Method for the continuous synthesis of titanium silicalite molecular sieve and use thereof

Abstract

The application belongs to the technical field of molecular sieve catalysts, and discloses a method for continuously synthesizing titanium-silicon molecular sieves and application thereof, which comprises a first ultrasonic reaction kettle, a second ultrasonic reaction kettle and a crystallization kettle connected in sequence. The first ultrasonic continuous kettle is used for receiving raw materials such as a silicon source, a titanium source and a template agent. The second ultrasonic continuous kettle is communicated with the outlet of the first ultrasonic reaction kettle, and is used for receiving the precursor sol. The inlet of the continuous crystallization unit is communicated with the outlet of the second ultrasonic reaction kettle, and titanium-silicon molecular sieve products are generated. Through the coupling of the double-ultrasonic-kettle connection and the continuous crystallization unit, the application realizes the continuous production of the whole process of precursor synthesis and crystallization, and significantly improves the synthesis efficiency and product quality of the titanium-silicon molecular sieves.

Description

Technical Field

[0001] This invention relates to a method for preparing titanium-silicon molecular sieves, and more particularly to a method for the rapid and continuous synthesis of titanium-silicon molecular sieves on a large scale, and the reaction apparatus used therein. Background Technology

[0002] Titanium-silicon molecular sieve (TS-1) is a heteroatom molecular sieve with an MFI topology. Its framework is partially replaced by titanium atoms, which gives it excellent performance in selectively catalyzing the oxidation of various organic compounds with hydrogen peroxide as an oxidant under mild conditions, such as olefin epoxidation, aromatic hydroxylation, and ketone ammonium oximeation. It is a key catalytic material in the field of green chemistry.

[0003] Traditional TS-1 synthesis methods are primarily batch hydrothermal synthesis methods, typically involving two stages: precursor preparation and crystallization. In the precursor preparation stage, silicon source, titanium source, template agent (such as tetrapropylammonium hydroxide, TPAOH), and water are mixed in a specific ratio for hydrolysis and prepolymerization. This stage demands extremely high uniformity of mixing. The titanium source (such as tetrabutyl titanate, TBOT) hydrolyzes very rapidly, easily leading to the formation of non-framework titanium species (such as anatase TiO2) due to excessively high local concentrations. These non-framework titanium species not only lack catalytic activity but also clog the molecular sieve channels, severely impacting the catalytic performance of TS-1. Traditional mechanically stirred tanks have limitations in micro-mixing, making it difficult to completely avoid the problem of localized over-concentration.

[0004] To improve precursor synthesis, studies have attempted to introduce ultrasonic technology into the precursor synthesis stage. The strong micro-stirring and micro-jets generated by ultrasonic cavitation can effectively suppress local over-concentration hydrolysis of the titanium source and promote uniform mixing of components at the molecular scale. For example, the preparation method of large-particle TS-1 titanium-silicon molecular sieves in Chinese patent application publication number CN108246362A adopts an ultrasonic pre-hydrolysis process. TBOT and isopropanol are mixed under ultrasonic vibration, and TEOS solution and TPAOH aqueous solution are mixed under ultrasonic vibration. The prepared TBOT mixed solution is slowly added dropwise to the TEOS mixed solution, stirred evenly, heated for hydrolysis to remove alcohol, and the alcohol is evaporated to obtain a mother liquor. The mother liquor is transferred to a high-pressure reactor, and nano-sized titanium-silicon molecular sieve powder is added as seed crystals. Crystallization is carried out using a programmed temperature rise method. The crystallized reaction mixture is filtered, washed, dried, and calcined to obtain large-particle TS-1 catalysts with a size of 2-50 μm.

[0005] However, existing ultrasound-assisted precursor synthesis methods are mostly batch operations, often employing only a single ultrasound treatment, making it difficult to ensure the completeness and uniformity of the synthesis reaction. Furthermore, precursor synthesis and subsequent crystallization processes are often separate batch operations, preventing continuous production and thus limiting the industrial production efficiency of TS-1. Summary of the Invention

[0006] One objective of this invention is to shorten the preparation time of titanium-silicon molecular sieves by combining two consecutive ultrasonic treatments with multi-stage crystallization, thereby achieving continuous and large-scale production. The final crystallized product exhibits high crystallinity and high performance consistency, and the yield of molecular sieves is improved.

[0007] The present invention provides a method for preparing a titanium-silicon molecular sieve, comprising the following steps: (1) Water, organic template agent, silicon source and titanium source are mixed and subjected to a first ultrasonic treatment to obtain mixed solution I; (2) Mixed solution I is subjected to a second ultrasonic treatment to obtain mixed solution II, wherein the power of the second ultrasonic treatment is lower than the power of the first ultrasonic treatment; (3) Crystallize the mixed solution II to obtain a crystallized solution; (4) The crystallization liquid is cooled, centrifuged, dried and calcined to obtain the titanium silicon molecular sieve catalyst.

