A continuous nucleation reaction device and its application in the preparation of layered double hydroxides

Abstract

The present invention discloses a continuous nucleation reaction device and its application in the preparation of layered double hydroxides. Based on the principle of heterogeneous nucleation reaction for preparing LDHs by a clean production process, the present invention adopts a continuous nucleation reaction device that can continuously feed and discharge materials and has functions of refining, grinding, peeling and dispersing. By using the high-speed collision of the dispersion medium to control the processes of solid-phase raw material dissolution - nucleation - peeling - crystallization, the rapid reduction of the particle size and the accelerated dissolution of the raw materials under high-energy collision during the continuous flow of the slurry are realized, promoting the rapid nucleation of reaction ions. At the same time, the LDHs crystal nuclei formed on the surface of the solid-phase raw materials are rapidly separated, accelerating the formation and uniform growth of crystal nuclei, and preparing LDHs products with high purity and uniform particle size distribution. This device significantly improves the reaction rate, reduces the reaction temperature, realizes continuous production, improves production efficiency and reduces production costs, and is very suitable for large-scale production.

Description

Technical Field:

[0001] The present invention belongs to the technical field of inorganic functional material preparation, and particularly relates to a continuous nucleation reaction device and its application in the preparation of layered double hydroxides. Background Art:

[0002] Layered double hydroxides (LDHs), also known as hydrotalcite, are a typical anionic layered material, and their chemical formula is [M 2+ 1-x M 3+ x (OH)2]A n- x / n ·mH2O, where M 2+ and M 3 + represent divalent and trivalent metal cations respectively, A n- is the interlayer anion, x is the molar fraction of M 3+ ions, and m is the number of crystal waters. The types and ratios of the LDHs lamellar elements and the types and amounts of the interlayer guests can be adjusted according to application requirements, so that a series of materials with special structures and properties can be prepared, which are widely used in the fields of catalysis, plastic additives, and environmental protection.

[0003] Patent (200710062650.9) proposes a method for preparing layered double hydroxides by a clean process. This method uses magnesium hydroxide and aluminum hydroxide as raw materials, and makes them react under high-temperature hydrothermal conditions in the reaction to produce LDHs products. This reaction is a typical heterogeneous nucleation reaction. The solid-phase raw materials first dissolve to form ions, and then precipitate and nucleate on the surface of magnesium hydroxide or aluminum hydroxide. The formed crystal nuclei further diffuse and grow along the interface between LDHs and the raw materials to form LDHs. Therefore, the particle size of the raw materials and the rapid peeling of the LDHs crystal nuclei from the raw materials have an important impact on the progress of the reaction and the morphology and size of the products. Generally, when using solid-phase raw materials to prepare LDHs, a stirring paddle type or high-shear reaction kettle is mostly used. However, in the preparation process, the traditional stirring paddle type reaction kettle cannot control the particle size of the raw materials and the peeling of the LDHs products from the raw material particles, which affects the uniformity of the LDHs nucleation and growth reaction, and impurities are likely to appear in the products and the particle size distribution is uneven; while the high-shear reaction kettle can control the particle size of the raw materials and can achieve the peeling of the LDHs products from the raw material particles, but due to the small working surface of the overall shear machine, there are problems such as low shear efficiency and uneven product particle size distribution. At the same time, when using a reaction kettle to prepare LDHs, it is mostly an intermittent reaction, resulting in an extended overall reaction time, a decrease in production efficiency, an increase in production costs, and limiting its further large-scale production. Summary of the Invention:

[0004] The present invention provides a continuous nucleation reaction device and applies it to the preparation of layered double hydroxides. By using a continuous nucleation reaction device with high-efficiency dispersion and exfoliation, a slurry of poorly soluble solid raw materials enters the reactor in a continuous feeding and discharging form, and reacts under high dispersion and strong exfoliation to produce LDHs products with high purity and uniform particle size distribution.

