Pseudo-boehmite and method for producing same, and use thereof

Abstract

The present application relates to the preparation field of pseudo-boehmite, and discloses a kind of pseudo-boehmite and its preparation method and application.The preparation method includes: (1) gas source is introduced into water and is pre-dissolved, to obtain solution;Wherein, the gas source is mixed gas containing CO2 Volume concentration is not more than 20%;The pH value of the solution is 4-6;(2) sodium metaaluminate solution is contacted with the solution to obtain mixed liquor containing set concentration sodium metaaluminate, and the gas source is introduced into the mixed liquor and is gelled to obtain reaction slurry;Wherein, the gas source is in the form of multiple bubbles in the mixed liquor with the speed of 2-30mm / s rises;(3) the reaction slurry is aged, and then the material after aging is filtered, washed and dried, to obtain pseudo-boehmite dry powder.The problem that low concentration CO2 is difficult to produce high-purity pseudo-boehmite is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing pseudoboehmite, more particularly, to a method for preparing pseudoboehmite with low concentration of CO2 and the pseudoboehmite prepared by the method, and the application of the pseudoboehmite. BACKGROUND

[0002] Pseudoboehmite (AlOOH·nH2O (0<n<1)) is widely used in petroleum refining processes, commonly used as a binder for catalytic cracking catalysts, and a precursor for hydrogenation catalyst and reforming catalyst carrier (γ-Al2O3). There are many methods for preparing pseudoboehmite, mainly including alcohol alumina hydrolysis method and precipitation method, etc. The carbonization method, which belongs to the category of precipitation method, i.e. NaAlO2-CO2 method, uses CO2 as a reaction raw material, which is consistent with the "double carbon target", in line with the theme of CO2 capture and utilization, and meets the requirements of green development in the era.

[0003] Because in the process of preparing pseudoboehmite by carbonization method, low concentration of CO2 is easy to cause hydrolysis reaction of sodium metavanadate (NaAlO2+2H2O→Al(OH)3+NaOH), thereby producing boehmite impurities. Therefore, in the prior art, the volume concentration of carbon dioxide for preparing pseudoboehmite by carbonization method is more than 30%:

[0004] CN111592022A discloses a method for preparing pseudoboehmite by carbonization method, using sodium aluminate solution with total alkali content of 45-55 g / L, aluminum oxide content of 40-45 g / L, and caustic coefficient α k of 1.5-1.7 as raw material, and introducing carbon dioxide gas with volume fraction of 35-40% and pressure of 0.85-0.9 kg / cm 2 , to obtain pseudoboehmite product with peptization index greater than 97%. In the method, the carbon dioxide gas is introduced for 9-11 minutes, the pH value of the gelation reaction is controlled to be 8-12, and the aging is performed at 90℃ or above for 2h or more. The raw material is a secondary washing solution, which realizes the reduction of water consumption and the recycling of secondary washing solution, and avoids environmental impact.

[0005] CN110304644A discloses a method for producing high-purity and high-stickiness pseudoboehmite, which uses high-purity sodium aluminate solution diluted with carbon dioxide gas with concentration of 30-50% to prepare high-purity pseudoboehmite wet filter cake, and then adds high-carbon alcohol additives after reslurry to react at 100-200℃ and pressure of 0.5-1 MPa for 2-24h to obtain high-purity and high-stickiness pseudoboehmite. The initial temperature of carbon dioxide gas reaction is 20-30℃, the final temperature is 25-50℃, and the carbon dioxide flow rate is 1-5m 3 / h, time 30-80 min. Wet filter cake pH = 7-7.5. The high-purity high-viscosity pseudo-boehmite is a reticular or lock-like polynuclear complex. The high-carbon alcohol additive is urea, and the addition mass is 0.5-2% of the wet filter cake. The obtained product has low impurity contents of silica, diiron trioxide and sodium oxide, good crystal form, large and controllable specific surface area and pore volume, and the data are better than those of SB powder.

