FR2990879A1 - PROCESS FOR DECARBONATING SMOKE. - Google Patents

Abstract

A process for decarbonating a smoke, such as carbon dioxide-containing hydrocarbon combustion smoke, comprising a step of contacting said smoke with an absorbent solution comprising, preferably consisting of, at least one amine , water and at least one thioalkanol C -C.

Description

METHOD FOR DECARBONATING SMOKE. TECHNICAL FIELD The present invention relates to a process for decarbonating fumes, in other words a process for removing carbon dioxide contained in fumes. The invention finds its application in the treatment of combustion fumes, including combustion fumes from the combustion of hydrocarbons for example in thermal power plants, and in various industries such as cement manufacturing, refining, steelmaking, petrochemicals, and the biomass industry. STATE OF THE PRIOR ART The deacidification of gaseous effluents such as natural gas, synthesis gases, combustion fumes, tail gases, and biomass fermentation gases is generally carried out by washing with a solvent. The physico-chemical characteristics of this solvent are closely related to the nature of the gaseous effluent to be treated and the solvent is generally chosen so that the treated gas meets a specific specification, so as to selectively remove an impurity, and so that the solvent is thermally and chemically stable vis-a-vis the various compounds present in the gaseous effluent. In the present, we are particularly interested in the decarbonation of fumes.

The typical composition in volume% of a gaseous effluent that can be qualified as smoke is generally the following, without taking into account the amount of water saturating this effluent under the temperature and pressure conditions in which it is placed. at disposal: - 60% to 95%, for example 80% to 92% by volume of nitrogen, - 2% to 25% by volume, for example 4% to 15% by volume of carbon dioxide, - 0.1 % to 10% by volume, for example 2% to 5% by volume of oxygen. Different impurities, such as sulfur oxides, nonionic oxides of nitrogen, argon, and particles may also be present in smaller amounts, these impurities generally represent less than 2% by volume of the total. effluent. The flue gas temperature is generally between 20 ° C and 180 ° C, the pressure is generally between 1 and 15 bar.

The treatment of fumes for their decarbonation imposes specific constraints on the solvent. Thus, the solvent must allow selective absorption of the carbon dioxide with respect to the nitrogen, it must be chemically stable especially with respect to the impurities of the effluent, namely essentially oxygen, sulfur oxides. SO. and NO oxides nitrogen, and it must have a low vapor pressure, to limit solvent losses at the top of the deacidification column.

The most widely used solvents today are aqueous solutions of primary, secondary or tertiary alkanolamines as described in the "Gas Purification" document of Arthur L. Kohl and Richard B. Nielsen, Gulf Professional Publishing, 1997.

The absorbed CO2 reacts with the alkanolamine present in solution, according to an exothermic reaction. The rate of the reaction, its exothermicity, the stability of the reaction products, and the corrosiveness of the solution decrease with the increase of the degree of substitution of the nitrogen atom of the alkanolamine molecule. Tertiary alkanolamines have the problem of a limited capacity, but also of a chemical association with slow CO2 in the face of the transfer phenomena, which implies that particular attention must be paid to the design of the absorbers. The secondary alkanolamines, and especially the primary alkanolamines, will therefore generally be preferred over tertiary alkanolamines, despite the higher risks of corrosion and chemical degradation of the solvent. By way of example, mention may be made of monoethanolamine (MEA) which, by virtue of its high absorption capacity, makes it possible to eliminate more than 90% of CO2 during the treatment of effluents which have low partial pressures of CO2, characteristics of the fumes. The regeneration of these aqueous solvents based on alkanolamine requires a substantial energy supply, corresponding to the heat of reaction between the alkanolamine and the acid gases, to the production of a quantity of vapor enabling the regeneration of the solvent to be carried out by " stripping ", and the sensible heat necessary to bring the solvent from the absorption temperature to the regeneration temperature. In addition to the aqueous solutions of alkanolamines, hot aqueous solutions of carbonates can be used as a solvent for the absorption of CO2 as mentioned in the document "Gas Purification" by Arthur L. Kohl and Richard B. Nielsen, Gulf Professional Publishing, 1997 already cited. The mode of action of hot aqueous solutions of carbonates is based on the absorption of CO2 in the aqueous solution, followed by the chemical reaction of CO2 with carbonates. It is known that the addition of additives makes it possible to optimize the effectiveness of the solvent. These additives are mostly primary or secondary amines, such as diethanolamine (DEA). Here again, the energy consumption of this process, especially during regeneration, remains too high. In contrast to processes which use aqueous solutions of alkanolamines or carbonates, and in which the selectivity of the solvent, particularly with respect to nitrogen, in the case of the treatment of fumes, is ensured by a reaction. other solvent decarbonation processes are based on a physical absorption of CO2 by the solvent.

