Process for the catalytic synthesis of para-xylene using a metal-modified mcm-22 molecular sieve

Abstract

The present application relates to a kind of metal modified MCM-22 molecular sieve catalytic synthesis of p-xylene method, belong to chemical catalysis technical field.The method with 2,5-dimethylfuran and acrylic acid as reactant, with metal modified MCM-22 molecular sieve as catalyst, in magnetic stirring tank, initial reaction pressure is normal pressure, reaction temperature is 150 ℃~190 ℃;Reaction time is 3h~10h, nitrogen is as the condition of protective gas is carried out.The metal modified MCM-22 molecular sieve obtained in the present application has high external specific surface characteristics, by the method of physical mixing and re-calcination, realize the synergistic effect of L acid site on metal oxide and MCM-22 surface B acid site, balance B acid, L acid site catalytic rate, speed up total reaction rate.99%2,5-DMF conversion rate and 98%PX selectivity can be obtained after reaction temperature is 150 ℃, reaction 10h.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalysis technology, specifically relating to a method and its application for catalyzing the synthesis of p-xylene (PX) from 2,5-dimethylfuran (2,5-DMF) and acrylic acid (AA) using metal-modified MCM-22 molecular sieve as a catalyst. Background Technology

[0002] p-Xylene (PX) is an important basic raw material in the aromatic hydrocarbon industry chain. It is mainly used in the oxidation reaction to synthesize purified terephthalic acid, which is then used to produce polyester products (such as synthetic fibers and plastics).

[0003] Traditional PX production processes heavily rely on fossil fuels, which are increasingly depleted. Therefore, obtaining PX from renewable biomass and its derivatives has attracted widespread attention. One of the best routes for PX synthesis is the Diels-Alder cycloaddition reaction of biomass-derived 2,5-DMF with the dienophile acrylic acid (AA), followed by dehydration and decarboxylation. This reaction offers advantages such as high yield and green sustainability, showing promising industrial application prospects. Numerous studies have found that this reaction requires synergistic catalysis from both Brønsted (B) and Lewis (L) acids, typically necessitating bifunctional catalysts. Silicate molecular sieves are widely used due to their high thermal stability and high specific surface area. However, although silicate molecular sieves possess both Brønsted (B) and Lewis (L) acid sites, the L acid sites are relatively fewer and weaker than the Brønsted (B) acid sites, leading to a mismatch in catalytic rates between the two and limiting the overall reaction rate.

[0004] Therefore, there is an urgent need to modulate the properties of the L acid sites in the catalyst, adjust the catalytic rates of B and L acids, and obtain a highly active molecular sieve catalyst for the synthesis of PX from 2,5-DMF. Summary of the Invention

[0005] This invention addresses the problem of low catalyst activity in the synthesis of PX from 2,5-DMF and AA by providing a metal-modified MCM-22 molecular sieve as a catalyst, which exhibits high catalytic performance in the synthesis of PX from 2,5-DMF and AA.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for synthesizing PX using metal-modified MCM-22 molecular sieve catalysis is characterized by using 2,5-DMF and AA as reactants, with metal-modified MCM-22 molecular sieve as the catalyst, wherein the molar ratio of 2,5-DMF to AA is 1:2 (the amount of 2,5-DMF is 7.5 mmol); the mass of the metal-modified MCM-22 molecular sieve catalyst is 5% of the total mass of the reactants; the reaction is carried out in a magnetically stirred tank; the reaction temperature is 150℃~190℃, the initial reaction pressure is atmospheric pressure, and nitrogen is used as a protective gas.

[0008] As a limitation of the present invention, the preparation method of the metal-modified MCM-22 molecular sieve catalyst of the present invention is as follows:

[0009] (1) The metal precursor and the undetemplated MCM-22(P) were ground evenly in a mortar and calcined in a muffle furnace at 550℃ for 8h to obtain Na-type modified MCM-22 molecular sieve.

[0010] (2) The Na-type modified MCM-22 molecular sieve obtained in step (1) is treated with 1.0 mol·L⁻¹ water. -1 The metal-modified MCM-22 molecular sieve was obtained by performing three ion exchanges with NH4Cl aqueous solution, followed by filtration, washing, drying, and calcination at 550℃ for 4 hours in a muffle furnace.

