P-modified MWW molecular sieve, method for preparing the same, and its use.

Abstract

This invention relates to the field of molecular sieves, and more particularly to P-modified MWW molecular sieves, methods for preparing them, and their use. The molecular sieve is A Pδ-7 / A P ≥40%, preferably A Pδ-7 / A P It indicates ≥50%, A Pδ-7 teeth, 31 This represents the peak area of ​​the P species signal peak with a chemical shift in the range of -22 ppm to 8 ppm in the P MAS NMR spectrogram, and A P teeth 31 This represents the total peak area of ​​all signal peaks in the P MAS NMR spectrogram. The catalyst containing the molecular sieve of the present invention has high levels of activity, selectivity, and stability, and excellent carbon deposition resistance.

Description

Detailed description of the invention

[0001] [Technical Field] This invention relates to the field of molecular sieves, and more particularly to p-modified MWW molecular sieves, methods for preparing the same, and their use, and more particularly to their application to the bio-based synthesis of p-xylene.

[0002] [Background technology] Since the beginning of the 21st century, countries around the world have been actively exploring new technologies that use biomass, a renewable resource, as a raw material. In the chemical industry, technologies are developing to replace conventional petroleum-based chemicals with bio-based chemicals. Paraxylene (PX) is one of the most important bulk chemicals. PX is primarily used to produce terephthalic acid through oxidation, the latter of which is further polymerized with ethylene glycol to produce polyethylene terephthalate polyester. Polyethylene terephthalate polyester is widely used in the polyester fiber and polyester plastics industries. China's demand for PX in 2021 was approximately 35 million tons. Currently, the majority of PX is derived from petroleum raw materials, but bio-based PX is beginning to be used in the production of renewable plastic bottles, polyester fibers, and other products. One promising route is to prepare PX from biomass-derived 2,5-dimethylfuran (DMF) and ethylene.

[0003] DMF and ethylene undergo a Diels-Alder cycloaddition reaction to produce the cycloaddition intermediate oxanorbornene, which is then dehydrated under an acid catalyst to produce PX and water. Since 2,5-hexadione and DMF can be converted to each other under acidic conditions, 2,5-hexadione can also be used as a starting material and react with ethylene under a solid acid catalyst to prepare PX. The following side reactions can occur in the reaction system in which DMF and ethylene react with each other to produce PX: (1) hydrolysis of DMF to 2,5-hexadione, and further dehydration to 3-methyl-2-cyclopenten-1-one; (2) alkylation side reaction, i.e., alkylation reaction with electron-rich molecules such as the cycloaddition intermediate ethylene, which produces an excess alkylation product of PX; (3) oligomerization side reaction, i.e., oligomerization of DMF or 2,5-hexadione itself; and (4) isomerization of the cycloaddition intermediate. DMF molecules are relatively reactive, and strong acids readily induce self-polymerization of DMF molecules, triggering hydrolysis and condensation side reactions of DMF. Appropriate acidity can satisfy the requirements for the main reaction, namely DA addition followed by dehydration, resulting in the acquisition of the target product, PX, with high selectivity. Therefore, catalyst materials should be designed to avoid strongly acidic sites, or modification methods may be used to remove strongly acidic sites on the catalyst. In addition, oligomerization side reactions can cause serious carbon deposition problems, leading to rapid deactivation of the catalyst material due to carbon deposition on the surface. Therefore, catalysts are required to have a large external specific surface area to withstand carbon deposition.

[0004] Conventional silicon-aluminum molecular sieves usually have a small external specific surface area and strong acidity. On the other hand, SCM-1 is a two-dimensional layered material with a very large external specific surface area, but the drawback of SCM-1 is its strong acidity. CN113831238A and CN113831308A have successfully prepared modified SCM-1 materials, Sn-Al-SCM-1 and Zr-Al-SCM-1, but strong acid sites still exist, and the problem of eliminating strong acid sites has not been solved. Such catalysts are difficult to catalyze the reaction of DMF and ethylene to prepare PX with high selectivity.

[0005] CN103814005A discloses a method for producing paraxylene, toluene and other compounds from renewable resources and ethylene by using a homogeneous metal salt as a Lewis acid catalyst. CN102482177B discloses the preparation of PX from DMF and ethylene by using pickled activated carbon as a catalyst. WO2014 / 043468A1 discloses the preparation of PX from DMF and ethylene by using a supported or unsupported metal salt catalyst. CN109569677B discloses the preparation of PX by using a phosphoric acid-type solid acid catalyst in the reaction of DMF and ethylene.

[0006] Other documents related to the background art 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, and such a solid catalyst should exhibit desired properties such as high activity, selectivity, and stability, and excellent resistance to carbon deposition.

[0008] 〔Summary of the Invention〕 To overcome the challenges of prior art in bio-based PX synthesis, such as the excessively high acid strength of molecular sieve catalysts reducing product selectivity and the susceptibility to loss of catalytic active sites resulting in low stability, the inventors diligently conducted research. As a result, they found that a novel class of P-modified MWW molecular sieves is particularly suitable for catalyzing the reaction of 2,5-dimethylfuran and / or 2,5-hexadione with ethylene to prepare p-xylene. The aforementioned molecular sieve catalyst exhibits high product selectivity, strong carbon deposition resistance, and high cycle stability. Therefore, the present invention was made.

[0009] A first aspect of the present invention is a compound of 40% or more, preferably 50% or more of A Pδ-7 / A P This provides a P-modified MWW molecular sieve that shows the ratio of [the specified values].

[0010] A second aspect of the present invention provides a method for preparing a molecular sieve, comprising performing P modification on an H-type MWW molecular sieve as a precursor, wherein, prior to the P modification, some or all of Al is optionally removed, and then a non-aluminum metal M is optionally grafted.

[0011] A third aspect of the present invention provides the use of a catalyst comprising a P-modified MWW molecular sieve when preparing paraxylene using 2,5-dimethylfuran and / or 2,5-hexadione as a starting material.

