CN108516568B - Production method of potassium nitrate - Google Patents
Production method of potassium nitrate Download PDFInfo
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- CN108516568B CN108516568B CN201810407668.6A CN201810407668A CN108516568B CN 108516568 B CN108516568 B CN 108516568B CN 201810407668 A CN201810407668 A CN 201810407668A CN 108516568 B CN108516568 B CN 108516568B
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D9/00—Nitrates of sodium, potassium or alkali metals in general
- C01D9/08—Preparation by double decomposition
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D9/00—Nitrates of sodium, potassium or alkali metals in general
- C01D9/16—Purification
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F5/00—Compounds of magnesium
- C01F5/26—Magnesium halides
- C01F5/30—Chlorides
Abstract
The invention discloses a method for producing potassium nitrate, which comprises the following steps: step (1): reacting magnesium oxide, potassium chloride and nitric acid; step (2): carrying out solid-liquid separation treatment on the reaction liquid in the step (1) to obtain a filtrate; and (3): mixing a cosolvent into the filtrate obtained in the step (2); and (4): and (4) carrying out solid-liquid separation on the crystallization feed liquid obtained in the step (3) to obtain potassium nitrate. The method has the advantages of easily available raw materials, low cost, green and environment-friendly process, and repeatedly recyclable cosolvent. Compared with the traditional double decomposition process, the product has higher purity, higher yield and wider application of the byproduct magnesium chloride, and simultaneously avoids the danger brought by using ammonium nitrate to the production and the inconvenience of raw material transportation.
Description
Technical Field
The invention relates to the technical field of inorganic chemical industry, in particular to a production method of high-purity potassium nitrate
Background
Potassium nitrate (KNO)3) The product is named as saltpeter and saltpeter, and is an important inorganic chemical product and a chlorine-nitrogen-and-potassium-free binary high-quality compound fertilizer. As an agricultural potassium fertilizer, the potassium nitrate is superior to potassium chloride in action. Has the effects of remarkably improving the quality of crops and increasing the yield and income. Potassium nitrate, which is not a fertilizer application, is a raw material for making black powder and is also used for a flame to produce a purple spark. The medicine industry can be used for producing penicillin sylvite, rifampicin and other medicines. Edible potassium nitrate is used as a colour former and preservative additive in the food industry. It can also be used as glass clarifying agent and for manufacturing glass shells of automobile lamps, optical glass, computer and television kinescope, etc. In addition, in the industries of chemical industry, tobacco industry, metallurgy and the like, potassium nitrate can also be used as a catalyst, cigarette paper manufacturing, a beneficiation agent and the like. At present, domestic methods for producing potassium nitrate mainly comprise a double decomposition method and an ion exchange method.
The double decomposition method generally adopts ammonium nitrate and potassium chloride as raw materials to prepare potassium nitrate and ammonium chloride as a byproduct. The method not only has high production cost and low price of the byproduct ammonium chloride, but also restricts the production of the potassium nitrate because the used raw material ammonium nitrate is a dangerous explosive and the nation takes strict restriction measures for the production and transportation of the ammonium nitrate.
The ion exchange method is to prepare potassium nitrate by carrying out ion exchange reaction on ammonium nitrate and potassium chloride. The method has the advantages of high product quality, high energy consumption, complex equipment structure and high investment cost.
Disclosure of Invention
Based on the problems existing in the technical background, the invention provides a method for producing high-purity potassium nitrate, aiming at improving the purity and yield of potassium nitrate.
A method for producing potassium nitrate comprises the following steps:
step (1): reacting magnesium oxide, potassium chloride and nitric acid;
step (2): carrying out solid-liquid separation treatment on the reaction liquid in the step (1) to obtain a filtrate;
and (3): mixing a cosolvent into the filtrate obtained in the step (2); the cosolvent is C1-C4 alcohol;
and (4): and (4) carrying out solid-liquid separation on the crystallization feed liquid (crystallization solution system) obtained in the step (3) to obtain potassium nitrate.
