A process for the preparation of 2,6-dimethylphenol by methylation of phenol and methanol with a catalyst of iron oxides, catalysts for the coproduction of o-cresol and their use

Abstract

The application belongs to the field of functional material preparation and catalysis technology, and discloses a preparation method of an iron oxide catalyst, which comprises the following steps: dissolving an iron precursor and a promoter in water respectively to form uniform aqueous solutions; mixing the two aqueous solution systems and stirring to make them uniformly mixed; continuously heating and stirring the mixed aqueous solution to evaporate water; drying the gel-like substance, and then calcining at a specified temperature for 5h to obtain the iron oxide catalyst. The method of the application obtains the iron oxide catalyst with high catalytic performance by calcining the mixture of the promoter and the iron precursor, and uses the iron oxide catalyst to catalyze the methylation reaction of phenol and methanol. The application improves the conversion rate and selectivity of the reaction by improving mass transfer, increasing the specific surface area and the content of acid sites, and has the advantages of simple operation, good repeatability, low cost, phenol conversion rate of 94.4%, product 2,6-dimethylphenol selectivity of 50.1%, and o-cresol selectivity of 49.2%.

Description

Technical Field

[0001] This invention belongs to the field of functional material preparation and catalysis technology, and in particular, a method and application of an iron oxide catalyst, a methylation catalyst for phenol and methanol to prepare 2,6-xylenol and a catalyst for the co-production of o-cresol. Background Technology

[0002] 2,6-Xylenol is a white crystalline powder at room temperature with a pungent odor. It is an intermediate used in organic synthesis and in fine chemical products such as preservatives, disinfectants, pharmaceuticals, solvents, and antioxidants. It is mainly used in the synthesis of polyphenylene oxide (PPO), 2,6-dimethylaniline, and antioxidants. o-Cresol is a colorless or pale yellow transparent liquid at room temperature with a pungent odor. It is mainly used in the synthesis of o-cresol formaldehyde resins and o-cresol formaldehyde epoxy resins. It can also be used to manufacture the herbicide 2,4-D, as well as fragrances, chemical reagents, and antioxidants.

[0003] Currently, the main methods for preparing 2,6-xylenol and o-cresol are natural separation and chemical synthesis. Natural separation methods primarily obtain them from coal tar and petroleum cracking products; however, due to limited resources and complex processes, this method cannot meet the demand. Chemical synthesis methods mainly include o-toluidine diazotization, toluene chlorination hydrolysis, toluene sulfonation alkali fusion, and phenol-methanol alkylation. The o-toluidine diazotization process is complex and uses intermittent production, making it unsuitable for large-scale production. Toluene chlorination hydrolysis yields readily available raw materials and easily separated products, but its process conditions are harsh and environmentally unfriendly. Toluene sulfonation alkali fusion requires large amounts of strong acids and bases, causing severe equipment corrosion and environmental pollution. Phenol-methanol alkylation is a green and environmentally friendly process with low cost and readily available raw materials, making it the most popular and widely used method in chemical synthesis.

[0004] Catalysts for the methylation reaction of phenol and methanol mainly include phosphates, sulfates, molecular sieves, and metal oxides. Phosphates and sulfates, as catalysts, primarily produce anisole as the main product, while the yields of 2,6-xylenol and o-cresol are low. Molecular sieves themselves possess a variety of medium- and strong methylation potentials. Because of their acidic sites, zeolites are prone to carbon deposition and deactivation during reactions, and the product distribution is complex. Most zeolites exhibit low ortho-product selectivity (the sum of the selectivities for o-cresol and 2,6-xylenol). In contrast, many metal oxides tend to undergo C-alkylation reactions on phenol to generate ortho-products. Furthermore, metal oxides have advantages such as long lifetime and good stability. Therefore, metal oxides are frequently used in research on the alkylation reactions of phenol and methanol to prepare ortho-products. Among numerous metal oxides, iron oxides and iron-based catalysts often exhibit excellent ortho-selectivity and stability.

[0005] The alkylation reaction of phenol and methanol is a gas-solid phase reaction. Due to the high temperature required during the reaction, the catalyst is prone to carbon deposition and deactivation. Furthermore, the low space velocity reduces the yield. In addition, improving the conversion rate of phenol and the selectivity for 2,6-xylenol are also important issues.

[0006] A search revealed no patent publications related to this invention's patent application. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and application for the preparation of 2,6-xylenol and o-cresol catalyst by methylation of iron oxide catalyst, phenol and methanol.

[0008] The technical solution adopted by this invention to solve its technical problem is:

[0009] A method for preparing an iron oxide catalyst, the method comprising the following steps:

[0010] (1) The iron precursor and the accelerator were dissolved in water respectively, and a homogeneous aqueous solution was formed after dissolution, resulting in two aqueous solutions;

[0011] (2) Mix the two aqueous solutions obtained in step (1) and stir to make them evenly mixed to obtain a mixed aqueous solution;

[0012] (3) The mixed aqueous solution obtained in step (2) is continuously heated and stirred to evaporate the water until a gel-like substance is obtained;

[0013] (4) The gel-like substance obtained in step (3) is dried and then calcined at a specified temperature for 5 hours to obtain an iron oxide catalyst.

