A gradient pore distribution alumina carrier and a preparation method thereof

Abstract

The present application aims to provide a gradient pore distribution alumina carrier and a preparation method thereof, and belongs to the technical field of alumina material synthesis. After calcination of pseudo-boehmite, the present application immerses the pseudo-boehmite into an organic alkali solution twice for hydrothermal treatment. During the hydrothermal treatment, the alumina grains are rehydrated and secondarily grown to form elliptical flaky pseudo-boehmite with a morphology. The elliptical flaky particles are stacked to form a large number of macropore channels. During the shaping of the carrier, the content of the elliptical flaky pseudo-boehmite in the mixture is adjusted to prepare the alumina carrier with gradient distribution of the channels. The alumina carrier has a high content of macropores in the shell layer, and the channels are wide. The pore structure is beneficial to the diffusion of macromolecular reactants to the inside of the carrier, and at the same time, the surface of the carrier has a strong anti-clogging ability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of synthesis of alumina materials, and particularly relates to a gradient pore distribution alumina carrier and a preparation method thereof. BACKGROUND

[0002] Active alumina as a good hydrogenation catalytic carrier material has a wide application in the oil refining industry. At present, with the increasing seriousness of the heavy and poor quality of crude oil, oil refining enterprises are faced with the problem of processing and utilizing a large amount of heavy and residual oil. Heavy and residual oil molecules have a complex three-dimensional structure, and the sulfur-containing aromatic side chains often form steric hindrance. In the hydrogenation catalytic process, heavy oil macromolecules are adsorbed and deposited on the surface or pore of the catalyst, so that the internal diffusion resistance of the reaction is increased, and the apparent activity of the catalyst is decreased.

[0003] CN104646008A discloses a poor-quality heavy oil hydrodesulfurization and demetallization catalyst and a preparation method thereof. The catalyst takes alumina as a carrier, and takes group VIII and group ⅥB elements, especially Ni-Mo, as active components. The catalyst has a pore volume of 0.61-0.70 mL / g, a specific surface area of 155-200 m 2 / g, and an average pore diameter of 13.0-18.0 nm. The preparation method of the catalyst is to treat the carrier particles after molding and calcination with acid solutions with continuously increasing concentrations. This method can improve the pore structure of the catalyst surface and the inside to a certain extent, but due to the limited effect of the acid, it is difficult to form larger macropore channels on the catalyst surface.

[0004] CN110935461A discloses a preparation method of a heavy oil hydrodemetallization catalyst. The preparation process of the catalyst includes: (1) mixing and kneading a physical pore expander, pseudo-boehmite and active metal components to form a modified alumina carrier SⅠ, drying and calcining; (2) unsaturatedly spraying and impregnating SⅠ with a hydrogenation active component impregnation solution I, and then drying and calcining to obtain a modified alumina carrier SⅡ; (3) mixing SⅡ, ammonium bicarbonate and water, and then performing sealed heat treatment, and then drying and calcining the material after heat treatment to obtain a carrier SⅢ; (4) supersaturatedly impregnating the carrier SⅢ with a hydrogenation active component impregnation solution II, and then drying and calcining to obtain the catalyst. The catalyst prepared by the method has a rod-like structure on the surface, and the open channels formed by the rod-like particles are used to adjust the pore structure of the catalyst surface, but the firmness of the rod-like particles on the surface of the catalyst combined with the carrier needs to be improved. SUMMARY

[0005] The purpose of the present application is to provide a gradient pore distribution alumina carrier and a preparation method thereof. The alumina carrier has a "core-shell" structure of gradient distribution, and the "shell layer" has a higher content of 0.5-1 μm pores. The alumina carrier is suitable for the field of heavy and residual oil hydroprocessing with high impurity content.

[0006] The application adopts the technical scheme as follows:

[0007] A gradient pore distribution alumina carrier, the pore of the alumina carrier is in a core-shell structure, the thickness of the core layer is 0.5-0.8r, the thickness of the shell layer is 0.2-0.5r, wherein r is the radius of the alumina carrier, i.e. the straight-line distance from the center of the alumina carrier to the outer surface, the average pore diameter of the shell layer is 0.5-1μm, and the average pore diameter of the core layer is 10-30nm.

