Modified tin-titanium-silicon molecular sieve catalyst, preparation method and application thereof, and method for preparing cresol through toluene hydroxylation

Abstract

The invention relates to the technical field of catalytic material synthesis, and discloses a preparation method of a modified tin-titanium-silicon molecular sieve catalyst, which comprises the following steps: S1, mixing a silicon source, a titanium source, a tin source, an alkali source, a template agent, a surfactant and water to obtain a first mixture; s2, performing hydrothermal reaction on the first mixture in the step S1, and washing, drying and roasting an obtained second mixture to obtain tin-titanium-silicon molecular sieve powder; and S3, mixing and contacting the tin-titanium-silicon molecular sieve powder obtained in the step S2 with an organic solution of organosiloxane, and then drying to obtain the modified tin-titanium-silicon molecular sieve catalyst. According to the modified tin-titanium-silicon molecular sieve catalyst provided by the invention, a catalytic activity center is mainly positioned in a molecular sieve pore channel, and when the catalyst is used for catalyzing a reaction for preparing cresol through toluene hydroxylation, effective shape-selective catalysis can be realized, so that the selectivity of o-cresol and p-cresol can be improved, and particularly the selectivity of the o-cresol can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic material synthesis, and in particular to a tin-titanium-silicon molecular sieve, a preparation method and application thereof, and a method for preparing cresol by hydroxylating toluene. Background Art

[0002] As an important fine chemical intermediate, cresol is widely used in industries such as medicine, pesticides, and spices. Cresol includes three isomers: o-cresol, m-cresol, and p-cresol. Single cresol has a higher market value. Initially, cresol was mostly obtained by fractionation from coal tar and waste liquid from washing petroleum fractions in oil refineries. This method has been gradually eliminated due to shortcomings such as non-renewable resources, complex production processes, numerous separation equipment, and low output. Current methods for synthesizing cresol mainly include sulfonation alkali fusion, chlorination hydrolysis, isopropylbenzene oxidation, phenol alkylation, diazotization hydrolysis, and direct oxidation. However, all of these methods have disadvantages such as easy environmental pollution, severe equipment corrosion, cumbersome reaction steps, many by-products, high production costs, low reaction conversion rates, and low cresol selectivity.

[0003] The hydroxylation of toluene to produce cresol is a promising green synthetic method that has garnered widespread attention. For example, CN1566052A discloses a method for producing cresol. This method uses H₂O₂ as an oxidant and utilizes titanium silicalite to catalyze the hydroxylation of toluene in a methanol medium. The method achieves a toluene conversion of 11%, a selectivity of 73% for o-cresol, 13% for m-cresol, and 14% for p-cresol. However, the reaction conversion rate is relatively low, and the selectivity for cresol is not high. Summary of the Invention

[0004] The present invention aims to overcome the problem of poor shape-selective catalytic effect in the prior art toluene hydroxylation reaction and provides a method for preparing a modified tin-titanium-silicon molecular sieve catalyst. The modified tin-titanium-silicon molecular sieve catalyst prepared by the present invention has catalytic active centers primarily located within the molecular sieve pores. When used to catalyze the hydroxylation of toluene to produce cresol, it can effectively perform shape-selective catalysis, thereby improving the overall selectivity of o-cresol and p-cresol, particularly improving the selectivity of o-cresol.

[0005] In order to achieve the above object, the present invention provides a method for preparing a modified tin-titanium-silicon molecular sieve catalyst, which comprises the following steps: S1, mixing a silicon source, a titanium source, a tin source, an alkali source, a template, a surfactant and water to obtain a first mixture; S2, subjecting the first mixture in step S1 to a hydrothermal reaction, washing, drying, and calcining the obtained second mixture to obtain a tin-titanium-silicon molecular sieve powder; S3. Mixing and contacting the tin-titanium-silicon molecular sieve powder described in step S2 with an organic solution of organosiloxane, and then drying to obtain a modified tin-titanium-silicon molecular sieve catalyst.

[0006] The second aspect of the present invention provides a modified tin-titanium-silicon molecular sieve catalyst prepared by the preparation method of the present invention.

[0007] The third aspect of the present invention provides use of the modified tin-titanium-silicon molecular sieve catalyst of the present invention in the hydroxylation of toluene to prepare cresol.

