Phase change absorbent for selectively removing hydrogen sulfide as well as preparation method and application of phase change absorbent

Abstract

The invention discloses a phase change absorbent for selectively removing hydrogen sulfide as well as a preparation method and application thereof, and the phase change absorbent comprises the following components in percentage by mass: 20-45% of cyclic amide tertiary amine, 5-10% of a catalyst, 1-5% of a catalyst, 1-5% of a catalyst and the balance of a solvent. 20%-50% of a hydrogen bond reconstruction type phase separation accelerant; and the balance of water. The molecular structure of the cyclic amide tertiary amine comprises a tertiary amine nitrogen atom used for carrying out acid-base reaction with H2S and an amide group used as a hydrogen bond acceptor, and the cyclic amide tertiary amine is used for reacting with H2S with high selectivity; the hydrogen bond reconstruction type phase separation accelerant is polyhydric alcohol containing two or more hydroxyl groups, after H2S is absorbed, an absorbent is induced to be subjected to liquid-liquid phase separation, a rich phase rich in H2S and a lean phase low in H2S content are formed, and then separation of the rich phase and the lean phase can be achieved through simple gravity or centrifugation. The phase change absorbent provided by the invention has the advantages of high H2S absorption selectivity, low regeneration energy consumption, simple preparation method and low operation cost, and is especially suitable for fine desulfurization of refinery dry gas and other complex acidic gases.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of energy saving and emission reduction and gas purification, and particularly relates to a phase change absorbent for selectively removing hydrogen sulfide and a preparation method and application thereof. BACKGROUND

[0002] In the industrial fields of natural gas, refinery gas and coal chemical industry, the gas raw material often contains acidic components such as H2S and CO2. Removing H2S is crucial for personnel safety, equipment and catalyst protection, product quality and environmental protection requirements. In many process applications, such as when refinery dry gas is used as fuel gas, only H2S removal is required, and there is no strict requirement for CO2 removal. Therefore, developing high selectivity desulfurization technology has significant economic value for reducing equipment investment and operating energy consumption.

[0003] Currently, alcohol amine method is widely used for selective desulfurization in industry, and tertiary amine aqueous solution represented by N-methyldiethanolamine (MDEA) is the mainstream technology. CN117323781A discloses an amine absorbent using MDEA as the main agent and compounding with an activator. This technology uses the kinetic characteristics that the reaction rate of MDEA with H2S is much faster than that with CO2 to achieve selective absorption. However, this kind of alcohol amine method with water as the main solvent generally has high regeneration energy consumption due to the high specific heat capacity and large latent heat of vaporization of water, and the amine solution is prone to degradation, foaming and other problems during long-term operation, affecting the long-term stable operation of the device.

[0004] In order to solve the above problems, researchers have made various improvements. One approach is to develop a composite solvent, and CN116407927A discloses an absorbent compounded by organic alcohol amine, organic solvent, oxidizing agent and inorganic salt, etc. This kind of absorbent improves the absorption performance through the synergistic effect of multiple components, but often has problems such as complex components, easy to have side reactions, high risk of solvent degradation, increased operating cost, etc. Another type of technology that attracts attention is phase change absorption technology, the core idea of which is that the absorbent can spontaneously form a rich phase rich in H2S and a lean phase lean in H2S after absorbing H2S, and only the rich phase needs to be treated during regeneration, which can greatly save energy. For example, CN108144415A discloses a phase change absorption liquid composed of organic amine and organic solvent. However, the existing phase change absorption technology still has some shortcomings, such as the precipitation of solid after absorption in some systems, which poses the risk of plugging pipelines and equipment; and some liquid-liquid phase separation systems have the problems of incomplete phase separation, low enrichment of H2S in the rich phase or interphase solvent entrainment loss, etc., which limit the full play of the energy saving effect.

