High-load liquid-liquid phase change absorbent for carbon dioxide capture and application of high-load liquid-liquid phase change absorbent

Abstract

The 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 of the high-load liquid-liquid phase change absorbent. The invention provides a high-load liquid-liquid phase change absorbent for carbon dioxide capture, the liquid-liquid phase change absorbent is a uniform solution composed of an accelerant, an activator, N-methyl pyrrolidone and water, and the weight ratio of N-methyl pyrrolidone to water is (2-3): 1; the sum of the weight of the activating agent and the accelerant accounts for 20-45wt% of the total weight of the liquid-liquid phase change absorbent, and the weight ratio of the activating agent to the accelerant is (0.3-4): 1. The invention also provides a carbon dioxide trapping method by using the high-load liquid-liquid phase change absorbent. The adsorption load of CO2 is high.

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 its application. Background Technique

[0002] Carbon Capture, Utilization and Storage (CCUS) technology mainly includes three links: CO 2 capture, CO 2 utilization and CO 2 storage. Among them, carbon capture is the core link and also the link with higher energy consumption and cost. How to improve the capture efficiency and reduce the capture cost is a current international research hotspot. Among them, amine solvents in chemical absorption method are the most mature carbon dioxide separation technology. Liquid absorption method has been commercialized, but the investment and operation costs are relatively high. Traditional amine solvent is 30wt% MEA (monoethanolamine), with an absorption capacity of 0.2 - 0.5mol CO 2 / mol amine, and the regeneration energy consumption is 3.4 - 4.0GJ / t CO 2 , having problems such as small absorption capacity, low recovery ability, and high desorption energy consumption. Compared with single-phase organic amine absorbents, phase change absorbents have a phase change behavior after absorbing CO 2 , and only need to regenerate the CO 2 rich phase, which can greatly reduce the volume of regenerated rich liquid and lower the regeneration energy consumption.

[0003] Chinese Patent CN118454438B discloses a carbon dioxide composite absorbent: the carbon dioxide composite absorbent is composed of a promoter, an alkanolamine as an activator, and a solvent; the sum of the weights of the promoter and the activator accounts for 20 - 60wt% 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 alkanolamine containing a primary amine group or a secondary amine group in its molecular structure, such as aminoethyl ethanolamine (AEEA), hydroxyethyl piperazine, 2-aminobutanol, ethanolamine (MEA, i.e., monoethanolamine); the solvent is a pure solvent or a mixed solvent. The organic solvent is sulfolane, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), methanol, n-propanol. In the mixed solvent, the volume ratio of the organic solvent to water is 0.5 - 3:1. The cyclic absorption load is high, but all the rich liquid needs to be desorbed and regenerated, requiring relatively high energy consumption.

[0004] Chinese Patent CN114011207B discloses a low - energy - consumption phase - change absorbent composed of N,N - dimethylethanolamine, anhydrous piperazine, n - butanol and water, which has a high rich - phase loading and excellent desorption performance. The desorption energy consumption is 1.61 GJ / t. However, the phase - separation time requires 12 h, the residence time of the bottom liquid is long, and a larger and special multi - stage phase - separator needs to be customized during industrial application, further increasing the equipment investment.

[0005] Chinese Patent CN116688726A discloses a solid - liquid phase - change carbon dioxide absorbent composed of hydroxyethyl ethylenediamine, 2 - amino - 2 - methyl - 1 - propanol and N - methylpyrrolidone, and its phase - change time node is controllable. Among them, hydroxyethyl ethylenediamine is used as an activator to adjust the generation time of the solid phase, avoiding the precipitation of products at low carbon dioxide loads, which may cause equipment blockage. The absorption capacity is only 0.49 - 0.55 molCO 2 / mol, and the solid - phase material needs to be transported by special equipment, and there is still a risk of blocking the equipment. Microwave heating is used to regenerate the solid phase, which is not suitable for further commercial applications.