[0005] The continuous nucleation reaction device described in the present invention is composed of a fixed hollow jacketed cylinder and a rotor inside the cylinder. The rotor is controlled by a motor to rotate; reaction dispersers are evenly distributed on the rotor, and the space between the cylinder and the rotor is filled with dispersion beads; a reactor slurry inlet is provided at one end of the hollow jacketed cylinder, and a reactor slurry outlet is provided at the other end. The reactor slurry inlet is connected to a feed pump, and a dynamic separator is provided at the reactor slurry outlet; a heating medium inlet and a heating medium outlet are provided in the hollow jacket layer of the hollow jacketed cylinder, and the reaction temperature inside the cylinder is controlled by heating medium circulation.

[0006] The reaction disperser is of disk type or rod pin type.

[0007] The material of the reaction disperser is zirconia ceramic or polyurethane.

[0008] The material of the dispersion beads is zirconia or alumina. The diameter of the dispersion beads is 0.05 - 1.2 mm, preferably 0.05 - 0.3 mm; the filling amount of the dispersion beads is 50 - 80% of the volume of the cylinder.

[0009] The aspect ratio (length to diameter ratio) of the hollow jacketed cylinder is 0.5 - 10.

[0010] The inner wall material of the hollow jacketed cylinder is stainless steel, zirconia ceramic or polyurethane plastic.

[0011] The gap size of the dynamic separator is 50 - 80% of the diameter of the dispersion beads.

[0012] A method for preparing a layered double hydroxide is as follows: Mix the hydroxide and / or oxide of M 2+ and the hydroxide and / or oxide of M 3+ , add deionized water and stir to obtain a slurry; start the continuous nucleation reaction device, pump the slurry into the continuous nucleation reaction device through a feed pump, and after the reaction is completed, the product obtained at the reactor slurry outlet is directly filtered and dried to obtain the layered double hydroxide.

[0013] The M 2+ is Mg 2+ , Zn 2+ , Ca 2+One or more of; M 3+ is Al 3+ , Cr 3+ One or two of them.

[0014] The M described above 2+ Hydroxide and / or oxide of M, M 3+ The molar ratio of the hydroxide and / or oxide of is 1-4.

[0015] A metal salt is also added to the slurry described above.

[0016] The metal salt described above is M 2+ and / or M 3+ Metal salt of, the anion of the metal salt is Cl - , NO3 - , CO3 2- , SO4 2- , PO4 3- One or more of them.

[0017] M 2+ The molar ratio of the hydroxide and / or oxide of M to the metal salt is 1-10.

[0018] The solid content of the slurry described above is 5-50%, preferably 10-30%.

[0019] The rotation speed of the continuous nucleation reaction device described above is set to 400-2000 rpm, preferably 1000-2000 rpm; the reaction temperature is 40-120 °C, preferably 60-100 °C.

[0020] The pumping speed of the slurry described above is 0.01-10 L / min.

[0021] The residence time of the slurry in the continuous nucleation reaction device described above is 0.1-12 h, preferably 2-4 h.

[0022] The interlayer anion of the layered double metal hydroxide described above is CO3 2- Or the corresponding anion of the added metal salt.

