Preparation method of food-grade potassium chloride

Abstract

The invention provides a preparation method of food-grade potassium chloride. The preparation method comprises the following steps: dissolving and filtering crude salt lake potassium to obtain a potassium chloride stock solution, adsorbing the potassium chloride stock solution by using a composite adsorbent comprising a carbon skeleton and grafting resin to obtain an adsorbed solution, carrying out negative pressure flash evaporation on the adsorbed solution to obtain a flash evaporation solution, and carrying out evaporation concentration, water washing and drying on the flash evaporation solution to obtain the food-grade potassium chloride. According to the method, crude potassium chloride prepared from a salt lake is used as a raw material, organic amine and inorganic ammonium impurities and heavy metal impurities such as lead and arsenic in the crude potassium chloride raw material are fully adsorbed by using a low-cost composite adsorbent, and then inorganic ammonium is converted into ammonia gas to be separated from a system through a negative pressure flash evaporation process; a small amount of soluble sodium salt and magnesium salt are washed through a washing process, indexes of the finally prepared potassium chloride product meet relevant national standards, equipment is simple, and industrial popularization is easy.

Description

Technical Field

[0001] The present invention relates to the technical field of potassium salts, and in particular, to a preparation method of food-grade potassium chloride. Background Art

[0002] With the improvement of living standards, the demand for products such as low-sodium salt products and low-sodium salt seasonings has increased rapidly, which has driven the stable growth of the consumption of upstream ingredients such as food-grade potassium chloride. At present, the raw materials for preparing food-grade potassium chloride are mostly sea salt and underground pure carnallite or underground pure sylvite. Due to factors such as marine pollution, the technology of preparing food-grade potassium chloride from sea salt raw materials poses challenges to food safety and brings concerns about food safety. When underground pure carnallite or underground pure sylvite is used as the raw material, due to the small reserves of high-quality raw materials and the high cost of developing and preparing food-grade potassium chloride from low-quality raw materials, the production capacity cannot be expanded.

[0003] At present, there are a certain number of studies on the process of preparing food-grade potassium chloride from crude potassium chloride raw materials in salt lake areas. The adsorption method is mostly used, and impurities in the potassium chloride raw materials are treated with adsorbents such as macroporous resins. However, no certain scale has been formed, the adsorption effect is not ideal, and the process is complex and the cost is high. Summary of the Invention

[0004] The main object of the present invention is to provide a preparation method of food-grade potassium chloride to solve the problems of complex process and high cost in preparing food-grade potassium chloride from salt lake brine in the prior art.

[0005] To achieve the above object, according to one aspect of the present invention, a preparation method of food-grade potassium chloride is provided, including the following steps: Step S1, dissolving and filtering crude potassium in the salt lake to obtain a potassium chloride stock solution; Step S2, adsorbing the potassium chloride stock solution with a composite adsorbent to obtain an adsorbed solution; Step S3, subjecting the adsorbed solution to negative pressure flash evaporation to obtain a post-flash evaporation solution; Step S4, evaporating and concentrating the post-flash evaporation solution to obtain potassium chloride crystals; Step S5, washing and drying the potassium chloride crystals in sequence to obtain food-grade potassium chloride; wherein the composite adsorbent includes a carbon skeleton and grafted resin.

[0006] Further, the grafted resin includes styrene cyclo-carboxylic acid resin and porous resin; preferably, the weight ratio of the styrene cyclo-carboxylic acid resin to the porous resin is 1:(0.1-100), more preferably 1:(0.3-30).

[0007] Further, the weight ratio of the carbon skeleton to the grafted resin is 1:(0.05-0.2), preferably 1:(0.08-0.13); and / or the adsorption capacity of the composite adsorbent for amine substances is 2-10 g / L, and the adsorption capacity for metal cations is 15-25 g / L.

[0008] Further, in step S2, the adsorption methods include static adsorption and / or dynamic adsorption. The dynamic adsorption includes one or more of single-column adsorption, continuous ion exchange adsorption, and adsorption tower adsorption.

[0009] Further, in static adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:(1 - 40), and the adsorption time is 1 - 6 h.

[0010] Further, in dynamic adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:(2 - 50), the solution flow rate is 1 - 10 Bv / h, and the adsorption temperature is 10 - 35 °C.

[0011] Further, in step S1, in the crude potassium from the salt lake, the weight percentage of potassium chloride ≥ 90%, the content of amine substances calculated as NH4 + is 100 - 1500 mg / kg, the heavy metal content calculated as Pb is 0 - 10 mg / kg, the arsenic content is 0 - 10 mg / kg, the weight percentage of sodium ions is 0.05 - 2%, and the weight percentage of magnesium ions is 0.05 - 2%; and / or the filtration methods include one or more of belt filtration, vacuum filtration, pressure filtration, and centrifugal filtration; and / or the mass concentration of the potassium chloride stock solution ≤ 27%.

[0012] Further, in step S3, the pressure of vacuum flashing is -0.06 - -0.1 MPa, the temperature is 65 - 100 °C, and the time is 30 - 300 s; preferably, the pressure of vacuum flashing is -0.07 - -0.1 MPa, the temperature is 65 - 90 °C, and the time is 30 - 60 s; more preferably, before vacuum flashing, step S3 further includes a step of adjusting the pH value of the post-adsorption liquid to 7.7 - 8.9; more preferably, after vacuum flashing, step S3 further includes a step of adjusting the pH value of the flashed liquid to 6.5 - 7.5.

