Y-type molecular sieve and method for synthesizing the same

Abstract

The application discloses a Y-type molecular sieve and a preparation method thereof, wherein the grain size of the molecular sieve is 20-100 nm, preferably 40-70 nm, and more preferably 50-60 nm; the molar ratio of silicon oxide to aluminum oxide in the molecular sieve is 4.5-7, preferably 5.0-6.5, and more preferably 6.0-6.5; and the proportion of 40-70 nm grains in the molecular sieve is 80%-95% as measured by a dynamic light electron scattering method, preferably 85%-93%. The Y-type molecular sieve provided by the application has small grains, a concentrated grain distribution, a high silicon-aluminum ratio and a Y molecular sieve with good hydrothermal stability, and can meet the demand of industrial production. When the Y-type molecular sieve is used for preparing a catalyst, the catalyst has stable performance.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Chinese Patent Application No. 202110019016.7, filed on January 7, 2021, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention belongs to the field of molecular sieve synthesis, and relates to a Y-type molecular sieve and its synthesis method, specifically to a Y-type molecular sieve with small crystal size and high silicon-to-aluminum ratio and its synthesis method. Background Technology

[0004] Y-type molecular sieves are molecular sieves with a FAU-type framework structure, where the interconnected pores of the octahedral zeolite cages form a three-dimensional channel structure. Due to their unique structure and properties, Y-type molecular sieves have been widely used in catalysis, gas separation, adsorption, and ion exchange in recent years. Y-type molecular sieves have been used in catalytic cracking (FCC) and hydrocracking for over 50 years. Their large specific surface area, large pore volume, abundant acid centers, and good thermal and chemical stability make them irreplaceable in industry.

[0005] The earliest Y-type molecular sieves used in industrial production were in the micrometer scale. However, due to the relatively long pores of micrometer-sized Y-type molecular sieves, secondary cracking easily occurs during the diffusion of product molecules within the pores in processes such as catalytic cracking, hydrocracking, and hydroisomerization, leading to a decrease in liquid yield. Furthermore, traditional Y-type molecular sieves, without post-treatment, have a very small external surface area, limiting their conversion of large polycyclic aromatic hydrocarbons. Small-crystal Y-type molecular sieves, with their larger external specific surface area while retaining the framework structure of Y-type molecular sieves, have attracted increasing attention.

[0006] Currently, there are several main methods for synthesizing small-crystal NaY molecular sieves:

[0007] 1. Adding a directing agent during the synthesis process alters the product properties by improving the agent's properties. For example, CN1033503C discloses a method for preparing small-crystal NaY molecular sieves. This method involves adding a sodium silicate solution to a conventional directing agent with a transmittance of less than 30% to prepare an improved directing agent with a transmittance greater than 70%. This improved directing agent is then added to the silica-alumina gel before crystallization to obtain small-crystal NaY molecular sieves with a SiO2 / Al2O3 ratio exceeding 5 and a crystallite size of several hundred nanometers. CN1032803C discloses a method for synthesizing small-crystal NaY molecular sieves, capable of producing NaY molecular sieves with crystallite sizes ranging from 100 to 500 nm. This method involves first crystallizing the silica-alumina gel at high temperature, then adding a directing agent after crystallization, followed by further crystallization to obtain the final product.

[0008] 2. The size of NaY molecular sieves can be reduced by adding surfactants or organic dispersants. For example, CN103449470B discloses a method for synthesizing highly stable small-crystal NaY molecular sieves. A high-alkali sodium aluminate solution is added to a water glass solution, stirred until homogeneous, and then poured into an aqueous solution of a surfactant. After aging, an improved directing agent is obtained. The directing agent is added to materials prepared according to a certain molar ratio, and crystallization is carried out for 8-72 hours to obtain small-crystal NaY molecular sieves. The crystal size is 100-400 nm. USP 3516786 synthesizes small-crystal NaY molecular sieves using organic solvents. Water-soluble solvents such as methanol, ethanol, dimethyl sulfoxide, and dimethylformamide can be added to the silicon or aluminum source before gel formation or after gel formation. The amount added is 0.1-20% of the gel amount. After crystallization, small-crystal NaY molecular sieves can be obtained.

[0009] 3. Methods to increase the alkalinity of the synthesis system. EP 0435625A2 proposes a method for directly synthesizing small-grained Y molecular sieves using high-alkali silica-alumina gel, achieving particle sizes down to tens of nanometers. This method first involves pouring an aqueous sodium aluminate solution into a high-alkali water glass solution and rotating it at 3000 rpm to homogenize the gel. After aging and crystallization, the product is obtained. However, the NaY molecular sieves obtained by this method have a relatively low SiO2 / Al2O3 ratio and poor hydrothermal stability, making them unsuitable for industrial application.

