CO2 pressure swing adsorption silica gel, preparation method and application thereof

Abstract

The application relates to the technical field of gas adsorption materials, in particular to CO2 pressure swing adsorption silica gel as well as a preparation method and application thereof. The CO2 pressure swing adsorption silica gel comprises a multi-stage channel silica gel carrier, the surface of the multi-stage channel silica gel carrier is sequentially grafted with an ionic liquid functional layer and a temperature-sensitive poly-N-isopropyl acrylamide layer, and a "ionic liquid core-temperature-sensitive shell" core-shell structure is formed; the preparation method comprises three steps of multi-stage channel silica gel carrier preparation, ionic liquid functional layer grafting and temperature-sensitive poly-N-isopropyl acrylamide layer grafting. The prepared adsorption silica gel has the characteristics of large adsorption capacity, high adsorption rate and good desorption effect, can be used for CO2 pressure swing adsorption processes in a wide gas humidity range environment, efficient adsorption and desorption can be realized by adjusting the temperature, pressure, gas velocity and other conditions of adsorption and desorption, the cycle stability is excellent, the existing defects of CO2 adsorption materials in actual application can be effectively solved, and the CO2 adsorption material has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas adsorption materials, in particular to a CO2 pressure swing adsorption silica gel and a preparation method and application thereof. BACKGROUND

[0002] Under the background of global energy saving and emission reduction and climate change, efficient separation of carbon dioxide (CO2) from various gas mixtures has become a research hotspot. Excessive emission of CO2 leads to the intensification of greenhouse effect, threatening ecological balance and sustainable development of human beings. Therefore, it is crucial to develop efficient CO2 adsorption technology.

[0003] At present, the commonly used CO2 adsorption methods in industry include liquid absorption method, membrane separation method and adsorption method. Although the liquid absorption method has high absorption efficiency, it has problems such as easy volatilization of absorbent, serious corrosion of equipment and large energy consumption in regeneration; the membrane separation method has high requirements for equipment, and the selectivity and stability of the membrane material are difficult to balance, and when treating high humidity gas, the membrane is easily polluted by water vapor, resulting in a decrease in separation performance; the adsorption method has been widely concerned due to its simple operation and low energy consumption, and traditional adsorbents such as activated carbon and zeolite have many shortcomings in CO2 adsorption. The adsorption selectivity of activated carbon is poor, the adsorption capacity of CO2 is limited, and in a high humidity environment, water will competitively occupy the adsorption sites, greatly reducing the adsorption effect of CO2; although zeolite has a certain adsorption selectivity, the pore size distribution is narrow, the diffusion resistance of gas is large, resulting in slow adsorption rate, and its adsorption capacity also cannot meet the demand of large-scale industrial application. SUMMARY

[0004] The purpose of the present application is to solve the problems existing in the prior art, and to provide a CO2 pressure swing adsorption silica gel and a preparation method and application thereof.

[0005] In order to achieve the above purpose, the present application provides a CO2 pressure swing adsorption silica gel, which comprises a multi-level pore silica gel carrier, the surface of the silica gel carrier is sequentially grafted with an ionic liquid functional layer and a temperature-sensitive poly-N-isopropyl acrylamide layer, forming a "ionic liquid core-temperature-sensitive shell" core-shell structure.

[0006] The silica gel carrier comprises a macropore with a pore size of 0.1-5 μm and a mesopore with a pore size of 3-5 nm multi-level pore structure.

[0007] The ionic liquid functional layer is fixed in the inner wall of the silica gel pore through covalent bond, and contains imidazole cation unit, the structural formula is: -CH2-CH-(Im + Br - )-, wherein Im + is 1-vinyl-3-ethyl imidazole cation.

[0008] The temperature-sensitive poly-N-isopropyl acrylamide layer is grafted on the surface and opening of the pores of the silica gel particles, and has a low critical solution temperature of 32 DEG C.

[0009] Preferably, the ionic liquid functional layer is covalently anchored by forming Si-O-Si bonds through condensation of 3-methacryloxypropyltrimethoxysilane with the silica gel surface silicon hydroxyl groups, and forming grafted polymer chains through radical reaction with 1-vinyl-3-ethyl imidazole bromide.

[0010] Preferably, the temperature-sensitive poly-N-isopropyl acrylamide layer is grafted through radical reaction, and after grafting, the poly-N-isopropyl acrylamide segments are in an expanded hydrated state below 32 DEG C and in a contracted hydrophobic state above 32 DEG C.

[0011] Further, the application also provides a preparation method of the above-mentioned CO2 pressure swing adsorption silica gel, and specifically comprises the following steps:

[0012] S1, preparation of a multi-level pore silica gel carrier: polyethylene glycol and triblock copolymer P123 are added into a hydrochloric acid solution, stirred at room temperature for 30-40 min, cooled to 0-10 DEG C, then tetraethyl orthosilicate is added, stirred for 1-2 h, ultrasonic degassing for 10-20 min, then sealed and placed in an oven at 60-70 DEG C for 18-24 h, then transferred into a stainless steel reaction kettle with a polytetrafluoroethylene lining, heated to 90-110 DEG C, reacted for 18-24 h, then dried at room temperature for 3 d, dried at 60 DEG C for 1 d, then heated to 450-550 DEG C at a rate of 3-5 DEG C / min in a muffle furnace, and calcined for 3-5 h to obtain a multi-level pore silica gel carrier;

[0013] S2, grafting of an ionic liquid functional layer: the multi-level pore silica gel carrier obtained in S1 is added with 3-methacryloxypropyltrimethoxysilane in tetrahydrofuran, heated to 70-80 DEG C, and reacted for 1-3 h, and the reaction process is shown in the following schematic diagram:

[0014] Formula (1), cooled to room temperature, and after the solid is filtered, washed and dried, 1-vinyl-3-ethyl imidazole bromide and benzoyl peroxide are added in toluene, heated to 100-120 DEG C, and reacted for 4-8 h, and the reaction process is shown in the following schematic diagram:

[0015] Formula (2), cooled to room temperature, and after the solid is filtered, washed and dried, a multi-level pore silica gel carrier containing an ionic liquid layer is obtained;

[0016] S3, temperature-sensitive poly-N-isopropylacrylamide layer grafting: under nitrogen protection, the multi-level channel silica gel carrier containing ionic liquid layer in S2 is added into a cyclohexanol / water mixed solution, ultrasonic dispersion is carried out for 20-30 min, N-isopropylacrylamide and azobisisobutyronitrile are added, stirring is carried out at room temperature for 1-3 h, then temperature is raised to 70-80 ℃, and reaction is carried out for 12-24 h, and a schematic diagram of the reaction process is as follows:

[0017] Formula (3), after cooling to room temperature, centrifugation, the solid is washed, dried to obtain CO2 pressure swing adsorption silica gel.