[0013] Further, in step S4, the evaporation and concentration methods include one or more of forced evaporation, single-effect evaporation, and multi-effect evaporation; and / or the concentration ratio of evaporation and concentration is 1:(3 - 40).

[0014] Further, in step S5, in water washing, the weight ratio of water to potassium chloride crystals is (0.5 - 15):100, preferably (2 - 8):100; and / or the drying methods include one or more of tray drying, hearth drying, and vacuum drying.

[0015] Applying the technical solution of the present invention, using the crude potassium chloride obtained from salt lakes as raw materials, first use a low-cost composite adsorbent to fully adsorb organic amine and inorganic ammonium impurities in the crude potassium chloride raw materials, and at the same time adsorb heavy metal impurities such as lead and arsenic. Then, through a negative pressure flash evaporation process, the inorganic ammonium is converted into ammonia and separated from the system. Through a washing process, a small amount of soluble sodium salts and magnesium salts are washed away. Thus, through the impurity removal process, impurities such as amines, heavy metals, sodium ions, and magnesium ions in the raw materials are removed. Finally, the indicators of the prepared potassium chloride product meet the relevant national standards. The method of the present invention can use a simple and feasible method to prepare high-quality food-grade potassium chloride from crude potassium chloride. The equipment is simple and easy to promote industrially, and can be directly applied to the large-scale industrial production of potassium salts. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0017] Figure 1 Shows the process flow chart of the preparation of food-grade potassium chloride according to Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0019] It should be noted that "food-grade potassium chloride" in the present invention refers to a product whose indicators meet "GB25585-2010 Potassium Chloride for Food Additives" and "QB 2554-2002 Potassium Chloride for Food Use".

[0020] As described in the background art of the present invention, there are problems of complex process and high cost in the prior art when preparing food-grade potassium chloride from salt lake brine. To solve the above problems, in a typical embodiment of the present invention, a method for preparing food-grade potassium chloride is provided, including the following steps: Step S1, dissolving and filtering the crude potassium from the salt lake to obtain a potassium chloride stock solution; Step S2, adsorbing the potassium chloride stock solution with a composite adsorbent to obtain an adsorbed solution; Step S3, subjecting the adsorbed solution to negative pressure flash evaporation to obtain a post-flash evaporation solution; Step S4, evaporating and concentrating the post-flash evaporation solution to obtain potassium chloride crystals; Step S5, washing and drying the potassium chloride crystals in sequence to obtain food-grade potassium chloride; wherein, the composite adsorbent includes a carbon skeleton and grafted resin.

[0021] Specifically, first dissolve the crude potassium from the salt lake, filter it to separate the insoluble substances in the solution, and obtain the potassium chloride stock solution; then adsorb the potassium chloride stock solution using a composite adsorbent including a carbon skeleton and grafted resin. The carbon skeleton provides a high specific surface area and good mechanical strength, while the grafted resin has excellent adsorption performance due to its rich active groups, so as to adsorb amine impurities (including organic amine impurities and inorganic ammonium impurities) and heavy metal impurities such as lead and arsenic in the solution, and obtain the post-adsorption solution; then perform vacuum flashing on the post-adsorption solution to convert inorganic ammonium into ammonia and remove it from the system, so as to separate the inorganic ammonium substances in the solution and obtain the post-flashing solution. Vacuum flashing can effectively evaporate at a lower temperature, reducing the thermal decomposition of potassium chloride at high temperature and the damage to equipment; finally, evaporate and concentrate the post-flashing solution, obtain potassium chloride crystals, wash them with water to remove sodium and magnesium ions in the potassium chloride crystals, and obtain food-grade potassium chloride with product indicators meeting the relevant national standards after drying.

[0022] The method of the present invention can realize the preparation of high-quality food-grade potassium chloride from crude potassium chloride by a simple and feasible method. The equipment is simple and easy to be popularized industrially, and can be directly applied to potassium salt production units in the northwest, improving the richness of products and the competitiveness of the potassium salt industry in the international market.

[0023] For the purpose of more favorably providing a high specific surface area and good mechanical strength for the composite adsorbent, in a preferred embodiment, the carbon skeleton includes one or more of porous carbon, biochar, and mesoporous carbon, and other common carbon materials can also be selected.

[0024] In a preferred embodiment, the grafted resin includes styrene cyclic carboxylic acid resin and porous resin; preferably, the weight ratio of the styrene cyclic carboxylic acid resin to the porous resin is 1:(0.1 - 100), more preferably 1:(0.3 - 30), and further preferably 1:(0.3 - 0.8) or 1:(3 - 30). Due to its unique molecular structure, the styrene cyclic carboxylic acid resin can effectively adsorb organic amine impurities and some heavy metal ions in the brine, while the porous resin has excellent adsorption performance for inorganic ammonium and heavy metals. The combination of the two can achieve the efficient removal of various impurities in the brine. By adjusting the weight ratio between the resins, the adsorption capacity of the adsorbent for different impurities can be optimized, thereby reducing the consumption of reagents and energy while ensuring product purity, reducing production costs. In addition, the use of this composite adsorbent can further reduce the complexity of multi-step treatment in the traditional process, improve production efficiency, facilitate large-scale production, further reduce costs, and enhance economic benefits and market competitiveness.

