A silicon-aluminum molecular sieve catalyst, its preparation method and application
By selectively adding aluminum to all-silica molecular sieves and using mechanical ball milling, the acidic site properties of the catalyst were controlled, solving the problems of low catalyst activity and selectivity, and improving the yield and selectivity of low-carbon olefins.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- FUZHOU UNIV
- Filing Date
- 2023-08-10
- Publication Date
- 2026-06-26
Smart Images
Figure SMS_3 
Figure SMS_4
Abstract
Description
Technical Field
[0001] This invention relates to the field of hydrocarbon catalyst cracking, specifically to a silica-alumina molecular sieve catalyst, its preparation method, and its application. Background Technology
[0002] Low-carbon olefins, including ethylene, propylene, and butene, are widely used in the production of important chemicals such as polyethylene, polypropylene, acrylonitrile, and phenol, and their global demand continues to increase. The development of the low-carbon olefin industry has a sustained impact on the national economy and living standards, with ethylene production serving as a key indicator of a country's petrochemical development level. In my country, low-carbon olefins mainly originate from steam cracking and catalytic cracking units. The former is a thermal cracking reaction, which suffers from high reaction temperatures (>800℃), high energy consumption, large CO2 emissions, low olefin yield, and difficulty in regulating product distribution. Catalytic cracking units are used to produce gasoline and diesel, generating large amounts of light alkanes as byproducts of low-carbon olefins. Catalytic thermal cracking technology, combining the advantages of steam cracking and catalytic cracking, shows broad application prospects and has become a new direction for the development of low-carbon olefin production technology. Currently, the bottleneck restricting the large-scale application of catalytic cracking technology for producing low-carbon olefins is the low activity and selectivity of the catalyst and its poor stability, leading to low low-carbon olefin yields and high process energy consumption. Process optimization alone cannot fundamentally solve the above problems. To achieve the production of more low-carbon olefins through catalytic cracking of light hydrocarbons, it is crucial to create highly active and selective catalytic thermal cracking catalysts for light hydrocarbons. This is of great significance for improving the utilization efficiency of my country's petroleum resources and promoting energy conservation and emission reduction in process industries.
[0003] CN115385357A discloses a method for preparing HZSM-5 molecular sieves. In an alkaline system containing a silicon source, an aluminum source, an organic template agent, and water, by adding special seed crystals and organic auxiliaries, the b-axis and c-axis lengths of the HZSM-5 molecular sieve can be controlled during crystallization. The resulting molecular sieve catalyst, modified with P and / or metals, exhibits high ethylene and propylene yields in the catalytic cracking reactions of light hydrocarbon feedstocks, primarily isoalkanes and cycloalkanes, ranging from C4 to C8. CN110372004A discloses a method for controlling the microscopic aluminum distribution of ZSM-5 molecular sieves and its application. This method uses Co ions to protect the ortho-aluminum sites in the ZSM-5 molecular sieve before post-treatment, thereby controlling the relative content of ortho-aluminum mono-aluminum in the ZSM-5 molecular sieve and increasing its relative content. Applying the Co-ion-protected ZSM-5 molecular sieve with its microscopic aluminum distribution modulated to C4 hydrocarbon cracking reactions yielded high C4 hydrocarbon activation capacity and high ethylene and propylene yields.
[0004] CN108689415A discloses a dealuminized H-ZSM-34 molecular sieve and its preparation method. This method involves conventional hydrothermal synthesis of NH4-ZSM-34 molecular sieve, followed by dealuminization treatment by adding the NH4-ZSM-34 to a Na2H2EDTA solution. The prepared dealuminized H-ZSM-34 molecular sieve exhibits a 73.7% conversion rate of methane to propylene in the reaction of methane to chloromethyl, a combined selectivity of 70.3% for ethylene and propylene, and a combined yield of 51.8% for ethylene and propylene.
[0005] Xia XA et al. designed mesoporous ZSM-5 zeolites using a dual-template synthesis strategy and investigated their performance in the catalytic cracking of n-octane to light olefins. The mesoporous ratio was systematically adjusted by the concentration of TBPOH. After introducing an appropriate amount of TBPOH template, the Al content of the tetrahedral coordination framework increased, attributed to the charge compensation effect of the TBP cation. The prepared catalyst exhibited a satisfactory C+2=~C4= light olefin selectivity of 70.4%, which is 5.0% higher than that of the conventional ZSM-5.