[0018] Preferably, the polyethylene glycol, triblock copolymer P123, tetraethyl orthosilicate and hydrochloric acid solution in S1 are in a weight ratio of 0.14-0.2:0.27-0.4:1:1.5-2.0.

[0019] Preferably, the concentration of the hydrochloric acid solution in S1 is 1 mol / L.

[0020] Preferably, the multi-level channel silica gel carrier, 3-methacryloyloxypropyltrimethoxysilane, 1-vinyl-3-ethylimidazole bromide, benzoyl peroxide, tetrahydrofuran and toluene in S2 are in a weight ratio of 1:0.2-0.4:0.2-0.3:0.005-0.015:8-12:8-12.

[0021] Preferably, the multi-level channel silica gel carrier containing ionic liquid layer, N-isopropylacrylamide, azobisisobutyronitrile and cyclohexanol / water mixed solution in S3 are in a weight ratio of 1:1.5-2.5:0.006-0.012:8-12.

[0022] Preferably, the cyclohexanol / water mixed solution in S3 refers to a mixture prepared by mixing cyclohexanol and water in a weight ratio of 1:19.

[0023] Further, the application also provides application of the above-mentioned CO2 pressure swing adsorption silica gel in a CO2 pressure swing adsorption process in a wide gas humidity range environment, and the application is characterized in that:

[0024] 0-30% gas humidity environment: the adsorption stage is carried out at 25 ℃ and normal pressure, the adsorption gas speed is 1500 Nm³ / h·m³, and the adsorption time is 180 s; the desorption stage is carried out at 45 ℃ and 0.1 bar, nitrogen is used for reverse blowing during the desorption process, the flow rate is 20% of the adsorption gas speed, the pressure is 0.1 bar, and the desorption time is 90 s;

[0025] 30-70% gas humidity environment: the adsorption stage is carried out at 25 DEG C, normal pressure, the adsorption gas speed is 2000 Nm 3 / h*m 3, the adsorption time is 150s; the desorption stage is carried out at 40 DEG C, 0.1 bar, nitrogen is used for reverse blowing during the desorption process, the flow rate is 40% of the adsorption gas speed, the pressure is 0.1 bar, the desorption time is 60s;

[0026] 70% above gas humidity environment: the adsorption stage is carried out at 25 DEG C, 1.2 bar, the adsorption gas speed is 1200 Nm 3 / h*m 3, the adsorption time is 240s; the desorption stage is carried out at 40 DEG C, 0.05 bar, nitrogen is used for reverse blowing during the desorption process, the flow rate is 80% of the adsorption gas speed, the pressure is 0.15 bar, the periodic blowing method of blowing for 10s and pausing for 5s is adopted, the desorption time is 120s.

[0027] Preferably, in the adsorption stage: the π electron cloud on the imidazole ring forms π-π interaction with the π bond of CO2 molecule, the quaternary ammonium cation N + of the imidazole ring produces electrostatic attraction with CO2, forms [Im + ……CO2] complex, at the same time, under low temperature (<32 DEG C), poly N-isopropyl acrylamide is in hydrophilic extended conformation, forms hydration layer, enhances the polarity of the silica gel surface, promotes the migration of CO2 molecules to the imidazole site; the amide group forms hydrogen bond with the carbonyl group of CO2, assists in fixing the adsorbed CO2;

[0028] In the desorption stage: under high temperature (>32 DEG C), isopropyl hydrophobic effect dominates, poly N-isopropyl acrylamide segment shrinks into a globular shape, the thickness decreases, the imidazole site wrapped is released, the space steric hindrance change produced by the conformational transition leads to the increase of pore size, directly reduces the diffusion resistance of CO2, the desorption rate is improved, at the same time, the imidazole ring is anchored on the silica gel surface through covalent bond, compared with physical impregnation, the cycle number can be greatly improved, the lower vapor pressure can also avoid the decomposition and loss of functional groups during desorption, and the imidazole group still has a high retention rate after multiple desorption.

[0029] The beneficial effects of the application are:

[0030] 1. The CO2 pressure swing adsorption silica gel prepared by the application has a unique "ionic liquid core-temperature sensitive shell" core-shell structure. The imidazole cation unit in the ionic liquid functional layer can be specifically combined with CO2 molecules through π-π interaction and electrostatic attraction, greatly enhancing the adsorption capacity. The temperature-sensitive poly N-isopropyl acrylamide layer is in an extended hydrated state at low temperature, enhancing the polarity of the silica gel surface and promoting the migration of CO2 molecules to the imidazole site. The amide group can also form a hydrogen bond with the carbonyl group of CO2, assisting in fixing the adsorbed CO2, further improving the adsorption effect and realizing efficient adsorption of CO2.

[0031] 2. The CO2 pressure swing adsorption silica gel prepared by the present application, when the temperature is higher than the low critical solution temperature of the temperature-sensitive poly-N-isopropyl acrylamide layer in the desorption stage, the layer changes from a hydrophilic extended state to a hydrophobic contracted state, and this conformational change not only releases the imidazole sites wrapped, making the [Im + The [Im

[0032] 3. The CO2 pressure swing adsorption silica gel prepared by the present application has a multi-level pore structure, including macropores and mesopores, the macropores provide a fast channel for gas transmission, and the mesopores increase the adsorption sites, ensuring that CO2 molecules can diffuse smoothly to the adsorption sites in different humidity environments; in a low humidity environment, the ionic liquid functional layer and the temperature-sensitive poly-N-isopropyl acrylamide layer can fully play a role; in a medium humidity environment, the appropriate amount of water promotes CO2 dissolution and diffusion under the action of the temperature-sensitive layer; in a high humidity environment, by adjusting the adsorption pressure, the temperature-sensitive layer and the multi-level pore structure work together to avoid water interference and maintain high adsorption performance, realizing effective adsorption in a wide humidity range.

