Process for preparing Ti-Beta zeolite based on gas-phase transport method and recyclable organic base

Abstract

The invention belongs to the technical field of petrochemical catalysis, and relates to a Ti-Beta zeolite preparation process capable of recycling organic alkali based on a gas-phase transport method. The method is mainly technically characterized by comprising the following steps: providing water vapor and weak organic alkali to assist a tetraethylammonium bromide template agent by gas phase transmission, and carrying out in-situ local desiliconization etching and repair reconstruction on hydroxyl nests of dealuminated Beta zeolite to prepare the Ti-Beta zeolite. The method has the advantages that the tetraethylammonium bromide template agent is combined with the volatile weak organic base, and the dissolved amount of silicate is limited by the pore channel condensation liquid and the zeolite solid surface liquid film which are generated by dealuminizing the Beta zeolite in saturated steam, so that controllable etching and desilicication of the dealuminized Beta zeolite hydroxyl nest are easier, and the admitting ability of the hydroxyl nest to large-volume titanium ions is improved. Local structure defects generated by controllable etching desilicication can be repaired by directly using quaternary ammonium cations provided by a TEABr template agent as a guiding agent, so that the method does not need fluoride or / and aluminum source assistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of petrochemical catalysis, and relates to a preparation process of Ti-Beta zeolite capable of recycling organic base based on gas-phase transport method. Background Art

[0002] So far, Ti-Beta zeolite has been prepared by various methods, including traditional hydrothermal method, dry gel conversion method (steam-assisted), topotactic 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 hydrogel. Usually, 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 preparing Ti-Beta zeolite by the traditional hydrothermal method, there are not only problems in the treatment of fluoride-containing wastewater, but also problems of high energy consumption and low efficiency. In addition, the introduction of a small amount of aluminum source will inevitably result in framework aluminum in the Ti-Beta zeolite framework, and a post dealumination 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 from hydrogel, but first the hydrogel is dried at low temperature to form a dry gel, and then Ti-Beta zeolite is synthesized by the dry gel conversion method. Since the conversion process of the dry gel is not carried out in the aqueous phase, but in the vapor generated by the vaporization of water, it is called steam-assisted dry gel conversion method. For example, the public 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: Using aerosol silica as the silicon source, preparing the titanium source with tetrabutyl titanate, deionized water and hydrogen peroxide solution, and preparing the aluminum source with sodium aluminate, sodium hydroxide and tetraethylammonium hydroxide solution. First, the aluminum source solution is added to the titanium source solution under vigorous stirring, and then the silicon source is added to the mixture, and 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. 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 18 h. 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 still a small amount of aluminum source needs to be introduced for auxiliary synthesis.

[0005] The main technical feature of the transformation method is that Ti-Beta zeolite is transformed from a zeolite with a completely different topological structure. For example, the open literature Chem. Commun., 2019, 55, 14279 reported a transformation method for preparing Ti-Beta zeolite. In this method, a layered Ti-MWW zeolite was used as the raw material. The Ti-MWW zeolite provides both the silicon source and the titanium source for the preparation of Ti-Beta. The procedure is as follows: First, the Ti-MWW zeolite and the fully dealuminated Beta seed crystals are added to an alkaline solution for degradation 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 templating agent (tetraethyl cation) and a fluoride mineralizing agent; the open literature (Research on the Synthesis and Catalytic Properties of Heteroatom Zeolites with BEA and FAU Topological Structures [D]. East China Normal University, 2018) has a more detailed description of the transformation of Ti-MWW to Ti-Beta. Another example is that the open literature Microporous and Mesoporous Materials 311 (2021) 110702 also reported a transformation method for preparing Ti-Beta zeolite. In this method, a ultrastable Y zeolite (USY, Si / Al = 6.0) was used as the starting material. First, the USY was dealuminated with 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 was repeated at least 2 - 3 times to make the obtained dealuminated USY (USY-DA) have a Si / Al molar ratio of more than 500 (analyzed by ICP). In this method, USY-DA is only used as the silicon source. Then, a mixture solution with the composition of 1.0SiO2:0.02TiO2:0.4TEAOH:0.2CTAB:0.5NH4F:7.5H2O was prepared with USY-DA, dealuminated Beta zeolite seed crystals (Beta-DA, Si / Al molar ratio ≥ 1900, dosage 10 wt% based on USY-DA), titanium source (TBOT), pore-forming agent (CTAB), templating agent TEAOH, and NH4F, and crystallized at 140 °C for 3 days to obtain Ti-Beta zeolite. Generally speaking, the transformation method for preparing Ti-Beta zeolite takes less time and has high product quality. However, the transformation method cannot dispense with the use of fluoride mineralizing agents.

[0006] The main technical feature of the isomorphous substitution method is to prepare Ti-Beta zeolite with dealuminated Beta zeolite. Specifically, on the premise of not destroying the crystal structure of dealuminated Beta zeolite, by using tetravalent titanium ions (Ti 4+)The hydroxyl nests of dealuminated Beta zeolite are implanted to prepare Ti-Beta zeolite. The isomorphous substitution method can be divided into three technical routes: gas-solid, solid-solid, and liquid-solid isomorphous substitution methods.

[0007] The gas-solid isomorphous substitution method uses volatile TiCl4 as the titanium source. Through an inert gas (such as N2) carrying TiCl4 to contact with the dealuminated Beta zeolite, the isomorphous substitution reaction is carried out at high temperature. The main problems of this method are the large operation difficulty, easy generation of non-framework titanium, and poor repeatability of catalyst preparation. Therefore, later, the solid-solid isomorphous substitution method and the liquid-solid isomorphous substitution method were proposed as improved technical routes.

[0008] The solid-solid isomorphous substitution method generally uses titanium dichloride cyclopentadienyl solid powder as the titanium source for the isomorphous substitution reaction of dealuminated Beta zeolite. For example, the Chinese invention patent (application number 202111439797.1) discloses a method for preparing Ti-Beta zeolite by isomorphous substitution. Its technical features are as follows: First, the Beta zeolite is completely dealuminated to obtain all-silicon Si-Beta zeolite. Then, the Si-Beta zeolite is pretreated by dehydration and removal of miscellaneous gases. After that, the pretreated Si-Beta zeolite and titanium dichloride cyclopentadienyl solid powder are uniformly mixed in an inert gas environment. The mixed powder is transferred to a covered flat-bottom crucible and evenly spread as thinly as possible in the flat-bottom crucible. The covered crucible containing the mixed powder is transferred to a vacuum environment for heating, so that the Ti metal in the precursor in the crucible is uniformly impregnated and loaded into the framework of the Si-Beta zeolite to obtain Ti-Beta zeolite. In order to make the dealuminated Beta zeolite and titanium dichloride cyclopentadienyl solid powder mix evenly, it is generally necessary to use a ball mill to fully process the mixture of dealuminated Beta zeolite and titanium dichloride cyclopentadienyl. For example, the use of a ball mill is involved in the open literature 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 literatures also involve the preparation of Ti-Beta zeolite by the solid-solid isomorphous substitution method: Chinese invention patent (application number 202011450442.8); Chinese invention patent (application number 202010855082.3); open literature Chinese Journal of Catalysis 42(2021)1176–1184; open literature Microporous and Mesoporous Materials 330(2022)111625; open literature Microporousand 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, and generally requires the use of a glove box.

[0009] The liquid-solid isomorphous substitution method preferably uses an ethanol solution of TiCl4 as the titanium source to carry out an isomorphous substitution reaction with dealuminated Beta zeolite. For example, the public literature Ind. Eng. Chem. Res. 2021, 60, 1219-1230 has detailed records of this method, and the key points are as follows: (1) Contact Al-β zeolite with Si / Al = 11 with an aqueous solution of 13 mol / L HNO3 and react at 100 °C for 24 h to obtain dealuminated Beta zeolite; (2) The dealuminated Beta zeolite is pre-treated by drying (110 °C, 2 h) and calcination (550 °C, 3 h) before use. Prepare a TiCl4 solution as the titanium source with ethanol dried by 3A zeolite (dehydrated for more than 24 h). Then, contact the ethanol solution of TiCl4 with the dealuminated Beta zeolite (grind) and carry out an isomorphous substitution reaction at room temperature to obtain Ti-Beta zeolite. The post-treatment of the Ti-Beta zeolite prepared by the above liquid-solid isomorphous substitution method includes drying (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, there are also reports in the public literature (Wang Yanan. Preparation, Characterization and Application Research of Ionic Liquids in Catalytic Fuel Desulfurization [D]. Tianjin University, 2010, Zhang Juan. Preparation, Characterization and Performance Research of Photocatalytic Oxidation Diesel Desulfurization Catalysts [D]. Tianjin University, 2008, and Chemical Engineering, Vol. 40, No. 10, 2012) on the preparation of Ti-Beta zeolite by the liquid-solid isomorphous substitution method using titanium sulfate (Ti(SO4)2) as the titanium source. When using Ti(SO4)2 as the titanium source in these public literatures, the step of acid dealumination of the zeolite is omitted, and Ti-Beta zeolite is directly prepared by carrying out an isomorphous substitution reaction between Al-Beta zeolite and Ti(SO4)2 solution. This method is based on the characteristic that the strong acidity of the Ti(SO4)2 solution enables dealumination and titanium supplementation to occur simultaneously in the liquid-solid reaction. However, when using Ti(SO4)2 as the titanium source to carry out the liquid-solid isomorphous substitution reaction on Al-Beta zeolite, effective removal of the framework aluminum of Beta zeolite cannot be achieved, and thus the degree of isomorphous substitution reaction of Ti 4+ ions is limited.

[0011] In fact, in the above-mentioned gas-solid, solid-solid and liquid-solid isomorphous substitution methods, there are all problems of limited degree of isomorphous substitution reaction of Ti 4+ ions. This is because the radius of the tetravalent titanium ion (Ti 4+ ) is greater than the radius of the trivalent aluminum ion (Al 3+ ) Therefore, the hydroxyl nest vacancies generated after removing Al 3+ from the Al-Beta zeolite framework are relatively small, which is not conducive to Ti4+ Implantation.

[0012] Theoretically, the structure reconstruction method can avoid the problems of the isomorphous substitution method. Although the structure reconstruction method also uses dealuminated Beta zeolite to prepare Ti-Beta zeolite, the structure reconstruction process occurs in the presence of a strongly alkaline TEAOH templating agent solution. Existing research has shown that the strongly alkaline TEAOH templating agent solution can completely dissolve (fragment) and recrystallize (structure reconstruction) the dealuminated Beta zeolite framework, which helps larger Ti 4+ ions combine with the fragmented Beta zeolite structure building units, so that when the framework recrystallizes, with the assembly of the structure building units, they can more easily enter the framework of Beta zeolite.

[0013] The open literature Catal. Sci. Technol., 2019, DOI: 10.1039 / C9CY00071B. reported the method for the rapid synthesis of Ti-Beta by the structure reconstruction method. The technical key points are as follows: (1) First, commercially available Al-Beta zeolite is fully dealuminated with 13 mol / L -1 HNO3 solution (dealumination conditions: liquid-solid ratio 50 ml / g -1 , 140 °C, 24 h); (2) The dealuminated Beta zeolite is dried (120 °C) and calcined (550 °C, 6 h) for post-treatment to prepare dealuminated Beta zeolite (Beta-DA) with a Si / Al molar ratio > 1900; (3) Using Beta-DA as the silicon source, TEAOH solution as the templating agent, and TBOT as the Ti source, a colloidal solution is prepared; (4) The colloidal solution is dissolved at 140 °C for 1 h; (5) The colloidal solution after the dissolution treatment is quenched, and then NH4F is added to it at room temperature to assist the recrystallization process. The chemical composition of the colloid before recrystallization is 1SiO2: 1 / x TBOT: (0.3 - 0.5)TEAOH: (4 - 7.5)H2O: 0.1NH4F; (6) Recrystallization is carried out at 140 °C, and highly crystalline Ti-Beta zeolite can be obtained within 1 h.

