CN113149026B - Preparation method of molecular sieve with stepped hole structure - Google Patents
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Abstract
The preparation method of the step hole molecular sieve comprises the following steps: (1) Dispersing a silicon source, an aluminum source and/or a phosphorus source and a template agent in water, stirring and mixing uniformly, placing the obtained mixture in a crystallization kettle, and heating in an oven for 0.5h-30d at a heating temperature of 5-300 ℃; (2) Taking the sample obtained in the step (1) out of the oven, filtering and separating, fully washing with deionized water and drying; (3) Roasting the dried sample obtained in the step (2) to remove the template agent in the molecular sieve, wherein the crystallinity of the obtained initial molecular sieve is 50-90%, and the completely crystallized sample is 100%; 4) And (3) carrying out hydrothermal treatment or chemical treatment on the sample obtained in the step (3) after the template agent is removed, and finally obtaining the step hole molecular sieve. The method realizes the regulation and control of the pore channel structure of the molecular sieve, simultaneously dissolves the compact and stable structure of the surface layer of the molecular sieve, and can improve the mass transfer and diffusion capacity of the molecular sieve to a greater extent.
Description
Technical Field
The invention belongs to the technical field of molecular sieve synthesis, and relates to a synthesis preparation method of a step hole molecular sieve.
Background
Molecular sieves are widely used in many fields such as adsorption, catalysis, separation, etc. because of their large specific surface, unique pore structure and excellent adjustable acid properties. The molecular sieves widely used in industry, such as MFI, FAU, MOR, BEA, are microporous materials, and the catalytic performance is limited due to weak mass transfer and diffusion capacity caused by narrow microporous orifices. Therefore, researchers take a series of measures to adjust the pore channel structure of the molecular sieve and improve the mass transfer and diffusion capacity of the molecular sieve. The adopted means mainly can be divided into the following categories, and the diffusion distance and the diffusion resistance of the nano-sized molecular sieve catalyst are shortened by synthesizing the nano-sized molecular sieve catalyst; introducing intragranular mesopores into the molecular sieve, for example, adopting a template agent in the synthesis process, and removing the template agent through roasting after the crystallization synthesis stage is finished; and adopting chemical treatment means to improve the pore channel structure of the molecular sieve.
The outer layer structure of the molecular sieve is relatively stable and dense, which has a certain effect on its mass transfer diffusion (Journal of Physical Chemistry C,2013,117 (48), 25545-25555). And in the subsequent chemical treatment process, the stable and compact shell is difficult to dissolve and break, so that chemical etching dissolves the inner structure of the molecular sieve crystal more (Chemistry of Materials,2019,31 (13), 4639-4648), and the compact shell structure of the outer layer is still well preserved (Journal of catalysis,278 (2011), 266-275). This phenomenon greatly limits the improvement of the molecular sieve diffusibility by the post-treatment method.
Thus, taking reasonable measures, the mass transfer performance of the microporous molecular sieve can be improved to a greater extent by removing the dense outer shell of the outer layer of the molecular sieve particles or converting the originally dense outer layer structure of the molecular sieve particles into a loose and porous structure while introducing the intragranular mesopores into the microporous molecular sieve (Angewandte Chemie International Edition,48 (2009), 533-538).
Disclosure of Invention
The surface structure of the molecular sieve is generally stable, and is difficult to dissolve and damage in the post-treatment process. Compared with the internal structure of the molecular sieve, the surface structure of the molecular sieve is better reserved after being treated by a conventional method, and the surface structure prevents molecules from diffusing in the molecular sieve in the catalytic adsorption separation process, so that the mass transfer capability of the molecular sieve is not improved. The invention is based on the knowledge of molecular sieve crystallization mechanism, utilizes the general rule in the crystallization process, regulates and controls the structural property of the initial molecular sieve by controlling the synthesis condition, realizes the property regulation of the molecular sieve particle surface layer, and based on the property regulation, carries out post-treatment operation to introduce step holes into the molecular sieve, simultaneously removes the compact structure of the molecular sieve surface layer, and remarkably improves the adsorption and diffusion capacities of the molecular sieve. The mass transfer capacity of the molecular sieve particles can be further improved by controlling the synthesis conditions and regulating and controlling the surface layer structure property of the molecular sieve particles so that the molecular sieve particles are greatly dissolved in the post-treatment process.
