Bimodal pore size distribution alumina, its preparation methods and applications

Abstract

This invention relates to the field of bimodal pore size distribution alumina preparation, and discloses a bimodal pore size distribution alumina, its preparation method, and its application. A method for preparing bimodal pore size distribution alumina includes the following steps: (1) hydrolyzing an alcohol solution containing aluminum alkoxy, and then removing at least a portion of the alcohol from the hydrolysis product to obtain an aluminum hydroxide slurry, wherein the molar ratio of alcohol to aluminum in the aluminum hydroxide slurry is 0.5-2.5; (2) dynamically aging the aluminum hydroxide slurry obtained in step (1), and then calcining it to obtain alumina; wherein the stirring rate of the dynamic aging is 300-800 rpm. The preparation method of bimodal pore size distribution alumina provided by this invention is simple, does not require additional pore-expanding agents or other additives, avoids the risk of introducing impurities into the product, and can obtain high-purity alumina.

Description

Technical Field

[0001] This invention relates to the field of bimodal pore size distribution alumina preparation, specifically to a bimodal pore size distribution alumina, its preparation method, and its application. Background Technology

[0002] Alumina materials, as catalyst supports, provide channels for mass transfer between reactants and products through their pores, while also offering binding sites for active centers. Large pore sizes in alumina materials facilitate rapid diffusion of reactant and product molecules, improving the utilization rate of active sites and inhibiting surface coking. Alumina supports with a hierarchical (bimodal or multimodal) pore size distribution can accommodate the diffusion requirements of molecules of different sizes in catalytic reactions, while maintaining a high specific surface area through the presence of small pores, which is beneficial for the dispersion of active metals. Clearly, alumina materials with a bimodal pore size distribution, as catalyst supports, can satisfy all the above advantages and promote advancements in catalyst technology in fields such as catalytic cracking, reforming, and hydrogenation.

[0003] The alkoxyaluminum hydrolysis method uses metallic aluminum and fatty alcohols as raw materials. Besides yielding high-purity alumina, it also allows for the adjustment of the alumina's pore structure by controlling the technical parameters of the preparation process. However, a series of studies have revealed that, without the addition of additives, it is difficult to achieve a bimodal pore size distribution in alumina products using traditional methods.

[0004] US3898322A proposes adjusting the pH of the aqueous solution during the hydrolysis step by adding ammonia or other organic and inorganic acids, and adding a certain amount of organic solvent (such as acetone), followed by aging at room temperature for at least 24 hours to obtain alumina with a bimodal pore size distribution. The most probable pore diameter reaches 25-80 nm, and macropores larger than 10 nm account for approximately 65-75% of the total volume. However, this method is time-consuming, and the introduced additives may introduce impurities into the product, affecting its purity.

[0005] CN104338562A discloses a bimodal porous alumina carrier and its preparation method. The method involves mixing hydrated alumina (PA and PB) containing boehmite with a modified alumina (PC) containing boehmite, molding, drying, and calcining. The resulting alumina has pores with diameters of 5-20 nm accounting for 30-60% of the total pore volume, and pores with diameters of 100-300 nm accounting for 15-45% of the total pore volume. However, this method is complex, has stringent requirements on the properties of the mixed raw materials, and the introduction of the modified material may introduce impurities into the product, affecting its purity.

[0006] CN102030351A discloses a macroporous alumina with a bimodal pore distribution and its preparation method. This alumina is prepared using a two-stage aging method, eliminating the need for pore-expanding agents and organic solvents, thus saving raw materials, simplifying the process, and significantly reducing production costs. In the obtained alumina, pores of 3.5-10 nm account for 20-55% of the total pore volume, with the most probable pore size located at 5-9 nm; pores of 20-80 nm account for 20-55% of the total pore volume, with the most probable pore size located at 30-60 nm. This method avoids the risk of introducing impurities into the product through the addition of additives; however, the two-stage aging operation is relatively complex, and the pH requirements for the aging slurry are quite stringent.

