Carbon dioxide capture anhydrous phase change system capable of realizing high-purity recovery of ionic liquid and application

Abstract

This invention discloses an anhydrous phase change system for carbon dioxide capture and its application, enabling high-purity recovery of ionic liquids. The anhydrous phase change system comprises a primary amine, an organic solvent, and an ionic liquid. The primary amine is monoethanolamine with a concentration controlled at 30 wt%, the organic solvent is n-butanol, and the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate or 1-butyl-3-methylimidazolium hexafluorophosphate. The anhydrous phase change system remains homogeneous before absorbing carbon dioxide and separates into a CO2-rich phase, an organic-poor phase, and an ionic liquid phase after absorption. The CO2-rich phase is regenerated by high-temperature heating. The organic-poor phase and the ionic liquid phase, along with the regenerated rich phase, participate in the next absorption or are directly recovered. This anhydrous phase change system for carbon dioxide capture overcomes the problem of low absorption load in traditional anhydrous phase change absorbents, achieves phase separation to reduce regeneration energy consumption, and effectively solves the problem of high-purity recovery of ionic liquids, demonstrating broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide capture technology, specifically relating to an anhydrous phase change system for carbon dioxide capture that enables high-purity recovery of ionic liquids and its application. Background Technology

[0002] Currently, carbon capture, utilization, and storage (CCUS) technology is the main and effective way to achieve CO2 emission reduction. Among them, the most mature CO2 capture technology is post-combustion chemical absorption, which can rapidly reduce CO2 emissions. However, traditional chemical absorption methods mainly use aqueous solutions of organic amines. Although they have high absorption efficiency and high desorption purity, they suffer from drawbacks such as high regeneration energy consumption, equipment corrosion, and absorbent degradation. Developing new absorbents is key to the further development of chemical absorption methods.

[0003] Phase change absorbents, as third-generation absorbents, offer significant advantages in reducing regeneration energy consumption. Existing phase change absorbents, after absorbing CO2, separate into two phases: a CO2-rich phase and an organic-poor phase. Regeneration only requires the CO2-rich phase, greatly reducing the regeneration volume and thus energy consumption. In aqueous phase change absorbents, the CO2-rich phase in a saturated solution is typically aqueous. The latent heat of vaporization of water accounts for a large proportion of regeneration energy consumption, preventing a significant reduction in energy consumption. Compared to aqueous phase change absorbents, anhydrous phase change absorbents achieve even lower regeneration energy consumption by eliminating the latent heat of vaporization of water; however, anhydrous phase change absorbents have lower absorption load and absorption rate. Therefore, it is necessary to improve the absorption characteristics of anhydrous phase change absorbents.

[0004] Ionic liquids, as a novel and green solvent, possess characteristics such as low vapor pressure, low volatility, wide liquid temperature range, and excellent electrochemical performance, and have been proven to promote the absorption of CO2 by organic amines. However, ionic liquids are expensive, and high-purity recovery of ionic liquids will be key to their widespread application. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the main objective of this invention is to provide an anhydrous phase change system for carbon dioxide capture that can achieve high-purity recovery of ionic liquids, thereby solving the problems of poor carbon dioxide absorption characteristics and difficulty in high-purity recovery of ionic liquids in traditional anhydrous phase change absorbents.

[0006] Another objective of this invention is to provide the application of the above-mentioned anhydrous phase change system for carbon dioxide capture that enables high-purity recovery of ionic liquids in CO2 absorption.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides an anhydrous phase change system for carbon dioxide capture that enables high-purity recovery of ionic liquids. The system consists of a primary amine, an organic solvent, and an ionic liquid. The primary amine is monoethanolamine (MEA), the organic solvent is n-butanol, and the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroboric acid [Bmim][BF4] and / or 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim][PF6].

[0009] The anhydrous phase change system for carbon dioxide capture described in this invention uses primary amine as the main absorbent, organic solvent as the phase-separating agent, and ionic liquid as the absorption promoter. These three components are mixed in different proportions to form a phase-separable anhydrous phase change absorbent, improving the absorption characteristics of the amine solution while maintaining phase separation. Compared to traditional phase change absorbents that only separate into two phases, this anhydrous phase change system remains a transparent homogeneous solution before CO2 absorption and separates into three phases after CO2 absorption: a CO2-rich phase, an organic-poor phase, and an ionic liquid phase. Only the CO2-rich phase needs to be regenerated, while the ionic liquid phase can be directly recovered in high purity for reuse, effectively solving the problem of ionic liquid recovery.

