Absorbent solution containing a mixture of 1,2-bis-(2-dimethylaminoethoxy)-ethane and of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol, and method of removing acid compounds from a gaseous effluent

Abstract

The invention relates to an absorbent solution for absorbing acid compounds, such as hydrogen sulfide and carbon dioxide, in a gaseous effluent, containing water and a mixture of amines comprising 1,2-bis-(2-dimethylaminoethoxy)-ethane and 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol, of respective formulas (I) and (II) below, and to a method of removing acid compounds contained in a gaseous effluent using this solution. ##STR00001##

Claims

1. An absorbent solution comprising: water; an amine mixture comprising 1,2-bis-(2-dimethylaminoethoxy)-ethane of formula (I) as follows: ##STR00016## and 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol of formula (II) as follows: ##STR00017## the absorbent solution for removing acid compounds contained in a gaseous effluent.

2. An absorbent solution as claimed in claim 1, comprising between 5 wt. % and 95 wt. % of amine mixture and between 5 wt. % and 95 wt. % of water.

3. An absorbent solution as claimed in claim 2, comprising between 10 wt. % and 90 wt. % of amine mixture and between 10 wt. % and 90 wt. % of water.

4. An absorbent solution as claimed in claim 1, wherein the mass concentration ratio of 1,2-bis-(2-dimethylaminoethoxy)-ethane to 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol ranges between 0.25 and 10.

5. An absorbent solution as claimed in claim 4, wherein the mass concentration ratio of 1,2-bis-(2-dimethylaminoethoxy)-ethane to 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol ranges between 0.5 and 2.

6. An absorbent solution as claimed in claim 1, further comprising between 5 wt. % and 50 wt. % of at least one additional amine, said additional amine being either a tertiary amine or a secondary amine having two secondary carbons at nitrogen alpha position or at least one tertiary carbon at nitrogen alpha position.

7. An absorbent solution as claimed in claim 6, wherein said additional amine is a tertiary amine selected from among the group made up of: N-methyldiethanolamine, triethanolamine, diethylmonoethanolamine, dimethylmonoethanolamine, ethyldiethanolamine, 2-(2-dimethylaminoethoxy)-ethanol, dimethylethylamine, dimethylethoxyethylamine, bis(dimethylaminoethyl)ether, and tetramethylethylenediamine.

8. An absorbent solution as claimed in claim 1, additionally comprise a non-zero amount less than 30 wt. % of at least one primary amine or secondary amine.

9. An absorbent solution as claimed in claim 8, wherein said primary or secondary amine is selected from among the group made up 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.

10. An absorbent solution as claimed in claim 1, further comprising at least one physical solvent selected from among the group made up of methanol, ethanol, 2-ethoxyethanol, triethylene glycoldimethylether, tetraethylene glycoldimethylether, pentaethylene glycoldimethylether, hexaethylene glycol-dimethylether, heptaethylene glycol-dimethylether, octaethylene glycoldimethylether, diethylene glycol 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 and tributyl phosphate.

11. A method of removing acid compounds contained in a gaseous effluent wherein an acid compound absorption stage is carried out by contacting the gaseous effluent with an absorbent solution as claimed in claim 1.

12. A method as claimed in claim 11, wherein the acid compound absorption stage is carried out at a pressure ranging between 1 bar and 200 bar, and at a temperature ranging between 20 C. and 100 C.

13. A method as claimed in claim 11, wherein an acid compound-laden absorbent solution is obtained after the absorption stage and at least one stage of regenerating said acid compound-laden absorbent solution is carried out at a pressure ranging between 1 bar and 10 bar, and at a temperature ranging between 100 C. and 180 C.

14. A method as claimed in claim 11, wherein the gaseous effluent is selected from among natural gas, syngas, combustion fumes, blast furnace fumes, refinery gas, cracked gas, combustible gas, acid gas from an amine plant, Claus tail gas, biomass fermentation gas, cement plant gas and incinerator fumes.

15. A method as claimed in claim 14, wherein the gaseous effluent is refinery gas comprising syngas.

16. A method as claimed in claim 11, implemented for selectively removing the H.sub.2S over the CO.sub.2 from a gaseous effluent comprising H.sub.2S and CO.sub.2.

17. A method as claimed in claim 16, wherein the gaseous effluent comprises natural gas.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other features and advantages of the invention will be clear from reading the description hereafter of embodiments given by way of non limitative example, with reference to the accompanying figures described hereafter:

(2) FIG. 1 is a block diagram of the implementation of an acid gas treating method, and

(3) FIG. 2 diagrammatically shows synthesis routes for 1,2-bis-(2-dimethylaminoethoxy)-ethane, 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol and a mixture of these two compounds.

DETAILED DESCRIPTION OF THE INVENTION

(4) The present invention aims to remove acid compounds from a gaseous effluent using an aqueous solution whose composition is detailed hereafter.

(5) Composition of the Absorbent Solution

(6) The absorbent solution used for removing the acid compounds contained in a gaseous effluent comprises at least: water, 1,2-bis-(2-dimethylaminoethoxy)-ethane of formula (I) as follows:

(7) ##STR00004## 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol of formula (II) as follows:

(8) ##STR00005##

(9) The total concentration of the amine mixture comprising 1,2-bis-(2-dimethylaminoethoxy)-ethane and 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol can be variable in the absorbent solution, ranging for example between 5 wt. % and 95 wt. %, preferably between 10 wt. % and 90 wt. %, more preferably between 20 wt. % and 60 wt. %, and most preferably between 25 wt. % and 50 wt. %, inclusive.