[0023] Beneficial effects: Based on the heterogeneous nucleation reaction principle of preparing LDHs by a clean production process, the present invention adopts a continuous nucleation reaction device that can achieve continuous feeding and discharging and has functions of raw material refinement, product exfoliation, and slurry uniform dispersion for the preparation of LDHs. During the reaction process, the high-speed collision of the dispersion medium is used to control the processes of solid-phase raw material dissolution - nucleation - exfoliation - crystallization, realizing the rapid reduction and accelerated dissolution of the particle size of the raw material under high-energy collision during the continuous flow of the slurry, promoting the rapid nucleation of reaction ions, and at the same time enabling the rapid separation of the LDHs nuclei formed on the surface of the solid-phase raw material, accelerating the formation and uniform growth of nuclei, and continuously preparing LDHs products with high purity and uniform particle size dispersion. The present invention continuously pumps the solid-phase insoluble slurry into the inner barrel of the reactor with functions of grinding refinement and slurry dispersion, and uniformly passes through the reactor at a certain flow rate at a certain reaction temperature for a certain reaction time. During this period, the zirconia bead dispersion medium in the reactor cylinder is driven by the dispersion disc on the high-speed rotor and rapidly refines and uniformly disperses the continuously flowing reaction slurry in the form of high-speed collision, accelerating the dissolution and dispersion of the solid-phase raw material in the liquid phase system, promoting the rapid nucleation of ions on the solid-phase raw material particles with a smaller particle size, and at the same time enabling the rapid separation of the generated LDHs nuclei from the raw material to promote the continuous progress of nucleation - exfoliation - growth, accelerating the growth of nuclei to form LDHs products with high purity, uniform particle size, and small size. Compared with the original reaction kettle reaction method, the use of this device can significantly improve the reaction rate, reduce the reaction temperature, which drops from 140 °C required by the reaction kettle to 80 °C, and at the same time realizes continuous production, improves production efficiency, reduces energy consumption, and is beneficial to the further large-scale production of LDHs. Brief description of the drawings:

[0024] Figure 1 is a schematic structural diagram of the continuous nucleation reaction device designed by the present invention: 1 - heating medium outlet, 2 - reactor slurry inlet, 3 - hollow jacketed cylinder, 4 - reactor slurry outlet, 5 - dynamic separator, 6 - pin-type reaction disperser, 7 - rotor, 8 - heating medium inlet, 9 - motor;

[0025] Figure 2 is the XRD spectrum of the layered double hydroxide obtained in Example 1;

[0026] Figure 3 is the laser particle size distribution diagram of the layered double hydroxide obtained in Example 1;

[0027] Figure 4 is the SEM spectrum of the layered double hydroxide obtained in Example 2;

[0028] Figure 5 is the laser particle size distribution diagram of the layered double hydroxide obtained in Comparative Example 1. Detailed implementation manners:

[0029] The continuous nucleation reaction device designed by the present invention consists of a fixed hollow jacketed cylinder body 3 and a rotor 7 inside the cylinder body. The rotor 7 is controlled to rotate by a motor 9. A rod-pin type reaction disperser 6 is evenly distributed on the rotor 7, and the space between the cylinder body and the rotor 7 is filled with dispersion beads. One end of the hollow jacketed cylinder body 3 is provided with a reactor slurry inlet 2, and the other end is provided with a reactor slurry outlet 4. The reactor slurry inlet 2 is connected to a feed pump, and a dynamic separator 5 is arranged at the reactor slurry outlet 4. A heating medium inlet 1 and a heating medium outlet 8 are arranged in the hollow jacket layer of the hollow jacketed cylinder body 3, and the reaction temperature and pressure inside the cylinder body are controlled by heating medium circulation.

[0030] Example 1:

[0031] The structural parameters of the continuous nucleation reaction device used in this example are as follows: the length of the cylinder body is 0.3 m, the length-diameter ratio of the cylinder body is 2, the internal volume of the device is 1 L, the material of the inner wall of the cylinder body is zirconia ceramic, a polyurethane rod-pin type reaction disperser, the diameter of the dispersion beads is 0.3 mm, the filling volume is 0.7 L, and the gap size of the dynamic separator is 0.12 mm. Circulating hot water is used as the heating medium for the hollow jacket of the cylinder body.

