A green process for mass production of ti-beta zeolite based on local structure reconstruction method

Abstract

The present application belongs to the field of petroleum chemical catalysis technology, and relates to a process for mass production of Ti-Beta zeolite based on local structure reconstruction method. The main technical features include: using water vapor assisted tetraethylammonium bromide template agent and alcohol amine weak organic base, and preparing Ti-Beta zeolite by local desilicon etching and repair reconstruction on the hydroxyl pit of dealuminated Beta zeolite. The benefits of the present application include: the combination of tetraethylammonium bromide template agent and alcohol amine weak organic base, and the limitation of the amount of silicate dissolved by the channel condensate liquid generated by dealuminated Beta zeolite and the liquid film on the surface of zeolite solid in saturated steam, which makes it easier to control the etching desilicon of the hydroxyl pit of dealuminated Beta zeolite and improves the receiving capacity of the hydroxyl pit to titanium ions with larger volume. The local structure defects generated by controllable etching desilicon can be directly repaired by using the quaternary ammonium cation provided by the TEABr template agent as a directing agent, so that the present application does not need to be assisted by fluoride or / and aluminum source.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of petrochemical catalysis technology, and relates to a green process for mass production of Ti-Beta zeolite based on a local structure reconstruction method. BACKGROUND

[0002] So far, Ti-Beta zeolite can be prepared by various methods, including traditional hydrothermal method, dry gel conversion method (steam assisted), crystal transformation method, isomorphous substitution method and 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 result in the presence of 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 Ti-Beta zeolite is synthesized by dry gel conversion method. Because the conversion process of the dry gel is not carried out in water but in steam, 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°C 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°C 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 be produced, 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 use an Al-Beta zeolite to perform an isomorphous substitution reaction with a 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 dealumination and titanium supplementation to occur simultaneously in the liquid-solid phase reaction. However, the liquid-solid isomorphous substitution reaction of Ti(SO4)2) with the Al-Beta zeolite cannot effectively remove the framework aluminum of the Beta zeolite, so that the Ti 4+ ion isomorphous substitution reaction occurs to a limited extent.

[0011] In fact, the gas-solid, solid-solid and liquid-solid isomorphous substitution methods described above all have the problem that the Ti 4+ ion isomorphous substitution reaction occurs to a limited extent. This is because the radius 4+ of the tetravalent titanium ion (Ti ) is larger than the radius of the trivalent aluminum ion (Al 3+ ). Therefore, the hydroxyl hole vacancies produced after the Al 3+ is removed from the framework of the Al-Beta zeolite are small, which is not conducive to 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: 65 wt% HNO3 solution, liquid-solid ratio 30, dealumination at reflux temperature for 12 h, 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 1.0 SiO2: xTEAOH: yTiO2: 0.5 NH4F: 7.0 H2O. The above gel solution is recrystallized at 140 °C for 1 day to obtain the Ti-Beta zeolite product. The post-treatment of Ti-Beta zeolite includes filtration, washing, drying (80 °C, overnight) and calcination (550 °C, 6 h).

[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 Zeolite, Hierarchical Pore Channel and Catalytic Performance Research [D]. Northwest University, 2021; Microporous and Mesoporous Materials 330 (2022) 111625; Ma Haikuo. Design and Synthesis of BEA Topology Heteroatom Zeolite and Its Catalytic Performance [D]. Yantai University, 2022; Pan Hong. Synthesis and Post-treatment Modification of Titanium Silicate Zeolite and Study on Its 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 wastewater is the main challenge for the industrial application of the existing structure reconstruction method. SUMMARY

[0016] The present application provides a green process for mass production of Ti-Beta zeolite based on a local structure reconstruction method.

[0017] In other words, the present application provides a green process for mass production of Ti-Beta zeolite by locally etching and reconstructing the hydroxyl pockets of dealuminated Beta zeolite without involving the use of fluoride or / and aluminum source, using a combination of steam assisted tetraethyl ammonium bromide (TEABr) template and alcohol amine weak organic base. The process has the following three most prominent technical features: (1) when preparing the hydrogel precursor for local structure reconstruction with dealuminated Beta zeolite and titanium source, it is required to add tetraethyl ammonium bromide (TEABr) as a template, and at the same time, add alcohol amine organic matter with high boiling point and good thermal stability as a weak base source, so as to replace the strong alkaline tetraethyl ammonium hydroxide (TEAOH) template used in the existing preparation process, so as to more easily avoid the complete dissolution and structure fragmentation of dealuminated Beta zeolite; (2) the hydrogel precursor is treated by spray drying to remove free water therein before local structure reconstruction, so as to be converted into a dry gel intermediate. Spray drying can convert a large amount of hydrogel precursor into a dry gel intermediate in a short time, which creates favorable conditions for mass production of Ti-Beta zeolite; (3) the local structure reconstruction process of the dry gel intermediate is carried out in a steam atmosphere in an autoclave, that is, under steam assistance. The steam is generated by the liquid water at the bottom of the autoclave which does not directly contact the dry gel intermediate.

[0018] The fundamental difference between the present application and the existing process for preparing Ti-Beta zeolite by structure reconstruction is that the starting point of the structure reconstruction is not the fragmented structure unit (long-range disorder, no characteristic diffraction peak of Beta zeolite in the XRD pattern) produced after the complete dissolution of the dealuminated Beta zeolite crystal, but the dealuminated Beta zeolite crystal as a whole (with complete characteristic diffraction peaks in the XRD pattern) whose hydroxyl pockets have been slightly etched by alcohol amine 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 a combination of tetraethyl ammonium bromide (TEABr) template and alcohol amine weak organic base to replace the strong alkaline tetraethyl ammonium hydroxide (TEAOH) template used in the existing preparation process. This not only helps to reduce the manufacturing cost of Ti-Beta zeolite, but also uses the flexible combination of template and weak organic base to unlock the TEA + cationic moiety and OH -The 1:1 ratio of the anion part is easy to achieve mild desilication etching of the hydroxyl pockets of the dealuminated Beta zeolite under weak alkalinity and to accelerate the structure reconstruction reaction under sufficient amount of structure directing agent. In particular, the TEABr template and the weak organic base of the alcohol amine used in the present application are high-thermal-stability and high-boiling-point organic substances, which are more resistant to high temperature than TEAOH, allowing the preparation of the dry gel intermediate to be performed by spray drying at a higher temperature, which is suitable for large-scale and rapid preparation of the dry gel intermediate, and thus has higher practical value.

[0019] It is found in the research that, because the process provided by the present application does not involve establishing the crystal structure of the Beta zeolite from scratch (i.e., does not involve Beta zeolite crystal growth), but only involves repairing the local structural defects left after the slightly etched hydroxyl pockets accept titanium ions, the process provided by the present application can prepare high-quality Ti-Beta zeolite with high skeletal titanium content and less non-skeletal titanium from dealuminated Beta zeolite through steam-assisted local structure reconstruction without the assistance of fluoride or / and aluminum source.

[0020] It is also found in the study that, for the present application, it is necessary to dry the hydrogel precursor to remove the free water therein and convert it into a dry gel intermediate before the local structure reconstruction is carried out, and then to make the dry gel intermediate to undergo the local structure reconstruction with the assistance of steam, so as to avoid the over-etching of the hydroxyl pits of the dealuminated Beta zeolite by the weakly alkaline solution of the alcohol amine type organic matter, and thus to avoid the partial disintegration of the crystal structure and the excessive fragmentation of the material. As known by those skilled in the art, the dissolution of the silicate solid in the alkaline solution exists a chemical equilibrium. But the greater the volume of the solution is, the more silicate solid is consumed to reach the equilibrium state. This means that, when the amount of the silicate solid (e.g. the dealuminated Beta zeolite) is certain, the greater the volume of the alkaline solution is, the greater the degree of dissolution of the silicate solid (e.g. the dealuminated Beta zeolite) is. However, for the present application, since the steam is in contact with the silicate solid, and the silicate fragments are non-volatile, the dissolution equilibrium of the silicate solid only involves the liquid film with a limited thickness on the surface of the silicate solid and the liquid water filled in the pores of the silicate solid due to the capillary condensation. Since 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 the liquid is limited, the silicate fragments that can be dissolved by the liquid film and the condensed liquid water in the pores are also limited. In addition, the drying of the hydrogel precursor to remove the free water therein and convert it into a dry gel intermediate before the local structure reconstruction is carried out, and then the structure reconstruction of the dry gel intermediate with the assistance of steam, is also beneficial to maximize the local structure reconstruction rate of the dealuminated Beta zeolite in the presence of the TEABr template and the alcohol amine type weak organic base composition, and thus to maximize the time for the preparation of the Ti-Beta zeolite by the structure reconstruction method. This is mainly because, under the conditions of the steam-assisted local structure reconstruction of the dry gel intermediate, the TEABr template molecules, the alcohol amine type weak organic base molecules and the soluble Beta zeolite structure units produced by the slight etching of the hydroxyl pits are all concentrated in the condensed liquid in the surface liquid film and the pores, which is beneficial to accelerate the recrystallization reaction.

[0021] The present application also has essential differences from the existing dry gel conversion method for the preparation of Ti-Beta zeolite. Although both the methods involve the steam assistance from the surface, the latter needs to undergo the crystallization process of the amorphous dry gel. The crystallization process of the dry gel with the assistance of steam can sometimes be carried out without the addition of the fluoride mineralizer, but the crystallization of the amorphous dry gel needs to be assisted by the introduction of the aluminum source without the addition of the fluoride mineralizer. Therefore, it is difficult to obtain the Ti-Beta zeolite with high performance by the existing dry gel conversion method.

