A method for surface modification of a shape-selective catalyst of MCM-22 molecular sieve

Abstract

The present invention relates to a method for surface modification of a MCM-22 molecular sieve shape-selective catalyst, belonging to the technical field of chemical engineering catalysis. In this preparation method, a macromolecular organic acid is selected to selectively remove the Al sites on the outer surface of the MCM-22 molecular sieve, and then a macromolecular silyl group is grafted onto the hydroxyl defect sites generated on the outer surface of the molecular sieve due to dealumination. This method can avoid blocking the pores of MCM-22, eliminate the outer surface acidity while retaining the internal activity of the molecular sieve, and reduce the pore mouth size, thereby obtaining a MCM-22 molecular sieve shape-selective catalyst with high activity, high selectivity and high stability. When this catalyst is applied to the reaction of alkylation of toluene with dimethyl carbonate to synthesize p-xylene, the activity of the catalyst remains 36% within 20 hours, and the selectivity can reach up to 66% at most.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical catalysis, and particularly relates to a method for surface modification of a shape-selective catalyst of MCM-22 molecular sieve for toluene alkylation reaction. Background Art

[0002] p-Xylene (PX) is one of the basic organic raw materials in the petrochemical industry, mainly used to produce polyester, and is widely used in fields such as chemical fibers, plastics, pharmaceuticals, and pesticides. At present, the main synthesis methods of PX include aromatics joint production, toluene disproportionation and alkylation transfer, xylene isomerization, etc. However, the above methods have disadvantages such as high operating costs, low toluene utilization rate, and harsh separation conditions. In recent years, the synthesis of p-xylene by toluene alkylation has good industrial application prospects due to its short process flow, high PX selectivity, economic efficiency, etc.

[0003] MCM-22 molecular sieve is a commonly used catalyst for toluene alkylation due to its high catalytic activity for toluene and good selectivity effect. However, a large number of acidic sites on the outer surface of MCM-22 molecular sieve are prone to catalyze the isomerization of PX, reducing the selectivity of PX. To further improve the selectivity of PX, generally, the acidic sites on its outer surface are eliminated by molecular sieve modification, the pore size of the molecular sieve is further modified, the isomerization reaction on the catalyst surface is inhibited, and the shape-selective performance of the molecular sieve is increased. Commonly used methods for modifying MCM-22 molecular sieve include chemical vapor deposition, chemical liquid deposition, metal oxide modification, and pre-carbon deposition methods. Although these methods can cover the acidic sites on the outer surface and modify the pore orifice size, due to the low selectivity of the deposited or loaded substances, there are often problems such as blocking the pores of the molecular sieve and covering the internal active sites of the molecular sieve, which in turn lead to a decrease in the activity and stability of the catalyst.

[0004] Therefore, it is necessary to develop a method for modifying MCM-22 catalyst that can improve the selectivity of p-xylene while maintaining high activity and high stability for toluene alkylation reaction. Summary of the Invention

[0005] Aiming at the disadvantages of the existing modification technologies, such as being prone to blocking the pores of MCM-22, covering the internal active sites of the molecular sieve, and having low catalytic activity and stability of MCM-22, the present invention provides a method for modifying MCM-22 catalyst that can improve the selectivity of p-xylene while maintaining high activity and high stability for toluene alkylation reaction.

[0006] To solve the above technical problems, the surface modification method of the shape-selective catalyst of MCM-22 molecular sieve of the present invention is carried out according to the following steps:

[0007] (1) Place the H-type MCM-22 molecular sieve in a macromolecular organic acid solution with a certain concentration;

[0008] (2) Stir in an oil bath at 90 °C for 3 - 12 h, then cool, filter by suction, and wash with water until neutral.

[0009] (3) After drying, place it in a muffle furnace, heat up to 500 °C, and calcine for 2 h to obtain MCM-22 with the outer surface Al sites removed.

[0010] (4) Place the MCM-22 zeolite with the outer surface Al sites removed obtained in step (3) in the polytetrafluoroethylene inner lining of a crystallization kettle, add a silylation reagent, where the mass ratio of the silylation reagent to the H-type MCM-22 zeolite is 0.5 - 2:1.

[0011] (5) After complete impregnation, put it into an oven at 120 - 200 °C, let it stand for 12 - 48 h, then cool, filter by suction, wash with acetone and water until neutral, and after drying, obtain the shape-selective catalyst of surface-modified MCM-22 zeolite.