[0011] As a further limitation of the present invention, the metal precursor in step (1) is any one of ZrOCl2·8H2O, Zn(NO3)2·6H2O or SnC2O4, and the metal-modified MCM-22 molecular sieve in step (2) is any one of ZrO2 / MCM-22, ZnO2 / MCM-22 or SnO2 / MCM-22.

[0012] As a further limitation of the present invention, the untemplated MCM-22(P) of the present invention is prepared by the following method:

[0013] (1) Dissolve 0.40g to 2.80g of NaOH in deionized water at room temperature, then add 1.66g of NaAlO2 and stir for 1h to obtain a clear and transparent solution;

[0014] (2) Then slowly add 6.94 g of hexamethyleneimine (HMI) to the solution obtained in step (1). After the addition is complete, continue stirring for 0.5 h. Under vigorous stirring conditions, slowly add 48.06 g of silica sol (25 wt%) using a peristaltic pump, add 0.12 g of seed crystals, and age in a water bath at 25 °C for 24 h to obtain a light milky yellow precursor. The molar ratio of the light milky yellow precursor is: 0.2 SiO2 : 0.0067 Al2O3 : 0.01~0.07 NaOH : 0.07 HMI : 6 H2O;

[0015] (3) The pale milky yellow precursor obtained in step (2) was transferred to a hydrothermal reactor and crystallized in an oven at 150°C for 7 days.

[0016] (4) The precursor after step (3) crystallization is filtered, washed and dried to obtain the undetemplated MCM-22(P).

[0017] By adopting the above technical solution, the present invention achieves the following beneficial effects compared with the prior art:

[0018] This invention provides a simple catalyst modification method. The metal-modified MCM-22 molecular sieve obtained by this invention has a high external specific surface area. Through physical mixing and calcination, the synergistic effect of the Lewis acid sites on the metal oxide and the Beta acid sites on the MCM-22 surface is achieved, balancing the catalytic rates of the Beta and Lewis acid sites and accelerating the overall reaction rate. At a reaction temperature of 150℃ and an initial reaction pressure of atmospheric pressure, after 10 hours of reaction, a maximum 2,5-DMF conversion of 99% and a PX selectivity of 98% can be obtained. Attached Figure Description

[0019] Figure 1 The XRD patterns of the metal-modified MCM-22 catalysts prepared in Examples 3, 6, and 9, and the MCM-22 prepared in Comparative Example 1, show characteristic diffraction peaks at approximately 2θ of 7.1°, 8.0°, 9.7°, 22.5°, 25.0°, and 26.0°, which are basically consistent with the MCM-22 patterns reported in the literature. There are no other impurity phases, which indicates that the loading of metal species does not affect the crystal structure of the MCM-22 molecular sieve.

[0020] The catalyst with a metal loading of 5% did not show the characteristic diffraction peaks of metal oxides (ZrO2, ZnO2, SnO2) in the XRD pattern, which may be due to the high dispersion of metal species on the MCM-22 molecular sieve.

[0021] Figure 2 The graph shows the catalytic activity of MCM-22 and Sn-MCM-22. As can be seen from the graph, the catalytic activity of the modified MCM-22 is significantly improved. Detailed Implementation

[0022] The present invention will be further described with reference to the following embodiments, but it should be understood that these embodiments are for illustrative purposes only and should not be construed as limiting the implementation of the present invention.

[0023] In this invention, metal-modified MCM-22 molecular sieves were prepared using different metal precursors. By adjusting the type and amount of metal precursors added during the preparation process, different modified MCM-22 molecular sieves can be obtained. Specific embodiments are as follows:

[0024] The preparation method of the precursor MCM-22(P) is carried out according to the following steps:

[0025] First, the precursor MCM-22(P) was synthesized by dissolving 0.40 g to 2.80 g of NaOH in 90.10 g of deionized water, then adding 1.66 g of NaAlO2 and stirring at room temperature for 1 h. Next, 6.94 g of HMI was added, and 48.06 g of silica sol (25 wt%) was slowly added dropwise under vigorous stirring. Then, 0.12 g of seed crystals was added, and the mixture was aged in a water bath at 25 °C for 24 h to obtain a pale milky yellow precursor. The molar ratio of the pale milky yellow precursor was: 0.2 SiO2 : 0.0067 Al2O3 : 0.01 to 0.07 NaOH : 0.07 HMI : 6 H2O.

