Amorphous silicon aluminum and preparation method and application thereof

Abstract

The present application relates to a kind of amorphous silicon aluminum and its preparation method and application, the alumina content in the amorphous silicon aluminum is 10%-90%, the silica content is 10%-90%, wherein, the pore volume characterized by N2 adsorption and desorption is 0.75~1.6mL / g, the specific surface area is 300~550m 2 / g, the most probable pore size is 6-15nm;200℃ pyridine infrared desorption is measured total acid amount is 150-300 μmol / g, B acid accounts for 15%-40% of total acid amount.The amorphous silicon aluminum uses pH swing method and hydrothermal treatment, compared with prior art, the amorphous silicon aluminum described in the present application has high specific surface area, high pore volume and high B acid content etc.Characteristics, and the most probable pore size is in suitable range, the carrier prepared by the amorphous silicon aluminum has higher strength.The preparation method described in the present application is simple, raw material is cheap and easy to obtain, suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of carrier materials and their preparation, specifically relating to an amorphous silicon-aluminum alloy, its preparation method, and its application. Background Technology

[0002] Amorphous silica-alumina, with its specific pore structure and surface area, is often used as a support for supported catalysts or as an active component in acid cracking, finding wide application in catalytic cracking and hydrocracking. The specific surface area, pore volume, acid strength, and acid distribution of amorphous silica-alumina significantly influence catalyst performance. Using amorphous silica-alumina supports with high specific surface area and large pore volume can improve the dispersion of the active component and enhance resistance to coking. However, the pore size of amorphous silica-alumina needs to be within a suitable range; larger is not always better. Currently, the optimal pore size for commonly used amorphous silica-alumina is 6-10 nm. Amorphous silica-alumina is mainly prepared by mixing and precipitating alumina and silica precursors, followed by filtration, washing, drying, and calcination. Different preparation methods result in significant differences in the physical and chemical properties of amorphous silica-alumina.

[0003] Currently, there are many methods for preparing amorphous silica-alumina. CN101820998A discloses an amorphous silica-alumina composition and its preparation and application methods. This involves adding aluminum sulfate, sodium silicate, and sodium aluminate solutions sequentially to a reaction vessel through pH adjustments. CN104870085A discloses a method for preparing a silica-alumina composition. After the pH oscillation process is complete, an alkali metal, typically sodium hydroxide, is added to the reaction system to increase the specific surface area of ​​the amorphous silica-alumina. CN105056928A discloses a method for preparing a controllable pore structure silica-alumina composite oxide. An aluminum source compound and a silicon source compound are neutralized into a gel at room temperature, followed by hydrothermal aging in a high-pressure reactor. This method can increase the specific surface area and pore volume of the catalyst; however, the most probable pore size also increases accordingly, typically exceeding 13 nm, approximately double the conventional pore size.

[0004] Although the above methods can all obtain amorphous silicon and aluminum with various properties, they still cannot meet the various requirements of various catalytic materials for the properties of the support. For example, it is impossible to obtain amorphous silicon and aluminum with high specific surface area, large pore volume, high acidity and suitable most probable pore size at the same time, especially when prepared using cheap and readily available raw materials and simple methods. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an amorphous silicon-aluminum material with specific pore and acidic characteristics, and also provides a method for preparing and applying this material. Specifically, this invention includes the following:

[0006] This invention provides an amorphous aluminum silicate with an alumina content of 10%-90% and a silica content of 10%-90%. The pore volume, characterized by N2 adsorption-desorption, is 0.75-1.6 mL / g, and the specific surface area is 300-550 m² / g. 2 / g, with a most probable pore size of 6-15nm; the total acid content determined by pyridine infrared desorption at 200℃ is 150-300μmol / g, with Brønsted acid accounting for 15%-40% of the total acid content.

