Composite catalyst and preparation method thereof, and preparation method of 2, 3, 6-tricresol

Abstract

The invention discloses a composite catalyst and a preparation method thereof, and a preparation method of 2, 3, 6-tricresol. The structural formula of the composite catalyst disclosed by the invention is Fe3O4-M-g-C3N4, wherein M is Fe2SiO4 and / or Fe2TiO5. The composite catalyst disclosed by the invention has the advantages of high catalytic activity, high catalyst stability, long service life and few byproducts in a reaction for preparing 2, 3, 6-tricresol; the components introduced into the composite catalyst are cheap, easy to obtain and harmless to a human body, the preparation process is safe and environment-friendly, the cost is low, the composite catalyst is safe to use, and the composite catalyst has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalysis for the synthesis of organic chemicals, specifically relating to a composite catalyst and its preparation method, and a method for preparing 2,3,6-trimethylphenol. Background Technology

[0002] 2,3,6-Tricresol is an important raw material for the production of vitamin E, polyphenylene ether engineering plastics, and plastic alloys. In addition, it is widely used in the production of food and feed additives, cosmetics, pesticides, and disinfectants. Currently, the commonly used large-scale industrial production method of 2,3,6-tricresol mainly achieves this through the methylation reaction of phenols. This involves using methanol as the methylating agent and m-cresol or 2,5-xylenol as the raw material, with the reaction completed under certain conditions through the action of a catalyst.

[0003] Commonly used catalyst systems are iron oxide-based and iron-containing composite oxide catalysts, but these catalysts have poor catalytic activity and stability. Currently, by introducing other components, the catalytic performance of ortho-methylation of phenols can be further adjusted. For example, US Patent 5128304A discloses a phenol alkylation catalyst with the composition Fe2O3-Cr2O3-SiO2-GeO2-K2CO3. This catalyst uses Fe2O3 as the main component and adjusts the reaction performance by doping with Cr2O3, SiO2, GeO2, and K2CO3. Chinese Patent CN101844968A further introduces Mn and In into the Fe-Cr-Si-Ge-K catalyst, and the resulting catalyst can achieve a yield of 96.8-97.6% of 2,3,6-trimethylphenol at a reaction temperature of 320℃. Other publicly disclosed catalyst compositions include Fe-Co-Cr-Al-Sn-Cs-Si (Chinese Patent CN101642711A), Fe-Mg-Ce-VK / Na (Chinese Patent CN104415761B), and Fe-Al-VP-Na / K / Ca (Chinese Patent CN120227887A). However, while these catalysts have made some progress in catalytic activity, their components involve relatively expensive (such as Ge and In) or toxic (such as Cr and V) elements, which are unfavorable for large-scale production from the perspectives of cost, safety, and environment. Summary of the Invention

[0004] This invention addresses the problems of poor catalyst performance, low stability, high cost, and the use of toxic elements in existing technologies for the preparation of 2,3,6-trimethylphenol. It provides a composite catalyst and its preparation method, as well as a method for preparing 2,3,6-trimethylphenol. The composite catalyst of this invention exhibits advantages such as high catalytic activity, high catalyst stability, long service life, and few byproducts in the preparation of 2,3,6-trimethylphenol. Furthermore, the components introduced into this composite catalyst are inexpensive, readily available, and harmless to the human body. The preparation process is safe, environmentally friendly, low-cost, and safe to use, showing promising application prospects.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0006] This invention provides a composite catalyst with the structural formula Fe3O4-Mg-C3N4, wherein M is Fe2SiO4 and / or Fe2TiO5.

[0007] In this invention, the "-" between Fe3O4, M, and g-C3N4 indicates that Fe3O4, M, and g-C3N4 are tightly connected at the microscale, meaning there is an interface between the different compounds, rather than a simple physical mixture. Introducing iron-based composite oxides Fe2SiO4 and / or Fe2TiO5 (M) into Fe3O4 acts as a barrier during aging, preventing the two Fe3O4 grains from ripening and growing, thus improving the catalyst's stability. Introducing g-C3N4 into the catalyst can further enhance its reactivity.

[0008] In this invention, the mass ratio of Fe3O4, M and g-C3N4 can be (70-100):(20-50):(35-55), for example 85:35:40, 95:25:40 or 75:35:50.

[0009] In this invention, M is preferably Fe2SiO4 and Fe2TiO5. The preferred mass ratio of Fe2SiO4 to Fe2TiO5 is (10-30):(10-20), for example, 25:10 or 15:10.

[0010] In this invention, the g-C3N4 can be prepared by high-temperature pyrolysis of nitrogen-containing organic compounds; the preparation of the g-C3N4 includes the following steps: heating the nitrogen-containing organic compound under a flowing inert atmosphere and reacting at a constant temperature.

[0011] The nitrogen-containing organic compound is preferably one or more of melamine, dicyandiamine, and urea.

