Preparation method and application of diamine porous ionic liquid

Abstract

The present invention belongs to the field of environmental protection technology, and in particular to a preparation method and application of a diamine porous ionic liquid. The preparation method first synthesizes a zeolite imidazole framework MEA@ZIF‑8 loaded by a hydrothermal method in situ; then an amine-functionalized imidazole ionic liquid [Amim][NTf2] with trifluoromethanesulfonyl imide as an anion is synthesized by an ion exchange method; finally, based on the principle of like dissolves like, [Amim][NTf2] is combined with MEA@ZIF‑8 by a solvent dispersion mixing method to prepare a diamine porous ionic liquid MEA@ZIF‑8‑Amim‑PIL. The diamine porous ionic liquid prepared by the present invention retains the excellent carbon capture performance of ionic liquid and ZIF‑8, and realizes the synergistic effect of the low-pressure CO2 high-density distribution of the liquid pores and the efficient electrostatic effect of the diamine group, which can be used for low-pressure flue gas carbon capture, has high regeneration efficiency, low energy consumption, and contributes to environmental protection.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental protection, and particularly relates to a preparation method of a diamine porous ionic liquid and application thereof. Background Art

[0002] Currently, the most mature and widely used CO2 capture process is the use of aqueous organic amines such as monoethanolamine, diethanolamine, and methyldiethanolamine to absorb CO2 from flue gas. It is widely used for industrial flue gas carbon removal. However, this method of amine-based CO2 absorption suffers from numerous challenges, including low regeneration efficiency, high desorption energy consumption, and absorbent corrosion. Consequently, the development of new, efficient absorbents and their associated absorption processes has become a research hotspot in carbon capture technology.

[0003] Porous ionic liquids (PILs) are a new class of porous materials with permanent pores and fluidity. They combine the shape selectivity and strong adsorption of porous solid materials with the rapid mass transfer, high designability, and stable kinetics of ionic liquids, showing immense promise for carbon capture. Among them, the third class of porous liquids, based on the ZIF-8 porous framework, has attracted considerable attention due to its simple preparation, easily tunable structure, and excellent performance. However, most pure ZIF-8 porous ionic liquids (ZIF-8-PILs) exhibit unsatisfactory performance for carbon capture from flue gases with low CO2 partial pressures due to their high viscosity, water instability, and insufficient active sites. Given the advantages of porous ionic liquids' easily tunable structure, the design and development of ZIF-8-PILs enriched with specific functional groups for tailored CO2 capture from low-pressure flue gases is highly desirable. To this end, researchers have introduced small amines with good CO2 solubility and absorption into the ZIF-8 framework in an effort to address these issues. However, the loading amount of a single small molecule amine in ZIF-8 is limited, and the electrostatic interaction between the monoamine-loaded ZIF-8 and the anions and cations of the ionic liquid in the porous ionic liquid structure is weak. The low-pressure flue gas CO2 absorption performance of monoamine ZIF-8-PILs has not achieved the ideal improvement effect.

[0004] In addition, studies have found that the introduction of amino functional groups such as primary and secondary amines into ionic liquids can effectively improve the electrostatic interaction between anions and cations, significantly enhancing CO2 absorption performance. However, most traditional amino-based ionic liquids have disadvantages such as high viscosity, large dosage, and poor CO2 solubility, making them unsuitable for industrial production.

[0005] Based on the existence of the above problems, there is an urgent need for a low-energy, high-regeneration-efficiency carbon capture agent that can not only increase the amino content in ZIF-8-PILs, but also regulate the interaction between the components of ZIF-8-PILs and improve the CO2 absorption performance of low-pressure flue gas, which is more conducive to environmental protection. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a diamine porous ionic liquid. The method uses MEA in situ loaded ZIF-8 (MEA@ZIF-8) as the porous framework of the porous ionic liquid, and an amine-functionalized imidazolium ionic liquid [Amim][NTf2] as the steric solvent of the porous ionic liquid. Based on the principle of like dissolves like, [Amim][NTf2] is combined with MEA@ZIF-8 using a solvent dispersion mixing method to prepare the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL. The present invention also provides the application of the diamine porous ionic liquid in low-pressure flue gas carbon capture.