[0033] 4. The ionic liquid functional layer of the CO2 pressure swing adsorption silica gel prepared by the present application is firmly fixed on the inner wall of the silica gel pore by covalent bond, compared with the physical impregnation method, the ionic liquid is not easy to fall off or decompose in the process of multiple adsorption-desorption cycles, ensuring the stability of the adsorption sites, the conformational change of the temperature-sensitive poly-N-isopropyl acrylamide layer has good reversibility and can repeatedly play a role in multiple cycles, and the multi-level pore structure remains stable in the cycle process and will not collapse or deform due to multiple uses, ensuring the stability of the overall performance of the material and long-term repeated use, reducing the use cost. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The cycle number-adsorption capacity change situation line graph of the CO2 pressure swing adsorption silica gel prepared for Example 1 in different gas humidity environments;

[0035] Figure 2 The cycle number-adsorption capacity change situation line graph of the CO2 pressure swing adsorption silica gel prepared for Example 2 in different gas humidity environments;

[0036] Figure 3 The cycle number-adsorption capacity change situation line graph of the CO2 pressure swing adsorption silica gel prepared for Example 3 in different gas humidity environments;

[0037] Figure 4A line graph of the change in the number of cycles-adsorption capacity of the CO2 pressure swing adsorption silica gel prepared for Comparative Example 1 under different gas humidity environments;

[0038] Figure 5 A line graph of the change in the number of cycles-adsorption capacity of the CO2 pressure swing adsorption silica gel prepared for Comparative Example 2 under different gas humidity environments;

[0039] Figure 6 A line graph of the change in the number of cycles-adsorption capacity of the CO2 pressure swing adsorption silica gel prepared for Comparative Example 3 under different gas humidity environments;

[0040] Figure 7 A line graph of the change in the number of cycles-adsorption capacity of the CO2 pressure swing adsorption silica gel prepared for Comparative Example 4 under different gas humidity environments;

[0041] Figure 8 A line graph of the change in the number of cycles-adsorption capacity of the CO2 pressure swing adsorption silica gel prepared for Comparative Example 5 under different gas humidity environments;

[0042] Figure 9 A line graph of the change in the number of cycles-adsorption capacity of the CO2 pressure swing adsorption silica gel prepared for Comparative Example 5 under different gas humidity environments;

[0043] Figure 10 A line graph of the change in the number of cycles-adsorption capacity of the CO2 pressure swing adsorption silica gel prepared for Comparative Example 5 under different gas humidity environments. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of the present application more clear and obvious, the present application is further described in detail below in combination with specific examples.

[0045] Example 1: A specific preparation method of a CO2 pressure swing adsorption silica gel, comprising the following steps:

[0046] (1) 140 g of polyethylene glycol and 270 g of triblock copolymer P123 were added to 1.5 kg of a hydrochloric acid solution with a concentration of 1 mol / L, stirred at room temperature for 30 min, cooled to 0°C, then 1 kg of tetraethyl orthosilicate was added, stirred for 1 h, and after ultrasonic degassing for 10 min, it was sealed and placed in an oven at 60°C for 18 h, then transferred to a stainless steel reaction kettle with a polytetrafluoroethylene liner, heated to 90°C, and reacted for 18 h, then dried at room temperature for 3 d, dried at 60°C for 1 d, then heated to 450°C at a rate of 3°C / min in a muffle furnace, and calcined for 3 h to obtain a hierarchical pore silica gel carrier;

[0047] (2) 800 g of the hierarchical porous silica support obtained in (1) and 160 g of 3-methacryloxypropyltrimethoxysilane were added to 6.4 kg of tetrahydrofuran, and the mixture was heated to 70°C and reacted for 1 h. After cooling to room temperature, the solid was filtered, washed, and dried, and then 160 g of 1-vinyl-3-ethylimidazolium bromide and 4 g of benzoyl peroxide were added to 6.4 kg of toluene, and the mixture was heated to 100°C and reacted for 4 h. After cooling to room temperature, the solid was filtered, washed, and dried to obtain a hierarchical porous silica support containing an ionic liquid layer;

[0048] (3) Under nitrogen protection, 800 g of the hierarchical porous silica support containing an ionic liquid layer obtained in (2) was added to 6.4 kg of a cyclohexanol / water mixed solution (prepared by mixing cyclohexanol and water at a weight ratio of 1:19), and the mixture was ultrasonically dispersed for 20 min. Then, 1.2 kg of N-isopropylacrylamide and 4.8 g of azobisisobutyronitrile were added, and the mixture was stirred at room temperature for 1 h, and then heated to 70°C and reacted for 12 h. After cooling to room temperature, the mixture was centrifuged, and the solid was washed and dried to obtain a CO2 pressure swing adsorption silica gel.

[0049] Example 2: A specific preparation method of a CO2 pressure swing adsorption silica gel, comprising the following steps:

[0050] (1) 170 g of polyethylene glycol and 335 g of triblock copolymer P123 were added to 1.8 kg of a 1 mol / L hydrochloric acid solution, and stirred at room temperature for 35 min. Then, the temperature was lowered to 5°C, and 1 kg of tetraethyl orthosilicate was added. The mixture was stirred for 1.5 h, ultrasonically degassed for 15 min, sealed, and then placed in an oven at 65°C for 21 h. Then, the mixture was transferred to a stainless steel reaction kettle with a polytetrafluoroethylene liner, heated to 100°C, and reacted for 21 h. After cooling to room temperature, the mixture was dried for 3 d, and then dried at 60°C for 1 d. Then, the mixture was heated to 500°C at a rate of 4°C / min in a muffle furnace, and calcined for 4 h to obtain a hierarchical porous silica support;

