P-modified metal-doped mww molecular sieves, methods of making and using the same

Abstract

This invention relates to the field of molecular sieves, specifically to a P-modified metal-doped MWW molecular sieve, its preparation method, and its applications. In this molecular sieve, A... Pδ‑7 / A P ≥50%, A Pδ‑7 represent 31 The peak area of ​​the P species signal peak at the terminal group with a P chemical shift of -7ppm ± 15ppm in the P MAS NMR spectrum, A P It represents 31 The peak area of ​​the total signal peak in the pMAS NMR spectrum. The molecular sieve of this invention has high activity, selectivity, and stability, and excellent resistance to carbon deposition.

Description

Technical Field

[0001] This invention relates to the field of molecular sieves, specifically to a P-modified metal-doped MWW molecular sieve, its preparation method, and its applications. Background Technology

[0002] Since the beginning of the 21st century, countries around the world have been actively seeking new technologies using biomass, a renewable resource, as raw materials. In the chemical industry, technologies that replace traditional petroleum-based chemicals with bio-based chemicals are flourishing. Paraxylene (PX) is one of the most important bulk chemicals, mainly used for the oxidation of terephthalic acid, which is further polymerized with ethylene glycol to produce polyethylene terephthalate (PET), widely used in the polyester fiber and polyester plastics industries. In 2021, China's PX demand was approximately 35 million tons. Currently, the vast majority of PX comes from petroleum feedstocks, but bio-based PX is beginning to appear in renewable plastic bottles and polyester fibers. One promising route is the production of PX from biomass-derived 2,5-dimethylfuran (DMF) and ethylene.

[0003] DMF and ethylene first undergo a Diels-Alder cycloaddition reaction to generate the cycloaddition intermediate oxadione. Subsequently, the intermediate undergoes a dehydration reaction under acid catalysis to generate PX and water. Since 2,5-hexanedione and DMF can interconvert under acidic conditions, 2,5-hexanedione can also be used as a raw material to prepare PX with ethylene under the catalysis of a solid acid. In the reaction system for generating PX, the side reactions include (1) the side reaction initiated by DMF hydrolysis, that is, DMF hydrolyzes to 2,5-hexanedione and further dehydrates to 3-methyl-2-cyclopenten-1-one; (2) the alkylation side reaction, that is, the cycloaddition intermediate undergoes an alkylation reaction with electron-rich molecules such as ethylene to generate the over-alkylated product of PX; (3) the oligomerization side reaction, the oligomerization reaction of DMF or 2,5-hexanedione itself; and (4) the isomerization of the cycloaddition intermediate. DMF molecules are relatively active, and strong acids easily cause the self-polymerization of DMF molecules and initiate the hydrolysis and condensation side reactions of DMF. Suitable acidity satisfies the main reaction, namely dehydration after DA addition, which allows for high selectivity in obtaining the product. Therefore, the design of catalytic materials should avoid strong acid sites, or modification methods should be used to eliminate strong acid sites on the catalyst. Furthermore, oligomerization side reactions cause severe coking problems, leading to rapid deactivation of the catalytic material due to surface coking. Therefore, a large external specific surface area is required to resist coking. Traditional silica-alumina molecular sieves typically have small external specific surface areas and strong acidity, but SCM-1, being a two-dimensional layered material, has a huge external specific surface area, but its weakness lies in its strong acidity. Although CN113831238A and CN113831308A successfully prepared modified SCM-1 materials Sn-Al-SCM-1 or Zr-Al-SCM-1, strong acid sites still exist. Without solving the problem of eliminating strong acid sites, the catalyst will struggle to achieve high selectivity in catalyzing the production of PX from DMF and ethylene.

[0004] CN103814005A reports the use of homogeneous metal salts as Lewis acid catalysts, which inevitably suffer from the disadvantages of difficulty in catalyst recovery and recycling, failing to meet the requirements of industrial production. CN102482177B reports acid-washed activated carbon, and WO2014 / 043468A1 reports supported metal salt catalysts. Using metal salts or acids as active sites for catalysts, or loading them onto a support, both suffer from the disadvantage of easy loss of active components, leading to a gradual decline in their recycling performance, also failing to meet the requirements of industrial production. CN109569677B reports the use of amorphous phosphate solid acids in the reaction of DMF and ethylene to prepare PX. Although it exhibits a high PX selectivity of 96%, the application prospects of such amorphous catalysts require further investigation.

[0005] In summary, existing technologies mainly suffer from problems such as unsuitable acidity of catalysts, excessively high acid strength of molecular sieve catalysts leading to low product selectivity or easy loss of catalyst active sites and poor stability, which pose challenges to practical industrial applications. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low product selectivity, easy loss of catalyst active sites, and poor stability caused by excessively high acid strength of molecular sieve catalysts in the prior art. This invention provides a P-modified metal-doped MWW molecular sieve, its preparation method, and its application. This molecular sieve has high product selectivity, strong resistance to carbon deposition, and high cycle stability.

[0007] To achieve the above objectives, a first aspect of the present invention provides a P-modified metal-doped MWW molecular sieve, wherein A in the molecular sieve... Pδ-7 / A P ≥50%.

[0008] 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: using H-type MWW molecular sieve as a matrix, optionally removing part or all of Al and optionally grafting non-aluminum metal M, and then modifying it with P.

[0009] The third aspect of the present invention provides the application of the molecular sieve described in the first aspect of the present invention as a catalyst in the preparation of p-xylene from 2,5-dimethylfuran and / or 2,5-hexanedione.