[0025] In the composite adsorbent of the present invention, a reasonable ratio of the carbon skeleton to the grafted resin is beneficial to making the adsorbent more efficient and economical in removing amine and heavy metal impurities in brine. In a preferred embodiment, the weight ratio of the carbon skeleton to the grafted resin is 1:(0.05 - 0.2), preferably 1:(0.08 - 0.13), and more preferably 1:(0.08 - 0.11); and / or the adsorption capacity of the composite adsorbent for amine substances is 2 - 10 g / L, and the adsorption capacity for metal cations is 15 - 25 g / L. A high adsorption capacity means that a smaller amount of adsorbent can be used to achieve deep removal of impurities, which is beneficial to reducing the replacement frequency and treatment volume of the adsorbent, saving costs. At the same time, this is also conducive to simplifying the process flow, improving production efficiency, and reducing energy consumption.

[0026] In a preferred embodiment, in step S2, the adsorption methods include static adsorption and / or dynamic adsorption. Dynamic adsorption includes one or more of single-column adsorption, continuous ion exchange adsorption, and adsorption tower adsorption. Static adsorption can be carried out at a lower flow rate, which is beneficial for the adsorbent to fully contact with the brine, deeply remove impurities, and improve the product purity. Dynamic adsorption can control the flow rate and the amount of adsorbent used, which is not only beneficial for realizing continuous production and improving production efficiency, but also can reduce the overall cost due to the regeneration and reuse of the adsorbent. The adsorption method can be flexibly adjusted according to the characteristics of the raw materials, the types and contents of impurities, and the production capacity requirements to optimize the adsorption process, which can not only improve the quality of food-grade potassium chloride, but also take into account economic benefits, effectively solve the complexity and high cost problems of the traditional process, and provide technical support for the preparation of high-quality potassium chloride from salt lake brine.

[0027] To further improve the impurity removal efficiency, precisely control the adsorption process, reduce the use of chemical reagents and energy consumption, thereby reducing production costs, making the preparation process of food-grade potassium chloride more economical and environmentally friendly, and facilitating large-scale industrial application. In a preferred embodiment, in static adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:(1 - 40), preferably 1:(30 - 40), and the adsorption time is 1 - 6 h, so as to promote the full adsorption of impurities and avoid resource waste and treatment complexity caused by excessive adsorbent.

[0028] For similar reasons, in a preferred embodiment, in dynamic adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:(2 - 50), preferably 1:(26 - 36), the solution flow rate is 1 - 10 Bv / h, and the adsorption temperature is 10 - 35 °C, which is more conducive to realizing continuous and efficient adsorption, reducing the production cycle, and improving the equipment utilization rate.

[0029] The raw material of crude potassium from salt lakes can use products of different grades produced in different sections of the salt lake area. The content indexes of amine substances, heavy metal indexes, and the contents of elements such as arsenic, sodium, and magnesium are determined according to the actual production situation. To further improve the adaptability of the process and the raw materials, in a preferred embodiment, in step S1, in the crude potassium from salt lakes, the weight percentage content of potassium chloride ≥ 90%, the content of amine substances calculated as NH4 + is 100 - 1500 mg / kg, the heavy metal content calculated as Pb is 0 - 10 mg / kg, the content of arsenic is 0 - 10 mg / kg, the weight percentage content of sodium ions is 0.05 - 2%, and the weight percentage content of magnesium ions is 0.05 - 2%; and / or the filtration method includes one or more of belt filtration, vacuum filtration, pressure filtration, and centrifugal filtration; and / or the mass concentration of the potassium chloride stock solution ≤ 27%. It should be noted that for the raw material of crude potassium from salt lakes with a potassium chloride content lower than the listed indexes and an impurity content higher than the listed indexes, through the process flow of the present invention, by appropriately adjusting the relevant process parameters during production, products meeting the standards can also be prepared.

[0030] For further preference based on the above reasons, in the crude potassium from salt lakes, the weight percentage content of potassium chloride is 93.8 - 98.3%, the content of amine substances calculated as NH4 + is 1040 - 1474 mg / kg, the heavy metal content calculated as Pb is 5 - 10 mg / kg, the content of arsenic is 2 - 10 mg / kg, the weight percentage content of sodium ions is 0.5 - 2%, and the weight percentage content of magnesium ions is 0.5 - 2%. Preferably, the mass concentration of the potassium chloride stock solution is 25 - 27%.

[0031] By optimizing the process parameters of vacuum flash evaporation and precisely adjusting the pH value, the process of preparing food - grade potassium chloride from salt lake brine can be significantly simplified and the cost can be reduced. In a preferred embodiment, in step S3, the pressure of vacuum flash evaporation is - 0.06 - - 0.1 MPa, the temperature is 65 - 100 °C, and the time is 30 - 300 s; preferably, the pressure of vacuum flash evaporation is - 0.07 - - 0.1 MPa, the temperature is 65 - 90 °C, and the time is 30 - 60 s; more preferably, before vacuum flash evaporation, step S3 further includes a step of adjusting the pH value of the post - adsorption solution to 7.7 - 8.9; more preferably, after vacuum flash evaporation, step S3 further includes a step of adjusting the pH value of the post - flash evaporation solution to 6.5 - 7.5. Appropriate vacuum flash evaporation pressure and time can promote the complete removal of inorganic ammonium substances and reduce subsequent treatment steps. Adjusting the pH value to the above range can not only promote the release of ammonium ions before flash evaporation but also maintain the stability of the solution and the adaptability of subsequent processes after flash evaporation, so as to optimize the flash evaporation process, improve efficiency, reduce energy consumption and reagent use, lower production costs, and make the preparation of food - grade potassium chloride more economically feasible. Food - grade sodium hydroxide or hydrochloric acid can be used for pH adjustment.

