Preparation method of MWW molecular sieve, MWW molecular sieve and application

Abstract

The invention relates to a preparation method of an MWW molecular sieve, the MWW molecular sieve and application of the MWW molecular sieve. Comprising the following steps: crystallizing a mixture containing a silicon source, an aluminum source, inorganic alkali or inorganic acid, a crystallization auxiliary agent, water and a structure-directing agent to obtain the MCM-56 molecular sieve, the original molar composition of the mixture is as follows: SiO2 / Al2O3 is equal to 10 to 300, OH <-> / SiO2 is equal to 0.01 to 1, M < + > / SiO2 is equal to 0.01 to 1, R / SiO2 is equal to 0.005 to 1.0, H2O / SiO2 is equal to 2 to 30, and D2O3 / SiO2 is equal to 0.01 to 3; wherein M is an alkali metal element, R is a structure-directing agent, D2O3 is a crystallization auxiliary agent, and D is a boron element or a gallium element; the structure directing agent is cyclohexylamine. Cyclohexylamine which is low in toxicity, low in price and easy to obtain serves as a template agent, and the MCM-56 molecular sieve is synthesized in one step through a hydrothermal crystallization method. The synthesis route is simple and feasible, the operation is controllable, and the production cost can be effectively reduced by using the cheap structure-directing agent.

Description

Technical Field

[0001] This application relates to a method for preparing MWW molecular sieves and the application of MWW molecular sieves, belonging to the field of catalytic chemistry. Background Technology

[0002] MWW family molecular sieves contain two relatively independent pore systems: intralayer ten-membered ring sinusoidal pores (0.41 nm × 0.51 nm) and interlayer twelve-membered ring supercages (1.82 nm × 0.71 nm × 0.71 nm). In addition, there are twelve-membered ring semi-supercages with a depth of 0.91 nm on the outer surface (Science 264 (1994) 1910-1913). The unique multi-pore coexistence structure of MWW molecular sieves makes them promising for industrial applications. They are widely used in the alkylation of benzene and olefins (Catal. Today 73 (2002) 3-22), catalytic cracking (J. Catal. 167 (1997) 438-446), isomerization (J. Catal. 158 (1996) 561-569), and aromatization (Chin. J. Catal. 23 (2002) 24-28). They are among the few molecular sieves that have been industrialized.

[0003] The MWW family of molecular sieves comprises numerous members, including MCM-22, MCM-49, MCM-56, MCM-36, ITQ-1, ITQ-2, ERB-1, SSZ-25, and SSZ-70. Among them, MCM-56 is a staggered MWW molecular sieve, with layers stacked in a disordered manner. This unique structure gives it a high external specific surface area and high external surface acid concentration, which not only shortens the reaction diffusion path but also provides a site for macromolecular reactants and transition states, exhibiting excellent catalytic performance. It overcomes the diffusion limitations inherent in molecular sieves as microporous crystals and has significant research value.

[0004] In 1994, patent US5362697 first reported the MCM-56 molecular sieve and its synthesis method, which used hexamethyleneimine (HMI) as a structure-directing agent (OSDA). However, HMI is highly toxic and expensive, and heavily reliant on imports. Therefore, researchers hoped to use a low-toxicity and inexpensive structure-directing agent to replace HMI. Patent CN104743570A disclosed that aniline can be used to partially replace HMI, reducing production costs while producing a stable MCM-56 molecular sieve that inhibits its transformation to MCM-49 molecular sieve. Gong Yanjun et al. found that introducing tetraethylammonium hydroxide (TEAOH) into the HMI system can broaden the synthesis range of the MCM-56 crystal phase and achieve a higher degree of separation between layers, exhibiting higher reactivity and a lower deactivation rate in the liquid-phase alkylation reaction of benzene and ethylene (Microporous Mesoporous Mater. 302 (2020) 110245). In addition, Wu Peng et al. also obtained MCM-56 molecular sieves by acid treatment of the two-dimensional layered precursor MCM-22P. This is because acid treatment removes some of the OSDA sites in the interlayer, thereby changing the orientation of the interlayer hydrogen bonds. (J.Phys.Chem.C113(2009)18753)