[0010] Through the above technical solution, the present invention has the following advantages:

[0011] The molecular sieve of this invention exhibits high activity, selectivity, and stability, with excellent resistance to carbon deposition. For example, using the molecular sieve of this invention as a catalyst, 2,5-dimethylfuran and / or 2,5-hexanedione can react with ethylene to efficiently and selectively convert to p-xylene (PX). The two-dimensional layered structure of the molecular sieve endows it with good mass transfer performance, facilitating the smooth progress of the reaction, while also possessing strong resistance to carbon deposition. Compared to molecular sieves without P modification, the acid strength is significantly reduced after modification, effectively minimizing the occurrence of strong acid-catalyzed alkylation, isomerization, and various polymerization side reactions. The content of key impurities (such as polyalkylbenzenes, isomerization products of cycloaddition intermediates, and oligomers of 2,5-dimethylfuran) is extremely low, achieving not only high PX selectivity but also greatly reducing the pressure of subsequent PX separation and purification. P modification not only forms new acidic sites with suitable acid strength and provides a small amount of Brønsted acid, but its binding with metals also plays a role in stabilizing the active sites of the catalyst. No significant change in catalyst activity was observed during catalyst recycling. Attached Figure Description

[0012] Figure 1 The XRD pattern of the P-Al-SCM-1 molecular sieve obtained in Example 1;

[0013] Figure 2 The image shows the SEM image of the P-Al-SCM-1 molecular sieve obtained in Example 1.

[0014] Figure 3 The P-Al-SCM-1 molecular sieve obtained in Example 1 31 P MAS NMR spectrum;

[0015] Figure 4 The NH3-TPD diagram of the P-Al-SCM-1 molecular sieve obtained in Example 1 is shown.

[0016] Figure 5 The image shows the Py-FTIR spectrum of the P-Al-SCM-1 molecular sieve obtained in Example 1. Detailed Implementation

[0017] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0018] In this invention, A Pδ-7 represent 31 The peak area of ​​the P species signal peak at the terminal group with a P chemical shift of -7ppm ± 15ppm in the P MAS NMR spectrum, A P It represents 31 The peak area of ​​the total signal peaks in the PMAS NMR spectrum.

[0019] This invention provides a P-modified metal-doped MWW molecular sieve, wherein A in the molecular sieve Pδ-7 / A P ≥50%.

[0020] The PM-MWW molecular sieve of this invention has high activity, selectivity, and stability, and excellent resistance to carbon deposition.

[0021] According to a preferred embodiment of the present invention, A in the molecular sieve Pδ-7 / A P ≥70%. For example, A in molecular sieves. Pδ-7 / A P It can be 70%, 80%, 90%, or 100%. By adopting the aforementioned preferred scheme, the activity, selectivity, stability, and resistance to carbon buildup can be further improved.

[0022] In this invention, the molecular sieve is in 31 The P MAS NMR spectrum also shows a signal peak with a P chemical shift at -26ppm±15ppm, which is the signal peak of P species in pyrophosphate and polyphosphate.

[0023] According to a preferred embodiment of the present invention, the metal in the molecular sieve is selected from at least one metal from Group IVB, Group VB, Group VIB, Group IIIA, and Group IVA, preferably from at least one metal from Al, Sn, Ti, W, Zr, Nb, Ta, and Ga, more preferably from at least one metal from Al, Sn, W, and Nb, and even more preferably from Sn. By adopting the aforementioned preferred embodiment, the activity, selectivity, and stability of the molecular sieve, as well as its resistance to carbon deposition, can be further improved.

[0024] According to a preferred embodiment of the present invention, the MWW molecular sieve is selected from at least one of MCM molecular sieves, ITQ molecular sieves, and SCM molecular sieves, preferably SCM molecular sieves.

[0025] According to a preferred embodiment of the present invention, the SCM-type molecular sieve is selected from SCM-1 molecular sieve and / or SCM-2 molecular sieve, preferably SCM-1.

[0026] According to a preferred embodiment of the present invention, the molecular sieve crystals have a two-dimensional layered structure. By adopting the aforementioned preferred embodiment, the activity, selectivity, stability, and resistance to carbon deposition of the molecular sieve can be further improved.

[0027] Two-dimensional layered structures refer to the thin nanosheet structure of MWW-type molecular sieves. This layered structure provides a large external specific surface area, which is beneficial for mass transfer.

[0028] According to a preferred embodiment of the present invention, the molecular sieve has an internal specific surface area of ​​80-300 m². 2 / g, preferably 100-200m 2 / g. By adopting the aforementioned preferred scheme, the activity, selectivity, stability, and resistance to carbon deposition of molecular sieves can be further improved.

[0029] According to a preferred embodiment of the present invention, the molecular sieve has an external specific surface area of ​​50-200 m². 2 / g, preferably 100-200m 2 / g. By adopting the aforementioned preferred scheme, the activity, selectivity, stability, and resistance to carbon deposition of molecular sieves can be further improved.

[0030] According to a preferred embodiment of the present invention, the Lewis / The ratio is not less than 1. By adopting the aforementioned preferred scheme, the activity, selectivity, stability, and resistance to carbon deposition of molecular sieves can be further improved.

[0031] According to a preferred embodiment of the present invention, the total acid content of the molecular sieve is 400-900 μmol / g, preferably 500-700 μmol / g, wherein the strong acid content is ≤15%, preferably ≤10%. By adopting the aforementioned preferred embodiment, the activity, selectivity, stability, and resistance to carbon deposition of the molecular sieve can be further improved.

[0032] According to a preferred embodiment of the present invention, the Si / metal molar ratio in the molecular sieve is 13-100, preferably 15-50. By adopting the aforementioned preferred embodiment, the activity, selectivity, stability, and resistance to carbon deposition of the molecular sieve can be further improved.

[0033] According to a preferred embodiment of the present invention, the Si / P molar ratio in the molecular sieve is 15-100, preferably 20-50. By adopting the aforementioned preferred embodiment, the activity, selectivity, stability, and resistance to carbon deposition of the molecular sieve can be further improved.

[0034] This invention provides a method for preparing the molecular sieve described herein. The method includes: using an H-type MWW molecular sieve as a matrix, optionally removing some or all of the Al, optionally grafting a non-aluminum metal, and then modifying it with P. The molecular sieve described above can be prepared using this method.

