A method for utilizing reaction heat during the preparation of magnesium nitrate

Abstract

The present invention discloses a method for utilizing reaction heat in the preparation process of magnesium nitrate, which relates to the technical field of magnesium nitrate production. After magnesium oxide and tap water are homogenized, they enter a first-stage tubular reactor together with nitric acid. After reacting at 118 - 123 °C for 1 - 1.2 minutes, they enter a second-stage tubular reactor, and nitric acid is supplemented. The reaction ends when the pH value in the second-stage tubular reactor reaches 4 - 5. The filtrate obtained by pressure filtering the reaction material is crystallized and centrifuged to obtain magnesium nitrate hexahydrate crystals. Among them, cold circulating water is introduced into the jacket of the first-stage tubular reactor, and when the water temperature reaches 95 - 98 °C, it is used as the heat supplement for the second-stage tubular reactor, fully utilizing the reaction heat, shortening the reaction time, and saving the production cost.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium nitrate production, and specifically relates to a method for utilizing reaction heat during the preparation of magnesium nitrate. Background Art

[0002] The existing magnesium nitrate production process mainly involves reacting magnesium oxide with nitric acid in a reaction kettle. After the reaction is completed, solid impurities such as silicate in the reaction solution are filtered out by means of plate and frame filtration, and then hexahydrate magnesium nitrate crystals are prepared through concentration, crystallization, and centrifugation processes.

[0003] The main defects of the existing process are as follows:

[0004] 1. A large amount of heat is released during the reaction of nitric acid with magnesium oxide. If the heat is not discharged in time, the feeding rate of nitric acid needs to be reduced, resulting in a very long reaction time and low production efficiency.

[0005] 2. During the subsequent pressure filtration and transfer of the magnesium nitrate solution, due to reasons such as temperature reduction or incomplete pipeline purging, a large amount of magnesium nitrate crystals will appear, causing blockage of the pipeline or the plate and frame filter press. Therefore, during the material transfer process, steam heating is required to prevent the material from crystallizing in the pipeline, which requires a large amount of steam and increases the production cost.

[0006] 3. Since the magnesium nitrate reaction kettle is generally a large reaction kettle of 20 m³, 40 m³, or even 80 m³, the stirring efficiency is low, and the magnesium oxide material cannot react completely, resulting in waste of materials. This situation can be seen from the magnesium oxide content in the filter mud produced by plate and frame filtration. Currently, the magnesium oxide content in the filter mud is between 5 - 8% w / w, resulting in a large amount of waste of magnesium oxide, low product yield, and high cost. Summary of the Invention

[0007] The technical problem to be solved by the present invention is: aiming at the deficiencies existing in the prior art, to provide a method for utilizing reaction heat during the preparation of magnesium nitrate, which improves the product yield and reduces the production cost.

[0008] To solve the above technical problem, the technical solution of the present invention is:

[0009] A method for utilizing reaction heat during the preparation of magnesium nitrate, comprising the following steps:

[0010] A: Magnesium oxide and tap water enter a homogenizing tank, and the materials are stirred and emulsified to obtain a magnesium oxide emulsion;

[0011] B: Magnesium oxide emulsion and nitric acid enter a one-stage tubular reactor together. Cold circulating water is added to the jacket of the one-stage tubular reactor at one time. When the water temperature in the jacket reaches 95 - 98 °C, the cold circulating water inlet of the jacket is opened again and its inlet flow rate is adjusted, and then the outlet of the jacket is opened to keep the temperature in the one-stage tubular reactor at 118 - 123 °C. The outlet water of the jacket is continuously transferred to the circulating water return tank. Control the feeding flow rates of the magnesium oxide emulsion and nitric acid to ensure that the residence time of the materials in the one-stage tubular reactor is 1 - 1.2 min;

[0012] C: The materials after reaction in the one-stage tubular reactor are transferred to a two-stage tubular reactor, and nitric acid is continuously added. The reaction ends when the pH value in the two-stage tubular reactor is 4 - 5. During the reaction process, the hot water in the circulating water return tank is introduced into the heat preservation interlayer of the two-stage tubular reactor to control the temperature in the two-stage tubular reactor between 80 - 90 °C;

