MWW molecular sieve, preparation method and application thereof, and preparation method of p-xylene

Abstract

The invention relates to the field of molecular sieves, in particular to an MWW molecular sieve, a preparation method and application thereof and a preparation method of p-xylene. The molecular sieve has a schematic chemical composition as shown in the formula of mSiO2.nAl2O3.pP2O5, in the formula, m / p is more than or equal to 10 and less than or equal to 100, and n / p is more than or equal to 0.2 and less than or equal to 1. The MWW molecular sieve provided by the invention has excellent stability, carbon deposition resistance and high selectivity, for example, the MWW molecular sieve has high selectivity in a reaction for preparing PX by contacting DMF and / or HDO with ethylene.

Description

Technical Field

[0001] The invention relates to the field of molecular sieves, and in particular to an MWW molecular sieve and a preparation method and application thereof, and a preparation method of p-xylene. Background Art

[0002] Molecular sieves are widely used in chemical catalytic reactions because of their large specific surface area, rich active sites and stable structure. Traditional molecular sieve catalysts are widely used in the field of petrochemicals, such as oil cracking, isomerization, and alkylation reactions, and they are usually highly acidic. In recent years, the technology of preparing chemicals using biomass as raw materials has emerged and developed, and traditional molecular sieves have been limited in the field of biomass catalytic conversion because their highly acidic sites are prone to cause a series of side reactions such as hydrolysis, condensation, and polymerization in an oxygen-rich environment of biomass. Therefore, the modification of molecular sieve catalysts to make them suitable for the field of biomass catalysis has received more and more attention. If you want to obtain the required acidity, starting from the original molecular sieve powder, it often takes several steps, such as the original molecular sieve powder needs to be roasted, ammonium exchanged, roasted, modified, and roasted. The present invention aims to obtain a molecular sieve catalyst with the required acid properties with as few modification steps as possible. And meet the reaction requirements, the catalyst structure is stable.

[0003] The framework of the molecular sieve is based on three-dimensional TO 4 (SiO 4 , AlO 4 The skeleton of aluminosilicate molecular sieve is composed of SiO 4 Tetrahedron and AlO 4 Tetrahedral composition, AlO 4 The charge balance is achieved by cations such as Na + , H + The framework properties of zeolite can be changed by cation exchange, and the tetracoordinated Al can further coordinate with other atoms to change the acid properties. During the synthesis of molecular sieves, organic structure directing agents are introduced into the pores to guide the synthesis of the molecular sieve crystal structure. When used as a catalyst, the organic structure directing agents need to be calcined to remove them and expose the active sites on the surface.

[0004] The molecular sieve with MWW structure is a two-dimensional layered structure with a bowl-shaped twelve-membered ring semi-supercage on the outer surface of its crystal. Its large external specific surface provides excellent mass transfer performance and has a strong potential to resist carbon deposition. It can be further developed and applied in the field of biomass catalysis. However, the strongly acidic molecular sieves widely used in the petrochemical field, such as ZSM-5, Beta, and Y, are too acidic. When used for catalytic conversion of biomass-derived raw materials, polymerization side reactions between raw materials are prone to occur, causing serious carbon deposition and rapid deactivation of the catalyst. For example, patent US20140296600A1 reports that H-type molecular sieves are used as catalysts to catalyze 2,5-dimethylfuran (DMF) and ethylene from biomass to prepare bio-based paraxylene (PX). When HY molecular sieve is used as a catalyst, the PX selectivity reaches 75%, and when H-Beta molecular sieve is used as a catalyst, the PX selectivity reaches 90%. Subsequent acid modification reduces the acid strength of the molecular sieve. For example, in patent US20190344252A1, a phosphoric acid-modified Beta molecular sieve was reported as a catalyst, and the PX selectivity reached 97%. The catalyst preparation method is to roast the synthesized Na-type Beta molecular sieve raw powder to remove the organic structure directing agent, ammonium exchange, roast to obtain H-Beta, and then load phosphoric acid and roast to obtain the final catalyst product after the strong acid completely removes Al. This preparation method is relatively cumbersome, and the active site of the obtained molecular sieve catalyst is a P-modified hydroxyl hole, which has poor chemical stability. The Beta molecular sieve is a three-dimensional structure, and the pores are easily blocked due to the occurrence of carbon deposition, causing the catalyst to be deactivated. Therefore, it is very important to find a simple modification method to obtain a catalyst with suitable acidity and excellent mass transfer to catalyze the preparation of PX from biomass-derived DMF and ethylene. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems in the prior art of low selectivity, severe carbon deposition and poor stability of molecular sieve catalysts used for preparing PX from 2,5-dimethylfuran (DMF) or 2,5-hexanedione (HDO) and ethylene. The present invention provides an MWW molecular sieve and a preparation method and application thereof, and a method for preparing paraxylene. The molecular sieve has excellent stability, resistance to carbon deposition and high selectivity for the reaction of preparing PX from DMF or HDO and ethylene.

[0006] In order to achieve the above object, the present invention provides a MWW molecular sieve having a formula of "mSiO 2 nAl 2 O 3 ·pP 2 O 5 ” is a schematic chemical composition shown in the formula, wherein 10≤m / p≤100, 0.2≤n / p≤1.

[0007] The second aspect of the present invention provides a method for preparing the molecular sieve described in the first aspect of the present invention, the method comprising: optionally removing the organic structure directing agent from the MWW molecular sieve precursor, contacting it with a phosphorus source in a first organic solvent, washing, drying and calcining.

