A silica microsphere with high specific surface area and large pore volume and its preparation method

Abstract

This invention relates to silica microspheres with high specific surface area and large pore volume, and their preparation method, belonging to the field of catalyst and preparation technology. The method involves dissolving a surfactant and sodium silicate in water to obtain a clear solution; then adding ethyl acetate to the obtained clear solution and allowing the mixture to stand or stir to react; after the reaction is complete, the mixture is sequentially subjected to centrifugation, washing, pulping, spray drying, and calcination to obtain silica microspheres with high specific surface area and large pore volume. The specific surface area of ​​the obtained silica microspheres is 380~530 m² / g. 2 / g, pore volume 1.8~2.3cm 3 / g, with a particle size of 40~60μm. This invention utilizes a uniform precipitation method combined with spray drying technology to significantly improve the specific surface area and pore volume of silica microspheres. It solves the problems of relatively harsh synthesis conditions and the difficulty in simultaneously achieving high specific surface area and large pore volume in conventional silica microspheres. It is suitable for catalysis, adsorption, separation and other fields, and has broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of catalyst and its preparation technology, specifically relating to a silica microsphere with high specific surface area and large pore volume and its preparation method. Background Technology

[0002] Silica gel has a wide range of applications. Among them, silica microspheres with high specific surface area and large pore volume are particularly suitable as supports for polyolefin catalysts, especially metallocene catalysts, due to their suitable pore volume, pore size, specific surface area, and good flowability. Currently, the mainstream silica microspheres used as polyolefin catalyst supports have a specific surface area of ​​approximately 300 m². 2 / g, pore volume approximately 1.8cm 3 / g, with a particle size of approximately 30~60μm.

[0003] There are various methods for preparing silica microspheres. The most common method is to use silicates and inorganic strong acids as raw materials, react them at a certain pH value to form a gel, and then obtain silica microspheres through aging, acid washing, water washing, drying or spray molding and calcination. Existing technologies such as patents CN113754798A, CN110732341A, and CN106622378B all first prepare gel raw materials, then crush them into slurry, and then obtain silica microspheres through spray drying. However, the silica microsphere carriers prepared by this traditional method have two shortcomings: (1) the reaction is violent and difficult to control during the sol-gel preparation process, and the local pH value is too low, resulting in uneven gel; (2) it is difficult for existing silica microspheres to have both high specific surface area and large pore volume at the same time, and the specific surface area is often sacrificed for the sake of large pore volume. Therefore, it is necessary to adopt a new method to prepare silica microspheres with high specific surface area, large pore volume, good strength and flowability to meet the requirements of catalyst carriers.

[0004] Homogeneous precipitation is a method in which raw materials uniformly precipitate under certain conditions. In this method, the precipitant added to the solution does not react immediately with the precipitated component, but rather is released uniformly and slowly throughout the system through a chemical reaction, thus causing the precipitate to be uniformly produced from the system. Compared with conventional precipitation synthesis methods, homogeneous precipitation is simpler and more effective. When using it to synthesize silicon dioxide, organic esters or strong acid-weak base salts are generally used as homogeneous precipitants.

[0005] There are already relevant patents and literature reports on silicone microspheres both domestically and internationally.

[0006] CN119897155A discloses a method for preparing silica microspheres used as catalyst supports. This method involves first adding beta molecular sieve modified powder to a water glass solution, mixing it with a sulfuric acid solution, and then using a high-pressure gas flow to atomize the acidified water glass into droplets, which are then rapidly converted into a gel. Following aging, acid washing, water washing, supercritical carbon dioxide drying, and calcination in an atmosphere furnace, silica microspheres with high specific surface area and large pore volume are obtained. However, this preparation process is complex, costly, and unsuitable for large-scale production.

