Method for producing potassium sulfate using metathesis process, potassium sulfate product and potash fertilizer

Abstract

The present disclosure relates to the field of potassium sulfate preparation methods, and provides a method for producing potassium sulfate using a metathesis process, a potassium sulfate product, and a potash fertilizer. The method comprises: using an ammonium sulfate solid and a potassium chloride solid as raw materials, and adding same in two steps to carry out a first-stage reaction and a second-stage reaction respectively; then, mixing with hot water to carry out a third-stage reaction, and then performing crystallization and separation to thoroughly remove impurities from a product and increase the content of K2O in the product. By means of the three-stage reaction process provided in the present disclosure, a potassium sulfate product with high K2O content and low chlorine content can be prepared, and the method is simple and easy to implement and is suitable for industrial application.

Description

Method for producing potassium sulfate by metathesis process, potassium sulfate product and potash fertilizer

[0001] Cross-reference to Related Applications

[0002] The present disclosure claims priority to the Chinese patent application No. 202411168750.X, filed on August 23, 2024, and entitled "Method for producing potassium sulfate by metathesis process, potassium sulfate product and potash fertilizer", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the field of potassium sulfate production methods, in particular, to a method for producing potassium sulfate by metathesis process, a potassium sulfate product and a potash fertilizer. BACKGROUND

[0004] Potassium sulfate is an important non-chlorine potash fertilizer, which can be used for economic crops such as tobacco, citrus, tea, grape, sugar beet, and sugarcane. The potassium element contained in potassium sulfate is one of the three major nutrients for plants. Potassium is a large amount of nutrient element required by plants, and is particularly suitable for chlorine-avoiding crops. It is a multi-nutrient and widely used fertilizer. In addition, potassium sulfate is also a basic chemical raw material, which is widely used in the pharmaceutical, glass and dye industries. Therefore, the demand for potassium sulfate is very large, and the industrial production capacity is often much smaller than the demand. It is of great practical significance to further study the production process of potassium sulfate.

[0005] Currently, the methods for producing potassium sulfate mainly include comprehensive utilization of potassium ore, comprehensive utilization of bitter brine, Mannheim method, and various conversion methods using sulfate and potassium chloride as raw materials. Among them, the comprehensive utilization of potassium ore and bitter brine is limited due to resource constraints. The most commonly used method for industrial production of potassium sulfate is the Mannheim process, which is the reaction of potassium chloride with sulfuric acid at high temperature. The raw materials are poured into a reaction furnace heated to above 500-600°C, and potassium bisulfate is produced by two-step reaction to produce potassium sulfate and hydrochloric acid. This method for producing potassium sulfate accounts for 40% to 50% of the global supply. However, the Mannheim process has problems such as large investment, high energy consumption, severe equipment corrosion, and poor sales of by-product hydrochloric acid, which also restricts its development. In addition, in order to neutralize the acid in the intermediate product, stone powder (mainly composed of calcium carbonate) is added to the potassium sulfate product produced by the Mannheim method, resulting in a small amount of calcium sulfate in the final potassium sulfate product, which cannot be fully water-soluble and cannot be used as a fully water-soluble fertilizer.

[0006] Using ammonium sulfate and potassium chloride as raw materials to convert and produce potassium sulfate has good economic and social benefits, and is increasingly valued because the price of potassium sulfate is much higher than that of potassium chloride, and the by-product potassium-containing ammonium chloride can be used as a raw material for compound fertilizer or directly used.

[0007] However, the main problems of the process for preparing potassium sulfate by using ammonium sulfate and potassium chloride as raw materials are that the K2O content of the potassium sulfate product is not high, and the chlorine ion content of the potassium sulfate product is high, which limits its further application. In addition, the existing process for preparing potassium sulfate by using ammonium sulfate and potassium chloride as raw materials also has the problems of complex process flow, large water consumption, and difficulty in industrial application.

[0008] In view of this, the present disclosure is proposed. SUMMARY

[0009] The purpose of the present disclosure is to provide a method for producing potassium sulfate by a metathesis process, a potassium sulfate product and a potassium fertilizer, aiming to provide a preparation process of a potassium sulfate product with high K2O content and low chlorine ion content.

[0010] The present disclosure is implemented as follows:

[0011] In a first aspect, the present disclosure provides a method for producing potassium sulfate by a metathesis process, comprising:

[0012] using ammonium sulfate solids and potassium chloride solids as raw materials, carrying out a first-stage reaction in a solution system, and then crystallizing and separating to obtain a primary potassium sulfate crude product;

[0013] using the primary potassium sulfate crude product, ammonium sulfate solids and potassium chloride solids as raw materials, carrying out a second-stage reaction in a solution system, and then crystallizing and separating to obtain a secondary potassium sulfate crude product;

[0014] mixing the secondary potassium sulfate crude product with hot water at a temperature of 80-98℃ to carry out a third-stage reaction, and then crystallizing and separating.

[0015] In an optional embodiment, the molar ratio of ammonium sulfate solids to potassium chloride solids used for the first-stage reaction is 1:(1.4-2.2), and the molar ratio of ammonium sulfate solids to potassium chloride solids used for the second-stage reaction is 1:(1.8-2.8).

[0016] In an optional embodiment, the process for obtaining the primary potassium sulfate crude product comprises: mixing and dissolving ammonium sulfate solids, secondary potassium sulfate crude product mother liquor and water to obtain an ammonium sulfate solution, mixing the ammonium sulfate solution and potassium chloride solids to carry out a first-stage reaction, and then crystallizing and separating at a reduced temperature to obtain the primary potassium sulfate crude product and a primary potassium sulfate crude product mother liquor; wherein the secondary potassium sulfate crude product mother liquor is obtained from the process for separating the secondary potassium sulfate crude product.

[0017] In an optional embodiment, the mass ratio of ammonium sulfate solids, secondary potassium sulfate crude product mother liquor and water is 1:(2.0-3.2):(0.2-1.0);

[0018] Preferably, the temperature of the first-stage reaction is controlled to be 60-90℃, and the reaction time is 1-3h;

[0019] Preferably, the crystallization temperature after the first-stage reaction is controlled to be 30-60°C, and the crystallization time is controlled to be 1-3h.

[0020] Preferably, the dissolution temperature is 60-90°C when preparing the ammonium sulfate solution.

[0021] In an alternative embodiment, the mother liquor of the primary potassium sulfate crude product is used to prepare the NK fertilizer by-product.

[0022] Preferably, the mother liquor of the primary potassium sulfate crude product is evaporated and concentrated to obtain a concentrated NK fertilizer mother liquor, and the concentrated NK fertilizer mother liquor is crystallized and separated to obtain NK fertilizer wet product and NK fertilizer mother liquor, and the NK fertilizer wet product is dried to obtain NK fertilizer product.

[0023] More preferably, the NK fertilizer mother liquor is recycled to the evaporation and concentration stage.

[0024] In an alternative embodiment, the process for obtaining the secondary potassium sulfate crude product comprises: dissolving the ammonium sulfate solid, the primary potassium sulfate crude product and the potassium sulfate product mother liquor to obtain a crystal slurry mixed solution, mixing the crystal slurry mixed solution and potassium chloride solid to perform a second-stage reaction, and then crystallizing and separating to obtain the secondary potassium sulfate crude product and secondary potassium sulfate crude product mother liquor, and using the secondary potassium sulfate crude product mother liquor to dissolve the ammonium sulfate solid in the first-stage reaction; wherein the potassium sulfate product mother liquor is obtained by crystallizing and separating after a third-stage reaction.

[0025] In an alternative embodiment, the mass ratio of the ammonium sulfate solid, the primary potassium sulfate crude product and the potassium sulfate product mother liquor is 1:(2.2-3.3):(4.8-6.2).

[0026] Preferably, the temperature of the second-stage reaction is controlled to be 60-90°C, and the reaction time is controlled to be 1-3h.

[0027] Preferably, the crystallization temperature after the second-stage reaction is controlled to be 30-60°C, and the crystallization time is controlled to be 1-3h.

[0028] Preferably, the dissolution temperature is 60-90°C when preparing the crystal slurry mixed solution.

[0029] In an alternative embodiment, the reaction temperature of the third-stage reaction is controlled to be 60-90°C, and the reaction time is controlled to be 0.5-2.0h.

[0030] Preferably, the mass ratio of the secondary potassium sulfate crude product to hot water is controlled to be 1:(0.8-1.2).

[0031] Preferably, after the third-stage reaction, crystallization is performed at 30-60°C for 1-3h, and then the potassium sulfate wet product and potassium sulfate product mother liquor are separated, and the potassium sulfate wet product is dried to obtain the potassium sulfate product.

[0032] More preferably, the potassium sulfate product mother liquor is used to dissolve the ammonium sulfate solid in the second reaction.

[0033] In a second aspect, the present disclosure provides a potassium sulfate product prepared by the method of any one of the preceding embodiments.

[0034] Preferably, the potassium sulfate product has a K2O content of 50.0wt%-51.5wt%, a chloride ion content of less than 0.3wt%, a moisture content of less than 0.5wt%, and a water insoluble content of less than 0.05wt%.

[0035] In a third aspect, the present disclosure provides a potassium fertilizer comprising the potassium sulfate product of the preceding embodiments.

