Method for synthesizing potassium nitrate at low temperature by taking air as raw material
By using air as raw material and reacting potassium ferrite at low temperature, potassium nitrate is directly synthesized, which solves the problems of high cost and demanding technical requirements of the existing potassium nitrate production methods, and realizes low-cost and efficient preparation of potassium nitrate.
Patent Information
- Application Number
- CN202411544707.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-31
- Publication Date
- 2025-01-24
AI Technical Summary
The existing potassium nitrate production methods are costly, have harsh technical requirements and harsh reaction conditions, making it difficult to achieve efficient and low-cost preparation.
Using air as the raw material, potassium ferrite reacts below 250°C. Through a series of steps including the synthesis of potassium ferrite, activation treatment, air reaction, product collection, concentration and purification, potassium nitrate is directly synthesized.
The low cost and efficient preparation of potassium nitrate is realized, and it has the characteristics of simple technical, high -efficiency, and safe and environmental protection.
Smart Images
Figure CN119349602A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of potassium nitrate preparation, and particularly relates to a method for synthesizing potassium nitrate at low temperature by taking air as a raw material. Background Art
[0002] Potassium nitrate is an extremely important inorganic material. It is not only widely used in industry, military, and fireworks, but also a high-quality nitrogen-potassium binary compound fertilizer in agriculture. It is all water-soluble nutrients and leaves no residue after fertilization. The production methods of potassium nitrate mainly include ammonium nitrate double decomposition method, potassium alkali neutralization method, nitrate ion exchange method, etc. Its preparation principle is mainly to separate and prepare chemical components such as potassium nitrate, potassium chloride, and ammonium chloride by using their solubility differences to form an element closed loop; then industrial potassium nitrate products are obtained through cooling crystallization, separation, washing, and purification.
[0003] The current production of potassium nitrate faces problems such as high cost, high technical requirements, and harsh reaction conditions. Therefore, in order to solve the above problems, it is necessary to develop new synthesis methods. Summary of the invention
[0004] In order to solve the cost problem of preparing potassium nitrate and overcome technical difficulties, the purpose of the present invention is to provide a method for synthesizing potassium nitrate at low temperature using air as a raw material. The present invention uses air as a raw material, uses potassium ferrite to react at a temperature below 250°C, and finally separates the reaction product to synthesize potassium nitrate. The method has the characteristics of low cost, simple technology and high reaction efficiency.
[0005] The method for synthesizing potassium nitrate at low temperature using air as a raw material of the present invention comprises the following steps:
[0006] S1. Synthesis of potassium ferrite crystals: add ferric chloride to ultrapure water and stir until completely dissolved, then slowly add potassium hydroxide to the ferric chloride solution and stir until the solution turns brown; transfer the resulting solution to a stainless steel kettle lined with polytetrafluoroethylene for hydrothermal reaction, cool naturally to room temperature after the reaction is completed, filter, wash the filtered product with ultrapure water and dry it naturally to obtain black hexagonal flaky potassium ferrite crystals;
[0007] S2. Activate the potassium ferrite crystals obtained in step S1: clean the potassium ferrite crystals with ultrapure water, then place the potassium ferrite crystals in hydrochloric acid or sulfuric acid and stir for 10 to 20 minutes for activation, filter out the potassium ferrite crystals, use ultrapure water and anhydrous ethanol to clean the activated potassium ferrite at room temperature, and then heat it in an oven at 150 to 170°C; take out the heated product and repeat the operation steps of "stirring the potassium ferrite crystals in hydrochloric acid or sulfuric acid aqueous solution - cleaning with ultrapure water and anhydrous ethanol - heating in an oven" 4 to 6 times, wherein the heating time in the oven is 3 to 5 hours for the first 3 to 4 repeated operations, and the heating time in the oven is 20 to 30 hours for the last 1 to 2 repeated operations, thereby completing the activation of the crystal surface and obtaining activated potassium ferrite crystals;
[0008] S3. Reaction using air: The activated potassium ferrite crystals obtained in step S2 were placed in a blast drying oven and reacted under an air atmosphere at a standard atmospheric pressure;
