Magnesium modified hierarchical pore zsm-5 type molecular sieve catalyst, preparation method and application thereof

Abstract

This invention relates to the field of catalyst technology, specifically a magnesium-modified hierarchical ZSM-5 molecular sieve catalyst, its preparation method, and its application. This magnesium-modified hierarchical ZSM-5 molecular sieve catalyst is prepared using the organic template agent N,N-dimethyldipropyltriamine, exhibiting a 90° cross-linked hierarchical structure. This structure enhances the diffusion rate of reactants and products, thereby improving catalytic activity. Furthermore, it possesses a large specific surface area, a short diffusion path, and good stability. The interconnected hierarchical pores of the molecular sieve allow for full utilization of their diffusion characteristics, resulting in excellent catalytic performance in the catalytic cracking of heavy oils. Additionally, the organic template agent used in this invention is significantly cheaper than the template agents used in the synthesis of specially morphological hierarchical porous molecular sieves in current literature, effectively solving the problem of poor catalytic performance and the difficulty in widespread application due to the use of expensive template agents in existing catalysts.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst, its preparation method, and its application. Background Technology

[0002] Catalytic cracking of heavy oil to produce low-carbon olefins and light gasoline and diesel fuels is an effective way to fully utilize heavy oil resources. Due to the characteristics of low-quality heavy oil, catalytic cracking catalysts are required to have high activity, reasonable pore size distribution, and good mechanical strength.

[0003] However, due to the severe diffusion resistance in the micropores of conventional molecular sieves, reactant molecules have difficulty entering the pores, resulting in low utilization of active sites and reduced catalytic activity and selectivity. Furthermore, for reactions involving macromolecules, carbon deposits generated by side reactions can deactivate the catalyst, significantly shortening the lifespan of the molecular sieve.

[0004] Hierarchical ZSM-5 molecular sieves not only possess the tunable acidity, good hydrothermal stability, and shape selectivity of microporous materials, but also the pore size advantages of mesoporous zeolites, making them promising candidates for macromolecular pyrolysis reactions. The main synthetic methods for hierarchical ZSM-5 molecular sieves include template agent methods and post-treatment methods.

[0005] Post-treatment methods typically use strong acids or bases to dealuminize and desilicate molecular sieves to obtain hierarchical porous structures. For example, Chinese patent document CN118179577A discloses an alkali-treated, metal-synergistic modified ZSM-5 molecular sieve catalyst. However, the alkali treatment in this patent causes partial collapse of the framework structure, damaging the molecular sieve's framework and resulting in a low yield and reduced catalytic performance. Utilizing soft templates, such as micelles, reverse micelles, and vesicles formed by surfactant molecules, is another important method for synthesizing porous and nanostructured materials. For instance, Chinese patent document CN108658093A discloses a method for preparing and applying hierarchical porous ZSM-5 molecular sieves, using hexadecyltrimethylammonium bromide as a template agent and employing a dry hydrothermal synthesis method to obtain hierarchical porous ZSM-5 molecular sieves. However, the synthesis steps for this template agent are cumbersome and costly, making large-scale application difficult. Summary of the Invention

[0006] This invention provides a magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst, its preparation method, and its application, overcoming the shortcomings of the prior art. It can effectively solve the problems of poor catalytic performance of existing molecular sieve catalysts and the difficulty in promoting their application due to the use of expensive template agents.

[0007] One of the technical solutions of this invention is achieved through the following measures: a magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst, obtained by the following method: The first step involves dissolving the alkali source, organic template agent, and first acid source in deionized water and stirring until homogeneous to obtain solution a. The second step is to dissolve the aluminum source in deionized water and stir to obtain an aluminum source solution; The third step is to add an aluminum source solution to solution a, then add a silicon source and stir to carry out a hydrothermal crystallization reaction to obtain reaction product b. After solid-liquid separation, drying and calcination, reaction product b is obtained to obtain hierarchical porous ZSM-5 molecular sieve. The fourth step involves stirring the hierarchical ZSM-5 molecular sieve with an ammonium chloride solution and performing ammonium exchange to obtain reaction product c. After solid-liquid separation, drying, and calcination, reaction product c is obtained as an ammonium-exchanged hierarchical ZSM-5 molecular sieve. Fifth step: Dissolve the second acid source and matrix in deionized water and stir to obtain solution d; In the sixth step, ammonium-exchanged hierarchical ZSM-5 molecular sieve, magnesium salt and binder are added to solution d in sequence and stirred to obtain gel e. After spray granulation, drying and calcination, gel e is obtained as magnesium-modified hierarchical ZSM-5 molecular sieve catalyst.

