EP0373983A1 - Process for the simultaneous elimination of CO2 and gasoline from a gaseous hydrocarbon mixture comprising methane, C2 and higher hydrocarbons and also CO2 - Google Patents

Abstract

The gas mixture to be treated (1) is washed (5) between 0 DEG C and -45 DEG C by means of a solvent (6) for CO2 and C3 and higher hydrocarbons to produce a methane stream (8) containing not more than 2 mol% of CO2 and a CO2-rich liquid phase (11) containing at least 80 mol% of C3 and higher hydrocarbons from the gas mixture (1). The liquid phase (11) is subjected to a demethanization (12, 17) producing a demethanized rich solvent (27) and a methane-rich gas phase (22), and then the rich solvent (27) is subjected to a regeneration producing a regenerated solvent (34) which is recycled into the washing zone (5), and a gas mixture (42) containing the CO2 and the C2 and higher hydrocarbons which are present in the methanized rich solvent, the said gas mixture being separated by regenerative washing with a C5 and higher hydrocarbon solvent, into a CO2-rich acidic gas stream containing, expressed as methane equivalent, less than 10 mol% of hydrocarbons, and into a C2 and higher hydrocarbon cut (48) containing at least 80 mol% of the C3 and higher hydrocarbons present in the gas to be treated (1).

Description

The invention relates to a process for simultaneous decarbonation and degassing of a gaseous mixture consisting mainly of hydrocarbons consisting of methane and C₂ and higher hydrocarbons and also containing CO₂ and optionally one or more non-sulfurized compounds with low boiling point such as H₂, CO, N₂ and argon.

The method according to the invention makes it possible to directly separate a gas mixture of the aforementioned type into three components, namely:
- a treated gas consisting mainly of methane and C₂ hydrocarbons and whose CO₂ molar content is at most equal to 2%,
a section of hydrocarbons containing at least 80 mol% of C₃ hydrocarbons and more present in the gas mixture to be treated, and
- a stream of acid gas consisting of CO₂ containing less than 10 mol% of hydrocarbons, expressed in methane equivalent, relative to CO₂.

Several processes are known, used industrially, for the treatment of gas mixtures as defined above and the main examples of which are represented by the various natural gases, which include a decarbonation operation, that is to say removal of CO₂ , and a degassing operation, that is to say a separation of heavy hydrocarbons for example in C₃ and above, from the gas mixture and make it possible to carry out the fractionation of said gas mixture into the three components mentioned above.
These decarbonation and degassing operations are generally carried out separately and are part of a succession of operations carried out on the gas mixture to be treated and mainly comprising an elimination of the acid gas CO₂, drying, adsorption of the water on a suitable solid such as a molecular sieve, a separation by cryogenic distillation between -30 ° C and -90 ° C associated or not with a solvent extraction in order to obtain the cut of natural gas liquid, and finally reheating the treated gas to ambient temperature in order to generally supply the commercial gas network.

In such a treatment scheme for a gas mixture of the natural gas type containing the above-mentioned constituents, the lowering of the temperature of the gas mixture is imposed by the sole production of the cut of natural gas liquid, no other operation being performed at this temperature level.

In this type of treatment scheme, carrying out series of operations, which are based on very different principles and are carried out at different temperature levels, has serious drawbacks. There is little possibility of thermal integration, which makes said treatment scheme extremely costly from an energy and investment point of view.

Also known are processes for treating gaseous mixtures of the natural gas type, which make it possible to simultaneously carry out the elimination of CO₂ contained in the gaseous mixture and the production of gaseous hydrocarbons and liquid hydrocarbons, the type of which is the process. known as the RYAN-HOLMES process and described, in particular, by J. RYAN and F. SCHAFFERT in the journal CHEMICAL ENGINEERING PROGRESS, October 1984, pages 53 to 56. In such a process, the natural gas to be treated, after having been dehydrated in a conventional manner and then refrigerated, is subjected to a low temperature distillation carried out in three or four successive stages.
In the three-stage embodiment, the dehydrated and refrigerated natural gas is separated, in a first column (demethanizer) at the head of which is injected an additive consisting of a liquid fraction of C₄ hydrocarbons and more, into a gas phase containing methane and lighter compounds and a liquid fraction containing C₂ and higher hydrocarbons and CO₂. This liquid fraction is separated, in a second column (de-ethanizer) into which a certain amount of the additive is also introduced, into a top fraction consisting of CO₂ and a bottom fraction containing the C en hydrocarbons and more. Said tail fraction is then separated, in a third column, into an overhead fraction consisting of a liquid cut of C₂ to C₄ hydrocarbons and into a tail fraction consisting of a liquid cut of C₄ and higher hydrocarbons, which contains the major part of the butanes and higher hydrocarbons present in the treated natural gas and from which the appropriate quantity is taken to constitute the additive injected in the first and second columns. The use of this additive avoids the crystallization of CO₂ at the top of the demethanizer and ensures the rupture of the azeotrope which forms between ethane and CO₂ and facilitates the separation of these compounds in the de-ethanizer. The aforementioned process is therefore essentially based on serial distillation operations.

The invention provides a process for simultaneous decarbonation and degassing of gas mixtures, which are available under an absolute pressure greater than 0.5 MPa and consist mainly of hydrocarbons consisting of methane and C₂ and higher hydrocarbons and also contain CO₂ and optionally one or more low-boiling non-sulfur compounds such as H₂, CO, N₂ and argon, such gas mixtures being, for example, of the natural gas type,
said process making it possible to achieve more easily and at lower cost, in comparison with known processes, the objective of separating the gaseous mixture into the three components, namely treated gas consisting mainly of methane, liquid fraction of hydrocarbons in majority of hydrocarbons in C₃ and above and containing, as necessary, a more or less large quantity of ethane and current of CO₂, which have the specifications defined above.

The process according to the invention is of the type of process which is described in the US-A-3770622 quotation and in which the gas mixture is brought into contact, in a washing zone, with a solvent consisting of a liquid which dissolves CO₂ and hydrocarbons in C₂ and above and which has on the one hand, at atmospheric pressure, a boiling temperature greater than 40 ° C and on the other hand, at - 30 ° C, a viscosity less than 0.1 Pa. s, by operating at a sufficiently low temperature and with a ratio of the flow rates of the gaseous mixture to be treated and of the solvent such that a treated gas consisting mainly of methane and having a molar CO₂ content of more equal to 2% and, on the other hand, a liquid phase called rich solvent and formed of the solvent enriched in CO₂ and in a fraction of hydrocarbons in C₂ and more containing at least 80 mol% of the hydrocarbons in C₃ and more present in the gas mixture to be treated, we subjects the rich solvent to at least partial demethanization treatment to produce a methane-depleted liquid phase called demethanized rich solvent and a methane-rich gas phase, which can optionally be combined with the gaseous mixture to be treated before bringing this into contact last with the solvent, the demethanized rich solvent is subjected to a treatment producing an acid gas stream, which contains almost all of the CO₂ present in the demethanized rich solvent, also producing a mixture of hydrocarbons called hydrocarbon cut and producing finally a regenerated solvent, which is recycled to the washing zone.

