Phase change absorbent for selectively removing hydrogen sulfide and preparation method and application thereof

Abstract

The application discloses a phase change absorbent for selectively removing hydrogen sulfide and a preparation method and application thereof. The phase change absorbent comprises the following components in mass fraction: 20-45% of a cyclic amide tertiary amine; 20-50% of a hydrogen bond reformation phase separation promoter; and the balance of water. The cyclic amide tertiary amine contains a tertiary amine nitrogen atom for acid-base reaction with H2S and an amide group as a hydrogen bond acceptor in a molecular structure, and is used for high-selectivity reaction with H2S. The hydrogen bond reformation phase separation promoter is a polyhydric alcohol containing two or more hydroxyl groups, and can induce liquid-liquid phase separation of the absorbent after absorbing H2S, so as to form a rich phase rich in H2S and a lean phase with less H2S content, and then the separation of the rich phase and the lean phase can be realized through simple gravity or centrifugation. The phase change absorbent has the advantages of high H2S absorption selectivity, low regeneration energy consumption, simple preparation method and low operation cost, and is particularly suitable for fine desulfurization of complex sour gas such as refinery dry gas.

Description

Technical Field

[0001] This invention belongs to the field of energy conservation, emission reduction and gas purification, specifically relating to a phase change absorbent for selectively removing hydrogen sulfide, its preparation method and application. Background Technology

[0002] In industrial sectors such as natural gas, refinery gas, and coal chemical processing, gaseous feedstocks often contain acidic components such as H2S and CO2. H2S removal is crucial for ensuring personnel safety, protecting equipment and catalysts, and meeting product quality and environmental requirements. In many processes, such as when refinery dry gas is used as fuel gas, only H2S removal is required, while CO2 removal is not strictly necessary. Therefore, developing highly selective desulfurization technologies has significant economic value in reducing equipment investment and operating energy consumption.

[0003] Currently, the amine method is widely used in industry for selective desulfurization, with tertiary amine aqueous solutions, represented by N-methyldiethanolamine (MDEA), being the mainstream technology. CN117323781A discloses an amine absorbent with MDEA as the main agent and a compound activator. This technology utilizes the kinetic characteristic that MDEA reacts with H2S at a much faster rate than with CO2 to achieve selective absorption. However, this type of amine method, which uses water as the main solvent, generally suffers from high regeneration energy consumption due to water's high specific heat capacity and large latent heat of vaporization, as well as problems such as degradation and foaming of the amine solution during long-term operation, affecting the long-term stable operation of the equipment.

[0004] To address these issues, researchers have implemented various improvements. One approach is to develop composite solvents. CN116407927A discloses an absorbent composed of organic alcohol amines, organic solvents, oxidants, and inorganic salts. These absorbents enhance absorption performance through the synergistic effect of multiple components, but often suffer from complex compositions, susceptibility to side reactions, high risk of solvent degradation, and increased operating costs. Another promising technology is phase change absorption technology. Its core idea is that after absorbing H2S, the absorbent spontaneously forms an H2S-rich phase and an H2S-poor phase, allowing for significant energy savings during regeneration by treating only the rich phase. For example, CN108144415A discloses a phase change absorbent composed of organic amines and organic solvents. However, existing phase change absorption technologies still have shortcomings. For instance, some systems precipitate solids after absorption, posing a risk of clogging pipelines and equipment; while some liquid-liquid phase separation systems suffer from incomplete phase separation, low H2S enrichment in the rich phase, or solvent entrainment losses between phases, limiting their full energy-saving effect.

[0005] Therefore, developing a novel desulfurization absorbent that combines high H2S selectivity with high absorption capacity, enables rapid and thorough liquid-liquid separation without solid phase precipitation after absorption, and has stable chemical properties and low regeneration energy consumption has become a pressing technical challenge in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of high regeneration energy consumption and limited selectivity in the existing amine-based desulfurization process, as well as the potential for incomplete phase separation, solid formation, solvent degradation, or poor system stability in existing phase change absorbent systems. Therefore, this invention aims to provide a novel phase change absorbent for selectively removing hydrogen sulfide based on a chemically induced hydrogen bond network reconstruction mechanism, along with its preparation method and applications, to achieve highly efficient selective capture of hydrogen sulfide and low-energy regeneration of the absorbent.

