A phase change absorbent for capturing CO2 and a method for capturing CO2.

Abstract

The application discloses a phase change absorbent for capturing CO2 and a method for capturing CO2, and the phase change absorbent is composed of tetramethylethylenediamine, hydroxyethyl ethylenediamine, 1-propanol and water. The phase change absorbent is homogeneous before absorption, and is converted into liquid-liquid two phases after absorption, the upper phase is mainly a tertiary amine and 1-propanol solution, and most of carbon dioxide products are concentrated in the lower phase aqueous solution. Since only the rich phase needs to be heated during desorption, the regeneration energy consumption can be effectively reduced. The use of the organic solvent 1-propanol to replace part of the aqueous solvent not only improves the solubility of CO2 in the phase change absorbent, but also can further reduce the rich liquid volume and thus reduce the regeneration energy consumption.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide capture and separation technology, specifically to a phase change absorbent for capturing CO2 and a method for capturing CO2. Background Technology

[0002] Common CO2 capture technologies typically include: pre-combustion capture, oxygen-enriched combustion, and post-combustion capture. Among these, post-combustion capture requires the least modification to existing equipment and is considered the most promising technology for CO2 capture.

[0003] Chemical absorption is a widely used industrial method for post-combustion CO2 capture. For example, monoethanolamine (MEA) is widely used in industrial CO2 capture due to its high absorption efficiency, large CO2 capacity, and renewability. However, traditional amine solvents are prone to problems such as high regeneration energy consumption, equipment corrosion, and amine degradation during absorption. Therefore, more and more researchers are dedicated to developing novel absorbents such as compound amines, phase change absorbents, ionic liquids (ILs), and eutectic solvents (DESs) to reduce CO2 capture costs.

[0004] Phase change absorbents refer to absorbents that are homogeneous solutions before CO2 absorption, but separate into two phases after CO2 absorption due to differences in the polarity or density of their components. Using phase change absorbents to capture CO2 concentrates the CO2 products in the rich phase. Regeneration only requires heating the rich phase, reducing the volume required for regeneration compared to other absorbents, thus significantly reducing energy consumption. The components of a two-phase solvent are typically a phase separator / active amine / water. Taking tertiary amine / primary / secondary amine / water as an example, after phase separation, the upper phase mainly consists of hydrophobic tertiary amine, while the lower phase is an aqueous solution of CO2 products. However, due to the properties of water, regeneration requires significant latent heat, and there are issues with electrochemical corrosion between the aqueous solution and pipelines. Compared to aqueous solutions, non-aqueous solutions have advantages such as higher boiling points and lower corrosivity to equipment. Using non-aqueous solvents to construct non-aqueous liquid-liquid phase change absorbents for CO2 capture is expected to provide a new approach for efficient, low-energy, and low-corrosion carbon capture technology.

[0005] Phase-rich regeneration costs constitute a major portion of CO2 capture expenses. Taking 30wt% monoethanolamine (MEA) aqueous solution capture as an example, the energy cost of phase-rich regeneration accounts for more than two-thirds of the total carbon capture operation cost. Even with phase change absorbers, energy consumption is 2-2.5 GJ / tCO2. To further reduce regeneration costs, catalytic phase-rich regeneration has become a new method to reduce regeneration energy consumption. Catalysts can be classified into homogeneous and heterogeneous catalysts based on whether the catalyst and reactants are in the same phase. Homogeneous catalysts mainly consist of inorganic acids (oxalic acid, sulfurous acid, etc.) or Lewis acid metal salts (such as copper chloride, nickel chloride, etc.). Although homogeneous catalysts also exhibit good catalytic performance, they are difficult to separate and cannot be reused, increasing catalytic costs. Heterogeneous catalysts are easy to separate, and those currently mainly used in catalytic research include molecular sieves, transition state metal oxides, carbonic anhydrases, metal-organic frameworks (MOFs), and organic covalent frameworks (COFs). Heterogeneous catalysts have exhibited extremely high catalytic performance, for example, SO42-. 2- / ZrO2-HZSM-5 catalysis reduces the MEA-CO2 regeneration temperature to below 98℃, reducing energy consumption by approximately 31% (Environmental Science & Technology, 2020, 54(21): 13944-13952). However, acidic catalysts have poor stability in alkaline environments, and it is necessary to improve catalyst stability while ensuring catalytic performance.

