US3317423A - Process for solvent extraction of aromatics from aromatic-paraffinic hydrocarbon mixture - Google Patents

Description

May 2, 1967 H. P. HEBE RT 3,317,423

PROCESS FOR SOLVENT EXTRACTION OF AROMATICS FROM AROMATIC-PARAFFINIC HYDROCARBON MIXTURE Filed Sept. 22, 1964 56 CONDENSER 53 4 PREHEATER I RAFHNATE STRIPPING 64 TOWER v REBOILER z; STEAM O f LEAN 58 RECYCLE ,I8 RAFFINATPE' EXTRACTER FURFURAL OIL IO l2 ALKYL ATE FEED MA E UP 1 2| 72 1 RECYCLE CONDENSER I 42 ALKYLATE 4O I 1 I 3 \HJ '7' n PREHEATER EXTRACT STRIPPING TOWER REBOILER STEAM 28h LEAN 'EXTRACT INVENTOR HUGH P- HEBERT mV ATTORNEY.

hydrocarbons, e.g., heavy United States Patent 3,317,423 PROCESS FOR SOLVENT EXTRACTION OF ARO- MATICS FROM AROMATIC-PARAFFINIC HY- DROCARBON MIXTURE Hugh P. Hebert, Princeton, N.J., assignor to Cities Service Oil Company, a corporation of Delaware Filed Sept. 22, 1964, Ser. No. 398,193

4 Claims. (Cl. 208327) "conducted at temperatures wherein both the raffinate and extract are in a fluid, easily handled liquid phase. The

aromatic hydrocarbons are dissolved by the solvent and separated from the mixture as the rich extract phase from which the aromatics are further separated by distillation and, in a commercial process, the solvent is recirculated to the extractor. The parafiinic and naphthenic hydrocarbons from the raffinate phase which also contain small quantities of the solvent are also generally processed by distillation in a commercial process with the solvent being recirculated to the extractor.

In the extraction of aromatics from relatively heavy gas oil, decant oil, etc., by the above procedure the temperature is often above 140 F. since at lower temperatures the rafiinate is a viscous or semi-solid gelatinous material which is difiicult to handle. When furfural is used as the solvent with the relatively heavy hydrocarbons at the temperatures required to keep the raffinate in a fluid liquid phase, the aromatic extract has low BMCI values. Additionally, separation of the relatively expensive furfural in the extract and in the rafiinate by distillation requires a substantial amount of steam.

It is an object of this invention to provide a process for preparing a carbon black feedstock having a high BMCI from relatively heavy hydrocarbons such as those boiling above 500 F.

It is another object of this invention to provide an economical process for preparing a high quality carbon black feedstock from hydrocarbons boiling above 500 F.

and economically separating the expensive solvent from the extract and raffinate phases by using furfural and a parafiinic hydrocarbon as dual solvents at relatively low extraction temperatures and separating the furfural together with the paraflinic solvent from the rafiinate and extract.

In accordance with a preferred embodiment of this invention, furfural together with certain paratfinic hydrocarbon solvents are employed as dual solvents for the extraction of aromatics from relatively heavy hydrocarbons at extraction temperatures below 140 F. The paraffinic hydrocarbon prevents gelling of the raffinate at these lower temperatures and facilitates extraction at lower temperatures with a consequent higher quality aromatic extract. Also the paraflinic hydrocarbon acts as a chaser for the furfural in distillations of the raftinate and extract phases which facilitates recovery of the furfural. The paraflinic solvent and furfural are separated from each other after the distillation by settling and decantation of the condensate of furfural and parafiinic solvent from the distillation. It should be noted that extraction at the lower temperaturesv produce a higher quality aromatic concentrate irrespective of the parafiinic hydrocarbon. Thus, extraction at 80 F. with furfural and the paraffinic solvent gives a concentrate having a higher BMCI value than such an extraction at F. or 140 F.