[0007] To achieve the above objectives, the first aspect of the present invention provides a phase change absorbent for selectively removing hydrogen sulfide. The phase change absorbent is a homogeneous aqueous solution formed by a cyclic amide tertiary amine, a hydrogen bond reconstruction phase separation promoter, and water in a specific ratio, and comprises the following components by mass fraction:

[0008] Cyclic amide tertiary amines: 20 wt.%~45 wt.%;

[0009] Hydrogen bond reconstruction phase separation promoter: 20 wt.%~50 wt.%;

[0010] The remainder is water;

[0011] The cyclic amide tertiary amine contains a tertiary amine nitrogen atom for acid-base reaction with H2S and an amide group (C=O) as a hydrogen bond acceptor in its molecular structure.

[0012] The hydrogen bond remodeling phase separation promoter is a polyol containing two or more hydroxyl groups (-OH).

[0013] As the core of this invention, the phase transition mechanism proposed in this invention is based on the following concept:

[0014] (1) The tertiary amine nitrogen atom in the cyclic amide tertiary amine ensures high reactivity to H2S (slow reaction with CO2), while the carbonyl oxygen (C=O) in the amide group acts as a strong hydrogen bond acceptor. Before absorbing H2S, it can form stable intermolecular hydrogen bonds with the hydrogen bond remodeling phase separation promoter, so that the whole system exists in a homogeneous liquid phase.

[0015] (2) The hydroxyl group in the hydrogen bond reconstructed phase separation promoter acts as a hydrogen bond donor, forming a hydrogen bond with the carbonyl oxygen of the cyclic amide tertiary amine, effectively "anchoring" the amine molecule and preventing its spontaneous separation from the aqueous phase.

[0016] (3) Phase transition mechanism: When the absorbent absorbs H2S, the nitrogen atom of the tertiary amine is protonated to form a quaternary ammonium cation (R3NH4+). + Based on the principle of inductive effect in quantum chemistry, the positive charge on the nitrogen atom draws electron cloud density away from the entire ring structure (including the distal amide group) through covalent bonds. This leads to a significant reduction in the lone pair electron cloud density on the carbonyl oxygen atom in the amide group, weakening its ability to act as a hydrogen bond acceptor. The stable hydrogen bonds originally formed with the phase separation promoter are thus disrupted or "broken." At this point, the protonated amine molecules (ionic salts) preferentially dissolve in water due to their strong polarity, forming a high-density, H2S-rich aqueous phase (i.e., the rich phase); while the "released," less polar phase separation promoter and unreacted amine molecules aggregate to form an independent, low-density, H2S-poor organic phase (i.e., the poor phase), thereby achieving liquid-liquid two-phase separation.

[0017] Furthermore, the molecular structure of the cyclic amide tertiary amine contains a tertiary amine functional group and an amide functional group, wherein the tertiary amine functional group is embedded in an alicyclic or heterocyclic structure.

[0018] As a preferred embodiment of the present invention, the cyclic amide tertiary amine is selected from at least one of N-formylpiperidine, N-acetylpiperidine, N-formylpyrrolidine, and N-acetylmorpholine.

[0019] Furthermore, the hydrogen bond remodeling phase separation promoter is selected from at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, and triethylene glycol.

[0020] In another preferred embodiment of the present invention, the mass ratio of the cyclic amide tertiary amine to the hydrogen bond remodeling phase separation promoter in the phase change absorber is 1:0.8 to 1:1.5.

[0021] Preferably, the cyclic amide tertiary amine is N-formylpiperidine (NFP). The tertiary nitrogen atom on its piperidine ring has suitable basicity and steric hindrance, ensuring selectivity for H2S; the formyl group (-CHO) provides the carbonyl oxygen necessary to realize the hydrogen bond switching mechanism of the present invention.

[0022] Preferably, the hydrogen bond reconstruction phase separation promoter is 1,3-propanediol. It has a short molecular chain, low viscosity, and two terminal hydroxyl groups, enabling it to form an effective hydrogen bond network with N-formylpiperidine. Furthermore, both 1,3-propanediol and NFP exhibit good chemical stability.

[0023] As a particularly preferred embodiment of the present invention, the phase change absorbent comprises the following components by mass fraction:

[0024] 30 wt.% to 40 wt.% of N-formylpiperidine;

[0025] 30 wt.% to 40 wt.% of 1,3-propanediol;

[0026] The remainder is water.

[0027] A second aspect of the present invention provides a method for preparing the above-mentioned phase change absorbent, comprising the following steps:

[0028] Under temperature conditions of 10–30°C, the measured amounts of compound amine absorbent, phase separation promoter, and water are sequentially added to a container equipped with a stirring device and stirred until a homogeneous and clear solution is formed, thus obtaining the phase change absorbent.