(10) The mass concentration ratio of tertiary diamine of formula (I) to tertiary monoamine of formula (II) preferably ranges between 0.25 and 10, more preferably between 0.5 and 2.

(11) According to an embodiment, the mass concentration ratio of tertiary diamine of formula (I) to tertiary monoamine of formula (II) ranges between 1.4 and 1.6.

(12) The absorbent solution can contain between 5 wt. % and 95 wt. % of water, preferably between 10 wt. % and 90 wt. %, more preferably between 40 wt. % and 80 wt. %, and most preferably between 50 wt. % and 75 wt. %, inclusive.

(13) The sum of the mass fractions expressed in wt. % of the various compounds of the absorbent solution is 100 wt. % of the absorbent solution.

(14) According to an embodiment, the absorbent solution further contains at least one additional amine that is a tertiary amine, such as N-methyldiethanolamine, triethanolamine, diethylmonoethanolamine, dimethylmonoethanolamine, ethyldiethanolamine, 2-(2-dimethylaminoethoxy)-ethanol, dimethylethylamine, dimethylethoxyethylamine, or a tertiary diamine such as bis(dimethylaminoethyl)ether or tetramethylethylenediamine, or a secondary amine with severe steric hindrance, this hindrance being defined by either the presence of two secondary carbons at nitrogen alpha position or at least one tertiary carbon at nitrogen alpha position. Said additional amine is understood to be any compound having at least one severely hindered tertiary or secondary amine function. The concentration of said severely hindered tertiary or secondary additional amine in the absorbent solution can range between 5 wt. % and 50 wt. %, preferably between 5 wt. % and 35 wt. %, more preferably between 5 wt. % and 25 wt. %.

(15) According to an embodiment, the absorbent solution can additionally comprise 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 wt. %, preferably below 15 wt. % and more preferably below 10 wt. % of said compound containing at least one primary or secondary amine function. Preferably, the absorbent solution comprises at least 0.5 wt. % of said compound containing at least one primary or secondary amine function. Said compound enables to accelerate the absorption kinetics of the CO.sub.2 and, in some cases, of the COS contained in the gas to be treated.

(16) A non-exhaustive list of compounds containing at least one primary or secondary amine function that can go into the formulation is given below: monoethanolamine, diethanolamine, N-butylethanolamine, aminoethylethanolamine, diglycolamine, piperazine, 1-methylpiperazine, 2-methylpiperazine, homopiperazine, N-(2-hydroxyethyl)piperazine, N-(2-aminoethyl)piperazine, morpholine, 3-(metylamino) propylamine, 1,6-hexanediamine and all the diversely N-alkylated derivatives thereof such as, for example, N,N-dimethyl-1,6-hexanediamine, N,N-dimethyl-1,6-hexanediamine, N-methyl-1,6-hexanediamine or N,N,N-trimethyl-1,6-hexanediamine.

(17) The absorbent solution comprising the mixture of 1,2-bis-(2-dimethylaminoethoxy)-ethane and 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol can also contain a mixture of additional primary and/or secondary amines as defined above.

(18) According to an embodiment, the absorbent solution contains organic compounds non reactive towards acid compounds (commonly referred to as physical solvents), which allow to increase the solubility of at least one or more acid compounds of the gaseous effluent. For example, the absorbent solution can comprise between 5 wt. % and 50 wt. % of physical solvent such as alcohols, ethers, ether alcohols, glycol and polyethylene glycol ethers, glycol thioethers, glycol and polyethylene glycol esters and alkoxyesters, glycerol esters, lactones, lactames, N-alkylated pyrrolidones, morpholine derivatives, morpholin-3-one, imidazoles and imidazolidinones, N-alkylated piperidones, cyclotetramethylenesulfones, N-alkylformamides, N-alkylacetamides, ether-ketones, alkyl carbonates or alkyl phosphates and derivatives thereof. By way of non limitative example, it can be a solvent or a mixture of several solvents selected from among methanol, ethanol, 2-ethoxyethanol, triethylene glycoldimethylether, tetraethylene glycoldimethylether, pentaethylene glycol-dimethylether, hexaethylene glycoldimethylether, heptaethylene glycol-dimethylether, octaethylene glycol-dimethylether, diethylene glycol butoxyacetate, glycerol triacetate, sulfolane, N-methylpyrrolidone, N-methylmorpholin-3-one, N,N-dimethylformamide, N-formyl-morpholine, N,N-dimethyl-imidazolidin-2-one, N-methyl-imidazole, ethylene glycol, diethylene glycol, triethylene glycol, thiodiglycol, propylene carbonate and tributylphosphate.

Synthesis of the Mixture of Compounds According to the Invention

Synthesis of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol

(19) The synthesis of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol can be achieved via all the routes allowed by organic chemistry. Without being exhaustive, the four routes described below, illustrated in FIG. 2, can be mentioned. In FIG. 2, the arrows show reaction steps, the reactions being numbered from (1) to (13). These are reaction schemes.