[0012] As a limitation of the present invention, the H-type MCM-22 zeolite described in the present invention is a self-made zeolite, and is specifically prepared according to the following steps:

[0013] (1) Dissolve 3.33 - 14.11 g of NaOH in deionized water, add 4.14 - 12.43 g of NaAlO2, and stir the solution until it is clear and transparent.

[0014] (2) Slowly add cyclohexylamine (HMI) and continue stirring. Slowly add silica sol using a peristaltic pump, and control the reactant ratio as: n(SiO2):n(Al2O3):n(NaOH):n(HMI):n(H2O) = 1:0.033 - 0.0167:0.15 - 0.35:0.35:35, and continue stirring to obtain a light milky yellow precursor.

[0015] (3) Pre-add MCM-22 seeds equivalent to 0.1% - 10% of the mass of SiO2 in the polytetrafluoroethylene inner lining of a crystallization kettle, transfer the precursor to the inner lining, and let it stand and crystallize in an oven at 120 - 170 °C for 7 days. After filtering by suction, washing, and drying, obtain a white powder without the template agent removed.

[0016] (4) Place the white powder obtained in step (3) in a muffle furnace, heat up to 550 °C, and calcine for 8 h to obtain Na-type MCM-22 zeolite.

[0017] (5) Ion-exchange the Na-type MCM-22 zeolite obtained in step (4) three times with 1 M NH4Cl solution, dry it, place it in a muffle furnace, heat up to 550 °C, and calcine for 4 h to obtain H-type MCM-22 zeolite.

[0018] As a definition of the present invention, the macromolecular organic acid in step (1) of the present invention is one of oxalic acid, citric acid, salicylic acid, and tartaric acid; the mass ratio of the H-type MCM-22 molecular sieve to the macromolecular organic acid solution is 10-100:1.

[0019] As a definition of the present invention, the silylating reagent in step (4) of the present invention is trimethylchlorosilane or triethylchlorosilane.

[0020] The shape-selective catalyst of the surface-modified MCM-22 molecular sieve of the present invention can be used for the alkylation of toluene and dimethyl carbonate to synthesize p-xylene. The specific application method is as follows: Place 1.0 g of the surface-modified MCM-22 molecular sieve shape-selective catalyst with a particle size of 20-30 mesh in a fixed-bed reactor, heat the vaporization chamber temperature to 150 °C, heat the reactor to 360-400 °C, and under the protection of inert gases Ar and N2, after the temperature reaches the set value, pump the raw materials toluene and dimethyl carbonate into the reactor at a molar ratio of 2-4:1 through a micro constant flow pump, and the mass space velocity is 5 h -1 , flow through the bed for reaction, and after condensation, obtain the reaction solution, and quantitatively analyze the toluene conversion rate and the selectivity of p-xylene by gas chromatography.

[0021] After adopting the above technical scheme, compared with other methods, the present invention has obtained the following beneficial effects:

[0022] By selecting macromolecular acids that are difficult to enter the pores and selectively removing the Al sites on the outer surface of the molecular sieve, the acidity on the outer surface can be accurately eliminated without affecting the active sites in the pores; selecting macromolecular silyl groups to selectively graft onto the hydroxyl defect sites generated on the outer surface of the molecular sieve due to Al removal can modify the pore mouth size without blocking the pores. This method can eliminate the acidity on the outer surface and modify the pore mouth size while avoiding blocking the pores of MCM-22 and retaining the internal activity of the molecular sieve, thereby obtaining an MCM-22 molecular sieve catalyst with high activity, high selectivity, and high stability. The shape-selective catalyst of the surface-modified MCM-22 molecular sieve can maintain an activity of 36% within 20 hours, and the selectivity can reach up to 66% at most. Description of the Drawings

[0023] Figure 1 is the infrared spectrum of the H-MCM-22 catalyst obtained in Example 1 and the C-TMCS-MCM-22 catalyst obtained in Example 8. It can be seen from the figure that compared with the unmodified H-MCM-22 catalyst, the modified C-TMCS-MCM-22 catalyst has a new absorption peak at 2964 cm -1 , which is the stretching vibration of the C-H bond in the methyl group, indicating that the silyl group has been successfully grafted onto the MCM-22 molecular sieve.

