Alumina carrier and preparation method thereof

Abstract

The invention discloses an alumina carrier and a preparation method thereof. The alumina carrier carbon provided by the invention is non-uniformly distributed in a carrier body phase, the content of a micron-sized pore channel micro-area C of the carrier body phase is 30-55 wt%, and the content of a non-micron-sized pore channel micro-area C is 1.5-6.5 wt%. The preparation method of the alumina carrier comprises the following steps: (1) uniformly mixing flour and an alkaline substance, performing grinding treatment, adding the ground material into an alumina precursor, performing uniform mixing, adding a proper amount of distilled water into the mixed material, performing mixing and kneading, and performing extrusion molding to obtain a molded body; and (2) heating the molded body in a closed container, drying the heated material, and roasting in an inert atmosphere to obtain the alumina carrier. The alumina carrier contains a certain amount of micron-sized pore channels, and the micron-sized pore channels are subjected to carbon modification treatment, so that the alumina carrier has more active sites and is suitable for catalyst carriers, adsorption-separation materials, energy storage materials and the like, the preparation process is simple, and industrial production is easy.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation, and specifically relates to an alumina carrier and its preparation method. Background Technology

[0002] Activated alumina, as a porous material, is widely used as a catalyst or support due to its excellent physicochemical properties. The pore structure of the support is a crucial factor determining the performance of hydrogenation catalysts; pore structure parameters such as specific surface area, pore size, and pore volume directly affect the catalyst's activity and lifespan.

[0003] Studies on alumina as a catalyst support have shown that it not only acts as an inert support but also promotes the formation of the active phase in hydrotreating catalysts. The strong interaction between Al₂O₃ and the active components is beneficial for the dispersion and stability of the active components during the reaction. However, the strong interaction between the strongly acidic sites on the Al₂O₃ surface and the active components often leads to the formation of nickel (or cobalt) aluminum spinel, which is difficult to sulfide and form a sulfide-state active phase, thus reducing catalytic activity. Therefore, to improve catalyst activity and efficiency, many studies have employed new materials as supports or modified alumina supports to improve the dispersion of the active phase and alter the interaction between the active phase and the support.

[0004] CN103055950A discloses a method for preparing spherical alumina. The method includes the following steps: mixing an aluminum source, polyethylene glycol, and at least one selected from low-carbon alcohols and water uniformly; adding low-carbon epoxy alkane to the mixture; molding the mixture into spheres using an oil column; and then aging, drying, and calcining to obtain macroporous alumina. The spherical alumina obtained by this method has a three-dimensional interconnected macroporous structure, with a pore size of 0.1-10.0 μm, a pore volume of 0.5-1.5 mL / g, and a specific surface area of ​​150-350 m². 2 / g. Although the alumina support prepared by this method has high pore volume and large macropore size, the preparation process is complex and costly. Moreover, the surface of the alumina support is not modified, which affects its activity.

[0005] CN114130380A discloses an alumina carrier molding method, the alumina carrier prepared therefrom, and its application. The alumina carrier molding process of this invention includes the following steps: (1) mixing alumina dry adhesive powder with starch and water, kneading and molding to obtain alumina wet strips; (2) heat-treating the alumina wet strips to obtain a gelatinized pore-expanding carrier; (3) drying and calcining the gelatinized pore-expanding carrier obtained in step (2) to obtain an alumina carrier. The alumina carrier prepared by this method has a small pore size, which is not conducive to the diffusion of macromolecular reactants, and also has the disadvantage of not modifying the surface of the alumina carrier.