[0022] It needs to be particularly emphasized that the green process for preparing Ti-Beta zeolite based on the local structure reconstruction method provided by the application is not a simple combination of the existing dry gel conversion method and the structure reconstruction method. The innovation and advancement of the application lie in the following aspects: firstly, the application uses a combination of tetraethylammonium bromide (TEABr) template agent and alcohol amine weak organic base to replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process, and at the same time, the amount of dissolved silicate is limited by the pore condensate liquid generated by the dealuminated Beta zeolite in the saturated steam and the liquid film on the surface of the zeolite solid, which is more conducive to the controlled etching and desiliconization of the hydroxyl pit of the dealuminated Beta zeolite, improves the accommodation capacity of the hydroxyl pit for titanium ions with large 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 controlled etching and desiliconization produces local structural defects, and the TEA + cations structural directing agent (SDA) can be quickly repaired in the weak alkaline environment generated by the alcohol amine organic matter, and the application is completely free from the troubles caused by the need to add fluoride or / and aluminum source for auxiliary structure reconstruction due to the structure reconstruction of Beta zeolite from amorphous silicate fragments in the existing process. In addition, since the TEABr template agent and the alcohol amine weak organic base are both high-thermal-stability and high-boiling-point organic matters, they are more resistant to high temperature than TEAOH, and are low in price and widely available, allowing the preparation of dry gel intermediates to be carried out by the spray drying method at a higher temperature, which is suitable for large-scale and rapid preparation of dry gel intermediates, and thus the process provided by the application has higher practical value.

[0023] The technical solution of the application is as follows:

[0024] A green process for preparing Ti-Beta zeolite in large quantities based on a local structure reconstruction method, the steps are as follows:

[0025] First step: preparing dealuminated Beta zeolite from Al-Beta zeolite

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

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

[0028] The Al-Beta zeolite refers to a silicon-aluminum Beta zeolite. The present application does not limit the grain size of the Al-Beta zeolite, nor does it limit the production process of the Al-Beta zeolite. However, in order to facilitate the implementation effect of the present application, the Al-Beta zeolite has the following limitations: 1) the Al-Beta zeolite has no impurity crystals; 2) the Al-Beta zeolite has good crystallization; and 3) the molar ratio of silicon-aluminum oxide (the molar ratio of SiO2 to Al2O3) of the Al-Beta zeolite is appropriate.

[0029] The presence or absence of impurity crystals in the Al-Beta zeolite can be checked and confirmed by X-ray polycrystalline powder diffraction (XRD) method. As known by those skilled in the art, the molar ratio of SiO2 to Al2O3 of the Al-Beta zeolite produced by the hydrothermal synthesis method is usually between 10 and 200 (US 3 308 069 (1967)). In the Al-Beta zeolite product with a lower molar ratio of SiO2 to Al2O3, there are generally MOR impurity crystals, while in the Al-Beta zeolite with a higher molar ratio of SiO2 to Al2O3, there are generally ZSM-5 zeolite impurity crystals. By sampling the Al-Beta zeolite and performing XRD analysis, and comparing the XRD pattern of the sample with the standard diffraction cards of Beta zeolite, MOR zeolite and ZSM-5 zeolite, it can be determined whether there are characteristic peaks of MOR zeolite and ZSM-5 zeolite impurity crystals in the XRD pattern of the sample, so as to know whether the Al-Beta zeolite is a 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 requires 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° to be compared 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 pockets 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, Ti-Al-Beta zeolite) as the oxidation reaction catalyst and weaken the advantage of the structural reconstruction method in the preparation of 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 high-temperature water vapor, EDTA complexing agent, organic acid solution, 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, considering the production cost, process complexity and difficulty in treatment of the waste liquid generated by dealumination of the dealuminated Beta zeolite.

[0039] Engineers familiar with the art can prepare the dealuminated Beta zeolite according to their experience or refer 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 preparing the dealuminated Beta zeolite by acid dealumination of the Al-Beta zeolite with an aqueous concentrated nitric acid solution, the concentration of the aqueous nitric acid 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 required molar ratio of SiO2 to Al2O3 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 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 hydrogel precursor for local structure reconstruction using the dealuminated Beta zeolite

[0041] In addition to the dealuminated Beta zeolite, other raw materials for preparing the hydrogel precursor for local structure reconstruction include: tetraethylammonium bromide (TEABr) template, alcohol amine weak organic base, titanium source, and deionized water.

[0042] The amount of the dealuminated Beta zeolite is calculated based on SiO2, and the amounts of the other raw materials satisfy the following conditions:

[0043] TEABr to SiO2 molar ratio: suitable range is 0.05-0.5; preferred range is 0.1-0.4; more preferred range is 0.2-0.3.

[0044] Alcohol amine to SiO2 molar ratio: suitable range is 0.1-0.5; preferred range is 0.15-0.4; more preferred range is 0.2-0.3.

[0045] H2O to SiO2 molar ratio: suitable range is 3-10; preferred range is 4-8; more preferred range is 5-6.

[0046] Si to Ti molar ratio: suitable range is 5-100; preferred range is 10-80; more preferred range is 15-50.

[0047] The alcohol amine weak organic base mainly refers to diethanolamine (boiling point 268.8℃) or triethanolamine (360℃), which is mainly because they are not only cheap and easy to obtain, but also have high boiling point, which can meet the requirement of the boiling point temperature of the alcohol amine weak organic base in the large-scale preparation of the dry gel intermediate by the spray drying method.

[0048] 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 - ions have poor stability; and tetraethylammonium chloride is not as cheap and easy to obtain as tetraethylammonium bromide. Therefore, the tetraethylammonium bromide is selected as the template agent in the present application on the basis of comprehensive consideration of the above factors.

[0049] The titanium source suitable for the present application is mainly an organic compound of titanium, such as tetrabutyl titanate (TBOT), tetraethyl titanate (TEOT), tetraisopropyl titanate (TPOT) or titanium acetylacetonate, etc. Since the cost of the titanium source has little effect on the production cost of the titanium silicalite in general, the selection of the titanium source should mainly consider whether it is conducive to the entry of titanium ions into the framework of the titanium silicalite and whether it can avoid the generation of non-framework titanium in the titanium silicalite to the maximum extent. Based on this principle, the titanium source of the present application is preferably tetrabutyl titanate (TBOT) and tetraethyl titanate (TEOT), and more preferably tetrabutyl titanate. The titanium source suitable for the present application can be stabilized by a common complexing agent in advance before use. For example, tetrabutyl titanate can be stabilized by an appropriate amount of isopropanol before use.

[0050] The operation of preparing the hydrogel precursor can be carried out at room temperature. The basic procedure is as follows: first, according to the amount of the dealuminated Beta zeolite and the selected molar ratio of H2O to SiO2, the molar ratio of the alcohol amine to SiO2, the molar ratio of Si to Ti and the molar ratio of TEABr to SiO2, the deionized water, the alcohol amine, the titanium source and the TEABr template are measured; then, the TEABr template is dissolved in water under stirring, and the titanium source is dissolved in the alcohol amine. Finally, the TEABr template solution and the dealuminated Beta zeolite are sequentially added to the weak alkaline solution containing the alcohol amine and the titanium source under stirring, and the reaction (slight desilication reaction) is carried out at room temperature for a period of time. The suitable range of the stirring reaction time is 0.5-12 h; the preferred range is 1-6 h; and the more preferred range is 2-4 h.

[0051] The TEABr template can be ionized in the aqueous solution to generate TEA + cations. We found in our research that the TEA + cations ionized from the TEABr template in the aqueous solution, like the TEA + cations ionized from the TEAOH template solution, can act as a structure directing agent (SDA) in the final stage of the preparation of the Ti-Beta zeolite, i.e. in the later stage of the vapor-assisted local structure reconstruction process, after the titanium ions are received by the local structural defects left by the slightly etched hydroxyl pits. While the weak alkaline OH - anions (R-NH2+ H2O → R-NH3 + + OH - ) produced by the hydrolysis of the alcohol amine weak organic base in the aqueous solution, can act as an etchant in the early stage of the preparation of the Ti-Beta zeolite, including the preparation process of the hydrogel precursor and the process of converting the hydrogel precursor into the dry gel intermediate by spray drying to remove the free water therein, and the initial stage of the vapor-assisted local structure reconstruction process (the autoclave heating process), and is responsible for the slight desilication of the hydroxyl pits of the dealuminated Beta zeolite. In the recommended molar ratio of TEABr to SiO2 and the molar ratio of the alcohol amine to SiO2 in the present application, the etching desilication effect of the weak alkaline aqueous solution provided by the alcohol amine organic matter can be assisted by the TEA + cations released from the TEABr template in the aqueous solution to promote the two local structure reconstruction reactions for preparing the Ti-Beta zeolite from the dealuminated Beta zeolite, including the etching desilication reaction of the hydroxyl pits and the recrystallization reaction of the silicate fragments.