[0005] In summary, the current synthesis of MCM-56 molecular sieves mainly uses HMI, which is highly toxic and expensive, as the OSDA, and introduces crystal growth regulators to control the crystallization process. Summary of the Invention

[0006] To address the problems existing in the prior art, this application synthesizes MCM-56 molecular sieves via hydrothermal crystallization using cyclohexylamine, a low-toxicity, inexpensive, and readily available template agent. The synthetic route is simple, easy to perform, and controllable. The use of inexpensive structure-directing agents can effectively reduce production costs, which is beneficial for its scale-up applications.

[0007] The method for preparing MWW molecular sieves provided in this application uses cyclohexylamine as a template agent and precisely controls the synthesis conditions by finely adjusting the molar composition of the raw materials to synthesize MCM-56 molecular sieves. The MCM-56 molecular sieves synthesized by this method are composed of disordered stacked nanosheets with a size of 150–500 nm and a thickness of 2.5 nm–10 nm.

[0008] According to one aspect of this application, a method for preparing MWW molecular sieve is provided, comprising the following steps: crystallizing a mixture containing a silicon source, an aluminum source, an inorganic base or inorganic acid, a crystallization aid, water and a structure directing agent to obtain MCM-56 molecular sieve;

[0009] The original molar composition of the mixture is:

[0010] SiO2 / Al2O3 = 10~300, OH - / SiO2=0.01~1, M + / SiO2=0.01~1,

[0011] R / SiO2=0.005~1.0, H2O / SiO2=2~30, D2O3 / SiO2=0.01~3;

[0012] Where M is an alkali metal element, R is a structure directing agent, D2O3 is a crystallization aid, and D is boron or gallium.

[0013] The structure-directing agent is cyclohexylamine.

[0014] Preferably, the mixture is obtained in the following order: silicon source, aluminum source, inorganic base or inorganic acid, crystallization aid, water, and structure directing agent.

[0015] Optionally, the silicon source is selected from at least one of silica sol, silica fume, tetraethyl orthosilicate, chromatography silica gel, water glass, and coarse-pore silica gel.

[0016] Preferably, the silicon source is selected from silica sol.

[0017] Optionally, the aluminum source is selected from at least one of aluminum chloride, sodium aluminate, aluminum nitrate, aluminum sulfate, aluminum powder, aluminum acetate, and boehmite.

[0018] Preferably, the aluminum source is selected from sodium aluminate.

[0019] Optionally, the inorganic base is selected from at least one of sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate.

[0020] Preferably, the inorganic base is selected from sodium hydroxide.

[0021] Optionally, the inorganic acid is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

[0022] Preferably, the inorganic acid is selected from sulfuric acid.

[0023] Optionally, the alkalinity of the raw material mixture can be adjusted by adding an inorganic base or an inorganic acid.

[0024] Optionally, the crystallization aid includes compounds of boron or gallium.

[0025] Optionally, the boron compound is selected from at least one of sodium tetraborate, boric acid, and sodium metaborate.

[0026] Optionally, the gallium compound is selected from at least one of gallium sulfate and gallium nitrate.

[0027] Preferably, the crystallization aid is selected from boric acid.

[0028] Optionally, the crystallization is dynamic crystallization.

[0029] Optionally, the dynamic crystallization is performed in a rotary oven.

[0030] Optionally, the temperature for dynamic crystallization is 100–200°C.

[0031] Optionally, the temperature for dynamic crystallization is independently selected from any value among 100℃, 110℃, 120℃, 130℃, 140℃, 145℃, 150℃, 160℃, 170℃, 180℃, 190℃, and 200℃, or a range between any two of the above points.

[0032] Optionally, the dynamic crystallization time is 48 to 288 hours.

