FR3014327A1 - ABSORBENT SOLUTION BASED ON N, N, N ', N'-TETRAMETHYL-1,6-HEXANEDIAMINE AND A SECONDARY DIAMINE OF THE ALKYLDIAMINE FAMILY AND METHOD FOR REMOVING ACIDIC COMPOUNDS FROM A GASEOUS EFFLUENT - Google Patents

Abstract

The invention relates to the removal of acidic compounds in a gaseous effluent in an absorption process using an aqueous solution of N, N, N ', N'-Tetramethyl-1,6-hexanediamine formulated with a particular secondary diamine , making it possible to obtain a monophasic absorbent solution under the absorption conditions of acid gases such as CO2. The invention is advantageously applicable to the treatment of natural gas and gas of industrial origin.

Description

Field of the Invention The present invention relates to the absorption of acidic compounds (H2S, 002, COS, CS2, mercaptans, ...) contained in a gas by means of an aqueous absorbing solution comprising the combination of a diamine tertiary, N, N, N ', N'-tetramethyl-1, 6-hexanediamine, and a particular secondary diamine, to obtain a monophasic absorbent solution under the acid gas absorption conditions such as the 002. The invention is advantageously applicable to the treatment of natural gas and gas of industrial origin.

PRIOR ART Treatment of gases of industrial origin The nature of the gaseous effluents that can be treated is diverse. Non-limiting examples include synthesis gases, combustion fumes, refinery gases, bottoms gases from the Claus process, biomass fermentation gases, cement gases and blast furnace gases. . All these gases contain acidic compounds such as carbon dioxide (002), hydrogen sulphide (H2S), carbon oxysulphide (COS), carbon disulfide (CS2) and mercaptans (RSH), mainly carbon dioxide. methyl mercaptan (CH3SH), ethyl mercaptan (CH3CH2SH) and propyl mercaptans (CH3CH2CH2SH). For example, in the case of combustion fumes, CO2 is the acid compound that is to be removed. Indeed, CO2 is one of the greenhouse gases largely produced by different human activities and has a direct impact on air pollution. In order to reduce the amount of CO2 emitted into the atmosphere, it is possible to capture the CO2 contained in a gaseous effluent. Natural gas processing In the case of natural gas, three main treatment operations are considered: deacidification, dehydration and degassing. The first step, which is deacidification, is aimed at the removal of acidic compounds such as 002, but also H2S, COS, CS2 and mercaptans (RSH), mainly methyl mercaptan (CH3SH). ethyl mercaptan (CH3CH2SH) and propyl mercaptans (CH3CH2CH2SH and CH3CH (CH3) SH). The generally accepted specifications for the deacidified gas are 2% of 002, or even 50 ppm of CO2, to then liquefy the natural gas; 4 ppm H2S, and 10 ppm to 50 ppm total sulfur. The dehydration step then controls the water content of the deacidified gas against transport specifications. Finally, the degassing stage of natural gas ensures the dew point of hydrocarbons in natural gas, again depending on transport specifications.

Deacidification is therefore often carried out first, in particular in order to eliminate toxic acid gases such as H 2 S in the first stage of the process chain and to avoid the pollution of the different unit operations by these acidic compounds, in particular the dehydration section and the heavier hydrocarbons condensation and separation section. Elimination of acidic compounds by absorption The deacidification of gaseous effluents, such as for example natural gas and combustion fumes, as well as synthesis gases, refinery gases, gases obtained at the bottom of the Claus process, fermentation gases Biomass, cement and high blast furnace gases are generally carried out by washing with an absorbent solution. The absorbent solution makes it possible to absorb the acid compounds present in the gaseous effluent (in particular H 2 S, mercaptans, O 2, COS, CS 2). The solvents commonly used today are aqueous solutions of primary, secondary or tertiary alkanolamine, in combination with a possible physical solvent. For example, document FR 2 820 430 can be cited which proposes processes for deacidification of gaseous effluents. For example, US Pat. No. 6,852,144 describes a method for removing acidic compounds from hydrocarbons. The method uses a water-methyldiethanolamine or water-triethanolamine absorbent solution containing a high proportion of a compound belonging to the following group: piperazine and / or methylpiperazine and / or morpholine. For example, in the case of the capture of 002, the absorbed CO2 reacts with the amine present in solution according to a reversible exothermic reaction, well known to those skilled in the art and leading to the formation of hydrogenocarbonates, carbonates and / or carbamates, allowing removal of CO2 in the gas to be treated. Similarly, for the removal of H2S in the gas to be treated, the absorbed H2S reacts with the amine present in solution according to a reversible exothermic reaction, well known to those skilled in the art and leading to the formation of hydrosulfide. Another essential aspect of industrial solvent gas or flue gas treatment operations is the regeneration step of the separating agent. Depending on the type of absorption (physical and / or chemical), regeneration by expansion, and / or distillation and / or entrainment by a vaporized gas called "stripping gas" is generally envisaged. One of the main limitations of the solvents commonly used today is the need to implement large absorbent solution flow rates, which results in significant energy consumption for the regeneration of the solvent, but also important equipment sizes (columns, pumps, etc.). This is particularly true in the case where the partial pressure of acid gases is low. For example, for an aqueous solution of MonoEthanolAmine at 30% by weight used for the capture of CO2 in post-combustion in a thermal power station smoke, where the partial pressure of CO2 is of the order of 0.1 bar, the energy of regeneration represents about 3.9 GJ per tonne of CO2 captured (reference case, CASTOR project, post-combustion capture pilot of the Esbjerg thermal power plant). Such energy consumption represents a considerable operating cost for the capture process of 002. In general, for the treatment of acid effluents comprising acidic compounds such as, for example, H 2 S, mercaptans, O 2, COS, SO 2, CS 2, The use of amine-based compounds is interesting because of their ease of use in aqueous solution. However, during the deacidification of these effluents, the absorbent solution can degrade, either by thermal degradation or by secondary reaction with the acid gases to be captured, but also with other compounds contained in the effluent, such as, for example, oxygen, SOx and NOx, contained in industrial fumes.

These degradation reactions are detrimental to the proper functioning of the process: decreased solvent efficiency, corrosion, foaming, etc. Due to these degradations, it is necessary to carry out a purification of the solvent by distillation and / or ion exchange, and to make amine bonds. By way of example, amine bonds in a post-combustion CO 2 capture process, using a 30% by weight absorbing solution of MonoEthanolAmine, represent 1.4 kg of amine per tonne of CO2 captured, which increases considerably the operating costs of a catchment unit. It is difficult to find a stable absorbent compound to remove acidic compounds in any type of effluent, and allow the deacidification process to operate at a lower cost. Document FR 2 934 172 discloses that N, N, N ', N'-tetramethyl-1,6-hexanediamine (TMHDA), alone or mixed with a few weight percentages of primary or secondary amines, is of great interest in all the processes for treating gaseous effluents for the removal of acidic compounds.

