NOVEL BETA-HYDROXYLATED TERTIARY DIAMINES, A PROCESS FOR THEIR SYNTHESIS AND THEIR USE FOR ELIMINATING ACID COMPOUNDS A GASEOUS EFFLUENT

Abstract

The invention relates to novel nitrogen compounds belonging to the family of tertiary diamines of general formula (I) below, wherein R is an alkanediyl radical (CH.sub.2)n with n=2, 3, 4, 5 or 6.

##STR00001##

The compound according to the invention is for example N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol or N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol. The invention also relates to the method for preparing them and to their use for removing acid compounds contained in a gaseous effluent.

Claims

1. A method of removing acid compounds contained in a gaseous effluent, comprising carrying out an acid compound absorption stage by contacting the gaseous effluent with an absorbent solution comprising water and at least one nitrogen compound belonging to the family of tertiary diamines meeting general formula (I) as follows: ##STR00013## wherein R is an alkanediyl radical (CH.sub.2)n with n=2, 3, 4, 5 or 6.

2. A method as claimed in claim 1, wherein the absorbent solution comprises between 5 wt. % and 95 wt. % of said at least one nitrogen compound, and between 5 wt. % and 95 wt. % of water.

3. A method as claimed in claim 1, wherein the absorbent solution additionally comprises between 5 wt. % and 95 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.

4. A method as claimed in claim 3, wherein said additional amine is a tertiary amine selected from among the group made up of: N-methyldiethanolamine, triethanolamine, diethylmonoethanolamine, dimethylmonoethanolamine, and ethyldiethanolamine.

5. A method as claimed in claim 1, wherein the absorbent solution also comprises a non-zero amount less than 30 wt. % of at least one additional amine such as a primary amine or a secondary amine.

6. A method as claimed in claim 5, wherein said additional 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-hexane-diamine, and N,N,N-trimethyl-1,6-hexanediamine.

7. A method as claimed in claim 1, wherein the absorbent solution furthermore comprises at least one physical solvent selected from the group made up of methanol, ethanol, 2-ethoxyethanol, triethylene glycoldimethylether, tetra-ethylene glycoldimethylether, pentaethylene glycoldimethylether, 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-methylimidazole, ethylene glycol, diethylene glycol, triethylene glycol, thiodiglycol and tributyl phosphate.

8. A method as claimed in claim 1, wherein the gaseous effluent is selected from among natural gas, syngases, combustion fumes, refinery gas, acid gas from an amine plant, Claus tail gas, biomass fermentation gas, cement plant gas and incinerator fumes.

9. A method as claimed in claim 1, 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, preferably natural gas.

10. A method as claimed in claim 1, wherein the absorbent solution comprises between 10 wt. % and 90 wt. % of said at least one nitrogen compound, and between 10 wt. % and 90 wt. % of water.

11. A method as claimed in claim 1, wherein, in general formula (I), n is equal to 2 and R is an ethylidene radical r1, named N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol and meeting the formula as follows: ##STR00014##

12. A method as claimed in claim 1, wherein, in general formula (I), n is equal to 4 and R is a butylidene radical r2, named N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol and meeting the formula as follows: ##STR00015##

13. 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 comprising water and at least one nitrogen compound obtained by a synthesis method comprising the following reactions: a first reaction of epoxidation of an alpha-omega-diene to achieve epoxidation of each one of the alkene functions of the alpha-omega-diene to oxirane functions so as to produce a diepoxyalkane, a second reaction of addition of two moles of dimethylamine and one molecule of the diepoxyalkane so as to produce a nitrogen compound belonging to the family of tertiary diamines meeting general formula (I) as follows: ##STR00016## wherein R is an alkanediyl radical (CH.sub.2)n with n=2, 3, 4, 5 or 6.

Description

BRIEF DESCRIPTION OF THE SOLE FIGURE

[0069] 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 figure described hereafter:

[0070] FIG. 1 is a block diagram of the implementation of an acid gas treating method.

[0071] In the diagrams of the present description illustrating the preparation of nitrogen compounds according to the invention, the arrows represent reaction stages. These are reaction schemes.

DETAILED DESCRIPTION OF THE INVENTION

[0072] The novel nitrogen compounds according to the invention are tertiary diamines meeting general formula (I) as follows:

##STR00005##

wherein R is an alkanediyl radical (CH.sub.2)n with n=2, 3, 4, 5 or 6.

[0073] In the present description, a tertiary diamine is understood to be a chemical compound comprising two amine functions which are tertiary amine functions.

[0074] In general formula (I), the hydroxyl groups are carried by carbon atoms at amine beta position.