[0006] Chinese patent application CN110801711A discloses a phase change absorbent for capturing carbon dioxide and a method for capturing carbon dioxide. The absorbent, based on 100% by volume, comprises a main absorbent of 25%-55%, a co-absorbent of 6%-45%, a phase-separating agent of 10%-40%, and water of 5%-25%. The phase-separating agent is 1-propanol. The main absorbent is a tertiary amine from the alcohol amine family. The co-absorbent is a primary or secondary amine having at least two amino groups. The method for capturing carbon dioxide using the aforementioned phase change absorbent involves contacting a carbon dioxide-containing gas with the phase change absorbent to saturate the absorbent with carbon dioxide. The saturated absorbent then separates into two liquid phases, with CO2 enriched in the lower liquid phase. This absorbent can achieve a small volume ratio of carbon dioxide-rich liquid phase after capturing carbon dioxide and low energy consumption for desorption. In addition, the absorbent also has a large absorption capacity and a fast absorption rate. However, the main absorbent selected in this literature is a tertiary amine. Compared with primary amine, the product formed by capturing CO2 with tertiary amine is easier to regenerate, but the reactivity of tertiary amine with CO2 is poor. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a phase change absorbent for capturing CO2 with low energy consumption and good reactivity with CO2, and a method for capturing CO2.

[0008] The present invention solves the above-mentioned technical problems through the following technical means:

[0009] A phase change absorbent for capturing CO2, comprising tetramethylethylenediamine (TMEDA), hydroxyethylethylenediamine (AEEA), 1-propanol and water.

[0010] Preferably, the components include 30-40% by mass of tetramethylethylenediamine, 30-40% by mass of hydroxyethylethylenediamine, and a total of 30% by mass of 1-propanol and water.

[0011] Preferably, the mass ratio of 1-propanol to water is 1-5:5-9.

[0012] Preferably, the mass ratio of 1-propanol to water is 3:7.

[0013] Beneficial effects: By specifically controlling the addition ratio of 1-propanol without further reducing the water solvent, the viscosity of the rich phase can be kept too high or even precipitate can be formed, and the regeneration energy consumption can be effectively reduced.

[0014] Preferably, the mass fraction of hydroxyethyl ethylenediamine is 30%, the mass fraction of tetramethyl ethylenediamine is 40%, the mass fraction of water is 21%, and the mass fraction of 1-propanol is 9%.

[0015] The present invention also proposes a method for capturing CO2 using the phase change absorbent for capturing CO2, comprising the following steps: contacting the phase change absorbent with a CO2-containing gas to absorb CO2, wherein the absorbent after absorbing CO2 is divided into upper and lower liquid phases, and CO2 is enriched in the lower liquid phase.

[0016] Preferably, during the CO2 absorption process, the absorption temperature is 40–60°C, the volume fraction of CO2 in the CO2-containing gas is 8–12%, and the liquid-to-gas ratio is 5–8 L / m³. 3 .

[0017] Preferably, the volume of the lower liquid phase is 35-75% of the total volume of the upper and lower liquid phases; the absorption load is not less than 2.4 mol (CO2) / kg (amine).

[0018] Preferably, the method further includes desorbing the lower liquid phase after CO2 absorption.

[0019] Preferably, the desorption is performed under heating.

[0020] Preferably, the desorption temperature is 90–120°C, the time is 30–90 min, and the desorption pressure is 1–1.1 atmospheres.

[0021] Preferably, the CO2 desorption rate is 55-75%.

[0022] Preferably, at a temperature of 120°C and a regeneration time of 90 min, the CO2 desorption rate reaches about 75%.

[0023] Preferably, a catalyst is added during the desorption process; the catalyst has a core-shell structure, with the core being MIL-125-NH2 and the shell being COF-LZU1; the core is the catalytic regeneration active host titanium-based MOFs MIL-125-NH2, and the shell is a stable organic covalent framework COF-LZU1 with acid and alkali resistance, which is covalently linked by pyromellitic methyl ether and p-phenylenediamine.

[0024] Beneficial effects: With the addition of a catalyst, CO2 is more easily desorbed under the same regeneration process conditions, and the CO2 desorption rate can reach 90-95%.