[0008] A fourth aspect of the present invention provides a method for preparing cresol by hydroxylation of toluene, characterized in that the method comprises: subjecting toluene, a solvent, and an oxidant to a contact reaction in the presence of the modified tin-titanium-silicon molecular sieve catalyst of the present invention.

[0009] The modified tin-titanium-silicon molecular sieve catalyst prepared by the present invention has catalytic active centers primarily located within the molecular sieve pores. When used to catalyze the hydroxylation of toluene to produce cresol, it is beneficial for improving the overall selectivity of o-cresol and p-cresol, particularly the selectivity of o-cresol. The present invention, on the one hand, adds a nonionic surfactant during the synthesis of the tin-titanium-silicon molecular sieve to enlarge the internal pores of the molecular sieve. On the other hand, by treating the outer surface of the tin-titanium-silicon molecular sieve with an organosiloxane, the oxidation reaction on the outer surface of the molecular sieve is effectively suppressed and the primary oxidation reaction is promoted within the molecular sieve pores, effectively improving the reaction conversion rate and the selectivity of o-cresol and p-cresol, particularly the selectivity of o-cresol. DETAILED DESCRIPTION

[0010] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0011] The present invention provides a method for preparing a modified tin-titanium-silicon molecular sieve catalyst, the method comprising: S1, mixing a silicon source, a titanium source, a tin source, an alkali source, a template, a surfactant and water to obtain a first mixture; S2, subjecting the first mixture in step S1 to a hydrothermal reaction, washing, drying, and calcining the obtained second mixture to obtain a tin-titanium-silicon molecular sieve powder; S3. Mixing and contacting the tin-titanium-silicon molecular sieve powder described in step S2 with an organic solution of organosiloxane, and then drying to obtain a modified tin-titanium-silicon molecular sieve catalyst.

[0012] In the present invention, the types of silicon sources can be selected from a wide range. The following exemplary description is provided, but the scope of the present invention is not limited thereto. According to a preferred embodiment of the present invention, the silicon source is one or more of tetramethyl orthosilicate, tetraethyl orthosilicate, tetra-n-propyl orthosilicate and tetra-n-butyl orthosilicate, preferably tetraethyl orthosilicate and / or tetramethyl orthosilicate.

[0013] In the present invention, there is no special requirement for the type of titanium source. The following exemplary description is given, but the scope of the present invention is not limited thereto. According to a preferred embodiment of the present invention, the titanium source is one or more of tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate and tetrabutyl titanate, preferably tetrabutyl titanate.

[0014] In the present invention, the types of tin sources can be selected from a wide range. The following exemplary description is provided, but the scope of the present invention is not limited thereto. According to a preferred embodiment of the present invention, the tin source is one or more of tin chloride, tin chloride pentahydrate, stannous chloride, stannous chloride dihydrate, calcium stannate, potassium stannate, sodium stannate, lithium stannate, stannous sulfate and stannous pyrophosphate, preferably tin chloride pentahydrate.

[0015] In the present invention, there is no special requirement for the type of alkali source. The following exemplary description is given, but the scope of the present invention is not limited thereto. According to a preferred embodiment of the present invention, the alkali source is an organic base, preferably one or more of tetrapropylammonium hydroxide and tetrabutylammonium hydroxide.

[0016] In the present invention, the types of templates can be selected from a wide range, which are exemplified below but do not limit the scope of the present invention. According to a preferred embodiment of the present invention, the template is an alkaline template, preferably one or more of ammonia, ethylamine, tetrapropylammonium hydroxide and triethanolamine, more preferably tetrapropylammonium hydroxide.

[0017] In the present invention, there is no special requirement for the type of surfactant. The following exemplary description is given, but the scope of the present invention is not limited thereto. According to a preferred embodiment of the present invention, the surfactant is a nonionic surfactant, preferably one or more of a polyol type, a polyether type, an alkyl alcohol amine type, and a polysorbate nonionic surfactant, more preferably a polysorbate nonionic surfactant, preferably one or more of Span 80, Span 60, Span 40, and Span 20.