First 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol production route

(20) According to this first route, the 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol is obtained by reaction of one mole of dimethylamine with one mole of triethyleneglycol according to a known condensation reaction (reaction 1). This reaction can for example be conducted in the presence of hydrogen and of a suitable catalyst under conditions known to the person skilled in the art. Selective production of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol via this route is promoted by the use of excess triethylene glycol. Triethylene glycol, which is the precursor in this reaction, is generally obtained by trimerization of ethylene oxide according to a conventional ring opening reaction in the presence of a water molecule. Triethylene glycol is an abundant and inexpensive industrial compound.

Second 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol production route

(21) According to this second route, the 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol is obtained through a reaction of halogenation, chlorination for example, of the triethylene glycol to 2-[2-(2-chloroethoxy)-ethoxy]-ethanol (reaction 3), with a conventional chlorination agent such as hydrochloric acid or thionyl chloride for example, then through a reaction of condensation of the 2-[2-(2-chloroethoxy)-ethoxy]-ethanol with dimethylamine (reaction 5). Selective production of 2-[2-(2-chloroethoxy)-ethoxy]-ethanol via this route can be promoted by the use of excess triethylene glycol.

Third 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol production route

(22) According to this third route, the 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol is obtained first by the reaction of one mole of ammonia with one mole of triethylene glycol according to a known condensation reaction (reaction 8) leading to 2-[2-(2-aminoethoxy)-ethoxy]-ethanol. The primary amine function thereof is subsequently methylated through the reaction of formaldehyde in the presence of hydrogen, generally by means of a suitable catalyst (reaction 10) under conditions known to the person skilled in the art. Selective production of 2-[2-(2-aminoethoxy)-ethoxy]-ethanol according to reaction 8 can be promoted by the use of excess triethylene glycol.

Fourth 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol production route

(23) According to this fourth route, the 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol is obtained by reaction of dimethylamine and ethylene oxide in order to obtain a dimethylaminoethoxypolyethoxyethanol, which is the product of the oligomerization of the ethylene oxide initiated by dimethylamine (reaction 12). The average degree of oligomerization of the mixture of products obtained depends on the molar ratio of ethylene oxide to dimethylamine. The production of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol requires a 3:1 theoretical molar ratio. Separation of this mixture of oligomers, notably by distillation, allows the 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol to be isolated (step 13).

Synthesis of 1,2-bis-(2-dimethylaminoethoxy)-ethane

(24) The synthesis of 1,2-bis-(2-dimethylaminoethoxy)-ethane (also referred to as bis-(2-dimethylaminoethoxy)-1,2-ethane in FIG. 2) can be achieved via all the routes allowed by organic chemistry. Without being exhaustive, the following three routes can be mentioned.

First 1,2-bis-(2-dimethylaminoethoxy)-ethane production route

(25) According to this first route, the 1,2-bis-(2-dimethylaminoethoxy)-ethane is obtained by reaction of one mole of dimethylamine with one mole of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol whose synthesis is described above, according to a known condensation reaction (reaction 2). This reaction can for example be conducted in the presence of hydrogen and of a suitable catalyst under conditions known to the person skilled in the art.

(26) 1,2-bis-(2-dimethylaminoethoxy)-ethane can also be obtained by conducting this reaction directly from triethylene glycol instead of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol, using 2 moles of dimethylamine, i.e. by combining reactions 1 and 2 in the same step.

Second 1,2-bis-(2-dimethylaminoethoxy)-ethane production route

(27) According to this second route, the 1,2-bis-(2-dimethylaminoethoxy)-ethane is obtained through a reaction of halogenation, chlorination for example, of the 2-[2-(2-chloroethoxy)-ethoxy]-ethanol whose synthesis is described above, to bis-(2-chloroethoxy)-1,2-ethane (reaction 4), with a conventional chlorination agent such as hydrochloric acid or thionyl chloride for example, then through a reaction of condensation of the bis-(2-chloroethoxy)-1,2-ethane with dimethylamine leading to 2-[2-(2-dimethylaminoethoxy)-ethoxy]-1-chloroethane, followed by the condensation reaction of the 2-[2-(2-dimethylaminoethoxy)-ethoxy]-1-chloroethane with dimethylamine, leading to 1,2-bis-(2-dimethylaminoethoxy)-ethane (sequence of reactions 6 and 7).

(28) 1,2-bis-(2-dimethylaminoethoxy)-ethane can also be obtained by conducting this reaction directly from triethylene glycol instead of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol, i.e. by combining reactions 3 and 4 in the same step, then 6 and 7 in the same step.

Third 1,2-bis-(2-dimethylaminoethoxy)-ethane production route

(29) According to this third route, the 1,2-bis-(2-dimethylaminoethoxy)-ethane is obtained first by the reaction of one mole of ammonia with one mole of 2-[2-(2-aminoethoxy)-ethoxy]-ethanol whose synthesis is described above, according to a known condensation reaction (reaction 9) leading to bis-(aminoethoxy)-1,2-ethane. The primary amine functions thereof are subsequently methylated through the reaction of formaldehyde in the presence of hydrogen, generally by means of a suitable catalyst (reaction 11) under conditions known to the person skilled in the art.