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

[0053] In the preparation of the hydrogel precursor stage, the role of the addition of deionized water is to ensure that the four components of the de-aluminized Beta zeolite, TEABr, alcohol amine weak organic base and titanium source form a uniform hydrogel precursor. Therefore, in the preparation stage of the hydrogel precursor, if the amount of water introduced is too low (i.e. the H2O / SiO2 ratio is too low), on the one hand it is difficult to ensure the uniformity of the hydrogel precursor, on the other hand it is also not conducive to the formation of a weak alkaline solution of alcohol amine organic matter, which is necessary for the necessary degree of silicon etching of the hydroxyl pit of the de-aluminized Beta zeolite. In order to adapt to the requirements of the flowability and viscosity of the hydrogel precursor in the preparation of the dry gel intermediate by spray drying, the minimum H2O / SiO2 ratio (the ratio of the amount of deionized water added to the amount of de-aluminized Beta zeolite (dry basis, calculated as SiO2)) of the hydrogel precursor should be much greater than the saturated water absorption rate of the de-aluminized Beta zeolite (the typical saturated water absorption rate of the de-aluminized Beta zeolite is generally 1.2 ml H2O / g dehydrated zeolite. Dehydrated zeolite is defined as a zeolite sample that is first dried overnight at 110°C, then calcined at 550°C for 3h. The saturated water absorption amount 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 there is no free water). And the maximum amount of deionized water, i.e. the maximum amount of deionized water, is mainly constrained by the time and energy consumption of the next step of removing free water from the hydrogel precursor by spray drying to convert it into a dry gel intermediate. The above is the main basis for determining the H2O / SiO2 molar ratio range of the present application. Step 3: removing free water from the hydrogel precursor by spray drying to convert it into a dry gel intermediate

[0054] The dry gel intermediate described in the present application refers to the product obtained after the hydrogel precursor is treated by spray drying to remove most of the free water. Compared with the hydrogel precursor, not only is most of the free water removed from the dry gel intermediate, but also the hydroxyl pit of the de-aluminized Beta zeolite has been further etched by the weak alkaline solution environment produced by the alcohol amine organic matter in the hydrogel precursor, and a small amount of silicon-oxygen tetrahedron (SiO4) has fallen off from the edge of the hydroxyl pit, becoming a soluble monomeric silicate or oligomeric silicate species. However, the content, structure and physicochemical properties of the organic matter (mainly TEABr template and alcohol amine organic matter) can be ignored.

[0055] In order to enable engineers in the field to have a more specific understanding of the spray drying process and the dry gel intermediate described in the present application, the present application provides a typical method for preparing a dry gel intermediate on a scale of several kilograms or more: a hydrogel precursor prepared according to the requirements described above in the present application is fed into a centrifugal spray drying tower at a hydrogel precursor feed rate of 20 Kg / h. The centrifugal spray drying tower is a common domestic equipment, the spray tower diameter is 2.5 meters, and the working speed of the rotary atomizer is 8000 min -1, the temperature of the hot air into the tower is 350℃, and the temperature of the exhaust air out of the tower is 120℃. The dry gel intermediate product is collected from the discharge port of the first and second cyclone separation towers. The analysis by the thermogravimetric (TG) instrument shows that the weight loss of the dry gel intermediate product prepared by the spray drying method due to the removal of free water occurs in a low temperature zone of 30-130℃; the weight loss due to the removal of bound water (water bound by pores and hydroxyl holes, etc.) occurs in a medium temperature zone of 130-166℃, and the weight loss due to the decomposition and removal of the TEABr template and the alcohol amine organic substances occurs in a high temperature zone above 166℃. The results show that the dry gel intermediate product prepared by the spray drying of the hydrogel precursor prepared according to the requirements of the present application still contains about 20wt% of water, mainly in the form of bound water, and little free water. The dry gel intermediate product is white in appearance, and the thermogravimetric analysis confirms that the content of the TEABr template and the alcohol amine organic substances in the dry gel intermediate product has not changed compared with the hydrogel precursor. Therefore, the dry gel intermediate product meeting the requirements of the present application can be prepared by further drying the hydrogel precursor prepared according to the requirements of the present application by the spray drying method.

[0056] For comparison, the present application further provides a typical method for preparing a dry gel intermediate product of an order of magnitude of less than 100g in a laboratory by a low temperature drying method: a hydrogel precursor prepared according to the requirements of the present application is placed in a common electric heating oven at 80℃, and dried and dehydrated to a constant weight state to become a white dry gel intermediate product after about 12h. The analysis data show that the dry gel intermediate product contains about 25wt% of water, mainly in the form of bound water, and little free water. Compared with the hydrogel precursor, the content of the TEABr template and the alcohol amine organic substances in the dry gel intermediate product has not changed, which is a dry gel intermediate product meeting the requirements of the present application.

[0057] Comparing the analysis results of the above two dry gel intermediate products can find that, according to the requirements of the present application, the hydrogel precursor is prepared by using tetraethylammonium bromide (TEABr) with a high boiling point and good thermal stability as a template, and adding alcohol amine organic substances with a high boiling point and good thermal stability as a weak base source, and using the combination of the two to replace the tetraethylammonium hydroxide (TEAOH) template with poor thermal stability used in the existing preparation process, so that the dry gel intermediate product meeting the present application can be prepared quickly and in large quantities at a higher temperature by using a spray drying equipment with high drying efficiency and strong processing capacity.

[0058] The spray drying is carried out at normal pressure; the total water content in the dry gel intermediate product is required to be between 15wt% and 25wt%, and the decomposition or removal of TEABr and alcohol amine weak organic bases in the drying process is prevented.

[0059] For spray drying, the feed rate of the hydrogel precursor, the rotational speed of the atomizer, the inlet air temperature and the outlet air temperature are adjustable parameters, but the adjustable range is small. Therefore, engineers in the field need to adjust the above parameters according to the size of the specific spray drying equipment and the water content of the hydrogel precursor, in order to achieve the best preparation effect of the dry gel intermediate. For the present application, the required dry gel intermediate has two characteristics: first, the content, structure and physicochemical properties of the organic matter (mainly TEABr template and alcohol amine organic matter) therein can be ignored; second, most of the free water in the hydrogel has been removed. In order to facilitate engineers in the field to judge whether the dry gel intermediate meets the requirements of the present application, the present application gives the following simplest judgment method: (1) judging whether the first characteristic is met from the color of the dry gel intermediate. If the color of the dry gel intermediate is white, it means that TEABr and alcohol amine organic matter have not decomposed and changed in structure during drying, meeting the first characteristic. If the color of the dry gel intermediate is light yellow or egg yolk, it means that TEABr or / and alcohol amine organic matter has decomposed and changed in structure during drying, not meeting the first characteristic; (2) taking a sample of the dry gel intermediate for thermogravimetric analysis, the sample has dehydration weight loss in the low temperature zone (free water removal zone) of 30-130°C and in the medium temperature zone (bound water removal zone) of 130-166°C, and the total weight loss rate is between 15-25%, indicating that the dehydration degree during low temperature drying is appropriate. If the total weight loss rate is >25%, it indicates that the dehydration degree during low temperature drying is not enough. If the total weight loss rate is <15%, it indicates that the dehydration degree during low temperature drying is too large. The dry gel intermediate prepared by spray drying method is generally in the form of microspheres and has good fluidity, which can be directly sealed for use.

[0060] Fourth step: steam-assisted partial structure reconstruction of the dry gel intermediate to prepare Ti-Beta zeolite

[0061] The reaction process of steam-assisted partial structure reconstruction of the dry gel intermediate to prepare Ti-Beta zeolite is carried out in an autoclave. The autoclave is provided with a support and a tray inside. The dry gel intermediate powder is placed on the tray, and the auxiliary steam is provided by vaporization of the liquid water at the bottom of the autoclave.

[0062] In this step, the amount of liquid water added at the bottom of the autoclave, as well as the reaction temperature and time of structure reconstruction, are the main influencing factors. For their value range, the present application requires the following:

[0063] The amount of liquid water added at the bottom of the autoclave is calculated as the mass ratio of H2O to dry gel intermediate (W H2O / W 干胶中间体 The suitable range of the mass ratio of H2O to dry gel intermediate is 1.5-3; the preferred range is 1.8-2.8; and the more preferred range is 2.0-2.5. The reaction temperature for the structure reconstruction is suitably in the range of 120-170°C, preferably in the range of 130-160°C, and more preferably in the range of 135-150°C.

[0065] The reaction time for the structure reconstruction is suitably in the range of 0.5-48h, preferably in the range of 4-24h, and more preferably in the range of 6-18h.

[0066] The above-mentioned condition ranges are selected to meet the needs of the reaction for the preparation of Ti-Beta zeolite by the steam-assisted partial structure reconstruction of the dry gel intermediate. The reaction process for the preparation of Ti-Beta zeolite by the steam-assisted partial structure reconstruction of the dry gel intermediate is described as follows to enable engineers in the field to better understand the above-mentioned condition ranges selected for the present application:

[0067] In the initial stage of the partial structure reconstruction process, i.e. in the heating-up stage of the autoclave, more and more liquid water at the bottom of the autoclave is changed into water vapor as the temperature in the autoclave is gradually increased, and the partial pressure of the steam in the autoclave is continuously increased. As a result, the dry gel intermediate powder on the tray is correspondingly provided with higher and higher water content due to the increasing infiltration of the water vapor. In this process, the dealuminated Beta zeolite, TEABr template, alcohol amine weak organic base in the dry gel, and the silicate fragments (soluble Beta zeolite structural units) produced by the slight etching of the weak alkaline solution of the alcohol amine organic matter in the hydrogel precursor during the preparation of the hydrogel precursor and the subsequent spray drying process will also be correspondingly changed. 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 form a liquid film with a certain thickness. Secondly, for the TEABr template and alcohol amine molecules in the dry gel intermediate which were originally in a dehydrated state, the main change is that they are dissolved in water again and ionized into TEA + cations and OH - anions, so that the capillary condensation liquid in the pores of the dealuminated Beta zeolite and the water film on the surface of the zeolite are both changed into an alkaline solution containing TEA + cations and OH + anions. The alkaline solution which is distributed throughout the pores of the dealuminated Beta zeolite will inevitably further etch and desiliconize the hydroxyl pits of the dealuminated Beta zeolite. In addition, for the silicate fragments (soluble Beta zeolite structural units) which have been produced in the dry gel intermediate by the slight etching of the weak alkaline solution of the alcohol amine organic matter in the hydrogel precursor during the preparation of the hydrogel precursor and the subsequent low-temperature drying process, the main change is that they are dissolved in the alkaline solution which is distributed throughout the pores of the dealuminated Beta zeolite, and delay the further etching and desiliconization of the hydroxyl pits of the dealuminated Beta zeolite in the alkaline solution.