[0005] Therefore, developing a new desulfurization absorbent with high H2S selectivity and high absorption capacity, which can realize fast and complete liquid-liquid separation without solid phase precipitation after absorption, and has stable chemical properties and low energy consumption in regeneration, has become a technical problem to be solved in the field. SUMMARY

[0006] The present application aims to overcome the problems of high energy consumption in regeneration, limited selectivity, and incomplete phase separation, solid formation, solvent degradation, or poor system stability in the existing phase change absorbent system in the alcohol amine method desulfurization process in the prior art. Therefore, the present application is dedicated to providing a new selective removal of hydrogen sulfide phase change absorbent based on the mechanism of hydrogen bond network reconstruction induced by chemical reaction and its preparation method and application, so as to realize efficient and selective capture of hydrogen sulfide and low energy consumption regeneration of the absorbent.

[0007] To achieve the above-mentioned purpose, the first aspect of the present application provides a phase change absorbent for selectively removing hydrogen sulfide, which is a homogeneous aqueous solution formed by a cyclic amide tertiary amine, a hydrogen bond reconstruction type phase separation promoter and water in a specific ratio, and includes the following components by mass fraction:

[0008] Cyclic amide tertiary amine: 20wt.% to 45wt.%;

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

[0010] The balance 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 the molecular structure;

[0012] The hydrogen bond reconstruction type phase separation promoter is a polyhydric alcohol containing two or more hydroxyl groups (-OH).

[0013] As the core of the present application, the phase change mechanism proposed in the present application is based on the following idea:

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

[0015] (2) The hydroxyl group in the hydrogen bond reconstruction type phase separation promoter acts as a hydrogen bond donor to form 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 water phase.

[0016] (3) Phase transition mechanism: when the absorbent absorbs H2S, the tertiary amine nitrogen atom is protonated to form a quaternary ammonium cation (R3NH + ). According to the principle of quantum chemistry, the positive charge on the nitrogen atom will absorb the electron cloud density from the entire ring structure (including the distal amide group) through the covalent bond. This results in a significant reduction in the lone pair electron cloud density of the carbonyl oxygen atom in the amide group, weakening its ability as a hydrogen bond acceptor. The stable hydrogen bond originally formed with the phase separation promoter is thus destroyed or "broken". At this time, the protonated amine molecule (ionic salt) preferentially dissolves in water due to its strong polarity, forming a high-density H2S-rich aqueous phase (i.e., the rich phase); while the "released" phase separation promoter and unreacted amine molecules, which have weaker polarity, aggregate to form a separate low-density H2S-lean organic phase (i.e., the lean phase), thus achieving liquid-liquid two-phase separation.

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

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

[0019] Further, 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.

[0020] As another preferred scheme of the present application, in the phase transition absorbent, 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.

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

[0022] Preferably, the hydrogen bond reconfiguration phase separation promoter is 1,3-propanediol. Its molecular chain is short and has low viscosity, and it has two terminal hydroxyl groups, which can form an effective hydrogen bond network with N-formylpiperidine, and it itself has good chemical stability with NFP.

[0023] As a particularly preferred technical scheme of the present application, the phase transition absorbent consists of the following components by mass fraction:

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

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

[0026] the balance being water.

[0027] The second aspect of the present application provides a preparation method of the phase change absorbent as described above, comprising the following steps:

[0028] Under the temperature condition of 10-30℃, metered composite amine absorbent, phase separation promoter and water are sequentially added into a container with stirring device, and stirred and mixed until a uniform and clear solution is formed, thereby obtaining the phase change absorbent.

[0029] The third aspect of the present application provides an application of the phase change absorbent as described above in selective removal of hydrogen sulfide in gas, comprising the following steps:

[0030] S1 absorption step: in the absorption tower, the raw gas containing hydrogen sulfide is contacted with the phase change absorbent in countercurrent, and the hydrogen sulfide in the raw gas is absorbed by the phase change absorbent, thereby obtaining the purified gas and the rich liquid absorbing hydrogen sulfide;

[0031] S2 phase separation step: the rich liquid obtained in step S1 is introduced into the phase separator to stand and stratify, thereby obtaining the upper H2S lean liquid with less H2S content and the lower H2S rich liquid rich in H2S;

[0032] S3 regeneration and circulation step: the H2S rich liquid obtained in step S2 is preheated and then sent into the regeneration tower to be heated and desorbed for regeneration, thereby obtaining the regenerated lean liquid and the high-concentration hydrogen sulfide gas; the H2S lean liquid obtained in step S2 is directly pumped or mixed with the regenerated lean liquid and then sent back to the absorption tower for circulation, and the high-concentration hydrogen sulfide gas desorbed from the top of the regeneration tower is sent to the downstream device.

