FR3036975A1 - PROCESS FOR REMOVING ACIDIC COMPOUNDS FROM A GASEOUS EFFLUENT WITH AN ABSORBENT SOLUTION BASED ON AMINOETHERS SUCH AS BIS- (3-DIMETHYLAMINOPROPOXY) -1,2-ETHANE - Google Patents

Abstract

The invention relates to a process for eliminating the acidic compounds contained in a gaseous effluent comprising contacting, in the absorption column C1, a gaseous effluent with an absorbent solution comprising water and at least one nitrogen compound of general formula ( I) wherein x is 0 or 1, and wherein R is selected from hydrogen or - (CH 2) 3 -N- (CH 3) 2 when x is 1, said solution absorbent material not containing N, N, N ', N'-tetramethyl-1,6-hexanediamine. For example, the nitrogen compound is bis (3-dimethylaminopropoxy) -1,2-ethane of the following formula:

Description

FIELD OF THE INVENTION The present invention relates to the field of deacidification processes of a gaseous effluent. The invention is advantageously applicable to the treatment of industrial gas and natural gas.

Co 1: Key Gas deacidification processes using aqueous solutions of amines are commonly used to remove the compounds Acids present in a gas, in particular carbon dioxide (002), hydrogen sulphide (H2S), l carbon oxysulfide (COS), carbon disulfide (CS2), sulfur dioxide (SO2) and mercaptans (RSH) such as trimethyl mercaptan (CH3SH), ethyl mercaptan (CH3CH2SH) and propyl mercaptan (CH3CH2CH2SH). The gas is deacidified by contact with the absorbent solution, and the absorbent solution is thermally regenerated. These acid gas deacidification processes are also commonly referred to as "solvent wash" with a so-called "chemical" solvent, as opposed to so-called "physical" solvent use for absorption that is not based on the realization of chemical reactions. A chemical solvent is an aqueous solution comprising a reagent that selectively reacts with the acidic compounds (H2S, CO2, COS, CS2, etc.) present in the treated gas to form salts, without reacting with the other nonacidic compounds of the gas . The treated gas after contact with the solvent is then depleted of acidic compounds, which are selectively transferred as salts into the solvent. The chemical reactions are reversible, which allows the solvent loaded with acid compounds to be subsequently deacidified, for example under the action of heat, to release on the one hand the acidic compounds in the form of gases, which can then be stored , transformed or used for various applications, and on the other hand to regenerate the solvent which returns to its initial state and can thus be reused for a new reaction phase with the acid gas to be treated. The reaction phase of the solvent with the acid gas is commonly called the absorption phase, and that where the solvent is deacidified is called the solvent regeneration phase. In general, the performance of the separation of acidic compounds from the gas, in this context, depends mainly on the nature of the chosen reversible reaction. Conventional acid gas deacidification processes are generally so-called "amine" processes, that is, they rely on the reactions of the acidic compounds with amines in solution. These reactions are part of the general framework of acid-base reactions. H2S, CO2. or COS are for example acidic compounds, especially in the presence of water, while amines are basic compounds. The mechanisms of the reactions and the nature of the salts obtained generally depend on the structure of the amines used. For example, US 6,852,144 discloses a method for removing acidic compounds from hydrocarbons using a water-N-methyldiethanolamine or water-triethanolamine absorbent solution containing a high proportion of a compound belonging to the following piperazine and / or methylpiperazine group. and / or morpholine. The performance of acid gas deacidification processes by washing with amines is directly dependent on the nature of the amine (s) present in the solvent. These amines can be primary, secondary or tertiary. They may have one or more equivalent or different amine functional groups per molecule. In order to improve the performance of the deacidification processes, amines that are always more efficient are continually being sought. A limitation of the absorbent solutions commonly used in deacidification applications is an insufficient selectivity of H2S absorption relative to CO2. In fact, in certain cases of deacidification of natural gas, a selective elimination of H 2 O is sought with a minimum of CO2 absorption. This constraint is particularly important for gases to be treated already containing a CO2 content of less than or equal to the desired specification. It then seeks a maximum H2S absorption capacity with a maximum selectivity of H2S absorption vis-à-vis the CO2. This selectivity makes it possible to maximize the amount of gas treated and to recover an acid gas at the outlet of the regenerator having the highest possible concentration of H 2 S, which limits the size of the units of the sulfur chain downstream of the treatment and guarantees a better 30 operation. In some cases, an H2O enrichment unit is needed to concentrate the acid gas in H2S. In this case, the most selective amine is also sought. Tertiary amines, such as N-methyldiethanolamine, or congested secondary amines 3036975 exhibiting slow reaction kinetics with CO2 are commonly used, but have limited selectivities at high H2S loading rates. It is well known to those skilled in the art that tertiary amines or secondary amines with severe steric hindrance have slower CO2 capture kinetics than uncompressed primary or secondary amines. In contrast, tertiary or secondary amines with severe steric hindrance have instantaneous H2S uptake kinetics, which allows for selective removal of H2S based on distinct kinetic performance. congested tertiary or secondary amines, in particular tertiary or secondary congested diamines, in solution for deacidifying acid gases. Among the applications of tertiary or secondary amines with a severe steric hindrance, US Pat. No. 4,405,582 describes a process for the selective absorption of sulphide gases by an absorbent containing a diaminoether whose at least one amine function is tertiary and whose other amine function is tertiary or secondary having a severe steric hindrance, the nitrogen atom being in the latter case linked either to at least one tertiary carbon or to two secondary carbon atoms. The two amine functions and the main chain carbons may be substituted by alkyl or hydroxyalkyl radicals.

US Patent 4,405,583 also discloses a method for selectively removing H2S in gases containing H2S and CO2 by an absorbent containing a diaminoether whose two secondary amine functions have a severe steric hindrance defined as above. The substituents of the amine functions and the main chain carbons may be substituted by alkyl and hydroxyalkyl radicals.