[0013] D: The reaction materials in the two-stage tubular reactor are transferred to a plate and frame filter press for pressure filtration. After the pressure filtration is completed, the filter mud is washed with the hot water in the heat preservation interlayer of the two-stage tubular reactor;

[0014] E: The filtrate after plate and frame pressure filtration is transferred to a crystallizer, cooled to 60 - 65 °C for crystallization, and then further cooled for crystal growth. When the temperature drops to 30 - 40 °C, centrifugation is carried out to obtain magnesium nitrate hexahydrate crystals.

[0015] Preferably, in step A, the weight ratio of magnesium oxide to tap water is 0.25 - 0.35:1, the stirring speed is 5000 - 8000 r / min, and the stirring time is 3 - 5 min.

[0016] Preferably, in step B, the volume ratio of the magnesium oxide emulsion to nitric acid is 1:0.9 - 0.95.

[0017] Preferably, in step B, the pressure in the upper cavity of the one-stage tubular reactor is 0.2 - 0.3 Mpa.

[0018] Preferably, in step C, the residence time of the materials in the two-stage tubular reactor is 2 - 3 min.

[0019] Preferably, in step C, the pressure in the top cavity of the two-stage tubular reactor is controlled at 0.1 - 0.2 Mpa.

[0020] Preferably, a first on-line pH sensor is provided at the front section (inlet) of the two-stage tubular reactor, and a second on-line pH sensor is provided on the pipeline between the two-stage tubular reactor and the plate and frame filter press. The addition amount of nitric acid in step C is adjusted according to the difference between the first on-line pH sensor and the second on-line pH sensor.

[0021] Preferably, in step D, the washing liquid after plate and frame pressure filtration is used for preparing the magnesium oxide emulsion.

[0022] Preferably, a large amount of magnesium nitrate is contained in the centrifugal mother liquor in step E, and it is recycled to the magnesium oxide emulsion preparation section and used as bottom water.

[0023] Preferably, the crystals of magnesium nitrate hexahydrate in step E are rinsed with purified water, and high-purity magnesium nitrate hexahydrate is obtained after drying.

[0024] Due to the adoption of the above technical solution, the beneficial effects of the present invention are as follows:

[0025] 1. The present invention adopts a one-stage tubular reactor, and the outer wall is cooled by circulating water, so that the reaction heat of nitric acid and magnesium oxide can be quickly released. Therefore, the reaction can proceed more quickly, greatly reducing the reaction time of magnesium oxide and nitric acid and improving the reaction efficiency.

[0026] 2. The heat released by the reaction of nitric acid and magnesium oxide is absorbed by the circulating water in the jacket of the one-stage tubular reactor. The circulating water is heated to about 95 - 98 °C and then used for the heating of the subsequent second-stage reaction. After the reaction, the temperature of the circulating water drops to about 80 °C, and then it is continuously used for operations such as plate-and-frame filter pressing insulation and pipeline flushing, which can better dissolve the magnesium nitrate crystals precipitated in the pipeline. Therefore, the utilization rate of heat is improved, the use of steam is reduced, and the energy consumption is greatly saved.

[0027] 3. The washing liquid generated by the heating circulating water for washing the plate-and-frame filter press is finally used as the preparation water for the magnesium oxide emulsion, greatly improving the utilization rate of water resources, avoiding material waste, saving energy, and at the same time improving the product yield.

[0028] 4. The present invention adopts a tubular reaction method. Compared with the kettle reaction, the stirring efficiency of the pipeline reaction is higher, and the situation of uneven material reaction will not occur. Therefore, the utilization rate of magnesium oxide can be greatly improved, and the content of magnesium oxide in the filter mud can be reduced.

