WO2015007970A1

WO2015007970A1 - Process for removing acidic compounds from a gaseous effluent with a dihydroxyalkylamine-based absorbent solution

Info

Publication number: WO2015007970A1
Application number: PCT/FR2014/051527
Authority: WO
Inventors: Bruno Delfort; Dominique Le Pennec; Julien Grandjean; Aurélie WENDER
Original assignee: IFP Energies Nouvelles
Priority date: 2013-07-18
Filing date: 2014-06-19
Publication date: 2015-01-22
Also published as: FR3008625B1; FR3008625A1

Abstract

A process for removing the acidic compounds contained in a gaseous effluent, consisting in bringing a gaseous effluent (1) into contact, in a column (C1), with an absorbent solution (4) composed of an aqueous solution of one or more dihydroxyalkylamines corresponding to the following formula (1):

Description

PROCESS FOR THE REMOVAL OF ACIDIC COMPOUNDS FROM A GASEOUS EFFLUENT WITH AN ABSORBENT SOLUTION BASED ON DYH Y D ROX Y AL K Y L AM INES

The present invention relates to the field of deacidification processes of a gaseous effluent. The invention is advantageously applicable to the treatment of industrial gases and natural gas, and in particular to the selective removal of H ₂ S with respect to C0 ₂ .

Absorption processes employing an aqueous amine solution are commonly used to remove the acidic compounds (in particular CO ₂ , H ₂ S, COS, CS ₂ , SO ₂ and mercaptans) present. in a gas. The gas is deacidified by contact with the absorbent solution, and the absorbent solution is thermally regenerated. For example, US 6,852,144 discloses a method for removing acidic compounds from hydrocarbons using a water-N-methyldiethanolamine or water-triethanolamine absorbent solution containing a high proportion of a compound belonging to the following group: piperazine and / or methylpiperazine and / or morpholine.

A limitation of the absorbent solutions commonly used in deacidification applications is an insufficient selectivity of absorption of H ₂ S with respect to C0 ₂ . In fact, in certain cases of deacidification of natural gas, selective removal of H ₂ S is sought with a minimum of C0 ₂ absorption. This constraint is particularly important for gases to be treated already containing a CO ₂ content less than or equal to the desired specification. A maximum absorption capacity of H ₂ S is then sought with a maximum selectivity of absorption of H ₂ S with respect to CO ₂ . This selectivity makes it possible to maximize the quantity of gas treated and to recover an acid gas at the outlet of the regenerator having the highest possible concentration of H ₂ S, which limits the size of the units of the sulfur chain downstream of the treatment and guarantees better operation. In some cases, an H ₂ S enrichment unit is needed to concentrate the acid gas in H ₂ S. In this case, the most selective amine is also sought. Tertiary amines, such as N- Methyldiethanolamine, or congested secondary cells with slow reaction kinetics with C0 ₂ are commonly used, but have selectivities limited to high H ₂ S loading rates. It is well known to those skilled in the art that tertiary amines or secondary amines with a severe steric hindrance have a kinetics of uptake of C0 ₂ slower than primary or secondary amines uncrowded. In contrast, tertiary or secondary amines with severe steric hindrance have instantaneous H ₂ S capture kinetics, which allows for selective removal of H ₂ S based on distinct kinetic performance.

Among the applications of secondary amines with a severe steric hindrance, US Pat. No. 4,405,581 describes a process for the selective absorption of sulphide gases by an absorbent containing secondary monoamines having a severe steric hindrance of which at least one of the substituents is a hydroxyalkyl group. The general formula of the secondary hydroxyalkyl monoamines proposed in US Pat. No. 4,405,581 imposes a severe steric hindrance in alpha of nitrogen, the nitrogen atom being bonded to at least one tertiary carbon or to two secondary carbon atoms.

US Patent 4,405,81 1 also describes a method for the selective removal of H ₂ S in gases containing H ₂ S and CO ₂ by an absorbent containing tertiary monoamines having a severe steric hindrance of which at least one of the substituents is a hydroxyalkyl group. The general formula of the tertiary hydroxyalkyl-monoamines proposed in US Pat. No. 4,405,81 1 also describes a severe steric hindrance in alpha of nitrogen, requiring that the nitrogen atom be bonded to at least one tertiary carbon atom if the two other carbon atoms in alpha of the nitrogen are primary or the nitrogen atom is bonded to a tertiary or secondary carbon, if the second carbon atom in alpha of the nitrogen is secondary and the third is primary . French patent application FR 2 982 170 describes a process for removing acidic compounds from a gaseous effluent with an amine-based absorbent solution having a severe steric hindrance. These molecules are selected from the group of tertiary or secondary monoamines possessing a steric hinderance in alpha of the nitrogen atom and belonging to the family of di- (hydroxyalkyl) monoamines. The general formula of the di- (hydroxyalkyl) monoamines secondary proposed in the patent application FR 2 982 170 requires that the two carbons in beta of nitrogen (in alpha hydroxyls) are primary or secondary, that is to say that they are linked to at least one hydrogen atom. In this case the alcohol functions are primary or secondary but never tertiary.