[0029] A third aspect of the present invention provides an application of the above-mentioned phase change absorbent in the selective removal of hydrogen sulfide from gases, comprising the following steps:

[0030] S1 Absorption Step: In the absorption tower, the raw gas containing hydrogen sulfide is brought into countercurrent contact with the phase change absorbent. The hydrogen sulfide in the raw gas is absorbed by the phase change absorbent, resulting in purified gas and a rich liquid that has absorbed hydrogen sulfide.

[0031] S2 phase separation step: The rich liquid obtained in step S1 is introduced into a phase separator and allowed to stand and separate into layers to obtain an upper layer of H2S-poor liquid with less H2S content and a lower layer of H2S-rich liquid enriched with H2S.

[0032] S3 Regeneration and Recycling Steps: The H2S rich solution obtained in step S2 is preheated and then sent to the regeneration tower for heating and desorption regeneration to obtain a regenerated lean solution and high-concentration hydrogen sulfide gas. The H2S lean solution obtained in step S2 is sent back to the absorption tower for recycling, either directly or mixed with the regenerated lean solution. The high-concentration hydrogen sulfide gas desorbed from the top of the regeneration tower is sent to the downstream unit.

[0033] Furthermore, in step S1, the temperature inside the absorption tower is 30℃~40℃, and the pressure is 0.1 MPa~5.0 MPa.

[0034] Furthermore, in step S3, the temperature inside the regeneration tower is 100℃~120℃, and the pressure is 0.1 MPa~1.0 MPa.

[0035] Compared with the prior art, the present invention has the following significant advantages:

[0036] (1) High selectivity for H2S and fast absorption efficiency: The absorbent prepared by this invention has excellent kinetic and thermodynamic properties. The cyclic amide tertiary amine retains high reactivity selectivity for H2S. At the same time, it can spontaneously separate phases after absorbing H2S, which greatly reduces the amount of absorbent circulating. This allows the system to operate at a higher total sulfur capacity in the rich liquid without affecting the purified gas index.

[0037] (2) Significantly reduced regeneration energy consumption: The phase separation chemical reaction of the system of the present invention is precisely triggered. Compared with the traditional system that relies on the difference in physical solubility, the phase separation is faster and more thorough. Since the H2S content of the depleted phase is very low, it can be directly recycled. Only the rich phase needs to be regenerated, and the energy saving effect is more than 30%.

[0038] (3) The system has high operational stability and no risk of blockage: The absorbent of the present invention forms a stable liquid-liquid two-phase after absorbing H2S, avoiding the solid phase precipitation problem that may occur in the prior art and eliminating the industrial operation risks such as equipment corrosion and blockage caused by it.

[0039] (4) Simple preparation and strong process adaptability: The preparation process of this invention is only a simple physical mixing, without the need for complex chemical reactions. It can be achieved by adding a phase separator on the basis of the amine process. It is easy to modify existing desulfurization equipment or apply it to new equipment, and has good prospects for promotion. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the performance evaluation device for hydrogen sulfide absorption by the absorbent in this invention.

[0041] Figure 2 This is a schematic diagram of the performance evaluation device for hydrogen sulfide desorption by the absorbent in this invention.

[0042] Figure 3 This is a graph showing the H2S absorption load of different phase change absorbents and traditional MDEA absorbent in this invention.

[0043] Figure 4 This is a bar chart showing the H2S content of the two phases (rich and poor) after phase separation of different phase change absorbents in this invention.

[0044] Figure 5 This is a graph showing the H2S absorption rate of different phase change absorbents and traditional MDEA absorbents in this invention.

[0045] Figure 6 This is a graph showing the phase change absorption load of the phase change absorber and the traditional MDEA absorber after multiple absorption-desorption cycles.

[0046] In the diagram: 1-H2S / CO2 mixed gas cylinder; 2-N2 gas cylinder; 3-Flow control device; 4-Gas mass flow controller; 5-Constant temperature water bath device; 6-Three-necked flask; 7-Thermocouple thermometer; 8-Condenser; 9-Drying tube; 10-Multifunctional gas analyzer; 11-Data collection device; 12-Tail gas washing bottle; 13-Magnetic stirring oil bath device; 14-Magnetic stirring rotor. Detailed Implementation

[0047] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0049] Unless otherwise stated, the experimental methods in the embodiments of the present invention are conventional methods; the reagents and materials used are commercially available products unless otherwise stated.