[0075] R is selected from among one of the following groups: [0076] r1: a 1,2-ethanediyl radical CH.sub.2CH.sub.2 when n=2. The nitrogen compound is then N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol having the following formula:

##STR00006## [0077] r2: a 1,4-butanediyl radical CH.sub.2CH.sub.2CH.sub.2CH.sub.2 when n=4. The nitrogen compound is then N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol having the following formula:

##STR00007## [0078] r3: a 1,3-propanediyl radical when n=3. The nitrogen compound is then N,N,N,N-tetramethyl-1,7-diamino-2,6-heptanediol having the following formula:

##STR00008## [0079] r4: a 1,5-pentanediyl radical when n=5. The nitrogen compound is then N,N,N,N-tetramethyl-1,9-diamino-2,8-nonanediol having the following formula:

##STR00009## [0080] r5: a 1,6-hexanediyl radical when n=6. The nitrogen compound is then N,N,N,N-tetramethyl-1,10-diamino-2,9-decanediol having the following formula:

##STR00010##

[0081] Advantageously, a compound according to the invention is N,N,N,N-(tetra-methyl)-1,6-diamino-2,5-hexanediol or N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octane-diol.

[0082] Synthesis of a Compound According to the Invention

[0083] The nitrogen compounds of general formula (I) can be prepared by carrying out the following reactions: [0084] a first epoxidation reaction of an alpha-omega-diene to achieve epoxidation of each one of the alkene functions of the alpha-omega-diene to oxirane functions so as to produce a diepoxyalkane, [0085] a second reaction of addition of two moles of dimethylamine and one molecule of the diepoxyalkane so as to produce the nitrogen compound according to general formula (I).

[0086] An alpha-omega-diene is understood to be a diene comprising two alkene functions at the ends, such as 1,5-hexadiene and 1,7-octadiene.

[0087] The synthesis of N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol is illustrated by Diagram A hereafter:

##STR00011##

[0088] A reaction of epoxidation of each one of the two alkene functions of the 1,5-hexadiene to oxirane functions is first conducted in order to obtain 1,2,5,6-diepoxyhexane. This epoxidation reaction can be carried out with any means known to the person skilled in the art for conducting epoxidation of a carbon-carbon double bond. A peroxide, a hydroperoxide, a peracid such as peracetic acid or 3-chloroperbenzoic acid, or a perester can be used for example. It is also possible to use the combination of an acid such as acetic acid and of a peroxide such as hydrogen peroxide allowing in-situ generation of a peracid. The reaction can be conducted under mild conditions, for example at a temperature close to ambient temperature, and in the presence of a solvent, which can be a chlorinated solvent such as dichloromethane or an aliphatic or aromatic hydrocarbon solvent. The epoxidation reaction of an unsaturation can also be performed by means of oxygen and of a suitable catalytic system.

[0089] Secondly, a reaction of addition of two moles of dimethylamine to one molecule of 1,2,5,6-diepoxyhexane to form N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol is carried out. This reaction can be conducted with excess dimethylamine. It is an exothermic reaction that is preferably performed with suitable temperature control. For example, the temperature is maintained within the 15 C./100 C. range.

[0090] The synthesis of N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol is illustrated by Diagram B below:

##STR00012##

[0091] This synthesis is based on the same reactions, the same procedures and the same conditions as those described above for preparing N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol, but using 1,7-octadiene instead of 1,5-hexadiene as the precursor for the first epoxidation reaction. The epoxidation reaction yields 1,2,7,8-diepoxyoctane used in the second addition reaction with dimethylamine.

[0092] The synthesis of the other compounds according to the invention, N,N,N,N-tetramethyl-1,7-diamino-2,6-heptanediol (R=r3, n=3), N,N,N,N-tetramethyl-1,9-diamino-2,8-nonanediol (R=r4, n=5) and N,N,N,N-tetramethyl-1,10-diamino-2,9-decanediol (R=r5, n=6), is based on the same reactions, the same procedures and the same conditions as those described above for preparing N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol or N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol, but by using the compounds listed in Table 1 below as the precursors and intermediate products of the reactions:

TABLE-US-00001 TABLE 1 Name of the compound of general Name of the Name of the formula(I) alpha-omega-diene diepoxyalkane N,N,N,N-tetramethyl-1,7- 1,6-heptadiene 1,2,6,7- diamino-2,6-heptanediol diepoxyheptane N,N,N,N-tetramethyl-1,9- 1,8-nonadiene 1,2,8,9- diamino-2,8-nonanediol diepoxynonane N,N,N,N-tetramethyl-1,10- 1,9-decadiene 1,2-9,10- diamino-2,9-decanediol diepoxydecane

[0093] Preferably, the first epoxidation reaction and the second addition reaction are conducted in two successive stages during the preparation of the nitrogen compounds according to the invention.

[0094] Use of the Compounds According to the Invention in the Treatment of Gaseous Effluents

[0095] The compounds according to the invention can be used in different fields of chemistry and they can be advantageously used in the treatment of gas of industrial origin and of natural gas.

[0096] The present invention aims to remove acid compounds from a gaseous effluent using an aqueous solution comprising at least one nitrogen compound according to general formula (I), and advantageously N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol and N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol. The solution is contacted with the gaseous effluent to remove acid compounds contained therein.

