Preparation method of carbon dioxide PAMAM grafted ionic liquid for oil gas purification

Abstract

The invention relates to the technical field of removal of carbon dioxide in oil gas, in particular to a preparation method of carbon dioxide PAMAM grafted ionic liquid for oil gas purification. Comprising the following steps: 1) activating carboxyl: dissolving 1-butyl-3-methylimidazole carboxylic acid in a solvent, adding dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and stirring at room temperature to generate active ester; 2) grafting PAMAM: adding PAMAM dendrimer into the solution, and reacting under the protection of nitrogen; and 3) purification: removing the dicyclohexylurea precipitate through centrifugation, and dialyzing the filtrate to remove the unreacted ionic liquid and small molecule byproducts to obtain the PAMAM grafted ionic liquid. The stability and durability of the absorbent are remarkably improved, the CO2 absorption efficiency is improved, the energy consumption of the absorbent per unit mass is reduced, and the preparation method is simple and controllable, mild in reaction condition and easy for large-scale production.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide removal in oil and gas, and in particular to a method for preparing a PAMAM grafted ionic liquid for purifying carbon dioxide from oil and gas. Background Art

[0002] With the acceleration of global industrialization, carbon dioxide emissions are increasing, leading to an increasingly severe greenhouse effect and harming the ecological environment. Carbon capture, utilization, and storage (CCUS) has become a key approach to achieving carbon neutrality. Chemical absorption, due to its maturity and widespread application, is considered the most promising carbon capture technology. Currently, alcoholamine absorbents such as monoethanolamine (MEA) and diethanolamine (DEA) are widely used due to their high affinity for carbon dioxide. However, these traditional absorbents suffer from volatilization, susceptibility to oxidative degradation, and high regeneration energy consumption.

[0003] As a new type of solvent, ionic liquids are considered ideal solvents for capturing carbon dioxide due to their adjustable structure and properties, extremely low vapor pressure, and low specific heat. However, pure ionic liquids still face many challenges in practical applications. First, their high cost limits their large-scale application. Second, ionic liquids generally have high viscosity, especially at high concentrations, resulting in poor compatibility with existing carbon capture devices in actual industrial operations. In addition, ionic liquids have a low absorption rate during the capture process, and their regeneration process consumes a lot of energy.

[0004] To address these challenges, researchers have begun exploring new composite absorbents. Among these, the combination of alcoholamine absorbents with functionalized ionic liquids has garnered considerable attention. This combination not only maintains the high affinity of the alcoholamine absorbent but also leverages the properties of the functionalized ionic liquid to improve absorption performance. However, designing a composite absorbent that effectively improves CO2 absorption efficiency while reducing regeneration energy consumption remains a key and challenging area of ​​research.

[0005] There are currently some invention patents to solve the problems of carbon dioxide capture efficiency and stability. For example, the Chinese patent document publication number CN113842749A discloses "A composite CO2 absorbent of alcoholamine and ionic liquid and its preparation method". The absorbent is made of a mixture of ionic liquid, ethanolamine and water, wherein the total concentration of ionic liquid and ethanolamine is 0.2-2.5 mol / L, and the molar ratio of ionic liquid to ethanolamine is 1:9-9:1. The absorbent can significantly improve the capture rate of CO2, quickly and efficiently capture CO2 in the mixed gas under low energy consumption conditions, and the preparation, use and regeneration process of the adsorbent are simple, and the operating conditions are easy to control. However, this patent still has the problem of how to further improve the absorption rate and absorption capacity of the absorbent.

[0006] Chinese patent publication number CN113842748A discloses "A Non-Aqueous Phase High-Boiling-Point Ionic Liquid-Piperazine Mixed CO2 Absorbent and Its Preparation Method." The absorbent is composed of a mixture of an alkylimidazole ionic liquid, piperazine, and a non-aqueous solvent. This invention not only replaces the traditional aqueous solvent system with an alcohol solvent system but also optimizes the active ingredients in the absorbent. This significantly increases the CO2 capture rate while achieving rapid and efficient capture of CO2 from mixed gases under low energy consumption. However, this patent still raises the question of how to further improve the absorbent's absorption capacity and reduce desorption costs.