[0008] Further, the specific surface area of the alumina carrier is 150-260m 2 / g, the pore volume is 0.75-1.1mL / g, the content of the pore with a diameter of 10-30nm accounts for 35%-55% of the total pore volume, and the content of the pore with a diameter of 0.5-1μm accounts for 15%-40% of the total pore volume.

[0009] A preparation method of a gradient pore distribution alumina carrier, comprising the following steps:

[0010] In the first step, the pseudo-boehmite is subjected to calcination treatment, and then the calcined material is immersed in an organic alkali solution I for low-temperature hydrothermal treatment, and then the treated material is subjected to liquid-solid separation;

[0011] In the second step, the separated solid material in the first step is again immersed in an organic alkali solution II for high-temperature hydrothermal treatment, and then the treated material is subjected to liquid-solid separation, drying to obtain pseudo-boehmite P1;

[0012] In the third step, the pseudo-boehmite P1 is mixed with pseudo-boehmite P2, and the mixture is subjected to rolling ball forming to obtain an alumina carrier precursor S1;

[0013] In the fourth step, the pseudo-boehmite P1 is mixed with pseudo-boehmite P3, and then the alumina carrier precursor S1 is mixed with the mixture, and then the mixture is subjected to rolling ball forming, and then the formed material is subjected to drying and calcination to obtain an alumina carrier.

[0014] Further, the pseudo-boehmite in the first step can be prepared by an existing method or purchased, and preferably is pseudo-boehmite prepared by an aluminum sulfate-sodium metaaluminate method, and the calcination temperature is 450-650℃, and the calcination time is 4-8 hours.

[0015] Further, the organic alkali solution I in the first step comprises one of tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide, and preferably is tetraethylammonium hydroxide, and the mass concentration of the organic alkali in the organic alkali solution I is 0.8%-2.0%.

[0016] Further, the low-temperature hydrothermal treatment in the first step is a sealed hydrothermal treatment in a high-pressure reaction kettle, the low-temperature hydrothermal treatment temperature is 80-120℃, and the treatment time is 1-4 hours.

[0017] Further, the organic alkali solution II in the second step comprises one of tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrapropylammonium hydroxide, preferably tetraethylammonium hydroxide, the organic alkali solution II is the same as or different from the organic alkali solution I, preferably the same, and the mass concentration of the organic alkali in the organic alkali solution II is 3.5%-12.5%.

[0018] Further, the high-temperature hydrothermal treatment in the second step is a sealed hydrothermal treatment in a high-pressure reaction kettle, the high-temperature hydrothermal treatment temperature is 140-180℃, the treatment time is 4-10 hours, the drying temperature is 100-160℃, and the drying time is 6-10 hours.

[0019] Further, the pseudo-boehmite P2 in the third step is in a granular form, the mesopore diameter is greater than 10nm, and the mass ratio of the pseudo-boehmite P1 to the pseudo-boehmite P2 is 1:19-1:9.

[0020] Further, the rolling ball forming in the third step is performed in a rotary table forming machine, the operation conditions are that the inclination angle of the rotary table is 35-70º, the rotary speed of the rotary table is 10-30rpm, the forming time of the material in the rotary table is 30-120min, and the radius of the alumina carrier precursor S1 is 0.5r-0.8r, wherein r is the radius of the final alumina material.

[0021] Further, the pseudo-boehmite P3 in the fourth step is in a granular form, the mesopore diameter is greater than 15nm, and the mass ratio of the pseudo-boehmite P1 to the pseudo-boehmite P3 is 7:3-9:1.

[0022] Further, the rolling ball forming in the fourth step is performed in a rotary table forming machine, the operation conditions are that the inclination angle of the rotary table is 35-70º, the rotary speed of the rotary table is 10-30rpm, and the forming time of the material in the rotary table is 20-120min.

[0023] Further, the drying temperature in the fourth step is 60℃-180℃, preferably 80℃-150℃, the drying time is 1-8 hours, preferably 2-6 hours, the calcination temperature is 450-800℃, preferably 500-750℃, and the calcination time is 2-8 hours, preferably 4-6 hours.