[0008] The third aspect of the present invention provides a use of the molecular sieve described in the first aspect of the present invention in the preparation of an adsorbent or a catalyst.

[0009] The fourth aspect of the present invention provides a use of the molecular sieve described in the first aspect of the present invention in the preparation of p-alkyl aromatics using furan raw materials and / or ketone raw materials.

[0010] The fifth aspect of the present invention provides a method for preparing para-xylene, comprising: contacting and reacting a 2,5-dimethylfuran raw material and / or a 2,5-hexanedione raw material with ethylene in the presence of a catalyst and an optional second organic solvent; wherein the catalyst comprises the molecular sieve described in the first aspect of the present invention;

[0011] Through the above technical solution, the present invention has the following advantages:

[0012] The MWW molecular sieve having the composition of the present invention has excellent stability, resistance to carbon deposition and high selectivity, for example, has high selectivity in the reaction of preparing PX by contacting DMF and / or HDO with ethylene. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is the XRD spectrum of the catalyst in Example 1;

[0014] Figure 2 is the NH of the catalyst in Example 1 3 -TPD curve;

[0015] Figure 3 is the Py-FTIR spectrum of the catalyst in Example 1;

[0016] Figure 4 is the catalyst in Example 1 27 Al NMR spectrum;

[0017] Figure 5 is the XRD spectrum of the catalyst in Example 6;

[0018] Figure 6 is the NH of the catalyst in Example 6 3 -TPD curve;

[0019] Figure 7 is the Py-FTIR spectrum of the catalyst in Example 6;

[0020] Figure 8 is the catalyst in Example 627 Al NMR spectrum. DETAILED DESCRIPTION

[0021] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0022] The present invention provides a MWW molecular sieve having a formula of "mSiO 2 nAl 2 O 3 ·pP 2 O 5 ” is a schematic chemical composition shown in the formula, wherein 10≤m / p≤100, 0.2≤n / p≤1.

[0023] The MWW molecular sieve having the composition of the present invention has excellent stability, resistance to carbon deposition and selectivity, for example, has high selectivity in the reaction of preparing PX by contacting DMF and / or HDO with ethylene.

[0024] According to a preferred embodiment of the present invention, the formula "mSiO 2 nAl 2 O 3 ·pP 2 O 5 ", 20≤m / n≤35, preferably 25≤m / n≤32, 10≤m / p≤60, 0.4≤n / p≤0.65. By adopting the above preferred scheme, the stability, carbon deposition resistance and selectivity of the MWW molecular sieve can be further improved.

[0025] According to a preferred embodiment of the present invention, the content of tetracoordinated aluminum in the molecular sieve accounts for no more than 15% of the total aluminum content, preferably no more than 12%. Tetracoordinated Al is Al in the molecular sieve framework that has not been modified by P. This active site has strong acidity, so it is required to adopt an effective modification method to modify it under the premise of ensuring its stability, reduce the content of tetracoordinated Al, that is, reduce the acidity of the molecular sieve, which can further improve the stability, carbon deposition resistance and selectivity of the MWW molecular sieve.

[0026] According to a preferred embodiment of the present invention, the crystals of the molecular sieve are two-dimensional layered structures. The two-dimensional layered structure refers to the thin nanosheet structure of the MWW molecular sieve, which provides a large external specific surface area and is conducive to mass transfer. By adopting the above preferred embodiment, the stability, carbon deposition resistance and selectivity of the MWW molecular sieve can be further improved.

[0027] According to a preferred embodiment of the present invention, the internal specific surface area of ​​the molecular sieve is not less than 30m 2 / g, preferably not less than 40m 2 By adopting the above preferred embodiment, the stability, carbon deposition resistance and selectivity of the MWW molecular sieve can be further improved.

[0028] According to a preferred embodiment of the present invention, the external specific surface area of ​​the molecular sieve is not less than 30m 2 / g, preferably not less than 50m 2 By adopting the above preferred embodiment, the stability, carbon deposition resistance and selectivity of the MWW molecular sieve can be further improved.

[0029] According to a preferred embodiment of the present invention, the Lewis / The ratio is 0.2-5.0, preferably 0.5-3.5. By adopting the above preferred solution, the stability, carbon deposition resistance and selectivity of the MWW molecular sieve can be further improved.

[0030] According to a preferred embodiment of the present invention, the total acid content of the molecular sieve is 300-1200 μmol / g, preferably 400-800 μmol / g. By adopting the above preferred scheme, the stability, carbon deposition resistance and selectivity of the MWW molecular sieve can be further improved.

[0031] In the present invention, as long as the molecular sieve having the aforementioned characteristics of the present invention can be prepared, there is no particular limitation on the preparation method thereof, and it may be a conventional preparation scheme in the art.

[0032] Preferably, the present invention provides a method for preparing the molecular sieve of the present invention, which comprises: optionally removing the organic structure directing agent from the MWW molecular sieve precursor, contacting it with a phosphorus source in a first organic solvent, washing, drying and calcining.

[0033] The catalyst of the present invention having excellent stability, carbon deposition resistance and selectivity can be prepared by the method of the present invention.

[0034] According to a preferred embodiment of the present invention, the preparation of the MWW molecular sieve precursor includes: preparing a crystallization liquid with a silicon source, an aluminum source, sodium hydroxide, an organic structure directing agent a, an organic structure directing agent b and water, and then hydrothermally crystallizing to obtain the MWW molecular sieve precursor.