[0014] Furthermore, the calcination temperature in step (4) is 300℃~500℃;

[0015] Alternatively, the molar ratio of iron precursor to accelerator in step (1) is 2:1 to 1:4.

[0016] Furthermore, the iron precursor is an iron-containing organic or inorganic compound, the accelerator is glycine, the calcination temperature in step (4) is 400°C, and the molar ratio of the iron precursor to the accelerator in step (1) is 1:2.

[0017] Furthermore, the iron-containing organic or inorganic compounds include ferric citrate, ferric oxalate, ferric nitrate, ferric acetylacetone, and ferric acetate.

[0018] Furthermore, the specific steps are as follows:

[0019] (1) The iron precursor and the accelerator were placed in water and heated and stirred at 90°C until they were completely dissolved to form a homogeneous aqueous solution, thus obtaining two aqueous solutions.

[0020] Each 1g of iron precursor is dissolved in 20mL of water;

[0021] (2) Mix the two aqueous solutions obtained in step (1), heat and stir at 90°C for 1 hour to make them evenly mixed, and obtain a mixed aqueous solution;

[0022] (3) The mixed aqueous solution obtained in step (2) is continuously heated and stirred for 2 hours to evaporate the water until a gel-like substance is obtained. The heating temperature is 80℃ and the stirring speed is 600r / min.

[0023] (4) The gel-like material obtained in step (3) is dried in an oven at 80°C for 12 hours, and then heated to the specified calcination temperature at a heating rate of 2°C / min and calcined for 5 hours to obtain an iron oxide catalyst.

[0024] The iron oxide catalyst was prepared by the method described above.

[0025] The application of iron oxide catalysts as described above in the catalytic methylation reaction of phenol and methanol.

[0026] The method for catalyzing the methylation reaction of phenol and methanol using iron oxides with high catalytic performance as described above includes the following steps:

[0027] 1) Sieve the iron oxide catalyst through a 60-80 mesh, mix it evenly with the quartz sand, and spread it evenly in the middle of the fixed bed reactor, using glass fiber as support;

[0028] For every 1g of catalyst, 4g of quartz sand is added;

[0029] 2) Phenol is dissolved in methanol as raw material and pumped into the preheater for vaporization by a micro plunger pump. Nitrogen is used as a carrier gas to transport the vaporized raw material into the reactor.

[0030] 3) Purge the preheater and reactor with nitrogen, raise the temperature to the specified temperature, heat for 3 hours to activate the catalyst, and then start the reaction;

[0031] 4) Collect the reaction products after condensation, and take a reaction sample every 1 hour.

[0032] Furthermore, the reaction conditions in step 2) are as follows:

[0033] The molar ratio of phenol to methanol was 1:3–13, the nitrogen flow rate was 10–50 mL / min, and the weight hourly space velocity (WHSV) was 0.5 h⁻¹. -1 ~2.0h -1 The preheater temperature is 300℃;

[0034] The reaction conditions in step 3) are as follows:

[0035] The reactor temperature is 310℃~390℃, the pressure is atmospheric pressure, and the reaction time is 8h~30h.

[0036] Furthermore, the reaction conditions in step 3) are as follows: reactor temperature is 330℃~370℃, nitrogen flow rate is 20~40mL / min, and reaction time is 10h~20h.

[0037] The advantages and positive effects of this invention are as follows:

[0038] 1. The method of this invention utilizes a uniform mixture of a promoter and an iron precursor, followed by calcination to obtain iron oxide with high catalytic performance. This iron oxide is then used to catalyze the methylation reaction of phenol and methanol. This invention improves the conversion rate and selectivity of the reaction by enhancing mass transfer, increasing specific surface area, and increasing the content of acidic sites. The method is simple to operate, has good reproducibility, low cost, and achieves a phenol conversion rate of up to 94.4%, a selectivity of 50.1% for 2,6-xylenol, and a selectivity of 49.2% for o-cresol.

[0039] 2. The method of the present invention solves the problems of easy catalyst deactivation and low selectivity of ortho-products in the methylation reaction of phenol and methanol, and provides a simple and convenient method for preparing iron oxide catalysts. This method is simple, easy to operate, and has a short time consumption, and can exhibit high catalytic performance in the methylation reaction of phenol and methanol.

[0040] 3. The iron oxide prepared by the method of the present invention has significantly improved acid strength, which is conducive to the occurrence of ortho-C-methylation reaction of phenol; by increasing the specific surface area of ​​the catalyst and reducing the particle size, more active sites are exposed on the catalyst, thereby improving the conversion rate and selectivity of the reaction.

[0041] 4. The iron oxide prepared by this invention has a larger specific surface area and a greater acidity, as evidenced by the larger specific surface area and greater acidity obtained from nitrogen adsorption isotherms and ammonia temperature-programmed desorption. The increased specific surface area improves the acidity and acid strength of the material, thus facilitating the C-methylation reaction of phenol.

