A modified molecular sieve, a preparation method and application thereof

Abstract

The application provides a modified molecular sieve and a preparation method and application thereof, and belongs to the technical field of molecular sieves. The preparation method of the modified molecular sieve comprises the following steps: uniformly mixing 5A molecular sieve and modified 4A molecular sieve to obtain mixed molecular sieve raw powder; slowly pouring a zinc nitrate hexahydrate solution and a 2-methyl imidazole solution into the mixed molecular sieve raw powder in sequence, stirring and reacting for 0.5-1.5 h, standing for 10-36 h, filtering and centrifugally separating after standing, collecting the solid, washing the solid with anhydrous ethanol, and drying to obtain the modified molecular sieve. The 4A molecular sieve is modified in multiple steps, then is compounded with the 5A molecular sieve, and then is modified by introducing a metal organic framework material, so that a composite material with high adsorption capacity and high cycle stability is finally formed.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve technology, specifically to a modified molecular sieve, its preparation method, and its application. Background Technology

[0002] Carbon dioxide (CO2), a major greenhouse gas, is considered a primary cause of global warming, ocean acidification, and a range of other environmental problems due to its excessive emissions. With rapid industrialization, the combustion of fossil fuels, cement production, and chemical processes have generated substantial CO2 emissions. Therefore, developing efficient and economical CO2 capture technologies has become a global research hotspot.

[0003] Among numerous carbon dioxide capture technologies, adsorption has shown broad application prospects in carbon dioxide purification due to its advantages such as low cost, high efficiency, simple process, low energy consumption, and no secondary pollution. The core of adsorption lies in the development of high-performance adsorption materials. Currently, common CO2 adsorption materials mainly include zeolite molecular sieves, metal-organic framework materials, activated carbon, and organic amine solid adsorbents. Among them, zeolite molecular sieves are widely used in gas separation due to their regular microporous structure, good thermal stability and mechanical strength, and relatively low cost. In particular, type A molecular sieves (such as 4A and 5A molecular sieves) exhibit a certain CO2 adsorption capacity under normal temperature and pressure because the cations in their framework can interact strongly with CO2 molecules through an electrostatic field. However, due to the strong hydrophilicity of both 4A and 5A molecular sieves, water vapor competition for adsorption is severe, leading to a significant decrease in their carbon dioxide adsorption capacity in high-humidity environments. MOFs are porous materials formed by the synergistic formation of metal ions or clusters with organic molecules (called linkers). Compared with traditional inorganic porous materials, they have tunable pore structures and larger specific surface areas, making them promising materials for CO2 capture. Summary of the Invention

[0004] In view of this, the present invention modifies 4A molecular sieve in multiple steps, then combines it with 5A molecular sieve, and introduces metal-organic framework materials for modification, ultimately forming a composite material with high adsorption capacity and high cycling stability.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention provides a method for preparing modified molecular sieves, comprising the following steps:

[0007] (1) Mix 5A molecular sieve and modified 4A molecular sieve evenly to obtain mixed molecular sieve raw powder for later use;

[0008] (2) Weigh a certain amount of 2-methylimidazole and add it to deionized water to obtain a 2-methylimidazole solution; weigh a certain amount of zinc nitrate hexahydrate and add it to deionized water to obtain a zinc nitrate hexahydrate solution;

[0009] (3) The zinc nitrate hexahydrate solution and the 2-methylimidazole solution were slowly poured into the mixed molecular sieve powder in sequence, and the reaction was stirred for 0.5-1.5 h. After standing for 10-36 h, the mixture was filtered and centrifuged to separate the solid. The solid was washed with anhydrous ethanol and dried to obtain the modified molecular sieve.

[0010] Furthermore, the preparation method of the modified 4A molecular sieve in step (1) is as follows:

[0011] (1) Add 4A molecular sieve, sodium dodecylbenzenesulfonate and tetraethyl orthosilicate to deionized water, place in a water bath at 50-80℃, and sonicate to obtain a mixture; add ammonia and benzyl dimethyl (2-hydroxyethyl) ammonium chloride to the mixture, react at 70-90℃ for 1-3 hours, wash thoroughly with ethanol aqueous solution after the reaction, centrifuge, dry to obtain modified intermediate product;

[0012] (2) Add the modified intermediate product to deionized water, stir evenly, then add aconitine and continue stirring to react. After the reaction is complete, filter and wash with deionized water 3 times, dry, and obtain modified 4A molecular sieve.

[0013] Further, in step (1), the mass ratio of 4A molecular sieve, sodium dodecylbenzenesulfonate, tetraethyl orthosilicate, deionized water, ammonia, and benzyl dimethyl (2-hydroxyethyl) ammonium chloride is (2-5):(0.5-1.0):(3-7):(100-200):(5-8):(1-3).