[0068] When the temperature of the autoclave is raised to a level sufficient to carry out the structural reconstruction reaction (recrystallization reaction), the concentration of silicate fragments (soluble Beta zeolite structural units) dissolved in the alkaline solution throughout the pores of the dealuminated Beta zeolite also reaches a maximum - the chemical equilibrium concentration. At this time, the etching desilication reaction of the hydroxyl pockets of the dealuminated Beta zeolite by the weakly alkaline solution produced by the alcohol amine organic matter in the dry gel intermediate is inhibited, and the entire closed system enters the later stage of the vapor-assisted local structural reconstruction process. The main features of this stage are: first, the titanium ions released by the titanium source in the dry gel intermediate begin to enter the etched hydroxyl pockets of the dealuminated Beta zeolite. The etched hydroxyl pockets increase in volume due to slight desilication, improving the ability to accommodate larger titanium ions. Because of this, the Ti-Beta zeolite process prepared by the vapor-assisted partial structural reconstruction method provided by the present application has the characteristic of high skeletal titanium content. Then, the silicate fragments (soluble Beta zeolite structural units) dissolved and concentrated in the alkaline solution throughout the pores of the dealuminated Beta zeolite, with a limited total amount of liquid, rapidly undergo local structural reconstruction reactions (recrystallization reactions) on the local structural defect sites left after the dealuminated Beta zeolite rapidly accommodates titanium ions under the action of the structure-directing agent (SDA) TEA + cations, and then carry out local structural reconstruction reactions (recrystallization reactions) on the local structural defect sites left after the dealuminated Beta zeolite rapidly accommodates titanium ions under the action of the structure-directing agent (SDA) TEA

[0069] In the present application, in order to achieve the reaction purpose and effect of the vapor-assisted dry gel intermediate local structural reconstruction for preparing Ti-Beta zeolite, the amount of water introduced into the bottom of the autoclave should at least enable the formation of vapor-liquid two-phase in the autoclave at the structural reconstruction reaction temperature. Because only under the condition of the coexistence of vapor-liquid two-phase, the pores of the dealuminated Beta zeolite will be filled with liquid water due to capillary condensation, and at the same time, the surface of the dealuminated Beta zeolite will also develop from monolayer to multilayer adsorption of water molecules, and finally form a liquid film with a certain thickness. As can be seen from the above, the liquid water condensed in the pores of the dealuminated Beta zeolite and the liquid film with a certain thickness formed on the surface of the zeolite are the support for the reaction process of each stage of the vapor-assisted dry gel intermediate local structural reconstruction, thereby realizing the phase interface micro-hydrothermal system for Ti-Beta zeolite preparation.

[0070] 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 at 120℃, 130℃, 140℃, 150℃, 160℃ and 170℃, the volume of the saturated water vapor in the autoclave is V (unit: m 3The equivalent mass of water vapor (unit: Kg) is about 1.1V, 1.3V, 1.6V, 1.8V, 2.2V and 2.5V, respectively, when the autoclave is filled with saturated water vapor.

[0071] For example, in the preparation of Ti-Beta zeolite by steam-assisted local structure reconstruction reaction of dry gel intermediates at 140℃, in order to form vapor-liquid two-phase in the autoclave at the structure reconstruction reaction temperature of 140℃, the minimum amount of water to be introduced into the bottom of the autoclave is estimated to be 1.6V+1.2W. Wherein 1.2 is the saturated water absorption rate of typical dealuminated Beta zeolite, and W is the weight of dry gel intermediates. For a laboratory small autoclave with a volume of 100ml, assuming that the amount of dry gel intermediates added is 10g (0.01Kg), in order to form vapor-liquid two-phase in the autoclave at the structure reconstruction reaction temperature of 140℃, the minimum amount of water to be introduced into the bottom of the autoclave is estimated to be 12.16g (1.6V=1.6x1x10 -4 Kg=0.16g; 1.2W=1.2x10x10 -3 Kg=12g). Therefore, in theory, as long as 12.16g or more of liquid water is added to the bottom of the autoclave in advance, and 10g of dry gel intermediates is added to the tray above the support, Ti-Beta zeolite can be prepared by steam-assisted local structure reconstruction reaction of dry gel intermediates at 140℃. Of course, in actual work, the threshold value of the amount of liquid water 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-autoclave yield requirement of Ti-Beta zeolite. Therefore, in order to facilitate engineers in the field, the present application finally recommends that W H2O / W 干胶中间体 The ratio of 1.5-3 is used as the appropriate water addition range for the preparation of Ti-Beta zeolite by steam-assisted local structure reconstruction reaction of dry gel intermediates.

[0072] After the steam-assisted local structure reconstruction reaction of dry gel intermediates is completed, the autoclave is treated by conventional hydrothermal synthesis of zeolite molecular sieves. When the temperature and pressure in the autoclave approach ambient temperature and pressure, the autoclave is opened and the Ti-Beta zeolite product is removed.

[0073] Step 5: Post-treatment of Ti-Beta zeolite product

[0074] The Ti-Beta zeolite product prepared by the method of the present application does not need to be filtered, washed, especially post-processed by defluorination and dealumination, but only needs to be subjected to conventional drying and calcination treatment to obtain the Ti-Beta zeolite product, i.e. after the steam-assisted partial structure reconstruction reaction of the dry gel intermediate is completed, the Ti-Beta zeolite product is collected from the tray in the autoclave, and then subjected to drying and calcination treatment. The purpose of calcination is to remove the TEABr template and alcohol amine organic matter in the product. Engineers familiar with the field can perform the post-processing operation according to common sense.

[0075] Advantages of the present application:

[0076] The present application provides a new process for preparing Ti-Beta zeolite, which uses dealuminated Beta zeolite as the main raw material, does not need to add fluoride or / and aluminum source for assistance, and mainly performs local desiliconization etching and repair reconstruction on the hydroxyl pits of the dealuminated Beta zeolite by means of the combination of steam-assisted tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base. The main technical innovation of the present application is that, first, the present application uses the combination of tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base 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 zeolite solid surface liquid film generated by the dealuminated Beta zeolite in the saturated steam, which is more conducive to the controllable etching desiliconization of the hydroxyl pits of the dealuminated Beta zeolite, improves the accommodation 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. Second, the controllable etching desiliconization produces local structural defects, and the TEA + cations in the solution ionized by the TEABr template can quickly repair the defects in the weak alkaline environment generated by the alcohol amine organic matter, and thus the present application completely gets rid of the troubles caused by the need to add fluoride or / and aluminum source for assisting the structure reconstruction due to the need to start from amorphous silicate fragments for the structure reconstruction of Beta zeolite in the existing process. In addition, since the TEABr template and the alcohol amine weak organic base are both high-thermal-stability and high-boiling-point organic matters, they are more resistant to high temperature than TEAOH, and are low in price and widely available, allowing the use of spray drying method to quickly, efficiently and massively prepare dry gel intermediates at a higher temperature, and thus the process provided by the present application has higher practical value. BRIEF DESCRIPTION OF DRAWINGS

[0077] Figure 1 is the XRD pattern of the dry gel intermediate prepared in Example 1.

[0078] Figure 2is the framework vibration Fourier transform infrared spectrogram of the Ti-Beta-1 sample prepared in Example 1.

[0079] Figure 3 is the X-ray polycrystalline powder diffraction (XRD) pattern of the Ti-Beta-1 sample prepared in Example 1.

[0080] Figure 4 is the framework vibration Fourier transform infrared spectrogram of the Ti-Beta-1-F-Com sample prepared in Comparative Example 1.

[0081] Figure 5 is the framework vibration Fourier transform infrared spectrogram of the Ti-Beta-2-Cl-Com sample prepared in Comparative Example 2.

[0082] Figure 6 is the framework vibration Fourier transform infrared spectrogram of the Ti-Beta-3-Cp-Com sample prepared in Comparative Example 3. DETAILED DESCRIPTION

[0083] The specific embodiments of the present application are further illustrated in the following with reference to the accompanying drawings and technical solutions.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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, 5 mmol of hydrogen peroxide (35%) and 50 mg of Ti-Beta zeolite catalyst are added to the flask, and then the reaction is started under vigorous stirring at 333 K for 2 hours. Finally, samples are taken from the reaction product, and composition analysis is performed using 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.

[0088] In addition, in the process of preparing Ti-Beta zeolite by the method of steam-assisted dealumination of Beta zeolite for local structure reconstruction, the following are involved: detection of impurity crystals in Al-Beta zeolite raw material, analysis of relative crystallinity and analysis of the SiO2 / Al2O3 molar ratio of the Al-Beta zeolite raw material; detection of residual aluminum content (expressed as the SiO2 / Al2O3 molar ratio) in the dealuminated Beta zeolite, and analysis of the water content, template content and dealuminated Beta zeolite crystal structure retention degree of the dry gel intermediate.

[0089] The detection of impurity crystals in the Al-Beta zeolite raw material and the characterization of the dealuminated Beta zeolite crystal structure retention degree of the dry gel intermediate can be performed by X-ray powder diffraction (XRD); the detection of the relative crystallinity of the Al-Beta zeolite raw material can be performed by measuring 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 SiO2 / Al2O3 molar ratio of the Al-Beta zeolite raw material can be detected by X-ray fluorescence spectroscopy (XRF); the residual aluminum content (expressed as the SiO2 / Al2O3 molar ratio) of the dealuminated Beta zeolite can be analyzed by inductively coupled plasma emission spectroscopy (ICP); and the water content and template content of the dry gel intermediate can be analyzed by thermogravimetric (TG) analysis.

[0090] The application will be further described by way of examples, but the application is not limited by these examples.

