US2567172A - Method of refining oil with a solvent - Google Patents

Description

Sept l1, 1951 G. B. ARNOLD ET AL METHOD OF REFINING OIL WITH A SOLVENT Filed Feb. 28, 1948 Nw hmm,

T To ENE V5 Patented Sept. 11,` 1951 METHOD F OIL WITH A VENT George B. Arnold, Glenham, and William E. Skelton, Beacon, N. Y., assignors to The Texas Company, New York, N. Y., a corporation of Delaware Application February 28, 1948, Serial No. 11,988

6 Claims.

This invention relates to a method of refining oil with a solvent liquid which is at least partially miscible with water at ordinary temperatures, and particularly relates to the recovery of the solvent from the oil by azeotropic distillation.

In accordance with the invention, a relatively low boiling feed oil, such as kerosene or gas oil,

is extracted with a selective solvent, such as furfural, under conditions effective to form extract and raflnate phases respectively. The raiinate phase comprises non-aromatic or relatively insoluble constituents of the oil mixed with a small proportion of the solvent, while the extract phase comprises the relatively aromatic and naphthenic constituents oi the oil dissolved in the main body of solvent.

The extract and rafnate phases are separately subjected to distillation in the presence of water vapor and an added quantity of low boiling oil so as to effect separation of solvent from oil. It is contemplated supplying suillcient steam or water. as well-as added oil, to the fractionating zones to form ternary water-oil-solvent azeotropes with all, or substantially all, of the solvent present in the extract and railinate phase mixtures. The added oil has a boiling temperature intermediate the boiling temperatures of the solvent and water. This added oil may be a fraction of the oil produced by the treatment, or may be obtained from an outside source.

The resulting distillates are cooled and condensed and then subjected to settling to form oil-rich, water-rich and solvent-rich liquid layers, respectively. The oil-rich liquid comprising added oil and small amounts oi solvent and water is removed and recycled to the azeotropic distillation zones as will be described with reference to the drawing.

The solvent-rich liquid comprising solvent and a small amount of dissolved water and oil is removed and recycled to the extraction zone. The water-rich liquid comprising water and a small amount of solvent is removed. part being recycled as reux to the fractionating zone, and the remainder subjected to fractional distillation to recover the residual solvent, the recovered solvent being returned to the extraction tower.

The invention is particularly useful in connection with the solvent refining or extraction of hydrocarbon oilsv boiling in thei'same tem-f`v4 perature range as the solvent or higher boiling than the solvent, and where the difference in boiling temperature between the solvent and the lowest honing constituents oi the oil ranges from (Cl. E36-14.48)

several degrees up to about F. 1n other words, the invention is useful in connection withthe treatment of oils wherein 'the difference between the initial true boiling point of the oil and the boiling temperature of the solvent is usually less than about '75 F. Where the difference is substantially greater than this, no particular problem exists in eiecting recovery of the solvent from the oil by conventional distillation methods.

An essential feature of the invention involves the addition to the distillation zone or zones of a substantial quantity of oil boiling between the boiling temperature of water and that of the solvent employed. For example, in the case of extraction with furfural, which boils at about 322 F., it is contemplated adding to the distillation zone or zones oil boiling within the range about 212 to 320 F. Any `petroleum fraction boiling in this range may be used, although a parafnic fraction is preferable since paraiilns appear to azeotrope better than aromatlcs. Hydrocarbons such as hexane, heptane, octane and the like, or mixtures thereof may be used 'as the added substance. The purpose of this added oil is to form an azeotrope of increased oil content and decreased water content, so that the distillation of the azeotrope from the feed mixture can be effected with greater economy in heat requirements. I

It has been observed that the ternary azeotrope obtained by distilling, in the presence of steam, the raffinate phase resulting from furi'ural extraction of a gas oil having an initial A. S. T. M. boiling point of about 458 F. will contain approximately 12% oil, 21% solvent, and 67% Water. On the other hand, the ternary azeotrope obtained by steam distillation of the raiiinate phase produced by furfural extraction of kerosene having an initial A. S. T. M. boiling point of about 322 F. contains approximately 33% oil, 21% solvent, and 46% water by volume. It will be understood, of course, that the true boiling point of hydrocarbon mixture is usually' about to 100 F. lower than the A. S. T. M. value.

