Preparation method and application of fluorine-modified Ti-MCM-68 molecular sieve

Abstract

The invention belongs to the technical field of Ti-containing molecular sieves, and particularly relates to a preparation method and application of a fluorine-modified Ti-MCM-68 molecular sieve. The preparation method provided by the invention comprises the following steps: carrying out hydro-thermal synthesis on an Al-MCM-68 matrix; the Al-MCM-68 matrix obtained in the step 1 is subjected to acid pickling dealumination and drying, and a dried sample deAl-MCM-68 molecular sieve is obtained; the deAl-MCM-68 molecular sieve obtained in the step 2 is subjected to fluorine-containing titanium source liquid-solid phase replacement and then is washed, dried and roasted, and finally the fluorine-modified Ti-MCM-68 molecular sieve is obtained. The fluorine-modified Ti-MCM-68 molecular sieve prepared by the method disclosed by the invention has high catalytic activity on H2O2 conversion in a hydroxylation reaction of anisole and H2O2, has high selectivity on p-hydroxyanisole, and has relatively long catalyst life.

Description

Technical Field

[0001] This invention belongs to the field of Ti-containing molecular sieve technology, and particularly relates to a method for preparing fluorine-modified Ti-MCM-68 molecular sieve and its application. Background Technology

[0002] p-Hydroxyanisole can be used as a polymerization inhibitor for acrylonitrile, acrylic acid, methacrylic acid, and other alkenyl monomers. Its advantage lies in its direct participation in ternary copolymerization after addition without removal, significantly simplifying the production process. This characteristic makes it irreplaceable in the polymer materials industry. It can also be used as a UV inhibitor and as an intermediate in pharmaceuticals, dyes, fragrances, and pesticides. o-Hydroxyanisole, also known as guaiacol, is an important fine chemical intermediate in the fragrance, pharmaceutical, agricultural, and dye industries. Among its many applications, the most important use of o-Hydroxyanisole is in the synthesis of vanillin.

[0003] In recent years, the process for preparing hydroxyanisole from anisole and hydrogen peroxide has gradually attracted attention. This process features mild reaction conditions, high yield, and water as the main byproduct, fully aligning with the principles of green chemistry and atom economy. Notably, p-hydroxyanisole has a significantly higher economic value than o-hydroxyanisole; therefore, optimizing the process to improve the ratio of p-hydroxyanisole to o-hydroxyanisole has become an important research direction for this reaction system.

[0004] Ti-containing molecular sieves are considered to be one of the most promising catalysts for hydroxylation reactions under mild conditions with H2O2 as the oxidant.

[0005] Heterogeneous catalytic systems outperform homogeneous catalytic systems in industrial operations. Heterogeneous catalysts are more stable and facilitate product separation and catalyst recovery / regeneration. However, heterogeneous catalytic reactions are affected by mass transfer and diffusion, and cannot simply exhibit the high activity and selectivity of homogeneous reactions. Existing molecular sieve catalysts still suffer from drawbacks such as low catalytic activity. Specifically, the ten-membered ring channel system of the existing TS-1 molecular sieve exhibits significant mass transfer resistance to guest molecules, resulting in low activity and para-selectivity in the hydroxylation of anisole. Although the existing Ti-MWW molecular sieve possesses sufficient tetracoordinate Ti species, it may lack suitable active centers for catalyzing hydroxylation reactions. When applied to the hydroxylation of anisole, the yield of hydroxyanisole is extremely low (<3%), making it a poor catalyst for anisole hydroxylation.

[0006] In 1999 (US Patent 6049018), Mobil disclosed a silica-alumina molecular sieve called MCM-68. This molecular sieve has an MSE-type topology with a 12×10×10 three-dimensional channel structure. The straight channels of the twelve-membered rings intersect perpendicularly with two independent and curved ten-membered ring channels, forming an 18×12-membered ring supercage accessible through the ten-membered ring channels. Due to its excellent three-dimensional channel structure, researchers began to explore this structure of titanium-silicon molecular sieve. Existing technologies disclose the synthesis of Ti-MCM-68 molecular sieves via a post-processing synthesis method, which involves acid leaching and dealuminization of the MCM-68 molecular sieve followed by gas-phase titanium tetrachloride replenishment. However, gas-solid phase replacement titanium replenishment still has many drawbacks: titanium tetrachloride is highly susceptible to hydrolysis, generating corrosive HCl acid mist, which can easily lead to dangerous accidents. Titanium replenishment requires temperatures above 500℃, which is not only very energy-intensive, but also places stringent requirements on the materials and process design of the reaction equipment, increasing the difficulty of industrial application.