• a) régénération du solvant riche déméthanisé produisant le solvant régénéré et un mélange gazeux contenant le CO₂ ainsi que les hydrocarbures en C₂ et plus présents dans le solvant riche déméthanisé et traitement dudit mélange gazeux pour produire le courant de gaz acide riche en CO₂ et la coupe d'hydrocarbures,
• b) - extraction sous forme liquide des hydrocarbures en C₂ et plus par mise en contact, dans une zone d'extraction, du solvant riche déméthanisé, soumis préalablement à une réfrigération, avec un solvant hydrocarboné, de manière à produire un solvant purifié renfermant la quasi-totalité du CO₂ présent dans le solvant riche déméthanisé et ayant une teneur en hydrocarbure, exprimée en équivalent méthane, inférieure à 10% molaire par rapport au CO₂ ainsi qu'un solvant hydrocarboné enrichi en hydrocarbures en C₂ et plus, puis régénération du solvant purifié pour produire d'une part le solvant régénéré et d'autre part le courant de gaz acide riche en CO₂ et fractionnement du solvant hydrocarboné enrichi par distillation en une fraction d'hydrocarbures en C₂ et plus constituant la coupe d'hydrocarbures et en le solvant hydrocarboné régénéré, qui est recyclé, après réfrigération, vers la zone d'extraction, et
• c) - refroidissement du solvant riche déméthanisé à une température suffisamment inférieure à la température régnant dans la zone de lavage pour provoquer une démixtion dudit solvant riche déméthanisé en deux fractions, à savoir une fraction liquide inférieure, qui renferme la quasi-totalité du CO₂ présent dans le solvant riche déméthanisé et possède une teneur en hydrocarbure, exprimée en équivalent méthane, inférieure à 10% molaire par rapport au CO₂ et qui constitue un solvant purifié, et une fraction liquide supérieure, qui constitue la coupe d'hydrocarbures en C₂ et plus, et régénération du solvant purifié pour produire d'une part le solvant régénéré et d'autre part le courant de gaz acide riche en CO₂.

The process according to the invention differs from the process of the US-A-3770622 citation, and is therefore characterized in that the treatment of the demethanized rich solvent is carried out so that the stream of acid gas which it produces contains, expressed in methane equivalent, less than 10 mol% of hydrocarbons relative to CO₂ and that the cut of hydrocarbons obtained consists of a mixture of hydrocarbons in C₂ and more containing at least 80 mol% of hydrocarbons in C₃ and more present in the gaseous mixture to be treated, said treatment of the demethanized rich solvent consisting of one or other of the following treatments a), b), c):

• a) regeneration of the demethanized rich solvent producing the regenerated solvent and a gaseous mixture containing CO₂ as well as the C₂ hydrocarbons and more present in the demethanized rich solvent and treatment of said gaseous mixture to produce the stream of acid gas rich in CO₂ and cutting hydrocarbons,
• b) - extraction in liquid form of C₂ and higher hydrocarbons by bringing into contact, in an extraction zone, the demethanized rich solvent, subjected beforehand to refrigeration, with a hydrocarbon solvent, so as to produce a purified solvent containing the almost all of the CO₂ present in the demethanized rich solvent and having a hydrocarbon content, expressed in methane equivalent, of less than 10 mol% relative to CO₂ as well as a hydrocarbon solvent enriched in C₂ hydrocarbons and more, then regeneration of the solvent purified to produce on the one hand the regenerated solvent and on the other hand the stream of acid gas rich in CO₂ and fractionation of the hydrocarbon solvent enriched by distillation into a fraction of hydrocarbons in C₂ and more constituting the cut of hydrocarbons and in regenerated hydrocarbon solvent, which is recycled, after refrigeration, to the extraction zone, and
• c) - cooling the demethanized rich solvent to a temperature sufficiently lower than the temperature prevailing in the washing zone to cause demixing of said demethanized rich solvent in two fractions, namely a lower liquid fraction, which contains almost all of the CO₂ present in the demethanized rich solvent and has a hydrocarbon content, expressed in methane equivalent, of less than 10 mol% relative to the CO₂ and which constitutes a purified solvent , and a higher liquid fraction, which constitutes the cut of hydrocarbons in C₂ and more, and regeneration of the purified solvent to produce on the one hand the regenerated solvent and on the other hand the stream of acid gas rich in CO₂.

By "methane equivalent" is meant according to the invention as many pseudo-molecules with a single carbon atom as there are carbon atoms in the considered hydrocarbon molecule.

The solvent, which is generally defined above for bringing it into contact with the gaseous mixture to be treated for the purpose of absorbing CO₂ and C en and higher hydrocarbons, preferably has a viscosity of less than 0.05 Pa.s.

les aldéhydes de formule

les esters de formules

les alcanols en C₁ à C₄, les diéthers de formule CH₃-O⁅C₂H₄O⁆

CH₃, les diéthers alcools de formule R₉O- C₂H₄- O - C₂H₄ - OH, les lactones de formule

et le carbonate de propylène, avec dans ces formules R₁ et R2, identiques ou différents, désignant un atome d'hydrogène ou un radical alcoyle en C₁ ou C₂, R₃ étant un radical alcoyle en C₃ ou C₄, R₆ étant un radical alcoyle en C₂ à C₄ ou un radical ⁅C₂H₄O⁆

R₈ avec R₈ désignant un radical alcoyle en C₁ ou C₂ et n étant égal à 1 ou 2, R₇ étant un radical alcoyle en C₁ ou C₂ ou un radical ⁅C₂H₄O⁆

R₈, R₉ désignant un radical alcoyle en C₁ à C₄ et p étant un nombre entier allant de 2 à 4.The solvent according to the invention may consist in particular of one or more liquid absorbents which are selective for CO₂ and used in anhydrous form or as a mixture with water, the said solvent (s) being chosen from the amides of formulas

aldehydes of formula

formula esters

Ccan to C₄ alkanols, diethers of formula CH₃-O⁅C₂H₄O⁆

CH₃, diether alcohols of formula R₉O- C₂H₄- O - C₂H₄ - OH, lactones of formula

and carbonate of propylene, with in these formulas R₁ and R2, identical or different, denoting a hydrogen atom or an alkyl radical in C₁ or C₂, R₃ being an alkyl radical in C₃ or C₄, R₆ being an alkyl radical in C₂ to C₄ or a radical ⁅C₂H₄O⁆

R₈ with R₈ denoting a C₁ or C₂ alkyl radical and n being equal to 1 or 2, R₇ being a Coy or C₂ alkyl radical or a ⁅C₂H₄O⁆ radical

R₈, R₉ denoting a C₁ to C₄ alkyl radical and p being an integer ranging from 2 to 4.

Nonlimiting examples of liquid organic absorbents corresponding to the above formulas are such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethoxymethane, diethoxymethane, dimethoxy-1,1 ethane, methanol, ethanol, ethylene dimethyl ether glycol, diethylene glycol dimethyl ether, ethylene glycol monomethyl ether, butyrolactone, propiolactone and propylene carbonate.

The contacting temperature of the gas mixture to be treated with the solvent in the washing zone is preferably between 0 ° C and -45 ° C.