Thus, it is seen that when the A. S. T. M. inltial yboilinglipoint of the oil is about 136 higher than qthe solvent, theternary azeotrope contains a much larger proportion of water thanwhere the A. S. T.' M. initialboiling point is only af "few l.degrees higher than the solvent boiling temperature.

In order to illustrate the invention in more detail, reference will now be made to the accompanying drawing comprising a flow diagram of the process as applied to the treatment of a cycle gas oil produced in the catalytic cracking of mineral oil and having an A. S. T. M. boiling range as follows:

I B. P. 458 5% 484 494 5% 530 End Point 622 through a pipe 4. The solvent comprises furfural and minor amounts of water and oil as a result of previous use in the process. It may contain about 15% oil and 3% water by volume. The solvent is introduced to the tower in the proportion of about one volume to two volumes of feed oil. The temperatures of the entering streams of oil and solvent are regulated, so that the temperature at the bottom of the tower is maintained at about 100 F. while the temperature at the top is maintained at about 150 F.

Under these conditions, extract and raiflnate phases are formed. The raiilnate phase comprises ol amounting to from about 60 to 80% by volume of the feed oil. The raiiinate phase is continuously removed from the upper portion of the tower through a pipe 5 and heat exchanger Ii to a fractionator 1. A parafiimic hydrocarbon, or a fraction of the railinate oil boiling below 300 F. is injected in the rafllnate phase stream from a pipe I 4 to which reference will be made later.

Heat may be supplied to the bottom of the fractionator either with open steam, a closed heating coil, or a combination of both. As will be mentioned later, provision is made for supplying reflux liquid to the top of the tower. Suflicient water is introduced to the tower either in the form of steam or water reflux or both to form the ternary-water-oil furfural azeotrope with all of the furfural present in the raffinate phase feed. The top of this tower is maintained at a temperature of about 205 to 250 F., and the bottom at a temperature of about 250 to 400 F. so that the solvent is completely, or substantially completely, distilled from the raiiinate oil. the solvent-free oil being discharged through a pipe 8.

The distillate comprising solvent, water and oil is removed through pipe 9 into a condenser I0 and then to a settling chamber II. The settler is maintained at a temperature of about '70 to 150 F.. and the condensate separates into oilrich, water-rich and solvent-rich liquid layers, respectively. These layers have the following approximate composition:

The oil-rich liquid layer amounting to about 35% of the mixture passing into the settler is continuously drawn off through a pipe I2, branch `vipes I3 and I4 through which it is conducted to pipe 5 for injection into fresh railinate phase 4 owing into the fractionator 1. This oil-rich phase is injected into the rafiinate phase in the proportion of about rs to l/2 volumes per volume of rafiinate phase. This injected oil comprises the added oil added to the railinate phase mixture for the purpose of obtaining a ternary azeotrope of decreased water content. This added oil may be added initially to the system from a source not shown through pipe I5, and any makeup required to compensate for losses during operation may be added through pipe I5.

The solvent-rich liquid is continuously drawn off from the settler I I through pipe 20 and returned to\ the upper portion of the extraction tower 3. Make-up solvent may be added from an outside source through pipe 2I.

Water-rich liquid is drawn off through pipe 25. and at least a portion thereof diverted through pipe 26 for recycling to the top of the fractionator 1 as refiux liquid. The non-recycled portion is drawn oi through pipe 21 to pipe 28 through which it is conducted to a fractionator 29 for the purpose of stripping residual solvent therefrom. The resulting distillate is conducted through pipe 3|, condenser 32 to settler 33 wherein separation into water and solvent layers occurs. The water layer is recycled to the fractionator, and the solvent layer is drawn off through pipe 35 for return to the extraction tower 3.