Another limitation of the absorbent solutions commonly used in total deacidification applications is the kinetics of C0 ₂ or COS pickup that are too slow. In the case where the desired specifications on the C0 ₂ or in COS are very advanced, one seeks a kinetics of reaction as fast as possible so as to reduce the height of the absorption column. This pressure equipment represents a significant part of the investment costs of the process.

Whether maximum C0 ₂ and maximum COD uptake kinetics are sought in a total deacidification application, or a minimum CO ₂ capture kinetics in a selective application, it is always desirable to use an absorbent solution having the largest cyclic capacity. possible. This cyclic capacity, denoted Δα corresponds to the load ratio difference (a denotes the number of moles of acid compounds absorbed _gas aci _d n e per kilogram of absorbent solution) between the absorbent solution supplied to the absorption column and the absorbent solution withdrawn at the bottom of said column. Indeed, the more the absorbent solution has a high cyclic capacity, the more the absorbent solution flow rate that must be used to deacidify the gas to be treated is limited. In gas treatment processes, the reduction of the absorbent solution flow rate also has a strong impact on the reduction of investments, especially in the dimensioning of the absorption column.

Another essential aspect of industrial gas treatment or flue gas treatment operations is the regeneration of the separating agent. According to the type of absorption (physical and / or chemical), regeneration by expansion, and / or by distillation and / or by entrainment by a vaporized gas called "stripping gas" is generally envisaged. The energy consumption necessary for the regeneration of the solvent can be very important, which is particularly true in the case where the partial pressure of acid gases is low, and represent a considerable operating cost for the CO ₂ capture process.

There is thus a need to provide compounds which are good candidates for the deacidification of gases, in particular for the selective removal of H ₂ S with respect to C0 ₂ , and which make it possible to operate at lower operating costs (of which regeneration energy) and investments (including the cost of the absorption column).

The inventors have demonstrated that tertiary or secondary monoamines of which at least one of the substituents is a hydroxyalkyl group and having a severe steric hindrance are not equivalent in terms of performance for their use in absorbent solution formulations for gas treatment. acids in an industrial process.

The present invention relates to the use of tertiary or secondary monoamines belonging to the family of di- (2-hydroxyalkyl) -monoamines and having a particular severe steric hindrance. The molecules according to the invention have the particularity that at least one of the two carbon atoms which are located in alpha of the hydroxyl group and in beta of the nitrogen atom is tertiary, that is to say that it does not is not bound to a hydrogen atom. In this case at least one of the alcohol functions is tertiary. In general, the present invention describes a process for removing the acidic compounds contained in a gaseous effluent, in which an absorption step of the acidic compounds is carried out by contacting the gaseous effluent with an absorbent solution comprising:

- some water

at least one nitrogen compound chosen from di- (2-hydroxyalkyl) monoamines corresponding to the following formula (I):

in which:

R1 is chosen from a hydrogen atom and an alkyl radical containing from 1 to 6 carbon atoms,

R2, R3, R4, R5, R6 and R7 are independently selected from a hydrogen atom and an alkyl radical of 1 to 6 carbon atoms, and

R8 and R9 are in no case hydrogen atoms and are independently selected from alkyl radicals having 1 to 6 carbon atoms.

This condition on R8 and R9 defines the particular severe steric hindrance of the compounds according to the invention.

In formula (I), it is the group R 1 which determines whether the compound is a secondary amine or a tertiary amine.

According to the invention, the nitrogenous compound may be chosen from the following compounds:

- 1 - [(2-hydroxyethyl) methylamino] -2-methyl-2-propanol

- 1, 1 '- (methylimino) -bis- [2-methyl-2-propanol]

2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol

2 - [(2-hydroxy-2-methylpropyl) amino] -1-butanol

; and - Bis (2-hydroxy-2-methylpropyl) amine

The absorbent solution may comprise between 5% and 95% by weight of said nitrogenous compound, preferably between 10% and 90% by weight of said nitrogenous compound, and between 5% and 95% by weight of water, and preferably between 10% and 90% by weight. weight of water.

