Carbon dioxide trapping agent as well as preparation method and application thereof

Abstract

The invention discloses a carbon dioxide trapping agent and a preparation method and application thereof, and relates to the technical field of chemical synthesis, the carbon dioxide trapping agent comprises the following components: 2-15 mL of diethanolamine, 6-20 mL of triethylene tetramine, 20-80 mL of tetraethylenepentamine, 2-15 mL of ethanolamine, 5-20 mL of triethanolamine, 10-50 mL of methanol, 1-10 mL of polyethyleneimine, 1-12 g of piperazine, and 2-10 mL of an initiator. The carbon dioxide trapping agent disclosed by the invention can simultaneously meet three conditions of high-efficiency trapping, low-cost absorption and normalized application (the temperature is-15 DEG C to 30 DEG C and the pressure is 101 kPa), and can be well compatible with and solve the bottleneck problems, namely economic benefit and cost, which troubles the development of a CCUS technology at present.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical synthesis, and in particular to a carbon dioxide capture agent and a preparation method and application thereof. Background Art

[0002] China is facing increasing international pressure to reduce emissions and domestic demand for emission reduction. It continues to promote the rapid upgrade of CCUS (carbon capture, utilization and storage) technology from a strategic reserve technology to a practical solution. Its technical positioning, development direction and future deployment need further research. Since my country's coal-based energy structure will be difficult to change fundamentally for a long time in the future, CO2 emissions will remain high for a long time. CCUS technology, as an emerging technology with large-scale CO2 emission reduction potential, is widely regarded as one of the important technologies for responding to global climate change and controlling greenhouse gas emissions. The development of CCUS technology is an important technical way for my country to reduce CO2 emissions in the long term. From the perspective of policy orientation and actual needs, CCUS technology will become a focus technology in the next few years, and it is very necessary to reserve technology in this field in advance.

[0003] Liquid amine absorption is a method widely used in industry. This method has high selectivity for CO2 absorption, but it has disadvantages such as high material consumption and corrosion of equipment. Pre-combustion capture technology and post-combustion capture technology have matured and reached the economically feasible stage, but there is still a disadvantage of high cost. The average cost of capture exceeds US$30 / ton of CO2, which seriously affects the deployment of CCUS technology. With good economic benefits, it is a key technology in the future research field of capture technology. Moreover, compared with high-concentration emission sources, low-concentration CO2 emission sources have to invest more in purification and compression costs, and the CO2 capture cost of high-concentration emission sources is lower. For this reason, most of the large-scale CCUS demonstration bases in China currently give priority to or have been deployed around coal-fired power plants and other factories with large CO2 emissions, and most of the global CCUS technology deployments are coal-fired power plants.

[0004] The principle of alcohol amine chemical absorption method is to use the reversible chemical reaction between organic alcohol amine and CO2 to remove CO2 from industrial tail gas. Due to the strong electrostatic and hydrogen bonding effects in the product, the viscosity of organic alcohol amine will increase sharply after absorbing CO2. Therefore, organic alcohol amine usually needs to be diluted in low-viscosity physical solvents such as water, ethanol, and sulfolane.

[0005] A new design concept of "chemical absorbent + chemical diluent", PEI / TEPA+[emim][AcO], PEI+[P 4444[2-F-PhO] mixed absorbent not only has high CO2 absorption capacity and fast CO2 absorption rate, but also has a less significant change in viscosity after CO2 absorption than pure PEI / TEPA. On the other hand, PEI / TEPA and [emim][AcO] / [P 4444 ][2-F-PhO] has extremely low volatility, making PEI / TEPA+[emim][AcO]P 4444 The ][2-F-PhO] mixed absorbent is safer and greener when used in the CO2 capture process.

