Air suspension granulation technique for preparing spherical magnesium nitrate hexahydrate

Abstract

This application discloses an air-suspension granulation technology for preparing spherical magnesium nitrate hexahydrate, belonging to the field of magnesium nitrate hexahydrate granulation technology. It includes magnesium nitrate hexahydrate purification and granulation. This application incorporates a hydrophobic agent to form a robust microscopic protective layer, which effectively blocks water molecule intrusion and has a low moisture absorption rate. Furthermore, the air-suspension granulation tower technology is redesigned to better handle surface free water, resulting in higher magnesium nitrate purity, better crystal form, and better applicability to various magnesium nitrate applications. The particle size of the magnesium nitrate hexahydrate particles prepared by this application can be adjusted according to the air velocity, ranging from 0.5 to 12 mm. This technology has a wide range of applications, low cost, high sphericity, and eliminates the need for subsequent separate processing of broken particles, reducing labor costs and improving production efficiency. The magnesium nitrate hexahydrate also exhibits high purity, few impurities, and high product quality.

Description

Technical Field

[0001] This application belongs to the field of magnesium nitrate hexahydrate granulation technology, and in particular relates to an air suspension granulation technology for preparing spherical magnesium nitrate hexahydrate. Background Technology

[0002] Most existing processes for producing magnesium nitrate hexahydrate involve reacting magnesium oxide with nitric acid. After the reaction, cooling crystallization is used to precipitate magnesium nitrate as magnesium nitrate hexahydrate. However, the magnesium oxide used in this process is industrial-grade magnesium oxide with a purity of 88-92%, containing a large amount of silicates and calcium ions (silicate content is approximately 6-8%, and calcium oxide content is approximately 1.5-2.5%). In normal production, silicates are filtered out as precipitates later, but calcium nitrate, being easily soluble, will follow the magnesium nitrate solution into the subsequent crystallization process. During the cooling crystallization process, it will crystallize out together with magnesium nitrate hexahydrate as calcium nitrate tetrahydrate. This results in a high calcium ion content in the industrial-grade magnesium nitrate, approximately 0.1-0.2%, which is converted to calcium nitrate tetrahydrate at a content of approximately 0.6-1.18%. This content significantly reduces the purity of magnesium nitrate hexahydrate, greatly limiting its application.

[0003] Currently, solid magnesium nitrate hexahydrate is produced or sold in the form of needle-shaped crystals. However, in certain situations (mostly by overseas customers), there is a greater demand for solid granular magnesium nitrate hexahydrate. Granular magnesium nitrate hexahydrate is less prone to clumping than needle-shaped magnesium nitrate hexahydrate, making it more convenient and faster to use. It also has the advantage of faster dissolution, making it more suitable for various industries. Therefore, the demand for granular magnesium nitrate hexahydrate among overseas customers has increased significantly.

[0004] According to existing data, only one domestic manufacturer currently uses high-tower granulation to prepare granular magnesium nitrate hexahydrate. This process involves reconstituted magnesium nitrate into an aqueous solution, heating it, and then transferring it through a nozzle to a high tower for granulation. A suitable anti-caking agent is then sprayed onto the solution to produce granular magnesium nitrate hexahydrate. While this process solves the problem of producing suitable granular magnesium nitrate hexahydrate, the presence of a large amount of calcium nitrate tetrahydrate results in poor crystal structure, easy breakage, and the need to add appropriate organic anti-caking agents. This limits its application in specific fields such as agriculture. Furthermore, during actual production, the solid material may break upon contact with the ground, requiring subsequent screening processes to produce suitable granular magnesium nitrate hexahydrate. The crushed magnesium nitrate hexahydrate is then recycled, with a success rate of only 30-35%. Repeating this process results in high energy consumption. Summary of the Invention

[0005] The purpose of this application is to provide an air suspension granulation technology for preparing spherical magnesium nitrate hexahydrate, so as to solve the technical problems of high calcium ion content and low purity of magnesium nitrate hexahydrate products in the prior art, the need to add additional agglomerating agents to prepare spherical magnesium nitrate, and low spherical formation rate.