[0025] Preferably, when adding catalyst for regeneration, the regeneration temperature is 90℃, the regeneration time is 40min, and the CO2 desorption rate reaches about 75%.

[0026] The core-shell catalyst of this invention comprises a core of MOFs (Metal-Oxygen-Fish) synthesized hydrothermally from tetrabutyl titanate and 2-aminoterephthalic acid with the addition of cyclohexanecarboxylic acid as a modifier, namely MIL-125-NH2. This MOF possesses numerous Li- and Beta-acid catalytic sites, as well as advantages such as large specific surface area and high porosity, providing good catalytic activity. Simultaneously, the -NH2 group serves as a bonding site for the outer shell COFs. The outer shell COFs are organically linked from trimesin and p-phenylenediamine, exhibiting alkali resistance. The core-shell structure material is obtained by solvothermal synthesis of a MOF solution containing trimesin and p-phenylenediamine.

[0027] The regeneration mechanism of the catalytically enriched phase in this invention is as follows: The catalyst core, MIL-125-NH2, contains Lewis acid sites (LAS) and Brønsted acid sites (BAS). The protons provided by the BAS convert AEEA-CO2- to AEEA-COOH. Then, metallic Ti provides empty orbitals that combine with the unique pair of electrons on the O atom, resulting in a longer NC bond length and weakened bond energy. Therefore, CO2 regeneration can occur even at low temperatures. Simultaneously, the LAS can also convert AEEA-COOH... + Deprotonation transfers protons to BAS, regenerating AEEA and BAS, and catalyzing the start of the next cycle.

[0028] Core-shell structured catalysts, due to their stable outer shell, improve the overall stability of the catalyst while ensuring the catalytic performance of the core. The absorbent of this invention exhibits excellent CO2 absorption performance, a short phase separation time, and the use of catalyst-assisted regeneration can further reduce regeneration energy consumption, thus showing broad application prospects.

[0029] The phase change absorbent for CO2 capture described in this invention is homogeneous before CO2 absorption and separates into two phases after CO2 absorption. The lower phase is rich in CO2 products, while the upper phase is poor in CO2, mainly composed of tertiary amines and organic solvents. The rich phase is simply sent to a desorption tower for catalyst-assisted regeneration, thus solving the problem of excessive energy consumption in existing absorbents.

[0030] The main absorbent of the phase change absorbent for CO2 capture described in this invention, hydroxyethyl ethylenediamine, contains primary amine (-NH2) and secondary amine (-NH-) groups, enhancing its CO2 absorption performance. This ensures both a rapid CO2 absorption rate and a high CO2 load. The phase-separating agent comprises the hydrophobic tertiary amine tetramethylethylenediamine and 1-propanol. Tetramethylethylenediamine not only acts as a phase separator but also serves as a regeneration active amine to promote CO2 absorption. Replacing some water with 1-propanol improves the solubility of CO2 in the solution and reduces the volume of the rich phase, thus decreasing regeneration energy consumption. Furthermore, replacing only a small amount of water avoids excessive viscosity of the rich phase, which could lead to precipitation and impede solution flow within the pipeline. Attached Figure Description

[0031] Figure 1 This is a transmission electron microscope image of the catalyst synthesized in Example 7 of the present invention;

[0032] Figure 2 This is a diagram illustrating the phase change mechanism of the phase change absorbent after absorbing CO2, as proposed in this invention.

[0033] Figure 3 This is a schematic diagram of the entire CO2 absorption-regeneration process in Embodiment 6 of the present invention; 1-washing tower; 2-absorption tower; 3-cooler; 4-circulation pump; 5-lean liquor heat exchanger; 6-phase separation tank; 7-first lean liquor pump; 8-rich liquor pump; 9-lean-rich liquor heat exchanger; 10-second lean liquor pump; 11-regeneration tower; 12-reflux pump; 13-condenser; 14-gas-liquid separator; 15-reboiler;

[0034] Figure 4 The diagrams show the phase separation of CO2 absorbed by the aqueous absorbents in Comparative Example 1 and Examples 1-5 of this invention, with different mass ratios. 100% represents Comparative Example 1, and 90%, 80%, 70%, 60%, and 50% represent Examples 1-5, respectively.

