METHOD FOR CAPTURING CO2

Abstract

The present invention addresses to a method that uses surface-active surfactants ionic liquids (ILs) with an affinity for water to capture CO.sub.2, especially ILs derived from surfactants, of low production cost, fluoride-free, causing a low environmental impact in its use and high yield of CO.sub.2 sorption. The CO.sub.2 sorption method consists of contacting a gas mixture with at least one of the described ILs, at the working temperature, pressure and partial pressure of CO.sub.2. The removal of CO.sub.2 is done by pressure reduction. ILs can be reused without loss of efficiency.

Claims

1- METHOD FOR CAPTURING CO.sub.2, characterized in that it comprises contacting a gaseous mixture containing CO.sub.2 with ionic liquids, under the process conditions of exhausted gases or natural gas, high or low pressures, in an absorption string.

2- THE METHOD according to claim 1, characterized in that ionic liquids are fluorine-free and have an affinity for water.

3- THE METHOD according to claim 1, characterized in that ionic liquids are chosen from 1-butyl-3-methylimidazolium lauryl sulfate ([bmim][C.sub.12SO.sub.4); 1-butyl-3-methylimidazolium lauryl ether sulfate ([bmim][C.sub.12ESO.sub.4]); 1-butyl-3-methylimidazolium lauryl benzene sulfonate ([bmim][C.sub.12BSO.sub.3]); 1-butyl-3-methylimidazolium lauroyl sarcosinate ([bmim][C.sub.12SAR]); tetra-n-butylammonium lauryl sulfate ([TBA][C.sub.12SO.sub.4]); tetra-n-butylammonium lauryl ether sulfate [TBA][C.sub.12ESO.sub.4]); tetra-n-butylammonium lauryl benzene sulfonate ( [TBA][C.sub.12BSO.sub.3]); and tetra-n-butylammonium lauroyl sarcosinate ( [TBA][C.sub.12SAR]).

4- THE METHOD according to claim 1, characterized in that desorption occurs by decompression in one or more stages.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0020] The present invention will be described in more detail below, with reference to the attached figures which, in a schematic manner and not limiting the inventive scope, represent examples of its embodiment. In the drawings, there are:

[0021] FIG. 1 illustrating the structures of the ionic liquids used in the present invention;

[0022] FIG. 2 illustrating a graph of CO.sub.2 sorption in ILs at a temperature of 30° C.;

[0023] FIG. 3 illustrating a graph of CO.sub.2 sorption in ILs at a temperature of 50° C.;

[0024] FIG. 4 illustrating a graph of sorption and desorption cycles of CO.sub.2 in [TBA][C.sub.12ESO.sub.4] at a temperature of 50° C.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The method of capturing CO.sub.2 according to the present invention consists of contacting the gas mixture containing CO.sub.2 with the ionic liquids, in the process conditions of exhausted gases or natural gas, high or low pressures, in an absorption string. Desorption occurs by decompression, which can be done in one or more stages. The negligible volatility, chemical and electrochemical stability of ILs reduce the potential for equipment corrosion and the constant need for sorbent make-up.

[0026] The ionic liquids used in the present invention, whose structures are represented in FIG. 1, are as follows: [0027] 1) 1-butyl-3-methylimidazolium lauryl sulfate: [bmim][C.sub.12SO.sub.4 ]; [0028] 2) 1-butyl-3-methylimidazolium lauryl ether sulfate: [bmim][C.sub.12ESO.sub.4]; [0029] 3) 1-butyl-3-methylimidazolium lauryl benzene sulfonate: [bmim][C.sub.12BSO.sub.3]; [0030] 4) 1-butyl-3-methylimidazolium lauroyl sarcosinate: [bmim][C.sub.12SAR]; [0031] 5) tetra-n-butylammonium lauryl sulfate: [TBA][C.sub.12SO.sub.4]; [0032] 6) tetra-n-butylammonium lauryl ether sulfate: [TBA][C.sub.12ESO.sub.4]; [0033] 7) tetra-n-butylammonium lauryl benzene sulfonate: [TBA][C.sub.12BSO.sub.3]; [0034] 8) tetra-n-butylammonium lauroyl sarcosinate: [TBA][C.sub.12SAR].