[0050] (1) Raw materials used in the examples

[0051] N-Formylpiperidine (NFP): Industrial grade, purity ≥99.0%, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0052] N-acetylpiperidine: analytical grade, purity ≥98.5%, purchased from Shanghai Maclean Biochemical Technology Co., Ltd.;

[0053] 1,3-Propanediol: Industrial grade, purity ≥99.0%, purchased from Dow Chemical Company;

[0054] 1,2-Propanediol: Industrial grade, purity ≥99.0%, purchased from Shandong Depu Chemical Co., Ltd.;

[0055] N-Methyldiethanolamine (MDEA): Industrial grade, purity ≥99.0%, purchased from BASF (China) Co., Ltd.

[0056] Simulated gases: H2S (99.9% purity), CO2 (99.9% purity), and N2 (99.99% purity), all prepared by mixing cylinder gases using a mass flow controller manufactured by Beijing Sevenstar Electronics Co., Ltd.

[0057] (2) Performance evaluation methods

[0058] (S1) Absorption performance evaluation:

[0059] refer to Figure 1The absorption device includes an H2S / CO2 mixed gas cylinder 1 and an N2 gas cylinder 2, a flow control device 3, a gas mass flow controller 4, a constant temperature water bath device 5, a 250mL three-necked flask 6 as the absorption bottle, a thermocouple thermometer 7, a condenser 8, a drying tube 9, a multifunctional gas analyzer 10, a data collection device 11, and a tail gas washing bottle 12. During the experiment, 200g of the absorbent to be tested was placed in the absorption bottle, and the absorption temperature was precisely controlled by the constant temperature water bath device 5. A simulated acidic gas was prepared according to the set ratio and entered the absorption bottle at a certain flow rate to fully contact the absorbent. At the same time, the temperature in the absorption bottle was monitored in real time using the thermocouple thermometer 7. After the tail gas was dried, it entered the multifunctional gas analyzer 10 to analyze the H2S and CO2 concentrations online. The H2S removal efficiency (η) was calculated according to formula (1):

[0060]

[0061] In the formula, C in and C out These represent the volume fractions of H2S in the inlet and outlet gases of the absorption device, respectively.

[0062] H2S absorption load (α) is defined as the number of moles of H2S absorbed per mole of amine after absorption saturation or a specified absorption time, and is obtained by chemical titration analysis of the absorbent-rich solution after H2S absorption.

[0063] H2S absorption rate (R) abs The absorption rate is defined as the amount of H2S absorbed per unit volume of absorbent per unit time, and its instantaneous absorption rate can be calculated by equation (2):

[0064]

[0065] In the formula, R abs (t) represents the instantaneous absorption rate at time t, in units of mol·g⁻¹. －1 ·min －1 Q represents the volumetric flow rate of the simulated gas, in L·min. －1 C in and C out These represent the volume fractions of H2S in the inlet and outlet gases, respectively; V M The molar volume of H2S gas under standard conditions is taken as 22.4 L·mol⁻¹. －1 m L The value represents the mass of the absorbent, expressed in grams (g).

[0066] (S2) Desorption performance evaluation:

[0067] refer to Figure 2The desorption apparatus includes an N2 cylinder 2, a flow control device 3, a gas mass flow controller 4, a magnetic stirring oil bath device 13, a 250mL three-necked flask 6 as the desorption bottle, a thermocouple thermometer 7, a condenser 8, a drying tube 9, a multi-functional gas analyzer 10, a data collection device 11, and a tail gas washing bottle 12. The absorbed rich liquid is added to the desorption bottle, which contains a magnetic stirring rotor 14. The oil bath device 13 heats the liquid to the desorption temperature (120℃), and the thermocouple thermometer 7 monitors the temperature inside the desorption bottle in real time. Simultaneously, a certain flow rate of N2 is used as stripping gas, bubbling from below the liquid surface. The desorbed acidic gas is condensed by the condenser 8 and the drying tube 9, and the H2S concentration is then detected online by the multi-functional gas analyzer 10 until the H2S concentration in the tail gas is below the detection limit.

[0068] Example 1: Preparation of absorbent A

[0069] At room temperature (25°C) and normal pressure, 80 g of N-formylpiperidine (NFP), 80 g of 1,3-propanediol, and 40 g of deionized water were added sequentially to a 500 mL beaker equipped with a magnetic stirrer. The magnetic stirrer was turned on and stirred at 300 rpm for 30 minutes until the solution was clear and transparent without layering, yielding absorbent A. In absorbent A, the mass fractions of N-formylpiperidine, 1,3-propanediol, and water were 40 wt.% and 20 wt.%, respectively.

