A synergistically modified molecular sieve with high selective adsorption performance and a preparation method thereof

Abstract

The application discloses a kind of synergistically modified molecular sieves with high selective adsorption performance and a preparation method thereof.The method comprises the following steps: treating 13X type molecular sieves with alkali to construct hierarchical pore structure, then performing metal cation exchange, then grafting amine-containing organosilicon compounds, and finally performing outer surface hydrophobic end-capping with hexamethyldisilazane.The obtained molecular sieves have CO2 adsorption capacity of 3.12 mmol / g at 25℃ and 1 bar, CO2 / N2 selectivity of 142, activity retention rate of 94.2% after 5 cycles, and water adsorption capacity as low as 3.6 wt%.Through the synergistic effect of hierarchical pore construction, metal exchange, amine grafting and hydrophobic end-capping, the application realizes high selectivity, high capacity, high humidity stability and good regeneration performance of the molecular sieves, and is suitable for CO2 / N2 and CO2 / CH4 mixed gas separation.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve materials technology, and in particular to a synergistically modified molecular sieve with high selective adsorption performance and its preparation method. Background Technology

[0002] Molecular sieves, due to their regular pore structure, large specific surface area, and tunable surface properties, have wide applications in gas adsorption and separation. However, unmodified molecular sieves have limited selective adsorption capacity for carbon dioxide, especially in complex gas mixtures (such as CO2 / N2 and CO2 / CH4), making efficient separation difficult. Existing technologies improve adsorption selectivity by introducing metal cations through ion exchange or by surface functionalization through organic amine grafting, but these single modification methods often have limitations: metal ion exchange offers limited improvement in adsorption capacity, and while amine functionalization can enhance the affinity for acidic CO2 gas, the amine groups easily clog the pores and have poor water resistance. Furthermore, conventional modification methods struggle to balance high selectivity and high adsorption capacity; the microporous structure of the molecular sieve is easily damaged or blocked during modification, leading to a decrease in adsorption kinetics.

[0003] To address these issues, some studies have attempted multi-step composite modification strategies, such as pore formation followed by grafting or metal-amine co-modification. However, existing composite modification methods still suffer from drawbacks such as complex processes, unclear synergistic effects, and insufficient hydrophobic stability, especially with significant degradation of adsorption performance under humid conditions. Therefore, developing a synergistic modification method for molecular sieves that combines high selectivity, high adsorption capacity, and good wet stability is of significant research and application value. Summary of the Invention

[0004] To address the aforementioned issues, this invention proposes a synergistically modified molecular sieve with high selective adsorption performance and its preparation method. Through a three-step synergistic modification process involving alkali treatment to construct hierarchical pores, introduction of metal cation exchange, and grafting with aminosilane, the selective adsorption performance of the molecular sieve for carbon dioxide is significantly improved.

[0005] This invention can be achieved through the following technical solutions: A method for preparing a synergistically modified molecular sieve with highly selective adsorption performance includes the following steps: S1. The 13X type molecular sieve powder is pulverized and passed through a 40-100 mesh sieve, dried at 80-150℃ for 2-24 hours, then activated at 250-350℃ under a nitrogen atmosphere for 1-8 hours, and contacted with a 0.2-0.5 mol / L sodium hydroxide solution at 50-70℃ for 0.5-2 hours to perform desilication treatment, thereby obtaining a hierarchical porous molecular sieve; the mesopore volume of the hierarchical porous molecular sieve is 0.10-0.30 cm3 / g, and the micropore volume retention rate is 70-90%; S2. The hierarchical porous molecular sieve is contacted with an exchange solution containing metal cations to perform ion exchange, thereby obtaining the first exchange molecular sieve; the ion exchange temperature is 60-80℃, the time is 2-12h, the concentration of the exchange solution is 0.01-1.0mol / L, the liquid-to-solid ratio is 5-50mL / g, and the number of exchanges is 1-3 times. S3. The first exchange molecular sieve is grafted with anamine-containing organosilicon compound under reflux in anhydrous toluene for 6-12 h to obtain anamine-functionalized molecular sieve; the amine-functionalized molecular sieve is contacted with hexamethyldisilazane in anhydrous toluene and reacted at 20-120℃ for 0.5-12 h to obtain a synergistically modified molecular sieve with high selective adsorption performance; the amine grafting and hexamethyldisilazane treatment are performed sequentially and without exchange.

