An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2, its preparation method, and its application.

Abstract

The application discloses a water-based liquid-liquid phase change absorbent for absorbing and capturing SO2, which comprises the following components in percentage by mass: 10-30% of an absorbent, 5-45% of a phase separation agent, 0.1-6% of a phase separation promoter, and 40-70% of water, wherein the sum of the mass percentage of the above components is 100%; the absorbent is a piperazine organic amine; the phase separation agent is an ether; and the phase separation promoter is an acid. The components are stirred and mixed uniformly in a closed container to obtain the water-based liquid-liquid phase change absorbent; the absorption temperature in application is 20-60 DEG C, and the desorption temperature is 90-120 DEG C. The water-based liquid-liquid phase change absorbent has the advantages of good cyclic absorption performance, high selectivity, low regeneration energy consumption, fast absorption rate, small volatilization loss of the absorbent, and can be directly used in an actual organic amine water solution desulfurization process without modification of the system, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of gas separation and environmental protection technology, and particularly relates to an absorbent for capturing SO2 through phase change absorption, specifically an aqueous liquid-liquid phase change absorbent for capturing SO2, its preparation method, and its application. Background Technology

[0002] Organic amine chemical absorption for SO2 separation has advantages such as high desulfurization efficiency, good selectivity, and no secondary pollutants, and has been widely used in industries such as steel, sulfuric acid, and non-ferrous smelting. However, during high-temperature thermal desorption, the sensible heat of the absorbent and the latent heat of water vaporization account for approximately 30% to 50% of the total energy consumption of desorption, resulting in high energy consumption. In recent years, researchers have reduced the energy consumption in SO2 desorption by designing novel organic amine structures, adding desorption promoters to improve the desorption rate, and developing efficient desorption processes.

[0003] Phase change absorbents are absorbents that undergo a phase change during or after the absorption of SO2, with SO2 concentrated in one of the phases. Only the SO2-rich phase needs to be desorbed, significantly reducing the volume of the regeneration solution and thus reducing regeneration energy consumption. Therefore, phase change absorbents are a class of absorbents with great energy-saving potential. Phase change absorption can be divided into liquid-liquid phase change absorption and liquid-solid phase change absorption according to the form of the absorption products. Chinese invention patent application "Ionic Liquid for Phase Change Absorption of Sulfur Dioxide (201810498673.2)" discloses an ionic liquid composed of organic cations and organic or inorganic anions. After absorbing SO2, it undergoes a liquid-solid phase change, requiring only the desorption of the solid, greatly reducing desorption energy consumption. Ionic liquids have characteristics such as high stability, tunable structure, and low volatility, but they have high viscosity, slow absorption rate, and high absorbent cost. Furthermore, the solids generated during phase change absorption can easily clog pipes, causing inconvenience in practical applications. Chinese invention patent application “A low-energy-consumption polyamine liquid-liquid phase change absorbent for carbon capture (202111486038.0)” discloses a liquid-liquid phase change absorbent using N,N-dimethylethanolamine (DMEA) as the absorbent. Water is used as the solvent to reduce the viscosity of the solution. The absorbent has a high rich phase loading and better desorption performance, but the phase separation agent n-butanol has a low boiling point and high volatility.

[0004] Currently, there are relatively few liquid-liquid phase change systems used for SO2 separation, and most of them are non-aqueous organic solvent phase change agents. These agents have high viscosity, poor heat and mass transfer efficiency, and high solvent volatility, which affects their SO2 absorption and desorption efficiency. Furthermore, in actual desulfurization processes, high-temperature flue gas needs to be cooled and dust-removed in a water scrubbing tower before entering the absorption tower, and the moisture in this gas can adversely affect the non-aqueous organic absorbent. Therefore, from an industrial application perspective, developing low-viscosity, water-soluble SO2 liquid-liquid phase change absorbents with low volatilization loss is of great significance for reducing the energy consumption of actual organic amine desulfurization systems. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art by providing an aqueous liquid-liquid phase change absorber for capturing SO2 with good cyclic absorption performance, high selectivity, and low energy consumption, as well as its preparation method and application.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is characterized in that: the aqueous liquid-liquid phase change absorbent comprises the following components by mass percentage: 10-30% absorbent, 5-45% phase separation agent, 0.1-6% phase separation promoter, and 40-70% water, wherein the sum of the mass percentages of the above components is 100%.

[0008] The absorbent is a piperazine organic amine;

[0009] The phase-separating agent is ether;

[0010] The phase separation promoter is an acid.

[0011] The piperazine organic amine has a mass percentage content of 15-25% in the aqueous liquid-liquid phase change absorbent.

[0012] The mass percentage of the phase-separating agent in the aqueous liquid-liquid phase change absorbent is 15-35%.

[0013] The phase separation promoter has a mass percentage content of 0.5% to 5% in the aqueous liquid-liquid phase change absorbent.

[0014] The water content in the aqueous liquid-liquid phase change absorbent is 45-65% by mass.

[0015] The piperazine organic amines mentioned are one or a mixture of two or more of N-hydroxyethyl piperazine (HEP), N,N-bis(2-hydroxyethyl) piperazine (BHEP), N,N-bis(2-hydroxypropyl) piperazine (HPP) or N-hydroxyethyl-N-hydroxypropyl piperazine (HEHPP).

