Aluminum-modified silica gel, its preparation method and application

Abstract

The application provides an aluminum-modified silica gel and a preparation method and application thereof, and the preparation method comprises the following steps: step 1, uniformly mixing a silicate solution, an aluminum-containing compound solution, an inorganic acid solution and a surfactant, and keeping constant temperature for a certain time; step 2, adjusting the pH value of the material in step 1 to 7-10, and aging; and step 3, washing, drying and calcining the material in step 2 to obtain the aluminum-modified silica gel. In the application, the aluminum-containing compound is added in the process of in-situ synthesis of the silica gel, the aluminum atoms can be introduced into the silica gel skeleton, the problem that the metallocene compound is easy to fall off from the surface of the silica gel is solved, meanwhile, in the synthesis process, the trivalent aluminum replaces the tetravalent silicon, the electron deficiency of the atom is increased, and the catalyst activity can be enhanced. In addition, due to the formation of the Al-O-Si bond on the surface of the aluminum-modified silica gel, the support force of the pore skeleton is enhanced, and the heat resistance of the silica gel is improved.

Description

Technical Field

[0001] This invention relates to the field of polyolefins, specifically to an in-situ synthetic aluminum-modified silica gel, its preparation method, and its application. Background Technology

[0002] Silica gel, as a support for olefin polymerization catalysts, can be used to prepare titanium-based, chromium-based, and metallocene catalysts used in Unipol's gas-phase polyethylene plant. It can also be used to prepare chromium-based catalysts used in Phillips' high-density polyethylene plant, as well as metallocene polypropylene catalysts. The global demand for supported silica gel is 3,000 tons / year, while the domestic demand is approximately 600 tons / year, all of which are imported, mainly from Grace and PQ in the United States, at a price of 100,000 yuan / ton. Ordinary silica gel cannot be used as a support for polyolefin catalysts. The technology for supporting silica gel for polyolefin catalysts is highly demanding and difficult to develop; therefore, the development of silica gel support preparation technology is urgent. Relevant patents for the preparation of supported silica gel include US4384086, US5073531, CN1287892, and CN106902799. Some existing technologies start from organic raw materials, resulting in high synthesis costs. Some existing technologies directly mix water glass and sodium silicate, but this has the disadvantage of difficulty in controlling the primary particle size of the gel, ultimately leading to unstable physicochemical properties in the final product.

[0003] Specifically, CN1287892 discloses a method for preparing aluminum-modified silica gel adsorbent material. Inorganic fiber paper is impregnated in water glass, then mixed with soluble aluminum salt to form an aqueous solution, and reacted for 12–24 hours. The reacted inorganic fiber paper is then removed, dried, and heat-treated to obtain the aluminum-modified silica gel adsorbent material. If used as a carrier for polyolefin catalysts, the pore volume must be at least 1 cm³. 3 The silica gel prepared by this method has a small pore volume, which limits the entry of metallocene compounds into the inner surface of the silica gel. It is difficult to increase the loading of metallocene compounds, so it is not suitable as a support for polyolefin catalysis.

[0004] CN106902799 discloses a method for preparing a high-alumina catalyst for melamine synthesis. After gelling with sodium silicate and sulfuric acid, the catalyst undergoes aging, pore expansion, acid soaking, and water washing to obtain a high specific surface area. The resulting silica gel has a specific surface area ≥300 m² / g. 2 / g, pore volume 0.4-0.7cm 3 / g; Although this technology improves the pore volume of the obtained silica gel to some extent through pore expansion treatment, it still has the problem of excessively small pore volume as a catalyst support for olefin polymerization. Summary of the Invention

[0005] The main objective of this invention is to provide an aluminum-modified silica gel, its preparation method, and its application, so as to overcome the defects of existing carrier silica gel, such as small pore volume, unstable physicochemical properties, and high synthesis cost.

[0006] To achieve the above objectives, the present invention provides a method for preparing aluminum-modified silicone, comprising the following steps:

[0007] Step 1: Mix the silicate solution, aluminum compound solution, inorganic acid solution and surfactant evenly, and maintain the temperature for a certain period of time.

[0008] Step 2: Adjust the pH value of the material from Step 1 to 7-10 and age it.

[0009] Step 3: Wash, dry and calcine the material from Step 2 to obtain aluminum-modified silica gel.

