Reaction heat utilization method in magnesium nitrate preparation process

Abstract

The invention discloses a reaction heat utilization method in a magnesium nitrate preparation process, and relates to the technical field of magnesium nitrate production, magnesium oxide and tap water are homogenized and then enter a first-section tubular reactor together with nitric acid, a reaction is carried out at 118-123 DEG C for 1-1.2 min, then the reaction product enters a second-section tubular reactor, nitric acid is supplemented until the pH value in the second-section tubular reactor is 4-5, the reaction is finished, and a reaction product is obtained; and crystallizing the filtrate obtained by filter pressing of the reaction material, and centrifuging to obtain magnesium nitrate hexahydrate crystals. Wherein cold circulating water is introduced into the jacket of the first-section tubular reactor, and when the water temperature reaches 95-98 DEG C, the cold circulating water is used as heat supplement of the second-section tubular reactor, so that the reaction heat is fully utilized, the reaction time is shortened, and the production cost is saved.

Description

Technical Field

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

[0002] The existing magnesium nitrate production process mainly uses magnesium oxide and nitric acid to react in a reactor. After the reaction is completed, solid impurities such as silicates in the reaction solution are filtered out by plate and frame filter press, and then magnesium nitrate hexahydrate crystals are prepared through concentration, crystallization and centrifugation processes.

[0003] The main defects of the existing process are as follows: 1. A large amount of heat is released during the reaction of nitric acid and magnesium oxide. If the heat is not discharged in time, the nitric acid feed rate needs to be reduced, resulting in a long reaction time and low production efficiency.

[0004] 2. In the subsequent filtration and transfer process of magnesium nitrate solution, a large amount of magnesium nitrate crystals will appear due to temperature reduction or incomplete pipeline purging, resulting in blockage of pipelines or plate and frame filter presses. Therefore, steam heating is required during the material transfer process to prevent the material from crystallizing in the pipeline, which will require a large amount of steam and increase production costs.

[0005] 3. Since the magnesium nitrate reactor is generally a large reactor of 20m³, 40m³, or even 80m³, its stirring efficiency is low, and the magnesium oxide material cannot be completely reacted, resulting in material waste. This can be seen from the magnesium oxide content in the filter mud produced by the plate and frame filter press. The current magnesium oxide content in the filter mud is between 5-8% w / w, resulting in a large amount of magnesium oxide waste, low product yield and high cost. Summary of the invention

[0006] The technical problem to be solved by the present invention is: in view of the deficiencies in the prior art, a method for utilizing reaction heat in a magnesium nitrate preparation process is provided, which improves the yield of the product and reduces the production cost.

[0007] In order to solve the above technical problems, the technical solution of the present invention is: A method for utilizing reaction heat in a magnesium nitrate preparation process comprises the following steps: 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; E: The filtrate after plate and frame filtration is transferred to a crystallizer, cooled to 60-65°C for crystallization, and then continued to cool for crystal cultivation. When the temperature drops to 30-40°C, centrifugation is performed to obtain crystals of magnesium nitrate hexahydrate.

[0008] 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.

[0009] Preferably, the volume ratio of the magnesium oxide emulsion to the nitric acid in step B is 1:0.9-0.95.

[0010] Preferably, the pressure of the upper cavity in the tubular reactor in step B is 0.2-0.3 MPa.

[0011] Preferably, in step C, the material stays in the two-stage tubular reactor for 2-3 minutes.

[0012] Preferably, in step C, the pressure of the top cavity of the second-stage tubular reactor is controlled at 0.1-0.2 MPa.

[0013] Preferably, a first online pH sensor is provided at the front section (inlet) 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, and 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.

[0014] Preferably, the washing liquid after washing the plate and frame filter press in step D is used to prepare magnesium oxide emulsion.

[0015] Preferably, the centrifuged mother liquor in step E contains a large amount of magnesium nitrate, which is recycled to the magnesium oxide emulsion preparation stage for use as bottom water.