[0042] 5. This invention utilizes the thermal decomposition of glycine and ferric citrate in a specific molar ratio to obtain a highly catalytically active iron oxide, which is then used as a catalyst for the methylation reaction of phenol and methanol. This invention improves the conversion rate and selectivity of the reaction by increasing the specific surface area, reducing the particle size, increasing the total acid content, and adjusting the ratio of medium-strong to strong acids. The process is simple, reproducible, low-cost, and yields a high amount of 2,6-xylenol. Attached Figure Description

[0043] Figure 1 This is a SEM image of the iron oxide catalyst in Example 1 of this invention;

[0044] Figure 2 The image shows the XRD pattern of the iron oxide catalyst in Example 1 of this invention.

[0045] Figure 3 This is the BET plot of the iron oxide catalyst in Example 1 of this invention;

[0046] Figure 4 The NH3-TPD diagram of the iron oxide catalyst in Example 1 of this invention is shown.

[0047] Figure 5 This is a SEM image of the iron oxide catalyst in Example 2 of this invention;

[0048] Figure 6 The image shows the XRD pattern of the iron oxide catalyst in Example 2 of this invention.

[0049] Figure 7 This is a diagram showing the water contact angle of the iron oxide catalyst in Example 2 of this invention;

[0050] Figure 8 This is the BET diagram of the iron oxide catalyst in Example 2 of this invention;

[0051] Figure 9 This is a SEM image of the iron oxide catalyst in Example 3 of this invention;

[0052] Figure 10 The image shows the XRD pattern of the iron oxide catalyst in Example 3 of this invention.

[0053] Figure 11 This is the BET plot of the iron oxide catalyst in Example 3 of this invention;

[0054] Figure 12 This is the NH3-TPD diagram of the iron oxide catalyst in Example 3 of this invention. Detailed Implementation

[0055] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0056] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0057] A method for preparing an iron oxide catalyst, the method comprising the following steps:

[0058] (1) The iron precursor and the accelerator were dissolved in water respectively, and a homogeneous aqueous solution was formed after dissolution, resulting in two aqueous solutions;

[0059] (2) Mix the two aqueous solutions obtained in step (1) and stir to make them evenly mixed to obtain a mixed aqueous solution;

[0060] (3) The mixed aqueous solution obtained in step (2) is continuously heated and stirred to evaporate the water until a gel-like substance is obtained;

[0061] (4) The gel-like substance obtained in step (3) is dried and then calcined at a specified temperature for 5 hours to obtain an iron oxide catalyst.

[0062] Preferably, the calcination temperature in step (4) is 300℃~500℃;

[0063] Alternatively, the molar ratio of iron precursor to accelerator in step (1) is 2:1 to 1:4.

[0064] Preferably, the iron precursor is an iron-containing organic or inorganic compound, the accelerator is glycine, the calcination temperature in step (4) is 400°C, and the molar ratio of the iron precursor to the accelerator in step (1) is 1:2.

[0065] Preferably, the iron-containing organic or inorganic compound includes ferric citrate, ferric oxalate, ferric nitrate, ferric acetylacetone, and ferric acetate.

[0066] Preferably, the specific steps are as follows:

[0067] (1) The iron precursor and the accelerator were placed in water and heated and stirred at 90°C until they were completely dissolved to form a homogeneous aqueous solution, thus obtaining two aqueous solutions.

[0068] Each 1g of iron precursor is dissolved in 20mL of water;

[0069] (2) Mix the two aqueous solutions obtained in step (1), heat and stir at 90°C for 1 hour to make them evenly mixed, and obtain a mixed aqueous solution;

[0070] (3) The mixed aqueous solution obtained in step (2) is continuously heated and stirred for 2 hours to evaporate the water until a gel-like substance is obtained. The heating temperature is 80℃ and the stirring speed is 600r / min.

[0071] (4) The gel-like material obtained in step (3) is dried in an oven at 80°C for 12 hours, and then heated to the specified calcination temperature at a heating rate of 2°C / min and calcined for 5 hours to obtain an iron oxide catalyst.

[0072] The iron oxide catalyst was prepared by the method described above.

[0073] The application of iron oxide catalysts as described above in the catalytic methylation reaction of phenol and methanol.

[0074] The method for catalyzing the methylation reaction of phenol and methanol using iron oxides with high catalytic performance as described above includes the following steps:

[0075] 1) Sieve the iron oxide catalyst through a 60-80 mesh, mix it evenly with the quartz sand, and spread it evenly in the middle of the fixed bed reactor, using glass fiber as support;

[0076] For every 1g of catalyst, 4g of quartz sand is added;

[0077] 2) Phenol is dissolved in methanol as raw material and pumped into the preheater for vaporization by a micro plunger pump. Nitrogen is used as a carrier gas to transport the vaporized raw material into the reactor.

[0078] 3) Purge the preheater and reactor with nitrogen, raise the temperature to the specified temperature, heat for 3 hours to activate the catalyst, and then start the reaction;

[0079] 4) Collect the reaction products after condensation, and take a reaction sample every 1 hour.

[0080] Preferably, the reaction conditions in step 2) are as follows:

[0081] The molar ratio of phenol to methanol was 1:3–13, the nitrogen flow rate was 10–50 mL / min, and the weight hourly space velocity (WHSV) was 0.5 h⁻¹. -1 ~2.0h -1 The preheater temperature is 300℃;

[0082] The reaction conditions in step 3) are as follows:

[0083] The reactor temperature is 310℃~390℃, the pressure is atmospheric pressure, and the reaction time is 8h~30h.

