that will better meet the needs of high-end precision agriculture in China. In particular, it provides reliable data for high-value chlorine-sensitive crops (such as tobacco, fruit, and tea), which is of positive significance for improving the quality and yield of cash crops and serving the development of modern agriculture. Attached Figure Description

[0027] Figure 1 This relates to the effect of furnace top temperature on the finished potassium sulfate product.

[0028] Figure 2 This relates to the effect of furnace temperature on the finished potassium sulfate product.

[0029] Figure 3 This describes the effect of concentrated sulfuric acid feed rate on the finished potassium sulfate product. Detailed Implementation

[0030] To make the technical solutions of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. It should be noted that the following embodiments are only used to better understand the technical solutions of the present invention and should not be construed as limiting the present invention.

[0031] Example 1: A process for improving the stability of potassium sulfate production: Potassium chloride and concentrated sulfuric acid are introduced into a Mannheim reactor. The flow rate of potassium chloride is set at 12% (open / load percentage), and the flow rate of concentrated sulfuric acid is set at 54.5-71.5% (open / load percentage). The reactor top temperature is 670-770℃, and the furnace temperature is 490-550℃. The reaction proceeds, followed by cooling, scraping, sieving, and pulverizing to obtain potassium sulfate. The hydrogen chloride gas generated during the reaction is discharged, and a 3% (w / w) dilute hydrochloric acid solution is prepared. This solution is then introduced into a fermenter containing *Bacillus flavus* (8% inoculum) and a culture medium (containing 110 g / L glucose, 25 g / L corn steep liquor, 7 g / L urea, 40 g / L ammonium sulfate, 32 g / L calcium carbonate, 0.8 g / L potassium dihydrogen phosphate, and 0.4 g / L magnesium sulfate). The pH of the fermentation system is controlled to 6.7 to induce acid production.

[0032] The effect of furnace temperature on the finished potassium sulfate product: The reaction conditions were controlled with furnace top temperatures of 670℃, 700℃, 730℃, and 770℃. The effects of furnace top temperature on the potassium oxide, chloride ion, and free acid content in the potassium sulfate samples are as follows: Figure 1 As shown.

[0033] Depend on Figure 1 It can be seen that as the furnace top temperature changes, the potassium oxide (potassium element converted from potassium sulfate product to potassium oxide) content gradually increases and then tends to level off, while the chloride ion (Cl) content... - The content of free acid gradually decreased and then showed an increasing trend, with a more significant change in the temperature range of 670-730℃. When the furnace top temperature was 730℃, potassium oxide and Cl... - The contents of free acid were 52.5%, 1.36%, and 2.38%, respectively, while the concentration of Cl in the range of 730-770℃ was... - The rate of change of free acid content increased, and the potassium oxide content in the product did not change significantly, so the influence no longer increased significantly. Therefore, the furnace top temperature was selected as 730℃.

[0034] The effect of furnace temperature on the finished potassium sulfate product: Furnace temperature is a core control parameter in the Mannheim process for potassium sulfate production, directly determining the extent of the core chemical reaction (KCl + H₂SO₄ → K₂SO₄ + HCl). Insufficient furnace temperature leads to slow reaction kinetics and incomplete conversion of raw materials, resulting in a lower potassium oxide content in the finished product. Unreacted potassium chloride and sulfuric acid, on the other hand, contribute to the low Cl₂ content. - Excessive free acid content severely impacts product yield. Therefore, precise control and optimization of furnace temperature are crucial for ensuring complete reaction, increasing product content, and reducing impurities. The effect of different furnace temperatures on potassium sulfate samples under the optimal furnace top temperature of 730℃ is shown in [reference needed]. Figure 2 .

[0035] from Figure 2 It can be seen that as the furnace temperature increases within the range of 490-550℃, the potassium oxide content initially rises and then decreases, while the Cl content... - The content of free acids showed a decreasing or fluctuating trend, with a relatively large rate of change; while at a temperature of 530℃, potassium oxide and Cl... - The free acid contents were 52.5%, 1.36%, and 2.38%, respectively; however, when the temperature was above 530℃, all three values ​​showed a fluctuating trend with no significant difference. Analysis indicates that a temperature of 530℃ is sufficient to meet the reaction conditions for potassium sulfate, while potassium oxide and Cl... - The free acid content also reached an optimal value. Once the temperature exceeded 530℃, the furnace temperature was no longer a limiting factor in the reaction process. Therefore, 530℃ was chosen as the optimal reaction temperature. This ensures a complete reaction while increasing the main product content and reducing impurities.

