A method for synthesizing a zsm-35 and zsm-5 composite structure zeolite

Abstract

The application discloses a synthesis method of ZSM-35 and ZSM-5 composite zeolite, the composite zeolite takes ZSM-35 as a core and takes ZSM-5 as a shell, and the synthesis method comprises the following steps: (1) uniformly mixing ZSM-35 zeolite, a silicon source, an aluminum source, a template agent, ammonium hydroxide, alcohol and water; then sequentially performing dynamic treatment and static treatment; then separating solid substances and drying the solid substances; (2) mixing the dried substances obtained in the step (1) with inorganic alkali and water, and evaporating water to prepare dry gel; (3) performing crystallization by adopting a gas phase crystallization method, and then performing separation, drying and calcination to obtain the composite zeolite. The ZSM-35 and ZSM-5 composite zeolite can keep the integrity and crystallinity of the ZSM-35 and ZSM-5 skeleton structures, and the core and the shell are combined closely, are not separated and are stable in structure.

Description

Technical Field

[0001] This invention belongs to the field of porous inorganic material preparation, and in particular relates to a method for synthesizing a ZSM-35 and ZSM-5 composite zeolite. Background Technology

[0002] Composite zeolite molecular sieves are co-crystallizations of two or more zeolite molecular sieves, or composite crystals possessing the structural characteristics of two or more zeolite molecular sieves. Composite molecular sieves can eliminate the disadvantages of single zeolites, possess the advantages of multiple zeolite composite structures, and exhibit synergistic effects in catalytic reactions.

[0003] CN101722034A discloses a method for preparing a mordenite / ZSM-5 core-shell molecular sieve material, which involves the following steps: 1) treating mordenite crystals in a modifier solution (the modifier is selected from at least one of ammonia, ethylamine, n-butylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, or tetrapropylammonium bromide); 2) adding the modified mordenite crystals into a ZSM-5 synthesis system and mixing them evenly; 3) hydrothermal crystallization at a temperature of 80-200℃, followed by filtration, washing, and calcination to obtain the mordenite / ZSM-5 core-shell molecular sieve. In this method, a large number of ZSM-5 nanoparticles are generated on the outer surface of the mordenite under the erosion of the modifier. These nanoparticles act as nucleation centers in the ZSM-5 crystallization synthesis system, promoting the growth of the ZSM-5 shell layer, ultimately forming fine ZSM-5 grains densely distributed on the outer surface of the mordenite.

[0004] One of the main problems with existing technologies for synthesizing core-shell composite zeolites is that, while maintaining the integrity of the ZSM-5 and ZSM-35 zeolite framework structures, either a core-shell structure cannot be formed, resulting in a composite molecular sieve that is mostly eutectic, or an unstable core-shell structure is formed, where the core zeolite and the shell zeolite easily separate into two independent states. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for synthesizing a ZSM-35 and ZSM-5 composite zeolite. This ZSM-35 and ZSM-5 composite zeolite maintains the integrity and crystallinity of the ZSM-35 and ZSM-5 framework structures, and exhibits a tight, non-separating core-shell bond and structural stability.

[0006] The first aspect of this invention provides a method for synthesizing a ZSM-35 and ZSM-5 composite zeolite, wherein the composite zeolite has ZSM-35 as the core and ZSM-5 as the shell, and the synthesis method includes:

[0007] (1) Mix ZSM-35 zeolite, silicon source, aluminum source, template agent, ammonium hydroxide, alcohol and water evenly; then perform dynamic treatment and static treatment in sequence; then separate the solid substances and dry them;

[0008] (2) The dried material obtained in step (1) is mixed with inorganic alkali and water, and then the water is evaporated to prepare dry glue;

[0009] (3) Crystallization is carried out by gas phase crystallization, followed by separation, drying and calcination to obtain composite zeolite.

[0010] In the method of the present invention, the particle size of the ZSM-35 zeolite in step (1) is 400-2500 nm, preferably 600-2300 nm.

[0011] In the method of this invention, the silicon source mentioned in step (1) is one or more of methyl orthosilicate, ethyl orthosilicate, and propyl orthosilicate, preferably ethyl orthosilicate. The silicon source decomposes into amorphous silica microparticles, which then combine with the aluminum source and template agent, and are then adsorbed onto the outer surface of the zeolite, ultimately forming a gel layer on the outer surface of the core zeolite in the form of a silica-alumina template agent microstructure.

[0012] In the method of the present invention, the aluminum source mentioned in step (1) is at least one of aluminum isopropoxide, aluminum butoxide, aluminum sec-butoxide, aluminum nitrate, aluminum sulfate, aluminum chloride, and sodium aluminate, preferably at least one of aluminum isopropoxide, aluminum nitrate, aluminum sulfate, and aluminum chloride.