[0084] Preferably, the reaction conditions in step 3) are: reactor temperature of 330℃~370℃, nitrogen flow rate of 20~40mL / min, and reaction time of 10h~20h.

[0085] Specifically, the relevant preparation and testing methods are as follows:

[0086] Example 1

[0087] A method for preparing iron oxide with high catalytic performance, comprising the following specific steps:

[0088] (1) Weigh 0.015 mol of ferric citrate and disperse it in 80 mL of deionized water. Heat and stir in a water bath at 90 °C until the ferric citrate is completely dissolved.

[0089] (2) Transfer the obtained aqueous solution to a flask, heat and stir in a water bath at 90°C for 1 hour to make it evenly mixed, and then transfer it to a beaker.

[0090] (3) Seal the beaker with plastic wrap and poke a certain number of holes to allow moisture to evaporate. Place the beaker in an 80°C water bath and heat and stir for 2 hours to evaporate the moisture until a gel-like substance is obtained. The rotation speed is 600 r / min.

[0091] (4) The gel-like substance obtained in step (3) was placed in an oven at 80°C and dried for 12 hours. The dried substance was then ground and calcined in a muffle furnace for 5 hours at a heating rate of 2°C / min and a calcination temperature of 450°C to obtain the final iron oxide, which was named C-1.

[0092] The specific steps of the method for catalytic methylation reaction of phenol and methanol using iron oxides as described above are as follows:

[0093] 1) Sieve the catalyst through a 60-80 mesh sieve, mix it evenly with quartz sand, and spread it evenly in the middle of the fixed bed reactor, using glass fiber as support;

[0094] The catalyst weighs 1g and the quartz sand weighs 4g.

[0095] 2) Phenol is dissolved in methanol as a raw material, with a molar ratio of phenol to methanol of 1:5. The solution is then pumped into a preheater for vaporization using a micro-plunger pump, with a weight hourly space velocity (WHSV) of 1 h⁻¹. -1 Nitrogen is used as a carrier gas to transport the gasified raw material into the reactor at a flow rate of 30 mL / min and a preheater temperature of 300℃.

[0096] 3) Before starting the reaction, purge the preheater and reactor with nitrogen and raise the temperature to the specified temperature. Heat for 3 hours to activate the catalyst, and then start the reaction. The reactor temperature is 350℃ and the reaction time is 10 hours.

[0097] 4) Collect the reaction products after condensation, and take a reaction sample every 1 hour.

[0098] The relevant tests are as follows:

[0099] 1. Performance testing of the iron oxide obtained in Example 1 of this invention

[0100] Figure 1 The image shown is a scanning electron microscope image of the iron oxide prepared in Example 1. The results show that the average size of the prepared material is 50.0 nm.

[0101] Figure 2 The image shows the XRD pattern of the iron oxide prepared in Example 1. The results show that the material has both hematite and magnetite crystal forms, and the peak shape indicates that the iron oxide has good crystallinity.

[0102] Figure 3 The image shows the nitrogen adsorption isotherm results for the iron oxide prepared in Example 1. The catalyst exhibits a type IV isotherm and an H3 hysteresis loop, indicating the presence of considerable mesopores. Due to the pore-forming and thermally decomposing effects of glycine, the specific surface area of ​​the material reaches 120 m². 2 ·g -1 .

[0103] Figure 4 The graph shows the ammonia-programmed temperature desorption results of the iron oxide prepared in Example 1. The catalyst exhibits the highest total acid content, reaching 1.02 mmol / g. Furthermore, most of the acids are moderately strong and strong, at 0.722 mmol / g and 0.168 mmol / g, respectively. This is beneficial for the C-alkylation reaction of phenol.

[0104] 2. The relevant comparative experiments are as follows:

[0105] Take 3-5 drops of the reaction product for GC analysis. Calculate the conversion rate and product selectivity; the results are shown in Table 1.

[0106] Ferric oxalate, ferric nitrate, ferric acetylacetone, and ferric acetate were selected as iron precursors in equal molar amounts, and other conditions were kept the same for comparative experiments. The reaction results are shown in Table 1. Comparative Example 1 used ferric oxalate as the iron precursor, Comparative Example 2 used ferric nitrate as the iron precursor, Comparative Example 3 used ferric acetylacetone as the iron precursor, and Comparative Example 4 used ferric acetate as the iron precursor.

[0107] Specifically, Comparative Example 1 uses a catalyst prepared with ferric oxalate as an iron precursor to catalyze the methylation reaction of phenol and methanol, resulting in the reaction system of Comparative Example 1. The remaining conditions are the same as those in the method for catalyzing the methylation reaction of phenol and methanol in Example 1. The prepared catalyst is named O-1. The preparation steps of this iron oxide are the same as steps (1) to (4) in the "Method for Preparing Iron Oxides" of Example 1.

