High-Load Liquid-Liquid Phase Change Absorbent for Carbon Dioxide Capture and Its Application

Abstract

The present invention belongs to the field of carbon dioxide capture and flue gas purification, and specifically relates to a high-load liquid-liquid phase-change absorbent for carbon dioxide capture and its application. The present invention provides a high-load liquid-liquid phase-change absorbent for carbon dioxide capture, the liquid-liquid phase-change absorbent being a homogeneous solution composed of a promoter, an activator, N-methylpyrrolidone, and water, wherein the weight ratio of N-methylpyrrolidone to water is 2 to 3:1; the sum of the weight of the activator and the promoter accounts for 20 to 45wt% of the total weight of the liquid-liquid phase-change absorbent, and the weight ratio of the activator to the promoter is 0.3 to 4:1. The present invention also provides a carbon dioxide capture method using the above-mentioned high-load liquid-liquid phase-change absorbent; the present invention has a high absorption load for CO2.

Description

Technical Field

[0001] The present invention belongs to the field of carbon dioxide capture and flue gas purification, and particularly relates to a high-load liquid-liquid phase change absorbent for carbon dioxide capture and application thereof. Background Art

[0002] Carbon capture, utilization, and storage (CCUS) technology primarily encompasses three steps: CO2 capture, CO2 utilization, and CO2 storage. Carbon capture is the core step, yet also the most energy-intensive and costly. Improving capture efficiency and reducing capture costs are current international research hotspots. Among these, amine-based solvents in chemical absorption are the most mature CO2 separation technology. Liquid absorption methods have been commercialized, but they suffer from high investment and operating costs. Traditional amine-based solvents use 30wt% MEA (monoethanolamine), with an absorption capacity of 0.2-0.5 molCO2 / mol amine and regeneration energy consumption of 3.4-4.0 GJ / tCO2. These solvents suffer from low absorption capacity, low recovery capacity, and high desorption energy consumption. Compared to single-phase organic amine absorbents, phase-change absorbents undergo a phase change after absorbing CO2, requiring only the CO2-rich phase for regeneration. This significantly reduces the volume of regenerated rich liquid and reduces regeneration energy consumption.

[0003] Chinese patent CN118454438B discloses a carbon dioxide composite absorbent. The carbon dioxide composite absorbent comprises a promoter, an alcoholamine as an activator, and a solvent. The combined weight of the promoter and activator accounts for 20-60 wt% of the total weight of the carbon dioxide composite absorbent, and the weight ratio of the promoter to the activator is 0.3-3:1. The promoter is tris(dimethylaminopropyl)hexahydrotriazine (i.e., 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine). The activator is an alcoholamine containing a primary or secondary amine group in its molecular structure, such as hydroxyethylethylenediamine (AEEA), hydroxyethylpiperazine, 2-aminobutanol, or ethanolamine (MEA, i.e., monoethanolamine). The solvent can be a pure solvent or a mixed solvent. The organic solvent is sulfolane, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), methanol, or n-propanol. In the mixed solvent, the volume ratio of the organic solvent to water is 0.5-3:1. The circulating absorption load is high, but all the rich liquid needs to be desorbed and regenerated, which requires high energy consumption.

[0004] Chinese patent CN114011207B discloses a low-energy phase-change absorbent composed of N,N-dimethylethanolamine, anhydrous piperazine, n-butanol, and water. It has a high rich-phase load and excellent desorption performance, with a desorption energy consumption of 1.61 GJ / t. However, the phase separation time is 12 hours, and the bottom liquid residence time is long. Industrial application requires the customization of a larger, special multi-stage phase separator, further increasing equipment investment.

[0005] Chinese patent CN116688726A discloses a solid-liquid phase-change carbon dioxide absorbent composed of hydroxyethylethylenediamine, 2-amino-2-methyl-1-propanol, and N-methylpyrrolidone, with a controllable phase transition time. The hydroxyethylethylenediamine acts as an activator to regulate the solid phase generation time, preventing product precipitation at low carbon dioxide loadings and equipment clogging. The absorption capacity is only 0.49 to 0.55 molCO2 / mol, and the solid phase material requires specialized equipment for transport, which still poses the risk of equipment clogging. Microwave heating is used to regenerate the solid phase, making it unsuitable for further commercial application.

