EP0379021B1 - Process for working up the raffinate fraction obtained in the extractine distillation of hydrocarbon mixtures - Google Patents

Process for working up the raffinate fraction obtained in the extractine distillation of hydrocarbon mixtures Download PDF

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Publication number
EP0379021B1
EP0379021B1 EP90100284A EP90100284A EP0379021B1 EP 0379021 B1 EP0379021 B1 EP 0379021B1 EP 90100284 A EP90100284 A EP 90100284A EP 90100284 A EP90100284 A EP 90100284A EP 0379021 B1 EP0379021 B1 EP 0379021B1
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EP
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Prior art keywords
raffinate
distillation column
coalescer
solvent
separation vessel
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EP90100284A
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German (de)
French (fr)
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EP0379021A1 (en
Inventor
Gerd Emmrich
Hans-Christoph Schneider
Ulrich Rüdel
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Krupp Koppers GmbH
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Krupp Koppers GmbH
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    • CCHEMISTRY; METALLURGY
    • C10PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10GCRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
    • C10G7/00Distillation of hydrocarbon oils
    • C10G7/08Azeotropic or extractive distillation
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S203/00Distillation: processes, separatory
    • Y10S203/90Particular type of heating
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S210/00Liquid purification or separation
    • Y10S210/05Coalescer

Definitions

  • the invention relates to a process for working up the raffinate of an extractive distillation of hydrocarbon mixtures, in which N-substituted morpholines, the substituents of which have no more than seven carbon atoms, are used as the selective solvent, the lower-boiling constituents of the hydrocarbon mixture serving as the feed product being used as raffinate withdrawn overhead from the extractive distillation column and the raffinate then distilled to recover the solvent residues contained therein and the resulting bottom product with a certain solvent content is withdrawn from the raffinate distillation column and separated into a light and a heavy phase in a separating container, whereupon the heavy phase is reintroduced into the extractive distillation column and the light phase into the raffinate distillation column.
  • the extractive distillation process described above has been known for a number of years and can be used for the separation of hydrocarbon mixtures of different compositions, for example for the separation of aromatics and non-aromatics or for the separation of olefins or diolefins and paraffins.
  • the process has become particularly useful using N-formylmorpholine as a selective solvent for obtaining highly pure aromatics proven.
  • the bottom product withdrawn from the extractive distillation column is normally passed into a downstream stripping column in which the hydrocarbons contained in it as extract are separated from the solvent by distillation.
  • the solvent is then withdrawn from the bottom of the stripping column and returned to the extractive distillation column for reuse.
  • the solvent is usually introduced or reintroduced at the top of the extractive distillation column.
  • the invention is therefore based on the object of eliminating this disadvantage.
  • coalescer In the coalescer, the very fine droplets of the heavy phase can unite to form large drops, which can then sink down without difficulty as a result of their higher sinking speed in the separating container.
  • a coalescer which is particularly suitable for carrying out the method according to the invention and its mode of action will be discussed below in connection with FIGS. 2 and 3.
  • the bottom product with a solvent content of 20 to 75% by weight is drawn off from the raffinate distillation column and cooled to a temperature of 20 to 70 ° C. before entering the coalescer.
  • the solvent content of the bottom product of the raffinate distillation can in this case be controlled via the bottom temperature or the temperature of the column heating at the bottom of the raffinate distillation column, since there is a clear relationship between the solvent content and the bottom temperature such that the bottom temperature rises with increasing solvent content, the bottom temperature setting is of course dependent on the boiling point of the solvent used and the composition of the hydrocarbon mixture to be worked up in the raffinate distillation column.
  • benzene is obtained from a crude benzene fraction obtained from pyrolysis gasoline by extractive distillation with N-formylmorpholine and a solvent content in the bottom product of the raffinate distillation column of 50% by weight
  • a bottom temperature is established.
  • the content of the same solvent in the bottom product is 75% by weight, the bottom temperature is approximately 125 ° C.
  • the flow diagram shown in FIG. 1 contains only the parts of the system that are absolutely necessary for the process explanation, while auxiliary devices such as pumps, circulation cookers, heat exchangers etc. are not shown.
  • the hydrocarbon mixture serving as the feed product which may already have been subjected to pre-distillation, is introduced through line 1 into the central part of the bottomed extractive distillation column 2.
  • the feed product is usually heated to just below the boiling point so that it evaporates immediately when it enters the extractive distillation column.
  • the selective solvent used is introduced at the top into the extractive distillation column 2 and flows down over the trays of this column, taking up the vaporous hydrocarbons of the extract.
  • the lower-boiling hydrocarbons which form the raffinate phase escape through line 4 at the top of the column and pass through this line into the middle part of the raffinate distillation column 19 provided with packing or trays.
  • the liquid bottom product of the extractive distillation column 2 consists of the solvent and the hydrocarbons of the extract dissolved therein and is withdrawn through line 5 from the extractive distillation column 2 and reaches the stripping column 6, in which these hydrocarbons are separated from the selective solvent by distillation.
  • the solvent is removed from the bottom of the column through line 7 and flows back through line 3 into the extractive distillation column 2 while the hydrocarbons to be extracted escape overhead from the stripping column 6 and pass through line 8 into column 9, in which their further Separation takes place.
  • the higher-boiling components can be drawn off through line 10 and the lower-boiling components can be drawn off through line 11.
  • the branch line 12 is provided in the area of the line 7, through which a partial amount of the solvent can reach the regeneration device 14 when the valve 13 is in the appropriate position.
  • the regenerated solvent is through line 15 again returned to the circuit (line 7), while the separated impurities are removed from the regeneration device through line 16.
  • the line 17 is finally used to supply fresh solvent.
  • the bottom product obtained in the raffinate distillation column 19 is drawn off via line 21 with a solvent content of 20 to 75% by weight, while hydrocarbons of the raffinate with a solvent content of less than 10 ppm are removed via line 2o from the raffinate distillation column 19 .
  • the withdrawn sump product passes via line 21 into the cooler 22, in which it undergoes the necessary cooling.
  • it is introduced via line 29 into the coalescer 3o, which is combined with the separating container 23 to form a structural unit.
  • the bottom product from the coalescer 3o therefore enters directly into the upper part of the separating tank 23, in which the interface controller 24 is installed in the central region.
  • the cooler 22 Since the amount of sump product flowing off via the line 21 is relatively small, the cooler 22 will not always be necessary for the cooling thereof required. If necessary, it is rather also possible to dispense with this cooler and to cool the bottom product in line 21 and in the separating container 23 in that the latter are not insulated or are equipped with a cooling jacket. Excessive cooling of the bottom product to a temperature below 20 ° C. is not appropriate, because it causes the heating energy requirement in the raffinate distillation column 19 and the extractive distillation column 2 would be increased unnecessarily. At a temperature between 2o and 7o ° C, the desired separation of the introduced bottom product into an upper and a lower phase takes place in the separating tank. The different composition of these two phases has already been mentioned above.
  • the withdrawal of the heavy phase (lower phase) from the separating tank 23 is controlled by the interface controller 24. This is done in such a way that the position of the interface between the heavy and the light phase influences the position of the interface controller 24, which is attached to a joint in a freely movable manner. As soon as the heavy phase has accumulated in the lower part of the separating tank 23 to such an extent that the interface between the heavy and light phases is at the same level as the interface controller 24, it assumes the horizontal position shown in the figure and actuates it when this position is reached Via the pulse line 27, the actuator 28 of the valve 26 in such a way that it is opened.
  • the valve 26 Since the valve 26 is installed in the line 25, the heavy phase is drawn off from the separating container 23 and can be combined with the solvent flowing in the line 3 via this line. If, on the other hand, the separating layer between the heavy and light phases in the separating container continues to decrease, the position of the separating layer regulator 24 changes accordingly downward and the valve 26 is closed or throttled in the manner described. The light phase (upper phase) is meanwhile removed from the separating tank 23 via the line 18 and returns to the bottom of the raffinate distillation column 19. It deviates from the circuit shown in the flow diagram of course, it is also possible not to combine the heavy phase drawn off through line 25 with the solvent in line 3, but rather to introduce it separately into the upper part of the extractive distillation column 2.
  • coalescer 3o which is connected to the associated separating container 23 to form a structural unit. It can be seen that the coalescer 3o is flanged onto the upper part of the separating container 23 so that the bottom product in the coalescing 3o can flow out of the raffinate distillation column 19 directly into the upper part of the separating container 23.
  • the reference symbols 18, 25 and 29 mark the connections for the corresponding lines and the reference symbol 24 the connection for the interface controller.
  • Fig. 3 finally shows a section through the coalescer 3o in the plane AB of Fig. 2. It can be seen in the figure that the interior of the coalescer 3o in this case is completely filled with corrugated metal plates 31 arranged one above the other. These corrugated iron plates 31 are arranged in the coalescer 3o in such a way that their grooves 32 run parallel to the longitudinal direction of the coalescer 3o. In addition, the corrugated metal plates 31 have a gradient of approximately 1% in the direction of the inlet opening to the separating container 23, so that the bottom product located in the coalescer 30 can easily flow into the separating container 23.
  • the corrugated metal plates 31 should preferably consist of pickled carbon steel because this material guarantees good wettability.
  • the channel 32 of a corrugated iron plate 31 is shown in FIG. 3 as a detailed illustration. The depth a of the grooves 32 should preferably be 20 mm.
  • coalescer 30 and the separating container 23 are combined to form one structural unit, which is undoubtedly the preferred embodiment. If special operational circumstances require it, it is also possible to arrange the coalescer 30 and the separating container 23 separately from one another.

