A catalyst for synthesizing 2,6-dimethylphenol and a preparation method thereof

Abstract

The application discloses a catalyst for synthesizing 2,6-dimethylphenol and a preparation method thereof, and relates to the technical field of organic synthesis catalysis. The catalyst comprises a composite catalytic system and an active component loaded in the composite catalytic system. The composite catalytic system is a mixed filler of cerium modified molecular sieves and molecularly imprinted polymers. The active component is a combination of iron salt and magnesium salt. The catalyst for synthesizing 2,6-dimethylphenol and the preparation method thereof can greatly improve the yield of 2,6-dimethylphenol through synergistic catalysis of the iron salt and the magnesium salt, shape selection and screening of the cerium modified molecular sieves and synergistic effect of the molecularly imprinted polymers, and is significantly superior to traditional catalysts. The selectivity of 2,6-dimethylphenol is significantly improved through the shape selection of the cerium modified molecular sieves and the selective adsorption of the molecularly imprinted polymers on o-cresol.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis catalysis technology, specifically to a catalyst for the synthesis of 2,6-dimethylphenol and its preparation method. Background Technology

[0002] 2,6-Dimethylphenol is an important organic chemical intermediate widely used in the synthesis of polyphenylene ether resins, epoxy resins, pharmaceutical intermediates, rubber antioxidants, and other products. Currently, the mainstream industrial process for synthesizing 2,6-dimethylphenol is the gas-phase alkylation reaction of phenol and methanol. This process has advantages such as readily available raw materials, mild reaction conditions, and environmental friendliness; however, the key issue is the poor performance of the catalyst. While various catalysts currently used in the industrial synthesis of 2,6-dimethylphenol from methanol and phenol have been applied, they still have significant shortcomings in terms of activity stability, selectivity control, resistance to carbon deposition, and process adaptability.

[0003] The catalysts used in the prior art for this reaction mainly include metal oxide catalysts and molecular sieve supported metal catalysts. For example, single HZSM-5 molecular sieve catalysts can suppress the formation of macromolecular byproducts to a certain extent by utilizing their shape selectivity, but they have problems such as uneven distribution of active centers and severe carbon deposition, which leads to a rapid decline in catalyst activity, short service life, and rapid decline in activity after continuous operation, requiring frequent regeneration or replacement. While catalysts supported on metal salts such as iron and magnesium can improve reaction activity, they produce a variety of byproducts (such as 2,4-dimethylphenol, 3,5-dimethylphenol, polyalkylated phenols, etc.), and the selectivity for the target product 2,6-dimethylphenol is less than 80%. In addition, traditional catalysts cannot effectively control the formation of the reaction byproduct o-cresol, resulting in low conversion rate of 2,6-dimethylphenol, low raw material utilization, many byproducts, difficult separation, and increased subsequent separation costs.

[0004] Therefore, developing a catalyst that combines high activity, high selectivity, strong stability, and high raw material utilization is key to solving the pain points in the synthesis process of 2,6-dimethylphenol and is of great significance to promoting technological progress in this field. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a catalyst for the synthesis of 2,6-dimethylphenol and its preparation method, solving the technical defects of existing catalysts such as severe carbon deposition and numerous by-products. This invention achieves multiple functional integrations of "catalytic activity - shape-selective sieving - carbon deposition inhibition - raw material reuse" through component composite synergistic design, significantly improving the reaction effect and achieving high selectivity, high activity and long lifespan. At the same time, it can effectively utilize the by-product o-cresol, significantly improving the yield of 2,6-dimethylphenol.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: a catalyst for synthesizing 2,6-dimethylphenol, comprising a composite catalytic system and an active component supported in the composite catalytic system, wherein the composite catalytic system is a mixture of cerium-modified molecular sieve and molecularly imprinted polymer, the active component is a combination of iron salt and magnesium salt, the mass fraction of cerium in the cerium-modified molecular sieve is 0.5%-5%, the total loading of the iron salt and magnesium salt is 5%-15% of the mass of the cerium-modified molecular sieve, and the molar ratio of the iron salt to the magnesium salt is 1:0.5-3, and the mixing mass ratio of the cerium-modified molecular sieve to the molecularly imprinted polymer is 1:0.2-1; The molecularly imprinted polymer is prepared using o-cresol as a template molecule, combined with functional monomers, crosslinking agents and initiators, and the molar ratio of template molecule, functional monomers and crosslinking agents is 1:2-8:10-40.