[0035] Figure 5 The diagram shows the volume ratio of the upper and lower phases after phase separation of the aqueous absorbent in Comparative Example 1 and Examples 1-5 of the present invention, containing different mass ratios; wherein, 100% represents Comparative Example 1, and 90%, 80%, 70%, 60%, and 50% represent Examples 1-5 respectively.

[0036] Figure 6The diagram shows the phase separation time and rich phase loading of aqueous absorbents with different mass ratios in Comparative Example 1 and Examples 1-5 of the present invention; wherein 100% represents Comparative Example 1, and 90%, 80%, 70%, 60%, and 50% represent Examples 1-5 respectively. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0039] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0040] Example 1

[0041] A phase change absorbent for capturing CO2 is a quaternary system composed of a main absorbent AEEA, a phase separation promoter TMEDA, 1-propanol, and a solvent water. The mass fractions of AEEA, TMEDA, and water are 30%, 40%, 27% (90% water content compared to the total mass of 1-propanol and water), and 3% 1-propanol. It is a homogeneous solution before absorbing carbon dioxide.

[0042] The absorbent was used to absorb simulated flue gas with a CO2 volume fraction of 12% at an absorption temperature of 40°C for 30 minutes. After absorption, the absorbent separated into two phases. The enriched phase was sent for desorption regeneration at a temperature of 120°C for 90 minutes.

[0043] Example 2

[0044] A phase change absorbent for capturing CO2 is a quaternary system composed of a main absorbent AEEA, a phase separation promoter TMEDA, 1-propanol, and a solvent water. The mass fractions of AEEA, TMEDA, and water are 30%, 40%, 24% (80% water content compared to the total mass of 1-propanol and water), and 6% 1-propanol. It is a homogeneous solution before absorbing carbon dioxide. The remaining absorption and desorption conditions are the same as in Example 1.

[0045] Example 3

[0046] A phase change absorbent for capturing CO2 is a quaternary system composed of a main absorbent AEEA, a phase separation promoter TMEDA, 1-propanol, and a solvent water. The mass fractions of AEEA, TMEDA, and water are 30%, 40%, 21% (70% water content compared to the total mass of 1-propanol and water), and 9% 1-propanol. It is a homogeneous solution before absorbing carbon dioxide. The remaining absorption and desorption conditions are the same as in Example 1.

[0047] Example 4

[0048] A phase change absorbent for capturing CO2 is a quaternary system composed of a main absorbent AEEA, a phase separation promoter TMEDA, 1-propanol, and a solvent water. The mass fractions of AEEA, TMEDA, and water are 30%, 40%, 18% (60% water content compared to the total mass of 1-propanol and water), and 12% 1-propanol. It is a homogeneous solution before absorbing carbon dioxide. The remaining absorption and desorption conditions are the same as in Example 1.

[0049] Example 5

[0050] A phase change absorbent for capturing CO2 is a quaternary system composed of a main absorbent AEEA, a phase separation promoter TMEDA, 1-propanol, and a solvent water. The mass fractions of AEEA, TMEDA, and water are 30%, 40%, 15% (50% water content compared to the total mass of 1-propanol and water), and 15% 1-propanol. It is a homogeneous solution before absorbing carbon dioxide. The remaining absorption and desorption conditions are the same as in Example 1.

[0051] Example 6

[0052] A complete CO2 absorption-regeneration process experiment using a phase change absorbent for CO2 capture. The method for capturing CO2 with the described phase change absorbent can be achieved by... Figure 3The process includes: 1) The phase change absorbent contacts CO2 gas in the absorption tower 2 in a counter-current manner. The captured flue gas enters the water washing tower 1 to wash away the volatile solution before being discharged. The cold water in the water washing tower 1 is cooled by the cooler 3 and is recycled by the circulating pump 4. 2) The phase change absorbent flows into the phase separation tank 6 from the bottom of the tower. The lean liquid enters the lean liquid cooler 5 through the first lean liquid pump 7 and mixes with the lean liquid at the outlet of the regeneration tower 11 before returning to the absorption tower 2. 3) The rich liquid flows into the lean-rich liquid heat exchanger 9 through the rich liquid pump 8 for heat exchange. The rich liquid after heat exchange enters the regeneration tower 11. The lean liquid in the lean-rich liquid heat exchanger 9 is obtained from the lean liquid flowing out of the regeneration tower 11 through the second lean liquid pump 10. 4) The rich liquid flows through the catalyst packing of Example 7 in the regeneration tower 11 for heating and desorption, releasing CO2 gas. The CO2 is condensed by the condenser 13 and separated into organic amines and water vapor in the gas-liquid separator 14 for further purification of the CO2 gas. The resulting amine solution is returned to the regeneration tower 11 via reflux pump 12 to replenish the absorbent. The regeneration tower 11 is heated by steam, which is generated by reboiler 15.