[0012] A fourth aspect of the present invention provides a biobased synthesis method for paraxylene, the method comprising reacting 2,5-dimethylfuran and / or 2,5-hexadione with ethylene in the presence of a catalyst comprising a P-modified MWW molecular sieve to obtain an effluent containing paraxylene; and separating the paraxylene.

[0013] The catalyst containing the molecular sieve of the present invention exhibits high activity, selectivity, and stability, and has excellent resistance to carbon deposition. For example, by using the catalyst of the present invention, 2,5-dimethylfuran and / or 2,5-hexadione react with ethylene, thereby being converted to paraxylene (PX) efficiently and with high selectivity. The two-dimensional layered structure of the molecular sieve is thought to provide the catalyst containing the molecular sieve with good mass transfer performance, contributing to the smooth progress of the reaction and providing strong resistance to carbon deposition. Compared with non-P-modified molecular sieves, the P-modified molecular sieve of the present invention has significantly reduced acid strength, and its appropriate acid strength can effectively reduce the occurrence of alkylation, isomerization, and various polymerization side reactions catalyzed by strong acids. As a result, the content of major impurities (polyalkylbenzene, isomerization products of cyclization intermediates, and oligomers of 2,5-dimethylfuran) is kept extremely low, achieving high selectivity of PX and significantly reducing the burden of subsequent separation and purification of PX. P modification not only forms a novel acidic site with appropriate acid strength, resulting in a small amount of Brønsted acid, but the bond between the P species and the metal also plays a role in stabilizing the catalyst's active site (no significant change in activity was observed when the catalyst was reused).

[0014] [Brief explanation of the drawing] Figure 1 shows the XRD pattern of the P-Al-SCM-1 molecular sieve obtained in Example 1.

[0015] Figure 2 is an SEM image of the P-Al-SCM-1 molecular sieve obtained in Example 1.

[0016] Figure 3 shows the P-Al-SCM-1 molecular sieve obtained in Example 1. 31 This is a P MAS NMR spectrum.

[0017] Figure 4 shows the NH3-TPD of the P-Al-SCM-1 molecular sieve obtained in Example 1.

[0018] Figure 5 shows the Py-FTIR spectrum of the P-Al-SCM-1 molecular sieve obtained in Example 1.

[0019] Figure 6 shows the 31 P MAS NMR spectrum of the P-Al-beta molecular sieve obtained in Comparative Example 1.

[0020] 〔Description of Preferred Embodiments〕 Neither the endpoints nor any values within the ranges disclosed herein are to be limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the end values of the individual ranges, the end values of the individual ranges and the individual point values therebetween, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed herein.

[0021] In a first aspect, the present invention provides a P-modified MWW molecular sieve exhibiting a ratio of 40% or more, preferably 50% or more of A Pδ-7 / A P , where A Pδ-7 represents 31 the peak area of the P signal peak having a chemical shift in the range of -22 ppm to 8 ppm in the P MAS NMR spectrogram, and A P represents 31 the total peak area of all signal peaks in the P MAS NMR spectrogram. The signal peaks in the range of -22 ppm to 8 ppm are considered to be due to P species that are linked to one or two metal atoms but not to other P, i.e., (M-O)PO(OH)2 and (M-O)2-PO(OH).

[0022] In a preferred embodiment, the molecular sieve exhibits a ratio of 70% or more of A Pδ-7 / A P . For example, the A Pδ-7 / A P ratio of the molecular sieve may be 70%, 80%, 90% or 100%.

[0023] 31In a P MAS NMR spectrogram, the molecular sieve of the present invention also exhibits signal peaks with chemical shifts in the range of -41 ppm to -11 ppm, which are P species signal peaks for pyrophosphates and polyphosphates.

[0024] In a preferred embodiment, the molecular sieve comprises a group of metals from the IVB, VB, VIB, IIIA, and IVA groups, preferably Al, Sn, Ti, W, Zr, Nb, Ta, and Ga, more preferably Al, Sn, W, and Nb, and more preferably Sn.

[0025] In a preferred embodiment, the MWW molecular sieve is at least one selected from the group consisting of MCM molecular sieves (e.g., MCM-22 disclosed in CN106517232B, which is incorporated by reference herein), ITQ molecular sieves (e.g., ITQ-2 disclosed in WO1997017290A1, which is incorporated by reference herein), and SCM molecular sieves (e.g., SCM-1 disclosed in CN104511271B, which is incorporated by reference herein), preferably SCM molecular sieves.

[0026] In a preferred embodiment, the SCM-type molecular sieve is an SCM-1 molecular sieve and / or an SCM-2 molecular sieve, preferably SCM-1.

[0027] In a preferred embodiment, the molecular sieve crystals are crystals with 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 that facilitates mass transfer.

[0028] In a preferred embodiment, the molecular sieve has a diameter of 80-300 m. 2 / g, preferably 100-200m 2 It has an internal specific surface area of ​​ / g.

[0029] In a preferred embodiment, the molecular sieve is 50-200 m 2 / g, preferably 100-200m 2 It has an external specific surface area of ​​ / g.

[0030] In a preferred embodiment, the molar ratio of Lewis acid to Brønsted acid in the molecular sieve is at least 1.

[0031] In a preferred embodiment, the molecular sieve has a total acid content of 400 to 900 μmol / g, preferably 500 to 700 μmol / g, where the strong acid content is ≤15 mol%, preferably ≤10 mol%, based on the total acid content.

[0032] In a preferred embodiment, the molecular sieve has a Si / metal molar ratio of 13 to 100, preferably 15 to 50.

[0033] In a preferred embodiment, the molecular sieve has a Si / P molar ratio of 15 to 100, preferably 20 to 50.

[0034] In a second aspect, the present invention provides a method for preparing a molecular sieve of the present invention, comprising performing P modification on an H-type MWW molecular sieve as a precursor, wherein some or all of the Al is optionally removed before the P modification, and then a non-aluminum metal is optionally grafted.