[0012] The inert atmosphere may be one or more of nitrogen, helium, and argon.

[0013] The heating rate can be 1-10℃ / min, for example 2℃ / min.

[0014] The target temperature for heating can be 500-650℃, for example, 550℃.

[0015] The isothermal reaction time can be 2-6 hours, for example, 4 hours.

[0016] This invention also provides a method for preparing a composite catalyst, comprising the following steps:

[0017] S1. Mix the first mixture and the second mixture to react and obtain a gel-like substance;

[0018] The first mixture includes an M source and a first solvent, wherein the M source is a titanium source and / or a silicon source;

[0019] The second mixture includes an iron source, g-C3N4, and a second solvent;

[0020] S2. Calcine and reduce the gelatinous substance.

[0021] In this invention, in step S1, the titanium source may be one or more of tetrabutyl titanate, tetraethyl titanate, and tetraisopropyl titanate.

[0022] In step S1 of this invention, the silicon source may be one or more of tetraethyl orthosilicate, methyl orthosilicate, and butyl orthosilicate.

[0023] In this invention, in step S1, the concentration of source M in the first mixture can be 0.1-2 mol / L, for example 0.4 mol / L, 0.6 mol / L, 1.2 mol / L or 1.4 mol / L.

[0024] In this invention, in step S1, the iron source can be one or more of ferric nitrate, ferric sulfate, and ferric chloride; the concentration of iron ions in the second mixture is preferably 0.5-2 mol / L, more preferably 1-2 mol / L, for example 1.2 mol / L, 1.4 mol / L, or 1.5 mol / L.

[0025] In this invention, in step S1, the first solvent can be a conventional organic solvent in the art that can dissolve the titanium source and / or silicon source, preferably ethanol; the first mixture is obtained under stirring conditions as is customary in the art.

[0026] In this invention, in step S1, the second solvent can be deionized water; the mass ratio of g-C3N4 to the second solvent can be 0.01-0.1, more preferably 0.02-0.06, for example 0.04; the second mixture is generally obtained under stirring conditions as is customary in the art, and the stirring time is preferably 30 min.

[0027] In this invention, in step S1, the mixing reaction may include a dropping step, wherein the dropping refers to adding the first mixture to the second mixture; the dropping time is preferably 1 to 20 minutes, more preferably 5 to 10 minutes, for example 5 minutes.

[0028] In this invention, in step S1, the mixing reaction can be carried out under stirring conditions to ensure a complete reaction; the stirring temperature is preferably 50-70℃, for example 60℃; the stirring time is preferably 0.5-4h, more preferably 1-2h, for example 1h.

[0029] In this invention, step S1 may include a drying step after the mixing reaction, wherein the drying temperature is preferably 90-110°C, for example 100°C.

[0030] In this invention, in step S2, the calcination temperature can be 350-650℃, preferably 400-600℃, for example 400℃, 500℃ or 600℃; the calcination time can be 2-12h, preferably 5-10h, more preferably 6-8h, for example 6h or 8h; the calcination is preferably carried out under a static air atmosphere; the calcination may also include a grinding and pulverizing step.

[0031] In this invention, in step S2, the reduction temperature can be 250-600℃, preferably 300-600℃, more preferably 350-550℃, for example 350℃, 400℃ or 550℃; the heating rate to the reduction temperature is preferably 1-10℃ / min, for example 2℃ / min; the reduction time can be 1-6h, preferably 2-5h, for example 2h or 4h; the reduction is preferably carried out in a reducing atmosphere, which can be a conventional reducing atmosphere in the art, preferably including hydrogen and / or carbon monoxide.

[0032] The present invention also provides a composite catalyst, which is prepared by the composite catalyst preparation method described above.

[0033] The present invention also provides a method for preparing 2,3,6-trimethylphenol, which uses the above-mentioned composite catalyst and the raw materials include 2,5-dimethylphenol.

[0034] In this invention, the preparation method of 2,3,6-trimethylphenol can employ a fixed-bed reaction. The fixed-bed reaction is conventional in the art, referring to a process where the raw material continuously flows into a fixed-bed reactor with a catalyst bed, and the product continuously flows out of the fixed-bed reactor, with the raw material reacting with the catalyst bed to generate the product.

[0035] In some embodiments of the present invention, the method for preparing the 2,3,6-trimethylphenol includes the following steps:

[0036] A vaporization mixture is continuously fed into a catalyst bed for reaction; wherein the vaporization mixture comprises 2,5-xylenol, methanol, and water; and the catalyst bed comprises the aforementioned composite catalyst.

[0037] The composite catalyst may be in the form of particles; the particles are obtained by compression, crushing and sieving in accordance with conventional methods in the art; the mesh size of the particles may be 60-80 mesh.

[0038] The amount of the composite catalyst used can be 30 mL.

[0039] The mass ratio of methanol, 2,5-xylenol and water can be (900-1000):(750-850):(100-200), for example, 960:800:136.