[0053] Absorber 2 flue gas flow rate 15m 3 / h, CO2 is absorbed using the absorbent from Example 3, with a liquid-to-gas ratio of 5L / m³. 3 The absorbent flow rate was 75 L / h, and the absorber tower temperature was 40℃. The regeneration tower 11 temperature was 100-105℃, and the effective catalyst mass was 40 g (excluding substrate mass). The CO2 content in the outlet flue gas of absorber tower 2 and regeneration tower 11 was monitored using a CO2 infrared analyzer to determine the CO2 capture rate and regeneration rate. The system operated continuously for three days, with the catalyst packing replaced once a day.

[0054] Example 7

[0055] A catalyst for phase-rich regeneration of a phase change absorbent for CO2 capture. The synthesis method of catalyst MIL-125-NH2: 1 mmol of tetrabutyl titanate and 1 mmol of cyclohexanecarboxylic acid (CHA) were added to 5 mL of a DMF-methanol mixed solvent (DMF to methanol volume ratio 9:1) and stirred for 15 minutes. Then, 1.5 mmol of 2-aminoterephthalic acid was added to the above solution, and stirring was continued for another 15 minutes. The reaction mixture was then transferred to a stainless steel autoclave lined with polytetrafluoroethylene and heated in an oven at 120 °C for 24 hours.

[0056] The synthesis method of the core-shell catalyst MIL-125-NH2@COF-LZU1 involves adding 200 mg MIL-125-NH2, 150 mg trimethylolpropoxide (TFB), and 150 mg p-phenylenediamine (PDA) to 75 mL of dioxane, followed by the addition of 7.5 mL of 3M acetic acid aqueous solution. The mixture is then poured into a stainless steel autoclave lined with polytetrafluoroethylene and heated in an oven at 120 °C for 72 hours. The catalyst morphology is as follows. Figure 1 As shown;

[0057] The rich phase produced in Example 3 and a core-shell catalyst comprising 1.25% of the mass of the rich phase were added to a beaker. The regeneration temperature was 90°C, and the regeneration time was 40 min.

[0058] Example 8

[0059] A phase change absorbent for capturing CO2 differs from Example 1 only in that: the mass fraction of AEEA is 35% and the mass fraction of TMEDA is 35%; the rest is the same as in Example 1.

[0060] Example 9

[0061] A phase change absorbent for capturing CO2 differs from Example 1 only in that: the mass fraction of AEEA is 40% and the mass fraction of TMEDA is 30%; the rest is the same as in Example 1.

[0062] Comparative Example 1

[0063] A liquid-liquid phase change absorbent for carbon dioxide capture is a ternary system consisting of a main absorbent AEEA, a phase separation promoter TMEDA, and a solvent water, wherein the mass fraction of AEEA is 30%, the mass fraction of TMEDA is 40%, and the mass fraction of water is 30% (the water content is 100% compared to the total mass of 1-propanol and water). It is a homogeneous solution before absorbing carbon dioxide. The absorption and desorption conditions are the same as in Example 1.

[0064] Comparative Example 2

[0065] Under catalyst-free conditions, the rich phase produced in Example 3 was sent for desorption regeneration. The regeneration temperature was 90°C, and the regeneration time was 40 min.

[0066] Comparative Example 3

[0067] The only difference from Example 1 is that its main absorbent is ethanolamine.

[0068] Comparative Example 4

[0069] The only difference from Example 1 is that its phase separation promoter is diethylethanolamine.

[0070] Experimental Example 1

[0071] The volume ratio of the two phases after CO2 absorption and phase separation of the phase change absorbents used in Examples 1-5, Examples 8-9 and Comparative Examples 1 and 3-4 was measured, as well as the CO2-rich phase load and phase separation time.