The washing zone advantageously consists of one or more washing columns containing the appropriate number of theoretical washing stages, said columns being, for example, of the type of tray columns or even packed columns. Advantageously, the temperature in each of the washing columns is kept substantially constant by indirect heat exchange, carried out at one or more points of the column in question, between the fluid medium contained in this column and a refrigerating fluid.

The demethanization treatment applied to the rich solvent is carried out, in particular, in two stages, namely a first stage in which the said rich solvent is subjected to a first expansion at an intermediate pressure capable of releasing a large fraction of the methane dissolved in said solvent to be demethanized and to produce a first gas rich in methane and a predemethanized fluid and a second step in which the predemethanized fluid is subjected to a second expansion then to a distillation so as to produce a second gas rich in methane and the demethanized rich solvent, the second methane-rich gas being compressed to the pressure of the first methane-rich gas and then mixed with the latter to form the methane-rich gas phase.

The methane-rich gas phase, resulting from the demethization treatment applied to the rich solvent, is advantageously compressed to the pressure of the gas mixture to be treated, then it is cooled and mixed with the gas mixture to be treated before the latter is brought into contact. with the solvent in the washing area.

In particular, when treatment a) is applied to the rich demethanized solvent, the treatment of the gaseous mixture containing CO₂ and C hydrocar and higher hydrocarbons, which is produced during the regeneration step of said treatment a), consists of washing said gaseous mixture by bringing this gaseous mixture into contact with a C₅ and higher hydrocarbon solvent in a washing space operating at low temperature so as to produce the stream of acid gas rich in CO₂ and a rich hydrocarbon solvent containing almost all of the C₂ and higher hydrocarbons contained in said gaseous mixture and practically free of CO₂, said washing being followed by regeneration of the rich hydrocarbon solvent to produce the cut of C₂ and higher hydrocarbons and a regenerated hydrocarbon solvent which is recycles to the washing space.

Advantageously, the regeneration of the demethanized rich solvent, carried out during treatment a), is carried out by reheating said solvent to a temperature close to ambient, by dividing the reheated solvent into first and second streams, by directing the first stream directly to a regeneration area, directing the second stream to said regeneration area after having heated it by indirect heat exchange with the regenerated solvent, and subjecting the solvent to distillation in the regeneration area. Said distillation can be carried out in the presence of a stream of inert gas, for example nitrogen, injected into the regeneration zone.

Advantageously, when treatment c) is applied to the demethanized rich solvent, the temperature, below the temperature prevailing in the washing zone, to which said demethanized rich solvent is cooled to achieve its demixing is more particularly between -25 °. C and -80 ° C.

The regeneration of the purified solvent produced in one or other of the treatments b) and c), which leads to the production of the stream of acid gas rich in CO₂ and having, expressed in methane equivalent, a hydrocarbon content of less than 10 % molar relative to CO₂, can be carried out by any treatment making it possible to release the gaseous compounds dissolved in a liquid. In particular, the regeneration of the purified solvent can be carried out by expansion of said purified solvent to a pressure greater than 100 kPa and for example between 150 kPa and 300 kPa and by stripping using an inert gas such as nitrogen. possibly associated with a heating of the purified solvent in the regeneration zone.
The regeneration of the purified solvent can also be carried out by heating the said purified solvent to a temperature close to ambient, by dividing the heated solvent into first and second streams, directing the first stream directly to a regeneration zone, by directing the second stream to this regeneration zone after having heated it by indirect heat exchange with the regenerated purified solvent, and by subjecting the solvent to distillation in the regeneration zone in order to produce the regenerated solvent and the regeneration current. acid gas rich in CO₂ supplied by the process.

When the gaseous mixture to be treated contains water and / or C₅ and higher hydrocarbons, it is advantageously subjected to a pretreatment intended to remove all or part of these compounds before being brought into contact with the solvent in the zone of washing.
This pretreatment can consist of a distillation possibly carried out in the presence of solvent, taken from the solvent injected into the washing zone, to produce the pretreated gas mixture having a C₆ hydrocarbon content and more than 0.1% by weight, a fraction of so-called heavy hydrocarbons containing almost all of the C₆ and more hydrocarbons and all or part of the C₅ hydrocarbons and, optionally, a liquid consisting of a mixture of solvent and water. Said distillation of the gas mixture is carried out at a temperature at least equal to the temperature prevailing in the washing zone.

The invention will be better understood on reading the description given below of several of its embodiments using the facilities shown schematically in Figures 1 to 3 of the accompanying drawing.

Referring to FIG. 1, the gas mixture to be treated arriving via line 1 is introduced into the lower part of a distillation column 2, in which said gas mixture is optionally distilled in the presence of solvent removed, through line 41 emerging in the upper part of column 2, on the regenerated solvent 38 brought to the washing column 5, before passage of said solvent in a refrigeration zone 39 mounted on the conduit 6 for injecting the regenerated solvent in said washing column 5 , so as to produce on the one hand a dried gaseous mixture, evacuated from column 2 by a line 3 and whose hydrocarbon content in C₆ and more is less than 0.1% by weight, and on the other hand a cut hydrocarbon containing almost all of the C₆ hydrocarbons and more and possibly all or part of the C₅ hydrocarbons, drawn off from column 2 by a pipe 4 and optionally a liquid drawn off column 2 through a conduit 54 and consisting of a mixture of solvent and water.

The dried gaseous mixture leaving column 2 through line 3 is introduced into the lower part of a washing column 5, for example of the plate column type, in which it is brought into contact, against the current, with regenerated cold solvent injected into the upper part of the column 5 via the line 6, after passing through the coolant 39, this contacting being carried out at a temperature of, for example, between 0 ° C. and -45 ° C., said temperature being controlled by passage of the liquid medium contained in column 5 in refrigerants 7. At the head of column 5, a treated gas consisting mainly of methane and depleted in CO₂ is removed, said treated gas being heated in a heating system 9 then directed, via a conduit 10, to a zone of use, while at the bottom of said column 5 is drawn off, via a conduit 11, a liquid phase consisting of the solvent enriched in CO₂ and other compounds absorbed and called rich solvent.

The dried gas mixture is brought into contact with the solvent in the washing column 5 at an appropriate temperature in the range 0 ° C. to -45 ° C. and with a ratio of the flow rates of the gas mixture to be treated and of solvent such that on the one hand the treated gas collected, through line 8, at the head of column 5 has a molar CO₂ content of at most equal to 2% and that on the other hand the rich solvent, flowing through line 11 , contains at least 80 mol% of C₃ and higher hydrocarbons present in the dried gas mixture introduced in column 5.

