WO2011138517A1

WO2011138517A1 - Absorbent solution based on ν,ν,ν',ν'-tetraethyl diethylenetriamine and method for removing acid compounds from a gaseous effluent

Info

Publication number: WO2011138517A1
Application number: PCT/FR2011/000218
Authority: WO
Inventors: Marc Jacquin; Marco De Oliveira Aleixo
Original assignee: IFP Energies Nouvelles
Priority date: 2010-05-06
Filing date: 2011-04-14
Publication date: 2011-11-10
Also published as: FR2959675A1; FR2959675B1

Abstract

The invention relates to the removal of acid compounds in a gaseous effluent in an absorption process using an aqueous solution of Ν,Ν,Ν',Ν'-tetraethyl diethylenetriamine. The invention can be advantageously used for processing natural gas and gases of industrial origin.

Description

ABSORBENT SOLUTION BASED ON Ν, Ν, Ν ', Ν'-

TETRAETHYLDIETHYLENETRIAMINE AND METHOD FOR REMOVING ACIDIC COMPOUNDS FROM A GASEOUS EFFLUENT

The present invention relates to the capture of acidic compounds (H ₂ S, C0 ₂ , COS, CS ₂ , mercaptans, etc.) contained in a gas by means of a particular triamine, Ν, Ν, Ν ', Ν'. -Tetraethyldiethylenetriamine, in the form of an absorbent aqueous solution. The invention is advantageously applicable to the treatment of natural gas and gas of industrial origin.

In order to limit the phenomenon of global warming, carbon dioxide is extracted from combustion fumes in order to be sequestered in an underground reservoir. In the case of natural gas, the content of carbon dioxide and hydrogen sulphide is reduced, for reasons of toxicity, to improve the calorific value of the gas and possibly to allow the liquefaction of natural gas for transport by ship.

Absorption processes employing an aqueous amine solution are commonly used to remove the acidic 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.

Absorbent solutions commonly used today are aqueous solutions of primary, secondary or tertiary alkanolamine, optionally in combination with a physical solvent. For example, document FR 2 820 430 can be cited which proposes processes for deacidification of gaseous effluents. No. 6,852,144, which describes a method for eliminating the acidic compounds of 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 C0 ₂ capture, the absorbed C0 ₂ reacts with the alkanolamine 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 elimination of C0 ₂ in the gas to be treated.

Similarly, for the removal of H ₂ S in the gas to be treated, the absorbed H ₂ S reacts with the alkanolamine present in solution according to a reversible exothermic reaction, well known to those skilled in the art and leading to the formation of hydrogen sulfide.

An essential aspect of the operations of treatment of gases or industrial fumes by absorbent solution resides in the regeneration of the separating agent. Depending on the type of absorption (physical and / or chemical), regeneration is generally carried out by expansion, and / or by distillation and by entrainment by a vaporized gas called "stripping gas".

One of the limitations of the absorbent solutions commonly used today is an energy consumption necessary for the regeneration of the absorbent solution which is too important. This is particularly true in the case where the partial pressure of acidic compounds is low. For example, for a 30% weight aqueous solution of MonoEthanolAmine used for the capture of C0 ₂ in post-combustion in a thermal power plant smoke, where the partial pressure of C0 ₂ is of the order of 0.12 bar, The regeneration energy represents about 3.7 GJ per tonne of CO ₂ captured. Such energy consumption represents a considerable operating cost for the C0 ₂ capture process.

It is well known to those skilled in the art that the energy required for the regeneration by distillation of a chemical absorbent solution can be broken down into three different positions: the energy required to heat the absorbing solution between the head and the bottom of the regenerator, the energy required to lower the partial pressure of acidic compounds in the regenerator by vaporizing a stripping gas, and finally the energy necessary to break the chemical bond between the amine and the acid compound.