[0006] CN114653351A discloses a method for preparing an alumina support, comprising the following steps: (1) mixing water, starch, and acid at 80-100℃ to obtain a colloid, then mixing the colloid, extrusion aid, and alumina precursor evenly, kneading, and extruding to obtain a molded product; (2) drying and calcining the molded product obtained in step (1) to obtain an alumina support. The alumina support prepared by the method of the present invention has a dual pore distribution of mesoporous and macroporous pores, with the macropore size distribution being 50-600 nm. Although the alumina support prepared by this method has macropores of 50-600 nm, the pore size will decrease due to metal and carbon deposition during the hydrogenation reaction, thereby affecting the diffusion of macromolecular reactants, and the surface of the alumina support is not modified in any way. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides an alumina support and its preparation method. The alumina support of this invention contains a certain amount of micron-sized pores, which are carbon-modified to have more active sites, making it suitable for use as a catalyst support, adsorption-separation material, energy storage material, etc. The preparation process is simple and easy for industrial production.

[0008] The alumina carrier of the present invention has the following properties: C content 5wt%-20wt%, Al2O3 content 80wt%-95wt%, and specific surface area 150-300m². 2 / g, pore volume 0.8-1.5mL / g, with 0.5-20μm micron-sized pores accounting for 20%-40% of the total pore volume.

[0009] The alumina carrier carbon of the present invention exhibits a non-uniform distribution in the carrier bulk phase. The carbon content in the micron-sized pore micro-regions of the carrier bulk phase is 30wt%-55wt%, while the carbon content in the non-micron-sized pore micro-regions is 1.5wt%-6.5wt%. Micron-sized pore micro-regions refer to regions with continuous through-holes larger than 0.5μm formed by particle packing, while non-micron-sized pore micro-regions refer to regions with tightly packed particles forming pores smaller than 200nm. Micron-sized and non-micron-sized pore micro-regions can be distinguished by observation using a scanning electron microscope.

[0010] The method for preparing the alumina support of the present invention includes the following steps: (1) Mix flour with alkaline substances evenly and grind to obtain pretreated powder. Then add the pretreated powder to the alumina precursor and mix evenly. Add an appropriate amount of distilled water to the mixture, knead, and extrude to form a molded body. (2) The molded body is placed in a sealed container for heat treatment. After heat treatment, the material is dried and calcined under an inert atmosphere to obtain an alumina carrier.

[0011] In the method of this invention, the flour mentioned in step (1) is wheat flour, wherein the protein content is 6%-20%, the starch content is 65%-75%, and the remainder consists of moisture, ash, enzymes, fat, and vitamins. It can be one or a mixture of high-gluten flour, medium-gluten flour, and low-gluten flour. In the method of the present invention, the alkaline substance in step (1) is one or more of LiOH, KOH and NaOH, and the mass ratio of the alkaline substance to flour is 2:100-10:100, preferably 4:100-8:100.

[0012] In the method of the present invention, the peak intensity of the XRD spectrum of the pretreated powder in step (1) at 2θ of 15º, 17º, 18º, and 23º is reduced by more than 60% compared with that of the flour raw material, preferably by 75%-90%. The average grain size D corresponding to the peak position at 2θ of 15º is 6.5-8.5 nm, where D=Kλ / (Bcosθ), K is the Scherrer constant, λ is the diffraction wavelength of the target material, B is the half-width of the diffraction peak, and θ is the diffraction angle. The grinding can be carried out using conventional grinding methods in the art, preferably in a ball mill, for a grinding time of 40-180 min, preferably 60-120 min.

[0013] In the method of the present invention, the alumina precursor in step (1) is a substance that can be transformed into γ-phase alumina after calcination, preferably boehmite, more preferably boehmite with a pore size of 10-30 nm, and the mass ratio of flour to alumina precursor is 10:100-30:100.

[0014] In the method of the present invention, the extrusion molding in step (1) can select the shape and size of the perforated plate as needed, and the shape of the molded body can be cylindrical strip, clover strip, four-leaf clover strip, etc., with a strip size of 0.1cm-0.5cm. The shape and size of the molded body are not limited to these.

[0015] In the method of the present invention, the sealed container in step (2) is preferably a sealed high-pressure autoclave, the volume of the molding material accounts for 30% to 70% of the total volume of the polytetrafluoroethylene liner of the high-pressure autoclave, the heating temperature is 40-90℃, and the heating time is 60-120min.