[0008] By performing two ultrasonic treatments with different powers, the precursors can react fully and completely, achieving high homogenization and complete reaction even for industrial-scale production. Furthermore, the short pre-crystallization treatment time for the precursors improves the efficiency of titanium-silicon molecular sieve production. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of the reaction apparatus for the continuous synthesis of titanium-silicon molecular sieves using ultrasound enhancement in Embodiment 1 of the present invention. Figure 2 This is a schematic diagram of the structure of the first ultrasonic continuous vessel in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the structure of the second ultrasonic continuous vessel in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the continuous crystallization unit in Embodiment 1 of the present invention; Figure 5 The ultraviolet-visible absorption spectrum of the driver in Example 1 of this invention; Figure 6 The X-ray diffraction (XRD) spectrum of the final TS-1 product in Embodiment 1 of the present invention; Figure 7 This is a scanning electron microscope (SEM) image of the final TS-1 product in Embodiment 1 of the present invention. Detailed Implementation

[0010] The preparation method of the titanium-silicon molecular sieve of the present invention is described in further detail below. This does not limit the scope of protection of this application, which is defined by the claims. Certain specific details disclosed provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will recognize that embodiments can be implemented using other materials, etc., without employing one or more of these specific details.

[0011] Unless the context requires otherwise, the terms "comprising" and "including" in the specification and claims shall be understood as open-ended and inclusive, meaning "including, but not limited to".

[0012] The terms "implementation," "an implementation," "another implementation," or "certain implementations" used in this specification refer to specific features, structures, or characteristics described in relation to the implementation, which are included in at least one implementation. Therefore, "implementation," "an implementation," "another implementation," or "certain implementations" do not necessarily all refer to the same implementation. Furthermore, specific features, structures, or characteristics can be combined in any way within one or more implementations. Each feature disclosed in this specification can be replaced by any alternative feature that provides the same, equivalent, or similar purpose. Therefore, unless otherwise specified, the disclosed features are merely general examples of equivalent or similar features.

[0013] Ultrasound definition: Ultrasound refers to the general term for sound with a frequency greater than 20 kHz.

[0014] The synthetic titanium-containing molecular sieve in this application includes an organic template agent, a silicon source, and a titanium source.

[0015] Definition of silicon source: The silicon source in this application is selected from water-soluble or water-soluble silicon-containing compounds.

[0016] Titanium source definition: The titanium source in this application is selected from water-soluble or water-soluble titanium-containing compounds.

[0017] All “pressure” in this application refers to gauge pressure.

[0018] In one embodiment, the organic template agent in this application includes, but is not limited to, one or a mixture of multiple substances such as ethylenediamine, tetraethylammonium hydroxide, n-butylamine, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetrapropylammonium bromide, and tetrabutylammonium bromide.

[0019] The silicon source includes, but is not limited to, tetraethyl orthosilicate and / or silica sol.

[0020] The titanium source includes, but is not limited to, one or a mixture of multiple substances such as tetrabutyl titanate, tetraethyl titanate, tetraisopropyl titanate, titanium trichloride, and titanium tetrachloride.

[0021] The ultrasound includes one or more mixed ultrasound sources.

[0022] During the crystallization stage, crystallization occurs under static hydrothermal conditions, with the precursor crystallized statically under high temperature and autogenous pressure for 24-72 hours. This process is time-consuming and energy-intensive. Furthermore, the presence of temperature and concentration gradients within the reactor during static crystallization leads to uneven particle size distribution in the titanium-silicon molecular sieve products.

[0023] The method for preparing the titanium-silicon molecular sieve of the present invention includes the following steps: (1) Water, organic template agent, silicon source and titanium source are mixed and subjected to a first ultrasonic treatment to obtain mixed solution I; (2) Mixed solution I is subjected to a second ultrasonic treatment to obtain mixed solution II, wherein the power of the second ultrasonic treatment is lower than the power of the first ultrasonic treatment; (3) Crystallize the mixed solution II to obtain a crystallized solution; (4) The crystallization liquid is cooled, centrifuged, dried and calcined to obtain the titanium silicon molecular sieve catalyst.

[0024] The power of the first ultrasonic treatment is 1 kW to 20 kW. The power of the second ultrasonic treatment is 1 kW to 15 kW.

[0025] Preferably, the power of the first ultrasonic treatment is greater than or equal to the power of the second ultrasonic treatment. Optionally, the power of the first ultrasonic treatment is 5 kW to 10 kW, and the power of the second ultrasonic treatment is 2 kW to 5 kW.

[0026] The frequency of the first ultrasonic treatment is 20 kHz-100 kHz. The frequency of the second ultrasonic treatment is 20 kHz-80 kHz.

[0027] Preferably, the frequency of the first ultrasonic treatment is greater than or equal to the frequency of the second ultrasonic treatment.

[0028] This invention fundamentally suppresses the local over-concentration hydrolysis of the titanium source by combining a first ultrasonic treatment with a second ultrasonic treatment, promotes the uniform mixing of the silicon source, titanium source and template agent at the molecular scale, enables the precursor sol to reach a highly homogenized and fully synthesized state, and significantly increases the proportion of active titanium species in the precursor.

[0029] In some embodiments, an immersion ultrasonic generator or a wall-mounted ultrasonic generator is used during the first ultrasonic treatment.

[0030] During the second ultrasonic treatment, a wall-mounted ultrasonic generator is used.

