Aluminum-rich hierarchical pore molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention provides an aluminum-rich hierarchical pore molecular sieve catalyst as well as a preparation method and application thereof, and relates to the technical field of catalyst preparation and application. According to the preparation method, an aluminum-rich molecular sieve (Si / Al = 2-10) matrix is sequentially subjected to skeleton modification, acid treatment and alkali treatment to obtain the hierarchical pore catalyst. Specifically, an aluminum-rich molecular sieve is subjected to framework modification through fluoride, Al site transformation and migration to the outer surface of the molecular sieve are promoted, then the effect of a scavenger is achieved through an acid medium, modified Al species are removed, and Al site modulation of the aluminum-rich molecular sieve can be achieved through the synergistic effect of fluoride and fluoride. And selectively removing Si species in combination with an alkali treatment strategy, and constructing intracrystalline mesopores to obtain the aluminum-rich hierarchical pore molecular sieve with micropores and intracrystalline mesopores at the same time. The hierarchical pore molecular sieve catalyst prepared by the method has rich mesoporous structures, adjustable pore size distribution and mesoporous degree, and shows high catalytic performance in glycerol dehydration reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation and application, and in particular to an aluminum-rich multi-level porous molecular sieve catalyst and a preparation method and application thereof. Background Art

[0002] Molecular sieves are widely used in separation, adsorption and catalysis. Their unique pore structure and acidity endow them with wide applications in basic chemicals, petrochemicals and fine chemicals. The relatively narrow pore structure of traditional microporous molecular sieves limits the catalytic conversion process involving macromolecular reactants or products. Introducing mesoporous structures into microporous molecular sieves to construct multi-level pore molecular sieves can effectively solve the above problems.

[0003] At present, the method for constructing mesopores in microporous molecular sieves is mainly post-treatment method (mainly including acid treatment and alkali treatment). Acid treatment can improve the hydrothermal stability of molecular sieves. However, this method can only produce endoplasmic mesopores and cannot significantly improve the mass transfer performance of molecular sieves. At the same time, acid treatment leads to a significant decrease in the Al content of the molecular sieve, resulting in a decrease in the number of acid sites in the molecular sieve. Alkali treatment, as a simple and easy post-treatment method, can construct a transparent multi-level pore structure in the microporous molecular sieve and also increase the Al content of the molecular sieve. However, the alkali treatment method has strict restrictions on the silicon-aluminum ratio of the initial microporous molecular sieve. When the silicon-aluminum atomic ratio is less than 25, the high concentration of aluminum sites in the molecular sieve causes a serious repulsive effect, which inhibits the etching and dissolution of the molecular sieve in the alkaline medium. In recent years, researchers have developed a water vapor treatment-alkali treatment bridging strategy to construct intracrystalline mesopores in aluminum-rich multi-level pore molecular sieves, but the silicon-aluminum ratio of its parent microporous molecular sieve ranges from 10 to 20. For aluminum-rich molecular sieves with lower silicon-aluminum ratios, new preparation methods need to be developed to construct multi-level pore channel structures.

[0004] In the prior art, the patent with publication number CN 116143140 A discloses an aluminum-rich multi-level porous mordenite molecular sieve and its preparation method. The method first uses a fluorine-containing medium to dealuminate and siliconize the microporous mordenite molecular sieve, then etches the dealuminate and siliconize molecular sieve with alkaline solution, and then obtains the hydrogen-type molecular sieve after ammonium exchange and calcination. The intracrystalline mesopores are successfully introduced into the microporous mordenite molecular sieve through the fluorination-alkali treatment bridging strategy, while the micropores and acidity of the molecular sieve are kept good. However, the mesopore size distribution provided in the application is relatively single, and the mesoporosity is low, with a mesopore volume of only 0.1~0.25 cm 3 / g, the average pore size distribution of the multi-level pore molecular sieve in the embodiment is only 8 nm, lacking effective means for adjusting the pore structure. Summary of the invention