[0007] This invention provides a method for preparing amorphous aluminum silicon, comprising the following steps:

[0008] (1) Prepare an acidic aluminum-containing solution and an alkaline solution, wherein the alkaline solution is an alkaline silicon-containing solution and optionally an alkali metal solution and / or an alkaline aluminum-containing solution, wherein the acidic aluminum-containing solution is an aluminum sulfate solution and / or an aluminum nitrate solution and / or an aluminum chloride solution, wherein the alkali metal solution is a sodium hydroxide solution, a potassium hydroxide solution, a sodium carbonate solution or a potassium carbonate solution, wherein the alkaline aluminum-containing solution is a sodium aluminate solution and / or a potassium aluminate solution, and wherein the alkaline silicon-containing solution is a sodium silicate solution or a silica sol;

[0009] (2) Add a certain amount of water to the reactor and heat it to the reaction temperature. Then, add a portion of acidic aluminum-containing solution and a portion of any alkaline solution alternately. Add the acidic aluminum-containing solution to make the pH of the mixed system 1.5-4.5 and add the alkaline solution to make the pH of the mixed system 8-11.5. The acidic aluminum-containing solution is added in 2-8 portions.

[0010] (3) The mixture obtained in step (2) is subjected to hydrothermal treatment. The treatment conditions include a temperature of 100-200℃ and a time of 0.5-12 hours.

[0011] (4) The solid product obtained by filtering the hydrothermal treatment mixture is dried and calcined in sequence to obtain the amorphous silicon aluminum.

[0012] Finally, the present invention also provides the application of the above-mentioned amorphous silicon-aluminum in catalyst supports.

[0013] Compared with existing technologies, the amorphous silicon-aluminum of this invention has characteristics such as high specific surface area, high pore volume, and high Brønsted acid content, and the most probable pore size is within a suitable range, resulting in a carrier with higher strength. The preparation method of this invention is simple, uses inexpensive and readily available raw materials, and is suitable for large-scale industrial production. Attached Figure Description

[0014] Figure 1 The images show the XRD patterns of amorphous silicon-aluminum prepared in Examples 1 and 2. Detailed Implementation

[0015] First, it should be noted that the endpoints and any values ​​of the ranges disclosed in this specification are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] In a first aspect, this invention provides an amorphous silica-alumina with specific pore characteristics, exhibiting high specific surface area and high pore volume, a suitable most probable pore size, and, as characterized by pyridine infrared desorption, a high total acid content and a relatively high content of Brønsted acid. Preferably, the alumina content is 15%-85%, and the silica content is 15%-85%; preferably, the pore volume characterized by N2 adsorption-desorption is 0.8-1.5 mL / g, and the specific surface area is 350-520 m² / g. 2 The most probable pore size is 7-13 nm; preferably, the total acid content measured by pyridine infrared desorption at 200℃ is 160-290 μmol / g, with Brønsted acid accounting for 18%-38% of the total acid content. The amorphous silica-alumina of this invention has high pore volume and high specific surface area, making it suitable as a catalyst support material. Simultaneously, the suitable most probable pore size ensures sufficient strength as a support material, while the high total acid content, especially the relatively high content of Brønsted acid, provides sufficient active acid centers to improve catalyst performance.

[0017] Regarding the content of silicon oxide and aluminum oxide in the amorphous silicon-aluminum alloy described in this invention, when the purity is sufficiently high, their sum is 100%. Generally, the sum of silicon oxide and aluminum oxide content is at least 95%. Factors causing the sum of their contents to be less than 100% may include small amounts of impurities in the raw materials or incomplete washing of salt during post-processing. In this invention, the sum of silicon oxide and aluminum oxide content is at least 95%, with the remainder being impurities, which may include elements such as sulfur, titanium, sodium, and iron.

[0018] To obtain the amorphous silicon-aluminum described in this invention, this invention also provides a method for preparing amorphous silicon-aluminum. The method mainly includes the steps of preparing an amorphous silicon-aluminum precursor and hydrothermally treating the precursor. The precursor preparation employs a pH swing method, specifically involving adding an acidic aluminum-containing component to the preparation system to lower the pH to an acidic range below 7, and then adding an alkaline solution to the preparation system to raise the pH to an alkaline range above 7, thereby causing the pH of the preparation mixture to change from a low acidic pH to a high alkaline pH or to cyclically between these two values. After one or more pH swings and the addition of materials is complete, the preparation mixture is hydrothermally treated, then filtered, dried, and calcined to obtain the amorphous silicon-aluminum described in this invention. The novel amorphous silicon-aluminum obtained using the method described in this invention possesses unique properties.