[0013] In the method of this invention, the template agent mentioned in step (1) is tetrapropylammonium hydroxide. The function of the template agent is to induce the other raw materials to form a shell zeolite.

[0014] In the method of the present invention, the alcohol mentioned in step (1) is at least one of ethanol, propanol, and butanol.

[0015] In the method of this invention, the mass ratio of the silicon source (SiO2) to ZSM-35 zeolite in step (1) is 1:9 to 22, preferably 1:10 to 20. The mass ratio of the silicon source (SiO2) to ammonium hydroxide is 1:0.9 to 2.2, preferably 1:1 to 2. The mass ratio of the silicon source (SiO2) to alcohol is 1:90 to 220, preferably 1:100 to 200. The mass ratio of the silicon source (SiO2) to water is 1:90 to 220, preferably 1:100 to 200, where water refers to all water in the mixing system of step (1), including water added separately and water introduced from other materials in solution form.

[0016] In the method of the present invention, the molar ratio of silicon source (SiO2), aluminum source (Al2O3), and template agent in step (1) is 17-60:1:2-11, preferably 20-50:1:3-10.

[0017] In the method of this invention, the silicon source and aluminum source need to be added to the synthesis system simultaneously in step (1), preferably slowly, to ensure that both are added slowly at the same time. This slow addition method can keep the proportion of silicon and aluminum materials in the system basically constant, and will not produce large clumps of gel, which is conducive to the formation of a stable and uniform silicon-aluminum gel structure.

[0018] In the method of this invention, the dynamic treatment in step (1) involves stirring the mixed liquid system for 1–15 hours, preferably 2–10 hours. The dynamic treatment must be carried out under certain temperature conditions, specifically 0–15°C, preferably 0–10°C. During the dynamic treatment, the silicon source hydrolyzes into amorphous silicon oxide, which then forms a micro-silica-alumina gel structure containing the template agent with the aluminum source and template agent in the solution. Due to the low ambient temperature, the silicon source transforms into amorphous silicon oxide at a slower rate, resulting in a slower formation of the micro-silica-alumina gel structure containing the template agent and a smaller gel size. This allows the zeolite sufficient time to adsorb the silica-alumina gel onto its outer surface. As time progresses, a silica-alumina gel layer gradually forms on the outer surface of the zeolite. If the ambient temperature is high, the silicon source hydrolysis rate is too fast, leading to excessively rapid aggregation and potentially larger gel clusters, which hinders zeolite adsorption of the gel, preventing the formation of the final core-shell structure.

[0019] In the method of this invention, the static treatment in step (1) involves allowing the mixed liquid system to stand still for 1 to 15 hours, preferably 2 to 10 hours. This standing process must be carried out under specific temperature conditions, specifically 18 to 35°C, preferably 20 to 30°C. The static treatment makes the gel layer adsorbed on the outer surface of the core zeolite more stable, increasing its bonding force with the zeolite and facilitating the formation of the final core-shell structure.

[0020] In the method of this invention, the separation described in step (1) refers to a conventional filtration operation, but only filtration is performed without washing the filter cake with any solvent. The drying conditions are generally drying at 80–150°C for 5–15 hours.

[0021] In the method of the present invention, the inorganic base mentioned in step (2) is at least one of sodium hydroxide and potassium hydroxide.

[0022] In the method of this invention, water and inorganic base are added in step (2) to form OH - The amounts of inorganic alkali added relative to the aluminum source added in step (1), calculated as Al2O3, are as follows: -The molar ratio of aluminum source (Al2O3) to water is 4–11:1:3000–7500, preferably 5–10:1:4000–7000.

[0023] In the method of the present invention, the temperature for evaporating water in step (2) is 80-130°C, preferably 100-120°C; the reaction time is unlimited until the water is evaporated.

[0024] In the method of this invention, the gas-phase crystallization method described in step (3) refers to the use of a support platform built into the reactor, which is far from the bottom of the reactor. The platform is where the dry gel of the reactants is placed, while the bottom of the reactor is filled with liquids such as water. The crystallization reaction carried out in this reactor is a gas-phase crystallization method. Raw materials such as aluminum and silicon sources form a dry gel of reactants and place it on the platform, while liquid substances such as water are placed at the bottom of the reactor. At high temperatures, some water evaporates into high-temperature water vapor and reacts with the dry gel in a crystallization reaction. The dry gel does not directly contact the liquid water, so the various reactants are macroscopically close to a static state during the reaction process. The synthesis mechanism of the crystallization reaction carried out at this time belongs to the solid-phase synthesis mechanism. The synthesis mechanism of the conventional hydrothermal crystallization reaction carried out in a large amount of water is a liquid-phase synthesis mechanism. All raw materials are surrounded by a large amount of water, and the reaction process is carried out in the vigorous movement of water. At this time, the core-shell structure material is easily separated by the violent impact of water and it is difficult to form a stable core-shell material. The solid-phase synthesis mechanism of this invention can overcome this disadvantage.