[0006] Therefore, developing a phase change absorption system with large absorption load, high cycle capacity and short phase separation time provides new ideas for further commercialization. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a high-load liquid-liquid phase-change absorbent for carbon dioxide capture and its application, wherein the phase-change absorbent has the excellent properties of large absorption load, high cycle absorption capacity and rapid phase separation.

[0008] In order to solve the above problems, the present invention provides a high-load liquid-liquid phase-change absorbent for carbon dioxide capture. The liquid-liquid phase-change absorbent is a solution (homogeneous solution) composed of a promoter, an activator, N-methylpyrrolidone (NMP) and water, wherein the weight ratio of N-methylpyrrolidone to water is 2-3:1; the sum of the weights of the activator and the promoter accounts for 20-45wt% of the total weight of the liquid-liquid phase-change absorbent, and the weight ratio of activator to promoter is 0.3-4:1.

[0009] Note: N-methylpyrrolidone acts as both a solvent and a phase separation inducer.

[0010] As an improvement of the high-load liquid-liquid phase change absorbent for carbon dioxide capture of the present invention:

[0011] The accelerator is tris(dimethylaminopropyl)hexahydrotriazine (i.e., 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine);

[0012] The activator is 2-methylpiperazine.

[0013] As a further improvement of the high-load liquid-liquid phase change absorbent for carbon dioxide capture of the present invention:

[0014] Tris(dimethylaminopropyl)hexahydrotriazine accounts for 9-20wt% of the total weight of the liquid-liquid phase change absorbent;

[0015] 2-Methylpiperazine accounts for 5-36 wt % of the total weight of the liquid-liquid phase change absorbent.

[0016] As a further improvement of the high-load liquid-liquid phase change absorbent for carbon dioxide capture of the present invention:

[0017] The liquid-liquid phase change absorbent is composed of 20 wt% of tris(dimethylaminopropyl)hexahydrotriazine, 10 wt% of 2-methylpiperazine, and 70 wt% of a mixed solvent, wherein the weight ratio of N-methylpyrrolidone to water is 2:1.

[0018] In the present invention, the promoter, activator, N-methylpyrrolidone (NMP) and water are mixed into a homogeneous solution by conventional stirring (for example, at 25±5°C and 300±50 rpm for 30±5 min) to obtain the high-load liquid-liquid phase change absorbent.

[0019] The present invention also provides a method for capturing carbon dioxide using the high-load liquid-liquid phase change absorbent, comprising the following steps:

[0020] 1) CO2 absorption process:

[0021] The gas containing CO2 is passed into the liquid-liquid phase change absorbent. The liquid-liquid phase change absorbent is a homogeneous solution before absorbing CO2. When the CO2 is absorbed to a certain load, a phase change phenomenon will occur, forming an immiscible liquid-liquid two-phase;

[0022] Note: Due to the airflow, the separation of the immiscible liquid-liquid two phases is incomplete;

[0023] This step 1) is carried out at a pressure of ≤110kPa (0~110kPa);

[0024] 2) CO2 rich liquid separation:

[0025] Stop the introduction of the CO2-containing gas, and allow the immiscible liquid-liquid phases obtained in step 1) to separate by standing (thereby achieving complete phase separation), forming upper and lower liquid layers;

[0026] The upper liquid is a CO2-poor phase (mainly composed of N-methylpyrrolidone), and the lower liquid is a CO2-rich phase (consisting of reaction products, water, and a small amount of N-methylpyrrolidone, with CO2 mainly concentrated in the lower liquid).

[0027] Note: The reaction products generally include R1R2NCOO - 、R1R2NH2 + 、HCO3 - wait;

[0028] 3) CO2 rich liquid regeneration:

[0029] The CO2-rich phase is taken out and heated for desorption, so that the CO2 in the CO2-rich phase is released (i.e., thereby achieving regeneration of the CO2-rich liquid). The result is named regenerated CO2-rich liquid (i.e., the rich phase after the CO2 is released);

[0030] The homogeneous solution formed by mixing the regenerated CO2 rich liquid and the CO2 lean phase obtained in step 2) is a recyclable liquid-liquid phase change absorbent.

[0031] That is, the recycled liquid-liquid phase change absorbent is subsequently recycled and reused to absorb CO2 again.

[0032] As an improvement to the carbon dioxide capture method of the present invention:

[0033] The absorption temperature in step 1) is 30-45°C;

[0034] The heating desorption temperature in step 3) is 90-120°C.