[0036] The present disclosure has the following beneficial effects:

[0037] The present disclosure uses ammonium sulfate solid and potassium chloride solid as raw materials, adds them in two steps for reaction, respectively performs a first reaction and a second reaction, then performs a third reaction with hot water, and then performs crystallization and separation, thereby fully removing impurities in the product and increasing the K2O content in the product. The three-reaction process provided by the present disclosure can prepare a potassium sulfate product with high K2O content and low chlorine content, and the method is simple and easy to implement, and is convenient for industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the present disclosure, and therefore should not be considered as limiting the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0039] FIG. 1 is a process flow diagram of a liquid-phase double decomposition method for preparing potassium sulfate according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be described clearly and completely. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be purchased on the market.

[0041] The embodiments of the present disclosure provide a method for producing potassium sulfate by a double decomposition process. Please refer to FIG. 1, which includes the following steps:

[0042] S1, first reaction

[0043] The solid ammonium sulfate and the solid potassium chloride are used as raw materials, the raw materials are dissolved, and then a first-stage reaction is performed in a solution system, after which the first-stage reaction product is obtained by cooling crystallization and separation. The first-stage reaction product is used in step S2 to perform a second-stage reaction, and the first-stage reaction product mother liquor is used in step S4 to prepare NK fertilizer.

[0044] In some embodiments, the step of the first-stage reaction comprises: mixing and dissolving the solid ammonium sulfate, the second-stage potassium sulfate crude product mother liquor, and water to obtain an ammonium sulfate solution, mixing the ammonium sulfate solution and the solid potassium chloride to perform the first-stage reaction, and then performing cooling crystallization and separation after sufficient reaction at a high temperature to obtain the first-stage potassium sulfate crude product and the first-stage potassium sulfate crude product mother liquor. The second-stage potassium sulfate crude product mother liquor is obtained from the process of separating the second-stage potassium sulfate crude product (i.e., the second-stage potassium sulfate crude product mother liquor). Since the second-stage potassium sulfate crude product mother liquor contains a large amount of ammonium chloride, the second-stage potassium sulfate crude product mother liquor is returned to the first-stage reaction. Since the first-stage potassium sulfate crude product mother liquor is used in step S4 to prepare NK fertilizer, it is beneficial to fully utilize the N in the raw materials.

[0045] In some embodiments, the molar ratio of the solid ammonium sulfate and the solid potassium chloride used in the first-stage reaction is 1:(1.4-2.2), such as 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, 1:2.1, 1:2.2, etc. It is appropriate for the molar ratio of the solid ammonium sulfate and the solid potassium chloride to be within the above range, so that the raw materials are fully reacted and the product yield is improved. The mass ratio of the solid ammonium sulfate, the second-stage potassium sulfate crude product mother liquor, and water can be 1:(2.0-3.2):(0.2-1.0), such as 1:2.0:0.2, 1:2.5:0.5, 1:3.0:0.8, 1:3.2:1.0, etc. By adjusting the amount of the second-stage potassium sulfate crude product mother liquor and water, the solid ammonium sulfate is fully dissolved, and the solid content of the solution is kept relatively appropriate, which promotes the reaction with potassium chloride.

[0046] In some embodiments, when preparing the ammonium sulfate solution, the dissolution temperature is 60-90°C, so that the solid ammonium sulfate is quickly dissolved. This process can be performed in a dissolution tank with a heating device to provide the heat required for dissolution. Specifically, the dissolution temperature can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc.

[0047] In some embodiments, the prepared ammonium sulfate solution and potassium chloride solid are simultaneously added to the reactor, the reaction is stirred, and the temperature of the first-stage reaction is controlled at 60-90°C for 1-3 h to allow the ammonium sulfate and potassium chloride to fully react and improve the utilization of raw materials. Specifically, the first-stage reaction can be carried out in a reactor with a heating device to maintain the reaction temperature as required. The temperature of the first-stage reaction can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc., and the reaction time can be 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, etc.

[0048] Further, after the high-temperature reaction, the solution in the reactor is transferred to a crystallizer, cooled and crystallized, the crystallization temperature is controlled at 30-60°C, and the crystallization time is 1-3 h to allow the potassium sulfate to be precipitated. Specifically, the crystallization temperature can be controlled at 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, etc., and the crystallization time can be 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, etc.

[0049] Further, the system after cooling and crystallization is subjected to solid-liquid separation, which can be carried out in a centrifuge. After separation, a first-stage potassium sulfate crude product and a first-stage potassium sulfate crude product mother liquor are obtained. The K2O content in the obtained first-stage potassium sulfate crude product is 41.0-44.0% (by mass, the same below).

[0050] S2, second-stage reaction

[0051] The first-stage potassium sulfate crude product, ammonium sulfate solid, and potassium chloride solid are used as raw materials, the raw materials are dissolved, and then a second-stage reaction is carried out in the solution system. After crystallization and separation, a second-stage potassium sulfate crude product and a second-stage potassium sulfate crude product mother liquor are obtained. The second-stage potassium sulfate crude product is used in the third-stage reaction, and the second-stage potassium sulfate crude product mother liquor is used to dissolve the ammonium sulfate solid in the first-stage reaction. By adding the ammonium sulfate solid and potassium chloride solid to the reaction kettle in two steps, the reactor efficiency is improved, the reaction degree of potassium chloride and ammonium sulfate is increased, the residence time of the material in the reaction kettle is shortened, the product quality is stable and has a certain degree of improvement. After the second-stage reaction, a second-stage potassium sulfate crude product with higher K2O content can be obtained.

[0052] In some embodiments, the step of the second-stage reaction comprises: mixing and dissolving the ammonium sulfate solid, the potassium sulfate first crude product and the potassium sulfate product mother liquor to obtain a crystal slurry mixed solution, mixing the crystal slurry mixed solution and the potassium chloride solid to perform the second-stage reaction, then cooling and crystallizing to precipitate the potassium sulfate solid, and after separation, obtaining the potassium sulfate second crude product and a potassium sulfate second crude product mother liquor. The potassium sulfate product mother liquor is obtained by crystallization and separation after the third-stage reaction, that is, the potassium sulfate product mother liquor is the mother liquor obtained after the potassium sulfate product is separated. Through the second-stage reaction, the unreacted potassium chloride in the potassium sulfate first crude product and the potassium sulfate product mother liquor can be fully reacted, so that the raw material utilization is more sufficient, the raw material consumption is reduced, and the product quality is improved to a certain extent. By recycling the mother liquor of the three reaction stages in the overall process, the purpose of zero emission is achieved, and the water consumption and process cost are also significantly reduced.

[0053] It should be noted that the traditional second-stage reaction is different from the scheme provided by the embodiments of the present disclosure that the ammonium sulfate solid and the potassium chloride solid are added in two stages. The traditional second-stage reaction is mostly to mix and react the potassium sulfate first crude product and the potassium chloride solution, while the present disclosure is to add the ammonium sulfate solid and the potassium chloride solid in two stages, which can further improve the K2O content in the product, and also can reduce the chlorine content in the product, so that the chlorine content is significantly lower than the existing level, which is conducive to widening the application range of the potassium sulfate product.

[0054] In some embodiments, the molar ratio of the ammonium sulfate solid and the potassium chloride solid used in the second-stage reaction is 1:(1.8-2.8), such as 1:1.8, 1:2.0, 1:2.2, 1:2.5, 1:2.8, etc. By controlling the amount of ammonium sulfate solid and potassium chloride solid used in the second-stage reaction, the K2O content in the potassium sulfate second crude product can be further improved.

[0055] Further, the mass ratio of the ammonium sulfate solid, the potassium sulfate first crude product and the potassium sulfate product mother liquor is 1:(2.2-3.3):(4.8-6.2), such as 1:2.2:4.8, 1:2.5:5.0, 1:2.8:5.1, 1:3.2:6.0, etc. By adjusting the amount of potassium sulfate first crude product and potassium sulfate product mother liquor, the ammonium sulfate solid can be fully dissolved, and the solid content of the solution can also be maintained within a suitable range, which is conducive to the full reaction of ammonium sulfate and potassium chloride. Specifically, the process of dissolving the ammonium sulfate solid can be carried out in a dissolving tank with a heating device to provide the heat required for dissolving.

[0056] Further, when preparing the crystal slurry mixed solution, the ammonium sulfate solid is dissolved with the potassium sulfate product mother liquor, and the crystal slurry mixed solution is heated to 60-90°C to quickly and fully dissolve the ammonium sulfate solid. Specifically, the temperature of the dissolving water can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc.

[0057] Further, the obtained crystal slurry solution and potassium chloride solid are added into the reactor at the same time, and the reaction is stirred, and the temperature of the second-stage reaction is controlled to be 60-90°C, and the reaction time is 1-3 hours, so that the ammonium sulfate and potassium chloride are fully reacted. Specifically, the second-stage reaction can be carried out in a reactor with a heating device to maintain the reaction temperature, and the reaction temperature can be controlled to be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc., and the reaction time can be 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, etc.