[0008] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions: The aforementioned alkaline source is one of potassium hydroxide, sodium hydroxide, and lithium hydroxide.

[0009] The aforementioned organic template agent is N,N-dimethyldipropyltriamine.

[0010] Both the first and second acid sources mentioned above are strong acids, specifically concentrated sulfuric acid and concentrated nitric acid.

[0011] The aluminum source mentioned above is one of aluminum sulfate, aluminum isopropoxide, and metakaolin.

[0012] The silicon source mentioned above is tetraethyl orthosilicate.

[0013] The matrix is ​​zeolite, which is one of kaolinite and boehmite.

[0014] The magnesium salt mentioned above is one of magnesium sulfate, magnesium nitrate, and magnesium chloride.

[0015] The above-mentioned adhesive is silica sol.

[0016] The mass ratio of the above-mentioned alkali source, organic template agent, first acid source, aluminum source and silicon source is (1.0 to 1.5): (1.5 to 2.5): (0.5 to 1.5): (0.1 to 0.3): (10 to 15).

[0017] In the second step above, the mass concentration of the aluminum source solution is 1% to 3%.

[0018] In the fourth step above, 25 mL to 35 mL of ammonium chloride solution with a concentration of 1 mol / L to 2 mol / L is added to each gram of multi-level porous ZSM-5 molecular sieve.

[0019] In the fifth step above, the mass ratio of the second acid source, the matrix, and the deionized water is (0.2 to 0.5): (5.0 to 5.5): (8 to 12).

[0020] In the sixth step above, the binder accounts for 2% to 3% of the mass of the ammonium-exchanged hierarchical porous ZSM-5 molecular sieve, and the magnesium salt accounts for 1% to 5% of the mass of the ammonium-exchanged hierarchical porous ZSM-5 molecular sieve.

[0021] In the sixth step above, the mass ratio of the ammonium-exchanged hierarchical porous ZSM-5 molecular sieve to solution d is (4.0 to 4.5): (10 to 20).

[0022] In the first step above, the stirring temperature is 40℃ to 50℃ and the stirring time is 1.0h to 1.5h.

[0023] In the third step above, during hydrothermal crystallization, the reaction temperature is 140℃ to 160℃, and the reaction time is 3 to 5 days.

[0024] In the fourth step above, during ammonium exchange, the reaction temperature is 60℃ to 65℃ and the reaction time is 2.0h to 2.5h.

[0025] In steps two, five, and six above, the stirring time is 0.5 h to 1.0 h.

[0026] In steps three, four, and six above, the drying temperature is 90℃ to 120℃ and the drying time is 4h to 12h; the calcination temperature is 500℃ to 600℃ and the reaction time is 6.0h to 6.5h.

[0027] The second technical solution of the present invention is achieved through the following measures: a method for preparing a magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst, which is carried out according to the following method: The first step involves dissolving the alkali source, organic template agent, and first acid source in deionized water and stirring until homogeneous to obtain solution a. The second step is to dissolve the aluminum source in deionized water and stir to obtain an aluminum source solution; The third step is to add an aluminum source solution to solution a, then add a silicon source and stir to carry out a hydrothermal crystallization reaction to obtain reaction product b. After solid-liquid separation, drying and calcination, reaction product b is obtained to obtain hierarchical porous ZSM-5 molecular sieve. The fourth step involves stirring the hierarchical ZSM-5 molecular sieve with an ammonium chloride solution and performing ammonium exchange to obtain reaction product c. After solid-liquid separation, drying, and calcination, reaction product c is obtained as an ammonium-exchanged hierarchical ZSM-5 molecular sieve. Fifth step: Dissolve the second acid source and matrix in deionized water and stir to obtain solution d; In the sixth step, ammonium-exchanged hierarchical ZSM-5 molecular sieve, magnesium salt and binder are added to solution d in sequence and stirred to obtain gel e. After spray granulation, drying and calcination, gel e is obtained as magnesium-modified hierarchical ZSM-5 molecular sieve catalyst.