[0031] Immersion ultrasonic generators can employ any existing technological structure, with the entire unit sealed and encapsulated in a rod shape, completely and directly immersed in the liquid, radiating ultrasound directly into the liquid without relying on the container wall for conduction; the rod shape is often referred to as an ultrasonic probe / vibrating rod. Wall-mounted ultrasonic generators are directly adhered to the bottom and / or sidewalls of the reactor's outer wall, without immersion in the liquid, and the ultrasound enters the liquid cavity through conduction via the metal of the container wall.

[0032] Immersion ultrasonic probes are inserted directly into the material inside the reactor, allowing acoustic energy to radiate directly to the reaction system through the probe tip. This method is characterized by extremely high energy density and concentrated effect. In the synthesis of titanium-silicon molecular sieve precursors, titanium sources (such as TBOT) hydrolyze extremely rapidly, readily self-aggregating to form non-framework titanium species such as anatase TiO2. Immersion probes and high-power ultrasound are first employed. The strong ultrasonic cavitation effect generates intense micro-stirring and shock waves, powerfully dissociating titanium source aggregates, accelerating mass transfer, and aligning the hydrolysis rates of the titanium and silicon sources. This prevents preemptive self-aggregation of titanium and achieves initial uniform dispersion of titanium hydroxyl species in the silica gel network. Then, wall-mounted ultrasonic transducers are evenly distributed on the outer wall of the reactor, allowing ultrasound waves to penetrate the material. After the first ultrasonic treatment, titanium hydroxyl groups have achieved initial uniform dispersion in the silica gel, but a small amount still fails to form a tightly mixed network with the silicon hydroxyl groups. The uniform and gentle action of the second wall-mounted ultrasound can further dissociate these residual titanium hydroxyl aggregates, making them more evenly dispersed in the silica gel. This provides more sufficient preconditions for titanium atoms to smoothly enter the molecular sieve framework during the subsequent hydrothermal crystallization process.

[0033] When using a dual-immersion ultrasonic reactor in series, after the precursor undergoes strong ultrasonication in the first reactor, the titanium hydroxyl species are initially and uniformly dispersed in the silica gel network. If the second reactor continues to use immersion ultrasonication of the same intensity, the sustained high-intensity cavitation effect will excessively shear the silica gel network, causing the uniformly dispersed titanium hydroxyl groups to peel off from the silica gel network and subsequently condense to form oligomers. These oligomers are difficult to dissociate during subsequent hydrothermal crystallization and cannot effectively enter the molecular sieve framework, ultimately leading to a decrease in the framework titanium content and an increase in non-framework titanium in the crystallized product, resulting in a decline in catalytic performance.

[0034] When using a dual-walled ultrasonic autoclave in series, the ultrasonic energy of the wall-mounted autoclave is dispersed and has a low intensity, which cannot complete the strong deagglomeration of titanium source agglomerates in the first stage. A large number of titanium source agglomerates cannot be effectively dispersed. These agglomerates cannot enter the framework during the subsequent crystallization process, resulting in an increase in non-framework titanium in the final product.

[0035] The pretreatment of the precursors in this invention is carried out under ultrasonic conditions, specifically under the first and second ultrasonic treatment conditions. After pretreatment, the precursors are placed in a crystallization kettle for hydrothermal crystallization.

[0036] The duration of the first ultrasonic treatment is 10 min to 120 min.

[0037] Optionally, the duration of the first ultrasound treatment is 20 min–40 min.

[0038] The second ultrasound treatment lasts for 5 to 60 minutes. Alternatively, the second ultrasound treatment lasts for 10 to 20 minutes.

[0039] Optionally, the time for the first ultrasound treatment is longer than the time for the second ultrasound treatment.

[0040] In some embodiments, water, organic template agent, silicon source, and titanium source are mixed to obtain a mixed solution, and the flow rate of the mixed solution during ultrasonic treatment and crystallization treatment is controlled at 100-180 mL / min.

[0041] Preferably, the flow rate is controlled at 120-150 mL / min.

[0042] The mixed solution of the present invention maintains the above flow rate during pretreatment. Combined with the two ultrasonic treatments of the present invention, the temperature field and concentration field gradients present in static crystallization are effectively eliminated, ensuring the uniformity of the crystallization process and the high crystallinity and narrow particle size distribution of the product.

[0043] In some embodiments, during steps (1) and (2), the temperature of the mixed solution is controlled at 20-60°C during the first and second ultrasonic treatments. o C. Optionally, in steps (1) and (2), during the first and second ultrasonic treatments, the temperature of the mixed solution is controlled at less than or equal to 40°C. o C.

[0044] In this invention, the molar ratio of silicon in the silicon source to titanium in the titanium source is 20-80:1.

[0045] Preferably, the molar ratio of silicon in the silicon source to titanium in the titanium source is 40-60:1. The molar ratio of silicon to organic template agent in the silicon source is 5-30:1.

[0046] Preferably, the molar ratio of silicon element in the silicon source to the organic template agent is 10-20:1. The molar ratio of silicon to water in the silicon source is 1:10-60.

[0047] Preferably, the molar ratio of silicon to water in the silicon source is 1:30-50.

[0048] In some implementations, the crystallization temperature in step (3) is controlled at 100°C-200°C.

[0049] Optionally, the crystallization temperature can be controlled between 150℃ and 180℃.

[0050] In some embodiments, in step (3), the mixed solution II undergoes two or more stages of crystallization.

