Mordenite molecular sieve as well as preparation method and application thereof

Abstract

The invention relates to the technical field of molecular sieve catalytic materials, in particular to a mordenite molecular sieve and a preparation method and application thereof.The preparation method comprises the following steps that in the presence of mordenite seed crystals and industrial byproduct salt, a reaction mixture containing a silicon source, an aluminum source, an alkali source and deionized water is subjected to crystallization treatment, and metal cation type mordenite is obtained; carrying out inorganic acid ion exchange treatment on the metal cation type mordenite to obtain hydrogen type mordenite; and carrying out surface modification treatment on the hydrogen-type mordenite, and then sequentially drying and roasting to obtain the mordenite molecular sieve. The method has the advantages that the industrial by-product salt is used as the mineralizing agent, and is cooperated with the guiding effect of the seed crystal to promote crystal nucleus formation and crystal growth of the mordenite molecular sieve and accelerate crystallization of the mordenite molecular sieve; the synthesized mordenite powder is subjected to low-concentration inorganic acid exchange treatment to prepare hydrogen-type mordenite, and a molecular sieve framework structure is reserved to the maximum extent. And carboxylic acid sodium salt is adopted to carry out outer surface acidity regulation and 12-membered ring orifice modification on the hydrogen-type mordenite molecular sieve, so that the hydrogen-type mordenite molecular sieve has high dimethylamine selectivity and good catalytic stability in methanol amination reaction, and has large-scale industrial application potential.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve catalytic materials technology, and in particular to a mordenite zeolite molecular sieve, its preparation method, and its application. Background Technology

[0002] Mordenite is a high-silica molecular sieve composed of parallel twelve-membered ring main channels (approximately 0.65 nm × 0.70 nm in diameter) and side-connected eight-membered ring channels (0.26 × 0.57 nm in diameter). This unique channel structure endows mordenite with excellent shape selectivity and acidity distribution characteristics, effectively overcoming the diffusion limitations of the single eight-membered ring channels in SSZ-13 and SAPO-34 molecular sieves, while avoiding the poor shape selectivity problem of macroporous molecular sieves (such as Y-type). Currently, mordenite shows promising application prospects in dimethyl ether carbonylation, toluene disproportionation, alkylation, and methanol amination.

[0003] CN120829167A discloses a method for preparing eight-membered ring aluminum-rich mordenite nanosheets, in which a silicon source, inorganic alkali, aluminum source, template agent, water, and metal additives are mixed and stirred in an ice-water bath to prepare an initial gel; then a one-stage hydrothermal crystallization, centrifugation, filtration, and drying are performed to obtain a metal cation-type mordenite molecular sieve; CN119898789A discloses a flower-like spherical mordenite and its preparation method, wherein the flower-like spherical mordenite is a self-assembled aggregate of multiple plate-like mordenite, and its synthesis requires mixing an aluminum source, a structure directing agent I, an alkali source, and water to obtain a mixed system I, then adding a silicon source and a structure directing agent II to the mixture I and stirring to obtain an initial gel, and then crystallizing, filtering, and washing to obtain a crystallized product; CN120698478A discloses a small-grained mordenite molecular sieve and its preparation method. The method employs a segmented crystallization process. First, a first gel containing a mixture of silicon source, aluminum source, template agent, and alkali source is crystallized and synthesized. Then, the slurry is mixed with a second gel containing a mixture of silicon source, aluminum source, template agent, and alkali source and crystallized again to obtain the product.

[0004] Although the above patents have produced relatively thin and small nanofiber zeolite products, improving the catalytic performance of the products, the synthesis steps are complex and require one or even two organic template agents, including but not limited to hexadecyltrimethylammonium bromide, amines, quaternary ammonium salts, alcohols, etc. This not only increases the production cost, but also greatly increases the difficulty of post-treatment of the products and production wastewater.

[0005] Therefore, existing techniques for preparing mordenite nanosheet molecular sieves generally rely on complex template agents (such as bifunctional template agents) or cumbersome processes (such as stepwise hydrothermal synthesis), resulting in problems such as multiple synthesis steps and long cycles. Furthermore, complex template agents are costly, polluting, and difficult to mass-produce, which seriously hinders their industrial application. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a mordenite molecular sieve, its preparation method, and its application. The invention employs an organic template-free method, utilizing inorganic sodium and potassium salts as mineralizing agents in the synthesis system. These agents, along with the guiding effect of seed crystals, accelerate the formation of mordenite nuclei and the rapid growth of crystals, resulting in highly crystalline nanosheet-like mordenite molecular sieves. Furthermore, sodium carboxylate solution is used to perform surface acid modification and twelve-membered ring pore modification on the hydrogen-form mordenite molecular sieve, enabling it to exhibit high methanol conversion and excellent dimethylamine selectivity in methanol amination reactions.

[0007] This invention is achieved through the following technical solution: On one hand, it provides a method for preparing mordenite molecular sieves, comprising the following steps: In the presence of mordenite seed crystals and industrial by-product salts, a reaction mixture containing silicon source, aluminum source, alkali source and deionized water is crystallized to obtain metal cationic mordenite. The metal cation-type mordenite was subjected to inorganic acid ion exchange treatment to obtain hydrogen-type mordenite H-MOR. The hydrogen-type mordenite zeolite was surface modified, and then dried and calcined in sequence to obtain mordenite molecular sieve MOR-SC.