With these solvents carrying out a physical absorption, such as, for example, chilled methanol or polyethylene glycols, it is generally found that it is necessary to use a large solvent flow rate, given the low absorption capacity of these solvents. under the operating conditions of the flue gas treatment. Another disadvantage of some of these solvents achieving physical absorption is also their instability in the presence of oxygen in the smoke to decarbonate. US-B2-6,579,343 discloses a method of purifying a gas in which the gas is contacted with an ionic liquid. The use of ionic liquids would selectively separate CO2 from nitrogen. The interest of these solvents is also their low vapor pressure and their thermal stability. But today, these molecules are not available on an industrial scale and remain at a high cost. As a result, these ionic liquids can not be considered today as a viable technological solution to the problem of the treatment of combustion fumes. GB-A-1388497 discloses a process for removing a compound selected from oxygen, iodine, methyl iodide, and oxides of carbon, sulfur and nitrogen having less than three atoms. oxygen, a gaseous mixture containing it, wherein the gaseous mixture is contacted in an absorption zone at a pressure above atmospheric pressure, with a liquid fluorocarbon. The gaseous mixture may include other compounds such as air, hydrocarbons such as methane and natural gas, and various impurities such as H2S hydrogen sulfide, ammonia, hydrogen or helium. Because of their structure, fluorocarbons are particularly suitable for decarbonation. Indeed, the presence of fluorine atoms on the carbon chain gives these molecules the property of absorbing carbon dioxide, which can be up to 500% by volume, at 25 ° C., this absorption of CO2 being performed selectively with respect to oxygen. These fluorocarbon solvents are, on the other hand, strongly penalized by their physicochemical properties such as density and viscosity. In addition, the modest absorption capacity of these solvents imposes the use of large volumes of solvents which is incompatible with an industrial implementation for the treatment of combustion fumes or natural gas. Moreover, the high cost of these molecules is also an obstacle to their implementation on a large scale.

In general, the problem common to all the solvents described above and which can be used on an industrial scale is the energy necessary for their regeneration.

This regeneration step, generally thermal, involves three mechanisms respectively related to the sensible heat of the absorbent solution, its heat of vaporization, and the enthalpy of binding between the absorbed species and the absorbent solution. The binding energy is all the more important because a chemical reaction makes it possible to shift the solubility equilibria. In the particular case of alkanolamines, it is thus more expensive to regenerate a very basic primary alkanolamine such as MonoEthanolAmine (MEA), than a tertiary amine such as MethylDiEthanolAmine (MDEA). The heat of vaporization of the solvent is to be taken into account since the thermal regeneration step requires the vaporization of a non-negligible fraction of the solvent, such as water, in order to achieve a "stripping" effect favoring the removal of the acid gases contained in the solvent to be regenerated. It should be noted that the "stripping" effect could be generated by an inert gas, but then the question of the availability of this inert gas, and especially of the process to be used to separate the CO2 from this inert gas at the outlet, would arise. of the regeneration step.

The distribution of the energy cost of the regeneration step between sensible heat, heat of vaporization and enthalpy of the absorbed gas-absorbent solution will essentially depend on the physicochemical properties of the absorbing solution. In order to reduce the energy input required for regeneration, documents FR-A-2898284, FR-A-2900842 and FR-A-2900843 propose the use of a chemical absorbent solution containing an alkanolamine whose reaction with CO2 are immiscible with non-carbonated alkanolamine. This property of the alkanolamine produces a demixing phenomenon, between a first phase containing the nonreactive alkanolamine on the one hand, and a second phase containing the salts resulting from the reaction between the alkanolamine and the CO2 on the other hand. Only the second phase is regenerated by distillation, which makes it possible to minimize the energy required for the regeneration of the absorbent solution.

