US3108942A - Dewaxing process - Google Patents

Description

Oct 29, 1.963 A. M,su vA ETAL DEWAXING PROCESS 2 Sheets-Sheet 1 Filed Dec. 29. 1959 Oct 29, 1963 A. M. SILVA ETAL DEWAXINGPROCESS 2 Sheets-Sheet 2 Filed Dec. 29, 1959 United States Patent O This invention relates -to the removal Lof wax or waxlike materials from mixtures containing the same. In `accordance with one embodiment this invention is directed to the dewaxing of waxy materials by a combination of operations involving solvent dewaxing and urea dewaxing or urea complex formation. In the practice of this invention the following materials or mixtures thereof can be dewaxed or fractionated by the removal of wax or waxlike materials the reform: waxy petroleum fractions such as waxy lubricating oils, fatty acids, fatty oils, vegetable oils, animal oils and fats and fish oils and the like.

In the solvent dewaxing of waxy petroleum streams and the like it is the practice to admix the waxy petroleum to be dewaxed with a liquid dewaxing solvent and -to cool the -resulting admixture to a suitable -low dewaxing temperature to precipitate a substantial portion of the waxy material. The resul-ting precipitated wax is then removed by ltration from the resulting dewaxed petroleum.

In :a urea `dewaxing or urea complex formation fractionation operation urea is added to a material containing components which are capable of `forming solid complexes with urea. These complexes, such las urea complexes with the straight chain ihydrocarbons, n-paraffins in the molecular weight range C6-C25 and higher, form at relatively low temperatures, such as a temperature in the range 50-150" F., more or less. The urea complex formation operation is usually carried out in the presence of an accelerator such as methanol, isopropyl alcohol, or mixtures thereof and the like, i.e. materials which tend to act both as a solvent for the urea and the mixture undergoing fractionation by urea complex formation thereby bringing about conditions wherein a more intimate contact takes place between the urea and the urea complex Vforming components of the mixture. Following the formation of the solid urea complexes these complexes are usually removed by ltration and then suitably treated in the presence of a solvent and at la relatively high temperature at which the complexes de'- compose, usually above about 150 F., to break the complex and to separate the urea from the complex forming components.

It is an object of this invention to provide an improved urea fractionation or complex formation operation.

It is another object of this invention to provide `an improved dewaxing operation involving in combination solvent dewaxing and urea complex formation.

Another object of this invention is to provide a process for dewaxing waxy petroleum streams.

Still another object of this invention is -to provide a combina-tion dewaxing operation whereby low pour point substantially completely dewaxed lubricating oils are obtained.

Yet another object of this invention is to provide an improved process for the fractionation of fatty `acids and 3,1859452 Patented Oct. 29, l963 rice oils and vegetable oils and animal oils and the like for the recovery of special wax-like materials therefrom.

How these yand other lobjects of this invention are attained will become apparent in the light of the accompanying disclosure made with reference to the accompanying drawings, wherein:

FIG. I is a schematic flow diagram of a dewaxing operation in accordance with the practice of this invention and applicable to the dewaxing of petroleum streams, and wherein:

FIG. II is a schematic flow diagram of another dewaxing process in accordance with this invention.

In accordance with at least one embodiment lof the practice of this invention at least one of the foregoing objects will be achieved.

It has now been discovered that `an improved fractionation or wax separation process involving urea complex formation is obtained by carrying out the urea complex formation operation in the presence of a dewaxing solvent and in the presence of a minor amount yof water dissolved in said dewaxing solvent. More particularly, in accordance with `this invention `an improved fractionation or dewaxing operation involving urea complex formation is effected by subjecting a mixture containing wax lor waxlike components, at least a portion of which form solid complexes with urea, to solvent dewaxing to precipitate said wax or said wax-like components. Following the precipitation of these wax or wax-like components the remaining mixture, now dissolved in the dewaxing solvent, is subjected to contact with urea in the presence of a minor amount of water, which is either extraneously added dur-ing or just prior to the urea contacting operation or which is 'already incorporated on the dewaxing solvent, even during the aforesaid solvent dewaxing operation. A minor amount of water incorporated in the dewaxing solvent, such as an amount of water in the range G25-2.5% by vol. based ron the dewaxing solvent or solvent plus the aforesaid remaining mixture, and dissolved therein, is usually suicient.