[0035] In a preferred embodiment, the H-MWW molecular sieve is prepared by a conventional method in the art, which includes calcining the MWW molecular sieve (e.g., an SCM-1 molecular sieve synthesized by the preparation method described in CN104511271B) to remove any structure-directing agent present therein, for example, by calcining in air or oxygen at 400-700°C for 1-6 hours, followed by ion exchange in an ammonium salt solution, and then recalcination. Here, the conditions for ion exchange and recalcination may be those conventionally selected in the art, for example, by ion exchange in a 1 mol / L NH4Cl solution at 80°C for 1 hour, repeated three times, and then recalcination in air or oxygen at 400-700°C for 1-6 hours to obtain H-MWW.

[0036] In the present invention, there are no particular limitations on the method for removing some or all of the Al. In a preferred embodiment, the method for removing some or all of the Al includes first subjecting the H-type MWW molecular sieve to steam hydrothermal treatment, and then washing it with an acid solution.

[0037] In the present invention, the acid solution has a wide range of options. Preferably, the acid solution is at least one selected from the group consisting of hydrochloric acid solution, oxalic acid solution, nitric acid solution, sulfuric acid solution, and phosphoric acid solution, and is preferably a nitric acid solution.

[0038] In the present invention, the conditions for the steam hydrothermal treatment may be conditions conventionally selected in the art. Preferably, an inert atmosphere is used as the condition for the steam hydrothermal treatment. An inert atmosphere refers to a gas that does not participate in the reaction, and in the present invention, this may be nitrogen, air, argon, etc. The role of this gas is to allow the water vapor to pass through the material.

[0039] In a preferred embodiment, the conditions for the steam hydrothermal treatment include a water vapor concentration in the gas phase of 10 to 100 mol%, preferably 30 to 70 mol%.

[0040] In a preferred embodiment, the conditions for the steam hydrothermal treatment include a temperature of 600 to 900°C, preferably 700 to 800°C.

[0041] In a preferred embodiment, the conditions for the steam hydrothermal treatment include a treatment time of 1 to 48 hours, preferably 6 to 12 hours.

[0042] In the present invention, the conditions for acid solution washing may be conditions conventionally selected in the art. Preferably, the conditions for acid solution washing include the concentration of the acid solution being 1 mol / L to 14 mol / L.

[0043] In a preferred embodiment, the cleaning conditions include a temperature of 20 to 120°C, preferably 80 to 110°C.

[0044] In a preferred embodiment, the cleaning conditions include a processing time of 6 to 48 hours, preferably 12 to 24 hours.

[0045] In a preferred embodiment, the cleaning conditions include the final Si / Al molar ratio at the end of the cleaning being 25 to 180, preferably 100 to 180.

[0046] In the present invention, the method for grafting the non-aluminum metal M may be a conventionally selected method in the art. In a preferred embodiment, the method for grafting the non-aluminum metal M is a solvent reflux method, which includes introducing a molecular sieve from which some or all of Al has been removed into an organic solution containing a source of the non-aluminum metal M, refluxing, followed by a first solid-liquid separation, a first washing, a first drying, and a first calcination.

[0047] In a preferred embodiment, the non-aluminum metal source M is a compound of at least one metal selected from the group consisting of 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 of tin tetrachloride, dimethyltin dichloride, niobium pentachloride, and tungsten hexachloride.

[0048] In a preferred embodiment, the organic solvent is at least one selected from the group consisting of alkanes, aromatic hydrocarbons, and halogenated hydrocarbons, for example, dichloromethane or n-hexane.

[0049] In a preferred embodiment, the grafted molecular sieve has a Si / M molar ratio of 13 to 100, preferably 15 to 50.

[0050] In a preferred embodiment, the first firing conditions include a temperature of 400 to 700°C, preferably 500 to 600°C.

[0051] In a preferred embodiment, the first firing conditions include a processing time of 3 to 12 hours, preferably 4 to 8 hours.

[0052] In the present invention, the conditions for the first solid-liquid separation, the first washing, and the first drying are not particularly limited, as long as the objectives of the present invention are achieved.

[0053] In the present invention, the P modification method may be a method conventionally selected in the art, such as impregnation. Alternatively, in a preferred embodiment, the P modification method includes optionally removing some or all of the Al, and then optionally grafting a non-aluminum metal M onto an MWW molecular sieve, which is then placed in an organic solution containing a phosphorus source, refluxed, followed by a second solid-liquid separation, a second washing, and a second calcination.

[0054] In a preferred embodiment, the phosphorus source is at least one selected from the group consisting of dimethylphosphonic acid, phosphorus oxychloride, methylphosphonic acid, trimethylphosphine oxide, trimethylphosphine, and phosphorus pentachloride.

[0055] In the present invention, the amount of phosphorus source added is not particularly limited, as long as the objective of the present invention is achieved. In a preferred embodiment, the amount of phosphorus source added is 0.05 to 1 mole, preferably 0.06 to 0.50 moles, and more preferably 0.07 to 0.30 moles, per mole of silicon in the molecular sieve.

[0056] In a preferred embodiment, the organic solvent of the organic solution is at least one selected from alkanes, aromatic hydrocarbons, and halogenated hydrocarbons. Examples of organic solvents include dichloromethane and n-hexane.

[0057] In the present invention, the reflux time for P modification is not particularly limited. The reflux time may be, for example, 0.5 to 12 hours.

[0058] In a preferred embodiment, after P modification, the molecular sieve has a Si / P molar ratio of 15 to 100, preferably 20 to 50.

[0059] In a preferred embodiment, the second firing condition includes a temperature of 400 to 700°C, preferably 500 to 600°C.

[0060] In a preferred embodiment, the second firing conditions include a processing time of 3 to 12 hours, preferably 4 to 8 hours.

