CN109970076B - Y-type molecular sieve with surface coated with silicon-aluminum mesoporous layer and preparation method thereof - Google Patents

Y-type molecular sieve with surface coated with silicon-aluminum mesoporous layer and preparation method thereof Download PDF

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CN109970076B
CN109970076B CN201711454281.8A CN201711454281A CN109970076B CN 109970076 B CN109970076 B CN 109970076B CN 201711454281 A CN201711454281 A CN 201711454281A CN 109970076 B CN109970076 B CN 109970076B
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郑金玉
王成强
罗一斌
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Sinopec Research Institute of Petroleum Processing
China Petroleum and Chemical Corp
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Abstract

A Y-type molecular sieve with a silicon-aluminum mesoporous layer coated on the surface is characterized in that a mesoporous structure grows on the surface of a Y-type molecular sieve crystal grain and coats the molecular sieve crystal grain, the particle size distribution is uniform, the particle size visible in a scanning electron microscope is 1-2 mu m, and diffraction peaks exist at 28 degrees, 38.5 degrees, 49 degrees and 65 degrees in an XRD spectrogram; a/b is 1.2-9.5, wherein a represents a shift of 500cm in a Raman (Raman) spectrum‑1B represents a Raman shift of 350cm‑1Spectral peak intensity of (a). The Y-type molecular sieve provided by the invention has the advantages of uniform particle size, smooth surface mesoporous structure, strong accessibility of macromolecules and gradient distribution characteristic of pore channel distribution.

Description

Y-type molecular sieve with surface coated with silicon-aluminum mesoporous layer and preparation method thereof
Technical Field
The invention relates to a Y-type molecular sieve with a silicon-aluminum mesoporous layer coated on the surface and a preparation method thereof, in particular to a Y-type molecular sieve which grows a mesoporous layer on the surface of a molecular sieve crystal grain and completely coats the mesoporous layer on the surface of the molecular sieve and a preparation method thereof.
Background
Catalytic cracking is an important process in petroleum refining, is widely applied to the petroleum processing industry, and plays a significant role in oil refineries. In the catalytic cracking process, heavy fractions such as vacuum distillates or residues of heavier components are reacted in the presence of a catalyst to convert into gasoline, distillates and other liquid cracked products and lighter gaseous cracked products of four carbons or less. The catalytic cracking reaction process follows a carbonium ion reaction mechanism, and therefore, an acidic catalytic material, particularly a catalytic material having a strong B acid center, needs to be used. Amorphous alumino-silicate material is an acidic catalytic material, which has both B and L acid centers, is the main active component in early catalytic cracking catalysts, but is gradually replaced by crystalline molecular sieves due to its lower cracking activity and higher required reaction temperature. Crystalline molecular sieves are porous materials with a pore size of less than 2nm and a special crystalline phase structure, and materials with a pore size of less than 2nm are named as microporous materials according to the definition of IUPAC, so that crystalline molecular sieves or zeolites generally belong to microporous materials, and the microporous molecular sieve materials have stronger acidity and higher structural stability due to complete crystal structures and special framework structures, show higher catalytic activity in catalytic reactions, and are widely applied to petroleum processing and other catalytic industries.
The Y-type molecular sieve is used as a typical microporous molecular sieve material, and is applied in the fields of catalytic cracking, hydrocracking and the like on a large scale due to the regular pore channel structure, good stability and strong acidity. When the modified Y-type molecular sieve is used in a catalytic cracking catalyst, certain modification treatment is usually required to be carried out on the Y-type molecular sieve, such as skeleton dealumination inhibition through rare earth modification, the structural stability of the molecular sieve is improved, the retention degree of acid centers is increased, and the cracking activity is further improved; or the framework silicon-aluminum ratio is improved through ultra-stabilization treatment, so that the stability of the molecular sieve is improved.
Along with the increasing exhaustion of petroleum resources, the trend of crude oil heaving and deterioration is obvious, the slag blending proportion is continuously improved, and the requirement of the market for light oil products is not reduced, so that in recent years, the deep processing of heavy oil and residual oil is more and more emphasized in the petroleum processing industry, a plurality of refineries begin to blend vacuum residual oil, even normal pressure residual oil is directly used as a cracking raw material, the catalytic cracking of heavy oil gradually becomes a key technology for improving economic benefits of oil refining enterprises, and the macromolecular cracking capability of a catalyst therein is a focus of attention. The Y-type molecular sieve is the most main cracking active component in the conventional cracking catalyst, but due to the smaller pore channel structure, the Y-type molecular sieve shows a relatively obvious pore channel limiting effect in macromolecular reaction, and also shows a certain inhibiting effect on the cracking reaction of macromolecules such as heavy oil or residual oil and the like. Therefore, for catalytic cracking of heavy oil, it is necessary to use a material having a large pore size, no diffusion limitation to reactant molecules, and a high cracking activity.