[0006] Preferably, the desilication treatment further includes acid washing, using a 0.05 mol / L hydrochloric acid solution, for 3 hours.

[0007] Preferably, the metal cation is Mg2+ or Ca2+.

[0008] Preferably, the ion exchange treatment further includes calcination activation, with a calcination temperature of 250-550℃ and a calcination time of 1-10h.

[0009] Preferably, the amine-containing organosilicon compound is selected from 3-aminopropyltriethoxysilane or 3-aminopropyltrimethoxysilane, and the amount used is 0.2-4.0 mmol / g molecular sieve.

[0010] Application of a synergistically modified molecular sieve with high selective adsorption performance in the separation of CO2 / N2 mixed gas and CO2 / CH4 mixed gas. The beneficial effects of this invention are: This invention significantly improves the selective adsorption performance of molecular sieves for carbon dioxide through a three-step synergistic modification process involving alkali treatment to construct hierarchical pores, metal cation exchange, and aminosilane grafting. Alkali treatment introduces mesopores while maintaining the microporous framework structure, forming bimodal channels that provide ample grafting space for amine groups, preventing micropore blockage and improving gas diffusion dynamics. The introduction of metal cations enhances the electric field strength within the channels, increasing the affinity for polar CO2 molecules through electrostatic interactions. Aminosilane grafting achieves chemisorption of CO2 through acid-base interactions. The synergistic effect of these three processes forms a hydrophobic layer on the outer surface of the molecular sieve, reducing water adsorption to below 4.5 wt%, effectively inhibiting the poisoning and competitive adsorption of water vapor on the active sites of amine groups, and ensuring the molecular sieve maintains high selectivity even in humid environments. The synergistically modified molecular sieve prepared by this invention has a CO2 adsorption capacity of 3.12 mmol / g and a CO2 / N2 selectivity of 142 under conditions of 25℃ and 1 bar. After 5 cycles, the activity retention rate is as high as 94.2%, and the 5% breakthrough time is 56.4 min. It has high selectivity, high adsorption capacity, high humidity stability and excellent cycle regeneration performance, and has broad application prospects in the field of CO2 / N2 and CO2 / CH4 mixed gas separation. Attached Figure Description

[0011] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 The BET specific surface area and structural parameters of the molecular sieve are given. Figure 2 This represents the static CO2 adsorption capacity of the molecular sieve. Figure 3 The study aimed to evaluate the CO2 / N2 selectivity, static water adsorption capacity, cycling stability, and dynamic CO2 adsorption breakthrough time of the molecular sieve. Detailed Implementation

[0012] The following provides a detailed description of the embodiments of the present invention: These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and processes. However, the scope of protection of the present invention is not limited to the following embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions.

[0013] Example 1: A method for preparing a synergistically modified molecular sieve with high selective adsorption performance, comprising the following steps: S1. The 13X type molecular sieve powder is pulverized and passed through a 40-mesh sieve, dried at 80℃ for 24 hours, then activated at 250℃ under a nitrogen atmosphere for 8 hours, contacted with a 0.2 mol / L sodium hydroxide solution at 50℃ for 2 hours for desilication treatment, and then treated with a 0.03 mol / L hydrochloric acid solution for 3 hours to obtain a hierarchical porous molecular sieve; the mesopore volume of the hierarchical porous molecular sieve is 0.10 cm3 / g, and the micropore volume retention rate is 90%; S2. The hierarchical porous molecular sieve was contacted with an exchange solution containing Mg2+ for ion exchange. The concentration of the exchange solution was 0.01 mol / L and the liquid-to-solid ratio was 5 mL / g. The exchange was carried out at 60℃ for 12 h, and the exchange was performed once. Then, it was calcined at 250℃ for 10 h to obtain the first exchange molecular sieve. S3. The first exchange molecular sieve was grafted with 3-aminopropyltriethoxysilane under reflux in anhydrous toluene for 6 h, with the amount of aminosilane being 0.2 mmol / g of molecular sieve, to obtain anamine-functionalized molecular sieve; the amine-functionalized molecular sieve was then contacted with hexamethyldisilazane in anhydrous toluene and reacted at 20 °C for 12 h to obtain a synergistically modified molecular sieve with high selective adsorption performance.

