PROCESS FOR THE TREATMENT OF A HYDROCARBON FEED CONTAINING HYDROGEN AND HYDROCARBONS

Abstract

The present invention concerns a process for the treatment of a hydrocarbon feed containing hydrogen and hydrocarbons including C.sub.1 to C.sub.4 hydrocarbons, comprising the following steps: separating the hydrocarbon feed into a gaseous phase and a liquid phase containing hydrocarbons; cooling the liquid phase obtained from step a) to a temperature of 45 C. or less using a cooling device; carrying out a first recontacting step on the cooled liquid phase with the gaseous phase in a counter-current column in order to recover a first gaseous effluent which is rich in hydrogen and a first liquid hydrocarbon effluent;
in which, before the cooling step b), the liquid phase obtained from step a) is pre-cooled by exchange of heat in an exchanger supplied with the first gaseous effluent and/or the first liquid hydrocarbon effluent obtained from step c).

Claims

1. A process for the treatment of a hydrocarbon feed containing hydrogen and hydrocarbons including C.sub.1 to C.sub.4 hydrocarbons, comprising the following steps: a) separating the hydrocarbon feed into a gaseous phase (6) and a liquid phase (4) containing hydrocarbons; b) cooling the liquid phase (4) obtained from step a) to a temperature of 45 C. or less using a cooling device (15); c) carrying out a first recontacting step on the cooled liquid phase (4) with the gaseous phase (6) in a counter-current column (16) in order to recover a first gaseous effluent (17) which is rich in hydrogen and a first liquid hydrocarbon effluent (18); d) carrying out a second recontacting step on the first liquid hydrocarbon effluent (18) with a recycle gas (21) and separating a second gaseous effluent (24) which is enriched in C.sub.1 and C.sub.2 hydrocarbons and a second liquid hydrocarbon effluent (27); e) fractionating the second liquid hydrocarbon effluent (27) obtained from step d) in a fractionation column (28) in a manner such as to separate a gaseous overhead fraction (30) and a liquid bottom fraction (29) containing hydrocarbons containing more than 4 carbon atoms; f) condensing the gaseous overhead fraction (30) obtained from step e) and separating a liquid phase (33) containing mainly C.sub.3 and C.sub.4 hydrocarbons and a gaseous phase (21) which is recycled to step d), in which, before the cooling step b), the liquid phase obtained from step a) is pre-cooled by exchange of heat in an exchanger (11) supplied with the first gaseous effluent (17) and/or the first liquid hydrocarbon effluent (18) obtained from step c).

2. The process according to claim 1 in which, before the cooling step b), the liquid phase (4) obtained from step a) undergoes an exchange of heat in an exchanger (11) supplied with the first gaseous effluent (17) and in which the gaseous phase (6) obtained from step a) undergoes an exchange of heat in an exchanger (13) supplied with the first liquid hydrocarbon effluent (18).

3. The process according to claim 1 in which, before the cooling step b), the liquid phase (4) obtained from step a) undergoes an exchange of heat in an exchanger (13) supplied with the first gaseous effluent (18) and in which the gaseous phase (6) obtained from step a) undergoes an exchange of heat in an exchanger (13) supplied with the first liquid hydrocarbon effluent (17).

4. The process according to claim 1, in which the liquid phase (4) obtained from step a) is cooled to a temperature of 0 C. or less using a cooling device (15).

5. The process according to claim 2, in which the gaseous phase obtained from step a) is cooled to a temperature of 0 C. or less using a cooling device, it being understood that said step for cooling the gaseous phase is carried out after the heat exchange step in accordance with claim 2.

6. The process according to claim 1, in which part or all of the second gaseous effluent (24) enriched in C.sub.1 and C.sub.2 hydrocarbons is recycled upstream of the first recontacting step.

7. The process according to claim 6, in which the second gaseous effluent (24) is recycled as a mixture with the gaseous phase (6) obtained from step a).

8. The process according to claim 1, in which the separation carried out in step d) is carried out with the aid of a separating drum.

9. The process according to claim 1, in which the first recontacting step is carried out at a temperature in the range 20 C. to 55 C.

10. The process according to claim 1, in which the first recontacting step is carried out at a pressure in the range 1.6 to 4 MPa.

11. The process according to claim 1, in which the second recontacting step is carried out at a temperature in the range 10 C. to 55 C.

