US2754342A - Aromatic hydrocarbon separation process - Google Patents

Description

July 10, 1956 R. o. sHELToN AROMATIC HYDROCARBON SEPARATION PROCESS Filed NOV. 5, 1951 ATTORNEYS Unted rates Patent AROMATIC HYDROCARBON SEPARATION PRCESS Russell 0. Shelton, Bartlesville, Okla., assigner to Phillips Petroleum Company, a corporation of Delaware Application November 5, 1951, Serial No. 254,915

7 Claims. (Cl. 260-674) This invention relates to improvements in the separation of aromatic hydrocarbons from a petroleum fraction and to the recovery or" substantially pure aromatic hydrocarbons from admixtures with non-aromatic hydrocarbons. In one of its aspects this invention relates to a method employing solvent extraction for the recovery of an aromatic hydrocarbon concentrate from a cracked gasoline containing aromatic hydrocarbons and olenic hydrocarbons. In still another of its aspects this invention is directed to a method for the recovery of an aromatic concentrate suitable for use as a blending stock by solvent extraction of a cracked gasoline, such as a catalytically cracked gasoline, containing substantial amounts of aromatic and olenic hydrocarbons. In still another of its aspects this invention relates to the solvent extraction of a cracked gasoline containing substantial amounts of oleinic and aromatic hydrocarbons with a liquid selective solvent for aromatic hydrocarbons.

In the production of gasoline or other low boiling hydrocarbons from crude oil or from a suitable cracking stock there is produced in admixture With parafiinic, eletinic and naphthenic hydrocarbons substantial amounts of aromatic hydrocarbons. By fractional distillation the aromatic hydrocarbon content can be increased up to about 50 per cent or more depending upon the composition of the petroleum fraction being separated. Furthur concentration by distillation to produce a substantially pure aromatic fraction is often impractical and for this reason further concentration of the aromatic hydrocarbons is usually accomplished by selective solvent extraction or by extractive distillation, employing in each instance a liquid selective solvent for the aromatic hydrocarbons. In a selective solvent extraction operation for the recovery of aromatic hydrocarbons it has been found that the presence of substantial amounts i. e. above about 50 per cent by volume total aromatic and olenic hydrocarbons cause the hydrocarbon fraction being treated to be miscible with the selective solvent, or at least to hinder phase separation. In order to obtain phase separation in such a selective solvent extraction operation a low temperature must frequently be employed.

In accordance with the present invention a petroleum fraction containing aromatic hydrocarbons and olelinic hydrocarbons is subjected to solvent extraction with a liquid selective solvent for aromatic hydrocarbons in the presence of a relatively high boiling petroleum fraction. In my invention I extract a light cracked gasoline containing oletinic and aromatic hydrocarbons With a liquid selective solvent for aromatic hydrocarbons, such as sulfur dioxide, furfural, nitrobenzene, phenols and the like, in the presence of a high boiling petroleum fraction, such as a gas-oil, which is suitable for use as a cracking stock for the production of the aforementioned light cracked gasoline. The addition of a high boiling petroleum fraction to the solvent extraction operation promotes phase separation in that it reduces the miscibility of the selective solvent in the particular petroleum fraction being treated for the recovery of an aromatic concentrate. The pres- Patented July l0, 1956 ent invention Will be better understood by referring to the accompanying drawing which is a ilow plan schematically illustrating a preferred embodiment of my invention.

Referring now to the drawing numeral 11 designates a feed line through which a light cracked gasoline boiling in the range -475 F. and containing olenic and aromatic hydrocarbons is introduced into extractor 12. Extractor 12 may be any type of suitable contacting device for a liquid-liquid solvent extraction operation and may comprise a combination of mixer-settler or a continuous contacting column. Into one end of extraction zone 12 is introduced via line 1 a liquid selective solvent for aromatic hydrocarbons such as sulfur dioxide. Into the other end of the extraction zone 12 a suitable high boiling petroleum fraction such as a gas oil boiling in the range S50-950 F. and suitable for use as a cracking stock and preferably low in aromatic hydrocarbons, usually below about l0 per cent by volume, is introduced via line 14. The solvent extraction operation carried out within extraction zone 12 may be concurrently or countercurrently. As shown in the accompanying drawing a countercurrent solvent extraction operation is being carried out. From one end of extraction zone 12 a raftinate phase is Withdrawn via line 16 and from the other end of extraction zone 12 an extract phase is withdrawn via line 18. Line 16 leads to a suitable separating or fractionating device such as flash tank 19 wherein sulfur dioxide is ashed and removed via line 2l). From the bottom of ilash tank 19 is removed via line 21 the remaining ratnate phase, now substantially free of sulfur dioxide, which is then passed to ranate fractionator 22, Within ralinate ractionator 22 the rainate phase is subjected to fractional distillation and a rainate product is removed overhead via line 23. From the bottom of fractionator 22 is removed via line 24 a bottoms fraction consisting substantially of the higher boiling petroleum fraction which was introduced into extraction zone 12 via line 14.