The extract phase is drawn off from the bottom of the lower 3 through pipe 40 to a fractionator 42 similar to fractionator 1. Added oil similar to that obtained through pipe I5, or a fraction of the extract oil product boiling below 300 F. may be injected from pipe I5A into the extract phase in the proportion of about l to 3 volumes per volume of extract phase.l The fractionator 42 is also provided with means for supplying heat to the bottom thereof either in the form of open steam or a closed heating coil or both, provision being made also for the introduction of reflux liquid. Water is injected into the fractionator to form a ternary furfuraloil-water-azeotrope with a minor portion of the extract oil. This azeotrope is thus removed as a distillate through pipe 43 and condenser 44 to a settling chamber 45 wherein it separates into oilrich, water-rich and solvent-rich liquid layers, respectively, each having a composition of approximately the same as those formed in the settler II. The oil-rich liquid containing added oil is drawn off through pipe 46, pipe 41 and pipe 48 through which it is injected into the stream of extract phase entering the fractionator 42.

The solvent-rich liquid is drawn oil from the settler through pipe 50 and returned through pipe 5I to the extraction tower 3.

The water-rich liquid is drawn oil' from the settler 45 through pipe 53 and diverted in part through pipe 54 as reflux to the fractionator 42. The remainder of this liquid is conducted to pipe 28' for treatment in the fractionator 29.

As indicated in the drawing, provision is made for conducting oil-rich liquid from either settler II or settler 45 to either of the fractionators 1 and 42. Thus, oil-rich liquid from pipe I2 can i be diverted through pipe I2A communicating with pipe 48. On the other hand, oil-rich liquid from pipe 41 can be diverted through pipe 41A for passage to the fractionator 1. This arrangement is feasible where the low boiling oils used in both fractionators 1 and 42 are of the same physical character; otherwise, added oils of dif-A ferent character may be used for azeotrope for-l mation in each tower. Provision may alsobo made for discharging oil-rich liquid from each settler.

The raiiinate oil discharged through pipe l will amount to about 60-70% of the feed oil entering through pipe I and will have the following characteristics:

,The extract oil discharged from the fractionator 42 through pipe 60 will amount to about {t0-40% of the feed oil and will have the following characteristics: l

'A'. P. I. Gravity 11.9 A. S. T. M. Distllatz'on v Degrees F. I. B. P 450 515 50% 542 90% 614 End Point 658 While the treatment of gas oil has been specifically referred to, nevertheless, the process is applicable to the treatment of other types of oil and also to the treatment of kerosene, the lowest boiling constituents of which may have a. true boiling point approximating or higher than that of the solvent used. In general, the invention has application to the treatment of hydrocarbon mixtures having an A. S. T. M. initial boiling temperature within the range about 350 to 500 F. and having an end boiling point ranging from about 400 to 650 F. It is contemplated that the invention has application to the treatment of oils derived from animal and vegetable sources. Specific conditions of temperature and solvent dosage may vary from those specifically mentioned, depending upon the character of the feed oil undergoing treatment and the degree of fractional separation desired.

The invention is particularly concerned with the use of relatively high boiling organic solvent liquids which are miscible, at least to some extent, with water, and with which constituents of the'oil feed in the presence of water form azeotropes. may be used. They may include other derivaamarga obtained from said extracting zone, a substantial Selective solvents other than furfural f tives of the furan group and other aldehydes such ture of the solvent being less than about 75 F.

