Method for preparing potassium nitrate

Abstract

The invention relates to a method for preparing potassium nitrate, which comprises the following steps: step 1, reacting a calcium nitrate solution with sodium sulfate to generate a sodium nitrate solution and calcium sulfate dihydrate, and separating the calcium sulfate dihydrate to obtain the sodium nitrate solution; 2, evaporating the sodium nitrate solution to obtain an evaporation completion solution; step 3, reacting the evaporated liquid with potassium chloride, and filtering after the reaction is completed to obtain filtrate; step 4, cooling and crystallizing the filtrate, and separating out a crystal substance of potassium nitrate; and 5, filtering the crystal substance, washing the obtained filter residue, and drying to obtain potassium nitrate.

Description

Technical Field

[0001] The present invention relates to the technical fields of chemical engineering and chemical fertilizers, and particularly to a method for producing potassium nitrate. Background Art

[0002] Potassium nitrate is an important inorganic compound, which is widely used in fields such as agricultural fertilizers, industrial catalysts, glass manufacturing, energy storage, food preservatives, and fireworks manufacturing. Especially in agriculture, as a high-purity nitrogen-potassium compound fertilizer, potassium nitrate has the advantages of good water solubility and no chloride ion residue, and plays a significant role in improving crop yield and quality. With the rapid development of modern agriculture and fine chemical industry, the market demand for potassium nitrate continues to grow, and there is an urgent need to develop efficient and low-cost production processes.

[0003] Currently, the main industrial methods for producing potassium nitrate include the double decomposition method of sodium nitrate and potassium chloride, the double decomposition method of ammonium nitrate and potassium chloride, the ion exchange method of ammonium nitrate and potassium chloride, and the magnesium nitrate method, etc. These traditional production methods have their own advantages and disadvantages: the double decomposition method of sodium nitrate and potassium chloride has the most mature process and high product quality, and the potassium nitrate yield can reach more than 98%. However, sodium nitrate comes from natural nitre or synthetic sodium nitrate, with limited raw material supply and relatively high price, resulting in high production costs; the ion exchange method of ammonium nitrate and potassium chloride has a mature process and good product quality, but has high equipment investment, high energy consumption, and due to ammonium nitrate being an explosive, the transportation and storage of ammonium nitrate are strictly controlled; the double decomposition method of ammonium nitrate and potassium chloride has a mature process, relatively simple operation, and low production costs, but the product quality is poor and it is only suitable for producing agricultural-grade potassium nitrate. Similarly, due to ammonium nitrate being an explosive, its use is restricted; the double decomposition method of magnesium nitrate and potassium chloride is the method adopted by most domestic small potassium nitrate production enterprises at present. Its advantage is that it avoids using ammonium nitrate as a raw material and uses magnesium nitrate or nitric acid and magnesium oxide as raw materials, with wide raw material sources and low prices. The disadvantages are that the potassium nitrate yield is less than 90%, low-temperature crystallization is required, the product quality is poor, and the by-product magnesium chloride is difficult to process, resulting in relatively high comprehensive production costs.

[0004] Producing potassium nitrate using calcium nitrate and potassium chloride has certain advantages. Both calcium nitrate and potassium chloride are chemical fertilizers, with easy availability and low prices. There have been previous patent reports in this regard. For example, directly producing potassium nitrate by the double decomposition reaction of calcium nitrate and potassium chloride has similar process conditions to the magnesium nitrate method, and the potassium nitrate yield is only 76%. Even when adding alcohols during the cooling crystallization process, the potassium nitrate yield is only 90%. The by-product calcium chloride contains a relatively high amount of potassium nitrate and is difficult to process. The above problems need to be solved urgently. Summary of the Invention

[0005] The present invention discloses a method for producing potassium nitrate, aiming to solve the technical problems existing in the prior art.

[0006] The present invention adopts the following technical solutions: A method for preparing potassium nitrate, characterized by comprising the following steps: Step 1: React a calcium nitrate solution with sodium sulfate to form a sodium nitrate solution and calcium sulfate dihydrate, separate the calcium sulfate dihydrate to obtain the sodium nitrate solution; Step 2: Evaporate the sodium nitrate solution to obtain an evaporation-complete liquid; Step 3: React the evaporation-complete liquid with potassium chloride, and after the reaction is completed, filter to obtain a filtrate; Step 4: Cool and crystallize the filtrate to precipitate potassium nitrate crystals; Step 5: Filter the crystals, wash the obtained filter residue, and dry it to obtain potassium nitrate.