[0006] Due to the simplicity of the synthesis method of amine solution and its strong absorption capacity, various researchers have carried out a large number of indoor experimental syntheses in recent years. For example: ①, 2M MAPA / 5M DEEA system, characterized by low vapor pressure, high loading capacity, energy consumption of 2.4GJ / ton of CO2, and high viscosity. ②, 2MBDA / 4M DEEA system, characterized by a 48% increase in circulation capacity, but high viscosity. ③, 5MTETA+DEEA system, characterized by a 40% higher circulation loading, a loading capacity of up to 0.92mol / mol, and a 30% lower energy consumption than MEA. ④, DETA+cyclopentane sulfone system, characterized by a 35% higher circulation loading, but very easy to phase separate. ⑤, PMDETA+DETA system, characterized by a loading capacity of up to 0.62mol / mol, a lower phase rich in 99.7% CO2, and low-temperature phase separation. ⑥, temperature-controlled lipophilic alcohol amine solution system, characterized by a low desorption temperature (80°C) and an energy consumption of 2.0GJ / ton of CO2. ⑦. DMCA15%+MCA15%; DMCA25%+PZ5%; DSBA15%+MCA15% systems are characterized by low desorption temperature (80°C), fast absorption rate, cyclic net load about 1.46 times higher than 30% MEA, and regeneration energy consumption of 2.48GJ / ton of CO2. ⑧. DMX-1 system is characterized by low reaction heat (about 60KJ / mol), good thermal stability, easy separation, and energy consumption of 2.3GJ / ton of CO2.

[0007] After NH3 absorbs CO2 with organic solvents such as ethanol, 1-propanol and N, N-dimethylformamide (DMF), the solid phase can enrich CO2 by 54%. Perry et al. investigated a good liquid-solid phase transition system: 1,3-bis(3-aminopropyl)-1,1,3,3-tetrasiloxane (GAP-0). After the absorbent is loaded with CO2, it changes from a low-viscosity liquid to a solid that is rich in a large amount of CO2. The process model of this system reduces the energy consumption from 30% of the MEA process to 18%. Recently, researchers have studied new polyamine absorbents (diethanolamine DEA, 2-amino-2-methyl-1-propanol AMP, dimethyldiethanolamine DMEE) using ionic liquids (tetramethylammonium glycine, [N1111][Gly]) as solvents, which have the advantages of easy liquid-solid phase transition, fast absorption rate, large loading capacity and low desorption temperature. At the same time, the liquid-solid phase separation behavior of polyamines (diethylenetriamine DETA, triethylenetetramine TETA, tetraethylenepentamine TEPA, etc.) after loading CO2 in organic solvents such as ethanol, diethylene glycol dimethyl ether, and N-methylpyrrolidone is also very obvious. In addition, the system has the advantages of fast absorption rate, large loading capacity and low desorption temperature.

[0008] Based on the above-listed technologies and process analysis of synthetic amine liquids, it can be seen that some of the above-mentioned agents tend to have higher CO2 absorption, some tend to have lower analysis energy consumption and analysis temperature, and some tend to reduce viscosity to improve mass transfer efficiency. Regardless of which emphasis is placed, there is currently no agent that can comprehensively solve the high adsorption, high analysis rate, high reuse rate and low analysis energy consumption of CO2 absorbents. Moreover, if the above-mentioned agents are purchased at an industrial level, a large economic cost investment is required, which seriously restricts the market promotion of such agents. Currently, these agents are only suitable for laboratory research stages, and are not suitable for on-site implementation. Therefore, there is a temporary lack of high-efficiency and low-cost CO2 capture agents with high market share and utilization rate on the market. Therefore, it is urgent to develop a high-efficiency and low-cost CO2 capture agent under normal conditions. Summary of the invention

[0009] The purpose of the present invention is to provide a carbon dioxide capture agent and its preparation method and application, which can simultaneously meet the three conditions of high-efficiency capture, low-cost absorption, and normalized (temperature -15℃~30℃, pressure 101kPa) application, and can be very well compatible and solve the bottleneck problem that currently plagues the development of CCUS technology - economic benefits and costs. Once the economic benefits and cost issues are resolved, it will release the domestic CCUS market demand, increase the breadth and depth of CCUS technology applications, and gain an upper hand in the market competition landscape.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] The invention provides a carbon dioxide capture agent. The formula of the carbon dioxide capture agent comprises: 2-15 mL of diethanolamine, 6-20 mL of triethylenetetramine, 20-80 mL of tetraethylenepentamine, 2-15 mL of ethanolamine, 5-20 mL of triethanolamine, 10-50 mL of methanol, 1-10 mL of polyethyleneimine, 1-12 g of piperazine and 2-10 mL of initiator.