[0035] In the present invention, as long as the purpose of the present invention can be achieved, there is no special requirement for the type of the organic structure directing agent a. According to a preferred embodiment of the present invention, the organic structure directing agent a is selected from at least one of N, N, N-trimethylammonium adamantane, hexamethyleneimine, piperidine, homopiperazine, dicyclohexylamine, and N, N-diethylcyclohexylamine, preferably N, N, N-trimethylammonium adamantane. By adopting the above preferred scheme, the stability, carbon deposition resistance and selectivity of the prepared MWW molecular sieve can be further improved.

[0036] In the present invention, as long as the purpose of the present invention can be achieved, there is no special requirement for the type of the organic structure directing agent b. According to a preferred embodiment of the present invention, the organic structure directing agent b is cyclohexylamine. By adopting the above preferred embodiment, the stability, carbon deposition resistance and selectivity of the prepared MWW molecular sieve can be further improved.

[0037] In the present invention, as long as the molecular sieve of the present invention can be obtained, there is no particular limitation on the amount of each substance in the crystallization solution. According to a preferred embodiment of the present invention, the silicon source in the crystallization solution is SiO 2 Aluminum source is Al 2 O 3 The molar ratio of sodium hydroxide, organic structure directing agent a, organic structure directing agent b and water is 1: 0.028-0.050: 0.07-0.22: 0.001-0.03: 0.051-0.10: 12-50; preferably 1: 0.029-0.048: 0.08-0.21: 0.001-0.028: 0.055-0.095: 14-40. By adopting the above preferred scheme, the stability, carbon deposition resistance and selectivity of the prepared MWW molecular sieve can be further improved.

[0038] In the present invention, the hydrothermal crystallization process is carried out in a conventional homogeneous reactor, and the hydrothermal crystallization conditions can be selected in a wide range. According to a preferred embodiment of the present invention, the hydrothermal crystallization conditions include: crystallization at 130-180°C for 0.5-2.0 days, preferably crystallization at 140-170°C for 0.75-2.00 days.

[0039] According to a preferred embodiment of the present invention, the crystallization method is dynamic crystallization, for example, stirring crystallization, and the preferred rotation speed is 10-100 rpm.

[0040] In the present invention, the preparation of the MWW molecular sieve precursor further comprises separation and washing after hydrothermal crystallization.

[0041] In the present invention, the conditions for removing the organic structure directing agent can be conventionally selected in the art. According to a preferred embodiment of the present invention, the conditions for removing the organic structure directing agent include: a temperature of 500-700°C, preferably 550-650°C.

[0042] According to a preferred embodiment of the present invention, the conditions for removing the organic structure directing agent include: a time of 3-12 hours, preferably 4-8 hours.

[0043] According to the present invention, the method of removing the organic structure directing agent is to perform calcination in an oxygen-containing atmosphere, and preferably the oxygen-containing atmosphere is air.

[0044] In the present invention, the contact conditions may be conventionally selected in the art. According to a preferred embodiment of the present invention, the contact conditions include: a temperature of 40-150°C, preferably 60-100°C.

[0045] According to a preferred embodiment of the present invention, the contacting conditions include: a time of 0.5-12 hours, preferably 3-6 hours.

[0046] In the present invention, the drying conditions can be conventionally selected in the art. According to a preferred embodiment of the present invention, the drying conditions include: a temperature of 50-100°C, preferably 80-100°C.

[0047] According to a preferred embodiment of the present invention, the drying conditions include: a time of 5-24 hours, preferably 6-12 hours.

[0048] In the present invention, the calcination conditions can be conventionally selected in the art. According to a preferred embodiment of the present invention, the calcination conditions include: a temperature of 400-800°C, preferably 500-700°C.

[0049] According to a preferred embodiment of the present invention, the calcination conditions include: a time of 0.5-12 hours, preferably 3-8 hours.

[0050] In the present invention, as long as the purpose of the present invention can be achieved, there is no special requirement for the type of the first organic solvent. According to a preferred embodiment of the present invention, the first organic solvent is selected from at least one of alkanes, aromatic hydrocarbons, and halogenated hydrocarbons.

[0051] According to a preferred embodiment of the present invention, the phosphorus source is selected from at least one of phosphoric acid, dimethylphosphonic acid, phosphorus oxychloride, and phosphorus pentachloride, preferably phosphorus oxychloride, dimethylphosphonic acid and / or phosphorus pentachloride. By adopting the above preferred embodiment, the stability, carbon deposition resistance and selectivity of the prepared MWW molecular sieve can be further improved.

[0052] In the present invention, there is no particular limitation on the concentration of the phosphorus source in the first organic solvent, as long as the purpose of the present invention can be achieved. According to a preferred embodiment of the present invention, the concentration of the phosphorus source in the first organic solvent is 0.005-0.5 mol / L.

[0053] In the present invention, the washing method after contacting with the phosphorus source in the first organic solvent can be a conventional choice in the art. According to a preferred embodiment of the present invention, the washing is performed using the first organic solvent of the present invention as a detergent.

[0054] The present invention provides an application of the molecular sieve of the present invention in the preparation of an adsorbent or a catalyst.

[0055] The present invention provides an application of the molecular sieve of the present invention in preparing para-alkyl aromatic hydrocarbons with furan raw materials and / or ketone raw materials.

[0056] The present invention provides a method for preparing paraxylene, comprising: contacting and reacting 2,5-dimethylfuran raw material and / or 2,5-hexanedione raw material with ethylene in the presence of a catalyst and an optional second organic solvent; wherein the catalyst contains the molecular sieve of the present invention.