[0010] The Y-type molecular sieves obtained by the above methods either have too low a silicon-to-aluminum ratio, large crystal size, or uneven particle size distribution, resulting in defects such as easy structural collapse, low catalytic activity, unstable performance, and short catalyst lifetime when used as catalyst supports. Summary of the Invention

[0011] To address the shortcomings of existing technologies, this invention provides a Y-type molecular sieve and its synthesis method. This Y-type molecular sieve has the advantages of high silicon-to-aluminum ratio, small crystal size, uniform particle size distribution, and good hydrothermal stability.

[0012] According to a first aspect of the present invention, the present invention provides a Y-type molecular sieve, wherein the crystal size of the molecular sieve is 20-100 nm, preferably 40-70 nm, more preferably 50-60 nm; the molar ratio of silicon oxide to aluminum oxide in the molecular sieve is 4.5-7, preferably 5.0-6.5, more preferably 6.0-6.5; and the proportion of 40-70 nm crystals in the molecular sieve is 80%-95%, preferably 85%-93%, as measured by dynamic photoelectron scattering method.

[0013] Preferably, the specific surface area of ​​the Y-type molecular sieve of the present invention is 800-950 m². 2 / g, preferably 850-920 m 2 / g, for example 810, 820, 830, 840, 850, 860, 870, 880, 890, 900, 905, 910, 914, 920, 930, 940, 948m 2 / g.

[0014] Preferably, the Y-type molecular sieve of the present invention has an external specific surface area of ​​100-200 m². 2 / g, preferably 150-180m 2 / g.

[0015] Preferably, the R value of the molecular sieve is 4-9, for example 4, 5, 6, 6.2, 6.5, 7, 7.3, 7.8, 8, 8.5, 9, where R = specific surface area / external specific surface area.

[0016] Preferably, the pore volume of the Y-type molecular sieve of the present invention is not less than 0.36 ml / g, preferably not less than 0.38 ml / g and not greater than 0.56 ml / g, preferably not greater than 0.53 ml / g, more preferably 0.43-0.53 ml / g, such as 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.50, 0.51, 0.52 ml / g.

[0017] The Y-type molecular sieve provided by this invention can be NaY or HY after ammonium exchange. When it is HY, after treatment at 700℃ and 0.1MPa high-temperature steam atmosphere for 2 hours, the crystallinity of the obtained molecular sieve is between 75-90%, preferably 83-88%.

[0018] When the molecular sieve is NaY, the hydrothermal stability of the Y-type molecular sieve is as follows: after ammonium exchange, after treatment in a high-temperature water vapor atmosphere of 700℃ and 0.1MPa for 2 hours, the crystallinity of the obtained molecular sieve is between 75-90%, preferably 83-88%.

[0019] The Y-type molecular sieve of this invention has the properties of both Y molecular sieve and nanomaterials due to its small particle size and large external specific surface area; it has good hydrothermal stability and is not prone to collapse due to its high silicon-to-aluminum ratio; and it has stable catalyst properties due to its uniform particle size distribution.

[0020] According to a second aspect of the present invention, the present invention provides a method for synthesizing Y-type molecular sieves, the method comprising the following steps:

[0021] (1) After mixing silicon source, aluminum source, alkali source and water, the first crystallization is carried out to obtain directing agent A. The characteristic diffraction peaks of Y molecular sieve cannot be observed in the XRD spectrum of directing agent A.

[0022] (2) Add one or more of silicon source, aluminum source, alkali source and water to the directing agent A to carry out a second crystallization to obtain directing agent B. The crystallinity of directing agent B is 5%-20%, preferably 8%-16%;

[0023] (3) Add one or more of silicon source, aluminum source, alkali source, and water to the directing agent B to carry out third crystallization;

[0024] In step (1), the molar ratio of Na2O to H2O is 0.01-0.045 lower than that of Na2O to H2O in step (2), preferably 0.01-0.035 lower, more preferably 0.015-0.030 lower, and even more preferably 0.02-0.026 lower.

[0025] In the method of the present invention, the Na2O:H2O molar ratio in the crystallization system for preparing the directing agent B, i.e., the system in step (2), is higher (0.01-0.04), preferably higher (0.015-0.035), and even more preferably higher (0.023-0.033) than the crystallization system formed after adding one or more of silicon source, aluminum source, alkali source, and water to the directing agent B.

[0026] In the above method, the silicon source is preferably one or more of water glass, silica sol, silicon dioxide, and sodium silicate; the aluminum source is preferably one or more of sodium aluminate, aluminum powder, aluminum hydroxide, and aluminum isopropoxide; and the alkali source is preferably one or more of sodium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide.

[0027] Distilled water is preferred.

