A binderless mww structure molecular sieve catalyst and its preparation method and application

Abstract

The application discloses a binder-free MWW structure molecular sieve catalyst and a preparation method and application thereof. The outer specific surface area of the catalyst is 200 m 2 / g or above, and the crystal thickness of the catalyst is 10 nm or below. The preparation method of the catalyst comprises the following steps: mixing an MWW molecular sieve raw powder, a binder and an alkali source to form a precursor; mixing and treating the precursor with cyclohexane and a low-carbon alcohol, and then separating; mixing the separated solid with a template agent and water, and then hydrothermally crystallizing to perform first calcination; performing ammonium exchange on the first calcination product, and then performing second calcination to obtain the MWW structure molecular sieve catalyst. The catalyst is used in the reaction of synthesizing cyclohexyl benzene from cyclohexene and benzene, and has higher product selectivity and reaction stability.

Description

Technical Field

[0001] This invention belongs to the field of MWW structured molecular sieve catalysts, specifically relating to a binder-free MWW structured molecular sieve catalyst, its preparation method, and its application. Background Technology

[0002] The molecular formula of cyclohexylbenzene (CHB) is C2. 12 H 16 Cyclohexylbenzene is used to produce phenol and cyclohexanone through oxidation and acid decomposition reactions. Currently, the main production processes for cyclohexylbenzene include the hydrogenation alkylation of benzene, the selective hydrogenation of biphenyl, and the FC alkylation of benzene and cyclohexene. Among these, the FC alkylation of benzene and cyclohexene uses benzene and cyclohexene as raw materials, and prepares cyclohexylbenzene under the action of acidic catalysts such as Lewis acids, ionic liquids, and zeolite molecular sieves. Zeolite molecular sieves, as a solid acid catalyst, can reduce separation costs while promoting green production, making them highly promising for industrial applications. Cyclohexylbenzene has a large molecular size and easily generates dicyclohexylbenzene byproducts with extremely large molecular sizes during synthesis. These byproducts are difficult to diffuse and tend to accumulate carbon at the pore openings of molecular sieves, clogging the pores and significantly reducing catalyst activity and lifespan. Therefore, increasing the diffusivity of the molecular sieve and possessing a larger external specific surface area is crucial.

[0003] MWW-structured molecular sieves are plate-like molecular sieves whose pore system comprises two sets of non-interconnected ten-membered ring channels (one set containing a twelve-membered ring cylindrical supercage) and a bowl-shaped twelve-membered ring semi-supercage located on the outer surface of the crystal. Its open bowl-shaped semi-supercage structure on the outer surface gives it a stronger benzene adsorption capacity compared to other molecular sieves and facilitates the diffusion of reactant molecules, making it an ideal alkylation catalyst.

[0004] In industrial production, molecular sieve powders are typically bonded together with binders to form a crystalline structure. Binders generally comprise about 40% of the total catalyst mass. However, commonly used catalyst binders are inert components, such as alumina, silica, and kaolin, which can clog the pores of the molecular sieve, weakening its adsorption capacity, increasing diffusion resistance, and affecting the diffusion performance of the reaction, leading to decreased reactivity and selectivity. Binder-free molecular sieves, on the other hand, are produced by thoroughly and uniformly mixing raw materials such as silicon and aluminum sources in a specific ratio in a solid phase, followed by crystallization with water vapor or an organic structure-directing agent, allowing binder molecules to grow crystals under solid-phase conditions. Because of the absence of a binder, they possess a larger specific surface area, resulting in superior performance in adsorption separation and catalytic reactions.

[0005] CN114162833A discloses a method for preparing thin-layer MCM-22 molecular sieve microspheres with a microporous mesoporous structure. This method involves adding a second template agent to form a "desert rose" morphology, and the catalyst made from this morphology can be used in the liquid-phase alkylation reaction of benzene and ethylene. However, the molecular sieve microspheres obtained by this method are 1-2 micrometers in size, and a binder component is still required when using the catalyst. This causes pore blockage of the molecular sieve, increases diffusion resistance, and makes it difficult for large molecules such as cyclohexylbenzene and dicyclohexylbenzene to diffuse, resulting in low product selectivity and a short catalyst lifespan.