[0051] (2) 800 g of the hierarchical porous silica support obtained in (1) and 240 g of 3-methacryloxypropyltrimethoxysilane were added to 8 kg of tetrahydrofuran, and the mixture was heated to 75°C and reacted for 2 h. After cooling to room temperature, the solid was filtered, washed, and dried, and then 200 g of 1-vinyl-3-ethylimidazolium bromide and 8 g of benzoyl peroxide were added to 8 kg of toluene, and the mixture was heated to 110°C and reacted for 6 h. After cooling to room temperature, the solid was filtered, washed, and dried to obtain a hierarchical porous silica support containing an ionic liquid layer;

[0052] (3) Under the protection of nitrogen, 800 g of the hierarchical porous silica gel carrier containing the ionic liquid layer obtained in (2) was added into 8 kg of a cyclohexanol / water mixed solution (prepared by mixing cyclohexanol and water at a weight ratio of 1:19) and ultrasonically dispersed for 25 min, then 1.6 kg of N-isopropyl acrylamide and 6.4 g of azobisisobutyronitrile were added, stirred at room temperature for 2 h, then heated to 75 ℃, and reacted for 18 h. After cooling to room temperature, centrifugation was performed, and the solid was washed and dried to obtain the CO2 pressure swing adsorption silica gel.

[0053] Example 3: A specific preparation method of the CO2 pressure swing adsorption silica gel, comprising the following steps:

[0054] (1) 200 g of polyethylene glycol, 400 g of triblock copolymer P123 were added into 2 kg of a hydrochloric acid solution with a concentration of 1 mol / L, stirred at room temperature for 40 min, cooled to 10 ℃, then 1 kg of tetraethyl orthosilicate was added, stirred for 2 h, ultrasonically degassed for 20 min, sealed, and then placed in an oven at 70 ℃ for 24 h. Then it was transferred into a stainless steel reaction kettle with a polytetrafluoroethylene liner, heated to 110 ℃, reacted for 24 h, dried at room temperature for 3 d, dried at 60 ℃ for 1 d, then heated to 550 ℃ at a rate of 5 ℃ / min in a muffle furnace, and calcined for 5 h to obtain the hierarchical porous silica gel carrier;

[0055] (2) 800 g of the hierarchical porous silica gel carrier obtained in (1) and 320 g of 3-methacryloxypropyltrimethoxysilane were added into 9.6 kg of tetrahydrofuran and heated to 80 ℃ for reaction for 3 h. After cooling to room temperature, the solid was filtered, washed, and dried, and then mixed with 240 g of 1-vinyl-3-ethylimidazole bromide and 12 g of benzoyl peroxide in 9.6 kg of toluene, heated to 120 ℃ for reaction for 8 h, cooled to room temperature, and then the solid was filtered, washed, and dried to obtain the hierarchical porous silica gel carrier containing the ionic liquid layer;

[0056] (3) Under the protection of nitrogen, 800 g of the hierarchical porous silica gel carrier containing the ionic liquid layer obtained in (2) was added into 9.6 kg of a cyclohexanol / water mixed solution (prepared by mixing cyclohexanol and water at a weight ratio of 1:19) and ultrasonically dispersed for 30 min, then 2 kg of N-isopropyl acrylamide and 9.6 g of azobisisobutyronitrile were added, stirred at room temperature for 3 h, then heated to 80 ℃, and reacted for 24 h. After cooling to room temperature, centrifugation was performed, and the solid was washed and dried to obtain the CO2 pressure swing adsorption silica gel.

[0057] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that 1-vinyl-3-ethylimidazole bromide is not grafted. The specific preparation process is as follows: a specific preparation method of the CO2 pressure swing adsorption silica gel, comprising the following steps:

[0058] (1) 170 g of polyethylene glycol, 335 g of triblock copolymer P123 were added into 1.8 kg of hydrochloric acid solution with a concentration of 1 mol / L, stirred at room temperature for 35 min, cooled to 5°C, then 1 kg of tetraethyl orthosilicate was added, stirred for 1.5 h, ultrasonic degassing for 15 min, then sealed and placed in an oven at 65°C for 21 h, then transferred into a stainless steel reaction kettle with a polytetrafluoroethylene liner, heated to 100°C, reacted for 21 h, then dried at room temperature for 3 d, dried at 60°C for 1 d, then heated to 500°C at a rate of 4°C / min in a muffle furnace, calcined for 4 h, to obtain a hierarchical porous silica gel carrier;

[0059] (2) 800 g of the hierarchical porous silica gel carrier obtained in (1) and 240 g of 3-methacryloyloxypropyltrimethoxysilane were added into 8 kg of tetrahydrofuran and heated to 75°C for 2 h, cooled to room temperature, and the solid was filtered, washed and dried to obtain a hierarchical porous silica gel carrier containing carbon-carbon double bonds;

[0060] (3) Under nitrogen protection, 800 g of the hierarchical porous silica gel carrier containing carbon-carbon double bonds obtained in (2) was added into 8 kg of a cyclohexanol / water mixed solution (mixed according to a weight ratio of 1:19) and ultrasonically dispersed for 25 min, then 1.6 kg of N-isopropyl acrylamide and 6.4 g of azobisisobutyronitrile were added, stirred at room temperature for 2 h, then heated to 75°C, reacted for 18 h, cooled to room temperature, centrifuged, and the solid was washed and dried to obtain a CO2 pressure swing adsorption silica gel.

[0061] Comparative Example 2: Comparative Example 2 differs from Example 2 in that N-isopropyl acrylamide is not grafted, and the specific preparation process is as follows: a specific preparation method of a CO2 pressure swing adsorption silica gel, comprising the following steps:

[0062] (1) 170 g of polyethylene glycol, 335 g of triblock copolymer P123 were added into 1.8 kg of hydrochloric acid solution with a concentration of 1 mol / L, stirred at room temperature for 35 min, cooled to 5°C, then 1 kg of tetraethyl orthosilicate was added, stirred for 1.5 h, ultrasonic degassing for 15 min, then sealed and placed in an oven at 65°C for 21 h, then transferred into a stainless steel reaction kettle with a polytetrafluoroethylene liner, heated to 100°C, reacted for 21 h, then dried at room temperature for 3 d, dried at 60°C for 1 d, then heated to 500°C at a rate of 4°C / min in a muffle furnace, calcined for 4 h, to obtain a hierarchical porous silica gel carrier;

[0063] (2) 800 g of the hierarchical porous silica support obtained in (1) and 240 g of 3-methacryloxypropyltrimethoxysilane were added to 8 kg of tetrahydrofuran, and the mixture was heated to 75 °C and reacted for 2 h. After cooling to room temperature, the solid was filtered, washed, and dried. Then, 200 g of 1-vinyl-3-ethylimidazole bromide and 8 g of benzoyl peroxide were added to 8 kg of toluene, and the mixture was heated to 110 °C and reacted for 6 h. After cooling to room temperature, the solid was filtered, washed, and dried to obtain the CO2 pressure swing adsorption silica gel.