[0032] In a preferred embodiment, in step S4, the evaporation concentration method includes one or more of forced evaporation, single-effect evaporation, and multi-effect evaporation; and / or the concentration ratio of evaporation concentration is 1:(3 - 40); preferably, when the adsorption method is static adsorption, the concentration ratio of evaporation concentration is 1:(20 - 40); when the adsorption method is dynamic adsorption, the concentration ratio of evaporation concentration is 1:(3.7 - 8.0). Forced evaporation accelerates the crystallization process of potassium chloride and shortens the production cycle by enhancing heat and mass transfer; single-effect evaporation is simple to operate and easy to control; multi-effect evaporation significantly reduces energy consumption through multiple utilization of heat energy, especially suitable for large-scale production. Optimization of the evaporation concentration ratio can enable efficient concentration of potassium chloride without causing resource waste, reduce dependence on energy during evaporation, and lower production costs.

[0033] For the purpose of effectively removing impurities such as sodium and magnesium ions on the surface of potassium chloride crystals, reducing secondary evaporation and increased energy consumption caused by excessive water use, and reducing waste of water resources, in a preferred embodiment, in step S5, in the water washing, the weight ratio of water to potassium chloride crystals is (0.5 - 15):100, preferably (2 - 8):100; and / or the drying method includes one or more of tray drying, hearth drying, and negative pressure drying. The choice of drying method, such as the uniformity of tray drying, the rapidity of hearth drying, and the efficiency of negative pressure drying, can be flexibly adjusted according to specific production conditions and product requirements, which is not only beneficial to improving drying efficiency, but also can reduce energy consumption during drying, and reduce equipment investment and maintenance costs.

[0034] Typical but non-limiting, the weight ratio of the carbon skeleton to the grafted resin is 1:0.05, 1:0.08, 1:0.10, 1:0.11, 1:0.13, 1:0.15, 1:0.18, 1:0.2 or a range value composed of any two of these numerical values.

[0035] Typical but non-limiting, the weight ratio of styrene ring carboxylic acid resin to porous resin is 1:0.1, 1:0.3, 1:0.5, 1:0.8, 1:1, 1:3, 1:5, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100 or a range value composed of any two of these numerical values.

[0036] Typical but non-limiting, in static adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:1, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40 or a range value composed of any two of these numerical values.

[0037] Typical but non-limiting, in dynamic adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:2, 1:5, 1:10, 1:15, 1:20, 1:26, 1:30, 1:36, 1:40, 1:45, 1:50 or a range value composed of any two of these values.

[0038] Typical but non-limiting, in step S3, the pressure of vacuum flashing is -0.06 MPa, -0.07 MPa, -0.08 MPa, -0.09 MPa, -0.1 MPa or a range value composed of any two of these values, the temperature is 65 °C, 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C or a range value composed of any two of these values, and the time is 30 s, 40 s, 50 s, 60 s, 80 s, 100 s, 150 s, 200 s, 250 s, 300 s or a range value composed of any two of these values.

[0039] Typical but non-limiting, in step S4, the concentration ratio of evaporation and concentration is 1:3, 1:3.7, 1:5, 1:8, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40 or a range value composed of any two of these values.

[0040] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0041] Example 1

[0042] The process flow chart of the preparation of food-grade potassium chloride is shown in Figure 1 .

[0043] The raw material of crude potassium from salt lake is sourced from Qinghai Salt Lake Industry Co., Ltd., with a potassium chloride content of 96.2%, an amine substance content (calculated as NH4 + ) of 1474 mg / kg, a heavy metal (calculated as Pb) content of 10 mg / kg, an arsenic content of 10 mg / kg, a sodium ion content of 1%, and a magnesium ion content of 2%.

[0044] In step S1, 1000 g of crude potassium from salt lake is taken and added with 2800 g of pure water to stir and dissolve to prepare a solution, which is vacuum filtered to obtain a potassium chloride stock solution with a mass concentration of 26%.

[0045] Step S2, adsorb the potassium chloride stock solution using a composite adsorbent; the composite adsorbent includes a carbon skeleton (which can be porous carbon) and grafted resin with a weight ratio of 1:0.09, and the grafted resin includes styrene ring carboxylic acid resin and porous resin with a weight ratio of 1:0.5. The adsorption capacity of the composite adsorbent for amine substances is 6 g / L, and the adsorption capacity for metal cations is 20 g / L; the adsorption method is dynamic adsorption, single-column adsorption. Take 90 mL of the adsorbent to fill the column. The volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:36, the solution flow rate is 2 Bv / h, the adsorption temperature is 25 °C, and all the liquid passes through the resin to obtain the post-adsorption liquid;

[0046] Step S3, adjust the pH value of the post-adsorption liquid to 7.7 with food additive potassium hydroxide, subject the post-adsorption liquid to negative pressure flash evaporation, with a pressure of -0.07 MPa, a temperature of 65 °C, and a time of 60 s to obtain the post-flash evaporation liquid, and adjust the pH value of the post-flash evaporation liquid to 7 with food additive hydrochloric acid;

[0047] Step S4, subject the post-flash evaporation liquid to forced evaporation with a concentration ratio of 1:3.8 to obtain potassium chloride crystals;

[0048] Step S5, wash the potassium chloride crystals, with the weight ratio of water to potassium chloride crystals being 5:100. After solid-liquid separation, perform chamber drying to obtain food-grade potassium chloride.