According to the IUPAC definition, a material with a pore size of 2-50 nm is a mesoporous (mesoporous) material, and the size range of macromolecules such as heavy oil or residual oil is in the pore size range, so that the research of mesoporous materials, particularly mesoporous silicon-aluminum materials, has attracted great interest to researchers in the catalysis field. Mesoporous materials are firstly developed and succeeded by Mobil Corporation in 1992 (Beck J S, Vartuli J Z, Roth W J et al, J.Am.Chem.Comm.Soc., 1992, 114, 10834-containing 10843) and named as M41S series mesoporous molecular sieves, including MCM-41(Mobil Corporation Material-41) and MCM-48, etc., wherein the pore diameter of the molecular sieves can reach 1.6-10 nm, and the mesoporous materials are uniform and adjustable, have concentrated pore diameter distribution, large specific surface area and pore volume and strong adsorption capacity; however, the pore wall structure of the molecular sieve is an amorphous structure, so that the molecular sieve has poor hydrothermal stability and weak acidity, cannot meet the operation conditions of catalytic cracking, and is greatly limited in industrial application.
In order to solve the problem of poor hydrothermal stability of mesoporous molecular sieves, part of research work focuses on increasing the thickness of the pore walls of the molecular sieves, and if a neutral template agent is adopted, the molecular sieve with thicker pore walls can be obtained, but the defect of weaker acidity still exists. In CN 1349929a, a novel mesoporous molecular sieve is disclosed, in which primary and secondary structural units of zeolite are introduced into the pore walls of the molecular sieve, so that the molecular sieve has the basic structure of the conventional zeolite molecular sieve, and the mesoporous molecular sieve has strong acidity and ultrahigh hydrothermal stability. However, the molecular sieve has the defects that a template agent with high price is required to be used, the aperture is only about 2.7nm, the molecular sieve still has large steric hindrance effect on macromolecular cracking reaction, the structure is easy to collapse under the high-temperature hydrothermal condition, and the cracking activity is poor.
In the field of catalytic cracking, silicon-aluminum materials are widely used due to their strong acid centers and good cracking properties. The proposal of the mesoporous concept provides possibility for the preparation of a novel catalyst, and the current research results mostly focus on the use of expensive organic template and organic silicon source, and mostly need to be subjected to a high-temperature hydrothermal post-treatment process. In order to reduce the preparation cost and obtain a porous material in the mesoporous range, more research efforts have been focused on the development of disordered mesoporous materials. US5,051,385 discloses a monodisperse mesoporous silicon-aluminum composite material, which is prepared by mixing acidic inorganic aluminum salt and silica sol and then adding alkali for reaction, wherein the aluminum content is 5-40 wt%, the aperture is 20-50 nm, and the specific surface area is 50-100 m2(ii) in terms of/g. US4,708,945 discloses first loading porous boehmite with silica particles orHydrating silicon oxide, carrying out hydrothermal treatment on the obtained compound at the temperature of more than 600 ℃ for a certain time to prepare the catalyst with silicon oxide loaded on the surface of the boehmite, wherein the silicon oxide is combined with hydroxyl of the transitional boehmite, and the surface area reaches 100-200 m2(iv) g, average pore diameter of 7 to 7.5 nm. A series of acidic cracking catalysts are disclosed in US4,440,872, some of which are supported on gamma-Al2O3Impregnating silane, and then roasting at 500 ℃ or treating with water vapor. In CN1353008A, inorganic aluminum salt and water glass are used as raw materials, stable and clear silicon-aluminum sol is formed through the processes of precipitation, washing, dispergation and the like, white gel is obtained through drying, and then the silicon-aluminum catalytic material is obtained through roasting for 1-20 hours at 350-650 ℃. CN1565733A discloses a mesoporous silicon-aluminum material which has a pseudo-boehmite structure, concentrated pore size distribution and a specific surface area of about 200-400 m2The mesoporous silicon-aluminum material has the advantages that the pore volume is 0.5-2.0 ml/g, the average pore diameter is 8-20 nm, the most probable pore diameter is 5-15 nm, an organic template agent is not needed in the preparation of the mesoporous silicon-aluminum material, the synthesis cost is low, the obtained silicon-aluminum material has high cracking activity and hydrothermal stability, and the high macromolecular cracking performance is shown in a catalytic cracking reaction.
