Liquid-liquid phase change absorbent and application thereof

Abstract

The invention discloses a liquid-liquid phase change absorbent and application thereof. The liquid-liquid phase change absorbent comprises the following components in percentage by mass: 20-50% of a main absorbent, 15-65% of a phase splitting agent, 1-15% of a crystallization inhibitor and 0-40% of water, wherein the total mass of the main absorbent is 100%; the crystallization inhibitor includes a combination of a carbonate and a heterocyclic amine. The phase change absorbent disclosed by the invention can be used for capturing CO2, can keep liquid-liquid phase change in a relatively wide temperature range, and can effectively inhibit crystallization, so that liquid-solid phase change can be avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of CO2 capture, and in particular to a liquid-liquid phase change absorbent and applications thereof. Background Art

[0002] To effectively curb the negative impact of CO2 on the environment, it is necessary to vigorously develop new technologies such as renewable energy. Furthermore, it is imperative to develop carbon capture, utilization, and storage (CCUS) as a short- to medium-term technology. Chemical absorption, currently the most predominant carbon emission reduction technology for coal-fired power plants, utilizes an absorption / regeneration process characterized by high efficiency, rapid speed, and high integration. However, adding the traditional ethanolamine absorption process to a coal-fired power plant will increase total investment by 30-50%, reduce power generation efficiency by nearly 10%, and increase electricity costs by 20-30%. Furthermore, losses due to absorbent degradation account for approximately 10% of the carbon capture cost. Clearly, the high energy consumption and high cost of chemical absorption pose significant challenges to the large-scale deployment of carbon capture equipment in coal-fired power plants. Consequently, research and development of low-cost, low-energy post-combustion carbon capture technologies has grown significantly, with chemical absorption accounting for 43% of the total.

[0003] Phase-change absorbent carbon capture technology has attracted increasing attention due to its potential to significantly reduce carbon capture energy consumption and equipment costs. After absorbing CO2, the phase-change absorbent separates into a CO2-rich phase and a CO2-lean phase. Since only the CO2-rich solvent requires regeneration, the low flow rate of regenerated solvent and the high partial pressure of CO2 in the desorber theoretically reduce carbon capture energy consumption to 0.79–0.9 GJ / t CO2. To further reduce energy consumption, increasing the concentration of active amine solvent in the absorbent is the most effective measure. Consequently, water-lean or anhydrous phase-change absorbents have seen rapid development. However, a major drawback of this technology is the increased viscosity of the CO2-rich phase after phase separation, which can even lead to a liquid-solid phase transition at or below room temperature. Since the solid phase is often a viscous or hydrophilic flocculent product, liquid-solid separation is difficult to achieve in industry and can easily lead to blockage of pipelines and valves, hindering the stable operation of the carbon capture process.

[0004] CN114011207B discloses a low-energy polyamine liquid-liquid phase change absorbent for carbon capture, with N,N-dimethylethanolamine (DMEA) as the main absorbent, n-butanol (n-BuOH) as a phase separator, anhydrous piperazine (PZ) as a promoter, and water as a solvent. CN112892160B discloses a phase change absorbent and its application in CO2 capture, with N-aminoethylpiperazine as the main absorbent, n-propanol as a phase separator, and water as a solvent. CN110141935B discloses a functionalized ionic liquid phase change system and application for CO2 capture, with functionalized ionic liquid diethylenetriamine triazole as the main absorbent, n-propanol as a phase separator, and water as a solvent. The common feature of these phase change absorbents is that water is used as a solvent, and a liquid-liquid phase change occurs at room temperature after absorbing CO2.

[0005] CN112107966B discloses a non-aqueous liquid-liquid phase-change absorbent for carbon dioxide capture and its application. The absorbent uses a primary alcoholamine as an absorption promoter and a mixture of dimethyl sulfoxide and pentamethyldiethylenetriamine as a composite organic solvent. The phase-change absorbent is characterized by being water-free and undergoing a liquid-liquid phase transition at room temperature after absorbing CO2.

[0006] CN108854459B discloses a low-energy, anhydrous CO2 phase-change absorbent, a regeneration method, and applications. The absorbent utilizes a single diamine compound containing both a primary amine (NH2-) and a tertiary amine (N-) at a 100% concentration, without any other organic solvents, water, or ionic liquids. CN115253601A discloses a solid-liquid phase-change two-phase amine absorbent for CO2 capture and its applications. The absorbent is a non-aqueous ternary system composed of triethylenetetramine, 2-amino-2-methyl-1-propanol, and N-methylformamide. These phase-change absorbents share the characteristics of being water-free and undergoing a solid-liquid phase transition at room temperature after absorbing CO2.