[0012] Preferably, the formula of the carbon dioxide capture agent includes: 8-15 mL of diethanolamine, 10-20 mL of triethylenetetramine, 30-80 mL of tetraethylenepentamine, 6-15 mL of ethanolamine, 5-20 mL of triethanolamine, 20-50 mL of methanol, 2-10 mL of polyethyleneimine, 5-12 g of piperazine, and 5-10 mL of initiator.

[0013] Preferably, the initiator is N-methyldiethanolamine.

[0014] The present invention also provides a method for preparing a carbon dioxide capture agent, the method comprising the following steps:

[0015] Add methanol and piperazine to the reactor and stir at room temperature. After piperazine is completely dissolved, add ethanolamine, diethanolamine, triethylenetetramine, tetraethylenepentamine and triethanolamine in sequence. After adding each agent, stir for 5 to 10 minutes before adding the next one. Then add polyethyleneimine and initiator. When the solution becomes a uniform and transparent solution, stop stirring and cool to room temperature to obtain the target product.

[0016] Preferably, the stirring conditions include: a stirring speed of 50 r / min to 60 r / min, and a stirring time of 5 min to 10 min.

[0017] The present invention also provides an application of a carbon dioxide capture agent, wherein the maximum saturated absorption capacity of CO2 of the carbon dioxide capture agent is 95.1 mg / g, which is 8 to 9 times that of monoethanolamine (MEA) under the same conditions; the maximum repeated absorption capacity is 91.4%, and the resolution rate is 98%.

[0018] Furthermore, when the carbon dioxide capture agent is used at a temperature of -15°C to 30°C and a pressure of 101 kPa, it can capture CO2 with a concentration of less than 5% in the air, and after being refrigerated and left to stand at -15°C for 120 days, there is no stratification, turbidity, or crystallization, and it can still maintain a relatively high low-temperature stability.

[0019] Technical effects and advantages of the present invention:

[0020] 1. The high-efficiency and low-cost carbon dioxide capture agent prepared by the present invention has the characteristics of good thermal stability, fast absorption rate, good selectivity, high capacity, good recyclability, etc. The absorption capacity of CO2 exceeds that of the traditional organic alcohol amine aqueous solution, and the maximum saturated absorption of CO2 can reach 21g. It is 8 to 9 times that of monoethanolamine (MEA) under the same conditions. At the same time, the test results of a third-party agency with CMA qualifications show that the performance indicators of the independently developed amine solution are better than those of similar products with high market share.

[0021] 2. The amine solution obtained by the saturated adsorption of carbon dioxide by the scavenger prepared by the present invention has no stratification, no turbidity, and no crystallization after being refrigerated at 6°C. According to the test, the independently developed amine solution can still maintain a high low-temperature stability at -15°C and after standing for 120 days, without stratification, no turbidity, and no crystallization.

[0022] Other features and advantages of the present invention will be described in the following description, and partly become obvious from the description, or be understood by implementing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 This is the reaction mechanism diagram of polyethyleneimine (PEI) and carbon dioxide (CO2);

[0025] Figure 2 Schematic diagram of the test device for CO2 saturation absorption capacity. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the steps. For example, some steps may be decomposed, while some steps may be combined or partially combined, so the actual execution order may change according to the actual situation.

[0028] The terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0029] In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or sub-modules is not necessarily limited to those steps or sub-modules explicitly listed, but may include other steps or sub-modules not explicitly listed or inherent to these processes, methods, products, or apparatuses.

[0030] In order to solve the shortcomings of the prior art, the present invention discloses a carbon dioxide capture agent. The formula of the carbon dioxide capture agent includes: 2-15 mL of diethanolamine, 6-20 mL of triethylenetetramine, 20-80 mL of tetraethylenepentamine, 2-15 mL of ethanolamine, 5-20 mL of triethanolamine, 10-50 mL of methanol, 1-10 mL of polyethyleneimine, 1-12 g of piperazine, and 2-10 mL of initiator N-methyldiethanolamine.

[0031] Furthermore, the formula of the carbon dioxide capture agent includes: 8-15 mL of diethanolamine, 10-20 mL of triethylenetetramine, 30-80 mL of tetraethylenepentamine, 6-15 mL of ethanolamine, 5-20 mL of triethanolamine, 20-50 mL of methanol, 2-10 mL of polyethyleneimine, 5-12 g of piperazine, and 5-10 mL of initiator.