[0058] Further, after the reaction is completed, the solution in the reactor is transferred into a crystallizer, and the solution is cooled and crystallized, and the crystallization temperature is controlled to be 30-60°C, and the crystallization time is 1-3 hours, so that the potassium sulfate in the system is precipitated. Specifically, the crystallization temperature can be controlled to be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, etc., and the crystallization time can be 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, etc.

[0059] Further, after the crystallization is completed, solid-liquid separation is performed to obtain the secondary potassium sulfate crude product and the secondary potassium sulfate crude product mother liquor. The solid-liquid separation method is not limited, and a centrifuge can be used for separation, but is not limited thereto. The K2O content of the secondary potassium sulfate crude product prepared by the disclosed embodiment is 45.0-48.0%.

[0060] S3, third-stage reaction

[0061] The secondary potassium sulfate crude product obtained in step S2 is mixed with hot water with a temperature of 80-98°C, and a third-stage reaction is performed, and after the high-temperature reaction, crystallization and separation are performed. Through the third-stage reaction, the K2O content in the product can be further improved, and the chlorine content in the product can be reduced.

[0062] In some embodiments, the secondary potassium sulfate crude product and hot water with a temperature meeting the requirements are added into the reactor, and the reaction is stirred, and the reaction temperature of the third-stage reaction is controlled to be 60-90°C, and the reaction time is 0.5-2.0 hours, so that the K2O content in the product can be further improved. Specifically, the temperature of the hot water used in the third-stage reaction can be 80°C, 85°C, 90°C, 95°C, 98°C, etc., the reaction temperature of the third-stage reaction can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, etc., and the reaction time can be 0.5h, 1.0h, 1.5h, 2.0h, etc., and the reaction process can be carried out in a reactor with a heating device to maintain the reaction temperature to meet the requirements.

[0063] In some embodiments, the mass ratio of the secondary potassium sulfate crude product to hot water is 1:(0.8-1.2), such as 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, etc. By adjusting the amount of hot water, the solid content before the reaction is more suitable, achieving the purpose of high-temperature water washing, and further improving the K2O content of the product. In order to obtain a potassium sulfate product with higher K2O content, the hot water and potassium chloride can be mixed to obtain a potassium chloride solution with a mass fraction of 1%-30%, and the potassium chloride solution is used for mixing reaction with the secondary potassium sulfate crude product.

[0064] Further, after the reaction with hot water is completed, the solution in the reactor is transferred into a crystallizer, and cooling and crystallization are performed to control the crystallization temperature to be 30-60°C and the crystallization time to be 1-3h, so that the potassium sulfate in the solution is precipitated. Specifically, the crystallization temperature can be 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, etc., and the crystallization time can be 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, etc.

[0065] Further, after the cooling and crystallization are completed, solid-liquid separation is performed to obtain a potassium sulfate wet product and a potassium sulfate product mother liquor. The potassium sulfate wet product is dried to obtain a potassium sulfate product with a water content meeting the requirements, and the potassium sulfate product mother liquor is used for dissolving ammonium sulfate solids in the second-stage reaction. The solid-liquid separation method is not limited and can be performed by using a centrifugal machine, but is not limited thereto.

[0066] It is detected that the K2O content of the potassium sulfate product prepared by the embodiments of the present disclosure is 50.0wt%-51.5wt%, the chloride ion content is less than 0.3wt%, the water content is less than 0.5wt%, and the water-insoluble content is less than 0.05wt%. The total yield of potassium oxide is greater than 75% based on the potassium sulfate product; and the total yield of potassium is greater than 99.9% based on the potassium sulfate and NK fertilizer product.

[0067] It should be noted that the process provided by the embodiments of the present disclosure has undergone pilot tests, and the product meets the above requirements. In many existing technologies, the process for preparing potassium sulfate from ammonium sulfate and potassium chloride as raw materials cannot meet the product requirements claimed by industrial tests, such as a K2O content that does not meet the standard, which is far lower than the product level obtained in the laboratory stage.

[0068] S4, preparation of NK fertilizer

[0069] The primary potassium sulfate crude product mother liquor is used for preparing NK fertilizer by-products, the primary potassium sulfate crude product mother liquor is further recovered, NK fertilizer by-products are produced, the utilization rate of raw materials is improved, and zero emission of the overall process is achieved.

[0070] In some embodiments, the potassium sulfate once crude mother liquor is concentrated by evaporation to obtain a concentrated NK fertilizer mother liquor, the concentrated NK fertilizer mother liquor is crystallized and separated to obtain NK fertilizer wet product and NK fertilizer mother liquor, the NK fertilizer wet product is dried to obtain NK fertilizer product, and the NK fertilizer mother liquor is recycled to the evaporation concentration stage. By further optimizing the process of preparing NK fertilizer by-products, the utilization rate of raw materials can be improved, and the K2O content of the obtained NK fertilizer product is higher. The NK fertilizer by-product production technology is mature, simple to operate, and the by-products can be used for sale, thereby reducing costs and improving economic benefits.

[0071] In some embodiments, the evaporation concentration method is not limited, and a traditional three-effect evaporation concentration process can be used, but is not limited thereto. The concentrated NK fertilizer mother liquor obtained after concentration is introduced into a cooling crystallizer, cooled, and a concentrated NK fertilizer crystal slurry solution is obtained. The concentrated NK fertilizer crystal slurry solution is separated to obtain NK fertilizer wet product and NK fertilizer mother liquor. The separation method is not limited, and a centrifugal method can be used, but is not limited thereto.

[0072] It is detected that the nutrient (N+K2O) content of the NK fertilizer product prepared in the embodiments of the present disclosure is greater than 34%, and the moisture content is less than 1.0%.

[0073] The production device used in the process method provided in the embodiments of the present disclosure can adopt various forms. For example, the reactor can adopt various forms, such as a bottom stirring reactor, a top stirring reactor, a jacketed reactor, an external circulation reactor, etc.; the crystallizer can adopt various forms, such as a bottom stirring crystallizer, a top stirring crystallizer, a jacketed crystallizer, an external circulation crystallizer, etc.; the evaporation system can also adopt various forms, such as a two- or three-effect countercurrent evaporation system, a two- or three-effect cocurrent evaporation system, etc.; and the drying equipment can adopt various forms of dryers, such as a fluidized bed (boiling bed) dryer, a disc dryer, an air flow dryer, etc.

[0074] The embodiments of the present disclosure provide a potassium sulfate product prepared by the method provided in the embodiments of the present disclosure. The K2O content of the potassium sulfate product is greater than 50wt%, the chlorine content is less than 1wt%, and the water content is less than 1.0wt%, which meets the requirements of GBT 20406-2017 agricultural potassium sulfate (see Table 1 for specific requirements).

[0075] Table 1 Requirements for agricultural potassium sulfate

[0076] The embodiments of the present disclosure also provide a potassium fertilizer including the potassium sulfate product. Since the K2O content of the potassium sulfate product is high and the chlorine content is low, the application range of the potassium fertilizer is wider.

[0077] The features and performances of the present disclosure are further described in detail below in combination with embodiments.

[0078] Example 1

[0079] The present embodiment provides a method for producing potassium sulfate by a double decomposition process, comprising the following steps:

[0080] (1) Ammonium sulfate solid, potassium sulfate secondary crude mother liquor and hot water at 95℃ are simultaneously added into a dissolving tank, and stirred and dissolved at 85℃ to obtain an ammonium sulfate solution. The mass ratio of the ammonium sulfate solid, the potassium sulfate secondary crude mother liquor and the water is 1:2.2:0.8, and the potassium sulfate mother liquor is from step (2). The ammonium sulfate solution and potassium chloride solid are simultaneously added into a reactor, stirred and reacted, the reaction temperature is 80℃, the reaction time is 1 hour, and the molar ratio of the ammonium sulfate solid and the potassium chloride solid is 1.0:1.8. The solution in the reactor enters a crystallizer, and is cooled and crystallized, the crystallization temperature is 50℃, and the crystallization time is 1 hour. The solution after the cooling and crystallization is completed enters a centrifuge to separate potassium sulfate primary crude and potassium sulfate primary crude mother liquor. The potassium sulfate primary crude enters step (2), and the potassium sulfate primary crude mother liquor goes to step (4) to prepare NK fertilizer by-products.

[0081] (2) The ammonium sulfate solid, the potassium sulfate primary crude and the potassium sulfate product mother liquor (from step (3)) are mixed, and stirred and dissolved at 85℃ to prepare a crystal slurry mixed solution. The mass ratio of the ammonium sulfate solid, the potassium sulfate primary crude and the potassium sulfate product mother liquor is 1:2.7:5.0. The crystal slurry mixed solution and potassium chloride solid are simultaneously added into a reactor, stirred and reacted, the reaction temperature is 80℃, the reaction time is 1 hour, and the molar ratio of the ammonium sulfate solid and the potassium chloride solid added in step (2) is 1:2.5. The solution in the reactor enters a crystallizer, and is cooled and crystallized, the crystallization temperature is 50℃, and the crystallization time is 1 hour. The solution after the cooling and crystallization is completed enters a centrifuge to separate potassium sulfate secondary crude and potassium sulfate secondary crude mother liquor. The potassium sulfate secondary crude enters step (3), and the potassium sulfate secondary crude mother liquor is recycled.