[0007] Therefore, there is an urgent need to develop a simple method to obtain high-purity alumina with a bimodal pore size distribution. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems existing in the prior art and provide a bimodal pore size distribution alumina, its preparation method, and its applications. The preparation method of bimodal pore size distribution alumina provided by this invention is simple, does not require the addition of pore-expanding agents or other additives, avoids the risk of introducing impurities into the product, and can obtain high-purity alumina.

[0009] To achieve the above objectives, the present invention provides a method for preparing alumina with a bimodal pore size distribution, the method comprising the following steps:

[0010] (1) Hydrolyze an alcohol solution containing aluminum alkoxy and then remove at least part of the alcohol from the hydrolysis product to obtain an aluminum hydroxide slurry, wherein the molar ratio of alcohol to aluminum in the aluminum hydroxide slurry is 0.5-2.5;

[0011] (2) The aluminum hydroxide slurry obtained in step (1) is subjected to dynamic aging and then calcined to obtain aluminum oxide;

[0012] The stirring rate for dynamic aging is 300-800 rpm.

[0013] A second aspect of the present invention provides an alumina prepared by the method described in the first aspect.

[0014] A third aspect of the present invention provides the application of the alumina described in the second aspect in the preparation of catalysts.

[0015] The beneficial effects of the present invention through the above technical solution include:

[0016] The preparation method of bimodal pore size distribution alumina provided by this invention is simple, does not require the addition of pore expanders or other additives, avoids the risk of introducing impurities into the product, and can obtain high-purity alumina suitable for a wide range of applications. Detailed Implementation

[0017] The endpoints and any values ​​of the ranges disclosed herein 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.

[0018] This invention provides a method for preparing alumina with a bimodal pore size distribution, the method comprising the following steps:

[0019] (1) Hydrolyze an alcohol solution containing aluminum alkoxy and then remove at least part of the alcohol from the hydrolysis product to obtain an aluminum hydroxide slurry, wherein the molar ratio of alcohol to aluminum in the aluminum hydroxide slurry is 0.5-2.5;

[0020] (2) The aluminum hydroxide slurry obtained in step (1) is subjected to dynamic aging and then calcined to obtain aluminum oxide;

[0021] The stirring rate for dynamic aging is 300-800 rpm.

[0022] The molar ratio of alcohol to aluminum in the aluminum hydroxide slurry of this invention is 0.5-2.5, preferably 0.5-1, for example 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, and any value within any range formed by any two of these values. This preferred embodiment is advantageous for obtaining alumina with a bimodal pore size distribution as described in this application, and also facilitates alcohol recovery.

[0023] The present invention does not impose a particular limitation on the solid content of the aluminum hydroxide slurry, and any conventional selection in the art is acceptable. Preferably, the solid content of the aluminum hydroxide slurry is 5-20 wt%.

[0024] The present invention does not have any particular limitation on the method of removing part of the alcohol in step (1). Conventional technical means in the art can be used as long as the alcohol can be separated from the system. The present invention does not limit this.

[0025] In this invention, the stirring rate for dynamic aging is 300-800 rpm, preferably 300-500 rpm, such as 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, 700 rpm, 750 rpm, 800 rpm, and any value within any range formed by any two of these values. This preferred embodiment is advantageous for obtaining alumina with a bimodal pore size distribution as described in this invention. When the stirring rate for dynamic aging is lower than this range, the alumina may not achieve a certain pore volume and macropore ratio, or even necessarily a bimodal pore size distribution; when the stirring rate for dynamic aging is higher than this range, the effect of increasing pore volume and macropore ratio is no longer significant, and energy consumption is high.

[0026] The dynamic aging conditions described in this invention can be performed using conventional methods in the art. Preferably, the dynamic aging conditions include: a temperature of 90-150℃, more preferably 90-120℃, such as 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, and any value within any range formed by any two of these values; and a time of 6-48h, more preferably 6-24h, such as 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h, 42h, 44h, 46h, 48h, and any value within any range formed by any two of these values. This preferred embodiment is more conducive to obtaining alumina with a bimodal pore size distribution and pore volume as described in this invention.

[0027] This invention does not impose any particular limitation on how to achieve dynamic aging; conventional techniques in the field can be used.

