FR3038906B1

FR3038906B1 - PROCESS FOR TREATING A HYDROCARBONATED LOAD CONTAINING HYDROGEN AND HYDROCARBONS

Info

Publication number: FR3038906B1
Application number: FR1501494A
Authority: FR
Inventors: Alexandre Pagot
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2015-07-15
Filing date: 2015-07-15
Publication date: 2019-06-21
Anticipated expiration: 2035-07-15
Also published as: BR102016015090A2; BR102016015090B1; CN106350107B; US20170015913A1; RU2715180C2; CN106350107A; FR3038906A1

Abstract

La présente invention concerne un procédé de traitement d'une charge hydrocarbonée contenant de l'hydrogène et des hydrocarbures incluant des hydrocarbures en C1 à C4, comprenant les étapes suivantes : • on sépare la charge hydrocarbonée en une phase gazeuse (6) et une phase liquide contenant des hydrocarbures (4); • on refroidit la phase liquide (4) issue de l'étape a) à une température inférieure ou égale à 45°C au moyen d'un dispositif de refroidissement (15); • on réalise un premier recontactage de la phase liquide (4) refroidie avec la phase gazeuse (6) dans une colonne (16) à contre-courant de manière à récupérer un premier effluent gazeux (17) riche en hydrogène et un premier effluent liquide d'hydrocarbures (18); dans lequel avant l'étape de refroidissement, on pré-refroidit la phase liquide issue de l'étape a) par échange thermique dans un échangeur (11) alimenté avec le premier effluent gazeux et/ou le premier effluent liquide d'hydrocarbures issus de l'étape c).The present invention relates to a process for treating a hydrocarbon feedstock containing hydrogen and hydrocarbons including C1 to C4 hydrocarbons, comprising the following steps: • the hydrocarbon feedstock is separated into a gaseous phase (6) and a phase hydrocarbon-containing liquid (4); The liquid phase (4) resulting from step a) is cooled to a temperature of less than or equal to 45 ° C. by means of a cooling device (15); A first recontacting of the cooled liquid phase (4) with the gaseous phase (6) is carried out in a countercurrent column (16) so as to recover a first gaseous effluent (17) rich in hydrogen and a first liquid effluent hydrocarbons (18); in which before the cooling step, the liquid phase resulting from step a) is pre-cooled by heat exchange in an exchanger (11) supplied with the first gaseous effluent and / or the first liquid hydrocarbon effluent from step c).

Description

The present invention relates to the field of treatment of effluents from petroleum or petrochemical conversion or refining units which comprise both hydrogen and hydrocarbons such as: methane, ethane, propane, butane, hydrocarbon fractions having from 5 to 11 carbon atoms (designated C5 - Ο14), and optionally heavier hydrocarbons such as hydrocarbons having 12 to 30 carbon atoms (C12-C30) or more, often in small amounts.

This may include the treatment of a catalytic reforming effluent or aromatisation of fractions having a distillation range in the field of gasoline (having essentially from 6 to 11 carbon atoms), which makes it possible to provide a aromatic reformate, a hydrogen-rich gas and a liquefied petroleum gas (or "LPG") essentially comprising hydrocarbons having three or four carbon atoms (propane and / or propylene and / or butane and / or butenes and / or butadiene, as well as their mixtures). The presence of C3 and C4 hydrocarbons in the catalytic reforming effluents is particularly related to the hydrocracking reactions which take place concomitantly with the dehydrogenation reactions. The invention is also applicable to dehydrogenation effluents, for example butane, or pentane, or higher hydrocarbons, for example fractions essentially comprising hydrocarbons having from 10 to 14 carbon atoms, the olefins of which are used in downstream for the manufacture of linear alkyl benzenes.

The process according to the invention can also be applied to the hydrotreating (and / or hydrodesulfurization and / or hydrodemetallization and / or total or selective hydrogenation) of all hydrocarbon cuts such as naphtha, gasoline, kerosene, light gas oil, heavy gas oil, vacuum distillate, vacuum residue. More generally, it is applicable to any effluent comprising hydrogen, light hydrocarbons (methane and / or ethane), C3 and C4 hydrocarbons and heavier hydrocarbons.