[0064] Comparative Example 3: Comparative Example 3 differs from Example 2 in that no polyethylene glycol was added in step (1).

[0065] Comparative Example 4: Comparative Example 4 differs from Example 2 in that no triblock copolymer P123 was added in step (1).

[0066] Comparative Example 5: Comparative Example 5 differs from Example 2 in that 1-vinyl-3-ethylimidazole bromide was loaded on the hierarchical porous silica support by physical impregnation. The specific preparation method is as follows: a specific preparation method of CO2 pressure swing adsorption silica gel, comprising the following steps:

[0067] (1) 170 g of polyethylene glycol and 335 g of triblock copolymer P123 were added to 1.8 kg of a 1 mol / L hydrochloric acid solution, stirred at room temperature for 35 min, cooled to 5 °C, and then 1 kg of tetraethyl orthosilicate was added. The mixture was stirred for 1.5 h, degassed by ultrasonic for 15 min, sealed, and then placed in an oven at 65 °C for 21 h. Then, the mixture was transferred to a stainless steel reaction kettle with a polytetrafluoroethylene liner, heated to 100 °C, and reacted for 21 h. After cooling to room temperature, the mixture was dried for 3 d and then dried at 60 °C for 1 d. Then, the mixture was heated to 500 °C at a rate of 4 °C / min in a muffle furnace and calcined for 4 h to obtain a hierarchical porous silica support;

[0068] (2) 800 g of the hierarchical porous silica support obtained in (1) and 240 g of 3-methacryloxypropyltrimethoxysilane were added to 8 kg of tetrahydrofuran, and the mixture was heated to 75 °C and reacted for 2 h. After cooling to room temperature, the solid was filtered, washed, and dried. Then, 200 g of 1-vinyl-3-ethylimidazole bromide and 8 g of benzoyl peroxide were added to 8 kg of toluene, and the mixture was heated to 110 °C and reacted for 6 h. After cooling to room temperature, the solid was filtered, washed, and dried to obtain the CO2 pressure swing adsorption silica gel.

[0069] (3) Add 800g of the multi-level porous silica carrier containing the thermosensitive poly(N-isopropylacrylamide) layer obtained in (2) and 200g of 1-vinyl-3-ethylimidazolium bromide to 8kg of toluene, stir at room temperature for 24h, centrifuge, and the solid is washed and dried to obtain CO2 pressure swing adsorption silica gel.

[0070] Specific application: A simulated gas containing 20% ​​CO2, 70% N2, and 10% O2 (by volume) was used. The humidity range was adjusted by adding water vapor. CO2 adsorption / desorption tests were conducted on silica gels prepared according to Examples 1-3 and Comparative Examples 1-5 at low (15%), medium (50%), and high (80%) humidity levels. The tests were performed according to the following requirements:

[0071] 0-30% gas humidity environment: The adsorption stage is carried out at 25℃ and normal pressure, with an adsorption gas velocity of 1500 Nm³ / h·m³ and an adsorption time of 180s; the desorption stage is carried out at 45℃ and 0.1 bar, with nitrogen back purging during desorption, a flow rate of 20% of the adsorption gas velocity, a pressure of 0.1 bar, and a desorption time of 90s.

[0072] 30-70% gas humidity environment: The adsorption stage is carried out at 25℃ and normal pressure, with an adsorption gas velocity of 2000 Nm³ / h·m³ and an adsorption time of 150s; the desorption stage is carried out at 40℃ and 0.1 bar, with nitrogen back purging during desorption, a flow rate of 40% of the adsorption gas velocity, a pressure of 0.1 bar, and a desorption time of 60s.

[0073] In an environment with a gas humidity of over 70%: the adsorption stage is carried out at 25℃ and 1.2 bar, with an adsorption gas velocity of 1200 Nm³ / h·m³ and an adsorption time of 240 s; the desorption stage is carried out at 40℃ and 0.05 bar, with nitrogen back-purge during desorption at a flow rate of 80% of the adsorption gas velocity and a pressure of 0.15 bar, using a periodic purging method of 10 s purging followed by a 5 s pause, and a desorption time of 120 s.

[0074] CO2 adsorption capacity is calculated using the formula q. Calculate, where C in / C out Where t is the inlet and outlet CO2 concentration (mol / m³), Q is the gas flow rate (m³ / h), and t is the outlet CO2 concentration (mol / m³). b M represents the breakthrough time (h), m represents the sample mass (kg), and M represents the breakthrough time. CO2 =44 g / mol, and the experimental results are shown in Table 1.

[0075] CO2 adsorption rate is calculated according to the formula v The calculations and experimental results are shown in Table 1.

[0076] The CO2 desorption rate is calculated according to the formula r = (q0- q1) / q0 wherein q0 is the CO2 adsorption capacity of the examples and comparative examples, q1 is the CO2 residual adsorption capacity of the examples and comparative examples after desorption (calculated by gas chromatography GC method), and q0- q1 is the CO2 desorption amount of the examples and comparative examples. 残留 The experimental results are shown in Table 1.