[0025] In the method of this invention, water is placed at the bottom of the reactor in step (3), wherein the water-to-reactor (volume ratio) is 8-25:100, preferably 10-20:100. During the reaction, some of the water at the bottom of the reactor evaporates into gas and participates in the crystallization reaction.

[0026] In the method of the present invention, the crystallization temperature in step (3) is 150-220°C, preferably 170-200°C; the crystallization time is 20-90h, preferably 30-80h.

[0027] In the method of the present invention, the separation in step (3) can be carried out by filtration, which usually includes multiple filtrations, generally 1 to 10 times.

[0028] In the method of the present invention, the drying temperature in step (3) is 80-150°C and the drying time is 1-20h.

[0029] In the method of this invention, the calcination in step (3) is a high-temperature calcination treatment at 400-600°C for 1-10 hours. The calcination needs to be carried out in air or oxygen.

[0030] A second aspect of the present invention provides a composite structure zeolite synthesized by the above-described synthesis method.

[0031] The composite zeolite of this invention contains two types of zeolite components: ZSM-5 zeolite and ZSM-35 zeolite. The two zeolites form a core-shell composite structure, with ZSM-35 zeolite as the core zeolite located at the center of the entire structure, and ZSM-5 zeolite as the shell layer, surrounding the outer surface of the core zeolite.

[0032] In the composite zeolite of this invention, the shell thickness is 20–350 nm.

[0033] The specific surface area of ​​the composite zeolite of this invention is 300–760 m². 2 / g, preferably 500-700m 2 / g.

[0034] This invention can provide structurally stable ZSM-35 and ZSM-5 core-shell composite zeolites, which not only possess the excellent properties of the two zeolites, but also produce unique composite properties. They can be used as adsorbents for separating gas and liquid mixtures, as catalyst supports or acid catalyst components, and are particularly suitable for the isomerization of 1-hexene and n-heptane.

[0035] Compared with the prior art, the core-shell composite zeolite and its synthesis method provided by the present invention have the following advantages:

[0036] The inventors discovered through research that when synthesizing core-shell ZSM-5 and ZSM-35 composite zeolites using the traditional liquid-phase hydrothermal synthesis method, ZSM-5 and ZSM-35 often exist in an independent state instead of a stable core-shell structure. Furthermore, the crystallinity of ZSM-35 zeolite is relatively low. They believe that one of the main reasons for this is that during the hydrothermal synthesis process, a large amount of liquid water is present in the synthesis system. Under the influence of heat, the water continuously impacts the synthesis product. When the structure of the synthesis product is not stable enough, it will cause the core-shell structure of the zeolite to separate, and it will also reduce the crystallinity of ZSM-35 zeolite. Further research by the inventors revealed that the method of this invention first prepares a silica-alumina gel-ZSM-35 zeolite composite with a core-shell structure, where the silica-alumina gel forms the shell and the ZSM-35 zeolite forms the core. Step (1) involves a liquid system containing a large amount of water and alcohols. Various raw materials are dissolved or dispersed in the aqueous phase and, after dynamic and static treatments, form a gel microstructure, which is uniformly and stably adsorbed onto the outer surface of the ZSM-35 core zeolite, resulting in a structurally stable gel-ZSM-35 zeolite composite. In the subsequent synthesis reaction, a vapor-phase crystallization method is used to directly transform the gel shell into a ZSM-5 zeolite shell, which then encapsulates the ZSM-35 zeolite, forming a core-shell structured stable ZSM-5 and ZSM-35 composite zeolite.

[0037] (2) In this invention, after the dried material obtained in step (1), an inorganic alkali and water are added to prepare a dry gel. This allows the inorganic alkali to bind with the gel shell layer in the core-shell structure of the gel-ZSM-35 zeolite. Due to the obstruction of the gel shell layer, the inorganic alkali cannot enter the pores of the core ZSM-35 zeolite. Therefore, in subsequent reactions, the inorganic alkali hardly damages the structure of the ZSM-35 zeolite, thus maintaining the integrity and high crystallinity of the ZSM-35 zeolite structure. In conventional hydrothermal methods, the inorganic alkali exists in liquid form in the synthesis system. Thus, during the crystallization reaction, the inorganic alkali can easily enter the pores of the ZSM-35 zeolite, damaging the structure of the core zeolite. Therefore, the method of this invention has the advantage of increasing the crystallinity of the core zeolite and improving the catalytic performance of the final product.