[0016] The piperazine organic amines mentioned are a mixture of N,N-bis(2-hydroxyethyl)piperazine (BHEP) and N-hydroxyethylpiperazine (HEP), or a mixture of N,N-bis(2-hydroxypropyl)piperazine (HPP) and N-hydroxyethylpiperazine (HEP).

[0017] The ether contains 6 to 10 C atoms and the ratio of C atoms to O atoms is greater than or equal to 2.

[0018] The ether is one or a mixture of two or more of the following: ethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol ethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, triethylene glycol ethyl ether, triethylene glycol dimethyl ether, dipropylene glycol monopropyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol dimethyl ether.

[0019] The ether is ethylene glycol monobutyl ether, or diethylene glycol diethyl ether, or diethylene glycol monobutyl ether, or a binary mixture of ethylene glycol monobutyl ether and diethylene glycol diethyl ether, or a binary mixture of ethylene glycol monobutyl ether and diethylene glycol monobutyl ether, or a binary mixture of diethylene glycol diethyl ether and diethylene glycol monobutyl ether, or a ternary mixture of ethylene glycol monobutyl ether, diethylene glycol diethyl ether, and diethylene glycol monobutyl ether.

[0020] The acid is an inorganic acid, an organic acid, or a mixture of inorganic and organic acids; wherein the inorganic acid is selected from one or more of sulfuric acid, phosphoric acid, or boric acid, and the organic acid is selected from one or more of oxalic acid, malonic acid, succinic acid, citric acid, or salicylic acid.

[0021] The mixture of inorganic and organic acids is preferably a mixture of sulfuric acid and organic acids.

[0022] A method for preparing an aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is characterized by: weighing the following components by mass percentage: 10-30% piperazine organic amine as absorbent, 5-45% ether as phase separation agent, 0.1-6% acid as phase separation promoter, and 40-70% water, wherein the sum of the mass percentages of the above components is 100%; and stirring and mixing the components evenly in a sealed container to obtain the aqueous liquid-liquid phase change absorbent.

[0023] An application of an aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is characterized in that: when the aqueous liquid-liquid phase change absorbent is used to separate and capture SO2 in waste gas, the absorption temperature is 20-60℃ and the desorption temperature is 90-120℃.

[0024] An application of an aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2, characterized in that: when the aqueous liquid-liquid phase change absorbent is used to separate and capture SO2 in waste gas, the absorption temperature is 30-50℃ and the desorption temperature is 100-110℃.

[0025] The interaction mechanism of the aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 provided by this invention is as follows:

[0026] This invention proposes a liquid-liquid phase change absorbent composed of piperazine organic amines as absorbents, ethers as phase-separating agents, acids as phase-separation promoters, and water. The piperazine organic amines in this absorbent exhibit good selectivity and cyclic absorption / desorption performance for SO2. The non-polar, non-volatile ether acts as the phase-separating agent; the oxygen atoms in the ether can bond with the hydrogen atoms of the organic amine and water molecules via hydrogen bonds, forming a stable spatial structure that is miscible. Hydrogen bonds are a weak electrostatic attraction and are easily broken by external forces such as heating or reactions. When SO2 is absorbed, the nitrogen atom on the piperazine group reacts with SO2, disrupting the hydrogen bonds between ether-amine-water molecules, reducing the solubility of the ether in water, causing it to aggregate in molecular form, and inducing liquid-liquid phase separation. The polar ammonium salt generated by the reaction of the acid and organic amine has a strong salting-out ability, competing with the organic solvent for free water and expelling the organic solvent. Furthermore, the polar ammonium salt further disrupts the hydrogen bond network between ether-amine-water molecules. These two effects jointly promote the liquid-liquid phase change during the absorption process. The solvent water not only reduces the viscosity of the solution, but also regulates the phase transition through hydrogen bonding with organic amines and ethers. Therefore, this liquid-liquid phase transition absorber rapidly separates into two phases after absorbing SO2. The ammonium salt formed by the reaction of SO2 with organic amines is enriched in the lower aqueous phase, while the upper aqueous phase has a very low SO2 content and is mainly composed of organic solvent ether and water. Only the SO2-rich liquid phase (lower aqueous phase) needs to be sent to the desorption tower for regeneration, significantly reducing desorption energy consumption. When the number of oxygen atoms in the ether is excessive, more hydrogen bonds are formed, resulting in stronger hydrophilicity and making phase separation difficult. Longer carbon chains reduce the hydrophilicity of the ether, enhance the nonpolarity of the solvent, and facilitate phase separation. Therefore, the ether used has 6–10 carbon atoms, with a carbon-to-oxygen ratio greater than or equal to 2.

[0027] The present invention has the following advantages over the prior art:

[0028] This invention creates a novel aqueous liquid-liquid phase change absorbent by mixing a specific phase-separating agent ether with a piperazine-based organic amine absorbent, a phase-separation promoter acid, and water in an appropriate ratio. This aqueous liquid-liquid phase change absorbent not only exhibits excellent cyclic absorption performance and high selectivity for SO2, but also boasts low regeneration energy consumption, fast absorption rate, and minimal absorbent volatilization loss. This solves the problems of high desorption energy consumption in existing non-phase change absorption systems and high viscosity and slow mass transfer rates in ionic liquid and organic solvent phase change absorbents. Furthermore, it can be directly applied to actual organic amine aqueous solution desulfurization processes without requiring system modifications, demonstrating promising application prospects.