[0006] CN107512727A discloses a method for preparing binder-free MWW-structured molecular sieves. This method crystallizes the binder into MCM-22 molecular sieves via gas-solid phase transition crystallization, solving the problems of long crystallization time and incomplete crystallization. Furthermore, it exhibits good catalytic activity in the liquid-phase alkylation reaction of benzene and ethylene. However, when this molecular sieve is used as a catalyst in the FC alkylation reaction of benzene and cyclohexene, the byproduct dicyclohexylbenzene rapidly deposits carbon at the pore openings, leading to a short catalyst lifespan. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a binder-free MWW-structured molecular sieve catalyst, its preparation method, and its applications. The MWW-structured molecular sieve catalyst is a high specific surface area, ultrathin layer, binder-free MWW-structured molecular sieve catalyst. This catalyst, used in the alkylation of cyclohexene with benzene to synthesize cyclohexylbenzene, exhibits higher product selectivity and reaction stability.

[0008] The first aspect of this invention provides a binder-free MWW-structured molecular sieve catalyst, wherein the catalyst has an external specific surface area of ​​200 m². 2 / g or more, preferably 200~280m 2 / g, wherein the crystal thickness of the catalyst is less than 10nm, preferably 3~8nm.

[0009] According to the present invention, the SiO2 / Al2O3 molar ratio of the binderless MWW structured molecular sieve catalyst is 20~80.

[0010] According to the present invention, the binder-free MWW structured molecular sieve catalyst has a specific surface area of ​​400~600 m². 2 / g.

[0011] According to the present invention, in the preparation of the binder-free MWW structured molecular sieve catalyst, the mass ratio of the binder (based on oxides) to the raw MWW structured molecular sieve powder (based on dry basis) is 0.5~12:1, preferably 1~9:1. The binder is preferably a silicon-containing binder or an aluminum-containing binder.

[0012] A second aspect of this invention provides a method for preparing the above-mentioned MWW-structured molecular sieve catalyst, comprising: (1) Mix MWW molecular sieve raw powder, binder and alkali source to form a precursor; (2) The precursor described in step (1) is mixed with cyclohexane and lower alcohols and then separated; (3) The solid obtained in step (2) is mixed with template agent and water and then hydrothermally crystallized, followed by the first calcination; (4) The calcination product obtained in step (3) is subjected to ammonium exchange and a second calcination to obtain the MWW structured molecular sieve catalyst.

[0013] According to the present invention, in step (1), the properties of the MWW molecular sieve raw powder are: SiO2 / Al2O3 molar ratio of 25~100; specific surface area of ​​350~550 m². 2 / g. The crystal thickness of the MWW molecular sieve raw powder is less than 15nm, preferably 3~10nm.

[0014] According to the present invention, in step (1), the molding is preferably extrusion molding. In step (1), during the mixing and molding process of the MWW molecular sieve powder, binder, and alkali source, molding aids, such as at least one of a pore-forming agent and a pectinic acid, may be added. The pore-forming agent includes at least one of guar gum powder and methylcellulose. The pectinic acid is preferably a nitric acid solution. The mass concentration of the nitric acid solution is 0.5% to 5%, preferably 1% to 3%.

[0015] According to the present invention, in step (1), the binder is preferably a silicon-containing binder and an aluminum-containing binder. The silicon-containing binder includes at least one selected from silica sol, silica fume, and silica powder. The aluminum-containing binder is an inorganic aluminum salt. The aluminum-containing binder includes at least one selected from sodium aluminate, aluminum sulfate, and aluminum nitrate.

[0016] According to the present invention, in step (1), the alkali source is an alkali with alkali metal and / or alkaline earth metal as cations; more preferably, the alkali source includes at least one of sodium hydroxide, potassium hydroxide and barium hydroxide.

