A polyamine-based functionalized ionic liquid, a preparation method and application thereof

Abstract

The application discloses a kind of polyamine functionalized ionic liquid and its preparation method and application, its molecular composition is its molecular composition is tetraethylene pentamine-caprolactam salt, molecular formula is [TEPAH][CPL], structural formula is as shown in formula I.Preparation method, preparation is simple, easy to operate and implement.The novel functionalized ionic liquid of the application as CO2 absorbent, in water, alcohol and ether etc.Solvent all has good solubility, and the ionic liquid solution formed can be used to capture or separate CO2 in gas.The absorbent not only has high CO2 absorption capacity, but also has the advantage of low energy consumption of regeneration.It can effectively overcome the defects of traditional organic amine and conventional ionic liquid absorption CO2, provide new ideas for the industrial application of ionic liquid in the future.

Description

Technical Field

[0001] This invention relates to the field of carbon dioxide capture and separation technology, specifically to a polyamine-functionalized ionic liquid, its preparation method, and its application in capturing or separating CO2 in mixed gases. Background Technology

[0002] CO2 capture mainly involves three methods: pre-combustion capture, oxygen-enriched combustion, and post-combustion capture. Post-combustion capture requires no modification to existing power plant processes and is applicable to any type of thermal power plant; CO2 capture technology can be directly incorporated into existing processes. Currently, chemical absorption is the most widely used carbon capture method among post-combustion capture technologies. While different chemical absorbents have their own characteristics, they also have their limitations. Organic amines, represented by monoethanolamine (MEA), are commonly used chemical absorbents. MEA reacts rapidly with CO2 and has high selectivity, but it suffers from drawbacks such as easy degradation and foaming, and strong corrosiveness. To overcome the shortcomings of single organic amines, mixed amines have emerged. Mixed amines combine the advantages of different types of organic amines, significantly improving the CO2 capture characteristics of this type of absorbent. However, in practical applications, the cost of heating and regenerating chemical absorbents is high. To reduce energy consumption and costs, two-phase amine absorbents with significant differences in affinity for solvents have been developed, which can reduce the volume of regenerated liquid and thus effectively reduce regeneration energy consumption. However, due to the inherent limitations of organic amines, the development of novel chemical absorbents with tunable structures and stable performance has become a research hotspot in the field of carbon dioxide capture technology.

[0003] Ionic liquids (ILs) are salts composed of cations and anions. Due to their tunable structure, low saturated vapor pressure, and high chemical and thermal stability, ionic liquids are considered the most promising novel CO2 absorbents. Conventional ionic liquids are classified into imidazole salts, amino acid salts, pyridine salts, pyrrole salts, and ammonium salts. However, conventional ionic liquids absorb CO2 primarily through physical absorption, resulting in slow absorption rates and low absorption capacity, which are unsuitable for capturing CO2 in flue gas with large volumes and low partial pressures. Therefore, based on research on conventional ionic liquids, researchers have obtained functionalized ionic liquids with special functions by adjusting the combination of cations and anions or introducing specific functionalized groups. Studies have shown that the more basic groups (amino, hydroxyl, and amino acid groups, etc.) in the structure of a functionalized ionic liquid, the higher its absorption load, i.e., the stronger its CO2 capture capacity. However, pure ionic liquids are usually very viscous at room temperature; excessive viscosity is detrimental to the absorption and desorption of ionic liquids and their industrial applications. Therefore, researchers have drawn inspiration from organic amine solutions, dissolving ionic liquids in solvents to reduce their viscosity and increase the solubility and mass transfer efficiency of CO2 in solution. Most existing ionic liquids are generally soluble in water, but their solubility in organic solvents such as alcohols is low or even non-soluble. Especially after reacting with CO2, ionic liquids tend to form high-viscosity sols or even precipitate solids, making it extremely difficult to achieve liquid-liquid phase separation. This limits the selection and development prospects of ionic liquid solutions. Therefore, further exploration is needed in the research and development of novel ionic liquids.