[0007] Therefore, the prior art has the following shortcomings: 1. Traditional alcohol amine absorbents such as monoethanolamine (MEA) and diethanolamine (DEA) are volatile, easily oxidized and degraded, and have high regeneration energy consumption, which limits their promotion in industrial applications; 2. Although pure ionic liquids have advantages such as adjustable structure and properties, extremely low vapor pressure and low specific heat, their high cost and high viscosity restrict their large-scale use in practical applications, especially at high concentrations, where they have poor compatibility with existing carbon capture devices. 3. Existing alcoholamine-ionic liquid composite absorbents still need to be further optimized in terms of improving CO2 absorption efficiency and reducing desorption costs. In particular, how to effectively improve the performance of ionic liquids while maintaining the high affinity of alcoholamine absorbents is the current research focus; 4. In the prior art, the compounding of ionic liquids and alcohol amine absorbents often adopts a simple physical mixing method, which lacks effective chemical bonding, resulting in poor compounding effect and difficulty in fully exerting the synergistic effect of the two. Summary of the Invention

[0008] The purpose of the present invention is to address the above-mentioned defects in the prior art and provide a method for preparing PAMAM grafted ionic liquid for oil and gas purification of carbon dioxide, which effectively solves the problems of traditional alcohol amine absorbents being easy to volatilize and easily oxidize and degrade, significantly improves the stability and durability of the absorbent, improves the CO2 absorption efficiency, and reduces the energy consumption per unit mass of the absorbent. In addition, the preparation method is simple and controllable, the reaction conditions are mild, and it is easy to scale up production.

[0009] The present invention provides a method for preparing a PAMAM grafted ionic liquid for oil and gas purification of carbon dioxide, and its technical solution is as follows: (1) Raw materials and reagents: PAMAM dendrimer: G4 generation was selected, which contains 64 primary amino groups on its surface; Carboxylic acid functionalized ionic liquid: 1-butyl-3-methylimidazole carboxylic acid, with a simplified structural formula of C4H9-NC3H3N-CH3-COOH; Dehydrating agent: dicyclohexylcarbodiimide, the structural formula is C6H 11 N=C=NC6H 11 ; Solvent: anhydrous dimethyl sulfoxide or N,N-dimethylformamide; (II) Reaction steps: 1) Activation of carboxyl groups: Dissolve 1.0 mol of 1-butyl-3-methylimidazole carboxylic acid in 100 mL of solvent, add 1.2 mol of dicyclohexylcarbodiimide, and stir at room temperature for 1 h at a stirring rate of 400 rpm. The reaction formula is as follows: C4H9-NC3H3N-CH3-COOH + C6H 11 N=C=NC6H 11 → C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ] +C6H 11 NHCONHC6H 11 The reaction generates O-acylisourea, the structural formula of which is: C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ]; Among them, cyclohexyl, the structural formula is: C6H 12 ; Dicyclohexylurea, the structural formula is: C6H 11 NHCONHC6H 11 ; 2) Grafting PAMAM: Add 212-285 g of PAMAM dendrimer to the solution obtained after activation of the carboxyl groups in step 1) above, and react at 40°C under nitrogen protection for 24 hours with a stirring rate of 200 rpm. The primary amino groups on the surface of the PAMAM dendrimer are covalently linked to the carboxylic acid functionalized ionic liquid via amide bonds; The reaction formula is as follows: C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ]+PAMAM-NH2→PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3+C6H 11 NHCONHC6H 11 ; 3) Purification: The dicyclohexylurea precipitate was first removed by centrifugation, and the filtrate was dialyzed to remove unreacted ionic liquid and small molecule by-products, wherein more than 90% of the molecules with a molecular weight cutoff of ≥3.5 kilodaltons were retained to obtain the PAMAM grafted ionic liquid PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3.