The French patent application filed by the applicant under the number 13 / 61,853 describes a deacidification process using a solution of a tertiary diamine, N, N, N ', N'-tetramethyl-1,6-hexanediamine ( TMHDA), combined with a diaminoether such as bis- (3-dimethylaminopropoxy) -1.2-ethane. Another limitation of the absorbent solutions commonly used in total deacidification applications is slow CO2 or COS capture kinetics. In the case where the desired specifications on CO2 or in COS are very advanced, the reaction kinetics are sought as fast as possible so as to reduce the height of the absorption column. This pressure equipment represents a significant part of the investment costs of the process. Whether CO2 uptake kinetics and maximum COS are sought in a total deacidification application, or a minimum CO2 capture kinetics in a selective application, it is always desirable to use an absorbent solution having the greatest possible cyclic capacity. . This cyclic capacity, denoted by Am, corresponds to the difference in charge ratio (a, denoting the number of moles of acidic compounds absorbed by acid absorption per kilogram of absorbent solution) between the absorbent solution withdrawn at the bottom of the absorption column and the absorbent solution feeding said column. Indeed, the more the absorbent solution has a high cyclic capacity, the more the flow of absorbent solution that must be used to deacidify the gas to be treated is limited. In gas treatment processes, the reduction of the absorbent solution flow also has a strong impact on the reduction of the investments, in particular with regard to the dimensioning of the absorption column. Another essential aspect of industrial gas treatment or flue gas treatment operations is the regeneration 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. The energy consumption necessary for the regeneration of the solvent can be very important, which is particularly true in the case where the partial pressure of acid gases is low, and represent a considerable operating cost for the CO2 capture process. It is well known to those skilled in the art that the energy required for the regeneration by distillation of an amine solution can be broken down into three different positions: the energy required to heat the absorbent solution between the head and the background of the regenerator, the energy required to lower the partial pressure of acid gas in the regenerator by vaporization of a stripping gas, and finally the energy necessary to break the chemical bond between the amine and the CO2.

These first two positions are proportional to the flow rates of absorbent solution that must be circulated in the unit to achieve a given specification. To reduce the energy consumption associated with the regeneration of the solvent, i | It is therefore preferable once again to maximize the cyclic capacity of the solvent. Indeed, the more the absorbent solution has a high cyclic capacity, the more the flow of absorbent solution that must be used to deacidify the gas to be treated is limited. There is thus a need, in the field of gas deacidification, to provide compounds which are good candidates for the removal of acidic compounds from a gaseous effluent, including, but not limited to, the selective removal of H2S compared to 002, which allows operating at lower operating costs (including regeneration energy) and investments (including the cost of the absorption column). The inventors have demonstrated that tertiary or secondary multiamines possessing a severe steric hindrance are not equivalent in terms of performance for their use in absorbent solution formulations for the treatment of acidic gases in an aqueous solution. industrial process. The present invention relates to the use, in the field of gas deacidification, of an aqueous absorbent solution comprising a nitrogen compound of general formula (1) below: said absorbent solution not comprising N, N, N N, N'-tetramethyl-1,6-hexanediamine (TMHDA).

The general formula (I) is detailed below. In particular, the subject of the present invention is the use, in the field of gas deacidification, of an aqueous absorbent solution comprising bis (3-dimethylaminopropoxy) -1,2-ethane of formula (11) above. below, having the general formula (1), said absorbent solution not containing N, N, N ', N'-tetramethyl-1,8-hexanediamine (TMHDA).

The inventors have demonstrated that the use of the compounds corresponding to this general formula (I), to which bis (3-dimethylaminopropoxy) -1,2-ethane in particular, responds in aqueous solution, said solution does not containing no TMHDA, makes it possible to obtain good performances in terms of cyclic capacity for acid gas absorption and absorption selectivity with respect to H2S, in particular an absorption selectivity vis-à-vis H 2 S is more important than reference amines such as N-methyldiethanolamine (MDEA) for equivalent or greater acidic cyclic absorption capacity.

In general, the invention relates to a process for the elimination of acidic compounds contained in a gaseous effluent, in which a step of absorption of the acidic compounds is carried out by contacting the effluent with an absorbent solution comprising water and at least one nitrogen compound of the following general formula (I): wherein x is 0 or 1, and wherein R is a hydrogen atom or - (CH 2) 3 -N- radical ( CH 3) 2 when x is 1, said absorbent solution not comprising N, N, N ', 1H-tetramethyl-1,6-hexanediamine. Preferably, said nitrogenous compound is bis- (3-dimethylaminopropoxy) -1,2-ethane. According to the invention, the absorbent solution may comprise between 5% and 95% by weight of said nitrogenous compound, preferably between 10% and 90% by weight of said nitrogenous compound, and between 5% and 95% by weight of water, and preferably between 10% and 90% by weight of water. The absorbent solution may further comprise from 5 to 95% by weight of at least one additional amine, said additional amine being either a tertiary amine or a secondary amine comprising two secondary carbons alpha to the amine atom. nitrogen or at least one tertiary carbon alpha to the nitrogen atom. Said additional amine may be a tertiary amine selected from the group consisting of: N-methylethiethanolamine; triethanolannine; diethylmonoethanolamine - dimethylmonoethanolamine; and - ethyldiethanolamine.