[0007] A method for preparing a diamine porous ionic liquid comprises the following steps:

[0008] Step 1: Synthesis of MEA@ZIF-8:

[0009] A mixed solution of ethanolamine and 2-methylimidazole was mixed with a methanol solution of zinc nitrate hexahydrate (Zn(NO3)·6H2O), and the mixture was subjected to a hydrothermal reaction and centrifugal drying to obtain white particles of MEA@ZIF-8.

[0010] Step 2: Synthesis of [Amim][NTf2] ionic liquid:

[0011] 1-Methylimidazole and 2-bromoethylamine hydrobromide are mixed and reacted in acetonitrile solvent; after the reaction, the product is recrystallized from ethanol and dried to obtain the intermediate [Amim][Br];

[0012] Subsequently, [Amim][Br] and Li[NTf2] were reacted in an acetonitrile-water mixed solvent, and the product was neutralized to pH = 7, and then washed and dried to obtain a light yellow [Amim][NTf2] ionic liquid;

[0013] Step 3: Synthesis of diamine porous ionic liquid:

[0014] MEA@ZIF-8 is used as the porous framework body and [Amim][NTf2] ionic liquid is used as the steric solvent. It is prepared by a simple solvent dispersion and mixing method. The specific steps are: MEA@ZIF-8 and [Amim][NTf2] are dispersed in methanol respectively, ultrasonically oscillated at room temperature to make them uniformly dispersed, the dispersed homogeneous solutions are mixed, and dried to obtain a diamine porous ionic liquid, namely MEA@ZIF-8-Amim-PIL.

[0015] Preferably, in step 1, the molar ratio of 2-methylimidazole to zinc nitrate hexahydrate is 8:1, the mass ratio of ethanolamine to zinc nitrate hexahydrate is 0-1:5, and the volume ratio of zinc nitrate hexahydrate to methanol is (0.1-0.5:50) mol / ml.

[0016] Preferably, in the step 1, the hydrothermal reaction temperature is 50-60° C., and the reaction time is 20-24 h; the drying temperature is 80-90° C., and the drying time is 20-24 h.

[0017] Preferably, in step 2, the molar ratio of 1-methylimidazole to 2-bromoethylamine hydrobromide is 1:1; and the usage ratio of 1-methylimidazole to acetonitrile is (0.1-0.5:50) mol / ml.

[0018] Preferably, in the step 2, the temperature of the mixed reaction in the acetonitrile solvent is 60-70° C., and the reaction time is 20-24 h; the drying temperature is 80-90° C., and the drying time is 20-24 h.

[0019] Preferably, in the step 2, the molar ratio of [Amim][Br] to Li[NTf2] is 1:1; the usage ratio of [Amim][Br] to acetonitrile-water mixed solvent is (0.1-0.5:50) mol / ml; in the acetonitrile-water mixed solvent, the volume ratio of acetonitrile to water is 1:1; and the solvent used for washing is a mixed solvent of methanol and chloroform.

[0020] Preferably, in the step 2, the reaction temperature in the acetonitrile-water mixed solvent is 25-30° C., the reaction time is 20-24 h; the volume ratio of methanol to chloroform is 9:1; the drying temperature is 80-90° C., and the drying time is 20-24 h; and neutralization is carried out using a NaOH solution.

[0021] Preferably, in step three, the mass ratio of MEA@ZIF-8 to [Amim][NTf2] is 0.05-0.1:1.

[0022] Preferably, in step three, the drying temperature is 80-90° C., and the drying time is 20-24 hours.

[0023] A diamine porous ionic liquid prepared by this invention is used in low-pressure flue gas carbon capture. Low-pressure CO₂ absorption testing of the porous ionic liquid was conducted using a gas adsorption instrument at room temperature and 0-1 bar. Prior to testing, the porous ionic liquid was vacuum desorbed at 80°C for 24 hours to remove water vapor and impurities. Repeating this CO₂ absorption-desorption process allows for the recycling of the diamine porous ionic liquid, reducing costs and contributing to green ecology and environmental protection.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The present invention adopts MEA@ZIF-8-Amim-PIL biamine porous ionic liquid as a low-pressure flue gas carbon capture agent, wherein the ionic liquid cation provides an -NH2 structure that chemically reacts with CO2; the imidazole ring in the MEA@ZIF-8 porous material can form an enhanced electrostatic interaction with CO2, and at the same time, the MEA loaded in ZIF-8 can chemically react with CO2 to form carbamate; in addition, there is a strong electrostatic interaction between the functional amine group of the ionic liquid cation and the loaded MEA; more importantly, the unique liquid pores of the porous ionic liquid can release more absorption active sites, achieving a high-density distribution of CO2 in the cavity microenvironment under low pressure; under the synergistic effect of the above advantages, the low-pressure flue gas CO2 absorption performance of the biamine porous ionic liquid is effectively improved. The biamine porous ionic liquid of the present invention not only realizes the strong electrostatic synergy of the biamine group, but also the unique liquid pores of the porous ionic liquid realize a high-density distribution of CO2 under low pressure, significantly improving the low-pressure flue gas CO2 absorption performance.

