CN111348657B - Ultrasonic-assisted titanium silicalite molecular sieve modification method - Google Patents
Ultrasonic-assisted titanium silicalite molecular sieve modification method Download PDFInfo
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Abstract
The invention discloses an ultrasonic-assisted titanium silicalite molecular sieve modification method, which comprises the steps of uniformly mixing a titanium silicalite molecular sieve with a modification reaction solution, placing the mixture in a crystallization kettle provided with an ultrasonic generator, crystallizing the mixture under the assistance of an ultrasonic field, and then washing, filtering, drying and roasting the mixture to obtain a modified titanium silicalite molecular sieve; wherein the power of the ultrasonic field is 40-160W or a multiple of 40-160W, and the multiple is the mass of the actually used titanium-silicon molecular sieve divided by 20g; the crystallization is carried out under the assistance of an ultrasonic field for 6-48 hours. The modification method of the titanium-silicon molecular sieve has universal applicability, is particularly suitable for alkali modified TS-1 with more treatment capacity, and has good catalytic performance and greatly improved stability after ultrasonic-assisted modification.
Description
Technical Field
The invention relates to the technical field of molecular sieve modification, in particular to an ultrasonic-assisted titanium-silicon molecular sieve modification method.
Background
The titanium silicon molecular sieve (TS-1) is prepared from Ti4 + Substitution of part of Si4 in all-silicon molecular sieves (Silicalite-1) + The zeolite molecular sieve with MFI structure is formed. Due to ion Ti4 + Has six coordination characteristics and potential of accepting electron pairs, so that the TS-1 molecular sieve has the following characteristics of H 2 O 2 Or the organic peroxide compound has good adsorption activation performance.
Cyclohexanone oxime is considered an important chemical production raw material, which is a key intermediate for producing nylon-6 monomer epsilon-Caprolactam (CPL). The company Monterdipe S.p.A. (EniChem S.p.A.) was successful in developing a cyclohexanone ammoximation process with cyclohexanone, ammonia and H in the 80 s of the 20 th century 2 O 2 Is prepared by cyclohexanone ammoximation reaction under the catalysis of titanium-silicon molecular sieve TS-1 as raw materialPreparing cyclohexanone oxime. The production process is simple, mild in condition, environment-friendly, high in reactant conversion rate and product selectivity, and greatly improved in industrial benefit, so that the development of the process is significant for industrial production of caprolactam. The titanium-silicon molecular sieve (TS-1) is also applied to other organic oxidation reactions, and has wide application potential.
In 1981, macro Taramasso et al disclosed for the first time that the hydrothermal crystallization method for synthesizing TS-1, the current synthesis conditions need to be strictly controlled, or non-framework titanium can be generated in addition to tetra-coordination framework titanium containing an active center, and the catalytic performance of the non-framework titanium can be negatively influenced. Firstly, the non-framework titanium does not have catalytic oxidation activity per se, and also can catalyze and decompose a reactant H in ammoxidation 2 O 2 Thereby affecting the conversion rate of the main reaction and the selectivity to the target product, resulting in the reduction of the TS-1 catalytic performance; secondly, the content of non-framework titanium is difficult to control, which results in poor activity stability of the titanium silicalite molecular sieve, thus restricting industrial application of TS-1.
In recent years, scientific researchers at home and abroad improve the catalytic performance of TS-1 through modification treatment. The modification method for TS-1 mainly comprises the following steps: acid modification, alkali modification and salt modification. Wherein, the alkali modification can play a role of reaming in TS-1, and a cavity structure is formed in the crystal, thereby reducing the diffusion limit of reactant and product molecules and further improving the catalytic performance of TS-1. Meanwhile, the alkali modification can promote the further improvement of the content of the framework titanium through the process of dissolving and recrystallizing the defect sites.
The patent US6475465B and CN1301599A propose a method for modifying TS-1 by organic alkali, which is characterized in that alcohol amine compound, quaternary ammonium base, fatty amine and other mixture are mixed with molecular sieve and water according to a certain proportion, and reacted for 3 hours to 3 days under the autogenous pressure of 150 ℃, wherein the TS-1 can be raw powder or acid modified TS-1.
