A process for the preparation of Ti-beta zeolite based on the gas phase transport method with reusable organic base

Abstract

The present application belongs to the field of petroleum chemical catalysis technology, and relates to a Ti-Beta zeolite preparation process based on a gas phase transmission method and a reusable organic base. Main technical features include: providing water vapor and a weak organic base auxiliary tetraethylammonium bromide template by gas phase transmission, and preparing Ti-Beta zeolite by in-situ local desilicon etching and repair and reconstruction of the hydroxyl pit of the dealuminized Beta zeolite. Benefits include: the combination of the tetraethylammonium bromide template and the volatile weak organic base, and the limitation of the amount of dissolved silicate by the channel condensate liquid generated by the dealuminized Beta zeolite and the liquid film on the zeolite solid surface in the saturated steam, which makes the controllable etching desilicon of the hydroxyl pit of the dealuminized Beta zeolite and the improvement of the receiving capacity of the hydroxyl pit to the relatively large titanium ions easier. The local structural defects generated by the controllable etching desilicon can be directly repaired by the quaternary ammonium cations provided by the TEABr template, so that the present application does not need fluoride or / and aluminum source auxiliary.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of petrochemical catalysis technology, and relates to a Ti-Beta zeolite preparation process based on a gas phase transmission method and a reusable organic base. BACKGROUND

[0002] So far, Ti-Beta zeolite can be prepared by various methods, including a traditional hydrothermal method, a dry gel conversion method (steam assisted), a crystal transformation method, a isomorphous substitution method and a structure reconstruction method.

[0003] The main technical feature of the traditional hydrothermal method is that Ti-Beta zeolite is produced by hydrothermal crystallization of a hydrogel, and a large amount of fluoride mineralizer needs to be added to the hydrogel, and even a small amount of aluminum source needs to be introduced for auxiliary synthesis. The crystallization process of the hydrogel is slow and time-consuming. Therefore, when Ti-Beta zeolite is prepared by the traditional hydrothermal method, not only is there a problem of treatment of fluoride-containing wastewater, but also there are problems of high energy consumption and low efficiency. In addition, the introduction of a small amount of aluminum source will inevitably cause framework aluminum in the Ti-Beta zeolite framework, and a post-dealuminization step needs to be added.

[0004] The main technical feature of the dry gel conversion method (steam assisted) is that Ti-Beta zeolite is not directly synthesized by a hydrogel, but a dry gel is first prepared by low-temperature drying of the hydrogel, and then the dry gel conversion method is used to synthesize Ti-Beta zeolite. Because the conversion process of the dry gel is not carried out in an aqueous phase, but in steam generated by water vaporization, it is called steam-assisted dry gel conversion method. For example, the published document J. Phys. Chem. B 1998, 102, 7126-7131 discloses a method for synthesizing Ti-Beta zeolite by dry gel conversion. The method is as follows: aerosol silica is used as a silicon source, tetrabutyl titanate, deionized water and hydrogen peroxide solution are used to prepare a titanium source, and sodium metaaluminate, sodium hydroxide and tetraethylammonium hydroxide solution are used to prepare an aluminum source. First, the aluminum source solution is added to the titanium source solution under vigorous stirring, and then the silicon source is added to the mixed solution, and the stirring is continued until a uniform colloidal solution is formed. Then, the colloidal solution is evaporated to dryness at 80℃ to obtain a dry gel. The composition of the dry gel is SiO2:TiO2:Al2O3:Na2O:TEAOH = 304:10:0.46:1.55:132.5. The crystallization is carried out in a special autoclave. The dry gel is placed on a tray, and deionized water is placed under the tray. The conversion of the dry gel is carried out at 175℃ for 18h. During this period, the dry gel is converted into Ti-Beta zeolite with the assistance of water vapor. Compared with the conventional hydrothermal method, the dry gel conversion method can be carried out without adding fluoride mineralizer, and the crystallization time is shorter, but a small amount of aluminum source still needs to be introduced for auxiliary synthesis.

[0005] The main technical feature of the crystal transformation method is that the Ti-Beta zeolite is transformed from a zeolite with a completely different topology. For example, the publication Chem. Commun., 2019, 55, 14279 reports a crystal transformation method for preparing Ti-Beta zeolite. In this method, a Ti-MWW zeolite with a layered structure is used as a raw material. The Ti-MWW zeolite provides both the silicon source and the titanium source for the preparation of Ti-Beta. The method is as follows: first, the Ti-MWW zeolite and the fully dealuminated Beta seeds are added to an alkaline solution for degradation, so as to become the structural building units for synthesizing Ti-Beta zeolite. Then, the degradation solution is crystallized into Ti-Beta zeolite with the assistance of a template agent (tetraethyl cation) and a fluoride mineralizer; the publication (Synthesis and Catalytic Performance of BEA and FAU Topology Zeolites with Heteroatoms[D]. East China Normal University, 2018) has a more detailed description of the crystal transformation of Ti-MWW to Ti-Beta. For another example, the publication Microporous and Mesoporous Materials 311 (2021) 110702 also reports a crystal transformation method for preparing Ti-Beta zeolite. In this method, a USY zeolite (USY, Si / Al = 6.0) is used as a starting raw material. First, the USY is dealuminated with a 6 mol / L nitric acid solution at reflux temperature (liquid-solid ratio 30, 12 h), filtered, washed, dried, and calcined. The above acid dealumination operation is repeated at least 2-3 times, so that the Si / Al molar ratio of the obtained dealuminated USY (USY-DA) reaches 500 or more (analyzed by ICP). In this method, the USY-DA is only used as a silicon source. Then, the USY-DA, dealuminated Beta zeolite seeds (Beta-DA, Si / Al molar ratio ≥ 1900, amount of 10 wt% based on USY-DA), a titanium source (TBOT), a pore-forming agent (CTAB), a template agent TEAOH, and NH4F are used to prepare a mixed solution with a composition of 1.0 SiO2: 0.02 TiO2: 0.4 TEAOH: 0.2 CTAB: 0.5 NH4F: 7.5 H2O, and crystallized at 140°C for 3 days to obtain Ti-Beta zeolite. Generally, the crystal transformation method for preparing Ti-Beta zeolite has less time consumption and high product quality. However, the crystal transformation method cannot get rid of the use of fluoride mineralizers.

[0006] The main technical feature of the isomorphous substitution method is to use a dealuminated Beta zeolite to prepare a Ti-Beta zeolite, specifically, under the premise of not destroying the crystal structure of the dealuminated Beta zeolite, by introducing tetravalent titanium ions (Ti 4+Ti-Beta zeolite is prepared by implanting titanium into the hydroxyl pockets of dealuminated Beta zeolite. The isomorphous substitution method is further divided into three technical routes, namely, gas-solid phase, solid-solid phase and liquid-solid phase isomorphous substitution methods.

[0007] The gas-solid phase isomorphous substitution method uses volatile TiCl4 as the titanium source, and TiCl4 is carried by inert gas (such as N2) to contact with the dealuminated Beta zeolite, and the isomorphous substitution reaction is carried out at high temperature. The main problem of this method is that the operation is difficult, non-framework titanium is easy to produce, and the repeatability of catalyst preparation is poor. Therefore, the solid-solid phase isomorphous substitution method and the liquid-solid phase isomorphous substitution method are proposed as improved technical routes.

[0008] The solid-solid isomorphous substitution method generally uses solid titanium dichloride powder as the titanium source to carry out isomorphous substitution reaction on dealuminated Beta zeolite. For example, the Chinese invention patent (application number 202111439797.1) discloses a method for preparing Ti-Beta zeolite by isomorphous substitution method, the technical features of which are: first, dealuminating Beta zeolite to obtain all-silicon Si-Beta zeolite, then pretreating the Si-Beta zeolite by dehydration and impurity removal, and then uniformly mixing the pretreated Si-Beta zeolite with solid titanium dichloride powder in an inert gas environment; transferring the mixed powder to a flat-bottomed crucible with a cover and uniformly spreading it as thinly as possible in the flat-bottomed crucible, and transferring the crucible with the mixed powder to a vacuum environment for heating, so that the Ti metal in the precursor in the crucible is uniformly impregnated into the framework of the Si-Beta zeolite to obtain Ti-Beta zeolite. In order to make the dealuminated Beta zeolite and the solid titanium dichloride powder mix uniformly, it is generally necessary to use a ball mill to fully treat the mixture of dealuminated Beta zeolite and titanium dichloride. For example, the use of a ball mill is involved in the following publications: Catal. Sci. Technol., 2019, DOI: 10.1039 / C9CY00957D, Green Chem., 2014, 16, 2281 and Chinese Journal of Catalysis 36 (2015) 906-912. In addition, the following documents also involve the use of solid-solid isomorphous substitution method to prepare Ti-Beta zeolite: Chinese invention patent (application number 202011450442.8); Chinese invention patent (application number 202010855082.3); publication Chinese Journal of Catalysis 42 (2021) 1176-1184; publication Microporous and Mesoporous Materials 330 (2022) 111625; publication Microporous and Mesoporous Materials 288 (2019) 109588. The Ti-Beta zeolite prepared by the solid-solid isomorphous substitution method has good quality, but the titanium source is relatively expensive, and the operation process needs to be carried out under the protection of inert gas, generally requiring the use of a glove box.

[0009] The liquid-solid isomorphous substitution method is preferably carried out by using an ethanol solution of TiCl4 as the titanium source to perform an isomorphous substitution reaction with the dealuminated Beta zeolite. For example, the method is described in detail in the published document Ind. Eng. Chem. Res. 2021, 60, 1219-1230, the main points of which are as follows: (1) an Al-beta zeolite with Si / Al = 11 is contacted with a 13 mol / L aqueous HNO3 solution and reacted at 100°C for 24 h to obtain a dealuminated Beta zeolite; (2) the dealuminated Beta zeolite is pretreated by drying (110°C, 2 h) and calcination (550°C, 3 h) before use. A solution of TiCl4 is prepared as the titanium source by using ethanol (dried over 3A zeolite for more than 24 h). Then, the ethanol solution of TiCl4 is contacted (ground) with the dealuminated Beta zeolite to perform an isomorphous substitution reaction at room temperature to obtain a Ti-Beta zeolite. The post-treatment of the Ti-Beta zeolite prepared by the above liquid-solid isomorphous substitution method includes a drying step (120°C, 3 h) and a calcination step (550°C, 3 h).

[0010] In addition to using an ethanol solution of TiCl4 as the titanium source, the published documents (Wang Yannan. Preparation, characterization and application of ionic liquid in catalytic desulfurization of fuel oil [D]. Tianjin University, 2010, Zhang Juan. Preparation, characterization and performance of photocatalytic oxidation of diesel desulfurization catalyst [D]. Tianjin University, 2008 and Chemical Engineering, 2012, Vol. 40, No. 10) report a method of using titanium sulfate (Ti(SO4)2) as the titanium source to prepare a Ti-Beta zeolite by the liquid-solid isomorphous substitution method. These published documents all omit the step of acid dealumination of the zeolite when using Ti(SO4)2) as the titanium source, and directly perform an isomorphous substitution reaction between the Al-Beta zeolite and the Ti(SO4)2) solution to prepare a Ti-Beta zeolite. This method is based on the strong acidity of the Ti(SO4)2) solution, which can enable the dealumination and titanium supplementation to occur simultaneously in the liquid-solid phase reaction. However, the liquid-solid isomorphous substitution reaction between the Ti(SO4)2) and the Al-Beta zeolite cannot effectively remove the framework aluminum of the Beta zeolite, and thus the Ti 4+ ion can only be partially substituted for the Al

[0011] In fact, the gas-solid, solid-solid and liquid-solid isomorphous substitution methods described above all have the problem that the substitution reaction of the Ti 4+ ion for the Al 4+ ion occurs to a limited extent. This is because the radius of the Ti ion is larger than the radius of the Al 3+ ion. Therefore, the hydroxyl hole vacancies generated after the Al 3+ ion is removed from the framework of the Al-Beta zeolite are small, which is not conducive to the substitution of the Ti4+ Implantation.

[0012] Theoretically, the structural reconstruction method can avoid the problems of the isomorphous substitution method. Although the structural reconstruction method also uses dealuminated Beta zeolite to prepare Ti-Beta zeolite, the structural reconstruction process occurs in the presence of a strongly alkaline TEAOH template solution. Existing research shows that the strongly alkaline TEAOH template solution contributes to the complete dissolution (fragmentation) and recrystallization (structural reconstruction) of the dealuminated Beta zeolite framework, which is beneficial to the formation of larger Ti... 4+ Ions combine with fragmented Beta zeolite structural building blocks, thus facilitating their entry into the Beta zeolite framework during framework recrystallization through the assembly of these building blocks.

[0013] The published paper Catal. Sci. Technol., 2019, DOI: 10.1039 / C9CY00071B. reported a method for rapid synthesis of Ti-Beta using the structure reconstruction method. The key technical points are as follows: (1) First, use 13 mol L -1 HNO3 solution was used to thoroughly remove aluminum from commercially available Al-Beta zeolite (removal conditions: liquid-to-solid ratio 50 ml / g). -1 (1) Drying (120℃, calcination (550℃, 6h) of dealubilized Beta zeolite to prepare dealubilized Beta zeolite (Beta-DA) with a Si / Al molar ratio >1900; (3) Using Beta-DA as the silicon source, TEAOH solution as the template agent, and TBOT as the Ti source, a colloidal solution was prepared; (4) The colloidal solution was dissolved at 140℃ for 1h; (5) The colloidal solution after dissolution was rapidly cooled, and then NH4F was added to it at room temperature to assist the recrystallization process. The chemical composition of the colloidal solution before recrystallization was 1SiO2:1 / x TBOT:(0.3-0.5)TEAOH:(4-7.5)H2O:0.1NH4F; (6) Recrystallization was carried out at 140℃, and highly crystalline Ti-Beta zeolite could be obtained within 1h.

[0014] A similar method is also reported in the publication Mater. Chem. Front., 2021, 5, 6101. The Si / Al molar ratio of the dealuminated Beta zeolite used is >1500 (dealumination conditions of Al-Beta zeolite: 65wt% HNO3 solution, liquid-solid ratio 30, dealumination at reflux temperature for 12h, repeated once). The specific procedure for preparing Ti-Beta zeolite using dealuminated Beta zeolite (Beta-DA) as the silicon source is as follows: first, Beta-DA is added to a strong alkaline TEAOH aqueous solution under stirring for 10 min. Then, TBOT is added dropwise. Finally, NH4F is added to the mixture to obtain a colloidal solution with a composition of 1.0SiO2:xTEAOH:yTiO2:0.5NH4F:7.0H2O. The above gel solution is recrystallized at 140℃ for 1 day to obtain the Ti-Beta zeolite product. The post-treatment of Ti-Beta zeolite includes filtration, washing, drying (80℃, overnight) and calcination (550℃, 6h).

