阅读说明：本技术 表面富铝的NaY分子筛及其制备方法 (NaY molecular sieve with aluminum-rich surface and preparation method thereof ) 是由 付强 李永祥 张成喜 胡合新 慕旭宏 舒兴田 于 2018-05-28 设计创作，主要内容包括：本公开涉及一种表面富铝的NaY分子筛及其制备方法,所述分子筛的表面SiO<Sub>2</Sub>/Al<Sub>2</Sub>O<Sub>3</Sub>的摩尔比为2.5～5,体相SiO<Sub>2</Sub>/Al<Sub>2</Sub>O<Sub>3</Sub>的摩尔比为6～10,所述分子筛的Al分布参数D满足：1.2≤D≤4,其中,D＝Al(S)/Al(C),Al(S)表示采用XPS方法测定的分子筛表面及表面以下2～6nm区域内的铝含量,Al(C)表示采用XRF方法测定的分子筛的整体铝含量。该NaY分子筛从颗粒表面到中心存在比常规分子筛更大的铝分布梯度。(The invention relates to a NaY molecular sieve with an aluminum-rich surface and a preparation method thereof, wherein the molar ratio of SiO2/Al2O3 on the surface of the molecular sieve is 2.5-5, the molar ratio of bulk SiO2/Al2O3 is 6-10, and the Al distribution parameter D of the molecular sieve meets the following requirements: d is not less than 1.2 and not more than 4, wherein D is Al (S)/Al (C), Al (S) represents the aluminum content of the surface and the area below the surface of the molecular sieve measured by XPS method, and Al (C) represents the whole aluminum content of the molecular sieve measured by XRF method. The NaY molecular sieve presents a greater aluminum distribution gradient from the surface of the particle to the center than conventional molecular sieves.)

1. The NaY molecular sieve with the aluminum-rich surface is characterized in that the molar ratio of SiO2/Al2O3 on the surface of the molecular sieve is 2.5-5, the molar ratio of bulk SiO2/Al2O3 is 6-10, and the Al distribution parameter D of the molecular sieve meets the following requirements: d is not less than 1.2 and not more than 4, wherein D is Al (S)/Al (C), Al (S) represents the aluminum content of the surface and the area below the surface of the molecular sieve measured by XPS method, and Al (C) represents the whole aluminum content of the molecular sieve measured by XRF method.

2. A process for preparing the NaY molecular sieve of claim 1, comprising the steps of:

a. mixing a directing agent with a first silicon source to obtain a first mixture, wherein the molar composition of the directing agent is Na 2O: A12O 3: SiO 2: H2O ═ 6 to 25: 1: (6-25): (200-400);

b. Mixing the first mixture obtained in the step a with a second silicon source, an aluminum source and water to obtain a second mixture;

c. Performing hydrothermal crystallization on the second mixture obtained in the step b, and collecting a solid product;

Wherein, calculated by SiO2, the weight ratio of the first silicon source to the second silicon source is 1: (0.01-12).

3. The method of claim 2, wherein in step a, the step of preparing the directing agent comprises: mixing sodium metaaluminate with water glass to obtain a third mixture, carrying out dynamic ageing and standing ageing on the third mixture, and then mixing the third mixture with water to obtain the directing agent;

Preferably, the dynamic ageing comprises: stirring and aging for 5-48 hours at 15-60 ℃; the standing and aging comprises the following steps: standing and aging for 5-48 hours at 15-60 ℃.

4. The method according to claim 2, wherein in step a, the first silicon source is at least one selected from water glass, colloidal silica and silica sol.

5. The method according to claim 2, wherein in the step a, when the first silicon source is a solid silicon source, the mixing is performed under stirring conditions, and the stirring time is 30-180 min.

6. The process of claim 2, wherein in step b, the molar composition of the second mixture is Na 2O: A12O 3: SiO 2: H2O ═ 2-6: 1: (8-20): (200-400).

7. The method according to claim 2, wherein in step b, the second silicon source is at least one selected from water glass, silica-alumina gel and silica-alumina sol; preferably, the molar ratio of SiO2/Al2O3 of the silicon-aluminum gel is 6-16, and the molar ratio of SiO2/Al2O3 of the silicon-aluminum sol is 6-16.