[0108] Comparative Example 2 uses a catalyst prepared with ferric nitrate as an iron precursor to catalyze the methylation reaction of phenol and methanol, resulting in the reaction system of Comparative Example 2. The remaining conditions for the catalytic methylation reaction of phenol and methanol are the same as those in the method for catalyzing the methylation reaction of phenol and methanol in Example 1. The prepared catalyst is named N-1. The preparation steps of this iron oxide are the same as steps (1) to (4) in the "Method for Preparing Iron Oxides" in Example 1.

[0109] Comparative Example 3 uses a catalyst prepared with iron acetylacetone as the iron precursor to catalyze the methylation reaction of phenol and methanol, resulting in the reaction system of Comparative Example 3. The remaining conditions for the catalytic methylation reaction of phenol and methanol are the same as those in the method for catalyzing the methylation reaction of phenol and methanol in Example 1. The prepared catalyst is named A-1. The preparation steps of this iron oxide are the same as steps (1) to (4) in the "Method for Preparing Iron Oxides" in Example 1.

[0110] Comparative Example 4 uses a catalyst prepared with ferric acetate as an iron precursor to catalyze the methylation reaction of phenol and methanol, resulting in the reaction system of Comparative Example 4. The remaining conditions for the methylation reaction of phenol and methanol are the same as those in the method for catalyzing the methylation reaction of phenol and methanol in Example 1. The catalyst obtained is named A-2. The preparation steps of this iron oxide are the same as steps (1) to (4) in the "Method for Preparing Iron Oxides" in Example 1.

[0111] Table 1

[0112]

[0113] As shown in Table 1, the order of catalytic performance of the catalysts is: C-1 > O-1 > A-1 > N-1 > A-2. The C-1 catalyst in Example 1 achieved a phenol conversion of 65.7%, a 2,6-xylenol selectivity of 37.4%, and an ortho-selectivity of 99.5%. Due to differences in anionic properties, the catalysts in the comparative examples and the examples exhibited different specific surface areas and particle sizes after calcination, as well as being affected by crystal forms, ultimately leading to different catalytic performances. The C-1 catalyst demonstrated the best catalytic performance due to its largest specific surface area, smallest particle size, and largest total acid content. A large specific surface area and small particle size are beneficial for improving mass transfer and exposing more active sites. This is beneficial for improving the phenol conversion and the 2,6-xylenol selectivity. The abundant medium-strong acid and strong acid content are favorable for catalyzing the C-methylation reaction of phenol to generate ortho-products. Furthermore, the ortho-selectivity of the reaction was found to be >99.5%, indicating that this catalyst is highly favorable for the ortho-C-methylation reaction of phenol. The order of catalytic performance of the catalysts in Table 1 is well correlated with their order of total acidity.

[0114] Example 2

[0115] A method for preparing iron oxide with high catalytic performance, comprising the following specific steps:

[0116] (1) Weigh 0.015 mol of ferric citrate and disperse it in 80 mL of deionized water. Heat and stir in a water bath at 90 °C until the ferric citrate is completely dissolved. Weigh 0.030 mol of glycine and disperse it in 30 mL of deionized water. Heat and stir in a water bath at 90 °C until the glycine is completely dissolved.

[0117] (2) The two homogeneous aqueous solutions were mixed in a flask and heated and stirred in a water bath at 90°C for 1 hour to make them evenly mixed. Then the mixture was transferred to a beaker.

[0118] (3) Seal the beaker with plastic wrap and poke a certain number of holes to allow moisture to evaporate. Place the beaker in an 80°C water bath and heat and stir for 2 hours to evaporate the moisture until a gel-like substance is obtained. The rotation speed is 600 r / min.

[0119] (4) The gel-like substance obtained in step (3) was placed in an oven at 80°C and dried for 12 hours. The dried substance was then ground and calcined in a muffle furnace for 5 hours at a heating rate of 2°C / min and a calcination temperature of 450°C to obtain the final iron oxide, which was named C-2.

[0120] The specific steps of the method for catalytic methylation reaction of phenol and methanol using iron oxides as described above are as follows:

[0121] 1) Sieve the catalyst through a 60-80 mesh sieve, mix it evenly with quartz sand, and spread it evenly in the middle of the fixed bed reactor, using glass fiber as support;

[0122] The catalyst weighs 1g and the quartz sand weighs 4g.

[0123] 2) Phenol is dissolved in methanol as a raw material, with a molar ratio of phenol to methanol of 1:7. The solution is then pumped into a preheater for vaporization using a micro-plunger pump, with a weight hourly space velocity (WHSV) of 1.2 h⁻¹. -1 Nitrogen is used as a carrier gas to transport the gasified raw material into the reactor at a flow rate of 20 mL / min and a preheater temperature of 300℃.

[0124] 3) Before starting the reaction, purge the preheater and reactor with nitrogen and raise the temperature to the specified temperature. Heat for 3 hours to activate the catalyst, and then start the reaction. The reactor temperature is 350℃ and the reaction time is 20 hours.

[0125] 4) Collect the reaction products after condensation, and take a reaction sample every 1 hour.

[0126] The relevant tests are as follows:

[0127] 1. Performance testing of the iron oxide obtained in Example 2 of this invention (same as Example 1).

[0128] Figure 5The image shows a scanning electron microscope (SEM) image of the iron oxide prepared in Example 2. The results show that the average size of the prepared material is 38.4 nm.