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  • Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • General Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Production Of Liquid Hydrocarbon Mixture For Refining Petroleum (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Description

Die Erfindung betrifft ein Verfahren zur Aufarbeitung des Raffinates einer Extraktivdestillation von Kohlenwasserstoffgemischen, bei der N-substituierte Morpholine, deren Substituenten nicht mehr als sieben C-Atome aufweisen, als selektives Lösungsmittel verwendet werden, wobei die leichter siedenden Bestandteile des als Einsatzprodukt dienenden Kohlenwasserstoffgemisches als Raffinat über Kopf aus der Extraktivdestillationskolonne abgezogen und das Raffinat daran anschließend zwecks Rückgewinnung der in ihm vorhandenen Lösungsmittelreste destilliert und das dabei anfallende Sumpfprodukt mit einem bestimmten Lösungsmittelgehalt aus der Raffinatdestillationskolonne abgezogen und in einem Scheidebehälter in eine leichte und eine schwere Phase getrennt wird, worauf die schwere Phase in die Extraktivdestillationskolonne und die leichte Phase in die Raffinatdestillationskolonne wiedereingeleitet wird.The invention relates to a process for working up the raffinate of an extractive distillation of hydrocarbon mixtures, in which N-substituted morpholines, the substituents of which have no more than seven carbon atoms, are used as the selective solvent, the lower-boiling constituents of the hydrocarbon mixture serving as the feed product being used as raffinate withdrawn overhead from the extractive distillation column and the raffinate then distilled to recover the solvent residues contained therein and the resulting bottom product with a certain solvent content is withdrawn from the raffinate distillation column and separated into a light and a heavy phase in a separating container, whereupon the heavy phase is reintroduced into the extractive distillation column and the light phase into the raffinate distillation column.

