FR2961114A1 - Removing carbon dioxide from flue gases, comprises a absorption step of contacting flue gases with an absorbent solution comprising water and diamine e.g. 1,2-bis(2-dimethylaminoethoxy)ethane and 1,2-bis(2-pyrolidinoethoxy)ethane - Google Patents

Abstract

Removing carbon dioxide from flue gases having carbon dioxide with a partial pressure of below 200 mbar, comprises a absorption step of contacting flue gases with an absorbent solution comprising water and at least one diamine including 1,2-bis(2-dimethylaminoethoxy)ethane, 1,2-bis(2-diethylaminoethoxy)ethane and 1,2-bis(2-pyrolidinoethoxy) ethane. An independent claim is included for the absorbent solution for removing carbon dioxide form flue gases.

Description

The present invention relates to the field of capturing CO2 contained in combustion fumes by means of an aqueous absorbent solution comprising diamines of the 1,2-bis (2-aminoethoxy) ethane family.

In order to limit the phenomenon of global warming, the carbon dioxide is extracted from the combustion fumes in order to be sequestered in an underground reservoir. Absorption processes employing an aqueous amine solution are commonly used to remove the acid compounds (in particular H 2 S, mercaptans, CO 2, COS, CS 2) present in a gas. The gas is purified by contact with the absorbent solution, and the absorbent solution is thermally regenerated. JP H08 257353 discloses a method of removing CO 2 in the flue gases, wherein the flue gases are contacted at atmospheric pressure with an aqueous solution containing a diamine compound of the general formula [1]: RIR2NCH2CH2OCH2CH2NR3R4 [1] wherein R1, R2, R3, R4 respectively denote lower alkyl groups of 1 to 3 carbons. More particularly, the diamine compound of interest is bis (2-dimethylaminoethyl) ether. This document describes the thermodynamic performances (charge rate and reaction enthalpy) of bis (2-dimethylaminoethyl) ether in contact with combustion fumes. However, this document does not describe the degradation performance of this molecule and is limited to the presence of an ethoxyethyl-CH2CH2-O-CH2CH2-unit in the structure of the diamine. US 4,556,546 discloses the use of compounds having the general formula R1 R2-N- (CH2CH2O) x-CH2CH2-NR3R4 in which at the end or at the ends of the ethoxyethyl chain a morpholine ring is found. bis (2-dimethylaminoethyl) ether. These compounds are used to purify gas streams comprising acidic compounds. Nevertheless, the main use of these solvents is either in the absence of water and the molecule then behaves like a physical solvent, either in the presence of water and in this case the intended application is the hydrolysis of the COS. The relative low basicity of morpholine-type amine functions makes these molecules bad candidates for capturing CO2.

It is difficult to find an absorbent compound for removing acid compounds in any type of effluent, and allowing the deacidification process to operate at a lower cost.

The present invention proposes to use one of the diamines of the group consisting of 1,2-bis (2-dimethylaminoethoxy) ethane, 1,2-bis (2-diethylaminoethoxy) ethane and 1,2-bis (2 -pyrolidinoethoxy) ethane, which have good stability and good CO2 capture capacity to reduce the cost of operation of the process.

In general, the present invention describes a method for removing CO2 contained in combustion smoke having a CO 2 partial pressure of less than 200 mbar, wherein a CO2 absorption step is carried out by contacting the smoke. with an absorbing solution comprising: water, and at least one of the group consisting of 1,2-bis (2-dimethylaminoethoxy) ethane, 1,2-bis (2-diethylaminoethoxy) ethane and the 1,2-bis (2-pyrolidinoéthoxy) ethane.

According to the invention, the absorbent solution may comprise between 10% and 90% by weight of diamine and between 10% and 90% by weight of water.