[0024] Figure 2The toluene conversion rate and PX selectivity obtained in Example 8 and Comparative Example 8 during the toluene alkylation reaction are shown in the figure. It can be seen that compared with the magnesium oxide supported on the C-MCM-22 catalyst prepared by the impregnation method, the toluene conversion rate and PX selectivity of the MCM-22 molecular sieve catalyst treated by dealumination and silanization are significantly improved and remain stable after 20 h of reaction. Detailed implementation mode

[0025] The present invention will be further described with reference to the following examples. However, it should be understood that these examples are only for illustrative purposes and should not be construed as limiting the implementation of the present invention.

[0026] Example 1

[0027] Self-made MCM-22 molecular sieve with SiO2 / Al2O3 of 30 was prepared according to the following molar ratio: n(SiO2):n(Al2O3):n(NaOH):n(HMI):n(H2O) = 1:0.033:0.15:0.35:35. First, 3.33 g of NaOH was dissolved in deionized water, and then 8.29 g of NaAlO2 was added. The solution was stirred until it was clear and transparent. Then, cyclohexylamine (HMI) was slowly added dropwise and stirring was continued. Then, silica sol was slowly added dropwise using a peristaltic pump to obtain a pale milky yellow precursor. 5% of the MCM-22 seeds by mass of SiO2 were pre-added to the polytetrafluoroethylene liner of the crystallization kettle. The precursor was transferred to the liner and then crystallized in an oven at 150 °C for 7 days. After filtration, washing, and drying, a white powder without template agent was obtained. It was placed in a muffle furnace, heated to 550 °C, and calcined for 8 h to obtain Na-type MCM-22 molecular sieve. Then, it was ion-exchanged three times with 1 M NH4Cl solution, dried, placed in a muffle furnace, heated to 550 °C, and calcined for 4 h to obtain H-MCM-22 molecular sieve.

[0028] Example 2

[0029] The H-type MCM-22 molecular sieve prepared in Example 1 was placed in an oxalic acid solution, where the mass ratio of the MCM-22 molecular sieve to the oxalic acid solution was 1:100. Stirring was carried out in an oil bath at 90 °C (with a reflux device) for 12 h, then it was cooled, filtered by suction, and washed with water until neutral. It was dried in an oven at 120 °C and finally placed in a muffle furnace, heated to 500 °C, and calcined for 2 h to obtain the C-MCM-22 catalyst.

[0030] Example 3

[0031] Using the H-type MCM-22 zeolite prepared in Example 1, place it in the polytetrafluoroethylene liner of the crystallization kettle, then add trimethylchlorosilane with a mass ratio twice that of the catalyst. After it is completely soaked, put it in an oven at 120 °C and let it stand for 12 h. Then, after cooling, suction filtration, washing with acetone and water until neutral, dry it in an oven at 120 °C to obtain the TMCS12-120-MCM-22 catalyst.

[0032] Example 4

[0033] Perform silylation treatment on the C-MCM-22 zeolite prepared in Example 2. Place the C-MCM-22 in the polytetrafluoroethylene liner of the crystallization kettle, then add triethylchlorosilane with a mass ratio twice that of the catalyst. After it is completely soaked, put it in an oven at 120 °C and let it stand for 12 h. Then, after cooling, suction filtration, washing with acetone and water until neutral, dry it in an oven at 120 °C to obtain the C-TESC12-120-MCM-22 catalyst.

[0034] Example 5

[0035] Perform silylation treatment on the C-MCM-22 zeolite prepared in Example 2. Place the C-MCM-22 in the polytetrafluoroethylene liner of the crystallization kettle, then add trimethylchlorosilane with a mass ratio twice that of the catalyst. After it is completely soaked, put it in an oven at 120 °C and let it stand for 12 h. Then, after cooling, suction filtration, washing with acetone and water until neutral, dry it in an oven at 120 °C to obtain the C-TMCS12-120-MCM-22 catalyst.

[0036] Example 6

[0037] Perform silylation treatment on the C-MCM-22 zeolite prepared in Example 2. Place the C-MCM-22 in the polytetrafluoroethylene liner of the crystallization kettle, then add trimethylchlorosilane with a mass ratio twice that of the catalyst. After it is completely soaked, put it in an oven at 160 °C and let it stand for 12 h. Then, after cooling, suction filtration, washing with acetone and water until neutral, dry it in an oven at 120 °C to obtain the C-TMCS12-160-MCM-22 catalyst.