Das vorstehend beschriebene Extraktivdestillationsverfahren ist bereits seit einer ganzen Reihe von Jahren bekannt und kann zur Trennung von Kohlenwasserstoffgemischen unterschiedlicher Zusammensetzung verwendet werden, beispielsweise zur Trennung von Aromaten und Nichtaromaten oder zur Trennung von Olefinen bzw. Diolefinen und Paraffinen. Im großtechnischen Maßstab hat sich das Verfahren insbesondere unter Verwendung von N-Formylmorpholin als selektivem Lösungsmittel zur Gewinnung von hochreinen Aromaten bewährt. Bei der Durchführung dieses Verfahrens wird normalerweise das aus der Extraktivdestillationskolonne abgezogene Sumpfprodukt in eine nachgeschaltete Abtreiberkolonne eingeleitet, in der die in ihm als Extrakt enthaltenen Kohlenwasserstoffe destillativ vom Lösungsmittel abgetrennt werden. Das Losungsmittel wird sodann aus dem Sumpf der Abtreiberkolonne abgezogen und zur Wiederverwendung in die Extraktivdestillationskolonne zurückgeführt. Hierbei erfolgt aus verfahrenstechnischen Gründen die Einleitung bzw. Wiedereinleitung des Lösungsmittels normalerweise am Kopf der Extraktivdestillationskolonne. Dadurch läßt es sich jedoch praktisch nicht vermeiden, daß das anfallende Raffinat noch gewisse Lösungsmittelreste enthält, wobei der Lösungsmittelgehalt im Raffinat bis zu 2 Gew.-% betragen kann. Aus Wirtschaftlichkeitsgründen und im Hinblick auf die Gewinnung eines möglichst reinen Raffinates ist es jedoch unerläßlich, diesen Lösungsmittelanteil im Raffinat möglichst weitgehend zurückzugewinnen.The extractive distillation process described above has been known for a number of years and can be used for the separation of hydrocarbon mixtures of different compositions, for example for the separation of aromatics and non-aromatics or for the separation of olefins or diolefins and paraffins. On a large industrial scale, the process has become particularly useful using N-formylmorpholine as a selective solvent for obtaining highly pure aromatics proven. When this process is carried out, the bottom product withdrawn from the extractive distillation column is normally passed into a downstream stripping column in which the hydrocarbons contained in it as extract are separated from the solvent by distillation. The solvent is then withdrawn from the bottom of the stripping column and returned to the extractive distillation column for reuse. For process engineering reasons, the solvent is usually introduced or reintroduced at the top of the extractive distillation column. However, this practically cannot prevent the resulting raffinate from still containing certain solvent residues, and the solvent content in the raffinate can be up to 2% by weight. For reasons of economy and with a view to obtaining as pure a raffinate as possible, however, it is essential to recover as much of this solvent content in the raffinate as possible.

Dies wäre sicher möglich, wenn man die Extraktivdestillationskolonne mit einem entsprechend hohen Raffinatrückfluß betreiben wurde. Im Gegensatz zur normalen Destillation ist jedoch bei der Extraktivdestillation ein derartiger Rückfluß aus folgenden Gründen unangebracht und deshalb zu vermeiden:

  • 1. Ein Raffinatrückfluß führt zu einer Verdünnung des Lösungsmittels und damit zu einer Selektivitätsminderung, wodurch die gewünschte Stofftrennung unnötig erschwert wird.
  • 2. Hochselektive Lösungsmittel - und hierzu gehören die eingangs genannten N-substituierten Morpholine - weisen nur ein begrenztes Lösevermögen für die abzutrennenden leichter siedenden Kohlenwasserstoffe auf. Ein Raffinatrückfluß kann deshalb dazu führen, daß sich auf den oberen Böden der Extraktivdestillationgskolonne zwei Flüssigphasen mit unterschiedlichen Dichten ausbilden, die einen störungsfreien Betrieb der Extraktivdestillationskolonne unmöglich machen.
This would certainly be possible if the extractive distillation column were operated with a correspondingly high raffinate reflux. In contrast to normal distillation, such a reflux is inappropriate for extractive distillation for the following reasons and should therefore be avoided:
  • 1. A raffinate reflux leads to a dilution of the solvent and thus to a reduction in selectivity, which unnecessarily complicates the desired separation.
  • 2. Highly selective solvents - and these include the N-substituted morpholines mentioned at the beginning - have only a limited solvency for the lower boiling hydrocarbons to be separated. Raffinate reflux can therefore lead to the formation of two liquid phases with different densities on the upper plates of the extractive distillation column, which make trouble-free operation of the extractive distillation column impossible.

Daher scheidet dieser an sich naheliegende Weg für die Rückgewinnung des Lösungsmittelanteiles aus dem Raffinat aus, und es muß stattdessen eine separate Rückgewinnung des Lösungsmittels aus dem Raffinat erfolgen. Diese kann zwar durch einfache Destillation des Raffinates in der Weise durchgeführt werden, daß das Raffinat als Kopfprodukt mit Lösungsmittelgehalten von < 1o ppm aus der Destillationskolonne abgezogen wird, während das auf fas 1oo %-ige Reinheit aufkonzentrierte Lösungsmittel aus dem Sumpf dieser Kolonne abgezogen und in die Extraktivdestillationskolonne zurückgeführt wird. Diese Arbeitsweise, bei der eine möglichst vollständige Trennung von Raffinat und Lösungsmittel angestrebt wird, erfordert jedoch einen hohen apparativen Aufwand (Destillationskolonne mit hoher Bodenzahl) und einen hohen Energieverbrauch.Therefore, this obvious route for the recovery of the solvent fraction from the raffinate is ruled out, and instead a separate recovery of the solvent from the raffinate must take place. Although this can be carried out by simple distillation of the raffinate in such a way that the raffinate is withdrawn as a top product with solvent contents of <10 ppm from the distillation column, while the solvent concentrated to almost 100% purity is withdrawn from the bottom of this column and into the extractive distillation column is recycled. However, this procedure, in which the complete separation of raffinate and solvent is sought, requires a high level of equipment (distillation column with a large number of plates) and high energy consumption.