[0082] (3) The potassium sulfate secondary crude obtained in step (2) and hot water at 95℃ are mixed according to a mass ratio of 1:0.9, and simultaneously added into a reactor, stirred and reacted, the reaction temperature is 80℃, and the reaction time is 1 hour. The solution in the reactor enters a crystallizer, and is cooled and crystallized, the crystallization temperature is 50℃, and the crystallization time is 1 hour. The solution after the cooling and crystallization is completed enters a centrifuge to separate potassium sulfate wet product and potassium sulfate product mother liquor. The potassium sulfate wet product is dried, and the potassium sulfate product mother liquor is recycled. The potassium sulfate wet product is dried by a dryer to obtain potassium sulfate product, the drying temperature is controlled at 110℃, and the drying time is 0.5-1h.

[0083] The K2O content of the potassium sulfate product is 50.8%, and the moisture content is 0.3%. The total yield of potassium oxide is 75.5% based on the potassium sulfate product. The potassium sulfate product can be completely dissolved, and the water-insoluble content is 0.03% (detection reference GB 6549-2011 Determination of water-insoluble content in potassium chloride). The chloride ion content in the potassium sulfate product is detected, and the detection result shows that the chloride ion content is 0.08%.

[0084] (4) The potassium sulfate primary crude product mother liquor obtained in step (1) is concentrated by three-effect evaporation to obtain a concentrated NK fertilizer mother liquor. The concentrated NK fertilizer mother liquor enters a cooling crystallizer, is cooled, and a concentrated NK fertilizer crystal slurry solution is obtained. The concentrated NK fertilizer crystal slurry solution is separated to obtain an NK fertilizer wet product and an NK fertilizer mother liquor. The NK fertilizer mother liquor is recycled to the three-effect evaporation concentration stage. The NK fertilizer wet product is dried by a dryer to obtain an NK fertilizer product.

[0085] The total N content of the NK fertilizer product is greater than 17.4%, the K2O content is greater than 17.9%, and the moisture content is 0.4%.

[0086] Example 2 (improve the reaction temperature of the dissolving tank and the reactor relative to example 1)

[0087] The present embodiment provides a method for producing potassium sulfate by a double decomposition process, comprising the following steps:

[0088] (1) Ammonium sulfate solid, potassium sulfate secondary crude product mother liquor, and hot water at 95°C are simultaneously added to a dissolving tank, and are stirred and dissolved at 95°C to obtain an ammonium sulfate solution. The mass ratio of the ammonium sulfate solid, the potassium sulfate secondary crude product mother liquor, and the water is 1:2.2:0.8, and the potassium sulfate mother liquor is from step (2). The ammonium sulfate solution and potassium chloride solid are simultaneously added to a reactor, and are stirred and reacted at a reaction temperature of 95°C for 1 hour. The molar ratio of the ammonium sulfate solid and the potassium chloride solid is 1.0:1.8. The solution in the reactor enters a crystallizer, is cooled and crystallized at a crystallization temperature of 50°C for 1 hour. The solution after cooling and crystallization enters a centrifuge to separate potassium sulfate primary crude product and potassium sulfate primary crude product mother liquor. The potassium sulfate primary crude product enters step (2), and the potassium sulfate primary crude product mother liquor is used to prepare an NK fertilizer by-product in step (4).

[0089] (2) The ammonium sulfate solid, the potassium sulfate primary crude product and the potassium sulfate product mother liquor (from step (3)) are mixed, dissolved by stirring at 95°C, and a crystal slurry mixed solution is prepared. The mass ratio of the ammonium sulfate solid, the potassium sulfate primary crude product and the potassium sulfate product mother liquor is 1:2.7:5.0. The crystal slurry mixed solution and the potassium chloride solid are simultaneously added to a reactor, stirred and reacted, the reaction temperature is 95°C, the reaction time is 1 hour, and the molar ratio of the ammonium sulfate solid and the potassium chloride solid added in step (2) is 1:2.5. The solution in the reactor is introduced into a crystallizer, cooled and crystallized, the crystallization temperature is 50°C, and the crystallization time is 1 hour. After the cooling and crystallization are completed, the solution is introduced into a centrifuge to separate the potassium sulfate secondary crude product and a potassium sulfate secondary crude product mother liquor. The potassium sulfate secondary crude product is introduced into step (3), and the potassium sulfate secondary crude product mother liquor is recycled.

[0090] (3) The potassium sulfate secondary crude product obtained in step (2) and hot water at 95°C are dosed according to a mass ratio of 1:0.9, and simultaneously added to a reactor, stirred and reacted, the reaction temperature is 95°C, and the reaction time is 1 hour. The solution in the reactor is introduced into a crystallizer, cooled and crystallized, the crystallization temperature is 50°C, and the crystallization time is 1 hour. After the cooling and crystallization are completed, the solution is introduced into a centrifuge to separate the potassium sulfate wet product and a potassium sulfate product mother liquor. The potassium sulfate wet product is dried, and the potassium sulfate product mother liquor is recycled.

[0091] The potassium sulfate wet product is dried by a dryer to obtain the potassium sulfate product, the drying temperature is controlled to be 110°C, and the drying time is 0.5-1h.

[0092] It is detected that the K2O content of the potassium sulfate product is 51.1%, and the moisture content is 0.3%. The total yield of potassium oxide reaches 75.2% based on the potassium sulfate product. The potassium sulfate product can be completely dissolved through a dissolution test, and the water-insoluble content is 0.03% (detection reference: determination of water-insoluble content in potassium chloride in GB 6549-2011). The chloride ion content in the potassium sulfate product is detected, and the detection result shows that the chloride ion content is 0.06%.

[0093] (4) The same as step (4) of example 1.

[0094] It is detected that the total N content of the NK fertilizer product is greater than 17.5%, the K2O content is greater than 17.6%, and the moisture content is 0.4%.

[0095] Example 3 (decrease the crystallization temperature of the crystallizer relative to example 1)

[0096] The example provides a method for producing potassium sulfate by a double decomposition process, including the following steps:

[0097] (1) Ammonium sulfate solid, potassium sulfate secondary crude mother liquor and hot water at 95℃ are simultaneously added into a dissolving tank, and dissolved under stirring at 85℃ to obtain an ammonium sulfate solution. The mass ratio of the ammonium sulfate solid, the potassium sulfate secondary crude mother liquor and the water is 1:2.1:0.8, and the potassium sulfate mother liquor is from step (2). The ammonium sulfate solution and potassium chloride solid are simultaneously added into a reactor, and reacted under stirring. The reaction temperature is 80℃, the reaction time is 1 hour, and the molar ratio of the ammonium sulfate solid to the potassium chloride solid is 1.0:1.8. The solution in the reactor is introduced into a crystallizer, and crystallized under cooling. The crystallization temperature is 40℃, and the crystallization time is 1 hour. The solution after the completion of the cooling crystallization is introduced into a centrifuge to separate potassium sulfate primary crude and potassium sulfate primary crude mother liquor. The potassium sulfate primary crude is introduced into step (2), and the potassium sulfate primary crude mother liquor is introduced into step (4) to prepare NK fertilizer by-products.

[0098] (2) Ammonium sulfate solid, potassium sulfate primary crude and potassium sulfate product mother liquor (from step (3)) are mixed, and dissolved under stirring at 85℃ to prepare a crystal slurry mixed solution. The mass ratio of the ammonium sulfate solid, the potassium sulfate primary crude and the potassium sulfate product mother liquor is 1:2.7:4.8. The crystal slurry mixed solution and potassium chloride solid are simultaneously added into a reactor, and reacted under stirring. The reaction temperature is 80℃, the reaction time is 1 hour, and the molar ratio of the ammonium sulfate solid to the potassium chloride solid added in step (2) is 1:2.5. The solution in the reactor is introduced into a crystallizer, and crystallized under cooling. The crystallization temperature is 40℃, and the crystallization time is 1 hour. The solution after the completion of the cooling crystallization is introduced into a centrifuge to separate potassium sulfate secondary crude and potassium sulfate secondary crude mother liquor. The potassium sulfate secondary crude is introduced into step (3), and the potassium sulfate secondary crude mother liquor is recycled.

[0099] (3) The potassium sulfate secondary crude obtained in step (2) and hot water at 95℃ are simultaneously added into a reactor according to a mass ratio of 1:0.9, and reacted under stirring. The reaction temperature is 80℃, and the reaction time is 1 hour. The solution in the reactor is introduced into a crystallizer, and crystallized under cooling. The crystallization temperature is 40℃, and the crystallization time is 1 hour. The solution after the completion of the cooling crystallization is introduced into a centrifuge to separate potassium sulfate wet product and potassium sulfate product mother liquor. The potassium sulfate wet product is dried, and the potassium sulfate product mother liquor is recycled. The potassium sulfate wet product is dried by a dryer to obtain potassium sulfate product. The drying temperature is controlled at 110℃, and the drying time is 0.5-1h.

[0100] The K2O content of the potassium sulfate product was detected to be 50.5%, and the moisture content was 0.3%. The total yield of potassium oxide was 76.5% based on the potassium sulfate product. The potassium sulfate product can be completely dissolved, and the water-insoluble content was 0.04% (detection reference GB 6549-2011 Determination of Water-insoluble Content in Potassium Chloride). The chloride ion content in the potassium sulfate product was detected, and the detection results showed that the chloride ion content was 0.25%.

