Process for the preparation of a deep eutectic solvent for absorbing carbon dioxide and a deep eutectic solvent

Abstract

The application provides a preparation method of a low eutectic solvent for absorbing carbon dioxide and the low eutectic solvent. The preparation method of the low eutectic solvent for absorbing carbon dioxide comprises the following steps: respectively drying piperazine and triethylene glycol to obtain pretreated piperazine and pretreated triethylene glycol; mixing the pretreated piperazine and the pretreated triethylene glycol in a proportion of 1:1-1:5 in terms of molar ratio to obtain a mixed solution; continuously introducing nitrogen into the mixed solution for a first specified time length to establish a nitrogen protective atmosphere in the mixed solution; placing the mixed solution in a sealed reaction bottle, heating and stirring at 70-80 DEG C for 2-3 h, and then naturally cooling to room temperature to obtain a transparent low eutectic solvent. The preparation method of the low eutectic solvent for absorbing carbon dioxide and the low eutectic solvent provided by the application can not only realize efficient and rapid CO2 absorption, but also has a simple preparation process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas separation, in particular to a preparation method of a deep eutectic solvent for absorbing carbon dioxide and the deep eutectic solvent. BACKGROUND

[0002] In recent years, the chemical absorption method has become the most promising CO2 capture solution due to its high capture efficiency, CO2 recovery purity (> 99%) and process maturity.

[0003] Deep eutectic solvents (DES) are low-melting mixtures formed by mixing a hydrogen bond acceptor (HBA) with a hydrogen bond donor (HBD) in a certain molar ratio through hydrogen bonding. The melting point of the mixture is significantly lower than that of any pure component. Due to its simple preparation, adjustable structure, low volatility and high thermal stability, it has broad application prospects in the fields of selective CO2 absorption and efficient and mild conversion, and provides a new research idea for the development of CO2 absorption technology. In recent years, how to improve the absorption capacity of deep eutectic solvents for CO2 has become a research hotspot. SUMMARY

[0004] Therefore, the present application provides a preparation method of a deep eutectic solvent for absorbing carbon dioxide and the deep eutectic solvent, so as to provide an absorbent with high absorption capacity for CO2 and capable of being recycled.

[0005] Specifically, the present application is realized by the following technical solutions:

[0006] The first aspect of the present application provides a preparation method of a deep eutectic solvent for absorbing carbon dioxide, which comprises:

[0007] Piperazine and tetraglyme are subjected to drying treatment respectively to obtain pretreated piperazine and pretreated tetraglyme;

[0008] The pretreated piperazine and the pretreated tetraglyme are mixed in a molar ratio of 1:1 to 1:5 to obtain a mixed solution;

[0009] Nitrogen gas is continuously introduced into the mixed solution for a first specified time period to establish a nitrogen protective atmosphere in the mixed solution;

[0010] The mixed solution is placed in a sealed reaction bottle and heated and stirred at 70 ℃ to 80 ℃ for 2 to 3 hours, and then naturally cooled to room temperature to obtain a transparent deep eutectic solvent.

[0011] The second aspect of the present application provides a deep eutectic solvent for absorbing carbon dioxide, which is prepared by any one of the preparation methods provided in the first aspect of the present application.

[0012] The third aspect of the present application provides a method for absorbing carbon dioxide by using a deep eutectic solvent, wherein the deep eutectic solvent is prepared by using any one of the preparation methods provided in the first aspect of the present application; the method for absorbing carbon dioxide by using a deep eutectic solvent comprises:

[0013] absorbing carbon dioxide gas by using the deep eutectic solvent at a temperature of 30-40℃.

[0014] The preparation method and the deep eutectic solvent for absorbing carbon dioxide provided in the present application first, by drying piperazine and triethylene glycol in advance, the residual water in the raw materials can be effectively removed, avoiding the competition of water molecules and hydrogen bond, so as to ensure the stability and reliability of the formation process of the deep eutectic solvent, further, in the mixing process, nitrogen is introduced for protection, which can prevent the components from being oxidized or absorbing carbon dioxide to generate impurities, and ensure the purity of the product, in addition, heating and stirring at a suitable temperature and fully reacting can help the formation of hydrogen bond network and the generation of deep eutectic system, finally, the transparent and stable deep eutectic solvent is obtained, which has high absorption capacity for CO2, good recycling effect, and can realize efficient and reversible absorption of CO2. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The flow chart of the first embodiment of the preparation method of the deep eutectic solvent for absorbing carbon dioxide provided in the present application is shown;

[0016] Figure 2 The state diagram of the deep eutectic solvent before and after absorbing carbon dioxide provided in an exemplary embodiment of the present application is shown;

[0017] Figure 3 The thermogravimetric analysis result diagram of the deep eutectic solvent provided in an exemplary embodiment of the present application is shown;

[0018] Figure 4 The refractive index diagram of the deep eutectic solvent provided in an exemplary embodiment of the present application is shown;

[0019] Figure 5 The diagram of the free volume of the deep eutectic solvent provided in an exemplary embodiment of the present application is shown. DETAILED DESCRIPTION

[0020] The exemplary embodiments will be described in detail herein, and the examples are shown in the accompanying drawings. When the following description refers to the accompanying drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all the embodiments consistent with the present application.

[0021] The following specific embodiments are given to introduce the technical solutions of the present application in detail.

[0022] Figure 1 The flow chart of the first embodiment of the preparation method of the eutectic solvent for absorbing carbon dioxide is provided in the present application. Please refer to Figure 1 The preparation method of the eutectic solvent for absorbing carbon dioxide provided in the present embodiment comprises:

[0023] S101, drying piperazine and triethylene glycol respectively to obtain pretreated piperazine and pretreated triethylene glycol.