[0006] To achieve the above objectives, the technical solution adopted in this application is: to provide an air suspension granulation technology for preparing spherical magnesium nitrate hexahydrate, specifically including the following steps:

[0007] (I) Purification of magnesium nitrate hexahydrate: Add magnesium nitrate hexahydrate to deionized water, heat and stir to dissolve; add magnesium carbonate and continue stirring; after stirring, filter the material to obtain filtrate;

[0008] (II) Granulation of magnesium nitrate hexahydrate: Transfer the filtrate to the storage container at the top of the suspension granulation tower, heat the storage container, turn on the blower at the middle air outlet, and open the discharge valve of the storage container to allow the filtrate to drip naturally and form coarse granules.

[0009] (III) Magnesium nitrate hexahydrate finished product: The coarse particles continue to drip into the lower part of the suspension granulation tower. A hydrophobic agent is sprayed onto the coarse particles through the spray system, and the bottom micro horizontal air outlet is opened to blow airflow obliquely upward, so that the coarse particles are briefly suspended after dripping. High-purity spherical magnesium nitrate hexahydrate product is obtained from the discharge port.

[0010] In one embodiment,

[0011] Step (3) The hydrophobic agent is an ethanol dispersion of fumed nano-silica and a silane coupling agent; the silane coupling agent is octyltriethoxysilane, hexyltriethoxysilane or isobutyltriethoxysilane;

[0012] The hydrophobic agent, by mass percentage, comprises 2-5% fumed silica, 0.5-3% silane coupling agent, and the balance ethanol, up to 100%.

[0013] The mass ratio of the hydrophobic agent to magnesium nitrate hexahydrate is 1:80-90.

[0014] In one embodiment,

[0015] Step (1): The mass ratio of deionized water to magnesium nitrate hexahydrate is 0.006-0.01:1.

[0016] In one embodiment,

[0017] Magnesium nitrate hexahydrate consists of 98.2-98.8% magnesium nitrate, 0.8-1.5% calcium nitrate tetrahydrate, and 0.1-0.6% free water.

[0018] In one embodiment,

[0019] Step (1) The amount of magnesium carbonate added is based on the detected calcium ion content. The calculation formula is: magnesium carbonate addition (kg) = (magnesium nitrate hexahydrate addition (kg) * calcium ion content (%) / 40) * 84.3 * 1.05.

[0020] In one embodiment,

[0021] Step (1): After adding magnesium carbonate, stir for 30 minutes; heat to 75-80 ℃.

[0022] In one embodiment,

[0023] Step (II) The temperature for heating is 60-80 ℃; the wind speed detected at the top of the suspension granulation tower is 1.5-8 m / s; Step (III) The wind speed of the airflow blown obliquely upward is 0.6-1.5 m / s.

[0024] In one embodiment,

[0025] The bottom of the suspension granulation tower is covered with a soft pad, and the formed magnesium nitrate hexahydrate solid falls into the soft pad, which is made of foamed resin.

[0026] In one embodiment,

[0027] The slope of the discharge port is 5°.

[0028] In one embodiment,

[0029] The purity of high-purity spherical magnesium nitrate hexahydrate products is 99.5-99.8%, and the spherical formation rate is 95-98%.

[0030] This application provides an air suspension granulation technology for preparing spherical magnesium nitrate hexahydrate, which has the following advantages compared with the prior art:

[0031] 1. This application incorporates a hydrophobic agent during the granulation process. Nano-silica, as an inorganic nanofiller, forms a framework of microscopically rough hydrophobic structure, providing a physical barrier and enhancing the hydrophobic effect through its large specific surface area. The silane coupling agent, on the one hand, binds to the hydroxyl groups on the surface of SiO2 and magnesium nitrate particles through hydrolyzed silanol bonds, and on the other hand, its long-chain alkyl groups are arranged outward, providing the main hydrophobic properties. The hydrophobic agent has moderate viscosity, is suitable for atomization, and is easy to implement in industry. The innovative "in-situ coating" technology enables the hydrophobic nano-SiO2 to be tightly bonded to the particle bulk material during the growth process, forming a strong microscopic protective layer. This protective layer can effectively block the intrusion of water molecules, has a low moisture absorption rate, and is far superior to traditional processes.