[0009] S4. Product collection: After the reaction in step S3 is completed, the activated potassium ferrite crystals are taken out and naturally cooled to room temperature, and then a small amount of ultrapure water is added to the potassium ferrite crystals so that the ultrapure water completely immerses the potassium ferrite crystals. After stirring for 10 to 20 minutes, the obtained suspension is allowed to stand for another 10 to 20 minutes, the activated potassium ferrite crystals are filtered out and retained separately, and the filtrate containing the target product potassium nitrate is collected;
[0010] The reaction formula is as follows:
[0011] 2K2Fe4O7+2N2+5O2=4KNO3+4Fe2O3
[0012] S5. Concentrating and drying the product: enriching the plurality of filtrates containing potassium nitrate obtained in step S4, and then drying the filtrate containing potassium nitrate in an oven at 25 to 90° C. to obtain a solid product containing potassium nitrate;
[0013] S6. Crystallization treatment of the solid product: the solid product containing potassium nitrate obtained in step S5 is heated at 240-280° C. in a muffle furnace for 1.5-5 h, and after naturally cooling to room temperature, a small amount of ultrapure water is added for recrystallization 2-4 times to obtain a recrystallized product; the recrystallization operation is as follows: a small amount of ultrapure water is added to completely dissolve the solid product, and then the ultrapure water is slowly evaporated at room temperature to allow the solid dissolved therein to naturally crystallize; a small amount of ultrapure water is added again to completely dissolve the solid product, and then the ultrapure water is slowly evaporated at room temperature to allow the solid dissolved therein to naturally crystallize; and so on, multiple recrystallization operations are performed;
[0014] S7. Purification of the recrystallized product by impurity removal: The recrystallized product obtained in step S6 is dissolved in water, and the content of carbonate (carbonate is formed by the reaction of potassium oxide on the surface of potassium ferrite with carbon dioxide in the air) in the solution is detected by carbonate test paper or other methods, and then barium acetate or calcium acetate in an amount equimolar to the carbonate is added to the solution, and stirred at room temperature for 3 to 5 minutes (no solid insoluble matter appears at this time), and the obtained mixture solution is dried to obtain a solid product containing potassium nitrate, and a small amount of ultrapure water is added to the obtained solid product. At this time, there is obvious solid insoluble matter (solid insoluble matter mainly refers to barium carbonate or calcium carbonate generated by the combination of carbonate and barium ions or calcium ions). The precipitation (mainly for the purpose of removing carbonate ions for purifying the product) appears, the solid insoluble matter is filtered out, and the excess water in the filtrate is dried to obtain a white solid product; the operation of "adding a small amount of ultrapure water to the obtained solid product - filtering to remove the solid insoluble matter - drying the excess water in the filtrate" is repeated for many times, until the ultrapure water is added to the obtained solid product to completely dissolve it and the solution becomes clear and transparent, the excess water in the filtrate is dried, and the solid product is washed with anhydrous ethanol for 2 to 4 times (the purpose of washing the solid product with ethanol is to remove potassium acetate impurities generated when adding barium acetate for impurity removal), the remaining ethanol is removed and a small amount of ultrapure water is added for recrystallization to obtain the potassium nitrate product;
[0015] The surface of the potassium ferrite activated crystals retained separately in step S4 has been passivated and needs to be activated again before the reaction can continue; that is, hydrochloric acid or sulfuric acid is added to the potassium ferrite activated crystals retained separately after filtration in step S4, and stirred for 10 to 20 minutes, and after the potassium ferrite crystals are filtered out, the acid-treated potassium ferrite is cleaned in turn with ultrapure water and anhydrous ethanol at room temperature, and then the operations of steps S2, S3, S4, S5, S6, and S7 are performed to obtain potassium nitrate products again; the operations of "adding hydrochloric acid or sulfuric acid aqueous solution and stirring - ultrapure water and anhydrous ethanol are cleaned - steps S2, S3, S4, S5, S6, and S7" are repeated to obtain potassium nitrate products multiple times; the reaction is repeated multiple times until the potassium ferrite activated crystals are basically consumed.