[0097] The method of removing acid compounds contained in a gaseous effluent according to the invention can in particular be implemented for selective removal of H.sub.2S over CO.sub.2 from a gaseous effluent comprising H.sub.2S and CO.sub.2, for example natural gas.

[0098] The method of removing acid compounds contained in a gaseous effluent according to the invention can also be advantageously implemented for CO.sub.2 capture from gas of industrial origin and from natural gas, for example combustion fumes.

[0099] Using beta-hydroxylated tertiary diamines according to the invention allows to obtain good performances in terms of cyclic capacity of acid gas absorption and/or of absorption selectivity towards H.sub.2S, notably higher absorption selectivity towards H.sub.2S than reference amines such as N-methyldiethanolamine (MDEA) for an equivalent or higher acid gas cyclic absorption capacity.

[0100] Composition of the Absorbent Solution

[0101] The absorbent solution used for removing the acid compounds contained in a gaseous effluent comprises: [0102] water, [0103] at least one nitrogen compound belonging to the family of tertiary diamines meeting general formula (I).

[0104] The absorbent solution can comprise N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol or N,N,N,N1-(tetramethyl)-1,8-diamino-2,7-octanediol, or a mixture of the two compounds.

[0105] The amines of general formula (I) can be in variable concentration 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.

[0106] 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.

[0107] The sum of the mass fractions expressed in wt. % of the various compounds of the absorbent solution is 100 wt. % of the absorbent solution.

[0108] According to one embodiment, the absorbent solution can furthermore contain at least one additional amine that is a tertiary amine, such as N-methyldiethanolamine, triethanolamine, diethylmonoethanolamine, dimethylmonoethanolamine or ethyl-diethanolamine, 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 95 wt. %, preferably between 5 wt. % and 50 wt. %, more preferably between 5 wt. % and 30 wt. %.

[0109] According to an embodiment, the amines of general formula (I) can 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 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 allows to accelerate the absorption kinetics of the CO.sub.2 and, in some cases, of the COS contained in the gas to be treated.

[0110] A non-exhaustive list of compounds containing at least one primary or secondary amine function that can go into the formulation is given below: [0111] monoethanolamine, [0112] diethanolamine, [0113] N-butylethanolamine, [0114] aminoethylethanolamine, [0115] diglycolamine, [0116] piperazine, [0117] 1-methylpiperazine, [0118] 2-methylpiperazine, [0119] homopiperazine, [0120] N-(2-hydroxyethyl)piperazine, [0121] N-(2-aminoethyl)piperazine, [0122] morpholine, [0123] 3-(metylamino)propylamine, [0124] 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-hexane-diamine, N-methyl-1,6-hexanediamine or N,N,N-trimethyl-1,6-hexane-diamine.

[0125] The absorbent solution comprising at least one compound according to the invention can contain a mixture of additional amines as defined above.

[0126] According to an embodiment, the absorbent solution can contain organic compounds non reactive towards the 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.

[0127] By way of non limitative example, it can be methanol, ethanol, 2-ethoxyethanol, triethylene glycoldimethylether, tetraethylene glycoldimethylether, pentaethylene glycol-dimethylether, hexaethylene glycoldimethylether, 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-methyl-imidazole, ethylene glycol, diethylene glycol, triethylene glycol, thiodiglycol, propylene carbonate, tributylphosphate.

[0128] Nature of the Gaseous Effluents

[0129] The absorbent solutions comprising at least one nitrogen compound according to the invention can be used for deacidizing the following gaseous effluents: natural gas, syngas, combustion fumes, refinery gas, acid gas from an amine plant, Claus tail gas, biomass fermentation gas, cement plant gas and incinerator fumes. 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), propyl-mercaptan (CH.sub.3CH.sub.2CH.sub.2SH)), COS, CS.sub.2, SO.sub.2.

[0130] 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 using the compounds 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 using the compounds 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.

[0131] The deacidizing method using the compounds 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.

[0132] The deacidizing method using the compounds 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 ppm CO.sub.2 so as to subsequently carry out liquefaction of the natural gas, less than 4 ppm H.sub.2S, and less than 50 ppm or even less than 10 ppm by volume of total sulfur.

[0133] Method of Removing Acid Compounds from a Gaseous Effluent

[0134] Using an aqueous solution comprising a compound according to general formula (I) 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.

[0135] 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.

[0136] 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.

[0137] The acid compound absorption stage can be carried out at a pressure in column C1 ranging between 1 and 200 bar, preferably between 1 and 120 bar, more 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.

[0138] 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.

[0139] 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.

[0140] 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 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 pressure lower than in absorption column C1 and higher than in 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.

[0141] 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

[0142] The examples below illustrate by way of non limitative example the synthesis of the compounds according to the invention, and some performances of these compounds 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

Synthesis of the Molecules According to the Invention

[0143] The examples hereafter illustrate the synthesis of the nitrogen compounds according to the invention, it being understood that all the synthesis possibilities for these molecules, regarding synthesis routes as well as the possible operating modes, are not described here.