[0007] Preferably, the iron salt is selected from one or more of ferric nitrate, ferric chloride, and ferric sulfate.

[0008] Preferably, the magnesium salt is selected from one or more of magnesium nitrate, magnesium chloride, and magnesium sulfate.

[0009] Preferably, the carrier of the cerium-modified molecular sieve is selected from HZSM-5 molecular sieve or Beta molecular sieve, and the raw material for preparing the cerium-modified molecular sieve is a cerium source compound, which is selected from cerium nitrate, cerium chloride or cerium oxalate.

[0010] Preferably, the functional monomer is one or more of methacrylic acid, acrylamide, or 4-vinylpyridine.

[0011] Preferably, the crosslinking agent is one of ethylene glycol dimethacrylate or divinylbenzene, and the initiator is one of azobisisobutyronitrile or benzoyl peroxide.

[0012] This invention also provides a method for preparing a catalyst for the synthesis of 2,6-dimethylphenol, specifically comprising the following steps: S1. Preparation of cerium-modified molecular sieves: The molecular sieve support is pretreated by calcining at 500-600℃ for 2-4h. After cooling, an aqueous solution of cerium source compound with a concentration of 0.1-1.0mol / L is added, and the mixture is stirred and impregnated at 50-80℃ for 4-12h. Then, the moisture is removed by vacuum drying, and the mixture is dried at 100-120℃ for 6-12h. Finally, the mixture is calcined at 550-650℃ for 3-6h to obtain cerium-modified molecular sieves. S2. Loading of active components: The cerium-modified molecular sieve prepared in step S1 is added to a mixed aqueous solution of iron salt and magnesium salt with a concentration of 0.05-0.5 mol / L. The mixture is stirred and impregnated at 60-90℃ for 6-18 h. After vacuum drying to remove water, it is dried at 110-130℃ for 8-16 h to obtain cerium-modified molecular sieve loaded with iron and magnesium salt. S3. Preparation of molecularly imprinted polymer: The template molecule o-cresol, functional monomer, and crosslinking agent are dissolved in an organic solvent, ultrasonically dispersed for 10-30 min, and nitrogen gas is introduced to remove oxygen for 20-40 min. Then, an initiator is added, and the mixture is polymerized at 60-80℃ for 8-24 h. After the reaction is completed, the product is ground and sieved, and the template molecule is removed by elution with an eluent. The washing continues until no o-cresol is detected in the eluent. After drying, the molecularly imprinted polymer is obtained. S4. Preparation of composite catalyst: The cerium-modified molecular sieve loaded with iron and magnesium salts obtained in step S2 is mixed with the molecularly imprinted polymer obtained in step S3 at a set mass ratio. 5%-15% of the total mass of the mixture is added as a binder. After stirring evenly, the mixture is extruded and dried at 120-150℃ for 4-8 hours, calcined at 500-600℃ for 2-4 hours, and then cooled to obtain the target catalyst.

[0013] Preferably, the binder in step S4 is either aluminum sol or silica sol.

[0014] Preferably, in step S3, the organic solvent is selected from toluene, acetonitrile, and chloroform, and the eluent is a mixed solution of methanol and acetic acid, with a volume ratio of methanol to acetic acid of 3-5:1.

[0015] The present invention also provides an application of a catalyst for the synthesis of 2,6-dimethylphenol in the synthesis of 2,6-dimethylphenol, specifically: the catalyst is packed into a fixed-bed reactor, using phenol and methanol as raw materials, with a raw material molar ratio of 1:2-1:6, a reaction temperature of 350-450℃, and a reaction pressure of 0.1-0.5MPa. After the raw materials are vaporized, they are introduced into the reactor for alkylation reaction to generate 2,6-dimethylphenol.