[0014] Furthermore, in step (1), the ultrasonic power is 30-50 kHz, and the ultrasonic treatment lasts for 10-25 min.

[0015] Furthermore, the concentration of the ethanol aqueous solution in step (1) is 20-30 wt%.

[0016] Furthermore, in step (2), the mass ratio of the modified intermediate product, deionized water, and aconitine is 1:(10-18):0.3-0.6.

[0017] Furthermore, the reaction described in step (2) lasts for 1-2 hours.

[0018] Furthermore, the drying temperature is 80-120℃, and the drying time is 1-5 hours.

[0019] Furthermore, the mass ratio of the 5A molecular sieve and the modified 4A molecular sieve in step (1) is 30-65:10-28.

[0020] Furthermore, the concentration of the 2-methylimidazole solution in step (2) is 0.8-2.0 mol / L.

[0021] Furthermore, the concentration of the zinc nitrate hexahydrate solution in step (2) is 0.1~0.6 mol / L.

[0022] Furthermore, the volume ratio of the zinc nitrate hexahydrate solution and the 2-methylimidazole solution in step (2) is 1:1.

[0023] Furthermore, in step (3), the mass ratio of the mixed solution composed of the 2-methylimidazole solution and the zinc nitrate hexahydrate solution to the mixed molecular sieve powder is 5-7:1-2.

[0024] Furthermore, the drying temperature in step (3) is 80-120℃, and the drying time is 18-36h.

[0025] The present invention also provides a modified molecular sieve prepared according to the method, and the application of the modified molecular sieve in the field of carbon dioxide adsorption.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention adjusts the pore structure of 4A molecular sieve by coating it with silica, thereby increasing the specific surface area of ​​the molecular sieve. It also increases the adsorption sites by grafting aconitic acid onto the sieve and further increases the specific surface area and porosity of the molecular sieve by combining it with ZIF-8 modification, providing more carbon dioxide adsorption sites. At the same time, it can also effectively inhibit water vapor competitive adsorption and improve the adsorption performance and adsorption stability of the molecular sieve for carbon dioxide in high humidity environments. Detailed Implementation

[0028] This invention provides a method for preparing modified molecular sieves, comprising the following steps:

[0029] (1) Mix 5A molecular sieve and modified 4A molecular sieve evenly to obtain mixed molecular sieve raw powder for later use;

[0030] (2) Weigh a certain amount of 2-methylimidazole and add it to deionized water to obtain a 2-methylimidazole solution; weigh a certain amount of zinc nitrate hexahydrate and add it to deionized water to obtain a zinc nitrate hexahydrate solution;

[0031] (3) The zinc nitrate hexahydrate solution and the 2-methylimidazole solution were slowly poured into the mixed molecular sieve powder in sequence, and the reaction was stirred for 0.5-1.5 h. After standing for 10-36 h, the mixture was filtered and centrifuged to separate the solid. The solid was washed with anhydrous ethanol and dried to obtain the modified molecular sieve.

[0032] In some embodiments of the present invention, the preparation method of the modified 4A molecular sieve in step (1) is as follows:

[0033] (1) Add 4A molecular sieve, sodium dodecylbenzenesulfonate and tetraethyl orthosilicate to deionized water, place in a water bath at 50-80℃, and sonicate to obtain a mixture; add ammonia and benzyl dimethyl (2-hydroxyethyl) ammonium chloride to the mixture, react at 70-90℃ for 1-3 hours, wash thoroughly with ethanol aqueous solution after the reaction, centrifuge, dry to obtain modified intermediate product;

[0034] (2) Add the modified intermediate product to deionized water, stir evenly, then add aconitine and continue stirring to react. After the reaction is complete, filter and wash with deionized water 3 times, dry, and obtain modified 4A molecular sieve.

[0035] In this invention, benzyl dimethyl (2-hydroxyethyl) ammonium chloride is used as a structure directing agent to guide the orderly deposition of silicon source on the surface of 4A molecular sieve, thereby improving the uniformity of deposition; ammonia provides amino groups, and this invention grafts aconitine onto the surface of 4A molecular sieve by introducing amino groups on the surface of 4A molecular sieve to react with carboxyl groups to form amide bonds.

[0036] In this invention, sodium dodecylbenzenesulfonate acts as a dispersant to prevent molecular sieve agglomeration and promote uniform surface modification; tetraethyl orthosilicate provides a silicon source, forming a core-shell material with 4A molecular sieve as the core and silica as the shell. The introduction of silica helps to adjust the pore structure of the 4A molecular sieve, increasing its specific surface area and thus enhancing its adsorption capacity for carbon dioxide. Simultaneously, the introduction of silica also improves the structural stability of the 4A molecular sieve and reduces the risk of cracking.