In der DE-A- 34 o9 o3o ist deshalb bereits vorgeschlagen worden, die destillative Abtrennung des Lösungsmittels von den Kohlenwasserstoffen des Raffinates nur unvollständig vorzunehmen und stattdessen aus der Raffinatdestillationskolonne ein Sumpfprodukt abzuziehen, das noch einen bestimmten Lösungsmittelgehalt aufweist. Anschließend wird dieses Sumpfprodukt nach entsprechender Kühlung in einen Scheidebehälter eingeleitet, in dem es in eine schwere und eine leichte Phase getrennt werden soll. Die schwere Phase besteht dabei im wesentlichen aus dem Lösungsmittel und den Kohlenwasserstoffen des Extraktes, die als Verunreinigung in das Raffinat gelangt sind. Sie kann auf Grund ihrer Zusammensetzung in die Extraktivdestillationskolonne zurückgeführt werden, während die leichte Phase, die die übrigen Bestandteile des Sumpfproduktes enthält, in die Raffinatdestillationskolonne wiedereingeleitet wird.DE-A-34 o9 o3o has therefore already proposed that the distillative removal of the solvent from the hydrocarbons of the raffinate is carried out only incompletely and instead a bottom product which still has a certain solvent content is taken off from the raffinate distillation column. Then, after appropriate cooling, this bottom product is introduced into a separating container in which it is placed in a heavy one and separate an easy phase. The heavy phase consists essentially of the solvent and the hydrocarbons of the extract, which have entered the raffinate as impurities. Because of its composition, it can be returned to the extractive distillation column, while the light phase, which contains the remaining constituents of the bottom product, is reintroduced into the raffinate distillation column.

Bei der Durchführung des vorstehend beschriebenen Verfahrens hat sich in der Praxis jedoch in einigen Fällen gezeigt, daß die Wirkungsweise des Scheidebehälters unzureichend war. Dies war vor allem dann festzustellen, wenn die Bestandteile der schweren Phase in dem aus der Raffinatdestillationskolonne abgezogenen Sumpfprodukt in Form von sehr feinen Tröpfchen vorlagen, deren Sinkgeschwindigkeit geringer war als die Aufsteigegeschwindigkeit der Bestandteile der leichten Phase. In diesem Falle wurden im unerwünschten Umfange Bestandteile der schweren Phase wieder mit zurück in die Raffinatdestillationskolonne gefördert und verschlechterten so die Trennleistung dieser Kolonne.When carrying out the method described above, however, it has been shown in practice in some cases that the operation of the vaginal container was inadequate. This was particularly noticeable when the heavy phase components were present in the bottom product drawn off from the raffinate distillation column in the form of very fine droplets whose rate of descent was lower than the rate of ascent of the light phase components. In this case, components of the heavy phase were conveyed back into the raffinate distillation column to an undesirable extent and thus worsened the separation performance of this column.

Der Erfindung liegt deshalb die Aufgabe zugrunde, diesen Nachteil zu beseitigen.The invention is therefore based on the object of eliminating this disadvantage.

Diese Aufgabe wird bei einem Verfahren der eingangs genannten Art erfindungsgemäß dadurch gelöst, daß das Sumpfprodukt aus der Raffinatdestillationskolonne vor dem Eintritt in den Scheidebehälter durch einen Koaleszer mit den im Patentanspruch 1 genannten Merkmalen geleitet wird.This object is achieved according to the invention in a process of the type mentioned at the outset by passing the bottom product from the raffinate distillation column through a coalescer with the features mentioned in patent claim 1 before it enters the separating tank.

In dem Koaleszer können sich die sehr feinen Tröpfchen der schweren Phase zu großen Tropfen vereinigen, die dann infolge ihrer höheren Sinkgeschwindigkeit im Scheidebehälter ohne Schwierigkeiten nach unten sinken können. Auf einen zur Durchführung des erfindungsgemäßen Verfahrens besonders geeigneten Koaleszer und dessen Wirkungsweise wird weiter unten im Zusammenhang mit Fig. 2 und 3 eingegangen werden.In the coalescer, the very fine droplets of the heavy phase can unite to form large drops, which can then sink down without difficulty as a result of their higher sinking speed in the separating container. A coalescer which is particularly suitable for carrying out the method according to the invention and its mode of action will be discussed below in connection with FIGS. 2 and 3.