[0070] Example 2: Preparation of absorbent B

[0071] The preparation method of the absorbent in this embodiment is basically the same as that in Example 1, except for the proportions of each component. Specifically, 40g of N-formylpiperidine, 100g of 1,3-propanediol, and 60g of deionized water are added sequentially to a beaker, and after mixing and stirring evenly, absorbent B is obtained. In the obtained absorbent B, the mass fraction of N-formylpiperidine is 20 wt.%, the mass fraction of 1,3-propanediol is 50 wt.%, and the mass fraction of water is 30 wt.

[0072] Example 3: Preparation of absorbent C

[0073] The preparation method of the absorbent in this embodiment is basically the same as that in Example 1, except for the proportions of each component. Specifically, 90g of N-formylpiperidine, 40g of 1,3-propanediol, and 70g of deionized water are added sequentially to a beaker, and after mixing and stirring evenly, absorbent C is obtained. In the obtained absorbent C, the mass fraction of N-formylpiperidine is 45 wt.%, the mass fraction of 1,3-propanediol is 20 wt.%, and the mass fraction of water is 35 wt.

[0074] Example 4: Preparation of absorbent D

[0075] The preparation method of the absorbent in this embodiment is basically the same as that in Example 1, except for the proportions of each component. Specifically, 70g of N-formylpiperidine, 70g of 1,3-propanediol, and 60g of deionized water are added sequentially to a beaker, and after mixing and stirring evenly, absorbent D is obtained. In the obtained absorbent D, the mass fraction of N-formylpiperidine is 35 wt.%, the mass fraction of 1,3-propanediol is 35 wt.%, and the mass fraction of water is 30 wt.

[0076] Example 5: Preparation of absorbent E

[0077] The preparation method of the absorbent in this embodiment is basically the same as that in Example 1, except for the proportions of each component. Specifically, 50g of N-formylpiperidine, 90g of 1,3-propanediol, and 60g of deionized water are added sequentially to a beaker, and after mixing and stirring evenly, absorbent E is obtained. In the obtained absorbent E, the mass fraction of N-formylpiperidine is 25 wt.%, the mass fraction of 1,3-propanediol is 45 wt.%, and the mass fraction of water is 30 wt.

[0078] Example 6: Preparation of absorbent F

[0079] This embodiment provides a phase change absorbent using different cyclic amide tertiary amines. The preparation method is basically the same as in Example 4, except that N-formylpiperidine is replaced with N-acetylpiperidine. Specifically, 70g of N-acetylpiperidine, 70g of 1,3-propanediol, and 60g of deionized water are added sequentially to a beaker, and after mixing and stirring evenly, absorbent F is obtained. In the obtained absorbent F, the mass fraction of N-acetylpiperidine is 35 wt.%, the mass fraction of 1,3-propanediol is 35 wt.%, and the mass fraction of water is 30 wt.

[0080] Example 7: Preparation of absorbent G

[0081] This embodiment provides a phase change absorbent using different hydrogen bond reconstruction phase separation promoters. Its preparation method is basically the same as in Example 4, except that 1,3-propanediol is replaced with 1,2-propanediol. Specifically, 70g of N-formylpiperidine, 70g of 1,2-propanediol, and 60g of deionized water are added sequentially to a beaker, and after mixing and stirring evenly, absorbent G is obtained. In the obtained absorbent G, the mass fraction of N-formylpiperidine is 35 wt.%, the mass fraction of 1,2-propanediol is 35 wt.%, and the mass fraction of water is 30 wt.

[0082] Comparative Example 1: Preparation of Absorbent H

[0083] This comparative example illustrates the case where a hydrogen bond remodeling phase separation promoter is lacking. Its preparation method is essentially the same as in Example 4, except that 1,3-propanediol is not added. Specifically, 140 g of N-formylpiperidine and 60 g of deionized water are added sequentially to a beaker, and after mixing and stirring until homogeneous, absorbent H is obtained. In the obtained absorbent H, the mass fraction of N-formylpiperidine is 70 wt.%, and the mass fraction of water is 30 wt.%.