[0049] Example 2

[0050] The raw material of crude potassium from salt lake is sourced from Qinghai Salt Lake Industry Co., Ltd., with a potassium chloride content of 95.0%, an amine substance content (calculated as NH4 + ) of 1300 mg / kg, a heavy metal (calculated as Pb) content of 6 mg / kg, an arsenic content of 3 mg / kg, a sodium ion content of 2%, and a magnesium ion content of 1.5%.

[0051] Step S1, take 500 g of crude potassium from salt lake, add 1350 g of pure water, stir and dissolve to prepare a solution, and perform vacuum filtration to obtain a potassium chloride stock solution with a mass concentration of 27%;

[0052] Step S2, adsorb the potassium chloride stock solution using a composite adsorbent; the composite adsorbent includes a carbon skeleton and grafted resin with a weight ratio of 1:0.09, and the grafted resin includes styrene ring carboxylic acid resin and porous resin with a weight ratio of 1:0.5. The adsorption capacity of the composite adsorbent for amine substances is 6 g / L, and the adsorption capacity for metal cations is 20 g / L; the adsorption method is dynamic adsorption, single-column adsorption. Take 48 mL of the adsorbent to fill the column. The volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:32, the solution flow rate is 3 Bv / h, the adsorption temperature is 27 °C, and all the liquid passes through the resin to obtain the post-adsorption liquid;

[0053] Step S3: Adjust the pH value of the post-adsorption liquid to 8.2 with food additive potassium hydroxide, subject the post-adsorption liquid to vacuum flashing at a pressure of -0.08 MPa, a temperature of 70 °C, and a time of 45 s to obtain the post-flashing liquid, and then adjust the pH value of the post-flashing liquid to 7 with food additive hydrochloric acid;

[0054] Step S4: Subject the post-flashing liquid to forced evaporation with a concentration ratio of 1:3.7 to obtain potassium chloride crystals;

[0055] Step S5: Wash the potassium chloride crystals with water at a weight ratio of water to potassium chloride crystals of 8:100, perform solid-liquid separation, and then conduct chamber drying to obtain food-grade potassium chloride.

[0056] Example 3

[0057] The raw material of crude potassium from salt lakes is sourced from Qinghai Salt Lake Industry Co., Ltd., with a potassium chloride content of 93.8%, an amine substance content (calculated as NH4 + ) of 1040 mg / kg, a heavy metal (calculated as Pb) content of 5 mg / kg, an arsenic content of 2 mg / kg, a sodium ion content of 0.5%, and a magnesium ion content of 1%.

[0058] Step S1: Take 800 g of crude potassium from salt lakes, add 2400 g of pure water, stir and dissolve to prepare a solution, and conduct vacuum filtration to obtain the potassium chloride stock solution with a mass concentration of 25%;

[0059] Step S2: Adsorb the potassium chloride stock solution with a composite adsorbent; the composite adsorbent includes a carbon skeleton and a grafted resin with a weight ratio of 1:0.11, and the grafted resin includes a styrene ring carboxylic acid resin and a porous resin with a weight ratio of 1:0.5. The adsorption capacity of the composite adsorbent for amine substances is 6 g / L, and the adsorption capacity for metal cations is 20 g / L; the adsorption method is static adsorption. Use 65 mL of the composite adsorbent, with a volume ratio of the composite adsorbent to the potassium chloride stock solution of 1:40, an adsorption time of 6 h, and an adsorption temperature of 25 °C to obtain the post-adsorption liquid;

[0060] Step S3: Adjust the pH value of the post-adsorption liquid to 8.3 with food additive potassium hydroxide, subject the post-adsorption liquid to vacuum flashing at a pressure of -0.1 MPa, a temperature of 90 °C, and a time of 30 s to obtain the post-flashing liquid, and then adjust the pH value of the post-flashing liquid to 7 with food additive hydrochloric acid;

[0061] Step S4: Subject the post-flashing liquid to forced evaporation with a concentration ratio of 1:40 to obtain potassium chloride crystals;

[0062] Step S5: Wash the potassium chloride crystals with water at a weight ratio of water to potassium chloride crystals of 3:100, perform solid-liquid separation, and then conduct chamber drying to obtain food-grade potassium chloride.

[0063] Example 4

[0064] The raw material of crude potassium from salt lakes is sourced from Qinghai Salt Lake Industry Co., Ltd. The potassium chloride content is 98.3%, the amine content (calculated as NH4 + ) is 1040 mg / kg, the heavy metal content (calculated as Pb) is 5 mg / kg, the arsenic content is 2 mg / kg, the sodium ion content is 0.5%, and the magnesium ion content is 0.5%.