[0037] In this invention, aconitic acid is an unsaturated tricarboxylic acid. On the one hand, some of the carboxyl groups on aconitic acid react with the introduced amino groups to form amide bonds, grafting aconitic acid onto the surface of 4A molecular sieves. On the other hand, the polycarboxyl structure of aconitic acid also interacts with carbon dioxide, increasing adsorption sites. In addition, the polycarboxyl structure of aconitic acid helps to form more micropores, thereby increasing the specific surface area and enhancing its physical adsorption of carbon dioxide.

[0038] In this invention, ZIF-8 modified mixed molecular sieves are used, which can increase the specific surface area and porosity of the molecular sieve, providing more carbon dioxide adsorption sites. Furthermore, the introduction of ZIF-8 can also improve the adsorption performance and stability of the molecular sieve for carbon dioxide under high humidity conditions.

[0039] Unless otherwise specified, all raw materials used in this invention are commercially available products in the art.

[0040] The present invention does not impose any special restrictions on the stirring method; any stirring method known to those skilled in the art that can achieve uniform mixing of the components is acceptable.

[0041] In some embodiments of the present invention, the mass ratio of the 4A molecular sieve, sodium dodecylbenzenesulfonate, tetraethyl orthosilicate, deionized water, ammonia, and benzyldimethyl (2-hydroxyethyl) ammonium chloride in step (1) is (2-5):(0.5-1.0):(3-7):(100-200):(5-8):(1-3). Preferably, the mass ratio of the 4A molecular sieve, sodium dodecylbenzenesulfonate, tetraethyl orthosilicate, deionized water, ammonia, and benzyldimethyl (2-hydroxyethyl) ammonium chloride in step (1) is (3-5):(0.6-0.8):(4-6):(120-180):(5-7):(1-2). More preferably, the mass ratio of the 4A molecular sieve, sodium dodecylbenzenesulfonate, tetraethyl orthosilicate, deionized water, ammonia, and benzyl dimethyl (2-hydroxyethyl) ammonium chloride in step (1) is 3:0.7:5:160:7:2.

[0042] This invention controls the mass ratio of 4A molecular sieve, sodium dodecylbenzenesulfonate, tetraethyl orthosilicate, deionized water, ammonia, and benzyl dimethyl (2-hydroxyethyl) ammonium chloride within the above-mentioned range, thereby constructing a uniform and non-clogging silica shell on the surface of the 4A molecular sieve, enhancing structural stability and helping to improve adsorption performance.

[0043] In some embodiments of the present invention, the ultrasonic power in step (1) is 30-50 kHz, and the ultrasonic treatment is 10-25 min. Preferably, the ultrasonic treatment in step (1) is 18 min.

[0044] In some embodiments of the present invention, the concentration of the ethanol aqueous solution in step (1) is 20-30 wt%. Preferably, the concentration of the ethanol aqueous solution in step (1) is 25 wt%.

[0045] In some embodiments of the present invention, the mass ratio of the modified intermediate product, deionized water, and aconitic acid in step (2) is 1:(10-18):0.3-0.6. Preferably, the mass ratio of the modified intermediate product, deionized water, and aconitic acid in step (2) is 1:(12-15):0.3-0.4. More preferably, the mass ratio of the modified intermediate product, deionized water, and aconitic acid in step (2) is 1:13:0.4.

[0046] This invention limits the mass ratio of modified intermediate product, deionized water, and aconitine to the above range, controls the grafting density of carboxyl groups, and prevents excessive modification from causing blockage of molecular sieve channels.

[0047] In some embodiments of the present invention, the reaction in step (2) takes 1-2 hours. Preferably, the reaction in step (2) takes 1.5 hours.

[0048] In some embodiments of the present invention, the drying temperature is 80-120°C and the drying time is 1-5 hours.

[0049] In some embodiments of the present invention, the mass ratio of the 5A molecular sieve to the modified 4A molecular sieve in step (1) is 30-65:10-28. Preferably, the mass ratio of the 5A molecular sieve to the modified 4A molecular sieve in step (1) is 35-57:13-21. More preferably, the mass ratio of the 5A molecular sieve to the modified 4A molecular sieve in step (1) is 43:15.

[0050] This invention limits the mass ratio of 5A molecular sieve and modified 4A molecular sieve within the above-mentioned range, which can optimize the selectivity for carbon dioxide and improve the adsorption capacity of the final product for carbon dioxide.