[0007] Based on its open pore structure and suitable Ti active sites for catalyzing hydroxylation reactions, Ti-MCM-68 possesses the potential for highly efficient catalysis of anisole hydroxylation reactions to prepare hydroxyanisole. From an industrial application perspective, developing a Ti-MCM-68 molecular sieve with suitable hydrophobicity, high para-selectivity, good catalytic activity, and long lifetime, and optimizing its titanium supplementation method, is of great significance. Summary of the Invention

[0008] In view of the shortcomings of the methods listed above, the purpose of this invention is to provide a method for preparing fluorine-modified Ti-MCM-68 molecular sieve and its application. The fluorine-modified Ti-MCM-68 molecular sieve prepared by the method of this invention has high catalytic activity for the conversion of H2O2 in the hydroxylation reaction of anisole and H2O2, high selectivity for p-hydroxyanisole, and a long catalyst lifetime.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing fluorine-modified Ti-MCM-68 molecular sieves: First, Al-MCM-68 matrix is ​​synthesized; then, it is subjected to acid washing, drying, and solid-phase displacement with fluorine-containing titanium source liquid; finally, it is obtained by washing, drying, and calcination to obtain fluorine-modified Ti-MCM-68 molecular sieves.

[0011] The specific preparation method is as follows:

[0012] (1) Hydrothermal synthesis of Al-MCM-68 parent material:

[0013] ① Preparation of reactants: Mix colloidal silica, deionized water, and Al(OH)3 in a polytetrafluoroethylene container and stir for 10 minutes. Add KOH aqueous solution to the solution and continue stirring for 30 minutes. Then add TEBOP. 2+ (I - )2 was used as a structure directing agent, and the mixture was stirred for another 4 hours. The molar composition of the resulting mixture was: SiO2:TEBOP 2+ (I - )2: KOH: Al(OH)3: H2O=1.0: 0.1~0.3: 0~0.5: 0.1~0.5: 15~40.

[0014] ② Hydrothermal crystallization: The mixture is placed in a polytetrafluoroethylene-lined autoclave and crystallized at 130–180°C for 14–18 days.

[0015] ③ Washing and drying: After cooling the autoclave to room temperature, centrifuge the mixture, then wash the obtained solid with deionized water several times, and dry it overnight to obtain MCM-68 white powder.

[0016] ④ High-temperature calcination: To remove the structure-directing agent clogging the pores of the molecular sieve, the synthesized MCM-68 was placed in a muffle furnace and heated stepwise according to the following steps: the temperature was increased from room temperature to 550–650℃ (heating rate of 1℃ / min) and maintained at the same temperature for 8–12 hours. Finally, the sample was cooled to room temperature to obtain the Al-MCM-68 parent sample.

[0017] (2) The Al-MCM-68 molecular sieve was placed in an acid solution of a certain concentration and ultrasonically treated to remove aluminum. After drying, the dried sample deAl-MCM-68 molecular sieve was obtained.

[0018] (3) Add hexafluorotitanic acid (H2TiF6) dropwise to a polytetrafluoroethylene container containing a certain amount of deionized water at a solid-liquid ratio of 1g:20mL, and slowly add the molecular sieve powder obtained in step (2) to the solution while stirring. Place the sealed polytetrafluoroethylene container in a water bath with stirring / sonication for a period of time. Filter the sample and wash it thoroughly with deionized water until the solution is neutral. Dry it at 100℃ overnight and then calcine it in a tube furnace to obtain sample F-Ti-MCM-68.

[0019] Preferably, the acid in step (2) is hydrochloric acid, sulfuric acid or nitric acid, more preferably nitric acid, and the concentration of the acid solution is 0.5 to 10 mol / L, the solid-liquid ratio is 1 g: 10 to 30 mL, and the acid treatment time is 1 to 4 h.

[0020] Preferably, the feed ratio (Si / Ti ratio) in step (3) is 10 to 40.

[0021] Preferably, the water bath temperature in step (3) is 20-100°C and the displacement reaction time is 1-8 hours.

[0022] Preferably, the roasting temperature in step (3) is 500-800℃ and the roasting time is 4-8h.

[0023] The present invention also provides an application of the above-mentioned molecular sieve as a catalyst in the reaction of hydroxylation of anisole to produce hydroxyanisole using hydrogen peroxide as an oxidant.

[0024] This invention can be carried out using batch, semi-continuous, and continuous methods. Various types of reactors can be used for the hydroxylation of anisole, including batch reactors, tubular reactors, fixed-bed reactors, and fluidized-bed reactors.

[0025] In addition, the aforementioned molecular sieve catalysts can be used directly, or they can be shaped and then used as fillers, depending on the reactor type. Common methods for shaping molecular sieve catalysts include extrusion molding, tableting, rotary granulation, and spray granulation.