[0004] In summary, ionic liquids possess advantages such as designable structure, tunable performance, and good stability, making them promising chemical absorbents for CO2 capture technology. Based on current research, this invention aims to develop a novel functionalized ionic liquid with good solubility, high absorption capacity, and low regeneration energy consumption. This will increase the diversity of subsequent ionic liquid solution construction and provide new ideas for the future industrial application of ionic liquids. Summary of the Invention

[0005] This invention provides a novel functionalized ionic liquid with good solubility, strong stability and high absorption load, for capturing or separating CO2 from mixed gases.

[0006] The polyamine-functionalized ionic liquid described in this invention exhibits excellent absorption performance and low regeneration energy consumption. Furthermore, this novel functionalized ionic liquid demonstrates good solubility in solvents such as water, alcohols, and ethers, and exhibits high thermal stability. Dissolving this novel functionalized ionic liquid in solvents for CO2 capture overcomes the shortcomings of traditional ionic liquids, such as high viscosity, low absorption capacity, and limited solubility, providing a new approach for the future industrial applications of ionic liquids.

[0007] The technical solution adopted by this invention to solve its technical problem is:

[0008] A polyamine-functionalized ionic liquid, whose molecular composition is tetraethylenepentamine-caprolactam salt, has the molecular formula [TEPAH][CPL] and its structural formula is shown in Formula I:

[0009]

[0010] Formula I

[0011] This invention also provides a novel method for preparing functionalized ionic liquids, which is simple to prepare and easy to operate and implement.

[0012] The method for preparing the novel functionalized ionic liquid includes the following steps:

[0013] The first step is to dissolve tetraethylenepentamine and caprolactam separately in anhydrous ethanol, and then stir with a magnetic stirrer until the solution is clear.

[0014] The second step involves mixing equal volumes of tetraethylenepentamine solution and caprolactam solution, and then heating the mixture at 1000–2000 rpm. -1 (1000~1500r·min -1 The reaction was carried out at a constant temperature for 18-30 h under stirring at a certain speed.

[0015] The third step involves removing unreacted raw materials and excess ethanol from the ionic liquid by vacuum distillation to obtain a novel functionalized ionic liquid, tetraethylenepentamine-caprolactam salt, namely [TEPAH][CPL].

[0016] In the first step, the molar ratio of tetraethylenepentamine to caprolactam is 2:1 to 1:2, and most preferably, the molar ratio of tetraethylenepentamine to caprolactam is 1:1. The concentration of anhydrous ethanol is 2-3 mol·L⁻¹. -1 .

[0017] In the second step, the constant temperature reaction conditions are 30~50℃. The optimal reaction temperature is set at 40℃, and the reaction time lasts for 24 hours.

[0018] In the third step, the conditions for vacuum distillation are as follows: three vacuum distillations at 60-75°C, each lasting 1.5-2 hours until constant weight is achieved. Preferably, the distillation temperature is 60°C, with 10% of the original volume of anhydrous ethanol added between each distillation.

[0019] In this invention, the cation used to synthesize the novel functionalized ionic liquid is a polyamine, TEPA. TEPA contains multiple amino groups, ensuring a high absorption capacity. Furthermore, the primary amine in TEPA has stronger reactivity than the secondary amine and is more readily combined with anions. The anion is a cyclic amide, CPL. The amide in CPL is weakly acidic and can form a salt compound with TEPA. Simultaneously, due to steric hindrance, CPL facilitates the regeneration of the ionic liquid after CO2 absorption saturation. The molar ratio of TEPA to CPL is 1:1, ultimately producing the product with the structure shown in Formula I, namely the functionalized ionic liquid tetraethylenepentamine-caprolactam salt [TEPAH][CPL]. The specific reaction equation is as follows:

[0020]

[0021] In this invention, when the novel functionalized ionic liquid is used as an absorbent, it can be dissolved in different solvents such as water, alcohol and ether to form an absorbent liquid, which is used to capture or separate CO2 in a mixed gas.

[0022] The volume percentage of CO2 in the mixed gas is 10%~15%. The mixed gas is passed into a solution containing a novel functionalized ionic liquid, and after the reaction, a CO2-saturated solution is obtained. The saturated solution is then regenerated by heating.