[0024] The beneficial effects of the present application are as follows:

[0025] The invention is to immerse the pseudo-boehmite after calcination into organic alkali solution twice for hydrothermal treatment, the alumina grains are rehydrated and secondary growth during the hydrothermal treatment, forming the elliptical flaky pseudo-boehmite with the morphology, and the elliptical flaky particles are stacked to form a large number of macroporous channels. When the carrier is formed, the content of the elliptical flaky pseudo-boehmite in the mixture is adjusted, so that the alumina carrier with gradient distribution of channels is prepared. The alumina carrier has high macropore content in the shell layer, and the channel is wide. The channel structure is beneficial to the diffusion of macromolecular reactants to the inside of the carrier, and at the same time, the carrier surface has strong anti-clogging ability. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a SEM diagram of the pseudo-boehmite P1 prepared in Example 1.

[0027] Figure 2 is a SEM diagram of the alumina carrier "shell layer" prepared in Example 1.

[0028] Figure 3 is a SEM diagram of the alumina carrier "core layer" prepared in Example 1. DETAILED DESCRIPTION

[0029] The technical solutions and technical effects of the invention are further illustrated below in combination with examples, but are not limited to the following examples.

[0030] Sample pore structure characterization: Micromeritics Trister 3000 nitrogen physical adsorption instrument was used to characterize the pore structure of the sample.

[0031] Distribution rate of pore diameter of 100 nm or more: the sample pore distribution was characterized by using the full-automatic mercury porosimeter of American Mac AutoPore9500.

[0032] Sample microstructure characterization: Hitachi SU8220 scanning electron microscope (SEM) was used to characterize the microstructure of the sample.

[0033] Method for measuring the average pore diameter of the alumina carrier "shell layer" and "core layer" of the invention: first, the pore volume, specific surface area and average pore diameter of the sample were determined by low-temperature nitrogen adsorption method (BET), then a certain amount of sample was placed in the catalyst attrition tester, and a certain amount of quartz sand was added to increase the attrition rate. When the sample is ground to a certain extent, the weight loss of the sample is measured and the pore structure is measured again. According to the relationship that the total pore volume and specific surface area of the sample are equal to the sum of each part, the pore volume and specific surface area of the part ground off can be calculated. At the same time, 40-80 samples were measured to calculate the average pore diameter.

[0034] Example 1

[0035] (1) The pseudo-boehmite prepared by aluminum sulfate-sodium metaaluminate method was calcined at 450°C for 4 hours. The calcined material was loaded into the inner liner of a high-pressure kettle made of polytetrafluoroethylene, and then a tetraethylammonium hydroxide solution with a concentration of 1.55 wt% was added to immerse the powder material completely. The mixture was stirred for 45 minutes, and then the high-pressure kettle was sealed and placed in an oven for hydrothermal treatment at 95°C for 3 hours. After the treatment, the sample was filtered.

[0036] (2) The filter cake obtained in step (1) was loaded into the inner liner of a high-pressure kettle again, and a tetraethylammonium hydroxide solution with a concentration of 9.5 wt% was added to immerse the material completely. The mixture was stirred for 45 minutes, and then the high-pressure kettle was sealed and subjected to hydrothermal treatment at 155°C for 8 hours. After the treatment, the material was washed and filtered, and the filter cake was dried at 140°C for 8 hours to obtain an ellipsoidal flaky pseudo-boehmite. The scanning electron microscope image of the sample is shown in Figure 1 .

[0037] (3) 500 grams of pseudo-boehmite P2 (with a pore size greater than 10 nm) and 38 grams of the ellipsoidal flaky pseudo-boehmite obtained in step (2) were mixed uniformly. The mixture was placed in a rotary table forming machine, the inclination angle of the rotary table was adjusted to 45°, and the rotation speed of the rotary table was set to 20 rpm. An appropriate amount of a 1% acetic acid aqueous solution was sprayed onto the material in the rotary table, and the material was formed in the rotary table for 60 minutes to obtain a spherical alumina carrier precursor S1 with a diameter of 3.0-5.0 mm.

