A carbon nanotube composite solvent, its preparation method, and a carbon dioxide capture system

Abstract

This invention relates to the field of flue gas treatment and carbon dioxide capture technology, and in particular to a carbon nanotube composite solvent, its preparation method, and a carbon dioxide capture system. The composite solvent comprises ethanolamine, piperazine, aminoethylpiperazine, functionalized carbon nanotubes, and deionized water, wherein the mass concentration of functionalized carbon nanotubes is 0.2 kg / m³. 3 ~0.8kg / m 3 During preparation, ultrasonic dispersion ensures long-term system stability and prevents precipitation. The supporting system includes an absorption tower and a regeneration tower, enabling semi-lean liquid circulation or standard absorption processes. This invention utilizes an organic amine complex system and functionalized carbon nanotubes with specific physical parameters to improve gas-liquid mass transfer efficiency. This invention can increase lean liquid absorption capacity, reduce system regeneration energy consumption, and maintain stable performance during continuous operation, effectively solving the problems of easy agglomeration of nanomaterials and high system energy consumption.

Description

Technical Field

[0001] This invention relates to the field of flue gas treatment and carbon dioxide capture technology, and particularly to a carbon nanotube composite solvent, its preparation method, and a carbon dioxide capture system. Background Technology

[0002] Developing efficient carbon dioxide capture technologies is of great significance for achieving energy conservation and emission reduction as well as ensuring industrial safety.

[0003] Currently, chemical absorption using organic amine solutions is the mainstream technology for capturing carbon dioxide from flue gas. To further improve capture efficiency, some attempts have emerged to combine nanomaterials with organic amine solutions. However, existing nanomaterial composite absorption systems have revealed several shortcomings in practical applications. First, these absorption systems generally have high desorption energy consumption, leading to the need for significant steam heat energy consumption during solvent regeneration, which significantly increases the overall processing cost of carbon capture. Second, the compatibility between nanomaterials and organic amines in existing technologies is poor, making it difficult to achieve ideal carbon dioxide capture rates. Furthermore, uneven dispersion of nanomaterials, powder accumulation, or precipitation are common during operation, which not only reduces gas-liquid mass transfer efficiency but may also clog equipment, affecting the continuous and stable operation of the system.

[0004] In order to reduce the heat load of carbon capture systems and improve processing efficiency, it is urgent to develop a new type of composite absorbent and supporting system that is stable, low in energy consumption and has high mass transfer efficiency. Summary of the Invention

[0005] This invention addresses the technical shortcomings of existing carbon dioxide capture technologies, such as high energy consumption for chemical absorbent regeneration, limited gas-liquid mass transfer rate, insufficient absorption capacity, and the instability of system operation caused by the easy aggregation and precipitation of nanomaterials in organic amine aqueous solutions. It provides a carbon nanotube composite solvent, its preparation method, and a carbon dioxide capture system.

[0006] On one hand, this invention provides a carbon nanotube composite solvent, the components of which include ethanolamine (MEA), piperazine (PZ), aminoethylpiperazine (AEP), and deionized water. The ethanolamine has a mass percentage concentration of 15wt%~30wt% in the composite solvent, providing a basic alkaline environment and serving as the primary chemical absorption site. The piperazine has a mass percentage concentration of 3wt%~10wt% in the composite solvent, acting as a reaction activator to accelerate the capture rate of carbon dioxide molecules using its secondary amine structure. The aminoethylpiperazine has a mass percentage concentration of 0.1wt%~1wt% in the composite solvent. The primary and secondary amine groups in the aminoethylpiperazine molecule can react rapidly with CO2, while its surface-active groups form a hydrogen bond network with the amine liquid molecules, improving the dispersion stability of functionalized carbon nanotubes (CNTs) in the amine liquid, enhancing the gas-liquid mass transfer effect, and providing high loading characteristics as a polyamine, combining the high reactivity of primary amines, the fast reaction rate of secondary amines, and the high loading characteristics of polyamines. If the AEP concentration is below 0.1 wt%, an effective hydrogen bond network cannot be formed; if it is above 1 wt%, the solution viscosity will increase, which will reduce mass transfer efficiency and increase regeneration energy consumption. The balance of the composite solvent is deionized water, and the total mass percentage of all components is 100%. Functionalized carbon nanotubes are also additionally dispersed in the composite solvent at a mass concentration of 0.2 kg / m³. 3 Up to 0.8kg / m 3 In this invention, the mass percentages of ethanolamine, piperazine, aminoethylpiperazine, and deionized water are all based on the total mass of the liquid phase components being 100%; functionalized carbon nanotubes are additional solid components dispersed in the liquid phase, and their mass concentration is based on the total volume of the composite solvent and is not included in the mass percentage of the liquid phase components.

[0007] Furthermore, the mass percentages of each component in the composite solvent are adjusted to achieve optimal adsorption-desorption equilibrium performance. Specifically, the mass percentage concentrations of ethanolamine, piperazine, aminoethylpiperazine, and functionalized carbon nanotubes are selected as follows: 20 wt%, 6 wt%, 0.5 wt%, and 0.6 kg / m³. 3 The composite solvent at this ratio exhibits extremely high reaction kinetic constants during the absorption phase and low energy consumption for chemical bond breaking during the regeneration phase.

[0008] The functionalized carbon nanotubes are selected from aminated carbon nanotubes, hydroxylated carbon nanotubes, and carboxylated carbon nanotubes. When the functionalized carbon nanotubes are aminated carbon nanotubes, the inner diameter of the aminated carbon nanotubes is 3 nm to 5 nm, the outer diameter is 8 nm to 15 nm, the length is 8 μm to 15 μm, and the specific surface area is not less than 210 m². 2 / g; When the functionalized carbon nanotubes are hydroxylated carbon nanotubes, the inner diameter of the hydroxylated carbon nanotubes is 5nm to 8nm, the outer diameter is 10nm to 15nm, the length is 2μm to 8μm, and the specific surface area is not less than 190m². 2 / g; When the functionalized carbon nanotubes are carboxylated carbon nanotubes, the inner diameter of the carboxylated carbon nanotubes is 3nm to 5nm, the outer diameter is 8nm to 15nm, the length is 5μm to 15μm, and the specific surface area is not less than 190m². 2 / g. The selection of functionalized carbon nanotubes with the specific aspect ratio and specific surface area mentioned above is mainly based on several practical considerations: multi-walled carbon nanotubes with an inner diameter of 3~8 nm and an outer diameter of 8~15 nm can control costs while improving gas-liquid mass transfer efficiency. The length is controlled at 2~15 μm; too long and they are prone to entanglement, aggregation, sedimentation, and blockage; too short and the aspect ratio and specific surface area will be significantly reduced. The specific surface area is not less than 190~210 m². 2 / g, which provides sufficient active sites. In addition, the introduction of amino, hydroxyl or carboxyl functional groups on the surface improves hydrophilicity and dispersion stability. With the synergistic effect of charge repulsion and steric hindrance, carbon nanotubes can be uniformly distributed in the circulating organic amine solution, thereby effectively avoiding particle accumulation, preventing filler blockage and maintaining mass transfer efficiency.

[0009] This invention also provides a method for preparing the above-mentioned carbon nanotube composite solvent, which ensures the long-term stability of the nanomaterials in amine solution through a physical dispersion process. The preparation method includes the following steps:

[0010] S1: According to the above-preset mass percentage ratio, add ethanolamine, piperazine and aminoethylpiperazine one by one to deionized water, and mechanically stir at room temperature with the stirring speed controlled at 300~500 rpm until all organic amine components are completely dissolved to form a uniform mixed amine aqueous solution.

[0011] S2: Weigh the pre-prepared functionalized carbon nanotubes and premix them with 5%~20% of the total mass of the mixed amine aqueous solution prepared in step S1. Perform ultrasonic dispersion treatment at a frequency of 40kHz to 50kHz for 15 to 40 minutes, controlling the system temperature to not exceed 50℃ using an ice-water bath cooling method. These process parameters are necessary to achieve a long-term stable system without precipitation. The cavitation effect generated by ultrasound breaks up the bound carbon nanotubes, allowing the functionalized groups on their surface to fully contact the amine molecules. When the proportion of the premixed amine aqueous solution is less than 5%, the carbon nanotubes cannot be sufficiently wetted, and they are still prone to aggregation after ultrasound. When the proportion is greater than 20%, the solid content of the premixed system is too low, and the carbon nanotubes cannot be fully dissociated by ultrasound.