[0016] In the method of the present invention, the drying temperature in step (2) is 90-150℃ and the drying time is 1-4 hours.

[0017] In the method of the present invention, the inert atmosphere in step (2) is one or more of argon, helium or nitrogen, preferably nitrogen, and the calcination temperature is 500-900℃ and the calcination time is 4-8 hours.

[0018] This invention involves grinding a mixture of flour and an alkaline substance. During grinding, the alkaline substance is adsorbed onto the surface of starch granules through hydrogen bonding. Under the combined action of mechanical force and the alkaline substance, it promotes the breakage of starch molecular bonds, generating shorter molecular chains and branched structures, thus improving the swelling, viscosity, and toughness of the starch. The pretreated powder is then formed with an alumina precursor. When the wet material is directly placed in a sealed high-pressure container for heating, the starch granules undergo deep fracture under the influence of the sealed environment, moisture, alkaline substance, and suitable temperature. This process induces water absorption, swelling, and foaming reactions, forming a micron-sized porous precursor within the carrier. The enhanced swelling, viscosity, and toughness of the starch facilitate the formation and structural integrity of the micron-sized porous precursor. Simultaneously, proteins and fats in the flour undergo degradation reactions in this environment, forming a uniform and continuous network structure. The generated gas has a good perforating effect, increasing the mesoporous content of the carrier while ensuring the continuous interconnection of micron-sized channels. During calcination, the micron-sized porous precursor undergoes a carbonization reaction in its micro-regions, forming a large number of carbon-modified and interconnected micron-sized channels. The carbon content in the micron-sized pore microregions of this alumina support material is significantly higher than that in the non-micron-sized pore microregions. This unique physicochemical property of the pore structure facilitates mass transfer and diffusion of macromolecules. Furthermore, it reduces the acid content on the surface of the micron-sized pore microregions of the alumina support, thereby enhancing the resistance to carbon deposition and metal deposition in heavy residue oil hydrodemetallization catalysts prepared using this alumina as a support. Simultaneously, the abundant functional groups on the surface of the micron-sized pore microregion carbon material increase the number of active sites on the alumina support surface, broadening the application areas and enhancing the activity of this support material. The carbon-containing alumina support of this invention has a simple preparation process and is easy to industrialize. This material can be widely used as a catalyst support, adsorption-separation material, and energy storage material. Attached Figure Description

[0019] Figure 1 The image shows the XRD pattern of the flour raw material and pretreated powder from Example 1.

[0020] Figure 2 This is a SEM image of the sample prepared in Example 1.

[0021] Figure 3 This is a schematic diagram of different micro-regions of the carrier.

[0022] Figure 4 The image shows the SEM image of the sample prepared for Comparative Example 1. Detailed Implementation

[0023] The technical solution and effects of the present invention will be further illustrated below with reference to the embodiments, but the invention is not limited to the following embodiments. In the present invention, wt% represents mass fraction.

[0024] The macroporous content in the sample was determined according to standard NB / T 14008-2021.

[0025] The pore structure of the sample was characterized using a scanning electron microscope (SEM). The specific operation was as follows: The microstructure of the carrier was characterized using a JSM-7500F SEM with an accelerating voltage of 5 kV, an accelerating current of 20 µA, and a working distance of 8 mm.

[0026] Method for determining the carbon content of the carrier phase: The carbon content of the carrier phase was determined according to the HG / T5594-2019 standard using an EMIA-20E infrared carbon-sulfur analyzer.