8. the process of claim 2, wherein in step b, the aluminum source is at least one selected from the group consisting of sodium metaaluminate, aluminum sulfate, aluminum chloride, aluminum nitrate and pseudoboehmite.

9. The method according to claim 2, wherein the aluminum element in the directing agent accounts for 3 to 30% of the aluminum element in the second mixture on an elemental basis and on a molar basis.

10. The method according to claim 2, wherein in step c, the hydrothermal crystallization conditions are as follows: the temperature is 90-100 ℃, and the time is 15-48 hours.

Technical Field

The invention relates to a NaY molecular sieve with an aluminum-rich surface and a preparation method thereof.

Background

At the end of the fifty years, Milton and Breck successfully synthesized Y-type molecular sieves, and the thermal stability and water stability of the NaY molecular sieve were improved because the SiO2/Al2O3 ratio in the structure of the NaY molecular sieve was greater than that of the X-type molecular sieve. In the early seventies, Grace company developed a guide agent method for synthesizing NaY molecular sieve, and water glass was used as a raw material to replace expensive silica sol, so that the process is simplified, and the growth cycle is shortened, thereby the NaY molecular sieve can be rapidly and widely applied to the fields of petrochemical industry, particularly petroleum cracking catalysis. Of the hundreds of molecular sieves that have been developed to date, the largest amount used industrially is the Y molecular sieve. At present, the synthesis of NaY molecular sieve mainly adopts a crystal gel method in industry. Due to the use and improvement of the crystal seed gel, the synthesis and crystallization time of the Y-type molecular sieve is greatly shortened, and a foundation is laid for the industrialization of the Y-type molecular sieve.

Y-type molecular sieves are FAU topologies, each unit cell consisting of 192 TO4(T ═ Si, a 1). The Y molecular sieve contains a supercage with the diameter of 1.2-1.3 nm, and the diameter of a twelve-membered ring orifice is as high as 0.74-0.75 nm. The commercial synthesis feed Y molecular sieve silica to alumina ratio is typically less than 2.8. According to the Loewenstein mechanism, the tetrahedral position immediately adjacent to the framework a1 atoms cannot be an a1 atom, so the nearest a1 atom around the a1 atom is only likely to be distributed para in its neighboring quaternary ring. Where the para-aluminum atoms of the A1 atoms in adjacent quaternary rings are called NNN-A1, the number of NNN-A1 per backbone aluminum may be 0, 1, 2, and 3. Characterization of NNN-A1 in the Y-dealuminated molecular sieve by 29Si MAS NMR revealed that the smaller the amount of Si (nAI) (n.gtoreq.2) in the molecular sieve, the greater the relative amount of 0-NNN-A1. Theoretical calculation studies on the framework aluminum of the molecular sieve show that as the number of NNN-A1 increases, the acidity of the molecular sieve gradually decreases, and only isolated aluminum atoms (0-NNN-A1) exhibit strong acid properties. The hydrothermal stability of the molecular sieve is also related to the content of framework aluminum in the molecular sieve, and as the content of framework aluminum in the molecular sieve is reduced, the unit cell of the molecular sieve is reduced, so that the molecular sieve has better thermal stability.