These first two stations are inversely proportional to the flow rates of absorbent solution that it is necessary to circulate in the unit to achieve a given specification. To reduce the energy consumption associated with the regeneration of the absorbent solution, it is therefore preferable to maximize the cyclic capacity of the absorbent solution.

The last item concerns the energy to be supplied to break the bond created between the amine used and the acid compound. To reduce the energy consumption associated with the regeneration of the absorbent solution, it is therefore preferable to minimize the ΔΗ linkage enthalpy. Nevertheless, it is not obvious to find an amine having a high cyclic capacity and a low reaction enthalpy. The best amine from an energy point of view is therefore that which has the best compromise between a strong cyclic capacity Δα and a low enthalpy of connection ΔΗ.

It is difficult to find an absorbent compound for removing acidic compounds in any type of effluent, and allowing the deacidification process to operate at a lower cost. Surprisingly, the Applicant has discovered that Ν, Ν, Ν ', Ν'-TetraEthylDiEthyleneTriAmine, commonly named TEDETA, is of great interest in all processes for treating gaseous effluents for the removal of acidic compounds.

In general, the present invention proposes a process for removing acidic compounds contained in a gaseous effluent in which an absorption step of the acidic compounds is carried out by contacting the gaseous effluent with an absorbent solution comprising:

- water, and

- Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine of formula:

According to the invention, the absorbent solution may comprise between 10% and 90% by weight of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine and between 10% and 90% by weight of water.

The absorbent solution may 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,

aminoethylethanolamine

diglycolamine,

piperazine

N- (2-hydroxyethyl) piperazine,

N-Methyl piperazine,

N-ethylpiperazine

N-propylpiperazine,

1,6-hexanediamine,

1,1,9,9-TetraMéthylDiPropylèneTriamine,

morpholine

piperidine

3- (methylamino) propylamine,

N-methylbenzylamine

Tetrahydroisoquinoline.

The absorbent solution may further comprise a physical solvent.

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 acid compounds can be carried out.

In the regeneration step, at least the following operations can be performed:

a) the absorbent solution loaded with acidic compounds is heated to cause the formation of two liquid phases, then ^"

b) separating the absorbent solution loaded with acidic compounds into two liquid fractions by phase separation to obtain a fraction enriched in acidic compounds and a depleted fraction in acidic compounds, then

c) recycling said depleted fraction of acidic compounds to form at least a portion of the absorbent solution implemented in the absorption step.

In addition, in the regeneration step, the following operation d) can be performed:

d) regenerating said fraction enriched in acidic compounds to obtain a regenerated fraction, and

in this case in step c), the depleted fraction can be recycled to acidic compounds and the regenerated fraction to form at least a portion of said absorbent solution implemented at the absorption step.

In step a), the absorbent solution loaded with acidic compounds can be heated at a temperature between 70 ° C and 110 ° C.

The process according to the invention can be implemented to treat one of the following gaseous effluents: natural gas, synthesis gases, combustion fumes, refinery gases, gases obtained at the bottom of the Claus process, Biomass fermentation gas, cement gas, incinerator fumes. For example, the gaseous effluent is a combustion smoke having a CO ₂ partial pressure of less than 200 mbar.

The present invention also relates to an absorbent solution for absorbing acidic compounds contained in a gaseous effluent, comprising an aqueous solution of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine.

The absorbent solution may comprise between 10% and 90% by weight of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine 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 can be chosen from the group formed by:

MonoEthanolAmine,.

aminoethylethanolamine

diglycolamine,

piperazine N- (2-hydroxyethyl) piperazine,

N-methyl piperazine,

N-ethylpiperazine

N-propylpiperazine,

1,6-hexanediamine,

1,1,9,9-TetraMéthylDiPropylèneTriamine,

morpholine

piperidine

3- (methylamino) propylamine,

N-methylbenzylamine

Tetrahydroisoquinoline.

The absorbent solution may further comprise a physical solvent.