[0008] Through the above technical solution, this invention synthesizes highly crystalline nanosheet-like mordenite molecular sieves without using any organic template agents, and prepares hydrogen-type mordenite using a mild acid washing process, thus preserving the original framework structure of the molecular sieve to the maximum extent. The acidic sites on the outer surface are reasonably controlled, and the pore size of the twelve-membered ring is also appropriately reduced. When used in methanol amination reaction, it can effectively reduce the catalytic reaction temperature and effectively improve the selectivity of dimethylamine, thereby increasing the product yield of dimethylamine.

[0009] Specifically, the preparation process of the reaction mixture includes the following steps: Step 1: Dissolve a certain amount of inorganic alkali source and industrial by-product salt in deionized water, stir until clear, then add aluminum source and continue stirring until clear; Step 2: Slowly add the silicon source to the solution obtained in step 1 to form a silica-alumina gel, and stir for 10-20 minutes to form a homogeneous gel. Step 3: Add the mordenite seed crystals and continue stirring for 30 minutes to obtain the reaction mixture.

[0010] Step 4: Transfer the reaction mixture to a hydrothermal reactor for hydrothermal crystallization. The hydrothermal crystallization temperature is 120-200℃, the crystallization time is 10-48h, and the crystallization rotation speed is 10-50HZ.

[0011] Step 5: After crystallization, the slurry undergoes solid-liquid separation and washing, followed by acid washing with a low concentration of inorganic acid. After acid washing, it is washed with deionized water until no Cl is present in the washing solution. - SO4 2- / NO3 - The acid-washed solid is placed in an oven at 80-100℃ and dried for a certain period of time to obtain hydrogen-form mordenite zeolite.

[0012] Step 6: Place the hydrogen-form mordenite in a sodium carboxylate solution of a certain concentration for surface modification and pore modification. After modification, solid-liquid separation, drying and calcination are required.

[0013] The above process consists of the basic steps in the synthesis of molecular sieves. The reaction mixture is an amorphous silica-alumina gel, which is alkaline and has a certain viscosity.

[0014] Further, in the reaction mixture, the silicon source is calculated as SiO2, the aluminum source as Al2O3, the alkali source as Na2O, and the industrial by-product salt is calculated as cations, in molar ratios as follows: SiO2 / Al2O3 = 10-30; H2O / SiO2 = 10-25; Na2O / SiO2 = 0.15-0.3; The molar ratio of the cations in the industrial by-product salt to SiO2 is 0.05-0.3; the amount of the mordenite seed crystals added is 1%-5% of the mass of SiO2.

[0015] Through the above technical solutions, the nanosheet-like silica zeolite molecular sieve prepared by the present invention has a high specific surface area and crystallinity.

[0016] In the aforementioned crystallization, inorganic acid solution ion exchange treatment, surface modification of hydrogen-form mordenite molecular sieves, and pore modification processes, the molar ratios in the synthesis process are key factors. Appropriate aging conditions, crystallization temperature, and time are crucial for synthesizing mordenite molecular sieves with regular nanosheet morphology. Molecular sieve crystallization is a highly complex chemical reaction process. Different molecular sieve crystallization processes require adjustments to the alkalinity, water volume, type and amount of organic template agent added. The requirements for these factors vary depending on the silicon-to-aluminum ratio range, but each has an optimal range. The molar ratios of the substances specified in this invention represent the optimal synthesis range derived from extensive experimental research.

[0017] Furthermore, the industrial by-product salt is selected from at least one of potassium chloride, sodium chloride, potassium sulfate, and sodium sulfate; sodium chloride, potassium chloride, anhydrous sodium sulfate, and potassium sulfate are all industrial by-product salts produced during wastewater treatment processes. In the molecular sieve synthesis described in this invention, they serve as mineralizing agents for crystal growth, mainly playing a key role in regulating crystal nucleation and growth, optimizing crystal phase structure, and improving crystallization efficiency; industrial wastewater contains a large amount of Na... + Direct ion emission leads to soil salinization, and sodium salts formed through evaporation crystallization have low economic benefits. Developing new application pathways can effectively improve their utilization value. In the synthesis of mordenite molecular sieves, adding an appropriate amount of industrial by-product salt as a mineralizing agent can effectively promote the entry of aluminum species into the molecular sieve framework, broaden the silica-alumina ratio range of the molecular sieve, and especially for mordenite with a low silica-alumina ratio, effectively inhibit the formation of impurity phases and improve the crystallinity of the product.

[0018] And / or, the silicon source is selected from at least one of silica sol, silica gel powder, sodium silicate, and fumed silica; the molecular sieve synthesized in this invention belongs to aluminosilicates, and the silicon source is an essential raw material. In the synthesis system, the silicon in the silicon source can form silicon-oxygen tetrahedra, which are the basic structural units of the molecular sieve.