[0026] Preferably, the hydroxylation reaction of anisole is carried out in the presence of a solvent, which is selected from protic and aprotic solvents. The protic solvent can be selected from water or alcohols, such as methanol, ethanol, and propanol, while the aprotic solvent can be acetone, acetonitrile, etc.

[0027] Preferably, the hydroxylation reaction temperature of anisole is 40–100°C.

[0028] Beneficial effects

[0029] This invention discloses a method for preparing fluorine-modified Ti-MCM-68 molecular sieves. Compared with the prior art, this invention has the following advantages:

[0030] (1) The hexafluorotitanic acid used in the preparation method of the present invention is not only inexpensive, but also introduces active Ti species into the molecular sieve framework through liquid-solid phase displacement, while providing the fluorine source required for modification. The operation is simple, the process is easy to control, the reaction conditions are mild, and the equipment requirements are low.

[0031] (2) The F in the inorganic titanium source used in the preparation method of the present invention - During liquid-solid phase displacement, occupying some vacancies on the surface of the molecular sieve can effectively prevent the formation of non-framework Ti, reduce the ineffective decomposition of hydrogen peroxide during the hydroxylation reaction, and improve the effective utilization rate of hydrogen peroxide.

[0032] (3) The fluorine-modified Ti-MCM-68 molecular sieve obtained in this invention has stronger Lewis acidity and hydrophobicity, and exhibits excellent catalytic performance and para-selectivity in the hydroxylation reaction of anisole.

[0033] (4) The fluorine element introduced in this invention can be stably anchored in the molecular sieve framework structure, exhibiting excellent structural stability. This stability not only significantly enhances the catalytic oxidation activity, but also effectively extends the catalyst's lifespan. Attached Figure Description

[0034] Figure 1 Example 1: XRD patterns of Al-MCM-68 matrix, deAl-MCM-68 sample after dealumination, and F-Ti-MCM-68 sample after titanium supplementation;

[0035] Figure 2 Compare the XRD patterns of Examples 1 and 2 (TS-1 and Ti-MWW);

[0036] Figure 3 Infrared spectral analysis results of pyridine adsorption in the samples of Example 1 and Comparative Examples 1-2;

[0037] Figure 4 Figure 1 shows the results of static water adsorption experiments on samples from Example 1 and Comparative Examples 1-2.

[0038] Figure 5 XPS image of the F-Ti-MCM-68 sample in Example 1. Detailed Implementation

[0039] The present invention will now be described in detail. Before proceeding with the description, it should be understood that the terminology used in this specification and the appended claims should not be construed as limited to its general or dictionary meaning, but rather should be interpreted according to the meaning and concept corresponding to the technical aspects of the invention, based on the principle that the inventors are allowed to appropriately define the terms for the best interpretation. Therefore, the description presented herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the invention. It should be understood that other equivalents or modifications can be obtained from it without departing from the spirit and scope of the invention.

[0040] The following embodiments are merely examples illustrating implementations of the present invention and do not constitute any limitation on the present invention. Those skilled in the art will understand that modifications made without departing from the spirit and concept of the present invention fall within the protection scope of the present invention. Unless otherwise specified, the reagents and instruments used in the following embodiments are commercially available products.

[0041] Example 1

[0042] A method for preparing fluorine-modified Ti-MCM-68 molecular sieve includes the following steps:

[0043] (1) Hydrothermal synthesis of Al-MCM-68 parent material:

[0044] ① Preparation of reactants: Mix colloidal silica, deionized water, and Al(OH)3 in a polytetrafluoroethylene container and stir for 10 minutes. Add KOH aqueous solution to the solution and continue stirring for 30 minutes. Then add TEBOP. 2+ (I - )2 was used as a structure directing agent, and the mixture was stirred for another 4 hours. The molar composition of the resulting mixture was: 1.0 SiO2, 0.1 TEBOP 2+ (I - )2, 0.375KOH, 0.1Al(OH)3, 30H2O.

[0045] ② Hydrothermal crystallization: The mixture is placed in a polytetrafluoroethylene-lined autoclave and crystallized at 160°C for 16 days.

[0046] ③ Washing and drying: After cooling the autoclave to room temperature, centrifuge the mixture, then wash the obtained solid with deionized water several times, and dry it overnight to obtain MCM-68 white powder.

[0047] ④ High-temperature calcination: To remove the structure-directing agent clogging the pores of the molecular sieve, the synthesized MCM-68 was placed in a muffle furnace and heated stepwise according to the following steps: the temperature was increased from room temperature to 650℃ (heating rate of 1℃ / min) and held at the same temperature for 10 hours. Finally, the sample was cooled to room temperature to obtain the Al-MCM-68 parent sample.