[0101] (4) The same as step (4) of Example 1.

[0102] The total N content of the NK fertilizer product was greater than 17.4%, the K2O content was greater than 17.9%, and the moisture content was 0.4%.

[0103] Example 4 (change the ratio of raw materials ammonium sulfate and potassium chloride in steps 1 and 2 relative to Example 1)

[0104] The present embodiment provides a method for producing potassium sulfate by a double decomposition process, comprising the following steps:

[0105] (1) Ammonium sulfate solid, potassium sulfate secondary crude product mother liquor and hot water at 95℃ are simultaneously added to a dissolving tank, and stirred and dissolved at 85℃ to obtain an ammonium sulfate solution. The mass ratio of ammonium sulfate solid, potassium sulfate secondary crude product mother liquor and water is 1:2.3:0.8, and the potassium sulfate mother liquor is from step (2). The ammonium sulfate solution and potassium chloride solid are simultaneously added to a reactor, stirred and reacted, the reaction temperature is 80℃, the reaction time is 1 hour, and the molar ratio of ammonium sulfate solid to potassium chloride solid is 1.0:2.0. The solution in the reactor enters a crystallizer, and is cooled and crystallized, the crystallization temperature is 50℃, and the crystallization time is 1 hour. The solution after cooling and crystallization is separated by a centrifuge to obtain potassium sulfate primary crude product and potassium sulfate primary crude product mother liquor. The potassium sulfate primary crude product enters step (2), and the potassium sulfate primary crude product mother liquor is used to prepare NK fertilizer by-product in step (4).

[0106] (2) Ammonium sulfate solid, potassium sulfate primary crude product and potassium sulfate product mother liquor (from step (3)) are mixed, and stirred and dissolved at 85℃ to prepare a crystal slurry mixed solution. The mass ratio of ammonium sulfate solid, potassium sulfate primary crude product and potassium sulfate product mother liquor is 1:2.7:5.2. The crystal slurry mixed solution and potassium chloride solid are simultaneously added to a reactor, stirred and reacted, the reaction temperature is 80℃, the reaction time is 1 hour, and the molar ratio of ammonium sulfate solid to potassium chloride solid added in step (2) is 1:2.7. The solution in the reactor enters a crystallizer, and is cooled and crystallized, the crystallization temperature is 50℃, and the crystallization time is 1 hour. The solution after cooling and crystallization is separated by a centrifuge to obtain potassium sulfate secondary crude product and potassium sulfate secondary crude product mother liquor. The potassium sulfate secondary crude product enters step (3), and the potassium sulfate secondary crude product mother liquor is recycled.

[0107] (3) Same as step (3) of example 1.

[0108] The K2O content of the potassium sulfate product was detected to be 50.6%, and the moisture content was 0.3%. The total yield of potassium oxide was 75.1% based on the potassium sulfate product. The potassium sulfate product could be completely dissolved, and the water-insoluble content was 0.04% (detection reference: determination of water-insoluble content in potassium chloride in GB 6549-2011). The chloride ion content in the potassium sulfate product was detected, and the detection result showed that the chloride ion content was 0.28%.

[0109] (4) Same as step (4) of example 1.

[0110] The total N content of the NK fertilizer product was greater than 17.2%, the K2O content was greater than 18.2%, and the moisture content was 0.4%.

[0111] Example 5: (relative to example 1, the amount of hot water is increased, and the mass ratio of the secondary potassium sulfate crude product to hot water is increased)

[0112] The present embodiment provides a method for producing potassium sulfate by a double decomposition process, comprising the following steps:

[0113] (1) Same as step (1) of example 1.

[0114] (2) Same as step (2) of example 1.

[0115] (3) The secondary potassium sulfate crude product obtained in step (2) and hot water at 95°C were mixed according to a mass ratio of 1:1.2 and simultaneously added to the reactor, and stirred and reacted, with a reaction temperature of 80°C and a reaction time of 1 hour. The solution in the reactor was transferred to a crystallizer, and cooled and crystallized, with a crystallization temperature of 50°C and a crystallization time of 1 hour. After the cooling and crystallization was completed, the solution was separated by a centrifuge to obtain a potassium sulfate wet product and a potassium sulfate product mother liquor. The potassium sulfate wet product was dried, and the potassium sulfate product mother liquor was recycled. The potassium sulfate wet product was dried by a dryer, to obtain a potassium sulfate product, with a drying temperature controlled at 110°C and a drying time of 0.5-1h.

[0116] The K2O content of the potassium sulfate product was detected to be 51.5%, and the moisture content was 0.3%. The total yield of potassium oxide was 75.1% based on the potassium sulfate product. The potassium sulfate product could be completely dissolved, and the water-insoluble content was 0.02% (detection reference: determination of water-insoluble content in potassium chloride in GB 6549-2011). The chloride ion content in the potassium sulfate product was detected, and the detection result showed that the chloride ion content was 0.04%.

[0117] (4) Same as step (4) of example 1.

[0118] Tests showed that the NK fertilizer product had a total N content greater than 17.3%, a K2O content greater than 17.7%, and a moisture content of 0.4%.

[0119] Example 6: (Compared to Example 1, in step (3), potassium chloride is first added to the water to prepare a potassium chloride solution, and then the crude potassium sulfate is washed twice.)

[0120] This embodiment provides a method for producing potassium sulfate using a metathesis process, including the following steps:

[0121] (1) Same as step (1) in Example 1.

[0122] (2) Same as step (2) in Example 1.

[0123] (3) The secondary crude potassium sulfate obtained in step (2) and hot water at 95°C are mixed at a mass ratio of 1:0.9. Hot water is added to the dissolving tank first, followed by solid potassium chloride, to prepare a 10% potassium chloride solution at 85°C. The pre-prepared potassium chloride solution and the secondary crude potassium sulfate are simultaneously added to the reactor, stirred, and reacted at 80°C for 1 hour. The solution in the reactor is then transferred to a crystallizer for cooling and crystallization at 50°C for 1 hour. After crystallization, the solution is centrifuged to separate the potassium sulfate wet product and the potassium sulfate mother liquor. The potassium sulfate wet product is dried, and the potassium sulfate mother liquor is recycled. The potassium sulfate wet product is dried in a dryer to obtain the potassium sulfate product, with the drying temperature controlled at 110°C and the drying time at 0.5-1 hour.

[0124] Testing revealed that the potassium sulfate product contained 51.2% K₂O and 0.3% moisture. The total yield of potassium oxide, based on the potassium sulfate product, reached 75.2%. Dissolution tests showed that the potassium sulfate product was completely soluble, with water-insoluble matter content measured at 0.05% (testing referenced GB 6549-2011, Determination of Water-Insoluble Matter Content in Potassium Chloride). The chloride ion content in the potassium sulfate product was measured at 0.39%.

[0125] (4) Same as step (4) in Example 1.

[0126] Tests showed that the NK fertilizer product had a total N content greater than 17.2%, a K2O content greater than 18.1%, and a moisture content of 0.4%.

[0127] Comparative Example 1

[0128] The main difference from Example 1 is that the reaction is a two-step process, without step (3), and both solid ammonium sulfate and solid potassium chloride are added in the first step. A 10% KCl solution is introduced in step (2) for the reaction.

[0129] The specific steps are as follows:

[0130] (1) Ammonium sulfate solid, potassium sulfate mother liquor and hot water at 95℃ are simultaneously added into a dissolving tank, and dissolved under stirring at 85℃ to obtain an ammonium sulfate solution. The mass ratio of the ammonium sulfate solid, the potassium sulfate product mother liquor and the water is 1:2.2:0.8, and the potassium sulfate product mother liquor is from step (2). The ammonium sulfate solution and potassium chloride solid are simultaneously added into a reactor, and reacted under stirring. The reaction temperature is 80℃, the reaction time is 1 hour, and the molar ratio of the ammonium sulfate solid and the potassium chloride solid is 1.0:2.0. The solution in the reactor is introduced into a crystallizer, and crystallized under cooling. The crystallization temperature is 50℃, and the crystallization time is 1 hour. The solution after the completion of the cooling crystallization is introduced into a centrifuge to separate potassium sulfate crude product and potassium sulfate crude product mother liquor. The potassium sulfate crude product is introduced into step (2), and the potassium sulfate crude product mother liquor is used to prepare NK fertilizer by-products.

[0131] (2) The potassium sulfate crude product obtained in step (1) and hot water at 95℃ are mixed according to a mass ratio of 1:1.4. Hot water is first added into a dissolving tank, and then potassium chloride solid is added to prepare a 10% KCl solution at 85℃. The potassium sulfate crude product is then added into the 10% KCl solution, and reacted at 80℃ for 1 hour. The solution in the reactor is introduced into a crystallizer, and crystallized under cooling. The crystallization temperature is 50℃, and the crystallization time is 1 hour. The solution after the completion of the cooling crystallization is introduced into a centrifuge to separate potassium sulfate wet product and potassium sulfate product mother liquor. The potassium sulfate is dried by a dryer to obtain potassium sulfate product. The drying temperature is controlled at 110℃, and the drying time is 0.5-1 hour. The potassium sulfate product mother liquor is recycled.