[0016] For step S2, the surfaces of the reactants are uniformly activated to remove surface impurities and expose the crystal faces involved in the reaction to the air, thereby promoting the reaction.
[0017] For step S3, the time required for the reaction varies at different reaction temperatures. When the temperature is low, the reaction is slow and the required reaction time is long; when the temperature is high, the crystal surface is rapidly deactivated and the reaction is interrupted quickly.
[0018] For step S5, since the product contains a small amount of impurities, the product color may be white, light yellow, or light brown.
[0019] For step S7, after adding barium acetate in equal moles to carbonate ions into the solution, the barium ions and carbonate ions are in a supersaturated state and cannot be completely precipitated. It is necessary to add water to the solid product obtained after drying the water and filter it again to remove the solid insoluble matter. This filtration is repeated 2 to 4 times until no solid insoluble matter is produced when water is added again, and then the subsequent operation can be carried out.
[0020] In the above steps, heating is completed in an oven. During heating, air circulation is required and the reactants are evenly spread in an open container to ensure that the reaction is as complete as possible.
[0021] Preferably, in step S1, the molar ratio of ferric chloride, ultrapure water and potassium hydroxide is 1:210-234:124-133; the temperature of the hydrothermal reaction is 180-220°C, and the reaction time is 50-60h.
[0022] Preferably, in step S2, the concentration of the hydrochloric acid aqueous solution is 3 to 6 mol / L, and the concentration of the sulfuric acid aqueous solution is 1.5 to 2.5 mol / L; the activation treatment operation is: using the hydrochloric acid or sulfuric acid aqueous solution to immerse the potassium ferrite crystals obtained in step S1 and stir for 10 to 20 minutes.
[0023] Preferably, in the step S3, the reaction temperature is 25 to 250° C., and the reaction time is 7 to 60 days; the reaction is carried out under normal pressure (i.e., 1 standard atmospheric pressure).
[0024] Preferably, in the step S4, after obtaining the reaction product, the operation of the next step must be carried out within 3 hours and cannot be retained for a long time.
[0025] Preferably, in step S7, the drying temperature is 25-90°C.
[0026] By adopting the above technical solution, natural crystallization can make the crystal grow slowly, so that colorless needle-shaped potassium nitrate crystals can be obtained in the end.
[0027] The beneficial effects of the present invention are as follows: the present invention provides a novel method for preparing potassium nitrate, which uses potassium ferrite (K2Fe4O7) and N2 and O2 in the air as raw materials, and directly synthesizes potassium nitrate through potassium ferrite activation pretreatment, reaction in the air, product collection, and product concentration and purification experimental steps. The present invention can react below 250°C. Unlike the traditional method for synthesizing potassium nitrate, which can only use nitric acid and nitric acid derivatives as raw materials, the method of the present invention can directly use air to synthesize potassium nitrate under normal pressure, and the reaction product is easy to enrich, the reaction cost is low, and it is safe and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 is the SEM image of potassium ferrite;
[0029] Figure 2 A photo of the potassium nitrate prepared by the present invention;
[0030] Figure 3 The XRD pattern of potassium nitrate prepared by the present invention;
[0031] Figure 4 Infrared image of potassium nitrate prepared by the present invention;
[0032] Figure 1 It shows that potassium ferrite crystals with hexagonal morphology were synthesized by this method;
[0033] Figure 2 , Figure 3 , Figure 4 It shows that the product of the present invention is potassium nitrate. DETAILED DESCRIPTION
[0034] The present application is further described in detail below in conjunction with specific embodiments.
[0035] Example 1
[0036] A method for synthesizing potassium nitrate at low temperature using air as a raw material, the specific steps are as follows:
[0037] S1. Synthesis of potassium ferrite crystals: 1.62 g of ferric chloride was added to 40 mL of ultrapure water and stirred until completely dissolved. Then 72 g of potassium hydroxide was slowly added to the ferric chloride solution and stirred for 5 min until the solution turned brown. The above solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel kettle and reacted at 200 ° C for 56 h. After the reaction was completed, it was cooled naturally at room temperature. The potassium ferrite was cleaned with ultrapure water and dried naturally to obtain black hexagonal flaky potassium ferrite crystals.
