US2593931A - Method of recovering selective solvents - Google Patents

Description

April 22, 1952 w. v. sTEARNS METHOD OF RECOVERING SELECTIVE SOLVENTS Filed Deo. 51, 1947 d.INVENTOR WALTER v. STEARNs ETT/.5? g' ATTORNEYS Patented Apr. 22, 1952 METHD F RECOVEEING SELECTV SOLVENTS Walter V. Stearns, White Piains, N. Y., assigner to TheM. W. Kellogg Co., -Iersey CitygN. J'.,.a

corporation of Delaware Application December 31, 1947, Serial No. 795,961

(Cl. EQ2-42) 9 Claims. l

This invention relates in general to the art of solvent fractionation of oils and more particularly to an improved process for separating the solvent from an oil fraction and from an antisolvent such as water. The invention is particularly concerned with the treatmentof petroleum oils, for example, petroleum oils boiling above the naphtha, kerosene, and gas oil ranges. The process of the present invention provides for separating the feed oil into atleast two fractions, an extract phase. of highlyl aromatic character and a raffinate phase containing oils more parafflnic than the original charge.

It is well known in the art to treat mineral oils, particularlyI petroleum. lubricating` oils, with solventswhich have theV ability to segregate the relatively more aromatic fractions from the relatively more parafflnic fractions. In these processesit is usual to employ solvent which have a preferential selectivity for the more aromatic type compounds, as for example, solvents of the class of phenol, cresol, aniline, nitro benzene, beta beta dichlor diethyl4 ether, furfuraL-and the like. Solvent mixtures offthe'se substances are employed` as well known mixtures containing materials of the class of liquefied normally gaseous hydrocarbons'. Solvent modifyingag'ents of the class of water,` alcohols and glycols, referredlto herein as'anti'so1vents are also used.

`In these processes it is the usual procedure to introduce theoil,. as for example `the. lubricating oil, into the bottom' of a solvent treatingl tower, since. it is usually lighter than` the solvent, and to introduce the solvent into. the top of the. tower. TheA oil being the lighter phase ows upwardly through the tower, intimately contacting the downlowing solvent; A` raffinate phase completely saturated with solvent is removed from thei upper part of theA tower and a solvent extract phase is` removed' from thelower part of the tower. It is, of course, desirable to'secure a rafiinate and extractA phaseA having as high a concentration as possible ofv the paraflinic materials: and aromatic materials respectively. It is, therefore, necessary to employv a solvent of suitable selectivity'. The` most commonly used solvent, phenol. does not have satisfactory selective characteristics unless. its solvent power is reduced by the addition of a suitable diluent, or anti-solvent such as water. The present inventionis concerned with an improved process for separating the extract phase Withdrawn from a solvent extraction step like that described above into itscomponents-of extract, solvent, andantisolvent. The protestof my invention isV a` distinct improvement over theV known processeslin'.

the art in that it isV possible to accomplish the fractionation process with about per cent less? solvent and an antif-solv'ent having a boilingpoint lower than that" of the extractmust be separated therefrom by evaporation. The system of' ein-` ploying furfura'l and water is an example. Furs therinore,` the process is applicable where the water;.or other material present in addition to the extract and solvent,. is an impurity to be separated rather than an anti-solvent serving a useful purpose.

The process of my invention may be readily understood by reference to the attached drawing showing apparatus suitable for its practice. For the purpose of illustrating this invention it is. assumed that the feed oil isV a petroleum oil (preferably, but not necessarily boiling' abovethe napntha and gas oil range):y and thesolvent is phenol which is typical of the l class having-f a preferential selectivity forv theA more: aromatic type compounds and having suitableN characteristics so that the solvent may be readily separated from the oil. The phenol extract phase comprised mostly of phenol.` but havingisubstanltial percentages of extract oil and water, enters the system through line Il) andY ist heated in two successive steps in heat exchangers' Il and l2 which causes the liquid extract to be` partially vaporize'd. lIhe liquid-vapor mixture is" introduced intofiash drum I3 `for'pu'rposes:of separating. phenol and" watervapors from` that partif of l the extract phase which` remains in liquidi condi tion. The vapors are withdrawn'from flash. drum I3 through overhead line llian'd introduced into a fractionation tower l5 which is provided with a number of bubble trays `indicated by'hor'iz'ontal dashed. lines' I6; l'lnval'norized liquidsV are: withdrawn fromllash drum IBtnrough line Il, passed through heat exchanger IE; andare introduced into fractionation tower l5" at a point several trays lower than that at which vapor line l4 enters tower l5. The flow of liquid throughfline Il is controlled by a' liquid level control valve I9, which opens and closes in response to variations in the position of liquid level' float 20 within tower l5. Shut-off valve 2li is provided for emergency use;