[0007] In a method for preparing potassium nitrate according to the present invention, in Step 1, the molar ratio of calcium nitrate to sodium sulfate in the calcium nitrate solution is 1:1.

[0008] In a method for preparing potassium nitrate according to the present invention, the sodium sulfate in Step 1 is sodium sulfate solid or sodium sulfate solution.

[0009] In a method for preparing potassium nitrate according to the present invention, the step of reacting a calcium nitrate solution with sodium sulfate to form a sodium nitrate solution and calcium sulfate dihydrate in Step 1 includes: adding sodium sulfate solid to a normal-temperature saturated sodium nitrate solution under normal temperature and pressure, stirring to form a slurry, and then adding the calcium nitrate solution to the sodium sulfate slurry and stirring for reaction for more than 30 minutes to form a sodium nitrate solution and calcium sulfate dihydrate.

[0010] In a method for preparing potassium nitrate according to the present invention, the mass percentage concentration of the calcium nitrate solution in Step 1 is 35-45%.

[0011] In a method for preparing potassium nitrate according to the present invention, the reaction temperature of the high-temperature complete liquid with potassium chloride is 90-100 °C, and the reaction time is greater than or equal to 15 minutes.

[0012] In a method for preparing potassium nitrate according to the present invention, Step 1 further includes washing the separated calcium sulfate dihydrate with water, and dissolving the washing liquid in calcium nitrate to obtain the calcium nitrate solution.

[0013] In a method for preparing potassium nitrate according to the present invention, the filtration temperature after the reaction in Step 3 is 85 °C.

[0014] In a method for preparing potassium nitrate according to the present invention, Step 3 further includes washing the filter residue obtained by filtration with hot water at 85 °C or above, and mixing the obtained washing liquid with the evaporation-complete liquid and then reacting with potassium chloride.

[0015] In a method for preparing potassium nitrate according to the present invention, the fifth step further includes a step of mixing the crystallization mother liquor obtained by filtering the crystallization product with the sodium nitrate solution in the second step and then evaporating.

[0016] The technical solution adopted by the present invention can achieve the following beneficial effects: The present invention mainly provides a method for preparing potassium nitrate. Based on using calcium nitrate and potassium chloride as raw materials to prepare potassium nitrate, an auxiliary material sodium sulfate is introduced to react with calcium nitrate to prepare a sodium nitrate solution, and then the sodium nitrate solution and potassium chloride are subjected to a metathesis reaction to prepare potassium nitrate; it solves the problems of difficult raw material supply and high price in the sodium nitrate method and low product yield in the calcium nitrate method. The potassium nitrate yield of this method reaches 98%. Compared with the traditional process, the production cost is greatly reduced, and the by-product calcium sulfate is a high-quality building material. Specific embodiments

[0017] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. In the description of the present invention, it should be noted that the term "or" is usually used in the sense of including "and / or" unless otherwise clearly specified in the content.

[0018] Unless clearly indicated to the contrary, the numerical parameters in this specification and the appended claims can be approximate values and can be changed according to the required characteristics obtained through the content of the present invention. Specifically, all the numbers representing the content of the composition, reaction conditions, etc. used in the specification and claims should be understood to be modified by the term "about" in all cases. Generally, the meaning it expresses is that it includes a change of ±10% in some embodiments, a change of ±5% in some embodiments, a change of ±1% in some embodiments, and a change of ±0.5% in some embodiments for a specific quantity.

[0019] Furthermore, the word "comprising" does not exclude the presence of materials or steps not listed in the claims. Ordinal numbers such as "first", "second", "third" and Arabic numerals, letters, etc. used in the specification and claims to modify corresponding elements or steps do not themselves mean the order in the manufacturing method. The use of these ordinal numbers is only used to clearly distinguish the steps.

[0020] In addition, unless specifically described or steps that must occur in sequence, the order of the above steps is not limited to the above list and can be changed or rearranged according to the required design. And the above embodiments can be mixed and used with each other or mixed and used with other embodiments based on considerations of design and reliability, that is, the technical features in different embodiments can be freely combined to form more embodiments.

[0021] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] To solve the problems existing in the prior art, an embodiment of the present application provides a method for preparing potassium nitrate.

[0023] A method for preparing potassium nitrate includes the following steps: Step 1: React calcium nitrate solution with sodium sulfate to generate sodium nitrate solution and calcium sulfate dihydrate, separate the calcium sulfate dihydrate, and obtain the sodium nitrate solution; Step 2: Evaporate the sodium nitrate solution; specifically, when the evaporation liquid reaches a specific gravity of d 100 = 1.544 (or 50.6 Be‘), the evaporation-completed liquid is obtained; Step 3: React the evaporation-completed liquid with potassium chloride, filter after the reaction is completed, and obtain a filtrate; Step 4: Cool and crystallize the filtrate to precipitate potassium nitrate crystals; Step 5: Filter the crystal slurry, wash the obtained filter residue, and dry it to obtain potassium nitrate.