[0038] S2. Activate the potassium ferrite crystals obtained in step S1: clean the potassium ferrite crystals with ultrapure water, then divide 10g of potassium ferrite crystals into 10 groups, each group is evenly spread in a culture dish with a diameter of 10cm, add 10mL, 5mol / L hydrochloric acid aqueous solution to each group and stir for 15min; filter out the remaining potassium ferrite, rinse the potassium ferrite after acid treatment with ultrapure water 3 times at room temperature, and rinse with anhydrous ethanol 3 times. Heat the washed potassium ferrite in a 160℃ oven, take out the product and repeat the operation steps of "adding hydrochloric acid aqueous solution to stir - cleaning with ultrapure water and anhydrous ethanol - heating in an oven" 5 times, wherein the heating time in the 160℃ oven for the first 4 repetitions is 3h, and the heating time in the 160℃ oven for the 5th repetition is 24h; thus, the activation of the crystal surface is completed to obtain potassium ferrite activated crystals.
[0039] S3. Reaction using air: Place the activated potassium ferrite crystals obtained in step S2 together with the culture dish into a 120°C forced air drying oven and react at a standard atmospheric pressure for 7 days.
[0040] S4. Product collection: After the reaction in step S3 is completed, the culture dishes containing potassium ferrite are taken out and naturally cooled to room temperature, 5 mL of ultrapure water is added to each culture dish, the culture dishes are shaken so that the water can completely immerse the reaction raw materials, and stirred for 15 minutes; the obtained suspension is allowed to stand for 15 minutes, the activated potassium ferrite crystals are filtered out and retained separately, and the filtrate is collected. The target product potassium nitrate is dissolved in the filtrate.
[0041] S5. Product concentration and drying: The 10 groups of solutions containing potassium nitrate obtained in step S4 are enriched and dried in an oven at 80° C. to obtain a solid product containing potassium nitrate.
[0042] S6. Crystallization of solid product: The solid containing potassium nitrate obtained in step S5 was placed in a muffle furnace, heated at 260° C. for 2 h, cooled naturally to room temperature, and then recrystallized three times by adding 10 mL of ultrapure water to obtain a recrystallized product.
[0043] S7. Recrystallization product impurity removal and purification: The recrystallization product obtained in step S6 is dissolved in water, and the content of carbonate in the solution is calculated according to the pH of the solution, and barium acetate in an amount equimolar to the carbonate is added to the solution. Stir at room temperature for 5 minutes and no solid insoluble matter appears. The mixture solution is placed in an oven at 80°C to dry the water, and then a small amount of water is added again. At this time, obvious solid insoluble matter appears, and the solid insoluble matter is removed by filtration. Dry the excess water in the filtrate to obtain a white solid product, repeat the operation of "adding a small amount of ultrapure water to the obtained solid product-filtering to remove solid insoluble matter-drying the excess water in the filtrate" 3 times; finally, add ultrapure water to the obtained solid product to make it completely dissolved and the solution is clear and transparent, and the excess water in the filtrate can be dried at 80°C, and then the white solid product is washed 3 times with anhydrous ethanol, and finally the remaining ethanol is removed and 5mL of ultrapure water is added for recrystallization to obtain the potassium nitrate product.
[0044] The surface of the potassium ferrite activated crystals remaining after the product is washed out in step S4 has been passivated, and needs to be activated again before the reaction can continue. Furthermore, in the potassium ferrite activated crystals remaining after filtering in step S4, 10 mL of a 5 mol / L hydrochloric acid aqueous solution is added to each culture dish and stirred for 15 minutes, the remaining potassium ferrite is filtered out, and the acid-treated potassium ferrite is cleaned in turn with ultrapure water and anhydrous ethanol at room temperature, and then the operations of steps S2, S3, S4, S5, S6, and S7 are performed to obtain a potassium nitrate product again; the operation of "adding hydrochloric acid or sulfuric acid aqueous solution and stirring - cleaning with ultrapure water and anhydrous ethanol - performing steps S2, S3, S4, S5, S6, and S7" can be repeated 5 times, and finally a potassium nitrate product with a mass of 25.6 mg and a mass fraction of 98% is obtained.
