EP2928582A1

EP2928582A1 - Absorbent solution made from amines belonging to the n-alkyl-hydroxypiperidine family and method for eliminating acid compounds from a gaseous effluent with such a solution

Info

Publication number: EP2928582A1
Application number: EP13808112.0A
Authority: EP
Inventors: Julien Grandjean; Bruno Delfort
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2012-12-07
Filing date: 2013-11-25
Publication date: 2015-10-14
Also published as: FR2999094A1; FR2999094B1; US20150314230A1; WO2014087075A1

Abstract

The invention relates to an absorbent solution comprising water and at least one amine belonging to the N-alkyl-hydroxypiperidine family, and a method implementing this solution for eliminating acid compounds contained in a gaseous effluent.

Description

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

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 6852144 discloses a method of removing acidic compounds from hydrocarbons. The method uses 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 recover an acid gas at the outlet of the regenerator having the highest concentration possible in H ₂ S, which limits the size of the units of the sulfur chain downstream of the treatment and guarantees a 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 MDEA), or congested secondary amines with slow reaction kinetics with C0 ₂ are commonly used, but have limited selectivities at high H ₂ S loading rates. 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 column of absorption column. This pressurized equipment, typically between 40 bars and 70 bars, 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 by Δα, corresponds to the difference in charge ratio (a designating the number of moles of acidic compounds absorbed n _{acid gas} per kilogram of absorbing solution) between the absorbent solution supplying the absorption column and the absorbent solution withdrawn in bottom of said column. Indeed, the more the absorbing solution has a strong cyclic capacity, the more the flow of absorbent solution that must be used to deacidify the gas to be treated is limited. In gas treatment processes, the reduction of the absorbent solution flow 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. Depending on the type of absorption (physical and / or chemical), regeneration by expansion, and / or distillation and / or entrainment by a vaporized gas called "stripping gas" is generally envisaged.

Another limitation of the absorbent solutions commonly used today is an energy consumption necessary for the regeneration of the solvent which is too important. This is particularly true in the case where the partial pressure of acid gases is low. For example, for an aqueous solution of 2-aminoethanol (or monoethanolamine or ethanolamine or MEA) at 30% by weight used for the capture of C0 ₂ post-combustion in a thermal power plant smoke, where the partial pressure of C0 ₂ is the order of 0.12 bar, the regeneration energy is about 3.7 GJ per tonne of CO ₂ captured. Such energy consumption represents a considerable operating cost for the C0 ₂ capture process. It is well known to those skilled in the art that the energy required for the regeneration by distillation of an amine solution can be broken down into three different positions: the energy required to heat the solvent between the head and the bottom of the regenerator, the energy necessary to lower the partial pressure of acid gas in the regenerator by vaporization of a stripping gas, and finally the energy necessary to break the chemical bond between the amine and the CO ₂ .

The first two stations are proportional to the flow rates of absorbent solution that must be circulated in the unit to achieve a given specification. To reduce the energy consumption associated with the regeneration of the solvent, it is therefore preferable once again to maximize the cyclic capacity of the solvent.

The last item concerns the energy to be supplied to break the bond created between the amine used and CO 2. To reduce the energy consumption associated with the regeneration of the absorbent solution, it is therefore preferable to minimize the ΔΗ linkage enthalpy. Nevertheless, it is not easy to find a solvent with a high cyclic capacity and a low reaction enthalpy. The best solution absorbing from an energy point of view is therefore that which will have the best compromise between a strong cyclic capacity Δα and a low enthalpy of connection ΔΗ.

The chemical stability of the absorbent solution is also a key aspect in the deacidification and gas treatment processes. The degradation behavior is a limitation for the commonly used absorbent solutions, especially under regeneration conditions at temperatures between 160 and 180 ° C envisaged in CO 2 capture processes. These conditions make it possible to recover CO 2 at a pressure of between 5 and 10 bars, making it possible to save energy on the compression of the CO 2 captured for the purpose of its transport and storage.

It is therefore difficult to find compounds, or a family of compounds, allowing the various deacidification processes to operate at lower operating costs (including regeneration energy) and investments (including the cost of the absorption column). .

It is well known to those skilled in the art that tertiary amines have a capture kinetics C0 ₂ slower than primary or secondary amines uncrowded. In contrast, tertiary amines have H ₂ S capture kinetics instantaneous, which allows for selective removal of H ₂ S based on distinct kinetic performance.

Among the applications of these tertiary amines, US Pat. No. 4,483,333 describes a process for the selective absorption of acid gases by an absorbent containing a tertiary alkanolamine or a tertiary aminoetheralcohol whose nitrogen is included in a heterocycle.

WO2009 / 1 10586A1 discloses an aqueous solution and a method for absorbing carbon dioxide from a gas, said aqueous solution containing at least one amine represented by the general formula below with n = 1 or 2, R 1 is an alkyl or hydroxyalkyl group and R ₂ in position 2 or 3 is hydrogen, alkyl or hydroxyalkyl, provided that at least one of R 1 and R ₂ is hydroxyalkyl.

