13X molecular sieve adsorbent and preparation method thereof

Abstract

The invention relates to the technical field of adsorbents, in particular to a 13X molecular sieve adsorbent and a preparation method thereof. The preparation method comprises the following steps: firstly, performing lanthanum ion replacement treatment on 13X molecular sieve raw powder, then generating an MFI molecular sieve coating layer on the surface of the 13X molecular sieve raw powder, etching by using sodium hydroxide to prepare a mesoporous structure, and then performing hydrophobic modification treatment on the mesoporous structure, so that water molecules are difficult to adsorb by the molecular sieve raw powder and mesoporous surfaces thereof due to a methyl group on the surface, and the molecular sieve raw powder and the mesoporous surfaces are not easy to adsorb; hydrogen bond connection cannot be formed, so that a rapid'adsorption-diffusion 'transfer process cannot be realized in molecular sieve raw powder, the polarity of carbon dioxide is far smaller than that of water molecules, the carbon dioxide cannot be repelled by methyl, and the diffusion of the carbon dioxide in mesopores is far higher than that in micropores due to the existence of the mesopores. Therefore, the carbon dioxide flux in the molecular sieve raw powder is effectively improved, and the carbon dioxide adsorption rate of the molecular sieve raw powder is improved.

Description

Technical Field

[0001] This invention relates to the field of adsorbent technology, specifically to a 13X molecular sieve adsorbent and its preparation method. Background Technology

[0002] In typical emission scenarios such as industrial exhaust gas and flue gas from coal-fired power plants, carbon dioxide generally exhibits low partial pressure. Although traditional Na-type 13X molecular sieve powder has a certain adsorption capacity for carbon dioxide due to its own structural characteristics, its inherent low silica-alumina ratio limits its adsorption capacity. Under humid conditions, polar water molecules compete with carbon dioxide for adsorption—that is, water molecules preferentially occupy adsorption active sites, resulting in a significant decrease in carbon dioxide adsorption capacity and a low adsorption capacity retention rate, making it difficult to meet the actual needs of efficient capture. Summary of the Invention

[0003] The purpose of this invention is to provide a 13X molecular sieve adsorbent and its preparation method to solve the problem of competitive adsorption of water vapor and carbon dioxide by 13X molecular sieve.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0005] In a first aspect, the present invention provides a method for preparing a 13X molecular sieve adsorbent, comprising the following steps:

[0006] a. Mix 13X molecular sieve raw powder with lanthanum nitrate solution, heat and stir, after stirring, filter, wash and dry, and calcine under nitrogen atmosphere to obtain La-13X molecular sieve raw powder;

[0007] b. Mix the template agent with deionized water, add the silicon source, stir and hydrolyze, then add the aluminum source and mix to obtain a silica-alumina gel. Then add La-13X molecular sieve powder to disperse, stir and treat, then heat and crystallize, dry and calcine to obtain calcined molecular sieve powder.

[0008] c. Add the calcined molecular sieve raw powder to the alkaline solution, heat and stir, then add dilute nitric acid dropwise to neutralize, filter, wash and dry, and then heat and calcine again to obtain mesoporous modified molecular sieve raw powder.

[0009] d. The mesoporous modified molecular sieve raw powder was impregnated in a hydrophobic modification solution, vacuum impregnated, centrifuged and dried, then heated and calcined in air atmosphere and cooled to obtain hydrophobic mesoporous modified 13X molecular sieve raw powder.

[0010] The hydrophobic mesoporous modified 13X molecular sieve raw powder was mixed with a binder, granulated, and dried to obtain 13X molecular sieve adsorbent.

[0011] Furthermore, in step a, the concentration of the lanthanum nitrate solution is 0.05~0.15 mol / L;

[0012] The lanthanum nitrate solution was adjusted to pH 4-4.6 by adding nitric acid solution dropwise.

[0013] The solid-liquid ratio of the 13X molecular sieve raw powder to the lanthanum nitrate solution is (0.5~1):10g / mL;

[0014] The silicon-to-aluminum ratio of the 13X molecular sieve raw powder is 2.0~3.0.

[0015] Furthermore, in step a, during the heating and stirring process, the heating temperature is 60~70℃ and the stirring time is 6~8h;

[0016] During heating and calcination, the calcination temperature is 520~550℃ and the calcination time is 2~3h.

[0017] Furthermore, in step b, the aluminum source is aluminum nitrate; the silicon source is ethyl silicate.

[0018] The template agent is tetrapropylammonium hydroxide, and the mass ratio of the template agent to deionized water is 1:(3~4).

[0019] Furthermore, in step b, the molar ratio of SiO2 / Al2O3 in the silica-alumina gel is 150~180; the molar ratio of template agent / SiO2 is 0.2~0.25.

[0020] The mass ratio of the La-13X molecular sieve powder to the silica-alumina gel is 10:(20~30).

[0021] Furthermore, in step b, the silicon source is added drop by drop;

[0022] During hydrolysis, the reaction should be stirred for 60-90 minutes at room temperature.

[0023] During the stirring process, the stirring temperature is 50~60℃ and the stirring time is 2~3 hours.

[0024] During the temperature rise crystallization process, the crystallization temperature is 160~170℃ and the crystallization time is 24~36h.

[0025] During heating and calcination, the calcination temperature is 500~550℃ and the calcination time is 4~6h.

