A method for the synthesis of modified alumina

Abstract

The application relates to the technical field of alumina modification, and particularly discloses a synthesis method of modified alumina, which aims to solve the problems of insufficient thermal stability of alumina and uneven dispersion of modified elements in the prior art.The method comprises the following steps: adding a metal organic compound into an aluminum sulfate aqueous solution in advance before the aluminum sulfate aqueous solution and a sodium metaaluminate aqueous solution are subjected to a parallel flow reaction; adding an aminopropylsilazane during the parallel flow reaction; after the parallel flow reaction is completed, adding a hydroxylated quaternary ammonium base into the generated pseudo-boehmite slurry to perform dispersion treatment, and then adding a silicon-containing compound to perform a doping reaction; and finally, calcining the pseudo-boehmite powder to obtain modified alumina.The in-situ and uniform modification of the alumina is realized by introducing the modified components with synergistic effects in different stages and in a specific order, the thermal stability of the final product is significantly improved, and the process flow is short and the cost benefit is high.

Description

Technical Field

[0001] This invention relates to the field of alumina modification technology, and more specifically, to a method for synthesizing modified alumina. Background Technology

[0002] Activated alumina, especially γ-Al₂O₃, is widely used as a catalyst support in petrochemicals, industrial catalysis, and automotive exhaust purification due to its large specific surface area, abundant porous structure, and low cost. However, conventional activated alumina is prone to phase transformation (such as from the γ phase to the θ phase and even the stable α phase) and particle sintering in high-temperature (e.g., above 1000℃) or high-temperature hydrothermal environments, leading to a sharp decrease in its specific surface area and pore volume, a reduction in catalytic active sites, and ultimately rendering it unusable. This is particularly prominent under harsh operating conditions such as automotive exhaust catalysis and catalytic combustion. Therefore, improving the thermal stability of activated alumina is a research hotspot in this field.

[0003] Currently, the mainstream method for improving the thermal stability of alumina is through doping modification, that is, introducing other elements (such as Si, La, Zr, Ti, etc.) to suppress its phase transformation and sintering. In existing technologies, the main methods for introducing modifying elements include impregnation and co-precipitation. Impregnation typically involves immersing solid alumina in a solution containing a precursor of the modifying element, but this method often leads to uneven distribution of the modifying element and unstable product performance. Although co-precipitation has been improved, for example by adding a modifier precursor to the alumina slurry, it is still difficult to achieve uniform dispersion of the modifying element because alumina particles are prone to agglomeration in aqueous media. Based on the above, this invention provides a method for synthesizing modified alumina. Summary of the Invention

[0004] To address the problems of insufficient thermal stability and uneven dispersion of modifying elements in existing alumina technologies, this invention provides a method for synthesizing modified alumina. This method achieves highly uniform dispersion of modifying elements by introducing multiple modifying components in stages and in a specific order during the in-situ synthesis of a boehmite precursor. This invention eliminates the need for modification after synthesizing boehmite powder or after calcination into alumina, effectively shortening the process flow and significantly improving the high-temperature thermal stability of the resulting alumina.

[0005] This invention provides a method for synthesizing modified alumina, employing the following technical solution: A method for synthesizing modified alumina includes the following steps: S1. Dissolve the organometallic compound in an alcohol solution to obtain solution 1. Add solution 1 to an aqueous aluminum sulfate solution, then add an aqueous sodium aluminate solution and carry out a neutralization reaction in parallel flow. During the neutralization reaction in parallel flow, add aminopropylsilazane. After the reaction is completed, a pseudoboehmite slurry is obtained. S2. Add hydroxylated quaternary ammonium base to the pseudoboehmite slurry and stir. Then, add sodium silicate under stirring to carry out the doping reaction. After the doping reaction is completed, filter, wash, and spray dry to obtain modified pseudoboehmite powder. S3. Modified alumina is obtained by calcining the modified boehmite powder.

[0006] Preferably, the organometallic compound in S1 is tetrabutyl titanate.

[0007] Preferably, the alcohol solution in S1 is at least one of ethanol, ethylene glycol, n-butanol, isopropanol, and tert-butanol.

[0008] Preferably, the alcohol solution in S1 is ethylene glycol.

[0009] Preferably, the neutralization reaction temperature in S1 is 62-85℃, the reaction time is 30-50 min, and the pH is 7-9.

[0010] Preferably, the aminopropylsilazane is added in S1 when the neutralization reaction has been underway for 10-20 minutes.