[0024] Specifically, piperazine (HBA) is an organic compound with the formula C4H 10 N2, wherein N contains a lone pair of electrons and can act as a hydrogen bond acceptor. Further, triethylene glycol (TEG) is a raw material with the formula C6H 14 O4, which contains two hydroxyl groups in its molecular structure, and the hydrogen of the hydroxyl group can act as a hydrogen bond donor (HBD).

[0025] In specific implementation, the drying equipment can be used to dry the piperazine, for example, a drying box or a vacuum drying box. In the present embodiment, the piperazine is placed in a vacuum drying box and dried at a temperature of 30-40 ℃ for 2-3 h to obtain pretreated piperazine. Similarly, the drying equipment can be used to dry the triethylene glycol. In the present embodiment, the triethylene glycol can be placed in a dryer and dried at room temperature for 10-12 h to obtain pretreated triethylene glycol.

[0026] It can be understood that drying the piperazine and triethylene glycol can effectively remove the water therein, avoiding affecting the hydrogen bond action in the subsequent process of forming the eutectic solvent, thereby ensuring accuracy and stability. In addition, drying can also improve the purity of the two raw materials, so that the obtained eutectic solvent has more excellent and stable performance.

[0027] S102, mixing the pretreated piperazine and pretreated triethylene glycol in a molar ratio of 1:1-1:5 to obtain a mixed solution.

[0028] Specifically, selecting a molar ratio of 1:1-1:5 can take into account the hydrogen bond action, the stability of the solution and the CO2 absorption performance at the same time. For example, when the molar ratio is 1:1, the active site density is high and the CO2 absorption capacity is strong, but the solution viscosity is relatively large. When the molar ratio is 1:5, the solution viscosity is relatively small, but the hydrogen bond action is weakened and the CO2 absorption capacity is reduced.

[0029] In a specific implementation, for example, in this embodiment, the pretreated piperazine and the pretreated triethylene glycol can be mixed in a molar ratio of 1:1 to obtain a mixed solution.

[0030] It can be understood that the above ratio range can not only ensure the formation of a stable and sufficient hydrogen bond network between the two, thereby effectively reducing the melting point of the mixed solution and promoting the generation of a transparent eutectic solvent. At the same time, the mixed solution in this ratio range can ensure good carbon dioxide absorption capacity and achieve rapid absorption of carbon dioxide.

[0031] S103, continuously introducing nitrogen into the mixed solution for a first specified duration to establish a nitrogen protective atmosphere in the mixed solution.

[0032] Specifically, the first specified duration is determined according to the experimental scale, the size of the container, and the nitrogen introduction rate, and is a duration for ensuring that air is completely exhausted. In this embodiment, the specific value of the first specified duration is not limited. In a specific implementation, for example, in a 10 mL conical flask, nitrogen is introduced at a rate of 5 mL / min until nitrogen bubbles continuously escape from the surface of the mixed solution or the overall mass of the test tube no longer increases, indicating that the first specified duration has been reached. In another embodiment, the first specified duration is set to 2-3 minutes.

[0033] It can be understood that continuously introducing nitrogen into the mixed solution can prevent the raw materials from being oxidized by air and reacting with water vapor in the air, ensuring that the heating process is in a more stable environment, thereby ensuring that the piperazine and the triethylene glycol are smoothly mixed in proportion, and ultimately preparing the eutectic solvent.

[0034] S104, placing the mixed solution in a sealed reaction bottle and heating and stirring at 70-80°C for 2-3 hours, and then naturally cooling to room temperature to obtain a transparent eutectic solvent.

[0035] Specifically, the sealed reaction bottle can isolate the mixed solution from external air, maintaining the airtightness and component stability of the reaction system. The sealed reaction bottle is usually a device with good airtightness and high temperature resistance. For example, conical flasks, round-bottom flasks, and screw-sealed reaction bottles. In this embodiment, a conical flask is used as the sealed reaction bottle.

[0036] In a specific implementation, in this step, the conical flask containing the piperazine and the triethylene glycol is placed in a constant-temperature magnetic heating jacket, heated and stirred at a temperature of 70-80°C for 2-3 hours until a homogeneous transparent solution is formed, the conical flask is taken out of the constant-temperature magnetic heating jacket, and cooled at room temperature, and then transferred to a reagent bottle.

[0037] Further, the temperature condition of 70 ℃-80 ℃ is selected, which can provide suitable kinetic energy for the mixing process and accelerate the hydrogen bond action. For example, at the temperature of 70 ℃, the raw materials can be prevented from volatilization while the hydrogen bond is formed. At the temperature of 80 ℃, the molecular kinetic energy can be further improved, and the reaction time can be shortened. Under the condition of 70 ℃-80 ℃, the stirring is performed for 2-3 h, and the system is naturally cooled to room temperature after the equilibrium is reached, so as to avoid the damage of the solution caused by the sudden change of temperature.

[0038] In the embodiment, the heating and stirring are performed at 80 ℃ for 2-3 h, and then the natural cooling to room temperature is performed, so as to obtain the transparent deep eutectic solvent (DES).

[0039] It should be noted that the strong hydrogen bond complex network is formed between the nitrogen atom of the piperazine and the hydroxyl group of the triethylene glycol, that is, the stable structure formed between the molecules through the hydrogen bond action can obtain the deep eutectic solvent.