[0040] The height of the catalyst bed can be 6.5~9cm, preferably 7~8cm, for example 7.5cm.

[0041] The temperature of the catalyst bed can be 310~330℃, for example 320℃.

[0042] The pressure of the catalyst bed can be 0.1 MPa.

[0043] The liquid hourly space velocity (LHSV) of the vaporized mixture introduced into the catalyst bed can be 0.8 to 1.2 h⁻¹. -1 For example, 1h -1 .

[0044] The vaporized mixture is obtained by vaporizing it through a vaporizer, which can be a coil with a length of 3-5m; the vaporization temperature can be 235~250℃, for example 250℃.

[0045] Preferably, the reaction is followed by a condensation step.

[0046] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0047] The reagents and raw materials used in this invention are all commercially available.

[0048] The positive and progressive effects of this invention are as follows:

[0049] (1) In the composite catalyst prepared by the present invention, the addition of g-C3N4 can improve the redox ability of iron species in Fe3O4, thereby improving the reaction activity; while the addition of iron-based composite oxide can improve the long-term stability of the catalyst.

[0050] (2) The composite catalyst prepared by the present invention can form Fe2SiO4 or Fe2TiO5 at a lower temperature, avoiding the reduction of catalyst performance caused by Fe3O4 sintering during the high-temperature mineralization process.

[0051] (3) The composite catalyst provided by the present invention exhibits excellent 2,5-dimethylphenol conversion rate in the reaction for preparing 2,3,6-trimethylphenol. It has the advantages of high catalytic activity, high catalyst stability, long service life and few by-products, and has good application prospects.

[0052] (4) The composite catalyst provided by the present invention exhibits excellent 2,3,6-trimethylphenol selectivity in the reaction for preparing 2,3,6-trimethylphenol. Excellent 2,3,6-trimethylphenol selectivity can reduce the generation of tetramethylphenol byproducts with no economic value in the reaction, thereby reducing unnecessary raw material consumption and lowering costs. The components Si and / or Ti introduced into the composite catalyst provided by the present invention are inexpensive, readily available and harmless to the human body. The preparation process is safe and environmentally friendly, low in cost and safe to use. Attached Figure Description

[0053] Figure 1 XRD patterns of carbon nitride-1, carbon nitride-2 and carbon nitride-3 prepared in this invention.

[0054] Figure 2 The XRD patterns are of catalyst-1, catalyst-2 and comparative catalyst-3 prepared in this invention.

[0055] Figure 3 This is a SEM image of catalyst-3 prepared in this invention.

[0056] Figure 4 The H2-TPR test results of catalyst-1 and catalyst-3 prepared in this invention are shown. Detailed Implementation

[0057] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0058] The preparation method of carbon nitride (g-C3N4) used in the following examples and comparative examples is as follows:

[0059] Weigh 30g of nitrogen-containing organic compound, place it in a tube furnace, introduce N2, heat it to 550℃ at a rate of 2℃ / min, hold it at 550℃ for 4h, cool it to room temperature and remove it to obtain carbon nitride (g-C3N4).

[0060] Three types of carbon nitride (g-C3N4) were prepared using this method, using melamine, dicyandiamine, and urea, respectively. The carbon nitrides obtained were named carbon nitride-1, carbon nitride-2, and carbon nitride-3, respectively.

[0061] In the following examples and comparative examples, the mass ratios of the components in the prepared composite catalysts were obtained in the following ways:

[0062] The content of each element in the prepared composite catalyst was determined by ICP-AES (Agilent 5110), and the composition of compounds in the composite catalyst was obtained by X-ray diffraction (XRD, Malvern Panaco, Aeris). The mass ratio of each compound was then calculated based on these analyses.

[0063] Example 1:

[0064] Preparation of composite catalysts:

[0065] S1. Weigh 7.16g of tetraethyl orthosilicate and add it to 20g of ethanol. Stir to dissolve and obtain the first mixture. Weigh 116.3g of ferric nitrate nonahydrate and 8g of carbon nitride-1 and add them to 200g of deionized water. Stir for 30min to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over a period of 5min. Stir at 60℃ for 1h to obtain a gel.

[0066] S2. After drying the gelatinous substance to a block shape at 100 °C, it was calcined at 500 °C for 6 hours under static air atmosphere. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 400 °C at a rate of 2 °C / min. The solid was then reduced at 400 °C for 2 hours to obtain catalyst-1.

[0067] In catalyst-1, the mass ratio of Fe3O4:Fe2SiO4:g-C3N4 is 85:35:40. For example... Figure 3 The XRD results shown confirm that catalyst-1 contains Fe3O4 and Fe2SiO4.

[0068] Example 2:

[0069] Preparation of composite catalysts:

[0070] S1. Weigh 10.65g of tetrabutyl titanate and add it to 20g of ethanol. Stir and dissolve to obtain the first mixture. Weigh 114.3g of ferric nitrate nonahydrate and 8g of carbon-2 nitride and add them to 200g of deionized water. Stir for 30 minutes to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over a period of 5 minutes. Stir at 60℃ for 1 hour to obtain a gel.