[0026] (2) The biamine porous ionic liquid of the present invention uses the zeolite imidazole skeleton ZIF-8 with in situ MEA loading as the porous framework body and the amino-functionalized imidazole trifluoromethanesulfonyl imide ionic liquid as the steric solvent. It is prepared based on the principle of like dissolves like and adopts a simple solvent dispersion and mixing method. It combines the shape selectivity and strong adsorption of porous solid materials and the rapid mass transfer, fluidity and stable kinetic properties of ionic liquid materials, thereby improving the absorption of low-pressure flue gas CO2, contributing to environmental protection, mitigating climate warming, etc.

[0027] (3) The present invention has a simple process, mild absorption conditions, high absorption capacity, high regeneration efficiency and low energy consumption, which is conducive to industrial application and provides a carbon capture agent for environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 1 and 2. Characterization spectra of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1; wherein a: infrared spectra of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1; b: XRD spectra of MEA@ZIF-8 in Example 1, ZIF-8 in Comparative Example 1 and fitted ZIF-8; c: N2 adsorption-desorption spectra of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1; d: thermogravimetric curves of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1.

[0029] Figure 2 The XPS spectra of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1 are shown in Figure 1; a: the full XPS spectra of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1; b: the N / C and N / Zn ratios of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1.2+ Comparison; c: C1s fine spectrum of MEA@ZIF-8 in Example 1; d: C1s fine spectrum of ZIF-8 in Comparative Example 1; e: N1s fine spectrum of MEA@ZIF-8 in Example 1; f: N1s fine spectrum of ZIF-8 in Comparative Example 1.

[0030] Figure 3 These are the SEM, EDS and TEM spectra of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1; wherein a: SEM image of ZIF-8 in Comparative Example 1; b: SEM and EDS images of ZIF-8 in Comparative Example 1; c: TEM image of MEA@ZIF-8 in Example 1; d: SEM and EDS images of MEA@ZIF-8 in Example 1.

[0031] Figure 4 is [Amim][NTf2] in Example 1 1 H NMR spectrum.

[0032] Figure 5 : Characterization spectra of the porous ionic liquid MEA@ZIF-8-Amim-PIL and the ionic liquid [Amim][NTf2] in Example 1; wherein a: infrared spectrum of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL and the ionic liquid [Amim][NTf2] in Example 1; b: XRD spectrum of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1 and the ZIF-8-Amim-PIL in Comparative Example 1; c: thermogravimetric curves of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL, the ionic liquid [Amim][NTf2] and the MEA@ZIF-8-Amim-PIL in Comparative Example 1; d: thermogravimetric curves of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1 a: Full XPS spectrum of a@ZIF-8-Amim-PIL; e: C1sXPS fine spectrum of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1; f: N1sXPS fine spectrum of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1.

[0033] Figure 6It is a comparison chart of the absorption performance of porous ionic liquids; wherein a: CO2 absorption capacity data chart of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1, MEA@ZIF-8 in Comparative Example 3 and ZIF-8 in Comparative Example 2; b: CO2 absorption capacity data chart of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1, the porous ionic liquid ZIF-8-Amim-PIL in Comparative Example 1 and the ionic liquid [Amim][NTf2] in Comparative Example 4; c: regeneration performance chart of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 2; d: infrared spectra of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1, the absorption saturated MEA@ZIF-8-Amim-PIL and the MEA@ZIF-8-Amim-PIL after 5 regeneration cycles and desorption treatment in Example 2. DETAILED DESCRIPTION

[0034] The accompanying drawings are for illustrative purposes only; they clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some, not all, of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0035] The raw materials, chemical reagents, instruments, etc. used in the present invention can be obtained through conventional commercial channels unless the manufacturer or source is clearly stated.