[0057] In the present invention, as long as the purpose of the present invention can be achieved, there is no special requirement for the type of the second organic solvent. According to a preferred embodiment of the present invention, the second organic solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, n-octane and tetrahydrofuran.

[0058] In the present invention, the conditions for the contact reaction can be selected in a wide range. According to a preferred embodiment of the present invention, the conditions for the contact reaction include: the mass concentration of the 2,5-dimethylfuran raw material and / or the 2,5-hexanedione raw material in the second organic solvent is not less than 5%, preferably not less than 15%.

[0059] According to a preferred embodiment of the present invention, the conditions of the contact reaction include: the mass ratio of the 2,5-dimethylfuran raw material and / or the 2,5-hexanedione raw material to the catalyst is (5-50):1, preferably (5-8):1.

[0060] According to a preferred embodiment of the present invention, the contact reaction conditions include: the reaction temperature is 200-320°C, preferably 235-270°C.

[0061] According to a preferred embodiment of the present invention, the contact reaction conditions include: the reaction time is 3-24h, preferably 6-12h.

[0062] According to a preferred embodiment of the present invention, the contact reaction conditions include: the pressure of ethylene is 1-6 MPa, preferably 2-4 MPa.

[0063] The present invention will be described in detail below through examples. In the following examples, the XRD spectra of the present invention were obtained on a D8 Advance X-ray diffractometer of Bruker, Germany, using a CuKα ray source.

[0064] NH 3 -TPD(NH 3 The programmed temperature desorption (TPD) curve was measured on an AMI-3300 instrument produced by Altamira. Before the test, the sample was pretreated at 550°C for 1 h, and ammonia was adsorbed at 100°C for 20 min before being subjected to programmed temperature desorption.

[0065] The ratio of L acid to B acid in the catalyst was determined by the pyridine adsorption infrared (py-FTIR) method. The py-FTIR spectrum was obtained on a Nicolet Model 710 spectrometer. The steps are as follows: (1) Sample preparation and pretreatment: about 14 mg of sample was pressed into a thin disc with a diameter of 13 mm and loaded into the sample tank, and then pretreated at 400°C for 2 h under vacuum conditions. After the sample tank was cooled to the corresponding temperature, the background spectrum was obtained by scanning; (2) Pyridine adsorption: pyridine was adsorbed in situ for 10 min and balanced for 5 min; c. Pyridine desorption: after the adsorption was completed, vacuum desorption was carried out at 150°C for 15 min, and the infrared absorption spectrum was scanned and recorded; the temperature was raised to the corresponding temperature to record the infrared spectrum. The difference spectrum before and after pyridine adsorption was the Py-FTIR spectrum.

[0066] The elemental composition and content of the molecular sieve were measured by an Agilent 725-ES inductively coupled plasma atomic emission spectrometer (ICP). The samples were digested with hydrofluoric acid, and the element content was based on moles.

[0067] solid 27 Al NMR ( 27 The Al-NMR spectra were obtained on a Varian 400MHz NMR solid state nuclear magnetic resonance spectrometer with a magnetic field strength of 9.4T and a resonance frequency of 400MHz. The peak with a chemical shift of about 50ppm corresponds to tetracoordinated aluminum, the peak with a chemical shift of about 38ppm corresponds to pentacoordinated aluminum, and the peak with a chemical shift of about -13ppm corresponds to hexacoordinated aluminum. The percentage of each peak area to the total peak area is the content of the corresponding coordinated aluminum.

[0068] The specific surface area and external specific surface area of ​​the molecular sieve were measured by nitrogen physical adsorption and desorption method: the adsorption and desorption curve was measured on Micromeretic ASAP2020M physical adsorption instrument, the total specific surface area was obtained by BET equation, and the external specific surface area was calculated by t-plot equation. Before the test, the sample was pretreated in vacuum at 350℃ for 6h.

[0069] The components of the reaction solution were analyzed qualitatively by gas chromatography-mass spectrometry (GC-MS), the instrument model was Agilent 7890A; the quantitative analysis was performed by gas chromatography (GC), the instrument model was Agilent 7890B, equipped with a hydrogen ion flame detector (FID) and a Wax polar capillary column. The quantitative analysis was based on the molar amount of each substance in the reaction solution measured by gas chromatography, and the calculation formula was as follows;

[0070] Conversion rate of 2,5-dimethylfuran (and / or 2,5-hexanedione) (%) = (molar amount of 2,5-dimethylfuran (and / or 2,5-hexanedione) participating in the reaction) / (molar amount of 2,5-dimethylfuran (and / or 2,5-hexanedione) initially added) × 100%;

[0071] The selectivity of the product PX (%) = (the molar amount of the product PX generated by the reaction) / (the molar amount of 2,5-dimethylfuran (and / or 2,5-hexanedione) participating in the reaction) × 100%.

[0072] Example 1

[0073] Silica sol, sodium aluminate, sodium hydroxide, N,N,N-trimethylammonium adamantanium (organic structure directing agent a), cyclohexylamine (organic structure directing agent b) and water were mixed at a material molar ratio of SiO 2 :Al 2 O 3 :NaOH:a:b:H 2 The mixed gel was prepared with a ratio of O=1:0.035:0.13:0.015:0.08:20, and transferred to a self-generated pressure hydrothermal crystallization reactor, and crystallized for 1 day at 170°C with a stirring speed of 20 rpm. Then it was centrifuged and washed, and dried at 80°C for 12 hours to finally obtain a well-crystallized molecular sieve raw powder.