State of the art

US Pat. No. 4,673,488 discloses a method for recovering light hydrocarbons from a hydrogen-containing reaction effluent resulting from a hydrocarbon feed conversion reaction which comprises: passing the partially condensed effluent comprising C5 + hydrocarbons, methane, ethane, propane, butane and hydrogen in a vapor-liquid separation zone which comprises at least two vapor-liquid separators and in which at least one vapor-liquid recontacting step is performed; Separating the effluent obtained after the vapor-liquid separation zone into a hydrogen-rich gas stream and a liquid hydrocarbon stream; • passing the liquid hydrocarbon stream in a fractionation zone comprising at least one fractionation column so as to recover a heavy hydrocarbon stream, a head vapor stream, and a liquid head flow; and recycling a portion of the overhead steam stream to said vapor-liquid separation zone.

Document FR 2 873 710 describes a method for the treatment of a hydrocarbon feedstock comprising a hydrocarbon liquid phase and a hydrogen-rich gas phase, in which: a) the feedstock is separated into a liquid and a gas, b) compressing at least a portion of the gas, which is then brought into contact with at least a portion of the liquid so as to recover a liquid and a gas rich in hydrogen, c) then fractionating the liquid from step b ) to obtain at least: a stabilized liquid substantially free of LPG and lighter products, a light liquid effluent comprising essentially LPG and a gaseous stream which is at least partly recycled, and wherein at least one of the gaseous streams from step a) or step c) is contacted against the current by an unstabilized liquid from steps a) or b). The unstabilized liquid is subcooled at least 10 ° C below its bubble point at the contact pressure.

The term "stabilized" for a reformate (or other stabilized liquid according to the invention) refers to a reformate (or other liquid) that has been distilled to remove most, and generally substantially all, 4-carbon compounds. or less (C4).

An object of the invention is to provide a method for maximizing the recovery of hydrogen and C3 and C4 hydrocarbons which may be better valued compared to a simple consumption as fuel in the refinery and which is more economical from the point energy perspective. Summary of the invention

The present invention therefore relates to a process for treating a hydrocarbon feedstock containing hydrogen and hydrocarbons including C1-C4 hydrocarbons, comprising the following steps: a) the hydrocarbon feedstock is separated into a gaseous phase and a liquid phase containing hydrocarbons; b) the liquid phase resulting from step a) is cooled to a temperature of less than or equal to 45 ° C by means of a cooling device; c) first recontacting the cooled liquid phase with the gas phase in a countercurrent column so as to recover a first gaseous effluent rich in hydrogen and a first liquid effluent of hydrocarbons; d) a second recontacting of the hydrocarbon liquid effluent with a recycle gas and separating a second hydrocarbon enriched effluent C1 and C2 and a second hydrocarbon liquid effluent; e) fractionating the second liquid hydrocarbon effluent from step d) into a fractionation column so as to separate a gaseous overhead fraction and a bottom liquid fraction containing hydrocarbons having more than 4 carbon atoms; f) the gaseous overhead fraction resulting from step e) is condensed and a liquid phase containing predominantly C 3 and C 4 hydrocarbons and a gaseous phase which is recycled in step d), in which prior to the stage, is separated off b) cooling, the liquid phase from step a) is pre-cooled by heat exchange in an exchanger fed with the first gaseous effluent and / or the first hydrocarbon liquid effluent from step c).

The term "recontacting" refers to an operation which makes it possible to extract compounds contained in a gaseous phase by means of a liquid phase which has an absorptive capacity through contacting between the two phases. For example, a recontacting can be ensured by making direct contact by in-line mixing of the liquid and gaseous phases or in a recontacting device dedicated to the unit operation.

The process according to the invention advantageously uses the frigories contained in the gaseous or liquid effluents generated in the reclumping stage carried out in a recontacting (or absorption) column to pre-cool the hydrocarbon liquid phase before the latter does not undergo cooling which makes it possible to reach the desired temperature for the recontacting step. The thermal integration thus makes it possible to significantly reduce the consumption of cold utility and therefore the overall energy consumption of the process. This thermal integration is all the more advantageous that the liquid hydrocarbon phase must be cooled to a temperature of less than or equal to 10 ° C, this cooling then requiring the implementation of a refrigeration unit which is an energy-consuming equipment.