[0014] The public literature Mater. Chem. Front., 2021, 5, 6101 also reported a similar method. The Si / Al molar ratio of the dealuminated Beta zeolite used was >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 was added to a strongly basic aqueous solution of TEAOH under stirring and stirred for 10 min. Then, TBOT was added dropwise thereto. Finally, NH4F was added to the mixture to obtain a colloidal solution with the composition of 1.0SiO2:xTEAOH:yTiO2:0.5NH4F:7.0H2O. The above gel solution was 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 public literatures are also related to the preparation of Ti-Beta zeolite by the structure reconstruction method: "Wang Bowen. Research on the Preparation and Catalytic Performance of MFI and BEA-Type Zeolites [D]. East China Normal University, 2021"; "You Qing. Preparation, Pore Multistaging and Catalytic Performance of Heteroatom Beta Zeolites [D]. Northwest University, 2021"; Microporous and Mesoporous Materials 330 (2022) 111625; "Ma Haikuo. Design and Synthesis of Heteroatom Zeolites with BEA Topology and Their Catalytic Performance [D]. Yantai University, 2022."; "Pan Huang. Synthesis, Post-treatment Modification and Epoxidation Performance of Titanium Silicate Zeolites [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 (first online published on January 27, 2022). Generally speaking, the structure reconstruction method is a Ti-Beta zeolite preparation method with relatively high industrial application value, and its main advantages are high framework titanium content, short preparation time and good preparation repeatability. However, the existing structure reconstruction method still needs to rely on the mineralization of a large amount of fluorides for assisted crystallization. The discharge of a large amount of high-fluoride wastewater is the main challenge for the industrial application of the existing structure reconstruction method. Summary of the Invention

[0016] The present invention provides a process for preparing Ti-Beta zeolite based on the gas-phase transport method with recyclable organic base.

[0017] In other words, the present invention provides a green process that does not involve the use of fluoride or / and aluminum source, uses vapor-phase transported water vapor and volatile weak organic base to assist tetraethylammonium bromide (TEABr) template agent to in-situ locally etch and desilicate the hydroxyl nests of dealuminated Beta zeolite and reconstruct the structure, can prepare a large amount of Ti-Beta zeolite and enable the reuse of the weak organic base. This process belongs to the in-situ local structure reconstruction method, that is, the local etching and desilication of the hydroxyl nests of dealuminated Beta zeolite by volatile weak organic base, the entry of titanium ions into the etched hydroxyl nests, and the recrystallization of TEA + The cation-directed silicate fragments recrystallize to repair the local structural defects left after the mildly etched hydroxyl nests accept titanium ions. The three reaction processes are carried out in-situ. This process has the following three most prominent technical features: (1) First, use titanium sulfate as the titanium source and tetraethylammonium bromide (TEABr) as the template agent to prepare an acidic aqueous solution containing titanium sulfate and tetraethylammonium bromide (TEABr), and perform equal-volume impregnation and drying treatment on dealuminated Beta zeolite to obtain the precursor of Ti-Beta zeolite; (2) The in-situ local structure reconstruction process of the Ti-Beta zeolite precursor is carried out in an autoclave. The water vapor and volatile organic base transported by vapor phase contact the precursor to assist tetraethylammonium bromide (TEABr) to achieve in-situ local etching and desilication and structure reconstruction reactions. The water vapor and volatile organic base are provided by the bottom liquid that does not directly contact the precursor of Ti-Beta zeolite; (4) After the preparation of Ti-Beta zeolite is completed, the volatile organic base can be redissolved in the bottom liquid by cooling the autoclave for recycling.

[0018] The fundamental difference between the present invention and the existing process for preparing Ti-Beta zeolite by structure reconstruction method is that the starting point of its structure reconstruction is not the fragmented structural units generated after the complete dissolution of the dealuminated Beta zeolite crystals (long-range disorder, no characteristic diffraction peaks of Beta zeolite in the XRD pattern), but the whole dealuminated Beta zeolite crystal with good long-range order of the Beta zeolite structure although the hydroxyl nests are mildly etched and desilicated by the volatile weak organic base (with complete characteristic diffraction peaks in the XRD pattern). Therefore, the structure reconstruction of the present invention belongs to local structure reconstruction. In addition, the present invention uses the combination of tetraethylammonium bromide (TEABr) template agent and volatile weak organic base to replace the strong basic tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process. This not only helps to reduce the manufacturing cost of Ti-Beta zeolite, but also uses the flexibility of the combination of the template agent and the weak organic base to unlock the TEA + cation part that acts as a structure-directing agent (SDA) and the OH -The 1:1 proportional relationship of the anionic part makes it easy to mildly desilicate and etch the hydroxyl nests of dealuminated Beta zeolite under weak alkalinity and also easy to accelerate the structure reconstruction reaction with a sufficient amount of structure-directing agent. In particular, when preparing the Ti-Beta zeolite precursor from dealuminated Beta zeolite in the present invention, the equal-volume impregnation method with an acidic aqueous solution containing titanium sulfate and TEABr template agent is adopted. The prepared precursor has a low water content and does not contain colloidal substances. Since tetraethylammonium bromide (TEABr) in the precursor has relatively high thermal stability, when drying the Ti-Beta zeolite precursor, conventional drying methods can be used, with a fast drying speed, avoiding the drying troubles encountered when preparing a dry gel intermediate using a hydrogel precursor. Moreover, since no weak organic base is introduced in the preparation of the Ti-Beta zeolite precursor in the present invention, instead, the volatile weak organic base is added in the form of an aqueous solution to the bottom of the autoclave. Only in the process of preparing Ti-Beta zeolite from the Ti-Beta precursor, the volatile weak organic base can contact the Ti-Beta zeolite precursor on the tray inside the autoclave in the form of gas-phase transport (vaporizing with water from the bottom liquid). Therefore, in the preparation stage of the Ti-Beta zeolite precursor, the hydroxyl nests of dealuminated Beta zeolite have not yet been mildly desilicated and etched by the volatile organic base. The mild etching and desilication of the hydroxyl nests of dealuminated Beta zeolite by the volatile organic base only occur in the process of preparing Ti-Beta zeolite from the Ti-Beta precursor. In this process, the local etching and desilication of the hydroxyl nests of dealuminated Beta zeolite by the volatile weak organic base, the entry of titanium ions into the etched hydroxyl nests, and the recrystallization of the TEAl + cation-directed silicate fragments to repair the local structural defects left after the etched hydroxyl nests accept titanium ions are carried out in situ. This is a unique feature of the present invention. Another unique feature of the present invention is that the use of the volatile organic base is not a one-time use, but most of it can be recycled and reused. In each use, the consumed part of the volatile organic base is only the dissolved part by the liquid film with a limited thickness on the crystal surface of the Ti-Beta zeolite product and the capillary condensed liquid with a limited total amount inside its pores. In short, the Ti-Beta zeolite preparation process provided by the present invention has a simple method, low cost, is suitable for large-scale preparation, and thus has higher practical value.

[0019] It was found in the research that because the process provided by the present invention does not involve establishing the crystal structure of Beta zeolite from scratch (i.e., does not involve the crystal growth of Beta zeolite), but only involves the repair of local structural defects left after titanium ions are accepted by the mildly etched hydroxyl nests, the process provided by the present invention can, without the assistance of fluoride or / and aluminum source, start from dealuminated Beta zeolite and carry out in-situ local desilication etching and structural reconstruction by gas-phase transporting water vapor and volatile organic base to assist tetraethylammonium bromide (TEABr), so as to prepare high-quality Ti-Beta zeolite with high framework titanium content and less non-framework titanium.

[0020] It was also found in the research that the gas-phase transport technical route adopted by the present invention not only provides a weak organic base for the in-situ local mild desilication etching of the hydroxyl nests of dealuminated Beta zeolite, but also provides important water vapor assistance for the in-situ local mild desilication etching of the hydroxyl nests of dealuminated Beta zeolite and the subsequent recrystallization of silicate fragments directed by TEA + cation to repair the local structural defects left after titanium ions are accepted by the mildly etched hydroxyl nests. The benefits of water vapor assistance include: (1) It is beneficial to avoid excessive desilication etching of the hydroxyl nests of dealuminated Beta zeolite by organic base. Those skilled in the art know that there is a chemical equilibrium in the dissolution of silicate solids in alkaline solutions. However, the larger the solution volume, the more silicate solids are consumed when reaching the equilibrium state. This means that when the feeding amount of silicate solids (such as dealuminated Beta zeolite) is fixed, the larger the volume of the alkali solution, the greater the dissolution degree of silicate solids (such as dealuminated Beta zeolite). However, for the present invention, since what contacts the silicate solids is steam and the silicate fragments are non-volatile, the dissolution equilibrium of silicate only involves the liquid film with a limited thickness on the surface of dealuminated Beta zeolite and the liquid water filled in its pores due to capillary condensation. Since the thickness of the liquid film on the solid surface and the pore volume of the zeolite are limited, that is, the total amount of liquid is limited, the silicate fragments that can be dissolved by the liquid water condensed in the liquid film and pores are also limited; (2) It is beneficial to increase the rate of the recrystallization reaction of silicate fragments directed by TEA + cation. That is, it is beneficial to minimize the time for preparing Ti-Beta zeolite by the local structure reconstruction method. This is mainly because under the conditions of gas-phase transporting water vapor and volatile weak organic base to assist local structure reconstruction, TEABr template molecules, volatile weak organic base molecules and soluble Beta zeolite structure units generated by mild etching of hydroxyl nests are all concentrated in the surface liquid film and the condensed liquid in the pores.

[0021] The present invention also has an essential difference from the existing process for preparing Ti-Beta zeolite by the dry gel conversion method. Although both methods involve steam assistance on the surface, the latter has to go through the crystallization process of amorphous dry gel. During the dry gel crystallization process assisted by steam, although it can sometimes be carried out without the addition of fluoride additives, the addition of an aluminum source is required to assist the crystallization of amorphous dry gel in the absence of fluoride mineralizer. Therefore, it is difficult to obtain high-performance Ti-Beta zeolite by the existing dry gel conversion method.

[0022] It should be particularly emphasized that the process for preparing Ti-Beta zeolite based on the gas-phase transport method with recyclable organic base provided by the present invention is not a simple combination of the existing dry gel conversion method and the structure reconstruction method. The innovation and advancement of the present invention lie in: First, the present invention uses the combination of tetraethylammonium bromide (TEABr) template and volatile weak organic base to replace the strongly basic tetraethylammonium hydroxide (TEAOH) template used in the existing preparation process. At the same time, by means of the pore condensate generated by dealuminating Beta zeolite in saturated steam and the liquid film on the surface of zeolite solid to limit the dissolution amount of silicate, it is easier to achieve the controllable etching and desilication of the hydroxyl nests of dealuminated Beta zeolite, improve the acceptance ability of the hydroxyl nests for larger titanium ions, 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 local structural defects generated by the controllable etching and desilication can be directly repaired quickly in the weakly basic environment generated by the volatile weak organic base with the TEA + cationic structure-directing agent (SDA) ionized by the TEABr template in the solution, completely getting rid of the trouble brought by the need to add fluoride or / and aluminum source for assisting structure reconstruction in the existing process due to the need to start from amorphous silicate fragments for the structure reconstruction of Beta zeolite. In addition, in the present invention, Ti-Beta zeolite is prepared by in-situ local construction and reconstruction from its precursor. The precursor is prepared by equal-volume impregnation of dealuminated Beta zeolite with an acidic aqueous solution of titanium sulfate and TEABr template. The water content in the Ti-Beta zeolite precursor is low and it does not contain colloidal substances. Therefore, only simple drying treatment is required during the preparation of the Ti-Beta zeolite precursor, with fast drying speed and reduced severity of the drying temperature range, suitable for large-scale preparation, and avoiding the drying trouble encountered when using hydrogel precursor to prepare dry gel intermediate. Moreover, in the present invention, the use of volatile organic base is not disposable, but most of it can be recycled and reused. In short, the process for preparing Ti-Beta zeolite provided by the present invention has the advantages of simple method, low cost, suitable for large-scale preparation, and thus higher practical value.

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

[0024] A preparation process of Ti-Beta zeolite capable of recycling organic base based on gas-phase transport method, the steps are as follows:

[0025] The first step: Prepare dealuminated Beta zeolite using Al-Beta zeolite as raw material

[0026] Engineers familiar with this field can, according to the requirements of the present invention, combine their own work experience and refer to the conventional acid dealumination methods in relevant literatures to prepare dealuminated Beta zeolite using Al-Beta zeolite as raw material. The requirements of the present invention are as follows:

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

[0028] The described Al-Beta zeolite refers to silica-alumina Beta zeolite. The present invention has no limitation on the crystal grain size of Al-Beta zeolite, nor on the production process of Al-Beta zeolite. However, in order to facilitate the implementation effect of the present invention, there are the following limitations on Al-Beta zeolite: 1) There are no impurity crystals in Al-Beta zeolite; 2) The crystallization of Al-Beta zeolite is good; 3) The molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) in Al-Beta zeolite is appropriate.