[0051] Alternatively, mixed solution II may undergo a first-stage crystallization and a second-stage crystallization sequentially, with the first-stage crystallization temperature being higher than the second-stage crystallization temperature. The first-stage crystallization temperature is 170℃-180℃, and the second-stage crystallization temperature is 160℃-170℃.

[0052] Optionally, mixed solution II undergoes a first-stage crystallization, a second-stage crystallization, and a third-stage crystallization sequentially, with the first-stage crystallization temperature being higher than the second-stage crystallization temperature, and the second-stage crystallization temperature being higher than the third-stage crystallization temperature. The first-stage crystallization temperature is 170℃-180℃, the second-stage crystallization temperature is 160℃-170℃, and the third-stage crystallization temperature is 150℃-160℃.

[0053] This application employs continuous multi-stage crystallization at different temperatures, separating the nucleation and growth processes of the crystal in both space and time. During crystallization, the material continuously flows forward and is renewed, ensuring that highly active precursor species remain in contact with each subsequent crystallization stage. This continuous supply method allows the grains to consistently receive the silicon and titanium sources needed to build the framework during the growth stage, guaranteeing the ordered arrangement of atoms in the crystal lattice and reducing lattice defects caused by insufficient material. This facilitates the effective entry of uniformly dispersed titanium species into the framework, resulting in highly crystalline titanium-silicon molecular sieves. In contrast, traditional single-stage static crystallization directly heats the precursor to the final temperature and maintains it throughout the process. In this process, explosive nucleation and crystal growth occur simultaneously and compete with each other. The silicon / titanium species must supply existing nuclei for growth while also facing the regeneration of new nuclei. The material is dispersed between the nucleation and growth processes, which can easily lead to lattice defects and a decrease in crystallinity.

[0054] During the crystallization process, the crystallization pressure is 0.5 MPa-2.5 MPa. The crystallization pressure can be the same in each crystallization stage.

[0055] The crystallization time is 4 h to 48 h, or alternatively, 4 h to 24 h.

[0056] In the two-stage crystallization process, the crystallization time is 4-12 hours.

[0057] In some implementations, in step (4), the cooling method is water cooling or natural cooling.

[0058] In some embodiments, the drying temperature in step (4) is not limited, as long as the moisture is evaporated to a certain extent. Preferably, the drying temperature is 60-100°C. o C, for example, 80 o C.

[0059] In some embodiments, in step (4), the temperature of the roasting process is controlled at 500-700°C. o C, for example, 550 o C.

[0060] The roasting time is 4-8 hours.

[0061] Preferably, during the roasting process, the heating rate is 2. o C / min, calcination temperature 500-700 o C.

[0062] In this invention, the centrifugal separation in step (4) uses the equipment and process conditions commonly used in the preparation of catalysts in the prior art.

[0063] On the other hand, the reaction apparatus for preparing titanium-silicon molecular sieves includes a first ultrasonic reactor, a second ultrasonic reactor connected to the first ultrasonic reactor, and a crystallization vessel connected to the second ultrasonic reactor. An immersion ultrasonic generator is provided in the first ultrasonic reactor, and a wall-mounted ultrasonic generator is provided in the second ultrasonic reactor.

[0064] A first feed inlet is provided at the top of the first ultrasonic reactor, and the first discharge outlet of the first ultrasonic reactor is connected to the second feed inlet of the second ultrasonic reactor. The second discharge outlet of the second ultrasonic reactor is connected to the precursor inlet of the crystallization reactor.

[0065] Optionally, a stirring device may be installed inside the second ultrasonic reactor.

[0066] The feed inlets of both the first and second ultrasonic reactors are located at the top, and the discharge outlets are located at the bottom.

[0067] Temperature control jackets are installed on the outer peripheral walls of the first and second ultrasonic reactors to control the temperature inside the reactors.

[0068] The crystallization vessel includes a first crystallization vessel and a second crystallization vessel. The first crystallization vessel has a first precursor inlet located at the upper part and a first precursor outlet located at the lower part; the second crystallization vessel has a second precursor inlet located at the upper part and a second precursor outlet located at the lower part. The first precursor outlet of the first crystallization vessel is connected to the second precursor inlet of the second crystallization vessel.

[0069] The titanium-silicon molecular sieve prepared in this application has applications in olefin epoxidation reaction systems. For example, the epoxidation of hexene to epoxide.

[0070] A method for epoxidizing olefins includes dispersing the titanium-silicon molecular sieve prepared according to this invention in hydrogen peroxide, then introducing hexene, and oxidizing the olefin to epoxides at a reaction temperature of 60°C. For example, hexene is epoxidized to hexane oxide.

[0071] Preferably, the mass ratio of titanium-silicon molecular sieve to hydrogen peroxide with a concentration of approximately 30% is 1:8.

[0072] Preferably, the pressure of the reaction system is 0.1 MPa.

[0073] In the reaction system, acetonitrile is chosen as the solvent.

[0074] When this catalyst is used in the hexene epoxidation reaction system, the selectivity of the resulting hexane oxide is all above 90%.