[0010] PAMAM grafted ionic liquid combines the amino activity of dendrimers with the synergistic effect of ionic liquids. The remaining ungrafted -NH2 on the PAMAM surface absorbs CO2 ammonium carbamate PAMAM-NH-COONH4. The ionic liquid enhances CO2 capture and absorption through physical dissolution and carboxylate activation to generate [Bmim][HCO3]. The PAMAM grafted ionic liquid undergoes a reversible reaction after heating, realizing the regeneration of the ionic liquid absorbent.

[0011] Preferably, the PAMAM dendrimer has a molecular weight of 14215 Da.

[0012] Preferably, the 1-butyl-3-methylimidazolecarboxylic acid [Bmim][COOH] has a purity of ≥99%.

[0013] Preferably, the dicyclohexylcarbodiimide DCC has a purity of ≥99%.

[0014] Preferably, the purity of the anhydrous dimethyl sulfoxide (DMSO) is ≥99.9%, and the purity of the N,N-dimethylformamide (DMF) is ≥99.8%.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention covalently grafts carboxylic acid-functionalized ionic liquids onto the surface of PAMAM dendrimers to form a stable chemically bonded structure. This effectively addresses the volatility and oxidative degradation issues of traditional alcoholamine absorbents, significantly improving their stability and durability. 2. The present invention uses an esterification reaction preparation process to achieve a closer bond between the ionic liquid and the PAMAM dendrimer, maintaining the basic structure of the ionic liquid while giving the PAMAM dendrimer new functions, achieving an organic combination of the advantages of both. 3. By adjusting the molar ratio of 1-butyl-3-methylimidazole carboxylic acid to PAMAM dendrimer, the present invention precisely controls the degree of grafting, ensures partial free amino groups, maintains CO2 chemical adsorption activity, improves amino group utilization, and reduces steric hindrance. 4. The compounded absorbent has a synergistic effect, utilizing the high affinity of the alcoholamine absorbent while enhancing the diffusion capacity of carbon dioxide through the functionalized ionic liquid, significantly improving the CO2 absorption efficiency; 5. Through the branched structure design and functionalization of PAMAM dendrimers, more adsorption sites are provided, the CO2 adsorption capacity is increased, and the energy consumption per unit mass of absorbent is reduced; 6. The amide bond-stabilized structural design reduces the desorption temperature of the absorbent, which is beneficial to improving the stability and service life of the absorbent under low temperature conditions; 7. Due to the modification of PAMAM dendrimers, the viscosity of the composite absorbent is significantly reduced, improving its fluidity and processing performance at high concentrations, and resolving the poor compatibility of pure ionic liquids with existing carbon capture devices in actual industrial operation. 8. The preparation method of the present invention is simple and controllable, the reaction conditions are mild, it is easy to scale up production, and it has good repeatability and reproducibility, providing a feasible technical solution for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the H NMR spectrum of the PAMAM grafted ionic liquid of Example 3; Figure 2 This is the infrared spectrum of the PAMAM grafted ionic liquid of Example 3. DETAILED DESCRIPTION