[0035] Note: The higher the desorption temperature, the better the regeneration efficiency, but the corresponding energy consumption is higher; therefore, the present invention preferably prefers 90~120℃.

[0036] As a further improvement of the carbon dioxide capture method of the present invention:

[0037] The time for standing and separating in step 2) is ≥ 2 minutes (generally 2 to 5 minutes).

[0038] Note: After 2 minutes, two immiscible liquid-liquid phases are formed. As the standing time increases, the two phases separate more completely and the rich liquid volume decreases further (change rate <1%). After phase separation, more than 93% of CO2 is enriched in the lower layer, and the rich phase accounts for about 65~68% of the volume.

[0039] As a further improvement of the carbon dioxide capture method of the present invention:

[0040] In the step 1), when CO2 is absorbed to full load (i.e., absorption saturation), step 1) is stopped.

[0041] Note: When the outlet gas flow rate is equal to the inlet gas flow rate, it is determined to be absorption saturation.

[0042] In the present invention, tris(dimethylaminopropyl)hexahydrotriazine serves as a high-alkalinity CO₂ absorbent, a certain proportion of N-methylpyrrolidone serves as a phase separation inducer to promote a liquid-liquid phase transition, and water serves as a solvent to further reduce the absorbent's viscosity. The liquid-liquid phase transition absorbent is a homogeneous solution before absorption and forms two immiscible liquid-liquid phases after absorption, with the CO₂-enriched phase located in the lower layer of the solution. N-methylpyrrolidone is an organic physical solvent with a strong affinity for CO₂. It does not participate in the CO₂ absorption reaction, but phase separates from the reaction products due to hydrogen bonding or hydrophobicity, residing in the upper layer of the solution after phase separation. After phase separation, only the rich phase needs to be sent to the regeneration tower. The lower the volume percentage of the rich phase, the smaller the amount of regenerated solution, the lower the sensible heat, and the lower the water content, which significantly reduces the latent heat of water evaporation, thereby reducing regeneration energy consumption.

[0043] The higher the concentration of amine in the liquid-liquid phase change absorbent, the greater the absorption capacity, but the viscosity of the CO2-enriched liquid phase will be further increased.

[0044] 2-Methylpiperazine as an activator can promote absorption by increasing the absorption rate. Compared with commonly used activators such as piperazine, 2-methylpiperazine has good water solubility, avoiding the problem of salt precipitation after liquid-liquid phase change absorbent absorbs CO2, and does not crystallize under all working conditions.

[0045] Compared with the prior art, the present invention has the following technical advantages:

[0046] (1) Tris(dimethylaminopropyl)hexahydrotriazine as a promoter can increase the absorption load. The high hydrophobicity and alkalinity of the tertiary amine in its molecule are conducive to reducing the viscosity of the rich liquid and promoting phase separation. After absorbing a certain load, the phase separation time is fast, as short as 2 minutes.

[0047] (2) The high-load liquid-liquid phase change absorbent of the present invention is a uniform solution composed of tris(dimethylaminopropyl)hexahydrotriazine, 2-methylpiperazine, N-methylpyrrolidine and water, with high boiling point and low vapor pressure N-methylpyrrolidone (NMP) as the main solvent, which has high thermal stability. After absorbing CO2, it forms an immiscible liquid-liquid two-phase under a certain load. The absorption load of the lower liquid relative to CO2 is 4.08~5.28mol / L, and the phase separation effect is the best, accounting for about 65~68% of the total volume. That is, only the rich liquid needs to be thermally decomposed and regenerated, which reduces the regeneration volume. The regeneration efficiency (the recovery of CO2 absorption capacity) is as high as 92.5%, and the cyclic absorption load is as high as 1.60molCO2 / molamine, which can greatly reduce the regeneration energy consumption. The regeneration energy consumption is 2.27~2.41GJ / t CO2, which is conducive to the promotion of industrial application. DETAILED DESCRIPTION

[0048] The present invention is further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0049] The performance test of the present invention is carried out by the following method:

[0050] Experiment 1: Absorption performance test (carbon dioxide capture method)

[0051] (1) CO2 absorption process:

[0052] At a constant temperature, CO2 gas was passed through a liquid-liquid phase-change absorbent to examine the absorbent's absorption capacity and phase separation. The liquid-liquid phase-change absorbent is a homogeneous solution before absorbing CO2. After absorbing a certain load of CO2, a phase change occurs, forming an immiscible liquid-liquid phase. Absorption is complete when the outlet gas flow rate equals the inlet gas flow rate, i.e., absorption saturation is achieved. The absorption rate is then calculated based on the flowmeter reading.