[0005] In view of the defects of the above-mentioned prior art, the purpose of the present invention is to provide a method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, which first modifies the framework of an aluminum-rich molecular sieve (Si / Al = 2~10) by fluoride to promote the transformation of the molecular sieve Al position and migration to the outer surface, and then removes the modified Al species through the acid medium as a "scavenger". The Al position of the aluminum-rich molecular sieve can be adjusted through the synergistic effect of the two; then, the alkaline treatment strategy is combined to selectively remove Si species, construct intracrystalline mesopores, and obtain an aluminum-rich multi-level porous molecular sieve with both micropores and intracrystalline mesopores. The introduced intracrystalline mesopores increase the contact opportunities between the reactants and the acid sites of the molecular sieve, and significantly improve the catalytic performance of the molecular sieve catalyst in the dehydration preparation reaction of glycerol.

[0006] The present invention can achieve the regulation of the mesopore diameter of the molecular sieve by adjusting the Al site of the molecular sieve. Specifically, by adjusting the modification level of the fluorine-containing medium and the selective removal of the modified Al site by acid treatment, the distribution and number of Al sites in the aluminum-rich molecular sieve can be regulated, and finally the Si species are selectively etched by the alkaline medium to construct intracrystalline mesopores. This application not only achieves the construction of a rich mesoporous structure in the aluminum-rich molecular sieve through the fluorination-acid etching-alkaline treatment bridging strategy, but also achieves the regulation of the mesopore diameter and mesoporous degree through the synergistic effect of skeleton modification and acid treatment, and the mesopore volume is significantly increased to 0.18~0.41 cm 3 / g, and the mesopore diameter can be adjusted in the range of 8~20 nm, which enriches the post-processing preparation technology and pore size modulation methods of aluminum-rich hierarchical pore molecular sieves.

[0007] The catalyst preparation method provided by the invention is simple, the pore size distribution and the mesopore degree are adjustable, the catalytic performance is high, and the catalyst has good industrialization prospects.

[0008] To achieve the above object, the present invention provides a method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, comprising the following steps: 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 at 80-140 °C for 6-48 h, and then place the dried sample in a muffle furnace and calcine at 450-700 °C for 1-5 hours; S2, acid treatment: putting the sample treated by fluorination in step S1 into an acidic medium solution at a temperature of 60-90°C, and heating for 15-90 min; centrifuging or filtering the treated sample to neutrality, drying at 80-140°C for 6-48 h, and then calcining at 450-700°C for 1-9 h; S3, alkali treatment: the sample treated with acid in step S2 is placed in an alkaline medium solution at a temperature of 60-90°C, and the heating duration is 15-90 min; the sample treated above is centrifuged or filtered and washed to neutrality, dried at 80-140°C for 6-48 h, and then calcined at 450-700°C for 1-9 h; 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.

[0009] 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.

[0010] Furthermore, in step S1, the fluoridation medium is one or more of ammonium fluoride, sodium fluoride, and potassium fluoride.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] Furthermore, in step S3, the alkaline medium is one or more of sodium hydroxide, potassium hydroxide, ammonia water, and sodium carbonate.

[0015] 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.

[0016] Furthermore, the average mesopore diameter of the aluminum-rich multi-level porous molecular sieve catalyst is 8-20 nm; the specific surface area of ​​the aluminum-rich multi-level porous molecular sieve catalyst is 357-432 m 2 / g; the pore volume of the aluminum-rich multi-level porous molecular sieve catalyst is 0.34~0.54 cm3 / 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.

[0017] The aluminum-rich multi-level porous molecular sieve catalyst is used in the process of dehydrating glycerol to prepare acrolein, which specifically comprises the following steps: in a reactor, glycerol is contacted with the aluminum-rich multi-level porous molecular sieve catalyst to undergo a dehydration reaction 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 .