[0026] The precursor was transferred to a hydrothermal reactor and allowed to crystallize in an oven at 150°C for 7 days. After filtration, washing, and drying, the precursor in the hydrothermal reactor yielded MCM-22(P) without template removal agent.

[0027] Example 1

[0028] 0.0523 g of ZrOCl2·8H2O and 2.0 g of MCM-22(P) were ground evenly in a mortar and calcined in a muffle furnace at 550 °C for 8 h to obtain Na-type 1% ZrO2 / MCM-22. Then, it was subjected to 1.0 mol·L⁻¹... -1 The NH4Cl aqueous solution was ion-exchanged three times, then dried and calcined in a muffle furnace at 550℃ for 4 hours to obtain H-type 1% ZrO2 / MCM-22.

[0029] Example 2

[0030] 0.0785 g of ZrOCl2·8H2O and 2.0 g of MCM-22(P) were ground evenly in a mortar and calcined in a muffle furnace at 550 °C for 8 h to obtain Na-type 3% ZrO2 / MCM-22. Then, it was subjected to 1.0 mol·L⁻¹... -1 The NH4Cl aqueous solution was ion-exchanged three times, then dried and calcined in a muffle furnace at 550℃ for 4 hours to obtain H-type 3% ZrO2 / MCM-22.

[0031] Example 3

[0032] 0.1308 g of ZrOCl2·8H2O and 2.0 g of MCM-22(P) were ground evenly in a mortar and calcined in a muffle furnace at 550 °C for 8 h to obtain Na-type 5% ZrO2 / MCM-22. Then, it was subjected to 1.0 mol·L⁻¹... -1 The NH4Cl aqueous solution was ion-exchanged three times, then dried and calcined in a muffle furnace at 550℃ for 4 hours to obtain H-type 5% ZrO2 / MCM-22.

[0033] Example 4

[0034] 0.0731 g of Zn(NO3)2·6H2O and 2.0 g of MCM-22(P) were ground evenly in a mortar and calcined in a muffle furnace at 550 °C for 8 h to obtain Na-type 1% Zr-MCM-22. Then, it was subjected to 1.0 mol·L⁻¹... -1 The NH4Cl aqueous solution was ion-exchanged three times, then dried and calcined in a muffle furnace at 550℃ for 4 hours to obtain H-type 1% ZnO2 / MCM-22.

[0035] Example 5

[0036] 0.2193 g of Zn(NO3)2·6H2O and 2.0 g of MCM-22(P) were ground evenly in a mortar and calcined in a muffle furnace at 550 °C for 8 h to obtain 3% ZnO2 / MCM-22. Then, it was further subjected to 1.0 mol·L⁻¹... -1 The NH4Cl aqueous solution was ion-exchanged three times, then dried and calcined in a muffle furnace at 550℃ for 4 hours to obtain H-type 3% ZnO2 / MCM-22.

[0037] Example 6

[0038] 0.3655 g of Zn(NO3)2·6H2O and 2.0 g of MCM-22(P) were ground evenly in a mortar and calcined in a muffle furnace at 550 °C for 8 h to obtain Na-type 5% ZnO2 / MCM-22. Then, it was subjected to 1.0 mol·L⁻¹... -1 The NH4Cl aqueous solution was ion-exchanged three times, then dried and calcined in a muffle furnace at 550℃ for 4 hours to obtain H-type 5% ZnO2 / MCM-22.

[0039] Example 7

[0040] 0.0274 g of Sn(NO3)2·6H2O and 2.0 g of MCM-22(P) were ground evenly in a mortar and calcined in a muffle furnace at 550 °C for 8 h to obtain Na-type 1% SnO2 / MCM-22. Then, it was subjected to 1.0 mol·L⁻¹... -1 The NH4Cl aqueous solution was ion-exchanged three times, then dried and calcined in a muffle furnace at 550℃ for 4 hours to obtain H-type 1% SnO2 / MCM-22.

[0041] Example 8

[0042] 0.0823 g of Sn(NO3)2·6H2O and 2.0 g of MCM-22(P) were ground evenly in a mortar and calcined in a muffle furnace at 550 °C for 8 h to obtain Na-type 3% SnO2 / MCM-22. Then, it was subjected to 1.0 mol·L⁻¹... -1 The NH4Cl aqueous solution was ion-exchanged three times, then dried and calcined in a muffle furnace at 550℃ for 4 hours to obtain H-type 3% SnO2 / MCM-22.