12. The process according to claim 1, in which the column (16) comprises in the range 5 to 15 theoretical plates.

13. The process according to claim 1, in which the hydrocarbon feed is an effluent from a catalytic reforming unit.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0037] Further characteristics and advantages of the invention will become apparent from the following description, given solely by way of non-limiting illustration and made with reference to the accompanying drawings, in which:

[0038] FIG. 1 is a flow diagram of a process in accordance with the invention, in accordance with a first embodiment;

[0039] FIG. 2 is a flow diagram of a process in accordance with the invention, in accordance with a second embodiment;

[0040] FIG. 3 is a flow diagram of a process which is not in accordance with the invention, representing a particular case described in the patent FR 2 873 710.

[0041] Similar elements are generally designated by identical reference numerals. Furthermore, the dashed lines or blocks denote optional elements.

[0042] The feed which 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 containing 10 to 14 carbon atoms, the olefins of which are used downstream for the manufacture of linear alkylbenzenes (generally termed LAB).

[0043] The process in accordance with the invention may also be applied to effluents from hydrotreatment units (hydrodesulphurization, hydrodemetallization, total or selective hydrogenation) of any hydrocarbon cuts such as naphtha, gasoline, kerosene, light gas oil, heavy gas oil, vacuum distillate, or vacuum residue. More generally, it is applicable to any effluent comprising hydrogen, light hydrocarbons (methane and/or ethane), LPGs (propane and/or butane) and heavier hydrocarbons.

[0044] Preferably, the process in accordance with the invention can be used to treat effluents obtained from catalytic reforming units.

[0045] Referring to FIG. 1, the hydrocarbon feed containing a gaseous phase comprising hydrogen and a hydrocarbon phase including C.sub.1, C.sub.2, C.sub.3 and C.sub.4 hydrocarbons is sent via the line 1 to a gas-liquid separation device 2 which may be a gas-liquid separator drum which is known to the person skilled in the art.

[0046] The separation device 2 allows recovering a gaseous phase 3 and a liquid hydrocarbon phase 4, respectively from the head and bottom of said device 2. As indicated in FIG. 1, the gaseous overhead fraction 3, which mainly contains hydrogen and light C.sub.1, C.sub.2, C.sub.3 and C.sub.4 hydrocarbons, may be divided into two streams 5 and 6. The stream 5 is recycled to a reaction unit located upstream, for example a catalytic reforming unit, as a recycle gas. The stream 6 of gas is compressed using a compressor 7 and then sent to a cooling system 8. The gas 6 is typically compressed to a pressure in the range 0.6 to 1.0 MPa.

[0047] The compressed gas 6 is optionally mixed with a recycle gas, supplied via the line 25, the origin of which is detailed below. The gas or mixture of gases is cooled to a temperature of less than 55 C., for example. The gas or mixture of gases obtained from the cooling system 8 (for example an air or water cooler) is transferred to a separator drum to recover a gas 10 which is purified of liquid hydrocarbons which have condensed by cooling.

[0048] The cooled gas 10 is compressed, using a compressor 7, to a pressure which is generally in the range 1.6 to 4.0 MPa.

[0049] The compressed gas 10 undergoes a low temperature recontacting step carried out in the presence of the liquid hydrocarbon phase 4 obtained from the gas-liquid separation device 2. As can be seen in FIG. 1, the compressed gas is initially pre-cooled using a cooler (air or water) 12, then undergoes indirect heat exchange using an exchanger 13 which is supplied via a cold stream which is described below. The gas may then advantageously be cooled using a cooling device (not shown), for example a chiller, in order to bring the gas to a temperature of 0 C. or less.

[0050] In accordance with the invention, the liquid hydrocarbon phase 4 is employed as an adsorbent liquid in the recontacting step. Thus, the liquid hydrocarbon phase 4 is initially pre-cooled by indirect heat exchange via an exchanger 11 which is supplied with a cold stream as described below. The pre-cooled liquid hydrocarbon phase 4 is then cooled to a temperature of 45 C. or less using a cooling device 15. Various types of cooling means may be used, depending on the temperature desired. As an example, an air or water cooler is used when the target temperature is in the range 20 C. to 45 C. Preferably, a chiller is used when the liquid hydrocarbon phase is to be cooled to a temperature of 20 C. or less, preferably to a temperature in the range 10 C. to 20 C.