[0026] Furthermore, in step c, the solid-liquid ratio of the calcined molecular sieve powder and the alkaline solution is 1:(10~15)g / mL;

[0027] The alkaline solution is a sodium hydroxide solution with a concentration of 0.15~0.2 mol / L;

[0028] During the heating and stirring process, the stirring temperature is 55~60℃ and the stirring time is 60~90min;

[0029] During heating and calcination, the calcination temperature is 500~550℃ and the calcination time is 4~6h.

[0030] Furthermore, in step d, the solid-liquid ratio of the mesoporous modified molecular sieve raw powder to the hydrophobic modified solution is 1:(10~20)g / mL;

[0031] The hydrophobic modification solution is an ethanol solution of methyltrimethoxysilane with a concentration of 2-5 wt%.

[0032] During vacuum impregnation, the vacuum is drawn to 80~100Pa, and the impregnation time is 1~3h;

[0033] During heating and roasting, the roasting temperature is 480~500℃ and the roasting time is 1~2h.

[0034] Furthermore, the mass ratio of the hydrophobic mesoporous modified 13X molecular sieve raw powder to the binder is (7.5~8):(2~2.5); the binder is any one or more of attapulgite, kaolin, and bentonite.

[0035] Secondly, the present invention also provides a 13X molecular sieve adsorbent prepared by the above method.

[0036] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0037] In order to improve the selective adsorption of carbon dioxide in humid gases by 13X molecular sieve powder under normal working conditions, this invention modifies the 13X molecular sieve powder.

[0038] This invention first uses 13X molecular sieve powder as raw material, mixing it with lanthanum nitrate solution. Under continuous stirring, lanthanum ions in the lanthanum nitrate solution will replace sodium ions in the 13X molecular sieve powder. Lanthanum ions have a +3 valence and a stronger electrostatic attraction with the negatively charged framework in the 13X molecular sieve powder. This can effectively inhibit the hydrolysis and dealuminization of the AlO4 tetrahedral structure, thereby significantly improving the framework stability of the 13X molecular sieve powder and avoiding the defect of framework collapse and decreased adsorption capacity caused by alkaline treatment in subsequent step c. At the same time, lanthanum ions can also effectively reduce the hydrolysis of the molecular sieve framework and inhibit the formation of silanol groups in the molecular sieve powder, thereby reducing the strong hydrophilic sites in the molecular sieve powder and reducing the hydrophilicity of the 13X molecular sieve powder. This reduces the phenomenon of water vapor competing with carbon dioxide for adsorption and causing a decrease in carbon dioxide adsorption rate when treating humid flue gas.

[0039] Based on this, the present invention further prepares an MFI molecular sieve shell layer on the surface of 13X molecular sieve raw powder. Using ethyl silicate as raw material, after alkaline hydrolysis in tetrapropylammonium hydroxide aqueous solution, it interacts again with aluminum ions of aluminum nitrate to generate silica-alumina oligomers. Then, La-13X molecular sieve raw powder is added to it. The active groups such as silanol groups remaining on the surface of La-13X molecular sieve raw powder will condense with the oligomers in the silica-alumina gel, thereby combining the silica-alumina gel with the molecular sieve raw powder. Moreover, this binding site will also play a nucleation role in the subsequent crystallization step, thereby ensuring that the free oligomers in the silica-alumina gel will preferentially generate crystals on the surface of La-13X molecular sieve raw powder, reducing the probability of generating free MFI crystal particles by nucleation alone, thereby maximizing the purity of the molecular sieve raw powder. After calcination to remove the template agent, calcined molecular sieve raw powder with a core-shell structure, the core being 13X molecular sieve raw powder and the shell being MFI molecular sieve raw powder is obtained.

[0040] Furthermore, this invention uses alkaline solution to treat the calcined molecular sieve powder. Since an MFI shell is formed on the surface of the molecular sieve powder after calcination, the MFI molecular sieve powder has higher skeleton stability and etching resistance compared to 13X molecular sieve powder. During etching, due to the barrier of the MFI shell, sodium hydroxide cannot directly contact the 13X molecular sieve powder body. Sodium hydroxide will preferentially etch the amorphous silicon and defect sites on the surface of the MFI shell, thereby forming a mesoporous structure. In order to avoid excessive etching of the MFI shell due to long-term treatment and excessive concentration, and to avoid sodium hydroxide affecting the structure of the 13X molecular sieve powder body, this invention also limits the treatment time and the concentration of sodium hydroxide solution to avoid excessive etching that damages the main structure of the MFI shell.

[0041] Furthermore, since molecular sieve powder is adsorbed using a porous structure, the preparation method of using an MFI shell to coat 13X molecular sieve powder to obtain a core-shell structure will inevitably cause the surface-generated MFI shell to partially block the pores of the 13X molecular sieve powder, thus causing a decrease in the adsorption capacity of the 13X molecular sieve powder. However, after etching with sodium hydroxide, the surface defects in the MFI shell will be etched and fused to form a mesoporous structure, reducing the blockage of the pores of the 13X molecular sieve powder, and thus partially restoring the adsorption capacity of the 13X molecular sieve powder.

[0042] Subsequently, this invention uses methyltrimethoxysilane, which has hydrophobic properties, as a modifier and mixes it with the mesoporous modified molecular sieve powder. The methyltrimethoxysilane combines with the residual silanol groups on the surface of the molecular sieve powder, thereby replacing the hydrophilic silanol groups with hydrophobic methyl groups. Furthermore, since the surface of the molecular sieve powder prepared by this invention already has a mesoporous structure with a pore size much larger than that of micropores, the problem of pore blockage caused by long-chain silane modification can be avoided. Thus, the surface of the molecular sieve powder can be fully hydrophobically modified without worrying about blockage causing a decrease in adsorption capacity.