[0043] Example 9

[0044] 0.1372 g of Sn(NO3)2·6H2O and 2.0 g of MCM-22(P) were ground evenly in a mortar and calcined in a muffle furnace at 550 °C for 8 h to obtain Na-type 5% SnO2 / MCM-22. Then, it was subjected to 1.0 mol·L⁻¹... -1 The NH4Cl aqueous solution was ion-exchanged three times, then dried and calcined in a muffle furnace at 550℃ for 4 hours to obtain H-type 5% SnO2 / MCM-22.

[0045] The catalysts obtained in Examples 1-9 above were applied in the reaction of 2,5-DMF and AA to synthesize PX, and the specific applications are as follows:

[0046] Example 10

[0047] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (by mass) of H-type 1% ZrO2 / MCM-22 was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150 °C, the initial pressure was atmospheric pressure, and the reaction time was 3 h. After the reaction was completed, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0048] Example 11

[0049] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (H-type) 3% ZrO2 / MCM-22 (equivalent to 5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150℃, the initial pressure was atmospheric pressure, and the reaction time was 3 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0050] Example 12

[0051] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (H-type) ZrO2 / MCM-22 (equivalent to 5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150℃, the initial pressure was atmospheric pressure, and the reaction time was 3 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0052] Example 13

[0053] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (by mass) of H-type 1% ZnO2 / MCM-22 was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150 °C, the initial pressure was atmospheric pressure, and the reaction time was 3 h. After the reaction was completed, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0054] Example 14

[0055] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (H-type) 3% ZnO2 / MCM-22 (equivalent to 5% of the total reactant mass) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150℃, the initial pressure was atmospheric pressure, and the reaction time was 3 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0056] Example 15

[0057] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (H-type) ZnO2 / MCM-22 (equivalent to 5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150℃, the initial pressure was atmospheric pressure, and the reaction time was 3 h. After the reaction was completed, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0058] Example 16

[0059] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (by mass) of H-type 1% SnO2 / MCM-22 was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150 °C, the initial pressure was atmospheric pressure, and the reaction time was 3 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0060] Example 17

[0061] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (H-type) 3% SnO2 / MCM-22 (equivalent to 5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150℃, the initial pressure was atmospheric pressure, and the reaction time was 3 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0062] Example 18

[0063] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% H-type SnO2 / MCM-22 (equivalent to 5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150℃, the initial pressure was atmospheric pressure, and the reaction time was 3 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0064] Example 19

[0065] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (H-type) 3% SnO2 / MCM-22 (equivalent to 5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150℃, the initial pressure was atmospheric pressure, and the reaction time was 5 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0066] Example 20

[0067] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (H-type) 3% SnO2 / MCM-22 (equivalent to 5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150℃, the initial pressure was atmospheric pressure, and the reaction time was 10 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0068] Example 21

[0069] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (H-type) 3% SnO2 / MCM-22 (equivalent to 5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 170℃, the initial pressure was atmospheric pressure, and the reaction time was 5 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0070] Example 22

[0071] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and 5% (H-type) 3% SnO2 / MCM-22 (equivalent to 5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 190℃, the initial pressure was atmospheric pressure, and the reaction time was 5 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0072] Undetemplated MCM-22(P) was calcined in a muffle furnace at 550 °C for 8 h to obtain Na-type MCM-22 molecular sieve. Using 1.0 mol·L⁻¹ -1 The NH4Cl aqueous solution was subjected to three ion exchanges, followed by filtration, washing, and drying. The mixture was then calcined in a muffle furnace at 550°C for 4 hours to obtain H-type MCM-22 molecular sieve.