According to one embodiment, before the cooling step b), the liquid phase resulting from step a) undergoes a heat exchange in an exchanger fed with the first cold gaseous effluent coming from the recontacting column (or from absorption) and the gaseous phase from step a) undergoes a heat exchange in an exchanger fed with the first cold hydrocarbon liquid effluent from the same recontacting column.

Alternatively, before the cooling step b), the liquid phase resulting from step a) undergoes a heat exchange in an exchanger fed with the cold hydrocarbon liquid effluent from the recontacting column and the gaseous phase of step a) undergoes a heat exchange in an exchanger fed with the cold gaseous effluent from the recontacting column.

These embodiments improve the thermal integration of the process by advantageously using the frigories of the first gaseous and liquid effluents (resulting from the recontacting step c)) to pre-cool the gaseous and liquid phases involved in step c)

In one embodiment, the liquid phase resulting from step a) is cooled to a temperature of less than or equal to 0 ° C. by means of a cooling device.

According to another embodiment, the gas phase resulting from step a) is cooled to a temperature of less than or equal to 0 ° C. by means of a cooling device, it being understood that said step of cooling the gaseous phase is performed after the heat exchange step if the latter exists.

According to a preferred embodiment, part or all of the second hydrocarbon enriched effluent C1 and C2 is recycled before the first recontacting step. Preferably, the second gaseous effluent is mixed with the gaseous phase resulting from step a) before the first recontacting step. The recycling of the second gaseous effluent to the first recontacting step notably makes it possible to improve the recovery yield of the C 3 and C 4 compounds, but also that of hydrogen.

Preferably, the separation carried out in step d) is carried out by means of a separation flask.

The first step of recontacting (step c)) is generally carried out at a temperature between -20 and 55 ° C, preferably at a temperature between -10 and 10 ° C.

The first recontacting step is carried out at a pressure of between 1.6 and 4 MPa.

Preferably, the second step of recontacting (step d)) is carried out at a temperature between 10 and 55 ° C. Preferably, the temperature of the second recontacting step is not controlled and results from the thermodynamic equilibrium after mixing the gaseous phase resulting from the stabilization step e) and the liquid resulting from the recontacting phase in the column (step c).

Preferably, the column used for the countercurrent recontacting comprises between 5 and 15 theoretical plates.

The process according to the invention is preferably implemented to treat a hydrocarbon feedstock which is an effluent from a catalytic reforming process.

Detailed description of the invention

The other features and advantages of the invention will become apparent on reading the following description, given solely by way of illustration and without limitation, and with reference to the drawings of the following figures: FIG. 1 is a schematic diagram of the process according to the invention according to a first embodiment; FIG. 2 is a block diagram of the method according to the invention according to a second embodiment; FIG. 3 is a block diagram of a process not in accordance with the invention, representing a particular case described in patent FR 2 873 710.

Similar items are generally referred to as identical reference signs. In addition, the dashed lines or blocks designate optional elements.

The feedstock that is treated by the process is, for example, an effluent from a catalytic reforming unit, dehydrogenation effluents, for example butane, or pentane, or higher hydrocarbons, for example fractions essentially comprising hydrocarbons having from 10 to 14 carbon atoms, whose olefins are used downstream for the manufacture of linear alkyl benzenes (commonly called LAB).

The process according to the invention can also be applied to effluents from hydrotreating units (hydrodesulfurization, hydrodemetallization, total or selective hydrogenation) of all hydrocarbon cuts such as naphtha, gasoline, kerosene, light gas oil, heavy gas oil, distillate under empty, vacuum residue. More generally, it is applicable to any effluent comprising hydrogen, light hydrocarbons (methane and / or ethane), LPG (propane and / or butane) and heavier hydrocarbons.

Preferably, the process according to the invention makes it possible to treat effluents originating from catalytic reforming units.