[0029] The aqueous phase change absorbent provided by this invention can quickly separate into two phases, liquid and liquid, after absorbing a certain amount of SO2. The phase separation agent is a low-polarity organic ether, the phase separation agent is a polar organic amine salt, and the phase change is water, which promotes the occurrence of phase change.

[0030] The piperazine organic amines and high-boiling-point ethers in the aqueous liquid-liquid phase change absorbent provided by this invention avoid the loss of absorbent and solvent due to volatility.

[0031] The phase separation promoter in the aqueous liquid-liquid phase change absorbent provided by this invention can reduce the volatilization loss of piperazine organic amines and increase the polarity of organic amine salts, thereby promoting the occurrence of phase change.

[0032] The aqueous phase change absorbent provided by this invention is an aqueous solution with low viscosity and excellent heat and mass transfer and transport performance. Attached Figure Description

[0033] Appendix Figure 1 Comparison diagram of SO2 and amine distribution in the rich and poor phases after absorption by the aqueous liquid phase change absorbents provided in Examples 4 to 9 of the present invention;

[0034] Appendix Figure 2 Comparison of the volume ratio of rich and poor phases and the distribution coefficient of SO2 in the rich and poor phases after absorption by the aqueous liquid phase change absorbents provided in Examples 4 to 9 of the present invention.

[0035] Appendix Figure 3 The aqueous liquid-liquid phase change absorber provided in Example 11 of the present invention provides solutions before and after absorption. 13 C NMR analysis results;

[0036] Appendix Figure 4 A comparison diagram of the cyclic loading in the cyclic absorption and desorption of the aqueous liquid-liquid phase change absorber provided in Example 15 of the present invention and Comparative Example 4;

[0037] Appendix Figure 5 A comparison chart of desorption rate and energy consumption in the cyclic absorption and desorption of the aqueous liquid-liquid phase change absorber provided in Example 15 of the present invention and Comparative Example 4. Detailed Implementation

[0038] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention and should be understood as being intended to better explain the invention, but not to limit the scope of the invention.

[0039] This invention provides an aqueous liquid-liquid phase change absorbent with good cyclic absorption and desorption performance, fast absorption rate, and low volatilization loss. By mass percentage, it comprises the following components: 10-30% piperazine organic amine as absorbent, 5-45% ether as phase separation agent, 0.1-6% acid as phase separation promoter, and 40-70% water, wherein the sum of the mass percentages of the above components is 100%.

[0040] Piperazine organic amines are one or a mixture of two or more of N-hydroxyethylpiperazine (HEP), N,N-bis(2-hydroxyethyl)piperazine (BHEP), N,N-bis(2-hydroxypropyl)piperazine (HPP) or N-hydroxyethyl-N-hydroxypropylpiperazine (HEHPP).

[0041] A preferred embodiment is that the piperazine organic amine is a mixture of N,N-bis(2-hydroxyethyl)piperazine (BHEP) and N-hydroxyethylpiperazine (HEP), or a mixture of N,N-bis(2-hydroxypropyl)piperazine (HPP) and N-hydroxyethylpiperazine (HEP).

[0042] The ether contains 6 to 10 carbon atoms and the ratio of carbon atoms to oxygen atoms is greater than or equal to 2. The ether is one or more of the following: ethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol ethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, triethylene glycol ethyl ether, triethylene glycol dimethyl ether, dipropylene glycol monopropyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol dimethyl ether.

[0043] A preferred embodiment is: the ether is ethylene glycol monobutyl ether, or diethylene glycol diethyl ether, or diethylene glycol monobutyl ether, or a binary mixture of ethylene glycol monobutyl ether and diethylene glycol diethyl ether, or a binary mixture of ethylene glycol monobutyl ether and diethylene glycol monobutyl ether, or a binary mixture of diethylene glycol diethyl ether and diethylene glycol monobutyl ether, or a ternary mixture of ethylene glycol monobutyl ether, diethylene glycol diethyl ether, and diethylene glycol monobutyl ether.

[0044] The acid is selected from one or more inorganic acids or organic acids. The inorganic acid is selected from one or more of sulfuric acid, phosphoric acid or boric acid, and the organic acid is selected from one or more of oxalic acid, malonic acid, succinic acid, citric acid or salicylic acid; in the mixed acid, a mixture of sulfuric acid and organic acid is preferred.

[0045] A preferred option is that the acid is sulfuric acid, or phosphoric acid, or succinic acid, or salicylic acid, or citric acid, or a binary mixture of sulfuric acid and phosphoric acid, or a binary mixture of sulfuric acid and succinic acid, or a binary mixture of sulfuric acid and citric acid, or a binary mixture of sulfuric acid and salicylic acid.

[0046] A method for preparing an aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 involves weighing the following components by mass percentage: 10-30% piperazine organic amine as absorbent, 5-45% ether as phase separation agent, 0.1-6% acid as phase separation promoter, and 40-70% water, wherein the sum of the mass percentages of the above components is 100%; the components are stirred and mixed evenly in a sealed container to obtain the aqueous liquid-liquid phase change absorbent.