[0091] Example 1: This example is used to illustrate that the green process for mass production of Ti-Beta zeolite according to the local structure reconstruction 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, mainly through the local etching and desilication of the hydroxyl pockets of dealuminated Beta zeolite by means of the combination of steam-assisted tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, can mass-produce Ti-Beta zeolite by replacing the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process with the combination of tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, while taking advantage of the pore condensate and zeolite solid surface liquid film generated by dealuminated Beta zeolite in saturated steam to limit the amount of silicate dissolved, more conveniently achieving controllable etching and desilication of the hydroxyl pockets of dealuminated Beta zeolite, achieving the purpose of mild etching and desilication of the hydroxyl pockets of dealuminated Beta zeolite and improving the acceptance capacity of the hydroxyl pockets for larger titanium ions, as well as avoiding the complete dissolution of dealuminated Beta zeolite crystals into fragmented structural units (amorphous) by strong alkaline TEAOH solution, thereby changing 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 etching and desilication of the hydroxyl pockets to accept 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, both TEABr template and alcohol amine weak organic base are high-thermal-stability and high-boiling-point organic substances, which are more resistant to high temperatures than TEAOH, allowing the preparation of dry gel intermediates to be carried out at higher temperatures by spray drying.

[0092] First step: preparation of dealuminated Beta zeolite from Al-Beta zeolite

[0093] (1) Al-Beta zeolite with a molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) of 25 was synthesized by the hydrothermal crystallization method provided by U.S. Patent US3 308 069 (1967) as the raw material for preparing dealuminated Beta zeolite. After the synthesized Al-Beta zeolite was subjected to conventional filtration, washing, drying (110°C, 12h) and template removal by calcination (540°C, 6h), TEM observation showed that the crystal size was less than 100 nanometers, belonging to nano-Beta zeolite; XRD examination showed that there were no any impurity crystals in it, and the BET specific surface area calculated from its nitrogen physical adsorption data was about 540m 2The Si / Al oxide molar ratio (mole ratio of SiO2to Al2O3) of the Beta zeolite mother substance is about 24, as measured by XRF, which meets the technical requirements of the Beta zeolite mother substance of the present application.

[0094] (2) Preparation of the dealuminated Beta zeolite.

[0095] First, a concentrated nitric acid solution with a molar concentration of 13 M was prepared. Then, 20 g of the Beta zeolite mother substance subjected to the drying and calcination treatment described above was added to a three-necked flask containing 400 ml of the 13 M concentrated nitric acid solution under stirring at a liquid-to-solid ratio of 20:1 (ml / g) to perform dealumination treatment. The dealumination temperature was 95°C, and the dealumination time was 20 h. During the dealumination reaction, the three-necked flask was kept in a reflux state. After the dealumination reaction was completed, the liquid was cooled to room temperature, and the solid product was recovered by filtration. Then, the dealuminated Beta zeolite was prepared by using a conventional water washing, drying (overnight at 110°C), and calcination treatment (550°C for 3 h). The Si / Al oxide molar ratio (mole ratio of SiO2to Al2O3) of the dealuminated Beta zeolite was 990, as measured by ICP, which meets the requirements of the present application. The dealuminated Beta zeolite was sealed and stored for later use, avoiding moisture absorption.

[0096] Second step, preparation of the hydrogel precursor for local structure reconstruction using the dealuminated Beta zeolite

[0097] The amount of the template agent was determined according to a TEABr / SiO2molar ratio (the number of moles of SiO2represents the number of moles of the dealuminated Beta zeolite) of 0.3, the amount of diethanolamine was determined according to a diethanolamine / SiO2molar ratio of 0.3, the amount of titanium tetrabutoxide (TBOT) was determined according to a Si / Ti molar ratio of 45, and the amount of deionized water was determined according to a H2O / SiO2molar ratio of 6, using tetraethylammonium bromide (TEABr) solid as the source of the template agent, diethanolamine as the weak organic base, and titanium tetrabutoxide (TBOT) as the titanium source.

[0098] The specific implementation is as follows: first, 10.72 Kg of tetraethylammonium bromide (TEABr), 5.36 Kg of diethanolamine, 1.29 Kg of titanium tetrabutoxide (TBOT), and 18.36 Kg of deionized water were weighed out, based on the use of 10 Kg of the dealuminated Beta zeolite. Then, the titanium source was mixed with diethanolamine under stirring, and then the aqueous solution of TEABr and deionized water was added to the mixture of the titanium source and diethanolamine, and stirred uniformly. Finally, all the dealuminated Beta zeolite was poured into the weak alkaline solution containing the titanium source, the TEABr template agent, and diethanolamine under stirring, and the reaction (slight dissolution of silica) was carried out at room temperature for 3 h to obtain the hydrogel precursor for local structure reconstruction to prepare Ti-Beta zeolite.

[0099] The third step involves removing free water from the hydrogel precursor through spray drying, transforming it into a dry gel intermediate.

[0100] Take 40 kg of the hydrogel precursor prepared in the second step, and then feed it into a centrifugal spray drying tower at a feed rate of 20 kg / h. The centrifugal spray drying tower is a common domestically produced device with a diameter of 2.5 meters and a rotary atomizer operating at a speed of 8000 min / min. -1 The inlet hot air temperature is 350℃, and the outlet exhaust temperature is 120℃. The dry rubber intermediate product is collected from the discharge ports of the primary and secondary cyclone separators. Approximately 30 kg of dry rubber intermediate is harvested. The XRD pattern of the dry rubber intermediate is attached. Figure 1 From the appendix Figure 1 As can be seen, the dry gel intermediate prepared according to the requirements of this invention retains the crystal structure of dealubilized Beta zeolite very well. Thermogravimetric analysis (TG) of the dry gel intermediate revealed that weight loss due to the removal of free water occurred in the low-temperature region of 30-130℃, weight loss due to the removal of bound water occurred in the medium-temperature region of 130-166℃, and weight loss due to the decomposition and removal of the TEABr template agent and diethanolamine occurred in the high-temperature region above 166℃. The results indicate that the prepared dry gel intermediate still contains approximately 20 wt.% water, of which free water accounts for about one-third and bound water accounts for about two-thirds. The dry gel intermediate is white in color and has a soft texture; the changes in the content, structure, and physicochemical properties of the organic matter (mainly the TEABr template agent and the weak organic base diethanolamine) are negligible. After gentle grinding in a mortar, it becomes powder, which meets the requirements of this invention, and is sealed for later use.

[0101] Step 4: Preparation of Ti-Beta zeolite by local structural reconstruction of steam-assisted dry gel intermediate.

[0102] The reaction process for preparing Ti-Beta zeolite by steam-assisted local structural reconstruction of a dry gel intermediate was carried out in a small laboratory autoclave with a volume of 100 ml. The autoclave was equipped with a support and a tray. A 10 g sample of the dry gel intermediate powder was placed on the tray, while the auxiliary steam was provided by the vaporization of liquid water at the bottom of the autoclave below the tray. The local structural reconstruction reaction was carried out in a conventional electric oven at a temperature of 140 °C for 12 h.

[0103] According to calculations, during the partial structural reconstruction of the steam-assisted dry gel intermediate in this small autoclave, more than 12.16g of liquid water was added to the bottom of the autoclave (at this time, W H2O / W 干胶中间体With a ratio of approximately 1.2, a gas-liquid two-phase reaction can occur at 140°C. However, in this case, the liquid phase mainly refers to the capillary condensate within the pores of the dealuminized Beta zeolite and the liquid film on the zeolite surface. To ensure that the local structural reconstruction reaction proceeds under suitable conditions with liquid water at the bottom of the reactor, W... H2O / W 干胶中间体 The ratio was increased to 2.0. Therefore, 20g of deionized water was added to the bottom of the vessel.

[0104] After the local structural reconstruction reaction was completed, the autoclave was cooled and depressurized according to the usual procedure for hydrothermal synthesis of zeolite molecular sieves. When the temperature and pressure inside the autoclave were close to the ambient temperature and pressure, the autoclave was opened and the Ti-Beta zeolite product was removed.

[0105] Step 5: Post-processing of Ti-Beta zeolite products

[0106] Since the Ti-Beta zeolite product prepared by the method of this invention does not require filtration and washing, nor does it require defluorination and dealumination post-treatment, it only needs to undergo conventional drying and calcination. The drying is carried out in an electric oven at 110°C for 12 hours; the calcination is carried out in a muffle furnace at 540°C for 6 hours. The resulting white powder is the Ti-Beta zeolite product, designated Ti-Beta-1.

[0107] The Si / Ti molar ratio of the Ti-Beta-1 sample was determined to be approximately 45 using XRF. The skeletal vibrational infrared spectrum of the Ti-Beta-1 sample is shown in the appendix. Figure 2 XRD pattern is attached. Figure 3 From the appendix Figure 2 The sample can be seen above at 960cm. -1 There is a clear characteristic absorption of skeletal titanium near the wavenumber, and its skeletal titanium content index value (I) 960 / I 800 The value is 1.17. Additionally, from the appendix... Figure 3 It is evident that the sample exhibits high crystallinity and is free of impurities. Furthermore, ultraviolet Raman spectroscopy characterization (excitation wavelength 325 nm) confirmed that the sample contains only a very small amount of anatase phase titanium dioxide (at wavelengths of 144, 390, and 635 cm⁻¹). -1 (A weak anatase structure titanium dioxide resonance peak is observed). The above results indicate that, according to the steam-assisted dealufted Beta zeolite local structure reconstruction method provided by this invention, high-quality Ti-Beta zeolite products were prepared from dealufted Beta zeolite without the assistance of fluorides and / or aluminum sources.

[0108] Comparative Example 1: This example is used to illustrate 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, dealuminated Beta zeolite, a large amount of tetraethylammonium hydroxide (TEAOH) template solution, titanium source and deionized water are made into 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 substance is cooled, and fluoride is added to it. Finally, the hydrogel amorphous substance is reheated to prepare Ti-Beta zeolite (synthetic Ti-Beta zeolite crystal) from amorphous substance under hydrothermal conditions. 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, and thus there are problems such as fluoride-containing wastewater, which is not conducive to industrial application.

