Aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture and its application

Abstract

The present invention 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 by weight percentage: 10 to 30 wt% of a piperazine organic amine as an absorbent, 5 to 45 wt% of an ester as a phase-separating agent, 0.5 to 8.0% of an acid as a phase-separation accelerator, and 40 to 75 wt% of water as a solvent, the sum of the weight percentages of the above components being 100%. The components are stirred and mixed evenly in a closed container to obtain an aqueous liquid-liquid phase-change absorbent; the absorption temperature during application is 20 to 60 ° C and the desorption temperature is 90 to 120 ° C. The aqueous liquid-liquid phase-change absorbent of the present invention can enrich more than 95% of SO2 and more than 96% of the absorbent in the lower liquid phase. Water as a solvent reduces the viscosity of the absorption liquid and accelerates the heat and mass transfer rate; it has the advantages of low desorption energy consumption, good cyclic absorption performance, low volatilization loss, and controllable phase-separation threshold.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas separation and environmental protection, and in particular relates to an absorbent for capturing SO2 by phase change absorption, specifically an aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture and its application. Background Art

[0002] At present, organic amine chemical absorption is widely used in industry to separate acidic components such as CO2, SO2, H2S, etc. in waste gas. This method has the advantages of high absorption efficiency, good selectivity, and recyclable absorbent. However, a large amount of water needs to be evaporated during high-temperature thermal regeneration of the absorbent, resulting in high energy consumption in the process.

[0003] Phase-change absorbents are a type of absorbent with great energy-saving potential and have attracted great attention. This type of absorbent is a uniform liquid phase before absorption. After absorbing CO2 or SO2, it transforms into two phases, causing CO2 or SO2 to be enriched in one of the phases. By desorbing the rich phase, the volume of the regeneration solution can be greatly reduced, thereby significantly reducing the regeneration energy consumption. The Chinese invention patent application "A phase-change absorption liquid for capturing SO2 (CN201710281328.9)" is a mixed solution composed of imidazole derivatives and organic solvents. After absorbing SO2, it separates into liquid-liquid or liquid-solid phases. The phase separation speed is fast, the regeneration energy consumption is low, and there are no problems such as degradation and corrosion. However, the solids formed during the absorption process may clog the pipeline, and the ionic liquid has high viscosity and high cost. E. Duan et al. used a binary mixture of water and caprolactam tetrabromide (CPL-TBAB) ionic liquid to absorb SO2. The mixture underwent a liquid-liquid phase transition, and the SO2-rich phase could be regenerated by heating under reduced pressure. However, its absorption capacity was low, only 0.52 g SO2 / g at 293 K, and the viscosity was still high, about 200 mPa·s. The Chinese invention patent application "A Phase Change Absorber and Its Application in Carbon Dioxide Capture (CN202110198459.7)" discloses a new phase-change absorbent composed of N-aminoethylpiperazine (AEP), n-propanol, and water. After saturation with CO2, a liquid-liquid phase transition occurred, with most of the carbon dioxide product concentrated in the lower liquid phase. Using water as a solvent avoided the formation of solid precipitates, but n-propanol has a low boiling point and large volatile losses.

[0004] Currently, there are many aqueous liquid-liquid phase change agents used for CO2 separation, but few for SO2 separation. Because the absorption mechanism of organic amines for SO2 differs from that for CO2, aqueous CO2 phase change absorbents cannot simply be used directly for SO2 phase change absorption. Furthermore, most phase change absorbents require a high absorption load, or even equilibrium absorption, to undergo phase separation, and the absorption load in actual industrial absorption towers is far from equilibrium. Therefore, the development of aqueous SO2 liquid-liquid phase change absorbents with strong absorption capacity, a low phase separation threshold, and controllable low viscosity and low volatility is of great significance for solving the high energy consumption problem of organic amine wet flue gas desulfurization. Summary of the Invention

[0005] The purpose of the present invention is to address the problems of high regeneration energy consumption of organic amine aqueous solutions, high viscosity of non-aqueous solvent phase change absorbents and large solvent volatilization losses, and to provide an aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture and its application, which has good SO2 absorption performance, low regeneration energy consumption, fast absorption rate and small absorbent volatilization losses, thereby providing a new economical and effective idea for industrial waste gas desulfurization.

[0006] The purpose of the present invention is to be solved by the following technical solutions:

[0007] A water-based liquid-liquid phase-change absorbent with a controllable phase separation threshold for SO2 capture, characterized in that the water-based liquid-liquid phase-change absorbent comprises the following components, calculated by weight percentage: 10-30 wt% of an absorbent, 5-45 wt% of a phase separation agent, 0.5-8.0% of a phase separation accelerator, and 40-75 wt% of water, where the sum of the weight percentages of the above components is 100%.

[0008] The absorbent is a piperazine organic amine;

[0009] The phase separation agent is an ester;

[0010] The phase separation accelerator is an acid.

[0011] The weight percentage of the absorbent in the aqueous liquid-liquid phase change absorbent is 15-25wt%.

[0012] The weight percentage of the phase separation agent in the aqueous liquid-liquid phase change absorbent is 15-40wt%.

[0013] The weight percentage of the phase separation accelerator in the aqueous liquid-liquid phase change absorbent is 2.0-6.5wt%.

[0014] The weight percentage of water in the aqueous liquid-liquid phase change absorbent is 50-65wt%.