The object of the present invention is to provide a process for the aftertreatment of molecular sieves, in particular for the aftertreatment modification of incompletely crystallized molecular sieves whose degree of crystallization is not more than 90%, preferably not more than 85%, more preferably not more than 80% relative to the corresponding completely crystallized molecular sieve.
Under the limiting conditions of the invention, the obtained incompletely crystallized molecular sieve sample can have the special crystal morphology of the molecular sieve with the topological structure and has a smooth and flat surface, but preferably, the crystal surface of the molecular sieve is rough and still in a rapid crystallization stage, and more amorphous species still exist in the obtained crystallized product. The crystal morphology is observed by a common scanning electron microscope method, and the invention has no special technical requirements. Wherein the mass ratio of the amorphous species in the final crystallized product (solid dry basis ratio after calcination at 550 ℃) is not less than 3%, preferably not less than 5%, more preferably not less than 8%.
The post-treatment method provided by the invention is characterized in that the crystal growth of the molecular sieve is controlled simultaneously, and the formation of a compact layer on the crystal surface of the molecular sieve is inhibited jointly through in-situ high-temperature alkali treatment. The dense layer is associated with two-dimensional growth in the later stages of molecular sieve crystallization. This stage of crystallization helps to form the characteristic crystal structure of the molecular sieve and reduces the formation of crystal defects such as twins and grain boundary tensions. But on the other hand, the formation of the surface compact layer is unfavorable for the framework dealumination, desilication and secondary pore formation of the molecular sieve in the post-treatment modification process.
In order to achieve the above purpose, the invention adopts the following specific scheme:
the preparation method of the step hole molecular sieve comprises the following steps:
(1) Dispersing a silicon source, an aluminum source and/or a phosphorus source and a template agent in water, stirring and mixing uniformly, placing the obtained mixture in a crystallization kettle, and heating in an oven for 0.5h-30d at a heating temperature of 5-300 ℃;
(2) Taking the sample obtained in the step (1) out of the oven, filtering and separating, fully washing with deionized water and drying;
(3) Roasting the dried sample obtained in the step (2) to remove the template agent in the molecular sieve, wherein the crystallinity of the obtained initial molecular sieve is 50-90%, and the completely crystallized sample is 100%;
(4) And (3) carrying out hydrothermal treatment or chemical treatment on the sample obtained in the step (3) after the template agent is removed, and finally obtaining the step hole molecular sieve.
The silicon source in the step (1) is one or more of silica sol, silicon dioxide, water glass, white carbon black and tetraethyl orthosilicate; the aluminum source is one or more of aluminum nitrate, aluminum sulfate, aluminum isopropoxide, pseudo-boehmite, aluminum oxide and aluminum hydroxide; the phosphorus source is one or more of phosphoric acid, phosphate and organic phosphine compounds; the template agent is an organic structure guiding agent or an inorganic structure guiding agent, wherein the organic structure guiding agent is one or more of tetramethylammonium hydroxide, tetrapropylammonium hydroxide, ethylenediamine and hexamethylenediamine, and the inorganic guiding agent is one or more of sodium hydroxide, potassium hydroxide and ammonia water.
The heating temperature in the step (1) is 30-250 ℃, and the heating time is 2 h-15 d.
And (3) a lining is arranged in the crystal bloom kettle in the step (1), and the lining is made of polytetrafluoroethylene.
The molecular sieve prepared by the method can be a molecular sieve crystal with any topological structure, and the composition of the molecular sieve can be a pure silicon molecular sieve or a molecular sieve containing other hetero atoms such as aluminum or phosphorus; preferably, the molecular sieve crystals are MFI, FAU, MOR, BEA, LTA molecular sieves.
