A method for preparing aluminum-rich Beta molecular sieve

Abstract

The present invention discloses a preparation method of aluminum-rich Beta molecular sieve, comprising the following steps: (1) performing a first hydrothermal reaction on a reaction mixture formed by mixing deionized water, an alkali source, a template and an aluminum source at a reaction temperature of 100-140° C., a reaction time of 6-24 hours and a stirring speed of 60-300 rpm; (2) adding a silicon source and a seed crystal in a prescribed amount to the mixed solution obtained in step (1), performing a second hydrothermal crystallization reaction at a reaction temperature of 140-160° C., a reaction time of 48-96 hours and a stirring speed of 60-300 rpm to obtain a Beta molecular sieve crystallization slurry; (3) filtering the Beta molecular sieve crystallization slurry obtained in step (2), washing with deionized water to a pH of 7-8, drying and calcining to obtain an aluminum-rich Beta molecular sieve containing an alkali metal; and (4) exchanging the product obtained in step (3) with ammonium, drying and calcining to obtain a hydrogen-type aluminum-rich Beta molecular sieve. The Beta molecular sieve obtained by the present invention has high productivity and yield.

Description

Technical Field

[0001] The present invention relates to the field of Beta molecular sieve preparation, in particular to a method for preparing aluminum-rich Beta molecular sieve. Background Art

[0002] The document "Aluminum-rich zeolite Beta, Zeolites, 1997, 19: 253-258" defines Beta molecular sieve containing 6 Al atoms in the unit cell as a stoichiometric molecular sieve, and its corresponding silicon-aluminum ratio (SiO2 / Al2O3) is 19.3. Beta molecular sieves with a silicon-aluminum ratio lower than 19.3 are further called aluminum-rich Beta molecular sieves.

[0003] The document "Preparation of aluminum-rich Beta zeolite, Microporous Materials, 1996, 5:289-297" reports a method for synthesizing aluminum-rich Beta molecular sieve by first preparing dry powdered silica gel and then recrystallizing it. The resulting product has a Si / Al ratio of 10.4. However, this method is prone to the formation of impurities such as hydrocalcium zeolite and analcime.

[0004] The patent with publication number WO9733830A1 and country of origin ES first disclosed the - and TEA + In a reaction system near neutral conditions, Beta molecular sieves with a wide range of Si / Al ratios (greater than 12.286) were synthesized. Using ethyl silicate and metallic aluminum powder as raw materials and tetraethylammonium hydroxide as a template, the method achieved a gel Si / Al ratio as low as 12, and the resulting Beta molecular sieve had a Si / Al ratio as low as 14.4. However, this method had very low yields and crystallinity.

[0005] A Chinese invention patent with publication number CN101096274B and invention name, "A method for preparing aluminum-rich beta zeolite," discloses a method for preparing aluminum-rich beta zeolite. The method comprises preparing a silicon-aluminum co-gel by incorporating a silicon source and an aluminum source in the presence of a hydrolyzing agent, aging the gel at 20 to 220°C and calcining the gel at 300 to 1400°C, and then crushing the gel to obtain a silicon-aluminum source. The silicon-aluminum source is then added to a solution consisting of tetraethylammonium cations, ammonium ions, fluoride ions, and water, and crystallized and the crystallized product is recovered to obtain the zeolite.

[0006] A Chinese invention patent with publication number CN101096275B and the invention name of "A method for synthesizing aluminum-rich beta zeolite" discloses a method for synthesizing beta zeolite. The method comprises impregnating a silicon source with an aqueous solution or acid solution containing an aluminum source, stirring until solidified, treating with or without ammonia water, and then aging and dehydrating the silicon source at 60 to 150°C. After grinding, the silicon source is calcined at 600 to 1400°C for 1 to 24 hours to obtain a silicon-aluminum source. A tetraethylammonium cation compound and hydrofluoric acid are then mixed and partially evaporated under normal pressure and not higher than 130°C or under vacuum conditions. The silicon-aluminum source is added to a concentrated mixture of tetraethylammonium hydroxide and hydrofluoric acid, and the resulting reaction mixture is hydrothermally crystallized to recover the crystallized product.

[0007] The above two methods both use high-temperature calcined silica-alumina co-gel as silica-alumina source to prepare aluminum-rich Beta molecular sieve under the action of fluoride, and the silicon-aluminum ratio of the obtained product is less than 20.

