Mixed solvent for carbon dioxide absorption and carbon dioxide absorption method

Abstract

The invention belongs to the technical field of carbon dioxide capture, and discloses a mixed solvent for carbon dioxide absorption and a carbon dioxide absorption method. The invention relates to a mixed solvent for carbon dioxide absorption. The mixed solvent is prepared from 3-methylaminopropylamine, isobutylamine, pentamethyldiethylenetriamine and water, wherein the concentration of the 3-methylaminopropylamine is 1.5 mol / L, the concentration of the isobutylamine is 0.5 mol / L, and the concentration of the pentamethyldiethylenetriamine is 3 mol / L. According to the invention, MAPA with high activity of primary amine and regulation and control functions of secondary amine, IBA with a unique space structure and a high-efficiency phase-splitting agent PMDETA are compounded in a pure water phase according to a specific proportion, so that an unexpected synergistic effect is generated. The technical prejudice that the capacity must be sacrificed when the viscosity is reduced is successfully broken through. The data of the embodiment shows that compared with the closest 2M3P system, the preferable solvent has the advantages that the rich phase viscosity is greatly reduced by 60%, the absorption capacity of 4.07 mol / kg is still kept, and the desorption efficiency is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide capture technology, and more specifically to mixed solvents for carbon dioxide absorption and methods for carbon dioxide absorption. Background Technology

[0002] In the context of climate change, carbon dioxide capture, utilization, and storage (CCVS) technologies are crucial for achieving carbon neutrality. Chemical absorption, especially amine absorption, is currently the most mature CO2 capture technology for coal-fired power plants and industrial processes. Monoethanolamine (MEA) aqueous solution is the benchmark absorbent, but its regeneration energy consumption is extremely high (typically >4.0 GJ / t CO2), resulting in high operating costs.

[0003] To reduce regeneration energy consumption, phase change absorbents have become a research hotspot. These absorbents undergo liquid-liquid phase separation after absorbing CO2, forming a CO2-rich phase and a CO2-poor phase. By regenerating only the smaller volume of the rich phase, the heat load is significantly reduced. For example, the 2M3P aqueous phase system (2 mol / L MAPA, 3 mol / L PMDETA) composed of 3-methylaminopropylamine (MAPA) and pentamethyldiethylenetriamine (PMDETA) has a high CO2 absorption capacity. However, this system suffers from excessively high viscosity in the rich phase (up to 320.7 mPa·s), leading to high mass transfer resistance and high pumping energy consumption, thus limiting its industrial application.

[0004] There has long been a difficult technical contradiction in this field, namely, the difficulty in simultaneously achieving "high absorption capacity", "low viscosity of the rich phase" and "low regeneration energy consumption". Researchers have tried various approaches: (1) Using non-aqueous solvents (such as DMSO): Although it can reduce viscosity, it introduces new problems such as solvent evaporation, high recycling costs, and poor equipment compatibility. (2) Adjusting the type and ratio of amines: However, there is a common technical bias that the introduction of multiple amines will lead to a complex reaction pathway, an increase in byproducts, and a decrease in system stability. The traditional view is that the introduction of multiple amines may cause competitive reactions and accelerate degradation. At the same time, it is also believed that in order to significantly reduce the viscosity of the rich phase, it is often necessary to sacrifice the CO2 absorption capacity.

[0005] Furthermore, in the regeneration of CO2 absorbents, there is a common technical practice and understanding in the field: to achieve efficient CO2 desorption, a relatively high regeneration temperature (typically above 380 K) is usually required. Whether it's the traditional MEA process or most improved phase change absorbent systems, the desorption tower operating temperature is set within this high-temperature range. This is mainly because high temperatures provide sufficient thermodynamic driving force for the decomposition of carbamates. Therefore, the notion that high temperatures are necessary for efficient desorption, and that low-temperature desorption (such as 363 K) is insufficient for efficient CO2 release, has become, to some extent, an inherent perception or technical bias among those skilled in the art, which also leads to persistently high energy consumption in the regeneration process.