[0019] In one specific embodiment, the concentration of the acidic aluminum-containing solution in step (1) is 50-120 g / L based on Al2O3, the concentration of the alkali metal solution is 1-100 g / L, the concentration of the alkaline aluminum-containing solution is 20-300 g / L based on Al2O3, and the concentration of the alkaline silicon-containing solution is 10-500 g / L based on SiO2.

[0020] In step (2), an acidic aluminum-containing solution is added to adjust the mixed system to acidic, preferably with a pH value of 2.0-4.0, and an alkaline solution is added to adjust the mixed system to alkaline, preferably with a pH value of 8.5-11.0.

[0021] According to the method of the present invention, the pH swing can have multiple cycles. Generally, the first step is to add an acidic aluminum-containing solution, and the last step is to add an alkaline solution. Preferably, there are 3-6 cycles. Accordingly, the acidic aluminum-containing solution in step (2) can be added in 3-6 batches.

[0022] If a fixed amount of solution is prepared, after the last addition of the acidic aluminum-containing solution, all the remaining alkaline solution is added. The pH value of the system after the last addition of the acidic aluminum-containing solution and the alkaline solution is not subject to the above restrictions.

[0023] The reaction conditions during the pH swing process are the conventional gelation reaction conditions. Generally, the reaction temperature is 25-90℃; it is preferred to carry out the reaction under stirring at a speed of 100-1000 rpm.

[0024] According to the present invention, the hydrothermal treatment in step (3) can improve the pore structure of the support. The inventors of the present invention have found that the combined use of pH swing method and hydrothermal method can not only increase the pore volume and specific surface area of ​​amorphous silica-alumina, but also maintain the most probable pore size of amorphous silica-alumina at a suitable level, and the acid strength of the support, especially the relative proportion of Brønsted acid, is relatively high, making it very suitable for use as a catalyst support. Under preferred conditions, the hydrothermal treatment conditions in step (3) are a temperature of 110-180°C and a time of 2-10 hours.

[0025] The pH swing preparation of amorphous silica-alumina precursors and hydrothermal treatment of this invention can be carried out in a single reactor, such as a reaction vessel. The reaction process is simple, the equipment investment is small, the raw materials are readily available, no template agent is required, the whole process is environmentally friendly, and it is very suitable for industrial production.

[0026] This invention also provides the application of the above-mentioned amorphous silicon-aluminum as a catalyst support, including mixing the amorphous silicon-aluminum with other optional heat-resistant inorganic oxides, extrusion aids, adhesives, additives, water, etc., and then molding it, followed by drying and optional calcination, to obtain a support containing the amorphous silicon-aluminum described in this invention. The other raw materials such as heat-resistant inorganic oxides and their dosages, molding methods, drying and calcination conditions, etc., are all conventional choices in the field and will not be described in detail here.

[0027] The invention will be further explained below through specific preferred embodiments, but it should be noted that the invention is not limited by the conditions of the embodiments. The main characterizing means used in the invention are as follows:

[0028] The composition of amorphous silicon and aluminum was determined by the following method: After the amorphous silicon and aluminum was pressed into sheets, the characteristic spectral lines of each element were measured using a Rigaku Electric Co., Ltd. 3271 X-ray fluorescence spectrometer. The elemental content of amorphous silicon and aluminum was semi-quantitatively analyzed using the external standard method to obtain the composition of Al2O3, SiO2, SO3, Na2O, etc. in the sample.

[0029] The acid content test method is as follows: 15 mg of amorphous aluminum silicate powder is pressed into a thin circular sheet and placed in an infrared sample cell, and then subjected to an infrared test at 450℃ for 10 minutes. -3 Pretreatment at Pa for 2 h. Then, a certain amount of pyridine was passed into the sample cell, and the sample was desorbed at 200 °C. The infrared spectrum at this desorption temperature was measured using a Fourier transform infrared spectrometer (ThermoFisher, NICOLET 6700), with values ​​at 1540 cm⁻¹. -1 The peak at 1450 cm⁻¹ represents the Brønsted acid site. -1 The peak at this location represents the L acid site. The amounts of Brønsted (B) and Lewis (L) acids can be calculated from the peak areas. The sum of the amounts of Brønsted (B) and Lewis (L) acids equals the total acid amount.

[0030] The N2 adsorption-desorption characterization method is as follows: N2 adsorption-desorption characterization is performed on a Micromeritics ASAP 2420 adsorption instrument. Before the test, about 0.3g of amorphous silica-alumina powder is taken and pretreated at 350℃ under vacuum for 10h.