[0035] The ILs proposed in this invention, as they are derived from low-cost and easily obtainable commercial surfactants, are much cheaper than the traditional commercial ILs supplied in the market. Its CO.sub.2 sorption capacity was determined on a thermomagnetic suspension microbalance (MSB). The test results showed a competitive sorption capacity with current commercial systems. The proposed ILs can be used in high or low pressure processes, in exhaust gas purification or natural gas purification, even with high partial pressures of carbon dioxide.

[0036] The costs for obtaining the ILs that are used in the CO.sub.2 capture method of the present invention are lower than [bmim][NTf .sub.2]. Normally, the value of an IL, when moving from the bench scale to the industrial scale, has a cost reduction of approximately 90%. With this premise, it is estimated a production cost close to R$ 1000.00/kg [bmim][NTf.sub.2], while the costs of the proposed ILs range from R$ 70.00/kg [TBA][Cl.sub.12ESO.sub.4 ] to R$ 435.00/kg [bmim][C.sub.12SAR]. The costs of capturing CO.sub.2 with ionic liquids are estimated at T=50° C. and P=50 bar (5.0 MPa), for comparison purposes (Table 1). The calculation considered only one CO.sub.2 capture cycle, although the ILs have a high regeneration capacity. The reference IL [bmim][NTf.sub.2] had a sorption cost of R$ 89.50/g CO.sub.2 captured. The [bmim][C.sub.12ESO.sub.4] and [TBA][C.sub.12SO.sub.4] achieve savings of 70 and 80%, respectively, in relation to the reference IL. The result shows that the CO.sub.2 capture method described in this invention overcomes one of the major limitations of the use of ionic liquids in a process, the high cost of the material.

TABLE-US-00001 TABLE 1 Cost estimate for using ILs to capture CO.sub.2. Cost economy of synthesis Sorbed amount Cost of sorption IL Price/kg* (%)** (g CO.sub.2 sorbed/kg IL) (R$/g captured CO.sub.2) [bmim][NTf.sub.2] R$ 10,000.00  — 111.73 89.50 [bmim][C.sub.12SO.sub.4] R$ 2,137.00 78.63 35.44 60.22 [bmim][C.sub.12ESO.sub.4] R$ 1,490.00 85.10 61.90 24.07 [bmim][C.sub.12BSO.sub.3] R$ 1,764.00 82.36 31.10 56.72 [bmim][C.sub.12SAR] R$ 4,356.00 56.44 18.65 233.56 [TBA][C.sub.12SO.sub.4] .sup. R$ 943.00 90.57 57.32 16.45 [TBA][C.sub.12ESO.sub.4] .sup. R$ 684.00 93.16 101.46 6.47 [TBA][C.sub.12BSO.sub.3] .sup. R$ 794.00 92.06 25.99 30.55 [TBA][C.sub.12SAR] R$ 2,779.00 72.21 97.38 28.53 *data based on 2021 values. **data based on 2021 values and as a comparison reference the [bmim][NTf.sub.2].

[0037] By means of the data and results shown, a capture process using ILs derived from surfactants is able to overcome several negative points for both the current capture process, using amine solutions, as well as the proposals aimed at the use of other ILs. In the first case, comparing with amine solutions, the process using ILs derived from surfactants only needs reduced pressure during the regeneration step, which will reduce the total cost of the capture process by a drastic energy reduction. Regarding the use of other ILs, as mentioned above, the cost of the solvent is the main negative point. However, the ILs derived from surfactants have a low cost, making them competitive in the market. The main advantage is the application of low-cost, non-fluorinated ILs, derived from common commercial surfactants, which have affinity and miscibility with water, so that these materials can be applied in aqueous solutions or dispersions, which tends to greatly increase the feasibility of its application in industrial processes. The use of ionic liquids as described in the invention can be applied at different stages in the purification processes of natural gas streams rich in CO.sub.2 and water.

