P-modified MWW molecular sieve, and preparation method therefor and use thereof

Abstract

The present invention relates to the field of molecular sieves, and particularly relates to a P-modified MWW molecular sieve, and a preparation method therefor and the use thereof. The molecular sieve shows APδ-7 / AP≥40%, and preferably ≥50%, wherein APδ-7 represents a peak area of a P-species signal peak, which has a chemical shift within the range of -22 ppm to 8 ppm in a 31P MAS NMR spectrogram, and AP represents the total peak area of all signal peaks in the 31P MAS NMR spectrogram. A catalyst which contains the molecular sieve of the present invention has high levels of activity, selectivity and stability, and has an excellent carbon deposition resistance capability.

Description

P-modified MWW molecular sieve and its preparation method and application Technical Field

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

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

[0003] DMF and ethylene first undergo a Diels-Alder cycloaddition reaction to form a cycloaddition intermediate, oxa-norbornene, which then undergoes a dehydration reaction under acid catalysis to produce PX and water. Since 2,5-hexanedione and DMF can be converted into each other under acidic conditions, 2,5-hexanedione can also be used as a raw material to react with ethylene under the catalysis of solid acid to prepare PX. In the reaction system where DMF and ethylene react to produce PX, side reactions include (1) DMF hydrolysis to 2,5-hexanedione and further dehydration to 3-methyl-2-cyclopentene-1-one; (2) alkylation side reaction, i.e., the cycloaddition intermediate undergoes an alkylation reaction with an electron-rich molecule such as ethylene to produce an over-alkylated product of PX; (3) oligomerization side reaction, i.e., the oligomerization reaction of DMF or 2,5-hexanedione itself; and (4) isomerization of the cycloaddition intermediate. DMF molecules are relatively active, and strong acids can easily cause self-polymerization of DMF molecules and trigger DMF hydrolysis and condensation side reactions. Appropriate acidity satisfies the primary reaction, DA addition, and subsequent dehydration, resulting in highly selective yield of the target product, PX. Therefore, strong acid sites should be avoided in catalytic material design or eliminated through modification. Furthermore, oligomerization side reactions can cause severe carbon deposition, which rapidly deactivates catalytic materials. Therefore, catalysts must possess a large external surface area to resist carbon deposition.

[0004] Traditional silica-alumina molecular sieves typically have a small external surface area and are highly acidic. However, SCM-1 is a two-dimensional layered material with a large external surface area, but its disadvantage is 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, and the problem of eliminating strong acid sites has not been solved. Such catalysts will not be able to catalyze the reaction of DMF and ethylene to produce PX with high selectivity.

[0005] CN103814005A discloses a method for producing paraxylene, toluene, and other compounds from renewable resources and ethylene using a homogeneous metal salt as a Lewis acid catalyst. CN102482177B discloses the production of PX from DMF and ethylene using acid-washed activated carbon as a catalyst. WO2014 / 043468A1 discloses the production of PX from DMF and ethylene using a supported or unsupported metal salt catalyst. CN109569677B discloses the use of a phosphate-based solid acid catalyst in the reaction of DMF and ethylene to produce PX.

[0006] Other documents related to background technology include CN107626341A, CN115385771A, CN102233274A, US20140194276A1 and CN109678172A.

[0007] However, there is still a need for a solid catalyst suitable for catalyzing the reaction of DMF and ethylene to produce PX, which exhibits desirable properties such as high activity, selectivity and stability and good resistance to carbon deposition.

[0008] SUMMARY OF THE INVENTION

[0009] To overcome the existing problems of low product selectivity and poor stability caused by the high acid strength of molecular sieve catalysts in bio-based PX synthesis, the present inventors conducted diligent research. As a result, they discovered a novel P-modified MWW molecular sieve that is particularly suitable for catalyzing the reaction of 2,5-dimethylfuran and / or 2,5-hexanedione with ethylene to produce p-xylene. This molecular sieve catalyst exhibits high product selectivity, strong resistance to carbon deposition, and high cyclic stability. This led to the completion of the present invention.

[0010] The first aspect of the present invention provides a P-modified MWW molecular sieve, wherein A Pδ-7 / A P ≥40%, preferably ≥50%.

[0011] The second aspect of the present invention provides a method for preparing the molecular sieve, which comprises: using H-type MWW molecular sieve as a matrix, optionally removing part or all of the Al and then optionally grafting a non-aluminum metal M, followed by P modification.

[0012] The third aspect of the present invention provides use of a catalyst comprising the P-modified MWW molecular sieve in the preparation of p-xylene using 2,5-dimethylfuran and / or 2,5-hexanedione as raw materials.

[0013] A fourth aspect of the present invention provides a bio-based paraxylene synthesis method, comprising reacting 2,5-dimethylfuran and / or 2,5-hexanedione with ethylene in the presence of a catalyst comprising the P-modified MWW molecular sieve to provide an effluent comprising paraxylene; and separating the paraxylene.