Disclosure of Invention
The inventor of the invention finds that as the microporous molecular sieve has the characteristics of complete crystal structure, strong acidity, excellent structural stability and high catalytic activity, mesoporous layers with smooth pore channels, small diffusion resistance and large pore diameters are grown on the surface of the microporous molecular sieve, the two structures are continuously communicated to form the gradient pore distribution characteristic, and the respective advantages of the two structures are enhanced. Based on this, the present invention was made.
Therefore, one of the purposes of the present invention is to provide a Y-type molecular sieve with a surface coated with a mesoporous structure, wherein the mesoporous structure grows on the surface of the molecular sieve, the two structures are connected with each other to form a composite structure, the regularity is higher, the particle size is more uniform, the surface mesoporous structure is unobstructed, the accessibility of macromolecules is strong, and the pore distribution presents a gradient distribution characteristic. The invention also aims to provide a preparation method of the Y-type molecular sieve.
The Y-type molecular sieve with the surface coated with the mesoporous structure is characterized in that the mesoporous structure grows on the surface of a Y-type molecular sieve crystal grain and coats the Y-type molecular sieve crystal grain, the particle size distribution is uniform, the particle size visible in a scanning electron microscope is 1-2 mu m, and the total specific surface area is 300-650 m2(ii) a total pore volume of 0.4 to 1.0cm3(ii)/g; diffraction peaks exist at 6.2 degrees, 10.1 degrees, 11.9 degrees, 15.7 degrees, 18.7 degrees, 20.4 degrees, 23.7 degrees, 27.1 degrees, 28 degrees, 31.4 degrees, 38.5 degrees, 49 degrees and 65 degrees in an XRD spectrogram. The chemical composition of the mesoporous layer is determined by the XPS method of surface chemistry, in atomic mass: 7-20% of aluminum and 5-12% of silicon; the a/b of the molecular sieve is 1.2-9.5, wherein a represents the shift of 500cm in a Raman (Raman) spectrum-1B represents a Raman shift of 350cm-1Spectral peak intensity of (a).
In the Y-type molecular sieve, the characteristic diffraction peaks appearing at the XRD spectrogram at 6.2 degrees, 10.1 degrees, 11.9 degrees, 15.7 degrees, 18.7 degrees, 20.4 degrees, 23.7 degrees, 27.1 degrees, 31.4 degrees and the like correspond to the FAU crystal phase structure of the Y-type molecular sieve, and the characteristic diffraction peaks appearing at the XRD spectrogram at 28 degrees, 38.5 degrees, 49 degrees and 65 degrees correspond to the pseudo-boehmite structure of the mesoporous layer.
In the Y-shaped molecular sieve, the wrinkled mesoporous structure can be seen to cover the surface of the crystal grains of the Y-shaped molecular sieve in a scanning electron microscope SEM picture, the granularity is uniform and is between 1 and 2 mu m, and the granularity is equivalent to the size of the crystal grains of the Y-shaped molecular sieve. The low-temperature nitrogen adsorption and desorption isotherm of the molecular sieve presents a typical IV type form and has mesoporous characteristics; the mesoporous layer is derived on the surface of the Y-type molecular sieve crystal grain in a crystal attachment growth mode.
The invention also provides a preparation method of the Y-type molecular sieve with the surface coated with the mesoporous structure, which comprises the following preparation steps: (1) preparing raw materials capable of synthesizing a NaY molecular sieve, uniformly mixing, and then performing static crystallization at the temperature of 95-105 ℃; (2) filtering and washing the slurry after the static crystallization to obtain a NaY molecular sieve filter cake; (3) adding water again into the NaY molecular sieve filter cake for pulping, uniformly dispersing, adding an aluminum source and an alkali solution into the NaY molecular sieve filter cake for reaction at the temperature of between 30 and 70 ℃ under the condition of violent stirring, and controlling slurry in the reaction processThe pH value of the system is between 9 and 11; (4) in terms of SiO, based on the weight of alumina contained in the added aluminum source and alkali solution2:Al2O3Adding a silicon source according to the weight ratio of (1-6), continuing to age for 1-8 hours at the temperature of 30-90 ℃, and recovering an aged product.