[0038] Example 7

[0039] Perform silylation treatment on the C-MCM-22 zeolite prepared in Example 2. Place the C-MCM-22 in the polytetrafluoroethylene liner of the crystallization kettle, then add trimethylchlorosilane with a mass ratio twice that of the catalyst. After it is completely soaked, put it in an oven at 200 °C and let it stand for 12 h. Then, after cooling, suction filtration, washing with acetone and water until neutral, dry it in an oven at 120 °C to obtain the C-TMCS12-200-MCM-22 catalyst.

[0040] Example 8

[0041] The C-MCM-22 molecular sieve prepared in Example 2 was subjected to silylation treatment. The C-MCM-22 was placed in the polytetrafluoroethylene liner of the crystallization kettle, and then trimethylchlorosilane with a mass ratio twice that of the catalyst was added. After it was completely soaked, it was placed in an oven at 200 °C and left standing for 24 h. Then, after cooling, suction filtration, washing with acetone and water until neutral, it was dried in an oven at 120 °C to obtain the C-TMCS24-200-MCM-22 catalyst.

[0042] Example 9

[0043] The C-MCM-22 molecular sieve prepared in Example 2 was subjected to silylation treatment. The C-MCM-22 was placed in the polytetrafluoroethylene liner of the crystallization kettle, and then trimethylchlorosilane with a mass ratio twice that of the catalyst was added. After it was completely soaked, it was placed in an oven at 200 °C and left standing for 48 h. Then, after cooling, suction filtration, washing with acetone and water until neutral, it was dried in an oven at 120 °C to obtain the C-TMCS48-200-MCM-22 catalyst.

[0044] The above examples were applied to the reaction of alkylation of toluene with dimethyl carbonate to synthesize p-xylene. The specific steps were as follows: 1.0 g of the surface-modified MCM-22 molecular sieve shape-selective catalyst with a particle size of 20-30 mesh was placed in a fixed-bed reactor. The temperature of the vaporization chamber was raised to 150 °C, and the temperature of the reactor was raised to 360-400 °C. Under the protection of inert gases Ar and N2, after the temperature reached the set value, the raw materials toluene and dimethyl carbonate were pumped into the reactor at a molar ratio of 2-4:1 by a micro constant flow pump, and the mass space velocity was 5 h -1 , flowed through the bed for reaction, and the reaction solution was obtained after condensation. The toluene conversion rate and the selectivity of p-xylene were quantitatively analyzed by gas chromatography. The reaction conditions, toluene conversion rate and p-xylene selectivity are shown in Table 1.

[0045] Table 1 Comparison of catalytic activities of different catalysts

[0046]

[0047] Comparative Example 1

[0048] A 5% SiO2-supported MCM-22 catalyst was prepared by the impregnation method. A certain amount of the H-type MCM-22 molecular sieve prepared in Example 1 was taken and placed in a tetraethyl orthosilicate solution. After it was mixed evenly, a cyclohexane solution with a mass ratio 10 times that of the molecular sieve was added. The mixed solution was stirred for 20 min, and then it was placed in an oil bath at 70 °C to be evaporated to dryness, and finally dried overnight in an oven at 120 °C to obtain the 5% SiO2 / MCM-22 catalyst.

[0049] Comparative Example 2

[0050] The 10% SiO₂ supported MCM-22 catalyst was prepared by the impregnation method. A certain amount of the H-type MCM-22 molecular sieve prepared in Example 1 was placed in a tetraethyl orthosilicate solution. After mixing evenly, a cyclohexane solution with a mass ratio of 10 times that of the molecular sieve was added. The mixed solution was stirred for 20 min, then evaporated to dryness in an oil bath at 70 °C, and finally dried overnight in an oven at 120 °C to obtain the 10% SiO₂ / MCM-22 catalyst.

[0051] Comparative Example 3

[0052] The 5% MgO supported MCM-22 catalyst was prepared by the incipient wetness impregnation method. A magnesium nitrate solution with a certain concentration was prepared. A certain amount of the H-MCM-22 molecular sieve prepared in Example 1 was placed in a beaker, and the magnesium nitrate solution was evenly dropped into the beaker containing the MCM-22 molecular sieve catalyst with a pipette. After complete absorption, it was left standing for 2 h, dried overnight in an oven at 80 °C, and finally calcined in a muffle furnace at 550 °C for 5 h to obtain the 5% MgO / MCM-22 catalyst.