[0018] In the present invention, there is no special requirement for the molar ratio of the silicon source, alkali source, water, surfactant, tin source and titanium source. The following is an exemplary explanation, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the molar ratio of the silicon source calculated as SiO2, the alkali source, water, surfactant, the tin source calculated as SnO2 and the titanium source calculated as TiO2 is 1: 0.05-0.6: 10-30: 0.001-0.02: 0.005-0.04: 0.005-0.04, preferably 1: 0.1-0.4: 15-25: 0.005-0.01: 0.01-0.03: 0.01-0.03.

[0019] In the present invention, the molar ratio of the tin source to the template agent can be selected in a wide range. The following exemplary description is provided, but the scope of the present invention is not limited thereto. According to a preferred embodiment of the present invention, the molar ratio of the tin source as anion to the template agent is 1:1-10, preferably 1:1-4.

[0020] In the present invention, there is no special requirement for the hydrothermal reaction process. According to a preferred embodiment of the present invention, the hydrothermal reaction includes a first heating and a second crystallization performed sequentially, and the temperature of the second crystallization is 40-170° C. higher than the temperature of the first heating.

[0021] In the present invention, the temperature range of the first heating is relatively wide, which is exemplified below but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the temperature of the first heating is 30-80°C, preferably 60-80°C.

[0022] In the present invention, the optional range of the first heating time is relatively wide, which is exemplified below but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the first heating time is 2-10 hours, preferably 6-8 hours.

[0023] In the present invention, there are no special requirements for the equipment used for the first heating, and it can be selected according to actual needs. For example, the first heating can be performed on a magnetic stirrer with a heating device. There are no special requirements for the magnetic stirrer, and common magnetic stirrers are applicable to the present invention, which will not be described in detail here.

[0024] In the present invention, the temperature range for the second crystallization is relatively wide, which is exemplified below but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the temperature for the second crystallization is 120-200°C, preferably 160-200°C.

[0025] In the present invention, the optional range of the second crystallization time is relatively wide, which is exemplified below but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the second crystallization time is 2-7 days, preferably 3-5 days.

[0026] In the present invention, there are no special requirements for the instruments and equipment used for the second crystallization, and they can be selected according to actual needs. For example, a stainless steel sealed hydrothermal reactor can be used for the second crystallization. There are no special requirements for the hydrothermal reactor, and commonly used hydrothermal reactors are applicable to the present invention. They can be selected according to actual needs and will not be described in detail here.

[0027] In the present invention, after the hydrothermal reaction is completed, the solid in the reaction mixture can be separated and taken out. There is no special requirement for the separation method, and it can be selected according to actual needs. For example, the solid can be separated by filtration.

[0028] In the present invention, the separated solid can be washed first. There is no special requirement for the type of washing liquid, which can be selected according to actual needs. For example, water can be used for washing.

[0029] In the present invention, there is no special requirement for the drying temperature. The following is an exemplary description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the drying temperature is 80-120°C.

[0030] In the present invention, there is no special requirement for the drying time. The following is an exemplary description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the drying time is 120-180 minutes.

[0031] In the present invention, there is no special requirement for the calcination temperature. The following is an exemplary description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the calcination temperature is 400-600°C.

[0032] In the present invention, there is no special requirement for the roasting time. The following is an exemplary description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the roasting time is 4-10 hours.

[0033] In the present invention, there are no special requirements for the instruments and equipment used in the drying and roasting processes. Commonly used drying equipment and roasting equipment can be applied to the present invention and can be selected according to actual needs. They will not be described in detail here.

[0034] According to a preferred embodiment of the present invention, step S1 comprises: mixing a silicon source, an alkali source, a titanium source, a surfactant and water, mixing the obtained third mixture with a tin source and stirring for 0.5-2 hours, and then adding a template to obtain the first mixture.

[0035] In the present invention, there is no special requirement for the type of organosiloxane. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the organosiloxane is a n -Si-(O-R') 4-n The compound of the structure, R and R' are each independently a C1-C3 alkyl group, preferably a methyl or ethyl group; n is 0, 1, 2 or 3, preferably 3.

[0036] According to a preferred embodiment of the present invention, the organosiloxane is one or more of methoxytrimethylsilane, ethoxytriethylsilane, ethoxytrimethylsilane and methoxytriethylsilane, preferably methoxytrimethylsilane.

[0037] In the present invention, there is no special requirement for the weight ratio of the organosiloxane to the tin-titanium-silicon molecular sieve powder. The following exemplary description is provided, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the weight ratio of the organosiloxane to the tin-titanium-silicon molecular sieve powder is 1:1-150, preferably 1:5-50, and more preferably 1:5-20.