The use of TEDETA to absorb acidic compounds, such as C0 ₂ , H ₂ S, COS, CS ₂ and mercaptans, contained in a gas makes it possible to limit the flow of absorbent solution used, from its high capacity, especially at low partial pressure of acidic compounds. Moreover, this amine has a relatively low reaction enthalpy. Finally, in a particular embodiment, the flow rates of absorbent solution can be further reduced, further reducing the costs associated with the regeneration of the solvent.

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, among which:

FIG. 1 represents the structural formula of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine,

FIG. 2 represents a schematic diagram of a process for the treatment of effluents containing acidic compounds,

FIG. 3 represents a schematic diagram of an effluent treatment process containing acidic compounds with fractional regeneration by heating.

The Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine, or TEDETA, is of interest in all acid gas treatment processes (natural gas, combustion fumes, etc.), in an aqueous absorbent solution composition. The present invention proposes to eliminate the acidic compounds of a gaseous effluent by using an absorbent compound in aqueous solution. The absorbent compound according to the invention, Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine, has an absorption capacity of acid gases (CO ₂ , H ₂ S, COS, SO ₂ , CS ₂ and mercaptans) which is larger. than the alkanolamines conventionally used. Indeed, Ν, Ν, Ν 'Ν'-Tétraéthyldiéthylènetriamine has the particularity to have a loading rate = n acid _gas / _n mine (a denotes the ratio between the number of moles of acid compounds absorbed n _{gas acid} by a portion of absorbent solution relative to the number of moles of amine _amine contained in said portion of absorbing solution) very important at low partial pressures of acidic compounds, for example at a CO ₂ partial pressure of less than 0 , 2 bar, compared to conventionally used alkanolamines. 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 deacidification unit in natural gas treatment and C0 ₂ capture applications contained in a smoke of combusion.

Synthesis of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine

The TEDETA used according to the invention may be prepared according to various synthetic routes known to those skilled in the art, which are diagrammed below:

For more details on how TEDETA is synthesized, refer to the following documents:

• Bulletin of the Chemical Society of France (1969), (4), 1161-70;

• Journal of the American Chemical Society (1954), 76, 303-5.

Nature of gaseous effluents

The absorbent solutions according to the invention can be used to deacidify the following gaseous effluents: natural gas, synthesis gases, combustion fumes, refinery gases, gases obtained at the bottom of the Claus process, the gases of fermentation of biomass, cement gas, incinerator fumes. These gaseous effluents contain one or more of the following acidic compounds: C0 ₂ , H ₂ S, mercaptans, COS, CS ₂ .

The present invention is particularly well adapted to the capture of CO ₂ 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 C0 ₂ capture unit according to the invention aims to reduce by 90% the C0 ₂ 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, TEDETA is well adapted to absorb C0 ₂ contained in combustion fumes comprising a low partial pressure of CO _{2 /} for example a CO ₂ partial pressure of less than 200 mbar.

The invention is also well suited to deacidify a natural gas. The natural gas consists mainly of gaseous hydrocarbons, but can contain several of the following acidic compounds: CO ₂ , H ₂ S, mercaptans mainly methyl mercaptan (CH ₃ SH), ethyl mercaptan. (CH ₃ CH ₂ SH) and propyl mercaptans (CH ₃ CH ₂ CH ₂ SH), COS, CS ₂ . The content of these compounds acid is very variable and can be up to 40% for C0 ₂ and H ₂ S. 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 and 120 bar. The invention can be implemented to achieve specifications generally imposed on the deacidified gas, which are 2% of C0 ₂ , or even 50 ppm of CO ₂ to subsequently liquefaction of natural gas and 4 ppm H ₂ S and 10 to 50 ppm total sulfur volume.

Composition of the absorbent aqueous solution

The Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine may be in a 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. .

The absorbent solution may contain between 10% and 90% by weight of water, preferably between 40% and 80% by weight of water, very preferably between 50% and 70% by weight of water.