EXAMPLES

[0038] Surfactant-derived ILs with an affinity for water proposed for application in CO.sub.2 capture are obtained from low-cost, easy-to-obtain and comprehensive commercial reagents. They can be used in an existing capture structure or with minor modifications, favoring the replacement of technology. ILs have the ability to sorb CO.sub.2 at high partial pressures, while amines require lower partial pressures. The regeneration of ILs can be done only by pressure difference, without the need for temperature, whereas amines need one more step in the process with great energy expense and constant make-up, which is the distillation step. Amines are primarily responsible for the corrosion effects (both in the absorption and regeneration unit) of the steels that form the process equipment, including AISI 304 and AISI 316 stainless steels, due to their highly reactive degradation products; in addition to not generating degradation compounds, ILs have the ability to form a protective film on equipment, making corrosion processes even more difficult.

[0039] The chemical structures of the ionic liquids proposed in this invention for the CO.sub.2 capture method are shown in FIG. 1.

[0040] CO.sub.2 sorption measurements were performed by gravimetry in a thermomagnetic suspension balance (MSB). The results of the tests in the isotherm at 30° C. and pressure variation from 0 to 60 bar (6.0 MPa) are shown in Table 2 and FIG. 2.

TABLE-US-00002 TABLE 2 Results of CO.sub.2 sorption in ILs at 30° C. of temperature. [bmim] [bmim] [bmim] [bmim] [bmim] [TBA] [TBA] [TBA] [TBA] Pressure* [NTf.sub.2] [C.sub.12SO.sub.4] [C.sub.12ESO.sub.4] [C.sub.12BSO.sub.3] [C.sub.12SAR] [C.sub.12SO.sub.4] [C.sub.12ESO.sub.4] [C.sub.12BSO.sub.3] [C.sub.12SAR] (bar = (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ 1/10 MPa) kg IL) kg IL) kg IL) kg IL) kg IL) kg IL) kg IL) kg IL) kg IL) −1 −1.13 −0.88 −2.57 −1.66 0.43 5.58 1.10 4.52 −0.80 5 17.72 −0.53 7.41 10.17 3.66 16.42 14.99 8.13 23.91 10 32.73 −0.62 16.34 18.79 6.60 30.50 28.73 11.80 36.54 15 46.32 0.67 26.38 27.74 14.01 39.11 42.35 15.39 52.06 20 61.51 6.58 34.93 36.16 16.79 51.34 55.31 18.72 67.87 25 78.10 17.76 43.96 44.41 18.72 60.02 69.49 22.60 83.28 30 94.67 33.67 50.68 53.67 17.45 74.81 83.60 26.08 98.77 35 110.21 52.38 58.20 63.77 21.79 83.48 98.06 27.18 112.97 40 125.15 68.30 65.98 72.42 26.30 95.61 112.99 34.05 127.64 45 144.13 80.25 75.23 81.34 28.78 105.47 127.16 37.93 144.51 50 158.02 89.68 80.57 91.09 30.96 118.40 140.59 42.00 160.03 55 171.21 84.50 33.53 126.70 153.37 174.57 60 184.02 84.07 34.48 133.75 172.71 180.62 *barometric pressure

[0041] The ILs that stood out the most at 30° C. were [bmim][NTf.sub.2] and [TBA][C.sub.12SAR] reaching 184.01 and 180.62 g CO.sub.2 sorbed/kg IL, respectively. Just below, showing great potential, due to the sorption cost (Table 1), there is [TBA][C.sub.12ESO.sub.4].

[0042] Table 3 and FIG. 3 show the results of CO.sub.2 sorption in the isotherm at 50° C. in ionic liquids. [TBA][C.sub.12ESO.sub.4] showed high CO.sub.2 sorption capacity, with linearity up to the highest pressure tested, showing no IL saturation in the tested range. The results are comparable to those achieved by [bmim] [NTf.sub.2 ], which is the IL of reference and with a much higher cost, as shown in Table 1.