[0010] The method for preparing aluminum-modified silicone according to the present invention, wherein the temperature of step 1 is kept at 40℃~90℃ and the holding time is 1-60min.

[0011] The method for preparing aluminum-modified silicone according to the present invention includes an aging temperature of 40℃~90℃ and an aging time of 1~8h in step 2.

[0012] The method for preparing aluminum-modified silica gel according to the present invention includes the following: the silicate solution is a sodium silicate solution; the aluminum-containing compound solution is an aqueous solution of at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, and aluminum phosphate; the inorganic acid solution is a solution of at least one of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid; and the surfactant is at least one of polyethylene glycol and polyacrylamide.

[0013] The method for preparing aluminum-modified silica gel according to the present invention, wherein the silicate solution is calculated as silicon dioxide, the aluminum-containing compound solution is calculated as aluminum, the inorganic acid solution is calculated as hydrogen ions, and the molar ratio of the silicate solution, the aluminum-containing compound solution, the inorganic acid and the surfactant is 1:0.001~0.1:1~1.2:0.001~0.1.

[0014] The method for preparing aluminum-modified silica gel according to the present invention, wherein step 2 adjusts the pH value by adding an alkaline solution to the material in step 1, wherein the alkaline solution is ammonia or sodium hydroxide solution.

[0015] The method for preparing aluminum-modified silica gel according to the present invention includes a drying temperature of 80-360℃ and a calcination temperature of 500-950℃.

[0016] The method for preparing aluminum-modified silica gel according to the present invention includes step 1, which involves mixing the silicate solution, the aluminum-containing compound solution, and the surfactant to form a mixed solution, and simultaneously adding the mixed solution and the inorganic acid solution to a reaction vessel at a volume flow ratio of 1:1 to 1:1.5 for constant temperature.

[0017] To achieve the above objectives, the present invention also provides aluminum-modified silica gel obtained by the above preparation method, wherein the aluminum content in the aluminum-modified silica gel is 0.1 wt% to 3.1 wt%, and the specific surface area of ​​the aluminum-modified silica gel is 230 to 380 m². 2 / g, pore volume 1~2.4cm 3 / g, with an average pore size of 10–20 nm.

[0018] To achieve the above objectives, the present invention further provides the application of the aforementioned aluminum-modified silica gel as a support in olefin polymerization catalysts.

[0019] The beneficial effects of this invention are:

[0020] (1) The method for preparing aluminum-modified silica gel by in-situ synthesis of the present invention involves adding an aluminum compound before the silica gel is formed, and adding aluminum atoms into the silica gel framework. Since the acidity of aluminum atoms is stronger than that of silicon atoms, when metallocene compounds are loaded, the metallocene compounds can be more easily adsorbed onto the inner surface of the silica gel, thereby increasing the loading of metallocene compounds and thus improving the activity of the catalyst, solving the problem that metallocene compounds are easy to fall off from the surface of silica gel.

[0021] (2) Isomorphic substitution of silicon by aluminum introduces aluminum into the silica gel framework. Trivalent aluminum replaces tetravalent silicon in the substitution process, creating a defect at the substitution site. This increases the electron deficiency of the atom, thus enhancing the Lewis acidity of the aluminum-modified silica gel. Compared to unmodified silica gel, the catalyst prepared using the aluminum-modified silica gel of this invention exhibits significantly enhanced activity, increasing catalytic activity by an order of magnitude.

[0022] (3) The formation of Al-O-Si bonds on the surface of aluminum-modified silica enhances the support of the pore framework and improves the heat resistance of the silica. The catalyst prepared using the aluminum-modified silica of this invention can still maintain high activity in polymerization reactions at temperatures exceeding 90°C. Detailed Implementation

[0023] The technical solution of the present invention will be described in detail below. The following embodiments are implemented under the premise of the technical solution of the present invention and a detailed implementation process is given. However, the protection scope of the present invention is not limited to the following embodiments. Structures or experimental methods that do not specify specific conditions in the following embodiments are generally performed under conventional conditions.

[0024] This invention provides a method for preparing aluminum-modified silicone, comprising the following steps:

[0025] Step 1: Mix the silicate solution, aluminum compound solution, inorganic acid solution and surfactant evenly, and maintain the temperature for a certain period of time.

[0026] Step 2: Adjust the pH value of the material from Step 1 to 7-10 and age it.