In one embodiment, Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine may be formulated with an activator. Preferably, this activator is chosen 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 of TEDETA can vary up to a maximum concentration of 20% by weight. Preferably, the activator content is limited to a value of less than 15% by weight, preferably less than 10% by weight. This type of formulation is particularly interesting in the case of capture of C0 ₂ in industrial fumes, or the treatment of natural gas containing C0 ₂ above the desired specification. Indeed, for this type of application, the primary or secondary amine function of the activator makes it possible to increase the capture kinetics of C0 ₂ by Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine, in order to reduce the size 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,

- AminoEthylEthanolAmine,

- DiGlycolAmine,

- Piperazine,

N- (2-Hydroxyethyl) piperazine,

N- (2-Aminoethyl) piperazine,

- N-MethylPiperazine,

N-ethylpiperazine

- N-PropylPiperazine,

1,6-HexaneDiAmine,

1,1,9,9-TetraMethylDiPropylenetriamine,

morpholine

- Piperidine,

3- (MetylAmino) PropylAmine,

- N-MethylBenzylAmine,

- TetraHydroIsoquinoline.

In one embodiment, the absorbent solution of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine contains other organic compounds. Thus, the absorbent solution according to the invention may contain organic compounds which are not reactive with respect to acidic compounds (commonly called "physical solvents"), which make it possible to increase the solubility in the absorbent solution of at least one or several 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-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. 2)

The implementation of an aqueous solution of TEDETA for deacidifying a gaseous effluent is carried out by performing an absorption step followed by a step. regeneration, for example by implementing the method of removal of acid compounds in a gaseous effluent shown schematically in Figure 2.

With reference to FIG. 2, the absorption step consists in bringing the gaseous effluent 1 into contact with the absorbent solution 4. The gaseous effluent 1 is introduced at the bottom of Cl, the absorbing solution is introduced at the top of Cl . The column Cl is provided with means of contacting between gas and liquid, for example a _^ bulk packing, structured packing or distillation trays. During contact, the amino functions of the TEDETA molecules of the absorbing solution react with the acidic compounds contained in the effluent so as to obtain a gaseous effluent depleted of acidic compounds 2 discharged at the top of Cl and an acid-enriched absorbent solution. 3 evacuated at the bottom of Cl to be regenerated.

The regeneration step consists in particular in heating and, optionally, in expanding, the absorbent solution enriched in acidic compounds in order to release the acidic compounds in gaseous form. The absorbent solution enriched in acidic compounds 3 is introduced into the heat exchanger E1, where it is heated by the stream 6 coming 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 the column C2, under the effect of contacting the absorbent solution arriving by 5 with the vapor produced by the reboiler, the acid compounds are released in gaseous form and discharged at the top of C2 through the pipe 7. The solution regenerated absorbent 6, that is to say depleted of acidic compounds 6 is cooled in El, then recycled to the column Cl through line 4. A demixing phenomenon for an absorbent solution of TEDETA, that is to say a separation of liquid-liquid phases within the absorbing solution, can be induced by an increase of the temperature, for charge rates of variables of the absorbent solution. Said demixing phenomenon can be controlled by the choice of the operating conditions of the process and / or the composition of the absorbent solution.

The demixing phenomenon can be exploited, in a variant of the process according to the invention (an example of which is described with reference to FIG. 3), by carrying out a fractional regeneration of the absorbing solution.

Process for removing acidic compounds in a gaseous effluent with fractional regeneration by heating (Fig. 3)

The absorbent compound according to the invention, Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine, has the particularity of being able to be used in a deacidification process with fractional regeneration by heating, for example as described by document F 2,898,284

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, for example by implementing the process for removing the acidic compounds in a gaseous effluent schematized in FIG.