[0007] CN117735560A discloses a mesoporous silica microsphere with ultra-high specific surface area, its preparation method and application. The method involves mixing a cationic surfactant, sodium silicate and ethyl acetate, allowing them to react statically, and then centrifuging, washing, drying and heat treatment under a nitrogen atmosphere to obtain mesoporous silica microspheres with ultra-high specific surface area. However, the purity, pore volume and particle size of the product are relatively low.

[0008] CN102382216A discloses a method for preparing a silica gel support for ethylene polymerization catalysts. The method involves mixing a water glass solution with a sulfuric acid solution, adding a complexing agent and a surfactant during the aging process, and then performing steps such as water washing and spray drying to prepare silica gel microspheres for polyolefin catalyst supports. However, this preparation process is relatively complex, the particle size distribution is relatively wide, and the morphology of the microspheres is not mentioned.

[0009] CN118083991A discloses a silica support, its preparation method, and its application. First, a silicate solution is mixed with a sulfuric acid solution for aging. Then, silicate and sulfuric acid are added to the mother liquor in a co-current manner, with an organic alcohol aqueous solution added during the process. This process is repeated multiple times, followed by washing with anhydrous ethanol and high-temperature activation to finally obtain silica microspheres for polyolefin catalyst support. However, this preparation process is relatively complex, the morphology of the microspheres is not mentioned, and the specific surface area and pore volume are relatively low.

[0010] US3652215 and US3652216 disclose a method for preparing macroporous silica gel for polyolefin catalyst support. The method involves first neutralizing sodium silicate with sulfuric acid, then washing with water, followed by pulping and washing with an organic solvent, and finally drying and calcining to obtain a specific surface area of ​​200-500 μm. 2 / g silica carrier, solvent recovery is the key obstacle to its industrialization, and the specific surface area and pore volume indicators need to be further optimized and improved.

[0011] The paper Colloid Polym. Sci. 2004, 282:1286 (Synthesis of hollow spherical silica with MCM-41 mesoporous structure) describes the preparation of high specific surface area mesoporous spherical silica gel by mixing sodium silicate with a low concentration of surfactant and using a homogeneous precipitation method; however, the product exhibits a hollow structure and a relatively low particle size. The paper Progress in Materials and Processes 2013, 602:259 (Preparation of the Silica Micro-Spheres by Chemical Precipitation Process) describes the preparation of silica microspheres by adding a blended surfactant to a sodium silicate solution and using ethyl acetate as a precipitant; however, both the particle size and pore volume require further improvement.

[0012] In summary, current domestic and international methods for preparing silica microspheres mainly utilize the traditional precipitation method involving the reaction of sodium silicate with strong inorganic acids. This method suffers from drawbacks such as relatively harsh synthesis conditions, complex preparation processes, and high costs. Furthermore, the challenge of simultaneously achieving high specific surface area and large pore volume in silica microspheres prepared using the homogeneous precipitation method remains unresolved. Simultaneously, to further improve the performance of polyolefin catalysts, there is an urgent need to develop new methods to prepare silica microspheres with even higher specific surface area and pore volume. Summary of the Invention

[0013] The purpose of this invention is to provide silica microspheres with high specific surface area and large pore volume, and a method for preparing the same. This invention utilizes a uniform precipitation method combined with spray drying technology to significantly improve the specific surface area and pore volume of silica microspheres, solving the problems of harsh reaction conditions and the difficulty in simultaneously achieving high specific surface area and large pore volume in conventional silica microspheres.

[0014] A method for preparing silica microspheres with high specific surface area and large pore volume, comprising the following steps:

[0015] (1) Dissolve the cationic surfactant and sodium silicate in water and stir until uniformly dispersed to obtain a clear solution;

[0016] (2) Add ethyl acetate to the clear solution obtained in step (1) and let it stand or stir to react;

[0017] (3) After the reaction in step (2) is completed, the reaction product is centrifuged, washed, dried, and pulped to obtain a solid-liquid mixture;

[0018] (4) The solid-liquid mixture obtained in step (3) is spray-dried to obtain a solid precursor;

[0019] (5) The solid precursor obtained in step (4) is calcined in air in stages to remove the surfactant, thereby obtaining the silica microspheres with high specific surface area and large pore volume.