[0061] In the present invention, the conditions for the second solid-liquid separation and the second washing are not particularly limited, as long as the objectives of the present invention are achieved.

[0062] While not bound by any particular theory, the microstructure (two-dimensional layered structure, thickness), pore structure, and acidity of the MWW molecular sieve are thought to make the MWW molecular sieve particularly suitable for modification by the P modification method of the present invention, resulting in a molecular sieve catalyst particularly suitable for the bio-based synthesis of PX.

[0063] In a preferred embodiment, the H-type MWW molecular sieve useful for the present invention is at least one of the H-type MCM molecular sieve, the H-type ITQ molecular sieve, and the H-type SCM molecular sieve; preferably the H-type SCM molecular sieve; more preferably the H-type SCM-1 molecular sieve and / or the H-type SCM-2 molecular sieve; and more preferably the H-type SCM-1 molecular sieve.

[0064] In a third aspect, the present invention provides the 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-hexadione as a starting material.

[0065] Reaction scheme: [ka]

[0066] In a fourth aspect, the present invention provides a biobased synthesis method for paraxylene, the method comprising reacting 2,5-dimethylfuran and / or 2,5-hexadione with ethylene in the presence of a catalyst comprising the P-modified MWW molecular sieve of the present invention to obtain an effluent containing paraxylene, and separating the paraxylene.

[0067] The formulation of the P-modified MWW molecular sieve of the present invention into catalysts suitable for use in industrial processes can be carried out according to techniques well known in the art. For example, the molecular sieve of the present invention is mixed with an appropriate amount of binder, and the mixture is molded, dried, and calcined to obtain a catalyst. The binder may be at least one of alumina, silica, titania, or their precursors. The mass of the binder may be 10-60%, for example 10-40%, of the mass of the molecular sieve. To facilitate molding, molding aids such as cellulose and water may also be introduced.

[0068] Drying and calcination in catalyst preparation can be carried out by conventional methods. Preferably, the drying conditions include a drying temperature of 90 to 160°C and a drying time of 6 to 15 hours, and the calcination conditions include an oxygen-containing atmosphere such as air, a calcination temperature of 300 to 550°C, and a calcination time of 2 to 5 hours.

[0069] Procedures and reaction conditions for reacting 2,5-dimethylfuran and / or 2,5-hexadione with ethylene in the presence of a molecular sieve catalyst to obtain an effluent containing p-xylene, as well as procedures and conditions for separating p-xylene from the reaction effluent, are well known in the art.

[0070] This disclosure, including the following examples, employs the following analytical and testing methods.

[0071] The components of the liquid reaction mixture are qualitatively analyzed using an Agilent 7890A gas chromatograph-mass spectrometer (GC-MS) from Agilent, Inc., USA. A wax polar capillary column is used for the chromatography. Quantitative analysis is performed using an Agilent 7890B gas chromatograph (GC) from Agilent, Inc., which is equipped with a hydrogen ion flame detector (FID) and a wax polar capillary column. A calibration curve is plotted using standard substances, and then the molar amounts of the sample components are measured. Based on the measured molar amounts of the substances, the conversion rate and selectivity of the substances are calculated.

[0072] The conversion rate of raw materials is calculated using the following formula: Raw material conversion rate (%) = (Molar amount of initial added raw material - Molar amount of unconverted raw material) / (Molar amount of initial added raw material) × 100%.

[0073] Product selectivity is calculated according to the following formula: Product selectivity (%) = (molar amount of product produced by the reaction) / (molar amount of initial added raw materials - molar amount of unconverted raw materials) × 100%.

[0074] In this specification, “raw material” means 2,5-dimethylfuran and / or 2,5-hexadione.

[0075] XRD patterns are acquired using a D8 Advance X-ray diffractometer, available from Bruker GmbH in Germany, with a CuKα radiation source (λ=1.54Å).

[0076] The composition of the molecular sieve is measured using an Agilent 725-ES inductively coupled plasma atomic emission spectrometer (ICP). The molecular sieve sample is dissolved in hydrofluoric acid, and the elemental content is expressed in molar terms.

[0077] Scanning electron microscope (SEM) images are acquired using the S-4800II field emission scanning electron microscope.

[0078] solid state 31 P Magic Angle Spin Nuclear Magnetic Resonance31 The P MAS NMR spectrum was acquired using a Varian 400 MHz NMR spectrometer, and H3PO4 was detected. 31 It is used as a reference for the chemical shift of phosphorus (P).

[0079] The NH3 programmed temperature desorption (NH3-TPD) experiment was performed using the TPD / TPR Altamira AMI-3300 instrument, and the total acid content was determined by calculation based on the obtained diagram.

[0080] The acid species of the catalyst is determined using pyridine adsorption infrared spectroscopy (py-FTIR). The py-FTIR spectrum is acquired using a Nicolet Model 710 spectrometer. The specific procedure is as follows: a) Sample preparation and pretreatment: Approximately 15 mg of the sample is compressed into a thin disc with a diameter of 13 mm and loaded into an infrared sample tank. The sample is then pretreated in a vacuum cell at 400°C for 2 hours; the sample is scanned at 100°C, 200°C, and 400°C to acquire the background spectrum. b) After the sample tank has cooled to room temperature, pyridine is adsorbed for 10 minutes; vacuum desorption is performed at 100°C for 10 minutes, and the infrared absorption spectrum is scanned and recorded; then the infrared absorption spectrum is scanned and recorded sequentially at 200°C and 400°C. The difference spectrum before and after pyridine adsorption is the acquired Py-FTIR spectrum. 1450 cm⁻¹ -1 The peak is the absorption peak of L acid, at 1540 cm. -1 The peak is the absorption peak of acid B. The total absorption peak area of ​​pyridine at 100°C is 1450 cm² for pyridine that has not been desorbed at 400°C. -1 and 1540cm -1 The ratio of the total absorption peak areas in each region is recorded as the strong acid ratio, and the ratio of the absorption peak area of ​​acid L to the absorption peak area of ​​acid B is recorded as the L / B ratio.