More particularly, a compound of interest is N-methyl-2-hydroxymethylpiperidine whose capture capacities and absorption rate are described. However, this document does not describe the performance of this molecule in terms of selective removal of H ₂ S in a gas containing H ₂ S and CO ₂ .

The inventors have found that tertiary alkanolamines whose nitrogen is included in a heterocycle are not equivalent in performance for their use in absorbent solution formulations for the treatment of acid gases in an industrial process.

Certain heterocyclic tertiary alkanolamine-type molecules have insufficient performances, in particular as regards the selective removal of H ₂ S in a gas containing H ₂ S and CO ₂ . On the other hand, other molecules make it possible to improve the absorption selectivity of H ₂ S relative to tertiary amines of reference, such as methyldiethanolamine. These same molecules also have acidic absorption performance, especially CO ₂ and a particularly high chemical stability. The present invention relates to the use of particular molecules belonging to the family of tertiary heterocyclic alkanolamines having a optimum performance between C02 capture capacity, selective removal of H ₂ S, and thermal stability, in the context of the deacidification of a gas. These molecules meet the general definition of N-alkyl-hydroxypiperidines. These heterocyclic tertiary alkanolamines have the particularity of having a single hydroxyl group directly bonded to one of the carbon atoms of the heterocycle, this heterocycle being a piperidine ring. More specifically, these molecules are N-alkyl-3-hydroxypiperidines and N-alkyl-4-hydroxypiperidines corresponding to the general formula (I):

The N-alkyl-hydroxypiperidines according to the invention are particularly distinguished from the document WO2009 / 1 10586A1 in which the R ₂ group can in no case be a hydroxyl group.

Another subject of the invention relates to a process for the elimination of acidic compounds contained in a gaseous effluent, in which an absorption step of the acidic compounds is carried out by bringing the effluent into contact with the absorbent solution according to the invention. .

The use of the N-alkyl-hydroxypiperidine compounds according to the invention makes it possible to obtain greater acid gas absorption capacities than the reference amines. This performance is increased due to greater basicity.

Moreover, the compounds according to the invention have a selectivity towards H ₂ S that is greater than the reference amines.

In addition, in the particular case of an application in natural gas treatment in which the absorbent solution contains a compound according to the invention mixed with a primary or secondary amine, the invention makes it possible to accelerate the absorption kinetics of the COS and C0 ₂ , relative to an MDEA solution containing the same amount of primary or secondary amine. This gain in COS and CO ₂ absorption kinetics results in savings on the cost of the absorption column in cases where removal of this compound at high specifications (1 ppm) is required.

In general, the subject of the present invention is an absorbent solution for removing acidic compounds contained in a gaseous effluent, comprising:

a - water;

b - at least one compound chosen from the group of N-alkyl-3-hydroxypiperidines and N-alkyl-4-hydroxypiperidines corresponding to the general formula (I):

in which the hydroxyl radical can be located in position 3 or in position 4 with respect to the nitrogen atom of the piperidine ring, and R is an alkyl radical containing one to six carbon atoms, and preferably one to three carbon atoms. carbon.

According to the invention, the nitrogenous compound may be chosen from the following compounds listed by way of non-limiting example of the formula en above

N-methyl-4-hydroxypiperidine N-methyl-3-hydroxypiperidine N-ethyl-3-hydroxypiperidine

According to the invention, the solution may comprise between 10% and 90% by weight of said nitrogenous compound, preferably between 20% and 60% by weight, very preferably between 25% and 50% by weight; and the solution may comprise between 10% and 90% by weight of water, preferably between 40% and 80% by weight of water, very preferably from 50% to 75% of water.

According to one embodiment, the solution may comprise an additional amine, said additional amine being a tertiary amine, such as methyldiethanolamine, or a secondary amine having two tertiary carbon atoms alpha to the nitrogen, or a secondary amine having at least one Quaternary carbon in alpha of nitrogen. In this case, the solution may comprise between 10% and 90% by weight of said additional amine, preferably between 10% and 50% by weight, very preferably between 10% and 30% by weight.

According to another embodiment, the solution may comprise a compound containing at least one primary or secondary amine function. In this case, the solution may comprise a concentration up to 30% by weight of said compound, preferably less than 15% by weight, preferably less than 10% by weight, and at least 0.5% by weight. The solution may comprise a concentration of at least 0.5% by weight of said compound. The compound can be chosen from:

monoethanolamine, N-butylethanolamine

aminoethylethanolamine

diglycolamine,

piperazine,

- 1-methylpiperazine

2-methylpiperazine

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.

According to the invention, the solution may comprise a physical solvent chosen from methanol and sulfolane.

The invention also relates to a process for removing acidic compounds contained in a gaseous effluent, in which an absorption step of the acidic compounds is carried out by contacting the effluent with an absorbent solution according to the invention.

According to the invention, the absorption step of the acid compounds can be carried out at a pressure between 1 bar and 120 bar, and at a temperature between 20 ^ and 100 ^<€.

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

Finally, the process can be implemented for the selective removal of H ₂ S from a gaseous effluent comprising H ₂ S and CO ₂ . Other features and advantages of the invention will be better understood and will become clear from reading the description given hereinafter with reference to the appended figures and described below.