Commercially directly synthesized Y-type molecular sieves are typically Na-type, have a framework silicon to aluminum (Si/Al) ratio of less than 2.8, and need to be subjected to sodium and aluminum removal before being added to the catalyst. The dealuminization process is of great importance to the application of the Y-type molecular sieve, the hydrothermal stability and the acid strength of the Y-type molecular sieve can be improved, and a secondary pore passage can be constructed in the molecular sieve. However, the dealumination process causes the distribution state of framework aluminum in the molecular sieve to change, which affects the acidity of the dealuminated Y molecular sieve. Research shows that the acid strength of the molecular sieve is gradually improved along with the dealumination of the molecular sieve, which shows that the framework aluminum atoms containing weak acid are easier to remove. The silicon-aluminum ratio of the directly synthesized NaY molecular sieve is lower. When the molecular sieve is subjected to moderate dealumination, n-NNN-A1(n ═ l, 2, 3) containing weak acid is preferentially removed, and 0-NNN-A1 containing strong acid is better retained, so that the dealumination increases the relative content of strong acid sites of the molecular sieve. When the aluminum atom in the FAU molecular sieve unit cell is greater than 64, the FAU molecular sieve does not contain 0-NNN-A1, and the molecular sieve does not contain strong acid sites. As dealumination proceeds, the amount of 0-NNN-A1 in the FAU molecular sieve gradually increases and the number of strong acid sites gradually increases. When the aluminum atom in the FAU molecular sieve unit cell is reduced to 29, the number of 0-NNN-A1 and the content of strong acid sites in the FAU molecular sieve are the largest. Continuing to dealuminate the Y molecule, 0-NNN-A1 instead decreased, resulting in a decrease in strong acid sites. Because the dealumination process selectively removes n-NNN-A1, the dealuminated Y molecular sieve has less n-NNN-A1, more 0-NNN-A1 and strong acid sites than the directly synthesized Y molecular sieve under the condition of the same silica-alumina ratio.

The dealumination process of the molecular sieve is a complicated process which is difficult to regulate, the dealumination of the aluminum is very sensitive to dealumination conditions, the dealumination degree of the surface and bulk phase of the catalyst is difficult to realize, the aluminum on the surface of the molecular sieve is usually easy to remove, and the dealumination conditions which are more rigorous are needed for removing the aluminum on the bulk phase of the molecular sieve, which can cause the collapse of the framework structure of the molecular sieve and the damage of micropores, so the aluminum distribution of the Y molecular sieve before dealumination modification has great influence on the pore structure and the acid property after dealumination.

The existing literature has less research on molecular sieves with aluminum-rich surfaces, especially NaY molecular sieves. CN1363517A discloses a method for synthesizing an aluminum-rich AFI type molecular sieve, which is to crystallize aluminum-rich gmelinite by adjusting the synthesis feed ratio. CN101096274A and CN101096275A disclose a method for synthesizing aluminum-rich Beta zeolite, in which a silica-alumina cogel is synthesized in the presence of a hydrolytic agent, or a silica-alumina source is prepared by impregnating a silicon source with an acidic alumina source, and the silica-alumina source is calcined and crushed to obtain the aluminum-rich Beta zeolite. In CN101274764A and CN101353168A, nano-sized aluminum-rich Beta zeolite is prepared by similar method or in the presence of fluorinion, and the method for preparing the aluminum-rich molecular sieve is realized in the process of primary hydrothermal synthesis. Early X-type molecular sieves, as described in USP2882244, although also belonging to the faujasite structure molecular sieves with very high aluminum content, were not used in catalytic processes in place of Y-type molecular sieves and aluminum-rich Y-type molecular sieves because they did not belong to the class of Y-type molecular sieves and have poor hydrothermal structural stability. CN102173436B discloses a method for preparing an aluminum-rich Y molecular sieve by a secondary hydrothermal synthesis method and carrying out rare earth modification. The method is characterized in that the molecular sieve is a high-surface-area rare earth Y molecular sieve which is prepared by uniformly mixing a NaY type molecular sieve with the same weight of colloids which are prepared from a silicon source and an aluminum source according to the mol ratio of Na2O/SiO2 of 0.3-0.5, SiO2/Al2O3 of 5-7 and H2O/Na2O of 40-70, performing hydrothermal synthesis for 0.5-4 hours at 60-110 ℃ to obtain the NaY molecular sieve rich in aluminum on the surface, performing hydrothermal exchange of rare earth ions, adjusting the pH value of slurry to 7-10 by using ammonia water, performing rare earth oxide deposition, performing vacuum roasting for 0.5-4 hours at 450-750 ℃ and the system pressure of 0.001-0.09 MPa, performing exchange by using an ammonium salt aqueous solution until the content of Na2O is not more than 1.0 weight percent, and preparing the rare earth Y molecular sieve with the RE2O3, wherein the BET content is not less than 10-20 weight percent, and the BET surface area is not less than 600 m/g; from the synthesis process, due to the lack of the directing agent, the aluminum element supplemented in the secondary hydrothermal synthesis is difficult to enter the Y molecular sieve framework to become framework aluminum.