Furfural is found to be more selective for the heavy aromatics at the lower temperatures. The paraffinic solvent also serves to strip paraflinic and naphthenic hydrocarbons from the rich extract phase and thus to further increase the quality of the aromatic extract.

The term BMCI as used herein is the abbreviation for the Bureau of Mines Correlation Index which is used to designate the quality and suitability of aromatic concentrates for carbon black production.

The double solvent system of this invention can be used in any suitable extraction system. For instance, the invention may be used in a single stage operation where the furfural, oil and paraflinic solventare thoroughly mixed together and then the resultant two phases allowed to separate in a settling tank and withdrawn separately, or in a continuous extraction system using an extraction column or contactor for counter-current extraction, or a centrifugal extraction unit.

The relatively heavy hydrocarbon feedstock employed in this invention is one boiling above 500 F., preferably above 600 F. and contains significant quantities of aromatic hydrocarbons (usually at least about 20 weight percent) and of paraffinic hydrocarbons (usually at least about 5 weight percent). Illustrative of such feedstocks there can be mentioned: heavy cycle oils, decant oils, virgin and coker heavy gas oils, and deasphalted gas oils. The aniline'nurnber of the feed can be from about 90 to about 180 and preferably from about to 170.

The preferred solvent for aromatics in the process of this invention is furfural. However, other normally liquid organic compounds which preferentially dissolve aromatic hydrocarbons from hydrocarbon mixtures containing the same in admixture with paraffinic or naphthenic hydrocarbons can also be employed. Thus another suitable solvent for the aromatics which can be employed in this invention is phenol.

The preferred solvents for parafiins are paraflinic solvents but other solvents which preferentially dissolve paraffin hydrocarbons from the above feedstock and are immiscible with the selected solvent for aromatics may be used.

Furfural is preferably used in ratios of about 0.1 to 5.0 volumes per volume of the relatively heavy hydrocarbon feedstock, preferably about 0.5 to 2.0 volumes. However. volume ratios beyond these may also be used.

The paraflinic solvent can be any paratfinic hydrocarbon oil within the boiling range of about250 F. to about 400 F. and preferably having a boiling range of about 300 F. to about 375 F. A saturated hydrocarbon such as heavy alkylate obtained from isobutane and propylene or butylene or amylene alkylation is particularly suitable as the parafiinic solvent. The volume of the paraffinic solvent can vary beneath 0.05 and 5.0 volumes per volume of feedstock (oil) and preferably between about 0.1 and 2.0, however, volume ratios beyond these can be employed.

The temperature range in the extractor can be from about 50 F. to 140 F., preferably from about 60 F. to about F. However, for optimum BMCI values it is preferred to use a temperature below 100 F. such as that from about 70 F. to about 95 F. Temperature differentials in the extraction unit can be attained by varying the temperature of the feed streams.

In a continuous extraction column the feed stock is preferably fed near the center, furfural near the rafiinate exit point and alkylate near the extract exit. The feed injection points can be varied to change the quality of the eflluent streams as desired. As mentioned hereinbefore, the extraction unit can also be a single stage mixer settler unit. Mixing in this latter case can be accomplished either with a mixing valve, centrifugal pump or with an impeller.

The accompanying drawing shows a preferred embodiment of the process. The relatively heavy hydrocarbon feedstock, as described hereinbefore, is charged into extraction column 12 through line intermediate the top and bottom of the column and contacted therein under counter-current flow conditions with furfural. The furfural is charged into the upper portion 14 of column 12 through line 18. Extraction column 12 has a suitable arrangement of conventional liquid-extraction equipment, not shown in the drawing, designed to obtain intimate contact between the liquid feedstock and liquid solvent.

A parafiinic solvent as described hereinbefore contacts the rich extract under counter-current fiow conditions in the extractor 12 to displace higher boiling feedstock paraffins from the rich extract stream prior to removal of the rich extract from the extraction column and to lower the viscosity of the rafiin'ate phase. The paraflinc solvent is charged into the process flow through line 20. Provisions are made in lines 18 and 20 for the introduction of furfural and alkylate make up through lines 68 and 21, respectively.