The preparation method provided by the invention innovatively combines the synthesis mode with the crystallization process, so that the purity and yield of the product can be improved. In addition, the method has the characteristics of easily obtained raw materials, low energy consumption, green and environment-friendly production process and the like.
According to the preparation method, the high-purity potassium nitrate can be obtained through crystallization by the synthesis method under the action of the cosolvent added in the crystallization process.
The research shows that the purity and the yield of the prepared potassium nitrate can be further improved under the appropriate preparation parameters of the step (1). Preferably, magnesium oxide and potassium chloride are added into nitric acid with the mass fraction of 50% -60%, the reaction temperature is controlled to be 60-110 ℃, and the pH value of the reaction solution is controlled to be 2-7.
Preferably, in step (1), the molar ratio of magnesium oxide, potassium chloride and nitric acid is 1: 2.
Preferably, in step (1), the reaction is carried out for 0.5 to 1.0 hour.
In the invention, the reaction solution obtained in the step (1) is filtered while hot to remove impurities, so that the filtrate is obtained.
The purity of the obtained potassium nitrate can be unexpectedly improved by combining the preparation method of the step (1) and the newly added cosolvent in the filtrate.
The cosolvent is alcohol which can be mixed and dissolved with water in an infinite ratio.
Preferably, the cosolvent is methanol and/or ethanol. Researches show that the yield of the product can be further improved by adopting the preferable material under the condition of ensuring high purity.
In the invention, in the step (3), the filtrate is cooled, cosolvent is added into the solution in the cooling process, and the solution is continuously stirred for cooling crystallization to ensure that potassium nitrate is fully precipitated.
Preferably, the mass of the cosolvent is not less than 0.5 times of the mass of the potassium chloride. Researches show that when the cosolvent is less added, the purity of the potassium nitrate is reduced.
More preferably, the mass of the cosolvent is 0.5-3 times of that of the potassium chloride.
The mass of the cosolvent is 0.5 to 2 times of that of the potassium chloride. The research shows that the purity of the product is higher and the yield of the product is further improved at the preferable adding amount.
Researches also find that the impurity content of the product can be further reduced and the purity and yield of the potassium nitrate can be improved by further controlling the adding temperature and the crystallization temperature of the cosolvent under the cosolvent.
Preferably, in the step (3), the temperature of the filtrate is reduced to 10-40 ℃, and then the cosolvent is mixed. It was surprisingly found by research that the co-solvent is added to the filtrate after the filtrate is cooled to the preferred temperature, which helps to improve the purity and yield of the product.
Preferably, in the step (3), the temperature of the filtrate is reduced to 10-20 ℃, and then the cosolvent is mixed. Under the optimal adding temperature, the yield and the purity of the obtained product can be further improved, the loss of the cosolvent can be reduced, and the cost is reduced.
In the invention, the synthesis process of the potassium nitrate, the cosolvent assisted crystallization and the control of the adding temperature are matched, the crystallization temperature is further controlled, and the yield can be obviously improved under the condition of ensuring good purity.
Preferably, in step (3), the temperature of crystallization is less than 20 ℃.
Further preferably, in the step (3), the temperature of crystallization is from-10 ℃ to 20 ℃.
More preferably, in the step (3), the temperature of crystallization is from-10 ℃ to 0 ℃. By matching with the process and the optimized crystallization temperature, the yield of the product can be improved to 95 percent or more, and the purity of the product can be improved to 99.7 percent or more.
Preferably, in the step (3), the crystallization time is 1.0-4.0 h.
And (4) carrying out solid-liquid separation on the system crystallized in the step (3), collecting a solid part, washing and drying to obtain the potassium nitrate.
Preferably, the washing liquid adopted in the washing process is a potassium nitrate solution; preferably a saturated aqueous solution of potassium nitrate.
The preparation method of the invention also comprises the following steps: and (4) distilling the liquid part obtained by solid-liquid separation in the step (4), recovering the cosolvent, continuing concentrating, cooling, crystallizing and separating to obtain a byproduct magnesium chloride and a circulating mother liquor.