The absorbent solution may further comprise between 0.5% and 20% by weight of an activator chosen from amines comprising at least one primary or secondary amine function. The activator may be selected from the group consisting of: MonoEthanolAmine, N-butylethanolamine, Aminoethylethanolamine, Diglycolamine, Piperazine, N- (2-hydoxyethyl) piperazine, N- (2-aminoethyl) piperazine, Morpholine, 3- (methylamino) propylamine.

After the absorption step, a gaseous effluent depleted in acidic compounds and an absorbent solution loaded with acid compounds is obtained, and at least one regeneration step of the absorbent solution loaded with acidic compounds can be carried out. Preferably, the regeneration is carried out at a temperature of between 160 ° C. and 180 ° C. and at a pressure of between 5 bars and 10 bars.

The present invention also discloses an absorbent solution for removing CO2 contained in a combustion smoke having a CO 2 partial pressure of less than 200 mbar comprising an aqueous solution of at least one diamine selected from the group consisting of bis (2-dimethylaminoethoxy) ethane, 1,2-bis (2-diethylaminoethoxy) ethane and 1,2-bis (2-pyrolidinoethoxy) ethane.

According to the invention, the absorbent solution may comprise between 10% and 90% by weight of diamine and between 10% and 90% by weight of water.

The absorbent solution may further comprise between 0.5% and 20% by weight of an activator chosen from amines comprising at least one primary or secondary amine function. The activator may be chosen from the group consisting of: - MonoEthanolAmine, - N-butylethanolamine, - Aminoethylethanolamine, Diglycolamine, - Piperazine, N- (2-hydroxyethyl) piperazine, N- (2-aminoethyl) piperazine, Morpholine, 3- (methylamino) propylamine.

The absorbent compounds according to the invention, that is to say 1,2-bis (2-dimethylaminoethoxy) ethane, 1,2-bis (2-diethylaminoethoxy) ethane and 1,2-bis (2- pyrolidinoethoxy) ethane have a greater CO2 absorption capacity than the alkanolamines conventionally used. Indeed, these diamines have the particularity to have a = ngaZ acid / namine loading ratio (a denoting the ratio between the number of moles of acidic compounds absorbed ngaZ acid by a portion of absorbent solution relative to the number of moles of amine namine contained in said portion of absorbent solution) very important at low partial pressures of acidic compounds, for example at a partial pressure of CO2 less than 0.2 bar, compared with alkanolamines conventionally used. The use of an aqueous absorbent solution according to the invention makes it possible to save on the investment cost and the regeneration costs of a unit for capturing the CO2 contained in a combustion smoke. In addition, 1,2-bis (2-dimethylaminoethoxy) ethane, 1,2-bis (2-diethylaminoethoxy) ethane and 1,2-bis (2-pyrolidinoethoxy) ethane have a low degradation rate at high temperature. compared to amine-based absorbent solutions of the prior art. Therefore, it is possible to regenerate the absorbent solution according to the invention at higher temperature and pressure, and thus produce an acid gas at higher pressure. This is particularly interesting in the case of the capture of CO2 contained in the fumes, where the acid gas must be compressed to be liquefied before injection into an underground reservoir.

Other characteristics and advantages of the invention will be better understood and will become clear from reading the description given below with reference to the drawings, in which: FIG. 1 gives different reaction schemes for synthesizing the diamines according to FIG. FIG. 2 represents a schematic diagram of a method for capturing CO2 contained in combustion fumes.

The present invention proposes to eliminate the CO2 contained in combustion fumes by using at least one diamine in aqueous solution, the diamine being chosen from the family of 1,2-bis (2-aminoethoxy) ethane and more precisely among: - 1,2-bis (2-dimethylaminoethoxy) ethane

0 ~ / ~ N ~, and / or 20 - 1,2-bis (2-diethylaminoethoxy) ethane NN, and / or - 1,2-bis (2-pyrolidinoethoxy) ethane.