[0028] According to a specific embodiment of the present invention, the method for synthesizing the Y-type molecular sieve specifically includes the following steps:

[0029] (1) Under stirring conditions, sodium aluminate, preferably an aluminum source, is dissolved in distilled water, and then water glass, preferably a silicon source, is added. After stirring evenly, sodium hydroxide is added and stirring is continued. The gel is then crystallized at a certain temperature for a period of time and then removed to obtain an incompletely crystallized Y molecular sieve solution, denoted as directing agent A. At this time, directing agent A contains some basic structural units and is in an amorphous phase. No characteristic diffraction peaks of Y molecular sieve are observed in the XRD pattern, that is, the crystallinity is 0.

[0030] (2) Under stirring conditions, a certain amount of silicon source, such as high-alkali water glass solution, and aluminum source, such as sodium aluminate solution, are added sequentially to the directing agent A obtained in step (1), stirred evenly, and crystallized at a constant temperature. The mixture is then removed and cooled to room temperature to obtain directing agent B. At this time, the crystallinity of directing agent B is 5%-20%, preferably 8%-16%.

[0031] (3) Under stirring conditions, low-alkali water glass and sodium aluminate solution are added to the directing agent B, and the mixture is kept at a constant temperature for crystallization. The resulting solid product is filtered, washed until neutral, and dried to obtain the product.

[0032] In this invention, high-alkali water glass and low-alkali water glass refer to the content of sodium hydroxide in the water glass solution, specifically based on the molar ratio of materials required for this step.

[0033] In the method of the present invention, the preferred material molar ratio in step (1) is (7-14)Na2O:Al2O3:(20-33)SiO2:(300-650)H2O, and more preferably (9-12)Na2O:Al2O3:(23-28)SiO2:(350-550)H2O.

[0034] In the method of the present invention, preferably, the crystallization temperature of step (1) is 70-100℃, more preferably 80-90℃, and the time is 4-12 hours, more preferably 6-10 hours.

[0035] In the method of the present invention, preferably, the directing agent A added in step (2) accounts for 25-38 wt% of the total mass of the directing agent B (based on the mass of Al2O3), more preferably 28-35 wt%. By controlling the directing agent A within the above-mentioned specific proportion range, the crystal size of the directing agent B can be controlled, thereby better ensuring that the crystal size of the obtained Y-type molecular sieve is within the required range and the particle size distribution is uniform.

[0036] In the method of the present invention, the molar ratio of the material of the directing agent B in step (2) is (17-26)Na2O:Al2O3:(13-19)SiO2:(400-618)H2O, preferably (21-24)Na2O:Al2O3:(15-17)SiO2:(400-550)H2O.

[0037] In the method of the present invention, the crystallization temperature in step (2) is 40-70℃, preferably 50-65℃, and the crystallization time is 15-41 hours, preferably 18-28 hours.

[0038] In the above method, the crystallization temperature during the preparation of directing agent A, i.e., the temperature of the first crystallization, is preferably higher (5-60℃) than the crystallization temperature during the preparation of directing agent B, i.e., the temperature of the second crystallization, and more preferably (15-40℃). By controlling the second crystallization to be carried out at a lower temperature, the crystal size of the molecular sieve is made smaller, and the formation of impurity crystals is avoided.

[0039] Preferably, the time for the first crystallization is 8-37 hours shorter than the time for the second crystallization, more preferably 8-22 hours.

[0040] In the method of the present invention, the mass of the directing agent B added in step (3) accounts for 45-65 wt% of the final sol (i.e. the material undergoing third crystallization) composition (based on the mass of Al2O3), preferably 50-60 wt%.

[0041] In the method of the present invention, after adding water glass and sodium aluminate solution in step (3), the final sol composition is (12-20)Na2O:Al2O3:(14-20)SiO2:(550-1050)H2O, preferably (14-17)Na2O:Al2O3:(16-18)SiO2:(650-950)H2O.

[0042] In the method of the present invention, the crystallization temperature of step (3) is 85-105℃, preferably 90-100℃, and the crystallization time is 6-13 hours, preferably 8-12 hours.

[0043] Preferably, the temperature of the third crystallization is 20-60°C higher than that of the second crystallization, and more preferably 35-50°C.

[0044] Preferably, the third crystallization time is 5-35 hours shorter than the second crystallization time, and more preferably 6-20 hours shorter.

[0045] According to a preferred embodiment of the present invention, the method further includes subjecting the product obtained from the third crystallization to one or more ammonium exchanges to obtain the desired HY molecular sieve.

[0046] The ammonium exchange can be carried out according to known methods and conditions, for example, by performing three ammonium exchanges using a 1.5 mol / L ammonium chloride solution at 70°C, with a solid-liquid ratio of 1:10 for each exchange. Further details are omitted here.