[0016] (III) Beneficial Effects This invention provides a catalyst for the synthesis of 2,6-dimethylphenol and a method for its preparation. Compared with the prior art, it has the following advantages: (1) The catalyst for the synthesis of 2,6-dimethylphenol and its preparation method, through the synergistic catalysis of iron salt and magnesium salt, the shape-selective sieving of cerium-modified molecular sieve and the synergistic effect of molecularly imprinted polymer, greatly improves the selectivity of 2,6-dimethylphenol, which is significantly better than traditional catalysts.

[0017] (2) The catalyst used to synthesize 2,6-dimethylphenol and its preparation method effectively inhibited carbon deposition in the catalyst through cerium modification, and the service life was greatly extended.

[0018] (3) The catalyst for the synthesis of 2,6-dimethylphenol and its preparation method significantly improve the selectivity of 2,6-dimethylphenol through the shape-selective effect of cerium-modified molecular sieve and the selective adsorption of o-cresol by molecularly imprinted polymer. The residence time is extended by the specific adsorption of o-cresol by molecularly imprinted polymer, so that the unreacted o-cresol is fully converted and the raw material loss is reduced. The molecularly imprinted polymer adsorbs o-cresol and promotes its re-alkylation, so that the by-product o-cresol is effectively converted into the target product and the raw material utilization rate is improved.

[0019] (4) The catalyst for the synthesis of 2,6-dimethylphenol and its preparation method are simple to prepare. The mature processes such as impregnation and polymerization are easy to operate, cost controllable, and easy to scale up for industrial production. Attached Figure Description

[0020] Figure 1 This is a flowchart of the preparation method of the catalyst used in the synthesis of 2,6-dimethylphenol according to the present invention; Figure 2 This is a bar chart comparing the selectivity of 2,6-dimethylphenol for each catalyst in this invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figures 1 to 2 The present invention provides five technical solutions: a catalyst for synthesizing 2,6-dimethylphenol and its preparation method, specifically including the following embodiments: Example 1: A method for preparing a catalyst for the synthesis of 2,6-dimethylphenol, comprising the following steps: S1. Preparation of cerium-modified HZSM-5 molecular sieve: Take 10g of HZSM-5 molecular sieve (silicon-to-aluminum ratio 50), place it in a muffle furnace, and calcine at 550℃ for 3h to remove surface adsorbed water and impurities. After cooling to room temperature, transfer it to a three-necked flask, add 50mL of aqueous solution containing 0.8g of cerium nitrate hexahydrate, and impregnate it at 60℃ and 200r / min for 8h. Remove the water by vacuum drying, place the solid product in an oven and dry at 110℃ for 10h, and finally place it in a muffle furnace again and calcine at 600℃ for 4h to obtain cerium-modified HZSM-5 molecular sieve with a cerium mass fraction of 2%. S2. Loading of active components: Weigh 8g of the cerium-modified HZSM-5 molecular sieve prepared in step S1, add 60mL of a mixed aqueous solution containing 1.2g of ferric nitrate nonahydrate and 0.6g of magnesium nitrate hexahydrate, stir and impregnate at 70℃ and 250r / min for 12h, remove moisture by vacuum drying, and dry at 120℃ for 12h to obtain the cerium-modified molecular sieve loaded with iron and magnesium salts; S3. Preparation of molecularly imprinted polymer: Weigh 0.5g of o-cresol, 1.8g of methacrylic acid, and 8.5g of ethylene glycol dimethacrylate in a molar ratio of 1:4:20. Dissolve in 50mL of toluene and ultrasonically disperse for 20min until homogeneous. Purge with nitrogen for 30min to remove oxygen from the system. Add 0.2g of azobisisobutyronitrile. Seal and place in a 70℃ constant temperature water bath for polymerization for 16h. After the reaction is complete, remove the product, grind and pass through an 80-mesh sieve. Elute with a methanol-acetic acid mixture (volume ratio 4:1) in a Soxhlet extractor for 8h until no o-cresol peak is detected in the eluent by high performance liquid chromatography (HPLC). Dry the product in a 60℃ vacuum drying oven for 8h to obtain the molecularly imprinted polymer. S4. Preparation of composite catalyst: The cerium-modified molecular sieve loaded with iron and magnesium salts obtained in step S2 is mixed with the molecularly imprinted polymer obtained in step S3 at a mass ratio of 1:0.5. 1.5g of aluminum sol binder is added and stirred evenly. The mixture is then extruded into strips (2mm in diameter) using an extruder. The formed catalyst is placed in an oven and dried at 130℃ for 6h. Subsequently, it is placed in a muffle furnace and calcined at 550℃ for 3h. After cooling to room temperature, the target catalyst C1 is obtained.