[0006] CN100348493C discloses a production process of pseudo-boehmite, which uses carbonization process (CO2 method) to produce pseudo-boehmite. 1-12 g of melamine is added to a sodium metaaluminate solution containing 10-120 g / L of alumina as a pore-expanding agent, and high-purity CO2 gas (volume concentration ≥98.5%) is used as a precipitant. The gelation pH value is 6.5-8.5, and the gelation temperature is 20-80℃. Pseudo-boehmite with large pore volume (0.7-1.6 mL / g), low bulk density (bulk density 0.15-0.5 g / mL) and good crystal phase is prepared. In the examples, the gibbsite content is less than 1%.

[0007] CN102838148B discloses a reactor and a method for preparing aluminum hydroxide. The method includes the reaction of a sodium metaaluminate solution with an alumina concentration of 10-60 g / L and CO2 gas with a volume concentration of 50-98% in a specific reactor at a temperature of 4-50℃. The CO2 gas is stopped when the pH value of the solution in the reactor reaches 9.5-11.5. Due to the small shear effect of the rotor rotation on the fluid in the reactor, the obtained aluminum hydroxide has uniform grain size and concentrated pore size distribution.

[0008] However, the industrial flue gas discharged by the petroleum refining industry, the power industry, the steel industry and the like in China has a large total amount of carbon emissions, and the CO2 concentration is low, usually less than 20%. Therefore, it is impossible to use the carbonization method to prepare pseudo-boehmite. Therefore, for the treatment of industrial flue gas, it is urgent to develop a method for preparing pseudo-boehmite from low-concentration CO2. SUMMARY

[0009] The purpose of the present application is to overcome the problem of how to prepare pseudo-boehmite from low-concentration CO2, and to provide a pseudo-boehmite, a preparation method and an application thereof. The provided method can prepare pseudo-boehmite without impurity crystals from low-concentration CO2.

[0010] In order to achieve the above-mentioned purpose, the present application provides a preparation method of pseudo-boehmite, wherein the preparation method comprises:

[0011] (1) introducing a gas source into water for pre-dissolution to obtain a solution; wherein the gas source is a mixed gas containing CO2 with a volume concentration of not more than 20%; and the pH value of the solution is 4-6;

[0012] (2) contacting a sodium metaaluminate solution with the solution to obtain a mixed solution containing sodium metaaluminate at a set concentration, and introducing the gas source into the mixed solution to perform a gelation reaction to obtain a reaction slurry; wherein the gas source rises in the mixed solution in the form of a plurality of bubbles at a speed of 2-30 mm / s;

[0013] (3) aging the reaction slurry, and then filtering, washing and drying the aged material to obtain pseudo-boehmite dry powder.

[0014] The second aspect of the present application provides a pseudo-boehmite prepared by the preparation method of the present application.

[0015] The third aspect of the present application provides an application of the pseudo-boehmite of the present application in petroleum refining.

[0016] Through the above technical solution, the method provided by the present application can realize the preparation of pseudo-boehmite by carbonization method using low-concentration CO2 gas, and the weak L acid content of the obtained pseudo-boehmite after calcination at 550℃ for 2h reaches more than 60% of the total L acid content, while the weak L acid content of conventional pseudo-boehmite is usually about 50%. The increase of the weak L acid ratio reduces the medium-strong L acid ratio. The further prepared catalytic cracking catalyst of the pseudo-boehmite can reduce the coke selectivity on the basis of good cracking performance. In the method provided by the present application, the pre-dissolution step and the rising speed of the bubbles formed by introducing low-concentration CO2 into the sodium metaaluminate solution during the gelation reaction are controlled, so as to realize the effective reaction of low-concentration CO2 and obtain pseudo-boehmite without impurity crystals. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 XRD spectra of pseudo-boehmite prepared for each of Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0018] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are understood to be approximate values. The exact numerical values of the endpoints of the ranges and the separate points are not to be construed as being strictly limited to the exact numerical values reported, but rather to have the weight of a range approximation. Any numerical range recited herein is intended to include all sub-ranges of the same numbers. For example, a range of 1-10 is intended to include all sub-ranges between and including the values 1-10, e.g., 1-6.1, 2.1-8.3, 3.5-7.7, 5.5-10, etc.