[0006] In view of this, the present invention is proposed. Summary of the Invention

[0007] The present invention aims to solve at least one of the above-mentioned technical problems, and provides a mixed solvent for carbon dioxide absorption and a method for carbon dioxide absorption.

[0008] To achieve the above objectives, the first technical solution adopted by the present invention is as follows: The mixed solvent used for carbon dioxide absorption consists of 3-methylaminopropylamine, isobutylamine, pentamethyldiethylenetriamine and water; wherein the concentration of 3-methylaminopropylamine is 1.5 mol / L, the concentration of isobutylamine is 0.5 mol / L and the concentration of pentamethyldiethylenetriamine is 3 mol / L.

[0009] Preferably, after absorbing carbon dioxide, the mixed solvent undergoes liquid-liquid phase separation, and the volume of the carbon dioxide-rich phase accounts for 30-45% of the total liquid volume.

[0010] The second technical solution adopted in this invention is: Methods for carbon dioxide absorption include: Under conditions of 300-310 K, a gas containing carbon dioxide is brought into contact with a mixed solvent to carry out an absorption reaction. After the absorption reaction is completed, the mixed solvent undergoes liquid-liquid phase separation, forming a carbon dioxide-rich phase and a carbon dioxide-poor phase; The carbon dioxide-rich phase is heated to 360-370 K for desorption, releasing carbon dioxide gas, and the carbon dioxide-lean phase is recovered. The mixed solvent is composed of 3-methylaminopropylamine, isobutylamine, pentamethyldiethylenetriamine and water.

[0011] Preferably, the concentration of 3-methylaminopropylamine is 1.5 mol / L, the concentration of isobutylamine is 0.5 mol / L, and the concentration of pentamethyldiethylenetriamine is 3 mol / L.

[0012] Preferably, the molar ratio of 3-methylaminopropylamine to isobutylamine is (1-4):1.

[0013] Preferably, the desorption is performed under inert gas purging conditions.

[0014] The third technical solution adopted in this invention is: A carbon dioxide absorption system for implementing any of the methods described above includes: An absorption tower is used to contact carbon dioxide-containing gas with a mixed solvent for an absorption reaction; the absorption tower has a rich liquid outlet. A desorption tower, connected to the rich liquid outlet of the absorption tower, is used to receive the rich phase liquid from the absorption tower that has absorbed carbon dioxide and undergone liquid-liquid phase separation, and to heat and desorb the rich phase liquid. A lean-rich liquid heat exchanger is connected between the rich liquid outlet of the absorption tower and the inlet of the desorption tower, and is used to exchange heat between the hot lean liquid flowing out of the desorption tower and the cold rich liquid flowing into the desorption tower. A condenser is connected to the top gas outlet of the desorption tower; A carbon dioxide compression unit is connected to the gas outlet of the condenser.

[0015] Preferably, the operating temperature of the absorption tower is 300-310 K, and the operating temperature of the desorption tower is 360-370 K.

[0016] Preferably, the heat recovery efficiency of the lean and rich liquid heat exchanger is not less than 75%.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves an unexpected synergistic effect by compounding MAPA (which possesses both the high activity of primary amines and the moderating function of secondary amines) with isobutylamine (IBA) (with its unique spatial structure) and the highly efficient phase-separating agent PMDETA in a specific ratio in a pure aqueous phase. This successfully breaks the technical prejudice that reducing viscosity must sacrifice capacity. Example data shows that, compared to the closest 2M3P system, the preferred solvent of this invention significantly reduces the viscosity of the rich phase by 60% while maintaining an absorption capacity as high as 4.07 mol / kg and significantly improving desorption efficiency.