[0047] The synthesis method provided by this invention first involves crystallization under conditions of high silicon-to-aluminum ratio and low alkalinity, resulting in the formation of a large number of incompletely crystallized nano-Y molecular sieve precursors in the solution. Then, a secondary crystallization is performed by increasing the alkalinity of the sol at a slightly lower temperature to obtain nano-seed crystals with smaller grains and a higher silicon-to-aluminum ratio. Based on this, a tertiary crystallization is performed under conditions of low alkalinity and high silicon-to-aluminum ratio to further increase the silicon-to-aluminum ratio and crystallinity, resulting in a more complete framework structure. This yields a Y molecular sieve with smaller, concentrated grains, a higher silicon-to-aluminum ratio, and good hydrothermal stability, meeting the needs of industrial production. Therefore, the synthesis method of this invention is suitable for industrial applications. Attached Figure Description

[0048] Figure 1 The XRD diffraction pattern of the directing agent A prepared in Example 1 is shown.

[0049] Figure 2 The XRD diffraction pattern of the directing agent B prepared in Example 1 is shown.

[0050] Figure 3 The XRD diffraction pattern of the Y-type molecular sieve prepared in Example 1 is shown.

[0051] Figure 4This is a 10kx SEM image of the Y-type molecular sieve prepared in Example 1.

[0052] Figure 5 This is a 50kx SEM image of the Y-type molecular sieve prepared in Example 1. Detailed Implementation

[0053] In the method of this invention, the crystallinity of directing agent A and directing agent B is measured by X-ray diffraction using the method of Chinese petrochemical industry standard SH / T0340-92.

[0054] The hydrothermal stability test of the Y-type molecular sieve refers to the crystallinity of the sample after hydrothermal treatment at 700℃ and 0.1MPa water vapor atmosphere for 2 hours. Higher crystallinity indicates better hydrothermal stability. The specific test method involves first performing three ammonium exchange cycles with a 1.5mol / L ammonium chloride solution at 70℃, with a solid-liquid weight ratio of 1:10 for each exchange. Then, the sample is placed under hydrothermal treatment at 700℃ and 0.1MPa water vapor atmosphere for 2 hours. Finally, the crystallinity of the sample after hydrothermal treatment is determined using X-ray diffraction according to the Chinese petrochemical industry standard SH / T0340-92.

[0055] The specific surface area and pore volume of the molecular sieve were measured using the N2-adsorption-desorption method. Before measurement, the sample was first heat-treated at 300℃ for 3 hours, and then subjected to nitrogen adsorption at 77K for testing. The specific surface area of ​​the molecular sieve was calculated using the BET method, and the total pore volume was measured at p / p 0 The surface area was measured at 0.98, and the external specific surface area was obtained using the t-Plot method.

[0056] The silicon-to-aluminum molar ratio of the molecular sieve framework was measured using X-ray diffraction. The cell parameter a0 was measured according to the Chinese petrochemical industry standard SH / T0339-92, and then substituted into Breck's formula Si / Al = ((192 × 0.00868) / (a0 − 24.191))–1 for calculation. The resulting silicon-to-aluminum molar ratio is expressed as SiO2 / Al2O3.

[0057] The crystal size of the molecular sieve was measured using a scanning electron microscope (SEM).

[0058] The particle size distribution of the molecular sieve was measured using the dynamic photoelectron scattering (DLS) method specified in GB / T 29022-2012.

[0059] The gel composition in each step is calculated based on the amount of material fed.

[0060] 1,3,5-Triisopropylbenzene (TIPB) was used as a model compound to test the catalytic cracking performance of the molecular sieve. The reaction was carried out in a fixed-bed reactor. 2g of sieved 20-40 mesh HY molecular sieve was weighed and loaded into the reactor. The catalyst was first purged with N2 at room temperature for 30 min at a flow rate of 50 mL / min. Then, the temperature was raised to 500℃ for activation. After activation, the temperature was lowered to 450℃, and the feedstock was introduced at a flow rate of 12 mL / h. The products were analyzed using an Agilent 7890B gas chromatograph (FID detector). Table 2 below shows the composition of the products collected after 48 hours of reaction in the stable period.

[0061] The preparation process and product performance of the method of the present invention will be further illustrated below with reference to the embodiments and comparative examples, but the following embodiments do not constitute a limitation on the method of the present invention.

[0062] Example 1

[0063] (1) Under stirring conditions, sodium aluminate was dissolved in distilled water, then water glass solution was added and stirred until the gel was uniform. Then sodium hydroxide solution was added and stirring was continued. The final gel composition was 9Na2O:Al2O3:23.0SiO2:550H2O. The gel was crystallized at 80℃ for 10h, then removed and cooled to room temperature to obtain directing agent A. XRD test did not observe any characteristic diffraction peaks belonging to Y molecular sieve.

[0064] (2) Under stirring conditions, water glass solution and sodium aluminate solution were added to directing agent A in sequence, and the resulting gel composition was 23Na2O:Al2O3:16SiO2:550H2O. Directing agent A accounted for 28wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 65℃ for 18h, then removed and cooled to room temperature, and this was designated as directing agent B, with a crystallinity of 13%.

