Controllable preparation method of silver-loaded hierarchical pore shaped adsorbent and application thereof in adsorption separation of ethane / ethylene

Abstract

The application discloses a controllable preparation method of silver-loaded hierarchical pore formed adsorbent and application of the silver-loaded hierarchical pore formed adsorbent in ethane / ethylene adsorption separation, and has the steps that 1) after an organic ligand is completely dissolved in a weak alkaline solution, CMC is added to continue stirring, a modified CMC suspension is obtained, and then vacuum freeze drying is carried out to obtain a modified CMC gel; 2) the modified CMC gel is directly immersed into a MOF precursor solution to perform a solvothermal reaction, and a silver-loaded hierarchical pore formed adsorbent is prepared; wherein the MOF precursor solution is a solution uniformly mixed by a metal ligand, silver tetrafluoroborate, an organic solvent, hydrochloric acid and water. The preparation process is simple and the condition is mild, the obtained adsorbent has adjustable mesopore size on the premise of keeping original micropore and structural stability, has good separation effect on ethane / ethylene, can be repeatedly used, and is suitable for large-scale industrial application.

Description

Technical Field

[0001] This invention belongs to the field of adsorbent technology, specifically relating to a controllable preparation method of a silver-loaded hierarchical pore-formed adsorbent and its application in ethane / ethylene adsorption and separation. Background Technology

[0002] Olefin purification alone accounts for 0.3% of global energy consumption; therefore, alkane / olefin separation has been highlighted as one of the seven most important chemical reactions. Ethylene is one of the most widely used feedstock molecules in the production of polymers and high-value organic chemicals. Industrially, the separation of ethylene from ethane / ethylene mixtures relies heavily on cryogenic distillation technology, but this technology is costly and energy-intensive. Using energy-efficient and environmentally friendly adsorption technology based on porous solid materials to separate C2H4 / C2H6 mixtures is an alternative. In this context, developing suitable porous adsorbents for ethane / ethylene separation has significant commercial implications.

[0003] As a novel type of porous material, metal-organic frameworks (MOFs) possess strong network chemistry properties and hold particular promise for the separation of light hydrocarbons. Especially in the adsorption and separation of C2H4 / C2H6 mixtures, their adsorption selectivity and capacity are higher than traditional adsorbents (such as zeolites and carbon-based adsorbents). Currently, most common C2H4 / C2H6 separations are achieved through thermodynamically driven separation, such as immobilizing metal ions (e.g., Cu(I) and Ag(I)) on the pores to form selective π-complexes with ethylene. However, MOFs generated by traditional solvothermal methods are generally microporous, which, although possessing a high specific surface area, face difficulties in mass transfer and encapsulating large guest molecules. Hierarchical pores (micropores / mesopores / macropores) constructed based on microporous MOFs not only promote mass transfer processes but also exhibit high specific surface areas, showing good potential in the separation of C2H4 / C2H6 mixtures. However, traditional hierarchical pore materials suffer from insufficient stability, and controlling the size of the mesopores remains challenging.

[0004] Although MOFs exhibit excellent performance in separating olefins / alkanes, most MOFs synthesized via traditional solvothermal methods are in powder form, resulting in significant pressure drops in adsorption beds and hindering large-scale industrial applications. Therefore, obtaining non-powdered MOF adsorbents is a crucial prerequisite for their industrial application. Currently, MOF material forming methods are broadly categorized into in-situ growth and post-forming methods. Post-forming involves shaping pre-formed crystalline powders, but this method often leads to partial collapse of the pore structure and a significant reduction in crystallinity. In-situ growth involves growing MOFs on a specific substrate, yielding a molded adsorbent loaded with MOFs after the synthesis reaction. This method offers advantages such as low cost and simplicity, preserving the original structure; however, the resulting composite material typically suffers from poor stability, low MOF particle loading, and a significant decrease in adsorption performance, resulting in poor olefin / alkane separation. Summary of the Invention

[0005] The purpose of this invention is to provide a controllable preparation method for a silver-loaded hierarchical pore-shaped adsorbent and its application in the adsorption and separation of ethane / ethylene. The resulting shaped adsorbent maintains the original micropores and structural stability while also having a controllable mesopore size, resulting in good separation effect for ethane / ethylene and the ability to be repeatedly recycled.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A controllable preparation method for a silver-loaded hierarchical pore-formed adsorbent is provided, comprising the following steps: 1) After the organic ligand is completely dissolved in a weakly alkaline solution, carboxymethyl cellulose (CMC) is added and stirring is continued to obtain a modified CMC suspension. Then, the modified CMC gel is obtained by vacuum freeze-drying. 2) The modified CMC gel obtained in step 1) is directly immersed in the precursor solution of MOF to carry out a solvothermal reaction to obtain a silver-loaded hierarchical pore-forming adsorbent; wherein the precursor solution of MOF is a solution of metal ligand, silver tetrafluoroborate (AgBF4), organic solvent, hydrochloric acid and water uniformly mixed.