[0084] Comparative Example 2: Preparation of Absorbent I

[0085] This comparative example uses a commonly used desulfurization absorbent in the prior art. Its preparation method is as follows: 60g of N-methyldiolamine (MDEA) and 140g of deionized water are added sequentially to a beaker, and after mixing and stirring evenly, a 30wt.% MDEA aqueous solution is obtained, denoted as absorbent I. In the obtained absorbent I, the mass fraction of N-methyldiolamine is 30wt.%, and the mass fraction of water is 70wt.%.

[0086] Application Example 1: Evaluation of the absorption and phase separation performance of absorbent AI

[0087] This application example is used to evaluate the performance of the absorbents prepared in Examples 1-7 and Comparative Examples 1-2 above.

[0088] Take 200g of each of the absorbents AG prepared in Examples 1-7 and HI prepared in Comparative Examples 1-2 and place them in a container as follows: Figure 1 In the absorption apparatus shown, absorption and phase separation experiments were conducted under the following uniform conditions:

[0089] Absorption temperature: 40℃;

[0090] Absorption pressure: atmospheric pressure;

[0091] Simulated gas composition: H2S 2 vol%, CO2 10 vol%, N2 88 vol%

[0092] Total gas flow rate: 500 mL·min -1 .

[0093] The absorption process lasted 60 minutes. During the absorption process, the H2S concentration in the outlet gas was continuously monitored, and the change in absorption load over time was calculated based on this, resulting in an H2S absorption load curve. The results are shown below. Figure 3 As shown. After absorption, record the final saturated H2S absorption load of the absorbent. Then, transfer the enriched solution after absorption to a 250 mL constant-temperature separatory funnel and let it stand at 40°C for 15 minutes to observe whether phase separation occurs. If phase separation occurs, record the volumes of the upper lean phase and the lower rich phase, and take samples from each. Analyze the H2S content of the two phases by titration. The results are shown below. Figure 4As shown in the table, the absorption performance and phase separation results of each absorbent are summarized in Table 1.

[0094] Table 1. Absorption performance and phase separation results of each absorbent

[0095]

[0096] As shown in Table 1, in Examples 1-7 of the present invention, liquid-liquid two-phase separation occurred after H2S absorption, and the volume ratio of the rich phase was less than 50% in all cases; while the absorbents in Comparative Examples 1 and 2 remained homogeneous throughout. This fully demonstrates the effectiveness of the technical solution of the present invention. Furthermore, the saturated H2S absorption load of all embodiments of the present invention was significantly higher than that of conventional MDEA aqueous solution (Comparative Example 2), exhibiting a higher absorption capacity.

[0097] Figure 3 The graphs show the H2S absorption load changes over time during the absorption process for the absorbents prepared in Examples 1-7 and Comparative Example 2. As can be seen from the graphs, the absorption load growth curves of the absorbents prepared in each example (Examples 1-7) are consistently above the curve of Comparative Example 2 (MDEA aqueous solution) throughout the entire absorption cycle. Furthermore, after 60 minutes of absorption, the final absorption load of each example (0.85-0.95 mol H2S / mol amine) is significantly higher than that of Comparative Example 2 (0.65 mol H2S / mol amine). The growth trend of the absorption load among the examples also corresponds to the final saturation load data in Table 1. From the slope trend of the curves, the curves of each example are generally steeper than the curve of Comparative Example 2 in the early stage of absorption, indicating that the absorbent of this invention can absorb H2S at a faster rate. This result demonstrates that the phase change absorbent provided by this invention has a higher thermodynamic absorption capacity than MDEA.

[0098] Figure 4 The figure shows the H2S content of the lean and rich phases after phase separation of the absorbents prepared in Examples 1-7 of this invention. As can be seen from the figure, the H2S loading of the rich phase in all examples of this invention reaches an extremely high level, exhibiting a significant H2S enrichment effect. In Examples 1-7, 95-98% of the H2S is enriched in the rich phase, and the rich phase loading is generally higher than 1.7 mol H2S / mol amine, with Example 3 reaching as high as 2.56 mol H2S / mol amine. This indicates that in the rich phase, the amine molecules almost reach the physical solubility limit after a 2:1 stoichiometric reaction with H2S, demonstrating a strong H2S capture ability. The H2S content in the lean phase is low, generally below 0.1 mol H2S / mol amine. This allows the lean phase to be directly recycled, achieving the energy-saving goal of regenerating only the high-concentration, small-volume rich phase.

[0099] Application Example 2: Evaluation of Absorption Kinetics

[0100] This application example is used to compare the absorption kinetics performance of the phase change absorbent prepared in different embodiments of the present invention with that of MDEA, a commonly used absorbent in the prior art.