[0081] The specific surface area and external specific surface area of ​​the molecular sieve were measured by nitrogen physicoadsorption and desorption methods. Adsorption and desorption curves were measured using a Micromeretic ASAP 2020M physicoadsorbent. The total specific surface area was determined by the BET formula, the external specific surface area by the t-plot formula, and the difference between the two was the internal specific surface area. Before measurement, the sample was pretreated in a vacuum at 350°C for 6 hours.

[0082] [Examples] The present invention will be described in detail below with reference to examples, but the scope of the present invention is not limited thereto.

[0083] [Example 1] According to the preparation method described in patent CN 104511271B, SCM-1 molecular sieve raw material powder was synthesized, then calcined to remove the structure-directing agent, followed by ion exchange and calcination to obtain H-SCM-1. ICP measurement confirmed that the molecular sieve had a silicon / aluminum ratio (atomic ratio) of 15.2.

[0084] The P-modified molecular sieve, P-Al-SCM-1, was prepared from H-SCM-1 using the following procedure: (1) High-temperature steam hydrothermal treatment of H-SCM-1 molecular sieve: Treated at 700°C for 10 hours under a nitrogen atmosphere and a water vapor partial pressure of 60%.

[0085] (2) Preparation of P-Al-SCM-1: The hydrothermally treated molecular sieve described above was directly refluxed in a dichloromethane solution containing a P source. Specifically, 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 silicon in the molecular sieve, and the molecular sieve content in the solution was 1 g per 50 mL of solution. A solid product was obtained by centrifugation and washing with dichloromethane. The solid product was calcined at 550 °C for 4 hours to obtain P-Al-SCM-1. ICP measurement showed that the Si / Al ratio was 15.2 and the Si / P ratio was 21.2. The XRD pattern is shown in Figure 1, which shows that the MWW topological structure is well maintained. The SEM image (see Figure 2) shows that the obtained molecular sieve has a two-dimensional layered structure, and BET measurement showed that the internal specific surface area was 93 m².2 / g, external specific surface area is 136m² 2 This indicates that the catalyst is / g 31 The P MAS NMR spectrum shows 77% A Pδ-7 / A P It possesses the following properties. Figure 4 shows the NH3-TPD curve, and the total acid content was calculated to be 684 μmol / g. Furthermore, the decrease in adsorbed NH3 above 300°C suggests that the strongly acidic sites are decreasing. The pyridine-IR spectrum (see Figure 5) showed that the overall L / B ratio at 100°C was 1.9. The pyridine molecules that do not desorb even at 400°C are those adsorbed to the strongly acidic sites, and therefore it was calculated that the strongly acidic sites account for 9%.

[0086] [Example 2] P-Al-SCM-1 molecular sieves were prepared according to the procedure described in Example 1, except that H-SCM-1 molecular sieves were treated in a nitrogen atmosphere at 600°C for 48 hours under a water vapor partial pressure of 50%. ICP measurement showed that the Si / Al ratio was 15.2 and the Si / P ratio was 20.5. BET measurement showed that the internal specific surface area was 105 m². 2 The value is / g, and the external specific surface area is 127m². 2 It was shown that this catalyst A Pδ-7 / A P It was found that the acid content was 72%. The total acid content calculated from the NH3-TPD curve was 674 μmol / g. The pyridine-IR spectrum showed an L / B ratio of 2.4, and it was calculated that the strongly acidic portion accounted for 12%.

[0087] [Example 3] A 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 refluxed in an n-hexane solution containing phosphorus oxychloride for 8 hours. ICP measurement showed that the Si / Al ratio was 15.2 and the Si / P ratio was 18.7. BET measurement showed that the internal specific surface area was 84 m². 2 The value is / g, and the external specific surface area is 108m². 2 It was shown that this catalyst A Pδ-7 / A P It was found that the acid content was 79%. The total acid content calculated from the NH3-TPD curve was 754 μmol / g. The pyridine-IR spectrum showed an L / B ratio of 1.8, and it was calculated that the strongly acidic portion accounted for 7%.

[0088] [Example 4] According to the preparation method described in Chinese Patent CN 104511271B, SCM-1 molecular sieve raw material powder was synthesized, then calcined to remove the structure-directing agent, followed by ion exchange and calcination to obtain H-SCM-1. ICP measurement confirmed that the silicon / aluminum ratio (atomic ratio) of the molecular sieve was 15.2.

[0089] The P-modified molecular sieve, P-Sn-SCM-1, was prepared from H-SCM-1 by the following procedure: (1) High-temperature steam hydrothermal treatment of H-SCM-1 molecular sieve: Treated at 900°C for 10 hours under a nitrogen atmosphere and a partial pressure of 10% water vapor. (2) Partial removal of Al using an acid solution: Hydrothermally treated H-SCM-1 molecular sieves were washed with 14M concentrated nitric acid at 120°C for 48 hours. The amount of molecular sieves in the acid solution was 1 g per 30 mL of acid solution. The final Si / Al ratio was measured to be 142.

[0090] (3) Preparation of Sn-SCM-1 by solvent reflux: The aluminum-free SCM-1 molecular sieves described above were refluxed in a dichloromethane solution of anhydrous SnCl4. The amount of molecular sieves in the solution was 1 g per 50 mL of solution. After that, they were washed with dichloromethane, dried, and calcined at 550°C for 4 hours to obtain Sn-SCM-1 molecular sieves.