[0065] Step S1: Take 10 Kg of crude potassium from salt lakes, add 30 Kg of pure water, stir and dissolve to prepare a solution, and then perform vacuum filtration to obtain the potassium chloride stock solution with a mass concentration of 25%.

[0066] Step S2: Adsorb the potassium chloride stock solution using a composite adsorbent. The composite adsorbent includes a carbon skeleton and grafted resin with a weight ratio of 1:0.08. The grafted resin includes styrene cyclic carboxylic acid resin and porous resin with a weight ratio of 1:0.5. The adsorption capacity of the composite adsorbent for amine substances is 6 g / L, and the adsorption capacity for metal cations is 20 g / L. The adsorption method is dynamic adsorption, continuous ion exchange adsorption. Take 1.3 L of the adsorbent to fill the column, with 3 columns in parallel for the adsorption zone. The volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:26, the solution flow rate is 4 Bv / h, and the adsorption temperature is 30°C. All the liquid passes through the resin to obtain the post-adsorption liquid.

[0067] Step S3: Adjust the pH value of the post-adsorption liquid to 8.0 using food additive potassium hydroxide, and perform negative pressure flash evaporation on the post-adsorption liquid at a pressure of -0.09 MPa, a temperature of 85°C, and a time of 35 s to obtain the post-flash evaporation liquid. Then, adjust the pH value of the post-flash evaporation liquid to 7 using food additive hydrochloric acid.

[0068] Step S4: Perform forced evaporation on the post-flash evaporation liquid with a concentration ratio of 1:4 to obtain potassium chloride crystals.

[0069] Step S5: Wash the potassium chloride crystals with water at a weight ratio of water to potassium chloride crystals of 2:100. After solid-liquid separation, perform chamber drying to obtain food-grade potassium chloride.

[0070] Example 5

[0071] The difference from Example 1 is that in Step S2, the potassium chloride stock solution is adsorbed using a composite adsorbent. The composite adsorbent includes a carbon skeleton and grafted resin with a weight ratio of 1:0.09. The grafted resin includes styrene cyclic carboxylic acid resin and porous resin with a weight ratio of 1:30. The adsorption capacity of the composite adsorbent for amine substances is 2 g / L, and the adsorption capacity for metal cations is 25 g / L. The adsorption method is static adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:1, the adsorption time is 1 h, and the adsorption temperature is 25°C to obtain the post-adsorption liquid.

[0072] Example 6

[0073] The difference from Example 1 lies in that in step S2, the potassium chloride stock solution is adsorbed using a composite adsorbent; the composite adsorbent includes a carbon skeleton and a grafted resin with a weight ratio of 1:0.13, the grafted resin includes a styrene cyclic carboxylic acid resin and a porous resin with a weight ratio of 1:3, the adsorption capacity of the composite adsorbent for amine substances is 10 g / L, and the adsorption capacity for metal cations is 15 g / L; the adsorption method is static adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:40, the adsorption time is 6 h, the adsorption temperature is 25 °C, and the post-adsorption solution is obtained.

[0074] Example 7

[0075] The difference from Example 1 lies in that in step S2, the potassium chloride stock solution is adsorbed using a composite adsorbent; the composite adsorbent includes a carbon skeleton and a grafted resin with a weight ratio of 1:0.13, the grafted resin includes a styrene cyclic carboxylic acid resin and a porous resin with a weight ratio of 1:30, the adsorption capacity of the composite adsorbent for amine substances is 2 g / L, and the adsorption capacity for metal cations is 25 g / L; the adsorption method is adsorption tower adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:2, the solution flow rate is 10 Bv / h, the adsorption temperature is 10 °C, and the post-adsorption solution is obtained.

[0076] Example 8

[0077] The difference from Example 1 lies in that in step S2, the potassium chloride stock solution is adsorbed using a composite adsorbent; the composite adsorbent includes a carbon skeleton and a grafted resin with a weight ratio of 1:0.11, the grafted resin includes a styrene cyclic carboxylic acid resin and a porous resin with a weight ratio of 1:30, the adsorption capacity of the composite adsorbent for amine substances is 10 g / L, and the adsorption capacity for metal cations is 15 g / L; the adsorption method is adsorption tower adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:50, the solution flow rate is 1 Bv / h, the adsorption temperature is 35 °C, and the post-adsorption solution is obtained.

[0078] Example 9

[0079] The difference from Example 1 is that

[0080] In step S3, the pH value of the post-adsorption solution is adjusted to 7.7 using food additive potassium hydroxide, the post-adsorption solution is subjected to vacuum flashing, the pressure is -0.06 MPa, the temperature is 65 °C, the time is 300 s, the post-flashing solution is obtained, and the pH value of the post-flashing solution is adjusted to 6.5 using food additive hydrochloric acid;

[0081] In step S4, the post-flashing solution is subjected to forced evaporation, and the concentration ratio is 1:3 to obtain potassium chloride crystals;

[0082] Step S5: Wash the potassium chloride crystals. The weight ratio of water to potassium chloride crystals is 0.5:100. After solid-liquid separation, perform hearth drying to obtain food-grade potassium chloride.

[0083] Example 10

[0084] The difference from Example 1 is that

[0085] In step S3, adjust the pH value of the post-adsorption liquid to 8.9 with food additive potassium hydroxide. Perform vacuum flashing on the post-adsorption liquid at a pressure of -0.1 MPa, a temperature of 100 °C, and a time of 30 s to obtain the flashed liquid. Adjust the pH value of the flashed liquid to 7.5 with food additive hydrochloric acid.

