A low-temperature regenerable absorbent based on extractant-enhanced CO2 desorption reaction and its application

Abstract

This invention relates to a low-temperature regenerable absorbent and its application method based on an extractant-enhanced CO2 desorption reaction, belonging to the field of carbon capture and gas-liquid separation technology. The absorbent is composed of a fatty amine, an extractant, and water, and exhibits a two-phase separation state during CO2 capture. The core mechanism by which this absorbent enhances CO2 desorption is the extraction effect of the extractant on the regenerated fatty amine, and the self-extraction effect of the fatty amine migrating to the organic phase after regeneration to restore its initial polarity. During CO2 desorption, the absorbent utilizes the extraction effect to achieve the separation and transfer of regenerated products, promoting a positive shift in the desorption reaction equilibrium, thus possessing great potential to improve absorbent regeneration efficiency and reduce CO2 desorption temperature and regeneration energy consumption.

Description

Technical Field

[0001] This invention relates to a low-temperature regenerable absorbent and its application method based on extractant-enhanced CO2 desorption reaction, belonging to the field of carbon capture and gas-liquid separation technology. Background Technology

[0002] Carbon dioxide capture and storage (CCS) has become an indispensable technological approach to addressing climate change and the only means to achieve low-carbon utilization of fossil fuels. Among existing carbon capture methods, chemical absorption based on organic amine solutions has become one of the mainstream technologies due to its wide adaptability and mature process. However, the core bottleneck for its commercial development lies in the high energy consumption of the absorbent regeneration process. Therefore, developing efficient and low-energy absorbents has become one of the key breakthroughs for the large-scale promotion of chemical absorption carbon capture technology.

[0003] Novel absorbent systems, such as biphase absorbents, ionic liquids, and low-aqueous absorbents, can reduce regeneration energy consumption by 30%-50% through phase change regulation or solvent modification. However, their potential for further energy consumption control within commercial development is limited. This is because the desorption temperature of absorbents generally remains in the 120-140℃ range, leading to significant consumption and irreversible losses of high-grade steam in the system. The synergistic effect between desorption temperature and regeneration energy consumption optimization becomes key to significantly reducing system energy consumption. Lowering the absorbent desorption temperature to below 100℃ allows for absorbent regeneration driven by industrial waste heat (50-100℃), thereby significantly reducing the energy consumption of carbon capture systems and improving economic efficiency. Furthermore, the high viscosity of the CO2-rich solution in the aforementioned absorbents remains a common challenge restricting their industrial application. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a low-temperature regenerable absorbent based on an extractant-enhanced CO2 desorption reaction and its application. This absorbent is a mixture of aliphatic amines, an extractant, and water, exhibiting a two-phase separation state during CO2 capture. In its fresh state, the upper organic phase of the absorbent is a mixture of aliphatic amines and the extractant, while the lower phase is an aqueous phase. After CO2 saturation absorption, the aliphatic amines in the organic phase react with CO2 to generate carbamates and carbonates, significantly increasing their polarity and dissolving into the aqueous phase, resulting in a significant reduction in the volume of the upper organic phase. During CO2 desorption, the absorbed products are regenerated as aliphatic amines and migrate to the upper organic phase, restoring the organic phase volume to its pre-CO2 absorption state. The core mechanism of this absorbent's enhanced CO2 desorption is the extraction effect of the extractant on the regenerated aliphatic amines, and the self-extraction effect of the regenerated aliphatic amines migrating to the organic phase after regaining their initial polarity. The absorbent utilizes the extraction effect during CO2 desorption to achieve the separation and transfer of regenerated products, driving a positive shift in the desorption reaction equilibrium, thus possessing great potential to improve absorbent regeneration efficiency and reduce CO2 desorption temperature and regeneration energy consumption.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows.