[0144] Example of N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol synthesis

[0145] 460.9 g (2.67 mol) of 3-chloroperbenzoic acid is added in four hours, in small fractions, to a solution of 75.0 g of 1,5-hexadiene in 1200 ml dichloromethane maintained between 0 C. and 5 C. After return to ambient temperature, the medium is filtered. The filtrate is washed twice with 750 ml of an aqueous 10% sodium sulfite solution, then with 750 ml of water. After distillation, 86.1 g of a product whose .sup.13C NMR spectrum (CDCl.sub.3) characterized by the below data matches that of 1,2,5,6-diepoxyhexane is obtained: [0146] 46.1 ppm:[CH.sub.2(O)CH]CH.sub.2CH.sub.2[CH(O)CH.sub.2] [0147] 50.8 ppm:[CH.sub.2(O)CH]CH.sub.2CH.sub.2[CH(O)CH.sub.2] [0148] 28.6 ppm:[CH.sub.2(O)CH]CH.sub.2CH.sub.2[CH(O)CH.sub.2] [0149] 28.2 ppm:[CH.sub.2(O)CH]CH.sub.2CH.sub.2[CH(O)CH.sub.2] [0150] 51.0 ppm:[CH.sub.2(O)CH]CH.sub.2CH.sub.2[CH(O)CH.sub.2] [0151] 46.1 ppm:[CH.sub.2(O)CH]CH.sub.2CH.sub.2[CH(O)CH.sub.2].

[0152] 85.0 g (0.74 mol) of 1,2,5,6-diepoxyhexane is added in two hours, while maintaining the temperature at 5 C., to 1636.0 g of an aqueous 40% dimethylamine solution. After return to ambient temperature, the excess dimethylamine and the water are removed. After distillation under reduced pressure, 115.0 g of a product whose .sup.13C NMR spectrum (CDCl.sub.3) characterized by the below data matches that of N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol is isolated. [0153] 45.3 ppm:(CH3).sub.2NCH.sub.2CH(OH)CH.sub.2CH.sub.2CH(OH)CH.sub.2N(CH.sub.3).sub.2 [0154] 30.8 ppm:(CH.sub.3).sub.2NCH.sub.2CH(OH)CH.sub.2CH.sub.2CH(OH)CH.sub.2N(CH.sub.3).sub.2 [0155] 67.0 ppm:(CH.sub.3).sub.2NCH.sub.2CH(OH)CH.sub.2CH.sub.2CH(OH)CH.sub.2N(CH.sub.3).sub.2 [0156] 65.3 ppm:(CH.sub.3).sub.2NCH.sub.2CH(OH)CH.sub.2CH.sub.2CH(OH)CH.sub.2N(CH.sub.3).sub.2 [0157] 65.3 ppm:(CH.sub.3).sub.2NCH.sub.2CH(OH)CH.sub.2CH.sub.2CH(OH)CH.sub.2N(CH.sub.3).sub.2 [0158] 66.7 ppm:(CH.sub.3).sub.2NCH.sub.2CH(OH)CH.sub.2CH.sub.2CH(OH)CH.sub.2N(CH.sub.3).sub.2 [0159] 31.1 ppm:(CH.sub.3).sub.2NCH.sub.2CH(OH)CH.sub.2CH.sub.2CH(OH)CH.sub.2N(CH.sub.3).sub.2 [0160] 45.3 ppm:(CH.sub.3).sub.2NCH.sub.2CH(OH)CH.sub.2CH.sub.2CH(OH)CH.sub.2N(CH.sub.3).sub.2

[0161] Example of N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol synthesis

[0162] 457.5 g (2.65 mol) of 3-chloroperbenzoic acid is added in four hours, in small fractions, to a solution of 100.0 g of 1,7-octadiene in 1200 ml dichloromethane maintained between 0 C. and 5 C. After return to ambient temperature, the medium is filtered. The filtrate is washed twice with 750 ml of an aqueous 10% sodium sulfite solution, then with 750 ml of water. After distillation, 110.0 g of a product whose .sup.13C NMR spectrum (CDCl.sub.3) characterized by the below data matches that of 1,2,7,8-diepoxyoctane is obtained: [0163] 45.6 ppm:[CH2(O)CH]CH2CH2CH2CH2[CH(O)CH2] [0164] 50.8 ppm:[CH2(O)CH]CH2CH2CH2CH2[CH(O)CH2] [0165] 31.4 ppm:[CH2(O)CH]CH2CH2CH2CH2[CH(O)CH2] [0166] 24.9 ppm:[CH2(O)CH]CH2CH2CH2CH2[CH(O)CH2] [0167] 24.9 ppm:[CH2(O)CH]CH2CH2CH2CH2[CH(O)CH2] [0168] 31.4 ppm:[CH2(O)CH]CH2CH2CH2CH2[CH(O)CH2] [0169] 50.8 ppm:[CH2(O)CH]CH2CH2CH2CH2[CH(O)CH2] [0170] 45.6 ppm:[CH2(O)CH]CH2CH2CH2CH2[CH(O)CH2].