[0035] According to a preferred embodiment of the present invention, the H-MWW molecular sieve is prepared using conventional methods in the art. The structure-directing agent in the MWW molecular sieve (e.g., the SCM-1 molecular sieve synthesized by the preparation method described in CN104511271B) is removed by calcination at 400-700°C for 1-6 hours in air or oxygen. After ion exchange in an ammonium salt solution, calcination is performed. The conditions for ion exchange and calcination can be conventionally selected in the art, for example, ion exchange at 80°C for 1 hour in a 1 mol / L NH4Cl solution, repeated 3 times. Finally, H-MWW is obtained by calcination again at 400-700°C for 1-6 hours in air or oxygen.

[0036] In this invention, there are no particular requirements for the method of removing some or all of the Al. According to a preferred embodiment of the invention, the method of removing some or all of the Al is as follows: first, the H-type MWW molecular sieve is subjected to hydrothermal treatment with steam, and then eluted with an acid solution. By adopting the aforementioned preferred scheme, the activity, selectivity, stability, and resistance to carbon deposition of the prepared molecular sieve can be further improved.

[0037] In this invention, the range of possible acid solutions is relatively wide. According to a preferred embodiment of this invention, the acid solution is selected from at least one of hydrochloric acid solution, oxalic acid solution, nitric acid solution, sulfuric acid solution and phosphoric acid solution, preferably nitric acid solution.

[0038] In this invention, the conditions for the water vapor hydrothermal treatment can be conventionally chosen in the art. According to a preferred embodiment of this invention, the conditions for the water vapor hydrothermal treatment include: conducting the treatment in an inert gas atmosphere, where the inert atmosphere refers to a gas that does not participate in the reaction, such as nitrogen, air, or argon in this invention. The role of the gas is to carry the water vapor through the material.

[0039] According to a preferred embodiment of the present invention, the conditions for the water vapor hydrothermal treatment include: a water vapor partial pressure of 10-100%, that is, the process can be carried out in pure water vapor, that is, in 100% water vapor partial pressure, preferably a water vapor partial pressure of 30-70%.

[0040] According to a preferred embodiment of the present invention, the conditions for the water vapor hydrothermal treatment include: a temperature of 600-900℃, preferably 700-800℃.

[0041] According to a preferred embodiment of the present invention, the conditions for the water vapor hydrothermal treatment include: a time of 1-48 hours, preferably 6-12 hours.

[0042] By employing the aforementioned preferred conditions for steam hydrothermal treatment, the activity, selectivity, stability, and resistance to carbon deposition of the prepared molecular sieve can be further improved.

[0043] In this invention, the elution conditions can be conventionally selected in the art. According to a preferred embodiment of the invention, the elution conditions include: the concentration of the acid solution is 1 mol / L-14 mol / L.

[0044] According to a preferred embodiment of the present invention, the elution conditions include a temperature of 20-120°C, preferably 80-110°C.

[0045] According to a preferred embodiment of the present invention, the elution conditions include a time of 6-48 hours, preferably 12-24 hours.

[0046] According to a preferred embodiment of the present invention, the elution conditions include elution to a Si / Al molar ratio of 25-180, preferably 100-180.

[0047] By adopting the aforementioned optimized elution conditions, the activity, selectivity, stability, and resistance to carbon deposition of molecular sieves can be further improved.

[0048] In this invention, the method for grafting non-aluminum metal M can be a conventional choice in the art. According to a preferred embodiment of the invention, the method for grafting non-aluminum metal M is a solvent reflux method, comprising: placing a molecular sieve with some or all of the Al removed in an organic solution containing a non-aluminum metal M source under reflux, followed by a first solid-liquid separation, a first washing, a first drying, and a first calcination. By adopting the aforementioned preferred scheme, the activity, selectivity, stability, and resistance to carbon deposition of the prepared molecular sieve can be further improved.

[0049] According to a preferred embodiment of the present invention, the non-aluminum metal M source is selected from a compound of at least one metal selected from Sn, Ti, W, Zr, Nb, Ta, and Ga, preferably a compound of Sn and / or W and / or Nb metals, and more preferably at least one selected from tin tetrachloride, dimethyltin dichloride, niobium pentachloride, and tungsten hexachloride.

[0050] According to a preferred embodiment of the present invention, the organic solvent is selected from at least one of alkanes, aromatic hydrocarbons, and halogenated hydrocarbons. For example, it may be dichloromethane or n-hexane.

[0051] According to a preferred embodiment of the present invention, the Si / M molar ratio in the grafted molecular sieve is 13-100, preferably 15-50.

[0052] According to a preferred embodiment of the present invention, the conditions for the first roasting include: a temperature of 400-700°C, preferably 500-600°C.

[0053] According to a preferred embodiment of the present invention, the conditions for the first roasting include: a time of 3-12 hours, preferably 4-8 hours.

[0054] By employing the aforementioned preferred method of grafting non-aluminum metal M, the activity, selectivity, stability, and resistance to carbon deposition of molecular sieves can be further improved.

[0055] In this invention, there are no special requirements for the conditions of the first solid-liquid separation, the first washing, and the first drying; as long as the purpose of this invention can be achieved.

[0056] In this invention, the method of P modification can be a conventional choice in the art. According to a preferred embodiment of the invention, the method of P modification is as follows: placing the molecular sieve grafted with non-aluminum metal M in an organic solution containing phosphorus source under reflux, followed by a second solid-liquid separation, a second washing, and a second calcination. By adopting the aforementioned preferred scheme, the activity, selectivity, stability, and resistance to carbon deposition of the prepared molecular sieve can be further improved.

[0057] According to a preferred embodiment of the present invention, the phosphorus source is selected from at least one of dimethylphosphoric acid, phosphorus oxychloride and phosphorus pentachloride.

[0058] In this invention, as long as the purpose of this invention can be achieved, there are no special requirements on the amount of phosphorus source added. According to a preferred embodiment of this invention, the amount of phosphorus source added is 1 / 20-1 of the molar amount of silicon in the molecular sieve.