The absorbent solution may further comprise a non-zero and less than 30% by weight amount of at least one additional amine being a primary amine or a secondary amine. Said additional primary or secondary amine may be 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, N'-dimethyl-1,6-hexanediamine; N-methyl-1,6-hexanediamine; and N, N ', N'-trimethyl-1,6-hexanediamine. The absorbent solution may further comprise at least one physical solvent selected from the group consisting of methanol, ethanol, 2-ethoxyethanol, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, pentaethylene glycol dimethyl ether, hexaethylene glycol dimethyl ether, heptaethylene glycol dimethyl ether, and octaethylene glycol dimethyl ether. diethylene glycol butoxyacetate, glycerol triacetate, sulfolane, N-methylpyrrolidone, N-methylmorpholin-3-one, N, N-dimethylformamide, N-formyl-morpholine, N, N-dimethylimidazolidin-2-one N-methylimidazole, ethyleneglycol, diethyleneglycol, triethyleneglycol, thiodiglycol, propylene carbonate, tributylphosphate.

Preferably, the absorption step of the acidic compounds is carried out at a pressure of between 1 bar and 200 bar, and at a temperature of between 20 ° C and 100 ° C. Preferably, an absorbent solution loaded with acid compounds is obtained after the absorption step, and at least one regeneration step of the absorbent solution loaded with acidic compounds is carried out at a pressure of between 1 bar and 10 bar and at 20 a temperature of between 100 ° C and 180 ° C. The gaseous effluent may be chosen from natural gas, synthesis gases, combustion fumes, refinery gases, acid gases from an amine unit, gases from a tail reduction unit of Claus process, biomass fermentation gases, cement gases, incinerator fumes.

The process according to the invention can be used to selectively remove H2S with respect to CO2 from a gaseous effluent comprising H2S and CO2. Advantageously, the process according to the invention is used for the selective removal of H2S with respect to CO2 contained in natural gas.

Preferably, the H2S is selectively removed from 002 in a ratio S of formula (a) below, said ratio being greater than 1.1. (a) In the formula (a), RiF2S is the H2S removal efficiency, said H2S rIH2S removal efficiency expressed according to the following formula (a1) IIH2s HS 'FG, c-Iralie - Ga: treats, X v 2: - ............._. (al) F xv 1/2's 'GUI15 / 7 // -' Galbruf 11co2 is the removal efficiency of 002, said 002 elimination yield, Ilco2 being expressed according to the following formula (a2) = I - " (a2) CO, x In the formulas (a1) and (a2), F is the molar flow rate of the gaseous effluent, raw or treated, and y is the mole fraction of acid gas H2S or CO2. , the ratio S is greater than 2, and is preferably greater than 2.5 Other objects and advantages of the invention will appear on reading the following description of examples of particular embodiments of the invention given By way of nonlimiting examples, the description being made with reference to the appended figure described below: Figure 1.3 represents a schematic diagram of the implementation of a method The present invention proposes to remove the acidic compounds from a gaseous effluent by using solute. aqueous ion whose composition is detailed below.

3036975 Composition of an absorbent solution The absorbent solution used for the removal of acidic compounds contained in a gaseous effluent comprises: water; At least one nitrogenous compound corresponding to the following general formula (I) in which x is equal to 0 or 1, and in which R is a hydrogen atom or a radical - (CH 2) 3 -N- (CH 3) When X is 1. According to the invention, the absorbent solution does not contain N, N, N ', N'-tetramethyl-1,6-hexanediamine (TMHDA), of the following formula: Nitrogen compound of the general formula (I) is bis (3-dimethylaminopropoxy) -1,2-ethane corresponding to the following formula (II): The formula (II) corresponds to the case of the general formula (I) where x is equal to 0. The nitrogen compound of general formula (I) may be in variable concentration in the absorbent solution, for example between 5% and 95% by weight, preferably between 10% and 90% by weight, and even more preferably between 20% and 90% by weight. And 60% by weight, and most preferably between 25% and 50% by weight, inclusive.

The absorbent solution may contain between 5% and 95% w / w, preferably between 10% and 90% w / w, more preferably between 40% and 80% w / w, and very preferred from 50% to 75% water, limits included. The sum of the mass fractions expressed as the weight of the various compounds of the absorbent solution is equal to 100% by weight of the absorbent solution. According to one embodiment, the absorbent solution may also contain at least one additional amine which is a tertiary amine such as N-methyldiethanolamine, triethanolamine, diethylmonoethanolannine, dimethylmonoethanolamine, or ethyldiethanolamine, or which is a secondary amine having a severe steric hindrance, this congestion being defined either by the presence of two secondary carbons alpha to the nitrogen atom, or by at least one tertiary carbon alpha to the nitrogen atom. By said additional amine is meant any compound having at least one tertiary amine or secondary amine function severely congested. Said additional amine is not N, N, N ', N'-tetramethyl-1,6-hexanediannine. The concentration of said tertiary or secondary secondary amine severely congested in the absorbent solution may be from 5% to 95% by weight, preferably from 5% to 50% by weight, very preferably from 5% to 30% by weight. 0 weight. According to one embodiment, the amines according to the general formula (I) may be formulated with one or more compounds containing at least one primary or secondary amine function. For example, the absorbent solution comprises up to a concentration of 30% by weight, preferably less than 15% by weight, preferably less than 10% by weight of said compound containing at least one primary or secondary amine function. Preferably, the absorbent solution comprises at least 0.5% by weight of said compound containing at least one primary or secondary amine function. Said compound makes it possible to accelerate the absorption kinetics of CO2 and, in certain cases, of the COS contained in the gas to be treated. A non-exhaustive list of compounds containing at least one primary or secondary amine function that may be included in the formulation is given below - monoethanolamine; diethanolamine; N-butylethanolamine; aminoethylethanolamine; 3036975 12 - diglycolamine; piperazine; 1-methylpiperazine; 2-methylpiperazine; Homopiperazine; N- (2-hydroxyethyl) piperazine; N- (2-aminoethyl) piperazine; morpholine; 3- (methylamino) propylamine; 1,6-hexanediamine and all its variously N-alkylated derivatives such as, for example, N, N1-dimethyl-1,6-hexanediamine, N, N'-dimethyl-1,6-hexanediamine, N-methyl-1 6-hexanediamine or N, N1, Nr-trinneyl-1,6-hexanediamine. It is noted that the TMHDA does not fit this definition because it is not a compound having a primary or secondary amine function.