[0006] Li C et al. synthesized B-Al-ZSM-5 zeolite with a variable Si / Al ratio by utilizing the structural preference of boron (B) to occupy certain positions at channel intersections, thus guiding Al positions into the 10R channels of ZSM-5. In a post-synthetic treatment, B was removed to produce an Al-rich ZSM-5 sample occupying the 10R channel positions. Several ZSM-5 samples were tested in the methanol-to-propylene reaction; the sample synthesized via the B-assisted method showed a longer catalytic lifetime, higher propylene yield, and lower alkane and aromatic yields.
[0007] Wu et al. prepared graded ZSM-5 zeolite using steam-assisted crystallization (SAC), and then modified the acidity of the zeolite with organosilane compounds. The resulting zeolite was finally used for butene catalytic cracking to produce propylene, achieving a high propylene yield of 40 wt%. The ZSM-5 zeolite prepared by the SAC method showed more acidic sites in the straight and sinusoidal channels, rather than at the channel intersections, which is beneficial for enhancing the reaction pathway for propylene production, while suppressing the main side reactions in butene catalytic cracking.
[0008] In existing technologies, the control of aluminum content in molecular sieves is usually achieved through post-treatment modification, including acid treatment and steam treatment. Although this can change the acid properties of molecular sieves, the process is relatively complicated. Catalysts obtained by changing the relative content of aluminum in molecular sieves through post-treatment usually have disadvantages such as poor connectivity of pores at all levels and disruption of the original microporous pore structure. Summary of the Invention
[0009] To address the shortcomings of the prior art, the present invention aims to provide a silica-alumina molecular sieve catalyst, its preparation method, and its application. The present invention synthesizes an all-silica molecular sieve by selectively adding aluminum to it, thereby giving the synthesized silica-alumina molecular sieve suitable acidity and a good pore structure. The ball milling process can create more defects on the outer surface of the all-silica molecular sieve, thereby increasing the space for aluminum to settle.
[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:
[0011] A method for preparing a silica-alumina molecular sieve catalyst, characterized by comprising the following steps:
[0012] (1) The silicon source, alkali source and template agent are mixed evenly in a water bath in a solvent to obtain a sol precursor. The sol precursor is subjected to hydrothermal crystallization reaction, washed, dried and calcined to obtain a molecular sieve catalyst precursor.
[0013] (2) The molecular sieve catalyst precursor obtained in step (1) is subjected to ammonium ion exchange treatment, followed by ion exchange, drying, and calcination to obtain the molecular sieve catalyst.
[0014] (3) Using the molecular sieve catalyst obtained in step (2) as a support, add an aluminum-containing salt compound, introduce aluminum into the molecular sieve catalyst support by mechanical ball milling, and then obtain the silicon-aluminum molecular sieve catalyst by calcination.
[0015] Preferably, in step (3), the mass ratio of the amount of aluminum-containing salt compound added to the molecular sieve catalyst is 1 to 15:5.
[0016] Preferably, the silicon source in step (1) includes one or more of silica sol, fumed silica, sodium silicate, and tetraethyl orthosilicate, and the alkali source is one or more of sodium hydroxide, sodium carbonate, and potassium hydroxide.
[0017] Preferably, the template agent in step (1) is one or more of tetrapropylammonium bromide and tetrapropylammonium hydroxide.
[0018] Preferably, the ammonium ion exchange raw material in step (2) is one of ammonium chloride and ammonium bicarbonate.
[0019] Preferably, the aluminum element in step (3) is one or more of organoaluminum compounds, inorganic aluminum compounds, or hydrates.
[0020] Preferably, the hydrothermal crystallization reaction temperature in step (1) is 180°C and the reaction time is 24h.
[0021] Preferably, the ball milling speed in step (3) is 360-1000 r / min and the time is 1-3 h.
[0022] Another object of the present invention is to provide a silica-alumina molecular sieve catalyst prepared by any of the above preparation methods.
[0023] The third objective of this invention is to provide an application of the aforementioned silica-alumina molecular sieve catalyst in the catalytic cracking of hydrocarbons to produce low-carbon olefins.