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

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

[0035] Compared with the prior art, the present application has the following remarkable beneficial effects:

[0036] (1) high selectivity and fast absorption efficiency: the absorbent prepared by the present application has excellent kinetic and thermodynamic properties, the cyclic amide tertiary amine retains high reaction selectivity to H2S, and can spontaneously phase separate after absorbing H2S, thereby greatly reducing the circulation amount of the absorbent, and enabling the system to operate at a higher total sulfur content of the rich liquid without affecting the purified gas index.

[0037] (2) The energy consumption of regeneration is significantly reduced: the phase separation chemical reaction of the system is triggered accurately, compared with the traditional system which relies on the difference in physical solubility, the phase separation is faster and more thorough, and since the H2S content in the lean 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 stability and no risk of blockage: the absorbent of the present application forms a stable liquid-liquid two-phase after absorbing H2S, avoiding the problem of solid phase precipitation in the prior art, and eliminating the industrial operation risks such as equipment corrosion and blockage caused thereby.

[0039] (4) The preparation is simple and the process is adaptable: the preparation process of the present application is only a simple physical mixing, without complex chemical reaction, only one phase separator needs to be added on the basis of the amine process to realize it, which is easy to modify or apply to new devices on the existing desulfurization device, and has good popularization prospect. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 It is a performance evaluation device structure schematic diagram of the absorbent in the present application for hydrogen sulfide absorption.

[0041] Figure 2 It is a performance evaluation device structure schematic diagram of the absorbent in the present application for hydrogen sulfide desorption.

[0042] Figure 3 It is a curve diagram of different phase change absorbents and traditional MDEA absorbents for H2S absorption load in the present application.

[0043] Figure 4 It is a columnar diagram of the H2S content of the lean and rich two phases after the phase separation of different phase change absorbents in the present application.

[0044] Figure 5 It is a curve diagram of different phase change absorbents and traditional MDEA absorbents for H2S absorption rate in the present application.

[0045] Figure 6 It is a curve diagram of the phase change absorbent and the traditional MDEA absorbent for phase change absorption load after a plurality of absorption-desorption cycles in the present application.

[0046] In the figure: 1-H2S / CO2 mixed gas bottle; 2-N2 gas bottle; 3-flow control device; 4-gas mass flow controller; 5-constant temperature water bath device; 6-three neck flask; 7-thermocouple thermometer; 8-condenser; 9-dry 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 DESCRIPTION

[0047] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work under the premise of the present application, belong to the scope of protection of the present application.

[0048] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work under the premise of the present application, belong to the scope of protection of the present application.

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

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

[0051] N-formylpiperidine (NFP): industrial grade, purity ≥ 99.0%, purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd.;

[0052] N-acetylpiperidine: analytical pure, purity ≥ 98.5%, purchased from Shanghai Macklin 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 gas: H2S (purity 99.9%), CO2 (purity 99.9%), N2 (purity 99.99%), all mixed and prepared by a mass flow controller produced by Beijing Qixing Huachuang Electronics Co., Ltd. from cylinder gas.

[0057] (2) Performance evaluation method

[0058] (S1) Absorption performance evaluation:

[0059] Reference Figure 1, the absorption device includes H2S / CO2 mixed gas cylinder 1 and N2 gas cylinder 2, flow control device 3, gas mass flow controller 4, constant temperature water bath device 5, 250 mL three-neck flask 6 as absorption bottle, thermocouple temperature meter 7, condenser 8, drying tube 9, multifunctional gas analyzer 10, data collection device 11 and tail gas washing bottle 12. During the experiment, 200 g of the to-be-tested absorbent is placed in the absorption bottle, and the absorption temperature is accurately controlled through the constant temperature water bath device 5. The simulated acid gas is prepared according to the set proportion, enters the absorption bottle at a certain flow rate, and fully contacts with the absorbent, and the thermocouple temperature meter 7 is used to monitor the temperature in the absorption bottle in real time. The tail gas is dried and then enters the multifunctional gas analyzer 10 for online analysis of H2S and CO2 concentrations. The H2S removal efficiency (η) is calculated according to formula (1):