[0020] Furthermore, in step (1), the cationic surfactant is one of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride; in the clear solution, the concentration of the cationic surfactant is 0.1~10wt%, and the concentration of sodium silicate is 0.1~10wt%.

[0021] In step (2), the concentration of ethyl acetate in the clear solution is 0.1~10wt%; the temperature for standing or stirring the reaction is 10~40℃, and the time for standing or stirring the reaction is 5~24h.

[0022] Furthermore, in step (3), the reaction product is washed by centrifugation with ethanol and water in sequence; the dried solid sample is added to water for slurrying, and the concentration of the solid sample in the solid-liquid mixture is 5~10wt%;

[0023] Furthermore, in step (4), the inlet temperature of the spray dryer is 180~260℃ and the outlet temperature is 80~130℃;

[0024] Furthermore, in step (5), the stepwise calcination involves first heating the temperature at a rate of 1~2℃ / min to 200~350℃ for 2~4h, and then heating the temperature at a rate of 2~5℃ / min to 500~600℃ for 3~8h.

[0025] The silica microspheres with high specific surface area and large pore volume described in this invention are prepared by the above-described preparation method.

[0026] Structural characterization of high specific surface area and large pore volume silica microspheres:

[0027] This invention utilizes a uniform precipitation method combined with spray drying technology to prepare silica microspheres with high specific surface area and large pore volume. The composition is SiO2, and the specific surface area is 380~530 m² / g. 2 / g, pore volume 1.8~2.3cm 3 / g, the silica gel exhibits a regular microsphere morphology with a particle size of 40~60μm ( Figure 1 ).

[0028] The preparation principle of high specific surface area and large pore volume silica microspheres:

[0029] This invention provides a method for preparing silica microspheres with high specific surface area and large pore volume. In the initial stage of the reaction, a cationic surfactant forms a micelle structure in water. After the introduction of sodium silicate, silicate ions are adsorbed onto the surface of the cationic surfactant micelles through electrostatic interaction, initially constructing an organic-inorganic composite structure. Subsequently, ethyl acetate is added and slowly hydrolyzes in the system, continuously releasing acetic acid and gradually lowering the pH value of the system, promoting controlled hydrolysis and condensation reactions of silicate ions. This slow acidification process effectively avoids uneven gelation caused by local over-acidity or excessively rapid reaction. As the reaction proceeds, silicate species aggregate and cross-link under the guidance of the micelle template, forming a composite with a mesoscopic structure. By adjusting the type and concentration of surfactant and the amount of ethyl acetate, the assembly behavior of the composite micelles can be precisely controlled, thereby optimizing the pore structure (including pore volume and specific surface area) of the final material. Subsequently, the above composite slurry is rapidly dried and shaped by spray drying to obtain precursor microspheres with certain mechanical strength and regular morphology. Finally, the organic template is gradually removed in an air atmosphere through a stepwise calcination process with programmed temperature rise. The low-temperature stage allows the surfactant to slowly decompose and carbonize, temporarily supporting the pores; the high-temperature stage further removes residual carbon and strengthens the silica skeleton, ultimately forming silica microspheres with high specific surface area, large pore volume and good thermal stability.

[0030] In summary, the present invention has the following advantages over the prior art:

[0031] 1. Ethyl acetate, as a weak acidic ester, slowly releases acetic acid during its hydrolysis process, which can effectively reduce the reaction rate of the sol-gel process and avoid uneven gelation caused by excessively low local pH values. This helps to form silica microspheres with uniform particle size distribution and regular structure. At the same time, the introduction of ethyl acetate also affects the pore structure of silica, thereby regulating the performance of the support and ultimately achieving the goal of improving catalytic activity.