[0007] CN105289209B discloses a mixed organic solution for capturing CO2 and SO2 acidic gases through phase change. The mixed organic solution is composed of an organic amine absorbent and an organic solvent, wherein the mass fraction of the organic amine absorbent is 5 to 35 parts, and the mass fraction of the organic solvent is 65 to 95 parts; the organic amine absorbent is one or a mixture of two or more of the following in any proportion: chain polyamines, diamines, sterically hindered amines, alcoholamines, and amides; and the organic solvent is one or a mixture of two or more of the following in any proportion: alcohols, ethers, ketones, and esters. After absorbing the acidic gas, the mixed organic solution undergoes a phase change (liquid-liquid phase change or liquid-solid phase change). The preferred temperature for absorbing carbon dioxide or sulfur dioxide is 25 to 55°C, and the preferred temperature for desorbing carbon dioxide or sulfur dioxide is 75 to 115°C. The absorption capacity and desorption rate of carbon dioxide and sulfur dioxide are high.

[0008] CN116236883A discloses an aqueous liquid-liquid phase-change absorbent with a controllable phase-separation threshold for SO2 capture. The aqueous liquid-liquid phase-change absorbent comprises the following components, measured by weight percentage: 10-30 wt% absorbent, 5-45 wt% phase-separation agent, 0.5-8.0% phase-separation accelerator, and 40-75 wt% water; the absorbent is a piperazine-type organic amine; the phase-separation agent is an ester; and the phase-separation accelerator is an acid. The aqueous liquid-liquid phase-change absorbent uses an ester as a phase-separation agent. Due to the difference in polarity between the absorbed ammonium salt and the ester, the two are immiscible, inducing a phase change. Furthermore, by varying the non-polarity and dosage of the ester, the time of phase change and the phase-separation threshold can be altered.

[0009] Existing phase-change absorbents can undergo a liquid-liquid phase transition at room temperature after absorbing CO2. However, these phase-change absorbents have the disadvantage of increasing the viscosity of the CO2-rich phase after the phase transition. Furthermore, at temperatures below room temperature, liquid-solid separation and precipitation can occur, resulting in a narrow temperature range for the liquid-liquid phase transition. Alternatively, existing phase-change absorbents undergo direct solid-liquid phase transition at room temperature, which means they are prone to solid precipitation, hindering the stable operation of the process system. Summary of the Invention

[0010] To address at least one of the aforementioned technical problems, the present invention provides a liquid-liquid phase-change absorbent and its application. The phase-change absorbent of the present invention can be used for CO2 capture, maintains liquid-liquid phase transition over a wide temperature range, and effectively inhibits crystallization, thereby preventing liquid-solid phase transition.

[0011] In order to achieve the above-mentioned objectives, the first aspect of the present invention provides a liquid-liquid phase change absorbent, which, based on the total mass of the liquid-liquid phase change absorbent as 100%, comprises: 20% to 50% of a main absorbent, 15% to 65% of a phase separator, 1% to 15% of a crystallization inhibitor, and 0% to 40% of water; wherein the crystallization inhibitor comprises a combination of a carbonate and a heterocyclic amine.

[0012] According to a specific embodiment of the present invention, preferably, the mass ratio of the carbonate ester to the heterocyclic amine is 1:3 to 3:1.

[0013] According to a specific embodiment of the present invention, preferably, the carbonate includes one or more of ethylene carbonate, propylene carbonate and fluoroethylene carbonate.

[0014] According to a specific embodiment of the present invention, preferably, the heterocyclic amine includes one or more of piperazines and morpholines. More preferably, the heterocyclic amine includes one or more of N-hydroxyethylpiperazine, N-aminoethylpiperazine, 2-morpholinoethanol and N-(2-aminoethyl)morpholine.

[0015] According to a specific embodiment of the present invention, preferably, the primary absorbent comprises one or more of a primary amine, a secondary amine, a sterically hindered amine, and a polyamine. More preferably, the primary absorbent comprises a polyamine. Further preferably, the primary absorbent comprises one or more of a diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0016] According to a specific embodiment of the present invention, preferably, the phase separation agent includes one or more of ethers, alcohols, sulfones and tertiary amines. More preferably, the phase separation agent includes one or more of alcohols and tertiary amines. Further preferably, the phase separation agent includes a tertiary amine containing an alcoholic hydroxyl group. Specifically, the tertiary amine containing an alcoholic hydroxyl group includes one or more of N-methyldiethanolamine, diethylaminoethanol and 3-dimethylamino-1-propanol.

[0017] According to a specific embodiment of the present invention, preferably, the liquid-liquid phase change absorbent is a homogeneous solution before absorbing CO2, and undergoes a liquid-liquid phase change after absorbing CO2, and is divided into a CO2-rich phase and a CO2-lean phase; wherein, the CO2-rich phase and the CO2-lean phase maintain liquid-liquid phase change at -20°C to 50°C and normal pressure conditions.

[0018] According to a specific embodiment of the present invention, preferably, the CO2-rich phase formed by the liquid-liquid phase-change absorbent after absorbing CO2 does not generate a solid phase at a temperature above -20°C and under normal pressure.

[0019] According to a specific embodiment of the present invention, preferably, the volume ratio of the CO2-rich phase and the CO2-lean phase formed by the liquid-liquid phase change absorbent after absorbing CO2 at 25°C and normal pressure is 0.56-2.47:1.