[0036] Example 1

[0037] 1. Preparation of MEA@ZIF-8-Amim-PIL porous ionic liquid

[0038] (1) Preparation of ethanolamine-loaded zeolitic imidazole framework (MEA@ZIF-8)

[0039] 3.29g of 2-methylimidazole and 0.48g of MEA were dissolved in 50ml of methanol, followed by the addition of 1.48g of Zn(NO₃)·6H₂O and the mixture was reacted at 50°C for 12h. After completion of the reaction, the reaction solution was centrifuged to obtain a white precipitate, which was washed three times with methanol and freeze-dried to obtain MEA@ZIF-8.

[0040] (2) Preparation of [Amim][NTf2] ionic liquid

[0041] 0.1 mol of methylimidazole, 0.1 mol of 2-bromoethylamine hydrobromide and 50 ml of acetonitrile were added to a 100 mL three-necked flask respectively. The mixture was refluxed at 60°C for 24 h under nitrogen protection. After the reaction was completed, the acetonitrile was removed by rotary evaporation. The product was recrystallized from ethanol and then dried at 80°C for 12 h to obtain the intermediate [Amim][Br].

[0042] Subsequently, 0.1 mol of the intermediate [Amim][Br] and 0.1 mol of Li[NTf2] were added to 50 mL of a 1:1 volume ratio acetonitrile-water mixed solvent, and the mixture was refluxed at 60°C for 24 h under nitrogen protection. The product was neutralized with NaOH to pH = 7, and then washed three times with a 9:1 volume ratio of methanol and chloroform mixed solvent, and then dried at 80°C for 24 h to obtain the aminoimidazole trifluoromethanesulfonyl imide ionic liquid [Amim][NTf2].

[0043] (3) Preparation of porous ionic liquid MEA@ZIF-8-Amim-PIL

[0044] 0.95 g [Amim][NTf2] ionic liquid and 0.05 g MEA@ZIF-8 were dissolved in 20 mL methanol respectively, and ultrasonically vibrated at room temperature to make them uniformly dispersed. The dispersed [Amim][NTf2] ionic liquid methanol solution and MEA@ZIF-8 methanol solution were ultrasonically vibrated at room temperature to make them uniformly mixed, and then dried at 80 ° C for 24 h to obtain the diamine porous ionic liquid MEA@ZIF-8-Ami m-PIL.

[0045] 2. Low-pressure CO2 absorption application of diamine porous ionic liquid. The specific method is as follows:

[0046] 0.1g of diamine porous ionic liquid MEA@ZIF-8-Amim-PIL was filled into the absorption tube and then heated to 80℃ under vacuum at a heating rate of 5℃ / min. The diamine porous ionic liquid was desorbed for 24 hours to remove impurity gases and solvents in the sample. After desorption, the absorption tube temperature was lowered to room temperature and CO2 absorption test was performed at 0-1 bar. The CO2 absorption content at 1 bar was 94.3mg / g. The specific results are shown in Figure 6 (b) shown.

[0047] The absorption saturated MEA@ZIF-8-Amim-PIL was detected by infrared, and its infrared spectrum is shown as follows: Figure 6 (d) shown.

[0048] Example 2

[0049] According to the low-pressure CO2 absorption application of MEA@ZIF-8-Amim-PIL in Example 1, the absorbent is MEA@ZIF-8-Amim-PIL after completing one desorption-adsorption process in Example 1. The desorption-adsorption process is repeated 4 times. The other conditions are the same as in Example 1. The specific method is as follows:

[0050] 0.1g of porous ionic liquid MEA@ZIF-8-Amim-PIL was filled into the absorption tube, and then heated to 80℃ at a heating rate of 5℃ / min under vacuum conditions. The porous ionic liquid was desorbed for 24 hours to remove impurity gases and solvents in the sample. After desorption, the temperature of the absorption tube was lowered to room temperature, and a CO2 absorption test was performed at 0-1 bar. The above CO2 desorption-absorption process was repeated 4 times. The CO2 absorption content remained basically unchanged at 1 bar. The specific results are as follows Figure 6 (c) shown.

[0051] The porous ionic liquid MEA@ZIF-8-Amim-PIL after 5 regeneration cycles and desorption treatment was subjected to infrared detection, and its infrared spectrum is shown as follows: Figure 6 (d) As shown in III.