[0010] The phase separation principle of the anhydrous phase change system for carbon dioxide capture that enables high-purity recovery of ionic liquids in this invention is as follows: The precipitation of the CO2-rich phase is due to the reaction of amine liquid with CO2 to form carbamate, which is separated from the organic solvent n-butanol by the salting-out effect; while the precipitation of ionic liquids is the combined effect of salting-out effect and MEA solubilizing effect. Ionic liquids [Bmim][BF4] and [Bmim][PF6] are slightly soluble or even insoluble in n-butanol. Only after the addition of MEA can they be uniformly distributed in n-butanol. As the absorption process proceeds, MEA is consumed, the solubilizing effect weakens, and the ionic liquid precipitates out. This provides a new approach for the efficient utilization and high-purity recovery of ionic liquids.

[0011] Furthermore, the mass fraction of the main absorbent MEA in the anhydrous phase change system is fixed at 30 wt%, the mass fraction of the ionic liquid varies from 2.5 wt% to 10 wt%, and the remainder is the organic solvent n-butanol.

[0012] Furthermore, the specific mass fractions of the ionic liquids are: [Bmim][BF4] is 7.5wt%-10wt%, and [Bmim][PF6] is 2.5wt%-10wt%.

[0013] Furthermore, the anhydrous phase change system exhibits phase separation characteristics: it remains homogeneous before absorbing carbon dioxide, and after absorbing carbon dioxide, it separates into three phases, including a CO2-rich phase, an organic-poor phase, and an ionic liquid phase.

[0014] Furthermore, the volume of the CO2-rich phase accounts for 30%-40% of the total volume.

[0015] This invention also provides the application of the above-mentioned anhydrous phase change system for carbon dioxide capture that enables high-purity recovery of ionic liquids in CO2 absorption. MEA is used as the main absorbent, n-butanol as the phase-separating agent, and the ionic liquids [Bmim][BF4] or [Bmim][PF6] as the absorption promoter. These three components are mixed in different proportions to form an anhydrous phase change absorbent capable of phase separation. This absorbent is used to absorb gases with a CO2 volume fraction of 5%-50%, at an absorption temperature of 40°C and a desorption temperature of 120°C, achieving both phase change and CO2 capture.

[0016] Compared with traditional anhydrous phase change absorbents, this invention uses ionic liquid as an absorption promoter. While ensuring the phase change characteristics of the system, it improves the absorption characteristics of the absorbent, increases the absorption load by 12%-23%, and accelerates the absorption rate by 15%-25%. After absorbing CO2, due to the combined effects of salting out and solubilization, the homogeneous solution separates into three phases—a CO2-rich phase, an organic-poor phase, and an ionic liquid phase. The precipitation of the high-purity ionic liquid phase can effectively solve the problem of difficult ionic liquid recovery, realize the high-purity recovery of ionic liquid, which is crucial for the reuse of ionic liquid and is more conducive to industrial promotion. Attached Figure Description

[0017] Figure 1 The images show a comparison of the phase separation of Examples 1 and 2 with those of Comparative Examples 1 and 2.

[0018] Figure 2 The Fourier transform infrared (FTIR) results are for the ionic liquid phases in Examples 1 and 2.

[0019] Figure 3 The changes in CO2 absorption load over time are shown in Examples 1 and 2, and Comparative Examples 1 and 2.

[0020] Figure 4 Examples 1 and 2 show the absorption rate, absorption load, and enhancement results compared to Comparative Example 1 under different ionic liquids. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1

[0023] This embodiment provides an anhydrous phase change system for carbon dioxide capture that enables high-purity recovery of ionic liquids. The system consists of a primary amine, an organic solvent, and an ionic liquid. The primary amine is MEA, the organic solvent is n-butanol, and the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroboric acid [Bmim][BF4]. The mass fraction of the main absorbent MEA is fixed at 30 wt%, the mass fractions of [Bmim][BF4] are 7.5 wt% and 10 wt%, respectively, and the remainder is the organic solvent n-butanol.