According to the invention, the absorbent solution comprising a nitrogen compound of general formula (1) may comprise a mixture of additional amines as defined above. According to one embodiment, the absorbent solution may contain organic compounds which are non-reactive with respect to acid 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, ethers, ether alcohols, glycol ethers and polyethylene glycol ethers, glycol thioethers, glycol esters and alkoxy esters, and the like. polyethylene glycol, glycerol esters, lactones, lactams, N-alkylated pyrrolidones, morpholine derivatives, morpholin-3-one, imidazoles and imidazolidinones, N-alkylated piperidones, cyclotetramethylenesulfones, N-8-alkylformamide, N-alkylacetamides, alkyl ketone ethers-ketones or alkyl phosphates and their derivatives. By way of example and without limitation, it may be methanol, [ethanol, 2-ethoxyethanol, triethyleneglycoldimethylether, tetraethyleneglycoldimethylether, pentaethyleneglycoldimethylether, hexaethyleneglycoldimethylether, heptaethyleneglycoldimethylether, octaethylene glycol dimethyl ether, diethylene glycol butoxyacetate, glycerol triacetate, sulfolane, N-methylpyrrolidone, N-methylmorpholin-3-one, N, N-dimethylformamide, N-formyl-morpholine, N N-dimethylimidazolidin-2-one, N-methylinnidazole, ethyleneglycol, diethyleneglycol, triethyleneglycol, thiodiglycol, propylene carbonate, tributylphosphate. Synthesis of Nitrogen Compounds of General Formula (I) Synthesis of Bis (3-dimethylaminopropoxy) -12-ethane Bis (3-dimethylaminopropoxy) -1,2-ethane can be prepared according to various known synthetic routes of the invention. skilled person. The bis- (3-dimethylaminopropoxy) -1,2-ethane may be prepared according to the following synthetic route, cited by way of non-limiting example. Bis (3-dimethylaminopropoxy) 1,2-ethane can be prepared in three stages, the first of which consists in the reaction of one mole of ethylene glycol with two moles of acrylonitrile, leading to 1,2- The nitrile functions of 1,2-bis (2-cyanoethoxy) ethane are then reduced in a second step to primary amine functions by hydrogenation in the presence of a suitable catalyst and sometimes ammonia to yield bis (3-aminopropoxy) 1,2-ethane The synthesis of bis (3-aminopropoxy) 1,2-ethane according to this sequence of two steps is described, for example, in US 4,313,004, US 5,075,507 and US 5,081,305 In a third step, the two primary amine functions of bis (3-aminopropoxy) 1,2-ethane are methylated, for example by reductive amination generally using formaldehyde, in the presence of hydrogen and a catalyst suitable for conducting bis (3-dimethylaminopropoxy) 1,2-ethan e) Synthesis of the compound of general formula (I) with x = 1 and R = H The compound of general formula (I) with x = 1 and R = H can be prepared according to different synthesis routes known to those skilled in the art . The compound of general formula (I) with x = 1 and R = H may be prepared according to the following synthetic route, cited by way of non-limiting example. The compound of general formula (I) with x = 1 and R = H may be prepared in three stages, the first of which consists in the reaction of one mole of glycerol with two moles of acrylonitrile, leading to 343- (2-cyanoethoxy). ) -2-hydroxypropoxy] propanenitrile.

The nitrile functions of 343- (2-cyanoethoxy) -2-hydroxypropoxyboropanenitrile are then reduced in a second step to primary amine functions by the action of hydrogen, in the presence of a suitable catalyst and sometimes ammonia to lead to the 1 3-bis (3-aminopropoxy) propan-2-ol. In a third step, the two primary amine functions of 1,3-bis (3-aminopropoxy) propan-2-ol are methylated, for example by reductive amination generally using formaldehyde, in the presence of hydrogen and catalyst suitable for yielding 2,14-dimethyl-6,10-dioxa-2,14-diazapentadecan-8-O. Synthesis of the Compound of Aeneral Formula (I) with X = R = - (CH 2) 1-NMe, The compound of general formula (I) with x = 1 and R = - (CH 2) 3 -NMe 2 be prepared according to different synthetic routes known to those skilled in the art. The compound of general formula (I) with x = 1 and R = - (CH 2) 3 -NMe 2 may be prepared according to the following synthetic route, cited by way of non-limiting example. The compound of general formula (I) with x = 1 and R = - (CH 2) 3 -NMe 2 can be prepared in three steps, the first of which consists in the reaction of one mole of glycerol with three moles of acrylonitrile, leading to 3 - {[1,3-bis (2-cyanoethoxy) propan-2-yl] oxylpropanenitrile. The nitrile functions of 34 [1,3-bis (2-cyanoethoxy) propan-2-yloxy} propanenitrile are then reduced in a second step to primary amine functions by the action of hydrogen, in the presence of a suitable catalyst and sometimes ammonia to yield 3 - {[1,3-bis (3-aminopropoxy) propan-2-yl] oxy} propan-1-amine.

In a third step, the three primary amine functions of 3 - ([1,3-bis (3-aminopropoxy) propan-2-yl] oxylpropan-1-amine are methylated, for example by reductive amination generally using formaldehyde. in the presence of hydrogen and a suitable catalyst to give 8- [3- (dimethylamino) propoxy] -2,14-dimethyl-6,10-dioxa-2,14-diazapentadecane.

Nature of the gaseous effluents According to the invention, the absorbent solutions can be used to deacidify the gaseous effluents following natural gas, synthesis gases, combustion fumes, refinery gases, acid gases derived from an amine unit, gases from a Claus process bottoms reduction unit, biomass fermentation gases, cement gases, incinerator fumes. These gaseous effluents contain one or more of the following acidic compounds: 002, H2S, mercaptans (for example methylmercaptan (CH3SH), ethylmercaptan (CH3CH2SH), propylnnercaptan (CH3CH2CH2SH)), COS, CS2, SO2.