[0019] And / or, the aluminum source is selected from at least one of aluminum sulfate octahydrate, sodium aluminate, aluminum isopropoxide, and aluminum nitrate; And / or, the alkali source is sodium hydroxide. The alkali source provides the necessary alkalinity for molecular sieve synthesis and has a stabilizing effect on silicate sols; simultaneously, the alkali metal cations in the inorganic alkali can balance the negative charge of the molecular sieve framework and also act as pore fillers; if H+ is used... + When other cations replace alkali metal cations, the sol may destabilize, leading to precipitation or solidification.

[0020] Furthermore, the crystallization treatment is carried out at a temperature of 120-200°C for a time of 10-48 hours; And / or, the crystallization process is carried out under stirring conditions at a speed of 10-50 rpm.

[0021] The crystallization process described above is a one-step crystallization method. To ensure better crystallization results, the reaction mixture must be aged at room temperature for 2 hours before crystallization. The crystallization temperature is 120-200℃, preferably 150-180℃, and the crystallization time is 10-48 hours, preferably 10-24 hours. The entire crystallization process is carried out under dynamic conditions, with a rotation speed of 10-50 rpm.

[0022] Furthermore, the inorganic acid is selected from at least one of hydrochloric acid, nitric acid, and sulfuric acid, and has a concentration of 0.1-1 mol / L; And / or, the solid-liquid ratio of the metal cation type mordenite to the inorganic acid solution is 1:5-1:20; And / or, the conditions for the ion exchange are: temperature of 15-35℃, time of 2-4h, and number of times of exchange 2.

[0023] Through the above technical solution, the acidic properties of the molecular sieve mainly originate from the bridged hydroxyl groups in the framework, and the directly synthesized molecular sieve framework is composed of Na... + In this case, the acidity is very weak and cannot provide the acidic centers required for the catalytic reaction. Therefore, it is necessary to remove the Na from the molecular sieve obtained by hydrothermal synthesis. + After ion exchange, it is replaced with protons H. + Only then can hydrogen-form molecular sieves suitable for catalytic reactions be obtained. The exchange of metal cation-form mordenite for hydrogen-form mordenite can be achieved through inorganic ammonium salt solution exchange or inorganic acid exchange. Generally, inorganic ammonium salt solution exchange requires a higher concentration of ammonium salt and must be carried out at an environment not lower than 80°C. NH4 + Mainly based on kinetic and thermodynamic effects, it enters the molecular sieve channels and interacts with Na. + Ion exchange occurs, and further high-temperature calcination is required after the exchange to neutralize the NH4+. + Hydrogen-form molecular sieves can only be obtained through thermal decomposition. This invention uses a low-concentration inorganic acid solution to wash the metal cation-form mordenite at room temperature. The H+ in the inorganic acid... + More readily reacts with Na in the zeolite framework + After the exchange process, only drying is required; high-temperature calcination is unnecessary. Using a lower concentration of inorganic acid for exchange minimizes damage to the original framework structure of the molecular sieve, preserving high crystallinity. Simultaneously, the acid washing process effectively removes impurities from the zeolite channels, clears the pore structure, improves micropore distribution, and thus enhances the accessibility of acidic centers.

[0024] The inorganic acid is selected from hydrochloric acid, nitric acid, and sulfuric acid, and the concentration of the inorganic acid is 0.1-1 mol / L, preferably 0.2-0.5 mol / L; the ratio of the synthesized metal cation type mordenite powder to the inorganic acid is 1:8-1:20, preferably 1:10-1:15, according to the solid-liquid ratio.

[0025] Furthermore, the surface modification treatment is a modification treatment using a sodium carboxylate salt solution; And / or, the sodium carboxylate is selected from at least one of sodium benzoate, sodium citrate, sodium oxalate, disodium EDTA, or tetrasodium EDTA; And / or, the concentration of the sodium carboxylate solution is 0.01-0.2 mol / L; the solid-liquid ratio of the hydrogen-form mordenite to the sodium carboxylate solution is 1:10-1:20; preferably 1:15.

[0026] Furthermore, the surface modification treatment conditions are as follows: modification temperature 30-60℃, modification time 1-5h, preferably 2-3h at 40-50℃, and one modification treatment is sufficient. After modification, solid-liquid separation is performed, followed by drying and calcination at 550-600℃ for 6-10h, preferably 8-10h at 570-580℃.

[0027] Another type of mordenite molecular sieve is provided, which is prepared by the above-mentioned method for preparing mordenite molecular sieve.

[0028] Furthermore, this molecular sieve has a plate-like morphology and a specific surface area of ​​450-600 m². 2 / g; the Na2O mass percentage of the molecular sieve is 0.4-0.6%; and / or, the Brønsted acid content on the outer surface of the molecular sieve is 10-30 μmol / g.

[0029] Finally, an application of mordenite molecular sieve in methanol amination reaction is provided, using the aforementioned mordenite molecular sieve as a catalyst.

[0030] Beneficial effects: This invention effectively promotes the formation of mordenite crystal nuclei and crystal growth by rationally utilizing industrial by-product salts as mineralizing agents for crystal growth and synergistically acting as seed crystals, thereby shortening the crystallization reaction time and improving production efficiency. Simultaneously, it effectively broadens the silica-alumina ratio range for synthesizing mordenite molecular sieves without organic templates, resulting in the preparation of mordenite molecular sieves with high crystallinity and high specific surface area. This overcomes the difficulties of existing methods for preparing nanosheet mordenite molecular sieves, which involve long synthesis times, complex synthesis steps, and the use of numerous organic templates.