[0065] (3) Under stirring conditions, water glass solution and sodium aluminate solution were added to directing agent B, and the final gel composition was 15Na2O:Al2O3:18SiO2:820H2O, with directing agent B accounting for 50wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 90℃ for 12h, cooled to room temperature, filtered and dried to obtain the final product. The XRD patterns of the crystallized products obtained in steps (1), (2) and (3) are shown below. Figure 1 , Figure 2 , Figure 3 As shown.

[0066] Example 2

[0067] (1) Under stirring conditions, sodium aluminate was dissolved in distilled water, then water glass solution was added and stirred until the gel was uniform. Then sodium hydroxide solution was added and stirring was continued. The final gel composition was 12.0Na2O:Al2O3:25SiO2:450H2O. The gel was crystallized at 90℃ for 6 hours, then removed and cooled to room temperature to obtain directing agent A. XRD test did not observe any characteristic diffraction peaks belonging to Y molecular sieve.

[0068] (2) Under stirring conditions, water glass solution and sodium aluminate solution were added to directing agent A in sequence, and the resulting gel composition was 21Na2O:Al2O3:17SiO2:440H2O. Directing agent A accounted for 35wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 50℃ for 28h, then removed and cooled to room temperature, and this was designated as directing agent B, with a crystallinity of 18%.

[0069] (3) Under stirring conditions, water glass solution and sodium aluminate solution were added to the directing agent B. The final gel composition was 14Na2O:Al2O3:17SiO2:950H2O, and the directing agent B accounted for 60wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 100℃ for 8h, cooled to room temperature, filtered and dried to obtain the final product.

[0070] Example 3

[0071] (1) Under stirring conditions, sodium aluminate was dissolved in distilled water, then water glass solution was added and stirred until the gel was uniform. Then sodium hydroxide solution was added and stirring was continued. The final gel composition was 10.5Na2O:Al2O3:28SiO2:350H2O. The gel was crystallized at 85℃ for 8 hours, then removed and cooled to room temperature to obtain directing agent A. XRD test did not observe any characteristic diffraction peaks belonging to Y molecular sieve.

[0072] (2) Under stirring conditions, water glass solution and sodium aluminate solution were added to directing agent A in sequence. The resulting gel composition was 21.5Na2O:Al2O3:15SiO2:400H2O, and directing agent A accounted for 33wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 60℃ for 25h, then removed and cooled to room temperature. This gel was designated as directing agent B, with a crystallinity of 14%.

[0073] (3) Under stirring conditions, water glass solution and sodium aluminate solution were added to the directing agent B. The final gel composition was 17Na2O:Al2O3:16SiO2:660H2O, and the directing agent B accounted for 55wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 100℃ for 10h, cooled to room temperature, filtered and dried to obtain the final product.

[0074] Example 4

[0075] (1) Under stirring conditions, sodium aluminate was dissolved in distilled water, then water glass solution was added and stirred until the gel was uniform. Then sodium hydroxide solution was added and stirring was continued. The final gel composition was 10Na2O:Al2O3:20SiO2:640H2O. The gel was crystallized at 70℃ for 12h, then removed and cooled to room temperature to obtain directing agent A. XRD test did not observe any characteristic diffraction peaks belonging to Y molecular sieve.

[0076] (2) Under stirring conditions, water glass solution and sodium aluminate solution were added to directing agent A in sequence. The resulting gel composition was 25.6Na2O:Al2O3:19SiO2:420H2O, and directing agent A accounted for 30wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 55℃ for 25h, then removed and cooled to room temperature. This gel was designated as directing agent B, with a crystallinity of 10%.

[0077] (3) Under stirring conditions, water glass solution and sodium aluminate solution were added to the directing agent B. The final gel composition was 20Na2O:Al2O3:18SiO2:950H2O, and the directing agent B accounted for 65wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 105℃ for 6h, cooled to room temperature, filtered and dried to obtain the final product.

[0078] Example 5

[0079] (1) Under stirring conditions, sodium aluminate was dissolved in distilled water, then water glass solution was added and stirred until the gel was uniform. Then sodium hydroxide solution was added and stirring was continued. The final gel composition was 14.0Na2O:Al2O3:33SiO2:520H2O. The gel was crystallized at 75℃ for 4 hours, then removed and cooled to room temperature to obtain directing agent A. XRD test did not observe any characteristic diffraction peaks belonging to Y molecular sieve.

[0080] (2) Under stirring conditions, water glass solution and sodium aluminate solution were added to directing agent A in sequence. The resulting gel composition was 17.0Na2O:Al2O3:16SiO2:400H2O, and directing agent A accounted for 25wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 70℃ for 15h, then removed and cooled to room temperature. This gel was designated as directing agent B, with a crystallinity of 20%.