[0015] The piperazine organic amine is one or a mixture of any proportion of two or more of N-aminoethylpiperazine (AEP), N-hydroxyethylpiperazine (HEP), N,N-bis(2-hydroxyethyl)piperazine (BHEP), N,N-bis(2-hydroxypropyl)piperazine (HPP) or N-hydroxyethyl-N-hydroxypropylpiperazine (HEHPP).

[0016] The phase separation agent is one or a mixture of two or more of glycerol triacetate (GT), triethyl citrate (TEC), and triethyl phosphate (TEP).

[0017] The acid is an inorganic acid, an organic strong acid, or a mixture of an inorganic acid and an organic strong acid; the inorganic acid is one or a mixture of two or more of sulfuric acid, phosphoric acid or boric acid, and the organic strong acid is one or a mixture of two or more of oxalic acid, citric acid, malonic acid or succinic acid.

[0018] The acid is sulfuric acid, or a mixture of sulfuric acid and phosphoric acid, or a mixture of sulfuric acid and a strong organic acid, that is, a mixture of an inorganic acid and a strong organic acid, preferably a mixture of sulfuric acid and an organic acid.

[0019] A water-based liquid-liquid phase-change absorbent with a controllable phase-separation threshold for SO2 capture, characterized in that the preparation method of the water-based liquid-liquid phase-change absorbent with a controllable phase-separation threshold is as follows: weigh the following components in percentage by weight: 10 to 30 wt% of a piperazine-type organic amine as an absorbent, 5 to 45 wt% of an ester as a phase-separation agent, 0.5 to 8.0 wt% of an acid as a phase-separation promoter, and 40 to 70 wt% of water as a solvent, wherein the sum of the weight percentages of the above components is 100%; stir and mix the components in a closed container to obtain the water-based liquid-liquid phase-change absorbent.

[0020] An application of an aqueous liquid-liquid phase-change absorbent with a controllable phase-separation threshold for SO2 capture, characterized in that when the aqueous liquid-liquid phase-change absorbent is used to separate and capture SO2 in exhaust gas, the absorption temperature is 20-60°C and the desorption temperature is 90-120°C. After absorbing SO2, the aqueous liquid-liquid phase-change absorbent separates into phases, with more than 95% of SO2 and more than 96% of the absorbent enriched in the lower liquid phase, and the phase-separation agent mainly enriched in the upper liquid phase.

[0021] When the aqueous liquid-liquid phase change absorbent is used to separate and capture SO2 in exhaust gas, the absorption temperature is 30-50°C and the desorption temperature is 100-110°C.

[0022] The interaction mechanism of the aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture provided by the present invention is:

[0023] The aqueous liquid-liquid phase-change absorbent of the present invention uses piperazine-type organic amine as the absorbent, and the hydrogen atom connected to the N atom in piperazine is replaced by a hydroxyalkyl group, which changes its pKa value and alkalinity, so that it has a stronger absorption capacity and selectivity for SO2; the cyclic structure of piperazine has a certain steric hindrance effect, and the generated absorption product has a relatively low stability, which can ensure that the aqueous liquid-liquid phase-change absorbent has a higher desorption performance.

[0024] The aqueous liquid-liquid phase-change absorbent of the present invention uses ester as a phase separator. Since the polarity of the absorbed product ammonium salt is somewhat different from that of the ester, the two are immiscible, inducing a phase change. By changing the non-polarity and dosage of the ester, the time when the phase change occurs and the phase separation threshold can be changed. In addition, the high boiling point and flash point of the ester can reduce the volatilization loss of the phase-change absorbent.

[0025] The aqueous liquid-liquid phase change absorbent of the present invention uses acid as a phase separation promoter. The acid reacts with piperazine organic amines to generate polar ammonium salts, which on the one hand promotes the occurrence of liquid-liquid phase change, reduces the SO2 load during phase separation, and regulates the phase separation threshold for phase change; in addition, it also improves the desorption efficiency of SO2.

[0026] The aqueous liquid-liquid phase change absorbent of the present invention uses water as a solvent. Water not only reduces the viscosity of the phase change absorbent and increases the heat and mass transfer rates, but also dissolves the absorption product and avoids the formation of solid precipitation. Therefore, the absorbent will quickly separate into two phases after absorbing SO2, wherein the ammonium salt generated by the reaction of SO2 with organic amine is enriched in the lower liquid phase, and the SO2 content in the upper water phase is very low, and the main components are organic solvent ester and water. It is only necessary to send the SO2-enriched phase (lower liquid phase) to the desorption tower for regeneration, thereby greatly reducing the desorption energy consumption.

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

[0028] The present invention forms a new absorbent-phase-separator-phase-separator-phase-separation-accelerator-water quaternary aqueous liquid-liquid phase-change absorbent by mixing a specific phase-separator ester with an absorbent piperazine organic amine, a phase-separation accelerator acid and water in appropriate proportions. After absorbing a certain amount of SO2, the quaternary aqueous liquid-liquid phase-change absorbent can quickly separate into liquid-liquid phases. Since the ester has a weak solubility for organic amine salts, more than 95% of SO2 is enriched in the lower liquid phase (rich phase) and the proportion of SO2 in the upper liquid phase (lean phase) is relatively small; the volume of the lower liquid phase accounts for approximately 60 to 85% of the total volume of the upper and lower liquid phases, and only the rich phase needs to be desorbed, which greatly saves desorption energy consumption.