With reference to FIG. 1, the hydrocarbon feedstock containing a gaseous phase comprising hydrogen and a hydrocarbon phase including C 1, C 2, C 3 and C 4 hydrocarbons is sent via line 1 into a gas-liquid separation device 2 which may be a gas-liquid separator flask known to those skilled in the art.

The separation device 2 makes it possible to recover a gaseous phase 3 and a hydrocarbon liquid phase 4, respectively at the top and at the bottom of said device 2. As indicated in FIG. 1, the gaseous fraction 3 at the top which contains mainly hydrogen and C1, C2, C3 and C4 light hydrocarbons can be divided into two streams 5 and 6. The stream 5 is recycled as a recycle gas into an upstream reaction unit, for example a catalytic reforming unit. As for the gas stream 6, it is compressed by means of the compressor 7 and then sent to a cooling system 8. The gas 6 is typically compressed to a pressure of between 0.6 and 1.0 MPa.

The compressed gas 6 is optionally mixed with a recycle gas brought in line 25, the origin of which is detailed below. The gas or gas mixture is cooled, for example, to a temperature below 55 ° C. The gas or gas mixture from the cooling system 8 (e.g., an air or water cooler) is transferred to a separator flask to recover a purified liquid hydrocarbon gas which has condensed by cooling.

The cooled gas 10 is compressed by means of the compressor 7 at a pressure generally between 1.6 and 4.0 MPa.

The compressed gas is subjected to a low temperature recontacting step in the presence of the hydrocarbon liquid phase 4 from the gas-liquid separation device 2. As shown in FIG. 1, the compressed gas is firstly cooled by means of a cooler (air or water) 12, then undergoes an indirect heat exchanger by means of an exchanger 13 which is fed with a cold flow described below. The gas can then be advantageously cooled by means of a cooling device (not shown), for example a refrigeration unit ("chiller" according to the English terminology) in order to bring the gas to a temperature less than or equal to 0 ° C.

According to the invention, the hydrocarbon liquid phase 4 is used as an absorbing liquid in the recontacting step. Thus the hydrocarbon liquid phase 4 is first pre-cooled by indirect heat exchange, via an exchanger 11 which is fed with a cold flow described below. The pre-cooled hydrocarbon liquid phase 4 is then cooled to a temperature of less than or equal to 45 ° C by means of a cooling device 15. Different types of cooling means can be used depending on the desired temperature. For example, an air or water cooler is used when the target temperature is between 20 and 45 ° C. It will be preferred to use a refrigeration unit ("chiller" according to the English terminology) when it is desired to cool the hydrocarbon liquid phase at a temperature of less than or equal to 20 ° C., preferably at a temperature comprised between between -10 and 20 ° C.

The gas 10 and the cooled liquid hydrocarbon phase 4 are brought into countercurrent contact in a recontacting (or absorption) column 16 which may comprise perforated or cap trays, or any other contact plate, or else be lined with structured packing elements or not (pall, raschig or other rings). The column may for example have a number of theoretical separation plates of between 5 and 15, preferably between 7 and 10. The recontacting consists in carrying out an absorption of the C1 to C4 hydrocarbons present in the gas by means of the liquid phase. of cooled hydrocarbons. In general, depending on the temperature of the gaseous and liquid phases which are brought into contact in the column, the recontacting step is carried out at a temperature between -20 and 55 ° C., preferably between -10 and 10 ° C. ° C.

From the recontacting column 16, which is generally operated at a pressure of between 1.6 and 4.0 MPa, a gaseous effluent rich in hydrogen is withdrawn via line 17. The cold gaseous effluent is used as a thermal fluid for the reactor. exchanger 11 which performs an indirect heat exchange with the hydrocarbon liquid phase 4, as described above. The cold liquid effluent discharged through the bottom of the column 16 via the line 18 is also used as thermal fluid to supply the exchanger 13 to pre-cool the gas phase 10. The use of cold fluids from the step of recontactage can significantly reduce the energy consumption of the cooling devices 14 and 15 and in particular the cooling device 15 which is necessary to achieve a cooling of the hydrocarbon liquid phase to increase its absorption capacity to be used as a liquid recontacting fluid.