[0029] Among them, whether there are impurity crystals in Al-Beta zeolite can be checked and confirmed by X-ray powder diffraction (XRD) method. People familiar with this field know that the molar ratio of SiO2 to Al2O3 of Al-Beta zeolite produced by hydrothermal synthesis method is usually between 10 and 200 (US3 308 069 (1967)). In Al-Beta zeolite products with a lower molar ratio of SiO2 to Al2O3, there may generally be mordenite (MOR) impurity crystals, while in Al-Beta zeolite with a higher molar ratio of SiO2 to Al2O3, there may generally be ZSM-5 zeolite impurity crystals. By sampling 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 judged 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 Al-Beta zeolite is a pure Beta zeolite phase.

[0030] In theory, the crystallization of Al-Beta zeolite can also be analyzed by XRD and measured by the relative crystallinity index. However, considering that the XRD relative crystallinity index needs to be obtained by comparing the sum of the intensities of the medium-intensity characteristic diffraction peaks of Al-Beta zeolite between 2θ = 7.6 - 8° and the highest-intensity characteristic diffraction peaks between 2θ = 22 - 23° with the sum of the intensities of the corresponding diffraction peaks of the reference sample (standard Beta zeolite with a crystallinity of 100%), and the reference sample has no unified definition; and considering that the intensities of the medium-intensity characteristic diffraction peaks of Al-Beta zeolite between 2θ = 7.6 - 8° and the highest-intensity characteristic diffraction peaks between 2θ = 22 - 23° are greatly affected by the processes and conditions of post-processing such as calcination. Therefore, using the XRD relative crystallinity index to determine whether the crystallization of the purchased or synthesized Al-Beta zeolite is good has poor universality. For this reason, the present invention recommends using the specific surface area index of Al-Beta zeolite to measure whether the crystallization of the purchased or synthesized Al-Beta zeolite meets the requirements. According to the 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 450m 2 / g. Engineers familiar with the art can use the conventional nitrogen physical adsorption method to first measure the nitrogen adsorption isotherm data of Al-Beta zeolite, and then calculate its BET specific surface area value according to the BET model. In short, the present invention requires that the BET specific surface area value of the used Al-Beta zeolite ≧ 450m 2 / g, indicating that its crystallization is good.

[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 in Al-Beta zeolite, that is, the higher the content of framework aluminum, the more the number of hydroxyl nests in dealuminated Beta zeolite, and the more the number of titanium ions that may be introduced into the framework during the steam-assisted local structure reconstruction process, which is beneficial to the preparation of Ti-Beta zeolite with a low Si / Ti ratio; on the other hand, it is more difficult to synthesize pure-phase Al-Beta zeolite with a very low molar ratio of SiO2 to Al2O3 by the hydrothermal method. Therefore, the suitable range of the molar ratio of SiO2 to Al2O3 of Al-Beta zeolite required by the present invention is between 10 - 200, the preferred range is between 20 - 100, and the more preferred range is between 25 - 60.

[0032] The molar ratio analysis of SiO2 and Al2O3 in Al-Beta zeolite can be carried out by traditional chemical analysis methods (titration method), or by X-ray fluorescence spectroscopy (XRF) method or inductively coupled plasma emission spectroscopy (ICP) method. The present invention recommends using the simple and rapid XRF method.

[0033] The Al-Beta zeolite meeting the requirements of the present invention can be obtained through commercial channels or synthesized by oneself. Engineers familiar with this field can also synthesize the Al-Beta zeolite meeting the requirements of the present invention according to their own experience and other literature reports.If synthesizing Al-Beta zeolite by oneself, the methods reported in the following invention patents and public documents can be selected: US3 308 069 (1967), EP187 522A2 (1986), US4 847 055 (1989), CN1 086 792A (filing date: September 20, 1993), CN1 108 213A (filing date: March 11, 1994), CN1 108 214A (filing date: March 11, 1994), CN1154 341A (filing date: January 11, 1996), CN1 154 242A (filing date: January 9, 1996), CN1 154 342A (filing date: January 11, 1996), CN1 268 545A (filing date: March 30, 1999), CN1 133 497C (filing date: March 30, 1999), CN1108 275C (filing date: September 10, 1999), CN1 100 004C (filing date: May 19, 2000), CN1 335 258A (filing date: February 28, 2001), CN1 116 227C (filing date: March 12, 2001), CN101 205 072B (filing date: December 18, 2006), 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) DOI10.1002 / 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 described above, to prepare dealuminated Beta zeolite based on Al-Beta zeolite, conventional acid dealumination methods can be used. The present invention requires that the molar ratio of SiO2 to Al2O3 of the dealuminated Beta zeolite be as high as possible, that is, all the framework aluminum in the Al-Beta zeolite should be removed as much as possible. For the dealuminated Beta zeolite meeting the requirements of the present invention, the suitable range of the molar ratio of SiO2 to Al2O3 is ≥700, the preferred range is ≥800, and the more preferred range is ≥900.

[0036] Since the molar ratio of SiO2 to Al2O3 of the dealuminated Beta zeolite is very high and the aluminum content is very low, the inductively coupled plasma emission spectrometry (ICP) method or atomic absorption (AA) method is required to accurately determine its molar ratio of SiO2 to Al2O3. The ICP method is recommended in the present invention.

[0037] When performing acid dealumination treatment on Al-Beta zeolite, efforts should be made to remove all the framework aluminum. The harm of excessive residual framework aluminum on the dealuminated Beta zeolite is that the strong acidity of the framework aluminum will significantly reduce the selectivity of Ti-Beta zeolite (more precisely, Ti-Al-Beta zeolite) as an oxidation reaction catalyst and weaken the advantages of the structure reconstruction method in preparing high-performance Ti-Beta zeolite.

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

[0039] Engineers familiar with the art can, based on their own experience or referring to the specific methods disclosed in the following literature, perform acid dealumination treatment on Al-Beta zeolite with an aqueous solution of concentrated nitric acid to prepare dealuminated Beta zeolite meeting the requirements of the present invention: Chemical Communications, 1998, 1: 87-88; Micropor. Mesopor. Mater., 1999, 31: 163-173; Micropor. Mesopor. Mater., 2001, 49: 103–109; Micropor. Mesopor. Mater., 2008, 110: 480–487; Micropor. Mesopor. Mater., 2012, 163: 122-130; ACS Catalysis, 2014, 4(8): 2801-2810. When using an aqueous solution of concentrated nitric acid to perform acid dealumination on Al-Beta zeolite to prepare dealuminated Beta zeolite, the concentration of the nitric acid aqueous solution, the ratio of the acid solution to the zeolite (liquid-solid ratio), and the temperature and time of the acid treatment are all important factors affecting the degree of acid dealumination of Al-Beta zeolite. The influence of the above factors on the dealumination of Al-Beta zeolite is ultimately reflected in the residual aluminum content of the dealuminated Beta zeolite. However, if the dealuminated Beta zeolite with a molar ratio of SiO2 to Al2O3 meeting the requirements cannot be obtained after one-time dealumination, it is entirely possible to make the molar ratio of SiO2 to Al2O3 of the dealuminated Beta zeolite meet the requirements of the present invention through secondary or even multiple supplementary dealuminations. The present invention recommends using 13M concentrated nitric acid as the dealumination acid solution and using the acid solution amount according to a liquid-solid ratio of 20:1 (ml / g). On this premise, the dealumination reaction is carried out at 95 °C for 20 h; after the dealumination reaction, the solid product is first recovered by solid-liquid separation, then the solid product is washed with water until the pH value is neutral, and then dried at a temperature of 80-200 °C for 3-24 h and calcined at a temperature of 500 °C - 600 °C for 3-8 h to obtain dealuminated Beta zeolite. After the dealumination of Al-Beta zeolite, due to the formation of a large number of hydroxyl nest lattice defect sites, its water absorption and moisture absorption capacity is stronger, and it should be sealed and stored for standby.

[0040] Step 2: Prepare the precursor for the in-situ local structure reconstruction method for preparing Ti-Beta zeolite by the equal-volume impregnation method

[0041] The Ti-Beta zeolite precursor described in the present invention refers to the product obtained by impregnating dealuminated Beta zeolite with an acidic aqueous solution containing tetraethylammonium bromide (TEABr) templating agent and titanium sulfate (Ti(SO4)2) in an equal volume, and then drying to remove the free water in the wet material. It should be emphasized that the purpose of the drying treatment is mainly to remove most of the free water in the impregnated wet material of the Ti-Beta zeolite precursor, but it cannot significantly change the content, structure and physical and chemical properties of the organic matter (TEABr templating agent) in the Ti-Beta zeolite precursor.

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

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

[0044] The present invention requires that when preparing the precursor of Ti-Beta zeolite by the equal-volume impregnation method, it can be carried out at room temperature; the dosages of tetraethylammonium bromide (TEABr) templating agent and titanium sulfate, the impregnation time and the drying conditions of the wet precursor material need to meet the following conditions:

[0045] Based on the dosage of dealuminated Beta zeolite in terms of SiO2, the dosages of other impregnation raw materials and the impregnation conditions are as follows:

[0046] The molar ratio of TEABr to SiO2: The suitable range is 0.05 - 0.5; the preferred range is 0.1 - 0.4; the more preferred range is 0.2 - 0.3.

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

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

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

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

[0051] The TEABr template agent can ionize to produce TEA + cations in aqueous solution. We found in the research that the TEA + cations generated by the ionization of the TEABr template agent in aqueous solution can, like the TEA + cations ionized from the TEAOH template agent solution, play the role of a structure - directing agent (SDA) in the final stage of preparing Ti - Beta zeolite, that is, in the later stage of the process of using gas - phase - transported water vapor and volatile weak organic bases to assist in local structure reconstruction, which is the process of repairing the local structural defects left after the slightly etched hydroxyl nests accept titanium ions. Engineers familiar with this 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 effects in aqueous solution. However, the problem is that tetraethylammonium fluoride will cause fluorine - containing wastewater; the price of tetraethylammonium iodide is relatively expensive and the I - ions have poor stability; tetraethylammonium chloride is not as cheap and easily available as tetraethylammonium bromide. Therefore, based on comprehensive consideration of the above factors, the present invention selects tetraethylammonium bromide as the template agent.

[0052] The silicon-titanium ratio of the Ti-Beta zeolite precursor, i.e., the Si / Ti molar ratio, determines the silicon-titanium ratio of the Ti-Beta zeolite prepared by the method of the present invention. According to the principle of the present invention, the titanium sulfate introduced when preparing the Ti-Beta zeolite precursor will release titanium ions when the local structure is reconstructed by gas-phase transmission of water vapor and volatile weak organic bases, and the latter enters the slightly etched dealuminated Beta zeolite hydroxyl pits, thereby converting the dealuminated Beta zeolite into Ti-Beta zeolite. Therefore, the maximum amount of titanium source used when preparing the Ti-Beta zeolite precursor can be estimated by the number of hydroxyl pits of the dealuminated Beta zeolite, or directly estimated by the silicon-aluminum ratio (SiO2 / Al2O3) of the Al-Beta zeolite raw material. For example, the lowest Si / Ti ratio of the Ti-Beta zeolite that can be prepared by using the dealuminated Beta zeolite prepared by the Al-Beta zeolite raw material with a SiO2 / Al2O3 ratio of 30 is 15. Therefore, when preparing a Ti-Beta zeolite precursor, the maximum amount of titanium source used should make the Si / Ti ratio of the precursor ≮15, otherwise excessive titanium source use will lead to an increase in non-framework titanium in the Ti-Beta zeolite product. Generally speaking, a framework titanium content in titanium silicalite is beneficial to the catalytic reaction within an appropriate range. On the one hand, a too low framework titanium content of titanium silicalite (i.e., the Si / Ti molar ratio is too high) is not conducive to catalyst activity, and the reason is needless to elaborate. On the other hand, a too high framework titanium content of titanium silicalite (i.e., the Si / Ti ratio is too low) is also not beneficial to increasing catalytic activity. This is because, in this case, diffusion control within the zeolite micropores 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 in the present invention.