[0038] (3) Based on step (2), this invention uses a vapor-phase crystallization method to prepare ZSM-35 and ZSM-5 core-shell composite zeolites, avoiding the severe impact of liquid water on the shell structure during the synthesis process and maintaining the stability of the shell structure. In conventional hydrothermal methods, even if core-shell ZSM-35 and ZSM-5 composite zeolites are formed, the ZSM-5 zeolite in the shell will be continuously impacted by liquid water and separate from the ZSM-35 zeolite, forming independent ZSM-35 and ZSM-5 zeolites. Attached Figure Description

[0039] Figure 1 A scanning electron microscope image of sample A1 obtained in Example 1;

[0040] Figure 2 A scanning electron microscope image of sample DA1 was obtained for Comparative Example 1;

[0041] Figure 3 The XRD pattern of sample A1 obtained in Example 1;

[0042] Figure 4 The XRD spectrum of sample DA1 was obtained for comparison example 1. Detailed Implementation

[0043] The technical solutions and effects of the present invention will be further illustrated below with reference to the embodiments, but the invention is not limited to the following embodiments.

[0044] The pore structure of the composite zeolite of this invention was characterized by N2 adsorption-desorption using a physical adsorption instrument from Micron Technology (USA). Prior to measurement, the sample was vacuum-treated at 300℃ for at least 4 hours. Parameters such as the total specific surface area were calculated using the BET formula.

[0045] The crystal phase structure and crystallinity of the composite zeolite of this invention were characterized by X-ray diffraction using a Rigaku D / max2500 X-ray diffractometer (Japan), with a Cu target, Kα radiation source, graphite monochromator, tube voltage of 40kV, tube current of 80mA, scanning range of 5° to 40°, step size of 0.1°, and scanning speed of 1° / min.

[0046] The thickness of the shell layer of the composite zeolite of this invention was characterized by high-resolution transmission electron microscopy. The high-resolution transmission electron microscope used was a JEOL JEM-2200FS field emission ultra-high resolution transmission electron microscope with an accelerating voltage of 200kV and a point resolution of 0.19nm.

[0047] Example 1

[0048] Take a clean beaker and add ZSM-35 zeolite (particle size 1200nm), tetrapropylammonium hydroxide solution (mass concentration 30%), distilled water, ethanol, and ammonium hydroxide solution (mass concentration 25%) according to the mass ratio (zeolite: silicon source as SiO2: ammonium hydroxide: alcohol: water = 15:1:1.2:150:150) and molar ratio (silicon source as SiO2: aluminum source as Al2O3: template agent = 38:1:6). Place the beaker in a circulating water system at 6℃. Then, slowly add tetraethyl orthosilicate solution and aluminum sulfate to the beaker simultaneously. Stir for 7 hours. Then, heat the water in the circulating water system to 25℃, stop stirring, and let it stand for 7 hours. Then, filter out the solid material and dry it at 110℃ for 12 hours.

[0049] Then, according to the molar ratio (inorganic base in OH-) - (Calculation: Aluminum source (Al2O3): Water = 7.5:1:5000) Add sodium hydroxide and distilled water and mix evenly; then evaporate the water at 110℃; then place on the support platform of the reactor, add distilled water to the bottom of the reactor according to the volume ratio (reactor:water = 10:100), and react at 170℃ for 80h; then filter the obtained sample several times, then place it in an oven to dry at 110℃ for 12h, and finally calcine in air at 400℃ for 10h. The obtained sample is numbered A1.

[0050] The XRD pattern of sample A1 is shown below. Figure 3 As shown in the figure, the composite material contains two types of crystals, namely ZSM-5 zeolite and ZSM-35 zeolite. According to Table 1, both types of crystals have high crystallinity and high specific surface area.

[0051] Scanning electron microscope image of sample A1 is shown below. Figure 1 ,Depend on Figure 1As can be seen, the sample has a core-shell structure. The particle size of the composite material is about 1600 nm. It consists of irregular particles with a rough outer shell, which is a rough ZSM-5 zeolite shell with a thickness of about 100 nm.

[0052] Example 2

[0053] Take a clean beaker and add ZSM-35 zeolite (particle size 1200nm), tetrapropylammonium hydroxide solution (mass concentration 30%), distilled water, propanol, and ammonium hydroxide solution (mass concentration 25%) according to the mass ratio (zeolite: silicon source as SiO2: ammonium hydroxide: alcohol: water = 10:1:1:100:100) and molar ratio (silicon source as SiO2: aluminum source as Al2O3: template agent = 20:1:3). Mix well. Place the beaker in a circulating water system at 0℃. Then slowly add propyl orthosilicate and aluminum sulfate to the beaker simultaneously. Stir for 10 hours. Then heat the water in the circulating water system to 20℃, stop stirring, and let stand for 10 hours. Then filter out the solid material and dry at 110℃ for 12 hours.