[0033] Optionally, the time for dynamic crystallization is independently selected from any value among 48h, 72h, 96h, 112h, 120h, 132h, 144h, 168h, 180h, 200h, 240h, and 288h, or a range between any two of the above points.

[0034] Optionally, the rotational speed of the rotary oven for dynamic crystallization is 10 to 100 revolutions per minute.

[0035] Optionally, the rotational speed of the dynamic crystallization rotary oven is independently selected from any value among 10 rpm, 30 rpm, 50 rpm, 60 rpm, 80 rpm, and 100 rpm, or a range between any two of the above.

[0036] Optionally, the crystallization process may further include aging.

[0037] Optionally, the aging process is dynamic aging.

[0038] Optionally, the dynamic aging is carried out in a rotary oven.

[0039] Optionally, the temperature for dynamic aging is 0–100°C.

[0040] Optionally, the temperature for dynamic aging is independently selected from any value among 0℃, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, and 100℃, or a range between any two of the above points.

[0041] Optionally, the dynamic aging time is 0 to 48 hours.

[0042] Optionally, the dynamic aging time is independently selected from any value among 0h, 1h, 2h, 2.5h, 3h, 4h, 5h, 60h, 70h, 80h, 36h, and 48h, or a range between any two of the above points.

[0043] Optionally, the rotation speed of the dynamic aging rotary oven is 10 to 100 revolutions per minute.

[0044] Optionally, the rotational speed of the dynamic aging rotary oven is independently selected from any value among 10 rpm, 30 rpm, 50 rpm, 60 rpm, 80 rpm, and 100 rpm, or a range between any two of the above.

[0045] Optionally, the crystallization process further includes separation and drying steps.

[0046] Optionally, the drying temperature is 80–120°C.

[0047] Optionally, the drying temperature is independently selected from any value among 80°C, 90°C, 100°C, 110°C, and 120°C, or a range between any two of the above points.

[0048] Optionally, the drying time is 10 to 24 hours.

[0049] Optionally, the drying time is independently selected from any value among 10h, 12h, 14h, 16h, 18h, 20h, 22h, and 24h, or a range between any two of the above points.

[0050] As a specific implementation method, a synthesis method for MCM-56 molecular sieve is provided, the specific steps of which are as follows:

[0051] A. Add the raw materials sequentially according to the order of silicon source, aluminum source, inorganic base, crystallization aid, deionized water, and structure directing agent, and stir thoroughly until uniformly mixed. Transfer the resulting gel mixture to a hydrothermal synthesis reactor. The original molar composition of the mixture is: silicon source / aluminum source = 10-300, OH... - / Silicon source = 0.01~1, M + / Silicon source = 0.01~1, D2O3 / silicon source = 0.01~3, H2O / silicon source = 2~30, cyclohexylamine / silicon source = 0.005~1.0; wherein the molar composition of the silicon source is SiO2; the molar composition of the aluminum source is Al2O3; M is an alkali metal element, and D2O3 is a crystallization aid;

[0052] B. After the raw materials are uniformly mixed, they are aged at a low temperature of 0-100℃ (10-100 rpm) for 0-48 hours.

[0053] C. Crystallize the aged mixture at a high temperature of 100-200℃ (10-100 rpm) for 48-288 hours;

[0054] D. Cool the reactor with tap water, centrifuge or filter to obtain solid product, and wash and dry the solid product to obtain MCM-56 molecular sieve raw powder.

[0055] In another aspect of this application, an MCM-56 molecular sieve prepared by the above-described preparation method is provided, wherein the MCM-56 molecular sieve is composed of disordered stacked nanosheets; the size of the nanosheets is 150–500 nm; and the thickness of the nanosheets is 2.5–10 nm.

[0056] Another aspect of this application provides an application of the MCM-56 molecular sieve prepared by the above-described method in the alkylation, alkyl transfer, disproportionation, isomerization, aromatization, and cracking of hydrocarbons.