Preferably, the recovered cosolvent is recycled and reused in the step (3), and the recycled mother liquor is reused in the step (1).
The invention relates to a more preferable production method of high-purity potassium nitrate, which comprises the following steps:
1) slowly adding solid magnesium oxide and potassium chloride into nitric acid with the mass fraction of 50% -60% according to a certain proportion, controlling the reaction temperature to be 60-110 ℃, controlling the pH value of a reaction solution to be 2-7, and reacting for 0.5-1.0 hour.
2) Filtering the reaction solution in the step 1) while the reaction solution is hot, and removing impurities in the feed liquid.
3) Cooling and crystallizing the filtrate obtained in the step 2). The temperature of the solution is reduced to-10-20 ℃ by cooling or freezing, a certain amount of organic cosolvent is added in the cooling process, and a large amount of potassium nitrate crystals are separated out by crystallization of the solution.
4) Filtering and separating the crystallization feed liquid in the step 3). Separating to obtain potassium nitrate and mother liquor I, washing and drying the solid to obtain the finished product of potassium nitrate.
5) Evaporating and concentrating the mother liquor I obtained in the step 4). Recycling the organic cosolvent and returning to be used (mechanically applied to the step 3));
6) cooling and crystallizing the feed liquid concentrated in the step 5) to separate out magnesium chloride hexahydrate crystals, carrying out solid-liquid separation to obtain magnesium chloride crystals and a mother liquid II, and returning the mother liquid II to the dissolution reaction kettle for use (mechanically applied to the step 1)).
The cosolvent added in the step 3) is methanol, ethanol or a mixed solvent of two solvents, the mass of the added cosolvent is 0.5-2.0 times of that of potassium chloride, and the optimal range is obtained through experimental optimization, the cosolvent is less and can influence the purity of potassium nitrate, and the cosolvent can reduce the yield of potassium nitrate and waste energy.
In the step 3), when the temperature of the feed liquid is reduced to 10-30 ℃, adding an alcohol cosolvent into the feed liquid; the temperature of the final crystallized potassium nitrate when being completely precipitated is controlled between-10 ℃ and 20 ℃.
According to the method, double decomposition reaction is carried out on magnesium oxide, potassium chloride and nitric acid to generate potassium nitrate and magnesium chloride, then cooling crystallization is carried out by utilizing the difference of the solubility of the potassium nitrate and the magnesium chloride along with the change of temperature, a certain amount of cosolvent is added in the crystallization process to improve the solubility of the magnesium chloride, and the crystallization difference of the magnesium chloride and the potassium nitrate is further amplified, so that the purity and the crystallization rate of the potassium nitrate are improved. The cosolvent is preferably methanol, ethanol or a mixed solvent of two solvents, and is added in the process of cooling and crystallizing the feed liquid, so that magnesium chloride is not precipitated in a solid form, and the solubility of potassium nitrate can be reduced, thereby greatly improving the crystal quantity of potassium nitrate and the purity of potassium nitrate, and remarkably improving the separation effect of products.
Advantageous effects
Compared with other process routes, the method of the invention comprises the following steps: the raw materials are easy to obtain, the cost is low, the process is green and environment-friendly, the separation effect of potassium nitrate and magnesium chloride is obviously improved by introducing the cosolvent, compared with the traditional double decomposition process, the obtained product has higher purity and yield, the by-product magnesium chloride has wider application, and the danger brought to production and the inconvenience of raw material transportation by using ammonium nitrate are avoided.
By the method, the purity of the potassium nitrate can reach 99.9 percent, and the yield of the product can reach more than 97 percent. And the operation is convenient, thus being beneficial to industrial scale-up production.
