Al-rich hierarchical porous molecular sieve catalyst, its preparation method and application

Abstract

The present invention provides a high-aluminum hierarchical zeolite catalyst, a preparation method thereof and an application thereof, relating to the technical fields of catalyst preparation and application. In this preparation method, a high-aluminum zeolite (Si / Al = 2 - 10) parent body is successively subjected to framework modification, acid treatment and alkali treatment to obtain a hierarchical pore catalyst. Specifically, fluoride is used to perform framework modification on the high-aluminum zeolite to promote the transformation of the Al sites in the zeolite and their migration to the outer surface, and then an acid medium acts as a "scavenger" to remove the modified Al species. Through the synergistic effect of the two, the modulation of the Al sites in the high-aluminum zeolite can be achieved; combined with the alkali treatment strategy, Si species are selectively removed to construct intracrystalline mesopores, and a high-aluminum hierarchical zeolite with both micropores and intracrystalline mesopores is obtained. The hierarchical zeolite catalyst prepared by this method has a rich mesoporous structure, adjustable pore size distribution and mesoporosity degree, and shows high catalytic performance in the glycerol dehydration reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation and application, and particularly relates to a high-aluminum hierarchical zeolite molecular sieve catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Zeolite molecular sieves are widely used in the fields of separation, adsorption, and catalysis. Their unique pore structure and acidity endow zeolite molecular sieves with extensive applications in basic chemical industry, petrochemical industry, fine chemical industry, and other fields. The relatively narrow pore structure of traditional microporous zeolite molecular sieves limits the catalytic conversion process involving large-molecule reactants or products. Introducing mesoporous structures into microporous zeolite molecular sieves to construct hierarchical zeolite molecular sieves can effectively solve the above problems.

[0003] At present, the main method for constructing mesopores in microporous zeolite molecular sieves is the post-treatment method (mainly including acid treatment and alkali treatment). Acid treatment can improve the hydrothermal stability of zeolite molecular sieves. However, this method can only generate encapsulated mesopores and cannot significantly improve the mass transfer performance of zeolite molecular sieves. At the same time, acid treatment causes a significant decrease in the Al content of zeolite molecular sieves, resulting in a decrease in the number of acid sites of zeolite molecular sieves. As a simple and easy post-treatment method, alkali treatment can construct a permeable hierarchical pore structure in microporous zeolite molecular sieves and can also increase the Al content of zeolite molecular sieves. However, the alkali treatment method has strict limitations on the silicon-aluminum ratio of the initial microporous zeolite molecular sieves. When the silicon-aluminum atomic ratio is less than 25, due to the severe repulsive effect caused by the high concentration of aluminum sites in zeolite molecular sieves, the etching and dissolution of zeolite molecular sieves in an alkaline medium are inhibited. In recent years, researchers have developed a steam treatment-alkali treatment bridging strategy to construct intracrystalline mesopores in high-aluminum hierarchical zeolite molecular sieves, but the silicon-aluminum ratio range of the parent microporous zeolite molecular sieves is 10-20. For high-aluminum zeolite molecular sieves with a lower silicon-aluminum ratio, new preparation methods need to be developed to construct hierarchical pore structures.

[0004] In the prior art, the patent with the publication number CN 116143140 A discloses a high-aluminum hierarchical mordenite zeolite molecular sieve and a preparation method thereof. This method first uses a fluorine-containing medium to perform dealumination and silicon supplementation on microporous mordenite zeolite molecular sieves, then performs alkali etching on the dealuminated and silicon-supplemented zeolite molecular sieves, and finally obtains a hydrogen-type zeolite molecular sieve after ammonium exchange and calcination treatments. By means of a fluorination-alkali treatment bridging strategy, intracrystalline mesopores are successfully introduced into microporous mordenite zeolite molecular sieves, and at the same time, the micropores and acidity of the zeolite molecular sieves are well maintained. However, the mesopore pore size distribution provided in this application is relatively single, and the mesopore porosity is low. The mesopore pore volume is only 0.1-0.25 cm 3 / g, and the average pore size distribution of the hierarchical zeolite molecular sieves in the examples is only 8 nm, lacking effective pore structure adjustment means. Summary of the Invention

[0005] Aiming at the defects of the above-mentioned existing technologies, the purpose of the present invention is to provide a preparation method of an aluminum-rich hierarchical zeolite catalyst. This method first modifies the framework of an aluminum-rich zeolite (Si / Al = 2 - 10) with fluoride to promote the transformation of the Al sites in the zeolite and their migration to the outer surface. Then, an acidic medium acts as a "scavenger" to remove the modified Al species. Through the synergistic effect of the two, the modulation of the Al sites in the aluminum-rich zeolite can be achieved. Combining with an alkali treatment strategy, Si species are selectively removed to construct intracrystalline mesopores, obtaining an aluminum-rich hierarchical zeolite with both micropores and intracrystalline mesopores. The introduced intracrystalline mesopores increase the contact opportunity between reactants and the acid sites of the zeolite, significantly improving the catalytic performance of the zeolite catalyst in the dehydration preparation reaction of glycerol.