[0051] In some embodiments of the present invention, the concentration of the 2-methylimidazole solution in step (2) is 0.8-2.0 mol / L. Preferably, the concentration of the 2-methylimidazole solution in step (2) is 1.5 mol / L.

[0052] In some embodiments of the present invention, the concentration of the zinc nitrate hexahydrate solution in step (2) is 0.1~0.6 mol / L. Preferably, the concentration of the zinc nitrate hexahydrate solution in step (2) is 0.3 mol / L.

[0053] In some embodiments of the present invention, the volume ratio of the zinc nitrate hexahydrate solution and the 2-methylimidazole solution in step (2) is 1:1.

[0054] In some embodiments of the present invention, the mass ratio of the mixed solution composed of the 2-methylimidazole solution and the zinc nitrate hexahydrate solution in step (3) to the mixed molecular sieve powder is 5-7:1-2. Preferably, the mass ratio of the mixed solution composed of the 2-methylimidazole solution and the zinc nitrate hexahydrate solution in step (3) to the mixed molecular sieve powder is 6.2:1.5.

[0055] In some embodiments of the present invention, the drying temperature in step (3) is 80-120°C and the drying time is 18-36 hours. Preferably, the drying temperature in step (3) is 100°C and the drying time is 24 hours.

[0056] The present invention also provides a modified molecular sieve prepared according to the method, and the application of the modified molecular sieve in the field of carbon dioxide adsorption.

[0057] The applications of the modified molecular sieve described in this invention include, but are not limited to, industrial waste gas treatment and air purification.

[0058] This invention improves the adsorption performance of the molecular sieve for carbon dioxide in high-humidity environments by introducing a hydrophobic ZIF-8 layer on the surface of the molecular sieve, effectively avoiding competitive adsorption of water vapor while allowing CO2 molecules to enter the interior through micropores. The invention also enhances the selective adsorption capacity of the molecular sieve for carbon dioxide through chemical grafting modification. Furthermore, the ZIF-8 modification and silica shell coating enhance the molecular sieve's resistance to hydrothermal aging, making it less prone to pulverization and deactivation during repeated adsorption and desorption processes, thus extending the cycle life of the molecular sieve.

[0059] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0060] Unless otherwise specified, the test methods or experimental methods described in the following examples are all conventional methods; unless otherwise specified, the raw materials and additives are obtained from conventional commercial sources or prepared by conventional methods.

[0061] In the following examples or comparative examples, the mixed solution in step (3) refers to a mixture of 2-methylimidazole solution and zinc nitrate hexahydrate solution. The volume ratio of the zinc nitrate hexahydrate solution to the 2-methylimidazole solution is 1:1.

[0062] Example 1

[0063] A method for preparing modified molecular sieves, the specific steps of which are as follows:

[0064] (1) Mix 5A molecular sieve and modified 4A molecular sieve at a mass ratio of 43:15 to obtain mixed molecular sieve raw powder for later use;

[0065] (2) Weigh a certain amount of 2-methylimidazole and add it to deionized water to obtain a 2-methylimidazole solution with a concentration of 1.5 mol / L; weigh a certain amount of zinc nitrate hexahydrate and add it to deionized water to obtain a zinc nitrate hexahydrate solution with a concentration of 0.3 mol / L.

[0066] (3) The 2-methylimidazole solution and zinc nitrate hexahydrate solution were slowly poured into the mixed molecular sieve powder in sequence. The mass ratio of the mixed solution to the mixed molecular sieve powder was 6.2:1.5. The mixture was stirred for 0.8 h and allowed to stand for 22 h. After standing, the mixture was filtered and centrifuged to separate the solid. The solid was washed three times with anhydrous ethanol and dried at 100 °C for 24 h to obtain the modified molecular sieve.

[0067] The preparation method of the modified 4A molecular sieve in step (1) is as follows:

[0068] (1) Add 4A molecular sieve, sodium dodecylbenzenesulfonate and tetraethyl orthosilicate to deionized water, place in a 60℃ water bath, and sonicate at 30kHz for 15 min to obtain a mixture; add ammonia and benzyl dimethyl (2-hydroxyethyl) ammonium chloride to the mixture, react at 80℃ for 2 h, wash thoroughly with 25wt% ethanol aqueous solution after reaction, centrifuge, dry at 100℃ for 2 h to obtain modified intermediate product;

[0069] The mass ratio of the 4A molecular sieve, sodium dodecylbenzenesulfonate, tetraethyl orthosilicate, deionized water, ammonia, and benzyl dimethyl (2-hydroxyethyl) ammonium chloride is 3:0.7:5:160:7:2.