The crystallinity of the starting molecular sieve obtained in step (3) is 60% to 90%, more preferably 65% to 85%, most preferably 70% to 80%, based on 100% of the fully crystallized sample; the relative crystallinity is measured by a conventional X-ray polycrystalline diffraction peak height method or a peak area method, and when the relative crystallinity is calculated, the same molecular sieve which is completely crystallized is selected as a reference sample, and the crystallinity is determined to be 100%. Preferably, the starting molecular sieve crystals have a rough surface and remain in the rapid crystallization stage, and amorphous species remain in the resulting crystallized product.
The temperature of the hydrothermal treatment in the step (4) is 200-800 ℃ and the time is 0.5-24 h.
The chemical treatment in the step (4) comprises acid treatment or alkali treatment, wherein the concentration of the used chemical reagent is 0.01-40 wt%, the solid-liquid ratio is 1:1-1:40, the temperature is 20-100 ℃, and the treatment time is 5 min-72 h.
In a preferred technical scheme, before the crystallization of the molecular sieve in the step (1) is finished, directly performing in-situ alkali treatment on the molecular sieve which is not completely crystallized; the alkali treatment is carried out at 20-120 ℃, preferably at a temperature difference of not more than 10 ℃ from the crystallization temperature of the molecular sieve, preferably at a temperature difference of not more than 5 ℃.
The beneficial technical effects of the invention are as follows:
(1) The method has wide applicability, is suitable for the improvement of various molecular sieves, and has wide application prospect;
(2) The method of the invention regulates the structure property of the initial molecular sieve by controlling the synthesis condition, realizes the property regulation of the molecular sieve particle surface layer, introduces step holes into the molecular sieve by performing post-treatment operation based on the property regulation, removes the compact structure of the molecular sieve surface layer, and obviously improves the adsorption and diffusion capacity.
(3) The method can be combined with various post-treatment methods, and the mass transfer capacity of the molecular sieve particles can be further improved by controlling the synthesis conditions and regulating the surface layer structure property of the molecular sieve particles so that the molecular sieve particles are largely dissolved in the post-treatment process.
Drawings
FIGS. 1.A and b are SEM images at 1 μm and 100nm, respectively, of a sample of the raw material molecular sieve MFI-1 of example 1;
FIGS. 2.A and b are SEM images at 1 μm and 100nm, respectively, of a sample of the MFI-R1 of the feedstock molecular sieve of comparative example 1;
FIG. 3 XRD patterns of the raw material molecular sieves in example 1 and comparative example 1;
FIG. 4 is an SEM photograph of the molecular sieves prepared in example 1 and comparative example 1, wherein a and b are SEM photographs at 1 μm and 100nm of the sample of comparative example 1, and c and d are SEM photographs at 1 μm and 100nm of the sample of example 1, respectively;
FIG. 5 SEM spectra of the molecular sieves of the raw materials of example 3 (a) and comparative examples 6 (b) -7 (c), all with scales of 100nm;
figure 6 XRD patterns of example 3, comparative examples 6 and 7;
FIG. 7 SEM spectra of samples after treatment of example 3 (a) and comparative example 6 (b), all on a scale of 100nm.
Detailed Description
For a better understanding of the present invention, the following description will further illustrate the present invention by using specific examples, but the present invention is not limited to the following examples.
Example 1
The preparation method of the MFI molecular sieve with the stepped holes comprises the following steps:
MFI molecular sieve as synthetic raw material: dispersing 2.5g of sodium hydroxide and 20.3g of tetrapropylammonium hydroxide in 450g of deionized water, stirring for 1h at room temperature to fully dissolve and uniformly mix; then adding 3.75g of aluminum nitrate nonahydrate, 52g of tetraethyl orthosilicate into the solution, and stirring for 24 hours at room temperature; after the molecular sieve precursors are fully hydrolyzed and uniformly mixed, transferring the molecular sieve precursors into a crystallization kettle with a Teflon lining, and placing the crystallization kettle in an oven and heating the crystallization kettle at 170 ℃ for 10 hours; taking out a sample, filtering and separating the sample, fully washing the sample by using deionized water, and drying the sample at 100 ℃ for 12 hours to obtain a raw material MFI molecular sieve MFI-1, wherein the relative crystallinity of the raw material MFI molecular sieve is 76%;
preparing a cascade pore MFI molecular sieve: dispersing the MFI-1 molecular sieve obtained in the step 1) in 0.3mol/l sodium hydroxide solution at 65 ℃ with the solid-liquid mass ratio of 1:30, and continuously stirring for 0.5h at a constant temperature. And after the reaction is finished, filtering the mixture, fully washing the obtained solid by using deionized water, and drying at 100 ℃ for 12 hours to obtain the step hole MFI molecular sieve.