[0011] Preferably, the aluminum sulfate concentration in S1, calculated as aluminum oxide, is 70-130 g / L.

[0012] Preferably, the concentration of sodium aluminate in S1 is 80-200 g / L, calculated as alumina.

[0013] Preferably, the mass ratio of organometallic compound, alcohol solution, aluminum sulfate aqueous solution, and aminopropylsilazane in S1 is (0.01-0.03):(0.08-0.15):1:(0.02-0.05).

[0014] Preferably, the hydroxylated quaternary ammonium base in S2 is 2-hydroxyethyltrimethylammonium hydroxide or hydroxypropyltrimethylammonium hydroxide.

[0015] Preferably, the hydroxylated quaternary ammonium base in S2 is 2-hydroxyethyltrimethylammonium hydroxide.

[0016] Preferably, the mass ratio of hydroxylated quaternary ammonium base, sodium silicate, and pseudoboehmite slurry in S2 is (0.009-0.04):(0.01-0.04):1.

[0017] Preferably, the stirring time after adding the hydroxylated quaternary ammonium base in S2 is 20-40 min.

[0018] Preferably, the doping reaction time in S2 is 30-60 min.

[0019] Preferably, the washing in step S2 is performed using deionized water or deionized water containing ammonium carbonate.

[0020] Preferably, in the ammonium carbonate-containing deionized water, the amount of ammonium carbonate added is 5-12% of the mass of the deionized water.

[0021] Preferably, the inlet temperature of the spray dryer in S2 is 180-200℃, the outlet temperature is 90-110℃, and the pressure is 0.4-0.8MPa.

[0022] Preferably, the calcination temperature in step S3 is 500-800℃, and the calcination time is 3-5h.

[0023] In summary, the present invention has the following beneficial effects: This invention pre-disperses a metal element (such as Ti) uniformly in an acidic aluminum source before the co-current reaction of aluminum sulfate aqueous solution and sodium aluminate aqueous solution. This ensures that the metal element can uniformly enter the alumina lattice and form a solid solution during the subsequent precipitation process, fundamentally increasing the phase transition temperature. During the co-current reaction, aminopropylsilazane is added, which hydrolyzes in the reaction system to generate silanol (-Si-OH) and amino (-NH2). The silanol condenses with the hydroxyl groups (Al-OH) on the surface of newly formed boehmite to form stable Al-O-Si covalent bonds, thus concentrating the silicon... The modified alumina particles are firmly anchored to the alumina surface, enhancing interfacial bonding and effectively inhibiting particle growth and sintering. After the co-current reaction, a hydroxylated quaternary ammonium base is first added to the generated boehmite slurry for dispersion treatment, effectively breaking up the agglomerates of boehmite particles and increasing their surface accessibility. Then, silicon is introduced for doping, so that the silica generated by hydrolysis uniformly coats the dispersed particle surface, forming a dense aluminosilicate "protective shell," further physically preventing high-temperature sintering. Silicon doping can also adjust the surface acidity. This invention achieves in-situ and uniform modification of alumina by introducing synergistic modifying components in a specific order at different stages, significantly improving the thermal stability of the final product, and has a short process flow and high cost-effectiveness.

[0024] This invention combines the precursor preparation and modification steps into one, avoiding the complex process of synthesizing powder first and then impregnating or calcining for modification in traditional methods. It significantly shortens the production cycle, reduces energy consumption, and has good prospects for industrial application. Attached Figure Description

[0025] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 The image shown is the XRD pattern of the product in Example 1 of this invention, where the horizontal axis represents the diffraction angle and the vertical axis represents the absorbance.

[0026] Figure 2This is an SEM image of the product in Example 1 of the present invention.

[0027] Figure 3 The image shown is the XRD pattern of the product in Example 2 of this invention, where the horizontal axis represents the diffraction angle and the vertical axis represents the absorbance.

[0028] Figure 4 This is an SEM image of the product in Example 2 of the present invention.

[0029] Figure 5 The image shown is the XRD pattern of the product in Example 3 of this invention, where the horizontal axis represents the diffraction angle and the vertical axis represents the absorbance.

[0030] Figure 6 This is a SEM image of the product in Example 3 of the present invention.

[0031] Figure 7 The image shows the XRD pattern of the product in Comparative Example 1 of this invention, where the horizontal axis represents the diffraction angle and the vertical axis represents the absorbance.