[0052] Comparative Example 1

[0053] The porous ionic liquid MEA@ZIF-8-Amim-PIL was prepared according to the method of Example 1, except that the porous framework was replaced with ZIF-8. The remaining conditions were the same as those of Example 1, and the specific method was as follows:

[0054] (1) Preparation of porous framework ZIF-8

[0055] 3.29g of 2-methylimidazole was dissolved in 50ml of methanol, followed by the addition of 1.48g of Zn(NO3)·6H2O. The mixture was reacted at 50°C for 12 hours. After completion of the reaction, the reaction solution was centrifuged to obtain a white precipitate, which was washed three times with methanol and freeze-dried to obtain ZIF-8.

[0056] (2) Preparation of porous ionic liquid ZIF-8-Amim-PIL

[0057] 0.95 g of [Amim][NTf2] ionic liquid and 0.05 g of ZIF-8 were dissolved in 20 mL of methanol respectively, and ultrasonically vibrated at room temperature to make them uniformly dispersed. The dispersed [Amim][NTf2] ionic liquid methanol solution and ZIF-8 methanol solution were ultrasonically vibrated at room temperature to make them uniformly mixed, and then dried at 80 ° C for 24 h to obtain porous ionic liquid ZIF-8-Amim-PIL.

[0058] According to the low-pressure CO2 absorption application of porous ionic liquid in Example 1, ZIF-8-Amim-PIL was selected as the porous ionic liquid, and the remaining steps were the same as Example 1. The CO2 absorption content at 1 bar was 82.4 mg / g.

[0059] Comparative Example 2

[0060] According to the low-pressure CO2 absorption application of porous ionic liquid in Example 1, ZIF-8 was selected as the adsorbent, and the remaining steps were the same as in Example 1. The CO2 absorption content was 27.4 mg / g at 1 bar. The specific results are as follows Figure 6 As shown in (a).

[0061] Comparative Example 3

[0062] According to the low-pressure CO2 absorption application of porous ionic liquid in Example 1, MEA@ZIF-8 was selected as the adsorbent, and the remaining steps were the same as in Example 1. The CO2 absorption content was 41.7 mg / g at 1 bar. The specific results are as follows Figure 6 As shown in (a).

[0063] Comparative Example 4

[0064] According to the low-pressure CO2 absorption application of porous ionic liquid in Example 1, the absorbent is selected from ionic liquid [Amim][NTf2], and the remaining steps are the same as in Example 1. The CO2 absorption content is 57.9 mg / g at 1 bar. The specific results are as follows Figure 6 (b) shown.

[0065] like Figure 1 As shown, Figure 1 (a) is the infrared spectrum of MEA@ZIF-8 (II) in Example 1 and ZIF-8 (I) in Comparative Example 1. It can be seen from the figure that the spectrum of MEA@ZIF-8 shows four imidazole characteristic peaks of ZIF-8 at 3136 cm -1 , 2924cm -1 , 1583cm -1 , 1146cm -1 and the coordination peak of Zn atom and imidazole nitrogen at 3136 cm -1 At the same time, MEA's 1566cm -1 -NH2 peak, 3100 and 3170 cm -1 NH stretching vibration peak and 3626cm -1 The OH characteristic peaks are also clearly visible, proving that MEA is successfully loaded into the ZIF-8 skeleton structure.

[0066] Figure 1(b) XRD spectra of MEA@ZIF-8 in Example 1, ZIF-8 in Comparative Example 1, and the fitted ZIF-8. As can be seen from the figure, all diffraction peaks of ZIF-8 in Comparative Example 1 match well with those of the fitted ZIF-8, indicating that ZIF-8 was successfully synthesized. Furthermore, the characteristic diffraction peaks of ZIF-8 are still observed in MEA@ZIF-8 without significant shift changes, indicating that the loading of MEA does not disrupt the crystal structure of ZIF-8.

[0067] Figure 1 (c) is the N2 adsorption-desorption curve of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1. As can be seen from the figure: the N2 adsorption-desorption isotherm of MEA@ZIF-8 shows a typical microporous structure, and the specific surface areas of the two can reach 1719 and 1311 m2 respectively. 2 / g, further indicating that there are a large number of microporous structures in the synthesized ZIF-8 and MEA@ZIF-8 that can serve as permanent pores.