[0077] Cyclic stability test: The CO2 adsorption / desorption test process of the silica gel prepared according to Examples 1-3 and Comparative Examples 1-5 is one cycle, and the cyclic stability test is carried out for one hundred cycles under low, medium and high humidity respectively, the change of the adsorption capacity is recorded, and the "cycle number-adsorption capacity" curves of Examples 1-3 and Comparative Examples 1-5 under low, medium and high humidity are drawn, and the experimental results are shown in Figures 1-8

[0078] Adsorption capacity and desorption rate test of Example 2 under different gas humidity environment: using simulated gas containing 20% CO2, 70% N2 and 10% O2, the gas humidity range is adjusted by adding water vapor, and the CO2 adsorption / desorption test of the silica gel prepared according to Example 2 is carried out under 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100% humidity respectively: the test is carried out according to the following requirements: the adsorption stage is carried out at 25°C and normal pressure, the adsorption gas speed is 2000 Nm³ / h·m³, and the adsorption time is 150s; the desorption stage is carried out at 40°C and 0.1 bar, and nitrogen is used for reverse blowing during the desorption process, the flow rate is 40% of the adsorption gas speed, the pressure is 0.1 bar, the desorption time is 60s, and the experimental results are shown in Figure 9 and Figure 10

[0079] Table 1 Adsorption capacity, adsorption rate and desorption rate test results

[0080]

[0081] Performance analysis:

[0082] From the experimental data in Table 1 and Figures 1-8 It can be seen from the experimental data in Table 1 and

[0083] ​​This may be because the imidazole cation units grafted on the surface of the silica gel prepared in Example 2 adsorb CO2 through π-π conjugation and electrostatic attraction, the π electron cloud of the imidazole ring forms a π-π interaction with the π bond of the CO2 molecule, and the quaternary ammonium cation N + of CO2 produces electrostatic attraction to form a stable [Im + ···CO2] complex, which directionally captures CO2 molecules, and this chemical adsorption can provide higher binding energy than physical adsorption, especially at low humidity (15%), the CO2 molecules directly interact with the imidazole sites, and the adsorption capacity is significantly higher than that of Comparative Example 1; at the same time, the ionic liquid is grafted and fixed in the pore channel of the silica gel by a chemical method, avoiding the loss of the ionic liquid by physical impregnation, such as in Comparative Example 5, ensuring that the adsorption capacity remains high in a high-humidity environment (80%) and is much higher than that of Comparative Example 5; finally, in the adsorption process at low temperature (25°C, <32°C), the temperature-sensitive layer is in a hydrophilic and relaxed hydration state, forming a polar surface, which enhances the migration ability of CO2 molecules to the imidazole sites, and the amide group forms a hydrogen bond with the carbonyl group of CO2 to assist fixation, further improving the adsorption capacity, even though the water content increases at medium humidity (50%), the multi-level pore channel provides sufficient diffusion paths, and the temperature-sensitive layer remains relaxed in the adsorption stage and does not block the pore openings, ensuring that CO2 molecules can still effectively contact the imidazole sites, and by increasing the adsorption pressure in a high-humidity environment (80%), the adsorption capacity is maintained at a high level through the use of partial pressure driving to enhance adsorption.

[0084] In terms of the adsorption rate, this may be because the silica gel prepared in Example 2 has a multi-level pore structure, in which the macropores serve as gas transmission channels and the mesopores provide abundant adsorption sites, shortening the diffusion distance of CO2 molecules in the pore channel, and the adsorption rate is above 96% at different humidities, which is significantly higher than that of Comparative Examples 3 and 4 (incomplete multi-level pore structure), proving the key role of multi-level pores in rapid gas diffusion; at the same time, in the adsorption process, the temperature is 25°C, and in different humidity environments, the relaxed conformation of the temperature-sensitive layer increases the polarity and hydrophilicity of the silica gel surface, promoting the conduction of CO2 at the gas-solid or gas-liquid-solid interface, making it easier for CO2 molecules to be captured by the adsorption sites, and the adsorption rate of Example 2 is much higher than that of Comparative Example 2 at high humidity, which reflects the role of the temperature-sensitive layer in reducing mass transfer resistance.

[0085] In terms of the desorption rate, this may be because when the temperature is raised to 40-45°C in the desorption stage, the temperature-sensitive layer of Example 2 changes from a hydrophilic and relaxed state to a hydrophobic and contracted state, producing a double effect:

[0086] 1. Pore expansion: The shrinkage of the temperature-sensitive layer reduces the steric hindrance of the pore opening, increases the pore size, directly reduces the diffusion resistance of CO2, and leads to an increase in desorption rate. The desorption rate of Example 2 is 97.2% at high humidity, while the desorption rate of Comparative Example 2 (without desorption auxiliary structure) is only 30.5%, showing the key role of conformational transition in desorption.

[0087] 2. Site exposure: The shrinkage of the temperature-sensitive layer releases the wrapped imidazole sites, making the [Im + ···CO2] complex more easily broken, combined with reduced pressure and nitrogen blowing, to achieve high-efficiency desorption.

[0088] In terms of cycle stability, Example 2 has excellent performance in cycle stability, which is mainly due to its unique functional groups and structure, and it also has different performances in different humidity environments:

[0089] The ionic liquid functional layer in Example 2 is covalently bonded to the inner wall of the silica gel pore, containing imidazole cation units. This covalent bonding method has higher stability compared to the physical impregnation method used in Comparative Example 5, where 1-vinyl-3-ethylimidazole bromide is loaded on the hierarchical pore silica gel carrier. In the process of multiple cycles, the covalently bonded ionic liquid is not easily detached or decomposed, ensuring that the number of imidazole sites interacting with CO2 remains stable. From a microscopic perspective, during each adsorption, the π-electron cloud of the imidazole ring forms a π-π interaction with the π-bond of the CO2 molecule, while the dipole moment of the quaternary ammonium cation N + forms a stable [Im + ···CO2] complex with the dipole moment of CO2; During desorption, although the temperature and pressure change, the imidazole cation units remain on the surface of the silica gel due to the stability of the covalent bond, allowing the material to maintain a high adsorption capacity after multiple cycles in different humidity environments.

[0090] The temperature-sensitive poly-N-isopropyl acrylamide layer is grafted on the surface and pore opening of the silica gel particles, with a low critical solution temperature of 32°C. During the adsorption stage, the temperature is 25°C, and the poly-N-isopropyl acrylamide is in a hydrophilic and relaxed conformation. During the desorption stage, the temperature is 40-45°C, and the isopropyl hydrophobic effect dominates, causing the poly-N-isopropyl acrylamide segments to shrink into a globular shape, releasing the wrapped imidazole sites. The change in steric hindrance caused by the conformational transition leads to an increase in pore size, directly reducing the diffusion resistance of CO2 and increasing the desorption rate. This conformational transition is reversible, and the temperature-sensitive poly-N-isopropyl acrylamide layer can repeatedly switch between relaxed and contracted states, ensuring the cycle stability of the material's adsorption and desorption performance in different humidity environments.