[0040] In addition, the piperazine or the triethylene glycol has a high melting point or viscosity, and when the two are mixed in a suitable proportion, the hydrogen bond complex action can disturb the ordered arrangement of the respective crystal lattices, so that the crystal lattice energy can be greatly reduced, thereby forming a stable liquid with a melting point much lower than that of the single component, that is, the deep eutectic solvent.

[0041] Further, in the present application, the heating and stirring under 70-80 ℃ can accelerate the rearrangement and stabilization of the hydrogen bond network. Under the condition of nitrogen protection and sealing, the interference of water and oxygen is avoided, and it is ensured that only the hydrogen bond action of the target molecule exists in the system. After cooling to room temperature, the hydrogen bond action is stably present, and the transparent and uniform deep eutectic solvent state is maintained.

[0042] The synergistic mechanism of the above experimental conditions (pre-drying, nitrogen protection atmosphere, molar ratio, temperature, and time) is briefly introduced as follows:

[0043] (1) The pre-drying is performed to remove the water interference and avoid the side reaction and the structural defect of the deep eutectic solvent

[0044] Specifically, piperazine (an amine-containing cyclic organic amine) and tetraglyme (an ether alcohol containing multiple hydroxyl groups) are both strong polar compounds, which are easy to absorb moisture in the air through hydrogen bonds, and the moisture will damage the preparation process in two ways: First, the amine group of piperazine has weak alkaline, if containing moisture, it will undergo weak hydrolysis with water (although the hydrolysis of piperazine is weak, but a small amount of moisture will still reduce its effective concentration); More importantly, moisture will compete with piperazine to bind to the hydroxyl group (-OH) of tetraglyme, and the formation of the eutectic solvent depends on the directional hydrogen bonding between the hydrogen bond donor (hydroxyl group of tetraglyme) and the hydrogen bond acceptor (amine group of piperazine), the presence of water will break this directional binding, leading to the difficulty in forming a stable hydrogen bond network structure, and the final product may appear turbidity, delamination. Second, if tetraglyme contains moisture, it will dilute its concentration, and the hydroxyl group of water will form an invalid hydrogen bond with itself, further weakening the interaction with piperazine; At the same time, during the subsequent heating process, the water may evaporate, causing pressure fluctuations in the reaction system, and destroying the stability of the sealed reaction.

[0045] Therefore, targeted drying can completely remove free water and absorbed water in the two components, laying a foundation for subsequent precise reactions.

[0046] (2) By nitrogen protection atmosphere, oxygen can be isolated, and component oxidation and byproduct generation can be inhibited

[0047] The key components in the reaction system are tetraglyme (containing ether bond and hydroxyl group) and piperazine (containing amine group), which are easy to undergo oxidation reaction with oxygen in the air under heating (70-80 ℃), the hydroxyl group of tetraglyme may be oxidized to aldehyde group (-CHO) or carboxyl group (-COOH) under heating, and the generated oxygen-containing compound will undergo amide reaction with the amino group of piperazine, generating a solid byproduct that is insoluble in the eutectic solvent.

[0048] In addition, the amine group (-NH-) of piperazine may also be oxidized to imine group (=N-) or nitro group (-NO2) at high temperature, which destroys its hydrogen bond acceptor function and cannot form a stable eutectic solvent with tetraglyme.

[0049] By continuously introducing nitrogen for a specified period of time, the air (especially oxygen) in the reaction system can be completely replaced, forming an inert protective layer on the surface of the mixed solution, blocking the oxidation reaction path from the root, and ensuring that the two components only undergo the target reaction of hydrogen bond combination without byproduct interference.

[0050] (3) By setting the molar ratio to 1:1-1:5, the hydrogen bond donor and acceptor ratio can be matched, and the stability and performance of the formed eutectic solvent can be regulated

[0051] The core of forming a eutectic solvent is that the hydrogen bond donor and hydrogen bond acceptor form a stable binary system through hydrogen bonds, and the molar ratio directly determines the integrity of the hydrogen bond network.

[0052] If the proportion of piperazine is too high, the unbound piperazine will exist in a free state, causing the melting point of the eutectic solvent to rise (losing the eutectic property), and the free piperazine is volatile, reducing the stability of the solvent;

[0053] If the proportion of triethylene glycol is too high, the proportion of unbound triethylene glycol will dilute the concentration of the eutectic solvent, weakening its CO2 absorption capacity (CO2 mainly reacts with the amine group of piperazine, and excessive triethylene glycol will reduce the density of the amine group).

[0054] By setting the molar ratio to 1:1-1:5, the amine group of piperazine can be precisely matched with the hydroxyl group of triethylene glycol, so that the amine group of piperazine can form hydrogen bonds with the hydroxyl group of triethylene glycol, building a dense and stable hydrogen bond network, which not only ensures the low melting point (liquid at room temperature) and transparency of the eutectic solvent, but also retains enough amine group sites for subsequent CO2 absorption.

[0055] (4) By setting the temperature to 70-80°C, the hydrogen bond reaction can be activated, and the components can be prevented from being damaged by high temperature

[0056] Specifically, the core role of temperature is to provide the activation energy required for hydrogen bond combination, while avoiding excessive heating that leads to component decomposition. If the temperature is insufficient, the kinetic energy of the two components is low, and the collision frequency of the hydroxyl group and the amine group is insufficient, which cannot overcome the energy barrier of hydrogen bond formation, resulting in a physical mixture (layered or turbid) that cannot form a unified eutectic solvent; if the temperature is too high, although it can accelerate the formation of hydrogen bonds, it will cause triethylene glycol to volatilize slightly (reduce the effective concentration); piperazine (boiling point 148.5°C, but volatile above 80°C) is lost with a small amount of nitrogen; the two components may undergo thermal decomposition (such as triethylene glycol ether bond rupture, generating small molecule alcohols), ultimately destroying the hydrogen bond network.