[0020] According to a specific embodiment of the present invention, preferably, the time for the liquid-liquid phase change absorbent to undergo liquid-liquid phase change after absorbing CO2 at 25°C and normal pressure is less than 3 minutes.

[0021] According to a specific embodiment of the present invention, preferably, the absorption load of the CO2-rich phase formed by the liquid-liquid phase-change absorbent after absorbing CO2 at 25°C and normal pressure is 2.34 to 3.47 molCO2 / kg CO2-rich phase.

[0022] According to a specific embodiment of the present invention, preferably, the CO2 desorption efficiency of the CO2-rich phase formed by the liquid-liquid phase change absorbent after absorbing CO2 is 70% to 90% at a temperature of 85°C to 100°C.

[0023] A second aspect of the present invention provides use of the above-mentioned liquid-liquid phase change absorbent in carbon dioxide capture.

[0024] The present invention has at least the following beneficial effects:

[0025] The present invention provides a liquid-liquid phase-change absorbent for CO2 capture. The phase-change absorbent of the present invention is a homogeneous solution before absorbing CO2; after absorbing CO2, liquid-liquid phase separation can occur quickly and significantly to form a CO2-rich phase and a CO2-lean phase; and the liquid-liquid phase change can be maintained over a wide temperature range (-20°C to 50°C); and crystallization can be effectively inhibited, thereby avoiding the occurrence of liquid-solid phase change. The present invention creatively introduces a combination of carbonate and heterocyclic amine into the phase-change absorbent as a crystallization inhibitor. A synergistic effect occurs between the carbonate and the heterocyclic amine. The cyclic functional groups they contain form large π bonds, which isolate or reduce the interaction between the reaction products after the phase-change absorbent absorbs CO2, thereby effectively inhibiting crystallization. This is something that other esters or other amines cannot achieve. At the same time, the strong polarity of carbonates and heterocyclic amines means that after phase separation, the crystallization inhibitor primarily acts in the CO2-rich phase, reducing the viscosity of the CO2-rich phase and effectively inhibiting the formation of crystals in the CO2-rich phase at low temperatures (≥-20°C). This, in turn, avoids the occurrence of liquid-solid phase transitions and facilitates the stable operation of the carbon capture system. Furthermore, the CO2-rich phase formed by the phase-change absorbent of the present invention after CO2 absorption can be rapidly and efficiently desorbed at low temperatures of 85°C to 100°C, with a desorption efficiency of 70% to 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 These are optical images of the liquid-liquid phase change absorbers of Example 1 and Comparative Examples 1 to 5 after being placed in the environment described in Test Example 2. DETAILED DESCRIPTION

[0027] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0028] It should be noted that, unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0029] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0030] According to a specific embodiment of the first aspect of the present invention, the present invention provides a liquid-liquid phase change absorbent, which comprises, based on the total mass of the liquid-liquid phase change absorbent as 100%, 20% to 50% of the main absorbent, such as but not limited to 20%, 25%, 30%, 35%, 40%, 45% or 50%, and a range of any two of the above specific values; 15% to 65% of the phase separation agent, such as but not limited to 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or more. %, 60% or 65%, etc., and ranges consisting of any two of the above specific values; crystallization inhibitor 1% to 15%, such as but not limited to 1%, 5%, 10% or 15%, etc., and ranges consisting of any two of the above specific values; water 0% to 40%, such as but not limited to 0%, 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40%, etc., and ranges consisting of any two of the above specific values; wherein the crystallization inhibitor comprises a combination of a carbonate and a heterocyclic amine. It will be understood by those skilled in the art that the liquid-liquid phase-change absorbent may include a main absorbent, a phase separation agent, and a crystallization inhibitor, but not water; alternatively, the liquid-liquid phase-change absorbent may also include a main absorbent, a phase separation agent, a crystallization inhibitor, and water. In other words, the liquid-liquid phase-change absorbent may contain water or not.

[0031] In some embodiments, the mass ratio of the carbonate to the heterocyclic amine is 1:3 to 3:1, such as but not limited to 1:1, 1:2, 1:3, 2:1 or 3:1, and preferably 1:2 to 2:1.

[0032] In some embodiments, the carbonate includes one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

[0033] In some embodiments, the heterocyclic amine includes one or more of piperazines and morpholines, etc. Preferably, the heterocyclic amine includes one or more of N-hydroxyethylpiperazine, N-aminoethylpiperazine, 2-morpholinoethanol and N-(2-aminoethyl)morpholine, etc.