[0018] The beneficial effects of the present invention are: 1. The preparation method of the aluminum-rich multi-level porous molecular sieve catalyst provided by the present invention constructs a rich mesoporous structure in the aluminum-rich molecular sieve through framework modification, Al position removal and Si etching bridging strategy. The aluminum-rich molecular sieve is modified by fluoride to achieve the transformation and migration of the Al position of the molecular sieve; with the cooperation of the "scavenger" acid medium, the non-framework aluminum species after the transformation and migration are removed; under the synergistic effect of the two, the Al position of the molecular sieve is modulated, triggering the spontaneous and controllable dissolution of the molecular sieve in the alkaline medium after fluorination-acid treatment. By adjusting the condition parameters of the fluorination-acid treatment, the mesopore diameter and mesoporous degree of the final multi-level porous molecular sieve can be adjusted.

[0019] 2. The aluminum-rich multi-level pore molecular sieve catalyst prepared by the present invention has a rich intracrystalline mesoporous structure, which increases the contact opportunity between reactants and active sites from the perspective of expanding diffusion channels and improving the diffusion of reactants, intermediates and products, and significantly improves the performance of glycerol dehydration reaction. The synergistic effect of the non-framework aluminum species and Brønsted sites significantly improves the yield of acrolein and acetaldehyde.

[0020] 3. The aluminum-rich multi-level porous molecular sieve catalyst provided by the present invention has simple operation steps and production equipment, low preparation cost, and is suitable for large-scale industrialization and industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the TEM image of the catalyst used in Comparative Example 1.

[0022] Figure 2 This is the TEM image of the catalyst prepared in Example 1.

[0023] Figure 3 BJH pore size distribution diagram of the catalysts prepared in Examples 1-4 and Comparative Example 1.

[0024] Figure 4This is the TEM image of the aluminum-rich multi-level porous molecular sieve catalyst prepared in Comparative Example 5.

[0025] Figure 5 This is the TEM image of the aluminum-rich multi-level porous molecular sieve catalyst prepared in Comparative Example 6.

[0026] Figure 6 This is the TEM image of the aluminum-rich multi-level porous molecular sieve catalyst prepared in Comparative Example 7.

[0027] Figure 7 The BJH pore size distribution diagram of the catalysts prepared in Comparative Examples 1-7.

[0028] Figure 8 The glycerol conversion results of the catalysts prepared in Examples 1-3 and Comparative Example 1 in the glycerol dehydration preparation reaction.

[0029] Fig. 9 The results are as follows for the acrolein yields of the catalysts prepared in Examples 1-3 and Comparative Example 1 in the glycerol dehydration reaction.

[0030] Fig.10 The acetaldehyde yield results of the catalysts prepared in Examples 1-3 and Comparative Example 1 in the glycerol dehydration preparation reaction. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0033] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0034] The steam treatment-alkali treatment bridging strategy can construct intracrystalline mesopores in aluminum-rich hierarchical pore molecular sieves, but the silicon-aluminum ratio of its parent microporous molecular sieve ranges from 10 to 20. For aluminum-rich molecular sieves with lower silicon-aluminum ratios, new preparation methods need to be developed to construct hierarchical pore structures.

[0035] The present invention provides a method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, comprising the following steps: 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 at 80-140 °C for 6-48 h, and then place the dried sample in a muffle furnace and calcine at 450-700 °C for 1-5 hours; Wherein, the fluoridation medium is one or more of ammonium fluoride, sodium fluoride and potassium fluoride.

[0036] 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.

[0037] S2, acid treatment: the sample treated by fluorination in step S1 is put into an acidic medium solution at a temperature of 60-90°C in proportion, and the heating duration is 15-90 min; the sample treated above is centrifuged or filtered and washed to neutrality, dried at 80-140°C for 6-48 h, and then calcined 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. The concentration of the acidic medium solution is 0.1-5.0 mol / L, and the volume of the acidic medium and the mass ratio of the microporous molecular sieve are (10-50) ml: 1 g.