[0017] According to the present invention, preferably, in step (1), the mass ratio of MWW molecular sieve raw powder, binder, and alkali source is 1:0.5~12:0.02~0.2, more preferably 1:1~9:0.05~0.1. Wherein, the MWW molecular sieve raw powder is based on the dry basis of MWW molecular sieve, and the binder is based on oxides.

[0018] According to the present invention, in step (1), the binder is preferably a silicon-containing binder and an aluminum-containing binder. The mass ratio of MWW molecular sieve raw powder, silicon-containing binder, aluminum-containing binder, and alkali source is 1:0.5~10:0.01~2:0.02~0.2, preferably 1:1~8:0.05~1:0.05~0.1. Wherein, the MWW molecular sieve raw powder is based on the dry basis of MWW molecular sieve, the silicon-containing binder is based on SiO2, and the aluminum-containing binder is based on Al2O3.

[0019] According to the present invention, preferably, in step (1), the mass ratio of MWW molecular sieve raw powder, pore-forming agent, and pectinic acid is 1:0.01~0.1:0.2~3, more preferably 1:0.01~0.05:0.5~2. Wherein, the MWW molecular sieve raw powder is based on the dry basis of MWW molecular sieve.

[0020] According to the present invention, in step (2), the low-carbon alcohol is selected from at least one of alcohols with C6 or less, preferably at least one of methanol, ethanol, and isopropanol.

[0021] According to the present invention, in step (2), the mass ratio of the precursor to cyclohexane and lower alcohol is 1:0.5~2:0.5~5; preferably 1:0.7~1.5:1~3.

[0022] According to the present invention, in step (2), the processing temperature is 40~90℃, and the processing time is 1~5h. The processing method is to let it stand in a mixed solution of cyclohexane and ethanol. The separation can be a conventional solid-liquid separation method.

[0023] According to the present invention, in step (3), the template agent includes at least one of hexamethyleneimine, piperidine, cyclohexylamine, aniline and piperazine.

[0024] According to the present invention, in step (3), the mass ratio of the solid obtained in step (2) to the template agent and water is 1:0.3~1.5:0.5~4, preferably 1:0.8~1.5:1~3.

[0025] According to the present invention, in step (3), the conditions for hydrothermal crystallization include: a crystallization temperature of 140~170℃, preferably 150~160℃; and a crystallization time of 24~60h, preferably 30~48h. The crystallization equipment is preferably a crystallization kettle. The conditions for the first calcination include: a calcination temperature of 500℃~550℃ and a calcination time of 3h~8h. Drying can be performed before calcination. The drying conditions are: a drying temperature of 80℃~150℃ and a drying time of 3h~12h.

[0026] According to the present invention, in step (4), the ammonium exchange is a treatment method in which the roasted product is immersed in an ammonium salt solution. The temperature of the ammonium exchange is 20℃~90℃, the time is 3h~6h, and it is repeated 2~4 times. The ammonium salt includes one or more of ammonium chloride, ammonium sulfate, ammonium nitrate, ammonium acetate, ammonium oxalate and ammonium phosphate, preferably ammonium nitrate.

[0027] According to the present invention, in step (4), the conditions for the second calcination include: a calcination temperature of 500℃~550℃ and a calcination time of 3h~8h. Drying can be performed before calcination. The drying conditions are: a drying temperature of 80℃~150℃ and a drying time of 3h~12h.

[0028] According to the present invention, the relative crystallinity of the MWW structured molecular sieve catalyst relative to the MWW molecular sieve raw powder is 90% or more, preferably 90% to 100%.

[0029] The third aspect of this invention provides the application of the above-described MWW structured molecular sieve catalyst or the catalyst prepared by the above preparation method in the reaction of cyclohexene and benzene alkylation to synthesize cyclohexylbenzene.

[0030] According to the present invention, the reaction conditions for the application are: a reaction temperature of 130~220℃, a reaction pressure of 1~4MPa, a benzene to cyclohexene molar ratio of 1~20, and a mass hourly space velocity (HHSV) based on cyclohexene of 0.2~4h. -1 .