The hydrogen-rich gas 17 is discharged from the treatment unit via line 19 after possibly passing through a guard bed 20 ("Guard bed") in order to adsorb the chlorine present in the gas. when the hydrocarbon feedstock treated by the process is a catalytic reforming effluent

According to the method, the liquid effluent 18 coming from the recontacting column 16 is used as a recontacting fluid in a second recontacting step which consists of bringing the said liquid effluent into contact with a gaseous recycle fluid brought by the line 21, so as to to improve the recovery of C3 and C4 (LPG) compounds and to remove methane and ethane from the process.

As indicated in FIG. 1, the second recontacting is performed by direct in-line mixing of the liquid effluent 18 with the recycle gas 21. The second recontacting step is carried out at a temperature higher than that of the first step of recontacting, which is generally between 10 and 55 ° C. This temperature results from the thermodynamic equilibrium of the absorption of the liquid 18 and the vapor 21. Preferably, no means of controlling the temperature (for example of the heat exchanger type) is used.

The gas / liquid mixture is transferred via line 22 to a separator tank 23 which is operated so as to maximize the recovery in the overhead gas of hydrogen and C 1 and C 2 hydrocarbons. The gaseous effluent containing hydrogen and C1 and C2 hydrocarbons is withdrawn via line 24 to be recycled in whole or in part in the process via line 25. The part of the gaseous effluent containing hydrogen and C1 and C2 hydrocarbons which is not recycled, is removed from the process via line 26. This gaseous effluent can be used in particular as a fuel gas in the refinery.

The recycling, in whole or in part, of the gaseous effluent containing hydrogen and C 1 and C 2 hydrocarbons upstream of the first recontacting step, for example as indicated in FIG. 1 mixed with compressed gas 6 from the separator tank 2 has the advantageous effect of improving the recovery efficiency of the hydrogen during the first recontacting step.

With reference to FIG. 1, by the bottom of the separation flask 23, a liquid effluent 27 containing essentially hydrocarbons having three and more than three carbon atoms (C3 +) and also a minor amount of C1 and C2 hydrocarbons is recovered. The liquid effluent 27 is heated before being sent to a stabilization unit which is operated so as to recover a stabilized hydrocarbon liquid effluent and a distillate mainly comprising C 3 and C 4 hydrocarbons. The stabilization unit comprises a distillation column 28 whose bottom is provided with a circulation pipe equipped with a recirculation circuit comprising a reboiler (not shown) and a discharge pipe 29 of the liquid effluent. stabilized. The overhead gas of the column 28 circulates in a conduit 30 connected to a condensing system comprising a cooling device 31 of the overhead gas and a reflux tank 32. The condensed liquid separated at the reflux tank 32 is discharged via the line 33 and is divided into two streams, a stream being recycled in column 28 by line 34 while the non-recycled complementary stream is discharged through line 35 out of the process as LPG stream. The residual gas withdrawn at the top of the uncondensed reflux flask 32 and potentially comprising substantial quantities of C3 and C4 hydrocarbons is discharged via line 21 and recycled to the process to undergo a step of recontacting with the liquid effluent. from the recontacting column 16, as mentioned above.

Still with reference to FIG. 1, the stabilized liquid effluent 29 recovered at the bottom of the distillation column 28 advantageously serves to feed an indirect heat exchanger system 36, 37 in order to preheat the liquid effluent 27 before it enters. in the distillation column 25. This thermal integration thus makes it possible to reduce the heating power required by the reboiler in order to operate the distillation column 28.

As indicated in FIG. 1, it is advantageous to have, upstream of the distillation column 28, a guard bed 38 configured to capture the chlorine possibly present in the liquid effluent 27 in the case where the hydrocarbon feedstock treated by the process is a catalytic reforming unit effluent.

FIG. 2 represents a schematic diagram of the method according to the invention according to a second embodiment.

The second embodiment differs from that of FIG. 1 in that on the one hand the hydrocarbon liquid phase 4 is pre-cooled by heat exchange in an exchanger 11 fed with a cold fluid which is the liquid effluent 18 from of the recontacting column 16 and, secondly, in that the compressed gas 10 is pre-cooled by indirect heat exchanger by means of an exchanger 13 which is fed by the hydrogen-rich off-gas stream 17 withdrawn at the top of the recontacting column 16.