[0059] According to a preferred embodiment of the present invention, the organic solvent is selected from at least one of alkanes, aromatic hydrocarbons, and halogenated hydrocarbons.

[0060] According to a preferred embodiment of the present invention, the Si / P molar ratio in the P-modified molecular sieve is 15-100, preferably 20-50.

[0061] According to a preferred embodiment of the present invention, the conditions for the second calcination include a temperature of 400-700°C, preferably 500-600°C.

[0062] According to a preferred embodiment of the present invention, the conditions for the second roasting include: a time of 3-12 hours, preferably 4-8 hours.

[0063] By employing the aforementioned preferred method of grafting non-aluminum metal M, the activity, selectivity, stability, and resistance to carbon deposition of molecular sieves can be further improved.

[0064] In this invention, there are no special requirements for the reflux time, which can be, for example, 0.5-12 hours.

[0065] In this invention, there are no special requirements for the conditions of the second solid-liquid separation and the second washing, as long as the purpose of this invention can be achieved.

[0066] In this invention, the microstructure (two-dimensional layered structure, thickness), pore structure, and acidity of the H-type MWW molecular sieve can all affect the product prepared by this invention. According to a preferred embodiment of this invention, the H-type MWW molecular sieve is selected from at least one of H-type MCM molecular sieves, ITQ molecular sieves, and SCM molecular sieves; preferably, it is an H-type SCM molecular sieve; more preferably, it is an H-type SCM-1 molecular sieve and / or an H-type SCM-2 molecular sieve, and even more preferably, it is an H-type SCM-1 molecular sieve. By adopting the aforementioned preferred scheme, the activity, selectivity, and stability of the molecular sieve, as well as its resistance to carbon deposition, can be further improved.

[0067] This invention provides an application of the molecular sieve described herein as a catalyst in the preparation of p-xylene using 2,5-dimethylfuran and / or 2,5-hexanedione as raw materials.

[0068] Reaction formula:

[0069]

[0070] In this invention, the components of the reaction solution were qualitatively analyzed using an Agilent 7890A gas chromatography-mass spectrometry (GC-MS) system from Agilent Technologies, USA, with a Wax polar capillary column. For quantification, an Agilent 7890B gas chromatograph (GC) from Agilent Technologies, USA, equipped with a flame ionization detector (FID) and a Wax polar capillary column, was used. The conversion rate and selectivity of the substances were calculated based on the molar amounts of the substances measured by gas chromatography.

[0071] In this invention, the formula for calculating the raw material conversion rate is:

[0072] Conversion rate of raw materials % = (molar amount of raw materials initially added - molar amount of raw materials remaining) / (molar amount of raw materials initially added) × 100%.

[0073] In this invention, the formula for calculating product selectivity is:

[0074] Product selectivity % = (molar amount of product generated in the reaction) / (molar amount of initial added raw material - molar amount of remaining raw material) × 100%.

[0075] In this invention, the XRD patterns were obtained using a Bruker D8 Advance X-ray diffractometer from Germany, employing a CuKα ray source.

[0076] In this invention, the elemental composition of the molecular sieve was determined by an Agilent 725-ES inductively coupled plasma atomic emission spectrometer (ICP). The molecular sieve sample was digested with hydrofluoric acid, and the elemental content was expressed in moles.

[0077] Scanning electron microscope (SEM) images were obtained using an S-4800II field emission scanning electron microscope.

[0078] solid 31 P-magic-angle rotational nuclear magnetic resonance (P-magic-angle rotational nuclear magnetic resonance) 31 The PMAS NMR spectrum was obtained using a Varian 400MHz NMR instrument, with H3PO4 used as the PMAS NMR spectra. 31 Reference for P chemical shift.

[0079] In this invention, the NH3 temperature-programmed desorption (NH3-TPD) experiment was conducted on a TPD / TPR Altamira AMI-3300 instrument, and the total acid content was calculated by fitting and peaking the obtained spectrum.

[0080] In this invention, the acid type of the catalyst is determined using pyridine adsorption-FTIR (py-FTIR). The py-FTIR spectrum is obtained on a Nicolet Model 710 spectrometer. The specific steps are as follows: a) Sample preparation and pretreatment: Approximately 15 mg of sample is compressed into a thin disc with a diameter of 13 mm and placed in the infrared sample cell; then, the sample is pretreated at 400℃ under vacuum conditions for 2 hours. The background spectrum is obtained by scanning the sample at 100℃, 200℃, and 400℃. b) After the sample cell cools to room temperature, pyridine is adsorbed for 10 minutes. Vacuum desorption is performed at 100℃ for 10 minutes, and the infrared absorption spectrum is scanned and recorded. The infrared absorption spectra are then scanned and recorded sequentially at 200℃ and 400℃. The difference spectrum before and after pyridine adsorption is the obtained Py-FTIR spectrum. (1450 cm⁻¹) -1 The absorption peak for L-acid is at 1540 cm⁻¹. -1 The peak at 1450 cm⁻¹ represents the absorption peak of Brønsted acid. Pyridine, which remained undesorbed at 400℃, also showed a peak at 1450 cm⁻¹. -1 and 1540cm -1 The ratio of the total absorption peak area at 100℃ to the total absorption peak area of ​​pyridine at 100℃ is the strong acid ratio.

[0081] The present invention will be described in detail below through embodiments.

[0082] Example 1

[0083] SCM-1 molecular sieve raw powder was synthesized according to the preparation method described in patent CN 104511271B. The structure directing agent was removed by calcination, and then ion exchange and calcination were performed to obtain H-SCM-1. The silicon-to-aluminum ratio (atomic ratio) of the molecular sieve was measured to be 15.2 by ICP.