(30) Bis-(aminoethoxy)-1,2-ethane can also be obtained directly from triethylene glycol instead of 2-[2-(2-aminoethoxy)-ethoxy]-ethanol, using 2 moles of ammonia for combining reactions 8 and 9.

Synthesis of a mixture of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol and 1,2-bis-(2-dimethylaminoethoxy)-ethane

(31) Within the context of the invention where it is desired to use mixtures of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol and 1,2-bis-(2-dimethylaminoethoxy)-ethane, it is possible to perform the synthesis of each one of these molecules separately using all the synthesis routes allowed for each molecule, as described above for example, then to mix the two molecules.

(32) Advantageously, the synthesis of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol and 1,2-bis-(2-dimethylaminoethoxy)-ethane can be conducted in the same steps and a mixture of these two molecules is then obtained.

(33) A mixture of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol and 1,2-bis-(2-dimethylaminoethoxy)-ethane can for example be obtained directly through the reaction of dimethylamine and triethylene glycol according to a known condensation reaction, by adjusting the dimethylamine/triethylene glycol ratio so as to obtain, according to reaction 1 and the sequence of reactions 1 and 2, a mixture of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol and 1,2-bis-(2-dimethylaminoethoxy)-ethane in the desired proportions. These reactions can for example be carried out in the presence of hydrogen and of a suitable catalyst under conditions abundantly mentioned in the literature.

(34) A mixture of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol and 1,2-bis-(2-dimethyl-aminoethoxy)-ethane can also be obtained directly through a reaction of halogenation, for example of chlorination of the triethylene glycol, by adjusting the chlorination agent/triethylene glycol ratio so as to obtain, according to reaction 3 and the sequence of reactions 3 and 4, a mixture of 2-[2-(2-chloroethoxy)-ethoxy]-ethanol and bis-(2-chloroethoxy)-1,2-ethane in the desired proportions. The reaction of the dimethylamine with this mixture of 2-[2-(2-chloroethoxy)-ethoxy]-ethanol and bis-(2-chloroethoxy)-1,2-ethane directly leads to the mixture of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol and 1,2-bis-(2-dimethylaminoethoxy)-ethane according to reactions 5 and 6 plus 7 that are carried out in the same step.

(35) A mixture of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol and 1,2-bis-(2-dimethyl-aminoethoxy)-ethane can also be obtained directly through the reaction of ammonia and triethylene glycol, according to a known condensation reaction, by adjusting the ammonia/triethylene glycol ratio so as to obtain, according to reaction 8 and the sequence of reactions 8 and 9, a mixture of 2-[2-(2-aminoethoxy)-ethoxy]-ethanol and bis-(aminoethoxy)-1,2-ethane in the desired proportions. The primary amine functions of the molecules making up this mixture are subsequently methylated by reaction of formaldehyde in the presence of hydrogen and generally by means of a suitable catalyst under conditions abundantly mentioned in the literature, so as to lead to the mixture of 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol and 1,2-bis-(2-dimethyl-aminoethoxy)-ethane in the desired proportions, according to reactions 10 and 11 that are carried out here in the same step.

(36) Nature of the Gaseous Effluents

(37) The absorbent solutions according to the invention can be used for deacidizing the following gaseous effluents: natural gas, syngas, combustion fumes, blast furnace fumes, refinery gas such as syngas, cracked gas, combustible gas commonly referred to as fuel gas, acid gas from an amine plant, Claus tail gas, biomass fermentation gas, cement plant gas and incinerator fumes.

(38) These gaseous effluents contain one or more of the following acid compounds: CO.sub.2, H.sub.2S, mercaptans (for example methylmercaptan (CH.sub.3SH), ethylmercaptan (CH.sub.3CH.sub.2SH), propylmercaptan (CH.sub.3CH.sub.2CH.sub.2SH)), COS, CS.sub.2, SO.sub.2.

(39) Combustion fumes are produced notably by the combustion of hydrocarbons, biogas, coal in a boiler or for a combustion gas turbine, for example in order to produce electricity. By way of illustration, a deacidizing method according to the invention can be implemented for absorbing at least 70%, preferably at least 80% or even at least 90% of the CO.sub.2 contained in combustion fumes. These fumes generally have a temperature ranging between 20 C. and 60 C., a pressure ranging between 1 and 5 bar, and they can comprise between 50 and 80% nitrogen, between 5 and 40% carbon dioxide, between 1 and 20% oxygen, and some impurities such as SOx and NOx if they have not been removed upstream from the deacidizing process. In particular, the deacidizing method according to the invention is particularly well suited for absorbing the CO.sub.2 contained in combustion fumes having a low CO.sub.2 partial pressure, for example a CO.sub.2 partial pressure below 200 mbar.

(40) The deacidizing method according to the invention can be implemented for deacidizing a syngas. Syngas contains carbon monoxide CO, hydrogen H.sub.2 (generally with a H.sub.2/CO ratio of 2), water vapour (generally at saturation at the wash temperature) and carbon dioxide CO.sub.2 (of the order of 10%). The pressure generally ranges between 20 and 30 bar, but it can reach up to 70 bar. It can also comprise sulfur-containing (H.sub.2S, COS, etc.), nitrogen-containing (NH.sub.3, HCN) and halogenated impurities.