[0071] S2. After drying the gelatinous substance to a block shape at 100 °C, it was calcined at 500 °C for 6 h in a static air atmosphere. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 400 °C at a rate of 2 °C / min, and held at 400 °C for 2 h to obtain catalyst-2.

[0072] In catalyst-2, the mass ratio of Fe3O4:Fe2TiO5:g-C3N4 is 85:35:40. For example... Figure 3 The XRD results shown confirm that catalyst-2 contains Fe3O4 and Fe2TiO5.

[0073] Example 3:

[0074] Preparation of composite catalysts:

[0075] S1. Weigh 5.11g of tetraethyl orthosilicate and 3.04g of tetrabutyl titanate, add them to 20g of ethanol, stir and dissolve to obtain the first mixture. Weigh 115.9g of ferric nitrate nonahydrate and 8g of carbon-1 nitride, add them to 200g of deionized water, stir for 30min to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over a period of 5min. Stir at 60℃ for 1h to obtain a gel-like substance.

[0076] S2. After drying the gelatinous substance to a block shape at 100 °C, it was calcined at 500 °C for 6 h in a static air atmosphere. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 400 °C at a rate of 2 °C / min, and held at 400 °C for 2 h to obtain catalyst-3.

[0077] The mass ratio of Fe3O4:Fe2SiO4:Fe2TiO5:g-C3N4 in catalyst-3 is 85:25:10:40.

[0078] Example 4:

[0079] Preparation of composite catalysts:

[0080] S1. Weigh 5.11g of tetraethyl orthosilicate and 3.04g of tetrabutyl titanate, add them to 20g of ethanol, stir and dissolve to obtain the first mixture. Weigh 115.9g of ferric nitrate nonahydrate and 8g of carbon-3 nitride, add them to 200g of deionized water to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over a period of 5 minutes. Stir at 60℃ for 1 hour to obtain a gel-like substance.

[0081] S2. After drying the gelatinous substance to a block shape at 100 °C, it was calcined at 500 °C for 6 h in a static air atmosphere. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 400 °C at a rate of 2 °C / min, and held at 400 °C for 2 h to obtain catalyst-4.

[0082] The mass ratio of Fe3O4:Fe2SiO4:Fe2TiO5:g-C3N4 in catalyst-4 is 85:25:10:40.

[0083] Example 5:

[0084] Preparation of composite catalysts:

[0085] S1. Weigh 3.07g of tetrabutyl orthosilicate and 3.04g of tetrabutyl titanate, add them to 20g of ethanol, stir and dissolve to obtain the first mixture. Weigh 118.6g of ferric nitrate nonahydrate and 8g of carbon-1 nitride, add them to 200g of deionized water, stir for 30min to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over 5min, stir at 60℃ for 1h to obtain a gel.

[0086] S2. After drying the gelatinous substance to a block shape at 100 °C, it was calcined at 500 °C for 6 h in a static air atmosphere. The resulting solid was then ground and pulverized, placed in a tube furnace, and H2 was introduced. The temperature was increased to 400 °C at a rate of 2 °C / min, and held at 400 °C for 2 h to obtain catalyst-5.

[0087] The mass ratio of Fe3O4:Fe2SiO4:Fe2TiO5:g-C3N4 in catalyst-5 is 95:15:10:40.

[0088] Example 6:

[0089] Preparation of composite catalysts:

[0090] S1. Weigh 5.11g of tetraethyl orthosilicate and 3.04g of tetrabutyl titanate, add them to 20g of ethanol, stir and dissolve to obtain the first mixture. Weigh 97.6g of ferric nitrate nonahydrate and 10g of carbon-1 nitride, add them to 200g of deionized water, stir for 30min to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over a period of 5min. Stir at 60℃ for 1h to obtain a gel-like substance.

[0091] S2. After drying the gelatinous substance to a block shape at 100℃, it is calcined at 500℃ for 6 h in a static air atmosphere. The resulting solid is ground and pulverized, then placed in a tube furnace, H2 is introduced, and the temperature is raised to 400℃ at a rate of 2℃ / min, and held at 400℃ for 2 h to obtain catalyst-6.

[0092] The mass ratio of Fe3O4:Fe2SiO4:Fe2TiO5:g-C3N4 in catalyst-6 is 75:25:10:50.

[0093] Example 7:

[0094] Preparation of composite catalysts:

[0095] S1. Weigh 5.11g of tetraethyl orthosilicate and 3.04g of tetrabutyl titanate, add them to 20g of ethanol, stir and dissolve to obtain the first mixture. Weigh 115.9g of ferric nitrate nonahydrate and 8g of carbon-1 nitride, add them to 200g of deionized water, stir for 30min to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over a period of 5min. Stir at 60℃ for 1h to obtain a gel-like substance.