[0006] The present invention can realize the regulation of the mesopore aperture of the zeolite through the modulation of the Al sites in the zeolite. Specifically, by controlling the modification level of the fluorine-containing medium and the selective removal of acid treatment of the Al sites after modification, the distribution and quantity of the Al sites in the aluminum-rich zeolite are modulated. Finally, the Si species are selectively etched by an alkaline medium to construct intracrystalline mesopores. Through the bridging strategy of fluorination - acid etching - alkali treatment, the present application not only realizes the construction of a rich mesoporous structure in the aluminum-rich zeolite, but also realizes the regulation of the mesopore aperture and the degree of mesopores through the synergistic effect of framework modification and acid treatment. The mesopore volume is significantly increased to 0.18 - 0.41 cm 3 / g, and the mesopore aperture can be adjusted within the range of 8 - 20 nm, enriching the post-treatment preparation technology and aperture modulation means of the aluminum-rich hierarchical zeolite.

[0007] The catalyst preparation method provided by the present invention is simple, with adjustable pore size distribution and degree of mesopores, high catalytic performance, and has good industrial application prospects.

[0008] To achieve the above object, the present invention provides a preparation method of an aluminum-rich hierarchical zeolite catalyst, including the following steps:

[0009] S1, fluorination treatment: Put the microporous zeolite sample into a fluorination medium solution, stir at room temperature for 5 - 10 h, then place the sample in an oven and dry at 80 - 140 °C for 6 - 48 h. Then place the dried sample in a muffle furnace and calcine at 450 - 700 °C for 1 - 5 hours;

[0010] S2, acid treatment: Put the sample after the fluorination treatment in step S1 into an acidic medium solution at a temperature of 60 - 90 °C, and heat for a duration of 15 - 90 min. Centrifuge or filter and wash the above-treated sample to neutral, dry at 80 - 140 °C for 6 - 48 h, and then calcine at 450 - 700 °C for 1 - 9 h;

[0011] S3, alkali treatment: putting the sample treated with acid in step S2 into an alkaline medium solution at a temperature of 60-90°C, and heating for 15-90 minutes; centrifuging or filtering the treated sample to neutrality, drying at 80-140°C for 6-48 hours, and then calcining at 450-700°C for 1-9 hours;

[0012] S4, ammonium exchange: the sample treated in step S3 is subjected to ammonium exchange with NH4NO3 or NH4Cl solution, and then calcined to finally obtain an aluminum-rich hierarchical pore molecular sieve catalyst.

[0013] Furthermore, in step S1, the concentration of the fluorinated medium solution is 0.01-1.0 mol / L, and the ratio of the volume of the fluorinated medium solution to the mass of the microporous molecular sieve sample is (1-5) ml: 1 g.

[0014] Furthermore, in step S1, the fluoridation medium is one or more of ammonium fluoride, sodium fluoride, and potassium fluoride.

[0015] Furthermore, in step S2, the concentration of the acidic medium solution is 0.1-5.0 mol / L, and the mass ratio of the volume of the acidic medium to the microporous molecular sieve is (10-50) ml: 1 g.

[0016] Furthermore, in step S2, the acidic medium is a mixed system of one or more of nitric acid, hydrochloric acid, formic acid, acetic acid, and citric acid.

[0017] Furthermore, in step S3, the concentration of the alkaline medium solution is 0.05-1.0 mol / L, and the mass ratio of the volume of the alkaline medium to the microporous molecular sieve is (10-50) ml: 1 g.

[0018] Furthermore, in step S3, the alkaline medium is one or more of sodium hydroxide, potassium hydroxide, ammonia water, and sodium carbonate.

[0019] The present invention also provides an aluminum-rich multi-level porous molecular sieve catalyst, which is prepared by the above-mentioned preparation method, and the silicon-aluminum atomic ratio of the microporous molecular sieve sample is Si / Al=2-10; the aluminum-rich multi-level porous molecular sieve catalyst contains both micropores and intracrystalline mesopores; the topological structure of the aluminum-rich multi-level porous molecular sieve is MOR type, FAU type or MFI type; the main component of the aluminum-rich multi-level porous molecular sieve catalyst is aluminosilicate molecular sieve.