[0091] (4) Under reflux conditions in a dichloromethane solution, the Sn-SCM-1 molecular sieve was treated with dimethylphosphonic acid for 1 hour. The amount of dimethylphosphonic acid added was 1 / 10 of the molar amount of silicon in the molecular sieve. A solid product was obtained by centrifugation and washing with dichloromethane. The solid product was calcined at 550°C for 4 hours to obtain P-Al-SCM-1. ICP measurement showed that the Si / Sn ratio was 35.3 and the Si / P ratio was 21.6. BET measurement showed that the internal specific surface area was 10¹ m². 2 The value is / g, and the external specific surface area is 116m². 2 It was shown that this catalyst A Pδ-7 / A P It was found that the acid content was 85%. The total acid content calculated from the NH3-TPD curve was 641 μmol / g. From the pyridine-IR spectrum, the L / B ratio was calculated to be 2.8, and the strongly acidic portion accounted for 6%.

[0092] [Example 5] P-Sn-SCM-1 was prepared according to the procedure described in Example 4, except that partial removal of Al using an acid solution was carried out at 80°C for 12 hours using 1M nitric acid, resulting in a final Si / Al ratio of 25.5. ICP measurement showed a Si / Sn ratio of 47.1 and a Si / P ratio of 28.9. BET measurement showed an internal specific surface area of ​​124 m². 2 The value is / g, and the external specific surface area is 178m². 2 It was shown that this catalyst A Pδ-7 / A P It was found that the acid content was 70%. The total acid content calculated from the NH3-TPD curve was 852 μmol / g. The pyridine-IR spectrum showed an L / B ratio of 2.2, and it was calculated that the strongly acidic portion accounted for 11%.

[0093] [Example 6] P-Sn-SCM-1 was prepared according to the procedure described in Example 4, except that reflux treatment with dimethyltin dichloride was used when preparing Sn-SCM-1. ICP measurement showed that the Si / Sn ratio was 42.6 and the Si / P ratio was 35.6. BET measurement showed that the internal specific surface area was 135 m². 2 The value is / g, and the external specific surface area is 168m². 2 It was shown that this catalyst A Pδ-7 / A P It was found that the acid content was 75%. The total acid content calculated from the NH3-TPD curve was 679 μmol / g. The pyridine-IR spectrum showed an L / B ratio of 3.1, and it was calculated that the strongly acidic portion accounted for 9%.

[0094] [Example 7] P-Ti-SCM-1 was prepared according to the procedure described in Example 4, except that the Ti-SCM-1 intermediate was prepared by refluxing a TiCl4 dichloromethane solution. ICP measurement showed that the Si / Ti ratio was 27.8 and the Si / P ratio was 23.6. BET measurement showed that the internal specific surface area was 145 m². 2 The value is / g, and the external specific surface area is 179m². 2 It was shown that this catalyst A Pδ-7 / A P It was found that the acid content was 76%. The total acid content calculated from the NH3-TPD curve was 705 μmol / g. The pyridine-IR spectrum showed an L / B ratio of 1.9, and it was calculated that the strongly acidic portion accounted for 8%.

[0095] [Example 8] P-Nb-SCM-1 was prepared according to the procedure described in Example 4, except that the Nb-SCM-1 intermediate was prepared by refluxing a dichloromethane solution of NbCl5. ICP measurement showed that the Si / Nb ratio was 29.0 and the Si / P ratio was 25.8. BET measurement showed that the internal specific surface area was 94 m². 2 The value is / g, and the external specific surface area is 141m². 2 It was shown that this catalyst A Pδ-7 / A P It was found that the acid content was 74%. The total acid content calculated from the NH3-TPD curve was 478 μmol / g. The pyridine-IR spectrum showed an L / B ratio of 2.1, and it was calculated that the strongly acidic portion accounted for 11%.

[0096] [Example 9] PW-SCM-1 was prepared according to the procedure described in Example 4, except that the W-SCM-1 intermediate was prepared by refluxing a dichloromethane solution of WCl6. ICP measurement showed that the Si / W ratio was 22.5 and the Si / P ratio was 20.6. BET measurement showed that the internal specific surface area was 85 m². 2 The value is / g, and the external specific surface area is 128m². 2 It was shown that this catalyst A Pδ-7 / A P It was found that the acid content was 78%. The total acid content calculated from the NH3-TPD curve was 490 μmol / g. The pyridine-IR spectrum showed an L / B ratio of 3.3, and it was calculated that the strongly acidic portion accounted for 9%.

[0097] [Example 10] Using the molecular sieve catalysts prepared in Examples 1-9 described above, a reaction was carried out to prepare PX from DMF and ethylene, under the following reaction 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°C, and the reaction time was 12 hours. 0.5 g of the catalyst from Examples 1-9, 3.0 g of DMF, and 17 g of n-heptane were placed in a magnetically stirred autoclave, and ethylene at 2.0 MPa was packed inside. The reaction was carried out at 250°C for 12 hours, and the liquid reaction mixture was analyzed by gas chromatography to measure the DMF conversion rate and PX selectivity. The results are shown in Table 1 below. [Table 1]

[0098] [Example 11] In this example, the P-Al-SCM-1 molecular sieve prepared in Example 1 was used as a catalyst. 0.5 g of the catalyst, 3.0 g of 2,5-hexadione (HDO), and 17 g of n-heptane were placed in a magnetically stirred autoclave, and ethylene at 2.0 MPa was packed inside. The reaction was carried out at 250°C for 12 hours, and analysis of the liquid reaction mixture by gas chromatography revealed that the conversion rate of HDO was 97.5% and the selectivity of PX was 96.5%.

[0099] This example demonstrates that HDO is also a useful raw material for the preparation of PX.

[0100] [Example 12] In this example, the P-Al-SCM-1 molecular sieve prepared in Example 1 was used as a catalyst. 2.0 g of the catalyst and 15.0 g of DMF were placed in a magnetically stirred autoclave, and ethylene at 6.0 MPa was packed into it. The reaction was carried out at 250°C for 12 hours, and analysis of the liquid reaction mixture by gas chromatography revealed that the DMF conversion rate was 48.2% and the PX selectivity was 92.3%.

[0101] This example demonstrates that in the preparation of PX, higher PX selectivity can be achieved by converting the starting materials in the presence of an organic solvent. However, in the absence of an organic solvent, high reactant and product concentrations can be achieved, and the yield per unit reactor volume is higher.

