Phase change absorbent for desulfurization and decarbonization of natural gas and preparation method of phase change absorbent

Abstract

The invention belongs to the technical field of natural gas purification, and particularly relates to a phase change absorbent for desulfurization and decarburization of natural gas and a preparation method thereof.The phase change absorbent is prepared from, by mass, 15%-60% of ionic liquid, 40%-85% of organic solvent and the balance water; wherein a cation donor of the ionic liquid is cyclic amine, and an anion donor of the ionic liquid is nitrogenous organic acid or nitrogenous organic acid salt; the cyclic amine-organic acid ionic liquid is used as an active component of the phase change absorbent, and the active component of the absorbent contains cyclic amido, so that the hydrolysis reaction of COS can be efficiently catalyzed, the COS is converted into H2S which is easily absorbed by the absorbent, and the efficient removal of the COS is realized; secondly, according to the content of the sulfide and the carbon dioxide in the natural gas, different kinds of organic acids are selected as anion donors of the ionic liquid, so that the alkalinity of the phase change absorbent is regulated and controlled, and the aim of efficiently removing the sulfide and the carbon dioxide in the natural gas is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of natural gas purification, and in particular relates to a phase change absorbent for natural gas desulfurization and decarbonization and a preparation method thereof. Background Art

[0002] As a clean energy, natural gas has an increasing share in the energy structure. The main components of acidic gas in natural gas are H2S, COS and CO2. High-content acidic gas will seriously corrode equipment and pipelines, causing the SO2 content in the flue gas of downstream users to exceed the standard, polluting the environment and causing great harm to human health. Therefore, the excessive acidic gas in natural gas must be removed.

[0003] At present, the existing natural gas desulfurization and decarbonization can be divided into dry and wet methods; among them, the dry method uses solid as the desulfurization agent, with high desulfurization efficiency, but regeneration is more difficult and the sulfur capacity is low, so it is less used; the wet method uses solution as the desulfurization agent, and the wet method can be divided into chemical absorption, physical absorption, physicochemical absorption and oxidation-reduction method; but the existing wet desulfurization and decarbonization processes often have high requirements for absorption conditions and poor purification effects.

[0004] Specifically, the chemical absorption method is based on reversible chemical reactions, and utilizes alkaline organic amines to react with acidic components (H2S, CO2) in natural gas to generate certain compounds to achieve the goal of desulfurization and decarbonization; when the absorbent that absorbs the acidic components increases the temperature and reduces the pressure, the generated compounds can be decomposed to release acidic gases; currently, the amine method is the most commonly used method for removing acidic components from natural gas. Commonly used amines include primary amines MEA (monoethanolamine) and diglycolamine (DGA), secondary amines DEA (diethanolamine), tertiary amines MDEA (N-methyldiethanolamine), sterically hindered amines, etc.; among them, MDEA is generally considered to be an absorbent with relatively low energy consumption and is widely used in natural gas purification; however, MDEA is easy to foam, and due to its weak alkalinity, when the pressure is low, it is easy to cause the H2S content in the purified gas to exceed the standard, and absorption requires high-pressure process conditions.

[0005] The physical absorption method utilizes the difference in solubility between sulfide and carbon dioxide in physical solvents to remove acidic components from natural gas, and is suitable for treating natural gas with a high content of acidic components. The physical absorption method has the advantages of absorbent that is not easy to deteriorate, small specific heat capacity, and high efficiency in removing organic sulfides (RSH, COS, CS2). However, the physical solvent has a large solubility for heavy hydrocarbons, which affects the calorific value of purified natural gas and subsequent sulfur recovery, and the purification effect of the physical absorption method is not good.