(41) The deacidizing method according to the invention can be implemented for deacidizing a natural gas. Natural gas predominantly consists of gaseous hydrocarbons, but it can contain some of the following acid compounds: CO.sub.2, H.sub.2S, mercaptans, COS, CS.sub.2. The proportion of these acid compounds is very variable and it can reach up to 70 vol. % for CO.sub.2 and up to 40 vol. % for H.sub.2S. The temperature of the natural gas can range between 20 C. and 100 C. The pressure of the natural gas to be treated can range between 10 and 200 bar. The invention can be implemented in order to reach specifications generally imposed on deacidized gas, which are less than 2% CO.sub.2, or even less than 50 vol.Math.ppm CO.sub.2 so as to subsequently carry out liquefaction of the natural gas, less than 4 vol.Math.ppm H.sub.2S, and less than 50 vol.Math.ppm or even less than 10 vol.Math.ppm total sulfur.

(42) Method of Removing Acid Compounds from a Gaseous Effluent

(43) Using an absorbent solution according to the invention for deacidizing a gaseous effluent is schematically done by carrying out an absorption stage followed by a regeneration stage, as shown in FIG. 1 for example.

(44) With reference to FIG. 1, the plant for deacidizing a gaseous effluent according to the invention comprises an absorption column C1 provided with means for contacting the gas and the liquid, for example a random packing, a structured packing or trays. The gaseous effluent to be treated is fed through a line 1 opening into the bottom of column C1. A line 4 allows the absorbent solution to be fed to the top of column C1. A line 2 allows the treated (deacidized) gas to be discharged and a line 3 allows the absorbent solution enriched in acid compounds following absorption to be sent to a regeneration column C2. This regeneration column C2 is provided with gas-liquid contacting internals, for example trays, random or structured packings. The bottom of column C2 is equipped with a reboiler R1 that provides the heat required for regeneration by vaporizing a fraction of the absorbent solution. The acid compound-enriched solution is fed to the top of regeneration column C2 through a line 5. A line 7 allows to discharge at the top of column C2 the gas enriched in acid compounds released upon regeneration, and a line 6 arranged in the bottom of column C2 allows the regenerated absorbent solution to be sent to absorption column C1. A heat exchanger E1 allows the heat of the regenerated absorbent solution from column C2 to be recovered so as to heat the acid compound-enriched absorbent solution leaving absorption column C1.

(45) The absorption stage consists in contacting the gaseous effluent delivered through line 1 with the absorbent solution delivered through line 4. Upon contact, the amine functions of the molecules according to general formula (I) of the absorbent solution react with the acid compounds contained in the effluent so as to obtain an acid compound-depleted gaseous effluent that is discharged through line 2 at the top of column C1 and an acid compound-enriched absorbent solution that is discharged through line 3 in the bottom of column C1 to be regenerated.

(46) The acid compound absorption stage can be carried out at a pressure in column C1 ranging between 1 and 200 bar, preferably between 20 and 100 bar for natural gas treatment, preferably between 1 and 3 bar for industrial fumes treatment, and at a temperature in column C1 ranging between 20 C. and 100 C., preferably between 30 C. and 90 C., or even between 30 C. and 60 C.

(47) The regeneration stage notably consists in heating and optionally in expanding the acid compound-enriched absorbent solution so as to release the acid compounds in gas form. The acid compound-enriched absorbent solution leaving column C1 is fed to heat exchanger E1 where it is heated by the stream circulating in line 6 and coming from regeneration column C2. The heated solution at the outlet of E1 is fed to regeneration column C2 through line 5.

(48) In regeneration column C2, under the effect of contacting the absorbent solution flowing in through line 5 with the vapour produced by the reboiler, the acid compounds are released in gas form and discharged at the top of column C2 through line 7. The regenerated absorbent solution, i.e. depleted in acid compounds, is discharged through line 6 and cooled in E1, then recycled to absorption column C1 through line 4.

(49) The regeneration stage can be carried out by thermal regeneration, optionally complemented by one or more expansion stages. For example, the acid compound-enriched absorbent solution discharged through line 3 can be sent to a first flash drum (not shown) prior to being sent to heat exchanger E1. In the case of a natural gas, expansion allows to obtain a gas discharged at the top of the drum that contains the major part of the aliphatic hydrocarbons co-absorbed by the absorbent solution. This gas can be optionally washed by a fraction of the regenerated absorbent solution and the gas thus obtained can be used as fuel gas. The flash drum preferably operates at a lower pressure than absorption column C1 and a higher pressure than regeneration column C2. This pressure is generally determined by the conditions of use of the fuel gas, and it is typically of the order of 5 to 15 bar. The flash drum operates at a temperature substantially identical to the temperature of the absorbent solution obtained in the bottom of absorption column C1.

(50) Regeneration can be carried out at a pressure in column C2 ranging between 1 and 5 bar, or even up to 10 bar, and at a temperature in column C2 ranging between 100 C. and 180 C., preferably between 110 C. and 170 C., more preferably between 120 C. and 140 C. Preferably, the regeneration temperature in column C2 ranges between 155 C. and 180 C. in cases where the acid gases are intended to be reinjected. Preferably, the regeneration temperature in column C2 ranges between 115 C. and 130 C. in cases where the acid gas is sent to the atmosphere or to a downstream treating process such as a Claus process or a tail gas treating process.