[0043] Furthermore, because the present invention performs hydrophobic modification on the surface of the molecular sieve powder, the methyl groups on the surface make it difficult for water molecules to be adsorbed by the molecular sieve powder and its mesoporous surface, and hydrogen bonds cannot be formed. Thus, the rapid "adsorption-diffusion" transfer process cannot be achieved in the molecular sieve powder. Carbon dioxide, on the other hand, is much less polar than water molecules and will not be repelled by methyl groups. Moreover, due to the presence of mesopores, the diffusion rate of carbon dioxide in the mesopores is much higher than that in the micropores, thereby effectively increasing the carbon dioxide flux in the molecular sieve powder and thus improving the adsorption rate of carbon dioxide by the molecular sieve powder. Attached Figure Description

[0044] Figure 1 This is a flowchart of the preparation method of the 13X molecular sieve adsorbent of the present invention;

[0045] Figure 2 This is a scanning electron microscope image of the hydrophobic mesoporous modified 13X molecular sieve raw powder prepared in Example 1 of the present invention;

[0046] Figure 3 These are pore size analysis diagrams of the hydrophobic mesoporous modified 13X molecular sieve raw powders prepared in Examples 1 and 3 and Comparative Example 3 of the present invention. Detailed Implementation

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] In the embodiments and comparative examples of this invention, the 13X molecular sieve raw powder used is commercially available KMK brand 13X molecular sieve raw powder, with a silica-alumina ratio of 2.0~3.0;

[0049] Example 1

[0050] A method for preparing a 13X molecular sieve adsorbent includes the following steps:

[0051] a. Add 13X molecular sieve raw powder to a 0.05 mol / L lanthanum nitrate solution at a solid-liquid ratio of 0.5:10 g / mL, heat to 60℃, and stir for 6 h. During stirring, control the pH of the mixture to 4.3~4.6. After stirring, filter out the 13X molecular sieve raw powder, wash the filter cake with deionized water until the washing liquid is neutral, dry at 120℃ for 10 h, and then calcine it at 550℃ for 3 h under a nitrogen atmosphere at a rate of 2℃ / min to obtain La-13X molecular sieve raw powder.

[0052] b. Dissolve tetrapropylammonium hydroxide in deionized water, slowly add ethyl silicate dropwise, stir and react at room temperature for 60 min to hydrolyze, then add aluminum nitrate, and continue stirring for 120 min to obtain aluminosilicate gel;

[0053] In the aluminosilicate gel, the mass ratio of tetrapropylammonium hydroxide to deionized water is 1:3;

[0054] The molar ratio of SiO2 / Al2O3 is 150; the molar ratio of tetrapropylammonium hydroxide / SiO2 is 0.2.

[0055] La-13X molecular sieve powder was added to the silica-alumina gel and ultrasonically dispersed and mixed for 60 min. The mixture was heated to 60 °C and stirred at 500 rpm for 3 h. The mixture was then transferred to a polytetrafluoroethylene-lined reactor and crystallized at 160 °C for 24 h. After the reactor cooled, the mixture was vacuum filtered and the filter cake was washed until the pH was 7-8. The filter cake was heated to 120 °C and dried for 12 h. The dried product was heated to 550 °C and calcined for 6 h. After cooling, the calcined molecular sieve powder was obtained.

[0056] The mass ratio of silica-alumina gel to La-13X molecular sieve powder is 2:1.

[0057] c. According to the solid-liquid ratio of 1:10 g / mL, the obtained calcined molecular sieve raw powder was added to a sodium hydroxide solution with a concentration of 0.15 mol / L, heated to 60℃, stirred at a rate of 300 rpm for 90 min, then added dilute nitric acid to neutralize the pH value to neutral, filtered, and the filter cake was washed with deionized water until neutral, then heated to 120℃ and dried for 12 h, then heated to 550℃ again and calcined for 4 h to obtain mesoporous modified molecular sieve raw powder;

[0058] d. According to the solid-liquid ratio of 1:10 g / mL, the mesoporous modified molecular sieve raw powder was impregnated in the hydrophobic modification solution, the vacuum was drawn to a pressure of 80 Pa, and the vacuum impregnation treatment was carried out for 3 h. After centrifugation, the powder was dried at 120℃ for 10 h, and then calcined at 500℃ for 2 h in air atmosphere. After cooling to room temperature, the hydrophobic mesoporous modified 13X molecular sieve raw powder was obtained.

[0059] The hydrophobic modification solution is a 2wt% ethanol solution of methyltrimethoxysilane.

[0060] The hydrophobic mesoporous modified 13X molecular sieve raw powder was mixed with bentonite binder, granulated and dried to obtain 13X molecular sieve adsorbent.

[0061] The mass ratio of the hydrophobic mesoporous modified 13X molecular sieve raw powder to the bentonite binder is 4:1.

[0062] Example 2

[0063] A method for preparing a 13X molecular sieve adsorbent includes the following steps:

[0064] Compared with Example 1, this example increases the concentration of lanthanum nitrate solution in step a, while the other steps remain unchanged;

[0065] a. Add 13X molecular sieve raw powder to a 0.15 mol / L lanthanum nitrate solution at a solid-liquid ratio of 0.5:10 g / mL, heat to 60℃, and stir for 6 h. During stirring, control the pH of the mixture to 4.3~4.6. After stirring, filter out the 13X molecular sieve raw powder, wash the filter cake with deionized water until the washing liquid is neutral, dry at 120℃ for 10 h, and then calcine it at 550℃ for 3 h under a nitrogen atmosphere at a rate of 2℃ / min to obtain La-13X molecular sieve raw powder.