[0081] (3) Under stirring conditions, water glass solution and sodium aluminate solution were added to the directing agent B. The final gel composition was 12Na2O:Al2O3:14SiO2:1050H2O, and the directing agent B accounted for 45wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 90℃ for 10h, cooled to room temperature, filtered and dried to obtain the final product.

[0082] Example 6

[0083] (1) Under stirring conditions, sodium aluminate was dissolved in distilled water, then water glass solution was added and stirred until the gel was uniform. Then sodium hydroxide solution was added and stirring was continued. The final gel composition was 7.0Na2O:Al2O3:26SiO2:300H2O. The gel was crystallized at 100℃ for 8 hours, then removed and cooled to room temperature to obtain directing agent A. XRD test did not observe any characteristic diffraction peaks belonging to Y molecular sieve.

[0084] (2) Under stirring conditions, water glass solution and sodium aluminate solution were added to directing agent A in sequence. The resulting gel composition was 23.0Na2O:Al2O3:13SiO2:615H2O, and directing agent A accounted for 38wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 40℃ for 16h, then removed and cooled to room temperature. This gel was designated as directing agent B, with a crystallinity of 10%.

[0085] (3) Under stirring conditions, water glass solution and sodium aluminate solution were added to the directing agent B. The final gel composition was 15Na2O:Al2O3:20SiO2:550H2O, and the directing agent B accounted for 55wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 85℃ for 10h, cooled to room temperature, filtered and dried to obtain the final product.

[0086] Example 7

[0087] (1) Under stirring conditions, sodium aluminate was dissolved in distilled water, then water glass solution was added and stirred until the gel was uniform. Then sodium hydroxide solution was added and stirring was continued. The final gel composition was 12Na2O:Al2O3:20SiO2:530H2O. The gel was crystallized at 90℃ for 6 hours, then removed and cooled to room temperature to obtain directing agent A. XRD test did not observe any characteristic diffraction peaks belonging to Y molecular sieve.

[0088] (2) Under stirring conditions, water glass solution and sodium aluminate solution were added to directing agent A in sequence, and the resulting gel composition was 17Na2O:Al2O3:14SiO2:420H2O. Directing agent A accounted for 35wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 60℃ for 31h, then removed and cooled to room temperature, and this was designated as directing agent B, with a crystallinity of 6%.

[0089] (3) Under stirring conditions, water glass solution and sodium aluminate solution were added to the directing agent B. The final gel composition was 20Na2O:Al2O3:16SiO2:800H2O, and the directing agent B accounted for 55wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 95℃ for 10h, cooled to room temperature, filtered and dried to obtain the final product.

[0090] Example 8

[0091] (1) Under stirring conditions, sodium aluminate was dissolved in distilled water, then water glass solution was added and stirred until the gel was uniform. Then sodium hydroxide solution was added and stirring was continued. The final gel composition was 12Na2O:Al2O3:25SiO2:500H2O. The gel was crystallized at 70℃ for 4 hours, then removed and cooled to room temperature to obtain directing agent A. XRD test did not observe any characteristic diffraction peaks belonging to Y molecular sieve.

[0092] (2) Under stirring conditions, water glass solution and sodium aluminate solution were added to directing agent A in sequence, and the resulting gel composition was 17Na2O:Al2O3:15SiO2:500H2O. Directing agent A accounted for 30wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 40℃ for 24h, then removed and cooled to room temperature, and this was designated as directing agent B, with a crystallinity of 10%.

[0093] (3) Under stirring conditions, water glass solution and sodium aluminate solution were added to the directing agent B. The final gel composition was 14.4Na2O:Al2O3:16SiO2:800H2O, and the directing agent B accounted for 62wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 100℃ for 6h, cooled to room temperature, filtered and dried to obtain the final product.

[0094] Example 9

[0095] (1) Under stirring conditions, sodium aluminate was dissolved in distilled water, then water glass solution was added and stirred until the gel was uniform. Then sodium hydroxide solution was added and stirring was continued. The final gel composition was 12Na2O:Al2O3:22SiO2:500H2O. The gel was crystallized at 80℃ for 5 hours, then removed and cooled to room temperature to obtain directing agent A. XRD test did not observe any characteristic diffraction peaks belonging to Y molecular sieve.

[0096] (2) Under stirring conditions, water glass solution and sodium aluminate solution were added to directing agent A in sequence, and the resulting gel composition was 25Na2O:Al2O3:17SiO2:500H2O. Directing agent A accounted for 35wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 60℃ for 9h, then removed and cooled to room temperature, and this was designated as directing agent B, with a crystallinity of 8%.

[0097] (3) Under stirring conditions, water glass solution and sodium aluminate solution were added to the directing agent B. The final gel composition was 20Na2O:Al2O3:18SiO2:800H2O, and the directing agent B accounted for 60wt% of the total gel mass (based on the percentage content of Al2O3 in the gel). The gel was crystallized at 90℃ for 13h, cooled to room temperature, filtered and dried to obtain the final product.