With reference to FIG. 3, the absorption step consists in bringing the gaseous effluent 1 into contact with the absorbent solution 4. The gaseous effluent 1 is introduced at the bottom of Cl, the absorbent solution is introduced at the top of the Cl. The column C1 is provided with means for contacting gas and liquid, for example loose packing, structured packing or distillation trays. During contact, the amino functions of the TEDETA molecules of the absorbing solution react with the acidic compounds contained in the effluent so as to obtain a gaseous effluent depleted of acidic compounds 2 discharged at the top of Cl and an acid-enriched absorbent solution. 3 evacuated at the bottom of Cl to be regenerated. The regeneration step consists in particular in heating and, optionally, in expanding, the absorbent solution enriched in acidic compounds in order to release the acidic compounds in gaseous form. The absorbent solution enriched in acidic compounds 3 is introduced into the heat exchanger E1, where it is heated by the stream 6 coming from the regeneration column C2. The heated solution at the outlet of El is introduced into the flask BS1.

The heating step consists in raising the temperature of the absorbent solution 3, passing through the heat exchanger E1, to obtain a two-phase solution 5. According to the invention, the aqueous solution of TEDETA has the property of forming two separable phases when heated above a threshold temperature which depends on the loading rate of acid compounds. Preferably, the absorbent solution is heated to a temperature above 70 ° C, preferably above 8 ° C. For example, it is heated to a temperature between 70 ° C and 110 ° C, preferably between 80 ° C and 100 ° C. Then a separation of the solution 2 into two liquid fractions is carried out in the flask BS1: a fraction enriched in acidic compounds and a fraction depleted in acidic compounds. The liquid-liquid separation step consists of separating the two phases obtained following the heating step by sending the fraction rich in acid compounds 12 to the regeneration column C2, and returning the lean fraction 14 to the column The fraction 14 can be cooled in the exchanger E3 before being introduced into the column C1 through the conduit 4. A gaseous fraction 13 can be released during the separation step and discharged at the head of the balloon. MB1.

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 the contacting of the absorbent solution arriving at 12 with the vapor produced by the reboiler, the acid compounds are released in gaseous form and discharged at the top of C2 through line 7. The regenerated absorbent solution 6, that is to say depleted in acidic compounds 6 is cooled in El, optionally in E2, and then recycled to column C1 via line 4. The deacidification processes according to the invention, in particular the processes described with reference to FIGS. 2 and 3, can be operated according to the operating conditions described below.

The absorption step of the acidic compounds, in the Cl column, 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 and 3 bars for the treatment of industrial fumes, and at a temperature between 30 ° C and 90 ° C.

The regeneration in column C2 can be carried out at a pressure of between 1 bar and 5 bar, or even up to 10 bar and at a temperature of between 100 ° C. and 180 ° C., preferably between 130 ° C. and 170 ° C.

Examples:

In the examples presented below, two aqueous solutions of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine are used, respectively at 30% by weight and 50% by weight. The performance of these absorbent solutions is compared to that of an aqueous solution of MonoEthanolAmine at 30% by weight, which constitutes the reference solvent for a post-combustion fume capture application, and that of an aqueous solution of 40% of methyl-ethanolamine. % weight which constitutes the reference absorbent solution for a natural gas treatment application.

Example 1: Capture Capacity

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 cm ³ by injections of pure CO ₂ from a reserve. The aqueous amine solution is previously drawn under vacuum before any CO ₂ injection. The pressure of the gas phase in the reactor is then monitored as a function of time following the CO ₂ injections. An overall material balance in the gas phase makes it possible to measure the charging rate of the absorbent solution, a corresponding to the number of moles acid gas absorbed by the _{∞2 η} solution divided by the number of moles of amine of the absorbent solution n _a m _in e-

By way of example, the charge levels obtained at 40 ° C. for different partial pressures of CO ₂ are compared between two absorbent solutions according to the invention, a 30% by weight absorbent solution of MonoEthanolAmine and an absorbent solution of MethylDiEthanolAmin. 40% by weight: Charge rate a = nn

Amine Concentration T (° C) ΡΡ∞2 - ΡΡ∞2 - PPc02 -

0.1 bar 0.3 bar 1 bar

TE D ETA 30% weight 40 1.7 1.9 2

TE D ETA 50% weight 40 1.4 1.4 1.7 X

MEA 30% weight 40 0.52 0.55 0.6

MDEA 40% wt 40 0.3 0.5 0.7 note: the value x for TEDETA 30% wt. At PP _C o2 = 1 bar was not measured.