[0027] Step 3: Wash, dry and calcine the material from Step 2 to obtain aluminum-modified silica gel.

[0028] This invention introduces aluminum atoms into the silica gel framework by adding an aluminum-containing compound during the in-situ synthesis of silica gel. Since aluminum atoms are more acidic than silicon atoms, they more easily adsorb metallocene compounds onto the inner surface of the silica gel when loaded, solving the problem of metallocene compounds easily detaching from the silica gel surface. Simultaneously, during the synthesis process, trivalent aluminum replaces tetravalent silicon, creating a defect at the substitution site, thereby increasing the electron deficiency of the atom and enhancing the Lewis acidity of the aluminum-modified silica gel, thus improving catalyst activity. Furthermore, the formation of Al-O-Si bonds on the surface of the aluminum-modified silica gel enhances the support of the porous framework and improves the heat resistance of the silica gel.

[0029] In one embodiment, the silicate solution is water glass or sodium silicate solution, the aluminum compound solution is an aqueous solution of at least one of aluminum sulfate, aluminum nitrate, aluminum chloride and aluminum phosphate, the inorganic acid solution is a solution of at least one of sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid, and the surfactant is at least one of polyethylene glycol and polyacrylamide.

[0030] In one embodiment, the silicate solution of the present invention is calculated as silicon dioxide, the aluminum compound solution is calculated as aluminum, and the inorganic acid solution is calculated as hydrogen ions. The molar ratio of the silicate solution, the aluminum compound solution, the inorganic acid solution and the surfactant is 1:0.001~0.1:1~1.2:0.001~0.1.

[0031] In this invention, the silicate solution, inorganic acid solution, aluminum-containing compound solution, and surfactant can be added to the reaction system in step 1 in any order. Preferably, the silicate solution, aluminum-containing compound solution, and surfactant form a homogeneous mixed solution, and then the mixed solution is mixed with the inorganic acid solution. For example, the mixed solution and the inorganic acid solution are added to the reaction system simultaneously at a volume flow ratio (i.e., addition rate ratio) of 1:1 to 1:1.5. This can increase the specific surface area and pore volume of the obtained silica gel.

[0032] In one embodiment, the temperature for constant temperature in step 1 is 40°C to 90°C, and the constant temperature time is 1 to 60 minutes.

[0033] Then, the pH value of the material after being kept at a constant temperature in step 1 is adjusted to 7-10, and then aged. This invention does not particularly limit the method of pH adjustment; for example, an alkaline solution may be added to the material in step 1 to bring the pH value to 7-10. In one embodiment, the alkaline solution is ammonia water, and this invention does not particularly limit the concentration of the ammonia water.

[0034] In another embodiment, the aging temperature in step 2 is 40℃~90℃, and the aging time is 1~8h. In yet another embodiment, the aging temperature is 70℃~80℃, and the aging time is 2~4h.

[0035] Then, the material from step 2 is washed until neutral, dried, and calcined to obtain aluminum-modified silica gel. This invention does not particularly limit the drying method, temperature, or calcination temperature. In one embodiment, the drying temperature is 120-360°C, and the calcination temperature is 500-700°C. The drying method is, for example, spray drying, with an inlet temperature of, for example, 250-380°C, an outlet temperature of, for example, 100-150°C, and a centrifugal speed of, for example, 4000-6000 rpm.

[0036] Aluminum-modified silica gel was prepared by the above method according to the present invention. The aluminum content in the aluminum-modified silica gel is 0.1 wt% to 3.1 wt%, and the specific surface area of ​​the aluminum-modified silica gel is 230 to 380 m². 2 / g, pore volume 1~2.4cm 3 / g, with an average pore size of 10–20 nm.

[0037] The aluminum-modified silica gel prepared by the method of the present invention has a large pore volume, making it suitable as a support for olefin polymerization catalysts, such as metallocene catalysts, chromium-based catalysts, or Ziegler-Natta catalysts.

[0038] In summary, this invention proposes an in-situ synthesis method for preparing aluminum-modified silica gel. This method is simple to operate, allows for controllable particle size and pore volume, and yields high output. The polyolefin catalyst prepared using the silica gel support of this invention exhibits high activity, nearly nine times higher than that of catalysts prepared using silica gel from abroad.

[0039] The following embodiments further illustrate the features of the present invention, but the scope of protection of the present invention is not limited to these embodiments.