Drawings
FIG. 1 is a process flow diagram of the present invention
Detailed Description
Example 1
Adding 1260 g of nitric acid with the mass fraction of 50% into a 2000 ml four-neck flask with a stirring and condensing pipe and a thermometer, slowly adding 195 g of magnesium oxide powder while stirring, controlling the pH value to be between 2 and 7, continuously stirring for 30 minutes after the magnesium oxide is added, slowly adding 745 g of solid potassium chloride, then introducing steam to heat and dissolve, controlling the temperature to be between 60 and 110 ℃ to completely dissolve the solid potassium chloride, then preserving heat for 1 hour at the temperature of between 100 and 110 ℃, and simultaneously evaporating part of water; then filtering while the solution is hot to remove impurities which cannot be contained in the solution; then transferring the filtrate into a 5000 ml flask with a stirring, thermometer and cooling bath for cooling crystallization, when the temperature of the feed liquid is reduced to 30 ℃, adding 400 g of methanol into the feed liquid, continuing stirring, reducing the temperature for crystallization, and stirring the crystals at 20 ℃ for 1 hour to completely separate out potassium nitrate; then, the solid is separated by suction filtration, and is washed by saturated potassium nitrate solution, and then the solid is dried to obtain 788 g of finished potassium nitrate product with yield of 78% and purity of 99.8%; the filtrate is distilled to recover methanol, evaporated, concentrated, crystallized, solid-liquid separated and dried to obtain 810 g of magnesium chloride hexahydrate, the yield is 80.0%, and the purity is 95.1%.
Example 2
Adding 1260 g of nitric acid with the mass fraction of 50% into a 2000 ml four-neck flask with a stirring and condensing pipe and a thermometer, slowly adding 195 g of magnesium oxide powder while stirring, controlling the pH value to be between 2 and 7, continuously stirring for 30 minutes after the magnesium oxide is added, slowly adding 745 g of solid potassium chloride, then introducing steam to heat and dissolve, controlling the temperature to be between 60 and 110 ℃ to completely dissolve the solid potassium chloride, then preserving heat for 1 hour at the temperature of between 100 and 110 ℃, and simultaneously evaporating part of water; then filtering while the solution is hot to remove impurities which cannot be contained in the solution; then transferring the filtrate into a 5000 ml flask with a stirring, thermometer and cooling bath for cooling crystallization, when the temperature of the feed liquid is reduced to 30 ℃, adding 600 g of methanol into the feed liquid, continuously stirring, reducing the temperature for crystallization, and stirring for crystallization for 1 hour when the temperature is reduced to-10 ℃ so as to completely separate out potassium nitrate; then, the solid is separated by suction filtration, and is washed by saturated potassium nitrate solution, and then the solid is dried to obtain 962 g of finished potassium nitrate product, the yield is 95.2 percent, and the purity is 99.7 percent; after the filtrate is distilled to recover methanol, 851 g of magnesium chloride hexahydrate is obtained by evaporation concentration, crystallization, solid-liquid separation and drying, the yield is 84.0 percent and the purity is 96.3 percent.
Example 3
1260 g of nitric acid with the mass fraction of 50 percent is added into a 2000 ml four-neck flask with a stirring and condensing tube and a thermometer, 195 g of magnesium oxide powder is slowly added under stirring, the PH value is controlled between 2 and 7, 745 g of solid potassium chloride is slowly added after the magnesium oxide is added and the stirring is continued for 30 minutes, then steam is introduced for heating and dissolving, the temperature is controlled between 60 ℃ and 110 ℃ to completely dissolve the solid potassium chloride, then the temperature is kept at 100 ℃ to 110 ℃ for 1 hour, and part of water is evaporated out at the same time; then filtering while the solution is hot to remove impurities which cannot be contained in the solution; then transferring the filtrate into a 5000 ml flask with a stirring, thermometer and cooling bath for cooling crystallization, when the temperature of the feed liquid is reduced to 20 ℃, adding 1000 g of methanol into the feed liquid, continuously stirring, reducing the temperature for crystallization, and stirring the crystals for 1 hour when the temperature is reduced to-10 ℃ so as to completely separate out potassium nitrate; then, the solid is separated by suction filtration, and is washed by saturated potassium nitrate solution, and then the solid is dried to obtain 974 g of finished potassium nitrate product, the yield is 96.4%, and the purity is 99.8%; after the filtrate is distilled to recover methanol, 860 g of magnesium chloride hexahydrate is obtained after evaporation concentration, crystallization, solid-liquid separation and drying, the yield is 85.0 percent, and the purity is 95.9 percent.