[0032] 2. Cationic surfactants can alter the pore structure and surface properties of silica gel, thereby increasing the catalyst loading and dispersibility. By controlling the type and amount of surfactant, the microstructure of the silica gel support can be optimized, ultimately improving the catalyst activity and selectivity.

[0033] 3. Spray drying is a rapid and efficient drying technology that can quickly convert sol into dried microspheres. By adjusting the process parameters of spray drying, the particle size and morphology of silica microspheres can be precisely controlled. Combined with the sustained-release effect of ethyl acetate, the structure and performance of the microspheres can be further optimized.

[0034] 4. Distributed calcination allows the surfactant to be removed slowly, supporting the pore walls, retaining mesopores, and increasing the specific surface area of ​​the material.

[0035] 5. The uniform precipitation method combined with spray drying enables silica microspheres to maintain a high specific surface area and pore volume, and to have good flowability; it can be used in the fields of adsorption, separation and catalysis. The preparation process is simple, economical and efficient and convenient, which is conducive to large-scale industrial production and has important practical application value and broad application prospects. Attached Figure Description

[0036] Figure 1 This is a scanning electron microscope image of the silica microspheres prepared in Example 1 of the present invention. Detailed Implementation

[0037] The following specific embodiments further illustrate the present invention: a high specific surface area, large pore volume silica microsphere and its preparation method.

[0038] Example 1:

[0039] Hexadecyltrimethylammonium bromide and sodium silicate were dissolved in water and stirred until uniformly dispersed to obtain a clear solution. The concentration of hexadecyltrimethylammonium bromide was 2.65 wt%, and the concentration of sodium silicate was 2.7 wt%. Ethyl acetate was then added, with a concentration of 5.75 wt% in the clear solution, and the mixture was allowed to stand at room temperature for 12 hours. After the reaction, the solid sample was washed with alternating centrifugation using ethanol and water, and then dried at 100 °C. The dried solid sample was then added to water and slurried to obtain a concentration of 8 wt%. The resulting solid-liquid mixture was spray-dried to obtain a solid precursor. The inlet temperature of the spray dryer was 210 °C, and the outlet temperature was 100 °C. The obtained solid precursor was placed in a muffle furnace and calcined at 300 °C for 3 hours at a heating rate of 1 °C / min, and then roasted at 550 °C for 6 hours at a heating rate of 2 °C / min to obtain silica microspheres, denoted as SG-1 (when calculating the amount of each raw material added, the mutual reactions between the raw materials during the addition process are not considered). The composition and physicochemical properties of SG-1 are shown in Table 1. Figure 1 As shown, the prepared silica microspheres SG-1 have a regular spherical shape, uniform size, and a particle size of 60 μm.

[0040] Example 2:

[0041] Tetradecyltrimethylammonium bromide and sodium silicate were dissolved in water and stirred until uniformly dispersed to obtain a clear solution. The concentration of tetradecyltrimethylammonium bromide was 2.65 wt%, and the concentration of sodium silicate was 2.7 wt%. Ethyl acetate was then added, with a concentration of 5.75 wt% in the clear solution, and the mixture was allowed to stand at room temperature for 12 hours. After the reaction, the solid sample was washed with alternating centrifugation using ethanol and water, and then dried at 100°C. The dried solid sample was then added to water and slurried to obtain a concentration of 8 wt%. The resulting solid-liquid mixture was spray-dried to obtain a solid precursor. The inlet temperature of the spray dryer was 210°C, and the outlet temperature was 100°C. The obtained solid precursor was placed in a muffle furnace and calcined at 300°C for 3 hours at a heating rate of 1°C / min, and then roasted at 550°C for 6 hours at a heating rate of 2°C / min to obtain silica microspheres, denoted as SG-2 (when calculating the amount of each raw material added, the mutual reactions between the raw materials during the addition process are not considered). The composition and physicochemical properties of SG-2 are shown in Table 1.