[0028] According to the present invention, preferably, the alkoxy-aluminum-containing alcohol solution in step (1) is prepared by reacting elemental aluminum with an alcohol.

[0029] This invention does not impose any particular limitation on the amount of each substance used, and can be carried out with reference to conventional methods in the art. Preferably, the molar ratio of elemental aluminum to alcohol is 1:3.2-4, more preferably 1:3.6-4. This preferred embodiment is beneficial for the complete reaction of elemental aluminum.

[0030] The present invention allows for a wide range of choices of alcohols, which can be conventional choices in the art. Preferably, the alcohol is a C2-C6 alcohol, such as ethanol, n-propanol, isopropanol, n-butanol, n-pentanol, isopentanol, n-hexanol, isohexanol, etc., and more preferably a C4-C6 alcohol.

[0031] The present invention allows for a wide range of choices of the aluminum element, which can be conventional choices in the art. Preferably, the aluminum element is selected from at least one of aluminum ingots, aluminum beads, aluminum foil, aluminum shavings, and aluminum wire.

[0032] Preferably, the purity of the elemental aluminum is not less than 99.9 wt%.

[0033] The present invention does not impose particular limitations on the reaction conditions, and can be carried out with reference to conventional methods in the art. Preferably, the reaction temperature is 20°C below the boiling point of the alcohol to the boiling point of the alcohol.

[0034] The present invention does not impose any particular limitation on the conditions for hydrolysis, and can be carried out with reference to conventional methods in the art. Preferably, the hydrolysis temperature in step (1) is 90-110°C.

[0035] The present invention does not impose any particular limitation on the amount of water used, and can be carried out with reference to conventional methods in the art. Preferably, the mass ratio of the alkoxyaluminum alcohol solution to water is 1:1.4-2.5.

[0036] The present invention does not particularly limit the calcination conditions in step (2), and can refer to conventional methods in the art. Preferably, the calcination conditions in step (2) include: a temperature of 450-600℃ and a time of 4-8 hours. The calcination is generally carried out in an air atmosphere, which may include a flowing atmosphere or a stationary atmosphere.

[0037] Preferably, the method further includes drying the aging product obtained in step (2) before calcining it.

[0038] The present invention does not impose any particular limitation on the drying conditions, and conventional methods in the art can be used, which will not be elaborated upon here.

[0039] According to the present invention, preferably, the alumina has a bimodal pore size distribution, the alumina includes micropores and macropores, the most probable pore diameter of the micropores is 5-12 nm, and the most probable pore diameter of the macropores is not less than 15 nm, preferably 15-40 nm.

[0040] According to the present invention, preferably, the pore volume of pores of 10 nm and above accounts for more than 40% of the total pore volume, and more preferably 60-85%.

[0041] A second aspect of the present invention provides an alumina prepared by the method described in the first aspect.

[0042] According to the present invention, preferably, the alumina has a bimodal pore size distribution, the alumina includes micropores and macropores, the most probable pore diameter of the micropores is 5-12 nm, and the most probable pore diameter of the macropores is not less than 15 nm, preferably 15-40 nm.

[0043] According to the present invention, preferably, the pore volume of pores of 10 nm and above accounts for more than 40% of the total pore volume, and more preferably 60-85%.

[0044] According to the present invention, preferably, the pore volume of the alumina is not less than 0.55 cm³. 3 / g, preferably 0.55-0.8cm 3 / g.

[0045] A third aspect of the present invention provides the application of the alumina described in the second aspect in the preparation of catalysts.

[0046] The alumina with a bimodal pore size distribution and a specific pore distribution described in this invention not only facilitates the rapid diffusion of reactant and product molecules of different sizes in catalytic reactions, but also improves the utilization rate of active sites, thereby enhancing the activity of catalysts prepared using the alumina described in this invention.

[0047] The present invention will be described in detail below through embodiments.

[0048] In the following embodiments, parameters such as pore volume, specific surface area, most probable pore diameter, and the proportion of pore volume of 10 nm and above to the total pore volume were measured using an Auto-sorb-6B six-station fully automated specific surface area and porosity analyzer manufactured by CANTA Corporation, USA. The specific surface area of ​​the sample was calculated using the BET equation, and the volume of N2 adsorbed by the sample at a relative pressure p / p0 = 0.98 was measured and converted to liquid nitrogen volume, which is the pore volume.