Nevertheless, most of the aqueous absorbent solutions comprising TMHDA, alone or mixed with a few weight percentages of primary or secondary amines, exhibit a liquid-liquid phase separation during the absorption of CO2 under the conditions of the absorber, also called demixing phenomenon in the present description. In the form of two separate phases, the flow of acidic compounds transferred from the gas to the absorbent solution is strongly impacted and the column height must be adapted accordingly. This phenomenon therefore poses implementation difficulties, and given the complexity of the system, is difficult to model. Surprisingly, the Applicant has demonstrated that the addition of a few percentages by weight of particular secondary diamines to an aqueous solution of TMHDA makes it possible to obtain a monophasic absorbent solution under the acid gas absorption conditions such as 002. DESCRIPTION OF THE INVENTION The object of the present invention is to overcome one or more of the disadvantages of the prior art by proposing a method for eliminating acid compounds, such as 002, H2S, COS, CS2 and mercaptans. of a gas employing an aqueous absorbent solution comprising the combination of two specific amines whose properties make it possible, while maintaining a monophasic absorbent solution under the acid gas absorption conditions, to limit the flow of absorbent solution to be used , in particular at low partial pressure of acid gas, and which have a very high stability. A first subject of the invention is an aqueous absorbing solution comprising the combination of N, N, N ', N'-tetramethyl-1,6-hexanediamine (TMHDA) of formula (I) and an activator of general formula (II). The present invention also relates to a process for the removal of acidic compounds contained in a gaseous effluent, such as natural gas and gases of industrial origin, comprising: a step of absorption of the acidic compounds by contacting the effluent with an aqueous solution comprising TMHDA and an activator of general formula (II). optionally at least one liquid-liquid separation step of the solution charged with acid gas after heating, allowing fractional regeneration of the absorbent solution. at least one regeneration step of the absorbent solution loaded with acidic compounds. The invention also relates to the application of said process for the removal of acidic compounds to the treatment of natural gas or the treatment of gas of industrial origin, in particular the capture of 002 after combustion. SUMMARY OF THE INVENTION The invention relates to an absorbent solution for absorbing acidic compounds from a gaseous effluent, comprising: - water; - N, N, N ', N'-tetramethyl-1, 6-hexanediamine of formula (I) N N (I) - at least one activator compound selected from secondary diamines corresponding to the general formula (II).

By secondary diamine is meant an amine comprising two amine functions and at least one of the two amine functions is a secondary amine function. According to the invention, the general formula (II) is of the form: ## STR1 ## in which: R 1 is a linear or branched alkyl or cycloalkyl group of 8 to 18 carbon atoms, the groups R2, R3, R4 and R5 are independently selected from one of the group consisting of: a hydrogen atom and an alkyl group of 1 to 4 carbon atoms, the groups R6 and R7 are independently selected from one of the group consisting of: a hydrogen atom and an alkyl group of 1 to 4 carbon atoms, - a is an integer between 1 and 5, including extremes. The absorbent solution advantageously comprises from 10% to 90% by weight, preferably from 20% to 60% by weight, of TMHDA, and a non-zero and less than 50% by weight, preferably less than 30% by weight, of said at least one activator compound according to general formula (II).

The absorbent solution may comprise from 10% to 90% by weight of water, preferably from 50% to 70% by weight of water. According to one embodiment of the absorbent solution, the mass fraction of water is between 55% and 69% by weight of the absorbent solution, and the mass fraction of amines is between 31% and 45% by weight of the solution. absorbent, said mass fraction of amines comprising H R3 a mixture of N, N, U, N-tetramethyl-1,6-hexanediamine and 1% and 10% by weight of said at least one activator compound according to general formula (II ). According to a preferred embodiment, the absorbent solution contains at least one activator corresponding to the general formula (II) and chosen from the group formed by: H NH 2 N- (1-octyl) -1,2-ethanediamine HN NH 2 N- (1-Decyl) -1,2-ethanediamine H NH 2 N- (1-dodecyl) -1,2-ethanediamine HN H 2 N- (1-decyl) -1,3-propanediamine According to one embodiment of the absorbent solution the solution further comprises at least one additional activator compound comprising a primary or secondary amine function, preferably in an amount of less than 15% by weight of the absorbing solution, selected from the group consisting of: - monoethanolamine; diethanolamine; n-butylethanolamine; aminoethylethanolamine; diglycolamine; piperazine; 1-methylpiperazine; 2-methylpiperazine; - homopiperazine; N- (2-hydroxyethyl) piperazine; N- (2-aminoethyl) piperazine; morpholine; 3- (methylamino) propylamine; 1,6-hexanediamine; N, N'-dimethyl-1,6-hexanediamine; N-methyl-1,6-hexanediamine; N, N ', N'-trimethyl-1,6-hexanediamine. The invention also relates to a process for eliminating the acidic compounds contained in a gaseous effluent, in which is carried out: a step of absorption of the acidic compounds by contacting the effluent with an absorbent solution according to the invention of in order to obtain a gaseous effluent depleted in acidic compounds and an absorbent solution loaded with acid compounds, - then a regeneration step in which at least a portion of the solution charged with acidic compounds is sent to a distillation column to release the acidic compounds. in the form of a gaseous effluent and obtain a regenerated absorbent solution. The absorption step is advantageously carried out so as to obtain a gaseous effluent depleted of acidic compounds and an absorbent solution loaded with monophasic acid compounds. In general, the absorption step of the acidic compounds is carried out at a pressure of between 1 bar and 120 bar, and at a temperature of between 20 ° C. and 100 ° C. Advantageously, the absorption step is carried out at a temperature of between 30 ° C. and 95 ° C., preferably between 30 ° C. and 60 ° C. In general, the thermal regeneration step is carried out at a pressure of between 1 bar and 10 bar and a temperature of between 100 ° C. and 180 ° C. In a variant of the process according to the invention, a first step of expansion of the absorbent solution loaded with acidic compounds is carried out before the regeneration step. In one embodiment of the process according to the invention, the absorption step is followed by at least one liquid-liquid separation step of the absorbent solution loaded with two-phase acidic compounds obtained after heating the absorbent solution, then at least one step of fractional regeneration of the absorbent solution loaded with acidic compounds. The invention also relates to a process according to the invention for the treatment of natural gas.

The invention also relates to a process according to the invention for the treatment of gases of industrial origin, preferably for the capture of 002.