[0057] The beneficial effects of this application include:

[0058] (1) This application uses cyclohexylamine, which is low in toxicity, inexpensive and readily available, as a template agent to synthesize MCM-56 molecular sieve in one step via hydrothermal crystallization. This synthetic route is simple and easy to implement, and the operation is controllable. The use of inexpensive structure-directing agents can effectively reduce production costs, which is conducive to its large-scale application.

[0059] (2) The method for preparing MCM-56 molecular sieves in this application can replace the sodium ions in the MCM-56 molecular sieves synthesized in this invention with other cations through ion exchange, thereby obtaining hydrogen-type, ammonium-type, zinc-type, and magnesium-type MCM-56 molecular sieves, which can then be applied to different catalytic reaction processes.

[0060] (3) The MCM-56 molecular sieve synthesized in this application can be applied to reactions such as alkylation, alkyl transfer, disproportionation, isomerization, aromatization, and cracking of hydrocarbons. Attached Figure Description

[0061] Figure 1 This is the X-ray diffraction pattern of the MCM-56 molecular sieve in Example 1 of this application.

[0062] Figure 2 The image shown is a scanning electron microscope image of the MCM-56 molecular sieve in Example 1 of this application, with a scale bar of 1 μm.

[0063] Figure 3 The nitrogen adsorption-desorption curves of the MCM-56 molecular sieve in Example 1 of this application are shown.

[0064] Figure 4 This is the X-ray diffraction pattern of the MCM-56 molecular sieve in Example 2 of this application.

[0065] Figure 5 The image shown is a scanning electron microscope image of the MCM-56 molecular sieve in Example 2 of this application, with a scale bar of 1 μm.

[0066] Figure 6 The X-ray diffraction pattern of the MCM-56 molecular sieve in Comparative Example 1 of this application is shown. Detailed Implementation

[0067] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0068] Unless otherwise specified, the raw materials and solvents used in the embodiments of this application were all purchased commercially.

[0069] The analysis method in the embodiments of this application is as follows:

[0070] The morphological characteristics of the samples were analyzed by scanning electron microscopy (SEM) using a Hitachi SU1510 instrument with an accelerating voltage of 15 kV.

[0071] The structural characteristics of the samples were analyzed by X-ray diffraction (XRD) testing. The analytical instrument was an Empyrean-100XRD diffractometer from Panaco GmbH, Netherlands. The test conditions were Cu Kα as the radiation source, tube voltage 40kV, tube current 40mA, and diffraction data were collected from 5° to 50° (2θ).

[0072] The textural properties of the samples were analyzed by nitrogen physical adsorption-desorption test, and the analysis instrument was a Micromeritics ASAP-2020HD88 surface area and pore structure analyzer.

[0073] The cyclohexene conversion rate and cyclohexylbenzene selectivity in the embodiments of this application are calculated as follows:

[0074] Cyclohexene conversion rate = (molar percentage of cyclohexene in reactants - molar percentage of cyclohexene in products) / molar percentage of cyclohexene in reactants

[0075] Cyclohexylbenzene selectivity = (molar percentage of cyclohexylbenzene in the product) / (sum of molar percentages of all products)

[0076] Example 1

[0077] Under stirring conditions, 19.65 g of silica sol (30.54 wt.% SiO2, 0.32 wt.% Na2O, 0.02 wt.% Al2O3, 69.12 wt.% H2O), 0.74 g of sodium aluminate (16.8 wt.% Al2O3, 24.0 wt.% Na2O, 59.2 wt.% H2O), 2.39 g of 0.1 g / ml sodium hydroxide solution, 1.11 g of boric acid (H3BO3, purity ≥99.5 wt.%), 19.41 g of deionized water, and 1.98 g of cyclohexylamine (CHA, purity ≥99 wt.%) were added to the reactor in sequence. The molar composition of the mixture was: SiO2 / Al2O3 = 50, Na2O / SiO2 = 0.09, H3BO3 / SiO2 = 0.18, H2O / SiO2 = 20, CHA / SiO2 = 0.2. The mixture was thoroughly stirred to ensure homogeneity, and the synthesis vessel was sealed. It was then dynamically aged at 60℃ (50 rpm) for 2 hours, followed by dynamic crystallization at 150℃ (50 rpm) for 96 hours. The reaction was quenched with tap water, and the solid product was obtained by centrifugation. It was then washed with deionized water until neutral. The product was dried overnight at 120℃ to obtain MCM-56 molecular sieve powder.