Example 4
1260 g of nitric acid with the mass fraction of 50 percent is added into a 2000 ml four-neck flask with a stirring and condensing tube and a thermometer, 195 g of magnesium oxide powder is slowly added under stirring, the PH value is controlled between 2 and 7, 745 g of solid potassium chloride is slowly added after the magnesium oxide is added and the stirring is continued for 30 minutes, then steam is introduced for heating and dissolving, the temperature is controlled between 60 ℃ and 110 ℃ to completely dissolve the solid potassium chloride, then the temperature is kept at 100 ℃ to 110 ℃ for 1 hour, and part of water is evaporated out at the same time; then filtering while the solution is hot to remove impurities which cannot be contained in the solution; then transferring the filtrate into a 5000 ml flask with a stirring, thermometer and cooling bath for cooling crystallization, when the temperature of the feed liquid is reduced to 20 ℃, adding 1500 g of methanol into the feed liquid, continuously stirring, reducing the temperature for crystallization, and stirring the crystals for 1 hour when the temperature is reduced to-10 ℃ so as to completely separate out potassium nitrate; then, the solid is separated by suction filtration, and is washed by saturated potassium nitrate solution, and then the solid is dried to obtain 981 g of finished potassium nitrate product, the yield is 97.1 percent, and the purity is 99.9 percent; after the filtrate is distilled to recover methanol, the mixture is evaporated, concentrated, crystallized, separated from solid and liquid and dried to obtain 858 g of magnesium chloride hexahydrate, the yield is 84.7 percent, and the purity is 95.1 percent.
Example 5
1260 g of nitric acid with the mass fraction of 50 percent is added into a 2000 ml four-neck flask with a stirring and condensing tube and a thermometer, 195 g of magnesium oxide powder is slowly added under stirring, the PH value is controlled between 2 and 7, 745 g of solid potassium chloride is slowly added after the magnesium oxide is added and the stirring is continued for 30 minutes, then steam is introduced for heating and dissolving, the temperature is controlled between 60 ℃ and 110 ℃ to completely dissolve the solid potassium chloride, then the temperature is kept at 100 ℃ to 110 ℃ for 1 hour, and part of water is evaporated out at the same time; then filtering while the solution is hot to remove impurities which cannot be contained in the solution; then transferring the filtrate into a 5000 ml flask with a stirring, thermometer and cooling bath for cooling crystallization, when the temperature of the feed liquid is reduced to 10 ℃, adding 1000 g of methanol into the feed liquid, continuously stirring, reducing the temperature for crystallization, and stirring the crystals for 1 hour when the temperature is reduced to-10 ℃ so as to completely separate out potassium nitrate; then, the solid is separated by suction filtration, and is washed by saturated potassium nitrate solution, and then the solid is dried to obtain 976 g of finished potassium nitrate product, the yield is 96.6%, and the purity is 99.8%; after the filtrate is distilled to recover methanol, 855 g of magnesium chloride hexahydrate is obtained after evaporation concentration, crystallization, solid-liquid separation and drying, the yield is 84.5 percent, and the purity is 96.0 percent.