[0018] This invention, through optimization of amine structure and phase separation behavior, achieves for the first time highly efficient regeneration of CO2-rich phases at significantly lower temperatures (360 K-370 K). Examples show that at a low temperature of 363 K, the desorption rate of this system reaches 59.3%, far exceeding the desorption rate (38.4%) of the traditional 2M3P system at the same temperature. When combined with purging with an inert gas (such as N2), the desorption rate can be further increased to over 98.5%. This demonstrates the feasibility of low-temperature, efficient desorption in the phase change system of this invention, opening a new path for significantly reducing the regeneration energy consumption of CO2 capture.

[0019] The present invention, through 10 consecutive absorption-desorption cycle experiments, showed that the absorption capacity decay was less than 6%, and no obvious byproducts were detected by infrared and NMR analysis. This strongly demonstrates that the precise formulation of the present invention successfully overcomes the inherent bias that polyamine mixing easily leads to instability and increased byproducts, showcasing excellent potential for industrial applications.

[0020] This invention features a low viscosity and good flowability of the rich-phase phase, and after system optimization, it can achieve efficient desorption at lower temperatures. Combined with energy integration design, the energy consumption for CO2 removal can be reduced to approximately 3.0 GJ / ton, which is about 35% lower than the traditional MEA process. The pure aqueous phase system of this invention avoids the problem of non-aqueous solvent recovery, has good compatibility with existing amine-based collection devices, and has low modification costs, making it particularly suitable for large-scale flue gas treatment scenarios such as coal-fired power plants and chemical plants. Attached Figure Description

[0021] Figure 1 The CO2 absorption rate of solvent systems with different MAPA and PMDETA concentration ratios in Example 6; Figure 2 The absorption rates of the system after replacing MAPA with different molar amounts of IBA in Example 6; Figure 3 The values ​​represent the desorption rates of the system after replacing MAPA with different molar amounts of IBA in Example 6. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, those skilled in the art can obtain the following results without creative effort: The first embodiment of the present invention provides a mixed solvent for carbon dioxide absorption, which is composed of 3-methylaminopropylamine, isobutylamine, pentamethyldiethylenetriamine and water; wherein the concentration of 3-methylaminopropylamine is 1.5 mol / L, the concentration of isobutylamine is 0.5 mol / L, and the concentration of pentamethyldiethylenetriamine is 3 mol / L.

[0023] 3-Methylaminopropylamine (MAPA): A primary absorption and phase separation promoter. Its primary amino group (-NH2) at one end of the molecule exhibits extremely high reactivity, rapidly reacting with CO2 to form carbamate, ensuring a high absorption rate. The secondary amino group (-NH-CH3) at the other end also participates in the reaction, but the resulting carbamate differs in stability from the primary amine. The presence of two amino groups with different reactivity and product stability within the molecule increases the complexity of the reaction products, providing the initial thermodynamic driving force for subsequent phase separation.

[0024] Isobutylamine (IBA): A viscosity modifier and phase separation promoter. As a simple short-chain primary amine, IBA can also rapidly absorb CO2. Its small molecular weight and unique isobutyl structure effectively disrupt the orderly arrangement of ion clusters in the rich phase after CO2 absorption, significantly altering the polarity and hydrogen bond network of the local microenvironment. Its introduction effectively inhibits the formation of large molecular ion clusters in the rich phase, thereby greatly reducing the viscosity of the rich phase. Simultaneously, its solubility differs from that of the CO2 reaction products of MAPA and PMDETA, further exacerbating the incompatibility of the system and accelerating the liquid-liquid phase transition.

[0025] Pentamethyldiethylenetriamine (PMDETA): A phase-separating and buffering agent. As a tertiary amine, PMDETA lacks an active hydrogen atom on its nitrogen atom and cannot directly react with CO2 to form stable carbamates. Its main function is to react with H2 in water... + This combination promotes the hydrolysis of CO2 to form bicarbonate (HCO3-). - The ionic products generated by this pathway are more hydrophilic. The presence of PMDETA directionally leads the reaction to generate two different types of products, one with stronger hydrophilicity and the other with stronger hydrophobicity, clearly widening the polarity difference between the components and acting as a key guiding factor for induced phase separation.