[0048] (2) Acid pickling and aluminum removal: The Al-MCM-68 matrix was placed in a container containing a 6 mol / L nitric acid solution and subjected to ultrasonic treatment. The solid-liquid ratio was 1 g: 20 mL, the acid pickling temperature was 30 °C, and the acid pickling time was 3 h. The solid obtained after ultrasonic treatment was washed with water and dried to obtain deAl-MCM-68.

[0049] (3) Liquid-solid phase displacement and calcination: H2TiF6 was added dropwise to a polytetrafluoroethylene container containing a certain amount of deionized water. While stirring, deAl-MCM-68 molecular sieve powder was slowly added to the solution at a solid-liquid ratio of 1g:20mL and a feed ratio (Si / Ti) of 15. The sealed polytetrafluoroethylene container was placed in a stirred 30℃ water bath for 2h. The sample was filtered and thoroughly washed with deionized water until the solution was neutral. After drying at 100℃ overnight, it was calcined in a tube furnace at 550℃ for 6h to obtain sample F-Ti-MCM-68.

[0050] Phase analysis of sample F-Ti-MCM-68 was performed using a Bruker D8 Advance X-ray diffractometer. The XRD pattern (...) Figure 1As can be seen, the Al-MCM-68 sample in the example showed characteristic diffraction peaks at 6.5°, 6.9°, 9.7°, 19.4°, 21.7°, 22.7°, and 27.4° corresponding to the

[101] ,

[110] ,

[200] ,

[400] ,

[420] ,

[105] , and

[440] crystal planes, indicating the formation of MCM-68 molecular sieve.

[0051] Depend on Figure 2 It can be seen that the deAl-MCM-68 sample after dealuminization and the F-Ti-MCM-68 after titanium supplementation still maintain a good MSE topology compared with the Al-MCM-68 parent. However, the breakage of aluminum-oxygen bonds during the dealuminization process leads to the broadening of diffraction peaks.

[0052] Example 2

[0053] A method for preparing fluorine-modified Ti-MCM-68 molecular sieve includes the following steps:

[0054] (1) Hydrothermal synthesis of Al-MCM-68 parent material:

[0055] ① Preparation of reactants: Mix colloidal silica, deionized water, and Al(OH)3 in a polytetrafluoroethylene container and stir for 10 minutes. Add KOH aqueous solution to the solution and continue stirring for 30 minutes. Then add TEBOP. 2+ (I - )2 was used as a structure directing agent, and the mixture was stirred for another 4 hours. The molar composition of the resulting mixture was: 1.0 SiO2, 0.3 TEBOP 2+ (I - )2, 0.5KOH, 0.5Al(OH)3, 40H2O.

[0056] ② Hydrothermal crystallization: The mixture is placed in a polytetrafluoroethylene-lined autoclave and crystallized at 180°C for 14 days.

[0057] ③ Washing and drying: After cooling the autoclave to room temperature, centrifuge the mixture, then wash the obtained solid with deionized water several times, and dry it overnight to obtain MCM-68 white powder.

[0058] ④ High-temperature calcination: To remove the structure-directing agent clogging the pores of the molecular sieve, the synthesized MCM-68 was placed in a muffle furnace and heated stepwise according to the following steps: the temperature was increased from room temperature to 550℃ (heating rate of 1℃ / min) and maintained at the same temperature for 8 hours. Finally, the sample was cooled to room temperature to obtain the Al-MCM-68 parent sample.

[0059] (2) Acid pickling and aluminum removal: The Al-MCM-68 matrix was placed in a container containing a 6 mol / L nitric acid solution and subjected to ultrasonic treatment. The solid-liquid ratio was 1 g: 20 mL, the acid pickling temperature was 30 °C, and the acid pickling time was 3 h. The solid obtained after ultrasonic treatment was washed with water and dried to obtain deAl-MCM-68.

[0060] (3) Liquid-solid phase displacement and calcination: H2TiF6 was added dropwise to a polytetrafluoroethylene container containing a certain amount of deionized water. While stirring, deAl-MCM-68 molecular sieve powder was slowly added to the solution at a solid-liquid ratio of 1g:20mL and a feed ratio (Si / Ti) of 25. The sealed polytetrafluoroethylene container was placed in a 30℃ water bath with ultrasound for 2 hours. The sample was filtered and thoroughly washed with deionized water until the solution was neutral. After drying at 100℃ overnight, it was calcined in a tube furnace at 600℃ for 6 hours to obtain sample F-Ti-MCM-68.