[0029] 5. The present invention adopts a two-stage tubular reaction method. By controlling the addition amount of nitric acid in the second-stage tubular reactor through an on-line pH meter, the subsequent reaction parameters can be quickly and accurately adjusted, improving the utilization rate of materials and reducing the labor cost at the same time. Specific Embodiments

[0030] The present invention will be further described below in conjunction with embodiments. Example 1

[0031] Step A: Magnesium oxide with a weight ratio of 0.35:1 (magnesium oxide content 90% w / w, addition amount 350 kg) and tap water (1 m³) are added to a 1500 L homogenizing tank, and the stirring speed is controlled at 5000 r / min, and the stirring time is 5 min to obtain a magnesium oxide emulsion, where the volume of the magnesium oxide emulsion is 1.26 m³.

[0032] Step B: Magnesium oxide emulsion and nitric acid solution (nitric acid content 60wt%, addition amount 1.2m³, mass 1650kg) with a volume ratio of 1:0.95 are put into a tubular reactor (diameter 60cm, length 10m), and the upper cavity pressure is controlled to be 0.2Mpa. Cold circulating water is added to the jacket at one time. When the water temperature reaches 95°C, the cold circulating water inlet flow rate is adjusted to 10L / min, and the water outlet is turned on to keep the temperature in the reactor at 118°C. The material is retained in the tubular reactor for 1.2min.

[0033] Step C: The reacted material is transferred to the second-stage tubular reactor (length 20m, diameter 60cm), and the residence time is 3min. The value of the first online pH sensor is 10.5, and the amount of nitric acid added is 250kg, which is monitored by the flow meter to ensure that it is added to the second-stage tubular reactor in equal proportions to ensure that the value of the second online pH sensor is 4.5. The hot water in the circulating water return tank is passed into the insulation interlayer of the second-stage tubular reactor at a flow rate of 15L / min, and the temperature is controlled at 80℃ and the top cavity pressure is controlled at 0.1Mpa.

[0034] Step D: The reaction material is transferred to a plate-frame filter press for filtration, and the filter mud is washed with hot water in the thermal insulation interlayer, and the washing liquid is used to prepare the magnesium oxide emulsion. The washing liquid (hot water in the thermal insulation interlayer) is used in an amount of 100 kg, and 106 kg of filter mud washing liquid is obtained.

[0035] Step E: The filtrate temperature of the plate and frame filter press is about 80°C. It is transferred to the crystallizer and cooled to 60°C. Magnesium nitrate hexahydrate crystals begin to appear. The temperature is further cooled to 30°C for centrifugation to obtain 1880kg of magnesium nitrate hexahydrate crystals with a purity of 99% and a yield of 93.25%. The crystals are rinsed with purified water (100kg) and dried to obtain 1860kg of high-purity magnesium nitrate hexahydrate with a purity of 99.5% and a yield of 92.26%. 960kg of the centrifuged mother liquor has a magnesium nitrate content of 20.42% w / w, which is returned to the magnesium oxide emulsion preparation section. After the crystals are rinsed, 120kg of washing liquid is obtained with a magnesium nitrate content of 8.33% w / w, which is returned to the magnesium oxide emulsion preparation section. Example 2

[0036] Step A: Add magnesium oxide (magnesium oxide content 90% w / w, added in an amount of 355 kg) and the application solution in Example 1 (centrifugal mother liquor + filter mud washing liquid + magnesium nitrate crystal washing liquid totaling 1180 kg) into a 1500L homogenizing tank, control the stirring speed to 6000 r / min, and the stirring time to 4 min to obtain a magnesium oxide emulsion with a total weight of 1535 kg and a volume of 1280 L.

[0037] Step B: Magnesium oxide emulsion and nitric acid solution (1650kg, nitric acid content 60wt%) with a volume ratio of 1:0.94 are introduced into a tubular reactor together, and the upper cavity pressure is controlled to be 0.25Mpa. Cold circulating water is added into the jacket at one time. When the water temperature reaches 96°C, the inlet flow rate of the cold circulating water is adjusted to 12L / min, and the water outlet is turned on to keep the temperature in the reactor at 120°C. The material is retained in the tubular reactor for 1.1min.