[0045] Example 2
[0046] A method for synthesizing potassium nitrate at low temperature using air as a raw material, the specific steps are as follows:
[0047] S1. Synthesis of potassium ferrite crystals: 1.62 g of ferric chloride was added to 40 mL of ultrapure water and stirred until completely dissolved. Then 72 g of potassium hydroxide was slowly added to the ferric chloride solution and stirred for 5 min until the solution turned brown. The above solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel kettle and reacted at 200 ° C for 56 h. After the reaction was completed, it was cooled naturally at room temperature. The potassium ferrite was cleaned with ultrapure water and dried naturally to obtain black hexagonal flaky potassium ferrite crystals.
[0048] S2. Activate the potassium ferrite crystals obtained in step S1: clean the potassium ferrite crystals with ultrapure water, then divide 10g of potassium ferrite crystals into 10 portions, evenly spread each portion in a culture dish with a diameter of 10cm, add 10mL, 5mol / L hydrochloric acid aqueous solution to each portion and stir for 15min; filter out the remaining potassium ferrite, rinse the acid-treated potassium ferrite with ultrapure water 3 times at room temperature, and rinse with anhydrous ethanol 3 times. Heat the washed potassium ferrite in a 160℃ oven, take out the product and repeat the "add hydrochloric acid aqueous solution and stir - clean with ultrapure water and anhydrous ethanol - heat in an oven" operation steps 5 times, wherein the heating time in a 160℃ oven is 3h for the first 4 repetitions, and the heating time in a 160℃ oven is 24h for the fifth repetition. At this point, the activation of the crystal surface is completed, and potassium ferrite activated crystals are obtained.
[0049] S3. Reaction using air: Place the activated potassium ferrite crystals obtained in step S2 together with the culture dish in a 160°C forced air drying oven and react at a standard atmospheric pressure for 10 days.
[0050] S4. Product collection: After the reaction in step S3 is completed, the culture dishes containing potassium ferrite are taken out and naturally cooled to room temperature, 5 mL of ultrapure water is added to each culture dish, the culture dishes are shaken so that the water can completely immerse the reaction raw materials, and stirred for 15 minutes; the obtained suspension is allowed to stand for 15 minutes, the activated potassium ferrite crystals are filtered out and retained separately, and the filtrate is collected. The target product potassium nitrate is dissolved in the filtrate.
[0051] S5. Product concentration and drying: The 10 groups of solutions containing potassium nitrate obtained in step S4 are enriched and dried in an oven at 80° C. to obtain a solid product containing potassium nitrate.
[0052] S6. Crystallization of solid product: The solid containing potassium nitrate obtained in step S5 was placed in a muffle furnace, heated at 260° C. for 2 h, cooled naturally to room temperature, and then recrystallized three times by adding 10 mL of ultrapure water to obtain a recrystallized product.
[0053] S7. Recrystallization product impurity removal and purification: The recrystallization product obtained in step S6 is dissolved in water, and the content of carbonate in the solution is calculated according to the pH of the solution, and barium acetate in an amount equimolar to the carbonate is added to the solution. Stir at room temperature for 5 minutes and no solid insoluble matter appears. The mixture solution is placed in an oven at 80°C to dry the water, and then a small amount of water is added again. At this time, obvious solid insoluble matter appears, and the solid insoluble matter is removed by filtration. Dry the excess water in the filtrate to obtain a white solid product, repeat the operation of "adding a small amount of ultrapure water to the obtained solid product-filtering to remove solid insoluble matter-drying the excess water in the filtrate" twice; finally, add ultrapure water to the obtained solid product to make it completely dissolved and the solution is clear and transparent, and the excess water in the filtrate can be dried at 80°C, and then the white solid product is washed twice with anhydrous ethanol. Finally, remove the remaining ethanol and add 5mL of ultrapure water for recrystallization to obtain a potassium nitrate product.