[0006] The physical and chemical absorption method is to mix alcohol amines, physical solvents and water to form an absorbent for natural gas desulfurization and decarbonization. It has the characteristics of both physical absorption and chemical absorption methods. The most typical representative is the sulfoneamine method, which combines sulfolane and MDEA or sulfolane and DIPA (diisopropanolamine). Its advantages are high acid gas load, high purification degree, and strong organic sulfur removal ability. However, the absorbent has a strong ability to absorb heavy hydrocarbons and is relatively expensive. Summary of the invention

[0007] In view of the technical problems existing in the prior art, the present invention provides a phase change absorbent for natural gas desulfurization and decarbonization and a preparation method thereof, so as to solve the technical problems that the existing wet desulfurization and decarbonization processes often have high absorption condition requirements and poor purification effects.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is: The present invention provides a phase change absorbent for natural gas desulfurization and decarbonization, which comprises, by mass fraction, 15%-60% of an ionic liquid, 40%-85% of an organic solvent and the remainder of water; wherein the cation donor of the ionic liquid is a cyclic amine, and the anion donor is a nitrogen-containing organic acid or a nitrogen-containing organic acid salt.

[0009] Furthermore, the cyclic amine is one of 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]-5-nonene, triethylenediamine, piperazine, morpholine and piperidine.

[0010] Furthermore, the nitrogen-containing organic acid is one of ethylenediaminetetraacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, lysine, alanine, aspartic acid and glycine.

[0011] Furthermore, the nitrogen-containing organic acid salt is one of disodium ethylenediaminetetraacetate, trisodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, tripotassium ethylenediaminetetraacetate and tetrapotassium ethylenediaminetetraacetate.

[0012] Furthermore, the organic solvent is one or a mixture of ethylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol methyl ether acetate, diethylene glycol butyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, ethyl acetate, butyl acetate and butyl propionate.

[0013] Furthermore, the absorption temperature of the phase change absorbent for natural gas desulfurization and decarbonization is 25-45°C.

[0014] Furthermore, the desorption temperature of the phase change absorbent for natural gas desulfurization and decarbonization is 80-120°C.

[0015] Furthermore, after absorbing sulfides and carbon dioxide in natural gas, the phase change absorbent for natural gas desulfurization and decarbonization changes from a uniform phase to a liquid-liquid two-phase; wherein the upper layer is a lean phase and the lower layer is a rich phase.

[0016] Furthermore, the molar ratio between the cation donor and the anion donor in the ionic liquid is 1:0.25-1.

[0017] The present invention also provides a method for preparing a phase change absorbent for natural gas desulfurization and decarbonization, comprising: The cation donor of the ionic liquid and the anion donor of the ionic liquid are mixed, dissolved in water, stirred and reacted in a water bath, and the water is dried by spin drying after the reaction to obtain the ionic liquid; The ionic liquid, the organic solvent and water are mixed evenly to obtain the phase change absorbent for natural gas desulfurization and decarbonization.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The phase-change absorbent for natural gas desulfurization and decarbonization provided by the present invention is prepared by using ionic liquid, organic solvent and water, and uses cyclic amine-organic acid ionic liquid as the active component of the phase-change absorbent. The active component of the absorbent contains cyclic amine groups, which can efficiently catalyze the hydrolysis reaction of COS, convert COS into H2S that is easily absorbed by the absorbent, and realize efficient removal of COS. Secondly, according to the content of sulfide and carbon dioxide in natural gas, different types of organic acids are selected as anion donors of the ionic liquid to adjust the alkalinity of the phase-change absorbent. Thereby achieving the goal of efficiently removing sulfide and carbon dioxide from natural gas; in the present invention, the phase change absorbent can efficiently remove sulfide (H2S, COS) and carbon dioxide from natural gas. After absorbing sulfide and carbon dioxide, the phase change absorbent changes from a uniform phase to a liquid-liquid two-phase, with the upper layer being a lean phase and the lower layer being a rich phase. Desorption only requires desorption of the lower rich phase, thereby significantly reducing the desorption and regeneration energy consumption of the absorbent; the phase change absorbent has good desulfurization and decarbonization effects; specifically, the total sulfur content (in terms of sulfur) in the tail gas after the absorbent treats natural gas is less than 20 mg / m 3 , hydrogen sulfide content is less than 6mg / m 3 , carbon dioxide (molar fraction) is less than 3%, meeting the index requirements of Class I natural gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of the performance evaluation device of the absorbent in the present invention; Figure 2 It is a schematic structural diagram of the desorption device of the absorbent in the present invention.