[0008] The Chinese invention patent with publication number 101205072B and the invention name "A method for synthesizing low silicon-aluminum ratio beta zeolite" discloses a method for preparing aluminum-rich beta zeolite by adding an aluminum source to beta zeolite having a silicon-aluminum molar ratio of 25-30 as a raw material. The silicon-aluminum ratio of the obtained product ranges from 4 to 15, and the silicon-aluminum ratio of the product prepared in the embodiment ranges from 7 to 15. This patent uses beta zeolite as a raw material, and the production cost is relatively high. Summary of the Invention

[0009] In view of the defects of the existing preparation methods of aluminum-rich Beta molecular sieves, the purpose of the present invention is to provide a preparation method of aluminum-rich Beta molecular sieves.

[0010] The technical solution of the present invention to solve the above technical problems is:

[0011] A method for preparing aluminum-rich Beta molecular sieve comprises the following steps:

[0012] (1) a reaction mixture formed by mixing deionized water, an alkali source, a template, and an aluminum source is subjected to a first hydrothermal reaction at a reaction temperature of 100 to 140° C., a reaction time of 6 to 24 hours, and a stirring speed of 60 to 300 rpm;

[0013] (2) adding the silicon source and seed crystals in the formulated amount to the mixed solution obtained in step (1), and performing a second hydrothermal crystallization reaction at a reaction temperature of 140 to 160° C., a reaction time of 48 to 96 h, and a stirring speed of 60 to 300 rpm to obtain a Beta molecular sieve crystallization slurry;

[0014] (3) The Beta molecular sieve crystallization slurry obtained in step (2) is filtered, washed with deionized water to a pH of 7 to 8, dried, and calcined to obtain an alkali metal-containing aluminum-rich Beta molecular sieve;

[0015] (4) The product obtained in step (3) is subjected to ammonium exchange, drying, and calcination to obtain a hydrogen-type aluminum-rich Beta molecular sieve.

[0016] Preferably, the silicon source is SiO2, the aluminum source is Al2O3, the alkali source is M2O, and the template is ROH.

[0017] Preferably, the molar ratio of SiO2, Al2O3, M2O, ROH and H2O is 8-22:1:0.5-1.5:1.6-5.5:120-330.

[0018] Preferably, the M2O is one of sodium hydroxide and potassium hydroxide.

[0019] Furthermore, the Al2O3 is selected from one of aluminum sol, aluminum hydroxide, and pseudo-boehmite; the ROH is a 25-35% by mass aqueous solution of tetraethylammonium hydroxide; the SiO2 is selected from one of silica gel, silica sol, and precipitated silica; and the seed crystal is a hydrogen-type Beta molecular sieve.

[0020] Preferably, the molar ratio of SiO2 to Al2O3 contained in the seed crystal is in the range of 20 to 30.

[0021] Preferably, the amount of seed crystals added in step (2) is 0.5-2% by mass of the SiO2 contained in the silicon source, and the seed crystals are added in the form of a suspension formed by dispersing the seed crystals in deionized water, with the mass fraction of the seed crystals in the seed crystal suspension being 10-20%. The seed crystals are dispersed in the deionized water to form a suspension to serve as a pre-dispersion agent.

[0022] Furthermore, in the step (3), the drying temperature is 90-120°C, and the drying time is 12-24 hours; the roasting temperature is 540-580°C, the holding time is 6-10 hours, and the roasting is carried out in a flowing air atmosphere, and the air flow rate is 1-5 L / min; in the step (4), the drying temperature is 90-120°C, and the drying time is 12-24 hours; the roasting temperature is 450-540°C, the holding time is 3-6 hours, and the roasting is carried out in a flowing air atmosphere, and the air flow rate is 1-5 L / min.

[0023] Furthermore, in the step (4), the ammonium salt used for ammonium exchange is selected from one of ammonium sulfate and ammonium nitrate; the mass fraction of the ammonium salt in the ammonium salt aqueous solution is 5-10%, the mass ratio of the ammonium salt aqueous solution to the molecular sieve during the ammonium exchange process is 7-12:1, the ammonium exchange temperature is 50-90°C, the number of ammonium exchanges is 2-3 times, and the ammonium exchange time is 0.5-3 hours.

[0024] The present invention discloses a method for preparing an aluminum-rich Beta molecular sieve. The method involves a first hydrothermal reaction of an aluminum source, a template, and an alkali source at a specific temperature, followed by the addition of a silicon source and a second hydrothermal crystallization reaction at a specific temperature. The crystallization raw materials used in the present method are all conventional, inexpensive, and readily available. Fluorine-containing raw materials are not required, making industrial production easy. XRF testing shows a silicon-to-aluminum ratio close to that of the feed, and the resulting Beta molecular sieve has a high yield and yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the X-ray powder diffraction pattern of the Beta molecular sieve powder prepared in Example 1;

[0026] Figure 2 This is a scanning electron microscope image of Beta molecular sieve prepared in Example 1;

[0027] Figure 3 is the X-ray powder diffraction pattern of the Beta molecular sieve powder prepared in Example 2;