[0031] Compared with the prior art, the advantages of the present invention are as follows: 1. The inventors discovered through research that the external specific surface area of ​​the binder-free MWW structured molecular sieve catalyst is 200m². 2 With a density of over / g and a crystal thickness of less than 10nm, it is used in the reaction of cyclohexene and benzene alkylation to synthesize cyclohexylbenzene. It not only has good activity, but also can significantly improve the selectivity and catalyst lifetime of cyclohexylbenzene.

[0032] 2. The inventors discovered that in existing technologies for preparing binder-free MWW-structured molecular sieve catalysts, a binder is typically added to the MWW molecular sieve powder to form the catalyst, followed by the conversion of the binder into molecular sieve crystals. This causes the converted crystals to preferentially grow on the surface of the original powder crystals, resulting in thicker molecular sieve catalyst crystals, reduced surface area, and impaired diffusion performance, thus affecting its application performance as a catalyst. Further research revealed that pretreating the catalyst precursor in a mixed solution of cyclohexane and lower alcohols at a specific temperature before the crystallization step facilitates the dehydration condensation of interlayer Si-OH groups in the MWW-structured molecular sieve during calcination, forming a three-dimensional structure. The molecular size of cyclohexane is similar to that of the organic template agent. The introduction of cyclohexane preemptively occupies the gaps between the layers of the MWW-structured molecular sieve, hindering the entry of organic template agent molecules into the interlayer space and inhibiting the superposition of the basic layers during crystallization, thereby controlling the crystal thickness. Simultaneously, the separation between layers increases the specific surface area and exposes more active acidic sites. By introducing ethanol to control the concentration of cyclohexane, excessive cyclohexane can be prevented from entering the molecular sieve channels, thus hindering the crystallization of the molecular sieve by the organic template agent and leading to incomplete crystallization of the MWW-structured molecular sieve. Furthermore, at a certain temperature, ethanol has a pre-crystallization effect on the catalyst precursor, significantly shortening the crystallization time and improving the crystallinity of the catalyst, ultimately yielding a high external specific surface area, ultrathin layer, binder-free MWW-structured molecular sieve catalyst.

[0033] 3. The high external specific surface area, ultra-thin layer binder-free MWW structure molecular sieve catalyst of the present invention is used in macromolecular alkylation reactions, such as the alkylation of cyclohexene and benzene to synthesize cyclohexylbenzene. It not only has good activity, but also can significantly improve the selectivity and catalyst lifetime of cyclohexylbenzene. Attached Figure Description

[0034] Figure 1 These are the reaction time-cyclohexene conversion curves for Example 1 and Comparative Example 1; Figure 2 These are X-ray diffraction images of Example 1 and Comparative Example 1; Figure 3 These are transmission electron microscope images of Cata-1 from Example 1; Figure 4 This is a transmission electron microscope image of Comparative Example 1, Cata-1b. Detailed Implementation

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] In this invention, X-ray diffraction (XRD) analysis of the samples was performed using a Bruker D8 Advanced X-ray diffractometer.

[0037] In this invention, the molecular sieve crystal thickness and transmission electron microscopy (TEM) patterns were determined using a JEOL-2010F electron microscope manufactured by Nippon Electron Ltd.

[0038] In this invention, the N2 adsorption-desorption isotherm was performed in a Micromeritics ASAP 2010 physical adsorption instrument under vacuum at 300 °C. The specific surface area of ​​the sample was calculated using the BET formula.

[0039] In this invention, the meaning of catalyst lifetime reaching several hours is: the time when the cyclohexene conversion rate is less than 80% is recorded as catalyst lifetime, i.e. catalyst deactivation.

[0040] In this invention, the room temperature is 25°C.