[0053] (2) CO2 rich liquid separation:

[0054] After the absorption of step (1) is completed, the CO2 gas is stopped from being introduced, and the mixture is allowed to stand for ≥2 minutes for phase separation to form an upper liquid layer and a lower liquid layer. The volume percentage and CO2 load of the upper liquid layer and the lower liquid layer are tested respectively.

[0055] The upper liquid is a CO2-poor phase (mainly composed of N-methylpyrrolidone), and the lower liquid is a CO2-rich phase (including reaction products, water, and a small amount of N-methylpyrrolidone, with CO2 mainly concentrated in the lower liquid).

[0056] (3) CO2 rich liquid regeneration:

[0057] After the CO2-rich phase is separated and taken out, the upper CO2-lean phase is retained for standby use. The regeneration process only requires heating and desorbing the CO2-rich phase, and regeneration (heating and desorption) is performed at a certain temperature; the CO2-rich phase after releasing CO2 is mixed with the CO2-lean phase obtained in step (2) to form a homogeneous solution and then recycled to absorb CO2 again.

[0058] In the above experiment 1:

[0059] The absorption temperature in step (1) is preferably set at 30-45°C, and the operating pressure does not exceed the maximum operating pressure of the instrument, preferably 0-110 kPa. After saturation absorption, a sample is taken for analysis of the CO2 concentration; the CO2 is then sent to a desorption bottle for desorption and regeneration. The regeneration temperature in step (3) is preferably set at 90-120°C. Afterwards, the next cycle test is performed. Generally speaking, the next cycle test is preferably performed when the regeneration degree of the carbon dioxide composite absorbent exceeds 90%.

[0060] Experiment 2: Cyclic Experiment Test

[0061] The carbon dioxide composite absorbent obtained from the desorption in Experiment 1 was subjected to a second absorption test using the same test apparatus, absorption temperature, and operating pressure as Experiment 1. After saturation, samples were taken and analyzed to calculate the absorbent's cyclic absorption capacity. Desorption and regeneration were then performed at the same regeneration temperature as Experiment 1, with samples taken and analyzed after each absorption and desorption cycle. Five cycles were performed to assess the absorbent's thermal stability. The calculation method for cyclic absorption capacity was the same as that used in Experiment 1.

[0062] Experiment 3: Energy Consumption Test

[0063] In the present invention, the energy consumption for regenerating the phase change absorbent is calculated by sensible heat, latent heat and reaction heat, and the unit is GJ / t CO2. The calculation method is a common method in the art and will not be repeated here.

[0064] The absorption load of the absorbents described in the following examples and comparative examples was tested. The carbon dioxide loading in the absorption solution was measured using acid-base titration before and after the experiment. The absorption and regeneration performance determination methods are commonly used in the art and will not be detailed here.

[0065] Example 1: A high-load liquid-liquid phase change absorbent for carbon dioxide capture

[0066] 9 wt % of tris(dimethylaminopropyl)hexahydrotriazine, 36 wt % of 2-methylpiperazine, and 55 wt % of a mixed solvent (the weight ratio of N-methylpyrrolidone to water in the mixed solvent is 3:1) were weighed and placed in a beaker, and stirred at 25° C. and 300 rpm for 30 min to form a homogeneous solution, thereby obtaining a high-load liquid-liquid phase change absorbent.

[0067] The absorption performance test was carried out according to Experiment 1. The parameters of step (1) were set as follows: absorption temperature was 30°C and pressure was 1.0 kPa. The measurement results were as follows: the standing time after absorption was 2 min, the volume proportion of the CO2-rich phase in the lower layer was 68%, the CO2 load was 5.28 mol / L, the maximum absorption load (absorption capacity) was 1.58 molCO2 / mol amine, 96% CO2 was enriched in the lower layer, the desorption temperature was 120°C, the regeneration degree was 90.7%, and the regeneration energy consumption was 2.41 GJ / t CO2;

[0068] The cycle experiment was carried out according to Experiment 2. The experimental conditions were the same as Experiment 1 corresponding to Example 1 above. The absorption temperature was set at 30°C and the regeneration temperature was set at 120°C. The measurement results showed that the absorption capacity after five cycles was 1.42 molCO2 / molamine.