Other features and advantages of the invention will be better understood and will become clear from reading the description given hereinafter with reference to the appended figures given by way of example: FIG. 1 represents a schematic diagram a process for treating acid gas effluents. FIG. 2 represents a schematic diagram of a process for treating acid gas effluents with fractional regeneration by heating. DETAILED DESCRIPTION OF THE INVENTION The present invention proposes to eliminate the acidic compounds of a gaseous effluent by using the combination of at least two types of amine compounds in aqueous solution. The absorbent solution is an aqueous solution based on TMHDA, which has the property of reacting reversibly with acidic compounds, such as H2S and 002. The TMHDA in aqueous phase, has the property of forming two separable liquid phases when it has absorbed a certain quantity of acidic compounds (demixing phenomenon), such as 002. In other words, the aqueous solution of TMHDA forms two liquid phases when its charge rate (number of moles of acid compounds captured one mole of amine of the absorbent solution) exceeds a demixing critical load rate, i.e., a loading rate threshold. When placed in contact in the absorption column, the loading rate of the absorbent solution increases as the acid compounds contained in the gas are absorbed. When introducing the aqueous solution of TMHDA into the absorption column, the solution is monophasic. In the absorption column, the loading rate of the absorbent solution may exceed the critical loading rate demixtion and the absorbent solution may separate into two phases. In the form of two separate phases, the flow of acidic compounds transferred from the gas to the solution would be strongly impacted and the column height should be adapted accordingly. This phenomenon therefore poses significant problems of implementation, and given the complexity of the system, is difficult to model. In order to maintain the monophasic absorbent solution in the absorption column, the present invention proposes mixing the TMHDA with specific activators which have the property of eliminating the demixing phenomenon by raising the loading rate to 002.

By activator compound is meant a compound that accelerates the absorption kinetics of the CO2 contained in the gas to be treated. The composition of the absorbent solution according to the invention is detailed later in the description. The aqueous compositions based on TMHDA activated by a secondary diamine of general formula (II) are of interest as an absorbent solution in all processes for treating acid gases (natural gas, combustion fumes, etc.).

TMHDA has a greater absorption capacity with acid gases (002, H2S, COS, SO2, CS2 and mercaptans) than the alkanolamines conventionally used. Indeed, the TMHDA has the particularity of having very high feed rates (a = ngaz acid / flamine) at low partial pressures of acid gas, compared with the alkanolamines conventionally used.

The addition of a few weight percentages of a secondary diamine of formula (II) to an aqueous solution of TMHDA only slightly modifies the filler levels obtained, particularly at a low partial pressure of acid gas. The use of an aqueous absorbent solution according to the invention therefore saves on the investment cost and the operating costs of a deacidification unit (gas treatment and capture of 002).

In addition, the TMHDA molecule is interesting for its resistance to degradation, especially thermal and in the presence of oxygen. Therefore, it is possible to regenerate the solvent at a higher temperature and thus to obtain an acid gas at higher pressure if this is of interest in the case of reinjection of acid gas. This is particularly interesting in the case of post-combustion CO2 capture where the gas to be treated contains oxygen and where acid gas must be compressed before reinjection and sequestration. The addition of a few weight percent of a secondary diamine of general formula (II) does not change this conclusion because, given its low concentration, the rate of degradation of this molecule is slow. Moreover, the secondary diamines of general formula (II) are also interesting for their resistance to degradation, especially in the presence of oxygen. The use of an aqueous absorbent solution according to the invention makes it possible to save on the operating costs of the deacidification unit, and on the investment cost and the operating costs associated with the compression of the acid gas.

Furthermore, the aqueous solutions of TMHDA activated by a secondary diamine of general formula (II) have the particularity of being able to be implemented in a deacidification process, with fractional regeneration by heating as described in document FR 2 898 284. .

The addition of a small amount of secondary diamines of general formula (II) to an aqueous solution of TMHDA makes it possible to control the phenomenon of demixing of the solution during the process. This makes it possible to obtain a monophasic absorbent solution under the acid gas absorption conditions such as CO2, and to obtain a phase separation at the outlet of the charge-effluent exchanger if this is desired. Synthesis of N, N, 1 ', N-tetramethyl-1,6-hexanediamine TMHDA can be prepared according to various synthetic routes known to those skilled in the art, described for example in JP 1998- 341556, EP 1998-105636, JP 1994-286224, JP 1993-25241, EP 1993-118476, EP 1988-309343, JP 1986-124298, JP 1985-147734, DE 19853523074, JP 1983-238221, and JP 1983-234589. . The reactions described in these documents are generally catalytic, with various catalyst compositions, for example platinum, palladium, rhodium, ruthenium, copper, nickel or cobalt derivatives. Some of these pathways identified from basic chemicals are shown below, noting generically [Cat.] The use of a catalyst. N H H NH [Cat.] N / 7 / N + H2O 100-200 ° C [Cat.] + H2O 100-250 ° C H2 1-5 bar I NE12 H [Cat.] H -2-i ## EQU1 ## NH3 50-250 ° C H2 5-350 bar Synthesis of secondary diamines of general formula (II) The secondary diamines of general formula (II) can be synthesized by any means allowed by organic chemistry. We can, without being exhaustive, mention the following three ways of synthesis. According to a first synthetic route, the secondary diamines of general formula (II) can be obtained by condensation reaction of a halide or a tosylate or of an alkyl mesylate with a diamine corresponding to the general formula (III ), wherein the groups and indices are defined as for the general formula (II), according to the first scheme shown below. ## STR3 ## In this scheme, the possible reactions of the -NR6R7 function are not represented, since the radicals R6 and R7 are not defined.When R6 and R7 are hydrogen atoms, the use of an excess of the diamine (III) will obtain the indicated product.

According to a second synthetic route, the secondary diamines of general formula (II) can be obtained by reaction of a suitable aldehyde or ketone with a diamine corresponding to the general formula (III). This reaction leads to the formation of an imine after removal of a molecule of water. Then the imine is hydrogenated using a suitable catalyst to yield a secondary diamine of general formula (II) according to the following general scheme wherein R8 or R9 may be a hydrogen atom and must be consistent with the definition of R1. R2 R4 k (R6 Is4R7 R2 R4 R6 R9 R2 R4 ki / R6 0 + H2N 8 \ R7 H2 \ R3 R5 R CH N / C = N R9 / H R9 R3 R3 R5 - -a with R1 = R5R9CH- e H2O R5 In this scheme, the possible reactions of the -NR6F17 function are not represented, since the radicals R6 and R7 are not defined.When R6 and R7 are hydrogen atoms, the use of an excess of the diamine (III) will obtain the indicated product.