[0053] Step 3: Prepare Ti-Beta zeolite by in-situ local structural reconstruction of Ti-Beta zeolite precursor using gas phase transport method

[0054] The reaction process of preparing Ti-Beta zeolite by in-situ local structural reconstruction is carried out in an autoclave. A bracket and a tray are provided inside the autoclave. The dried Ti-Beta zeolite precursor is placed on the tray, and the water vapor and volatile weak organic base used for gas phase transmission are provided by the vaporization of the aqueous solution at the bottom of the autoclave under the tray. The organic base is n-butylamine. The reason why the present invention chooses n-butylamine as the volatile weak organic base is mainly because it has a relatively suitable boiling point (77.8°C), is not only cheap and easy to obtain, but also easy to vaporize and recover, and is easy to operate. Other small molecular fatty amines such as methylamine, ethylamine, etc. are not suitable for selection. The main problem is that the boiling point is too low and the volatility is too high, which is not good for the working environment.

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

[0056] The addition amount of the liquid water at the bottom of the autoclave is based on the mass ratio of the liquid water at the bottom of the autoclave to the precursor (W H2O / W 前驱体 ratio). The suitable range of the mass ratio of the liquid water at the bottom of the autoclave to the precursor is: 1.5 - 3; the preferred range is: 1.8 - 2.8; the more preferred range is: 2.0 - 2.5.

[0057] The dosage of the weakly volatile organic base is based on the mass percentage concentration of the organic base in the aqueous solution. The suitable range of the percentage concentration of the organic base in the aqueous solution is: 10 - 60%; the preferred range is: 20 - 50%; the more preferred range is: 30 - 40%.

[0058] The suitable range of the reaction temperature for the structure reconstruction is: 120 - 170 °C; the preferred range is: 130 - 160 °C; the more preferred range is: 135 - 150 °C.

[0059] The suitable range of the reaction time for the structure reconstruction is: 0.5 - 48 h; the preferred range is: 4 - 24 h; the more preferred range is: 6 - 18 h.

[0060] The selection of the above condition ranges is to meet the requirements of the reaction for in-situ local structure reconstruction of Ti-Beta zeolite by the gas-phase transport method. To enable engineers in the field to better understand the selection of the above condition ranges made in the present invention, the reaction process for in-situ local structure reconstruction of Ti-Beta zeolite by the gas-phase transport method is described as follows:

[0061] In the initial stage of the in-situ local structure reconstruction process, that is, during the heating stage of the autoclave, as the temperature inside the autoclave gradually rises, more and more liquid water at the bottom of the autoclave and the weakly volatile organic base turn into vapor, and the vapor pressure inside the autoclave continuously rises accordingly. As a result, the dry gel intermediate powder above the tray obtains a correspondingly higher water content and weakly volatile organic base content due to the infiltration of more and more water vapor and weakly volatile organic base. During this process, the dealuminated Beta zeolite, TEABr template agent, and weakly organic base in the Ti-Beta zeolite precursor will undergo the following changes: First, 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 surface of the zeolite will develop from a monolayer to a multilayer of water molecule adsorption, eventually forming a liquid film with a certain thickness. Second, for the TEABr template agent molecules originally in the dehydrated state in the precursor, their main change is to redissolve in water and ionize TEA + cations. In addition, the weakly volatile organic base transported into the Ti-Beta zeolite precursor through the gas phase will dissolve in the capillary condensed liquid in the zeolite pores and the water film on the zeolite surface, and hydrolyze to produce alkalinity (R-NH2 + H2O → R-NH3 + + OH -), thus turning the capillary condensed liquid in the zeolite channels and the water film on the zeolite surface into a weakly basic solution containing TEA + The weakly basic solution that permeates both inside and outside the channels of dealuminated Beta zeolite will inevitably undergo an etching and desilication reaction with the hydroxyl nests of dealuminated Beta zeolite, resulting in mild etching of the hydroxyl nests and the production of silicate fragments (soluble Beta zeolite structure units) that dissolve in the weakly basic solution permeating both inside and outside the channels of dealuminated Beta zeolite. As the concentration of silicate fragments (soluble Beta zeolite structure units) dissolved in the weakly basic solution permeating both inside and outside the channels of dealuminated Beta zeolite increases, the further etching and desilication reaction of the weakly basic solution on the hydroxyl nests of dealuminated Beta zeolite is retarded.

[0062] When the temperature of the autoclave rises high enough to carry out the structure reconstruction reaction (recrystallization reaction), the concentration of silicate fragments (soluble Beta zeolite structure units) dissolved in the weakly basic solution permeating both inside and outside the channels of dealuminated Beta zeolite will also reach the highest point - the chemical equilibrium concentration. At this time, the etching and desilication reaction of the weakly basic solution produced by the weak organic base in the precursor on the hydroxyl nests of dealuminated Beta zeolite is inhibited, and the entire closed system enters the later stage of the in-situ local structure reconstruction process. The main features of this stage are: First, the titanium ions released from the titanium source in the precursor begin to enter the etched hydroxyl nests of dealuminated Beta zeolite. The etched hydroxyl nests have an increased volume due to mild desilication, improving their ability to accommodate larger titanium ions. For this reason, the process for preparing Ti-Beta zeolite by the vapor transport of water vapor and volatile weak organic base local structure reconstruction method provided by the present invention has the characteristic of a high framework titanium content. Then, the silicate fragments (soluble Beta zeolite structure units) dissolved and concentrated in the weakly basic solution with a limited total liquid volume permeating both inside and outside the channels of dealuminated Beta zeolite, under the action of TEA + cations with a structure-directing effect (SDA), quickly carry out a local structure reconstruction reaction (recrystallization reaction) at the local structural defect sites left after the hydroxyl nests of dealuminated Beta zeolite accept titanium ions to repair the structural defects.

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

[0064] According to the saturated vapor pressure of water vapor, when the temperatures inside the autoclave are 120 °C, 130 °C, 140 °C, 150 °C, 160 °C and 170 °C respectively, the saturated water vapor pressures generated by the liquid water added to the bottom of the autoclave are 198.5 kPa, 247.5 kPa, 295.0 kPa, 355.1 kPa, 431.3 kPa and 517.8 kPa in sequence. Regarding the saturated water vapor inside the autoclave as an ideal gas approximately, when the volume of the autoclave is V (unit: m 3 ) and is filled with saturated water vapor at 120 °C, 130 °C, 140 °C, 150 °C, 160 °C and 170 °C, the reduced masses of water vapor (unit: Kg) are approximately 1.1V, 1.3V, 1.6V, 1.8V, 2.2V and 2.5V in sequence.

[0065] Taking the preparation of Ti-Beta zeolite by in-situ local structure reconstruction reaction by vapor-phase transport method at 140 °C as an example, in order to enable the formation of a vapor-liquid two-phase inside the autoclave at the structure reconstruction reaction temperature of 140 °C, the estimated minimum amount of water to be introduced in advance to the bottom of the autoclave is: 1.6V + 1.2W. Among them, 1.2 is the saturated water absorption rate of typical dealuminated Beta zeolite, and W is the weight of the Ti-Beta zeolite precursor. For a laboratory small autoclave with a volume of 100 ml, assuming the addition amount of the Ti-Beta zeolite precursor is 10 g (0.01 Kg), in order to enable the formation of a vapor-liquid two-phase inside the small autoclave at the structure reconstruction reaction temperature of 140 °C, the estimated minimum value of the amount of water to be introduced in advance to the bottom of the autoclave is 12.16 g (1.6V = 1.6×1×10 -4 Kg = 0.16 g; 1.2W = 1.2×10×10 -3Kg = 12 g). Therefore, theoretically, as long as more than 12.16 g of liquid water is added in advance to the bottom of the small autoclave, and 10 g of Ti-Beta zeolite precursor is added to the tray above the support, Ti-Beta zeolite can be prepared by in-situ local structure reconstruction reaction using the vapor transport method at 140 °C. Of course, in actual work, the threshold value of the bottom liquid volume that should 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 (the height of the support and the size of the tray), and the single autoclave production requirement of Ti-Beta zeolite. Therefore, for the convenience of engineers in this field, the present invention finally recommends using W H2O / W 沸石前驱体 The ratio of 1.5 - 3 is used as the appropriate range of the bottom liquid usage amount in the stage of preparing Ti-Beta zeolite by in-situ local structure reconstruction reaction using the vapor transport method.

[0066] After the in-situ local structure reconstruction reaction is completed, the autoclave is cooled and depressurized in accordance with the usual practice of conventional hydrothermal synthesis of zeolite molecular sieves. When the temperature and pressure in the autoclave approach the ambient temperature and pressure, the autoclave is opened, the Ti-Beta zeolite product is taken out, and after the volume and concentration of the bottom liquid are measured, it is recycled.

[0067] Step 4: Post-treatment of the Ti-Beta zeolite product

[0068] The Ti-Beta zeolite product prepared by the method of the present invention does not require post-treatment of defluorination and dealumination, and only needs to be subjected to conventional water washing, drying, and calcination treatments to obtain the Ti-Beta zeolite product. Among them, the purpose of water washing is to remove a small amount of sulfate radicals introduced by the titanium source. The purpose of calcination is to remove the TEABr template agent and volatile weak organic bases in the product. Engineers familiar with this field can perform the post-treatment operations according to common sense.

[0069] Advantages of the present invention:

[0070] The present invention provides a green process for preparing Ti-Beta zeolite in large quantities. The process mainly uses dealuminated Beta zeolite as the raw material, without adding fluoride or / and aluminum source for assistance. It mainly utilizes the gas-phase transport pathway to provide water vapor and weak organic base to assist the tetraethylammonium bromide (TEABr) template agent, in-situ locally etching and repairing the hydroxyl nests of dealuminated Beta zeolite. The main technological innovation of the present invention lies in: firstly, using the combination of tetraethylammonium bromide (TEABr) template agent and volatile weak organic base to replace the strongly basic tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process. At the same time, by means of the pore condensation liquid generated by dealuminated Beta zeolite in saturated steam and the liquid film on the zeolite solid surface to limit the dissolution amount of silicate, it is easier to achieve controllable etching and desilication of the hydroxyl nests of dealuminated Beta zeolite, improve the acceptance ability of the hydroxyl nests for larger titanium ions, and thus is more conducive to the preparation of high-performance Ti-Beta zeolite with high framework titanium content and low non-framework titanium content. Secondly, the controllable etching and desilication generates local structural defects, which can be directly repaired quickly in the weakly basic environment generated by the volatile weak organic base with the TEA + cationic structure-directing agent (SDA) ionized by the TEABr template agent in the solution, completely getting rid of the trouble brought by the need to add fluoride or / and aluminum source for auxiliary structure reconstruction in the existing process due to the need to reconstruct the Beta zeolite structure starting from amorphous silicate fragments. In addition, in the present invention, Ti-Beta zeolite is prepared by in-situ local construction and reconstruction of the dried precursor. The precursor is prepared by isovolume impregnation of dealuminated Beta zeolite with an acidic aqueous solution of titanium sulfate and TEABr template agent. The water content of the Ti-Beta zeolite precursor is low and it does not contain colloidal substances. Therefore, only simple drying treatment is required when preparing the Ti-Beta zeolite precursor, the drying speed is fast, the strictness of the drying temperature range is reduced, it is suitable for large-scale preparation, and it avoids the drying trouble encountered when using hydrogel precursor to prepare dry gel intermediate. Moreover, in the present invention, the use of volatile organic base is not disposable, but most of it can be recycled and reused. In short, the Ti-Beta zeolite preparation process provided by the present invention has the advantages of simple method, low cost, being suitable for large-scale preparation, and thus having higher practical value. Description of the Drawings

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

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

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

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

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

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

[0077] The following further illustrates the detailed implementation manners of the present invention in combination with the accompanying drawings and technical solutions.

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

[0079] In terms of characterizing the physical and chemical properties of the Ti-Beta zeolite product, the focus can be on characterizing the titanium content, framework titanium content, non-framework titanium content, and relative crystallinity.