[0038] In the present invention, there is no special requirement for the type of organic solvent. The following exemplary description is given, but the scope of the present invention is not limited thereto. According to a preferred embodiment of the present invention, the organic solvent is an organic aprotic solvent, preferably one or more of cyclohexane, n-hexane and acetone, more preferably cyclohexane and acetone, and the volume ratio of cyclohexane to acetone is 0.8-1.1:1.

[0039] In the present invention, the concentration of the organosiloxane in the organic solution of the organosiloxane can be selected in a wide range. The following exemplary description is provided, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the concentration of the organosiloxane in the organic solution of the organosiloxane is 0.01-0.1 g / mL, preferably 0.01-0.05 g / mL.

[0040] In step S3 of the present invention, the mixing contact time can be selected in a wide range, which is exemplified below but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the mixing contact time in step S3 is 12-36 hours, preferably 24-36 hours.

[0041] In step S3 of the present invention, there is no special requirement for the drying method. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the drying is performed by vacuum rotary evaporation in step S3.

[0042] In step S3 of the present invention, there is no special requirement for the drying temperature. The following is an exemplary description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the drying temperature in step S3 is 50-90°C.

[0043] In step S3 of the present invention, there is no special requirement for the drying time. The following is an exemplary description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the drying time in step S3 is 2-6 hours.

[0044] In step S3 of the present invention, there is no special requirement for the drying pressure. The following is an exemplary description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the drying pressure in step S3 is 50-100 kPa.

[0045] The present invention provides a modified tin-titanium-silicon molecular sieve catalyst prepared by the preparation method described herein. The modified tin-titanium-silicon molecular sieve catalyst provided herein has catalytic active centers primarily located within the molecular sieve pores. When used to catalyze the hydroxylation of toluene to produce cresol, it provides effective shape-selective catalysis, particularly improving selectivity for o-cresol.

[0046] The present invention provides application of the modified tin-titanium-silicon molecular sieve catalyst in the hydroxylation of toluene to prepare cresol.

[0047] The invention provides a method for preparing cresol by hydroxylation of toluene. The method comprises: subjecting toluene, a solvent and an oxidant to a contact reaction in the presence of the modified tin-titanium-silicon molecular sieve catalyst of the invention.

[0048] In the present invention, there is no special requirement for the type of solvent. The following exemplary description is given, but the scope of the present invention is not limited thereto. According to a preferred embodiment of the present invention, the solvent is one or more of methanol, acetone, methyl isobutyl ketone and cyclohexanone, preferably methanol.

[0049] In the present invention, there is no special requirement for the type of oxidant. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the oxidant is an H2O2 aqueous solution with a concentration of 30-50wt%.

[0050] In the present invention, the mass ratio of the catalyst to toluene can be selected in a wide range. The following is an exemplary description, but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the mass ratio of the catalyst to toluene is 5-10:100.

[0051] In the present invention, the molar ratio of toluene to H2O2 can be selected in a wide range, which is exemplified below but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the molar ratio of toluene to H2O2 is 3-5:1.

[0052] In the present invention, the molar ratio of the solvent to H2O2 can be selected in a wide range, which is exemplified below but does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the molar ratio of the solvent to H2O2 is 5-10:1.

[0053] In the contact reaction of the present invention, there is no special requirement for the reaction temperature. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the reaction temperature in the contact reaction is 25-80°C.

[0054] In the contact reaction of the present invention, there is no special requirement for the reaction time. The following is an exemplary description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the reaction time in the contact reaction is 3-24 hours.

[0055] The modified tin-titanium-silicon molecular sieve catalyst prepared by the present invention has catalytic active centers primarily located within the molecular sieve pores. When used to catalyze the hydroxylation of toluene to produce cresol, it is beneficial for improving the overall selectivity of o-cresol and p-cresol, particularly the selectivity of o-cresol. The present invention, on the one hand, adds a nonionic surfactant during the synthesis of the tin-titanium-silicon molecular sieve to enlarge the internal pores of the molecular sieve. On the other hand, by treating the outer surface of the tin-titanium-silicon molecular sieve with an organosiloxane, the oxidation reaction on the outer surface of the molecular sieve is effectively suppressed and the primary oxidation reaction is promoted within the molecular sieve pores, effectively improving the reaction conversion rate and the selectivity of o-cresol and p-cresol, particularly the selectivity of o-cresol.