[0006] Therefore, developing a phase - change absorption system with a large absorption load, high cycle capacity and short phase - separation time provides new ideas for further commercial applications. 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. This phase - change absorbent has excellent properties of large absorption load, high cycle absorption capacity and rapid phase separation.

[0008] 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. 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 - 45 wt% of the total weight of the liquid - liquid phase - change absorbent, and the weight ratio of the activator:promoter = 0.3 - 4:1.

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

[0010] As an improvement to the high - load liquid - liquid phase - change absorbent for carbon dioxide capture of the present invention: The promoter is tris(dimethylaminopropyl)hexahydro - 1,3,5 - triazine (i.e., 1,3,5 - tris(dimethylaminopropyl)hexahydro - 1,3,5 - triazine); The activator is 2 - methylpiperazine.

[0011] As a further improvement to the high - load liquid - liquid phase - change absorbent for carbon dioxide capture of the present invention: The content of tris(dimethylaminopropyl)hexahydrotriazine in the liquid-liquid phase change absorbent is 9-20 wt% of the total weight of the liquid-liquid phase change absorbent; The content of 2-methylpiperazine in the liquid-liquid phase change absorbent is 5-36 wt% of the total weight of the liquid-liquid phase change absorbent.

[0012] As a further improvement of the high-load liquid-liquid phase change absorbent for carbon dioxide capture in the present invention: The liquid-liquid phase change absorbent is composed of 20 wt% tris(dimethylaminopropyl)hexahydrotriazine, 10 wt% 2-methylpiperazine, and 70 wt% mixed solvent, and the weight ratio of N-methylpyrrolidone to water in the mixed solvent is 2:1.

[0013] In the present invention, the promoter, activator, N-methylpyrrolidone (NMP), and water are mixed into a homogeneous solution by a conventional stirring method (for example, stirring at 25±5°C and 300±50 rpm for 30±5 min) to obtain the high-load liquid-liquid phase change absorbent.

[0014] The present invention also provides a carbon dioxide capture method using the above high-load liquid-liquid phase change absorbent, including the following steps: 1) CO 2 Absorption process: The gas containing CO 2 is introduced into the liquid-liquid phase change absorbent. The liquid-liquid phase change absorbent is a homogeneous solution before absorbing CO 2 . When the CO 2 absorption reaches a certain load, a phase change phenomenon will occur, forming two immiscible liquid-liquid phases; Note: Due to the gas flow, the separation of the two immiscible liquid-liquid phases is incomplete; This step 1) is carried out under a pressure of ≤110 kPa (0-110 kPa); 2) CO 2 Rich liquid separation: Stop introducing the gas containing CO 2 , and let the two immiscible liquid-liquid phases obtained in step 1) stand for separation (so as to achieve complete phase separation), forming upper and lower layer liquids; The upper layer liquid is the CO 2 lean phase (mainly composed of N-methylpyrrolidone), and the lower layer liquid is the CO 2 rich phase (composed of reaction products, water, and a small amount of N-methylpyrrolidone, etc., and CO 2 is mainly enriched in the lower layer liquid); Note: The reaction products generally include R 1 R 2 NCOO - 、R 1 R2 NH 2 + 、HCO 3 - etc.; 3) CO 2 Rich solution regeneration: Take out CO 2 from the rich phase for heating desorption so that CO 2 in the rich phase of CO 2 is released (i.e., thus realizing the regeneration of the rich solution of CO 2 ), and the obtained is named the regenerated rich solution of CO 2 (i.e., the rich phase after releasing CO 2 ); The regenerated rich solution of CO 2 and the CO 2 lean phase obtained in step 2) are mixed to form a homogeneous solution, which is a recyclable liquid-liquid phase change absorbent.

[0015] That is, the recyclable liquid-liquid phase change absorbent is recycled and reused subsequently to absorb CO 2 .

[0016] As an improvement to the carbon dioxide capture method of the present invention: The absorption temperature in step 1) is 30~45°C; The heating desorption temperature in step 3) is 90~120°C.