[0060]

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

[0062] The H2S absorption load (α) is defined as the number of moles of H2S absorbed by each mole of amine after reaching absorption saturation or a specified absorption time, which is obtained by chemical titration analysis of the rich liquid of the absorbed H2S.

[0063] The H2S absorption rate (R abs ) is defined as the number of moles of H2S absorbed by the absorption agent per unit volume per unit time, and the instantaneous absorption rate can be calculated by formula (2):

[0064]

[0065] In the formula, R abs (t) is the instantaneous absorption rate at time t, with the unit of mol·g －1 ·min －1 ; Q is the volume flow rate of the simulated gas, with the unit of L·min －1 ; C in and C out are the volume fractions of H2S in the inlet and outlet gases, respectively; V M is the molar volume of H2S gas under standard conditions, taking 22.4 L·mol －1 , and m L is the mass of the absorbent, with the unit of g.

[0066] (S2) Desorption performance evaluation:

[0067] Reference Figure 2, the desorption device includes a N2 cylinder 2, a flow control device 3, a gas mass flow controller 4, a magnetic stirring oil bath device 13, a 250 mL three-neck flask 6 as a desorption bottle, a thermocouple temperature detector 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. The absorbed rich liquid is added to the desorption bottle, which has a magnetic stirring rotor 14, heated to the desorption temperature (120°C) by the magnetic stirring oil bath device 13, and the temperature in the desorption bottle is detected in real time by the thermocouple temperature detector 7. At the same time, N2 with a certain flow rate is used as stripping gas to bubble from below the liquid surface, and the desorbed acidic gas is condensed and dried by the condenser 8 and the drying tube 9, and then the H2S concentration is detected online by the multifunctional gas analyzer 10 until the H2S concentration in the tail gas is lower than the detection limit.

[0068] Example 1: Preparation of absorbent A

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

[0070] Example 2: Preparation of absorbent B

[0071] The preparation method of the absorbent of this example is basically the same as that of Example 1, except for the ratio of the components. Specifically, 40g of N-formylpiperidine, 100g of 1,3-propanediol and 60g of deionized water were sequentially added to a beaker, and after being mixed and stirred uniformly, absorbent B was obtained. In the obtained absorbent B, the mass fraction of N-formylpiperidine was 20wt.%, the mass fraction of 1,3-propanediol was 50wt.% and the mass fraction of water was 30wt.%.

[0072] Example 3: Preparation of absorbent C

[0073] The preparation method of the absorbent of this example is basically the same as that of Example 1, except for the ratio of the components. Specifically, 90g of N-formylpiperidine, 40g of 1,3-propanediol and 70g of deionized water were sequentially added to a beaker, and after being mixed and stirred uniformly, absorbent C was obtained. In the obtained absorbent C, the mass fraction of N-formylpiperidine was 45wt.%, the mass fraction of 1,3-propanediol was 20wt.% and the mass fraction of water was 35wt.%.

[0074] Example 4: Preparation of absorbent D

[0075] The preparation method of the absorbent of the present example is basically the same as that of Example 1, except for the proportion of each component. Specifically, 70 g of N-formylpiperidine, 70 g of 1,3-propanediol and 60 g of deionized water are sequentially added into a beaker, and after being uniformly mixed and stirred, 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 of the present example is basically the same as that of Example 1, except for the proportion of each component. Specifically, 70 g of N-formylpiperidine, 70 g of 1,3-propanediol and 60 g of deionized water are sequentially added into a beaker, and after being uniformly mixed and stirred, 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.%.