[0070] (2) Add the modified intermediate product to deionized water, stir evenly, then add aconitine and continue stirring for 1 hour. After the reaction is completed, filter and wash with deionized water 3 times. Dry at 110℃ for 5 hours to obtain modified 4A molecular sieve. The mass ratio of the modified intermediate product, deionized water and aconitine is 1:13:0.4.

[0071] Example 2

[0072] A method for preparing modified molecular sieves, the specific steps of which are as follows:

[0073] (1) Mix 5A molecular sieve and modified 4A molecular sieve at a mass ratio of 35:13 to obtain mixed molecular sieve raw powder for later use;

[0074] (2) Weigh a certain amount of 2-methylimidazole and add it to deionized water to obtain a 2-methylimidazole solution with a concentration of 1.5 mol / L; weigh a certain amount of zinc nitrate hexahydrate and add it to deionized water to obtain a zinc nitrate hexahydrate solution with a concentration of 0.3 mol / L.

[0075] (3) The 2-methylimidazole solution and zinc nitrate hexahydrate solution were slowly poured into the mixed molecular sieve powder in sequence. The mass ratio of the mixed solution to the mixed molecular sieve powder was 5:1. The mixture was stirred for 0.8 h and allowed to stand for 10 h. After standing, the mixture was filtered and centrifuged to separate the solid. The solid was washed three times with anhydrous ethanol and dried at 100 °C for 24 h to obtain the modified molecular sieve.

[0076] The preparation method of the modified 4A molecular sieve in step (1) is as follows:

[0077] (1) Add 4A molecular sieve, sodium dodecylbenzenesulfonate and tetraethyl orthosilicate to deionized water, place in a 55°C water bath, and sonicate at 30 kHz for 10 min to obtain a mixture; add ammonia and benzyl dimethyl (2-hydroxyethyl) ammonium chloride to the mixture, react at 70°C for 3 h, wash thoroughly with 25 wt% ethanol aqueous solution after reaction, centrifuge, dry at 90°C for 2 h to obtain the modified intermediate product;

[0078] The mass ratio of the 4A molecular sieve, sodium dodecylbenzenesulfonate, tetraethyl orthosilicate, deionized water, ammonia, and benzyl dimethyl (2-hydroxyethyl) ammonium chloride is 3:0.6:4:120:5:1.

[0079] (2) Add the modified intermediate product to deionized water, stir evenly, then add aconitine and continue stirring for 1 hour. After the reaction is completed, filter and wash with deionized water 3 times. Dry at 80°C for 5 hours to obtain modified 4A molecular sieve. The mass ratio of the modified intermediate product, deionized water and aconitine is 1:12:0.3.

[0080] Example 3

[0081] A method for preparing modified molecular sieves, the specific steps of which are as follows:

[0082] (1) Mix 5A molecular sieve and modified 4A molecular sieve at a mass ratio of 30:11 to obtain mixed molecular sieve raw powder for later use;

[0083] (2) Weigh a certain amount of 2-methylimidazole and add it to deionized water to obtain a 2-methylimidazole solution with a concentration of 1.9 mol / L; weigh a certain amount of zinc nitrate hexahydrate and add it to deionized water to obtain a zinc nitrate hexahydrate solution with a concentration of 0.1 mol / L.

[0084] (3) The 2-methylimidazole solution and zinc nitrate hexahydrate solution were slowly poured into the mixed molecular sieve powder in sequence. The mass ratio of the mixed solution to the mixed molecular sieve powder was 5:1. The mixture was stirred for 0.5 h and allowed to stand for 10 h. After standing, the mixture was filtered and centrifuged to separate the solid. The solid was washed three times with anhydrous ethanol and dried at 80 °C for 24 h to obtain the modified molecular sieve.

[0085] The preparation method of the modified 4A molecular sieve in step (1) is as follows:

[0086] (1) Add 4A molecular sieve, sodium dodecylbenzenesulfonate and tetraethyl orthosilicate to deionized water, place in a 50℃ water bath, and sonicate at 30kHz for 25 min to obtain a mixture; add ammonia and benzyl dimethyl (2-hydroxyethyl) ammonium chloride to the mixture, react at 70℃ for 3 h, wash thoroughly with 20wt% ethanol aqueous solution after reaction, centrifuge, dry at 80℃ for 2 h to obtain modified intermediate product;

[0087] The mass ratio of the 4A molecular sieve, sodium dodecylbenzenesulfonate, tetraethyl orthosilicate, deionized water, ammonia, and benzyl dimethyl (2-hydroxyethyl) ammonium chloride is 2:0.5:3:100:5:1.