[0028] Figure 4 This is a scanning electron microscope image of Beta molecular sieve prepared in Example 2;

[0029] Figure 5 is the X-ray powder diffraction pattern of the powder Beta molecular sieve prepared in Example 5;

[0030] Figure 6 This is a scanning electron microscope image of Beta molecular sieve prepared in Example 5;

[0031] Figure 7 This is the X-ray powder diffraction pattern of the Beta molecular sieve powder prepared in Comparative Example 1;

[0032] Figure 8 This is the X-ray powder diffraction pattern of the Beta molecular sieve prepared in Comparative Example 2. DETAILED DESCRIPTION

[0033] The following will be combined with the accompanying drawings in the embodiments of the present application to clearly describe the technical solutions in the embodiments of the present application. Obviously, the embodiments described are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of this application.

[0034] Example 1

[0035] This embodiment provides a method for preparing aluminum-rich Beta molecular sieve, comprising the following steps:

[0036] (1) 606.75 g of deionized water was weighed, 24.39 g of solid sodium hydroxide was added and stirred to dissolve, and then 563.28 g of a 25 wt % aqueous solution of tetraethylammonium hydroxide and 287.45 g of an aluminum sol having an Al2O3 content of 21.2 wt % were added. After stirring and mixing, the mixture was placed in a hydrothermal crystallization reactor for the first hydrothermal reaction for 24 hours at a reaction temperature of 100° C. and a stirring speed of 60 rpm.

[0037] (2) To the mixture after the reaction, 318.80 g of silica gel with a SiO2 content of 90.12 wt% and 14.37 g of a 10 wt% Beta seed suspension were added. After stirring and mixing, a second hydrothermal reaction was carried out in a hydrothermal crystallization reactor at a reaction temperature of 140° C. and a stirring speed of 60 rpm for 96 hours. The Beta seed was a hydrogen-type Beta molecular sieve produced by Tianjin Nanhua Catalyst Co., Ltd. The Beta seed suspension was formed by dispersing the seed crystals in deionized water.

[0038] The amount of Beta seed suspension added was 0.5% of the mass of SiO2 contained in the silica gel, and the molar ratio of SiO2 to Al2O3 in the seed crystals was approximately 20.69. The molar ratio of SiO2:Al2O3:Na2O:ROH:H2O in the secondary crystallization reaction slurry was 8.00:1.00:0.50:1.60:120.00.

[0039] (3) After the crystallization reaction is completed, the obtained crystallized product is filtered and recovered, washed with deionized water until the pH is 7-8, and dried at 90°C for 24 hours. Figure 1 The powder X-ray diffraction pattern of the crystallized product shows that the product has typical Beta molecular sieve structural characteristics. Figure 2 This is a scanning electron microscope image of the crystallized product. The grain size of Beta molecular sieve ranges from about 100 to 300 nm.

[0040] The dried crystallized product was placed in a muffle furnace, heated to 540° C. and calcined for 10 hours in a flowing air atmosphere with an air flow rate of 1 L / min and a heating rate of 2° C. / min.

[0041] (4) After the calcination, the mass of the obtained product is weighed, and a 5% ammonium nitrate aqueous solution with a mass fraction of 12 times the weight of the molecular sieve is added. Under stirring conditions, the ammonium exchange reaction is carried out. The ammonium exchange temperature is 50°C, the number of exchanges is 3 times, and the ammonium exchange time for each time is 3 hours. After the exchange is completed, it is dried at 90°C for 24 hours. The dried product is placed in a muffle furnace and heated to 450°C in a flowing air atmosphere and calcined for 6 hours. The air flow rate is 1L / min and the heating rate is 2°C / min. After the second calcination is completed, continue to cool to 40-60°C in an air atmosphere, collect the calcined product to prepare the hydrogen-type aluminum-rich Beta molecular sieve.

[0042] X-ray fluorescence spectroscopy (XRF) test shows that the SiO2 / Al2O3 ratio of the hydrogen-type aluminum-rich Beta molecular sieve is 7.2. Calculated based on the silicon-aluminum ratio of the feed, the utilization rate of the silicon source is about 90%.

[0043] Example 2

[0044] This embodiment provides a method for preparing aluminum-rich Beta molecular sieve, comprising the following steps:

[0045] (1) 759.83 g of deionized water was weighed, 40.72 g of potassium hydroxide solid was added and stirred to dissolve, and then 398.96 g of a 35 wt % aqueous solution of tetraethylammonium hydroxide and 285.03 g of an aluminum sol having an Al2O3 content of 21.2 wt % were added. After stirring and mixing, the mixture was placed in a hydrothermal crystallization reactor for the first hydrothermal reaction for 6 hours at a reaction temperature of 140° C. and a stirring speed of 300 rpm.