[0012] S3: Transfer the ultrasonically dispersed premixed liquid to a constant temperature stirred tank and add the remaining mixed amine aqueous solution. Continue mechanical stirring at a temperature of 30~45℃ for 2~3 hours to allow the system to reach a thermodynamically stable state and obtain a carbon nanotube composite solvent without precipitation.

[0013] On the other hand, the present invention also provides a carbon dioxide capture system that uses the above-mentioned carbon nanotube composite solvent as an absorbent. The system includes an absorption tower, a recovery tank, a recovery pump, a recovery cooler, a lean liquid cooler, a rich liquid pump, a first lean-rich liquid heat exchanger, a lean liquid pump, a regeneration tower, a condenser, a reflux pump, a gas-liquid separator, a reboiler, a second lean-rich liquid heat exchanger, a semi-lean liquid pump, and a semi-lean liquid cooler. The absorption tower is divided into an upper absorption zone and a lower absorption zone. The bottom of the absorption tower has a raw material gas inlet and a rich liquid outlet, the middle has a semi-lean liquid inlet, and the top... The absorber is equipped with a washing liquid inlet, a reflux outlet, and a top vapor outlet. The top vapor outlet of the absorber is connected to the vapor inlet of the recovery cooler. The condensate outlet of the recovery cooler is connected to the inlet of the recovery tank. The outlet of the recovery tank is connected to the reflux outlet at the top of the absorber via a recovery pump. The rich liquid outlet at the bottom of the absorber is connected to the inlet of the rich liquid pump. The outlet of the rich liquid pump is divided into two paths: the first path connects to the upper-middle inlet of the regeneration tower via the tube side of the second lean-rich liquid heat exchanger, and the second path connects to the middle inlet of the regeneration tower via the tube side of the first lean-rich liquid heat exchanger. The rich liquid pump delivers a cold medium, flowing through the tube side of the second lean-rich liquid heat exchanger and the first lean-rich liquid heat exchanger. A semi-lean liquid outlet is located in the middle of the regeneration tower, connected to the semi-lean liquid inlet in the middle of the absorption tower via a semi-lean liquid pump, the shell side of the second lean-rich liquid heat exchanger, and a semi-lean liquid cooler. The semi-lean liquid pump delivers a hot medium, flowing through the shell side of the second lean-rich liquid heat exchanger and exchanging heat with the rich liquid in the tube side. A lean liquid outlet is located at the bottom of the regeneration tower, connected to the lean liquid pump and the first lean-rich liquid heat exchanger. The shell side and lean liquid cooler are connected to the washing liquid inlet at the top of the absorption tower; the lean liquid pump delivers the lean liquid as a heat medium, which flows through the shell side of the first lean-rich liquid heat exchanger and exchanges heat with the rich liquid in the tube side; the reboiler is connected to the bottom of the regeneration tower and is used to provide a heat source for gas stripping for rich liquid regeneration; the gas phase outlet at the top of the regeneration tower is connected in sequence to the gas phase inlet of the condenser and the feed inlet of the gas-liquid separator; the liquid phase outlet of the gas-liquid separator is connected to the top reflux port of the regeneration tower via a reflux pump, and the gas phase outlet of the gas-liquid separator is the carbon dioxide product gas output port.

[0014] This invention also provides a second carbon dioxide capture system, using the aforementioned carbon nanotube composite solvent as the absorbent. The system includes an absorption tower, a recovery tank, a recovery pump, a recovery cooler, a lean liquid cooler, a rich liquid pump, a first lean-rich liquid heat exchanger, a lean liquid pump, a regeneration tower, a condenser, a reflux pump, a gas-liquid separator, and a reboiler. The absorption tower has a raw material gas inlet and a rich liquid outlet at its bottom, and a washing liquid inlet, a reflux outlet, and a top gas phase outlet at its top. The top gas phase outlet of the absorption tower is connected to the gas phase inlet of the recovery cooler, the condensate outlet of the recovery cooler is connected to the liquid inlet of the recovery tank, and the liquid outlet of the recovery tank... The recovery pump is connected to the reflux port at the top of the absorption tower; the rich liquid outlet at the bottom of the absorption tower is connected to the inlet of the rich liquid pump, and the outlet of the rich liquid pump is connected to the upper inlet of the regeneration tower via the tube side of the first lean-rich liquid heat exchanger; the rich liquid pumped by the rich liquid pump is a cold medium that flows through the tube side of the first lean-rich liquid heat exchanger; the bottom of the regeneration tower is provided with a lean liquid outlet, which is connected to the washing liquid inlet at the top of the absorption tower via the lean liquid pump, the shell side of the first lean-rich liquid heat exchanger, and the lean liquid cooler; the lean liquid pumped by the lean liquid pump is a hot medium that flows through the shell side of the first lean-rich liquid heat exchanger and exchanges heat with the rich liquid in the tube side.

[0015] The reboiler is connected to the bottom of the regeneration tower and is used to provide a heat source for gas stripping during rich liquid regeneration. The gas phase outlet at the top of the regeneration tower is connected in sequence to the gas phase inlet of the condenser and the feed inlet of the gas-liquid separator. The liquid phase outlet of the gas-liquid separator is connected to the top reflux port of the regeneration tower via a reflux pump, and the gas phase outlet of the gas-liquid separator is the carbon dioxide product gas output port.

[0016] Furthermore, the absorption temperature inside the absorption tower is controlled between 35°C and 55°C; the regeneration temperature at the bottom of the regeneration tower is controlled between 115°C and 120°C.

[0017] Depending on the application scenario, the system can be implemented using two optional process flows:

[0018] Process 1 is implemented in a semi-lean liquid circulation mode. In this mode, the absorber is divided into an upper absorption zone and a lower absorption zone. The feed gas enters from the bottom of the absorber and first contacts the semi-lean liquid from the regeneration tower in the lower absorption zone to complete the initial absorption. Subsequently, the gas rises to the upper absorption zone and contacts the deep regeneration lean liquid from the bottom of the regeneration tower to complete the deep decarbonization. The rich liquid at the bottom of the absorber is transported by a rich liquid pump and heated by heat exchange with the hot lean liquid in the rich-lean liquid heat exchanger. Then, it is divided into two streams and enters the regeneration tower: the first stream enters the upper part of the regeneration tower for partial regeneration to produce semi-lean liquid. The temperature of the hot semi-lean liquid at the outlet of the regeneration tower is 102~108℃ and the pressure is 30~100kPaG. After heat exchange and cooling, the temperature of the hot semi-lean liquid drops to 70~80℃ and is sent into the absorber. The second stream enters the middle part of the regeneration tower for complete regeneration. The first stream of rich liquor enters the upper part of the regeneration tower, where it comes into contact with the rising stripping steam in the lower section to complete preliminary regeneration, forming a semi-lean liquor. The second stream of rich liquor enters the middle of the regeneration tower, where it undergoes deep regeneration under the high-temperature stripping action of the reboiler at the bottom of the tower, forming a lean liquor. The stepped inlet design enables stepped utilization of heat and reduces regeneration energy consumption.

[0019] Process 2 is implemented in the standard absorption mode. In this mode, the feed gas comes into countercurrent contact with the lean liquid in the absorption tower. The rich liquid generated at the bottom of the tower is heated by the lean-rich liquid heat exchanger and then enters the top of the regeneration tower. In the regeneration tower, gas-liquid mass transfer desorption is carried out by the heat provided by the reboiler. The desorbed carbon dioxide is condensed at the top of the tower and then output. The regenerated lean liquid is pumped back to the absorption tower for recycling.

[0020] The system also includes a temperature control unit, which is located inside the absorption tower and the regeneration tower. This unit controls the absorption temperature in the absorption tower between 35°C and 55°C, and the regeneration temperature at the bottom of the regeneration tower between 115°C and 120°C. Key operating parameters of the carbon dioxide capture system are regulated by an automated control system. Maintaining the absorption temperature in the absorption tower between 35°C and 55°C facilitates the chemical bonding between the composite solvent and carbon dioxide molecules, improving absorption efficiency. After the carbon nanotube composite solvent absorbs carbon dioxide, the rich solution is regenerated by heating at a temperature of 115°C to 120°C. The optimal absorption temperature in the absorption tower is 35°C to 45°C. This temperature range matches the typical emission temperature of industrial flue gas from coal-fired power plants and steel mills, eliminating the need for additional deep cooling of the raw gas and significantly reducing the system's pretreatment energy consumption. When the absorption temperature exceeds 55°C, the reverse desorption reaction rate of CO2 and amine molecules accelerates significantly, reducing the effective absorption capacity of the solvent. Therefore, the upper limit of the absorption temperature is controlled at 55°C.