In the preparation process, the raw materials for synthesizing the NaY molecular sieve in the step (1) are usually directing agent, water glass, sodium metaaluminate, aluminum sulfate and deionized water, and the adding proportion of the directing agent, the water glass, the sodium metaaluminate, the aluminum sulfate and the deionized water can be the charging proportion of the conventional NaY molecular sieve, for example, Na can be added2O：Al2O3：SiO2：H2O is 1.5-8: 1: 5-18: 100 to 500, the charge ratio of NaY molecular sieve for preparing special performance, for example, the charge ratio of NaY molecular sieve for preparing large or small crystal grains, is not particularly limited as long as NaY molecular sieve having FAU crystal phase structure can be obtained. The guiding agent can be prepared according to the prior art (US3639099 and US3671191), and the guiding agent is prepared by mixing a silicon source, an aluminum source, alkali liquor and deionized water according to (15-18) Na2O:Al2O3:(15～17)SiO2:(280～380)H2Mixing the components according to the molar ratio of O, uniformly stirring, and standing and aging for 0.5-48 h at room temperature to 70 ℃. In the feeding proportion of the NaY molecular sieve, Al in the guiding agent2O3The content of (A) is based on the total charge Al2O33 to 15%, preferably 5 to 10% of the total amount. The static crystallization in the step (1) is carried out for 8-50 hours, preferably 10-40 hours, and more preferably 15-35 hours.
In the preparation process, the aluminum source in the step (3) is selected from one or more of aluminum nitrate, aluminum sulfate and aluminum chloride; the alkali solution is one or more selected from ammonia water, potassium hydroxide, sodium hydroxide and sodium metaaluminate. When sodium metaaluminate is used as the alkali solution, the alumina content is counted in the total alumina content. The reaction temperature in the step (3) is 30-70 ℃, and preferably 35-65 ℃.
In the preparation process, the silicon source in the step (4) is selected from one or more of water glass, sodium silicate, tetraethoxysilane, tetramethoxysilane and silicon oxide. The aging temperature is 30-90 ℃, preferably 40-80 ℃, and the aging time is 1-8 hours, preferably 2-7 hours. Said recovery usually comprises the steps of filtration, washing and drying, well known to the person skilled in the art and not described in more detail here.
The Y-type molecular sieve with the surface coated with the mesoporous structure provided by the invention simultaneously contains the microporous structure and the mesoporous structure, and the silicon-aluminum mesoporous layer is derived and grown on the surface of the Y-type molecular sieve and coated on the surface of the molecular sieve, so that the granularity is more uniform, the mesoporous structure on the surface is unobstructed, a continuous gradient channel structure is formed with the internal molecular sieve, and the accessibility of macromolecules is enhanced.
Drawings
FIG. 1 is a scanning electron microscope SEM photograph of the Y-type molecular sieve with the surface coated with the mesoporous structure.
FIG. 2 is a SEM image of a typical NaY molecular sieve.
FIG. 3 is an X-ray diffraction pattern of the Y-type molecular sieve with the surface coated with the mesoporous structure.
Fig. 4 is a low-temperature nitrogen adsorption and desorption isotherm of the Y-type molecular sieve with the surface coated with the mesoporous structure of the invention.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.
The SEM was a Hitachi S4800 field emission SEM, Japan, with an accelerating voltage of 5kV, and the spectra were collected and processed with Horiba 350 software.
The phase of the sample was determined by X-ray diffraction.
The physicochemical data of the specific surface, the pore structure and the like of the sample are measured by adopting a low-temperature nitrogen adsorption-desorption method.
The chemical composition of the mesoporous layer is determined by X-ray photoelectron spectroscopy.
The laser Raman (Raman) spectrum adopts LabRAM HR UV-NIR laser confocal Raman spectrometer of HORIBA company, Japan, the wavelength of an excitation light source is 325nm, an ultraviolet 15-time objective lens, a confocal pinhole is 100 mu m, and the spectrum scanning time is 100 s.
Example 1
This example illustrates a Y-type molecular sieve with a surface coated with mesoporous structure and its preparation.
Under the condition of vigorous stirring, water glass, aluminum sulfate, sodium metaaluminate, guiding agent and deionized water are mixed according to 7.5SiO2：Al2O3：2.15Na2O：190H2Mixing the molar ratio of O to form NaY molecular sieve gel, wherein the mass ratio of the guiding agent is 5%, continuously stirring for 1 hour at room temperature, placing the gel in a crystallization kettle for static crystallization treatment for 40 hours at 100 ℃, quickly cooling after crystallization, and filtering and washing crystallized slurry to obtain a NaY molecular sieve filter cake; adding water again to the obtained NaY molecular sieve filter cake for pulping, dispersing uniformly, and then stirring Al vigorously at 30 DEG C2(SO4)3Solution (concentration 89 gAl)2O3/L) and NaAlO2Solution (concentration 156 gAl)2O3/L) is added into the mixture to react, the pH value of a slurry system in the reaction process is controlled to be 9.5, and after the mixture is added for a certain time, Al is used according to the mixture2(SO4)3Solution and NaAlO2Total Al in solution2O3By weight, in terms of SiO2:Al2O31:2.3 weight ratio, the desired water glass solution (concentration 100g SiO)2and/L) adding the mixture into a reaction system, continuing to age for 6 hours at 70 ℃, filtering after the aging is finished, washing and drying at 120 ℃ to obtain the Y-type molecular sieve with the surface-coated mesoporous structure, which is recorded as SAYN-1.