[0132] It is detected that the K2O content of the potassium sulfate product reaches 50.1%. The total yield of potassium oxide is 70.2% based on the potassium sulfate product. The potassium sulfate product can be completely dissolved according to a dissolution test, and the water-insoluble content is 0.05% (detection reference: determination of water-insoluble content in potassium chloride in GB 6549-2011). The chloride ion content in the potassium sulfate product is detected, and the detection result shows that the chloride ion content is 0.45%.

[0133] Although the K2O content of the product can reach 50.0% which meets the first-grade product requirement of the national standard of potassium sulfate by using the two-step method, the total yield of potassium oxide is low due to the large amount of water used in the two-step method.

[0134] Comparative Example 2

[0135] The main difference from Example 1 is that the two-step method is used, step (3) is not performed, and the ammonium sulfate solid and the potassium chloride solid are both added in the first step. The potassium sulfate crude product is directly washed with water in step (2).

[0136] The specific steps are as follows:

[0137] (1) Ammonium sulfate solid, potassium sulfate mother liquor and hot water at 95℃ are simultaneously added into a dissolving tank, and stirred and dissolved at 85℃ to obtain an ammonium sulfate solution. The mass ratio of the ammonium sulfate solid, the potassium sulfate product mother liquor and the water is 1:2.2:0.8, and the potassium sulfate product mother liquor is from step (2). The ammonium sulfate solution and potassium chloride solid are simultaneously added into a reactor, and stirred and reacted at a reaction temperature of 80℃ for 1 hour. The molar ratio of the ammonium sulfate solid and the potassium chloride solid is 1.0:2.0. The solution in the reactor is introduced into a crystallizer, and cooled and crystallized at a crystallization temperature of 50℃ for 1 hour. The solution after the cooling and crystallization is introduced into a centrifuge to separate a potassium sulfate crude product and a potassium sulfate crude product mother liquor. The potassium sulfate crude product is introduced into step (2), and the potassium sulfate crude product mother liquor is used to prepare a NK fertilizer by-product.

[0138] (2) The potassium sulfate crude product obtained in step (1) and hot water at 95℃ are mixed according to a mass ratio of 1:1.4. Hot water is first added into a dissolving tank, and then the potassium sulfate crude product is added. The solution is reacted at 80℃ for 1 hour. The solution in the reactor is introduced into a crystallizer, and cooled and crystallized at a crystallization temperature of 50℃ for 1 hour. The solution after the cooling and crystallization is introduced into a centrifuge to separate a potassium sulfate wet product and a potassium sulfate product mother liquor. The potassium sulfate is dried by a dryer to obtain a potassium sulfate product. The drying temperature is controlled at 110℃, and the drying time is 0.5-1 hour. The potassium sulfate product mother liquor is recycled.

[0139] It is detected that the K2O content of the potassium sulfate product reaches 48.2%. The total yield of potassium oxide is 69.5% based on the potassium sulfate product. The potassium sulfate product can be completely dissolved by a dissolution test, and the water insoluble content is 0.06% (detection reference: determination of water insoluble content in potassium chloride in GB 6549-2011). The chloride ion content in the potassium sulfate product is detected, and the detection result shows that the chloride ion content is 0.45%.

[0140] The K2O content of the product does not reach 50.0% required by the national standard first-grade potassium sulfate by using the two-step method. Meanwhile, the total yield of potassium oxide is also low due to the large amount of water used in the two-step method.

[0141] Comparative Example 3

[0142] The difference from Example 1 is that the high-temperature water is not used for washing in step (3), and the low-temperature water is used for washing, and then separated and dried directly.

[0143] The specific steps are as follows:

[0144] (1) The same as step (1) in Example 1.

[0145] (2) The same as step (2) in Example 1.

[0146] (3) The secondary potassium sulfate crude product obtained in step (2) and hot water at 60°C were mixed according to a mass ratio of 1:0.9, and water washing was performed at 50°C. After 1 hour of reaction, the wet potassium sulfate product and the potassium sulfate product mother liquor were separated by centrifugation. The wet potassium sulfate product was dried, and the potassium sulfate product mother liquor was recycled. The dried crystals (drying temperature and time were the same as in Example 1) were obtained to obtain the potassium sulfate product.

[0147] The K2O content of the potassium sulfate product was detected to be 49.1%. The total yield of potassium oxide was 76.1% based on the potassium sulfate product. The potassium sulfate product was tested by a dissolution test, and the water-insoluble content was detected to be 0.07% (detection reference: determination of water-insoluble content in potassium chloride in GB 6549-2011). The chloride ion content in the potassium sulfate product was detected, and the detection results showed that the chloride ion content was 0.42%.

[0148] The method uses low-temperature washing, and the K2O content of the product does not reach the 50.0% requirement of the first-grade potassium sulfate in the national standard.

[0149] Comparative Example 4

[0150] The difference from Example 1 is that, in step (3), after washing with hot water, no crystallization is performed, and the product is directly separated and dried.

[0151] The specific steps are as follows:

[0152] (1) The same as step (1) in Example 1.

[0153] (2) The same as step (2) in Example 1.

[0154] (3) The secondary potassium sulfate crude product obtained in step (2) and hot water at 95°C were mixed according to a mass ratio of 1:0.9, and water washing was performed at 80°C. After 1 hour of reaction, the wet potassium sulfate product and the potassium sulfate product mother liquor were separated by centrifugation. The wet potassium sulfate product was dried, and the potassium sulfate product mother liquor was recycled. The dried crystals (drying temperature and time were the same as in Example 1) were obtained to obtain the potassium sulfate product.

[0155] The K2O content of the potassium sulfate product was detected to be 51.3%. The total yield of potassium oxide was 67% based on the potassium sulfate product. The potassium sulfate product was tested by a dissolution test, and the water-insoluble content was detected to be 0.04% (detection reference: determination of water-insoluble content in potassium chloride in GB 6549-2011). The chloride ion content in the potassium sulfate product was detected, and the detection results showed that the chloride ion content was 0.06%.

[0156] The method uses high-temperature washing, and the product quality is good, but the total yield of potassium oxide is low because no low-temperature crystallization is performed.

[0157] Comparative Example 5

[0158] The difference from Example 1 is that the reaction of step (2) and step (3) is not carried out, and a traditional one-step reaction process is adopted, in which the ammonium sulfate solution and potassium chloride solution are reacted.

[0159] The specific steps are as follows:

[0160] (1) Ammonium sulfate solid and hot water at 95°C are simultaneously added to a dissolving tank, stirred and dissolved to obtain an ammonium sulfate solution. The mass ratio of ammonium sulfate solid to water is 1:2.4. The ammonium sulfate solution and potassium chloride solid are simultaneously added to a reactor, stirred and reacted. The reaction temperature is 80°C, the reaction time is 1 hour, and the molar ratio of ammonium sulfate solid to potassium chloride solid is 1.0:2.0.

[0161] (2) The solution in the reactor enters a crystallizer, is cooled and crystallized, the crystallization temperature is 50°C, and the crystallization time is 1 hour. The solution after cooling and crystallization enters a centrifuge to separate to obtain potassium sulfate wet product and potassium sulfate mother liquor.

[0162] (3) The potassium sulfate wet product is dried, and the dried crystals (drying temperature and time are the same as in Example 1) are obtained to obtain potassium sulfate product.

[0163] The detection shows that the K2O content of the potassium sulfate product reaches 44.5%. The total yield of potassium oxide is 69.5% based on the potassium sulfate product. The potassium sulfate product can be completely dissolved according to the dissolution test, and the water-insoluble content is 0.09% (detection reference: determination of water-insoluble content in potassium chloride in GB 6549-2011). The detection of chloride ion content in the potassium sulfate product shows that the chloride ion content is 1.9%.

[0164] The product quality is poor, the K2O content is low, and the chloride ion content is high by using the traditional one-step method to react the ammonium sulfate solution and potassium chloride solid. Further purification is needed to prepare a product that meets the national standard requirements of potassium sulfate.

[0165] Comparative Example 6

[0166] The difference from Example 1 is that the reaction of step (2) and step (3) is not carried out, and a traditional one-step reaction process is adopted, in which the ammonium sulfate solution and potassium chloride solution are reacted.

[0167] The specific steps are as follows:

[0168] (1) Ammonium sulfate solid and hot water at 95℃ are simultaneously added into a dissolving tank, stirred and dissolved to obtain an ammonium sulfate solution, wherein the mass ratio of the ammonium sulfate solid to water is 1:1.36. Potassium chloride solid and hot water at 95℃ are simultaneously added into a dissolving tank, stirred and dissolved to obtain a potassium chloride solution, wherein the mass ratio of the potassium chloride solid to water is 1:2.28. The ammonium sulfate solution and the potassium chloride solution are simultaneously added into a reactor, stirred and reacted, the reaction temperature is 80℃, the reaction time is 1 hour, and the molar ratio of the ammonium sulfate solid to the potassium chloride solid is 1.0:2.0.

[0169] (2) The solution in the reactor is introduced into a crystallizer, cooled, crystallized, the crystallization temperature is 50℃, and the crystallization time is 1 hour. The solution after the cooling and crystallization is introduced into a centrifuge to separate to obtain a potassium sulfate wet product and a potassium sulfate mother liquor. The potassium sulfate wet product is dried to obtain a potassium sulfate product.