[0073] Comparative Example 1

[0074] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹.-1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and H-type MCM-22 (equivalent to 5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 150℃, the initial pressure was atmospheric pressure, and the reaction time was 5 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0075] Comparative Example 2

[0076] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and H-type MCM-22 (5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 170℃, the initial pressure was atmospheric pressure, and the reaction time was 5 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0077] Comparative Example 3

[0078] 2,5-DMF and AA were mixed at a molar ratio of 1:2, with a 2,5-DMF concentration of 0.3 mol·L⁻¹. -1 The concentration of AA is 0.6 mol·L⁻¹ -1 The solvent was n-heptane, and the total reaction volume was 25 mL. The mixture was transferred to a magnetically stirred reactor, and H-type MCM-22 (equivalent to 5% of the total mass of the reactants) was added. The reactor was purged three times with high-purity nitrogen. The reaction temperature was 190℃, the initial pressure was atmospheric pressure, and the reaction time was 5 h. After the reaction, the reactor was cooled in an ice-water bath. The main product was PX, and the byproducts were 2,5-hexanedione and 2,5-dimethylbenzoic acid.

[0079] The specific surface area and catalytic activity of the catalysts obtained in Examples 1-9 and those used in Comparative Examples 1-3 are compared, as shown in Table 1 below:

[0080] Table 1 Comparison of catalytic activity between Examples 10-22 and Comparative Examples 1-3

[0081]

[0082]

[0083] Table 1 shows that the catalytic activity of MCM-22 molecular sieve changed after modification. The most effective modified metal precursor was SnC2O4, with the best catalytic activity observed at a metal loading of 3%. However, the catalytic activity decreased when the loading reached 5%, possibly because the Sn species covered some of the Brønsted acid sites on the outer surface of the molecular sieve. Compared to Comparative Example 3, under the same reaction conditions, the 2,5-DMF conversion and PX selectivity of the H-type 3% SnO2 / MCM-22 were 15% and 19% higher, respectively, demonstrating a significant advantage.

[0084] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A process for the catalytic synthesis of para-xylene from o-xylene and methanol using a metal-modified MCM-22 molecular sieve, characterized in that The method uses 2,5-dimethylfuran and acrylic acid as reactants, and a metal-modified MCM-22 molecular sieve as a catalyst, wherein the molar ratio of 2,5-dimethylfuran to acrylic acid is 1:2; the mass of the metal-modified MCM-22 molecular sieve is 5% of the total mass of the reactants; the reaction is carried out in a magnetic stirring tank; the reaction temperature is 150-190°C, the initial reaction pressure is normal pressure, and the reaction time is 3-10 hours; and nitrogen is used as a protective gas. The metal-modified MCM-22 molecular sieve is any one of ZrO2 / MCM-22, ZnO / MCM-22 or SnO2 / MCM-22, and the preparation method is as follows: (1) uniformly grinding a metal precursor and a MCM-22(P) without removing a template in a mortar, and calcining in a muffle furnace at 550°C for 8 hours to obtain a Na-modified MCM-22 molecular sieve; (2) the Na-type modified MCM-22 molecular sieve obtained in step (1) is ion exchanged with 1.0 mol·L -1 NH4Cl aqueous solution for 3 times, and then is subjected to suction filtration, washing, drying, and calcination at 550 DEG C for 4 h in a muffle furnace to obtain the metal-modified MCM-22 molecular sieve.

2. The process for the catalytic synthesis of para-xylene according to claim 1, characterized in that The metal precursor in step (1) is any one of ZrOCl2·8H2O, Zn(NO3)2·6H2O or SnC2O4.

3. The process for the catalytic synthesis of para-xylene according to claim 1, characterized in that The MCM-22(P) without removing a template in step (1) is prepared as follows: (1) dissolving 0.40-2.80g of NaOH in deionized water at room temperature, then adding 1.66g of NaAlO2, and stirring for 1 hour to obtain a clear and transparent solution; (2) then slowly adding 6.94g of hexamethylene imine HMI to the solution obtained in step (1), continuing to stir for 0.5 hours after the addition is completed, slowly adding 48.06g of 25wt% silica sol under the condition of vigorous stirring using a peristaltic pump, adding 0.12g of seed crystals, and aging in a 25°C water bath for 24 hours to obtain a light yellowish brown precursor, wherein the molar ratio of the light yellowish brown precursor is: 0.2SiO2:0.0067Al2O3:0.01-0.07NaOH:0.07HMI:6H2O; (3) transferring the light yellowish brown precursor obtained in step (2) to a hydrothermal reaction kettle, and placing in a 150°C oven for crystallization for 7 days; (4) after the precursor crystallized in step (3) is subjected to suction filtration, washing and drying, the MCM-22(P) without removing a template is obtained.

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