EP0087832B2 - Process for the removal of aromatic compounds from hydrocarbons - Google Patents

Description

The invention relates to a process for removing aromatic compounds from hydrocarbon mixtures with a boiling range of 30 to 300 ° C by liquid-liquid extraction with a selective solvent and generation of an aromatic-free raffinate, regeneration of the loaded solvent (extract) by re-extraction with a non-aromatic hydrocarbon , the boiling point of which is lower than that of the selective solvent, distillative separation of the aromatics from the non-aromatic re-extraction agent and removal of solvent residues from the raffinate and the removed aromatics by water washing.

It is known to obtain the aromatics (extract) dissolved in the selective solvent after the extraction by re-extraction with a low-boiling non-aromatic hydrocarbon (re-extraction agent). The resulting mixture of low-boiling non-aromatic hydrocarbons (re-extraction agent) and re-extracted aromatics (re-extract) is separated by distillation (DE-A-1 545 383).

This method has the disadvantage that, when extracted with the selective solvent, owing to the different distribution factors of the aromatic hydrocarbons to be separated off, the amount of solvent must be such that even the most poorly soluble aromatic hydrocarbon is still extracted. On the other hand, the amount of reextractant must be measured in the re-extraction so that even the aromatic hydrocarbon which is most soluble in the solvent is still re-extracted. As a result, the amount of the re-extracting agent is substantially larger than the amount of the raffinate, and this re-extracting agent must be distilled off from the extracted aromatic hydrocarbons. This requires a considerable amount of heat.

Another disadvantage is that the lowest-boiling constituent of the hydrocarbon mixture to be freed from the aromatics must have a boiling point which is at least 30, if possible 50 ° C higher than the boiling point of the re-extracting agent in order to ensure an economical distillative separation between extract and To achieve re-extraction. The boiling point of the reactant should not be lower than 50 ° C, if possible, in order to allow economical condensation during the distillation. The hydrocarbon mixture must therefore have an initial boiling point of 100 to 120 ° C. It is not possible to separate the aromatics from mixtures with a boiling range from 30 to 300 ° C. using the known method.

In the known process of DE-A-2 035 324, aromatics are separated from a hydrocarbon mixture, the aim being to obtain pure aromatics. After a first extraction of the aromatics with solvent, in a second extraction step heavy non-aromatics are displaced from the extract with water and light non-aromatics, some of which are recirculated and originate from the feedstock.

The invention has for its object to completely remove the aromatics from a hydrocarbon mixture in which they interfere. The purity of the aromatics separated is not important here. In the process mentioned in the introduction, the object is achieved in that a mixture of N-methylpyrrolidone and water is used as the selective solvent, that aromatic solvent is extracted from the extract as an extract, this solvent is mixed with solvent-containing water flowing out of the water washes, the mixture relinquishes the re-extraction, withdraws from the sump of the re-extraction the solvent which has been freed from aromatics and contains water and re-extracting agent and gives up to a distillation in which the re-extracting agent is separated from the solvent together with water, so that the top product of the re-extraction containing the re-extracting agent, aromatics and solvent residues Feeds distillation column, withdraws re-extraction agent from the top and returns it to the re-extraction, derives a mixture of aromatics and solvent residues from the bottom of the distillation column and gives up the water wash, the used, solvent-containing Washing water containing tel is mixed with the mixture supplied for re-extraction, and that aromatics are removed from the water wash. Design options for this method result from the subclaims.

The advantages achieved by the invention are, in particular, that aromatic compounds from hydrocarbon mixtures with a boiling point above 300 ° C. can be obtained in a simple and particularly economical manner by liquid-liquid extraction with a selective solvent, regeneration of the loaded solvent by re-extraction with a non-aromatic hydrocarbon and separation of the aromatics from the non-aromatic re-extractant.

The addition of water according to the invention to the aromatic-laden solvent from the extraction shifts the distribution factors between the hydrocarbon phase and the solvent phase towards the hydrocarbon phase. Such a shift means that the necessary amount of Reextractant is significantly reduced. This saves thermal energy for distilling off the re-extraction agent from the extract.