[0038] S3, alkali treatment: the sample treated with acid in step S2 is put into an alkaline medium solution at a temperature of 60-90°C in proportion, and the heating duration is 15-90 min; the sample treated above is centrifuged or filtered and washed to neutrality, dried at 80-140°C for 6-48 h, and then roasted at 450-700°C for 1-9 h; Wherein, the alkaline medium is one or more of sodium hydroxide, potassium hydroxide, ammonia water, and sodium carbonate.

[0039] 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.

[0040] 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.

[0041] Among them, the ammonium exchange temperature conditions are 60~90℃, the exchange time is 15-90 min, the exchange times are 1~5 times, the drying temperature is 80~140℃, the drying time is 6~48 h, the roasting temperature is 450~700℃, and the roasting time is 1~9 h.

[0042] The present invention also provides an aluminum-rich multi-level pore molecular sieve catalyst, which is prepared by the above-mentioned preparation method, and the silicon-aluminum atomic ratio of the microporous molecular sieve sample used in the aluminum-rich multi-level pore molecular sieve catalyst is Si / Al=2-10. The aluminum-rich multi-level pore molecular sieve catalyst contains both micropores and intracrystalline mesopores; the topological structure of the aluminum-rich multi-level pore molecular sieve is MOR type, FAU type or MFI type. The main component of the aluminum-rich multi-level pore molecular sieve catalyst is aluminosilicate molecular sieve.

[0043] The average mesopore diameter of aluminum-rich hierarchical mordenite molecular sieve is 8-20 nm; the specific surface area of ​​aluminum-rich hierarchical mordenite molecular sieve catalyst is 357~432 m 2 / g; the pore volume of the aluminum-rich hierarchical 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.

[0044] The aluminum-rich multi-level porous molecular sieve catalyst is used in the process of dehydrating glycerol to prepare acrolein, which specifically comprises the following steps: in a reactor, glycerol is contacted with the aluminum-rich multi-level porous molecular sieve catalyst to undergo a dehydration reaction 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 .

[0045] The preparation method of the aluminum-rich multi-level porous molecular sieve catalyst provided by the present invention is described below in conjunction with specific examples. Unless otherwise specified, the raw materials and reagents in the examples of the present application are purchased through commercial channels.

[0046] Example 1 This embodiment provides a method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, comprising the following steps: 1) Fluorination treatment: 20 g of mordenite molecular sieve (MOR), 0.24 g of ammonium fluoride and 60 ml of water were placed in a beaker and stirred at room temperature for 8 h. The treated sample was placed in an oven and dried at 120 °C for 12 h, and then calcined in a muffle furnace at 550 °C for 3 h; wherein the Si / Al atomic ratio of mordenite molecular sieve is 7.9.

[0047] 2) Acid treatment: Prepare an aqueous solution containing 1 M nitric acid, take 300 ml into a flask, place it in a water bath and heat it to 80°C, then add 15 g of molecular sieve treated with nitric acid, stir for 60 min, and the solid-liquid ratio is 1 / 20; wash the reaction product with deionized water until it is neutral, dry it at 120°C for 12 h, and calcine it at 550°C in a muffle furnace for 3 h; 3) Alkali treatment: prepare 0.2 M sodium hydroxide, take 150 ml in a polypropylene flask, place it in a water bath and heat it to 60°C, add 5 g of molecular sieve treated with nitric acid, stir for 30 min, 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; 4) Ammonium exchange: The molecular sieve obtained above was added to 0.8 M ammonium chloride solution with a solid-liquid ratio of 1 / 20, and magnetically stirred at 80°C for 2 hours. The exchange was repeated 3 times, and then the reaction product was filtered and washed with deionized water, dried at 120°C for 8 h, and calcined at 550°C for 3 h. It was recorded as aluminum-rich hierarchical porous molecular sieve catalyst A.