[0072] Experimental Methods: Following the absorbent preparation methods described in Examples 1-5, 8-9, and Comparative Examples 1 and 3-4, 25g of absorbent was prepared and a gas with a CO2 volume fraction of 12% was introduced. Absorption was carried out at 40°C for 30 minutes. During the absorption process, the phase separation was observed and the separation time was recorded. After absorption, the gas was introduced into an infrared CO2 analyzer to continuously monitor the CO2 content. After absorption, the gas was transferred to a graduated cylinder and allowed to stand for stratification. The volume ratio of the upper and lower phases was measured. The absorption load of the CO2-rich phase was determined by titration.

[0073] Figure 4 and Figure 5 The effect of water content on the phase separation ratio of Examples 1-5 and Comparative Example 1 is shown. It can be seen that phase separation occurred in both Examples 1-5 and Comparative Example 1 after CO2 absorption. The volume of the CO2-rich phase ranged from 35% to 75%, and the volume ratio decreased as the water content of the solvent formulation decreased. This is because 1-propanol has a certain degree of hydrophobicity, while the CO2 product is highly polar. Under the influence of the CO2 product, 1-propanol and water separated. The higher the mass ratio of 1-propanol, the lower the volume ratio of the lower phase. Indeed, in Comparative Example 1, with a water content of 100%, the rich phase volume ratio was the highest, approaching 75%. During CO2 regeneration, only the lower phase needs to be sent for desorption; therefore, using 1-propanol to adjust the absorbent can further reduce the energy consumption for phase change absorbent regeneration.

[0074] Figure 6 The effect of moisture content on the absorption load and phase separation time of Examples 1-5 and Comparative Example 1 is shown. From Figure 6 As can be seen, the phase separation time increases with increasing water content, and phase separation is maintained even after absorption. A shorter phase separation time means lower phase separation conditions in the absorbent, reducing the impact of changes in the absorber's operating conditions on the absorbent's phase separation. Furthermore, the absorption load reaches its maximum of 2.5 mol / kg at a water content of 70%. This is because excessively high water content leads to an excessively large mass of the aqueous phase in the lower phase, which is detrimental to CO2 concentration, while excessively low water content increases the viscosity of the rich phase, which is unfavorable for CO2 mass transfer. Therefore, an equilibrium is reached at a water content of around 70%, resulting in the optimal absorption load.

[0075] Table 1 below shows the phase separation time and absorption load of the absorbents described in Examples 1, 8-9, and Comparative Examples 3-4. The higher the concentration of AEEA, the higher the absorption load, increasing from 2.19 mol / kg in Example 1 to 2.41 mol / kg in Example 8, and then to 2.53 mol / kg in Example 9. This is because AEEA has a higher reactivity with CO2 than TMEDA. However, the increase in AEEA concentration also has a significant impact on the viscosity of the enriched phase, showing a clear increasing trend. Higher viscosity increases the pump power. Compared with Example 1, the phase separation time of Comparative Examples 3 and 4 is significantly increased, demonstrating the excellent phase separation performance of AEEA as the main absorbent and TMEDA as a phase separation promoter.

[0076] Table 1

[0077]

[0078] Experiment Example 2

[0079] The regeneration performance of the phase change absorbent described in Examples 1-5, Example 7, and Comparative Examples 1-2 was measured. This experiment measured the regeneration performance of the phase change absorbent and the improvement in regeneration performance of Example 3 by adding a catalyst, using pyrolysis regeneration.

[0080] Experimental Method: The absorption steps described in Example 1 were repeated. The obtained absorbent was used for regeneration. During the regeneration process, 100% N2 was introduced to remove the desorbed CO2 from the regeneration device. The regeneration temperature was 90 or 120°C, and the regeneration time was 40 or 90 minutes. The desorbed gas was passed through an infrared CO2 analyzer to monitor the CO2 content at all times. The CO2 load after desorption was determined by titration.