[0017] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0018] Example 1: The present invention provides a method for preparing a PAMAM grafted ionic liquid for purifying carbon dioxide from oil and gas, comprising the following steps: (1) Raw materials and reagents: PAMAM dendrimer: G4 generation is selected, with 64 primary amino groups on the surface and a molecular weight of approximately 14215Da; Carboxylic acid functionalized ionic liquid: 1-butyl-3-methylimidazole carboxylic acid, with a structural formula of C4H9-NC3H3N-CH3-COOH, purity ≥99%; Dehydrating agent: dicyclohexylcarbodiimide, whose structural formula is C6H 11 N=C=NC6H 11 , purity ≥99%; Solvent: Anhydrous dimethyl sulfoxide, purity ≥99.9%; (II) Reaction steps: 1) Activation of carboxyl groups: 1.0 mol of 1-butyl-3-methylimidazole carboxylic acid was dissolved in 100 mL of anhydrous dimethyl sulfoxide, and 1.2 mol of dicyclohexylcarbodiimide was added. The mixture was stirred at room temperature for 1 hour to generate O-acylisourea. During the reaction, magnetic stirring was intermittent at a stirring rate of 400 rpm. The reaction formula is as follows: C4H9-NC3H3N-CH3-COOH + C6H 11 N=C=NC6H 11 → C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ] +C6H 11 NHCONHC6H 11 The reaction generates O-acylisourea, the structural formula of which is: C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ]; Cyclohexyl, the structural formula is C6H 12 ; Dicyclohexylurea, its structural formula is C 13 H 24 N2O; Among them, the by-product dicyclohexylurea precipitates out; 2) Grafting PAMAM: 212 g of PAMAM dendrimer with 64 primary amino groups on its surface was added to the solution obtained after activation of the carboxyl groups in step 1) above. The reaction was carried out at 40°C under nitrogen protection for 24 hours with a stirring rate of 200 rpm. The primary amino groups on the surface of the PAMAM dendrimer are covalently linked to the carboxylic acid functionalized ionic liquid via amide bonds; The reaction formula is as follows: C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ]+PAMAM-NH2→PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3+C6H 11 NHCONHC6H 11 ; 3) Purification: The dicyclohexylurea precipitate was first removed by centrifugation, and the filtrate was dialyzed to remove unreacted ionic liquid and small molecular by-products, with a molecular weight cut-off of 3.5 kilodaltons or more to obtain the PAMAM grafted ionic liquid PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3.

[0019] Example 2: The present invention provides a method for preparing a PAMAM grafted ionic liquid for purifying carbon dioxide from oil and gas, comprising the following steps: (1) Raw materials and reagents: PAMAM dendrimer: G4 generation is selected, with 64 primary amino groups on the surface and a molecular weight of approximately 14215Da; Carboxylic acid functionalized ionic liquid: 1-butyl-3-methylimidazole carboxylic acid, with a simplified structural formula of C4H9-NC3H3N-CH3-COOH, purity ≥99%; Dehydrating agent: dicyclohexylcarbodiimide, the structural formula is C6H 11 N=C=NC6H 11 , purity ≥99%; Solvent: N, N-dimethylformamide, purity ≥ 99.8%; (II) Reaction steps: 1) Activation of carboxyl groups: 1.0 mol of 1-butyl-3-methylimidazole carboxylic acid was dissolved in 100 mL of anhydrous N,N-dimethylformamide, 1.2 mol of dicyclohexylcarbodiimide was added, and the mixture was stirred at room temperature for 1 hour to generate O-acylisourea; during the reaction, the stirring rate was controlled at 400 rpm; The reaction formula is as follows: C4H9-NC3H3N-CH3-COOH + C6H 11 N=C=NC6H 11 → C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ] +C6H 11 NHCONHC6H 11 The reaction generates O-acylisourea, the structural formula of which is: C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ]; Cyclohexyl, the structural formula is C6H 12 ; Dicyclohexylurea, its structural formula is C 13 H 24 N2O; Among them, the by-product dicyclohexylurea precipitates out; 2) Grafting PAMAM: 256 g of PAMAM dendrimer, containing 64 primary amino groups on its surface, was added to the solution obtained by activating the carboxyl groups in step 1) above. The reaction was carried out under nitrogen protection at 40°C for 24 hours with a stirring rate of 200 rpm. The primary amino groups on the surface of the PAMAM dendrimer are covalently linked to the carboxylic acid functionalized ionic liquid via amide bonds; The reaction formula is as follows: C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ]+PAMAM-NH2→PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3+C6H 11 NHCONHC6H 11 ; 3) Purification: The dicyclohexylurea precipitate was first removed by centrifugation, and the filtrate was dialyzed to remove unreacted ionic liquid and small molecular by-products, with a molecular weight cut-off of 3.5 kilodaltons or more to obtain the PAMAM grafted ionic liquid PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3.