[0019] The first aspect of the present application provides a preparation method of pseudo-boehmite, wherein the preparation method comprises:

[0020] (1) introducing a gas source into water for pre-dissolution to obtain a solution; wherein the gas source is a mixed gas containing CO2 at a volume concentration of not more than 20%; and the pH value of the solution is 4-6;

[0021] (2) contacting the sodium metaaluminate solution with the solution to obtain a mixed solution containing sodium metaaluminate at a set concentration, and introducing the gas source into the mixed solution to perform a gelation reaction to obtain a reaction slurry; wherein the gas source rises in the form of multiple bubbles in the mixed solution at a speed of 2-30 mm / s;

[0022] (3) aging the reaction slurry, and then filtering, washing, and drying the aged material to obtain pseudo-boehmite dry powder.

[0023] In some embodiments of the present application, for a gas source with low concentration of CO2, the solution of dissolved CO2 obtained by the pre-dissolution is reacted with the sodium metaaluminate solution to perform a gelation reaction, which can effectively inhibit the hydrolysis of sodium metaaluminate and promote the initial nucleation of pseudo-boehmite crystals. Preferably, the volume concentration of CO2 in the gas source is 5-20%. This concentration is lower than the value that can be achieved by the carbonation method in the prior art. The gas source can be obtained by adjusting a high-concentration CO2 gas, or can be obtained from industrial flue gas, such as FCC regeneration flue gas, thermal power plant flue gas, steel plant flue gas, boiler flue gas, combustion furnace flue gas, and calcination furnace flue gas.

[0024] In some embodiments of the present application, preferably, the temperature of the pre-dissolution is room temperature-50°C. In the present application, the room temperature is 25±5°C.

[0025] In some embodiments of the present application, preferably, the pH value of the solution is 4.2-5.5. More preferably, the pH value is 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5.0, 5.1, 5.2, 5.3, 5.4, 5.5, and any value within the range defined by any two of the above values. In the present application, the solution obtained by the pre-dissolution has dissolved CO2 in an amount such that the pH value of the solution meets the above conditions, which is beneficial to inhibiting the hydrolysis of sodium metaaluminate and promoting the initial nucleation of pseudo-boehmite crystals in the subsequent gelation reaction process, and reducing the generation of impurity crystals.

[0026] In some embodiments of the present application, preferably, the concentration of sodium metaaluminate in the mixed solution is 10-40 g / L, preferably 15-35 g / L, in terms of aluminum oxide. At this concentration, the sodium metaaluminate solution can be matched with low-concentration CO2, and the generation of impurity crystals in the reaction process can be avoided.

[0027] In some embodiments of the present application, in step (2), the gas source is introduced into the mixture in the form of bubbles to participate in the gelation reaction. The gas source rises in the form of bubbles in the mixed solution at a speed of 2-30 mm / s, for example, 4-20 mm / s; preferably, the gas source rises in the form of bubbles in the mixed solution at a speed of 8-15 mm / s. A gas distribution plate can be arranged in the reactor in which the gelation reaction is carried out, and the gas source forms bubbles upward from the bottom of the reactor through the gas distribution plate. The gas distribution plate can be a ring-shaped gas disperser, in which circular gas distribution holes are arranged in a ring shape on the distribution plate, and the size and number of the gas distribution holes are determined according to the actual situation such as the gas inlet amount and the required gas flow rate of the reactor. The flow pattern of the bubbles in the reactor is in the category of bubbling flow or pulsating flow, which avoids too high a gas speed so that CO2 cannot be diffused into the emulsion phase of the mixed solution in time to participate in the gelation reaction and is taken out of the reaction zone. Within the above-mentioned gas speed range, sufficient CO2 gas residence time and CO2 gas content in the mixture are ensured, and the mass transfer between gas and liquid is enhanced. At the same time, the pre-dissolution and control of the rising speed of CO2 bubbles improve the selectivity of the production of pseudoboehmite by carbonation method from the reaction kinetics, and solve the problem that it is difficult to produce high-purity pseudoboehmite with low-concentration CO2. The speed can be measured by a conductive probe bubble measuring instrument or a visual method.

[0028] In some embodiments of the present application, preferably, the pH value of the reaction slurry is 9-11. Controlling the pH value can avoid the generation of impurities, and at the same time, the appropriate reaction of the gas source and the sodium metaaluminate solution is controlled.

[0029] In some embodiments of the present application, preferably, the temperature of the gelation reaction is not more than 50°C, and is preferably 0-50°C.