[0029] The quaternary aqueous liquid-liquid phase change absorbent of the present invention uses a high-boiling-point, low-volatile ester as a phase separator. The addition of the ester replaces part of the water, thereby reducing the water content in the enriched phase and lowering the heat of evaporation of water. As a physical solvent, the ester can promote the physical diffusion of sulfur dioxide in the solution and improve the ability of the phase change solution to absorb sulfur dioxide. Since both amine molecules and ester molecules can form intermolecular hydrogen bonds with water molecules, an organic amine-ester-water hydrogen bond network with a certain polarity is formed. When the organic amine reacts with SO2 to generate a polar ammonium salt, the ester has a certain non-polarity. Due to the difference in polarity, the original equilibrium is broken, and the solution spontaneously changes to an immiscible turbid state and is divided into two liquid phases. When the non-polarity of the ester is stronger, or the amount of ester used is larger, the polarity difference between the amine salt generated by the reaction of the organic amine with SO2 and the ester is greater, the time required for phase separation is shorter, and the amine salt concentration at this time, i.e., the phase separation load of the absorbent, is smaller, thereby changing the size of the phase separation threshold.

[0030] The phase separation accelerator of the present invention is an acid, which reacts with a piperazine-type organic amine to generate a polar organic amine salt, which can not only reduce the volatilization loss of the organic amine, but also change the hydrogen bond network of amine-ester-water in the quaternary aqueous liquid-liquid phase change absorbent, regulate the polarity of the solution, and promote the occurrence of phase change; when the acidity of the phase separation accelerator is stronger (the pKa value is smaller) and the concentration is higher, the polarity of the generated organic amine salt is stronger, the polarity difference with the ester is greater, the time required for phase separation is shorter, the phase separation load at this time is smaller, and the size of the phase separation threshold is changed.

[0031] The piperazine organic amine-ester-acid-water quaternary aqueous liquid-liquid phase change absorbent of the present invention regulates the hydrogen bond network between amine-ester-water and the non-polarity of the solution by adjusting the polarity and dosage of the phase separation agent ester, changing the strength and dosage of the phase separation accelerator acid, and the synergistic effect of the phase separation agent ester and the phase separation accelerator acid, thereby promoting the occurrence of phase change, thereby changing the phase separation threshold and being able to regulate the phase separation threshold.

[0032] The phase-change absorbent provided by the present invention is an aqueous solution with low viscosity and excellent heat and mass transfer and transportation performance. The aqueous liquid-liquid phase-change absorbent has good cyclic absorption performance for SO2, high selectivity, fast absorption rate, small absorbent volatilization loss, and low desorption energy consumption, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Attachment Figure 1 A comparison chart of the saturated absorption capacity and phase-separated absorption capacity of the aqueous liquid-liquid phase-change absorbents provided in Examples 1 to 7 of the present invention and the absorbents provided in Comparative Examples 1 and 2;

[0034] Attachment Figure 2 The aqueous liquid-liquid phase change absorbent provided in Example 6 of the present invention absorbs the solution before and after 13 C NMR analysis results;

[0035] Attachment Figure 3 A comparison chart of cyclic loads in cyclic absorption and desorption performance of the aqueous liquid-liquid phase change absorbents provided in Examples 1 to 7 of the present invention and the absorbents provided in Comparative Examples 1 and 2;

[0036] Attachment Figure 4 This is a comparison chart of the desorption rate and energy consumption in the cyclic absorption and desorption performance of the aqueous liquid-liquid phase change absorbent provided by Examples 1 to 7 of the present invention and the absorbent provided by Comparative Examples 1 to 2. DETAILED DESCRIPTION

[0037] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention. It should be understood that the examples are for better explanation of the present invention, but are not intended to limit the scope of the present invention.

[0038] The present invention provides an aqueous liquid-liquid phase change absorbent for SO2 capture with good cyclic absorption and desorption performance, fast absorption rate, and small volatilization loss, and with a controllable phase separation threshold. The absorbent comprises the following components, calculated by weight percentage: 10 to 30 wt% of an absorbent, 5 to 45 wt% of a phase separation agent, 0.5 to 8.0% of a phase separation promoter, and 40 to 75 wt% of water, wherein the sum of the weight percentages of the above components is 100%. The absorbent is N-aminoethylpiperazine (AEP), N-hydroxyethylpiperazine (HEP), N,N-bis(2-hydroxyethyl)piperazine (BHEP), N,N-bis(2-hydroxypropyl)piperazine (HPP), or N-hydroxyethylpiperazine (HEP). -N-hydroxypropylpiperazine (HEHPP) or a mixture of two or more thereof in any proportion; the phase separator is triethyl phosphate (TEP), glyceryl triacetate (GT), or triethyl citrate (TEC); the acid is an inorganic acid, a strong organic acid, or a mixture of an inorganic acid and an organic strong acid; wherein the inorganic acid is sulfuric acid, phosphoric acid, or boric acid or a mixture of two or more thereof; and the strong organic acid is oxalic acid, citric acid, malonic acid, or succinic acid or a mixture of two or more thereof; the preferred embodiment of the inorganic acid is a mixture of sulfuric acid and phosphoric acid, and the preferred embodiment of the mixture of the inorganic acid and the strong organic acid is a mixture of sulfuric acid and an organic strong acid.