Bei der Durchführung des erfindungsgemäßen Verfahrens ist es zweckmäßig, wenn das Sumpfprodukt mit einem Lösungsmittelgehalt von 2o bis 75 Gew.-% aus der Raffinatdestillationskolonne abgezogen und vor dem Eintritt in den Koaleszer bis auf eine Temperatur von 20 bis 7o°C gekühlt wird. Der Lösungsmittelgehalt des Sumpfproduktes der Raffinatdestillation kann hierbei über die Sumpftemperatur bzw. die Temperatur der Kolonnenbeheizung am Sumpf der Raffinatdestillationskolonne gesteuert werden, da zwischen dem Lösungsmittelgehalt und der Sumpftemperatur eine eindeutige Beziehung derart besteht, daß mit steigendem Lösungsmittelgehalt die Sumpftemperatur ansteigt, wobei die sich einstellende Sumpftemperatur natürlich von der Siedetemperatur des verwendeten Lösungsmittels und der Zusammensetzung des in der Raffinatdestillationskolonne aufzuarbeitenden Kohlenwasserstoffgemisches abhängig ist. So stellt sich beispielsweise bei der Gewinnung von Benzol aus einer aus Pyrolysebenzin gewonnenen Rohbenzolfraktion durch Extraktivdestillation mit N-Formylmorpholin bei einem Lösungsmittelgehalt im Sumpfprodukt der Raffinatdestillationskolonne von 50 Gew.-% eine Sumpftemperatur von ca. 1oo°C ein. Liegt dagegen der Gehalt des gleichen Lösungsmittels im Sumpfprodukt bei 75 Gew.-%, so beträgt die Sumpftemperatur ca. 125°C.When carrying out the process according to the invention, it is expedient if the bottom product with a solvent content of 20 to 75% by weight is drawn off from the raffinate distillation column and cooled to a temperature of 20 to 70 ° C. before entering the coalescer. The solvent content of the bottom product of the raffinate distillation can in this case be controlled via the bottom temperature or the temperature of the column heating at the bottom of the raffinate distillation column, since there is a clear relationship between the solvent content and the bottom temperature such that the bottom temperature rises with increasing solvent content, the bottom temperature setting is of course dependent on the boiling point of the solvent used and the composition of the hydrocarbon mixture to be worked up in the raffinate distillation column. For example, when benzene is obtained from a crude benzene fraction obtained from pyrolysis gasoline by extractive distillation with N-formylmorpholine and a solvent content in the bottom product of the raffinate distillation column of 50% by weight, a bottom temperature of approximately 100 ° C. is established. On the other hand, if the content of the same solvent in the bottom product is 75% by weight, the bottom temperature is approximately 125 ° C.

Selbstverständlich können anstelle der Temperaturmessung auch analytische Methoden, wie z.B. die Gaschromatographie, zur Ermittlung und Kontrolle des Lösungsmittelgehaltes des Sumpfproduktes herangezogen werden.Of course, instead of temperature measurement, analytical methods such as gas chromatography can be used to determine and control the solvent content of the bottom product.

Weitere Einzelheiten des beanspruchten Verfahrens sowie des zu seiner Durchführung verwendeten Koaleszers ergeben sich aus den vorliegenden Unteransprüchen und sollen nachfolgend an Hand der Abbildungen erläutert werden. Hierbei zeigen:

Fig. 1
ein Fließschema zur Durchführung des Verfahrens,
Fig. 2
einen Koaleszer mit dem dazugehörigen Scheidebehalter
und
Fig. 3
einen Schnitt in der Ebene A-B von Fig. 2.
Further details of the claimed method and of the coalescer used to carry it out result from the present subclaims and will be explained below with reference to the figures. Here show:
Fig. 1
a flow chart for carrying out the process,
Fig. 2
a coalescer with the associated scabbard
and
Fig. 3
a section in the plane AB of Fig. 2nd

Das in Fig. 1 dargestellte Fließschema enthält dabei nur die für die Verfahrenserläuterung unbedingt erforderlichen Anlagenteile, während Nebeneinrichtungen, wie beispielsweise Pumpen, Umlaufkocher, Wärmetauscher etc., nicht dargestellt sind. Das als Einsatzprodukt dienende Kohlenwasserstoffgemisch, das gegebenenfalls bereits einer Vordestillation unterworfen worden sein kann, wird durch die Leitung 1 in den mittleren Teil der mit Böden versehenen Extraktivdestillationskolonne 2 eingeleitet. Das Einsatzprodukt ist dabei normalerweise bis dicht unterhalb des Siedepunktes erhitzt, so daß es beim Eintritt in die Extraktivdestillationskolone sofort verdampft. Durch die Leitung 3 wird das verwendete selektive Lösungsmittel am Kopf in die Extraktivdestillationskolonne 2 eingeleitet und fließt über die Böden dieser Kolonne herab nach unten, wobei es die dampfförmigen Kohlenwasserstoffe des Extraktes aufnimmt. Die leichter siedenden Kohlenwasserstoffe, die die Raffinatphase bilden, entweichen durch Leitung 4 am Kopf der Kolonne und gelangen über diese Leitung in den mittleren Teil der mit Füllkörpern oder Böden versehenen Raffinatdestillationskolonne 19.The flow diagram shown in FIG. 1 contains only the parts of the system that are absolutely necessary for the process explanation, while auxiliary devices such as pumps, circulation cookers, heat exchangers etc. are not shown. The hydrocarbon mixture serving as the feed product, which may already have been subjected to pre-distillation, is introduced through line 1 into the central part of the bottomed extractive distillation column 2. The feed product is usually heated to just below the boiling point so that it evaporates immediately when it enters the extractive distillation column. Through line 3 the selective solvent used is introduced at the top into the extractive distillation column 2 and flows down over the trays of this column, taking up the vaporous hydrocarbons of the extract. The lower-boiling hydrocarbons which form the raffinate phase escape through line 4 at the top of the column and pass through this line into the middle part of the raffinate distillation column 19 provided with packing or trays.

