Ionic liquid and compound absorbent containing same

Abstract

The invention provides an ionic liquid and a compound absorbent containing the same. The ionic liquid is tetraethylammonium hydroxide amino acid salt; the compound absorbent comprises the ionic liquid and imidazole.

Description

Technical Field

[0001] The present invention relates to the technical field of gas separation and purification, and particularly relates to an ionic liquid for absorbing carbon dioxide and a compound absorbent containing the same. Background Art

[0002] The continuous increase in fossil fuel consumption has led to a year-on-year increase in CO2 emissions. It has become a global consensus to jointly address climate change. Currently, the main CO2 capture methods include solvent absorption method, adsorption separation method, membrane separation method, cryogenic liquefaction separation method, etc. Among them, the alkanolamine absorption method is the most mature, using aqueous solutions such as monoethanolamine (MEA) and methyldiethanolamine (MDEA) as absorbents, but there are problems such as large solvent loss and high regeneration energy consumption. Ionic liquids have the characteristics of low vapor pressure, adjustable structure design, and adjustable properties such as polar acids and bases. At the same time, the specific heat capacity of ionic liquids is usually lower than that of MEA and water, that is, the sensible heat used for solvent heating during desorption can be reduced, providing a new way for efficient and low-energy CO2 capture and separation. Functional ionic liquids such as amino group, carboxylic acid group, and nitrogen heterocyclic group have been reported successively, and their CO2 absorption performance is significantly better than that of conventional ionic liquids. Among them, amino acid functional ionic liquids have a higher absorption capacity and good regeneration performance, but usually have high viscosity, and their viscosity increases significantly after absorbing CO2, seriously affecting the mass transfer effect, and there is still a problem of high energy consumption during regeneration, which limits their industrial application. Summary of the Invention

[0003] One aspect of the present invention provides an ionic liquid, which is tetraethylammonium hydroxide amino acid salt.

[0004] In a specific embodiment, the tetraethylammonium hydroxide amino acid salt is tetraethylammonium hydroxide glycinate and / or tetraethylammonium hydroxide sarcosinate.

[0005] Another aspect of the present invention provides a method for preparing the ionic liquid as described in one aspect of the present invention, which includes the following steps:

[0006] 1) Mix an amino acid with water to obtain an amino acid aqueous solution;

[0007] 2) Dropwise add an aqueous solution of tetraethylammonium hydroxide to the amino acid aqueous solution, react, and obtain a reaction solution after the reaction ends;

[0008] 3) Remove the water in the reaction solution to obtain the ionic liquid.

[0009] In a specific embodiment, the molar ratio of the amino acid to the tetraethylammonium hydroxide is 1:1.

[0010] In a specific embodiment, in step 2), the reaction temperature is the natural ambient temperature, and the reaction time is 10 to 24 h.

[0011] In a specific embodiment, water in the reaction solution is first removed using a rotary evaporator, followed by vacuum drying, and finally the ionic liquid is obtained.

[0012] In a specific embodiment, in step 3), the temperature of the vacuum drying is 50 to 80 °C, and the time is 24 to 48 h.

[0013] The third aspect of the present invention provides a composite absorbent, which includes the ionic liquid as described in the first aspect of the present invention and imidazole.

[0014] In a specific embodiment, the imidazole is N-methylimidazole.

[0015] In a specific embodiment, the mass ratio of the ionic liquid to the organic solvent is 2:1 to 1:4.

[0016] The fourth aspect of the present invention provides the use of the ionic liquid as described in the first aspect of the present invention or the composite absorbent as described in any one of the second aspect of the present invention in the absorption of carbon dioxide.

[0017] In a specific embodiment, the use is for the absorption of carbon dioxide in natural gas, shale gas, coalbed methane, and biogas.

[0018] Advantages of the present invention:

[0019] Compared with the prior art, the ionic liquid of the present invention has better carbon dioxide absorption performance. After being compounded with N-methylimidazole, it realizes the absorption of carbon dioxide without water. The two can produce a synergistic effect, greatly improving the carbon dioxide absorption performance, especially greatly shortening the equilibrium time of carbon dioxide absorption, and remaining liquid after absorbing carbon dioxide, and thus can have good recycling performance. At the same time, the use cost is greatly reduced, breaking through the problems of high viscosity and high energy consumption, providing a new way for CO2 capture and separation. Specific embodiments

[0020] The following further illustrates the present invention in conjunction with embodiments, but the embodiments of the present invention are only exemplary descriptions, and in no case do they constitute a limitation to the present invention.