[0069] Example 2: A high-load liquid-liquid phase change absorbent for carbon dioxide capture

[0070] 20 wt % of tris(dimethylaminopropyl)hexahydrotriazine, 10 wt % of 2-methylpiperazine, and 70 wt % of a mixed solvent (the weight ratio of N-methylpyrrolidone to water in the mixed solvent is 2:1) were weighed and placed in a beaker, and stirred at 25° C. and 300 rpm for 30 minutes to form a homogeneous solution, thereby obtaining the high-load liquid-liquid phase change absorbent.

[0071] The absorption performance test was carried out according to Experiment 1. The parameters of step (1) were set as follows: the absorption temperature was 30°C and the pressure was 110 kPa. The measurement results were as follows: the standing time after the absorption was 3 minutes, the volume proportion of the CO2-rich phase in the lower layer was 67%, the CO2 load was 4.99 mol / L, the maximum absorption load was 1.78 molCO2 / mol amine, 94% CO2 was enriched in the lower layer, the desorption temperature was 110°C, the regeneration degree was 92.5%, and the regeneration energy consumption was 2.37 GJ / t CO2;

[0072] The cyclic experiment was carried out according to Experiment 2. The experimental conditions were the same as Experiment 1 corresponding to Example 2 above. The absorption temperature was set to 30°C and the regeneration temperature was set to 110°C. The measurement results showed that the absorption capacity after five cycles was 1.60 molCO2 / molamine.

[0073] Example 3: A high-load liquid-liquid phase change absorbent for carbon dioxide capture

[0074] 20 wt % of tris(dimethylaminopropyl)hexahydrotriazine, 10 wt % of 2-methylpiperazine, and 70 wt % of a mixed solvent (the weight ratio of N-methylpyrrolidone to water in the mixed solvent is 3:1) were weighed and placed in a beaker, and stirred at 25° C. and 300 rpm for 30 minutes to form a homogeneous solution, thereby obtaining the high-load liquid-liquid phase change absorbent.

[0075] The absorption performance test was carried out according to Experiment 1. The parameters of step (1) were set as follows: the absorption temperature was 45°C and the pressure was 50 kPa. The measurement results were as follows: the standing time after the absorption was 5 minutes, the volume proportion of the CO2-rich phase in the lower layer was 65%, the CO2 load was 5.09 mol / L, the maximum absorption load was 1.61 molCO2 / mol amine, 95% CO2 was enriched in the lower layer, the desorption temperature was 90°C, the regeneration degree was 91.9%, and the regeneration energy consumption was 2.27 GJ / t CO2;

[0076] The cycle experiment was carried out according to Experiment 2. The experimental conditions were the same as Experiment 1 corresponding to Example 3 above. The absorption temperature was set to 45°C and the regeneration temperature was set to 90°C. The measurement results showed that the absorption capacity after five cycles was 1.47 molCO2 / molamine.

[0077] Example 4: A high-load liquid-liquid phase change absorbent for carbon dioxide capture

[0078] 15 wt % of tris(dimethylaminopropyl)hexahydrotriazine, 5 wt % of 2-methylpiperazine, and 80 wt % of a mixed solvent (the weight ratio of N-methylpyrrolidone to water in the mixed solvent is 2:1) were weighed and placed in a beaker, and stirred at 25° C. and 300 rpm for 30 minutes to obtain a homogeneous solution, thereby obtaining the high-load liquid-liquid phase change absorbent.

[0079] The absorption performance test was carried out according to Experiment 1. The parameters of step (1) were set as follows: the absorption temperature was 40°C and the pressure was 10 kPa. The measurement results were as follows: the standing time after the absorption was 2 min, the volume proportion of the CO2-rich phase in the lower layer was 66%, the CO2 load was 4.08 mol / L, the maximum absorption load was 1.55 molCO2 / mol amine, 93% CO2 was enriched in the lower layer, the desorption temperature was 110°C, the regeneration degree was 92.1%, and the regeneration energy consumption was 2.30 GJ / t CO2;

[0080] The cyclic experiment was carried out according to Experiment 2. The experimental conditions were the same as Experiment 1 corresponding to Example 4 above. The absorption temperature was set to 40°C and the regeneration temperature was set to 110°C. The measurement results showed that the absorption capacity after five cycles was 1.40 molCO2 / molamine.