[0061] Example 3

[0062] A method for preparing fluorine-modified Ti-MCM-68 molecular sieve includes the following steps:

[0063] (1) Hydrothermal synthesis of Al-MCM-68 parent material:

[0064] ① Preparation of reactants: Mix colloidal silica, deionized water, and Al(OH)3 in a polytetrafluoroethylene container and stir for 10 minutes. Add KOH aqueous solution to the solution and continue stirring for 30 minutes. Then add TEBOP. 2+ (I - )2 was used as a structure directing agent, and the mixture was stirred for another 4 hours. The molar composition of the resulting mixture was: 1.0 SiO2, 0.2 TEBOP 2+ (I - )2, 0.1KOH, 0.3Al(OH)3, 15H2O.

[0065] ② Hydrothermal crystallization: The mixture is placed in a polytetrafluoroethylene-lined autoclave and crystallized at 130°C for 18 days.

[0066] ③ Washing and drying: After cooling the autoclave to room temperature, centrifuge the mixture, then wash the obtained solid with deionized water several times, and dry it overnight to obtain MCM-68 white powder.

[0067] ④ High-temperature calcination: To remove the structure-directing agent clogging the pores of the molecular sieve, the synthesized MCM-68 was placed in a muffle furnace and heated stepwise according to the following steps: the temperature was increased from room temperature to 600℃ (heating rate of 1℃ / min) and held at the same temperature for 12 hours. Finally, the sample was cooled to room temperature to obtain the Al-MCM-68 matrix.

[0068] (2) Acid pickling and aluminum removal: The Al-MCM-68 matrix was placed in a container containing a 4 mol / L nitric acid solution and subjected to ultrasonic treatment. The solid-liquid ratio was 1 g: 20 mL, the acid pickling temperature was 30 °C, and the acid pickling time was 3 h. The solid obtained after ultrasonic treatment was washed with water and dried to obtain deAl-MCM-68.

[0069] (3) Liquid-solid phase displacement and calcination: H2TiF6 was added dropwise to a polytetrafluoroethylene container containing a certain amount of deionized water. While stirring, deAl-MCM-68 molecular sieve powder was slowly added to the solution at a solid-liquid ratio of 1g:20mL and a feed ratio (Si / Ti) of 40. The sealed polytetrafluoroethylene container was placed in a stirred 60℃ water bath for 2h. The sample was filtered and thoroughly washed with deionized water until the solution was neutral. After drying at 100℃ overnight, it was calcined in a tube furnace at 550℃ for 6h to obtain sample F-Ti-MCM-68.

[0070] Example 4

[0071] A method for preparing fluorine-modified Ti-MCM-68 molecular sieve includes the following steps:

[0072] (1) Hydrothermal synthesis of Al-MCM-68 parent material:

[0073] ① Preparation of reactants: Mix colloidal silica, deionized water, and Al(OH)3 in a polytetrafluoroethylene container and stir for 10 minutes. Add KOH aqueous solution to the solution and continue stirring for 30 minutes. Then add TEBOP. 2+ (I - )2 was used as a structure directing agent, and the mixture was stirred for another 4 hours. The molar composition of the resulting mixture was: 1.0 SiO2, 0.1 TEBOP 2+ (I - )2, 0.375KOH, 0.1Al(OH)3, 30H2O.

[0074] ② Hydrothermal crystallization: The mixture is placed in a polytetrafluoroethylene-lined autoclave and crystallized at 160°C for 16 days.

[0075] ③ Washing and drying: After cooling the autoclave to room temperature, centrifuge the mixture, then wash the obtained solid with deionized water several times, and dry it overnight to obtain MCM-68 white powder.

[0076] ④ High-temperature calcination: To remove the structure-directing agent clogging the pores of the molecular sieve, the synthesized MCM-68 was placed in a muffle furnace and heated stepwise according to the following steps: the temperature was increased from room temperature to 650℃ (heating rate of 1℃ / min) and held at the same temperature for 10 hours. Finally, the sample was cooled to room temperature to obtain the Al-MCM-68 parent sample.

[0077] (2) Acid pickling and aluminum removal: The Al-MCM-68 matrix was placed in a container containing a 2 mol / L nitric acid solution and subjected to ultrasonic treatment. The solid-liquid ratio was 1 g: 20 mL, the acid pickling temperature was 30 °C, and the acid pickling time was 3 h. The solid obtained after ultrasonic treatment was washed with water and dried to obtain deAl-MCM-68.