[0049] Example 1

[0050] 0.5 mol of aluminum shavings with a purity of 99.996% by mass and 1.8 mol of n-hexanol were added to the reaction vessel as raw materials. The temperature was raised to 140℃ to initiate the reaction. The temperature was controlled at 145℃ for 60 minutes to allow the aluminum shavings to react completely to form a n-hexanol solution of aluminum hexoxy.

[0051] A solution of 197 g of aluminum hexoxy in n-hexanol was added to 300 mL of deionized water and hydrolyzed at 90 °C. Then, a portion of the alcohol was separated from the system, resulting in an aluminum hydroxide slurry with n... 醇 / n Al=1, with a solid content of 7wt%. The aluminum hydroxide slurry was transferred to a closed aging vessel equipped with mechanical stirring for aging under the following conditions: temperature 120℃, time 20h, and stirring speed 300rpm. The aged product was dried at 120℃ for 12h and then calcined at 550℃ for 6h to obtain alumina with a bimodal pore size distribution. The relevant physicochemical properties of the alumina are shown in Table 1.

[0052] Example 2

[0053] 0.5 mol of aluminum shavings with a purity of 99.996% by mass and 1.8 mol of n-hexanol were added to the reaction vessel as raw materials. The temperature was raised to 140℃ to initiate the reaction. The temperature was controlled at 145℃ for 60 minutes to allow the aluminum shavings to react completely to form a n-hexanol solution of aluminum hexoxy.

[0054] A solution of 197 g of aluminum hexoxy in n-hexanol was added to 300 mL of deionized water and hydrolyzed at 90 °C. Then, a portion of the alcohol was separated from the system, resulting in an aluminum hydroxide slurry with n... 醇 / n Al =0.8, with a solid content of 7.2 wt%. The aluminum hydroxide slurry was transferred to a closed aging vessel equipped with mechanical stirring for aging under the following conditions: temperature 100℃, time 12 h, and stirring speed 500 rpm. The aged product was dried at 120℃ for 12 h and then calcined at 550℃ for 6 h to obtain alumina with a bimodal pore size distribution. The physicochemical properties of the alumina are shown in Table 1.

[0055] Example 3

[0056] 0.5 mol of aluminum shavings with a purity of 99.996% by mass and 1.8 mol of n-butanol were added to the reaction vessel as raw materials. The temperature was raised to 110°C to initiate the reaction. The temperature was controlled at 115°C for 60 minutes to allow the aluminum shavings to react completely to generate a n-butoxyaluminum n-butanol solution.

[0057] A solution of 147 g of aluminum butoxygenate in n-butanol was added to 300 mL of deionized water and hydrolyzed at 90 °C. Then, a portion of the alcohol was separated from the system, resulting in an aluminum hydroxide slurry with n... 醇 / n Al =0.5, with a solid content of 7.6 wt%. The aluminum hydroxide slurry was transferred to a closed aging vessel equipped with mechanical stirring for aging under the following conditions: temperature 120℃, time 20 h, and stirring speed 500 rpm. The aged product was dried at 120℃ for 12 h and then calcined at 550℃ for 6 h to obtain alumina with a bimodal pore size distribution. The relevant physicochemical properties of the alumina are shown in Table 1.

[0058] Example 4

[0059] The method of Example 1 was followed, except that the aging temperature was changed to 150°C and the aging time was changed to 12 hours, resulting in alumina with a bimodal pore size distribution. The relevant physicochemical properties of the alumina are shown in Table 1.

[0060] Comparative Example 1

[0061] The method of Example 1 was followed, except that instead of dynamic aging, static aging was used to obtain alumina with a bimodal pore size distribution. The relevant physicochemical properties of the alumina product are shown in Table 1.

[0062] Comparative Example 2

[0063] The method described in Example 1 was followed, except that instead of dynamic aging, static aging was used at a temperature of 90°C for 6 hours to obtain alumina with a bimodal pore size distribution. The relevant physicochemical properties of the alumina product are shown in Table 1.