[0032] Preparation method of layered double metal hydroxides: Weigh 3 kg of CaO, CaCl2·2H2O and Al(OH)3 in a molar ratio of 3:1:2 and add them to a beaker, then add 7 kg of deionized water to prepare a slurry with a solid content of 30% and stir it. Turn on the continuous nucleation reaction device, set the rotor speed to 1800 rpm, the reaction temperature inside the cylinder body to 80 °C, the reaction pressure to 0.1 MPa, adjust the slurry feeding speed so that the reaction residence time of the slurry in the reaction device is 2 h. The product obtained from the outlet is centrifuged and dried at 60 °C for 8 hours to obtain layered double metal hydroxides with the molecular formula Ca4Al2(OH) 12 Cl2·4H2O.

[0033] The crystal structure of the product was characterized by an XRD-6000 type X-ray powder diffractometer from Shimadzu Corporation, Japan. Figure 2 is the XRD pattern. It can be seen from the figure that characteristic diffraction peaks of Ca4Al2(OH) 12 Cl2·4H2O appear at around 2θ = 11.7°, 23.4°, 34.5° and 60.8°. Moreover, the peak shapes are sharp and the baseline is low and flat, indicating that the crystal structure of the product is complete and there are no impurities.

[0034] The particle size of the sample was measured using a Malvern 2000 type laser particle size analyzer from the UK. Figure 3 is the laser particle size distribution diagram. It can be seen from the figure that the particle size distribution D of the product50 is 0.366 μm, D 90 is 0.693 μm.

[0035] Example 2:

[0036] The structural parameters of the continuous nucleation reaction device used in this example: the length of the cylinder body is 0.8 m, the aspect ratio of the cylinder body is 4, the internal volume of the device is 10 L, the material of the inner wall of the cylinder body is zirconia ceramics, polyurethane rod pin type reaction disperser, the diameter of the dispersion beads is 0.40 mm, the filling volume is 8 L, and the gap size of the dynamic separator is 0.20 mm. Circulating hot water is used as the heating medium for the hollow jacket of the cylinder body.

[0037] Preparation method of layered double metal hydroxide: Weigh 2.5 kg of CaO, MgCl2·6H2O and Al(OH)3 in a molar ratio of 5:1:2 and add them to a beaker. Then add 7.5 kg of deionized water to prepare a slurry with a solid content of 20% and continuously stir. Start the continuous nucleation reaction device, set the rotation speed to 2000 rpm, the reaction temperature in the cylinder body to 60 °C, the reaction pressure to atmospheric pressure, adjust the slurry feeding speed so that the reaction residence time of the slurry in the reaction device is 3 h. Then the product slurry obtained from the discharge port is centrifuged and dried at 60 °C for 8 hours to obtain a layered double metal hydroxide with the molecular formula Ca5MgAl2(OH) 12 Cl2·4H2O.

[0038] The grain size and morphology were observed by a supra55 type scanning electron microscope of ZEISS Company, Germany. Figure 4 This is the SEM photo. As can be seen from the figure, the prepared product has a flaky structure and is regular, with uniform particle size.

[0039] Example 3:

[0040] The structural parameters of the continuous nucleation reaction device used in this example: the length of the cylinder body is 0.75 m, the aspect ratio of the cylinder body is 2.5, the internal volume of the device is 30 L, the material of the inner wall of the cylinder body is zirconia ceramics, polyurethane rod pin type reaction disperser, the diameter of the dispersion beads is 0.2 mm, the filling volume is 24 L, and the gap size of the dynamic separator is 0.12 mm. Circulating hot water is used as the heating medium for the hollow jacket of the cylinder body.

[0041] Preparation method of layered double hydroxide: Weigh 0.6 kg of Mg(OH)2 and Al(OH)3 in a molar ratio of 2:1 and add them to a beaker. Then add 9.4 kg of deionized water to prepare a slurry with a solid content of 6% and continuously stir. Start the continuous nucleation reaction device, set the rotation speed to 2000 rpm, set the reaction temperature in the cylinder to 100 °C, the reaction pressure to 0.1 MPa, adjust the slurry feeding speed so that the reaction residence time of the slurry in the reactor is 2.5 h. Then, the product slurry obtained from the discharge port is centrifuged and dried at 60 °C for 8 hours to obtain layered double hydroxide with the molecular formula Mg4Al2(OH) 12 Cl2·4H2O.