Syntheses of diamines according to the invention

1,2-bis (2-dimethylaminoethoxy) ethane, 1,2-bis (2-diethylaminoethoxy) ethane and 1,2-bis (2-pyrolidinoethoxy) ethane can be, for example, but not only, prepared according to the reactions or sequences of reactions illustrated by the reaction scheme shown in FIG. 1. With reference to FIG. 1, the compounds according to the invention can be obtained by reacting a secondary amine R1 R2NH or a mixture of secondary amines corresponding to the general formula R1 R2NH on triethylene glycol according to a well-known condensation reaction (reaction referenced 2). This reaction can for example be carried out in the presence of hydrogen and a suitable catalyst under conditions abundantly cited in the literature. The triethylene glycol which is the precursor in this reaction is generally obtained by trimerization of ethylene oxide according to a conventional ring opening reaction in the presence of a molecule of water (reaction referenced 1). Triethylene glycol is an abundant and inexpensive industrial compound. The compounds according to the invention can also be obtained firstly by the reaction of ammonia with triethylene glycol according to a well-known condensation reaction (reaction referenced 3) leading to 1,2-bis (2-aminoethoxy) ethane called also 1,8-diamino-3,6-dioxaoctane, the primary amine functions of the latter being then N-alkylated by reaction of an aldehyde in the presence of hydrogen and generally using a suitable catalyst ( reaction referenced 4) under conditions abundantly cited in the literature. The compounds according to the invention can also be obtained firstly by the halogenation reaction of, for example, the chlorination of triethylene glycol with 1,2-bis (2-chloroethoxy) ethane (reaction referenced 5) with a conventional chlorination agent such as for example hydrochloric acid or thionyl chloride, and then by a condensation reaction (reaction referenced 6) with a secondary amine R1 R2NH or a mixture of secondary amines corresponding to the general formula RI R2NH. The compounds according to the invention can also be obtained by condensation reaction of a dialkylamino-2-ethanol with a 1,2-dihaloethane such as 1,2-dichloroethane (reaction referenced 7) or by condensation reaction of a dialkylamino-2-haloethane such a 2-chloro-N, N'-dialkylethylamine optionally in the form of a hydrohalide with ethylene glycol (reaction referenced 8).

In the scheme of FIG. 1, R1 and R2 represent for example a methyl radical, an ethyl radical or when R1 and R2 are linked to each other a 1,4-butylene radical -CH2-CH2-CH2-CH2-. Similarly, R 1 R 2 NH may represent, for example, dimethylamine or diethylamine or pyrrolidine. R can represent a hydrogen atom or a methyl radical.

Nature of the qazeux effluents to be treated by the process according to the invention

Absorbent solutions according to the invention are particularly well suited to the capture of CO2 contained in the combustion fumes. The combustion fumes are produced in particular by the combustion of hydrocarbons, biogas, coal in a boiler or for a combustion gas turbine, for example for the purpose of producing electricity. By way of illustration, a CO2 capture unit according to the invention aims to reduce by 90% the CO2 emissions of a thermal power station. These fumes generally have a temperature of between 20 and 60 ° C., a pressure of between 1 and 5 bar and may comprise between 50 and 80% of nitrogen, between 5 and 40% of carbon dioxide, and between 1 and 20% of carbon dioxide. oxygen, and some impurities such as SOx and NOx, if they have not been removed downstream of the deacidification process. In particular, the absorbent solution according to the invention is well adapted to absorb the CO2 contained in combustion fumes comprising a low partial pressure of CO 2, for example a CO 2 partial pressure of less than 200 mbar. Composition of the absorbent solution