[0047] An application of an aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2, wherein when the aqueous liquid-liquid phase change absorbent is used to separate and capture SO2 in waste gas, the absorption temperature is 20-60℃, preferably 30-50℃; and the desorption temperature is 90-120℃, preferably 100-110℃.

[0048] The aqueous liquid-liquid phase change absorbent provided by this invention can be used for the separation and capture of SO2 in the exhaust gas of coal-fired power plants, sulfuric acid plants, hydrometallurgical plants, and other factories.

[0049] The phase change absorption-desorption process for SO2 is as follows: Simulated flue gas with a SO2 volume fraction of 0.1%-15% and the remainder being N2 is prepared in a gas distribution tank. The sulfur-containing flue gas is then passed into an organic amine phase change solution. The absorption temperature is maintained at 25–60℃, and the absorption reaction lasts for 3–6 hours. After SO2 absorption, the gas spontaneously separates into two phases. The lower aqueous phase is the SO2-enriched phase, containing most of the organic amine salts resulting from the reaction with SO2, water, and a small amount of phase-separating agent. The upper aqueous phase is the SO2-depleted phase, containing a small amount of organic amine salts resulting from the reaction with SO2, water, and a large amount of phase-separating agent.

[0050] The upper and lower aqueous phases after SO2 absorption are separated, and the lower aqueous phase is sent for desorption regeneration. The desorption regeneration temperature is 100-120℃, and the time is 0.5-3.5h. The desorbed SO2 is recovered and reused. The lean amine solution after the rich phase regeneration is mixed with the upper aqueous phase to obtain an aqueous phase change absorbent for cyclic absorption of SO2.

[0051] In addition to SO2, the simulated flue gas described in this invention also contains nitrogen, which is used as a carrier gas to introduce SO2 into the absorbent.

[0052] The components of the aqueous phase change absorbent provided by this invention can be prepared in the laboratory or obtained through procurement.

[0053] In the embodiments provided by this invention, the organic amine N,N-bis(2-hydroxypropyl)piperazine (HPP), also known as 1,4-bis(2-hydroxypropyl)piperazine, was prepared by the method described in step A of Example 1 in CN101584961A; the organic amine N-hydroxyethyl-N-hydroxypropylpiperazine (HEHPP), also known as 1-(2-hydroxyethyl)-4-(2-hydroxypropyl)piperazine, was prepared by the method described in Example CN103638779A; other reagents were purchased from China National Pharmaceutical Group Corporation.

[0054] Example 1

[0055] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is composed of N,N-bis(2-hydroxyethyl)piperazine (BHEP) as the absorbent, triethylene glycol dimethyl ether as the phase-separating agent, boric acid as the phase-separating promoter, and water. The BHEP comprises 20% by mass, the triethylene glycol dimethyl ether 25% by mass, the boric acid 3.5% by mass, and the remainder is water, with the sum of the mass percentages of the above components being 100%.

[0056] 100g of the liquid absorbent was used to absorb simulated flue gas containing 1.23% SO2. The flow rate of the simulated flue gas was 1.62 L / min, the absorption temperature was 25℃, and the absorption time was 240 min. The SO2-rich phase (or downstream aqueous phase) after absorption was sent for desorption regeneration at 100℃ for 180 min.

[0057] The method for detecting SO2 concentration in the upper and lower aqueous phases after absorption by the liquid-liquid absorbent is iodometric titration, and the viscosity is determined by rotational viscometer.

[0058] Absorption capacity (AQ) refers to the amount of SO2 absorbed per unit volume of amine, expressed in mol SO2 / mol amine.

[0059] Cyclic load EQ is the difference between the SO2 load of the rich solution obtained after SO2 absorption and the SO2 load of the lean solution obtained after desorption. That is, the number of moles of SO2 desorbed from each mole of organic amine in one absorption-desorption cycle, with the unit being mol SO2 / mol amine.

[0060] The distribution coefficient is the ratio of the molar concentration of SO2 in the enriched phase to the molar concentration of SO2 in the lean phase after absorption.

[0061] The desorption rate DE during the desorption process is the amount of SO2 desorbed / the amount of SO2 in the amine-rich solution before desorption × 100%.

[0062] The energy consumption Q in the desorption process refers to the amount of electricity consumed to desorb a unit mass of SO2, and the unit is GJ / t.

[0063] Example 2

[0064] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is disclosed, comprising N,N-bis(2-hydroxyethyl)piperazine (BHEP) as the absorbent, triethylene glycol dimethyl ether as the phase-separating agent, phosphoric acid as the phase-separating promoter, and water. The mass fractions of BHEP are 20%, triethylene glycol dimethyl ether is 25%, phosphoric acid is 3.5%, and the remainder is water, with the sum of the mass percentages of the above components being 100%. The remainder is the same as in Example 1.

[0065] Example 3

[0066] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is disclosed, comprising N,N-bis(2-hydroxyethyl)piperazine (BHEP) as the absorbent, triethylene glycol dimethyl ether as the phase-separating agent, sulfuric acid as the phase-separating promoter, and water. The mass fraction of BHEP is 20%, the mass fraction of triethylene glycol dimethyl ether is 25%, the mass fraction of sulfuric acid is 3.5%, and the remainder is water, with the sum of the mass percentages of the above components being 100%. The rest is the same as in Example 1.