[0014] The catalyst comprising the molecular sieve of the present invention shows high activity, selectivity and stability, and has excellent resistance to carbon deposition. For example, by adopting the catalyst of the present invention, 2,5-dimethylfuran and / or 2,5-hexanedione can be efficiently and selectively converted into para-xylene (PX) with ethylene reaction. It is believed that the two-dimensional layered structure of the molecular sieve gives the catalyst comprising the molecular sieve good mass transfer performance, which is conducive to the smooth progress of the reaction and has strong resistance to carbon deposition. Compared with the molecular sieve without P modification, the acid strength of the molecular sieve modified by P of the present invention is greatly reduced, and its suitable acid strength effectively reduces the occurrence of strong acid-catalyzed alkylation, isomerization and various polymerization side reactions, so that the content of key impurities (such as polyalkylbenzenes, isomerization products of cycloaddition intermediates, oligomers of 2,5-dimethylfuran) is extremely low, which not only achieves high PX selectivity, but also greatly reduces the pressure of subsequent separation and purification of PX. P modification not only forms new acidic sites with suitable acid strength and provides a small amount of B acid, but the combination of P species and metal also plays a role in stabilizing the active sites of the catalyst (no significant change in activity is observed after the catalyst is recycled).

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG1 is an XRD pattern of the P-Al-SCM-1 molecular sieve obtained in Example 1;

[0017] FIG2 is a SEM image of the P-Al-SCM-1 molecular sieve obtained in Example 1;

[0018] Figure 3 shows the P-Al-SCM-1 molecular sieve obtained in Example 1. 31 P MAS NMR spectra;

[0019] FIG4 is an NH3-TPD diagram of the P-Al-SCM-1 molecular sieve obtained in Example 1;

[0020] FIG5 is a Py-FTIR graph of the P-Al-SCM-1 molecular sieve obtained in Example 1;

[0021] Figure 6 shows the P-Al-Beta molecular sieve obtained in Comparative Example 1. 31 P MAS NMR spectrum.

[0022] DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The endpoints of the ranges and any values ​​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 endpoints of each range, the endpoints of each range and 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 to be specifically disclosed herein.

[0024] In the first aspect, the present invention provides a P-modified MWW molecular sieve, which exhibits A Pδ-7 / A P ≥40%, preferably ≥50%, of which A Pδ-7 represent 31 The peak area of ​​the P signal peak with a chemical shift ranging from -22 ppm to 8 ppm in the P MAS NMR spectrum, A P represent 31 The total peak area of ​​all signal peaks in the P MAS NMR spectrum is as follows: It is believed that the signal peaks in the range of -22 ppm to 8 ppm can be attributed to P species that are connected to a single or two metal atoms but not to another P, namely (MO)PO(OH)2 and (MO)2-PO(OH).

[0025] In some preferred embodiments, the molecular sieve exhibits A Pδ-7 / A P ≥70%. For example, molecular sieve A Pδ-7 / A P It can be 70%, 80%, 90% or 100%.

[0026] The molecular sieve of the present invention is 31 There are also signal peaks with chemical shifts ranging from -41 ppm to -11 ppm in the P MAS NMR spectrum, which are the P species signal peaks of pyrophosphate and polyphosphate.

[0027] In some preferred embodiments, the molecular sieve comprises at least one doping metal selected from the group consisting of Group IVB, Group VB, Group VIB, Group IIIA, and Group IVA metals, preferably Al, Sn, Ti, W, Zr, Nb, Ta, and Ga, further preferably Al, Sn, W, and Nb, and more preferably Sn.

[0028] In some preferred embodiments, the MWW molecular sieve is selected from at least one of MCM molecular sieves (such as MCM-22 in CN 106517232 B, the disclosure of which is incorporated herein by reference), ITQ molecular sieves (such as ITQ-2 in WO1997017290A1, the disclosure of which is incorporated herein by reference), and SCM molecular sieves (such as SCM-1 in CN104511271B, the disclosure of which is incorporated herein by reference), preferably SCM molecular sieves.

[0029] In some preferred embodiments, the SCM-type molecular sieve is SCM-1 molecular sieve and / or SCM-2 molecular sieve, preferably SCM-1.

[0030] In some preferred embodiments, the molecular sieve crystals have a two-dimensional layered structure. The two-dimensional layered structure refers to the thin nanosheet structure of the MWW molecular sieve. This layered structure provides a large external specific surface area, which is beneficial for mass transfer.

[0031] In some preferred embodiments, the internal specific surface area of ​​the molecular sieve is 80-300m 2 / g, preferably 100-200m 2 / g.

[0032] In some preferred embodiments, the external specific surface area of ​​the molecular sieve is 50-200 m 2 / g, preferably 100-200m 2 / g.

[0033] In some preferred embodiments, the Lewis acid / The molar ratio of the acid is not less than 1.

[0034] In some preferred embodiments, 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 mol%, preferably ≤10 mol%, based on the total acid content.

[0035] In some preferred embodiments, the Si / metal molar ratio in the molecular sieve is 13-100, preferably 15-50.

[0036] In some preferred embodiments, the Si / P molar ratio in the molecular sieve is 15-100, preferably 20-50.

[0037] In a second aspect, the present invention provides a method for preparing the molecular sieve of the present invention, which comprises: using H-type MWW molecular sieve as a matrix, optionally removing part or all of the Al and then optionally grafting a non-aluminum metal, and then performing P modification.