[0057] By setting the temperature to 70-80°C, sufficient kinetic energy can be provided to the molecules to promote efficient combination of the hydroxyl group and the amine group to form a hydrogen bond network, and to avoid component volatilization and decomposition, ensuring complete reaction and stable product.

[0058] (5) By setting the reaction time to 2-3 h, the hydrogen bond reaction can be fully ensured, and insufficient or excessive reaction can be avoided

[0059] Specifically, the purpose of heating and stirring is to promote the uniform mixing of the two components, ensure that the piperazine is in sufficient contact with the tetraglyme and form hydrogen bonds. If the time is insufficient, the mixed solution is not completely uniform, the piperazine or tetraglyme in the local area is excessive, the hydrogen bond network is incomplete, the product may have microscopic stratification (appearance turbidity), and the unreacted components lead to unstable performance of the final formed eutectic solvent; and if the time is too long, although no side reactions will occur (with nitrogen protection and dry basis), but it will increase the energy consumption, and long time stirring may cause slight fluctuations in the system temperature (affect the consistency of hydrogen bond combination).

[0060] By setting the reaction time to 2-3 h, the molecular level uniform mixing of the two components can be achieved by stirring at a temperature of 70-80 °C, ensuring complete hydrogen bond reaction and forming a single, transparent eutectic solvent system. Subsequent natural cooling to room temperature can solidify the hydrogen bond network and maintain a stable form.

[0061] It can be understood that each condition does not act independently, but forms a layer-by-layer progressive synergistic relationship, ultimately achieving efficient preparation of the eutectic solvent.

[0062] Specifically, after drying to remove water, the system only contains piperazine or tetraglyme, at which time nitrogen protection can precisely isolate oxygen (without the need to resist the dual interference of water and oxygen), maximizing the inhibition of oxidative side reactions; further, without the interference of water and byproducts, the molar ratio of 1:1-1:5 can precisely correspond to the hydrogen bond binding sites of piperazine or tetraglyme, avoiding impurities occupying the binding sites and ensuring that the hydrogen bond network is formed according to the target ratio; finally, precise proportion matching makes molecular collision more efficient, further accelerating the reaction at an activation temperature of 70-80 °C, and the reaction can be completed within 2-3 h without the need to extend the time.

[0063] In summary, by removing water through drying, isolating oxygen with nitrogen, matching the hydrogen bond sites, providing activation energy at a temperature, and ensuring complete reaction within a certain time, the five conditions work together to ultimately form a transparent, stable, and byproduct-free eutectic solvent, and the amine group sites of piperazine are preserved, ensuring high-efficiency CO2 absorption performance in the future.

[0064] The application provides a preparation method of a low eutectic solvent for absorbing carbon dioxide. First, the raw materials are pre-dried to remove the residual water, so that the water molecules do not compete with the hydrogen bonds, thereby ensuring the stability and reliability of the low eutectic solvent formation process. Nitrogen is introduced during the mixing process to prevent oxidation or absorption of carbon dioxide to generate impurities, thereby ensuring the purity of the product. Heating and stirring at an appropriate temperature and sufficient reaction help to form a hydrogen bond network and a low eutectic system, and finally a transparent and stable low eutectic solvent is obtained. The prepared low eutectic solvent can realize efficient and rapid CO2 absorption, and the preparation process is simple.

[0065] Further, the application also provides a low eutectic solvent for absorbing carbon dioxide, which is prepared by the preparation method of any one of the first aspect of the application.

[0066] In addition, the application also provides a method for absorbing carbon dioxide by using a low eutectic solvent. The method for absorbing carbon dioxide by using a low eutectic solvent provided by the application is introduced as follows.

[0067] Specifically, the method for absorbing carbon dioxide by using a low eutectic solvent provided by the application is prepared by any one of the preparation methods of the first aspect of the application. The method for absorbing carbon dioxide by using a low eutectic solvent comprises the following steps.

[0068] The low eutectic solvent absorbs carbon dioxide gas at a temperature of 30-40℃.

[0069] It should be noted that the absorption mechanism of CO2 mainly includes physical absorption and chemical absorption, which are as follows.

[0070] (1) Physical absorption mechanism

[0071] The piperazine and triethylene glycol molecules contain multiple hydroxyl groups, which can form a stable hydrogen bond network with piperazine. This network provides a polar and highly ordered microenvironment, making it easier for CO2 molecules to dissolve and diffuse.

[0072] Further, the low eutectic solvent has a large polarity, which can effectively increase the solubility of CO2 in the solvent and realize physical dissolution under van der Waals force and dipole interaction. In addition, it can be understood that the physical absorption process is a fast and reversible process, and the absorption rate is fast.

[0073] (2) Chemical absorption mechanism

[0074] The piperazine molecule contains primary / secondary amine groups. In the presence of CO2, the amine group reacts with CO2 to form carbamate or carbonate complex.

[0075] Further, the hydroxyl group of triethylene glycol can form a hydrogen bond with the generated carbamate ion to reduce the dissociation tendency and enhance the stability of chemical absorption.

[0076] It can be understood that the chemical absorption process has high selectivity and absorption capacity, and can achieve a large degree of CO2 fixation.