[0015] The following publications also relate to the preparation of Ti-Beta zeolite by structure reconstruction method: Wang Bowen. Preparation of MFI and BEA Type Zeolites and Study on Their Catalytic Performance[D]. East China Normal University, 2021; You Qing. Preparation of Heteroatom Beta Zeolites, Hierarchical Pore Channel and Catalytic Performance[D]. Northwest University, 2021; Microporous and Mesoporous Materials 330 (2022) 111625; Ma Haikuo. Design and Synthesis of BEA Topology Heteroatom Zeolites and Their Catalytic Performance[D]. Yantai University, 2022; Pan Hong. Synthesis and Post-treatment Modification of Titanium Silicate Zeolites and Study on Their Epoxidation Performance[D]. East China Normal University, 2022; New J. Chem., 2021, 45, 10303; Chemical Industry Progress https: / / doi.org / 10.16085 / j.issn.1000-6613.2021-2097 (2022-01-27 Online First). In general, the structure reconstruction method is a relatively industrially valuable method for preparing Ti-Beta zeolite, and the main advantages are high titanium content in the framework, short preparation time, and good preparation repeatability. However, the existing structure reconstruction method still needs to be assisted by the mineralization of a large amount of fluoride for crystallization. The discharge of a large amount of high-fluorine-containing wastewater is the main challenge for the industrial application of the existing structure reconstruction method. SUMMARY

[0016] The present application provides a Ti-Beta zeolite preparation process based on a gas phase transport method using reusable organic bases.

[0017] In other words, the present application provides a green process for in-situ local etching and structure reconstruction of the hydroxyl pockets of dealuminated Beta zeolite without using fluoride or / and aluminum source, with the assistance of water vapor and volatile weak organic base vapor phase transmission and tetraethyl ammonium bromide (TEABr) template, which can produce Ti-Beta zeolite in large quantities and recycle the weak organic base. The process belongs to in-situ local structure reconstruction method, that is, the local etching and desilication of the hydroxyl pockets of dealuminated Beta zeolite by volatile weak organic base, the entry of titanium ions into the etched hydroxyl pockets, and the in-situ local structure reconstruction of the Ti-Beta zeolite precursor by TEA + The cation-directed recrystallization of silicate fragments repairs the local structural defects left after the Ti ions are received by the slightly etched hydroxyl pockets, and the three reaction processes are carried out in situ. The process has the following three most prominent technical features: (1) first, using titanium sulfate as the titanium source, tetraethyl ammonium bromide (TEABr) as the template, preparing an acidic aqueous solution containing titanium sulfate and tetraethyl ammonium bromide (TEABr), and then carrying out equal volume impregnation and drying treatment on the dealuminated Beta zeolite to obtain the Ti-Beta zeolite precursor; (2) the in-situ local structure reconstruction process of the Ti-Beta zeolite precursor is carried out in an autoclave, and the water vapor and volatile organic base are contacted with the precursor by vapor phase transmission, and tetraethyl ammonium bromide (TEABr) is used to assist the in-situ local etching and desilication and structure reconstruction reaction. The water vapor and volatile organic base are provided by the bottom liquid of the autoclave which does not directly contact the Ti-Beta zeolite precursor; (4) after the preparation of Ti-Beta zeolite is completed, the volatile organic base can be redissolved in the bottom liquid of the autoclave by cooling to be recycled.

[0018] The present application is fundamentally different from the existing process for preparing Ti-Beta zeolite by structure reconstruction in that the starting point of the structure reconstruction is not the fragmented structure units (long-range disorder, no characteristic diffraction peaks of Beta zeolite in the XRD pattern) produced after the dealuminated Beta zeolite crystals are completely dissolved, but the dealuminated Beta zeolite crystals as a whole (with complete characteristic diffraction peaks in the XRD pattern) whose hydroxyl pockets have been slightly etched by volatile weak organic base but the long-range order of the Beta zeolite structure is still well maintained, so the structure reconstruction of the present application belongs to local structure reconstruction. In addition, the present application uses tetraethyl ammonium bromide (TEABr) template combined with volatile weak organic base instead of the strong alkaline tetraethyl ammonium hydroxide (TEAOH) template used in the existing preparation process, which not only helps to reduce the cost of Ti-Beta zeolite production, but also uses the flexibility of the combination of template and weak organic base to unlock the TEA + The cation part and the OH -The 1:1 ratio of the anion part is easy to achieve mild etching of the hydroxyl pockets of the dealuminated Beta zeolite and to accelerate the structure reconstruction reaction under sufficient amount of structure directing agent. Especially, the acid aqueous solution containing titanium sulfate and TEABr template is used in the preparation of the Ti-Beta zeolite precursor by the equal-volume impregnation method, and the prepared precursor has low water content and does not contain colloidal substances. Since the tetraethylammonium bromide (TEABr) in the precursor has high thermal stability, the conventional drying method can be used for the drying treatment of the Ti-Beta zeolite precursor, the drying speed is fast, and the drying trouble encountered in the preparation of the dry gel intermediate using the hydrogel precursor is avoided. Moreover, the volatile weak organic base is not introduced in the preparation of the Ti-Beta zeolite precursor, but is added in the form of an aqueous solution at the bottom of the autoclave. Only in the process of preparing Ti-Beta zeolite from the Ti-Beta zeolite precursor, the volatile weak organic base can contact with the Ti-Beta zeolite precursor on the tray in the autoclave in the form of gas phase transmission (vaporization from the bottom liquid together with water). Therefore, in the preparation stage of the Ti-Beta zeolite precursor, the hydroxyl pockets of the dealuminated Beta zeolite have not been subjected to mild etching of the volatile organic base. The mild etching of the volatile organic base to the dealuminated Beta zeolite hydroxyl pocket only occurs in the process of preparing Ti-Beta zeolite from the Ti-Beta zeolite precursor. In this process, the local etching of the volatile weak organic base to the dealuminated Beta zeolite hydroxyl pocket, the entry of titanium ions into the etched hydroxyl pocket, and the TEA + The cation-directed recrystallization of the silicate fragments repairs the local structural defects left after the dealuminated Beta zeolite hydroxyl pockets accept titanium ions, and the three reaction processes are carried out in situ. This is a unique feature of the present application. Another unique feature of the present application is that the use of volatile organic bases is not one-time, but most of them can be recycled for reuse. In each use, the consumed part of the volatile organic base is only the dissolved part of the limited thickness liquid film on the crystal surface of the Ti-Beta zeolite product and the limited amount of capillary condensed liquid inside the pore. In summary, the Ti-Beta zeolite preparation process provided by the present application has the advantages of simple method, low cost, and is suitable for large-scale preparation, and thus has higher practical value.

[0019] In the research, it is found that, because the process provided by the present application does not involve establishing the crystal structure of Beta zeolite from scratch (i.e. does not involve Beta zeolite crystal growth), but only involves repairing the local structural defects left after the titanium ions are received by the slightly etched hydroxyl pits, the process provided by the present application can start from the dealuminated Beta zeolite to prepare high-quality Ti-Beta zeolite with high framework titanium content and less non-framework titanium by in-situ local etching desilication and structure reconstruction with the assistance of vapor phase transmission of water vapor and volatile organic base tetraethylammonium bromide (TEABr).

[0020] In the research, it is also found that, the vapor phase transmission technology route adopted by the present application not only provides weak organic base for in-situ local mild desilication etching of the dealuminated Beta zeolite hydroxyl pits, but also provides weak organic base for the subsequent entry of titanium ions into the etched hydroxyl pits, TEA + The cation-directed silicate fragment recrystallization repairs the local structural defects left after the titanium ions are received by the slightly etched hydroxyl pits, and provides important water vapor assistance. The benefits of water vapor assistance include: (1) It is beneficial to avoid over-desilication etching of the dealuminated Beta zeolite hydroxyl pits by the organic base. As known by those skilled in the art, the dissolution of silicate solid in alkaline solution has a chemical equilibrium. But the larger the solution volume, the more silicate solid needs to be consumed to reach the equilibrium state. This means that when the amount of silicate solid (such as dealuminated Beta zeolite) is constant, the larger the volume of alkaline solution, the greater the degree of dissolution of the silicate solid (such as dealuminated Beta zeolite). However, for the present application, since the silicate solid is in contact with steam, and the silicate fragments are non-volatile, the dissolution equilibrium of the silicate only involves the liquid film with limited thickness on the surface of the dealuminated Beta zeolite and the condensed liquid water in the pores of the zeolite. Because the thickness of the liquid film on the surface of the solid and the pore volume of the zeolite are limited, i.e. the total amount of liquid is limited, the silicate fragments that can be dissolved by the condensed liquid water in the liquid film and the pores are also limited; (2) It is beneficial to increase the rate of cation-directed silicate fragment recrystallization reaction. That is, it is beneficial to maximize the time reduction of the local structure reconstruction method for preparing Ti-Beta zeolite. This is mainly because, under the conditions of vapor phase transmission of water vapor and volatile weak organic base assisted local structure reconstruction, the TEABr template molecules, volatile weak organic base molecules and soluble Beta zeolite structural units produced by the slight etching of the hydroxyl pits are concentrated in the condensed liquid in the surface liquid film and the pores. + The cation-directed silicate fragment recrystallization repairs the local structural defects left after the titanium ions are received by the slightly etched hydroxyl pits, and provides important water vapor assistance. The benefits of water vapor assistance include: (1) It is beneficial to avoid over-desilication etching of the dealuminated Beta zeolite hydroxyl pits by the organic base. As known by those skilled in the art, the dissolution of silicate solid in alkaline solution has a chemical equilibrium. But the larger the solution volume, the more silicate solid needs to be consumed to reach the equilibrium state. This means that when the amount of silicate solid (such as dealuminated Beta zeolite) is constant, the larger the volume of alkaline solution, the greater the degree of dissolution of the silicate solid (such as dealuminated Beta zeolite). However, for the present application, since the silicate solid is in contact with steam, and the silicate fragments are non-volatile, the dissolution equilibrium of the silicate only involves the liquid film with limited thickness on the surface of the dealuminated Beta zeolite and the condensed liquid water in the pores of the zeolite. Because the thickness of the liquid film on the surface of the solid and the pore volume of the zeolite are limited, i.e. the total amount of liquid is limited, the silicate fragments that can be dissolved by the condensed liquid water in the liquid film and the pores are also limited; (2) It is beneficial to increase the rate of cation-directed silicate fragment recrystallization reaction. That is, it is beneficial to maximize the time reduction of the local structure reconstruction method for preparing Ti-Beta zeolite. This is mainly because, under the conditions of vapor phase transmission of water vapor and volatile weak organic base assisted local structure reconstruction, the TEABr template molecules, volatile weak organic base molecules and soluble Beta zeolite structural units produced by the slight etching of the hydroxyl pits are concentrated in the condensed liquid in the surface liquid film and the pores.

[0021] The present application is also essentially different from the existing dry gel transformation method for preparing Ti-Beta zeolite. Although both methods involve steam assistance, the latter involves a crystallization process of amorphous dry gel. The crystallization process of dry gel under steam assistance can sometimes be carried out without adding fluoride mineralizer, but requires the introduction of aluminum source to assist the crystallization of amorphous dry gel without adding fluoride mineralizer. Therefore, it is difficult to obtain high-performance Ti-Beta zeolite by the existing dry gel transformation method.

[0022] It needs to be particularly emphasized that the Ti-Beta zeolite preparation process based on the vapor phase transport method provided by the present application is not a simple combination of the existing dry gel transformation method and structure reconstruction method. The innovation and advancement of the present application lies in the following aspects: first, the present application uses tetraethylammonium bromide (TEABr) template combined with volatile weak organic base to replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process, and at the same time, with the help of the pore condensation liquid generated by the dealuminated Beta zeolite in saturated steam and the liquid film on the surface of the zeolite solid, the amount of dissolved silicate is limited, making it easier to achieve controllable etching and desiliconization of the hydroxyl pit of the dealuminated Beta zeolite, improving the acceptance ability of the hydroxyl pit for titanium ions with larger volume, and thus more conducive to the preparation of high-performance Ti-Beta zeolite with high framework titanium content and low non-framework titanium content. Second, the controllable etching and desiliconization produces local structural defects, which can be directly repaired by TEA + cations ionized from the TEABr template in solution in a weakly alkaline environment generated by volatile weak organic base, completely eliminating the troubles caused by the need to reconstruct the Beta zeolite structure from amorphous silicate fragments in the existing process, thus requiring the addition of fluoride or / and aluminum source for auxiliary structure reconstruction. In addition, in the present application, Ti-Beta zeolite is prepared by in-situ local construction and reconstruction from its precursor. The precursor is prepared by impregnating dealuminated Beta zeolite with an equal volume of acidic aqueous solution of titanium sulfate and TEABr template. The Ti-Beta zeolite precursor has low water content and does not contain colloidal substances, so only simple drying treatment is required when preparing the Ti-Beta zeolite precursor, the drying speed is fast, the temperature range is not harsh, it is suitable for mass production, and the drying troubles encountered when using hydrogel precursors to prepare dry gel intermediates are avoided. Furthermore, in the present application, the use of volatile organic base is not one-time, but most of it can be recycled and reused. In summary, the Ti-Beta zeolite preparation process provided by the present application has the advantages of simple method, low cost, and suitability for mass production, thus having higher practical value.

[0023] The technical solutions of the present application are as follows:

[0024] A Ti-Beta zeolite preparation process based on gas phase transmission method and using reusable organic base, the steps are as follows:

[0025] First step: using Al-Beta zeolite as raw material to prepare dealuminated Beta zeolite

[0026] Engineers familiar with the field can prepare dealuminated Beta zeolite from Al-Beta zeolite as raw material according to the requirements of the present application, combined with their own work experience and reference to the conventional acid dealuminization method in the relevant literature. The requirements of the present application are as follows:

[0027] (1) Selecting Al-Beta zeolite raw material

[0028] The Al-Beta zeolite refers to silicon-aluminum Beta zeolite. The present application has no limitation on the crystal size of Al-Beta zeolite, and has no limitation on the production process of Al-Beta zeolite. However, in order to facilitate the implementation effect of the present application, the Al-Beta zeolite has the following limitations: 1) No impurity crystal in Al-Beta zeolite; 2) Good crystallization of Al-Beta zeolite; 3) Suitable molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) of Al-Beta zeolite.