[0068] Figure 1 (d) shows the thermogravimetric curves of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1. As can be seen from the figure, ZIF-8 exhibits no significant mass loss below 450°C, demonstrating its good thermal stability. MEA@ZIF-8 exhibits slight mass loss due to the addition of MEA to the framework, demonstrating successful MEA loading into the ZIF-8 framework.

[0069] like Figure 2 The XPS spectra of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1 are shown in FIG. Figure 2 As can be seen in (a), the XPS spectra of ZIF-8 and MEA@ZIF-8 show characteristic peaks of Zn, C and N at 1022 eV, 1045 eV, 400 and 280, respectively. Figure 2 As shown in (b), the N / C and N / Zn element ratios in MEA@ZIF-8 are slightly increased compared with those in ZIF-8. Figure 2 (c) is the C1s fine spectrum of MEA@ZIF-8 in Example 1, Figure 2 (d) is the C1s fine spectrum of ZIF-8 in Comparative Example 1. In addition, the N1s fine spectrum of MEA@ZIF-8 shows a new NH peak. Figure 2 (e) and (f) show that MEA has been successfully loaded into the ZIF-8 skeleton structure.

[0070] Figure 3 TEM, SEM and EDS spectra of MEA@ZIF-8 in Example 1 and ZIF-8 in Comparative Example 1. Figure 3As can be seen from (a), ZIF-8 is in the form of hexagonal blocks with uniform particle size. Figure 3 As can be seen from (b), the EDS patterns of C, N, and Zn are evenly distributed, indicating that ZIF-8 was successfully prepared. Figure 3 As can be seen in Figures 3(c) and 3(d), the MEA@ZIF-8 particle size decreases, the surface becomes rougher, and the shape becomes more irregular. This is primarily due to the accelerated nucleation and growth of ZIF-8 caused by the introduction of MEA. These results further demonstrate the successful loading of MEA into the ZIF-8 framework. Furthermore, the SEM and TEM spectra of MEA@ZIF-8 clearly show that the particle edges tend to be blurred or even agglomerated, while the XRD pattern shows that the crystallinity of MEA@ZIF-8 remains largely unchanged. Based on this, we speculate that the in situ synthesis strategy plays a significant role in maintaining the structural integrity of MEA@ZIF-8.

[0071] Figure 4 is the ionic liquid [Amim][NTf2] in Example 1 1 H NMR spectrum. The figure shows that the hydrogen shifts on the imidazole ring of 1-methylimidazole are located at 7.52 and 7.48 ppm, respectively, the side chain methyl hydrogen is located at 3.93 ppm, and the active hydrogen of -NH2 is located at 4.32 and 4.27 ppm. These results, combined with the ionic liquid structure, confirm the successful synthesis of [Amim][NTf2].

[0072] Figure 5 (a) is the infrared spectra of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL(Ⅲ), ionic liquid [Amim][NTf2](Ⅱ) and Li[NTf2](Ⅰ) in Example 1. It can be seen from the figure that compared with [Amim][NTf2], the spectrum of MEA@ZIF-8-Amim-PIL has the highest peaks at 421 and 1024 cm -1 The Zn-N bond and CN bond absorption peaks of ZIF-8 were observed at the bottom, respectively, proving that the porous ionic liquid MEA@ZIF-8-Amim-PIL was successfully prepared by combining [Amim][NTf2] with MEA@ZIF-8.

[0073] Figure 5 (b) XRD spectra of the porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1 and ZIF-8 in Comparative Example 1. The figure shows that the XRD spectrum of MEA@ZIF-8-Amim-PIL shows a broad peak of [Amim][NTf2] and typical characteristic peaks of ZIF-8 with no significant shift, indicating that the porous framework structure remains stable and undamaged in the porous ionic liquid.

[0074] Figure 5(c) shows the thermogravimetric spectra of the porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1, [Amim][NTf2] in Comparative Example 4, and ZIF-8-Amim-PIL in Comparative Example 1. The figure shows that the addition of the porous framework MEA@ZIF-8 and ZIF-8 does not reduce the thermal stability of the ionic liquid [Amim][NTf2], further confirming the structural stability of the porous ionic liquid during synthesis.