[0171] 100.0 g (0.70 mol) of 1,2,7,8-diepoxyoctane is added in two hours, while maintaining the temperature at 5 C., to 769.0 g of an aqueous 40% dimethylamine solution. After return to ambient temperature, the excess dimethylamine and the water are removed. After distillation under reduced pressure, 143.0 g of a product whose .sup.13C NMR spectrum (CDCl.sub.3) characterized by the below data matches that of N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol is isolated. [0172] 45.3 ppm:(CH3)2NCH2CH(OH)CH2CH2CH2CH2CH(OH)CH2N(CH3)2 [0173] 65.4 ppm:(CH3)2NCH2CH(OH)CH2CH2CH2CH2CH(OH)CH2N(CH3)2 [0174] 66.7 ppm:(CH3)2NCH2CH(OH)CH2CH2CH2CH2CH(OH)CH2N(CH3)2 [0175] 34.7 ppm:(CH3)2NCH2CH(OH)CH2CH2CH2CH2CH(OH)CH2N(CH3)2 [0176] 25.7 ppm:(CH3)2NCH2CH(OH)CH2CH2CH2CH2CH(OH)CH2N(CH3)2 [0177] 25.7 ppm:(CH3)2NCH2CH(OH)CH2CH2CH2CH2CH(OH)CH2N(CH3)2 [0178] 34.7 ppm:(CH3)2NCH2CH(OH)CH2CH2CH2CH2CH(OH)CH2N(CH3)2 [0179] 66.7 ppm:(CH3)2NCH2CH(OH)CH2CH2CH2CH2CH(OH)CH2N(CH3)2 [0180] 65.4 ppm:(CH3)2NCH2CH(OH)CH2CH2CH2CH2CH(OH)CH2N(CH3)2 [0181] 45.3 ppm:(CH3)2NCH2CH(OH)CH2CH2CH2CH2CH(OH)CH2N(CH3)2.

Example 2

CO.SUB.2 .Absorption Rate of an Amine Formulation for a Selective Absorption Method

[0182] Comparative CO.sub.2 absorption tests are carried out with different absorbent solutions: [0183] an absorbent solution comprising 49 wt. % N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol according to the invention in water, [0184] an aqueous solution of N-methyldiethanolamine (MDEA) with 47 wt. % MDEA, which is the reference absorbent solution for selective removal in gas treatment, [0185] an aqueous solution of 1,2-bis-(pyrrolidinylethoxy)-ethane with 50 wt. % 1,2-bis-(pyrrolidinylethoxy)-ethane, which is a diaminoether with two tertiary amine functions according to the general formula of U.S. Pat. No. 4,405,582 but has no alcohol function and does not fall within general formula (I) according to the invention, [0186] an aqueous solution of 1,2-bis-(tertiobutylaminoethoxy)-ethane with 40 wt. % 1,2-bis-(tertiobutylaminoethoxy)-ethane, which is a diaminoether with two secondary functions having severe steric hindrance of the nitrogen atoms according to the general formula of U.S. Pat. No. 4,405,583, with no alcohol function and which does not fall within general formula (I) according to the invention, [0187] an aqueous solution of N,N,N,N-tetramethyl-1,6-hexanediamine (TMHDA) with 50 wt. % TMHDA, which is a tertiary diamine disclosed in patent FR-2,934,172, but which has no alcohol function and does not fall within general formula (I) according to the invention.

[0188] For each test, the CO.sub.2 flow absorbed by the aqueous absorbent solution is measured in a closed reactor of Lewis cell type. 200 g solution is fed into the closed reactor at a controlled temperature of 50 C. Four successive CO.sub.2 injections are carried out from 100 to 200 mbar in the vapour phase of the 200 cm.sup.3-volume reactor. The gas phase and the liquid phase are stirred at 100 rpm and entirely characterized from the hydrodynamic point of view. For each injection, the CO.sub.2 absorption rate is measured through pressure variation in the gas phase. A global transfer coefficient Kg is thus determined using a mean of the results obtained for the four injections.

[0189] The results obtained are shown in Table 2 hereafter in relative absorption rate by comparison with the reference aqueous absorbent solution comprising 47 wt. % MDEA, 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).

TABLE-US-00002 TABLE 2 Concen- CO.sub.2 relative tration absorption rate at Compound (wt. %) 50 C. MDEA 47 1.00 1,2-bis-(pyrrolidinylethoxy)-ethane 50 1.43 (according to U.S. Pat. No. 4,405,582) 1,2-bis-(tertiobutylaminoethoxy)-ethane 40 1.74 (according to U.S. Pat. No. 4,405,583) TMHDA (according to FR-2,934,172) 50 2.72 N,N,N,N-(tetramethyl)-1,6-diamino- 49 0.87 2,5-hexanediol

[0190] 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 and compared to the absorbent solutions with some molecules of the prior art. It therefore appears that the exemplified compound 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.