[0064] Comparative Example 3

[0065] The method was carried out according to Example 1, except that a portion of the alcohol in the system was separated, resulting in n in the aluminum hydroxide slurry. 醇 / n Al =0.3. The relevant physicochemical properties of the alumina product are shown in Table 1.

[0066] Comparative Example 4

[0067] The method was carried out according to Example 1, except that the mechanical stirring rate was 200 rpm. The relevant physicochemical properties of the alumina product are shown in Table 1.

[0068] Table 1

[0069]

[0070] As shown in Table 1, the method described in this invention can produce alumina with bimodal pore size distribution and a specific pore distribution. The alumina of this invention not only facilitates the rapid diffusion of reactant and product molecules of different sizes in catalytic reactions, but also improves the utilization rate of active sites, thereby enhancing the activity of the catalyst prepared using the alumina of this invention.

[0071] In addition, the preparation method of bimodal pore size distribution alumina provided by the present invention is simple, does not require the addition of pore expanders or other additives, avoids the risk of introducing impurities into the product, and can obtain high-purity alumina.

[0072] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing alumina with a bimodal pore size distribution, the method comprising the following steps: (1) Hydrolyze an alcoholic solution containing aluminum alkoxy and then remove at least part of the alcohol from the hydrolysis product to obtain an aluminum hydroxide slurry, wherein the molar ratio of alcohol to aluminum in the aluminum hydroxide slurry is 0.5-2.5; (2) The aluminum hydroxide slurry obtained in step (1) is subjected to dynamic aging and then calcined to obtain aluminum oxide; The stirring rate for the dynamic aging process is 300-800 rpm. The conditions for dynamic aging include a temperature of 90-150℃. The alumina prepared by the method has a bimodal pore size distribution. The alumina includes micropores and macropores. The most probable pore diameter of the micropores is 5-12 nm, and the most probable pore diameter of the macropores is not less than 15 nm. In the alumina prepared by the method described above, the pore volume of pores with a diameter of 10 nm or larger accounts for more than 40% of the total pore volume.

2. The preparation method according to claim 1, wherein, The molar ratio of alcohol to aluminum in aluminum hydroxide slurry is 0.5-1.

3. The preparation method according to claim 1, wherein, The solid content of the aluminum hydroxide slurry is 5-20 wt%.

4. The preparation method according to claim 1, wherein, The stirring rate for dynamic aging is 300-500 rpm.

5. The preparation method according to claim 1, wherein, The conditions for dynamic aging include: a temperature of 90-150℃ and a time of 6-48h.

6. The preparation method according to claim 5, wherein, The conditions for dynamic aging include: a temperature of 90-120℃ and a time of 6-24h.

7. The preparation method according to any one of claims 1-6, wherein, The alkoxy-containing aluminum alcohol solution in step (1) is prepared by reacting elemental aluminum with an alcohol.

8. The preparation method according to claim 7, wherein, The molar ratio of elemental aluminum to alcohol is 1:3.2-4; The alcohol is a C4-C6 alcohol.

9. The preparation method according to claim 7, wherein, The reaction temperature is 20°C below the alcohol boiling point to the alcohol boiling point.

10. The preparation method according to any one of claims 1-6, wherein, The hydrolysis temperature in step (1) is 90-110℃; The mass ratio of the alkoxy-aluminum alcohol solution to water is 1:1.4-2.

5.

11. The preparation method according to any one of claims 1-6, wherein, The roasting conditions in step (2) include: a temperature of 450-600℃ and a time of 4-8h.

12. The preparation method according to any one of claims 1-6, wherein, In the alumina prepared by the method described above, the pore volume of pores with a diameter of 10 nm or larger accounts for 60-85% of the total pore volume.

13. An alumina prepared by the method of any one of claims 1-12.

14. The alumina according to claim 13, wherein, The pore volume of the alumina is not less than 0.55 cm³. 3 / g.

15. The alumina according to claim 14, wherein, The alumina has a pore volume of 0.55-0.8 cm³. 3 / g.

16. The use of alumina according to any one of claims 13-15 in the preparation of a catalyst.

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