[0021] The present invention also provides an application of the above-mentioned carbon nanotube composite solvent in the treatment of carbon dioxide capture in flue gas from coal-fired power plants, blast furnace gas from steel plants, or tail gas from chemical plants.

[0022] Compared with the prior art, the beneficial effects of the present invention are manifested in the following aspects:

[0023] 1. This invention introduces functionalized carbon nanotubes with specific physical specifications, thereby introducing a large number of micro-disturbance sources into the liquid phase. The functionalized carbon nanotubes, with their high aspect ratio one-dimensional nanostructure and high specific surface area, form dispersed nano-disturbances in the liquid phase, inducing local micro-disturbances at the gas-liquid interface and reducing the thickness of the gas-liquid boundary layer. Simultaneously, their surface-active groups can assist in the adsorption of CO2 molecules and their transfer to the amine molecule reaction sites in the liquid phase, achieving a synergistic effect of physical adsorption and chemical absorption, significantly improving the mass transfer flux of CO2 from the gas phase to the liquid phase. After adding aminated carbon nanotubes, this composite solvent, compared to a ternary basic amine solution without functionalized carbon nanotubes, increases the lean-liquid absorption capacity. This improvement directly translates to a reduction in the packing height of the absorption tower while achieving the same capture rate, thus lowering the initial cost of the device.

[0024] 2. This invention solves the technical challenge of easy agglomeration of nanomaterials in a strong electrolyte amine solution environment by limiting the ultrasonic dispersion time and screening the inner diameter, outer diameter, and length of carbon nanotubes. After continuous cycling for a period of time, the composite solvent exhibits a low decrease in absorption capacity, and no significant powder accumulation or precipitation is observed in system dead zones or on the surface of heat exchangers. This stability ensures long-term continuous and stable operation of industrial-scale equipment, reducing downtime due to maintenance and cleaning. Specifically, the specific aspect ratio and surface-modified carbon nanotubes improve interfacial compatibility; the hydrogen bonding network of AEP improves dispersion stability; and the premixing and stepwise ultrasonic process achieves complete dissociation of carbon nanotubes. These three factors synergistically solve the agglomeration and precipitation problem.

[0025] 3. This invention employs a ternary complex system of ethanolamine, piperazine, and aminoethylpiperazine. Aminoethylpiperazine, acting as a polyamine activator, exhibits primary and secondary amine groups in its molecular structure that react rapidly with CO2. Simultaneously, it forms a synergistic reaction network with ethanolamine and piperazine, accelerating the CO2 hydration rate and increasing the CO2 saturation loading of the solution. Furthermore, aminoethylpiperazine can improve the interfacial compatibility of functionalized carbon nanotubes in the amine solution through hydrogen bonding, enhancing the dispersion stability of the system and further strengthening the gas-liquid mass transfer effect. It also provides high loading characteristics as a polyamine, combining the high reactivity of primary amines, the fast reaction rate of secondary amines, and the high loading capacity of polyamines. With a formulation of 6% PZ + 20% MEA + 0.5% AEP, a stable spatial arrangement is formed between the three organic amine molecules and the functionalized carbon nanotubes, allowing carbon dioxide molecules to be rapidly activated by piperazine and captured and immobilized by ethanolamine and aminoethylpiperazine after entering the liquid phase. This multi-component synergistic effect ensures a high capture rate while endowing the solvent with strong antioxidant and anti-degradation capabilities. The surface-active groups of aminoethylpiperazine improve the interfacial compatibility between carbon nanotubes and organic amine aqueous solutions, enhancing system compatibility through hydrogen bonding networks and preventing stratification mismatch between nanomaterials and amine solutions. Furthermore, the ternary composite system (MEA+PZ+AEP) optimizes the CO2 binding energy distribution and reduces the energy consumption for desorption chemical bond breaking; functionalized carbon nanotubes enhance gas-liquid mass transfer, accelerate desorption kinetics, and shorten the residence time in the rich solution regeneration process; these two factors synergistically reduce regeneration energy consumption.

[0026] 4. In the semi-lean liquor circulation process of this invention, the regeneration of the semi-lean liquor in the regeneration tower relies on the heat at the tower outlet, which not only makes full use of heat but also reduces the consumption of circulating cooling water in the tower top condenser. This energy cascade utilization design concept matches the low energy consumption characteristics of carbon nanotubes, further improving the economic efficiency of the entire capture system.

[0027] 5. This invention utilizes the synergistic effect of a ternary complex amine system (MEA+PZ+AEP), combined with the strengthening effect of functionalized carbon nanotubes on the gas-liquid mass transfer interface, to improve the reaction kinetic constant during the absorption stage. During the regeneration stage, the CO2 binding energy distribution of different amines in the ternary amine system is more rational, and the polyamine structure of AEP helps reduce desorption energy consumption during regeneration. Compared with the traditional MEA single amine liquid system, the system's regeneration energy consumption is significantly reduced.

[0028] In summary, this invention, through the compounding of chemical components in a composite solvent, the screening of the physical properties of functionalized carbon nanotubes, and the systematic optimization of the preparation process and circulation flow, constructs a carbon dioxide capture scheme that combines high mass transfer, low energy consumption, and strong stability. This scheme effectively controls operating costs and equipment maintenance difficulty while improving the carbon dioxide capture rate, providing a concrete and feasible technical path for large-scale carbon dioxide emission reduction in the industrial sector. Attached Figure Description

[0029] Figure 1 This is a process flow diagram of a carbon dioxide capture system using a semi-lean liquid circulation mode in one embodiment of the present invention.

[0030] Figure 2 This is a process flow diagram of the carbon dioxide capture system using the standard absorption mode in step two of this embodiment of the invention.

[0031] The attached figures are labeled as follows:

[0032] 1. Absorber; 2. Recovery tank; 3. Recovery pump; 4. Recovery cooler; 5. Lean liquor cooler; 6. Rich liquor pump; 7. First lean-rich liquor heat exchanger; 8. Lean liquor pump; 9. Regeneration tower; 10. Condenser; 11. Reflux pump; 12. Gas-liquid separator; 13. Reboiler; 14. Second lean-rich liquor heat exchanger; 15. Semi-lean liquor pump; 16. Semi-lean liquor cooler. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] This invention provides a method for preparing a carbon nanotube composite solvent, the specific preparation steps of which are as follows:

[0035] S1: According to the required mass percentage ratio, first add deionized water to the mixing vessel, then add ethanolamine, piperazine, and aminoethylpiperazine sequentially. In the preferred formulation of this embodiment, the mass percentage concentration of ethanolamine is controlled at 20 wt%, the mass percentage concentration of piperazine is controlled at 6 wt%, the mass percentage concentration of aminoethylpiperazine is controlled at 0.5 wt%, and the remainder is deionized water. Start the mechanical stirring device at room temperature, set the speed to 400 rpm, and continue stirring until the mixed amine solution becomes transparent and homogeneous.

[0036] S2: Weigh the pre-determined mass of functionalized carbon nanotubes. Based on experimental screening, the addition amount of functionalized carbon nanotubes was set to 0.6 kg / m³. 3The functionalized carbon nanotubes are selected from aminated carbon nanotubes, hydroxylated carbon nanotubes, or carboxylated carbon nanotubes. Specifically, the aminated carbon nanotubes have an inner diameter of 3 to 5 nm, an outer diameter of 8 to 15 nm, a length of 8 to 15 μm, and a specific surface area of ​​not less than 210 m². 2 / g. Hydroxylated carbon nanotubes exhibit an inner diameter of 5 to 8 nm, an outer diameter of 10 to 15 nm, a length of 2 to 8 μm, and a specific surface area of ​​not less than 190 m². 2 / g. Carboxylated carbon nanotubes exhibit an inner diameter of 3 to 5 nm, an outer diameter of 8 to 15 nm, a length of 5 to 15 μm, and a specific surface area of ​​not less than 190 m². 2 / g. The weighed functionalized carbon nanotubes are pre-mixed with a mixed amine aqueous solution accounting for 5%~20% of the total mass of the mixed amine aqueous solution prepared in step S1, and then subjected to ultrasonic dispersion treatment. The frequency of the ultrasonic dispersion treatment is 40kHz to 50kHz, the duration is set to 15min to 40min, and the system temperature is controlled not to exceed 50℃. According to the stability test results, the ultrasonic time is set to be no less than 15min. When the ultrasonic time reaches 15min to 20min, due to the local high-energy impact force generated by the ultrasonic cavitation effect, the carbon nanotube binding body is fully dissociated, and the surface functional groups form a stable hydrogen bond network with amine molecules, thus maintaining a precipitation-free state even after standing for 24h. If the ultrasonic time is less than 10min, the system will show a precipitation problem when the addition amount exceeds 0.4kg / m³. 3 At this time, obvious black particle deposits will appear.