[0056] In the present invention, toluene conversion and cresol selectivity were analyzed using gas chromatography, and the analysis results were quantified using the internal standard method, with naphthalene as the internal standard. The chromatographic analysis conditions were: an Agilent-6890 chromatograph, an HP-5 capillary column, an injection volume of 0.5 μL, and an injection port temperature of 280°C. The column temperature was maintained at 100°C for 2 minutes, then increased to 200°C at a rate of 15°C / min and maintained there for 3 minutes. The FID detector was set at a detector temperature of 300°C.

[0057] The toluene conversion rate is calculated as follows: toluene conversion rate = (toluene molar amount in raw material - toluene molar amount in product) / toluene molar amount in raw material × 100%; The formula for calculating o-cresol selectivity is: o-cresol selectivity = molar amount of o-cresol in the product / total molar amount of the product × 100%; The formula for calculating the p-cresol selectivity is: p-cresol selectivity = molar amount of p-cresol in the product / total molar amount of the product × 100%.

[0058] Preparation Example 1 The modified tin-titanium-silicon molecular sieve catalyst was prepared by the following steps: S1. Tetraethyl orthosilicate: tetrapropylammonium hydroxide: deionized water: polysorbate nonionic surfactant Span 80: tetrabutyl titanate are mixed in a molar ratio of 1:0.2:20:0.01:0.02, and stirred at room temperature; while the mixture is being stirred, tin chloride pentahydrate is added and stirred for 1 hour to obtain a colorless transparent solution (the molar ratio of tetraethyl orthosilicate to tin chloride pentahydrate is 1:0.02), wherein tetraethyl orthosilicate is calculated as SiO2, tin chloride pentahydrate is calculated as SnO2, and tetrabutyl titanate is calculated as TiO2; then, a template agent tetrapropylammonium hydroxide is added in an amount equimolar to the chloride ions in the tin chloride pentahydrate to obtain a first mixture; S2, placing the first mixture on a magnetic stirrer, heating at 70° C. for 6 hours, placing the resulting mixture in a stainless steel sealed reactor, and performing a crystallization reaction at 160° C. for 3 days to obtain a second mixture; S3. Filter the second mixture to remove the solid, wash the obtained solid with water, dry it at 110° C. for 120 min, and then calcine it in air at 550° C. for 6 h to obtain tin-titanium-silicon molecular sieve powder.

[0059] S4. Add the tin titanium silicate molecular sieve powder into 100 mL of cyclohexane solution containing 2 g of methoxytrimethylsilane, with the weight ratio of the organosiloxane to the tin titanium silicate molecular sieve powder being 1:10. Stir and disperse the reaction for 24 hours, then dry the dispersion by rotary evaporation under reduced pressure in a water bath (temperature of 50°C, time of 3 hours, pressure of 50 kPa) to obtain a modified tin titanium silicate molecular sieve catalyst.

[0060] Preparation Example 2 The modified tin-titanium-silicon molecular sieve catalyst was prepared by the following steps: S1. Tetrabutyl orthosilicate: tetrabutylammonium hydroxide: deionized water: polyol-type nonionic surfactant glycerol fatty acid ester: tetraethyl titanate are mixed in a molar ratio of 1:0.5:30:0.02:0.04, and stirred at room temperature; during the stirring of the above mixture, stannous chloride is added and stirred for 1 hour to obtain a colorless transparent solution (the molar ratio of tetrabutyl orthosilicate to stannous chloride is 1:0.04), wherein tetrabutyl orthosilicate is calculated as SiO2, stannous chloride is calculated as SnO2, and tetraethyl titanate is calculated as TiO2; then, a template agent ethylamine is added at a molar ratio of 1:10 to chloride ions in stannous chloride to obtain a first mixture; S2, placing the first mixture on a magnetic stirrer, heating at 50° C. for 10 hours, placing the resulting mixture in a stainless steel sealed reactor, and performing a crystallization reaction at 140° C. for 6 days to obtain a second mixture; S3. Filter the second mixture to remove the solid, wash the obtained solid with water, dry it at 110° C. for 120 min, and then calcine it in air at 550° C. for 6 h to obtain tin-titanium-silicon molecular sieve powder.