FIG. 1 represents a schematic diagram of a process for treating acid gas effluents.

FIG. 2 represents a synthesis scheme of an N-alkyl-hydroxypiperidine according to the invention from a picoline.

FIG. 3 represents a synthesis scheme of the N-methyl-4-hydroxypiperidine according to the invention starting from methyl acrylate.

The present invention provides an aqueous solution and a process for removing acidic compounds from a gaseous effluent.

The aqueous solution according to the invention comprises at least one nitrogen compound chosen from the group of N-alkyl-3-hydroxypiperidines and N-alkyl-4-hydroxypiperidines

The molecules according to the invention can be synthesized using all the routes allowed by organic chemistry. For each of the molecules of the invention, some may be cited without being exhaustive.

The N-alkyl-hydroxypiperidines of the invention can be synthesized by any pathway permitted by organic chemistry. By way of example, the synthesis can be carried out from widely available industrial products which are the 3 or 4-methylpyridines also called 3 or 4-picolines according to a general reaction scheme illustrated in FIG.

The ammoxidation reaction of the 3 or 4-picolines (reaction 1) leads to 3 or 4 cyanopyridines which are then converted into 3 or 4-pyridinecarboxamides according to basic hydrolysis (reaction 2). The 3 or 4-pyridinecarboxamides can then be converted to 3 or 4-aminopyridines in basic medium and in the presence for example of sodium hypochlorite according to the so-called "Hofman reaction" reaction (reaction 3). The 3 or 4-aminopyridines can then be converted into 3 or 4-hydroxypyridines in a diazotization reaction which is carried out in the presence of alkaline nitrite, for example sodium nitrite followed by acid hydrolysis (reaction 4). The 3 or 4-hydroxypyridines obtained are then subjected to a hydrogenation of the aromatic ring (reaction 5). This well-known reaction leads to 3 or 4-hydroxypiperidines also called 3- or 4-piperidinols. Finally, the 3 or 4-hydroxypiperidines will undergo a so-called N-alkylation (reaction 6) to yield 1-alkyl-3 or 4-hydroxypiperidines. This N-alkylation reaction may be carried out for example by condensation of the 3 or 4-hydroxypiperidines with an alkyl halide. Preferably, this N-alkylation reaction will be carried out by condensation of the 3 or 4-hydroxypiperidines with either an alcohol, an aldehyde or a ketone in the presence of hydrogen and a suitable catalyst.

In the case of the molecules of the invention which meet the definition of N-alkyl-4-hydroxypiperidines, an advantageous synthetic route is to perform the multistep synthesis from a plentiful and inexpensive industrial precursor which is methyl acrylate according to a general reaction scheme illustrated in FIG. 3 applied here to one of the preferred molecules of the invention which is 1-methyl-4-hydroxypiperidine.

The addition of one mole of methylamine to 2 moles of methyl acrylate leads to methyl-di- (2- (methylcarboxy) ethyl) amine (reaction 1), which is then subjected to a cyclization reaction called "reaction of Dieckman "to lead to 1-methyl-3-methylcarboxy-4-piperidone (reaction 2). This reaction is carried out in a basic medium, generally with an alkaline alkoxide, and requires a subsequent neutralization step. The ester function of 1-methyl-3-methylcarboxy-4-piperidone is then acid-hydrolyzed to yield 3-carboxy-1-methyl-4-piperidone (reaction 3). From this product, 1-methyl-4-piperidone is obtained by carrying out a decarboxylation reaction according to a well-known procedure (reaction 4). Finally, the carbonyl function of 1-methyl-4-piperidone is hydrogenated to yield 1-methyl-4-hydroxypiperidine (reaction 5). This sequence of reactions illustrated here with methylamine as a precursor may be applied to any other primary amine to yield the family of 1-alkyl-4-hydroxypiperidines.

Composition of the absorbent solution

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

b - at least one molecule selected from the group of N-alkyl-3-hydroxypiperidines and N-alkyl-4-hydroxypiperidines corresponding to the general formula (I):

R being an alkyl radical containing one to six carbon atoms, and preferably one to three carbon atoms.

The hydroxyl radical may be located at the 3-position or at the 4-position with respect to the nitrogen atom of the piperidine ring.

For example, the absorbent solution according to the invention may comprise a compound te corresponding to the general formula (I), chosen from the following compounds:

According to the invention, the alkylaminopiperazine may be in variable concentration in the absorbent solution, for example between 10% and 90% by weight, preferably between 20% and 60% by weight, very preferably between 25% and 50% by weight.

The absorbent solution may contain from 10% to 90% by weight of water, preferably from 40% to 80% by weight of water, very preferably from 50% to 75% water.

c - According to one embodiment, the absorbent solution may also contain a tertiary amine, for example methyldiethanolamine, triethanolamine, diethylmonoethanolamine, dimethylmonoethanolamine, ethyldiethanolamine, or secondary having a severe steric hindrance, this bulk being defined either by the presence of two tertiary carbons in alpha of the nitrogen, or by at least one quaternary carbon in alpha of the nitrogen. The concentration of tertiary amine or secondary amine severely congested in the absorbent solution may be between 10% and 90% by weight, preferably between 10% and 50% by weight, very preferably between 10% and 30% by weight. According to one embodiment, the absorbent solution may contain a compound 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 as monoethanolamine,

N-butylethanolamine

aminoethylethanolamine

diglycolamine,

piperazine,

1 - methylpiperazine

2- methylpiperazine

N- (2-hydroxyethyl) piperazine,

N- (2-aminoethyl) piperazine,

morpholine

3- (methylamino) propylamine.

