阅读说明：本技术 一种无氟条件下高硅Beta沸石分子筛的合成方法 (Method for synthesizing high-silicon Beta zeolite molecular sieve under fluorine-free condition ) 是由 纪红兵 姜久兴 王永庆 严丹萍 马飞 于 2019-11-20 设计创作，主要内容包括：本发明公开了一种无氟条件下高硅Beta沸石分子筛的合成方法。该方法通过浓溶胶制备、加Beta分子筛晶种、恒温加热晶化等制备工艺得到高硅Beta沸石分子筛。本发明避免了高毒性氟物种的使用,所合成出的Beta分子筛具有高硅铝比和高结晶度。本发明具有环境友好、价格低廉、工艺简单等优点。(The invention discloses a method for synthesizing a high-silicon Beta zeolite molecular sieve under a fluorine-free condition. The method obtains the high-silicon Beta zeolite molecular sieve by the preparation processes of thick sol preparation, Beta molecular sieve seed crystal addition, constant-temperature heating crystallization and the like. The invention avoids the use of highly toxic fluorine species, and the synthesized Beta molecular sieve has high silicon-aluminum ratio and high crystallinity. The invention has the advantages of environmental protection, low price, simple process and the like.)

1. A method for synthesizing a high-silicon Beta zeolite molecular sieve under a fluorine-free condition is characterized by comprising the following steps:

dissolving a template agent and an alkali source together, adding a silicon source, stirring and mixing at room temperature to form concentrated sol, adding Beta zeolite seed crystals into the concentrated sol, controlling the water content within the molar ratio of the silicon source to the water =5 ~ 12, transferring to a reaction kettle, heating in an oven at constant temperature for crystallization reaction, cooling at room temperature after the reaction is finished, and performing suction filtration and drying on the obtained product to obtain the high-silicon Beta zeolite molecular sieve.

2. The synthesis method according to claim 1, wherein the raw materials are added in a molar ratio of silicon source to alkali source to template =1:0.1 ~ 5:0.3 ~ 6.

3. The synthesis method according to claim 1, wherein the silicon source is white carbon black, silica sol, tetramethyl silicate or tetraethyl silicate, the alkali source is sodium hydroxide, and the template agent is tetraethylammonium hydroxide.

4. The synthesis method of claim 1, wherein the Beta molecular sieve seed crystal is added in an amount of 1 ~ 15% of the mass of the silicon source.

5. The synthesis method of claim 1, wherein the crystallization reaction temperature is 120 ~ 200 ℃ and the crystallization reaction time is 1 ~ 6 days.

Technical Field

The invention belongs to the field of molecular sieve preparation, and particularly relates to a method for synthesizing a high-silicon Beta zeolite molecular sieve by concentrated sol under a fluorine-free condition.

Background

Zeolite Beta was first synthesized by Mobil corporation of america in 1967 in the strongly basic system of tetraethylammonium hydroxide by hydrothermal crystallization (USP 308069). Because of the unique three-dimensional 12-membered ring cross channel structure and good thermal stability and hydrothermal stability, the Beta zeolite used as a catalyst shows excellent catalytic performance in the petroleum refining and petrochemical processes of hydrocracking, dewaxing, aromatic alkylation, olefin hydration and the like, and is an important industrial zeolite molecular sieve.

The structure of zeolite Beta molecular sieves was not published by J. Newsam et al (1988)Proc. R. Soc. London Ser. A-Math. Phys. Eng. Sci.1988,420375-Zeolites1988,8446-. The framework of zeolite Beta is shown to have 3 isomers, A, B, C. the ratio of polymorph A to polymorph B in conventional zeolite Beta crystals is about 45: 55.