[0030] In some embodiments of the present application, preferably, the conditions of the aging include: the aging temperature is 60-100°C, and is preferably 80-90°C; the aging time is 30-240 min, and is preferably 60-120 min. The above-mentioned conditions of the aging can meet the requirement of promoting the growth of crystals.

[0031] In some embodiments of the present application, preferably, the washing is washing the filter cake obtained by filtration with deionized water, and the washing is ended when the pH value of the deionized water reaches 7-7.5. The conditions of the drying include: the drying temperature is 60-120°C, and is preferably 70-100°C; the drying time is 2-6 hours, and is preferably 2-4 hours.

[0032] The second aspect of the present application provides a pseudoboehmite prepared by the preparation method of the present application.

[0033] In some embodiments of the present application, preferably, the crystallinity of the pseudoboehmite is 75% or more, and the crystallite size of the pseudoboehmite is 3-4 nm. The crystallinity and the crystallite size are determined by X-ray powder diffraction (XRD) according to the standard methods of RIPP 145-90 and RIPP 146-90 (see Petroleum and Chemical Industry Analysis Methods (RIPP Test Methods), edited by Yang Cuiding et al., Science Press, published in 1990).

[0034] In some embodiments of the present application, preferably, the pore volume of the pseudoboehmite is not less than 0.30 mL / g, the specific surface area is 350 m 2 / g or more, the Na2O content is lower than 0.1 wt%, the peptization index is greater than 96%, and after the pseudoboehmite is calcined at 550°C for 2 h, the ratio of the weak L acid amount to the total L acid amount is not less than 60%. That is, the strong L acid amount is low.

[0035] The specific surface area and the total pore volume are determined by the BET method.

[0036] The Na2O content is determined by X-ray fluorescence spectroscopy.

[0037] The determination of the peptization index (DI): 5 g of the pseudoboehmite with a particle size of less than 200 mesh (dry basis) is placed in a 250 mL conical flask, an appropriate amount of deionized water is added and stirred, an appropriate amount of hydrochloric acid is added, and after stirring for a certain period of time, it is allowed to stand and settle for 24 h. After pouring off the upper suspension, it is dried and calcined, the mass of the sample (W) is determined, and the peptization index DI = (5-W) / 5 x 100% is calculated.

[0038] The acid amount data of the pseudoboehmite after calcination at 550°C for 2 h are obtained by pyridine infrared spectroscopy test, the total acid amount is obtained by desorption at 250°C, and the weak acid amount is the difference between the total acid amount and the medium-strong acid amount desorbed at 350°C.

[0039] The pseudoboehmite does not contain gibbsite impurities in its phase. For example, the XRD spectrum of the pseudoboehmite does not show the spectrum peaks of gibbsite impurities.

[0040] The third aspect of the present application provides an application of the pseudoboehmite of the present application in petroleum refining. The pseudoboehmite can be used in the preparation of petroleum refining catalysts, such as hydrogenation catalysts, reforming catalysts, isomerization catalysts, adsorbents, and adjuvants.

[0041] Preferably, the application is in a catalytic cracking catalyst. When the catalytic cracking reaction is carried out, the coke selectivity can be reduced.

[0042] In the present application, the pH values of the solutions are measured at 25°C.

[0043] The present application will be described in detail by way of examples. The crystallinity and crystallite size of the pseudoboehmite prepared in the following examples were determined by X-ray powder diffraction (XRD) using the standard methods of RIPP 145-90 and RIPP 146-90 (see Petroleum and Chemical Industry Analysis Methods (RIPP Test Methods), edited by Yang Cuiding et al., Science Press, 1990). The formula for calculating the crystallite size is: where K = 1.075, λ is the wavelength of the anode radiation Kα1 spectrum, β1 is the integral width of the diffraction peak of the (130) crystal plane of the pseudoboehmite, and θ is the Bragg diffraction angle of the diffraction peak. The content of the boehmite impurity phase was determined according to RIPP 138-90.