[0040] 1. Raw material specifications and sources

[0041] Water glass (modulus 3.2-3.5, SiO2 content 25%, Sinopec Catalyst Changling Branch); concentrated sulfuric acid (95.0-98.0 wt%, Sinopharm reagent); hydrochloric acid (36.0-38.0 wt%, Sinopharm reagent); nitric acid (65.0-68.0 wt%, Sinopharm reagent); ammonia (25.0-28.0 wt%, Sinopharm reagent); sodium hydroxide (purity ≥96.0%, Sinopharm reagent); polyethylene glycol (1 mol / L, Sinopharm reagent); aluminum sulfate (purity ≥99.0%, Sinopharm reagent); aluminum nitrate nonahydrate (purity ≥99.0%, Sinopharm reagent); 955 silica gel (Grace); except for water glass and polyethylene glycol, which are chemically pure, all other reagents are analytical grade.

[0042] 2. Analysis and Characterization

[0043] To test the particle size distribution of silica gel using a Malvern MS2000, distilled water was poured into a 1000ml beaker, and the standard operating procedure (SOP) was initiated. Optical path calibration was performed, and laser intensity was measured. When the test procedure prompted for sample addition, a small amount of silica gel was carefully added to the measuring cell until the required opacity was achieved. Measurement was then initiated, and the instrument automatically provided the particle size distribution.

[0044] The pore structure of silica gel was determined using a Konta Autosorb-1 physical adsorption analyzer. A certain amount of silica gel sample was placed in an analytical tube and desorbed for more than 4 hours at 120°C in the degassing system. The sample was then transferred to the analytical system, where the adsorbent and adsorbate reached dynamic equilibrium under liquid nitrogen temperature and gradient relative pressure. The relationship between relative equilibrium pressure and nitrogen adsorption was plotted as an isotherm. The specific surface area of ​​the silica gel was calculated using the multi-point BET method based on the measured isotherm, and the pore volume and pore size distribution were determined using the BJH method.

[0045] The morphology of the silica support was tested using a Hitachi HT7800 transmission electron microscope and a FEI Apreo 2 scanning electron microscope.

[0046] The metal content of silica gel was tested using a Thermo Fisher iCAP6300 inductively coupled plasma spectrometer (ICP) with a pump speed of 13 rpm, a plasma gas velocity of 15.0 L / min, an auxiliary gas velocity of 1.50 L / min, and an atomizing gas pressure of 200 kPa.

[0047] Example 1

[0048] (1) Mix 200 mL of 1 mol / L water glass solution, 9 mL of 0.1 mol / L aluminum sulfate solution and 0.5 g of polyethylene glycol 600 thoroughly;

[0049] (2) The mixed solution obtained in step (1) and 210 mL of 1 mol / L sulfuric acid were added to the reaction vessel at the same rate, with a dropping rate of 5 mL / min and a temperature of 40 °C. The temperature was kept constant for 30 min. This step is acid hydrolysis.

[0050] (3) Add ammonia solution to the material obtained in step (2), adjust the pH value to 7, keep the temperature at 40℃, and age for 4 hours;

[0051] (4) The material obtained in step (3) is washed with distilled water until neutral, then dried and calcined to obtain aluminum-modified silica gel;

[0052] (5) Select the spray drying method: inlet temperature 350℃, outlet temperature 120℃, centrifugal speed 5000rpm. Silica gel was calcined at 600℃ for 4 hours to obtain product 1.

[0053] Example 2

[0054] The difference from Example 1 is that the temperature in steps (2) and (3) is set to 60°C to obtain product 2.

[0055] Example 3

[0056] The difference from Example 1 is that the temperature in steps (2) and (3) is set to 90°C to obtain product 3.

[0057] Example 4

[0058] (1) Add 200 mL of 1 mol / L water glass solution, 33 mL of 0.1 mol / L aluminum sulfate solution and 0.5 g of polyethylene glycol 600 as the base solution to the reaction vessel and turn on the stirrer;

[0059] (2) Add 210 mL of 1 mol / L sulfuric acid to the reaction vessel at a rate of 5 mL / min, set the temperature to 40℃, and maintain the temperature for 30 min; this step is acid hydrolysis.

[0060] (3) Same as step (3) in Example 1

[0061] (4) Same as step (4) in Example 1

[0062] (5) Same as step (5) in Example 1, to obtain product 4.