It is seen therefore that in ,accordance with one embodiment this invention involves a fractionation process employing two special `dewaxing or fractionation steps: (l) a solvent dewaxing operation wherein the mixture undergoing fractionation is cont-acted with a dewaxing solvent under conditions to effect the precipitation of solid wax or wax-like materials therefrom `and (2) after separation of these solid wax or wax-like componen-ts, such as by ltration, the remaining mother liquor lor filtrate is contacted with urea under complex forming condi-tions to form solid urea complexes with lthe wax or wax-like components in the mother liquor which are capable of forming solid complexes with urea.

In accordance with a particular embodiment of this invention the resulting formed solid urea complexes are separated, such as by filtration, and the remain-ing filtrate fractionated by distillation to separate dewaxed material and dewaxing solvent therefrom. The dewaxing solvent, especially the aromatic hydrocarbon portion or wax solvent portion thereof, is then employed to break or decompose the previously separated urea complexes to yield solid urea and wax or wax-like components dissolved in the aromatic hydrocarbon portion of the dewaxing solven-t.

In a solvent dewaxing operation the dewaxing solvent employed, particularly in the practice of this invention, is an admixture of a normally liquid aliphatic ketone, an anti-solvent or non-solvent for wax, such as an aliphatic ketone containing from 3 to 12 carbon atoms per molecule and a normally liquid aromatic hydrocarbon, a wax solvent, such as an aromatic hydrocarbon containing from 6 to 12 carbon atoms per molecule. Suitable aliphatic ketones which make up a dewaxing solvent for use in accordance with this invention include acetone, methyl ethyl ketone, ethyl ethyl ketone, methyl isobutyl ketone, ethyl isobutyl ketone, methyl isopropyl ketone, methyl n-butyl ketone, propyl n-butyl ketone, propyl isobutyl ketone, and the various lower and higher molecular weight homologs, and mixtures thereof.

Suitable normally liquid aromatic hydrocarbons which make up a dewaxing solvent employed in the practice of this invention include benzene, toluene, the xylenes, ortho-xylene, meta-xylene `and para-xylene, ethylbenzene lalong with the various other monoor poly-alkyl or hydrocarbyl substituted benzenes containing up to 12 carbon atoms per molecule.

In the practice of this invention it is preferred to employ as the dewaxing solvent a mixture of methyl ethyl ketone and toluene, such as a 50/50 mixture or a mixture containing 20-80% by vol. aliphatic ketone such as methyl ethyl ketone, or other suitable aliphatic ketone or mixtures thereof, and Sil-20% by vol. aromatic hydrocarbon such as toluene or other suitable normally liquid aromatic hydrocarbon. Y

In the actual solvent dewaxing operation the mixture containing wax or wax-like materials, such as a waxy petroleum fraction or a mixture of fatty oils or fatty acids, is contacted with a suitable dewaxing solvent, usually in an amount 0.5-10.0, more frequently in the range 1 6, parts by vol. dewaxing solvent per part by vol. mixture undergoing dewaxing.

The dewaxing operation is carried out at a relatively low temperature, such as a temperature in the range 30 F. down to about 40 F., more or less, the actual dewaxing temperature employed depending upon the particular mixture to be dewaxed, the make up or composition of the dewaxing solvent employed, the amount of wax or wax-like components in the mixture undergoing dewaxing and the amount of wax or wax-like components desired to be precipitated during the dewaxing operation.

Following the dewaxing operation the resulting precipitated wax or wax-like components are separated, usually by iiltration, to yield a slack wax or relatively crude wax product fraction and a mother liquor or iiltrate. Following this wax separation operation the wax is then usually recovered as product by suitable treatment which might involve wax repulping or an additional dewaxing (deoiling) operation.