[0020] Furthermore, the average mesopore diameter of the aluminum-rich multi-level porous molecular sieve catalyst is 8 to 20 nm; the specific surface area of the aluminum-rich multi-level porous molecular sieve catalyst is 357 to 432 m 2 / g; the pore volume of the aluminum-rich multi-level porous molecular sieve catalyst is 0.34 to 0.54 cm3 / g; wherein, the micropore volume is 0.13 - 0.16 cm 3 / g, and the intracrystalline mesopore volume is 0.18 - 0.41 cm 3 / g.

[0021] The aluminosilicate hierarchical zeolite catalyst is used in the process of dehydrating glycerol to prepare acrolein, and specifically includes the following steps: in a reactor, glycerol contacts with the aluminosilicate hierarchical zeolite catalyst, and a dehydration reaction occurs to generate acrolein and acetaldehyde; the reaction temperature of the glycerol is 260 - 400 °C, the reaction pressure is 0.1 - 0.5 MPa, and the space velocity is 1.25 h -1 .

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The preparation method of the aluminosilicate hierarchical zeolite catalyst provided by the present invention constructs a rich mesoporous structure in the aluminosilicate zeolite through the strategies of framework modification, Al displacement removal, and Si etching bridging. By modifying the aluminosilicate zeolite with fluoride, the transformation and migration of the Al sites in the zeolite can be achieved; in cooperation with the "scavenger" acid medium, the non-framework aluminum species after transformation and migration are removed; under the synergistic effect of the two, the modulation of the Al sites in the zeolite is realized, triggering the spontaneous and controllable dissolution of the zeolite after fluorination-acid treatment in the alkaline medium. By adjusting the condition parameters of the fluorination-acid treatment, the mesopore aperture and mesopore degree of the final hierarchical zeolite can be adjusted.

[0024] 2. The aluminosilicate hierarchical zeolite catalyst prepared by the present invention has a rich intracrystalline mesoporous structure, which improves the contact opportunity between the reactants and the active sites from the perspective of expanding the diffusion channels and enhancing the diffusion of reactants, intermediates, and products, and significantly improves the performance of the glycerol dehydration reaction. The formed non-framework aluminum species and under the synergistic effect of the sites, significantly improve the yields of acrolein and acetaldehyde.

[0025] 3. The operation steps and production device of the aluminosilicate hierarchical zeolite catalyst provided by the present invention are simple, the preparation cost is low, and it is suitable for large-scale industrialization and industrial application. Description of the Drawings

[0026] Figure 1 TEM image of the catalyst used in Comparative Example 1.

[0027] Figure 2 TEM image of the catalyst prepared in Example 1.

[0028] Figure 3 BJH pore size distribution diagrams of the catalysts prepared in Examples 1 - 4 and Comparative Example 1.

[0029] Figure 4TEM image of the aluminum-rich hierarchical zeolite catalyst prepared in Comparative Example 5.

[0030] Figure 5 TEM image of the aluminum-rich hierarchical zeolite catalyst prepared in Comparative Example 6.

[0031] Figure 6 TEM image of the aluminum-rich hierarchical zeolite catalyst prepared in Comparative Example 7.

[0032] Figure 7 BJH pore size distribution diagram of the catalysts prepared in Comparative Examples 1-7.

[0033] Figure 8 Glycerol conversion results of the catalysts prepared in Examples 1-3 and Comparative Example 1 in the glycerol dehydration preparation reaction.

[0034] Figure 9 Acrolein yield results of the catalysts prepared in Examples 1-3 and Comparative Example 1 in the glycerol dehydration preparation reaction.

[0035] Figure 10 Acetaldehyde yield results of the catalysts prepared in Examples 1-3 and Comparative Example 1 in the glycerol dehydration preparation reaction. Detailed implementation manners

[0036] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Here, it should also be noted that in order to avoid obscuring the present invention due to unnecessary details, only the structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, while other details less related to the present invention are omitted.

[0038] In addition, it should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0039] The steam treatment-alkali treatment bridging strategy can construct intracrystalline mesopores in aluminum-rich hierarchical zeolites, but the silica-alumina ratio range of its parent microporous zeolites is 10-20. For aluminum-rich zeolites with a lower silica-alumina ratio, new preparation methods need to be developed to construct hierarchical pore channel structures.

[0040] The present invention provides a preparation method for an aluminum-rich hierarchical zeolite catalyst, comprising the following steps:

[0041] S1, Fluorination treatment: Put the microporous molecular sieve sample into the fluorination medium solution, stir at room temperature for 5 - 10 h, then place the sample in an oven and dry it at 80 - 140 °C for 6 - 48 h. Then put the dried sample into a muffle furnace and calcine it at 450 - 700 °C for 1 - 5 hours;

[0042] Among them, the fluorination medium is one or more of ammonium fluoride, sodium fluoride, and potassium fluoride.