EXAMPLES

(51) The examples below illustrate, by way of non limitative example, some of the performances of the compounds according to formulas (I) and (II) in admixture when used in aqueous solution for removing acid compounds, such as CO.sub.2 or H.sub.2S, contained in a gaseous effluent by contacting the gaseous effluent with the solution.

Example 1: H2S Absorption Capacity of Aqueous Amine Solutions for an Acid Gas Treating Method

(52) The H.sub.2S absorption capacity performances at 40 C. of an aqueous solution of 1,2-bis-(2-dimethylaminoethoxy)-ethane in admixture with 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol according to the invention (solution (e)), containing 30 wt. % 1,2-bis-(2-dimethylaminoethoxy)-ethane and 20 wt. % 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol, are compared with the following solutions: solution (a): an aqueous MDEA solution containing 50 wt. % MDEA, which is a reference absorbent solution for selective removal in gas treatment; solution (c): an aqueous solution according to the prior art (U.S. Pat. No. 4,405,582) of 1,2-bis-(2-dimethylaminoethoxy)-ethane containing 30 wt. % 1,2-bis-(2-dimethylaminoethoxy)-ethane; solution (b): an aqueous solution according to the prior art (U.S. Pat. No. 4,405,582) of 1,2-bis-(2-dimethylaminoethoxy)-ethane containing 50 wt. % 1,2-bis-(2-dimethylaminoethoxy)-ethane; solution (d): an aqueous solution according to the prior art (U.S. Pat. No. 4,405,582) of a mixture of 1,2-bis-(2-dimethylaminoethoxy)-ethane and MDEA, containing 30 wt. % 1,2-bis-(2-dimethylaminoethoxy)-ethane in admixture with 20 wt. % MDEA.

(53) An absorption test is carried out at 40 C. on these aqueous amine solutions in a thermostat-controlled equilibrium cell. This test consists in injecting into the equilibrium cell, previously filled with degassed aqueous amine solution, a known amount of acid gas, H.sub.2S in this example, then in waiting for the equilibrium state to be reached. The amounts of acid gas absorbed in the aqueous amine solution are then deduced from the temperature and pressure measurements by means of material and volume balances. The solubilities are conventionally represented in form of H.sub.2S partial pressures (in bar) as a function of the H.sub.2S loading (in mol of H.sub.2S/kg absorbent solution and in mol of H.sub.2S/mol of amine).

(54) In the case of deacidizing a H.sub.2S-containing natural gas, the H.sub.2S partial pressures encountered in acid gases typically range between 0.1 and 1 bar. By way of example, in this industrial range, Table 1 hereafter compares the H.sub.2S loadings obtained at 40 C. for various H.sub.2S partial pressures between the MDEA absorbent solution (a), the absorbent solution according to the invention (e), and the other three aqueous solutions according to U.S. Pat. No. 4,405,582 (b), (c) and (d).

(55) TABLE-US-00001 TABLE 1 Loading at 40 C. Wt. % Wt. % [amine (mole H.sub.2S/kg) solvent Solution Amines in diamine amine Wt. % function] P = 0.1 P = 0.3 P = 1 reference aqueous solution (I) (II) MDEA (mole/kg) bar bar bar (a) MDEA 0% 0% 50% 4.20 0.88 1.64 2.91 (b) Diamine I: 1,2-bis-(2- 50% 0% 0% 4.90 0.14 0.39 1.95 dimethylaminoethoxy)- ethane (according to patent U.S. Pat. No. 4,405,582) (c) Diamine I: 1,2-bis-(2- 30% 0% 0% 2.94 0.99 1.98 2.69 dimethylaminoethoxy)- ethane (according to patent U.S. Pat. No. 4,405,582) (d) Diamine I: 1,2-bis-(2- 30% 0% 20% 4.62 0.80 1.78 3.39 dimethylaminoethoxy)- ethane + MDEA (according to patent U.S. Pat. No. 4,405,582) (e) Diamine I: 1,2-bis-(2- 30% 20% 0% 4.07 1.46 2.32 3.52 dimethylaminoethoxy)- ethane + monoamine II: 2-[2-(2- dimethylaminoethoxy)- ethoxy]-ethanol

(56) At 40 C., whatever the H.sub.2S partial pressure, the absorption capacity of the aqueous solution according to the invention (e) is higher than that of the reference MDEA solution containing the same percentage by weight of amine and a higher amine function concentration. This capacity gain allows to distinguish the formulation according to the invention (e) from the formulations according to the prior art based on 1,2-bis-(2-dimethylaminoethoxy)-ethane and/or MDEA.

(57) Indeed, at a 0.1 bar partial pressure, the H.sub.2S loading is 1.46 mol/kg in the absorbent solution according to the invention (e) and 0.88 mol/kg in the reference MDEA absorbent solution (a). At a H.sub.2S partial pressure of 0.1 bar, the difference between the H.sub.2S loadings of the two absorbent solutions is 0.58 mol/kg with an absorption capacity for the absorbent solution according to the invention (e) increased by 66% in relation to the reference MDEA absorbent solution (a) containing the same percentage by weight of amine and with yet a higher amine function concentration.