[0026] Before absorbing CO2, MAPA, IBA, PMDETA, and water form a homogeneous molecular dispersion system. After CO2 absorption, the system simultaneously contains: a hydrophobic component, mainly composed of carbamate ion pairs formed by MAPA and IBA; and a hydrophilic component, mainly composed of bicarbonate ions generated by PMDETA, as well as excess unreacted PMDETA and water molecules. These two types of components have vastly different polarities and hydrogen bonding abilities, making them unable to stably co-dissolve in the same liquid phase. According to the principle of "like dissolves like," the system spontaneously separates into two liquid phases to achieve a lower Gibbs free energy: a CO2-rich phase, mainly composed of concentrated hydrophobic carbamates, resulting in higher viscosity and density, but significantly improved flowability due to the viscosity-reducing effect of IBA; and a CO2-poor phase, mainly containing hydrophilic bicarbonates, unreacted PMDETA, and a large amount of water, with low viscosity and a small CO2 loading.

[0027] This invention constructs a highly efficient "absorption-phase separation-regeneration" cycle system through synergistic innovation at three levels: molecular structure design, precise phase behavior control, and system energy integration. The key lies in the unique synergistic effect of MAPA, IBA, and PMDETA in a pure aqueous phase, thereby overcoming three long-standing technical biases.

[0028] This invention overcomes the technical prejudice that mixing multiple amines leads to complex reaction pathways, increased byproducts, and decreased stability. A common concern in the field is that introducing multiple amines (such as MAPA, IBA, and PMDETA) complicates competing reactions, increases side reaction pathways, accelerates solvent degradation, and affects the long-term stability of the system. This invention, through precise molecular selection and ratio control (especially the molar ratio of primary to tertiary amine concentrations), not only avoids chaotic competition but also constructs a stable system with complementary and mutually buffering reactions.

[0029] This invention breaks the technical prejudice that reducing the viscosity of the rich phase must come at the cost of sacrificing absorption capacity. Traditional phase change absorbents are generally constrained by the technical trade-off between viscosity and capacity, because high capacity usually depends on the formation of high concentrations of reaction products, which tend to form dense ionic networks, leading to a surge in viscosity. To reduce the viscosity of the rich phase, it is often necessary to reduce the concentration of active amine or the depth of reaction, thereby sacrificing capacity. This invention successfully breaks this inherent perception through the synergistic effect of the MAPA / IBA / PMDETA ternary structure. Experimental data show that while the introduction of IBA significantly reduces the viscosity of the rich phase (from 320.7 mPa·s to 128.9 mPa·s), the CO2 loading of the rich phase increases instead of decreasing, reaching a high level of 0.92 mol / mol amine.

[0030] This invention overcomes the technical prejudice that low-temperature desorption is difficult to achieve efficient CO2 release. Traditional processes often employ high-temperature (>380 K) regeneration, while in this invention, the volume to be regenerated is significantly reduced. The secondary aminocarbamates generated by MAPA and the primary aminocarbamates generated by IBA have inherently lower thermal stability than the carbamates generated by MEA. Simultaneously, the presence of PMDETA causes some CO2 in the system to exist in the form of weaker-binding bicarbonates, which are easily decomposed at lower temperatures (363 K). Furthermore, the low viscosity means less ion diffusion resistance during desorption, making it easier for CO2 bubbles to form and desorb, thereby accelerating desorption kinetics and further improving desorption efficiency.

[0031] In some preferred embodiments, after absorbing carbon dioxide, the mixed solvent undergoes liquid-liquid phase separation, and the volume of the carbon dioxide-rich phase accounts for 30-45% of the total liquid volume.