[0021] Example 1

[0022] Add 0.2 mol of glycine to a 500 ml round-bottom flask, then add 150 ml of deionized water to dissolve it. Then, while stirring, slowly add an aqueous solution containing 0.2 mol of tetraethylammonium hydroxide dropwise through a constant-pressure dropping funnel. The reaction temperature is controlled at 25 °C by a water bath, and the reaction time is 48 h. After the reaction is completed, a reaction mixture is obtained. The mixture is evaporated to remove the remaining deionized water at 60 °C using a rotary evaporator, and then vacuum dried at 60 °C for 48 h to obtain an ionic liquid, which is determined to be tetraethylammonium glycinate ([N 2222 [Gly]).

[0023] Among them, the results of nuclear magnetic resonance analysis are as follows: 1 H NMR (600 MHz, D2O): 1.18 (m, 12H, CH3C), 3.08 (s, 2H, CH2COO), 3.18 ppm (q, 8H, CH2N); 13C NMR (600 MHz, D2O): 6.53, 44.67, 51.87, 53.8, 181.45 ppm.

[0024] Example 2

[0025] Add 0.2 mol of sarcosine to a 500 ml round-bottom flask, then add 150 ml of deionized water to dissolve it. Then, while stirring, slowly add an aqueous solution containing 0.2 mol of tetraethylammonium hydroxide dropwise through a constant-pressure dropping funnel. The reaction temperature is controlled at 25 °C by a water bath. The reaction time is 48 h. After the reaction is completed, a reaction mixture is obtained. The mixture is evaporated to remove the remaining deionized water at 60 °C using a rotary evaporator, and then vacuum dried at 60 °C for 48 h to obtain an ionic liquid, which is determined to be tetraethylammonium sarcosinate ([N 2222 [Sar]).

[0026] Among them, the results of nuclear magnetic resonance analysis are as follows: 1 H NMR (600 MHz, D2O): 1.18 (m, 12H, CH3C), 2.21 (s, 3H, CH3N), 3.03 (d, 2H, CH2COO), 3.17 (q, 8H, CH2N); 13 13C NMR (600 MHz, D2O): 6.53, 34.31, 51.87, 53.8, 179.58 ppm.

[0027] Example 3

[0028] Mix [N 2222 [Gly] and N-methylimidazole uniformly at a mass ratio of 2:1 to prepare a compound absorbent 1#, where the mass content of the ionic liquid is 66.7 wt%.

[0029] Example 4

[0030] Mix [N 2222 [Gly] and N-methylimidazole evenly at a mass ratio of 3:2 to prepare the composite absorbent 2#, where the mass content of the ionic liquid is 60.0 wt%.

[0031] Example 5

[0032] Mix [N 2222 [Gly] and N-methylimidazole evenly at a mass ratio of 1:1 to prepare the composite absorbent 3#, where the mass content of the ionic liquid is 50.0 wt%.

[0033] Example 6

[0034] Mix [N 2222 [Gly] and N-methylimidazole evenly at a mass ratio of 1:2 to prepare the composite absorbent 4#, where the mass content of the ionic liquid is 33.3 wt%.

[0035] Example 7

[0036] Mix [N 2222 [Gly] and N-methylimidazole evenly at a mass ratio of 1:3 to prepare the composite absorbent 5#, where the mass content of the ionic liquid is 25.0 wt%.

[0037] Example 8

[0038] Mix [N 2222 [Gly] and N-methylimidazole evenly at a mass ratio of 1:4 to prepare the composite absorbent 6#, where the mass content of the ionic liquid is 20.0 wt%.

[0039] Example 9

[0040] Mix [N 2222 [Sar] and N-methylimidazole evenly at a mass ratio of 2:1 to prepare the composite absorbent 7#, where the mass content of the ionic liquid is 66.7 wt%.