The added water has to be evaporated again from the solvent, but this does not result in additional heating costs because this evaporated water is used to wash out solvent from raffinate and extract. The course of these water washes is then used to increase the water content of the solvent after the extraction and before the re-extraction. This combination is an essential part of the idea according to the invention that the amount of heat to be applied for the evaporation of the water is used at two points, namely water washing and the shifting of the distribution factors, with very different effects.

The process also has the advantage that the aromatics can also be separated from hydrocarbon mixtures with an initial boiling point below 100 ° C., for example 30 ° C. For this purpose, according to the invention, the low-boiling fractions are first distilled off from the solvent loaded with the aromatic extract before it is led to the re-extraction in a distillation column. Then only the higher-boiling parts of the extract remain for the re-extraction, and these have a sufficiently large difference in boiling temperature to the re-extracting agent that it can be separated from the re-extract with a low reflux ratio.

• Fig. 1 das erfindungsgemässe Verfahren für ein Einsatzprodukt mit einem Siedebereich von 120 bis 300° C;
• Fig. 2 das erfindungsgemässe Verfahren für ein Einsatzprodukt mit einem Siedebereich von 30 bis 300° C.

The invention is shown schematically and for example in the drawings and is described in more detail below. Show it:

• 1 shows the method according to the invention for a feed product with a boiling range from 120 to 300.degree.
• 2 shows the method according to the invention for a feed product with a boiling range from 30 to 300 ° C.

• 1. Zufuhr des Einsatzproduktes;
• 2. Extraktor zur Flüssig-Flüssig-Extraktion;
• 3. aromatenfreies Raffinat; 4. Extraktor für Raffinat-Wasserwäsche;
• 5. Abzug Raffinat;
• 6. unbeladenes selektives Lösungsmittel zur Extraktion 2;
• 7. beladenes Lösungsmittel mit niedrigerem Wassergehalt aus der Extraktion 2;
• 8. beladenes Lösungsmittel mit höherem Wassergehalt zur Flüssig-Flussig-Reextraktion 9;
• 10. Zufuhr unbeladenes Reextraktionsmittel zur Flüssig-Flüssig-Reextraktion 9;
• 11. Abzug beladenes Reextraktionsmittel zur Reextraktionsmittel-Destillation 12; .
• 13. Abzug Kopfprodukt der Destillationskolonne 12;
• 14. Rückfluss auf Destillationskolonne 12;
• 15. lösungsmittelhaltiger Extrakt als Ablauf der Destillationskolonne 12;
• 16. Extraktor für Extraktwasserwäsche;
• 17. Abzug gewaschener Extrakt;
• 18. regeneriertes mit Reextraktionsmittel gesättigtes Lösungsmittel mit höherem Wassergehalt zur Lösungsmittelstripperdestillation 19;
• 20. Abzug Kopfprodukt der Lösungsmittelstripperdestillation 19;
• 21. Flüssigabscheider;
• 22. Abzug Reextraktionsmittel vom Flüssigabscheider 21;
• 23. Rücklauf auf die Lösungsmittelstripperdestillation 19;
• 24. Wasserablauf vom Abscheider 21 zum Extraktor für Extraktwasserwäsche 16;
• 25. Ablauf lösungsmittelhaltiges Waschwasser aus Extraktor für Extraktwasserwäsche 16;
• 26. Wasserabzug aus Abscheider 21 zum Extraktor für Raffinat-Wasserwäsche 4;
• 27. Ablauf von lösungsmittelhaltigem Waschwasser aus dem Extraktor für Raffinat- Wasserwäsche 4;
• 28. Zuführung von lösungsmittelhaltigem Waschwasser zum beladenen Lösungsmittel mit niedrigerem Wassergehalt 7 zur Herstellung eines Lösungsmittels mit höherem Wassergehalt 8 für die Reextraktion 9;
• 29. Destillationskolonne zu Abtrennung der niedrigsiedenden Teile des Extraktes;
• 30. Abzug Kopfprodukt der Destillationskolonne 29;
• 31. Flüssigabscheider;
• 32. Abzug niedrigsiedender Teil des Extraktes;
• 33. Rücklauf auf Destillationskolonne 29;
• 35. lösungsmittelhaltiges Wasser zur Destillationskolonne 29.

