WO2014209585A1 - Procédé permettant l'élimination d'hydrocarbures lourds d'un solvant de distillation extractive - Google Patents

Procédé permettant l'élimination d'hydrocarbures lourds d'un solvant de distillation extractive Download PDF

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Publication number
WO2014209585A1
WO2014209585A1 PCT/US2014/041517 US2014041517W WO2014209585A1 WO 2014209585 A1 WO2014209585 A1 WO 2014209585A1 US 2014041517 W US2014041517 W US 2014041517W WO 2014209585 A1 WO2014209585 A1 WO 2014209585A1
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WIPO (PCT)
Prior art keywords
solvent
extractive distillation
unit
stream
lle
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Application number
PCT/US2014/041517
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English (en)
Inventor
Robert G. TINGER
Dana L. Pilliod
Robert A. SCHAEFER
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Exxonmobil Chemical Patents Inc.
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Application filed by Exxonmobil Chemical Patents Inc. filed Critical Exxonmobil Chemical Patents Inc.
Publication of WO2014209585A1 publication Critical patent/WO2014209585A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D11/00—Solvent extraction
    • B01D11/04—Solvent extraction of solutions which are liquid

Definitions

  • the invention relates to an extractive distillation process for the separation of aromatics from non-aromatics and a method for purifying the extractive distillation solvent. More specifically, the invention relates to the recovery of a purified extractive distillation solvent from a solvent-rich stream comprising solvent and heavy hydrocarbon contaminants.
  • Aromatic hydrocarbons such as benzene, toluene and xylenes (collectively, "BTX"), serve as important building blocks for a variety of plastics, foams and fibers. Often these compounds are produced via catalytic reformation of naphtha through steam cracking of naphtha or gas oils, or other methods where substantial amounts of non-aromatic compounds are present.
  • the useful aromatic hydrocarbons may be separated from the non-aromatic hydrocarbons by, for example, solvent extraction.
  • solvent extraction technique that is well known to those of ordinary skill in the art is the sulfolane process developed by UOP and Shell Oil Co. The process uses tetrahydrothiophene- 1, 1 -dioxide (or sulfolane) as a solvent and water as a co-solvent to preferentially extract the desired BTX compounds from non-aromatic hydrocarbons.
  • other solvents having similar properties may also be used (e.g., glycols).
  • One embodiment of the sulfolane process uses extractive distillation, wherein a hydrocarbon feed containing aromatic and non-aromatic compounds is fed to a multistage distillation tower in which a circulating solvent (e.g., sulfolane) is present.
  • a circulating solvent e.g., sulfolane
  • the solvent changes the relative volatility of the aromatic/non-aromatic compounds such that aromatic compounds can be separated from the non-aromatic compounds.
  • the non-aromatic compounds are fractionated overhead, while the aromatic compounds exit out the bottom of the tower along with the higher boiling solvent.
  • the aromatic compounds are then separated from the solvent in another multistage column, such that the majority of the desired aromatic compounds are fractionated overhead while the majority of the solvent is recovered out the bottom of the tower.
  • the solvent is then recycled back to the extractive distillation tower.
  • LLE liquid-liquid extraction
  • a feed consisting of aromatic/non-aromatic compounds is mixed with a solvent (e.g., sulfolane) in a multistage tower.
  • the solvent has a low affinity for non-aromatic compounds and high carbon number aromatic compounds, allowing these compounds to be preferentially rejected from the solvent.
  • a method for preventing the buildup of light impurities in an LLE unit is disclosed in PCT Patent Application Publication No. WO 2013/081730, and a method for preventing the buildup of light impurities in an LLE and/or extractive distillation unit is disclosed in U.S. Patent Application No. 13/683,588.
  • a method for limiting the buildup of molecular oxygen and chlorides in both extractive distillation and liquid-liquid extraction processes is disclosed in U.S. Patent No. 8,471,088.
  • the present inventors have discovered that taking a portion of extractive distillation solvent contaminated with heavy compounds that cannot be removed in an extractive distillation process, processing this portion in an LLE unit to remove the heavy compounds, and returning the cleaned solvent back to the extractive distillation unit is an effective means of maintaining solvent purity in the extractive distillation process.
  • the LLE unit can either be an adjacent unit to the extractive distillation unit, or a unit that has capacity to process solvent contaminated with heavy compounds, and to which the contaminated feed can be transported.