[0102] [Example 13] In this example, the P-Al-SCM-1 molecular sieve prepared in Example 1 was used as a catalyst. 1.0 g of catalyst, 3.0 g of HDO, and 17 g of n-hexane were placed in a magnetically stirred autoclave, and ethylene at 3.0 MPa was packed into it. The reaction was carried out at 250°C for 24 hours, and analysis of the liquid reaction mixture by gas chromatography revealed that the HDO conversion rate was 98.2% and the PX selectivity was 96.7%.

[0103] [Example 14] In this example, the P-Al-SCM-1 molecular sieve prepared in Example 1 was used as a catalyst. 0.5 g of catalyst, 3.0 g of DMF, and 17.0 g of tetrahydrofuran were placed in a magnetically stirred autoclave, and ethylene at 4.0 MPa was packed into it. The reaction was carried out at 300°C for 3 hours, and analysis of the liquid reaction mixture by gas chromatography revealed that the DMF conversion rate was 95.2% and the PX selectivity was 97.0%.

[0104] The experimental results of Examples 13 and 14 demonstrated that these commonly used organic solvents are suitable for this reaction. In Example 14, it was found that raising the reaction temperature to 300°C could increase the reaction temperature and shorten the reaction time, but the drawback is that the reactor needs to have better heat resistance.

[0105] [Example 15] In this example, the P-Al-SCM-1 molecular sieve prepared in Example 1 was used as a catalyst. 0.5 g of the catalyst, 3.0 g of HDO, and 17 g of tetrahydrofuran were placed in a magnetically stirred autoclave, and ethylene at 1.0 MPa was packed into it. The reaction was carried out at 270°C for 24 hours, and analysis of the liquid reaction mixture by gas chromatography revealed that the HDO conversion rate was 98.1% and the PX selectivity was 96.1%.

[0106] [Example 16] In this example, the P-Al-SCM-1 molecular sieve prepared in Example 1 was used as a catalyst. 0.5 g of catalyst, 3.0 g of DMF, and 17 g of tetrahydrofuran were placed in a magnetically stirred autoclave, and ethylene at 3.0 MPa was packed into it. The reaction was carried out at 235°C for 24 hours, and analysis of the liquid reaction mixture by gas chromatography revealed a DMF conversion rate of 94.3% and a PX selectivity of 96.7%.

[0107] [Example 17] In this example, the cycle activity of the P-Al-SCM-1 molecular sieve catalyst prepared in Example 1 was tested in the reaction to prepare PX from DMF and ethylene. The reaction conditions were as follows: 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°C; and the reaction time was 12 hours. 0.5 g of catalyst, 3.0 g of DMF, and 17 g of n-heptane were placed in a magnetically stirred autoclave, and ethylene at 2.0 MPa was packed into it. The reaction was carried out at 250°C for 12 hours, and the liquid reaction mixture was analyzed by gas chromatography to measure the DMF conversion rate and the selectivity of PX. After the reaction was complete, the spent catalyst was separated by centrifugation, calcined to remove carbon deposits, and reused in the next cycle. The results are shown in Table 2 below. It was found that the DMF conversion rate and the selectivity of PX remained essentially unchanged for at least 5 cycles, confirming the excellent recycling stability of the catalyst.

[0108] [Table 2]

[0109] [Example 18] In step (2), P modification was carried out by the incipient wetness impregnation method using a dimethyl phosphoric acid solution in dichloromethane, and the amount of P source added was 1 / 10 of the molar amount of silicon in the molecular sieve, except that the procedure was repeated as in Example 1. After impregnation, the material was dried and calcined at 550°C for 4 hours to obtain P-Al-SCM-1. ICP measurement showed that the Si / Al ratio was 15.2 and the Si / P ratio was 10.0. BET measurement showed that the internal specific surface area was 81 m². 2 The value is / g, and the external specific surface area is 102m². 2 It was shown that this catalyst is / g 31 The P MAS NMR spectrum is A Pδ-7 / A PThe figure was 43%. The total acid content calculated from the NH3-TPD curve was 863 μmol / g. The pyridine-IR spectrum showed an L / B ratio of 1.1, and it was calculated that the strongly acidic portion accounted for 8%.

[0110] 0.5 g of catalyst, 3.0 g of DMF, and 17 g of n-heptane were added to a magnetically stirred autoclave, and ethylene at 2.0 MPa was packed inside. The reaction was carried out at 250°C for 12 hours, and analysis of the liquid reaction mixture by gas chromatography revealed a DMF conversion rate of 90.2% and a PX selectivity of 76%.

[0111] [Comparative Example 1] Example 1 was repeated, except that a P-modified molecular sieve, P-Al-beta, was obtained using a beta molecular sieve available from Tianjin Nanhua Catalyst Co., Ltd.

[0112] ICP measurements showed a Si / Al ratio of 18.8 and a Si / P ratio of 24.3. BET measurements revealed an internal specific surface area of ​​271 m². 2 The value is / g, and the external specific surface area is 19m². 2 It was shown that the value was / g. Figure 6 shows the catalyst 31 The P MAS NMR spectrum is shown. Figure 6 is A Pδ-7 / A P This indicates that it is 31%. The total acid content calculated from the NH3-TPD curve was 598 μmol / g. The pyridine-IR spectrum showed that the L / B ratio was 1.4, and it was calculated that the strongly acidic portion accounted for 19%.

[0113] 0.5 g of catalyst, 3.0 g of DMF, and 17 g of n-heptane were placed in a magnetically stirred autoclave, and ethylene at 2.0 MPa was packed inside. The reaction was carried out at 250°C for 12 hours, and analysis of the liquid reaction mixture by gas chromatography revealed a DMF conversion rate of 77.1% and a PX selectivity of 68.2%.

