PROCESS FOR SEPARATION OF AROMATIC HYDROCARBONS FROM A MIXED HYDROCARBON STREAM

Abstract

The present invention relates to a process for the separation of aromatic hydrocarbons from a hydrocarbon feed stream comprising contacting a hydrocarbon feed stream with a solvent for aromatics (aromatics solvent) to provide an aromatics-laden solvent stream and subjecting the aromatics-laden solvent stream to solvent regeneration to provide regenerated aromatics solvent and an aromatics stream.

Claims

1. Process for separation of aromatic hydrocarbons from a hydrocarbon feed stream comprising the steps of: (a) contacting a gaseous hydrocarbon feed stream with aromatics solvent to provide a gaseous hydrocarbon-solvent mixture; (b) reducing the temperature of the gaseous hydrocarbon-solvent mixture to a temperature wherein the aromatics solvent is at least partially in liquid phase and the not absorbed hydrocarbons are in gas phase; (c) subjecting the thus obtained cooled hydrocarbon-solvent mixture to a separation to provide an aromatics-laden solvent stream and a gaseous stream; and (d) subjecting the aromatics-laden solvent stream to solvent regeneration to provide regenerated aromatics solvent and an aromatics stream.

2. The process according to claim 1, wherein in step (c) the separation comprises gas-liquid separation.

3. The process according to claim 2, wherein the gaseous stream obtained by gas-liquid separation is subjected either to: at least one further cooling step; or a compression step, optionally with another subsequent cooling step, and subjecting the thus obtained cooled or compressed, or optionally cooled and compressed stream, to a second gas-liquid separation to provide a further aromatics-laden solvent stream and a second gaseous stream.

4. The process according to claim 3, wherein the gaseous stream obtained by gas-liquid separation is subjected to a compression step followed by at least one cooling step, wherein the compression step comprises a first compression stage after which the partially compressed stream is contacted with aromatics solvent and the thus obtained mixture is subjected to a gas-liquid separation to provide a further aromatics-laden solvent stream and a partially compressed gaseous stream that is subsequently subjected to a second compression stage.

5. The process according to claim 3, wherein the gaseous stream obtained by gas-liquid separation is subjected to a compression step followed by at least one cooling step, wherein between the compression step and the cooling step additional aromatics solvent is fed to the compressed stream.

6. The process according to claim 3, wherein the gaseous stream obtained by gas-liquid separation is subjected to a compression step followed by at least one cooling step, wherein the thus obtained compressed and cooled stream has a pressure of 1500-4000 kPa.

7. The process according to claim 1, wherein the gaseous stream is contacted with aromatics solvent in an aromatics absorption column to provide a further aromatics-laden solvent stream and an aromatics free effluent.

8. The process according to claim 1, wherein step (a) comprises spraying liquid aromatics solvent into the gaseous hydrocarbon feed stream, wherein the gaseous hydrocarbon feed stream has a higher temperature than the aromatics solvent, thereby evaporating said aromatics solvent.

9. The process according to claim 1, wherein in step (b) the temperature of the gaseous hydrocarbon-solvent mixture is reduced to 25-70 C.

10. The process according to claim 1, wherein the regenerated aromatics solvent obtained in step (d) is recycled to the aromatics solvent used in the process.

11. The process according to claim 7, wherein aromatics solvent provided by the solvent regeneration is recycled to the aromatics absorption column.

12. The process according to claim 1, wherein one or more of the aromatics-laden solvent streams are only partially subjected to solvent regeneration, wherein the remaining part of said one or more aromatics-laden solvent streams that are not subjected to solvent regeneration are cooled and recycled to the aromatics solvent used in the process.

13. The process according to claim 12, wherein said remaining part of the one or more aromatics-laden solvent streams that are not subjected to solvent regeneration are used as the aromatics solvent feed.

14. The process according to claim 1, wherein the aromatics solvent has a boiling point of 200 C. or more at ambient pressure.

15. The process according to claim 1, wherein the aromatics solvent is selected from the group consisting of methyl naphthalene, ethyl naphthalene, propyl naphthalene, di-methyl naphthalene, methyl ethyl naphthalene, di-ethyl naphthalene, methyl propyl naphthalene, ethyl propyl naphthalene, di-propyl naphthalene, tetralin, decalin, toluene, xylenes, decane, undecane, dodecane, tridecane, tetradecane and sulfolane.

16. The process according to claim 1, wherein the gaseous hydrocarbon feed stream is produced by alkane aromatization.

17. The process according to claim 1, wherein the gaseous hydrocarbon feed stream comprises at least 1 wt-% aromatic hydrocarbons.

Description

DESCRIPTION OF THE FIGURES

[0061] FIG. 1: The gaseous hydrocarbon feed stream (1) is contacted with aromatics solvent (2) to provide a gaseous hydrocarbon-solvent mixture that is sent to cooler (A) in which a mixed hydrocarbon-solvent stream (3) is generated with a temperature at which the aromatics solvent is at least partially in liquid phase and the not absorbed hydrocarbons are in gas phase. Stream (3) is sent to separator (B) in which the thus obtained cooled hydrocarbon-solvent mixture (3) is subjected to a separation to provide an aromatics-laden solvent stream (4) and a gaseous stream (12). The thus obtained aromatics-laden solvent stream (4) is subjected to solvent regeneration in solvent regeneration column (C) to provide regenerated aromatics solvent (13) and an aromatics stream (14). The regenerated aromatics solvent (13) may be used as the aromatics solvent used in the process and process installation of the present invention.