[0061] S4. Add the tin titanium silicate molecular sieve powder into 100 mL of n-hexane solution containing 6 g of methoxytriethylsilane, with the weight ratio of the organosiloxane to the tin titanium silicate molecular sieve powder being 1:100. Stir and disperse the reaction for 12 hours, then dry the dispersion by rotary evaporation under reduced pressure in a water bath (temperature of 60°C, time of 2 hours, pressure of 50 kPa) to obtain a modified tin titanium silicate molecular sieve catalyst.

[0062] Preparation Example 3 The modified tin-titanium-silicon molecular sieve catalyst was prepared by the following steps: S1. Tetramethyl orthosilicate: tetrabutylammonium hydroxide: deionized water: polysorbate nonionic surfactant Span 80: tetrabutyl titanate are mixed in a molar ratio of 1:0.3:25:0.008:0.03, and stirred at room temperature; while the mixture is being stirred, tin chloride pentahydrate is added and stirred for 1 hour to obtain a colorless transparent solution (the molar ratio of tetramethyl orthosilicate to tin chloride pentahydrate is 1:0.03), wherein tetramethyl orthosilicate is calculated as SiO2, tin chloride pentahydrate is calculated as SnO2, and tetrabutyl titanate is calculated as TiO2; and then tetrapropylammonium hydroxide as a template is added in a molar ratio of 1:3 to chloride ions in tin chloride pentahydrate to obtain a first mixture; S2, placing the first mixture on a magnetic stirrer, heating at 70° C. for 6 hours, placing the resulting mixture in a stainless steel sealed reactor, and performing a crystallization reaction at 180° C. for 4 days to obtain a second mixture; S3. Filter the second mixture to remove the solid, wash the obtained solid with water, dry it at 110° C. for 120 min, and then calcine it in air at 550° C. for 6 h to obtain tin-titanium-silicon molecular sieve powder.

[0063] S4. Add the tin titanium silicate molecular sieve powder into 100 mL of cyclohexane solution containing 4 g of methoxytrimethylsilane, with the weight ratio of the organosiloxane to the tin titanium silicate molecular sieve powder being 1:20. Stir and disperse the reaction for 24 hours. Then, dry the dispersion by rotary evaporation under reduced pressure in a water bath (temperature of 50°C, time of 3 hours, pressure of 50 kPa) to obtain a modified tin titanium silicate molecular sieve catalyst.

[0064] Preparation Example 4 The modified tin-titanium-silicon molecular sieve catalyst was prepared by the following steps: S1. Tetrapropyl orthosilicate: tetrapropylammonium hydroxide: deionized water: polyether nonionic surfactant fatty alcohol polyoxyethylene ether: tetramethyl titanate are mixed in a molar ratio of 1:0.05:20:0.005:0.01, and stirred at room temperature; during the stirring of the above mixture, stannous sulfate is added and stirred for 1 hour to obtain a colorless transparent solution (the molar ratio of tetrapropyl orthosilicate to stannous sulfate is 1:0.01), wherein tetrapropyl orthosilicate is calculated as SiO2, stannous sulfate is calculated as SnO2, and tetramethyl titanate is calculated as TiO2; then, a template ammonia water is added at a molar ratio of 1:5 to sulfate ions in stannous sulfate to obtain a first mixture; S2, placing the first mixture on a magnetic stirrer, heating at 70° C. for 5 hours, placing the resulting mixture in a stainless steel sealed reactor, and crystallizing at 150° C. for 4 days to obtain a second mixture; S3. Filter the second mixture to remove the solid, wash the obtained solid with water, dry it at 110° C. for 120 min, and then calcine it in air at 550° C. for 6 h to obtain tin-titanium-silicon molecular sieve powder.

[0065] S4. Add the tin titanium silicate molecular sieve powder into 100 mL of acetone solution containing 10 g of ethoxytrimethylsilane, with the weight ratio of the organosiloxane to the tin titanium silicate molecular sieve powder being 1:2. Stir and disperse the reaction for 36 hours. Then, dry the dispersion by rotary evaporation under reduced pressure in a water bath (temperature of 60°C, time of 3 hours, pressure of 50 kPa) to obtain a modified tin titanium silicate molecular sieve catalyst.