[0038] Step C: The reacted material is transferred to the second-stage tubular reactor with a residence time of 2.5 min. The value of the first online pH sensor is 11.0, and the value of the second online pH sensor is 4.9 by adding 250 kg of nitric acid. The hot water in the circulating water return tank is passed into the insulation interlayer of the second-stage tubular reactor at a flow rate of 18 L / min, and the temperature is controlled at 85 ° C. The top cavity pressure is controlled at 0.15 MPa.

[0039] Step D: The reaction material is transferred to a plate-frame filter press for filtration, and the filter mud is washed with hot water in the insulation interlayer, and the washing liquid is used to prepare the magnesium oxide emulsion. The filter mud is washed with 100 kg of hot water, and the solution after washing weighs 110 kg.

[0040] Step E: The temperature of the filtrate of the plate and frame filter press is about 82°C. It is transferred to the crystallizer and cooled to 62°C for crystallization. It is further cooled to 35°C for centrifugation to obtain 2040kg of magnesium nitrate hexahydrate crystals with a purity of 99.2% and a yield of 99.80%. The crystals are rinsed with 100kg of purified water and dried to obtain 2020kg of high-purity magnesium nitrate hexahydrate with a purity of 99.6% and a yield of 98.82%. 1240kg of the centrifuged mother liquor with a magnesium nitrate content of 16.69% w / w is returned to the magnesium oxide emulsion preparation section. After the crystals are rinsed, 120kg of rinsing water is obtained. It is applied back to the magnesium oxide emulsion preparation section. Example 3

[0041] Step A: Add magnesium oxide (magnesium oxide content 90% w / w, added in an amount of 365 kg) and 1470 kg of the coating liquid in Example 2 into a 1500 L homogenizing tank, control the stirring speed to 8000 r / min, and the stirring time to 3 min to obtain a magnesium oxide emulsion.

[0042] Step B: Magnesium oxide emulsion and nitric acid solution (1620 kg, nitric acid content 60 wt%) with a volume ratio of 1:0.90 are introduced into a tubular reactor together, and the upper cavity pressure is controlled to be 0.3 MPa. Cold circulating water is added to the jacket at one time. When the water temperature reaches 98°C, the inlet flow rate of the cold circulating water is adjusted to 15 L / min, and the water outlet is turned on to keep the temperature in the reactor at 123°C. The material is retained in the tubular reactor for 1 min.

[0043] Step C: The reacted materials are transferred to a second-stage tubular reactor with a residence time of 2 min. The value of the first on-line pH sensor is 10.0. By adding 210 kg of nitric acid, the value of the second on-line pH sensor is ensured to be 4.5. The hot water in the circulating water return tank is introduced into the heat preservation interlayer of the second-stage tubular reactor at a flow rate of 20 L / min, and the temperature is controlled at 90 °C. The pressure in the top cavity is controlled at 0.2 Mpa.

[0044] Step D: The reaction materials are transferred to a plate and frame filter press for pressure filtration. The filter mud is washed with 100 kg of hot water in the heat preservation interlayer to obtain 110 kg of washing liquid, and the washing liquid is used for preparing the magnesium oxide emulsion.

[0045] Step E: The 3500 kg of pressure filtrate from the plate and frame filter press at a temperature of 85 °C is transferred to a crystallizer, cooled to 65 °C for crystallization, and then further cooled to 32 °C for centrifugation to obtain 2040 kg of magnesium nitrate hexahydrate crystals with a purity of 99.5% and a yield of 97.14%. The crystals are rinsed with 100 kg of purified water and dried to obtain 2020 kg of high-purity magnesium nitrate hexahydrate with a purity of 99.8% and a yield of 96.19%. The 1300 kg of centrifugation mother liquor with a magnesium nitrate content of 19.76% w / w is recycled to the magnesium oxide emulsion preparation section. The 120 kg of rinsing water obtained after crystal rinsing is recycled to the magnesium oxide emulsion preparation section. Example 4

[0046] Step A: Magnesium oxide (magnesium oxide content 90% w / w, addition amount 380 kg) and 1530 kg of the recycled liquid in Example 3 are added to a 1500 L homogenizing tank, and the stirring speed is controlled at 7000 r / min with a stirring time of 4.5 min to obtain a magnesium oxide emulsion.