Due to the selective solubility of the aromatic component in the furfural solvent relative to other hydrocarbons in the feed stock, the aromatics tend to transfer into a solvent phase leaving a solvent immiscible hydrocarbon rafiinate phase relatively lean in aromatics and comprising other classes of hydrocarbons such as parafiins present in the feedstock. The relatively dense extract phase gravitates downwardly into the lower portion of column 12 flowing counter-currently against a stream of the paraffinic solvent tending to flow into the upper portion of column 12.

The rich extract phase which tends to flow downwardly through the column due to its relatively greater density in comparison to the hydrocarbon feedstock is withdrawn from the bottom of extraction column 12 through line 16. It is then heated in preheater 22 and transferred through line 24 into extract stripping tower 26. The extract stripping tower, as well as the raifinate stripping tower which will be mentioned hereinafer, can be any of several types of fractionation towers suited for stripping the lower boiling furfural (B.P. 329 F.) and paraflinic solvent (B.P. 250 F. to 400 F.) from the higher boiling hydrocarbon feed (boiling above 500 F.). Extract stripping tower 26 is heated at a temperature suflicient to distill oif the furfural and paraffinic solvent from the aromatics. The preferred paraflinic solvent boils at about the same or slightly higher temperatures (300 F. to 375 F.) than the furfural and acts as a stripping agent for furfural, thus reducing the need for steam stripping. The solvents pass out of stripping tower 26 through the condenser 38 wherein they are cooled and condensed to the liquid phase and subsequently drawn through line 40 into settling tank 42 where the solvents separate into two distinct phases at temperatures of from about 80 F. to about 120 F. The upper phase in separator 42 is the paraifinic solvent and this is drawn off and conducted into .line 20 for recycling into extraction column 12. A portion of such solvent may be recycled to the tower 26 through a line 72. Provision is made for adding paraffinic solvent to line 20 for makeup. The lower phase in the separator 42 is furfural which may be recycled to the extractor 12 via lines 65 and 18. Lean extract comprising the aromatic fraction from the rich solvent phase is removed from stripping tower 26 through lines 28 and 34. A portion of the lean extract is heated in a reboiler 32 and recirculated into the bottom of the extract stripping tower through a line 30 in order to maintain distillation temperature.

The rafiinate from extractor 12 is heated in a preheater 48 and conducted to stripping tower 50 through a line 46. Lean rafiinate is conducted out of the bottom of this tower. A portion of the lean raflinate is heated in a reboiler 62 and recirculated into the lower portion via a line 60 whereas the remainder is passed out of the process through a line 58. The paraifinic solvent and furfural are passed off overhead in the vapor phase from the rafiinate stripping tower 50 through a line 52, through a condenser 53 and into a settling tank 54 where the two liquid solvents separate into a lower furfural phase and an upper paraffinic solvent phase. The parafiinic solvent is drawn oil the top of the settling tank through a line 56 and is fed into recycle alkylate line 20 except for a portion returned to tower 50 through a line 71. The furfural from the bottom of tank 54 is passed through lines 64 and 18 for recycling into the extractor.

The rich solvent phase conducted out of extractor 12 contains minor quantities of paraffinic solvent which is easily separated in the process. The rafiinate phase conducted out of extractor 12 can contain minor quantities of furfural which is also easily separated in the process. The separation of the furfural and parafiinic solvent from both the rich extract and the raffinate phase is performed by distillation wherein the paraffinic solvent aids in the stripping off of the more expensive furf-ural. The paraffinic solvent and furf-ural are then easily separated from each other by settling. The rich extract phase will often contain from about 5% to about 25% of parafiinic solvent by volume but normally from about 8% to about 20% of paraffinic solvent by volume. The rafiinate from the extractor can contain from about 0.5% to about 10% of furfnral by volume and normally from about 1% to about 6% by volume of furfural.

