Preparation method of hierarchical pore ZSM-5 molecular sieve

Abstract

The invention discloses a preparation method of a multi-level pore ZSM-5 molecular sieve. The preparation method comprises: adding a template agent, a seed crystal, an R crystallization regulator in sequence to a mixed solution of deionized water, an alkali source and an aluminum source, adding a silicon source dropwise, and stirring to obtain a mixed sol; wherein the seed crystal is a nano ZSM-5 molecular sieve with a grain size of 50 to 500 nm, and the mass ratio of the seed crystal to the mass of SiO2 is 0.05 to 1.0:1; the molar ratio of each component in the mixed sol is SiO2:Al2O3:template agent:M2O:H2O:R crystallization regulator=1:0.001 to 0.04:0.01 to 0.1:0.05 to 0.3:15 to 60:0.01 to 1; the mixed sol obtained in the above steps is hydrothermally crystallized at 120 to 200°C for 30 to 80 hours, and the product is cooled, separated, washed, dried, and calcined to obtain the multi-level pore ZSM-5 molecular sieve. The multi-level pore ZSM-5 molecular sieve prepared by the preparation method of the present invention has a small particle size and a large number of interconnected intercrystalline mesoporous structures between the particles.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve preparation, and particularly relates to a method for preparing a multi-level pore ZSM-5 molecular sieve. Background Art

[0002] ZSM-5 zeolite molecular sieve contains ten-membered rings, with the basic structural unit consisting of eight five-membered rings. Its crystal structure belongs to the orthorhombic system. ZSM-5 zeolite molecular sieve has a unique structure, with its pores representing its cavities. The framework consists of two intersecting pore systems, with the straight cylindrical pores being elliptical. The crystal structure of ZSM-5 zeolite molecular sieve is very stable. It has been widely used in ion exchange, adsorption separation, and shape selectivity.

[0003] ZSM-5 zeolite is commonly used in heavy oil cracking, aromatization, benzene-methanol alkylation, and methanol conversion to light olefins. However, ZSM-5 zeolite itself has a microporous structure and is susceptible to carbon deposition and deactivation during the reaction. Introducing mesopores into ZSM-5 zeolite would reduce deactivation and significantly extend its catalytic life.

[0004] Chinese patent CN112875721A discloses a method for rapidly preparing mesoporous ZSM-5 molecular sieve macrostructures. The method involves thoroughly mixing a dilute solution containing ZSM-5 seed crystals with starch or cyclodextrin, an aluminum source, a silicon source, and a template to form a slurry. The slurry is then extruded and combined to form a sheet or strip. The sheet or strip is placed in a wheel-drawer container and then treated under a high-temperature, high-pressure steam atmosphere to convert both the silicon source and the aluminum source into ZSM-5 macrostructures. The product is then calcined in an oxygen-containing gas atmosphere to produce the mesoporous ZSM-5 macrostructure. However, the preparation method is complex and the product quality is low.

[0005] Chinese patent CN110028080A discloses a method for rapidly crystallizing and synthesizing highly crystalline mesoporous ZSM-5 molecular sieves. The method includes precursor preparation, crystallization, filtration, drying, and calcination. Two crystallization methods are available. Method one uses a dry gel conversion method to prepare the precursor, utilizing the autogenous pressure of ethanol for crystallization. Method two uses saturated steam to heat the precursor in a sealed container for crystallization. The saturated steam temperature for crystallization is 160-180°C, and the crystallization time is 1-6 hours. During the crystallization process, a silicon source and a template are added to the precursor in a molar ratio of 1:(0.01-0.5) by mass. The initial precursor to silicon source mass ratio is 2-15%. However, this preparation method is complex and the product quality is not high.

[0006] Chinese patent CN 110217804 A discloses a method for preparing a ZSM-5 molecular sieve, comprising the following steps: (1) mixing a first silicon source, a first aluminum source, a first alkali source, a first template, a seed crystal, urea, and water, and then aging the mixture to obtain a gel; (2) sequentially subjecting the gel to low-temperature crystallization and high-temperature crystallization; and (3) drying and calcining the solid product obtained by the high-temperature crystallization in step (2); the low-temperature crystallization temperature is 90-130° C., the high-temperature crystallization temperature is 150-180° C., the seed crystal is a spherical ZSM-5 molecular sieve containing a second template, and the seed crystal is obtained by crystallization at 100-135° C. However, the preparation process of this method is complex and is not easy to be industrially operated.