[0041] Example 10

[0042] Mix [N 2222 [Sar] and N-methylimidazole evenly at a mass ratio of 3:2 to prepare the composite absorbent 8#, where the mass content of the ionic liquid is 60.0 wt%.

[0043] Example 11

[0044] Mix [N 2222[Sar] and N-methylimidazole were mixed evenly at a mass ratio of 1:1 to prepare the compound absorbent No. 9, in which the mass content of the ionic liquid was 50.0 wt%.

[0045] Example 12

[0046] Mix [N 2222 [Sar] and N-methylimidazole evenly at a mass ratio of 1:2 to prepare the compound absorbent No. 10, in which the mass content of the ionic liquid is 33.3 wt%.

[0047] Example 13

[0048] Mix [N 2222 [Sar] and N-methylimidazole evenly at a mass ratio of 1:3 to prepare the compound absorbent No. 11, in which the mass content of the ionic liquid is 25.0 wt%.

[0049] Example 14

[0050] Mix [N 2222 [Sar] and N-methylimidazole evenly at a mass ratio of 1:4 to prepare the compound absorbent No. 12, in which the mass content of the ionic liquid is 20.0 wt%.

[0051] Comparative Example 1

[0052] N-methylimidazole.

[0053] Test Example 1

[0054] In a self-made absorption bottle with an inner diameter of 3.0 cm, 5.0 g of the ionic liquid [N 2222 [Gly] prepared in Example 1, the ionic liquid [N 2222 [Sar] prepared in Example 2, the compound absorbents prepared in Examples 3 to 14, the ionic liquid [N 1111 [Gly] prepared in Comparative Example 1, N-methylimidazole in Comparative Example 2, and the compound absorbent prepared in Comparative Example 3 were added respectively. Then, pure CO2 was introduced with a gas flow rate of 100 ml / min, a temperature of 40 °C, and a pressure of 0.1 MPa. The weight of the absorption bottle was weighed at regular intervals until the mass no longer changed, the equilibrium time of CO2 absorption was recorded, and the absorption capacity for CO2 was calculated. The results are shown in Table 1.

[0055] Table 1

[0056] Example <![CDATA[Absorption capacity for CO2]]> Absorption equilibrium time / min Morphology after absorption equilibrium Example 1 <![CDATA[0.130g CO2 / g]]> 2543 Solid state Example 2 <![CDATA[0.109 g CO2 / g]]> 200 Solid state Example 3 <![CDATA[0.132g CO2 / g]]> 60 Liquid state Example 4 <![CDATA[0.128 g CO2 / g]]> 50 Liquid state Example 5 <![CDATA[0.108g CO2 / g]]> 45 Liquid state Example 6 <![CDATA[0.076g CO2 / g]]> 20 Liquid state Example 7 <![CDATA[0.060g CO2 / g]]> 15 Liquid state Example 8 <![CDATA[0.050g CO2 / g]]> 10 Liquid state Example 9 <![CDATA[0.134 g CO2 / g]]> 60 Liquid state Example 10 <![CDATA[0.120g CO2 / g]]> 55 Liquid state Example 11 <![CDATA[0.100g CO2 / g]]> 40 Liquid state Example 12 <![CDATA[0.068g CO2 / g]]> 20 Liquid state Example 13 <![CDATA[0.055 g CO2 / g]]> 15 Liquid state Example 14 <![CDATA[0.045g CO2 / g]]> 10 Liquid state Comparative example 1 <![CDATA[0.004 g CO2 / g]]> 15 Liquid state

[0057] According to the results in Table 1, the products of Examples 3 to 14 solve the problem of becoming solid after adsorbing CO2 and greatly shorten the equilibrium time for CO2 absorption. For example, the adsorption equilibrium of Example 1 was reached at 2543 min, and it became solid after adsorbing CO2; the adsorption equilibrium of Example 2 was reached at 200 min, and it became solid after adsorbing CO2; while for Examples 3 to 14, the absorption reached equilibrium at 10 to 60 min and remained liquid after adsorbing CO2.