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

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

[0082] In addition, in the process of preparing Ti-Beta zeolite by in-situ local structure reconstruction method of gas-phase transport-assisted dealumination of Beta zeolite, it also involves the detection of impurity crystals, the analysis of relative crystallinity, and the analysis of the silica-alumina ratio (molar ratio of SiO2 to Al2O3) of the Al-Beta zeolite raw material; the detection of the residual aluminum content (expressed as the molar ratio of SiO2 to Al2O3) in the dealuminated Beta zeolite, and the analysis and characterization of the water content, template agent content, and the retention degree of the crystal structure of the dealuminated Beta zeolite in the Ti-Beta zeolite precursor prepared by the impregnation method.

[0083] Among them, the detection of impurity crystals in the Al-Beta zeolite raw material and the characterization of the retention degree of the crystal structure of the dealuminated Beta zeolite in the precursor can be carried out by the X-ray powder diffraction (XRD) method; the detection of the relative crystallinity of the Al-Beta zeolite raw material can be achieved by measuring the nitrogen physical adsorption data of the sample, calculating the BET total surface area value of the sample on this basis, and drawing a conclusion; the silica-alumina ratio (molar ratio of SiO2 to Al2O3) of the Al-Beta zeolite raw material can be detected by the X-ray fluorescence spectroscopy (XRF) method; the residual aluminum content (expressed as the molar ratio of SiO2 to Al2O3) in the dealuminated Beta zeolite can be analyzed by inductively coupled plasma emission spectroscopy (ICP); the analysis of the water content and template agent content in the precursor is carried out by the thermogravimetric (TG) method.

[0084] The present invention will be further described below by way of examples, but the present invention is not limited by these examples.

[0085] Example 1: This example is used to illustrate the preparation process of Ti-Beta zeolite with recyclable organic base based on the gas-phase transport method provided by the present invention. That is, dealuminated Beta zeolite is used as the main raw material, without involving the use of fluoride or / and aluminum source. Mainly using the gas-phase transport pathway to provide water vapor and weak organic base to assist tetraethylammonium bromide (TEABr) template agent, in-situ local desilication etching and repair and reconstruction of the hydroxyl nests of dealuminated Beta zeolite can be carried out, a large amount of Ti-Beta zeolite can be prepared and the weak organic base can be recycled. The green process can replace the strong basic tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process by combining tetraethylammonium bromide (TEABr) template agent with volatile weak organic base. At the same time, by means of the pore condensate generated by dealuminated Beta zeolite in saturated steam and the liquid film on the surface of the zeolite solid to limit the dissolution amount of silicate, it is more convenient to realize the controllable desilication etching of the hydroxyl nests of dealuminated Beta zeolite, achieve the purpose of mild desilication etching of the hydroxyl nests of dealuminated Beta zeolite and improve the acceptance ability of the hydroxyl nests for larger titanium ions, and avoid the complete dissolution of dealuminated Beta zeolite crystals by strong basic TEAOH solution into fragmented structural units (amorphous substances). Thus, the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) is changed to repair the local defects of Ti-Beta zeolite crystals, that is, to repair the local structural defects left after the hydroxyl nests with mild etching accept titanium ions (the present invention). Because the present invention avoids reconstructing the Ti-Beta zeolite structure starting from amorphous fragmented structural units, high-quality Ti-Beta zeolite can be prepared from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source. In addition, in the present invention, Ti-Beta zeolite is prepared by in-situ local construction and reconstruction from a dried Ti-Beta zeolite precursor. The precursor is prepared by isovolume impregnation of dealuminated Beta zeolite with an acidic aqueous solution of titanium sulfate and TEABr template agent. The water content in the Ti-Beta zeolite precursor is low and it does not contain colloidal substances. Therefore, only simple drying treatment is required when preparing the Ti-Beta zeolite precursor, which is suitable for large-scale preparation.

[0086] The first step is to prepare dealuminated Beta zeolite using Al-Beta zeolite as the raw material

[0087] (1) According to the hydrothermal crystallization method provided by US Patent US3 308 069 (1967), synthesize Al-Beta zeolite with a molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) of 25 by oneself as the raw material for preparing dealuminated Beta zeolite. After the synthesized Al-Beta zeolite is subjected to conventional filtration, washing, drying (110 °C, 12 h) and calcination to remove the template agent (540 °C, 6 h), its crystal grain size is observed by TEM to be less than 100 nanometers, belonging to nano-Beta zeolite; no impurity crystals are found by XRD inspection, and its BET specific surface area is calculated from its nitrogen physical adsorption data to be about 540 m 2 / g, and its molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) is measured by XRF to be about 24, meeting the technical requirements of the Beta zeolite raw material for this invention.

[0088] (2) Prepare dealuminated Beta zeolite.

[0089] First, prepare a concentrated nitric acid solution with a molar concentration of 13M. Then, according to the liquid-solid ratio of 20:1 (ml / g), 20 g of the Beta zeolite matrix after the above-mentioned drying and calcination treatment is added to a three-necked flask containing 400 ml of 13M concentrated nitric acid solution under stirring for dealumination treatment. The dealumination temperature is 95 °C and the dealumination time is 20 h. During the dealumination reaction, the three-necked flask is kept in a reflux state. After the dealumination reaction is completed, the liquid material is cooled to room temperature and then filtered to recover the solid product. Then, it is subjected to conventional water washing, drying (overnight at 110 °C) and calcination treatment (550 °C, 3 h) to obtain dealuminated Beta zeolite. The molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) of the dealuminated Beta zeolite is measured by ICP to be 990. It meets the requirements of this invention. Seal and store for later use to avoid moisture absorption.

[0090] Second step: Prepare the precursor for in-situ local structure reconstruction method to prepare Ti-Beta zeolite by the equal-volume impregnation method

[0091] Use tetraethylammonium bromide (TEABr) solid as the template agent source and titanium sulfate (Ti(SO4)2) as the titanium source. Determine the template agent dosage according to the TEABr / SiO2 molar ratio (using the number of moles of SiO2 to represent the number of moles of dealuminated Beta zeolite) of 0.3; determine the dosage of titanium sulfate (Ti(SO4)2) according to the Si / Ti molar ratio of 50; determine the volume of the equal-volume impregnation solution according to the dosage of dealuminated Beta zeolite and the saturated water absorption rate of dealuminated Beta zeolite.

[0092] The specific procedures are as follows: First, taking 10 g of dealuminated Beta zeolite as the dosage, 10.72 g of tetraethylammonium bromide (TEABr) template agent and 0.82 g of titanium sulfate (Ti(SO4)2) are respectively weighed. The template agent and titanium sulfate are prepared into a 12 ml acidic aqueous solution with deionized water (the saturated water absorption rate of dealuminated Beta zeolite is calculated as 1.2 ml H2O / g of dehydrated zeolite). Then, the dealuminated Beta zeolite is impregnated isovolumetrically at room temperature with the acidic impregnation solution containing TEABr template agent and titanium sulfate. The impregnation is carried out statically in a closed container, and the impregnation time is 4 h. After the isovolumetric impregnation is completed, the precursor wet material is dried. The drying temperature is 80 °C and the drying time is 12 h. The dried solid product, namely the Ti-Beta zeolite precursor, is about 27 g and is sealed for standby.

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

[0094] In the third step, the Ti-Beta zeolite is prepared by in-situ local structure reconstruction of the Ti-Beta zeolite precursor using the vapor transport method

[0095] The reaction process of preparing the Ti-Beta zeolite by in-situ local structure reconstruction is carried out in a laboratory small autoclave with a volume of 100 ml. There are brackets and trays inside the autoclave. Take 10 g of the dried Ti-Beta zeolite precursor and place it on the tray, and the water vapor and volatile weak organic base (n-butylamine) for vapor transport are provided by vaporization of the bottom aqueous solution under the tray. The local structure reconstruction reaction is carried out in a common electric heating oven with the temperature set at 140 °C for 12 h.

[0096] According to calculations, when preparing Ti-Beta zeolite by in-situ local structure reconstruction of Ti-Beta zeolite precursor using the gas-phase transport method in this small autoclave, more than 12.16 g of liquid water is added to the bottom of the autoclave (at this time, the W H2O / W 沸石前驱体 ratio is about 1.2), and a gas-liquid two-phase can appear at 140 °C. However, in this case, the liquid phase mainly refers to the capillary condensed liquid in the channels of dealuminated Beta zeolite and the liquid film on the zeolite surface. To make the local structure reconstruction reaction proceed under suitable conditions with liquid water at the bottom of the autoclave, the W H2O / W 沸石前驱体 ratio is increased to 2.0. Therefore, 20 g of deionized water is added to the bottom of the autoclave, and at the same time, 13.3 g of n-butylamine is added to make the percentage concentration of n-butylamine in the aqueous solution reach 40%.

[0097] After the local structure reconstruction reaction is completed, in accordance with the usual practice of conventional hydrothermal synthesis of zeolite molecular sieves, the autoclave is cooled and depressurized. When the temperature and pressure in the autoclave are close to the ambient temperature and pressure, the autoclave is opened and the Ti-Beta zeolite product is taken out.

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

[0099] The Ti-Beta zeolite product prepared by the method of the present invention does not require defluorination and dealumination post-treatment, but a small amount of sulfate ions brought in by the titanium source (titanium sulfate) needs to be removed by simple water washing. Then, the washed Ti-Beta zeolite product is subjected to conventional drying and calcination treatments. The drying is carried out in an electric oven at a drying temperature of 110 °C and a drying time of 12 h; the calcination is carried out in a muffle furnace at a calcination temperature of 540 °C and a calcination time of 6 h. The obtained white powder is the Ti-Beta zeolite product, designated as Ti-Beta-1.

[0100] The Si / Ti molar ratio of the Ti-Beta-1 sample measured by the XRF method is about 50. The infrared spectrum of the framework vibration of the Ti-Beta-1 sample is shown in Figure 2 , and the XRD pattern is shown in Figure 3 . It can be seen from Figure 2 that this sample has an obvious characteristic absorption of framework titanium near the wave number of 960 cm -1 , and its framework titanium content index value (I 960 / I 800 ) is 1.08. In addition, it can be seen from Figure 3 that this sample has a high crystallinity and no impurity crystals. In addition, after being characterized by ultraviolet Raman spectroscopy (excitation light source wavelength 325 nm), it is confirmed that this sample only contains a very small amount of anatase-phase titanium dioxide (at 144, 390, 635 cm -1There is a resonance peak of weakly crystalline anatase titanium dioxide at this position). The above results indicate that, according to the process of local structure reconstruction of dealuminated Beta zeolite by gas-phase transmission of water vapor and volatile weak organic bases provided by the present invention, high-quality Ti-Beta zeolite products were prepared from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source.

[0101] Comparative Example 1: This example is used to illustrate that according to the existing structure reconstruction process (reference: "Wang Bowen. Preparation and Catalytic Performance of MFI and BEA Zeolites [D]. East China Normal University, 2021"), that is, first, dealuminated Beta zeolite, a large amount of tetraethylammonium hydroxide (TEAOH) templating agent solution, a titanium source, and deionized water are made into a hydrogel. Then, the hydrogel is hydrothermally pretreated at a higher temperature so that the dealuminated Beta zeolite in it is completely dissolved by the large amount of strongly basic TEAOH solution and becomes fragmented structural units with amorphous properties. Then, the hydrogel belonging to the amorphous substance is cooled, and fluoride is added to it. Finally, the hydrogel amorphous substance is reheated to carry out structure reconstruction from the amorphous substance under hydrothermal conditions to prepare Ti-Beta zeolite (synthesize Ti-Beta zeolite crystals), which is also an effective way to prepare Ti-Beta zeolite. However, when preparing Ti-Beta zeolite according to the existing structure reconstruction process, the assistance of fluoride is required, so there are practical problems such as fluoride-containing wastewater that are not conducive to industrial applications.

[0102] First step, prepare dealuminated Beta zeolite using Al-Beta zeolite as raw material

[0103] Repeat the steps for preparing dealuminated Beta zeolite in Example 1, using an Al-Beta zeolite raw material without hetero-crystalline phase, crystal grain size less than 100 nm, BET specific surface area of about 540 m 2 / g, and a molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) of about 24 to prepare dealuminated Beta zeolite with a molar ratio of SiO2 to Al2O3 of 990 by acid dealumination, and store it sealed for later use.