  • the invention is directed to a method for recovering a purified solvent in a process for the separation of aromatic and non-aromatic hydrocarbons, comprising: (a) introducing a solvent-rich stream comprising solvent and at least one heavy contaminant, wherein said heavy contaminant has a boiling point in the range of between that of said non-aromatic hydrocarbons and said solvent, into a liquid-liquid extraction (LLE) unit; and (b) recovering from said LLE unit: (i) a contaminated stream comprising said heavy contaminant from said solvent-rich stream and (ii) a purified solvent stream.
  • said solvent-rich stream is continuously or intermittently transported to said LLE unit (e.g., via vehicle, via piping, etc.). Any combination of continuous and/or intermittent transfer between said extractive distillation unit and said LLE unit is possible.
  • said LLE unit is integrated with said extractive distillation unit.
  • a more specific embodiment of the invention is a method for separating aromatic hydrocarbons from a feedstock comprising aromatic and non-aromatic hydrocarbons, the method comprising: (a) introducing a feedstock comprising aromatic and non-aromatic hydrocarbons into a multistage extractive distillation column, feeding a circulating solvent into said column, recovering a raffinate stream comprising non-aromatic hydrocarbons overhead from said column, and removing a rich solvent stream comprising said circulating solvent and aromatic hydrocarbons from the bottom of said column; (b) feeding said rich solvent stream into a fractionating column, recovering an extract stream comprising aromatic hydrocarbons overhead from said fractionating column and a contaminated solvent-rich stream from the bottom of said fractionating column; and (c) directing at least a portion of said contaminated solvent-rich stream to a liquid-liquid extraction (LLE) unit on a batch basis to yield: (i) a contaminated stream comprising a portion of said solvent and at least one contaminant and (ii) a pur
  • FIGURE 1 depicts on the left-hand scale data showing the accumulation of heavy waste products over a three month timeframe in a sulfolane solvent used for the separation of aromatics from a hydrocarbon feedstock in an extractive distillation process.
  • the right-hand scale of the figure depicts data showing the corresponding decrease in solvent purity.
  • FIGURE 2 depicts data showing the comparative projected decrease in purity of a sulfolane solvent used for the separation of aromatics from a hydrocarbon feedstock in an extractive distillation process with and without the addition of a periodic batch purge to an LLE unit.
  • FIGURE 3 depicts a schematic view of two parallel systems comprising an extractive distillation process and a liquid-liquid extraction process. These systems are connected via a solvent exchange conduit.
  • FIGURE 4 depicts a schematic view of an embodiment of the two parallel systems of FIGURE 3 comprising an extractive distillation process and a liquid-liquid extraction process. These systems are connected via a solvent exchange conduit.
  • FIGURE 5 depicts data showing the comparative projected decrease in purity of a sulfolane solvent used for the separation of aromatics from a hydrocarbon feedstock in an extractive distillation process with and without the addition of a periodic batch purge to an LLE unit.
  • This invention provides an improved extractive distillation process for recovering aromatic hydrocarbons from non-aromatic hydrocarbons in feed mixtures containing heavy hydrocarbon contaminants.
  • the term "heavy contaminant” refers to any hydrocarbon (e.g., aromatic) having a boiling point between that of the separated non-aromatics and the extractive distillation solvent and "boiling point" may refer to the normal boiling point or the effective boiling point.
  • heavy contaminants comprise C 9+ aromatic hydrocarbons.
  • this invention relates to an improved extractive-distillation process for recovering aromatic hydrocarbons including benzene, toluene, and xylenes (BTX aromatics) from C6-Cs petroleum streams.
  • this invention is directed toward the regeneration, recovery and purification of the extractive distillation solvent used to recover aromatics from non- aromatics in feed mixtures containing heavy hydrocarbons.
  • contaminated stream refers to a stream containing some amount of contaminant, especially heavy contaminant.
  • purified solvent refers to solvent from which some amount of contaminant has been removed.
  • introducing applies to feed streams originating from an external source to the system containing the relevant process unit as opposed to a circulating recycle stream. This distinction particularly serves to distinguish the claimed invention from the prior art as disclosed in U.S. Patent No.