Example 2
The preparation method of the MFI molecular sieve with the stepped holes comprises the following steps:
MFI molecular sieve as synthetic raw material: dispersing 2.5g of sodium hydroxide in 150g of deionized water, stirring for 1h at room temperature to fully dissolve and uniformly mix; then adding 3.75g of aluminum nitrate nonahydrate, 52g of tetraethyl orthosilicate into the solution, and stirring for 24 hours at room temperature; after the molecular sieve precursor is fully hydrolyzed and uniformly mixed, adding 50mgMFI molecular sieve seed crystal into the mixture, stirring the mixture for 30min to uniformly mix the molecular sieve seed crystal, transferring the molecular sieve precursor into a crystallization kettle with a Teflon lining, placing the crystallization kettle into an oven, and heating the crystallization kettle at 170 ℃ for 8h; taking out a sample, filtering and separating the sample, fully washing the sample by using deionized water, and drying the sample at 100 ℃ for 12 hours to obtain a raw material molecular sieve MFI-2 with a relative crystallinity of 78%;
preparing a cascade pore MFI molecular sieve: dispersing the MFI-2 molecular sieve obtained in the step 1) in 0.3mol/l sodium hydroxide solution at 65 ℃ with the solid-liquid mass ratio of 1:30, and continuously stirring for 30min at a constant temperature. And after the reaction is finished, filtering the mixture, fully washing the obtained solid by using deionized water, and drying at 100 ℃ for 12 hours to obtain the step hole MFI molecular sieve.
Example 3
The preparation method of the step hole ultrastable Y-type molecular sieve comprises the following steps:
synthetic raw material Y-type molecular sieve: 20.60g of sodium metaaluminate solution (21.0 wt% Na) 2 O,3.20wt％Al 2 O 3 ) And 20.90g of water glass (28.45% by weight of SiO) 2 ,8.89wt％Na 2 O) uniformly dispersing the mixture in 8.60g of deionized water, stirring for 30min, and standing and aging for 16h after the mixture is fully and uniformly mixed; 50g of the above mixture, 75.86g of water glass, 16.88g of sodium metaaluminate were uniformly dispersed in 25g of deionized water, and after stirring for 5 hours, 51.05g of an aluminum sulfate solution (7.60 wt% Al) was added thereto 2 O 3 ) Stirring for 1 hr, and placing the gel in a beltHeating the inside of the crystallization kettle with the fluorine dragon lining for 10 hours at 98 ℃; taking out a sample, filtering and separating the sample, fully washing the sample by using deionized water, and drying the sample at 100 ℃ for 12 hours to obtain a raw material molecular sieve Y-1, wherein the relative crystallinity of the raw material molecular sieve Y-1 is 72%;
preparing a step hole ultrastable Y molecular sieve: adding 30g of the gY molecular sieve obtained in the step 1) and 30g of ammonium chloride into 300 g of distilled water, uniformly stirring, and then stirring and exchanging for 1h at 90 ℃. During the exchange, 1mol/L hydrochloric acid solution is adopted to adjust the pH value of the exchange slurry to 3.0 and keep the pH value. Filtering and washing after exchange is finished to obtain an ammonium exchange product; and (3) placing the molecular sieve subjected to ammonium ion exchange treatment in a hydrothermal furnace at 650 ℃, and roasting for 4 hours in a 100% water vapor atmosphere to obtain the step hole ultrastable Y molecular sieve.