[0039] A preferred solution is: an aqueous liquid-liquid phase change absorbent with a controllable phase separation threshold for SO2 capture, which includes the following components, calculated by weight percentage: 15-25wt% absorbent, 15-40wt% phase separation agent, 2.0-6.5wt% phase separation promoter, 50-65wt% water, and the sum of the weight percentages of the above components is 100%.

[0040] A water-based liquid-liquid phase-change absorbent with a controllable phase-separation threshold for SO2 capture. The preparation method of the water-based liquid-liquid phase-change absorbent is as follows: weigh the following components in percentage by weight: 10 to 30 wt% of a piperazine-type organic amine as an absorbent, 5 to 45 wt% of an ester as a phase-separating agent, 0.5 to 8.0 wt% of an acid as a phase-separation accelerator, and 40 to 70 wt% of water as a solvent, wherein the sum of the weight percentages of the above components is 100%; and stir and mix the components in a closed container to obtain the water-based liquid-liquid phase-change absorbent.

[0041] The invention discloses an application of an aqueous liquid-liquid phase-change absorbent with a controllable phase separation threshold for SO2 capture. When the aqueous liquid-liquid phase-change absorbent is used to separate and capture SO2 in exhaust gas, the absorption temperature is 20-60°C, preferably 30-50°C, and the desorption temperature is 90-120°C, preferably 100-110°C. After absorbing SO2, the aqueous liquid-liquid phase-change absorbent separates into phases, and more than 95% of the SO2 and more than 96% of the absorbent are enriched in the lower liquid phase.

[0042] The aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture provided by the present invention can be used to separate and capture SO2 in exhaust gas from coal-fired power plants, sulfuric acid plants, hydrometallurgical plants and other factories.

[0043] The phase-change absorption and desorption process for SO2 using an aqueous liquid-liquid phase-change absorbent with a controllable phase-separation threshold for SO2 capture is as follows: simulated flue gas with a SO2 volume fraction of 0.1% to 15% and the remainder being N2 is placed in a gas distribution tank. The sulfur-containing flue gas is then passed through an organic amine phase-change solution at an absorption temperature of 25 to 60°C for 1 to 6 hours. After absorbing SO2, the aqueous liquid-liquid phase-change absorbent spontaneously separates into two phases: a lower aqueous phase, a SO2-rich phase, containing most of the organic amine salts resulting from the reaction of the organic amine with SO2, water, and a small amount of a phase-separating agent; and an upper aqueous phase, a SO2-lean phase, containing a small amount of the organic amine salts resulting from the reaction of the organic amine with SO2, water, and a large amount of a phase-separating agent.

[0044] After SO2 absorption, the upper and lower aqueous phases are separated, with the lower aqueous phase being sent for desorption and regeneration. The desorption and regeneration process takes place at a temperature of 100-120°C for 0.5-3.5 hours, and the desorbed SO2 is recycled. The lean amine solution after rich phase regeneration is mixed with the upper aqueous phase to produce a new aqueous liquid-liquid phase change absorbent for cyclic SO2 absorption.

[0045] The simulated flue gas provided by the present invention contains nitrogen in addition to SO2. The nitrogen is used as a carrier gas to pass SO2 into the absorbent.

[0046] The components of the aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture provided by the present invention can be prepared in a laboratory or obtained through purchase.

[0047] In the examples provided herein, 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 steps described in Example 1 in CN103638779A; and other reagents were purchased from China National Pharmaceutical Group.

[0048] Example 1

[0049] A water-based liquid-liquid phase-change absorbent with a controllable phase-separation threshold for SO2 capture is disclosed. The absorbent comprises 15 wt% of bishydroxyethylpiperazine (BHEP), 20 wt% of triethyl phosphate (TEP), 2.0 wt% of sulfuric acid (H2SO4), a phase-separation promoter, and the balance is water (H2O), the sum of the weight percentages of the above components being 100%. In a closed container, BHEP, TEP, and H2SO4 are added to H2O according to set weight percentages, and the mixture is stirred and uniformly mixed to prepare a BHEP-TEP-H2SO4-H2O quaternary water-based liquid-liquid phase-change absorbent.

[0050] Example 2

[0051] A water-based liquid-liquid phase-change absorbent with a controllable phase separation threshold for SO2 capture is prepared by replacing the phase separation agent in Example 1 with triacetin (GT) with the remaining components remaining the same to prepare a BHEP-GT-H2SO4-H2O quaternary water-based liquid-liquid phase-change absorbent.

[0052] Example 3

[0053] A water-based liquid-liquid phase-change absorbent with a controllable phase separation threshold for SO2 capture is prepared by replacing the phase separation agent in Example 1 with triethyl citrate (TEC) with the remaining components remaining the same to prepare a quaternary water-based liquid-liquid phase-change absorbent BHEP-TEC-H2SO4-H2O.

[0054] Example 4

[0055] A water-based liquid-liquid phase-change absorbent with a controllable phase separation threshold for SO2 capture is prepared by replacing the phase separation accelerator in Example 1 with phosphoric acid, while keeping all other properties the same, to prepare a BHEP-TEP-H3PO4-H2O quaternary water-based liquid-liquid phase-change absorbent.

[0056] Example 5

[0057] A water-based liquid-liquid phase-change absorbent with a controllable phase-separation threshold for SO2 capture is prepared by replacing the phase-separation accelerator in Example 1 with boric acid, while keeping all other properties the same, to prepare a BHEP-TEP-H3BO4-H2O quaternary water-based liquid-liquid phase-change absorbent.

