Phase behavior controllable absorbent for carbon dioxide capture and preparation method and application thereof

Abstract

The invention discloses a phase behavior controllable absorbent for carbon dioxide capture and a preparation method and application thereof, and belongs to the technical field of gas separation. The phase behavior controllable absorbent is in a homogeneous phase before absorbing CO2, liquid-liquid two phases are formed in the CO2 absorbing process, and CO2 is absorbed to be saturated and recovered to be in the homogeneous phase; the diethylenetriamine phase-splitting regulator comprises 20-35% of diethylenetriamine serving as a main agent, 15-35% of phase-splitting regulator and the balance of water, wherein the split-phase regulating agent is diethylaminoethanol and pentamethyldiethylenetriamine, and the mass ratio of the diethylaminoethanol to the pentamethyldiethylenetriamine is (1: 4)-(4: 1). The preparation method of the phase behavior controllable absorbent for carbon dioxide capture comprises the following steps: preparing the raw materials in proportion, and uniformly mixing to obtain the phase behavior controllable absorbent. The invention discloses application of the phase behavior controllable absorbent in treatment of carbon dioxide-containing gas and a method for capturing carbon dioxide by adopting the phase behavior controllable absorbent. According to the phase behavior controllable absorbent disclosed by the invention, the CO2 absorption rate is increased, the CO2 capture energy consumption is reduced, and the one-time investment of equipment is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas separation, and in particular relates to a phase-behavior controllable absorbent for carbon dioxide capture, and a preparation method and application thereof. Background Art

[0002] As the global warming problem intensifies, countries have pledged to work together to control global warming to within 1.5℃ above pre-industrial levels. To achieve the above temperature control goals, global carbon dioxide emissions must be reduced by more than 80% by 2050. Carbon capture, storage and utilization (CCUS) is a necessary means to achieve this goal. It is expected that CCUS will offset 10%-20% of current global carbon emissions by 2050. At present, chemical absorption is the most mature technology for industrial applications to capture CO2, but the high cost of CO2 capture limits the large-scale application of chemical absorption.

[0003] In order to reduce the energy consumption of CO2 capture by chemical absorption, researchers have developed a series of chemical absorbents with phase separation characteristics in order to achieve low-energy carbon capture. The more commonly used CO2 absorbents in the prior art are chemical absorbents with phase separation characteristics. They are homogeneous before absorbing CO2. After absorbing CO2, they form liquid-liquid or liquid-solid phases. Only the CO2-enriched phase enters the regeneration unit, reducing the processing capacity of the regeneration unit, thereby reducing the energy consumption of CO2 capture. The above absorbents need to be equipped with a phase separator due to phase separation when absorbing CO2, which increases the process and corresponding equipment and cannot be directly applied to existing devices. The Chinese patent application "An organic amine phase change absorbent and its application" (application number 202311180531.9, published on December 1, 2023) proposes an organic amine phase change absorbent, which includes an organic amine mixed solution, a phase separation inducer, an oxygen inhibitor and water. The organic amine mixed solution includes a mixed solution of N,N-diethylethanolamine and diethylenetriamine. The Chinese patent application "Anhydrous liquid-liquid phase change absorbent for capturing carbon dioxide" (application number 202210697935.4, published on December 29, 2023) proposes an anhydrous liquid-liquid phase change absorbent for absorbing carbon dioxide in flue gas. The absorbent is composed of primary amine, tertiary amine and organic solvent. The primary amine refers to diglycolamine, n-propanolamine or butanolamine. The tertiary amine is pentamethyldiethylenetriamine, tetramethylpropylenediamine or tetramethylethylenediamine, and the organic solvent is propylene glycol, 1,4-butanediol, 1,3-propylene glycol or ethylene glycol.

[0004] Another type of chemical absorbent with phase separation characteristics is homogeneous before and after absorbing CO2. Only during the desorption process, two phases are formed due to the increase in temperature. The amine in the upper liquid phase plays an extraction role, promoting the desorption of the absorbent, thereby reducing energy consumption. Based on the theory of thermal phase change, a series of phase change absorbents composed of lipophilic amines have been developed. Lipophilic amines generally have a large viscosity and have a greater impact on the CO2 absorption rate. Typical lipophilic amines include DMCA and dipropylamine (Zhang, J., Y. Qiao, and D. W. Agar, Intensification of low temperature thermomorphic biphasic amine solvent regeneration for CO2 capture. Chemical Engineering Research and Design, 2012. 90 (6): p. 743-749.).