[0075] The method for preparing titanium-silicon molecular sieves provided by this invention shortens the reaction time of the titanium-silicon molecular sieve by employing two consecutive ultrasonic treatments and multi-stage crystallization treatments, and by controlling the ultrasonic conditions each time. In industrial-scale production, the final product, the titanium-silicon molecular sieve, exhibits uniform crystallinity and particle size distribution, indicating stable performance of the product from continuous industrial production.

[0076] In the preparation of titanium-silicon molecular sieves, not only are organic solvents and surfactants completely avoided, reducing the environmental impact of the production process, but also continuous production of the entire process of precursor synthesis and crystallization is achieved through the coupling of dual ultrasonic reactors in series with a continuous crystallization unit. While effectively suppressing the formation of non-framework titanium, the synthesis efficiency and process stability are greatly improved, truly achieving green, efficient and continuous industrial production.

[0077] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or fractions are by weight.

[0078] The units in the weight-volume percentages of this invention are well known to those skilled in the art, for example, referring to the weight of the solute in 100 ml of solution.

[0079] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as are familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0080] Combined with appendix Figure 1-4 This invention discloses one embodiment of the reaction apparatus for preparing titanium-silicon molecular sieves. The reaction apparatus includes a first ultrasonic reactor 11 and a second ultrasonic reactor 12, as well as a first crystallization reactor 21 and a second crystallization reactor 22 connected in sequence. The connection method of the reactors is the same as the flow direction of the materials.

[0081] The first feed inlet is located at the top of the first ultrasonic reactor 11, and the first discharge outlet is located at the bottom of the first ultrasonic reactor 11. An ultrasonic probe 113 is installed inside the first ultrasonic reactor 11, and the ultrasonic probe 113 extends into the reactor 11 at a position below the first feed inlet. For example, the ultrasonic probe is located in the middle position between the first feed inlet and the first discharge outlet.

[0082] The second feed inlet is located at the top of the second ultrasonic reactor 12, and the second discharge outlet is located at the bottom of the second ultrasonic reactor 12. An ultrasonic transducer 123 is installed on the outer periphery of the second ultrasonic reactor 12, and the ultrasonic transducer 123 is located at the bottom of the second ultrasonic reactor. A stirring device 124 is installed inside the second ultrasonic reactor 12.

[0083] Temperature control jackets 125 are fitted on the outer peripheral walls of the first ultrasonic reactor 11 and the second ultrasonic reactor 12. For example, water or steam at a certain temperature is introduced into the jacket to heat the substances in the reactor.

[0084] A transfer pump is installed between the first crystallization vessel 21 and the second crystallization vessel 22. Both the first and second crystallization vessels are covered with temperature-controlled jackets, and water vapor or heat transfer oil flows into the jackets to circulate and independently control the crystallization temperature of each vessel.

[0085] During the reaction, the reactants enter the first ultrasonic reactor 11 through the first feed inlet, where the mixture is treated by an ultrasonic probe. They then enter the second ultrasonic reactor 12, where the mixture is treated by an ultrasonic transducer mounted on the outer wall. Subsequently, they sequentially enter the first crystallization reactor 21 and the second crystallization reactor 22 for continuous, staged crystallization. After further cooling, drying, and calcination, the titanium-silicon molecular sieve catalyst is obtained. Example 1

[0086] Preparation of titanium-silicon molecular sieves

[0087] Titanium-silicon molecular sieves were prepared using the above-described reaction apparatus, which included two-stage ultrasonication and two-stage crystallization treatment.

[0088] Tetraethyl orthosilicate (TEOS), tetrabutyl titanate (TBOT), tetrapropylammonium hydroxide (TPAOH, 25 wt%), and deionized water were mixed in a molar ratio of 1:0.020:0.2:35. The mixture was continuously fed into the first ultrasonic reactor at a flow rate of 150 mL / min. The temperature inside the first ultrasonic reactor was controlled at 30°C. The ultrasonic probe had an ultrasonic frequency of 20 kHz and a power of 6 kW. The average residence time of the material in the reactor was 30 minutes.

[0089] The precursor sol in the first ultrasonic reactor is discharged through the first outlet and flows into the second ultrasonic reactor. The temperature in the second ultrasonic reactor is controlled at 30°C, the ultrasonic frequency of the ultrasonic transducer is 20 kHz, the power is 3 kW, and the stirring speed in the second ultrasonic reactor is 200 rpm. The average residence time of the material in the reactor is 20 minutes.

[0090] The precursor sol in the second ultrasonic reactor is discharged through the second outlet and flows into the first crystallization reactor. Inside the first crystallization reactor, the temperature is 180℃, the pressure is 0.9 MPa, the stirring speed is 150 rpm, and the average residence time is 12 hours. The material in the first crystallization reactor then flows into the second crystallization reactor, where the temperature is 160℃, the pressure is 0.9 MPa, the stirring speed is 150 rpm, and the average residence time is 12 hours.

[0091] The crystallized product flowing out of the second crystallization reactor was cooled, washed with deionized water until neutral, centrifuged, dried at 80°C for 12 hours, and finally calcined at 550°C for 6 hours to remove the template agent, yielding the TS-1 molecular sieve product. Compared with existing technologies, this invention uses a dual-ultrasonic continuous reactor to enhance the synthesis of the precursor, effectively suppressing the self-polymerization of titanium sources and the formation of non-framework titanium, allowing more titanium species to enter the molecular sieve framework. Simultaneously, the continuous crystallization unit ensures more complete precursor conversion, avoiding losses caused by material transfer and waste liquid discharge during batch operations. Experimental results show that the solid yield of TS-1 prepared by the method of this invention is higher than that of the traditional hydrothermal method.