[0086] In step S4, perform forced evaporation on the flashed liquid with a concentration ratio of 1:3.5 to obtain potassium chloride crystals.

[0087] In step S5, wash the potassium chloride crystals. The weight ratio of water to potassium chloride crystals is 15:100. After solid-liquid separation, perform chamber drying to obtain food-grade potassium chloride.

[0088] Example 11

[0089] The difference from Example 1 is that in step S2, adsorb the potassium chloride stock solution with a composite adsorbent. The composite adsorbent includes a carbon skeleton (which can be porous carbon) and a grafted resin with a weight ratio of 1:0.05. The grafted resin includes a styrene cyclic carboxylic acid resin and a porous resin with a weight ratio of 1:0.1. The adsorption capacity of the composite adsorbent for amine substances is 6 g / L, and the adsorption capacity for metal cations is 20 g / L. The adsorption method is dynamic adsorption, single-column adsorption. Take 90 mL of the adsorbent to fill the column. The volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:36, the solution flow rate is 2 Bv / h, and the adsorption temperature is 25 °C. All the liquid passes through the resin to obtain the post-adsorption liquid.

[0090] Example 12

[0091] The difference from Example 1 is that in step S2, adsorb the potassium chloride stock solution with a composite adsorbent. The composite adsorbent includes a carbon skeleton (which can be porous carbon) and a grafted resin with a weight ratio of 1:0.2. The grafted resin includes a styrene cyclic carboxylic acid resin and a porous resin with a weight ratio of 1:100. The adsorption capacity of the composite adsorbent for amine substances is 6 g / L, and the adsorption capacity for metal cations is 20 g / L. The adsorption method is dynamic adsorption, single-column adsorption. Take 90 mL of the adsorbent to fill the column. The volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:36, the solution flow rate is 2 Bv / h, and the adsorption temperature is 25 °C. All the liquid passes through the resin to obtain the post-adsorption liquid.

[0092] Comparative Example 1

[0093] Example 1 of Chinese Patent Application CN 115771905A.

[0094] Comparative Example 2

[0095] The difference from Example 1 is that the composite adsorbent is an equal amount of carbon framework.

[0096] Comparative Example 3

[0097] The difference from Example 1 is that the composite adsorbent is an equal amount of grafted resin.

[0098] Comparative Example 4

[0099] The difference from Example 1 is that adsorption is not carried out using the composite adsorbent.

[0100] Comparative Example 5

[0101] The difference from Example 1 is that in step S3, atmospheric flash evaporation is carried out.

[0102] The potassium chloride products prepared in the above examples and comparative examples were subjected to content testing. The testing method refers to "GB25585-2010 Food Additive Potassium Chloride" or "QB 2554-2002 Edible Potassium Chloride", and the results are shown in Table 1.

[0103] Table 1

[0104] / Weight percentage of potassium chloride in the product Impurity content Example 1 99.9％ Meet the requirements Example 2 99.9％ Meet the requirements Example 3 99.8％ Meet the requirements Example 4 99.8％ Meet the requirements Example 5 99.7％ Meet the requirements Example 6 99.6％ Meet the requirements Example 7 99.6％ Meet the requirements Example 8 99.5％ Meet the requirements Example 9 99.5％ Meet the requirements Example 10 99.5％ Meet the requirements Example 11 99.1％ Meet the requirements Example 12 99.2％ Meet the requirements Comparative Example 1 95.0％ Meet the requirements Comparative Example 2 91.8％ Do not meet the requirements Comparative Example 3 95.1％ Meet the requirements Comparative Example 4 85.9％ Do not meet the requirements Comparative Example 5 92.5％ Meet the requirements

[0105] It can be seen that in Comparative Example 1 for the removal of amine substances, chemical oxidation, precipitation method plus adsorption method are used, that is, by reacting the solution after adjusting the pH with phosphate ions and magnesium ions to form magnesium ammonium phosphate, and then adsorbing magnesium ammonium phosphate with activated carbon, and the desorbed magnesium ammonium phosphate is used as the product. In each example of the present application for the removal of amine substances, a two-step method is adopted, that is, first the removal of organic amine substances is completed through the adsorption process, and then the removal of inorganic ammonium ions is completed through the process of flash evaporation after adding alkali. The purpose of adding alkali in the flash evaporation process is to convert ammonium ions into free ammonia molecules by adjusting the pH. Since the boiling point of ammonia molecules is below 100 °C, the separation of potassium chloride solution and inorganic ammonium can be completed through flash evaporation in a short time.

[0106] The purpose of the adsorption process in Comparative Example 1 is to adsorb magnesium ammonium phosphate, and the purpose of the adsorption process in each example of the present application is to adsorb organic amines; the purpose of the flash evaporation process in Comparative Example 1 is to cooperate with the subsequent multiple-effect evaporation to complete the pre-concentration process, and the purpose of the flash evaporation process in each example of the present application is to remove inorganic ammonium substances that have been converted into free ammonia molecules in the solution through negative-pressure flash evaporation.