[0031] The XRD characterization method was as follows: a certain amount of amorphous aluminum silicate powder was pressed into sheets, and the crystal form of the sample was determined using a Philips XPERT series X-ray powder diffractometer. The test conditions were: Cu Kα rays (Kα = 0.154 nm), operating current 30 mA, operating voltage 40 kV, Ni filter, and scanning range 2θ = 5° to 70°.

[0032] The radial crushing strength test method is as follows: a 5mm carrier is placed horizontally between the two platforms of the particle strength tester, and a load is applied evenly to it until the carrier is destroyed. The applied pressure when the particles are crushed is recorded.

[0033] Example 1

[0034] In this embodiment, the aluminum sulfate solution had a concentration of 104 g / L (Al2O3), a free acid concentration of 3 g H2SO4 / L, and a Fe2O3 concentration ≤150 mg / L; the sodium aluminate solution had a concentration of 220 g / L (Al2O3) and a Na2O concentration of 227 g / L; and the sodium silicate solution had a concentration of 300 g / L (SiO2). During the preparation process, 500 mL of water was first added to the reactor and heated to 55°C. Then, aluminum sulfate, sodium aluminate, and sodium silicate solutions were added sequentially according to the order in Table 1. The pH of the liquid after each step is also listed in Table 1. After each addition, the mixture was stirred for 5 minutes at a stirring speed of 600 rpm. After the addition was complete, the liquid was transferred to a high-pressure reactor and hydrothermally heated at 140°C for 4 hours. After the hydrothermal step, the sample was filtered, washed, dried at 120°C for 12 hours, and calcined at 600°C for 3 hours. XRD characterization confirmed it as amorphous aluminum silicate. Figure 1 The physicochemical properties are shown in Table 5.

[0035] Table 1

[0036] step Components pH of the liquid after addition 1 Deionized water 6.9 2 Aluminum sulfate 3.0 3 Sodium aluminate 10.2 4 Aluminum sulfate 3.1 5 Sodium silicate 9.5 6 Aluminum sulfate 3.0 7 Sodium aluminate 10.6

[0037] Comparative Example 1

[0038] The pH swing preparation process (steps 1-7) of Comparative Example 1 was completely identical to that of Example 1. The resulting mixture was directly filtered, washed, dried, and calcined under the same drying and calcination conditions as in Example 1. XRD characterization revealed it to be amorphous silica-alumina. The physicochemical properties of the amorphous silica-alumina prepared in Comparative Example 1 are shown in Table 5.

[0039] Comparative Example 2

[0040] Comparative Example 2 used the same raw material concentration and dosage as Example 1, but did not use the pH swing method for gelation. In the preparation process, 500 mL of water was first added to the reaction vessel and heated to 55°C. Then, aluminum sulfate, sodium aluminate, and sodium silicate solutions were simultaneously added to the reaction vessel and stirred for 30 minutes at a stirring speed of 600 rpm. After the addition was complete, the liquid was transferred to a high-pressure reactor and hydrothermally heated at 140°C for 4 hours. After the hydrothermal step, the sample was filtered, washed, dried at 120°C for 12 hours, and calcined at 600°C for 3 hours. XRD characterization revealed it to be amorphous aluminum silicate, and its physicochemical properties are shown in Table 5.

[0041] Example 2

[0042] In this embodiment, the aluminum sulfate solution had a concentration of 104 g / L (Al2O3), a free acid concentration of 3 g H2SO4 / L, and a Fe2O3 concentration ≤150 mg / L; the sodium aluminate had a concentration of 220 g / L (Al2O3) and a Na2O concentration of 227 g / L; and the sodium silicate had a concentration of 300 g / L (SiO2). During preparation, 200 mL of water was first added to the reactor and heated to 55°C. Then, aluminum sulfate, sodium aluminate, and sodium silicate were added sequentially according to the order in Table 2. The pH of the liquid after each step is also listed in Table 2. After each addition, the mixture was stirred for 5 minutes at a stirring speed of 600 rpm. After the addition was complete, the mixture was transferred to a high-pressure reactor and hydrothermally heated at 140°C for 4 hours. After the hydrothermal step, the sample was filtered, washed, dried at 120°C for 12 hours, and calcined at 600°C for 3 hours. XRD characterization confirmed it as amorphous aluminum silicate. Figure 1 The physicochemical properties are shown in Table 5.