[0067] Comparative Example 1

[0068] BHEP and triethylene glycol dimethyl ether were directly dissolved in water to prepare an aqueous solution with a BHEP mass fraction of 20% and a triethylene glycol dimethyl ether mass fraction of 25% as the absorbent. The rest was the same as in Example 1.

[0069] Table 1. Effect of acid on the absorption and desorption performance of absorbent.

[0070]

[0071]

[0072] As shown in Table 1, in Examples 1 and 2, when boric acid and phosphoric acid were used as phase separation promoters, the amine-rich liquid after absorption did not separate into phases, but liquid-liquid phase separation occurred after heating to a certain temperature. In Example 3, when sulfuric acid was used as a phase separation promoter, liquid-liquid phase separation occurred after absorption. Furthermore, although the absorption capacity of organic amines decreased after adding acid as a phase separation promoter, the desorption rate and cycle absorption capacity both increased, and the desorption energy consumption was significantly reduced.

[0073] Because the nitrogen atom in piperazine organic amines and the ether bond in the phase-separating agent can form hydrogen bonds with water molecules, the absorbent is a homogeneous solution before absorption. When the acid reacts with the organic amine to form an amine salt, the highly polar ammonium salt disrupts the interaction forces and hydrogen bonds between the amine, water, and ether. Due to the self-association ability of water and the salting-out effect of the ammonium salt, the absorbent undergoes phase separation. Heating further breaks the hydrogen bonds between the ether and water molecules, promoting phase separation. The stronger the polarity of the acid and the stronger the polarity of the ammonium salt, the greater the salting-out effect, and the more favorable the phase separation. That is, sulfuric acid has a good phase separation promoting effect. Considering the absorption capacity, cyclic absorption capacity, desorption rate, and energy consumption, sulfuric acid provides a suitable phase transition temperature when used as a phase separation promoter.

[0074] Example 4

[0075] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is composed of N,N-di(2-hydroxypropyl)piperazine (HPP) and N-hydroxyethylpiperazine (HEP) as absorbents, diethylene glycol diethyl ether as a phase-separating agent, sulfuric acid as a phase-separating promoter, and water. The mass fractions of HPP, HEP, diethylene glycol diethyl ether, and sulfuric acid are 16%, 4.0%, with the remainder being water. The sum of the mass percentages of the above components is 100%.

[0076] 100g of the absorbent was used to absorb simulated flue gas containing 1.0% SO2. The flow rate of the simulated flue gas was 1.22L / min, the absorption temperature was 40℃, and the absorption time was 180min. The SO2-rich phase (or downstream aqueous phase) after absorption was sent for desorption regeneration at 100℃ for 120min.

[0077] Among them, the distribution rate D of SO2 S This refers to the SO2 loading in the enriched phase being 100% of the total SO2 loading in the amine solution;

[0078] Partition ratio D of organic amines A This refers to the percentage of amines in the enriched phase relative to the total amine content multiplied by 100%.

[0079] Absorption rate refers to the amount of SO2 absorbed per unit time, expressed in mol / s, and is determined using the initial rate method.

[0080] Example 5

[0081] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is disclosed, comprising N,N-bis(2-hydroxypropyl)piperazine (HPP) and N-hydroxyethylpiperazine (HEP) as absorbents, diethylene glycol dibutyl ether as a phase-separating agent, sulfuric acid as a phase-separating promoter, and water. Specifically, the mass fraction of HPP is 18%, the mass fraction of HEP is 2%, the mass fraction of diethylene glycol dibutyl ether is 16%, the mass fraction of sulfuric acid is 4.0%, and the remainder is water, with the sum of the mass percentages of the above components being 100%. The remainder is the same as in Example 4.

[0082] Example 6

[0083] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is disclosed, comprising N,N-bis(2-hydroxypropyl)piperazine (HPP) and N-hydroxyethylpiperazine (HEP) as absorbents, diethylene glycol dimethyl ether as a phase-separating agent, sulfuric acid as a phase-separating promoter, and water. Specifically, the mass fraction of HPP is 18%, the mass fraction of HEP is 2%, the mass fraction of diethylene glycol dimethyl ether is 16%, the mass fraction of sulfuric acid is 4.0%, and the remainder is water, with the sum of the mass percentages of the above components being 100%. The remainder is the same as in Example 4.

[0084] Example 7

[0085] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is disclosed, comprising N,N-bis(2-hydroxypropyl)piperazine (HPP) and N-hydroxyethylpiperazine (HEP) as absorbents, triethylene glycol ethyl ether as a phase-separating agent, sulfuric acid as a phase-separating promoter, and water. Specifically, the mass fraction of HPP is 18%, the mass fraction of HEP is 2%, the mass fraction of triethylene glycol ethyl ether is 16%, the mass fraction of sulfuric acid is 4.0%, and the remainder is water, with the sum of the mass percentages of the above components being 100%. The remainder is the same as in Example 4.

[0086] Example 8

[0087] An aqueous liquid-liquid phase change absorbent for SO2 separation and capture is composed of N,N-bis(2-hydroxypropyl)piperazine (HPP) and N-hydroxyethylpiperazine (HEP) as absorbents, tetraethylene glycol methyl ether as a phase separation agent, sulfuric acid as a phase separation promoter, and water. Specifically, the mass fraction of BHEP is 18%, the mass fraction of HEP is 2%, the mass fraction of triethylene glycol methyl ether is 16%, the mass fraction of sulfuric acid is 4.0%, and the remainder is water, with the sum of the mass percentages of the above components being 100%. The rest is the same as in Example 4.