[0107] For the removal of amine substances in Comparative Example 1, it is necessary to adjust the pH and then add magnesium ions and sodium phosphate. At the same time, a strong oxidant also needs to be added, and the addition amounts of magnesium ions, phosphate ions and oxidant are all in excess for the raw materials, which has the risk of introducing other impurities. In each example of the present application, with the pH value as the calibration parameter, the potassium hydroxide and hydrochloric acid added can generate potassium chloride through a neutralization reaction, and hydrogen ions and hydroxide ions generate water, without introducing other ions except potassium and chlorine during the entire impurity removal process.

[0108] As can be seen from the above, compared with the comparative examples, each example of the present invention uses the crude potassium chloride obtained from salt lakes as the raw material. First, a low-cost composite adsorbent is used to fully adsorb organic amine and inorganic ammonium impurities in the crude potassium chloride raw material, and at the same time, heavy metal impurities such as lead and arsenic are adsorbed. Then, through a negative pressure flash evaporation process, inorganic ammonium is converted into ammonia and separated from the system. Through a washing process, a small amount of soluble sodium salts and magnesium salts are washed away, so as to remove impurities such as amines, heavy metals, sodium ions and magnesium ions in the raw material through an impurity removal process. Finally, the obtained potassium chloride product indexes meet the relevant national standards, and the weight percentage content of potassium chloride in the product is above 99%. The method of the present invention can use a simple and feasible method to prepare high-quality food-grade potassium chloride from crude potassium chloride. The equipment is simple and easy to be popularized industrially, and can be directly applied to the large-scale industrial production of potassium salts.

[0109] In addition, it can be seen that when all process parameters are within the preferred range of the present invention, the comprehensive effect is better.

[0110] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing food grade potassium chloride, characterized in that: The following steps are involved: Step S1, dissolving crude potassium from salt lake, filtering, and obtaining potassium chloride stock solution; Step S2, using a composite adsorbent to adsorb the potassium chloride stock solution to obtain an adsorbed liquid; Step S3, flash evaporating the adsorbed liquid under negative pressure to obtain a flashed liquid; Step S4, evaporating and concentrating the flashed liquid to obtain potassium chloride crystals; Step S5, washing and drying the potassium chloride crystals in sequence to obtain the food-grade potassium chloride; Wherein, the composite adsorbent comprises a carbon skeleton and a grafted resin.

2. The preparation method according to claim 1, characterized in that: The grafting resin includes styrene ring carboxylic acid resin and porous resin; Preferably, the weight ratio of the styrene ring carboxylic acid resin to the porous resin is 1:(0.1-100), more preferably 1:(0.3-30).

3. The preparation method according to claim 1 or 2, characterized in that: The weight ratio of the carbon skeleton to the grafting resin is 1:(0.05-0.2), preferably 1:(0.08-0.13); and / or The composite adsorbent has an adsorption capacity of 2 to 10 g / L for amine substances and an adsorption capacity of 15 to 25 g / L for metal cations.

4. The preparation method according to any one of claims 1 to 3, characterized in that In the step S2, the adsorption method includes static adsorption and / or dynamic adsorption, and the dynamic adsorption includes one or more of single column adsorption, continuous cross-linking adsorption and adsorption tower adsorption.

5. The preparation method according to claim 4, characterized in that: In the static adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:(1-40), and the adsorption time is 1-6 hours.

6. The preparation method according to claim 4 or 5, characterized in that: In the dynamic adsorption, the volume ratio of the composite adsorbent to the potassium chloride stock solution is 1:(2-50), the solution flow rate is 1-10 Bv / h, and the adsorption temperature is 10-35°C.

7. The preparation method according to any one of claims 1 to 6, characterized in that In the step S1, The crude potassium in the salt lake has a potassium chloride content of ≥90% by weight, and NH4 + The content of amine substances in terms of Pb is 100-1500 mg / kg, the content of heavy metals in terms of Pb is 0-10 mg / kg, the content of arsenic is 0-10 mg / kg, the weight percentage of sodium ions is 0.05-2%, and the weight percentage of magnesium ions is 0.05-2%; and / or The filtering method includes one or more of belt filtration, vacuum filtration, filter press and centrifugal filtration; and / or The mass concentration of the potassium chloride stock solution is ≤27%.

8. The preparation method according to any one of claims 1 to 7, characterized in that In the step S3, The negative pressure flash evaporation has a pressure of -0.06 to -0.1 MPa, a temperature of 65 to 100°C, and a time of 30 to 300 seconds; preferably, the negative pressure flash evaporation has a pressure of -0.07 to -0.1 MPa, a temperature of 65 to 90°C, and a time of 30 to 60 seconds; More preferably, before the negative pressure flash evaporation, the step S3 further comprises the step of adjusting the pH value of the adsorbed liquid to 7.7 to 8.9; More preferably, after the negative pressure flash evaporation, the step S3 further comprises the step of adjusting the pH value of the post-flash evaporation liquid to 6.5-7.

5.

9. The preparation method according to any one of claims 1 to 8, characterized in that: In the step S4, The evaporation and concentration method includes one or more of forced evaporation, single-effect evaporation and multiple-effect evaporation; and / or The concentration ratio of the evaporation concentration is 1:(3-40).

10. The preparation method according to any one of claims 1 to 9, characterized in that: In the step S5, In the water washing, the weight ratio of water to the potassium chloride crystals is (0.5-15):100, preferably (2-8):100; and / or The drying method includes one or more of box drying, hearth stone drying and negative pressure drying.

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