This configuration makes it easier to balance the flow rates of the gaseous and liquid effluents that supply the exchangers 11 and 13 as a function of the needs and / or the availability of the frigories to pre-cool the gaseous and liquid phases that are brought into contact in the column. .

Example

Example 1 (comparative) illustrates the operation of a treatment process illustrated in FIG. 3, in which the gaseous phase 6 and the hydrocarbon liquid phase 4 are cooled to a temperature of 0 ° C. by means of two refrigerating units before being contacted countercurrent in the recontacting column 16. It will also be noted that the gaseous effluent 24 produced in the second recontacting step is not recycled to the first recontacting step.

The treated hydrocarbon feedstock is an effluent (or reformate) resulting from catalytic reforming, the composition of which is given in Table 1:

Table 1: Composition of the reformate

The hydrocarbon feedstock is first treated in a separator tank 2 in order to separate a gaseous phase 6 predominantly containing hydrogen and a liquid phase 4 containing hydrocarbons.

The gaseous phase 6 resulting from the separation step is compressed by compressors 7 with intermediate cooling necessary for the proper operation of the compressors and is sent to the first recontacting step with the liquid phase 4 resulting from the separation step. The gaseous and liquid phases which have an initial temperature of about 100 and 40 ° C respectively are cooled to a temperature of 0 ° C by means of the refrigerating units 14 and 15. The cooled gaseous and liquid phases are brought into countercurrent contact in a recontacting column 16 comprising 9 trays

theoretical which is operated at a pressure of 3.1 MPa. From the recontacting column, a gas rich in hydrogen and a liquid phase containing hydrocarbons is withdrawn. The liquid phase 18 is then contacted with a recycle gas phase 21 from the reflux flask of the distillation column. The second recontacting is operated in line and the mixture is separated in a separator tank 23 at a pressure of 1.6 MPa so as to provide a gas 24 which is not recycled at the first recontacting and a liquid phase 27.

The liquid phase 27 is fractionated in a fractionation column 28 (or stabilization column) so as to recover a gaseous overhead fraction 30 and a stabilized bottom liquid fraction 29 containing hydrocarbons having more than 4 carbon atoms. This column is operated with a pressure of 1.6 MPa and a temperature of 43 ° C. to the reflux tank.

The overhead gas fraction 30 is condensed in a reflux flask from which a liquid phase 33 containing condensed C 3 -C 4 hydrocarbons (LPG) and a gas phase 21 which is recycled at the second recontacting is separated.

Table 2 groups the recovery rates of the different products of the streams generated by the method of Example 1.

Table 2

EXAMPLE 2 Example 2 illustrates the process for treating a hydrocarbon feedstock according to the invention with reference to FIG. 1. It differs from Example 1 in that the gas 24 obtained at the end of the second recontacting is totally recycled at the first recontacting and in that the phase

compressed gas 6 is cooled by indirect heat exchange via an exchanger 13 fed with the liquid effluent 18 from the recontacting column 16 and in that the hydrocarbon liquid phase is pre-cooled by an exchanger 11 fed with the effluent gas 17 from the recontacting column 16 and then cooled by means of the refrigerating unit 15 at a temperature of 0 ° C.

The temperatures, at the inlet of the recontacting column, of the liquid and gaseous phases are respectively 0 ° C. and 40 ° C.

The other operating conditions mentioned in Example 1 are kept identical for Example 2.

Table 3 gives the recovery rates of the different products of the streams generated by the method of Example 2.

Table 3

Example 3 Example 3 is based on the process according to the invention according to FIG.

Compared to FIG. 1, example 3 differs in that the liquid 4 and gaseous phases 10 are first pre-cooled by heat exchange with a heat exchanger supplied respectively with the liquid effluent 18 and the gaseous effluent. 17, then cooled with the refrigerating units 14 and 15 to reach a temperature of 0 ° C at the inlet of the recontacting column 16.