Fractionation tower l 5 effectively separates the phenol extract phase into a liquid fraction of pure phenol and oil, and a vapor phase which is an azeotropic mixture of water and phenol. The phenol and oil phase is withdrawn from the bottom of tower I5 through line 22 and pumped by pump 23 to an upper section 24 of tower I5. Upper section 24 is entirely separated from balance of tower I5 by separating partition 25 and is used for the separation of phenol and oil.`

The phenol-water vapor is withdrawn from the upper end of the lower section of tower I5 through line 21, cooled and condensed by heat exchanger 28, and stored in phenolic water storage drum 29. Control valve 29a regulates lthe withdrawal of phenolic water vapor through line 21 and is automatically controlled in response to pressure conditions within lower section of tower I5 by a conventional pressure responsive means 29h so as to maintain a desired pressure Within tower I5. line 30 and pump 3| to tower I5 to serve as a reflux liquid, the amount of reflux being controlled by a control valve 32 and a flow controller 33 preferably operated by temperature control means 34.

In order to conveniently maintain a proper amount of phenolic water in phenolic water storage drum 29 a supply line 35 is connected to reflux line 3i] for either withdrawing or adding phenolic water. In case the amount of phenolic Water becomes excessive, it may be withdrawn through line 36 which connects storage line 35 with reflux line .35 on the high pressure side of pump 3l. A valve 3l in line 35 is automatically operated through conventional operating means :1.

38 by liquid level control float 3Q within phenolic water storage drum 29 so as to maintain a substantially constant level therein. If it is desired to introduce additional phenolic water for phenol recovery, it may be introduced into the system by opening valve 46.

It will be understood, of course, that flash drum I3 could be eliminated and that the incoming phenol extract could be introduced as a mixture of liquid and vapor coming directly from line I into tower I5. However, employment of flash drum I3 for separating the liquid and vapor and introducing them into the tower I at different levels increases the efficiency of the fractionation and makes possible the use of heat in heat exchanger I5 where it is most urgently needed.

A liquid level recorder may be usefully employed to indicate the liquid level in the bottom of tower I5.

The flow of the water-free mixture of phenol and oil through line 22 to upper section 24 is controlled automatically by ow control valve 4I and, if necessary, is mixed with additional phenol introduced through line 42. Inside upper section 24 phenol oil mixture passes downwardly through a series of bubble trays 43 under substantially higher pressure and temperature conditions than existed in the water fractionating section I5.v A substantial amount of liquid is retained in a trapout section 44, the liquid level being recorded by liquid level recorder 45. Liquid is continuously withdrawn from trapout section 44 through line 45 and circulated by pump 4". through a furnace 48 and back to the bottom of upper section 24 via line 4S. Dual flow controllers 50 and 5I are provided to control the rate of circulation through furnace 48. The bull; of the phenol is Vaporized in the furnace 48 and the vapor is collected in. the upper ash section Some phenolic water is returned by 24 of the tower I5. The vapors separated here ow upwardly through the vapor passages 52 and the trays 43 in which the vapor is desuperheated and some phenol is vaporized from the descending feed stream.

The phenol vapor from above the trays 43 leaves the tower by means of line 53 and is passed to reboiler 54 in which it is totally condensed. The heat given on in this condensation vaporizes phenol from the downflowing stream flowing from the tower by means of line 55; the stream flowing in line 5o is then returned to the tower for separation. Some of this vapor is employed in the tower for vaporizing the phenolwater azeotrope. The excess vapor is withdrawn through line 65. Liquid phenol is withdrawn via line Ell, through valve 5I at a rate controlled by liquid-level controller 52. Likewise, the withdrawal of vapors from upper flash section 24 through line 53 is controlled by means of valve 53 which is controlled automatically in response to the pressure-control means 54.