[0078] Figure 1 This is the XRD pattern of the MCM-56 molecular sieve raw powder prepared in Example 1. Figure 1 It can be seen that the product is a pure phase MCM-56 molecular sieve with high crystallinity.

[0079] Figure 2 These are scanning electron microscope images of the MCM-56 molecular sieve prepared in Example 1. Figure 2 It can be seen that the prepared MCM-56 molecular sieve exhibits the typical plate-like morphology of MWW molecular sieve, with the size of the plates ranging from 150 to 300 nm and the thickness ranging from 2.5 to 10 nm.

[0080] Figure 3 The N2 adsorption-desorption curves of the MCM-56 molecular sieve prepared in Example 1 are shown below. Figure 3 It can be concluded that the adsorption isotherm of the sample is a type IV isotherm, in which a hysteresis loop appears in the range of P / P0 from 0.6 to 1.0, indicating the presence of mesopores or macropores in the sample.

[0081] Example 2

[0082] Under stirring conditions, 19.65 g of silica sol (30.62 wt.% SiO2, 0.32 wt.% Na2O, 0.03 wt.% Al2O3, 69.03 wt.% H2O), 0.74 g of aluminum sulfate (Al2(SO4)3·18H2O, purity ≥98 wt.%), 6.85 g of 0.1 g / ml potassium hydroxide solution, 1.73 g of boric acid (H3BO3, purity ≥99.5 wt.%), 4.39 g of deionized water, and 3.97 g of cyclohexylamine (CHA, purity ≥99 wt.%) were added to the reactor in the following order: SiO2 / Al2O3 = 80, Na2O / SiO2 = 0.1, H3BO3 / SiO2 = 0.28, H2O / SiO2 = 14, CHA / SiO2 = 0.4. Stir thoroughly to ensure homogeneity, then seal the synthesis vessel. Aged dynamically at 80°C (60 rpm) for 1 hour, then crystallized dynamically at 160°C (60 rpm) for 132 hours. Quench the reaction with tap water, and centrifuge to obtain the solid product. Wash with deionized water until neutral. Dry overnight at 120°C to obtain MCM-56 molecular sieve raw powder.

[0083] Figure 4 This is the XRD pattern of the MCM-56 molecular sieve raw powder prepared in Example 2. Figure 4 It can be seen that the product is a pure phase MCM-56 molecular sieve with high crystallinity.

[0084] Figure 5 These are scanning electron microscope images of the MCM-56 molecular sieve prepared in Example 2. Figure 5 It can be seen that the product has the typical plate-like morphology of MWW molecular sieve, with the size of the plates ranging from 200 to 500 nm and the thickness ranging from 2.5 to 10 nm.

[0085] Example 3

[0086] Under stirring conditions, 2.11 g of silica (95 wt.% dry basis), 0.12 g of aluminum nitrate (Al(NO3)3·9H2O, purity ≥99.0 wt.%), 6.24 g of 0.1 g / ml sodium hydroxide solution, 1.53 g of sodium tetraborate (Na2B4O7·10H2O, purity ≥99.9 wt.%), 16.09 g of deionized water, and 0.99 g of cyclohexylamine (CHA, purity ≥99 wt.%) were added to the reactor in the following order: SiO2 / Al2O3 = 100, Na2O / SiO2 = 0.08, Na2B4O7 / SiO2 = 0.04, H2O / SiO2 = 20, CHA / SiO2 = 0.2. The mixture was stirred thoroughly until homogeneous, and then the reactor was sealed. The mixture was dynamically aged at 50°C (50 rpm) for 1 hour, followed by dynamic crystallization at 150°C (50 rpm) for 120 hours. The reaction was quenched with tap water, and the solid product was obtained by centrifugation. The solid product was then washed with deionized water until neutral. The solid product was dried overnight at 120°C to obtain MCM-56 molecular sieve powder.