The absorbent solution according to the invention is composed of an aqueous solution comprising one or more of the following diamines: 1,2-bis (2-dimethylaminoethoxy) ethane 1,2-bis (2-diethylaminoethoxy) ethane 1,2-bis (2-pyrolidinoethoxy) ethane OO / c) ~~ N1 ~ 10 The diamines according to the invention can be in variable concentration, for example between 10% and 90% by weight, preferably between 20% and 60% by weight, very preferred between 30% and 50% by weight, in the aqueous solution. The absorbent solution may contain from 10% to 90% by weight of water, preferably from 40% to 80% by weight of water, very preferably from 50% to 70% water. In one embodiment, the one or more diamines are formulated with an activator. Preferably, this activator is selected from another amine, containing at least one primary or secondary amine function. The absorbent solution according to the invention may contain at least 0.5% by weight of activator. The concentration of activator in the aqueous solution according to the invention can vary up to a maximum concentration of 20% by weight. Preferably, the activator content is limited to less than 15% by weight, preferably less than 10% by weight. This type of formulation is particularly interesting in the case of CO2 capture in industrial fumes. Indeed, for this type of application, the primary or secondary amine function of the activator makes it possible to increase the CO2 capture kinetics by the diamine or diamines of the invention, in order to reduce the size of the equipment. Preferably, the activator is selected from primary or secondary amines. A non-exhaustive list of compounds that can be used as activators is given below: Monoethanolamine, N-butylethanolamine, aminoethylethanolamine, diglycolamine, piperazine, N- (2-hydroxyethyl) piperazine, N- (2-aminoethyl) piperazine, Morpholine, 3- (methylamino) propylamine.

Of course, the sum of the contents of the various elements constituting the absorbent solution according to the invention is equal to 100% by weight.

Process for removing CO2 The use of an aqueous solution according to the invention for absorbing the CO2 contained in a combustion smoke is carried out by carrying out an absorption step followed by a regeneration step, for example by setting the process for the elimination of the acidic compounds in a gaseous effluent shown schematically in FIG.

With reference to FIG. 2, the absorption step consists of putting the combustion smoke 1 in contact with the absorbent solution 4. The smoke 1 is introduced at the bottom of Cl, the absorbent solution is introduced at the top of Cl. Column Cl is provided with means for contacting gas and liquid, for example loose packing, structured packing or distillation trays. During the contact, the amine functions of the diamines of the absorbent solution react with the CO2 contained in the combustion smoke so as to obtain a gaseous effluent depleted in CO2 2 discharged at the top of Cl and an absorbent solution enriched in the CO 2 evacuated in the bottom of Cl to be regenerated. The regeneration step consists in particular in heating and, optionally, relaxing, the absorbent solution enriched in CO2 in order to release the CO2 in gaseous form. The absorbent solution enriched with CO2 3 is introduced into the heat exchanger El, where it is heated by the stream 6 from the regeneration column C2. The heated solution at the outlet of El is introduced into the regeneration column C2.

The regeneration column C2 is equipped with internal contacting between gas and liquid, for example trays, loose or structured packings. The bottom of column C2 is equipped with a reboiler which provides the heat necessary for regeneration by vaporizing a fraction of the absorbing solution. In column C2, under the effect of contacting the absorbent solution arriving by 5 with the steam produced by the reboiler, the CO2 is released in gaseous form and discharged at the top of C2 through line 7. The absorbent solution regenerated 6, that is to say depleted in acidic compounds 6 is cooled in El, then recycled in the column Cl through line 4. The acidic compounds absorption step in Cl can be carried out at a pressure between 1 bar and 10 bar, preferably between 1 and 3 bar for the treatment of industrial fumes, and at a temperature between 20 ° C and 100 ° C, preferably between 30 ° C and 90 ° C, or between 30 and 60 ° C. The regeneration in C2 can be carried out at a pressure of between 1 bar and 10 bar and at a temperature between 100 ° C and 180 ° C, preferably between 120 ° C and 170 ° C. Preferably, the regeneration can be carried out at a temperature of between 155 ° C. and 180 ° C. and at a pressure of between 5 and 10 bars in the case where it is desired to reinject the CO2 into an underground reservoir. Preferably, the regeneration temperature is between 115 ° C and 130 ° C in cases where the CO2 is sent to the atmosphere.