Since the vapor entering line 55 cornes from a point within fractionation tower l5 under the last bubble tray Ia, it is substantially pure phenol because all the water has been removed by vaporization at a higher point within the tower I5 and all the oil is liquid under temperature and pressure conditions within tower I5. The heat contained in the phenol vapor is usefully employed in heat exchanger I2 as a means.

for heating the incoming extract phase, at a rate which may be governed by valve 5l' valve 6l may be controlled by temperature-responsive means 68 to divert phenol vapor through line 56 if temperatures seem to justify it. The rate of vapor withdrawal from line 55 may be controlled by line 65 which is itself controlled according to the pressure within tower I5 by means of pressure-responsive means lil. If the phenol vapor were not removed at this point it would rise through tower I5 until liquefied in the upper portion thereof. In so doing it would transmit heat to the various bubble trays higher up in the tower but the heat thus transferred would nct serve a particularly useful purpose since tower I5 generally has an excess of heat, but would rather require more reflux and more cooling water. The same heat is much more usefully employed in partially vaporizing the extract phase coming in through line l0. Moreover, all phenol, an excess of that required for the constant boiling of phenolic-water mixture from tower I5 withdrawn through line 2l' would eventually have to nd its way from tower l5 through line 22 to upper section24 as in a phenol-oil mixture. It would then be necessary for the capacity of upper section 24 and furnace 48 to be sufficiently great to distill off all of the phenol not removed in the phenolicwater mixture. In accordance with the present invention, however, a substantial portion of the phenol is separated from the oil in the lower portion of tower I5 rather than in upper section 24 so that the duty imposed on upper section 24 and furnace 43 is much smaller as a result. It is possible, therefore, to effect substantial savings in initial investment and operation of upper section 24 and furnace 43.

An example of these savings shown in the design of a large refinery unit for phenol treating East Texas deasphalted oil resulted in great economies which can be illustrated by the following figures:

In a phenol treating plant having a capacity of 6,160 barrels per stream day the extract phase consisted of Ph. 5L. 1222,530 lbs. Aper hr., water 1l,450'lbs.'1per hr., extract oil ,24,000 lbs. `per hr.,

`total `257,980 lbs. per hr. This extract phase left the vphenol counter-current extraction tower at a temperature of 220 F. and, at this temperature, entered heat exchanger I2. Heat exchanger I2 operatesundera duty of 16,704,000B. t.\u. per` hr. and increases the temperature ofthe extract phase mixture to 310 F. -to produce the following mixture, Ph. V. 1890 lbs. per hr., steam 3510 lbs-per hr., Ph. L. 227,332 lbs. per ihr., water 8,251 lbs. per hr., extract oil, 24,000 lbs. .per hr., total 264,983 lbs. per hr. -At a temperature of 310 F. and a pressure ofi5 lbs. gauge the extract phase is separated into vapors passing through line I4 which consist of Ph. V. 1890 lbs. per hr., steam 3510 lbs. per Thr., total `5400 lbs. per hr., and liquids entering the tower through line Il which consist of Ph. L. 227,332 ibs. per hr., water 8,251 lbs. per hr., extract oil 24,000 lbs. per hr., total 259,583 lbs. per hr. Tower I5 is'maintained at a pressure of 5 lbs. gauge and has a temperature gradient ranging from 230 F. at the upper end near point at which the azeotropic vapors leave through line 21 to a temperature of 380 F. in the bottom portion of tower I5 near the point at which liquid phenol and oil is withdrawn through line 22. The lower end of dryer tower I5 ismaintained at 380 F. by circulating 305,000 lbs. per hour of 'liquid through heat exchanger 54 in which 30,500,000 B. t. u. per hour are transi ferred from phenol vapor in line 53 to phenol oil liquid in line 55 with the result that the phenol vapor is condensed and the phenol-oil liquid loses about half its phenol in the form of phenol vapor part of which passes upwardly through bubble trays I6 and part is withdrawn through line 65 `in order to achieve the efficiencies which the present invention has for its object.

85,270 lbs. per hour of phenol vapor at a teinperature of 380 F. is withdrawn through line 85 and condensed in heat exchanger I2 to `phenol liquid at 380 F., thus providing 16,604,000 pounds per hour for the partial vaporization of incoming extract phase.

Within dryer tower I5, the extract phase is separated into azeotropic Vapor withdrawn through line 21 which consists of Ph. V. 1886 lbs. per hr., steam 14,113 lbs. per hr., total 15,999 lbs. per hour. This constant boiling Amixture is about 89% steam and 11% phenol vapor at a pressure 5 lbs. gauge. All of the water is removed from the extract phase in this manner.

` Dry extract solution will be withdrawn from the bottom of the tower through line 22 at the rate of Ph. L. 142,380 lbs. per hr., extract oil 24,000 lbs. per hr., total 166,380 lbs. per hour.