[0046] (2) To the mixture after the reaction, 316.12 g of silica gel with a SiO2 content of 90.12 wt% and 28.49 g of a 20 wt% Beta seed suspension were added. After stirring and mixing, a second hydrothermal reaction was carried out in a hydrothermal crystallization reactor at a reaction temperature of 160° C. and a stirring speed of 300 rpm for 48 hours. The Beta seed was a hydrogen-type Beta molecular sieve produced by Tianjin Nanhua Catalyst Co., Ltd. The Beta seed suspension was formed by dispersing the seed crystals in deionized water.

[0047] The amount of Beta seed suspension added was 2% of the mass of SiO2 contained in the silica gel, and the molar ratio of SiO2 to Al2O3 in the seed crystals was approximately 30.45. The molar ratio of SiO2:Al2O3:K2O:ROH:H2O in the secondary crystallization reaction slurry was 8.00:1.00:0.60:1.60:120.00.

[0048] (3) After the crystallization reaction is completed, the obtained crystallized product is filtered and recovered, washed with deionized water until the pH is 7-8, and dried at 120°C for 12 hours. Figure 3 The powder X-ray diffraction pattern of the crystallized product shows that the product has typical Beta molecular sieve structural characteristics. Figure 4 This is a scanning electron microscope image of the crystallized product. The grain size of Beta molecular sieve ranges from about 200 to 400 nm.

[0049] The dried crystallized product was placed in a muffle furnace, heated to 580° C. and calcined for 6 hours in a flowing air atmosphere with an air flow rate of 5 L / min and a heating rate of 2° C. / min.

[0050] (4) After the calcination, the mass of the obtained product is weighed, and a 10% ammonium nitrate aqueous solution with a mass fraction of 7 times the weight of the molecular sieve is added. Under stirring conditions, an ammonium exchange reaction is carried out. The ammonium exchange temperature is 90°C, the number of exchanges is 2, and the ammonium exchange time for each time is 0.5 hours. After the exchange is completed, it is dried at 120°C for 12 hours. The dried product is placed in a muffle furnace and heated to 540°C in a flowing air atmosphere and calcined for 3 hours. The air flow rate is 5L / min and the heating rate is 2°C / min. After the second calcination is completed, continue to cool to 40-60°C in an air atmosphere, collect the calcined product to prepare the hydrogen-type aluminum-rich Beta molecular sieve.

[0051] The SiO2 / Al2O3 ratio of the hydrogen-type aluminum-rich Beta molecular sieve tested by XRF is 7.0. Calculated based on the silicon-aluminum ratio of the feed, the utilization rate of the silicon source is about 88%.

[0052] Example 3

[0053] This embodiment provides a method for preparing aluminum-rich Beta molecular sieve, comprising the following steps:

[0054] (1) Weigh 322.25 g of deionized water, add 27.02 g of sodium hydroxide solid and stir to dissolve, then continue to add 505.39 g of 30 wt% tetraethylammonium hydroxide aqueous solution and 57.50 g of aluminum hydroxide with 65.20 wt% Al2O3 content, stir and mix evenly, and place in a hydrothermal crystallization reactor at a reaction temperature of 120°C and a stirring speed of 180 rpm to carry out the first hydrothermal reaction for 16 hours.

[0055] (2) To the mixture after the reaction, 890.06 g of silica sol with a SiO2 content of 29.79 wt% and 17.68 g of a 15 wt% Beta seed suspension were added. After stirring and mixing, a second hydrothermal reaction was carried out in a hydrothermal crystallization reactor at a reaction temperature of 145° C. and a stirring speed of 180 rpm for 72 hours. The Beta seed was a hydrogen-type Beta molecular sieve produced by Tianjin Nanhua Catalyst Co., Ltd. The Beta seed suspension was formed by dispersing the seed crystals in deionized water.

[0056] The amount of Beta seed suspension added was 1.0% of the mass of SiO2 contained in the silica sol, and the molar ratio of SiO2 to Al2O3 in the seed crystals was approximately 24.63. The molar ratio of SiO2:Al2O3:Na2O:ROH:H2O in the secondary crystallization reaction slurry was 12.00:1.00:0.90:2.80:200.00.

[0057] (3) After the crystallization reaction is completed, the resulting crystallized product is filtered and recovered, washed with deionized water to a pH of 7 to 8, and dried at 100° C. for 18 hours. The powder X-ray diffraction pattern of the crystallized product shows that the product has typical Beta molecular sieve structural characteristics.

[0058] The dried crystallized product was placed in a muffle furnace, heated to 550° C. and calcined for 7 hours in a flowing air atmosphere with an air flow rate of 2 L / min and a heating rate of 2° C. / min.