[0058] Test Example 2

[0059] In a self-made absorption bottle with an inner diameter of 3.0 cm, 5.0 g of the compound absorbent prepared in Example 4 was added respectively, and then pure CO2 was introduced with a gas flow rate of 100 ml / min, a temperature of 40 to 80 °C (see Table 2 for details), and a pressure of 0.02 to 0.1 MPa. The weight of the absorption bottle was weighed at regular intervals until the mass no longer changed, and the absorption reached equilibrium in about 60 min. The absorption capacity for CO2 was calculated, and the results are shown in Table 2.

[0060] Table 2

[0061] Temperature (°C) Pressure (MPa) <![CDATA[CO2 uptake (g CO2 / g absorbent)]]> 50 0.10 0.122 60 0.10 0.121 70 0.10 0.117 80 0.10 0.115 40 0.08 0.126 40 0.06 0.120 40 0.04 0.105 40 0.02 0.101

[0062] According to the results in Table 2, it can be seen that the increase in temperature and the decrease in pressure lead to a decrease in the absorption amount.

[0063] Test Example 3

[0064] In a self-made absorption bottle with an inner diameter of 3.0 cm, 5.0 g of the compound absorbent prepared in Examples 3 to 14 was added, and then pure CO2 was introduced with a gas flow rate of 100 ml / min, a temperature of 40 °C, and a pressure of 0.1 MPa. The weight of the absorption bottle was weighed at regular intervals until the mass no longer changed, and the absorption reached equilibrium in about 60 min. The absorption capacity of the absorbent for CO2 was calculated. After absorption, N2 was introduced with a flow rate of 300 ml / min and a desorption temperature of 120 °C. After about 6 h of desorption, the CO2 absorbed by the absorbent was basically completely released. According to the above steps, the absorption-desorption cycle was carried out 3 times, and the absorption capacity of the absorbent for CO2 was calculated respectively. The results of Example 3 are shown in Table 3.

[0065] Table 3

[0066]

[0067] Test Example 4

[0068] The viscosities of the products of Examples 1 to 14 were measured using a viscometer, and some of the results are shown in Table 4.

[0069] Table 4

[0070]

[0071] As can be seen from the results in Table 4, the viscosities of the products in Examples 3 to 12 are significantly lower than the viscosities of the ionic liquids before compounding.

[0072] Although the present invention has been described with reference to specific embodiments, those skilled in the art should understand that various changes can be made without departing from the true spirit and scope of the present invention. In addition, various changes can be made to the subject matter, spirit and scope of the present invention to adapt to specific situations, materials, material compositions and methods. All such changes are included within the scope of the claims of the present invention.

Claims

1. An ionic liquid, which is tetraethylammonium hydroxide amino acid salt.

2. The ionic liquid according to claim 1, wherein The tetraethylammonium hydroxide amino acid salt is tetraethylammonium hydroxide glycinate and / or tetraethylammonium hydroxide sarcosinate.

3. A method for preparing the ionic liquid according to claim 1 or 2, which comprises the following steps: 1) Mix an amino acid with water to obtain an aqueous amino acid solution; 2) Dropwise add an aqueous solution of tetraethylammonium hydroxide to the aqueous amino acid solution, react, and obtain a reaction solution after the reaction ends; 3) Remove the water in the reaction solution to obtain the ionic liquid.

4. The method according to claim 3, characterized in that, The molar ratio of the amino acid to the tetraethylammonium hydroxide is 1:

1.

5. The method according to claim 3, characterized in that, In step 2), the reaction temperature is the natural ambient temperature, and the reaction time is 10 to 24 h.

6. The method according to claim 3, wherein In step 3), first remove the water in the reaction solution by a rotary evaporator, then vacuum dry, and finally obtain the ionic liquid; Preferably, in step 3), the temperature of the vacuum drying is 50 to 80 °C, and the time is 24 to 48 h.

7. A compound absorbent, which comprises the ionic liquid according to claim 1 or 2 and imidazole.

8. The composite absorbent according to claim 7, wherein The imidazole is N-methylimidazole.

9. The compound absorbent according to claim 7, wherein The mass ratio of the ionic liquid to the organic solvent is 2:1 to 1:

4.

10. Use of the ionic liquid according to claim 1 or 2 or the compound absorbent according to any one of claims 7 to 9 in the absorption of carbon dioxide; Preferably, the use is for the absorption of carbon dioxide in natural gas, shale gas, coalbed methane and biogas.

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