[0044] The specific surface area and total pore volume of the prepared pseudoboehmite were determined by the BET method using an ASAP 2405N V1.01 automatic adsorption instrument of the American Micromeritics Company, a low-temperature static nitrogen adsorption capacity method, and a sample in a 1.33 x 10 -2 Pa, vacuum degassing at 300°C for 4 h, and determination of the adsorption-desorption isotherm of the sample at 77.4 K using N2 as the adsorption medium. The specific surface area (SBET) of the sample was calculated according to the BET formula, the volume of N2 adsorbed by the sample at a relative pressure p / p0 = 0.98 was determined, and it was converted to the volume of liquid nitrogen, i.e., the total pore volume.

[0045] The Na2O content was determined by X-ray fluorescence spectroscopy.

[0046] Determination of the peptization index (DI): 5 g of the pseudoboehmite having a particle size of less than 200 mesh (dry basis) was placed in a 250 mL conical flask, an appropriate amount of deionized water was added and stirred, an appropriate amount of hydrochloric acid was added, and after stirring for a certain period of time, it was allowed to stand and settle for 24 h. After pouring off the upper suspension, it was dried and calcined, the mass of the sample (W) was determined, and the peptization index DI = (5 - W) / 5 x 100% was calculated.

[0047] The acid amount data of the pseudoboehmite after calcination at 550°C for 2 h were obtained by pyridine infrared spectroscopy testing, the total acid amount was obtained by desorption at 250°C, and the weak acid amount was the difference between the total acid amount and the medium-strong acid amount obtained by desorption at 350°C.

[0048] Example 1

[0049] Deionized water was added to a reactor and pre-dissolved at room temperature (about 25°C) by passing in CO2 gas with a volume concentration of 5% to obtain a CO2-containing solution with a pH value of 5.2; then a sodium aluminate solution was added to the solution to prepare a mixture with a sodium aluminate concentration of 15 g / L (calculated as Al2O3), and CO2 gas with a volume concentration of 5% was passed into the mixture formed, and the flow rate was adjusted so that the rising speed of the bubbles formed by the gas distribution plate in the mixture was 10 mm / s, and a gelation reaction was carried out at room temperature, and the end point pH value of the reaction slurry obtained was controlled to be 10.8. The slurry obtained was aged, the aging temperature was controlled at 80°C, and the aging time was 60 min. After aging was completed, the product was filtered, washed, and the filter cake obtained was dried at 100°C for 3 hours to obtain a pseudoboehmite powder A1, and the physicochemical properties are shown in Table 1.

[0050] Example 2

[0051] Deionized water was added to a reactor and pre-dissolved at room temperature (about 25°C) by passing in CO2 gas with a volume concentration of 10% to obtain a CO2-containing solution with a pH value of 4.8; then a sodium aluminate solution was added to the solution to prepare a mixture with a sodium aluminate concentration of 20 g / L (calculated as Al2O3), and CO2 gas with a volume concentration of 10% was passed into the mixture formed, and the flow rate was adjusted so that the rising speed of the bubbles formed by the gas distribution plate in the mixture was 8 mm / s, and a gelation reaction was carried out at room temperature, and the end point pH value of the reaction slurry obtained was controlled to be 10.5. The slurry obtained was aged, the aging temperature was controlled at 80°C, and the aging time was 80 min. After aging was completed, the product was filtered, washed, and the filter cake obtained was dried at 100°C for 3 hours to obtain a pseudoboehmite powder A2, and the physicochemical properties are shown in Table 1.

[0052] Example 3

[0053] Deionized water was added to a reactor and pre-dissolved at room temperature (about 25°C) by passing in industrial flue gas with a CO2 volume concentration of 15% to obtain a CO2-containing solution with a pH value of 4.5; then a sodium aluminate solution was added to the solution to prepare a mixture with a sodium aluminate concentration of 25 g / L (calculated as Al2O3), and industrial flue gas with a CO2 volume concentration of 15% was passed into the mixture formed, and the flow rate was adjusted so that the rising speed of the bubbles formed by the gas distribution plate in the mixture was 12 mm / s, and a gelation reaction was carried out at 50°C, and the end point pH value of the reaction slurry obtained was controlled to be 10. The slurry obtained was aged, the aging temperature was controlled at 90°C, and the aging time was 80 min. After aging was completed, the product was filtered, washed, and the filter cake obtained was dried at 100°C for 3 hours to obtain a pseudoboehmite powder A3, and the physicochemical properties are shown in Table 1.