The absorbent solution may further comprise between 5% and 95% by weight of at least one additional amine being either a tertiary amine or a secondary amine comprising two secondary carbon atoms alpha to the nitrogen atom, or a secondary amine comprising at least one tertiary carbon alpha to the nitrogen atom.

Said additional amine may be a tertiary amine selected from the group consisting of:

N-methyldiethanolamine;

triethanolamine;

diethylmonoethanolamine;

dimethylmonoethanolamine;

ethyldiethanolamine.

The absorbent solution may further comprise a non-zero amount and less than 30% by weight of at least one additional amine being a primary amine or a secondary amine.

Said additional primary or secondary amine may be chosen from the group consisting of:

monoethanolamine;

diethanolamine;

n-butylethanolamine;

aminoethylethanolamine;

diglycolamine;

piperazine;

1-methylpiperazine;

2-methylpiperazine;

homopiperazine;

N- (2-hydroxyethyl) piperazine; N- (2-aminoethyl) piperazine;

morpholine;

3- (methylamino) propylamine;

1,6-hexanediamine;

N, N'-dimethyl-1,6-hexanediamine;

N-methyl-1,6-hexanediamine;

N, N ', N'-trimethyl-1,6-hexanediamine.

The absorbent solution may further comprise a physical solvent selected from methanol and sulfolane.

The absorption step of the acidic compounds can be carried out at a pressure between 1 bar and 120 bar, and at a temperature between 20 ° C and 100 ° C.

After the absorption step, an absorbent solution loaded with acid compounds can be obtained, and at least one regeneration step of the absorbent solution loaded with acidic compounds can be carried out at a pressure of between 1 bar and 10 bar and at a pressure of temperature between 100 ° C and 180 ° C.

The gaseous effluent may be chosen from natural gas, synthesis gases, combustion fumes, refinery gases, acid gases from an amine unit, gases from a tail reduction unit of Claus process, biomass fermentation gases, cement gases, incinerator fumes.

The process according to the invention can be implemented to selectively remove H ₂ S with respect to C0 ₂ from a gaseous effluent comprising H ₂ S and CO ₂ .

The use of the di- (2-hydroxyalkyl) -monoamine compounds according to the invention makes it possible to obtain good performances in terms of the cyclic capacity of absorption of acid gases and of absorption selectivity with respect to the H ₂ S, in particular a higher absorption selectivity for H ₂ S than reference amines such as N-methyldiethanolamine (MDEA) for an equivalent or greater cyclic acid absorption capacity. . Other characteristics and advantages of the invention will be better understood and will become clear from reading the description given hereinafter with reference to FIG. 1 showing a block diagram of the implementation of a treatment method. of acid gases.

The present invention proposes to eliminate the acidic compounds of a gaseous effluent by implementing in aqueous solution at least one compound selected from the group of tertiary or secondary monoamines belonging to the family of di- (2-hydroxyalkyl) -monoamines and possessing a particular severe steric hindrance.

Composition of the absorbent solution

The absorbent solution used in the process according to the invention comprises:

a - water;

b - at least one molecule chosen from the group of di- (2-hydroxyalkyl) -monoamines having the particularity that at least one of the two carbon atoms which are located in alpha of the hydroxyl groups and in beta of the atom of Nitrogen is tertiary, ie it is not bound to a hydrogen atom.

The di- (2-hydroxyalkyl) monoamines used according to the invention correspond to the general formula

(I) in which:

R2, R3, R4, R5, R6 and R7 are independently chosen from a hydrogen atom and an alkyl radical containing from 1 to 6 carbon atoms, and

- R8 and R9 are in no case hydrogen atoms and are independently selected from alkyl radicals containing 1 to 6 carbon atoms. This condition on R8 and R9 defines the particular severe steric hindrance of the compounds according to the invention. In formula (I), it is the group R 1 which determines whether the compound is a secondary amine or a tertiary amine.

Preferably, the absorbent solution implemented according to the invention comprises at least one of the compounds covered by the formula (I) cited below:

- 1 - [(2-hydroxyethyl) methylamino] -2-methyl-2-propanol

1, 1 '- (methylimino) -bis- [2-methyl-2-propanol]

■

2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol

2 - [(2-hydroxy-2-methylpropyl) amino] -1-butanol

Bis (2-hydroxy-2-methylpropyl) amine

The amines according to general formula (I) may be in variable concentration in the absorbent solution, for example between 5% and 95% by weight, preferably between 10% and 90% by weight, more preferably between 20% and 60% by weight. and very preferably between 25% and 50% by weight.