Das flüssige Sumpfprodukt der Extraktivdestillationskolonne 2 besteht aus dem Lösungsmittel und den darin gelösten Kohlenwasserstoffen des Extraktes und wird durch die Leitung 5 aus der Extraktivdestillationskolonne 2 abgezogen und gelangt in die Abtreiberkolonne 6, in der diese Kohlenwasserstoffe destillativ vom selektiven Lösungsmittel abgetrennt werden. Das Lösungsmittel wird durch die Leitung 7 aus dem Kolonnensumpf entfernt und fließt über die Leitung 3 wieder in die Extraktivdestillationskolonne 2 zurück während die zu gewinnenden Kohlenwasserstoffe über Kopf aus der Abtreiberkolonne 6 entweichen und durch die Leitung 8 in die Kolonne 9 gelangen, in der ihre weitere Auftrennung erfolgt. So können beispielsweise durch die Leitung 1o die höhersiedenden Bestandteile und durch die Leitung 11 die niedrigersiedenden Bestandteile abgezogen werden. Da sich im Laufe der Zeit im verwendeten Lösungsmittel Verunreinigungen anreichern können, ist im Bereich der Leitung 7 die Abzweigleitung 12 vorgesehen, durch die bei entsprechender Stellung des Ventils 13 eine Teilmenge des Lösungsmittels zur Regeneriereinrichtung 14 gelangen kann. Das regenerierte Lösungsmittel wird durch die Leitung 15 wieder in den Kreislauf (Leitung 7) zurückgeführt, während die ausgeschiedenen Verunreinigungen durch die Leitung 16 aus der Regeneriereinrichtung entfernt werden. Die Leitung 17 dient schließlich der Zufuhr von frischem Lösungsmittel.The liquid bottom product of the extractive distillation column 2 consists of the solvent and the hydrocarbons of the extract dissolved therein and is withdrawn through line 5 from the extractive distillation column 2 and reaches the stripping column 6, in which these hydrocarbons are separated from the selective solvent by distillation. The solvent is removed from the bottom of the column through line 7 and flows back through line 3 into the extractive distillation column 2 while the hydrocarbons to be extracted escape overhead from the stripping column 6 and pass through line 8 into column 9, in which their further Separation takes place. For example, the higher-boiling components can be drawn off through line 10 and the lower-boiling components can be drawn off through line 11. Since impurities can accumulate in the solvent used over time, the branch line 12 is provided in the area of the line 7, through which a partial amount of the solvent can reach the regeneration device 14 when the valve 13 is in the appropriate position. The regenerated solvent is through line 15 again returned to the circuit (line 7), while the separated impurities are removed from the regeneration device through line 16. The line 17 is finally used to supply fresh solvent.