The main difficulty of this technology lies in the control of the demixing phenomenon which must not penalize the transfer phenomena, which can lead to a limitation of the amount of CO2 that can be absorbed by a given volume of absorbent solution. In addition, the similarities between the physicochemical properties of the two phases, in particular their densities, have a notable impact on the size and type of the device to be used to achieve the separation of the two phases, and a complex device of large dimension must therefore be provided. In view of the foregoing, therefore, there is a need for a decarbonation process of a carbon dioxide-containing smoke with an absorbent solution, which can be removed by absorption, with high efficiency. the carbon dioxide of this smoke, which has a high selectivity, for the removal of carbon dioxide from nitrogen, which uses an absorbent solution prepared with reagents readily available in large quantities and low cost and having the appropriate physicochemical properties (eg density, viscosity, vapor pressure) for its use in such a process. Finally, there is a need for a process in which the energy input required during the regeneration step of the absorbent solution is less, thereby decreasing the overall energy consumption of the process and the costs of the decarbonation process. fumes. The object of the present invention is to provide a process for decarbonating fumes containing carbon dioxide which, among other things, meets this need. The object of the present invention is still to provide a process for decarbonating a smoke which does not have the disadvantages, defects, limitations and disadvantages of the processes of the prior art, and which solves the problems of the processes of the art. prior. SUMMARY OF THE INVENTION This and other objects are achieved, in accordance with the invention, by a process for decarbonating a carbon dioxide-containing smoke, comprising a step of contacting said smoke with an absorbent solution comprising, preferably consisting of, at least one amine, water and at least one C 2 -C 4 thioalkanol. The process according to the invention is fundamentally different from the processes of the prior art in that it uses a specific absorbent solution, and in some cases new, for the treatment of specific gaseous effluents that are fumes. Some of the absorbent solutions used in the process according to the invention are certainly already known and have been used in a process for simultaneously removing mercaptans and other acid gases. However, this process, which was the subject of the application WO-A1-2007 / 083012 (FR-A1-2896244) is exclusively used for the treatment of gaseous mixtures, such as natural gases, essentially consisting of hydrocarbons, and containing little or no nitrogen and oxygen. Such gaseous mixtures are totally different from the fumes treated by the process according to the invention, which generally contain a major proportion of nitrogen and a large proportion of oxygen. Furthermore, while in the process of the application WO-A1-2007 / 083012 (FR-A1-2896244) it is sought to simultaneously eliminate the mercaptans and all the other acid gases, the process according to the invention is designed to eliminate, selectively absorb CO2 relative to nitrogen in fumes. Surprisingly, it has been demonstrated that the absorbent solutions preferably comprise at least one amine, water and at least one C 2 -C 4 thioalkanol, some of which have already been used for the total purification of Essentially hydrocarbon-based gas mixtures containing mercaptans and / or acid gases as impurities could also be successfully used to selectively remove the CO2 contained in fumes from the nitrogen. All the absorbent solutions used in the process according to the invention, whether they are already known, such as the absorbing water-diethanolamine-thiodiglycol solution, or not, have the advantage of having a high reactivity vis-à- CO2 and a high selectivity to preferentially absorb the CO2 contained in fumes, compared to nitrogen. It is entirely surprising that absorbent solutions which are suitable for the overall and non-selective removal of all acid gases from substantially hydrocarbon gas mixtures may also be suitable for the selective removal of CO2 from nitrogen from fumes which are specific gaseous mixtures essentially nitrogenous and free from hydrocarbons. Indeed, the problems which arise during the treatment of gaseous hydrocarbon mixtures are, obviously, totally different from those which arise during the treatment of gaseous mixtures such as fumes, because of the totally different composition of each of them. these gas mixtures.

Specific problems posed by the treatment of fumes also come from their low pressure, generally less than 15 bar. The decarbonation process of a smoke according to the invention meets the needs mentioned above, it does not have the disadvantages, defects, limitations and disadvantages of the processes of the prior art, and it provides a solution to the problems of the processes of the invention. prior art. In particular, it has been shown that, surprisingly, the addition according to the invention, of a C2-C4 thioalkanol, such as TDG, to an absorbent solution containing water and an amine, used in a The process of decarbonating fumes led to a significant energy saving during the step of regenerating said absorbent solution. These energy gains are obtained while maintaining a high selectivity of the absorbent solution vis-à-vis the CO2 compared to nitrogen. Without wishing to be bound by any theory, it appears that the thioalkanol, which can be described as cosolvent, affects the interactions between the CO2 and the absorbing solution. Since the bonding energy between the CO2 and the amine in solution is reduced, the energy required for the regeneration of the absorbent solution used in the process according to the invention is less.

Tests carried out in a pilot plant have shown that the water-DEATDG absorbent solution used according to the invention for the decarbonation of a representative gaseous effluent - because of its CO2 content - of a combustion smoke, made it possible to to obtain the selective removal of CO2 with respect to nitrogen, and that this absorbing solution, because of the addition of TDG, also made it possible to achieve a considerable energy saving, namely a saving in energy of 15%. %, during the regeneration step of the absorbent solution relative to a water-DEA absorbing solution without TDG used for the treatment of this same gaseous effluent. The same performances for the treatment of fumes are presented both by the new absorbent solutions containing a thioalkanol and by the already known absorbent solutions containing a thioalkanol used in the process according to the invention.

The method according to the invention makes it possible to reduce the capital expenditure ("CAPEX") and operating expenses ("OPEX") of the flue gas treatment installations, in particular combustion fumes, in particular by virtue of the energy savings during combustion. regeneration step due to the optimization of the absorbent solution implemented. The absorbent solution used in the process according to the invention also has all the appropriate physicochemical properties (for example low vapor pressure, viscosity and low density) which make it particularly suitable for optimum use in absorption columns including existing absorption columns. The smoke to be treated by the process according to the invention may be any smoke containing at least carbon dioxide. Generally, the smoke to be treated comprises, in percentages by volume relative to the total volume of the smoke: 10 - 60% to 95% by volume, for example 85% to 92% by volume, nitrogen, - 2% to 25% by volume. % by volume, for example 4% to 15% by volume, of carbon dioxide, 0.1% to 10% by volume, for example 2% to 5% by volume, of oxygen. The smoke to be treated may further comprise one or more impurities selected from Sulfur oxides, NO oxides, argon, and solid particles. Generally, the impurity (s) represent (s) in total less than 2% by volume of the total volume of the smoke to be treated. As already mentioned above, the smoke to be treated, prior to the step of bringing it into contact with the absorbent solution, can undergo a quenching treatment, generally carried out with water in particular. to remove solid particles and / or filtration, for example using 30 electrostatic filters.