[0024] This anhydrous phase change system for carbon dioxide capture remains homogeneous before absorbing carbon dioxide and separates into three phases after absorption: a CO2-rich phase, an organic-poor phase, and an ionic liquid phase. Only the CO2-rich phase needs to be thermally desorbed at 120°C, which greatly reduces the desorption energy consumption. The absorption temperature is 40°C, and the system absorbs gas with a CO2 volume fraction of 10%.

[0025] Example 2

[0026] This embodiment provides an anhydrous phase change system for carbon dioxide capture that enables high-purity recovery of ionic liquids. The system consists of a primary amine, an organic solvent, and an ionic liquid. The primary amine is MEA, the organic solvent is n-butanol, and the ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim][PF6]. The main absorbent MEA has a fixed mass fraction of 30 wt%, and the mass fractions of [Bmim][PF6] are 2.5 wt%, 5 wt%, 7.5 wt%, and 10 wt%, respectively. The remainder is the organic solvent n-butanol, and the rest is the same as in Example 1.

[0027] Comparative Example 1

[0028] This comparative example uses a 30wt% MEA-n-butanol anhydrous solution, which separates into two phases after absorbing CO2: a CO2-rich phase and an organic-poor phase.

[0029] Comparative Example 2

[0030] This comparative example uses a 30wt% MEA-water solution, which does not separate after absorbing CO2.

[0031] I. Phase separation of systems after CO2 absorption in Examples 1 and 2 and Comparative Examples 1 and 2

[0032] Method: 30g of the following absorbents were placed in a bubbling absorption device: MEA-n-butanol-[Bmim][BF4] anhydrous phase change absorbent from Example 1, MEA-n-butanol-[Bmim][PF6] anhydrous phase change absorbent from Example 2, MEA-n-butanol anhydrous solution from Comparative Example 1, and MEA-aqueous solution from Comparative Example 2. The absorption temperature of the bubbling absorption device was controlled at 40°C by a water bath. A gas containing 10% CO2 volume fraction was introduced until the absorbent was saturated. The saturated absorbent was then allowed to stand for 24 hours to separate the phases, and the phase separation of different absorbents was obtained. The components of the phase separation were qualitatively analyzed by Fourier transform infrared spectroscopy.

[0033] The results are as follows Figure 1 As shown, Examples 1 and 2 both separated into three phases after absorbing CO2, while Comparative Example 1 only separated into two phases: the milky white phase was the CO2-rich phase, and the transparent solution was the organic-poor phase. Comparative Example 2 did not separate into phases after absorbing CO2. Compared to Comparative Example 1, the saturated solutions of Examples 1 and 2 separated into three phases. The additional phase shown in the diagram was analyzed using Fourier transform infrared spectroscopy (FTIR), and the results are as follows. Figure 2 As shown in the diagram, one phase in the block diagram has been proven to be an ionic liquid phase, thereby enabling high-purity recovery of the ionic liquid. In Example 1, the ionic liquid phase appears between the organic-poor phase and the CO2-rich phase, while in Example 2, the ionic liquid phase appears at the bottom of the CO2-rich phase.

[0034] The precipitation of the three phases is mainly due to the combined effects of the salting-out effect of carbamate and the solubilizing effect of MEA. MEA reacts with CO2 to form carbamate, which precipitates out of the organic solvent due to salting-out, forming a CO2-rich phase. Ionic liquids [Bmim][BF4] and [Bmim][PF6] can exist stably and uniformly in the organic solvent with the solubilizing effect of MEA. However, as MEA is consumed, the solubilizing effect weakens, and the ionic liquids gradually precipitate to form an ionic liquid phase. The precipitation of the ionic liquid phase demonstrates that the anhydrous phase change system of this invention can achieve high-purity recovery of ionic liquids.