[0028] The third technical solution of the present invention is achieved through the following measures: the application of a magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst in heavy oil catalytic cracking reaction.

[0029] This invention utilizes the organic template N,N-dimethyldipropyltriamine to prepare a magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst. This catalyst exhibits a 90° cross-linked hierarchical structure, reducing diffusion resistance and increasing diffusion rates of reactants and products, thereby enhancing catalytic activity. Furthermore, it possesses a large specific surface area, a short diffusion path, and good stability. The interconnected hierarchical pores of the molecular sieve fully utilize their diffusion characteristics, resulting in excellent catalytic performance in the catalytic cracking of heavy oils. In addition, the organic template used in this invention is significantly cheaper than the templates used in the synthesis of specially morphological hierarchical porous molecular sieves in current literature, effectively solving the problem of poor catalytic performance and the difficulty in widespread application due to the use of expensive templates in existing catalysts. Attached Figure Description

[0030] Figure 1 This is the X-ray diffraction (XRD) pattern of the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of this invention.

[0031] Figure 2 This is a scanning electron microscope (SEM) image of the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of the present invention.

[0032] Figure 3 This is a graph showing the N2 adsorption-desorption curves of the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of this invention.

[0033] Figure 4 This is a comparison chart showing the conversion rates of vacuum wax oil as a catalyst feedstock for the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of this invention.

[0034] Figure 5 This is a comparison chart of the yield of the target product from vacuum wax oil, the catalyst feedstock for the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of this invention.

[0035] Figure 6 This is a comparison chart of the amount of coke produced after the catalytic reaction of the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of this invention. Detailed Implementation

[0036] This invention is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemicals mentioned in this invention are well-known and commonly used chemical reagents and chemicals in the prior art; unless otherwise specified, all percentages in this invention are mass percentages; unless otherwise specified, all solutions in this invention are aqueous solutions with water as the solvent, for example, hydrochloric acid solution is an aqueous solution of hydrochloric acid; room temperature in this invention generally refers to a temperature between 15°C and 25°C, generally defined as 25°C.

[0037] The present invention will be further described below with reference to embodiments: Example 1: The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst was obtained by the following method: The first step involves dissolving the alkali source, organic template agent, and first acid source in deionized water and stirring until homogeneous to obtain solution a. The second step is to dissolve the aluminum source in deionized water and stir to obtain an aluminum source solution; The third step is to add an aluminum source solution to solution a, then add a silicon source and stir to carry out a hydrothermal crystallization reaction to obtain reaction product b. After solid-liquid separation, drying and calcination, reaction product b is obtained to obtain hierarchical porous ZSM-5 molecular sieve. The fourth step involves stirring the hierarchical ZSM-5 molecular sieve with an ammonium chloride solution and performing ammonium exchange to obtain reaction product c. After solid-liquid separation, drying, and calcination, reaction product c is obtained as an ammonium-exchanged hierarchical ZSM-5 molecular sieve. Fifth step: Dissolve the second acid source and matrix in deionized water and stir to obtain solution d; In the sixth step, ammonium-exchanged hierarchical ZSM-5 molecular sieve, magnesium salt and binder are added to solution d in sequence and stirred to obtain gel e. After spray granulation, drying and calcination, gel e is obtained as magnesium-modified hierarchical ZSM-5 molecular sieve catalyst.