[0170] It is detected that the K2O content of the potassium sulfate product reaches 50.5%. The total yield of potassium oxide is 36.8% based on the potassium sulfate product. The potassium sulfate product can be completely dissolved through a dissolution test, and the water-insoluble content is 0.02% (detection reference: determination of water-insoluble content in potassium chloride in GB 6549-2011). The chloride ion content in the potassium sulfate product is detected, and the detection result shows that the chloride ion content is 0.30%.

[0171] In the one-step method, the ammonium sulfate solution and the potassium chloride solution are reacted, the product quality can reach 50.0% of the first-grade product of the national standard of potassium sulfate, but the yield of potassium oxide is extremely low.

[0172] In summary, the method for producing potassium sulfate provided by the disclosed embodiments, the potassium sulfate product and the potassium fertilizer are prepared from potassium chloride and ammonium sulfate through three steps, and the potassium sulfate product with a K2O content greater than 50% is obtained.

[0173] The product has the following advantages:

[0174] (1) The potassium oxide content of the prepared potassium sulfate product can reach greater than 50wt% (50-52%), the chlorine content is less than 1wt% (may be less than 0.3%), the water content is less than 1.0wt%, and the water-insoluble content is less than 0.05%, which is higher than the requirement of the first-grade product of the national standard GBT 20406-2017 agricultural potassium sulfate crystalline.

[0175] (2) The yield of potassium oxide is greater than 75% based on the potassium sulfate main product; the yield of potassium oxide reaches more than 99.9% based on the potassium sulfate product and the NK fertilizer; and the nutrient (N+K2O) content of the byproduct NK fertilizer is greater than 34%, which meets the market demand and can be directly sold as a binary compound fertilizer.

[0176] (3) The potassium sulfate product prepared by the present disclosure is a fully water-soluble product, and the water-insoluble content is less than 0.05%. The potassium sulfate product produced by the Mannheim method on the current market contains calcium insoluble due to the addition of stone powder (calcium carbonate and calcium hydroxide) to neutralize the unreacted sulfuric acid during the reaction, and the water-insoluble content of the product is about 0.2-0.5%, which cannot achieve full water solubility. It will block the sprayer and block the pipeline after a long time. If you want to be fully water-soluble, you must use potassium hydroxide or potassium carbonate to neutralize sulfuric acid, resulting in high cost. The potassium sulfate product prepared by the present disclosure can achieve full water solubility, good delivery and spraying effect, and is more suitable for application in spray fertilization.

[0177] (4) The process of the present disclosure has low chlorine ion content in the potassium sulfate product. The chlorine ion content of the mainstream potassium sulfate product on the market is 1.0-2.0%, and the chlorine ion content of the potassium sulfate product produced by the present disclosure can be less than 0.3%. The chlorine ion content is reduced by more than 70%, and the chlorine ion content is better than the national standard GBT 20406-2017 Agricultural Potassium Sulfate Crystalline Superior Product. Although chlorine is a trace element necessary for plants, high chlorine ion content can harm many chlorine-averse crops, and large amounts of chlorine ions entering the soil can accelerate soil salinization. Potassium sulfate is suitable for plants sensitive to chlorine elements and drought-prone areas. Therefore, potassium sulfate products with low chlorine content are more widely applicable to crops, and also have better protection for the soil.

[0178] (5) The potassium sulfate product prepared by the present disclosure has uniform particle size distribution and good flowability after drying, and does not need to add anti-caking agents. It still has good loose type and flowability after long-term storage.

[0179] (6) The by-product of the process of the present disclosure is NK fertilizer, which has a total nutrient content (N+K2O) of more than 34% and a water content of less than 1.0%. The by-product production technology is mature, and the NK fertilizer can be directly sold as a binary compound fertilizer, or can be used to produce a ternary compound fertilizer by adding phosphorus (P), thereby achieving the effect of reducing production cost and improving economic benefit. The by-product of the conventional Mannheim method is hydrochloric acid, which has a limited sales range and low economic benefit.

[0180] The preparation method and process have the following advantages:

[0181] (1) The method provided by the present disclosure realizes continuous, large-scale and industrial production by preparing potassium sulfate products with K2O content greater than 50.0% through a three-step process using potassium chloride and ammonium sulfate as raw materials and adopting a double decomposition reaction. The process of each step is simple, and compared with the existing mature industrialized technology (Mannheim potassium sulfate technology), the production device is a normal pressure equipment, the operation is safe, the reaction process is carried out at a lower temperature, and there is no environment of strong acid and strong base, so the equipment is not easy to be corroded, and no toxic gas is generated, which is more energy-saving and environment-friendly.

[0182] (2) The three-step method has more advantages compared with the traditional two-step method:

[0183] The two-step method: in the first step, ammonium sulfate solution and potassium chloride solid are reacted to prepare potassium sulfate crude product (K2O content is between 42%-44%), in the second step, hot water or potassium chloride solution (mass fraction of potassium chloride in the solution is between 1%-30%) is used to wash the reaction to prepare potassium sulfate product, when the ratio of potassium sulfate crude product and water is 1:0.9-1.0, the K2O content of the prepared potassium sulfate product is about 49.0%, and when the ratio of potassium sulfate crude product and water is increased to 1:1.4-1.5, the potassium sulfate product with K2O content of about 50.1% can be prepared. The two-step method needs to introduce about 2.4 tons of fresh water for preparing 1.0 ton of potassium sulfate product.

[0184] The three-step method: ammonium sulfate and potassium chloride are added in two steps, and in the third step, water or potassium chloride solution (mass fraction of potassium chloride in the solution is between 1%-20%) is used to wash the reaction to prepare potassium sulfate product; the K2O content of the potassium sulfate primary crude product obtained in the first step is between 42.0-43.5%, and the K2O content of the potassium sulfate secondary crude product prepared in the second step is between 45.0-47.0%; since the K2O content of the potassium sulfate secondary crude product is already above 45.0%, after washing with 0.9 times of hot water in the third step, the potassium sulfate product with K2O content greater than 50.5% can be prepared, and by slightly increasing the washing water amount to 1.1 times, the potassium sulfate product with K2O content greater than 51.0% can be prepared. By adopting the stepwise feeding reaction and dissolving ammonium sulfate solid with mother liquor, the amount of fresh water is reduced, and about 2.0 tons of water (more than 80% of which is recovered secondary steam condensate) is needed for preparing 1.0 ton of potassium sulfate product by the three-step method, which is 176% less than the fresh water amount in the two-step method. The fresh water finally enters the evaporation system, is separated after high-temperature evaporation by consuming steam, and the reduction of water amount can reduce the consumption of steam, so that the purpose of energy saving and consumption reduction is achieved, and the production cost is reduced.

[0185] In addition, in the method, the raw materials of ammonium sulfate and potassium chloride are added in two stages, the concentration of each stage is reduced, which is beneficial to the full reaction of the raw materials, and the solution concentration is reduced, which is also beneficial to the transportation of the solution. The K2O content of the primary potassium sulfate product is 42.0-43.5%, the K2O content of the secondary potassium sulfate product is 45.0-47.0%, and the mass ratio of the secondary potassium sulfate product to water is 1:0.9-1.2 during the third washing step, so that the potassium sulfate product with a K2O content greater than 50.5% can be prepared. If the two-step method is used, through repeated laboratory experiments, the K2O content of the potassium sulfate product can only reach more than 50.0% by using 1.4-1.5 times the amount of washing water of the crude product, and the quality is not stable. If the K2O content of the potassium sulfate product is greater than 50.5%, the amount of washing water needs to be increased to more than 1.7 times. The three-step method not only saves water, but also has stable and reliable quality.

[0186] (3) Advantages of the third stage reaction:

[0187] Since the K2O content of the secondary potassium sulfate product is 45.0-47.0%, the third step can be used to wash the product with water to prepare potassium sulfate product with a K2O content greater than 50.5%, and the chloride ion content is less than 0.3%. The chloride ion content of most of the products prepared in the experiment can be less than 0.1%. Therefore, in order to further improve the K2O content of the potassium sulfate product, a potassium chloride solution (the mass fraction of potassium chloride in the solution is between 1% and 30%) can be used to wash the product after the reaction to prepare the potassium sulfate product. Washing with a potassium chloride solution can increase the K2O content of the potassium sulfate product, but it can also slightly increase the chloride ion content of the product. For example, washing the secondary potassium sulfate product with a potassium chloride solution with a potassium chloride mass fraction of 10% can increase the chloride ion content to 0.3-0.5%, and the potassium sulfate content can also increase to 50.8-51.2%. Therefore, for products with relatively low chloride ion content requirements, a potassium chloride solution with a relatively high potassium chloride mass fraction (between 1% and 30%) can be used to wash the secondary potassium sulfate product to prepare a potassium sulfate product with relatively high K2O content and chloride ion content. However, the chloride ion content is still better than the requirement of the national standard GBT 20406-2017 Agricultural Potassium Sulfate Crystalline First Grade, which requires that the chloride ion content be less than 2.0%.