[0031] This invention uses sodium carboxylate solution to regulate the acid properties of the outer surface of hydrogen-form mordenite molecular sieve and modify the pore size of the twelve-membered ring, which can effectively reduce the occurrence of side reactions and improve the selectivity of dimethylamine.

[0032] The method of this invention is simple and low-cost, does not use any organic template agents, reduces the difficulty of industrial synthesis and post-processing, is environmentally friendly, and is suitable for industrial mass production. Attached Figure Description

[0033] Figure 1 The XRD patterns of the hydrogen-form mordenite molecular sieves obtained in each embodiment are shown below. Figure 2 The XRD patterns of the hydrogen-form mordenite molecular sieves obtained in each comparative example are shown. Figure 3 SEM image of the hydrogen-type mordenite molecular sieve obtained in Example 1; Figure 4This is a SEM image of the hydrogen-type mordenite molecular sieve obtained in Example 2; Figure 5 This is a SEM image of the hydrogen-type mordenite molecular sieve obtained in Example 3; Figure 6 SEM image of the hydrogen-form mordenite molecular sieve obtained in Comparative Example 1. Figure 7 The image shows the SEM image of the hydrogen-type mordenite molecular sieve obtained in Comparative Example 3. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise stated, all percentages, ratios, proportions, or parts are by weight.

[0036] Unless otherwise specified, the reagents and raw materials used in the embodiments and comparative examples of this invention are commercially available.

[0037] Example 1: Add 18.8g of deionized water to the reactor and start stirring. Then add 3.7813g of sodium hydroxide, 5.498g of aluminum sulfate octadechydrate, and 2.8958g of sodium chloride sequentially. Stir for 10 minutes after each addition to ensure all materials are dissolved. Then, slowly add 33g of silica sol while stirring, and continue stirring until the mixture reaches a relatively thin consistency. Add 0.297g of mordenite seed crystals and allow to age at room temperature for 2 hours. After aging, transfer the mixture to a hydrothermal reactor and crystallize at 150℃ for 24 hours, maintaining a rotation speed of 30 rpm throughout the crystallization process. After crystallization, once the temperature has dropped below 80℃, open the reactor and centrifuge, wash, and dry the slurry.

[0038] The silica-alumina gel has the following composition: SiO2 / Al2O3=20, Na2O / SiO2=0.275, H2O / SiO2=15, NaCl / SiO2=0.3, and the amount of seed crystals added is 3% of the mass of SiO2.

[0039] The washed and dried powder was exchanged in a 0.5 mol / L sulfuric acid solution with a solid-liquid ratio of 1:10. The exchange was carried out at room temperature for 2 hours, and the exchange was repeated twice. After filtration, washing, and drying at 80°C, the hydrogen form sample was obtained.

[0040] The obtained sample was tested by X-ray diffraction, and the results showed that it was a pure-phase mordenite molecular sieve. Figure 1 The crystal morphology of the obtained product is shown in the figure. Figure 3 It is in the form of highly dispersible nanosheets with a thickness of 20-50 nm.

[0041] Hydrogen-form mordenite powder was added to a 0.02 mol / L sodium citrate solution and stirred at 50°C for 2 hours at a solid-liquid ratio of 1:15. After filtration, it was dried at 100°C and calcined in a muffle furnace at 580°C for 8 hours to obtain a catalyst for methanol amination.

[0042] Example 2: Add 53.22g of deionized water to the reactor and start stirring. Then add 1.4689g of sodium hydroxide, 1.4291g of sodium aluminate, and 2.1521g of sodium sulfate sequentially. Stir for 10 minutes after each addition to ensure all materials are dissolved. Then, slowly add 9.67g of silica gel powder while stirring, stirring until a relatively thin consistency is reached. Add 0.36g of mordenite seed crystals and age at room temperature for 2 hours. After aging, transfer to a hydrothermal reactor and crystallize at 170℃ for 12 hours, maintaining a rotation speed of 30 rpm throughout the crystallization process. After crystallization, cool the mixture to below 80℃ with cold water, open the reactor, and centrifuge, wash, and dry the slurry.

[0043] The composition of the silica-alumina gel is SiO2 / Al2O3=25, Na2O / SiO2=0.18, H2O / SiO2=20, Na2SO4 / SiO2=0.1, and the amount of seed crystals added is 4% of the mass of SiO2.

[0044] The washed and dried powder was subjected to ion exchange treatment in a 0.4 mol / L nitric acid solution. The solid-liquid ratio of the molecular sieve powder to the nitric acid solution was 1:10. The exchange was carried out at room temperature for 2 hours, and the exchange was repeated twice. After filtration, washing, and drying at 80℃, the hydrogen form sample was obtained.

[0045] The obtained sample was tested by X-ray diffraction, and the results showed that it was a pure-phase mordenite molecular sieve. Figure 1 The crystal morphology of the obtained product is shown in the figure. Figure 4 It is in the form of highly dispersible nanosheets with a thickness of 20-50 nm.