[0081] Example 5: A high-load liquid-liquid phase change absorbent for carbon dioxide capture

[0082] 15 wt % of tris(dimethylaminopropyl)hexahydrotriazine, 15 wt % of 2-methylpiperazine, and 70 wt % of a mixed solvent (the weight ratio of N-methylpyrrolidone to water in the mixed solvent is 2:1) were weighed and placed in a beaker, and stirred at 25° C. and 300 rpm for 30 minutes to form a homogeneous solution, thereby obtaining the high-load liquid-liquid phase change absorbent.

[0083] The absorption performance test was carried out according to Experiment 1. The parameters of step (1) were set as follows: the absorption temperature was 30°C and the pressure was 10 kPa. The measurement results were as follows: the standing time after the absorption was 2 minutes, the volume proportion of the CO2-rich phase in the lower layer was 66%, the CO2 load was 4.13 mol / L, the maximum absorption load was 1.46 molCO2 / mol amine, 94% CO2 was enriched in the lower layer, the desorption temperature was 110°C, the regeneration degree was 90.1%, and the regeneration energy consumption was 2.33 GJ / t CO2;

[0084] The cycle experiment was carried out according to Experiment 2. The experimental conditions were the same as Experiment 1 corresponding to Example 5 above. The absorption temperature was set to 30°C and the regeneration temperature was set to 110°C. The measurement results showed that the absorption capacity after five cycles was 1.31 molCO2 / molamine.

[0085] The CO2 cyclic loading of the phase-change absorbent prepared in Examples 1 to 5 was maintained at ≥1.31 molCO2 / molamine after five cycles, and the desorption efficiency of each desorption was as high as over 90%, indicating that the absorbent had good stability, excellent desorption performance, and stable regeneration, with a regeneration energy consumption of 2.27~2.41 GJ / t CO2.

[0086] Comparative Example 1

[0087] 30 wt% ethanolamine and 70 wt% water were weighed and placed in a beaker based on the total weight percentage of the absorbent. The mixture was stirred at 25°C and 300 rpm for 30 minutes to form a homogeneous solution, thereby obtaining a conventional commercial (30 wt% MEA) carbon dioxide absorbent.

[0088] The absorption performance test was carried out according to Experiment 1. The parameters of step (1) were set as follows: the absorption temperature was 30°C and the pressure was 1 kPa. The measurement results showed that after the absorption was completed, the standing time was more than 5 minutes, there was no phase change and stratification phenomenon, the maximum absorption load was 0.59 molCO2 / molamine, the desorption temperature was 120°C, the regeneration degree was 60%, and the regeneration energy consumption was 3.81 GJ / t CO2;

[0089] The cyclic experiment was carried out according to Experiment 2. The experimental conditions were the same as Experiment 1 corresponding to the above Comparative Example 1. The absorption temperature was set to 30°C and the regeneration temperature was set to 120°C. The measurement results showed that the absorption capacity after five cycles was 0.26 molCO2 / molamine.

[0090] Comparative Example 2

[0091] Compared with Example 2, the weight ratio of N-methylpyrrolidone:water in the mixed solvent was changed from "2:1" to "1:1", and the amount of the mixed solvent remained unchanged; the rest was the same as Example 2.

[0092] The absorption performance test was carried out according to Experiment 1. The parameters of step (1) were set as follows: absorption temperature was 30°C and pressure was 110 kPa. The test results showed that after the absorption was completed, the standing time was more than 5 minutes, there was no phase change and stratification phenomenon, the maximum absorption load was 1.44 molCO2 / molamine, the regeneration degree was 90.4% when the desorption temperature was 110°C, and the regeneration energy consumption was 2.9 GJ / tCO2;

[0093] The cyclic experiment was carried out according to Experiment 2. The experimental conditions were the same as Experiment 1 corresponding to Comparative Example 2. The absorption temperature was set to 30°C and the regeneration temperature was set to 110°C. The measurement results showed that the absorption capacity after five cycles was 1.21 molCO2 / molamine.

[0094] Comparative Example 3

[0095] Relative to Example 2, the "mixed solvent consists of N-methylpyrrolidone: water in a weight ratio of 2:1" is changed to "N-methylpyrrolidone is used alone as the solvent", and the amount of solvent remains unchanged, i.e., 70 wt % N-methylpyrrolidone; the rest is the same as Example 2.