[0042] Example 3:

[0043] Hexadecyltrimethylammonium chloride and sodium silicate were dissolved in water and stirred until uniformly dispersed to obtain a clear solution. The concentration of hexadecyltrimethylammonium chloride was 2.65 wt%, and the concentration of sodium silicate was 2.7 wt%. Ethyl acetate was then added, with a concentration of 5.75 wt% in the clear solution, and the mixture was allowed to stand at room temperature for 12 hours. After the reaction, the solid sample was washed with alternating centrifugation using ethanol and water, and then dried at 100°C. The dried solid sample was then slurried in water to a concentration of 8 wt%. The resulting solid-liquid mixture was spray-dried to obtain a solid precursor. The inlet temperature of the spray dryer was 210°C, and the outlet temperature was 100°C. The obtained solid precursor was placed in a muffle furnace and calcined at 300°C for 3 hours at a heating rate of 1°C / min, and then roasted at 550°C for 6 hours at a heating rate of 2°C / min to obtain silica microspheres, designated SG-3 (the interactions between the raw materials during the addition process were not considered when calculating the amount of each raw material added). The composition and physicochemical properties of SG-3 are shown in Table 1.

[0044] Example 4:

[0045] Tetradecyltrimethylammonium chloride and sodium silicate were dissolved in water and stirred until uniformly dispersed to obtain a clear solution. The concentration of tetradecyltrimethylammonium chloride was 2.65 wt%, and the concentration of sodium silicate was 2.7 wt%. Ethyl acetate was then added to achieve a concentration of 5.75 wt% in the clear solution, and the mixture was allowed to stand at room temperature for 12 hours. After the reaction, the solid sample was washed with alternating centrifugation using ethanol and water, and then dried at 100°C. The dried solid sample was then slurried in water to a concentration of 8 wt%. The resulting solid-liquid mixture was spray-dried to obtain a solid precursor. The inlet temperature of the spray dryer was 210°C, and the outlet temperature was 100°C. The obtained solid precursor was placed in a muffle furnace and calcined at 300°C for 3 hours at a heating rate of 1°C / min, followed by calcination at 550°C for 6 hours at a heating rate of 2°C / min to obtain silica microspheres, designated SG-4 (the interactions between the raw materials during the addition process were not considered when calculating the amount of each raw material added). The composition and physicochemical properties of SG-4 are shown in Table 1.

[0046] Example 5:

[0047] Hexadecyltrimethylammonium bromide and sodium silicate were dissolved in water and stirred until uniformly dispersed to obtain a clear solution. The concentration of hexadecyltrimethylammonium bromide was 3.5 wt%, and the concentration of sodium silicate was 2.7 wt%. Ethyl acetate was then added, with a concentration of 5.75 wt% in the clear solution, and the mixture was allowed to stand at room temperature for 12 hours. After the reaction, the sample solid was washed with alternating centrifugation using ethanol and water, and then dried at 100°C. The dried solid sample was then added to water and slurried to a concentration of 8 wt%. The resulting solid-liquid mixture was spray-dried to obtain a solid precursor. The inlet temperature of the spray dryer was 210°C, and the outlet temperature was 100°C. The obtained solid precursor was placed in a muffle furnace and calcined at 300°C for 3 hours at a heating rate of 1°C / min, followed by calcination at 550°C for 6 hours at a heating rate of 2°C / min to obtain silica microspheres, designated SG-5 (the interactions between the raw materials during the addition process were not considered when calculating the amount of each raw material added). The composition and physicochemical properties of SG-5 are shown in Table 1.