[0104] Second step, prepare a hydrogel precursor for structure reconstruction using dealuminated Beta zeolite

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

[0106] The specific procedure is as follows: First, based on the dosage of 10 g dealuminated Beta zeolite, 30 g of 25 wt.% tetrapropylammonium hydroxide (TEAOH) aqueous solution and 1.16 g of tetrabutyl titanate (TBOT) are weighed respectively. Then, under stirring, the titanium source and the TEAOH template agent solution are mixed to prepare a uniform alkaline solution containing the titanium source and the TEAOH template agent. Finally, under stirring, all the dealuminated Beta zeolite is poured into the alkaline solution containing the titanium source and the TEAOH template agent, and stirred at room temperature for reaction (mild desilication reaction) for 3 h to obtain a hydrogel (with a H2O / SiO2 molar ratio of about 7.4) for the structural reconstruction to prepare Ti-Beta zeolite.

[0107] The third step, hydrothermal pretreatment of the hydrogel

[0108] All the hydrogel prepared in the second step is loaded into a small laboratory autoclave with a PTFE liner for hydrothermal pretreatment. The pretreatment is carried out in a common electric heating oven with the temperature set at 140 °C, and the pretreatment time is 1 h. After the pretreatment, the autoclave is taken out of the oven and quenched with water to room temperature. A small amount of the sample is taken out after opening the autoclave for the detection of the retention degree of the Beta zeolite crystal structure (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 basically completely dissolved by the strongly alkaline TEAOH solution with a large dosage and has become fragmented structural units with an amorphous nature.

[0109] The fourth step, using fluoride to assist the hydrothermally treated hydrogel for structural reconstruction to prepare Ti-Beta zeolite

[0110] The fluoride used in this example is ammonium fluoride (NH4F). The addition amount of ammonium fluoride is calculated according to F - / SiO2 = 0.2. The specific procedure is as follows: Weigh accurately the ammonium fluoride solid, and then add all the ammonium fluoride solid powder into the autoclave, and manually stir it to dissolve and mix it well with the hydrogel after hydrothermal pretreatment (in which the crystal structure of the dealuminated Beta zeolite has been completely dissolved and destroyed and has become fragmented structural units with an amorphous nature (in a state of long-range disorder)). Finally, reseal the autoclave for hydrothermal crystallization treatment, and the hydrothermal crystallization treatment is at 140 °C and the crystallization time is 12 h. After the crystallization is completed, the autoclave is taken out of the oven and quenched with water to room temperature.

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

[0112] In this example, the crystallization product obtained in the fourth step needs to go through four post-treatment steps of filtration, repeated water washing, drying, and calcination in sequence to obtain the Ti-Beta zeolite product, coded as Ti-Beta-1-F-Com (Com represents the comparative example).

[0113] In this example, the reason for repeatedly washing the crystallization product with water is to remove the F-ion impurities in the Ti-Beta zeolite product. Obviously, in this example, the fluorides in the crystallization mother liquor and a large amount of washing liquor will cause problems in the treatment of wastewater.

[0114] The Si / Ti molar ratio of the Ti-Beta-1-F-Com sample measured by the XRF method is about 50. The infrared spectrum of the framework vibration of the Ti-Beta-1-F-Com sample is shown in Figure 4 . From Figure 4 it can be seen that the sample also has obvious characteristic absorption of framework titanium near the wavenumber of 960 cm -1 . By comparing with Example 1, it can be seen that the existing structure reconstruction process is also an effective way to prepare Ti-Beta zeolite. However, when preparing Ti-Beta zeolite by the existing structure reconstruction process, the assistance of fluoride is required, so there are practical problems such as fluoride-containing wastewater that are not conducive to industrial applications.

[0115] Comparative Example 2: This example is used to illustrate that according to the method of the existing liquid-solid isomorphous substitution process (Ind. Eng. Chem. Res. 2021, 60, 1219-1230), that is, first contacting dealuminated Beta zeolite with an anhydrous ethanol solution of titanium tetrachloride at room temperature, and performing a short ultrasonic oscillation treatment, then evaporating the ethanol solvent in the feed liquid, and then drying and calcining the solid product to obtain Ti-Beta zeolite. However, due to the small size of the hydroxyl nests in dealuminated Beta zeolite (the space left by migrating out a framework Al 3+ ion), it is not easy to accept the larger-sized Ti 4+ ion (the ionic radius of Ti 4+ ion is while the ionic radius of Al 3+ ion is ), so when preparing Ti-Beta zeolite by this method, the framework titanium content is low.

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

[0117] Repeat the preparation steps of dealuminated Beta zeolite in Example 1, using a zeolite without hetero-crystalline phase, crystal grain size less than 100 nanometers, and BET specific surface area of about 540 m 2Al-Beta zeolite raw material with a molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) of about 24 was used to prepare dealuminated Beta zeolite with a molar ratio of SiO2 to Al2O3 of 990 by acid dealumination, and it was sealed and stored for later use.

[0118] In the second step, an anhydrous ethanol solution of titanium tetrachloride was prepared.

[0119] In the glove box, 6 mL of TiCl4 was quickly extracted with a pipette and transferred to 100 mL of anhydrous ethanol, and then an ethanol solution of TiCl4 with a concentration of 0.5 mol / L was prepared for later use.

[0120] In the third step, a liquid-solid isomorphous substitution reaction was carried out at room temperature.

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

[0122] Then, 10 g of dry dealuminated Beta zeolite was poured into 30 ml of the impregnation solution, stirred evenly to obtain a reactant slurry. Then, the reactant slurry was transferred to an ultrasonic oscillator, and an ultrasonic-assisted liquid-solid isomorphous substitution reaction was carried out at room temperature. The reaction time was 20 min.

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

[0124] In the fourth step, the Ti-Beta zeolite product was obtained by post-treating the product of the liquid-solid isomorphous substitution reaction.

[0125] The post-treatment steps mainly include conventional drying (120 °C, overnight) and calcination (540 °C, 3 h). The Ti-Beta zeolite prepared in this example was designated as Ti-Beta-2-Cl-Com. The Si / Ti molar ratio of the Ti-Beta-2-Cl-Com sample was measured to be about 50 by the XRF method. The infrared spectrum of the framework vibration of the Ti-Beta-2-Cl-Com sample is shown in Figure 5 . From Figure 5 it can be seen that the sample also has a characteristic absorption of framework titanium near the wave number of 960 cm -1 However, compared with Example 1, it can be seen that the intensity of the characteristic absorption peak of framework titanium of the Ti-Beta-2-Cl-Com sample prepared by this method is weaker, indicating that its framework titanium content is lower.

[0126] Comparative Example 3: This example is used to illustrate the method of the existing solid-solid isomorphic substitution process (Microporous and Mesoporous Materials 288(2019)109588), that is, first, dealuminated Beta zeolite and titanium dichloride solid powder are fully ground and uniformly mixed under the protection of inert gas. Then, the solid mixture is calcined to obtain Ti-Beta zeolite. Similarly, due to the small size of the hydroxyl nests in dealuminated Beta zeolite (the space left by migrating out a framework Al 3+ ion), it is not easy to accommodate larger Ti 4+ ions (Ti 4+ ion radius is while the radius of Al 3+ ion is ), so when preparing Ti-Beta zeolite by this method, the framework titanium content is also low.

[0127] First step: Prepare dealuminated Beta zeolite using Al-Beta zeolite as raw material

[0128] Repeat the preparation steps of dealuminated Beta zeolite in Example 1. Use an Al-Beta zeolite raw material without hetero-crystalline phase, crystal grain size less than 100 nm, BET specific surface area of about 540 m 2 / g, and a molar ratio of silicon-aluminum oxide (molar ratio of SiO2 to Al2O3) of about 24. Through acid dealumination, dealuminated Beta zeolite with a molar ratio of SiO2 to Al2O3 of 990 is prepared and stored sealed for later use.

[0129] Second step: Prepare the precursor mixture by grinding the solid powders of dealuminated Beta zeolite and titanium dichloride

[0130] First, calculate according to the preparation of Ti-Beta zeolite with a Si / Ti molar ratio of 50 using 10 g of dealuminated Beta zeolite. Accurately weigh 0.85 g of titanium dichloride solid powder in the glove box.

[0131] Then, carefully grind the dry dealuminated Beta zeolite powder and titanium dichloride solid powder in a mortar in the glove box to obtain the precursor mixture.

[0132] Third step: Prepare Ti-Beta zeolite by calcining the precursor mixture

[0133] The precursor mixture was quickly placed in a crucible and spread thinly. After covering the crucible, it was placed in a muffle furnace for calcination treatment (540 °C, 3 h). The obtained white solid powder was the Ti-Beta zeolite product, coded as Ti-Beta-3-Cp-Com. The Si / Ti molar ratio of the Ti-Beta-2-Cp-Com sample was measured to be approximately 50 by the XRF method. The skeletal vibration infrared spectrum of the Ti-Beta-3-Cp-Com sample is shown in Figure 6 . It can be seen from Figure 6 that this sample also has a characteristic absorption of framework titanium near the wavenumber of 960 cm -1 . However, compared with Example 1, it can be seen that the intensity of the characteristic absorption peak of framework titanium in the Ti-Beta-3-Cp-Com sample prepared by this method is weak, indicating that its framework titanium content is low.

[0134] Example 2: This example is used to illustrate the preparation process of Ti-Beta zeolite with recyclable organic base based on the gas-phase transport method provided by the present invention, that is, using dealuminated Beta zeolite as the main raw material, without involving the use of fluoride or / and aluminum source for assistance, mainly using the gas-phase transport pathway to provide water vapor and weak organic base to assist the tetraethylammonium bromide (TEABr) template agent, in-situ locally etching and repairing the hydroxyl nests of dealuminated Beta zeolite, which can prepare a large amount of Ti-Beta zeolite and enable the recycling of weak organic base. The green process can replace the strong basic tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process by combining the tetraethylammonium bromide (TEABr) template agent with volatile weak organic base. At the same time, by means of the pore condensation liquid generated by dealuminated Beta zeolite in saturated steam and the liquid film on the surface of zeolite solid to limit the dissolution amount of silicate, it is more convenient to achieve the controllable etching and desilication of the hydroxyl nests of dealuminated Beta zeolite, so as to achieve the purpose of slightly etching and desilication of the hydroxyl nests of dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl nests to larger titanium ions, and to avoid the complete dissolution of dealuminated Beta zeolite crystals by strong basic TEAOH solution into fragmented structural units (amorphous substances), thereby changing the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) into the repair of local defects of Ti-Beta zeolite crystals, that is, the repair of the local structural defects left after the slightly etched hydroxyl nests accept titanium ions (the present invention). Among them, when in-situ locally reconstructing the structure of Ti-Beta zeolite precursor to prepare Ti-Beta zeolite by gas-phase transport method, it is allowed to change the amount of liquid water added to the bottom of the autoclave within a certain range without changing the beneficial effects of the present invention. In short, because the present invention avoids reconstructing the Ti-Beta zeolite structure starting from amorphous fragmented structural units, high-quality Ti-Beta zeolite can be prepared from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source. In addition, in the present invention, Ti-Beta zeolite is prepared by in-situ local construction and reconstruction of the dried Ti-Beta zeolite precursor. The precursor is prepared by isovolumetric impregnation of dealuminated Beta zeolite with an acidic aqueous solution of titanium sulfate and TEABr template agent. The water content in the Ti-Beta zeolite precursor is low and it does not contain colloidal substances, so only simple drying treatment is required during the preparation of the Ti-Beta zeolite precursor, which is suitable for large-scale preparation.

[0135] Repeat Example 1, but when in-situ locally reconstructing the structure of Ti-Beta zeolite precursor to prepare Ti-Beta zeolite by gas-phase transport method in the third step, the amount of liquid water (W H2O / W 沸石前驱体The ratios were changed to 1.5, 2.5, and 3.0 in sequence, that is, the amounts of deionized water added to the bottom of the kettle were 15 g, 25 g, and 30 g in sequence. To keep the concentration of n-butylamine in the bottom liquid of the kettle unchanged (40%), the amounts of n-butylamine added to the bottom liquid of the kettle were approximately 10 g, 17 g, and 20 g in sequence. The infrared spectra of the framework vibrations of the prepared Ti-Beta zeolite samples all had obvious characteristic absorptions of framework titanium near the wavenumber of 960 cm -1 and the framework titanium content index values (I 960 / I 800 ) were 1.03, 1.05, and 1.02 in sequence.