The absorbent solution may contain between 5% and 95% by weight of water, preferably between 10% and 90% by weight of water, more preferably between 40% and 80% by weight of water, and very preferably 50% by weight. 75% water. According to one embodiment, the absorbent solution may further contain at least one additional amine which is a tertiary amine such as methyldiethanolamine, triethanolamine, diethylmonoethanolamine, dimethylmonoethanolamine, or ethyldiethanolamine, or which is a secondary amine having a severe steric hindrance, this congestion being defined either by the presence of two secondary carbons in alpha of nitrogen, or by at least one tertiary carbon in alpha of nitrogen. The concentration of tertiary or secondary secondary amine severely encumbered in the absorbent solution may be between 5% and 95% by weight, preferably between 5% and 50% by weight, very preferably between 5% and 30% by weight.

According to one embodiment, the amines according to the 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% by weight, preferably less than 15% by weight, preferably less than 10% by weight of said compound containing at least one primary or secondary amine function. Preferably, the absorbent solution comprises at least 0.5% by weight of said compound containing at least one primary or secondary amine function. Said compound makes it possible to accelerate the absorption kinetics of the COS and, in certain cases, the CO ₂ contained in the gas to be treated.

A non-exhaustive list of compounds containing at least one primary or secondary amine function that may be included in the formulation is given below:

monoethanolamine;

diethanolamine;

N-butylethanolamine;

aminoethylethanolamine;

diglycolamine;

piperazine;

1-methylpiperazine;

2-methylpiperazine;

homopiperazine;

N- (2-hydroxyethyl) piperazine; N- (2-aminoethyl) piperazine;

morpholine;

3- (methylamino) propylamine;

1,6-hexanediamine and all its variously N-alkylated derivatives such as for example N, N'-dimethyl-1,6-hexanediamine, N-methyl-1,6-hexanediamine or N, N ', N' trimethyl-1,6-hexanediamine.

The absorbent solution according to the invention may comprise a mixture of additional amines as defined above.

According to one embodiment, the absorbent solution may contain a physical solvent chosen from methanol and sulfolane.

Synthesis of a molecule according to the general formula of the invention

The molecules of the invention can be synthesized according to any route permitted by organic chemistry. Among these, the reactions of addition of ammonia, primary alkylamines or primary or secondary monoalkanolamines with more or less substituted epoxides can be cited without being exhaustive.

The reaction of adding a primary or secondary amine to an epoxide is a well-known reaction of organic chemistry. It is used industrially in particular to manufacture N-methylethanolamine by reaction of methylamine and ethylene oxide. When it is desired from a primary amine to obtain a secondary alkanolamine by reaction with an epoxide, it is recommended to operate with an excess of amine in order to disadvantage the obtaining of the di-addition compound which would be an amine unwanted tertiary. When it is desired from a secondary amine to obtain a tertiary alkanolamine by reaction with an epoxide, it is possible to operate with equimolar amounts or with an excess of one or the other of the reagents. Excess reagents can be separated from the desired product at the end of the reaction and recycled to the process.

The reaction of adding an amine to an epoxide is an exothermic reaction that generally requires control of the reaction temperature. She is carried out for example between -10 ° C and 140 ° C depending on nature and the reactivity of the amine and the epoxide considered.

This reaction can be carried out in the absence or in the presence of a solvent. When a solvent is used, it may be selected from conventional solvents used in organic chemistry. It may be for example but not limited to water or an alcohol such as methanol, ethanol or isopropanol.

This reaction generally does not require a catalyst although some compounds such as tertiary amines, quaternary ammonium salts or metal derivatives may be used.

Nature of gaseous effluents

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

The combustion fumes are produced in particular by the combustion of hydrocarbons, biogas, coal in a boiler or for a combustion gas turbine, for example for the purpose of producing electricity. By way of illustration, the method according to the invention can be used to absorb at least 70%, preferably at least 80% or even at least 90% of the CO ₂ contained in the combustion fumes. These fumes generally have a temperature of between 20 ° C. and 60 ° C., a pressure of between 1 and 5 bar and may comprise between 50 and 80% of nitrogen, between 5% and 40% of carbon dioxide, and between 1% and 5%. and 20% oxygen, and some impurities such as SOx and NOx, if they have not been removed upstream of the deacidification process. In particular, the process according to the invention is particularly well adapted to absorb the CO ₂ contained in combustion fumes comprising a low CO ₂ partial pressure, for example a CO ₂ partial pressure of less than 200 mbar. The process according to the invention can be used to deacidify a synthesis gas. The synthesis gas contains carbon monoxide CO, hydrogen H ₂ (generally in a ratio H ₂ / CO equal to 2), water vapor (generally at saturation at the temperature where the washing is carried out) and carbon dioxide C0 ₂ (of the order of ten percent). The pressure is generally between 20 and 30 bar, but can reach up to 70 bar. It may also contain sulfur (H ₂ S, COS, etc.), nitrogen (NH ₃ , HCN) and halogenated impurities.