[0047] Step B: The magnesium oxide emulsion and nitric acid solution (1680 kg, nitric acid content 60 wt %) with a volume ratio of 1:0.90 enter a first-stage tubular reactor together, and the pressure in the upper cavity is controlled at 0.28 Mpa. Cold circulating water is added to the jacket at one time. When the water temperature reaches 97 °C, the inlet flow rate of the cold circulating water is adjusted to 13 L / min, and the outlet is opened to keep the temperature in the reactor at 121 °C. The residence time of the materials in the first-stage tubular reactor is 1.15 min.

[0048] Step C: The reacted materials are transferred to a second-stage tubular reactor with a residence time of 2.8 min. The value of the first on-line pH sensor is 9.5, and 120 kg of nitric acid is added to make the value of the second on-line pH sensor 5.0. The hot water in the circulating water return tank is introduced into the heat preservation interlayer of the second-stage tubular reactor at a flow rate of 16 L / min, and the temperature is controlled at 88 °C. The pressure in the top cavity is controlled at 0.18 Mpa.

[0049] Step D: The reaction materials are transferred to a plate and frame filter press for pressure filtration. The filter mud is washed with hot water in the heat-insulating interlayer to obtain 110 kg of washing liquid, and the washing liquid is used to prepare magnesium oxide emulsion.

[0050] Step E: The filtrate of 3480 kg obtained from the plate and frame filter press has a temperature of 83°C and is transferred to a crystallizer to cool down to 63°C for crystallization. It is further cooled down to 34°C for centrifugation to obtain 2200 kg of magnesium nitrate hexahydrate crystals with a purity of 99.3% and a yield of 100.54%. The crystals are rinsed with 100 kg of purified water to obtain 120 kg of washing liquid. After rinsing, 2180 kg of high-purity magnesium nitrate hexahydrate is obtained with a purity of 99.7% and a yield of 99.63%. The centrifugation mother liquor is 1220 kg with a magnesium nitrate content of 20.21%, which is recycled to the magnesium oxide emulsion preparation section.

[0051] It can be seen from the data of the above examples that:

[0052] In the present invention, the application of the one-stage tubular reactor combined with cooling by circulating water greatly shortens the reaction time of magnesium oxide and nitric acid. Taking Example 1 as an example, the residence time of the materials in the one-stage tubular reactor is only 1.2 min. Compared with the traditional process, the reaction efficiency is greatly improved, indicating that the tubular reactor combined with cooling by circulating water can effectively accelerate the reaction process.

[0053] The heat utilization rate is greatly improved: The heat generated by the reaction of nitric acid and magnesium oxide is absorbed by the circulating water, and the heated circulating water is fully used for subsequent heating of the second-stage reaction, heat preservation of the plate and frame filter press, pipeline flushing, etc. In Example 2, for example, the hot water in the circulating water return tank is introduced into the heat-insulating interlayer of the second-stage tubular reactor at a flow rate of 18 L / min, realizing the cascade utilization of heat, reducing the use of steam, and effectively saving energy consumption.

[0054] The water resource utilization rate is improved and there is no material waste: The heated circulating water is used for the washing liquid generated by washing the plate and frame filter press, and finally used as the preparation water for magnesium oxide emulsion; the centrifugation mother liquor is recycled to the magnesium oxide emulsion preparation section as bottom water. These series of operations make full use of water resources, reduce waste, and at the same time improve the product yield. In Example 3, the yield of magnesium nitrate hexahydrate crystals reaches 97%, and the yield of high-purity magnesium nitrate hexahydrate reaches 96%, fully reflecting the advantages of this method in terms of resource utilization and product yield.

[0055] The utilization rate of magnesium oxide is significantly improved: By adopting the tubular reaction mode, the problems of low stirring efficiency and uneven material reaction in the traditional kettle reaction are solved. From the results of each example, the magnesium oxide content in the filter mud is significantly reduced, indicating that the utilization rate of magnesium oxide is greatly improved and material waste is reduced.

