US2312912A - Solvent refining of oil and recovery of the solvent - Google Patents

Description

March 2, 1943.` w. KIERSTED, JR

SOLVENT REFINING OF OIL AND RECOVERY OF THE SOLVENT Filed .May l0, 1941 20.. mzmoumm rl-..

WYNKOOP KlEIZTED I2.

lNvENToR O mu |10. .IIIIIUL E23 Mug. .rUmbxU J O a Lus Patented Mar. 2, 1943 SOLVENT REFINING OF O11 AND RECOVERY F THE SOLVENT Wynkoop Kiersted, Jr., Scarsdale, N. Y., assigner, by mesne assignments, to The Texas Company,

New York, N. Y., a corporation o! Delaware Application May 10, 1941, Serial No. 392,842

7 Claims. l(Cl. 202--57) This invention relates to solvent reiining of oils and more particularly to the recovery of the solvent from the rened oil for reuse in the process.

This application is a continuation in part of my pending application Serial No. 389,704, iiled April 22, 1941, for Solvent reiining of hydrocarbon oil and recovery of the solvent.

More specifically the present invention involves a modiiication of the method of solvent recovery disclosed in Kiersted and Scoville Patent No. 2,186,298, granted January 9, 1940, for Solvent refining of hydrocarbon oil and recovery of the solvent.

As disclosed in this patent hydrocarbon oil is extracted with a relatively high boiling solventl such as iurfural, nitrobenzene, phenol, dichlorethyl ether, etc.,.whlch is at least partially miscible with water at ordinary temperatures. As a result of the extraction the oil and solvent mixture is separated into extract and raiiinate phases, each of the resulting phases comprising oil and solvent liquid. The solvent is distilled from each phase in part at least by resorting to relatively high temperatures. I'he iinal portion of the solvent is stripped from the oil with the aid of steam.

With solvents of the foregoing character it is desirable to distill as much of the solvent as possible from the oil without the aid of steam so as to obtain the solvent in substantially dry form. The presence of water in the solvent is usually undesirable because it reduces the solvent capacity oi the solvent from constituents of mineral oil.

However, when a selective solvent of the foregoing character is removed from lubricating oil, for example, by vaporization in the absence of a distilling aid a substantial amount of the solvent still remains in the oil and must be distilled therefrom with the help of a distilling aid such as steam. Therefore, that portion of the solvent which is recovered with the aid of steam will contain an appreciable amount of water and provision must be made for removing the water as .completely as possible, particularlyin those cases where the full solvent capacity of the solvent is desired. ,i

For these reasons it is desirable, therefore, to conduct as muchof the distillation as possible without the aid of steam. However, with certain types of oils which normally contain acidic or unstable constituents, if the distillation is carried out under conditions or in apparatus such that the oil and solvent or a portion thereof -is permitted to remain at elevated temperatures,

' namely, in the range 450 to 500 F. for a substantial period of time then some deterioration or decompositon of the constituents of the oilsolvent mixture occurs. This is particularly true with respect to the extract phase mixture such as obtained in the solvent extraction of lubricating oil stocks due to concentration of the acidic or unstable bodies in the extract by virtue of the extraction process.

Decomposition of the unstable bodies and accumulation of acidic bodies in the system, while relatively 'small in extent, is nevertheless undesirable since some loss of the solvent will result.V

It appears that the undesirable products of de. compostion include bodies exerting an appreciable corrosive eiect up'on steel apparatus. Moreover, there are indications that tne'accumulation and retention of these decomposition products in the solvent being recycled through the process may in some instances accelerate to some extent the deterioration or decomposition of the oil and solvent mixture during exposure to eleva-ted temperatures.

For example, when distilling furfural from an extract phase produced in the extraction of lubricating oil distillate stock derived from Penn'- sylvania crude wherein the extract phase mixture has been exposed to temperatures' in the range 450 to 460 F. for a substantial period of time, i. e., about 60 minutes, a small amount of material is formed, most of which boils within a temperature rangek intermediate theboiling temperature of the solvent and that of the ex- 'tract oil, and this material may include small amounts of organic acids such as acetic, pro- 1 picnic and butyric acids. The nature of the reoration of the equipment action giving rise to formation of these undesirable bodies is not'| fully understood. It is thought that the products may possibly be the result or decomposition of the extract oil or of reaction between the solvent and hydrocarbon constituents of the extract oil or between the solvent and decompostion products of the extract oil.