The patent CN101850986A proposes a mixed modification method, which is characterized in that TS-1 is added into a mixed solution of inorganic alkali and organic alkali according to a certain proportion, and the mixture reacts for 2 to 360 hours at the temperature of 80 to 200 ℃ and under autogenous pressure, wherein the organic alkali is quaternary ammonium alkali and aliphatic amine compound, and the inorganic alkali is ammonia water, sodium hydroxide, potassium hydroxide and the like. The patent CN1268400A proposes a method for modifying TS-1 by using aqueous solution of metal salt or other mixture, which is characterized in that the aqueous solution of metal salt and TS-1 are mixed according to a certain proportion, reacted for 6-100h at 30-100 ℃, then dried at 110-200 ℃, then programmed to be heated to 200-800 ℃ and baked for 2-20h.
The invention provides a titanium silicalite molecular sieve modification method, which comprises the steps of uniformly mixing an alkali solution containing an organic chelating agent with a titanium silicalite molecular sieve according to a certain proportion, reacting in a closed reaction kettle, filtering, washing, drying and roasting the obtained product to obtain the TS-1 molecular sieve modified by the alkali solution containing the organic chelating agent.
Patent CN103073022B proposes a modification method of titanium silicalite molecular sieve, comprising the following steps: (1) primary modification: mixing titanium-silicon molecular sieve with ammonia water, ammonium nitrate and water, reacting at a certain temperature, washing with water, and drying; (2) secondary modification: mixing the titanium-silicon molecular sieve after primary modification with sulfur-containing metal salt and water, reacting at a certain temperature, washing with water, and drying; and (3) roasting the titanium-silicon molecular sieve subjected to secondary modification at a high temperature. The invention is especially suitable for TS-1 synthesized by a classical system, and the modified molecular sieve has good catalytic performance on cyclohexanone ammoximation.
In the process of modifying the titanium-silicon molecular sieve by alkali in the prior art, as the molecular sieve and alkali liquor are not uniformly contacted when being stood and crystallized in a hydrothermal synthesis kettle, when the molecular sieve is more loaded, the solid-liquid separation phenomenon is obvious, the modification effect is directly influenced, and the catalytic performance of the molecular sieve is not obviously improved.
Therefore, there is an urgent need to find a modification method of the titanium silicalite molecular sieve to improve the performance of the titanium silicalite molecular sieve.
Disclosure of Invention
The invention provides an ultrasonic-assisted titanium-silicon molecular sieve modification method, which aims at the defect of poor effect of the titanium-silicon molecular sieve modification method in the prior art.
The technical scheme provided by the invention is as follows:
the ultrasonic-assisted titanium silicalite molecular sieve modification method comprises the steps of uniformly mixing a titanium silicalite molecular sieve with a modification reaction solution, placing the mixture in a crystallization kettle provided with an ultrasonic generator, crystallizing under the assistance of an ultrasonic field, and then washing, filtering, drying and roasting to obtain a modified titanium silicalite molecular sieve;
wherein the power of the ultrasonic field is 40-160W or a multiple of 40-160W, and the multiple is the mass of the actually used titanium-silicon molecular sieve divided by 20g; the crystallization is carried out under the assistance of an ultrasonic field for 6-48 hours.
In recent years, ultrasonic waves, which have cavitation effect and promote homogenization of a precursor and nucleation, have been introduced as an auxiliary means into material synthesis and have been widely used. The ultrasonic wave has preliminary research results on the effect caused by the crystallization process, and the energy of the ultrasonic wave is utilized to control the crystallization process, so that the nucleation and growth process can be promoted, and the crystallization process is more optimized. The inventor introduces ultrasonic waves as auxiliary means into the hydrothermal crystallization process to avoid molecular sieve deposition and achieve mesoscopic uniform mixing with alkali modified liquid, and simultaneously utilizes the cavitation effect of the ultrasonic waves, namely the extremely large energy and huge pressure released at the moment of collapse of countless tiny cavity bubbles generated in a medium, so as to accelerate the dissolution and recrystallization rate of the molecular sieve, greatly improve the catalytic performance of the titanium-silicon molecular sieve, slow down the attenuation of the activity of the molecular sieve and improve the stability of the molecular sieve.