[0101] The absorbent AG prepared in Examples 1-7 and the absorbent I (30wt% MDEA aqueous solution) prepared in Comparative Example 2 were respectively placed in Figure 1 In the absorption apparatus shown, an absorption experiment was conducted under the same absorption conditions as in Application Example 1. Throughout the absorption process, the H2S concentration in the outlet gas was continuously monitored, and the instantaneous H2S absorption rate of each absorbent at different times was calculated according to Equation (2) in the performance evaluation method. The results are as follows: Figure 5 As shown.

[0102] Figure 5 This is a graph showing the absorption rate of H2S by the absorbent AG prepared in Examples 1-7 of this invention and the absorbent I prepared in Comparative Example 2. Figure 5 It can be seen that the H2S absorption rate curves of the absorbent AG prepared in Examples 1-7 of this invention are significantly higher than those of absorbent I in Comparative Example 2 throughout the entire absorption cycle. In the initial absorption stage, the peak absorption rate of the absorbents in each embodiment of this invention is between 2.3 × 10⁻⁶. -5 Up to 2.5×10 -5 mol·g －1 ·min －1 In contrast, the peak absorption rate of absorbent I in Comparative Example 2 was only about 1.8 × 10⁻⁶. -5 mol·g －1 ·min －1 As can be seen from the curve shape, the absorbent of the present invention, especially absorbent C prepared in Example 3, exhibits a longer high-rate absorption plateau period. The absorption rate of absorbent C only begins to decrease significantly after about 30 minutes, while the absorption rate of absorbent I prepared in Comparative Example 2 enters a continuous decline phase after about 10 minutes.

[0103] The above results show that the series of phase change absorbents described in this invention have significantly faster absorption kinetics and higher sustained absorption capacity compared with the existing absorbent MDEA, which is of great significance for improving the treatment efficiency of industrial plants and extending the operating cycle.

[0104] Furthermore, combining the results of Examples 1-2, it can be seen that among Examples 1-7, Example 4 has the best saturated loading and absorption rate for hydrogen sulfide. However, compared to Example 3, its saturated absorption loading is only increased by 0.1 mol H2S / mol amine, but it requires an increase of 10 wt% in the amount of organic amine used. Therefore, considering both performance and cost, the absorbent D prepared in Example 4 is the preferred formulation of this invention. The performance and cycle stability of absorbent D under different process conditions are further investigated below.

[0105] Application Example 3: Performance Evaluation under Different Process Conditions

[0106] This application example aims to investigate the performance of the absorbent of the present invention under different process operating conditions. Absorbent D prepared in Example 4 was selected, and absorption experiments were conducted at different absorption temperatures and pressures, simulating the same gas composition and flow rate as in Application Example 1.

[0107] (1) Temperature effect: The absorption pressure was fixed at atmospheric pressure, and absorption experiments were conducted at 30℃, 40℃ and 50℃ respectively.

[0108] (2) Pressure effect: The absorption temperature was fixed at 40℃. By installing a back pressure valve at the tail gas pipeline of the absorption system, the system pressure was controlled at 0.5 MPa and 1.0 MPa respectively for the absorption experiment.

[0109] The experimental results are summarized in Table 2.

[0110] Table 2. Performance of absorbent D prepared in Example 4 under different process conditions

[0111]

[0112] As shown in Table 2, the absorbent D prepared in Example 4 of this invention maintains extremely high H2S removal efficiency and absorption load over a wide temperature range of 30-50℃. Furthermore, under pressurized conditions, the absorption performance is further improved, and the co-absorption of CO2 remains at a very low level, demonstrating that the phase change absorbent of this invention has excellent selectivity for H2S and broad adaptability to various operating conditions.

[0113] Application Example 4: Cyclic Stability Test

[0114] This application example is used to verify the long-term performance of the absorbent of the present invention.

[0115] The absorbent D prepared in Example 4 of this invention and the absorbent I prepared in Comparative Example 2 were subjected to six consecutive absorption-desorption cycle experiments.

[0116] Absorption conditions: Same as in Application Example 1, each time absorption until saturation.

[0117] Regeneration conditions: Take the saturated rich liquid after absorption (for absorbent D, only take its lower rich phase liquid; for absorbent I, take the same mass of rich liquid as the rich phase liquid of absorbent D), and regenerate it at 120℃ and normal pressure using the following method... Figure 2 The desorption apparatus shown is used at a rate of 50 mL / min. －1 The N2 is stripped and regenerated for 60 minutes.