[0032] The second embodiment of the present invention provides a method for absorbing carbon dioxide, comprising: Under conditions of 300-310 K, a gas containing carbon dioxide is brought into contact with a mixed solvent to carry out an absorption reaction. After the absorption reaction is completed, the mixed solvent undergoes liquid-liquid phase separation, forming a carbon dioxide-rich phase and a carbon dioxide-poor phase; The carbon dioxide-rich phase is heated to 360-370 K for desorption, releasing carbon dioxide gas, and the carbon dioxide-lean phase is recovered. The mixed solvent is composed of 3-methylaminopropylamine, isobutylamine, pentamethyldiethylenetriamine and water.

[0033] After carbon dioxide gas undergoes an absorption reaction with the mixed solvent, the solution spontaneously separates into a rich phase with high CO2 loading and small volume, and a lean phase with low CO2 loading and large volume. The mixed solvent used has a strong driving force for phase separation, a fast speed, and a clear interface. Its specific amine combination and the polar differentiation generated after reacting with CO2 ensure the spontaneity and quality of phase separation.

[0034] In this embodiment of the invention, the desorption temperature is 360-370 K, which is significantly lower than the desorption temperature of over 380 K typically used in traditional MEA processes and most phase change absorbers. Its feasibility stems from the following: In the rich phase of this invention, the carbamate generated from the primary amines of IBA and MAPA, and the bicarbonate generated with the promotion of PMDETA, have optimized thermal stability, possessing sufficient decomposition driving force at a lower temperature; the low viscosity (e.g., 128.9 mPa·s) rich phase reduces heat transfer and CO2 bubble desorption resistance, further promoting desorption kinetics.

[0035] In some preferred embodiments, desorption is performed under inert gas purging conditions, and the synergistic effect of the mixed solvent and inert gas purging is excellent. For example, at 363 K, the desorption rate is 59.3% with thermal desorption alone, but it jumps to over 98.5% after combining with N2 purging. This proves that the mixed solvent of the present invention is not only suitable for low-temperature desorption, but also can produce a synergistic effect with conventional enhancement methods, ensuring the final desorption efficiency at low temperatures.

[0036] In some specific embodiments, the carbon dioxide-containing gas consists of carbon dioxide and nitrogen with a volume fraction of 12%.

[0037] The third embodiment of the present invention provides a carbon dioxide absorption system for implementing any of the methods described above, comprising: An absorption tower is used to contact carbon dioxide-containing gas with a mixed solvent for an absorption reaction; the absorption tower has a rich liquid outlet. A desorption tower, connected to the rich liquid outlet of the absorption tower, is used to receive the rich phase liquid from the absorption tower that has absorbed carbon dioxide and undergone liquid-liquid phase separation, and to heat and desorb the rich phase liquid. A lean-rich liquid heat exchanger is connected between the rich liquid outlet of the absorption tower and the inlet of the desorption tower, and is used to exchange heat between the hot lean liquid flowing out of the desorption tower and the cold rich liquid flowing into the desorption tower. A condenser is connected to the top gas outlet of the desorption tower; A carbon dioxide compression unit is connected to the gas outlet of the condenser.

[0038] The absorption system provided by this invention allows for spontaneous liquid-liquid phase separation of the CO2-loaded solvent at the bottom of the absorption tower or in the connected pipeline / tank after absorption is completed. The separated carbon dioxide-rich phase is then transported to the lean-rich liquid heat exchanger through the rich liquid outlet.

[0039] The lean-rich liquid heat exchanger is used to recover energy from the circulating liquid between the absorption tower and the desorption tower, thereby achieving low-energy carbon dioxide absorption and desorption operations. The heat recovery efficiency of the lean-rich liquid heat exchanger is not less than 75%.