EXAMPLE 1 Syntheses of Amines According to the Invention By way of example, a synthetic procedure is described for a few molecules according to the invention.

As an indication, the following examples illustrate the synthesis of certain molecules of the invention, it being understood that all the possibilities of synthesis of these molecules both at the level of the synthetic routes considered and the possible procedures are not here described.

Synthesis of 1,2-bis (2-dimethylaminoethoxy) ethane 10 g (53.4 mmol) of 1,2-bis (2-chloroethoxy) ethane and 50 ml of ethanol are introduced into an autoclave reactor and then the vacuum in the reactor is charged with 19.2 g (427.8 mmol) of dimethylamine while controlling the temperature. The medium is then brought to 80 ° C. for 7 hours with stirring.

After returning to ambient temperature and degassing the excess dimethylamine, 4.5 g of sodium hydroxide are added in pellet which is allowed to react for 30 minutes and then filtration is carried out followed by distillation of the filtrate. The fraction distilling between 60 ° C and 72 ° C is collected under a pressure of 0.3 mbar. 9.4 g (86% yield) of a product according to the structure of 1,2-bis (2-dimethylaminoethoxy) ethane are obtained according to NMR analysis. 1H-NMR (CDCl3): 1.6ppm (s): CH3; 1.8 ppm (tr): (CH3) 2N-CH2CH2-O-CH2CH2-O-CH2CH2-N (CH3) 2 2.9ppm (tr): (CH3) 2N-CH2CH2-O-CH2CH2-O-CH2CH2-N (CH 3) 2 3.0 ppm (s): (CH 3) 2 N -CH 2 CH 2 -O-CH 2 CH 2 -O-CH 2 CH 2 -N (CH 3) 2 13 C NMR (CDCl 3): 45.4 ppm: CH 3 58.4 ppm: (CH 3 ) 2N-CH 2 CH 2 -O-CH 2 CH 2 -O-CH 2 CH 2 -N (CH 3) 2 68.9 ppm: (CH 3) 2 N -CH 2 CH 2 -O-CH 2 CH 2 -O-CH 2 CH 2 -N (CH 3) 2 69.9 ppm: (CH 3) 2N In a 1 liter flask, 86.5 g (462 mmol) of 1,2-bis (2-pyrolidinoethoxy) ethane were added. bis (2-chloroethoxy) ethane and 215 ml of ethanol, then 262.7 g of pyrrolidine (3.7 moles) keeping the temperature below 40 ° C. The medium is then brought to 80 ° C. for 7 hours with stirring and then the more volatile compounds are evaporated under reduced pressure. After returning to ambient temperature, 38.8 g of sodium hydroxide in pellet is added to 150 ml of water which is allowed to react for 30 minutes, then the aqueous phase is eliminated and the organic phase is distilled off. The fraction distilling between 128 ° C. and 134 ° C. is collected under a pressure of 0.4 mbar. 102.3 g of a product conforming to the structure of 1,2-bis (2-pyrolidinoethoxy) ethane (yield 86%) are obtained.