[0109] First step, using Al-Beta zeolite as raw material to prepare dealuminated Beta zeolite

[0110] Repeat the dealuminated Beta zeolite preparation step of Example 1, using Al-Beta zeolite raw material with no impurity crystal 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.

[0111] Second step, using dealuminated Beta zeolite to prepare hydrogel precursor for structure reconstruction

[0112] Use 25wt.% tetrapropylammonium hydroxide (TEAOH) aqueous solution as template source, use tetrabutyl titanate (TBOT) as titanium source, and determine the amount of template solution according to TEAOH / SiO2 molar ratio (the number of moles of SiO2 represents the number of moles of dealuminated Beta zeolite) is 0.3; according to Si / Ti molar ratio is 50 to determine the amount of tetrabutyl titanate (TBOT); the amount of water brought in by TEAOH template is determined by H2O / SiO2 molar ratio.

[0113] The specific method is as follows: first, 30 g of 25 wt.% tetrapropylammonium hydroxide (TEAOH) aqueous solution and 1.16 g of tetrabutyl titanate (TBOT) are weighed out according to the amount of 10 g of dealuminated Beta zeolite; then, the titanium source and the TEAOH template solution are mixed under stirring to prepare a uniform alkaline solution containing the titanium source and the TEAOH template; finally, all the dealuminated Beta zeolite is poured into the alkaline solution containing the titanium source and the TEAOH template under stirring, and the reaction (slight dissolution of silica) is stirred at room temperature for 3 h to obtain a hydrogel (H2O / SiO2molar ratio is about 7.4) for the preparation of Ti-Beta zeolite by structure reconstruction.

[0114] Third step, hydrothermal pretreatment of the hydrogel

[0115] 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 heating oven with a temperature setting of 140°C, and the pretreatment time is 1 h. 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 retention degree 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 large amount of strong alkaline TEAOH solution, and has become a fragmented structural unit with amorphous properties.

[0116] Fourth step, preparation of Ti-Beta zeolite by structure reconstruction of the hydrogel assisted by fluoride

[0117] 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 method 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 the ammonium fluoride and mix it uniformly with the hydrogel after the hydrothermal pretreatment (in which the crystal structure of the dealuminated Beta zeolite has been completely dissolved and destroyed, and has become 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 12 h. After the crystallization is completed, the autoclave is taken out of the oven and cooled to room temperature with water.

[0118] Fifth step, post-treatment of the Ti-Beta zeolite product

[0119] 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).

[0120] 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.

[0121] 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 in the appendix. Figure 4 From the appendix 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.

[0122] 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.

[0123] The first step is to prepare dealubilized Beta zeolite using Al-Beta zeolite as raw material.

[0124] 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.

[0125] The second step is to prepare an anhydrous ethanol solution of titanium tetrachloride.

[0126] 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.

[0127] The third step involves carrying out a liquid-solid isomorphic substitution reaction at room temperature.

[0128] 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.

[0129] 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.

[0130] After the reaction was completed, the ethanol solvent was recovered by vacuum evaporation at 80°C, and the solid product was collected.

[0131] The fourth step involves post-processing the liquid-solid isomorphous substitution reaction product to obtain the Ti-Beta zeolite product.

[0132] 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 in the appendix. Figure 5 From the appendix 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.

[0133] 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 (a 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.

[0134] First step, preparing dealuminated Beta zeolite from Al-Beta zeolite

[0135] 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.

[0136] Second step, preparing a precursor mixture by grinding the solid powder of dealuminated Beta zeolite and dichlorotitanocene

[0137] 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.

[0138] Then, put the dealuminated Beta zeolite powder and the solid powder of dichlorotitanocene in a dry state into a mortar in the glove box and grind them carefully to obtain a precursor mixture.

[0139] Third step, preparing Ti-Beta zeolite by calcining the precursor mixture

[0140] 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 also has a skeletal titanium characteristic absorption near 960 cm"1. However, as compared with Example 1, it can be seen that the skeletal titanium characteristic absorption peak of the Ti-Beta-3-Cp-Com sample prepared by the method is weaker, indicating that the skeletal titanium content is lower. Figure 6 . As can be seen from Figure 3, the sample also has a skeletal titanium characteristic absorption near 960 cm"1. However, as compared with Example 1, it can be seen that the skeletal titanium characteristic absorption peak of the Ti-Beta-3-Cp-Com sample prepared by the method is weaker, indicating that the skeletal titanium content is lower. -1 . As can be seen from Figure 3, the sample also has a skeletal titanium characteristic absorption near 960 cm"1. However, as compared with Example 1, it can be seen that the skeletal titanium characteristic absorption peak of the Ti-Beta-3-Cp-Com sample prepared by the method is weaker, indicating that the skeletal titanium content is lower.

[0141] Example 2: This example is used to illustrate that the green process for mass production of Ti-Beta zeolite according to the local structure reconstruction 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, mainly through the local etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite and the structure reconstruction by means of the combination of steam-assisted tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, can mass-produce the green process of Ti-Beta zeolite, which can replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process with the combination of tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, while taking advantage of the pore condensate and zeolite solid surface liquid film generated by the dealuminated Beta zeolite in saturated steam to limit the amount of dissolved silicate, more conveniently achieve the controllable etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite, achieve the purpose of mild etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite and improving the acceptance capacity of the hydroxyl pockets for 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, i.e. the repair of local structural defects left after the mild etching and desilication of the hydroxyl pockets for titanium ions (the present application). Among them, when repairing and reconstructing, i.e. when repairing the local structural defects left after the mild etching and desilication of the hydroxyl pockets for titanium ions with the assistance of water vapor, 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 reconstructing the Ti-Beta zeolite structure from amorphous fragmented structural units. In addition, both the TEABr template and the alcohol amine weak organic base are high-temperature stable and high-boiling-point organic substances, which are more resistant to high temperatures than TEAOH, allowing the preparation of dry gel intermediates to be carried out at higher temperatures by spray drying.

[0142] Example 1 was repeated, but in the fourth step of steam-assisted local structure reconstruction of the dry gel intermediate to prepare Ti-Beta zeolite, the amount of liquid water (W H2O / W 干胶中间体 ) added to the bottom of the kettle was changed to 1.5, 2.5 and 3.0, respectively. The Ti-Beta zeolite samples prepared had obvious skeletal titanium characteristic absorption near 960 cm -1 -1 in the skeletal vibration infrared spectrum, and the skeletal titanium content index (I 960 / I 800 ) was 1.12, 1.10 and 1.13, respectively.

[0143] Example 3: This example is used to illustrate that the green process for mass production of Ti-Beta zeolite according to the local structure reconstruction 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, mainly through the local etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite and the structure reconstruction by using the combination of tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, can mass-produce the green process of Ti-Beta zeolite, which can replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process by using the combination of tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, while taking advantage of the pore condensate and zeolite solid surface liquid film generated by the dealuminated Beta zeolite in saturated steam to limit the amount of silicate dissolved, more conveniently achieve the controllable etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite, achieve the purpose of mild etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite and improving the acceptance capacity of the hydroxyl pockets for titanium ions with larger volume, and avoid the dealuminated Beta zeolite crystals being completely dissolved by the strong alkaline TEAOH solution to become fragmented structural units (amorphous), 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 etching and desilication of the hydroxyl pockets (the present application) accepting titanium ions. Among them, when repairing and reconstructing, i.e. when repairing the local structural defects left after the mild etching and desilication of the hydroxyl pockets accepting titanium ions with the assistance of water vapor, the temperature and time of the reconstruction reaction 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, both the TEABr template and the alcohol amine weak organic base are high-temperature stable and high-boiling-point organic substances, which are more resistant to high temperatures than TEAOH, allowing the preparation of dry gel intermediates to be carried out at higher temperatures by using the spray drying method.

[0144] Example 1 was repeated, but when preparing Ti-Beta zeolite by steam-assisted local structure reconstruction of the dry gel intermediate in the fourth step, the temperature and time of the reconstruction reaction were changed to 120℃×48h, 130℃×24h, 150℃×6h, 160℃×2h and 170℃×0.5h, respectively. The Ti-Beta zeolite samples prepared had obvious framework titanium characteristic absorption near 960cm -1 in the infrared spectrum of the framework vibration, and the framework titanium content index (I 960 / I 800 ) was 1.15, 1.14, 1.12, 1.12 and 1.16, respectively.

[0145] Example 4: This example is used to illustrate that the green process for mass production of Ti-Beta zeolite according to the local structure reconstruction 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, mainly through the local etching and reconstruction of the hydroxyl pockets of the dealuminated Beta zeolite by means of the combination of steam-assisted tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, can mass-produce Ti-Beta zeolite by replacing the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process with a combination of tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, while taking advantage of the pore condensate and zeolite solid surface liquid film generated by the dealuminated Beta zeolite in saturated steam to limit the amount of silicate dissolved, to more conveniently achieve controllable etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite, to achieve the purpose of mild etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite and improving the acceptance capacity of the hydroxyl pockets for larger titanium ions, 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 repair of local structural defects left after the mild etched hydroxyl pockets accept titanium ions (the present application). In the preparation of the hydrogel precursor, the amount of tetraethylammonium bromide (TEABr) template 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 reconstructing the Ti-Beta zeolite structure from amorphous fragmented structural units. In addition, both the TEABr template and the alcohol amine weak organic base are high-temperature stable and high-boiling-point organic substances, which are more resistant to high temperatures than TEAOH, allowing the preparation of dry gel intermediates to be carried out at higher temperatures by spray drying.