[0046] Hydrogen-form mordenite powder was added to a 0.04 mol / L sodium benzoate solution and stirred at 40°C for 2 hours at a solid-liquid ratio of 1:15. After filtration, the solution was dried at 100°C and calcined in a muffle furnace at 580°C for 8 hours to obtain a catalyst for methanol amination.

[0047] Example 3: Add 27.0g of deionized water to the reactor, start stirring, and add 4.4429g of aluminum sulfate octahydrate and 1.1183g of potassium chloride. After stirring and clarifying, slowly add 22.48g of sodium silicate, stirring until a relatively thin state is reached. Then slowly add 3.18g of silica sol and 0.3g of mordenite seed crystals, and stir and age at room temperature for 2 hours. After aging, transfer to a hydrothermal reactor and crystallize at 170℃ for 12 hours, maintaining a rotation speed of 30 rpm during the crystallization process. After crystallization, when the temperature drops below 80℃, open the reactor, centrifuge, wash, and dry the slurry.

[0048] The silica-alumina gel has the following composition: SiO2 / Al2O3=15, Na2O / SiO2=0.29, H2O / SiO2=25, KCl / SiO2=0.15, and the amount of seed crystals added is 5% of the mass of SiO2.

[0049] The washed and dried powder was exchanged in a 0.3 mol / L hydrochloric acid solution with a solid-liquid ratio of 1:10 to sulfuric acid solution. The exchange was carried out at room temperature for 2 hours, and the exchange was repeated twice. After filtration, washing, and drying at 80°C, the hydrogen form sample was obtained.

[0050] The obtained sample was tested by X-ray diffraction, and the results showed that it was a pure-phase mordenite molecular sieve. Figure 1 .

[0051] Hydrogen-form mordenite powder was added to a 0.05 mol / L sodium oxalate solution and stirred at 50°C for 2 hours at a solid-liquid ratio of 1:15. After filtration, it was dried at 100°C and then calcined in a muffle furnace at 580°C for 8 hours to obtain a catalyst for methanol amination.

[0052] Example 4: Add 33.85g of deionized water to the reactor and start stirring. Add 2.6657g of aluminum sulfate octadechydrate and 1.0457g of potassium sulfate. After stirring and clarifying, slowly add 27.29g of sodium silicate. Stir until a relatively thin consistency is reached, then slowly add 0.9028g of silica gel powder and 0.216g of mordenite seed crystals. Aging is carried out at room temperature with stirring for 2 hours. After aging, transfer the mixture to a hydrothermal reactor. Crystallization temperature is 180℃, and crystallization time is 10 hours. After crystallization, when the temperature drops below 80℃, open the reactor and centrifuge, wash, and dry the slurry.

[0053] The composition of the silica-alumina gel is SiO2 / Al2O3=30, Na2O / SiO2=0.3, H2O / SiO2=25, K2SO4 / SiO2=0.05, and the amount of seed crystals added is 3% of the mass of SiO2.

[0054] The washed and dried powder was exchanged in a 0.3 mol / L nitric acid solution with a solid-liquid ratio of 1:15 to sulfuric acid solution. The exchange was carried out at room temperature for 2 hours, and the exchange was repeated twice. After filtration, washing, and drying at 80°C, the hydrogen form sample was obtained.

[0055] The obtained sample was tested by X-ray diffraction, and the results showed that it was a pure-phase mordenite molecular sieve. Figure 1 .

[0056] Hydrogen-form mordenite powder was added to a 0.02 mol / L sodium citrate solution and stirred at 50°C for 2 hours at a solid-liquid ratio of 1:15. After filtration, it was dried at 100°C and calcined in a muffle furnace at 580°C for 8 hours to obtain a catalyst for methanol amination.

[0057] Example 5: Add 18.57g of deionized water to the reactor and start stirring. Then, add 3.4375g of sodium hydroxide, 2.1471g of aluminum nitrate, and 1.755g of sodium chloride sequentially, stirring for 10 minutes after each addition to ensure each material is completely dissolved. Next, while stirring, slowly add 30g of silica sol, followed by 0.27g of mordenite seed crystals. Aging is carried out at room temperature for 2 hours. After aging, transfer the mixture to a hydrothermal reactor and crystallize at 150℃ for 24 hours, maintaining a rotation speed of 30 rpm throughout the crystallization process. After crystallization, once the temperature drops below 80℃, open the reactor and centrifuge, wash, and dry the slurry.

[0058] The silica-alumina gel has the following composition: SiO2 / Al2O3=28, Na2O / SiO2=0.275, H2O / SiO2=15, NaCl / SiO2=0.2, and the amount of seed crystals added is 3% of the mass of SiO2.

[0059] The washed and dried powder was exchanged in a 0.5 mol / L sulfuric acid solution with a solid-liquid ratio of 1:10. The exchange was carried out at room temperature for 2 hours, and the exchange was repeated twice. After filtration, washing, and drying at 80°C, the hydrogen form sample was obtained.

[0060] The obtained sample was tested by X-ray diffraction, and the results showed that it was a pure-phase mordenite molecular sieve. Figure 1 .