  • upstream and downstream define the sequencing between process units, wherein feed enters the upstream process unit prior to entering the downstream process unit.
  • FIGURE 1 graphically depicts the accumulation of heavy hydrocarbons over a three month period in a traditional extractive distillation process using sulfolane as the extractive distillation solvent.
  • the present invention contemplates the accumulation of heavy hydrocarbons introduced to the system through the feed mixtures, as opposed to being generated by reactions within the system as indicated by prior art.
  • the solvent purity generally decreased over the three month timeframe from an initial purity of approximately 99.6 wt.% to a final purity of approximately 97.3 wt.%. Intermittent increases in purity were observed around day 80 and day 100 on FIGURE 1 corresponding to a reduction in the solvent regenerator temperature. The solvent reached a minimum in purity towards the end of the three month period, at 96.5 wt.%.
  • FIGURE 1 shows that the level of Cg + hydrocarbons increased from an initial level of about 0.2 wt.% to a final level of about 0.7 wt.% and the level of unknown heavies increased from an initial level of about 0.1 wt.% to about 1.9 wt.%.
  • An object of the present invention is to prevent such a decrease in solvent purity by removing Cg + hydrocarbons and unknown heavies before accumulation can occur.
  • a hydrocarbon feed containing a mixture of aromatic and non- aromatic hydrocarbons is introduced via conduit 1 of FIGURE 3 into extractive distillation system 21 containing an extractive distillation solvent (e.g., sulfolane) in a closed system loop to produce a product stream (such as BTX aromatics) exiting the system via conduit 2 and a second stream comprised mostly of non-aromatic hydrocarbons exiting the system via conduit 28.
  • extractive distillation solvent e.g., sulfolane
  • a hydrocarbon feed containing a mixture of aromatic and non-aromatic hydrocarbons is introduced via conduit 3 into liquid-liquid extraction system 22 containing an extraction solvent (e.g., sulfolane) in a closed system loop to produce a product stream (such as BTX aromatics) exiting the system via conduit 4 and a second stream comprised mostly of non-aromatic hydrocarbons exiting the system via conduit 29.
  • an extraction solvent e.g., sulfolane
  • a product stream such as BTX aromatics
  • FIGURE 4 A more specific embodiment of the invention is depicted schematically in FIGURE 4. For purposes of clarity, only the main processing units have been included in this diagram.
  • a feed containing aromatic and non-aromatic hydrocarbons is introduced into a middle portion of extractive distillation column 23 of FIGURE 4 via conduit 6 and a solvent-rich stream is fed into an upper portion of the column via conduit 7.
  • a non-aromatic hydrocarbon rich stream is recovered from the upper portion of the extractive-distillation column via conduit 8.
  • a solvent-rich stream containing the solvent, aromatic hydrocarbons, and heavy contaminant is recovered from a bottom portion of the extractive distillation column via conduit 9, and is fed into a middle portion of solvent- recovery fractionating column 24.
  • An aromatic rich stream is recovered from an upper portion of the solvent-recovery fractionating column via conduit 10.
  • a solvent-rich stream containing solvent and heavy contaminant is removed from a bottom portion of the solvent- recovery column via conduit 11 and recycled into the extractive distillation column via conduit 7.
  • a feed containing aromatic and non-aromatic hydrocarbons is introduced into liquid-liquid extraction (LLE) column 25 via conduit 12 and a solvent-rich stream is fed into the unit via conduit 13.
  • LLE liquid-liquid extraction
  • a non-aromatic hydrocarbon rich stream containing the majority of the heavy contaminant(s) is recovered from the upper portion of the LLE unit via conduit 14.
  • a solvent-rich stream comprising the solvent, aromatic hydrocarbons and residual non-aromatic hydrocarbons is recovered from a bottom portion of the LLE column via conduit 15 and is fed into a middle portion of stripper column 26.
  • a stream comprising the residual non- aromatic hydrocarbons along with aromatic hydrocarbons is removed from an upper portion of the stripper column via conduit 16 and recycled into the LLE unit.
  • the recycle stream of non-aromatic hydrocarbons and aromatic hydrocarbons may enter the LLE column 25 at a location below the feed entry point, above the feed entry point, at the same location the feed is introduced, or any combination thereof.
  • a solvent-rich stream containing a majority of the aromatic hydrocarbons is recovered from the bottom portion of the stripper unit via conduit 17 and fed into a middle portion of solvent-recovery fractionating column 27.
  • An aromatic rich stream is recovered from an upper portion of the solvent-recovery fractionating column via conduit 18.