[0023] Catalyst C1 was packed into a fixed-bed reactor to synthesize 2,6-dimethylphenol by alkylation of phenol and methanol. The reaction conditions were: phenol to methanol molar ratio of 1:4, reaction temperature of 400℃, and reaction pressure of 0.3MPa. After continuous operation for 24 hours, the catalytic performance test results were as follows: the selectivity of 2,6-dimethylphenol was 93.2%, the yield was 85.3%, the conversion rate of phenol was 91.5%, and the yield of the final product o-cresol was 6.22%.

[0024] Example 2: A method for preparing a catalyst for the synthesis of 2,6-dimethylphenol, specifically: in step S1, the amount of cerium nitrate hexahydrate added is 0.4 g, and the cerium mass fraction is 1%; in step S2, the amount of ferric nitrate nonahydrate added is 1.0 g, the amount of magnesium nitrate hexahydrate added is 0.8 g, and the molar ratio of iron salt to magnesium salt is 1:1; the other steps are exactly the same as in Example 1, to obtain catalyst C2.

[0025] Catalytic performance test results: phenol conversion rate was 88.7%, 2,6-dimethylphenol selectivity was 91.5%, and yield was 81.2%; the yield of the final product o-cresol was 7.54%.

[0026] Example 3: A method for preparing a catalyst for the synthesis of 2,6-dimethylphenol, specifically: in step S1, the molecular sieve support is changed to a Beta molecular sieve (silicon-to-aluminum ratio 30); in step S4, the mass ratio of the cerium-modified molecular sieve loaded with iron and magnesium salts to the molecularly imprinted polymer is 1:0.3; the other steps are exactly the same as in Example 1, and catalyst C3 is obtained.

[0027] Catalytic performance test results: phenol conversion rate 86.3%, 2,6-dimethylphenol selectivity 92.1%, yield 79.5%; the yield of the final product o-cresol is 6.82%.

[0028] Example 4: A catalyst for synthesizing 2,6-dimethylphenol, comprising a composite catalytic system and an active component supported in the composite catalytic system. The composite catalytic system is a mixed packing of cerium-modified molecular sieve and molecularly imprinted polymer. The active component is a combination of iron salt and magnesium salt. The mass fraction of cerium in the cerium-modified molecular sieve is 0.5%. The total loading of iron salt and magnesium salt is 5% of the mass of the cerium-modified molecular sieve, and the molar ratio of iron salt to magnesium salt is 1:0.5. The mixing mass ratio of cerium-modified molecular sieve and molecularly imprinted polymer is 1:0.2. The iron salt is a combination of ferric nitrate, ferric chloride, and ferric sulfate. The magnesium salt is a combination of magnesium nitrate, magnesium chloride, and magnesium sulfate. The support for the cerium-modified molecular sieve is HZSM-5 molecular sieve. The raw material for preparing the cerium-modified molecular sieve is a cerium source compound, which is cerium chloride. Molecularly imprinted polymers are prepared using o-cresol as a template molecule, combined with functional monomers, crosslinking agents, and initiators. The molar ratio of the template molecule, functional monomer, and crosslinking agent is 1:2:10. The functional monomer is a combination of methacrylic acid, acrylamide, and 4-vinylpyridine. The crosslinking agent is ethylene glycol dimethacrylate, and the initiator is azobisisobutyronitrile.