[0092] The obtained TS-1 molecular sieve was analyzed by ultraviolet spectroscopy, refer to the attached figure. Figure 5 The results showed that the prepared molecular sieve exhibited a typical four-coordinated framework titanium characteristic absorption peak at 220 nm, while no corresponding signal of non-framework titanium was detected at 320 nm, indicating that the molecular sieve contained almost no non-framework titanium species.

[0093] The TS-1 molecular sieve obtained in this embodiment was analyzed by X-ray diffraction and scanning electron microscopy (SEM), as shown in the attached figure. Figure 6 and 7 .

[0094] right Figure 6 Analysis of the XRD pattern showed that the product obtained in Example 1 of the present invention exhibited typical MFI topological diffraction peaks at 2θ of 7.8°, 8.8°, 23.1°, 23.8° and 24.3°, and no other crystalline phase impurity peaks were detected.

[0095] Based on the combined XRD and SEM characterization results, the method for preparing titanium-silicon molecular sieves in this application has yielded nano-TS-1 molecular sieves with high crystallinity and uniform grain size while shortening the crystallization cycle. Example 2

[0096] The method and process parameters for preparing titanium-silicon molecular sieves in this embodiment are basically the same as in Example 1, except that the ultrasonic power of the first ultrasonic continuous reactor is changed from 6 kW to 8 kW, while the other conditions remain the same. The ultraviolet spectral analysis of the finally prepared TS-1 molecular sieve shows that the prepared molecular sieve exhibits a typical four-coordinate framework titanium characteristic absorption peak at 220 nm, while no corresponding signal of non-framework titanium is detected at 320 nm, indicating that the molecular sieve contains almost no non-framework titanium species. Example 3

[0097] The method and process parameters for preparing titanium-silicon molecular sieves in this embodiment are basically the same as in Example 1, except that the ultrasonic power of the second ultrasonic continuous reactor is changed from 3 kW to 5 kW, while the other conditions remain the same. The ultraviolet spectral analysis of the finally prepared TS-1 molecular sieve shows that the prepared molecular sieve exhibits a typical four-coordinate framework titanium characteristic absorption peak at 220 nm, while no corresponding signal of non-framework titanium is detected at 320 nm, indicating that the molecular sieve contains almost no non-framework titanium species. Example 4

[0098] The method and process parameters for preparing titanium-silicon molecular sieves in this embodiment are basically the same as in Example 1, except that the continuous crystallization unit consists of two reactors connected in series, with temperatures of 175℃ and 155℃ respectively, while the other conditions remain the same. The UV spectral analysis of the finally prepared TS-1 molecular sieve shows that it exhibits a typical four-coordinate framework titanium characteristic absorption peak at 220 nm, while no corresponding signal of non-framework titanium was detected at 320 nm, indicating that the molecular sieve contains almost no non-framework titanium species. Example 5

[0099] The method and process parameters for preparing titanium-silicon molecular sieves in this embodiment are basically the same as in Example 1, except that the continuous crystallization unit consists of three reactors connected in series, with temperatures of 175℃, 170℃, and 165℃ respectively, and a residence time of 8 h for each reactor, for a total residence time of 24 h. The rest are the same. The UV spectral analysis of the finally prepared TS-1 molecular sieve shows that the prepared titanium-silicon molecular sieve exhibits a typical four-coordinate framework titanium characteristic absorption peak at 220 nm, while no corresponding signal of non-framework titanium was detected at 320 nm, indicating that the molecular sieve contains almost no non-framework titanium species. Comparative Example 1

[0100] The method and process parameters for preparing titanium-silicon molecular sieves in this comparative example are basically the same as in Example 1. The same raw material ratio is used, the ultrasonic generator of the first ultrasonic reactor is turned off, the mixed raw materials flow directly into the second ultrasonic reactor and remain there for 50 minutes, and the material discharged from the second ultrasonic reactor flows directly into the first crystallization reactor. Other conditions are the same as in Example 1. The UV spectral analysis of the finally prepared TS-1 molecular sieve shows that the prepared molecular sieve exhibits a typical four-coordinate framework titanium characteristic absorption peak at 220 nm, while a corresponding signal of non-framework titanium is detected at 320 nm, indicating that the molecular sieve contains non-framework titanium species. Comparative Example 2

[0101] The method and process parameters for preparing titanium-silicon molecular sieves in this comparative example are basically the same as in Example 1. The same raw material ratio is used, the ultrasonic generator in the second ultrasonic reactor is turned off, the residence time in the first ultrasonic reactor is 50 minutes, and the material discharged from the first ultrasonic reactor flows directly into the first crystallization reactor. Other conditions are the same as in Example 1. The UV spectral analysis of the finally prepared TS-1 molecular sieve shows that the prepared molecular sieve exhibits a typical four-coordinate framework titanium characteristic absorption peak at 220 nm, while a weak corresponding signal of non-framework titanium is detected at 320 nm, indicating that there are trace amounts of non-framework titanium species in this molecular sieve. Comparative Example 3