Upper section 24 operates under a pressure of 25 lbs. per square inch with a temperature of about 435 F. at the upper end and 560 F. at the lower end. Phenol vapor is withdrawn at the rate of 40,500 lbs. per hour through line 53 and condensed in dryer tower reboiler 54. The extract oil product withdrawn from the bottom of upper section 24 contains some phenol the proportion being about as follows: Ph. L. 1880 lbs. per hr., extract oil 24,000 lbs. per hr., total 25,880 lbs. per hour. The remainder of the phenol may be separated from the extract oil by any conventional means for instance, by steam stripping.

It will be seen that almost 1/3 of the phenol is separated from the extract in the lower part of dryer tower I5. The consequent lowering of duty on upper section 24 and furnace 48 results in a saving in the cost of the furnace which usual- 6 ly 'runs about 4 or v5 times the total cost of the heat exchanger I2 and reboiler-54.

Moreover, the cooler which was formerly `12e-- quired to cool the phenol after recovery is no longer needed. In previous installations all 'of the phenol passed through -furnace 48 with the result that a great deal of heat was introduced into the system; under the 'present invention a large proportion of the phenol is "withdrawn through line 65 vand the duty `on furnace 48 is greatly reduced so that less heat is introduced into the system and the necessity for cooling phenol is eliminated.

The annual savings because of reduced consumption of the fuel gas from thefurnace and the-addition of water to the phenol cooler results in the reduction of operating costs which far'exceeds the initial savings in capital investment. While the process of the following invention is particularly applicable to the treatment of heavy petroleum oil fraction to separate themore aromatic components from the more paralliniqit is to be understood that the process may be usefully employed in other solvent fractionationprocesses in which it is necessary to recover an `extract from an extract phase containing an extract, a lower-boiling solvent, andan anti-solvent.

I claim:

1. In the fractionation of a solvent extract solution containing extract, `a `lower-boiling solventand an anti-solvent which has a boiling l point lower than said solvent, wherein said solution is subjected to fractional distillation in a vertically extended fractionation yzone to separate a top distillate fraction lcontaining substantially all of said anti-solvent, and wherein a residue yof solvent and extract is withdrawn from `the lower end of said fractionation zone, the improvement which includes'the stepsiof: withdrawing a liquid sidestream from said fractionation zone at a vpoint sufficiently below the point of introduction of said solvent extract solution to obtain a liquid substantially free of said anti-solvent; heating said liquid sidestream 'tovaporize a substantial part of the solvent content thereof; returning at least part of saidsolvent vapor to said fractionation zone at a point not higher than the point of withdrawal of said liquid sidestream, and withdrawing a vapor sidestream of substantially pure solvent from said fractionation zone at a point sufficiently below the point of introduction of said extract solution and suiicientl'y near the point of introduction of said solvent vapor to be substantially free of said anti-solvent.

2. A method as described in claim 1 in which said solvent is a phenol and said anti-solvent is water.

3. A method as described in claim 1 in which said solvent is furfural and said anti-solvent is water.

4. A method as described in claim 1 in which said bottoms liquid is heated sufliciently to vaporize a maximum of substantially pure solvent vapor; a portion of said solvent vapor is permitted to rise through said first fractional distillation tower to provide distillation heat therein; and the excess of said solvent vapor is with drawn in said vapor sidestream.

5. The combination as described in claim 1 in which said solvent vapor stream from said fractional distillation zone is at least partially condensed by indirect heat exchange with said solvent extract solution prior to the introduction of said extract phase into said first fractional distillation zone.

v(i. In the fractionation of a solvent extract solution containing extract, a lower-boiling solvent, and an anti-solvent which has a boiling point lower than said solvent, wherein said solution is subjected to a first fractional distillation in a vertically extended fractionation zone to separate a top distillate fraction containing substantially all of said anti-solvent, and wherein the residue of said rst fractionation is withdrawn from the lower end of said fractionation zone and subjected to a second fractional distillation to separate substantially pure solvent vapor, the improvement which includes the steps of withdrawing a liquid sidestream from said fractionation zone at a point sufficiently below the point of introduction of said solvent extract solution to obtain a liquid substantially free of said anti-solvent; passing said liquid sidestream through a reboiler in indirect heat exchange with said solvent vapor from said second fractional distillation tb vaporize a substantial part of the solvent content of said liquid sidestream; returning at least part of said solvent vapor to said fractionation zone at a point not higher than the point of withdrawlal of said liquid sidestream; and withdrawing a vapor sidestream of substantially pure solvent from said fractionation zone at a point sufficiently below the point of introduction of said extract solution and sufficiently near the point of introduction of said solvent vapor` to be substantially free of said antisolvent.