[0059] (4) After the calcination, the mass of the obtained product is weighed, and a 7% ammonium sulfate aqueous solution with a mass fraction of 10 times the weight of the molecular sieve is added. Under stirring conditions, the ammonium exchange reaction is carried out. The ammonium exchange temperature is 70°C, the number of exchanges is 3, and the ammonium exchange time for each time is 1 hour. After the exchange is completed, it is dried at 100°C for 18 hours. The dried product is placed in a muffle furnace and heated to 500°C in a flowing air atmosphere and calcined for 4 hours. The air flow rate is 2L / min and the heating rate is 2°C / min. After the second calcination is completed, continue to cool to 40-60°C in an air atmosphere, collect the calcined product to prepare the hydrogen-type aluminum-rich Beta molecular sieve.

[0060] The SiO2 / Al2O3 ratio of the hydrogen-type aluminum-rich Beta molecular sieve tested by XRF is 10.7. Calculated based on the silicon-aluminum ratio of the feed, the utilization rate of the silicon source is about 89%.

[0061] Example 4

[0062] This embodiment provides a method for preparing aluminum-rich Beta molecular sieve, comprising the following steps:

[0063] (1) Weigh 244.57 g of deionized water, add 24.16 g of sodium hydroxide solid and stir to dissolve, then continue to add 514.97 g of 30 wt% tetraethylammonium hydroxide aqueous solution and 42.07 g of aluminum hydroxide with 65.20 wt% Al2O3 content, stir and mix well, and place in a hydrothermal crystallization reactor at a reaction temperature of 120°C and a stirring speed of 180 rpm to carry out the first hydrothermal reaction for 16 hours.

[0064] (2) To the mixture after the reaction, 976.69 g of silica sol with a SiO2 content of 29.79 wt% and 19.40 g of a Beta seed suspension containing 15 wt% of the mixture were added. After stirring and mixing, a second hydrothermal reaction was carried out in a hydrothermal crystallization reactor at a reaction temperature of 145° C. and a stirring speed of 180 rpm for 72 hours. The Beta seed was a hydrogen-type Beta molecular sieve produced by Tianjin Nanhua Catalyst Co., Ltd. The Beta seed suspension was formed by dispersing the seed crystals in deionized water.

[0065] The amount of Beta seed suspension added was 1.0% of the mass of SiO2 contained in the silica sol, and the molar ratio of SiO2 to Al2O3 in the seed crystals was approximately 24.63. The molar ratio of SiO2:Al2O3:Na2O:ROH:H2O in the secondary crystallization reaction slurry was 18.00:1.00:1.10:3.90:270.00.

[0066] (3) After the crystallization reaction is completed, the resulting crystallized product is filtered and recovered, washed with deionized water to a pH of 7 to 8, and dried at 100° C. for 18 hours. The powder X-ray diffraction pattern of the crystallized product shows that the product has typical Beta molecular sieve structural characteristics.

[0067] The dried crystallized product was placed in a muffle furnace, heated to 550° C. and calcined for 7 hours in a flowing air atmosphere with an air flow rate of 2 L / min and a heating rate of 2° C. / min.

[0068] (4) After the calcination, the mass of the obtained product is weighed, and a 7% ammonium sulfate aqueous solution with a mass fraction of 10 times the weight of the molecular sieve is added. Under stirring conditions, the ammonium exchange reaction is carried out. The ammonium exchange temperature is 70°C, the number of exchanges is 3, and the ammonium exchange time for each time is 1 hour. After the exchange is completed, it is dried at 100°C for 18 hours. The dried product is placed in a muffle furnace and heated to 500°C in a flowing air atmosphere and calcined for 4 hours. The air flow rate is 2L / min and the heating rate is 2°C / min. After the second calcination is completed, continue to cool to 40-60°C in an air atmosphere, collect the calcined product to prepare the hydrogen-type aluminum-rich Beta molecular sieve.

[0069] The SiO2 / Al2O3 ratio of the hydrogen-type aluminum-rich Beta molecular sieve tested by XRF is 16.6. Calculated based on the silicon-aluminum ratio of the feed, the utilization rate of the silicon source is about 92%.

[0070] Example 5

[0071] This embodiment provides a method for preparing aluminum-rich Beta molecular sieve, comprising the following steps:

[0072] (1) 759.44 g of deionized water was weighed, 24.74 g of solid sodium hydroxide was added and stirred to dissolve, and then 629.44 g of a 30 wt % aqueous solution of tetraethylammonium hydroxide and 32.61 g of pseudo-boehmite with a 72.90 wt % Al 2 O 3 content were added. After stirring and mixing, the mixture was placed in a hydrothermal crystallization reactor for a first hydrothermal reaction for 16 hours at a reaction temperature of 120° C. and a stirring speed of 180 rpm.