The rich solvent circulating in the conduit 11 is introduced, after passage through the expansion valve 12, into the upper part of an expansion tank 13 in which a first methane-rich gas separates, which is removed at the head of the flask 13 by a conduit 14, and a predemethanized rich solvent, which is withdrawn from the bottom of the flask 13 by a conduit 15. Said predemethanized rich solvent is subjected to a second expansion through an expansion valve 16 followed by a distillation in a distillation column 17 provided with a reboiler 18, so as to produce a second gas rich in methane, which is evacuated at the top of the column 17 by a conduit 19, and a liquid phase depleted in methane, called demethanized rich solvent, which is drawn off at the bottom of the column 17 by a pipe 27. The second methane-rich gas circulating in the pipe 19 is caused to pass into a compressor 20 from which it leaves, via a pipe 21, to a pressure substantially equal to that of the first methane-rich gas passing through line 14, then these two methane-rich gases are mixed in line 22 and the gas phase resulting from this mixture is recycled, by means of a compressor 23 whose the outlet is extended by a line 24, a cooler 25 and a line 26, in the line 3 for supplying the dried gas mixture to the washing column 5.

The demethanized rich solvent, withdrawn from the column 17 by the conduit 27, passes through an expansion valve 29 then a heating system 28, in which it is brought to a temperature close to ambient, then it is brought to a column 33 regeneration provided with a reboiler 40 after being divided into a first stream 30, which is introduced directly into the regeneration column 33, and a second stream 31, which is introduced into said regeneration column after having been reheated in an exchanger indirect heat 35. The regeneration can be carried out in the presence of a stream of inert gas, in particular a stream of nitrogen, injected into the lower part of the column 33 through a conduit 43. Said regeneration produces, on the one hand, a regenerated solvent drawn off at the bottom of the column 33, through a pipe 34, and used in the heat exchanger 35, to heat the second stream 31 of solvent rich in methanis to be regenerated, before being recycled, by the pump 37 and the pipe 38, to the washing column 5, and on the other hand a gaseous mixture discharged at the top of the column 33, by a pipe 42, and containing the CO₂ as well as C₂ and more hydrocarbons present in the demethanized rich solvent.

The gaseous mixture passing through the conduit 42 is washed against the current, in a washing tower 47 provided with a condenser 46 at the head and a reboiler 70 at the bottom and operating at low temperature, using a hydrocarbon solvent in C₅ and no longer brought to the washing tower 47 via a pipe 53, said washing producing, on the one hand, a stream 44 of acid gas rich in CO₂, which contains almost all of the CO₂ present in the rich solvent demethanized and has, expressed in methane equivalent, a hydrocarbon content of less than 10 mol% relative to CO₂, and, on the other hand, a rich hydrocarbon solvent 45 practically free of CO₂ and containing almost all of the hydrocarbons C₂ and more present in the gas mixture arriving via line 42.

The rich hydrocarbon solvent 45 is brought to a regeneration column 49 in which said solvent 45 is subjected to distillation to produce, on the one hand, a fraction of hydrocarbons 48 constituting the cut of C₂ hydrocarbons and more containing at least 80 mol% of the C₃ hydrocarbons and more contained in the gas to be treated brought to the washing column 5 by the line 3, and, on the other hand, a regenerated hydrocarbon solvent 50, which is recycled, by the pump 51, to the regeneration column 47 after refrigeration in the system 52 and passage in the conduit 53.

The embodiment of the method according to the invention, which is illustrated in FIG. 2, differs from the embodiment illustrated in FIG. 1 only by the treatment of the demethanized rich solvent available at the outlet of the expansion valve 29 mounted on the line 27 through which the demethanized rich solvent is withdrawn from the demethanization column 17. The operations carried out in column 2, as well as the operations for bringing the gas to be treated into contact with the solvent in column 5 for washing and demethanization of the rich solvent are therefore identical to those described with reference to FIG. 1.

The demethanized rich solvent, expanded by passage through the expansion valve 29, is refrigerated in the refrigerating system 40 with the result of the demixing of said solvent into two liquid phases, namely an upper hydrocarbon phase and a lower phase consisting of the solvent containing the majority CO₂ and a certain amount of hydrocarbons. The assembly is introduced into an extraction tower 56, in which it is brought into contact, against the current, with a refrigerated hydrocarbon solvent injected, through a conduit 57, into the lower part of the extraction tower and with a stream of regenerated solvent introduced into the tower 56 through a conduit 63, so as to produce, on the one hand, a purified solvent containing almost all of the CO₂ present in the demethanized rich solvent, said purified solvent being drawn off at the bottom of the extraction tower 56 by a conduit 58 on which is mounted an expansion valve 60, and, on the other hand, a hydrocarbon solvent enriched in C₂ hydrocarbons and more containing little CO₂, said solvent being removed at the head of the extraction tower 56 by a conduit 59.

The enriched hydrocarbon solvent 59 is introduced into a regeneration column 49 in which said solvent is fractionated by distillation into a fraction of C₂ and higher hydrocarbons, which is evacuated at the top of said column 49 by a conduit 48 and constitutes the cut d hydrocarbons C₂ and more containing at least 80 mol% of hydrocarbons C₃ and more contained in the gas to be treated brought to the washing column 5 by line 3, and in a regenerated hydrocarbon solvent withdrawn from column 49 by a line 50, which regenerated hydrocarbon solvent is recycled by the pump 51, through the refrigerant system 61 and the conduit 57, to the extraction tower 56.

At the outlet of the expansion valve 60, the purified solvent circulating in the conduit 58 is introduced into the upper part of a regeneration column 62 provided with a heater 69, in which said purified solvent is subjected to a regeneration comprising a stripping using a stream of inert gas, for example a stream of nitrogen, injected into the lower part of the column 62 through a conduit 43. Said regeneration produces, on the one hand, a regenerated solvent 34, which is recycled by means of a pump 37 and a pipe 38 to the washing column 5 through the heat exchanger 39 and the pipe 6, and, on the other hand, a stream 44 of acid gas rich in CO₂ , which contains almost all of the CO₂ present in the demethanized rich solvent and has, expressed in methane equivalent, a hydrocarbon content of less than 10 mol% relative to CO₂.
Part of the cold regenerated solvent passing through line 38 is diverted through line 63 to be injected into the extraction tower 56 at a point in this tower located above the injection point of the demethanized rich solvent circulating in the line 27.

In the embodiment of the process according to the invention, which is illustrated in FIG. 3, the gaseous mixture to be treated, arriving via a pipe 1, is introduced into the lower part of a washing column 5, for example of the type column with plates, in which it is brought into contact, against the current, with a solvent injected into the upper part of the column 5 through a conduit 6, this bringing into contact being carried out at a temperature of, for example, between 0 ° C and -45 ° C. At the top of column 5, a treated gas consisting mainly of methane and depleted in CO₂ is collected, via a line 8, while at the bottom of said column, a liquid phase is drawn off, via line 11, formed of the solvent enriched in CO₂ and other compounds absorbed and called rich solvent. The gas mixture to be treated is brought into contact with the solvent in column 5 at an appropriate temperature in the range 0 ° C to -45 ° C and with a ratio of the flow rates of the gas mixture to be treated and of solvent such as on the one hand, the treated gas collected, via line 8, at the head of column 5 has a molar CO₂ content of at most equal to 2% and, on the other hand, the rich solvent passing through line 11 contains at least 80 molar% of C₃ and higher hydrocarbons present in the gas mixture to be treated.

The treated gas, collected by line 8 at the temperature prevailing in the washing column 5, can be delivered to a distribution network after reheating or undergo beforehand, if necessary, one or more additional treatments to perfect its purification. The temperature profile in column 5 is checked by means of the refrigerants 7 through which the liquid medium contained in column 5 passes.