(58) This gain still is 47% in relation to solution (c) according to the prior art containing the same percentage by weight (30%) of 1,2-bis-(2-dimethylaminoethoxy)-ethane as the formulation according to the invention (e). On the other hand, the absorption capacity of aqueous solution (b) containing 50 wt. % 1,2-bis-(2-dimethylaminoethoxy)-ethane according to the prior art decreases by 84% in relation to the reference MDEA solution (a) containing the same percentage by weight of amine and with yet a lower amine function concentration. Similarly, the H.sub.2S absorption capacity for a 0.1 bar partial pressure of the aqueous solution according to the prior art (d) containing 30 wt. % 1,2-bis-(2-dimethylaminoethoxy)-ethane and 20 wt. % MDEA decreases by 9% in relation to the reference MDEA solution (a) containing the same percentage by weight of amine (50%) and with yet a lower amine function concentration.

(59) At a H.sub.2S partial pressure of 0.3 bar, the H.sub.2S loading difference between the absorbent solution according to the invention (e) and the reference MDEA solution (a) reaches 41% in favour of the absorbent solution according to the invention. This gain still is 17% in relation to an aqueous solution (c) containing the same percentage by weight (30%) of 1,2-bis-(2-dimethylaminoethoxy)-ethane as the formulation according to the invention (e). The H.sub.2S loading difference still is 30% in relation to aqueous solution (e) according to the prior art containing the same percentage by weight of 1,2-bis-(2-dimethylaminoethoxy)-ethane (30%), the same percentage by weight of amine (50%) and yet a higher amine function concentration than the formulation according to the invention (e). On the other hand, the absorption capacity of solution (b) according to the prior art decreases by 76% in relation to the reference MDEA solution (a) containing the same percentage by weight of amine (50%) and with yet a lower amine function concentration.

(60) At a H.sub.2S partial pressure of 1 bar, the H.sub.2S loading difference between the absorbent solution according to the invention (e) and the reference MDEA solution (a) reaches 21% in favour of the absorbent solution according to the invention. This gain still is 31% in relation to an aqueous solution (c) containing the same percentage by weight (30%) of 1,2-bis-(2-dimethylaminoethoxy)-ethane as the formulation according to the invention (e). It still is 4% in relation to aqueous solution (d) according to the prior art containing the same percentage by weight of 1,2-bis-(2-dimethylaminoethoxy)-ethane (30%), the same percentage by weight of amine (50%) and yet a higher amine function concentration than the formulation according to the invention (e). On the other hand, the absorption capacity of aqueous solution (b) containing 50 wt. % 1,2-bis-(2-dimethylaminoethoxy)-ethane according to the prior art decreases by 33% in relation to the reference MDEA solution (a) containing the same percentage by weight of amine and with yet a lower amine function concentration.

(61) It can thus be observed that, unlike other solutions of the prior art, the solution according to the invention (e) has a higher H.sub.2S absorption capacity than the reference 50 wt. % MDEA aqueous solution (a) and than the various exemplified solutions according to the prior art, at 40 C., in the H.sub.2S partial pressure range between 0.1 and 1 bar corresponding to a partial pressure range representative of usual industrial conditions. It appears that the exemplified absorbent solution according to the invention allows to reduce the solvent flow rates required in H.sub.2S-containing gas deacidizing applications in relation to the reference MDEA absorbent solution or to other solutions of the prior art.

Example 2: CO2 Absorption Capacity of Amine Formulations for an Acid Gas Treating Method

(62) The CO.sub.2 absorption capacity performances at 40 C. of an aqueous solution of 1,2-bis-(2-dimethylaminoethoxy)-ethane in admixture with 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol according to the invention, containing 30 wt. % 1,2-bis-(2-dimethylaminoethoxy)-ethane and 20 wt. % 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol (solution (e)), are compared with those of: an aqueous MDEA solution containing 47 wt. % MDEA, which is a reference absorbent solution for selective removal in gas treatment (solution (f)); and an aqueous solution of 1,2-bis-(2-dimethylaminoethoxy)-ethane (according to U.S. Pat. No. 4,405,582) containing 30 wt. % 1,2-bis-(2-dimethylaminoethoxy)-ethane (solution (c)).

(63) An absorption test is carried out at 40 C. on aqueous amine solutions in a thermostat-controlled equilibrium cell according to the same method of operation as the one described in the previous example, by replacing the H.sub.2S by CO.sub.2.

(64) In the case of natural gas deacidizing, the CO.sub.2 partial pressures encountered in acid gases are typically greater than or equal to 1 bar. By way of example, in this industrial range, Table 2 hereafter compares the CO.sub.2 loadings obtained at 40 C. for a 1 bar CO.sub.2 partial pressure between the 47 wt. % MDEA aqueous solution (f), the solution according to the invention (e) and the aqueous solution according to the prior art (c).