[0096] S2. After drying the gelatinous substance to a block shape at 100 °C, it was calcined at 600 °C for 8 h in a static air atmosphere. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 550 °C at a rate of 2 °C / min, and held at 550 °C for 4 h to obtain catalyst-7.

[0097] The mass ratio of Fe3O4:Fe2SiO4:Fe2TiO5:g-C3N4 in catalyst-7 is 85:25:10:40.

[0098] Example 8:

[0099] Preparation of composite catalysts:

[0100] S1. Weigh 5.11g of tetraethyl orthosilicate and 3.04g of tetrabutyl titanate, add them to 20g of ethanol, stir and dissolve to obtain the first mixture. Weigh 115.9g of ferric nitrate nonahydrate and 8g of carbon-1 nitride, add them to 200g of deionized water, stir for 30min to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over a period of 5min. Stir at 60℃ for 1h to obtain a gel-like substance.

[0101] S2. After drying the gelatinous substance to a block shape at 100 °C, it was calcined at 400 °C for 6 h in a static air atmosphere. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 350 °C at a rate of 2 °C / min, and held at 350 °C for 4 h to obtain catalyst-8.

[0102] The mass ratio of Fe3O4:Fe2SiO4:Fe2TiO5:g-C3N4 in catalyst-8 is 85:25:10:40.

[0103] Comparative Example 1:

[0104] Catalyst preparation:

[0105] S1. Weigh 7.16g of tetraethyl orthosilicate and add it to 20g of ethanol. Stir to dissolve and obtain the first mixture. Weigh 116.8g of ferric nitrate nonahydrate and add it to 200g of deionized water. Stir for 30 minutes to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over a period of 5 minutes. Stir at 60℃ for 1 hour to obtain a gel.

[0106] S2. The gelatinous substance was dried to a block shape at 100 °C and then calcined at 500 °C for 6 h in a static air atmosphere. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 400 °C at a rate of 2 °C / min, and held at 400 °C for 2 h to obtain comparative catalyst-1.

[0107] In contrast, the mass ratio of Fe3O4 to Fe2SiO4 in catalyst-1 is 85:35.

[0108] Comparative Example 2:

[0109] Catalyst preparation:

[0110] S1. Weigh 89.0g of ferric nitrate nonahydrate and 8g of carbon nitride-1, add them to 200g of deionized water, and stir at 60℃ to obtain a paste.

[0111] S2. The paste was dried to block form at 100 °C and then calcined at 500 °C for 6 h in static air. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 400 °C at a rate of 2 °C / min, and held at 400 °C for 2 h to obtain comparative catalyst-2.

[0112] In contrast, the mass ratio of Fe3O4 to g-C3N4 in catalyst-2 is 85:40.

[0113] Comparative Example 3:

[0114] Catalyst preparation:

[0115] 116.9 g of ferric nitrate nonahydrate was weighed and calcined at 500 °C for 6 h in static air. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 400 °C at a rate of 2 °C / min and held at 400 °C for 2 h to obtain Fe3O4, i.e., comparative catalyst-3.

[0116] Comparative Example 4:

[0117] Catalyst preparation:

[0118] S1. Weigh 20g of tetraethyl orthosilicate and add it to 20g of ethanol. Stir to dissolve and obtain the first mixture. Weigh 79.3g of ferric nitrate nonahydrate and add it to 200g of deionized water. Stir for 30 minutes to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over a period of 5 minutes. Stir at 60℃ for 1 hour to obtain a gel.

[0119] S2. After drying the gelatinous substance to a block shape at 100 °C, it was calcined at 500 °C for 6 h in a static air atmosphere. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 400 °C at a rate of 2 °C / min, and held at 400 °C for 2 h to obtain Fe2SiO4, i.e., comparative catalyst-4.

[0120] Comparative Example 5:

[0121] Catalyst preparation:

[0122] S1. Weigh 5.11g of tetraethyl orthosilicate and 3.04g of tetrabutyl titanate, add them to 20g of ethanol, stir and dissolve to obtain the first mixture. Weigh 115.9g of ferric nitrate nonahydrate and 8g of carbon-1 nitride, add them to 200g of deionized water, stir for 30min to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over a period of 5min. Stir at 60℃ for 1h to obtain a gel-like substance.

[0123] S2. The gelatinous substance was dried to a block shape at 100 °C and then calcined at 500 °C for 6 h in a static air atmosphere. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 200 °C at a rate of 2 °C / min, and held at 200 °C for 2 h to obtain comparative catalyst-5.

[0124] In contrast, the mass ratio of Fe3O4:Fe2SiO4:Fe2TiO5:g-C3N4 in catalyst-5 is 85:25:10:40.