According to a third synthetic route, in the particular case where the secondary diamine of general formula (II) is an N-alkyl-1,3-propanediamine, it is possible to prepare the diamine by addition reaction of a primary alkylamine on acrylonitrile to obtain initially a N-alkyl-3-aminopropionitrile, which after a hydrogenation reaction of the nitrile function leads to the desired diamine according to the following general scheme. The nature of the gaseous effluents The absorbent solutions according to the invention can be used to deacidify the following gaseous effluents: natural gas, synthesis gases, combustion fumes, gases, and the like. Refinery gas, tail gas Claus process, biomass fermentation gas, cement gas, incinerator fumes. These gaseous effluents contain one or more of the following acidic compounds: CO2, H2S, mercaptans, COS, CS2. 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. These fumes have a temperature of between 20 ° C. and 60 ° C., a pressure of between 1 bar and 5 bar and can have between 50% and 80% nitrogen, between 5% and 10%, and 40% carbon dioxide, between 1% and 20% oxygen, and some impurities such as SOx and NOx, if they have not been removed downstream of the process. acidification. Natural gas consists mainly of gaseous hydrocarbons, but may contain several of the following acidic compounds: 002, H2S, mercaptans, COS, CS2. The content of these acidic compounds is very variable and can be up to 40% for CO2 and H2S. The temperature of the natural gas can be between 20 ° C and 100 ° C. The pressure of the natural gas to be treated may be between 10 bar and 120 bar.

Composition of the absorbent aqueous solution The TMHDA may be in variable concentration, for example between 10% and 90% by weight, preferably between 20% and 60% by weight, very preferably between 30% and 50% by weight, in the aqueous solution. , terminals included.

The activator compounds of general formula (II) have a non-zero concentration, for example less than 50% by weight, or even less than 30% by weight, preferably less than 20% by weight, very preferably less than 10% by weight, in the aqueous solution, terminals included. Preferably, the absorbent solution comprises at least 0.5% by weight of one or more activator compounds of general formula (II), preferably at least 1%. The sum of the mass fractions expressed in% by weight of the various compounds of the absorbent solution is equal to 100% by weight of the absorbent solution.

A non-exhaustive list of activator compounds of general formula (II) is given below: N- (1-octyl) -1,2-ethanediamine; N- (1-decyl) -1,2-ethanediamine; N- (1-dodecyl) -1,2-ethanediamine; N- (1-décyI) -1,3-propanediamine. The absorbent solution may contain at least 10% by weight of water, in general between 10% and 90% by weight of water, very preferably between 50% by weight and 70% by weight of water, for example between 55% to 50% by weight. 69% weight of water. In a very preferred mode, the absorbent solution according to the invention contains from 55% to 69% by weight of water, from 31% to 45% by weight of amines comprising TMHDA mixed with at least one secondary diamine of general formula (II) as an activator, the activator representing between 1% and 10% by weight of the final absorbent solution. In one embodiment, the absorbent solution according to the invention may contain, in addition to the TMHDA and at least one diamine of general formula (II), at least one activator compound containing at least one primary or secondary amine function, selected from the group consisting of: monoethanolamine; diethanolamine; N-butylethanolamine; aminoethylethanolamine; Diglycolamine; piperazine; 1-methyl-piperazine; 2-methylpiperazine; homopiperazine; N- (2-hydroxyethyl) piperazine; N- (2-aminoethyl) piperazine; morpholine; 3- (methylamino) propylamine; 1,6-hexanediamine; N, N'-dimethyl-1,6-hexanediamine; N-methyl-1,6-hexanediamine; N, N ', N'-trimethyl-1,6-hexanediamine.

For example, the absorbent solution comprises between 0.5% and up to a concentration of 15% by weight of the absorbent solution, preferably less than 10% by weight, preferably less than 5% by weight of said activator compound chosen from the list below. above, terminals included. Absorbent solutions according to the invention are particularly useful in the case of CO2 capture in industrial flue gases, or treatment of natural gas containing CO2 above the desired specification. Indeed, for this type of applications, it is sought to increase the capture kinetics of 002, in order to reduce the height of the absorption columns. In one embodiment, the secondary diamine-activated TMHDA-based absorbent solution of the general formula (II) may also include other organic compounds, which are non-reactive with respect to the acidic compounds (commonly referred to as "physical solvents"). , which make it possible to increase the solubility of at least one or more acidic compounds of the gaseous effluent. For example, the absorbent solution may comprise between 5% and 50% by weight of physical solvent such as alcohols, glycol ethers, lactams, N-alkylated pyrrolidones, N-alkylated piperidones, cyclotetramethylenesulfone, N-alkylated alkylformamides, N-alkylacetamides, ethers-ketones or alkyl phosphates and their derivatives. By way of example and without limitation, it may be methanol, tetraethyleneglycoldimethylether, sulfolane or N-formyl morpholine. Process for removing acidic compounds in a gaseous effluent (FIG 1) The implementation of an absorbent solution for deacidifying a gaseous effluent is carried out schematically by carrying out an absorption step followed by a regeneration step . The absorption step consists of contacting the gaseous effluent containing the acidic compounds to be removed with the absorbent solution in an absorption column C1. The gaseous effluent to be treated (1) and the absorbent solution (4) feed the column Cl. During contact, the organic compounds provided with an amine function of the absorbent solution (4) react with the acidic compounds contained in the effluent (1) so as to obtain a gaseous effluent depleted in acidic compounds ( 2) which leaves at the top of column C1 and an acid-enriched absorbent solution (3) which leaves at the bottom of column C1. The absorbent solution enriched in acidic compounds (3) is sent to an exchanger E1, where it is heated by the stream (6) from the regeneration column C2. The absorbent solution charged and heated at the outlet of the exchanger E1 (5) feeds the distillation column (or regeneration column) C2 in which the regeneration of the absorbent solution loaded with acidic compounds takes place. The regeneration step therefore consists in particular in heating and, optionally, expanding, the absorbent solution enriched in acidic compounds in order to release the acidic compounds which come out at the top of column C2 in gaseous form (7). The regenerated absorbent solution, that is to say depleted in acidic compounds (6), leaves at the bottom of the column C2, then passes into the exchanger E1, in which it gives heat to the flow (3) as previously described. . The regenerated and cooled absorbent solution (4) is then recycled to the absorption column C1. The absorption step of the acidic compounds can be carried out at a pressure of between 1 bar and 120 bar, preferably between 20 bar and 100 bar for the treatment of a natural gas, preferably between 1 bar and 3 bar for treatment of industrial fumes, and at a temperature between 20 ° C and 100 ° C, preferably between 30 ° C and 95 ° C, even more preferably between 30 ° C and 90 ° C, and even more preferably included between 30 ° C and 60 ° C. Indeed, the process according to the invention has an excellent capacity of absorption of acidic compounds when the temperature in the absorption column Cl is between 30 ° C and 60 ° C. Generally, the temperature varies in the absorber as a function of the temperature of the introduced fluids and the exothermicity of the reactions. The temperature of the absorbent solution supplying the absorber is such that the solution is monophasic on arrival at the absorber head. It is preferably strictly less than 60 ° C, and still more preferably less than 55 ° C. The regeneration step of the process according to the invention can be carried out by thermal regeneration, optionally supplemented by one or more expansion steps. It is possible to carry out, before the regeneration step, a first step of relaxing the absorbent solution loaded with acidic compounds. It is also possible to perform a second expansion step of the absorbent solution loaded with acid compounds, the second expansion step being carried out after the first expansion step and before the regeneration step, the absorbent solution being heated before undergoing the second step of relaxation. Given the high stability of the TMHDA, it is possible to regenerate the absorbent solution according to the invention at high temperature in a distillation column. In general, the thermal regeneration step is carried out at a temperature of between 100 ° C. and 180 ° C., preferably between 130 ° C. and 170 ° C., and at a pressure of between 1 bar and 10 bar. Preferably, the regeneration in the distillation column is carried out at a temperature of between 155 ° C. and 165 ° C. and at a pressure of between 6 bar and 8.5 bar in the case where it is desired to reinject the acid gases. . Preferably, the regeneration in the distillation column is carried out at a temperature of 115 ° C. and 130 ° C. and at a pressure of between 1.7 bar and 3 bar in the case where the acid gas is sent to the atmosphere. or in a downstream treatment process, such as a Claus process or a tail gas treatment process. Moreover, a demixing phenomenon for a given absorbent solution (separation of liquid-liquid phases within the absorbing solution) can be induced by a rise in temperature. Said demixing phenomenon can be controlled by the choice of the operating conditions of the process and / or the composition of the absorbent solution. In this case, variants (FIG 2) of the process according to the invention can be implemented, in particular a fractional regeneration by heating the absorbent solution. Process for removing acidic compounds in a gaseous effluent with fractional regeneration by heating (FIG 2) The implementation of an absorbent solution for deacidifying a gaseous effluent is carried out schematically by performing an absorption step, followed by a step of heating the absorbent solution, followed by a liquid-liquid separation step of the absorbent solution, followed by a regeneration step. The absorption step comprises contacting the gaseous effluent containing the acidic compounds to be removed with the absorbent solution in a C1 absorption column. The gaseous effluent to be treated (1) and the absorbent solution (4) feed the column C1. During contact, the organic compounds provided with an amine function of the absorbent solution (4) react with the acidic compounds contained in the effluent (1) so as to obtain a gaseous effluent depleted in acidic compounds (2) which comes out in Column head C1 and an absorbent solution enriched in acidic compounds (3) which leaves at the bottom of column C1. The heating step consists in raising the temperature of the absorbent solution (3), for example in a heat exchanger E1, to obtain a two-phase solution (5). The two-phase solution (5) is sent to a decanter BS1, in which the liquid-liquid separation step consists of separating the two phases obtained in the heating step by sending the phase 30 rich in acid gas ( 12) to the regeneration column C2, and returning the lean phase acid gas (14), after possible passage in an exchanger E3, to the absorption column C1. The gas phase released by heating the absorbent solution (3) in the exchanger E1 is separated from the liquid phases in BS1 and discharged through the pipe (13). The regeneration step thus consists in particular in heating in the distillation column C2 and, optionally, in expanding, the absorbent solution enriched in acidic compounds (12) in order to release the acidic compounds which come out at the top of column C2 in gaseous form ( 7). The regenerated absorbent solution, that is to say depleted in acidic compounds (6), leaves at the bottom of the column C2, then passes into the exchanger E1, in which it gives heat to the flow (3) as previously described. . The regenerated and cooled absorbent solution (4), after optional passage in a new exchanger E2, is then recycled to the absorption column C1. At the bottom of the distillation column C2, a portion of the absorbent solution is withdrawn through the conduit (10), heated in the reboiler R1, and then reintroduced into the bottom of the column C2 via the conduit (11).