[0054] Then, according to the molar ratio (inorganic base in OH-) - (Calculation: Aluminum source (Al2O3): Water = 5:1:4000) Add sodium hydroxide and distilled water and mix evenly; then evaporate the water at 110℃; then place on the support platform of the reactor, add distilled water to the bottom of the reactor according to the volume ratio (reactor:water = 10:100), react at 170℃ for 80h; then filter the obtained sample several times, then place it in an oven to dry at 110℃ for 12h, and finally calcine in air at 400℃ for 10h. The obtained sample is numbered A2.

[0055] Sample A2 has a core-shell structure and contains two types of crystals: ZSM-5 zeolite and ZSM-35 zeolite. Both types of crystals have high crystallinity and high specific surface area.

[0056] Example 3

[0057] Take a clean beaker and add ZSM-35 zeolite (1200nm), tetrapropylammonium hydroxide solution (mass concentration 30%), distilled water, propanol, and ammonium hydroxide solution (mass concentration 25%) according to the mass ratio (zeolite: silicon source as SiO2: ammonium hydroxide: alcohol: water = 20:1:2:200:200) and molar ratio (silicon source as SiO2: aluminum source as Al2O3: template agent = 50:1:10). Mix well. Place the beaker in a circulating water system at 10℃. Then, slowly add tetraethyl orthosilicate solution and aluminum sulfate to the beaker simultaneously. Stir for 2 hours. Then, heat the water in the circulating water system to 30℃, stop stirring, and let it stand for 2 hours. Then, filter out the solid material and dry it at 110℃ for 12 hours.

[0058] Then, according to the molar ratio (inorganic base in OH-) - (Calculation: Aluminum source (Al2O3): Water = 5:1:4000) Add sodium hydroxide and distilled water and mix evenly; then evaporate the water at 110℃; then place on the support platform of the reactor, add distilled water to the bottom of the reactor according to the volume ratio (reactor:water = 20:100), react at 200℃ for 30h; then filter the obtained sample several times, then place it in an oven to dry at 110℃ for 12h, and finally calcine in air at 400℃ for 10h. The obtained sample is numbered as follows.

[0059] Sample A3 has a core-shell structure and contains two types of crystals: ZSM-5 zeolite and ZSM-35 zeolite. Both types of crystals have high crystallinity and high specific surface area.

[0060] Example 4

[0061] Take a clean beaker and add ZSM-35 zeolite (particle size 1200nm), tetrapropylammonium hydroxide solution (mass concentration 30%), distilled water, ethanol, and ammonium hydroxide solution (mass concentration 25%) according to the mass ratio (zeolite: silicon source as SiO2: ammonium hydroxide: alcohol: water = 13.5:1:1.2:120:165) and molar ratio (silicon source as SiO2: aluminum source as Al2O3: template agent = 38:1:7). Place the beaker in a circulating water system at 6℃. Then, slowly add tetraethyl orthosilicate and aluminum chloride to the beaker simultaneously. Stir for 7 hours. Then, heat the water in the circulating water system to 25℃, stop stirring, and let it stand for 7 hours. Then, filter out the solid material and dry it at 110℃ for 12 hours.

[0062] Then, according to the molar ratio (inorganic base in OH-) - (Calculation: Aluminum source (Al2O3): Water = 6.8:1:5500) was added to potassium hydroxide and distilled water and mixed evenly; then the water was evaporated at 110℃; then the mixture was placed on the support platform of the reactor, and distilled water was added to the bottom of the reactor according to the volume ratio (reactor:water = 13:100), and the reaction was carried out at 170℃ for 75h; the obtained sample was filtered several times, then placed in an oven and dried at 110℃ for 12h, and finally calcined in air at 400℃ for 10h. The obtained sample was numbered A4.

[0063] Sample A4 has a core-shell structure and contains two types of crystals: ZSM-5 zeolite and ZSM-35 zeolite. Both types of crystals have high crystallinity and high specific surface area.

[0064] Example 5

[0065] Take a clean beaker and add ZSM-35 zeolite (particle size 1200nm), tetrapropylammonium hydroxide solution (mass concentration 30%), distilled water, ethanol, and ammonium hydroxide solution (mass concentration 25%) according to the mass ratio (zeolite: silicon source as SiO2: ammonium hydroxide: alcohol: water = 18.3:1:1.7:110:135) and molar ratio (silicon source as SiO2: aluminum source as Al2O3: template agent = 38:1:3.8). Mix well. Place the beaker in a circulating water system at 6℃. Then slowly add tetraethyl orthosilicate and aluminum nitrate to the beaker simultaneously. Stir for 5 hours. Then heat the water in the circulating water system to 22℃, stop stirring, and let stand for 5 hours. Then filter out the solid material and dry at 110℃ for 12 hours.