[0038] In some preferred embodiments, the H-MWW molecular sieve is prepared by conventional methods in the art, including calcination to remove the structure directing agent in the MWW molecular sieve (e.g., the SCM-1 molecular sieve synthesized by the preparation method described in CN104511271B), for example, calcination at 400-700°C in air or oxygen for 1-6 hours; then ion exchange in an ammonium salt solution and calcination again, wherein the ion exchange and re-calcination conditions can be conventionally selected in the art, for example, exchange in a 1 mol / L NH4Cl solution at 80°C for 1 hour, repeated 3 times, and then calcined again in air or oxygen at 400-700°C for 1-6 hours to obtain H-MWW.

[0039] In the present invention, there is no particular limitation on the method for removing part or all of the Al. In some preferred embodiments, the method for removing part or all of the Al comprises: first subjecting the H-type MWW molecular sieve to a steam hydrothermal treatment, and then eluting with an acid solution.

[0040] In the present invention, the acid solution can be selected from a wide range. Preferably, the acid solution is at least one selected from hydrochloric acid solution, oxalic acid solution, nitric acid solution, sulfuric acid solution and phosphoric acid solution, preferably nitric acid solution.

[0041] In the present invention, the conditions for the steam hydrothermal treatment may be conventionally selected in the art. Preferably, the steam hydrothermal treatment is performed in an inert atmosphere. The inert atmosphere refers to a gas that does not participate in the reaction, and in the present invention, for example, may be nitrogen, air, argon, etc. The function of the gas is to carry the water vapor through the material.

[0042] In some preferred embodiments, the conditions for the water vapor hydrothermal treatment include: a water vapor concentration in the gas phase of 10-100 mol %, preferably a water vapor concentration of 30-70 mol %.

[0043] In some preferred embodiments, the conditions of the steam hydrothermal treatment include: a temperature of 600-900°C, preferably 700-800°C.

[0044] In some preferred embodiments, the conditions of the water vapor hydrothermal treatment include: a time of 1-48 hours, preferably 6-12 hours.

[0045] In the present invention, the conditions for the acid solution elution can be conventionally selected in the art. Preferably, the conditions for the acid solution elution include: the concentration of the acid solution is 1 mol / L-14 mol / L.

[0046] In some preferred embodiments, the elution conditions include: a temperature of 20-120°C, preferably 80-110°C.

[0047] In some preferred embodiments, the elution conditions include: a time of 6-48 hours, preferably 12-24 hours.

[0048] In some preferred embodiments, the elution conditions include: eluting to a Si / Al molar ratio of 25-180, preferably 100-180.

[0049] In the present invention, the method for grafting the non-aluminum metal M can be a conventional choice in the art. In some preferred embodiments, the method for grafting the non-aluminum metal M is a solvent reflux method, comprising: placing the molecular sieve from which some or all of the Al has been removed in 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.

[0050] In some preferred embodiments, 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, and more preferably at least one selected from tin tetrachloride, dimethyltin dichloride, niobium pentachloride, and tungsten hexachloride.

[0051] In some preferred embodiments, the organic solvent is at least one selected from alkanes, aromatic hydrocarbons, and halogenated hydrocarbons, for example, dichloromethane or n-hexane.

[0052] In some preferred embodiments, the Si / M molar ratio in the grafted molecular sieve is 13-100, preferably 15-50.

[0053] In some preferred embodiments, the conditions for the first calcination include: a temperature of 400-700°C, preferably 500-600°C.

[0054] In some preferred embodiments, the conditions for the first calcination include: a time of 3-12 hours, preferably 4-8 hours.

[0055] In the present 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 the present invention can be achieved.

[0056] In the present invention, the P modification method can be a conventional method in the art, such as an impregnation method. Alternatively, in some preferred embodiments, the P modification method comprises: placing the MWW molecular sieve, from which some or all of the Al has been optionally removed and then optionally grafted with a non-aluminum metal M, under reflux in an organic solution containing a phosphorus source, followed by a second solid-liquid separation, a second washing, and a second calcination.

[0057] In some preferred embodiments, the phosphorus source is at least one selected from dimethylphosphonic acid, phosphorus oxychloride, methylphosphonic acid, trimethylphosphine oxide, trimethylphosphine and phosphorus pentachloride.

[0058] In the present invention, as long as the purpose of the present invention can be achieved, there is no particular requirement for the amount of the phosphorus source added. In some preferred embodiments, the amount of the phosphorus source added is 0.05 mol to 1 mol, preferably 0.06 to 0.50 mol, more preferably 0.07 to 0.30 mol, relative to 1 mol of silicon in the molecular sieve.

[0059] In some preferred embodiments, the organic solvent of the organic solution is at least one selected from alkanes, aromatic hydrocarbons, and halogenated hydrocarbons. Examples of the organic solvent are dichloromethane and n-hexane.

[0060] In the present invention, there is no particular requirement for the reflux time of P modification. The reflux time can be, for example, 0.5-12 hours.

[0061] In some preferred embodiments, the Si / P molar ratio in the P-modified molecular sieve is 15-100, preferably 20-50.

[0062] In some preferred embodiments, the conditions for the second calcination include: a temperature of 400-700°C, preferably 500-600°C.

[0063] In some preferred embodiments, the second calcination conditions include: a time of 3-12 hours, preferably 4-8 hours.

[0064] In the present invention, there is no particular requirement for the conditions of the second solid-liquid separation and the second washing, as long as the purpose of the present invention can be achieved.