[0037] S3: Add the premixed solution after ultrasonic dispersion in step S2 to the remaining mixed amine aqueous solution, and continue mechanical stirring at 30℃ to 45℃ for 2h to 3h to obtain carbon nanotube composite solvent.

[0038] Based on the above-mentioned composite solvent, this invention provides two different system operation processes. (See attached diagram.) Figure 1 The diagram shows process one provided by this invention, namely the semi-lean liquid circulation mode. This system is mainly applied in industrial scenarios that are extremely sensitive to energy consumption and require deep decarbonization. Its specific operating principle and process are described below:

[0039] The carbon nanotube composite solvent absorption and regeneration system for carbon dioxide capture in flue gas of this invention mainly consists of an absorption tower 1, a recovery tank 2, a recovery pump 3, a recovery cooler 4, a lean liquid cooler 5, a rich liquid pump 6, a first lean-rich liquid heat exchanger 7, a lean liquid pump 8, a regeneration tower 9, a condenser 10, a reflux pump 11, a gas-liquid separator 12, a reboiler 13, a second lean-rich liquid heat exchanger 14, a semi-lean liquid pump 15, and a semi-lean liquid cooler 16. These components are connected sequentially via process pipelines to synergistically achieve efficient carbon dioxide absorption and solvent recycling and regeneration. Two units of both the recovery pump 3 and the reflux pump 11 are provided, one in operation and one on standby, to ensure continuous and stable system operation. The system also includes a demineralized water makeup line connected to the top of the recovery tank 2 to replenish water lost during system operation and maintain solvent water balance. The absorption tower 1 is the core equipment for carbon dioxide absorption. Its top gas phase outlet is connected to the recovery cooler 4. The condensate outlet of the recovery cooler 4 is connected to the recovery tank 2. The liquid phase outlet of the recovery tank 2 is connected back to the upper part of the absorption tower 1 via the recovery pump 3, forming a solvent recovery and reflux loop at the top of the absorption tower. This loop is used to recover the solvent entrained at the top of the tower and maintain the water balance inside the tower. The lower part of the absorption tower 1 has a raw material gas (i.e., flue gas) inlet, and the top of the tower has a purified gas outlet, used to input the flue gas to be treated and output the purified gas after decarbonization. The bottom liquid phase outlet of the absorption tower 1 is connected to the inlet of the rich liquid pump 6. The outlet of the rich liquid pump 6 is divided into two process pipelines. The first pipeline is connected to the tube-side inlet of the second lean-rich liquid heat exchanger 14, and the second pipeline is connected to the tube-side inlet of the first lean-rich liquid heat exchanger 7. The tube-side outlet of the second lean-rich liquid heat exchanger 14 is connected to the upper inlet of the regeneration tower 9, and the tube-side outlet of the first lean-rich liquid heat exchanger 7 is connected to the middle part of the regeneration tower 9. The second rich liquid, after being heated by heat exchange between the first rich-lean liquid heat exchanger 7 and the high-temperature lean liquid from the bottom of the regeneration tower 9, enters the middle of the regeneration tower 9 for deep regeneration. The first rich liquid, after being heated by heat exchange between the second rich-lean liquid heat exchanger 14 and the high-temperature semi-lean liquid from the middle of the regeneration tower 9, enters the upper middle part of the regeneration tower 9 for partial regeneration. The regeneration tower 9 is provided with an upper regeneration zone and a lower regeneration zone. The first rich liquid, after being preheated by the second rich-lean liquid heat exchanger 14, enters the lower part (upper middle inlet) of the upper regeneration zone of the regeneration tower 9, and comes into contact with the rising steam from the lower section for preliminary regeneration. After removing some CO2, it forms a semi-lean liquid. Most of the semi-lean liquid is discharged from the semi-lean liquid outlet in the middle of the regeneration tower 9, and a small part of the semi-lean liquid continues to flow downwards and merges with the second rich liquid to complete deep regeneration in the lower regeneration zone. The middle part of the regeneration tower 9 is provided with a semi-lean liquid outlet for discharging the semi-lean liquid that has completed preliminary regeneration. The pipeline design of pressurizing before heat exchange can effectively avoid flash vaporization of semi-lean liquid during heat exchange, prevent cavitation of semi-lean liquid pump, and ensure long-term continuous and stable operation of the system.The regeneration tower 9 is the core equipment for rich liquor regeneration. A reboiler 13 is installed at its bottom, with a steam inlet and a condensate outlet for introducing external steam to provide a heat source for rich liquor stripping regeneration. A semi-lean liquor outlet is located in the middle of the regeneration tower 9, connected to the inlet of a semi-lean liquor pump 15. The outlet of the semi-lean liquor pump 15 is connected to the shell-side inlet of the second rich-lean-lean liquor heat exchanger 14. The shell-side outlet of the second rich-lean-lean liquor heat exchanger 14 is cooled by a semi-lean liquor cooler 16 and then reconnected to the middle inlet of the absorption tower 1, forming a semi-lean liquor circulation loop. A lean liquor outlet is located at the bottom of the regeneration tower 9, connected to the shell-side inlet of the absorption tower 1. The inlet of the liquid pump 8 is connected to the shell-side inlet of the first lean-rich liquid heat exchanger 7, and the shell-side outlet of the first lean-rich liquid heat exchanger 7 is connected back to the upper part of the absorption tower 1 after passing through the lean liquid cooler 5, forming a lean liquid circulation loop; the gas phase outlet at the top of the regeneration tower 9 is connected in sequence to the gas phase inlet of the condenser 10 and the feed inlet of the gas-liquid separator 12; the liquid phase outlet of the gas-liquid separator 12 is connected back to the top of the regeneration tower 9 via the reflux pump 11, forming a regeneration tower reflux loop, and the gas phase outlet of the gas-liquid separator 12 is used to output the captured carbon dioxide product gas, completing the overall structure of the system.