[0129] Figure 6 The image shows the XRD pattern of the iron oxide prepared in Example 2. The results show that the material has both hematite and magnetite crystal forms, and the peak shape proves that the iron oxide has good crystallinity.

[0130] Figure 7 The image shows the nitrogen adsorption isotherm results for the iron oxide prepared in Example 2. The catalyst exhibits a type IV isotherm and an H3 hysteresis loop, indicating the presence of considerable mesopores. Due to the pore-forming and thermally decomposing effects of glycine, the specific surface area of ​​the material reaches 138 m². 2 ·g -1 .

[0131] Figure 8 The graph shows the ammonia-programmed temperature desorption results of the iron oxide prepared in Example 2. The catalyst exhibits the highest total acid content, reaching 1.14 mmol / g. Furthermore, most of the acids are moderately strong and strong, at 0.724 mmol / g and 0.206 mmol / g, respectively. This is beneficial for the C-alkylation reaction of phenol.

[0132] 2. The relevant comparative experiments are as follows:

[0133] Take 3-5 drops of the reaction product for GC analysis. Calculate the conversion rate and product selectivity; the results are shown in Table 2.

[0134] Using maleic anhydride of the same molar amount and glycine of different molar ratios as promoters, and with other conditions remaining the same, as comparative experiments, the reaction results are shown in Table 2. Comparative Example 5 used 0.0075 mol of glycine as the promoter, Comparative Example 6 used 0.06 mol of glycine as the promoter, and Comparative Example 7 used 0.03 mol of maleic anhydride as the promoter.

[0135] Specifically, Comparative Example 5 used a catalyst prepared with 0.0075 mol of glycine as a promoter to catalyze the methylation reaction of phenol and methanol, resulting in the reaction system of Comparative Example 5. The remaining conditions were the same as those in the method for catalyzing the methylation reaction of phenol and methanol in Example 2. The prepared catalyst was named C-2-1. The preparation steps of this iron oxide were the same as steps (1) to (4) in the "Method for Preparing Iron Oxides" of Example 2.

[0136] Comparative Example 6 used a catalyst prepared with 0.06 mol of glycine as a promoter to catalyze the methylation reaction of phenol and methanol, resulting in the reaction system of Comparative Example 5. The remaining conditions were the same as those in the method for catalyzing the methylation reaction of phenol and methanol in Example 2. The prepared catalyst was named C-2-2. The preparation steps of this iron oxide were the same as steps (1) to (4) in the "Method for Preparing Iron Oxides" of Example 2.

[0137] Specifically, Comparative Example 7 uses a catalyst prepared with maleic anhydride as a promoter to catalyze the methylation reaction of phenol and methanol, resulting in the reaction system of Comparative Example 7. The remaining conditions are the same as those in the method for catalyzing the methylation reaction of phenol and methanol in Example 2. The prepared catalyst is named C-3. The preparation steps of this iron oxide are the same as steps (1) to (4) in the "Method for Preparing Iron Oxides" of Example 2.

[0138] Table 2

[0139]

[0140] Table 2 shows the reaction results of iron oxide catalysts prepared using different promoters. The results show that when maleic anhydride is used as a promoter, the catalytic performance remains almost unchanged. This indicates that maleic anhydride as a promoter does not contribute to the increase in specific surface area or total acidity. However, when an appropriate amount of glycine is used as a promoter, the conversion rate of phenol increases to 86.4%, and the selectivity of 2,6-xylenol increases to 42.7%. This is because glycine releases heat during decomposition, promoting the thermal decomposition of ferric citrate. Furthermore, glycine decomposition helps the catalyst form pores, thereby increasing the specific surface area and reducing the particle size. However, when the amount of glycine added is small, it does not significantly increase the specific surface area or form pores, so C-2-1 does not significantly improve the catalytic performance. Conversely, excessive glycine releases too much heat during thermal decomposition, leading to sintering and agglomeration of the catalyst, which in turn reduces the specific surface area and the number of acidic sites. In summary, mixing ferric citrate and glycine in an appropriate molar ratio can increase the specific surface area and reduce the particle size of the calcined catalyst. This facilitates mass transfer and exposes active sites. Consequently, the catalyst exhibits significantly improved performance in medium- and strong acids, as well as a substantial increase in total acid content. This is a key reason for the enhanced catalytic performance, as it promotes the conversion of phenol and the C-methylation reaction.

[0141] Example 3

[0142] A method for preparing iron oxide with high catalytic performance, comprising the following specific steps:

[0143] (1) Weigh 0.015 mol of ferric citrate and disperse it in 80 mL of deionized water. Heat and stir in a water bath at 90 °C until the ferric citrate is completely dissolved. Weigh 0.03 mol of glycine and disperse it in 30 mL of deionized water. Heat and stir in a water bath at 90 °C until the glycine is completely dissolved.

[0144] (2) The two homogeneous aqueous solutions were mixed in a flask and heated and stirred in a water bath at 90°C for 1 hour to make them evenly mixed. Then the mixture was transferred to a beaker.