[0043] [TBA][C.sub.12SAR] showed competitive CO.sub.2 sorption capacity, although its production cost is higher than the cost of [TBA][C.sub.12ESO.sub.4]. The ILs [TBA][C.sub.12ESO.sub.4] and [TBA][C.sub.2SO.sub.4] also showed good C.sub.2 sorption capacities, reaching 50% of the sorption capacity of [bmim][NTf.sub.2], showing the potential of these ILs for use in CO.sub.2 capture plants. It is concluded that the anion [C.sub.12ESO.sub.4 ], both for the cation [bmim].sup.+and for the cation [TBA].sup.+, presents good results. In the isotherm at 50° C., the CO.sub.2 sorption values are lower than in the isotherm at 30° C. This result was already expected due to the fact that, with an increase in temperature, the kinetic energy of the molecules increases, facilitating the desorption of the gas. The differential of the method of capturing CO.sub.2 using ILs is the capacity of integral regeneration of the material.

TABLE-US-00003 TABLE 3 Results of CO.sub.2 sorption in ILs at 50° C. of temperature. [bmim] [bmim] [bmim] [bmim] [bmim] [TBA] [TBA] [TBA] [TBA] Pressure* [NTf.sub.2] [C.sub.12SO.sub.4] [C.sub.12ESO.sub.4] [C.sub.12BSO.sub.3] [C.sub.12SAR] [C.sub.12SO.sub.4] [C.sub.12ESO.sub.4] [C.sub.12BSO.sub.3] [C.sub.12SAR] (bar = (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ (g CO.sub.2/ 1/10 MPa) kg IL) kg IL) kg IL) kg IL) kg IL) kg IL) kg IL) kg IL) kg IL) −1 2.10 −1.91 3.24 −3.20 −4.34 5.42 1.54 −2.48 3.47 5 16.14 3.16 9.82 4.19 −2.26 10.85 13.10 1.37 19.49 10 27.50 8.30 16.25 10.48 −0.18 10.77 23.33 3.91 28.68 15 38.99 12.09 22.49 17.13 1.50 22.64 32.95 7.43 37.15 20 50.83 15.87 28.61 23.63 2.99 28.78 42.91 10.78 47.72 25 58.35 20.38 34.13 29.94 4.96 36.10 51.60 14.22 58.04 30 69.99 23.92 40.42 36.76 7.27 35.60 60.12 18.22 64.99 35 81.45 27.52 46.41 43.40 10.12 43.43 70.50 22.71 73.28 40 91.71 30.84 50.86 49.74 13.64 49.25 81.53 26.75 82.19 45 102.14 33.31 56.51 55.86 16.54 50.50 90.57 32.17 93.89 50 111.74 35.45 61.91 63.31 18.65 57.32 101.47 42.86 97.38 55 121.56 65.32 22.33 55.69 109.82 60 130.87 67.86 25.22 62.48 113.19 *barometric pressure

[0044] FIG. 4 shows the results obtained with 80 cycles of sorption/desorption of CO.sub.2 in [TBA][C.sub.12ESO.sub.4] at 50° C. of temperature.

[0045] Thus, the cost reduction of the CO.sub.2 capture method using the proposed ILs is proven. The regeneration of ILs [TBA][C.sub.12ESO.sub.4] takes place by reducing the pressure at room temperature, with reduced energy consumption when compared to the use of amines, as there will be no need to heat the solvent in the regeneration step. As the vapor pressure of ILs is practically negligible, there is no need for continuous make-up, as is done with amines, reducing the operational cost of the process. When keeping a comparison between the ILs and the amines, in relation to the stability of the compounds during the process, there are other advantages: amines undergo thermal and chemical degradation forming compounds of high chemical reactivity and toxicity (such as formaldehydes), whereas the ILs described in this patent are stable in oxidizing and CO.sub.2 atmospheres. In addition, such compounds generated in the degradation of amines (HSS—heat stable salts) are mainly responsible for the corrosion effects of the steels that form the process equipment, including stainless steels AISI 304 and AISI 316 (both in the absorption unit and in regeneration). In addition to not generating degradation compounds, ILs have the ability to form a protective film on equipment, making corrosion processes even more difficult.

[0046] It should be noted that, although the present invention has been described in relation to the attached drawings, it may undergo modifications and adaptations by technicians skilled on the subject, depending on the specific situation, but provided that it is within the inventive scope defined herein.