[0020] Example 3: The present invention provides a method for preparing a PAMAM grafted ionic liquid for purifying carbon dioxide from oil and gas, comprising the following steps: (1) Raw materials and reagents: PAMAM dendrimer: G4 generation is selected, with 64 primary amino groups on the surface and a molecular weight of approximately 14215Da; Carboxylic acid functionalized ionic liquid: 1-butyl-3-methylimidazole carboxylic acid, with a simplified structural formula of C4H9-NC3H3N-CH3-COOH, purity ≥99%; Dehydrating agent: dicyclohexylcarbodiimide, the structural formula is C6H 11 N=C=NC6H 11 , purity ≥99%; Solvent: Anhydrous dimethyl sulfoxide, purity ≥99.9%; (II) Reaction steps: 1) Activation of carboxyl groups: 1.0 mol of 1-butyl-3-methylimidazole carboxylic acid was dissolved in 100 mL of anhydrous dimethyl sulfoxide, and 1.2 mol of dicyclohexylcarbodiimide was added. The mixture was stirred at room temperature for 1 hour to generate O-acylisourea. During the reaction, magnetic stirring was intermittent at a stirring rate of 400 rpm. The reaction formula is as follows: C4H9-NC3H3N-CH3-COOH + C6H 11N=C=NC6H 11 → C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ] +C6H 11 NHCONHC6H 11 The reaction generates O-acylisourea, the structural formula of which is: C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ]; Cyclohexyl, the structural formula is C6H 12 ; Dicyclohexylurea, its structural formula is C 13 H 24 N2O; Among them, the by-product dicyclohexylurea precipitates out; 2) Grafting PAMAM: 285 g of PAMAM dendrimer, containing 64 primary amino groups on its surface, was added to the solution obtained by activating the carboxyl groups in step 1) above. The reaction was carried out under nitrogen protection at 40°C for 24 hours with a stirring rate of 200 rpm. The primary amino groups on the surface of the PAMAM dendrimer are covalently linked to the carboxylic acid functionalized ionic liquid via amide bonds; The reaction formula is as follows: C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ]+PAMAM-NH2→PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3+C6H 11 NHCONHC6H 11 ; 3) Purification: The dicyclohexylurea precipitate was first removed by centrifugation, and the filtrate was dialyzed to remove unreacted ionic liquid and small molecular by-products, with a molecular weight cut-off of 3.5 kilodaltons or more to obtain the PAMAM grafted ionic liquid PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3.

[0021] In order to further verify the structure of the PAMAM grafted ionic liquid, the structure of Example 3 was characterized by infrared and nuclear magnetic resonance. Figure 1 (1H-NMR spectrum of PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3) and Figure 2(Infrared spectrum of PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3) shown.

[0022] Depend on Figure 1 The results show that the peak at δ = 1.65 ppm is the proton peak of the -NH2 at the end of the PAMAM macromolecular chain, the peak at δ = 8.02 ppm is the proton peak of the -NH-, the peak at δ = 7.73 ppm is the proton peak of the -NH- position adjacent to the carbonyl group of the imidazole group, the peak at δ = 7.84 ppm is the proton peak of the double bond of the imidazole group, and the peak at δ = 8.33 ppm is the proton peak of the meta position of the imidazole group. Characterization by H NMR spectroscopy confirmed that the product has the expected molecular structure characteristics, preliminarily indicating that the PAMAM grafted ionic liquid PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3 was successfully prepared through this reaction.

[0023] Depend on Figure 2 The results show that 1683cm -1 The characteristic peak of amide bond NH is at 1590 cm -1 The characteristic peak of CN is at 1533cm -1 、1465 cm -1 The absorption peak of imidazole ring is at 3300~2500cm -1 The carboxyl vibration peak at is weak and almost invisible, indicating the successful association of PAMAM molecules and 1-butyl-3-methylimidazole carboxylic acid molecules. Figure 1 The results of H-NMR spectrum fully prove that the preparation of Example 3 is successful.