Topologically, zeolite Beta belongs to the same family as Mordenite (Mordenite), ZSM-12 zeolites. When Beta zeolite is synthesized in a conventional strong alkaline hydrothermal system, the silicon-aluminum-to-atomic silicon-aluminum ratio (Si/Al) molecular ratio (SiO) of silicon alumina₂/Al₂O₃) The range is very limited by the Si/a 1. Mordenite (Mordenite) heterocrystals are often produced at Si/A1 atomic ratios below 15, and ZSM-12 zeolite and ZSM-5 zeolite heterocrystals are often produced when high silica to alumina ratio Beta zeolite is synthesized at Si/A1 atomic ratios above 30, particularly 50- ∞. And the Beta zeolite with high silicon-aluminum ratio or full silicon has high stability, hydrothermal stability and hydrophobicity, and has a plurality of potential applications as a carrier or an adsorbent of a metal-loaded catalyst and the like.

European patent application EP0095303A1, EP0094827B1 in 1982 and U.S. patent US4554065 in 1985 propose a method for increasing the silicon-aluminum ratio of Beta zeolite by dealumination with inorganic acid, however, for industrial application, the direct obtainment of high-silicon or all-silicon Beta zeolite by hydrothermal synthesis can reduce the production cost, avoid the pollution of inorganic acid emission to the environment, and has obvious practical value.

In 1990, the united states patent of inventions (US4923690) disclosed a direct hydrothermal synthesis of high silicon zeolite Beta. The method is technically characterized in that white carbon black or silica gel is used as a silicon source, sodium aluminate is used as an aluminum source, tetraethylammonium cation is used as a template agent, sodium chloride is selectively added, and crystallization is carried out at the temperature of 90-200 ℃ to obtain the product with the Si/Al atomic ratio of 10-500 (SiO corresponds to the molecular ratio of silicon to aluminum)₂/Al₂O₃Silica to alumina ratio, 20-1000. For ease of comparison, the molecular ratio is converted uniformly to the atomic ratio hereinafter. ) Beta zeolite with relative crystallinity of 30-90%. When the silicon-aluminum ratio is increased, the crystallinity is reduced and the crystallization is incomplete.

In 1992, the U.S. patent application (US5164169) disclosed a direct hydrothermal synthesis of high silicon zeolite Beta. The method is technically characterized in that white carbon black is used as a silicon source, sodium aluminate is used as an aluminum source, a chelating agent such as triethanolamine and tetraethylammonium ions is used as a template agent, high-purity Beta seed crystal is added to be crystallized at the temperature of 70-175 ℃, and the Beta zeolite with the silicon-aluminum atomic ratio Si/Al of 100-500 and higher purity can be obtained. However, the specific surface area of the Beta molecular sieve is obviously reduced while the silicon-aluminum ratio is improved, and in addition, because triethanolamine and tetraethylammonium fluoride are used in the patent, the practicability of the patent is influenced due to safety reasons.

In 1994, chinese patent invention (CN1086792A, CN1086793A) disclosed a method for direct hydrothermal synthesis of zeolite Beta. The method is technically characterized in that active silicon dioxide/water glass is used as a silicon source, tetraethyl ammonium hydroxide is used as a template agent, sodium carbonate is added, and crystallization is carried out for 30 hours at 140 ℃ in a static kettle to obtain the Beta zeolite with the silicon-aluminum ratio of 19.1. It is worth noting that although the SiO ingredient is formulated₂/Al₂O₃= infinity, but no all-silicon or high-silicon zeolite Beta has been synthesized.