This example shows the significant loading rates that can be obtained thanks to an absorbent solution according to the invention, comprising 30 and 50% by weight of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine, especially for low partial pressures of acid gases. . It is also possible to compare the capacity of the absorbent solution, not in terms of feed rate, but in mole of CO ₂ per kilogram of aqueous amine solution (mol / kg), which is a more meaningful quantity for the process, since sets the flow rates of absorbent solution in the unit. The number of mol _C o2 / kg is expressed from the charge rate a by the following relation:

α · 10 · ί]

molC02 / kg = -

M

where [A] is the concentration of amine in weight%, and M is the molar mass of the amine.

Again, taking into account the concentration and the molar mass of the amine, it is seen that an absorbent solution based on TEDETA is more efficient than an absorbent solution based on MEA or MDEA. If we go into more detail, we note that a solution of 30% by weight TEDETA and a MEA solution at 30% weight or C0 ₂ capture capacities, in mol of C0 ₂ per kilogram of absorbing solution , almost equivalent. Nevertheless, TEDETA has an enthalpy of reaction with respect to C0 ₂ which is of the order of 70 kJ / mol, whereas MEA has an enthalpy of reaction with respect to C0 ₂ of the order of 90 kJ / mol. . The use of TEDETA thus allows a better compromise between C0 ₂ capture capacity and reaction enthalpy.

Example 2 Liquid-Liquid Phase Separation

Depending on the composition of the absorbent solution based on Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine, the composition of the gas to be treated and the temperature of the absorbent solution, liquid-liquid phase separation can occur (demixing phenomenon ). The conditions (concentration, operating conditions of pressure and temperature) in which demixing occurs for a given absorbent solution are determined by laboratory tests (perfectly stirred gas-liquid reactors). The formulation can then be used in a deacidification process with fractional regeneration by heating, as described with reference to FIG. 3. An absorbent solution based on Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine is particularly suitable for this type of process because it allows rapid liquid-liquid phase separation.

For example, at 40 ° C. and for a CO ₂ partial pressure of 0.1 bar, a solvent composed of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine at the level of 30 or 50% by weight is monophasic.

Nevertheless, by raising the temperature, a solvent composed of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine at a level of 30 or 50% by weight loaded under the conditions mentioned above can become diphasic for a temperature greater than 60 °. C, and can be used in a deacidification process with fractional regeneration. To further illustrate these remarks, one can take the case of two absorbent solutions, one at 30% by weight and the other at 50% by weight of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine. These two absorbent solutions, in a conventional implementation (FIG 2), already have increased performance compared to the reference absorbent solutions that are MEA and MDEA (see Example 1). The two TEDETA-based absorbent solutions are contacted at a total pressure of 1 bar with a gas having a CO ₂ partial pressure of 0.1 bar at 40 ° C. and then in a second stage are heated through a heat exchanger at a temperature of 90 ° C, at which temperature is achieved a relaxation, either at 1 bar total or 2.5 bar total. Under these conditions, the absorbent solution can be monophasic or diphasic. If the absorbing solution is two-phase, then a liquid-liquid phase separation can be carried out in order to relieve the regeneration step as proposed by the process described with reference to FIG. 3. The table below presents the various cases of figure, indicating the reduction of flow of absorbent solution to the regenerator.