In this case the smoke brought into contact with an absorbent solution during the step of bringing said smoke into contact with an absorbent solution generally does not contain solid particles and is saturated with water. The smoke to be treated is generally supplied at a temperature of between 20 ° C. and 180 ° C., and at a pressure generally below 15 bar. The process according to the invention is more particularly applicable to the decarbonation of combustion fumes and especially fumes from the combustion of hydrocarbons, for example gas, oil or coal. The process according to the invention makes it possible to eliminate 85% to 98% by volume of the CO2 of the smoke to be treated, generally from 88% to 92%. According to the invention, the smoke is contacted with an absorbent solution comprising, preferably at least one amine, water and at least one C2-C4 thioalkanol. The C2-C4 thioalkanol has the formula RS- (C2-C4) alkylene-OH where R is any group, for example an alkyl group (generally C1-C6) or an alcohol group or a thiol group or a alkylthioalkanol group (generally C1 to C6). According to a preferred embodiment, the C2-C4 thioalkanol is a dimeric molecule. An example of a C2 to C4 thioalkanol which can be used according to the invention is ethylene dithioethanol of formula (HO-CH2-CH2) -S- (CH2-CH2) -S- (CH2-CH2-OH). The preferred thioalkanol is thiodiethylene glycol or thiodiglycol (TDG) which is the compound of formula S (CH2-CH2-O11). In addition to TDG, other C2-C4 thioalkanols may also be used according to the invention, in particular methylthioethanol. It is also possible to use a mixture of several thioalkanols.

Any amine may be used in the absorbent solution whether it is a primary, secondary, or tertiary, cyclic, or aromatic amine. However, the amine used should generally be soluble in water at the concentrations used in the absorbent solution. For the purposes of the invention, the term "primary amine" generally means a compound comprising at least one primary amine function. For the purposes of the invention, the term "secondary amine" generally means a compound comprising at least one secondary amine function. For the purposes of the invention, the term "tertiary amine" generally means a compound comprising at least one tertiary amine function and preferably comprising only tertiary amine functions. These primary, secondary or tertiary amines may be chosen from aliphatic amines, cyclic amines or others. Examples of amines which can be used according to the invention are given in particular in document US-Al-2010/0288125, or in document FR-A-2 898 284 to the description of which reference may be made. Preferably, the at least one amine is chosen from alkanolamines.

These alkanolamines can be primary, secondary, or tertiary. Recall that the alkanolamines are amines comprising at least one hydroxyalkyl group bonded to the nitrogen atom.

Tertiary alkanolamines may be trialkanolamines, alkyldialkanolamines or dialkylalkanolamines. The secondary alkanolamines may be dialkanolamines, or alkylalkanolamines, and the primary alkanolamines are monoalkanolamines. The alkyl groups and the hydroxyalkyl groups of the alkanolamines can be linear or branched and generally comprise from 1 to 10 carbon atoms, preferably the alkyl groups comprise from 1 to 4 carbon atoms, and the hydroxyalkyl groups comprise from 2 to 4 carbon atoms. carbon. Examples of these alkanolamines are 2-aminoethanol (monoethanolamine, MEA), N, N-bis (2-hydroxethyl) amine (diethanolamine, DEA), N, N-bis (2-hydroxypropyl) amine (diisopropanolamine, DIPA). ), tris (2-hydroxyethyl) amine (triethanolamine, TEA), tributanolamine, bis (2-hydroxyethyl) methylamine (methyldiethanolamine, MDEA), 2-diethylaminoethanol (diethylethanolamine, DEEA), 2-dimethylaminoethanol (dimethylethanolamine) DMEA), 3-dimethylamino-1-propanol (N, N-dimethylpropanolamine), 3-diethylamino-1-propanol, 2-diisopropylaminoethanol (DIEA), N, N-bis (2-hydroxypropyl) methylamine ( methyldiisopropanolamine, MDIPA), 2-amino-2-methyl-1-propanol (AMP), 1-amino-2-methyl-propan-2-ol, 2-amino-1-butanol (2-AB). Examples of tertiary amines and especially tertiary alkanolamines are given in US-Al-2008/0025893 to the description of which we can refer.