[0078] (3) Liquid-solid phase displacement and calcination: H2TiF6 was added dropwise to a polytetrafluoroethylene container containing a certain amount of deionized water. While stirring, deAl-MCM-68 molecular sieve powder was slowly added to the solution at a solid-liquid ratio of 1g:20mL and a feed ratio (Si / Ti) of 50. The sealed polytetrafluoroethylene container was placed in an 80℃ water bath with stirring and reacted for 2h. The sample was filtered and thoroughly washed with deionized water until the solution was neutral. After drying at 100℃ overnight, it was calcined in a tube furnace at 550℃ for 6h to obtain sample F-Ti-MCM-68.

[0079] Comparative Example 1

[0080] This comparative example synthesizes TS-1 molecular sieve according to the method described in US Patent (US4410501A): A certain amount of tetraethyl silicate (TEOS) was added dropwise to an aqueous solution of tetrapropylammonium hydroxide (TPAOH) while stirring to form a silica sol. Simultaneously, tetrabutyl titanate (TBOT) was dissolved in ethanol and slowly added dropwise to the silica sol. The pH of the system was adjusted to alkaline with ammonia water, and the mixture was stirred for several hours to form a mixed gel with a molar ratio of 1SiO2:0.025TiO2:0.25TPAOH:4EtOH:18H2O. The gel was transferred to an autoclave and crystallized at 80°C for 24 hours, followed by crystallization at 170°C for 48 hours. After crystallization, the gel was filtered, washed, dried, and calcined at 550°C for 6 hours to obtain a white powder sample, TS-1.

[0081] Comparative Example 2

[0082] This comparative example synthesizes Ti-MWW molecular sieves according to the method described in the literature (J. Phys. Chem. B., 2001, 105: 2897–2905): A certain amount of piperidine (PI) was dissolved in deionized water, and the solution was divided into two equal portions. Tetrabutyl titanate (TBOT) was added to one portion under vigorous stirring, and boric acid was added to the other portion under vigorous stirring. The mixture was stirred for 30 min to hydrolyze TBOT. Simultaneously, a certain amount of silica was divided into two equal portions and slowly added to solutions containing titanium and boron, respectively. The mixture was stirred for 1 h to form two homogeneous gels. Subsequently, the two gels were mixed and stirred for 1.5 h to obtain a gel with a molar composition of 1SiO2:0.02TiO2:0.67B2O3:1.4PI:19H2O. The obtained gel was transferred to an autoclave and heated at 100 r / min, first at 130 °C for 1 day, then at 150 °C for 1 day, and finally at 170 °C for 5 days. After crystallization, the sample was filtered, washed, dried, and calcined at 530℃ for 10 h. The synthesized product was then placed in a 6 mol / L nitric acid solution with a solid-liquid ratio of 1 g:20 mL and acid-washed at 100℃ for 20 h. Subsequently, the acid-treated sample was calcined again at 530℃ to obtain sample Ti-MWW. XRD patterns showed that Comparative Example 1 sample exhibited characteristic diffraction peaks at 7.9°, 8.9°, 22.9°, 23.8°, and 24.4°, indicating the formation of TS-1 molecular sieve. Comparative Example 2 sample exhibited characteristic peaks at 7.2°, 8.0°, 9.6°, 14.4°, 16.0°, 22.7°, 23.7°, and 26.1°, indicating the formation of Ti-MWW molecular sieve.

[0083] Application examples

[0084] The performance of the F-Ti-MCM-68 molecular sieves prepared in Examples 1-4 and the TS-1 and Ti-MWW molecular sieves prepared in Comparative Examples 1 and 2 as anisole hydroxylation catalysts was evaluated.

[0085] The results are summarized in Table 1.

[0086] The measurement method and calculation formulas for each value are shown below.

[0087] Determination Method: The F-Ti-MCM-68 molecular sieves prepared in Examples 1-4 were tableted, crushed, and sieved. A 40-60 mesh shaped catalyst was used as a catalyst bed, with a catalyst dosage of 10 g. The catalyst bed was loaded into a fixed-bed reactor. The molar ratio of anisole to hydrogen peroxide (27.5%) was 2:1, the concentration of anisole was 15 wt%, and ethanol was used as the solvent. After mixing, the mixture was pumped through a high-pressure pump at an anisole space velocity of 1.0 h⁻¹. -1The product enters the reaction system at a flow rate of 0.5 MPa, the reaction temperature is 70°C, and the pressure is 0.5 MPa. A collection tank is connected to the reactor outlet for product collection. The product is quantified by gas chromatography.

[0088] In the embodiments of the present invention, an Agilent gas chromatograph was used to determine the contents of anisole, o-hydroxyanisole and p-hydroxyanisole in the system by external standard method, and hydrogen peroxide was determined by iodometric method.