The process according to the invention can be implemented to deacidify a natural gas. Natural gas mainly consists of hydrocarbon gas, but may contain several compounds following acids: C0 _2, H ₂ S, mercaptans, COS, CS _2. The content of these acidic compounds is very variable and can be up to 40% for C0 ₂ and H ₂ S. The temperature of the natural gas can be between 20 ° C and 100 ° C. The pressure of the natural gas to be treated may be between 10 and 120 bar. The invention can be implemented to achieve specifications generally imposed on the deacidified gas, which are less than 2% of C0 ₂ , or even less than 50 ppm of C0 ₂ to then achieve liquefaction of natural gas and less than 4 ppm H ₂ S, and less than 50 ppm, or even less than 10 ppm, total sulfur volume.

Process for removing acidic compounds in a gaseous effluent

The implementation of an aqueous solution comprising a compound according to general formula (I) for deacidifying a gaseous effluent is carried out schematically by performing an absorption step followed by a regeneration step, for example as represented by Figure 1.

With reference to FIG. 1, the deacidification plant for a gaseous effluent according to the invention comprises an absorption column C1 provided with means for contacting gas and liquid, for example a loose packing, a structured packing or plates. The gaseous effluent to be treated is conveyed via a pipe 1 opening at the bottom of column C1. A pipe 4 allows the introduction of the absorbent solution at the top of the column C1. A pipe 2 allows the evacuation of the treated gas (deacidified), and a pipe 3 conveys the absorbent solution enriched in acidic compounds following absorption to a regeneration column C2. This regeneration column C2 is equipped with internal contacting between gas and liquid, for example trays, loose or structured packings. The bottom of the column C2 is equipped with a reboiler R1 which provides the heat necessary for the regeneration by vaporizing a fraction of the absorbing solution. The solution enriched in acidic compounds is introduced at the top of the regeneration column C2 via a line 5. A line 7 makes it possible to evacuate at the top of the column C2 the gas enriched in acid compounds released during the regeneration, and a line 6 arranged at the bottom of the column C2 makes it possible to send the regenerated absorbent solution to the absorption column C1. A heat exchanger E1 makes it possible to recover the heat of the regenerated absorbent solution issuing from column C2 in order to heat the absorbent solution enriched in acidic compounds leaving the absorption column C1.

The absorption step consists of contacting the gaseous effluent arriving via line 1 with the absorbent solution arriving via line 4. During contact, the amine functions of the molecules according to general formula (I) of the absorbent solution react with the acidic compounds contained in the effluent so as to obtain a gaseous effluent depleted of acidic compounds which is discharged through line 2 at the top of the column C1 and an absorbent solution enriched in acidic compounds discharged through line 3 at the bottom of the column C1 to be regenerated.

The absorption step of the acidic compounds can be carried out at a pressure in the column C1 of between 1 bar and 120 bar, preferably between 20 bar and 100 bar for the treatment of a natural gas, preferably between 1 bar and 3 bar for the treatment of industrial fumes, and at a temperature in the column C1 of between 20 ° C and 100 ° C, preferably between 30 ° C and 90 ° C, or between 30 and 60 ° C.

The regeneration step consists in particular in heating and, optionally, in expanding, the absorbent solution enriched in acidic compounds in order to release the acidic compounds in gaseous form. The absorbent solution enriched in acidic compounds leaving the column C1 is introduced into the heat exchanger E1, where it is heated by the flow flowing in the pipe 6 from the regeneration column C2. The heated solution at the outlet of E1 is introduced into the regeneration column C2 via line 5. In the regeneration column C2, under the effect of contacting the absorbent solution arriving via line 5 with the vapor produced by the reboiler, the acid compounds are released in gaseous form and discharged at the top of column C2 by the 7. The absorbent solution regenerated, that is to say depleted in acidic compounds, is discharged through line 6 and is cooled in E1, then recycled to the absorption column C1 via line 4.

The regeneration step of the process according to the invention can be carried out by thermal regeneration, optionally supplemented by one or more expansion steps.

The regeneration can be carried out at a pressure in the column C2 of between 1 bar and 5 bar, or even up to 10 bar and at a temperature in the column C2 of between 100 ° C. and 180 ° C. In a preferred manner, the regeneration temperature in the column C2 is between 155 ° C. and 180 ° C. in the case where it is desired to reinject the acid gases.