[0038] Example 2: As an optimization of the above example, the alkali source is one of potassium hydroxide, sodium hydroxide and lithium hydroxide.

[0039] Example 3: As an optimization of the above examples, the organic template agent is N,N-dimethyldipropyltriamine.

[0040] Example 4: As an optimization of the above example, both the first acid source and the second acid source are strong acids, and the strong acid is one of concentrated sulfuric acid and concentrated nitric acid.

[0041] Example 5: As an optimization of the above examples, the aluminum source is one of aluminum sulfate, aluminum isopropoxide and metakaolin.

[0042] Example 6: As an optimization of the above examples, the silicon source is tetraethyl orthosilicate.

[0043] Example 7: As an optimization of the above examples, the matrix is ​​zeolite, which is one of kaolinite and pseudoboehmite.

[0044] Example 8: As an optimization of the above examples, the magnesium salt is one of magnesium sulfate, magnesium nitrate and magnesium chloride.

[0045] Example 9: As an optimization of the above examples, the binder is silica sol.

[0046] Example 10: As an optimization of the above example, the mass ratio of the alkali source, organic template agent, first acid source, aluminum source and silicon source is (1.0 to 1.5): (1.5 to 2.5): (0.5 to 1.5): (0.1 to 0.3): (10 to 15).

[0047] Example 11: As an optimization of the above example, in the second step, the mass concentration of the aluminum source solution is 1% to 3%.

[0048] Example 12: As an optimization of the above example, in the fourth step, 25 mL to 35 mL of ammonium chloride solution with a concentration of 1 mol / L to 2 mol / L is added to each gram of multi-level porous ZSM-5 molecular sieve.

[0049] Example 13: As an optimization of the above example, in the fifth step, the mass ratio of the second acid source, the matrix and the deionized water is (0.2 to 0.5): (5.0 to 5.5): (8 to 12).

[0050] Example 14: As an optimization of the above example, in the sixth step, the binder accounts for 2% to 3% of the mass of the ammonium-exchanged hierarchical porous ZSM-5 molecular sieve, and the magnesium salt accounts for 1% to 5% of the mass of the ammonium-exchanged hierarchical porous ZSM-5 molecular sieve.

[0051] Example 15: As an optimization of the above example, in the sixth step, the mass ratio of ammonium-exchanged hierarchical ZSM-5 molecular sieve to solution d is (4.0 to 4.5): (10 to 20).

[0052] Example 16: As an optimization of the above example, in the first step, the stirring temperature is 40°C to 50°C and the stirring time is 1.0h to 1.5h.

[0053] Example 17: As an optimization of the above example, in the third step, during hydrothermal crystallization, the reaction temperature is 140°C to 160°C and the reaction time is 3 to 5 days.

[0054] Example 18: As an optimization of the above example, in the fourth step, during ammonium exchange, the reaction temperature is 60°C to 65°C and the reaction time is 2.0h to 2.5h.

[0055] Example 19: As an optimization of the above example, in the second, fifth and sixth steps, the stirring time is 0.5h to 1.0h.

[0056] Example 20: As an optimization of the above example, in steps three, four and six, the drying temperature is 90°C to 120°C and the drying time is 4h to 12h; during calcination, the reaction temperature is 500°C to 600°C and the reaction time is 6.0h to 6.5h.

[0057] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes N,N-dimethyldipropyltriamine, an organic template agent, as a raw material to prepare a magnesium-modified hierarchical ZSM-5 molecular sieve catalyst with a magnesium (wt%) loading between 0.18% and 0.72%. It combines the advantages of strong acidity and high stability of microporous molecular sieves with the strong mass transfer capacity of mesoporous molecular sieves, thereby improving the diffusion rate of reactants and products and enhancing catalytic activity, exhibiting excellent catalytic performance.