[0014] Example 2: A method for preparing a synergistically modified molecular sieve with high selective adsorption performance, comprising the following steps: S1. The 13X type molecular sieve powder is pulverized and passed through a 70-mesh sieve, dried at 115℃ for 13 hours, then activated at 300℃ under a nitrogen atmosphere for 4.5 hours, contacted with 0.35 mol / L sodium hydroxide solution at 60℃ for 1.25 hours for desilication treatment, and then treated with 0.03 mol / L hydrochloric acid solution for 3 hours to obtain a hierarchical porous molecular sieve; the mesopore volume of the hierarchical porous molecular sieve is 0.20 cm3 / g, and the micropore volume retention rate is 80%; S2. The hierarchical porous molecular sieve was contacted with an exchange solution containing Ca2+ for ion exchange. The concentration of the exchange solution was 0.505 mol / L and the liquid-to-solid ratio was 27.5 mL / g. The exchange was carried out at 70℃ for 7 h, and the exchange was repeated twice. Then, it was calcined at 400℃ for 5.5 h to obtain the first exchange molecular sieve. S3. The first exchange molecular sieve was grafted with 3-aminopropyltrimethoxysilane under reflux in anhydrous toluene for 9 h, with the amount of aminosilane being 2.1 mmol / g of molecular sieve, to obtain anamine-functionalized molecular sieve; the amine-functionalized molecular sieve was then contacted with hexamethyldisilazane in anhydrous toluene and reacted at 70 °C for 6.25 h to obtain a synergistically modified molecular sieve with high selective adsorption performance.

[0015] Example 3: A method for preparing a synergistically modified molecular sieve with high selective adsorption performance, comprising the following steps: S1. The 13X type molecular sieve powder is pulverized and passed through a 100-mesh sieve, dried at 150℃ for 2 hours, then activated at 350℃ under a nitrogen atmosphere for 1 hour, and contacted with a 0.5 mol / L sodium hydroxide solution at 70℃ for 0.5 hours for desilication treatment. Finally, it is treated with a 0.03 mol / L hydrochloric acid solution for 3 hours to obtain a hierarchical porous molecular sieve. The mesopore volume of the hierarchical porous molecular sieve is 0.30 cm³ / g, and the micropore volume retention rate is 70%. S2. The hierarchical porous molecular sieve was contacted with an exchange solution containing Mg2+ for ion exchange. The concentration of the exchange solution was 1.0 mol / L and the liquid-to-solid ratio was 50 mL / g. The exchange was carried out at 80℃ for 2 h and the number of exchanges was 3. Then, it was calcined at 550℃ for 1 h to obtain the first exchange molecular sieve. S3. The first exchange molecular sieve was grafted with 3-aminopropyltriethoxysilane in anhydrous toluene for 12 h under reflux, with the amount of aminosilane being 4.0 mmol / g of molecular sieve, to obtain anamine-functionalized molecular sieve; the amine-functionalized molecular sieve was then contacted with hexamethyldisilazane in anhydrous toluene and reacted at 120 °C for 0.5 h to obtain a synergistically modified molecular sieve with high selective adsorption performance.