[0066] Example 3

[0067] A method for preparing a 13X molecular sieve adsorbent includes the following steps:

[0068] Compared with Example 2, this example increases the concentration of sodium hydroxide solution in step c, while the other steps remain unchanged;

[0069] c. According to the solid-liquid ratio of 1:10 g / mL, the obtained calcined molecular sieve raw powder was added to a sodium hydroxide solution with a concentration of 0.2 mol / L, heated to 60℃, stirred at a rate of 300 rpm for 90 min, then added dilute nitric acid to neutralize the pH value to neutral, filtered, and the filter cake was washed with deionized water until neutral, then heated to 120℃ and dried for 12 h, then heated to 550℃ again and calcined for 4 h to obtain mesoporous modified molecular sieve raw powder;

[0070] d. According to the solid-liquid ratio of 1:10 g / mL, the mesoporous modified molecular sieve raw powder was impregnated in the hydrophobic modification solution, the vacuum was drawn to a pressure of 80 Pa, and the vacuum impregnation treatment was carried out for 3 h. After centrifugation, the powder was dried at 120℃ for 10 h, and then calcined at 500℃ for 2 h in air atmosphere. After cooling to room temperature, the hydrophobic mesoporous modified 13X molecular sieve raw powder was obtained.

[0071] The hydrophobic modification solution is a 2wt% ethanol solution of methyltrimethoxysilane.

[0072] Example 4

[0073] A method for preparing a 13X molecular sieve adsorbent includes the following steps:

[0074] Compared with Example 3, this example increases the concentration of the hydrophobic modification solution in step d, while the other steps remain unchanged;

[0075] d. According to the solid-liquid ratio of 1:10 g / mL, the mesoporous modified molecular sieve raw powder was impregnated in the hydrophobic modification solution, the vacuum was drawn to a pressure of 80 Pa, and the vacuum impregnation treatment was carried out for 3 h. After centrifugation, the powder was dried at 120℃ for 10 h, and then calcined at 500℃ for 2 h in air atmosphere. After cooling to room temperature, the hydrophobic mesoporous modified 13X molecular sieve raw powder was obtained.

[0076] The hydrophobic modification solution is a 5 wt% ethanol solution of methyltrimethoxysilane.

[0077] The hydrophobic mesoporous modified 13X molecular sieve raw powder was mixed with bentonite binder, granulated and dried to obtain 13X molecular sieve adsorbent.

[0078] The mass ratio of the hydrophobic mesoporous modified 13X molecular sieve raw powder to the bentonite binder is 4:1.

[0079] Example 5

[0080] A method for preparing a 13X molecular sieve adsorbent includes the following steps:

[0081] a. Add 13X molecular sieve raw powder to a 0.15mol / L lanthanum nitrate solution at a solid-liquid ratio of 1:10 g / mL, heat to 70℃, and stir for 8 hours. During stirring, control the pH of the mixture to 4.3~4.6. After stirring, filter out the 13X molecular sieve raw powder, wash the filter cake with deionized water until the washing liquid is neutral, dry at 120℃ for 10 hours, and then calcine it at 520℃ for 2 hours under a nitrogen atmosphere at a rate of 2℃ / min to obtain La-13X molecular sieve raw powder.

[0082] b. Dissolve tetrapropylammonium hydroxide in deionized water, slowly add ethyl silicate dropwise, stir and react at room temperature for 60 min to hydrolyze, then add aluminum nitrate, and continue stirring for 120 min to obtain aluminosilicate gel;

[0083] In the aluminosilicate gel, the mass ratio of tetrapropylammonium hydroxide to deionized water is 1:4;

[0084] The molar ratio of SiO2 / Al2O3 is 180; the molar ratio of tetrapropylammonium hydroxide / SiO2 is 0.25.

[0085] La-13X molecular sieve powder was added to the silica-alumina gel and ultrasonically dispersed and mixed for 60 min. The mixture was heated to 50 °C and stirred at 500 rpm for 2 h. The mixture was then transferred to a polytetrafluoroethylene-lined reactor and crystallized at 170 °C for 36 h. After the reactor cooled, the mixture was vacuum filtered and the filter cake was washed until the pH was 7. The filter cake was heated to 120 °C and dried for 12 h. The dried product was heated to 500 °C and calcined for 4 h. After cooling, the calcined molecular sieve powder was obtained.

[0086] The mass ratio of silica-alumina gel to La-13X molecular sieve powder is 3:1.

[0087] c. According to the solid-liquid ratio of 1:15 g / mL, the obtained calcined molecular sieve raw powder was added to a sodium hydroxide solution with a concentration of 0.2 mol / L, heated to 55℃, stirred at a rate of 300 rpm for 60 min, then added dilute nitric acid to neutralize the pH value to neutral, filtered, and the filter cake was washed with deionized water until neutral, then heated to 120℃ and dried for 12 h, then heated to 500℃ again and calcined for 4 h to obtain mesoporous modified molecular sieve raw powder;

[0088] d. According to the solid-liquid ratio of 1:20 g / mL, the mesoporous modified molecular sieve raw powder was impregnated in the hydrophobic modification solution, the vacuum was drawn to a pressure of 80 Pa, and the vacuum impregnation treatment was carried out for 3 h. After centrifugation, the powder was dried at 120℃ for 10 h, and then calcined at 480℃ for 1 h in air atmosphere. After cooling to room temperature, the hydrophobic mesoporous modified 13X molecular sieve raw powder was obtained.