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 deacidification process according to the invention can be used to absorb at least 70%, preferably at least 80% or even at least 90% of the CO2 contained in the combustion fumes. These fumes generally have a temperature of between 20 ° C. and 60 ° C., a pressure of between 1 and 5 bar and may comprise between 50 ° C. and 80% of nitrogen, and between 5% and 40 ° C. of carbon dioxide. , between 1% and 20% oxygen, and some impurities such as SOx and NOx, if they have not been removed upstream of the deacidification process. In particular, the deacidification process according to the invention is particularly well adapted to absorb the CO2 contained in combustion fumes having a low partial pressure of 002, for example a partial pressure of CO2 of less than 200 mbar. The deacidification process according to the invention can be used to deacidify a synthesis gas. The synthesis gas contains carbon monoxide CO, hydrogen dihydrogen H 2 (generally in a H 2 / CO ratio equal to 2), water vapor (generally at saturation at the temperature where the wash is effected and killed). carbon dioxide CO2 (of the order of about ten percent), the pressure is generally between 20 and 30 bar, but can reach up to 70 bar, and it can contain, in addition, sulfur impurities (H2S, COS, etc.), nitrogen (NH3, HCN) and halogenated, The deacidification process according to the invention can be used to deacidify a natural gas.Natural gas is mainly composed of gaseous hydrocarbons, but can contain several the following acidic compounds: 002, H2S, mercaptans, COS, C82 The content of these acidic compounds is very variable and can be up to 70% by volume for CO2 and up to 40% by volume for H2S The temperature of the natural gas can be between 20 ° C and 1 00 ° C. The pressure of the natural gas to be treated can be between 10 and 200 bar. The invention can be implemented to achieve specifications generally imposed on the deacidified gas, which are less than 296 of CO2, or even less than 50 ppm of CO2 to then achieve a liquefaction of natural gas and less than 4 ppm of H2S, and less than 50 ppm, or even less than 10 ppm, total sulfur volume. Process for eliminating acidic compounds in a gaseous effluent The use of an aqueous solution comprising at least one nitrogen compound of general formula (I), such as bis (3-dimethylaminopropoxy) -1,2-ethane, and having no TMHDA, to deacidify a gaseous effluent is carried out schematically by performing an absorption step followed by a regeneration step, for example as shown in Figure 1. Referring to Figure 1, the deacidification plant of a gaseous effluent according to the invention comprises an absorption column C1 provided with contact means 15 between gas and liquid, for example loose packing, structured packing or trays. The gaseous effluent to be treated is conveyed via a pipe 1 opening at the bottom of column C1. A pipe 4 allows the introduction of the absorbing solution at the top of the column C1. A pipe 2 allows the evacuation of the treated gas (deacidified), and a pipe 3 makes it possible to convey the absorbent solution enriched in acid compounds following the absorption to a regeneration column 02. This regeneration column C2 is equipped with gas and liquid contacting interiors, for example trays, loose or structured packings. The bottom of the column C2 is equipped with a reboiler R1 which provides the heat necessary for regeneration by vaporizing a fraction of the absorbent solution. The solution enriched in acidic compounds is introduced at the top of the regeneration column C2 via a pipe 5. A pipe 7 makes it possible to discharge at the top of the column C2 the gas enriched in acidic compounds released during the regeneration, and a pipe 6 arranged at the bottom column C2 makes it possible to send the regenerated absorbent solution to the absorption column C1. A heat exchanger E1 allows the heat of the regenerated absorbent solution from the column C2 to be recovered to heat the absorbent solution enriched in acidic compounds leaving the absorption column C1.

The absorption step consists in bringing the gaseous effluent arriving via line 1 into contact with the absorbent solution arriving via line 4. During contact, the amine functions of the molecules of the absorbent solution react with the acidic compounds. contained in the effluent so as to obtain a gaseous effluent depleted of acidic compounds which is discharged through line 2 at the top of column C1 and an acid-enriched absorbent solution discharged via line 3 at the bottom of column C1 for to be regenerated. The absorption step of the acidic compounds can be carried out at a pressure in the Cl column of between 1 bar and 200 bar, preferably between 20 bar and 100 bar for the treatment of a natural gas, preferably between 1 bar and 3 bar for the treatment of industrial fumes, and at a temperature in the Cl column between 20 ° C and 100 ° C, preferably between 30 ° C and 90 ° C, or between 30 and 60 ° C. 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 leaving the column C1 is introduced into the heat exchanger E1, where it is heated by the flow flowing in the pipe 6 from the regeneration column C2. The heated solution at the outlet of El is introduced into the regeneration column C2 via line 5. In regeneration column C2, under the effect of bringing the absorbent solution arriving via line 5 into contact with the vapor produced by the reboiler, the acidic compounds are released in gaseous form and discharged at the top of column C2 through line 7. The regenerated absorbent solution, that is to say depleted in acidic compounds, is evacuated via line 6 and is cooled in E1 'and then recycled to the absorption column C1 via line 4. The regeneration step can be carried out by thermal regeneration, optionally supplemented by one or more expansion steps. For example, the absorbent solution enriched in acidic compounds discharged through the pipe 3 can be sent to a first expansion tank (not shown) before it passes through the heat exchanger E1. In the case of a natural gas, the expansion makes it possible to obtain a gas evacuated at the top of the flask containing most of the aliphatic hydrocarbons co-absorbed by the absorbing solution. This gas may optionally be washed with a fraction of the regenerated absorbent solution and the gas thus obtained may be used as a fuel gas. The expansion flask preferably operates at a pressure lower than that of the absorption column C1 and greater than that of the regeneration column C2. This pressure is generally set by the conditions of use of the fuel gas, and is typically of the order of 5 to 15 bar. The expansion flask operates at a temperature substantially identical to that of the absorbing solution obtained at the bottom of the absorption column C1.