[0017] Note: The higher the desorption temperature, the better the regeneration efficiency, but the corresponding energy consumption is higher; therefore, the present invention preferably selects 90~120°C.

[0018] As a further improvement to the carbon dioxide capture method of the present invention: The static separation time in step 2) is ≥2 min (generally 2~5 minutes).

[0019] Note: After 2 min, two immiscible liquid-liquid phases can be formed. Increasing the static separation time makes the two-phase separation more complete, and the volume of the rich solution is further reduced (change rate <1%). After phase separation, more than 93% of CO 2 is enriched in the lower layer, and the volume ratio of the rich phase is about 65~68%.

[0020] As a further improvement to the carbon dioxide capture method of the present invention: In step 1), when absorbing CO 2 to full load (i.e., absorption saturation), stop step 1).

[0021] Note: When the outlet gas flow rate is equal to the inlet gas flow rate, it is determined as absorption saturation.

[0022] In the present invention: Tris(dimethylaminopropyl)hexahydrotriazine is used as a highly alkaline CO 2 absorbent, a certain proportion of N-methylpyrrolidone is used as a phase separation inducer to promote liquid-liquid phase change, and water is used as a solvent to further reduce the viscosity of the absorbent; the liquid-liquid phase change absorbent is a homogeneous solution before absorption and forms immiscible liquid-liquid two phases after absorption, and the phase enriched with CO 2 is in the lower layer of the solution. N-methylpyrrolidone is an organic physical solvent with a strong affinity for CO 2 and does not participate in the CO 2 absorption reaction. Due to hydrogen bonding or hydrophobicity, it undergoes phase separation with the reaction products and is located in the upper layer of the solution after phase separation. After the solution is phase-separated, only the rich phase needs to be sent to the regeneration tower. The lower the volume ratio of the rich phase, the smaller the corresponding amount of the regenerated solution, the lower the sensible heat, and the less the water content, which can significantly reduce the latent heat of water evaporation and thus reduce the regeneration energy consumption.

[0023] The higher the amine concentration of the promoter and activator in the liquid-liquid phase change absorbent, the greater the absorption capacity, but it will further increase the viscosity of the liquid phase enriched with CO 2 .

[0024] 2-Methylpiperazine is used as an activator, which 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 the liquid-liquid phase change absorbent absorbs CO 2 and no crystallization under all operating conditions.

[0025] Compared with the prior art, the present invention has the following technical advantages: (1) Tris(dimethylaminopropyl)hexahydrotriazine is used as a promoter to increase the absorption load. The hydrophobicity and alkalinity of the high-content tertiary amine in its molecule are beneficial to reducing the viscosity of the rich liquid and promoting phase separation. After absorbing to a certain load, the phase separation time is fast, as short as 2 minutes.

[0026] (2) The high-load liquid-liquid phase change absorbent of the present invention is a homogeneous solution composed of tris(dimethylaminopropyl)hexahydrotriazine, 2-methylpiperazine, N-methylpyrrolidone and water. N-methylpyrrolidone (NMP) with a high boiling point and low vapor pressure is used as the main solvent and has high thermal stability; when absorbing CO 2 and forming immiscible liquid-liquid two phases at a certain load, the absorption load of the lower liquid phase for CO 2 is 4.08 - 5.28 mol / 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, reducing the regeneration volume. The regeneration efficiency (the recovery degree of the CO 2 absorption capacity) is as high as 92.5%, and the cyclic absorption load is as high as 1.60 mol CO 2 / mol amine can greatly reduce the regeneration energy consumption, and the regeneration energy consumption is 2.27 - 2.41 GJ / t CO 2 , which is conducive to the industrial application and promotion. Specific embodiments

[0027] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto: The performance test of the present invention is carried out by the following method: Experiment 1. Absorption performance test (carbon dioxide capture method) (1) CO 2 Absorption process: At a certain temperature, CO 2 gas is introduced into the liquid-liquid phase change absorbent to investigate the absorption capacity of the absorbent and the phase separation situation. The liquid-liquid phase change absorbent is a homogeneous solution before absorbing CO 2 , and a phase change phenomenon occurs after absorbing CO 2 at a certain load, forming two immiscible liquid-liquid phases; when the outlet gas flow rate is equal to the inlet gas flow rate, the absorption is completed, that is, after absorption saturation, the absorption rate is calculated according to the reading of the flow meter.