[0088] Example 9

[0089] An aqueous liquid-liquid phase change absorbent for SO2 separation and capture is composed of N,N-bis(2-hydroxypropyl)piperazine (HPP) and N-hydroxyethylpiperazine (HEP) as absorbents, diethylene glycol diethyl ether and diethylene glycol monobutyl ether as phase separation agents, sulfuric acid as a phase separation promoter, and water. Specifically, the mass fraction of BHEP is 18%, the mass fraction of HEP is 2%, the mass fractions of diethylene glycol diethyl ether and diethylene glycol monobutyl ether are both 8%, the mass fraction of sulfuric acid is 4.0%, and the remainder is water, with the sum of the mass percentages of the above components being 100%. The rest is the same as in Example 4.

[0090] Comparative Example 2

[0091] N,N-bis(2-hydroxypropyl)piperazine (HPP) and N-hydroxyethylpiperazine (HEP) were directly dissolved in water to prepare an aqueous solution with a mass fraction of 18% HPP and 2% HEP as the absorbent. The mass fraction of sulfuric acid was 4.0%, and the rest was the same as in Example 4.

[0092] Table 2. Effects of various ethers on absorption phase separation

[0093]

[0094]

[0095] Table 2 shows that the mixed amine aqueous solution of HPP and HEP absorbs SO2 into a homogeneous solution, and the addition of ether causes a phase change. Since the amount of ether used is relatively small, it has almost no effect on the absorption capacity of the absorbent for SO2, but the cyclic absorption capacity and desorption rate are improved, and energy consumption is significantly reduced. Because tetraethylene glycol dimethyl ether has a long carbon chain, the viscosity of the solution increases, leading to a decrease in desorption rate and cyclic absorption capacity. (Appendix) Figure 1 The distribution of SO2 and amine in the rich phase after absorption by the liquid-liquid phase change absorbents of Examples 4-9 is described, with appendices. Figure 2 The volume percentages of the lean and rich phases after absorption by the liquid-liquid phase change absorbers in Examples 4-9, as well as the distribution coefficient of SO2 in the lean and rich phases, are described. (See Table 2 and Appendix.) Figure 1 and attached Figure 2 It can be seen that: (1) When ether is used as a phase separation agent, the distribution rate of SO2 and amine in the rich phase is greater than 90%, that is, SO2 and amine are mainly enriched in the lower aqueous phase (rich phase), and the concentration in the upper aqueous phase (poor phase) is very low. Due to the high concentration and small volume of SO2 in the rich phase, the desorption rate is increased and the energy consumption is reduced; when diethylene glycol diethyl ether is used as a phase separation agent, the distribution coefficient of SO2 is as high as 27.5, the distribution rate of SO2 in the rich liquid is as high as 99.9%, and there is almost no SO2 in the poor phase. (2) The phase separation ability of ether is related to its structure. When the carbon-oxygen atom ratio in the ether is greater than 2, phase separation can be achieved at a lower temperature; when the carbon-oxygen atom ratio is equal to 2, the longer the carbon chain, the stronger its nonpolarity, and the lower the required phase separation temperature. Therefore, diethylene glycol dimethyl ether requires the highest phase separation temperature. (3) When diethylene glycol diethyl ether and diethylene glycol monobutyl ether are mixed into a binary ether, its absorption performance and phase separation performance are between the two ethers.

[0096] The addition of ether to the system slightly increased the viscosity of the absorbent, and the viscosity of the enriched phase after absorption increased further, but remained low at around 10 mPa·s, while the absorption rate decreased slightly. Based on comprehensive analysis of absorption capacity, cyclic absorption capacity, desorption rate, energy consumption, and phase separation performance, the piperazine-based organic amine phase change absorption system using diethylene glycol diethyl ether and diethylene glycol monobutyl ether as phase separation agents showed better performance.

[0097] Example 10

[0098] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is disclosed. This absorbent is composed of N,N-bis(2-hydroxyethyl)piperazine (BHEP) as the absorbent, diethylene glycol diethyl ether as the phase-separating agent, sulfuric acid as the phase-separating promoter, and water. Specifically, the mass fraction of BHEP is 20%, the mass fraction of diethylene glycol diethyl ether is 15%, the mass fraction of sulfuric acid is 0.5%, and the remainder is water. The sum of the mass percentages of the above components is 100%. The rest is the same as in Example 4.

[0099] Example 11

[0100] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is disclosed, comprising N,N-bis(2-hydroxyethyl)piperazine (BHEP) as the absorbent, diethylene glycol diethyl ether as the phase-separating agent, sulfuric acid as the phase-separating promoter, and water. The mass fractions of BHEP, diethylene glycol diethyl ether, and sulfuric acid are 20% and 0.5%, respectively, with the remainder being water. The sum of the mass percentages of these components is 100%. The remainder is the same as in Example 4.

[0101] Example 12

[0102] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is disclosed, comprising N,N-bis(2-hydroxyethyl)piperazine (BHEP) as the absorbent, diethylene glycol diethyl ether as the phase-separating agent, sulfuric acid as the phase-separating promoter, and water. The mass fraction of BHEP is 20%, the mass fraction of diethylene glycol diethyl ether is 25%, the mass fraction of sulfuric acid is 0.5%, and the remainder is water, with the sum of the mass percentages of the above components being 100%. The remainder is the same as in Example 4.