[0016] Preferably, the crystals of magnesium nitrate hexahydrate in step E are rinsed with purified water and dried to obtain high-purity magnesium nitrate hexahydrate.

[0017] Due to the adoption of the above technical solution, the beneficial effects of the present invention are: 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 released quickly, so that the reaction can be carried out more quickly, greatly reducing the reaction time of magnesium oxide and nitric acid and improving the reaction efficiency.

[0018] 2. The heat released by the reaction of nitric acid and magnesium oxide is absorbed by the circulating water in the jacket of the first stage tubular reactor. The circulating water is heated to about 95-98°C and then used for the subsequent second stage reaction heating. After the reaction, the circulating water temperature drops to about 80°C and then continues to be used for plate and frame filter press insulation and pipeline flushing, which can better dissolve the magnesium nitrate crystals crystallized in the pipeline. Therefore, the utilization rate of heat is improved, the use of steam is reduced, and energy consumption is greatly saved.

[0019] 3. The washing liquid produced by the heated circulating water for washing the plate and frame filter press is finally used as the preparation water of the magnesium oxide emulsion, which greatly improves the utilization rate of water resources, avoids material waste, saves energy, and also improves the yield of the product.

[0020] 4. The present invention adopts a tubular reaction method. Compared with a kettle reaction, the pipeline reaction has a higher stirring efficiency and does not cause uneven material reaction. Therefore, the utilization rate of magnesium oxide can be greatly improved and the content of magnesium oxide in the filter mud can be reduced.

[0021] 5. The present invention adopts a two-stage tubular reaction mode, and controls the amount of nitric acid added in the two-stage tubular reactor by an online pH meter, which can quickly and accurately adjust subsequent reaction parameters, improve material utilization, and reduce labor costs. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the embodiments. Example 1

[0023] Step A: Add magnesium oxide (magnesium oxide content 90% w / w, added amount 350 kg) and tap water (1 m³) in a weight ratio of 0.35:1 into a 1500 L homogenizing tank, control the stirring speed to 5000 r / min, and the stirring time to 5 min to obtain magnesium oxide emulsion, wherein the volume of the magnesium oxide emulsion is 1.26 m³.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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

[0033] 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.

[0034] 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.

[0035] Step C: The reacted material is transferred to the second-stage tubular reactor with a residence time of 2 min. The value of the first online pH sensor is 10.0. By adding 210 kg of nitric acid, the value of the second online pH sensor is ensured to be 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 20 L / min, and the temperature is controlled at 90 ° C. The top cavity pressure is controlled at 0.2 Mpa.

[0036] Step D: The reaction material is transferred to a plate and frame filter press for filtration, and the filter mud is washed with 100 kg of hot water in the thermal insulation interlayer to obtain 110 kg of washing liquid, which is used to prepare magnesium oxide emulsion.

[0037] Step E: 3500kg of the filtrate from the plate and frame filter press is at 85°C, transferred to a crystallizer and cooled to 65°C for crystallization, and then cooled to 32°C for centrifugation to obtain 2040kg of magnesium nitrate hexahydrate crystals with a purity of 99.5% and a yield of 97.14%. The crystals are rinsed with 100kg of purified water, and after drying, 2020kg of high-purity magnesium nitrate hexahydrate is obtained with a purity of 99.8% and a yield of 96.19%. 1300kg of the centrifuged mother liquor, with a magnesium nitrate content of 19.76% w / w, is returned to the magnesium oxide emulsion preparation section. After the crystals are rinsed, 120kg of rinsing water is obtained, which is returned to the magnesium oxide emulsion preparation section. Example 4

[0038] Step A: Add magnesium oxide (magnesium oxide content 90% w / w, added in an amount of 380 kg) and 1530 kg of the coating liquid in Example 3 into a 1500 L homogenizing tank, control the stirring speed to 7000 r / min, and the stirring time to 4.5 min to obtain a magnesium oxide emulsion.