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

The absorbent solution 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 unit Claus process bottoms, biomass fermentation gases, cement gases, incinerator fumes. These gaseous effluents contain one or more acidic compounds: CO 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 and 60 ° C., a pressure of between 1 and 5 bar and may comprise between 50 and 80% of nitrogen, between 5 and 40% of carbon dioxide, and between 1 and 20% of carbon dioxide. oxygen, and some impurities such as SOx and NOx, if they have not been removed 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. Process for removing acidic compounds in a gaseous effluent

The invention also relates to a process for deacidifying a gaseous effluent from the aqueous solution according to the invention. This process is carried out, schematically, by performing an absorption step followed by a regeneration step, for example as shown in FIG.

With reference to FIG. 1, the absorption step consists of bringing the gaseous effluent 1 into contact with the absorbent solution 4. The gaseous effluent 1 is introduced at the bottom of C1, the absorbent solution is introduced at the head of C1 . Column C1 is provided with gas-liquid contacting means, for example loose packing, structured packing or distillation trays. During contact, the amine functions of the molecules of the absorbent solution react with the acidic compounds contained in the effluent, so as to obtain a gaseous effluent depleted of acidic compounds 2 discharged at the head of C1, and an acid-enriched absorbent solution. 3 evacuated at the bottom of C1 to be regenerated.

The regeneration step consists in particular in heating and, optionally, in expanding, the absorbent solution enriched in acidic compounds in order to release the acidic compounds in gaseous form. The absorbent solution enriched in acidic compounds 3 is introduced into the heat exchanger E1, where it is heated by the stream 6 from the regeneration column C2. The heated solution at the outlet of E1 is introduced into the regeneration column C2. The regeneration column C2 is equipped with internal contacting between gas and liquid, for example trays, loose or structured packings. The bottom of column C2 is equipped with a reboiler R1 which provides the heat necessary for regeneration by vaporizing a fraction of the absorbent solution. In the column C2, under the effect of contacting the absorbent solution arriving by 5 with the vapor produced by the reboiler, the acid compounds are released in gaseous form and discharged at the top of C2 through the pipe 7. The solution regenerated absorbent 6, that is to say depleted in acidic compounds 6 is cooled in E1, then recycled in column C1 through line 4.

The absorption step of the acidic compounds can be carried out at a pressure in 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 C1 of between 20% and 80%, preferably between 30 ° C and 90 ° C, or even between 30 and 60 ° C.

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 C2 of between 1 bar and 5 bar, or even up to 10 bar, and at a temperature in C2 of between Ι ΟΟ'Ό and 180 ° C., preferably of between 130 ° and 170 ° C. vs. Preferably, the regeneration temperature in C2 is between 155 ° C and Ι δΟ'Ό in the case where it is desired to reinject the acid gases. Preferably, the regeneration temperature in C2 is between 115 ° C and 130 ° in the case where the acid gas is sent to the atmosphere or in a downstream treatment process, such as a Claus process or a treatment method. of tail gas.

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 contains, in addition, sulfur impurities (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. The natural gas consists mainly of gaseous hydrocarbons, but can contain several of the following acidic compounds: C0 ₂ , H ₂ S, mercaptans, COS, CS2. The content of these acidic compounds is very variable and can be up to 40% for CO ₂ and H ₂ S. The temperature of the natural gas can be between 20 ° and 100 ° C. The pressure of the natural gas to be treated may be between 10 and 120 bar. The invention can be implemented to achieve specifications generally imposed on the deacidified gas, which are 2% of C0 ₂ , or even 50 ppm of C0 ₂ to then perform a liquefaction of natural gas and 4 ppm H ₂ S and 10 to 50 ppm volume of total sulfur.

EXAMPLE 1 Ability and Selectivity of H ₂ S Elimination of a Gaseous Effluent Containing H ₂ S and CO ₂ by Solutions of N-methyl-4-hydroxypiperidine, N-methyl-3-hydroxypiperidine and N-ethyl -4-hydroxypiperidine:

An absorption test is carried out at 40 ° C. on aqueous amine solutions in a perfectly stirred open reactor on the gas side.

For each solution, the absorption is carried out in a liquid volume of 50 cm ³ by bubbling a gaseous stream consisting of a nitrogen mixture: carbon dioxide: hydrogen sulphide of 89: 10: 1 in volume proportions, of a flow rate of 30NL / h for 90 minutes.

At the end of the test, the H ₂ S feedstock content obtained (a = mole of H ₂ S / kg of solvent) and the absorption selectivity for C0 _{2 were} measured.