[0020] Among them, 10 simulated natural gas bottle, 11 gas mass flow controller, 12 gas flow display A, 13 iron stand A, 14 water bath, 15 absorption bottle, 16 gas chromatograph A, 17 drying tube A, 18 gas mass flow meter, 19 gas flow display B, 110 tail gas absorption bottle A, 111 raw gas sampling valve, 112 tail gas sampling valve; 20 iron stand B, 21 magnetic stirring oil bath, 22 condenser, 23 desorption bottle, 24 thermometer, 25 drying tube B, 26 gas flow meter, 27 gas flow display C, 28 sampling valve, 29 gas chromatograph B, 210 tail gas absorption bottle B. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail in the following specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] The present invention provides a phase change absorbent for natural gas desulfurization and decarbonization, comprising, by mass fraction, 15%-60% of an ionic liquid, 40%-85% of an organic solvent and the remainder of water; wherein the cation donor of the ionic liquid is a cyclic amine, and the anion donor is a nitrogen-containing organic acid or a nitrogen-containing organic acid salt.

[0023] In the present invention, the cyclic amine is one of 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]-5-nonene, triethylenediamine, piperazine, morpholine and piperidine; the nitrogen-containing organic acid is one of ethylenediaminetetraacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, lysine, alanine, aspartic acid and glycine; the nitrogen-containing organic acid salt is one of disodium ethylenediaminetetraacetate, trisodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, tripotassium ethylenediaminetetraacetate and tetrapotassium ethylenediaminetetraacetate.

[0024] In the present invention, the organic solvent is one or a mixture of ethylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol methyl ether acetate, diethylene glycol butyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, ethyl acetate, butyl acetate and butyl propionate; and the water is purified water, distilled water or tap water.

[0025] The preparation method of the phase change absorbent for natural gas desulfurization and decarbonization according to the present invention comprises the following steps: The cation donor of the ionic liquid and the anion donor of the ionic liquid are mixed, water is added to dissolve them, and the mixture is stirred for reaction in a water bath. After the reaction, the water is dried by spin drying to obtain the ionic liquid; wherein the molar ratio between the cation donor and the anion donor in the ionic liquid is 1:0.25-1; then, the ionic liquid, the organic solvent and water are evenly mixed to obtain the phase change absorbent for natural gas desulfurization and decarbonization; wherein the addition of water is beneficial to the hydrolysis reaction of carbonyl sulfide and can reduce the viscosity of the phase change absorbent.

[0026] It should be noted that when the phase change absorbent for natural gas desulfurization and decarbonization is applied to the removal process of H2S, COS and CO2 in natural gas, its absorption temperature is 25-45°C and the absorption pressure is 101.325kPa; after absorbing sulfides and carbon dioxide in natural gas, the phase change absorbent for natural gas desulfurization and decarbonization changes from a uniform phase to a liquid-liquid two-phase; wherein the upper layer is a lean phase and the lower layer is a rich phase; during desorption, only the lower layer rich liquid after absorbing the acidic gas needs to be desorbed, and the desorption temperature of the phase change absorbent is 80-120°C.

[0027] Comparative Example 1 30g of MEA and 70g of dimethyl sulfoxide were placed in a beaker, stirred and mixed to prepare an absorbent, and the prepared absorbent was added into an absorbent performance evaluation device for absorption experiment; wherein, the absorption temperature was 40°C, the flow rate of the natural gas sample was 200mL / min, and the absorption was stopped after 180min; the content of each component in the natural gas sample is shown in Table 1.