[0038] (4) 500 grams of pseudo-boehmite P3 (with a pore size greater than 15 nm) and 2000 grams of the ellipsoidal flaky pseudo-boehmite obtained in step (2) were mixed uniformly. The mixture and the spherical alumina carrier precursor S1 prepared in step (3) were placed in a rotary table forming machine, the inclination angle of the rotary table was adjusted to 45°, and the rotation speed of the rotary table was set to 20 rpm. An appropriate amount of a 1% acetic acid aqueous solution was sprayed onto the material in the rotary table, and the material was formed in the rotary table for 40 minutes. The obtained spherical carrier was dried at 120°C for 4 hours and then calcined at 650°C for 5 hours to obtain the alumina carrier A-1 of the present application. The properties of the carrier are shown in Table 1, the scanning electron microscope image of the "shell layer" of the cross section of the carrier is shown in Figure 2 , and the scanning electron microscope image of the "core layer" is shown in Figure 3 .

[0039] Example 2

[0040] The same as example 1, except that the concentration of tetraethylammonium hydroxide in step (1) is 1.25 wt%, the hydrothermal treatment temperature is 105℃, and the treatment time is 2 hours. The concentration of tetraethylammonium hydroxide in step (2) is 7.5 wt%, the hydrothermal treatment temperature is 165℃, and the treatment time is 6.5 hours. The oval flake-like pseudoboehmite added in step (3) is 43 grams, and the rolling ball forming time is 70 min. The oval flake-like pseudoboehmite added in step (4) is 2800 grams, and the rolling ball forming time is 30 min, to obtain the alumina carrier A-2 of the present application, and the carrier properties are shown in Table 1.

[0041] Example 3

[0042] The same as example 1, except that the concentration of tetraethylammonium hydroxide in step (1) is 0.95 wt%, the hydrothermal treatment temperature is 115℃, and the treatment time is 1 hour. The concentration of tetraethylammonium hydroxide in step (2) is 12 wt%, the hydrothermal treatment temperature is 145℃, and the treatment time is 9.5 hours. The oval flake-like pseudoboehmite added in step (3) is 49 grams, and the rolling ball forming time is 65 min. The oval flake-like pseudoboehmite added in step (4) is 1500 grams, and the rolling ball forming time is 35 min, to obtain the alumina carrier A-3 of the present application, and the carrier properties are shown in Table 1.

[0043] Example 4

[0044] The same as example 1, except that the concentration of tetraethylammonium hydroxide in step (1) is 1.85 wt%, the hydrothermal treatment temperature is 85℃, and the treatment time is 4 hours. The concentration of tetraethylammonium hydroxide in step (2) is 4.5 wt%, the hydrothermal treatment temperature is 175℃, and the treatment time is 5 hours. The oval flake-like pseudoboehmite added in step (3) is 32 grams, and the rolling ball forming time is 75 min. The oval flake-like pseudoboehmite added in step (4) is 4500 grams, and the rolling ball forming time is 25 min, to obtain the alumina carrier A-4 of the present application, and the carrier properties are shown in Table 1.

[0045] Comparative Example 1

[0046] The same as example 1, except that the tetraethylammonium hydroxide in step (1) and step (2) is replaced by the same amount of ammonia water, and no oval flake-like particles are formed in the material after hydrothermal treatment, to obtain the comparative alumina carrier A-5, and the carrier properties are shown in Table 1.

[0047] Comparative Example 2

[0048] The same as example 1, except that the tetraethylammonium hydroxide in step (1) and step (2) is replaced by the same amount of sodium hydroxide, and no oval flake-like particles are formed in the material after hydrothermal treatment, to obtain the comparative alumina carrier A-6, and the carrier properties are shown in Table 1.

[0049] Comparative Example 3

[0050] The same as in Example 1, except that when the carrier roll ball is formed, the raw material used for the "core layer" is all pseudo-boehmite P2 and the raw material used for the "shell layer" is all pseudo-boehmite P3, to obtain comparative alumina carrier A-7, and the carrier properties are shown in Table 1.

[0051] Table 1 Alumina carrier properties

[0052]

[0053] From the data in Table 1, it can be seen that the pore structure of the alumina carrier prepared by the method of the present application is gradient distribution, i.e. the pore size on the surface of the carrier is larger and the content of 0.5-1 μm pores is high. From the data in Table 1, it can be seen that the pore size of the "core layer" of the alumina carrier prepared by the method of the present application is smaller than that of the "shell layer", which is beneficial to the diffusion of the reactants. Figure 2 It can be seen that the pore of the "shell layer" of the alumina carrier prepared by the method of the present application is open, which is beneficial to the diffusion of the macromolecular reactants.