[0006] A low-temperature regenerative absorbent based on extractant-enhanced CO2 desorption reaction, wherein the absorbent is composed of aliphatic amine, extractant and water, wherein the mass fraction of aliphatic amine in the absorbent is 10%~50% and the mass fraction of extractant is 10%~30%; The oil-water partition coefficient (Log P) of the fatty amine is 1.2~3.5; The extractant has a boiling point ≥100℃, an aqueous solubility ≤1%, and does not react chemically with CO2.

[0007] Preferably, the fatty amine is one or more of N,N'-di-tert-butylethylenediamine (DTBEDA), N,N-dimethylcyclohexylamine (DMCA), and 2-dibutylaminoethanol (DBAE).

[0008] Preferably, the extractant is one or more selected from tributyl phosphate (TBP), butyl acetate, amyl acetate, and isoamyl acetate.

[0009] Preferably, the mass fraction of fatty amines in the absorbent is 15% to 30%.

[0010] Preferably, the mass fraction of the extractant in the absorbent is 15% to 20%.

[0011] Preferably, the absorbent is suitable for capturing CO2 in a mixed gas containing CO2, with an absorption temperature of 25~60℃ and a typical CO2 loading of 0.80~1.50 mol CO2 / mol amine.

[0012] Preferably, after CO2 absorption saturation, the absorbent is extracted and regenerated by heating and desorption, with a regeneration temperature of 50~120℃ and a typical regeneration efficiency of over 89%; more preferably, the regeneration temperature is 70~90℃.

[0013] Preferably, the absorbent exists in two separate states before absorbing CO2: an upper organic phase and a lower aqueous phase. The upper organic phase consists of aliphatic amines and an extractant. After CO2 absorption, the aliphatic amines in the upper organic phase react with CO2 and dissolve into the lower aqueous phase, reducing the volume of the organic phase. After CO2 desorption, the absorption product is regenerated into aliphatic amines, which migrate to the upper organic phase through the combined effects of the extractant and the self-extraction of the aliphatic amines, increasing the volume of the organic phase and reversibly restoring it to its state before CO2 absorption.

[0014] An application of a low-temperature regenerable absorbent based on an extractant-enhanced CO2 desorption reaction is disclosed, wherein the absorbent is used in industrial chemical absorption carbon capture. Pretreated flue gas enters from the bottom of the absorption tower and reacts with the low-temperature regenerable absorbent at atmospheric pressure. After the reaction is complete, the flue gas exits from the top of the tower, and the low-temperature regenerable absorbent is recovered via a water washing tower. Fresh low-temperature regenerable absorbent is injected from the top of the absorption tower and reacts with carbon dioxide inside the tower to produce products such as carbonates and bicarbonates. Subsequently, the carbon dioxide-rich liquid exits from the bottom of the tower, is preheated by a lean-rich liquid heat exchanger, and is pumped to the top of a stripping tower for regeneration. During this process, carbon dioxide is released and, through condensation and separation, high-purity carbon dioxide is obtained for subsequent compression, storage, and transportation. The regenerated absorbent flows out from the bottom of the stripping tower, is cooled, and returned to the absorption tower for recycling. The heat required for the absorbent regeneration process is provided by a reboiler at the bottom of the stripping tower.

[0015] Beneficial effects This invention provides a low-temperature regenerable absorbent based on an extractant-enhanced CO2 desorption reaction and its application. The core mechanism of CO2 desorption enhancement is the extractant's extraction effect on aliphatic amines, and the self-extraction effect of the aliphatic amines migrating to the organic phase after regeneration to restore their initial polarity. The extraction effect drives the CO2 desorption reaction equilibrium towards the decomposition and separation of the absorption products, enabling efficient regeneration of the absorbent under low-temperature conditions, and possessing great potential to reduce the regeneration temperature and energy consumption of the absorbent.