The rich solvent circulating in the conduit 11 is introduced, after passing through an expansion valve 12, into the upper part of the demethanization column 17, consisting of a reboiling distillation column 18 and in which the rich solvent is divided into a gaseous phase rich in methane, which is removed at the top of column 17 by a conduit 22, and in a liquid phase depleted in methane, called demethanized rich solvent, which is drawn off at the bottom of column 17 by a conduit 27 .

The demethanized rich solvent is brought into a refrigeration zone 64, in which it is cooled to a temperature of, for example, between -25 ° C and -80 ° C and sufficiently lower than the temperature prevailing in the washing zone for cause a demixing of said rich solvent demethanized into two fractions, which separate, in a separator 65, into a lower liquid fraction withdrawn from the separator by a conduit 66, said fraction being called purified solvent and consisting of the solvent containing almost all of the CO₂ present in the demethanized rich solvent and having a hydrocarbon content, expressed in methane equivalent, of less than 10 mol% relative to CO₂, and in a higher liquid fraction, called C₂ and more hydrocarbon fraction and containing at least 80 molar% of C₃ and higher hydrocarbons present in the gaseous mixture to be treated arriving via line 1, said hydroc cut arbours being evacuated from the separator 65 by a conduit 48.

The purified solvent circulating in the conduit 66 is introduced, after passage through an expansion valve 67, into the upper part of a regeneration column 68 provided with a heater 69, in which the said purified solvent is subjected to regeneration by stripping using a stream of inert gas, for example a stream of nitrogen, injected into the lower part of the column 68 through a pipe 43.
Said regeneration produces, on the one hand, a regenerated solvent 34, which is recycled by means of a pump 37 and a conduit 38 to the washing column 5 through a heat exchanger 39 and the conduit 6, and, on the other hand, a stream 44 of acid gas rich in CO₂, which contains almost all of the CO₂ present in the demethanized rich solvent and has a hydrocarbon content, expressed in methane equivalent, of less than 10 mol% relative to CO₂ .

The embodiment illustrated by FIG. 3 could also be adapted to include the steps of pretreatment of the gaseous mixture to be treated and demethanization in two stages, which include the embodiments illustrated in FIGS. 1 and 2.

To complete the above description, two examples of implementation of the method according to the invention are given below, without implied limitation.

EXAMPLE 1 :

Using an installation similar to that shown diagrammatically in FIG. 1 of the appended drawing and operating as described above, a gas mixture having the following molar composition was treated: . CO₂ : 18% . Methane : 71.5% . Ethane : 5.1% . Propane : 1.8% . Butane : 1.8% . Hexane : 1.8%

The gaseous mixture to be treated, arriving via line 1 with a flow rate of 10,000 kmol / h, a temperature of 30 ° C and a pressure of 5,000 kPa was introduced into column 2 for removal of C en and higher hydrocarbons. In this example, the gas mixture to be treated being dry, no addition of solvent was carried out via line 41.

Via line 4 of column 2, 352 kmol / h of a heavy hydrocarbon fraction having a pressure of 5,000 kPa and a temperature equal to 30 ° C. was discharged, said fraction having the following composition: . CO₂ : 9.26% . Methane : 18% . Ethane : 5.01% . Propane : 4.71% . Butane : 12.05% . Hexane : 50.97%

Via line 3 at the head of column 2, 9648 kmol / h of a pretreated gas mixture having a temperature of -20 ° C. and a pressure of 4950 kPa were discharged, said pretreated gas mixture having the following molar composition: . CO₂ : 18.32% . Methane : 73.45% . Ethane : 5.10% . Propane : 1.69% . Butane : 1.43% . Hexane : 0.01%

The pretreated gas mixture was brought into contact with 6000 kmol / h of solvent consisting of a mixture of methanol and water in a molar ratio equal to 95: 5 and having a pressure of 5000 kPa and a temperature equal to -30 ° C. , said contacting being carried out in a washing column 5 comprising 14 plates and operating at -30 ° C under a pressure of 4900 kPa. The refrigerants 7 fitted to the washing column 5 made it possible to maintain the temperature in said column at the desired value.

At the head of column 5, 7,405 kmol / h were evacuated through line 8 of a treated gas having a pressure of 4,900 kPa and a temperature of -30 ° C, said treated gas having the following molar composition: . CO₂ : 1.42% . Methane : 95.67% . Ethane : 2.90% . Methanol : 0.01%

At the bottom of the washing column 5, 9,182 kmol / h of rich solvent having a temperature of -30 ° C. and a pressure of 4,900 kPa were withdrawn through line 11, said rich solvent having the following molar composition: . CO₂ : 21.15% . Methane : 6.11% . Ethane : 3.99% . Propane : 1.88% . Butane : 1.52% . Methanol : 62.07% . Water : 3.27%

The treated gas, discharged through line 8, was warmed up to ambient temperature in the heat exchanger system 9, which makes it possible to ensure the refrigeration of the solvent in the refrigerant 39. The heated treated gas is directed through line 10 to an expedition pipeline.

The demethanization of the rich solvent firstly involved a first expansion of said solvent at a pressure of 3000 kPa, the expanded relaxed solvent supplying the expansion tank 13 in which 362 kmol / h of a first gas containing 68 mol% of methane were produced. , which was discharged at the head of the flask 13 through line 14, and a predemethanized rich solvent withdrawn from said flask through line 15 and whose molar methane content was reduced from 6.11% to 3.57%. The premethanized rich solvent, the temperature of which was equal to -33.6 ° C., was expanded in valve 16 and then fed to the distillation column 17 comprising 10 plates and operating at 1800 kPa. Column 17 produced 577 kmol / h of a second methane-rich gas, evacuated through line 19 under a pressure of 1800 kPa and a temperature of -37 ° C, and a demethanized rich solvent withdrawn from column 17 through line 27 with a flow rate of 8243 kmol / h, a pressure of 1800 kPa and a temperature of -8.2 ° C.

The demethanized rich solvent had the following molar composition: . CO₂ : 20.16% . Methane : 0.03% . Ethane : 3.37% . Propane : 1.98% . Butane : 1.67% . Methanol : 69.13% . Water : 3.64%

The second methane-rich gas was compressed in compressor 20 to the pressure of the first methane-rich gas, namely 3000 kPa. The compressed gas leaving the compressor 20, via the conduit 21, was mixed with the first methane-rich gas to form the methane-rich gas phase 22, which was then compressed, in the compressor 23, until the pressure of the gaseous mixture at treating, namely 5000 kPa, said compressed gas phase being added through line 24, the refrigerant 25 and line 26, to the pretreated gas mixture circulating in line 3.

The compressed methane-rich gaseous phase passing through line 26 had a temperature of -20 ° C, a pressure of 5,000 kPa and a flow rate of 938 kmol / h.