[0007] According to the above scheme, in step 1), the organic ligand is a mixture of terephthalic acid (H2BDC) and BDC-X, with a molar ratio of 1:0.25-4; wherein BDC-X is 2,5-dihydroxyterephthalic acid (BDC-(OH)2), 2-aminoterephthalic acid (BDC-NH2), or 2-sulfonic acid monosodium terephthalate (BDC-SO3Na).

[0008] According to the above scheme, in step 1), the pH of the weakly alkaline solution is no greater than 8.5. Preferably, it is one of ammonia water, sodium carbonate solution, or sodium bicarbonate solution.

[0009] According to the above scheme, in step 1), the molar mass ratio of organic ligand to CMC is 0.5-2 mmol: 400 mg; the volume mass ratio of weak alkaline solution to CMC is 15-25 mL: 400 mg.

[0010] According to the above scheme, in step 1), vacuum freeze drying is performed for 24-48 hours.

[0011] According to the above scheme, in step 2), the organic solvent is one of N,N-dimethylacetamide, dimethyl sulfoxide, or tetrahydrofuran.

[0012] According to the above scheme, in step 2), the metal ligand is either zirconium tetrachloride or hafnium tetrachloride.

[0013] According to the above scheme, in step 2), the volume ratio of organic solvent, hydrochloric acid and water in the MOF precursor solution is 1-20:1:1-10, and the concentration (mass percentage, wt%) of hydrochloric acid is 10%-35%. According to the above scheme, in step 2), the molar ratio of metal ligand to HCl in hydrochloric acid in the MOF precursor solution is 1:15-30; the molar ratio of metal ligand to silver tetrafluoroborate (AgBF4) is 1:1-5.

[0014] According to the above scheme, in step 2), the mass ratio of the modified CMC gel to AgBF4 is 2:1-4.

[0015] According to the above scheme, in step 2), the solvothermal reaction conditions are: 45-65℃, reaction time 12-24 h, and the entire process of step 2) is carried out under light-protected conditions. This invention provides an application of the above-mentioned silver-loaded hierarchical pore-forming adsorbent in ethane / ethylene gas separation.

[0016] According to the above scheme, the silver-loaded hierarchical pore-forming adsorbent is activated by being kept at 50-80 ℃ for 8-12 hours before ethane / ethylene gas separation.

[0017] This invention provides a controllable preparation method for a silver-loaded hierarchical pore-forming adsorbent. The method involves first modifying a CMC gel with organic ligands, then mixing it with a MOF precursor solution containing metal ligands, silver tetrafluoroborate, organic solvents, hydrochloric acid, and water for solvothermal preparation. The modification of the CMC gel with organic ligands better promotes the in-situ growth of the MOF on the gel substrate surface. The organic solvent, hydrochloric acid, and water are used to generate mesopores. By controlling the type and amount of organic solvent, the mesopore size is adjustable and controllable (4.0 nm-12 nm), which not only accelerates the gas mass transfer rate and increases the specific surface area but also exposes more metal sites, facilitating gas adsorption. Simultaneously, the in-situ introduction of Ag functional sites enhances the interaction between the adsorbent and ethylene, improving the ethylene / ethane selectivity.

[0018] The beneficial effects of this invention are as follows: 1. This invention provides a controllable preparation method for a silver-loaded hierarchical pore-forming adsorbent. The method promotes in-situ growth of MOFs by modifying CMC gel with organic ligands, generating mesopores with adjustable sizes. Simultaneously, Ag functional sites are introduced in situ. The resulting adsorbent exhibits good stability and excellent ethane / ethylene separation performance. The adsorption performance of the gel after forming decreases only slightly compared to before forming, resulting in good separation efficiency and the ability to separate high-purity ethylene. Furthermore, it possesses good regeneration performance, allowing for repeated recycling and demonstrating significant potential for industrial applications.

[0019] 2. The preparation process of this invention is simple and the conditions are mild. The gel raw material, carboxymethyl cellulose, is inexpensive and readily available, resulting in low cost and facilitating large-scale industrial production. Attached Figure Description

[0020] Figure 1 The images show the XRD patterns of the silver-loaded hierarchical pore-forming adsorbents prepared in Examples 1-3 and Comparative Example 4.