[0054] The surface of the potassium ferrite activated crystals remaining after the product is washed out in step S4 has been passivated, and needs to be activated again before the reaction can continue. Further, in the potassium ferrite activated crystals remaining after filtering in step S4, each culture dish is added with 10mL, 5mol / L hydrochloric acid aqueous solution and stirred for 15min, the remaining potassium ferrite is filtered out, and the acid-treated potassium ferrite is cleaned with ultrapure water and anhydrous ethanol in turn at room temperature, and then the operations of steps S3, S4, S5, S6, and S7 are performed to obtain potassium nitrate products again; repeat the operation of "adding hydrochloric acid or sulfuric acid aqueous solution and stirring-cleaning with ultrapure water and anhydrous ethanol-performing steps S3, S4, S5, S6, and S7" for 3 times. Finally, a potassium nitrate product with a mass of 11.8mg and a mass fraction of 96% is obtained.
[0055] Example 3
[0056] A method for synthesizing potassium nitrate at low temperature using air as a raw material, the specific steps are as follows:
[0057] S1. Synthesis of potassium ferrite crystals: 1.62 g of ferric chloride was added to 40 mL of ultrapure water and stirred until completely dissolved. Then 72 g of potassium hydroxide was slowly added to the ferric chloride solution and stirred for 5 min until the solution turned brown. The above solution was transferred to a 100 mL polytetrafluoroethylene-lined stainless steel kettle and reacted at 200 ° C for 56 h. After the reaction was completed, it was cooled naturally at room temperature. The potassium ferrite was cleaned with ultrapure water and dried naturally to obtain black hexagonal flaky potassium ferrite crystals.
[0058] S2. Activate the potassium ferrite crystals obtained in step S1: clean the potassium ferrite crystals with ultrapure water, then divide 4g of potassium ferrite crystals into 2 portions, each portion is evenly spread in a culture dish with a diameter of 10cm, and each portion is added to 10mL, 5mol / L hydrochloric acid aqueous solution and stirred for 15min; filter out the remaining potassium ferrite, rinse the potassium ferrite after acid treatment with ultrapure water 3 times at room temperature, and rinse with anhydrous ethanol 3 times. Heat the washed potassium ferrite in a 160℃ oven, take out the product and repeat the operation steps of "adding hydrochloric acid aqueous solution and stirring - cleaning with ultrapure water and anhydrous ethanol - heating in an oven" 5 times, wherein the heating time in a 160℃ oven is 3h for the first 4 repetitions, and the heating time in a 160℃ oven is 24h for the fifth repetition. At this point, the activation of the crystal surface is completed, and potassium ferrite activated crystals are obtained.
[0059] S3. Reaction using air: The activated potassium ferrite crystals obtained in step S2 together with the culture dish are placed in dry air with a humidity of less than 25% for reaction for 45 days.
[0060] S4. Product collection: After the reaction in step S3 is completed, add 5 mL of ultrapure water to each culture dish, shake the culture dish so that the water can completely immerse the reaction raw materials, and stir for 15 minutes; let the resulting suspension stand for 15 minutes, filter out the potassium ferrite activated crystals and keep them separately, collect the filtrate, and the target product potassium nitrate is dissolved in the filtrate.
[0061] S5. Product concentration and drying: The two groups of potassium nitrate-containing solutions obtained in step S4 are enriched and dried in an oven at 80° C. to obtain a solid product containing potassium nitrate.
[0062] S6. Crystallization of solid product: The solid containing potassium nitrate obtained in step S5 was placed in a muffle furnace, heated at 260° C. for 2 h, cooled naturally to room temperature, and then recrystallized three times by adding 10 mL of ultrapure water to obtain a recrystallized product.