[0023] Since CO2 capture technology is generally applied after denitrification and desulfurization processes, the gas temperature will have a certain impact on the absorption solution. Therefore, the preferred gas temperature is 30~60℃.

[0024] The concentration of the novel functionalized ionic liquid in the ionic liquid solution can be adjusted according to actual needs. The saturated solution can be regenerated by heating, and the regenerated solution can be recycled. The regeneration conditions for the saturated solution are: regeneration temperature of 100~120℃ and regeneration time of 30~120min.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] Traditional organic amine MEAs are prone to oxidation, degradation, foaming, and strong corrosiveness, while conventional ionic liquids have low absorption capacity, limited solubility, and high viscosity. This invention develops a novel functionalized ionic liquid containing multiple amine groups, exhibiting highly efficient CO2 absorption performance. Simultaneously, this ionic liquid demonstrates strong stability and good solubility in various solvents such as water, alcohols, and ethers, increasing the diversity of subsequent ionic liquid solution construction. This novel functionalized ionic liquid overcomes the shortcomings of traditional organic amines and ionic liquids, providing new ideas for the future industrial application of ionic liquids, thus facilitating their industrial promotion.

[0027] The novel functionalized ionic liquid of this invention, used as a CO2 absorbent, exhibits excellent solubility in solvents such as water, alcohols, and ethers. The resulting ionic liquid solution can be used to capture or separate CO2 from gases. This absorbent not only possesses high CO2 absorption capacity but also exhibits good stability and reusability, and is easily regenerated with low regeneration energy consumption. It effectively overcomes the shortcomings of traditional organic amines and conventional ionic liquids in CO2 absorption, providing a new approach for the future industrial application of ionic liquids. Attached Figure Description

[0028] Figure 1 Thermogravimetric analysis (TGA) curve of the novel functionalized ionic liquid [TEPAH][CPL] of this invention;

[0029] Figure 2 This is a comparison chart of the absorption performance of the novel functionalized ionic liquid solution of the present invention with MEA and conventional ionic liquid solutions;

[0030] Figure 3 This is a comparison chart of the regeneration energy consumption of the novel functionalized ionic liquid solution and the MEA solution of the present invention. Detailed Implementation

[0031] In industrial applications, due to the large volume of actual flue gas and the heat it carries, which alters the temperature of the absorption solution, the temperature of the absorption solution can be assumed to equal the flue gas temperature once the system stabilizes. Therefore, in the following embodiments, a water bath is used to control the temperature of the absorption solution to reflect the temperature of the test gas.

[0032] Example 1: Synthesis of Novel Functionalized Ionic Liquids

[0033] The first step involved dissolving tetraethylenepentamine (TEPA) and caprolactam (CPL) separately in anhydrous ethanol to prepare a 2.5 mol·L⁻¹ solution. -1 Ethanol solution: Equal volumes of TEPA ethanol solution and CPL ethanol solution were mixed, and the mixture was heated at 1500 r·min. -1 The reaction was carried out at a constant temperature of 40°C for 24 hours with stirring at a certain speed.

[0034] The second step involves vacuum distillation of the reacted solution at 60°C for 1.5 h until constant weight. Then, 10% anhydrous ethanol is added, and the solution is distilled again at 60°C for 1.5 h. This process is repeated three times to remove unreacted raw materials and excess ethanol from the ionic liquid. The resulting novel functionalized ionic liquid, tetraethylenepentamine-caprolactam salt, is obtained as [TEPAH][CPL].