[0028] Table 1 Content of each component in laboratory simulated natural gas

[0029] It should be noted that the component content percentages of CH4, CO2, and H2S in Table 1 are all volume percentages.

[0030] As attached Figure 1 As shown, the performance evaluation device of the absorbent includes a simulated natural gas bottle 10, a gas mass flow controller 11, a gas flow display A12, an iron stand A13, a water bath 14, an absorption bottle 15, a gas chromatograph A16, a drying tube 17A, a gas mass flow meter 18, a gas flow display B19, a tail gas absorption bottle A, a raw gas sampling valve 111 and a tail gas sampling valve 112.

[0031] The simulated natural gas bottle 10 stores a natural gas sample, and the outlet of the simulated natural gas bottle 10 is connected to the inlet of the gas mass flow controller 12; the outlet of the gas mass flow controller 12 is arranged in two ways, one of which is connected to the bottom inlet of the absorption bottle 15, and the other is connected to the inlet of the raw gas sampling valve 111; wherein, the output end of the gas mass flow controller 11 is connected to the input end of the gas flow display A12.

[0032] The absorption bottle 15 is installed on the iron frame A13, and the absorption bottle 15 is placed in the water bath 14; wherein, the sand core pore size of the absorption bottle 15 is 10-30μm; the top outlet of the absorption bottle 15 is connected to the inlet of the drying tube 17, and the other end of the drying tube 17 is connected to the inlet of the gas mass flowmeter 18; wherein, the filler of the drying tube 17 is color-changing silica gel; the outlet of the gas mass flowmeter 18 is connected to the inlet of the tail gas absorption bottle A110, and the absorption liquid in the tail gas absorption bottle A110 is sodium hydroxide solution.

[0033] The outlet of the raw gas sampling valve 111 is connected to the inlet of the tail gas sampling valve 113, and the outlet of the tail gas sampling valve 113 is connected to the inlet of the gas mass flow meter 18; the output end of the gas mass flow meter 18 is connected to the input end of the gas flow display B19; a first sampling port is arranged between the raw gas sampling valve 111 and the tail gas sampling valve 112, and the first sampling port is connected to the inlet of the gas chromatograph A16.

[0034] The absorbent that absorbed H2S, COS and CO2 was transferred to the desorption device for desorption experiment. The desorption temperature was 120℃ and the stirring rate was 500r / min. The desorption was stopped when no gas flowed out. Figure 2 As shown, the desorption device includes an iron frame B20, a magnetic stirring oil bath 21, a condenser 22, a desorption bottle 23, a thermometer 24, a drying tube B25, a gas flow meter 26, a gas flow display C27, a sampling valve 28, a gas chromatograph B29 and a tail gas absorption bottle 210.

[0035] The desorption bottle 23 is installed on the iron frame B20, and the bottom of the desorption bottle 23 is placed in the magnetic stirring oil bath 21; one end of the condenser 22 is connected to the top outlet of the desorption bottle 23, and the other end of the condenser 22 is connected to the inlet of the drying tube B25; wherein the filler in the drying tube B25 is color-changing silica gel; the thermometer 24 is inserted into the desorption bottle 23.

[0036] The outlet of the drying tube B25 is connected to the inlet of the gas flow meter 26, and the outlet of the gas flow meter 26 is divided into two paths, one of which is connected to the inlet of the sampling valve 28, and the other is connected to the inlet of the tail gas absorption bottle 210; the input end of the gas flow display C27 is connected to the output end of the gas flow meter 26, and the inlet of the gas chromatograph B29 is connected to the outlet of the sampling valve 28; the absorption liquid in the tail gas absorption bottle 210 is a sodium hydroxide solution.

[0037] Experimental results: In Comparative Example 1, the contents of various components in the tail gas absorbed by the absorbent and the desulfurization and decarbonization rates are shown in Table 2, and the amount of acid gas desorbed by the absorbent and the contents of various components in the desorbed gas are shown in Table 8.

[0038] Table 2 Content of various components in tail gas absorbed by absorbent and desulfurization and decarbonization rate of comparative example 1

[0039] Comparative Example 2 30g of MDEA and 70g of dimethyl sulfoxide were placed in a beaker and stirred to mix evenly to prepare an absorbent. The prepared absorbent was added into an absorption bottle for absorption experiment at an absorption temperature of 40°C and a natural gas flow rate of 200mL / min. The absorption was stopped after 180min. The absorbent that absorbed H2S, COS and CO2 was transferred to a desorption bottle for desorption experiment at a desorption temperature of 120°C and a stirring rate of 500r / min. Desorption was stopped when no gas flowed out.

[0040] It should be noted that the absorbent performance evaluation device, natural gas sample and desorption device used in Comparative Example 2 are the same as those in Comparative Example 1 above, and will not be described in detail here.

[0041] Experimental results: In Comparative Example 2, the contents of various components in the tail gas absorbed by the absorbent and the desulfurization and decarbonization rates are shown in Table 3, and the amount of acid gas desorbed by the absorbent and the contents of various components in the desorbed gas are shown in Table 8.

[0042] Table 3 Content of various components in tail gas absorbed by absorbent in comparative example 2 and desulfurization and decarbonization rate

[0043] Example 1 This embodiment 1 provides a phase change absorbent for natural gas desulfurization and decarbonization, including 1,8-diazabicyclo[5.4.0]undec-7-ene, ethylenediaminetetraacetic acid and ethylene glycol butyl ether acetate.

[0044] The method for preparing the phase change absorbent for natural gas desulfurization and decarbonization comprises the following steps: Mix 20 g of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) and 10 g of EDTA (ethylenediaminetetraacetic acid) in a flask, add an appropriate amount of water to dissolve them, stir and react at a water bath temperature of 40°C for 24 hours, and after the reaction, dry the water on a rotary evaporator to obtain DBU-EDTA ionic liquid.

[0045] 30 g of DBU-EDTA ionic liquid, 10 g of water and 60 g of ethylene glycol butyl ether acetate were placed in a beaker, stirred and mixed evenly, and a phase change absorbent for natural gas desulfurization and decarbonization was prepared.

[0046] The prepared phase change absorbent for natural gas desulfurization and decarbonization was placed in a performance evaluation device for phase change absorbent to carry out an absorption experiment; the absorption temperature of the absorption experiment was 40°C, the natural gas flow rate was 200mL / min, and the absorption was stopped after 180min; the absorbent that absorbed H2S, COS and CO2 was transferred to a desorption bottle for a desorption experiment, the desorption temperature was 120°C, the stirring rate was 500r / min, and the desorption was stopped when no gas flowed out.

[0047] Experimental results: In this Example 1, the content of each component in the tail gas absorbed by the absorbent and the desulfurization and decarbonization rate are shown in Table 4, and the amount of acid gas desorbed by the absorbent and the content of each component in the desorbed gas are shown in Table 9.

[0048] Table 4 Content of various components in tail gas absorbed by absorbent and desulfurization and decarbonization rate of Example 1

[0049] Example 2 This embodiment 2 provides a phase change absorbent for natural gas desulfurization and decarbonization, including 1,8-diazabicyclo[5.4.0]undec-7-ene, glycine and diethylene glycol butyl ether acetate.

[0050] The method for preparing the phase change absorbent for natural gas desulfurization and decarbonization comprises the following steps: 20 g of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) and 10 g of Gly (glycine) were mixed in a flask, and an appropriate amount of water was added to dissolve them. The mixture was stirred and reacted at a water bath temperature of 40°C for 24 hours. After the reaction, the water was dried on a rotary evaporator to obtain a DBU-Gly ionic liquid.

[0051] 30 g of DBU-Gly ionic liquid, 5 g of water and 65 g of diethylene glycol butyl ether acetate were placed in a beaker, stirred and mixed evenly, and a phase change absorbent for natural gas desulfurization and decarbonization was prepared.

[0052] The prepared phase change absorbent for natural gas desulfurization and decarbonization was placed in a performance evaluation device for phase change absorbent to carry out an absorption experiment; the absorption temperature of the absorption experiment was 40°C, the natural gas flow rate was 200mL / min, and the absorption was stopped after 180min; the absorbent that absorbed H2S, COS and CO2 was transferred to a desorption bottle for a desorption experiment, the desorption temperature was 120°C, the stirring rate was 500r / min, and the desorption was stopped when no gas flowed out.

[0053] Experimental results: In this Example 2, the content of each component in the tail gas absorbed by the absorbent and the desulfurization and decarbonization rate are shown in Table 5, and the amount of acid gas desorbed by the absorbent and the content of each component in the desorbed gas are shown in Table 9.

[0054] Table 5 Content of various components in tail gas absorbed by absorbent and desulfurization and decarbonization rate of Example 2

[0055] Example 3 This embodiment 3 provides a phase change absorbent for natural gas desulfurization and decarbonization, including 1,5-diazabicyclo[4.3.0]-5-nonene, disodium ethylenediaminetetraacetate and butyl acetate.

[0056] The method for preparing the phase change absorbent for natural gas desulfurization and decarbonization comprises the following steps: Mix 15 g of DBN (1,5-diazabicyclo[4.3.0]-5-nonene) and 10 g of EDTA-2Na (disodium ethylenediaminetetraacetate) in a flask, add an appropriate amount of water to dissolve them, stir and react at a water bath temperature of 40°C for 24 hours, and after the reaction is completed, dry the water on a rotary evaporator to obtain DBN-EDTA-2Na ionic liquid.

[0057] 25 g of DBN-EDTA-2Na ionic liquid, 5 g of water and 70 g of butyl acetate were placed in a beaker, stirred and mixed evenly, and a phase change absorbent for natural gas desulfurization and decarbonization was prepared.

[0058] The prepared phase change absorbent for natural gas desulfurization and decarbonization was placed in a performance evaluation device for phase change absorbent to carry out an absorption experiment; the absorption temperature of the absorption experiment was 40°C, the natural gas flow rate was 200mL / min, and the absorption was stopped after 180min; the absorbent that absorbed H2S, COS and CO2 was transferred to a desorption bottle for a desorption experiment, the desorption temperature was 120°C, the stirring rate was 500r / min, and the desorption was stopped when no gas flowed out.

[0059] Experimental results: In this Example 3, the content of each component in the tail gas absorbed by the absorbent and the desulfurization and decarbonization rate are shown in Table 6, and the amount of acid gas desorbed by the absorbent and the content of each component in the desorbed gas are shown in Table 9.

[0060] Table 6 Content of various components in tail gas absorbed by absorbent and desulfurization and decarbonization rate of Example 3

[0061] Example 4 This embodiment 4 provides a phase change absorbent for natural gas desulfurization and decarbonization, including 1,5-diazabicyclo[4.3.0]-5-nonene, aspartic acid and propylene glycol ethyl ether acetate.

[0062] The method for preparing the phase change absorbent for natural gas desulfurization and decarbonization comprises the following steps: Mix 15 g of DBN (1,5-diazabicyclo[4.3.0]-5-nonene) and 8 g of Asp (aspartic acid) in a flask, add an appropriate amount of water to dissolve them, stir and react at a water bath temperature of 40°C for 24 hours, and after the reaction, dry the water on a rotary evaporator to obtain DBN-Asp ionic liquid.

[0063] 23 g of DBN-Asp ionic liquid, 2 g of water and 75 g of propylene glycol ethyl ether acetate were placed in a beaker, stirred and mixed evenly, and a phase change absorbent for natural gas desulfurization and decarbonization was prepared.

[0064] The prepared phase change absorbent for natural gas desulfurization and decarbonization was placed in a performance evaluation device for phase change absorbent to carry out an absorption experiment; the absorption temperature of the absorption experiment was 40°C, the natural gas flow rate was 200mL / min, and the absorption was stopped after 180min; the absorbent that absorbed H2S, COS and CO2 was transferred to a desorption bottle for a desorption experiment, the desorption temperature was 120°C, the stirring rate was 500r / min, and the desorption was stopped when no gas flowed out.

[0065] Experimental results: In this Example 4, the content of each component in the tail gas absorbed by the absorbent and the desulfurization and decarbonization rate are shown in Table 7, and the amount of acid gas desorbed by the absorbent and the content of each component in the desorbed gas are shown in Table 9.

[0066] Table 7 Content of various components in tail gas absorbed by absorbent in Example 4 and desulfurization and decarbonization rate

[0067] It should be noted that the total sulfur content in Table 2-7 refers to the amount of H2S, COS, and CS2 converted into S. The calculation formula is:

[0068] In the formula, is the total sulfur content, in mg / m 3 ; is the hydrogen sulfide content, in mg / m3 ; is the carbonyl sulfide content, in mg / m 3 ; is the carbon disulfide content, in mg / m 3 ; The relative molecular mass of hydrogen sulfide is 34.08; The relative molecular mass of carbonyl sulfide is 60.07; The relative molecular mass of carbon disulfide is 76.14; The relative atomic mass of sulfur is 32.065.

[0069] The desulfurization rate refers to the efficiency of removing total sulfur within a certain period of time, and the calculation formula is:

[0070] In the formula, is the total sulfur content in the raw gas, in mg / m 3 ; is the total sulfur content in the tail gas after absorption, in mg / m 3 .

[0071] The decarbonization rate refers to the efficiency of removing carbon dioxide within a certain period of time, and the calculation formula is:

[0072] In the formula, is the volume of raw gas entering the absorption bottle, in mL; is the volume percentage of carbon dioxide in the raw gas; is the volume of tail gas after absorption, in mL; It is the volume percentage of carbon dioxide in the exhaust gas after absorption.

[0073] Table 8 Amount of acid gas desorbed by comparative absorbent and content of each component

[0074] Table 9 Amount of acid gas desorbed by absorbent and content of each component in Example

[0075] It can be seen from the data in Tables 2-7 that the desulfurization and decarbonization rate of the phase change absorbent for natural gas desulfurization and decarbonization provided by the embodiment of the present invention is significantly higher than that of the traditional absorbents MDEA and MEA, and the total sulfur content (in terms of sulfur) in the absorbed tail gas is less than 10 mg / m 3 , hydrogen sulfide content is less than 6mg / m 3 , carbon dioxide (molar fraction) is less than 3%, meeting the national index requirements for Class I natural gas.

[0076] It can be seen from the data in Tables 8 and 9 that the desorption energy consumption of the phase-change absorbent for natural gas desulfurization and decarbonization provided by the embodiment of the present invention is significantly lower than that of the traditional absorbents MEA and MDEA. MEA can desorb acidic gas only at a temperature of 140°C, and the desorption temperature is relatively high, resulting in relatively high energy consumption; MDEA can desorb at 120°C, but the sulfide content in the desorbed gas is relatively low, indicating that the sulfide desorption effect is relatively poor; the phase-change absorbent for natural gas desulfurization and decarbonization provided by the present invention has a relatively low sulfide content in the lean phase desorbed gas, while a relatively high sulfide content in the rich phase desorbed gas, indicating that the sulfide absorbed by the absorbent is mainly concentrated in the rich phase, so only the rich phase needs to be desorbed during desorption; the rich phase volume ratio of the phase-change absorbent for natural gas desulfurization and decarbonization provided by the embodiment of the present invention is lower than 45%, which can significantly reduce the desorption energy consumption.

[0077] The phase-change absorbent for natural gas desulfurization and decarbonization described in the present invention can efficiently remove sulfides (H2S, COS) and carbon dioxide from natural gas. After the absorbent absorbs sulfides and carbon dioxide, the absorbent changes from a uniform phase to a liquid-liquid two-phase, with the upper layer being a lean phase and the lower layer being a rich phase. Desorption only requires desorption of the lower rich phase, thereby significantly reducing the desorption and regeneration energy consumption of the absorbent. In the present invention, different types of organic acids can be selected to adjust the alkalinity of the absorbent according to the content of sulfides and carbon dioxide in natural gas, thereby achieving the goal of efficiently removing sulfides and carbon dioxide from natural gas. In addition, the active component of the absorbent contains cyclic amine groups, which can efficiently catalyze the hydrolysis reaction of COS, convert COS into H2S that is easily absorbed by the absorbent, and achieve efficient removal of COS.

[0078] The above embodiment is only one of the implementation methods that can realize the technical solution of the present invention. The scope of protection claimed by the present invention is not limited only to this embodiment, but also includes changes, replacements and other implementation methods that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention.

Claims

1. A phase change absorbent for natural gas desulfurization and decarbonization, characterized in that: The composition comprises, by mass fraction, 15%-60% of an ionic liquid, 40%-85% of an organic solvent and the remainder of water; wherein the cation donor of the ionic liquid is a cyclic amine, and the anion donor is a nitrogen-containing organic acid or a nitrogen-containing organic acid salt.

2. A phase change absorbent for natural gas desulfurization and decarbonization according to claim 1, characterized in that: The cyclic amine is one of 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]-5-nonene, triethylenediamine, piperazine, morpholine and piperidine.

3. A phase change absorbent for natural gas desulfurization and decarbonization according to claim 1, characterized in that: The nitrogen-containing organic acid is one of ethylenediaminetetraacetic acid, ethylene glycol bis(2-aminoethyl ether)tetraacetic acid, lysine, alanine, aspartic acid and glycine.

4. A phase change absorbent for natural gas desulfurization and decarbonization according to claim 1, characterized in that: The nitrogen-containing organic acid salt is one of disodium ethylenediaminetetraacetate, trisodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, tripotassium ethylenediaminetetraacetate and tetrapotassium ethylenediaminetetraacetate.

5. The phase change absorbent for natural gas desulfurization and decarbonization according to claim 1, characterized in that: The organic solvent is one of ethylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate, ethylene glycol methyl ether acetate, diethylene glycol butyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, ethyl acetate, butyl acetate and butyl propionate, or a mixture of several of them.

6. A phase change absorbent for natural gas desulfurization and decarbonization according to claim 1, characterized in that: The absorption temperature of the phase change absorbent used for natural gas desulfurization and decarbonization is 25-45°C.

7. A phase change absorbent for natural gas desulfurization and decarbonization according to claim 1, characterized in that: The desorption temperature of the phase change absorbent for natural gas desulfurization and decarbonization is 80-120°C.

8. The phase change absorbent for natural gas desulfurization and decarbonization according to claim 1, characterized in that: After absorbing sulfide and carbon dioxide in natural gas, the phase change absorbent for natural gas desulfurization and decarbonization changes from a uniform phase to a liquid-liquid two-phase; wherein the upper layer is a lean phase and the lower layer is a rich phase.

9. The phase change absorbent for natural gas desulfurization and decarbonization according to claim 1, characterized in that: The molar ratio between the cation donor and the anion donor in the ionic liquid is 1:0.25-1.

10. A method for preparing a phase change absorbent for natural gas desulfurization and decarbonization according to any one of claims 1 to 9, characterized in that: include: The cation donor of the ionic liquid and the anion donor of the ionic liquid are mixed, water is added to dissolve them, and the mixture is stirred in a water bath for reaction. After the reaction, the water is dried by spin drying to obtain the ionic liquid; The ionic liquid, the organic solvent and water are mixed evenly to obtain the phase change absorbent for natural gas desulfurization and decarbonization.

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