[0098] Comparative Example 1

[0099] Y-type molecular sieves were prepared according to the method of Example 9, except that directing agent B was not prepared. Instead, water glass solution and sodium aluminate solution were directly added to directing agent A under stirring conditions for final crystallization. Directing agent A accounted for 60 wt% of the total gel mass (based on the percentage of Al2O3 in the gel), and the final gel composition was 20Na2O:Al2O3:18SiO2:800H2O.

[0100] Comparative Example 2

[0101] Y-type molecular sieves were prepared according to the method of Example 9, except that directing agent A was not prepared. Instead, directing agent B was prepared directly according to the gel composition of 25Na2O:Al2O3:17SiO2:500H2O, and then directing agent B was added for final crystallization. Directing agent B accounted for 60wt% of the total gel mass (based on the percentage of Al2O3 in the gel), and the final gel composition was 20Na2O:Al2O3:18SiO2:800H2O.

[0102] Comparative Example 3

[0103] Y-type molecular sieves were prepared according to the method of Example 9, except that the gel composition of step (2) was 37Na2O:Al2O3:17SiO2:500H2O.

[0104] Comparative Example 4

[0105] Y-type molecular sieves were prepared according to the method of Example 9, except that the temperature of isothermal crystallization in step (1) was 70°C and the time was 24 hours, and the crystallinity of the directing agent A was 25% as determined by XRD.

[0106] Comparative Example 5

[0107] Y-type molecular sieves were prepared according to the method of Example 9, except that the isothermal crystallization temperature in step (2) was 65°C and the time was 50 hours. XRD test showed that the crystallinity of the directing agent B was 45%.

[0108] The product properties of the above embodiments and comparative examples are shown in Table 1.

[0109] Table 1. Structural properties of products in the examples and comparative examples.

[0110]

[0111] Table 2 Catalytic performance of products in the Examples and Comparative Examples

[0112]

[0113] As can be seen from the results in Table 1 above, the Y-type molecular sieve provided by this invention has small and concentrated crystallite distribution, a high silicon-to-aluminum ratio, and good hydrothermal stability, which can meet the needs of industrial production. The catalyst exhibits stable performance when used in catalyst preparation.

[0114] As can be seen from the results in Table 2 above, the Y-type molecular sieve provided by this invention exhibits excellent cracking activity for the macromolecular reactant 1,3,5-triisopropylbenzene. This molecular sieve has a small crystal size, concentrated particle size distribution, and abundant acidic sites on its outer surface, which is beneficial for the cracking of macromolecular reactants into low-molecular-weight products (isopropylbenzene and benzene). This molecular sieve also exhibits good diffusion performance for macromolecular reactants, is less prone to carbon buildup, and is conducive to long-term operation.

Claims

1. A method for synthesizing Y-type molecular sieves, characterized in that: The molecular sieve has a crystallite size of 20-100 nm, a silica / alumina molar ratio of 4.5-6.5, and the proportion of 40-70 nm crystallites in the molecular sieve, as measured by dynamic photoelectron scattering, is 80-95%. The synthesis method of the Y-type molecular sieve includes the following steps: (1) After mixing silicon source, aluminum source, alkali source and water, the first crystallization is carried out to obtain directing agent A. No characteristic diffraction peaks belonging to Y molecular sieve can be observed in the XRD spectrum of directing agent A. (2) Add one or more of silicon source, aluminum source, alkali source, and water to the directing agent A to carry out a second crystallization to obtain directing agent B. The crystallinity of directing agent B is 5%-20%. (3) Add one or more of silicon source, aluminum source, alkali source, and water to the directing agent B to carry out third crystallization; In step (1), the molar ratio of Na2O to H2O is 0.01-0.045 lower than that in step (2). The temperature of the first crystallization is 5-60℃ higher than that of the second crystallization, and the time of the first crystallization is 8-37 hours shorter than that of the second crystallization. The crystallization temperature of step (1) is 70-100℃ and the time is 4-12 hours; the crystallization temperature of step (2) is 40-70℃ and the crystallization time is 15-41 hours.

2. The method according to claim 1, characterized in that, The molar ratio of Na2O:H2O in step (1) is 0.015-0.03 lower than that in step (2).

3. The method according to claim 1, characterized in that, The molar ratio of Na2O:H2O in step (1) is 0.02-0.026 lower than that in step (2).

4. The method according to claim 1, characterized in that, The molar ratio of Na2O:H2O in step (2) is 0.01-0.04 higher than that in step (3).

5. The method according to claim 4, characterized in that, The molar ratio of Na2O to H2O in step (2) is 0.015-0.035 higher than that in step (3).

6. The method according to claim 4, characterized in that, The molar ratio of Na2O to H2O in step (2) is 0.023-0.033 higher than that in step (3).