  • a substantially contaminant- free solvent-rich stream is removed from a bottom portion of the solvent-recovery fractionating column via conduit 19 and recycled into the LLE unit via conduit 13.
  • a portion of solvent in conduit 11 periodically or continuously exits the extractive distillation system via conduit 20 (consisting of piping, for instance) and enters the LLE column 25 in order to be purified and an equal amount of solvent exits the liquid-liquid extraction system via conduit 20 and enters extractive distillation unit 23.
  • Conduit 20 is represented by a dashed line to indicate that this conduit may or may not comprise a physical connection (for instance, solvent transfer between systems may be accomplished via trucking).
  • Conduit 5 in FIGURE 3 and conduit 20 in FIGURE 4 allowing for solvent exchange may consist of a variety of transportation means, including but not limited to vehicular transport (e.g., trucking), transportation via watercraft (e.g., ship or barge), or piping.
  • tanks may be used to store and cool solvent before it is introduced into the appropriate system.
  • the solvent-rich stream recovered from the extractive distillation unit is not mixed with the solvent-rich stream from the LLE unit in a single tank to keep the LLE-recovered solvent substantially free of the heavy contaminants in the extractive distillation-recovered solvent.
  • two parallel pipes may be constructed allowing for simultaneous solvent transfer between systems.
  • a single pipe may be constructed and solvent transfer may be accomplished in batches wherein solvent from one system is transported to the other system and afterward the direction of pipe flow is reversed to allow for solvent transfer to the original system.
  • Solvent transfer may occur continuously or in periodic batches.
  • the liquid-liquid extraction (LLE) unit is located contiguous to the extractive distillation process (for convenience of further integration, such as of heat exchangers, common feed, and the like) and a portion of extractive distillation solvent is continuously processed through the LLE and recycled to the extractive distillation unit.
  • the LLE is a stand-alone unit and solvent is transferred in batch quantities.
  • solvent batch transfer occurs once every 25 days as depicted in FIGURE 2.
  • FIGURE 2 shows that in a traditional extractive distillation process with no solvent purge, the purity of the extractive distillation solvent is simulated to decrease from approximately 97% to 80% (17%) within a 350 day timeframe.
  • FIGURE 2 shows that by adding a purge every 25 days (consisting of sending a portion of solvent to an LLE unit to be purified and recycled to the extractive distillation unit), the decrease in solvent purity over the same timeframe of 350 days is simulated to diminish to approximately only a 4% decrease.
  • solvent transfer occurs more frequently than once every 25 days.
  • the solvent transfer rate in said preferred embodiments can be determined by one of ordinary skill in the art in possession of the present disclosure.
  • FIGURE 5 shows that continuous purging maintains the solvent purity at about 97%, while batch purging once every 7 days maintains the solvent purity at about 95.5%, which is sufficiently high for unit performance.
  • Batch purging also has another benefit. Continuous purging transfers approximately 288,000 m 3 of solvent per month, whereas purging once every 7 days transfers only about 120 m 3 of solvent per month. Therefore, considering the significant savings in transferring less solvent per month and that batch purging maintains a sufficient solvent purity for optimal unit performance, batch purging is more efficient and preferred over continuous purging.
  • the extraction solvent is any liquid that preferentially extracts aromatic hydrocarbons over non-aromatic hydrocarbons.
  • the boiling point of the extraction solvent should be higher than the boiling point of the aromatic hydrocarbons being extracted (i.e., it should have a boiling point of at least 100°C and preferably between about 200°C and about 300°C) so that it is not evaporated during stripping.
  • the preferred extraction solvent is sulfolane, available as Sulfolane WTM from Chevron Phillips Chemical Company, Bartlesville, Okla., USA.
  • the solvent is selected from glycols, such as di-, tri-, and tetraethylene glycol, and nitrogen-containing species such as N-methyl pyrrolidine. Mixtures of such solvents can be used.
  • the feed mixture containing aromatic and non- aromatic hydrocarbons is recognized to contain heavy hydrocarbon "contaminants”
  • the feed mixture is supplied to a LLE system, as opposed to an extractive distillation system, for separation. Because the LLE system more effectively separates the heavy hydrocarbon "contaminants,” the transfer of solvent from the extractive distillation system to the LLE system for purification can be done on a less frequent basis.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