[0016] The absorbent not only exhibits excellent CO2 capture performance, with a CO2 absorption loading of 0.80~1.50 mol CO2 / mol amine, but also achieves a regeneration efficiency of 89.86%~89.88% at 90℃. After CO2 saturation absorption, the absorbent remains a two-phase system, with the upper organic matter acting as the extractant, and the absorption products mainly uniformly dispersed in the aqueous phase, exhibiting a low solution viscosity.

[0017] The absorbent combines the advantages of high CO2 loading and low saturated viscosity, and its high regeneration efficiency under low temperature conditions provides a new solution for reducing absorbent regeneration energy consumption and matching low-grade industrial heat sources, which can significantly reduce the system energy consumption of CO2 capture in power plants, steel plants, cement plants and other facilities. Attached Figure Description

[0018] Figure 1 The phase change of TBP / DMCA low-temperature regenerable absorbent during CO2 capture.

[0019] Figure 2 The phase change of TBP / DTBEDA low-temperature regenerable absorbent during CO2 capture.

[0020] Figure 3A comparison chart of CO2 capture performance of different types of absorbents. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments.

[0022] In the following examples or comparative examples, the prepared absorbent is used for capture in a mixture containing CO2, and the method steps include: The first step is to bubble a mixture of CO2 into a three-necked flask containing an absorbent at a temperature of 25-60°C until the absorbent is saturated, at which point the bubbling of the CO2 mixture is stopped. The second step involves transferring the three-necked flask containing the absorbent obtained in the first step to an oil bath at a temperature of 50-120°C. The absorbent is then stirred until it is completely regenerated, at which point heating is stopped.

[0023] Example 1 This example provides a low-temperature regenerative absorbent based on an extractant-enhanced CO2 desorption reaction. The absorbent system consists of a fatty amine, an extractant, and water. The mass concentrations of the fatty amine N,N-dimethylcyclohexylamine (DMCA) and the extractant tributyl phosphate (TBP) are both 15%.

[0024] Example 2 This example provides a low-temperature regenerable absorbent based on an extractant-enhanced CO2 desorption reaction. The absorbent system consists of a fatty amine, an extractant, and water. The fatty amine N,N'-di-tert-butylethylenediamine (DTBEDA) and the extractant TBP both have a mass concentration of 15%.

[0025] Comparative Example 1 In this comparative example, the absorbent was composed of ethanolamine (MEA) and water, with an ethanolamine mass concentration of 30%. The absorbent was in a homogeneous state before, after, and after CO2 absorption, and its CO2 absorption capacity was only 0.5 mol CO2 / mol amine. Under the regeneration condition of 100℃, the regeneration efficiency was only 67.3%.

[0026] Prepare 50g of the absorbents from Examples 1 and 2, namely TBP / DMCA and TBP / DTBEDA, respectively, and transfer them to bubble absorption bottles. Place the absorption bottles in a constant temperature water bath at 40°C to maintain a constant temperature. Start the test in a mixed gas with a CO2 volume ratio of 15% until the absorbent reaches saturation. Then transfer the saturated absorbent to an oil bath and regenerate it at 90°C. Figure 1 and Figure 2The phase changes of TBP / DMCA and TBP / DTBEDA absorbents during CO2 capture are shown. It can be observed that in the fresh solvent state, both the TBP / DMCA and TBP / DTBEDA single-extraction systems exhibit a two-phase separation, with an organic phase on top and an aqueous phase on the bottom. After CO2 saturation absorption, the volume of the upper organic phase in these single-extraction systems significantly decreases, mainly due to the reaction of aliphatic amines DMCA and DTBEDA with CO2 to form carbamates and carbonates that dissolve in the lower aqueous phase, while the upper organic phase primarily consists of the extractant TBP. After CO2 desorption, the volume of the upper organic phase significantly increases, indicating that the extraction effect of TBP on DMCA and DTBEDA, as well as the self-extraction effect of DMCA and DTBEDA, promotes the transfer of regenerated aliphatic amines to the organic phase.