[0032] The present invention also discloses a method for preparing a carbon dioxide capture agent, comprising the following steps:

[0033] Add methanol and piperazine into the reaction kettle and stir. After the piperazine is completely dissolved, add ethanolamine, diethanolamine, triethylenetetramine, tetraethylenepentamine and triethanolamine into the reaction kettle in order. After each agent is added, stir at a speed of 50r / min to 60r / min for 5min to 10min before adding the next one. Then add polyethyleneimine and initiator N-methyldiethanolamine. When the solution completely becomes a uniform and transparent solution, stop stirring and cool to room temperature to obtain the target product.

[0034] The present invention also discloses an application of a carbon dioxide capture agent, wherein the maximum saturated absorption capacity of CO2 of the carbon dioxide capture agent is 95.1 mg / g, which is 8 to 9 times that of monoethanolamine (MEA) under the same conditions; the maximum repeated absorption capacity is 91.4%, and the resolution rate is 98%.

[0035] Furthermore, when the capture agent is used at a temperature of -15°C to 30°C and a pressure of 101 kPa, it can capture CO2 with a concentration of less than 5% in the air, and after being refrigerated and left to stand at -15°C for 120 days, there is no stratification, turbidity, or crystallization, and it can still maintain a high low-temperature stability.

[0036] Among them, the mechanism and chemical equation of the reaction between some formula components and CO2 are as follows:

[0037] ①. The chemical equation for the reaction between N-methyldiethanolamine (45% MDEA) and carbon dioxide is as follows:

[0038]

[0039]

[0040]

[0041] ②. Tetraethylenepentamine (TEPA) and carbon dioxide can undergo a variety of reactions:

[0042]

[0043]

[0044] ③. Monoethanolamine (MEA) and carbon dioxide can react as follows:

[0045]

[0046] ④. Methanol and carbon dioxide can react as follows:

[0047]

[0048] ⑤. Polyethyleneimine (PEI) has abundant primary, secondary and tertiary amines on its molecular chain. The adsorption reaction with CO2 begins with the lone pair of electrons on the primary or secondary amine attacking the positively charged carbon atom on CO2 to form amphoteric particles, which then react with another non-tertiary amine, water molecules or other hydroxide ions to form a metastable carbamate structure ( Figure 1 ). The adsorption reaction equation of primary amine or secondary amine is:

[0049] CO2+RNH2→RNH2-CO2;

[0050] RNH2-CO2+B→RNHCOO - +BH + ;

[0051] In the above formula, B represents another non-tertiary amine amine group, water molecule or hydroxide ion. Tertiary amine captures CO2 by promoting the reaction of CO2 molecules with water molecules to form bicarbonate. The reaction equation is:

[0052] R3N+H2O+CO2→R3NH + +HCO3 - ;

[0053] ⑥. Piperazine 5% and carbon dioxide can produce the following reaction:

[0054]

[0055]

[0056] Embodiment 1:

[0057] Example 1 of the present invention discloses a carbon dioxide capture agent, the formula of which includes: 15 mL of diethanolamine, 20 mL of triethylenetetramine, 80 mL of tetraethylenepentamine, 15 mL of ethanolamine, 20 mL of triethanolamine, 50 mL of methanol, 10 mL of polyethyleneimine, 12 g of piperazine, and 10 mL of initiator.

[0058] Embodiment 1 of the present invention also discloses a method for preparing a carbon dioxide capture agent, comprising the following steps:

[0059] Add 50 mL of methanol and 12 g of piperazine into the reactor and stir. After the piperazine is completely dissolved, add 15 mL of ethanolamine, 15 mL of diethanolamine, 20 mL of triethylenetetramine, 80 mL of tetraethylenepentamine and 20 mL of triethanolamine in sequence. After adding each agent, stir at a speed of 50 r / min for 5 minutes. Then add 10 mL of polyethyleneimine and 10 mL of initiator N-methyldiethanolamine. When the solution completely becomes a uniform and transparent solution, stop stirring and cool to room temperature to obtain the target product.