[0053] Comparative Example 4

[0054] The 10% MgO supported MCM-22 catalyst was prepared by the incipient wetness impregnation method. A magnesium nitrate solution with a certain concentration was prepared. A certain amount of the H-MCM-22 molecular sieve prepared in Example 1 was placed in a beaker, and the magnesium nitrate solution was evenly dropped into the beaker containing the MCM-22 molecular sieve catalyst with a pipette. After complete absorption, it was left standing for 2 h, dried overnight in an oven at 80 °C, and finally placed in a muffle furnace, heated to 550 °C, and calcined for 5 h to obtain the 10% MgO / MCM-22 catalyst.

[0055] Comparative Example 5

[0056] The 15% MgO supported MCM-22 catalyst was prepared by the incipient wetness impregnation method. A magnesium nitrate solution with a certain concentration was prepared. A certain amount of the H-MCM-22 molecular sieve prepared in Example 1 was placed in a beaker, and the magnesium nitrate solution was evenly dropped into the beaker containing the MCM-22 molecular sieve catalyst with a pipette. After complete absorption, it was left standing for 2 h, dried overnight in an oven at 80 °C, and finally placed in a muffle furnace, heated to 550 °C, and calcined for 5 h to obtain the 15% MgO / MCM-22 catalyst.

[0057] Comparative Example 6

[0058] The 5% MgO-supported C-MCM-22 catalyst was prepared by the equal-volume impregnation method. A magnesium nitrate solution with a certain concentration was prepared. A certain amount of the C-MCM-22 molecular sieve prepared in Example 2 was placed in a beaker. The magnesium nitrate solution was evenly dropped into the beaker containing the C-MCM-22 molecular sieve catalyst with a pipette. After it was completely absorbed, it was left standing for 2 h, dried overnight in an oven at 80 °C, and finally placed in a muffle furnace. The temperature was raised to 550 °C and calcined for 5 h to obtain the 5% MgO / C-MCM-22 catalyst.

[0059] Comparative Example 7

[0060] The 10% MgO-supported C-MCM-22 catalyst was prepared by the equal-volume impregnation method. A magnesium nitrate solution with a certain concentration was prepared. A certain amount of the C-MCM-22 molecular sieve prepared in Example 2 was placed in a beaker. The magnesium nitrate solution was evenly dropped into the beaker containing the C-MCM-22 molecular sieve catalyst with a pipette. After it was completely absorbed, it was left standing for 2 h, dried overnight in an oven at 80 °C, and finally placed in a muffle furnace. The temperature was raised to 550 °C and calcined for 5 h to obtain the 10% MgO / C-MCM-22 catalyst.

[0061] Comparative Example 8

[0062] The 15% MgO-supported C-MCM-22 catalyst was prepared by the equal-volume impregnation method. A magnesium nitrate solution with a certain concentration was prepared. A certain amount of the C-MCM-22 molecular sieve prepared in Example 2 was placed in a beaker. The magnesium nitrate solution was evenly dropped into the beaker containing the C-MCM-22 molecular sieve catalyst with a pipette. After it was completely absorbed, it was left standing for 2 h, dried overnight in an oven at 80 °C, and finally placed in a muffle furnace. The temperature was raised to 550 °C and calcined for 5 h to obtain the 15% MgO / C-MCM-22 catalyst.

[0063] The above comparative examples were applied to the reaction of alkylation of toluene with dimethyl carbonate to synthesize p-xylene. The specific steps were as follows: 1.0 g of a surface-modified MCM-22 molecular sieve shape-selective catalyst with a particle size of 20 - 30 mesh was placed in a fixed-bed reactor. The temperature of the vaporization chamber was raised to 150 °C, and the temperature of the reactor was raised to 400 °C. Under the protection of inert gases Ar and N2, after the temperature reached the set value, the raw materials toluene and dimethyl carbonate were pumped into the reactor at a molar ratio of 4:1 by a micro constant-flow pump, and the mass space velocity was 5 h -1 , flowed through the bed for reaction, and the reaction solution was obtained after condensation. The toluene conversion rate and the selectivity of p-xylene were quantitatively analyzed by gas chromatography. The reaction conditions, toluene conversion rate, and p-xylene selectivity are shown in Table 2.