[0077] Further, in a possible implementation, after the low eutectic solvent absorbs the carbon dioxide gas at a temperature of 30-40 ℃, the method further comprises:

[0078] The low eutectic solvent that has absorbed the carbon dioxide is heated to desorb the low eutectic solvent and the carbon dioxide gas, so as to reuse the desorbed low eutectic solvent and collect the desorbed carbon dioxide gas.

[0079] Optionally, in a possible implementation, the heating treatment temperature is 70 ℃-90 ℃.

[0080] It can be understood that when the low eutectic solvent that has absorbed the carbon dioxide is heated to 70 ℃-90 ℃, the CO2 molecules physically dissolved in the solvent will escape due to the increase of the system temperature. In addition, the thermal energy destroys the van der Waals force and hydrogen bond interaction between CO2 and solvent molecules, thereby reducing the solubility of CO2 in the solvent, so that CO2 is released in the form of gas. Further, the carbamate / hydrogen carbonate complex generated by the reaction of the piperazine amino group and CO2 will decompose under heating conditions. In summary, the desorption function is achieved.

[0081] Specifically, Figure 2 The low eutectic solvent before and after absorbing carbon dioxide according to an example embodiment of the present application is shown in the state diagram, wherein, Figure 2 (A) of FIG. in the diagram before absorption, Figure 2 (B) of FIG. in the diagram after absorption, Figure 2 (C) of FIG. in the diagram after desorption. Please refer to Figure 2 It can be seen that before absorption, the low eutectic solvent in the three-necked flask is in a transparent liquid state. After absorption, white turbid substances appear in the three-necked flask, indicating the interaction between the low eutectic solvent and carbon dioxide. After desorption, the liquid in the three-necked flask returns to a transparent liquid state, indicating that the absorbed carbon dioxide is released from the solvent.

[0082] According to the foregoing description, it can be understood that the eutectic solvent generated in the embodiment can be recycled by absorption and desorption. The eutectic solvent can capture carbon dioxide by chemical absorption and physical absorption at low temperature, and release carbon dioxide by destroying weak binding force and reversible chemical bonds by heat energy at high temperature. The eutectic solvent not only has high absorption performance, but also can be regenerated and recycled by temperature adjustment at low energy consumption.

[0083] The following specific embodiments are given to introduce the technical solutions of the present application in detail:

[0084] Embodiment 1

[0085] The piperazine was placed in a vacuum drying oven and dried at a temperature of 30-40 °C for 2-3 h. The tetraglyme was placed in a desiccator and dried at room temperature for 10-12 h. Piperazine and tetraglyme were weighed according to a molar ratio of 1:1, and then the weighed piperazine and tetraglyme were added to a conical flask and uniformly mixed. Nitrogen was then introduced for 5-10 min. Further, the conical flask containing the piperazine and tetraglyme was placed in a constant-temperature magnetic heating jacket and heated and stirred at 80 °C for 2 h (during the heating process, the conical flask was in a sealed state). A uniform transparent solution was formed in the flask to obtain the eutectic solvent.

[0086] Further, after the eutectic solvent was prepared, a carbon dioxide absorption test was performed. Specifically, the eutectic solvent was placed in a gas absorption device, pure carbon dioxide was introduced into the gas absorption device at a rate of 20 mL / min, and nitrogen was introduced into the gas absorption device at a rate of 50 mL / min. At 40 °C, the mixed gas was mixed with the eutectic solvent until the CO2 concentration detected at the outlet end of the gas absorption device was constant, and a mixed solution absorbing carbon dioxide was obtained (it should be noted that the mixed gas composed of carbon dioxide and nitrogen enters the gas absorption device from the inlet end, reacts with the eutectic solvent in the gas absorption device, and is further discharged through the outlet end. The gas detection device is provided at the outlet end to detect the concentration of carbon dioxide. During the absorption process, the concentration of carbon dioxide first decreases and then increases, and when the increase stops, it means complete absorption). The absorption capacity of carbon dioxide was calculated by weighing with an electronic balance. In this embodiment, the calculated absorption capacity of carbon dioxide was 0.121 g CO2 / g DES.

[0087] It should be noted that in the present application, the absorption capacity of carbon dioxide (g CO2 / g DES) is calculated according to the following formula:

[0088] ;

[0089] ;

[0090] : mass of CO2 absorbed (g);

[0091] : mass of the absorber plus absorbent before absorption (g);

[0092] : mass of the absorber plus absorbent after absorption (g);

[0093] : mass of the absorbent (g); in this application, the absorbent is a deep eutectic solvent.

[0094] Further, pure nitrogen gas is passed into the mixed solution in which carbon dioxide is absorbed at a flow rate of 45 mL / min, and desorption experiments are carried out under the condition of heating and stirring at 90℃. Whether desorption is ended is determined by the change in the concentration of carbon dioxide at the outlet end. When the CO2 concentration gradually increases and increases to remain unchanged, it is determined that desorption is ended. At this time, the desorption rate is calculated. In this embodiment, it is calculated that the desorption rate is 99%.

[0095] It should be noted that in this embodiment, the desorption rate is calculated according to the following formula:

[0096] Desorption efficiency = (moles of CO2 absorbed by the deep eutectic solvent) / (moles of CO2 in the deep eutectic solvent before desorption)

[0097] : moles of CO2 absorbed by the deep eutectic solvent;

[0098] : moles of CO2 remaining in the deep eutectic solvent after desorption.