[0032] Figure 8 This is a SEM image of the product in Comparative Example 1 of the present invention.

[0033] Figure 9 The image shows the XRD pattern of the product in Comparative Example 2 of this invention, where the horizontal axis represents the diffraction angle and the vertical axis represents the absorbance.

[0034] Figure 10 This is a SEM image of the product in Comparative Example 2 of the present invention.

[0035] Figure 11 The image shows the XRD pattern of the product in Comparative Example 3 of this invention, where the horizontal axis represents the diffraction angle and the vertical axis represents the absorbance.

[0036] Figure 12 This is a SEM image of the product in Comparative Example 3 of the present invention. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise specified, all materials and reagents used in this invention are commercially available.

[0039] Examples 1-3 provide a method for synthesizing modified alumina.

[0040] Example 1 A method for synthesizing modified alumina specifically includes the following steps: S1. At room temperature, 1.2 g of tetrabutyl titanate and 10 g of ethanol were weighed and mixed to prepare solution 1. Solution 1 was dissolved in 110 g of aluminum sulfate aqueous solution. At 65 °C, 113 g of sodium aluminate aqueous solution was added and the neutralization reaction was carried out in parallel flow. The pH of the reaction was controlled at 8 and the reaction time was 45 min. When the neutralization reaction was carried out for 15 min, 2.3 g of aminopropylsilazane was added to the reaction system. After the reaction was completed, a pseudoboehmite slurry was obtained, in which the concentration of aluminum sulfate (calculated as alumina) was 103 g / L and the concentration of sodium aluminate (calculated as alumina) was 180 g / L. S2. Add 3g of 2-hydroxyethyltrimethylammonium hydroxide to 223g of pseudoboehmite slurry and stir for 20min. Then, add 4g of sodium silicate under stirring to carry out the doping reaction. Stir for 60min until the doping reaction is completed. The slurry is then separated into solid and liquid by a vacuum filtration pump and washed with deionized water. The slurry is then filtered to reduce the impurity content. The filtered and washed filter cake is mixed with water and spray-dried. The inlet temperature is controlled at 190℃, the outlet temperature at 100℃ and the pressure at 0.5MPa to obtain modified pseudoboehmite powder. S3. Modified alumina was obtained by calcining the modified boehmite powder at 800℃ for 3 hours.

[0041] Example 2 A method for synthesizing modified alumina specifically includes the following steps: S1. At room temperature, 1.2 g of tetrabutyl titanate and 10 g of ethanol were weighed and mixed to prepare solution 1. Solution 1 was dissolved in 110 g of aluminum sulfate aqueous solution. At 85 °C, 113 g of sodium aluminate aqueous solution was added and carried out in parallel flow for neutralization reaction. The reaction pH was controlled at 8 and the reaction time was 30 min. When the neutralization reaction was carried out for 10 min, 2.3 g of aminopropylsilazane was added to the reaction system. After the reaction was completed, a pseudoboehmite slurry was obtained, in which the aluminum sulfate concentration was 103 g / L (calculated as alumina) and the sodium aluminate concentration was 180 g / L (calculated as alumina). S2. Add 3g of 2-hydroxyethyltrimethylammonium hydroxide to 223g of pseudoboehmite slurry and stir for 20min. Then, add 4g of sodium silicate under stirring to carry out the doping reaction. Stir for 60min until the doping reaction is completed. The slurry is then separated into solid and liquid by a vacuum filtration pump, washed with deionized water, and filtered to reduce the impurity content in the slurry. The filter cake after filtration and washing is mixed with water and spray-dried. The inlet temperature is controlled at 180℃, the outlet temperature at 90℃, and the pressure at 0.7MPa to obtain modified pseudoboehmite powder. S3. Modified alumina was obtained by calcining the modified boehmite powder at 800℃ for 3 hours.