[0118] After each cycle, the saturated H2S absorption load of the regenerated absorbent was tested. The experimental results are as follows: Figure 6 As shown, and summarized in Table 3.

[0119] Table 3. Cyclic stability test data

[0120]

[0121] Depend on Figure 6 The results and data in Table 3 show that after 6 cycles, the H2S absorption load decay rate of absorbent D prepared in Example 4 of this invention was only 1.1%. In contrast, the absorption load decay rate of absorbent I prepared in Comparative Example 2 reached 6.2%. Liquid chromatography analysis showed that the concentrations of NFP and 1,3-propanediol in the regenerated lean solution of Example 4 remained essentially unchanged, and no obvious degradation products were detected. These results fully demonstrate that the absorbent system described in this invention possesses excellent chemical and thermal stability, enabling it to support long-term industrial applications.

[0122] In summary, the phase change absorbent and its application method provided by this invention exhibit significant beneficial effects in terms of selectivity, absorption capacity, regeneration energy consumption, and operational stability.

[0123] The above embodiments are merely one of the implementation methods for achieving the technical solution of the present invention. The scope of protection claimed by the present invention is not limited to this embodiment, but also includes any variations, substitutions and other implementation methods that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention.

[0124] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. Furthermore, various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the spirit of the present invention, and should also be regarded as the content disclosed by the present invention.

[0125] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A phase change absorbent for selective removal of hydrogen sulfide, characterized by, The phase change absorbent comprises the following components by mass fraction: Cyclic amide tertiary amine: 20% to 45%; Hydrogen bond reconfiguration phase separation promoter: 20% to 50%; The balance is water; The cyclic amide tertiary amine contains a tertiary amine nitrogen atom for acid-base reaction with H2S and an amide group as a hydrogen bond acceptor in the molecular structure; the cyclic amide tertiary amine is selected from at least one of N-formylpiperidine, N-acetylpiperidine, N-formylpyrrolidine and N-acetylmorpholine; The hydrogen bond reconfiguration phase separation promoter is a polyhydric alcohol containing two or more hydroxyl groups.

2. The phase change sorbent for selective removal of hydrogen sulfide according to claim 1, wherein The hydrogen bond reconfiguration phase separation promoter is selected from at least one of ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol and triethylene glycol.

3. The phase change sorbent for selective removal of hydrogen sulfide according to claim 1, wherein The mass ratio of the cyclic amide tertiary amine to the hydrogen bond reconfiguration phase separation promoter is 1:0.8 to 1:1.

5.

4. The phase change sorbent for selective removal of hydrogen sulfide according to claim 1, wherein The cyclic amide tertiary amine is N-formylpiperidine, and the hydrogen bond reconfiguration phase separation promoter is 1,3-propanediol.

5. The phase change sorbent for selective removal of hydrogen sulfide according to claim 1, wherein The phase change absorbent comprises, by mass fraction: 30% to 40% of N-formylpiperidine; 30% to 40% of 1,3-propanediol, and the balance is water.

6. A method for producing a phase change absorbent for selectively removing hydrogen sulfide according to any one of claims 1 to 5, characterized by, The method comprises the following steps:

7. Use of the phase change absorbent according to any one of claims 1 to 5 for the selective removal of hydrogen sulfide from a gas, characterized in that, The method comprises the following steps: S1 absorption step: in an absorption tower, a raw gas containing hydrogen sulfide is brought into countercurrent contact with the phase change absorbent, and the hydrogen sulfide in the raw gas is absorbed by the phase change absorbent to obtain a purified gas and a rich liquid that has absorbed hydrogen sulfide; S2 phase separation step: the rich liquid obtained in step S1 is introduced into a phase separator to stand and separate into a lower layer rich phase liquid rich in H2S and an upper layer lean phase liquid with less H2S; S3 regeneration and circulation step: the rich phase liquid obtained in step S2 is preheated and then sent into a regeneration tower for heating desorption regeneration to obtain regenerated lean liquid and high-concentration hydrogen sulfide gas; the lean phase liquid obtained in step S2 is directly pumped or mixed with the regenerated lean liquid and then sent back to the absorption tower for recycling.

8. Use according to claim 7, characterized in that, In step S1, the temperature in the absorption tower is 30°C to 40°C, and the pressure is 0.1 MPa to 5.0 MPa.

9. Use according to claim 7, characterized in that, In step S3, the temperature in the regeneration tower is 100°C to 120°C.

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