[0091] The multi-level pore silica gel carrier of Example 2 has a multi-level pore structure of macropores and mesopores, the macropores provide a fast transmission channel for the gas, enabling the CO2 molecules to quickly reach the inside of the material; the mesopores provide abundant adsorption sites, increasing the contact area with CO2. This multi-level pore structure can effectively function under different humidity environments. Under low humidity environment, gas diffusion is relatively easy, and the multi-level pore structure ensures that CO2 molecules can smoothly reach the functional areas of the ionic liquid functional layer and the temperature-sensitive poly-N-isopropyl acrylamide layer; under high humidity environment, although water may occupy part of the pore space, the presence of macropores and mesopores still provides diffusion paths for CO2 molecules, avoiding the decline in adsorption performance caused by water blockage. At the same time, the multi-level pore structure remains stable during the cycle process and does not collapse or deform due to repeated adsorption and desorption, ensuring the stability of the overall performance of the material.

[0092] Performance under different humidity environments

[0093] Low humidity environment (15%): Under low humidity environment, the adsorption capacity of Example 2 is high and the cycle stability is good, because the ionic liquid functional layer can fully exert its specific interaction with CO2, the temperature-sensitive poly-N-isopropyl acrylamide layer is in a relaxed hydrated state at low temperature, enhancing the polarity of the silica gel surface and promoting the adsorption of CO2. Moreover, due to the low humidity, the interference of water on the adsorption and desorption process is small, and the functional groups and structure of the material can stably function, and the adsorption capacity changes little after multiple cycles.

[0094] Medium humidity environment (50%): Under medium humidity environment, the appropriate amount of water helps the dissolution and diffusion of CO2 under the hydration of the temperature-sensitive poly-N-isopropyl acrylamide layer, further improving the adsorption efficiency. At the same time, the synergistic effect of the ionic liquid functional layer and the temperature-sensitive poly-N-isopropyl acrylamide layer remains stable, and the multi-level pore structure ensures the transmission of the gas, so that the material can maintain high adsorption capacity and good cycle stability during multiple cycles.

[0095] High humidity environment (80%): High humidity environment is a challenge for adsorption materials, but Example 2 still shows good performance. Although water competes with CO2 for adsorption, increasing the adsorption pressure can increase the adsorption driving force of CO2. The temperature-sensitive poly-N-isopropyl acrylamide layer can still maintain a relaxed state under high humidity to provide an adsorption channel for CO2, and can effectively shrink during the desorption stage to release the adsorption sites. The multi-level pore structure can also effectively disperse water under high humidity, avoiding the blockage of pores caused by water aggregation, thereby ensuring that the material still has high adsorption capacity and good cycle stability after multiple cycles under high humidity environment.

[0096] FromFigure 9 and Figure 10 From the data changes of the adsorption capacity and desorption rate, it can be predicted that the CO2 PSA silica gel prepared in Example 2 has excellent application suitability and high efficiency in different adsorption / desorption processes under different gas humidity environments. Under the gas humidity environment of 0-10%, the adsorption capacity rises rapidly with the increase of gas humidity and maintains at a high level, and the desorption rate is also at a high level. This may be because, in the unique "ionic liquid core-temperature sensitive shell" core-shell structure of the silica gel, the imidazole cation unit in the ionic liquid functional layer can specifically bind with CO2 molecules, and is less disturbed by other molecules at low humidity, so it can fully play its role. At the same time, although the temperature-sensitive poly-N-isopropyl acrylamide layer does not change significantly in conformation due to humidity, it can still provide a certain polar adsorption auxiliary effect. During the desorption stage, the poly-N-isopropyl acrylamide layer will also shrink to a certain extent as the temperature rises, and the desorption rate can still be maintained at a high level with the cooperation of nitrogen blowing in the process.

[0097] In the gas humidity range of 10-80%, the adsorption capacity and desorption rate are relatively stable. On the one hand, the multi-level pore structure of the silica gel carrier provides good transmission channels for the gas, so that CO2 can reach the adsorption site smoothly. On the other hand, the appropriate amount of water vapor promotes the dissolution and diffusion of CO2 under the action of the temperature-sensitive layer. The presence of the temperature-sensitive layer can also assist adsorption and desorption through conformational changes during the adsorption and desorption processes, so that the silica gel can work efficiently and continuously in this humidity range.

[0098] In the gas humidity environment of 80-100%, the adsorption capacity and desorption rate decrease significantly. This is because a large number of water molecules will compete with CO2 for adsorption sites, and part of the pores will be occupied by water, hindering the diffusion and adsorption of CO2. However, through the desorption conditions set in the experiment, i.e. using 40°C and 0.1 bar conditions during the desorption stage, and through nitrogen reverse blowing (flow rate is 40% of the adsorption gas speed), the adverse effects of high humidity can be overcome to a certain extent. The temperature rise promotes the shrinkage of the temperature-sensitive layer, releasing the occupied adsorption sites, and the nitrogen blowing can effectively remove CO2 and part of the water vapor. Although the performance of the silica gel has decreased significantly, combined with the desorption process under high gas humidity environment and the data in Table 1, it can be predicted that the adsorption / desorption process under different gas humidity environments using the silica gel of the present application can meet the basic requirements of CO2 adsorption and desorption in actual use. In summary, based on the adaptability to different humidity environments brought by the unique structure and the reasonable desorption condition setting, the CO2 PSA silica gel prepared in Example 2 is applicable in a wide range of gas humidity, and can provide reliable solutions for various industrial scenarios involving CO2 separation.