This selectivity S is defined as follows:

H ₂ s (Concentration of gas mixture C0 ₂ ) a _co (concentration of gas mixture H ₂ S) Under the conditions of the test described here S ⁼ 10 ^χ - ^~ .

By way of example, it is possible to compare the degree of charge and the selectivity between an absorbent solution of N-methyl-4-hydroxypiperidine at 50% by weight according to the invention, of N-methyl-3-hydroxypiperidine at 50% by weight. weight according to the invention and N-ethyl-4-hydroxypiperidine at 49% by weight according to the invention and an absorbent solution of methyldiethanolamine (MDEA) at 47% by weight, reference compound for the elimination H ₂ S selective gas treatment, and an absorbent solution of 50% (N-methyl-3-hydroxymethyl) piperidine, heterocyclic tertiary amine cited in US Patent 4,483,833 and belonging to the general formula cited in WO2009 / 1 105586 and separate from the invention.

Table 1

This example illustrates the gains in the degree of charge and selectivity that can be achieved with an absorbent solution according to the invention, comprising 50% by weight of N-methyl-4-hydroxypiperidine or 50% by weight of N-methyl-3-hydroxypiperidine. or 49% by weight of N-ethyl-4-hydroxypiperidine compared to the reference absorbent solution (MDEA 47%) This example illustrates that heterocyclic tertiary alkanolamines are not all equivalent in terms of selectivity. Indeed, (N-methyl-3-hydroxymethyl) piperidine (second entry of Table 1) does not belong to the group of N-alkyl-hydroxypiperidines unlike the molecules of the invention. It does not bring a gain in selectivity compared to the reference absorbent solution (MDEA 47%).

It therefore appears that the molecules claimed have particular performance and improved in terms of charge rate and selectivity.

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

A comparative CO 2 absorption test was carried out with an absorbent solution of 50% by weight N-methyl-4-hydroxypiperidine according to the invention relative to an aqueous solution of methyldiethanolamine at 47% by weight.

These solutions are also compared to a 50% wt.% Solution of N-methyl-2-hydroxymethylpiperidine, a molecule described in WO2009 / 1 105586 and according to US Pat. US patent specification 4,483,833 and various solutions of compounds described in US Patent 4,483,833 and according to the definition of WO2009 / 1 105586: a solution of N- (2-hydroxyethyl) -pyrolidine at 50 wt%, a solution of N- (2-hydroxyethyl) -piperidine at 45% by weight, a solution of N-methyl-2-hydroxyethylpiperidine at 45% by weight.

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 oxysulfide 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 of 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 2 as the relative absorption rate of the reference formulation methyldiethanolamine 47%, this relative absorption rate being defined by the ratio of the overall transfer coefficient of the solvent to the overall transfer coefficient of the reference formulation.

Table 2 Examination of the results shows, under these test conditions, a rate of absorption of CO2 by the formulation based on N-methyl-4-hydroxypiperidine according to the invention slower than the reference formulation MDEA, unlike to the other molecules cited in the prior art. It therefore appears that the molecule exemplified according to the invention is of particular interest and improved in the case of a selective deacidification in which it is sought to limit the kinetics of C02 absorption.

Example 3. CO 2 absorption rate of an activated formulation

The absorption rate of CO ₂ is compared with an absorbent solution containing 39% by weight of methyldiethanolamine and 6.7% by weight of piperazine in water to an absorbent solution according to the invention containing 39% by weight of N-methyl-4-hydroxypiperidine. and 6.7 wt% piperazine in water.

In each test, a gas containing CO 2 is contacted with the absorbing liquid by operating in a vertical falling film reactor provided in its upper part with a gas outlet and an inlet for the liquid and in its lower part. an inlet for the gas and an outlet for the liquid. Through the gas inlet, a gas containing 10% CO 2 and 90% nitrogen is injected at a flow rate of between 30 and 50 Nl / h and the liquid inlet is introduced with a flow rate of 0.5 l / h. Through the gas outlet, a CO 2 depleted gas is evacuated and the liquid outlet is evacuated and the CO 2 enriched liquid is evacuated.

The absolute pressure and the liquid temperature at the outlet are respectively equal to 1 bar and 40 ^<€.

For each test, the flow of C0 ₂ absorbed between the gas inlet and the gas outlet is measured as a function of the incoming gas flow rate: for each gas flow setpoint: 30 - 35 - 40 - 45 - 50 Nl / h, the gas incoming and outgoing are analyzed by infrared ray absorption techniques in the gas phase to determine their C0 ₂ content. From all these measurements, by performing two ups and downs of the range of flow rates, the overall transfer coefficient Kg is deduced, characterizing the absorption speed of the absorbing liquid.

The operating conditions specific to each test and the results obtained are presented in Table 3. Composition of the aqueous absorbent solution

Tertiary amine Activator

Concentration Concentration

Nature Nature Speed

(% by weight) (% by weight)

relative absorption of C02

MDEA 39 Piperazine 6.7 1

N-methyl-4-hydroxypiperidine

(according to the invention) 39 piperazine 6.7 1, 24

Table 3

Examination of the results in Table 3 shows the improved rate of absorption of CO 2 exhibited by the absorbent solutions according to the invention compared with those of the control absorbent solution containing an MDEA-piperazine mixture known to those skilled in the art. .