[0087] Example 4

[0088] Under stirring conditions, 29.40 g of water glass (20.41 wt.% SiO2, 6.50 wt.% Na2O, 0.09 wt.% Al2O3, 73.00 wt.% H2O), 1.98 g of sodium aluminate (16.8 wt.% Al2O3, 24.0 wt.% Na2O, 59.2 wt.% H2O), 19.89 g of 0.1 g / ml hydrochloric acid solution, 1.73 g of boric acid (H3BO3, purity ≥99.5 wt.%), 2.69 g of deionized water, and 3.97 g of cyclohexylamine (CHA, purity ≥99 wt.%) were added to the reactor in sequence. The molar composition of the mixture was: SiO2 / Al2O3 = 30, Na2O / SiO2 = 0.10, H3BO3 / SiO2 = 0.07, H2O / SiO2 = 25, CHA / SiO2 = 0.4. The mixture was thoroughly stirred to ensure homogeneity, and the synthesis vessel was sealed. It was dynamically aged at 80℃ (60 rpm) for 4 hours, followed by dynamic crystallization at 150℃ (60 rpm) for 96 hours. The reaction was quenched with tap water, and the solid product was obtained by centrifugation. It was then washed with deionized water until neutral. The product was dried overnight at 120℃ to obtain MCM-56 molecular sieve raw powder.

[0089] Example 5

[0090] Under stirring conditions, 6.45 g of solid silica gel (93 wt.% dry basis), 0.30 g of sodium aluminate (16.8 wt.% Al₂O₃, 24.0 wt.% Na₂O, 59.2 wt.% H₂O), 10.00 g of 0.1 g / ml sodium hydroxide solution, 15.45 g of boric acid (H₃BO₃, purity ≥99.5 wt.%), 22.40 g of deionized water, and 3.97 g of cyclohexylamine (CHA, purity ≥99 wt.%) were added to the reactor in the following order: SiO₂ / Al₂O₃ = 200, Na₂O / SiO₂ = 0.125, H₃BO₃ / SiO₂ = 2.5, H₂O / SiO₂ = 18, CHA / SiO₂ = 0.4. The mixture was stirred thoroughly until homogeneous, and then the reactor was sealed. The product was dynamically aged at 50℃ (30 rpm) for 2.5 h, and then dynamically crystallized at 140℃ (30 rpm) for 72 h. The reaction was quenched with tap water, and the solid product was obtained by centrifugation. It was then washed with deionized water until neutral. The product was dried overnight at 120℃ to obtain MCM-56 molecular sieve raw powder.

[0091] Example 6

[0092] Under stirring conditions, 21.13 g of tetraethyl orthosilicate (28.4 wt.% SiO2), 0.24 g of aluminum nitrate (Al(NO3)3·9H2O, purity ≥99.0 wt.%), 7.19 g of 0.1 g / ml sodium hydroxide solution, 7.42 g of boric acid (H3BO3, purity ≥99.5 wt.%), 33.20 g of deionized water, and 15.20 g of cyclohexylamine (CHA, purity ≥99 wt.%) were added to the reactor in the following order: SiO2 / Al2O3 = 150, Na2O / SiO2 = 0.10, H3BO3 / SiO2 = 1.2, H2O / SiO2 = 20, CHA / SiO2 = 0.5. The mixture was stirred thoroughly until homogeneous, and then the reactor was sealed. The mixture was dynamically aged at 50℃ (60 rpm) for 3 hours, and then dynamically crystallized at 145℃ (60 rpm) for 144 hours. The reaction was quenched with tap water, and the solid product was obtained by centrifugation. The solid product was then washed with deionized water until neutral. The raw MCM-56 molecular sieve powder was obtained by drying at 120℃ overnight.