[0066] Then, according to the molar ratio (inorganic base in OH-) - (Calculation: Aluminum source (Al2O3): Water = 9.5:1:6500) Add sodium hydroxide and distilled water and mix evenly; then evaporate the water at 110℃; then place on the support platform of the reactor, add distilled water to the bottom of the reactor according to the volume ratio (reactor:water = 16:100), and react at 170℃ for 85h; then filter the obtained sample several times, then place it in an oven to dry at 110℃ for 12h, and finally calcine in air at 400℃ for 10h. The obtained sample is numbered A5.

[0067] Sample A5 has a core-shell structure and contains two types of crystals: ZSM-5 zeolite and ZSM-35 zeolite. Both types of crystals have high crystallinity and high specific surface area.

[0068] Comparative Example 1

[0069] The only difference from Example 1 is that the preparation of the silica-alumina gel-zeolite composite was not carried out under the temperature conditions of the present invention.

[0070] Take a clean beaker and add ZSM-35 zeolite (particle size 1200nm), tetrapropylammonium hydroxide solution (mass concentration 30%), distilled water, ethanol, and ammonium hydroxide solution (mass concentration 25%) according to the mass ratio (zeolite: silicon source as SiO2: ammonium hydroxide: alcohol: water = 15:1:1.2:150:150) and molar ratio (silicon source as SiO2: aluminum source as Al2O3: template agent = 38:1:6). Place the beaker in a circulating water system at 6℃. Then, slowly add tetraethyl orthosilicate and aluminum sulfate to the beaker simultaneously. Stir for 7 hours. Then, heat the water in the circulating water system to 55℃, stop stirring, and let it stand for 7 hours. Then, filter out the solid material and dry it at 110℃ for 12 hours.

[0071] Then, according to the molar ratio (inorganic base in OH-) -(Calculation: Aluminum source (Al2O3): Water = 7.5:1:5000) Add sodium hydroxide and distilled water and mix evenly; then evaporate the water at 110℃; then place on the support platform of the reactor, add distilled water to the bottom of the reactor according to the volume ratio (reactor:water = 10:100), and react at 170℃ for 80h; then filter the obtained sample several times, then place it in an oven to dry at 110℃ for 12h, and finally calcine in air at 400℃ for 10h. The obtained sample is numbered DA1.

[0072] The XRD pattern of sample DA1 is shown below. Figure 4 As shown in the figure, the composite material contains two types of crystals, namely ZSM-5 zeolite and ZSM-35 zeolite. According to Table 2, ZSM-35 has a low crystallinity and a slightly lower specific surface area.

[0073] Scanning electron microscope image of sample DA1 is shown below. Figure 2 ,Depend on Figure 2 As can be seen, the sample contains two types of zeolite. The larger crystals are from ZSM-35 zeolite, approximately 1.2 micrometers in size, with relatively clear crystal edges and a disc-like morphology. The smaller crystals are from ZSM-5 zeolite, approximately 3 to 500 nanometers in size, with a granular morphology. This indicates that the synthesized product exists in an independent state, rather than a core-shell structure. The independent existence of the two zeolites in Comparative Example 1 suggests that the method is not stable enough, and it is possible that the synthesized core-shell structure dissociates into an independent state during the preparation process.

[0074] Comparative Example 2

[0075] The only difference from Example 1 is that the conventional liquid-phase hydrothermal crystallization synthesis method is used.

[0076] Take a clean beaker and add ZSM-35 zeolite (particle size 1200nm), tetrapropylammonium hydroxide solution (mass concentration 30%), distilled water, ethanol, and ammonium hydroxide solution (mass concentration 25%) according to the mass ratio (zeolite: silicon source as SiO2: ammonium hydroxide: alcohol: water = 15:1:1.2:150:150) and molar ratio (silicon source as SiO2: aluminum source as Al2O3: template agent = 38:1:6). Place the beaker in a circulating water system at 6℃. Then, slowly add tetraethyl orthosilicate and aluminum sulfate to the beaker simultaneously. Stir for 7 hours. Then, heat the water in the circulating water system to 25℃, stop stirring, and let it stand for 7 hours. Then, filter out the solid material and dry it at 110℃ for 12 hours.

[0077] Then, according to the molar ratio (inorganic base in OH-) -(Calculated as Al2O3: water = 7.5:1:5000) Sodium hydroxide and distilled water were added and mixed evenly; then the mixture was placed in a reaction vessel and reacted at 170℃ for 80h; the resulting sample was filtered several times, then placed in an oven and dried at 110℃ for 12h, and finally calcined in air at 400℃ for 10h. The resulting sample was numbered DA2.

[0078] Sample DA2 is in an independent state and contains two types of crystals, namely ZSM-5 zeolite and ZSM-35 zeolite. Both crystals have low crystallinity, and ZSM-35 has too much crystallinity loss and low specific surface area.