[0043] The concentration of the fluorination medium solution is 0.01 - 1.0 mol / L, and the ratio of the volume of the fluorination medium solution to the mass of the microporous molecular sieve sample is (1 - 5) ml: 1 g.

[0044] S2, Acid treatment: Put the sample after the fluorination treatment in step S1 into the acidic medium solution at a temperature of 60 - 90 °C according to a certain proportion, and heat for 15 - 90 min; Centrifuge or filter and wash the above - treated sample until it is neutral, dry it at 80 - 140 °C for 6 - 48 h, and then calcine it at 450 - 700 °C for 1 - 9 h;

[0045] Among them, the acidic medium is a mixed system of one or more of nitric acid, hydrochloric acid, formic acid, acetic acid, and citric acid. The concentration of the acidic medium solution is 0.1 - 5.0 mol / L, and the ratio of the volume of the acidic medium to the mass of the microporous molecular sieve is (10 - 50) ml: 1 g.

[0046] S3, Alkali treatment: Put the sample after the acid treatment in step S2 into the alkaline medium solution at a temperature of 60 - 90 °C according to a certain proportion, and heat for 15 - 90 min; Centrifuge or filter and wash the above - treated sample until it is neutral, dry it at 80 - 140 °C for 6 - 48 h, and then calcine it at 450 - 700 °C for 1 - 9 h;

[0047] Among them, the alkaline medium is one or more of sodium hydroxide, potassium hydroxide, ammonia water, and sodium carbonate. The concentration of the alkaline medium solution is 0.05 - 1.0 mol / L, and the ratio of the volume of the alkaline medium to the mass of the microporous molecular sieve is (10 - 50) ml: 1 g.

[0048] S4, Ammonium exchange: Use NH4NO3 or NH4Cl solution to perform ammonium exchange on the sample after the treatment in step S3, and then calcine it to finally obtain the aluminum - rich hierarchical pore molecular sieve catalyst.

[0049] Among them, the ammonium exchange temperature condition is 60 - 90 °C, the exchange time is 15 - 90 min, the number of exchange times is 1 - 5 times, the drying temperature is 80 - 140 °C, the drying time is 6 - 48 h, the calcination temperature is 450 - 700 °C, and the calcination time is 1 - 9 h.

[0050] The present invention also provides a high-aluminum hierarchical zeolite molecular sieve catalyst, which is prepared by the aforementioned preparation method. The silicon-aluminum atomic ratio of the microporous zeolite molecular sieve sample used in this high-aluminum hierarchical zeolite molecular sieve catalyst is Si / Al = 2-10. This high-aluminum hierarchical zeolite molecular sieve catalyst contains both micropores and intracrystalline mesopores at the same time; the topological structure of the high-aluminum hierarchical zeolite molecular sieve is of MOR type, FAU type or MFI type. The main component of this high-aluminum hierarchical zeolite molecular sieve catalyst is aluminosilicate molecular sieve.

[0051] The average mesopore diameter of the high-aluminum hierarchical mordenite zeolite molecular sieve is 8-20 nm; the specific surface area of the high-aluminum hierarchical zeolite molecular sieve catalyst is 357-432 m 2 / g; the pore volume of the high-aluminum hierarchical zeolite molecular sieve catalyst is 0.34-0.54 cm 3 / g; among them, the micropore volume is 0.13-0.16 cm 3 / g, and the pore volume of the intracrystalline mesopores is 0.18-0.41 cm 3 / g.

[0052] This high-aluminum hierarchical zeolite molecular sieve catalyst is used in the process of dehydrating glycerol to prepare acrolein, and specifically includes the following steps: In a reactor, glycerol contacts with the high-aluminum hierarchical zeolite molecular sieve catalyst, and a dehydration reaction occurs to generate acrolein and acetaldehyde; the reaction temperature of the glycerol is 260-400 °C, the reaction pressure is 0.1-0.5 MPa, and the space velocity is 1.25 h -1 .

[0053] The following specifically describes the preparation method of the high-aluminum hierarchical zeolite molecular sieve catalyst provided by the present invention. Unless otherwise specified, the raw materials and reagents in the examples of this application are all purchased through commercial channels.

[0054] Example 1

[0055] This example provides a preparation method of a high-aluminum hierarchical zeolite molecular sieve catalyst, including the following steps:

[0056] 1) Fluorination treatment: Put 20 g of mordenite zeolite molecular sieve (MOR), 0.24 g of ammonium fluoride and 60 ml of water in a beaker, stir at room temperature for 8 h, place the treated sample in an oven and dry it at 120 °C for 12 h, and then calcine it in a muffle furnace at 550 °C for 3 h; among them, the Si / Al atomic ratio of the mordenite zeolite molecular sieve is 7.9.