Comparative example 1
Dispersing 2.5g of sodium hydroxide and 20.3g of tetrapropylammonium hydroxide in 450g of deionized water, stirring for 1h at room temperature to fully dissolve and uniformly mix; then adding 3.75g of aluminum nitrate nonahydrate, 52g of tetraethyl orthosilicate into the solution, and stirring for 24 hours at room temperature; after the molecular sieve precursors are fully hydrolyzed and uniformly mixed, transferring the molecular sieve precursors into a crystallization kettle with a Teflon lining, and placing the crystallization kettle in an oven and heating the crystallization kettle at 170 ℃ for 18 hours; taking out a sample, filtering and separating the sample, fully washing the sample by using deionized water, and drying the sample at 100 ℃ for 12 hours to obtain a raw material molecular sieve MFI-R1, wherein the relative crystallinity of the raw material molecular sieve is 95%;
preparing a cascade pore MFI molecular sieve: dispersing the MFI-R1 molecular sieve obtained in the step 1) in 0.3mol/l sodium hydroxide solution at 65 ℃ with the solid-liquid mass ratio of 1:30, and continuously stirring for 30min at a constant temperature. After the completion, the mixture was filtered, and the obtained solid was thoroughly washed with deionized water and dried at 100 ℃ for 12 hours to obtain the cascade pore MFI molecular sieve described in comparative example 1.
Comparative example 2
Dispersing 2.5g of sodium hydroxide and 20.3g of tetrapropylammonium hydroxide in 450g of deionized water, stirring for 1h at room temperature to fully dissolve and uniformly mix; then adding 3.75g of aluminum nitrate nonahydrate, 52g of tetraethyl orthosilicate into the solution, and stirring for 24 hours at room temperature; after the molecular sieve precursors are fully hydrolyzed and uniformly mixed, transferring the molecular sieve precursors into a crystallization kettle with a Teflon lining, and placing the crystallization kettle in an oven and heating the crystallization kettle at 170 ℃ for 30 hours; taking out a sample, filtering and separating the sample, fully washing the sample by using deionized water, and drying the sample at 100 ℃ for 12 hours to obtain a raw material MFI molecular sieve MFI-R2, wherein the relative crystallinity of the raw material MFI molecular sieve MFI-R2 is 92%;
preparing a cascade pore MFI molecular sieve: dispersing the MFI-1 molecular sieve obtained in the step 1) in 0.3mol/l sodium hydroxide solution at 65 ℃ with the solid-liquid mass ratio of 1:30, and continuously stirring for 30min at a constant temperature. After the completion, the mixture was filtered, and the obtained solid was thoroughly washed with deionized water and dried at 100 ℃ for 12 hours to obtain the cascade pore MFI molecular sieve described in comparative example 2.
Comparative example 3
Dispersing 2.5g of sodium hydroxide and 20.3g of tetrapropylammonium hydroxide in 450g of deionized water, stirring for 1h at room temperature to fully dissolve and uniformly mix; then adding 3.75g of aluminum nitrate nonahydrate, 52g of tetraethyl orthosilicate into the solution, and stirring for 24 hours at room temperature; after the molecular sieve precursors are fully hydrolyzed and uniformly mixed, transferring the molecular sieve precursors into a crystallization kettle with a Teflon lining, and placing the crystallization kettle in an oven and heating the crystallization kettle at 180 ℃ for 10 hours; taking out a sample, filtering and separating the sample, fully washing the sample by using deionized water, and drying the sample at 100 ℃ for 12 hours to obtain a raw material MFI molecular sieve MFI-R3, wherein the relative crystallinity of the raw material MFI molecular sieve MFI-R3 is 92%;
preparing a cascade pore MFI molecular sieve: dispersing the MFI-1 molecular sieve obtained in the step 1) in 0.3mol/l sodium hydroxide solution at 65 ℃ with the solid-liquid mass ratio of 1:30, and continuously stirring for 30min at a constant temperature. After the completion, the mixture was filtered, and the obtained solid was thoroughly washed with deionized water and dried at 100 ℃ for 12 hours to obtain the cascade pore MFI molecular sieve described in comparative example 3.