Example I A selective solvent extraction system embodying the preferred arrangement of apparatus described in the accompanying diagrammatic drawing is provided for the extraction of decant oil having a gravity of 14.1" API, an initial boiling point of 605 F., and containing more than 20 weight percent aromatics and more than 5 weight percent parafiins, by the use of furfural and a paraffinic solvent having a boiling range of from about 300 F. to about 375 F. This parafiinic solvent is a heavy alkylate fraction prepared from the alkylation of isobutane and propylene.

Decant oil at a rate of 1,000 barrels per day (b.p.d.) is fed into the midsection of extractor 12 from line 10. Furfural at the rate of 500 b.p.d. is fed into the upper portion of extractor 12 through line 18 whereas alkylate at the rate of 460 b.p.d. is fed into the bottom portion of extractor 12. The extractor 12 is maintained at atmospheric pressure and a temperature of F: Raffinate comprising paraffinic and naphthenic hydrocarbons together with a major portion of alkylate and a minor portion of furfural fed into the extractor is drawn oif the top of the extractor through line 46. The rafiinate in line 46 is conducted into the raffinate stripping tower 50 after the temperature of the rafiinate is raised to 440 F. by 'preheater 48. The upper portion of the rafiinate stripping tower is maintained at a temperature of 275 F. whereas the bottom of this tower is maintained at a temperature of 450 F. Lean rafiinate containing the nonaromatic hydrocarbons of the feed and substantially free of the solvents is withdrawn from rafiinate stripping tower through line 58 and out of the process at a rate of 618.5 b.p.d. The lean raifinate has an API gravity of 29.5 The temperature in the lower portion of the raflinate stripping tower is maintained by recirculating a part of the lean ratfinate through line 60 and heater 62.

The raflinate stripping stripping tower is maintained at 3 (p.s.i.a.) pounds per square inch absolute. The alkylate together with small quantities of furfural is distilled out of tower 50 through line 52, and the vapors are cooled in condenser 53'prior to introduction into settling tank or tower 54 which is maintained at F. The condenser 53 isalso provided with means, not shown in the drawing, for drawing the vacuum maintained in tower 5 50. The alkylate is drawn off the top of settling tank 54 at a rate of 328 b.p.d. through line 56 which joins the re cycle alkylate feed line 20 whereas furfural is drawn off the bottom of tank 54 at a rate of 30 b.p.d. and is passed into furfural recycle line 18.

Extract, comprising aromatics in the decant feed, a major portion of the furfural and a minor portion of the alkylate fed into extractor 12 is withdrawn from the bottom of the extractor through line 16. This rich extract is conducted into extract stripping tower 26 after being heated to 440 F. by preheater 22. Extract stripping tower 26 is maintained at a pressure of 3 p.s.i.a., a temperature of 260 F. at its upper portion and 450 F. at its lower portion. Lean extract of aromatic hydrocarbons substantially free of furfural and alkylate is conducted out of the bottom of tower 26 through line 28. A portion of the lean extract is recirculated into tower 26 after passing through reboiler 32 whereas the remainder of the lean extract is passed out of the process through line 34 at the rate of 381.5 b.p.d. This lean extract has a BMCI of 147 and a specific gravity of 1.1356. Furfural and small quantities of alkylate are distilled off in tower 26 and are conducted through condenser 38 and finally into settler 42 which is maintained at 110 F. The alkylate forms the upper phase in the settling tank or tower 42 and is drawn off at the rate of 132 b.p.d. by line 20. The furfural settles to the bottom of tank 42 and is drawn off at the rate of 470 b.p.d. through line 65 which feeds into furfural recycle conduit 18.

Example II The following Table I shows the effect of temperature and the use of a parafiinic solvent on values of extracts in the processing of the decant oil described in Example I above. The process employed was that of the above Example I except for the variables shown in the table.