[0056] Precise control of reaction parameters: Through two-stage tubular reaction and by using an online pH meter to control the addition amount of nitric acid in the second-stage tubular reactor, the reaction parameters can be adjusted quickly and precisely. In each embodiment, nitric acid is supplemented according to the numerical difference between the first online pH sensor and the second online pH sensor, achieving precise control of the reaction, improving the material utilization rate, and reducing the labor cost at the same time.

[0057] It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A method for utilizing reaction heat in a magnesium nitrate preparation process, characterized in that The following steps are involved: A: Magnesium oxide and tap water enter the homogenizing tank, stir and emulsify the materials to obtain magnesium oxide emulsion; B: Magnesium oxide emulsion and nitric acid enter a tubular reactor together, and cold circulating water is added to the jacket of the tubular reactor at one time. When the water temperature in the jacket reaches 95-98°C, the cold circulating water inlet of the jacket is opened again and its inlet flow rate is adjusted, and then the outlet of the jacket is opened to keep the temperature in the tubular reactor at 118-123°C. The outlet water of the jacket is continuously transferred to the circulating water return tank, and the feed flow rate of magnesium oxide emulsion and nitric acid is controlled to ensure that the material retention time in the tubular reactor is 1-1.2min; C: The materials after the reaction in the first-stage tubular reactor are transferred to the second-stage tubular reactor, and nitric acid is continuously added. When the pH value in the second-stage tubular reactor is 4-5, the reaction ends. During the reaction, the hot water in the circulating water return tank is passed into the insulation interlayer of the second-stage tubular reactor to control the temperature in the second-stage tubular reactor between 80-90°C; D: The reaction materials in the two-stage tubular reactor are transferred to a plate-frame filter press for filtration. After the filtration is completed, the filter mud is washed with hot water in the insulation interlayer of the two-stage tubular reactor. The washing liquid after washing in the plate-frame filter press is used to prepare magnesium oxide emulsion; E: The filtrate after plate and frame filtration is transferred to the crystallizer, cooled to 60-65℃ for crystallization, and then continued to cool for crystal cultivation. When the temperature drops to 30-40℃, it is centrifuged to obtain crystals of magnesium nitrate hexahydrate. The mother liquor from the centrifuge is returned to the magnesium oxide emulsion preparation section for use as bottom water.

2. The method for utilizing reaction heat in a magnesium nitrate preparation process as claimed in claim 1, wherein: In step A, the weight ratio of magnesium oxide to tap water is 0.25-0.35:1, the stirring speed is 5000-8000 r / min, and the stirring time is 3-5 min.

3. A method for utilizing reaction heat in a magnesium nitrate preparation process as claimed in claim 1, characterized in that: The volume ratio of the magnesium oxide emulsion to the nitric acid in step B is 1:0.9-0.

95.

4. The method for utilizing reaction heat in a magnesium nitrate preparation process as claimed in claim 1, wherein: In step B, the pressure of the upper cavity in the tubular reactor is 0.2-0.3 MPa.

5. The method for utilizing reaction heat in a magnesium nitrate preparation process as claimed in claim 1, characterized in that: In step C, the material stays in the two-stage tubular reactor for 2-3 minutes.

6. The method for utilizing reaction heat in a magnesium nitrate preparation process as claimed in claim 1, characterized in that: In step C, the pressure of the top cavity of the second-stage tubular reactor is controlled at 0.1-0.2 MPa.

7. The method for utilizing reaction heat in a magnesium nitrate preparation process as claimed in claim 1, characterized in that: A first online pH sensor is provided at the front section of the two-stage tubular reactor, and a second online pH sensor is provided on the pipeline between the two-stage tubular reactor and the plate and frame filter press. The amount of nitric acid added in step C is adjusted according to the difference between the first online pH sensor and the second online pH sensor.

8. The method for utilizing reaction heat in a magnesium nitrate preparation process as claimed in claim 1, characterized in that: The crystals of magnesium nitrate hexahydrate in step E are rinsed with purified water and dried to obtain high-purity magnesium nitrate hexahydrate.