[0074] The above molecular sieve raw powder was P-modified: 1.0 g of the above molecular sieve raw powder was added to 30 mL of phosphorus oxychloride toluene solution (the concentration of phosphorus oxychloride was 0.01 M), and treated at 100°C for 3 hours. After cooling, it was washed with toluene, dried at 80°C for 12 hours, and calcined in air at 550°C for 4 hours to obtain a P-modified MWW molecular sieve catalyst. The XRD pattern of the obtained catalyst is shown in the figure below: Figure 1 The structure of MWW molecular sieve is shown in Figure 1. The internal specific surface area measured by BET is 40 m 2 / g, external specific surface area is 52m 2 / g. ICP measured the Si / Al molar ratio to be 17.1 and the P / Al molar ratio to be 2.3. 3 -TPD curve as Figure 2 As shown in Figure 2, the total acid content is 417 μmol / g. Figure 3 As shown, the ratio of L acid to B acid is 3.1. 27 Al-NMR Figure 4 As shown, the content of tetracoordinated Al is 10%, the content of pentacoordinated Al is 41%, and the content of hexacoordinated Al is 49%.

[0075] Example 2

[0076] Silica sol, sodium aluminate, sodium hydroxide, N,N,N-trimethylammonium adamantanium (organic structure directing agent a), cyclohexylamine (organic structure directing agent b) and water were mixed at a material molar ratio of SiO 2 :Al 2 O 3 :NaOH:a:b:H 2 The mixed gel was prepared with a ratio of O=1:0.038:0.18:0.025:0.06:35, and transferred to a self-generated pressure hydrothermal crystallization reactor, and crystallized for 2 days at 140°C and a stirring speed of 20 rpm. Then it was centrifuged and washed, and dried at 80°C for 12 hours to finally obtain a well-crystallized molecular sieve raw powder.

[0077] The above molecular sieve raw powder was P-modified: 1.0 g of the above molecular sieve raw powder was added to 30 mL of phosphorus pentachloride n-octane solution (the concentration of phosphorus pentachloride was 0.01 M), and treated at 60°C for 6 hours. After cooling, it was washed with n-octane, dried at 80°C for 12 hours, and calcined in air at 550°C for 4 hours to obtain a P-modified MWW molecular sieve catalyst. The XRD pattern of the obtained catalyst is similar to Figure 1 The internal specific surface area of ​​the catalyst measured by BET is 124 m 2 / g, external specific surface area is 96m 2 / g. The Si / Al molar ratio measured by ICP was 15.8, and the P / Al molar ratio was 1.7. 3 -TPD measured the total acid content to be 569 μmol / g. Py-FTIR measured the ratio of L acid to B acid to be 2.5. 27 Al-NMR measured that the content of tetracoordinated aluminum was 0, the content of pentacoordinated Al was 24%, and the content of hexacoordinated Al was 76%.

[0078] Example 3

[0079] Silica sol, sodium aluminate, sodium hydroxide, N,N,N-trimethylammonium adamantanium (organic structure directing agent a), cyclohexylamine (organic structure directing agent b) and water were mixed at a material molar ratio of SiO 2 :Al 2 O 3 :NaOH:a:b:H 2 The mixed gel was prepared with a ratio of O=1:0.041:0.18:0.025:0.06:15, and transferred to a self-generated pressure hydrothermal crystallization reactor, and crystallized for 1.25 days at 150°C and a stirring speed of 20 rpm. Then it was centrifuged and washed, and dried at 80°C for 12 hours to finally obtain a well-crystallized molecular sieve raw powder.

[0080] The above molecular sieve raw powder was P-modified: 1.0 g of the above molecular sieve raw powder was added to 30 mL of dimethylphosphoric acid 1-chlorobutane solution (the concentration of dimethylphosphoric acid was 0.01 M), and treated at 80°C for 3 hours. After cooling, it was washed with 1-chlorobutane, dried at 80°C for 12 hours, and calcined in air at 550°C for 4 hours to obtain a P-modified MWW molecular sieve catalyst. The XRD pattern of the obtained catalyst is similar to Figure 1 The internal specific surface area of ​​the catalyst measured by BET is 78m 2 / g, external specific surface area is 91m 2 / g. The Si / Al molar ratio measured by ICP was 13.2, and the P / Al molar ratio was 2.1. 3 -TPD measured the total acid content to be 603 μmol / g. Py-FTIR measured the ratio of L acid to B acid to be 2.4. 27 Al-NMR measured that the content of tetracoordinated aluminum was 0, the content of pentacoordinated Al was 12%, and the content of hexacoordinated Al was 88%.

[0081] Example 4

[0082] The molecular sieve raw powder in Example 1 was modified with P: 1.0 g of the molecular sieve raw powder was added to 30 mL of 1,2-dichloroethane solution of phosphorus pentachloride (the concentration of phosphorus pentachloride was 0.01 M), and treated at 80°C for 3 h. After cooling, it was washed with 1,2-dichloroethane, dried at 80°C, and calcined in air at 550°C for 4 h to obtain a P-modified MWW molecular sieve catalyst. The XRD pattern of the obtained catalyst is similar to Figure 1 The internal specific surface area of ​​the catalyst measured by BET is 112 m 2 / g, external specific surface area is 111m 2 / g. The Si / Al molar ratio measured by ICP was 17.1, and the P / Al molar ratio was 1.7. 3 -TPD measured the total acid content to be 498 μmol / g. Py-FTIR measured the ratio of L acid to B acid to be 2.8.27 Al-NMR measured that the content of tetracoordinated aluminum was 8%, the content of pentacoordinated Al was 32%, and the content of hexacoordinated Al was 60%.