[0103] Example 13

[0104] The absorption reaction temperature was 50°C, and the rest was the same as in Example 11.

[0105] Example 14

[0106] The absorption reaction temperature was 60°C, and the rest was the same as in Example 11.

[0107] Comparative Example 3

[0108] N,N-bis(2-hydroxyethyl)piperazine (BHEP) was directly dissolved in water to prepare an aqueous solution with a mass fraction of 20% BHEP as the absorbent. The mass fraction of sulfuric acid was 0.5%, and the rest was the same as in Example 10.

[0109] Table 3. Effects of diethylene glycol diethyl ether dosage and temperature on absorption phase separation.

[0110]

[0111] In Examples 10-14, phase separation occurred approximately 10 minutes after SO2 absorption, with SO2 partitioning rates exceeding 99% and amine partitioning rates exceeding 98% in the rich phase. Comparing Comparative Example 3 with Examples 10-12, it was found that a higher mass fraction of diethylene glycol diethyl ether in the phase change absorbent slightly reduced the amount of SO2 absorbed. This is mainly due to the increased viscosity of the absorbent, which reduces mass transfer efficiency; the higher the mass fraction of diethylene glycol diethyl ether, the more pronounced this effect. However, with increasing diethylene glycol diethyl ether mass fraction, the cyclic load and desorption rate significantly improved, regeneration energy consumption significantly decreased, and the lower phase volume ratio also decreased. Comparing Examples 13 and 14 with Example 11, it was found that increased temperature had almost no effect on the lower phase volume ratio, but the absorption and desorption effects worsened, similar to the pattern observed with homogeneous absorbents without phase change.

[0112] Appendix Figure 3 For the solution before and after absorption in Example 11 13 C NMR analysis results. (Attached) Figure 3 Peaks 1, 2, and 3 in the figure represent the chemical shifts of the C atom in the piperazine ring of BHEP; peaks 2 and 3 represent the chemical shifts of the C atom in the branched hydroxyethyl group; peaks a, b, c, and d represent the chemical shifts of the C atom in diethylene glycol diethyl ether. (From the appendix...) Figure 3 It can be observed that diethylene glycol diethyl ether hardly reacts with SO2 and is mainly concentrated in the upper aqueous phase; the ammonium salt of BHEP reacting with SO2 is mainly enriched in the lower aqueous phase (enriched phase), while some diethylene glycol diethyl ether also dissolves in the lower aqueous phase.

[0113] Example 15

[0114] An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 is composed of N,N-bis(2-hydroxyethyl)piperazine (BHEP) as the absorbent, diethylene glycol diethyl ether as the phase-separating agent, sulfuric acid as the phase-separating promoter, and water. The BHEP comprises 15% by mass, the diethylene glycol diethyl ether 20% by mass, the sulfuric acid 4.5% by mass, and the remainder is water, with the sum of the mass percentages of the above components being 100%.

[0115] 100g of the absorbent was used to absorb simulated flue gas containing 1.5% SO2. The flow rate of the simulated flue gas was 1.25 L / min, the absorption temperature was 40℃, and the absorption time was 180 min. The SO2-rich phase after absorption was sent for desorption regeneration at 100℃ for 120 min. The desorbed liquid phase was mixed with the absorbed lean liquid phase to restore the solution to a homogeneous phase, and then the absorption and desorption cycle was repeated. The volatility of the absorbent was determined as follows: 100g of absorbent was added to the absorption bottle, and N2 was introduced at a flow rate of 800 ml / min. The mass of the absorbent was weighed at regular intervals, and the weight loss rate was calculated.

[0116] Comparative Example 4

[0117] N,N-bis(2-hydroxyethyl)piperazine (BHEP) was directly dissolved in water to prepare an aqueous solution with a BHEP mass fraction of 15% as the absorbent, wherein the mass fraction of sulfuric acid was 4.5%. The rest was the same as in Example 15.

[0118] Figure 4 and Figure 5 The cyclic absorption and desorption performance of the absorbent prepared in Example 15 was compared with that of Comparative Example 4. The results showed that the cyclic loading EQ of the absorbent did not change significantly with the increase of absorption-desorption cycles; the EQ of Example 15 remained at approximately 0.88 mol / mol, an increase of about 8.7% compared to Comparative Example 4; the desorption rate was greater than 96%, an increase of about 6.1% compared to Comparative Example 4; and the average energy consumption was approximately 265.7 GJ / t, a decrease of about 19.5% compared to Comparative Example 4. After four cycles of absorption, the lower aqueous phase accounted for 80.2% of the total volume, the SO2 concentration ratio of the lower and upper aqueous phases was 12.21, and the SO2 partition rate in the enriched phase was greater than 99%, indicating that the absorbent has stable regenerability and good partitioning performance.