[0064] Table 2 Comparison of catalytic activities of examples and comparative examples

[0065]

[0066] It can be seen from Table 1 and Table 2 that the MCM-22 catalyst treated by dealumination and silylation is used in the present invention to catalyze the reaction of toluene and dimethyl carbonate to produce p-xylene. Compared with the catalyst prepared by the impregnation method, the selectivity of p-xylene can be improved under the condition that the conversion rate of toluene remains basically unchanged. The selectivity of p-xylene can reach 66%, significantly improving the yield of p-xylene.

[0067] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. Use of a surface-modified MCM-22 molecular sieve shape-selective catalyst in the alkylation of toluene with dimethyl carbonate to synthesize p-xylene, characterized in that, The surface-modified MCM-22 molecular sieve shape-selective catalyst is prepared by the following method: (1) Place the H-type MCM-22 molecular sieve in a macromolecular organic acid solution with a certain concentration; (2) Stir in an oil bath at 90 °C for 3 - 12 h, then cool, filter by suction, and wash with water until neutral; (3) After drying, place it in a muffle furnace, heat up to 500 °C, and calcine for 2 h to obtain the MCM-22 molecular sieve with the outer surface Al sites removed; (4) Place the MCM-22 molecular sieve with the outer surface Al sites removed obtained in step (3) in the PTFE liner of a crystallization kettle, and add a silylation reagent, where the mass ratio of the silylation reagent to the MCM-22 molecular sieve is 0.5 - 2:1; the silylation reagent is trimethylchlorosilane or triethylchlorosilane; (5) After complete impregnation, place it in an oven at 120 - 200 °C, stand for 12 - 48 h, then cool, filter by suction, wash with acetone and water until neutral, and dry to obtain the surface-modified MCM-22 molecular sieve shape-selective catalyst.

2. The application according to claim 1, wherein The H-type MCM-22 molecular sieve described above is a self-made molecular sieve, and this molecular sieve is specifically prepared according to the following steps: (1) Dissolve 3.33 - 14.11 g of NaOH in deionized water, add 4.14 - 12.43 g of NaAlO2, and stir the solution until it is clear and transparent; (2) Slowly dropwise add cyclohexylamine HMI and continue stirring, and slowly dropwise add silica sol using a peristaltic pump, controlling the molar ratio of the reactants as: SiO2:Al2O3:NaOH:HMI:H2O = 1:0.033 - 0.0167:0.15 - 0.35:0.35:35, and continue stirring to obtain a light milky yellow precursor; (3) Pre-add MCM-22 seeds accounting for 0.1% - 10% of the mass of SiO2 in the PTFE liner of a crystallization kettle, transfer the precursor to the liner, stand for crystallization in an oven at 120 - 170 °C for 7 days, filter by suction, wash, and dry to obtain a white powder without the template agent removed; (4) Place the white powder obtained in step (3) in a muffle furnace, heat up to 550 °C, and calcine for 8 h to obtain the Na-type MCM-22 molecular sieve; (5) The Na-type MCM-22 molecular sieve obtained in step (4) is ion-exchanged three times with 1 mol•L -1 NH4Cl solution, dried, placed in a muffle furnace, heated to 550 °C, and calcined for 4 h to obtain the H-type MCM-22 molecular sieve.

3. The application according to claim 1, characterized in that The macromolecular organic acid described in step (1) is one of oxalic acid, citric acid, salicylic acid, or tartaric acid.

4. The application according to claim 1, wherein The mass ratio of the H-type MCM-22 molecular sieve to the macromolecular organic acid solution in step (1) is 10 - 100:

1.

5. The application according to claim 1, wherein The specific application method of the surface-modified MCM-22 molecular sieve shape-selective catalyst is as follows: Place 1.0 g of the surface-modified MCM-22 molecular sieve shape-selective catalyst with a particle size of 20-30 mesh in a fixed-bed reactor. Heat the vaporization chamber temperature to 150 °C and the reactor temperature to 360-400 °C. Under the protection of inert gases Ar and N2, after the temperature reaches the set value, pump the raw materials toluene and dimethyl carbonate into the reactor through a micro constant flow pump at a molar ratio of 2-4:1, and the mass space velocity is 5 h -1 . Flow through the bed for reaction, and after condensation, obtain the reaction liquid. Use gas chromatography to quantitatively analyze the toluene conversion rate and the selectivity of p-xylene.

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