[0043] Table 2

[0044] step Components pH of the liquid after addition 1 Deionized water 7.2 2 Aluminum sulfate 3.0 3 Sodium aluminate 10.0 4 Aluminum sulfate 3.0 5 Sodium silicate 10.0 6 Aluminum sulfate 3.0 7 Sodium aluminate 10.5 8 Aluminum sulfate 3.3 9 Sodium aluminate 10.4

[0045] Comparative Example 3

[0046] The pH swing preparation process (steps 1-9) of Comparative Example 3 was completely identical to that of Example 2. The resulting mixture was directly filtered, washed, and calcined without undergoing high-pressure hydrothermal treatment. The filtration, washing, and calcination conditions of Comparative Example 3 were completely identical to those of Example 2. The physicochemical properties of the amorphous aluminum silicate prepared in Comparative Example 2 are shown in Table 5.

[0047] Example 3

[0048] In this embodiment, the aluminum sulfate solution had a concentration of 80 g / L (Al2O3); sodium aluminate had a concentration of 180 g / L (Al2O3); and Na2O had a concentration of 187 g / L. The sodium silicate had a mass fraction of 200 g / L (SiO2). During preparation, 1000 mL of water was first added to the reactor and heated to 40°C. Then, aluminum sulfate, sodium aluminate, and sodium silicate were added sequentially according to the order in Table 3. The pH of the liquid after each step is also listed in Table 3. After each addition, the mixture was stirred for 5 minutes at a stirring speed of 400 rpm. After the addition was complete, the mixture was transferred to a high-pressure reactor and hydrothermally heated at 130°C for 5 hours. After the hydrothermal step, the sample was filtered, washed, dried at 120°C for 12 hours, and calcined at 550°C for 3 hours. XRD characterization revealed it to be amorphous aluminum silicate, and its physicochemical properties are shown in Table 5.

[0049] Table 3

[0050] step Components pH of the liquid after addition 1 Deionized water 6.8 2 Aluminum sulfate 2.5 3 Sodium aluminate 9.0 4 Aluminum sulfate 3.0 5 Sodium silicate 9.0 6 Aluminum sulfate 3.5 7 Sodium aluminate 9.7 8 Aluminum sulfate 3.8 9 Sodium silicate 10.1

[0051] Example 4

[0052] In this embodiment, the aluminum sulfate solution had a concentration of 90 g / L (Al₂O₃); the sodium hydroxide solution had a concentration of 25 g / L; the sodium aluminate solution had a concentration of 200 g / L (Al₂O₃); and the Na₂O concentration was 205 g / L. The sodium silicate solution had a concentration of 250 g / L (SiO₂). During the preparation process, 1000 mL of water was first added to the reactor and heated to 60°C. Then, aluminum sulfate, sodium aluminate, sodium silicate, and sodium hydroxide were added sequentially according to the order shown in Table 4. The pH of the liquid after each step is also listed in Table 4. After each addition, the mixture was stirred for 5 minutes at a stirring speed of 700 rpm. After the addition was complete, the mixture was transferred to a high-pressure reactor and hydrothermally heated at 120°C for 7 hours. After the hydrothermal step, the sample was filtered, washed, dried at 120°C for 12 hours, and calcined at 600°C for 3 hours. XRD characterization revealed it to be amorphous aluminum silicate, and its physicochemical properties are shown in Table 5.

[0053] Table 4

[0054] step Components pH of the liquid after addition 1 Deionized water 7.2 2 Aluminum sulfate 2.8 3 Sodium aluminate 10.5 4 Aluminum sulfate 3.0 5 Sodium silicate 9.4 6 Aluminum sulfate 3.7 7 Sodium aluminate 10.0 8 Aluminum sulfate 3.4 9 Sodium hydroxide 9.5

[0055] Table 5

[0056]

[0057] Example 5

[0058] Take 80g of uncalcined amorphous silica-alumina from Example 1, add 20g of boehmite, 3g of guar gum powder, 110mL of water, and 2mL of concentrated nitric acid, mix thoroughly, and continue kneading into a plastic body on a twin-screw extruder. Then, extrude it into butterfly-shaped strips with a diameter of 1.6 mm. After drying the wet strips at 120℃ for 4 hours, calcine them at 600℃ for 3 hours to obtain the carrier. The radial crushing strength was tested to be 25 N / mm.