Disclosure of Invention

The purpose of the present disclosure is to provide a surface aluminum-rich NaY molecular sieve having a larger aluminum distribution gradient from the particle surface to the center than conventional molecular sieves, and a method for preparing the same.

To achieve the above object, a first aspect of the present disclosure: the NaY molecular sieve with the surface rich in aluminum is provided, the molar ratio of SiO2/Al2O3 on the surface of the molecular sieve is 2.5-5, the molar ratio of SiO2/Al2O3 in a bulk phase is 6-10, and the Al distribution parameter D of the molecular sieve meets the following requirements: d is not less than 1.2 and not more than 4, wherein D is Al (S)/Al (C), Al (S) represents the aluminum content of the surface and the area below the surface of the molecular sieve measured by XPS method, and Al (C) represents the whole aluminum content of the molecular sieve measured by XRF method.

In a second aspect of the present disclosure: there is provided a process for preparing a NaY molecular sieve according to the first aspect of the present disclosure, the process comprising the steps of:

a. mixing a directing agent with a first silicon source to obtain a first mixture, wherein the molar composition of the directing agent is Na 2O: A12O 3: SiO 2: H2O ═ 6 to 25: 1: (6-25): (200-400);

b. Mixing the first mixture obtained in the step a with a second silicon source, an aluminum source and water to obtain a second mixture;

c. Performing hydrothermal crystallization on the second mixture obtained in the step b, and collecting a solid product;

Wherein, calculated by SiO2, the weight ratio of the first silicon source to the second silicon source is 1: (0.01-12).

Optionally, in step a, the preparation step of the targeting agent comprises: mixing sodium metaaluminate with water glass to obtain a third mixture, carrying out dynamic ageing and standing ageing on the third mixture, and then mixing the third mixture with water to obtain the directing agent;

Preferably, the dynamic ageing comprises: stirring and aging for 5-48 hours at 15-60 ℃; the standing and aging comprises the following steps: standing and aging for 5-48 hours at 15-60 ℃.

Optionally, in step a, the first silicon source is at least one selected from water glass, colloidal silica and silica sol.

Optionally, in step a, when the first silicon source is a solid silicon source, the mixing is performed under a stirring condition, and the stirring time is 30-180 min.

Alternatively, in step b, the molar composition of the second mixture is Na 2O: A12O 3: SiO 2: H2O ═ 2-6: 1: (8-20): (200-400).

Optionally, in step b, the second silicon source is at least one selected from water glass, silica-alumina gel and silica-alumina sol; preferably, the molar ratio of SiO2/Al2O3 of the silicon-aluminum gel is 6-16, and the molar ratio of SiO2/Al2O3 of the silicon-aluminum sol is 6-16.

Optionally, in step b, the aluminum source is at least one selected from sodium metaaluminate, aluminum sulfate, aluminum chloride, aluminum nitrate and pseudo-boehmite.

Optionally, the aluminum element in the guiding agent accounts for 3-30% of the aluminum element in the second mixture in terms of elements and moles.

Optionally, in step c, the conditions of the hydrothermal crystallization are as follows: the temperature is 90-100 ℃, and the time is 15-48 hours.

According to the technical scheme, the guiding agent is firstly contacted with the silicon source to form local high-silicon concentration, so that a crystal nucleus with high silicon atoms can be formed, the silicon source is consumed faster than an aluminum source in the subsequent crystal grain growth, the silicon atom concentration is reduced faster, the silicon-aluminum ratio on the surface of the crystal nucleus is gradually reduced, and the NaY molecular sieve with aluminum-rich surface is finally prepared and has a larger framework aluminum distribution gradient than that of a conventional molecular sieve from the particle surface to the center. The method provided by the disclosure does not need additional template agent or additive, the used raw materials are cheap and easily available, the preparation can be successfully carried out by one-time hydrothermal crystallization, and the process is simple and easy to implement.

Additional features and advantages of the disclosure will be set forth in the detailed description which follows.