TABLE I.YIELD AND BMCI VALUES ON EXTRACTS WITH AND WITHOUT ALKYLATE ADDITION [Decant oil] Temp, Furlural Alkylate BMCI of F. Oil Oil Extract 1 350375 F. Alkylate.

2 301375 F. Alkylate.

400 F. and finally separating the aromatic components from the furfural.

2. A process for producing an aromatic concentrate from hydrocarbon feedstock boiling above 500 F. and containing at least about 20 weight percent aromatic hydrocarbons and at least about 5 weight percent paraffinic hydrocarbons which comprises: (a) counter-currently contacting said feedstock in an extraction zone maintained at a temperature throughout said zone of from about F. to about F. with furfural to extract the aromatic components therefrom, thereby forming a paraffinic rafiinate containing minor quantities of furfural and an aromatic extract containing minor quantities of parafiins from the feedstock; (b) counter-currently contacting said extract in said zone with a substantially saturated parafiinic hydrocarbon solvent having a boiling range of from about 250 F. to about 400 F., thereby stripping additional parafiinic feedstock therefrom and removing a major portion of said parafiinic solvent and thus stripped paraflinic feedstock in admixture with the rafiinate from said zone; (c) removing the aromatic extract together with a major portion of the furfural and a minor portion of the parafiinic solvent from said zone; (d) distilling the withdrawn rafiinate mixture to separate a mixture of parafiinic solvent and furfural therefrom; (e) distilling the withdrawn extract to sepa rate a mixture of furfural and paraffinic solvent therefrom; (f) settling thus separated mixtures of furfural and paraiiinic solvent to form separate phases of furfural and parafiinic solvent; and (g) separately recovering furfural and parafiinic solvent from step (f).

3. The process of claim 2 in which the mixtures formed in steps (d) and (e) are treated by condutcing the distilled parafiini-c solvent and furfural separated from the raflinate phase to a settling zone maintained at a temperature of from about 70 F. to about 95 F. to thereby form in said settling zone an upper parafiin solvent phase and a lower furfural phase, conducting the distilled furfural and parafiin solvent separated from the extract phase to a settling zone maintained at a temperature of from about 70 F. to about 95 F. to thereby form in said zone an upper paraffinic solvent phase and a lower furfural phase, separately drawing off the parafiinic solvent phase from furfural phase in each of said settling zones and returning both the paraflnic solvent and the furfural therefrom to the extraction zone.

4. The process of claim 3 wherein from about 0.1 to 5 volumes of furfural and from about 0.05 to 5 volumes of the paraffinic solvent are employed per volume of hydrocarbon feedstock.

References Cited by the Examiner FOREIGN PATENTS 2/ 1959 Great Britain.

DELBERT E. GANTZ, Primary Examiner. H. LEVINE, C. R. DAVIS, Assistant Examiners.

Claims (1)

1. A PROCESS FOR PRODUCING AN AROMATIC CONCCENTRATE FROM HYDROCARBON FEEDSTOCK BOILING ABOVE 500*F. AND CONTAINING SUGNIFICANT QUANTITIES OF BOTH PARAFFINIC AND AROMATIC CONSTITUENTS WHICH COMPRISES CONTACTING SAID FEEDSTOCK IN A COUNTERCURRENT EXTRACTION ZONE MAINTAINED AT A TEMPERATURE THROUGHOUT SAID ZONE OF FROM ABOUT 70*F. TO ABOUT 95*F. WITH FURFURAL, THEREBY FORMING A PARAFFINIC RAFFINATE AND AN AROMATIC EXTRACT CONTAINING A SMALL AMOUNT OF PARAFFINS, COUNTER-CURRENTLY CONTRACTING SAID EXTRACT IN SAID ZONE WITH A PARAFFINIC HYDROCARBON HAVING A BOILING POINT OF FROM ABOUT 250*F. TO ABOUT 400*F. AND FINALLY SEPARATING THE AROMATIC COMPONENTS FROM THE FURFURAL.

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