[0058] Example 6

[0059] A water-based liquid-liquid phase-change absorbent with a controllable phase-separation threshold for SO2 capture is disclosed. The absorbent comprises 15 wt% of bishydroxyethylpiperazine (BHEP), 20 wt% of triethyl phosphate (TEP), 3.5 wt% of sulfuric acid (H2SO4), a phase-separation promoter, and the remainder is water (H2O), with the sum of the weight percentages of the above components being 100%. In a closed container, BHEP, TEP, and H2SO4 are added to H2O according to set weight percentages, and the mixture is stirred and uniformly mixed to prepare a BHEP-TEP-H2SO4-H2O quaternary water-based liquid-liquid phase-change absorbent.

[0060] Example 7

[0061] A quaternary aqueous liquid-liquid phase-change absorbent with a controllable phase separation threshold for SO2 capture is prepared by changing the weight percentage of the phase separation agent TEP in Example 6 to 25wt%, adding 15wt% of the absorbent bishydroxyethylpiperazine (BHEP), 3.5wt% of the phase separation promoter sulfuric acid (H2SO4), and the balance being water (H2O) to form a BHEP-TEP-H2SO4-H2O aqueous liquid-liquid phase-change absorbent.

[0062] Comparative Example 1

[0063] A BHEP-H2SO4-H2O ternary solution without ester as a phase separation agent was used as the absorbent, and the rest was the same as in Example 1.

[0064] Comparative Example 2

[0065] A BHEP-TEP-H2O ternary solution without adding acid as a phase separation accelerator was used as the absorbent, and the rest was the same as in Example 1.

[0066] Experimental Example 1

[0067] The phase separation effect and absorption performance of the aqueous liquid-liquid phase change absorbents provided in Examples 1 to 7 and the absorbents provided in Comparative Examples 1 and 2 after absorbing SO2 were measured.

[0068] Method: Prepare the corresponding absorbent according to the components and methods of Examples 1 to 7 and Comparative Examples 1 to 2, and take 80g of each absorbent and add it to a bubbling absorber. After the absorber is heated to a constant temperature at 40°C, simulated flue gas containing 1.2% SO2 by volume at a flow rate of 1.35L / min is introduced into the absorbent to test the absorption performance. If the solution becomes turbid during the absorption process, stop the gas introduction, record the phase separation time, let it stand, separate the SO2-rich phase from the SO2-lean phase, and measure the volume and SO2 concentration of each phase. Then, combine the two phases and continue to introduce gas absorption until saturation is reached. The volume and SO2 concentration of the SO2-lean and SO2-rich liquid phases are measured.

[0069] The SO2 concentration in the absorption liquid is determined by iodine titration, and the viscosity of the absorbent is measured by a rotational viscometer.

[0070] Absorption capacity AQ refers to the amount of SO2 absorbed by a unit amount of amine, and the unit is mol SO2 / mol amine;

[0071] Absorption capacity AQ during phase separation 分相 It refers to the amount of SO2 absorbed by a unit amount of amine during absorption phase separation, and the unit is mol SO2 / mol amine;

[0072] The SO2 distribution rate in the rich phase refers to the ratio of the number of moles of SO2 in the rich phase to the total number of moles of SO2 absorbed, and the unit is %;

[0073] The volume proportion of the lower phase refers to the ratio of the SO2-rich phase to the total volume of the solution, expressed in %.

[0074] The results are shown in Table 1. In Example 1, TEP was added as a phase separator, and liquid-liquid separation occurred after 45 minutes of absorption. However, in Comparative Example 1, which did not add a phase separator, no liquid-liquid separation occurred even after saturation absorption. In Examples 2 and 3, the addition of highly non-polar triacetin (GT) and triethyl citrate (TEC), respectively, significantly shortened the time it took for phase separation to occur. This indicates that phase separators play a crucial role in determining whether liquid-liquid separation occurs when the BHEP aqueous solution absorbs SO2. Although triethyl phosphate (TEP) was added as a phase separator in Comparative Example 2, no acid was added, and phase separation still required a relatively long absorption time. However, in Example 1, the addition of acid significantly shortened the time it took for phase separation to occur, demonstrating that acid promotes phase separation.

[0075] After SO₂ absorption in Example 1, the volume of the enriched phase accounts for 77.2% of the total volume, meaning that the regeneration liquid processing capacity is reduced by approximately 22.8% compared to the homogeneous absorbent without TEP. Approximately 96% or more of the SO₂ and 97% or more of the bis(hydroxyethylpiperazine) (BHEP) are enriched in the lower liquid phase (the enriched phase), while the concentrations of SO₂ and bis(hydroxyethylpiperazine) (BHEP) in the upper liquid phase (the lean phase) are very low. Therefore, the absorbent can be recycled by simply desorbing the enriched phase. Under the same desorption conditions, regeneration energy consumption is significantly reduced. Furthermore, compared to the conventional organic amine homogeneous absorbent, Comparative Example 1, the viscosity of the enriched phase after absorption in Comparative Example 2 and Examples 1 to 7, which incorporate a phase separation agent, increases somewhat, but the low viscosity remains relatively low. The aqueous liquid-liquid phase-change absorbent with a controllable phase separation threshold for SO₂ capture provided by the present invention exhibits excellent heat and mass transfer and transport performance.