[0041] In this invention, the formulas for calculating the single-pass conversion rate of cyclohexene and the selectivity of cyclohexylbenzene are as follows: Cyclohexene conversion rate = (total product - cyclohexene) / total amount of all product components × 100% Cyclohexylbenzene selectivity = cyclohexylbenzene / total amount of all components in the product × 100%. Example 1

[0042] (1) MWW molecular sieve raw powder, silica sol, sodium aluminate, sodium hydroxide, guar gum powder, and 2% nitric acid aqueous solution were uniformly mixed in a mass ratio of 1:6:0.2:0.1:0.01:0.5, wherein the MWW molecular sieve raw powder was on a dry basis, the silica sol was based on SiO2, and the sodium aluminate was based on Al2O3. The mixture was then extruded into strips using a cloverleaf perforated plate, dried at 120°C, and cooled to room temperature to obtain the MWW structured molecular sieve catalyst precursor. The properties of the MWW molecular sieve raw powder were: SiO2 / Al2O3 molar ratio of 30 and specific surface area of ​​447 m². 2 / g. The crystal thickness of the MWW molecular sieve raw powder is 8nm.

[0043] (2) The catalyst precursor obtained in step (1) is added to a mixed solution of cyclohexane and ethanol, with a mass ratio of catalyst precursor to cyclohexane and ethanol of 1:0.5:2.5; the mixture is treated at 60°C for 3 hours, and then solid-liquid separation is performed.

[0044] (3) The solid obtained in step (2) is placed in a crystallization vessel with hexamethyleneimine and water in a mass ratio of 1:1.5:2. The crystallization temperature is 150℃ and the crystallization time is 48h. The product obtained by crystallization is separated into solid and liquid. The solid obtained is dried at 120℃ for 5h and calcined at 550℃ for 4h.

[0045] (4) The calcined product obtained in step (3) was exchanged with an aqueous solution of ammonium chloride in a water bath at 30°C for 1 h according to the mass ratio of molecular sieve (dry basis): ammonium chloride: water = 1:1:10. After centrifugation, the exchange was repeated twice, followed by centrifugation, washing with water, drying at 120°C for 5 h, and calcining at 550°C for 4 h to obtain a binder-free MWW molecular sieve catalyst, denoted as Cata-1.

[0046] The properties of the MWW molecular sieve catalyst Cata-1 are as follows: external specific surface area is 203 m². 2 / g, crystal thickness is 7 nm, SiO2 / Al2O3 molar ratio is 33.

[0047] The catalyst testing conditions were: a reaction temperature of 160℃, a reaction pressure of 3 MPa, a benzene to cyclohexene molar ratio of 10, and a mass hourly space velocity (MHV) of 2 h⁻¹ based on cyclohexene. -1 Under the given conditions, the test results are shown in Table 2. Example 2

[0048] Compared with the catalyst preparation method of Example 1, the difference in Example 2 is that step (2) is changed to adding the catalyst precursor obtained in step (1) to a mixed solution of cyclohexane and ethanol, with a mass ratio of catalyst precursor to cyclohexane and ethanol of 1:1:3; the mixture is treated at 80°C for 1 h, and then separated. The final molecular sieve catalyst is designated Cata-2.

[0049] The properties of the MWW molecular sieve catalyst Cata-2 are as follows: external specific surface area is 239 m². 2 / g, crystal thickness is 5nm, SiO2 / Al2O3 molar ratio is 33.

[0050] The catalyst testing conditions were the same as in Example 1. The test results are shown in Table 2. Example 3

[0051] (1) MWW molecular sieve raw powder, silica sol, aluminum sulfate, sodium hydroxide, guar gum powder, and 4% nitric acid aqueous solution were uniformly mixed in a mass ratio of 1:4:0.1:0.08:0.02:0.5, wherein the MWW molecular sieve raw powder was on a dry basis, the silica sol was based on SiO2, and the aluminum sulfate was based on Al2O3. The mixture was then extruded into strips using a cloverleaf perforated plate, dried at 100°C, and cooled to room temperature to obtain the MWW structured molecular sieve catalyst precursor. The properties of the MWW molecular sieve raw powder were: SiO2 / Al2O3 molar ratio of 40 and specific surface area of ​​463 m². 2 / g. The crystal thickness of the MWW molecular sieve raw powder is 7nm.

[0052] (2) The catalyst precursor obtained in step (1) is added to a mixed solution of cyclohexane and isopropanol, with a mass ratio of catalyst precursor to cyclohexane and isopropanol of 1:0.8:3; the mixture is treated at 50°C for 3 hours, and then solid-liquid separation is performed.