[0039] Step B: Magnesium oxide emulsion and nitric acid solution (1680 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 0.28 MPa. Cold circulating water is added to the jacket at one time. When the water temperature reaches 97°C, the cold circulating water inlet flow rate is adjusted to 13 L / min, and the water outlet is turned on to keep the temperature in the reactor at 121°C. The material is retained in the tubular reactor for 1.15 min.

[0040] Step C: The reacted material is transferred to the second-stage tubular reactor with a residence time of 2.8 min. The value of the first online pH sensor is 9.5, and 120 kg of nitric acid is added to make the value of the second online pH sensor 5.0. 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 16 L / min, and the temperature is controlled at 88 ° C and the top cavity pressure is controlled at 0.18 Mpa.

[0041] Step D: The reaction material is transferred to a plate and frame filter press for filtration, and the filter mud is washed with hot water in the thermal insulation interlayer to obtain 110 kg of washing liquid, which is used to prepare magnesium oxide emulsion.

[0042] Step E: 3480 kg of the filtrate obtained by the plate and frame filter press is at a temperature of 83°C, transferred to a crystallizer and cooled to 63°C for crystallization, and then cooled 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 elution, 2180 kg of high-purity magnesium nitrate hexahydrate is obtained with a purity of 99.7% and a yield of 99.63%. 1220 kg of the centrifuged mother liquor with a magnesium nitrate content of 20.21% is returned to the magnesium oxide emulsion preparation section.

[0043] From the data of the above embodiment, it can be seen that: The application of a one-stage tubular reactor in the present invention combined with circulating water cooling greatly shortens the reaction time of magnesium oxide and nitric acid. Taking Example 1 as an example, the retention time of the material in the one-stage tubular reactor is only 1.2 minutes. Compared with the traditional process, the reaction efficiency is greatly improved, which shows that the tubular reactor combined with circulating water cooling can effectively accelerate the reaction process.

[0044] 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 the subsequent second-stage reaction heating, plate and frame filter press insulation, and pipeline flushing. As in Example 2, 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 18L / min, which realizes the cascade utilization of heat, reduces the use of steam, and effectively saves energy consumption.

[0045] The utilization rate of water resources is improved and there is no waste of materials: the heated circulating water is used to wash the washing liquid produced by the plate and frame filter press, and finally used as the preparation water of the magnesium oxide emulsion; the centrifuged mother liquor is returned to the magnesium oxide emulsion preparation section for use as bottom water. This series of operations makes full use of water resources, reduces waste, and also improves 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%, which fully reflects the advantages of this method in resource utilization and product yield.

[0046] The utilization rate of magnesium oxide is significantly improved: the use of tubular reaction mode solves the problems of low stirring efficiency and uneven material reaction in traditional kettle reaction. From the results of each embodiment, the content of magnesium oxide in the filter mud is significantly reduced, indicating that the utilization rate of magnesium oxide has been greatly improved and material waste has been reduced.

[0047] Precise control of reaction parameters: Through two-stage tubular reaction, and using an online pH meter to control the amount of nitric acid added in the two-stage tubular reactor, the reaction parameters can be adjusted quickly and accurately. In each embodiment, nitric acid is added according to the difference in the values ​​of the first online pH sensor and the second online pH sensor, which achieves precise control of the reaction, improves material utilization, and reduces labor costs.

[0048] It should be understood that these embodiments are only used to illustrate the present invention and are not used 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 limited by the appended claims of the 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; E: The filtrate after plate and frame filtration is transferred to a crystallizer, cooled to 60-65°C for crystallization, and then continued to cool for crystal cultivation. When the temperature drops to 30-40°C, centrifugation is performed to obtain crystals of magnesium nitrate hexahydrate.

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 washing liquid after washing the plate and frame filter press in step D is used to prepare magnesium oxide emulsion.

9. The method for utilizing reaction heat in a magnesium nitrate preparation process as claimed in claim 1, characterized in that: The centrifuged mother liquor in step E is returned to the magnesium oxide emulsion preparation stage for use as bottom water.

10. The method for utilizing reaction heat in a magnesium nitrate preparation process according to 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.