[0048] Preparation of acrolein by dehydration of glycerol: About 1 g of the aluminum-rich multi-level porous molecular sieve catalyst A prepared in Example 1 was placed in the constant temperature section of the reaction tube, and the remaining space was filled with quartz sand. The catalyst was then heated to 450°C in a nitrogen atmosphere for pretreatment, and then cooled to the reaction temperature of 320°C for stabilization, and then glycerol aqueous solution was introduced, with nitrogen as the carrier gas. Before the raw materials entered the reaction tube, they were first vaporized in a 190°C vaporization chamber, and the air velocity was 1.25 h / min based on glycerol. -1 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 3 .

[0049] Comparative Example 1 Comparative Example 1 provides a method for preparing acrolein by dehydrating glycerol, which is mainly different from Example 1 in that the untreated mordenite molecular sieve (Si / Al=7.9) in Example 1 is used, and the specific process is as follows: 1) About 1 g of Mordenite molecular sieve (MOR) was loaded into the constant temperature section of the reaction tube, and the remaining part was filled with quartz sand. The catalyst was then heated to 450°C in a nitrogen atmosphere for pretreatment, and then the reaction temperature was lowered to 320°C for stabilization, and then propylene glycol aqueous solution was introduced, with nitrogen as the carrier gas. Before the raw material entered the reaction tube, it was first vaporized in a 190°C vaporization chamber, with an air velocity of 1.25 h-1 based on propylene glycol. 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 3 .

[0050] Figure 1 This is a 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.

[0051] Figure 2This is a TEM image of the aluminum-rich hierarchical 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 rich mesoporous structure.

[0052] It was proved that the intracrystalline mesopores of the multi-level pore molecular sieve in Example 1 were prepared by fluorination treatment, acid treatment and base treatment bridging strategy.

[0053] Comparative Example 2 Comparative Example 2 provides a method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, which is mainly different from Example 1 in that step 2) acid treatment, step 3) alkali treatment, and step 4) ammonium exchange are not performed, and only the mordenite molecular sieve is subjected to fluorination treatment. The other steps are substantially the same as those in Example 1 and will not be repeated here.

[0054] The fluorinated catalyst was then used in the process of dehydrating glycerol to produce acrolein, and the product was analyzed using an FID detector equipped with an FID detector, with n-pentanol as the internal standard. Figure 7 .

[0055] Comparative Example 3 Comparative Example 3 provides a method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, which is mainly different from Example 1 in that step 1) fluorination treatment, step 3) alkali treatment, and step 4) ammonium exchange are not performed, and only the mordenite molecular sieve is subjected to acid treatment. The other steps are substantially the same as those in Example 1 and will not be repeated here.

[0056] The acid-treated catalyst was then used in the process of dehydrating glycerol to produce acrolein, and 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 .

[0057] Comparative Example 4 Comparative Example 4 provides a method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, which is mainly different from Example 1 in that step 1) fluorination treatment and step 2) acid treatment are not performed, and only alkali treatment and ammonium exchange are performed on the mordenite molecular sieve. The other steps are generally the same as those in Example 1 and will not be repeated here.

[0058] The treated catalyst was then used in the process of dehydrating glycerol to produce acrolein, and 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 .

[0059] Comparative Example 5 Comparative Example 5 provides a method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, which is mainly different from Example 1 in that step 2) acid treatment is not performed, and the other steps are generally the same as Example 1 and will not be repeated here.

[0060] The treated catalyst was then used in the process of dehydrating glycerol to produce acrolein, and 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 .

[0061] Figure 4 This is a TEM image of the molecular sieve sample prepared in Comparative Example 5. It can be seen that in the absence of the acid treatment step, the surface of the prepared molecular sieve sample is smooth and flat, and there is no obvious mesoporous structure. This shows that only the fluorination-alkali treatment combination cannot construct intracrystalline mesopores in the aluminum-rich molecular sieve.

[0062] Comparative Example 6 Comparative Example 6 provides a method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, which is mainly different from Example 1 in that step 3) alkaline treatment and step 4) ammonium exchange are not performed, and the other steps are generally the same as Example 1 and will not be repeated here.