[0053] (3) The solid obtained in step (2) is placed in a crystallization vessel with hexamethyleneimine and water in a mass ratio of 1:1.5:2. The crystallization temperature is 160℃ and the crystallization time is 48h. The product obtained by crystallization is separated into solid and liquid. The solid is dried at 100℃ for 5h and calcined at 550℃ for 4h.

[0054] (4) The calcined product obtained in step (3) was exchanged with an aqueous solution of ammonium chloride in a water bath at 50°C for 1 h according to the mass ratio of molecular sieve (dry basis): ammonium chloride: water = 1:1:10. After centrifugation, the exchange was repeated twice, followed by centrifugation, washing with water, drying at 120°C for 5 h, and calcining at 550°C for 4 h to obtain a binder-free MWW molecular sieve catalyst, denoted as Cata-3.

[0055] The properties of the MWW molecular sieve catalyst Cata-3 are as follows: external specific surface area is 221 m². 2 / g, crystal thickness is 7 nm, SiO2 / Al2O3 molar ratio is 38.

[0056] The catalyst testing conditions were the same as in Example 1. The test results are shown in Table 2. Example 4

[0057] Compared with the catalyst preparation method of Example 3, the difference of Example 4 is that in step (1), the mass ratio of MWW molecular sieve raw powder, silica sol, aluminum sulfate, sodium hydroxide, guar gum powder and 4% nitric acid aqueous solution is changed to 1:8:0.2:0.08:0.02:0.5, and the molecular sieve catalyst obtained is denoted as Cata-4.

[0058] The properties of the MWW molecular sieve catalyst Cata-4 are as follows: external specific surface area is 236 m².2 / g, crystal thickness is 7 nm, SiO2 / Al2O3 molar ratio is 42.

[0059] The catalyst testing conditions were the same as in Example 1. The test results are shown in Table 2. Example 5

[0060] Compared with the catalyst preparation method of Example 3, the difference in Example 5 is that the properties of the MWW molecular sieve raw powder in step (1) are: SiO2 / Al2O3 molar ratio of 80 and specific surface area of ​​488 m². 2 / g. The crystal thickness of the MWW molecular sieve raw powder is 8nm, and the final molecular sieve catalyst is designated Cata-5.

[0061] The properties of the MWW molecular sieve catalyst Cata-5 are as follows: external specific surface area of ​​216 m². 2 / g, crystal thickness is 7 nm, SiO2 / Al2O3 molar ratio is 52.

[0062] The catalyst testing conditions were the same as in Example 1. The test results are shown in Table 2. Comparative Example 1

[0063] Compared with the catalyst preparation method of Example 1, the difference of Comparative Example 1 is that step (2) is omitted. The resulting catalyst is denoted as Cata-1b.

[0064] The properties of the MWW molecular sieve catalyst Cata-1b are as follows: external specific surface area is 127 m². 2 / g, crystal thickness is 20nm, SiO2 / Al2O3 molar ratio is 33.

[0065] The test was conducted under the same conditions as in Example 1, and the evaluation results are shown in Table 2. Comparative Example 2

[0066] According to the method in Example 1 of CN 111099621B, the MWW-structured ultrathin nanosheet molecular sieve Cata-2b was prepared.

[0067] The MWW molecular sieve catalyst has the following properties: external surface area of ​​186 m². 2 / g, crystal thickness is 6nm, molar ratio is 35.

[0068] The test was conducted under the same conditions as in Example 1, and the evaluation results are shown in Table 2. Comparative Example 3

[0069] Compared with the catalyst preparation method of Example 1, the difference of Comparative Example 3 is that only cyclohexane is added in step (2), and no ethanol is added. The resulting catalyst is denoted as Cata-3b.

[0070] The properties of the MWW molecular sieve catalyst Cata-3b are as follows: external specific surface area of ​​173 m². 2 / g, crystal thickness is 7nm, SiO2 / Al2O3 molar ratio is 33.

[0071] The test was conducted under the same conditions as in Example 1, and the evaluation results are shown in Table 2.