[0125] Comparative Example 6:

[0126] Catalyst preparation:

[0127] S1. Weigh 5.11g of tetraethyl orthosilicate and 3.04g of tetrabutyl titanate, add them to 20g of ethanol, stir and dissolve to obtain the first mixture. Weigh 115.9g of ferric nitrate nonahydrate and 8g of carbon-1 nitride, add them to 200g of deionized water, stir for 30min to obtain the second mixture. Quickly add the first mixture dropwise to the second mixture over a period of 5min. Stir at 60℃ for 1h to obtain a gel-like substance.

[0128] S2. The gelatinous substance was dried to a block shape at 100 °C and then calcined at 500 °C for 6 h in a static air atmosphere. The resulting solid was ground and pulverized, then placed in a tube furnace, H2 was introduced, and the temperature was increased to 650 °C at a rate of 2 °C / min, and held at 650 °C for 2 h to obtain comparative catalyst-6.

[0129] In contrast, the mass ratio of Fe3O4:Fe2SiO4:Fe2TiO5:g-C3N4 in catalyst-6 is approximately 85:25:10:40.

[0130] Comparative Example 7

[0131] Catalyst preparation:

[0132] Weigh 8.5g Fe3O4 (i.e., comparative catalyst-3), 3.5g Fe2SiO4 (i.e., comparative catalyst-4) and 4.5g carbon nitride-1, mix them physically with a scraper for 20 minutes, then put them into a bottle and shake on a shaker for 10 minutes to obtain comparative catalyst-7.

[0133] Comparative Example 8

[0134] Catalyst preparation:

[0135] Weigh out 55g of ferric nitrate nonahydrate, 0.88g of chromium nitrate nonahydrate, 0.32g of germanium tetrachloride, 0.63g of manganese nitrate tetrahydrate, 0.73g of sodium silicate nonahydrate, and 3.5g of indium trichloride, dissolve them in 1000mL of water, and stir continuously. Adjust the pH of the solution to 7.0 using 10% ammonia water, then heat to 90℃ and maintain the pH at 7.5~8.0 while stirring for 1h. Let stand overnight, filter, and repeatedly wash the filter cake with deionized water. Dry the filter cake at 120℃ for 24h. Crush the resulting solid and soak it in 20mL of 1% potassium carbonate solution for 24h. Filter, dry the resulting solid at 120℃ for 14h, and then calcine it at 470℃ for 5h to obtain comparative catalyst-8.

[0136] Example 1

[0137] The prepared catalyst-3 was observed using a scanning electron microscope (ZEISS Sigma 300, Germany), and the results are as follows: Figure 1 As shown, a large number of fine particles exist on the surface of the catalyst, which is conducive to the adsorption reaction of gas molecules and enhances the catalytic performance of the catalyst.

[0138] X-ray diffraction (XRD, Malvern Panaco, Aeris) was performed on the prepared carbon nitride-1, carbon nitride-2, carbon nitride-3, catalyst-1, catalyst-2, and comparative catalyst-3. The results are as follows: Figure 2 and Figure 3 As shown. From Figure 2 It can be seen that the carbon nitride-1, carbon nitride-2, and carbon nitride-3 prepared in this invention are graphitic carbon nitrides (g-C3N4). From Figure 3 It can be seen that catalyst-1 contains Fe3O4 and Fe2SiO4, catalyst-2 contains Fe3O4 and Fe2TiO5, and catalyst-3 contains only Fe3O4, without Fe2SiO4 or Fe2TiO5.

[0139] Example 2

[0140] The catalysts prepared in the above-mentioned examples and comparative examples were compressed into tablets, crushed, and sieved to obtain 60-80 mesh particles for use in the reaction of 2,5-xylenol to 2,3,6-trimethylphenol. This reaction is a fixed-bed reaction, in which the raw materials continuously flow into the reactor and the products continuously flow out of the reactor, that is, the raw materials react with the catalyst bed to generate the products.

[0141] The specific steps are as follows:

[0142] 30 mL of catalyst was placed in the bed of a fixed-bed reactor (Shanghai Yanzheng Experimental Instrument Co., Ltd.) to obtain a catalyst bed. Methanol, 2,5-xylenol, and water were mixed at a mass ratio of 960:800:136, and then vaporized in a vaporizer (a coil heated to 250°C, approximately 3-5 meters long) to obtain a vaporized mixture. The vaporized mixture was then vaporized at a liquid air velocity of 1 h⁻¹. -1 A catalyst bed (7.5 cm high, 320 °C, 0.1 MPa) was introduced for the reaction. The reacted material was collected in a condenser to obtain the product 2,3,6-trimethylphenol.

[0143] The obtained 2,3,6-trimethylphenol content was analyzed by external standard method using a gas chromatograph (Shimadzu Corporation, GC-2014C). The conversion rate and selectivity of 2,3,6-trimethylphenol were calculated according to the following formula.