[0058] This invention is the first to apply a magnesium-modified hierarchical ZSM-5 molecular sieve catalyst to heavy oil cracking. It utilizes the mesoporous structure to improve conversion and increases the yield of small-molecule olefins and aromatics (propylene, gasoline, and diesel). Furthermore, current methods for preparing hierarchical molecular sieves use expensive template agents, hindering industrial application. This invention utilizes the low-cost organic template agent N,N-dimethyldipropyltriamine to synthesize the magnesium-modified hierarchical ZSM-5 molecular sieve catalyst. This reduces synthesis costs while significantly improving diffusion performance and catalytic performance in heavy oil cracking, effectively addressing the problems of poor catalytic performance and the reliance on expensive template agents in existing molecular sieve catalysts, which hinder widespread adoption.

[0059] Example 21: The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst was obtained by the following method: First, 1.3g of alkali source (sodium hydroxide), 2g of organic template agent (N,N-dimethyldipropyltriamine) and 1mL of primary acid source (concentrated sulfuric acid) were dissolved in 15mL of deionized water and stirred at 45℃ for 1h to obtain solution a; The second step involves dissolving 0.19 g of aluminum source (aluminum sulfate) in 10 mL of deionized water and stirring at room temperature for 0.5 h to obtain an aluminum source solution. The third step involves adding an aluminum source solution to solution a, followed by 11.32g of a silicon source (tetraethyl orthosilicate). The mixture is first rapidly stirred at 60°C for 0.5h, and then subjected to a hydrothermal crystallization reaction at 150°C for 3 days to obtain reaction product b. The reaction product is then subjected to solid-liquid separation, dried at 100°C for 6h, and then calcined in a muffle furnace at 550°C for 6h to obtain a hierarchical porous ZSM-5 molecular sieve. In the fourth step, 1g of hierarchical ZSM-5 molecular sieve was mixed with 30mL of 1.5mol / L ammonium chloride solution and stirred at 60℃ for 2.0h to obtain reaction product c. Product c was subjected to solid-liquid separation, dried at 100℃ for 6h, and then calcined in a muffle furnace at 550℃ for 6.0h to obtain ammonium-exchanged hierarchical ZSM-5 molecular sieve. Fifth step: Dissolve 0.3g of the second acid source (concentrated nitric acid) and 5.3g of the matrix (pseudoboehmite) in 10g of deionized water and stir for 0.5h to obtain solution d; In step six, 4.3 g of ammonium-exchanged hierarchical ZSM-5 molecular sieve, 0.05 g of magnesium salt (magnesium nitrate), and 0.12 g of binder (silica sol, mass concentration of 30%) were added sequentially to solution d and stirred at room temperature for 1 h to obtain gel e. Gel e was spray-granulated, dried overnight at 100 °C, and then calcined in a muffle furnace at 550 °C for 6.0 h to obtain magnesium-modified hierarchical ZSM-5 molecular sieve catalyst, wherein the loading of metallic magnesium (wt%) was 0.18%.

[0060] Example 22: The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst differs from that in Example 21 in that "0.05g magnesium salt (magnesium nitrate)" is replaced with "0.1g magnesium salt (magnesium nitrate)," which means the loading of metallic magnesium (wt%) is 0.36%. All other steps are the same.

[0061] Example 23: The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst differs from that in Example 21 in that "0.05g magnesium salt (magnesium nitrate)" is replaced with "0.2g magnesium salt (magnesium nitrate)," which means the loading of metallic magnesium (wt%) is 0.72%. All other steps are the same.

[0062] Comparative example: This conventional microporous ZSM-5 molecular sieve catalyst was obtained by the following method: S1, 0.3g of the second acid source (concentrated nitric acid) and 5.3g of the matrix (pseudoboehmite) were dissolved in 10g of deionized water and stirred for 0.5h to obtain a mixed solution; S2, 4.3g ZSM-5 molecular sieve, 0.1g magnesium salt (magnesium nitrate) and 0.12g binder (silica sol, mass concentration of 30%) were added to the mixture and stirred at room temperature for 1h to obtain a gel. The gel was spray granulated, dried overnight at 100℃, and then calcined in a muffle furnace at 550℃ for 6.0h to obtain a microporous ZSM-5 molecular sieve catalyst.