[0027] Method for determining the carbon content in the carrier micro-regions: The carbon content in the carrier micro-regions was measured using SEM-EDS. During measurement, the carrier was cut into 1-2 mm pieces and adhered to the SEM stage, ensuring that the cross-section of the carrier was perpendicular to the electron beam of the SEM. During the measurement process, 20 micrometer-level pore micro-regions and 20 non-micrometer-level pore micro-regions were randomly selected from the carrier cross-section, and the carbon content of different micro-regions was measured. The average value was taken as the carbon content of different micro-regions. Example 1

[0028] (1) Weigh 30 g of medium-gluten wheat flour (protein content 8.8%, carbohydrate content 67.6%) and 2.1 g of sodium hydroxide. Mix the above materials evenly and grind the mixture in a grinder for 75 minutes. Then add 160 g of boehmite (pore size 17.5 nm) to the mixture and mix evenly. Add distilled water and knead the material into a plastic body. Extrude the plastic body into strips. The XRD patterns of the wheat flour raw material and the pretreated powder are shown in the figure. Figure 1 The average grain size D of the pretreated powder peak position 2θ is 15º, which corresponds to a grain size D of 6.9 nm. (2) Place the wet material from step (1) directly into the autoclave, with the material accounting for 50% of the volume of the autoclave's reaction liner. After the autoclave is sealed, heat it at 75°C for 90 minutes. After heating, dry the material at 120°C for 4 hours. (3) Place the dried material from step (2) into a tube furnace, introduce nitrogen into the tube furnace to completely replace the air in the furnace chamber, and calcine at 600°C for 6 hours under a nitrogen atmosphere to obtain alumina support S1. The properties of the support are shown in Table 1, and the scanning electron microscope image of the cross-section of the support is shown in Table 1. Figure 1 ,Depend on Figure 1 It is evident that abundant micron-sized interconnected channels are formed in the carrier. Example 2

[0029] Same as Example 1, except that in step (1), sodium hydroxide is replaced with potassium hydroxide, the amount of potassium hydroxide added is 1.8 g, the grinding time is 90 minutes, and the amount of boehmite added is 128 g. In step (2), the heating temperature is 60℃ and the heating time is 100 minutes. Alumina carrier S2 is obtained, and the properties of the carrier are shown in Table 1. Example 3

[0030] Same as Example 1, except that in step (1), the amount of sodium hydroxide added is 2.4 g, the grinding time is 65 minutes, and the amount of boehmite added is 240 g. In step (2), the heating temperature is 85℃ and the heating time is 75 minutes. Alumina support S3 was obtained, and the properties of the support are shown in Table 1. Example 4

[0031] Same as Example 1, except that in step (1), the amount of sodium hydroxide added is 1.5 g, the grinding time is 115 minutes, and the amount of boehmite added is 105 g. In step (2), the heating temperature is 45℃ and the heating time is 115 minutes. Alumina support S4 was obtained, and the properties of the support are shown in Table 1.

[0032] Comparative Example 1 Same as Example 1, except that in step (1), flour and boehmite are mixed, and then the same amount of alkaline substance is added in solution during molding to obtain alumina carrier S5. The properties of the carrier are shown in Table 1, and the scanning electron microscope image of the cross-section of the carrier is shown in Table 1. Figure 3 ,Depend on Figure 3 It is evident that no abundant micron-sized interconnected channels were formed in the carrier.

[0033] Comparative Example 2 Same as Example 1, except that the wet material after molding in step (2) was not placed in a sealed container for heating treatment, but was directly placed in an oven for forced air heating treatment to obtain alumina carrier S6. No abundant micron-level through channels were formed in the carrier. The properties of the carrier are shown in Table 1.

[0034] Comparative Example 3 Same as Example 1, except that in step (1) sodium hydroxide was replaced with the same amount of ammonium bicarbonate to prepare alumina support S7. No abundant micron-sized interconnected channels were formed in the support. The properties of the support are shown in Table 1.

[0035] Table 1 Properties of Carbon-Containing Alumina Carriers Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 carrier S1 S2 S3 S4 S5 S6 S7 C content, % 13.6 15.5 8.7 17.3 14.2 13.8 13.1 <![CDATA[Al2O3 content, %]]> 86.4 84.5 91.3 82.7 85.8 86.2 86.9 <![CDATA[Specific surface area, m 2 / g]]> 213 226 208 221 211 209 215 Pore ​​volume, mL / g 1.12 1.08 1.15 1.17 0.89 0.94 0.91 Content of 0.5-20μm pores, % 23.6 25.8 20.9 27.5 0.8 6.9 1.4 C content in micron-sized pore micro-regions, wt% 41.2 42.6 38.7 45.3 ─ ─ ─ C content in non-micron-sized pore micro-regions, wt% 2.6 3.7 1.8 4.2 ─ ─ ─ As can be seen from Table 1, the carbon-containing macroporous alumina support prepared by the method of this invention has a high content of 0.5-20 μm pores, and the carbon is non-uniformly distributed in the bulk phase of the support. Figure 1 It can be seen that the carrier material prepared by the present invention has good micron-level pore connectivity.