Comparative example 4
Dispersing 2.5g of sodium hydroxide and 20.3g of tetrapropylammonium hydroxide in 450g of deionized water, stirring for 1h at room temperature to fully dissolve and uniformly mix; then adding 3.75g of aluminum nitrate nonahydrate, 52g of tetraethyl orthosilicate into the solution, and stirring for 24 hours at room temperature; after the molecular sieve precursor is fully hydrolyzed and uniformly mixed, 50mg of MFI molecular sieve seed crystal is added into the mixture, the mixture is stirred for 30min to uniformly mix, a molecular sieve precursor is transferred into a crystallization kettle with a Teflon lining, and the crystallization kettle is placed in an oven and heated for 18h at 170 ℃; taking out a sample, filtering and separating the sample, fully washing the sample by using deionized water, and drying the sample at 100 ℃ for 12 hours to obtain a raw material MFI molecular sieve MFI-R4, wherein the relative crystallinity of the raw material MFI molecular sieve MFI-R4 is 90%;
preparing a cascade pore MFI molecular sieve: dispersing the MFI-1 molecular sieve obtained in the step 1) in 0.3mol/l sodium hydroxide solution at 65 ℃ with the solid-liquid mass ratio of 1:30, and continuously stirring for 30min at a constant temperature. After the completion, the mixture was filtered, and the obtained solid was thoroughly washed with deionized water and dried at 100 ℃ for 12 hours to obtain the cascade pore MFI molecular sieve described in comparative example 4.
Comparative example 5
Dispersing 2.5g of sodium hydroxide and 20.3g of tetrapropylammonium hydroxide in 450g of deionized water, stirring for 1h at room temperature to fully dissolve and uniformly mix; then adding 3.75g of aluminum nitrate nonahydrate, 52g of tetraethyl orthosilicate into the solution, and stirring for 24 hours at room temperature; after the molecular sieve precursor is fully hydrolyzed and uniformly mixed, 50mg of MFI molecular sieve seed crystal is added into the mixture, the mixture is stirred for 30min to uniformly mix, a molecular sieve precursor is transferred into a crystallization kettle with a Teflon lining, and the crystallization kettle is placed in an oven and heated for 30h at 170 ℃; taking out a sample, filtering and separating the sample, fully washing the sample by using deionized water, and drying the sample at 100 ℃ for 12 hours to obtain a raw material MFI molecular sieve MFI-R5, wherein the relative crystallinity of the raw material MFI molecular sieve MFI-R5 is 95%;
preparing a cascade pore MFI molecular sieve: dispersing the MFI-1 molecular sieve obtained in the step 1) in 0.3mol/l sodium hydroxide solution at 65 ℃ with the solid-liquid mass ratio of 1:30, and continuously stirring for 30min at a constant temperature. After the completion, the mixture was filtered, and the obtained solid was thoroughly washed with deionized water and dried at 100 ℃ for 12 hours to obtain the cascade pore MFI molecular sieve described in comparative example 5.
Comparative example 6
Synthesizing a raw material Y-type molecular sieve: 20.60g of sodium metaaluminate solution (21.0 wt% Na) 2 O,3.20wt％Al 2 O 3 ) And 20.90g of water glass (28.45% by weight of SiO) 2 ,8.89wt％Na 2 O) uniformly dispersing the mixture in 8.60g of deionized water, stirring for 30min, and standing and aging for 16h after the mixture is fully and uniformly mixed; 50g of the mixture, 75.86g of water glass and 16.88g of sodium metaaluminate are uniformly dispersed in 25g of deionized water, and stirred for 5 hoursTo this was added 51.05g of an aluminum sulfate solution (7.60 wt% Al 2 O 3 ) Stirring for 1h, and heating the gel in a crystallization kettle with a Teflon lining at 98 ℃ for 12h; taking out a sample, filtering and separating the sample, fully washing the sample by using deionized water, and drying the sample at 100 ℃ for 12 hours to obtain a raw material Y-type molecular sieve Y-R1, wherein the relative crystallinity of the raw material Y-type molecular sieve Y-R1 is 93%;
preparing a step hole ultrastable Y molecular sieve: adding 30g of the g Y-R1 molecular sieve obtained in the step 1) and 30g of ammonium chloride into 300 g of distilled water, stirring uniformly, and then stirring and exchanging for 1h at 90 ℃. During the exchange, 1mol/L hydrochloric acid solution is adopted to adjust the pH value of the exchange slurry to 3.0 and keep the pH value. Filtering and washing after exchange is finished to obtain an ammonium exchange product; and (3) placing the molecular sieve subjected to ammonium ion exchange treatment in a hydrothermal furnace at 650 ℃, and roasting for 4 hours in a 100% water vapor atmosphere to obtain the step hole ultrastable Y molecular sieve in comparative example 6.