[0078] Example 6: Preparation of absorbent F

[0079] The present example provides a phase change absorbent using a different cyclic amide tertiary amine. The preparation method thereof is basically the same as that of Example 4, except that N-formylpiperidine is replaced by N-acetylpiperidine. Specifically, 70 g of N-acetylpiperidine, 70 g of 1,3-propanediol and 60 g of deionized water are sequentially added into a beaker, and after being uniformly mixed and stirred, 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] The present example provides a phase change absorbent using a different hydrogen bond reconfiguration type phase separation promoter. The preparation method thereof is basically the same as that of Example 4, except that 1,3-propanediol is replaced by 1,2-propanediol. Specifically, 70 g of N-formylpiperidine, 70 g of 1,2-propanediol and 60 g of deionized water are sequentially added into a beaker, and after being uniformly mixed and stirred, 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] The present comparative example is used to illustrate the case where the hydrogen bond reconfiguration phase separation promoter is absent. It is prepared in substantially the same manner as Example 4, except that 1,3-propanediol is not added. Specifically, 140 g of N-formylpiperidine and 60 g of deionized water are sequentially added to a beaker, and after being mixed and stirred uniformly, an 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] The present comparative example is a desulfurization absorbent commonly used in the prior art. It is prepared in the following manner: 60 g of N-methyldiethanolamine (MDEA) and 140 g of deionized water are sequentially added to a beaker, and after being mixed and stirred uniformly, a 30 wt.% MDEA aqueous solution is obtained, which is denoted as absorbent I. In the obtained absorbent I, the mass fraction of N-methyldiethanolamine is 30 wt.%, and the mass fraction of water is 70 wt.%.

[0086] Application Example 1: Evaluation of absorption and phase separation performance of absorbents A-I

[0087] The present application example is used to evaluate the performance of each absorbent prepared in Examples 1-7 and Comparative Examples 1-2 described above.

[0088] The absorbents A-G prepared in Examples 1-7 and the absorbents H-I prepared in Comparative Examples 1-2 are each taken 200 g and placed in an absorption device as shown in Figure 1 The absorption and phase separation experiments are carried out under the following uniform conditions:

[0089] Absorption temperature: 40°C;

[0090] Absorption pressure: atmospheric pressure;

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

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

[0093] The absorption process lasts for 60 minutes. During the absorption process, the H2S concentration in the outlet gas is continuously monitored, and the absorption load change with time is calculated accordingly, and a H2S absorption load curve is plotted, as shown in Figure 3 After the absorption is completed, the final saturated H2S absorption load of the absorbent is recorded. Subsequently, the rich liquid after absorption is transferred to a 250 mL constant temperature separatory funnel, and is allowed to stand at 40°C for 15 minutes, and whether phase separation occurs is observed. If phase separation occurs, the volumes of the upper lean phase and the lower rich phase are recorded, and samples are taken respectively, and the H2S contents of the two phases are analyzed by titration, and the results are shown in Figure 4The 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] From the results in Table 1, it can be seen that Examples 1-7 of the present application all undergo liquid-liquid two-phase separation after absorbing H2S, and the volume ratio of the rich phase is less than 50%; while the absorbents of Comparative Examples 1 and 2 are always in a homogeneous phase. This fully confirms the effectiveness of the technical solution of the present application. At the same time, the saturated H2S absorption load of all examples of the present application is significantly higher than that of the conventional MDEA aqueous solution (Comparative Example 2), showing a higher absorption capacity.

[0097] Figure 3 The curves of H2S absorption load over time during the absorption process of the absorbents prepared in Examples 1-7 of the present application and the absorbent prepared in Comparative Example 2. From the figure, it can be seen that the absorption load growth curves of the absorbents prepared in each example (Examples 1-7) of the present application are all above the curve of Comparative Example 2 (MDEA aqueous solution) in the entire absorption period, and 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). Among each example, the growth trend of the absorption load also corresponds to the final saturated load data in Table 1. From the slope change trend of the curve, the curve of each example of the present application is generally steeper than that of Comparative Example 2 in the early stage of absorption, indicating that the absorbent of the present application can absorb H2S at a faster rate. This result shows that the phase change absorbent provided by the present application has a higher thermodynamic absorption capacity than MDEA.