[0032] 2. This application presents a new technology for air suspension granulation towers, which can better treat surface free water and produce magnesium nitrate with higher purity and better crystal form, making it more suitable for various applications of magnesium nitrate.

[0033] 3. The magnesium nitrate hexahydrate particles prepared in this application can be produced with a particle size range of 0.5-12 mm by adjusting the wind speed. This results in a wide range of applications, low cost, and high pellet formation rate. No further processing of broken particles is required, reducing labor costs and improving production efficiency. The magnesium nitrate hexahydrate has high purity and better crystallinity. Pressure filtration treatment results in extremely low calcium ion content and fewer impurities, leading to high product quality. Due to the high purity and better crystallinity of the product, the magnesium nitrate hexahydrate solid prepared by this process has stronger compressive strength, an extremely low breakage rate, and a higher yield. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of a suspension granulation tower.

[0036] Figure 2 This is a process flow diagram.

[0037] Explanation of symbols in the diagram:

[0038] 1. Feed pipe; 2. Drip tray; 3. Middle air outlet; 4. Bottom slightly horizontal air outlet; 5. Bottom gentle slope; 6. Discharge port; 7. Tower body. Detailed Implementation

[0039] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, this application will be further described in detail. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit this application.

[0040] Example 1

[0041] The suspension granulation tower structure used in the air suspension granulation technology for preparing spherical magnesium nitrate hexahydrate in this application is as follows: Figure 1As shown, the structure includes a tower body 7. Material enters the tower body 7 through a feed pipe 1. The tower body 7 is 18 m high. Material drips from the dripping plate 2 through the feed pipe 1. The dripping plate 2 can be changed according to customer needs based on its aperture size. Simultaneously, the airflow speed of the central air outlet 3 and the bottom micro-lateral air outlet 4 can be adjusted to prevent incomplete condensation or breakage during dripping. The central air outlet 3 is at a 75° angle to the horizontal plane, providing a stronger airflow to better dry the moisture in the material. The bottom micro-lateral air outlet 4 has a smaller airflow and is at a 15° angle to the horizontal plane; its purpose is primarily to reduce the material's falling speed, thus creating a better flow pattern in the middle and bottom sections. The airflow is parallel, reducing the material's falling speed and preventing breakage. It also increases the material's residence time in the air, resulting in better drying. The bottom slope 5 uses a one-time molded foamed resin coating at a 5° angle to the horizontal plane, effectively cushioning the impact of the material's fall. Due to the slope, the material automatically flows towards the discharge port 6. The discharge port 6 is controlled by a valve connected to a weighing scale, allowing for weighing during packaging. An automatic packaging and weighing system can also be used for added convenience.

[0042] Example 2

[0043] An air suspension granulation technique for preparing spherical magnesium nitrate hexahydrate, such as Figure 2 As shown, the specific steps include:

[0044] (I) Purification of magnesium nitrate hexahydrate: Add 200 kg of deionized water to the dissolving kettle, add 30 t of solid magnesium nitrate hexahydrate to the dissolving kettle, heat to 78 ℃ and stir to dissolve. After the material is completely dissolved, transfer the material to the magnesium nitrate refining kettle, add 119.5 kg of magnesium carbonate powder under the heat preservation condition, stir and react for 30 min. After stirring, filter the material to obtain the filtrate.

[0045] Testing revealed that the solid magnesium nitrate hexahydrate comprised 98.8% magnesium nitrate, 1.06% calcium nitrate tetrahydrate, and 0.14% free water, with a calcium ion content of 0.18%.

[0046] (II) Granulation of magnesium nitrate hexahydrate: Transfer the filtrate to the suspension granulation temporary storage tank, heat the storage container to 80 ℃, turn on the blowers at the middle air outlet 3 and the bottom micro-lateral air outlet 4 of the suspension granulation tower, set the air velocity of the middle air outlet 3 to 3 m / s, and the air velocity of the bottom micro-lateral air outlet 4 to 0.8 m / s; after the air velocity stabilizes, open the valve of the feed pipe 1 at the top of the suspension granulation tower, so that the filtrate drips naturally into the suspension granulation tower through the drip plate 2 with a diameter of 2 mm, forming coarse granules;