[0007] Catalysis, 2011, 32:11-12, reports a two-end crystallization method for synthesizing ZSM-5 molecular sieves without an organic template. The first crystallization stage employed high-temperature pre-crystallization for nucleation, while the second stage employed low-temperature crystallization to synthesize the molecular sieve. However, the resulting ZSM-5 molecular sieve product was an aggregate without hierarchical pores.

[0008] The existing ZSM-5 molecular sieve preparation method has various defects or deficiencies. Therefore, it is necessary to provide a new multi-level pore ZSM-5 molecular sieve preparation method. Summary of the Invention

[0009] In view of the defects of the above-mentioned technology, the purpose of the present invention is to provide a method for preparing a multi-level pore ZSM-5 molecular sieve, by using nano ZSM-5 molecular sieve as a crystal seed, nano ZSM-5 molecular sieve as a crystal seed has a strong structure-guiding effect, and can quickly induce small-grain ZSM-5 zeolite to form a certain size agglomerate in the early stage of crystallization; by R crystallization regulator, alkalinity is released in the later stage of crystallization, and intercrystalline mesopores that are evenly distributed and connected are gently etched. The multi-level pore ZSM-5 molecular sieve obtained by the preparation method of the present invention has a small particle size, and there are a large number of connected intercrystalline mesoporous structures between the particles.

[0010] To achieve the above object, the solution adopted by the present invention is a method for preparing a multi-level pore ZSM-5 molecular sieve, comprising the following steps:

[0011] (1) Adding a template, a seed crystal, an R crystallization regulator, and a silicon source dropwise to a mixed solution of deionized water, an alkali source, and an aluminum source in sequence, and stirring uniformly to obtain a mixed sol;

[0012] The seed crystal is a nano ZSM-5 molecular sieve with a grain size of 50 to 500 nm, and the mass ratio of the seed crystal to SiO2 is 0.05 to 1.0:1; the deionized water is calculated as H2O, the alkali source is calculated as M2O, M is Na or K, the aluminum source is calculated as Al2O3, and the silicon source is calculated as SiO2. The molar ratio of the components in the mixed sol is SiO2:Al2O3:template:M2O:H2O:R crystallization regulator=1:0.001 to 0.04:0.01 to 0.1:0.05 to 0.3:15 to 60:0.01 to 1;

[0013] (2) The mixed sol obtained in step (1) is subjected to hydrothermal crystallization at 120-200° C. for 30-80 hours, and the product is cooled, separated, washed, dried, and calcined to obtain the multi-level pore ZSM-5 molecular sieve.

[0014] Preferably, in the preparation method of the present invention, the mass ratio of the seed crystal to the mass of SiO2 is 0.1 to 0.5:1.

[0015] Preferably, in the preparation method of the present invention, the silicon source is selected from at least one of silica sol, ethyl orthosilicate, sodium silicate, and white carbon black.

[0016] Preferably, in the preparation method of the present invention, the R crystallization regulator is selected from at least one of formamide, carbonamide, N,N-dimethylformamide and N,N-dimethylacetamide.

[0017] Preferably, in the preparation method of the present invention, the drying temperature is 80-120° C., and the drying time is 12-24 hours; the roasting temperature is 500-600° C., and the roasting time is 6-12 hours.

[0018] Preferably, in the preparation method of the present invention, the aluminum source is selected from at least one of aluminum isopropoxide, pseudo-boehmite, sodium metaaluminate, aluminum nitrate, and aluminum sulfate.

[0019] Preferably, in the preparation method of the present invention, the template is at least one selected from tetramethylammonium hydroxide, tetramethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium hydroxide and tetraethylammonium bromide.

[0020] Preferably, in the preparation method of the present invention, the alkali source is sodium hydroxide and / or potassium hydroxide.