These include N-methyldiethanolamine (MDEA), N, N-diethylethanolamine (DEEA), N, N-dimethylethanolamine (DMEA), 2-diisopropylaminoethanol (DIEA), N, N, N, N'-Tetramethylpropanediamine (TMPDA), N, N, N ', N'-tetraethylpropanediamine (TEPDA), dimethylamino-2-dimethylamino-ethoxyethane (Niax), and N, N-dimethyl-N', N'-diethylethylenediamine (DMDEEDA). Examples of tertiary alkanolamines which can be used in the process according to the invention are also given in US-Al-2010/0288125, to the description of which reference may be made. These include tris (2-hydroxyethyl) amine (triethanolamine, TEA), tris (2-hydroxypropyl) amine (triisopropanol), tributylethanolamine (TEA), bis (2-hydroxyethyl) methylamine (methyldiethanolamine, MDEA), 2-diethylaminoethanol (diethylethanolamine, DEEA), 2-dimethylaminoethanol (dimethylethanolamine DMEA), 3-dimethylamino-1-propanol, 3-diethylamino-1-propanol, 2-diisopropylaminoethanol (DIEA), N, N-bis (2-hydroxypropyl) methylamine (methyldiisopropanolamine, MDIPA). Other examples of tertiary alkanolamines which can be used in the process according to the invention are given in US-A-5,209,914 to the description of which reference may be made. These include N-methyldiethanolamine, triethanolamine, N-ethyldiethanolamine, 2-dimethylaminoethanol, 2-dimethylamino-1-propanol, 3-dimethylamino-1-propanol, 1-dimethylamino-2-propanol, N-methyl-N- ethylethanamine, 2-diethylaminoethanol, 3-dimethylamino-1-butanol, 3-dimethylamino-2-butanol, N-methyl-N-isopropylethanolamine, N-methyl-N-ethyl-3-amino-1-propanol, 4-dimethylamino 1-butanol, 4-dimethylamino-2-butanol, 3-dimethylamino-2-methyl-1-propanol, 1-dimethylamino-2-methyl-2-propanol, 2-dimethylamino-1-butanol and 2-dimethylamino-2 -methyl-1-propanol.

The amine may also be selected from aminoethers. Examples of such aminoethers are 2-2- (Aminoethoxy) ethanol (AEE), 2- (2-t-butylaminoethoxy) ethanol (EETB), and 3-methoxypropyldimethylamine. The amine may also be chosen from saturated 3, 5, 6, or 7-membered heterocycles comprising at least one NH group contained in the ring.

The ring may optionally further comprise one or two other heteroatoms in the ring chosen from nitrogen and oxygen, and may be optionally substituted by one or more substituents chosen from alkyl radicals containing from 1 to 6 carbon atoms such as ethyl or methyl radicals, aminoalkyl radicals comprising 1 to 6 carbon atoms, and hydroxyalkyl groups comprising 1 to 6 carbon atoms. Examples of such heterocycles are piperazine, 2-methylpiperazine, N-methylpiperazine, N-ethylpiperazine, Naminoethylpiperazine (AEPZ), aminopropylpiperazine, N-hydroxyethylpiperazine (HEP), homopiperazine, bis (hydroxyethyl) piperazine, piperidine, aminoethylpiperidine (AEPD), aminopropylpiperidine, furfurylamine (FA) and morpholine (MO). The amine used according to the invention may also be chosen from polyamines, such as the alkylene polyamines, in particular the alkylenes diamines, the tertiary bis (diamines) and the polyalkylene polyamines. Among the diamines of alkylenes, mention may be made of hexamethylenediamine, 1,4-diaminobutane, 1,3-diaminopropane, 2,2-dimethyl-1,3-diaminopropane, 3-methylaminopropylamine, N (2 hydroxyethyl) ethylenediamine, 3 (dimethylaminopropylamine) (DMAPA), 3 (diethylamino) propylamine, and N, N'-bis (2-hydroxyethyl) ethylene diamine. Among the tertiary bis (diamines), mention may be made of N, N, N ', N'-tetramethylethylenediamine, N, N-diethyl-N', N'-dimethylethylenediamine, N, N, N ', N', tetraethylethylenediamine, N, N, N ', N'-tetramethyl-1,3-propanediamine (TMPDA), N, N, N', N'-tetraethyl-1,3-propanediamine (TEPDA), N, N-dimethyl- N, N'-diethylethylenediamine (DMDEEDA), 1-dimethylamino-2-dimethylaminoethoxyethane (bis [2- (dimethylamino) ethyl] ether, mentioned in the document US-Al-2010/0288125 to the description of which one will be able to refer. Among the polyalkylene polyamines, mention may be made of dipropylenetriamine (DTPA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), hexamethylenediamine (HMDA), tris (3-aminopropyl) amine, and tris (2-aminoethyl) amine. In one embodiment, the absorbent solution comprises only amines comprising only tertiary amine groups and / or sterically hindered amine groups. Preferred amines comprising only tertiary amine groups are tris (2-hydroxyethyl) amine (triethanolamine, TEA), tris (2-hydroxypropyl) amine (triisopropanol), tributanolamine, bis (2-hydroxyethyl) methylamine (methyldiethanolamine, MDEA), 2-diethylaminoethanol (diethylethanolamine, DEEA), 2-dimethylaminoethanol (dimethylethanolamine DMEA), 3-dimethylamino-1-propanol, 3-diethylamino-1-propanol, 2-diisopropylaminoethanol (DIEA) N, N-bis (2-hydroxypropyl) methylamine (methyldiisopropanolamine, MDIPA).

Preferred amines comprising only sterically hindered amine groups are 2-amino-2-methyl-1-propanol (AMP) and 1-amino-2-methylpropan-2-ol.