[0084] The steps for preparing P-modified P-Al-SCM-1 molecular sieves from H-SCM-1 are as follows:

[0085] (1) Select the above-mentioned H-SCM-1 molecular sieve for high-temperature water vapor hydrothermal treatment, and treat it for 10h at 700℃ nitrogen atmosphere and 60% water vapor partial pressure;

[0086] (2) Preparation of P-Al-SCM-1: The hydrothermally treated molecular sieve was refluxed in dichloromethane solution and treated with dimethylphosphoric acid for 1 h. The amount of P source added was 1 / 10 of the molar amount of silicon in the molecular sieve. After centrifugation and washing with dichloromethane, a solid product was obtained and calcined at 550 °C for 4 h to obtain P-Al-SCM-1. The Si / Al ratio was measured to be 15.2 and the Si / P ratio was 21.2 by ICP. The XRD pattern is shown below. Figure 1 As shown, the MWW topology remains well preserved, and SEM ( Figure 2 The data shows that it has a two-dimensional layered structure, and the internal specific surface area measured by BET is 93 m². 2 / g, with an external specific surface area of ​​136m² 2 / g. For example... Figure 3 As shown, the catalyst 31 A of the PMAS NMR spectrum Pδ-7 / A P It is 77%. The NH3-TPD spectrum is as follows: Figure 4 As shown, the calculated total acidity is 684 μmol / g. The low NH3 adsorption at temperatures above 300℃ indicates a limited number of strong acid sites. (Pyridine infrared spectrum) Figure 5 The results show that the overall L / B ratio is 1.9 at 100℃. The pyridine molecules that remain undesorbed at 400℃ are adsorbed at strong acid sites, and the calculated proportion of strong acid is 9%.

[0087] Example 2

[0088] Unlike Example 1, the H-SCM-1 molecular sieve was treated at 600°C in a nitrogen atmosphere with a partial pressure of 50% water vapor for 48 hours, while other steps remained the same to obtain the P-Al-SCM-1 molecular sieve. ICP measurements showed a Si / Al ratio of 15.2 and a Si / P ratio of 20.5. BET measurements showed an internal specific surface area of ​​105 m². 2 / g, with an external specific surface area of ​​127m² 2 / g. Catalyst A Pδ-7 / A P The total acid content was 72%. NH3-TPD calculations yielded a total acid content of 674 μmol / g. The pyridine infrared spectrum showed an L / B ratio of 2.4, indicating a strong acid content of 12%.

[0089] Example 3

[0090] Unlike Example 1, the sample was refluxed in hexane and treated with phosphorus oxychloride for 8 hours. The amount of P source added was 1 / 10 of the molar amount of silicon in the molecular sieve. After centrifugation and washing with hexane, a solid product was obtained and calcined at 550°C for 4 hours, with other steps remaining the same, to obtain P-Al-SCM-1 molecular sieve. ICP measurements showed a Si / Al ratio of 15.2 and a Si / P ratio of 18.7. BET measurements showed an internal specific surface area of ​​84 m². 2 / g, with an external specific surface area of ​​10⁸ m² 2 / g. Catalyst A Pδ-7 / A P The total acid content was 79%. NH3-TPD calculations yielded a total acid content of 754 μmol / g. The pyridine infrared spectrum showed an L / B ratio of 1.8, indicating a strong acid content of 7%.

[0091] Example 4

[0092] SCM-1 molecular sieve raw powder was synthesized according to the preparation method described in patent CN 104511271B. The structure directing agent was removed by calcination, and then ion exchange and calcination were performed to obtain H-SCM-1. The silicon-to-aluminum ratio (atomic ratio) of the molecular sieve was measured to be 15.2 by ICP.

[0093] P-modified P-Sn-SCM-1 was prepared from H-SCM-1. Al could be removed to varying degrees to obtain P-Sn-SCM-1 molecular sieves.

[0094] The steps are as follows:

[0095] (1) H-SCM-1 molecular sieve was subjected to high-temperature water vapor hydrothermal treatment at 900℃ in nitrogen atmosphere and 10% water vapor partial pressure for 10h.

[0096] (2) Al was partially eluted with acid solution. Concentrated nitric acid 14M was used to elute at 120℃ for 48h, and the final Si / Al ratio was measured to be 142.

[0097] (3) Sn-SCM-1 was obtained by solvent reflux method. The SCM-1 molecular sieve after Al removal was placed in anhydrous SnCl4 CH2Cl2 solution for reflux, then washed with CH2Cl2, dried and calcined at 550℃ for 4h to obtain Sn-SCM-1.

[0098] (4) The Sn-SCM-1 molecular sieve was refluxed in dichloromethane solution and treated with dimethylphosphoric acid for 1 h, with the amount of P source added being 1 / 10 of the molar amount of silicon in the molecular sieve. After centrifugation and washing with dichloromethane, a solid product was obtained, which was then calcined at 550 °C for 4 h to obtain P-Al-SCM-1. ICP analysis showed a Si / Sn ratio of 35.3 and a Si / P ratio of 21.6. BET analysis showed an internal specific surface area of ​​10¹ m². 2 / g, with an external specific surface area of ​​116m² 2 / g. Catalyst A Pδ-7 / A P The percentage was 85%. NH3-TPD calculations yielded a total acid content of 641 μmol / g. The pyridine infrared spectrum showed an L / B ratio of 2.8, indicating a strong acid content of 6%.

[0099] Example 5

[0100] Unlike Example 4, Al was partially eluted with an acid solution using 1M nitric acid at 80°C for 12 hours, resulting in a final Si / Al ratio of 25.5. Other steps remained the same to obtain P-Sn-SCM-1. ICP analysis showed a Si / Sn ratio of 47.1 and a Si / P ratio of 28.9. BET analysis determined the internal specific surface area to be 124 m². 2 / g, with an external specific surface area of ​​178m² 2 / g. Catalyst A Pδ-7 / A P The percentage is 70%. NH3-TPD calculations yielded a total acid content of 852 μmol / g. The pyridine infrared spectrum showed an L / B ratio of 2.2, indicating a strong acid content of 11%.