[0024] The above-mentioned PAMAM grafted ionic liquid PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3 has the following structural characteristics: (1) The butyl substituent of 1-butyl-3-methylimidazole carboxylic acid [Bmim][COOH] is hydrophobic and enhances the interaction with CO2; (2) PAMAM and 1-butyl-3-methylimidazole carboxylic acid [Bmim][COOH] are covalently linked through ester groups to form a stable chemical bond; (3) The amino dispersibility of PAMAM is improved, reducing the steric effect.

[0025] Advantages of the above-mentioned PAMAM grafted ionic liquid PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3: (1) When combined with traditional alcohol amine absorbents, it can significantly improve the absorption efficiency and desorption rate of CO2; (2) In industrial applications, it can directly replace traditional absorbents and be used for carbon dioxide removal in oil and gas purification; (3) It has good durability and stability and can be reused many times; (4) It has low energy consumption and is easy to regenerate.

[0026] The comparative tests of the embodiments and comparative examples mentioned in the present invention are as follows: Comparative Example 1: Using dendritic polymer PAMAM G4 as a carbon dioxide absorbent; Comparative Example 2: Monoethanolamine MEA was used as the carbon dioxide absorbent; Comparative Example 3: Alcoholamine ionic liquid: [Bmim][BF4]-MEA as a carbon dioxide absorbent.

[0027] Absorption experiment test: In order to evaluate the absorption capacity of the absorbent for carbon dioxide in the examples and comparative examples, a CO2 bubbling absorption device was selected to measure the CO2 absorption load. At the beginning of absorption, pure CO2 gas was released from the CO2 cylinder and regulated by a mass flow meter to stabilize the gas flow at 150 ml / min. The gas was then passed into the bubbling absorption bottle to contact with the absorbent to carry out the CO2 absorption reaction. The volume of the absorbent was fixed at 30 g. The bubbling absorption bottle was placed in a constant temperature water bath, and the CO2 absorption was measured by setting the water bath temperature. The absorbed gas flowed out from the outlet of the bottle top, and the outlet gas passed through a wet flow meter, and the data was recorded every two minutes. When the flow rate read by the wet flow meter was consistent with the set inlet flow rate, it was considered that the absorption of the solution had reached saturation, and the experiment was stopped.

[0028] Table 1 Adsorption capacity of absorbent for CO2

[0029] As can be seen from the results in Table 1, the adsorption capacities of Examples 1 to 3 are all relatively high, exceeding 5.00 mol CO2 / mol, and the time to saturation is all over 40 minutes. The adsorption capacity of the conventional CO2 adsorbent monoethanolamine MEA in Comparative Example 2 and the alcoholamine ionic liquid in Comparative Example 3 does not exceed 0.50 mol CO2 / mol. The PAMAM grafted ionic liquid is a multi-amino chemical adsorption with a large molecular weight, providing more carbon dioxide adsorption sites, and can effectively improve the CO2 adsorption capacity compared with Comparative Examples 2 and 3. When PAMAM G4 is used alone as an adsorbent, its capacity can reach 4.21 mol CO2 / mol. After further combining with the ionic liquid, its adsorption capacity is further enhanced. The PAMAM grafted ionic liquid has a synergistic effect, utilizing the high affinity of PAMAM and enhancing the diffusion capacity of carbon dioxide through the functionalized ionic liquid, significantly improving the CO2 absorption efficiency and improving the utilization rate of amino groups compared to using only the dendritic polymer PAMAM as a CO2 absorbent. The above data fully prove that the CO2 absorption efficiency of ionic liquid grafted with PAMAM is significantly improved.