[0028] (2) CO 2 Rich liquid separation: After the absorption in step (1) is completed, the introduction of CO 2 gas is stopped, and the mixture is allowed to stand for ≥2 min for phase separation. The separated upper liquid and lower liquid are respectively tested for the volume percentage and CO 2 load.

[0029] The upper liquid is the CO 2 lean phase (mainly composed of N-methylpyrrolidone), and the lower liquid is the CO 2 rich phase (including reaction products, water and a small amount of N-methylpyrrolidone, and CO 2 is mainly enriched in the lower liquid); (3) CO 2 Rich liquid regeneration: After the CO 2 rich phase is separated and taken out, the upper CO 2 lean phase is reserved for standby. The regeneration process only needs to heat and desorb the CO 2 rich phase, and regeneration (heating and desorption) is carried out at a certain temperature; the CO 2 released after rich phase and the CO 2 lean phase obtained in step (2) are mixed to form a homogeneous solution and then recycled to absorb CO 2 again.

[0030] In the above Experiment 1: The absorption temperature in step (1) is preferably set at 30~45°C, and the operating pressure does not exceed the maximum working pressure of the instrument, preferably 0~110 kPa. After absorption saturation, a sample is taken for analysis of the CO 2 concentration; then it is sent to a desorption bottle for desorption regeneration. The regeneration temperature in step (3) is preferably set at 90~120°C. After that, the next cycle experiment test is carried out. Generally, when the regeneration degree of the carbon dioxide composite absorbent preferably exceeds 90%, the next cycle experiment test is carried out.

[0031] Experiment 2: Cycle experiment test The carbon dioxide composite absorbent obtained by desorption in Experiment 1 is absorbed again under the same test device, absorption temperature and operating pressure experimental conditions as in Experiment 1. After absorption saturation, a sample is taken for analysis, and the cyclic absorption capacity of the absorbent is calculated; then it is desorbed and regenerated at the same regeneration temperature as in Experiment 1. After each absorption and desorption, a sample is taken for analysis, and a total of five cycle tests are carried out to investigate the thermal stability of the absorbent. The calculation method of the cyclic absorption capacity is the same as the absorption capacity calculation method in Experiment 1 above.

[0032] Experiment 3: Energy consumption test In the present invention, the energy consumption for regenerating the phase change absorbent is calculated through sensible heat, latent heat and reaction heat, with the unit of GJ / t CO 2 , and the calculation method is a commonly used method in the art and will not be elaborated here.

[0033] Test the absorption load of the absorbents described in the following examples and comparative examples. Before and after the experiment, the carbon dioxide load in the absorption liquid is measured using the acid-base titration method. The determination methods of absorption and regeneration performance are commonly used methods in the art and will not be elaborated here.

[0034] Example 1: A high-load liquid-liquid phase change absorbent for carbon dioxide capture By weight percentage of the total absorbent, 9 wt% tris(dimethylaminopropyl)hexahydrotriazine, 36 wt% 2-methylpiperazine, and 55 wt% mixed solvent (the weight ratio of N-methylpyrrolidone to water in the mixed solvent is 3:1) are respectively weighed and placed in a beaker. Stir at 25°C and 300 rpm for 30 min to form a homogeneous solution, obtaining a high-load liquid-liquid phase change absorbent.