[0016] Example 4: A method for preparing a synergistically modified molecular sieve with high selective adsorption performance, comprising the following steps: S1. The 13X type molecular sieve powder is pulverized and passed through a 60-mesh sieve, dried at 110℃ for 12 hours, then activated at 300℃ under a nitrogen atmosphere for 4 hours, contacted with a 0.3 mol / L sodium hydroxide solution at 60℃ for 1 hour for desilication treatment, and then treated with a 0.03 mol / L hydrochloric acid solution for 3 hours to obtain a hierarchical porous molecular sieve; the mesopore volume of the hierarchical porous molecular sieve is 0.18 cm3 / g, and the micropore volume retention rate is 82%; S2. The hierarchical porous molecular sieve was contacted with an exchange solution containing Mg2+ for ion exchange. The concentration of the exchange solution was 0.2 mol / L and the liquid-to-solid ratio was 20 mL / g. The exchange was carried out at 70℃ for 6 h, and the exchange was repeated twice. Then, it was calcined at 400℃ for 5 h to obtain the first exchange molecular sieve. S3. The first exchange molecular sieve was grafted with 3-aminopropyltriethoxysilane in anhydrous toluene for 8 h under reflux, with the amount of aminosilane being 1.5 mmol / g of molecular sieve, to obtain anamine-functionalized molecular sieve; the amine-functionalized molecular sieve was then contacted with hexamethyldisilazane in anhydrous toluene and reacted at 80 °C for 4 h to obtain a synergistically modified molecular sieve with high selective adsorption performance.

[0017] Comparative Example 1: The difference between this comparative example and Example 1 is that no sodium hydroxide desilication treatment is performed.

[0018] A method for preparing a synergistically modified molecular sieve with highly selective adsorption performance includes the following steps: S1. The raw powder of 13X molecular sieve is crushed and passed through a 40-mesh sieve, dried at 80℃ for 24h, and then activated at 250℃ under a nitrogen atmosphere for 8h. Without sodium hydroxide desilication treatment, it is treated with 0.03mol / L hydrochloric acid solution for 3h to obtain activated molecular sieve without pores. S2. The activated molecular sieve was contacted with an exchange solution containing Mg2+ for ion exchange. The concentration of the exchange solution was 0.01 mol / L and the liquid-to-solid ratio was 5 mL / g. The exchange was carried out at 60℃ for 12 h, and the exchange was performed once. Then, it was calcined at 250℃ for 10 h to obtain the first exchange molecular sieve. S3. The first exchange molecular sieve was grafted with 3-aminopropyltriethoxysilane in anhydrous toluene for 6 h, and the amount of aminosilane was 0.2 mmol / g molecular sieve to obtain amine-functionalized molecular sieve; the amine-functionalized molecular sieve was contacted with hexamethyldisilazane in anhydrous toluene and reacted at 20 °C for 12 h to obtain synergistically modified molecular sieve.

[0019] Comparative Example 2: The difference between this comparative example and Example 1 is that no metal cation exchange treatment is performed.

[0020] A method for preparing a synergistically modified molecular sieve with highly selective adsorption performance includes the following steps: S1. The 13X type molecular sieve powder is pulverized and passed through a 40-mesh sieve, dried at 80℃ for 24 hours, then activated at 250℃ under a nitrogen atmosphere for 8 hours, contacted with a 0.2 mol / L sodium hydroxide solution at 50℃ for 2 hours for desilication treatment, and then treated with a 0.03 mol / L hydrochloric acid solution for 3 hours to obtain a hierarchical porous molecular sieve; the mesopore volume of the hierarchical porous molecular sieve is 0.10 cm3 / g, and the micropore volume retention rate is 90%; S2. Without performing metal cation exchange treatment, the hierarchical porous molecular sieve obtained in step S1 is directly calcined at 250°C for 10 hours and then used as the raw material for the next step. S3. The molecular sieve obtained in step S2 is refluxed and grafted with 3-aminopropyltriethoxysilane in anhydrous toluene for 6 h. The amount of aminosilane used is 0.2 mmol / g of molecular sieve to obtain amine-functionalized molecular sieve. The amine-functionalized molecular sieve is contacted with hexamethyldisilazane in anhydrous toluene and reacted at 20 °C for 12 h to obtain synergistically modified molecular sieve.

[0021] Comparative Example 3: The difference between this comparative example and Example 1 is that it does not undergo hexamethyldisilazane hydrophobic end-capping treatment.