The molar composition of said methane-rich gas phase flowing in line 26 was as follows: . CO₂ : 29.80% . Methane : 59.50% . Ethane : 9.45% . Propane : 0.97% . Butane : 0.26% . Methanol : 0.02%

The demethanized rich solvent, after expansion in the valve 29 and reheating in the reheating system 28, had a temperature of 10 ° C and a pressure of 800 kPa. Said heated solvent was then divided into a first stream 30 having a flow rate of 4533 kmol / h, which was directed directly to the regeneration column 33, and into a second stream 31, which was heated to 70 ° C. in the heat exchanger. heat 35 before being conveyed to the regeneration column 33. This column operated under a pressure of 700 kPa and included 18 plates, the currents 30 and 31 being injected respectively at the plates 8 and 12, counted from the top of the column.

The regeneration column 33 produced at the head a gaseous mixture containing CO₂ and the hydrocarbons in C₂ and more, which was evacuated via line 42 with a temperature of -14 ° C, a pressure of 700 kPa and a flow rate of 2244 kmol / h and at the bottom a regenerated solvent withdrawn from the regeneration column 33 through the pipe 34.

The gas mixture passing through line 42 had the following molar composition: . CO₂ : 74.07% . Methane : 0.12% . Ethane : 12.36% . Propane : 7.28% . Butane : 6.13% . Hexane : 0.04%

The regenerated solvent is cooled by passage through the heat exchanger 35, then recompressed to a pressure of 5000 kPa by the pump 37, and it is then directed through the conduit 38 on the one hand in a major quantity to the washing column 5 , through the refrigerant 39 and the conduit 6.

The gas mixture passing through line 42 was washed against the current in washing tower 47 using a hydrocarbon solvent consisting mainly of hexane. Tower 47 had 35 trays and operated under a pressure of 700 kPa with a temperature of -30 ° C at the head at the level of refrigerant 46.
The supply of tower 47 with solvent, via line 53, and in gaseous mixture, through line 42, was carried out respectively on the first plate and on plate 21 of said tower. The washing tower 47 produced at the head a stream of acid gas 44 rich in CO₂ and having a hydrocarbon content, expressed in methane equivalent, of less than 10 mol% relative to CO₂, said stream of acid gas having a temperature of -30 ° C, a pressure of 650 kPa and a flow rate of 1685 kmol / h, and in the background a hydrocarbon solvent 45 with reduced CO₂ content having a temperature of 95.8 ° C, a pressure of 730 kPa and a flow rate of 5059 kmol / h.

The molar composition of the acid gas stream 44 was as follows: . CO₂ : 98.65% . Methane : 0.15% . Ethane : 0.98% . Butane : 0.05% . Hexane : 0.17%

The rich hydrocarbon solvent 45 had the following molar composition: . Ethane : 5.16% . Propane : 3.23% . Butane : 3.69% . Hexane : 87.91%

The fractionation of the rich hydrocarbon solvent 45 in column 49 provided with 28 trays and operating under a pressure of 600 kPa produced at the head 561 kmol / h of a cut of hydrocarbons 48 in C₂ and more having a temperature of 18 ° C and a pressure of 600 kPa and at the bottom 4500 kmol / h of regenerated hydrocarbon solvent having a temperature of 142.7 ° C and a pressure of 670 kPa, said solvent containing, in mole, 98.89% of hexane and 1.11 % butane.

The molar composition of the C₂ and higher hydrocarbon cut 48 was as follows: . CO₂ : 0.02% . Ethane : 46.49% . Propane : 29.10% . Butane : 24.37% . Hexane : 0.02%

EXAMPLE 2 :

Using an installation similar to that shown diagrammatically in FIG. 2 of the appended drawing and operating as described above, a gas mixture having the same composition, temperature, pressure and flow rate as the gas mixture of Example 1 was treated.

The pretreatment of said gaseous mixture, in column 2, in order to remove the C₆ and higher hydrocarbons therefrom was carried out under the conditions of Example 1 and said column 2 was removed on the one hand, via line 3, a pretreated gas mixture and on the other hand, via line 4, a heavy hydrocarbon fraction having the same composition, temperature, pressure and flow rate characteristics as those of the pretreated gas mixture and of the heavy hydrocarbon fraction obtained in Example 1.

The pretreated gas mixture was brought into contact with 11,500 kmol / h of solvent having a temperature of -20 ° C. and a pressure of 5000 kPa and containing, by mole, 82.34% of methanol, 14.67% of water and 2.88 hexane, said contacting being carried out in a washing column 5 comprising 14 plates and operating at -20 ° C under a pressure of 4900 kPa. The refrigerants 7 fitted to the washing column 5 made it possible to maintain the temperature in said column at the desired value.

At the head of column 5, 7,499 kmol / h of a treated gas having a pressure of 4,900 kPa and a temperature of -20 ° C. were discharged via line 8, said treated gas having the following molar composition: . CO₂ : 1.68% . Methane : 94.44% . Ethane : 3.78% . Methanol : 0.02%

The treated gas, discharged through line 8, was warmed up to ambient temperature in the heat exchanger system 9, the heated treated gas being directed, through line 10, to a shipping pipeline.

At the bottom of the washing column, 14655 kmol / h of rich solvent having a temperature of -20 ° C. and a pressure of 4900 kPa were withdrawn via line 11, said rich solvent having the following molar composition: . CO₂ : 13.64% . Methane : 3.70% . Ethane : 2.10% . Propane : 1.23% . Butane : 0.98% . Hexane : 2.24% . Methanol : 64.61% . Water : 11.51%

The demethanization of the rich solvent firstly involved a first expansion of said solvent at a pressure of 3000 kPa, the expanded rich solvent supplying the expansion tank 13 in which 401 kmol / h of a first gas containing 64 mol% of methane, which was removed at the head of the flask 13 via the line 14, and a predemethanized rich solvent withdrawn from the said flask through the line 15 and whose molar methane content has been reduced from 3.70 to 2.01%. The premethanized rich solvent, the temperature of which was equal to -22.5 ° C., was expanded in valve 16 and then fed to the distillation column 17 comprising 10 plates and operating at 1800 kPa.
Column 17 produced 604 kmol / h of a second methane-rich gas, evacuated via line 19 under a pressure of 1800 kPa and at a temperature of -25 ° C, and a demethanized solvent withdrawn from column 17, through conduit 27, with a flow rate of 13,649 kmol / h, a temperature of 1 ° C and a pressure of 1,800 kPa.

The demethanized rich solvent passing through line 27 had the following molar composition: . CO₂ : 12.11% . Methane : 0.03% . Ethane : 1.53% . Propane : 1.20% . Butane : 1.01% . Hexane : 2.39% . Methanol : 69.37% . Water : 12.36%

The second methane-rich gas was compressed in compressor 20 to the pressure of the first methane-rich gas, namely 3000 kPa. The compressed gas leaving the compressor 20, via the conduit 21, was mixed with the first methane-rich gas to form the methane-rich gas phase 22, which was then compressed, in the compressor 23, until the pressure of the gaseous mixture at treating, namely 5000 kPa, said compressed gas phase being added through line 24, the refrigerant 25 and line 26, to the pretreated gas mixture circulating in line 3.