[0054] Example 4

[0055] Deionized water was added to a reactor and pre-dissolved at room temperature (about 25°C) by passing CO2 gas with a volume concentration of 20% to obtain a CO2-containing solution with a pH value of 4.5. Then, a sodium aluminate solution was added to the solution to prepare a mixture with a sodium aluminate concentration of 35 g / L (calculated as Al2O3), and CO2 gas with a volume concentration of 20% was simultaneously passed through the mixture. The flow rate was adjusted so that the rising speed of the gas bubbles formed by the gas distribution plate in the mixture was 15 mm / s. The gelation reaction was carried out at 40°C, and the end point pH value of the obtained reaction slurry was controlled to be 10. The obtained slurry was aged at an aging temperature of 90°C for 100 min. After aging, the product was filtered, washed, and the obtained filter cake was dried at 100°C for 3 hours to obtain pseudoboehmite powder A4. The physicochemical properties are shown in Table 1.

[0056] Example 5

[0057] Deionized water was added to a reactor and pre-dissolved at room temperature (about 25°C) by passing CO2 gas with a volume concentration of 5% to obtain a CO2-containing solution with a pH value of 5.2. Then, a sodium aluminate solution was added to the solution to prepare a mixture with a sodium aluminate concentration of 15 g / L (calculated as Al2O3), and CO2 gas with a volume concentration of 5% was simultaneously passed through the mixture. The flow rate was adjusted so that the rising speed of the gas bubbles formed by the gas distribution plate in the mixture was 4 mm / s. The gelation reaction was carried out at 30°C, and the end point pH value of the obtained reaction slurry was controlled to be 10.8. The obtained slurry was aged at an aging temperature of 80°C for 60 min. After aging, the product was filtered, washed, and the obtained filter cake was dried at 100°C for 3 hours to obtain pseudoboehmite powder A5. The physicochemical properties are shown in Table 1.

[0058] Example 6

[0059] Deionized water was added to a reactor and 10% by volume CO2 gas was bubbled therethrough to perform pre-dissolution at room temperature (about 25°C) to obtain a CO2-containing solution having a pH value of 4.8. Then, a sodium aluminate solution was added to the solution to prepare a mixture having a sodium aluminate concentration of 20 g / L (calculated as Al2O3), and 10% by volume CO2 gas was simultaneously bubbled therethrough to the mixture, and the flow rate was adjusted so that the rising speed of the bubbles formed by the gas distribution plate in the mixture was 20 mm / s, and a gelation reaction was performed at room temperature. The end point pH value of the obtained reaction slurry was controlled to be 10.5. The obtained slurry was aged at an aging temperature of 80°C for 80 min. After aging, the product was filtered, washed, and the obtained filter cake was dried at 100°C for 3 hours to obtain a pseudoboehmite powder A6. The physicochemical properties of the product are shown in Table 1.

[0060] Comparative Example 1

[0061] 10% by volume CO2 gas was bubbled at 25°C into a sodium aluminate solution having a concentration of 20 g / L (calculated as Al2O3), the flow rate was adjusted so that the rising speed of the bubbles formed by the gas distribution plate in the formed mixture was 8 mm / s, and a gelation reaction was performed at room temperature (about 25°C). The end point pH value of the obtained reaction slurry was controlled to be 10.5. The obtained slurry was aged at an aging temperature of 80°C for 80 min. After aging, the product was filtered, washed, and the obtained filter cake was dried at 100°C for 3 hours to obtain a product D1. The physicochemical properties of the product are shown in Table 1.

[0062] Comparative Example 2

[0063] Deionized water was added to a reactor and 10% by volume CO2 gas was bubbled therethrough to perform pre-dissolution at room temperature (about 25°C) to obtain a CO2-containing solution having a pH value of 4.8. Then, a sodium aluminate solution was added to the solution to prepare a mixture having a sodium aluminate concentration of 20 g / L (calculated as Al2O3), and 10% by volume CO2 gas was simultaneously bubbled therethrough to the formed mixture, and the flow rate was adjusted so that the rising speed of the bubbles formed by the gas distribution plate in the mixture was 40 mm / s, and a gelation reaction was performed at room temperature. The end point pH value of the obtained reaction slurry was controlled to be 10.5. The obtained slurry was aged at an aging temperature of 80°C for 80 min. After aging, the product was filtered, washed, and the obtained filter cake was dried at 100°C for 3 hours to obtain a product D2. The physicochemical properties of the product are shown in Table 1.

