Preparation method of low-silicon-doped pseudo-boehmite and aluminum oxide

Abstract

The invention relates to a method for preparing a high-purity thermally stable catalyst carrier, which is based on C3-C6 aluminum alkoxide hydrolysate and aluminosilicate, the content of SiO2 is 0.5-11% by weight, and the method comprises the following steps: preparing a pseudo-boehmite filter cake by using aluminum alkoxide hydrolysis, and then carrying out tetraethoxysilane hydrolysis to obtain a silicon-deposited silicon-aluminum compound. And carrying out heat treatment and separation on the silicon-aluminum compound, and finally drying or calcining to obtain the low-silicon-doped pseudo-boehmite and aluminum oxide. The invention aims to prepare pseudo-boehmite with low silicon content and aluminum oxide, and the pore structure property and stability of the pseudo-boehmite are adjusted by adding silicon without changing the original crystal phase. According to the method, estersil is added for deposition and heat treatment before high-purity pseudo-boehmite is dried, only silicon and alcohol are introduced in the process, no impurities are introduced, and the obtained catalyst carrier is adjustable in pore structure and specific surface and pure in crystalline phase. The preparation method is simple in process and good in product quality and can be widely applied to the field of catalysis.

Description

Technical Field

[0001] The invention belongs to a chemical production process, and in particular relates to a method for preparing low-silicon doped pseudo-boehmite and alumina. Background Art

[0002] The present invention relates to a method for preparing a high-purity, thermally stable catalyst carrier by mixing pseudo-boehmite with a silicate compound in an aqueous medium and then drying or calcining the obtained product. The SiO2 weight of the catalyst carrier is 0.5-10% silicon content.

[0003] According to the latest research results, the role of the support material for the active components is more important, because the support not only allows the fine distribution of the active components on the surface and achieves an ideal mass transfer through a specific pore structure, but also the SiO2 content and acidity have a synergistic effect with the catalytic active substances as a function of the pore size. For the use of catalyst supports such as desulfurization, denitrification, alkane oxidative dehydrogenation, hydrocracking and various isomerization reactions, the support material with alumina crystal structure is more preferred than zeolite. It is necessary to adjust the aluminum silicon compound accordingly according to the specific surface area and pore volume using the SiO2 content. Silica doping can change the pore structure of alumina, stabilize the oxygen lattice of γ-Al2O3, and delay the formation of α-Al2O3. The study of thermal stability and hydrothermal stability not only shows the applicability of Si-doped pseudo-boehmite in catalytic reactions in the presence of high temperature steam, but also helps to better understand the structural characteristics of these aluminas with improved thermal stability.

[0004] CN201710945388.6 uses an alcohol-water mixture to hydrolyze organic alcohol aluminum, and the product is filtered and hydrolyzed, then dried and calcined to obtain a macroporous-mesoporous aluminosilicate catalyst carrier, which improves the flow and diffusion performance of the material and effectively prevents catalyst blockage and poisoning during the reaction. The disadvantage is that alcohol needs to be added to assist hydrolysis, which increases the post-processing steps and safety.

[0005] CN201710945334.X replaces alcohol water with acetonitrile aqueous solution, realizes the construction of hierarchical pore three-dimensional mesoporous structure in the aluminosilicate catalyst carrier, improves the flow and diffusion performance of the material, and effectively prevents the catalyst from clogging and poisoning during the reaction. This method requires the addition of organic solvents to assist hydrolysis, which increases the post-processing steps and safety Summary of the invention

[0006] A method for preparing low-silicon doped pseudo-boehmite and alumina is based on C3-C6 alcohol aluminum hydrolyzate plus silicoaluminosilicate, with SiO2 content of 0.5-11% by weight, and the steps include: preparing pseudo-boehmite filter cake by alcohol aluminum hydrolysis, and then hydrolyzing ethyl orthosilicate to obtain silicon-deposited silicon-aluminum composite. Then the silicon-aluminum composite is heat-treated and separated, and finally dried or calcined to obtain low-silicon doped pseudo-boehmite and alumina. The purpose of the present invention is to prepare a pseudo-boehmite and alumina with low silicon content, and adjust the pore structure properties and stability of the pseudo-boehmite by adding silicon, while not changing the original crystal phase. The method is to add silicon ester to deposit and heat-treat the high-purity pseudo-boehmite before drying, and only silicon and alcohol are introduced in the process, and no other impurities are introduced. The pore structure and specific surface of the obtained catalyst carrier are adjustable, and the crystal phase is pure. The preparation method is simple in process, good in product quality, and can be widely used in the field of catalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1-5 The XRD of silicon-doped pseudo-boehmite prepared in Example 1-5 is shown.

[0008] Figure 6-10 The XRD of silicon-doped aluminum alumina prepared in Example 1-5. DETAILED DESCRIPTION

[0009] Embodiment 1: First, add 20g of aluminum n-hexyl alcohol into a four-necked flask and heat it to 85°C, add 20g of water, hydrolyze for 1h, add 10g of n-hexanol, hydrolyze for 3h, separate the alcohol and water at 100°C to obtain a white slurry, filter, add the filter cake into a flask, add 20g of water, heat it to 85°C, dropwise add an ethanol solution of orthosilicate, the mass ratio of ethyl orthosilicate to ethanol is 1:10, add 0.5g of ethyl orthosilicate, continue to hydrolyze for 4h, and obtain a white sol; heat treat at 100°C for 2h, filter the mixture, put the gel material into an oven at a temperature of 110°C and dry it for 8h to obtain a silicon-aluminum pseudo-boehmite powder; heat the powder in a muffle furnace for 3h to 550°C and maintain calcination for 3h to obtain a silicon-doped alumina finished product.