Claims

1. An alumina carrier, characterized in that... It has the following properties: carbon content 5wt%-20wt%, Al2O3 content 80wt%-95wt%, and micron-sized channels of 0.5-20μm accounting for 20%-40% of the total pore volume; carbon is non-uniformly distributed in the carrier phase, with the carbon content of the micron-sized channel micro-regions in the carrier phase being 30wt%-55wt%, and the carbon content of the non-micron-sized channel micro-regions being 1.5wt%-6.5wt%; the micron-sized channel micro-regions refer to the regions with continuous through-holes larger than 0.5μm formed by particle packing, and the non-micron-sized channel micro-regions refer to the regions with pores smaller than 200nm formed by densely packed particles.

2. The alumina carrier according to claim 1, characterized in that: Specific surface area 150-300m² 2 / g, pore volume 0.8-1.5mL / g.

3. A method for preparing the alumina carrier according to claim 1 or 2, characterized in that... The following contents are included: (1) Mix flour and alkaline substances evenly and grind them to obtain pretreated powder. Then add the pretreated powder to the alumina precursor and mix evenly. Add an appropriate amount of distilled water to the mixture and knead and extrude to form a molded body; (2) Place the molded body in a sealed container for heating treatment. After heating treatment, the material is dried and calcined under an inert atmosphere to obtain an alumina carrier.

4. The method according to claim 3, characterized in that: The flour mentioned in step (1) is wheat flour, with a protein content of 6%-20% and a starch content of 65%-75%.

5. The method according to claim 3, characterized in that: The alkaline substance mentioned in step (1) is one or more of LiOH, KOH, and NaOH, and the mass ratio of the alkaline substance to flour is 2:100-10:100, preferably 4:100-8:

100.

6. The method according to claim 3, characterized in that: The XRD pattern of the pretreated powder in step (1) shows that the peak intensity of the diffraction peaks at 2θ of 15º, 17º, 18º, and 23º is reduced by more than 60% compared with that of the flour raw material, preferably by 75%-90%. The average grain size D corresponding to the peak position at 2θ of 15º is 6.5-8.5 nm, where D=Kλ / (Bcosθ), K is the Scherrer constant, λ is the diffraction wavelength of the target material, B is the half-width of the diffraction peak, and θ is the diffraction angle.

7. The method according to claim 3, characterized in that: The grinding in step (1) is carried out in a ball mill for a grinding time of 40-180 min, preferably 60-120 min.

8. The method according to claim 3, characterized in that: The alumina precursor mentioned in step (1) is a substance that transforms into γ-phase alumina after calcination, preferably boehmite, more preferably boehmite with a pore size of 10-30 nm, and the mass ratio of flour to alumina precursor is 10:100-30:

100.

9. The method according to claim 3, characterized in that: The sealed container in step (2) is preferably a sealed high-pressure reactor. The volume of the molding material accounts for 30% to 70% of the total volume of the polytetrafluoroethylene liner of the high-pressure reactor. The heating temperature is 40-90℃ and the heating time is 60-120min.

10. The method according to claim 3, characterized in that: The drying temperature in step (2) is 90-150℃ and the drying time is 1-4 hours; the inert atmosphere in step (2) is one or more of argon, helium or nitrogen, preferably nitrogen; the calcination temperature is 500-900℃ and the calcination time is 4-8 hours.

11. The application of the alumina support as described in claim 1 or 2 in the fields of catalysis and adsorption.

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