[0029] This invention also provides a method for preparing a catalyst for the synthesis of 2,6-dimethylphenol, specifically including the following steps: S1. Preparation of cerium-modified molecular sieve: The molecular sieve support was pretreated by calcining at 500℃ for 2h. After cooling, an aqueous solution of cerium source compound with a concentration of 0.1mol / L was added. The mixture was stirred and impregnated at 50℃ for 4h. Then, the water was removed by vacuum drying. The mixture was dried at 100℃ for 6h. Finally, it was calcined at 550℃ for 3h to obtain the cerium-modified molecular sieve. S2, Loading of active components: The cerium-modified molecular sieve prepared in step S1 was added to a mixed aqueous solution of iron salt and magnesium salt with a concentration of 0.05 mol / L, stirred and impregnated at 60°C for 6 h, vacuum dried to remove moisture, and dried at 110°C for 8 h to obtain cerium-modified molecular sieve loaded with iron and magnesium salt. S3. Preparation of molecularly imprinted polymer: The template molecule o-cresol, functional monomer, and crosslinking agent were dissolved in an organic solvent, ultrasonically dispersed for 10 min, and nitrogen gas was introduced to remove oxygen for 20 min. Then, an initiator was added, and the mixture was polymerized at 60℃ for 8 h. After the reaction was completed, the product was ground and sieved. The template molecule was removed by elution with an eluent. The washing was continued until no o-cresol was detected in the eluent. After drying, the molecularly imprinted polymer was obtained. The organic solvent was toluene, and the eluent was a mixed solution of methanol and acetic acid with a volume ratio of 3:1. S4. Preparation of composite catalyst: The cerium-modified molecular sieve loaded with iron and magnesium salts obtained in step S2 is mixed with the molecularly imprinted polymer obtained in step S3 at a set mass ratio. 5% of the total mass of the mixture is added as a binder. After stirring evenly, the mixture is extruded and dried at 120°C for 4 hours, calcined at 500°C for 2 hours, and cooled to obtain the target catalyst C4. The binder is aluminum sol.

[0030] This invention also provides a method for preparing a catalyst for the synthesis of 2,6-dimethylphenol. The application of the prepared catalyst in the synthesis of 2,6-dimethylphenol is as follows: the catalyst is packed into a fixed-bed reactor, using phenol and methanol as raw materials with a raw material molar ratio of 1:2, a reaction temperature of 350°C, and a reaction pressure of 0.1 MPa. After vaporization, the raw materials are introduced into the reactor for alkylation reaction to generate 2,6-dimethylphenol.

[0031] Example 5: A catalyst for synthesizing 2,6-dimethylphenol, comprising a composite catalytic system and an active component supported in the composite catalytic system. The composite catalytic system is a mixed packing of cerium-modified molecular sieve and molecularly imprinted polymer. The active component is a combination of iron salt and magnesium salt. The mass fraction of cerium in the cerium-modified molecular sieve is 5%. The total loading of iron salt and magnesium salt is 15% of the mass of the cerium-modified molecular sieve, and the molar ratio of iron salt to magnesium salt is 1:3. The mixing mass ratio of cerium-modified molecular sieve to molecularly imprinted polymer is 1:1. The iron salt is a combination of ferric nitrate and ferric chloride, and the magnesium salt is a combination of magnesium nitrate and magnesium chloride. The support for the cerium-modified molecular sieve is selected from HZSM-5 molecular sieve, and the raw material for preparing the cerium-modified molecular sieve is a cerium source compound, wherein the cerium source compound is cerium oxalate. Molecularly imprinted polymers are prepared using o-cresol as a template molecule, combined with functional monomers, crosslinking agents, and initiators. The molar ratio of the template molecule, functional monomer, and crosslinking agent is 1:8:40. The functional monomer is a combination of methacrylic acid and 4-vinylpyridine, the crosslinking agent is ethylenedivinylbenzene, and the initiator is benzoyl peroxide.