Examples

Example 1 Synthesis of the Molecules According to the Invention

The following examples illustrate the synthesis of the preferred molecules of the invention, it being understood that all the possibilities of synthesis of these molecules both at the level of the synthetic routes and the possible operating modes are not here described.

1 - ((2-Hydroxyethylammon ylamino) -2-methyl-2-propanol

To 150.0 g (1.97 moles) of 2- (methylamino) ethanol in 300 ml of ethanol, 171.1 g (0.987 moles) of dimethyl-1, 1-oxirane are introduced with stirring over one hour and a half. at a temperature maintained below 22 ° C. The ethanol and the excess of 2- (methylamino) ethanol are then distilled off and, after distillation under reduced pressure, 134.1 g of 1 - [(2-hydroxyethyl) methylamino] -2-methyl-2 are collected. - Propanol whose structure is confirmed by NMR analysis.

2-i (2-Hydroxy-2-methylpropyl) aminol-2-methyl-1-propanol To 267.0 g (3.0 moles) of 2-amino-2-methyl-1-propanol, 108.0 g (1.5 moles) of dimethyl-1,1-diol are introduced with stirring over 1.5 hours. oxirane at a temperature maintained below 20 ° C. The excess of 2-amino-2-methyl-1-propanol is then distilled off under reduced pressure and the residual product is recrystallized from ethyl acetate to give after drying 226.5 g of 2 - [( 2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol whose structure is confirmed by NMR analysis.

1, 1 '- (Methylimino) -bis- [2-methyl-2-propanoll]

To a solution of 226.0 g (3.12 moles) of dimethyl-1, 1-oxirane in 200 ml of water is added with stirring in two hours 80.6 g (1.04 mol) of monomethylamine in solution. aqueous at a temperature maintained below 10 ° C. After returning to ambient temperature, the excess epoxide and the water are removed by evaporation. After distillation under reduced pressure, 151 g of 1,1 '- (methylimino) -bis- [2-methyl-2-propanol], the structure of which is confirmed by NMR analysis, are collected.

Bis (2-hydroxy-2-methylpropyl) amine

To a solution of 1,129.0 g of 20% ammonia and 400 ml of ethanol, 247.0 g (3.4 mole) of dimethyl-1, 1-oxirane are added with stirring over two hours. temperature kept below 20 ° C. After cooling to room temperature, excess ammonia, ethanol and water are removed by evaporation. After distillation under reduced pressure, 133 g of 1, 1 '- (methylimino) -bis- [2-methyl-2-propanol] and 56 g of 1-amino-2-methyl-2-propanol are collected. reacted with dimethyl-1, 1-oxirane to give 1,1 '- (methylimino) -bis- [2-methyl-2-propanol]. In total, 184 g of 1,1 '- (methylimino) -bis- [2-methyl-2-propanol] are obtained, the structure of which is confirmed by NMR analysis.

2 - [(2-hydroxy-2-methylpropyl) aminol-1-butanol

To a solution of 267.0 g (3.0 moles) of 2-amino-1-butanol in 300 ml of ethanol, 108.0 g (1.5 moles) of dimethyl are introduced with stirring over 1.5 hours. -1, 1-oxirane at a temperature maintained between 10 ° C and 20 ° C. Ethanol and excess 2-amino-1-butanol are then removed by evaporation and collected after distillation under reduced pressure 165.8 g of 2 - [(2-hydroxy-2-methylpropyl) amino] -1-butanol whose structure is confirmed by NMR analysis.

Example 2: CO absorption rate? an amine formulation for a selective absorption process.

Comparative tests for the absorption of C0 ₂ by various absorbent solutions according to the invention of 2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol, of 1 - [(2- hydroxyethyl) methylamino] -2-methyl-2-propanol, 2 - [(2-hydroxy-2-methylpropyl) amino] -1-butanol and Bis (2-hydroxy-2-methylpropyl) amine at 50% by weight.

in water relative to an aqueous solution of N-methyldiethamolamine

(MDEA) 47% by weight in MDEA, which is the reference solvent for selective removal in gas treatment.

These solutions are also compared with a solution of 50% by weight terbutylethanolamine in water, mono (hydroxyalkyl) secondary amine with a severe steric hindrance of the nitrogen atom according to the general formula of US Pat. No. 4,405,581 but which has a only alcohol function does not enter the formula (I) according to the invention. They are also compared to a solution of N-methyl-N-isopropyl-3-amino-1-propanol at 50% by weight in water, tertiary mono (hydroxyalkyl) amine with a severe steric hindrance of the atom of nitrogen according to the general formula of US Patent 4,405,81 1 but which has a single alcohol function does not fall within the formula (I) according to the invention. They are finally compared with solutions of N- (2'-hydroxyethyl) -2-amino-2-methyl-1-propanol and N- (2'-hydroxypropyl) -2-amino-2-methyl-1-propanol at 50% by weight in water, di- (2-hydroxyalkyl) -monoamines with a severe steric hindrance of the nitrogen atom and preferred molecules according to the claims of document FR 2 982 170 but whose carbons in alpha of Hydroxide functions do not meet the definition of formula (I) according to the invention.