In accordance with the present invention provision is made for removing these undesirable bodies, not presentin the solvent prior to extr'fctivel contact with the raw oil asfan intermediate step in the recovery of the solvent from the oil and for eliminating them from the system thereby avoiding loss of solvent, and deteridue to corrosive action of such bodies.

Provision is alsoincluded for subjecting the reconstituents thereiroml of acidic bodies to treatment, immediately after their liberation in the system, with soda ash solution for the purpose of removing the undesired Different methods oi accomplishing this treatment may be employed as hereinafter described.

To facilitate further description of the invention reference will now be made to the flow dia- Y gram shown in the accompanying drawing.

index or so-called naphthenic constituents of the oil dissolved in the bulk oi the solvent accumulates in the bottom oi the tower, while the rafflnate phase comprising high viscosity index or socalled. parailinic constituents mixed with asmall proportion oi the solvent accumulates'in the top of the tower. l

The extract phase is withdrawn and passed through a heater or heat exchanger 2 wherein the temperature is raised.

The heated mixture is introduced to a :dash tower 3 maintained at sustantially atmospheric pressure, the lower portion of the tower being at a temperature of about 330 F. The vaporized material removed from the top of the tower represents about 40 or 45% of the total solvent contained in the extract phase, and this vaporized solvent may contain about 1 to 2% oi water most of which enters the system in the charge oil.

The unvaporized liquid is drawn oil from the bottom ofthe tower 3 through aheater 4 to a second tower 5, usually maintained under a pressure'of about 30 pounds gauge. The oil and solventrmixture enters the tower at a temperature of about 450 to 460 F. so as to maintain a temperature of about 430 F. at the bottom of the tower.

is indicated in the drawing the heated mixture of oil and solvent may be introduced to the midportion of the tower 5. The hot mixture entering the tower is caused to flow over suitable bailles provided within the lower portion of the tower. Due to the elevated temperature a substantial portion of the mixture is` vaporized including a large proportion o! the solvent. The

vapors rise through the upper portion of the tower which is provided with a number of conventional bubble trays.

During passage through the trays partial condensation occurs as a result of cooling due to the introduction of a reflux liquid through a pipe 6 solvent thus removed at this point may amount to about 50 to 55% of the total solvent contained in the extract phase, volume basis.

'I'he unvapor-ized liquid collecting in 'the 'botcovered solvent containing substantial amountstom of the tower 5 is drawn of! and introducedl to a third tower vI0 maintained under lan absolute pressure .of about 1 to 5 pounds and with a temperature of about 400 F.' in the bottom of `the tower. An additional quantity of solvent, namely Aabout 4 to 10% by volume of the original solvent,

is removed in a dry condition from the top o! the tower.

The unvaporizedresidue collecting in the bottom of the tower I0 still contains a small amount of solvent usually less than 1%. This residue is introduced to astripping tower Il wherein the remaining solvent is stripped out with the aid of steam. 'I'he residue from this stripping action comprises extract oil substantially tree from solvent while the vaporized material comprises a Y mixture of solvent and water.

The solvent and water vapor is condensed in a introduced to a separator I3 at a. temperature ot about 160 F. for example. In the' separator the hot condensate separates into upper and lower layers respectively rich in water and solvent. For

example, the upper layer may contain about 13% furfural while the lower layer comprises about 90% furfural.

According to one method of procedure, the lower layer is withdrawn and introduced through a pipe I3a to a treater I4 wherein it is brought into countercurrent contact with a soda ash solution containing about 10% by weight of soda ash. The treated mixture is drawn of! from the bottom of the vessel I4 to a scrubbing vessel I5 wherein it is subjected to washing with water to remove any remaining traces of soda. The washing step may be bypassed if desired.