(65) TABLE-US-00002 TABLE 2 Loading at 40 C. (mole Solu- CO.sub.2/kg) solvent tion Wt. % Wt. % for a 1 bar CO.sub.2 refer- Amines in diamine amine Wt. % partial pressure ence aqueous solution (I) (II) MDEA PCO.sub.2 = 1 bar (f) MDEA 0% 0% 47% 2.73 (c) Diamine I: 1,2- 30% 0% 0% 2.67 bis-(2-dimethyl- aminoethoxy)- ethane (accord- ing to patent U.S. Pat. No. 4,405,582) (e) Diamine I: 1,2- 30% 20% 0% 3.25 bis-(2-dimethyl- aminoethoxy)- ethane + mono- amine II: 2-[2- (2-dimethyl- aminoethoxy)- ethoxy]-ethanol

(66) At 40 C., for a 1 bar CO.sub.2 partial pressure, the absorption capacity of the aqueous solution according to the invention (e) is higher than that of the reference solution (f) containing the same percentage by weight of amine and a higher amine function concentration. This capacity gain allows to distinguish the formulation according to the invention from the formulations according to the prior art based on 1,2-bis-(2-dimethylaminoethoxy)-ethane.

(67) Indeed, at a 1 bar partial pressure, the CO.sub.2 loading is 3.25 mol/kg in the absorbent solution according to the invention (e) and 2.73 mol/kg in the absorbent MDEA solution (f). The difference between the CO.sub.2 loadings of the two absorbent solutions is 0.52 mol/kg with an absorption capacity for the absorbent solution according to the invention (e) increased by 19% in relation to the reference MDEA absorbent solution (f). On the other hand, the absorption capacity of the aqueous solution according to the prior art (c) has decreased by 2% in relation to the reference MDEA solution (f).

(68) It can thus be observed that, unlike another solution of the prior art, the aqueous solution according to the invention (e) has a higher CO.sub.2 absorption capacity than the MDEA aqueous solution (f) and than the solution according to the prior art (c), at 40 C., in a 1 bar CO.sub.2 partial pressure range within a partial pressure range representative of usual industrial conditions. It appears that the exemplified absorbent solution according to the invention (e) allows to reduce the solvent flow rates required in CO.sub.2-containing gas deacidizing applications in relation to the reference MDEA absorbent solution or to other solutions of the prior art.

Example 3: CO2 Absorption Rate of an Amine Formulation for a Selective Absorption Method

(69) A comparative measurement of the CO.sub.2 absorption rate is performed between an absorbent solution containing 30 wt. % 1,2-bis-(2-dimethylaminoethoxy)-ethane and 20 wt. % 2-[2-(2-dimethylaminoethoxy)-ethoxy]-ethanol according to the invention (solution (e)), and an aqueous solution of N-methyldiethanolamine (MDEA) with 47 wt. % MDEA (solution (f)), which is the reference absorbent solution for selective removal in gas treatment.

(70) For each test, the CO.sub.2 flow absorbed by the aqueous absorbent solution is measured in a stirred closed reactor at a controlled temperature of 40 C. 50 g of solution are fed to the closed reactor. A CO.sub.2 injection is carried out at 1 bar in the vapour phase of the 50 cm.sup.3-volume reactor. The gas phase and the liquid phase are stirred at 600 rpm. The CO.sub.2 absorption rate is measured through pressure variation in the gas phase. A global transfer coefficient Kg is thus determined.

(71) The results obtained are shown in Table 3 hereafter in relative absorption rate in relation to the reference MDEA aqueous absorbent solution (f), this relative absorption rate being defined by the ratio of the global transfer coefficient of the absorbent solution tested to the global transfer coefficient of the reference absorbent solution (with MDEA).

(72) TABLE-US-00003 TABLE 3 CO.sub.2 relative Solution absorption rate a reference Absorbent solution at 50 C. (f) 47 wt. % MDEA 1.00 (e) 30 wt. % 1,2-bis-(2-dimethyl- 0.91 aminoethoxy)-ethane + 20 wt. % 2-[2-(2-dimethyl- aminoethoxy)-ethoxy]-ethanol

(73) The results show, under these test conditions, a slower rate of absorption of CO.sub.2 by the absorbent solution according to the invention compared to the reference formulation with MDEA (f). It therefore appears that the exemplified absorbent solution according to the invention surprisingly is of particular and improved interest in the case of selective deacidizing of a gaseous effluent where the CO.sub.2 absorption kinetics is to be limited.

(74) The H.sub.2S absorption capacity of the exemplified absorbent solution according to the invention being higher than that of a MDEA aqueous solution (see Example 1 above), it appears that the exemplified absorbent solution according to the invention (e) allows to reduce the absorbent solution flow rates required in selective deacidizing applications (H.sub.2S over CO.sub.2) for absorbing a given flow of H.sub.2S while reducing the flow of co-absorbed CO.sub.2 in relation to the reference MDEA absorbent solution.

APPENDIX: LIST OF THE MOLECULES REPRESENTED IN FIG. 2

(75) TABLE-US-00004 Ref. Name Formula P1 2-[2-(2-dimethylaminoethoxy)-ethoxy]- ethanol P2 1,2-bis-(2-dimethylaminoethoxy)-ethane Or bis-(2-dimethylaminoethoxy)-1,2-ethane P3 dimethylaminoethoxypolyethoxyethanol P4 2-[2-(2-aminoethoxy)-ethoxy]-ethanol P5 bis-(aminoethoxy)-1,2-ethane 0 P6 Triethylene glycol P7 2-[2-(2-chloroethoxy)-ethoxy]-ethanol P8 bis-(2-chloroethoxy)-1,2-ethane P9 2-[2-(2-dimethylaminoethoxy)-ethoxy]-1- chloroethane P10 Dimethylamine (CH.sub.3).sub.2NH P11 Ethylene oxide