[0089] The hydrophobic modification solution is a 5 wt% ethanol solution of methyltrimethoxysilane.

[0090] The hydrophobic mesoporous modified 13X molecular sieve raw powder was mixed with bentonite binder, granulated and dried to obtain 13X molecular sieve adsorbent.

[0091] The mass ratio of the hydrophobic mesoporous modified 13X molecular sieve raw powder to the bentonite binder is 3:1.

[0092] Comparative Example 1

[0093] A method for preparing a 13X molecular sieve adsorbent includes the following steps:

[0094] Compared with Example 1, this comparative example did not perform the original step a treatment, but only used 13X molecular sieve raw powder for the next step, while the other steps remained unchanged;

[0095] b. Dissolve tetrapropylammonium hydroxide in deionized water, slowly add ethyl silicate dropwise, stir and react at room temperature for 60 min to hydrolyze, then add aluminum nitrate, and continue stirring for 120 min to obtain aluminosilicate gel;

[0096] In the aluminosilicate gel, the mass ratio of tetrapropylammonium hydroxide to deionized water is 1:3;

[0097] The molar ratio of SiO2 / Al2O3 is 150; the molar ratio of tetrapropylammonium hydroxide / SiO2 is 0.2.

[0098] Add 13X molecular sieve powder to the silica-alumina gel and ultrasonically disperse and mix for 60 min. Heat the mixture to 60℃ and continue stirring at 500 rpm for 3 h. Transfer the mixture to a polytetrafluoroethylene-lined reactor and crystallize at 160℃ for 24 h. After the reactor cools, vacuum filter and wash the filter cake until the pH is 7-8. Heat the filter cake to 120℃ and dry for 12 h. Heat the dried product to 550℃ and calcine for 6 h. After cooling, obtain the calcined molecular sieve powder.

[0099] The mass ratio of silica-alumina gel to La-13X molecular sieve powder is 2:1.

[0100] c. According to the solid-liquid ratio of 1:10 g / mL, the obtained calcined molecular sieve raw powder was added to a sodium hydroxide solution with a concentration of 0.15 mol / L, heated to 60℃, stirred at a rate of 300 rpm for 90 min, then added dilute nitric acid to neutralize the pH value to neutral, filtered, and the filter cake was washed with deionized water until neutral, then heated to 120℃ and dried for 12 h, then heated to 550℃ again and calcined for 4 h to obtain mesoporous modified molecular sieve raw powder;

[0101] d. According to the solid-liquid ratio of 1:10 g / mL, the mesoporous modified molecular sieve raw powder was impregnated in the hydrophobic modification solution, the vacuum was drawn to a pressure of 80 Pa, and the vacuum impregnation treatment was carried out for 3 h. After centrifugation, the powder was dried at 120℃ for 10 h, and then calcined at 500℃ for 2 h in air atmosphere. After cooling to room temperature, the hydrophobic mesoporous modified 13X molecular sieve raw powder was obtained.

[0102] The hydrophobic modification solution is a 2wt% ethanol solution of methyltrimethoxysilane.

[0103] Eight parts of hydrophobic mesoporous modified 13X molecular sieve raw powder were mixed with two parts of bentonite binder, granulated and dried to obtain 13X molecular sieve adsorbent.

[0104] The mass ratio of the hydrophobic mesoporous modified 13X molecular sieve raw powder to the bentonite binder is 4:1.

[0105] Comparative Example 2

[0106] A method for preparing a 13X molecular sieve adsorbent includes the following steps:

[0107] Compared with Example 1, this comparative example did not perform the original step b treatment, but only used La-13X molecular sieve raw powder for step c treatment, and the other steps remained unchanged;

[0108] a. Add 13X molecular sieve raw powder to a 0.05 mol / L lanthanum nitrate solution at a solid-liquid ratio of 0.5:10 g / mL, heat to 60℃, and stir for 6 h. During stirring, control the pH of the mixture to 4.3~4.6. After stirring, filter out the 13X molecular sieve raw powder, wash the filter cake with deionized water until the washing liquid is neutral, dry at 120℃ for 10 h, and then calcine it at 550℃ for 3 h under a nitrogen atmosphere at a rate of 2℃ / min to obtain La-13X molecular sieve raw powder.

[0109] c. According to the solid-liquid ratio of 1:10 g / mL, the La-13X molecular sieve raw powder was added to a sodium hydroxide solution with a concentration of 0.15 mol / L, heated to 60℃, stirred at a rate of 300 rpm for 90 min, then diluted nitric acid was added dropwise to neutralize the pH value to neutral, filtered, and the filter cake was washed with deionized water until neutral, then heated to 120℃ and dried for 12 h, then heated to 550℃ again and calcined for 4 h to obtain the mesoporous modified molecular sieve raw powder;

[0110] d. According to the solid-liquid ratio of 1:10 g / mL, the mesoporous modified molecular sieve raw powder was impregnated in the hydrophobic modification solution, the vacuum was drawn to a pressure of 80 Pa, and the vacuum impregnation treatment was carried out for 3 h. After centrifugation, the powder was dried at 120℃ for 10 h, and then calcined at 500℃ for 2 h in air atmosphere. After cooling to room temperature, the hydrophobic mesoporous modified 13X molecular sieve raw powder was obtained.