The extract phase removed from extraction zone 12 via line 18 is passed into a suitable separating or fractionating device such as ash tank 26. Sulfur dioxide is removed via line 28 by flashing. From the bottom of flash tank 26 is recovered via line 29 the remaining extract phase which is then passed into extract fractionator 30. An extract product is recovered overhead from fractionator 30 via line 31. The extract recovered via line 31 is an aromatic hydrocarbon concentrate and is substantially enriched with respect to aromatic hydrocarbons over the aromatic hydrocarbon content found in the feed which was introduced into extractor 12 via line 11. From the bottom of fractionator 30 is removed via line 32 the remaining portion of the high boiling petroleum fraction introduced into extractor 12 via line 14. The portions of the high boiling petroleum fraction in line 32 and 24 are admixed in line 33 and then introduced into a cracking zone 34. Cracking zone 34 may be any suitable cracking zone either catalytic or noncatalytic, if catalytic, either a fixed, moving or iiuidized bed catalytic cracking zone. Associated with cracking Zone 34 are various separation zones and equipment, not shown, such as fractionators, extractors, etc. The heavy products from the cracking Zone 34 and its accompanying separation zones are removed via line 36 and a light cracked gasoline fraction is removed via line 11 to feed extractor 12.

One advantage of operating in accordance with the present invention is that the high boiling petroleum fraction used as a stripping medium with extractor 12 and recovered later on can be used as a cracking stock. This is particularly desirable since impurities tend to build up in the stripping medium if the stripping medium were to be recycled within the process. According to my invention however, the recovered stripping medium or higher boiling petroleum fraction is passed directly to a cracking operation wherein any impurities or undesirable constituents such as sulfur compounds which may have been picked up during the solvent extraction step are destroyed or cifectively removed.

In a typical operation in accordance with the present invention a petroleum fraction such as a light cracked gasoline having Ya boiling range ofY 114 F.-430 F. and containing about 30 per cent by volume paraflins, 5l per cent by volume olenic hydrocarbons, 8 per cent by volume naphthenic hydrocarbons and 11 per cent by volume aromatic hydrocarbons is solvent extracted with liquid sulfur dioxide. Sulfur dioxide is supplied at a rate of 4.88 (about pounds per pound of gasoline feed. The higher boiling petroleum fraction such as a gas oil having a boiling range within 600 F.900 F. and which is suitable for use as a cracking stock in a catalytic or non-catalytic cracking operation, is introduced as a stripping oilY at the bottom of the extractor at the rate of 1.11 (about l) pound per pound of gasoline feed. This higher boiling petroleum fraction is preferably low in aromatic hydrocarbon content, preferably less than per cent by volume since aromatic hydrocarbons are undesirable in a catalytic cracking stock. The temperature in the extractor may be in the range 0-70 F., preferably between -30 F. The pressure within the extractor may range from 30-70 p. s. i. g., preferably about 40 p. s. i. g. but sulcient to maintain the sulfur dioxide in the liquid phase. The raiiinate phase removed from the extractor comprises 0.48 pound sulfur dioxide, 0.98 pound stripping oil and 0.63 pound of hydrocarbons in the gasoline boiling range, all on the basis of 1 pound of gasoline feed. One or more stages of ashing may be employed to separate the SO2 from the hydrocarbons, or the separation may be made more completely by fractionation. The remaining hydrocarbons after SO2 removal are then fractionated to separate a rainate product from the stripping oil. The rainate product has a boiling range between 128 F. and 438 F. and comprises 36 per cent by volume parainic hydrocarbons, 44 per cent by Volume olenic hydrocarbons, 16 per cent by volume naphthenic hydrocarbons and 4 per cent by volume aromatic hydrocarbons. The extract phase removed from the extractor contains 4.40 pounds of sulfur dioxide, 0.13 pound of stripping oil and 0.37 pound of gasoline hydrocarbons, per pound of feed. After sulfur dioxide removal from the extract phase the light hydrocarbons are separated from the stripping oil by fractionation. An extract product is recovered having a boiling range within 130 F. and 425 F. and contains 6 per cent by volume parainic hydrocarbons, 57 per cent by .volume olenic hydrocarbons, 8. per cent by volume naphthenic hydrocarbons and 29 per cent by volume aromatic hydrocarbons. The stripping oil streams recovered from the railinate and extract phases are then combined and employed as feed in the cracking operation for the production of additional feed.