[0030] Desorption Test: To evaluate the carbon dioxide desorption capacity of the absorbents in the Examples and Comparative Examples, desorption experiments were conducted on the saturated alcoholamine solutions. A three-necked flask heating method was used. The saturated absorbent was poured into a three-necked flask, a serpentine condenser and a thermometer were inserted, and the flask was placed in an oil bath. The temperature was adjusted to the desired desorption temperature (100-130°C). After heating at atmospheric pressure until the temperature stabilized, the desorption time was recorded using a stopwatch. In this experiment, the desorption temperature was set at 120°C, and the CO2 desorption amount and time were recorded.

[0031] Table 2 Desorption capacity of absorbent for CO2

[0032] As shown in Table 2, the desorption capacities of the examples are also high, generally around 5.00 mol CO₂ / mol, and the desorption time is also above 75 minutes. The desorption capacities of the conventional CO₂ adsorbents, monoethanolamine MEA (Comparative Example 2) and alcoholamine ionic liquid (Comparative Example 3), are significantly lower, below 0.50 mol CO₂ / mol. This is primarily due to the lower CO₂ adsorption capacity of conventional CO₂ adsorbents, resulting in lower desorption capacities. The desorption results demonstrate that the PAMAM grafted ionic liquid is able to rapidly and stably desorb adsorbed CO₂.

[0033] The PAMAM grafted ionic liquid was then subjected to continuous adsorption-desorption cycles. The experimental results showed that after 50 consecutive cycles, the PAMAM grafted ionic liquid's CO₂ adsorption capacity remained above 5.00 mol CO₂ / mol, and the desorption capacity remained above 4.80 mol CO₂ / mol, showing almost no loss in adsorption and desorption capabilities. In contrast, the commonly used monoethanolamine (MEA) showed a decrease in adsorption capacity of over 70% and a decrease in desorption capacity of over 80% after 50 consecutive cycles. These reductions fully demonstrate that the PAMAM grafted ionic liquid significantly improves the stability and durability of the absorbent.

[0034] Loading capacity evaluation: The CO2 absorbed by the reagent was displaced using a 0.1 mol / L dilute H2SO4 solution. The volumetric loading of the reagent absorbed CO2 was measured using the communicating vessel principle. Load titration experiments were conducted to measure the CO2-rich solution loading and regeneration temperature for the Examples and Comparative Examples, and the experimental data were recorded. The regeneration temperature refers to the temperature required to restore the adsorption / absorption capacity of the absorbent after it has adsorbed or absorbed CO2 by heating it with a higher temperature source, releasing CO2. This temperature reflects the energy consumption required by the absorbent.

[0035] Table 3 CO2 load capacity test

[0036] From the above data, it can be seen that the PAMAM of Comparative Example 1 has a low regeneration temperature and low energy consumption, the monoethanolamine MEA of Comparative Example 2 has a high regeneration energy consumption, and Comparative Example 3 achieves carbon dioxide desorption under lower temperature conditions, which can reduce the heat energy demand during the regeneration process. The rich liquid loading capacity of Example 3 is the largest, which is 19.03 L CO2 / L solution, much higher than the comparative example. This is related to the fact that multiple amino groups in its molecular structure provide more reaction sites. A higher volume loading capacity means that more CO2 can be absorbed in the same volume of solution. Comprehensive absorption, desorption, and loading experiments show that Examples 1-3 have significantly lower regeneration temperatures than traditional amine solvents such as MEA, achieving the purpose of absorbing carbon dioxide and regenerating to reduce energy consumption.