[0072] Table 1. Nitrogen adsorption-desorption characterization data for each catalyst. Cata-1 513 203 0.999 0.147 Cata-2 544 239 1.048 0.154 Cata-3 538 221 1.115 0.154 Cata-4 523 236 1.006 0.161 Cata-5 501 216 1.011 0.142 Cata-1b 456 127 0.926 0.169 Cata-2b 498 186 0.988 0.150 Cata-3b 405 173 0.869 0.128 Note: In Table 1, S BET It refers to the total specific surface area, S external V refers to the external specific surface area. total V refers to the total orifice volume. micro It refers to the pore volume of micropores.

[0073] Table 2 Evaluation results of each catalyst example Example 1 99 89 1150 Example 2 99 86 1060 Example 3 99 86 1180 Example 4 99 87 1130 Example 5 99 89 1050 Comparative Example 1 99 78 650 Comparative Example 2 99 76 540 Comparative Example 3 99 84 390

Claims

1. A binder-free MWW structured molecular sieve catalyst, wherein the catalyst has an external specific surface area of ​​200 m². 2 / g or more, and the crystal thickness of the catalyst is less than 10nm; The preparation method of binder-free MWW structured molecular sieve catalysts includes: (1) Mix MWW molecular sieve raw powder, binder and alkali source to form a precursor; (2) The precursor described in step (1) is mixed with cyclohexane and lower alcohols and then separated; (3) The solid obtained in step (2) is mixed with template agent and water and then hydrothermally crystallized, followed by the first calcination; (4) The calcination product obtained in step (3) is subjected to ammonium exchange and a second calcination to obtain the MWW structured molecular sieve catalyst; In step (2), the mass ratio of the precursor to cyclohexane and lower alcohols is 1:0.5~2:0.5~5; In step (2), the processing temperature is 40~90℃ and the processing time is 1~5h.

2. The catalyst according to claim 1, characterized in that, The binderless MWW structured molecular sieve catalyst has a SiO2 / Al2O3 molar ratio of 20 to 80.

3. The catalyst according to claim 1, characterized in that, The catalyst has an external specific surface area of ​​200~280m². 2 / g, the crystal thickness of the catalyst is 3~8nm.

4. The catalyst according to claim 1, characterized in that, The binder-free MWW-structured molecular sieve catalyst has a specific surface area of ​​400-600 m². 2 / g.

5. A method for preparing the binderless MWW structured molecular sieve catalyst according to any one of claims 1 to 4, comprising: (1) Mix MWW molecular sieve raw powder, binder and alkali source to form a precursor; (2) The precursor described in step (1) is mixed with cyclohexane and lower alcohols and then separated; (3) The solid obtained in step (2) is mixed with template agent and water and then hydrothermally crystallized, followed by the first calcination; (4) The calcination product obtained in step (3) is subjected to ammonium exchange and a second calcination to obtain the MWW structured molecular sieve catalyst; In step (2), the mass ratio of the precursor to cyclohexane and lower alcohols is 1:0.5~2:0.5~5; In step (2), the processing temperature is 40~90℃ and the processing time is 1~5h.

6. The preparation method according to claim 5, characterized in that, In step (1), the properties of the MWW molecular sieve raw powder are: SiO2 / Al2O3 molar ratio of 25~100, and specific surface area of ​​350~550 m². 2 / g, wherein the crystal thickness of the MWW molecular sieve raw powder is less than 15nm.

7. The preparation method according to claim 5, characterized in that, In step (1), the crystal thickness of the MWW molecular sieve raw powder is 3~10nm.

8. The preparation method according to claim 5, characterized in that, In step (1), the adhesive includes a silicon-containing adhesive and an aluminum-containing adhesive; the aluminum-containing adhesive is an inorganic aluminum salt. And / or, in step (1), the alkali source is an alkali with alkali metal and / or alkaline earth metal as cations; And / or, in step (3), the template agent includes at least one of hexamethyleneimine, piperidine, cyclohexylamine, aniline and piperazine.