[0065] Without being bound by a particular theory, it is believed that the microstructure (two-dimensional layered structure, thickness), pore structure and acidity of the MWW molecular sieve make it particularly suitable for modification using the P modification method of the present invention to provide a molecular sieve catalyst particularly suitable for bio-based PX synthesis.

[0066] In some preferred embodiments, the H-type MWW molecular sieve used in the present invention is at least one selected from H-type MCM molecular sieve, H-type ITQ molecular sieve, and H-type SCM molecular sieve; preferably, H-type SCM molecular sieve; further preferably, H-type SCM-1 molecular sieve and / or H-type SCM-2 molecular sieve, and more preferably H-type SCM-1.

[0067] In a third aspect, the present invention provides a use of a catalyst comprising the molecular sieve of the present invention in the preparation of p-xylene using 2,5-dimethylfuran and / or 2,5-hexanedione as raw materials.

[0068] Reaction formula:

[0069] In a fourth aspect, the present invention provides a bio-based paraxylene synthesis method, comprising reacting 2,5-dimethylfuran and / or 2,5-hexanedione with ethylene in the presence of a catalyst comprising the P-modified MWW molecular sieve of the present invention to provide an effluent comprising paraxylene; and separating the paraxylene.

[0070] The P-modified MWW molecular sieve of the present invention can be compounded into a catalyst suitable for use in an industrial process according to techniques known in the art. For example, the molecular sieve of the present invention can be mixed with an appropriate amount of a binder, molded, and then dried and calcined to obtain the catalyst. The binder can be at least one of aluminum oxide, silicon oxide, titanium oxide, and their precursors. The binder can account for 10-60% of the molecular sieve's mass, for example, 10-40%. To aid molding, molding aids such as cellulose and water can also be introduced.

[0071] The drying and calcination during catalyst preparation can be performed in conventional manners. Preferably, the drying conditions include: a drying temperature of 90-160°C for 6-15 hours; and the calcination conditions include: performing the calcination in an oxygen-containing atmosphere, such as air, at a temperature of 300-550°C for 2-5 hours.

[0072] The procedures and reaction conditions for reacting 2,5-dimethylfuran and / or 2,5-hexanedione with ethylene in the presence of a molecular sieve catalyst to provide an effluent comprising p-xylene, and the procedures and conditions for separating p-xylene from the reaction effluent are known in the art.

[0073] In this disclosure, including the following examples, the following analytical and testing methods were employed: Qualitative analysis of reaction solution components was performed using an Agilent 7890A gas chromatograph-mass spectrometer (GC-MS) with a Wax polar capillary column. Quantitative analysis was performed using an Agilent 7890B gas chromatograph (GC) equipped with a flame ion detector (FID) and a Wax polar capillary column. Standards were used to construct calibration curves, and the molar amounts of sample components were determined. The conversion rate and selectivity were calculated based on the measured molar amounts.

[0074] The formula for calculating the raw material conversion rate is: Raw material conversion rate % = (initially added raw material molar amount - remaining raw material molar amount) / (initially added raw material molar amount) × 100%.

[0075] The product selectivity is calculated as follows: Product selectivity % = (molar amount of product generated by the reaction) / (molar amount of the raw material initially added - molar amount of the remaining raw material) × 100%.

[0076] Here, the term "raw material" refers to 2,5-dimethylfuran and / or 2,5-hexanedione.

[0077] The XRD spectra were obtained on a Bruker D8Advance X-ray diffractometer from Germany using a CuKα radiation source.

[0078] The composition of the molecular sieves was measured by an Agilent 725-ES inductively coupled plasma atomic emission spectrometer (ICP). The molecular sieve samples were digested with hydrofluoric acid, and the element contents were measured in moles.

[0079] Scanning electron microscopy (SEM) images were obtained on a S-4800II field emission scanning electron microscope.

[0080] solid 31 P magic angle spinning nuclear magnetic resonance ( 31 P MAS NMR) spectra were obtained on a Varian 400 MHz NMR instrument, and H3PO4 was used as 31 P chemical shift reference.

[0081] NH3 temperature-programmed desorption (NH3-TPD) experiments were carried out on a TPD / TPR Altamira AMI-3300 instrument, and the total acid content was calculated from the obtained spectra.

[0082] The pyridine adsorption infrared (py-FTIR) method was used to determine the type of catalyst acid, and the py-FTIR spectrum was obtained on a Nicolet Model 710 spectrometer. The specific operation steps are as follows: a. Sample preparation and pretreatment: about 15 mg of sample was pressed into a thin disc with a diameter of 13 mm and placed in an infrared sample tank; then the sample was pretreated at 400°C in a vacuum cell for 2 hours. The sample was scanned at 100°C, 200°C, and 400°C to obtain a background spectrum. b. After the sample tank was cooled to room temperature, pyridine was adsorbed for 10 minutes. Vacuum desorption was carried out at 100°C for 10 minutes, and the infrared absorption spectrum was scanned and recorded. The infrared absorption spectrum was scanned and recorded at 200°C and 400°C in sequence. The difference spectrum before and after pyridine adsorption is the obtained Py-FTIR spectrum. 1450cm -1 The absorption peak of L acid is at 1540 cm -1 The absorption peak of pyridine at 400℃ is 1450cm -1 and 1540cm -1 The ratio of the total absorption peak area of ​​L acid to the total absorption peak area of ​​pyridine at 100°C is the strong acid ratio, and the ratio of the absorption peak area of ​​L acid to the absorption peak area of ​​B acid is recorded as the L / B ratio.