[0111] The hydrophobic modification solution is a 2wt% ethanol solution of methyltrimethoxysilane.

[0112] After mixing the hydrophobic mesoporous modified 13X molecular sieve raw powder with bentonite binder, the mixture was granulated and dried to obtain 13X molecular sieve adsorbent.

[0113] The mass ratio of the hydrophobic mesoporous modified 13X molecular sieve raw powder to the bentonite binder is 4:1.

[0114] Comparative Example 3

[0115] A method for preparing a 13X molecular sieve adsorbent includes the following steps:

[0116] Compared with Example 1, this comparative example did not perform step c, but only used calcined molecular sieve raw powder for step d, and the other steps remained unchanged;

[0117] a. Add 13X molecular sieve raw powder to a 0.05 mol / L lanthanum nitrate solution at a solid-liquid ratio of 0.5:10 g / mL, heat to 60℃, and stir for 6 h. During stirring, control the pH of the mixture to 4.3~4.6. After stirring, filter out the 13X molecular sieve raw powder, wash the filter cake with deionized water until the washing liquid is neutral, dry at 120℃ for 10 h, and then calcine it at 550℃ for 3 h under a nitrogen atmosphere at a rate of 2℃ / min to obtain La-13X molecular sieve raw powder.

[0118] b. Dissolve tetrapropylammonium hydroxide in deionized water, slowly add ethyl silicate dropwise, stir and react at room temperature for 60 min to hydrolyze, then add aluminum nitrate, and continue stirring for 120 min to obtain aluminosilicate gel;

[0119] In the aluminosilicate gel, the mass ratio of tetrapropylammonium hydroxide to deionized water is 1:3;

[0120] The molar ratio of SiO2 / Al2O3 is 150; the molar ratio of tetrapropylammonium hydroxide / SiO2 is 0.2.

[0121] La-13X molecular sieve powder was added to the silica-alumina gel and ultrasonically dispersed and mixed for 60 min. The mixture was heated to 60 °C and stirred at 500 rpm for 3 h. The mixture was then transferred to a polytetrafluoroethylene-lined reactor and crystallized at 160 °C for 24 h. After the reactor cooled, the mixture was vacuum filtered and the filter cake was washed until the pH was 7-8. The filter cake was heated to 120 °C and dried for 12 h. The dried product was heated to 550 °C and calcined for 6 h. After cooling, the calcined molecular sieve powder was obtained.

[0122] The mass ratio of silica-alumina gel to La-13X molecular sieve powder is 2:1.

[0123] d. According to the solid-liquid ratio of 1:10 g / mL, the calcined molecular sieve raw powder was impregnated in a hydrophobic modification solution, the vacuum was drawn to a pressure of 80 Pa, and the vacuum impregnation treatment was carried out for 3 h. After centrifugation, the powder was dried at 120℃ for 10 h, and then calcined at 500℃ for 2 h in air atmosphere. After cooling to room temperature, the hydrophobic mesoporous modified 13X molecular sieve raw powder was obtained.

[0124] The hydrophobic modification solution is a 2wt% ethanol solution of methyltrimethoxysilane.

[0125] The hydrophobic mesoporous modified 13X molecular sieve raw powder was mixed with bentonite binder, granulated and dried to obtain 13X molecular sieve adsorbent.

[0126] The mass ratio of the hydrophobic mesoporous modified 13X molecular sieve raw powder to the bentonite binder is 4:1.

[0127] Comparative Example 4

[0128] A method for preparing 13X molecular sieve raw powder includes the following steps:

[0129] Compared with Example 1, this comparative example did not prepare hydrophobic mesoporous modified 13X molecular sieve raw powder, but only used 13X molecular sieve raw powder for step S2 treatment;

[0130] According to the mass ratio, 8 parts of 13X molecular sieve raw powder and 2 parts of bentonite binder are mixed, granulated and dried to obtain 13X molecular sieve adsorbent.

[0131] Performance testing:

[0132] According to HG / T 2690-2012 "13X Molecular Sieve Raw Powder", the hydrophobic mesoporous modified 13X molecular sieve raw powder prepared in Examples 1-5 and Comparative Examples 1-4 of this invention were subjected to static carbon dioxide adsorption tests at pressures of 2 mmHg and 250 mmHg using the static gravimetric method, and the detection temperature was 25℃.

[0133] The dynamic adsorption rate of carbon dioxide was detected by HG / T 2691-2024 for the 13X molecular sieve adsorbents prepared in Examples 1-5 and Comparative Examples 1-4 of this invention. During the detection, the volume fraction of CO2 at the inlet was 450 × 10⁻⁶. -6 When the volume fraction of CO2 at the outlet exceeds 1×10 -6 At that time, the dynamic CO2 breakthrough time was recorded to obtain the dynamic CO2 adsorption capacity. Then, based on the dynamic CO2 breakthrough time and the dynamic CO2 adsorption capacity, the amount of adsorption per unit volume of molecular sieve adsorbent sample per unit time was calculated to obtain the dynamic adsorption rate.

[0134] The 13X molecular sieve adsorbents prepared in Examples 1-5 and Comparative Examples 1-4 of this invention were placed in an environment with a relative humidity of 55% and an ambient temperature of 30°C and allowed to stand for equilibration for 24 hours to simulate a humid environment. After this, the static carbon dioxide adsorption capacity of 2 mmHg was tested again according to HG / T 2690-2012, and the capacity retention rate was calculated using the following formula:

[0135]

[0136] The test results are shown in Table 1 below.