[0035] According to Experiment 1, the absorption performance test is carried out. The set parameters in step (1) are: absorption temperature is 30°C, pressure is 1.0 kPa, and the obtained measurement results are: the static time after absorption is 2 min, and the volume fraction of the lower-layer CO 2 rich phase is 68%, and the CO 2 loading is 5.28 mol / L, and the maximum absorption load (absorption capacity) is 1.58 mol CO 2 / mol amine, 96% CO 2 Enriched in the lower layer, when the desorption temperature is 120 °C, the regeneration degree is 90.7%, and the regeneration energy consumption is 2.41 GJ / t CO 2 ; The cyclic experiment was measured according to Experiment 2. The experimental conditions were the same as those of 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 measured results showed that the absorption capacity after five cycles was 1.42 mol CO 2 / mol amine.

[0036] Example 2. A high-load liquid-liquid phase change absorbent for carbon dioxide capture By weight percentage of the total absorbent, 20 wt% tris(dimethylaminopropyl)hexahydrotriazine, 10 wt% 2-methylpiperazine, and 70 wt% mixed solvent (the weight ratio of N-methylpyrrolidone to water in the mixed solvent is 2:1) were weighed and placed in a beaker. Stir at 25 °C and 300 rpm for 30 min to mix into a homogeneous solution to obtain the high-load liquid-liquid phase change absorbent.

[0037] The absorption performance was tested according to Experiment 1. The specific parameters set in step (1) were: the absorption temperature was 30 °C and the pressure was 110 kPa. The measured results showed that the static time after absorption was 3 min, and the volume fraction of the lower-layer CO 2 rich phase was 67%, and the CO 2 loading was 4.99 mol / L, and the maximum absorption load was 1.78 mol CO 2 / mol amine, 94% CO 2 Enriched in the lower layer, when the desorption temperature is 110 °C, the regeneration degree is 92.5%, and the regeneration energy consumption is 2.37 GJ / t CO 2 ; The cyclic experiment was measured according to Experiment 2. The experimental conditions were the same as those of Experiment 1 corresponding to Example 2 above. The absorption temperature was set at 30 °C and the regeneration temperature was set at 110 °C. The measured results showed that the absorption capacity after five cycles was 1.60 mol CO 2 / mol amine.

[0038] Example 3. A high-load liquid-liquid phase change absorbent for carbon dioxide capture By weight percentage of the total absorbent, 20 wt% tris(dimethylaminopropyl)hexahydrotriazine, 10 wt% 2-methylpiperazine, and 70 wt% mixed solvent (the weight ratio of N-methylpyrrolidone to water in the mixed solvent is 3:1) were weighed and placed in a beaker. Stir at 25 °C and 300 rpm for 30 min to mix into a homogeneous solution to obtain the high-load liquid-liquid phase change absorbent.

[0039] The absorption performance was tested according to Experiment 1. The specific parameter settings in step (1) were as follows: the absorption temperature was 45 °C, and the pressure was 50 kPa. The measurement results were as follows: the standing time after absorption was 5 min, and the volume fraction of the lower-layer CO 2 rich phase was 65%, and the CO 2 loading was 5.09 mol / L. The maximum absorption load was 1.61 mol CO 2 / mol amine. 95% of the CO 2 was enriched in the lower layer. When the desorption temperature was 90 °C, the regeneration degree was 91.9%, and the regeneration energy consumption was 2.27 GJ / t CO 2 ; The cyclic experiment was measured according to Experiment 2. The experimental conditions were the same as those of Experiment 1 corresponding to Example 3 above. The absorption temperature was set at 45 °C, and the regeneration temperature was 90 °C. The measurement results were as follows: the absorption capacity after five cycles was 1.47 mol CO 2 / mol amine.

[0040] Example 4: A high-load liquid-liquid phase change absorbent for carbon dioxide capture By weight percentage of the total absorbent, 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 was 2:1) were weighed and placed in a beaker. They were stirred at 25 °C and 300 rpm for 30 min to be uniformly mixed to obtain a homogeneous solution, thus obtaining the high-load liquid-liquid phase change absorbent.