The regeneration can be carried out at a pressure in the column C2 of between 1 bar and 5 bar, or even up to 10 bar and at a temperature in the column C2 of between 100 ° C. and 180 ° C., preferably between 110 ° C. and 180 ° C. ° C .: 1 170 ° C, more preferably between 120 ° C and 140 ° C. Preferably, the regeneration temperature in column C2 is between 155 ° C. and 180 ° C. in the case where it is desired to reinject the acid gases. Preferably, the regeneration temperature in column C2 is between 115 ° C and 130 ° C in cases 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. The process according to the invention advantageously allows selective removal of the H2S vis-à-vis the CO in the gas to be treated. Preferably, the process is carried out for the selective removal of H2S with respect to CO2 from natural gas comprising H2S and CO2. The H2S absorption selectivity for CO2 can be expressed by the S ratio of the removal efficiencies of the two gases: (a) These removal efficiencies are expressed respectively as 11, S r ( In these expressions, F denotes the molar flow rate of the gaseous effluent, whether crude or treated. y denotes the molar fraction of acid gas, H2S or 002. According to the invention, the elimination selectivity of the H2S with respect to the CO is greater than 1.1, preferably greater than 2, and even more preferably higher at 2.5 The examples below illustrate, in a nonlimiting manner, the synthesis of a nitrogen compound of general formula (I), bis (3-dimethylaminopropoxy) -1,2-ethane, as well as some of the performances of this compound when used in aqueous solution, without TMHDA, to eliminate acid compounds, such as CO2 or H2S, contained s in a gaseous effluent by contacting the gaseous effluent with the solution. EXAMPLE 1 Synthesis of Bis (3-dimethylaminopropoxy) -1,2-ethane At the laboratory scale, the synthesis of bis (3-dimethylaminopropoxy) -1,2-ethane is carried out as follows. 90.0 g (0.511 mol) of 1,2-bis (3-aminopropoxy) ethane and 0.5 g of a platinum-on-carbon catalyst are charged to an autoclave reactor. The reactor is then purged by the introduction of hydrogen up to 5 bar followed by degassing under reduced pressure. The operation is repeated 3 times. 250 g of an aqueous solution of formaldehyde at 37% by weight are then slowly introduced. The reactor is then stirred for 5 hours at 120 ° C. under a pressure of 20 bar of hydrogen. After returning to ambient temperature, the catalyst is filtered to isolate the liquid phase. The previous operation is reproduced and then the two liquid phases are joined and distilled. 137.3 g of a product whose NMR-13C spectrum detailed below is consistent with that of bis (3-dimethylaminopropoxy) -1,2-ethane are collected. 44.7 ppm: (CH 3) 2 N -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -O-CH 2 -CH 2 -CH 2 -N (CH 3) 2 55.8 ppm: (Cl-13) 2 N-Cl-12 CF12-CH2-O-CH2-Cl2-O-CH2-CF12-CF12-N (CF13) 2 27.2 ppm. (CH 3) 2 N-Cl-12-CF-12-Cl-12-Cl-12-CH 2 -O-CH 2 -CH 2 -Cl-12-N (CF 13) 2 68.7 ppm: (Cl-13) 2N-CH 2 -CH2-CF12-O-CH2-CH2-CH2-O-CF12-CF12-CH2-N (CH3) 69.4ppm: (C1-C13) 2N-CF12-CF-12-CF12-O-CH2-CH2-O -CH2-C112-CF12-N (CH3) 2 3036975 EXPRrIni 7: Cn:) Absorption activity of H2S of an amine formulation for a process of trapping acid gas Performance of absorption capacity of H2S at 40 ° C of an aqueous solution of bis (3-dimethylaminopropoxy) -1,2-ethane according to the invention, containing 30% by weight of bis (3-dimethylaminopropoxy) -1,2-ethane , and not containing TMHDA, is compared with that of an aqueous solution of MDEA containing 50% by weight of MDEA, which constitutes a reference absorbent solution for a selective elimination in gas treatment. An absorption test at 40 ° C is carried out on aqueous amine solutions in a thermostatic equilibrium cell. This test consists in injecting into the equilibrium cell, previously filled with degassed aqueous amine solution, a known quantity of acid gas, of the H 2 S in this example, and then waiting for the establishment of the state of balanced. The quantities of acid gas absorbed in the aqueous amine solution are then deducted from the temperature and pressure measurements by means of material and volume balances. The solubilities are conventionally represented in the form of H 2 S partial pressures (in bar) as a function of the H 2 S feed rate (in moles of H 2 S / kg of absorbent solution and in moles of H 2 S / mol of amine). ). In the case of selective deacidification in natural gas treatment, the partial H 2 S pressures encountered in the acid gases are typically between 0.05 and 0.15 bar, at a temperature of 40 ° C. By way of example, in this industrial range, the rates of H2S feedstock obtained at 40 ° C. for various partial H 2 S pressures between the absorbent solution of MDEA at 50% by weight and the absorbent solution of bis (3-dimethylaminopropoxy) -1,2-ethane at 30 wt. Aqueous solution of bi,> (3-dimethylaminopropoxy) -1,2-ethane at 30% by weight at 40 ° C. Aqueous solution of MDEA at 50% by weight at 40 ° C. Charge rate in H2S (mol / kg) Partial pressure in H2S / bah 0.05 0.15 n 1.25 0 0 1.31 1.70 0.21 0.15 1 47 1.90 0.26 Loading rate in H2S (mol / mol of amine) Charge rate in H2S H2S (mol / kg) (nnol / mol) Table 1 3036975 21 At 40 ° C., whatever the partial pressure of H2S, the absorption capacity of the aqueous solution of bis- (3- dimethylaminopropoxy) -1.2-ethane according to the invention is greater than that of the MDEA solution: in fact, at a partial pressure of 0.05 bar, the loading rate of H2S is 1.25 mol / kg in the solution absorbent of bis- (3-dimethylaminopropoxy) -1,2-ethane and 0.64 mol / kg in the reference MDEA absorbent solution At a partial pressure of 0.10 bar H 2 S, the difference between the H2S load of the two absorbent solutions is 0.82 mol / kg with abso capacity for the absorbing solution of bis (3-dimethylaminopropoxy) -1,2-ethane increased by 93% over the reference MDEA absorbent solution. At a partial H 2 S pressure of 0.15 bar, the difference in H 2 S feed ratio between the two absorbent solutions is still 77% in favor of the bis (3-dimethylaminopropoxy) -1,2 absorbent solution. - ethane. It is therefore found that the aqueous solution of bis (3-dimethylaminopropoxy) -1,2-ethane at 30% by weight has a higher capacity to absorb H 2 S than the reference aqueous solution of MDEA at 50% by weight of at 40 ° C, in the range of 15 H 2 S partial pressures between 0.05 and 0.15 bar corresponding to a partial pressure range representative of the usual industrial conditions. Example 3: Calculation of a tray absorber. Investigation of a Maximum Selectivity of Absorption of H2S Relative to CO2 The process of absorption of the process according to the invention is carried out to treat a natural gas whose pressure at the inlet of the absorber is of 71.9 bar and the temperature of 31.2 ° C. The molar composition of the natural gas at the inlet of the absorber is as follows: 85% mol of methane, 4.9% mol of ethane, 1.41% of propane, 0.26% of isobutane, 0, 59% n-butane, 0.15% isopentane, 0.30% n-pentane and 0.14% n-hexane. The gas also contains 0.09% of water, 2.53% of nitrogen and 2.13% of CO2 and 2.49% of H2S. The specifications for the treated gas are 2 ppmv for H2S and 2% mol for CO2. A selectivity of removal of H2S with respect to maximum CO2 is therefore required. The raw gas, at a flow rate of 19 927 kmol / h, is contacted countercurrently with an aqueous solution of regenerated amine. characterized by filler levels of 7.10-4 moles of H2S per mole of amine and 3.10-3 moles of CO 2 per mole of amine, in an absorber 30 equipped with 4-way flap trays, the spacing between trays being 60 cm. The temperature of the regenerated amine solution at the top of the absorber is 44.6 ° C. The absorber is modeled by n real trays taking into account rigorously the geometry of the trays, on each of which the acid gas flows are calculated using the approach of the double film. An iterative calculation makes it possible to resolve the material and thermal balances plateau by plateau and to calculate, according to the number of plateaux n, the acid gas concentration and the temperature profiles in the absorber. The absorber is sized by the number of trays needed to achieve the required 2ppm 2 H 2 S specification in the treated gas. For each calculation, this number of plates n is obtained as well as the corresponding CO2 concentration in the treated gas. It is recalled that the selectivity of H2S absorption with respect to CO2 is defined by the ratio S of the elimination efficiencies of the two gases: (a) These elimination efficiencies are respectively expressed by H, S F. ## EQU1 ## wherein F denotes the molar flow rate of acid gas, crude or treated, y denotes the molar fraction of gas. acid, H2S or CO2 Table 2 below compares the results obtained by calculation for an absorption step using an aqueous solution of MDEA containing 47% by weight of MDEA according to the reference method to those obtained using an aqueous solution of bis- (3-dimethylaminopropoxy) -1,2-ethane at 50% by weight, and not containing TMHDA, according to the method of the invention. (a1) 3036975 Table 2 This example illustrates the gain in selectivity of 15% obtained with the process according to the invention using a formulation of 1 Bis (3-dimethylaminopropoxy) -1,2-ethane at 50 wt% without TMHDA, relative to the reference method.