[0060] Embodiment 2:

[0061] Example 2 of the present invention discloses a carbon dioxide capture agent, the formula of which includes: 10 mL of diethanolamine, 15 mL of triethylenetetramine, 40 mL of tetraethylenepentamine, 8 mL of ethanolamine, 10 mL of triethanolamine, 20 mL of methanol, 5 mL of polyethyleneimine, 6 g of piperazine, and 8 mL of initiator.

[0062] Embodiment 2 of the present invention also discloses a method for preparing a carbon dioxide capture agent, comprising the following steps:

[0063] Add 20 mL of methanol and 6 g of piperazine into the reactor and stir. After the piperazine is completely dissolved, add 8 mL of ethanolamine, 10 mL of diethanolamine, 15 mL of triethylenetetramine, 40 mL of tetraethylenepentamine and 10 mL of triethanolamine in sequence. After adding each agent, stir at a speed of 50 r / min for 5 minutes. Then add 5 mL of polyethyleneimine and 8 mL of initiator N-methyldiethanolamine. When the solution completely becomes a uniform and transparent solution, stop stirring and cool to room temperature to obtain the target product.

[0064] Embodiment 3:

[0065] Example 3 of the present invention discloses a carbon dioxide capture agent, the formula of which includes: 8 mL of diethanolamine, 15 mL of triethylenetetramine, 50 mL of tetraethylenepentamine, 6 mL of ethanolamine, 5 mL of triethanolamine, 30 mL of methanol, 2 mL of polyethyleneimine, 5 g of piperazine, and 5 mL of initiator.

[0066] Embodiment 3 of the present invention also discloses a method for preparing a carbon dioxide capture agent, comprising the following steps:

[0067] Add 30 mL of methanol and 5 g of piperazine into the reactor and stir. After the piperazine is completely dissolved, add 6 mL of ethanolamine, 8 mL of diethanolamine, 15 mL of triethylenetetramine, 50 mL of tetraethylenepentamine and 5 mL of triethanolamine into the reactor and stir at a speed of 50 r / min for 5 min. Then add 2 mL of polyethyleneimine and 5 mL of initiator N-methyldiethanolamine. When the solution completely becomes a uniform and transparent solution, stop stirring and cool to room temperature to obtain the target product.

[0068] Embodiment 4:

[0069] Example 4 of the present invention discloses a carbon dioxide capture agent, the formula of which includes: 15 mL of diethanolamine, 10 mL of triethylenetetramine, 30 mL of tetraethylenepentamine, 10 mL of ethanolamine, 15 mL of triethanolamine, 20 mL of methanol, 2 mL of polyethyleneimine, 8 g of piperazine, and 10 mL of initiator.

[0070] Embodiment 4 of the present invention also discloses a method for preparing a carbon dioxide capture agent, comprising the following steps:

[0071] Add 20 mL of methanol and 8 g of piperazine into the reactor and stir. After the piperazine is completely dissolved, add 10 mL of ethanolamine, 15 mL of diethanolamine, 10 mL of triethylenetetramine, 30 mL of tetraethylenepentamine and 15 mL of triethanolamine into the reactor. After adding each agent, stir at a speed of 50 r / min for 5 minutes. Then add 2 mL of polyethyleneimine and 10 mL of initiator N-methyldiethanolamine. When the solution completely becomes a uniform and transparent solution, stop stirring and cool to room temperature to obtain the target product.

[0072] Test example:

[0073] The present invention is to develop a highly efficient and low-cost CO2 capture agent for CCUS, so its main technical indicators are CO2 saturated absorption capacity, saturated absorption liquid viscosity, CO2 resolution rate, and CO2 repeated absorption capacity, a total of 4 technical indicators.

[0074] 1. The method for testing the CO2 saturation absorption is to test the carbon dioxide absorption efficiency of the sample on a stainless steel carbon dioxide absorption device commonly used in the art. First, prepare the required test solution and put it into the carbon dioxide absorption bottle. Figure 2 Then weigh its initial weight and record it as m1, then introduce a certain amount of CO2 gas from the long tube, stop the ventilation after 20 minutes, measure the mass of CO2 absorbed by the test gas washing bottle and record it as m2, and the calculation formula of saturated absorption is as follows.