EXAMPLE 2 Capacity for Capturing Amines According to the Invention The performances (ie CO2 capture capacity) are compared in particular with that of an aqueous solution of MonoEthanolAmin at 30% by weight, which constitutes the reference solvent for an application of capture of CO2 contained in post-combustion fumes. An absorption test is carried out on aqueous amine solutions in a perfectly stirred closed reactor whose temperature is controlled by a control system. For each solution, the absorption is carried out in a liquid volume of 50 cm3 by pure CO2 injections from a reserve. The solvent solution is previously drawn under vacuum before any CO2 injection. The pressure of the gas phase in the reactor is then monitored as a function of time following the CO2 injections. An overall material balance on the gas phase makes it possible to measure the degree of charge of the solvent a = nb of mole acid compound / nb of mole amine. By way of example, compare in Table 1 the filler levels (a = nb of acid compound / nb of mole amine) obtained at 40 ° C for various partial pressures of CO2 between absorbent solutions of 1,2-bis (2-dimethylaminoethoxy) ethane and 1,2-bis (2-pyrolidinoethoxy) ethane according to the invention and an absorbent solution of MonoEthanolAmine at 30% by weight for post-combustion CO 2 capture application. To go from a size of the charge rate obtained in the laboratory to a characteristic quantity of the process, some calculations are necessary, and are explained below for the two applications concerned. In the case of post-combustion CO 2 capture application, the partial pressures of CO 2 in the effluent to be treated are typically 0.1 bar with a temperature of 40 ° C., and it is desired to remove 90% of the acid gas. The cyclic capacity Da expressed in moles of CO 2 per kg of solvent is calculated, considering that the solvent reaches its maximum thermodynamic capacity at the bottom of the absorption column aPPCO 2 = 0.1 bar and must at least be regenerated below its capacity. thermodynamic under the conditions of the column head aPPCO2 = 0.01 bar to achieve 90% reduction of CO2. Aa = (aPPCO2 = o, lbar - aPPco2 = o, o1bar). [A] - 10 / M where [A] is the concentration of amine expressed in% by weight, and M is the molar mass of the amine in g / mol.

Charge rate = nCO2 / namine Name Generic Concentration T PPCO2 = PPco2 Da (mol AH (° C) 0.1 bar = 0.01 CO2 / kg (kJ / mol bar Solvent) CO2) MEA 30% weight 40 0.52 0.44 0.38 92 1,2-bis (2-30% by weight) 40 1.01 0.21 1.18 62 dimethylaminoethoxy) ethane 1,2-bis (2-30% by weight 1.45 0.41 1.22 61 pyrolidinoethoxy) ethane Table 1

This example shows the higher loading rates that can be obtained thanks to an absorbent solution according to the invention, comprising 30% by weight of molecules according to the invention. Moreover, for a post-combustion flue gas capture application in which the partial pressure of CO 2 in the effluent to be treated is 0.1 bar, this example illustrates the greatest cyclical capacity in moles of CO2 per kilogram of solvent obtained thanks to a Absorbent solution according to the invention, comprising 10% by weight of molecules according to the invention to achieve a felling rate of 90% at the outlet of the absorber. In this application, where the energy associated with the regeneration of the solvent is critical, it can be observed that the amines according to the invention make it possible to obtain a much better compromise than the MEA, in terms of cyclic capacity and reaction enthalpy. . EXAMPLE 3 Stability of an Amine Solution According to the Invention The compounds according to the invention have the particularity of being particularly resistant to the degradations which may occur in a deacidification unit.

A degradation test is carried out on aqueous solutions of amine in a closed reactor whose temperature is controlled by a control system. For each solution, the test is carried out in a liquid volume of 50 cm 3 injected into the reactor. The solvent solution is previously drawn under vacuum before any gas injection and the reactor is then placed in a heating shell at the set temperature and stirred magnetically. The gas in question is then injected at the desired partial pressure. This pressure is added to the initial pressure due to the vapor pressure of the aqueous amine solution. Different degradation conditions are tested: thermal degradation: in the absence of acid gas only the temperature of the test is kept constant and the vapor pressure of the solvent is measured. degradation under CO2: CO2 is injected so as to reach a partial pressure of 20 bar degradation under 02: air is injected under a partial pressure of 20 bar, which gives an oxygen partial pressure of 4.2 bars. Table 2 below gives the degradation rate TD under CO2 and O 2 degradation of 2-bis (2-dimethylaminoethoxy) ethane according to the invention, and bis (2-dimethylaminoethyl) ether as well as MEA as reference amines, under different conditions, for a period of 15 days, defined by the equation below: TD (%) = [Al- [Al ° where [A] is the concentration of the compound in the degraded sample, and [A] ° is the concentration of the compound in the undegraded solution. The concentrations [A] and [A] ° are determined by gas chromatography. [Aldegradation rate T Amine Concentration (° C) PPCO2 = 20 bar PP02 = 4.2 bar MEA 30% weight 140 42% 21 0/0 bis (2-50% weight 140 32% 12% diethylaminoethyl) ether 1,2-bis (2-50% wt. 140 6% 9% dimethylaminoethoxy) ethane Table 2