The absorption step of the acidic compounds can be carried out at a pressure of between 1 bar and 120 bar, preferably between 20 bar and 100 bar for the treatment of a natural gas, preferably between 1 bar and 3 bar for treatment of industrial fumes, and at a temperature between 20 ° C and 100 ° C, preferably between 30 ° C and 95 ° C, even more preferably between 30 ° C and 90 ° C, and even more preferably included between 30 ° C and 60 ° C. Indeed, the process according to the invention has an excellent capacity of absorption of acidic compounds when the temperature in the absorption column Cl is between 30 ° C and 60 ° C. Generally, the temperature varies in the absorber as a function of the temperature of the introduced fluids and the exothermicity of the reactions. The temperature of the absorbent solution supplying the absorber is such that the solution is monophasic on arrival at the absorber head. It is preferably strictly less than 60 ° C, and still more preferably less than 55 ° C.

The regeneration step of the process according to the invention can be carried out by thermal regeneration, optionally supplemented by one or more expansion steps. It is possible to carry out, before the regeneration step, a first step of relaxing the absorbent solution loaded with acidic compounds. It is also possible to perform a second expansion step of the absorbent solution loaded with acid compounds, the second expansion step being carried out after the first expansion step and before the regeneration step, the absorbent solution being heated before undergoing the second step of relaxation. Given the high stability of the TMHDA, it is possible to regenerate the absorbent solution according to the invention at high temperature in a distillation column. In general, the thermal regeneration step is carried out at a temperature of between 100 ° C. and 180 ° C. and at a pressure of between 1 bar and 10 bar. Preferably, the regeneration in the distillation column is carried out at a temperature of between 155 ° C. and 165 ° C. and at a pressure of between 6 bar and 8.5 bar in the case where it is desired to reinject the acid gases. . Preferably, the regeneration in the distillation column is carried out at a temperature of 115 ° C. and 130 ° C. and at a pressure of between 1.7 bar and 3 bar in the case where the acid gas is sent to the atmosphere. or in a downstream treatment process, such as a Claus process or a tail gas treatment process. Examples Absorbent solutions used in these examples are aqueous solutions of TMHDA in combination with a compound of general formula (II). The compounds of general formula (II) used as examples are: N- (1-octyl) -1,2-ethanediamine (OEDA), N- (1-decyl) -1,2-ethanediamine (DEDA) ), N- (1-dodecyl) -1,2-ethanediamine (DoDEDA), N- (1-decyl) -1,3-propanediamine (DPDA).