[0144] The calculation methods for the relevant effect parameters are as follows:

[0145] (1) Conversion rate of 2,3,6-trimethylphenol (%) = (molar amount of 2,5-dimethylphenol consumed in the reaction / molar amount of 2,5-dimethylphenol added to the reaction) × 100%.

[0146] (2) Selectivity of 2,3,6-trimethylphenol (%) = (molar amount of 2,3,6-trimethylphenol generated in the reaction / theoretically generated molar amount of 2,3,6-trimethylphenol) × 100%.

[0147] Table 1 shows the conversion and selectivity results for each catalyst, where reaction time refers to the time during which the catalyst is continuously used for the reaction.

[0148] Table 1. Conversion of 2,5-xylenol and selectivity of 2,3,6-trimethylphenol for each catalyst

[0149]

[0150]

[0151]

[0152] The reduction rates of 2,5-xylenol conversion and 2,3,6-trimethylphenol selectivity were calculated based on the results of each catalyst at 24 h and 240 h, and the results are shown in Table 2.

[0153] Table 2. Reduction rate of 2,5-xylenol conversion and 2,3,6-trimethylphenol selectivity for each catalyst

[0154]

[0155] The catalysts prepared in the various embodiments of the present invention all exhibit high conversion rates and high selectivity in the reaction of 2,5-xylenol to 2,3,6-trimethylphenol; and have excellent long-term stability: after 240 hours of continuous reaction, the conversion rate of the catalysts prepared in each embodiment decreased by less than 4%, and in some preferred embodiments by less than 1%, while the selectivity decreased by less than 1%.

[0156] The catalytic activity results compared with those of catalyst-7 show that the physical mixture has poor catalytic performance. This is because there are fewer contact surfaces and weaker interactions between the substances at the microscopic scale.

[0157] The results of comparison with catalyst-8 show that although the catalyst prepared using the existing technology has good conversion rate and selectivity at 24h, the conversion rate and selectivity begin to decrease after 48h. In contrast, the catalyst of the present application embodiment can still maintain good conversion rate and selectivity after 240h, has higher stability, and a longer service life.

[0158] Example 3

[0159] Tests were conducted using H2-TPR (McMerrittek, AutoChem III), and the results are as follows: Figure 4 As shown. The specific test method is as follows:

[0160] Weigh 200 mg of sample and place it in a U-shaped quartz tube. Dry the sample by increasing the temperature from room temperature to 100 °C at a programmed rate of 10 °C / min. Purge the sample with He gas (50 mL / min) for 1 h, cool it to 50 °C, and then introduce a 10% H2 / Ar mixed gas (50 mL / min) for 0.5 h. After the baseline stabilizes, heat the sample to 800 °C in a 10% H2 / Ar gas stream at a rate of 10 °C / min. Detect the reducing gas using a TCD.

[0161] H2-TPR tests were performed on catalyst-1 and control catalyst-3 using the above test method. The results showed that the reduction peak of catalyst-1 shifted towards the low temperature direction, indicating that the iron species in catalyst-1 were easier to reduce. This suggests that the addition of g-C3N4 promoted the redox performance of iron oxide.

[0162] The catalyst-1 was subjected to reduction-oxidation-reduction test: (1) The catalyst sample was subjected to H2-TPR test using the above H2-TPR test method and marked as "first reduction"; (2) The temperature was lowered to 300℃, and 20% O2 / Ar (50 mL / min) was introduced to oxidize the catalyst sample for 1 h, and the above H2-TPR test steps were repeated and marked as "second reduction"; (3) The temperature was lowered to 300℃, and 20% O2 / Ar (50 mL / min) was introduced to oxidize the catalyst sample for 1 h, and the above H2-TPR test steps were repeated and marked as "third reduction".

[0163] The results showed that after the reduction-oxidation cycle, the reduction curves of the "second reduction" and "third reduction" of catalyst-1 did not change significantly compared with the "first reduction", indicating that catalyst-1 has good redox stability.

[0164] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A composite catalyst, characterized in that, Its structural formula is Fe3O4-Mg-C3N4, where M is Fe2SiO4 and / or Fe2TiO5.

2. The composite catalyst as described in claim 1, characterized in that, The mass ratio of Fe3O4, M and g-C3N4 is (70-100):(20-50):(35-55), for example 85:35:40, 95:25:40 or 75:35:50; And / or, when M is Fe2SiO4 and Fe2TiO5, the mass ratio of Fe2SiO4 to Fe2TiO5 is preferably (10-30):(10-20), for example 25:10 or 15:

10.

3. The composite catalyst as described in claim 1, characterized in that, The preparation of g-C3N4 includes the following steps: heating a nitrogen-containing organic compound under a flowing inert atmosphere and reacting at a constant temperature; The nitrogen-containing organic compound is preferably one or more of melamine, dicyandiamine, and urea. The inert atmosphere is one or more of nitrogen, helium and argon; The heating rate is 1-10℃ / min, for example, 2℃ / min; The target heating temperature is 500-650℃, for example, 550℃; The isothermal reaction time is 2-6 hours, for example, 4 hours.