Example 3

H.SUB.2.S Absorption Capacity of a N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol Formulation for an Acid Gas Treating Method

[0191] The H.sub.2S absorption capacity performances at 40 C. of an aqueous solution of N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol according to the invention, containing 49 wt. % N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol, are compared with those of an MDEA aqueous solution containing 50 wt. % MDEA, which is a reference absorbent solution for deacidizing H.sub.2S-containing gas.

[0192] An absorption test is carried out at 40 C. on 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).

[0193] In the case of deacidizing in natural gas treatment, the H.sub.2S partial pressures encountered in acid gases typically range between 0.1 and 1 bar at a temperature of 40 C. By way of example, in this industrial range, Table 3 hereafter compares the H.sub.2S loadings obtained at 40 C. for various H.sub.2S partial pressures between the 50 wt. % MDEA absorbent solution and the 49 wt. % N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol absorbent solution.

TABLE-US-00003 TABLE 3 49 wt. % N,N,N,N-(tetramethyl)- 50 wt. % 1,6-diamino-2,5-hexanediol MDEA aqueous aqueous solution at 40 C. solution at 40 C. H.sub.2S H.sub.2S H.sub.2S partial loading H.sub.2S loading H.sub.2S pressure (mol/mol loading (mol/mol loading (bar) amine) (mol/kg) amine) (mol/kg) 0.10 0.94 2.26 0.21 0.88 1.00 1.75 4.20 0.69 2.95

[0194] At 40 C., whatever the H.sub.2S partial pressure, the absorption capacity of the N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol aqueous solution according to the invention is higher than that of the MDEA solution. At a H.sub.2S partial pressure of 0.10 bar, the difference between the H.sub.2S loadings of the two absorbent solutions is 1.38 mol/kg, with an absorption capacity for the N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol absorbent solution increased by 157% in relation to the reference MDEA absorbent solution. At a H.sub.2S partial pressure of 1 bar, the H.sub.2S loading increase for the N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol absorbent solution still is 42% in relation to the reference MDEA absorbent solution. It can thus be observed that the 49 wt. % N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol aqueous solution has a higher H.sub.2S absorption capacity than the reference 50 wt. % MDEA aqueous solution 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.

[0195] It thus appears that this exemplified molecule according to the invention allows to reduce the absorbent solution flow rates required in H.sub.2S-containing gas deacidizing applications compared to the reference MDEA absorbent solution.

[0196] CO.sub.2 absorption being slower in an aqueous solution of N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol than in a MDEA aqueous solution (see Example 2 above) and the acid gas, notably H.sub.2S, absorption capacity being equivalent or higher with the N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol absorbent solution in relation to a MDEA aqueous solution as illustrated in the present example, it appears that this exemplified molecule according to the invention allows to reduce the absorbent solution flow rates required in selective deacidizing applications (H.sub.2S/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.

Example 4

H.SUB.2.S Absorption Capacity of a N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol Formulation for an Acid Gas Treating Method

[0197] The H.sub.2S absorption capacity performances at 40 C. of an aqueous solution of

[0198] N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol according to the invention containing 50 wt. % of N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol are compared with those of an MDEA aqueous solution containing 50 wt. % MDEA, which is a reference absorbent solution for deacidizing H.sub.2S-containing gas.

[0199] An absorption test is carried out at 40 C. according to the operating mode described in the previous example.

[0200] In the case of natural gas treatment deacidizing, the H.sub.2S partial pressures encountered in acid gases typically range between 0.1 and 1 bar, at a temperature of 40 C. By way of example, in this industrial range, Table 4 hereafter compares the H.sub.2S loadings obtained at 40 C. for various H.sub.2S partial pressures between the 50 wt. % MDEA absorbent solution and the 50 wt. % N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol absorbent solution.

TABLE-US-00004 TABLE 4 50 wt. % N,N,N,N-(tetramethyl)- 50 wt. % 1,8-diamino-2,7-octanediol MDEA aqueous aqueous solution at 40 C. solution at 40 C. H.sub.2S H.sub.2S H.sub.2S partial loading H.sub.2S loading H.sub.2S pressure (mol/mol loading (mol/mol loading (bar) amine) (mol/kg) amine) (mol/kg) 0.10 1.04 2.25 0.21 0.88 1.00 1.82 3.92 0.69 2.95

[0201] At 40 C., whatever the H.sub.2S partial pressure, the absorption capacity of the N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol aqueous solution according to the invention is higher than that of the MDEA solution. At a H.sub.2S partial pressure of 0.10 bar, the difference between the H.sub.2S loadings of the two absorbent solutions is 1.37 mol/kg, with an absorption capacity for the N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol absorbent solution increased by 156% in relation to the reference MDEA absorbent solution. At a H.sub.2S partial pressure of 1 bar, the H.sub.2S loading increase for the N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol absorbent solution still is 33% in relation to the reference MDEA absorbent solution. It can thus be observed that the 50 wt. % N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol aqueous solution has a higher H.sub.2S absorption capacity than the reference 50 wt. % MDEA aqueous solution 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.