[0042] Example 3 A method for synthesizing modified alumina specifically includes the following steps: S1. At room temperature, 1.1 g of tetrabutyl titanate and 12 g of ethanol were weighed and mixed to prepare solution 1. Solution 1 was dissolved in 110 g of aluminum sulfate aqueous solution. At 65 °C, 113 g of sodium aluminate aqueous solution was added and the neutralization reaction was carried out in parallel flow. The pH of the reaction was controlled at 8 and the reaction time was 45 min. When the neutralization reaction was carried out for 15 min, 2.3 g of aminopropylsilazane was added to the reaction system. After the reaction was completed, a pseudoboehmite slurry was obtained, in which the concentration of aluminum sulfate (calculated as alumina) was 103 g / L and the concentration of sodium aluminate (calculated as alumina) was 180 g / L. S2. Add 3.88g of 2-hydroxyethyltrimethylammonium hydroxide to 223g of pseudoboehmite slurry and stir for 20min. Then, add 4.2g of sodium silicate under stirring to carry out the doping reaction. Stir for 60min until the doping reaction is completed. The slurry is then separated into solid and liquid by a vacuum filtration pump, washed with deionized water, and filtered to reduce the impurity content in the slurry. The filter cake after filtration and washing is mixed with water and spray-dried. The inlet temperature is controlled at 190℃, the outlet temperature at 100℃, and the pressure at 0.5MPa to obtain modified pseudoboehmite powder. S3. Modified alumina was obtained by calcining the modified boehmite powder at 800℃ for 3 hours.

[0043] To verify the comprehensive performance of the modified alumina prepared in Examples 1-3 of this invention, the applicant set up Comparative Examples 1-5, as follows: Comparative Example 1 A method for synthesizing modified alumina specifically includes the following steps: Under the conditions of S1 and 65℃, 110g of aluminum sulfate aqueous solution and 113g of sodium aluminate aqueous solution were carried out in parallel flow for neutralization reaction for 45min. When the neutralization reaction was carried out for 15min, 2.3g of aminopropylsilazane was added to the reaction system. After the reaction was completed, a pseudoboehmite slurry was obtained, wherein the concentration of aluminum sulfate was 103g / L based on alumina and the concentration of sodium aluminate was 180g / L based on alumina. S2. Add 3g of 2-hydroxyethyltrimethylammonium hydroxide to 223g of pseudoboehmite slurry and stir for 20min. Then, add 4g of sodium silicate under stirring to carry out the doping reaction. Stir for 60min until the doping reaction is completed. The slurry is then separated into solid and liquid by a vacuum filtration pump and washed with deionized water. The slurry is then filtered to reduce the impurity content. The filtered and washed filter cake is mixed with water and spray-dried. The inlet temperature is controlled at 190℃, the outlet temperature at 100℃ and the pressure at 0.5MPa to obtain modified pseudoboehmite powder. S3. Modified alumina was obtained by calcining the modified boehmite powder at 800℃ for 3 hours.

[0044] Comparative Example 2 A method for synthesizing modified alumina specifically includes the following steps: S1. At room temperature, 1.2 g of tetrabutyl titanate and 10 g of ethanol were weighed and mixed to prepare solution 1. Solution 1 was dissolved in 110 g of aluminum sulfate aqueous solution. At 65 °C, 113 g of sodium aluminate aqueous solution was added in parallel flow to carry out a neutralization reaction. The reaction pH was controlled at 8 and the reaction time was 45 min. After the reaction was completed, a pseudoboehmite slurry was obtained, in which the aluminum sulfate concentration was 103 g / L (calculated as alumina) and the sodium aluminate concentration was 180 g / L (calculated as alumina). S2. Add 3g of 2-hydroxyethyltrimethylammonium hydroxide to 223g of pseudoboehmite slurry and stir for 20min. Then, add 4g of sodium silicate under stirring to carry out the doping reaction. Stir for 60min until the doping reaction is completed. The slurry is then separated into solid and liquid by a vacuum filtration pump and washed with deionized water. The slurry is then filtered to reduce the impurity content. The filtered and washed filter cake is mixed with water and spray-dried. The inlet temperature is controlled at 190℃, the outlet temperature at 100℃ and the pressure at 0.5MPa to obtain modified pseudoboehmite powder. S3. Modified alumina was obtained by calcining the modified boehmite powder at 800℃ for 3 hours.