[0035] II. Absorption characteristics and enhancement effects of CO2 absorption in the systems of Examples 1 and 2 and Comparative Examples 1 and 2

[0036] Method: 30g of each of the following absorbents were placed in a bubbling absorption device: MEA-n-butanol-[Bmim][BF4] anhydrous phase change absorbent from Example 1, MEA-n-butanol-[Bmim][PF6] anhydrous phase change absorbent from Example 2, MEA-n-butanol anhydrous solution from Comparative Example 1, and MEA-aqueous solution from Comparative Example 2. The absorption temperature of the bubbling absorption device was controlled at 40°C by a water bath. A gas containing 10% CO2 volume fraction was introduced until the absorbent was saturated. The CO2 content in the tail gas was monitored to obtain the change in absorption rate of different absorbents over time. The absorption characteristics of the absorbents were obtained by integrating the relationship between absorption rate and time. By comparing with Comparative Example 1, the absorption enhancement factor values, absorption load enhancement factor E1, and absorption rate enhancement factor E2 of the absorbents in Examples 1 and 2 were obtained. This allowed for the determination of the enhancement effect of the anhydrous phase change system for carbon dioxide capture that enables high-purity recovery of ionic liquids in this invention. When the enhancement factor is greater than 1, it indicates that the ionic liquid has the function of improving absorption characteristics.

[0037] The results are as follows Figure 3 As shown, the absorption load of Examples 1, 2, Comparative Example 1, and Comparative Example 2 changes over time. Examples 1 and 2 have higher absorption loads and absorption rates than the comparative examples, and can approach saturation more quickly, which can effectively improve the absorption characteristics of traditional absorbents. Figure 4 The specific enhancement effect is illustrated by the enhancement factors. The enhancement factors E1 and E2 in Examples 1 and 2 are both greater than 1 and change with the concentration of the ionic liquid, but are always greater than 1. This proves that the anhydrous phase change system proposed in this invention improves the absorption characteristics of the absorbent, increases the absorption load by 12%-23%, and accelerates the absorption rate by 15%-25%. It has excellent absorption characteristics while ensuring three-phase separation.

[0038] The above are merely preferred embodiments of the present invention, but the present invention should not be limited to the content disclosed in these embodiments. Therefore, any equivalents or modifications made without departing from the spirit of the present invention fall within the scope of protection of the present invention.

Claims

1. A carbon dioxide capture anhydrous phase change system capable of high purity recovery of ionic liquid, characterized in that, The anhydrous phase change system for carbon dioxide capture consists of a primary amine, an organic solvent, and an ionic liquid. The primary amine has a mass fraction of 30 wt%, the ionic liquid has a mass fraction of 2.5 wt%-10 wt%, and the remainder is an organic solvent. The primary amine is monoethanolamine, the organic solvent is n-butanol, and the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroboric acid [Bmim][BF4] and / or 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim][PF6].

2. The anhydrous phase change system for carbon dioxide capture capable of high-purity recovery of ionic liquids according to claim 1, characterized in that, The ionic liquid [Bmim][BF4] has a mass fraction of 7.5wt%-10wt%, and the ionic liquid [Bmim][PF6] has a mass fraction of 2.5wt%-10wt%.

3. The anhydrous phase change system for carbon dioxide capture capable of high-purity recovery of ionic liquids according to claim 1, characterized in that, The anhydrous phase change system for carbon dioxide capture remains homogeneous before absorbing carbon dioxide, and separates into three phases after absorbing carbon dioxide, including a CO2-rich phase, an organic-poor phase, and an ionic liquid phase.

4. The anhydrous phase change system for carbon dioxide capture capable of high-purity recovery of ionic liquids according to claim 3, characterized in that, The volume of the CO2-rich phase accounts for 30%-40% of the total volume.

5. The anhydrous phase change system for carbon dioxide capture capable of high-purity recovery of ionic liquids according to claim 3, characterized in that, The CO2-rich phase is regenerated by high-temperature heating, and the organic-poor phase and ionic liquid phase, together with the regenerated rich phase, participate in the next absorption or direct recovery.

6. The anhydrous phase change system for carbon dioxide capture capable of high-purity recovery of ionic liquids according to claim 3, characterized in that, The ionic liquid phase is a high-purity ionic liquid component.

7. The application of the anhydrous phase change system for carbon dioxide capture capable of high-purity recovery of ionic liquids as described in any one of claims 1-6, characterized in that, It is used to absorb gases with a CO2 volume fraction of 5%-50%, with primary amine as the main absorbent, n-butanol as the organic solvent as the phase separation agent, and ionic liquids [Bmim][BF4] or [Bmim][PF6] as the absorption promoter.

8. The application of the anhydrous phase change system for carbon dioxide capture capable of high-purity recovery of ionic liquids according to claim 7, characterized in that, The absorption temperature is 40℃ and the desorption temperature is 120℃, achieving phase change and CO2 capture in the system.

Images