[0146] Example 1 was repeated, but in the second step, when preparing the hydrogel precursor for local structure reconstruction with dealuminated Beta zeolite, the TEABr / SiO2molar ratio (the number of moles of dealuminated Beta zeolite expressed in moles of SiO2) was changed to 0.05, 0.1, 0.2, 0.25, 0.4 and 0.5 in turn, and the amount of tetraethylammonium bromide (TEABr) was 1.79 Kg, 3.57 Kg, 7.14 Kg, 8.93 Kg, 14.29 Kg and 17.86 Kg in turn. On the basis of the above hydrogel precursor, the free water in the hydrogel precursor was removed by spray drying to convert it into a dry gel intermediate, and further Ti-Beta zeolite was prepared by steam-assisted local structure reconstruction of the dry gel intermediate. The Ti-Beta zeolite samples prepared had obvious framework titanium characteristic absorption near 960 cm -1 in the skeleton vibration infrared spectrum, and the skeleton titanium content index value (I 960 / I 800 ) fluctuated between 1.1 and 1.2.

[0147] Example 5: This example is used to illustrate that the green process for mass production of Ti-Beta zeolite according to the local structure reconstruction 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, mainly through the local etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite by means of the combination of steam-assisted tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, can mass-produce Ti-Beta zeolite by replacing the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process with the combination of tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, while taking advantage of the pore condensate and zeolite solid surface liquid film generated by the dealuminated Beta zeolite in saturated steam to limit the amount of dissolved silicate, more conveniently achieving controllable etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite, achieving the purpose of mild etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite and improving the acceptance capacity of the hydroxyl pockets for larger titanium ions, as well as avoiding the complete dissolution of the dealuminated Beta zeolite crystals into fragmented structural units (amorphous substances) by the strong alkaline TEAOH solution, thereby changing 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 etching and desilication of the hydroxyl pockets to accept titanium ions (the present application). Among them, the amount of diethanolamine weak organic base can be changed within a certain range when preparing the hydrogel precursor, 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, both the TEABr template and the alcohol amine weak organic base are high-temperature stable and high-boiling-point organic substances, which are more resistant to high temperatures than TEAOH, allowing the preparation of dry gel intermediates to be carried out at higher temperatures by spray drying.

[0148] Example 1 was repeated, but when preparing the hydrogel precursor for local structure reconstruction with dealuminated Beta zeolite in the second step, the diethanolamine / SiO2 molar ratio (expressed in moles of SiO2 as the moles of dealuminated Beta zeolite) was changed to 0.1, 0.2, 0.25, 0.4 and 0.5 in turn, and the amount of diethanolamine weak organic base was 1.79 Kg, 3.58 Kg, 4.47 Kg, 7.15 Kg and 8.94 Kg in turn. On the basis of the above hydrogel precursor, the free water in the hydrogel precursor was removed by spray drying to convert it into a dry gel intermediate, and Ti-Beta zeolite was further prepared by steam-assisted local structure reconstruction of the dry gel intermediate. The Ti-Beta zeolite samples prepared had a skeletal vibration infrared spectrum at 960 cm -1There are obvious skeleton titanium characteristic absorption peaks near 1,000 cm 960 / I 800 ) between 1.1 and 1.2.

[0149] Example 6: This example is used to illustrate that the green process for mass production of Ti-Beta zeolite according to the local structure reconstruction 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, mainly through the local etching and desilication of the hydroxyl pits of dealuminated Beta zeolite by the combination of steam-assisted tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, a green process for mass production of Ti-Beta zeolite, can replace the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process with the combination of tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, while taking advantage of the pore condensate and zeolite solid surface liquid film generated by dealuminated Beta zeolite in saturated steam to limit the amount of dissolved silicate, to more conveniently achieve controllable etching and desilication of the hydroxyl pits of dealuminated Beta zeolite, to achieve the purpose of mild etching and desilication of the hydroxyl pits of dealuminated Beta zeolite and improving the acceptance capacity of the hydroxyl pits for larger titanium ions, 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 repair of local structural defects left after the mild etched hydroxyl pits accept titanium ions (the present application). Among them, triethanolamine is allowed to be used as a weak organic base when preparing the hydrogel precursor 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, both TEABr template and alcohol amine weak organic base are high-thermal-stability and high-boiling-point organic substances, which are more resistant to high temperature than TEAOH, allowing the preparation of dry gel intermediates to be carried out at a higher temperature by spray drying.

[0150] Example 1 is repeated, but when preparing the hydrogel precursor for local structure reconstruction with dealuminated Beta zeolite in the second step, triethanolamine is used instead of diethanolamine as a weak organic base, and the amount of triethanolamine used is 7.61 Kg. On the basis of this hydrogel precursor, the free water in the hydrogel precursor is removed by spray drying to convert it into a dry gel intermediate, and Ti-Beta zeolite is further prepared by steam-assisted local structure reconstruction of the dry gel intermediate. The prepared Ti-Beta zeolite sample has skeleton vibration infrared spectrum peaks at 960 cm -1There is an obvious skeleton titanium characteristic absorption near the wave number, and the skeleton titanium content index value (I 960 / I 800 ) is 1.17.

[0151] Example 7: This example is used to illustrate that the green process for mass production of Ti-Beta zeolite according to the local structure reconstruction 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, mainly through the local etching and desilication of the hydroxyl pits of the dealuminated Beta zeolite by the combination of steam-assisted tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, a green process for mass production of Ti-Beta zeolite can be achieved by replacing the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process with a combination of tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, while taking advantage of the pore condensate and zeolite solid surface liquid film generated by the dealuminated Beta zeolite in saturated steam to limit the amount of silicate dissolved, to more conveniently achieve controllable etching and desilication of the hydroxyl pits of the dealuminated Beta zeolite, to achieve the purpose of mild etching and desilication of the hydroxyl pits of the dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl pits for larger titanium ions, 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 repair of local structural defects left after the mild etched hydroxyl pits accept titanium ions (the present application). Among them, the amount of deionized water can be changed within a certain range without changing the beneficial effects of the present application when preparing the hydrogel precursor. 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, both the TEABr template and the alcohol amine weak organic base are high-temperature stable and high-boiling-point organic substances, which are more resistant to high temperatures than TEAOH, allowing the preparation of dry gel intermediates to be carried out at higher temperatures by spray drying.

[0152] Example 1 was repeated, but in the second step, when preparing the hydrogel precursor for local structure reconstruction with dealuminated Beta zeolite, the H2O / SiO2 molar ratio (the number of moles of dealuminated Beta zeolite is expressed by the number of moles of SiO2) was changed to 3, 4, 8 and 10 in turn, and the amount of deionized water was 9.18 Kg, 12.24 Kg, 24.48 Kg and 30.6 Kg in turn. On the basis of the above hydrogel precursor, the free water in the hydrogel precursor was removed by spray drying to convert it into a dry gel intermediate, and Ti-Beta zeolite was further prepared by steam-assisted local structure reconstruction of the dry gel intermediate. The Ti-Beta zeolite samples prepared had obvious skeleton titanium characteristic absorption near 960 cm -1 in the skeleton vibration infrared spectrum, and the skeleton titanium content index value (I 960 / I 800 ) fluctuated between 1.1-1.2.

[0153] Example 8: This example is used to illustrate that the green process for mass production of Ti-Beta zeolite according to the local structure reconstruction 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, mainly through the local etching and reconstruction of the hydroxyl pockets of the dealuminated Beta zeolite by means of the combination of steam-assisted tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, can mass-produce Ti-Beta zeolite by replacing the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process with a combination of tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, while taking advantage of the pore condensate and zeolite solid surface liquid film generated by the dealuminated Beta zeolite in saturated steam to limit the amount of silicate dissolved, to more conveniently achieve controllable etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite, to achieve the purpose of mild etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite and improving the acceptance capacity of the hydroxyl pockets for larger titanium ions, as well as 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), 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 pockets accept titanium ions (the present application). Among them, different titanium sources can be used, the Si / Ti molar ratio can be changed within a certain range, and the stirring time can be changed 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, both the TEABr template and the alcohol amine weak organic base are high-temperature stable and high-boiling-point organic substances, which are more resistant to high temperatures than TEAOH, allowing the preparation of dry gel intermediates to be carried out by spray drying at a higher temperature.

[0154] Example 1 was repeated, but in the second step, when preparing the hydrogel precursor for local structure reconstruction of the dealuminated Beta zeolite, 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 successively, while the stirring time was changed to 12 h, 6 h, 4 h, 2 h and 0.5 h successively, and the titanium source used in preparing the above hydrogel precursor was changed to tetraethyl titanate, tetraisopropyl titanate, titanium acetylacetonate, a complex of tetrabutyl titanate and isopropanol with a molar ratio of 1:5 and a complex of tetraethyl titanate and isopropanol with a molar ratio of 1:8 successively. On the basis of the above hydrogel precursor, the free water in the hydrogel precursor was removed by spray drying to convert it into a dry gel intermediate, and further Ti-Beta zeolite was prepared by steam-assisted local structure reconstruction of the dry gel intermediate. The Ti-Beta zeolite samples prepared had obvious framework titanium characteristic absorption near 960 cm -1 in the infrared spectrum of the framework vibration, and the index value (I 960 / I 800 ) of the framework titanium content thereof varied between 0.85 and 1.2. Overall, as the Si / Ti molar ratio increased, the index value (I 960 / I 800 ) of the framework titanium content of the Ti-Beta zeolite samples tended to decrease.