[0057] 2) Acid treatment: Prepare an aqueous solution containing 1 M nitric acid, take 300 ml and place it in a flask, heat it to 80 °C in a water bath, then add 15 g of the zeolite molecular sieve after nitric acid treatment, stir for 60 min, and the solid-liquid ratio is 1 / 20; wash the reaction product with deionized water until neutral, dry it at 120 °C for 12 h, and calcine it in a muffle furnace at 550 °C for 3 h;

[0058] 3) Alkali treatment: Prepare a solution containing 0.2 M sodium hydroxide, take 150 ml and place it in a polypropylene flask, and heat it in a water bath to 60 °C. Then add 5 g of the molecular sieve treated with nitric acid, stir for 30 min, and the solid-liquid ratio is 1 / 30; wash the reaction product with deionized water until neutral, dry at 120 °C for 12 h, and calcine at 550 °C for 3 h;

[0059] 4) Ammonium exchange: Add the obtained molecular sieve above to a 0.8 M ammonium chloride solution, with a solid-liquid ratio of 1 / 20, stir magnetically at 80 °C for 2 hours, repeat the exchange 3 times, then filter and wash the reaction product with deionized water, dry at 120 °C for 8 h, and calcine at 550 °C for 3 h, denoted as the aluminum-rich hierarchical porous molecular sieve catalyst A.

[0060] Preparation of acrolein by glycerol dehydration:

[0061] Load about 1 g of the aluminum-rich hierarchical porous molecular sieve catalyst A prepared in Example 1 in the isothermal section of the reaction tube, and fill the remaining part with quartz sand. Then pre-treat the catalyst by heating it to 450 °C in a nitrogen atmosphere, and then reduce the temperature to the reaction temperature of 320 °C and stabilize it. Then start to introduce the glycerol aqueous solution. Using nitrogen as the carrier gas, the raw material is vaporized in a vaporization chamber at 190 °C before entering the reaction tube. The space velocity is 1.25 h -1 , and the product is analyzed using an FID detector equipped with an FID detector, with n-pentanol as the internal standard. The reaction performance test results are shown in Figure 3 .

[0062] Comparative Example 1

[0063] Comparative Example 1 provides a method for preparing acrolein by glycerol dehydration. The main difference from Example 1 is mainly that: the mordenite molecular sieve (Si / Al = 7.9) untreated in Example 1 is used. The specific process is as follows:

[0064] 1) Load about 1 g of mordenite molecular sieve (MOR) in the isothermal section of the reaction tube, and fill the remaining part with quartz sand. Then pre-treat the catalyst by heating it to 450 °C in a nitrogen atmosphere, and then reduce the temperature to the reaction temperature of 320 °C and stabilize it. Then start to introduce the glycerol aqueous solution. Using nitrogen as the carrier gas, the raw material is vaporized in a vaporization chamber at 190 °C before entering the reaction tube. The space velocity is 1.25 h-1 based on glycerol, and the product is analyzed using an FID detector equipped with an FID detector, with n-pentanol as the internal standard. The reaction performance test results are shown in Figure 3 .

[0065] Figure 1 is the TEM image of the mordenite molecular sieve in Comparative Example 1. It can be seen that the microporous molecular sieve has a smooth surface and no obvious mesoporous structure is observed.

[0066] Figure 2 TEM image of the aluminum-rich hierarchical zeolite molecular sieve catalyst prepared in Example 1. It can be seen that after fluorination treatment, acid treatment, and alkali treatment, the catalyst has a rough surface and a rich mesoporous structure.

[0067] It is proved that the intracrystalline mesopores of the hierarchical zeolite molecular sieve in Example 1 are prepared by the bridging strategy of fluorination treatment, acid treatment, and alkali treatment.

[0068] Comparative Example 2

[0069] Comparative Example 2 provides a preparation method of an aluminum-rich hierarchical zeolite molecular sieve catalyst. The main difference from Example 1 is that: the acid treatment in step 2), the alkali treatment in step 3), and the ammonium exchange in step 4) are not carried out, and only the mordenite molecular sieve is fluorinated. The other steps are substantially the same as those in Example 1 and will not be elaborated here.

[0070] Then, the fluorinated catalyst is used in the process of glycerol dehydration to prepare acrolein. The product is analyzed by an FID detector equipped with an FID detector, and n-pentanol is used as the internal standard. The reaction performance test results are shown in Figure 7 .