7. The method according to claim 1 or 4, characterized in that, The molar ratio of materials in step (1) is (7-14)Na2O:Al2O3:(20-33)SiO2:(300-650)H2O.

8. The method according to claim 7, characterized in that, The molar ratio of materials in step (1) is (9-12)Na2O:Al2O3:(23-28)SiO2:(350-550)H2O.

9. The method according to claim 1, characterized in that, The temperature of the first crystallization is 15-40℃ higher than that of the second crystallization, and the time of the first crystallization is 8-22 hours shorter than that of the second crystallization.

10. The method according to claim 1, characterized in that, The crystallization temperature in step (1) is 80-90℃ and the time is 6-10 hours.

11. The method according to claim 1, characterized in that, Based on the mass of Al2O3, the directing agent A added in step (2) accounts for 25-38 wt% of the total mass of directing agent B.

12. The method according to claim 11, characterized in that, Based on the mass of Al2O3, the directing agent A added in step (2) accounts for 28-35 wt% of the total mass of directing agent B.

13. The method according to claim 1, characterized in that, In step (2), the molar ratio of the directing agent B is (17-26)Na2O:Al2O3:(13-19)SiO2:(400-618)H2O.

14. The method according to claim 13, characterized in that, In step (2), the molar ratio of the directing agent B is (21-24)Na2O:Al2O3: (15-17)SiO2: (400-550)H2O.

15. The method according to claim 1, characterized in that, The crystallization temperature in step (2) is 50-65℃ and the crystallization time is 18-28 hours.

16. The method according to claim 1, characterized in that, Based on the mass of Al2O3, the mass of the directing agent B added in step (3) accounts for 45-65 wt% of the composition mass of the material undergoing the third crystallization.

17. The method according to claim 16, characterized in that, Based on the mass of Al2O3, the mass of the directing agent B added in step (3) accounts for 50-60 wt% of the composition mass of the material undergoing the third crystallization.

18. The method according to claim 1, characterized in that, The composition of the material undergoing the third crystallization in step (3) is (12-20)Na2O:Al2O3:(14-20)SiO2:(550-1050)H2O.

19. The method according to claim 18, characterized in that, The composition of the material undergoing the third crystallization in step (3) is (14-17)Na2O:Al2O3: (16-18)SiO2: (650-950)H2O.

20. The method according to claim 1, characterized in that, The crystallization temperature in step (3) is 80-105℃ and the crystallization time is 6-13 hours.

21. The method according to claim 20, characterized in that, The crystallization temperature in step (3) is 90-100℃ and the crystallization time is 8-12 hours.

22. The method according to claim 1, characterized in that, The silicon sources mentioned in steps (1), (2) and (3) may be the same or different, and each can be one or more of water glass, silica sol, silicon dioxide, and sodium silicate. The aluminum sources mentioned in steps (1), (2) and (3) may be the same or different, and each can be one or more of sodium aluminate, sodium aluminate, aluminum powder, aluminum hydroxide, and aluminum isopropoxide. The alkali sources mentioned in steps (1), (2), and (3) may be the same or different, and each may be one or more of sodium hydroxide, tetraethylammonium hydroxide, and tetrapropylammonium hydroxide.

23. Y-type molecular sieve prepared by any one of claims 1-22.

24. The molecular sieve according to claim 23, characterized in that, The molecular sieve has an R value of 4.5-9.5, where R = specific surface area / external specific surface area.

25. The molecular sieve according to claim 23, characterized in that, The molecular sieve has a crystal size of 40-70 nm and a silicon oxide / alumina molar ratio of 5-6.

5. The proportion of 40-70 nm crystals in the molecular sieve, as measured by dynamic photoelectron scattering, is 85-93%.

26. The molecular sieve according to claim 23, characterized in that, The molecular sieve has a crystal size of 40-70 nm and a silica / alumina molar ratio of 6-6.

5.

27. The molecular sieve according to claim 23, characterized in that, The molecular sieve has an R value of 4.5-6, where R = specific surface area / external specific surface area.

28. The molecular sieve according to claim 23, characterized in that, The specific surface area of ​​the molecular sieve is 800-950 m². 2 / g, with an external specific surface area of ​​100-200m² 2 / g, with a pore volume of 0.38-0.56ml / g.

29. The molecular sieve according to claim 28, characterized in that, The specific surface area of ​​the molecular sieve is 850-920 m². 2 / g, with an external specific surface area of ​​150-180m² 2 / g, with a pore volume of 0.43-0.53ml / g.

30. The molecular sieve according to any one of claims 23-29, characterized in that, The molecular sieve, after being treated at 700℃ and 0.1MPa high-temperature steam atmosphere for 2 hours, has a crystallinity between 75% and 90%.

31. The molecular sieve according to claim 30, characterized in that, The molecular sieve, after being treated at 700℃ and 0.1MPa high-temperature steam atmosphere for 2 hours, has a crystallinity between 83% and 89%.

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