[0029] Among them, whether there is an impurity crystal in the Al-Beta zeolite can be checked and confirmed by X-ray powder diffraction (XRD) method. As known by those skilled in the art, the molar ratio of SiO2 to Al2O3 of Al-Beta zeolite produced by hydrothermal synthesis method is usually between 10-200 (US3 308 069 (1967)). In the Al-Beta zeolite product with lower molar ratio of SiO2 to Al2O3, there is generally MOR impurity crystal, and in the Al-Beta zeolite with higher molar ratio of SiO2 to Al2O3, there is generally ZSM-5 zeolite impurity crystal. By sampling and XRD analysis of Al-Beta zeolite, and comparing the XRD pattern of the sample with the standard diffraction card of Beta zeolite, MOR zeolite and ZSM-5 zeolite, it can be judged whether there are characteristic peaks of MOR zeolite and ZSM-5 zeolite impurity crystal in the XRD pattern of the sample, so as to know whether the Al-Beta zeolite is pure Beta zeolite phase.

[0030] In theory, the crystallization of Al-Beta zeolite can also be analyzed by XRD, using the relative crystallinity index as a measure. However, the XRD relative crystallinity index needs to be compared with the sum of the intensities of the medium-intensity characteristic diffraction peaks of Al-Beta zeolite at 2θ = 7.6-8° and the highest-intensity characteristic diffraction peaks at 2θ = 22-23° with the sum of the intensities of the corresponding diffraction peaks of a reference sample (standard Beta zeolite with a crystallinity of 100%), and the reference sample is not uniformly defined; and the intensities of the medium-intensity characteristic diffraction peaks of Al-Beta zeolite at 2θ = 7.6-8° and the highest-intensity characteristic diffraction peaks at 2θ = 22-23° are greatly affected by the process and conditions of post-processing such as calcination. Therefore, the XRD relative crystallinity index is not suitable for determining whether the purchased or synthesized Al-Beta zeolite is well crystallized. Therefore, the present application recommends using the specific surface area index of Al-Beta zeolite to measure whether the purchased or synthesized Al-Beta zeolite meets the requirements. According to our statistical results of the literature reported values of the specific surface area data of Al-Beta zeolite, the BET specific surface area value of well-crystallized Al-Beta zeolite produced by the hydrothermal synthesis method is generally not less than 450 m 2 / g. Engineers familiar with the field can first measure the nitrogen adsorption isotherm data of Al-Beta zeolite by conventional nitrogen physical adsorption method, and then calculate the BET specific surface area value according to the BET model. In summary, the present application requires that the BET specific surface area value of the Al-Beta zeolite used is ≧ 450 m 2 / g, indicating that it is well crystallized.

[0031] The molar ratio of SiO2 to Al2O3 is a key index of Al-Beta zeolite. This is because, on the one hand, the lower the molar ratio of SiO2 to Al2O3 of Al-Beta zeolite, i.e. the higher the content of framework aluminum, the more the number of hydroxyl pits of dealuminated Beta zeolite, and the more the number of framework titanium ions that can be introduced in the steam-assisted local structure reconstruction process, which is beneficial to the preparation of Ti-Beta zeolite with low Si / Ti ratio; on the other hand, it is difficult to synthesize pure phase Al-Beta zeolite with a very low molar ratio of SiO2 to Al2O3 by the hydrothermal method. Therefore, the present application requires that the molar ratio of SiO2 to Al2O3 of Al-Beta zeolite is in the range of 10-200, preferably in the range of 20-100, and more preferably in the range of 25-60.

[0032] The SiO2to Al2O3molar ratio of the Al-Beta zeolite can be analyzed by traditional chemical analysis (titration), or by X-ray fluorescence spectroscopy (XRF) or inductively coupled plasma emission spectroscopy (ICP). The present application recommends the use of the simple and fast XRF method.

[0033] Al-Beta zeolites meeting the requirements of the present application can be obtained commercially or synthesized by the skilled person. Al-Beta zeolites meeting the requirements of the present application can also be synthesized by the skilled person on the basis of his own experience and other literature reports.If Al-Beta zeolite is synthesized by oneself, the following methods reported in the invention patents and open literature can be selected: US3 308 069(1967), EP187 522A2(1986), US4 847 055(1989), CN1 086 792A(1993.9.20), CN1 108 213A(1994.3.11), CN1 108 214A(1994.3.11), CN1154 341A(1996.1.11), CN1 154 242A(1996.1.9), CN1 154 342A(1996.1.11), CN1 268 545A(1999.3.30), CN1 133 497C(1999.3.30), CN1108 275C(1999.9.10), CN1 100 004C(2000.5.19), CN1 335 258A(2001.2.28), CN1 116 227C(2001.3.12), CN101 205 072B(2006.12.18), Chem.Comm., 1996, 625; J.Mater.Chem., 1998, 8(9), 2137-2145; Microporous and Mesoporous Materials 21(1998)305-313; Applied Catalysis A-GENERAL, 166(1998), 97-103; Microporous and Mesoporous Materials 48(2001)23-29; Microporous and Mesoporous Materials 56(2002)1-10.; Journal of Molecular Catalysis A: Chemical 252(2006)76-84; Microporous and Mesoporous Materials 94(2006)1-8; J.Mater.Sci. 41(2006)1861-1864; Cryst.Res.Technol. 44, No. 4, 379-385(2009) DOI 10.1002 / crat.200800474; Microporous and Mesoporous Materials 143(2011)97-103; RSC Adv. 2019, 9, 3653-3660.

[0034] (2) Preparation of Dealuminated Beta Zeolite

[0035] As mentioned above, the dealuminated Beta zeolite can be prepared from the Al-Beta zeolite by using the conventional acid dealumination method. The present invention requires that the dealuminated Beta zeolite has as high as possible molar ratio of SiO2 to Al2O3, i.e. the framework aluminum of the Al-Beta zeolite should be removed as much as possible. The dealuminated Beta zeolite meeting the requirement of the present invention has a molar ratio of SiO2 to Al2O3 in the range of ≧ 700, preferably in the range of ≧ 800, and more preferably in the range of ≧ 900.

[0036] Because the dealuminated Beta zeolite has very high molar ratio of SiO2 to Al2O3 and very low aluminum content, the molar ratio of SiO2 to Al2O3 of the dealuminated Beta zeolite should be determined by using the inductively coupled plasma emission spectroscopy (ICP) method or the atomic absorption (AA) method. The present invention recommends the use of the ICP method.

[0037] When the Al-Beta zeolite is subjected to the acid dealumination treatment, the framework aluminum of the Al-Beta zeolite should be removed as much as possible. The harm of the dealuminated Beta zeolite having excessive residual framework aluminum is that the strong acidity of the framework aluminum will significantly reduce the selectivity of the Ti-Beta zeolite (more accurately, the Ti-Al-Beta zeolite) as the oxidation reaction catalyst and weaken the advantage of the structural reconstruction method in the preparation of the high performance Ti-Beta zeolite.

[0038] Although the framework aluminum of the Al-Beta zeolite is easy to remove so that the dealumination method using the high temperature water vapor, the EDTA complexing agent, the organic acid solution, the inorganic acid (concentrated hydrochloric acid, concentrated nitric acid) solution, or any combination of the above different methods can be used to prepare the dealuminated Beta zeolite meeting the requirement of the present invention from the Al-Beta zeolite, the present invention recommends the use of the concentrated nitric acid aqueous solution dealumination method to prepare the dealuminated Beta zeolite meeting the requirement of the present invention in consideration of the production cost, the process complexity and the difficulty in the treatment of the waste liquid generated by the dealumination.

[0039] The skilled engineer can prepare the dealuminated Beta zeolite according to the requirements of the present application by using concentrated nitric acid aqueous solution to dealuminate Al-Beta zeolite according to his own experience or by referring to the specific methods disclosed in the following documents: Chemical Communications, 1998, 1: 87-88; Micropor. Mesopor. Mater., 1999, 31: 163-173; Micropor. Mesopor. Mater., 2001, 49: 103-109; Micropor. Mesopor. Mater., 2008, 110: 480-487; Micropor. Mesopor. Mater., 2012, 163: 122-130; ACS Catalysis, 2014, 4(8): 2801-2810. When using concentrated nitric acid aqueous solution to dealuminate Al-Beta zeolite to prepare dealuminated Beta zeolite, the concentration of the nitric acid aqueous solution, the ratio of the acid solution to the zeolite (liquid-solid ratio), and the temperature and time of the acid treatment are important factors affecting the degree of acid dealumination of the Al-Beta zeolite. The effects of the above factors on the dealumination of the Al-Beta zeolite are ultimately reflected in the residual aluminum content of the dealuminated Beta zeolite. However, if the dealuminated Beta zeolite with a molar ratio of SiO2 to Al2O3 that meets the requirements of the present application cannot be obtained after one dealumination, the molar ratio of SiO2 to Al2O3 of the dealuminated Beta zeolite can be made to meet the requirements of the present application by secondary or even multiple supplemental dealumination. The present application recommends using 13M concentrated nitric acid as the dealumination acid and using the acid solution in a liquid-solid ratio (ml / g) of 20:1. Under this premise, the dealumination reaction is carried out at 95°C for 20h; after the dealumination reaction is completed, the solid product is first recovered by solid-liquid separation, then the solid product is washed with water to neutral pH, and then the solid product is dried at a temperature of 80-200°C for 3-24h and calcined at a temperature of 500°C-600°C for 3-8h to obtain the dealuminated Beta zeolite. After dealumination of the Al-Beta zeolite, the zeolite has a stronger water absorption and moisture absorption capacity due to the generation of a large number of hydroxyl lattice defect sites, and should be stored in a sealed manner for use.

[0040] Second step: preparation of a precursor for in-situ local structure reconstruction method Ti-Beta zeolite by equal volume impregnation method

[0041] The Ti-Beta zeolite precursor of the present application refers to the product obtained after the dealuminated Beta zeolite is impregnated with an equal volume of acidic aqueous solution containing tetraethylammonium bromide (TEABr) template and titanium sulfate (Ti(SO4)2) and then dried to remove free water in the impregnated wet dealuminated Beta zeolite. It is important to note that the purpose of the drying treatment is mainly to remove most of the free water in the impregnated wet Ti-Beta zeolite precursor, but the content, structure and physicochemical properties of the organic matter (TEABr template) in the Ti-Beta zeolite precursor should not be significantly changed.

[0042] Therefore, in addition to the dealuminated Beta zeolite, the impregnation raw materials for preparing the Ti-Beta zeolite precursor by the equal volume impregnation method at room temperature include tetraethylammonium bromide (TEABr) template, titanium sulfate and deionized water.

[0043] The preparation of the Ti-Beta zeolite precursor by the equal volume impregnation method can be carried out at room temperature. The basic procedure is as follows: first, determine the volume of the equal volume impregnation solution according to the amount of the dealuminated Beta zeolite and the saturated water absorption rate of the dealuminated Beta zeolite (the typical saturated water absorption rate of the dealuminated Beta zeolite is generally 1.2 ml H2O / g dehydrated zeolite. The dehydrated zeolite is defined as a zeolite sample that is first dried at 110°C overnight and then calcined at 550°C for 3h. The saturated water absorption of a certain amount of dehydrated zeolite is the amount of deionized water consumed when the dehydrated zeolite is titrated with deionized water until all the samples are uniformly wet but no free water appears); then, according to the selected molar ratio of TEABr to SiO2 and the molar ratio of Si to Ti, weigh the TEABr template and titanium sulfate, and prepare an acidic impregnation solution containing the TEABr template and titanium sulfate with deionized water; finally, impregnate the dealuminated Beta zeolite with the acidic impregnation solution containing the TEABr template and titanium sulfate at room temperature. The impregnation is carried out statically in a closed container. After the equal volume impregnation is completed, the wet precursor is subjected to drying treatment, and the Ti-Beta zeolite precursor is obtained. The dried Ti-Beta zeolite precursor is sealed for use.

[0044] The present application requires that the preparation of the Ti-Beta zeolite precursor by the equal volume impregnation method be carried out at room temperature; the amounts of tetraethylammonium bromide (TEABr) template and titanium sulfate, the impregnation time and the drying conditions of the wet precursor need to meet the following conditions:

[0045] The amount of the dealuminated Beta zeolite is calculated based on SiO2, and the amounts of other impregnation raw materials and the impregnation conditions are as follows:

[0046] The molar ratio of TEABr to SiO2 is in the range of 0.05-0.5, preferably in the range of 0.1-0.4, and more preferably in the range of 0.2-0.3.

[0047] Si to Ti molar ratio: suitable range is 5-100; preferred range is 10-80; more preferred range is 15-50.

[0048] Immersion time: suitable range is 0.5-12h; preferred range is 1-6h; more preferred range is 2-4h.

[0049] Low temperature drying temperature range of the precursor wet material: suitable range is 30℃-170℃; preferred range is 50℃-150℃; more preferred range is 80℃-120℃.

[0050] Low temperature drying time range of the precursor wet material: suitable range is 0.5h-24h; preferred range is 3h-18h; more preferred range is 6h-12h.

[0051] TEABr template agent can be ionized in aqueous solution to produce TEA + Cations. We found in our research that TEA + Cations produced by ionization of TEABr template agent in aqueous solution can act as TEA + Cations produced by ionization of TEAOH template agent solution, can act as structure directing agents (SDA) in the last stage of Ti-Beta zeolite preparation, i.e. in the repair process of local structural defects left after the titanium ions are accepted by the slightly etched hydroxyl pockets in the later stage of the process assisted by gas phase transmission of water vapor and volatile weak organic base, which is the post-etching process. Engineers familiar with the field know that, in addition to tetraethylammonium bromide, other tetraethylammonium halides, such as tetraethylammonium fluoride, tetraethylammonium chloride and tetraethylammonium iodide, can also release TEA + Cations with structure directing effect in aqueous solution. However, the problem is that tetraethylammonium fluoride will cause fluorine-containing wastewater; tetraethylammonium iodide is relatively expensive and I - Cations have poor stability; tetraethylammonium chloride is not as cheap and easy to obtain as tetraethylammonium bromide. Therefore, the present application chooses tetraethylammonium bromide as the template agent on the basis of comprehensive consideration of the above factors.