The titanium silicalite molecular sieve used in the present invention may be a titanium silicalite molecular sieve prepared by any method known in the art, for example, the method described in Zeolite, 1992, vol.12943-950, J.chem.Soc., chem Commun.,1992,123-124, or a commercially available titanium silicalite molecular sieve.
The crystallization kettle can be any suitable hydrothermal reaction kettle capable of adding an ultrasonic field in the prior art.
The modification method can be applied to a solid-liquid molecular sieve modification method of an alkaline liquid medium.
Preferably, in one embodiment of the present invention, the modification reaction solution is an aqueous alkali solution.
More preferably, the molar ratio of titanium silicalite, base and water is 1:0.02 to 0.6:3 to 20.
Preferably, in the modification method of the titanium silicalite molecular sieve according to the present invention, the base is an organic base or an inorganic base, or a mixture of both, and the mixing molar ratio is 1:1 to 50.
More preferably, in an embodiment of the present invention, the organic base is one or more selected from urea, a quaternary ammonium base compound, an alcohol amine compound, or an aliphatic amine compound; the inorganic base is one or more selected from ammonia water, potassium hydroxide, sodium hydroxide or ammonium nitrate.
More specifically, the organic base may be, for example, ethylamine, ethylenediamine, n-butylamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and the like.
In the titanium silicalite molecular sieve modification method of the present invention, other additives may be included in the aqueous alkali solution to enhance the properties of the modified molecular sieve, for example, organic chelating agents such as one or more selected from the group consisting of citric acid, tartaric acid, glutamic acid, ethylenediamine triacetic acid, ethylenediamine tetraacetic acid, nitrilotriacetic acid, 1, 2-cyclohexanediamine tetraacetic acid, trans-1, 2-cyclohexanediamine tetraacetic acid, diethylenetriamine pentaacetic acid, hydroxyethylethylenediamine triacetic acid and triethylenetetramine hexaacetic acid.
Preferably, in an embodiment of the present invention, the crystallization temperature is 90 to 200 ℃ and the reaction time is 6 to 48 hours.
Preferably, in an embodiment of the present invention, the washing with deionized water is to be neutral; the drying is that the drying is carried out for 2 to 5 hours at the temperature of 100 to 150 ℃; the roasting temperature is 500-600 ℃ and the time is 3-10 hours.
Preferably, in an embodiment of the present invention, the amount of the titanium silicalite molecular sieve added is 10% to 50% of the volume of the crystallization kettle.
In another aspect of the present invention, there is provided a modified titanium silicalite molecular sieve prepared by the above-described modification process.
The titanium-silicon molecular sieve catalyst can be used for cyclohexanone ammoximation reaction to prepare cyclohexanone oxime, and other catalyst such as olefin epoxidation, phenol hydroxylation, ketone ammoximation and alcohol oxidation.
The beneficial effects of the invention are as follows:
the modification method of the titanium-silicon molecular sieve has universal applicability, is particularly suitable for alkali modified TS-1 with more treatment capacity, and has good catalytic performance and greatly improved stability after ultrasonic-assisted modification.
Drawings
FIG. 1 is a transmission electron microscope image of a TS-1 molecular sieve raw powder that has not been treated by the method of the present invention;
FIG. 2 is a transmission electron micrograph of a modified TS-1 molecular sieve loaded at 2 g.
FIG. 3 is a transmission electron microscope image of a TS-1 molecular sieve with a loading of 20g after ultrasonic-assisted modification.
Detailed Description
The invention discloses an ultrasonic-assisted titanium-silicon molecular sieve modification method, and a person skilled in the art can properly improve the process parameters by referring to the content of the invention. It is to be particularly pointed out that all similar substitutes and modifications apparent to those skilled in the art are deemed to be included in the invention and that the relevant person can make modifications and appropriate alterations and combinations of what is described herein to make and use the technology without departing from the spirit and scope of the invention.
In the present invention, unless otherwise indicated, scientific and technical terms used herein have the meanings commonly understood by one of ordinary skill in the art.
In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail with reference to specific embodiments.
The TS-1 molecular sieves used in this example were prepared according to the synthetic methods proposed by Thangraj et al (J. Chem. Soc., chem Commun.,1992, 123-124). 20g of tetraethyl orthosilicate is dripped into 24g of tetrapropylammonium hydroxide aqueous solution (mass fraction is 25%), hydrolysis is carried out at room temperature until the solution is clear, 1g of tetrabutyl titanate is dissolved in 6.5g of isopropanol, the titanium source mixed solution is slowly dripped into the silicon source hydrolysis solution under stirring, the reaction is carried out at 60 ℃ for 1h, the temperature is increased to 80 ℃ for 3h, the ethanol is removed, the glue solution is transferred to a hydrothermal synthesis kettle for standing crystallization for 72h, washing is carried out until the solution is neutral, drying is carried out for 4h, and roasting is carried out at 550 ℃ for 6h.
The transmission electron microscope image is shown in figure 1, and the TS-1 molecular sieve has a uniform micropore structure.
Example 1: modification of titanium silicalite molecular sieves
The mixed solution of 20g of TS-1 molecular sieve and 16.8g of tetrapropylammonium hydroxide aqueous solution (mass fraction is 25%), 18g of water is filled into a reaction kettle, under the self-generating pressure, the reaction temperature is 180 ℃, the ultrasonic field power is 60W, the ultrasonic time is 12 hours, the hydrothermal treatment is carried out for 24 hours, then deionized water is used for washing to pH value of 7-8, drying is carried out at 120 ℃ for 4 hours, and roasting is carried out at 550 ℃ for 5 hours.
The transmission electron microscope image is shown in fig. 3.
Example 2: modification of titanium silicalite molecular sieves
A mixed solution of 20g of TS-1 molecular sieve and 12.9g of tetrabutylammonium hydroxide aqueous solution (the mass fraction is 40%), 38g of water is filled into a reaction kettle, the reaction temperature is 160 ℃ under the self-generating pressure, the ultrasonic field power is 50W, the ultrasonic time is 7 hours, the hydrothermal treatment is carried out for 36 hours, then deionized water is used for washing to pH value of 7-8, the mixture is dried for 5 hours at 120 ℃, and the mixture is baked for 8 hours at 550 ℃.
Example 3: modification of titanium silicalite molecular sieves
20g of TS-1 molecular sieve and 14.5g of tetramethylammonium hydroxide aqueous solution (mass fraction 25%),
putting 40g of water mixed solution into a reaction kettle, under the self-generating pressure, the reaction temperature is 190 ℃, the ultrasonic field power is 40W, the ultrasonic time is 10 hours, the hydrothermal treatment is 30 hours, then the water mixed solution is washed to pH value of 7-8 by deionized water, the water mixed solution is dried for 4 hours at 120 ℃, and the water mixed solution is baked for 4 hours at 550 ℃.
Example 4: modification of titanium silicalite molecular sieves
A mixed solution of 20g of TS-1 molecular sieve, 12.5g of ammonia water solution and 52g of water is put into a reaction kettle, and under the self-generated pressure, the reaction temperature is 170 ℃, the ultrasonic field power is 55W, the ultrasonic time is 12 hours, the hydrothermal treatment is 36 hours, then deionized water is used for washing to pH value of 7-8, and the mixture is dried at 120 ℃ for 3 hours and baked at 550 ℃ for 4 hours.
Example 5: modification of titanium silicalite molecular sieves
A mixed solution of 20g of TS-1 molecular sieve, 1.1g of potassium hydroxide and 60g of water is put into a reaction kettle, and under the self-generated pressure, the reaction temperature is 160 ℃, the ultrasonic field power is 100W, the ultrasonic time is 24 hours, the hydrothermal treatment is 40 hours, then deionized water is used for washing to pH value of 7-8, and the mixture is dried at 120 ℃ for 3 hours and baked at 550 ℃ for 6 hours.
Example 6: modification of titanium silicalite molecular sieves
A mixed solution of 20g of TS-1 molecular sieve, 2.3g of potassium hydroxide and 80g of water is put into a reaction kettle, and under the self-generated pressure, the reaction temperature is 170 ℃, the ultrasonic field power is 50W, the ultrasonic time is 48 hours, the hydrothermal treatment is carried out for 48 hours, then deionized water is used for washing to pH value of 7-8, and the mixture is dried at 120 ℃ for 3 hours and baked at 550 ℃ for 8 hours.
Comparative example 1: preparation of unmodified molecular sieves
TS-1 molecular sieves were prepared according to the synthetic method proposed by Thangaraj et al (J. Chem. Soc., chem Commun.,1992, 123-124). 20g of tetraethyl orthosilicate is dripped into 24g of tetrapropylammonium hydroxide aqueous solution (mass fraction is 25%), hydrolysis is carried out at room temperature until the solution is clear, 1g of tetrabutyl titanate is dissolved in 6.5g of isopropanol, the titanium source mixed solution is slowly dripped into the silicon source hydrolysis solution under stirring, the reaction is carried out at 60 ℃ for 1h, the temperature is increased to 80 ℃ for 3h, the ethanol is removed, the glue solution is transferred to a hydrothermal synthesis kettle for standing crystallization for 72h, washing is carried out until the solution is neutral, drying is carried out for 4h, and roasting is carried out at 550 ℃ for 6h.
The transmission electron microscope image is shown in figure 1, and the TS-1 molecular sieve has a uniform micropore structure.
Comparative example 2: alkali modification of small amounts of molecular sieves
A mixed solution of 2g of TS-1 molecular sieve and 1.68g of tetrapropylammonium hydroxide aqueous solution (mass fraction is 25%), 1.8g of water is filled into a reaction kettle, the reaction temperature is 180 ℃ under the self-generating pressure, the reaction is treated for 48 hours, then deionized water is used for washing to pH 7-8, the reaction kettle is dried for 4 hours at 120 ℃, and the reaction kettle is baked for 3 hours at 550 ℃.
The transmission electron microscope image is shown in fig. 2, and a large number of hollows and depressions with different sizes of 10-80nm appear in the modified molecular sieve, and the hollows and depressions reduce the diffusion resistance of the reaction and the products, thereby being beneficial to improving the catalytic activity and prolonging the service life of the molecular sieve.
Comparative example 3: alkali modification of a large number of molecular sieves
A mixed solution of 20g of TS-1 molecular sieve and 16.8g of tetrapropylammonium hydroxide aqueous solution (mass fraction is 25%), 18g of water is filled into a reaction kettle, the reaction temperature is 180 ℃ under the self-generating pressure, the reaction is treated for 48 hours, then deionized water is used for washing to pH 7-8, the reaction kettle is dried for 4 hours at 120 ℃, and the reaction kettle is roasted for 3 hours at 550 ℃.
Experimental example: evaluation of catalytic Properties of titanium silicalite molecular sieves TS-1 before and after modification
The catalytic performance of the samples was evaluated using cyclohexanone ammoximation as a probe reaction. And (3) carrying out continuous raw material liquid sample injection reaction in a three-neck flask with a condensing tube in a constant-temperature water bath at 80 ℃. The reaction solution was taken once an hour and analyzed by an Agilent 7890B gas chromatograph, and the catalytic activity of the TS-1 molecular sieve was expressed in terms of cyclohexanone conversion.
Reaction conditions: hydrogen peroxide (H) 2 O 2 ) The molar ratio of cyclohexanone is 1.2, ammonia (NH) 3 ) Cyclohexanone (C) 6 H 10 O) molar ratio of 2.2, t-butanol (C) 4 H 9 OH)/Cyclohexanone (C) 6 H 10 O) mass ratio of 2.5, tert-butanol (C) 4 H 9 OH)/deionized water (H) 2 The mass ratio of the O) is 1, the dosage of the TS-1 molecular sieve is 0.5-1% of the mass of the reaction liquid, and the feed rate of the raw materials is 90g/h.
Chromatographic conditions: the chromatographic column adopts an HP-5 capillary column (0.32mm x 30mx 0.25 mu m), the FID detector is nitrogen, the carrier gas is nitrogen, the temperature of the FID detector is 270 ℃, the temperature of a sample inlet is 240 ℃, the temperature of the column is 120 ℃ for 4min, and then the temperature is raised to 190 ℃ at the rate of 20 ℃ min < -1 >, and the temperature is kept for 11min.
The conversion rate of cyclohexanone is calculated by adopting a normalization method, and the conversion rate is calculated as follows:
wherein n is Oxime compounds Representing the amount of a substance reacting to form cyclohexanone oxime, n Ketone compounds Representing the amount of unreacted cyclohexanone material.
The experimental results are shown in tables 1 and 2.
TABLE 1 catalytic Activity of cyclohexanone oxime reaction catalyst
Table 2 list of specific surface area, pore volume and pore size of samples
Comparing BET data of different samples, it can be clearly seen that the number of mesopores of the molecular sieve after alkali modification is increased, the average pore diameter is increased, and the number and the size of mesopores influence the diffusion rate of reactants and products, thus determining the service life of the molecular sieve. When the alkali modification treatment capacity is more, the modification effect is poorer because the modification liquid is not uniformly contacted with the molecular sieve, and the ultrasonic wave is introduced in the crystallization stage, so that the layering effect can be improved, and the catalytic activity and the service life of the molecular sieve can be improved.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (10)
1. The ultrasonic-assisted titanium-silicon molecular sieve modification method is characterized in that titanium-silicon molecular sieve and modification reaction solution are uniformly mixed and then placed in a crystallization kettle provided with an ultrasonic generator, crystallization is carried out under the assistance of an ultrasonic field, and then the modified titanium-silicon molecular sieve is obtained through washing, filtering, drying and roasting;
wherein the power of the ultrasonic field is 40-160W or a multiple of 40-160W, and the multiple is the mass of the actually used titanium-silicon molecular sieve divided by 20g;
the crystallization is carried out under the assistance of an ultrasonic field for 6-48 hours.
2. The method for modifying a titanium silicalite molecular sieve according to claim 1, wherein the modifying reaction solution is an alkali solution.
3. The method for modifying a titanium silicalite molecular sieve according to claim 2, wherein the modifying reaction solution is an aqueous alkali solution.
4. The method for modifying a titanium silicalite molecular sieve according to claim 3, wherein the molar ratio of titanium silicalite molecular sieve, base and water is 1:0.02 to 0.6:3 to 20.
5. The method for modifying a titanium silicalite molecular sieve according to any one of claims 2 to 4, wherein the base is an organic base or an inorganic base, or a mixture of both.
6. The method for modifying a titanium silicalite molecular sieve according to claim 5, wherein the organic base is one or more selected from urea, quaternary ammonium base compounds, alcohol amine compounds and aliphatic amine compounds; the inorganic base is one or more selected from ammonia water, potassium hydroxide, sodium hydroxide or ammonium nitrate.
7. The method for modifying a titanium silicalite molecular sieve according to claim 1, wherein the crystallization temperature is 90-200 ℃ and the reaction time is 6-48 hours.
8. The method for modifying a titanium silicalite molecular sieve according to claim 1, wherein the washing with water is washing with deionized water to neutrality; the drying is that the drying is carried out for 2 to 5 hours at the temperature of 100 to 150 ℃; the roasting temperature is 500-600 ℃ and the time is 3-10 hours.
9. The method for modifying a titanium silicalite molecular sieve according to claim 1, wherein the adding amount of the titanium silicalite molecular sieve is 10% -50% of the volume of the crystallization kettle.
10. A modified titanium silicalite molecular sieve prepared by the modification process of any one of claims 1-9.
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