[0075]

[0076] 2. The viscosity of the saturated absorption liquid is tested using a viscosity tester that complies with national standards.

[0077] 3. The CO2 resolution rate is operated by vacuum evaporation. First, weigh the mass m2 of the absorption liquid after saturated CO2 adsorption, and then place the liquid saturated with CO2 adsorption in a vacuum evaporation thermostat, adjust the test pressure to -1atm, and raise the temperature to 85°C. Then collect the gas at the outlet of the instrument and perform gas chromatography analysis. When the CO2 concentration in the gas chromatography test does not change three times, it is considered that the resolution is complete. Then weigh the mass m3 of the absorption liquid after resolution. The calculation formula of the resolution rate is as follows.

[0078]

[0079] 4. The test method for repeated absorption of CO2 is consistent with the test method for absorption rate.

[0080] The sample numbers corresponding to the above-mentioned Examples 1 to 5 are respectively recorded as 1#, 2#, 3#, and 4#. The test results of Examples 1 to 4 are shown in Table 1 below.

[0081] Table 1 Test results of various technical indicators of Examples 1 to 4

[0082]

[0083] Internationally renowned brands of amine liquid and domestically renowned brands of amine liquid were selected for performance index comparison, and the corresponding test results and reports were issued by an authoritative testing agency. The specific results are shown in Table 2 below.

[0084] Table 2 Comparative test data of amine liquid performance

[0085]

[0086]

[0087] It can be seen from the experimental results that the amine liquid independently synthesized and developed in Example 4 of the present invention is far superior to other products in terms of the four indicators of CO2 saturated absorption capacity, saturated absorption liquid viscosity, CO2 resolution rate, and CO2 repeated absorption capacity, and the market price is much lower than the selling prices of the other two types of amine liquids, and has extremely high economic and market promotion value.

[0088] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A carbon dioxide capture agent, characterized in that: The formula composition of the carbon dioxide capture agent includes: 2-15 mL of diethanolamine, 6-20 mL of triethylenetetramine, 20-80 mL of tetraethylenepentamine, 2-15 mL of ethanolamine, 5-20 mL of triethanolamine, 10-50 mL of methanol, 1-10 mL of polyethyleneimine, 1-12 g of piperazine, and 2-10 mL of initiator.

2. A carbon dioxide capture agent according to claim 1, characterized in that: The formula composition of the carbon dioxide capture agent includes: 8-15 mL of diethanolamine, 10-20 mL of triethylenetetramine, 30-80 mL of tetraethylenepentamine, 6-15 mL of ethanolamine, 5-20 mL of triethanolamine, 20-50 mL of methanol, 2-10 mL of polyethyleneimine, 5-12 g of piperazine, and 5-10 mL of initiator.

3. A carbon dioxide capture agent according to claim 1 or 2, characterized in that: The initiator is N-methyldiethanolamine.

4. A method for preparing a carbon dioxide capture agent according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: Add methanol and piperazine to the reactor and stir at room temperature. After piperazine is completely dissolved, add ethanolamine, diethanolamine, triethylenetetramine, tetraethylenepentamine and triethanolamine in sequence. After adding each agent, stir for 5 to 10 minutes before adding the next one. Then add polyethyleneimine and initiator. When the solution becomes a uniform and transparent solution, stop stirring and cool to room temperature to obtain the target product.

5. The method for preparing a carbon dioxide capture agent according to claim 4, characterized in that: The stirring conditions include: a stirring speed of 50 r / min to 60 r / min, and a stirring time of 5 min to 10 min.

6. A use of the carbon dioxide capture agent according to any one of claims 1 to 3, characterized in that: The maximum saturated absorption capacity of CO2 of the carbon dioxide capture agent is 95.1 mg / g, which is 8 to 9 times that of monoethanolamine (MEA) under the same conditions; the maximum repeated absorption capacity is 91.4%, and the resolution rate is 98%.

7. The use of a carbon dioxide capture agent according to claim 6, characterized in that: When used at a temperature of -15°C to 30°C and a pressure of 101 kPa, the carbon dioxide capture agent can capture CO2 with a concentration of less than 5% in the air, and after being refrigerated and left to stand at -15°C for 120 days, there is no stratification, turbidity, or crystallization, and the agent can still maintain a relatively high low-temperature stability.

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