[0145] (3) Seal the beaker with plastic wrap and poke a certain number of holes to allow moisture to evaporate. Place the beaker in an 80°C water bath and heat and stir for 2 hours to evaporate the moisture until a gel-like substance is obtained. The rotation speed is 600 r / min.

[0146] (4) The gel-like substance obtained in step (3) was placed in an oven at 80°C and dried for 12 hours. The dried substance was then ground and calcined in a muffle furnace for 5 hours at a heating rate of 2°C / min and a calcination temperature of 400°C to obtain the final iron oxide, which was named C-2-400.

[0147] The specific steps of the method for catalytic methylation reaction of phenol and methanol using iron oxides as described above are as follows:

[0148] 1) Sieve the catalyst through a 60-80 mesh sieve, mix it evenly with quartz sand, and spread it evenly in the middle of the fixed bed reactor, using glass fiber as support;

[0149] The catalyst weighs 1g and the quartz sand weighs 4g.

[0150] 2) Phenol is dissolved in methanol as a raw material, with a molar ratio of phenol to methanol of 1:7. The solution is then pumped into a preheater for vaporization using a micro-plunger pump, with a weight hourly space velocity (WHSV) of 1.2 h⁻¹. -1 Nitrogen is used as a carrier gas to transport the gasified raw material into the reactor at a flow rate of 20 mL / min and a preheater temperature of 300℃.

[0151] 3) Before starting the reaction, purge the preheater and reactor with nitrogen and raise the temperature to the specified temperature. Heat for 3 hours to activate the catalyst, and then start the reaction. The reactor temperature is 350℃ and the reaction time is 20 hours.

[0152] 4) Collect the reaction products after condensation, and take a reaction sample every 1 hour.

[0153] The relevant tests are as follows:

[0154] 1. Performance testing of the iron oxide obtained in Example 3 of this invention (same as Example 1).

[0155] Figure 9The image shows a scanning electron microscope (SEM) image of the iron oxide prepared in Example 3. The results show that the average size of the prepared material is 30.4 nm.

[0156] Figure 10 The image shows the XRD pattern of the iron oxide prepared in Example 3. The results show that the material has both hematite and magnetite crystal forms, and the peak shape proves that the iron oxide has good crystallinity.

[0157] Figure 11 The image shows the nitrogen adsorption isotherm results for the iron oxide prepared in Example 3. The catalyst exhibits a type IV isotherm and an H3 hysteresis loop, indicating the presence of considerable mesopores. Due to the pore-forming and thermally decomposing effects of glycine, the specific surface area of ​​the material reaches 152 m². 2 ·g -1 .

[0158] Figure 12 The graph shows the ammonia-programmed temperature desorption results of the iron oxide prepared in Example 3. The catalyst exhibits the highest total acid content, reaching 1.28 mmol / g. Furthermore, most of the acids are moderately strong and strong, at 0.811 mmol / g and 0.264 mmol / g, respectively. This is beneficial for the C-alkylation reaction of phenol.

[0159] 2. The relevant comparative experiments are as follows:

[0160] Take 3-5 drops of the reaction product for GC analysis. Calculate the conversion rate and product selectivity; the results are shown in Table 3.

[0161] Catalysts obtained at different calcination temperatures were used as comparative experiments under the same other conditions. The reaction results are shown in Table 2. Comparative Example 8 was calcined at 300℃, and Comparative Example 9 was calcined at 500℃.

[0162] Specifically, Comparative Example 8 uses a catalyst prepared at a calcination temperature of 300°C to catalyze the methylation reaction of phenol and methanol, resulting in the reaction system of Comparative Example 8. The remaining conditions are the same as those in the method for catalyzing the methylation reaction of phenol and methanol in Example 3. The prepared catalyst is named C-2-300. The preparation steps of this iron oxide are the same as steps (1) to (4) in the "Method for Preparing Iron Oxides" of Example 3.

[0163] Comparative Example 9 uses a catalyst prepared at a calcination temperature of 500°C to catalyze the methylation reaction of phenol and methanol, resulting in the reaction system of Comparative Example 9. The remaining conditions for the catalytic methylation reaction of phenol and methanol are the same as those in the method for catalyzing the methylation reaction of phenol and methanol in Example 3. The prepared catalyst is named C-2-500. The preparation steps of this iron oxide are the same as steps (1) to (4) in the "Method for Preparing Iron Oxides" of Example 3.

[0164] Table 3

[0165]

[0166] Among them, the mass of the product is measured by the calibrated area normalization method:

[0167] Where, m r The product quality is f, where f is the relative correction factor and m is m. s For the mass of phenol, A r For the peak area of ​​the product, A s This represents the peak area of ​​phenol.

[0168] The conversion rate of the reaction is calculated using the following formula:

[0169] The selectivity of 2,6-xylenol is calculated using the following formula:

[0170] Table 3 shows the reaction results of iron oxide catalysts prepared at different calcination temperatures. The results indicate that the iron oxide exhibits the best catalytic performance at a calcination temperature of 400℃, with a phenol conversion rate of 94.4% and a 2,6-xylenol selectivity of 50.1%. However, both excessively high and low calcination temperatures lead to a decrease in conversion rate. This is because excessively high calcination temperatures cause catalyst sintering, resulting in larger particle sizes and reduced specific surface area. This reduces the number of active sites on the catalyst, thus causing a decrease in catalytic performance. The decrease in catalytic performance at excessively low calcination temperatures is mainly due to two factors: firstly, the low temperature reduces the crystallinity of the sample; secondly, the low calcination temperature reduces porosity, thus affecting mass transfer and the utilization of active sites.