[0010] Embodiment 2: First, add 20g of n-hexyl aluminum into a four-necked flask, add 20g of water at a water bath temperature of 80°C, hydrolyze for 1h, add 10g of n-hexanol, and hydrolyze for 3h. Perform alcohol-water separation at 105°C to obtain a white slurry. After filtration, add the filter cake into the flask, add 20g of water, heat up to 80°C, dropwise add an alcohol solution of orthosilicate, add ethyl orthosilicate in a mass ratio of 1:10 to ethanol, add 1.2g of ethyl orthosilicate, and continue to hydrolyze for 4h to obtain a white sol; heat treat at 100°C for 3h, sol, filter, and place the gel material in an oven at a temperature of 110°C for drying for 8h to obtain a silicon-aluminum composite powder; heat the powder in a muffle furnace for 3h to 550°C and maintain calcination for 3h to obtain a silicon-doped alumina finished product.

[0011] Embodiment 3: First, add 20g of n-hexanol aluminum into a four-necked flask at a water bath temperature of 75°C, add 20g of water, and after 1h of relieving, add 10g of n-hexanol, and then hydrolyze for 3h. Perform alcohol-water separation at 100°C to obtain a white slurry. After filtration, add the filter cake to the flask, add 20g of water, raise the temperature to 75°C, dropwise add an alcohol solution of orthosilicate, and add ethyl orthosilicate to ethanol in a mass ratio of 1:10. Add 1.2g of ethyl orthosilicate, and continue to hydrolyze for 4h to obtain a white sol; heat treat at 100°C for 3h, filter, and place the gel material in an oven at a temperature of 110°C for drying for 8h to obtain a silicon-aluminum composite powder; raise the temperature of the powder in a muffle furnace for 3h to 550°C and maintain calcination for 3h to obtain a silicon-doped alumina finished product.

[0012] Embodiment 4: First, 20g of aluminum n-hexyl alcohol was added to a four-necked flask, the water bath temperature was 90°C, 20g of water was added, 10g of n-hexanol was added after hydrolysis for 1h, and then hydrolysis was carried out for 3h. Alcohol-water separation was carried out at 100°C to obtain a white slurry. After filtration, the filter cake was added to the flask, 20g of water was added, the temperature was raised to 90°C, and an orthosilicate alcohol solution was added dropwise. The mass ratio of ethyl orthosilicate to ethanol was 1:10. 1.2g of ethyl orthosilicate was added, and hydrolysis was continued for 4h to obtain a white sol. The sol was heat treated at 100°C for 3h, filtered, and the gel material was placed in an oven at a temperature of 110°C for drying for 8h to obtain a silicon-aluminum composite powder; the powder was heated in a muffle furnace for 3h to 550°C and maintained for calcination for 3h to obtain a silicon-doped alumina finished product.

[0013] Embodiment 5: First, 20g of n-hexyl aluminum was added to a four-necked flask, the water bath temperature was 95°C, 20g of water was added, 10g of n-hexanol was added after hydrolysis for 1h, and then hydrolysis was carried out for 3h. Alcohol-water separation was carried out at 100°C to obtain a white slurry. After filtration, the filter cake was added to the flask, 20g of water was added, the temperature was raised to 95°C, and an orthosilicate alcohol solution was added dropwise, the mass ratio of ethyl orthosilicate to ethanol was 1:10, 1.2g of ethyl orthosilicate was added, and hydrolysis was continued for 4h to obtain a white sol; heat treatment was carried out at 100°C for 3h, filtered, and the gel material was placed in an oven at a temperature of 110°C for drying for 8h to obtain a silicon-aluminum composite powder; the powder was heated in a muffle furnace for 3h to 550°C and maintained for calcination for 3h to obtain a silicon-doped alumina finished product.

[0014] Table 1 Sample pore structure data

[0015]

Claims

1. A method for preparing a high-purity, thermally stable catalyst support based on a C3-C6 alcohol aluminum hydrolyzate plus a silicate, wherein the SiO2 content is 0.5-11% by weight, comprising the following steps: The first step is to hydrolyze aluminum alcohol to prepare pseudo-boehmite filter cake, and then ethyl orthosilicate is deposited to obtain a silicon-deposited silicon-aluminum composite. In the second step, the silicon-aluminum composite is heat-treated at a temperature of 90-130° C. for 2-24 hours. After separating the alcohol and water, the solid is dried or calcined.

2. The method according to claim 1, characterized in that When hydrolyzing C3-C6 aluminum alkoxide, C6 aluminum alkoxide is preferred.

3. The method according to claim 1, characterized in that When hydrolyzing C3-C6 aluminum alcohol, the water used is high-purity water, the hydrolysis is carried out during stirring, the hydrolysis temperature is 80-95° C., and the hydrolysis time is 0.5-4h.

4. The method according to claim 1, characterized in that The mixture obtained after hydrolysis is subjected to alcohol-water separation at a separation temperature of 70-110°C.

5. The method according to claim 1, characterized in that The slurry after separation of alcohol and water is filtered to obtain a filter cake.

6. The method according to claim 1, characterized in that The temperature of adding ethyl orthosilicate ethanol solution is 80-95°C, and the deposition time is 0.5-4h.

7. The method according to claim 1, characterized in that After separation, the solid is dried at 110-120°C for 6-8 hours, calcined at 550-600°C for 4-7 hours.

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