[0071] Comparative Example 3

[0072] Comparative Example 3 provides a preparation method of an aluminum-rich hierarchical zeolite molecular sieve catalyst. The main difference from Example 1 is that: the fluorination treatment in step 1), the alkali treatment in step 3), and the ammonium exchange in step 4) are not carried out, and only the mordenite molecular sieve is acid-treated. The other steps are substantially the same as those in Example 1 and will not be elaborated here.

[0073] Then, the acid-treated catalyst is used in the process of glycerol dehydration to prepare acrolein. The product is analyzed by an FID detector equipped with an FID detector, and n-pentanol is used as the internal standard. The reaction performance test results are shown in Figure 7 .

[0074] Comparative Example 4

[0075] Comparative Example 4 provides a preparation method of an aluminum-rich hierarchical zeolite molecular sieve catalyst. The main difference from Example 1 is that: the fluorination treatment in step 1) and the acid treatment in step 2) are not carried out, and only the mordenite molecular sieve is alkali-treated and ammonium-exchanged. The other steps are substantially the same as those in Example 1 and will not be elaborated here.

[0076] Then, the treated catalyst is used in the process of glycerol dehydration to prepare acrolein. The product is analyzed by an FID detector equipped with an FID detector, and n-pentanol is used as the internal standard. The reaction performance test results are shown in Figure 7 .

[0077] Comparative Example 5

[0078] Comparative Example 5 provides a method for preparing an aluminum-rich hierarchical zeolite catalyst. The main difference from Example 1 is mainly that: the acid treatment in step 2) is not carried out, and the other steps are substantially the same as those in Example 1, which will not be elaborated here.

[0079] Then, the treated catalyst was used in the process of glycerol dehydration to prepare acrolein. The product was analyzed using an FID detector equipped with an FID detector, with n-pentanol as the internal standard. The reaction performance test results are shown in Figure 7 .

[0080] Figure 4 is the TEM image of the zeolite sample prepared in Comparative Example 5. It can be seen that when the acid treatment step is missing, the surface of the prepared zeolite sample is smooth and flat, without an obvious mesoporous structure. This shows that only the fluorination-alkali treatment combination cannot construct intracrystalline mesopores in the aluminum-rich zeolite.

[0081] Comparative Example 6

[0082] Comparative Example 6 provides a method for preparing an aluminum-rich hierarchical zeolite catalyst. The main difference from Example 1 is mainly that: the alkali treatment in step 3) and the ammonium exchange in step 4) are not carried out, and the other steps are substantially the same as those in Example 1, which will not be elaborated here.

[0083] Then, the treated catalyst was used in the process of glycerol dehydration to prepare acrolein. The product was analyzed using an FID detector equipped with an FID detector, with n-pentanol as the internal standard. The reaction performance test results are shown in Figure 7 .

[0084] Figure 5 is the TEM image of the zeolite sample prepared in Comparative Example 6. It can be seen that when the alkali treatment step is missing, the surface of the prepared zeolite sample is smooth and flat, without an obvious mesoporous structure. This shows that only the fluorination-acid treatment combination cannot construct intracrystalline mesopores in the aluminum-rich zeolite.

[0085] Comparative Example 7

[0086] Comparative Example 7 provides a method for preparing an aluminum-rich hierarchical zeolite catalyst. The main difference from Example 1 is mainly that: the fluorination treatment in step 1) is not carried out, and the other steps are substantially the same as those in Example 1, which will not be elaborated here.

[0087] Then, the treated catalyst was used in the process of glycerol dehydration to prepare acrolein. The product was analyzed using an FID detector equipped with an FID detector, with n-pentanol as the internal standard. The reaction performance test results are shown in Figure 7 .

[0088] Figure 6TEM image of the molecular sieve sample prepared in Comparative Example 7. It can be seen that in the absence of the fluorination treatment step, the surface of the prepared molecular sieve sample is smooth and flat, without an obvious mesoporous structure. This indicates that only the combination of acid treatment and alkali treatment cannot construct intracrystalline mesopores in the aluminum-rich molecular sieve.

[0089] Examples 2 - 4

[0090] Examples 2 - 4 provide a preparation method of an aluminum-rich hierarchical pore molecular sieve catalyst. Compared with Example 1, the difference lies in that the dosage of the fluorination medium in step S1 and the dosage of the acid medium in step S2 are changed, as shown in the following table. The rest is generally the same as in Example 1 and will not be elaborated here.

[0091] The aluminum-rich hierarchical pore molecular sieve catalyst samples prepared in Examples 1 - 4 and Comparative Examples 1 - 7 were tested, and the surface and pore parameters were measured by a Micromeritics ASAP - 2020 physical adsorption instrument.