[0027] Figure 3 This study aimed to improve the CO2 capture performance of low-temperature regenerable absorbents based on extractants to enhance the CO2 desorption reaction. Compared to MEA absorbents, TBP / DTBEDA and TBP / DTBEDA absorbents exhibited superior CO2 absorption performance, with CO2 absorption loadings reaching 0.59 mol / mol and 0.81 mol / mol, respectively. Furthermore, both the TBP / DMCA and TBP / DTBEDA single-extraction systems demonstrated high CO2 desorption efficiencies of 89.86% and 89.88% respectively at a regeneration temperature of 90℃, significantly higher than the 67.3% desorption efficiency of MEA absorbents at 100℃. This indicates that the extractant is beneficial for achieving efficient regeneration of aliphatic amines under low-temperature conditions.

[0028] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A low-temperature regenerable absorbent based on extractant-enhanced CO2 desorption reaction, characterized in that: The absorbent is composed of a fatty amine, an extractant, and water, wherein the mass fraction of the fatty amine in the absorbent is 10% to 50%, and the mass fraction of the extractant is 10% to 30%. The oil-water partition coefficient of the fatty amine is 1.2~3.5; The extractant has a boiling point ≥100℃, an aqueous solubility ≤1%, and does not react chemically with CO2.

2. The low-temperature regenerative absorbent based on extractant-enhanced CO2 desorption reaction according to claim 1, characterized in that: The fatty amine is one or more of N,N'-di-tert-butylethylenediamine, N,N-dimethylcyclohexylamine, and 2-dibutylaminoethanol.

3. The low-temperature regenerative absorbent based on extractant-enhanced CO2 desorption reaction according to claim 1, characterized in that: The extractant is one or more of tributyl phosphate, butyl acetate, amyl acetate, and isoamyl acetate.

4. The low-temperature regenerative absorbent based on extractant-enhanced CO2 desorption reaction according to claim 1, characterized in that: The mass fraction of fatty amines in the absorbent is 15% to 30%.

5. The low-temperature regenerative absorbent based on extractant-enhanced CO2 desorption reaction according to claim 1, characterized in that: The mass fraction of the extractant in the absorbent is 15% to 20%.

6. The low-temperature regenerative absorbent based on extractant-enhanced CO2 desorption reaction according to claim 1, characterized in that: The absorbent is suitable for capturing CO2 in mixed gases containing CO2, with an absorption temperature of 25~60℃ and a typical CO2 loading of 0.80~1.50 mol CO2 / mol amine.

7. A low-temperature regenerative absorbent based on extractant-enhanced CO2 desorption reaction as described in claim 1 or 6, characterized in that: After CO2 absorption saturation, the absorbent is extracted and regenerated by heating and desorption. The regeneration temperature is 50~120℃, and the typical regeneration efficiency is over 89%.

8. The low-temperature regenerative absorbent based on extractant-enhanced CO2 desorption reaction according to claim 7, characterized in that: The regeneration temperature is 70~90℃.

9. The low-temperature regenerative absorbent based on extractant-enhanced CO2 desorption reaction according to claim 1, characterized in that: Before absorbing CO2, the absorbent exists in two separate states: an upper organic phase and a lower aqueous phase. The upper organic phase consists of aliphatic amines and an extractant. After CO2 absorption, the aliphatic amines in the upper organic phase react with CO2 and dissolve into the lower aqueous phase, reducing the volume of the organic phase. After CO2 desorption, the absorption products are regenerated into aliphatic amines, which migrate to the upper organic phase through the combined effects of the extractant's extraction effect and the aliphatic amine's self-extraction effect, increasing the volume of the organic phase and reversibly restoring it to its state before CO2 absorption.

10. The application of a low-temperature regenerable absorbent based on extractant-enhanced CO2 desorption reaction as described in any one of claims 1 to 9, characterized in that: The absorbent is used for carbon capture in industrial chemical absorption methods.

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