[0061] Hydrogen-form mordenite powder was added to a 0.06 mol / L disodium EDTA solution, and stirred at 40°C for 2 hours at a solid-liquid ratio of 1:15. After filtration, it was dried at 100°C and calcined in a muffle furnace at 580°C for 8 hours to obtain a catalyst for methanol amination.

[0062] Comparative Example 1: A mordenite molecular sieve was synthesized according to the method in Example 1 of patent CN106672998A. At room temperature, under magnetic stirring, silica sol, sodium hydroxide, water, and N-methylpiperidine were mixed in a certain proportion, then hydrothermally heated at 100°C for 24 hours. After cooling to room temperature, sodium aluminate powder was added to the solution and stirred until homogeneous. The mixture was then subjected to ultrasonication (0.5 KW / L) and magnetic stirring at 35°C for 2 hours, and finally crystallized at 175°C for 100 hours in a reaction vessel.

[0063] The silica-aluminum gel has the following composition: SiO2 / Al2O3=20, Na2O / SiO2=0.4, H2O / SiO2=45, and N-methylpiperidine / SiO2=0.10.

[0064] The washed and dried powder was exchanged in a 0.5 mol / L sulfuric acid solution with a solid-liquid ratio of 1:10. The exchange was carried out at room temperature for 2 hours, and the exchange was repeated twice. After filtration, washing, and drying at 80°C, the hydrogen form sample was obtained.

[0065] Hydrogen-type mordenite powder was added to a 0.02 mol / L sodium citrate solution and stirred at 50°C for 2 hours at a solid-liquid ratio of 1:15. After filtration, it was dried at 100°C and then calcined in a muffle furnace at 580°C for 8 hours to obtain a catalyst for methanol amination.

[0066] Compared with Example 1, Comparative Example 1 adopted the formulation of Example 1 (patent CN106672998A) and the post-processing method of this invention. The obtained sample, tested by X-ray diffraction, was a pure-phase mordenite molecular sieve, but with relatively low crystallinity. Figure 2 The appearance of the obtained product is shown in the figure. Figure 5 It is in the form of nanosheets, but is relatively large in size, with a major axis length of 500-900 nm.

[0067] Comparative Example 2: Add 34.98g of deionized water to the reactor and start stirring. Then, add 3.4375g of sodium hydroxide, 2.749g of aluminum sulfate octadechydrate, and 0.9653g of sodium chloride sequentially. Stir for 10 minutes after each addition to ensure all materials are dissolved. Next, slowly add 33g of silica sol while stirring until a relatively thin consistency is reached. Then, add 0.297g of mordenite seed crystals and age at room temperature for 2 hours. After aging, transfer to a hydrothermal reactor and crystallize at 150℃ for 24 hours, maintaining a rotation speed of 30 rpm. After crystallization, once the temperature drops below 80℃, open the reactor and centrifuge, wash, and dry the slurry.

[0068] The silica-alumina gel has the following composition: SiO2 / Al2O3=40, Na2O / SiO2=0.25, H2O / SiO2=20, seed crystal / SiO2=3%, and NaCl / SiO2=0.1.

[0069] The washed and dried powder was exchanged in a 0.5 mol / L sulfuric acid solution with a solid-liquid ratio of 1:10. The exchange was carried out at room temperature for 2 hours, and the exchange was repeated twice. After filtration, washing, and drying at 80°C, the hydrogen form sample was obtained.

[0070] Comparative Example 2, compared to Example 1, increased the silica-to-alumina ratio to 40, exceeding the scope of the claims. The resulting sample, tested by X-ray diffraction, was identified as a FER molecular sieve, not a mordenite zeolite molecular sieve. (See attached image) Figure 2 .

[0071] Comparative Example 3: Add 19.33g of deionized water to the reactor and start stirring. Then add 3.7812g of sodium hydroxide and 4.398g of aluminum sulfate octadechydrate sequentially, stirring for 10 minutes after each addition to ensure each material is completely dissolved. Next, slowly add 33g of silica sol while stirring, and continue stirring until the mixture reaches a relatively thin consistency. Then add 0.297g of mordenite seed crystals and age at room temperature for 2 hours. After aging, transfer the mixture to a hydrothermal reactor. Crystallize at 170℃ for 12 hours, maintaining a rotation speed of 30 rpm throughout the crystallization process. After crystallization, once the temperature drops below 80℃, open the reactor and centrifuge, wash, and dry the slurry.

[0072] The composition of the silica-alumina gel is SiO2 / Al2O3=25, Na2O / SiO2=0.275, H2O / SiO2=15, and the amount of seed crystals added is 3% of the mass of SiO2.

[0073] The washed and dried powder was exchanged in a 0.5 mol / L sulfuric acid solution with a solid-liquid ratio of 1:10. The exchange was carried out at room temperature for 2 hours, and the exchange was repeated twice. After filtration, washing, and drying at 80°C, the hydrogen form sample was obtained.