[0034] In some embodiments, the main absorbent includes one or more of primary amines, secondary amines, sterically hindered amines and polyamines. The structural formula of the primary amine is: R1-NH2, wherein R1 can be, for example, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted aryl derivative. The structural formula of the secondary amine is: R2-NH-R3, wherein R2 and R3 can be the same or different, and R2 and R3 can be, for example, independently substituted or unsubstituted alkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted aryl groups, or a substituted or unsubstituted aryl derivative. The sterically hindered amine is an amine with steric hindrance, that is, an amine with at least one bulky substituent (such as a nonlinear substituent) on the nitrogen atom. The polyamine is a compound containing two or more amino groups, and its structural formula can be: R-(NH-R') n -X; wherein R and R' may be the same or different, and R and R' may be, for example, each independently a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, or a substituted or unsubstituted aryl group; X may be NH2 (primary amine), NHR" (secondary amine) or NR"R"' (tertiary amine); n is an integer greater than 1. Preferably, the main absorbent includes a polyamine. Specifically, the main absorbent includes one or more of diethylenetriamine, triethylenetetramine and tetraethylenepentamine.

[0035] In some embodiments, the phase separation agent includes one or more of ethers, alcohols, sulfones, and tertiary amines. The ethers may include one or more of monoethers and polyethers, and their structural formula may be: R4-O-(R5-O) m -R6; wherein R4, R5 and R6 may be the same or different, and R4, R5 and R6 may be, for example, independently substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl, or substituted or unsubstituted aryl derivatives, etc.; m is an integer greater than 0 or 1, representing a repeating unit of an ether group. The alcohols may include one or more of monohydric alcohols, dihydric alcohols, polyhydric alcohols and alcohol polymers, etc.; for example, ethylene glycol, polyethylene glycol, etc. The structural formula of the sulfones is: R7-SO2-R8, wherein R7 and R8 may be the same or different, and R7 and R8 may be, for example, independently substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted aryl, or substituted or unsubstituted aryl derivatives, etc. The structural formula of the tertiary amine is: R9-NR 10 -R 11 , among which R9, R 10 and R 11 Can be the same or different, R9, R 10 and R 11For example, each of them can be independently a substituted or unsubstituted alkyl, a substituted or unsubstituted alkenyl, a substituted or unsubstituted aryl, or a substituted or unsubstituted aryl derivative. Preferably, the phase separating agent comprises one or more of alcohols and tertiary amines. More preferably, the phase separating agent comprises a tertiary amine containing an alcoholic hydroxyl group. Specifically, the tertiary amine containing an alcoholic hydroxyl group comprises one or more of N-methyldiethanolamine, diethylaminoethanol, and 3-dimethylamino-1-propanol.

[0036] In some embodiments, based on the total mass of the liquid-liquid phase change absorbent as 100%, it includes: 20% to 50% of a main absorbent, 15% to 65% of a phase separator, 1% to 15% of a crystallization inhibitor, and 0% to 39% of water; wherein the crystallization inhibitor includes a combination of a carbonate and a heterocyclic amine, and the mass ratio of the carbonate to the heterocyclic amine is 1:2 to 2:1; the main absorbent includes one or more of tetraethylene pentamine, triethylene tetramine, and 3-methylaminopropylamine, preferably including one or two of tetraethylene pentamine and triethylene tetramine; the phase separator includes one or more of 3-dimethylamino-1-propanol, N-methyldiethanolamine, and ethylene glycol, preferably including one or more of 3-dimethylamino-1-propanol and N-methyldiethanolamine; the carbonate includes one or both of ethylene carbonate and fluoroethylene carbonate; the heterocyclic amine includes one or both of N-hydroxyethylpiperazine and N-(2-aminoethyl)morpholine.

[0037] In some embodiments, the liquid-liquid phase change absorbent is a homogeneous solution before absorbing CO2, and undergoes a liquid-liquid phase change after absorbing CO2, dividing into a CO2-rich phase and a CO2-lean phase; wherein the CO2-rich phase and the CO2-lean phase maintain a liquid-liquid phase change under conditions of -20°C to 50°C and normal pressure (i.e., 101.325KPa). The absorption gas used in the specific test is a mixed gas containing CO2, which includes 12% CO2 by volume and the remainder nitrogen. In other words, the gas absorbed by the phase change absorbent is the mixed gas containing CO2.

[0038] In some embodiments, the liquid-liquid phase change absorbent forms a CO2-rich phase after absorbing CO2 (ie, absorbing the aforementioned CO2-containing mixed gas) without generating a solid phase at temperatures above -20°C and normal pressure.

[0039] In some embodiments, the volume ratio of the CO2-rich phase and the CO2-lean phase formed by the liquid-liquid phase change absorbent after absorbing CO2 (i.e., absorbing the above-mentioned CO2-containing mixed gas) at 25°C and normal pressure is 0.56-2.47:1.

[0040] In some embodiments, the liquid-liquid phase change absorbent absorbs CO2 (i.e., absorbs the aforementioned CO2-containing mixed gas) for a liquid-liquid phase change (i.e., the time it takes for the CO2-rich phase and the CO2-lean phase to separate and stabilize) at 25°C and atmospheric pressure for a time of 3 minutes or less. It should be noted that the term "3 minutes or less" refers to the phase separation time observed during the static state after absorption is complete.

[0041] In some embodiments, the viscosity of the CO2-rich phase formed by the liquid-liquid phase-change absorbent after absorbing CO2 (ie, absorbing the above-mentioned mixed gas containing CO2) at 25°C and normal pressure is less than 100 mPa·s.