[0101] Example 6

[0102] Unlike Example 4, dimethyltin dichloride was used for reflux in the preparation of Sn-SCM-1, while other steps remained the same to obtain P-Sn-SCM-1. ICP measurements showed a Si / Sn ratio of 42.6 and a Si / P ratio of 35.6. BET measurements showed an internal specific surface area of ​​135 m². 2 / g, with an external specific surface area of ​​168m² 2 / g. Catalyst A Pδ-7 / A P The total acid content was 75%. NH3-TPD calculations yielded a total acid content of 679 μmol / g. The pyridine infrared spectrum showed an L / B ratio of 3.1, indicating a strong acid content of 9%.

[0103] Example 7

[0104] Unlike Example 4, Ti-SCM-1 was prepared using TiCl4 reflux, while other steps remained the same to obtain P-Ti-SCM-1. ICP measurements showed a Si / Ti ratio of 27.8 and a Si / P ratio of 23.6. BET measurements showed an internal specific surface area of ​​145 m². 2 / g, with an external specific surface area of ​​179m² 2 / g. Catalyst A Pδ-7 / A P The total acid content was 76%. NH3-TPD calculations yielded a total acid content of 705 μmol / g. The pyridine infrared spectrum showed an L / B ratio of 1.9, indicating a strong acid content of 8%.

[0105] Example 8

[0106] Unlike Example 4, Nb-SCM-1 was prepared using NbCl5 reflux, while other steps remained the same to obtain P-Nb-SCM-1. ICP measurements showed a Si / Nb ratio of 29.0 and a Si / P ratio of 25.8. BET measurements showed an internal specific surface area of ​​94 m². 2 / g, with an external specific surface area of ​​141m² 2 / g. Catalyst A Pδ-7 / A P The total acid content was 74%. NH3-TPD calculations yielded a total acid content of 478 μmol / g. The pyridine infrared spectrum showed an L / B ratio of 2.1, indicating a strong acid content of 11%.

[0107] Example 9

[0108] Unlike Example 4, WCl6 was used for reflux in the preparation of W-SCM-1, while other steps remained the same to obtain PW-SCM-1. ICP measurements showed a Si / W ratio of 22.5 and a Si / P ratio of 20.6. BET measurements showed an internal specific surface area of ​​85 m². 2 / g, with an external specific surface area of ​​128m² 2 / g. Catalyst A Pδ-7 / A P The total acid content was 78%. NH3-TPD calculations yielded a total acid content of 490 μmol / g. The pyridine infrared spectrum showed an L / B ratio of 3.3, indicating a strong acid content of 9%.

[0109] Example 10

[0110] The molecular sieve catalysts from Examples 1-9 were used in the reaction of DMF and ethylene to prepare PX under the following conditions: the reaction solvent was n-heptane, the mass concentration of DMF in the solvent was 15%; the mass ratio of DMF to catalyst was 6:1; the reaction temperature was 250℃; and the reaction time was 12 h. 0.5 g of the catalyst from Examples 1-9, 3.0 g of DMF, and 17 g of n-heptane were added to a magnetically stirred high-pressure reactor, and ethylene was introduced at 2.0 MPa. The reaction was carried out at 250℃ for 12 h. The DMF conversion and PX selectivity of the reaction solution were calculated by gas phase analysis, as shown in Table 1.

[0111] Table 1

[0112] Catalyst number DMF conversion rate (%) PX selectivity (%) Example 1 98.1 97.4 Example 2 98.3 96.9 Example 3 97.0 97.7 Example 4 97.1 98.0 Example 5 96.9 95.4 Example 6 98.1 97.7 Example 7 93.5 94.9 Example 8 97.6 92.8 Example 9 96.7 94.1

[0113] Example 11

[0114] Using the P-Al-SCM-1 molecular sieve from Example 1 as a catalyst, 0.5 g of catalyst, 3.0 g of 2,5-hexanedione (HDO), and 17 g of n-heptane were added to a magnetically stirred high-pressure reactor, and ethylene was introduced at 2.0 MPa. The reaction was carried out at 250 °C for 12 h to obtain a reaction solution. The HDO conversion rate was calculated to be 97.5% and the PX selectivity was 96.5% by gas phase analysis.

[0115] Experiments have shown that HDO is also an effective raw material in the preparation of PX.

[0116] Example 12

[0117] Using the P-Al-SCM-1 molecular sieve from Example 1 as a catalyst, 2.0 g of catalyst and 15.0 g of DMF were added to a magnetically stirred high-pressure reactor, and 6.0 MPa of ethylene was introduced. The reaction was carried out at 250 °C for 12 h to obtain a reaction solution. The reaction solution was analyzed by gas phase analysis and the DMF conversion rate was calculated to be 48.2%, and the PX selectivity was 92.3%.

[0118] Experiments revealed that higher PX selectivity can be achieved in the preparation of PX in the presence of organic solvents. However, the absence of organic solvents allows for higher reaction solution and product concentrations, resulting in higher yield per unit reactor volume.

[0119] Example 13

[0120] Using the P-Al-SCM-1 molecular sieve from Example 1 as a catalyst, 1.0 g of catalyst, 3.0 g of HDO, and 17 g of n-hexane were added to a magnetically stirred high-pressure reactor, and ethylene was introduced at 3.0 MPa. The reaction was carried out at 250 °C for 24 h to obtain a reaction solution. The HDO conversion rate was calculated to be 98.2% and the PX selectivity was 96.7% by gas phase analysis.

[0121] Example 14

[0122] Using the P-Al-SCM-1 molecular sieve from Example 1 as a catalyst, 0.5 g of catalyst, 3.0 g of DMF and 17.0 g of tetrahydrofuran were added to a magnetically stirred high-pressure reactor, and 4.0 MPa of ethylene was introduced. The reaction was carried out at 300 °C for 3 h to obtain a reaction solution. The reaction solution was analyzed by gas phase analysis and the DMF conversion rate was calculated to be 95.2% and the PX selectivity was 97.0%.