[0093] Example 7

[0094] Under stirring conditions, 21.13 g of tetraethyl orthosilicate (28.4 wt.% SiO2), 1.50 g of sodium aluminate (16.8 wt.% Al2O3, 24.0 wt.% Na2O, 59.2 wt.% H2O), 5.05 g of 0.1 g / ml sodium hydroxide solution, 2.16 g of boric acid (H3BO3, purity ≥99.5 wt.%), 48.79 g of deionized water, and 0.99 g of cyclohexylamine (CHA, purity ≥99 wt.%) were added to the reactor in the following order: SiO2 / Al2O3 = 40, Na2O / SiO2 = 0.08, H3BO3 / SiO2 = 0.35, H2O / SiO2 = 30, CHA / SiO2 = 0.1. The mixture was stirred thoroughly until homogeneous, and then the reactor was sealed. The mixture was dynamically aged at 50℃ (60 rpm) for 5 hours, and then dynamically crystallized at 150℃ (60 rpm) for 168 hours. The reaction was quenched with tap water, and the solid product was obtained by centrifugation. The solid product was then washed with deionized water until neutral. The solid product was dried overnight at 120℃ to obtain MCM-56 molecular sieve powder.

[0095] The XRD patterns of the MCM-56 molecular sieves prepared in Examples 3-7 of this application are similar to those in Example 1, showing that they are well-crystallized MCM-56 molecular sieves.

[0096] Comparative Example 1

[0097] Referring to the method in US Pat. (1994) 5362697, MCM-56 molecular sieve was synthesized using hexamethyleneimine as a structure-directing agent. The specific operation was as follows: Under stirring conditions, 19.65 g of silica sol (30.54 wt.% SiO2, 0.32 wt.% Na2O, 0.02 wt.% Al2O3, 69.12 wt.% H2O), 2.59 g of sodium aluminate (16.8 wt.% Al2O3, 24.0 wt.% Na2O, 59.2 wt.% H2O), 3.53 g of 0.1 g / ml sulfuric acid solution, 16.10 g of deionized water, and 3.47 g of hexamethyleneimine (HMI, purity ≥99 wt.%) were added to the reaction vessel in sequence. The molar composition of the mixture was: SiO2 / Al2O3 = 23, Na2O / SiO2 = 0.08, H2O / SiO2 = 19.2, HMI / SiO2 = 0.35. The mixture was thoroughly stirred to ensure homogeneity, and the synthesis vessel was sealed. It was dynamically aged at 60℃ (50 rpm) for 2 hours, followed by dynamic crystallization at 140℃ (50 rpm) for 40 hours. The reaction was quenched with tap water, and the solid product was obtained by centrifugation. It was then washed with deionized water until neutral. The product was dried overnight at 120℃ to obtain MCM-56 molecular sieve raw powder.

[0098] Figure 6The image shows the XRD pattern of the MCM-56 molecular sieve powder prepared in Comparative Example 1. Figure 6 It can be seen that the product is MCM-56 molecular sieve.

[0099] Test Example 1

[0100] The MCM-56 molecular sieves prepared in Examples 1-3 and Comparative Example 1 of this application were used to test the performance of the liquid-phase alkylation reaction of benzene and cyclohexene. The MCM-56 molecular sieves were placed in a fixed-bed reactor, and benzene and cyclohexene were introduced into the reactor to produce cyclohexylbenzene. The test conditions were: reaction temperature (T) 160℃, reaction pressure (P) 1.5MPa, benzene to cyclohexene molar ratio (B / CH) 10:1, and cyclohexene space velocity (WHSV). CH ) is 2h -1 The reaction products were collected and their composition was analyzed using an Agilent 7890A chromatographic analyzer equipped with a PONA column and an FID detector.