[0083] Example 5

[0084] The molecular sieve powder in Example 1 was modified with P: 1.0 g of the molecular sieve powder was added to 30 mL of an aqueous solution of phosphoric acid (the concentration of phosphoric acid was 0.01 M) and treated at 60°C for 12 h. After cooling, it was washed with water, dried at 80°C, and calcined in air at 550°C for 4 h to obtain a P-modified MWW molecular sieve catalyst. The XRD pattern of the obtained catalyst was similar to Figure 1 The internal specific surface area of ​​the catalyst measured by BET is 147 m 2 / g, external specific surface area is 114m 2 / g. ICP measured the Si / Al molar ratio to be 17.1 and the P / Al molar ratio to be 1.4. 3 -TPD measured the total acid content to be 408 μmol / g. Py-FTIR measured the ratio of L acid to B acid to be 2.4. 27 Al-NMR measured that the content of tetracoordinated aluminum was 12%, the content of pentacoordinated Al was 31%, and the content of hexacoordinated Al was 57%.

[0085] Example 6

[0086] The molecular sieve raw powder in Example 1 was P-modified: that is, the molecular sieve raw powder containing the organic structure directing agent was first calcined at 550°C in air to remove the organic structure directing agent. Then it was added to 30mL of phosphorus oxychloride toluene solution (the concentration of phosphorus oxychloride was 0.01M) and treated at 110°C for 6h. After cooling, it was washed with toluene, dried at 80°C for 12h, and calcined in air at 550°C for 4h to obtain a P-modified MWW molecular sieve catalyst. The XRD pattern of the obtained catalyst is shown as follows: Figure 5 As shown, it is the structure of MWW molecular sieve, and the internal specific surface area measured by BET is 76m 2 / g, external specific surface area is 88m 2 / g. ICP measured the Si / Al molar ratio to be 17.1 and the P / Al molar ratio to be 2.3. 3 -TPD curve as Figure 6 As shown in Figure 2, the total acid content is 564 μmol / g. Figure 7 As shown, the ratio of L acid to B acid is 0.6. 27 Al-NMR Figure 8 As shown, the content of tetracoordinated Al is 0, the content of pentacoordinated Al is 0%, and the content of hexacoordinated Al is 100%.

[0087] Example 7

[0088] The difference from Example 6 is that the P modification process was carried out at 60°C for 3 h, and other conditions remained the same. Figure 1 The internal specific surface area of ​​the catalyst measured by BET is 104m 2 / g, external specific surface area is 111m 2 / g. ICP measured the Si / Al molar ratio to be 17.1 and the P / Al molar ratio to be 1.6. 3 -TPD measured the total acid content to be 487 μmol / g. Py-FTIR measured the ratio of L acid to B acid to be 1.1. 27 Al-NMR measured that the content of tetracoordinated aluminum was 10%, the content of pentacoordinated Al was 32%, and the content of hexacoordinated Al was 58%.

[0089] Example 8

[0090] The MCM-22 molecular sieve product (product number NKF-10H) of Tianjin Nanhua Catalyst Co., Ltd. was used for P modification. The modification method was the same as in Example 1 to obtain a P-modified MWW molecular sieve catalyst. The XRD pattern of the obtained catalyst was Figure 1 Similar to MWW molecular sieve structure. The internal specific surface area measured by BET is 116m 2 / g, external specific surface area is 43m 2 / g. ICP measured the Si / Al molar ratio to be 14.7 and the P / Al molar ratio to be 2.2. 3 -TPD measured the total acid content to be 594 μmol / g. Py-FTIR measured the ratio of L acid to B acid to be 1.6. 27 Al-NMR measured that the content of tetracoordinated aluminum was 0, the content of pentacoordinated Al was 8%, and the content of hexacoordinated Al was 92%.

[0091] Example 9

[0092] The molecular sieve catalyst in the above-mentioned Examples 1-8 was used for the reaction of preparing PX from DMF and ethylene. The reaction operation was as follows: 0.5 g of the catalyst in the above-mentioned Examples 1-8, 3.0 g of DMF and 17 g of n-heptane were added to a magnetically stirred high-pressure reactor, filled with 2.0 MPa of ethylene and heated to 250°C, and reacted at 250°C for 12 hours. After the reaction, the reaction liquid was analyzed by gas chromatography to calculate the molar amount of each substance. The calculated DMF conversion rate and PX selectivity are shown in Table 1.

[0093] Table 1

[0094] Catalyst No. DMF conversion rate (%) PX selectivity (%) Example 1 92.2 95.5 Example 2 93.2 96.4 Example 3 92.1 96.9 Example 4 94.1 96.3 Example 5 88.9 86.0 Example 6 96.1 97.6 Example 7 93.5 96.3 Example 8 89.7 91.4

[0095] Example 10

[0096] 0.5 g of the catalyst in Example 1, 3.0 g of 2,5-hexanedione (HDO) and 17 g of n-heptane were added to a magnetically stirred high-pressure reactor, filled with 2.0 MPa of ethylene and heated to 250° C., and reacted at 250° C. for 12 hours. After the reaction, the reaction liquid was analyzed by gas chromatography to calculate the molar amount of each substance, and the calculated DMF conversion rate was 96.5%, and the PX selectivity was 94.1%.