[0079] Comparative Example 3

[0080] The only difference from Example 1 is the method of adding the inorganic base.

[0081] Take a clean beaker and prepare the following ingredients according to the mass ratio (zeolite: silicon source (SiO2): ammonium hydroxide: alcohol: water = 15:1:1.2:150:150) and molar ratio (inorganic base as OH⁻). - The following mixture was prepared: silicon source (SiO2): aluminum source (Al2O3): template agent = 7.5:38:1:6. Sodium hydroxide, ZSM-35 zeolite (1200nm), tetrapropylammonium hydroxide solution (30% by mass), distilled water, ethanol, and ammonium hydroxide solution (25% by mass) were added and mixed thoroughly. The beaker was placed in a circulating water system at 6°C. Tetraethyl orthosilicate and aluminum sulfate were then slowly added to the beaker simultaneously. The mixture was stirred for 7 hours. The water in the circulating water system was then heated to 25°C, stirring was stopped, and the mixture was allowed to stand for 7 hours. The solid material was then filtered out and dried at 110°C for 12 hours.

[0082] The sample was then placed on the support platform of the reactor, and distilled water was added to the bottom of the reactor at a volume ratio of 10:100 (reactor:water = 10:100). The reaction was carried out at 170°C for 80 hours. The resulting sample was then filtered several times and dried in an oven at 110°C for 12 hours. Finally, it was calcined in air at 400°C for 10 hours. The resulting sample was numbered DA3.

[0083] Sample DA3 is in an independent state and contains two types of crystals, namely ZSM-5 zeolite and ZSM-35 zeolite. Both crystals have low crystallinity, and ZSM-35 has too much crystallinity loss and low specific surface area.

[0084] Table 1. Physicochemical properties of the samples obtained in each embodiment.

[0085]

[0086] Note: In this invention, the crystallinity of ZSM-35 zeolite and ZSM-5 zeolite samples in Example 1 is 100%, respectively. The relative crystallinity of ZSM-35 zeolite in all samples is obtained by comparing the crystallinity of ZSM-35 zeolite in the sample with that in Example 1. The relative crystallinity of ZSM-5 zeolite in all samples is obtained by comparing the crystallinity of ZSM-5 zeolite in the sample with that in Example 1. The shell thicknesses given in Table 1 are approximate thicknesses.

[0087] Table 2 Physicochemical properties of each comparative sample

[0088]

[0089]

[0090] Note: In this invention, the crystallinity of ZSM-35 zeolite and ZSM-5 zeolite samples in Example 1 is 100%, respectively. The relative crystallinity of ZSM-35 zeolite in all samples is obtained by comparing the crystallinity of ZSM-35 zeolite in the sample with that in Example 1, and the relative crystallinity of ZSM-5 zeolite in all samples is obtained by comparing the crystallinity of ZSM-5 zeolite in the sample with that in Example 1.

[0091] Application examples

[0092] The catalytic performance of the material was investigated by isomerization of 1-hexene and n-heptane.

[0093] The materials prepared in Examples 1-5, Comparative Examples 1, 2, and 3 were respectively used to prepare catalysts Cat1-Cat5, DCat1, DCat2, and DCat3 using conventional methods. The catalyst preparation process involved conventional ammonium ion exchange to form a hydrogen-type molecular sieve, which became the catalyst.

[0094] The material properties were evaluated in a micro fixed-bed reactor at a reaction temperature of 400℃, a reaction pressure of 0.4MPa, and a mass hourly space velocity of 12h⁻¹. -1 Hydrogen space velocity 3500 h -1 The raw materials are a mixture of 1-hexene and n-heptane, with 1-hexene comprising 10% by mass. Isohexene selectivity is used as the catalytic performance indicator. Isohexene selectivity is calculated as the percentage by mass of isohexene in all products.

[0095] Table 3 Evaluation Results

[0096]

[0097]

Claims

1. A method for synthesizing a ZSM-35 and ZSM-5 composite zeolite, wherein the composite zeolite has ZSM-35 as the core and ZSM-5 as the shell, the synthesis method comprising: (1) Mix ZSM-35 zeolite, silicon source, aluminum source, template agent, ammonium hydroxide, alcohol and water evenly; Then it undergoes dynamic processing and static processing in sequence; Then the solid material is separated and dried; (2) The dried material obtained in step (1) is mixed with inorganic alkali and water, and then the water is evaporated to prepare dry glue; (3) Crystallization was carried out by vapor phase crystallization, followed by separation, drying and calcination to obtain composite zeolite; The dynamic treatment in step (1) involves stirring the mixture system for 1 to 15 hours, and the temperature of the dynamic treatment is 0 to 15°C. The static treatment in step (1) involves allowing the mixture system to stand still for 1 to 15 hours, and the temperature of the standing system is 18 to 35°C. The crystallization temperature in step (3) is 150-220℃ and the crystallization time is 20-90h.