[0040] The cyclic control method of this carbon dioxide absorption system adjusts the gas-liquid ratio based on the feedback signal formed by the carbon dioxide concentration in the gas at the outlet of the absorption tower, so that the carbon dioxide concentration is kept below 1%, and the desorption rate is kept stable within the error range of no more than 5% by the closed-loop adjustment of the temperature feedback signal and the valve opening.

[0041] The following detailed descriptions of the mixed solvents used for carbon dioxide absorption, the carbon dioxide absorption methods, and their effects are illustrated through several specific examples.

[0042] Example 1: Mixed solvent for carbon dioxide absorption and method for carbon dioxide absorption The mixed solvent composition is: MAPA 1.5 mol / L, IBA 0.5 mol / L, PMDETA 3 mol / L, with deionized water as the solvent, and a total volume of 300 mL.

[0043] Carbon dioxide absorption method: Under constant temperature of 303 K, a CO2 / N2 mixed gas with a volume fraction of 12% was contacted with a mixed solvent for absorption reaction. After the reaction lasted for 60 min, the system changed from a single phase to a two-phase system. The volume fraction of the CO2-rich phase accounted for about 35% of the total liquid, and its color was slightly turbid, indicating that liquid-liquid phase separation occurred. The viscosity of the rich phase was 128.9 mPa·s, and the CO2 loading was 4.07 mol / kg.

[0044] The enriched phase was separated and desorbed. After heating at 363 K for 30 min, CO2 was completely released with a desorption rate of 100% and a gas purity >99%. The lean solution was cooled and recycled. After five cycles, the absorption capacity remained above 0.85 mol CO2 / mol amine, and the system viscosity and absorption rate remained basically stable, indicating that the system has excellent regeneration performance and cycle stability.

[0045] Example 2: Effect of CO2 concentration and liquid phase ratio on phase behavior Using the mixed solvent from Example 1, the CO2 volume fraction was varied to 8%, 12%, and 15%. The CO2 / N2 mixed gas was contacted with the mixed solvent for absorption reaction, and the reaction was carried out at 303 K for 90 min. The results showed that when the CO2 volume fraction was ≥12%, the system rapidly underwent liquid-liquid phase separation after 30 min of absorption; at lower concentrations, only slight turbidity and incomplete phase separation occurred. The highest CO2 loading in the rich phase reached 0.92 mol CO2 / mol amine.

[0046] The rich phase was heated to 363 K and held for 40 min, and the desorption rate was measured to be 98.5%, with heat consumption reduced by about 28% compared to the single amine solvent. This indicates that the mixed amine system can stably achieve reversible phase change absorption under industrial flue gas (12–15% CO2) conditions, thus improving energy efficiency.

[0047] Example 3: Regulation of absorption rate by different primary amine ratios Three mixed solvents were prepared: Group A (MAPA:IBA = 3:1), Group B (MAPA:IBA = 2:1), and Group C (MAPA:IBA = 1:1), all maintaining PMDETA at 3 mol / L and a constant total amine concentration. Absorption was performed at 303 K and 12% CO2 for 90 min. The experiment showed that Group A had the fastest absorption rate, with a 45% decrease in CO2 concentration within 30 min; Group C had a slightly slower absorption rate, but more pronounced phase separation and a clearer separation of the enriched phase.

[0048] All three enriched phases were desorbed at 363 K. Desorption of group A was completed within 20 min, while groups B and C required 25 min and 30 min, respectively. The results indicate that a higher MAPA ratio is beneficial for accelerating the absorption reaction, while the introduction of IBA enhances the phase separation driving force, achieving an optimized balance between absorption rate and phase separation performance.

[0049] Example 4: Regeneration and Cyclic Performance Testing of Mixed Solvents The mixed solvent from Example 1 was used for 10 cycles of testing. Each cycle's absorption conditions were 303 K, CO2 volume fraction 12%, and time 60 min; the desorption conditions were 363 K and time 30 min. The absorption capacity and regeneration rate of the rich solution were measured after each cycle. The results showed that the absorption capacity remained stable at 0.85–0.88 mol CO2 / mol amine in the first to fifth cycles, and remained at 0.80 mol CO2 / mol amine in the tenth cycle, with a decrease of less than 6%.