[0092] First, the sample was desorbed under vacuum at 350 °C for 10 h, and then a nitrogen adsorption - desorption experiment was carried out at the liquid nitrogen temperature (-196 °C). The total specific surface area of the sample was calculated by the Brunauer - Emmett - Teller (BET) theoretical model, where the cross-sectional area of the N2 molecule was taken as 0.162 nm 2 ; the total pore volume of the sample was calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.995; the micropore specific surface area and micropore pore volume of the sample were obtained according to the t-plot method; the mesopore pore size distribution of the sample was obtained by analyzing the adsorption branch data of the nitrogen adsorption - desorption isotherm using the BJH model. The silicon-aluminum atomic ratio of the sample was determined by an X-ray fluorescence spectrometer (XRF). The test results are shown in Figure 3 , and the test data are shown in the following table.

[0093]

[0094] As can be seen from the above table, a rich intracrystalline mesoporous structure was successfully introduced into the aluminum-rich molecular sieve through fluorination - acid treatment - alkali treatment. By changing the degree of fluorination and the level of acid treatment, the average mesopore pore size of the molecular sieve can be adjusted within the range of 8 - 20 nm, and at the same time, the mesopore degree can be adjusted, and the mesopore pore volume can reach up to 0.41 cm 3 / g.

[0095] Figure 3 BJH pore size distribution diagrams of the catalysts prepared in Examples 1 - 4 and Comparative Example 1. Comparing Example 1 with Comparative Example 1, it can be seen that a rich intracrystalline mesoporous structure was successfully introduced into the aluminum-rich molecular sieve through fluorination treatment, acid treatment, alkali treatment, and ammonium exchange.

[0096] The test results of Comparative Examples 1 - 7 are shown inFigure 7 , the test data are shown in the following table.

[0097]

[0098] Figure 7 It is the BJH pore size distribution diagram of the catalysts prepared in Comparative Examples 1-7. It can be seen that neither single fluorination treatment, acid treatment, alkali treatment, ammonium exchange, nor any binary or ternary combination can construct intracrystalline mesopores in the aluminum-rich zeolite.

[0099] It should be emphasized that Figure 7 in Comparative Example 5 and Comparative Example 7 are the BJH pore size distribution diagrams of the molecular sieve catalysts prepared without acid treatment and fluorination treatment, respectively. It can be seen that whether the acid treatment step or the fluorination treatment step is missing, a rich mesoporous structure cannot be constructed in the aluminum-rich zeolite. This further confirms the importance of the synergistic effect of fluorination treatment and acid treatment in constructing mesopores and adjusting the mesopore aperture in the aluminum-rich zeolite.

[0100] Figure 8 and Figure 9 are the glycerol conversion rate and acrolein yield diagrams of the molecular sieve catalysts in Examples 1-3 and Comparative Example 1. It can be seen that the catalytic performance of the microporous molecular sieve in Comparative Example 1 is relatively low, and the glycerol conversion rate and acrolein yield are only 17.7% and 11.0% respectively. After being treated by the fluorination treatment, acid treatment and alkali treatment bridging strategy, the glycerol dehydration performance of the hierarchical pore molecular sieve catalysts prepared in Examples 1-3 is significantly improved, and the glycerol conversion rate and acrolein yield are increased to 90.6% - 95.8% and 50.0% - 55.2% respectively.

[0101] Figure 10 is the acetaldehyde yield diagram of the molecular sieve catalysts in Examples 1-3 and Comparative Example 1. The acetaldehyde yield of the microporous molecular sieve in Comparative Example 1 is only 1.6%. After the fluorination treatment - acid treatment - alkali treatment bridging strategy, the acetaldehyde yields of the hierarchical pore molecular sieve catalysts prepared in Examples 1 - 3 are significantly increased to 21.0% - 24.0%. This is because the non-framework aluminum species formed during the fluorination treatment and the synergistic effect of the acid sites realize the conversion of glycerol and the formation of acetaldehyde, proving that the catalyst prepared by this strategy has a high glycerol conversion efficiency and the production efficiency of the main product acrolein, and can also promote the formation of acetaldehyde. This catalyst not only realizes the high-value utilization of glycerol, but also opens up a new production route for the preparation of acetaldehyde.

[0102] It can be known from the experiment that the fluorination medium can be one or more of ammonium fluoride, sodium fluoride, and potassium fluoride.

[0103] The acidic medium can be a mixed system of one or more of nitric acid, hydrochloric acid, formic acid, acetic acid, and citric acid. The alkaline medium can be one or more of sodium hydroxide, potassium hydroxide, ammonia water, and sodium carbonate.