The SEM photo of the SAYN-1 is shown in figure 1, the SEM photo of a typical NaY molecular sieve is shown in figure 2, and the comparison of figures 1 and 2 shows that the SAYN-1 sample has uniform particle size distribution, the particle size of 1-2 μm and a wrinkled structure on the surface, which indicates that the SAYN-1 is a material with a wrinkled mesoporous structure growing on the surface of the crystal grains of the NaY molecular sieve.
The XRD spectrum of the SAYN-1 is shown in fig. 3, and diffraction peaks appear at 6.2 °, 10.1 °, 11.9 °, 15.7 °, 18.7 °, 20.4 °, 23.7 °, 27.1 °, 28 °, 31.4 °, 38.5 °, 49 ° and 65 °, wherein the characteristic diffraction peaks marked ^ correspond to the FAU crystal phase structure of the Y-type molecular sieve and the characteristic diffraction peaks marked a-corresponds to the pseudo-boehmite structure of the mesoporous layer.
The low temperature nitrogen desorption isotherm of SAYN-1 is shown in FIG. 4, and exhibits a typical type IV form with mesoporous characteristics having a total specific surface area of 516m2(ii)/g, total pore volume 0.92cm3/g。
The surface chemical composition of SAYN-1 was determined by XPS method, and the atomic mass was 13.6% for aluminum and 7.1% for silicon. Raman (Raman) spectrometry with a/b of 2.1, wherein a represents a 500cm shift in the Raman (Raman) spectrum-1B represents a Raman shift of 350cm-1Spectral peak intensity of (a).
Example 2
This example illustrates a Y-type molecular sieve with a surface coated with mesoporous structure and its preparation.
The preparation of NaY molecular sieve is the same as example 1 except that the crystallization treatment time is 35 hours; adding water again to the NaY molecular sieve filter cake, pulping, dispersing uniformly, and adding AlCl at 50 ℃ under vigorous stirring3Solution (concentration 60 gAl)2O3/L) and ammonia water (mass fraction 25%) are added into the mixture for reaction, the pH value of a slurry system in the reaction process is controlled to be 10.5, and after the mixture is added for a certain time, according to the used AlCl3Al of solution2O3By weight, in terms of SiO2:Al2O31:5.7 by weight, the desired water glass solution (concentration 100g SiO)2and/L) adding the mixture into a reaction system, continuing to age for 4 hours at 50 ℃, filtering after the aging is finished, washing and drying at 120 ℃ to obtain the Y-type molecular sieve with the surface-coated mesoporous structure, which is recorded as SAYN-2.
The scanning electron microscope photo of the SAYN-2 has the characteristics shown in figure 1, the particle size distribution is uniform, the particle size is 1-2 mu m, and the surface of the NaY molecular sieve crystal grain is coated with a wrinkled mesoporous structure.
The XRD spectrum of SAYN-2 has the characteristics shown in figure 3, and contains FAU crystal phase structure and pseudo-boehmite structure.
Low temperature of SAYN-2The nitrogen adsorption and desorption isotherm has the characteristics shown in figure 4, is in the form of IV isotherms and has mesoporous characteristics, and the total specific surface area is 572m2In terms of a total pore volume of 0.5cm3/g。
The surface chemical composition of SAYN-2 was determined by XPS method, and the atomic mass was 18.4% for aluminum and 5.7% for silicon. Raman (Raman) spectroscopy, which gave an a/b of 6.3.
Example 3
This example illustrates a Y-type molecular sieve with a surface coated with mesoporous structure and its preparation.
Under the condition of vigorous stirring, water glass, aluminum sulfate, sodium metaaluminate, guiding agent and deionized water are mixed according to 8.5SiO2：Al2O3：2.65Na2O：210H2Mixing the molar ratio of O to form NaY molecular sieve gel, wherein the mass ratio of the guiding agent is 5%, continuously stirring for 1 hour at room temperature, placing the gel in a crystallization kettle for static crystallization treatment at 100 ℃ for 20 hours, quickly cooling after crystallization, and filtering and washing crystallized slurry to obtain a NaY molecular sieve filter cake; adding water again into the obtained NaY molecular sieve filter cake, pulping, dispersing uniformly, and stirring vigorously at 40 deg.C to obtain Al (NO)3)3Solution (concentration 50 gAl)2O3/L) and ammonia water are added into the mixture at the same time for reaction, the pH value of a slurry system in the reaction process is controlled to be 9.0, and after a certain time, the pH value is adjusted according to the Al (NO) used3)3Al of solution2O3By weight, in terms of SiO2:Al2O3Adding the needed tetraethoxysilane into a reaction system according to the weight ratio of 1:3, continuing to age for 4 hours at 80 ℃, filtering after the aging is finished, washing and drying at 120 ℃ to obtain the Y-type molecular sieve with the surface coated mesoporous structure, which is recorded as SAYN-3.