Comparative example 7
Synthesizing a raw material Y-type molecular sieve: 20.60g of sodium metaaluminate solution (21.0 wt% Na) 2 O,3.20wt％Al 2 O 3 ) And 20.90g of water glass (28.45% by weight of SiO) 2 ,8.89wt％Na 2 O) uniformly dispersing the mixture in 8.60g of deionized water, stirring for 30min, and standing and aging for 16h after the mixture is fully and uniformly mixed; 50g of the above mixture, 75.86g of water glass, 16.88g of sodium metaaluminate were uniformly dispersed in 25g of deionized water, and after stirring for 5 hours, 51.05g of an aluminum sulfate solution (7.60 wt% Al) was added thereto 2 O 3 ) Stirring for 1h, and heating the gel in a crystallization kettle with a Teflon lining at 98 ℃ for 18h; taking out a sample, filtering and separating the sample, fully washing the sample by using deionized water, and drying the sample at 100 ℃ for 12 hours to obtain a raw material Y-type molecular sieve Y-R2, wherein the relative crystallinity of the raw material Y-type molecular sieve Y-R2 is 96%;
preparing a step hole ultrastable Y molecular sieve: adding 30g of the g Y-R2 molecular sieve obtained in the step 1) and 30g of ammonium chloride into 300 g of distilled water, stirring uniformly, and then stirring and exchanging for 1h at 90 ℃. During the exchange, 1mol/L hydrochloric acid solution is adopted to adjust the pH value of the exchange slurry to 3.0 and keep the pH value. Filtering and washing after exchange is finished to obtain an ammonium exchange product; and (3) placing the molecular sieve subjected to ammonium ion exchange treatment in a hydrothermal furnace at 650 ℃, and roasting for 4 hours in a 100% water vapor atmosphere to obtain the step hole ultrastable Y molecular sieve in comparative example 7.
Characterization was performed on the samples obtained in examples 1-3 and comparative examples 1-7, and the characterization parameters of the obtained samples are shown in Table 1.
Table 1 summary of sample structural parameters for examples and comparative examples
XRD analysis is carried out on the samples involved in the examples by using a Bruker D8 ADVANCE X-ray powder diffractometer, and the relative crystallinity of each sample is calculated by taking the crystallinity of the completely crystallized sample as 100%; the pore structure adopts Quadraorb-evo TM Analytical characterization, calculation of the specific surface by BET method, total pore volume in terms of sample at relative pressure P/P 0 Adsorption capacity at 0.99 is calculated, and micropore volume is calculated by a t-plot method; SEM pictures the surface topography of the samples of the examples and comparative examples was obtained by using Japanese Electron (JEOL) 7900F.
As shown in table 1, the catalyst prepared by the method of the invention has rough and porous surface, and the catalyst obtained by post-treatment of the completely crystallized raw material molecular sieve has smooth surface, which shows that the method of the invention has remarkable inhibition effect on the formation of the surface compact layer of the surface molecular sieve crystal of the catalyst; more importantly, the increase of mesoporous volume of the molecular sieve catalyst prepared by the method (the mesoporous volume of the final molecular sieve catalyst minus the mesoporous volume of the raw material molecular sieve) is obviously larger than that of the raw material molecular sieve which is completely crystallized or has higher crystallization degree after post-treatment.