The preferred amine of the absorbent solution according to the invention is chosen from MEA, DEA, DIPA, and mixtures thereof. In one embodiment, the absorbent solution comprises, preferably, water, at least one tertiary amine, at least one activator, and at least one C2-C4 thioalkanol. Preferably, the tertiary amine is selected from tertiary alkanolamines. Examples of tertiary amines and in particular tertiary alkanolamines have already been given above. Preferably, in this embodiment, the tertiary amine is selected from N-methyldiethanolamine (MDEA), triethanolamine (TEA), tributanolamine (TBA), and mixtures thereof. The activator may be selected from any activator known to those skilled in the art, but may preferably be selected from primary amines and secondary amines, more preferably the activator may be selected from primary alkanolamines and secondary alkanolamines. Examples of primary and secondary amines and especially primary and secondary alkanolamines have already been given above.

The activator may also be chosen from saturated 3, 5, 6, or 7-membered heterocycles comprising at least one NH group contained in the ring already mentioned above.

Examples of activators are given in US-Al-2008/0025893, these are 3-methylaminopropylamine (MAPA), piperazine, 2-methylpiperazine, N-methylpiperazine, homopiperazine, piperidine, and morpholine. Other examples of activators that can be used in the process according to the invention are given in document WO-A1-2004 / 071624: it is piperazine, hydroxyethylpiperazine (HEP), and bis (hydroxyethyl) piperazine, and mixtures thereof. Still other examples of activators that can be used in the process according to the invention are given in US-A-5,209,914; US-A-5,277,885; and US-A-5,348,714, these are polyamines such as dipropylenetriamine (DPTA), diethylenetriamine (DETA), triethylenetetramine (TETA) and tetraethylenepentamine (TEPA). Other activators mentioned in these documents which can be used in the process according to the invention are aminoethylethanolamine (AEEA), hexamethylenediamine (HMDA), dimethylaminopropylamine (DMAPA) and 1,2-diaminocyclohexane (DACH) as well as methoxypropylamine (MOPA), ethoxypropylamine, aminoethylpiperazine (AEPZ), aminopropylpiperazine, aminoethylpiperidine (AEPD), aminopropylpiperidine, furfurylamine (FA) and ethylmonoethanolamine (EMEA). In a preferred embodiment, the activator is chosen from monoethanolamine (MEA), butylethanolamine (BEA), diethanolamine (DEA), aminoethylethanolamine (AEEA), piperazine, hydroxyethylpiperazine (HEP), aminoethylpiperazine (AEP), and mixtures thereof. Advantageously, in this embodiment, or the absorbent solution comprises water, at least one tertiary amine, at least one activator and at least one C 2 -C 4 thioalkanol, the thioalkanol is preferably chosen from ethylene dithioethanol or ThioDiGlycol (TDG).

Generally, the absorbent solution preferably comprises: from 20% to 60%, preferably from 30% to 50%, more preferably from 35% to 45% by weight, based on the total mass of the absorbent solution at least one amine; from 20% to 60%, preferably from 30% to 50%, more preferably from 35% to 45% by weight, based on the total weight of the absorbent solution, of water; from 10% to 40%, preferably from 10% to 30%, more preferably from 10% to 20% by mass relative to the total mass of the absorbent solution, of at least one thioalkanol. Of these absorbent solutions, the absorbent solutions that include MEA as the amine, TDG as the thioalkanol, and water in the aforementioned proportions are preferred.

A most preferred absorbent solution is the absorbent solution consisting of water, MEA, and TDG in the respective proportions of 45%, 40%, and 15% by weight.

In the embodiment where the absorbent solution comprises water, at least one tertiary amine, at least one activator and at least one C2-C4 thioalkanol, the absorbent solution generally comprises, preferably, is constituted by: 35% to 45% by weight, based on the total mass of the absorbent solution, of at least one tertiary amine; from 4% to 12% by weight relative to the total mass of the absorbent solution of at least one activator chosen preferably from primary amines and secondary amines; the total content of tertiary amine and activator being from 38% to 50% by weight relative to the total mass of the absorbent solution, the total concentration of tertiary amine and activator being between 3.8 and 4.2 mol / L; from 10% to 20% by weight relative to the total mass of the absorbent solution of at least one C 2 to C 4 thioalkanol; - the rest of water to reach 100% by mass. This absorbent solution comprises specific components in specific amounts. Indeed, this absorbent solution advantageously comprises a mixture of specific amines, namely a mixture of a tertiary amine and a primary or secondary amine acting as an activator. Each of these amines, tertiary on the one hand, and primary or secondary on the other hand respectively, is present in a specific amount, defined by a narrow range, and the mixture of these amines is also present in a specific amount also defined by a narrow beach. The other components of the mixture, namely water and C2-C4 thioalkanol are also present in specific amounts, defined by narrow ranges. In this embodiment, a preferred absorbent solution is a solution consisting of water, MDEA, HEP and / or piperazine and TDG, in the proportions of 35%, 42% and 8%, respectively. , and 15% by weight. Advantageously, the contacting step is carried out at a temperature of 20 ° C to 100 ° C, preferably 25 ° C to 50 ° C and a pressure of 1 to 15 bar. Advantageously, the decarbonation process as described above further comprises, after the contacting step, a regeneration step 25 of the absorbent solution loaded with CO2. Advantageously, this regeneration step of the absorbent solution is carried out at a pressure of 0 to 5 bar, preferably 1 to 2.5 bar, more preferably 1 to 2 bar, and at a temperature of 100 ° C. to 30 bar. 140 ° C.