[0076] Table 1 Comparison of phase separation between Examples 1-7 and Comparative Examples 1-2

[0077]

[0078] Attachment Figure 1 The saturated absorption capacity and phase separation absorption capacity of the aqueous liquid-liquid phase change absorbent provided in Examples 1 to 7 and the absorbent provided in Comparative Examples 1 and 2 are described. Figure 1 , it is concluded that: (1) Comparing Example 1 with Example 2 and Example 3, it can be seen that when the amount of phase separation agent is the same, when triacetin (GT) and triethyl citrate (TEC) are used as phase separation agents, phase separation occurs quickly after absorption, and the AQ of triacetin (GT) and triethyl citrate (TEC) are 分相 Much smaller than the AQ of triethyl phosphate (TEP) 分相 ; This is because there is no charged group in the molecule of triacetin, and its polarity is the weakest; triethyl phosphate and triethyl citrate both contain charged phosphate or carboxylic acid groups, but the polarity of the phosphate group is stronger than the carboxylic acid group, and the carbon chain length of triethyl phosphate is shorter than that of triethyl citrate, so the polarity of triethyl phosphate is much greater than that of triethyl citrate, so triethyl phosphate is miscible with water, while triacetin (GT) and triethyl citrate (TEC) have very low solubility in water; that is, the stronger the non-polarity of the phase separation agent ester, the shorter the phase separation time required, AQ 分相 (2) Comparing Example 6 and Example 7, it can be seen that the greater the amount of phase separation agent TEP is used, the shorter the time required for phase separation and the phase separation threshold AQ 分相 (3) Comparing Example 1 with Example 4 and Example 5, it can be seen that when the amount of acid is the same, since the pKa1 of sulfuric acid, phosphoric acid and boric acid are -3.01, 2.12 and 9.24 respectively, the stronger the acidity of the phase separation accelerator, the shorter the required phase separation time, and AQ分相 In addition, since the stronger the acidity, the more intense the reaction with the organic amine, the lower the effective concentration of the organic amine that absorbs SO2, and therefore the smaller the absorption capacity AQ; (4) Comparing Example 1 and Example 6, it can be seen that when the amount of the phase separation accelerator acid is increased, the phase separation time is reduced, and AQ 分相 The above (1)-(4) illustrate that the aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture provided by the embodiments of the present invention can control the phase separation threshold of the phase change by adjusting the type and amount of the phase separation agent ester in the liquid-liquid phase change absorbent, as well as the type and amount of the accelerator acid, so as to meet the requirements of industrial production when treating low SO2 concentration inlet gas, and avoid the disadvantage that many liquid-liquid phase change absorbents need to absorb saturation before phase separation occurs; (5) From Example 1, Example 4, and Example 5 in Table 1, As shown in Example 5, the type and amount of the phase separation promoter acid have little effect on the volume fraction of the rich phase, the SO2 distribution rate of the rich phase, and the distribution rate of the amine, while the type and amount of the phase separation agent ester have a greater effect on the volume fraction of the rich phase, the SO2 distribution rate of the rich phase, and the distribution rate of the amine; (6) The AQ of the aqueous liquid-liquid phase change absorbents provided in Examples 1, 4, and 5 are all higher than those of the conventional homogeneous absorbents, such as the AQ of Comparative Example 1. This is because triethyl phosphate, as a physical solvent, can promote the physical diffusion of sulfur dioxide in the solution and improve the ability of the phase change solution to absorb sulfur dioxide. However, the AQ of the aqueous liquid-liquid phase change absorbents provided in Examples 2 and 3 is lower than that of Comparative Example 1. This is because the solution viscosity increases after the addition of triacetin (GT) and triethyl citrate (TEC), which is not conducive to the absorption and mass transfer reaction.

[0079] The phase-change absorbent of the piperazine-based organic amine-ester-acid-water quaternary aqueous liquid-liquid phase change absorbent of the present invention is as follows: the nitrogen atoms in the piperazine-based organic amine and the ester groups in the phase-change agent can form hydrogen bonds with water molecules, resulting in the absorbent being a homogeneous solution before absorption; when the acid reacts with the organic amine to form an amine salt, the polarity of the ammonium salt destroys the interaction and hydrogen bonds between the amine, water, and ester. The polarity of the absorbed ammonium salt differs from that of the ester, making them insoluble, thus inducing a phase change. When the non-polarity of the phase-change agent ester is stronger or the amount used is larger, the polarity difference between the amine salt and the ester generated by the reaction of the organic amine with SO2 is greater, which facilitates phase separation. Specifically, triacetin (GT) and triethyl citrate (TEC) facilitate phase separation. When the polarity of the accelerator acid is stronger or the amount used is larger, the polarity of the ammonium salt is stronger, the polarity difference and salting-out effect are greater, and phase separation is also more facilitated. Specifically, sulfuric acid has a better phase-separation-promoting effect.

[0080] Attachment Figure 2 The aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture provided in Example 6 has the following characteristics: 13C NMR analysis results. Peak 1 in the figure is the chemical shift of the C atom on the piperazine ring of BHEP, peaks 2 and 3 are the chemical shifts of the C atom in the branched hydroxyethyl group; peaks a and b are the chemical shifts of the C atom in triethyl phosphate. Figure 2 It can be found that in the upper liquid phase (lean phase), there is only a small amount of ammonium salt, mainly triethyl phosphate (TEP); in the lower liquid phase (rich phase), it is mainly ammonium salts from the reaction of BHEP and SO2, and only a small amount of triethyl phosphate (TEP) is dissolved in the rich phase; therefore, SO2 is mainly enriched in the lower liquid phase, and as the amount of phase separation agent triethyl phosphate (TEP) increases, the volume of the rich phase decreases.