In either case the alkali treated liquid mixture is then conducted to a fractionator i6 advantageously operated under about atmospheric pressure. The temperature at the top of the tower is maintained at about 220 to 260 F. while the temperature at the bottom of the tower is maintainedv at about 330 F. Heat may be supplied to the bottom of the tower by means of a closed coil I1, or instead a portion of the dry solvent vapor removed from the tower 5 may f be injected through a pipe I8.' The wet solvent fractionator I6.

Prior.to introducing this wet solvent to the fractionator I6 it may be passed through a condenser, not shown, wherein the bulk of the selective solvent is condensed. 'I'he thus partially condensed mixture may then be conducted to a separator to effect separation between the condensate and the vapor. The condensate may be introduced to the bottom of the fractionator while the uncondensed vapor containing water is introduced to the midportion of the fractionator I6.

The unvaporized liquid collecting in the bottom of the fractionator I6 is composed of solvent substantially free from Water while the vapor leaving the top of the fractionator comprises a mixture of solvent and water containing about 45% furfural. The latter upon condensation is advantageously recycled to the separator I3 as will be mentioned again.

The upper layer formed ln the separator I3 is withdrawn and introduced to the upper portion rofa fractionator I9, open steam being admittedrto the bottom of this fractionator to act as a stripping agent. A temperature of about 215 to 225 F. is maintained in the bottom of the fractionator while a temperature of 212 F. is maintained in the top of the fractionator..

The unvaporized liquid collecting in the bottom of this fractionator is water substantially free from solvent and is withdrawn from the system. The vapor `removed from the top of 4 the `fractionator comprises a mixture of furfural and water containing about 35% furfural. This vapor is advantageously combinedwith that from the iractionator I6, the resulting mixture condensed in a condenser 20 and the condensate returned .through pipe ZI to the separator I3.

Used or partially spent alkali accumulating at the top of the treating vessel I4 may be mixed with the water layer drawn off from the top of the separator I3 and the combined mixture charged to the fractionator I9. Likewise the water used in the scrubbing vessel I5 may be introduced to the fractionator I9 as indicated. In this way the solvent liquid contained in the spent alkali and scrubbing water is recovered therefrom.

If it is desired to omit the alkali treatment, the solvent phase is conducted directly from the phase drawn on.' from the separator I3 maybe omitted. Instead the intermediate condensate drawn olf through pipe 8 from the tower 5 may be subjected to alkali or other chemical treatment in order to remove acidic bodies. In such case the intermediate condensate containing the acidic bodies cooled'if necessary is conducted through a pipe 24 to the treater I4 wherein it is treated with soda ash solution. The treatedI condensate is then conducted through a pipe 25 to the separator I3 wherein it commingles with the solvent layer accumulating therein.

Treatment of the extract phase has been described because the unstable reactive material contained in the oil charged to vessel I has been found to be concentrated by the treating process in the extract. However, if such reactive or unstable material appears inthe raflinate phase of any stock treated, then instead of employing 4separate operations, the wet solvent removed from the raffinate oil may be combined with the separator I3'through a bypass pipe 22 to the fractionator I6. y

The intermediate condensate drawn off through the pipe 8 from the tower E is advantageously commingled with the distillates from the fractlonators I6 and I9 passing to the condenser 2D and to the separator I3.

In actual operation a recording flow controller 23 may be placed in the line 8 so as t0 provide for drawing off liquid from the pan 'I at a uni` form rate.

The amount so -withdrawn is adjusted so that the liquid so withdrawn will contain substantially all of the decomposition products which maybe formed as a result of exposure of the solvent-oil mixture to elevated temperawet solvent from the extract phase and the two treated simultaneously for the removal or neutralization of acidic bodies.

While reference has been specically made above to the recovery of the selective solvent from a mixture of the solvent and a mineral oil, nevertheless it is contemplated that the invention is applicable'to the recovery of a solvent -liquid from admixture with other oils and fatty oil or fatty acid substances including vegetable, animal and sh oils, fats, waxes and the like,

' and wherein as a result ofthe solvent rening tures in the heater 4 and the lower portion of l the tower 5.