[0063] Example 5

[0064] (1) Add 210 mL of 1 mol / L sulfuric acid as the base solution to the reaction vessel and turn on the stirrer;

[0065] (2) Mix 200 mL of 1 mol / L water glass solution, 33 mL of 0.1 mol / L aluminum sulfate solution and 0.5 g of polyethylene glycol 600 evenly, and then add it to the reaction vessel at a rate of 5 mL / min. Set the temperature to 40℃ and keep it constant for 30 min.

[0066] (3) Same as step (3) in Example 1

[0067] (4) Same as step (4) in Example 1

[0068] (5) Same as step (5) in Example 1, to obtain product 5.

[0069] Example 6

[0070] (1) Mix 200 mL of 1 mol / L sodium silicate solution, 133 mL of 0.1 mol / L aluminum nitrate solution and 1 g of polyethylene glycol 2000 thoroughly;

[0071] (2) The mixed solution obtained in step (1) and 210 mL of 1 mol / L hydrochloric acid were added to the reaction vessel at the same rate, with a dropping rate of 10 mL / min and a temperature of 70℃, and the temperature was kept constant for 60 min.

[0072] (3) Add sodium hydroxide solution to the material obtained in step (2), adjust the pH value to 7, keep the temperature at 40℃, and age for 2 hours;

[0073] (4) Same as step (4) in Example 1

[0074] (5) Same as step (5) in Example 1, to obtain product 6.

[0075] Example 7

[0076] (1) Mix 200 mL of 1 mol / L sodium silicate solution, 67 mL of 0.1 mol / L aluminum chloride solution and 0.5 g of polyacrylamide evenly;

[0077] (2) The mixed solution obtained in step (1) and 210 mL of 1 mol / L hydrochloric acid were added to the reaction vessel at a rate of 1:1.5. The hydrochloric acid solution was added at a rate of 15 mL / min, and the temperature was set at 70℃ and kept constant for 10 min.

[0078] (3) Add ammonia solution to the material obtained in step (2), adjust the pH value to 7, keep the temperature at 90℃, and age for 8 hours;

[0079] (4) Same as step (4) in Example 1

[0080] (5) Same as step (5) in Example 1, to obtain product 7.

[0081] Comparative Example 1

[0082] Commercial silica gel (unmodified silica gel) was purchased, and its particle size and specific surface area were tested and compared with the aluminum-modified silica gel prepared in the embodiments of the present invention. The results are shown in Table 1.

[0083] Table 1

[0084]

[0085] As shown in Table 1, the specific surface area and pore volume of the silicone product prepared by the method of the present invention are comparable to those of the comparative silicone Grace955, and the specific surface area is even greater than 300 m². 2 / g, pore volume greater than or equal to 1.7cm 3 / g, superior to the comparative silica Grace955; the addition of aluminum is beneficial to increasing the specific surface area and pore volume of silica; the specific surface area of ​​products 1-3 decreases with increasing preparation temperature. The specific surface area of ​​product 4 is only 273m². 2 / g, which is lower than the specific surface area of ​​the product by 1-3. The difference between the two is due to the different feeding methods of acid hydrolysis, indicating that the latter feeding method is better.

[0086] Example 8

[0087] The silica gels of Examples 1-7 and Comparative Example 1 were used to support zirconium dichlorophenocene (overloading was used here to ensure that as much zirconium dichlorophenocene as possible was loaded onto the silica gel, and the theoretical loading amount of zirconium dichlorophenocene in the examples and the comparative example was the same) to prepare catalysts 1-7 and comparative catalyst 1; and under normal pressure, 5 mL of MAO and 0.045 g of catalyst were added, and polymerization was carried out at 60 °C for 1 hour. The monomer for polymerization was ethylene. The activity results of the catalysts are shown in Table 2.

[0088] Example 9

[0089] In Example 1 and Comparative Example 1, silica gel was used to support chromium oxide (overloading was used here to ensure that as much chromium oxide as possible was loaded onto the silica gel, and the theoretical loading of chromium oxide was the same in both examples and comparative examples) to prepare catalyst 7A and comparative catalyst 1A, respectively. Under conditions of 2 MPa, 5 mL of triethylaluminum and 0.04 g of catalyst were added, and polymerization was carried out at 85 °C for 1 hour. The monomer used for polymerization was ethylene. The catalyst activity results are shown in Table 3. The actual zirconium / chromium content of the catalysts in the examples was determined by ICP.