[0042] In some embodiments, the absorption load of the CO2-rich phase formed by the liquid-liquid phase change absorbent after absorbing CO2 (i.e., absorbing the above-mentioned CO2-containing mixed gas) at 25°C and normal pressure is 2.34 to 3.47 molCO2 / kg CO2-rich phase.

[0043] In some embodiments, the liquid-liquid phase change absorbent forms a CO2-rich phase after absorbing CO2 (ie, absorbing the aforementioned CO2-containing mixed gas) and has a CO2 desorption efficiency of 70% to 90% at a temperature of 85°C to 100°C.

[0044] In some embodiments, the liquid-liquid phase change absorbent can be prepared by mixing the components in a conventional manner in the art. For example, the preparation method of the liquid-liquid phase change absorbent may include the following steps: mixing the main absorbent, phase separator, crystallization inhibitor, and optionally added water at 60-80°C under stirring conditions, and continuously stirring until a homogeneous solution (i.e., a clear liquid) is formed to obtain the liquid-liquid phase change absorbent. There is no special restriction on the mixing order of the main absorbent, phase separator, crystallization inhibitor, and optionally added water, and it can be routinely adjusted by those skilled in the art; after each component is added, it can be stirred for a period of time until the liquid becomes clear.

[0045] According to a specific embodiment of the second aspect of the present invention, the present invention provides the use of the above-mentioned liquid-liquid phase change absorbent in carbon dioxide capture.

[0046] The phase-change absorbent of the present invention is a homogeneous solution before absorbing CO2; after absorbing CO2, the polarity of the main absorbent of the present invention increases, and the polarity difference with the phase separator of the present invention becomes larger. At the same time, the reaction heat is released during the absorption of CO2, which increases the temperature of the absorbent and destroys the weak mutual hydrogen bonding between the components in the absorbent. Therefore, after absorbing CO2, the phase-change absorbent of the present invention undergoes liquid-liquid phase separation, forming a CO2-rich phase and a CO2-lean phase. In addition, due to the synergistic effect between the main absorbent (especially polyamine), the phase separator (especially a tertiary amine containing an alcoholic hydroxyl group) and the crystallization inhibitor (a combination of a carbonate and a heterocyclic amine) of the present invention, the phase-change absorbent of the present invention can quickly and significantly undergo liquid-liquid phase separation and maintain liquid-liquid phase separation over a wide temperature range (-20°C to 50°C). The CO2-rich phase of the present invention mainly contains the main absorbent, the crystallization inhibitor, a small amount of the phase separator and optionally contained water; the CO2 content in the CO2-rich phase accounts for 70vol% to 90vol% of the total CO2 absorbed by the phase-change absorbent. The CO₂-lean phase of the present invention primarily comprises a phase separation agent and, optionally, a small amount of water. The rapid phase separation characteristics of the phase-change absorbent of the present invention improve its utilization efficiency and CO₂ capture efficiency. Furthermore, the phase-change absorbent of the present invention has the advantage of a long shelf life. It remains clear and homogeneous even when stored sealed at -20 to 25°C and normal pressure for extended periods (over 72 hours, up to one month).

[0047] At the same time, the present invention creatively introduces a combination of carbonate and heterocyclic amine as a crystallization inhibitor in the phase change absorbent. A synergistic effect occurs between the carbonate and heterocyclic amine. The cyclic functional groups they contain form large π bonds, which cut off or reduce the interaction between the reaction products after the absorbent absorbs CO2, thereby effectively inhibiting crystallization, which is something that other esters or other amines cannot achieve. At the same time, the strong polarity of carbonate and heterocyclic amine makes the crystallization inhibitor mainly act in the CO2-rich phase after the absorbent is separated, reducing the viscosity of the CO2-rich phase and effectively inhibiting the formation of crystals in the CO2-rich phase under low temperature (≥-20°C) conditions, thereby avoiding the occurrence of liquid-solid phase change, which is beneficial to the stable operation of the carbon capture system. In addition, the carbonate in the crystallization inhibitor of the present invention reduces the melting point of the CO2-rich phase, and synergistically changes the hydrogen bond network structure in the CO2-rich phase with the heterocyclic amine, which is also beneficial to inhibiting crystallization.

[0048] In industry, the phase-change absorbent of the present invention can absorb a CO2-containing mixed gas with a CO2 volume content of 400ppm to 20vol%, and the absorption temperature can be 25°C to 45°C. The CO2-lean phase formed by the phase-change absorbent of the present invention after absorbing CO2 can be directly transported back to the inlet of the absorption tower, mixed with the lean liquid and further cooled before entering the absorption tower to capture CO2; the CO2-rich phase can be transported to the desorption tower for desorption after passing through the lean-rich liquid heat exchanger. Due to the synergistic effect between the main absorbent (especially polyamine), phase separator (especially tertiary amine containing alcoholic hydroxyl group) and crystallization inhibitor (combination of carbonate and heterocyclic amine) of the present invention, the CO2-rich phase formed by the phase-change absorbent of the present invention after absorbing CO2 can achieve rapid and efficient desorption under low temperature conditions of 85°C to 100°C, and the desorption efficiency is 70% to 90%. On the one hand, this low-temperature desorption can effectively utilize waste heat or low-quality heat sources in industry, thereby reducing the heat consumption of absorbent regeneration; on the other hand, this low-temperature desorption reduces the thermal degradation loss of the absorbent, reduces the vapor pressure of the absorbent, and reduces the volatility loss of the absorbent.