The compressed methane-rich gas phase passing through line 26 had a temperature of -20 ° C, a pressure of 5000 kPa and a flow rate of 1006 kmol / h. The molar composition of said methane-rich gas phase flowing in line 26 was as follows: . CO₂ : 34.31% . Methane : 53.50% . Ethane : 9.84% . Propane : 1.70% . Butane : 0.53% . Hexane : 0.09% . Methanol : 0.03%

The demethanized rich solvent, expanded in the valve 29 and refrigerated at -40 ° C in the refrigerant system 40, was brought into contact, against the current, in the liquid / liquid extraction tower 56 with a refrigerated hydrocarbon solvent with content predominantly hexane, said hydrocarbon solvent consisting, in mole, of 95.77% hexane, 1.11% butane and 3.12% methanol. The extraction tower 56 included 31 trays and was supplied on the first tray with 5000 kmol / h of regenerated solvent supplied by line 63 with a temperature of -40 ° C, on tray 21 by the rich demethanized solvent from the system refrigeration 40 and on the plate 31 by the refrigerated hydrocarbon solvent based on hexane supplied by line 57 with a flow rate of 1600 kmol / h. This extraction produced 2079 kmol / h of a rich hydrocarbon solvent having a temperature of -40 ° C and a pressure of 1200 kPa, said rich hydrocarbon solvent being evacuated at the top of tower 56 via line 59, and 18069 kmol / h purified solvent withdrawn from the bottom of said tower, via line 58, at a temperature of -40 ° C. and under a pressure of 1200 kPa.

The molar composition of the rich hydrocarbon solvent passing through line 59 was as follows: . CO₂ : 0.14% . Methane : 0.13% . Ethane : 9.19% . Propane : 7.79% . Butane : 6.62% . Hexane : 73.72% . Methanol : 2.40%

The molar composition of the purified solvent passing through line 58 was as follows: . CO₂ : 9.16% . Methane : 0.01% . Ethane : 0.10% . Propane : 0.01% . Hexane : 2.42% . Methanol : 74.91% . Water : 13.40%

By fractionation of the enriched hydrocarbon solvent 59 in the regeneration column 49 comprising 28 plates and operating at 700 kPa, there was produced on the one hand, at the top of column 49, 497 kmol / h of a C coupe hydrocarbon fraction and plus having a temperature of 28 ° C and a pressure of 700 kPa, which was evacuated via line 48, and on the other hand, at the bottom of said column, 1600 kmol / h of regenerated hydrocarbon solvent having a temperature of 142 , 7 ° C and a pressure of 670 kPa, which is drawn off through line 50.

The C₂ and higher hydrocarbon section, evacuated via line 48, had the following molar composition: . CO₂ : 0.59% . Methane : 0.54% . Ethane : 38.40% . Propane : 32.58% . Butane : 27.67% . Hexane : 0.20% . Methanol : 0.02%.

The regenerated hydrocarbon solvent passing through line 50 contained, by mole, 95.77% hexane, 1.11% butane and 3.12% methanol. Said solvent was brought, in the pump 51, to a pressure of 1200 kPa, then refrigerated at -40 ° C in the refrigerant system 61 before being recycled, via the conduit 57, to the extraction tower 56.

The purified solvent coming from line 58 of the extraction tower 56 is expanded to a pressure of 200 kPa in the expansion valve 60, then it is introduced into the regeneration column 62 for the purpose of regeneration. Said column 62, comprising 14 plates and operating under a pressure of 200 kPa, is supplied on the first plate with the purified solvent to be regenerated and on the last plate by a stream of nitrogen supplied, via line 43, with a flow rate of 650 kmol / h. The heater 69, which is provided with said column 62, was located on the seventh plate.

The regeneration of the purified solvent produced, on the one hand, 2289 kmol / h of a stream of acid gas rich in CO₂, said stream being discharged through line 44 at the head of column 62 and, on the other hand, a solvent regenerated withdrawn from the bottom of the column 62 through the conduit 34.

The stream of CO₂-rich acid gas discharged through line 44 had a pressure of 200 kPa and a temperature of -47.5 ° C and it had the following molar composition: . CO₂ : 71.64% . Methane : 0.05% . Ethane : 0.77% . Propane : 0.04% . Hexane : 0.40% . Methanol : 0.06% . Nitrogen : 27.04%.

The regenerated solvent circulating in the conduit 34 was brought to the pressure of 5000 kPa by passage through the pump 37, then divided into two parts, namely a major part recycled to the washing column 5 after passage through the heat exchanger system 39 and the conduit 6 and a part brought into the extraction tower 56 by the conduit 63.

Claims (13)

1 - Process for the simultaneous decarbonation and degassing of a gas mixture, which has an absolute pressure greater than 0.5 MPa and mainly contains hydrocarbons consisting of methane and C₂ hydrocarbons and above and also includes CO comporte and possibly one or more compounds unsulphides with low boiling point such as H₂, CO, N₂ and Ar, in which the gas mixture is brought into contact, in a washing zone (5), with a solvent (6) consisting of a liquid, which dissolves preferably CO₂ and hydrocarbons C₂ and above and which has on the one hand, at atmospheric pressure, a boiling temperature greater than 40 ° C and on the other hand, at -30 ° C, a viscosity less than 0, 1 Pa.s, operating at a sufficiently low temperature and with a ratio of the flow rates of the gaseous mixture to be treated and of the solvent such that a treated gas (8) consisting mainly of methane and present is produced ant a molar CO₂ content at most equal to 2% and, on the other hand, a liquid phase called rich solvent (11) and formed of the solvent enriched in CO₂ and in a fraction of hydrocarbons in C₂ and more containing at least 80 molar% of C₃ and higher hydrocarbons present in the gas mixture to be treated, the rich solvent is subjected to an at least partial demethanization treatment (12, 17) to produce a methane-depleted liquid phase called demethanized rich solvent (27) and a methane-rich gas phase (22) and the demethanized rich solvent is subjected to a treatment (55) producing an acid gas stream (44), which contains the CO₂ present in the demethanized rich solvent, also producing a mixture of hydrocarbons called hydrocarbon cut (48) and finally producing a regenerated solvent (34), which is recycled to the washing zone (5), said process being characterized in that the treatment of the demethan rich solvent isé est produced in such a way that the stream of acid gas which it produces contains, expressed in methane equivalent, less than 10 mol% of hydrocarbons relative to CO₂ and that the resulting cut of hydrocarbons consists of a mixture of C₂ hydrocarbons and more containing at least 80 mol% of C₃ hydrocarbons and more present in the gas mixture to be treated, said treatment to which the demethanized rich solvent is subjected consisting of one or other of the treatments a), b), c) following: a) - regeneration (33) of the demethanized rich solvent producing the regenerated solvent (34) and a gaseous mixture (42) containing the CO₂ as well as the C₂ hydrocarbons and more present in the demethanized rich solvent (27) and treatment (47, 49) of said gaseous mixture (42) to produce the stream of acid gas (44) rich in CO₂ and the cut of hydrocarbons (48), b) - extraction in liquid form of C₂ and higher hydrocarbons by bringing into contact, in an extraction zone (56), the demethanized rich solvent (27), subjected beforehand to refrigeration (40), with a hydrocarbon solvent ( 57), so as to produce a purified solvent (58) containing almost all of the CO₂ present in the demethanized rich solvent and having a hydrocarbon content, expressed in methane equivalent, of less than 10 mol% relative to the CO₂ as well as a hydrocarbon solvent enriched (59) with C₂ hydrocarbons and more, then regeneration (62) of the purified solvent to produce on the one hand the regenerated solvent (34) and on the other hand the stream of acid gas (44) rich in CO₂ and fractionation of the enriched hydrocarbon solvent (59) by distillation (49) into a fraction of C₂ hydrocarbons and more constituting the hydrocarbon fraction (48) and in the regenerated hydrocarbon solvent (50), which is recycled, after refrigeration (61), to the extraction zone (56), and c) cooling the demethanized rich solvent to a temperature sufficiently lower than the temperature prevailing in the washing zone (5) to cause a demixing (64,65) of said demethanized rich solvent into two fractions, namely a lower liquid fraction (66) , which contains almost all of the CO₂ present in the demethanized rich solvent and has a hydrocarbon content, expressed in methane equivalent, of less than 10 mol% relative to CO₂ and which constitutes a purified solvent, and a higher liquid fraction, which constitutes the cut of hydrocarbons (48) in C₂ and above, and regeneration (68) of the purified solvent (66) to produce on the one hand the regenerated solvent (34) and on the other hand the stream of acid gas (44) rich in CO₂. 2 - Process according to claim 1, characterized in that the solvent brought into contact with the gaseous mixture to be treated has a viscosity, at -30 ° C, less than 0.05 Pa.s. 3 - Process according to claim 1 or 2 characterized in that the solvent brought into contact with the gaseous mixture to be treated in the washing zone (5) consists of one or more liquid organic absorbents, used in anhydrous form or in mixture with water, the said absorbent (s) being chosen from the amides of formulas