The invention can be implemented in any conventional absorption and regeneration installation using chemical absorbent solutions. Such an installation is described in particular in document WO-A1-2007 / 083012 to the description of which reference may be made. Any gas-liquid contact apparatus may be used to perform the contacting, absorption step. In particular, any type of column can be used as an absorption column. It may be in particular a perforated plate column, a valve column or a column with bells. Packed, loose or structured columns can also be used. It is also possible to use in-line or static solvent mixers. In what follows, the terms "absorption column" or "column" are used for simplification to denote the liquid-liquid contact apparatus, but it is understood that any liquid-liquid contact device can be used. to perform the absorption step. Thus, can the step of contacting the smoke with the absorbent solution, or absorption step, be carried out in an absorption column at a temperature generally from 20 ° C to 100 ° C, preferably from 25 ° C to 50 ° C. The pressure in the absorption column is generally from 1 to 15 bar.

The absorption is carried out by contacting the fumes with the absorbent solution at a flow rate of fumes generally of 3x106 Nm3 / day to 30x106 Nm3 / day and a flow of absorbent solution generally from 5000 to 50000 m3 / day. Advantageously, as already mentioned, the decarbonation process as described above further comprises a regeneration step of the absorbent solution loaded with CO2.

This regeneration step of the absorbent solution is generally carried out at a pressure of 0 to 5 bar, preferably 1 to 2.5 bar, and at a temperature of 100 ° C to 140 ° C. The regeneration step of the absorbent solution is carried out conventionally by heating and separating the absorbed CO2 from the solution in a regeneration column. In fact, the solution of amines loaded with CO 2 -this rich amine-from the bottom of the absorption column is then reheated in an amine / amine exchanger by the hot amine of the bottom of the regenerator, and possibly partially vaporized, then recycled to feed the regeneration column. The regenerated amine which is thus also called poor amine is then recycled to the absorption step. A reboiler generates steam that travels upstream in the regeneration column, causing CO2. This desorption is favored by the low pressure and the high temperature prevailing in the regenerator.

At the top of the regeneration column, the gases are cooled in a condenser. The condensed water is separated from the CO2 in a reflux flask and returned either to the top of the regeneration column or directly to the lean amine solution tank. The regenerated amine which is therefore also called poor amine is then recycled to the absorption stage. A semi-regenerated mode of operation can also be envisaged. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS In what follows, the invention is described with reference to the following example, given by way of illustration and not limitation. Example. In this example, carried out in a pilot plant, it is shown that the addition of TDG to an absorbent solution comprising water and DEA makes it possible to obtain a high removal rate of CO 2 in a representative gas mixture. smoke at the boiler outlet, and a decrease in the steam consumption used for the regeneration of the absorbent solution. Brief description of the pilot installation. The pilot plant for washing gas treatment used in this example makes it possible to treat from 50 to 1500 Nm 3 / h of gas under a pressure of 10 to 40 bar with a solvent flow rate of 100 to 3500 L / h and it comprises: an absorption loop, composed of a column containing 11 trays each of a diameter of 20 cm, and a system of compressors, ejectors and exchangers ensuring the circulation of the gas. - A flash section composed of a balloon and a recovery pump. a regeneration section consisting of a packed column with a diameter of 30 cm, a preheater, a steam reboiler, a recovery pump, a water-cooled condenser, a condenser head with a cold group, and a decompression of the acid gas. A storage section composed of a water cooler, a storage tank and a recovery pump. Test conditions and results. Absorption. The tests were carried out at a pressure of 2 bar absolute. The gas flow rate to be treated is set at 150 kg / h. The gas to be treated consists mainly of nitrogen and carbon dioxide 002. The concentration of CO2 is 9% by volume, a typical composition of a smoke at the boiler outlet. The gas is saturated with water at a temperature of 40 ° C and a pressure of 2 bar absolute.

The gas is brought into contact with the absorbent solution in the absorption column. The solvent flow rate is set at 400 L / h for the tests.

The tests were carried out with a water-DEA-TDG absorbent solution 45-40-15% by mass supplied at 45 ° C. The CO2 contents of the gas to be treated and the treated gas (gas at the end of the treatment) are measured by gas chromatography. Under the conditions described above, a removal rate of 91% was measured during the tests. - Regeneration.