Table 1 below details the compositions of these examples. Formulation A TMHDA (30% wt) + OEDA (10% wt) + H2O Formulation B TMHDA (30% wt) + DEDA (10% wt) + H2O Formulation C TMHDA (30% wt) + DoDEDA (10% wt) + H2O Formulation D TMHDA (30% wt) + DPDA (10% wt) + H2O Table 1 Absorbent solution is also used in these examples an aqueous solution of TMHDA in combination with a compound of general formula (II), the N- (1-decyl) -1,2-ethanediamine (DEDA) and with piperazine (Pz). This formulation is detailed in Table 2 below: Formulation E TMHDA (30% wt) + DEDA (5% wt) + Pz (5% wt) + H2O Table 2 In the first example described below, it is presented the synthesis protocol of the compounds of general formula II used in the composition of formulations A to E. In the second example described below, it is shown that the physicochemical properties of formulations A to E (ie demixing temperature) at different CO2 loading rates are very different from those of aqueous solutions of TMHDA in combination with a primary or secondary amine not responding to the general formula (II). The aqueous solution chosen for illustration is a solution of TMHDA in combination with piperazine, the composition of which is detailed in Table 3 below. Reference 1 TMHDA (30% wt) + Pz (10% wt) + H20 Table 3 Finally, in the third example described hereinafter, the stability of formulation E is compared with that of an aqueous solution of TMHDA at 35.degree. % weight, and that of an aqueous solution of MonoEthanolAmine at 30% weight. In the formulations given in Tables 1, 2, 3 and 6, the sum of the mass fractions expressed in% by weight of the various compounds and of water is equal to 100% by weight of the absorbent solution. EXAMPLE 1 Synthesis Protocols Synthesis of N- (1-octyl) -1,2-ethanediamine To a solution of 72.0 g (1.2 moles) of ethylenediamine in 150 ml of toluene is added 57.9 g. (0.3 mole) 1-bromooctane in 150 ml ethanol. The medium is kept under reflux with stirring for 3 hours. After returning to ambient temperature, 12.6 g (0.315 mol) of sodium hydroxide in 50 ml of water are added. After filtration, the organic phase is separated, and the aqueous phase is extracted with 4 times 50 ml of ether. The organic fractions are combined and after distillation, 48.6 g of a product whose 13C-NMR spectrum (CDCl3), given below, is consistent with that of N- (1-octyl) -1, are obtained. 2-ethanediamine. 52.1 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH3 49.3 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2 31.2 ppm: H2N-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2 CH2-CH2-CH3 29.6 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH3 28.9 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2- CH2-CH2-CH2-CH3 28.6 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH3 26.7 ppm: H2N-CH2-CH2-NH-CH2-CH2- CH2-CH2-CH2-CH2-CH3 21.9 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH3 13.3 ppm: H2N-CH2-CH2-NH-CH2 -CH2-CH2-CH2-CH2-CH2-CH3 Synthesis of N- (1-decyl) -1,2-ethanediamine To a solution of 72.0 g (1.2 moles) of ethylenediamine in 150 ml of To the ethanol is added 66.3 g (0.3 mole) of 1-bromodecane in 50 ml of ethanol. The medium is kept under reflux with stirring for 3 hours. After returning to ambient temperature, 12.6 g (0.315 mol) of sodium hydroxide in 50 ml of water are added. After filtration, the organic phase is separated, and the aqueous phase is extracted with 4 times 50 ml of ether. The organic fractions are combined and, after distillation, 41.0 g of a product whose 13C-NMR (CDCl3) spectrum given below is consistent with that of N- (1-decyl) -1 are obtained. 2-ethanediamine. 41.1 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 49.3 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 52.1 ppm: H 2 N -CH 2 -CH 2 -NH-CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 31.2 ppm H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 29.6 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2 -CH2-CH2-CH2-CH2-CH3 28.9 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 28.9 ppm: H2N-CH2 -CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 28.9 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2 28.6 ppm: H 2 N -CH 2 -CH 2 -NH-CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 26.7 ppm: H 2 N -CH 2 -CH 2 -NH -CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 21.9 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2 13.4 ppm: H2N-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 Synthesis of N- (1-dodecyl) -1,2-ethanediamine To a solution of 72.0 g (1.2 moles) of ethylenediamine in 150 ml of ethanol is added 74.7 g (0.3 moles) of 1-bromododecane in 50 ml of ethanol. The medium is kept under reflux with stirring for 3 hours. After returning to ambient temperature, 12.6 g (0.315 mol) of sodium hydroxide in 50 ml of water are added. After filtration, the organic phase is separated off, and after distillation, 40.0 g of a product whose 13C-NMR (CDCl3) spectrum is in conformity with that of N- (1-dodecyl) -1,2-ethanediamine are obtained. . Synthesis of N- (1-decyl) -1,3-propanediamine To a solution of 83.6 g (1.1 moles) of 1,3-propanediamine in 150 ml of ethanol is added 50.0 g (0.22 g). mole) of 1-bromodecane in 50 ml of ethanol. The medium is kept under reflux with stirring for 3 hours. After returning to ambient temperature, 9.5 g (0.23 mol) of sodium hydroxide in 50 ml of water are added. After filtration, the organic phase is separated, and after distillation 20.0 g of a product whose 13C-NMR spectrum (CDCl3), given below, is obtained in accordance with that of N- (1-decyl). -1,3-propanediamine. 40.1 ppm: H2N-CH2-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 33.4 ppm: H2N-CH2-CH2-CH2-NH-CH2 47.4 ppm: H2N-CH2-CH2-CH2-NH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2 49.6 ppm: H2N-CH2-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 31.3 ppm: H2N-CH2-CH2-CH2-NH 29.6 ppm: H 2 N -CH 2 -CH 2 -CH 2 -NH-CH 2 -CH 2 -CH 2 -CH 2 CH 2 -CH 3 29.0 ppm: H 2 N -CH 2 -CH 2 -CH 2 -NH-CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 29.0 ppm: H 2 N -CH 2 -CH 2 -CH 2 -NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 29.0 ppm: H2N-CH2-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2 28.7 ppm: H 2 N -CH 2 -CH 2 -CH 2 -NH-CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 26.8 ppm: H 2 N -CH 2 -CH 2 -CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 22.1 ppm: H2N-CH2-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2 13.5 ppm: H2N-CH2-CH2-CH2-NH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3-CH3-CH3-CH2-CH2-CH2-CH3 Example 2: Demixing temperatures. Effect of CO2 charge rate. The demixing phenomenon can be controlled by the nature of the activator that is added to an aqueous solution of TMHDA.

Depending on the composition of the absorbent solution based on TMHDA, the possible presence of a primary or secondary amine, the composition of the gas to be treated (ie the partial pressure of 002) and the temperature of the absorbent solution, a liquid phase separation -liquid can occur (demixing phenomenon). In the laboratory, the temperature at which demixing occurs for a given formulation (ie concentrations of amines and given water) is determined at a given loading rate (expressed in moles of CO2 per kg of formulation before loading) by increasing gradually the temperature. Each formulation is first charged with CO2 at room temperature by sweeping about 30 g of a virgin formulation sample with a flow rate of 20NL / h of CO2 until a loading rate of 2 moles of CO2 per kg is reached. virgin solution, the rate of charge being controlled by weighing. About 15 g of the resulting charged solution is mixed with the corresponding amount of virgin solution to obtain a solution having a feed rate of 1 mole of CO2 per mole of virgin solution. For each formulation, three samples corresponding to the virgin solution, the solution charged with CO2 at 1 mol / kg and at 2 mol / kg are immersed in a thermostatically controlled oil bath whose temperature is regulated to within one degree Celsius. . For each solution, the temperature at which a phase separation is observed, in successive temperature increments, from 40 ° C to 55 ° C, in increments of 5 ° C, from 55 ° C to 65 ° C in increments of 1 ° C, and 65 ° C to 95 ° C, in increments of 5 ° C.