[0024] In the method for preparing potassium nitrate of the present invention, based on using calcium nitrate and potassium chloride as raw materials to prepare potassium nitrate, an auxiliary material sodium sulfate is introduced to react with calcium nitrate to prepare sodium nitrate solution, and then the sodium nitrate solution and potassium chloride are subjected to a metathesis reaction to prepare potassium nitrate; it solves the problems of difficult raw material supply and high price in the sodium nitrate method and low product yield in the calcium nitrate method. The potassium nitrate yield of this method reaches 98%. Compared with the traditional process, the production cost is greatly reduced, and the by-product calcium sulfate is a high-quality building material.

[0025] In some preferred embodiments, the molar ratio of calcium nitrate to sodium sulfate in the calcium nitrate solution in Step 1 is 1:1; based on this, the reaction is ensured to be complete, and the remaining reactants are avoided from contaminating the sodium nitrate solution.

[0026] In some preferred embodiments, the sodium sulfate in Step 1 is sodium sulfate solid or sodium sulfate solution; preferably, the sodium sulfate is sodium sulfate solid. Since the solubility of solid Na2SO4 in the sodium nitrate saturated solution is small, Na2SO4 gradually dissolves during the reaction, avoiding the outburst of CaSO4·2H2O crystal nuclei.

[0027] In some preferred embodiments, the step of reacting calcium nitrate solution with sodium sulfate to form sodium nitrate solution and calcium sulfate dihydrate in step one includes: adding solid sodium sulfate to a normal-temperature saturated sodium nitrate solution under normal temperature and pressure, stirring to form a slurry, and then adding the calcium nitrate solution to the sodium sulfate slurry and stirring for more than 30 minutes to form a sodium nitrate solution and calcium sulfate dihydrate. Based on this, on the one hand, using a saturated sodium nitrate solution to disperse solid sodium sulfate avoids using water for dissolution and reduces the evaporation amount; on the other hand, the solubility of sodium sulfate in the saturated sodium nitrate solution is small, and when the calcium nitrate solution is added to the sodium sulfate slurry, no crystal nuclei will burst, ensuring the normal filtration of calcium sulfate subsequently.

[0028] In some preferred embodiments, the mass percentage concentration of the calcium nitrate solution in step one is 35 - 45%; thus, when preparing with the calcium sulfate washing solution, which contains about 8% NaNO3, when using a calcium nitrate solution with this concentration, the sodium nitrate solution after the reaction of the calcium nitrate solution and sodium sulfate is about 47% and will not crystallize, and the amount of evaporated water is small.

[0029] Preferably, the mass percentage concentration of the calcium nitrate solution is 37%.

[0030] In some preferred embodiments, the reaction temperature of the high-temperature completed liquid with potassium chloride is 90 - 100 °C, and the reaction time is greater than or equal to 15 minutes; this ensures sufficient reaction.

[0031] In some preferred embodiments, step one further includes washing the separated calcium sulfate dihydrate with water and dissolving the washing solution in calcium nitrate to obtain a sodium nitrate solution step; in this way, the digestion washing water is balanced.

[0032] In some preferred embodiments, the filtration temperature after the reaction in step three is 85 °C; when the temperature exceeds 85 °C, after potassium nitrate is saturated, the solution viscosity is high and filtration is difficult, and when the temperature is lower than 85 °C, the solubility of potassium nitrate is small, the product is less, and the production efficiency is low.

[0033] In some preferred embodiments, step three further includes washing the filter residue obtained by filtration with hot water above 85 °C and mixing the obtained washing solution with the evaporation completed liquid and then reacting with potassium chloride. The sodium chloride washing solution has a high sodium chloride content and a low potassium nitrate content. Returning to this step is beneficial for the reaction of potassium nitrate. The NaCl dissolved from the washing salt in the previous cycle will also precipitate and be filtered out at this time, avoiding entering the evaporation system.

[0034] In some preferred embodiments, step five further includes filtering the crystallized product and mixing the obtained crystallization mother liquor with the sodium nitrate solution in step two for evaporation. Since a certain amount of water is consumed when washing the filter residue (KNO3), the sodium chloride content in the potassium nitrate crystallization mother liquor is relatively less than that in the washing brine. Returning the crystallization mother liquor for evaporation balances the washing water and reduces the amount of sodium chloride precipitated during the evaporation process.

[0035] Specifically, the specific gravity of the evaporation-complete liquid concentration is d 100 = 1.544 (or 50.6 Be‘); at this time, the high-temperature complete liquid contains NO3 - at 40 - 43%, preferably 42.5%; solid NaCl is 3 - 6%.

[0036] Example 1 Step 1: Take 400 g of Ca(NO3)2·4H2O (the following concentrations are all mass percentage concentrations) and stir it into 350 g of the washing liquid of calcium sulfate dihydrate (calcium washing liquid (containing 10.68% NaNO3)) to obtain a calcium nitrate solution with a concentration of 36.8%; Step 2: Take another 240 g of Na2SO4 and stir it in 2000 g of saturated sodium nitrate solution (NaNO3 is 47%) to obtain a slurry. Add the calcium nitrate solution in Step 1 to the sodium sulfate slurry and stir and react at room temperature for 30 minutes, then vacuum filter to obtain 2613 g of filtrate. The filtrate contains 46.92% NaNO3; wash the filter residue four times with 350 ml of water to obtain 368 g of wet filter residue CaSO4·2H2O. The filter residue contains 21.1% water and 0.0005% NaN03; the calcium washing liquid is 354 g, containing 11.1% NaNO3, and is used for preparing calcium nitrate in the next batch; Step 3: Take 575 g of the sodium nitrate filtrate (NaNO3 is 46.92%) obtained in Step 2 and mix it with 581 g of 20°C potassium nitrate crystallization mother liquor (the mother liquor contains 17.01% NaCl, 19.74% KNO3, 11.5% NaNO3) and evaporate to 740 g to obtain the evaporation-complete liquid. The evaporation temperature is 100°C (the evaporation-complete liquid contains 7.56% NaCl, 15.5% KNO3, 45.41% NaNO3, 31.53% H2O, and solid NaCl is 6%); Step 4: Mix 740 g of the evaporation-complete liquid with 155 g of the washing liquid (containing 26.5% NaCl, 6.79% KNO3, 1.38% NaNO3, 65.33% H2O), heat to 100°C, then add 236 g of KCl (K2O is 62%) and react for 15 minutes, then hot filter to obtain 892 g of filtrate; wash the filter residue NaCl with 110 mml of 90°C hot water to obtain 145 g of wet filter residue NaCl (containing 9.3% water and 0.17% K2O) and 183 g of washing liquid (containing 8.03% KNO3, 1.34% NaNO3, 24.47% NaCl, 66.16% H2O); Step 5: Add 60 ml of water to 892 g of the high-temperature filtrate and cool it to 20°C; Step 6: Vacuum filter the crystallization slurry from Step 5 to obtain 640 g of potassium nitrate crystallization mother liquor (NaCl is 19.31%, KNO3 is 21.57%, NaNO3 is 8.08%, and H2O is 51.24%). The potassium nitrate crystallization mother liquor is used to return to Step 3 and mix with the sodium nitrate solution for evaporation. Rinse the potassium nitrate solid with 75 ml of water to obtain 252 g of wet potassium nitrate. After drying, 236.9 g of potassium nitrate is obtained, which contains 0.32% Cl and 99.5% KNO3.

[0037] In this example, the residual sodium nitrate content in calcium sulfate dihydrate (dry basis) is 0.0006%, the potassium nitrate content in the product is 99.5%, the K2O content in the by-product sodium chloride is 0.19% (dry basis), and the yield of potassium nitrate is 99%. After drying and dehydration, calcium sulfate dihydrate can be used as a gypsum mold and building decoration material.

[0038] Example 2 The difference between this example and Example 1 is that in Step 4, heat to 90 °C and then add 236 g of KCl (K2O is 62%) and react for 15 minutes; the rest is the same as in Example 1.

[0039] In this example, the residual sodium nitrate content in calcium sulfate dihydrate (dry basis) is 0.0006%, the potassium nitrate content in the product is 99.56%, the K2O content in the by-product sodium chloride is 0.22% (dry basis), and the yield of potassium nitrate is 99.2%.

[0040] Example 3 The difference between this example and Example 1 is that in Step 4, heat to 95 °C and then add 236 g of KCl (K2O is 62%) and react for 15 minutes; the rest is the same as in Example 1.

[0041] In this example, the residual sodium nitrate content in calcium sulfate dihydrate (dry basis) is 0.0005%, the potassium nitrate content in the product is 99.13%, the K2O content in the by-product sodium chloride is 0.23% (dry basis), and the yield of potassium nitrate is 99.2%.