[0136] Example 3: This example is used to illustrate the preparation process of Ti-Beta zeolite with recyclable organic base based on the gas-phase transport method provided by the present invention, that is, using dealuminated Beta zeolite as the main raw material, without involving the use of fluoride or / and aluminum source for assistance, mainly using the gas-phase transport pathway to provide water vapor and weak organic base to assist the tetraethylammonium bromide (TEABr) template agent, in-situ locally desilicate and repair and reconstruct the hydroxyl nests of dealuminated Beta zeolite, which can prepare a large amount of Ti-Beta zeolite and enable the recycling of weak organic base. The green process can replace the strong basic tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process by combining the tetraethylammonium bromide (TEABr) template agent with a volatile weak organic base. At the same time, by means of the pore condensation liquid generated by dealuminated Beta zeolite in saturated steam and the liquid film on the zeolite solid surface to limit the dissolution amount of silicate, it is more convenient to achieve the controllable desilication by etching the hydroxyl nests of dealuminated Beta zeolite, so as to achieve the purpose of slightly etching and desilicating the hydroxyl nests of dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl nests for larger titanium ions, and to avoid the complete dissolution of dealuminated Beta zeolite crystals by the strong basic TEAOH solution and becoming fragmented structural units (amorphous substances), thereby changing the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) into the repair of local defects of Ti-Beta zeolite crystals, that is, repairing the local structural defects left after the hydroxyl nests with slightly etched titanium ions are accepted (the present invention). Among them, when using the gas-phase transport method to in-situ locally reconstruct the structure of the Ti-Beta zeolite precursor to prepare Ti-Beta zeolite, 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 invention. In short, because the present invention avoids reconstructing the Ti-Beta zeolite structure starting from amorphous fragmented structural units, high-quality Ti-Beta zeolite can be prepared from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source. In addition, in the present invention, Ti-Beta zeolite is prepared by in-situ local construction and reconstruction of a dried Ti-Beta zeolite precursor. The precursor is prepared by equal-volume impregnation of dealuminated Beta zeolite with an acidic aqueous solution of titanium sulfate and TEABr template agent. The Ti-Beta zeolite precursor has a low water content and does not contain colloidal substances, so only simple drying treatment is required during the preparation of the Ti-Beta zeolite precursor, which is suitable for large-scale preparation.

[0137] Repeat Example 1, but when using the gas-phase transport method to in-situ locally reconstruct the structure of the Ti-Beta zeolite precursor to prepare Ti-Beta zeolite in the third step, change the temperature and time of the reconstruction reaction to: 120 °C × 48 h, 130 °C × 24 h, 150 °C × 6 h, 160 °C × 2 h, and 170 °C × 0.5 h in sequence. Then, the skeletal vibration infrared spectrum of the prepared Ti-Beta zeolite sample is at 960 cm -1There are obvious characteristic absorptions of framework titanium near the wave number, and the index values (I 960 / I 800 ) of the framework titanium content are 0.99, 1.00, 0.98, 1.10, and 1.08 in sequence.

[0138] Example 4: This example is used to illustrate the preparation process of Ti-Beta zeolite that can recycle organic bases based on the gas-phase transport method provided by the present invention, that is, using dealuminated Beta zeolite as the main raw material, without involving the use of fluoride or / and aluminum source for assistance, mainly using the gas-phase transport path to provide water vapor and weak organic bases to assist the tetraethylammonium bromide (TEABr) template agent, in-situ locally etching and repairing the hydroxyl nests of dealuminated Beta zeolite, a green process that can prepare a large amount of Ti-Beta zeolite and enable the recycling of weak organic bases. It can replace the strong basic tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process by combining the tetraethylammonium bromide (TEABr) template agent with a volatile weak organic base. At the same time, by means of the pore condensate generated by dealuminated Beta zeolite in saturated steam and the liquid film on the zeolite solid surface to limit the dissolution amount of silicate, it is more convenient to achieve the controllable etching and desilication of the hydroxyl nests of dealuminated Beta zeolite, to achieve the purpose of slightly etching and desilicating the hydroxyl nests of dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl nests for larger titanium ions, and to avoid the complete dissolution of dealuminated Beta zeolite crystals by the strong basic TEAOH solution into fragmented structural units (amorphous substances). Thus, turning the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) into repairing the local defects of Ti-Beta zeolite crystals, that is, repairing the local structural defects left after the hydroxyl nests with slight etching accept titanium ions (the present invention). Among them, when preparing the Ti-Beta zeolite precursor for in-situ local structure reconstruction by the equal-volume impregnation method, the amount of the tetraethylammonium bromide (TEABr) template agent is allowed to be changed within a certain range without changing the beneficial effects of the present invention. In short, because the present invention avoids reconstructing the Ti-Beta zeolite structure starting from amorphous fragmented structural units, high-quality Ti-Beta zeolite can be prepared from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source. In addition, in the present invention, Ti-Beta zeolite is prepared by in-situ local construction and reconstruction from the dried Ti-Beta zeolite precursor. The precursor is prepared by equal-volume impregnation of dealuminated Beta zeolite with an acidic aqueous solution of titanium sulfate and the TEABr template agent. The Ti-Beta zeolite precursor has a low water content and does not contain colloidal substances, so only simple drying treatment is required during the preparation of the Ti-Beta zeolite precursor, which is suitable for large-scale preparation.

[0139] Repeat Example 1, but when preparing the Ti-Beta zeolite precursor for in-situ local structure reconstruction by the equal-volume impregnation method in the second step, successively change the TEABr / SiO2 molar ratio (expressing the molar number of dealuminated Beta zeolite in terms of the molar number of SiO2) to 0.05, 0.1, 0.2, 0.25, 0.4, and 0.5. The prepared Ti-Beta zeolite precursor is further made into Ti-Beta zeolite by in-situ local structure reconstruction through the gas-phase transport method. For the prepared Ti-Beta zeolite samples, the infrared spectra of the framework vibrations all have obvious characteristic absorptions of framework titanium near the wavenumber of 960 cm -1 and the index value (I 960 / I 800 ) of the framework titanium content fluctuates between 0.9 and 1.0.

[0140] Example 5: This example is used to illustrate the preparation process of Ti-Beta zeolite with recyclable organic base based on the gas-phase transport method provided by the present invention, that is, using dealuminated Beta zeolite as the main raw material, without involving the use of fluoride or / and aluminum source for assistance, mainly using the gas-phase transport pathway to provide water vapor and weak organic base to assist the tetraethylammonium bromide (TEABr) template agent, in-situ locally etching and repairing the hydroxyl nests of dealuminated Beta zeolite, which can prepare a large amount of Ti-Beta zeolite and enable the recycling of weak organic base. The green process can replace the strong basic tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process by combining the tetraethylammonium bromide (TEABr) template agent with volatile weak organic base. At the same time, by means of the pore condensation liquid generated by dealuminated Beta zeolite in saturated steam and the liquid film on the surface of zeolite solid to limit the dissolution amount of silicate, it is more convenient to achieve the controllable etching and desilication of the hydroxyl nests of dealuminated Beta zeolite, so as to achieve the purpose of slightly etching and desilication of the hydroxyl nests of dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl nests to larger titanium ions, and to avoid the complete dissolution of dealuminated Beta zeolite crystals by strong basic TEAOH solution and becoming fragmented structural units (amorphous substances), thereby changing the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) into repairing the local defects of Ti-Beta zeolite crystals, that is, repairing the local structural defects left after the slightly etched hydroxyl nests accept titanium ions (the present invention). Among them, when preparing the Ti-Beta zeolite precursor for in-situ local structure reconstruction by the equal-volume impregnation method, the Si / Ti molar ratio and impregnation time are allowed to be changed within a certain range without changing the beneficial effects of the present invention. In short, because the present invention avoids reconstructing the Ti-Beta zeolite structure starting from amorphous fragmented structural units, high-quality Ti-Beta zeolite can be prepared from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source. In addition, in the present invention, Ti-Beta zeolite is prepared by in-situ local construction and reconstruction of the dried Ti-Beta zeolite precursor. The precursor is prepared by equal-volume impregnation of dealuminated Beta zeolite with an acidic aqueous solution of titanium sulfate and TEABr template agent. The Ti-Beta zeolite precursor has a low water content and does not contain colloidal substances, so only simple drying treatment is required during the preparation of the Ti-Beta zeolite precursor, which is suitable for large-scale preparation.

[0141] Repeat Example 1, but when preparing the Ti-Beta zeolite precursor for in-situ local structure reconstruction by the equal-volume impregnation method in the second step, successively change the Si / Ti molar ratio (the number of moles of dealuminated Beta zeolite represented by the number of moles of SiO2) to 60, 70, 80, 90, and 100, and at the same time successively change the impregnation time to 12 h, 8 h, 6 h, 2 h, and 0.5 h. The prepared zeolite precursor is further made into Ti-Beta zeolite by in-situ local structure reconstruction through the vapor transport method. For the prepared Ti-Beta zeolite samples, the infrared spectrum of the framework vibration has obvious characteristic absorption of framework titanium near the wavenumber of 960 cm -1 and the index value of its framework titanium content (I 960 / I 800 ) varies between 0.8 and 1.0. Generally, with the increase of the Si / Ti molar ratio, the index value of the framework titanium content (I 960 / I 800 ) of the Ti-Beta zeolite samples shows a decreasing trend.

[0142] Example 6: This example is used to illustrate the preparation process of Ti-Beta zeolite with recyclable organic base based on the gas-phase transport method provided by the present invention, that is, using dealuminated Beta zeolite as the main raw material, without involving the use of fluoride or / and aluminum source for assistance, mainly using the gas-phase transport path to provide water vapor and weak organic base to assist the tetraethylammonium bromide (TEABr) template agent, in-situ locally etching and repairing the hydroxyl nests of dealuminated Beta zeolite, which can prepare a large amount of Ti-Beta zeolite and enable the recycling of weak organic base. The green process can replace the strong basic tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process by combining the tetraethylammonium bromide (TEABr) template agent with volatile weak organic base. At the same time, by means of the pore condensation liquid generated by dealuminated Beta zeolite in saturated steam and the liquid film on the zeolite solid surface to limit the dissolution amount of silicate, it is more convenient to achieve the controllable etching and desilication of the hydroxyl nests of dealuminated Beta zeolite, so as to achieve the purpose of slightly etching and desilication of the hydroxyl nests of dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl nests to larger titanium ions, and to avoid the complete dissolution of dealuminated Beta zeolite crystals by strong basic TEAOH solution into fragmented structural units (amorphous substances). Thus, the synthesis of Ti-Beta zeolite crystals (traditional structure reconstruction method) is changed to repair the local defects of Ti-Beta zeolite crystals, that is, to repair the local structural defects left after the hydroxyl nests with slight etching accept titanium ions (the present invention). Among them, when preparing the Ti-Beta zeolite precursor for in-situ local structure reconstruction by the equal-volume impregnation method, the drying temperature and time of the wet material after equal-volume impregnation are allowed to be changed within a certain range without changing the beneficial effects of the present invention. In short, because the present invention avoids reconstructing the Ti-Beta zeolite structure starting from amorphous fragmented structural units, high-quality Ti-Beta zeolite can be prepared from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source. In addition, in the present invention, Ti-Beta zeolite is prepared by in-situ local construction and reconstruction from the dried Ti-Beta zeolite precursor. The precursor is prepared by equal-volume impregnation of dealuminated Beta zeolite with an acidic aqueous solution of titanium sulfate and TEABr template agent. The Ti-Beta zeolite precursor has a low water content and does not contain colloidal substances, so only simple drying treatment is required during the preparation of the Ti-Beta zeolite precursor, which is suitable for large-scale preparation.

[0143] Repeat Example 1, but when preparing the Ti-Beta zeolite precursor for in-situ local structure reconstruction by the equal-volume impregnation method in the second step, successively change the drying treatment conditions of the wet material after equal-volume impregnation to 50 °C × 24 h (drying under slightly negative pressure), 60 °C × 12 h (drying under slightly negative pressure), 70 °C × 16 h, 100 °C × 6 h, 120 °C × 3 h, 150 °C × 1 h, and 170 °C × 0.5 h. The prepared zeolite precursor is further made into Ti-Beta zeolite by in-situ local structure reconstruction through the gas-phase transport method. For the prepared Ti-Beta zeolite sample, its skeletal vibration infrared spectrum has obvious characteristic absorption of framework titanium near the wavenumber of 960 cm -1 and its framework titanium content index value (I 960 / I 800 ) fluctuates between 0.9 and 1.0.