and wherein the feed oil is subjected to contact in an extraction zone with a water-miscible organic solvent liquid, extract and railinate 7 phases are formed, said phases separately removed from the extraction zone. each of said quantity of added oil boiling intermediate the boiling temperature of water and the solvent and capable of ternary azeotrope formation therewith, passing the resulting mixture into a steam distillation column, effecting distillation thereof in the presence of steam, the amounts of steam and added oil being suillcient to form ternary water-oil-solvent azeotropes with substantially all of the solvent present in the removed phase passing to the steam distillation column',l removing resulting ternary azeotropes as a distillate from said distillation column, said distillate containing substantially less water than when the distillation is effected in the absence of said added oil, separately removing from the distillation zone a residual liquid of product oil substantially completely free from solvent, discharging said residual liquid, subjecting said distillate to condensation, subjecting the resulting condensate to settling in a settling zone at a temperature in the range about to 150 F.. forming in said settling zone ollrich, water-rich and solvent-rich layers, respectively, withdrawing liquid from each of said layers,'recycling withdrawn water-rich liquid as reflux to the upper portion of said column and recycling withdrawn oil-rich liquid to the lower portion of said distillation column to re-supply said added oil. y

' 2. The method according to claim 1 in which the feed oil to the extraction zone is a hydrocarbon oil boiling -in the range about 350 to 650 F.

3.A In the solvent rening of kerosene and light gas oil, the difference between the initial true boiling point of the oil and the boiling temperature of the solvent being less than about F. and wherein thefeed oil is subjected to contact extraction zone with a. water miscible organic solvent liquid, extract and raiiinate phases are formed, said phases separately removed from the extraction zone, each of said phases comprising oil and solvent, and the removed phases separately treated to remove solvent from the oil for reuse in the extraction zone, the method of treating said removed phases comprising passing a removed phase as obtained from said extraction zone to the lower portion of a distilling column, introducing steam and an added oil boiling intermediate the boiling 'temperatures of water and said solvent and capable of ternary azeotropic formation therewith to the lower portion of said column in amounts suilicient to form ternary water-oil-solvent azeotropes with substantially all of the solvent present in the removed phase entering said column, removing resulting ternary azeotropesv as a distillate from said column, said distillate containing substantially less water than when the distillation is eifectedin the absence of said added oil, separately removing from the column a residual liquid of product oil substantially completely lfree from solvent, discharging said residual `liquid. subjecting said distillate to condensation, subjectingthe resulting condensate to settling in a settling zone at a temperature in the range about 70 to 150 F., forming in said settling zone oil-rich, water-rich and solvent-rich liquid layers, respectively, withdrawing liquid from each of said layers, recycling withdrawn water-rich liquid as reilux to the upper portion of said column, and recycling withdrawn oil-rich liquid to the lower portionl of said column to supply said added oil.

4. In the solvent refining of kerosene and light gas oil with furfural in an extraction zone thereby forming extract and railinate phase mixtures,

respectively, the method of treating said phases after separate removal from the extraction zone comprising passing a removed phase to a distillation column, introducing steam and an added oil boiling intermediate the boiling temperatures of water and furfural andcapable of ternary azeotrope formation therewith to the lower portion of said column in amounts suflicient to form ternary water-oil-solvent azeotropes with substantially all of the solvent present in the phase mixture passing to said column from the extraction zone, removing resulting ternary azeotropes as a distillate from said column, said distillate containing substantially less water than when the distillation is effected in the absence oi' said added oil, separately removing from the distillation column a residual liquid of product oil substantially completely free from solvent, discharging said residual liquid, subjecting said distillate to condensation, subjecting the resulting condensate to settling in a settling zone at a temperature in the range about 70 to 150 F., forming in said settling zone 011-. rich, water-rich and solvent-rich layers, respec-l tively, withdrawing liquid from each of said layers. recycling Withdrawn water-rich'liquid 'as reflux to the upper portion of said column, and recycling withdrawn oil-rich liquid to the lower portion of said column to supply said added oil. 5. The method according to claim 3 in which the feed oil-to the extraction zone is a hydroi-I gbolrvi oil boiling in the range about 350 to 6. The method according to claim 3 in which the added oil boils in the range of about 212 to 320 F.