[0202] It therefore appears that the exemplified molecule according to the invention allows to reduce the absorbent solution flow rates required in H.sub.2S-containing gas deacidizing applications in relation to the reference MDEA absorbent solution.

Example 5

CO.SUB.2 .Absorption Capacity of a N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol Formulation for an Acid Gas Treating Method

[0203] The CO.sub.2 absorption capacity performances at 40 C. of an aqueous solution of N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol according to the invention, containing 49 wt. % N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol, are compared with those of an MDEA aqueous solution containing 47 wt. % MDEA, which is a reference absorbent solution for deacidizing CO.sub.2-containing gas.

[0204] An absorption test is carried out at 40 C. according to the operating mode described in the previous examples, the acid gas being CO.sub.2 instead of H.sub.2S.

[0205] In the case of deacidizing in natural gas treatment, the CO.sub.2 partial pressures encountered in acid gases typically range between 0.1 and 1 bar at a temperature of 40 C. By way of example, in this industrial range, Table 5 below compares the CO.sub.2 loadings obtained at 40 C. for various CO.sub.2 partial pressures between the 47 wt. % MDEA absorbent solution and the 49 wt. % N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol absorbent solution.

TABLE-US-00005 TABLE 5 49 wt. % N,N,N,N-(tetramethyl)- 47 wt. % 1,6-diamino-2,5-hexanediol MDEA aqueous aqueous solution at 40 C. solution at 40 C. CO.sub.2 CO.sub.2 CO.sub.2 partial loading CO.sub.2 loading CO.sub.2 pressure (mol/mol loading (mol/mol loading (bar) amine) (mol/kg) amine) (mol/kg) 0.10 0.88 2.12 0.22 0.88 1.00 1.65 3.95 0.69 2.74

[0206] At 40 C., whatever the CO.sub.2 partial pressure, the absorption capacity of the N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol aqueous solution according to the invention is higher than that of the MDEA solution. At a CO.sub.2 partial pressure of 0.10 bar, the difference between the CO.sub.2 loadings of the two absorbent solutions is 1.24 mol/kg with an absorption capacity for the N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol absorbent solution increased by 141% in relation to the reference MDEA absorbent solution. At a CO.sub.2 partial pressure of 1 bar, the CO.sub.2 loading increase for the N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol absorbent solution still is 44% in relation to the reference MDEA absorbent solution. It can thus be observed that the 49 wt. % N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol aqueous solution has a higher CO.sub.2 absorption capacity than the reference 47 wt. % MDEA aqueous solution at 40 C., in the CO.sub.2 partial pressure range between 0.1 and 1 bar corresponding to a partial pressure range representative of usual industrial conditions.

[0207] It thus appears that this exemplified molecule according to the invention allows to reduce the absorbent solution flow rates required in CO.sub.2-containing gas deacidizing applications compared to the reference MDEA absorbent solution.

Example 6

CO.SUB.2 .Absorption Capacity of a N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol Formulation for an Acid Gas Treating Method

[0208] The CO.sub.2 absorption capacity performances at 40 C. of an aqueous solution of N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol according to the invention containing 47 wt. % of N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol are compared with those of an MDEA aqueous solution containing 47 wt. % MDEA, which is a reference absorbent solution for deacidizing CO.sub.2-containing gas.

[0209] An absorption test is carried out at 40 C. according to the operating mode described in the previous examples, the acid gas being CO.sub.2.

[0210] In the case of natural gas treatment deacidizing, the CO.sub.2 partial pressures encountered in acid gases typically range between 0.1 and 1 bar, at a temperature of 40 C. By way of example, in this industrial range, Table 6 hereafter compares the CO.sub.2 loadings obtained at 40 C. for various CO.sub.2 partial pressures between the 47 wt. % MDEA absorbent solution and the 47 wt. % N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol absorbent solution.