[0047] (III) Magnesium nitrate hexahydrate finished product: The coarse particles continue to drip into the lower part of the suspension granulation tower. A hydrophobic agent is sprayed onto the coarse particles through the spray system. The coil air duct at the bottom of the suspension granulation tower is opened, and the airflow is blown out obliquely upward from the bottom micro-horizontal air outlet 4, so that the coarse particles can be suspended briefly after dripping to this point. The material is suspended in the tower body 7 for 4 seconds and then falls to the ground. The bottom of the suspension granulation tower is covered with a soft pad. The formed magnesium nitrate hexahydrate solid falls into the soft pad and flows out from the discharge port 6 to obtain high-purity spherical magnesium nitrate hexahydrate product.

[0048] Composition of the hydrophobic agent: by mass percentage, 3% fumed nano silica, 1.5% octyltriethoxysilane, ethanol added to 100%, and the amount of hydrophobic agent used is 353 kg;

[0049] The high-purity spherical magnesium nitrate hexahydrate has an average particle size of 3.5 mm. Its content was tested and found to be: magnesium nitrate hexahydrate content of 99.6%, calcium ion content of 0.06% (equivalent to calcium nitrate tetrahydrate content of 0.35%), free water content of 0.05%, and moisture absorption rate of 0.8% after being placed in an environment with a relative humidity of 80% for 48 hours. The spherical formation rate was 96.8%.

[0050] Example 3

[0051] An air suspension granulation technique for preparing spherical magnesium nitrate hexahydrate specifically includes the following steps:

[0052] (I) Purification of magnesium nitrate hexahydrate: Add 180 kg of deionized water to the dissolving kettle, add 30 t of solid magnesium nitrate hexahydrate to the dissolving kettle, heat to 80 ℃ and stir to dissolve. After the material is completely dissolved, transfer the material to the magnesium nitrate refining kettle, add 139.4 kg of magnesium carbonate powder under the heat preservation condition, stir and react for 30 min. After stirring, filter the material to obtain the filtrate.

[0053] Testing revealed that the solid magnesium nitrate hexahydrate comprised 98.4% magnesium nitrate, 1.24% calcium nitrate tetrahydrate, and 0.36% free water, with a calcium ion content of 0.21%.

[0054] Pressure filtration can remove insoluble matter. At this time, calcium ions will precipitate out in the form of calcium carbonate, which greatly reduces the calcium ion content in the solution. After magnesium carbonate reacts with calcium nitrate, the resulting magnesium nitrate remains in the solution, which improves the purity of magnesium nitrate in the later stage.

[0055] (II) Granulation of magnesium nitrate hexahydrate: Transfer the filtrate to the suspension granulation temporary storage tank, heat the storage container to 80 ℃, turn on the blowers at the middle air outlet 3 and the bottom micro-lateral air outlet 4 of the suspension granulation tower, set the air velocity of the middle air outlet 3 to 4.2 m / s, and the air velocity of the bottom micro-lateral air outlet 4 to 1.1 m / s; after the air velocity stabilizes, open the valve of the feed pipe 1 at the top of the suspension granulation tower, so that the filtrate drips naturally into the suspension granulation tower through the drip plate 2 with a diameter of 2.8 mm, forming coarse granules;

[0056] (III) Finished Magnesium Nitrate Hexahydrate: The coarse particles continue to drip into the lower part of the suspension granulation tower. A hydrophobic agent is sprayed onto the coarse particles through a spray system. The coiled air duct at the bottom of the suspension granulation tower is opened, and the airflow is blown upward at an angle from the bottom micro-horizontal air outlet 4. This allows the coarse particles to be briefly suspended after dripping to this point, which can better remove the free water on the surface of the magnesium nitrate hexahydrate particles and also provide better buoyancy support for the magnesium nitrate hexahydrate solid. The material is suspended in the tower body 7 for 4 seconds before falling to the ground. The bottom of the suspension granulation tower is covered with a soft pad, and the formed magnesium nitrate hexahydrate solid falls into the soft pad, which provides better support after the magnesium nitrate hexahydrate solid falls to the ground. At the same time, the slope of the discharge port 6 is low, so the material that falls to the ground can flow out smoothly from the discharge port 6, preventing the magnesium nitrate hexahydrate particles from colliding and breaking due to the accumulation at the bottom. The magnesium nitrate hexahydrate solid flows out from the discharge port 6, resulting in a high-purity spherical magnesium nitrate hexahydrate product.