[0096] The absorption performance test was carried out according to Experiment 1. The parameters of step (1) were set as follows: the absorption temperature was 30°C and the pressure was 110 kPa. The measurement results showed that after the absorption was completed, the standing time was more than 2 minutes, and the phase transition was stratified into liquid and solid phases, with the lower layer being the solid phase, and the next test experiment could not be carried out.

[0097] Regeneration energy consumption is primarily composed of three components: the absorbent's sensible heat of regeneration, the heat of desorption of the CO2 product, and the latent heat removed by the regeneration gas. In the present invention, the solvent ratio is crucial for phase change behavior. When the weight ratio of N-methylpyrrolidone:water in Comparative Example 2 was reduced to 1:1, the absorbent absorbed CO2 without undergoing phase change and stratification. Regeneration required heating of the entire absorbent, resulting in a higher energy consumption of 2.9 GJ / t CO2 compared to the liquid-liquid phase-change absorbent of Example 2. This is primarily due to increased sensible heat. The phase-change absorbent of the present invention only requires regeneration of the CO2-rich lower phase, thereby reducing the amount of regeneration solution and, consequently, the sensible heat.

[0098] The 30 wt% ethanolamine solution in Comparative Example 1 is a common commercial absorbent that undergoes no phase change after absorption and has a relatively high energy consumption of 3.81 GJ / t CO2. Comparing Comparative Examples 1 and 2, tris(dimethylaminopropyl)hexahydrotriazine exhibits a lower heat of reaction and a higher absorption capacity. The absorption load in Comparative Example 2 is 2.45 times that of Comparative Example 1, while the desorption rate is as high as 90%, demonstrating superior absorption performance. Furthermore, the addition of N-methylpyrrolidone reduces the latent heat of evaporation of water, significantly lowering the regeneration latent heat. Overall, compared to Comparative Example 1, the regeneration energy consumption in Comparative Example 2 is reduced by 23.9%.

[0099] Combining Examples 1 and 3, the content of 2-methylpiperazine in Example 1 increased, the absorption load and regeneration rate decreased slightly, and the regeneration energy consumption increased by 0.14 GJ / t CO2. This is due to the higher reaction heat of 2-methylpiperazine, and desorption requires more thermal energy, that is, the corresponding desorption heat is higher.

[0100] Combining Examples 2 and 3, the proportion of N-methylpyrrolidone in Example 3 was increased, and the absorption load decreased by 9.6%. This was because the addition of the organic solvent reduced the alkalinity of the absorbent, and the energy consumption was also reduced.

[0101] Combining Examples 4 and 5, the increased content of 2-methylpiperazine in Example 5 resulted in decreased absorption load and regeneration rate, and increased regeneration energy consumption.

[0102] Comparative Example 4-1

[0103] The "2-methylpiperazine" in Example 2 was replaced with "piperazine" and the content remained unchanged at 10 wt %; the rest was the same as Example 2.

[0104] Absorption performance tests were conducted according to Experiment 1. The results showed that the absorbent containing piperazine (PZ) slowly produced a white cream-like substance upon introduction of carbon dioxide, which eventually turned into a solid. This precluded further testing.

[0105] Comparative Example 4-2

[0106] The "2-methylpiperazine" in Example 2 was replaced with "hydroxyethylpiperazine" and the content remained unchanged at 10 wt %; the rest was the same as Example 2.

[0107] The absorption performance test was carried out according to Experiment 1. After the absorption was completed, the standing time was 3 minutes. The volume proportion of the CO2-rich phase in the lower layer was 75%, the CO2 load was 1.55 mol / L, the maximum absorption load was 1.07 molCO2 / mol amine, 87% CO2 was enriched in the lower layer, the desorption temperature was 110°C, the regeneration degree was 72%, and the regeneration energy consumption was 3.2 GJ / t CO2.

[0108] The cyclic experiment was carried out according to Experiment 2. The experimental conditions were the same as Experiment 1 corresponding to Comparative Example 4-2 above. The absorption temperature was set to 30°C and the regeneration temperature was set to 110°C. The measurement results showed that the absorption capacity after five cycles was 0.72 molCO2 / molamine.

[0109] Comparative Example 5-1

[0110] The "N-methylpyrrolidone" in the mixed solvent of Example 2 was replaced with "dimethyl sulfoxide (DMSO)", the amount used remained unchanged, and the rest was the same as Example 2.