[0045] Comparative Example 3 A method for synthesizing modified alumina specifically includes the following steps: S1. At room temperature, 1.2 g of tetrabutyl titanate and 10 g of ethanol were weighed and mixed to prepare solution 1. Solution 1 was dissolved in 110 g of aluminum sulfate aqueous solution. At 65 °C, 113 g of sodium aluminate aqueous solution was added and the neutralization reaction was carried out in parallel flow. The pH of the reaction was controlled at 8 and the reaction time was 45 min. When the neutralization reaction was carried out for 15 min, 2.3 g of aminopropylsilazane was added to the reaction system. After the reaction was completed, a pseudoboehmite slurry was obtained, in which the concentration of aluminum sulfate (calculated as alumina) was 103 g / L and the concentration of sodium aluminate (calculated as alumina) was 180 g / L. S2. Stir 223g of pseudoboehmite slurry for 20min, then add 4g of sodium silicate under stirring to carry out the doping reaction. Stir for 60min until the doping reaction is completed. The slurry is then separated into solid and liquid by a vacuum filtration pump, washed with deionized water, and filtered to reduce the impurity content in the slurry. The filter cake after filtration and washing is mixed with water and spray-dried. The inlet temperature is controlled at 190℃, the outlet temperature at 100℃, and the pressure at 0.5MPa to obtain modified pseudoboehmite powder. S3. Modified alumina was obtained by calcining the modified boehmite powder at 800℃ for 3 hours.

[0046] Comparative Example 4 A method for synthesizing modified alumina specifically includes the following steps: S1. At room temperature, 1.2 g of tetrabutyl titanate and 10 g of ethanol were weighed and mixed to prepare solution 1. 110 g of aluminum sulfate aqueous solution was taken and 113 g of sodium aluminate aqueous solution was added to the reaction system at 65 °C for a neutralization reaction. The pH of the reaction was controlled at 8 and the reaction time was 125 min. When the neutralization reaction was in progress for 15 min, solution 1, 2.3 g of aminopropylsilazane, 3 g of 2-hydroxyethyltrimethylammonium hydroxide, and 4 g of sodium silicate were added to the reaction system. After the reaction was completed, a pseudoboehmite slurry was obtained, in which the concentration of aluminum sulfate (calculated as alumina) was 103 g / L and the concentration of sodium aluminate (calculated as alumina) was 180 g / L. S2. The slurry is subjected to solid-liquid separation by a vacuum filtration pump, washed with deionized water, and filtered to reduce the impurity content in the slurry. The filter cake after filtration and washing is mixed with water and spray-dried. The inlet temperature is controlled at 190℃, the outlet temperature at 100℃, and the pressure at 0.5MPa to obtain modified pseudoboehmite powder. S3. Modified alumina was obtained by calcining the modified boehmite powder at 800℃ for 3 hours.

[0047] Comparative Example 5 A method for synthesizing modified alumina specifically includes the following steps: S1. At room temperature, 1.2 g of tetrabutyl titanate and 10 g of ethanol were weighed and mixed to prepare solution 1. Solution 1 was dissolved in 110 g of aluminum sulfate aqueous solution. At 65 °C, 113 g of sodium aluminate aqueous solution was added and the neutralization reaction was carried out in parallel flow. The pH of the reaction was controlled at 8 and the reaction time was 45 min. When the neutralization reaction was carried out for 15 min, 3 g of 2-hydroxyethyltrimethylammonium hydroxide was added to the reaction system and stirred for 20 min. Then, 4 g of sodium silicate was added under stirring to carry out the doping reaction. After the reaction was completed, a pseudoboehmite slurry was obtained, in which the aluminum sulfate concentration was 103 g / L based on alumina and the sodium aluminate concentration was 180 g / L based on alumina. S2. Add 2.3g of aminopropylsilazane to 223g of pseudoboehmite slurry, stir for 60min, then separate the solid and liquid in the slurry by vacuum filtration pump, wash with deionized water, and filter to reduce the impurity content in the slurry. After filtration and washing, add water and stir evenly for spray drying. Control the inlet temperature to 190℃, the outlet temperature to 100℃, and the pressure to 0.5MPa to obtain modified pseudoboehmite powder. S3. Modified alumina was obtained by calcining the modified boehmite powder at 800℃ for 3 hours.

[0048] Performance testing The comprehensive properties of the modified alumina powders prepared in Examples 1-3 and Comparative Examples 1-3 of this invention were tested respectively, as follows: The specific surface area and pore volume of modified alumina powder before and after aging at 1200℃ for 10 hours were tested by the BET method, and the results are shown in Table 1.

[0049] Table 1: From Table 1 and Appendix Figure 1-12 As can be seen from the results, the modified alumina prepared in Examples 1-3 has significantly better overall performance than that of Comparative Examples 1-3, exhibiting high specific surface area and pore volume, and significant advantages in thermal stability, thus possessing broad market prospects.