aldehydes of formula

formula esters

Ccan to C₄ alkanols, diethers of formula CH₃ O⁅C₂ H₄O ⁆

CH₃, the alcohol diethers of formula R₉O - C₂H₄ - O - C₂H₄-OH, the lactones of formula

and propylene carbonate, with in these formulas R₁ and R₂, identical or different, designating a hydrogen atom or a C₁ or C₂ alkyl radical, R₃ being a C₃ or C₄ alkyl radical, R₆ being a C₂ alkyl radical to C₄ or a radical ⁅C₂H₄O⁆

R₈ with R₈ denoting a C₁ or C₂ alkyl radical and n representing 1 or 2, R₇ being a C₁ or C₂ alkyl radical or a ⁅C₂H₄O⁆ radical

R₈, R₉ denoting a C₁ to C₄ alkyl radical and p being an integer ranging from 2 to 4. 4 - Method according to one of claims 1 to 3, characterized in that the contacting temperature of the gas mixture to be treated with the solvent, in the washing zone (5), is between 0 ° C and -45 ° C. 5 - Method according to one of claims 1 to 4, characterized in that the demethanization treatment applied to the rich solvent (11) is carried out in two stages, namely a first step in which said rich solvent is subjected to a first expansion (12, 13) capable of releasing a large fraction of the methane dissolved in said solvent and of producing a first gas rich in methane (14) and a premethanized fluid (15) and a second step in which the premethanized fluid is subjected to a second expansion (16) then distillation (17) so as to produce a second methane-rich gas (19) and the demethanized rich solvent (27), the second methane-rich gas being compressed to the pressure of the first rich gas in methane and then mixed with the latter to constitute the gas phase (22) rich in methane. 6 - Method according to one of claims 1 to 5, characterized in that the gas phase (22) rich in methane is compressed to the pressure of the gas mixture to be treated, then it is cooled (25) and mixed with the mixture gaseous to be treated before the latter is brought into contact with the solvent in the washing zone (5). 7 - Method according to one of claims 1 to 6, characterized in that one applies the treatment a) to the demethanized rich solvent (27) and the gaseous mixture (42) is subjected resulting from the regeneration step of said treatment a) washing by bringing this gaseous mixture into contact with a C₅ hydrocarbon solvent and more in a washing space (47) operating at low temperature so as to produce the stream of acid gas (44) rich in CO₂ and a rich hydrocarbon solvent (45) containing almost all hydrocarbons C₂ and more contained in the gas mixture (42), said washing being followed by a regeneration (49) of the rich hydrocarbon solvent to produce the cut of hydrocarbons (48) in C₂ and more and a regenerated hydrocarbon solvent ( 50) which is recycled to the washing space after having refrigerated it (52). 8 - Method according to one of claims 1 to 7, characterized in that the treatment is applied a) to the demethanized rich solvent (27) and the regeneration of said demethanized rich solvent is carried out, constituting the first step of this treatment, by heating (28) said solvent to a temperature close to ambient, then dividing the heated solvent into a first (30) and a second (31) streams, directing the first stream (30) directly to a regeneration zone (33), by directing the second stream (31) towards said regeneration zone after having heated it by indirect heat exchange (35) with the regenerated solvent (34) and by subjecting the solvent to distillation in the regeneration zone (33). 9 - Process according to claim 8, characterized in that the distillation of the solvent in the regeneration zone (33) is carried out in the presence of a stream of inert gas (43), for example nitrogen, injected into said zone. 10 - Method according to one of claims 1 to 6, characterized in that treatment c) is applied to the demethanized rich solvent (27) and in that the temperature, lower than the temperature prevailing in the washing zone, to which the demethanized rich solvent is cooled to cause its demixing is between -25 ° C and -80 ° C. 11 - Method according to one of claims 1 to 6, characterized in that treatment b) or c) is applied to the demethanized rich solvent and in that the regeneration of the purified solvent is carried out by expansion of said solvent until a pressure greater than 100 kPa, in particular between 150 kPa and 300 kPa and by stripping (43) by means of an inert gas such as nitrogen possibly associated with a heating (69) of the purified solvent in the regeneration column. 12 - Method according to one of claims 1 to 6, characterized in that one applies the treatment b) or c) to the demethanized rich solvent and in that the regeneration of the purified solvent (58) consists in reheating (28) said solvent up to a temperature close to ambient, dividing the heated solvent into first (30) and second (31) streams, directing the first stream (30) directly to a regeneration zone (33), direct the second stream (31) to this regeneration zone after having heated it by indirect heat exchange (35) with the regenerated purified solvent (34) and to subject the purified solvent to distillation in the regeneration zone (33) for the purpose of producing the stream of acid gas (44) rich in CO₂ and the regenerated solvent (34). 13 - Method according to one of claims 1 to 12, characterized in that, the gas mixture to be treated containing water and / or C₅ hydrocarbons and more, said gas mixture is subjected to a pretreatment consisting of a distillation (2) carried out at a temperature at least equal to that prevailing in the washing zone (5) and, optionally, in the presence of solvent, taken from the solvent brought to the washing zone (5), to produce a fraction (4 ) of so-called heavy hydrocarbons and containing almost all of the C₆ hydrocarbons and more and possibly all or part of the C₅ hydrocarbons, a pretreated gas mixture (3) having a C₆ hydrocarbon content and more than 0.1% by weight and, optionally, a liquid (54) consisting of a mixture of solvent and water.

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