Published literature in 1996Chem, Commun, 1996,2365 reports a direct hydrothermal synthesis of all-silicon Process for zeolite Beta. The method is technically characterized in that tetraethoxysilane is used as a silicon source, tetraethylammonium hydroxide is used as a template agent, and hydrofluoric acid is used as a mineralizer. The greatest contribution here is the direct synthesis of low-defect Beta, but the large-scale application of the method is severely hampered by the introduction of the highly toxic hydrofluoric acid as a mineralizer. In the context of the subsequent reports,Top.Catal.1999,9, 59–76，Micropor. Mesopor. Mater.2006，90，237-245,Catal. Today2002,74, 271-279,Stud. Surf. Sci. Catal.,2004,154,725-730,Chem. Mater.2004,4, 725-730，Chem. Mater.2005,17, 4374-4385，3218-3223Micropor. Mesopor.Mater.2006，93，55-61，Micropor. Mesopor.Mater.2006，89，88-95，Angew. Chem. Int. Ed.2006,45,8013-8015，Micropor. Mesopor. Mater.,2007，100，118-127，Chem. Mater.2008,203218-3223 and the patents of the invention (CN1290654, CN101311116A, CN101462738A, CN105800634A, CN1096417C, CN101311116A) use a series of quaternary ammonium salts as organic structure directing agents to synthesize high silicon or all-silicon zeolites, but due to the same problems, the use of fluorine-containing systems causes serious environmental pollution problems in industrial production, thereby limiting the application of these methods.

Chinese patent (CN1154341A, CN1154342A) discloses a method for synthesizing Beta zeolite, which is technically characterized in that silica gel with any pore diameter and 20 ~ 300 meshes is used as a silicon source, the silica gel is mixed with a working solution consisting of an aluminum source, a sodium source, a tetraethylammonium cation source and water to wet the surfaces of silica gel particles with the working solution, and then crystallization reaction is carried out in two or more stepsActa Phys.- Chim. Sin.2008, crystallizing 24, 1192-1198 at the temperature of 180 ℃ for 12 to 32 hours in a standing still to obtain the Beta zeolite with the silicon-aluminum ratio ranging from 24 to 452. Although the method greatly reduces the dosage of the template agent and synthesizes the Beta zeolite with high silica-alumina ratio, the application of the Beta zeolite is influenced by complicated operation steps.

Thereafter, the literatureMicropor. Mesopor. Mater.1999，28519-530 reports a method for direct hydrothermal synthesis of all-silicon Beta zeolite by using an alkali system. The method is technically characterized in that white carbon black is used as a silicon source, a non-corresponding isomer of 4,4' -trimethylenebis (1-benzyl-1-methylpiperidine) quaternary ammonium salt cation is used as a structure directing agent, and the all-silicon Beta zeolite is synthesized by crystallizing for 2-16 days in a standing kettle at 135-150 ℃. The preparation process of the template agent involved in the method is complex.

Open literatureChem. Commun.,2001, 1486-1487 reports a direct hydrothermal synthesis of the all-silicon zeolite Beta C-type. It is technically characterized by that it uses tetraethyl orthosilicate as silicon source and uses DABMe (OH) as silicon sourceCrystallizing the template agent (namely-N-methyl quaternary ammonium base of triethylene diamine) at 150 ℃ for 12 days, and carrying out hydrothermal synthesis to obtain the BEC zeolite. Also, the templating agents involved in this process are quite expensive.

Open literatureACS Appl. Mater. Interfaces2017,927273-27283, which are respectively suitable for acid treatment dealuminization method, crystal transformation method, fluorine system and alkali system synthesis to synthesize the all-silicon Beta zeolite. The problems of the acid treatment method and the fluorine system method have been mentioned above and will not be described in detail. Similar to the Chinese patent (CN106430230A), the crystal transformation method needs to synthesize pure silicon ITQ-1 first, and two expensive templates, namely N, N, N-trimethy-1-adamaramium hydroxide or hexamethynimine, are used, so that the crystal transformation method has no industrialization prospect. In the case of the base system synthesis used herein, too large a quantity of seed crystals (10% relative to SiO) is used₂Dosage), also limiting its scale-up applications.