'7. In the fractionation of a solvent extract solution containing extract, a lower-boiling solvent, and `an anti-solvent which has a boiling point lower than said solvent, wherein said solution is subjected to a rst fractional distillation ina vertically extended fractionation zone to separate a top distillate fraction containing substantially all of said anti-solvent, and wherein the residue of said first fractionation is withdrawn from the lower end of saidiractionation zone and subjected to a second fractional distillation to separate substantially pure solvent vapor. the improvement which includes the steps of withdrawing `a liquid sidestream from said fractionation zone at a point suiciently below the point of introduction of said solvent extract solution toobtain a liquid substantially free of vsaid anti-solvent; passing said liquid sidestream through a reboiler in indirect heat exchange with said solvent vapor from said second fractional distillation to vaporize a substantial part of the solvent content of .said liquid sidestream; returning at least part of said solvent vapor to said fractionation zone at a point not higher than the point of withdrawal oi said liquid sidestream; and withdrawing a vapor sidestream of substantially pure solvent from said fractionation zone below the point of withdrawal of said liquid sidestream.

8. In the fractionation of a` solvent extract solution containing extract, a lower-boiling solvent, and an anti-solvent which has a boiling point lower than said solvent, wherein said solution is subjected to a first fractional distillation in a vertically extended fractionation zone to.

separate a top distillate fraction containing substantially all of said anti-solvent, and wherein the residue of said rst fractionation is withdrawn from the lower end of said fractionation zone and subjected to a second fractional distillation to separate substantially pure solvent vapor, the improvement which includes the steps of withdrawing a liquid sidestream from said fractionation zone at a point sufficiently below the point of introduction of said solvent extract solution to obtain a liquid substantially free of said anti-solvent; passing said liquid sidestream through a reboiler in indirect heat exchange with said solvent vapor from said second fractional distillation to vaporize a substantial part of the solvent content of said liquid sidestream; returning at least part of said solvent vapor to said fractionation zone at a point not higher than the point of withdrawal of said liquid sidestream; withdrawing a vapor sidestream of substantially pure solvent from said fractionation zone at a point sufficiently below the point of introduction of said extract solution and suflciently near the point of introduction of said solvent vapor to besubstantially free of said anti-solvent; and passing at least part of said solvent vapor through a reboiler in indirect heat exchange with incoming solvent extract solution to condense said vapor and heat said solution prior to the introduction of the latter into said fractionation zone.

9. A method as described in claim 6 in which temperatures lower than the boiling point of said solvent are maintained in the region of said fractional distillation Zone from which said top distillate fraction is withdrawn; and temperatures at or above the boiling point of said solvent are maintained in the region in which said solvent vapor is introduced into said fractionation zone.

WALTER V. STEARNS.

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

UNITED STATES PATENTS Number Name Date 2,111,822 Sullivan Mar. 22, 1938 2,115,401 Shifer Apr. 26, 1938 2,167,730 Smoley Aug. 1, 1939 2,168,570 Kraft Aug. 8, 1939 2,178,506 Weir Oct. 31, 1939 2,185,311 Ragatz et al Jan. 2, 1940 2,312,912 Kiersted Mar. 2. 1943

Claims (1)

1. IN THE FRACTIONATION OF A SOLVENT EXTRACT LSOLUTION CONTAINING EXTRACT, A LOWER-BOILING SOLVENT AND AN ANTI-SOLVENT WHICH HAS A BOILING POINT LOWER THAN SAID SOLVENT, WHEREIN SAID SOLUTION IS SUBJECTED TO FRACTIONAL DISTILLATION IN A VERTICALLY EXTENDED FRACTIONATION ZONE TO SEPARATE A TOP DISTILLTE FRACTION CONTAINING SUBSTANTIALLY ALL OF SAID ANTI-SOLVENT, AND WHEREIN A RESIDUE OF SOLVENT AND EXTRACT IS WITHDRAWN FROM THE LOWER END OF SAID FRACTIONATION ZONE, THE IMPROVEMENT WHICH INCLUDES THE STEPS OF: WITHDRAWING A LIQUID SIDESTREAM FROM SAID FRACTIONATION ZONE AT A POINT SUFFICIENTLY BELOW THE POINT OF INTRODUCTION OF SAID SOLVENT EXTRACT SOLUTION TO OBTAIN A LIQUID SUBSTANTIALLY FREE TO SAID ANTI-SOLVENT; HEATING SAID LIQUID SIDESTREAM TO VAPORIZE A SUBSTANTIAL PART OF THE SOLVENT CONTENT THEREOF; RETURNING AT LEAST PART OF SAID SOLVENT VAPOR TO SAID FRAC-

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