Table 3 below gives the degradation rate TD of the solvent under thermal degradation, for a temperature of 180 ° C., in the absence of acid gas, which is representative of the degradations that could occur at the bottom of the regenerator, if wishes to obtain a high pressure acid gas for reinjection applications. Degradation rate Amine Concentration T (° C) Solvent vapor pressure bis (2-dimethylaminoethyl) ether 50% weight 180 35% 1,2-bis (2-50% weight 180 3% dimethylaminoethoxy) ethane Table 3 This example shows that the use of the compounds according to the invention, as amine in an absorbent solution makes it possible to obtain a low degradation rate compared to the amine-based absorbent solutions of the prior art (MonoEthanolAmine and bis (2-dimethylaminoethyl) )ether). Therefore, it is possible to regenerate the solvent at a higher temperature and thus to obtain an acid gas at higher pressure. This is particularly interesting in the case of post-combustion CO2 capture where the acid gas must be compressed to be liquefied before reinjection.

Claims (10)

CLAIMS1) A method for removing the CO2 contained in a combustion smoke having a partial pressure of CO2 of less than 200 mbar, in which a CO2 absorption step is carried out by contacting the combustion smoke with an absorbing solution comprising: water, and at least one diamine of the group consisting of 1,2-bis (2-dimethylaminoethoxy) ethane, 1,2-bis (2-diethylaminoethoxy) ethane and 1,2-bis (2-pyrolidinoéthoxy) ethane. 2) The method of claim 1, wherein the absorbent solution comprises between 10% and 90% by weight of diamine and between 10% and 90% by weight of water. 3) Method according to one of the preceding claims, wherein the absorbent solution comprises between 0.5% and 20% by weight of an activator selected from amines comprising at least one primary or secondary amine function. 4) Process according to claim 3, wherein the activator is selected from the group consisting of: MonoEthanolAmine, N-butylethanolamine, Aminoethylethanolamine, Diglycolamine, Piperazine, N- (2-hydroxyoxy) piperazine, N- (2- aminoethyl) Piperazine, Morpholine, 3- (methylamino) propylamine. 5) Method according to one of the preceding claims, wherein after the absorption step is obtained a gaseous effluent depleted of acidic compounds and an absorbent solution loaded with acidic compounds, and performs at least one step of regeneration of the solution absorbent charged with acidic compounds. 6) Process according to claim 7, wherein the regeneration is carried out at a temperature between 160 ° C and 180 ° C and at a pressure between 5 bar and 10 bar. 7) Absorbent solution for removing CO2 contained in a combustion smoke having a CO 2 partial pressure of less than 200 mbar comprising an aqueous solution of at least one diamine selected from the group consisting of 1,2-bis (2) dimethylaminoethoxy) ethane, 1,2-bis (2-diethylaminoethoxy) ethane and 1,2-bis (2-pyrolidinoethoxy) ethane. 8. Absorbent solution according to claim 7, wherein the absorbent solution comprises between 10% and 90% by weight of diamine and between 10% and 90% by weight of water. 9) Absorbent solution according to one of claims 7 and 8, wherein the absorbent solution comprises between 0.5% and 20% by weight of an activator selected from amines comprising at least one primary or secondary amine function. The absorbent solution of claim 9, wherein the activator is selected from the group consisting of: MonoEthanolAmine, N-butylethanolamine, 19Aminoethylethanolamine, Diglycolamine, Piperazine, N- (2-hydroxyethyl) piperazine, N- (2) -aminoethyl) Piperazine, - Morpholine, 3- (methylamino) propylamine.