Open literatureJ.Inorg. Mater.,2018,339,963-968 synthesized zeolite Beta from all-silicon by a single template synthesis method, i.e., a seed-guided vapor assisted crystallization (SAC). The method is technically characterized in that white carbon black is used as a silicon source, tetraethylammonium hydroxide is used as a template agent, Beta crystal seeds with the ratio of sodium hydroxide to silicon to aluminum being 28 are added, the raw materials are stirred into paste, then the paste is placed into a 60 ℃ oven to be dried into dry glue and smashed, the dry glue is placed into a porous sieve made of polytetrafluoroethylene, a proper amount of water is placed into the bottom of a 45 mL stainless steel reaction kettle, and the sieve filled with the dry glue is fixed in the middle of the reaction kettle by a stainless steel wire without contacting with the water. And (4) screwing the kettle button, putting the kettle button into a preheated oven at 150 ℃, and standing and crystallizing at constant temperature for about 48 hours to obtain the all-silicon Beta zeolite sample. Open literatureAngew. Chem. Int. Ed.2018,573607-3611 also uses a steam assisted crystallization method to realize the synthesis of the all-silicon Beta zeolite molecular sieve, but because the reaction kettle of the steam assisted crystallization method is too complex, the operation is not easy, and the industrial value is influenced.

Chinese patent (CN107804856) discloses a direct synthesis method of Beta zeolite molecular sieve with high silica-alumina ratio under a fluorine-free system, which is characterized in that sodium salt or ammonium salt of phosphoric acid is used as a mineralizer, and an organic silicon source silane coupling agent is also used. The silane coupling agent is expensive, and the practical value of the method is influenced.

In the above synthesis of zeolite Beta, although carried out under fluorine-free conditions, there are two significant problems: the silicon-aluminum ratio of the synthesized Beta zeolite product is not high; complex operation, complex device and difficult realization of industrial production.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for synthesizing a high-silicon Beta zeolite molecular sieve under the fluorine-free condition without adding a fluorine-containing mineralizer in an aging stage.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for synthesizing a high-silicon Beta zeolite molecular sieve under a fluorine-free condition comprises the following steps:

dissolving a template agent and an alkali source together, adding a silicon source, stirring and mixing at room temperature to form concentrated sol, adding Beta molecular sieve seed crystals into the concentrated sol, controlling the water content, transferring the mixture to a reaction kettle, heating the mixture in a drying oven at constant temperature to perform crystallization reaction, cooling at room temperature after the reaction is finished, and performing suction filtration and drying on the obtained product to obtain the high-silicon Beta zeolite molecular sieve (Si/Al =200 ~ ∞).

In the above synthesis method, the raw materials are preferably added in a molar ratio of silicon source, alkali source and template =1:0.1 ~ 5:0.3 ~ 6.

Preferably, in the above synthesis method, the silicon source is white carbon black, silica sol, tetramethyl silicate or tetraethyl silicate, the alkali source is sodium hydroxide, and the template agent is tetraethylammonium hydroxide.

Preferably, in the above synthesis method, the amount of the Beta molecular sieve seed crystal added is 1 ~ 15% of the mass of the silicon source.

Preferably, in the above synthesis method, the crystallization reaction temperature is 120 ~ 200 ℃, and the crystallization reaction time is 1 ~ 6 days.

Compared with the prior art, the invention has the beneficial effects that:

1. the method for synthesizing the high-silicon Beta zeolite molecular sieve by using the concentrated sol under the fluorine-free condition avoids the use of high-toxicity fluorine species and greatly reduces the synthesis risk.

2. The invention can synthesize the Beta molecular sieve with high crystallinity and silicon-aluminum ratio of 200 ~ ∞ within 48 hours, and promotes the wide application of the high-silicon Beta molecular sieve.

3. The inorganic raw materials adopted by the invention are environment-friendly, the price is low, the operation steps are simple and feasible, and the method has important significance in the field of actual chemical production.

Drawings

FIG. 1: XRD spectrum of the product of example 1.

FIG. 2: SEM spectrum of the product of example 1.

FIG. 3: the nitrogen sorption and desorption isotherms of the product of example 1.

Detailed Description

The invention is described in further detail below with reference to the following detailed description and accompanying drawings: