Ternary composite absorbent, application thereof and method for separating mixed gas of CO2 and CH4

Abstract

The invention relates to the technical field of natural gas purification and gas separation, and discloses a ternary composite absorbent and application thereof, and a method for separating mixed gas of CO2 and CH4. The ternary composite absorbent consists of a first component, a second component and a solvent, the first component is 2-amino-2-methyl-1-propyl alcohol, and the second component is 2-amino-2-methyl-1-propyl alcohol; the second component is selected from at least one of piperazine, triethylene glycol, N-methyl pyrrolidone and 2-methylimidazole; the solvent is ethylene glycol. The ternary composite absorbent provided by the invention further inhibits CH4 co-absorption while ensuring the CO2 absorption capacity, can realize higher beta selectivity, and can be regenerated and recycled under the condition of lower temperature rise.

Description

Technical Field

[0001] This invention relates to the field of natural gas purification and gas separation technology, specifically to a ternary composite absorbent and its application, and a method for separating a mixture of CO2 and CH4. Background Technology

[0002] Currently, amine absorption processes are widely used in industry for CO2 removal. However, traditional single-amine or diamine systems still have shortcomings in terms of absorption capacity, selectivity, and regeneration energy consumption, making it difficult to simultaneously achieve high CO2 absorption capacity and low CH4 solubility requirements. The high regeneration energy consumption and limited mass transfer of traditional water-based alcoholamine systems have prompted researchers to develop low-aqueous / non-aqueous solvent systems and compound amine systems. In alcoholamine absorption, by compounding different amines or adding auxiliaries, the absorption rate and cycle capacity can be improved to some extent, while reducing regeneration energy consumption.

[0003] However, existing amine absorption systems generally suffer from the following problems: limited CO2 absorption capacity, requiring a high circulation rate; certain solubility for CH4, resulting in the loss of effective gas; insufficient system selectivity, making it difficult to meet the requirements for efficient separation; and lack of quantitative screening basis for formulation selection. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of limited CO2 absorption capacity and low selectivity for separating CO2 and CH4 in the existing amine absorption system.

[0005] To achieve the above objectives, a first aspect of the present invention provides a ternary composite absorbent for separating a mixture of CO2 and CH4, the ternary composite absorbent comprising a first component, a second component, and a solvent; based on the total mass of the ternary composite absorbent, the content of the first component is 10-20 wt%, the content of the second component is 5-40 wt%, and the content of the solvent is 40-85 wt%. The first component is 2-amino-2-methyl-1-propanol; The second component is selected from at least one of piperazine, triethylene glycol, N-methylpyrrolidone, and 2-methylimidazole; The solvent is ethylene glycol.

[0006] The second aspect of the present invention provides the application of the ternary composite absorbent described in the first aspect in the field of natural gas purification.

[0007] A third aspect of the present invention provides a method for separating a mixture of CO2 and CH4 gases, the method comprising: Under pressure conditions of 0.3-1.3 MPa, a solution containing a ternary composite absorbent is contacted with a mixed gas containing CO2 and CH4 to achieve the separation of CO2 and CH4. The ternary composite absorbent is the ternary composite absorbent described in the first aspect.

[0008] This invention develops a novel multi-component synergistic absorption system. By synergistically combining the first and second components and using ethylene glycol as a solvent to regulate the differences in viscosity and solubility, a ternary composite absorbent is constructed. This composite absorbent has the advantages of higher selectivity β value and strong controllability. Furthermore, it has the potential for mild regeneration and low-energy desorption, and the raw materials for the formulation are readily available. While ensuring CO2 absorption capacity, it further inhibits CH4 co-absorption, achieving higher β value selectivity and regenerability under low temperature rise conditions. Detailed Implementation

[0009] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0010] As previously described, a first aspect of the present invention provides a ternary composite absorbent for separating a mixture of CO2 and CH4, the ternary composite absorbent comprising a first component, a second component, and a solvent; based on the total mass of the ternary composite absorbent, the content of the first component is 10-20 wt%, the content of the second component is 5-40 wt%, and the content of the solvent is 40-85 wt%. The first component is 2-amino-2-methyl-1-propanol; The second component is selected from at least one of piperazine, triethylene glycol, N-methylpyrrolidone, and 2-methylimidazole; The solvent is ethylene glycol.

[0011] According to a particularly preferred embodiment, based on the total mass of the ternary composite absorbent, the content of the first component is 10-15 wt%, the content of the second component is 5-10 wt%, and the content of the solvent is 75-85 wt%. In this preferred embodiment, the ternary composite absorbent provided by the present invention can achieve a trade-off optimization between selectivity, capacity, viscosity, and operability.

[0012] According to a particularly preferred embodiment, the second component is selected from at least one of piperazine, triethylene glycol, and 2-methylimidazole. In this preferred embodiment, the ternary composite absorbent provided by the present invention can achieve good absorption selectivity.

[0013] According to a particularly preferred embodiment, the first component is 2-amino-2-methyl-1-propanol; the second component is piperazine; and the solvent is ethylene glycol. In this preferred embodiment, piperazine, as a promoter, can improve the absorption kinetics and separation performance of the 2-amino-2-methyl-1-propanol system. By adjusting the ratio of 2-amino-2-methyl-1-propanol to piperazine, the ternary composite absorbent provided by the present invention can achieve a higher selectivity β value.

[0014] The present invention does not impose any particular requirements on the preparation method of the ternary composite absorbent; it is sufficient to mix the first component, the second component, and the solvent evenly. Exemplarily, the first component, the second component, and the solvent can be subjected to a first mixing process at a stirring speed of 500 rpm for 5 minutes.

[0015] The preparation method of the ternary composite absorbent provided by this invention has advantages such as being engineering-friendly and having simple preparation steps.

[0016] As previously stated, the second aspect of the present invention provides the application of the ternary composite absorbent described in the first aspect in the field of natural gas purification.

[0017] The ternary composite absorbent provided by this invention uses common raw materials and has a simple preparation process, making it suitable for the purification of natural gas / methane sources or the separation of other CO2-containing mixed gases.

[0018] As previously described, a third aspect of the present invention provides a method for separating a mixture of CO2 and CH4 gases, the method comprising: Under pressure conditions of 0.3-1.3 MPa, a solution containing a ternary composite absorbent is contacted with a mixed gas containing CO2 and CH4 to achieve the separation of CO2 and CH4. The ternary composite absorbent is the ternary composite absorbent described in the first aspect.

[0019] Preferably, in the mixed gas, the volume ratio of CO2 to CH4 is 1:2-4.

[0020] The solution containing the ternary composite absorbent described in this invention is either a ternary composite absorbent or a solution formed by the ternary composite absorbent and water.

[0021] Preferably, the concentration of the ternary composite absorbent in the solution is 30-100 wt%, more preferably 30-60 wt%.

[0022] According to a particularly preferred embodiment, the concentration of the ternary composite absorbent in the solution is 45-55 wt%. In this preferred embodiment, by adjusting the concentration of the ternary composite absorbent, the ternary composite absorbent provided by the present invention can achieve a trade-off optimization between selectivity, capacity, viscosity, and operability.

[0023] Preferably, the solution containing the ternary composite absorbent also contains water.

[0024] According to a particularly preferred embodiment, the contact temperature is 25-35°C. In this preferred case, combining the thermal instability of the 2-amino-2-methyl-1-propanol reaction product with the low heat load characteristics of the non-aqueous / low-aqueous system, the ternary composite absorbent provided by the present invention has the potential for mild regeneration and low-energy desorption.

[0025] Preferably, the separation selectivity β value of CO2 and CH4 is 460-1100.

[0026] The separation selectivity β value in this invention is the core indicator for evaluating the separation ability of separation media such as adsorbents to separate CO2 and CH4. The larger the β value, the stronger the separation selectivity and the more significant the preferential permeation / adsorption capacity for CO2.

[0027] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, all instruments used are commercially available, and all raw materials used are commercially available analytical grade pharmaceuticals. In the following examples, unless otherwise specified, the reaction temperature is at room temperature, which refers to 24±1℃.

[0028] In the following examples, the total mass of the ternary composite absorbent is 10g.

[0029] Example 1 (1) The first component, the second component and the solvent are mixed to obtain a ternary composite absorbent; The conditions for the first mixing are: stirring speed of 500 rpm and time of 5 min; (2) The ternary composite absorbent is brought into contact with a mixed gas (composed of CO2 and CH4 in a volume ratio of 1:3.165) to achieve the separation of CO2 and CH4; Contact conditions: temperature 25℃, pressure 0.7MPa; The types and amounts of raw materials and process parameters in this embodiment are shown in Table 1.

[0030] Examples 2-6 The same process as in Example 1 was used, except that the types and amounts of raw materials and process parameters were different. All other steps were the same as in Example 1, as detailed in Table 1.

[0031] Example 7 (1) The first component, the second component and the solvent are mixed to obtain a ternary composite absorbent; The conditions for the first mixing are: stirring speed of 500 rpm and time of 5 min; (2) The ternary composite absorbent is mixed with water for a second time to obtain a solution containing the ternary composite absorbent; (3) The solution containing the ternary composite absorbent is contacted with a mixed gas (composed of CO2 and CH4 in a volume ratio of 1:3.165) to achieve the separation of CO2 and CH4; Contact conditions: temperature 25℃, pressure 0.7MPa; The types and amounts of raw materials and process parameters in this embodiment are shown in Table 1.

[0032] Examples 8-12 The same process as in Example 7 was used, except that the types of raw materials, the amount of raw materials used, and the process parameters were different. All other steps were the same as in Example 7, as detailed in Table 1.

[0033] Table 1

[0034] Comparative Example 1 The same procedure as in Example 1 was used, except that the second component was triazole, and the remaining steps were the same as in Example 1.

[0035] Comparative Example 2 The procedure was the same as in Example 1, except that the second component was N-methyldiethanolamine, and the remaining steps were the same as in Example 1.

[0036] Comparative Example 3 The same procedure as in Example 1 was used, except that the second component was monoethanolamine, and the remaining steps were the same as in Example 1.

[0037] Comparative Example 4 The same process as in Example 4 was used, except that the amount of the first component was 6.67 wt% and the amount of the second component was 13.33 wt%, and the remaining steps were the same as in Example 5.

[0038] Test case The products from the above embodiments and comparative examples were tested, and the separation performance of the ternary composite absorbent for mixed gases is shown in Table 2.

[0039] y 1 (mole%)This indicates the mole fraction of CO2 in the gas phase at equilibrium; the lower the value, the higher the purity of CH4 after separation. x 1 (mole%) It represents the apparent mole fraction of CO2 in the solution of the gemstone vessel at equilibrium. The higher the value, the more CO2 the ternary composite absorbent absorbs. y 1 (mole%) , x 1 (mole%) The testing method is gas chromatography.

[0040] The formulas for calculating Sc1_CO2 and Sc2_CH4 are as follows: .in, Gas solubility coefficient; : The apparent amount of each gas in the solution at equilibrium (1 is CO2, 2 is CH4). : Absorbent volume; : Pressure in the sapphire vessel at equilibrium; : The mole fraction of each substance in the gas phase at equilibrium (1 is CO2, 2 is CH4).

[0041] The formula for calculating the selectivity β value is: .in, Selectivity; : Apparent mole fraction of each gas in the solution at equilibrium (1 is CO2, 2 is CH4). : The mole fraction of each substance in the gas phase at equilibrium (1 is CO2, 2 is CH4).

[0042] The formula for calculating CO2 capture rate is: .in, CO2 capture rate; The apparent amount of CO2 in the solution at equilibrium in the gem-shaped vessel; : The total amount of CO2 entering the gem-quality vessel.

[0043] Table 2

[0044] As can be seen from the results in Table 2, the ternary composite absorbent provided by the present invention has a higher selectivity β value when separating mixed gases containing CO2 and CH4, and has the potential for mild regeneration and low-energy desorption.

[0045] By comparing Examples 1 to 4 and Comparative Examples 1 to 3, it can be seen that when separating mixed gases, the 2-amino-2-methyl-1-propanol / piperazine / ethylene glycol system of Example 4 has the highest absorption selectivity of 681.3338, and its CO2 capture rate is also relatively high.

[0046] 2-Amino-2-methyl-1-propanol has advantages in regeneration performance but weak kinetics. Piperazine has high reactivity and can be used as a promoter to improve absorption kinetics and enhance cycling performance.

[0047] By comparing Examples 4-6 and Comparative Example 4, it can be seen that when separating mixed gases, different ratios of 2-amino-2-methyl-1-propanol and piperazine show little difference in the solubility of CH4, but significant differences in absorption selectivity. When the ratio of 2-amino-2-methyl-1-propanol to piperazine is 3:1 and 2:1, the absorption selectivity is relatively high; however, considering all factors... y 1 (mol%)、x 1 (mole%) The overall performance is better when the dosage ratio is 2:1; while when the dosage ratio is 1:2, the absorption selectivity is only 315.5572.

[0048] Comparative examples 7-10 show that when the ternary composite absorbent is diluted with water to different concentrations, when the ratio of 2-amino-2-methyl-1-propanol to piperazine is 2:1 and the concentration of the ternary composite absorbent in the solution is 50wt%, the absorption system has a relatively low solubility for CH4 and a relatively high solubility for CO2.

[0049] By comparing Examples 8 and 11-12, it can be seen that at a lower temperature, when the ratio of 2-amino-2-methyl-1-propanol to piperazine is 2:1 and the concentration of the ternary composite absorbent in the solution is 50wt%, the absorption selectivity of the absorption system is already high enough, the CO2 capture rate reaches a certain level, and the absorption effect is good.

[0050] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A ternary composite absorbent for separating a mixture of CO2 and CH4, characterized in that, The ternary composite absorbent is composed of a first component, a second component, and a solvent; based on the total mass of the ternary composite absorbent, the content of the first component is 10-20 wt%, the content of the second component is 5-40 wt%, and the content of the solvent is 40-85 wt%. The first component is 2-amino-2-methyl-1-propanol; The second component is selected from at least one of piperazine, triethylene glycol, N-methylpyrrolidone, and 2-methylimidazole; The solvent is ethylene glycol.

2. The ternary composite absorbent according to claim 1, characterized in that, Based on the total mass of the ternary composite absorbent, the content of the first component is 10-15 wt%, the content of the second component is 5-10 wt%, and the content of the solvent is 75-85 wt%.

3. The ternary composite absorbent according to claim 1 or 2, characterized in that, The first component is 2-amino-2-methyl-1-propanol; the second component is piperazine; and the solvent is ethylene glycol.

4. The application of the ternary composite absorbent according to any one of claims 1-3 in the field of natural gas purification.

5. A method for separating a mixture of CO2 and CH4, characterized in that, The method includes: Under pressure conditions of 0.3-1.3 MPa, a solution containing a ternary composite absorbent is contacted with a mixed gas containing CO2 and CH4 to achieve the separation of CO2 and CH4. The ternary composite absorbent is the ternary composite absorbent according to any one of claims 1-3.

6. The method according to claim 5, characterized in that, In the mixed gas, the volume ratio of CO2 to CH4 is 1:2-4.

7. The method according to claim 5 or 6, characterized in that, The concentration of the ternary composite absorbent in the solution is 30-100 wt%, preferably 30-60 wt%.

8. The method according to claim 5 or 6, characterized in that, The concentration of the ternary composite absorbent in the solution is 45-55 wt%.

9. The method according to claim 5 or 6, characterized in that, The contact temperature is 25-35℃.

10. The method according to claim 5 or 6, characterized in that, The separation selectivity β value between CO2 and CH4 is 460-1100.

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