[0024] Compared with the prior art, the beneficial effects of the present invention are:
[0025] 1. The purpose of this invention is to provide a method for synthesizing silica-alumina molecular sieves by "mechanical ball milling". By synthesizing all-silica molecular sieves, aluminum is selectively added to the all-silica molecular sieves, so that the synthesized silica-alumina molecular sieves have suitable acid properties and good pore structure. The ball milling process can form more defects on the outer surface of the all-silica molecular sieves, thereby increasing the space for aluminum to settle.
[0026] 2. Hydrocarbon catalytic cracking follows the carbocation reaction mechanism under acidic site catalysis. That is, hydrocarbon molecules form carbocation intermediates at acidic sites, and the carbocation intermediates undergo β-cleavage to generate low-carbon olefins. However, acidic sites are not only active sites for cracking reactions, but also active sites for reactions such as hydrogen transfer, isomerization, and condensation coke formation. By introducing aluminum, the acidic site properties on the catalyst surface can be selectively controlled, reducing the acidic sites in the catalyst channels and thus suppressing side reactions as much as possible to improve the selectivity and yield of low-carbon olefins. The occurrence form of aluminum on the molecular sieve surface (dispersion, site state, and interaction with the molecular sieve) can be controlled to achieve efficient catalysis of acidic centers in the catalytic cracking of hydrocarbons to produce low-carbon olefins.
[0027] 3. ZSM-5 molecular sieve catalysts have a large number of The acidic sites exhibit high activity in the catalytic cracking of hydrocarbons to produce low-carbon olefins; however, the surface of ZSM-5 molecular sieves... The acidic sites originate from the coordinated unsaturated aluminum atoms in the framework of ZSM-5 molecular sieves. These framework aluminum atoms are mostly located within the micropores of the sieve, and the resulting acidic sites are also within these micropores. The diameter of the ZSM-5 micropores (0.51 × 0.56 nm) is similar to the diameter of low-carbon olefin molecules. These narrow micropores restrict the diffusion of low-carbon olefin products from the inside to the outside, leading to secondary reactions such as polymerization, cyclization, dehydrogenation, and aromatization of the generated olefins, thereby reducing the selectivity and yield of low-carbon olefins. Therefore, designing and preparing ZSM-5 catalysts with abundant acidic sites on the outer surface and micropore openings is crucial for improving the yield of low-carbon olefins. This invention employs a mechanochemical method to dope all-silica molecular sieves with aluminum, distributing the acidity on the outer surface of the sieve, reducing side reactions, and thus improving the selectivity and yield of low-carbon olefins. This achieves the preparation of a molecular sieve catalyst with high catalytic cracking activity for hydrocarbons and high olefin selectivity. Detailed Implementation
[0028] The following detailed description, in conjunction with embodiments of the present invention, will focus on preferred embodiments.
[0029] This invention relates to a method for preparing a silica-alumina molecular sieve catalyst, wherein the matrix is a microporous molecular sieve, and the method for producing microporous molecular sieves is well known to researchers in the art; the molecular sieve is synthesized using a method well known to researchers in the art. The final aluminum content, calculated by weight, is 1-150% of the molecular sieve.
[0030] Example 1
[0031] A method for preparing a silica-alumina molecular sieve catalyst includes the following steps:
[0032] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol, and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a homogeneous sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ using a 1:10 mass ratio of 1MNH4Cl solution for 2h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst.
[0033] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 1g aluminum nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Al@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-1.
[0034] Example 2
[0035] A method for preparing a silica-alumina molecular sieve catalyst includes the following steps:
[0036] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol, and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a homogeneous sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ using a 1:10 mass ratio of 1MNH4Cl solution for 2h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst.
[0037] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 5g aluminum nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min. The jar was opened and manually stirred every 30 minutes to prevent the sample from settling. The Al@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-2.
[0038] Example 3
[0039] A method for preparing a silica-alumina molecular sieve catalyst includes the following steps:
[0040] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol, and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a homogeneous sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ using a 1:10 mass ratio of 1MNH4Cl solution for 2h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst.
[0041] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 15g aluminum nitrate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Al@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-3.
[0042] Example 4
[0043] A method for preparing a silica-alumina molecular sieve catalyst includes the following steps:
[0044] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol, and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a homogeneous sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ using a 1:10 mass ratio of 1MNH4Cl solution for 2h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst.
[0045] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 1g aluminum sulfate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Al@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-4.
[0046] Example 5
[0047] A method for preparing a silica-alumina molecular sieve catalyst includes the following steps:
[0048] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol, and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ with 1M NH4Cl solution at a mass ratio of 1:10 for 2h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst.