[0064] Comparative Example 3

[0065] The 10% (volume concentration) CO2 gas was introduced into the 20 g / L (Al2O3) sodium metaaluminate solution at 25°C, the flow rate was adjusted so that the rising speed of the bubbles formed by the gas distribution plate in the formed mixture was 40 mm / s, and the gelation reaction was carried out at normal temperature (about 25°C); the end point pH value of the obtained reaction slurry was controlled to be 10.5. The obtained slurry was aged, the aging temperature was controlled to be 80°C, and the aging time was 80 min. After the aging was completed, the product was filtered, washed, and the obtained filter cake was dried at 100°C for 3 hours, and the obtained product was D3, and the physicochemical properties are shown in Table 1.

[0066] Comparative Example 4

[0067] The deionized water was added into the reactor, and the 10% (volume concentration) CO2 gas was introduced for pre-dissolution at normal temperature (about 25°C) to obtain the CO2-containing solution with a pH value of 6.3; then the sodium metaaluminate solution was added into the solution to prepare the mixture with a sodium metaaluminate concentration of 20 g / L (Al2O3), and the 10% (volume concentration) CO2 gas was introduced into the formed mixture, and the flow rate was adjusted so that the rising speed of the bubbles formed by the gas distribution plate in the mixture was 8 mm / s, and the gelation reaction was carried out at normal temperature; the end point pH value of the obtained reaction slurry was controlled to be 10.5. The obtained slurry was aged, the aging temperature was controlled to be 80°C, and the aging time was 80 min. After the aging was completed, the product was filtered, washed, and the obtained filter cake was dried at 100°C for 3 hours, and the obtained product was D4, and the physicochemical properties are shown in Table 1.

[0068] Table 1: Pseudo-boehmite performance indexes

[0069] Number A1 A2 A3 A4 A5 A6 Alumina trihydrate content, wt% 0 0 0 0 0 0 Crystallinity, % 78.2 80.3 81.6 82.4 75.4 76.6 Grain size, nm 3.3 3.4 3.7 3.6 3.4 3.2 Na20 content, % 0.0769 0.0827 0.0792 0.0734 0.0689 0.0747 Specific surface area, m 2 / g]] 436.44 392.36 407.95 379.85 410.27 422.12 Total pore volume, mL / g 0.37 0.38 0.38 0.4 0.38 0.37 DI, % 96.25 96.64 98.11 97.83 97.23 96.68 Total L acid after calcination, pmol / g 94 87 98 91 90 86 Weak L acid after calcination, pmol / g 61 56 65 59 58 55 Weak L acid ratio, % 64.9 64.4 66.3 64.8 64.4 64.0

[0070] Note: DI: dissolution index,

[0071] Table 1 (continued)

[0072]

[0073]

[0074] The XRD spectra of the products A1, D1, D2, D3 are shown in Figure 1It can be seen that in the comparative example 1, no CO2 pre-dissolution is adopted, in the comparative example 2, the bubble rising speed is too fast, and in the comparative example 3, no CO2 pre-dissolution is adopted and the bubble rising speed is too fast, and each of the products obtained generates gibbsite impurities (2θ = 19°, 20°, 41°, 53°); and the XRD spectrum of the A1 does not have the characteristic peaks of the gibbsite impurities, and the pseudo-boehmite without impurities is prepared. In the comparative example 1, no pre-dissolution is adopted, and the hydrolysis reaction of sodium aluminate cannot be effectively inhibited, and the gibbsite impurities are generated. The control of the bubble rising speed will also affect the technical effects of the present application. In addition, the pH value of the solution obtained by the pre-dissolution in the comparative example 4 is greater than 6, and the experimental results also cannot avoid the generation of the impurities, and the quality of the pseudo-boehmite obtained is affected, which is worse than the embodiments of the present application. The pseudo-boehmite obtained out of the scope of the present application contains impurities, and the DI is too low to meet the use standard of the catalytic cracking catalyst.