[0021] The preparation method of the present invention uses nano ZSM-5 molecular sieve as a seed crystal with a grain size of 50 to 500 nm. Due to its small particle size and large specific surface area, the nano seed crystals have more induction points and a larger number of nuclei during the crystallization process, thereby making the synthesized multi-level porous ZSM-5 molecular sieve grain size smaller. A crystallization regulator is used to release alkalinity in the late stage of crystallization, gently etching uniformly distributed and connected intercrystalline mesopores, and forming a nano-aggregate structure with intercrystalline mesopores.

[0022] The multi-level pore ZSM-5 molecular sieve prepared by the preparation method disclosed in the present invention has high crystallinity, and the size of the small particles of the multi-level pore ZSM-5 molecular sieve is about 45 to 75 nm. The particles are uniform and have a regular and uniform morphology. The small particles aggregate to form an agglomerate structure with intercrystalline mesopores. The multi-level pore ZSM-5 molecular sieve has interconnected intercrystalline mesopores, resulting in a multi-level pore zeolite with abundant intercrystalline mesopore active centers. The product can easily diffuse and has access to more catalyst active centers, maintaining excellent catalytic performance in the catalytic reaction and having a long life. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the XRD diffraction pattern of sample 1# obtained in Example 1.

[0024] Figure 2 These are the SEM and TEM images of sample 1# obtained in Example 1.

[0025] Figure 3 This is the adsorption isotherm of sample 1# obtained in Example 1.

[0026] Figure 4 This is the adsorption isotherm of sample 1#-1 obtained in Comparative Example 1. DETAILED DESCRIPTION

[0027] The following is a detailed description of the embodiments of the present invention: This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and processes. However, the protection scope of the present invention is not limited to the following embodiments. The experimental methods in the following embodiments where specific conditions are not specified are generally based on conventional conditions.

[0028] Unless otherwise specified, the test methods described in the following examples are conventional methods; the reagents and compounds described are commercially available unless otherwise specified.

[0029] Source of raw materials: In the present invention, the nano ZSM-5 molecular sieve can be purchased from commercial channels as a seed crystal, or can be prepared from the existing technology (such as Tan Kexin, Luan Guoyan, Pei Donghan. Synthesis of nano-scale ZSM-5 molecular sieve by pre-crystallization liquid method [J]. Chemical Technology and Development, 2016, 45(12): 5-7., the preparation method disclosed in CN1303816A), or the nano ZSM-5 molecular sieve with an average particle diameter of 105 nm prepared in Example 5 of patent CN1303816A can be used.

[0030] Analytical methods:

[0031] X-ray diffraction (XRD) analysis of the samples: The analytical instrument was a Rigaku Smartlab 9KW X-ray diffractometer, and the analysis conditions were CuKα radiation power supply, tube voltage 40 kV, tube current 100 mA, scanning step 0.02°, and scanning range 2θ = 4 to 40°.

[0032] The morphology of the samples was observed by scanning electron microscopy (SEM) using a Hitachi S-4800 field emission electron microscope.

[0033] The pore characteristics of the samples were determined by N2 physical adsorption using a Micromeritics TriStar II 3020 surface area and porosity analyzer.

[0034] Comparative Example 1

[0035] The aluminum source is sodium metaaluminate, the alkali source is sodium hydroxide, the silicon source is silica sol, the template is tetramethylammonium bromide, and the seed crystals are 50 nm ZSM-5 molecular sieves. The raw materials are measured according to the molar ratio of SiO2:Al2O3:template:MO:H2O=1:0.04:0.05:0.1:30 in the sol. The amount of SiO2 in the silica sol is 500 mmol. The mass ratio of the nano-ZSM-5 molecular sieve seed crystals to the SiO2 is 0.1:1.

[0036] Sodium hydroxide and sodium aluminate were added to deionized water in sequence and stirred evenly at room temperature. Then, a template dosage of tetramethylammonium bromide was added, followed by the addition of nano ZSM-5 molecular sieve seed crystals. Finally, silica sol was added dropwise and stirred evenly to obtain a mixed gel. The mixed gel was then transferred to a high-pressure reactor with a polytetrafluoroethylene liner, and the oven temperature was set at 150°C for 50 hours for crystallization. After the crystallization was completed, it was naturally cooled, filtered and separated, washed with deionized water, dried in an oven at 100°C for 12 hours, and then calcined in a muffle furnace at 500°C for 6 hours to obtain ZSM-5 molecular sieve, which was recorded as sample 1#-1.

