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BR-102025016038-A2 - METHOD FOR PRODUCING POTASSIUM SULFATE BY METATHESIS PROCESS, POTASSIUM SULFATE PRODUCT AND POTASSIUM FERTILIZER

BR102025016038A2BR 102025016038 A2BR102025016038 A2BR 102025016038A2BR-102025016038-A2

Abstract

This disclosure describes a method for the production of potassium sulfate by metathesis, a potassium sulfate product, and a potassium fertilizer, and relates to the field of potassium sulfate preparation methods. Solid ammonium sulfate and solid potassium chloride are used as raw materials, added in two steps for the reaction: a first-stage reaction and a second-stage reaction, respectively. Subsequently, a third-stage reaction is carried out with hot water, and crystallization and separation are performed, so that impurities in the product are completely removed and, at the same time, the K2O content in the product is increased. The potassium sulfate product with a high K2O content and low chlorine content can be prepared by means of the three-stage reaction process provided in this disclosure, the method being simple, easy to implement, and convenient for industrial application.

Inventors

  • Pingfu Sun
  • Guocai Liu

Assignees

  • MiGao Century Engineering Technology (Chengdu) Limited Company

Dates

Publication Date
20260310
Application Date
20250731
Priority Date
20240823

Claims (10)

  1. 1. Method for producing a potassium sulfate characterized by the metathesis process, comprising: taking a solid ammonium sulfate and a solid potassium chloride as raw materials, carrying out a first-stage reaction in a solution system and then crystallizing and separating, so as to obtain a primary crude potassium sulfate; taking the primary crude potassium sulfate, the solid ammonium sulfate and the solid potassium chloride as raw materials, carrying out a second-stage reaction in a solution system and then crystallizing and separating, so as to obtain a secondary crude potassium sulfate, and mixing the secondary crude potassium sulfate with hot water at 80 °C - 98 °C, carrying out a third-stage reaction and then crystallizing and separating.
  2. 2. Method according to claim 1, characterized in that the molar ratio of solid ammonium sulfate to solid potassium chloride for the first-stage reaction is 1:(1.4-2.2), and the molar ratio of solid ammonium sulfate to solid potassium chloride for the second-stage reaction is 1:(1.8-2.8).
  3. 3. A method according to claims 1 or 2, characterized by a process for obtaining primary crude potassium sulfate, comprises: mixing and dissolving solid ammonium sulfate, a mother liquor of secondary crude potassium sulfate, and water to obtain an ammonium sulfate solution; mixing the ammonium sulfate solution and solid potassium chloride to conduct the first-stage reaction; then cooling until crystallization and separating, so as to obtain primary crude potassium sulfate and a mother liquor of primary crude potassium sulfate, wherein the mother liquor of secondary crude potassium sulfate is obtained by a separation process and obtaining secondary crude potassium sulfate.
  4. 4. Method according to claim 3, characterized in that the mass ratio of solid ammonium sulfate, crude secondary potassium sulfate mother liquor and water is 1:(2.0-3.2):(0.2-1.0); preferably, the temperature of the first-stage reaction is controlled at 60 °C - 90 °C and the reaction time is controlled at 1 h - 3 h; preferably, the crystallization temperature after the first-stage reaction is controlled at 30 °C - 60 °C and the crystallization time is controlled at 1 h - 3 h, and preferably, when preparing the ammonium sulfate solution, the dissolution temperature is 60 °C - 90 °C.
  5. 5. Method according to claim 3, characterized in that the primary crude potassium sulfate mother liquor is used to prepare an NK fertilizer by-product; preferably, the primary crude potassium sulfate mother liquor is evaporated and concentrated to obtain a concentrated NK fertilizer mother liquor, the concentrated NK fertilizer mother liquor is crystallized and separated to obtain a wet NK fertilizer product and an NK fertilizer mother liquor, and the wet NK fertilizer product is dried to obtain an NK fertilizer product, and in a more preferred way, the NK fertilizer mother liquor is returned to an evaporation and concentration stage for recycling.
  6. 6. A method according to claim 3, characterized by a process for obtaining secondary crude potassium sulfate, comprises: mixing and dissolving solid ammonium sulfate, primary crude potassium sulfate, and a mother liquor of potassium sulfate product to obtain a mixed crystalline paste solution; mixing the mixed crystalline paste solution with solid potassium chloride for a second-stage reaction and then cooling until crystallization and separation, so as to obtain secondary crude potassium sulfate and the mother liquor of secondary crude potassium sulfate; and using the mother liquor of secondary crude potassium sulfate to dissolve the solid ammonium sulfate in the first-stage reaction, wherein the mother liquor of potassium sulfate product is obtained by crystallization and separation after the third-stage reaction.
  7. 7. Method according to claim 6, characterized in that the mass ratio of solid ammonium sulfate, primary crude potassium sulfate and potassium sulfate mother liquor is 1:(2.2-3.3):(4.8-6.2); preferably, the second stage reaction temperature is controlled at 60 °C - 90 °C and the reaction duration is controlled at 1 h - 3 h; preferably, the crystallization temperature after the second stage reaction is controlled at 30 °C - 60 °C and the crystallization duration is controlled at 1 h - 3 h, and preferably, when preparing the mixed crystalline paste solution, the dissolution temperature is 60 °C - 90 °C.
  8. 8. Method according to claim 1, characterized in that the reaction temperature of the third-stage reaction is controlled at 60 °C - 90 °C and the reaction duration is controlled at 0.5 h - 2.0 h; In a preferred manner, a mass ratio of secondary crude potassium sulfate to hot water is controlled at 1: (0.8-1.2); in a preferred manner, the hot water and potassium chloride are first mixed to obtain a potassium chloride solution with a mass fraction of 1%-30%, and then the potassium chloride solution is used to mix and react with the secondary crude potassium sulfate; in a preferred manner, after the third-stage reaction, a crystallization is conducted at 30 °C - 60 °C for 1 h - 3 h, followed by a separation to obtain a wet potassium sulfate product and a mother liquor of potassium sulfate product, and the wet potassium sulfate product is dried to obtain a potassium sulfate product, and in a more preferred manner, the mother liquor of potassium sulfate product is used to dissolve the solid ammonium sulfate in the second-stage reaction.
  9. 9. Potassium sulfate product, characterized in that the potassium sulfate product is prepared by the method according to any one of claims 1 to 8, and in a preferred manner, the K2O content of the potassium sulfate product is 50.0% by weight - 51.5% by weight, the chloride ion content is less than 0.3% by weight, the moisture content is less than 0.5% by weight, and the water-insoluble matter content is less than 0.05% by weight.
  10. 10. Potash fertilizer, characterized in that the potash fertilizer comprises the potassium sulfate product according to claim 8 or 9.