Example 3: Stability

The molecule of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine has the particularity of being resistant to degradation that may occur in a deacidification unit. The table below gives the degradation rate TD of the absorbing solution, under different conditions, for a duration of 15 days, defined by the equation below:

[A min e] - [A min e] °

TD (%)

[Friend] ° where [Amine] is the concentration of amine in the sample of degraded absorbent solution, and [Amine] ⁰ is the concentration of amine initially present in the sample of non-degraded absorbent solution.

This example shows that the use of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine, as an amine in an absorbent solution makes it possible to obtain a degradation rate equivalent to that of the amine-based absorbent solutions of the prior art (MethylDiEthanolAmine and MonoEthanolAmine).

Claims

claims

1. A process for eliminating the acidic compounds contained in a gaseous effluent in which an absorption step of the acidic compounds is carried out by contacting the gaseous effluent with an absorbent solution comprising:

- water, and

- ', Ν'-tetraethyldiethylenetriamine of formula:

2. The method of claim 1, wherein the absorbent solution comprises between 10% and 90% by weight of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine 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.

The method of claim 3, wherein the activator is selected from the group consisting of:

- MonoEthano Amine,

- AminoEthylEthanolAmine,

- DiGlycolAmine,

- Piperazine,

N- (2-Hydroxyethyl) piperazine,

- N-MethylPiperazine,

- N-EthylPiperazine,

- N-PropylPiperazine,

1,6-hexanediamine,

1,1,9,9-TetraMethylDiPropylene triamine, s

21

- Morpholine,

- Piperidine,

3- (MethylAmino) PropylAmine,

- N-MethylBenzylAmine,

- TetraHydroIsoquinoline.

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.

The method according to claim 6, wherein at the regeneration step at least the following operations are performed:

a) the absorbent solution loaded with acid compounds is heated to cause the formation of two liquid phases, then

¾>) the absorbent solution charged with acidic compounds is separated into two liquid fractions by phase separation to obtain a fraction enriched in acidic compounds and a fraction depleted in acidic compounds, then

7. The method of claim 6, wherein at the regeneration step is carried out at least the following operation:

in which in operation c), the fraction depleted in is recycled. acidic compounds and the regenerated fraction to form at least a portion of said absorbent solution implemented in the absorption step.

8. Method according to one of claims 6 and 7, wherein in step a), the absorbent solution loaded with acid compounds is heated at a temperature between 70 ° C and 110 ^o C.

9. Method according to one of the preceding claims, wherein the gaseous effluent is selected from the following gaseous effluents: natural gas, synthesis gas, combustion fumes, refinery gas, gas obtained, tail Claus process, biomass fermentation gases, cement gases, incinerator fumes.

10. Method according to one of the preceding claims, wherein the gaseous effluent is a combustion smoke having a CO ₂ partial pressure of less than 200 mbar.

11. Absorbent solution for absorbing acidic compounds contained in a gaseous effluent, comprising an aqueous solution of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine and comprising between 0.5% and 20% by weight of an activator chosen from amines comprising at least one primary or secondary amine function.

The absorbent solution according to claim 11, comprising between 10% and 90% by weight of Ν, Ν, Ν ', Ν'-tetraethyldiethylenetriamine and between 10% and 90%.

, weight of water.

Absorbent solution according to one of claims 11 and 12, wherein the activator is selected from the group consisting of:

- MonoEthanolAmine,

- AminoEthylEthanolAmine,

- DiGlycolAmine,

- Piperazine,

N- (2-Hydroxyethyl) piperazine,

- N-MethylPiperazine,

- N-Ethylipiperazine,

- N-PropylPiperazine,

1,6-HexaneDiAmine,

1,1,9,9-TetraMéthylDiPropylèneTriamine,

- Morpholine,

piperidine 3- (ethylAmino) PropylAmine,

-. N-methylbenzylamine

- TetraHydroIsoquinoline.

14. Absorbent solution according to one of claims 11 to 13, comprising a physical solvent.