[0057] Composition of the hydrophobic agent: by mass percentage, fumed nano silica accounts for 2%, hexyltriethoxysilane accounts for 0.5%, ethanol is added to 100%, and the amount of hydrophobic agent is 375 kg.

[0058] The high-purity spherical magnesium nitrate hexahydrate has an average particle size of 5.2 mm. Its content was tested and found to be: magnesium nitrate hexahydrate content of 99.5%, calcium ion content of 0.07% (equivalent to calcium nitrate tetrahydrate content of 0.41%), and free water content of 0.09%. After being placed in an environment with a relative humidity of 80% for 48 hours, the moisture absorption rate was 1.2%, and the spherical formation rate was 98.3%.

[0059] Example 4

[0060] An air suspension granulation technique for preparing spherical magnesium nitrate hexahydrate specifically includes the following steps:

[0061] (I) Purification of magnesium nitrate hexahydrate: Add 220 kg of deionized water to the dissolving kettle, add 30 t of magnesium nitrate hexahydrate solid to the dissolving kettle, heat to 75 ℃ and stir to dissolve. After the material is completely dissolved, transfer the material to the magnesium nitrate refining kettle. Under the heat preservation condition, add 100 kg of magnesium carbonate powder and 2 kg of magnesium carbonate-based flocculant and stir to react for 30 min. After stirring, filter the material to obtain the filtrate.

[0062] Testing revealed that the solid magnesium nitrate hexahydrate comprised 98.6% magnesium nitrate, 0.88% calcium nitrate tetrahydrate, and 0.52% free water, with a calcium ion content of 0.15%.

[0063] (II) Granulation of magnesium nitrate hexahydrate: Transfer the filtrate to the suspension granulation temporary storage tank, heat the storage container to 60 ℃, turn on the blowers at the middle air outlet 3 and the bottom micro-lateral air outlet 4 of the suspension granulation tower, set the air velocity of the middle air outlet 3 to 6 m / s, and the air velocity of the bottom micro-lateral air outlet 4 to 1.4 m / s; after the air velocity stabilizes, open the valve of the feed pipe 1 at the top of the suspension granulation tower, so that the filtrate drips naturally into the suspension granulation tower through the drip plate 2 with a diameter of 3.5 mm, forming coarse granules;

[0064] (III) Magnesium nitrate hexahydrate finished product: The coarse particles continue to drip into the lower part of the suspension granulation tower. A hydrophobic agent is sprayed onto the coarse particles through the spray system. When the filtrate begins to drip, the coil air duct at the bottom of the suspension granulation tower is opened, and the airflow is blown out obliquely upward from the bottom micro-horizontal air outlet 4, so that the coarse particles can be suspended briefly after dripping to this point. The material is suspended in the tower body 7 for 4 seconds and then falls to the ground. The bottom of the suspension granulation tower is covered with a soft pad. The formed magnesium nitrate hexahydrate solid falls into the soft pad and flows out from the discharge port 6 to obtain high-purity spherical magnesium nitrate hexahydrate product.

[0065] Composition of the hydrophobic agent: by mass percentage, fumed nano silica accounts for 5%, isobutyltriethoxysilane accounts for 3%, ethanol is added to 100%, and the amount of hydrophobic agent is 333 kg.

[0066] The high-purity spherical magnesium nitrate hexahydrate has an average particle size of 8.6 mm. Its content was tested as follows: magnesium nitrate hexahydrate content was 99.8%, calcium ion content was 0.03% (equivalent to calcium nitrate tetrahydrate content of 0.18%), and free water content was 0.02%. After being placed in an environment with a relative humidity of 80% for 48 hours, the moisture absorption rate was 0.5%, the sphericity rate was 96.8%, and the sphericity formation rate was 98.8%.