[0063] The treated catalyst was then used in the process of dehydrating glycerol to produce acrolein, and 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 .

[0064] Figure 5 This is a TEM image of the molecular sieve sample obtained in Comparative Example 6. It can be seen that in the absence of the alkali treatment step, the surface of the molecular sieve sample is smooth and flat, and there is no obvious mesoporous structure. This shows that only the fluorination treatment-acid treatment combination cannot construct intracrystalline mesopores in the aluminum-rich molecular sieve.

[0065] Comparative Example 7 Comparative Example 7 provides a method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, which is mainly different from Example 1 in that step 1) fluorination treatment is not performed, and the other steps are generally the same as Example 1 and will not be repeated here.

[0066] The treated catalyst was then used in the process of dehydrating glycerol to produce acrolein, and 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 .

[0067] Figure 6This is a TEM image of the molecular sieve sample obtained in Comparative Example 7. It can be seen that in the absence of the fluorination treatment step, the surface of the molecular sieve sample is smooth and flat, and there is no obvious mesoporous structure. This shows that only the combination of acid treatment and alkali treatment cannot construct intracrystalline mesopores in the aluminum-rich molecular sieve.

[0068] Embodiment 2-4 Example 2-4 provides a method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, which is different from Example 1 in that the amount of the fluorination medium in step S1 and the amount of the acid medium in step S2 are changed, as shown in the following table. The rest is roughly the same as Example 1 and will not be repeated here.

[0069] The aluminum-rich multi-level porous 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.

[0070] First, the sample was desorbed at 350 °C under vacuum for 10 h, and then nitrogen adsorption-desorption experiments were performed at liquid nitrogen temperature (-196 °C). The total specific surface area of ​​the sample was calculated using 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 is calculated by the nitrogen adsorption at the relative pressure P / P0=0.995; The micropore specific surface area and micropore volume of the sample are calculated by the t-plot method; The mesopore pore size distribution of the sample is 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 is determined by an X-ray fluorescence spectrometer (XRF). The test results are shown in Figure 3 , test data see the table below.

[0071] As can be seen from the table above, 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 diameter of the molecular sieve can be adjusted within the range of 8-20 nm. At the same time, the degree of mesopores can be adjusted, and the maximum mesopore volume can reach 0.41 cm 3 / g.

[0072] Figure 3 The BJH pore size distribution diagram of the catalysts prepared in Examples 1-4 and Comparative Example 1. Comparison of Example 1 with Comparative Example 1 shows that abundant intracrystalline mesoporous structures are successfully introduced into the aluminum-rich molecular sieve through fluorination treatment, acid treatment, alkali treatment and ammonium exchange.

[0073] The test results of Comparative Examples 1-7 are shown in Figure 7 , test data see the table below.

[0074] Figure 7 The BJH pore size distribution diagram of the catalyst prepared in Comparative Examples 1 to 7. It can be seen that fluorination treatment, acid treatment, alkali treatment, ammonium exchange or any binary or ternary combination alone cannot construct intracrystalline mesopores in the aluminum-rich molecular sieve.

[0075] It should be emphasized that Figure 7 Comparative Examples 5 and 7 are BJH pore size distribution diagrams of molecular sieve catalysts obtained without acid treatment and fluorination treatment, respectively. It can be seen that whether it is the lack of acid treatment or the lack of fluorination treatment steps, it is impossible to construct a rich mesoporous structure in the aluminum-rich molecular sieve. It further confirms the importance of the synergistic effect of fluorination treatment and acid treatment in constructing mesopores and adjusting the mesopore pore size in aluminum-rich molecular sieves.

[0076] Figure 8 and Fig. 9 The glycerol conversion rate and acrolein yield of the molecular sieve catalyst in Examples 1-3 and Comparative Example 1 are shown in Figure 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 fluorination treatment, acid treatment and alkali treatment bridging strategy treatment, the glycerol dehydration performance of the multi-level porous molecular sieve catalyst 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.