The scanning electron microscope photo of SAYN-3 has the characteristics shown in figure 1, the particle size distribution is uniform, the particle size is 1-2 mu m, and the surface of the NaY molecular sieve crystal grain is coated with a wrinkled mesoporous structure.
The XRD spectrum of SAYN-3 has the characteristics shown in figure 3, and contains FAU crystal phase structure and pseudo-boehmite structure.
Low in SAYN-3The isothermal nitrogen adsorption and desorption isotherm has the characteristics shown in figure 4, is in the form of IV isotherms, has mesoporous characteristics, and has a total specific surface area of 559m2(ii)/g, total pore volume 0.66cm3/g。
The surface chemical composition of SAYN-3 was determined by XPS method, and the atomic mass was 13.3% for aluminum and 7.4% for silicon. Raman (Raman) spectroscopy, with an a/b of 2.5.
Example 4
This example illustrates a Y-type molecular sieve with a surface coated with mesoporous structure and its preparation.
The preparation of NaY molecular sieve is the same as example 3, except that the crystallization treatment time is 48 hours; adding water again to the obtained NaY molecular sieve filter cake for pulping, dispersing uniformly, and then stirring Al vigorously at room temperature2(SO4)3Solution and NaAlO2Adding the solution into the reaction kettle simultaneously to react, controlling the pH value of a slurry system to be 9.8 in the reaction process, and adding Al according to the used Al after a certain time2(SO4)3Solution and NaAlO2Total Al of solution2O3By weight, in terms of SiO2:Al2O3Adding the needed tetraethoxysilane into a reaction system according to the weight ratio of 1:1.5, continuing to age for 8 hours at 60 ℃, filtering after the aging is finished, washing and drying at 120 ℃ to obtain the Y-type molecular sieve with the surface coated mesoporous structure, which is recorded as SAYN-4.
The scanning electron microscope photo of SAYN-4 has the characteristics shown in figure 1, the particle size distribution is uniform, the particle size is 1-2 mu m, and the surface of the NaY molecular sieve crystal grain is coated with a wrinkled mesoporous structure.
The XRD spectrum of SAYN-4 has the characteristics shown in figure 3, and contains FAU crystal phase structure and pseudo-boehmite structure.
The low-temperature nitrogen adsorption and desorption isotherm of SAYN-4 has the characteristics shown in figure 4, is in the form of IV isotherms, has mesoporous characteristics and has the total specific surface area of 595m2In terms of/g, total pore volume of 0.41cm3/g。
SAYN-4 surface chemical composition measured by XPS method, aluminum 11.4% by atomic mass, silicon 8.7%. Raman (Raman) spectroscopy, with an a/b of 7.2.
Example 5
This example illustrates a Y-type molecular sieve with a surface coated with mesoporous structure and its preparation.
The preparation of NaY molecular sieve is the same as example 3, except that the crystallization treatment time is 32 hours; adding water again into the obtained NaY molecular sieve filter cake, pulping, dispersing uniformly, and stirring vigorously at 35 deg.C to obtain Al (NO)3)3Solution and NaAlO2Adding the solution into the slurry to react, controlling the pH value of the slurry system to be 10.7 in the reaction process, and adding Al (NO) according to the use after a certain time3)3Solution and NaAlO2Total Al of solution2O3By weight, in terms of SiO2:Al2O3Adding the required water glass solution into a reaction system according to the weight ratio of 1:1, continuing to age at 75 ℃ for 2 hours, filtering after the aging is finished, washing and drying at 120 ℃ to obtain the Y-type molecular sieve with the surface coated mesoporous structure, which is recorded as SAYN-5.
The scanning electron microscope photo of SAYN-5 has the characteristics shown in figure 1, the particle size distribution is uniform, the particle size is 1-2 mu m, and the surface of the NaY molecular sieve crystal grain is coated with a wrinkled mesoporous structure.
The XRD spectrum of SAYN-5 has the characteristics shown in figure 3, and contains FAU crystal phase structure and pseudo-boehmite structure.