[0063] S7. Recrystallization product impurity removal and purification: The recrystallization product obtained in step S6 is dissolved in water, and the content of carbonate in the solution is calculated according to the pH of the solution, and barium acetate is added to the solution in an amount equimolar to the carbonate. Stir at room temperature for 5 minutes and no solid insoluble matter appears. The mixture solution is placed in an oven at 80°C to dry the water, and then a small amount of water is added again. At this time, obvious solid insoluble matter appears, and the solid insoluble matter is removed by filtration. Dry the excess water in the filtrate to obtain a white solid product, repeat the operation of "adding a small amount of ultrapure water to the obtained solid product-filtering to remove solid insoluble matter-drying the excess water in the filtrate" 3 times; finally, ultrapure water is added to the obtained solid product to make it completely dissolved and the solution is clear and transparent, and the excess water in the filtrate can be dried at 80°C, and then the white solid product is washed 3 times with anhydrous ethanol. Finally, remove the remaining ethanol and add 5mL of ultrapure water for recrystallization to obtain a potassium nitrate product with a mass of 2.1mg and a mass fraction of 98%.
[0064] Compared with Example 1, Example 2 changes the reaction conditions of step S3, the number of repeated filtration times and anhydrous ethanol washing times in step S7, and the number of repeated reactions, and the quality and purity of the product are changed; compared with Example 1, Example 3 changes the amount of potassium ferrite used in step S2, the reaction conditions of step S3, and the number of repeated steps S7. In Example 3, no repeated reactions are performed, and the product purity is the same, with only a change in quality.
Claims
1. A method for synthesizing potassium nitrate at low temperature using air as a raw material, the steps are as follows: S1. Synthesis of potassium ferrite crystals: add ferric chloride to ultrapure water and stir until completely dissolved, then slowly add potassium hydroxide to the ferric chloride solution and stir until the solution turns brown; transfer the resulting solution to a stainless steel kettle lined with polytetrafluoroethylene for hydrothermal reaction, cool naturally to room temperature after the reaction is completed, filter, wash the filtered product with ultrapure water and dry it naturally to obtain black hexagonal flaky potassium ferrite crystals; S2. Activate the potassium ferrite crystals obtained in step S1: clean the potassium ferrite crystals with ultrapure water, then place the potassium ferrite crystals in hydrochloric acid or sulfuric acid and stir for 10 to 20 minutes for activation, filter out the potassium ferrite crystals, use ultrapure water and anhydrous ethanol to clean the activated potassium ferrite at room temperature, and then heat it in an oven at 150 to 170°C; take out the heated product and repeat the operation steps of "stirring the potassium ferrite crystals in hydrochloric acid or sulfuric acid aqueous solution - cleaning with ultrapure water and anhydrous ethanol - heating in an oven" 4 to 6 times, wherein the heating time in the oven is 3 to 5 hours for the first 3 to 4 repeated operations, and the heating time in the oven is 20 to 30 hours for the last 1 to 2 repeated operations, thereby completing the activation of the crystal surface to obtain activated potassium ferrite crystals; S3. Reaction using air: The activated potassium ferrite crystals obtained in step S2 were placed in a blast drying oven and reacted under an air atmosphere at a standard atmospheric pressure; S4. Product collection: After the reaction in step S3 is completed, the activated potassium ferrite crystals are taken out and naturally cooled to room temperature, and then a small amount of ultrapure water is added to the potassium ferrite crystals so that the ultrapure water completely immerses the potassium ferrite crystals. After stirring for 10 to 20 minutes, the obtained suspension is allowed to stand for another 10 to 20 minutes, the activated potassium ferrite crystals are filtered out and retained separately, and the filtrate containing the target product potassium nitrate is collected; The reaction formula is as follows: 2K2Fe4O7+2N2+5O2=4KNO3+4Fe2O3, S5. Concentrating and drying the product: enriching the plurality of filtrates containing potassium nitrate obtained in step S4, and then drying the filtrate containing potassium nitrate in an oven at 25 to 90° C. to obtain a solid product containing potassium nitrate; S6. Crystallization treatment of the solid product: the solid product containing potassium nitrate obtained in step S5 is heated at 240-280° C. in a muffle furnace for 1.5-5 h, and after naturally cooling to room