[0067] This application provides an air-suspension granulation technology for preparing spherical magnesium nitrate hexahydrate. The "in-situ coating" technology allows hydrophobic nano-SiO2 to tightly bond with the particle bulk material during growth, forming a robust microscopic protective layer. This protective layer effectively blocks water molecule intrusion, exhibiting low moisture absorption, far superior to traditional processes. The redesigned air-suspension granulation tower technology better handles surface free water, resulting in higher purity and better crystal form of magnesium nitrate, making it more suitable for various applications. The magnesium nitrate hexahydrate particles prepared by this application can be produced with a particle size range of 0.5-12 mm by adjusting the airflow rate, offering wide applicability, low cost, and high sphericity. It eliminates the need for subsequent separate processing of broken particles, reducing labor costs and improving production efficiency. The magnesium nitrate hexahydrate has high purity and few impurities, resulting in high product quality. If the customer has no requirements regarding other impurities, an appropriate amount of flocculant can be added, and the final product purity can reach over 99.8%.

[0068] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An air suspension granulation technology for preparing spherical magnesium nitrate hexahydrate, characterized in that, Specifically, the following steps are included: (I) Purification of magnesium nitrate hexahydrate: Add magnesium nitrate hexahydrate to deionized water, heat and stir to dissolve; add magnesium carbonate and continue stirring; after stirring, filter the material to obtain filtrate; (ii) Granulation of magnesium nitrate hexahydrate: The filtrate is transferred to the storage container at the top of the suspension granulation tower, the storage container is heated, the blower at the middle air outlet is turned on, and the discharge valve of the storage container is opened to allow the filtrate to drip naturally and form coarse granules. (III) Magnesium nitrate hexahydrate finished product: The coarse particles continue to drip into the lower part of the suspension granulation tower. A hydrophobic agent is sprayed onto the coarse particles through a spray system, and the bottom micro-horizontal air outlet is opened to blow airflow obliquely upward, so that the coarse particles are briefly suspended after dripping. High-purity spherical magnesium nitrate hexahydrate product is obtained from the discharge port. The amount of magnesium carbonate added in step (I) is based on the detected calcium ion content, and the calculation formula is: magnesium carbonate addition (kg) = (magnesium nitrate hexahydrate addition (kg) * calcium ion content (%) / 40) * 84.3 * 1.05; the stirring time after adding magnesium carbonate in step (I) is 30 min; the heating temperature is 75-80 ℃; the heating temperature in step (II) is 60-80 ℃; the wind speed detected at the top of the suspension granulation tower is 1.5-8 m / s; the wind speed of the airflow blown obliquely upward in step (III) is 0.6-1.5 m / s; The hydrophobic agent is an ethanol dispersion of fumed nano-silica and a silane coupling agent; the silane coupling agent is octyltriethoxysilane, hexyltriethoxysilane, or isobutyltriethoxysilane; the hydrophobic agent, by mass percentage, comprises 2-5% fumed nano-silica, 0.5-3% silane coupling agent, and the balance being ethanol, up to 100%; the mass ratio of the hydrophobic agent to magnesium nitrate hexahydrate is 1:80-90.

2. The air suspension granulation technology for preparing spherical magnesium nitrate hexahydrate according to claim 1, characterized in that, The mass ratio of deionized water and magnesium nitrate hexahydrate in step (1) is 0.006-0.01:

1.

3. The air suspension granulation technology for preparing spherical magnesium nitrate hexahydrate according to claim 1, characterized in that, The hexahydrate magnesium nitrate comprises 98.2-98.8% magnesium nitrate, 0.8-1.5% calcium nitrate tetrahydrate, and 0.1-0.6% free water.

4. The air suspension granulation technology for preparing spherical magnesium nitrate hexahydrate according to claim 1, characterized in that, The bottom of the suspension granulation tower is covered with a soft mat, and the formed magnesium nitrate hexahydrate solid falls into the soft mat, which is made of foamed resin.

5. The air suspension granulation technology for preparing spherical magnesium nitrate hexahydrate according to claim 1, characterized in that, The slope of the discharge port is 5°.

6. The air suspension granulation technology for preparing spherical magnesium nitrate hexahydrate according to claim 1, characterized in that, The purity of the high-purity spherical magnesium nitrate hexahydrate product is 99.5-99.8%, and the spherical formation rate is 95-98%.

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