For example, when recovering furfural from an extractphase produced in extracting Pennsylvania lubricating oil stock with furfural the amount of liquid continuously drawn off from the pan 1 advantageously vamounts to about' 2 to 4% by volume of the solvent extract mixture entering the tower 5.

By commingling this withdrawn liquid with the water rich vapors entering the condenser 20, a portion of the acidic bodies is thus transv ferred to the water phase discharged from the top of the separator I3, and ultimately removed as constituents of the water discharged from the bottom of the fractionator I9. Advantage is thus taken of the water contained in the solvent to eliminate some of the acidic bodies from the solvent recovery system.

A portion of the acidic bodies remain in equilibrium with the furfuralfin the condensate passing from the condenser 20. By continuous recycling of this condensate through the separator I3 and the fractionator I6 additional poror solvent reco"ery operation there is a concentration of acidic bodies in either the rainate or extract phase.

Selective solvents, such as furfural are now employed for extracting and refining fatty oils and fatty acids such as are usedin the preparation` of foods, soaps, paints. varnishes and enamels. Examples of such other oils include linseedoil, tung oil, soy-bean oil, cottonseed oil, etc. Numerous other oil substances may be mentioned including fatty acids, fatty 'acid mixtures and mixtures of fats and oils, as well as rosin l and rosin oils.

mate 250 to 300 F., while the pressures may be tions of these acidic bodies (that is, where alkali treatment of the solvent phase is omitted) are removed in the distillate from the fractionator I6 and are ultimately transferred to the water layer/of the separator I3 and from there conducted to the fractionator I9 from the bottom of which these bodies are ultimately discharged from the system. As previously mentioned the solvent phase may be treated with alkali to remove the acidic bodies contained in the solvent.

I ing liquid is introduced to the tower above this may be employed satisfactorily.

of the order of 10 to 100 mm. absolute.

The apparatus illustrated in the drawing includes atmospheric, pressure and vacuum towers. However, it is contemplated that a less number of towers and in some instances a single tower In 'any case, regardless of the operating pressure, it is necessary to maintain a temperature at least in one of the towers which is substantially above the vapor-liquid equilibrium temperature of furfural at the prevailing pressure which results in vaporizing the acidic bodies boiling intermediate between furfural and the oil. Therefore, a coolpoint in order to form a reiiux condensate containing the undesirable acidic bodies. The re- However, the alkali treatment of the solvent sulting condensate having the acidic bodies concentrated therein is withdrawn from the system for neutralization.

Obviously, many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. In the recovery of a high boiling selective solvent such as furfural from a mixture of oil and solvent obtained in extracting oil with the solvent, said mixture, after exposure to elevated temperatures sufiiciently high to vaporize solvent therefrom, containing bodies corrosive to steel, the steps comprising heating the mixture of il and solvent to a temperature substantially above the boiling temperature of the solvent, passing the heated mixture to a distilling column wherein substantial vaporization of the mixture including a large proportion of the solvent occurs in the substantial absence of steam, subjecting the vaporized portion to partial condensation to form an intermediate condensate comprising corrosive bodies boiling substantially into the range intermediate that cf the -oil and the oil solvent and which were not present in the solvent prior to extractiva contact with the ra'w oil, withdrawing said intermediate condensate,

removing the uncondensed solvent, withdrawing the unvaporized portion of the heated mixture of oil and solvent, distilling remaining solvent therefrom under relatively lessv severe temperature conditions, recovering said removed uncondensed solvent and said distilled remaining solvent substantially free from said corrosive bodies, and returning the so recovered solvent for extracting fresh feed oil.

2. In the recovery of a high boiling selective solvent such as furfural from a mixture of oil and solvent obtained'in extracting oil with the solvent, said mixture, after exposure to elevated temperatures suiiiciently high` to vaporize solvent therefrom, containing bodies corrosive to steel, the steps comprising heating the mixture of oil and solvent to a temperature substantially above the boiling temperature of the solvent, passing the heated `mixture to a distilling column wherein substantial vaporization of the mixture including a large proportion of the solvent occurs in the substantial absence of steam, subjecting the vaporized portion to partial condensation to form an intermediate condensate comprising solvent and corrosive bodies boiling severe temperature conditions, chemically treat-- ing the withdrawn intermediate condensate to l remove said corrosive bodies, commingling the resulting treated solvent with saidremaining solvent distilled frorn the oil, and returning said commingled solvent for extracting fresh feed oil.