[0081] Experimental Example 2

[0082] After the aqueous liquid-liquid phase change absorbents provided in Examples 1 to 7 and the absorbents provided in Comparative Examples 1 to 2 absorbed SO2 and separated into phases, the desorption rate DE, desorption energy consumption Q and cycle load EQ of the SO2-rich phase were detected.

[0083] Method: Repeat the absorption steps for each absorbent in Experimental Example 1 to obtain an absorption liquid that has reached the absorption endpoint. Allow the liquid to stand for phase separation, and regenerate the SO2-rich lower liquid phase by thermal desorption at a regeneration temperature of 104°C for 60 minutes.

[0084] Among them, the cycle load EQ is the difference between the SO2 load of the rich liquid obtained after the absorption liquid absorbs SO2 and the SO2 load of the lean liquid obtained after desorption, that is, the number of moles of SO2 desorbed from each mole of organic amine in one absorption and desorption cycle, and the unit is mol SO2 / mol amine.

[0085] The desorption rate DE of the desorption process is the amount of SO2 desorbed / the amount of SO2 in the rich solution before desorption × 100%.

[0086] The energy consumption Q of the desorption process refers to the power consumption for desorbing unit mass of SO2, and its unit is GJ / t.

[0087] Results: As attached Figure 3 and 4As shown, compared with Comparative Example 1, the cyclic load EQ and DE of the liquid-liquid phase change absorbent provided by Examples 1 to 7 are both improved. For example, the desorption energy consumption Q of Example 1 is reduced by more than 28% compared with the homogeneous absorbent, indicating that the aqueous liquid-liquid phase change absorbent of the present invention has a high cyclic absorption capacity while overcoming the defect of high regeneration energy consumption of the homogeneous absorbent, which is conducive to large-scale industrial application. Comparing Examples 1 to 3, it can be seen that the EQ and DE of triethyl phosphate (TEP) as the phase separation agent are larger, Q is smaller, and it is a homogeneous phase before absorption, which has better effect in actual production applications. Comparing Examples 1, 4 and 5 with Comparative Example 2, it can be seen that the acidity of the phase separation promoter has little effect on the regeneration energy consumption, but the stronger the acidity, the smaller the EQ, the significantly increased DE, and the faster the desorption rate. Taking all factors into consideration, when sulfuric acid is used as the phase separation promoter and triethyl phosphate is used as the phase separation agent, its promoting effect on phase separation and desorption is the best.

[0088] Example 8

[0089] A water-based liquid-liquid phase-change absorbent with a controllable phase-separation threshold for SO2 capture is disclosed. The absorbent comprises 15 wt% of a main absorbent, bishydroxyethylpiperazine (BHEP), 5 wt% of a secondary absorbent, bishydroxypropylpiperazine (HPP), 25 wt% of a phase-separation agent, triethyl phosphate (TEP), 5.5 wt% of a phase-separation accelerator, sulfuric acid (H2SO4), and the remainder is water (H2O), the sum of the weight percentages of the above components being 100%. In a sealed container, BHEP, HPP, TEP, and H2SO4 are added to H2O according to set weight percentages, and the mixture is stirred and uniformly mixed to prepare a BHEP-HPP-TEP-H2SO4-H2O five-component water-based liquid-liquid phase-change absorbent.

[0090] Comparative Example 3

[0091] The BHEP-HPP-H2SO4-H2O quaternary solution without the phase separator TEP was used as the homogeneous absorbent, and the rest was the same as in Example 8.

[0092] Experimental Example 3

[0093] The cyclic absorption and desorption performance and volatility of SO2 of the BHEP-HPP-TEP-H2SO4-H2O five-component aqueous liquid-liquid phase change absorbent of Example 8 and the BHEP-HPP-H2SO4-H2O homogeneous absorbent of Comparative Example 3 were measured.

[0094] Method: Take 100g of the absorbent provided in Example 8 and Comparative Example 3 respectively, and use them to absorb simulated flue gas containing a SO2 concentration of 0.8%. The flow rate of the simulated flue gas is 1.35L / min, the absorption temperature is 40°C, and the absorption time is 180min. The SO2-rich phase after absorption is sent for desorption and regeneration. The regeneration temperature is 104°C and the regeneration time is 100min. The desorbed liquid phase is mixed with the absorbed lean liquid phase, and the solution is restored to a homogeneous phase, and then cyclic absorption and desorption are carried out. The method for determining the volatility of the absorbent is as follows: add 100g of absorbent to the absorption bottle, pass N2 at a flow rate of 800ml / min, weigh the mass of the absorbent at regular intervals, and calculate the weight loss rate.

[0095] Results: Table 2 shows the cyclic absorption and desorption performance of the five-component aqueous liquid-liquid phase-change absorbent prepared in Example 8 and the BHEP-HPP-H2SO4-H2O homogeneous absorbent of Comparative Example 3. The results show that the absorbent's cyclic loading (EQ) does not change significantly with increasing absorption and desorption cycles. The aqueous liquid-liquid phase-change absorbents provided by the present invention exhibit higher cyclic loadings than the homogeneous absorbents. The EQ of Example 8 remains at approximately 0.967 mol / mol, an increase of approximately 9.3% compared to Comparative Example 3. The desorption rate is approximately 97.3%, an increase of approximately 7.4% compared to Comparative Example 3. The average energy consumption is approximately 147 GJ / t, a decrease of approximately 30% compared to Comparative Example 3. After four absorption cycles, the lower liquid phase (enriched phase) accounts for 63.4% of the total volume, and the SO2 distribution ratio in the enriched phase is greater than 95%. This demonstrates that the aqueous liquid-liquid phase-change absorbent with a controllable phase separation threshold for SO2 capture provided by the present invention exhibits stable regeneration and excellent SO2 enrichment and distribution performance.