[0032] This invention also provides a method for preparing a catalyst for the synthesis of 2,6-dimethylphenol, specifically including the following steps: S1. Preparation of cerium-modified molecular sieve: The molecular sieve support was pretreated by calcining at 600℃ for 4h. After cooling, an aqueous solution of cerium source compound with a concentration of 1.0mol / L was added. The mixture was stirred and impregnated at 80℃ for 12h. Then, the water was removed by vacuum drying. The mixture was dried at 120℃ for 12h. Finally, it was calcined at 650℃ for 6h to obtain the cerium-modified molecular sieve. S2. Loading of active components: The cerium-modified molecular sieve prepared in step S1 is added to a mixed aqueous solution of iron salt and magnesium salt with a concentration of 0.5 mol / L, stirred and impregnated at 90℃ for 18 h, vacuum dried to remove moisture, and dried at 130℃ for 16 h to obtain cerium-modified molecular sieve loaded with iron and magnesium salt. S3. Preparation of molecularly imprinted polymer: The template molecule o-cresol, functional monomer, and crosslinking agent were dissolved in an organic solvent, ultrasonically dispersed for 30 min, and nitrogen gas was introduced to remove oxygen for 40 min. Then, an initiator was added, and the mixture was polymerized at 80℃ for 24 h. After the reaction was completed, the product was ground and sieved. The template molecule was removed by elution with an eluent. The washing continued until no o-cresol was detected in the eluent. After drying, the molecularly imprinted polymer was obtained. The organic solvent was chloroform, and the eluent was a mixed solution of methanol and acetic acid with a volume ratio of 5:1. S4. Preparation of composite catalyst: The cerium-modified molecular sieve loaded with iron and magnesium salts obtained in step S2 is mixed with the molecularly imprinted polymer obtained in step S3 at a set mass ratio. 15% of the total mass of the mixture is added as a binder. After stirring evenly, the mixture is extruded and dried at 150°C for 8 hours, calcined at 600°C for 4 hours, and cooled to obtain the target catalyst C5. The binder is silica sol.

[0033] This invention also provides a method for preparing a catalyst for the synthesis of 2,6-dimethylphenol. The application of the prepared catalyst in the synthesis of 2,6-dimethylphenol is as follows: the catalyst is packed into a fixed-bed reactor, using phenol and methanol as raw materials with a raw material molar ratio of 1:6, a reaction temperature of 450°C, and a reaction pressure of 0.5 MPa. After vaporization, the raw materials are introduced into the reactor for alkylation reaction to generate 2,6-dimethylphenol.

[0034] Comparative Example 1: Without cerium modification, other conditions were the same as in Example 1, yielding catalyst D1. Catalytic performance test results showed: phenol conversion rate 80.2%, 2,6-dimethylphenol selectivity 88.6%, yield 71%; the yield of the final product, o-cresol, was 9.14%. Comparative Example 2: Without the addition of molecularly imprinted polymer, and under the same conditions as Example 1, catalyst D2 was obtained. The catalytic performance test results were as follows: phenol conversion rate 74.5%, 2,6-dimethylphenol selectivity 90.3%, yield 67.3%; the yield of the final product o-cresol was 7.23%. Comparative Example 3: Using a single iron salt as the active component (without magnesium salt), and with other conditions the same as in Example 1, catalyst D3 was obtained. The catalytic performance test results were as follows: phenol conversion rate 82.6%, 2,6-dimethylphenol selectivity 82.1%, yield 67.8%; the yield of the final product o-cresol was 14.8%.

[0035] Comparative Example 4: 2,6-Dimethylphenol was synthesized using a traditional zeolite catalyst, designated as catalyst D4. Catalytic performance tests showed the following results: phenol conversion rate 78.5%, 2,6-dimethylphenol selectivity 65.2%, and yield 60.7%; the yield of the final product, o-cresol, was 27.3%, yielding catalyst D3. Catalytic performance test: C1-C3 and D1-D4 catalysts were loaded into a fixed-bed reactor (inner diameter 10 mm, length 500 mm) with a loading amount of 5 g. The reaction conditions were: molar ratio of o-cresol to methanol 1:4, reaction temperature 400℃, reaction pressure 0.3 MPa. After continuous operation for 24 h, the product composition was detected and the results are shown in Table 1.

[0036] Table 1 Catalytic performance test data As shown in Table 1, the catalytic activity of the preparations made using the methods of Examples 1-3 of this invention showed better performance in the phenol conversion, 2,6-dimethylphenol selectivity, 2,6-dimethylphenol yield, and the yield of the final product o-cresol during the performance testing. Furthermore, Example 1 exhibited the highest phenol conversion, 2,6-dimethylphenol selectivity, and 2,6-dimethylphenol yield. Therefore, Example 1 is the optimal real-time solution. Figure 2 It can be intuitively demonstrated that the selectivity of the catalysts prepared by the preparation methods of Examples 1-3 of the present invention is significantly better than that of the catalysts prepared by Comparative Examples 1-4. Furthermore, the yield of the final product o-cresol of the catalysts prepared by the preparation methods of Examples 1-3 of the present invention is lower than that of Comparative Examples 1-4, with the catalyst prepared in Example 1 having the lowest yield of the final product o-cresol. It can be seen that the molecularly imprinted polymers in Examples 1-3 of the present invention have a certain adsorption effect on the byproduct o-cresol and the ability to convert it into 2,6-dimethylphenol.