[0042] Comparative Example 1:

[0043] Using the same formula as in Example 1, with a slurry solid content (the molar ratio of CaO, CaCl2·2H2O and Al(OH)3 is 3:1:2, a total of 3 kg is added to a beaker, and then 7 kg of deionized water is added to prepare a slurry with a solid content of 30%) to react in an ordinary reaction kettle to prepare Ca4Al2(OH) 12 Cl2·4H2O. The preparation conditions of the reaction kettle are a stirring speed of 500 rpm, a reaction temperature of 120 °C, a reaction pressure of 0.2 MPa, and a reaction time of 6 h. After the reaction, the obtained product slurry is centrifuged and dried at 60 °C for 8 hours.

[0044] The particle size distribution of the sample was measured using a Malvern 2000 laser particle size analyzer from the UK. Figure 5 It is the laser particle size distribution diagram of the product of Comparative Example 1. As can be seen from the figure, the particle size distribution D 50 of the LDHs product prepared by Comparative Example 1 using an ordinary reaction kettle is 8.03 μm, and D 90 is 20.44 μm, which is significantly larger than the particle size distribution of the product in Example 1.

[0045] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a layered composite metal hydroxide, characterized in that, The specific operation of the preparation method is as follows: Mix the hydroxide and / or oxide of M 2+ with the hydroxide and / or oxide of M 3+ , add deionized water and stir to obtain a slurry; Start the continuous nucleation reaction device, pump the slurry into the continuous nucleation reaction device through a feed pump, after the reaction is completed, directly filter and dry the product obtained at the slurry outlet of the reactor to obtain the layered double hydroxide; The reaction device is composed of a fixed hollow jacketed cylinder body and a rotor inside the cylinder body. The rotor is controlled by a motor to rotate. The rotor is equipped with reaction dispersers evenly distributed thereon, and the space between the cylinder body and the rotor is filled with dispersion beads. One end of the hollow jacketed cylinder body is provided with a reactor slurry inlet, and the other end is provided with a reactor slurry outlet. The reactor slurry inlet is connected to a feed pump, and a dynamic separator is arranged at the reactor slurry outlet. The hollow jacket layer of the hollow jacketed cylinder body is provided with a heating medium inlet and a heating medium outlet, and the reaction temperature inside the cylinder body is controlled by heating medium circulation. The reaction disperser is of disc type or rod pin type. The material of the dispersion beads is zirconia or alumina, and the diameter of the dispersion beads is 0.05 - 1.2 mm. The filling amount of the dispersion beads is 50 - 80% of the volume of the cylinder body. The described M 2+ is one or more of Mg 2+ , Zn 2+ , Ca 2+ ; M 3+ is one or two of Al 3+ , Cr 3+ ; The molar ratio of the hydroxide and / or oxide of the described M 2+ to the hydroxide and / or oxide of M 3+ is 1 - 4; A metal salt is further added to the described slurry; the metal salt is M 2+ and / or M 3+ metal salt, and the anion of the metal salt is Cl - , NO3 - , CO3 2- , SO4 2- , PO4 3- one or more of; the molar ratio of the hydroxide and / or oxide of M 2+ to the metal salt is 1-10; The clearance size of the dynamic separator is 50 - 80% of the diameter of the dispersion beads. The rotation speed of the continuous nucleation reaction device is set at 1000 - 2000 rpm; the reaction temperature is 40 - 80 °C. The residence time of the slurry in the continuous nucleation reaction device is 2 - 4 h.

2. The preparation method according to claim 1, characterized in that, The aspect ratio of the hollow jacketed cylinder body is 0.5 - 10.

3. The preparation method according to claim 1, wherein The solid content of the slurry is 5 - 50%.

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