[0096] Table 2 Circular absorption and desorption performance of SO2 in Example 8 and Comparative Example 3

[0097]

[0098] The five-component aqueous liquid-liquid phase-change absorbent provided in Example 8 had a rich phase viscosity of 13.2 mPa.s after the fourth absorption. Although slightly higher than the rich phase viscosity of 9.6 mPa.s in Comparative Example 4, the viscosity of this example was still relatively low. In a weight loss experiment, the weight loss rate of the homogeneous absorbent in Comparative Example 3 was 8.98% after 6 hours, while the weight loss rate of the phase-change absorbent in Example 8 was 7.62%, a reduction of approximately 15.1% in volatilization loss. This indicates that the piperazine-based organic amine aqueous liquid-liquid phase-change absorption system using TEP as a phase separator and sulfuric acid as a phase separation accelerator significantly reduces desorption energy consumption while maintaining a high cyclic absorption capacity. Furthermore, the absorbent exhibits low volatilization losses, suggesting promising prospects for practical application.

[0099] The above embodiments are merely illustrative of the present invention. Obviously, the present invention is not limited to the described embodiments. Based on the embodiments of the present invention, those skilled in the art may make various modifications. However, any modifications that are equivalent to or similar to the intent of the claims of the present invention fall within the scope of protection of the present invention. Any technology not covered by the present invention may be implemented using existing technologies.

Claims

1. An aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture, characterized by: The aqueous liquid-liquid phase change absorbent comprises the following components by weight percentage: 10-30 wt% of an absorbent, 5-45 wt% of a phase separation agent, 0.5-8.0% of a phase separation accelerator, and 40-75 wt% of water, wherein the sum of the weight percentages of the above components is 100%. The absorbent is a piperazine organic amine; the piperazine organic amine is one or a mixture of two or more of N-aminoethylpiperazine, N-hydroxyethylpiperazine, N,N-bis(2-hydroxyethyl)piperazine, N,N-bis(2-hydroxypropyl)piperazine or N-hydroxyethyl-N-hydroxypropylpiperazine in any proportion; The phase separation agent is an ester; the ester is one or a mixture of two or more of glycerol triacetate (GT), triethyl citrate (TEC), and triethyl phosphate (TEP); The phase separation accelerator is an acid; the acid is an inorganic acid, an organic strong acid, or a mixture of an inorganic acid and an organic strong acid; the inorganic acid is one or a mixture of two of sulfuric acid and phosphoric acid, and the organic strong acid is one or a mixture of two or more of oxalic acid, citric acid, malonic acid or succinic acid.

2. The aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture according to claim 1, characterized in that: The weight percentage of the absorbent in the aqueous liquid-liquid phase change absorbent is 15-25wt%.

3. The aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture according to claim 1, characterized in that: The weight percentage of the phase separation agent in the aqueous liquid-liquid phase change absorbent is 15-40wt%.

4. The aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture according to claim 1, characterized in that: The weight percentage of the phase separation accelerator in the aqueous liquid-liquid phase change absorbent is 2.0-6.5wt%.

5. The aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture according to claim 1, characterized in that: The weight percentage of water in the aqueous liquid-liquid phase change absorbent is 50-65wt%.

6. The aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture according to claim 1, characterized in that: The acid is sulfuric acid, or a mixture of sulfuric acid and phosphoric acid, or a mixture of sulfuric acid and an organic strong acid.

7. The aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture according to any one of claims 1 to 6, characterized in that: The preparation method of the aqueous liquid-liquid phase-change absorbent with a controllable phase separation threshold is as follows: weigh the following components by weight percentage: 10 to 30 wt% of a piperazine-type organic amine as an absorbent, 5 to 45 wt% of an ester as a phase separation agent, 0.5 to 8.0 wt% of an acid as a phase separation accelerator, and 40 to 70 wt% of water as a solvent, where the sum of the weight percentages of the above components is 100%; stir and mix the components in a closed container to obtain the aqueous liquid-liquid phase-change absorbent.

8. Use of an aqueous liquid-liquid phase change absorbent with a controllable phase separation threshold for SO2 capture according to any one of claims 1 to 6, characterized in that: When the aqueous liquid-liquid phase-change absorbent is used to separate and capture SO2 from exhaust gas, the absorption temperature is 20-60°C and the desorption temperature is 90-120°C. After absorbing SO2, the aqueous liquid-liquid phase-change absorbent separates into phases, and more than 95% of SO2 and more than 96% of the absorbent are enriched in the lower liquid phase.

9. The use of the aqueous liquid-liquid phase change absorbent with controllable phase separation threshold for SO2 capture according to claim 8, characterized in that: When the aqueous liquid-liquid phase change absorbent is used to separate and capture SO2 in exhaust gas, the absorption temperature is 30-50°C and the desorption temperature is 100-110°C.

Images