[0097] Embodiment 11

[0098] 0.5 g of the catalyst in Example 6, 3.0 g of 2,5-hexanedione (HDO) and 17 g of n-heptane were added to a magnetically stirred high-pressure reactor, filled with 2.0 MPa of ethylene and heated to 250° C., and reacted at 250° C. for 12 hours. After the reaction, the reaction liquid was analyzed by gas chromatography to calculate the molar amount of each substance, and the calculated DMF conversion rate was 98.4%, and the PX selectivity was 96.8%.

[0099] Examples 10 and 11 illustrate that HDO can replace the raw material DMF in the preparation of PX, and molecular sieves modified with P by different methods can obtain PX with high selectivity and high activity.

[0100] Example 12

[0101] The molecular sieve catalyst in the above-mentioned Example 6 was used for the reaction of preparing PX from DMF and ethylene, and its cyclic reaction performance was tested: 0.5 g of the catalyst in the above-mentioned Example 6, 3.0 g of DMF and 17 g of n-heptane were added to a magnetically stirred high-pressure reactor, filled with 2.0 MPa of ethylene and heated to 250°C, and reacted at 250°C for 12 hours. After the reaction, the reaction liquid was analyzed by gas chromatography to calculate the molar amount of each substance, and the DMF conversion rate and PX selectivity were calculated. The catalyst solid was recovered, dried, and calcined at 550°C to remove carbon deposits before being put into the next cycle. The results are shown in Table 2, and the catalyst has good cyclic performance.

[0102] Table 2

[0103] Cycle times DMF conversion rate (%) PX selectivity (%) 1 96.1 97.6 2 94.2 97.2 3 93.2 96.7 4 93.4 96.4 5 93.0 96.5

[0104] Comparative Example 1

[0105] The molecular sieve raw powder in Example 1 is not P-modified, but the molecular sieve raw powder is calcined to remove the template agent, ammonium ion exchange, and calcined to obtain the hydrogen-type molecular sieve. The specific operation is to calcine the molecular sieve raw powder at 550°C in air to remove the organic structure directing agent, and then in 0.5M NH 4 The catalyst was exchanged with Cl solution for 3 times (1h at 80℃), centrifuged, washed and calcined to obtain H-type molecular sieve. Figure 1Similar to MWW molecular sieve structure. The internal specific surface area measured by BET is 365m 2 / g, external specific surface area is 119m 2 / g. The Si / Al molar ratio was 17.1 as measured by ICP. 3 -TPD measured the total acid content to be 961 μmol / g. Py-FTIR measured the ratio of L acid to B acid to be 0.7. 27 Al-NMR measured that the content of tetracoordinated aluminum was 82%, the content of pentacoordinated Al was 0%, and the content of hexacoordinated Al was 18%.

[0106] 0.5 g of the above catalyst, 3.0 g of DMF and 17 g of n-heptane were added to a magnetically stirred high-pressure reactor, filled with 2.0 MPa of ethylene and heated to 250°C, and reacted at 250°C for 12 hours. After the reaction, the reaction liquid was analyzed by gas chromatography to calculate the molar amount of each substance, and the calculated DMF conversion rate was 98.2% and the PX selectivity was 48.6%.

[0107] Comparative Example 2

[0108] The difference from Example 1 is that 1.0 g of molecular sieve powder is added to 30 mL of phosphorus oxychloride toluene solution (the concentration of phosphorus oxychloride is 0.002 M), and the other steps remain the same. Figure 1 Similar to MWW molecular sieve structure. The internal specific surface area measured by BET is 124m 2 / g, external specific surface area is 115m 2 / g. The Si / Al molar ratio measured by ICP was 17.1, and the P / Al molar ratio was 0.7. 3 -TPD measured the total acid content to be 575 μmol / g. Py-FTIR measured the ratio of L acid to B acid to be 0.8. 27 Al-NMR measured the content of tetracoordinated aluminum to be 70%, pentacoordinated Al to be 24%, and hexacoordinated Al to be 6%.

[0109] 0.5 g of the above catalyst, 3.0 g of DMF and 17 g of n-heptane were added to a magnetically stirred high-pressure reactor, filled with 2.0 MPa of ethylene and heated to 250°C, and reacted at 250°C for 12 hours. After the reaction, the reaction liquid was analyzed by gas chromatography to calculate the molar amount of each substance, and the calculated DMF conversion rate was 96.2%, and the PX selectivity was 61.6%.

[0110] Comparative Example 3

[0111] The Na-type Beta molecular sieve product (product number NKF-6-25NA) of Tianjin Nanhua Catalyst Co., Ltd. was used for P modification according to treatment method II. That is, the product was added to 30 mL of phosphorus oxychloride toluene solution (the concentration of phosphorus oxychloride was 0.01 M) and treated at 110°C for 6 hours. After cooling, it was washed with toluene, dried at 80°C, and calcined in air at 550°C for 4 hours to obtain a P-modified Beta molecular sieve catalyst. The internal specific surface area measured by BET was 358m 2 / g, external specific surface area is 20m 2 / g. ICP measured the Si / Al molar ratio to be 13.2 and the P / Al molar ratio to be 3.4. 3 -TPD measured the total acid content to be 523 μmol / g. Py-FTIR measured the ratio of L acid to B acid to be 0.8. 27 Al-NMR measured that the content of tetracoordinated aluminum was 65, the content of pentacoordinated Al was 6%, and the content of hexacoordinated Al was 29%.