[0049] The present invention will be specifically described below with reference to Examples. However, the present invention is not limited to these Examples and can be implemented with various modifications within the scope of the gist of the present invention.

[0050] Example 1

[0051] This embodiment provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent as 100%, the absorbent comprises: 20% tetraethylenepentamine, 40% 3-dimethylamino-1-propanol, 5% N-hydroxyethylpiperazine, 5% fluoroethylene carbonate, and the balance water. The above components, in the stated amounts, are added to a 250 ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this embodiment.

[0052] Example 2

[0053] This embodiment provides a liquid-liquid phase-change absorbent. The absorbent comprises, based on the total mass of the absorbent as 100%, 50% tetraethylenepentamine, 15% 3-dimethylamino-1-propanol, 5% N-hydroxyethylpiperazine, 5% fluoroethylene carbonate, and the balance water. The components are added in the aforementioned amounts to a 250ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this embodiment.

[0054] Example 3

[0055] This embodiment provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent as 100%, the absorbent comprises: 25% tetraethylenepentamine, 65% 3-dimethylamino-1-propanol, 5% N-hydroxyethylpiperazine, and 5% fluoroethylene carbonate. These components, in the stated proportions, are added to a 250ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this embodiment.

[0056] Example 4

[0057] This embodiment provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent as 100%, the absorbent comprises: 20% tetraethylenepentamine, 40% 3-dimethylamino-1-propanol, 10% N-hydroxyethylpiperazine, 5% fluoroethylene carbonate, and the balance water. The above components are added to a 250 ml three-mouthed round-bottom flask equipped with a mechanical stirrer, heated to 60-80°C, and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this embodiment.

[0058] Example 5

[0059] This embodiment provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent as 100%, the absorbent comprises: 20% tetraethylenepentamine, 40% 3-dimethylamino-1-propanol, 5% N-hydroxyethylpiperazine, 10% fluoroethylene carbonate, and the balance water. The above components, in the stated amounts, are added to a 250ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this embodiment.

[0060] Example 6

[0061] This embodiment provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent as 100%, the absorbent comprises: 20% tetraethylenepentamine, 40% 3-dimethylamino-1-propanol, 0.5% N-hydroxyethylpiperazine, 0.5% fluoroethylene carbonate, and the balance water. The above components, in the stated amounts, are added to a 250ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this embodiment.

[0062] Example 7

[0063] This embodiment provides a liquid-liquid phase-change absorbent. The absorbent comprises, based on the total mass of the absorbent as 100%, 20% triethylenetetramine, 40% N-methyldiethanolamine, 5% N-(2-aminoethyl)morpholine, 5% ethylene carbonate, and the balance water. The components are added in the aforementioned amounts to a 250 ml three-mouthed round-bottom flask with a mechanical stirrer. The flask is heated to 60-80° C. and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this embodiment.

[0064] Example 8

[0065] This embodiment provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent as 100%, the absorbent comprises: 20% tetraethylenepentamine, 40% 3-dimethylamino-1-propanol, 2.5% N-hydroxyethylpiperazine, 2.5% fluoroethylene carbonate, and the balance water. The above components, in the stated amounts, are added to a 250ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this embodiment.

[0066] Example 9

[0067] This embodiment provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent being 100%, the absorbent comprises: 20% tetraethylenepentamine, 40% ethylene glycol, 5% N-hydroxyethylpiperazine, 5% fluoroethylene carbonate, and the balance water. The above components, in the stated amounts, are added to a 250ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this embodiment.

[0068] Example 10

[0069] This embodiment provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent as 100%, the absorbent comprises: 20% 3-methylaminopropylamine, 40% 3-dimethylamino-1-propanol, 5% N-hydroxyethylpiperazine, 5% fluoroethylene carbonate, and the balance water. The above components, in the stated amounts, are added to a 250 ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this embodiment.

[0070] Comparative Example 1

[0071] This comparative example provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent as 100%, the absorbent comprises: 20% tetraethylenepentamine, 40% 3-dimethylamino-1-propanol, 5% N-hydroxyethylpiperazine, and the balance water. The components, in the aforementioned proportions, are added to a 250ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this comparative example.

[0072] This comparative example is compared with Example 1. The main difference from Example 1 is that fluoroethylene carbonate, a crystallization inhibitor, is not used.