[0073] (2) To the mixture after the reaction, 359.05 g of precipitated silica with an SiO2 content of 85.84 wt% and 20.54 g of a 15 wt% Beta seed suspension were added. After stirring and mixing, a second hydrothermal reaction was carried out in a hydrothermal crystallization reactor at a reaction temperature of 145° C. and a stirring speed of 180 rpm for 72 hours. The Beta seed was a hydrogen-type Beta molecular sieve produced by Tianjin Nanhua Catalyst Co., Ltd. The Beta seed suspension was formed by dispersing the seed crystals in deionized water.

[0074] The amount of Beta seed suspension added was 1.0% of the mass of SiO2 contained in the silica sol, and the molar ratio of SiO2 to Al2O3 in the seed crystals was approximately 24.63. The molar ratio of SiO2:Al2O3:Na2O:ROH:H2O in the secondary crystallization reaction slurry was 22.00:1.00:1.30:5.50:300.00.

[0075] (3) After the crystallization reaction is completed, the obtained crystallized product is filtered and recovered, washed with deionized water until the pH is 7-8, and dried at 100°C for 18 hours. Figure 5 The powder X-ray diffraction pattern of the crystallized product shows that the product has typical Beta molecular sieve structural characteristics. Figure 6 This is a scanning electron microscope image of the crystallized product. The grain size of Beta molecular sieve ranges from about 100 to 300 nm.

[0076] The dried crystallized product was placed in a muffle furnace, heated to 550° C. and calcined for 7 hours in a flowing air atmosphere with an air flow rate of 2 L / min and a heating rate of 2° C. / min.

[0077] (4) After the calcination, the mass of the obtained product is weighed, and a 7% ammonium sulfate aqueous solution with a mass fraction of 10 times the weight of the molecular sieve is added. Under stirring conditions, the ammonium exchange reaction is carried out. The ammonium exchange temperature is 70°C, the number of exchanges is 3, and the ammonium exchange time for each time is 1 hour. After the exchange is completed, it is dried at 100°C for 18 hours. The dried product is placed in a muffle furnace and heated to 500°C in a flowing air atmosphere and calcined for 4 hours. The air flow rate is 2L / min and the heating rate is 2°C / min. After the second calcination is completed, continue to cool to 40-60°C in an air atmosphere, collect the calcined product to prepare the hydrogen-type aluminum-rich Beta molecular sieve.

[0078] The SiO2 / Al2O3 ratio of the hydrogen-type aluminum-rich Beta molecular sieve tested by XRF is 19.2. Calculated based on the silicon-aluminum ratio of the feed, the utilization rate of the silicon source is about 87%.

[0079] Example 6

[0080] This embodiment provides a method for preparing aluminum-rich Beta molecular sieve, comprising the following steps:

[0081] (1) 829.33 g of deionized water was weighed, 37.22 g of potassium hydroxide solid was added and stirred to dissolve, and then 574.36 g of a 30 wt% aqueous solution of tetraethylammonium hydroxide and 30.31 g of pseudo-boehmite with a 72.90 wt% Al2O3 content were added. After stirring and mixing, the mixture was placed in a hydrothermal crystallization reactor for a first hydrothermal reaction for 16 hours at a reaction temperature of 120°C and a stirring speed of 180 rpm.

[0082] (2) To the mixture after the reaction, 333.69 g of precipitated silica with an SiO2 content of 85.84 wt% and 19.10 g of a 15 wt% Beta seed suspension were added. After stirring and mixing, a second hydrothermal reaction was carried out in a hydrothermal crystallization reactor at a reaction temperature of 145° C. and a stirring speed of 180 rpm for 72 hours. The Beta seed was a hydrogen-type Beta molecular sieve produced by Tianjin Nanhua Catalyst Co., Ltd. The Beta seed suspension was formed by dispersing the seed crystals in deionized water.

[0083] The amount of Beta seed suspension added was 1.0% of the mass of SiO2 contained in the silica sol, and the molar ratio of SiO2 to Al2O3 in the seed crystals was approximately 24.63. The molar ratio of SiO2:Al2O3:K2O:ROH:H2O in the secondary crystallization reaction slurry was 22.00:1.00:1.50:5.40:330.00.

[0084] (3) After the crystallization reaction is completed, the resulting crystallized product is filtered and recovered, washed with deionized water to a pH of 7 to 8, and dried at 100° C. for 18 hours. The powder X-ray diffraction pattern of the crystallized product shows that the product has typical Beta molecular sieve structural characteristics.

[0085] The dried crystallized product was placed in a muffle furnace, heated to 550° C. and calcined for 7 hours in a flowing air atmosphere with an air flow rate of 2 L / min and a heating rate of 2° C. / min.