[0035] In this invention, the cation used to synthesize the novel functionalized ionic liquid is a polyamine, TEPA. TEPA contains multiple amine groups, ensuring a high absorption capacity. Furthermore, the primary amine in TEPA is more reactive than the secondary amine and more readily binds to the anion. The anion is CPL, which contains a cyclic amide structure. CPL is weakly acidic and can form a salt compound with TEPA. The specific reaction equation for this novel functionalized ionic liquid is as follows:

[0036]

[0037] To further confirm that the reactant is indeed a functionalized ionic liquid [TEPAH][CPL], rather than a mixture of the two raw materials, the reaction product was characterized by thermogravimetric analysis and compared with TEPA. The results are as follows: Figure 1 As shown. By Figure 1 The results show that [TEPAH][CPL] and TEPA lose 10% of their weight at temperatures of 198.5℃ and 142.8℃, respectively, while [TEPAH][CPL] and TEPA lose 1.7% and 7.8% of their weight, respectively, at 120℃. These results indicate that the product after the reaction is a new substance distinct from TEPA, rather than a mixture of the two. Furthermore, [TEPAH][CPL] exhibits higher thermal stability than TEPA.

[0038] Example 2: Use of novel functionalized ionic liquids as CO2 absorbents

[0039] [TEPAH][CPL] was dissolved in a mixed solution of ethylene glycol (EG) and diethylene glycol dimethyl ether (DGDE) to prepare a 0.5 mol·L⁻¹ solution. -1 The ionic liquid solution was placed in a constant temperature water bath at 40°C until it reached the set temperature of 40°C, and then set aside for later use.

[0040] Comparative Example 1:

[0041] Monoethanolamine (MEA) was dissolved in water to prepare a 5 mol·L⁻¹ solution. -1 MEA solution (i.e., MEA mass fraction of 30%). Place the MEA solution in a constant temperature water bath at 40℃ to bring it to the set temperature of 40℃, and set it aside for later use.

[0042] A 30 wt% MEA aqueous solution was used to absorb CO2 under the same conditions as Comparative Example 1.

[0043] Comparative Example 2:

[0044] Tetramethylamine-caprolactam salt ([N) 1111 [CPL]) was dissolved in water to prepare a 0.5 mol / L ionic liquid solution. This [N]1111 The [CPL] aqueous solution was placed in a constant temperature water bath at 40℃ to reach the set temperature of 40℃, and then set aside. [N] 1111 The structure of [CPL] is shown in Equation 2.

[0045] Using 0.5 mol·L -1 [N 1111 [CPL] aqueous solution absorbs CO2 under the same conditions as Comparative Example 2.

[0046]

[0047] Formula 2

[0048] Experimental Example 1: Absorption Performance of Novel Functionalized Ionic Liquid Solution [TEPAH][CPL] / EG / DGDE

[0049] At 40 °C, 25 mL of the [TEPAH][CPL] / EG / DGDE solution from Example 2, 30 wt% MEA aqueous solution from Comparative Example 1 and Comparative Example 2, and 0.5 mol·L⁻¹ were taken respectively. -1 [N 1111 [CPL] aqueous solutions were poured into separate 50 mL bubbling absorption flasks and placed in a 40 °C constant temperature water bath. A mixed gas containing 15% (V / V) CO2 was then introduced until the solution was saturated, with a gas flow rate of 240 mL / min. The outlet flow rate of the bubbling absorption flasks was measured using a soap film flow meter. The absorption rate and absorption load of the absorption solution were calculated based on the difference in gas inlet and outlet flow rates. The results are as follows: Figure 2 As shown.

[0050] Depend on Figure 2 It can be seen that MEA aqueous solution and [N] 1111 The absorption loads of the [CPL] aqueous solution were 0.52 mol / mol and 0.80 mol / mol, respectively, while the [TEPAH][CPL] / EG / DGDE solution was 1.86 mol / mol, significantly higher than the two solutions in the comparative example. This demonstrates that the novel functionalized ionic liquid in this invention has a significant advantage in CO2 absorption performance compared to traditional organic amines and conventional ionic liquids.

[0051] Experimental Example 2: Regeneration Energy Consumption of Novel Functionalized Ionic Liquid Solution [TEPAH][CPL] / EG / DGDE

[0052] Besides absorption performance, the regeneration energy consumption of absorbents is also an important indicator for evaluating their quality and economic efficiency. In CO2 capture, the regeneration energy consumption of absorbents accounts for approximately 25-40% of the total energy consumption of carbon capture. Excessive regeneration energy consumption will significantly increase the operating cost of carbon capture technology. Therefore, the industrial application potential of a novel absorbent is closely related to its regeneration energy consumption.

