US2550058A - Production of oil-free wax and dewaxed oil from wax-bearing lubricating oil stock with a dewaxing solvent liquid - Google Patents

Description

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P. GEE FREE WAX AND DEWAXED OIL FRO WAX-BEARING LUBRICATING OIL STOCK WITH A DEWAXING SOLVENT LIQUID Filed July 15 PRODUCTION OF OIL QQQ QUSQQS URN hTToEuEYs April 24, 1951 Patented Apr. 24, 1951 PRODUCTION OF OIL-FREE WAX AND DE- WAXED OIL FROM WAX-BEARING LUBRI- CATING OIL STOCK WITH A DEWAXING SOLVENT LIQUID William Provine Gee, Plainfield, N. J assignor to Texaco Development Corporation, New York, N. Y., a corporation of Delaware Application July 15, 1948, Serial No. 38,864

9 Claims.

This invention relates to the production of oilfree wax and dewaxed oil from wax-bearing lubricating oil stocks by continuous filtration in the presence of a dewaxing solvent liquid.

The invention contemplates employing a dewaxing solvent liquid, advantageously a mixture of wax antisolvent liquid and an oil solvent liquid which exerts substantially complete solvent action upon oil but substantially no solvent action upon wax constituents of the mixture at dewaxing temperatures in the region of F. and below, and in which solvent liquid mixture water is at least partiall miscible at the temperatures employed in the process. The wax-bearing lubrieating oil stock and solvent liquid, substantially free from water, are chilled to and separated at a predetermined dewaxing temperature to produce dewaxed oil dissolved in solvent liquid and wax retaining solvent and a small amount of oil.

The Wax is re-dissolved in a further quantity of the solvent liquid and subjected to a secondary separation at a temperature substantially above the aforesaid dewaxing temperature, but in this secondary separation a small amount of water is incorporated in the mixture undergoing separation such that the solvent liquid exerts selective action as between the wax and the retained oil.

I have found that in solvent dewaxing operations involving both dewaxing of oils and recrystallization of the resultant Wax to produce marketable waxes in the same unit, it is difiicult and may be impossible to realize enicient results in the recrystallization step because the solvent liquid mixture necessarily common to both operations may not be best suited for the recrystallization step. This may be particularly true when the feed oil is a highly refined oil or one of high viscosity so that the amount of wax antisolvent component in the solvent mixture, for example, ketone, must be maintained at a relatively low value in order to obtain suitable miscibility of the oil in the solvent liquid at the required dewaxing temperature.

For example, a high viscosity, highly refined residual oil from Pennsylvania crude may require that the methylethyl ketone content of the conventional ketone-commercial benzol dewaxing solvent liquid mixture be held to a maximum of about 35% by volume of the solvent liquid mixture in order to avoid formation of two liquid phases when the mixture is cooled to the required devvaxing temperature, which may be in the range of about 0 F. and substantially below. On the other hand, if solvent of this low ketone content is used to recrystallize the Wax resulting from the dewaxing of this charge oil in order to produce marketable wax, the solvent has too great a solvent power for the wax with the result that poor fractionation of the wax occurs, accompanied by a low yield of product and a low filter ing rate.

Accordingly, my invention involves modifying the common solvent either prior to, during, or both prior to and during the recrystallization operation by incorporating water therein. Ad vantageously, the solvent liquid mixture employed in the recrystallization operation may comprise a portion of the solvent liquid from the normal solvent recovery which contains an appreciable quantity of water, as a resultof the employment of steam distillation in the recovery. Additional water from an extraneous source may be added, if such is required.

Recrystallization of the wax to produce a marketable product is normally conducted at a temperature above the freezing point of the water from the solvent mixture, for example, in the range about plus 20 F. to plus 50 F., and, therefore, the water does not crystallize to form ice, but instead remains in solution to modify the solvent in order that more efficient crystallization is obtained.

In order to describe the invention in more detail, reference will now be made to the accompanying drawing comprising a flow diagram for the process.

The wax-bearing lubricating oil stock is drawn from a source, not shown, through pipe I to a chilling coil 2 of conventional design. Solvent liquid, for example, a mixture of about 35% methylethyl ketone and commercial benzol, is conducted through pipe 3 and injected into the wax-bearing oil stream flowing through the chiller. This solvent may be mixed in the proportion of about '3 to 4 volumes of solvent per volume of oil. The entire amount may be mixed with the oil prior to introduction to the chiller or advantageously may be added incrementally during flow through the chilling system. If desired, the initial cooling may be in the substantial absence of solvent.