[0074] Comparative Example 3, compared to Example 1, did not contain any mineralizer. X-ray diffraction analysis of the obtained sample showed that the main phase was mordenite molecular sieve, but the crystallinity was low, with some amorphous material present. Figure 6 Some amorphous substances can be observed on the crystal surface, see Figure 2 The crystal morphology of the obtained product is shown in the figure. Figure 6 As can be seen from the figure, the flaky mordenite is relatively large in size, with a thickness of 300-500 nm, and there are some flocculent substances at the edges, which are incompletely crystallized amorphous silica-alumina gel.

[0075] Comparative Example 4: Add 33.85g of deionized water to the reactor, start stirring, add 2.6657g of aluminum sulfate octadechydrate and 1.0457g of potassium sulfate, stir until clear, then slowly add 27.29g of sodium silicate, stirring until a relatively thin consistency is reached, then slowly add 0.9028g of silica gel powder, and age at room temperature for 2 hours. After aging, transfer to a hydrothermal reactor, crystallize at 180℃ for 10 hours, maintaining a rotation speed of 30 rpm during crystallization. After crystallization, once the temperature drops below 80℃, open the reactor, centrifuge, wash, and dry the slurry.

[0076] The composition of the silica-alumina gel is SiO2 / Al2O3=30, Na2O / SiO2=0.3, H2O / SiO2=25, K2SO4 / SiO2=0.05, and seed crystal / SiO2=3%.

[0077] Comparative Example 4, compared to Example 4, did not include mordenite seed crystals. The resulting sample, as determined by X-ray diffraction, was a completely amorphous material. Figure 2 .

[0078] Effect Example The following tests were performed on Examples 1 to 5 and Comparative Examples 1 to 4: 1) XRD test of the synthesized and dried sample: The crystal structure of the powder sample after washing and drying was tested by X-ray diffraction.

[0079] Test results are available Figure 1 and Figure 2 . Figure 1 It includes the XRD curves of five samples obtained in Examples 1 to 5, from... Figure 1 As can be seen from the curves, the samples obtained in Examples 1 to 5 were all pure-phase mordenite molecular sieves. Figure 2 As can be seen from the curves, the product obtained in Comparative Example 1 is a pure phase mordenite molecular sieve, the product obtained in Comparative Example 2 is a FER molecular sieve, the main phase of the product obtained in Comparative Example 3 is mordenite, but the crystallinity is low and there is a certain amount of amorphous material, and Comparative Example 4 cannot synthesize a molecular sieve and is completely amorphous.

[0080] 2) Morphology test of hydrogen-type nanosheet samples: The crystal morphology of the washed and dried powder samples was tested by scanning electron microscopy.

[0081] Test results are available Figures 3 to 6 ; Figure 3 , Figure 4The scanning electron microscope (SEM) images of the samples obtained in Examples 1 and 2 show that the obtained products are nanosheet-like mordenite molecular sieves with high crystal dispersion, clear edges, and a nanosheet thickness of 20-50 nm, consistent with the high crystallinity in the XRD pattern. Figure 5 The image shows a scanning electron microscope (SEM) image of the product obtained in Comparative Example 1. It can be seen from the image that the long axis of the nanosheets is significantly longer, ranging from 500 to 900 nm. Figure 6 The image shows a scanning electron microscope (SEM) image of the product obtained in Comparative Example 3. It can be seen from the image that the sheet-like sample is not nanoscale and has obvious flocculent material at the edges. This is some incompletely crystallized amorphous silica-alumina gel. This result is consistent with... Figure 2 The lower diffraction peaks of the three curves in the comparative example remain consistent.

[0082] 3) Preparation of hydrogen-form nanosheet samples: The washed and dried powder was exchanged in a 0.5 mol / L sulfuric acid solution, with a solid-liquid ratio of 1:10. The exchange was carried out at room temperature for 2 hours, repeated twice, followed by filtration, washing, and drying at 80℃ to obtain the hydrogen-form sample. This step is a routine procedure for preparing hydrogen-form molecular sieves.

[0083] The elemental composition of the hydrogen-form nanosheet samples was tested using X-ray fluorescence spectrometry. The silica-to-alumina ratio and sodium oxide percentage of the samples are shown in Tables 1 and 2. As can be seen from Table 1, this invention can synthesize mordenite molecular sieves with a silica-to-alumina ratio ranging from 10 to 30. The Na₂O content in all samples is around 0.4-0.6%, which is at a low level, indicating that the exchange process is relatively thorough.

[0084] 4) Acid characterization analysis of hydrogen-type nanosheet samples: The prepared hydrogen-type nanosheet sample powder was pressed into tablets in a mold and crushed into small particles of 20×40 mesh. Using nitrogen as a medium, the pyridine infrared temperature-programmed adsorption and desorption were used to test the Brønsted acid content on the outer surface of the hydrogen-type nanosheet sample.

[0085] The test results are shown in Table 2. Table 2 shows that as the silicon-to-aluminum ratio (S / A ratio) of the samples increases, the content of Brønsted acid (B acid) on the outer surface of the samples gradually decreases, which is consistent with the variation of the acid properties of molecular sieves with the S / A ratio. Through acid property characterization tests, samples with a suitable S / A ratio range can be screened for catalytic reactions based on the amount of acid required.