Example 6
The cosolvent is changed into ethanol:
1260 g of nitric acid with the mass fraction of 50 percent is added into a 2000 ml four-neck flask with a stirring and condensing tube and a thermometer, 195 g of magnesium oxide powder is slowly added under stirring, the PH value is controlled between 2 and 7, 745 g of solid potassium chloride is slowly added after the magnesium oxide is added and the stirring is continued for 30 minutes, then steam is introduced for heating and dissolving, the temperature is controlled between 60 ℃ and 110 ℃ to completely dissolve the solid potassium chloride, then the temperature is kept at 100 ℃ to 110 ℃ for 1 hour, and part of water is evaporated out at the same time; then filtering while the solution is hot to remove impurities which cannot be contained in the solution; then transferring the filtrate into a 5000 ml flask with a stirring, thermometer and cooling bath for cooling crystallization, when the temperature of the feed liquid is reduced to 30 ℃, adding 1000 g of ethanol into the feed liquid, continuously stirring, reducing the temperature for crystallization, and stirring the crystals for 1 hour when the temperature is reduced to-10 ℃ so as to completely separate out potassium nitrate; then, the solid is separated by suction filtration, and is washed by saturated potassium nitrate solution, and then the solid is dried to obtain 976 g of finished potassium nitrate product, the yield is 96.6%, and the purity is 99.7%; after the filtrate is distilled to recover ethanol, 860 g of magnesium chloride hexahydrate is obtained after evaporation concentration, crystallization, solid-liquid separation and drying, the yield is 83.7 percent and the purity is 95.6 percent.
Example 7
Example of addition of cosolvent when cooling to 40 ℃:
1260 g of nitric acid with the mass fraction of 50 percent is added into a 2000 ml four-neck flask with a stirring and condensing tube and a thermometer, 195 g of magnesium oxide powder is slowly added under stirring, the PH value is controlled between 2 and 7, 745 g of solid potassium chloride is slowly added after the magnesium oxide is added and the stirring is continued for 30 minutes, then steam is introduced for heating and dissolving, the temperature is controlled between 60 ℃ and 110 ℃ to completely dissolve the solid potassium chloride, then the temperature is kept at 100 ℃ to 110 ℃ for 1 hour, and part of water is evaporated out at the same time; then filtering while the solution is hot to remove impurities which cannot be contained in the solution; then transferring the filtrate into a 5000 ml flask with a stirring, thermometer and cooling bath for cooling crystallization, when the temperature of the feed liquid is reduced to 40 ℃, adding 1000 g of methanol into the feed liquid, continuously stirring, reducing the temperature for crystallization, and stirring the crystals for 1 hour when the temperature is reduced to-10 ℃ so as to completely separate out potassium nitrate; then, carrying out suction filtration and separation on the solid, washing the solid by using a saturated potassium nitrate solution, and then drying the solid to obtain 972 g of a finished potassium nitrate product, wherein the yield is 96.2%, and the purity is 99.7%; after the filtrate is distilled to recover methanol, 850 g of magnesium chloride hexahydrate is obtained after evaporation concentration, crystallization, solid-liquid separation and drying, the yield is 84.0 percent and the purity is 95.4 percent.
Example 8
Examples of methanol addition greater than the proportional Range
1260 g of nitric acid with the mass fraction of 50 percent is added into a 2000 ml four-neck flask with a stirring and condensing tube and a thermometer, 195 g of magnesium oxide powder is slowly added under stirring, the PH value is controlled between 2 and 7, 745 g of solid potassium chloride is slowly added after the magnesium oxide is added and the stirring is continued for 30 minutes, then steam is introduced for heating and dissolving, the temperature is controlled between 60 ℃ and 110 ℃ to completely dissolve the solid potassium chloride, then the temperature is kept at 100 ℃ to 110 ℃ for 1 hour, and part of water is evaporated out at the same time; then filtering while the solution is hot to remove impurities which cannot be contained in the solution; then transferring the filtrate into a 5000 ml flask with a stirring, thermometer and cooling bath for cooling crystallization, when the temperature of the feed liquid is reduced to 30 ℃, adding 2000 g of methanol into the feed liquid, continuing stirring, reducing the temperature for crystallization, and when the temperature is reduced to-10 ℃, stirring for crystallization for 1 hour to ensure that potassium nitrate is completely separated out; then, the solid is separated by suction filtration, and is washed by saturated potassium nitrate solution, and then the solid is dried to obtain 962 g of finished potassium nitrate product, the yield is 95.2 percent, and the purity is 99.9 percent; the filtrate is distilled to recover methanol, evaporated, concentrated, crystallized, solid-liquid separated and dried to obtain 857 g of magnesium chloride hexahydrate, the yield is 84.7%, and the purity is 95.1%.
Comparative example 1
When the temperature is reduced to-10 ℃, adding a cosolvent:
1260 g of nitric acid with the mass fraction of 50 percent is added into a 2000 ml four-neck flask with a stirring and condensing tube and a thermometer, 195 g of magnesium oxide powder is slowly added under stirring, the PH value is controlled between 2 and 7, 745 g of solid potassium chloride is slowly added after the magnesium oxide is added and the stirring is continued for 30 minutes, then steam is introduced for heating and dissolving, the temperature is controlled between 60 ℃ and 110 ℃ to completely dissolve the solid potassium chloride, then the temperature is kept at 100 ℃ to 110 ℃ for 1 hour, and part of water is evaporated out at the same time; then filtering while the solution is hot to remove impurities which cannot be contained in the solution; then transferring the filtrate into a 5000 ml flask with a stirring, thermometer and cooling bath for cooling crystallization, when the temperature of the feed liquid is reduced to-10 ℃, adding 1000 g of methanol into the feed liquid, continuously stirring for cooling crystallization, and when the temperature is reduced to-10 ℃, stirring for crystallization for 1 hour to ensure that potassium nitrate is completely separated out; then, the solid is separated by suction filtration, and is washed by saturated potassium nitrate solution, and then the solid is dried to obtain 987 g of finished potassium nitrate product, the yield is 97.7%, and the purity is 98.9%; after the filtrate is distilled to recover methanol, 852 g of magnesium chloride hexahydrate is obtained after evaporation concentration, crystallization, solid-liquid separation and drying, the yield is 84.2 percent and the purity is 95.8 percent.
Comparative example 2
Blank examples without co-solvent:
1260 g of nitric acid with the mass fraction of 50 percent is added into a 2000 ml four-neck flask with a stirring and condensing tube and a thermometer, 195 g of magnesium oxide powder is slowly added under stirring, the PH value is controlled between 2 and 7, 745 g of solid potassium chloride is slowly added after the magnesium oxide is added and the stirring is continued for 30 minutes, then steam is introduced for heating and dissolving, the temperature is controlled between 60 ℃ and 110 ℃ to completely dissolve the solid potassium chloride, then the temperature is kept at 100 ℃ to 110 ℃ for 1 hour, and part of water is evaporated out at the same time; then filtering while the solution is hot to remove impurities which cannot be contained in the solution; then transferring the filtrate into a 5000 ml flask with a stirring, thermometer and cooling bath for cooling crystallization, and stirring the crystallization for 1 hour when the temperature of the feed liquid is reduced to-10 ℃ so as to completely precipitate potassium nitrate; then, the solid is separated by suction filtration, and is washed by saturated potassium nitrate solution, and then the solid is dried to obtain 957 g of finished potassium nitrate product, the yield is 94.7%, and the purity is 89.1%; the filtrate is evaporated, concentrated, crystallized, separated from solid and liquid and dried to obtain 834 g of magnesium chloride hexahydrate with the yield of 82.4 percent and the purity of 92.6 percent.
Comparative example 3
Examples of methanol addition less than the proportional range
1260 g of nitric acid with the mass fraction of 50 percent is added into a 2000 ml four-neck flask with a stirring and condensing tube and a thermometer, 195 g of magnesium oxide powder is slowly added under stirring, the PH value is controlled between 2 and 7, 745 g of solid potassium chloride is slowly added after the magnesium oxide is added and the stirring is continued for 30 minutes, then steam is introduced for heating and dissolving, the temperature is controlled between 60 ℃ and 110 ℃ to completely dissolve the solid potassium chloride, then the temperature is kept at 100 ℃ to 110 ℃ for 1 hour, and part of water is evaporated out at the same time; then filtering while the solution is hot to remove impurities which cannot be contained in the solution; then transferring the filtrate into a 5000 ml flask with a stirring, thermometer and cooling bath for cooling crystallization, when the temperature of the feed liquid is reduced to 30 ℃, adding 200 g of methanol into the feed liquid, continuously stirring, reducing the temperature for crystallization, and stirring for crystallization for 1 hour when the temperature is reduced to-10 ℃ so as to completely separate out potassium nitrate; then, the solid is separated by suction filtration, and is washed by saturated potassium nitrate solution, and then the solid is dried to obtain 980 g of finished potassium nitrate product, the yield is 97.0 percent, and the purity is 99.1 percent; the filtrate is distilled to recover methanol, evaporated, concentrated, crystallized, solid-liquid separated and dried to obtain 857 g of magnesium chloride hexahydrate, the yield is 84.7%, and the purity is 95.6%.