[0059] Comparative Example 4

[0060] 80g of uncalcined amorphous silica-alumina from Comparative Example 2 was taken, and additives and solutions were added according to the conditions of Example 5. A carrier was prepared under the same conditions. Its radial crushing strength was tested to be 17 N / mm.

Claims

1. An amorphous aluminum silicate, wherein the alumina content is 10%-90% and the silicon oxide content is 10%-90%, wherein, The pore volumes, characterized by N2 adsorption-desorption, ranged from 0.75 to 1.6 mL / g, and the specific surface areas ranged from 300 to 550 m² / g. 2 / g, with the most probable pore size being 6-15nm; the total acid content determined by pyridine infrared desorption at 200℃ was 160-290 μmol / g, with Brønsted acid accounting for 18%-38% of the total acid content, and the Brønsted acid content being 40.6-59.2 μmol / g.

2. The amorphous silicon-aluminum according to claim 1, wherein, The alumina content is 15%-85%, and the silicon dioxide content is 15%-85%.

3. The amorphous silicon-aluminum according to claim 1, wherein, The pore volumes characterized by N2 adsorption-desorption were 0.8–1.5 mL / g, and the specific surface areas were 350–520 m² / g. 2 / g, with a most probable pore size of 7-13nm.

4. A method for preparing amorphous aluminum silica according to claim 1, comprising the following steps: (1) Prepare an acidic aluminum-containing solution and an alkaline solution, wherein the alkaline solution is an alkaline silicon-containing solution, or an alkaline silicon-containing solution and an alkali metal solution, or an alkaline silicon-containing solution and an alkaline aluminum-containing solution, or an alkaline silicon-containing solution, an alkali metal solution and an alkaline aluminum-containing solution; The acidic aluminum-containing solution is an aluminum sulfate solution and / or an aluminum nitrate solution and / or an aluminum chloride solution; The alkali metal solution is a sodium hydroxide solution, potassium hydroxide solution, sodium carbonate solution, or potassium carbonate solution; the alkaline aluminum-containing solution is a sodium aluminate solution and / or a potassium aluminate solution; the alkaline silicon-containing solution is a sodium silicate solution or silica sol. (2) Add a certain amount of water to the reactor and heat it to the reaction temperature. Then, add a portion of acidic aluminum-containing solution and a portion of any alkaline solution alternately. Add the acidic aluminum-containing solution to make the pH of the mixed system 1.5-4.5 and add the alkaline solution to make the pH of the mixed system 8-11.

5. The acidic aluminum-containing solution is added in 2-8 portions. (3) The mixture obtained in step (2) is subjected to hydrothermal treatment. The treatment conditions include a temperature of 100-200℃ and a time of 0.5-12 hours. (4) The solid product obtained by filtering the hydrothermal treatment mixture is dried and calcined in sequence to obtain the amorphous silicon aluminum.

5. The method according to claim 4, wherein, In step (1), the concentration of the acidic aluminum-containing solution, calculated as Al2O3, is 50-120 g / L; the concentration of the alkali metal solution is 1-100 g / L; the concentration of the alkaline aluminum-containing solution, calculated as Al2O3, is 20-300 g / L; and the concentration of the alkaline silicon-containing solution, calculated as SiO2, is 10-500 g / L.

6. The method according to claim 4, wherein, In step (2), an acidic aluminum-containing solution is added to make the pH of the mixed system 2.0-4.0, and an alkaline solution is added to make the pH of the mixed system 8.5-11.

0.

7. The method according to claim 4, wherein, In step (2), the acidic aluminum-containing solution is added in 3-6 portions.

8. The method according to claim 4, wherein, The reaction temperature in step (2) is 25-90℃.

9. The method according to claim 8, wherein, The protected step (2) is carried out at a stirring speed of 100-1000 rpm.

10. The method according to claim 4, wherein, The drying conditions in step (4) include: temperature 100-180℃, time 6-24 hours; the calcination conditions are: temperature 400-800℃, time 0.5-12 hours.

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