[0005] However, the above absorbent has the problem of low carbon dioxide absorption rate, and because liquid-liquid or liquid-solid two-phases are formed after absorbing CO2, special liquid-liquid or liquid-solid separation equipment is required for separation before the absorbent is regenerated, which increases the process flow and requires large one-time equipment investment. Therefore, providing an absorbent with a high absorption rate and low equipment investment, which can be directly used on the basis of the original equipment, has become a problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0006] One of the purposes of the present invention is to provide a phase behavior controllable absorbent for carbon dioxide capture, which is homogeneous before absorbing CO2, forms liquid-liquid two-phases during the CO2 absorption process, and returns to homogeneous after absorbing CO2 to saturation. The phase behavior characteristics of homogeneous phase-liquid-liquid two-phase-homogeneous phase during the CO2 absorption process of the absorbent are utilized to increase the CO2 absorption rate of the absorbent, thereby improving its absorption performance and reducing the CO2 capture energy consumption, and reducing the one-time investment of the equipment.

[0007] The second object of the present invention is to provide a method for preparing the absorbent with controllable phase behavior.

[0008] The third object of the present invention is to provide an application of the absorbent with controllable phase behavior.

[0009] A fourth object of the present invention is to provide a method for capturing carbon dioxide using the phase behavior controllable absorbent.

[0010] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0011] The present invention discloses a phase-behavior controllable absorbent for carbon dioxide capture, wherein the phase-behavior controllable absorbent is homogeneous before absorbing CO2, forms liquid-liquid two phases during the CO2 absorption process, and recovers to a homogeneous phase after absorbing CO2 to saturation;

[0012] The phase behavior controllable absorbent comprises, by weight, 20-35% of a main agent, diethylenetriamine, 15-35% of a phase regulating agent, and the remainder is water;

[0013] The phase separation regulator is diethylaminoethanol and pentamethyldiethylenetriamine, and the mass ratio thereof is 1:4 to 4:1.

[0014] In some embodiments of the present invention, the phase behavior controllable absorbent comprises 20-30% of diethylenetriamine as a main agent, 20-35% of a phase regulating agent, and the remainder is water, calculated on a mass basis.

[0015] In some embodiments of the present invention, the phase behavior controllable absorbent is homogeneous before absorbing CO2. During the CO2 absorption process, a liquid-liquid two phase begins to form when the CO2 load is 0.8-2.5 mol / kg. The CO2 absorption continues, and the homogeneous phase is restored when the CO2 load reaches 4.0-5.0 mol / kg.

[0016] In one embodiment of the present invention, the phase behavior controllable absorbent is homogeneous before absorbing CO2. During the CO2 absorption process, the CO2 load begins to form liquid-liquid two phases at 0.95 mol / kg. The CO2 absorption continues, and the CO2 load reaches 4.59 mol / kg and the homogeneous phase is restored.

[0017] In one embodiment of the present invention, the phase behavior controllable absorbent is homogeneous before absorbing CO2. During the CO2 absorption process, the CO2 load begins to form liquid-liquid two phases at 1.41 mol / kg. The CO2 absorption continues, and the CO2 load reaches 4.37 mol / kg and the homogeneous phase is restored.

[0018] In one embodiment of the present invention, the phase behavior controllable absorbent is homogeneous before absorbing CO2, and during the CO2 absorption process, the CO2 load begins to form liquid-liquid two phases at 2.24 mol / kg, and the CO2 absorption continues, and the CO2 load reaches 4.25 mol / kg to restore the homogeneous phase. In some embodiments of the present invention, the phase behavior controllable absorbent is homogeneous before absorbing CO2, and the CO2 partial pressure rises to 2-5 kPa to begin to form liquid-liquid two phases, and the CO2 partial pressure is further increased to 7-13 kPa to restore the homogeneous phase.