It is well known that urea is capable of forming solid complexes with molecules having a substantially straight chain conguration, such as the normal paraliins, the normal oleiins, fatty acids, etc. It is also well known that thio-urea is capable of forming solid complexes with molecules which have a relatively slightly branched molecular configuration, such as the isoparaflins, the isoolens, etc.

Urea readily forms solid complexes with straight chain hydrocarbons, particularly the straight chain parainic hydrocarbons having a molecular weight in the range C6-C25, at relatively low temperatures, such as a ternperature in the range 40-150 F., usually in the range 60-l25 F. It has been observed that among those components which are capable of forming solid complexes with urea the higher molecular weight component is capable of forming complexes with urea at a temperature higher than the relatively low molecular weight component. Although emphasis has been made herein of the fact that urea forms solid complexes with straight chain hydrocarbons, as indicated hereinbefore, it is also known that urea is capable of forming solid complexes with non-hydrocarbon materials but which possess a substantially straight chain molecular configuration, such as the straight chain fatty acids, fatty alcohols, in the molecular weight range C55-C25 and higher and accordingly the practice of this invention, as indicated hereinabove, is also applicable to the fractionation of mixtures containing these materials.

In a urea fractionation operation formation of solid urea complexes is expedited by the presence of a solvent which is a mutual solvent for urea and for the mixture or components thereof which are capable of forming solid urea complexes. Accordingly in a urea fractionation operation it is usual to employ materials such as methanol, isopropanol, isobutanol and ethanol, and the like in order to expedite urea complex formation.

Following the separation of the solid urea complexes, in the usual type of fractionation process involving urea complex formation the solid urea complexes are decomposed into their respective components, urea and the wax or wax-like materials complexing therewith by heat, such as by exposing the urea complexes to a temperature at which the complexes are not stable, such as a temperature above about 150 F., e.g. a temperature in the range 15G-250 F. Alternatively the urea complexes maybe decomposed or broken by contact with a solvent for urea such as water. Usually a combination of heat and a solvent, either a urea solvent or a solvent for the other wax or wax-like component of the complex, is employed.

Referring now in detail to the drawings, and in particular to FIG. I thereof which schematically illustrates one embodiment of the practice of this invention, as applied to the dewaxing of a waxy petroleum fraction, a waxy petroleum oil in the lubricating oil boiling range, such as a petroleum fraction having a boiling range in the range SOO-900 F., more or less, is supplied from a source, not indicated, via line 11 into solvent dewaxing unit 12 wherein it is contacted and admixed with a dewaxing solvent, such as a 50-50 mixture of methyl ethyl ketone and toluene in the proportions 3 parts by vol. de-

Waxing solvent to l part by vol. waxy oil. The admixture is chilled to a suitable low temperature, such as a temperature in the range 40 to minus 40 F. to precipitate the waxy hydrocarbons therefrom, the dewaxing solvent being supplied from a source, not shown, to solvent dewaxing unit 12 via line 14. The resulting admixture of solid wax, dewaxing solvent with the partially dewaxed oil dissolved therein is supplied from solvent dewaxing unit 12 via line 15 to iilter 16. Desirably filter 16, as schematically illustrated, is a rotary dewaxing lter. Within filter 16 the solid wax is separated and removed via line 18 as slack wax for eventual treatment and recovery of a product wax. The iltrate, dewaxing solvent containing the partially dewaxed oil dissolved therein, is removed from iilter 16 via line 19 and introduced into urea dewaxing unit 20.

Within urea dewaxing unit 2i) the filtrate is admixed with urea supplied thereto from a suitable source, not shown, via line 2li. The urea introduced into urea de# waxing unit 2o is supplied in the form of solid urea, or in the form of a supersaturated solution or slurry, such as admixed with additional dewaxing solvent, or component thereof or charge oil which has already been solvent dewaxed and urea fractionated in accordance with this invention. Also Water from a suitable source, not shown, is introduced into urea dewaxing unit 20 via line 22. The amount of water from the extraneous source thus introduced into urea dewaxing unit 20 is added in a relatively minor amount as compared with the filtrate or dewaxing solvent therein, and is in the range G25-2.5% by vol. based on the tiltrate or dewaxing solvent.