[0050] Infrared spectroscopy and NMR analysis showed that the absorbent molecular structure did not undergo significant degradation, and no obvious byproducts were generated in the system. This indicates that the MAPA(IBA)-PMDETA-water mixed solvent has excellent chemical stability and cycle durability, making it suitable for industrial continuous absorption-desorption systems.

[0051] Example 5: Operation of a CO2 capture device based on mixed solvents A CO2 capture device is constructed, including an absorption tower, a desorption tower, a lean-rich liquid heat exchanger, a condenser, and a CO2 compression unit. The absorption tower is used to contact carbon dioxide-containing gas with a mixed solvent for absorption; the absorption tower has a rich liquid outlet. The desorption tower is connected to the rich liquid outlet of the absorption tower and is used to receive the rich phase liquid from the absorption tower, which has absorbed carbon dioxide and undergone liquid-liquid phase separation, and to heat and desorb the rich phase liquid. The lean-rich liquid heat exchanger is connected between the rich liquid outlet of the absorption tower and the inlet of the desorption tower, and is used to exchange heat between the hot lean liquid flowing out of the desorption tower and the cold rich phase liquid flowing into the desorption tower. The condenser is connected to the top gas outlet of the desorption tower. The CO2 compression unit is connected to the gas outlet of the condenser.

[0052] The inlet gas of the absorber was simulated coal-fired flue gas (12% CO2, balance N2, 8% humidity), with a bottom temperature of 303 K, a top temperature of 298 K, and a gas-liquid ratio of 1200. The desorption tower operated at 363 K, and the gas at the top of the tower condensed before entering the CO2 compression unit. The mixed solvent used was an aqueous solution of 1.5 mol / L MAPA, 0.5 mol / L IBA, and 3 mol / L PMDETA.

[0053] Actual measurement data shows that the CO2 removal rate can reach 94%, and the CO2 concentration in the gas after removal is reduced to 0.7%; the energy consumption for CO2 removal is about 3.0 GJ / ton of CO2, which is about 35% lower than that of the traditional MEA process. This indicates that the system can achieve efficient CO2 capture and recycling with low energy consumption and has significant potential for engineering applications.

[0054] Example 6: Comparison of the properties of different mixed solvents and their carbon dioxide absorption effects For the sake of brevity, the solvent composition will be represented by abbreviations below, where "M" represents MAPA, "P" represents PMDETA, and "I" represents IBA. The number before the letter indicates its molar concentration (mol / L). For example, "1M4P" represents an aqueous solution composed of 1 mol / L MAPA and 4 mol / L PMDETA; "1.5M0.5I3P" represents an aqueous solution composed of 1.5 mol / L MAPA, 0.5 mol / L IBA, and 3 mol / L PMDETA.

[0055] Using solvent systems with different MAPA and PMDETA concentration ratios (see Table 1), carbon dioxide absorption was performed according to the capture device and operating parameters in Example 5. The CO2 loading, volume, ratio of rich to lean phase, and viscosity of the rich phase in the resulting enriched phase are shown in Table 1. The CO2 absorption rate is as follows: Figure 1 As shown.

[0056] Table 1. Volume ratio of enriched and depleted phases and viscosity of enriched phase in the system under different amine concentration ratios. .

[0057] Different concentrations of IBA were added to the solvent systems of MAPA and PMDETA to form mixed solvent systems (see Table 2). Carbon dioxide absorption was performed according to the capture device and operating parameters in Example 5. The phase change behavior and CO2 loading of the mixed solvent system before and after absorption are shown in Table 2. The absorption and desorption characteristics and physical properties of some solvent systems are compared in Table 3. The absorption and desorption rates are as follows: Figure 2 , 3 As shown.