[0051] The gas 10 and the cooled liquid hydrocarbon phase 4 are brought into counter-current contact in a recontacting (or absorption) column 16 which may comprise perforated or bubble plates, or any other contacting plate, or may even be packed with structured or unstructured packing elements (Pall rings, Raschig rings or the like). As an example, the column may have in the range 5 to 15 theoretical separation plates, preferably in the range 7 to 10. Recontacting consists of absorbing the C.sub.1 to C.sub.4 hydrocarbons present in the gas with the aid of the cooled liquid hydrocarbon phase. 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 in the range 20 C. to 55 C., preferably in the range 10 C. to 10 C.

[0052] A gaseous effluent which is rich in hydrogen is withdrawn via the line 17 from the recontacting column 16, which is generally operated at a pressure in the range 1.6 to 4.0 MPa.

[0053] The cold gaseous effluent is used as a thermal fluid for the exchanger 11 which carries out indirect heat exchange with the liquid hydrocarbon phase 4, as described above. The cold liquid effluent evacuated via the line 18 from the bottom of the column 16 is also used as a thermal fluid in order to supply the exchanger 13 to pre-cool the gaseous phase 10.

[0054] The use of cold fluids obtained from the recontacting step means that the energy consumption of the cooling devices 14 and 15, and in particular of the cooling device 15, which is necessary in order to cool the liquid hydrocarbon phase in order to increase its absorption capacity for use as the recontacting liquid fluid, can be substantially reduced.

[0055] The hydrogen-rich gas 17 is evacuated from the treatment unit via the line 19 after optionally being passed through a guard bed 20 in order to adsorb the chlorine present in the gas when the hydrocarbon feed treated by the process is a catalytic reforming effluent.

[0056] In accordance with the process, the liquid effluent 18 obtained from the recontacting column 16 is used as a recontacting fluid in a second recontacting step which consists of bringing said liquid effluent into contact with a gaseous recycle fluid supplied via the line 21, in order to improve the recovery of C.sub.3 and C.sub.4 compounds (LPG) and to evacuate methane and ethane from the process.

[0057] As indicated in FIG. 1, the second recontacting step is carried out by direct contact by in-line mixing of the liquid effluent 18 with the recycle gas 21. The second recontacting step is carried out at a temperature which is higher than that of the first recontacting step, which is generally in the range 10 C. to 55 C. This temperature results from the thermodynamic equilibrium between the absorption of liquid 18 and the vapour 21. Preferably, no temperature control means (for example of the heat exchanger type) are used.

[0058] The gas/liquid mixture is transferred via the line 22 to a separator drum 23 which is operated in a manner such as to maximize the overhead recovery of gaseous hydrogen and C.sub.1 and C.sub.2 hydrocarbons. The gaseous effluent containing hydrogen and C.sub.1 and C.sub.2 hydrocarbons is withdrawn via the line 24 for recycling in its entirety or in part to the process, via the line 25. The portion of the gaseous effluent containing hydrogen and the C.sub.1 and C.sub.2 hydrocarbons which is not recycled is evacuated from the process via the line 26. This gaseous effluent may in particular be used as a fuel gas in the refinery.

[0059] Recycling all or a portion of the gaseous effluent containing hydrogen and C.sub.1 and C.sub.2 hydrocarbons upstream of the first recontacting step, for example as indicated in FIG. 1, as a mixture with the compressed gas 6 obtained from the separator drum 2, has the advantageous effect of improving the yield of hydrogen recovered during the first recontacting step.

[0060] Referring now to FIG. 1, a liquid effluent 27 essentially containing hydrocarbons containing three or more than three carbon atoms (C.sub.3.sup.+) and also, to a lesser extent, C.sub.1 and C.sub.2 hydrocarbons, is recovered via the bottom of the separator drum 23. The liquid effluent 27 is heated before being sent to a stabilization unit which is operated in a manner such as to recover a stabilized liquid hydrocarbon effluent and a distillate comprising mainly C.sub.3 and C.sub.4 hydrocarbons. The stabilization unit comprises a distillation column 28 the bottom of which is provided with a circulating line equipped with a recirculation circuit comprising a reboiler (not shown) and a conduit 29 for evacuation of stabilized liquid effluent. The overhead gas from the column 28 moves in a conduit 30 connected to a condensation system comprising a device 31 for cooling the overhead gas and a reflux drum 32. The condensed liquid separated in the reflux drum 32 is evacuated via the line 33 and is divided into two streams, one stream being recycled to the column 28 via the line 34, while the complementary stream which has not been recycled is evacuated via the line 35 out of the process, as a LPG stream. The residual gas withdrawn overhead from the reflux drum 32, which has not been condensed and potentially comprises non-negligible quantities of C.sub.3 and C.sub.4 hydrocarbons, is evacuated via the line 21 and recycled to the process in order to undergo a recontacting step with the liquid effluent 18 obtained from the recontacting column 16, as detailed above.