[0036] The effect of concentrated sulfuric acid and potassium chloride feed flow rates on the finished potassium sulfate product: According to the stoichiometric ratio (2KCl + H₂SO₄ → K₂SO₄ + 2HCl), if sulfuric acid is in excess, it will lead to an increase in the free acid content in the reaction system, causing the product to have excessive acidity, caking, and a yellow color; if potassium chloride is in excess, it will cause unreacted chloride ions (Cl₂) to... - Residues remain in the product, leading to insufficient main content (potassium oxide) and unqualified chloride ion levels. Therefore, achieving a precise and stable ratio of the flow rates of both is a crucial prerequisite for ensuring complete reaction and obtaining high-purity potassium sulfate. The effects of KCl and H2SO4 feed flow rates on the potassium oxide, chloride ion, and free acid content in potassium sulfate samples under the conditions of a furnace top temperature of 730℃ and a furnace internal temperature of 530℃ are shown in [the figure]. Figure 3 .

[0037] Depend on Figure 3 It can be seen that, under the condition of potassium chloride flow rate of 12%, with the change of H2SO4 feed flow rate, the potassium oxide content shows a trend of increasing and then gradually leveling off.- The content of free acid showed an increase followed by a gradual decrease, with a more significant change observed at a concentrated sulfuric acid flow rate of 70.5%. Potassium oxide and Cl... - The contents of potassium oxide and free acid were 52.4%, 1.17%, and 2.12%, respectively. However, the change slowed down when the content was further increased to 71.5%. Furthermore, the content of potassium oxide and Cl in the product... - Since the content of free acid did not change significantly, a feed flow rate of 70.5% for concentrated sulfuric acid was selected to ensure complete reaction and obtain high-purity potassium sulfate.

[0038] The effect of byproduct hydrochloric acid on lysine fermentation: Under optimal furnace and top temperatures, and feed rates of concentrated sulfuric acid and potassium chloride, the feasibility of using byproduct hydrochloric acid for amino acid fermentation was verified using the acid production rate of the finished lysine product as an indicator. Under conditions of a furnace temperature of 530℃, a furnace top temperature of 730℃, and a concentrated sulfuric acid feed rate of 70.5%, the resulting byproduct hydrochloric acid was applied to lysine fermentation. Six parallel batches were measured to verify its application effect, and the results are shown in Table 1.

[0039] Table 1. Effect of hydrochloric acid (byproduct) on lysine fermentation As shown in Table 1, the application of hydrochloric acid in lysine fermentation resulted in an acid production rate of 235.5 g / L and a conversion rate of 72.7%, both within the reasonable range for lysine fermentation and achieving good results. This indicates that the byproduct hydrochloric acid has high purity, significant application value, and can maintain the pH value within a reasonable range, making it suitable for normal application in lysine fermentation without negatively impacting product stability.

Claims

1. A process for improving the stability of potassium sulfate production, characterized in that, The process is as follows: potassium chloride and concentrated sulfuric acid are introduced into the reactor, and the furnace temperature is controlled in stages to carry out the reaction. The reaction is then cooled, scraped, sieved, and crushed to obtain potassium sulfate product. The hydrogen chloride gas generated during the reaction is discharged to make a dilute hydrochloric acid solution, which is then introduced into a fermenter containing yellow short bacteria and culture medium for fermentation and acid production.

2. The process for improving the stability of potassium sulfate production according to claim 1, characterized in that, The flow rate of potassium chloride in the reactor is set to 12-14% of the total flow rate.

3. The process for improving the stability of potassium sulfate production according to claim 1, characterized in that, The flow rate of the concentrated sulfuric acid is set to a percentage of 54.5-71.5%.

4. The process for improving the stability of potassium sulfate production according to claim 1, characterized in that, The furnace top temperature is 670-770℃, and the furnace internal temperature is 490-550℃.

5. The process for improving the stability of potassium sulfate production according to claim 1, characterized in that, The potassium in the finished potassium sulfate product is converted to potassium oxide, with a potassium oxide content of ≥52%, a chloride ion content of ≤2.0%, and a free acid content of ≤3.0%.

6. The process for improving the stability of potassium sulfate production according to claim 1, characterized in that, The dilute hydrochloric acid solution is introduced into the fermenter to control the pH of the fermentation system to 6.5-6.8, and the mass fraction of the dilute hydrochloric acid solution is 2-6%.

7. The process for improving the stability of potassium sulfate production according to claim 1, characterized in that, The culture medium includes glucose, corn steep liquor, urea, ammonium sulfate, calcium carbonate, potassium dihydrogen phosphate, and magnesium sulfate.

8. The process for improving the stability of potassium sulfate production according to claim 1, characterized in that, The fermentation temperature is 30-32℃.

9. The process for improving the stability of potassium sulfate production according to claim 1, characterized in that, The acid production rate of the fermentation is ≥226 g / L, and the conversion rate is ≥69.8%.

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