Zur Durchführung des erfindungsgemäßen Verfahrens wird das in der Raffinatdestillationskolonne 19 anfallende Sumpfprodukt mit einem Lösungsmittelgehalt von 2o bis 75 Gew.-% über die Leitung 21 abgezogen, während Kohlenwasserstoffe des Raffinates mit einem Lösungsmittelgehalt unter 1o ppm über die Leitung 2o aus der Raffinatdestillationskolonne 19 entfernt werden. Das abgezogene Sumpfprodukt gelangt über die Leitung 21 in den Kühler 22, in dem es die erforderliche Abkühlung erfährt. Danach wird es über die Leitung 29 in den Koaleszer 3o eingeleitet, der mit dem Scheidebehälter 23 zu einer baulichen Einheit zusammengefaßt ist. Aus dem Koaleszer 3o tritt deshalb das Sumpfprodukt unmittelbar in den Oberteil des Scheidebehälters 23 ein, in dem im mittleren Bereich der Trennschichtregler 24 installiert ist. Da die über die Leitung 21 abfließende Sumpfproduktmenge verhältnismäßig klein ist, wird für deren erforderliche Abkühlung nicht in jedem Falle der Kühler 22 notwendig sein. Gegebenenfalls ist es vielmehr auch möglich, auf diesen Kühler zu verzichten und die Abkühlung des Sumpfproduktes in der Leitung 21 und im Scheidebehälter 23 dadurch vorzunehmen, daß dieselben nicht isoliert sind bzw. mit einem Kühlmantel ausgestattet sind. Eine zu starke Abkühlung des Sumpfproduktes auf eine Temperatur unter 2o°C ist nicht angebracht, weil dadurch der Heizenergiebedarf in der Raffinatdestillationskolonne 19 und der Extraktivdestillationskolonne 2 unnötig erhöht werden würde. Bei einer Temperatur zwischen 2o und 7o°C erfolgt im Scheidebehälter die gewünschte Trennung des eingeleiteten Sumpfproduktes in eine Ober- und eine Unterphase. Auf die unterschiedliche Zusammensetzung dieser beiden Phasen ist bereits weiter oben hingewiesen worden. Der Abzug der schweren Phase (Unterphase) aus dem Scheidebehälter 23 wird dabei durch den Trennschichtregler 24 gesteuert. Dies geschieht in der Weise, daß die Lage der Trennschicht zwischen der schweren und der leichten Phase die Stellung des Trennschichtreglers 24, der an einem Gelenk frei beweglich befestitigt ist, beeinflußt. Sobald sich die schwere Phase im unteren Teil des Scheidebehälters 23 soweit angereichert hat, daß sich die Trennschicht zwischen schwerer und leichter Phase auf der gleichen Höhe wie der Trennschichtregler 24 befindet, nimmt dieser die in der Abbildung eingezeichnete waagerechte Stellung ein und betätigt bei Erreichen dieser Stellung über die Impulsleitung 27 den Stellantrieb 28 des Ventils 26 in der Weise, daß dieses geöffnet wird. Da das Ventil 26 in der Leitung 25 installiert ist, wird damit schwere Phase aus dem Scheidebehälter 23 abgezogen und kann über diese Leitung mit dem in der Leitung 3 fließenden Lösungsmittel vereinigt werden. Sinkt dagegen die Trennschicht zwischen schwerer und leichter Phase im Scheidebehälter weiter nach unten, so verändert sich die Stellung des Trennschichtreglers 24 entsprechend nach unten und das Ventil 26 wird dadurch in der beschriebenen Art und Weise geschlossen bzw. gedrosselt. Die leichte Phase (Oberphase) wird indessen über die Leitung 18 aus dem Scheidebehälter 23 entfernt und gelangt in den Sumpf der Raffinatdestillationskolonne 19 zurück. In Abweichung von der im Fließschema dargestellten Schaltung ist es natürlich auch möglich, die durch die Leitung 25 abgezogene schwere Phase nicht mit dem Lösungsmittel in der Leitung 3 zu vereinigen, sondern getrennt von diesem in den Oberteil der Extraktivdestillationskolonne 2 einzuleiten.To carry out the process according to the invention, the bottom product obtained in the raffinate distillation column 19 is drawn off via line 21 with a solvent content of 20 to 75% by weight, while hydrocarbons of the raffinate with a solvent content of less than 10 ppm are removed via line 2o from the raffinate distillation column 19 . The withdrawn sump product passes via line 21 into the cooler 22, in which it undergoes the necessary cooling. Then it is introduced via line 29 into the coalescer 3o, which is combined with the separating container 23 to form a structural unit. The bottom product from the coalescer 3o therefore enters directly into the upper part of the separating tank 23, in which the interface controller 24 is installed in the central region. Since the amount of sump product flowing off via the line 21 is relatively small, the cooler 22 will not always be necessary for the cooling thereof required. If necessary, it is rather also possible to dispense with this cooler and to cool the bottom product in line 21 and in the separating container 23 in that the latter are not insulated or are equipped with a cooling jacket. Excessive cooling of the bottom product to a temperature below 20 ° C. is not appropriate, because it causes the heating energy requirement in the raffinate distillation column 19 and the extractive distillation column 2 would be increased unnecessarily. At a temperature between 2o and 7o ° C, the desired separation of the introduced bottom product into an upper and a lower phase takes place in the separating tank. The different composition of these two phases has already been mentioned above. The withdrawal of the heavy phase (lower phase) from the separating tank 23 is controlled by the interface controller 24. This is done in such a way that the position of the interface between the heavy and the light phase influences the position of the interface controller 24, which is attached to a joint in a freely movable manner. As soon as the heavy phase has accumulated in the lower part of the separating tank 23 to such an extent that the interface between the heavy and light phases is at the same level as the interface controller 24, it assumes the horizontal position shown in the figure and actuates it when this position is reached Via the pulse line 27, the actuator 28 of the valve 26 in such a way that it is opened. Since the valve 26 is installed in the line 25, the heavy phase is drawn off from the separating container 23 and can be combined with the solvent flowing in the line 3 via this line. If, on the other hand, the separating layer between the heavy and light phases in the separating container continues to decrease, the position of the separating layer regulator 24 changes accordingly downward and the valve 26 is closed or throttled in the manner described. The light phase (upper phase) is meanwhile removed from the separating tank 23 via the line 18 and returns to the bottom of the raffinate distillation column 19. It deviates from the circuit shown in the flow diagram of course, it is also possible not to combine the heavy phase drawn off through line 25 with the solvent in line 3, but rather to introduce it separately into the upper part of the extractive distillation column 2.

Fig. 2 zeigt den Koaleszer 3o, der mit dem dazugehörigen Scheidebehälter 23 zu einer baulichen Einheit verbunden ist. Man erkennt, daß der Koaleszer 3o hierbei am Oberteil des Scheidebehälters 23 angeflanscht ist, so daß das im Koaleszer 3o befindliche Sumpfprodukt aus der Raffinatdestillationskolonne 19 unmittelbar in den Oberteil des Scheidebehälters 23 abfließen kann. Die Bezugszeichen 18, 25 und 29 markieren die Anschlüsse für die entsprechenden Leitungen und das Bezugszeichen 24 den Anschluß für den Trennschichtregler.2 shows the coalescer 3o, which is connected to the associated separating container 23 to form a structural unit. It can be seen that the coalescer 3o is flanged onto the upper part of the separating container 23 so that the bottom product in the coalescing 3o can flow out of the raffinate distillation column 19 directly into the upper part of the separating container 23. The reference symbols 18, 25 and 29 mark the connections for the corresponding lines and the reference symbol 24 the connection for the interface controller.

Fig. 3 stellt schließlich einen Schnitt durch den Koaleszer 3o in der Ebene A-B von Fig. 2 dar. Man erkennt auf der Abbildung, daß der Innenraum des Koaleszers 3o in diesem Falle vollständig mit übereinander angeordneten Wellblechplatten 31 ausgefüllt ist. Diese Wellblechplatten 31 sind dabei so im Koaleszer 3o angeordnet, daß deren Rinnen 32 parallel zur Längsrichtung des Koaleszers 3o verlaufen. Außerdem weisen die Wellblechplatten 31 in Richtung auf die Eintrittsöffnung zum Scheidebehälter 23 ein Gefälle von ca. 1 % auf, so daß das im Koaleszer 3o befindliche Sumpfprodukt ohne weiteres in den Scheidebehälter 23 abfließen kann. Die Wellblechplatten 31 sollen dabei vorzugsweise aus gebeiztem Kohlenstoffstahl bestehen, weil dieses Material eine gute Benetzbarkeit garantiert. Die Rinne 32 einer Wellblechplatte 31 ist in Fig. 3 als Detaildarstellung wiedergegeben. Die Tiefe a der Rinnen 32 soll vorzugsweise 2o mm betragen.Fig. 3 finally shows a section through the coalescer 3o in the plane AB of Fig. 2. It can be seen in the figure that the interior of the coalescer 3o in this case is completely filled with corrugated metal plates 31 arranged one above the other. These corrugated iron plates 31 are arranged in the coalescer 3o in such a way that their grooves 32 run parallel to the longitudinal direction of the coalescer 3o. In addition, the corrugated metal plates 31 have a gradient of approximately 1% in the direction of the inlet opening to the separating container 23, so that the bottom product located in the coalescer 30 can easily flow into the separating container 23. The corrugated metal plates 31 should preferably consist of pickled carbon steel because this material guarantees good wettability. The channel 32 of a corrugated iron plate 31 is shown in FIG. 3 as a detailed illustration. The depth a of the grooves 32 should preferably be 20 mm.