The data set forth in the foregoing operation were obtained without the use of an enriching section in the extractor, the feed and sulfur dioxide merely being mixed and introduced into the stripping section. With the use of an enriching section the aromatic hydrocarbon content of the rainate would have been reduced considerably and the concentration of aromatic hydrocarbons in the extract would have been increased.

The petroleum fraction which is advantageously solvent extracted in accordance with the process of this invention to produce an aromatic concentrate is preferably a gasolinev boiling range hydrocarbon material such as a cracked gasolinehaving a boiling range within 100 F. and 475 F. The process of this invention is particularly applicableto. cracked gasoline which contains substantial amounts of aromatic and olenic hydrocarbons, especially whereinv the total aromatic hydrocarbons and olenic hydrocarto obtain without resorting toy rather low temperatures and other extreme undesirable conditions. The process of this invention is particularly applicable to the treatment of a cracked gasoline fraction with which at a temperap ture within the range 0-770 F., especially above 20 F.

phase separation between a selective solvent for aromatic hydrocarbons (such as SO2) and said cracked gasoline fraction is not obtainable.

The higher boiling petroleum fraction which is used as a stripping liquid in accordance with the process of my invention is preferably a gas oil having a boiling range within 550 F. and 950 F. This higher boiling fraction is preferably substantially free of aromatic hydrocarbons and is preferably suitable for use as a cracking stock either in a catalytic or non-catalytic cracking operation.

As will be evident to those skilled in the art upon read-- ing this disclosure many substitutions, moditications and operational changes may be made without departing from the spirit or scope of this disclosure and invention.

claim:

1. A process for the production of an aromatic hydrocarbon concentrate from a light cracked gasoline containing above about 50 per cent by volume olefinic hydrocarbons and aromatic hydrocarbons which comprises solvent extracting in an extraction zone and light cracked gasoline with a selective solvent for aromatic hydrocarbons; introducing into said extraction zone a higher boiling petroleum fraction substantially free of aromatic hydrocarbons and having a boiling point range within 550 F. and 950 F.; extract phase and a raffinate phase; removing said selective Solvent and said higher boiling petroleum fraction from said extract phase to yield an extract substantially enriched with respect to aromatic hydrocarbons; subjecting the resulting removed higher boiling petroleum fraction to cracking in a cracking zone and recovering therefrom a light cracked gasoline containing olenic hydrocarbons and aromatic hydrocarbons.

2. A process for the production of an aromatic hydrocarbon concentrate from a light cracked gasoline having a boiling point range within F. and 475 F. and wherein the aromatic hydrocarbon-olefinic hydrocarbon content amounts to at least about 50% by volume which comprises solvent extracting said light crackedV gasoline at a temperature in the range 0-70 F. with liquid sulfur dioxide in the presence of a gas oil having a boiling point range within 550 F. and 950 F. and containing less than 10 per cent by volume aromatic hydrocarbons; separately recovering anextract phase and a raffinate phase; removing sulfur dioxide and said gas oil from said extract phase to yield an extract substantially enriched with respect to aromatic hydrocarbons; subjecting the resulting removed gas oil to cracking in a cracking zone and recovering therefrom a light cracked gasoline containingV oleiinic hydrocarbons and aromatic hydrocarbons.

3. A process for the production of an aromatic hydrocarbon concentrate from a light cracked gasoline containing above about 50 per cent by volume oleiinic hydrocarbons and aromatic hydrocarbons which comprises solvent extractingl said light cracked gasoline with a selective solvent for aromatic hydrocarbons in the presence or" a higher boiling petroleum fraction containing less than l() per centr by volume aromatic hydrocarbon and having a boilingpoint range within 550 F'. and 950 F.; separately recovering an extract phase and a rainate phase; removing said selective solvent and said higher separately recovering an boiling petroleum fraction from said extract phase to yield-an extract substantially enriched with respect to aromatic hydrocarbons; subjecting the resulting removed higher boiling petroleum fraction to cracking in a cracking zone; recovering therefrom a light cracked gasoline containing olenic hydrocarbons and aromatic hydrocarbons and recyclinfy at least a portion of the recovered light cracked gasoline to the aforesaid solvent extraction Step.