[0112] 0.5 g of the above catalyst, 3.0 g of DMF and 17 g of n-heptane were added to a magnetically stirred high-pressure reactor, filled with 2.0 MPa of ethylene and heated to 250°C, and reacted at 250°C for 12 hours. After the reaction, the reaction liquid was analyzed by gas chromatography to calculate the molar amount of each substance, and the calculated DMF conversion rate was 87.5% and the PX selectivity was 68.3%.

[0113] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A MWW molecular sieve, characterized in that: The molecular sieve has a schematic chemical composition as shown in the formula "mSiO2·nAl2O3·pP2O5", wherein 10≤m / p≤100, 0.2≤n / p≤1.

2. The molecular sieve according to claim 1, wherein In the formula "mSiO2·nAl2O3·pP2O5", 20≤m / n≤35, preferably 25≤m / n≤32; 10≤m / p≤60, 0.4≤n / p≤0.

65.

3. The molecular sieve according to claim 1 or 2, wherein: The proportion of the tetracoordinated aluminum content in the molecular sieve to the total aluminum content is not higher than 15%, preferably not higher than 12%.

4. The molecular sieve according to any one of claims 1 to 3, wherein The crystals of the molecular sieve are two-dimensional layered structures; and / or The internal specific surface area of ​​the molecular sieve is not less than 30m 2 / g, preferably not less than 40m 2 / g; and / or The external specific surface area of ​​the molecular sieve is not less than 30m 2 / g, preferably not less than 50m 2 / g; and / or The Lewis / The ratio is 0.2-5.0, preferably 0.5-3.5; and / or The total acid content of the molecular sieve is 300-1200 μmol / g, preferably 400-800 μmol / g.

5. The method for preparing the molecular sieve according to any one of claims 1 to 4, characterized in that: The method comprises: optionally removing the organic structure directing agent from the MWW molecular sieve precursor, contacting it with a phosphorus source in a first organic solvent, washing it, drying it, and calcining it.

6. The preparation method according to claim 5, wherein: The preparation of the MWW molecular sieve precursor comprises: preparing a crystallization liquid with a silicon source, an aluminum source, sodium hydroxide, an organic structure directing agent a, an organic structure directing agent b and water, and then performing hydrothermal crystallization to obtain the MWW molecular sieve precursor; Preferably The organic structure directing agent a is selected from at least one of N,N,N-trimethylammonium adamantane, hexamethyleneimine, piperidine, homopiperazine, dicyclohexylamine, and N,N-diethylcyclohexylamine, preferably N,N,N-trimethylammonium adamantane; and / or The organic structure directing agent b is cyclohexylamine.

7. The preparation method according to claim 5 or 6, wherein: In the crystallization solution, the molar ratio of the silicon source as SiO2, the aluminum source as Al2O3, sodium hydroxide, the organic structure directing agent a, the organic structure directing agent b and water is 1: 0.028-0.050: 0.07-0.22: 0.001-0.03: 0.051-0.10: 12-50; preferably 1: 0.029-0.048: 0.08-0.21: 0.001-0.028: 0.055-0.095: 14-40.

8. The preparation method according to any one of claims 5 to 7, wherein: The conditions of the hydrothermal crystallization include: crystallization at 130-180° C. for 0.5-2.0 days, preferably crystallization at 140-170° C. for 0.75-2.00 days; and / or The conditions for removing the organic structure directing agent include: The temperature is 500-700°C, preferably 550-650°C; and / or The time is 3-12h, preferably 4-8h; and / or The contact conditions include: The temperature is 40-150°C, preferably 60-100°C; and / or The time is 0.5-12h, preferably 3-6h; and / or The drying conditions include: The temperature is 50-100°C, preferably 80-100°C; and / or The time is 5-24h, preferably 6-12h; and / or The conditions for the calcination include: The temperature is 400-800°C, preferably 500-700°C; and / or The time is 0.5-12h, preferably 3-8h.

9. The preparation method according to any one of claims 5 to 8, wherein: The first organic solvent is selected from at least one of alkanes, aromatic hydrocarbons, and halogenated hydrocarbons; and / or The phosphorus source is selected from at least one of phosphoric acid, dimethyl phosphoric acid, phosphorus oxychloride, and phosphorus pentachloride, preferably at least one of phosphorus oxychloride, phosphorus pentachloride, and dimethyl phosphoric acid.

10. Use of the molecular sieve according to any one of claims 1 to 4 in the preparation of an adsorbent or a catalyst.

11. Use of the molecular sieve according to any one of claims 1 to 4 in the preparation of p-alkyl aromatics from furan raw materials and / or ketone raw materials.

12. A method for preparing p-xylene, characterized in that: The method comprises: contacting and reacting a 2,5-dimethylfuran raw material and / or a 2,5-hexanedione raw material with ethylene in the presence of a catalyst and an optional second organic solvent; Wherein, the catalyst contains the molecular sieve according to any one of claims 1 to 4; Preferably, The second organic solvent is selected from at least one of n-hexane, cyclohexane, n-heptane, n-octane and tetrahydrofuran; and / or The conditions of the contact reaction include: The mass concentration of the 2,5-dimethylfuran raw material and / or the 2,5-hexanedione raw material in the second organic solvent is not less than 5%, preferably not less than 15%; and / or The mass ratio of the 2,5-dimethylfuran raw material and / or the 2,5-hexanedione raw material to the catalyst is (5-50):1, preferably (5-8):1; and / or The reaction temperature is 200-320°C, preferably 235-270°C; and / or The reaction time is 3-24h, preferably 6-12h; and / or The pressure of ethylene is 1-6 MPa, preferably 2-4 MPa.

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