The embodiment shows that the potassium nitrate product produced by the method can meet or exceed the requirement of high-quality products according to the national GB-1918-.
From the above examples and comparative examples it can be seen that: 1) good potassium nitrate yields and purities were obtained with methanol and ethanol as co-solvents (examples 2 and 6). However, the boiling point of ethanol is high, the separation and recovery are difficult, the energy consumption is high, and the price of ethanol is high, so the corresponding cost is higher than that of methanol; has the advantages that: the toxicity of the ethanol is lower than that of the methanol, and the loss of the ethanol is less than that of the methanol; methanol is preferred from the viewpoint of overall economy. 2) Good product yield and purity can be obtained even if the feed liquid temperature is above 30 ℃, for example, the cosolvent is added at 40 ℃, but the cosolvent loss is large due to the influence of high temperature, so that the cosolvent is optimally added at 30 ℃ by comparison (examples 1-7). 3) When the temperature is reduced to-10 ℃, the cosolvent is added, the purity of the potassium nitrate product is low, the essence is that part of magnesium chloride is separated out along with the potassium nitrate product, the purity of the product is influenced, and the cosolvent does not play the due role (comparative example 1). 4) The blank example without the cosolvent has low yield and low purity of potassium nitrate, and the requirement of the product purity is difficult to achieve after refining (comparative example 2). 6) The adding amount of the cosolvent is lower than the range of the invention, and the yield and the purity are also influenced; the yield and the purity of the potassium nitrate product are not obviously improved when the potassium nitrate is higher than the range of the invention (examples 1-4 and comparative example 3).
Claims (7)
1. The method for producing potassium nitrate is characterized by comprising the following steps of:
step (1): adding magnesium oxide and potassium chloride into nitric acid with the mass fraction of 50% -60%, controlling the reaction temperature at 60-110 ℃, and controlling the pH value of the reaction liquid at 2-7;
step (2): carrying out solid-liquid separation treatment on the reaction liquid in the step (1) to obtain a filtrate;
and (3): cooling the filtrate obtained in the step (2) to 10-40 ℃, mixing with a cosolvent, and crystallizing; wherein the cosolvent is C1-C4 alcohol; the mass of the cosolvent is not less than 0.5 time of that of the potassium chloride; the crystallization temperature is-10 ℃ to 0 ℃;
and (4): and (4) carrying out solid-liquid separation on the crystallization feed liquid obtained in the step (3) to obtain potassium nitrate.
2. The method for producing potassium nitrate according to claim 1, wherein the cosolvent is methanol and/or ethanol.
3. The method for producing potassium nitrate according to claim 1, wherein the mass of the cosolvent is 0.5 to 3 times the mass of the potassium chloride.
4. The method for producing potassium nitrate according to claim 1, wherein the crystallization time in the step (3) is 1.0 to 4.0 hours.
5. The method for producing potassium nitrate according to claim 1, wherein in the step (1), the molar ratio of magnesium oxide, potassium chloride and nitric acid is 1:2: 2.
6. The method for producing potassium nitrate according to any one of claims 1 to 5, wherein the liquid fraction obtained by the solid-liquid separation in the step (4) is distilled, the cosolvent is recovered, and then concentration and temperature reduction crystallization are carried out to separate the byproduct magnesium chloride and the circulating mother liquor.
7. The method for producing potassium nitrate according to claim 6, wherein the recovered cosolvent is recycled and reused in the step (3), and the recycled mother liquor is reused in the step (1).
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