Detailed Description

The following describes in detail specific embodiments of the present disclosure. It should be understood that the detailed description and specific examples, while indicating the present disclosure, are given by way of illustration and explanation only, not limitation.

The first aspect of the disclosure: the NaY molecular sieve with the surface rich in aluminum is provided, the molar ratio of SiO2/Al2O3 on the surface of the molecular sieve is 2.5-5, the molar ratio of SiO2/Al2O3 in a bulk phase is 6-10, and the Al distribution parameter D of the molecular sieve meets the following requirements: d is not less than 1.2 and not more than 4, wherein D is Al (S)/Al (C), Al (S) represents the aluminum content of the surface and the area below the surface of the molecular sieve measured by XPS method, and Al (C) represents the whole aluminum content of the molecular sieve measured by XRF method.

The meaning and test methods for the surface SiO2/Al2O3 ratio and bulk SiO2/Al2O3 ratio of molecular sieves are well known to those skilled in the art and the determination of the aluminum content of molecular sieves using the XPS method and the XRF method are also well known to those skilled in the art in light of this disclosure and will not be described in detail herein.

The NaY molecular sieve with the aluminum-rich surface has a larger framework aluminum distribution gradient from the particle surface to the center than that of a conventional molecular sieve, and the catalyst surface and the bulk phase have the same aluminum content after dealumination modification when the molecular sieve is prepared by adopting the NaY molecular sieve, so that the NaY molecular sieve with the aluminum-rich surface is beneficial to obtaining larger catalyst surface mesoporous volume.

in a second aspect of the present disclosure: there is provided a process for preparing a NaY molecular sieve according to the first aspect of the present disclosure, the process comprising the steps of:

a. mixing a directing agent with a first silicon source to obtain a first mixture, wherein the molar composition of the directing agent is Na 2O: A12O 3: SiO 2: H2O ═ 6 to 25: 1: (6-25): (200-400);

b. Mixing the first mixture obtained in the step a with a second silicon source, an aluminum source and water to obtain a second mixture;

c. Performing hydrothermal crystallization on the second mixture obtained in the step b, and collecting a solid product;

Wherein, calculated by SiO2, the weight ratio of the first silicon source to the second silicon source is 1: (0.01-12).

According to the method, the guiding agent is firstly contacted with the silicon source to form local high-silicon concentration, so that a crystal nucleus with high silicon atoms can be formed, the silicon source is consumed faster than an aluminum source in subsequent crystal grain growth, the silicon atom concentration is reduced faster, the silicon-aluminum ratio on the surface of the crystal nucleus is gradually reduced, and the NaY molecular sieve with rich aluminum on the surface is finally prepared, wherein the distribution gradient of framework aluminum is larger than that of a conventional molecular sieve from the particle surface to the center of the NaY molecular sieve.

In step a, the directing agent is a conventional species well known to those skilled in the art for preparing NaY molecular sieves, and can be prepared by the procedures in the prior art according to the present disclosure. For example, the step of preparing the directing agent may comprise: mixing a silicon source (such as sodium silicate), an aluminum source (such as sodium metaaluminate) and optional water according to the ratio of (6-25) calculated by oxide to Na 2O: A12O 3: (6-25) SiO 2: (200-400) mixing the components in the molar ratio of H2O uniformly, and standing for 0.5-48 hours at the temperature of room temperature to 70 ℃ to obtain the guiding agent. In a preferred embodiment of the present disclosure, in order to obtain more desirable effects, the preparation step of the directing agent comprises: and mixing sodium metaaluminate with water glass to obtain a third mixture, carrying out dynamic ageing and standing ageing on the third mixture, and then mixing the third mixture with water to obtain the directing agent. Further, the dynamic aging may include: stirring and aging for 5-48 hours at 15-60 ℃; the standing aging may include: standing and aging for 5-48 hours at 15-60 ℃. The dynamic aging is beneficial to more fully mixing the sodium metaaluminate and the water glass, and after standing and aging, water can be added under the condition of stirring until the required molar ratio of the directing agent is reached. The guiding agent prepared by the preferred embodiment is more beneficial to synthesizing the NaY molecular sieve with aluminum-rich surface.