Upon 4admixture of the urea with the filtrate in the presence of water within urea dewaxing unit 20' urea conn plex formation between the urea and the waxy straight chain hydrocarbons contained in the partially dewaxed oil within the iiltrate takes place substantially immedi.

ately, the urea complex formation being substantially complete in less than about 30 minutes, such as in about 2-20 minutes.

Following the for-mation of the solid urea complexes the resulting admixture of urea-wax complexes, plus dewaxed oil Iand dewaxing solvent, together with any excess urea (the urea is desirably employed in an amount in substantial excess over that required to form complexes with all the waxy straight chain hydrocarbons in the oil introduced into urea dewaxing unit 20) is supplied from urea dewaxing uni-t 20 via line 24 to filter 25. Desirably filter 2S is of substantially the same construction as filter 16 and may be a vacuum rotary filter or a pressure rotary filter. Within ,filter 25 the solid urea-wax complexes are separated yand recovered therefrom via line 26 and -the remaining filtrate or mother liquor is recovered from filter 25 via line 28.

The urea-wax complexes recovered from filter 215 via line 26 are introduced into urea-wax complex breaker 29 wherein, desirably, it is subjected to an elevated complex-breaking temperature, such as a temperature of at least about 150 F., such as a temperature in the range G-200 F., e.g. 170 F., in the presence of a Wax solvent which is also a non-solvent for urea. The wax solvent is added to complex breaker 29 'from ya source, not shown, -via line 3i?. -In accordance with a particu-lar embodiment of the practice of this invention the wax solvent employed within complex breaker 29 is the same as the wax solvent or aromatic hydrocarbon employed as a component of the dewaxing solvent employed within the solvent `dewaxing unit 12. Accordingly the wax solvent supplied via line 3G to complex breaker 29 is toluene.

Within complex breaker 29 ldue to the application of heat in the presence of the added wax solvent, toluene, the urea-wax complex is decomposed into solid urea and wax which is dissolved in the wax solvent. The resulting solution of wax in the wax solvent, toluene, is recovered from complex breaker 29 via line 31 for the eventual treatment and recovery of a product wax. The solid urea resulting from the breaking of lthe urea-wax complexes is removed from complex breaker 29 via line 32 and recycled via line 21 to urea dewaxing unit 20 to contact additional partiaily dewaxed oil for the removal of additional waxy hydrocarbons therefrom.

The filtrate comprising dewaxed oil `and dewaxing solvent is recovered from filter 2S via line 2S and supplied to methyl ethyl ketone stripper 34 wherein methyl ethyl ketone is recovered overhead via line 35 and advantageously recycled to solvent dewaxing unit 12 via line 14 to contact additional waxy oil feed.

The bottoms issuing from methyl ethyl ketone stripper 34 via line 36 and comprising dewaxed oil and toluene is supplied to toluene stripper 38 wherein toluene is recovered overhead via line 39 for recycle via line 14- to solvent dewaxing `unit 12 to contact additional waxy oil feed. Desirably a portion of the toluene recovered overhead from toluene stripper 38 via line 39 is supplied via line 40 and line Sii to complex breaker 29 to contact the urea-wax complexes therein to effect their decomposition.

As indicated hereinabove water from an extraneous source, not shown, is added to urea dewaxing unit via line 22 and is incorporated in the urea dewaxing reaction admixture therein. In the preferred practice of this invention this water added to urea dewaxing unit 20 is recovered during the dewaxing solvent recovery steps, especially in the methyl ethyl ketone recovered overhead via line 35 from lmethyl ethyl ketone stripper 34 and recycled via line 14 to the solvent dewaxing unit 12. ln accordance with this preferred embodiment it is seen that the oil-containing fil-trate supplied via line 19 to the urea dewaxing unit 20 will already contain the desirable requisite amount of water dissolved therein.