[0052] The Si / Ti molar ratio of the Ti-Beta zeolite precursor determines the Si / Ti molar ratio of the Ti-Beta zeolite prepared by the method of the present application. According to the principle of the present application, the titanium sulfate introduced in the preparation of the Ti-Beta zeolite precursor will release titanium ions during the local structure reconstruction by vapor phase transport of water vapor and a volatile weak organic base, which will enter the hydroxyl pockets of the slightly etched dealuminated Beta zeolite, thus converting the dealuminated Beta zeolite into Ti-Beta zeolite. Therefore, the maximum amount of the titanium source used in the preparation of the Ti-Beta zeolite precursor can be estimated by the number of the hydroxyl pockets of the dealuminated Beta zeolite, or directly by the Si / Al ratio (SiO2 / Al2O3) of the Al-Beta zeolite raw material. For example, the minimum Si / Ti ratio of the Ti-Beta zeolite that can be prepared from the dealuminated Beta zeolite prepared from the Al-Beta zeolite raw material with a SiO2 / Al2O3 ratio of 30 is 15. Therefore, the maximum amount of the titanium source used in the preparation of the Ti-Beta zeolite precursor should make the Si / Ti ratio of the precursor ≮ 15, otherwise, the excessive amount of the titanium source will result in an increase in the non-framework titanium in the Ti-Beta zeolite product. In general, the content of the framework titanium in the titanium silicalite within a suitable range is beneficial to catalytic reactions. On the one hand, the content of the framework titanium in the titanium silicalite that is too low (i.e., the Si / Ti molar ratio is too high) is not conducive to the activity of the catalyst, and there is no need to elaborate the reason. On the other hand, the content of the framework titanium in the titanium silicalite that is too high (i.e., the Si / Ti ratio is too low) is also not conducive to the increase in the catalytic activity. This is because, in this case, the diffusion control in the micropores of the zeolite will become the rate-controlling step of the catalytic reaction. The above is the main basis for determining the Si / Ti molar ratio range of the present application.

[0053] Step 3: Preparation of Ti-Beta zeolite by in-situ local structure reconstruction of the Ti-Beta zeolite precursor by vapor phase transport method

[0054] The reaction process of the in-situ local structure reconstruction for preparing the Ti-Beta zeolite is carried out in an autoclave. The autoclave is provided with a support and a tray inside. The dried Ti-Beta zeolite precursor is placed on the tray, and the water vapor and the volatile weak organic base for vapor phase transport are provided by the vaporization of the water solution at the bottom of the autoclave. The organic base is n-butylamine. The present application selects n-butylamine as the volatile weak organic base mainly because it has a relatively suitable boiling point (77.8°C), is cheap and easy to obtain, and is easy to vaporize and recover, which is convenient for operation. Other small molecule fatty amines such as methylamine and ethylamine are not suitable, mainly because the boiling point is too low and the volatility is too high, which is not conducive to the working environment.

[0055] In this step, the amount of liquid water added at the bottom of the autoclave, the amount of the volatile weak organic base, and the reaction temperature and time of the structure reconstruction are the main influencing factors. For their value ranges, the present application requires the following:

[0056] The amount of liquid water added to the autoclave is preferably in the range of 0.5 to 5 mL per gram of precursor, more preferably in the range of 1 to 3 mL per gram of precursor, and most preferably in the range of 1.5 to 2.5 mL per gram of precursor. H2O 前驱体 The amount of liquid water added to the autoclave is preferably in the range of 0.5 to 5 mL per gram of precursor, more preferably in the range of 1 to 3 mL per gram of precursor, and most preferably in the range of 1.5 to 2.5 mL per gram of precursor.

[0057] The amount of volatile weak organic base is preferably in the range of 10 to 60% by mass, more preferably in the range of 20 to 50% by mass, and most preferably in the range of 30 to 40% by mass.

[0058] The reaction temperature for the structural reconstruction is preferably in the range of 120 to 170°C, more preferably in the range of 130 to 160°C, and most preferably in the range of 135 to 150°C.

[0059] The reaction time for the structural reconstruction is preferably in the range of 0.5 to 48 hours, more preferably in the range of 4 to 24 hours, and most preferably in the range of 6 to 18 hours.

[0060] The above ranges of conditions are selected to meet the requirements of the reaction for the in-situ partial structural reconstruction of Ti-Beta zeolite by the vapor phase transport method. The above ranges of conditions are described in detail as follows to enable engineers in the field to better understand the reaction process for the in-situ partial structural reconstruction of Ti-Beta zeolite by the vapor phase transport method.

[0061] In the initial stage of the in-situ partial structural reconstruction, i.e. in the temperature rising stage of the autoclave, more and more of the liquid water and the volatile weak organic base in the autoclave become vapor as the temperature in the autoclave gradually rises, and the vapor pressure in the autoclave continuously rises. As a result, the dry gel intermediate powder on the tray is correspondingly provided with higher and higher water content and volatile weak organic base content due to the increasing infiltration of water vapor and the volatile weak organic base. In this process, the dealuminated Beta zeolite, the TEABr template and the weak organic base in the Ti-Beta zeolite precursor will undergo the following changes: firstly, for the dealuminated Beta zeolite, on the one hand, its pores will be filled with liquid water due to capillary condensation, and on the other hand, the adsorption of water molecules on the zeolite surface will develop from a monolayer to a multilayer, and finally a liquid film with a certain thickness will be formed. Secondly, for the TEABr template molecules in the precursor which are originally in a dehydrated state, the main change is that they are dissolved in water again and ionize to produce TEA + cations. In addition, the volatile weak organic base transported into the Ti-Beta zeolite precursor by the vapor phase will dissolve in the capillary condensed liquid in the pores of the zeolite and the water film on the surface of the zeolite, and hydrolyze to produce alkali (R-NH2+ H2O → R-NH3 + + OH - ​) and the water film on the surface of the zeolite, thus both the capillary condensed liquid in the zeolite channels and the water film on the surface of the zeolite are changed into the weakly basic solution containing TEA + The weakly basic solution permeating the inside and outside of the pores of the dealuminated Beta zeolite will inevitably react with the hydroxyl pockets of the dealuminated Beta zeolite to cause slight etching of the hydroxyl pockets and dissolution of the silicate fragments (soluble Beta zeolite structural units) in the weakly basic solution permeating the inside and outside of the pores of the dealuminated Beta zeolite. As the concentration of the silicate fragments (soluble Beta zeolite structural units) dissolved in the weakly basic solution permeating the inside and outside of the pores of the dealuminated Beta zeolite increases, the further etching and desilication reaction of the weakly basic solution on the hydroxyl pockets of the dealuminated Beta zeolite is retarded.

[0062] When the temperature of the autoclave is raised to a level sufficient for the structural reconstruction reaction (recrystallization reaction) to occur, the concentration of the silicate fragments (soluble Beta zeolite structural units) dissolved in the weakly basic solution permeating the inside and outside of the pores of the dealuminated Beta zeolite also reaches a maximum - the chemical equilibrium concentration. At this time, the etching and desilication reaction of the weakly basic solution produced by the weak organic base in the precursor on the hydroxyl pockets of the dealuminated Beta zeolite is inhibited, and the entire closed system enters the later stage of the in situ local structural reconstruction process. The main features of this stage are: first, the titanium ions released by the titanium source in the precursor begin to enter the etched hydroxyl pockets of the dealuminated Beta zeolite. The etched hydroxyl pockets have increased in volume due to slight desilication, thereby improving their ability to accommodate the relatively large titanium ions. For this reason, the process for preparing Ti-Beta zeolite provided by the local structural reconstruction method using gas-phase transport of water vapor and volatile weak organic bases has the characteristic of high skeletal titanium content. Then, the silicate fragments (soluble Beta zeolite structural units) dissolved and concentrated in the weakly basic solution with a limited total amount of liquid permeating the inside and outside of the pores of the dealuminated Beta zeolite, under the action of the structure-directing agent (SDA) TEA + Under the action of the cations, the local structural reconstruction reaction (recrystallization reaction) occurs rapidly on the local structural defect sites left after the rapid accommodation of the titanium ions in the hydroxyl pockets of the dealuminated Beta zeolite, thereby repairing the structural defects.

[0063] In the present application, in order to achieve the reaction purpose and effect of in-situ local structure reconstruction of Ti-Beta zeolite by vapor phase transport method, the amount of water introduced in advance to the bottom of the autoclave should at least enable the formation of vapor-liquid two phases in the interior of the autoclave at the structure reconstruction reaction temperature. Because only under the condition of coexistence of vapor-liquid two phases, the pores of dealuminated Beta zeolite will be filled with water due to capillary condensation, and at the same time, the surface of dealuminated Beta zeolite will develop from monolayer to multilayer due to water molecule adsorption, and finally form a liquid film with certain thickness. As can be seen from the above, the liquid water condensed in the pores of dealuminated Beta zeolite and the liquid film with certain thickness formed on the surface of the zeolite are the support for the reaction process of each stage of in-situ local structure reconstruction of dealuminated Beta zeolite, thereby realizing the phase interface micro-hydrothermal system for the preparation of Ti-Beta zeolite.

[0064] According to the saturated vapor pressure of water vapor, when the temperature in the autoclave is 120℃, 130℃, 140℃, 150℃, 160℃ and 170℃ respectively, the saturated water vapor pressure generated by the liquid water added to the bottom of the autoclave is 198.5kPa, 247.5kPa, 295.0kPa, 355.1kPa, 431.3kPa and 517.8kPa respectively. If the saturated water vapor in the autoclave is approximated as an ideal gas, then when the autoclave with a volume of V (unit: m 3 ) is filled with saturated water vapor at 120℃, 130℃, 140℃, 150℃, 160℃ and 170℃, the equivalent mass (unit: Kg) of water vapor is about 1.1V, 1.3V, 1.6V, 1.8V, 2.2V and 2.5V respectively.

[0065] Taking the preparation of Ti-Beta zeolite by in-situ local structure reconstruction reaction at 140℃ by vapor phase transport method as an example, in order to enable the formation of vapor-liquid two phases in the interior of the autoclave at the structure reconstruction reaction temperature of 140℃, the minimum amount of water introduced in advance to the bottom of the autoclave is estimated to be 1.6V+1.2W. Among them, 1.2 is the saturated water absorption rate of typical dealuminated Beta zeolite, and W is the weight of Ti-Beta zeolite precursor. For a laboratory small autoclave with a volume of 100ml, assuming that the amount of Ti-Beta zeolite precursor added is 10g (0.01Kg), in order to enable the formation of vapor-liquid two phases in the interior of the autoclave at the structure reconstruction reaction temperature of 140℃, the minimum amount of water introduced in advance to the bottom of the autoclave is estimated to be 12.16g (1.6V=1.6x1x10 -4 Kg=0.16g; 1.2W=1.2x10x10 -3Kg = 12 g). Therefore, theoretically, as long as 12.16 g or more of liquid water is added to the bottom of the small autoclave in advance, and 10 g of Ti-Beta zeolite precursor is added to the tray above the support, Ti-Beta zeolite can be prepared by in-situ local structure reconstruction reaction by gas phase transmission method at 140℃. Of course, in actual work, the threshold value of the amount of liquid to be introduced into the bottom of the autoclave in advance can be appropriately increased according to the volume of the autoclave, the size of the internal components (support height and tray size), and the single-pot yield requirement of Ti-Beta zeolite. Therefore, in order to facilitate engineers in the field, the present application finally recommends using W H2O / W 沸石前驱体 The ratio of 1.5-3 is the appropriate range of the amount of liquid at the bottom of the autoclave for the preparation of Ti-Beta zeolite by in-situ local structure reconstruction reaction by gas phase transmission method.

[0066] After the in-situ local structure reconstruction reaction is completed, the autoclave is treated by reducing the temperature and pressure according to the conventional practice of hydrothermal synthesis of zeolite molecular sieves. When the temperature and pressure in the autoclave approach the ambient temperature and pressure, the autoclave is opened, the Ti-Beta zeolite product is taken out, and the bottom liquid is recycled after volume and concentration determination.

[0067] Fourth step: post-treatment of Ti-Beta zeolite product

[0068] The Ti-Beta zeolite product prepared by the method of the present application does not need to be treated by de-fluorination and de-alumination, and only needs to be treated by conventional water washing, drying and calcination to obtain Ti-Beta zeolite product. Among them, the purpose of water washing is to remove a small amount of sulfate introduced by the titanium source. The purpose of calcination is to remove the TEABr template and volatile weak organic base in the product. Engineers familiar with the field can perform the post-treatment operation according to common sense.

[0069] Advantages of the present application:

[0070] The present application provides a green process for preparing Ti-Beta zeolite in large quantities by using dealuminated Beta zeolite as the main raw material, without adding fluoride or / and aluminum source for assistance, mainly using the gas phase transmission pathway to provide water vapor and weak organic base to assist tetraethylammonium bromide (TEABr) template, and in-situ locally etching and repairing and reconstructing the hydroxyl pits of the dealuminated Beta zeolite. The main technical innovation of the present application is that, firstly, the combination of tetraethylammonium bromide (TEABr) template and volatile weak organic base is used to replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process, and at the same time, the amount of silicate dissolved is limited by the pore condensate and the liquid film on the surface of the zeolite solid generated by the dealuminated Beta zeolite in the saturated steam, which makes it easier to achieve controllable etching and desiliconization of the hydroxyl pits of the dealuminated Beta zeolite, improves the acceptance capacity of the hydroxyl pits for titanium ions with larger volume, and thus is more conducive to the preparation of high-performance Ti-Beta zeolite with high framework titanium content and low non-framework titanium content. Secondly, the controllable etching and desiliconization produces local structural defects, which can be quickly repaired in the weak alkaline environment generated by the volatile weak organic base by using TEABr template ionized in the solution + cations (SDA), which completely eliminates the troubles caused by the need to add fluoride or / and aluminum source for assisting the structural reconstruction in the existing process due to the need to start from amorphous silicate fragments for the reconstruction of Beta zeolite structure. In addition, in the present application, Ti-Beta zeolite is prepared by in-situ local construction and reconstruction from a dried precursor. The precursor is prepared by impregnating dealuminated Beta zeolite with an equal volume of acidic aqueous solution of titanium sulfate and TEABr template. The Ti-Beta zeolite precursor has low water content and does not contain colloidal substances, so only simple drying treatment is required when preparing the Ti-Beta zeolite precursor, the drying speed is fast, the harshness of the drying temperature range is reduced, it is suitable for mass production, and the drying troubles encountered when using hydrogel precursors to prepare dry gel intermediates are avoided. Furthermore, in the present application, the use of volatile organic bases is not one-time, but most of them can be recycled and reused. In summary, the Ti-Beta zeolite preparation process provided by the present application has the advantages of simple method, low cost, and suitability for mass production, and thus has higher practical value. BRIEF DESCRIPTION OF DRAWINGS

[0071] Figure 1 is the XRD pattern of the Ti-Beta zeolite precursor prepared in Example 1.