According to the results of these laboratory tests, the absorbing solution can be implemented in a deacidification process as described in FIG. 1, or in a deacidification process with split regeneration by heating, as described in FIG. The examples below make it possible to demonstrate the importance of the structure of the activator, of the respective concentration of the activator according to the invention and of another activator according to the prior art. 2-N Structure of the activator The laboratory tests are carried out for formulations having a total concentration of 40% by weight of amines: 30% by weight of TMHDA and 10% of a secondary diamine corresponding to the general formula (II) ) in the case of formulations A to D, and - 30% by weight of TMHDA and 10% by weight of piperazine in the case of reference formulation 1. Table 4 below summarizes the results obtained for different formulations.

Temperature at which phase separation is observed (° C) Blank solution Charge rate: Charge rate: 1 mole CO2 / kg 2 mole CO2 / kg Reference 1 55 25 25 Formulation A 65 Single phase at 95 ° C Single phase at 95 ° C Formulation B 60 Single phase at 95 ° C Single phase at 95 ° C Formulation C 60 Single-phase at 95 ° C Single-phase at 95 ° C Formulation D 60 Single-phase at 95 ° C A single phase at 95 ° C Table 4 It can be observed from Table 4 above that an amount equal to 10% by weight of an activator of general formula (II) makes it possible to completely eliminate the demixing phenomenon in the operating conditions of the absorber, the latter being observed in the case of the reference formulation containing an activator not corresponding to the general formula (II) (piperazine). Indeed, the temperature in the absorber generally varies between the temperature of the virgin amine feeding the absorber, preferably strictly less than 60 ° C, and a maximum temperature generally not exceeding 95 ° C, and preferably between 30 ° C and 60 ° C. Formulations A to D are therefore of interest since they make it possible to have a monophasic absorbent solution under the operating conditions corresponding to the absorber. Formulations A to D loaded at 2 mol / kg, that is under conditions characteristic of the outlet of the charge / effluent exchanger, are monophasic at 95 ° C., and are therefore particularly advantageous for being used in a deacidification process. as described in FIG. 1. 2-B / Composition of the solution of activator compounds (mixture of piperazine and an activator of general formula (II)) The laboratory tests are carried out for a formulation E having a total concentration of 40% by weight of amines: 30% by weight of TMHDA and 10% by weight of a mixture of a secondary diamine corresponding to the general formula (II) and piperazine. This formulation E is compared with reference 1 containing 30% by weight of TMHDA and 10% by weight of piperazine (Pz), as well as with formulation B containing 30% by weight of TMHDA and 10% by weight of secondary amine according to the formula ( II).

Composition of the activators (in% Temperature at which a weight of the absorbing solution is observed) phase separation (° C) According to the formula Other Blank solution 1 mole CO2 / kg 2 mole CO2 / kg general (II) Reference 1 0 Pz 10 % 55 25 25 Formulation B DEDA 10% 0 60 One single 95 phase single phase 95 Formulation E DEDA 5% Pz 5% 56 64 85 Table 5 It can be seen from Table 5 above that between 5% and 10% of the activators of general formula (II) in combination with piperazine to reach a total activator concentration of 10% by weight (formulation E) makes it possible to completely eliminate the demixing phenomenon under the operating conditions of the absorber which is observed in the case of reference formulation 1 containing as sole activator piperazine at a concentration of 10% by weight. Formulation E is therefore advantageous because it makes it possible to have a monophasic absorbent solution under the operating conditions corresponding to the absorber.

Formulation E charged to 2 mol / kg, that is to say under conditions characteristic of the outlet of the charge / effluent exchanger, is two-phase at a temperature greater than or equal to 90 ° C., typically encountered after the passage in the charge / effluent exchanger in a deacidification process, and is therefore particularly advantageous for being carried out in a deacidification process with fractional regeneration by heating, as described in FIG. 2. In this example, it can be seen that the combination of piperazine with an activator corresponding to the general formula (II) (formulation E) lowers the demixing temperature for a given loading rate, while maintaining the monophasic solution under the conditions of the absorber whatever the charge rate .

A liquid-liquid phase separation occurs at 85 ° C in the case of formulation E containing 5% by weight of piperazine and 5% by weight of DEDA and loaded at 2 mole / kg, while formulation B containing 10% of DEDA is monophasic at 95 ° C for the same charge rate. While formulation B is monophasic at 95 ° C, the proportion of higher liquid phase (lean phase) is 43% by volume for formulation E at the same temperature. Formulation E is therefore particularly advantageous for being used in a deacidification process with fractional regeneration by heating as described in FIG. 2, in which a decantation step after passage through the charge-effluent exchanger operating at 95 ° C. would reduce the flow of solvent in the regenerator by 43% compared to the formulation B used in a deacidification process as described in FIG. 1. Example 3: Stability The TMHDA molecule has the particularity of being very resistant to degradation that may occur in a deacidification unit. Activators of general formula (II) also have the distinction of being very resistant to damage that may occur in a deacidification unit.

By way of example, the formulation E according to the invention is compared with an aqueous solution at 30 ° A> weight of monoethanolamine (MEA) and an aqueous solution at 35% by weight of TMHDA. This example shows that the stability of formulations containing activators according to the invention in combination with TMHDA is comparable to the stability of a solution of TMHDA without activator. It also demonstrates that the formulations according to the invention have a significantly improved stability compared to a MEA solution at 30% by weight. The degradation tests of an amine in aqueous solution are carried out according to the following procedure: 100 g of absorbing solution are placed in a glass reactor surmounted by a condenser to prevent evaporation of the water. The reactor is heated to 80 ° C in an electric heating block. The solution is stirred at 1000 rpm by a magnetic bar. The presence of counter blades prevents the formation of a vortex. A gas is brought into contact with the solution by means of a dip tube for 7 days at atmospheric pressure. The gas flow rate entering the dip tube is a mixture of a gas flow rate of 0.033 Nl / h of CO2 and 7 Nl / h of atmospheric air. This gaseous mixture, produced in a mixing chamber, contains CO2, nitrogen and oxygen, the oxygen content in the gas being about 21%. Gas chromatographic analysis of the absorbent solution tested is carried out before the test and at the end of the test. The chromatographic method uses a polar column, a carrier gas, helium and FID (Flame Induced Detection) detection. This analysis makes it possible to determine a proportion of degradation products that appeared during the test. This proportion of the degradation products (% PD) formed is expressed in percentages of areas of the peaks observed on the chromatogram. It can therefore be calculated as follows: PD - r Total Area - Ame rs Area r Total Area - Ame nt Area Total Area Total Area, 1 End of Test / Before Test Amine Area main peak area for a 30 wt% MEA solution or a 35 wt% TMHDA solution or the sum of the areas of the three main peaks in the case of formulation E containing 30 wt% TMHDA, 7 wt% secondary diamine according to general formula (II) and 3% by weight of piperazine.