[0019] In one embodiment of the present invention, the phase behavior controllable absorbent is homogeneous before absorbing CO2, and the CO2 partial pressure rises to 2.6 kPa to begin to form liquid-liquid two phases, and the CO2 partial pressure is further increased to 12.5 kPa to restore the homogeneous phase.

[0020] In one embodiment of the present invention, the phase behavior controllable absorbent is homogeneous before absorbing CO2, and the CO2 partial pressure rises to 3.2 kPa to begin to form liquid-liquid two phases, and the CO2 partial pressure is further increased to 8.7 kPa to restore the homogeneous phase.

[0021] In one embodiment of the present invention, the phase behavior controllable absorbent is homogeneous before absorbing CO2, and the CO2 partial pressure rises to 4.7 kPa to begin to form liquid-liquid two phases, and the CO2 partial pressure is further increased to 7.1 kPa to restore the homogeneous phase.

[0022] The method for preparing the above-mentioned absorbent with controllable phase behavior for capturing carbon dioxide disclosed in the present invention comprises the following steps: preparing various raw materials in proportion and mixing them evenly to obtain the absorbent with controllable phase behavior.

[0023] The application of the above-mentioned phase-behavior controllable absorbent for capturing carbon dioxide disclosed in the present invention is application in treating carbon dioxide-containing gas.

[0024] In some embodiments of the present invention, the volume fraction of carbon dioxide in the carbon dioxide-containing gas is 7% to 20%.

[0025] The present invention discloses a method for capturing carbon dioxide, which uses the above-mentioned absorbent with controllable phase behavior to absorb carbon dioxide-containing gas.

[0026] In some embodiments of the present invention, after the controllable phase behavior absorbent absorbs CO2 until saturation and homogeneity is restored, the CO2 is desorbed by heating, and the desorbed and regenerated controllable phase behavior absorbent is returned to the absorption process for recycling for CO2 absorption.

[0027] In the phase behavior controllable absorbent of the present invention, the main agent diethylenetriamine and the phase regulator have relatively different oil-water partition coefficients. The main agent is a relatively hydrophilic polyamine, and when the CO2 partial pressure is low, it mainly absorbs CO2 to produce amino carbonates; the phase regulator is a relatively hydrophobic tertiary amine, which reacts slowly with CO2 and reacts less with CO2 at low partial pressures. The phase separation process is as follows: when the CO2 concentration is low, the main agent absorbs CO2, and the generated amino carbonate salt precipitation effect precipitates the relatively hydrophobic phase regulator to form a liquid-liquid two-phase; as the CO2 partial pressure increases, although the main agent continues to absorb CO2, the phase regulator reacts more with CO2, reducing the originally precipitated phase regulator to form a homogeneous phase.

[0028] The change in pressure does not directly affect the solubility of the substance, but rather the substance reacts with CO2 to form a salt that is more soluble in water.

[0029] If the CO2 partial pressure remains unchanged or decreases, the homogeneous absorbent will re-form into two phases. For example, the absorbent will be homogeneous after absorbing 15% CO2 and saturated; if purged with N2, the homogeneous absorbent will have liquid-liquid two phases.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The absorbent of the present invention has the characteristic of controllable phase separation. By adjusting the CO2 load and CO2 partial pressure during the carbon dioxide capture process, the phase behavior of the absorbent is manifested as homogeneous phase-liquid-liquid phase separation-homogeneous phase, thereby achieving controllable phase behavior.

[0032] The phase behavior controllable absorbent of the present invention exhibits phase behavior characteristics of homogeneous phase-liquid-liquid two-phase-homogeneous phase during the CO2 absorption process, realizes gas-liquid-liquid three-phase mass transfer enhancement in the liquid-liquid two-phase stage, increases the CO2 absorption rate, and further improves its absorption performance and reduces CO2 capture energy consumption.

[0033] The phase behavior controllable absorbent of the present invention can be directly used on the original absorption and desorption equipment without the need to configure separate liquid-liquid or liquid-solid separation equipment. Compared with the industrial application of other phase behavior controllable absorbents, the one-time equipment investment is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of phase change during the process of absorbing carbon dioxide by the absorbent of the present invention.