[0075] From the data of the examples 1-6 and table 1, it can be seen that the pseudo-boehmite with the crystallinity of more than 75% (the value of the pseudo-boehmite obtained under the preferred conditions of the present application is higher), the grain size of 3-4 nm, the pore volume of not less than 0.30 mL / g, the specific surface area of more than 350 m 2 / g, the Na2O content of less than 0.1%, and the peptization index DI of more than 96% can be obtained by using the preparation method of the present application. After the pseudo-boehmite is calcined at 550°C for 2h, the proportion of the weak L acid amount in the total L acid amount is not less than 60%, that is, the strong L acid amount is small. If the CO2 pre-dissolution is not adopted and / or the bubble flow rate is not controlled, the gibbsite impurities will be generated in the product of the pseudo-boehmite due to the lower volume concentration of the CO2 gas, the peptization index is low, the strength of the catalyst is affected, and the prepared catalyst cannot be applied.

[0076] The pseudo-boehmite provided by the present application is further applied to the preparation of the catalytic cracking catalyst, and the catalytic cracking catalyst prepared has a lower coke yield when the catalytic cracking reaction is carried out due to the reduction of the strong L acid amount and the increase of the weak L acid amount in the matrix, which is beneficial to improve the selectivity of the catalytic cracking catalyst.

[0077] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as the disclosed content of the present application, and all belong to the protection scope of the present application.

Claims

1. A method for preparing pseudoboehmite, characterized in that, The preparation method includes: (1) The gas source is introduced into water for pre-dissolution to obtain a solution; wherein the gas source is a mixed gas containing a CO2 volume concentration of not more than 20%; the pH value of the solution is 4-6; (2) The sodium aluminate solution is contacted with the solution to obtain a mixture containing a set concentration of sodium aluminate, and the gas source is introduced into the mixture to carry out a gelation reaction to obtain a reaction slurry; wherein the gas source rises in the mixture in the form of multiple bubbles at a speed of 2-30 mm / s. (3) The reaction slurry is aged, and the aged material is filtered, washed and dried to obtain boehmite dry powder.

2. The preparation method according to claim 1, wherein, The CO2 volume concentration in the gas source is 5-20%.

3. The preparation method according to claim 1, wherein, The pre-dissolution temperature is room temperature - 50°C.

4. The preparation method according to any one of claims 1-3, wherein, The pH value of the solution is 4.2-5.

5.

5. The preparation method according to any one of claims 1-3, wherein, The concentration of sodium aluminate in the mixture, calculated as alumina, is 10-40 g / L.

6. The preparation method according to claim 5, wherein, The concentration of sodium aluminate in the mixture, calculated as alumina, is 15-35 g / L.

7. The preparation method according to any one of claims 1-3, wherein, The gas source rises in the mixture in the form of multiple bubbles at a speed of 8-15 mm / s.

8. The preparation method according to any one of claims 1-3, wherein, The pH value of the reaction slurry is 9-11.

9. The preparation method according to any one of claims 1-3, wherein, The temperature of the gelation reaction is no greater than 50°C.

10. The preparation method according to claim 9, wherein, The temperature of the gelation reaction is 0-50℃.

11. The preparation method according to any one of claims 1-3, wherein, The aging conditions include: an aging temperature of 60-100℃ and an aging time of 30-240 min.

12. The preparation method according to claim 11, wherein, The aging conditions include: an aging temperature of 80-90℃ and an aging time of 60-120 minutes.

13. A pseudoboehmite prepared by the preparation method according to any one of claims 1-12.

14. The pseudoboehmite according to claim 13, wherein, The crystallinity of the pseudoboehmite is above 75%, and the grain size of the pseudoboehmite is 3-4 nm.

15. The pseudoboehmite according to claim 14, wherein, The pseudoboehmite has a crystallinity of over 75% and a grain size of 3-4 nm; the pseudoboehmite has a pore volume of not less than 0.30 mL / g and a specific surface area of ​​over 350 m². 2 The content of Na2O is less than 0.1wt%, and the gel solubility index is greater than 96%; after the pseudoboehmite is calcined at 550℃ for 2h, the proportion of weak L acid content to total L acid content is not less than 60%.

16. The use of boehmite as described in any one of claims 13-15 in petroleum refining.

17. The application of boehmite in petroleum refining according to claim 16, wherein, The application described is in catalytic cracking catalysts.

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