[0063] Experimental Example 1: Structural characterization analysis of the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of the present invention.

[0064] Experimental Methods: The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared in Example 21 of this invention was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption-desorption curve analysis. X-ray diffraction (XRD) analysis was performed using an X'Pert PRO MPD diffractometer (Panalytical, Netherlands) with Cu target Kα radiation as the light source, tube voltage 40 kV, tube current 40 mA, and a scan step size of 0.0167. Diffraction patterns were recorded within the 2θ range of 5° to 75°. Scanning electron microscopy (SEM) analysis was performed using a Hitachi S-4800 scanning electron microscope (Japan), with magnifications ranging from 30x to 800,000x and accelerating voltages from 0.5 kV to 30 kV. The N2 adsorption-desorption curves were obtained using an ASAP 2460 physical adsorption instrument manufactured by Micromeritics. Before testing, the samples were degassed at 300℃ for 6 hours, and then the adsorption-desorption isotherms were measured at a low temperature of -196.15℃ using high-purity nitrogen as the adsorption medium.

[0065] Experimental results: The X-ray diffraction (XRD) pattern of the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of this invention is shown below. Figure 1 As shown, from Figure 1 It can be seen that there is a set of doublets between 2θ = 3° and 8°, and another set of doublets between 2θ = 22° and 26°, which are consistent with the structural characteristics of MFI-type zeolite molecular sieves. Furthermore, no impurity peaks are observed, indicating that the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst prepared by the method of this invention is an MFI-type zeolite molecular sieve (ZSM-5 molecular sieve). The scanning electron microscope (SEM) image of the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of this invention is shown below. Figure 2 As shown, from Figure 2 It can be concluded that the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of the present invention is composed of pine needle-like structures with a thickness of 50 nm to 100 nm stacked together; the N2 adsorption-desorption curve of the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of the present invention is shown in the figure below. Figure 3 As shown, from Figure 3It can be concluded that an adsorption hysteresis loop exists in the N2 adsorption-desorption curve, indicating that the structure reflected in the curve is a plate-like particulate material with a certain degree of mesoporous structure. Furthermore, based on the curve integral, the specific surface area of ​​the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of this invention is 512 m². 2 / g.

[0066] Experimental Example 2: Investigating the application of the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of the present invention in the catalytic cracking reaction of heavy oil.

[0067] Experimental Methods: The catalytic performance of the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalysts prepared in Examples 21 to 23 of this invention was evaluated in a riser reactor for heavy oil catalytic cracking. The reactant was vacuum-pressed wax oil, the reaction temperature was 600℃, and the mass hourly space velocity (WHSV) was 8 h⁻¹. -1 The properties of the reactant vacuum wax oil are shown in Table 1. The gaseous products of the heavy oil catalytic cracking reaction were analyzed using a SCION GC 456 gas chromatograph, and the liquid products were analyzed using an Agilent 4890D gas chromatograph to obtain the content of the target product. The yield of the target product was calculated based on the content. The amount of coke produced in the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst after the reaction was measured using an infrared sulfur and carbon analyzer. A comparative example was used as a control.