[0101] The test results are shown in Table 1.

[0102] Table 1. Performance test results of MCM-56 molecular sieve in the liquid-phase alkylation reaction of benzene and cyclohexene.

[0103]

[0104] As shown in Table 1, the MCM-56 molecular sieve synthesized using cyclohexylamine as a structure-directing agent and with the introduction of crystallization aids exhibits stronger catalytic activity and better stability under the same reaction conditions in the liquid-phase alkylation reaction of benzene and cyclohexene, compared to the traditional MCM-56 molecular sieve synthesized using hexamethyleneimine as a structure-directing agent. The selectivity for cyclohexylbenzene remains the same. This is because the MCM-56 synthesized by the method described in this application has higher crystallinity, a larger external specific surface area, shortened mass transfer pathways, and exposed more active sites. The preparation method described in this application is simple, easy to implement, and controllable. The use of a low-toxicity, inexpensive, and readily available structure-directing agent can effectively reduce production costs and has excellent prospects for industrial application.

[0105] Unless otherwise specified, all figures appearing in this application specification and claims, such as active components, temperature and time, conversion rates, etc., should not be construed as absolutely precise values. Due to the standard deviation of measurement techniques, the measured values ​​inevitably contain a certain degree of experimental error.

[0106] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for preparing MWW molecular sieves, characterized in that, The process includes the following steps: crystallizing a mixture containing a silicon source, an aluminum source, an inorganic base or an inorganic acid, a crystallization aid, water, and a structure directing agent to obtain MCM-56 molecular sieve; The original molar composition of the mixture is as follows: SiO2 / Al2O3=10~300,OH - / SiO2=0.01~1,M + / SiO2=0.01~1, R / SiO2=0.005~1.0, H2O / SiO2=2~30, D2O3 / SiO2=0.01~3; Where M is an alkali metal element, R is a structure directing agent, D2O3 is a crystallization aid, and D is boron or gallium. The structure-directing agent is cyclohexylamine.

2. The preparation method according to claim 1, characterized in that, The silicon source is selected from at least one of silica sol, silica fume, tetraethyl orthosilicate, chromatography silica gel, water glass, and coarse-pore silica gel.

3. The preparation method according to claim 1, characterized in that, The aluminum source is selected from at least one of aluminum chloride, sodium aluminate, aluminum nitrate, aluminum sulfate, aluminum powder, aluminum acetate, and boehmite.

4. The preparation method according to claim 1, characterized in that, The inorganic base is selected from at least one of sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate.

5. The preparation method according to claim 1, characterized in that, The inorganic acid is selected from at least one of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

6. The preparation method according to claim 1, characterized in that, The crystallization aid includes compounds of boron or gallium; The boron compound is selected from at least one of sodium tetraborate, boric acid, and sodium metaborate; The gallium compound is selected from at least one of gallium sulfate and gallium nitrate.

7. The preparation method according to claim 1, characterized in that, The crystallization is dynamic crystallization; Preferably, the temperature for dynamic crystallization is 100–200°C; The dynamic crystallization time is 48–288 hours; Preferably, the crystallization process further includes aging. The aging process described is dynamic aging. The temperature for dynamic aging is 0–100℃; The dynamic aging time is 0–48 hours.

8. The preparation method according to claim 1, characterized in that, The crystallization process also includes separation and drying steps; Preferably, the drying temperature is 80–120°C; The drying time is 10 to 24 hours.

9. An MCM-56 molecular sieve prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The MCM-56 molecular sieve is composed of randomly stacked nanosheets; The nanosheets have a size of 150–500 nm; The thickness of the nanosheet is 2.5–10 nm.

10. The application of the MCM-56 molecular sieve prepared by the preparation method according to any one of claims 1 to 8 in the alkylation, alkyl transfer, disproportionation, isomerization, aromatization and cracking of hydrocarbons.

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