[0144] Example 7: This example is used to illustrate the preparation process of Ti-Beta zeolite with recyclable organic base based on the gas-phase transport method provided by the present invention. That is, dealuminated Beta zeolite is used as the main raw material, without involving the use of fluoride or / and aluminum source for assistance. Mainly using the gas-phase transport pathway to provide water vapor and weak organic base to assist tetraethylammonium bromide (TEABr) template agent, in-situ local desilication etching and repair and reconstruction of the hydroxyl nests of dealuminated Beta zeolite can be carried out, a large amount of Ti-Beta zeolite can be prepared, and a green process for recycling weak organic base can be achieved. The strong basic tetraethylammonium hydroxide (TEAOH) template agent used in the existing preparation process can be replaced by the combination of tetraethylammonium bromide (TEABr) template agent and volatile weak organic base. At the same time, by means of the pore condensation liquid generated by dealuminated Beta zeolite in saturated steam and the liquid film on the zeolite solid surface to limit the dissolution amount of silicate, the controllable desilication etching of the hydroxyl nests of dealuminated Beta zeolite can be more conveniently realized, so as to achieve the purpose of slightly etching and desilicating the hydroxyl nests of dealuminated Beta zeolite and improving the acceptance ability of the hydroxyl nests for larger titanium ions, and the purpose of avoiding the complete dissolution of dealuminated Beta zeolite crystals by strong basic TEAOH solution and becoming fragmented structural units (amorphous substances). Thus, synthesizing Ti-Beta zeolite crystals (traditional structure reconstruction method) becomes repairing the local defects of Ti-Beta zeolite crystals, that is, repairing the local structural defects left after the slightly etched hydroxyl nests accept titanium ions (the present invention). Among them, when preparing the Ti-Beta zeolite precursor for in-situ local structure reconstruction by the equal-volume impregnation method, Al-Beta zeolite raw materials with different silicon-aluminum ratios are allowed to be used to prepare dealuminated Beta zeolite, and the Si / Ti molar ratio used in the preparation of the zeolite precursor by the equal-volume impregnation method can be correspondingly changed according to the number of hydroxyl nests of dealuminated Beta zeolite, without changing the beneficial effects of the present invention. In short, because the present invention avoids reconstructing the Ti-Beta zeolite structure starting from amorphous fragmented structural units, high-quality Ti-Beta zeolite can be prepared from dealuminated Beta zeolite without the assistance of fluoride or / and aluminum source. In addition, in the present invention, Ti-Beta zeolite is prepared by in-situ local construction and reconstruction from the dried Ti-Beta zeolite precursor. The said precursor is prepared by equal-volume impregnation of dealuminated Beta zeolite with an acidic aqueous solution of titanium sulfate and TEABr template agent. The water content in the Ti-Beta zeolite precursor is low and it does not contain colloidal substances. Therefore, only simple drying treatment is required when preparing the Ti-Beta zeolite precursor, which is suitable for large-scale preparation.

[0145] Repeat Example 1. However, when preparing dealuminated Beta zeolite using Al-Beta zeolite as the raw material in the first step, first synthesize Al-Beta zeolite with a silica-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3) of 10, 20, 40, 60, 80, 100, 150, and 200 by the hydrothermal crystallization method provided in US Patent US3 308 069 (1967) as the raw material for preparing dealuminated Beta zeolite. After the synthesized Al-Beta zeolite is subjected to conventional filtration, washing, drying (110 °C, 12 h), and calcination to remove the template agent (540 °C, 6 h), TEM is used to observe that its average crystal grain size belongs to the nanometer level and the small crystal grain (less than 1 μm) level. As the silica-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3) increases, the crystal grain size increases; XRD method is used to check and no any impurity crystals are found therein. Its BET specific surface area calculated from its nitrogen physical adsorption data is higher than 500 m 2 / g; the silica-aluminum oxide molar ratio (molar ratio of SiO2 to Al2O3) measured by XRF method is 10, 20, 38, 57, 72, 94, 136, and 189 in sequence, meeting the technical requirements of the Beta zeolite raw material of the present invention. Acid dealumination is carried out on the above Al-Beta zeolite to prepare dealuminated Beta zeolite. The molar ratio of SiO2 to Al2O3 of the obtained dealuminated Beta zeolite is 751, 770, 870, 861, 855, 932, 1088, and 960 in sequence, meeting the technical requirements of the dealuminated Beta zeolite of the present invention.

[0146] The precursor of Ti-Beta zeolite is prepared from the above dealuminated Beta zeolite by the equal-volume impregnation method, and then Ti-Beta zeolite is further prepared by in-situ local structure reconstruction through the gas-phase transport method. Among them, when preparing the precursor of zeolite using dealuminated Beta zeolite with different numbers of hydroxyl nests, in the order of decreasing number of hydroxyl nests of dealuminated Beta zeolite, that is, in the order of increasing silica-aluminum ratio of the Al-Beta zeolite raw material (in the order from 10, 20, 38, 57, 72, 94, 136 to 189), the Si / Ti molar ratio of the hydrogel is changed to 5, 10, 15, 25, 60, 70, 80, and 110 in sequence. For the prepared Ti-Beta zeolite samples, the infrared spectrum of the framework vibration has obvious characteristic absorption of framework titanium near the wave number of 960 cm -1 The content index value (I 960 / I 800 ) of the framework titanium is between 0.8 and 1.1. Generally, as the Si / Ti molar ratio increases, the content index value (I 960 / I 800 ) of the framework titanium in the Ti-Beta zeolite samples shows a decreasing trend.

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

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

[0149] In this example, 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 cyclohexene conversions of the above Ti-Beta zeolite catalysts were 37%, 26%, 46%, and 47% in sequence, and the selectivities of cyclohexene oxide were 90%, 81%, 84%, and 82% in sequence.

Claims

1. A process for preparing Ti-Beta zeolite with recyclable organic base based on gas phase transmission method, characterized in that: Here are the steps: Step 1: Prepare dealuminated Beta zeolite using Al-Beta zeolite as raw material (1) Selection of Al-Beta zeolite raw materials The Al-Beta zeolite is a silicon-aluminum Beta zeolite. The Al-Beta zeolite has the following restrictions: 1) there is no impurity crystal 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 ≥ 450m 2 / g; 3) the molar ratio of silicon aluminum oxide of Al-Beta zeolite, that is, the molar ratio of SiO2 to Al2O3 is 10-200; (2) Preparation of dealuminated Beta zeolite Aluminum Beta zeolite is prepared by using an acid dealumination method based on Al-Beta zeolite, and the molar ratio of SiO2 to Al2O3 in the dealumination Beta zeolite is required to be ≥700; Step 2: Preparation of precursors for in-situ local structural reconstruction of Ti-Beta zeolite by isovolumetric impregnation The precursor of Ti-Beta zeolite is prepared by an equal volume impregnation method at room temperature; the impregnation raw materials include tetraethylammonium bromide TEABr template, titanium sulfate and deionized water; The specific steps are as follows: first, according to the amount of dealuminated Beta zeolite and the saturated water absorption rate of dealuminated Beta zeolite, the volume of the equal volume impregnation solution is determined; then, according to the selected molar ratio of TEABr to SiO2 and the molar ratio of Si to Ti, TEABr template and titanium sulfate are weighed, and an acidic impregnation solution containing TEABr template and titanium sulfate is prepared with deionized water; finally, the dealuminated Beta zeolite is impregnated with the acidic impregnation solution containing TEABr template and titanium sulfate at room temperature in equal volumes; The impregnation is carried out statically in a closed container; after the equal volume impregnation is completed, the precursor wet material is dried to obtain the precursor of Ti-Beta zeolite; The amount of dealuminated Beta zeolite is calculated based on SiO2. The amounts of other impregnation raw materials and the impregnation conditions are as follows: TEABr to SiO2 molar ratio: 0.05-0.5; Si to Ti molar ratio: 5-100; Immersion time: 0.5-12h; Precursor wet material drying temperature: 30℃-170℃; Precursor wet material drying time: 0.5h-24h; Step 3: Prepare Ti-Beta zeolite by in-situ local structural reconstruction of Ti-Beta zeolite precursor using gas phase transport method The reaction process of preparing Ti-Beta zeolite by in-situ local structural reconstruction is carried out in an autoclave; a support and a tray are provided inside the autoclave; a dried Ti-Beta zeolite precursor is placed on the tray, and water vapor and volatile weak organic base for gas phase transmission are provided by evaporation of aqueous solution at the bottom of the autoclave under the tray; the organic base is n-butylamine; The parameter requirements are as follows: The amount of the liquid water added to the kettle bottom is calculated based on the mass ratio of the liquid water to the precursor. The mass ratio of the liquid water to the precursor is in the range of 1.5-3. The amount of the volatile weak organic base is calculated based on the mass percentage concentration of the organic base in the aqueous solution, and the mass percentage concentration of the organic base in the aqueous solution ranges from 10 to 60%. The reaction temperature range for structural reconstruction is: 120-170°C; The reaction time range of structural reconstruction is: 0.5-48h; Step 4: Post-treatment of Ti-Beta zeolite product The post-treatment of the Ti-Beta zeolite product includes water washing, drying and calcination to obtain the Ti-Beta zeolite product.

2. A process for preparing Ti-Beta zeolite with recyclable organic base based on gas phase transmission method according to claim 1, characterized in that: In the first step (1), the molar ratio of silicon to aluminum oxide of the Al-Beta zeolite, that is, the molar ratio of SiO2 to Al2O3, is 20-100.

3. A process for preparing Ti-Beta zeolite with recyclable organic base based on gas phase transmission method according to claim 2, characterized in that: In the first step (1), the molar ratio of silicon to aluminum oxide of the Al-Beta zeolite, that is, the molar ratio of SiO2 to Al2O3, is 25-60.

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

5. A process for preparing Ti-Beta zeolite with recyclable organic base based on gas phase transmission method according to claim 4, characterized in that: In the first step (2), the molar ratio of SiO2 to Al2O3 of the dealuminated Beta zeolite is required to be in the range of ≧900.

6. A process for preparing Ti-Beta zeolite with recyclable organic base based on gas phase transmission method according to claim 1, characterized in that: In the second step, the parameter conditions are as follows: TEABr to SiO2 molar ratio: 0.1-0.4; Si to Ti molar ratio: 10-80; Immersion time: 1-6h; Precursor wet material drying temperature: 50℃-150℃; Precursor wet material drying time: 3h-18h.

7. A process for preparing Ti-Beta zeolite with recyclable organic base based on gas phase transmission method according to claim 6, characterized in that: In the second step, the parameter conditions are as follows: TEABr to SiO2 molar ratio: 0.2-0.3; Si to Ti molar ratio: 15-50; Soaking time: 2-4h; Precursor wet material drying temperature: 80℃-120℃; Precursor wet material drying time: 6h-12h.

8. The process for preparing Ti-Beta zeolite with recyclable organic base based on gas phase transmission method according to claim 1, characterized in that: In the third step, the parameter requirements are as follows: The amount of the liquid water added to the kettle bottom is calculated based on the mass ratio of the liquid water to the precursor. The mass ratio of the liquid water to the precursor is in the range of 1.8-2.

8. The amount of the volatile weak organic base is calculated based on the mass percentage concentration of the organic base in the aqueous solution, and the mass percentage concentration of the organic base in the aqueous solution ranges from 20 to 50%. The reaction temperature range for structural reconstruction is: 130-160°C; The reaction time range of structural reconstruction is: 4-24h.

9. A process for preparing Ti-Beta zeolite with recyclable organic base based on gas phase transmission method according to claim 8, characterized in that: In the third step, the parameter requirements are as follows: The amount of the liquid water added to the kettle bottom is calculated based on the mass ratio of the liquid water to the precursor, and the mass ratio of the liquid water to the precursor is in the range of 2.0-2.5; The amount of the volatile weak organic base is calculated based on the mass percentage concentration of the organic base in the aqueous solution, and the mass percentage concentration of the organic base in the aqueous solution ranges from 30% to 40%. The reaction temperature range for structural reconstruction is: 135-150°C; The reaction time range of structural reconstruction is: 6-18h.

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