[0072] Figure 2 is the framework vibration Fourier transform infrared spectrum of the Ti-Beta-1 sample prepared in Example 1.

[0073] Figure 3is the X-ray powder diffraction (XRD) pattern of the Ti-Beta-1 sample prepared in Example 1.

[0074] Figure 4 is the framework vibration Fourier transform infrared spectrum of the Ti-Beta-1-F-Com sample prepared in Comparative Example 1.

[0075] Figure 5 is the framework vibration Fourier transform infrared spectrum of the Ti-Beta-2-Cl-Com sample prepared in Comparative Example 2.

[0076] Figure 6 is the framework vibration Fourier transform infrared spectrum of the Ti-Beta-3-Cp-Com sample prepared in Comparative Example 3. DETAILED DESCRIPTION

[0077] The specific embodiments of the present application are further described in the following in conjunction with the drawings and technical solutions.

[0078] The implementation effects of the present application can be evaluated from two aspects of characterizing the physicochemical properties of the prepared Ti-Beta zeolite product and detecting its catalytic performance in the cyclohexene epoxidation reaction.

[0079] In the characterization of the physicochemical properties of the Ti-Beta zeolite product, the titanium content, the framework titanium content, the non-framework titanium content and the relative crystallinity can be characterized.

[0080] Among them, the titanium content is detected by X-ray fluorescence spectroscopy (XRF); the framework titanium content can be characterized by framework vibration Fourier transform infrared spectroscopy (FT-IR); and the non-framework titanium content can be characterized by ultraviolet resonance Raman spectroscopy (UV-Raman) with an excitation light source wavelength of 325 nm.

[0081] The cyclohexene epoxidation reaction is carried out in a 25 mL round-bottom flask equipped with a condenser and a magnetic stirrer. The method is as follows: first, 10 mmol of cyclohexene, 10 mL of acetonitrile, 10 mmol of hydrogen peroxide (35%) and 100 mg of Ti-Beta zeolite catalyst are added to the flask, and then the reaction is started under vigorous stirring at 353 K for 1 hour. Finally, samples are taken from the reaction product, and composition analysis is performed by a gas chromatograph (Shimadzu GC-2014C) equipped with a hydrogen flame ionization detector (FID) and a DB-WAX capillary column (30 m x 0.32 mm, 30 μm). The conversion of cyclohexene and the selectivity of epoxycyclohexane are calculated by external standard method.

[0082] In addition, in the process of preparing Ti-Beta zeolite by the method of in-situ partial structure reconstruction of dealuminated Beta zeolite assisted by vapor phase transport method, the following analyses are also involved: detection of impurity crystals in Al-Beta zeolite raw material, analysis of relative crystallinity and analysis of Si / Al ratio (molar ratio of SiO2 to Al2O3); detection of residual aluminum content (expressed as molar ratio of SiO2 to Al2O3) in dealuminated Beta zeolite, analysis and characterization of water content, template content and the degree of structure retention of dealuminated Beta zeolite in the Ti-Beta zeolite precursor prepared by impregnation method.

[0083] In the above, the detection of impurity crystals in Al-Beta zeolite raw material and the characterization of the degree of structure retention of dealuminated Beta zeolite in the precursor can be performed by X-ray powder diffraction (XRD) method; the detection of relative crystallinity of Al-Beta zeolite raw material can be performed by determining the nitrogen physical adsorption data of the sample, on the basis of which the BET total surface area value of the sample is calculated to draw a conclusion; the Si / Al ratio (molar ratio of SiO2 to Al2O3) of Al-Beta zeolite raw material can be detected by X-ray fluorescence spectroscopy (XRF); the residual aluminum content (expressed as molar ratio of SiO2 to Al2O3) of dealuminated Beta zeolite can be analyzed by inductively coupled plasma emission spectroscopy (ICP); and the analysis of water content and template content in the precursor can be performed by thermogravimetric (TG) method.

[0084] The application will be further described by the following examples, but the application is not limited by these examples.

[0085] Example 1: This example is used to illustrate that the Ti-Beta zeolite preparation process based on the gas phase transport method provided by the present application, i.e. using dealuminated Beta zeolite as the main raw material, does not involve the use of fluoride or / and aluminum source, mainly utilizes the gas phase transport pathway to provide water vapor and weak organic base auxiliary tetraethylammonium bromide (TEABr) template agent, and can greatly prepare Ti-Beta zeolite and make the weak organic base get the green process of recycling. The combination of tetraethylammonium bromide (TEABr) template agent and volatile weak organic base can replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process, and at the same time, with the help of the channel condensate generated by the dealuminated Beta zeolite in the saturated steam and the zeolite solid surface liquid film limiting the amount of silicate dissolved, the controllable etching desilication of the hydroxyl cavity of the dealuminated Beta zeolite can be more conveniently realized, the purpose of slightly etching desilication of the hydroxyl cavity of the dealuminated Beta zeolite and improving the receiving capacity of the hydroxyl cavity for titanium ions with larger volume is achieved, and the purpose of avoiding the dealuminated Beta zeolite crystals from being completely dissolved by the strong alkaline TEAOH solution into fragmented structural units (amorphous substances) is achieved, so that the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) is changed into the repair of local defects of Ti-Beta zeolite crystals, i.e. the repair of local structural defects left after the slightly etched hydroxyl cavity receives titanium ions (the present application). The present application can prepare high-quality Ti-Beta zeolite from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source, because it avoids the reconstruction of Ti-Beta zeolite structure from amorphous fragmented structural units. In addition, in the present application, Ti-Beta zeolite is prepared by in-situ local construction reconstruction from dried Ti-Beta zeolite precursor. The precursor is prepared by impregnating dealuminated Beta zeolite with an equal volume of acidic aqueous solution of titanium sulfate and TEABr template agent. The Ti-Beta zeolite precursor has low water content and does not contain colloidal substances, so only simple drying treatment is required when preparing the Ti-Beta zeolite precursor, which is suitable for large-scale preparation.

[0086] First step, preparing dealuminated Beta zeolite from Al-Beta zeolite

[0087] (1) Following the hydrothermal crystallization method provided in US Patent 3,308,069 (1967), Al-Beta zeolite with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of 25 was synthesized as a raw material for preparing dealuminized Beta zeolite. After conventional filtration, washing, drying (110℃, 12h), and calcination to remove the template agent (540℃, 6h), the synthesized Al-Beta zeolite was observed by TEM to have a grain size of less than 100 nm, classifying it as nano-Beta zeolite. XRD analysis revealed no impurities. Calculations based on its nitrogen physical adsorption data showed a BET specific surface area of ​​approximately 540 m². 2 The molar ratio of silicon-aluminum oxide (SiO2 to Al2O3) was approximately 24, as determined by XRF, which meets the technical requirements of this invention for Beta zeolite raw materials.

[0088] (2) Preparation of dealuminized Beta zeolite.

[0089] First, a concentrated nitric acid solution with a molar concentration of 13M was prepared. Then, 20g of the dried and calcined Beta zeolite precursor, prepared as described above, was added to a three-necked flask containing 400ml of 13M concentrated nitric acid solution under stirring, at a liquid-to-solid ratio of 20:1 (ml / g). The dealuminization process was carried out at 95℃ for 20 hours. During the dealuminization reaction, the three-necked flask was kept under reflux. After the dealuminization reaction was completed, the solution was cooled to room temperature and filtered to recover the solid product. Then, the product was washed with water, dried (overnight at 110℃), and calcined (550℃, 3 hours) to obtain dealuminated Beta zeolite. The molar ratio of silicon-aluminum oxides (SiO2 to Al2O3) in the dealuminated Beta zeolite was determined to be 990 by ICP, which meets the requirements of this invention. Store in a sealed container for later use, avoiding moisture absorption.

[0090] Step 2: Precursor for in-situ local structural reconstruction of Ti-Beta zeolite prepared using the equal-volume impregnation method.

[0091] Tetraethylammonium bromide (TEABr) solid was used as the template agent source, and titanium sulfate (Ti(SO4)2) was used as the titanium source. The amount of template agent was determined according to a TEABr / SiO2 molar ratio (expressing the number of moles of dealubilized Beta zeolite in terms of the number of moles of SiO2) of 0.3; the amount of titanium sulfate (Ti(SO4)2) was determined according to a Si / Ti molar ratio of 50; and the volume of the equal volume impregnation solution was determined according to the amount of dealubilized Beta zeolite and the saturated water absorption rate of dealubilized Beta zeolite.

[0092] The specific method is as follows: first, with the dosage of 10 g of dealuminated Beta zeolite, tetraethyl ammonium bromide (TEABr) template 10.72 g, titanium sulfate (Ti(SO4)2) 0.82 g are weighed respectively, and the template and titanium sulfate are prepared into 12 ml of acidic aqueous solution with ionized water (the saturated water absorption rate of dealuminated Beta zeolite is 1.2 ml H2O / g of dehydrated zeolite). Then, the dealuminated Beta zeolite is impregnated with the acidic impregnation solution containing the TEABr template and titanium sulfate at room temperature. The impregnation is carried out statically in a closed container, and the impregnation time is 4 h. After the equal-volume impregnation is completed, the precursor wet material is subjected to drying treatment. The drying temperature is 80°C, and the drying time is 12 h. The solid product after drying, i.e. Ti-Beta zeolite precursor, is about 27 g, which is sealed for use.

[0093] The XRD pattern of the Ti-Beta zeolite precursor is shown in Figure 1 . It can be seen from the XRD pattern that the Ti-Beta zeolite precursor prepared according to the requirements of the present application retains the crystal structure of the dealuminated Beta zeolite well. Figure 1 The Ti-Beta zeolite precursor is subjected to weight loss analysis by a thermogravimetric analyzer (TG), and it is found that the weight loss of the Ti-Beta zeolite precursor caused by the removal of free water occurs in the low-temperature zone of 30-130°C, the weight loss caused by the removal of bound water occurs in the medium-temperature zone of 130-166°C, and the weight loss caused by the decomposition and removal of the TEABr template occurs in the high-temperature zone above 166°C. The results show that the Ti-Beta zeolite precursor prepared still contains about 20 wt.% of water, of which the free water accounts for about one third, and the bound water accounts for about two thirds. The Ti-Beta zeolite precursor is white in color and soft in texture, and the changes in the content, structure and physicochemical properties of the organic matter (TEABr template) therein can be ignored. After being lightly ground with a mortar, it becomes a powder, which meets the requirements of the present application and is sealed for use.

[0094] In the third step, the Ti-Beta zeolite is prepared by in-situ partial structure reconstruction of the Ti-Beta zeolite precursor by gas phase transmission

[0095] The reaction process of the in-situ partial structure reconstruction for preparing the Ti-Beta zeolite is carried out in a laboratory small high-pressure kettle with a volume of 100 ml. The inside of the high-pressure kettle is provided with a support and a tray. 10 g of the Ti-Beta zeolite precursor after drying treatment is placed on the tray, and the water vapor and volatile weak organic base (n-butylamine) for gas phase transmission are provided by vaporization of the aqueous solution at the bottom of the kettle. The partial structure reconstruction reaction is carried out in a general electric heating oven with a temperature setting of 140°C, and the duration is 12 h.

[0096] According to the calculation, when the Ti-Beta zeolite precursor is in-situ locally restructured in the small autoclave by the gas phase transport method, 12.16 g or more of liquid water is added to the bottom of the autoclave (at this time, W H2O / W 沸石前驱体 is about 1.2), and the gas-liquid two-phase appears at 140°C. In this case, the liquid phase mainly refers to the capillary condensed liquid in the pore of the dealuminated Beta zeolite and the liquid film on the surface of the zeolite. In order to make the local restructuring reaction proceed under the appropriate condition of liquid water at the bottom of the autoclave, W H2O / W 沸石前驱体 is increased to 2.0. Therefore, 20 g of deionized water is added to the bottom of the autoclave, and 13.3 g of n-butylamine is added to make the percentage concentration of n-butylamine in the aqueous solution reach 40%.

[0097] After the local restructuring reaction is completed, the autoclave is treated by lowering the temperature and pressure according to the conventional method for hydrothermally synthesizing zeolite molecular sieves. When the temperature and pressure in the autoclave approach the ambient temperature and pressure, the autoclave is opened, and the Ti-Beta zeolite product is taken out.

[0098] Fourth step, post-treatment of the Ti-Beta zeolite product

[0099] The Ti-Beta zeolite product prepared by the method of the present application does not need to be treated by de-fluorination and de-alumination, but needs to be washed with water to remove a small amount of sulfate ions brought in by the titanium source (titanium sulfate). Then, the Ti-Beta zeolite product washed with water is treated by conventional drying and calcination. The drying is performed in an electric oven at a drying temperature of 110°C for 12 h, and the calcination is performed in a muffle furnace at a calcination temperature of 540°C for 6 h. The obtained white powder is the Ti-Beta zeolite product, which is designated as Ti-Beta-1.

[0100] The Si / Ti molar ratio of the Ti-Beta-1 sample is about 50, which is measured by the XRF method. The infrared spectrum of the framework vibration of the Ti-Beta-1 sample is shown in Figure 2 , and the XRD pattern is shown in Figure 3 . It can be seen from Figure 2 that the sample has obvious framework titanium characteristic absorption near 960 cm -1 , and the framework titanium content index value (I 960 / I 800 ) is 1.08. In addition, it can be seen from Figure 3 that the sample has high crystallinity and no impurity crystal. In addition, it is confirmed by the ultraviolet Raman spectrum characterization (excitation light source wavelength 325 nm) that the sample contains only a small amount of anatase titanium dioxide (at 144, 390, 635 cm -1The results show that the Ti-Beta zeolite product with high quality is prepared from the dealuminated Beta zeolite without the assistance of fluoride and / or aluminum source by the process of the partial structure reconstruction method of the dealuminated Beta zeolite assisted by the vapor phase transmission of water vapor and the weakly volatile organic base.