3. In the solvent extraction of oil with a high boiling selective solvent which is partially miscible with water at ordinary temperature wherein as a result of the extraction a mixture of solvent and oil is produced, said mixture, after exposure to elevated temperatures suiiiciently high to vaporize solvent therefrom, containing bodies corrosive to steel, the method of recovering the solvent from the oil for reuse in treating fresh feed oil which comprises heating a `mixture of the solvent and oil to an elevated temperature substantially Aabove the boiling temperature of the solvent, vaporizing a substantial portion of the heated mixture including a large portion of the solvent in the substantial absence of steam, subjecting the vaporized portion to partial condensation to form an intermediate condensate comprising materials boiling. substantially in the range intermediate that of the oil and the solvent, removing said intermediate condensate, removing uncondensed solvent, withdrawing the unvaporized portipn of the heated mixture of oil and solvent, distilling remaining solvent from the withdrawn heated mixture with the aid oi' steam to form a distillate mixture of solvent and water, subjecting said distillate mixture to settling in a separating zone to form phases rich in water and solvent respectively, separately treating each phase to separate therefrom a fraction comprising water containing a substantial amount of solvent, recycling said fraction to the aforesaid porize solvent therefrom, containing bodies corrosive to steel, the method of recovering the solvent from the oil for reuse in treating fresh feed oil which comprises heating a mixture of the solvent and oil to an elevated temperature substantially above the boiling temperature of the solvent, vaporizing a substantial portion of the heated mixture including a large DOrtion of the solvent in the substantial absence of steam, subjecting the vaporized portion to partial condensation to form an intermediate condensate comprising materials boiling substantially in the range intermediate that of the oil and the solvent, removing said intermediate condensate, removing uncondensed solvent, withdrawing the unvaporized portion of the heated mixture of oil and solvent, distilling remaining solvent from 'the withdrawn heated mixture with the aid of steam tolform a hot condensate of solvent and water, introducing saidcondensate to a separator, forming therein phases respectively rich in water and solvent, introducing the water-rich phase to a distilling column, distilling therefrom a distillate comprising solvent mixed with a smaller proportion of water, withdrawing the unvaporized portion consisting essentially of water, introducing said solvent rich phase 'to a separate distilling column, distilling therefrom a distillate comprising water mixed with a small proportion of solvent. withdrawing the unvaporized liquid comprising treated solvent from said separate distilling column, condensing the distillates produced from both said columns, conducting the condensed distillate to the aforesaid separator for further separation into phases and commingling said intermediate condensate with said condensed distillate.

5. The method according to claim 4 in which the solvent comprises furfural.

6. In the solvent extraction of oil with a high boiling selective solvent which is partially miscible with water at ordinary temperature wherein as a result of the extraction a mixture of solvent and oil is produced, said mixture, after` exposure to elevated temperatures sufficiently high to vaporize solvent therefrom, containing bodies corrosive to steel, the method of recovering the solvent from the oil for reuse in treating fresh feed oil which comprises heating a mixture of the solvent and oil to an elevated tem- Y solvent and water, introducing. said distiilateto a separator, forming therein phases respectively rich in water and solvent, introducing the waterrich phase to a distilling column, distilling therefrom solvent mixed with a smaller proportion of water than that in the Water-rich phase, withfdrawing the unvaporized portion consisting essentially of water, introducing said solvent-rich phase to a separate distilling column, distilling therefrom water mixed with a smaller proportion of a solvent than that in the solvent-rich phase, withdrawing unvaporized solvent substantially free from water from the bottom of said separare distiilng column, condensing the distillate produced from both said columns, conducting the condensed distillate to the aforesaid sepn arator for further separation into phases in the presence of fresh. solvent-water condensate and commingling said intermediate condensate with the condensed distillate from said columns.`

7.The method according to claim 6 in which the solventl comprises furfural.

. WYNKOOP KIERSTED, JX.

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