[0037] Example 1

[0038] The aluminum source is sodium metaaluminate, the alkali source is sodium hydroxide, the silicon source is silica sol, the template is tetramethylammonium bromide, the seed crystal is a ZSM-5 molecular sieve with a grain size of 50 nm, and the crystallization modifier is carbonamide. The raw materials are measured according to the molar ratio of SiO2:Al2O3:template:M2O:H2O:R crystallization modifier in the sol = 1:0.04:0.05:0.1:30:0.5. The amount of SiO2 in the silica sol is 500 mmol. The mass ratio of the nano-ZSM-5 molecular sieve seed crystal to SiO2 is 0.1:1.

[0039] Sodium hydroxide and sodium aluminate were added to deionized water in sequence and stirred evenly at room temperature. Then, a template dosage of tetramethylammonium bromide was added, followed by the addition of nano ZSM-5 molecular sieve seed crystals, followed by carbonamide, and finally, silica sol was added dropwise and stirred evenly to obtain a mixed gel. The mixed gel was then transferred to a high-pressure reactor with a polytetrafluoroethylene liner, and the oven temperature was set at 150°C for 50 hours for crystallization. After the crystallization was completed, it was naturally cooled, filtered and separated, washed with deionized water, dried in an oven at 100°C for 12 hours, and then calcined in a muffle furnace at 500°C for 6 hours to obtain a multi-level pore ZSM-5 molecular sieve, recorded as sample 1#.

[0040] Example 2

[0041] The operation was the same as in Example 1, except that the mass ratio of the nano ZSM-5 molecular sieve seed crystal to SiO2 was 0.1:0.5, and a multi-level pore ZSM-5 molecular sieve was obtained, which was recorded as sample 2#.

[0042] Example 3

[0043] The operation was the same as in Example 1, except that the mass ratio of the nano ZSM-5 molecular sieve seed crystal to SiO2 was 0.1:0.75, and a multi-level pore ZSM-5 molecular sieve was obtained, which was recorded as sample 3#.

[0044] Example 4

[0045] The operation was the same as in Example 1, except that aluminum isopropoxide was selected as the aluminum source, ethyl orthosilicate was selected as the silicon source, and tetrapropylammonium bromide was selected as the template agent to obtain a multi-level pore ZSM-5 molecular sieve, which was recorded as sample 4#.

[0046] Example 5

[0047] The operation was the same as in Example 1, except that tetrapropylammonium hydroxide was used as the template to obtain a multi-level pore ZSM-5 molecular sieve, which was recorded as sample 5#.

[0048] Example 6

[0049] The operation was the same as in Example 1, except that potassium hydroxide was used as the alkali source to obtain a multi-level pore ZSM-5 molecular sieve, which was recorded as sample 6#.

[0050] Example 7

[0051] The operation was the same as in Example 1, except that the crystallization temperature was selected to be 170° C., and a multi-level pore ZSM-5 molecular sieve was obtained, which was recorded as sample 7#.

[0052] Example 8

[0053] The operation was the same as in Example 1, except that the molar ratio of SiO2:Al2O3 was adjusted to 1:0.004, and a multi-level pore ZSM-5 molecular sieve was obtained, which was recorded as sample 8#.

[0054] Example 9

[0055] The operation was the same as in Example 1, except that the molar ratio of SiO2:Al2O3 was adjusted to 1:0.001, and a multi-level pore ZSM-5 molecular sieve was obtained, which was recorded as sample 9#.

[0056] Example 10

[0057] The operation was the same as in Example 1, except that the molar ratio of SiO2:R crystallization regulator was adjusted to 1:0.1, and a multi-level pore ZSM-5 molecular sieve was obtained, which was recorded as sample 10#.

[0058] Example 11

[0059] The operation was the same as in Example 1, except that the molar ratio of SiO2:R crystallization regulator was adjusted to 1:1, and a multi-level pore ZSM-5 molecular sieve was obtained, which was recorded as sample 11#.

[0060] Example 12

[0061] The operation was the same as in Example 1, except that only N,N-dimethylformamide was used as the R crystallization regulator to obtain a multi-level pore ZSM-5 molecular sieve, which was recorded as sample 12#.