[0083] The specific surface area and external specific surface area of ​​the molecular sieve were measured using nitrogen physical adsorption and desorption. Adsorption and desorption curves were obtained on a Micromeretic ASAP2020M physical adsorption instrument. The total specific surface area was calculated using the BET equation, and the external specific surface area was calculated using the t-plot equation. The difference between the two was the internal specific surface area. Prior to testing, the samples were pretreated at 350°C in vacuum for 6 hours. Example

[0084] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited thereto.

[0085] Example 1

[0086] SCM-1 molecular sieve powder was synthesized according to the preparation method described in patent CN 104511271B, calcined to remove the structure-directing agent, and then ion exchanged and calcined to obtain H-SCM-1. ICP analysis revealed a silicon-to-aluminum atomic ratio of 15.2.

[0087] The steps for preparing P-modified P-Al-SCM-1 molecular sieve from H-SCM-1 are as follows:

[0088] (1) High-temperature steam hydrothermal treatment of H-SCM-1 molecular sieve: treatment at 700°C in a nitrogen atmosphere and 60% water vapor partial pressure for 10 h;

[0089] (2) Preparation of P-Al-SCM-1: The hydrothermally treated molecular sieve was directly refluxed in a dichloromethane solution containing a P source, i.e., a dimethylphosphonic acid solution was added and treated for 1 hour. The amount of P source added was 1 / 10 of the molar amount of molecular sieve silicon, and the content of molecular sieve in the solution was 1g molecular sieve / 50mL solution. Centrifugation and washing with dichloromethane gave a solid product, which was calcined at 550°C for 4 hours to obtain P-Al-SCM-1. ICP measured the Si / Al ratio to be 15.2 and the Si / P ratio to be 21.2. The XRD spectrum is shown in Figure 1, and the MWW topological structure is still well maintained. SEM (Figure 2) shows that it is a two-dimensional layered structure, and BET measured the internal specific surface area to be 93m 2 / g, external specific surface area is 136m 2 / g. As shown in Figure 3, the catalyst 31 A of P MAS NMR spectrum Pδ-7 / A P The NH3-TPD spectrum is shown in Figure 4, and the calculated total acid content is 684 μmol / g. The low NH3 adsorption above 300°C indicates a low concentration of strong acid sites. The pyridine infrared spectrum (Figure 5) shows an overall L / B ratio of 1.9 at 100°C. The pyridine molecules that remain undesorbed at 400°C are adsorbed on strong acid sites, resulting in a calculated strong acid content of 9%.

[0090] Example 2

[0091] The P-Al-SCM-1 molecular sieve was prepared according to the procedure described in Example 1, except that the H-SCM-1 molecular sieve was treated at 600°C in a nitrogen atmosphere at a 50% water vapor partial pressure for 48 hours. The Si / Al ratio was 15.2 and the Si / P ratio was 20.5 by ICP. The internal specific surface area was 105 m 2 / g, external specific surface area is 127m 2 / g. The 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 infrared spectrum of pyridine showed an L / B ratio of 2.4, indicating a calculated strong acid content of 12%.

[0092] Example 3

[0093] P-Al-SCM-1 molecular sieve was prepared according to the procedure described in Example 1, except that it was refluxed in n-hexane and treated with phosphorus oxychloride for 8 h. ICP measured the Si / Al ratio to be 15.2 and the Si / P ratio to be 18.7. BET measured the internal specific surface area to be 84 m 2 / g, external specific surface area is 108m 2 / g. The catalyst A Pδ-7 / A P The total acid content was 79%. NH3-TPD analysis yielded a total acid content of 754 μmol / g. The infrared spectrum of pyridine revealed an L / B ratio of 1.8, indicating a calculated strong acid content of 7%.

[0094] Example 4

[0095] SCM-1 molecular sieve raw powder was synthesized according to the preparation method described in patent CN 104511271B, and the structure directing agent was removed by calcination. 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 by ICP to be 15.2.

[0096] The P-modified molecular sieve P-Sn-SCM-1 is prepared from H-SCM-1 by the following steps:

[0097] (1) High-temperature steam hydrothermal treatment of H-SCM-1 molecular sieve: treatment at 900°C in a nitrogen atmosphere and 10% water vapor partial pressure for 10 h.

[0098] (2) Partial elution of Al with acid solution: 14 M concentrated nitric acid was used for elution at 120 °C for 48 h. The amount of molecular sieve in the acid solution was 1 g molecular sieve / 30 mL acid solution. The final Si / Al ratio was measured to be 142.

[0099] (3) Preparation of Sn-SCM-1 by solvent reflux method: The Al-removed SCM-1 molecular sieve was placed in a solution of anhydrous SnCl₄ in CH₂Cl₂ at a concentration of 1 g of molecular sieve per 50 mL of solution. The product was then washed with CH₂Cl₂, dried, and calcined at 550°C for 4 h to obtain Sn-SCM-1.