[0021] Figure 2 The N2 adsorption-desorption curves (top) and pore size distribution diagrams (bottom) of the silver-loaded hierarchical pore-forming adsorbents prepared in Examples 1-3 and Comparative Example 4 are shown.

[0022] Figure 3 The silver-loaded hierarchical pore-forming adsorbent prepared in Example 3 is shown in the image. Figure 3 The upper right corner of image b shows an optical photograph of the silver-loaded hierarchical pore-formed adsorbent.

[0023] Figure 4 The adsorption curves of ethane / ethylene for the silver-loaded hierarchical pore-forming adsorbents prepared in Example 3 and Comparative Examples 1-3 at 298 K are shown. Pressure: 0-1 bar.

[0024] Figure 5The graph shows the cyclic adsorption capacity of ethylene at 298 K for the silver-loaded hierarchical pore-formed adsorbent prepared in Example 3. Detailed Implementation

[0025] To make the objectives, methods, and advantages of the present invention clearer, the present invention will now be further described in conjunction with embodiments, but is not limited thereto.

[0026] Example 1 A controllable preparation method for a silver-loaded hierarchical pore-formed adsorbent is provided, comprising the following steps: 1) Weigh 161 mg of monosodium 2-sulfonic terephthalate and 66 mg of terephthalic acid and add them to 40 mL of ammonia water with pH 8 and stir until dissolved. Then add 800 mg of carboxymethyl cellulose and stir until a homogeneous and transparent suspension is formed. Then quickly freeze with liquid nitrogen and freeze-dry the resulting ice gel under vacuum for 24 h to obtain the modified SO3Na-CMC gel.

[0027] 2) Weigh out 181 mg of zirconium tetrachloride, 200 mg of silver tetrafluoroborate, 18 mL of N,N-dimethylacetamide (DMA), 2 mL of 30% hydrochloric acid, and 6 mL of water, and add them to a reaction vessel. Sonicate at room temperature for 10 min to obtain the MOF precursor solution. Then add 400 mg of the gel obtained in step 1), and subsequently incubate at 60°C. o The solvothermal reaction was carried out in an oven at C for 24 hours. After the reaction was completed, the product was removed, washed three times with ethanol, and finally dried at 80°C. o The MOF-loaded gel, i.e., the silver-loaded hierarchical pore-forming adsorbent, was obtained by vacuum drying at C for 12 h, denoted as HP-UiO-66-SO3Ag@CMC-1. The entire process was carried out under light-protected conditions.

[0028] like Figure 2 The N2 adsorption-desorption curve of the gel obtained in this embodiment is a type IV curve, and there is an obvious hysteresis loop in the curve, indicating that the gel has a mesoporous structure with a mesoporous size of 4.0 nm.

[0029] Example 2 A controllable preparation method for a silver-loaded hierarchical pore-formed adsorbent is provided, comprising the following steps: 181 mg of zirconium tetrachloride, 200 mg of silver tetrafluoroborate, 18 mL of dimethyl sulfoxide (DMSO), 2 mL of 30% hydrochloric acid, and 6 mL of water were weighed and added to a reaction vessel. The mixture was sonicated at room temperature for 10 min to obtain a MOF precursor solution. Then, 400 mg of the gel obtained in step 1) of Example 1 was added, followed by reaction at 60°C. o The solvothermal reaction was carried out in an oven at C for 24 hours. After the reaction was completed, the product was removed, washed three times with ethanol, and finally dried at 80°C. oThe MOF-loaded gel, i.e., the silver-loaded hierarchical pore-forming adsorbent, was obtained by vacuum drying at C for 12 h, denoted as HP-UiO-66-SO3Ag@CMC-2. The entire process was carried out under light-protected conditions.

[0030] like Figure 2 The N2 adsorption-desorption curve of the gel obtained in this embodiment is a type IV curve, and there is an obvious hysteresis loop in the curve, indicating that the gel has a mesoporous structure with a mesoporous size of 10.4 nm. Example 3 181 mg of zirconium tetrachloride, 200 mg of silver tetrafluoroborate, 36 mL of dimethyl sulfoxide (DMSO), 2 mL of 30% hydrochloric acid, and 6 mL of water were weighed and added to a reaction vessel. The mixture was sonicated at room temperature for 10 min to obtain a MOF precursor solution. Then, 400 mg of the gel obtained in step 1) of Example 1 was added, followed by reaction at 60°C. o The solvothermal reaction was carried out in an oven at C for 24 hours. After the reaction was completed, the product was removed, washed three times with ethanol, and finally dried at 80°C. o The MOF-loaded gel, i.e., the silver-loaded hierarchical pore-forming adsorbent, was obtained by vacuum drying at C for 12 h, denoted as HP-UiO-66-SO3Ag@CMC-3. The entire process was carried out under light-protected conditions.