Description

TECHNICAL FIELD [0001] This disclosure relates to the field of methods for preparing potassium sulfate, in particular, to a method for producing potassium sulfate by a metathesis process, a potassium sulfate product and a potash fertilizer. Prior art [0002] Potassium sulfate is an important chlorine-free potash fertilizer suitable for commercial crops such as tobacco, citrus, tea, grapes, beet and sugarcane; the potassium it contains is one of the three main plant nutrients, and potassium is an essential macronutrient for plants, particularly beneficial for chlorine-sensitive crops, thus making potassium sulfate a multi-nutrient fertilizer with wide applications. Furthermore, potassium sulfate is a fundamental chemical feedstock widely used in industries such as pharmaceuticals, glass and dyes. As a result, the demand for potassium sulfate is very high, often leading to a situation where industrial production capacity falls far short of demand. Further research into potassium sulfate production processes is of significant practical importance. [0003] Currently, the main methods for producing potassium sulfate include the comprehensive utilization method of potassium ores, the comprehensive utilization method of bitters, the Mannheim method, and various conversion methods that use potassium sulfates and potassium chloride as raw materials. Among these, the application of the comprehensive utilization of potassium ore and bitters is limited due to resource constraints. The most commonly used method for the industrial production of potassium sulfate is the Mannheim process, i.e., potassium chloride reacts with sulfuric acid at elevated temperatures. Raw materials are fed into a reaction furnace heated above 500 °C - 600 °C, and potassium sulfate and hydrochloric acid are produced by the two-step reaction of potassium bisulfate. This method for producing potassium sulfate accounts for 40% to 50% of the global supply. However, the Mannheim process has disadvantages, such as high investment costs, significant energy consumption, severe equipment corrosion, and low marketability of the hydrochloric acid byproduct, which also limits its development. Furthermore, in the Mannheim process, in order to neutralize the acid in the intermediate product, limestone powder is added (the main component being calcium carbonate), resulting in traces of calcium sulfate in the final potassium sulfate product, making the product not fully soluble in water, thus preventing its use as a fully water-soluble fertilizer. [0004] In the method of using ammonium sulfate and potassium chloride as raw materials to produce potassium sulfate, since the price of potassium sulfate is much higher than that of potassium chloride, the ammonium chloride byproduct containing potassium can be used as a raw material for compound fertilizer or applied directly, thus providing the method with good economic and social benefits, and has therefore received increasing attention. [0005] However, currently, the main problems in the process of preparing potassium sulfate from ammonium sulfate and potassium chloride are: the K2O content in the potassium sulfate product is not high enough, while the chloride ion content in the potassium sulfate product is relatively high, thus limiting its future application. Furthermore, the existing process for preparing potassium sulfate from ammonium sulfate and potassium chloride still presents some problems, such as complex process flow, high water consumption, and difficult industrial application. [0006] In view of the above, the present disclosure is proposed. SUMMARY [0007] The objectives of this disclosure are to provide a method for producing potassium sulfate by a metathesis process, a potassium sulfate product and a potash fertilizer, and to provide a preparation process for the potassium sulfate product with a high K2O content and low chloride ion content. [0008] This announcement is made as follows. [0009] In the first aspect, a method for producing potassium sulfate by the metathesis process is provided in the present disclosure, including: taking solid ammonium sulfate and solid potassium chloride as raw materials, carrying out a first-stage reaction in a solution system and then crystallizing and separating in order to obtain a primary crude potassium sulfate; taking primary crude potassium sulfate, solid ammonium sulfate and solid potassium chloride as raw materials, carrying out a second-stage reaction in a solution system and then crystallizing and separating in order to obtain a secondary crude potassium sulfate, and mixing the secondary crude potassium sulfate with hot water at 80 °C - 98 °C, carrying out a third-stage reaction and then crystallizing and separating. [0010] In an optional embodiment, the molar ratio of solid ammonium sulfate to solid potassium chloride for the first-stage reaction is 1: (1.4-2.2), and the molar ratio of solid ammonium sulfate to solid potassium chloride for the second-stage