[0075] Figure 5 (d, e, f) are the XPS spectra, C 1s XPS fine spectra, and N 1s XPS spectra of the porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1. The figures show that the full XPS spectrum of MEA@ZIF-8-Amim-PIL exhibits distinct characteristic peaks at 1022 eV (Zn 2p), 689 eV (F 1s), 533 eV (O 1s), 400 eV (N 2p), 285 eV (C 1s), and 167 eV (S 2p). The coexistence of the Zn 2p and F, O, and S characteristic peaks demonstrates the effective combination of [Amim][NTf2] with MEA@ZIF-8, successfully preparing MEA@ZIF-8-Amim-PIL. In addition, the slight changes in the C1s and N1s fine spectra of MEA@ZIF-8-Amim-PIL compared with MEA@ZIF-8 indicate the existence of strong non-covalent interactions between [Amim][NTf2] in the porous ionic liquid MEA@ZIF-8-Amim-PIL and MEA@ZIF-8, which may be caused by the transfer or redistribution of electron density during the interaction.

[0076] Figure 6 (a) shows the CO2 absorption capacity data for the porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1, MEA@ZIF-8 in Comparative Example 3, and ZIF-8 in Comparative Example 2. The figure shows that within the range of 0 to 1 bar, the CO2 adsorption capacity of MEA@ZIF-8 and ZIF-8 shows a linear upward trend. The CO2 adsorption capacity of MEA@ZIF-8 at 1 bar is 41.68 mg / g, significantly higher than the 27.36 mg / g of ZIF-8. This indicates that MEA significantly improves CO2 adsorption performance. Compared with MEA@ZIF-8 and ZIF-8, the CO2 adsorption capacity of MEA@ZIF-8-Amim-PIL is significantly increased, reaching 94.3 mg / g at 1 bar, equivalent to 5 times the CO2 adsorption capacity of ZIF-8, indicating that the ionic liquid [Amim][NTf2] plays a significant role in improving CO2 adsorption performance.

[0077] Figure 6(b) shows the CO2 absorption capacity data for the porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 1, the ionic liquid [Amim][NTf2] in Comparative Example 4, and the porous ionic liquid ZIF-8-Amim-PIL in Comparative Example 1. The figure shows that the CO2 absorption capacity of MEA@ZIF-8-Amim-PIL, ZIF-8-Amim-PIL, and [Amim][NTf2] also shows an upward trend in the 0-1 bar range. Compared with [Amim][NTf2], the CO2 absorption capacity of the two porous ionic liquids is significantly improved, indicating that the porous channels of the liquid play an important role in improving the CO2 adsorption capacity. In addition, the CO2 absorption capacity of MEA@ZIF-8-Amim-PIL is significantly higher than that of ZIF-8-Amim-PIL, indicating that the efficient electrostatic effect of the functionalized diamine groups also plays a significant role in improving the CO2 adsorption capacity.

[0078] Figure 6 (c) shows the regeneration performance of the porous ionic liquid MEA@ZIF-8-Amim-PIL in Example 2. As can be seen from the figure, the CO2 absorption capacity remains almost unchanged after five regeneration cycles, indicating that the porous ionic liquid MEA@ZIF-8-Amim-PIL of the present invention has good cyclic stability and is expected to be a highly efficient industrial CO2 capture agent.

[0079] Figure 6 (d) is the infrared spectra of the diamine porous ionic liquid MEA@ZIF-8-Amim-PIL (I) in Example 1, the absorption saturated MEA@ZIF-8-Amim-PIL (II) and the MEA@ZIF-8 / [Amim][NTf2] (III) after 5 regeneration cycles and desorption treatment in Example 2. It can be seen from the figure that the FT-IR spectrum of the porous ionic liquid MEA@ZIF-8-Amim-PIL after absorbing CO2 is at 1547 cm -1 There appears a + This result is consistent with literature reports, indicating that CO2 forms a strong interaction with the functionalized diamine groups. Therefore, we can speculate that the permanent liquid channels of the porous ionic liquid provide efficient storage space for the reversible action of CO2, thereby significantly improving CO2 capture performance. Furthermore, the FT-IR of MEA@ZIF-8-Amim-PIL remains essentially unchanged before and after regeneration, indicating that the structural composition of the characteristic groups of the porous ionic liquid remains unchanged before and after regeneration, further demonstrating the good regeneration stability of the porous ionic liquid described in this invention.