[0099] Example 2

[0100] Piperazine is placed in a vacuum drying oven and dried at a temperature of 30-40℃ for 2-3 h. Triethylene glycol is placed in a desiccator and dried at room temperature for 10-12 h. Piperazine and triethylene glycol are weighed according to a molar ratio of 1:2, and the weighed piperazine and triethylene glycol are added to a conical flask and uniformly mixed, and then nitrogen gas is introduced for 5-10 min. Further, the conical flask containing piperazine and triethylene glycol is placed in a constant-temperature magnetic heating jacket, heated and stirred at 80℃ for 2 h (during the heating process, the conical flask is in a sealed state), and a uniform transparent solution is formed in the flask to obtain a deep eutectic solvent.

[0101] ​Further, after the deep eutectic solvent is prepared, a carbon dioxide absorption test is performed. Specifically, the deep eutectic solvent is placed in a gas absorption device, pure carbon dioxide is introduced into the gas absorption device at a rate of 20 mL / min, and nitrogen is introduced into the gas absorption device at a rate of 50 mL / min. At 40°C, the mixed gas is fully mixed with the deep eutectic solvent until the CO2 concentration detected at the outlet end of the gas absorption device is constant, and a mixed solution in which carbon dioxide is absorbed is obtained. The absorption capacity of carbon dioxide is calculated by weighing with an electronic balance. In this embodiment, it is determined by calculation that the absorption capacity of carbon dioxide is 0.097 g CO2 / g DES.

[0102] Further, pure nitrogen is introduced into the mixed solution in which carbon dioxide is absorbed at a flow rate of 45 mL / min, and a desorption experiment is performed under heating and stirring conditions at 85°C. Whether the desorption is complete is determined by the change in the concentration of carbon dioxide at the outlet end. When the CO2 concentration gradually increases and then remains constant, it is determined that the desorption is complete. At this time, the desorption rate is calculated. In this embodiment, it is determined by calculation that the desorption rate is 98%.

[0103] Example 3

[0104] Piperazine is placed in a vacuum drying oven and dried at a temperature of 30-40°C for 2-3 h. Triethylene glycol is placed in a desiccator and dried at room temperature for 10-12 h. Piperazine and triethylene glycol are weighed in a molar ratio of 1:3, and the weighed piperazine and triethylene glycol are added to a conical flask and uniformly mixed, and then nitrogen is introduced for 5-10 min. Further, the conical flask containing piperazine and triethylene glycol is placed in a constant-temperature magnetic heating jacket, heated and stirred at 70°C for 2 h (during the heating process, the conical flask is in a sealed state), and a uniform transparent solution is formed in the flask to obtain a deep eutectic solvent.

[0105] Further, after the deep eutectic solvent is prepared, a carbon dioxide absorption test is performed. Specifically, the deep eutectic solvent is placed in a gas absorption device, pure carbon dioxide is introduced into the gas absorption device at a rate of 20 mL / min, and nitrogen is introduced into the gas absorption device at a rate of 50 mL / min. At 40°C, the mixed gas is fully mixed with the deep eutectic solvent until the CO2 concentration detected at the outlet end of the gas absorption device is constant, and a mixed solution in which carbon dioxide is absorbed is obtained. The absorption capacity of carbon dioxide is calculated by weighing with an electronic balance. In this embodiment, it is determined by calculation that the absorption capacity of carbon dioxide is 0.064 g CO2 / g DES.

[0106] Furthermore, pure nitrogen gas was introduced into the mixed solution that had absorbed carbon dioxide at a flow rate of 45 mL / min, and a desorption experiment was conducted under heating and stirring conditions at 85°C. The end of the desorption was determined by the change in the concentration of carbon dioxide at the outlet. When the CO2 concentration gradually increased and then remained constant, the desorption was considered to be complete. At this point, the desorption rate was calculated. In this embodiment, the desorption rate was determined to be 95%.

[0107] Example 4

[0108] Piperazine was placed in a vacuum drying oven and dried at 30–40 °C for 2–3 h. Tetraethylene triethylene glycol was placed in a desiccator and dried at room temperature for 10–12 h. Piperazine and tetraethylene triethylene glycol were weighed in a molar ratio of 1:1 and added to an Erlenmeyer flask, mixed thoroughly, and then nitrogen gas was introduced for 5–10 min. Further, the Erlenmeyer flask containing piperazine and tetraethylene triethylene glycol was placed in a constant-temperature magnetic heating mantle and heated and stirred at 70 °C for 2 h (the Erlenmeyer flask remained sealed during heating) until a homogeneous and transparent solution formed in the flask, yielding the eutectic solvent.

[0109] Furthermore, after preparing the eutectic solvent, a carbon dioxide absorption test was conducted. Specifically, the eutectic solvent was placed in a gas absorption device, and pure carbon dioxide was introduced into the gas absorption device at a rate of 20 mL / min, while nitrogen gas was introduced into the gas absorption device at a rate of 50 mL / min. At 40 °C, the mixed gas and the eutectic solvent were thoroughly mixed until the CO2 concentration detected at the outlet of the gas absorption device remained constant, resulting in a mixed solution that had absorbed carbon dioxide. The absorption capacity of carbon dioxide was calculated by weighing using an electronic balance. In this embodiment, the calculated absorption capacity of carbon dioxide was determined to be 0.042 g CO2 / g DES.

[0110] Furthermore, pure nitrogen gas was introduced into the mixed solution that had absorbed carbon dioxide at a flow rate of 45 mL / min, and a desorption experiment was conducted under heating and stirring conditions at 90°C. The end of the desorption was determined by the change in the concentration of carbon dioxide at the outlet. When the CO2 concentration gradually increased and then remained constant, the desorption was considered to be complete. At this point, the desorption rate was calculated. In this embodiment, the desorption rate was determined to be 96%.