[0022] S1. The 13X type molecular sieve powder is pulverized and passed through a 40-mesh sieve, dried at 80℃ for 24 hours, then activated at 250℃ under a nitrogen atmosphere for 8 hours, contacted with a 0.2 mol / L sodium hydroxide solution at 50℃ for 2 hours for desilication treatment, and then treated with a 0.03 mol / L hydrochloric acid solution for 3 hours to obtain a hierarchical porous molecular sieve; the mesopore volume of the hierarchical porous molecular sieve is 0.10 cm3 / g, and the micropore volume retention rate is 90%; S2. The hierarchical porous molecular sieve was contacted with an exchange solution containing Mg2+ for ion exchange. The concentration of the exchange solution was 0.01 mol / L and the liquid-to-solid ratio was 5 mL / g. The exchange was carried out at 60℃ for 12 h, and the exchange was performed once. Then, it was calcined at 250℃ for 10 h to obtain the first exchange molecular sieve. S3. The first exchange molecular sieve was grafted with 3-aminopropyltriethoxysilane in anhydrous toluene for 6 hours. The amount of aminosilane used was 0.2 mmol / g of molecular sieve to obtain anamine-functionalized molecular sieve. Without hexamethyldisilazane hydrophobic end-capping treatment, the synergistically modified molecular sieve was obtained directly.

[0023] Performance testing 1. BET specific surface area and structural parameters The determination was carried out in accordance with the GB / T 19587-2017 standard.

[0024] Table 1. BET specific surface area and structural parameters of molecular sieves

[0025] As shown in Table 1, all examples 1-4 constructed hierarchical pore structures with BET specific surface areas ranging from 328.7 to 385.6 m² / g, micropore volumes ranging from 0.18 to 0.22 cm³ / g, mesopore volumes ranging from 0.10 to 0.30 cm³ / g, micropore volume retention rates ranging from 70% to 90%, and average pore sizes ranging from 0.68 to 0.79 nm. With increasing alkali treatment intensity (from 0.2 mol / L, 50°C, 2 h in Example 1 to 0.5 mol / L, 70°C, 0.5 h in Example 3), mesopore volumes increased from 0.10 cm³ / g to 0.30 cm³ / g, micropore volume retention rates decreased from 90% to 70%, BET specific surface areas decreased from 385.6 m² / g to 328.7 m² / g, and average pore sizes increased from 0.68 nm to 0.79 nm. This indicates that the degree of mesopore introduction can be precisely adjusted by regulating the alkali treatment conditions, achieving the controllable construction of dual-modal channels while maintaining the microporous framework structure. Example 4, using moderate alkali treatment conditions (0.3 mol / L, 60℃, 1 h), achieved comprehensive performance with a mesopore volume of 0.18 cm³ / g, a micropore volume retention rate of 82%, and a BET specific surface area of ​​371.5 m² / g, demonstrating good pore structure balance.

[0026] In contrast, Comparative Example 1, which was not subjected to alkali treatment for desilication, had the highest BET specific surface area (412.8 m2 / g), the largest micropore volume (0.25 cm3 / g), and the smallest average pore size (0.61 nm). This indicates that it still maintains a complete pure microporous structure without bimodal channels. This will make it difficult for aminosilane molecules to enter the micropores during subsequent amino grafting, and they are prone to clogging the channels.

[0027] 2 CO2 static adsorption capacity 1.0 g of molecular sieve sample was activated at 300℃ for 2 h. The activated sample was placed in the sample tube of the adsorption instrument and high-purity CO2 gas was gradually introduced under constant temperature of 25℃. The equilibrium adsorption amount under different pressures was recorded.

[0028] Table 2. Static CO2 adsorption capacity of molecular sieves

[0029] Table 2 shows that the static CO2 adsorption capacity of Examples 1-4 at 25℃ and 1 bar was 2.80-3.12 mmol / g, and the static CO2 adsorption capacity at 25℃ and 0.15 bar was 1.52-1.68 mmol / g. This indicates that the three-step synergistic modification strategy of the present invention, which involves alkali treatment to construct hierarchical pores, metal cation exchange, and aminosilane grafting, effectively improves the CO2 adsorption capacity of the molecular sieve. The underlying mechanism is as follows: the mesopores in the hierarchical pore structure provide sufficient grafting space for the amino groups, avoiding micropore blockage; the introduction of Mg2+ or Ca2+ enhances the electric field strength within the pores, improving the affinity for polar CO2 molecules through electrostatic interaction; and the amino functional groups achieve chemisorption of CO2 through acid-base interactions. The synergistic effect of these three factors enables the molecular sieve to exhibit excellent CO2 capture performance under both atmospheric and low-pressure conditions.