[0040] When using the above system for flue gas carbon dioxide capture, the carbon nanotube composite solvent prepared in this invention is first injected into each loop of the system. After the system is filled with solvent and leaks are eliminated, the system is started. The raw gas to be treated (molar percentage: CO2 11.80%, O2 5.14%, N2 66.74%, H2O 16.32%, temperature 40℃, pressure 0.02MPaG) enters the absorption tower 1 through the raw gas inlet at the bottom. The raw gas flows through the absorption tower 1 from bottom to top, and first comes into countercurrent contact with the semi-lean liquid entering from the middle of the tower in the lower section of the absorption tower 1. The semi-lean liquid absorbs part of the CO2 in the raw gas, completing the coarse removal. Carbonization process: The gas after coarse decarbonization continues to rise to the upper section of absorption tower 1, where it comes into countercurrent contact with the lean liquid entering from the top of the tower. The lean liquid deeply absorbs the remaining CO2 in the gas, completing the fine decarbonization process. The purified gas at the top of the tower after two stages of absorption is washed and recovered, and then sent out of the system from the purified gas outlet at the top of absorption tower 1. At the same time, the gaseous stream carrying solvent drawn from the top of absorption tower 1 is sent to the recovery cooler 4. After cooling and separation, the condensate enters the recovery tank 2. The gas phase merges with the purified gas at the top of the tower and is sent out. The condensate in the recovery tank 2 is pressurized by the recovery pump 3 and sent back to the upper part of absorption tower 1 as the top reflux liquid, realizing the recovery and utilization of solvent and the stable maintenance of water balance in the tower. The rich liquid discharged from the bottom of the absorption tower 1, which has absorbed a large amount of CO2, is pressurized by the rich liquid pump 6 and divided into two streams. The first stream of rich liquid is sent to the second lean-rich liquid heat exchanger 14 to exchange heat with the high-temperature semi-lean liquid from the regeneration tower 9, recovering the heat of the semi-lean liquid to preheat the rich liquid. The preheated rich liquid is then sent to the upper part of the regeneration tower 9. The second stream of rich liquid is sent to the first lean-rich liquid heat exchanger 7 to exchange heat with the high-temperature lean liquid from the bottom of the regeneration tower 9, recovering the heat of the lean liquid to preheat the rich liquid. The preheated rich liquid is then sent to the middle part of the regeneration tower 9. External steam is introduced into the reboiler 13 at the bottom of regeneration tower 9 to heat the lean liquor at the bottom of the tower and generate stripping steam. The steam flows upward through regeneration tower 9, providing sufficient heat for the regeneration of the rich liquor. The first stream of rich liquor fed into the upper part of regeneration tower 9 undergoes partial regeneration under the action of the rising steam, removing some CO2 and forming a semi-lean liquor in the middle of regeneration tower 9. After being pressurized by the semi-lean liquor pump 15, part of the semi-lean liquor is first sent to the second lean-rich liquor heat exchanger 14 to exchange heat with the cold rich liquor to recover waste heat, and then cooled to a suitable absorption temperature by the semi-lean liquor cooler 16 before finally being sent to the middle of absorption tower 1 as the lower... The washing liquid from the initial coarse decarbonization is recycled, while a small portion of the semi-lean liquid remains in regeneration tower 9 to continue participating in the deep regeneration process. The second rich liquid, fed into the middle of regeneration tower 9, undergoes deep regeneration under the continuous stripping action of rising steam until the CO2 purification degree of the lean liquid reaches the process index, forming lean liquid at the bottom of regeneration tower 9. After being pressurized by lean liquid pump 8, the lean liquid is sent to the first lean-rich liquid heat exchanger 7 to exchange heat with the rich liquid and recover heat. Subsequently, it is sent to lean liquid cooler 5 to be cooled to 40°C and sent to the upper part of absorption tower 1 to be recycled as the washing liquid for the upper fine decarbonization, thus realizing the recycling absorption of lean liquid.The acidic regeneration gas (mainly CO2) discharged from the top of regeneration tower 9 is sent to condenser 10 to be cooled to 40°C. The cooled regeneration gas is then sent to gas-liquid separator 12 for gas-liquid separation. The high-purity CO2 product gas obtained from the separation is sent out of the system from the gas phase outlet of gas-liquid separator 12 for recycling. The condensate obtained from the separation is pressurized by reflux pump 11 and sent back to the top of regeneration tower 9 as reflux to maintain the water balance and operational stability in regeneration tower 9, and further improve the purity of CO2 product gas. The entire process achieves efficient capture of flue gas CO2 through the coordinated operation of various components and the enhanced gas-liquid mass transfer effect of carbon nanotube composite solvent, while effectively reducing solvent regeneration energy consumption and system investment costs.

[0041] See attached document Figure 2 As shown, this is the second process provided by the present invention, namely the standard absorption and regeneration mode. Unlike the first process, this mode has a relatively simplified structure and is suitable for conditions where space is limited or feed gas fluctuates. The carbon nanotube composite solvent absorption and regeneration system (process two) for capturing carbon dioxide in flue gas according to the present invention mainly consists of an absorption tower 1, a recovery tank 2, a recovery pump 3, a recovery cooler 4, a lean liquid cooler 5, a rich liquid pump 6, a first lean-rich liquid heat exchanger 7, a lean liquid pump 8, a regeneration tower 9, a condenser 10, a reflux pump 11, a gas-liquid separator 12, and a reboiler 13. These components are connected sequentially through process pipelines to synergistically achieve efficient carbon dioxide absorption and solvent recycling and regeneration. The absorption tower 1 is the core equipment for carbon dioxide absorption. Its top gas phase outlet is connected to the recovery cooler 4. The condensate outlet of the recovery cooler 4 is connected to the recovery tank 2. The liquid phase outlet of the recovery tank 2 is connected back to the upper part of the absorption tower 1 via the recovery pump 3, forming a solvent recovery and reflux loop at the top of the absorption tower. This loop is used to recover the solvent entrained at the top of the tower and maintain the water balance inside the tower. The lower part of the absorption tower 1 is equipped with a raw material gas inlet, and the top of the tower is equipped with a purified gas outlet, used to input the flue gas to be treated and output the purified gas after decarbonization. The bottom liquid phase outlet of the absorption tower 1 is connected to the inlet of the rich liquid pump 6. The outlet of the rich liquid pump 6 is connected to the tube-side inlet of the first lean-rich liquid heat exchanger 7. The tube-side outlet of the first lean-rich liquid heat exchanger 7 is connected to the upper inlet of the regeneration tower 9. The regeneration tower 9 is the core equipment for rich liquid regeneration. A reboiler 1 is installed at the bottom of the tower. 3. The reboiler 13 is equipped with a steam inlet and a condensate outlet for introducing external steam to provide a heat source for the stripping and regeneration of the rich liquid. The bottom of the regeneration tower 9 is equipped with a lean liquid outlet, which is connected to the inlet of the lean liquid pump 8. The outlet of the lean liquid pump 8 is connected to the shell-side inlet of the first lean-rich liquid heat exchanger 7. The shell-side outlet of the first lean-rich liquid heat exchanger 7 is connected back to the upper part of the absorption tower 1 after passing through the lean liquid cooler 5, forming a lean liquid circulation loop. The gas phase outlet at the top of the regeneration tower 9 is connected to the inlet of the condenser 10. The outlet of the condenser 10 is connected to the gas-liquid separator 12. The liquid phase outlet of the gas-liquid separator 12 is connected back to the top of the regeneration tower 9 through the reflux pump 11, forming a regeneration tower reflux loop. The gas phase outlet of the gas-liquid separator 12 is used to output the captured carbon dioxide product gas, completing the overall structure of the system.

[0042] When using the above system for flue gas carbon dioxide capture, the carbon nanotube composite solvent prepared in this invention is first injected into each loop of the system. After the system is filled with solvent and leaks are eliminated, the system is started. The raw gas to be treated (molar percentage: CO2 11.80%, O2 5.14%, N2 66.74%, H2O 16.32%, temperature 40℃, pressure 0.02MPaG) enters the absorption tower 1 through the raw gas inlet at the bottom. The raw gas flows from bottom to top through the absorption tower 1, and combines with the regenerated lean gas entering from the top of the tower. In the countercurrent contact of the liquid and lean liquid, the carbon dioxide in the feed gas is fully absorbed to complete the decarbonization process. After the purified gas at the top of the absorption tower is washed and recovered, it is sent out of the system from the purified gas outlet at the top of the absorption tower 1. At the same time, the gaseous stream containing solvent drawn from the top of the absorption tower 1 is sent to the recovery cooler 4. After cooling and separation, the condensate enters the recovery tank 2. The gas phase merges with the purified gas at the top of the tower and is sent out. The condensate in the recovery tank 2 is pressurized by the recovery pump 3 and sent back to the upper part of the absorption tower 1 as the top reflux liquid, so as to realize the recovery and utilization of solvent and the stable maintenance of water balance in the tower. The rich liquid, which has absorbed a large amount of carbon dioxide, is discharged from the bottom of the absorption tower 1 and then pressurized by the rich liquid pump 6 before being sent to the first lean-rich liquid heat exchanger 7. It exchanges heat with the high-temperature lean liquid from the bottom of the regeneration tower 9 to recover heat from the lean liquid and preheat the rich liquid. The preheated rich liquid is then sent to the upper part of the regeneration tower 9 for heating and stripping regeneration until the carbon dioxide purification degree of the lean liquid at the bottom of the tower reaches the process index. External steam is introduced into the reboiler 13 at the bottom of the regeneration tower 9 to heat the lean liquid at the bottom of the tower and generate stripping steam. The steam flows from bottom to top through the regeneration tower 9, providing sufficient heat for the regeneration of the rich liquid and ensuring the stable operation of the regeneration process. The acidic regeneration gas (mainly carbon dioxide) discharged from the top of regeneration tower 9 is sent to condenser 10 for cooling to 40°C. The cooled regeneration gas is then sent to gas-liquid separator 12 for gas-liquid separation. The high-purity carbon dioxide product gas obtained from the separation is sent out of the system from the gas phase outlet of gas-liquid separator 12 for recycling. The condensate obtained from the separation is pressurized by reflux pump 11 and sent back to the top of regeneration tower 9 as reflux to maintain the water balance and operational stability within regeneration tower 9, further improving the purity of the carbon dioxide product gas. The qualified lean liquid obtained at the bottom of regeneration tower 9 is pressurized by lean liquid pump 8 and sent to the first lean-rich liquid heat exchanger 7 to exchange heat with the rich liquid and recover heat. It is then sent to lean liquid cooler 5 for cooling to 40°C and finally sent to the upper part of absorption tower 1 as washing liquid for recycling within the absorption tower, realizing the cyclic absorption of lean liquid. The entire process relies on the enhanced gas-liquid mass transfer effect of carbon nanotube composite solvent, effectively improving the carbon dioxide absorption capacity, reducing solvent regeneration energy consumption, simplifying the process flow, and reducing system investment and operating costs. In industrial-scale preparation, a pipeline-type continuous ultrasonic dispersion device is used in conjunction with an online constant-temperature stirring vessel to achieve continuous preparation of the composite solvent, ensuring that carbon nanotubes are uniformly dispersed in a large volume of amine solution and meeting the long-cycle operation requirements of the industrial circulation system.