temperature, a small amount of ultrapure water is added for recrystallization 2-4 times to obtain a recrystallized product; the recrystallization operation is as follows: a small amount of ultrapure water is added to completely dissolve the solid product, and then the ultrapure water is slowly evaporated at room temperature to allow the solid dissolved therein to naturally crystallize; a small amount of ultrapure water is added again to completely dissolve the solid product, and then the ultrapure water is slowly evaporated at room temperature to allow the solid dissolved therein to naturally crystallize; and so on, multiple recrystallization operations are performed; S7. Purification of the recrystallized product by impurity removal: the recrystallized product obtained in step S6 is dissolved in water, the carbonate content in the solution is detected by carbonate test paper or other methods, and then barium acetate or calcium acetate in an amount equimolar to the carbonate is added to the solution, and the mixture is stirred at room temperature for 3 to 5 minutes. The obtained mixture solution is dried to obtain a solid product containing potassium nitrate, a small amount of ultrapure water is added to the obtained solid product, the solid insoluble matter is filtered out, and the excess water in the filtrate is dried to obtain a white solid product; the operation of "adding a small amount of ultrapure water to the obtained solid product - filtering out the solid insoluble matter - drying the excess water in the filtrate" is repeated for many times until the solution becomes clear and transparent after ultrapure water is added to the obtained solid product to completely dissolve it, the excess water in the filtrate is dried, and the solid product is washed with anhydrous ethanol for 2 to 4 times, the remaining ethanol is removed, and a small amount of ultrapure water is added for recrystallization to obtain the potassium nitrate product.
2. A method for synthesizing potassium nitrate at low temperature using air as a raw material as claimed in claim 1, characterized in that: The surface of the potassium ferrite activated crystals retained separately in step S4 has been passivated, and potassium nitrate products can be further prepared after reactivation; that is, hydrochloric acid or sulfuric acid is added to the potassium ferrite activated crystals retained separately after filtration in step S4, and stirred for 10 to 20 minutes, and after the potassium ferrite crystals are filtered out, the acid-treated potassium ferrite is cleaned in turn with ultrapure water and anhydrous ethanol at room temperature, and then the operations of steps S2, S3, S4, S5, S6, and S7 are performed to obtain potassium nitrate products again; the potassium nitrate product can be obtained multiple times by repeating the operations of "adding hydrochloric acid or sulfuric acid aqueous solution and stirring - cleaning with ultrapure water and anhydrous ethanol - performing steps S2, S3, S4, S5, S6, and S7"; the reaction is repeated multiple times until the potassium ferrite activated crystals are basically consumed.
3. A method for synthesizing potassium nitrate at low temperature using air as a raw material as claimed in claim 1, characterized in that: In step S1, the molar ratio of ferric chloride, ultrapure water and potassium hydroxide is 1:210-234:124-133; the temperature of the hydrothermal reaction is 180-220°C, and the reaction time is 50-60h.
4. A method for synthesizing potassium nitrate at low temperature using air as a raw material as claimed in claim 1, characterized in that: In step S2, the concentration of the hydrochloric acid aqueous solution is 3-6 mol / L, and the concentration of the sulfuric acid aqueous solution is 1.5-2.5 mol / L; the operation of the activation treatment is: immersing the potassium ferrite crystals obtained in step S1 with the hydrochloric acid or sulfuric acid aqueous solution and stirring for 10-20 minutes.
5. A method for synthesizing potassium nitrate at low temperature using air as a raw material as claimed in claim 1, characterized in that: In step S3, the reaction temperature is 25 to 250° C., and the reaction time is 7 to 60 days; the reaction is carried out under 1 standard atmospheric pressure.
6. A method for synthesizing potassium nitrate at low temperature using air as a raw material as claimed in claim 1, characterized in that: In step S4, after obtaining the reaction product, the next step must be performed within 3 hours.
7. A method for synthesizing potassium nitrate at low temperature using air as a raw material as claimed in claim 1, characterized in that: In step S5, the drying temperature is 25-90°C.
8. A method for synthesizing potassium nitrate at low temperature using air as a raw material as claimed in claim 1, characterized in that: In step S7, the drying temperature is 25-90°C.