[0099] The above description is only the preferred embodiment of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can make equivalent substitutions or changes according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A CO2 pressure swing adsorption silica gel, characterized in that, It includes a multi-level porous silica carrier, on the surface of which an ionic liquid functional layer and a thermosensitive poly(N-isopropylacrylamide) layer are sequentially grafted to form an "ionic liquid core-thermosensitive shell" core-shell structure. The silicone carrier has a multi-level pore structure including macropores with a pore size of 0.1-5μm and mesopores with a pore size of 3-5nm; The ionic liquid functional layer is covalently fixed to the inner wall of the silica gel channel and contains imidazole cation units with the structural formula: -CH2-CH-(Im + Br - )-, where Im + It is a 1-vinyl-3-ethylimidazolium cation; The thermosensitive poly(N-isopropylacrylamide) layer is grafted onto the surface of the silica particles and the pore openings, and has a low critical melting temperature of 32°C. The ionic liquid functional layer is covalently anchored by Si-O-Si bonds formed by the condensation of 3-methacryloxypropyltrimethoxysilane with silanol groups on the surface of silica gel, and forms a graft polymer chain with 1-vinyl-3-ethylimidazolium bromide through a free radical reaction. The thermosensitive poly(N-isopropylacrylamide) layer is grafted via a free radical reaction. After grafting, the poly(N-isopropylacrylamide) segments are in a stretched hydrated state below 32°C and in a contracted hydrophobic state above 32°C.

2. The method for preparing CO2 pressure swing adsorption silica gel according to claim 1, characterized in that, Includes the following steps: S1. Preparation of multi-level porous silica support: Polyethylene glycol and triblock copolymer P123 were added to hydrochloric acid solution and stirred at room temperature for 30-40 min. The temperature was then lowered to 0-10℃, and tetraethyl orthosilicate was added. The mixture was stirred for 1-2 h and ultrasonically degassed for 10-20 min. After sealing, it was placed in an oven at 60-70℃ and dried for 18-24 h. Then, it was transferred to a stainless steel reactor with a polytetrafluoroethylene liner, heated to 90-110℃, and reacted for 18-24 h. After drying at room temperature for 3 days and at 60℃ for 1 day, it was then calcined in a muffle furnace at a rate of 3-5℃ / min to 450-550℃ for 3-5 h to obtain the multi-level porous silica support. S2, grafting of ionic liquid functional layer: The hierarchical porous silica support obtained in S1 is added to tetrahydrofuran with 3-methacryloxypropyltrimethoxysilane and heated to 70-80℃ for 1-3h. After cooling to room temperature, the solid is filtered, washed and dried. Then, it is reacted with 1-vinyl-3-ethylimidazolium bromide and benzoyl peroxide in toluene and heated to 100-120℃ for 4-8h. After cooling to room temperature, the solid is filtered, washed and dried to obtain a hierarchical porous silica support containing an ionic liquid layer. S3, Grafting of thermosensitive poly(N-isopropylacrylamide) layer: Under nitrogen protection, the multi-level porous silica support containing the ionic liquid layer in S2 is added to a cyclohexanol / water mixed solution and ultrasonically dispersed for 20-30 min. Then, N-isopropylacrylamide and azobisisobutyronitrile are added, and the mixture is stirred at room temperature for 1-3 h. Then, the temperature is raised to 70-80℃ and the reaction is carried out for 12-24 h. After cooling to room temperature, the mixture is centrifuged, and the solid is washed and dried to obtain CO2 pressure swing adsorption silica gel.

3. The method for preparing CO2 pressure swing adsorption silica gel according to claim 2, characterized in that, In S1, the weight ratio of polyethylene glycol, triblock copolymer P123, tetraethyl orthosilicate, and hydrochloric acid solution is 0.14-0.2:0.27-0.4:1:1.5-2.

0.

4. The method for preparing CO2 pressure swing adsorption silica gel according to claim 2, characterized in that, The concentration of the hydrochloric acid solution in S1 is 1 mol / L.

5. The method for preparing CO2 pressure swing adsorption silica gel according to claim 2, characterized in that, The multi-level porous silica carrier, 3-methacryloyloxypropyltrimethoxysilane, 1-vinyl-3-ethylimidazolium bromide, benzoyl peroxide, tetrahydrofuran, and toluene in S2 are present in a weight ratio of 1:0.2-0.4:0.2-0.3:0.005-0.015:8-12:8-12.

6. The method for preparing CO2 pressure swing adsorption silica gel according to claim 2, characterized in that, The S3 contains a multi-level porous silica carrier with an ionic liquid layer, N-isopropylacrylamide, azobisisobutyronitrile, and a cyclohexanol / water mixed solution in a weight ratio of 1:1.5-2.5:0.006-0.012:8-12.

7. The method for preparing CO2 pressure swing adsorption silica gel according to claim 2, characterized in that, The cyclohexanol / water mixed solution in S3 refers to a mixture of cyclohexanol and water at a weight ratio of 1:

19.

8. The application of the CO2 pressure swing adsorption silica gel according to claim 1 in the CO2 pressure swing adsorption process under a wide range of gas humidity conditions, characterized in that: 0 < gas humidity environment < 30%: The adsorption stage is carried out at 25℃ and normal pressure, with an adsorption gas velocity of 1500 Nm³ / h·m³ and an adsorption time of 180s; the desorption stage is carried out at 45℃ and 0.1 bar, with nitrogen back purging during desorption, a flow rate of 20% of the adsorption gas velocity, a pressure of 0.1 bar, and a desorption time of 90s. 30% < gas humidity environment < 70%: The adsorption stage is carried out at 25℃ and normal pressure, with an adsorption gas velocity of 2000 Nm³ / h·m³ and an adsorption time of 150s; the desorption stage is carried out at 40℃ and 0.1 bar, with nitrogen back purging during desorption, a flow rate of 40% of the adsorption gas velocity, a pressure of 0.1 bar, and a desorption time of 60s. In an environment with 70% or less gas humidity: the adsorption stage is carried out at 25℃ and 1.2 bar, with an adsorption gas velocity of 1200 Nm³ / h·m³ and an adsorption time of 240 s; the desorption stage is carried out at 40℃ and 0.05 bar, with nitrogen back-purge at a flow rate of 80% of the adsorption gas velocity and a pressure of 0.15 bar, using a periodic purging method of 10 s purging followed by a 5 s pause, and a desorption time of 120 s.

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