[0080] The Chinese meanings of the English abbreviations in this invention are:

[0081] ZIF-8: zeolite imidazole framework material, transition metal zinc ion (Zn 2+ ) and 2-methylimidazole ligand, the English full name is Zeolitic Imidazolate Framework-8;

[0082] PILs: porous ionic liquids;

[0083] ZIF-8-PILs: porous ionic liquids made of zeolitic imidazolate frameworks;

[0084] [Amim][NTf2]: aminoimidazole trifluoromethanesulfonyl imide ionic liquid;

[0085] MEA: ethanolamine;

[0086] Li[NTf2]: lithium trifluoromethanesulfonyl imide;

[0087] Zn(NO3)·6H2O: zinc nitrate hexahydrate;

[0088] MEA@ZIF-8: ethanolamine-supported zeolitic imidazole framework;

[0089] [Amim][Br]: 1-methyl-3-allylimidazolium bromide;

[0090] MEA@ZIF-8-Amim-PIL: diamine porous ionic liquid.

[0091] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A method for preparing a diamine porous ionic liquid, characterized in that: The steps include: Step 1: Synthesis of MEA@ZIF-8: A mixed solution of ethanolamine and 2-methylimidazole was mixed with a methanol solution of Zn(NO3)•6H2O, and subjected to hydrothermal reaction followed by centrifugal drying to obtain white particles of MEA@ZIF-8. Step 2: Synthesis of [Amim][NTf2] ionic liquid: 1-Methylimidazole and 2-bromoethylamine hydrobromide are mixed and reacted in acetonitrile solvent; after the reaction, the product is recrystallized from ethanol and dried to obtain the intermediate [Amim][Br]; Subsequently, [Amim][Br] was reacted with Li[NTf2] in an acetonitrile-water mixed solvent, and the product was neutralized to pH = 7, and then washed and dried to obtain a light yellow [Amim][NTf2] ionic liquid; Step 3: Synthesis of diamine porous ionic liquid: MEA@ZIF-8 was used as the porous framework and [Amim][NTf2] ionic liquid was used as the steric solvent. MEA@ZIF-8 and [Amim][NTf2] were dispersed in methanol respectively. Ultrasonic oscillation was performed at room temperature to uniformly disperse them. The dispersed homogeneous solutions were mixed and dried to obtain the diamine porous ionic liquid, namely MEA@ZIF-8-Amim-PIL. The molar ratio of 2-methylimidazole to zinc nitrate hexahydrate is 8:1, the mass ratio of ethanolamine to zinc nitrate hexahydrate is 0-1:5, and the volume ratio of zinc nitrate hexahydrate to methanol is (0.1-0.5:50) mol / ml. The molar ratio of 1-methylimidazole to 2-bromoethylamine hydrobromide is 1:1; the dosage ratio of 1-methylimidazole to acetonitrile is (0.1-0.5:50) mol / ml; The molar ratio of [Amim][Br] to Li[NTf2] is 1:1; the amount ratio of [Amim][Br] to the acetonitrile-water mixed solvent is (0.1-0.5:50) mol / ml; the volume ratio of acetonitrile to water in the acetonitrile-water mixed solvent is 1:1; the washing solvent is a mixed solvent of methanol and chloroform; and the neutralization is carried out with a NaOH solution. The mass ratio of MEA@ZIF-8 to [Amim][NTf2] is 0.05-0.1:

1.

2. The method for preparing a diamine porous ionic liquid according to claim 1, characterized in that: In the step 1, the hydrothermal reaction temperature is 50-60° C., and the reaction time is 20-24 hours; the drying temperature is 80-90° C., and the drying time is 20-24 hours.

3. The method for preparing a diamine porous ionic liquid according to claim 1, wherein: In the step 2, the temperature of the mixed reaction in the acetonitrile solvent is 60-70° C., and the reaction time is 20-24 hours; the drying temperature is 80-90° C., and the drying time is 20-24 hours.

4. The method for preparing a diamine porous ionic liquid according to claim 1, characterized in that: In the step 2, the reaction temperature in the acetonitrile-water mixed solvent is 25-30° C., the reaction time is 20-24 h; the volume ratio of methanol to chloroform is 9:1; the drying temperature is 80-90° C., and the drying time is 20-24 h.

5. The method for preparing a diamine porous ionic liquid according to claim 1, characterized in that: In the step 3, the drying temperature is 80-90° C., and the drying time is 20-24 hours.

6. Use of the diamine porous ionic liquid prepared by the preparation method according to any one of claims 1 to 5 in low-pressure flue gas carbon capture.

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