[0061] Still with reference to FIG. 1, the stabilized liquid effluent 29 recovered from 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 the distillation column 28. This thermal integration can thus be used to reduce the heat energy which has to be supplied to the reboiler in order to operate the distillation column 28.

[0062] As indicated in FIG. 1, it is advantageous to provide a guard bed 38 upstream of the distillation column 28 configured to capture any chlorine which might be present in the liquid effluent 27 in the case in which the hydrocarbon feed treated by the process is a catalytic reforming unit effluent.

[0063] FIG. 2 represents a flow diagram of the process in accordance with the invention, in accordance with a second embodiment.

[0064] The second embodiment differs from that of FIG. 1 in that on the one hand, the liquid hydrocarbon phase 4 is pre-cooled by heat exchange in an exchanger 11 supplied with cold fluid which is the liquid effluent 18 obtained from the recontacting column 16, and on the other hand in that the compressed gas 10 is pre-cooled by indirect heat exchange using an exchanger 13 which is supplied with hydrogen-rich gaseous effluent 17 withdrawn from the head of the recontacting column 16.

[0065] This configuration means that it is easier to equilibrate the flow rates of the gaseous and liquid effluents which are supplied to the exchangers 11 and 13 as a function of requirements and/or the availability of frigories to pre-cool the gaseous and liquid phases which are brought into contact in the column.

[0066] Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

[0067] In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

[0068] The entire disclosures of all applications, patents and publications, cited herein and of corresponding French application No. 15/01.494 filed Jul. 15, 2015, are incorporated by reference herein.

EXAMPLE

Example 1

[0069] Example 1 (comparative) illustrates the function of a treatment process illustrated in FIG. 3, in which the gaseous phase 6 and the liquid hydrocarbon phase 4 are cooled to a temperature of 0 C. using two chillers before being brought into counter-current contact in a recontacting column 16. It should also be noted that the gaseous effluent 24 produced in the second recontacting step is not recycled to the first recontacting step.

[0070] The treated hydrocarbon feed was an effluent (or reformate) obtained from catalytic reforming and had the composition given in Table 1:

TABLE-US-00001 TABLE 1 Composition of reformate Kg/h Reformate H2 7 200 C1 1 540 C2 2 540 C3 4 660 C4 branched 2 840 C4 linear 2 860 C5+ 178 360 Total Kg/h 200 000

[0071] The hydrocarbon feed was initially treated in a separator drum 2 in order to separate a gaseous phase 6 containing mainly hydrogen and a liquid phase 4 containing hydrocarbons.

[0072] The gaseous phase 6 obtained from the separation step was compressed by compressors 7 with the intermediate cooling steps necessary for the compressors to function properly, and was sent to the first recontacting step with the liquid phase 4 obtained from the separation step. The gaseous and liquid phases, which had an initial temperature of approximately 100 C. and 40 C. respectively, were cooled to a temperature of 0 C. using the cooling plants 14 and 15. The cooled gaseous and liquid phases were brought into counter-current contact in a recontacting column 16 comprising 9 theoretical plates which was operated at a pressure of 3.1 MPa. A hydrogen-rich gas 17 and a liquid phase 18 containing hydrocarbons were withdrawn from the recontacting column. The liquid phase 18 was then brought into contact with a gaseous recycle phase 21 which came from the reflux drum of the distillation column. The second recontacting step was operated in-line and the mixture was separated in a separator drum 23 at a pressure of 1.6 MPa in a manner such as to provide a gas 24 which was not recycled to the first recontacting step, and a liquid phase 27.

[0073] The liquid phase 27 was fractionated in a fractionation column 28 (or stabilization column) so as to recover a gaseous overhead fraction 30 and a stabilized liquid bottom fraction 29 containing hydrocarbons containing more than 4 carbon atoms. This column was operated at a pressure of 1.6 MPa and a temperature of 43 C. in the reflux drum.