The low-temperature nitrogen adsorption and desorption isotherm of SAYN-5 has the characteristics shown in figure 4, is in the form of IV isotherms, has mesoporous characteristics and has a total specific surface area of 420m2(ii)/g, total pore volume 0.62cm3/g。
The surface chemical composition of SAYN-5 was determined by XPS method, and it was found that aluminum was 7.5% and silicon was 11.5% by atomic mass. Raman (Raman) spectroscopy, which gave an a/b of 1.8.
Example 6
This example illustrates a Y-type molecular sieve with a surface coated with mesoporous structure and its preparation.
The preparation of the NaY molecular sieve is the same as that of the example 1, except that the crystallization treatment time is 24 hours; adding water again into the obtained NaY molecular sieve filter cake for pulping, dispersing uniformly, and then stirring Al (NO) vigorously at room temperature3)3Adding the solution and ammonia water simultaneously, controlling pH value of slurry system at 10.1, adding Al (NO) according to the amount of the solution3)3Al of solution2O3By weight, in terms of SiO2:Al2O3Adding the needed tetraethoxysilane into a reaction system according to the weight ratio of 1:1.8, continuing to age at 65 ℃ for 6 hours, filtering after the aging is finished, washing and drying at 120 ℃ to obtain the Y-type molecular sieve with the surface coated mesoporous structure, which is recorded as SAYN-6.
The scanning electron microscope photo of SAYN-6 has the characteristics shown in figure 1, the particle size distribution is uniform, the particle size is 1-2 mu m, and the surface of the NaY molecular sieve crystal grain is coated with a wrinkled mesoporous structure.
The XRD spectrum of SAYN-6 has the characteristics shown in figure 3, and contains FAU crystal phase structure and pseudo-boehmite structure.
The low-temperature nitrogen adsorption and desorption isotherm of SAYN-6 has the characteristics shown in figure 4, is in the form of IV isotherms, has mesoporous characteristics and has the total specific surface area of 588m2In terms of/g, total pore volume of 0.78cm3/g。
The surface chemical composition of SAYN-6 was determined by XPS method, and was 13.5% by atomic mass of aluminum and 9.5% by atomic mass of silicon. Raman (Raman) spectroscopy, which gave an a/b of 5.9.
Example 7
This example illustrates a Y-type molecular sieve with a surface coated with mesoporous structure and its preparation.
The preparation of NaY molecular sieve is the same as example 1 except that the crystallization treatment time is 45 hours; adding water again to the NaY molecular sieve filter cake, pulping, dispersing uniformly, and adding AlCl under vigorous stirring at 60 deg.C3Solution and NaAlO2Adding the solution into the reaction kettle simultaneously for reaction, controlling the pH value of a slurry system to be 10.8 in the reaction process, and adding AlCl according to the use after a certain time3Solution and NaAlO2Total Al of solution2O3By weight, in terms of SiO2:Al2O3Adding the required tetraethoxysilane into the reaction system according to the weight ratio of 1:4, continuing to age for 3 hours at 50 ℃, and finishing the agingAnd filtering, washing and drying at 120 ℃ to obtain the Y-type molecular sieve with the surface coated mesoporous structure, which is marked as SAYN-7.
The scanning electron microscope photo of SAYN-7 has the characteristics shown in figure 1, the particle size distribution is uniform, the particle size is 1-2 mu m, and the surface of the NaY molecular sieve crystal grain is coated with a wrinkled mesoporous structure.
The XRD spectrum of SAYN-7 has the characteristics shown in figure 3, and contains FAU crystal phase structure and pseudo-boehmite structure.
The low-temperature nitrogen adsorption and desorption isotherm of SAYN-7 has the characteristics shown in figure 4, is in the form of IV isotherms, has mesoporous characteristics and has a total specific surface area of 474m2(ii)/g, total pore volume 0.81cm3/g。
The surface chemical composition of SAYN-7 was determined by XPS method, and calculated by atomic mass, it was 16.1% for aluminum and 7.7% for silicon. Raman (Raman) spectroscopy, which gave an a/b of 9.3.
Example 8
This example illustrates a Y-type molecular sieve with a surface coated with mesoporous structure and its preparation.
The preparation of NaY molecular sieve is the same as that of example 1, except that the crystallization treatment time is 38 hours; adding water again into the obtained NaY molecular sieve filter cake for pulping, and stirring vigorously at 55 ℃ to obtain AlCl3Solution and NaAlO2Adding the solution into the reaction kettle simultaneously for reaction, controlling the pH value of a slurry system to be 9.7 in the reaction process, and adding AlCl according to the use after a certain time3Solution and NaAlO2Total Al of solution2O3By weight, in terms of SiO2:Al2O3Adding the required water glass solution into a reaction system according to the weight ratio of 1:1.2, continuing to age at 55 ℃ for 8 hours, filtering after the aging is finished, washing and drying at 120 ℃ to obtain the Y-type molecular sieve with the surface coated with the mesoporous structure, which is recorded as SAYN-8.