[0030] In contrast, the CO2 adsorption capacity of Comparative Example 1 (pore-forming without alkali treatment) was significantly lower than that of the examples, with adsorption capacities of only 2.31 mmol / g and 1.04 mmol / g at 1 bar and 0.15 bar, respectively. This indicates that without desilication treatment, the molecular sieve only has a microporous structure, and amine grafting mainly occurs at the pore openings and outer surfaces. The grafting amount is limited and easily clogs the pores, resulting in insufficient adsorption sites. At the same time, the diffusion resistance increases, and the adsorption performance decreases significantly. The adsorption capacity of Comparative Example 2 (without metal cation exchange) (2.52 mmol / g at 1 bar and 1.21 mmol / g at 0.15 bar) was significantly lower than that of the examples. This indicates that the lack of metal ion exchange weakens the electric field strength within the pores, reduces the electrostatic capture ability of CO2, and thus affects the overall adsorption performance. Comparative Example 3 (without hydrophobic end-capping treatment) showed an adsorption capacity of only 0.15 mmol / g at 0.15 bar, far lower than that of the other examples (1.52-1.68 mmol / g), and this sample exhibited extremely strong hygroscopicity during the test. This indicates the key role of hydrophobic end-capping treatment: the surface of the unmodified molecular sieve is rich in silanol groups, which readily adsorb water vapor in humid environments (even if the test gas is high-purity CO2, the sample will still be exposed to air during transfer and loading). Water molecules compete with CO2 for adsorption sites, and the competitive effect of water vapor is more significant under low-pressure conditions, leading to a sharp decrease in CO2 adsorption capacity.

[0031] 3 CO2 / N2 selectivity Molecular sieve samples were loaded into a fixed-bed adsorption column, and a CO2 / N2 mixture (volume ratio 15:85, simulating flue gas composition) was prepared. The mixture was introduced at a constant flow rate under conditions of 25°C and 1 bar. The composition of the outlet gas was monitored online using a gas chromatograph, the breakthrough curve was recorded, and the breakthrough time of CO2 and N2 was calculated.

[0032] 4 Static water adsorption capacity The determination was carried out in accordance with the GB / T 6287-2021 standard.

[0033] 5 Cyclic stability Accurately weigh approximately 1.0 g of molecular sieve sample, activate it at 300℃ for 2 h under a nitrogen atmosphere, cool it, and place it in a desiccator for later use. Take approximately 0.5 g of the activated sample, weigh it accurately, and determine the initial static adsorption capacity of CO2 at 25℃ and 1 bar, denoted as Q1. After the determination, place the sample in a tube furnace, heat it to 120℃ under nitrogen purging, and desorb at this temperature for 2 h. Cool it to room temperature under nitrogen protection, and determine the static adsorption capacity of CO2 for the second cycle under the same conditions, denoted as Q2. Repeat the above desorption, regeneration, and adsorption determination operations to determine the static adsorption capacity of CO2 for the third, fourth, and fifth cycles, denoted as Q3, Q4, and Q5, respectively. Before each determination, the sample mass should be re-weighed and corrected using the following formula: Qncorrection = Qnmeasured × (m1 / mn), where m1 is the sample mass at the first determination and mn is the sample mass at the nth determination. The activity retention rate after the nth cycle is calculated using the following formula: Activity retention rate n (%) = (Qn / Q1) × 100%.

[0034] 6. CO2 dynamic adsorption breakthrough time The determination was carried out in accordance with the HG / T 2691-2024 standard.

[0035] Table 3 Performance test results of molecular sieves

[0036] As shown in Table 3, the synergistically modified molecular sieves prepared in Examples 1-4 all exhibited excellent CO2 adsorption and separation performance. Among them, Example 2 showed the best overall performance, with a CO2 / N2 selectivity of 142, an activity retention rate of 94.2% after 5 cycles, a 5% breakthrough time of 56.4 min, and an equilibrium water adsorption capacity of only 3.6 wt% under conditions of 25℃ and 50% relative humidity, indicating that it possesses high selectivity, high stability, and excellent hydrophobic properties.