[0049] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 5g aluminum sulfate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min. The jar was opened and manually stirred every 30 minutes to prevent the sample from settling. The Al@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-5.
[0050] Example 6
[0051] A method for preparing a silica-alumina molecular sieve catalyst includes the following steps:
[0052] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol, and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ with 1M NH4Cl solution at a mass ratio of 1:10 for 2h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst.
[0053] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 15g aluminum sulfate and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Al@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-6.
[0054] Example 7
[0055] A method for preparing a silica-alumina molecular sieve catalyst includes the following steps:
[0056] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol, and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a homogeneous sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ using a 1:10 mass ratio of 1MNH4Cl solution for 2h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst.
[0057] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 1g of pseudoboehmite and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Al@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-7.
[0058] Example 8
[0059] A method for preparing a silica-alumina molecular sieve catalyst includes the following steps:
[0060] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol, and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a homogeneous sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ using a 1:10 mass ratio of 1MNH4Cl solution for 2h. After drying, the process was repeated twice and then calcined to obtain the Silicate-1 molecular sieve catalyst.
[0061] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 5g pseudoboehmite and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Al@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-8.
[0062] Example 9
[0063] A method for preparing a silica-alumina molecular sieve catalyst includes the following steps:
[0064] (1) Preparation of Silicate-1 molecular sieve catalyst: 193.32g of deionized water, 4g of sodium hydroxide, 66.667g of silica sol and 13.33g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40℃ and stirred until a uniform sol system was formed. Then, it was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 180℃ for 24h. After crystallization, it was washed, dried and calcined. Then, it was subjected to ammonium ion exchange with 1MNH4Cl solution at a mass ratio of 1:10 in a magnetically stirred water bath at 80℃ for 2h. After drying, the process was repeated twice and then calcined to obtain Silicate-1 molecular sieve catalyst.
[0065] (2) The 5g Silicate-1 molecular sieve catalyst matrix obtained in step (1) was mixed with 15g pseudoboehmite and added to an agate ball mill jar. The mixture was ball milled for 2 hours at a speed of 360r / min, with manual stirring every 30 minutes to prevent the sample from settling. The Al@Silicate-1 molecular sieve catalyst was obtained by calcination and named C-9.
[0066] Comparative Example 1
[0067] ZSM-5 molecular sieve produced by Nankai Catalyst Plant was selected as a comparative example, and the product was named D-1.
[0068] Comparative Example 2
[0069] Preparation of Silicate-1 molecular sieve catalyst: 193.32 g of deionized water, 4 g of sodium hydroxide, 66.667 g of silica sol, and 13.33 g of tetrapropylammonium bromide were added to a magnetically stirred water bath at 40 °C and stirred until a homogeneous sol system was formed. The mixture was then transferred to a hydrothermal reactor lined with polytetrafluoroethylene (PTFE) and crystallized at 180 °C for 24 h. After crystallization, the catalyst was washed, dried, and calcined. Ammonium ion exchange was then performed for 2 h in a magnetically stirred water bath at 80 °C using a 1:10 mass ratio of 1 M NH4Cl solution. After drying, this process was repeated twice, followed by calcination to obtain the Silicate-1 molecular sieve catalyst, named D-2.
[0070] Comparative Example 3
[0071] 48.3g of deionized water, 1g of sodium hydroxide, 16.667g of silica sol, 3.33g of tetrapropylammonium bromide, and 0.355g of sodium aluminate were added to a magnetically stirred water bath at 250℃ and stirred until a homogeneous sol system was formed. Then, the mixture was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner and crystallized at 170℃ for 24 hours. After crystallization, the mixture was washed, dried, and calcined. Then, ammonium ion exchange was performed in a magnetically stirred water bath at 80℃ with a 1:10 mass ratio of 1MNH4Cl solution for 2 hours. After drying, the process was repeated twice and then calcined to obtain the HZSM-5 molecular sieve catalyst with a silicon-to-aluminum ratio of 40, named D-3.