[0031] like Figure 2 , Figure 3 The N2 adsorption-desorption curves and SEM images show that the gel obtained in this example has a distinct mesoporous structure with a mesoporous size of 9.2 nm, and it has a good separation effect when applied to the adsorption and separation of ethane / ethylene.

[0032] The gel prepared in Example 3 was subjected to adsorption separation of ethane / ethylene. The specific steps were as follows: Weigh 120 mg of the obtained HP-UiO-66-SO3Ag@CMC-3, and heat it at 80°C. o The gel was dried under vacuum at C for about 10 h to obtain the activated gel, and then its single-component adsorption curves for ethane and ethylene were tested at 298 K.

[0033] Figure 4The adsorption curves of the silver-loaded hierarchical pore-formed adsorbents prepared for Examples 3 and 1-3 for ethane / ethylene at 298 K and 0-1 bar are shown in the figures. The figures show that at 0 bar, the adsorption capacity of the formed adsorbent for both ethylene and ethane is 0. With increasing pressure, especially in the low-pressure region, the adsorption curve for ethylene is steeper than that for ethane, indicating that the formed adsorbent can rapidly adsorb ethylene, and the adsorption capacity for ethylene is much higher than that for ethane, demonstrating that the formed adsorbent has preferential adsorption performance for ethylene. Specifically, the adsorption capacities of the formed adsorbent for ethylene and ethane at 298 K and 1 bar are 2.3 mmol / g and 1.3 mmol / g, respectively. IAST calculations show a C2H4 / C2H6 selectivity of 6.2, indicating good ethane / ethylene separation performance. By comparison Figure 4 The adsorption curves show that, compared to the adsorption curves before molding, the adsorption amounts of ethylene and ethane after molding are only slightly reduced. This indicates that the MOF can grow on the gel and has a high loading capacity, maintaining a high level of adsorption for ethane and ethylene.

[0034] Figure 5 The graph shows the cyclic adsorption capacity of ethylene by the silver-loaded hierarchical pore-shaped adsorbent prepared in Example 3 at 298 K. The graph shows that the adsorption capacity of ethylene by the shaped adsorbent did not change significantly in five consecutive adsorption cycles, indicating that the obtained shaped adsorbent has good recyclability.

[0035] Comparative Example 1 The preparation of HP-UiO-66-SO3H-3 powder includes the following steps: 181 mg of zirconium tetrachloride, 36 mL of dimethyl sulfoxide (DMSO), 2 mL of 30% hydrochloric acid, and 6 mL of water were weighed and added to a reaction vessel. The mixture was sonicated at room temperature for 10 min to obtain a MOF precursor solution, which was then subjected to a reaction at 60 °C. o The solvothermal reaction was carried out in an oven at C for 24 hours. After the reaction was completed, the product was removed, washed three times with ethanol, and finally dried at 80°C. o C. Vacuum drying for 12 h yielded a powdered MOF, denoted as HP-UiO-66-SO3H-3 powder.

[0036] Comparative Example 2 The preparation of HP-UiO-66-SO3Ag-3 powder includes the following steps: 181 mg of zirconium tetrachloride, 200 mg of silver tetrafluoroborate, 36 mL of dimethyl sulfoxide (DMSO), 2 mL of 30% hydrochloric acid, and 6 mL of water were weighed and added to a reaction vessel. The mixture was sonicated at room temperature for 10 min to obtain a MOF precursor solution, which was then subjected to a reaction at 60 °C. o The solvothermal reaction was carried out in an oven at C for 24 hours. After the reaction was completed, the product was removed, washed three times with ethanol, and finally dried at 80°C. o The MOF was obtained by vacuum drying at C for 12 h, and was designated as HP-UiO-66-SO3Ag-3 powder. The entire process was carried out under light-protected conditions.