[0100] (4) Treat Sn-SCM-1 molecular sieve with dimethylphosphonic acid under reflux in dichloromethane solution for 1 hour, wherein the amount of dimethylphosphonic acid added is 1 / 10 of the molar amount of molecular sieve silicon. Centrifuge and wash with dichloromethane to obtain a solid product, which is calcined at 550°C for 4 hours to obtain P-Al-SCM-1. ICP measured the Si / Sn ratio to be 35.3 and the Si / P ratio to be 21.6. BET measured the internal specific surface area to be 101m 2 / g, external specific surface area is 116m 2 / g. The catalyst A Pδ-7 / A P The total acid content was calculated to be 85%. NH3-TPD analysis yielded a total acid content of 641 μmol / g. The infrared spectrum of pyridine showed an L / B ratio of 2.8, indicating a calculated strong acid content of 6%.

[0101] Example 5

[0102] P-Sn-SCM-1 was prepared according to the procedure described in Example 4, except that 1 M nitric acid was used at 80°C for 12 h to partially elute the Al. The final Si / Al ratio was 25.5. ICP measured the Si / Sn ratio to be 47.1 and the Si / P ratio to be 28.9. The internal surface area was 124 m 2 / g, external specific surface area is 178m 2 / g. The catalyst A Pδ-7 / A P The total acid content was calculated to be 70%. NH3-TPD analysis yielded a total acid content of 852 μmol / g. The infrared spectrum of pyridine showed an L / B ratio of 2.2, indicating a calculated strong acid content of 11%.

[0103] Example 6

[0104] P-Sn-SCM-1 was prepared according to the procedure described in Example 4, except that dimethyltin dichloride was used for reflux during the preparation of Sn-SCM-1. The Si / Sn ratio was 42.6 and the Si / P ratio was 35.6 by ICP. The internal surface area was 135 m 2 / g, external specific surface area is 168m 2 / g. The catalyst A Pδ-7 / A PThe total acid content was calculated to be 75%. NH3-TPD analysis yielded a total acid content of 679 μmol / g. The infrared spectrum of pyridine showed an L / B ratio of 3.1, indicating a calculated strong acid content of 9%.

[0105] Example 7

[0106] P-Ti-SCM-1 was prepared according to the procedure described in Example 4, except that a reflux solution of TiCl4 in dichloromethane was used to prepare the Ti-SCM-1 intermediate. The Si / Ti ratio was 27.8 and the Si / P ratio was 23.6 by ICP. The internal surface area was 145 m 2 / g, external specific surface area is 179m 2 / g. The 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 infrared spectrum of pyridine showed an L / B ratio of 1.9, indicating a calculated strong acid content of 8%.

[0107] Example 8

[0108] P-Nb-SCM-1 was prepared according to the procedure described in Example 4, except that a reflux solution of NbCl5 in dichloromethane was used to prepare the Nb-SCM-1 intermediate. The Si / Nb ratio was 29.0 and the Si / P ratio was 25.8 by ICP. The internal surface area was 94 m 2 / g, external specific surface area is 141m 2 / g. The 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 infrared spectrum of pyridine showed an L / B ratio of 2.1, indicating a calculated strong acid content of 11%.

[0109] Example 9

[0110] PW-SCM-1 was prepared according to the procedure described in Example 4, except that a solution of WCl6 in dichloromethane was refluxed to prepare the W-SCM-1 intermediate. The Si / W ratio was 22.5 and the Si / P ratio was 20.6 as determined by ICP. The internal surface area was 85 m 2 / g, external specific surface area is 128m 2 / g. The 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 infrared spectrum of pyridine showed an L / B ratio of 3.3, indicating a calculated strong acid content of 9%.

[0111] Example 10

[0112] The molecular sieve catalysts from Examples 1-9 were used in the reaction to produce PX from DMF and ethylene. The reaction conditions were as follows: n-heptane as the reaction solvent, a 15% DMF concentration in the solvent, a 6:1 DMF to catalyst mass ratio, a temperature of 250°C, and a reaction time of 12 hours. 0.5 g of the catalyst from Examples 1-9, 3.0 g DMF, and 17 g n-heptane were added to a magnetically stirred autoclave, which was then charged with 2.0 MPa of ethylene. The reaction was carried out at 250°C for 12 hours. The DMF conversion and PX selectivity were calculated by gas phase analysis of the reaction solution, as shown in Table 1.

[0113] Table 1

[0114] Example 11

[0115] Using the P-Al-SCM-1 molecular sieve in Example 1 as a catalyst, 0.5 g of the 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 2.0 MPa of ethylene was added. The reaction was carried out at 250° C. for 12 h to obtain a reaction liquid. The reaction liquid was analyzed by gas phase analysis to obtain an HDO conversion rate of 97.5% and a PX selectivity of 96.5%.

[0116] This example demonstrates that HDO is also an effective raw material in the preparation of PX.

[0117] Example 12

[0118] Using the P-Al-SCM-1 molecular sieve in Example 1 as a catalyst, 2.0 g of the catalyst and 15.0 g of DMF were added to a magnetically stirred autoclave, and 6.0 MPa of ethylene was added. The reaction was carried out at 250° C. for 12 h to obtain a reaction liquid. The reaction liquid was analyzed by gas phase analysis to obtain a DMF conversion of 48.2% and a PX selectivity of 92.3%.