The foregoing is merely illustrative and explanatory of the principles of the invention, as various modifications and additions may be made to the specific embodiments described, or similar thereto, by those skilled in the art, without departing from the principles of the invention or beyond the scope of the appended claims.
Claims (7)
1. The preparation method of the step hole molecular sieve comprises the following steps:
(1) Dispersing a silicon source, an aluminum source and/or a phosphorus source and a template agent in water, stirring and mixing uniformly, placing the obtained mixture in a crystallization kettle, and heating in an oven for 0.5h-30d at a heating temperature of 5-300 ℃;
(2) Taking the sample obtained in the step (1) out of the oven, filtering and separating, fully washing with deionized water and drying;
(3) Roasting the dried sample obtained in the step (2) to remove the template agent in the molecular sieve, wherein the crystallinity of the obtained initial molecular sieve is 60-90%, and the completely crystallized sample is 100%;
(4) Carrying out hydrothermal treatment or chemical treatment on the sample obtained in the step (3) after the template agent is removed, and finally obtaining the step hole molecular sieve;
the molecular sieve prepared by the method can be a molecular sieve crystal with any topological structure, and the composition of the molecular sieve can be a pure silicon molecular sieve or a molecular sieve containing other hetero atoms such as aluminum or phosphorus; the molecular sieve crystals are MFI, FAU, MOR, BEA, LTA molecular sieves;
the relative crystallinity is measured by adopting a conventional X-ray polycrystalline diffraction peak height method or a peak area method, and when the relative crystallinity is calculated, the same molecular sieve which is completely crystallized is selected as a reference sample, and the crystallinity is considered to be 100%;
before the crystallization of the molecular sieve in the step (1) is finished, directly carrying out alkali treatment on the molecular sieve which is not completely crystallized in situ; the alkali treatment is carried out at 20-120 ℃, and the temperature difference between the alkali treatment temperature and the crystallization temperature of the molecular sieve is not more than 10 ℃;
the temperature of the hydrothermal treatment in the step (4) is 200-800 ℃ and the time is 0.5-24 h;
the chemical treatment comprises acid treatment or alkali treatment, wherein the concentration of the used chemical reagent is 0.01-40 wt%, the solid-liquid ratio is 1:1-1:40, the temperature is 20-100 ℃, and the treatment time is 5 min-72 h;
the surface of the initial molecular sieve crystal is rough and still in a rapid crystallization stage, and amorphous species still exist in the obtained crystallization product.
2. The method of claim 1, wherein the silicon source in step (1) is one or more of silica sol, silica, water glass, white carbon black, and tetraethyl orthosilicate; the aluminum source is one or more of aluminum nitrate, aluminum sulfate, aluminum isopropoxide, pseudo-boehmite, aluminum oxide and aluminum hydroxide; the phosphorus source is one or more of phosphoric acid, phosphate and organic phosphine compounds; the template agent is an organic structure guiding agent or an inorganic structure guiding agent, wherein the organic structure guiding agent is one or more of tetramethylammonium hydroxide, tetrapropylammonium hydroxide, ethylenediamine and hexamethylenediamine, and the inorganic guiding agent is one or more of sodium hydroxide, potassium hydroxide and ammonia water.
3. The method according to claim 1, wherein the heating temperature in step (1) is 30 to 250 ℃ and the heating time is 2 hours to 15 days.
4. The method of claim 1, wherein the crystallization kettle in step (1) has a liner, and the liner is made of polytetrafluoroethylene.
5. The method of claim 1, wherein the starting molecular sieve obtained in step (3) has a crystallinity of from 65 to 85% based on 100% of the fully crystallized sample.
6. The method of claim 1, wherein the starting molecular sieve obtained in step (3) has a crystallinity of from 70 to 80% based on 100% of the fully crystallized sample.
7. The method of claim 1, wherein the temperature difference between the alkali treatment temperature and the crystallization temperature of the molecular sieve in step (1) is not more than 5 ℃.
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| CN115367769B (en) * | 2022-07-18 | 2023-07-04 | 常州工学院 | Preparation method and application of high-crystallinity hierarchical pore SAPO-56 zeolite molecular sieve |
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