[0066] Preparation Example 5 Compared with Example 1, the difference is that in step S1, the molar ratio of tetraethyl orthosilicate, tetrapropylammonium hydroxide, deionized water, polysorbate nonionic surfactant Span 80, and tetrabutyl titanate is adjusted to 1:0.05:10:0.001:0.005, and the molar ratio of tetraethyl orthosilicate to tin chloride pentahydrate is adjusted to 1:0.005.

[0067] Preparation Example 6 Compared with Example 1, the difference is that in step S1, the molar ratio of chloride ions in tin chloride pentahydrate to the template agent tetrapropylammonium hydroxide is adjusted to 1:6.

[0068] Preparation Example 7 Compared with Example 1, the difference is that in step S1, the template agent is adjusted from tetrapropylammonium hydroxide to triethanolamine.

[0069] Preparation Example 8 Compared with Example 1, the difference is that the first heating is not performed in step S2, and the first mixture is directly placed in a stainless steel sealed reactor and crystallized at 160° C. for 3 days to obtain a second mixture.

[0070] Preparation Example 9 Compared with Example 1, the difference is that in step S3, the weight ratio of the organosiloxane to the tin-titanium-silicon molecular sieve powder is adjusted to 1:50.

[0071] Preparation Example 10 Compared with Example 1, the difference is that in step S3, the organosiloxane is adjusted from methoxytrimethylsilane to ethoxytriethylsilane.

[0072] Preparation Example 11 Compared with Example 1, the difference is that in step S3, the organic solvent is adjusted from cyclohexane to acetone.

[0073] Preparation Example 12 Compared with Example 1, the difference is that in step S3, the organic solvent is adjusted from cyclohexane to a mixed solvent of cyclohexane and acetone with a volume ratio of 1:1.

[0074] Comparative Example 1 Compared with Example 1, the difference is that the polysorbate nonionic surfactant Span 80 is not added in step S1.

[0075] Comparative Example 2 The steps S1 to S3 in Example 1 were followed, but the organosiloxane modification treatment in step S4 was omitted.

[0076] Test Case The catalysts prepared in each preparation example and each comparative example were used to evaluate the reaction performance of toluene hydroxylation to produce cresol, according to the following steps: Toluene, methanol solvent, a 30 wt% H₂O₂ aqueous solution, and a catalyst were added to a three-necked flask equipped with a condenser reflux system for reaction. The weight ratio of catalyst to toluene was 10:100, the molar ratio of toluene to H₂O₂ was 3:1, and the molar ratio of methanol to H₂O₂ was 6:1. The reaction temperature was 70°C and the reaction time was 5 hours. The results for toluene conversion, o-cresol selectivity, and p-cresol selectivity are listed in Table 1.

[0077] Table 1

[0078] The above describes preferred embodiments of the present invention, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the specific technical features in any appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preparing a modified tin-titanium-silicon molecular sieve catalyst, characterized in that: The method comprises the following steps: S1, mixing a silicon source, a titanium source, a tin source, an alkali source, a template, a surfactant and water to obtain a first mixture; S2, subjecting the first mixture in step S1 to a hydrothermal reaction, washing, drying, and calcining the obtained second mixture to obtain a tin-titanium-silicon molecular sieve powder; S3. Mixing and contacting the tin-titanium-silicon molecular sieve powder described in step S2 with an organic solution of organosiloxane, and then drying to obtain a modified tin-titanium-silicon molecular sieve catalyst.