The implementation of the process according to the invention described here also makes it possible to reduce by 15% the solvent flow rate used. This results in a decrease in the diameter of the column, from 3.51 to 3.41m. The number of trays needed to achieve a 2ppm H2S specification in the treated gas is also reduced from 16 to 12 trays. 350 -3; rz Tr- Yco2 [% molsec] YH2S [ppm molsec]% H2S% removal% 002 H2S / CO2 selectivity 1,38 2 100,0% 37% 2,67 100,0% 43% 2,33 2 Lt, JibPi solvent m3 / 17. / Diameter jrn] Number of plates Forrrular5 <rrn according to the invert, -, n 1,26 3,51 3,41 16 12 3036975 24 Example 4: Calculation of a absorbe trays . Search for a Maximum Acid Gas Absorption Capacity (HyS and CO: 1 The absorption step of the process according to the invention is carried out to treat a natural gas whose pressure at the inlet of the absorber is of 66.8 bar and the temperature of 43.5 ° C. The molar composition of the natural gas at the inlet of the absorber is as follows: 84.62 mol% of methane, 2.44 mol% of ethane , 1.37% propane, 0.31% isobutane, 0.67% n-butane, 0.25% isopentane, 0.28% n-pentane and 0.37% n-hexane. It also contains 0.11% of nitrogen and 5.51% of CO2 and 4.05% of H2S.The specifications for the treated gas are 2 ppmv for H2S and 296nno for 002. In this case, the flow rate of the abso solution should be minimized by using a total removal of H2S and a CO2 removal efficiency of 66% .The raw gas at a flow rate of 15025 kmol / h is brought into contact with countercurrent with an aqueous solution of regenerated amine, characterized p ar charge rates of 7.10-4 moles of H2S per mole of amine and 3.10-3 moles of CO2 per mole of amine, in an absorber 15 equipped with 4-pass flap trays, the spacing between trays being 60cm. The temperature of the regenerated amine solution at the top of the absorber is 57.7 ° C. The absorber is modeled as in the previous example. The absorber is dimensioned by the number of trays necessary to achieve the required specification of 2% CO2 in the treated gas. This number of plates n is obtained for each calculation, as is the residual H2S content of less than 2 ppm. Table 3 below compares the results obtained by calculation for an absorption step using an aqueous solution of MDEA containing 46% by weight of MDEA according to the reference method to those obtained by using an aqueous solution of bisphenol. (2-dimethylaminopropoxy) -1,2-ethane at 50% by weight, and not containing TMHDA, according to the method of the invention.