[0037] Comparative Example 3 The preparation of HP-UiO-66-SO3H@CMC-3 includes the following steps: 181 mg of zirconium tetrachloride, 36 mL of dimethyl sulfoxide (DMSO), 2 mL of 30% hydrochloric acid, and 6 mL of water were weighed and added to a reaction vessel. The mixture was sonicated at room temperature for 10 min to obtain a MOF precursor solution. Then, 400 mg of the gel obtained in step 1) of Example 1 was added, followed by reaction at 60°C. o The solvothermal reaction was carried out in an oven at C for 24 hours. After the reaction was completed, the product was removed, washed three times with ethanol, and finally dried at 80°C. o C. Vacuum drying for 12 h yielded a MOF-loaded gel, i.e., a hierarchical pore-forming adsorbent, denoted as HP-UiO-66-SO3H@CMC-3.

[0038] Comparative Example 4 A controllable preparation method for a silver-loaded molded adsorbent is provided, comprising the following steps: 181 mg of zirconium tetrachloride, 200 mg of silver tetrafluoroborate, 2 mL of 30% hydrochloric acid, and 6 mL of water were weighed and added to a reaction vessel without adding any organic solvent. The mixture was sonicated at room temperature for 10 min to obtain a MOF precursor solution. Then, 400 mg of the gel obtained in step 1) of Example 1 was added, followed by incubation at 60°C. o The solvothermal reaction was carried out in an oven at C for 24 hours. After the reaction was completed, the product was removed, washed three times with ethanol, and finally dried at 80°C. o The MOF-loaded gel was obtained by vacuum drying at C for 12 h, denoted as UiO-66-SO3Ag@CMC. The entire process was carried out under light-protected conditions.

[0039] like Figure 2 The N2 adsorption-desorption curve of the gel obtained in this comparative example is a typical microporous curve with no hysteresis loop, indicating that the gel has a microporous structure.

[0040] The silver-loaded hierarchical pore-forming adsorbent prepared by the method of this invention has good flexibility and its adsorption performance can be well preserved, which can meet the conditions for industrial application and can be used on a large scale in industry.

[0041] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A controllable preparation method for a silver-loaded hierarchical pore-forming adsorbent, characterized in that, Includes the following steps: 1) After the organic ligand is completely dissolved in a weakly alkaline solution, carboxymethyl cellulose is added and stirring is continued to obtain a modified carboxymethyl cellulose suspension. Then, the modified carboxymethyl cellulose gel is obtained by vacuum freeze drying. Wherein: the organic ligand is a mixture of terephthalic acid and BDC-X, and BDC-X is 2,5-dihydroxyterephthalic acid, 2-aminoterephthalic acid or monosodium 2-sulfonic terephthalate. 2) The modified carboxymethyl cellulose gel obtained in step 1) is directly immersed in the precursor solution of MOF to carry out a solvothermal reaction, thereby obtaining the silver-loaded hierarchical pore-forming adsorbent; wherein: the precursor solution of MOF is a solution of metal ligand, silver tetrafluoroborate, organic solvent, hydrochloric acid and water uniformly mixed; the metal ligand is one of zirconium tetrachloride or hafnium tetrachloride; the organic solvent is one of N,N-dimethylacetamide, dimethyl sulfoxide or tetrahydrofuran.

2. The controllable preparation method according to claim 1, characterized in that, In step 1), the molar ratio of terephthalic acid to BDC-X is 1:0.25-4.

3. The controllable preparation method according to claim 1, characterized in that, In step 1), the pH of the weakly alkaline solution is no greater than 8.

5.

4. The controllable preparation method according to claim 1, characterized in that, In step 1), the molar mass ratio of the organic ligand to carboxymethyl cellulose is 0.5-2 mmol: 400 mg; the volume mass ratio of the weakly alkaline solution to carboxymethyl cellulose is 15-25 mL: 400 mg.

5. The controllable preparation method according to claim 1, characterized in that, In step 2), the volume ratio of organic solvent, hydrochloric acid and water in the MOF precursor solution is 1-20:1:1-10, and the concentration of hydrochloric acid is 10%-35%.

6. The controllable preparation method according to claim 1, characterized in that, In step 2), the molar ratio of the metal ligand to HCl in the hydrochloric acid in the MOF precursor solution is 1:15-30; the molar ratio of the metal ligand to silver tetrafluoroborate is 1:1-5.

7. The controllable preparation method according to claim 1, characterized in that, In step 2), the mass ratio of the modified carboxymethyl cellulose gel to silver tetrafluoroborate is 2:1-4.

8. The controllable preparation method according to claim 1, characterized in that, In step 2), the solvothermal reaction conditions are: 45-65℃, reaction time 12-24 h; the entire process of step 2) is carried out under light-protected conditions.

9. The application of a silver-loaded hierarchical pore-forming adsorbent prepared by the preparation method according to any one of claims 1-8 in the separation of ethane / ethylene gas.

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