[0037] Carbon deposition test: After 24 hours of reaction, the carbon deposition of the catalysts prepared in Example 1 and Comparative Examples 1-3 was tested by thermogravimetric analysis (TGA), and the results are shown in Table 2.

[0038] Table 2 Carbon Deposition Test Data As shown in Table 2, cerium modification was used in all three examples of the present invention: Example 1, Comparative Example 2, and Comparative Example 3. Therefore, the amount of carbon deposits tested was much lower than that of Comparative Example 1 without cerium modification. Furthermore, the catalyst prepared by the method of Example 1 had the lowest amount of carbon deposits. Therefore, Example 1 is the best example.

[0039] Verification of the mechanism of action of the molecularly imprinted polymer: To verify the selective adsorption capacity of the molecularly imprinted polymer for o-cresol, the following experiment was conducted: A 0.1 mol / L o-cresol solution was mixed with the molecularly imprinted polymer of this invention, stirred for 2 hours, centrifuged, and the concentration of o-cresol in the solution was measured. A non-molecularly imprinted polymer was used as a control. Specific results are shown in Table 3.

[0040] Table 3. Adsorption capacity of molecularly imprinted polymers for o-cresol As shown in Table 3, the molecularly imprinted polymer adsorbs o-cresol five times more than the ordinary polymer, confirming its selective adsorption capacity for o-cresol.

[0041] The catalyst of this invention solves the core problems of traditional 2,6-dimethylphenol synthesis catalysts, such as severe carbon buildup, numerous by-products, and low raw material utilization. It has advantages such as high activity, high selectivity, strong stability, and industrial feasibility. It can be widely used in the industrial production of 2,6-dimethylphenol synthesized by alkylation of phenol and methanol. It can significantly improve product yield and extend equipment operating cycle, and has important economic value and social benefits.

[0042] This invention significantly improves the conversion rate of phenol and the selectivity of 2,6-dimethylphenol through synergistic catalysis of iron and magnesium salts, shape-selective sieving of cerium-modified molecular sieves, and synergistic effects of molecularly imprinted polymers. These improvements are significantly superior to traditional catalysts. Cerium modification effectively inhibits catalyst carbon deposition and greatly extends its service life. The shape-selective effect of cerium-modified molecular sieves and the selective adsorption of o-cresol by molecularly imprinted polymers significantly improve the selectivity of 2,6-dimethylphenol. The extended residence time due to the specific adsorption of o-cresol by molecularly imprinted polymers ensures the complete conversion of incompletely reacted o-cresol, reducing raw material loss. The adsorption of o-cresol by molecularly imprinted polymers and its promotion of re-alkylation effectively converts the byproduct o-cresol into the target product, improving raw material utilization. The preparation process is simple, employing mature processes such as impregnation and polymerization reactions, making it easy to operate, cost-controllable, and suitable for industrial-scale production.

[0043] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0044] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0045] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A catalyst for the synthesis of 2,6-dimethylphenol, characterized in that: The invention includes a composite catalytic system and an active component supported in the composite catalytic system. The composite catalytic system is a mixed filler of cerium-modified molecular sieve and molecularly imprinted polymer. The active component is a combination of iron salt and magnesium salt. The mass fraction of cerium in the cerium-modified molecular sieve is 0.5%-5%. The total loading of iron salt and magnesium salt is 5%-15% of the mass of the cerium-modified molecular sieve. The molar ratio of iron salt to magnesium salt is 1:0.5-3. The mixing mass ratio of cerium-modified molecular sieve to molecularly imprinted polymer is 1:0.2-1. The molecularly imprinted polymer is prepared using o-cresol as a template molecule, combined with functional monomers, crosslinking agents and initiators, and the molar ratio of template molecule, functional monomers and crosslinking agents is 1:2-8:10-40.