[0053] Take 200 mL of the [TEPAH][CPL] / EG / DGDE solution from Example 2 and place it in a closed vapor-liquid equilibrium reactor. Measure the pressure difference change of the absorbent solution after absorbing CO2 in the reactor at different temperatures (40~60℃) to obtain the vapor-liquid equilibrium (VLE) curve of the absorbent solution, and then calculate the heat of reaction of the solution. Measure the evaporation rate of the solvent and the specific heat capacity of the solution to calculate the sensible heat and latent heat data. Combining the values ​​of the heat of reaction, sensible heat, and latent heat, evaluate the regeneration energy consumption of the [TEPAH][CPL] / EG / DGDE solution. The results are as follows: Figure 3 As shown.

[0054] Depend on Figure 3 It is evident that the sensible heat gradually decreases and stabilizes with increasing CO2 desorption, while the latent heat gradually increases with CO2 desorption, but the latent heat value is very small. The regeneration energy consumption of the [TEPAH][CPL] / EG / DGDE solution first decreases and then increases with increasing CO2 desorption, reaching a minimum of 1.88 GJ / t CO2 at 1.20 mol / mol. From a desorption capacity of 0.30 to 1.40 mol / mol, the regeneration energy consumption of the solution is lower than that of the traditional MEA aqueous solution (3.80 GJ / t CO2) (Kim H., et al. Environmental Science & Technology, 2015, 49, 1478-1485.). This indicates that the regeneration energy consumption of the novel functionalized ionic liquid in this invention is lower than that of traditional organic amines, demonstrating significant energy-saving advantages.

[0055] The novel functionalized ionic liquids [TEPAH][CPL] were synthesized by the inventors. The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention.

Claims

1. The application of polyamine-functionalized ionic liquids in the capture or separation of carbon dioxide in mixed gases, characterized in that, The polyamine-functionalized ionic liquid has a molecule that is tetraethylenepentamine-caprolactam salt, with the molecular formula [TEPAH][CPL], and its structural formula is shown in Formula I: Formula I.

2. The application according to claim 1, characterized in that, The preparation method of the polyamine-functionalized ionic liquid includes the following steps: The first step is to dissolve tetraethylenepentamine and caprolactam separately in anhydrous ethanol, add magnetic stirring until the solution is clear, and obtain tetraethylenepentamine solution and caprolactam solution; The second step is to mix the tetraethylenepentamine solution and the caprolactam solution, and then heat the mixture at 1000~2000 r·min. -1 The reaction was carried out at a constant temperature for 18-30 h with stirring at a certain speed. The third step involves removing unreacted raw materials and excess ethanol from the product of the second step by vacuum distillation to obtain the polyamine-functionalized ionic liquid tetraethylenepentamine-caprolactam salt, namely [TEPAH][CPL].

3. The application according to claim 2, characterized in that, In the first step, the molar ratio of tetraethylenepentamine to caprolactam is 2:1 to 1:

2.

4. The application according to claim 2, characterized in that, In the first step, the concentration of the tetraethylenepentamine solution is 2-3 mol·L⁻¹. -1 The concentration of the caprolactam solution is 2-3 mol·L⁻¹. -1 .

5. The application according to claim 2, characterized in that, In the second step, the temperature of the isothermal reaction is 30~50℃.

6. The application according to claim 2, characterized in that, In the third step, the conditions for vacuum distillation are: vacuum distillation several times at 60~75℃, each time for 1.5~2 hours until constant weight.

7. The application according to claim 1, characterized in that, Includes the following steps: A mixed gas containing carbon dioxide is passed into a solution containing a polyamine-functionalized ionic liquid to obtain a CO2-saturated solution, which is then regenerated by heating.

8. The application according to claim 7, characterized in that, The solution containing the polyamine-functionalized ionic liquid absorbs CO2 at a temperature of 30~60℃; The volume percentage of CO2 in the carbon dioxide-containing mixed gas is 10% to 15%.

9. The application according to claim 7, characterized in that, The saturated solution is regenerated at a temperature of 100~120 °C for 30~120 min.

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