[0058] Table 2 Phase transition behavior of the system after adding IBA regulation .

[0059] Table 3 Comparison of absorption and desorption characteristics and physical properties of the system after adding IBA modulation. .

[0060] This embodiment also compared the physical properties of the system after adding amines of different molecular weights (AP, IPA, MEA, PA) to a mixed solvent system of MAPA and PMDETA and replacing MAPA. The specific results are shown in Table 4.

[0061] Table 4. Physical properties of the system after replacing MAPA with amines of different molecular weights. .

[0062] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A mixed solvent for carbon dioxide absorption, characterized in that, It is composed of 3-methylaminopropylamine, isobutylamine, pentamethyldiethylenetriamine and water; wherein the concentration of 3-methylaminopropylamine is 1.5 mol / L, the concentration of isobutylamine is 0.5 mol / L and the concentration of pentamethyldiethylenetriamine is 3 mol / L.

2. The mixed solvent for carbon dioxide absorption as described in claim 1, characterized in that, After absorbing carbon dioxide, the mixed solvent undergoes liquid-liquid phase separation, with the resulting carbon dioxide-rich phase accounting for 30-45% of the total liquid volume.

3. A method for absorbing carbon dioxide, characterized in that, Include: Under conditions of 300-310 K, a gas containing carbon dioxide is brought into contact with a mixed solvent to carry out an absorption reaction. After the absorption reaction is completed, the mixed solvent undergoes liquid-liquid phase separation, forming a carbon dioxide-rich phase and a carbon dioxide-poor phase; The carbon dioxide-rich phase is heated to 360-370 K for desorption, releasing carbon dioxide gas, and the carbon dioxide-lean phase is recovered. The mixed solvent is composed of 3-methylaminopropylamine, isobutylamine, pentamethyldiethylenetriamine and water.

4. The carbon dioxide absorption method as described in claim 5, characterized in that, In the mixed solvent, the concentration of 3-methylaminopropylamine is 1.5 mol / L, the concentration of isobutylamine is 0.5 mol / L, and the concentration of pentamethyldiethylenetriamine is 3 mol / L.

5. The carbon dioxide absorption method as described in claim 3, characterized in that, The carbon dioxide-containing gas consists of carbon dioxide and nitrogen with a volume fraction of 12%.

6. The carbon dioxide absorption method as described in claim 3, characterized in that, The volume of the carbon dioxide-rich phase accounts for 30-45% of the total liquid volume in both the carbon dioxide-rich and carbon dioxide-poor phases formed.

7. The carbon dioxide absorption method as described in claim 3, characterized in that, The desorption is carried out under inert gas purging conditions.

8. A carbon dioxide absorption system for implementing any one of the absorption methods described in claims 3-7, characterized in that, include: An absorption tower is used to contact carbon dioxide-containing gas with a mixed solvent for an absorption reaction; the absorption tower has a rich liquid outlet. A desorption tower, connected to the rich liquid outlet of the absorption tower, is used to receive the rich phase liquid from the absorption tower that has absorbed carbon dioxide and undergone liquid-liquid phase separation, and to heat and desorb the rich phase liquid. A lean-rich liquid heat exchanger is connected between the rich liquid outlet of the absorption tower and the inlet of the desorption tower, and is used to exchange heat between the hot lean liquid flowing out of the desorption tower and the cold rich liquid flowing into the desorption tower. A condenser is connected to the top gas outlet of the desorption tower; A carbon dioxide compression unit is connected to the gas outlet of the condenser.

9. The carbon dioxide absorption system as described in claim 7, characterized in that, The operating temperature of the absorption tower is 300-310 K, and the operating temperature of the desorption tower is 360-370 K.

10. The carbon dioxide absorption system as described in claim 7, characterized in that, The heat recovery efficiency of the lean and rich liquid heat exchanger shall not be less than 75%.

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