[0089] The conversion rate of anisole, the selectivity of p-hydroxyanisole, and the effective utilization rate of hydrogen peroxide are calculated using the following formulas:

[0090]

[0091]

[0092] The catalytic results of the molecular sieves in Examples 1-4 in the hydroxylation reaction of anisole are shown in Table 1:

[0093] Table 1. Catalytic results of molecular sieves in the hydroxylation reaction of anisole in Examples 1-4.

[0094]

[0095] As can be seen from the data in Table 1, the fluorine-modified Ti-MCM-68 molecular sieve prepared in this invention exhibits significant advantages in the hydroxylation reaction of anisole. Compared with the TS-1 molecular sieve of Comparative Example 1, the anisole conversion rates of Examples 1-4 are significantly higher. For example, the anisole conversion rate of Example 2 reaches 60.2%, which is much higher than the 36.5% of Comparative Example 1. This indicates that the molecular sieve of this invention has a stronger catalytic conversion ability for anisole.

[0096] Regarding the selectivity for p-hydroxyanisole, Examples 1-4 were all higher than Comparative Example 1, with Example 2 reaching 78.8% and Comparative Example 1 only reaching 63.4%, indicating that the molecular sieve of the present invention can more effectively promote the reaction toward the formation of p-hydroxyanisole.

[0097] Regarding the effective utilization rate of hydrogen peroxide, Examples 1-4 were also higher than Comparative Example 1, with Example 2 reaching 82.8% and Comparative Example 1 only reaching 50.8%. This indicates that the molecular sieve of the present invention can utilize hydrogen peroxide more efficiently, improving the utilization efficiency of raw materials. Compared with the Ti-MWW molecular sieve of Comparative Example 2, the advantages are even more obvious. The anisole conversion rate of Comparative Example 2 was only 2.8%, far lower than that of Examples 1-4, with almost no actual catalytic effect.

[0098] Experimental example

[0099] (1) Using a Bruker Tensor 27 infrared spectrometer, saturated adsorption infrared experiments of pyridine (Py) probe molecules were performed on the samples in Example 1 and Comparative Examples 1-2 to determine the Lewis acid strength.

[0100] Following the method used in the reference (Microporous and Mesoporous Materials 335(2022)111840), the sample was first subjected to a high vacuum of 473K (<10 -4 Activation was performed under (Pa) conditions for 2 h. After collecting background spectra at 323 K, excess pyridine was added to the sample, and the sample was kept at 323 K for 30 min to reach equilibrium. Physico- and chemi-adsorbed pyridine was desorbed by vacuum at 323 K for 30 min, followed by FTIR spectra collection. Pyridine interacting with Lewis acids was detected at 1445 cm⁻¹. -1 An absorption peak appears nearby. The presence and intensity of this peak can be used to determine whether the sample contains Lewis acid and its strength.

[0101] The experimental results are as follows Figure 3 As shown, the samples of Comparative Examples 1, 2 and the Example were measured at 1445 cm⁻¹. -1 Absorption peaks were observed at all locations, indicating that all samples contained Lewis acids. The figure also shows that the example sample exhibited an absorption peak at 1445 cm⁻¹. -1 The absorption peak intensity at this location is higher than that of Comparative Examples 1 and 2, indicating that the sample obtained by this method has stronger Lewis acidity.

[0102] (2) Conduct a static water adsorption experiment to test the hydrophobicity of the sample.

[0103] First, the molecular sieve sample was dried overnight at 100℃, then kept at a constant temperature of 35℃ and placed in a sealed vacuum desiccator containing a fixed amount of water. After the sample was in equilibrium adsorption in saturated water vapor for 2 days, the amount of water adsorbed was measured. The water adsorption rate (X) was calculated using the following formula:

[0104] X=(m wet -m dry ) / m dry ×100%

[0105] The experimental results are as follows Figure 4 As shown, compared with Al-MCM-68 matrix, Comparative Example 1 (TS-1) and Comparative Example 2 (Ti-MWW), the water adsorption rate of Example 1 (F-Ti-MCM-68 molecular sieve) is reduced, indicating that it has a certain degree of hydrophobicity.

[0106] (3) The sample from Example 1 was analyzed using a Shimadzu Kratos AXIS Supra X-ray photoelectron spectrometer, and the results are as follows: Figure 5 As shown, the peak at 687.33 eV is the F1S peak, indicating the presence of fluorine in the sample. Furthermore, the XRD pattern shows that the characteristic peaks of the F-Ti-MCM-68 molecular sieve are consistent with the structure of pure MSE, and the introduction of fluorine did not cause peak shift, indicating that fluorine atoms are embedded in the framework through chemical bonds rather than through simple physical adsorption. This structural integrity also provides evidence for the stable anchoring of fluorine.

[0107] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions claimed by the present invention.