Example 4: Capture capacity of N-methyl-4-hydroxypiperidine

The performance of the C0 ₂ capture capacity of the N-methyl-4-hydroxypiperidine according to the invention is compared in particular with those of an aqueous solution of MonoEthanolAmine at 30% by weight, which constitutes the reference solvent for a capture application. of C0 ₂ contained in post-combustion fumes. They are also compared with those of a solution of aqueous N-methyl-2-hydroxymethylpiperidine, cited in US Patent 4,405,582 containing the same weight percentage of tertiary diamine and piperazine. An absorption test is carried out on aqueous amine solutions in a perfectly stirred closed reactor whose temperature is controlled by a control system. For each solution, the absorption is carried out in a liquid volume of 50 cm ³ by injections of pure CO ₂ from a reserve. The solvent solution is previously drawn under vacuum before any CO ₂ injection. The pressure of the gas phase in the reactor is measured and an overall material balance on the gas phase makes it possible to measure the solvent loading rate a = nb of mole acid gas / nb of amine mole.

By way of example, the feed rates (a = nb of mole acid gas / nb of amine mole) obtained at 40 ° C. for various partial pressures of CO ₂ between an aqueous solution of N-methyl- 4-hydroxypiperidine 30% by weight according to the invention, an aqueous solution of N-methyl-2-hydroxymethylpiperidine molecule described in the document WO2009 / 1 105586 at 30% by weight and an aqueous solution of MonoEthanolAmine, at 30% by weight for a post-combustion C0 ₂ capture application.

To go from a quantity of the charge rate obtained in the laboratory to a characteristic quantity of the process, some calculations are necessary, and are explained below for the intended application:

In the case of an application of CO ₂ capture in post-combustion, the partial pressures of CO ₂ in the effluent to be treated are typically 0.1 bar with a temperature of 40 ° C., and it is desired to slaughter 90 % of the acid gas. The cyclic capacity Δα _Ρ0 expressed in moles of C0 ₂ per kg of solvent is calculated, considering that the solvent reaches its maximum thermodynamic capacity at the bottom of the absorption column and must at least be regenerated below its thermodynamic capacity under the conditions of the column head bar to achieve 90% reduction of C0 ₂ .

AOC _pc = {(Xppco) '[^]' 10 M

where [A] is the concentration of amine expressed in% by weight, and M is the molar mass of the amine in g / mol, are the feed ratios (mole C0 ₂ / mole of amine) of the solvent in equilibrium respectively with a partial pressure of 0.1 bar and 0.01 bar of CO ₂ .

The reaction enthalpy can be obtained by calculation from several CO ₂ absorption isotherms by applying the Van't Hoff law.

Table 4 For post-combustion fume extraction application where the partial pressure of C0 ₂ in the effluent to be treated is 0.1 bar, this example illustrates the greater cyclic capacity obtained thanks to an absorbing solution of N-methyl-4-hydroxypiperidine according to the invention, comprising 30% by weight of molecules to achieve a felling rate of 90% at the absorber outlet. In this application where the energy associated with the regeneration of the solution is critical, it can be observed that the amine according to the invention makes it possible to obtain a much better compromise than the MEA, in terms of cyclic capacity and heat transfer. reaction. There is also a gain in terms of cyclic capacity and reaction enthalpy of N-methyl-4-hydroxypiperidine according to the invention compared to N-methyl-2-hydroxymethylpiperidine described in WO2009 / 1 105586.

EXAMPLE 5 Capacity for C0 ₂ Capture of Solutions of N-Methyl-4-hydroxypiperidine Activated with Piperazine Application to post-combustion flue gas treatment

The performance of C0 ₂ capture capacity of an aqueous solution of N-methyl-4-hydroxypiperidine according to the invention in a mixture with piperazine is compared in particular with those of an aqueous solution of monoethanolamine at 30% by weight, which constitutes the reference solvent for a CO ₂ capture application contained in post-combustion fumes. They are also compared with those of an aqueous solution of N-methyl-2-hydroxymethylpiperidine, described in document WO2009 / 1 105586 containing the same weight percentage of tertiary amine and piperazine.

The absorption tests carried out are as described in the previous example. By way of example, the feed rates (a = nb of mole acid gas / mole of amine) obtained at 40 ° C. for various partial pressures of C0 ₂ between an absorbent solution of N-methyl are compared in Table 5. -4-hydroxypiperidine according to the invention to 39% by weight and containing 6.7% by weight of piperazine to accelerate the uptake kinetics of C0 ₂ in the post-combustion, an absorbent solution of monoethanolamine to 30% by weight, as well as an absorbent solution of N-methyl-2-hydroxymethylpiperidine at 39% by weight and containing 6.7% by weight of piperazine.