[0068] Experimental results: The conversion rate of vacuum wax oil, the catalytic feedstock, to the magnesium-modified hierarchical ZSM-5 molecular sieve catalyst of this invention is as follows: Figure 4 As shown, from Figure 4 It can be seen that, compared with the comparative examples, the conversion rate of vacuum wax oil, the catalyst feedstock of the magnesium-modified hierarchical ZSM-5 molecular sieve catalyst prepared in Examples 21 to 23 of the present invention, is significantly improved. At the same time, the conversion rate of vacuum wax oil, the catalyst feedstock of the magnesium-modified hierarchical ZSM-5 molecular sieve catalyst prepared in Example 23 of the present invention, is the highest. In addition, the conversion rates of vacuum wax oil, the catalyst feedstock of the magnesium-modified hierarchical ZSM-5 molecular sieve catalyst prepared in Examples 21 to 23 of the present invention, from high to low, are Example 23 > Example 22 > Example 21. The yield of the target product from vacuum wax oil, a catalyst feedstock for the magnesium-modified hierarchical ZSM-5 molecular sieve catalyst of this invention, is shown in Table 2 and... Figure 5 As shown in Table 2 and Figure 5 It can be seen that the yields of propylene, gasoline, and diesel in the target products of the magnesium-modified hierarchical ZSM-5 molecular sieve catalyst feedstock vacuum wax oil prepared in Examples 20 to 22 of the present invention are all higher than those in the comparative example. At the same time, the yield of propylene in the target products of the magnesium-modified hierarchical ZSM-5 molecular sieve catalyst feedstock vacuum wax oil prepared in Examples 20 to 22 of the present invention, from high to low, is Example 22 > Example 23 > Example 21. The amount of coke produced after catalytic reaction by the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of this invention is as follows: Figure 6 As shown, from Figure 6 It can be seen that the amount of coke produced after the reaction of the magnesium-modified hierarchical ZSM-5 molecular sieve catalysts prepared in Examples 20 to 22 of the present invention is higher than that of the comparative example, indicating that the magnesium-modified hierarchical ZSM-5 molecular sieve catalysts of the present invention have higher catalytic activity and can better promote the reaction. At the same time, the amount of coke produced after the catalytic reaction of the magnesium-modified hierarchical ZSM-5 molecular sieve catalysts prepared in Examples 20 to 22 of the present invention, from high to low, is Example 23 > Example 22 > Example 21.

[0069] Therefore, the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst of the present invention exhibits the best catalytic performance when the loading of metallic magnesium (wt%) is between 0.36% and 0.72%.

[0070] In summary, the magnesium-modified hierarchical ZSM-5 molecular sieve catalyst prepared by the organic template agent N,N-dimethyldipropyltriamine exhibits a 90° cross-coexisting hierarchical structure, which reduces the diffusion resistance of reactants and products, increases their diffusion rates, and thus enhances catalytic activity. Furthermore, it possesses a large specific surface area, a short diffusion path, and good stability. The interconnected hierarchical pores of the molecular sieve allow for full utilization of their diffusion characteristics, resulting in excellent catalytic performance in the catalytic cracking of heavy oils. Moreover, the organic template agent used in this invention is significantly cheaper than the template agents used in the synthesis of specially morphological hierarchical porous molecular sieves in current literature, effectively solving the problem of poor catalytic performance and the difficulty in widespread application of existing molecular sieve catalysts due to the use of expensive template agents.

[0071] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst, obtained by the following method: The first step involves dissolving the alkali source, organic template agent, and first acid source in deionized water and stirring until homogeneous to obtain solution a. The second step is to dissolve the aluminum source in deionized water and stir to obtain an aluminum source solution; The third step is to add an aluminum source solution to solution a, then add a silicon source and stir to carry out a hydrothermal crystallization reaction to obtain reaction product b. After solid-liquid separation, drying and calcination, reaction product b is obtained to obtain hierarchical porous ZSM-5 molecular sieve. The fourth step involves stirring the hierarchical ZSM-5 molecular sieve with an ammonium chloride solution and performing ammonium exchange to obtain reaction product c. After solid-liquid separation, drying, and calcination, reaction product c is obtained as an ammonium-exchanged hierarchical ZSM-5 molecular sieve. Fifth step: Dissolve the second acid source and matrix in deionized water and stir to obtain solution d; In the sixth step, ammonium-exchanged hierarchical ZSM-5 molecular sieve, magnesium salt and binder are added to solution d in sequence and stirred to obtain gel e. After spray granulation, drying and calcination, gel e is obtained as magnesium-modified hierarchical ZSM-5 molecular sieve catalyst.

2. The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst according to claim 1, characterized in that... The alkaline source is one of potassium hydroxide, sodium hydroxide, and lithium hydroxide; or / and the organic template agent is N,N-dimethyldipropyltriamine; or / and both the first and second acid sources are strong acids, and the strong acid is one of concentrated sulfuric acid and concentrated nitric acid.