[0041] The absorption performance was tested according to Experiment 1. The specific parameter settings in step (1) were as follows: the absorption temperature was 40 °C, and the pressure was 10 kPa. The measurement results were as follows: the standing time after absorption was 2 min, and the volume fraction of the lower-layer CO 2 rich phase was 66%, and the CO 2 loading was 4.08 mol / L. The maximum absorption load was 1.55 mol CO 2 / mol amine. 93% of the CO 2 was enriched in the lower layer. When the desorption temperature was 110 °C, the regeneration degree was 92.1%, and the regeneration energy consumption was 2.30 GJ / t CO 2 ; The cyclic experiment was measured according to Experiment 2. The experimental conditions were the same as those of Experiment 1 corresponding to Example 4 above. The absorption temperature was set at 40 °C, and the regeneration temperature was 110 °C. The measurement results were as follows: the absorption capacity after five cycles was 1.40 mol CO 2 / mol amine.

[0042] Example 5: A high-load liquid-liquid phase change absorbent for carbon dioxide capture Weigh 15 wt% tris(dimethylaminopropyl)hexahydrotriazine, 15 wt% 2-methylpiperazine, and 70 wt% mixed solvent (the weight ratio of N-methylpyrrolidone to water in the mixed solvent is 2:1) respectively based on the total weight percentage of the absorbent, place them in a beaker, and stir at 25 °C and 300 rpm for 30 min to mix into a homogeneous solution, obtaining the high-load liquid-liquid phase change absorbent described above.

[0043] Perform the absorption performance test according to Experiment 1. The specific parameter settings in step (1) are as follows: the absorption temperature is 30 °C and the pressure is 10 kPa. The obtained measurement results are as follows: the standing time after absorption is 2 min, and the lower-layer CO 2 rich phase volume fraction is 66%, and the CO 2 loading is 4.13 mol / L, and the maximum absorption load is 1.46 mol CO 2 / mol amine, and 94% of the CO 2 is enriched in the lower layer. When the desorption temperature is 110 °C, the regeneration degree is 90.1%, and the regeneration energy consumption is 2.33 GJ / t CO 2 ; The cyclic experiment is measured according to Experiment 2. The experimental conditions are the same as those in Experiment 1 corresponding to Example 5 above. Set the absorption temperature to 30 °C and the regeneration temperature to 110 °C. The obtained measurement results are as follows: the absorption capacity after five cycles is 1.31 mol CO 2 / mol amine.

[0044] The CO 2 cyclic loading of the phase change absorbents prepared in Examples 1 to 5 is maintained at ≥1.31 mol CO 2 / mol amine after five cycles, and the desorption efficiency of each desorption can reach over 90%. This indicates that the absorbent has good stability, excellent desorption performance, and stable renewable properties, and the regeneration energy consumption is 2.27 - 2.41 GJ / t CO 2 .

[0045] Comparative Example 1, Weigh 30 wt% ethanolamine and 70 wt% water respectively based on the total weight percentage of the absorbent, place them in a beaker, and stir at 25 °C and 300 rpm for 30 min to mix into a homogeneous solution, obtaining a traditional commercial (30 wt% MEA) carbon dioxide absorbent.

[0046] Perform the absorption performance test according to Experiment 1. The specific parameter settings in step (1) are as follows: the absorption temperature is 30 °C and the pressure is 1 kPa. The obtained measurement results are as follows: the standing time after absorption is more than 5 min, there is no phase change stratification phenomenon, and the maximum absorption load is 0.59 mol CO 2 / mol amine, when the desorption temperature is 120 °C, the regeneration degree is 60%, and the regeneration energy consumption is 3.81 GJ / t CO 2 ; The cyclic experiment was measured according to Experiment 2. The experimental conditions were the same as those of Experiment 1 corresponding to Comparative Example 1 above. The absorption temperature was set at 30 °C and the regeneration temperature was set at 120 °C. The measurement results obtained were as follows: the absorption capacity after five cycles was 0.26 mol CO 2 / mol amine.

[0047] Comparative Example 2, Compared with Example 2, the weight ratio of N-methylpyrrolidone to 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.