In Fig. 2 sind, wie bereits gesagt wurde, der Koaleszer 3o und der Scheidebehälter 23 zu einer baulichen Einheit zusammengefaßt, was zweifellos die bevorzugte Ausführungsform darstellt. Wenn es besondere betriebliche Gegebenheiten erfordern, ist es aber auch möglich, den Koaleszer 3o und den Scheidebehälter 23 getrennt voneinander anzuordnen.2, as has already been said, the coalescer 30 and the separating container 23 are combined to form one structural unit, which is undoubtedly the preferred embodiment. If special operational circumstances require it, it is also possible to arrange the coalescer 30 and the separating container 23 separately from one another.

Claims (2)

  1. Process for working up the raffinate from an extractive distillation of hydrocarbon mixtures, in which N-substituted morpholines, whose substituents have not more than seven carbon atoms, are used as selective solvent, the lower-boiling constituents of the hydrocarbon mixture used as feedstock being taken off as raffinate from the extractive distillation column over the top and the raffinate then being distilled for recovery of the solvent residues present therein and the bottom product thus obtained being taken off at a certain solvent content from the raffinate distillation column and being separated in a separation vessel into a light phase and a heavy phase, whereupon the heavy phase is recycled to the extractive distillation column and the light phase is reintroduced into the raffinate distillation column, characterised in that the bottom product from the raffinate distillation column (19) is, before it enters the separation vessel (23), passed through a coalescer (30) whose interior is completely filled with superposed corrugated metal plates (31) of pickled carbon steel, the corrugated metal plates (31) being arranged in such a way that their channels (32) run parallel to the longitudinal direction of the coalescer (30) and also have a slight downward gradient towards the outlet port.
  2. Coalescer with superposed internals for carrying out the process according to Claim 1, characterised in that the same is combined with the separation vessel (23) to form a constructional unit, the coalescer (30) being flanged to the upper part of the separation vessel (23) and the corrugated metal plates (31) whose channels (32) running parallel to the longitudinal direction of the coalescer (3) have a depth of 20 mm, having a downward gradient of 1% in the direction of the inlet port of the separation vessel (23).
EP90100284A 1989-01-20 1990-01-08 Process for working up the raffinate fraction obtained in the extractine distillation of hydrocarbon mixtures Expired - Lifetime EP0379021B1 (en)

Applications Claiming Priority (2)

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DE3901587A DE3901587A1 (en) 1989-01-20 1989-01-20 METHOD FOR PROCESSING THE REFINED OF AN EXTRACTIVE DISTILLATION OF HYDROCARBON MIXTURES
DE3901587 1989-01-20

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EP0379021A1 EP0379021A1 (en) 1990-07-25
EP0379021B1 true EP0379021B1 (en) 1993-09-15

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DE4101848A1 (en) * 1991-01-23 1992-07-30 Krupp Koppers Gmbh METHOD FOR SEPARATING AROMATES FROM HYDROCARBON MIXTURES OF ANY AROMATE CONTENT
DE4109632A1 (en) * 1991-03-23 1992-09-24 Krupp Koppers Gmbh METHOD FOR SEPARATING AROMATES BY EXTRACTIVE DISTILLATION
CA2146759A1 (en) * 1992-10-28 1994-05-11 George T. Chen High purity benzene production using extractive distillation
US9005405B2 (en) 2012-03-01 2015-04-14 Cpc Corporation, Taiwan Extractive distillation process for benzene recovery
US9221729B1 (en) * 2015-02-23 2015-12-29 Allnew Chemical Technology Company Extractive distillation for aromatics recovery
CN116574531B (en) * 2023-07-13 2023-10-27 大庆亿鑫化工股份有限公司 Furnace type device and production process for producing petroleum ether

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CA512198A (en) * 1955-04-26 H. Engel Karl Azeotropic distillation of hydrocarbon oils
US2376870A (en) * 1941-03-28 1945-05-29 Allied Chem & Dye Corp Azeotropic distillation of hydro-carbon oils
US4081355A (en) * 1970-08-12 1978-03-28 Krupp-Koppers Gmbh Process for recovering highly pure aromatics from a mixture of aromatics and non-aromatics
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DE3409030A1 (en) * 1984-03-13 1985-09-19 Krupp Koppers GmbH, 4300 Essen METHOD FOR SEPARATING AROMATES FROM HYDROCARBON MIXTURES OF ANY AROMATE CONTENT
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DE59002673D1 (en) 1993-10-21
US5031754A (en) 1991-07-16
DE3901587A1 (en) 1990-07-26
CA2008029A1 (en) 1990-07-20
KR0141364B1 (en) 1998-06-15
KR900011881A (en) 1990-08-02
JPH02232295A (en) 1990-09-14
EP0379021A1 (en) 1990-07-25
ES2047158T3 (en) 1994-02-16
JP2768528B2 (en) 1998-06-25

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