Claims

1. A method for preparing fluorine-modified Ti-MCM-68 molecular sieve, characterized in that, Includes the following steps: (1) Hydrothermal synthesis of Al-MCM-68 parent material; (2) The Al-MCM-68 matrix obtained in step 1 is acid-washed to remove aluminum and dried to obtain the dried sample deAl-MCM-68 molecular sieve. (3) The deAl-MCM-68 molecular sieve obtained in step 2 is subjected to solid-phase replacement with fluorine-containing titanium source liquid, and then washed, dried and calcined to finally obtain fluorine-modified Ti-MCM-68 molecular sieve.

2. The method for preparing fluorine-modified Ti-MCM-68 molecular sieve according to claim 1, characterized in that, Step 1, the hydrothermal synthesis of Al-MCM-68 matrix, specifically includes the following steps: Preparation of reactants: Colloidal silica, deionized water, and Al(OH)3 are mixed and stirred in a polytetrafluoroethylene container. KOH aqueous solution is added to the solution and stirring continues. Then, TEBOP is added. 2+ (I - )2 is used as a structure directing agent, and stirring is continued to obtain a mixture; Hydrothermal crystallization: The mixture is placed in an autoclave for crystallization; Washing and drying: After cooling the autoclave to room temperature, the mixture was centrifuged, and the solid obtained was washed several times with deionized water and dried overnight to obtain MCM-68 white powder. High-temperature calcination: The synthesized MCM-68 was calcined at high temperature; then, the sample was cooled to room temperature to obtain the Al-MCM-68 matrix.

3. The method for preparing fluorine-modified Ti-MCM-68 molecular sieve according to claim 2, characterized in that, In the reaction material preparation step, the molar ratio of each component in the final mixture is SiO2:TEBOP. 2+ (I - )2:KOH:Al(OH)3:H2O=1.0:0.1~0.3:0~0.5:0.1~0.5:15~40; In the hydrothermal crystallization step, the mixture is placed in a high-pressure reactor and crystallized at 130~180℃ for 14~18 days; In the high-temperature calcination step, the synthesized MCM-68 is placed in a muffle furnace and heated stepwise according to the following steps: the temperature is raised from room temperature to 550~650℃ at a heating rate of 1℃ / min, and maintained at the same temperature for 8~12h.

4. The method for preparing fluorine-modified Ti-MCM-68 molecular sieve according to claim 1, characterized in that, The acid in step 2 is one or more of hydrochloric acid, sulfuric acid, or nitric acid; preferably nitric acid; the concentration of the acid solution is 0.5-10 mol / L, the solid-liquid ratio is 1 g: 10-30 mL, and the acid treatment time is 1-4 h.

5. The method for preparing fluorine-modified Ti-MCM-68 molecular sieve according to claim 1, characterized in that, The specific method for solid-phase displacement of the fluorinated titanium source liquid in step 3 is as follows: hexafluorotitanic acid is added dropwise to a polytetrafluoroethylene container containing a certain amount of deionized water, and the molecular sieve powder obtained in step 2 is slowly added to the solution while stirring. The sealed polytetrafluoroethylene container is then placed in a water bath with stirring / ultrasound for a period of time for displacement reaction.

6. The method for preparing fluorine-modified Ti-MCM-68 molecular sieve according to claim 5, characterized in that, Molecular sieve powder was added to the solution at a solid-liquid ratio of 1g:20mL; the feed ratio was Si:Ti = 1:10-40; the water bath temperature during the displacement reaction was 20-100℃, and the displacement reaction time was 1-8h.

7. The method for preparing fluorine-modified Ti-MCM-68 molecular sieve according to claim 1, characterized in that, The roasting temperature in step 3 is 500–800℃, and the roasting time is 4–8 hours.

8. Fluorine-modified Ti-MCM-68 molecular sieve prepared by any one of the methods described in claims 1-7.

9. The application of the fluorine-modified Ti-MCM-68 molecular sieve according to claim 8, characterized in that, It is used as a catalyst in the hydroxylation of anisole to produce hydroxyanisole using hydrogen peroxide as an oxidant.

10. The application of the fluorine-modified Ti-MCM-68 molecular sieve according to claim 9, characterized in that, The molecular sieve catalyst can be used directly or, depending on the reactor type, can be formed and then used as a filler. The forming methods for the molecular sieve catalyst include extrusion molding, tableting, rotary granulation, and spray granulation. The anisole hydroxylation reaction is carried out in the presence of a solvent, which includes protic and aprotic solvents. Protic solvents include water and alcohol solvents; alcohol solvents include methanol, ethanol, and propanol; aprotic solvents include acetone and acetonitrile. The anisole hydroxylation reaction temperature is 40–100°C.

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