[0048] The absorption performance test was carried out according to Experiment 1. The specific parameters selected in step (1) were as follows: the absorption temperature was 30 °C and the pressure was 110 kPa. The measurement results obtained were as follows: the standing time after absorption was more than 5 min, there was no phase change and layering phenomenon, and the maximum absorption load was 1.44 mol CO 2 / mol amine, when the desorption temperature is 110 °C, the regeneration degree is 90.4%, and the regeneration energy consumption is 2.9 GJ / t CO 2 ; The cyclic experiment was measured according to Experiment 2. The experimental conditions were the same as those of Experiment 1 corresponding to Comparative Example 2 above. The absorption temperature was set at 30 °C and the regeneration temperature was set at 110 °C. The measurement results obtained were as follows: the absorption capacity after five cycles was 1.21 mol CO 2 / mol amine.

[0049] Comparative Example 3, Compared with Example 2, "the mixed solvent is composed of N-methylpyrrolidone and water with a weight ratio of 2:1" was changed to "using N-methylpyrrolidone alone as the solvent", and the amount of the solvent remained unchanged, that is, 70 wt% of N-methylpyrrolidone; the rest was the same as Example 2.

[0050] The absorption performance test was carried out according to Experiment 1. The specific parameters selected in step (1) were as follows: the absorption temperature was 30 °C and the pressure was 110 kPa. The measurement results obtained were as follows: the standing time after absorption was more than 2 min, and phase change occurred and layered into a liquid-solid two-phase state. The lower layer was a solid phase, and the next test experiment could not be carried out.

[0051] The regeneration energy consumption mainly consists of three parts: the sensible heat of the absorbent regeneration, CO 2The desorption reaction heat of the product and the latent heat carried away by the regeneration gas. In the present invention, the solvent ratio is the key to the phase change behavior. When the weight ratio of N-methylpyrrolidone to water in Comparative Ratio 2 is reduced to 1:1, there is no phase change and stratification phenomenon after the absorbent absorbs carbon dioxide. During regeneration, all the absorbent needs to be heated, and compared with the liquid-liquid phase change absorbent in Example 2, the energy consumption is relatively high at 2.9 GJ / t CO 2 , mainly due to the increase in sensible heat. For the phase change absorbent of the present invention, only the lower phase rich in CO 2 needs to be regenerated, so the amount of regenerated solution can be reduced and thus the sensible heat can be decreased.

[0052] In Comparative Ratio 1, the 30 wt% ethanolamine solution is a common commercial absorbent. There is no phase change after absorption, and the energy consumption is relatively high at 3.81 GJ / t CO 2 . Comparing Comparative Ratio 1 and 2, the reaction heat of tris(dimethylaminopropyl)hexahydrotriazine is lower and the absorption capacity is larger. The absorption load of Comparative Ratio 2 is 2.45 times that of Comparative Ratio 1 and the desorption rate is as high as 90%. It has better absorption performance. At the same time, N-methylpyrrolidone is added to reduce the latent heat of vaporization of water, significantly reducing the latent heat of regeneration. In summary, compared with Comparative Ratio 1, the regeneration energy consumption of Comparative Ratio 2 is reduced by 23.9%.

[0053] Combining Example 1 and 3, as the content of 2-methylpiperazine in Example 1 increases, the absorption load and regeneration rate slightly decrease, and the regeneration energy consumption increases by 0.14 GJ / t CO 2 , which is due to the relatively high reaction heat of 2-methylpiperazine. More thermal energy is required for desorption, that is, the corresponding desorption heat is higher.

[0054] Combining Example 2 and 3, as the proportion of N-methylpyrrolidone in Example 3 increases, the absorption load decreases by 9.6%, which is due to the addition of an organic solvent reducing the alkalinity of the absorbent. At the same time, the energy consumption also decreases.

[0055] Combining Example 4 and 5, as the content of 2-methylpiperazine in Example 5 increases, the absorption load and regeneration rate decrease, and the regeneration energy consumption increases.

[0056] Comparative Ratio 4-1, In Example 2, change "2-methylpiperazine" to "piperazine", and the content remains unchanged at 10 wt%; the rest is the same as Example 2.