Table 4 gives the recovery rates of the different products of the streams generated by the method of Example 3.

Table 4

By comparing the results of Example 1 with those of Examples 2 and 3, it can be seen that the pre-cooling of the gaseous and liquid phases with a cold fluid coming from the recontacting column makes it possible to significantly reduce the energy consumption in the exchangers 14 and 15. The process also makes it possible to improve the recovery rate of C3 and C4 hydrocarbons in the liquid stream 33 and hydrogen in the stream 17, in particular by recycling the gas obtained after separation gas / liquid effluent recovered after the second recontacting step. Example 2 compared to Example 3 highlights the advantage of removing the refrigerating unit which cools the gas phase entering the recontacting column. This embodiment thus makes it possible to limit the consumption of cold utility without significantly impacting the recovery of the C3 and C4 products (loss of only 0.8% by weight on the recovery of the C3-C4 cut).

Claims

A process for treating a hydrocarbon feed containing hydrogen and hydrocarbons including C1 to C4 hydrocarbons, comprising the following steps: a) separating the hydrocarbon feedstock into a gaseous phase (6) and a liquid phase containing hydrocarbons (4); b) cooling the liquid phase (4) from step a) to a temperature of less than or equal to 45 ° C by means of a cooling device (15); c) a first recontacting of the cooled liquid phase (4) with the gas phase (6) in a column (16) against the current so as to recover a first gaseous effluent (17) rich in hydrogen and a first effluent hydrocarbon liquid (18); d) a second recontacting of the first hydrocarbon liquid effluent (18) with a recycle gas (21) is carried out and a second hydrocarbon effluent (24) enriched in C1 and C2 hydrocarbons and a second hydrocarbon liquid effluent ( 27); e) the second hydrocarbon liquid effluent (27) from step d) is fractionated in a fractionation column (28) so as to separate a gaseous overhead fraction (30) and a bottom liquid fraction (29); containing hydrocarbons having more than 4 carbon atoms; f) the gaseous overhead fraction (30) resulting from step e) is condensed and a liquid phase (33) containing predominantly C 3 and C 4 hydrocarbons and a gaseous phase (21) which is recycled to the stage is separated off d), wherein before the cooling step b), the liquid phase (4) resulting from step a) undergoes a heat exchange in an exchanger (11) fed with the first gaseous effluent (17) and in which the gas phase (6) resulting from step a) undergoes a heat exchange in an exchanger (13) fed with the first hydrocarbon liquid effluent (18), or in which before the cooling step b), the liquid phase (4) resulting from step a) undergoes a heat exchange in an exchanger (13) fed with the first hydrocarbon liquid effluent (18) and wherein the gaseous phase (6) resulting from step a) is subjected to heat exchange in an exchanger (13) fed with the first gaseous effluent (17) -

2. Method according to claim 1, wherein the liquid phase (4) from step a) is cooled to a temperature of less than or equal to 0 ° C by means of a cooling device (15).

3. Method according to claims 1 or 2, wherein the gaseous phase from step a) is cooled to a temperature of 0 ° C or lower by means of a cooling device, it being understood that said cooling step the gas phase is carried out after the heat exchange step.

4. Method according to one of the preceding claims, wherein a portion or all of the second enriched gaseous effluent (24) C1 and C2 hydrocarbons is recycled before the first recontacting step.

5. The method of claim 4, wherein the second gaseous effluent (24) is recycled in admixture with the gaseous phase (6) from step a).

6. Method according to one of the preceding claims, wherein the separation in step d) is performed by means of a separation flask.

7. Method according to one of the preceding claims, wherein the first recontacting step is carried out at a temperature between -20 and 55 ° C.

8. Method according to one of the preceding claims, wherein the first recontacting step is performed at a pressure between 1.6 and 4 MPa.

9. Method according to one of the preceding claims, wherein the second recontacting step is performed at a temperature between 10 and 55 ° C.

10. Method according to one of the preceding claims, wherein the column (16) comprises between 5 and 15 theoretical plates.

11. Method according to one of the preceding claims, wherein the hydrocarbon feedstock is an effluent of a catalytic reforming process.