It means:

• 1. supply of the feed product;
• 2. Extractor for liquid-liquid extraction;
• 3. aromatic-free raffinate; 4. extractor for raffinate water wash;
• 5. Raffinate deduction;
• 6. unloaded selective solvent for extraction 2;
• 7. loaded solvent with lower water content from extraction 2;
• 8. loaded solvent with higher water content for liquid-liquid re-extraction 9;
• 10. supply of unloaded re-extraction agent for liquid-liquid re-extraction 9;
• 11. Discharge of loaded reextractant for reextractant distillation 12; .
• 13th deduction top product of the distillation column 12;
• 14. reflux to distillation column 12;
• 15. solvent-containing extract as the outlet from the distillation column 12;
• 16. Extractor for extract water washing;
• 17. Extract washed extract;
• 18. regenerated solvent saturated with re-extractant with a higher water content for solvent stripper distillation 19;
• 20. Deduction of overhead product from solvent stripper distillation 19;
• 21. liquid separator;
• 22. Deduction of re-extractant from the liquid separator 21;
• 23. Return to the solvent stripper distillation 19;
• 24. Water drainage from separator 21 to extractor for extract water wash 16;
• 25. Outflow of solvent-containing wash water from extractor for extract water wash 16;
• 26. Water withdrawal from separator 21 to extractor for raffinate water wash 4;
• 27. Outflow of solvent-containing wash water from the extractor for raffinate water wash 4;
• 28. supply of solvent-containing wash water to the loaded solvent with a lower water content 7 for the production of a solvent with a higher water content 8 for the re-extraction 9;
• 29. distillation column to separate the low-boiling parts of the extract;
• 30th deduction top product of the distillation column 29;
• 31. liquid separator;
• 32. deduction of low-boiling part of the extract;
• 33. reflux to distillation column 29;
• 35. solvent-containing water to the distillation column 29.

Example 1:

1, 1000 kg / h of a kerosene feed of the boiling point 120 to 300 ° C. with 15 to 20% by weight of aromatics are introduced into the lower part of the extractor 2 via line 1. Over 6, 4000 kg / h of N-methyl-pyrrolidone (NMP) with 6% by weight of water are added to an upper base of the extractor 2 as a selective solvent. The extraction is carried out at 50 ° C. 790 kg / h of a raffinate with 1 to 5% by weight of aromatics and about 5% by weight of solvent are drawn off via line 3 and transferred to the raffinate water wash 4. Over 5 750 kg / h of washed raffinate leave the plant.

From the bottom of the extractor 2, loaded solvent with a lower water content is drawn off via line 7. About 300 kg / h of solvent-containing water from the raffinate water wash 4 via line 27 and from the extract water wash 16 via line 25 are added to this solvent via line 28 added. This additive contains 200 kg / h of water and increases the water content of the solvent from 6 to 11% by weight. The loaded solvent with a water content of 11% by weight is fed via line 8 to the top of the reextraction column 9.

1200 kg / h of n-hexane are fed to the column 9 as a re-extraction agent in the lower part via line 10. If the water content of the solvent had not been increased according to the invention from 6% by weight to 11% by weight, the amount of n-hexane should have been 2500 kg / h.

The loaded re-extraction agent is withdrawn via line 11 and fed to the distillation column 12.

Solvent-containing extract is drawn off via line 15 and led to extract water wash 16. There, the solvent components are washed out of line 24 with 100 kg / h of water. The solvent-water mixture leaves the extract water wash 16 via line 25.

Via line 17, 250 kg / h of washed extract with an aromatic content of 50 to 70% by weight leave the plant. The reextraction column 9 leaves the regenerated solvent via line 18 and is led to the stripper distillation column 19. There the dissolved hexane and part of the water are distilled off via line 20. The condensate is separated in the separator 21.