Charge rates are as defined in the previous example. The cyclic capacity Δα _Ρ0 expressed in moles of CO ₂ per kg of solvent is calculated in the same manner as in Example 2:

AOC _pc = [pCppco) '[^]' 10 M where [A] is the total concentration of amine expressed as% by weight, and in the case of amine mixtures, M is the average molar mass of the amine mixture in g / mol:

M = [A _T] / ([A _T] / M _{AT +} [PZ] / Mpz)

where [A _T ], [PZ] are the concentrations of tertiary amine and piperazine, expressed in weight%, M _AT and M _PZ are respectively the molar masses of the tertiary amine and piperazine in mol / kg

Table 5

For post-combustion fume extraction application where the partial pressure of C0 ₂ in the effluent to be treated is 0.1 bar, this example illustrates the greater cyclic capacity obtained thanks to the absorbent solution according to the invention, comprising 39% weight of N-methyl-4-hydroxypiperidine according to the invention and 6.7% by weight of piperazine to achieve a felling rate of 90% at the outlet of the absorber compared to MEA 30% by weight.

There is also a gain in terms of the cyclic capacity of the formulation according to the invention compared to the formulation containing the same weight percentage of N-methyl- 2-hydroxymethylpiperidine described in WO2009 / 1 105586 and the same weight percentage of piperazine.

Example 6 Absorption capacity of CO ₂ of solutions of N-methyl-4-hydroxypiperidine activated with piperazine. Application to decarbonation in natural gas treatment

The performance of the absorption capacity of C0 ₂ of an aqueous solution of N-methyl-4-hydroxypiperidine according to the invention in a mixture with piperazine is compared in particular with those of an aqueous solution of methyldiethanolamine mixed with piperazine containing the same weight percentage of tertiary amine and piperazine, known to those skilled in the art to remove CO ₂ in the treatment of natural gas. They are also compared with those of an aqueous solution of N-methyl-2-hydroxymethylpiperidine, described in document WO2009 / 1 105586 containing the same weight percentage of tertiary amine and piperazine.

The absorption tests carried out are as described in the previous example.

By way of example, the feed rates (a = nb of mole acid gas / mole of amine mole) obtained at 40 ° C. for a partial pressure of CO ₂ equal to 3 bar between an absorbent solution of N-methyl-4-hydroxypiperidine according to the invention at 39% by weight and containing 6.7% by weight of piperazine, an absorbent solution of methyldiethanolAmin at 39% by weight and containing 6.7% by weight of piperazine, as well as an absorbent solution of N-methyl-2-hydroxymethylpiperidine at 39% by weight and containing 6.7% by weight of piperazine.

In the case of a decarbonation application in natural gas treatment, the partial pressures of C0 ₂ are typically centered between 1 and 10 bar with a temperature of 40 ^q C, and it is desired to eliminate almost all the C0 ₂ for liquefaction of natural gas. To compare the different solvents, the maximum cyclic capacity Aa _LN G, max expressed in moles of CO ₂ per kg of solvent is calculated, considering that the solvent reaches its maximum thermodynamic capacity at the bottom of the absorption column. and is fully regenerated under the conditions of the column head.

Δΰ ^ σ {a) '[A] · 10 /

where [A] is the total concentration of amine expressed in weight%, and in the case of amine mixtures, M is the average molar mass of the mixture of amines in g / mol: M = [A _T] / ([A _T] / M _{AT +} [PZ] / Mpz)

is the charge ratio (mole C0 ₂ / mole of amine) of the solvent in equilibrium respectively with a partial pressure of 3 bar of CO ₂ .

Table 6 For a total decarbonation application in natural gas treatment, this example illustrates the greater cyclic capacity obtained thanks to the absorbent solution according to the invention, comprising 39% by weight of N-methyl-4-hydroxypiperidine according to the invention. and 6.7% by weight of piperazine relative to the reference formulation containing 39% by weight of MDEA and 6.7% by weight of piperazine.

There is also a gain in terms of cyclic capacity of the formulation according to the invention compared to the formulation containing the same weight percentage of N-methyl-2-hydroxymethylpiperidine described in WO2009 / 1 105586 and the same weight percentage of piperazine. Example 7 Stability of an Amine Solution According to the Invention

The amines used according to the invention have the particularity of being particularly resistant to the degradations that may occur in a deacidification unit. A degradation test is carried out on aqueous solutions of amine in a closed reactor whose temperature is controlled by a control system. For each solution, the test is carried out in a liquid volume of 50 cm ³ injected into the reactor. The solvent solution is previously drawn under vacuum before any gas injection and the reactor is then placed in a heating shell at the set temperature and stirred magnetically. The gas in question is then injected at the desired partial pressure. This pressure is added to the initial pressure due to the vapor pressure of the aqueous amine solution. Different degradation conditions are tested:

- degradation under C0 ₂ C0 ₂ is injected so as to attain a partial pressure of 20 bar

degradation under 0 ₂ : air is injected under a partial pressure of 20 bars, which gives an oxygen partial pressure of 4.2 bars.

Table 7 gives the degradation rate TD, by degradation under C0 ₂ , of N-methyl-4-hydroxymethylpiperidine according to the invention, and of N-methyl-2-hydroxymethylpiperidine described in document WO2009 / 1 105586 as well as the MEA as reference amines, for a duration of 15 days, defined by the equation below:

[A] - [A] °

TD (%) =

[A] where [A] is the concentration of the compound in the degraded sample, and [A] ⁰ is the concentration of the compound in the non-degraded solution. The concentrations [A] and [A] ⁰ are determined by gas phase chromatography.