[0035] Figure 2 This is a comparison chart of the CO2 absorption rate of Experimental Example 1. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention are described to facilitate those skilled in the art to understand the present invention, but it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0037] Example 1

[0038] This example discloses the preparation of the phase behavior controllable absorbent of the present invention, which is as follows: diethylenetriamine (DETA), diethylaminoethanol (DEEA), pentamethyldiethylenetriamine (PMDETA) and water are mixed to prepare 80g of absorbent, wherein the mass fraction of DETA is 20%, the mass fraction of DEEA and PMDETA is 35%, the mass ratio of DEEA to PMDETA is 1:2.5, and the mass fraction of water is 45%.

[0039] The absorbent prepared in this example absorbs a mixed gas with a CO2 content of 15v% at 40°C. The results show that the absorbent is homogeneous before absorbing CO2; it forms a liquid-liquid two-phase when absorbing CO2 to 0.95mol / kg, and the corresponding CO2 partial pressure is 2.6kPa; it continues to absorb CO2 to a load of 4.59mol / kg and recovers to a homogeneous phase, and the corresponding CO2 partial pressure is 12.5kPa. Phase behavior during CO2 absorption: homogeneous phase-liquid-liquid two-phase-homogeneous phase.

[0040] Comparative Example 1

[0041] Different absorbents were prepared and each absorbent was used to absorb a mixed gas with a CO2 content of 15v% at 40°C to investigate its phase behavior during the CO2 absorption process. The composition ratio of each absorbent and its phase behavior during the CO2 absorption process are shown in Table 1.

[0042] Table 1 Composition of different absorbents and their phase behavior during CO2 absorption

[0043] Serial number Main agent, content Phase regulator, content Phase separation regulator ratio <![CDATA[Phase behavior of CO2 absorption]]> 1 MEA, 20% DEEA and PMDETA, 35% 1:2.5 Always uniform 2 DETA, 20% MDEA, 35% - Always uniform 3 DETA, 10% DEEA and PMDETA, 35% 1:2.5 Always uniform 4 DETA, 20% DEEA, 40% - Homogeneous-liquid-liquid two-phase 5 DETA, 20% PMDETA, 35% - Homogeneous-liquid-liquid two-phase 6 DETA, 20% DEEA and PMDETA, 35% 1:6 Homogeneous-liquid-liquid two-phase 7 DETA, 20% DEEA and PMDETA, 50% 1:1 Homogeneous-liquid-liquid two-phase

[0044] In Table 1, the balance of each absorbent is water.

[0045] Example 2

[0046] This embodiment discloses the preparation of the phase behavior controllable absorbent of the present invention, which is specifically as follows: DETA, DEEA, PMDETA and water are mixed to prepare 80g of absorbent, wherein the mass fraction of DETA is 30%, the sum of the mass fractions of DEEA and PMDETA is 20%, the mass ratio of DEEA and PMDETA is 3:1, and the mass fraction of water is 50%.

[0047] The absorbent prepared in this example absorbs a mixed gas with a CO2 content of 15% at 40°C. The results show that the absorbent is homogeneous before absorbing CO2; when absorbing CO2 to 1.41 mol / kg, liquid-liquid two phases are formed, and the corresponding CO2 partial pressure is 3.2 kPa; CO2 is continuously absorbed until the load is 4.37 mol / kg and the homogeneous phase is restored, and the corresponding CO2 partial pressure is 8.7 kPa. Phase behavior during CO2 absorption: homogeneous phase-liquid-liquid two phases-homogeneous phase.

[0048] Comparative Example 2

[0049] DETA, DEEA, PMDETA and water are mixed to prepare 80g of absorbent, wherein the mass fraction of DETA is 30%, the sum of the mass fractions of DEEA and PMDETA is 12%, the mass ratio of DEEA and PMDETA is 3:1, and the mass fraction of water is 58%.

[0050] The absorbent prepared in this comparative example was used to absorb a mixed gas with a CO2 content of 15% at 40° C. The results showed that the absorbent was always in a homogeneous phase during the CO2 absorption process.