[0062] Taking the sample 1# obtained in Example 1 as an example, the XRD diffraction pattern of the sample 1# is as follows: Figure 1 As shown, from Figure 1 It can be seen that the multi-level pore ZSM-5 molecular sieve synthesized by the preparation method of the present invention has a high crystallinity, while the multi-level pore ZSM-5 molecular sieve synthesized by the comparative example 1 did not obtain.

[0063] Taking the sample 1# obtained in Example 1 as an example, the SEM and TEM images of the sample 1# are as follows: Figure 2 As shown, from Figure 2It can be seen that the size of the obtained hierarchical pore ZSM-5 molecular sieve small particles is about 45 to 75 nm, and the particles are uniform. The small particle aggregates have an agglomerate structure with intercrystalline mesopores.

[0064] Taking the sample 1# obtained in Example 1 as an example, the adsorption isotherm of the sample 1# is as follows: Figure 3 As shown, from Figure 3 It can be seen that the sample has an obvious hysteresis loop in the medium specific pressure region, indicating that the multi-level pore ZSM-5 molecular sieve small particles have aggregated to form an agglomerate structure with intercrystalline mesopores. However, Comparative Example 1 did not obtain a multi-level pore ZSM-5 molecular sieve. Figure 4 shown.

[0065] In summary, the preparation method of the multi-level pore ZSM-5 molecular sieve provided by the present invention has a high degree of crystallinity, a small particle size of about 45 to 75 nm, and uniform particles with a regular and uniform morphology. The small particles are aggregated to form an agglomerate structure. The ZSM-5 molecular sieve has interconnected intercrystalline mesopores to obtain a multi-level pore zeolite, and the intercrystalline mesopore active centers are rich, the product can easily diffuse and is close to the catalyst active center. It can maintain excellent catalytic performance in the catalytic reaction and has a long life.

[0066] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-level pore ZSM-5 molecular sieve, characterized in that: The following steps are involved: (1) Adding a template, a seed crystal, an R crystallization regulator, and a silicon source dropwise to a mixed solution of deionized water, an alkali source, and an aluminum source in sequence, and stirring uniformly to obtain a mixed sol; The seed crystal is a nano ZSM-5 molecular sieve with a grain size of 50 to 500 nm, and the mass ratio of the seed crystal to SiO2 is 0.05 to 1.0:1; the deionized water is calculated as H2O, the alkali source is calculated as M2O, M is Na or K, the aluminum source is calculated as Al2O3, and the silicon source is calculated as SiO2. The molar ratio of the components in the mixed sol is SiO2:Al2O3:template:M2O:H2O:R crystallization regulator=1:0.001 to 0.04:0.01 to 0.1:0.05 to 0.3:15 to 60:0.01 to 1; (2) hydrothermally crystallizing the mixed sol obtained in step (1) at 120-200° C. for 30-80 h, cooling, separating, washing, drying, and calcining the product to obtain the hierarchical ZSM-5 molecular sieve; Wherein, the R crystallization regulator is selected from at least one of formamide, carbonamide, N,N-dimethylformamide and N,N-dimethylacetamide; the template agent is selected from at least one of tetramethylammonium hydroxide, tetramethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, tetraethylammonium hydroxide and tetraethylammonium bromide.

2. The method for preparing a multi-level pore ZSM-5 molecular sieve according to claim 1, wherein: The mass ratio of the seed crystal to SiO2 is 0.1-0.5:

1.

3. The method for preparing a multi-level pore ZSM-5 molecular sieve according to claim 1, wherein: The silicon source is selected from at least one of silica sol, ethyl orthosilicate, sodium silicate and white carbon black.

4. The method for preparing a multi-level pore ZSM-5 molecular sieve according to claim 1, wherein The drying temperature is 80-120° C., and the drying time is 12-24 hours; the roasting temperature is 500-600° C., and the roasting time is 6-12 hours.

5. The method for preparing the multi-level pore ZSM-5 molecular sieve according to claim 1, wherein The aluminum source is selected from at least one of aluminum isopropoxide, pseudo-boehmite, sodium metaaluminate, aluminum nitrate, and aluminum sulfate.

6. The method for preparing a multi-level pore ZSM-5 molecular sieve according to claim 1, wherein: The alkali source is sodium hydroxide and / or potassium hydroxide.

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