[0037] The above descriptions are merely some preferred embodiments of the present invention. Anyone skilled in the art may be able to modify the above-described technical solutions or convert them into equivalent technical solutions. Therefore, any corresponding simple modifications or equivalent transformations based on the technical solutions of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a PAMAM grafted ionic liquid for purifying carbon dioxide from oil and gas, characterized by: The following steps are involved: (1) Raw materials and reagents: PAMAM dendrimer: G4 generation was selected, which contains 64 primary amino groups on its surface; Carboxylic acid functionalized ionic liquid: 1-butyl-3-methylimidazole carboxylic acid, with a simplified structural formula of C4H9-NC3H3N-CH3-COOH; Dehydrating agent: dicyclohexylcarbodiimide, the structural formula is C6H 11 N=C=NC6H 11 ; Solvent: anhydrous dimethyl sulfoxide or N,N-dimethylformamide; (II) Reaction steps: 1) Activation of carboxyl groups: Dissolve 1.0 mol of 1-butyl-3-methylimidazole carboxylic acid in 100 mL of solvent, add 1.2 mol of dicyclohexylcarbodiimide, and stir at room temperature for 1 h at a stirring rate of 400 rpm. The reaction formula is as follows: <h2 style=";text-align:left;direction:ltr">C4H9-NC3H3N-CH3-COOH + C6H<h2 style=";text-align:left;direction:ltr"> 11 <h2 style=";text-align:left;direction:ltr"> N=C=NC6H<h2 style=";text-align:left;direction:ltr"> 11 <h2 style=";text-align:left;direction:ltr"> → <h2 style=";text-align:left;direction:ltr">C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> )-NH-C6H<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> ] +C6H<h2 style=";text-align:left;direction:ltr"> 11 <h2 style=";text-align:left;direction:ltr"> NHCONHC6H<h2 style=";text-align:left;direction:ltr"> 11 The reaction generates O-acylisourea, the structural formula of which is: C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H 12 )-NH-C6H 12 ]; Among them, cyclohexyl, the structural formula is: C6H 12 ; Dicyclohexylurea, the structural formula is: C6H 11 NHCONHC6H 11 ; 2) Grafting PAMAM: Add 212-285 g of PAMAM dendrimer to the solution obtained after activation of the carboxyl groups in step 1) above, and react at 40°C under nitrogen protection for 24 hours with a stirring rate of 200 rpm. The primary amino groups on the surface of the PAMAM dendrimer are covalently linked to the carboxylic acid functionalized ionic liquid via amide bonds; The reaction formula is as follows: <h2 style=";text-align:left;direction:ltr">C4H9-NC3H3N-CH3-[C(=O)-OC(=N-C6H<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> )-NH-C6H<h2 style=";text-align:left;direction:ltr"> 12 <h2 style=";text-align:left;direction:ltr"> ]+PAMAM-NH2→PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3+C6H<h2 style=";text-align:left;direction:ltr"> 11 <h2 style=";text-align:left;direction:ltr"> NHCONHC6H<h2 style=";text-align:left;direction:ltr"> 11 <h2 style=";text-align:left;direction:ltr"> ; 3) Purification: The dicyclohexylurea precipitate was first removed by centrifugation, and the filtrate was dialyzed to remove unreacted ionic liquid and small molecule by-products, wherein more than 90% of the molecules with a molecular weight cutoff of ≥3.5 kilodaltons were retained to obtain the PAMAM grafted ionic liquid PAMAM-NH-C(=O)-C4H9-NC3H3N-CH3.

2. The method for preparing a PAMAM grafted ionic liquid for oil and gas purification of carbon dioxide according to claim 1, characterized in that: The PAMAM dendrimer has a molecular weight of 14215 Da.

3. The method for preparing a PAMAM grafted ionic liquid for oil and gas purification of carbon dioxide according to claim 2, characterized in that: The 1-butyl-3-methylimidazole carboxylic acid has a purity of ≥99%.

4. The method for preparing a PAMAM grafted ionic liquid for purifying carbon dioxide from oil and gas according to claim 3, wherein: The dicyclohexylcarbodiimide has a purity of ≥99%.

5. The method for preparing a PAMAM grafted ionic liquid for purifying carbon dioxide from oil and gas according to claim 4, characterized in that: The purity of the anhydrous dimethyl sulfoxide is ≥99.9%, and the purity of N,N-dimethylformamide is ≥99.8%.

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