[0051] Example 3

[0052] This embodiment discloses the preparation of the phase behavior controllable absorbent of the present invention, which is specifically as follows: DETA, DEEA, PMDETA and water are mixed to prepare 80g of absorbent, wherein the mass fraction of DETA is 32%, the sum of the mass fractions of DEEA and PMDETA is 16%, the mass ratio of DEEA and PMDETA is 1:1, and the mass fraction of water is 52%.

[0053] The absorbent prepared in this example absorbs a mixed gas with a CO2 content of 15v% at 40°C. The results show that the absorbent is homogeneous before absorbing CO2; it forms a liquid-liquid two-phase when absorbing CO2 to 2.24mol / kg, and the corresponding CO2 partial pressure is 4.7kPa; it continues to absorb CO2 until the load is 4.25mol / kg and recovers to a homogeneous phase, and the corresponding CO2 partial pressure is 7.1kPa. Phase behavior during CO2 absorption: homogeneous phase-liquid-liquid two-phase-homogeneous phase.

[0054] Comparative Example 3

[0055] DETA, DEEA, PMDETA and water are mixed to prepare 80g of absorbent, wherein the mass fraction of DETA is 32%, the sum of the mass fractions of DEEA and PMDETA is 12%, the mass ratio of DEEA and PMDETA is 2:1, and the mass fraction of water is 56%.

[0056] The absorbent prepared in this comparative example was used to absorb a mixed gas with a CO2 content of 15% at 40° C. The results showed that the absorbent was always in a homogeneous phase during the CO2 absorption process.

[0057] Example 4

[0058] This embodiment discloses the preparation of the phase behavior controllable absorbent of the present invention, which is specifically as follows: DETA, DEEA, PMDETA and water are mixed to prepare 80g of absorbent, wherein the mass fraction of DETA is 25%, the sum of the mass fractions of DEEA and PMDETA is 30%, the mass ratio of DEEA and PMDETA is 1:4, and the mass fraction of water is 45%.

[0059] The absorbent prepared in this example absorbs a mixed gas with a CO2 content of 15v% at 40°C. The results show that at 40°C, the phase behavior of the mixed gas with a CO2 content of 15% during the absorption of CO2 is: homogeneous phase-liquid-liquid two-phase-homogeneous phase.

[0060] Comparative Example 4

[0061] DETA and water were mixed to prepare 80 g of absorbent, wherein the mass fraction of DETA was 25% and the mass fraction of water was 75%.

[0062] The absorbent was used to absorb a mixed gas with a CO2 content of 15v% at 40°C. It was found that the absorbent was always homogeneous during the CO2 absorption process.

[0063] Comparative Example 5

[0064] DETA, DEEA, PMDETA and water are mixed to prepare 80g of absorbent, wherein the mass fraction of DETA is 25%, the sum of the mass fractions of DEEA and PMDETA is 15%, the mass ratio of DEEA and PMDETA is 1:4, and the mass fraction of water is 60%.

[0065] The absorbent was used to absorb a mixed gas with a CO2 content of 15v% at 40°C. It was found that the absorbent was always homogeneous during the CO2 absorption process.

[0066] Comparative Example 6

[0067] DETA, PMDETA and water were mixed to prepare 80 g of absorbent, wherein the mass fraction of DETA was 25%, the mass fraction of PMDETA was 40%, and the mass fraction of water was 35%.

[0068] The absorbent absorbs a mixed gas with a CO2 content of 15v% at 40°C. Phase behavior during CO2 absorption: homogeneous phase - liquid-liquid two phases.

[0069] Test Example 1

[0070] This test example examines the CO2 absorption rate of the absorbents of Example 4, Comparative Example 4, Comparative Example 5 and Comparative Example 6. The experimental conditions are as follows: 40°C, 80g absorbent, 15v% CO2 mixed gas as the gas source, and 800rpm magnetic stirring.

[0071] At the same absorption time, the lower the outlet CO2 content, the faster the CO2 absorption rate of the absorbent.