[0123] Experiments in Examples 13 and 14 showed that commonly used organic solvents are suitable for this reaction. As demonstrated in Example 22, increasing the reaction temperature to 300°C shortens the reaction time; however, this places higher demands on the reactor's high-temperature resistance.

[0124] Example 15

[0125] Using the P-Al-SCM-1 molecular sieve from Example 1 as a catalyst, 0.5 g of catalyst, 3.0 g of HDO, and 17 g of tetrahydrofuran were added to a magnetically stirred high-pressure reactor, and 1.0 MPa of ethylene was introduced. The reaction was carried out at 270 °C for 24 h to obtain a reaction solution. The HDO conversion rate was calculated to be 98.1% and the PX selectivity was 96.1% by gas phase analysis.

[0126] Example 16

[0127] Using the P-Al-SCM-1 molecular sieve from Example 1 as a catalyst, 0.5 g of catalyst, 3.0 g of DMF and 17 g of tetrahydrofuran were added to a magnetically stirred high-pressure reactor, and ethylene at 3.0 MPa was introduced. The reaction was carried out at 235 °C for 24 h to obtain a reaction solution. The reaction solution was analyzed by gas phase analysis and the DMF conversion rate was calculated to be 94.3% and the PX selectivity was 96.7%.

[0128] Example 17

[0129] The cyclic activity of the P-Al-SCM-1 molecular sieve catalyst in Example 1 above for the preparation of PX from DMF and ethylene was tested under the following conditions: the reaction solvent was n-heptane, the mass concentration of DMF in the solvent was 15%; the mass ratio of DMF to catalyst was 6:1; the reaction temperature was 250℃; and the reaction time was 12 h. 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, and ethylene was introduced at 2.0 MPa. The reaction was carried out at 250℃ for 12 h. The DMF conversion and PX selectivity of the reaction solution were calculated by gas phase analysis. After the reaction, the used catalyst was obtained by centrifugation, calcined to remove carbon deposits, and then fed into the next cycle. Its performance is shown in Table 2. It can be seen that the DMF conversion and PX selectivity remained essentially unchanged, indicating that the catalyst exhibits excellent cyclic stability.

[0130] Table 2

[0131] Loop count DMF conversion rate (%) PX selectivity (%) 1 98.1 97.4 2 98.0 97.6 3 98.3 97.0 4 97.5 97.3 5 98.0 97.3

[0132] Example 18

[0133] Unlike Example 1, in step (2), the P modification was performed using an equal-volume impregnation method. The amount of P source added was 1 / 10 of the molar amount of silicon in the molecular sieve. The mixture was impregnated with a dichloromethane solution of dimethylphosphoric acid, dried, and calcined at 550°C for 4 hours to obtain P-Al-SCM-1. ICP measurements showed a Si / Al ratio of 15.2 and a Si / P ratio of 10.0. BET measurements showed an internal specific surface area of ​​81 m². 2 / g, with an external specific surface area of ​​102m² 2 / g. The catalyst 31 A of the PMAS NMR spectrum Pδ-7 / A P The total acid content was 43%. NH3-TPD calculations yielded a total acid content of 863 μmol / g. The pyridine infrared spectrum showed an L / B ratio of 1.1, indicating a strong acid content of 8%. 0.5 g of this catalyst, 3.0 g of DMF, and 17 g of n-heptane were added to a magnetically stirred high-pressure reactor, which was then charged with ethylene at 2.0 MPa. The reaction was carried out at 250 °C for 12 h. Gas phase analysis of the reaction solution showed a DMF conversion of 90.2% and a PX selectivity of 76%.

[0134] Comparative Example 1

[0135] Unlike Example 1, P-Al-Beta was obtained using Beta molecular sieves from Tianjin Nanhua Catalyst Co., Ltd. The steps for preparing P-modified P-Al-Beta molecular sieves from its H-Beta were exactly the same as in Example 1.

[0136] ICP measurements showed a Si / Al ratio of 18.8 and a Si / P ratio of 24.3. BET measurements showed an internal specific surface area of ​​271 m². 2 / g, with an external specific surface area of ​​19m² 2 / g. The catalyst 31 A of the PMAS NMR spectrum Pδ-7 / A P The total acid content was 31%. NH3-TPD calculations yielded a total acid content of 598 μmol / g. The pyridine infrared spectrum showed an L / B ratio of 1.4, indicating a strong acid content of 19%. 0.5 g of this catalyst, 3.0 g of DMF, and 17 g of n-heptane were added to a magnetically stirred high-pressure reactor, which was then charged with ethylene at 2.0 MPa. The reaction was carried out at 250 °C for 12 h. Gas phase analysis of the reaction solution showed a DMF conversion of 77.1% and a PX selectivity of 68.2%.

[0137] The results of the examples show that the molecular sieve prepared by the method of the present invention has a rich external specific surface area and suitable acidity, especially exhibiting excellent catalytic properties in reacting 2,5-dimethylfuran and / or 2,5-hexanedione with ethylene to produce p-xylene. It demonstrates significantly better performance compared to the catalysts in the comparative examples.

[0138] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A P-modified metal-doped MWW molecular sieve, characterized in that, A in this molecular sieve Pδ-7 / A P ≥50%, A Pδ-7 represent 31 The peak area of ​​the P species signal peak at the terminal group with a P chemical shift of -7ppm ± 15ppm in the P MAS NMR spectrum, A P It represents 31 The peak area of ​​the total signal peak in the PMAS NMR spectrum, the total acidity of the molecular sieve is 400-900 µmol / g, of which the strong acid content is ≤15%.

2. The molecular sieve according to claim 1, wherein, A in the molecular sieve Pδ-7 / A P ≥70%; and / or The metal in the molecular sieve is selected from at least one metal from Group IVB, Group VB, Group VIB, Group IIIA, and Group IVA; and / or The MWW molecular sieve is selected from at least one of MCM molecular sieves, ITQ molecular sieves, and SCM molecular sieves.