[0119] This example demonstrates that, in the preparation of PX, converting the raw materials in the presence of an organic solvent can achieve higher PX selectivity. However, in the absence of an organic solvent, higher reaction solution and product concentrations can be achieved, resulting in higher yields per unit reactor volume.

[0120] Example 13

[0121] Using the P-Al-SCM-1 molecular sieve in Example 1 as a catalyst, 1.0 g of the catalyst, 3.0 g of HDO, and 17 g of n-hexane were added to a magnetically stirred autoclave, and 3.0 MPa of ethylene was introduced. The reaction was carried out at 250° C. for 24 h to obtain a reaction liquid. Gas phase analysis of the reaction liquid showed that the HDO conversion was 98.2%, and the PX selectivity was 96.7%.

[0122] Example 14

[0123] Using the P-Al-SCM-1 molecular sieve in Example 1 as a catalyst, 0.5 g of the catalyst, 3.0 g of DMF and 17.0 g of tetrahydrofuran were added to a magnetically stirred autoclave, and 4.0 MPa of ethylene was added. 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 to obtain a DMF conversion of 95.2% and a PX selectivity of 97.0%.

[0124] The experimental results of Examples 13 and 14 confirm that commonly used organic solvents are suitable for this reaction. As shown by increasing the reaction temperature to 300°C in Example 14, increasing the reaction temperature can shorten the reaction time, but the disadvantage is that it places higher requirements on the high temperature resistance of the reactor.

[0125] Example 15

[0126] Using the P-Al-SCM-1 molecular sieve in Example 1 as a catalyst, 0.5 g of the catalyst, 3.0 g of HDO, and 17 g of tetrahydrofuran were added to a magnetically stirred autoclave, and 1.0 MPa of ethylene was introduced. The reaction was carried out at 270° C. for 24 h to obtain a reaction solution. Gas phase analysis of the reaction solution showed that the HDO conversion was 98.1% and the PX selectivity was 96.1%.

[0127] Example 16

[0128] Using the P-Al-SCM-1 molecular sieve in Example 1 as a catalyst, 0.5 g of the catalyst, 3.0 g of DMF and 17 g of tetrahydrofuran were added to a magnetically stirred autoclave, and 3.0 MPa of ethylene was added. 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 to obtain a DMF conversion rate of 94.3% and a PX selectivity of 96.7%.

[0129] Example 17

[0130] The cyclic reaction activity of the P-Al-SCM-1 molecular sieve catalyst described in Example 1 was tested for the preparation of PX from DMF and ethylene. The reaction conditions were as follows: n-heptane as the reaction solvent, a 15% DMF concentration in the solvent, a 6:1 DMF to catalyst mass ratio, a temperature of 250°C, and a reaction time of 12 hours. 0.5 g of the catalyst, 3.0 g of DMF, and 17 g of n-heptane were added to a magnetically stirred autoclave, and ethylene was introduced at 2.0 MPa. The reaction was carried out at 250°C for 12 hours. The DMF conversion and PX selectivity were calculated by gas analysis. After the reaction, the spent catalyst was centrifuged, calcined to remove carbon deposits, and then reused in the next cycle. The performance is shown in Table 2. The DMF conversion and PX selectivity remained essentially unchanged over at least five cycles, demonstrating the catalyst's excellent cyclic stability.

[0131] Table 2

[0132] Example 18

[0133] The difference from Example 1 is that the P modification in step (2) adopts the equal volume impregnation method, the amount of P source added is 1 / 10 of the molar amount of molecular sieve silicon, the dimethylphosphoric acid dichloromethane solution is impregnated, dried, and calcined at 550°C for 4h to obtain P-Al-SCM-1. The Si / Al ratio measured by ICP is 15.2, and the Si / P ratio is 10.0. The internal specific surface area measured by BET is 81m 2 / g, external specific surface area is 102m 2 / g. The catalyst 31 A of P MAS NMR spectrum Pδ-7 / A P The total acid content was 43%. NH3-TPD analysis revealed a total acid content of 863 μmol / g. The infrared spectrum of pyridine revealed an L / B ratio of 1.1, indicating a calculated strong acid content of 8%. 0.5 g of the catalyst, 3.0 g of DMF, and 17 g of n-heptane were added to a magnetically stirred autoclave and charged with 2.0 MPa of ethylene. The reaction was carried out at 250°C for 12 h. Gas chromatography analysis of the reaction solution revealed a DMF conversion of 90.2% and a PX selectivity of 76%.

[0134] Comparative Example 1

[0135] The difference from Example 1 is that P-Al-Beta was obtained by using Beta molecular sieve from Tianjin Nanhua Catalyst Co., Ltd. The steps for preparing P-modified P-Al-Beta molecular sieve from H-Beta were exactly the same as those in Example 1.

[0136] The Si / Al ratio measured by ICP was 18.8, and the Si / P ratio was 24.3. The internal specific surface area measured by BET was 271 m 2 / g, external specific surface area is 19m 2 / g. The catalyst 31 The P MAS NMR spectrum is shown in Figure 6, where A Pδ-7 / A P The total acid content was 31%. NH3-TPD analysis revealed a total acid content of 598 μmol / g. The infrared spectrum of pyridine revealed an L / B ratio of 1.4, indicating a calculated strong acid content of 19%. 0.5 g of the catalyst, 3.0 g of DMF, and 17 g of n-heptane were added to a magnetically stirred autoclave and charged with 2.0 MPa of ethylene. The reaction was carried out at 250°C for 12 hours. Gas chromatography analysis of the reaction solution revealed a DMF conversion of 77.1% and a PX selectivity of 68.2%.