[0098] Figure 4 The H2S contents of the lean and rich phases after the absorbents prepared in Examples 1-7 of the present application undergo phase separation. From the figure, it can be seen that the H2S load of the rich phase of all examples of the present application reaches an extremely high level, showing a significant H2S enrichment effect. In Examples 1-7, 95-98% of H2S is enriched in the rich phase, and the rich phase load is generally higher than 1.7 mol H2S / mol amine, among which the rich phase load of Example 3 is as high as 2.56 mol H2S / mol amine. This shows that in the rich phase, the amine molecules have almost reached the physical solubility limit after a 2:1 stoichiometric reaction with H2S, showing a strong H2S capture capacity. The H2S content in the lean phase is low, generally less than 0.1 mol H2S / mol amine. This allows the lean phase to be directly recycled, achieving the energy-saving goal of regenerating only the rich phase with high concentration and small volume.

[0099] Application Example 2: Absorption Kinetics Evaluation

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

[0101] The absorbents A-G prepared in Examples 1-7, and the absorbent I (30wt% MDEA aqueous solution) prepared in Comparative Example 2, were respectively placed in the absorption device shown in Figure 1 , and the absorption experiments were carried out under the same absorption conditions as in Application Example 1. During the entire 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 formula (2) in the performance evaluation method, and the results are shown in Figure 5 .

[0102] Figure 5 The curves of the H2S absorption rates of the absorbents A-G prepared in Examples 1-7 of the present application and the absorbent I prepared in Comparative Example 2 are shown in Figure 5 It can be seen that the H2S absorption rate curves of the absorbents A-G prepared in Examples 1-7 of the present application are significantly higher than that of the absorbent I of Comparative Example 2 throughout the absorption period. In the initial stage of absorption, the peak absorption rate of the absorbents of each embodiment of the present application is between 2.3×10 -5 and 2.5×10 -5 mol·g －1 ·min －1 ; in contrast, the peak absorption rate of the absorbent I of Comparative Example 2 is only about 1.8×10 -5 mol·g －1 ·min －1 . From the curve shape, it can be seen that the absorbents of the present application, especially the absorbent C prepared in Example 3, exhibit a longer high-rate absorption plateau. The absorption rate of absorbent C does not begin to decrease significantly until about 30 minutes, while the absorption rate of the absorbent I prepared in Comparative Example 2 enters a sustained decline stage after about 10 minutes.

[0103] The above results show that the series of phase change absorbents described in the present application have significantly faster absorption kinetics and higher sustained absorption capacity compared to the existing absorbent MDEA, which is of great significance for improving the processing efficiency and prolonging the operation period of industrial devices.

[0104] In addition, in combination with the results of Application Example 1-2, it can be seen that in Example 1-7, the saturated loading capacity and absorption rate of hydrogen sulfide of Example 4 are both optimal, but compared with Example 3, the saturated absorption loading is only increased by 0.1 mol H2S / mol amine, but the amount of organic amine used needs to be increased by 10 wt%. Therefore, in terms of comprehensive performance and cost, the absorbent D prepared in Example 4 is the preferred formula of the present application. The performance of absorbent D under different process conditions and the cycle stability are further investigated below.

[0105] Application Example 3: Performance investigation under different process conditions

[0106] The present application example aims to investigate the performance of the absorbent of the present application under different process operating conditions. The absorbent D prepared in Example 4 is selected to carry out absorption experiments under different absorption temperatures and absorption pressures, and the simulation gas composition and flow rate are the same as those in Application Example 1.

[0107] (1) Temperature effect: absorption experiments are carried out at 30℃, 40℃ and 50℃, respectively, with the absorption pressure fixed at atmospheric pressure.

[0108] (2) Pressure effect: absorption experiments are carried out by controlling the system pressure at 0.5 MPa and 1.0 MPa, respectively, with the absorption temperature fixed at 40℃, by installing a back pressure valve at the tail gas line of the absorption system.