3. The molecular sieve according to claim 2, wherein, The metal in the molecular sieve is selected from at least one of Al, Sn, Ti, W, Zr, Nb, Ta, and Ga; and / or The MWW molecular sieve is an SCM type molecular sieve.

4. The molecular sieve according to claim 3, wherein, The metal in the molecular sieve is at least one selected from Al, Sn, W, and Nb; and / or The SCM-type molecular sieve is selected from SCM-1 molecular sieve and / or SCM-2 molecular sieve.

5. The molecular sieve according to claim 4, wherein, The SCM-type molecular sieve is SCM-1.

6. The molecular sieve according to claim 1, wherein, The molecular sieve crystals have a two-dimensional layered structure; and / or The molecular sieve has an internal specific surface area of ​​80-300 m². 2 / g; and / or The molecular sieve has an external specific surface area of ​​50-200 m². 2 / g; and / or The Lewis / Brønsted ratio of the molecular sieve is not less than 1; and / or The total acid content of the molecular sieve is 400-900 µmol / g, of which the content of strong acid is ≤10%.

7. The molecular sieve according to claim 6, wherein, The molecular sieve has an internal specific surface area of ​​100-200 m². 2 / g; and / or The molecular sieve has an external specific surface area of ​​100-200 m². 2 / g.

8. The molecular sieve according to claim 1, wherein, The molecular sieve has a Si / metal molar ratio of 13-100; and / or The Si / P molar ratio in the molecular sieve is 15-100.

9. The molecular sieve according to claim 8, wherein, The molecular sieve has a Si / metal molar ratio of 15-50; and / or The Si / P molar ratio in the molecular sieve is 20-50.

10. A method for preparing the molecular sieve according to any one of claims 1-9, characterized in that, Using H-type MWW molecular sieve as the parent material, after removing some or all of the Al and grafting non-aluminum metals, P modification is performed.

11. The preparation method according to claim 10, wherein, The method for removing part or all of Al is as follows: first, the H-type MWW molecular sieve is subjected to hydrothermal treatment with steam, and then eluted with an acid solution.

12. The preparation method according to claim 11, wherein, The acid solution is selected from at least one of hydrochloric acid solution, oxalic acid solution, nitric acid solution, sulfuric acid solution, and phosphoric acid solution; and / or The conditions for the steam hydrothermal treatment include: The partial pressure of water vapor is 10-100%; and / or Temperatures of 600-900℃; and / or The time is 1-48 hours; and / or The elution conditions include: The concentration of the acid solution is 1 mol / L-14 mol / L; and / or Temperature is 20-120℃; and / or The time is 6-48 hours; and / or Elution was performed until the Si / Al molar ratio was 25-180.

13. The preparation method according to claim 12, wherein, The acid solution is a nitric acid solution; and / or The conditions for the steam hydrothermal treatment include: The partial pressure of water vapor is 30-70%; and / or Temperature is 700-800℃; and / or The time is 6-12 hours; and / or The elution conditions include: The temperature is 80-110℃; and / or The time is 12-24 hours; and / or Elute until the Si / Al molar ratio is 100-180.

14. The preparation method according to claim 10, wherein, The method for grafting non-aluminum metal M is a solvent reflux method, which includes: placing a molecular sieve with some or all of the Al removed into an organic solution containing a non-aluminum metal M source for reflux, followed by a first solid-liquid separation, a first washing, a first drying, and a first calcination.

15. The preparation method according to claim 14, wherein, The non-aluminum metal M source is selected from a compound of at least one metal selected from Sn, Ti, W, Zr, Nb, Ta, and Ga; and / or The organic solvent is selected from at least one of alkanes, aromatic hydrocarbons, and halogenated hydrocarbons; and / or The Si / M molar ratio in the grafted molecular sieve is 13-100; and / or The conditions for the first roasting include: The temperature is 400-700℃; and / or The time is 3-12 hours.

16. The preparation method according to claim 15, wherein, The Si / M molar ratio in the grafted molecular sieve is 15-50; and / or The conditions for the first roasting include: The temperature is 500-600℃; and / or The time is 4-8 hours.

17. The preparation method according to claim 10, wherein, The method of P modification is as follows: the molecular sieve grafted with non-aluminum metal M is placed in an organic solution containing phosphorus source and refluxed, followed by a second solid-liquid separation, a second washing, and a second calcination.

18. The preparation method according to claim 17, wherein, The phosphorus source is selected from at least one of dimethylphosphoric acid, phosphorus oxychloride and phosphorus pentachloride; and / or The organic solvent is selected from at least one of alkanes, aromatic hydrocarbons, and halogenated hydrocarbons; and / or The Si / P molar ratio in the P-modified molecular sieve is 15-100. and / or The conditions for the second roasting include: The temperature is 400-700℃; and / or The time is 3-12 hours.

19. The preparation method according to claim 18, wherein, The Si / P molar ratio in the P-modified molecular sieve is 20-50; and / or The conditions for the second roasting include: The temperature is 500-600℃; and / or The time is 4-8 hours.

20. The preparation method according to claim 10, wherein, The H-type MWW molecular sieve is selected from at least one of H-type MCM molecular sieves, ITQ molecular sieves, and SCM molecular sieves.

21. The preparation method according to claim 20, wherein, The H-type MWW molecular sieve is an H-type SCM molecular sieve.

22. The preparation method according to claim 21, wherein, The H-type MWW molecular sieve is either H-type SCM-1 molecular sieve or H-type SCM-2 molecular sieve.

23. The preparation method according to claim 22, wherein, The H-type MWW molecular sieve is H-type SCM-1.

24. The molecular sieve according to any one of claims 1-9 as a catalyst in the catalytic preparation of p-xylene from 2,5-dimethylfuran and / or 2,5-hexanedione.

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