The hexane leaves the separator 21 via line 22. Of the separated water, 100 kg / h are fed via line 24 to the extract water wash 16 and via line 26 to the raffinate water wash 4. In addition, a small part of the water flows as reflux to the top of the stripper distillation column 19. At the bottom of the column 19, 4 kg / h of N-methylpyrrolidone with 6% by weight of water are drawn off via line 6. From the distillation column 12, vapors are drawn off and condensed at the head via line 13. The condensate is partly returned via line 14 to the top of the column as reflux. The rest is fed together with the hexane from line 22 via line 10 to the reextraction column 9.

Example 2:

2 1000 kg / h of a kerosene feed of the boiling point 30 to 300 ° C. with 15 to 20% by weight of aromatics are introduced into the lower part of the extractor 2 via line 1. As in Example 1, 64,000 kg / h of N-methylpyrrolidone with 6% by weight of water are fed in via line. The raffinate leaves the system via line 3, water wash 4 and line 5 in an amount of 750 kg / h and with an aromatic content of 1 to 5% by weight.

From the bottom of the extractor 2, loaded solvent with a lower water content is drawn off via line 7 and fed into the distillation column 29 approximately in the middle. 300 kg / h of solvent-containing water from the raffinate water wash 4 via line 27 and the extract water wash via line 25 are fed to the distillation column 29 in the lower part via line 28. This product contains 200 kg / h of water and increases the water content of the solvent, which leaves the bottom of the distillation column 29 via line 8, from 6 to 11% by weight.

At the top of the distillation column 29, the vapors are drawn off via line 30, condensed and separated into a hydrocarbon phase and a water phase in the separator 31. The hydrocarbon phase is the low-boiling part of the extract and leaves the plant in an amount of 75 kg / h with an aromatic content of 50 to 70% by weight. If this low-boiling part of the extract had not been distilled off, some of it would have remained in the re-extracting agent and would ultimately have left the system together with the raffinate via the solvent circuit, so that dearomatization would have been much worse. The azeotropically entrained water is passed via line 33 as reflux to the top of the distillation column 29. The remaining extract leaves the plant in an amount of 175 kg / h with an aromatic content of 50 to 70% by weight via line 17. The rest of the procedure is the same as in Example 1.

Claims (6)

1. A process of removing aromatic compounds from mixed hydrocarbons having a boiling range from 30 to 300°C by liquid-liquid extraction (2) with a selective solvent and production of a raffinate which is free of aromatic compounds, regeneration of the laden solvent (extract) by re-extraction (9) with a non-aromatic hydrocarbon which has a lower boiling point than the selective solvent, distillative separation of the aromatic compounds from the non-aromatic re-extractant and removal of residual solvent from he raffinate and the removed aromatic compounds by washing with water (4,16). characterized in that a mixture of N-methyl pyrrolidone and water is used as a selective solvent, an extract consisting of a solvent which contains aromatic compounds is withdrawn from the extracting unit (2), that solvent is mixed with solvent-containing water which is drained from the water washers (4, 16), the mixture is fed to the re-extracting unit (9), the solvent from which the aromatic compounds have been removed and which contains water and re-extractant is withdrawn from the sump of the re-extracting unit and is fed to a distillation unit (19), in which the re-extractant together with water is separated from the solvent, the overhead product from the re-extracting unit, containing re-extractant, aromatic compounds and residual solvent, is fed to a distillation column (12), from which re-extract is withdrawn overhead and is returned to the re-extracting unit, a mixture of aromatic compounds and residual solvent is withdrawn from the sump of the distillation column (12) and is fed to the water washer (16), solvent-containing spent wash water from the water washer is admixed to the mixture that is fed to the re-extracting unit, and aromatic compounds are withdrawn from the water washer (16).

2. A process according to claim 1, characterized in that water is added to the selective solvent after the extraction and before the re-extraction in an amount of 1 to 20 % by weight of the selective solvent.

3. A process according to claim 2, characterized in that water is added in an amount of 5 to 10 % by weight of the selective solvent.

4. A process according to any of claims 1 to 3, characterized in that the low-boiling part of the extract is distilled off after the extraction and before the re-extraction.

5. A process according to any of claims 1 to 4, characterized in that n-hexane is used as a non-aromatic hydrocarbon for re-extraction.

6. A process according to any of claims 1 to 4, characterized in that n-heptane is used as a non-aromatic hydrocarbon for re-extraction.

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