[0086] (4) After the calcination, the mass of the obtained product is weighed, and a 7% ammonium sulfate aqueous solution with a mass fraction of 10 times the weight of the molecular sieve is added. Under stirring conditions, the ammonium exchange reaction is carried out. The ammonium exchange temperature is 70°C, the number of exchanges is 3, and the ammonium exchange time for each time is 1 hour. After the exchange is completed, it is dried at 100°C for 18 hours. The dried product is placed in a muffle furnace and heated to 500°C in a flowing air atmosphere and calcined for 4 hours. The air flow rate is 2L / min and the heating rate is 2°C / min. After the second calcination is completed, continue to cool to 40-60°C in an air atmosphere, collect the calcined product to prepare the hydrogen-type aluminum-rich Beta molecular sieve.

[0087] The SiO2 / Al2O3 ratio of the hydrogen-type aluminum-rich Beta molecular sieve tested by XRF is 19.7. Calculated based on the silicon-aluminum ratio of the feed, the utilization rate of the silicon source is about 90%.

[0088] Comparative Example 1

[0089] This comparative example provides a preparation method of aluminum-rich Beta molecular sieve. The only difference between this comparative example 1 and Example 1 is that the preparation method adopts a one-step hydrothermal reaction to prepare the crystallized product.

[0090] The specific experimental steps of Comparative Example 1 are as follows:

[0091] (1) Weigh 606.75 g of deionized water, add 24.39 g of sodium hydroxide solid and stir to dissolve, then continue to add 563.28 g of 25 wt% tetraethylammonium hydroxide aqueous solution and 287.45 g of aluminum sol with 21.2 wt% Al2O3 content, and stir to mix evenly.

[0092] (2) To the above mixture were added 318.80 g of silica gel having a SiO2 content of 90.12 wt% and 14.37 g of a 10 wt% Beta seed suspension. After stirring and mixing, the mixture was subjected to a hydrothermal reaction in a hydrothermal crystallization reactor at a temperature of 140° C. and a stirring speed of 60 rpm for 96 hours. The remaining steps were the same as in Example 1.

[0093] Figure 7The powder X-ray diffraction pattern of the crystallized product shows that the product has an amorphous structure and has no characteristic peaks of the Beta molecular sieve structure.

[0094] Comparative Example 2

[0095] This comparative example provides a method for preparing aluminum-rich Beta molecular sieve. The only difference between this comparative example 1 and Example 5 is that the preparation method adopts a one-step hydrothermal reaction to prepare the crystallized product.

[0096] The specific experimental steps of Comparative Example 2 are as follows:

[0097] (1) Weigh 759.44 g of deionized water, add 24.74 g of solid sodium hydroxide and stir to dissolve, then continue to add 629.44 g of 30 wt% tetraethylammonium hydroxide aqueous solution and 32.61 g of pseudo-boehmite with 72.90 wt% Al2O3 content, and stir to mix evenly.

[0098] (2) To the above mixture were added 359.05 g of precipitated silica having an SiO2 content of 85.84 wt% and 20.54 g of a 15 wt% Beta seed suspension. After stirring and mixing, the mixture was subjected to a hydrothermal reaction in a hydrothermal crystallization reactor at a temperature of 145° C. and a stirring speed of 180 rpm for 72 hours. The remaining steps were the same as in Example 5.

[0099] Figure 8 The powder X-ray diffraction pattern of the crystallized product shows that the product has characteristic peaks of Beta molecular sieve structure, but also has many impurity crystal peaks.

[0100] Comparative Example 3

[0101] This comparative example provides a method for preparing aluminum-rich Beta molecular sieve. The only difference between this comparative example 1 and Example 1 is that the order of adding silica gel and aluminum sol is interchanged. The preparation method of this comparative example is as follows:

[0102] (1) 606.75 g of deionized water was weighed, 24.39 g of solid sodium hydroxide was added and stirred to dissolve, and then 563.28 g of a 25 wt % aqueous solution of tetraethylammonium hydroxide and 318.80 g of silica gel with a SiO2 content of 90.12 wt % were added and stirred to mix evenly. The mixture was then placed in a hydrothermal crystallization reactor at a reaction temperature of 100° C. and a stirring speed of 60 rpm for a first hydrothermal reaction for 24 hours.

[0103] (2) To the mixture after the reaction, 287.45 g of an aluminum sol having a 21.2 wt% Al2O3 content and 14.37 g of a 10 wt% Beta seed suspension were added. After stirring and mixing, a second hydrothermal reaction was carried out in a hydrothermal crystallization reactor at a reaction temperature of 140°C and a stirring speed of 60 rpm for 96 hours. The remaining steps were the same as in Example 1.