[0155] Example 9: This example is used to illustrate that the green process for mass production of Ti-Beta zeolite according to the local structure reconstruction 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, mainly through the local etching and reconstruction of the hydroxyl pockets of the dealuminated Beta zeolite by means of the combination of steam-assisted tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, can mass-produce Ti-Beta zeolite by replacing the strong alkaline tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process with a combination of tetraethylammonium bromide (TEABr) template and alcohol amine weak organic base, while taking advantage of the pore condensate and zeolite solid surface liquid film generated by the dealuminated Beta zeolite in saturated steam to limit the amount of silicate dissolved, to more conveniently achieve controllable etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite, to achieve the purpose of mild etching and desilication of the hydroxyl pockets of the dealuminated Beta zeolite and improving the acceptance capacity of the hydroxyl pockets for larger titanium ions, as well as 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), 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 etching and desilication of the hydroxyl pockets to accept titanium ions (the present application). Among them, when preparing the hydrogel precursor, it is allowed to use Al-Beta zeolite raw materials with different silicon-aluminum ratios to prepare dealuminated Beta zeolite, and the Si / Ti molar ratio of the hydrogel precursor can be changed accordingly according to the number of hydroxyl pockets 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 reconstructing the Ti-Beta zeolite structure from amorphous fragmented structural units. In addition, both the TEABr template and the alcohol amine weak organic base are high-temperature stable and high-boiling-point organic substances, which are more resistant to high temperatures than TEAOH, allowing the preparation of dry gel intermediates to be carried out at higher temperatures by spray drying.

[0156] Example 1 was repeated, but in the first step of preparing dealuminated Beta zeolite from Al-Beta zeolite as raw material, Al-Beta zeolites with SiO2 / Al2O3 molar ratios 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 raw materials for preparing dealuminated Beta zeolite. After the above-synthesized Al-Beta zeolites were subjected to conventional filtration, washing, drying (110°C, 12h) and calcination to remove 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 increasing SiO2 / Al2O3 molar ratio; no any impurity crystal was found by XRD method, and the BET specific surface area calculated from the nitrogen physical adsorption data of the Al-Beta zeolites was all higher than 500 m2 / g; and the SiO2 / Al2O3 molar ratios of the Al-Beta zeolites measured by XRF were 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 Al-Beta zeolites were subjected to acid dealumination to prepare dealuminated Beta zeolite, and the SiO2 / Al2O3 molar ratios of the obtained dealuminated Beta zeolite were 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 dealuminated Beta zeolite from Al-Beta zeolite as raw material, Al-Beta zeolites with SiO2 / Al2O3 molar ratios 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 raw materials for preparing dealuminated Beta zeolite. After the above-synthesized Al-Beta zeolites were subjected to conventional filtration, washing, drying (110°C, 12h) and calcination to remove 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 increasing SiO2 / Al2O3 molar ratio; no any impurity crystal was found by XRD method, and the BET specific surface area calculated from the nitrogen physical adsorption data of the Al-Beta zeolites was all higher than 500 m2 / g; and the SiO2 / Al2O3 molar ratios of the Al-Beta zeolites measured by XRF were 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 Al-Beta zeolites were subjected to acid dealumination to prepare dealuminated Beta zeolite, and the SiO2 / Al2O3 molar ratios of the obtained dealuminated Beta zeolite were 751, 770, 870, 861, 855, 932, 1088 and 960, respectively, which met the technical requirements of the dealuminated Beta zeolite of the present application.

[0157] The above dealuminated Beta zeolite was used to prepare a hydrogel precursor, then the free water in the hydrogel precursor was removed by spray drying to convert it into a dry gel intermediate, and finally the Ti-Beta zeolite was prepared by further steam-assisted local structure reconstruction of the dry gel intermediate. In the preparation of the hydrogel precursor 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 hydroxyl pockets of the dealuminated Beta zeolite, i.e. in the order from low to high of the Si / Al 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 obvious framework titanium characteristic absorption at 960 cm -1 -1 of the infrared spectrum of the framework vibration, and the framework titanium content index value (I 960 / I 800 ) thereof varied between 0.8 and 1.5. Overall, with the increase of the Si / Ti molar ratio, the framework titanium content index value (I 960 / I 800 ) of the Ti-Beta zeolite samples showed a decreasing trend.

[0158] Example 10: 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.

[0159] 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, 5 mmol of hydrogen peroxide (35%) and 50 mg of Ti-Beta zeolite catalyst were added to the flask, and then the reaction was started under vigorous stirring at 333 K for 2 hours. 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 epoxy cyclohexane were calculated by the external standard method.

[0160] 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 31%, 22%, 44%, 43% in turn, and the selectivities of epoxy cyclohexane were 90%, 82%, 86%, 85% in turn.

Claims

1. A green process for mass production of Ti-Beta zeolite based on local structure reconstruction method, 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 Dealuminated Beta zeolite is prepared from Al-Beta zeolite by acid dealumination method, and the molar ratio of SiO2 to Al2O3 in the dealuminated Beta zeolite is required to be ≥ 700; Step 2: Preparation of hydrogel precursor for local structure reconstruction from dealuminated Beta zeolite Other raw materials for preparing the hydrogel precursor include: tetraethylammonium bromide (TEABr) template, alcohol amine weak organic base, titanium source and deionized water; The amount of dealuminated Beta zeolite is calculated based on SiO2, and the amount of other raw materials meets the following conditions: Molar ratio of TEABr to SiO2: 0.05-0.5; Molar ratio of alcohol amine to SiO2: 0.1-0.5; Molar ratio of H2O to SiO2: 3-10; Molar ratio of Si to Ti: 5-100; The alcohol amine weak organic base is diethanolamine or triethanolamine; The titanium source is tetrabutyl titanate, tetraethyl titanate, tetraisopropyl titanate or titanium acetylacetonate; The operation of preparing the hydrogel precursor can be carried out at room temperature; the specific steps are as follows: first, according to the amount of dealuminated Beta zeolite and the selected molar ratio of H2O to SiO2, molar ratio of alcohol amine to SiO2, molar ratio of Si to Ti and molar ratio of TEABr to SiO2, count the deionized water, alcohol amine, titanium source and TEABr template; then, under stirring, dissolve the TEABr template in water, and dissolve the titanium source in alcohol amine; finally, under stirring, add the TEABr template solution and dealuminated Beta zeolite to the weak alkaline solution containing alcohol amine and titanium source, and stir at room temperature; the stirring reaction time is 0.5-12h; Step 3: Removal of free water in the hydrogel precursor by spray drying to convert it into dry gel intermediate The spray drying is carried out at normal pressure; the total water content in the dry gel intermediate is required to be between 15-25wt%, and the decomposition or removal of TEABr and alcohol amine weak organic base during the drying process is prevented; Step 4: Preparation of Ti-Beta zeolite by steam-assisted local structure reconstruction of dry gel intermediate The reaction process of preparing Ti-Beta zeolite by steam-assisted local structure reconstruction of dry gel intermediate is carried out in an autoclave; the autoclave is provided with a support and a tray inside; the dry gel intermediate powder is placed on the tray, and the auxiliary steam is provided by vaporization of liquid water at the bottom of the autoclave; The parameters are as follows: The amount of liquid water at the bottom of the autoclave is calculated based on the mass ratio of H2O to dry gel intermediate, and the mass ratio of H2O to dry gel intermediate is in the range of 1.5-3; The reaction temperature for structure reconstruction is in the range of 120-170℃; The reaction time for structure reconstruction is in the range of 0.5-48h; Step 5: Post-treatment of Ti-Beta zeolite product After the reaction of steam-assisted local structure reconstruction of dry gel intermediate is completed, the Ti-Beta zeolite product is collected from the tray in the autoclave, and then it is dried and calcined to obtain the Ti-Beta zeolite product.

2. A green process for mass production of Ti-Beta zeolite based on local structure reconstruction method according to claim 1, characterized in that, In step (1), the molar ratio of silicon and aluminum oxides in Al-Beta zeolite, i.e., the molar ratio of SiO2 to Al2O3, is 20-200.

3. A green process for mass production of Ti-Beta zeolite based on local structure reconstruction method according to claim 2, characterized in that, In step (1), the molar ratio of silicon and aluminum oxides in Al-Beta zeolite, i.e., the molar ratio of SiO2 to Al2O3, is 25-60.

4. A green process for mass production of Ti-Beta zeolite based on local structure reconstruction method according to claim 1, characterized by, In step (2), the molar ratio of SiO2 to Al2O3 in the dealuminated Beta zeolite is ≥800.

5. A green process for mass production of Ti-Beta zeolite based on local structure reconstruction method according to claim 4, characterized in that, In step (2), the molar ratio of SiO2 to Al2O3 in the dealuminated Beta zeolite is ≥900.

6. A green process for mass production of Ti-Beta zeolite based on local structure reconstruction method according to claim 1, characterized by, In the second step, The molar ratio of TEABr to SiO2 is 0.1-0.

4. Molar ratio of alkanolamine to SiO2: 0.15-0.4; Molar ratio of H2O to SiO2: 4-8; Si to Ti molar ratio: 10-80; The titanium source is tetrabutyl titanate or tetraethyl titanate; The stirring reaction time ranges from 1 to 6 hours.

7. A green process for mass production of Ti-Beta zeolite based on local structure reconstruction method according to claim 6, characterized by, In the second step, The molar ratio of TEABr to SiO2 is 0.2-0.

3. Molar ratio of alkanolamine to SiO2: 0.2-0.3; Molar ratio of H2O to SiO2: 5-6; Si to Ti molar ratio: 15-50; The titanium source is tetrabutyl titanate. The stirring reaction time ranges from 2 to 4 hours.

8. A green process for mass production of Ti-Beta zeolite based on local structure reconstruction method according to claim 1, characterized by, In the fourth step, The amount of liquid water added to the bottom of the vessel is based on the mass ratio of H2O to the dry gel intermediate, and the range of the mass ratio of H2O to the dry gel intermediate is 1.8-2.

8. The reaction temperature range for structural reconstruction is 130-160℃; The reaction time range for structural reconstruction is 4-24 hours.

9. A green process for mass production of Ti-Beta zeolite based on local structure reconstruction method according to claim 8, characterized by, In the fourth step, The amount of liquid water added to the bottom of the vessel is based on the mass ratio of H2O to the dry gel intermediate, and the range of the mass ratio of H2O to the dry gel intermediate is 2.0-2.

5. The reaction temperature range for structural reconstruction is 135-150℃; The reaction time range for structural reconstruction is 6-18 hours.

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