2. The preparation method according to claim 1, wherein The silicon source is one or more of tetramethyl orthosilicate, tetraethyl orthosilicate, tetra-n-propyl orthosilicate and tetra-n-butyl orthosilicate, preferably tetraethyl orthosilicate and / or tetramethyl orthosilicate; and / or The titanium source is one or more of tetramethyl titanate, tetraethyl titanate, tetraisopropyl titanate and tetrabutyl titanate, preferably tetrabutyl titanate; and / or The tin source is one or more of tin chloride, tin chloride pentahydrate, stannous chloride, stannous chloride dihydrate, calcium stannate, potassium stannate, sodium stannate, lithium stannate, stannous sulfate and stannous pyrophosphate, preferably tin chloride pentahydrate; and / or The alkaline source is an organic base, preferably one or more of tetrapropylammonium hydroxide and tetrabutylammonium hydroxide; and / or The template agent is an alkaline template agent, preferably one or more of ammonia, ethylamine, tetrapropylammonium hydroxide and triethanolamine, more preferably tetrapropylammonium hydroxide; and / or The surfactant is a nonionic surfactant, preferably one or more of polyol type, polyether type, alkyl alcohol amine type, and polysorbate nonionic surfactant, more preferably a polysorbate nonionic surfactant; and / or The molar ratio of the silicon source as SiO2, the alkali source, water, the surfactant, the tin source as SnO2 and the titanium source as TiO2 is 1:0.05-0.6:10-30:0.001-0.02:0.005-0.04:0.005-0.04, preferably 1:0.1-0.4:15-25:0.005-0.01:0.01-0.03:0.01-0.03; and / or The molar ratio of the tin source as anion to the template is 1:1-10, preferably 1:1-4.

3. The preparation method according to claim 1 or 2, wherein The hydrothermal reaction includes a first heating and a second crystallization, wherein the temperature of the second crystallization is 40-170°C higher than the temperature of the first heating; Preferably, The first heating conditions include: a temperature of 30-80°C, preferably 60-80°C; and / or a heating time of 2-10 hours, preferably 6-8 hours; and / or The conditions for the second crystallization include: a temperature of 120-200° C., preferably 160-200° C.; and / or a time of 2-7 days, preferably 3-5 days.

4. The preparation method according to any one of claims 1 to 3, wherein Drying temperature is 80-120°C; and / or Drying time is 120-180 minutes; and / or calcination temperature is 400-600°C; and / or The roasting time is 4-10h.

5. The preparation method according to any one of claims 1 to 4, wherein The step S1 comprises: mixing a silicon source, an alkali source, a titanium source, a surfactant and water, then mixing with a tin source, and then adding a template to obtain the first mixture.

6. The preparation method according to any one of claims 1 to 5, wherein The organosiloxane contains R n -Si-(O-R') 4-n A compound of the structure, R and R' are each independently a C1-C3 alkyl group, preferably a methyl group or an ethyl group; n is 0, 1, 2 or 3, preferably 3; Preferably, the organosiloxane is one or more of methoxytrimethylsilane, ethoxytriethylsilane, ethoxytrimethylsilane and methoxytriethylsilane, preferably methoxytrimethylsilane; and / or The weight ratio of the organosiloxane to the tin-titanium-silicon molecular sieve powder is 1:1-150, preferably 1:5-50, more preferably 1:5-20; and / or The organic solvent is an organic aprotic solvent, preferably one or more of cyclohexane, n-hexane and acetone, more preferably cyclohexane and acetone, with the volume ratio of cyclohexane to acetone being 0.8-1.1:1; and / or In the organic solution of the organosiloxane, the concentration of the organosiloxane is 0.01-0.1 g / mL, preferably 0.01-0.05 g / mL; and / or The mixing contact time is 12-36 hours, preferably 24-36 hours; and / or The drying conditions include: drying by vacuum rotary evaporation, and / or drying at a temperature of 50-90° C., and / or drying for 2-6 hours, and / or drying at a pressure of 50-100 kPa.

7. The modified tin-titanium-silicon molecular sieve catalyst prepared by the preparation method according to any one of claims 1 to 6.

8. Use of the modified tin-titanium-silicon molecular sieve catalyst according to claim 7 in the hydroxylation of toluene to produce cresol.

9. A method for preparing cresol by hydroxylation of toluene, characterized in that: The method comprises: in the presence of the modified tin-titanium-silicon molecular sieve catalyst according to claim 7, subjecting toluene, a solvent and an oxidant to a contact reaction.

10. The method according to claim 9, wherein: The solvent is one or more of methanol, acetone, methyl isobutyl ketone and cyclohexanone, preferably methanol; and / or The oxidant is a H2O2 aqueous solution with a concentration of 30-50wt%; and / or The mass ratio of the catalyst to toluene is 5-10:100; and / or The molar ratio of toluene to H2O2 is 3-5:1; and / or The molar ratio of the solvent to H2O2 is 5-10:1; and / or The reaction temperature is 25-80°C; and / or The reaction time is 3-24h.

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