[0043] The system described in this invention exhibits significant technical advantages in practical operation. Firstly, regarding mass transfer performance, the introduction of carbon nanotubes of a specific size into the 20wt% MEA + 6wt% PZ + 0.5wt% AEP compound system optimizes the solvent kinetics during the absorption phase. The high specific surface area of ​​the carbon nanotubes provides physical adsorption sites for carbon dioxide molecules, which are subsequently chemically immobilized by surrounding organic amine molecules. This physicochemical synergy enhances the absorption capacity of the lean solution.

[0044] Secondly, in terms of energy saving and consumption reduction, this invention significantly reduces steam consumption during the regeneration process by improving the thermal properties of the solvent. Functionalized carbon nanotubes, with their high aspect ratio one-dimensional nanostructure and high specific surface area, form dispersed nano-perturbations in the liquid phase, inducing local micro-perturbations at the gas-liquid interface, reducing the thickness of the gas-liquid boundary layer, significantly accelerating the CO2 desorption kinetics, and shortening the residence time of the rich liquid in the regeneration tower. Simultaneously, their surface-active groups can assist in the adsorption of CO2 molecules, achieving a synergistic effect of physical adsorption and chemical absorption, resulting in higher regeneration rates at the same regeneration temperature, or achieving the target regeneration rate with lower regeneration energy consumption.

[0045] Furthermore, this invention addresses the stability bottleneck of nanomaterials in industrial applications. By limiting the ultrasonic dispersion time to no less than 15 minutes and using a specific concentration of aminoethylpiperazine, the surface charge of carbon nanotubes reaches a dynamic equilibrium. This is demonstrated by the fact that during a 48-hour continuous stability experiment, the absorption capacity showed only minor fluctuations, and no black precipitate or powder accumulation was observed on the surfaces of the entire system's pipelines, pumps, valves, and heat exchangers. This high stability ensures the reliability of the system during long-term operation, avoiding unplanned downtime caused by packing blockage or equipment wear.

[0046] Furthermore, the process flow of the present invention does not have strict requirements on the pressure of the raw gas. Stable and efficient CO2 capture can be achieved as long as the gauge pressure of the raw gas is not lower than 5 kPaG. It is suitable for the micro-positive pressure emission conditions of most industrial flue gas in coal-fired power plants, steel plants, chemical plants, etc. No additional high-pressure booster equipment is required, which reduces the system's equipment investment and operating power consumption.

[0047] In specific application scenarios, such as flue gas treatment in coal-fired power plants, the carbon dioxide concentration in the raw gas is approximately 11.8%. When using Process 1 for capture, the liquid-to-gas ratio within the absorption tower 1 can be precisely controlled by adjusting the flow ratio of the semi-lean liquid pump 15 and the lean liquid pump 8. The system also includes a temperature control unit, which is located within the absorption tower and the regeneration tower. This unit controls the absorption temperature within the absorption tower 1 between 35°C and 55°C, and the regeneration temperature at the bottom of the regeneration tower 9 between 115°C and 120°C. Under these process conditions—with the absorption temperature controlled between 35°C and 55°C and the regeneration temperature maintained between 115°C and 120°C—the system can achieve a carbon dioxide capture rate of over 90%, and the purity of the produced carbon dioxide reaches over 99.5%.

[0048] By comparing different types of carbon nanotubes, it can be found that aminated carbon nanotubes show the most outstanding performance in improving absorption capacity, with a capacity of 0.6 kg / m³. 3 The optimal addition amount represents the optimal process point for this invention. While hydroxylated and carboxylated carbon nanotubes are slightly less effective than aminated carbon nanotubes in increasing absorption capacity, their regeneration energy consumption is significantly lower than that of the base amine solution without added carbon nanotubes, reaching, for example, 1.26 t / tCO2 and 1.27 t / tCO2 respectively in process one. This demonstrates that the functionalized carbon nanotube composite solvent described in this invention has broad formulation applicability and excellent industrialization prospects.

[0049] Example 1

[0050] Weigh out 20 wt% ethanolamine, 6 wt% piperazine, and 0.5 wt% aminoethylpiperazine, add water to make up to 100 wt%, and mix to obtain the basic amine solution. Add 0.2 kg / m³ of water to the basic amine solution. 3 Aminated carbon nanotubes were first premixed with 8% (by mass) of a base amine solution, followed by ultrasonic dispersion at a frequency of 42 kHz for 15 minutes, with the system temperature controlled to not exceed 50°C. The mixture was then transferred to a solution tank and stirred for 2 hours until homogeneous, yielding a carbon nanotube composite solvent. This composite solvent was used for CO2 capture in flue gas from process one, with an absorption temperature of 40°C and a regeneration temperature of 115–120°C.

[0051] Example 2

[0052] Weigh out 20 wt% ethanolamine, 6 wt% piperazine, and 0.5 wt% aminoethylpiperazine, add water to make up to 100 wt%, and mix to obtain the basic amine solution. Add 0.4 kg / m³ of water to the basic amine solution. 3Aminated carbon nanotubes were first premixed with a base amine solution comprising 10% of the total mass of the base amine solution, and then ultrasonically dispersed at a frequency of 43 kHz for 15 minutes, with the system temperature controlled to not exceed 50°C. The mixture was then transferred to a solution tank and stirred for 2 hours until homogeneous, yielding a carbon nanotube composite solvent. This composite solvent was used for CO2 capture in flue gas from process one, with an absorption temperature of 40°C and a regeneration temperature of 115–120°C.

[0053] Example 3

[0054] Weigh out 20 wt% ethanolamine, 6 wt% piperazine, and 0.5 wt% aminoethylpiperazine, add water to make up to 100 wt%, and mix to obtain the basic amine solution. Add 0.6 kg / m³ of water to the basic amine solution. 3 Aminated carbon nanotubes were first premixed with a base amine solution comprising 15% of the total mass of the base amine solution, and then ultrasonically dispersed at a frequency of 40 kHz for 18 minutes, with the system temperature controlled to not exceed 50°C. The mixture was then transferred to a solution tank and stirred for 2 hours until homogeneous, yielding a carbon nanotube composite solvent. This composite solvent was used for CO2 capture in flue gas from process one, with an absorption temperature of 40°C and a regeneration temperature of 115–120°C.

[0055] Example 4

[0056] Weigh out 20 wt% ethanolamine, 6 wt% piperazine, and 0.5 wt% aminoethylpiperazine, add water to make up to 100 wt%, and mix to obtain the basic amine solution. Add 0.8 kg / m³ of water to the basic amine solution. 3 Aminated carbon nanotubes were first premixed with a base amine solution comprising 20% ​​of the total mass of the base amine solution, and then ultrasonically dispersed at a frequency of 50 kHz for 20 minutes, with the system temperature controlled to not exceed 50°C. The mixture was then transferred to a solution tank and stirred for 2 hours until homogeneous, yielding a carbon nanotube composite solvent. This composite solvent was used for CO2 capture in flue gas from process one, with an absorption temperature of 40°C and a regeneration temperature of 115–120°C.

[0057] Example 5

[0058] Weigh out 20 wt% ethanolamine, 6 wt% piperazine, and 0.5 wt% aminoethylpiperazine, add water to make up to 100 wt%, and mix to obtain the basic amine solution. Add 0.6 kg / m³ of water to the basic amine solution. 3Hydroxylated carbon nanotubes were first premixed with a base amine solution comprising 12% of the total mass of the base amine solution, and then ultrasonically dispersed at a frequency of 45 kHz for 15 minutes, with the system temperature controlled to not exceed 50°C. The mixture was then transferred to a solution tank and stirred for 2 hours until homogeneous, yielding a carbon nanotube composite solvent. This composite solvent was used for CO2 capture in flue gas from process one, with an absorption temperature of 40°C and a regeneration temperature of 115–120°C.