[0042] Example 4 In this example, the residual sodium nitrate content in calcium sulfate dihydrate (dry basis) is 0.0005%, the potassium nitrate content in the product is 99.07%, the K2O content in the by-product sodium chloride is 0.14% (dry basis), and the yield of potassium nitrate is 99%.

[0043] Example 5 The difference between this example and Example 1 is that in Step 4, rinse with hot water at 80 °C, and the rest is the same as in Example 1.

[0044] In this example, the residual sodium nitrate content in calcium sulfate dihydrate (dry basis) is 0.0006%, the potassium nitrate content in the product is 99.5%, the K2O content in the by-product sodium chloride is 0.26% (dry basis), and the yield of potassium nitrate is 99%.

[0045] Example 6 The difference between this example and Example 1 is that in Step 4, the reaction is carried out for 20 minutes, and the rest is the same as in Example 1.

[0046] In this example, the residual sodium nitrate content in calcium sulfate dihydrate (dry basis) is 0.0009%, the potassium nitrate content in the product is 99.48%, the K2O content in the by-product sodium chloride is 0.21% (dry basis), and the yield of potassium nitrate is 99.2%.

[0047] Comparative Example 1 The difference between this comparative example and Example 1 is that in Step 2, another 240 g of Na2SO4 is taken and stirred in 2000 g of water to obtain a slurry, and the rest is the same as in Example 1.

[0048] In this example, the residual sodium nitrate content in calcium sulfate dihydrate (dry basis) is 0.04%, the potassium nitrate content in the product is 99.55%, the K2O content in the by-product sodium chloride is 0.26% (dry basis), and the yield of potassium nitrate is 99.2%.

[0049] The embodiments of the present invention have been described above. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit and scope protected by the claims of the present invention, and all of them belong to the protection scope of the present invention.

Claims

1. A method for preparing potassium nitrate, characterized in that, It includes the following steps: Step 1: React calcium nitrate solution with sodium sulfate to form sodium nitrate solution and calcium sulfate dihydrate, separate the calcium sulfate dihydrate to obtain sodium nitrate solution; Step 2: Evaporate the sodium nitrate solution to obtain an evaporation-complete liquid; Step 3: React the evaporation-complete liquid with potassium chloride, and filter after the reaction is completed to obtain a filtrate; Step 4: Cool and crystallize the filtrate to precipitate potassium nitrate crystals; Step 5: Filter the crystals, wash the obtained filter residue, and dry it to obtain potassium nitrate.

2. A method for preparing potassium nitrate according to claim 1, characterized in that, In Step 1, the molar ratio of calcium nitrate in the calcium nitrate solution to the sodium sulfate is 1:

1.

3. A method for preparing potassium nitrate according to claim 1, characterized in that, The sodium sulfate in Step 1 is sodium sulfate solid or sodium sulfate solution.

4. A method for preparing potassium nitrate according to claim 1, characterized in that, The step of reacting calcium nitrate solution with sodium sulfate to form sodium nitrate solution and calcium sulfate dihydrate in Step 1 includes: adding sodium sulfate solid to a normal-temperature saturated sodium nitrate solution under normal temperature and pressure, stirring to form a slurry, and then adding the calcium nitrate solution to the sodium sulfate slurry and stirring for reaction for more than 30 minutes to form sodium nitrate solution and calcium sulfate dihydrate.

5. A method for preparing potassium nitrate according to claim 1, characterized in that, The mass percentage concentration of the calcium nitrate solution in Step 1 is 35 - 45%.

6. A method for preparing potassium nitrate according to claim 1, characterized in that, In Step 3, the reaction temperature of the high-temperature complete liquid with potassium chloride is 90 - 100 °C, and the reaction time is greater than or equal to 15 minutes.

7. A method for preparing potassium nitrate according to claim 1, characterized in that, Step 1 further includes washing the separated calcium sulfate dihydrate with water, and dissolving the washing liquid with calcium nitrate to obtain the calcium nitrate solution.

8. A method for preparing potassium nitrate according to claim 1, characterized in that, The filtration temperature after the reaction in Step 3 is 85 °C.

9. A method for preparing potassium nitrate according to claim 1, characterized in that, Step 3 further includes washing the filter residue obtained by filtration with hot water above 85 °C, and mixing the obtained washing liquid with the evaporation-complete liquid and then reacting with potassium chloride.

10. A method for preparing potassium nitrate according to claim 1, characterized in that, Step 5 further includes mixing the crystal mother liquor obtained by filtering the crystals with the sodium nitrate solution in Step 2 and evaporating.