4. A method for preparing a composite catalyst, characterized in that, It includes the following steps: S1. Mix the first mixture and the second mixture to react and obtain a gel-like substance; The first mixture includes an M source and a first solvent, wherein the M source is a titanium source and / or a silicon source; The second mixture includes an iron source, g-C3N4, and a second solvent; S2. Calcine and reduce the gelatinous substance.

5. The method for preparing the composite catalyst as described in claim 4, characterized in that, In step S1, the titanium source is one or more of tetrabutyl titanate, tetraethyl titanate, and tetraisopropyl titanate. And / or, in step S1, the silicon source is one or more of tetraethyl orthosilicate, methyl orthosilicate, and butyl orthosilicate; And / or, in step S1, the concentration of source M in the first mixture is 0.1-2 mol / L, for example 0.4 mol / L, 0.6 mol / L, 1.2 mol / L or 1.4 mol / L; And / or, in step S1, the iron source is one or more of ferric nitrate, ferric sulfate, and ferric chloride; And / or, in step S1, the concentration of iron ions in the second mixture is 0.5-2 mol / L, preferably 1-2 mol / L, for example 1.2 mol / L, 1.4 mol / L or 1.5 mol / L.

6. The method for preparing the composite catalyst as described in claim 4, characterized in that, In step S1, the first solvent is ethanol; And / or, in step S1, the second solvent is deionized water; And / or, in step S1, the mass ratio of g-C3N4 to the second solvent is 0.01-0.1, preferably 0.02-0.06, for example 0.04; And / or, in step S1, the second mixture is obtained under stirring conditions, wherein the stirring time is preferably 30 min; In step S1, the mixing reaction includes the step of adding the first mixture dropwise to the second mixture, wherein the dropwise addition time is preferably 1 to 20 minutes, more preferably 5 to 10 minutes, for example 5 minutes; And / or, in step S1, the mixing reaction is carried out under stirring conditions, the stirring temperature is preferably 50-70°C, for example 60°C; the stirring time is preferably 0.5-4h, more preferably 1-2h, for example 1h; And / or, in step S1, the mixing reaction is followed by a drying step, wherein the drying temperature is preferably 90-110°C, for example 100°C.

7. The method for preparing the composite catalyst as described in claim 4, characterized in that, In step S2, the calcination temperature is 350-650℃, preferably 400-600℃, for example 400℃, 500℃ or 600℃; And / or, in step S2, the calcination time is 2-12 hours, preferably 5-10 hours, more preferably 6-8 hours, for example 6 hours or 8 hours; And / or, in step S2, the calcination is carried out under a static air atmosphere; And / or, in step S2, the calcination process includes a grinding and pulverizing step; And / or, in step S2, the reduction temperature is 250-600℃, preferably 300-600℃, more preferably 350-550℃, for example 350℃, 400℃ or 550℃; And / or, in step S2, the heating rate to the reduction temperature is 1-10 °C / min, for example 2 °C / min; And / or, in step S2, the reduction time is 1-6 hours, preferably 2-5 hours, for example 2 hours or 4 hours; And / or, in step S2, the reduction is carried out in a reducing atmosphere, which preferably includes hydrogen and / or carbon monoxide.

8. A composite catalyst prepared by any one of the methods described in claims 4-7.

9. A method for preparing 2,3,6-trimethylphenol, characterized in that, The composite catalyst used is any one of claims 1-3 and 8, and the raw material includes 2,5-dimethylphenol.

10. The method for preparing 2,3,6-trimethylphenol as described in claim 9, characterized in that, The preparation method of the 2,3,6-trimethylphenol includes the following steps: A vaporization mixture is continuously fed into a catalyst bed for reaction; wherein the vaporization mixture comprises 2,5-xylenol, methanol, and water; and the catalyst bed comprises a composite catalyst as described in any one of claims 1-3 and 8. The composite catalyst is preferably in the form of particles; the particles are preferably obtained by tableting, crushing, and sieving; the mesh size of the particles is preferably 60-80 mesh. The preferred amount of the composite catalyst is 30 mL; The preferred mass ratio of methanol, 2,5-xylenol and water is (900-1000):(750-850):(100-200), for example, 960:800:

136. The height of the catalyst bed is preferably 6.5-9 cm, more preferably 7-8 cm, for example 7.5 cm; The temperature of the catalyst bed is preferably 310~330℃, for example 320℃; The pressure of the catalyst bed is preferably 0.1 MPa; The liquid hourly space velocity (LHSV) of the vaporized mixture introduced into the catalyst bed is preferably 0.8 to 1.2 h⁻¹. -1 For example, 1h -1 ; The vaporized mixture is obtained by vaporization in a vaporizer, and the vaporization temperature is preferably 235~250℃, for example 250℃; Preferably, the reaction is followed by a condensation step.

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