[0088] (2) Add the modified intermediate product to deionized water, stir evenly, then add aconitine and continue stirring for 1 hour. After the reaction is completed, filter and wash with deionized water 3 times. Dry at 80°C for 5 hours to obtain modified 4A molecular sieve. The mass ratio of the modified intermediate product, deionized water and aconitine is 1:10:0.3.

[0089] Example 4

[0090] A method for preparing modified molecular sieves, the specific steps of which are as follows:

[0091] (1) Mix 5A molecular sieve and modified 4A molecular sieve at a mass ratio of 57:21 to obtain mixed molecular sieve raw powder for later use;

[0092] (2) Weigh a certain amount of 2-methylimidazole and add it to deionized water to obtain a 2-methylimidazole solution with a concentration of 1.5 mol / L; weigh a certain amount of zinc nitrate hexahydrate and add it to deionized water to obtain a zinc nitrate hexahydrate solution with a concentration of 0.3 mol / L.

[0093] (3) The 2-methylimidazole solution and zinc nitrate hexahydrate solution were slowly poured into the mixed molecular sieve powder in sequence. The mass ratio of the mixed solution to the mixed molecular sieve powder was 7:2. The mixture was stirred for 1.5 h and allowed to stand for 36 h. After standing, the mixture was filtered and centrifuged to separate the solid. The solid was washed three times with anhydrous ethanol and dried at 100 °C for 24 h to obtain the modified molecular sieve.

[0094] The preparation method of the modified 4A molecular sieve in step (1) is as follows:

[0095] (1) Add 4A molecular sieve, sodium dodecylbenzenesulfonate and tetraethyl orthosilicate to deionized water, place in an 80℃ water bath, and sonicate at 30kHz for 25 min to obtain a mixture; add ammonia and benzyl dimethyl (2-hydroxyethyl) ammonium chloride to the mixture, react at 90℃ for 1 h, wash thoroughly with 25wt% ethanol aqueous solution after reaction, centrifuge, dry at 120℃ for 1 h to obtain the modified intermediate product;

[0096] The mass ratio of the 4A molecular sieve, sodium dodecylbenzenesulfonate, tetraethyl orthosilicate, deionized water, ammonia, and benzyl dimethyl (2-hydroxyethyl) ammonium chloride is 5:0.8:6:180:7:2.

[0097] (2) Add the modified intermediate product to deionized water, stir evenly, then add aconitine and continue stirring for 2 hours. After the reaction is completed, filter and wash with deionized water 3 times. Dry at 120℃ for 3 hours to obtain modified 4A molecular sieve. The mass ratio of the modified intermediate product, deionized water and aconitine is 1:15:0.4.

[0098] Example 5

[0099] A method for preparing modified molecular sieves, the specific steps of which are as follows:

[0100] (1) Mix 5A molecular sieve and modified 4A molecular sieve at a mass ratio of 65:28 to obtain mixed molecular sieve raw powder for later use;

[0101] (2) Weigh a certain amount of 2-methylimidazole and add it to deionized water to obtain a 2-methylimidazole solution with a concentration of 1.5 mol / L; weigh a certain amount of zinc nitrate hexahydrate and add it to deionized water to obtain a zinc nitrate hexahydrate solution with a concentration of 0.6 mol / L.

[0102] (3) The 2-methylimidazole solution and zinc nitrate hexahydrate solution were slowly poured into the mixed molecular sieve powder in sequence. The mass ratio of the mixed solution to the mixed molecular sieve powder was 7:2. The mixture was stirred for 1.5 h and allowed to stand for 36 h. After standing, the mixture was filtered and centrifuged to separate the solid. The solid was washed three times with anhydrous ethanol and dried at 120 °C for 24 h to obtain the modified molecular sieve.

[0103] The preparation method of the modified 4A molecular sieve in step (1) is as follows:

[0104] (1) Add 4A molecular sieve, sodium dodecylbenzenesulfonate and tetraethyl orthosilicate to deionized water, place in an 80℃ water bath, and sonicate at 30kHz for 10 min to obtain a mixture; add ammonia and benzyl dimethyl (2-hydroxyethyl) ammonium chloride to the mixture, react at 90℃ for 1 h, wash thoroughly with 30wt% ethanol aqueous solution after reaction, centrifuge, dry at 120℃ for 1 h to obtain modified intermediate product;

[0105] The mass ratio of the 4A molecular sieve, sodium dodecylbenzenesulfonate, tetraethyl orthosilicate, deionized water, ammonia, and benzyl dimethyl (2-hydroxyethyl) ammonium chloride is 5:1.0:7:200:8:3.