For each test, the C0 ₂ absorption flux is measured by the aqueous solution in a closed reactor, such as a Lewis cell. 200 g of solution is introduced into the closed reactor, regulated at a temperature of 50 ° C. Four successive injections of carbon dioxide of 100 to 200 mbar are carried out in the vapor phase of the reactor having a volume of 200 cm ³ . The gas phase and the liquid phase are stirred at 100 revolutions / minute and fully characterized from the hydrodynamic point of view. For each injection, the rate of absorption of the carbon dioxide is measured by variation pressure in the gas phase. An overall transfer coefficient Kg is thus determined by an average of the results obtained on the four injections.

The results obtained are shown in Table 1 below in terms of the rate of absorption relative to the reference formulation N-methyldiethamolamine (MDEA) at 47% by weight in MDEA, this relative absorption rate being defined by the ratio of the overall transfer of the solvent to the overall transfer coefficient of the reference formulation.

- Table 1 - The examination of the results shows, under these test conditions, a rate of absorption of C0 ₂ by the absorbent solutions according to the invention slower than the reference formulation MDEA, and with respect to certain molecules of the prior art. It thus appears that the molecules exemplified according to the invention are of particular interest and improved in the case of a selective deacidification of a gaseous effluent in which it is sought to limit the kinetics of C0 ₂ absorption.

Example 3 Absorption Capacity of the HpS of an Amine Formulation for a Selective Absorption Process

Absorption capacity performance of H ₂ S at 40 ° C of an aqueous solution of 2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol, according to the invention , containing 50% by weight of 2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol are compared with those of an aqueous solution of N-methyldiethamolamine (MDEA) containing 50% by weight MDEA, which is the reference solvent for selective removal in gas treatment.

An absorption test at 40 ° C. is carried out on aqueous amine fractions within a thermostatically controlled equilibrium cell. This test consists in injecting into the equilibrium cell, previously filled with degassed aqueous amine solution, a known quantity of acid gas (here hydrogen sulphide) and then waiting for the establishment of the equilibrium state. The quantities of acid gas absorbed in the solvent are then deduced from the temperature and pressure measurements by means of material and volume balances. The solubilities are conventionally represented in the form of H ₂ S partial pressures (in bar) as a function of the feed rate in H ₂ S (in mol of H ₂ S / kg of solvent and in mol of H ₂ S / mol of amine).

In the case of selective deacidification in natural gas treatment, the partial H ₂ S pressures encountered in the acid gases are typically between 0.05 and 0.5 bar, at a temperature of 40 ° C. By way of example, in this industrial range, the H ₂ S loading rates obtained at 40 ° C. for various partial H ₂ S pressures are compared in table 2 between an absorbent solution of MDEA at 50% by weight and an absorbent solution of 2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol at 50% by weight.

Aqueous solution of 2 - [(2-hydroxy-2-

Aqueous solution of methylpropyl) amino-MDEA] -2- 50% by weight at 40 ° C

50% methyl-1-propanol

weight at 40 ° C

Rate of

Pressure Rate

load in H ₂ S load in load partial load rate in

(mol / mol H ₂ S (mol / mol in H ₂ S (mol / kg) H ₂ S (bar) H ₂ S (mol / kg)

amine) of amine)