GEORGE B. ARNOLD. WILLIAM E. SKELTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,139,240 McFarland Dec. 6, 1938' 2,154,189 Weir Apr. 11, 1939 2,154,372 Bosing Apr. 11, 1939 2,168,570 Kraft Aug. 8, 1939 2,216,933 Atkins Oct. 8, 1940 2,381,996 Bloomer Aug. 14, 1945 2,465,959 Tindall Mar. 29, 1949 2,475,147 Manley July 5, 1949

Claims (1)

1. IN THE SOLVENT REFINING OF KEROSENE AND LIGHT GAS OIL, THE DIFFERENCE BETWEEN THE INITIAL TRUE BOILING POINT OF THE OIL AND THE BOILING TEMPERATURE OF THE SOLVENT BEING LESS THAN ABOUT 75* F. AND WHEREIN THE FEED OIL IS SUBJECTED TO CONTACT IN AN EXTRACTION ZONE WITH A WATER-MISCIBLE ORGANIC SOLVENT LIQUID, EXTRACT AND RAFFINATE PHASES ARE FORMED, SAID PHASES SEPARATELY REMOVED FROM THE EXTRACTION ZONE, EACH OF SAID PHASE COMPRISING OIL AND SOLVENT AND THE REMOVED PHASE SEPARATELY TREATED TO RECOVER SOLVENT FROM THE OIL FOR RE-USE IN THE EXTRACTION ZONE, THE METHOD OF TREATING SAID REMOVED PHASES COMPRISING COMMINGLING WITH A REMOVED PHASE AS OBTAINED FROM SAID EXTRACTING ZONE, A SUBSTANTIAL QUANTITY OF ADDED OIL BOILING INTERMEDIATE THE BOILING TEMPERATURE OF WATER AND THE SOLVENT AND CAPABLE OF TERNARY AZEOTROPE FORMATION THEREWITH, PASSING THE RESULTING MIXTURE INTO A STEAM DISTILLATION COLUMN, EFFECTING DISTILLATION THEREOF IN THE PRESENCE OF STEAM, THE AMOUNTS OF STEAM AND ADDED OIL BEING SUFFICIENT TO FORM TERNARY WATER-OIL-SOLVENT AZEOTROPES WITH SUBSTANTIALLY ALL OF THE SOLVENT PRESENT IN THE REMOVED PHASE PASSING TO THE STEAM DISTILLATION COLUMN, REMOVING RESULTING TERNARY AZEOTROPES AS A DISTILLATE FROM SAID DISTILLATION COLUMN, SAID DISTILLATE CONTAINING SUBSTANTIALLY LESS WATER THAN WHEN THE DISTILLATION IS EFFECTED IN THE ABSENCE OF SAID ADDED OIL, SEPARATELY REMOVING FROM THE DISTILLATION ZONE A RESIDUAL LIQUID OF PRODUCT OIL SUBSTANTIALLY COMPLETELY FREE FROM SOLVENT, DISCHARGING SAID RESIDUAL LIQUID, SUBJECTING SAID DISTILLATE TO CONDENSATION, SUBJECTING THE RESULTING CONDENSATE TO SETTLING IN A SETTLING ZONE AT A TEMPERATURE IN THE RANGE ABOUT 70 TO 150* F., FORMING IN SAID SETTLING ZONE OILRICH, WATER-RICH AND SOLVENT-RICH LAYERS, RESPECTIVELY, WITHDRAWING LIQUID FROM EACH OF SAID LAYERS, RECYCLING WITHDRAWN WATER-RICH LIQUID AS REFLUX TO THE UPPER PORTION OF SAID COLUMN AND RECYCLING WITHDRAWN OIL-RICH LIQUID TO THE LOWER PORTION OF SAID DISTILLATION COLUMN TO RE-SUPPLY SAID ADDED OIL.

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