Product, dewaxed oil is recovered as a bottoms product via line 41 from toluene stripper 38.

Referring now in detail to FIG. II of the drawings which schematically illustrates vanother embodiment of the practice of this invention and wherein the same reference numbers employed in FIG. I have also been employed to designate the same or comparable equipment, the embodiment schematically illustrated in FIG. II differing from that illustrated in FIG. I in the treatment of the urea complex reaction admixture containing excess urea, solid urea-wax complexes, dewaxed oil and dewaxing solvent issuing kfrom the urea dewaxing unit, the primary difference residing in the fractionation of the urea complex reaction mixture to separate therefrom the ketone component of the dewaxing solvent prior to the separation therefrom of the solid urea-wax complex. As indicated in IFIG. II waxy oil is supplied via line 11 to solvent dewaxing unit 12 wherein it is contacted with dewaxing solvent supplied via line 14. The resulting admixture of solid wax, partially dewaxed oil and dewaxing solvent is supplied `from solvent dewaxing unit 12 via line 15 to filter 16. The separated wax is recovered there-from as slack wax, via line 13 for the eventual recovery of product wax.

The filtrate comprising partially dewaxed oil and dewaxing solvent recovered from filter 16 via line 19 is suppiied to urea dewaxing unit 20 wherein it is contacted with an excess of solid urea introduced thereinto via line 21. Additionally water is supplied, as may be required, via line 22 to urea dewaxing unit '20 so that the -dewaxing solvent therein is saturated with respect to water or contains an amount of water dissolved therein in the range (12S-2.5 by vol. based on the filtrate or the dewaxing solvent.

There is recovered from urea dewaxing unit 20 a resulting react-ion admixtur comprising excess solid ureaq solid urea-wax complexes, dewaxed oil and dewaxing solvent. The reaction adrnixture is supplied from urea dewaxing unit 2.0 via line 24 to methyl ethyl ketone stripper 34 which lis operated under conditions, preferably under vacuum, so as to avoid exposing the ureawax complexes therein to a temperature high enough to decompose these complexes. Desirably methyl ethyl ketone stripper 34 is operated under conditions by cmploying a reduced pressure therein such that the ureawax complexes therein are not exposed to a temperature in excess of F., but at a temperature sufficient to distill overhead methyl ethyl ketone which is desirably recycled via line 35 and line 14 to solvent dewaxing unit 12 to contact additional waxy oil feed.

There is recovered as bottoms from methyl ethyl ketone stripper 34 the remaining reaction admixture comprising excess urea, solid urea-wax complexes, dewaxed oil and the remaining component of the dewaxing solvent, toluene. This bottoms fraction is recovered from methyl ethyl ketone stripper 34 via line 36 and transferred to pump 37 which transfers the aforesaid bottoms admixture via line 43 to filter 25.

Within filter 2.5 the excess of so'lid urea and the solid urea complexes are separated and recovered therefrom via line 26 and transferred to urea-wax complex breaker 29'. Within complex breaker 29 the urea-wax complexes are contacted with wax solvent, preferably the wax solvent component, toluene, of the dewaxing solvent supplied via line 30 under complex-breaking conditions, such as a temperature of at least about 150 F. to effect decomposition of the urea-wax complexes into their respective components, solid urea and wax. The wax is dissolved in the wax solvent employed within complex breaker 29 and is recovered therefrom via line y31 for eventual treatment and recovery as a product wax fraction. The urea thus regenerated from the urea-wax complexes within complex breaker 29 is separately recovered and transferred via line 32; and line 21 to urea dewaxing unit 2.0J to contact additional partially dewaxed oil supplied thereto from dewaxing filter 16 and line 19.