[0050] Comparative Example 1 and Comparative Example 1: After lacking titanium doping, the sample underwent high-temperature aging at 1200℃, and the specific surface area decreased from 180 m² / s². 2 / g plummeted to 140m 2 / g, and the pore volume also decreased significantly. This proves that the pre-introduction of metallic elements before the formation of pseudoboehmite plays an indispensable role in suppressing high-temperature phase transformation and stabilizing the material structure.

[0051] Comparative Example 1 and Comparative Example 2: Without aminopropylsilazane, a key interfacial anchoring agent, the high-temperature stability of the samples deteriorated significantly, with the specific surface area reduced to only 120 m² after aging. 2 / g. This indicates that introducing the first silicon protective layer through chemical bonding during particle growth is one of the core steps to achieve high stability.

[0052] Comparative Example 1 and Comparative Example 3: In the absence of the highly efficient dispersant hydroxylated quaternary ammonium base, even with the subsequent addition of sodium silicate, the performance of the samples after aging deteriorated significantly, with the specific surface area decreasing to 115 m². 2 / g, with particularly severe pore volume loss. This fully demonstrates that the addition of hydroxylated quaternary ammonium base ensures the uniform and effective formation of the second silicon protective shell, thereby producing a synergistic effect with the first two modification steps.

[0053] Comparative Example 1 with Comparative Examples 4 and 5: When titanium metal, aminopropylsilazane, hydroxylated quaternary ammonium base and sodium silicate are added to the reaction system simultaneously (i.e., without staged addition); or when titanium metal, aminopropylsilazane, hydroxylated quaternary ammonium base and sodium silicate are added to the reaction system in a different order than that specified in Example 1 (i.e., not in a specific order), the overall performance of the prepared sample will decrease significantly.

[0054] In summary, the "four-in-one" in-situ modification method proposed in this invention, which introduces titanium, aminopropylsilazane, hydroxylated quaternary ammonium base and sodium silicate in stages and in a specific order, has each step that is interconnected and indispensable. Through synergistic effect, it endows alumina with unexpectedly excellent high-temperature thermal stability and solves the problems in the prior art.

[0055] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for synthesizing modified alumina, characterized in that, Includes the following steps: S1. Dissolve the organometallic compound in an alcohol solution to obtain solution 1. Add solution 1 to an aqueous aluminum sulfate solution, then add an aqueous sodium aluminate solution and carry out a neutralization reaction in parallel flow. During the neutralization reaction in parallel flow, add aminopropylsilazane. After the reaction is completed, a pseudoboehmite slurry is obtained. S2. Add hydroxylated quaternary ammonium base to the pseudoboehmite slurry and stir. Then, add sodium silicate under stirring to carry out the doping reaction. After the doping reaction is completed, filter, wash, and spray dry to obtain modified pseudoboehmite powder. S3. Modified alumina is obtained by calcining the modified boehmite powder. The organometallic compound in S1 is tetrabutyl titanate.

2. The method for synthesizing modified alumina according to claim 1, characterized in that, The alcohol solution in S1 is at least one of ethanol, ethylene glycol, n-butanol, isopropanol, and tert-butanol.

3. The method for synthesizing modified alumina according to claim 1, characterized in that, The neutralization reaction temperature in S1 is 62-85℃, the reaction time is 30-50 min, and the pH is 7-9.

4. The method for synthesizing modified alumina according to claim 1, characterized in that, The concentration of aluminum sulfate, calculated as aluminum oxide, is 70-130 g / L.

5. The method for synthesizing modified alumina according to claim 1, characterized in that, The concentration of sodium aluminate in S1, calculated as alumina, is 80-200 g / L.

6. The method for synthesizing modified alumina according to claim 1, characterized in that, The mass ratio of organometallic compound, alcohol solution, aluminum sulfate aqueous solution, and aminopropylsilazane in S1 is (0.01-0.03):(0.08-0.15):1:(0.02-0.05).

7. The method for synthesizing modified alumina according to claim 1, characterized in that, The hydroxylated quaternary ammonium base in S2 is 2-hydroxyethyltrimethylammonium hydroxide or hydroxypropyltrimethylammonium hydroxide.

8. The method for synthesizing modified alumina according to claim 1, characterized in that, The mass ratio of hydroxylated quaternary ammonium base, sodium silicate, and pseudoboehmite slurry in S2 is (0.009-0.04):(0.01-0.04):

1.

9. The method for synthesizing modified alumina according to claim 1, characterized in that, The roasting temperature in S3 is 500-800℃, and the roasting time is 3-5h.

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