Claims

1. A gradient pore distribution alumina support, characterized by: The alumina carrier has a core-shell structure, the thickness of the core layer is 0.5-0.8r, the thickness of the shell layer is 0.2-0.5r, wherein r is the radius of the alumina carrier, i.e. the straight-line distance from the center of the alumina carrier to the outer surface, the average pore size of the shell layer is 0.5-1μm, and the average pore size of the core layer is 10-30nm; The preparation method of the gradient pore distribution alumina carrier comprises the following steps: In the first step, the pseudo-boehmite is subjected to calcination treatment, and then the calcined material is immersed in an organic alkali solution I for low-temperature hydrothermal treatment, and then the treated material is subjected to liquid-solid separation; In the second step, the separated solid material is again immersed in an organic alkali solution II for high-temperature hydrothermal treatment, and then the treated material is subjected to liquid-solid separation and drying to obtain pseudo-boehmite P1; In the third step, the pseudo-boehmite P1 is mixed with pseudo-boehmite P2, and the mixture is subjected to ball rolling to obtain an alumina carrier precursor S1; In the fourth step, the pseudo-boehmite P1 is mixed with pseudo-boehmite P3, and then the alumina carrier precursor S1 is mixed with the mixture, and the mixture is subjected to ball rolling to obtain an alumina carrier; In the first step, the organic alkali solution I is tetramethylammonium hydroxide or tetrapropylammonium hydroxide, and the mass concentration of the organic alkali in the organic alkali solution I is 0.8%-2.0%; In the first step, the low-temperature hydrothermal treatment is a sealed hydrothermal treatment in a high-pressure reaction kettle, the low-temperature hydrothermal treatment temperature is 80-120℃, and the treatment time is 1-4 hours; In the second step, the organic alkali solution II is tetramethylammonium hydroxide or tetrapropylammonium hydroxide, and the organic alkali solution II is the same as or different from the organic alkali solution I, and the mass concentration of the organic alkali in the organic alkali solution II is 3.5%-12.5%; In the second step, the high-temperature hydrothermal treatment is a sealed hydrothermal treatment in a high-pressure reaction kettle, the high-temperature hydrothermal treatment temperature is 140-180℃, the treatment time is 4-10 hours, the drying temperature is 100-160℃, and the drying time is 6-10 hours; In the third step, the pseudo-boehmite P2 is in the form of particles, and the average pore size is greater than 10nm, and the mass ratio of the pseudo-boehmite P1 to the pseudo-boehmite P2 is 1:19-1:9; In the fourth step, the pseudo-boehmite P3 is in the form of particles, and the average pore size is greater than 15nm, and the mass ratio of the pseudo-boehmite P1 to the pseudo-boehmite P3 is 7:3-9:

1.

2. The gradient pore size distribution alumina support of claim 1, wherein: The specific surface area of the alumina support is 150-260 m 2 / g, the pore volume is 0.75-1.1 mL / g, the content of channels with a diameter of 10-30 nm is 35%-55%, and the content of channels with a diameter of 0.5-1 μm is 15%-40%.

3. The gradient pore size distribution alumina support of claim 1, wherein: In the first step, the pseudo-boehmite is prepared by an aluminum sulfate-sodium metaaluminate method or purchased, and the calcination temperature is 450-650℃, and the calcination time is 4-8 hours.

4. The gradient pore size distribution alumina support of claim 1, wherein: In the third step, the ball rolling is performed in a rotating disc forming machine, and the operation conditions are as follows: the inclination angle of the rotating disc is 35-70º, the rotating speed of the rotating disc is 10-30rpm, the forming time of the material in the rotating disc is 30-120min, and the radius of the alumina carrier precursor S1 is 0.5r-0.8r.

5. The gradient pore distributed alumina support of claim 3, wherein: In the fourth step, the ball rolling is performed in a rotating disc forming machine, and the operation conditions are as follows: the inclination angle of the rotating disc is 35-70º, the rotating speed of the rotating disc is 10-30rpm, and the forming time of the material in the rotating disc is 20-120min. The drying temperature in the fourth step is 60-180℃, and the drying time is 1-8 hours; the calcination temperature is 450-800℃, and the calcination time is 2-8 hours.

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