[0101] Comparative Example 1: This example is used to illustrate the practice of the existing structure reconstruction method process (reference: Wang Bowen. Preparation of MFI, BEA type zeolite and its catalytic performance research[D]. East China Normal University, 2021), that is, first, the dealuminated Beta zeolite, a large amount of tetraethylammonium hydroxide (TEAOH) template solution, titanium source and deionized water are made into a hydrogel. Then, the hydrogel is hydrothermally pretreated at a high temperature, so that the dealuminated Beta zeolite in it is completely dissolved by a large amount of strong alkaline TEAOH solution and becomes a fragmented structure unit with amorphous properties. Then, the hydrogel amorphous material is cooled and fluoride is added to it. Finally, the hydrogel amorphous material is reheated to prepare Ti-Beta zeolite (synthetic Ti-Beta zeolite crystals) by structure reconstruction under hydrothermal conditions starting from the amorphous material. It is also an effective way to prepare Ti-Beta zeolite. However, the preparation of Ti-Beta zeolite according to the existing structure reconstruction method process requires the assistance of fluoride, thus there are actual problems such as fluoride-containing wastewater that are not conducive to industrial application.

[0102] First step, preparing dealuminated Beta zeolite from Al-Beta zeolite

[0103] Repeat the dealuminated Beta zeolite preparation step of Example 1, using Al-Beta zeolite raw material without impurity crystal phase, crystal size less than 100 nanometers, BET specific surface area about 540 m 2 / g, and the molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) about 24, to prepare dealuminated Beta zeolite (molar ratio of SiO2 to Al2O3 990), which is sealed and stored for use.

[0104] Second step, preparing hydrogel precursor for structure reconstruction from dealuminated Beta zeolite

[0105] Use 25wt.% tetrapropylammonium hydroxide (TEAOH) aqueous solution as the template source, use tetrabutyl titanate (TBOT) as the titanium source, determine the amount of template solution according to the TEAOH / SiO2 molar ratio (the number of moles of SiO2 represents the number of moles of dealuminated Beta zeolite) is 0.3; determine the amount of tetrabutyl titanate (TBOT) according to the Si / Ti molar ratio is 50; the amount of water brought in by the TEAOH template determines the H2O / SiO2 molar ratio.

[0106] The procedure is as follows: first, 25wt.% of tetrapropylammonium hydroxide (TEAOH) aqueous solution 30g, tetrabutyl titanate (TBOT) 1.16g are weighed out respectively, based on the amount of 10g dealuminated Beta zeolite. Then, the titanium source and TEAOH template solution are mixed under stirring to prepare a uniform basic solution containing the titanium source and TEAOH template; finally, all the dealuminated Beta zeolite is poured into the basic solution containing the titanium source and TEAOH template under stirring, and the reaction (slight dissolution of silica) is stirred at room temperature for 3h to obtain a hydrogel (H2O / SiO2molar ratio about 7.4) for the preparation of Ti-Beta zeolite by structure reconstruction.

[0107] Third step, hydrothermal pretreatment of the hydrogel

[0108] The hydrogel prepared in the second step is completely loaded into a laboratory small autoclave with a polytetrafluoroethylene lining for hydrothermal pretreatment. The pretreatment is carried out in a common electric oven with a temperature setting of 140°C, and the pretreatment time is 1h. After the pretreatment is completed, the autoclave is taken out of the oven and cooled to room temperature with water. A small amount of sample is taken out of the autoclave for detection of the degree of retention of the crystal structure of Beta zeolite (XRD method). The detection results show that after the hydrothermal pretreatment at a relatively high temperature of 140°C, the two main characteristic diffraction peaks of Beta zeolite at 2θ = 7.7° and 22.5° on the XRD pattern of the hydrogel sample have basically disappeared. This indicates that the crystal structure of the dealuminated Beta zeolite has been completely dissolved by the relatively large amount of strong alkaline TEAOH solution, and has become a fragmented structural unit with amorphous properties.

[0109] Fourth step, preparation of Ti-Beta zeolite by structure reconstruction of the hydrogel assisted by fluoride

[0110] In this example, the fluoride used is ammonium fluoride (NH4F). The amount of ammonium fluoride added is calculated according to F - / SiO2= 0.2. The specific procedure is as follows: the solid ammonium fluoride is accurately weighed, then the ammonium fluoride solid powder is completely added into the autoclave, and manual stirring is performed to dissolve it and mix it uniformly with the hydrogel after hydrothermal pretreatment (in which the crystal structure of the dealuminated Beta zeolite has been completely dissolved and destroyed, becoming a fragmented structural unit with amorphous properties (in a long-range disordered state)). Finally, the autoclave is resealed for hydrothermal crystallization treatment, and the hydrothermal crystallization treatment is carried out at 140°C for 12h. After the crystallization is completed, the autoclave is taken out of the oven and cooled to room temperature with water.

[0111] Fifth step, post-treatment of the Ti-Beta zeolite product

[0112] In this example, the crystallized product obtained in the fourth step needs to go through four post-processing steps in sequence: filtration, repeated washing, drying and calcination, to obtain the Ti-Beta zeolite product, designated as Ti-Beta-1-F-Com (Com indicates comparative example).

[0113] In this example, the reason for repeatedly washing the crystallized product with water is to remove F- ion impurities from the Ti-Beta zeolite product. Clearly, in this case, the fluoride in the crystallization mother liquor and the large amount of washing solution would cause wastewater that is difficult to treat.

[0114] The Si / Ti molar ratio of the Ti-Beta-1-F-Com sample was determined to be approximately 50 using XRF. The skeletal vibrational infrared spectrum of the Ti-Beta-1-F-Com sample is shown below. Figure 4 .from Figure 4 The sample can be seen above at 960cm. -1 There is also obvious skeletal titanium characteristic absorption near the wavenumber. A comparison with Example 1 shows that the existing structure reconstruction method is also an effective route for preparing Ti-Beta zeolite. However, the existing structure reconstruction method requires the assistance of fluorides to prepare Ti-Beta zeolite, thus presenting practical problems such as fluoride-containing wastewater, which are detrimental to industrial applications.

[0115] Comparative Example 2: This example illustrates the existing liquid-solid isomorphic substitution process (Ind. Eng. Chem. Res. 2021, 60, 1219-1230). First, dealubilized Beta zeolite is contacted with an anhydrous ethanol solution of titanium tetrachloride at room temperature and briefly subjected to ultrasonic vibration. Then, the ethanol solvent in the solution is evaporated, and the solid product is dried and calcined to obtain Ti-Beta zeolite. However, due to the small size of the hydroxyl clusters in dealubilized Beta zeolite (a framework Al migrates out),... 3+ The space left by ions does not easily accommodate larger Ti particles. 4+ Ions (Ti) 4+ ionic radius is And Al 3+ ionic radius is Therefore, when preparing Ti-Beta zeolite using this method, the skeletal titanium content is low.

[0116] The first step is to prepare dealubilized Beta zeolite using Al-Beta zeolite as raw material.

[0117] Repeat the preparation steps of dealuminized Beta zeolite in Example 1, using a phase-free material with a grain size of less than 100 nm and a BET specific surface area of ​​approximately 540 m². 2Al-Beta zeolite raw material with a silicon-aluminum oxide molar ratio (SiO2 to Al2O3 molar ratio) of approximately 24 was prepared by acid dealuminization to produce dealuminated Beta zeolite with a SiO2 to Al2O3 molar ratio of 990, which was then sealed and stored for later use.

[0118] The second step is to prepare an anhydrous ethanol solution of titanium tetrachloride.

[0119] In the glove box, use a pipette to extract 6 mL of TiCl4 and quickly transfer it to 100 mL of anhydrous ethanol to prepare a 0.5 mol / L TiCl4 ethanol solution for later use.

[0120] The third step involves carrying out a liquid-solid isomorphic substitution reaction at room temperature.

[0121] First, based on the calculation of preparing Ti-Beta zeolite with a Si / Ti molar ratio of 50 using 10g of dealuated Beta zeolite, 6.8ml of solution was extracted from the 0.5mol / L TiCl4 ethanol solution prepared in the second step, and diluted to 30ml with anhydrous ethanol. The resulting solution became the impregnation solution.

[0122] Then, 10g of dried dealuated Beta zeolite was poured into 30ml of impregnation solution and stirred until homogeneous to obtain a reaction slurry. Next, the reaction slurry was transferred to an ultrasonic oscillator and subjected to an ultrasonic-assisted liquid-solid isomorphic substitution reaction at room temperature for 20 minutes.

[0123] After the reaction was completed, the ethanol solvent was recovered by vacuum evaporation at 80°C, and the solid product was collected.

[0124] The fourth step involves post-processing the liquid-solid isomorphous substitution reaction product to obtain the Ti-Beta zeolite product.

[0125] The post-processing steps mainly consist of conventional drying (120℃, overnight) and calcination (540℃, 3h). The Ti-Beta zeolite prepared in this example is designated Ti-Beta-2-Cl-Com. The Si / Ti molar ratio of the Ti-Beta-2-Cl-Com sample was determined to be approximately 50 using XRF. The skeletal vibrational infrared spectrum of the Ti-Beta-2-Cl-Com sample is shown below. Figure 5 .from Figure 5 The sample can be seen above at 960cm. -1 There is also characteristic absorption of skeletal titanium near the wavenumber, but compared with Example 1, it can be seen that the characteristic absorption peak intensity of skeletal titanium in the Ti-Beta-2-Cl-Com sample prepared by this method is weaker, indicating that its skeletal titanium content is lower.

[0126] Comparative Example 3: This example is used to illustrate the process according to the prior art solid-solid isomorphous substitution method (Microporous and Mesoporous Materials 288 (2019) 109588), i.e. first, the dealuminated Beta zeolite and the solid powder of dichlorotitanocene are thoroughly ground and uniformly mixed under inert gas protection. Then the solid mixture is calcined to obtain Ti-Beta zeolite. Similarly, since the hydroxyl pocket size of the dealuminated Beta zeolite is small (one framework Al 3+ ion leaves a space), it is not easy to accommodate the larger volume Ti 4+ ion (Ti 4+ ion radius is and Al 3+ ion radius is ), so the content of framework titanium in Ti-Beta zeolite prepared by this method is also low.

[0127] First step, preparing dealuminated Beta zeolite from Al-Beta zeolite

[0128] The dealuminated Beta zeolite preparation step of Example 1 is repeated, using Al-Beta zeolite raw material with no impurity phase, crystal size less than 100 nanometers, BET specific surface area about 540 m 2 / g, and molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) about 24, to prepare dealuminated Beta zeolite with a molar ratio of SiO2 to Al2O3 of 990 by acid dealumination, and seal and store for later use.

[0129] Second step, preparing a precursor mixture by grinding the solid powder of dealuminated Beta zeolite and dichlorotitanocene

[0130] First, according to the calculation of preparing Ti-Beta zeolite with a Si / Ti molar ratio of 50 using 10 g of dealuminated Beta zeolite, accurately weigh 0.85 g of solid powder of dichlorotitanocene in the glove box.

[0131] Then, put the dealuminated Beta zeolite powder in a dry state and the solid powder of dichlorotitanocene in the glove box into a mortar and grind them carefully to obtain a precursor mixture.

[0132] Third step, preparing Ti-Beta zeolite by calcining the precursor mixture

[0133] The precursor mixture was quickly spread into a crucible and the crucible was covered and placed in a muffle furnace for calcination (540°C, 3h). The white solid powder obtained was the Ti-Beta zeolite product, designated Ti-Beta-3-Cp-Com. The Si / Ti molar ratio of the Ti-Beta-2-Cp-Com sample was about 50 as measured by XRF. The skeletal vibration infrared spectrum of the Ti-Beta-3-Cp-Com sample is shown in Figure 3. Figure 6 As can be seen from Figure 3, the sample has a skeletal titanium characteristic absorption near 960 cm Figure 6 As can be seen from Figure 3, the sample has a skeletal titanium characteristic absorption near 960 cm -1 As can be seen from Figure 3, the sample has a skeletal titanium characteristic absorption near 960 cm

[0134] Example 2: This example is used to illustrate that the Ti-Beta zeolite preparation process based on the vapor phase transport method provided by the present application, i.e. using dealuminated Beta zeolite as the main raw material, does not involve the use of fluoride or / and aluminum source for assistance, mainly utilizes the vapor phase transport pathway to provide water vapor and weak organic base auxiliary tetraethylammonium bromide (TEABr) template agent, and can greatly prepare Ti-Beta zeolite and make the weak organic base get the green process of recycling. The combination of tetraethylammonium bromide (TEABr) template agent and volatile weak organic base can replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process, and at the same time, with the help of the channel condensate generated by the dealuminated Beta zeolite in the saturated steam and the zeolite solid surface liquid film to limit the amount of silicate dissolved, it is more convenient to achieve the controllable etching desilication of the hydroxyl pit of the dealuminated Beta zeolite, achieve the purpose of mild etching desilication of the hydroxyl pit of the dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl pit to titanium ions with larger volume, and avoid the dealuminated Beta zeolite crystals being completely dissolved by the strong alkaline TEAOH solution into fragmented structural units (amorphous substances), so as to change the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) into the repair of local defects of Ti-Beta zeolite crystals, that is, the repair of local structural defects left after the mild etched hydroxyl pit accepts titanium ions (the present application). When the Ti-Beta zeolite is prepared by in-situ local structure reconstruction of the Ti-Beta zeolite precursor by the vapor phase transport method, the amount of liquid water added to the bottom of the kettle can be changed within a certain range without changing the beneficial effects of the present application. In short, the present application can prepare high-quality Ti-Beta zeolite from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source, because it avoids the reconstruction of Ti-Beta zeolite structure from amorphous fragmented structural units. In addition, in the present application, the Ti-Beta zeolite is prepared by in-situ local construction reconstruction from the dried Ti-Beta zeolite precursor. The precursor is prepared by impregnating the dealuminated Beta zeolite with an equal volume of acidic aqueous solution of titanium sulfate and TEABr template agent. The Ti-Beta zeolite precursor has low water content and does not contain colloidal substances, so only simple drying treatment is required when preparing the Ti-Beta zeolite precursor, which is suitable for mass production.