TABLE-US-00006 TABLE 6 47 wt. % N,N,N,N-(tetramethyl)- 47 wt. % 1,8-diamino-2,7-octanediol MDEA aqueous aqueous solution at 40 C. solution at 40 C. CO.sub.2 CO.sub.2 CO.sub.2 partial loading CO.sub.2 loading CO.sub.2 pressure (mol/mol loading (mol/mol loading (bar) amine) (mol/kg) amine) (mol/kg) 0.10 1.02 2.06 0.22 0.88 1.00 1.82 3.68 0.69 2.74

[0211] At 40 C., whatever the CO.sub.2 partial pressure, the absorption capacity of the N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol aqueous solution according to the invention is higher than that of the MDEA solution. At a CO.sub.2 partial pressure of 0.10 bar, the difference between the CO.sub.2 loadings of the two absorbent solutions is 1.18 mol/kg with an absorption capacity for the N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol absorbent solution increased by 134% in relation to the reference MDEA absorbent solution. At a CO.sub.2 partial pressure of 1 bar, the CO.sub.2 loading increase for the N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol absorbent solution still is 34% in relation to the reference MDEA absorbent solution. It can thus be observed that the 47 wt. % N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol aqueous solution has a higher CO.sub.2 absorption capacity than the reference 47 wt. % MDEA aqueous solution at 40 C., in the CO.sub.2 partial pressure range between 0.1 and 1 bar corresponding to a partial pressure range representative of usual industrial conditions.

[0212] It therefore appears that this exemplified molecule according to the invention allows to reduce the absorbent solution flow rates required in CO.sub.2-containing gas deacidizing applications in relation to the reference MDEA absorbent solution.

Example 7

Capture Capacity of N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol and N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol aqueous Solutions. Application to Post-Combustion Fumes Treatment

[0213] The CO.sub.2 capture capacity performances of the N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol and N, N, N ,N -(tetramethyl)-1,8-diamino-2,7-octanediol according to the invention are notably compared with those of a 30 wt. % MonoEthanolAmine (MEA) aqueous solution which is a reference solvent in capture applications for CO.sub.2 contained in post-combustion fumes. An absorption test is first carried out on aqueous amine solutions according to the operating mode described above.

[0214] By way of example, Table 7 compares the loadings (=nb of mol acid gas/nb of mol amine) obtained at 40 C. for various CO.sub.2 partial pressures between a 49 wt. % N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol aqueous solution according to the invention, a 47 wt. % N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol aqueous solution according to the invention and a 30 wt. % MonoEthanolAmine aqueous solution for a post-combustion CO.sub.2 capture application.

[0215] To switch from one loading quantity obtained in the laboratory to a quantity characteristic of the method, some calculations are necessary and explained below for the intended application.

[0216] In the case of a post-combustion CO.sub.2 capture application, the CO.sub.2 partial pressures in the effluent to be treated are typically 0.1 bar with a temperature of 40 C., and 90% of the acid gas is to be abated. The cyclic capacity PC expressed in mol of CO.sub.2 per kg of solvent is calculated, considering that the solvent reaches a loading in the absorption column bottom corresponding to an equilibrium partial pressure at 40 C. equal to 50% of the partial pressure in the effluent to be treated, i.e. PPCO.sub.2=0.05 bar, and needs at least to be regenerated to a loading corresponding to an equilibrium partial pressure equal to 50% of the pressure in the column top conditions, i.e. to PPCO.sub.2=0.005 bar, to achieve 90% CO.sub.2 abatement.

.sub.PC=(.sub.PPCO2-0,005bar.sub.PPCO2-0,005bar).Math.[A].Math.10/M

where [A] is the amine concentration expressed in wt. %, M the molar mass of the amine in g/mol, and .sub.PPCO2=0,005bar and .sub.PPCO2=0,005bar are the loadings (mol CO.sub.2/mol amine) of the solvent at equilibrium with a CO.sub.2 partial pressure of 0.05 bar and 0.005 bar respectively.

[0217] The reaction enthalpy can be obtained by calculation from several CO.sub.2 absorption isotherms by applying Van't Hoff's law.

TABLE-US-00007 TABLE 7 Loading = n.sub.CO2/n.sub.amine .sub.PC T P.sub.PCO2 = P.sub.PCO2 = (mol.sub.CO2/kg H Generic name Concentration ( C.) 0.05 bar 0.005 bar Solvent) (kJ/mol.sub.CO2) MEA 30 wt. % 40 0.50 0.41 0.47 92 N,N,N,N-(tetramethyl)-1,6- 49 wt. % 40 0.62 0.18 1.07 74 diamino-2,5-hexanediol (according to the invention) N,N,N,N-(tetramethyl)-1,8- 47 wt. % 40 0.70 0.19 1.02 73 diamino-2,7-octanediol (according to the invention)

[0218] For a post-combustion fumes capture application where the CO.sub.2 partial pressure in the effluent to be treated is 0.1 bar, this example illustrates the higher cyclic capacity obtained with 49 wt. % N,N,N,N-(tetramethyl)-1,6-diamino-2,5-hexanediol and 47 wt. % N,N,N,N-(tetramethyl)-1,8-diamino-2,7-octanediol absorbent solutions according to the invention, allowing to reach a 90% abatement ratio at the absorber outlet. In this application where the energy associated with the regeneration of the solution is critical, it can be noted that the amine according to the invention allows to obtain a much better compromise than MEA in terms of cyclic capacity and reaction enthalpy.