[0119] Compared with the homogeneous absorbent in Comparative Example 4, the viscosity of the rich phase after the fourth absorption in Example 15 was 10.6 mPa·s, while the viscosity of the rich liquid after absorption in Comparative Example 4 was 6.5 mPa·s. The viscosity of this example is still relatively low. In the volatility experiment, the weight loss rate of the homogeneous absorbent in Comparative Example 4 was measured to be 8.68% after 6 hours, while the weight loss rate of the phase change absorbent in Example 15 was 7.22%, with a reduction in volatilization loss of approximately 16.8%. It can be seen that the piperazine organic amine phase change absorption system using ether as a phase separation agent and sulfuric acid as a phase separation promoter not only greatly reduces desorption energy consumption but also reduces the volatilization loss of the absorbent during the absorption process, which has significant practical application value in industry.

[0120] This invention creates a novel aqueous liquid-liquid phase change absorbent by mixing a specific phase-separating agent ether with a piperazine-based organic amine absorbent, a phase-separation promoter acid, and water in an appropriate ratio. This aqueous liquid-liquid phase change absorbent not only exhibits excellent cyclic absorption performance and high selectivity for SO2, but also boasts low regeneration energy consumption, fast absorption rate, and minimal absorbent volatilization loss. This solves the problems of high desorption energy consumption in existing non-phase change absorption systems and high viscosity and slow mass transfer rates in ionic liquid and organic solvent phase change absorbents. Furthermore, it can be directly applied to actual organic amine aqueous solution desulfurization processes without requiring system modifications, demonstrating promising application prospects.

[0121] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention. Technologies not covered in this invention can be implemented using existing technologies.

Claims

1. An aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2, characterized in that: This aqueous liquid-liquid phase change absorbent comprises, by mass percentage, the following components: 10–30% absorbent, 5–45% phase separation agent, 0.1–6% phase separation promoter, and 40–70% water, wherein the sum of the mass percentages of the above components is 100%. The absorbent is a piperazine organic amine; The phase-separating agent is an ether, wherein the number of C atoms in the ether is 6 to 10 and the ratio of the number of C atoms to the number of O atoms is greater than or equal to 2; The phase separation promoter is an acid; The piperazine organic amines mentioned are one or a mixture of two or more of N-hydroxyethyl piperazine, N,N-bis(2-hydroxyethyl) piperazine, N,N-bis(2-hydroxypropyl) piperazine or N-hydroxyethyl-N-hydroxypropyl piperazine; The ether is one or a mixture of two or more of the following: ethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol ethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, triethylene glycol ethyl ether, triethylene glycol dimethyl ether, dipropylene glycol monopropyl ether, triethylene glycol monobutyl ether, and tetraethylene glycol dimethyl ether. The acid is an inorganic acid, an organic acid, or a mixture of inorganic and organic acids; wherein the inorganic acid is selected from one or more of sulfuric acid, phosphoric acid, or boric acid, and the organic acid is selected from one or more of oxalic acid, malonic acid, succinic acid, citric acid, or salicylic acid.

2. The aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 according to claim 1, characterized in that: The piperazine organic amine has a mass percentage content of 15-25% in the aqueous liquid-liquid phase change absorbent.

3. The aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 according to claim 1, characterized in that: The mass percentage of the phase-separating agent in the aqueous liquid-liquid phase change absorbent is 15-35%.

4. The aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 according to claim 1, characterized in that: The mass percentage of the phase separation promoter in the aqueous liquid-liquid phase change absorbent is 0.5-5%.

5. The aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 according to claim 1, characterized in that: The water content in the aqueous phase change absorbent is 45-65% by mass.

6. The aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 according to claim 1, characterized in that: The piperazine organic amines mentioned are a mixture of N,N-bis(2-hydroxyethyl)piperazine and N-hydroxyethylpiperazine, or a mixture of N,N-bis(2-hydroxypropyl)piperazine and N-hydroxyethylpiperazine.

7. The aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 according to claim 1, characterized in that: The ether is ethylene glycol monobutyl ether, or diethylene glycol diethyl ether, or diethylene glycol monobutyl ether, or a binary mixture of ethylene glycol monobutyl ether and diethylene glycol diethyl ether, or a binary mixture of ethylene glycol monobutyl ether and diethylene glycol monobutyl ether, or a binary mixture of diethylene glycol diethyl ether and diethylene glycol monobutyl ether, or a ternary mixture of ethylene glycol monobutyl ether, diethylene glycol diethyl ether, and diethylene glycol monobutyl ether.

8. The aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 according to claim 1, characterized in that: The mixture of inorganic and organic acids is a mixture of sulfuric acid and organic acids.

9. A method for preparing an aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 as described in any one of claims 1-8, characterized in that: Weigh the following components by mass percentage: 10-30% piperazine organic amine as absorbent, 5-45% ether as phase separation agent, 0.1-6% acid as phase separation promoter, and 40-70% water. The sum of the mass percentages of the above components is 100%. Mix the components evenly in a sealed container to obtain the aqueous liquid-liquid phase change absorbent.

10. An application of an aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 as described in any one of claims 1-8, characterized in that: When the aqueous liquid-liquid phase change absorbent is used to separate and capture SO2 in waste gas, the absorption temperature is 20-60℃ and the desorption temperature is 90-120℃.

11. The application of the aqueous liquid-liquid phase change absorbent for absorbing and capturing SO2 according to claim 10, characterized in that: When the aqueous liquid-liquid phase change absorbent is used to separate and capture SO2 in waste gas, the absorption temperature is 30-50℃ and the desorption temperature is 100-110℃.

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