0.05 0.21 0.64 0.15 0.64

0.10 0.29 0.91 0.21 0.88

0.26 0.54 1, 67 0.35 1, 47

0.49 0.69 2.14 0.51 2.12

- Table 2 -

At 40 ° C., for a partial pressure in h S of 0.05 bar, the absorption capacity of the two aqueous solutions of amine (2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl- 1-propanol and N-methyldiethanolamine) is equivalent with a loading rate in H ₂ S of 0.64 mol / kg. When the H ₂ S partial pressure increases, it is found that the absorbing solution of 2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol is more capacitive than the absorbent solution of MDEA. In fact, at a partial pressure of 0.1 bar, the loading rate in H ₂ S is 0.91 mol / kg in the absorbent solution of 2 - [(2-hydroxy-2-methylpropyl) amino] -2 -methyl-1-propanol and 0.88 mol / kg in the reference MDEA absorbent solution. At a H ₂ S partial pressure of 0.26 bar, the difference between the H ₂ S loading rates of the two absorbent solutions is 0.2 mol / kg with a greater absorption capacity for the absorbent solution of 2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol. At a H ₂ S partial pressure of 0.49 bar, the H ₂ S loading rates of the two absorbent solutions are again equivalent. It is therefore found that the aqueous solution of 2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol at 50% by weight has a higher H ₂ S absorption capacity than the 50% by weight aqueous reference methyldiethanolamine solution at 40 ° C, in the range of H ₂ S partial pressures between 0.05 and 0.5 bar corresponding to a partial pressure range representative of the usual industrial conditions. The absorption of C0 ₂ being slower in an aqueous solution of 2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol than in an aqueous solution of MDEA (Example 2 above) and the equivalent or greater absorption capacity of acidic gases, especially H ₂ S, of the 2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol absorbent solution with respect to a aqueous solution of MDEA as illustrated in the present example, it appears that the molecule exemplified according to the invention makes it possible to reduce the flow rates of absorbent solution to be used on applications of selective deacidification (H ₂ S / CO ₂ ) to absorb a given flow rate of H ₂ S while reducing the flow rate of coabsorbed C0 ₂ relative to the reference MDEA absorbent solution.

Claims

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

- some water;

in which :

R8 and R9 are independently selected from alkyl radicals having 1 to 6 carbon atoms.

The process according to claim 1, wherein the nitrogen compound is selected from the following compounds:

- 1 - [(2-hydroxyethyl) methylamino] -2-methyl-2-propanol

'- (methylimino) bis [2-methyl-2-propanol]

2 - [(2-hydroxy-2-methylpropyl) amino] -2-methyl-1-propanol

- - [(2-hydroxy-2-methylpropyl) amino] -1-butanol

-hydroxy-2-methylpropyl) amine

3. Method according to one of claims 1 and 2, wherein the absorbent solution comprises between 5% and 95% by weight of said nitrogenous compound, preferably between 10% and 90% by weight of said nitrogenous compound, and between 5% and 95%. weight of water, and preferably between 10% and 90% by weight of water.

4. Method according to one of the preceding claims, wherein the absorbent solution further comprises between 5% and 95% by weight of at least one additional amine, said additional amine being either a tertiary amine or a secondary amine comprising two carbons secondary in alpha of the nitrogen atom or at least one tertiary carbon in alpha of the nitrogen atom.

The process according to claim 4, wherein said additional amine is a tertiary amine selected from the group consisting of:

N-methyldiethanolamine;

triethanolamine;

diethylmonoethanolamine;

dimethylmonoethanolamine; and

ethyldiethanolamine.

6. Method according to one of the preceding claims, wherein the absorbent solution further comprises a non-zero amount and less than 30% by weight. at least one additional amine is a primary amine or a secondary amine.

The method of claim 6, wherein said additional amine is selected from the group consisting of:

monoethanolamine;

diethanolamine;

N-butylethanolamine;

aminoethylethanolamine;

e diglycolamine;

piperazine;

1-methylpiperazine;

2-methylpiperazine;

homopiperazine;

N- (2-hydroxyethyl) piperazine;

N- (2-aminoethyl) piperazine;

morpholine;

3- (methylamino) propylamine;

has 1,6-hexanediamine;

N, N'-dimethyl-1,6-hexanediamine;

N-methyl-1,6-hexanediamine; and

N, N ', N'-trimethyl-1,6-hexanediamine.

8. Method according to one of the preceding claims, wherein the absorbent solution further comprises a physical solvent selected from methanol and sulfolane.

9. Method according to one of the preceding claims, wherein the step of absorbing the acidic compounds is carried out at a pressure between 1 bar and 120 bar, and at a temperature between 20 ° C and 100 ° C.

10. Method according to one of the preceding claims, wherein there is obtained an absorbent solution loaded with acid compounds after the absorption step, and at least one step of regenerating said absorbent solution loaded with acidic compounds at a pressure between 1 bar and 10 bar and at a temperature between 100 ° C and 180 ° C. is carried out.

5 1 1. Process according to one of the preceding claims, in which the gaseous effluent is chosen from natural gas, synthesis gases, combustion fumes, refinery gases, acid gases derived from an amine unit, gases from a reduction unit at the bottom of the Claus process, biomass fermentation gases, cement gases, incinerator fumes.

o

12. Method according to one of claims 1 to 1 1, implemented for the selective removal of H ₂ S with respect to C0 ₂ of a gaseous effluent comprising H ₂ S and C0 ₂ . 5