[0090] Example 10

[0091] The silica gels of Example 1 and Comparative Example 1 were used to support chromium oxide (overloading was used here to ensure that as much chromium oxide as possible was loaded onto the silica gel, and the theoretical loading of chromium oxide in the examples and comparative examples was the same) to prepare catalyst 7B and comparative catalyst 1B, respectively; and under 1.5 MPa conditions, 5 mL of triethylaluminum and 0.04 g of catalyst were added, and polymerization was carried out at 90 °C for 1 hour. The monomers were ethylene and hexene. The catalyst activity results are shown in Table 3.

[0092] Table 2

[0093]

[0094]

[0095] Table 3

[0096]

[0097] As shown in Tables 2 and 3, the catalyst prepared by the method of this invention exhibits a significant increase in zirconium and chromium loading compared to the comparative catalyst, increasing by more than 2 to 3 times. Simultaneously, the polymerization activity is increased by one order of magnitude, with catalyst 1 showing the highest polymerization activity, 80 times higher than the comparative catalyst. This is because, during the silica gel preparation process, aluminum atoms are added in situ into the silica gel framework. Since aluminum atoms are more acidic than silicon atoms, when zirconium and chromium compounds are loaded, they can be more easily adsorbed onto the inner surface of the silica gel, increasing the loading and thus enhancing the catalyst activity.

[0098] As shown in Table 3, the chromium catalyst 7B prepared by the method of this invention still exhibits high activity at 90℃, exceeding that of comparative catalyst 1B by one order of magnitude. This is because the formation of Al-O-Si bonds on the surface of the aluminum-modified silica gel in this invention enhances the support of the pore framework and improves the heat resistance of the silica gel.

[0099] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing aluminum-modified silica gel, characterized in that, Includes the following steps: Step 1: Mix the silicate solution, aluminum compound solution, inorganic acid solution and surfactant evenly, and keep it at a constant temperature for a certain period of time. The constant temperature is 40℃~90℃ and the constant temperature time is 1-60 min. Step 2: Add an alkaline solution to the material from Step 1 to adjust the pH value of the material from Step 1 to 7-10, and then age it. Step 3: Wash, dry and calcine the material from Step 2 to obtain aluminum-modified silica gel; Wherein, the silicate solution is calculated as silicon dioxide, the aluminum-containing compound solution is calculated as aluminum, the inorganic acid solution is calculated as hydrogen ions, and the molar ratio of the silicate solution, the aluminum-containing compound solution, the inorganic acid solution and the surfactant is 1:0.001~0.1:1~1.2:0.001~0.

1.

2. The method for preparing aluminum-modified silica gel according to claim 1, characterized in that, Step 2: Aging temperature is 40℃~90℃, aging time is 1~8 h.

3. The method for preparing aluminum-modified silica gel according to claim 1, characterized in that, The silicate solution is a sodium silicate solution, the aluminum-containing compound solution is an aqueous solution of at least one of aluminum sulfate, aluminum nitrate, aluminum chloride, and aluminum phosphate, the inorganic acid solution is a solution of at least one of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, and the surfactant is at least one of polyethylene glycol and polyacrylamide.

4. The method for preparing aluminum-modified silica gel according to claim 1, characterized in that, In step 2, the alkaline solution is ammonia or sodium hydroxide solution.

5. The method for preparing aluminum-modified silica gel according to claim 1, characterized in that, The drying temperature is 80-360℃, and the calcination temperature is 500-950℃.

6. The method for preparing aluminum-modified silica gel according to claim 1, characterized in that, Step 1 is as follows: the silicate solution, the aluminum-containing compound solution and the surfactant are mixed to form a mixed solution, and the mixed solution and the inorganic acid solution are simultaneously added to the reaction vessel at a volume flow ratio of 1:1 to 1:1.5 and kept at a constant temperature.

7. The aluminum-modified silica gel obtained by the preparation method according to any one of claims 1-6, characterized in that, The aluminum-modified silica gel contains 0.1 wt% to 3.1 wt% aluminum, and has a specific surface area of ​​230 to 380 m². 2 / g, pore volume 1~2.4 cm 3 / g, with an average pore size of 10~20 nm.

8. The application of the aluminum-modified silica gel as a support in olefin polymerization catalysts as described in claim 7.

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