According to the present disclosure, in step a, the first silicon source may be various inorganic silicon sources commonly used for preparing NaY molecular sieve, and for example, may be at least one selected from water glass, colloidal silica and silica sol. In one embodiment of the present disclosure, when the first silicon source is a solid silicon source (e.g., colloidal silicon dioxide), the mixing is preferably performed under stirring conditions, and the stirring time may be 30 to 180 min; in this way, the solid silicon source can be better mixed with the directing agent, thereby achieving the objectives of the present disclosure. In other embodiments of the present disclosure, when the first silicon source is a liquid silicon source (e.g., water glass, silica sol, etc.), the mixing in step a may be a concurrent mixing of a directing agent and the first silicon source, and may be performed under rapid stirring conditions.

According to the present disclosure, in step b, the second silicon source may be the same as or different from the first silicon source. In order to obtain the desired effect, the second silicon source is generally a liquid silicon source, and may be at least one selected from the group consisting of water glass, silica-alumina gel, and silica-alumina sol, for example. More preferably, the molar ratio of SiO2/Al2O3 of the silicon-aluminum gel is 6-16, and the molar ratio of SiO2/Al2O3 of the silicon-aluminum sol is 6-16. When the first mixture is mixed with the second silicon source, the aluminum source and the water, a cocurrent mixing mode can be adopted, and the mixing can be carried out under the condition of rapid stirring; further, a second source of silicon, aluminum, and water may be added concurrently with the first mixture at a location spaced further apart from the first mixture for mixing.

In accordance with the present disclosure, in step b, the aluminum source may be a conventional kind for preparing NaY molecular sieve, for example, at least one selected from the group consisting of sodium metaaluminate, aluminum sulfate, aluminum chloride, aluminum nitrate and pseudo-boehmite. The water may be deionized or distilled water.

according to the present disclosure, in step b, the molar composition of the second mixture may be Na 2O: A12O 3: SiO 2: H2O ═ 2-6: 1: (8-20): (200-400). And the aluminum element in the guiding agent accounts for 3-30% of the aluminum element in the second mixture in terms of elements and moles.

According to the present disclosure, in step c, the conditions of the hydrothermal crystallization may be conventional conditions for synthesizing NaY molecular sieve, and the present disclosure is not particularly limited, for example: the temperature can be 90-100 ℃ and the time can be 15-48 hours.

The present disclosure is further illustrated below by reference to examples and comparative examples, but the scope of the present disclosure is not limited to these examples only.

In each of the examples and comparative examples, the relative crystallinity of NaY molecular sieve was determined using a SIMADU XRD6000 type X-ray diffractometer under the following experimental conditions: CuKa radiation, tube pressure 40kv and tube current 40 mA. The relative crystallinity was determined according to SH/T0340-92 standard method (compilation of standards for the chemical industry, published by the Chinese standards Press, 2000).

The surface SiO2/Al2O3 molar ratio of the molecular sieve is measured by an XPS method, the method simultaneously measures the aluminum content (Al (S)) in a region 2-6 nm below the surface and the surface of a sample, a Perkin-Elmer PHI 5000ESCA Systemm X-ray photoelectron spectrometer is used as a test instrument, Al K alpha (1486.6 eV) is used as a light source, and the pressure of an analysis chamber is less than 10-7Pa during measurement. The sample was Ar + ion etched for 15min prior to measurement to remove oxides generated during sample processing. The binding energies of all elements were corrected for with contaminated carbon (EC16 ═ 284.6eV), and the specific test methods were described in the "journal of catalysis, 11(2), 1993: 127.

The bulk SiO2/Al2O3 molar ratio of the molecular sieve and the overall aluminum content of the molecular sieve, i.e., Al (C), were determined by X-ray fluorescence spectroscopy (XRF). The test apparatus was a 3271E model X-ray fluorescence spectrometer manufactured by Nippon Denshi electric motors industries, Ltd. The test process is as follows: and (3) detecting the spectral line intensity of each element by using a scintillation counter and a proportional counter for the rhodium target with the excitation voltage of 50kV and the excitation current of 50mA, and quantitatively analyzing the SiO2 content and the Al2O3 content of the sample.