The absorbent solution used, charged with CO2, was then sent to the regeneration section of the pilot plant. The absorbent solution was regenerated necessary and sufficient to obtain a CO 2 removal rate of greater than 90% in the absorption section. Under the conditions imposed by the characteristics of the pilot plant, it is necessary to use 100 kg of steam at 4 bar per ton of absorbing solution. Under the same conditions of use in the absorption and regeneration sections, the use of an absorbent solvent solution water-DEA 60-40% by mass requires according to the measurements the implementation of 119 kg of steam by ton of solvent.5

Claims (21)

REVENDICATIONS1. A process for decarbonating a carbon dioxide containing smoke, comprising a step of contacting said smoke with an absorbent solution comprising, preferably consisting of, at least one amine, water and at least one C2 thioalkanol C4. 2. Method according to claim 1, wherein the smoke to be treated comprises, in percentages by volume relative to the total volume of the smoke to be treated: 60% to 95% by volume, for example 85% to 92% by volume, nitrogen, 2% to 25% by volume, for example 4% to 15% by volume, of carbon dioxide, 0.1% to 10% by volume, for example 2% to 5% by volume, 'oxygen. 20 3. The process according to claim 2, wherein the smoke to be treated further comprises one or more impurities selected from sulfur oxides, nonionic nitrogen oxides, argon, and particulates. solid. 4. The process according to claim 3, wherein the impurity (s) represent (s) in total less than 2% by volume of the total volume of the smoke to be treated. 5. Method according to any one of the preceding claims, wherein prior to the step of contacting the absorbent solution, the smoke to be treated, undergoes extinguishing treatment, and / or filtration, for example to using electrostatic filters. 6. A process according to any one of the preceding claims wherein the fume to be treated is supplied at a temperature of from 20 ° C to 180 ° C, and at a pressure of less than 15 bar. 7. A process according to any one of the preceding claims, wherein the smoke is selected from combustion fumes, including fumes from the combustion of hydrocarbons, for example gas, oil, or coal. 8. A process according to any one of the preceding claims, wherein the thioalkanol is ethylene dithioethanol ThioDiglycol (TDG). 9. A process according to any one of the preceding claims, wherein the at least one amine is selected from alkanolamines. The process according to claim 9, wherein the amine is selected from among MEA, DEA, DIPA, and mixtures thereof. 30 11. A method according to any one of the preceding claims, wherein the absorbent solution preferably comprises: from 20% to 60%, preferably from 30% to 50%, more preferably from 35% to 45%; % by weight relative to the total mass of the absorbent solution, of at least one amine; from 20% to 60%, preferably from 30% to 50%, more preferably from 35% to 45% by weight, relative to the total mass of the absorbent solution, of water; from 10% to 40%, preferably from 10% to 30%, more preferably from 10% to 20% by mass relative to the total mass of the absorbent solution, of at least one thioalkanol. The process of claim 11 wherein the absorbent solution is water, MEA, and TDG in the respective proportions of 45%, 40%, and 15% by weight. 13. A process according to any one of the preceding claims, wherein the absorbing solution comprises, preferably, water, at least one tertiary amine, at least one activator, and at least one C2-thioalkanol. C4. 14. The process as claimed in claim 13, in which the absorbing solution preferably comprises: from 35% to 45% by mass, relative to the total mass of the absorbent solution, of at least one tertiary amine ; From 4% to 12% by weight relative to the total mass of the absorbent solution of at least one activator preferably chosen from primary amines and secondary amines; the total content of tertiary amine and activator being from 38% to 50% by weight relative to the total mass of the absorbent solution, and the total concentration of tertiary amine and activator being between 3.8 and 4.2 mol / L; from 10% to 20% by weight relative to the total mass of the absorbent solution of at least one C 2 to C 4 thioalkanol; - and the rest of water to reach 100% by weight. 15. The method of claim 13 or 14, wherein the tertiary amine is selected from tertiary alkanolamines. 16. Process according to any one of claims 13 to 15, in which the activator is chosen from primary amines and secondary amines, preferably from primary alkanolamines and secondary alkanolamines. 17. A process according to any one of claims 13 to 16, wherein the tertiary amine is selected from N-methyldiethanolamine (MDEA), triethanolamine (TEA), tributanolamine and mixtures thereof, and the activator is selected from monoethanolamine (MEA), butylethanolamine (BEA), diethanolamine (DEA), aminoethylethanolamine (AEEA), piperazine, hydroxyethylpiperazine, aminoethylpiperazine and mixtures thereof. 18. A process according to any one of claims 13 to 17, wherein the absorbing solution is water, MDEA, HEP and / or piperazine and TDG, in the respective proportions of %, 42%, 8%, and 15% by weight. 19. A process according to any one of the preceding claims, wherein the contacting step is carried out at a temperature of 20 ° C to 100 ° C, preferably 25 ° C to 50 ° C and at a pressure of 20 ° C. 1 to 15 bar. The method of any of the preceding claims which further comprises a step of regenerating the absorbent solution charged with CO2 after the contacting step. 21. The method of claim 20, wherein the regeneration step of the absorbent solution is carried out at a pressure of 0 to 5 bar, preferably 1 to 2.5 bar, more preferably 1 to 2 bar, and a temperature of 100 ° C to 140 ° C.