[0135] Example 2: This example is used to illustrate that the Ti-Beta zeolite preparation process based on the vapor phase transport method provided by the present application, i.e. using dealuminated Beta zeolite as the main raw material, does not involve the use of fluoride or / and aluminum source for assistance, mainly utilizes the vapor phase transport pathway to provide water vapor and weak organic base auxiliary tetraethylammonium bromide (TEABr) template agent, and can greatly prepare Ti-Beta zeolite and make the weak organic base get the green process of recycling. The combination of tetraethylammonium bromide (TEABr) template agent and volatile weak organic base can replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process, and at the same time, with the help of the channel condensate generated by the dealuminated Beta zeolite in the saturated steam and the zeolite solid surface liquid film to limit the amount of silicate dissolved, it is more convenient to achieve the controllable etching desilication of the hydroxyl pit of the dealuminated Beta zeolite, achieve the purpose of mild etching desilication of the hydroxyl pit of the dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl pit to titanium ions with larger volume, and avoid the dealuminated Beta zeolite crystals being completely dissolved by the strong alkaline TEAOH solution into fragmented structural units (amorphous substances), so as to change the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) into the repair of local defects of Ti-Beta zeolite crystals, that is, the repair of local structural defects left after the mild etched hydroxyl pit accepts titanium ions (the present application). When the Ti-Beta zeolite is prepared by in-situ local structure reconstruction of the Ti-Beta zeolite precursor by the vapor phase transport method, the amount of liquid water added to the bottom of the kettle can be changed within a certain range without changing the beneficial effects of the present application. In short, the present application can prepare high-quality Ti-Beta zeolite from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source, because it avoids the reconstruction of Ti-Beta zeolite structure from amorphous fragmented structural units. In addition, in the present application, the Ti-Beta zeolite is prepared by in-situ local construction reconstruction from the dried Ti-Beta zeolite precursor. The precursor is prepared by impregnating the dealuminated Beta zeolite with an equal volume of acidic aqueous solution of titanium sulfate and TEABr template agent. The Ti-Beta zeolite precursor has low water content and does not contain colloidal substances, so only simple drying treatment is required when preparing the Ti-Beta zeolite precursor, which is suitable for mass production. H2O / W 沸石前驱体The amount of deionized water added to the bottom of the reactor was changed to 15 g, 25 g and 30 g, respectively, and the amount of n-butylamine added to the bottom of the reactor was changed to 10 g, 17 g and 20 g, respectively, to keep the concentration of n-butylamine in the bottom liquid unchanged (40%). The skeletal vibration infrared spectra of the prepared Ti-Beta zeolite samples had obvious skeletal titanium characteristic absorption near 960 cm -1 The skeletal titanium content index (I 960 / I 800 ) of the prepared Ti-Beta zeolite samples was 1.03, 1.05 and 1.02, respectively.

[0136] Example 3: This example is used to illustrate that the Ti-Beta zeolite preparation process based on the vapor phase transport method provided by the present application, i.e. using dealuminated Beta zeolite as the main raw material, does not involve the use of fluoride or / and aluminum source for assistance, mainly utilizes the vapor phase transport pathway to provide water vapor and weak organic base auxiliary tetraethylammonium bromide (TEABr) template agent, can greatly prepare Ti-Beta zeolite and can make the green process of the weak organic base to be recycled, can replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process by using tetraethylammonium bromide (TEABr) template agent combined with volatile weak organic base, at the same time, with the help of the channel condensate generated by the dealuminated Beta zeolite in the saturated steam and the zeolite solid surface liquid film to limit the amount of silicate dissolved, more conveniently realize the controllable etching desilication of the hydroxyl pit of the dealuminated Beta zeolite, achieve the purpose of mild etching desilication of the hydroxyl pit of the dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl pit to the titanium ions with larger volume, and the purpose of avoiding the dealuminated Beta zeolite crystal to be completely dissolved into fragmented structural units (amorphous substances) by the strong alkaline TEAOH solution, so as to change the synthesis of Ti-Beta zeolite crystal (traditional structure reconstruction method) into the local defect repair of Ti-Beta zeolite crystal, i.e. repair the local structural defects left after the mild etched hydroxyl pit accepts titanium ions (the present application). In the preparation of Ti-Beta zeolite by in-situ local structure reconstruction of Ti-Beta zeolite precursor by vapor phase transport method, the temperature and time of the reconstruction reaction can be changed within a certain range without changing the beneficial effects of the present application. In short, the present application can prepare high-quality Ti-Beta zeolite from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source, because it avoids the reconstruction of Ti-Beta zeolite structure from amorphous fragmented structural units. In addition, in the present application, Ti-Beta zeolite is prepared by in-situ local construction reconstruction from dried Ti-Beta zeolite precursor. The precursor is prepared by impregnating dealuminated Beta zeolite with an equal volume of acidic aqueous solution of titanium sulfate and TEABr template agent. The Ti-Beta zeolite precursor has low water content and does not contain colloidal substances, so only simple drying treatment is required during the preparation of Ti-Beta zeolite precursor, which is suitable for large-scale production.

[0137] Example 1 is repeated, but in the preparation of Ti-Beta zeolite by in-situ local structure reconstruction of Ti-Beta zeolite precursor by vapor phase transport method in the third step, the temperature and time of the reconstruction reaction are changed to 120°C x 48h, 130°C x 24h, 150°C x 6h, 160°C x 2h and 170°C x 0.5h, respectively. The prepared Ti-Beta zeolite sample has a skeleton vibration infrared spectrum at 960 cm -1There are obvious skeleton titanium characteristic absorption peaks around 550 cm"1, 620 cm"1and 710 cm"1, and the skeleton titanium content index value (I 960 / I 800 ) are 0.99, 1.00, 0.98, 1.10 and 1.08, respectively.

[0138] Example 4: This example is used to illustrate that the Ti-Beta zeolite preparation process based on the gas phase transmission method provided by the present application, i.e. using dealuminated Beta zeolite as the main raw material, does not involve the use of fluoride or / and aluminum source for assistance, mainly utilizes the gas phase transmission pathway to provide water vapor and weak organic base auxiliary tetraethyl ammonium bromide (TEABr) template agent, and can greatly prepare Ti-Beta zeolite and make the weak organic base get recycled green process. The weak organic base can be replaced by the combination of tetraethyl ammonium bromide (TEABr) template agent and volatile weak organic base to replace the strong alkaline tetraethyl ammonium hydroxide (TEAOH) template agent used in the existing preparation process, and at the same time, with the help of the channel condensate generated by the dealuminated Beta zeolite in the saturated steam and the zeolite solid surface liquid film to limit the amount of silicate dissolved, it is more convenient to achieve the controllable etching desilication of the hydroxyl pit of the dealuminated Beta zeolite, to achieve the purpose of mild etching desilication of the hydroxyl pit of the dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl pit to titanium ions with larger volume, and to avoid the dealuminated Beta zeolite crystals being completely dissolved by the strong alkaline TEAOH solution into fragmented structural units (amorphous substances), so as to change the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) into the repair of local defects of Ti-Beta zeolite crystals, i.e. the local structural defects left after the mild etched hydroxyl pit accepts titanium ions (the present application). In the preparation of the Ti-Beta zeolite precursor for in-situ local structure reconstruction method by equal volume impregnation method, the amount of tetraethyl ammonium bromide (TEABr) template agent can be changed within a certain range without changing the beneficial effects of the present application. In short, the present application can prepare high-quality Ti-Beta zeolite from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source, because it avoids the reconstruction of Ti-Beta zeolite structure from amorphous fragmented structural units. In addition, in the present application, Ti-Beta zeolite is prepared by in-situ local construction reconstruction from dried Ti-Beta zeolite precursor. The precursor is prepared by equal volume impregnation of dealuminated Beta zeolite with acidic aqueous solution of titanium sulfate and TEABr template agent. The water content in the Ti-Beta zeolite precursor is low and does not contain colloidal substances, so only simple drying treatment is required when preparing the Ti-Beta zeolite precursor, which is suitable for mass production.

[0139] Example 1 was repeated, but in the second step, the preparation of Ti-Beta zeolite precursor for in-situ local structure reconstruction method by equal volume impregnation method, the TEABr / SiO2 molar ratio (expressed by the number of moles of SiO2 the number of moles of dealuminated Beta zeolite) was changed to 0.05, 0.1, 0.2, 0.25, 0.4 and 0.5 in turn. The prepared Ti-Beta zeolite precursor was further in-situ local structure reconstruction by gas phase transmission method to prepare Ti-Beta zeolite. The prepared Ti-Beta zeolite samples, their skeleton vibration infrared spectra have obvious skeleton titanium characteristic absorption near 960 cm -1 -1, 820 cm-1 and 470 cm-1, and their skeleton titanium content index value (I 960 / I 800 ) fluctuates between 0.9-1.0.

[0140] Example 5: This example is used to illustrate that the Ti-Beta zeolite preparation process based on the vapor phase transport method provided by the present application, i.e. using dealuminated Beta zeolite as the main raw material, without involving the use of fluoride or / and aluminum source for assistance, mainly utilizing the vapor phase transport pathway to provide water vapor and weak organic base auxiliary tetraethylammonium bromide (TEABr) template, can greatly prepare Ti-Beta zeolite and make the weak organic base get the green process of recycling, which can replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process by combining tetraethylammonium bromide (TEABr) template with volatile weak organic base, while taking advantage of the pore condensate generated by dealuminated Beta zeolite in saturated steam and the zeolite solid surface liquid film to limit the amount of silicate dissolved, more conveniently achieve the controllable etching desilication of the hydroxyl pocket of dealuminated Beta zeolite, achieve the purpose of mild etching desilication of the hydroxyl pocket of dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl pocket for titanium ions with larger volume, and avoiding the dealuminated Beta zeolite crystals being completely dissolved by the strong alkaline TEAOH solution into fragmented structural units (amorphous materials), so as to change the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) into the repair of local defects of Ti-Beta zeolite crystals, i.e. the repair of local structural defects left after the mild etched hydroxyl pocket accepts titanium ions (the present application). In the preparation of the Ti-Beta zeolite precursor for in-situ local structure reconstruction method by the equal volume impregnation method, the Si / Ti molar ratio and the impregnation time are allowed to be changed within a certain range without changing the beneficial effects of the present application. In short, the present application can prepare high-quality Ti-Beta zeolite from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source, because it avoids reconstructing the Ti-Beta zeolite structure from amorphous fragmented structural units. In addition, in the present application, the Ti-Beta zeolite is prepared by in-situ local construction reconstruction from the dried Ti-Beta zeolite precursor. The precursor is prepared by using sulfuric acid titanium and TEABr template acidic aqueous solution to impregnate dealuminated Beta zeolite in equal volume. The water content in the Ti-Beta zeolite precursor is low and does not contain colloidal substances, so that only simple drying treatment is required when preparing the Ti-Beta zeolite precursor, which is suitable for mass production.

[0141] Example 1 was repeated, but in the second step, the Si / Ti molar ratio (expressed by the number of moles of SiO2to the number of moles of dealuminated Beta zeolite) was changed to 60, 70, 80, 90 and 100, respectively, while the impregnation time was changed to 12 h, 8 h, 6 h, 2 h and 0.5 h, respectively, for the preparation of Ti-Beta zeolite precursor for in-situ local structure reconstruction method by equal volume impregnation method. The prepared zeolite precursor was further in-situ locally structure reconstructed to Ti-Beta zeolite by gas phase transportation method. The prepared Ti-Beta zeolite samples had obvious skeleton titanium characteristic absorption at 960 cm -1 nearby in their skeleton vibration infrared spectra, and their skeleton titanium content index value (I 960 / I 800 ) varied between 0.8 and 1.0. Generally, with the increase of Si / Ti molar ratio, the skeleton titanium content index value (I 960 / I 800 ) of Ti-Beta zeolite samples showed a decreasing trend.

[0142] Example 6: This example is used to illustrate that the Ti-Beta zeolite preparation process based on the gas phase transport method provided by the present application, i.e. using dealuminated Beta zeolite as the main raw material, without involving the use of fluoride or / and aluminum source for assistance, mainly utilizing the gas phase transport pathway to provide water vapor and weak organic base auxiliary tetraethylammonium bromide (TEABr) template, can greatly prepare Ti-Beta zeolite and make the weak organic base get the green process of recycling, which can replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process by combining tetraethylammonium bromide (TEABr) template with volatile weak organic base, while taking advantage of the pore condensate generated by dealuminated Beta zeolite in saturated steam and the zeolite solid surface liquid film to limit the amount of silicate dissolved, more conveniently achieve the controllable etching desilication of the hydroxyl pocket of dealuminated Beta zeolite, achieve the purpose of mild etching desilication of the hydroxyl pocket of dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl pocket for titanium ions with larger volume, and avoiding the dealuminated Beta zeolite crystals being completely dissolved by the strong alkaline TEAOH solution into fragmented structural units (amorphous materials), so as to change the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) into the repair of local defects of Ti-Beta zeolite crystals, i.e. the repair of local structural defects left after the mild etched hydroxyl pocket accepts titanium ions (the present application). In the preparation of the Ti-Beta zeolite precursor for in-situ local structure reconstruction method by the equal volume impregnation method, the drying temperature and time of the wet material after equal volume impregnation are allowed to be changed within a certain range without changing the beneficial effects of the present application. In short, the present application can prepare high-quality Ti-Beta zeolite from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source, because it avoids reconstructing the Ti-Beta zeolite structure from amorphous fragmented structural units. In addition, in the present application, Ti-Beta zeolite is prepared by in-situ local construction reconstruction from dried Ti-Beta zeolite precursor. The precursor is prepared by equal volume impregnation of dealuminated Beta zeolite with an acidic aqueous solution of titanium sulfate and TEABr template. The Ti-Beta zeolite precursor has low water content and does not contain colloidal substances, so only simple drying treatment is required when preparing the Ti-Beta zeolite precursor, which is suitable for large-scale production.

[0143] Example 1 was repeated, but in the second step, the Ti-Beta zeolite precursor for in situ local structure reconstruction method was prepared by equal volume impregnation method, and the drying treatment conditions of the equal volume impregnated post-wetting material were changed to 50°C x 24h (drying under micro negative pressure), 60°C x 12h (drying under micro negative pressure), 70°C x 16h, 100°C x 6h, 120°C x 3h, 150°C x 1h and 170°C x 0.5h in sequence. The prepared zeolite precursor was further in situ locally structure reconstructed into Ti-Beta zeolite by gas phase transmission method. The prepared Ti-Beta zeolite sample had obvious skeleton titanium characteristic absorption near 960 cm -1 and 1030 cm 960 -1in its skeleton vibration infrared spectrum, and its skeleton titanium content index value (I 800 / I ) fluctuated between 0.9 and 1.0.