[0062] FIG. 2: More particularly, the separator (B) of FIG. 1 may comprise of different sub-steps, including gas-liquid separation, compression, cooling and aromatics absorption sub-steps. For instance, the separation may comprise a gas-liquid separation (D). The gaseous stream (5) that is obtained by the gas-liquid separation (D) may be subjected to compression, comprising one or more compression stages (E). The thus obtained compressed stream (6) may be subjected to further cooling in a compressed stream cooler (F) to provide a compressed and cooled stream (7) that may be subjected to a second gas-liquid separation (G) to provide a second aromatics-laden solvent stream (8) and a compressed gaseous stream obtained from second gas-liquid separation (9). The gaseous stream obtained from the first gas-liquid separation, optionally after being subjected to compression and/or cooling and/or a second gas-liquid separation as described above, may be fed to an aromatics absorption column (H) which further comprises an aromatics solvent feed (11) to produce a further (for instance a third) aromatics-laden solvent stream (10) and an effluent (12) that is substantially free of aromatics. As used herein, an effluent that is substantially free of aromatics comprises no more than 0.5 wt-% aromatics, preferably no more than 500 ppmw aromatics and most preferably no more than 50 ppmw aromatics. The ratio between naphthalene and aromatics solvent in the not yet condensed portion of the gaseous stream during the optional cooling and compression will shift towards naphthalene, if the aromatics solvent has a lower volatility than naphthalene, for instance which is the case for a-methyl naphthalene. This may create a combination of temperature, pressure and naphthalene content of the gas phase at which naphthalene may desublimate from the gas-phase or precipitate from the condensate although aromatics solvent is added upstream. Staged addition of aromatics solvent to the gaseous stream upstream of the aromatics absorption column, for instance via the aromatics solvent feed (15) to the partially compressed stream and/or the aromatics solvent feed (17) to the compressed stream, will ensure that the conditions which allow the deposition of solid naphthalene are avoided. All aromatics-laden solvent streams, for instance the aromatics-laden solvent stream (4) obtained from the first gas-liquid separator (D) and/or the aromatics-laden solvent stream (8) obtained from the second gas-liquid separator (G) and/or the aromatics-laden solvent stream (10) obtained from the aromatics absorption column (H) and/or the aromatics-laden solvent stream (16) obtained from the partially compressed stream from compressor (E), may be combined and subjected to solvent regeneration in solvent regeneration column (C) to provide regenerated aromatics solvent (13) and an aromatics stream (14).

[0063] FIG. 3: More particularly, the aromatics solvent flow rate in stream (2) and/or stream (15) and/or stream (17) to the gaseous stream upstream of the aromatics absorption column (H) may be partially decoupled from the aromatics solvent absorption-regeneration loop originating from the aromatics absorption column by a short solvent cycle with the additional solvent cycle cooler (I). The liquid solvent-naphthalene mixture collected from the gas-liquid separators downstream of the effluent cooler(s), for instance the aromatics-laden solvent stream (4) obtained from the first gas-liquid separator (D) and/or the aromatics-laden solvent stream (8) obtained from the second gas-liquid separator (G) and/or the aromatics-laden solvent stream (16) obtained from the partially compressed stream from compressor (E), is cooled in cooler (I) and recycled to the aromatics solvent dosing points to the gaseous stream upstream of the aromatics absorption column such as via stream (2) and/or stream (15) and/or stream (17). Only a portion of naphthalene-laden solvent is returned to the solvent regeneration column via stream (18) and made up by regenerated solvent via stream (19). The portion of the naphthalene-laden solvent that is not returned to the solvent regeneration may be cooled and recycled to the process via stream (20).

[0064] The following alpha-numerical references are used in FIGS. 1-3 Units: [0065] (A) Hydrocarbon-solvent mixture cooler [0066] (B) Separator [0067] (C) Solvent regeneration column [0068] (D) First gas-liquid separator [0069] (E) Compressor comprising one or more compression stages and optionally an intermediate gas-liquid separator [0070] (F) Compressed stream cooler [0071] (G) Second gas-liquid separator [0072] (H) Aromatics absorption column [0073] (I) Solvent cycle cooler

[0074] Streams: [0075] (1) Gaseous hydrocarbon feed stream [0076] (2) Aromatics solvent feed to gaseous mixed hydrocarbon feed stream [0077] (3) Cooled hydrocarbon-solvent mixture [0078] (4) First aromatics-laden solvent stream [0079] (5) Gaseous stream obtained from first gas-liquid separation [0080] (6) Compressed stream [0081] (7) Compressed and cooled stream [0082] (8) Second aromatics-laden solvent stream [0083] (9) Compressed gaseous stream obtained from second gas-liquid separation [0084] (10) Third aromatics-laden solvent stream [0085] (11) Aromatics solvent feed to aromatics absorption column [0086] (12) Effluent that is substantially free of aromatics [0087] (13) Regenerated aromatics solvent [0088] (14) Aromatics stream [0089] (15) Aromatics solvent feed to partially compressed stream [0090] (16) Fourth aromatics-laden solvent stream [0091] (17) Aromatics solvent feed to compressed stream [0092] (18) Aromatics solvent return [0093] (19) Aromatics solvent make-up [0094] (20) Cooled aromatics solvent recycle