[0171] In summary, the iron oxide catalyst prepared in this invention is obtained by reacting ferric citrate and glycine in an appropriate molar ratio at a suitable calcination temperature. Scanning electron microscopy (SEM) images show that the material size is approximately 18.4–39.4 nm. XRD patterns show that the material exhibits both hematite and magnetite crystal forms. Depending on the iron precursor, promoter, and calcination temperature, nitrogen adsorption-desorption testing determined the specific surface area of ​​the material to be 16.4 m². 2 ·g -1 up to 152m 2 ·g -1 The total acidity of the material, as measured by ammonia temperature-programmed desorption, ranged from 0.256 mmol / g to 1.28 mmol / g.

[0172] This invention, by controlling the molar ratio of glycine to ferric citrate, the type of iron precursor, the type of promoter, and the calcination temperature of the catalyst, ultimately explores a simple and rapid method for preparing iron oxide catalysts and efficiently catalyzing the methylation of phenol and methanol to produce 2,6-xylenol. The introduction of glycine as a promoter into the appropriate iron precursor significantly increases the amount of medium-strong and strong acids in the catalyst, making the ortho-C-methylation reaction of phenol more likely to occur, thereby improving the selectivity of 2,6-xylenol. Under the combined action of glycine and ferric citrate, the specific surface area and total acidity of the material are increased, resulting in higher catalytic performance.

[0173] Meanwhile, as can be seen from Examples 1-3 and Comparative Examples 1-9, there is a synergistic effect between ferric citrate, glycine in step (1) and calcination temperature in step (4) of the method of the present invention. In particular, when the molar ratio of ferric citrate to glycine in step (1) is 1:2 and the calcination temperature in step (4) is 400℃, the synergistic effect among these three is very significant, which can significantly improve the conversion rate of phenol and the selectivity of 2,6-xylenol of the prepared iron oxide catalyst. The conversion rate of phenol reached 94.4%, and the selectivity of 2,6-xylenol was 50.1%.

[0174] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for preparing an iron oxide catalyst, characterized in that: The preparation method includes the following steps: (1) Place the iron precursor and the accelerator in water, heat and stir at 90°C until they are completely dissolved to form a homogeneous aqueous solution, and obtain two aqueous solutions; Each 1 g of iron precursor is dissolved in 20 mL of water; (2) Mix the two aqueous solutions obtained in step (1), heat and stir at 90°C for 1 h to make them evenly mixed, and obtain a mixed aqueous solution; (3) The mixed aqueous solution obtained in step (2) is continuously heated and stirred for 2 h to evaporate the water until a gel-like substance is obtained. The heating temperature is 80 °C and the stirring speed is 600 r / min. (4) The gel-like material obtained in step (3) is dried in an oven at 80 °C for 12 h, and then calcined at a heating rate of 2 °C / min to a specified calcination temperature for 5 h to obtain an iron oxide catalyst. The iron precursor is ferric citrate, the accelerator is glycine, the calcination temperature in step (4) is 400 °C, and the molar ratio of the iron precursor to the accelerator in step (1) is 1:

2.

2. The iron oxide catalyst prepared by the method described in claim 1.

3. The application of the iron oxide catalyst as described in claim 2 in the catalytic methylation reaction of phenol and methanol.

4. The method for catalyzing the methylation reaction of phenol and methanol using the iron oxide catalyst as described in claim 2, characterized in that: Includes the following steps: 1) The iron oxide catalyst is sieved through a 60-80 mesh, mixed evenly with quartz sand, and then spread evenly in the middle of the fixed bed reactor, supported by glass fiber. For every 1 g of catalyst, 4 g of quartz sand is added; 2) Phenol is dissolved in methanol as raw material and pumped into the preheater for vaporization by a micro plunger pump. Nitrogen is used as a carrier gas to transport the vaporized raw material into the reactor. 3) Purge the preheater and reactor with nitrogen, raise the temperature to the specified temperature, heat for 3 hours to activate the catalyst, and then start the reaction; 4) The reaction products are collected after condensation, and a reaction sample is taken every 1 hour.

5. The method according to claim 4, characterized in that: The reaction conditions in step 2) are as follows: The molar ratio of phenol to methanol was 1:3–13, the nitrogen flow rate was 10–50 mL / min, and the weight hourly space velocity (WHSV) was 0.5 h⁻¹. -1 ~2.0 h -1 The preheater temperature is 300 ℃; The reaction conditions in step 3) are as follows: The reactor temperature was 310 ℃~390 ℃, the pressure was atmospheric pressure, and the reaction time was 8 h~30 h.

6. The method according to claim 5, characterized in that: The reaction conditions in step 3) are: reactor temperature of 330 ℃~370 ℃, nitrogen flow rate of 20~40 mL / min, and reaction time of 10 h~20 h.

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