[0059] Example 6

[0060] Weigh out 20 wt% ethanolamine, 6 wt% piperazine, and 0.5 wt% aminoethylpiperazine, add water to make up to 100 wt%, and mix to obtain the basic amine solution. Add 0.6 kg / m³ of water to the basic amine solution. 3 Carboxylated carbon nanotubes were first premixed with a base amine solution comprising 18% of the total mass of the base amine solution, and then ultrasonically dispersed at a frequency of 40 kHz for 15 minutes, with the system temperature controlled to not exceed 50°C. The mixture was then transferred to a solution tank and stirred for 2 hours until homogeneous, yielding a carbon nanotube composite solvent. This composite solvent was used for CO2 capture in flue gas from process one, with an absorption temperature of 40°C and a regeneration temperature of 115–120°C.

[0061] Comparative Example 1

[0062] A mixed solvent of 26.5 wt% ethanolamine and 73.5 wt% water was prepared and stirred until homogeneous, without the addition of carbon nanotubes, piperazine, or aminoethylpiperazine. This solvent was used for CO2 capture in the flue gas of Process 2, with an absorption temperature of 40℃ and a regeneration temperature of 115~120℃.

[0063] Comparative Example 2

[0064] A mixed solvent of 12 wt% piperazine, 14.5 wt% ethanolamine, and 73.5 wt% water was prepared and stirred until homogeneous, without the addition of carbon nanotubes or aminoethylpiperazine. This solvent was used for CO2 capture in the flue gas of Process 2, with an absorption temperature of 40℃ and a regeneration temperature of 115~120℃.

[0065] Comparative Example 3

[0066] A mixed solvent of 25.5 wt% ethanolamine, 1 wt% aminoethylpiperazine, and 73.5 wt% water was prepared and stirred until homogeneous, without the addition of carbon nanotubes or piperazine. This solvent was used for CO2 capture in the flue gas of Process 2, with an absorption temperature of 40℃ and a regeneration temperature of 115~120℃.

[0067] Comparative Example 4

[0068] A mixed solvent of 20 wt% ethanolamine, 6 wt% piperazine, 0.5 wt% aminoethylpiperazine, and 73.5 wt% water was prepared and stirred until homogeneous, without adding any carbon nanotubes. This solvent was used for CO2 capture in the flue gas of Process 2, with an absorption temperature of 40℃ and a regeneration temperature of 115~120℃.

[0069] Comparative Example 5

[0070] Weigh out 20 wt% ethanolamine, 6 wt% piperazine, and 0.5 wt% aminoethylpiperazine, add water to make up to 100 wt%, and mix to obtain the basic amine solution. Add 0.1 kg / m³ of water to the basic amine solution. 3 Aminated carbon nanotubes were first premixed with a base amine solution comprising 5% of the total mass of the base amine solution, and then ultrasonically dispersed for 15 minutes at a frequency of 40 kHz, with the system temperature controlled to not exceed 50°C. The mixture was then transferred to a solution tank and stirred for 2 hours until homogeneous, yielding a carbon nanotube composite solvent. This composite solvent was used for CO2 capture in flue gas from process one, with an absorption temperature of 40°C and a regeneration temperature of 115–120°C.

[0071] The following experiments were conducted using the above embodiments, and the specific experimental data are as follows:

[0072] The ultrasonic time was adjusted for the addition of 0~0.8 kg / m 3 Aminated CNTs, 0.6 kg / m 3 Hydroxylated CNTs and 0.6 kg / m 3 The effect of the complex solvent on carboxylated CNTs was investigated. After ultrasonication, the mixture was allowed to stand for 24 hours to observe whether any precipitation occurred. The experimental results are shown in Table 1. For the 0.2~0.8 kg / m³ complex protected by this invention... 3 Functionalized carbon nanotube composite solvents with concentration ranges showing no precipitation after 24 hours of standing for ultrasonic dispersion time ≥15 min ensure long-term system stability. While shorter ultrasonic times at lower concentrations can achieve no precipitation, they cannot cover the stability requirements across the entire concentration range. This invention selects 15 min as the minimum ultrasonic time to cover concentrations of 0.2–0.8 kg / m³. 3 The use of composite solvents across the full concentration range ensures long-term, precipitation-free stability for all formulations within the protection range. It should be noted that test results may fluctuate under different process conditions.

[0073] Table 1. Effect of ultrasonic time on the stability of composite solvents

[0074]

[0075] When the carbon nanotube concentration is below 0.2 kg / m 3At this time, the gas-liquid mass transfer enhancement effect is weak, and the improvement in absorption capacity and regeneration energy consumption is limited, failing to achieve the optimal technical effect of this invention; 0.2-0.8 kg / m 3 Within the concentration range, the absorption capacity first increases and then decreases with increasing concentration, at 0.6 kg / m³. 3 This is the optimal amount to add.

[0076] In processes one and two, the effects of different carbon nanotubes on solvent performance were investigated. The results are shown in Tables 2 and 3. The solvents containing 0–0.8 kg / m³ of carbon nanotubes were selected. 3 Aminated CNTs, 0.6 kg / m 3 Hydroxylated CNTs and 0.6 kg / m 3 A complex solvent for carboxylated CNTs, wherein 0.6 kg / m 3 Aminated CNTs composite solvents exhibit the best absorption and regeneration performance.

[0077] Table 2. Effects of adding different carbon nanotubes on the performance of the composite solvent in Process 1.

[0078]

[0079] Table 3. Effects of adding different carbon nanotubes on the performance of the composite solvent in Process 2.

[0080]

[0081] In summary, compared to ternary basic amine solutions without added carbon nanotubes, the composite solvent of the preferred formulation of this invention, under standard absorption mode, increases the effective absorption capacity of lean liquor circulation by 4.3% and reduces regeneration energy consumption by 11.9%; under semi-lean liquor circulation mode, it increases the effective absorption capacity of lean liquor circulation by 2.3% and reduces regeneration energy consumption by 11.6%. The effective absorption capacity in the table represents the actual CO2 absorption amount achieved by the lean liquor in the corresponding process flow when the system is running continuously and stably. Process 1 is a semi-lean liquor cascade regeneration process, with a higher degree of lean liquor regeneration, therefore its effective absorption capacity is higher than that of the standard regeneration process in Process 2.

[0082] During long-term operation, the absorption capacity of the composite solvent decreased by only 1.9% after 48 hours, demonstrating good stability. Experimental data are shown in Table 4.

[0083] Table 4, Process 2, 0.6 kg / m 3 Absorption stability of aminated CNT complex solvents

[0084]

[0085] After 48 hours of continuous operation, the particle size of the composite solvent was measured. The average particle size of the carbon nanotubes showed no significant change, and the system exhibited no precipitation or agglomeration, verifying the long-term stability of the dispersion system. The data in the table are online detection data during continuous system operation. The numerical fluctuation within ±2% is considered a normal systematic error in industrial online detection. Overall, the absorption capacity of the composite solvent did not decrease significantly, demonstrating excellent long-term operational stability.

[0086] By comparing the lean solution absorption capacity of ratios 1-4, piperazine, ethanolamine, and aminoethylpiperazine showed a synergistic effect in the decarbonization process. Among them, 6 wt% piperazine, 20 wt% ethanolamine, and 0.5 wt% aminoethylpiperazine exhibited the best lean solution absorption performance. The experimental data are shown in Table 5.

[0087] Table 5. Absorption capacity of the composite solvents in Comparative Examples 1-4

[0088]

[0089] In summary, this invention constructs a highly efficient, low-energy-consumption, and long-term stable carbon dioxide capture platform through specific chemical component compounding, nanomaterial specification screening, specific dispersion preparation processes, and a dual-mode selectable process flow. This system not only performs excellently on a laboratory scale, but its compatibility with low-pressure feed gas and significant reduction in regeneration heat load make it extremely valuable for carbon emission reduction retrofitting in heavy industries such as steel, power, and chemicals.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A carbon nanotube composite solvent, characterized in that, The liquid phase component of the composite solvent includes ethanolamine, piperazine, aminoethylpiperazine, and deionized water; wherein, based on the total mass percentage of the liquid phase components, the concentration of ethanolamine is 15wt% to 30wt%, the concentration of piperazine is 3wt% to 10wt%, the concentration of aminoethylpiperazine is 0.1wt% to 1wt%, and the balance is deionized water; the composite solvent also disperses functionalized carbon nanotubes, and the mass concentration of the functionalized carbon nanotubes in the composite solvent is 0.2 kg / m³. 3 Up to 0.8kg / m 3 ; The functionalized carbon nanotubes are one of aminated carbon nanotubes, hydroxylated carbon nanotubes, or carboxylated carbon nanotubes; when the functionalized carbon nanotubes are aminated carbon nanotubes, the inner diameter of the aminated carbon nanotubes is 3 nm to 5 nm, the outer diameter is 8 nm to 15 nm, the length is 8 μm to 15 μm, and the specific surface area is not less than 210 m². 2 / g; When the functionalized carbon nanotubes are hydroxylated carbon nanotubes, the inner diameter of the hydroxylated carbon nanotubes is 5nm to 8nm, the outer diameter is 10nm to 15nm, the length is 2μm to 8μm, and the specific surface area is not less than 190m². 2 / g; When the functionalized carbon nanotubes are carboxylated carbon nanotubes, the inner diameter of the carboxylated carbon nanotubes is 3nm to 5nm, the outer diameter is 8nm to 15nm, the length is 5μm to 15μm, and the specific surface area is not less than 190m². 2 / g.