4. A process in accordance with claim 2 wherein gas oil is removed from said raiinate phase subjected to cracking in said cracking zone along with the gas oil removed from said extract phase.

5. A process for the production of an aromatic concentrate from a light cracked gasoline containing above about 50 per cent by volume oleiinic hydrocarbons and aromatic hydrocarbons which comprises solvent extracting said light cracked gasoline with a selective solvent for aromatic hydrocarbons in the presence of a higher boiling petroleum fraction having a boiling range Within 550 F. and 950 F. and containing less than 10 per cent by volume aromatic hydrocarbons; separately recovering an extract phase and a raffinate phase; removing said selective solvent and said higher boiling petroleum fraction from said extract phase to yield an extract substantially enriched with respect to aromatic hydrocarbons; removing said selective solvent and said higher boiling petro leum fraction from said raffinate phase; subjecting the higher boiling petroleum fraction removed from said extract and ranate phases to cracking in a cracking zone; and recovering from said cracking zone a light cracked gasoline containing olelinic hydrocarbons and aromatic hydrocarbons.

6. A process in accordance With claim 5 wherein at least a portion of the recovered light cracked gasoline is recycled to the solvent extraction step.

7. A process for the production of an aromatic hydrocarbon concentrate from a light cracked gasoline containing above about per cent by volume olenic hydrocarbons and aromatic hydrocarbons which comprises solvent extracting in an extraction zone said light cracked gasoline with a selective solvent for aromatic hydrocarbons; introducing into said extraction zone a higher boiling petroleum fraction containing less than 10 per cent by volume aromatic hydrocarbons and having a boiling point in the range of 550 F. to 950 F.; separutely recovering an extract phase and a rafnate phase; removing said selective solvent and said higher boiling petroleum fraction from said extract phase to yield an extract substantially enriched with respect to aromatic hydrocarbons; subjecting the resulting removed higher boiling petroleum fraction to cracking in a cracking zone and recovering therefrom a light cracked gasoline containing olefinic hydrocarbons and aromatic hydrocarbons.

References Cited in the lile of this patent UNITED STATES PATENTS 2,064,842 Lowry et a1. Dec. 22, 1936 2,366,570 Souders et al. Jan. 2, 1945 2,379,334 Atwell lune 26, 1945 2,380,853 Linn et al July 3l, 1945 2,410,166 Kimball Oct. 29, 1946 OTHER REFERENCES Francis: industrial and Eng. Chem., vol. 36, pages 764-771 (August, 1944; 8 pages).

Francis: Industrial and Eng. Chem., vol. 36, pages 1096-1104 ,December 1944; 9 pages).

Sachanen: Chemical Constituents of Petroleum (1945), page 201, Reinhold, N. Y., publishers.

Claims (1)

1. A PROCESS FOR THE PRODUCTION OF AN AROMATIC HYDROCARBON CONCENTRATE FROM A LIGHT CRACKED GASOLINE CONTAINING ABOVE ABOUT 50 PER CENT BY VOLUME OLEFINIC HYDROCARBONS AND AROMATIC HYDROCARBONS WHICH COMPRISES SOLVENT EXTRACTING IN AN EXTRACTION ZONE AND LIGHT CRACKED GASOLINE WITH A SELECTIVE SOLVENT FOR AROMATIC HYDROCARBONS; INTRODUCING INTO SAID EXTRACTION ZONE A HIGHER BOILING PETROLEUM FRACTION SUBSTANTIALLY FREE OF AROAMTIC HYDROCARBONS AND HAVING A BOILING POINT RANGE WITHIN 550* F. AND 950* F.; SEPARATELY RECOVERING AN EXTRACT PHASE AND A RAFFINATE PHASE; REMOVING SAID SELECTIVE SOLVENT AND SAID HIGHER BOILING PETROLEUM FRACTION FROM SAID EXTRACT PHASE TO YIELD AN EXTRACT SUBSTANTIALLY ENRICHED WITH RESPECT TO AROMATIC HYDROCARBONS; SUBJECTING THE RESULTING REMOVED HIGHER BOILING PETROLEUM FRACTION TO CRACKING IN A CRACKING ZONE AND RECOVERING THEREFROM A LIGHT CRACKED GASOLINE CONTAINING OLEFINIC HYDROCARBONS AND AROMATIC HYDROCARBONS.

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