The scanning electron microscope photo of SAYN-8 has the characteristics shown in figure 1, the particle size distribution is uniform, the particle size is 1-2 mu m, and the surface of the NaY molecular sieve crystal grain is coated with a wrinkled mesoporous structure.
The XRD spectrum of SAYN-8 has the characteristics shown in figure 3, and contains FAU crystal phase structure and pseudo-boehmite structure.
The low-temperature nitrogen adsorption and desorption isotherm of SAYN-8 has the characteristics shown in figure 4, is in the form of IV isotherms, has mesoporous characteristics and has a total specific surface area of 391m2(ii)/g, total pore volume 0.90cm3/g。
The surface chemical composition of SAYN-8 was determined by XPS method, and was 9.4% by atomic mass of aluminum and 10.1% by atomic mass of silicon. Raman (Raman) spectroscopy, which gave an a/b of 1.4.

Claims (11)

1. A Y-type molecular sieve with a silicon-aluminum mesoporous layer coated on the surface is characterized in that a mesoporous structure grows on the surface of a Y-type molecular sieve crystal grain and coats the molecular sieve crystal grain, the particle size distribution is uniform, the particle size visible in a scanning electron microscope is 1-2 mu m, and diffraction peaks exist at 28 degrees, 38.5 degrees, 49 degrees and 65 degrees in an XRD spectrogram; a/b is 1.2-9.5, wherein a represents a shift of 500cm in a Raman (Raman) spectrum-1B represents a Raman shift of 350cm-1Spectral peak intensity of (a).
2. The Y-type molecular sieve having a surface-coated with a silicon-aluminum mesoporous layer according to claim 1, characterized in that the total specific surface area is 300 to 650m2(ii) a total pore volume of 0.4 to 1.0cm3/g。
3. The Y-type molecular sieve having a surface-coated silico-aluminous mesoporous layer according to claim 1, wherein said silico-aluminous mesoporous layer has a chemical composition in terms of atomic mass: 7-20% of aluminum and 5-12% of silicon.
4. The Y-type molecular sieve surface-coated with a mesoporous layer of silico-alumina according to claim 1, wherein said molecular sieve has a low temperature nitrogen desorption isotherm in the type IV typical form.
5. The Y-type molecular sieve having a surface coated with a mesoporous layer comprising silicon and aluminum according to claim 1, wherein said mesoporous layer comprising silicon and aluminum is derived by epimorphic growth on the surface of the Y-type molecular sieve grains.
6. The method for preparing the Y-type molecular sieve with the surface coated with the silicon-aluminum mesoporous layer as claimed in any one of claims 1 to 5, comprising the following preparation steps: (1) preparing raw materials capable of synthesizing a NaY molecular sieve, uniformly mixing, and then carrying out static crystallization for 8-50 hours at the temperature of 95-105 ℃; (2) filtering and washing the slurry after the static crystallization to obtain a NaY molecular sieve filter cake; (3) adding water into the NaY molecular sieve filter cake again for pulping, uniformly dispersing, adding an aluminum source and an alkali solution into the NaY molecular sieve filter cake at the temperature of between 30 and 70 ℃ under the condition of vigorous stirring for reaction, and controlling the pH value of a slurry system in the reaction process to be between 9 and 11; (4) in terms of SiO, based on the weight of alumina contained in the added aluminum source and alkali solution2:Al2O3Adding a silicon source according to the weight ratio of (1-6), continuing to age for 1-8 hours at the temperature of 30-90 ℃, and recovering an aged product.
7. The process according to claim 6, wherein the raw materials for synthesizing the NaY molecular sieve in step (1) are directing agent, water glass, sodium metaaluminate, aluminum sulfate and deionized water.
8. The process according to claim 6, wherein the aluminum source in the step (3) is one or more selected from the group consisting of aluminum nitrate, aluminum sulfate and aluminum chloride.
9. The process according to claim 6, wherein the alkali solution in the step (3) is one or more selected from the group consisting of aqueous ammonia, potassium hydroxide and sodium hydroxide, or the alkali is replaced with sodium metaaluminate.
10. The process according to claim 6, wherein, when the alkali is replaced with sodium metaaluminate in the step (3), the alumina content is calculated from the alumina content in the step (4).
11. The method according to claim 6, wherein the silicon source in the step (4) is one or more selected from the group consisting of water glass, sodium silicate, tetraethoxysilane, tetramethoxysilane and silicon oxide.
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