[0137] Table 1. Performance test results of the examples and comparative examples

[0138]

[0139] Additionally, the pore size of the hydrophobic mesoporous modified 13X molecular sieve raw powders prepared in Examples 1, 3, and Comparative Example 3 was analyzed using the DFT method. The results are shown in [Figure 1]. Figure 3 .

[0140] As can be seen from the data in Table 1, by comparing the data of Example 1 and Example 2, after increasing the concentration of lanthanum nitrate solution, the exchange of lanthanum ions between the 13X molecular sieve powder and the solution is enhanced. More sodium ions are replaced, and more lanthanum ions are loaded in the framework, which makes the framework of 13X molecular sieve more stable and reduces the hydrophilicity of the molecular sieve framework. This avoids the dealuminization and collapse of the framework in subsequent steps, thus ensuring that more micropores remain in the molecular sieve to adsorb gas.

[0141] As can be seen from the data in Example 3, after increasing the concentration of sodium hydroxide solution, the static adsorption capacity of the molecular sieve powder decreased, while the dynamic adsorption rate increased further. This is because increasing the concentration of sodium hydroxide solution increases the etching intensity of the molecular sieve powder, which in turn leads to the further etching of the micropores in the molecular sieve powder to form mesoporous structures. This results in a decrease in the specific surface area of ​​the molecular sieve powder and a decrease in the static adsorption capacity. However, due to the increase in mesoporous structures, the diffusion rate of carbon dioxide in the mesopores is much higher than that in the micropores, thereby effectively increasing the carbon dioxide flux in the molecular sieve powder and thus improving the adsorption rate of carbon dioxide by the molecular sieve powder.

[0142] The data in Example 4 show that after increasing the concentration of the hydrophobic modified solution, the content of hydrophobic groups introduced on the surface of the molecular sieve increases, making it difficult for water molecules to be adsorbed by the molecular sieve powder and its mesoporous surface, and thus preventing the formation of hydrogen bonds, thereby reducing the competition between water molecules and carbon dioxide molecules during the adsorption process of the molecular sieve.

[0143] The data in Example 5 show that even after reducing the amount of hydrophobic mesoporous modified 13X molecular sieve powder added and changing the parameters of various modification schemes, the molecular sieve adsorbent prepared by this invention still has a significantly higher adsorption rate and water resistance advantage compared with the traditional 13X molecular formula adsorbent.

[0144] Data from Example 1 and Comparative Example 1 show that without lanthanum ion replacement, the framework strength of the molecular sieve powder decreases. Furthermore, without the coordination effect of lanthanum ions to inhibit the formation of silanol groups in the molecular sieve framework, its hydrophilicity increases, leading to a decrease in capacity retention in humid environments. During sodium hydroxide etching, although there is an MFI shell structure on the outside, a certain degree of etching collapse still occurs, causing the pores of the molecular sieve to be blocked, thus resulting in a decrease in the adsorption capacity of the molecular sieve.

[0145] In Comparative Example 2, since step b was not performed, no MFI shell was formed on the surface of the molecular sieve powder. Therefore, during alkaline etching in step c, sodium hydroxide directly contacts the 13X molecular sieve. Although a mesoporous structure is formed, due to the low silicon-to-aluminum ratio of the 13X molecular sieve, prolonged etching will cause dealuminization of the 13X molecular sieve, leading to framework collapse and blockage of the pores in the molecular sieve. This ultimately results in a severe decrease in the static adsorption capacity in Comparative Example 2.

[0146] As can be seen from the data of Example 1, Comparative Example 3 and Comparative Example 4, without step c, the final synthesized molecular sieve powder is a core-shell structure molecular sieve with a layer of MFI molecular sieve covering 13X molecular sieve because it has not undergone alkaline etching. Without the sodium hydroxide etching process to generate a mesoporous structure, it cannot assist the diffusion of carbon dioxide gas. Furthermore, the pore size of the MFI molecular sieve is mostly 0.55 nm, which is much smaller than the 0.9~1 nm micropores of the 13X molecular sieve. Moreover, the MFI shell is grown directly on the surface of the 13X molecular sieve in situ. This process itself will cause partial blockage of the pores of the 13X molecular sieve, thereby further reducing the number of micropores and increasing the difficulty of diffusion. Therefore, even compared with the unmodified 13X molecular sieve in Comparative Example 4, the dynamic adsorption rate of Comparative Example 3 still shows a significant decrease.

[0147] The data from Comparative Example 4 show that the adsorption capacity is significantly improved compared to Example 1. This is because the sample used in Comparative Example 4 was made by directly mixing and granulating unmodified 13X molecular sieve powder with a binder. Compared to Example 1, the surface of the unmodified 13X molecular sieve powder in Comparative Example 4 did not form a layer of MFI molecular sieve shell. Therefore, the micropores on the surface of the 13X molecular sieve powder were not covered by MFI molecular sieve, resulting in more unblocked micropore structures and a larger adsorption area, thus leading to a higher adsorption capacity. However, since its surface lacks mesoporous structures, the dynamic adsorption rate of Comparative Example 4 decreased significantly compared to Example 1. Furthermore, because the pure 13X molecular sieve contains many polar sites, water vapor easily competes with carbon dioxide for adsorption during the adsorption process, resulting in a significant decrease in the capacity retention rate of Comparative Example 4.