[0077] Fig.10 The acetaldehyde yield graph of the molecular sieve catalysts of 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-base treatment bridging strategy, the acetaldehyde conversion rate of the multi-level porous molecular sieve catalysts obtained in Examples 1-3 is significantly improved to 21.0%-24.0%. This is because the synergistic effect of the non-framework aluminum species formed during the fluorination treatment and the Brønsted acid center realizes the conversion of glycerol and the formation of acetaldehyde, proving that the catalyst treatment obtained by this strategy has a higher 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 added value utilization of glycerol, but also opens up a new production route for the preparation of acetaldehyde.

[0078] Experiments show that the fluoridation medium can be one or more of ammonium fluoride, sodium fluoride, and potassium fluoride.

[0079] 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.

[0080] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing an aluminum-rich multi-level porous molecular sieve catalyst, characterized in that: The steps include: 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 at 80-140 °C for 6-48 h, and then place the dried sample in a muffle furnace and calcine at 450-700 °C for 1-5 hours; S2, acid treatment: putting the sample treated by fluorination in step S1 into an acidic medium solution at a temperature of 60-90°C, and heating for 15-90 min; centrifuging or filtering the treated sample to neutrality, drying at 80-140°C for 6-48h, and then calcining at 450-700°C for 1-9h; 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 min; centrifuging or filtering the treated sample to neutrality, drying at 80-140°C for 6-48h, and then calcining at 450-700°C for 1-9h; 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.

2. The method for preparing the aluminum-rich multi-level porous molecular sieve catalyst according to claim 1, characterized in that: 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.

3. The method for preparing the aluminum-rich multi-level porous molecular sieve catalyst according to claim 1, characterized in that: In step S1, the fluoridation medium is one or more of ammonium fluoride, sodium fluoride, and potassium fluoride.

4. The method for preparing the aluminum-rich multi-level porous 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 volume of the acidic medium to the microporous molecular sieve is (10-50) ml: 1 g.

5. The method for preparing the aluminum-rich multi-level porous molecular sieve catalyst according to claim 1, characterized in that: 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.

6. The method for preparing the aluminum-rich multi-level porous molecular sieve catalyst according to claim 1, characterized in that: 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.

7. The method for preparing the aluminum-rich multi-level porous molecular sieve catalyst according to claim 1, characterized in that: In step S3, the alkaline medium is one or more of sodium hydroxide, potassium hydroxide, ammonia water, and sodium carbonate.

8. An aluminum-rich multi-level porous molecular sieve catalyst, prepared by the preparation method of the aluminum-rich multi-level porous molecular sieve catalyst according to any one of claims 1 to 7, characterized in that: 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.

9. The aluminum-rich multi-level porous molecular sieve catalyst according to claim 8, characterized in that: The average mesopore diameter of the aluminum-rich multi-level porous molecular sieve catalyst is 8-20 nm; the specific surface area of ​​the aluminum-rich multi-level porous molecular sieve catalyst is 357-432 m 2 / g; the pore volume of the aluminum-rich multi-level porous 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.

10. An application of an aluminum-rich multi-level porous molecular sieve catalyst, characterized in that: The aluminum-rich multi-level porous molecular sieve catalyst is prepared according to the preparation method described in any one of claims 1 to 7 or is the aluminum-rich multi-level porous molecular sieve catalyst described in any one of claims 8 to 9; the aluminum-rich multi-level porous molecular sieve catalyst is used in the process of dehydrating glycerol to prepare acrolein, which specifically comprises the following steps: in a reactor, glycerol is contacted with the aluminum-rich multi-level porous molecular sieve catalyst to undergo a dehydration reaction to generate acrolein and acetaldehyde; the reaction temperature of the glycerol is 260 to 400°C, the reaction pressure is 0.1 to 0.5 MPa, and the space velocity is 1.25 h -1 .

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