[0144] Example 7: This example is used to illustrate that the Ti-Beta zeolite preparation process based on the vapor phase transport method provided by the present application, i.e. using dealuminated Beta zeolite as the main raw material, does not involve the use of fluoride or / and aluminum source for assistance, mainly utilizes the vapor phase transport pathway to provide water vapor and weak organic base auxiliary tetraethylammonium bromide (TEABr) template agent, and can greatly prepare Ti-Beta zeolite and make the weak organic base green process for reuse. The weak organic base can be replaced by the combination of tetraethylammonium bromide (TEABr) template agent and volatile weak organic base to replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process, and at the same time, with the help of the channel condensate generated by the dealuminated Beta zeolite in the saturated steam and the zeolite solid surface liquid film to limit the amount of silicate dissolved, it is more convenient to achieve the controllable etching desilication of the hydroxyl pit of the dealuminated Beta zeolite, achieve the purpose of mild etching desilication of the hydroxyl pit of the dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl pit to titanium ions with larger volume, and avoiding the dealuminated Beta zeolite crystal being completely dissolved by the strong alkaline TEAOH solution into a fragmented structural unit (amorphous material), so as to change the synthesis of Ti-Beta zeolite crystal (traditional structure reconstruction method) into the repair of local defects of Ti-Beta zeolite crystal, i.e. the local structural defects left after the mild etched hydroxyl pit accepts titanium ions (the present application). In the preparation of the Ti-Beta zeolite precursor for in-situ local structure reconstruction method by the equal volume impregnation method, the dealuminated Beta zeolite can be prepared by using Al-Beta zeolite raw material with different silicon aluminum ratios, and the Si / Ti molar ratio used in the preparation of the zeolite precursor by the equal volume impregnation method can be changed accordingly according to the amount of the hydroxyl pit of the dealuminated Beta zeolite, without changing the beneficial effects of the present application. In short, the present application can prepare high-quality Ti-Beta zeolite from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source, because it avoids the reconstruction of Ti-Beta zeolite structure from amorphous fragmented structural units. In addition, in the present application, Ti-Beta zeolite is prepared by in-situ local construction reconstruction from dried Ti-Beta zeolite precursor. The precursor is prepared by using sulfuric acid titanium and TEABr template agent acidic aqueous solution to impregnate dealuminated Beta zeolite. The water content in the Ti-Beta zeolite precursor is low and does not contain colloidal substances, so that only simple drying treatment is required during the preparation of the Ti-Beta zeolite precursor, which is suitable for mass production.

[0145] Example 1 was repeated, but in the first step of preparing the dealuminated Beta zeolite from the Al-Beta zeolite, the Al-Beta zeolites with a silica-to-alumina molar ratio (molar ratio of SiO2 to Al2O3) of 10, 20, 40, 60, 80, 100, 150 and 200 were first synthesized according to the hydrothermal crystallization method provided in U.S. Patent No. 3 308 069 (1967) as the raw material for preparing the dealuminated Beta zeolite. After the above-synthesized Al-Beta zeolites were subjected to the conventional filtration, washing, drying (110°C, 12h) and calcination for removing the template (540°C, 6h), it was observed by TEM that the average crystal size of the Al-Beta zeolites was in the nanometer and small crystal (less than 1 μm) levels, and the crystal size increased with the increase of the silica-to-alumina molar ratio (molar ratio of SiO2 to Al2O3); and it was found by XRD that there was no any impurity crystal in the Al-Beta zeolites, and the BET specific surface area of the Al-Beta zeolites was calculated from the nitrogen physical adsorption data to be higher than 500 m2 / g; and the silica-to-alumina molar ratio (molar ratio of SiO2 to Al2O3) of the Al-Beta zeolites was measured by XRF to be 10, 20, 38, 57, 72, 94, 136 and 189, respectively, which met the technical requirements of the Beta zeolite raw material of the present application. The above-synthesized Al-Beta zeolites were subjected to acid dealumination to prepare the dealuminated Beta zeolite, and the molar ratio of SiO2 to Al2O3 of the dealuminated Beta zeolite was 751, 770, 870, 861, 855, 932, 1088 and 960, respectively, which met the technical requirements of the dealuminated Beta zeolite of the present application. 2 Example 1 was repeated, but in the first step of preparing the dealuminated Beta zeolite from the Al-Beta zeolite, the Al-Beta zeolites with a silica-to-alumina molar ratio (molar ratio of SiO2 to Al2O3) of 10, 20, 40, 60, 80, 100, 150 and 200 were first synthesized according to the hydrothermal crystallization method provided in U.S. Patent No. 3 308 069 (1967) as the raw material for preparing the dealuminated Beta zeolite. After the above-synthesized Al-Beta zeolites were subjected to the conventional filtration, washing, drying (110°C, 12h) and calcination for removing the template (540°C, 6h), it was observed by TEM that the average crystal size of the Al-Beta zeolites was in the nanometer and small crystal (less than 1 μm) levels, and the crystal size increased with the increase of the silica-to-alumina molar ratio (molar ratio of SiO2 to Al2O3); and it was found by XRD that there was no any impurity crystal in the Al-Beta zeolites, and the BET specific surface area of the Al-Beta zeolites was calculated from the nitrogen physical adsorption data to be higher than 500 m2 / g; and the silica-to-alumina molar ratio (molar ratio of SiO2 to Al2O3) of the Al-Beta zeolites was measured by XRF to be 10, 20, 38, 57, 72, 94, 136 and 189, respectively, which met the technical requirements of the Beta zeolite raw material of the present application. The above-synthesized Al-Beta zeolites were subjected to acid dealumination to prepare the dealuminated Beta zeolite, and the molar ratio of SiO2 to Al2O3 of the dealuminated Beta zeolite was 751, 770, 870, 861, 855, 932, 1088 and 960, respectively, which met the technical requirements of the dealuminated Beta zeolite of the present application.

[0146] The dealuminated Beta zeolites were used to prepare the precursors of Ti-Beta zeolites by the equal-volume impregnation method, and then the Ti-Beta zeolites were further prepared by the gas phase transmission method in situ and local structure reconstruction. In the preparation of the precursors of the zeolites from the dealuminated Beta zeolites with different numbers of hydroxyl pockets, the Si / Ti molar ratio of the hydrogel was changed to 5, 10, 15, 25, 60, 70, 80 and 110 in the order from more to less of the number of the hydroxyl pockets of the dealuminated Beta zeolites, i.e. in the order from low to high of the silica-to-alumina ratio of the Al-Beta zeolite raw material (in the order of 10, 20, 38, 57, 72, 94, 136 and 189). The Ti-Beta zeolite samples prepared had the obvious framework titanium characteristic absorption at 960 cm -1 nearby in the framework vibration infrared spectrum, and the framework titanium content index value (I 960 / I 800 ) thereof varied between 0.8 and 1.1. Overall, the framework titanium content index value (I 960 / I 800 ) of the Ti-Beta zeolite samples tended to decrease with the increase of the Si / Ti molar ratio.

[0147] Example 8: This example is used to illustrate the process of preparing Ti-Beta zeolite by the steam-assisted dealumination and partial structure reconstruction method of Beta zeolite according to the present application, and the prepared Ti-Beta zeolite has excellent catalytic performance for the epoxidation reaction of cyclohexene and hydrogen peroxide.

[0148] The cyclohexene epoxidation reaction was carried out in a 25 mL round-bottom flask equipped with a condenser and a magnetic stirrer. The following steps were taken: first, 10 mmol of cyclohexene, 10 mL of acetonitrile, 10 mmol of hydrogen peroxide (35%) and 100 mg of Ti-Beta zeolite catalyst were added to the flask, and then the reaction was started under vigorous stirring at 353 K for 1 hour. Finally, samples were taken from the reaction product, and the composition was analyzed by gas chromatography (Shimadzu GC-2014C) equipped with a hydrogen flame ionization detector (FID) and a DB-WAX capillary column (30 m x 0.32 mm, 30 μm). The conversion of cyclohexene and the selectivity of epoxycyclohexane were calculated by the external standard method.

[0149] In this example, the four Ti-Beta zeolites (Ti-Beta-1, Ti-Beta-1-F-Com, Ti-Beta-2-Cl-Com and Ti-Beta-3-Cp-Com) prepared in Example 1 and Comparative Examples 1-3 were selected as catalysts to catalyze the epoxidation reaction of cyclohexene and hydrogen peroxide. The results showed that under the same reaction conditions, the conversion rates of cyclohexene for the above Ti-Beta zeolite catalysts were 37%, 26%, 46% and 47%, respectively, and the selectivities of epoxycyclohexane were 90%, 81%, 84% and 82%, respectively.

Claims

1. A process for the preparation of Ti-Beta zeolite based on the gas phase transport method with recyclable organic bases, characterized by, The steps are as follows: Step 1: Preparation of dealuminated Beta zeolite from Al-Beta zeolite (1) Selection of Al-Beta zeolite raw material The Al-Beta zeolite refers to a silicon-aluminum Beta zeolite; the Al-Beta zeolite has the following restrictions: 1) no impurity crystals in the Al-Beta zeolite; 2) the crystallization of the Al-Beta zeolite is good, that is, the BET specific surface area value of the Al-Beta zeolite is greater than or equal to 450 m 2 / g; 3) the molar ratio of silicon-aluminum oxide of the Al-Beta zeolite, that is, the molar ratio of SiO2 to Al2O3 is 10-200; (2) Preparation of dealuminated Beta zeolite The dealuminated Beta zeolite is prepared from Al-Beta zeolite by using acid dealuminating method, and the molar ratio of SiO2 to Al2O3 in the dealuminated Beta zeolite is required to be in the range of ≧700; Step 2: Preparation of precursor for in-situ local structure reconstruction method of Ti-Beta zeolite by equal-volume impregnation method The precursor for Ti-Beta zeolite is prepared by equal-volume impregnation method at room temperature; the impregnation raw materials include tetraethylammonium bromide (TEABr) template, titanium sulfate and deionized water. The specific steps are as follows: first, according to the amount of dealuminated Beta zeolite and the saturated water absorption rate of dealuminated Beta zeolite, the volume of equal-volume impregnation liquid is determined; then, according to the selected molar ratio of TEABr to SiO2 and the molar ratio of Si to Ti, TEABr template and titanium sulfate are weighed, and an acidic impregnation liquid containing TEABr template and titanium sulfate is prepared by using deionized water; finally, the dealuminated Beta zeolite is impregnated with the acidic impregnation liquid containing TEABr template and titanium sulfate at room temperature; The impregnation is carried out statically in a closed container; after the equal-volume impregnation is completed, the precursor wet material is dried to obtain the precursor for Ti-Beta zeolite; The amount of dealuminated Beta zeolite is calculated based on SiO2, and the amounts and impregnation conditions of other impregnation raw materials are as follows: Molar ratio of TEABr to SiO2: 0.05-0.5; Molar ratio of Si to Ti: 5-100; Impregnation time: 0.5-12h; Drying temperature of precursor wet material: 30℃-170℃; Drying time of precursor wet material: 0.5h-24h; Step 3: Preparation of Ti-Beta zeolite by in-situ local structure reconstruction of Ti-Beta zeolite precursor by gas phase transmission method The reaction process of in-situ local structure reconstruction for preparing Ti-Beta zeolite is carried out in an autoclave; the inside of the autoclave is provided with a support and a tray; the dried Ti-Beta zeolite precursor is placed on the tray, and the water vapor and volatile weak organic base for gas phase transmission are provided by vaporization of the water solution at the bottom of the autoclave; the organic base is n-butylamine; The parameters are as follows: The amount of liquid water at the bottom of the autoclave is calculated based on the mass ratio of liquid water at the bottom of the autoclave to the precursor, and the mass ratio of liquid water at the bottom of the autoclave to the precursor is in the range of 1.5-3; The amount of volatile weak organic base is calculated based on the mass percentage concentration of organic base in aqueous solution, and the mass percentage concentration of organic base in aqueous solution is in the range of 10-60%; The reaction temperature range for structure reconstruction is 120-170℃; The reaction time range for structure reconstruction is 0.5-48h; Step 4: Post-treatment of Ti-Beta zeolite product The post-treatment of Ti-Beta zeolite product includes water washing, drying and calcination to obtain Ti-Beta zeolite product.

2. A process for the preparation of Ti-Beta zeolite based on the gas phase transport method of reusable organic bases according to claim 1, characterized by, In step 1(1), the molar ratio of silicon-aluminum oxide of Al-Beta zeolite, i.e. the molar ratio of SiO2 to Al2O3, is 20-100.

3. A process for the preparation of Ti-Beta zeolite based on the gas phase transport method of reusable organic bases according to claim 2, characterized by, In the first step (1), the silica alumina oxide molar ratio of the Al-Beta zeolite, i.e. the molar ratio of SiO2 to Al2O3, is 25-60.

4. The process for the preparation of Ti-Beta zeolite based on gas phase transport method of reusable organic base according to claim 1, characterized in that, In the first step (2), the SiO2 to Al2O3 molar ratio of the dealuminated Beta zeolite is required to be in the range of ≧800.

5. A process for the preparation of Ti-Beta zeolite based on the gas phase transport method of reusable organic bases according to claim 4, characterized by, In the first step (2), the SiO2 to Al2O3 molar ratio of the dealuminated Beta zeolite is required to be in the range of ≧900.

6. A process for the preparation of Ti-Beta zeolite based on gas phase transport method of reusable organic base as claimed in claim 1 wherein, In the second step, the parameter conditions are as follows: ​ TEABr to SiO2 molar ratio: 0.1-0.4; Si to Ti molar ratio: 10-80; Impregnation time: 1-6h; Precursor wet material drying temperature: 50-150℃; Precursor wet material drying time: 3-18h.

7. A process for the preparation of Ti-Beta zeolite based on the gas phase transport method of reusable organic bases according to claim 6, characterized by, In the second step, the parameter conditions are as follows: TEABr to SiO2 molar ratio: 0.2-0.3; Si to Ti molar ratio: 15-50; Impregnation time: 2-4h; Precursor wet material drying temperature: 80-120℃; Precursor wet material drying time: 6-12h.

8. The process for the preparation of Ti-Beta zeolite based on gas phase transport method of reusable organic base according to claim 1, characterized by, In the third step, the parameters are required as follows: The amount of liquid water at the bottom of the kettle is in the range of 1.8-2.8 in terms of the mass ratio of the liquid water at the bottom of the kettle to the precursor; The amount of weak volatile organic base is in the range of 20-50% in terms of the mass percentage concentration of the organic base in the aqueous solution; The reaction temperature range for structure reconstruction is 130-160℃; The reaction time range for structure reconstruction is 4-24h.

9. A process for the preparation of Ti-Beta zeolite based on the gas phase transport method of reusable organic bases according to claim 8, characterized by, In the third step, the parameters are required as follows: The amount of liquid water at the bottom of the kettle is in the range of 2.0-2.5 in terms of the mass ratio of the liquid water at the bottom of the kettle to the precursor; The amount of weak volatile organic base is in the range of 30-40% in terms of the mass percentage concentration of the organic base in the aqueous solution; The reaction temperature range for structure reconstruction is 135-150℃; The reaction time range for structure reconstruction is 6-18h.

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