[0072] The results are attached Figure 1 As shown. Figure 1 It can be seen that the CO2 absorption rate of the absorbent of Example 4 is significantly higher than that of Comparative Examples 4, 5 and 6.

[0073] Summarize:

[0074] In the present application, the phase behavior controllable absorbent of homogeneous-liquid-liquid two-phase-homogeneous phase requires a quaternary system of DETA, DEEA, PMDETA and water, and the content of the main agent and the phase regulating agent and the ratio of the phase regulating agent are within the prescribed conditions. Replacing the main agent (Comparative Example 1 (1)), replacing the phase regulating agent (Comparative Example 1 (2)), the content of the main agent and the phase regulating agent is not within the prescribed range (Comparative Example 1 (3) and (7)), non-quaternary system (Comparative Example 1 (4) and (5)) and the ratio of the phase regulating agent is not within the prescribed range (Comparative Example 1 (6)) cannot achieve the phase behavior of homogeneous-liquid-liquid two-phase-homogeneous phase during CO2 absorption.

[0075] The absorbent of the present invention has a faster CO2 absorption rate and lower CO2 capture energy consumption.

[0076] The phase behavior controllable absorbent of the present invention can be directly desorbed and regenerated on the original absorption equipment without the need to configure separate liquid-liquid or liquid-solid separation equipment and desorption and regeneration equipment, and the one-time equipment investment is small.

[0077] The above description is only a preferred embodiment of the present invention, which is merely illustrative of the present invention and does not limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made by ordinary technicians in this field to the technical solution of the present invention should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A phase behavior controllable absorbent for carbon dioxide capture, characterized in that: The phase behavior controllable absorbent is homogeneous before absorbing CO2, forms liquid-liquid two phases during the CO2 absorption process, and recovers to a homogeneous phase after absorbing CO2 until saturation; The phase behavior controllable absorbent comprises, by weight, 20-35% of a main agent, diethylenetriamine, 15-35% of a phase regulating agent, and the remainder is water; The phase separation regulator is diethylaminoethanol and pentamethyldiethylenetriamine, and the mass ratio thereof is 1:4 to 4:

1.

2. The phase behavior controllable absorbent for carbon dioxide capture according to claim 1, characterized in that: The phase behavior controllable absorbent comprises, by weight, 20-30% of a main agent, diethylenetriamine, 20-35% of a phase separation regulator, and the remainder is water.

3. A phase behavior controllable absorbent for carbon dioxide capture according to claim 1 or 2, characterized in that: The phase behavior controllable absorbent is homogeneous before absorbing CO2. During the CO2 absorption process, liquid-liquid two phases begin to form when the CO2 load is 0.8-2.5 mol / kg. The CO2 absorption continues and the homogeneous phase is restored when the CO2 load reaches 4.0-5.0 mol / kg.

4. A phase behavior controllable absorbent for carbon dioxide capture according to claim 1 or 2, characterized in that: The phase behavior controllable absorbent is homogeneous before absorbing CO2. When the CO2 partial pressure rises to 2-5 kPa, liquid-liquid two phases begin to form. The homogeneous phase is restored by continuing to increase the CO2 partial pressure to 7-13 kPa.

5. The method for preparing a phase behavior controllable absorbent for carbon dioxide capture according to any one of claims 1 to 4, characterized in that: Prepare various raw materials in proportion and mix them evenly to obtain the absorbent with controllable phase behavior.

6. The use of the phase behavior controllable absorbent for carbon dioxide capture according to any one of claims 1 to 4, characterized in that: Application in the treatment of gases containing carbon dioxide.

7. The use according to claim 6, characterized in that: The volume fraction of carbon dioxide in the carbon dioxide-containing gas is 7% to 20%.

8. A method for capturing carbon dioxide, characterized in that: The carbon dioxide-containing gas is absorbed by using the phase behavior controllable absorbent described in any one of claims 1 to 4.

9. A method for capturing carbon dioxide according to claim 8, characterized in that: After the phase-behavior controllable absorbent absorbs CO2 until saturation and homogeneity is restored, the CO2 is desorbed by heating. The desorbed and regenerated phase-behavior controllable absorbent returns to the absorption process for recycling and CO2 absorption.

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