[0106] (2) Add the modified intermediate product to deionized water, stir evenly, then add aconitine and continue stirring for 2 hours. After the reaction is completed, filter and wash with deionized water 3 times. Dry at 120℃ for 3 hours to obtain modified 4A molecular sieve. The mass ratio of the modified intermediate product, deionized water and aconitine is 1:18:0.6.

[0107] Comparative Example 1

[0108] The difference from Example 1 is that the modified 4A molecular sieve is replaced with an equal amount of 4A molecular sieve, while the other steps are the same as in Example 1.

[0109] Comparative Example 2

[0110] The difference from Example 1 is that step (2) was not set in the preparation process of modified 4A molecular sieve, while the other steps are the same as in Example 1.

[0111] Comparative Example 3

[0112] The difference from Example 1 is that citric acid is used to replace aconitic acid in equal amounts, while the other steps are the same as in Example 1.

[0113] Comparative Example 4

[0114] The difference from Example 1 is that the concentration of the 2-methylimidazole solution is 0.7 mol / L, while the rest of the steps are the same as in Example 1.

[0115] Comparative Example 5

[0116] The difference from Example 1 is that the concentration of the 2-methylimidazole solution is 2.1 mol / L, while the rest of the steps are the same as in Example 1.

[0117] Comparative Example 6

[0118] The difference from Example 1 is that steps (2) and (3) are not set in the preparation process of the modified molecular sieve, that is, the modified molecular sieve is a mixture of 5A molecular sieve and modified 4A molecular sieve, and the remaining steps are the same as in Example 1.

[0119] Comparative Example 7

[0120] A method for preparing modified molecular sieves, the specific steps of which are as follows:

[0121] (1) Mix 5A molecular sieve and modified 4A molecular sieve at a mass ratio of 43:15 to obtain mixed molecular sieve raw powder for later use;

[0122] (2) Weigh a certain amount of 2-methylimidazole and add it to methanol to obtain a 2-methylimidazole solution with a concentration of 1.5 mol / L; weigh a certain amount of cobalt nitrate hexahydrate and add it to methanol to obtain a cobalt nitrate solution with a concentration of 0.3 mol / L;

[0123] (3) The 2-methylimidazole solution and the cobalt nitrate hexahydrate solution were slowly poured into the mixed molecular sieve powder in sequence. The volume ratio of the 2-methylimidazole solution and the cobalt nitrate hexahydrate solution was 1:1. The mass ratio of the mixed solution of the 2-methylimidazole solution and the cobalt nitrate hexahydrate solution to the mixed molecular sieve powder was 6.2:1.5. The mixture was stirred for 0.8 h and allowed to stand for 22 h. After standing, the mixture was filtered and centrifuged to separate the solids. The solids were washed three times with anhydrous ethanol and dried at 100 °C for 24 h to obtain the modified molecular sieve.

[0124] The preparation method of the modified 4A molecular sieve is the same as in Example 1.

[0125] Test Example 1

[0126] The modified molecular sieves provided in each embodiment and comparative example were subjected to performance tests.

[0127] The test method is as follows: Weigh 10g of the modified molecular sieve sample to be tested and place it in a fixed-bed reactor. First, heat the fixed-bed reactor to 120℃ under an argon atmosphere and keep it at that temperature for 1 hour to remove the adsorbed moisture and other impurities from the sample. Then, lower the system temperature to 45℃ and keep it at that temperature for 20 minutes. Next, introduce a mixed gas of carbon dioxide / nitrogen (15Vol.%CO2 + 85Vol.%N2) saturated with water vapor at 45℃ into the reactor until the concentration no longer changes. Test the adsorption performance of the modified molecular sieve for carbon dioxide in a high-humidity environment and perform 10 cycles of the test.

[0128] The compressive strength was expressed as the axial breaking pressure of the sample, and the compressive strength of the modified molecular sieves provided in each embodiment and comparative example was tested.

[0129] The test results are shown in Table 1.

[0130] Table 1

[0131] Group Carbon dioxide adsorption amount (wt. %) Carbon dioxide adsorption amount after 10 cycles (wt. %) Compressive strength (MPa) Example 1 8.8 8.7 123.7 Example 2 8.2 8.1 121.6 Example 3 8.7 8.4 120.9 Example 4 8.1 8.0 121.5 Example 5 8.3 8.2 122.3 Comparative Example 1 5.3 3.6 105.8 Comparative Example 2 5.8 4.7 119.7 Comparative Example 3 7.6 7.2 120.3 Comparative Example 4 6.2 5.8 120.1 Comparative Example 5 5.9 5.0 121.4 Comparative Example 6 4.5 2.8 100.6 Comparative Example 7 6.3 5.1 124.9