[0048] Comparative Example 1:

[0049] Sodium silicate was dissolved in water and stirred until uniformly dispersed to obtain a clear solution. The concentration of sodium silicate was 2.7 wt%. Ethyl acetate was then added, with a concentration of 5.75 wt% in the clear solution, and the mixture was allowed to stand at room temperature for 12 hours. After the reaction, the solid sample was washed with alternating centrifugation using ethanol and water, and dried at 100 °C. The dried solid sample was then added to water and slurried to obtain a concentration of 8 wt%. The resulting solid-liquid mixture was spray-dried to obtain a solid precursor. The inlet temperature of the spray dryer was 210 °C, and the outlet temperature was 100 °C. The obtained solid precursor was placed in a muffle furnace and calcined at 300 °C for 3 hours at a heating rate of 1 °C / min, followed by calcination at 550 °C for 6 hours at a heating rate of 2 °C / min to obtain silica microspheres, denoted as DB-1 (when calculating the amount of each raw material added, the mutual reactions between the raw materials during the addition process were not considered). The composition and physicochemical properties of DB-1 are shown in Table 1.

[0050] Comparative Example 2:

[0051] For commercially available silicone microspheres, we selected Grace's Davison 955 model silicone, denoted as DB-2.

[0052] Table 1: Property data of silica microspheres obtained in Examples 1-5 and Comparative Examples 1-2

[0053]

[0054] As can be seen from Table 1, the specific surface area, pore volume, and particle size of the silica microspheres prepared in Examples 1-5 are much larger than those in Comparative Examples 1-2. This indicates that silica microspheres with high specific surface area and large pore volume can be efficiently prepared by using sodium silicate as raw material, employing a uniform precipitation method, and combining it with spray drying technology. These silica microspheres have broad application prospects in the fields of catalysis, adsorption, and separation.

Claims

1. A method for preparing silica gel microspheres with high specific surface area and large pore volume, characterized in that: The steps are as follows, (1) dissolving the cationic surfactant and sodium silicate in water, stirring to uniformly disperse, to obtain a clear solution; (2) adding ethyl acetate to the clear solution obtained in step (1), and standing or stirring to react; (3) after the reaction in step (2) is completed, centrifugal washing of the reaction product is carried out with ethanol and water in sequence; then the dried solid sample is added to water to perform beating, and the concentration of the solid sample in the solid-liquid mixture is 5-10wt%; (4) spray drying the solid-liquid mixture obtained in step (3) to obtain a solid precursor; the inlet temperature of the spray dryer is 180-260℃, and the outlet temperature is 80-130℃; (5) calcining the solid precursor obtained in step (4) in an air atmosphere, first at a temperature increasing rate of 1-2 ℃ / min to 200-350 ℃ for 2-4 h, and then at a temperature increasing rate of 2-5 ℃ / min to 500-600 ℃ for 3-8 h to remove the surfactant, to obtain the silica gel microspheres with high specific surface area and large pore volume; the silica gel microspheres have a composition of SiO2, a specific surface area of 380-530 m 2 / g, a pore volume of 1.8-2.3 cm 3 / g, and a regular microspherical morphology with a particle size of 40-60 μm. (5) calcining the solid precursor obtained in step (4) in an air atmosphere, first at a temperature increasing rate of 1-2 ℃ / min to 200-350 ℃ for 2-4 h, and then at a temperature increasing rate of 2-5 ℃ / min to 500-600 ℃ for 3-8 h to remove the surfactant, to obtain the silica gel microspheres with high specific surface area and large pore volume; the silica gel microspheres have a composition of SiO2, a specific surface area of 380-530 m 2 / g, a pore volume of 1.8-2.3 cm 3 / g, and a regular microspherical morphology with a particle size of 40-60 μm.

2. The method of claim 1, wherein the silica gel microspheres have a high specific surface area and a large pore volume. In step (1), the cationic surfactant is one of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride; in the clear solution, the concentration of the cationic surfactant is 0.1-10wt%, and the concentration of sodium silicate is 0.1-10wt%.

3. The method of claim 1, wherein the silica gel microspheres have a high specific surface area and a large pore volume. In step (2), the concentration of ethyl acetate in the clear solution is 0.1-10wt%; the temperature for standing or stirring to react is 10-40℃, and the time for standing or stirring to react is 5-24h.

4. A silica gel microsphere with high specific surface area and large pore volume, characterized in that: is prepared by the preparation method of any one of claims 1-3.

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