9. The preparation method according to claim 8, characterized in that, In step (1), the silicon-containing binder includes at least one of silica sol, silica fume and silica powder; the aluminum-containing binder includes at least one of sodium aluminate, aluminum sulfate and aluminum nitrate. And / or, in step (1), the alkali source includes at least one of sodium hydroxide, potassium hydroxide and barium hydroxide.

10. The preparation method according to claim 5, characterized in that, In step (1), the mass ratio of MWW molecular sieve raw powder, binder, and alkali source is 1:0.5~12:0.02~0.2; wherein, the MWW molecular sieve raw powder is based on the dry basis of MWW molecular sieve, and the binder is based on oxides; And / or, in step (3), the mass ratio of the solid obtained in step (2) to the template agent and water is 1:0.3~1.5:0.5~4.

11. The preparation method according to claim 5, characterized in that, In step (1), the mass ratio of MWW molecular sieve raw powder, binder, and alkali source is 1:1~9:0.05~0.1; wherein, the MWW molecular sieve raw powder is based on the dry basis of MWW molecular sieve, and the binder is based on oxides; And / or, in step (3), the mass ratio of the solid obtained in step (2) to the template agent and water is 1:0.8~1.5:1~3.

12. The preparation method according to claim 5, 8, or 10, characterized in that, In step (1), the binder is a silicon-containing binder and an aluminum-containing binder. The mass ratio of MWW molecular sieve raw powder, silicon-containing binder, aluminum-containing binder and alkali source is 1:0.5~10:0.01~2:0.02~0.

2. Among them, the MWW molecular sieve raw powder is based on the dry basis of MWW molecular sieve, the silicon-containing binder is based on SiO2, and the aluminum-containing binder is based on Al2O3.

13. The preparation method according to claim 12, characterized in that, In step (1), the mass ratio of MWW molecular sieve raw powder, silicon-containing binder, aluminum-containing binder, and alkali source is 1:1~8:0.05~1:0.05~0.1; wherein, MWW molecular sieve raw powder is based on dry MWW molecular sieve, silicon-containing binder is based on SiO2, and aluminum-containing binder is based on Al2O3.

14. The preparation method according to claim 5, characterized in that, In step (2), the low alcohol is selected from at least one of alcohols below C6; and / or, in step (2), the mass ratio of the precursor to cyclohexane and the low alcohol is 1:0.7~1.5:1~3.

15. The preparation method according to claim 14, characterized in that, In step (2), the lower alcohol is at least one of methanol, ethanol, and isopropanol.

16. The preparation method according to claim 5, characterized in that, In step (3), the conditions for hydrothermal crystallization include: crystallization temperature of 140~170℃; crystallization time of 24~60h; and / or, the conditions for the first calcination include: calcination temperature of 500℃~550℃ and calcination time of 3h~8h.

17. The preparation method according to claim 16, characterized in that, Its features are, In step (3), the conditions for hydrothermal crystallization include: crystallization temperature of 150~160℃ and crystallization time of 30~48h.

18. The preparation method according to claim 5, characterized in that, In step (4), the conditions for the second roasting include: roasting temperature of 500℃~550℃ and roasting time of 3h~8h.

19. The preparation method according to claim 5, characterized in that, The relative crystallinity of the MWW structured molecular sieve catalyst relative to the MWW molecular sieve raw powder is over 90%.

20. The preparation method according to claim 19, characterized in that, The relative crystallinity of the MWW structured molecular sieve catalyst relative to the MWW molecular sieve raw powder is 90%~100%.

21. The application of the MWW structured molecular sieve catalyst according to any one of claims 1 to 4 or the catalyst prepared by any one of the preparation methods according to claims 5 to 20 in the reaction of cyclohexene and benzene alkylation to synthesize cyclohexylbenzene.

22. The application according to claim 21, characterized in that, The reaction conditions for this application are: reaction temperature of 130~220℃, reaction pressure of 1~4MPa, benzene to cyclohexene molar ratio of 1~20, and mass hourly space velocity (MHV) based on cyclohexene of 0.2~4h. -1 .

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