[0081] Table 2 below shows the loading and cyclic loading after desorption of the rich phase described in Examples 1-5, Example 7, and Comparative Examples 1-2. It can be seen that at the same temperature (120℃) and regeneration time (90 min), the cyclic loading for a water content of 70-100% is basically similar. Within the 70%-75% range, the regeneration rate of Example 3 (70% water content) is around 70%. When the water content is 50% and 60%, the regeneration rate begins to decrease, to 57% and 66% respectively. This is because the low water content results in excessively high viscosity of the rich phase, hindering stirring and heat transfer efficiency. Compared with Comparative Example 2, Example 7 with added catalyst shows a significant effect in assisting the regeneration of the rich phase. Under the conditions of a regeneration temperature of 90℃ and a heating time of 40 min, the regeneration rate is increased from 41% to 73%, an increase of approximately 138%. This indicates that the catalyst of the present invention has good catalytic performance for the regeneration of this liquid-liquid phase change absorbent.

[0082] Table 2

[0083]

[0084]

[0085] Experimental Example 3

[0086] Table 3 below shows the results of the phase change absorbent prepared according to the proportions in Example 3 during the full-process experiment in Example 6, when the CO2 volume concentration in the flue gas was 12% and the flue gas flow rate was 15m³ / h. 3 Under the condition of / h, it can operate stably for 3 days, and the CO2 capture rate and CO2 regeneration rate remain stable at over 90%. This indicates that the absorbent formulation and catalyst can adapt to continuous operation and remain stable for a long time, and have certain industrial application prospects.

[0087] Table 3

[0088]

[0089] The mechanism by which the phase change absorbent of the present invention can separate into phases after absorbing CO2 can be derived from... Figure 2 To illustrate: The phase-separating agents tetramethylethylenediamine (TED) and 1-propanol possess a certain degree of hydrophobicity. When a certain proportion of primary / secondary amines are added to TDD, 1-propanol, and their aqueous solutions, they can be mixed into a single phase and uniformly distributed in the solution system. After the primary / secondary amines react with CO2, they form highly polar products such as carbamates and protonated amines. These products gradually attract water molecules surrounding the TDD and 1-propanol, disrupting the original system's steady state. When the product concentration is sufficiently high, only a small amount of water molecules remain around the TDD and 1-propanol, forming two phases with different polarities. Because TDD and 1-propanol have a lower density than the aqueous phase, after phase separation, the primary and secondary amines and their CO2 product aqueous solution are in the lower phase, while the unreacted TDD and 1-propanol appear in the upper phase. Afterward, only the lower phase needs to be regenerated.

[0090] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for capturing CO2 using a phase change absorbent, characterized in that: Includes the following steps: The phase change absorbent is contacted with a CO2-containing gas to absorb CO2. After CO2 absorption, the absorbent separates into two liquid phases, with CO2 concentrated in the lower liquid phase. The lower liquid phase after CO2 absorption is then desorbed. The phase change absorbent for capturing CO2 is composed of tetramethylethylenediamine, hydroxyethylethylenediamine, 1-propanol, and water. In the phase change absorbent components for capturing CO2, the mass percentage of tetramethylethylenediamine is 30-40%, the mass percentage of hydroxyethylethylenediamine is 30-40%, and the total mass percentage of 1-propanol and water is 30%. A catalyst is also added during the desorption process. The catalyst has a core-shell structure, with the core being MIL-125-NH2 and the shell being COF-LZU1.

2. The method for capturing CO2 using a phase change absorbent according to claim 1, characterized in that: The mass ratio of 1-propanol to water is 1-5:5-9.

3. The method for capturing CO2 using a phase change absorbent according to claim 2, characterized in that: The mass ratio of 1-propanol to water is 3:

7.

4. The method for capturing CO2 using a phase change absorbent for capturing CO2 according to any one of claims 1-3, characterized in that: The mass fraction of hydroxyethyl ethylenediamine is 30%, the mass fraction of tetramethyl ethylenediamine is 40%, the mass fraction of water is 21%, and the mass fraction of 1-propanol is 9%.

5. The method for capturing CO2 using a phase change absorbent according to claim 1, characterized in that: During the CO2 absorption process, the absorption temperature is 40~60℃, the volume fraction of CO2 in the CO2-containing gas is 8~12%, and the liquid-to-gas ratio is 5~8 L / m³. 3 .

6. The method for capturing CO2 using a phase change absorbent according to claim 1, characterized in that: The desorption temperature is 90~120℃, the time is 30min~90min, and the desorption pressure is 1~1.1 atmospheres.

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