[0148] And by Figure 3 As can be seen, in Examples 1, 3, and Comparative Example 3 of the present invention, the number of mesopores was effectively increased after sodium hydroxide etching. Examples 1 and 3 were treated with sodium hydroxide solutions of different concentrations. After treatment with a higher concentration of sodium hydroxide, the number of micropores in Example 3 decreased, while the mesopore content increased significantly. Comparative Example 3, on the other hand, was not treated with sodium hydroxide at all. Without sodium hydroxide treatment, the MFI molecular sieve coating layer on its surface would cover the pore size of the 13X molecular sieve, resulting in a significant reduction in the number of usable through-holes, which in turn led to a reduction in the number of mesopores and micropores in Comparative Example 3.

[0149] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a 13X molecular sieve adsorbent, characterized in that, Includes the following steps: a. Mix 13X molecular sieve raw powder with lanthanum nitrate solution, heat and stir, after stirring, filter, wash and dry, and calcine under nitrogen atmosphere to obtain La-13X molecular sieve raw powder; b. Mix the template agent with deionized water, add the silicon source, stir and hydrolyze, then add the aluminum source and mix to obtain a silica-alumina gel. Then add La-13X molecular sieve powder to disperse, stir and treat, then heat and crystallize, dry and calcine to obtain calcined molecular sieve powder. c. Add the calcined molecular sieve raw powder to the alkaline solution, heat and stir, then add dilute nitric acid dropwise to neutralize, filter, wash and dry, and then heat and calcine again to obtain mesoporous modified molecular sieve raw powder. d. The mesoporous modified molecular sieve raw powder was impregnated in a hydrophobic modification solution, vacuum impregnated, centrifuged and dried, then heated and calcined in air atmosphere and cooled to obtain hydrophobic mesoporous modified 13X molecular sieve raw powder. The hydrophobic mesoporous modified 13X molecular sieve raw powder was mixed with a binder, granulated, and dried to obtain 13X molecular sieve adsorbent.

2. The method for preparing a 13X molecular sieve adsorbent according to claim 1, characterized in that: In step a, the concentration of the lanthanum nitrate solution is 0.05~0.15 mol / L; The lanthanum nitrate solution was adjusted to pH 4-4.6 by adding nitric acid solution dropwise. The solid-liquid ratio of the 13X molecular sieve raw powder to the lanthanum nitrate solution is (0.5~1):10g / mL; The silicon-to-aluminum ratio of the 13X molecular sieve raw powder is 2.0~3.

0.

3. The method for preparing a 13X molecular sieve adsorbent according to claim 1, characterized in that: In step a, during the heating and stirring process, the heating temperature is 60~70℃ and the stirring time is 6~8h; During heating and calcination, the calcination temperature is 520~550℃ and the calcination time is 2~3h.

4. The method for preparing a 13X molecular sieve adsorbent according to claim 1, characterized in that: In step b, the aluminum source is aluminum nitrate; the silicon source is ethyl silicate. The template agent is tetrapropylammonium hydroxide, and the mass ratio of the template agent to deionized water is 1:(3~4).

5. The method for preparing a 13X molecular sieve adsorbent according to claim 1, characterized in that: In step b, the molar ratio of SiO2 / Al2O3 in the silica-alumina gel is 150~180; the molar ratio of template agent / SiO2 is 0.2~0.

25. The mass ratio of the La-13X molecular sieve powder to the silica-alumina gel is 10:(20~30).

6. The method for preparing a 13X molecular sieve adsorbent according to claim 1, characterized in that: In step b, the silicon source is added drop by drop; During hydrolysis, the reaction should be stirred for 60-90 minutes at room temperature. During the stirring process, the stirring temperature is 50~60℃ and the stirring time is 2~3 hours. During the temperature rise crystallization process, the crystallization temperature is 160~170℃ and the crystallization time is 24~36h. During heating and calcination, the calcination temperature is 500~550℃ and the calcination time is 4~6h.

7. The method for preparing a 13X molecular sieve adsorbent according to claim 1, characterized in that: In step c, the solid-liquid ratio of the calcined molecular sieve powder and the alkaline solution is 1:(10~15)g / mL; The alkaline solution is a sodium hydroxide solution with a concentration of 0.15~0.2 mol / L; During the heating and stirring process, the stirring temperature is 55~60℃ and the stirring time is 60~90min; During heating and calcination, the calcination temperature is 500~550℃ and the calcination time is 4~6h.

8. The method for preparing a 13X molecular sieve adsorbent according to claim 1, characterized in that: In step d, the solid-liquid ratio of the mesoporous modified molecular sieve raw powder to the hydrophobic modified solution is 1:(10~20)g / mL; The hydrophobic modification solution is an ethanol solution of methyltrimethoxysilane with a concentration of 2-5 wt%. During vacuum impregnation, the vacuum is drawn to 80~100Pa, and the impregnation time is 1~3h; During heating and roasting, the roasting temperature is 480~500℃ and the roasting time is 1~2h.

9. The method for preparing a 13X molecular sieve adsorbent according to claim 1, characterized in that: The mass ratio of the hydrophobic mesoporous modified 13X molecular sieve raw powder to the binder is (7.5~8):(2~2.5); the binder is any one or more of attapulgite, kaolin, and bentonite.

10. A 13X molecular sieve adsorbent obtained by the preparation method according to any one of claims 1 to 9.

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