La présente invention concerne un procédé de distillation extractive pour récupérer des hydrocarbures aromatiques à partir d'hydrocarbures non aromatiques dans des mélanges d'alimentation contenant au moins une quantité mesurable de contaminants d'hydrocarbures lourds, chaque contaminant étant caractérisé comme ayant un point d'ébullition dans la plage d'entre ceux des hydrocarbures non aromatiques séparés et du solvant de distillation extractive utilisé pour récupérer et purifier des hydrocarbures aromatiques. Selon l'invention, un procédé de distillation extractive perfectionné est décrit pour la récupération d'hydrocarbures aromatiques comprenant le benzène, le toluène et les xylènes à partir de courants contenant des hydrocarbures lourds en (C9+) ainsi que des hydrocarbures lourds d'indentité inconnue. De façon plus spécifique, cette invention concerne la régénération et la récupération du solvant de distillation extractive à partir d'un courant riche en solvant contenant au moins une quantité mesurable de contaminants d'hydrocarbures lourds à l'aide d'extraction liquide-liquide.
PCT/US2014/041517 2013-06-28 2014-06-09 Procédé permettant l'élimination d'hydrocarbures lourds d'un solvant de distillation extractive WO2014209585A1 (fr)

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US201361840761P 2013-06-28 2013-06-28
US61/840,761 2013-06-28

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1021498B1 (fr) * 1997-09-03 2004-11-17 GTC Technology, Inc Processus de separation de composes aromatiques
US20060124509A1 (en) * 2004-12-10 2006-06-15 Van Nuland Marcus Lambertus H Process for mitigating acids in a system for separating aromatic hydrocarbons from a hydrocarbon feedstream
US20100300939A1 (en) * 2009-06-02 2010-12-02 Uop Llc Process for Removing a Contaminant from an Aromatic Selective Solvent
KR20110015546A (ko) * 2008-04-10 2011-02-16 씨피씨 코포레이션, 타이완 방향족 회수를 위한 신규한 에너지 효율적이고 처리량을 향상시키는 추출 공정
US20120197057A1 (en) * 2011-01-31 2012-08-02 John Joseph Monson Solvent Quality Control in Extraction Processes
US20120247943A1 (en) * 2011-03-31 2012-10-04 Uop Llc Aromatics recovery by extractive distillation

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1021498B1 (fr) * 1997-09-03 2004-11-17 GTC Technology, Inc Processus de separation de composes aromatiques
US20060124509A1 (en) * 2004-12-10 2006-06-15 Van Nuland Marcus Lambertus H Process for mitigating acids in a system for separating aromatic hydrocarbons from a hydrocarbon feedstream
KR20110015546A (ko) * 2008-04-10 2011-02-16 씨피씨 코포레이션, 타이완 방향족 회수를 위한 신규한 에너지 효율적이고 처리량을 향상시키는 추출 공정
US20100300939A1 (en) * 2009-06-02 2010-12-02 Uop Llc Process for Removing a Contaminant from an Aromatic Selective Solvent
US20120197057A1 (en) * 2011-01-31 2012-08-02 John Joseph Monson Solvent Quality Control in Extraction Processes
US20120247943A1 (en) * 2011-03-31 2012-10-04 Uop Llc Aromatics recovery by extractive distillation

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