2. The catalyst for synthesizing 2,6-dimethylphenol according to claim 1, characterized in that: The iron salt is selected from one or more of ferric nitrate, ferric chloride, and ferric sulfate.

3. The catalyst for synthesizing 2,6-dimethylphenol according to claim 1, characterized in that: The magnesium salt is selected from one or more of magnesium nitrate, magnesium chloride, and magnesium sulfate.

4. The catalyst for synthesizing 2,6-dimethylphenol according to claim 1, characterized in that: The carrier of the cerium-modified molecular sieve is selected from either HZSM-5 molecular sieve or Beta molecular sieve, and the raw material for preparing the cerium-modified molecular sieve is a cerium source compound, which is selected from either cerium nitrate, cerium chloride, or cerium oxalate.

5. The catalyst for synthesizing 2,6-dimethylphenol according to claim 1, characterized in that: The functional monomer is one or more of methacrylic acid, acrylamide, or 4-vinylpyridine.

6. The catalyst for synthesizing 2,6-dimethylphenol according to claim 1, characterized in that: The crosslinking agent is one of ethylene glycol dimethacrylate or divinylbenzene, and the initiator is one of azobisisobutyronitrile or benzoyl peroxide.

7. A method for preparing the catalyst for the synthesis of 2,6-dimethylphenol as described in any one of claims 1-6, characterized in that: Specifically, the following steps are included: S1. Preparation of cerium-modified molecular sieves: The molecular sieve support is pretreated by calcining at 500-600℃ for 2-4h. After cooling, an aqueous solution of cerium source compound with a concentration of 0.1-1.0mol / L is added, and the mixture is stirred and impregnated at 50-80℃ for 4-12h. Then, the moisture is removed by vacuum drying, and the mixture is dried at 100-120℃ for 6-12h. Finally, the mixture is calcined at 550-650℃ for 3-6h to obtain cerium-modified molecular sieves. S2, Loading of active components: The cerium-modified molecular sieve prepared in step S1 is added to a mixed aqueous solution of iron salt and magnesium salt with a concentration of 0.05-0.5 mol / L, stirred and impregnated at 60-90℃ for 6-18 h, and then vacuum dried to obtain cerium-modified molecular sieve loaded with iron and magnesium salt. S3. Preparation of molecularly imprinted polymer: The template molecule o-cresol, functional monomer, and crosslinking agent are dissolved in an organic solvent, ultrasonically dispersed for 10-30 min, and nitrogen gas is introduced to remove oxygen for 20-40 min. Then, an initiator is added, and the mixture is polymerized at 60-80℃ for 8-24 h. After the reaction is completed, the product is ground and sieved, and the template molecule is removed by elution with an eluent. The washing continues until no o-cresol is detected in the eluent. After drying, the molecularly imprinted polymer is obtained. S4. Preparation of composite catalyst: The cerium-modified molecular sieve loaded with iron and magnesium salts obtained in step S2 is mixed with the molecularly imprinted polymer obtained in step S3 at a set mass ratio. 5%-15% of the total mass of the mixture is added as a binder. After stirring evenly, the mixture is extruded and dried at 120-150℃ for 4-8 hours, calcined at 500-600℃ for 2-4 hours, and then cooled to obtain the target catalyst.

8. The method for preparing a catalyst for synthesizing 2,6-dimethylphenol according to claim 7, characterized in that: The binder in step S4 is either aluminum sol or silica sol.

9. A method for preparing a catalyst for synthesizing 2,6-dimethylphenol according to claim 7, characterized in that, In step S3, the organic solvent is selected from toluene, acetonitrile, and chloroform, and the eluent is a mixed solution of methanol and acetic acid, with a volume ratio of methanol to acetic acid of 3-5:

1.

10. The application of a catalyst prepared by the method for preparing a catalyst for the synthesis of 2,6-dimethylphenol as described in claim 7 in the synthesis of 2,6-dimethylphenol, characterized in that, Specifically, the catalyst is loaded into a fixed-bed reactor, using phenol and methanol as raw materials with a raw material molar ratio of 1:2-1:6, a reaction temperature of 350-450℃, and a reaction pressure of 0.1-0.5MPa. After vaporization, the raw materials are fed into the reactor for alkylation reaction to produce 2,6-dimethylphenol.

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