[0104] The powder X-ray diffraction pattern of the product shows that the product has an amorphous structure and has no characteristic peaks of Beta molecular sieve structure.

[0105] Comparative Example 4

[0106] This comparative example provides a method for preparing an aluminum-rich Beta molecular sieve. The only difference between this comparative example 1 and Example 1 is the molar ratio of the raw materials in the secondary crystallization reaction slurry. In this comparative example, the molar ratio of SiO₂:Al₂O₃:Na₂O:ROH:H₂O in the secondary crystallization reaction slurry is 6.00:1.00:0.5:1.6:100.0, with all other parameters being the same as in Example 1.

[0107] The powder X-ray diffraction pattern of the product shows that the product has an amorphous structure and has no characteristic peaks of Beta molecular sieve structure.

[0108] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of this application, ordinary technicians in this field can also make many forms without departing from the purpose of this application and the scope of protection of the claims, all of which are within the protection of this application.

Claims

1. A method for preparing aluminum-rich Beta molecular sieve, characterized in that: The steps include: (1) a reaction mixture formed by mixing deionized water, an alkali source, a template, and an aluminum source is subjected to a first hydrothermal reaction at a reaction temperature of 100 to 140°C, a reaction time of 6 to 24 hours, and a stirring speed of 60 to 300 rpm; (2) adding a silicon source and a seed crystal to the mixed solution obtained in step (1), and performing a second hydrothermal crystallization reaction at a reaction temperature of 140 to 160° C., a reaction time of 48 to 96 h, and a stirring speed of 60 to 300 rpm to obtain a Beta molecular sieve crystallization slurry; (3) The Beta molecular sieve crystallization slurry obtained in step (2) is filtered, washed with deionized water to a pH of 7-8, dried, and calcined to obtain an alkali metal-containing aluminum-rich Beta molecular sieve; (4) The product obtained in step (3) is subjected to ammonium exchange, drying, and calcination to obtain a hydrogen-type aluminum-rich Beta molecular sieve; The silicon source is SiO2, the aluminum source is Al2O3, the alkali source is M2O, and the template is ROH; The molar ratio of SiO2, Al2O3, M2O, ROH and H2O is 8~22: 1: 0.5~1.5: 1.6~5.5: 120~330.

2. The method for preparing an aluminum-rich Beta molecular sieve according to claim 1, wherein: In the M2O, M is an alkali metal sodium or potassium, and the alkali metal source is one of sodium hydroxide and potassium hydroxide.

3. The method for preparing an aluminum-rich Beta molecular sieve according to claim 1, characterized in that: The Al2O3 is selected from one of aluminum sol, aluminum hydroxide, and pseudo-boehmite; the ROH is a 25-35% by mass aqueous solution of tetraethylammonium hydroxide; the SiO2 is selected from one of silica gel, silica sol, and precipitated silica; and the seed crystal is hydrogen-type Beta molecular sieve.

4. The method for preparing an aluminum-rich Beta molecular sieve according to claim 3, characterized in that: The molar ratio of SiO2 to Al2O3 contained in the seed crystal is in the range of 20-30.

5. The method for preparing an aluminum-rich Beta molecular sieve according to claim 3, characterized in that: The amount of seed crystals added in step (2) is 0.5-2% of the mass of SiO2 contained in the silicon source, and the seed crystals are added in the form of a suspension formed by dispersing the seed crystals in deionized water, and the mass fraction of the seed crystals in the seed crystal suspension is 10-20%.

6. The method for preparing an aluminum-rich Beta molecular sieve according to claim 1, characterized in that: The drying temperature in step (3) is 90-120°C, and the drying time is 12-24 hours; the roasting temperature is 540-580°C, and the holding time is 6-10 hours. The roasting is carried out in a flowing air atmosphere with an air flow rate of 1-5 L / min.

7. The method for preparing an aluminum-rich Beta molecular sieve according to claim 1, characterized in that: In the step (4), the ammonium salt used for the ammonium exchange is selected from ammonium sulfate and ammonium nitrate; the mass fraction of the ammonium salt in the ammonium salt aqueous solution is 5-10%, the mass ratio of the ammonium salt aqueous solution to the molecular sieve during the ammonium exchange process is 7-12:1, the ammonium exchange temperature is 50-90°C, the number of ammonium exchanges is 2-3 times, and the ammonium exchange time is 0.5-3 hours.

8. The method for preparing an aluminum-rich Beta molecular sieve according to claim 1, characterized in that: The drying temperature in step (4) is 90-120°C, and the drying time is 12-24 hours; the roasting temperature is 450-540°C, and the holding time is 3-6 hours. The roasting is carried out in a flowing air atmosphere with an air flow rate of 1-5 L / min.

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