The filtrate recovered from filter 25 and comprising substantially completely dewaxed oil together with resid- ,ual dewaxing solvent, now-substantially only toluene, is

supplied via line 28 to toluene stripper 38. Toluene is recovered overhead therefrom via line 39 and is recycled lvia line 14 to solvent de-waxing unit 12 to contact additional waxy oil feed. Further, desirably a portion of the toluene stripper 33 via lline 39 is transferred via line 40 and line 39 to complex breaker 29 to serve as the wax solvent therein to decompose the urea-wax complexes. Product, dewaxed oil is recovered from toluene stripper 38 via line 41.

As in the case of the combination dewaxing operations schematically illustrated in FIG. I the dewaxing solvent, particularly the methyl ethyl ketone recovered overhead via line 35 from methyl ethyl ketone stripper 34, ccntains substantially all of the water originally supplied to urea dewaxing unit via line Z2. that suicient water is maintained and recycled within the system so that the addition of extraneous water to urea dewaxing unit 20 via line 22 need not always be required save to the extent necessary to maintain the desired water concentration, G-2.5% by vol. in the filtrate or dewaxing solvent and as may be required to make up actual physical losses, physical or in the recovered products.

The following is exemplary of the practice of this invention and of the advantages derivable therefrom. A light paratnic lubricating oil was solvent dewaxed by employing a 50/50 mixture of methyl ethyl ketone and toluene at a solvent to oil dosage of 3:1, the solvent dewaxing operation being carried out at a temperature in the range 0 to 30 F. Following the solvent dewaxing operation the filtrate therefrom, after separation of the precipitated Wax, containing dewaxed oil and dewaxing solvent was contacted with granular solid urea in an amount of about 17.5% by wt. based on the filtrate and in the presence of 1.25% by vol. of water based on the .dewaxing solvent. The urea contacting operation was carried out at ambient temperature of about 75 F. Substantially immediately upon contact of the urea with the water-containing `filtrate urea complex formation occurred ,and the urea complex formation reaction was substantially completely finished in less than about l0 minutes, the contacting operation between the urea and the filtrate being carried out under agitation or stirring.

Following the contacting operation the resulting solid urea-wax complexes were separated and decomposed in the presence of hot -toluene at a temperature of about 170 F. Solid urea was thereupon recovered from this urea-Wax breaking operation and recycled to contact additional filtrate containing partially dewaxed oil and dewaxing solvent. The results of these tests are set forth in accompanying Table No. 1.

Urea dewaxing operations as applied tothe ltrate recovered from a solvent dewaxing operation and containing partially dewaxed oil and dewaxing solvent (SO/50 mixture of methyl ethyl ketone and toluene) were carried out both in the presence and in the absence of water. It was observed that in a urea dewaxing operation carried out in accordance with the practice of this invention wherein the dewaxing solvent contained a m It is seen therefore amount of water dissolvedtherein, such as an amount of water in the range G25-2.5% by vol., e.g. 0.9-1.25% by Vol., based on the dewaxing solvent, complexes of urea-wax were substantially immediately formed upon contact with urea and the urea-wax complex formation reaction was completed in about l0 minutes. On the other hand, when the urea dewaxing operations were carried out in the substantially complete absence of water even after 13 hours of contact with urea the urea-wax` complex formation operation was not yet complete. In another test to show the iniluence of water upon the ureawax complex formation reaction it was observed that when a relatively large amount of water was present within the urea complex formation reaction admixture, such as an amount of water of about 10% by vol. based on the reaction admixture or filtrate, the urea complex formation reaction was retarded. lt is desirable therefore that theamount of water employed to enhance and improve the urea complex formation reaction be maintained at a relatively low level, such as an amount in the range 0.25-2.5% by vol. based on the dewaxing solvent or the filtrate containing oil and dewaxing solvent.

As will be apparent to those skilled in the art many changes, modifications and alterations may be made in the practice of this invention without departing from the spirit or scope thereof.