[0111] Example 5

[0112] Piperazine was placed in a vacuum drying oven and dried at 30–40 °C for 2–3 h. Tetraethylene triethylene glycol was placed in a desiccator and dried at room temperature for 10–12 h. Piperazine and tetraethylene triethylene glycol were weighed in a molar ratio of 1:1 and added to an Erlenmeyer flask, mixed thoroughly, and then nitrogen gas was introduced for 5–10 min. Further, the Erlenmeyer flask containing piperazine and tetraethylene triethylene glycol was placed in a constant-temperature magnetic heating mantle and heated and stirred at 70 °C for 2 h (the Erlenmeyer flask remained sealed during heating) until a homogeneous and transparent solution formed in the flask, yielding the eutectic solvent.

[0113] Furthermore, after preparing the eutectic solvent, a carbon dioxide absorption test was conducted. Specifically, the eutectic solvent was placed in a gas absorption device, and pure carbon dioxide was introduced into the gas absorption device at a rate of 20 mL / min, while nitrogen gas was introduced at a rate of 50 mL / min. At 40 °C, the mixed gas and the eutectic solvent were thoroughly mixed until the CO2 concentration detected at the outlet of the gas absorption device remained constant, resulting in a mixed solution that had absorbed carbon dioxide. The absorption capacity of carbon dioxide was calculated by weighing using an electronic balance. In this embodiment, the calculated absorption capacity of carbon dioxide was determined to be 0.039 g CO2 / g DES.

[0114] Furthermore, pure nitrogen gas was introduced into the mixed solution that had absorbed carbon dioxide at a flow rate of 45 mL / min, and a desorption experiment was conducted under heating and stirring conditions at 90°C. The end of the desorption was determined by the change in the concentration of carbon dioxide at the outlet. When the CO2 concentration gradually increased and then remained constant, the desorption was considered to be complete. At this point, the desorption rate was calculated. In this embodiment, the desorption rate was determined to be 96%.

[0115] Example 6

[0116] Following the steps described above, the eutectic solvent from Example 1 was used for five cycles of absorption and desorption. The absorption capacity of the eutectic solvent for CO2 remained essentially stable. Specific results are shown in the table below:

[0117] Table 1. Experimental results of CO2 absorption in eutectic solvent after 5 cycles

[0118] Cycles Absorption capacity (g CO2 / g DES) 1 0.121 2 0.11 3 0.106 4 0.08 5 0.07

[0119] Furthermore, to further verify the performance of the eutectic solvent prepared in this application, its thermal stability was determined using a thermogravimetric analyzer (Netzsch TG 209 F3, Germany). The specific results are as follows: Figure 3 As shown ( Figure 3 (A thermogravimetric analysis result diagram of a eutectic solvent shown in an exemplary embodiment of this application); wherein, Figure 3In this context, PZ represents piperazine; TEG represents tetraethylene triethylene glycol; PE / TEG (1:1) indicates a eutectic solvent prepared as shown in Example 1 with a molar ratio of piperazine to tetraethylene triethylene glycol of 1:1; PE / TEG (1:2) indicates a eutectic solvent prepared as shown in Example 2 with a molar ratio of piperazine to tetraethylene triethylene glycol of 1:2; PE / TEG (1:3) indicates a eutectic solvent prepared as shown in Example 3 with a molar ratio of piperazine to tetraethylene triethylene glycol of 1:3; PE / TEG (1:4) indicates a eutectic solvent prepared as shown in Example 4 with a molar ratio of piperazine to tetraethylene triethylene glycol of 1:4; and PE / TEG (1:5) indicates a eutectic solvent prepared as shown in Example 5 with a molar ratio of piperazine to tetraethylene triethylene glycol of 1:5. Please refer to... Figure 3 Eutectic solvents exhibit good thermal stability up to 300 °C. They do not decompose due to temperature increases during absorption or desorption, thus maintaining good stability.

[0120] Furthermore, the refractive index of the eutectic solvents prepared in Examples 1 to 5 was tested using an Abbe refractometer, specifically as follows: Figure 4 As shown ( Figure 4 This is a schematic diagram illustrating the refractive index of a eutectic solvent as shown in an exemplary embodiment of this application. Furthermore, based on the refractive index, the free volume of the eutectic solvent can be calculated, and the specific calculation process is as follows:

[0121] Relative molecular mass:

[0122] ;

[0123] Molar volume:

[0124] ;

[0125] Mohr's refractive index:

[0126] ;

[0127] Free volume:

[0128] ;

[0129] in, The relative molecular mass of the synthesized DES is given in g / mol.

[0130] The relative molecular mass of the hydrogen bond acceptor used is in g / mol.

[0131] The relative molecular mass of the hydrogen bond donor used is in g / mol;

[0132] The number of moles of hydrogen bond acceptors used, in mol;

[0133] The number of moles of hydrogen bond donors used, in mol;

[0134] The molar volume of the synthesized eutectic solvent is given in cm³ / mol.

[0135] The density of the synthesized eutectic solvent is given in g / cm³. 3 ;

[0136] is the molar refractive index of the synthesized eutectic solvent, cm³ / mol;

[0137] The refractive index of the synthesized eutectic solvent;

[0138] denoted as the free volume of the synthesized eutectic solvent, in cm³ / mol.

[0139] Furthermore, calculations show that the free volume of the eutectic solvent is as follows: Figure 5 As shown ( Figure 5 (This is a schematic diagram illustrating the free volume of a eutectic solvent in an exemplary embodiment of this application. Please also specify the parameters.) Figure 4 and Figure 5 Both refractive index and free volume show a linear relationship with temperature; as temperature increases, refractive index decreases and free volume increases. The free volume of all eutectic solvents increases with increasing temperature, following the same trend. Furthermore, the free volume also increases with increasing TEG proportion, indirectly confirming that TEG primarily plays a role in the physical absorption of carbon dioxide.