[0114] As is evident from the results of the examples, the molecular sieves prepared by the method of the present invention have a relatively large external specific surface area and appropriate acidity, and exhibit excellent properties, particularly when catalyzing the reaction of 2,5-dimethylfuran and / or 2,5-hexadione with ethylene to produce p-xylene. Compared with the catalysts of the comparative examples, the molecular sieves of the present invention achieve significantly better results.

[0115] While preferred embodiments of the present invention have been described in detail above, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including combining various technical features in any other suitable manner. These simple modifications and combinations are also considered to be within the scope of disclosure of the present invention and fall within the scope of protection of the present invention. [Brief explanation of the drawing]

[0116] [Figure 1] Figure 1 shows the XRD pattern of the P-Al-SCM-1 molecular sieve obtained in Example 1. [Figure 2] Figure 2 is an SEM image of the P-Al-SCM-1 molecular sieve obtained in Example 1. [Figure 3] Figure 3 shows the 31P MAS NMR spectrum of the P-Al-SCM-1 molecular sieve obtained in Example 1. [Figure 4] Figure 4 shows the NH3-TPD of the P-Al-SCM-1 molecular sieve obtained in Example 1. [Figure 5] Figure 5 shows the Py-FTIR spectrum of the P-Al-SCM-1 molecular sieve obtained in Example 1. [Figure 6] Figure 6 shows the 31P MAS NMR spectrum of the P-Al-beta molecular sieve obtained in Comparative Example 1.

Claims

1. A 40% or more, preferably 50% or more Ｐδ－７ / A Ｐ This is a P-modified MWW molecular sieve showing the ratio, and A Ｐδ－７ teeth ３１ P represents the peak area of ​​signal peaks with chemical shifts in the range of -22 ppm to 8 ppm in the MAS NMR spectrogram, and A Ｐ teeth ３１ P-MAS represents the total peak area of ​​all signal peaks in an NMR spectrogram, and is a P-modified MWW molecular sieve.

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

3. The crystals of the molecular sieve have a two-dimensional layered structure; and / or The molecular sieve has an internal specific surface area of 80 to 300 m ２ / g, preferably 100 to 200 m ２ / g; and / or The molecular sieve is 50 to 200 m ２ / g, preferably 100-200m ２ Having an external specific surface area of ​​ / g; and / or The molar ratio of Lewis acid to Brønsted acid in the molecular sieve is at least 1; and / or The molecular sieve according to claim 1 or 2, wherein the molecular sieve has a total acid content of 400 to 900 μmol / g, preferably 500 to 700 μmol / g, and the strong acid content is ≤15%, preferably ≤10%, based on the total acid content.

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

5. A method for preparing a molecular sieve according to any one of claims 1 to 4, comprising performing P modification on an H-type MWW molecular sieve as a precursor, wherein, prior to the P modification, some or all of Al is optionally removed, and then a non-aluminum metal is optionally grafted.

6. A method for removing some or all of Al includes first subjecting an H-type MWW molecular sieve to steam hydrothermal treatment, and then washing it with an acid solution; Preferably, the acid solution is at least one selected from the group consisting of hydrochloric acid solution, oxalic acid solution, nitric acid solution, sulfuric acid solution, and phosphoric acid solution, and is preferably a nitric acid solution; and / or The conditions for the steam-hydrothermal treatment include the following: The water vapor concentration in the gas phase is 10 to 100 mol%, preferably 30 to 70 mol%; and / or The temperature is 600 to 900°C, preferably 700 to 800°C; and / or The processing time is 1 to 48 hours, preferably 6 to 12 hours; and / or The cleaning conditions include the following: The concentration of the acid solution is 1 mol / L to 14 mol / L; and / or The temperature is 20 to 120°C, preferably 80 to 110°C; and / or The processing time is 6 to 48 hours, preferably 12 to 24 hours; and / or The method according to claim 5, wherein the final Si / Al molar ratio at the end of the washing is 25 to 180, preferably 100 to 180.

7. The method for grafting the non-aluminum metal M is a solvent reflux method, comprising: introducing a molecular sieve from which some or all of Al has been removed into an organic solution containing a source of the non-aluminum metal M, then refluxing; followed by 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 the group consisting of Sn, Ti, W, Zr, Nb, Ta, and Ga; and / or The organic solvent is at least one selected from the group consisting of alkanes, aromatic hydrocarbons, and halogenated hydrocarbons; and / or The molecular sieve after grafting has a Si / M molar ratio of 13 to 100, preferably 15 to 50; and / or The first firing conditions include the following: The temperature is 400 to 700°C, preferably 500 to 600°C; and / or The method according to claim 5 or 6, wherein the processing time is 3 to 12 hours, preferably 4 to 8 hours.

8. The method for the P modification includes optionally removing some or all of Al, then optionally grafting a non-aluminum metal M onto a molecular sieve, then placing the sieve into an organic solution containing a phosphorus source, then refluxing, followed by a second solid-liquid separation, a second washing, and a second calcination; preferably, The phosphorus source is at least one selected from the group consisting of dimethylphosphonic acid, phosphorus oxychloride, methylphosphonic acid, trimethylphosphine oxide, trimethylphosphine, and phosphorus pentachloride; and / or The organic solvent is at least one selected from the group consisting of alkanes, aromatic hydrocarbons, and halogenated hydrocarbons; and / or The molecular sieve after P modification has a Si / P molar ratio of 15 to 100, preferably 20 to 50; and / or The second firing conditions include the following: The temperature is 400 to 700°C, preferably 500 to 600°C; and / or The method according to any one of claims 5 to 7, wherein the processing time is 3 to 12 hours, preferably 4 to 8 hours.

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

10. A bio-based method for synthesizing paraxylene, comprising reacting 2,5-dimethylfuran and / or 2,5-hexadione with ethylene in the presence of a catalyst comprising a P-modified MWW molecular sieve according to any one of claims 1 to 4 to obtain an effluent containing paraxylene, and separating the paraxylene.

Images