[0111] The absorption performance test was carried out according to Experiment 1. After the absorption was completed, the standing time was 3 minutes, there was no stratification, the maximum absorption load was 1.34 molCO2 / molamine, the desorption temperature was 110℃, the regeneration degree was 88%, and the regeneration energy consumption was 3.3 GJ / tCO2;

[0112] The cyclic experiment was carried out according to Experiment 2. The experimental conditions were the same as Experiment 1 corresponding to Example 5-1 above. The absorption temperature was set to 30°C and the regeneration temperature was set to 110°C. The measurement results showed that the absorption capacity after five cycles was 1.07 molCO2 / molamine.

[0113] Comparative Example 5-2

[0114] The "N-methylpyrrolidone" in the mixed solvent of Example 2 was replaced with "N,N-dimethylformamide (DMF)", the amount used remained unchanged, and the rest was the same as Example 2.

[0115] The absorption performance test was carried out according to Experiment 1. After the absorption was completed, the system was allowed to stand for 5 minutes without stratification. The maximum absorption load was 1.41 molCO2 / molamine. When the desorption temperature was 110°C, the regeneration degree was 86%, and the next test was not carried out.

[0116] Finally, it should be noted that the above examples are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above examples and is subject to numerous variations. All variations that can be directly derived or conceived by a person of ordinary skill in the art from the disclosure of the present invention are considered to be within the scope of protection of the present invention.

Claims

1. A high-load liquid-liquid phase change absorbent for carbon dioxide capture, characterized by: The liquid-liquid phase change absorbent is a solution composed of a promoter, an activator, N-methylpyrrolidone and water, wherein the weight ratio of N-methylpyrrolidone to water is 2-3:1; the sum of the weights of the activator and the promoter accounts for 20-45wt% of the total weight of the liquid-liquid phase change absorbent, and the weight ratio of activator to promoter is 0.3-4:1; the promoter is tris(dimethylaminopropyl)hexahydrotriazine; and the activator is 2-methylpiperazine.

2. The high-load liquid-liquid phase-change absorbent for carbon dioxide capture according to claim 1, characterized in that: Tris(dimethylaminopropyl)hexahydrotriazine accounts for 9-20wt% of the total weight of the liquid-liquid phase change absorbent; 2-Methylpiperazine accounts for 5-36 wt% of the total weight of the liquid-liquid phase change absorbent.

3. The high-load liquid-liquid phase-change absorbent for carbon dioxide capture according to claim 1 or 2, characterized in that: The liquid-liquid phase change absorbent is composed of 20 wt % of tris(dimethylaminopropyl)hexahydrotriazine, 10 wt % of 2-methylpiperazine, and 70 wt % of a mixed solvent, wherein the weight ratio of N-methylpyrrolidone to water is 2:

1.

4. A method for capturing carbon dioxide, characterized in that: Using the high-load liquid-liquid phase change absorbent according to any one of claims 1 to 3 comprises the following steps: 1) CO2 absorption process: The gas containing CO2 is passed into the liquid-liquid phase change absorbent. The liquid-liquid phase change absorbent is a homogeneous solution before absorbing CO2. When the CO2 is absorbed to a certain load, a phase change phenomenon will occur, forming an immiscible liquid-liquid two phases. 2) CO2 rich liquid separation: Stop the introduction of the CO2-containing gas, and allow the immiscible liquid-liquid phases obtained in step 1) to separate by standing, forming upper and lower liquid layers; The upper liquid is a CO2-poor phase, and the lower liquid is a CO2-rich phase; 3) CO2 rich liquid regeneration: The CO2-rich phase is taken out and heated for desorption, so that the CO2 in the CO2-rich phase is released, and the result is named as the regenerated CO2-rich liquid; The homogeneous solution formed by mixing the regenerated CO2-rich liquid and the CO2-lean phase obtained in step 2) is a recyclable liquid-liquid phase change absorbent.

5. The carbon dioxide capture method according to claim 4, characterized in that: The absorption temperature in step 1) is 30-45°C; The heating desorption temperature in step 3) is 90-120°C.

6. A method for capturing carbon dioxide according to claim 5, characterized in that: The standing separation time in step 2) is ≥2 min.

7. A method for capturing carbon dioxide according to any one of claims 4 to 6, characterized in that: In the step 1), when CO2 is absorbed to full load, step 1) is stopped.