[0140] In addition, to verify the effectiveness of the above preparation method, relevant comparative experiments were also conducted in this application. The relevant comparative experiments are described below:

[0141] Comparative Example 1

[0142] Piperazine and tetraethylene glycol were dried separately to obtain pretreated piperazine and pretreated tetraethylene glycol. The pretreated piperazine and pretreated tetraethylene glycol were mixed in a molar ratio of 2:1 to obtain a mixed solution. Nitrogen gas was continuously introduced into the mixed solution for a first specified time to establish a nitrogen protective atmosphere in the mixed solution. The mixed solution was placed in a sealed reaction flask and heated and stirred at 80 °C for 2 h, and then naturally cooled to room temperature. The product was a solid-liquid mixture, and no eutectic solvent was synthesized.

[0143] Comparative Example 2:

[0144] Eutectic solvents were prepared using other raw materials, and the carbon dioxide absorption capacity of the prepared eutectic solvents was measured using the aforementioned method. The specific results are shown in Table 2.

[0145] Table 2 Carbon dioxide absorption capacity of eutectic solvents prepared from various raw materials (DES represents eutectic solvent)

[0146] Serial number Raw material Carbon dioxide absorption capacity (g CO2 / g DES) 1 Imidazole and tetrabutylammonium chloride in a molar ratio of 1 : 1 0.01 2 Imidazole and triethylene glycol in a molar ratio of 1 : 1 0.02 3 Piperazine and triethylene glycol in a molar ratio of 1 : 1 0.12

[0147] Please refer to Table 2. The preparation method provided in this embodiment produces a eutectic solvent with good carbon dioxide absorption capacity.

[0148] Referring to the descriptions in the preceding embodiments, it will be understood that the method provided in this application has at least the following advantages:

[0149] (1) This application provides a method for absorbing carbon dioxide using a eutectic solvent, which achieves efficient CO2 absorption and significantly improves the CO2 absorption rate. This method has the potential for large-scale industrial application and provides theoretical support for the development of efficient and low-cost CO2 absorbents.

[0150] (2) This application achieves both process simplification and enhanced absorption efficiency by using a eutectic solvent. The eutectic solvent has the outstanding advantages of simple preparation process and high chemical stability, effectively reducing system complexity and operating costs.

[0151] (3) The desorption temperature of the eutectic solvent described in this application after absorbing CO2 is as low as 75~90 ℃, and the desorption rate is higher than 95%, which has excellent regeneration stability and energy consumption economy.

[0152] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a eutectic solvent for absorbing carbon dioxide, characterized in that, The preparation method includes: Piperazine and tetraethylene glycol were dried separately to obtain pretreated pipeazine and pretreated tetraethylene glycol. Pretreated piperazine and pretreated tetraethylene glycol were mixed in a molar ratio of 1:1 to 1:5 to obtain a mixed solution; Nitrogen gas is continuously introduced into the mixed solution for a first specified time to establish a nitrogen protective atmosphere in the mixed solution; The mixed solution was placed in a sealed reaction flask and heated and stirred at 70 ℃~80 ℃ for 2~3 h, and then naturally cooled to room temperature to obtain a transparent eutectic solvent.

2. The method according to claim 1, characterized in that, Pretreated piperazine and pretreated tetraethylene glycol were mixed in a molar ratio of 1:1 to 1:5 to obtain a mixed solution comprising: Pretreated piperazine and pretreated tetraethylene glycol were mixed in a molar ratio of 1:1 to obtain a mixed solution.

3. The method according to claim 2, characterized in that, The mixed solution was placed in a sealed reaction flask and heated and stirred at 70 ℃~80 ℃ for 2~3 h, then allowed to cool naturally to room temperature to obtain a transparent eutectic solvent, comprising: The mixed solution was placed in a sealed reaction flask and heated and stirred at 80 °C for 3 h, and then naturally cooled to room temperature to obtain a transparent eutectic solvent.

4. The method according to claim 1, characterized in that, The piperazine is dried, including: Piperazine was placed in a vacuum drying oven and dried at 30–40 °C for 2–3 h to obtain pretreated piperazine.

5. The method according to claim 1, characterized in that, The process of drying triethylene glycol includes: Tetraethylene glycol was placed in a desiccator and dried at room temperature for 10–12 h to obtain pretreated tetraethylene glycol.

6. A eutectic solvent, characterized in that, The eutectic solvent is used to absorb carbon dioxide, and the eutectic solvent is prepared using the preparation method according to any one of claims 1-5.

7. A method for absorbing carbon dioxide using a eutectic solvent, characterized in that, The eutectic solvent is prepared using the preparation method according to any one of claims 1-5; the method for absorbing carbon dioxide using the eutectic solvent includes: Carbon dioxide gas was absorbed using a eutectic solvent at a temperature of 30 ℃ to 40 ℃.

8. The method according to claim 7, characterized in that, After absorbing carbon dioxide gas using a eutectic solvent at a temperature of 30°C to 40°C, the method further includes: The eutectic solvent that has absorbed carbon dioxide is heated to desorb the eutectic solvent and carbon dioxide gas, so that the desorbed eutectic solvent can be reused and the desorbed carbon dioxide gas can be collected.

9. The method according to claim 8, characterized in that, The heat treatment temperature is 70 ℃~90 ℃.

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