2. The synthesis method according to claim 1, characterized in that, The particle size of the ZSM-35 zeolite mentioned in step (1) is 400~2500nm.

3. The synthesis method according to claim 1, characterized in that, The particle size of the ZSM-35 zeolite mentioned in step (1) is 600~2300nm.

4. The synthesis method according to claim 1, characterized in that, The silicon source mentioned in step (1) is one or more of methyl orthosilicate, ethyl orthosilicate, and propyl orthosilicate; the aluminum source is at least one of aluminum isopropoxide, aluminum butoxide, aluminum sec-butoxide, aluminum nitrate, aluminum sulfate, aluminum chloride, and sodium aluminate; the template agent is tetrapropylammonium hydroxide; and the alcohol is at least one of ethanol, propanol, and butanol.

5. The synthesis method according to claim 4, characterized in that, The silicon source mentioned in step (1) is tetraethyl orthosilicate; the aluminum source is at least one of aluminum isopropoxide, aluminum nitrate, aluminum sulfate, and aluminum chloride.

6. The synthesis method according to claim 1, characterized in that, In step (1), the mass ratio of silicon source (SiO2) to ZSM-35 zeolite is 1:9~22; the mass ratio of silicon source (SiO2) to ammonium hydroxide is 1:0.9~2.2; the mass ratio of silicon source (SiO2) to alcohol is 1:90~220; the mass ratio of silicon source (SiO2) to water is 1:90~220; and / or, in step (1), the molar ratio of silicon source (SiO2), aluminum source (Al2O3), and template agent is 17~60:1:2~11.

7. The synthesis method according to claim 6, characterized in that, In step (1), the mass ratio of silicon source (SiO2) to ZSM-35 zeolite is 1:10~20; the mass ratio of silicon source (SiO2) to ammonium hydroxide is 1:1~2; the mass ratio of silicon source (SiO2) to alcohol is 1:100~200; the mass ratio of silicon source (SiO2) to water is 1:100~200; and / or, in step (1), the molar ratio of silicon source (SiO2), aluminum source (Al2O3), and template agent is 20~50:1:3~10.

8. The synthesis method according to claim 1, characterized in that, In step (1), the silicon source and aluminum source are added to the synthesis system slowly at the same time to ensure that both are added at the same time.

9. The synthesis method according to claim 1, characterized in that, In the dynamic treatment described in step (1), the stirring time is 2 to 10 hours and the temperature of the dynamic treatment is 0 to 10°C; and / or, in the static treatment described in step (1), the settling time is 2 to 10 hours and the settling temperature is 20 to 30°C.

10. The synthesis method according to claim 1, characterized in that, The drying conditions described in step (1) are drying at 80-150°C for 5-15 hours; and / or the temperature for evaporating moisture described in step (2) is 80-130°C.

11. The synthesis method according to claim 10, characterized in that, The temperature for evaporating water in step (2) is 100~120℃.

12. The synthesis method according to claim 1, characterized in that, The inorganic base mentioned in step (2) is at least one of sodium hydroxide and potassium hydroxide.

13. The synthesis method according to claim 1, characterized in that, In step (2), the inorganic base is OH- - The molar ratio of aluminum source (Al2O3) to water is 4~11:1:3000~7500.

14. The synthesis method according to claim 13, characterized in that, In step (2), the inorganic base is OH- - The molar ratio of aluminum source (Al2O3) to water is 5-10:1:4000-7000.

15. The synthesis method according to claim 1, characterized in that, In step (3), water is placed at the bottom of the reactor in the gas phase crystallization method, wherein the water-to-reactor volume ratio is 8~25:100; and / or the crystallization temperature is 150~220℃; and the crystallization time is 20~90h.

16. The synthesis method according to claim 1, characterized in that, In the gas phase crystallization method described in step (3), water is placed at the bottom of the reactor, wherein the water-to-reactor volume ratio is 10~20:

100.

17. The synthesis method according to claim 15, characterized in that, In step (3), the crystallization temperature is 170-200℃ and the crystallization time is 30-80h.

18. The synthesis method according to claim 1, characterized in that, The drying temperature in step (3) is 80-150℃ and the drying time is 1-20h; and / or, the calcination in step (3) is a high-temperature calcination treatment at 400-600℃ for 1-10h.

19. The ZSM-35 and ZSM-5 composite zeolite synthesized by any of the synthesis methods described in claims 1-18.

20. The composite zeolite according to claim 1, characterized in that, The thickness of the shell layer in the composite zeolite is 20~350nm.

21. The composite zeolite according to claim 1, characterized in that, The specific surface area of ​​the composite zeolite is 300–760 m². 2 / g.

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