[0137] The results of the examples demonstrate that the molecular sieve prepared using the method of the present invention possesses a substantial external specific surface area and suitable acidity, particularly excellent performance in catalyzing the reaction of 2,5-dimethylfuran and / or 2,5-hexanedione with ethylene to produce p-xylene. This performance is significantly superior to that of the catalyst used in the comparative example.

[0138] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A P-modified MWW molecular sieve, It is characterized in that The molecular sieve showed A Pδ-7 / A P ≥40%, preferably ≥50%, A Pδ-7 represent 31 The peak area of ​​the signal peak with a chemical shift in the range of -22 ppm to 8 ppm in the P MAS NMR spectrum, A P represent 31 P is the total peak area of ​​all signal peaks in the MAS NMR spectrum.

2. The molecular sieve according to claim 1, in, The molecular sieve A Pδ-7 / A P ≥ 70%; and / or The molecular sieve comprises at least one doping metal selected from the group consisting of Group IVB, Group VB, Group VIB, Group IIIA, Group IVA metals, preferably Al, Sn, Ti, W, Zr, Nb, Ta, Ga, more preferably Al, Sn, W and Nb; and / or The MWW molecular sieve is at least one selected from MCM molecular sieves, ITQ molecular sieves, and SCM molecular sieves, preferably SCM molecular sieves, and further preferably, the SCM molecular sieve is selected from SCM-1 molecular sieves and / or SCM-2 molecular sieves, more preferably SCM-1.

3. The molecular sieve according to claim 1 or 2, in, The crystals of the molecular sieve are two-dimensional layered structures; and / or The internal specific surface area of ​​the molecular sieve is 80-300m 2 / g, preferably 100-200m 2 / g; and / or The external specific surface area of ​​the molecular sieve is 50-200m 2 / g, preferably 100-200m 2 / g; and / or Lewis acid of the molecular sieve / The molar ratio of the acid is not less than 1; and / or 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%, based on the total acid content.

4. The molecular sieve according to any one of claims 1 to 3, in, The Si / metal molar ratio in the molecular sieve is 13-100, preferably 15-50; and / or The Si / P molar ratio in the molecular sieve is 15-100, preferably 20-50.

5. A method for preparing the molecular sieve according to any one of claims 1 to 4, It is characterized in that The method comprises: performing P modification on an H-type MWW molecular sieve as a matrix, wherein before the P modification, part or all of Al is optionally removed and then a non-aluminum metal is optionally grafted.

6. The preparation method according to claim 5, in, The method for removing part or all of Al is: first subjecting the H-type MWW molecular sieve to a steam hydrothermal treatment, and then subjecting it to an acid solution elution; preferably, 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; and / or The conditions of the steam hydrothermal treatment include: The water vapor concentration in the gas phase is 10-100 mol %, preferably 30-70 mol %; and / or The temperature is 600-900°C, preferably 700-800°C; and / or The time is 1-48h, preferably 6-12h; and / or The elution conditions include: The concentration of the acid solution is 1 mol / L-14 mol / L; and / or The temperature is 20-120°C, preferably 80-110°C; and / or The time is 6-48h, preferably 12-24h; and / or The elution is performed to a Si / Al molar ratio of 25-180, preferably 100-180.

7. The preparation method according to claim 5 or 6, in, The method for grafting non-aluminum metal M is a solvent reflux method, comprising: placing the molecular sieve from which some or all of Al has been removed in an organic solution containing a non-aluminum metal M source for reflux, and then performing a first solid-liquid separation, a first washing, a first drying, and a first calcination; preferably, The non-aluminum metal M source is 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, preferably 15-50; and / or The first calcination conditions include: The temperature is 400-700°C, preferably 500-600°C; and / or The time is 3-12h, preferably 4-8h.

8. The preparation method according to any one of claims 5 to 7, in, The P modification method is: placing the molecular sieve from which some or all of Al is optionally removed and a non-aluminum metal M is optionally grafted, in an organic solution containing a phosphorus source for reflux, followed by a second solid-liquid separation, a second washing, and a second calcination; preferably, The phosphorus source is selected from at least one of dimethylphosphonic acid, phosphorus oxychloride, methylphosphonic acid, trimethylphosphine oxide, trimethylphosphine 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, preferably 20-50; and / or The second calcination conditions include: The temperature is 400-700°C, preferably 500-600°C; and / or The time is 3-12h, preferably 4-8h.

9. The preparation method according to any one of claims 5 to 8, in, The H-type MWW molecular sieve is at least one of H-type MCM molecular sieves, ITQ molecular sieves, and SCM molecular sieves; preferably, H-type SCM molecular sieves; further preferably, H-type SCM-1 molecular sieves and / or H-type SCM-2 molecular sieves, and more preferably, H-type SCM-1.

10. A method for synthesizing bio-based p-xylene, comprising reacting 2,5-dimethylfuran and / or 2,5-hexanedione with ethylene in the presence of a catalyst comprising the P-modified MWW molecular sieve described in any one of claims 1 to 4 to provide an effluent comprising p-xylene; and separating the p-xylene.

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