In the case of the pre-test solution, the difference between the total area and the main peaks comes from the impurities of each amine. In the case of the solution after the test, the difference between the total area and the main peaks comes from the impurities and degradation products formed during the test, the latter therefore being evaluated by the formula above. Table 6 below shows the percentages of formed degradation products visible by the chromatographic method. Formulation% PD MEA 30% + H2O 23% TMHDA 35% + H2O 1% TMHDA 30% + DEDA 5% + Pz 5% + H2O (Formulation E according to the invention) 1, 8% Table 6 The results in Table 6 confirm the aqueous solutions according to the invention have a comparable stability to a solution of TMHDA without activators, and about 20 times more stable than a solution of MEA at 30% by weight.

It is clear that the activators according to the invention mixed with piperazine and TMHDA do not modify the stability of the formulation with respect to a solution of TMHDA without activator at 80 ° C. in the presence of CO2 and oxygen. The formation of degradation products detected by gas chromatography reaches, for a total concentration of 40% by weight of amines with activators, a level comparable to that observed for a solution containing 35% by weight of TMHDA without activators. to say close to 1%, is considered of the order of uncertainty of the measure which is 0.3%. Since the TMHDA molecule is interesting for its resistance to degradation, in particular thermal and in the presence of oxygen, it may be advantageous to use it in combination with a diamine of general formula (II), to regenerate the solvent at a higher temperature. and therefore obtain an acid gas at higher pressure if this is of interest in the case of reinjection of acid gas. This is particularly interesting in the case of post-combustion CO2 capture where the gas to be treated contains oxygen and where the acid gas must be compressed before reinjection and sequestration. The use of an aqueous absorbent solution according to the invention makes it possible to save on the operating costs of the deacidification unit, and on the investment cost and the operating costs associated with the compression of the acid gas.

Claims (15)

REVENDICATIONS1. Absorbent solution for absorbing acidic compounds of a gaseous effluent comprising: - water - N, N, N ', N'-tetramethyl-1,6-hexanediamine of formula (I), NN (I) at least one activator compound chosen from secondary diamines corresponding to the following general formula (II): ## STR2 ## in which: R 1 is a linear or branched alkyl or cycloalkyl group of 8 to 18 carbon atoms, the groups R2, R3, R4 and R5 are chosen independently from one of the elements of the group consisting of: a hydrogen atom and an alkyl group of 1 to 4 carbon atoms, the R6 and R7 groups are chosen independently among one of the elements of the group consisting of: a hydrogen atom and an alkyl group of 1 to 4 carbon atoms, - a is an integer between 1 and 5, including extreme values. An absorbent solution according to claim 1, comprising from 10% to 90% by weight, preferably from 20% to 60% by weight, of N, N, N ', N'-tetramethyl-1,6-hexanediamine, and an amount of non-zero and less than 50% by weight, preferably less than 30% by weight, of said at least one activator compound according to general formula (II). 3. Absorbent solution according to one of claims 1 and 2, comprising from 10% to 90% by weight of water, preferably from 50% to 70% by weight of water. 4. Absorbent solution according to one of the preceding claims, comprising a mass fraction of water between 55% and 69% by weight of the absorbent solution, and a mass fraction of amines between 31% and 45% by weight of the solution. absorbent, said mass fraction of amines comprising a mixture of N, N, N ', N'-tetramethyl-1,6-hexanediamine and 1% and 10% by weight of said at least one activator compound according to general formula (II) . 5. Absorbent solution according to one of the preceding claims, wherein the activator compound of general formula (II) is selected from the group consisting of: - N- (1-octyI) -1,2-ethanediamine H 1 \ 11 N- (1-Decyl) -1,2-ethanediamine H NH 2 - N- (1-dodecyl) -1,2-ethanediamine H - N- (1-decyl) -1,3-propanediamine H H2 Absorbent solution according to one of the preceding claims, further comprising at least one additional activator compound comprising a primary or secondary amine function, preferably in an amount of less than 15% by weight of the absorbent solution selected from the group consisting of : monoethanolamine; diethanolamine; N-butylethanolamine; aminoethylethanolamine, diglycolamine; piperazine; 1-methyl-piperazine; 2-methylpiperazine; homopiperazine; N- (2-hydroxyethyl) piperazine; N- (2-aminoethyl) piperazine; morpholine; 3- (methylamino) propylamine; 1,6-hexanediamine; N, N'-dimethyl-1,6-hexanediamine; N-methyl-1,6-hexanediamine; N, N ', N'-trimethyl-1,6-hexanediamine 7. A process for removing the acidic compounds contained in a gaseous effluent, in which is carried out: a step of absorption of the acidic compounds by contacting the effluent with an absorbent solution according to one of claims 1 to 6; so as to obtain a gaseous effluent depleted of acidic compounds and an absorbent solution loaded with acid compounds, - then a regeneration step in which at least a portion of the solution charged with acidic compounds is sent to a distillation column to release the compounds acids in the form of a gaseous effluent and obtain a regenerated absorbent solution. 8. The method of claim 7, wherein the absorbent solution loaded with acid compounds obtained during the absorption step is monophasic. 9. Method according to one of claims 7 and 8, wherein the absorption step of the acidic compounds is carried out at a pressure between 1 bar and 120 bar, and at a temperature between 20 ° C and 100 ° C . The process according to claim 9, wherein the step of absorbing the acidic compounds is carried out at a temperature of between 30 ° C and 95 ° C, preferably between 30 ° C and 60 ° C. 11. The method according to one of claims 7 to 10, wherein the regeneration step is carried out at a pressure of between 1 bar and 10 bar and a temperature of between 100 ° C and 180 ° C. 12. Method according to one of claims 7 to 11, wherein is carried out, before the regeneration step, a first step of expansion of the absorbent solution loaded with acidic compounds. 13. Method according to one of claims 7 to 12, wherein the absorption step is followed by at least one liquid-liquid separation step of the absorbent solution loaded with two-phase acidic compounds obtained after heating the absorbent solution. and then at least one step of fractional regeneration of the absorbent solution loaded with acidic compounds. 14. Process for treating natural gas according to one of claims 7 to 13. 15. Process for the treatment of industrial gases according to one of claims 7 to 13, preferably for the capture of 002.15