[0132] As shown in Table 1, the modified molecular sieves prepared in Examples 1-5 of this invention exhibit high adsorption capacity for carbon dioxide in high-humidity environments, along with excellent cyclic adsorption stability and mechanical properties, significantly outperforming Comparative Examples 1-7. Experimental data from Comparative Examples 1 and 2 indicate that the final products prepared from unmodified 4A molecular sieves or 4A molecular sieves lacking aconitic acid modification have poor adsorption performance and compressive strength. Experimental data from Comparative Example 3 show that the adsorption performance and compressive strength of the mixed molecular sieve deteriorated after replacing aconitic acid with other raw materials in equal amounts. Experimental data from Comparative Examples 4 and 5 show that adding a specific proportion of 2-methylimidazole achieves the best results; when the proportion is higher or lower than the range defined in this invention, the adsorption performance and compressive strength of the mixed molecular sieve deteriorate. Experimental data from Comparative Example 6 show that the molecular sieve lacking ZIF-8 modification exhibits a significant decrease in carbon dioxide adsorption capacity, cyclic adsorption stability, and compressive strength in high-humidity environments. The experimental data of Comparative Example 7 show that although the molecular sieve products prepared by modification with other types of metal-organic framework materials have higher mechanical properties, their adsorption capacity for carbon dioxide and cyclic adsorption stability are poor in high humidity environments.

[0133] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a modified molecular sieve, characterized in that, Includes the following steps: (1) Mix 5A molecular sieve and modified 4A molecular sieve evenly to obtain mixed molecular sieve raw powder for later use; (2) Weigh a certain amount of 2-methylimidazole and add it to deionized water to obtain a 2-methylimidazole solution; weigh a certain amount of zinc nitrate hexahydrate and add it to deionized water to obtain a zinc nitrate hexahydrate solution; (3) The zinc nitrate hexahydrate solution and the 2-methylimidazole solution were slowly poured into the mixed molecular sieve powder in sequence, and the reaction was stirred for 0.5-1.5 h. After standing for 10-36 h, the mixture was filtered and centrifuged to separate the solid. The solid was washed with anhydrous ethanol and dried to obtain the modified molecular sieve.

2. The method for preparing the modified molecular sieve according to claim 1, characterized in that, The preparation method of the modified 4A molecular sieve in step (1) is as follows: (1) Add 4A molecular sieve, sodium dodecylbenzenesulfonate and tetraethyl orthosilicate to deionized water, place in a water bath at 50-80℃, and sonicate to obtain a mixture; add ammonia and benzyl dimethyl (2-hydroxyethyl) ammonium chloride to the mixture, react at 70-90℃ for 1-3 hours, wash thoroughly with ethanol aqueous solution after the reaction, centrifuge, dry to obtain modified intermediate product; (2) Add the modified intermediate product to deionized water, stir evenly, then add aconitine and continue stirring to react. After the reaction is complete, filter and wash with deionized water 3 times, dry, and obtain modified 4A molecular sieve.

3. The method for preparing the modified molecular sieve according to claim 2, characterized in that, The mass ratio of the 4A molecular sieve, sodium dodecylbenzenesulfonate, tetraethyl orthosilicate, deionized water, ammonia, and benzyl dimethyl (2-hydroxyethyl) ammonium chloride in step (1) is (2-5):(0.5-1.0):(3-7):(100-200):(5-8):(1-3).

4. The method for preparing the modified molecular sieve according to claim 2, characterized in that, The mass ratio of the modified intermediate product, deionized water, and aconitine in step (2) is 1:(10-18):0.3-0.

6.

5. The method for preparing the modified molecular sieve according to claim 1, characterized in that, In step (1), the mass ratio of the 5A molecular sieve to the modified 4A molecular sieve is 30-65:10-28.

6. The method for preparing the modified molecular sieve according to claim 1, characterized in that, The concentration of the 2-methylimidazole solution in step (2) is 0.8-2.0 mol / L.

7. The method for preparing the modified molecular sieve according to claim 1, characterized in that, The concentration of the zinc nitrate hexahydrate solution in step (2) is 0.1~0.6 mol / L.

8. The method for preparing the modified molecular sieve according to claim 1, characterized in that, The volume ratio of the zinc nitrate hexahydrate solution and the 2-methylimidazole solution in step (2) is 1:

1.

9. The method for preparing the modified molecular sieve according to claim 1, characterized in that, The mass ratio of the mixed solution composed of the 2-methylimidazolium solution and the zinc nitrate hexahydrate solution in step (3) to the mixed molecular sieve raw powder is 5-7:1-2.

10. The modified molecular sieve prepared by the method according to any one of claims 1-9.