Amine Concentration T ( ^< C) TD (%)

ME 30% weight 140 42%

N-methyl-2-hydroxymethylpiperidine (described

in the document 50% weight 140 1 1% WO2009 / 1 105586)

N-methyl-4-hydroxymethylpiperidine (according to 50% weight 1%

the invention)

Table 7

Table 8 gives the degradation rate TD, by degradation under 0 ₂ , of the N-methyl-4-hydroxymethylpiperidine according to the invention, as well as the MEA as reference amine, for a period of 15 days, defined as above:

PP ₀₂ = 4.2 bar

Amine Concentration T (° C) TD (%)

MEA 30% weight 140 21%

N-methyl-4-hydroxymethylpiperidine (according to 50% weight 140 2%

the invention)

Table 8

Table 9 gives the degradation rate TD, by degradation under C0 ₂ of the N-methyl-4-hydroxymethylpiperidine according to the invention and piperazine mixed with the latter in an absorbent solution, and the MDEA as reference amine. , and piperazine mixed with the latter in another absorbent solution for a period of 15 days, the degradation rate of each amine being defined as above:

TD Tertiary amine TD piperazine (%)

Absorbent solution T ( ^< C)

(%)

MDEA 39% + piperazine 6.7% 140 13% 43%

N-methyl-4-hydroxymethylpiperidine 39% + 140 5% 8%

piperazine 6.7%

Table 9

This example shows that the use of the compounds according to the invention, as amine in an absorbing solution makes it possible to obtain a low degradation rate compared to amine-based absorbent solutions of the prior art (monoethanolamine and N-methyl2 -hydroxymethylpiperidine described in WO2009 / 1 105586).

In mixture with piperazine, it also indicates a lower degradation rate of the compounds according to the invention as well as piperazine mixed with them, in comparison with methyldiethanolamine mixed with piperazine.

Therefore, it is possible to regenerate the absorbent solution at higher temperature and thus to obtain an acid gas at higher pressure. This is particularly interesting in the case of C0 ₂ capture in post-combustion or decarbonation applications in natural gas treatment in which the acid gas must be compressed to be liquefied before reinjection.

Claims

An absorbent solution for removing acidic compounds contained in a gaseous effluent, comprising:

a - water;

Absorbent solution according to claim 1, wherein the compound is selected from the following compounds:

3. Absorbent solution according to one of the preceding claims, comprising between 10% and 90% by weight of said compound, preferably between 20% and 60% by weight, very preferably between 25% and 50% by weight.

4. Absorbent solution according to one of the preceding claims, comprising between 10% and 90% by weight of water, preferably between 40% and 80% by weight of water, very preferably from 50% to 75% of water. water.

Absorbent solution according to one of the preceding claims, comprising an additional amine, said additional amine being a tertiary amine, such as methyldiethanolamine, or a secondary amine having two carbons. Tertiary in alpha of nitrogen, or a secondary amine having at least one quaternary carbon in alpha of nitrogen.

Absorbent solution according to claim 5, comprising between 10% and 90% by weight of said additional amine, preferably between 10% and 50% by weight, very preferably between 10% and 30% by weight.

7. Absorbent solution according to one of the preceding claims, comprising a compound containing at least one primary or secondary amine function.

8. Absorbent solution according to claim 7, comprising a concentration up to 30% by weight of said compound, preferably less than 15% by weight, preferably less than 10% by weight, and at least 0.5% by weight.

9. Absorbent solution according to one of claims 7 and 8, comprising a concentration of at least 0.5% by weight of said compound.

10. Absorbent solution according to one of claims 7 to 9, wherein said compound is selected from:

- Monoethanolamine,

N-butylethanolamine

aminoethylethanolamine

diglycolamine,

piperazine

- 1-methylpiperazine

2-methylpiperazine

N- (2-hydroxyethyl) piperazine,

N- (2-aminoethyl) piperazine,

morpholine

3- (methylamino) propylamine.

11. Absorbent solution according to one of the preceding claims, comprising a physical solvent selected from methanol and sulfolane.

12. 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 effluent with an absorbent solution according to any one of claims 1 to 1 .

13. The method of claim 12, 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.

14. Process according to any one of claims 12 and 13, wherein, after the absorption step, a gaseous effluent depleted of acidic compounds and an absorbent solution loaded with acidic compounds are obtained, and at least one step is carried out. regeneration of the absorbent solution loaded with acidic compounds.

15. The method of claim 14, wherein the regeneration step is carried out at a pressure between 1 bar and 10 bar and a temperature between 100 ^< C and 180 ^< C.

16. Method according to one of claims 12 to 15, wherein the gaseous effluent is selected from natural gas, synthesis gas, combustion fumes, refinery gases, acid gases from a unit with Amines, gases from a Claus process bottling reduction unit, biomass fermentation gases, cement gases, incinerator fumes.

17. Method according to one of claims 12 to 16, implemented for the selective removal of H ₂ S from a gaseous effluent comprising H ₂ S and CO ₂ .