[0073] Comparative Example 2

[0074] This comparative example provides a liquid-liquid phase-change absorbent. The absorbent comprises, based on the total mass of the absorbent as 100%, 20% tetraethylenepentamine, 40% 3-dimethylamino-1-propanol, 5% fluoroethylene carbonate, and the balance water. The components are added in the aforementioned amounts to a 250ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this comparative example.

[0075] This comparative example is compared with Example 1. The main difference from Example 1 is that N-hydroxyethylpiperazine, a crystallization inhibitor, is not used.

[0076] Comparative Example 3

[0077] This comparative example provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent as 100%, the absorbent comprises: 20% tetraethylenepentamine, 40% 3-dimethylamino-1-propanol, 5% N-hydroxyethylpiperazine, 5% ethyl acetate, and the balance water. The components, in the aforementioned proportions, are added to a 250ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this comparative example.

[0078] This comparative example is compared with Example 1. The main difference from Example 1 is that the fluoroethylene carbonate in the crystallization inhibitor is replaced by ethyl acetate.

[0079] Comparative Example 4

[0080] This comparative example provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent as 100%, the absorbent comprises: 20% tetraethylenepentamine, 40% 3-dimethylamino-1-propanol, 5% N-hydroxyethylpiperazine, 5% glyceryl triacetate, and the balance water. The components, in the aforementioned proportions, are added to a 250ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this comparative example.

[0081] This comparative example is compared with Example 1. The main difference from Example 1 is that the fluoroethylene carbonate in the crystallization inhibitor is replaced by triacetin.

[0082] Comparative Example 5

[0083] This comparative example provides a liquid-liquid phase-change absorbent. Based on the total mass of the liquid-liquid phase-change absorbent as 100%, the absorbent comprises: 20% tetraethylenepentamine, 40% 3-dimethylamino-1-propanol, 5% triethylenetetramine, 5% fluoroethylene carbonate, and the balance water. The components, in the aforementioned proportions, are added to a 250ml three-mouthed round-bottom flask equipped with a mechanical stirrer. The flask is heated to 60-80°C and stirred at 1000 rpm for 10-30 minutes until the liquid becomes clear and a homogeneous solution is formed, thereby obtaining the liquid-liquid phase-change absorbent of this comparative example.

[0084] This comparative example is compared with Example 1. The main difference from Example 1 is that N-hydroxyethylpiperazine in the crystallization inhibitor is replaced by triethylenetetramine.

[0085] Test Example 1

[0086] 100 ml of the phase change absorbent provided in the above embodiment and comparative example were respectively taken and placed in a container. At 25 ° C and normal pressure, a mixed gas containing CO2 (including 12% CO2 by volume and the remainder nitrogen) was introduced into the phase change absorbent. The mixed gas flow rate was 300 ml / min until the phase change absorbent absorbed CO2 and reached saturation. Then, the introduction of the mixed gas containing CO2 was stopped. The method for judging whether the absorption of CO2 reached saturation was as follows: using an infrared gas analyzer, real-time monitoring of the CO2 volume concentration in the gas flowing out of the phase change absorbent was performed. When the CO2 volume concentration in the outflowing gas was close to the CO2 volume concentration in the mixed gas containing CO2 introduced, and the data was stable and no longer changed, it was indicated that the absorption reached saturation. Then the mixture was allowed to stand and the time for the separation of the CO2-rich phase and the CO2-lean phase was recorded (i.e., the time from the stop of the introduction of the mixed gas containing CO2 to the time when the volume of the two phases no longer changed). The volume of the CO2-rich phase and the CO2-lean phase and the CO2 absorption load in the CO2-rich phase were tested. Among them, the test method for CO2 absorption load adopts the conventional acid-base titration method. Take an appropriate amount of CO2-rich phase, add sulfuric acid to it, and calculate the CO2 absorption load based on the volume of CO2 released.

[0087] The results of the above tests are shown in Table 1 below.

[0088] Table 1

[0089]

[0090] It can be seen from Table 1 that the phase-change absorbents of each embodiment of the present invention can quickly and obviously undergo liquid-liquid phase separation after absorbing CO2, and the phase separation time is less than 3 minutes; and the volume ratio of the CO2-rich phase and the CO2-lean phase is less than 2.3:1, and the proportion of the CO2-rich phase is not high, which can reduce the desorption energy consumption; moreover, the phase-change absorbents of each embodiment of the present invention also have a higher CO2 absorption load.

[0091] Test Example 2

[0092] The method in Test Example 1 was used to make the phase change absorbents provided in the above embodiments and comparative examples absorb CO2, and the formed CO2-rich phase and CO2-lean phase were placed in environments of 25°C, 5°C, 0°C, -10°C, -20°C, and 50°C, respectively, with the placement time in each temperature environment being 4 hours. During this process, the CO2-rich phase and the CO2-lean phase were observed to see whether they maintained liquid-liquid phase separation. Furthermore, the CO2-rich phase was observed to see whether crystals appeared in the environments of 25°C, 5°C, 0°C, -10°C, -20°C, and 50°C. If crystals appeared, the phase was transferred to an environment of 60°C to see whether the crystals dissolved in the environment of 60°C.