3036975 Formua 25 bise- 1,2etharm? ###, ## STR2 ##, ## STR2 ## [ppm molsec] DEBUID:, solvent ', 1773 / h] [m] (4 asses) Jb Trays Table 3 The implementation of the process according to the invention described here makes it possible to reduce by 17% the flow rate of absorbing solution set This results in a decrease in the diameter of the column, from 3.90 to 3.81m.

The number of trays needed to achieve a 2% GO 2 specification in the treated gas is also reduced from 28 to 24 trays.

Claims (15)

REVENDICATIONS1. Process for the removal of acidic compounds contained in a gaseous effluent, in which a step of absorption of the acidic compounds is carried out by contacting the effluent with an absorbing solution comprising: - water, - at least one compound nitrogen compound of the following general formula (I) wherein x is 0 or 1, and wherein R is a hydrogen atom or a - (CH2) 3-N- (CH3) 2 radical when x is 1, said absorbent solution not containing N, N, N, 1, 11-tetramethyl-1,6-hexanediamine. 2. The process as claimed in claim 1, wherein said nitrogenous compound is bis (3-dimethylaminopropoxy) -1,2-ethane of the following formula (II). 3. Method according to one of the preceding claims, wherein the absorbent solution comprises between 5% and 95% by weight of said nitrogen compound, preferably between 10% and 90% by weight of said nitrogen compound, and between 5 ° / 0 and 95% weight of water, and preferably between 10% and 90% by weight of water. 4. Method according to one of the preceding claims, wherein the absorbent solution further comprises between 5% and 95% by weight of at least one additional amine, said additional amine being either a tertiary amine or a secondary amine comprising two carbons secondary in alpha of the nitrogen atom or at least one tertiary carbon in alpha of the nitrogen atom. 3036975 27 The process according to claim 4, wherein said additional amine is a tertiary amine selected from the group consisting of: N-methyldiethanolannine; triethanolamine; Diethylmonoethanolamine; dimethylmonoethanolannine; and - ethyldiethanolamine. 6. The process according to one of the preceding claims, wherein the absorbing solution further comprises a non-zero and less than 30% by weight of at least one additional amine being a primary amine or a secondary amine. The method of claim 6, wherein said additional primary or secondary amine is selected from the group consisting of - monoethanolamine; diethanolamine; N-butylethanolamine; aminoethylethanolamine; diglycolannine; 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-hexanediannine; N, N'-dimethyl-1,6-hexanediannine, N-methyl-1,6-hexanediamine and N, N, N'-trimethyl-1,6-hexanediamine. 8. Method according to one of the preceding claims, wherein the absorbent solution 5 further comprises at least one physical solvent selected from the group consisting of methanol, ethanol, 2-ethoxyethanol, triethyleneglycoldimethylether, tetraethyleneglycoldimethylether, pentaethyleneglycoldimethylether, hexaethyleneglycoldimethylether, heptaethyleneglycoldimethylether, octaethyleneglycoldimethylether, diethyleneglycol butoxyacetate, glycerol triacetate, sulfolane, N-methylpyrrolidone, N-methylmorpholin-3-one, N, N-dimethylformamide, N-formyl-morpholine, N, N-dimethyl-imidazolidin-2-one, N-methylimidazole, ethylene glycol, diethylene glycol, triethylene glycol, thiodiglycol, propylene carbonate, tributyl phosphate. 9. Process according to one of the preceding claims, in which the step of absorption of the acidic compounds is carried out at a pressure of between 1 bar and 200 bar, and at a temperature of between 20 ° C. and 100 ° C. 10. Method according to one of the preceding claims, wherein there is obtained an absorbent solution loaded with acidic compounds after the absorption step, and at least one regeneration step of said absorbent solution loaded with 20 acid compounds is carried out at a temperature of pressure between 1 bar and 10 bar and at a temperature between 100 ° C and 180 ° C. 11. Method according to one of the preceding claims, wherein the gaseous effluent is selected from natural gas, synthesis gas, combustion fumes, refinery gases, acid gases from an amine unit, gases from a Claus process bottling reduction unit, biomass fermentation gases, cement gases, incinerator fumes. 12. Method according to one of the preceding claims, implemented for the selective removal of H2S relative to CO2 from a gaseous effluent comprising H2S and CO2, preferably natural gas. 3036975 29 13. The method of claim 12, implemented for the selective removal of H2S relative to CO2 contained in natural gas. 14. Process according to any one of claims 12 and 13, in which the H2S is selectively removed relative to CO2 in a ratio S of the following formula (a): ## STR2 ## H2S removal efficiency, said H2S H2S removal efficiency being expressed according to the following formula (a1): ## STR2 ## wherein: removal of 002, said 002 elimination yield, TICO2 FGazirclu (a2) expressed according to the following formula (a2): qco, - x Gcc'.hrlit 10 F being the molar flow rate of the gaseous effluent, crude or treated; y being the molar fraction of acid gas H2S or 002, said ratio S being greater than 1.1, 15. The method of claim 14, wherein the ratio S is greater than 2, and preferably greater than 2.5. H, S "X Y Galiralié (al)