[0086] Evaluation of methanol amination catalytic performance: The hydrogen-form nanosheet mordenite molecular sieve modified with sodium carboxylate was evaluated for methanol amination under the conditions of reaction temperature 260-380℃, N / C molar ratio 2.5, and mass hourly space velocity 1.5 / h.

[0087] The test results are shown in Table 2.

[0088] Table 1. Physicochemical properties of hydrogen-form samples obtained from each embodiment and comparative example.

[0089] The crystallinity of the sample from Example 2 was selected as the benchmark for relative crystallinity and set at 100%.

[0090] Table 2. Na₂O content and methanol amination catalytic performance of the hydrogen-form samples obtained from each example and comparative example after modification with sodium carboxylate solution.

[0091] In summary, this invention effectively promotes the formation of mordenite crystal nuclei and crystal growth by rationally utilizing industrial by-product salts as mineralizing agents for crystal growth and synergistically acting as seed crystals. This shortens the crystallization reaction time and improves production efficiency. Simultaneously, it effectively broadens the silica-alumina ratio range for synthesizing mordenite molecular sieves without organic templates, resulting in mordenite molecular sieves with high crystallinity and high specific surface area. This effectively overcomes the difficulties of existing methods for preparing nanosheet mordenite molecular sieves, such as long synthesis times, complex synthesis steps, and the use of numerous organic templates. Furthermore, the method of this invention is simple, low-cost, and does not use any organic templates, reducing the difficulty of industrial synthesis and post-processing. It is environmentally friendly and suitable for industrial mass production.

[0092] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing mordenite molecular sieves, characterized in that, Includes the following steps: In the presence of mordenite seed crystals and industrial by-product salts, a reaction mixture containing silicon source, aluminum source, alkali source and deionized water is crystallized to obtain metal cationic mordenite. The metal cation-type mordenite was subjected to inorganic acid ion exchange treatment to obtain hydrogen-type mordenite. The hydrogen-type mordenite zeolite was surface modified, and then dried and calcined in sequence to obtain mordenite zeolite molecular sieve.

2. The method for preparing mordenite molecular sieve according to claim 1, characterized in that, In the reaction mixture, the silicon source is calculated as SiO2, the aluminum source as Al2O3, the alkali source as Na2O, and the industrial by-product salt is calculated as cations, in molar ratios: SiO2 / Al2O3 = 10-30; H2O / SiO2 = 10-25; Na2O / SiO2 = 0.15-0.3; The molar ratio of the cations to SiO2 in the industrial by-product salt is 0.05-0.3; the amount of the mordenite seed crystals added is 1%-5% of the mass of SiO2.

3. The method for preparing mordenite molecular sieve according to claim 1, characterized in that, The industrial by-product salt is selected from at least one of potassium chloride, sodium chloride, potassium sulfate, and sodium sulfate; And / or, the silicon source is selected from at least one of silica sol, silica gel powder, sodium silicate, and fumed silica; And / or, the aluminum source is selected from at least one of aluminum sulfate octahydrate, sodium aluminate, aluminum isopropoxide, and aluminum nitrate; And / or, the alkali source is sodium hydroxide.

4. The method for preparing mordenite molecular sieve according to claim 1, characterized in that, The crystallization treatment is carried out at a temperature of 120-200℃ for 10-48 hours. And / or, the crystallization process is carried out under stirring conditions at a speed of 10-50 rpm.

5. The method for preparing mordenite molecular sieve according to claim 1, characterized in that, The inorganic acid is selected from at least one of hydrochloric acid, nitric acid, and sulfuric acid, and has a concentration of 0.1-1 mol / L; And / or, the solid-liquid ratio of the metal cation type mordenite to the inorganic acid solution is 1:5-1:20; And / or, the conditions for the ion exchange are: temperature of 15-35℃, time of 2-4h, and number of times of exchange 2.

6. The method for preparing mordenite molecular sieve according to claim 1, characterized in that, The surface modification treatment is a modification treatment using sodium carboxylate salt solution; And / or, the sodium carboxylate is selected from at least one of sodium benzoate, sodium citrate, sodium oxalate, disodium EDTA, or tetrasodium EDTA; And / or, the concentration of the sodium carboxylate solution is 0.01-0.2 mol / L; the solid-liquid ratio of the hydrogen-form mordenite to the sodium carboxylate solution is 1:10-1:

20.

7. The method for preparing mordenite molecular sieve according to claim 1, characterized in that, The surface modification treatment conditions are: modification temperature 30-60℃, modification time 1-5h, modification times 1; calcination temperature 550-600℃, calcination time 6-10h.

8. A mordenite molecular sieve, characterized in that, The molecular sieve is prepared by the method for preparing mordenite molecular sieve according to any one of claims 1-7.

9. The mordenite molecular sieve according to claim 8, characterized in that, This molecular sieve has a plate-like morphology and a specific surface area of ​​450-600 m². 2 / g; the Na2O mass percentage of the molecular sieve is 0.4-0.6%; and / or, the Brønsted acid content on the outer surface of the molecular sieve is 10-30 μmol / g.

10. An application of a mordenite molecular sieve in methanol amination reaction, characterized in that, The silicate zeolite molecular sieve of claim 9 is used as a catalyst.

Images