[0102] The method and process parameters for preparing titanium-silicon molecular sieves in this comparative example are basically the same as in Example 1, using the same raw material ratio and feed rate, but the ultrasonic generators of the first and second ultrasonic reactors are turned off, while other conditions remain the same. The UV spectral analysis of the final product showed that no characteristic absorption peak of four-coordinated framework titanium was detected at 220 nm, while a corresponding signal of non-framework titanium was detected at 320 nm, indicating that the product contains non-framework titanium species. This product does not belong to the titanium-silicon molecular sieve category. Comparative Example 4

[0103] The method and process parameters for preparing titanium-silicon molecular sieves in this comparative example are basically the same as in Example 1. The same raw material ratio and feed rate are used. After collecting the ultrasonic raw material, it is intermittently hydrothermally crystallized at 170℃ (i.e., the material is static in the crystallization vessel) for 24 hours, with all other conditions remaining the same. The UV spectral analysis of the finally prepared TS-1 molecular sieve shows that it exhibits a typical four-coordinate framework titanium characteristic absorption peak at 220 nm, while no corresponding signal of non-framework titanium is detected at 320 nm, indicating that the molecular sieve contains almost no non-framework titanium species. Comparative Example 5

[0104] The method for preparing titanium-silicon molecular sieves in this comparative example is the traditional hydrothermal method, and the amount of molecular sieve synthesized is at the small-scale level. The precursor was prepared according to the molar ratio of the raw materials in Example 1. First, 5.16 g of the template agent tetrapropylammonium hydroxide (TPAOH, 25% aqueous solution) was mixed with 16.13 g of deionized water and stirred for 30 min. Then, the first mixed solution in the beaker was placed in an air-tight glove box filled with nitrogen. Next, 6.6 g of tetraethyl orthosilicate (TEOS) was slowly added dropwise (1 g / min) to the first mixed solution, with continuous stirring during the addition. After the addition was completed, stirring was continued at 45°C for 1 h to obtain the second mixed solution. Subsequent processes were carried out entirely in an air-tight glove box. 0.216 g of tetrabutyl titanate (TBOT) was slowly added dropwise to 4 g of isopropanol. After the addition was completed, the mixture was stirred at room temperature (25°C) for 3 min to obtain the third mixed solution. Subsequently, the third mixed solution was slowly added dropwise (0.1 g / min) to the second mixed solution. After the addition was complete, the mixture was stirred for 1 hour at room temperature (25°C) to obtain the fifth mixed solution. The temperature of the fifth mixed solution was raised to 80°C and evaporated for 5 hours to remove alcohol. During the alcohol removal process, deionized water was slowly added dropwise to maintain a constant solution volume, resulting in the sixth mixed solution. The sixth mixed solution was quickly transferred to a crystallization vessel and statically crystallized at 170°C for 24 hours. The product after crystallization was processed as in Example 1 to obtain TS-1 molecular sieve. The UV spectral analysis of the finally prepared TS-1 molecular sieve showed that the prepared molecular sieve exhibited a typical four-coordinate framework titanium characteristic absorption peak at 220 nm, while no corresponding signal of non-framework titanium was detected at 320 nm, indicating that the molecular sieve contained almost no non-framework titanium species. Comparative Example 6

[0105] The method and process parameters for preparing titanium-silicon molecular sieves in this comparative example are basically the same as those in Comparative Example 5, with the variable being the mass of the raw materials magnified 100 times. The UV spectral analysis of the final prepared TS-1 molecular sieve showed that it exhibited a typical four-coordinated framework titanium characteristic absorption peak at 220 nm, while a corresponding signal of non-framework titanium was detected at 320 nm, indicating that the product contains non-framework titanium species. Comparative Example 7

[0106] The method and process parameters for preparing titanium-silicon molecular sieves in this comparative example are basically the same as in Example 1, using the same raw material ratio and feed rate, but the ultrasonic power of both the first and second ultrasonic reactors is 6 kW, and other conditions are the same. The UV spectral analysis of the finally prepared TS-1 molecular sieve showed that the molecular sieve detected a characteristic absorption peak of four-coordinate framework titanium at 220 nm, while no corresponding signal of non-framework titanium was detected at 320 nm, indicating that the molecular sieve contains almost no non-framework titanium species. Comparative Example 8

[0107] The method and process parameters for preparing titanium-silicon molecular sieves in this comparative example are basically the same as in Example 1, using the same raw material ratio and feed rate, but the ultrasonic power of both the first and second ultrasonic reactors is 3 kW, and other conditions are the same. The UV spectral analysis of the finally prepared TS-1 molecular sieve showed that the prepared molecular sieve detected a characteristic absorption peak of four-coordinate framework titanium at 220 nm, while a weaker signal corresponding to non-framework titanium was detected at 320 nm, indicating that the molecular sieve contains a small amount of non-framework titanium species. Comparative Example 9

[0108] The method and process parameters for preparing titanium-silicon molecular sieves in this comparative example are basically the same as in Example 1, using the same raw material ratio and feed rate, but the crystallization temperature is 170℃, and other conditions are the same. The UV spectral analysis of the finally prepared TS-1 molecular sieve showed that the molecular sieve detected a characteristic absorption peak of four-coordinate framework titanium at 220 nm, while no corresponding signal of non-framework titanium was detected at 320 nm, indicating that the molecular sieve contains almost no non-framework titanium species.

[0109] To quantitatively evaluate the effect of this invention on improving the yield of molecular sieves, the yield was calculated using the following formula: Yield = (Mass of molecular sieve / Theoretically total mass of molecular sieve produced from feed) * 100% Table 1. Yield results of each embodiment and comparative example

[0110] Experimental Example 1 This experimental example shows the reaction results of the synthesized titanium-silicon molecular sieve in the hexene epoxidation in the examples and comparative examples, as shown in Table 1. The reaction conditions included: 0.2 g of molecular sieve, 15.6 g of acetonitrile solvent, 1.2 g of 1-hexene, and 1.6 g of hydrogen peroxide (30 wt%) were placed in a 50 mL batch reactor. Magnetic stirring was used to promote uniform mixing of the reactants. The reaction temperature was 60 °C, and the reaction time was 3 h. The resulting solid-liquid mixture was separated by centrifugation, and the liquid was then analyzed by gas chromatography. The results are shown in Table 2 below.

[0111] Under the condition that the reaction conditions are met, samples of the prepared titanium-silicon molecular sieve synthesized in Example 1 were taken at 5 time points. The time interval between the second sampling and the first sampling was 6 hours. The time intervals between the third, fourth, fifth and sixth sampling and the first sampling were 12 hours, 24 hours, 48 ​​hours and 72 hours, respectively. The titanium-silicon molecular sieves prepared in Example 1 were subjected to hexene epoxidation reaction using the above method. The reaction performance results are shown in Table 3.

[0112] Calculation formula

[0113] In the examples and comparisons, the formula for calculating the effective utilization rate of hydrogen peroxide is: Hydrogen peroxide utilization rate = (Molar amount of hydrogen peroxide converted (excluding ineffective decomposition) / Molar amount of hydrogen peroxide added) * 100% Selectivity for hexane oxide = (Molar amount of hexane oxide in the product / Total molar amount of all products) * 100%

[0114] Table 2 Results of reactions in each embodiment and comparative example

[0115]

[0116] Table 3 Results of product reaction performance obtained from continuous reaction in Example 1

[0117] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the substantive technical content of the present invention. The substantive technical content of the present invention is broadly defined within the scope of the claims. Any technical entity or method implemented by others that is completely identical to or an equivalent modification of the claims is considered to be covered within the scope of the claims.

Claims

1. A method for continuous synthesis of titanium-silicon molecular sieves, comprising the following steps: (1) Water, organic template agent, silicon source, and titanium source are mixed and subjected to a first ultrasonic treatment to obtain mixed solution I, wherein, The first ultrasonic treatment uses an immersion ultrasonic generator; (2) Mixed solution I is subjected to a second ultrasonic treatment to obtain mixed solution II. The second ultrasonic treatment is performed using a wall-mounted ultrasonic generator. The power of the second ultrasonic treatment is lower than that of the first ultrasonic treatment, and the time of the first ultrasonic treatment is longer than that of the second ultrasonic treatment. (3) Mixed solution II is subjected to first-stage crystallization and second-stage crystallization in sequence to obtain crystallized solution. The temperature of first-stage crystallization is 170℃-180℃, and the temperature of second-stage crystallization is 160℃-170℃. The temperature of first-stage crystallization is higher than that of second-stage crystallization. (4) The crystallization solution is cooled, centrifuged, dried and calcined to obtain a titanium-silicon molecular sieve catalyst; The power of the first ultrasonic treatment is 1 kW-20 kW, and the time of the first ultrasonic treatment is 20 min-40 min. The power of the second ultrasonic treatment is 1 kW-15 kW, and the duration of the second ultrasonic treatment is 10 min-20 min; The frequency of the first ultrasonic treatment is 20 kHz-100 kHz, and the frequency of the second ultrasonic treatment is 20 kHz-80 kHz. The frequency of the first ultrasonic treatment is greater than or equal to the frequency of the second ultrasonic treatment.

2. The method for titanium-silicon molecular sieves according to claim 1, characterized in that, Water, organic template agent, silicon source, and titanium source are mixed to obtain a mixed solution. The flow rate of the mixed solution during the first ultrasonic treatment, the second ultrasonic treatment, and the crystallization treatment is controlled at 100-180 mL / min.

3. The method for titanium-silicon molecular sieves according to claim 1, characterized in that, In steps (1) and (2), the temperature of the mixed solution is controlled at 20-60 ℃ during the first and second ultrasonic treatments.

4. The method for making titanium-silicon molecular sieves according to any one of claims 1-3, characterized in that, In the two-stage crystallization process, the crystallization time is 4-12 h.

5. The method for making titanium-silicon molecular sieves according to any one of claims 1-3, characterized in that, The molar ratio of silicon in the silicon source to titanium in the titanium source is 20-80:1; The molar ratio of silicon to organic template agent in the silicon source is 5-30:1; and The molar ratio of silicon to water in the silicon source is 1:10-60.

6. The method for making titanium-silicon molecular sieves according to any one of claims 1-3, characterized in that, In step (4), the temperature of the roasting process is controlled at 500-700 ℃; The roasting time is 4-8 hours.

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