[0093] The results of the above tests are as follows Figure 1and as shown in Table 2 below.

[0094] Table 2

[0095]

[0096]

[0097] Depend on Figure 1 As can be seen from Table 2, the phase-change absorbents of the various embodiments of the present invention can maintain a liquid-liquid phase transition over a wide temperature range (-20°C to 50°C) after absorbing CO2, and effectively suppress the formation of crystals in the CO2-rich phase at low temperatures (≥-20°C), thereby avoiding the occurrence of liquid-solid phase transition. However, the phase-change absorbents of the comparative examples do not possess the wide temperature phase transition characteristics of the embodiments, and instead form crystals at low temperatures. These crystals do not dissolve upon heating, hindering the stable operation of the carbon capture process.

[0098] Test Example 3

[0099] The method in Test Example 1 was used to make the phase change absorbents provided in the above embodiments and comparative examples absorb CO2, separate the formed CO2-rich phase, and heat it to different temperatures (85°C, 90°C, 95°C, 100°C) for desorption. The desorption time was 150 minutes. The desorption efficiency under different desorption temperature conditions is shown in Table 3 below.

[0100] Table 3

[0101]

[0102]

[0103] As can be seen from Table 3, the CO2-rich phase formed by the phase-change absorbent of each embodiment of the present invention after absorbing CO2 can be quickly and efficiently desorbed under low temperature conditions of 85°C to 100°C, with a desorption efficiency of 70% to 90%.

[0104] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A liquid-liquid phase change absorbent, which comprises, based on the total mass of the liquid-liquid phase change absorbent being 100%, a main Absorbent 20% to 50%, phase separator 15% to 65%, crystallization inhibitor 1% to 15% and water 0% to 40%; Wherein, the crystallization inhibitor comprises a combination of carbonate and heterocyclic amine.

2. The liquid-liquid phase-change absorbent according to claim 1, wherein: The mass ratio of the carbonate to the heterocyclic amine is 1:3 to 3:

1.

3. The liquid-liquid phase change absorbent according to claim 1, wherein: The carbonate includes one or more of ethylene carbonate, propylene carbonate and fluoroethylene carbonate.

4. The liquid-liquid phase-change absorbent according to claim 1, wherein: The heterocyclic amine includes one or more of piperazine and morpholine; Preferably, the heterocyclic amine includes one or more of N-hydroxyethylpiperazine, N-aminoethylpiperazine, 2-morpholinoethanol and N-(2-aminoethyl)morpholine.

5. The liquid-liquid phase change absorbent according to claim 1, wherein: The main absorbent includes one or more of primary amines, secondary amines, sterically hindered amines and polyamines; Preferably, the primary absorbent comprises a polyamine; More preferably, the main absorbent includes one or more of diethylenetriamine, triethylenetetramine and tetraethylenepentamine. The liquid-liquid phase-change absorbent according to claim 1 , wherein: The phase separation agent includes one or more of ethers, alcohols, sulfones and tertiary amines; Preferably, the phase separation agent comprises one or more of alcohols and tertiary amines; More preferably, the phase separation agent comprises a tertiary amine containing an alcoholic hydroxyl group; More preferably, the tertiary amine containing alcoholic hydroxyl group includes one or more of N-methyldiethanolamine, diethylaminoethanol and 3-dimethylamino-1-propanol.

7. The liquid-liquid phase-change absorbent according to claim 1, wherein: The liquid-liquid phase change absorbent is a homogeneous solution before absorbing CO2, and undergoes a liquid-liquid phase change after absorbing CO2, dividing into a CO2-rich phase and a CO2-lean phase; wherein, the CO2-rich phase and the CO2-lean phase maintain liquid-liquid phase change under conditions of -20°C to 50°C and normal pressure.

8. The liquid-liquid phase-change absorbent according to claim 7, wherein: The liquid-liquid phase change absorbent forms a CO2-rich phase after absorbing CO2, and no solid phase is generated at a temperature above -20°C and under normal pressure.

9. The liquid-liquid phase-change absorbent according to claim 7, wherein: The volume ratio of the CO2-rich phase and the CO2-lean phase formed by the liquid-liquid phase change absorbent after absorbing CO2 at 25°C and normal pressure is 0.56-2.47:1; Preferably, the liquid-liquid phase change absorbent undergoes a liquid-liquid phase change time of less than 3 minutes after absorbing CO2 at 25°C and normal pressure; Preferably, the absorption load of the CO2-rich phase formed by the liquid-liquid phase-change absorbent after absorbing CO2 at 25°C and normal pressure is 2.34 to 3.47 molCO2 / kg CO2-rich phase.

10. The liquid-liquid phase-change absorbent according to claim 7, wherein: The liquid-liquid phase-change absorbent forms a CO2-rich phase after absorbing CO2, and the CO2 desorption efficiency at a temperature of 85° C. to 100° C. is 70% to 90%.

11. Use of the liquid-liquid phase change absorbent according to any one of claims 1 to 10 in carbon dioxide capture.

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