[0074] The gaseous overhead fraction 30 was condensed in a reflux drum, from which a liquid phase 33 containing condensed C.sub.3-C.sub.4 hydrocarbons (LPG) and a gaseous phase 21, which was recycled to the second recontacting step, were separated.

[0075] Table 2 records the recoveries for the various stream products generated by the process of Example 1.

TABLE-US-00002 TABLE 2 Example 1 (FIG. 3) Consumption of chillers 14 and 15 to cool the gaseous 8.5 MW phase and the liquid hydrocarbon phase to 0 C. Recovery of hydrogen originating from streams 4 and 6 99.3% by wt in gas (17) Recovery of C.sub.3 and C.sub.4 hydrocarbons originating from 82.2% by wt streams 4 and 6 in liquid hydrocarbon phase (33) Recovery of C.sub.5.sup.+ hydrocarbons originating from streams 99.7% by wt 4 and 6 in stabilized stream (29)

Example 2

[0076] Example 2 illustrates the process for the treatment of a hydrocarbon feed in accordance with the invention and is made with reference to FIG. 1. It differs from Example 1 in that the gas 24 obtained from the second recontacting step was recycled in its entirety and in that the compressed gaseous phase 6 was cooled by indirect heat exchange via an exchanger 13 supplied with liquid effluent 18 obtained from the recontacting column 16 and in that the liquid hydrocarbon phase was pre-cooled with an exchanger 11 supplied with gaseous effluent 17 obtained from the recontacting column 16, then cooled using the chiller 15 to a temperature of 0 C.

[0077] The temperatures of the liquid and gaseous phases at the inlet to the recontacting column were respectively 0 C. and 40 C.

[0078] The other operating conditions mentioned in Example 1 were kept the same for Example 2.

[0079] Table 3 provides the recoveries of the various stream products generated by the process of Example 2.

TABLE-US-00003 TABLE 3 Example 2 (FIG. 1) Consumption of chiller 15 to cool the gaseous phase 2.8 MW and the liquid hydrocarbon phase to 0 C. Recovery of hydrogen originating from streams 4 and 6 100.0% by wt in gas (17) Recovery of C.sub.3 and C.sub.4 hydrocarbons originating from 83.1% by wt streams 4 and 6 in liquid hydrocarbon phase (33) Recovery of C.sub.5.sup.+ hydrocarbons originating from streams 99.7% by wt 4 and 6 in stabilized stream (29)

Example 3

[0080] Example 3 is based on the process of the invention according to FIG. 2.

[0081] Compared with FIG. 1, Example 3 differs in that the liquid 4 and gaseous 10 phases were initially pre-cooled by heat exchange with a heat exchanger supplied respectively with liquid effluent 18 and with gaseous effluent 17, then cooled with the chillers 14 and 15 in order to reach a temperature of 0 C. at the inlet to the recontacting column 16.

[0082] Table 4 provides the recoveries for the various products of the stream generated by the process of Example 3.

TABLE-US-00004 TABLE 4 Example 3 (FIG. 2) Consumption of chillers 14 and 15 to cool the gaseous 4.2 MW phase and the liquid hydrocarbon phase to 0 C. Recovery of hydrogen originating from streams 4 and 6 100.0% by wt in gas (17) Recovery of C.sub.3 and C.sub.4 hydrocarbons originating from 83.9% by wt streams 4 and 6 in liquid hydrocarbon phase (33) Recovery of C.sub.5.sup.+ hydrocarbons originating from streams 99.7% by wt 4 and 6 in stabilized stream (29)

[0083] Comparing the results of Example 1 with those of Examples 2, and 3, it can be seen that pre-cooling the gaseous and liquid phases with a cold fluid obtained from the recontacting column can significantly reduce the energy consumption in the chillers 14 and 15. The process can also be used to improve the degree of recovery of the C.sub.3 and C.sub.4 hydrocarbons in the liquid stream 33 and of hydrogen in the stream 17, in particular by recycling the gas obtained after gas/liquid separation of the effluent recovered after the second recontacting step.

[0084] A comparison of Example 2 with Example 3 shows the importance of dispensing with the cooling device which cools the gaseous phase entering the recontacting column. This embodiment can thus be used to limit the consumption of cold utilities without having a significant impact on the recovery of C.sub.3 and C.sub.4 hydrocarbons (loss of only 0.8% by weight in the recovery of C.sub.3 and C.sub.4 hydrocarbons).

[0085] The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

[0086] From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.