[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 can be seen from Table 2, the absorbent D prepared in Example 4 of the present application maintains extremely high H2S removal efficiency and absorption loading in a wide temperature range of 30-50℃. At the same time, under pressurized conditions, the absorption performance is further improved, and the CO2 co-absorption amount still maintains at a very low level, proving that the phase change absorbent of the present application has excellent selectivity for H2S and wide process condition adaptability.

[0113] Application Example 4: Cycle stability test

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

[0115] The absorbent D prepared in Example 4 of the present application and the absorbent I prepared in Comparative Example 2 are selected to carry out absorption-desorption cycle experiments for 6 times in succession.

[0116] Absorption conditions: same as Application Example 1, saturated absorption each time.

[0117] Regeneration condition: take the rich liquid after absorption saturation (for absorbent D, only take its lower rich phase liquid; for absorbent I, take the rich liquid with the same mass as the rich phase liquid of absorbent D), use the desorption device as shown in Figure 2 at 120℃, atmospheric pressure, and 50mL·min －1 N2stripping regeneration for 60 minutes.

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

[0119] Table 3. Cycle stability test data

[0120]

[0121] From the results of Figure 6 and the data in Table 3, it can be seen that after 6 cycles, the H2S absorption load attenuation rate of the absorbent D prepared in Example 4 is only 1.1%. The absorption load attenuation rate of the absorbent I prepared in Comparative Example 2 is 6.2%. Liquid chromatography analysis shows that the concentrations of NFP and 1,3-propanediol in the regenerated lean liquid of Example 4 are basically unchanged, and no obvious degradation products are detected. This result fully proves that the absorbent system described in the present application has excellent chemical stability and thermal stability, and can support long-period industrial applications.

[0122] In summary, the phase change absorbent and its application method provided by the present application have significant beneficial effects in selectivity, absorption capacity, regeneration energy consumption, and operation stability.

[0123] The above examples are only one of the implementation manners capable of implementing the technical solutions of the present application, and the scope of protection claimed by the present application is not limited to the above embodiment only, but also includes any changes, substitutions and other implementation manners easily thought of by those skilled in the art within the technical scope disclosed by the present application.

[0124] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations. In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, it should be considered as disclosed by the present application.

[0125] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

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

2. The phase change absorbent for selectively removing hydrogen sulfide according to claim 1, characterized in that, 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.

3. The phase change absorbent for selectively removing hydrogen sulfide according to claim 1, characterized in that, The mass ratio of the cyclic amide tertiary amine to the hydrogen bond remodeling phase separation promoter is from 1:0.8 to 1:1.

5.

4. The phase change absorbent for selectively removing hydrogen sulfide according to claim 1, characterized in that, The cyclic amide tertiary amine is N-formylpiperidine, and the hydrogen bond reconstruction phase separation promoter is 1,3-propanediol.

5. The phase change absorbent for selectively removing hydrogen sulfide according to claim 1, characterized in that, The phase change absorbent comprises, by mass fraction: 30%–40% N-formylpiperidine; 30%–40% 1,3-propanediol; and the balance being water.

6. A method for preparing a phase change absorbent for selectively removing hydrogen sulfide as described in any one of claims 1 to 5, characterized in that, The process includes the following steps: Under a temperature of 10–30°C, a measured amount of cyclic amide tertiary amine, hydrogen bond reconstruction 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.

7. An application of the phase change absorbent according to any one of claims 1 to 5 in the selective removal of hydrogen sulfide from a gas, characterized in that, Includes the following steps: 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. 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 lean phase liquid with less H2S content and a lower layer of rich phase liquid enriched with H2S. S3 Regeneration and Recycling Steps: The rich phase liquid obtained in step S2 is preheated and then sent to the regeneration tower for heating and desorption regeneration to obtain regenerated lean liquid and high-concentration hydrogen sulfide gas; the lean phase liquid obtained in step S2 is sent back to the absorption tower for recycling, either directly or mixed with the regenerated lean liquid.

8. The application according to claim 7, characterized in that, In step S1, the temperature inside the absorption tower is 30℃~40℃ and the pressure is 0.1 MPa~5.0 MPa.

9. The application according to claim 7, characterized in that, In step S3, the temperature inside the regeneration tower is 100℃~120℃.

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