[0104] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of an aluminum-rich hierarchical porous molecular sieve catalyst, characterized in that, It includes the following steps: S1, fluorination treatment: Put the microporous molecular sieve sample into a fluorination medium solution, stir at room temperature for 5 - 10 h, then place the sample in an oven and dry it at 80 - 140 °C for 6 - 48 h, and then place the dried sample in a muffle furnace and calcine it at 450 - 700 °C for 1 - 5 h; the fluorination medium is one or more of ammonium fluoride, sodium fluoride, and potassium fluoride; The silicon-aluminum atomic ratio of the microporous molecular sieve sample is Si / Al = 2 - 10; S2, acid treatment: Put the sample after the fluorination treatment in step S1 into an acidic medium solution at a temperature of 60 - 90 °C, and heat for a duration of 15 - 90 min; centrifuge or filter and wash the above-treated sample until it is neutral, dry it at 80 - 140 °C for 6 - 48 h, and then calcine it at 450 - 700 °C for 1 - 9 h; the acidic medium is a mixed system of one or more of nitric acid, hydrochloric acid, formic acid, acetic acid, and citric acid; S3, alkali treatment: Put the sample after the acid treatment in step S2 into an alkaline medium solution at a temperature of 60 - 90 °C, and heat for a duration of 15 - 90 min; centrifuge or filter and wash the above-treated sample until it is neutral, dry it at 80 - 140 °C for 6 - 48 h, and then calcine it at 450 - 700 °C for 1 - 9 h; S4, ammonium exchange: Perform ammonium exchange on the sample after being treated in step S3 with an NH4NO3 or NH4Cl solution, and then calcine it to finally obtain an aluminum-rich hierarchical pore molecular sieve catalyst.

2. The preparation method of the aluminum-rich hierarchical porous molecular sieve catalyst according to claim 1, characterized in that: In step S1, the concentration of the fluorination medium solution is 0.01 - 1.0 mol / L, and the ratio of the volume of the fluorination medium solution to the mass of the microporous molecular sieve sample is (1 - 5) ml:1 g.

3. The preparation method of the aluminum-rich hierarchical pore molecular sieve catalyst according to claim 1, characterized in that: In step S2, the concentration of the acidic medium solution is 0.1 - 5.0 mol / L, and the mass ratio of the acidic medium to the mass of the microporous molecular sieve is (10 - 50) ml:1 g.

4. The preparation method of the aluminum-rich hierarchical pore molecular sieve catalyst according to claim 1, wherein: In step S3, the concentration of the alkaline medium solution is 0.05 - 1.0 mol / L, and the mass ratio of the alkaline medium to the mass of the microporous molecular sieve is (10 - 50) ml:1 g.

5. The preparation method of the aluminum-rich hierarchical porous molecular sieve catalyst according to claim 1, wherein: In step S3, the alkaline medium is one or more of sodium hydroxide, potassium hydroxide, ammonia water, and sodium carbonate.

6. An aluminum-rich hierarchical porous molecular sieve catalyst, prepared by the preparation method of the aluminum-rich hierarchical porous molecular sieve catalyst according to any one of claims 1-5, characterized in that: The silicon-aluminum atomic ratio of the microporous molecular sieve sample is Si / Al = 2 - 10; the aluminum-rich hierarchical pore molecular sieve catalyst contains both micropores and intracrystalline mesopores; the topological structure of the aluminum-rich hierarchical pore molecular sieve is MOR type, FAU type, or MFI type; the main component of the aluminum-rich hierarchical pore molecular sieve catalyst is aluminosilicate molecular sieve.

7. The aluminum-rich hierarchical porous molecular sieve catalyst according to claim 6, wherein: The average mesopore diameter of the aluminum-rich hierarchical zeolite catalyst is 8 - 20 nm; the specific surface area of the aluminum-rich hierarchical zeolite catalyst is 357 - 432 m 2 / g; the pore volume of the aluminum-rich hierarchical zeolite catalyst is 0.34 - 0.54 cm 3 / g; wherein, the micropore volume is 0.13 - 0.16 cm 3 / g, and the pore volume of the intracrystalline mesopores is 0.18 - 0.41 cm 3 / g.

8. Application of an aluminum-rich hierarchical porous molecular sieve catalyst, characterized in that, The aluminosilicate hierarchical pore molecular sieve catalyst is prepared by the preparation method according to any one of claims 1-5 or is the aluminosilicate hierarchical pore molecular sieve catalyst according to any one of claims 6-7; the aluminosilicate hierarchical pore molecular sieve catalyst is used in the process of dehydrating glycerol to prepare acrolein and acetaldehyde, and specifically includes the following steps: in a reactor, glycerol contacts with the aluminosilicate hierarchical pore molecular sieve catalyst, and a dehydration reaction occurs to generate acrolein and acetaldehyde; the reaction temperature of the glycerol is 260-400 °C, the reaction pressure is 0.1-0.5 MPa, and the space velocity is 1.25 h -1 .

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