[0057] According to Experiment 1 for absorption performance testing, the obtained measurement results: After carbon dioxide is introduced into the absorbent added with piperazine (PZ), a white cream-like substance is slowly generated and finally turns into a solid. The next test experiment cannot be carried out.

[0058] Comparative Ratio 4-2, Change "2-methylpiperazine" in Example 2 to "hydroxyethylpiperazine", and keep the content unchanged at 10 wt%; the rest is the same as Example 2.

[0059] Perform the absorption performance test according to Experiment 1. After absorption, let it stand for 3 minutes. The lower layer is CO 2 The volume fraction of the rich phase is 75%, and CO 2 The loading is 1.55 mol / L, and the maximum absorption load is 1.07 mol CO 2 / mol amine, and 87% of CO 2 is enriched in the lower layer. When the desorption temperature is 110 °C, the regeneration degree is 72%, and the regeneration energy consumption is 3.2 GJ / t CO 2 ; The cyclic experiment is measured according to Experiment 2. The experimental conditions are the same as those of Experiment 1 corresponding to Comparative Example 4-2 above. Set the absorption temperature to 30 °C and the regeneration temperature to 110 °C. The obtained measurement results: the absorption capacity after five cycles is 0.72 mol CO 2 / mol amine.

[0060] Comparative Example 5-1, Change "N-methylpyrrolidone" in the mixed solvent of Example 2 to "dimethyl sulfoxide (DMSO)", keep the dosage unchanged, and the rest is the same as Example 2.

[0061] Perform the absorption performance test according to Experiment 1. After absorption, let it stand for 3 minutes, and it does not separate into layers. The maximum absorption load is 1.34 mol CO 2 / mol amine. When the desorption temperature is 110 °C, the regeneration degree is 88%, and the regeneration energy consumption is 3.3 GJ / t CO 2 ; The cyclic experiment is measured according to Experiment 2. The experimental conditions are the same as those of Experiment 1 corresponding to Example 5-1 above. Set the absorption temperature to 30 °C and the regeneration temperature to 110 °C. The obtained measurement results: the absorption capacity after five cycles is 1.07 mol CO 2 / mol amine.

[0062] Comparative Example 5-2, Change "N-methylpyrrolidone" in the mixed solvent of Example 2 to "N,N-dimethylformamide (DMF)", keep the dosage unchanged, and the rest is the same as Example 2.

[0063] Perform the absorption performance test according to Experiment 1. After absorption, let it stand for 5 minutes, and it does not separate into layers. The maximum absorption load is 1.41 mol CO 2 / mol amine. When the desorption temperature is 110 °C, the regeneration degree is 86%, and no further test is carried out.

[0064] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A high-load liquid-liquid phase change absorbent for carbon dioxide capture, characterized in that: 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: promoter = 0.3-4:

1.

2. The high-load liquid-liquid phase change absorbent for carbon dioxide capture according to claim 1, characterized in that: The accelerator is tris(dimethylaminopropyl)hexahydrotriazine; The activator is 2-methylpiperazine.

3. The high-load liquid-liquid phase change absorbent for carbon dioxide capture according to claim 2, 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.

4. The high-load liquid-liquid phase change absorbent for carbon dioxide capture according to any one of claims 1 to 3, 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 in the mixed solvent is 2:

1.

5. A method for capturing carbon dioxide, characterized in that: Using the high-load liquid-liquid phase change absorbent as described in any one of claims 1 to 4, comprising 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 to form an immiscible liquid-liquid two phases. 2) CO2 rich liquid separation: Stop passing the gas containing CO2, so that the immiscible liquid-liquid two phases obtained in step 1) are allowed to stand and separate to form 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 for heating and desorption, so that the CO2 in the CO2-rich phase is released, and the obtained liquid 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.

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

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

8. A method for capturing carbon dioxide according to any one of claims 5 to 7, characterized in that: In the step 1), when CO2 is absorbed to full load, step 1) is stopped.