2. The carbon nanotube composite solvent according to claim 1, characterized in that, Based on the total mass percentage of the liquid phase components, the ethanolamine has a mass percentage concentration of 20 wt%, the piperazine has a mass percentage concentration of 6 wt%, the aminoethylpiperazine has a mass percentage concentration of 0.5 wt%, and the balance is deionized water; the functionalized carbon nanotubes have a mass concentration of 0.6 kg / m³ in the composite solvent. 3 .

3. A method for preparing a carbon nanotube composite solvent as described in claim 1 or 2, characterized in that, Includes the following steps: S1: Add ethanolamine, piperazine and aminoethylpiperazine to deionized water in proportion and stir mechanically to form a homogeneous mixed amine aqueous solution; S2: Weigh functionalized carbon nanotubes and premix them with a mixed amine aqueous solution accounting for 5% to 20% of the total mass of the mixed amine aqueous solution prepared in step S1. Perform ultrasonic dispersion treatment. The frequency of the ultrasonic dispersion treatment is 40 kHz to 50 kHz, the duration is 15 min to 40 min, and the system temperature is controlled not to exceed 50 ℃. S3: Add the premixed solution after ultrasonic dispersion in step S2 to the remaining mixed amine aqueous solution, and continue mechanical stirring at 30℃ to 45℃ for 2h to 3h to obtain carbon nanotube composite solvent.

4. The method for preparing the carbon nanotube composite solvent according to claim 3, characterized in that, The mechanical stirring speed in step S1 is 300 rpm to 500 rpm.

5. A carbon dioxide capture system, characterized in that, Using the carbon nanotube composite solvent as described in claim 1 or 2 as the absorbent, the system includes an absorption tower (1), a recovery tank (2), a recovery pump (3), a recovery cooler (4), a lean liquid cooler (5), a rich liquid pump (6), a first lean-rich liquid heat exchanger (7), a lean liquid pump (8), a regeneration tower (9), a condenser (10), a reflux pump (11), a gas-liquid separator (12), a reboiler (13), a second lean-rich liquid heat exchanger (14), a semi-lean liquid pump (15), and a semi-lean liquid cooler (16). The absorption tower (1) is divided into an upper absorption zone and a lower absorption zone. The bottom of the absorption tower (1) is provided with a raw material gas inlet and a rich liquid outlet, the middle is provided with a semi-lean liquid inlet, and the top is provided with a washing liquid inlet, a reflux port and a tower top gas phase outlet. The gas phase outlet at the top of the absorption tower (1) is connected to the gas phase inlet of the recovery cooler (4), the condensate outlet of the recovery cooler (4) is connected to the inlet of the recovery tank (2), and the outlet of the recovery tank (2) is connected to the reflux port at the top of the absorption tower (1) via the recovery pump (3). The rich liquid outlet at the bottom of the absorption tower (1) is connected to the inlet of the rich liquid pump (6). The outlet of the rich liquid pump (6) is divided into two paths. The first path is connected to the upper middle inlet of the regeneration tower (9) through the tube side of the second lean-rich liquid heat exchanger (14), and the second path is connected to the middle inlet of the regeneration tower (9) through the tube side of the first lean-rich liquid heat exchanger (7). The rich liquid transported by the rich liquid pump (6) is a cold medium that flows through the tube side of the second lean-rich liquid heat exchanger (14) and the first lean-rich liquid heat exchanger (7). The regeneration tower (9) is provided with a semi-lean liquid outlet in the middle. The semi-lean liquid outlet is connected to the semi-lean liquid inlet in the middle of the absorption tower (1) via a semi-lean liquid pump (15), the shell side of the second lean-rich liquid heat exchanger (14), and a semi-lean liquid cooler (16). The semi-lean liquid pumped by the semi-lean liquid pump (15) is a heat medium that flows through the shell side of the second lean-rich liquid heat exchanger (14) and exchanges heat with the rich liquid in the tube side. The bottom of the regeneration tower (9) is provided with a lean liquid outlet, which is connected to the washing liquid inlet at the top of the absorption tower (1) via a lean liquid pump (8), the shell side of the first lean-rich liquid heat exchanger (7), and a lean liquid cooler (5). The lean liquid pumped by the lean liquid pump (8) is a heat medium that flows through the shell side of the first lean-rich liquid heat exchanger (7) and exchanges heat with the rich liquid in the tube side. The reboiler (13) is connected to the bottom of the regeneration tower (9) to provide a heat source for gas stripping for rich liquid regeneration; the gas phase outlet at the top of the regeneration tower (9) is connected in sequence to the gas phase inlet of the condenser (10) and the feed inlet of the gas-liquid separator (12). The liquid phase outlet of the gas-liquid separator (12) is connected to the top reflux port of the regeneration tower (9) via a reflux pump (11), and the gas phase outlet of the gas-liquid separator (12) is the carbon dioxide product gas output port.

6. A carbon dioxide capture system, characterized in that, Using the carbon nanotube composite solvent as described in claim 1 or 2 as the absorbent, the system includes an absorption tower (1), a recovery tank (2), a recovery pump (3), a recovery cooler (4), a lean liquid cooler (5), a rich liquid pump (6), a first lean-rich liquid heat exchanger (7), a lean liquid pump (8), a regeneration tower (9), a condenser (10), a reflux pump (11), a gas-liquid separator (12), and a reboiler (13). The absorption tower (1) is provided with a raw material gas inlet and a rich liquid outlet at the bottom, and a washing liquid inlet, a reflux port and a tower top gas phase outlet at the top. The gas phase outlet at the top of the absorption tower (1) is connected to the gas phase inlet of the recovery cooler (4), the condensate outlet of the recovery cooler (4) is connected to the inlet of the recovery tank (2), and the outlet of the recovery tank (2) is connected to the reflux port at the top of the absorption tower (1) via the recovery pump (3). The rich liquid outlet at the bottom of the absorption tower (1) is connected to the inlet of the rich liquid pump (6), and the outlet of the rich liquid pump (6) is connected to the upper inlet of the regeneration tower (9) through the tube side of the first lean-rich liquid heat exchanger (7); the rich liquid transported by the rich liquid pump (6) is a cold medium that flows through the tube side of the first lean-rich liquid heat exchanger (7). The bottom of the regeneration tower (9) is provided with a lean liquid outlet, which is connected to the washing liquid inlet at the top of the absorption tower (1) via a lean liquid pump (8), the shell side of the first lean-rich liquid heat exchanger (7), and a lean liquid cooler (5). The lean liquid pumped by the lean liquid pump (8) is a heat medium that flows through the shell side of the first lean-rich liquid heat exchanger (7) and exchanges heat with the rich liquid in the tube side. The reboiler (13) is connected to the bottom of the regeneration tower (9) to provide a heat source for gas stripping for rich liquid regeneration; the gas phase outlet at the top of the regeneration tower (9) is connected in sequence to the gas phase inlet of the condenser (10) and the feed inlet of the gas-liquid separator (12). The liquid phase outlet of the gas-liquid separator (12) is connected to the top reflux port of the regeneration tower (9) via a reflux pump (11), and the gas phase outlet of the gas-liquid separator (12) is the carbon dioxide product gas output port.

7. The carbon dioxide capture system according to claim 5 or 6, characterized in that, The system also includes a temperature control unit, which is used to control the absorption temperature in the absorption tower (1) to 35°C to 55°C and the regeneration temperature at the bottom of the regeneration tower (9) to 115°C to 120°C.

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