We claim:

1. A method of ydewaxing a waxy petroleum oil fraction which comprises contacting said waxy petroleum oil fraction with a dewaxing solvent consisting essentially of toluene and methyl ethyl ketone and a minor amount of water in the range 0.9-2.5% by vol. dissolved therein, the aforesaid contacting operation *being carried out at a relatively low temperature suicient to precipitate a substantial amount of wax from said waxy petroleum fraction, sepa-rating the resulting precipitated wax, recovering a liquid stre-am comprising dewaxed petroleum fraction dissolved in said dewaxing solvent yand containing said minor amount of water, contacting said liquid stream with urea under complex forming 4conditions to form solid urea complexes with the straight chain hydrocarbons in the resulting dewaxed petroleum fraction and separating the resulting solid urea complexes.

2. A method of :dewaxing a waxy petroleum oil fraction which comprises contacting said waxy petroleum oil fraction with a dewaxing solvent consisting essentially of toluene Iand methyl ethyl ketone and a minor lamount of water in the range (L9-2.5% by vol. dissolved therein, the aforesaid contacting operation being carried out at a relatively low temperature sufficient to precipitate a substantial amount of wax from said waxy petroleum oil fraction, separating vthe resulting precipitated wax, recovering a liquid stream comprising dewaxed petroleum oil fraction dissolved -in said dewaxing solvent and containing said rninor amount of water, cont-acting said liquid stream with urea under `complex formation conditions to form solid urea complexes with the straight chain hydrocarbons in the resulting dewaxed petroleum oil fraction, subjecting the resulting ladrnixture of urea, solid urea complexes, dewaxed petroleum oil fraction and dewaxing solvent to vacuum distillation to remove the methyl ethyl ketone therefrom, separating by filtration the solid urea `complexes and decomposing the separated solid urea complexes by contact wit-h toluene under complex breaking conditions to yield solid urea and recovering the resulting solid urea.

3. A method -as claimed in `claim 2 wherein the toluene used to decompose said separated urea complexes is separated by distillation from the resulting remaining admixture xafter separation of Isaid separated urea complexes therefrom.

4. A method in accordance with claim 3 wherein `the urea formed during the decomposition of the urea cominorplexes is separated and recycled to contact additional waxy petroleum fraction for the removal of w-axy straight chain hydrocarbons therefrom.

5. A method of dewaxing Ia waxy petroleum' oil tfraction which 4comprises admixing said mixture with -a de- Waxing solvent consisting essentially of methylehhylketone and toluene `and containing 0.9 to 1.25 vol. percent of Water therein to precipitate a substantial amount of lWax from said waxy petroleum oil fraction, separating the resulting precipitate, contacting the resulting mother liquor containing said dewaxing solvent containing said minor amount or" water therein with urea under conditions to effect the formation of sol-id urea complexes with 10 l the Wax remaining :in said mother liquor `and separating the resulting solid urea complexes.

References Cited in the file of this patent UNITED STATES PATENTS 2,577,202 Lien et al. Dec. 4, 1951 2,734,849 Gross etal Feb. 14, 1956 2,742,401 Knchen Apr. 17, 1956 2,786,015 Axe Mar. 19, 1957 2,823,172 Rumlberger et `al Feb. `11, 1958 2,862,868 Brown et al Dec. 2, 1958 2,913,390 Brunstrum Nov. 17, 1959

Claims (1)

1. A METHOD OF DEWAXING A WAXY PETROLEUM OIL FRACION WHICH COMPRISES CONTACTING SAID WAXY PETROLEUM OIL FRACTION WITH A DEWAXING SOLVENT CONSISTING ESSENTIALLY OF TOLUENE AND METHYL ETHYL KETONE AND A MINOR AMOUNT OF WATER IN THE RANGE 0.9-2.5% BY VOL. DISSOLVED THEREIN, THE AFORESAID CONTACTING OPERATION BEING CARRIED OUT AT A RELATIVELY LOW TEMPERATURE SUFFICIENT TO PRECIPITATE A SUBSTANTIAL AMOUNT OF WAX FROM SAID WAXY PETROLEUM FRACTION, SEPARATING THE RESULTING PRECIPITATED WAX, RE-

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