[0072] Results Analysis
[0073] Table 1. Texture property parameters of Examples 1-9 and Comparative Examples 1-2
[0074]
[0075] Table 1 shows the texture properties of Examples 1-9 and Comparative Examples 1-2 of the present invention. As can be seen from the N2 physical adsorption-desorption test results, the pore structure of each example does not change much. Among them, Comparative Example 1 is a microporous material and Comparative Example 2 is a micro-mesoporous material. When Comparative Example 2 is used as the matrix material of each example, the total pore volume, micropore volume and mesopore volume do not change much, maintaining the original pore structure of the matrix material, maintaining good pore connectivity, and having good diffusion performance for catalytic products.
[0076] Table 2 shows the data for the catalytic cracking reaction of n-butane at a reaction temperature of 640℃:
[0077] Table 2. Data on the catalytic cracking reaction of n-butane in Examples 1-9 and Comparative Examples 1-3
[0078]
[0079] As can be seen from the performance evaluation data of Examples 1-9 and Comparative Examples 1-3, the catalysts in the examples of the present invention have good performance in hydrocarbon catalytic cracking reactions, and have higher selectivity and yield of low-carbon olefins than those in the comparative examples, indicating that the synthesis of silica-alumina molecular sieves by mechanochemical method can effectively increase their catalytic cracking activity.
[0080] In summary, this invention synthesizes an all-silica molecular sieve and selectively adds aluminum to it, giving the synthesized silica-alumina molecular sieve suitable acid properties and a good pore structure. The ball milling process can create more defects on the outer surface of the all-silica molecular sieve, thereby increasing the space for aluminum to settle. By selectively controlling the acidic site properties on the catalyst surface through the introduction of aluminum, the acidic sites in the catalyst pores are reduced, thereby suppressing the occurrence of side reactions as much as possible to improve the selectivity and yield of low-carbon olefins. By controlling the occurrence form of aluminum on the molecular sieve surface (dispersion, settlement state, and interaction with the molecular sieve), the acidic centers can achieve highly efficient catalysis in the catalytic cracking of hydrocarbons to prepare low-carbon olefins.
[0081] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.
Claims
1. A method for preparing a silica-alumina molecular sieve catalyst, characterized in that, Includes the following steps: (1) The silicon source, alkali source and template agent are mixed evenly in a water bath in a solvent to obtain a sol precursor. The sol precursor is subjected to hydrothermal crystallization reaction, washed, dried and calcined to obtain a molecular sieve catalyst precursor. (2) The molecular sieve catalyst precursor obtained in step (1) is subjected to ammonium ion exchange treatment, dried and calcined to obtain the molecular sieve catalyst; (3) Using the molecular sieve catalyst obtained in step (2) as a support, add an aluminum-containing salt compound, introduce aluminum into the molecular sieve catalyst support by mechanical ball milling, and then calcinate to obtain a silicon-aluminum molecular sieve catalyst. In step (3), the mass ratio of the amount of aluminum-containing salt compound added to the molecular sieve catalyst is 1~15:
5.
2. The method for preparing the silica-alumina molecular sieve catalyst according to claim 1, characterized in that, The silicon source mentioned in step (1) is one or more of silica sol, fumed silica, sodium silicate, and tetraethyl orthosilicate, and the alkali source is one or more of sodium hydroxide, sodium carbonate, and potassium hydroxide.
3. The method for preparing the silica-alumina molecular sieve catalyst according to claim 1, characterized in that, The template agent mentioned in step (1) is one or more of tetrapropylammonium bromide and tetrapropylammonium hydroxide.
4. The method for preparing the silica-alumina molecular sieve catalyst according to claim 1, characterized in that, The ammonium ion exchange raw material mentioned in step (2) is one of ammonium chloride and ammonium bicarbonate.
5. The method for preparing the silica-alumina molecular sieve catalyst according to claim 1, characterized in that, The aluminum element mentioned in step (3) is one or more of organoaluminum compounds, inorganic aluminum compounds, or hydrates.
6. The method for preparing the silica-alumina molecular sieve catalyst according to claim 1, characterized in that, In step (1), the hydrothermal crystallization reaction temperature is 180℃ and the reaction time is 24h.
7. The method for preparing the silica-alumina molecular sieve catalyst according to claim 1, characterized in that, The ball milling speed in step (3) is 360~1000 r / min, and the time is 1~3 h.
8. A silica-alumina molecular sieve catalyst prepared by the preparation method according to any one of claims 1-7.
9. The application of the silica-alumina molecular sieve catalyst according to claim 8 in the catalytic cracking of hydrocarbons to produce low-carbon olefins.