[0188] (4) Advantages of step-by-step dissolution of ammonium sulfate:

[0189] In the present disclosure, in the preparation of the primary potassium sulfate crude product, the secondary potassium sulfate crude product mother liquor and fresh water are used to dissolve ammonium sulfate. By introducing the secondary potassium sulfate crude product mother liquor, the secondary potassium sulfate crude product mother liquor is recycled, and the amount of fresh water is reduced. The primary potassium sulfate crude product mother liquor is concentrated by evaporation and then used to prepare NK fertilizer. Since the amount of fresh water is reduced, the amount of water that needs to be evaporated is also reduced, which reduces the consumption of steam and achieves energy saving and consumption reduction.

[0190] In the present disclosure, in the preparation of the secondary potassium sulfate crude product, the potassium sulfate product mother liquor is used to dissolve ammonium sulfate. The dissolution of ammonium sulfate does not require the introduction of fresh water, which realizes the recycling of the potassium sulfate product mother liquor and reduces the introduction of fresh water in the system. The separated secondary potassium sulfate crude product mother liquor is used in the preparation of the primary potassium sulfate crude product. Since the fresh water introduced eventually needs to be evaporated and separated from the NK fertilizer evaporation system, the purpose of reducing steam consumption is achieved, and energy saving and consumption reduction are realized.

[0191] (5) Advantages in environmental protection and energy consumption:

[0192] By reasonably adjusting the amount of mother liquor at each step, all the mother liquor is recycled within the market system, achieving water balance and total solution balance between each process of potassium sulfate. As a result, no process solution or secondary steam condensate needs to be discharged.

[0193] In terms of energy consumption, the present project realizes the dynamic balance of the solution amount at each step of potassium sulfate production through two feeding and optimized solution (mother liquor) distribution without additional evaporation devices, and the water evaporation amount per ton of potassium sulfate is significantly reduced. According to the Chinese national standard GB29439-2012 "Standard Energy Consumption Value of Potassium Sulfate", the advanced value of energy consumption for producing potassium sulfate from resource-type potassium-containing brine by water-salt system method is 350 kgce / t, and the advanced value of energy consumption for producing potassium sulfate by mirabilite method, which is also a processing type, is 460 kgce / t. In terms of potassium sulfate products, the energy consumption of the present project is 185 kgce / t, which is much lower than the advanced value of energy consumption of potassium sulfate by water-salt system method.

[0194] (6) Innovation in industrialization

[0195] The reaction temperature of the method of the present disclosure is 70-95℃, which can be directly achieved by steam heating. The cooling and crystallization temperature is 30-50℃, which can be directly achieved by cooling circulating water. The process is simple and has low energy consumption.

[0196] In the present disclosure, the potassium chloride raw material is added to the reaction kettle in two steps in proportion, which improves the efficiency of the reactor, increases the reaction degree of potassium chloride and ammonium sulfate, shortens the residence time of the material in the reaction kettle, improves the production efficiency, and ensures the stability of the product quality.

[0197] The whole production process of the present disclosure is a liquid phase reaction system, all reactions and crystallization occur in the liquid phase, all reaction solutions and crystal slurries can be transported by pumps, which is convenient for transportation and beneficial to industrialized scale-up production. In the process flow, the reactors and crystallizers are in a new form, which improves the reaction efficiency and shortens the reaction time by modifying the existing reactors and crystallizers, and the product also has good quality and suitable particle size distribution.

[0198] The above is only the preferred embodiment of the present disclosure and is not intended to limit the present disclosure. For those skilled in the art, the present disclosure can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure. Industrial applicability

[0199] The present disclosure provides a method for producing potassium sulfate by double decomposition process, potassium sulfate product and potassium fertilizer. The method for producing potassium sulfate by double decomposition process provided by the present disclosure comprises: taking ammonium sulfate solid and potassium chloride solid as raw materials, carrying out a first reaction in a solution system, and then crystallizing and separating to obtain a first crude potassium sulfate product; taking the first crude potassium sulfate product, ammonium sulfate solid and potassium chloride solid as raw materials, carrying out a second reaction in a solution system, and then crystallizing and separating to obtain a second crude potassium sulfate product; mixing the second crude potassium sulfate product with hot water with a temperature of 80-98℃, carrying out a third reaction, and then crystallizing and separating. The above method takes ammonium sulfate solid and potassium chloride solid as raw materials, adds them into the reaction in two steps, respectively carries out a first reaction and a second reaction, and then carries out a third reaction with hot water, crystallizes and separates, fully removes impurities in the product, and at the same time increases the K2O content in the product, which is simple in method, high in quality of potassium fertilizer, and has a wide application prospect in process.

Claims

1. A method of producing potassium sulfate by a metathesis process, characterized in that, Comprise: A first-stage reaction is carried out in a solution system using ammonium sulfate solids and potassium chloride solids as raw materials, followed by crystallization and separation to obtain a first crude potassium sulfate product; A second-stage reaction is carried out in a solution system using the first crude potassium sulfate product, ammonium sulfate solids and potassium chloride solids as raw materials, followed by crystallization and separation to obtain a second crude potassium sulfate product; The second crude potassium sulfate product is mixed with hot water at a temperature of 80-98℃ to carry out a third-stage reaction, followed by crystallization and separation.

2. The method of claim 1, wherein, The molar ratio of the ammonium sulfate solids to the potassium chloride solids used in the first-stage reaction is 1:(1.4-2.2), and the molar ratio of the ammonium sulfate solids to the potassium chloride solids used in the second-stage reaction is 1:(1.8-2.8).

3. The method according to claim 1 or 2, characterized in that, The process for obtaining the first crude potassium sulfate product comprises: dissolving the ammonium sulfate solids, the second crude potassium sulfate product mother liquor and water to obtain an ammonium sulfate solution, mixing the ammonium sulfate solution with the potassium chloride solids to carry out the first-stage reaction, followed by cooling crystallization and separation to obtain the first crude potassium sulfate product and a first crude potassium sulfate product mother liquor; wherein the second crude potassium sulfate product mother liquor is obtained from the process of separating the second crude potassium sulfate product.

4. The method of claim 3, wherein, The mass ratio of the ammonium sulfate solids, the second crude potassium sulfate product 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 60-90℃, and the reaction time is 1-3h; Preferably, the crystallization temperature after the first-stage reaction is controlled at 30-60℃, and the crystallization time is 1-3h; Preferably, the dissolution temperature is 60-90℃ when preparing the ammonium sulfate solution.

5. The method of claim 3, wherein, The first crude potassium sulfate product mother liquor is used to prepare NK fertilizer by-products; Preferably, the first crude potassium sulfate product 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 NK fertilizer wet products and a NK fertilizer mother liquor, and the NK fertilizer wet products are dried to obtain NK fertilizer products; More preferably, the NK fertilizer mother liquor is recycled to the evaporation and concentration stage.

6. The method of claim 3, wherein, The process for obtaining the second crude potassium sulfate product comprises: dissolving the ammonium sulfate solids, the first crude potassium sulfate product and a potassium sulfate product mother liquor to obtain a crystal slurry mixed solution, mixing the crystal slurry mixed solution with the potassium chloride solids to carry out the second-stage reaction, followed by cooling crystallization and separation to obtain the second crude potassium sulfate product and a second crude potassium sulfate product mother liquor, and the second crude potassium sulfate product mother liquor is used to dissolve the ammonium sulfate solids in the first-stage reaction; wherein the potassium sulfate product mother liquor is obtained from the crystallization and separation after the third-stage reaction.

7. The method of claim 6, wherein, The mass ratio of the ammonium sulfate solids, the first crude potassium sulfate product and the potassium sulfate product mother liquor is 1:(2.2-3.3):(4.8-6.2); Preferably, the temperature of the second-stage reaction is controlled at 60-90℃, and the reaction time is 1-3h; Preferably, the crystallization temperature after the second-stage reaction is controlled at 30-60℃, and the crystallization time is 1-3h; Preferably, the dissolution temperature is 60-90℃ when preparing the crystal slurry mixed solution.

8. The method of claim 1, wherein, The reaction temperature of the three-stage reaction is controlled at 60-90°C, and the reaction time is 0.5-2.0h; Preferably, the mass ratio of the secondary crude potassium sulfate to the hot water is 1:(0.8-1.2); Preferably, the hot water and potassium chloride are mixed to obtain a potassium chloride solution with a mass fraction of 1-30%, and the potassium chloride solution is used to mix and react with the secondary crude potassium sulfate; Preferably, after the three-stage reaction, crystallization is carried out at 30-60°C for 1-3h, and then the wet potassium sulfate product and a potassium sulfate product mother liquor are separated, and the wet potassium sulfate product is dried to obtain the potassium sulfate product; More preferably, the potassium sulfate product mother liquor is used to dissolve the ammonium sulfate solid in the second-stage reaction.

9. A potassium sulfate product characterized in that, Prepared by the method of any one of claims 1-8; Preferably, the K2O content of the potassium sulfate product is 50.0-51.5wt%, the chloride ion content is less than 0.3wt%, the moisture content is less than 0.5wt%, and the water-insoluble content is less than 0.05wt%.

10. A potassium fertilizer, characterized in that, The potassium sulfate product of claim 8 or 9. The potassium sulfate product of claim 8 or 9.

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