[0037] Comparative Example 1, without alkali treatment to create pores, maintained a pure microporous structure with no bimodal channels. Amine grafting was mainly concentrated on the outer surface, resulting in a CO2 / N2 selectivity of only 30. After 5 cycles, the activity retention rate dropped to 81.8%, indicating that without a hierarchical pore structure, amine groups easily clog micropore channels, increasing diffusion resistance and significantly reducing adsorption kinetics and cycling stability. Comparative Example 2, without metal cation exchange, lacked non-framework metal sites within the molecular sieve channels. Although treated with alkali pore creation and amine grafting, it lacked metal-amine synergy, resulting in a CO2 / N2 selectivity of only 53, far lower than Example 1. This demonstrates that the introduction of metal cations plays an irreplaceable role in enhancing CO2 affinity and improving selectivity. Comparative Example 3, which was not treated with hexamethyldisilazane hydrophobic end-capping, had a water adsorption capacity as high as 36.8 wt%, which is about 9 times that of Example 1 (4.1 wt%). Under high humidity conditions, water vapor competed with CO2 for adsorption, resulting in a CO2 / N2 selectivity of only 78% and a breakthrough time of only 42.3 min, both of which were significantly worse than those of Example 1. This indicates that hydrophobic end-capping treatment on the outer surface is crucial for suppressing competitive adsorption of water vapor and improving adsorption selectivity and breakthrough time in humid environments.

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a synergistically modified molecular sieve with highly selective adsorption performance, characterized in that, Includes the following steps: S1. The 13X type molecular sieve powder is pulverized and passed through a 40-100 mesh sieve, dried at 80-150℃ for 2-24 hours, then activated at 250-350℃ under a nitrogen atmosphere for 1-8 hours, and contacted with a 0.2-0.5 mol / L sodium hydroxide solution at 50-70℃ for 0.5-2 hours to perform desilication treatment, thereby obtaining a hierarchical porous molecular sieve; the mesopore volume of the hierarchical porous molecular sieve is 0.10-0.30 cm3 / g, and the micropore volume retention rate is 70-90%; S2. The hierarchical porous molecular sieve is contacted with an exchange solution containing metal cations to perform ion exchange, thereby obtaining the first exchange molecular sieve; the ion exchange temperature is 60-80℃, the time is 2-12h, the concentration of the exchange solution is 0.01-1.0mol / L, the liquid-to-solid ratio is 5-50mL / g, and the number of exchanges is 1-3 times. S3. The first exchange molecular sieve is grafted with anamine-containing organosilicon compound under reflux in anhydrous toluene for 6-12 h to obtain anamine-functionalized molecular sieve; the amine-functionalized molecular sieve is contacted with hexamethyldisilazane in anhydrous toluene and reacted at 20-120℃ for 0.5-12 h to obtain a synergistically modified molecular sieve with high selective adsorption performance; the amine grafting and hexamethyldisilazane treatment are performed sequentially and without exchange.

2. The method for preparing the synergistically modified molecular sieve with high selective adsorption performance according to claim 1, characterized in that, The desilication process also includes acid washing, using a 0.05 mol / L hydrochloric acid solution for 3 hours.

3. The method for preparing the synergistically modified molecular sieve with high selective adsorption performance according to claim 1, characterized in that, The metal cation is Mg2+ or Ca2+.

4. The method for preparing the synergistically modified molecular sieve with high selective adsorption performance according to claim 1, characterized in that, The ion exchange treatment is followed by calcination activation, with a calcination temperature of 250-550℃ and a calcination time of 1-10h.

5. The method for preparing the synergistically modified molecular sieve with high selective adsorption performance according to claim 1, characterized in that, The amine-containing organosilicon compound is selected from 3-aminopropyltriethoxysilane or 3-aminopropyltrimethoxysilane, and the amount used is 0.2-4.0 mmol / g molecular sieve.

6. The application of the synergistically modified molecular sieve prepared by the method according to any one of claims 1-5 in the separation of CO2 / N2 mixed gas and CO2 / CH4 mixed gas.

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