3. The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst according to claim 1 or 2, characterized in that... The aluminum source is one of aluminum sulfate, aluminum isopropoxide, and metakaolin; or / and the silicon source is tetraethyl orthosilicate; or / and the matrix is ​​zeolite, which is one of kaolin and boehmite.

4. The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst according to claim 1, 2, or 3, characterized in that... The magnesium salt is one of magnesium sulfate, magnesium nitrate and magnesium chloride; or / and the binder is silica sol.

5. The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst according to any one of claims 1 to 4, characterized in that... The mass ratio of the alkali source, organic template agent, first acid source, aluminum source, and silicon source is 1.0 to 1.5:1.5 to 2.5:0.5 to 1.5:0.1 to 0.3:10 to 15; or / and, in the second step, the mass concentration of the aluminum source solution is 1% to 3%; or / and, in the fourth step, 25 mL to 35 mL of ammonium chloride solution with a concentration of 1 mol / L to 2 mol / L is added to each gram of multi-level porous ZSM-5 molecular sieve.

6. The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst according to any one of claims 1 to 5, characterized in that... In step 5, the mass ratio of the second acid source, matrix, and deionized water is 0.2 to 0.5: 5.0 to 5.5: 8 to 12; or / and in step 6, the binder accounts for 2% to 3% of the mass of the ammonium-exchanged hierarchical porous ZSM-5 molecular sieve, and the magnesium salt accounts for 1% to 5% of the mass of the ammonium-exchanged hierarchical porous ZSM-5 molecular sieve; or / and in step 6, the mass ratio of the ammonium-exchanged hierarchical porous ZSM-5 molecular sieve to solution d is 4.0 to 4.5: 10 to 20.

7. The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst according to any one of claims 1 to 6, characterized in that... In the first step, the stirring temperature is 40℃ to 50℃ and the stirring time is 1.0h to 1.5h; or / and in the third step, during hydrothermal crystallization, the reaction temperature is 140℃ to 160℃ and the reaction time is 3 days to 5 days; or / and in the fourth step, during ammonium exchange, the reaction temperature is 60℃ to 65℃ and the reaction time is 2.0h to 2.5h.

8. The magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst according to any one of claims 1 to 7, characterized in that... In steps two, five, and six, the stirring time is 0.5 h to 1.0 h; or / and in steps three, four, and six, the drying temperature is 90 °C to 120 °C and the drying time is 4 h to 12 h; during calcination, the reaction temperature is 500 °C to 600 °C and the reaction time is 6.0 h to 6.5 h.

9. The method for preparing the magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst according to any one of claims 2 to 8, characterized in that... Perform the following steps: The first step involves dissolving the alkali source, organic template agent, and first acid source in deionized water and stirring until homogeneous to obtain solution a. The second step is to dissolve the aluminum source in deionized water and stir to obtain an aluminum source solution; The third step is to add an aluminum source solution to solution a, then add a silicon source and stir to carry out a hydrothermal crystallization reaction to obtain reaction product b. After solid-liquid separation, drying and calcination, reaction product b is obtained to obtain hierarchical porous ZSM-5 molecular sieve. The fourth step involves stirring the hierarchical ZSM-5 molecular sieve with an ammonium chloride solution and performing ammonium exchange to obtain reaction product c. After solid-liquid separation, drying, and calcination, reaction product c is obtained as an ammonium-exchanged hierarchical ZSM-5 molecular sieve. Fifth step: Dissolve the second acid source and matrix in deionized water and stir to obtain solution d; In the sixth step, ammonium-exchanged hierarchical ZSM-5 molecular sieve, magnesium salt and binder are added to solution d in sequence and stirred to obtain gel e. After spray granulation, drying and calcination, gel e is obtained as magnesium-modified hierarchical ZSM-5 molecular sieve catalyst.

10. The application of a magnesium-modified hierarchical porous ZSM-5 molecular sieve catalyst according to any one of claims 1 to 8 in the catalytic cracking reaction of heavy oil.

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