The chilled mixture at a temperature of about minus 15 F. is introduced through pipe 4 to a continuous rotary vacuum drum filter 5 of conventional design. Filtration is effected at about minus 15 F. q

The resulting filtrate comprising dewaxed oil of about 0 F. to minus 15 F. pour test dissolved in the main body of solvent liquid, is discharged ture, the amounts so recycled being sufiicient to maintain the desired ratio of liquids, to solids in the mixture undergoing filtration.

The column I is operated so as to distill the bulk of the solvent from the filtrate as a substantially water-free distillate. This distillate is conducted through pipe 9, condenser Hi and pipe II to a storage tank l2 for reuse.

The distillation residue is drawn off from the bottom of the column I through pipe I5. This residue comprises dewaxed oil containing a relatively small proportion ofisolvent liquid, for example, about 2 to 3% by volume of the mixture flowing through pipe l5. This residue is conducted to a stripping column lfi'wherein the residual solvent is distilled from the dewaxed oil with the aid of steam, thereby recovering the residual solvent in the form of a wet distillate, comprising about 80% water, which is removed through a pipe l8 and a condenser l9. This condensate is conducted through pipes 20 and 2! to a wax mix surge tank 22, to which reference will be made later.

The wax cake discharged from the filter is conducted through a pipe 25 to a receiver 26 from which it is conducted through a pipe 27, heater 28 and pipe 29'to the aforesaid surge tank 22. This tank is maintained at a temperature of about 130 F. and wet solvent liquid is supplied thereto through pipe 2 I, already referred to, and also ketone concentrate through pipe 30, referred to later. The temperature is maintained sufiiciently high to efiect complete solution of the wax in the solvent.

Since water is being introduced with the solvent flowing through pipe 2|, provision is made for phase separation. Thus, a layer of water containing some dissolved solvent accumulates in the bottom of the tank 22, while an upper layer of waxy hydrocarbon dissolved in solvent collects in the upper portion of the tank.

The hydrocarbon-solvent layer is, drawn off through pipe 3| into pipe 32, wherein it may be mixed with an additional quantity of dry solvent, if necessary in order to obtain the desired solvent dosage. From pipe 32 the mixture flows into pipe 35 and through cooler 36, wherein it is cooled to about +50 F. The resulting cooled mixture flows through pipe 31 to a secondary filter 50.

Provision may be made for diverting some of the fresh wax cake mixture flowing through pipe 29 into the pipe 35 as indicated, and likewise, provision may be made for drawing off through pipe 38 excess water layer accumulating in the bottom of the tank 22.. A portion of this withdrawn water layer may be diverted through pipe 39. for mixing with the stream flowing through pipe 35 in order to assure sufficient water to realize the desired modifying action. This. water may range from about 0.3 to 1.0% by weight of the'solvent in the mixture passing to the. secondary filter, the solvent amounting to from 6 to volumes per volume of slack wax.

That portion of the withdrawn water layer which is not divertedthrough pipe 39 is conducted through pipe 40 to a solvent .fractionator II. The water layer flowing through pipe 40 may comprise about 90% water and 10% solvent and is substantially free from benzol and toluol. The purpose of this fractionator is to concentrate the ketone and eliminate the accumulati l The excess water is discharged The distillate of excess water. from the system through pipe 42.

comprising about -90% ketone is conducted through pipe 63, condenser 44 and pipe 55, com municating with the previously mentioned pipe 30.

Returning to the filter 50; this filtration is effected at a temperature of about +50 F. to produce a secondary filtrate and a secondary filter cake. The secondary filtrate is conducted through a pipe 5| to an evaporating column 52, wherein the bulk of the solvent is removed as a distillate containing a fractional per cent of water through-pipe 53. This distillate is condensed in condenser 54 and conducted through pipe 55 to the storage tank l2a.

The distillation residue from column 52 flows through pipe 56 to a stripping column 5?, wherein the residual solvent is stripped, leaving a residue of slop wax or a mixture of oil and low melting point wax which is discharged through pipe 58. The distillation is eifected in the presence of steam, thereby obtaining a wet distillate containing approximately 80% water which is removed through pipe 58, condenser 65 and pipe 6!, which communicates with pipe 2|, and by which this wet distillate is passed into the surge tank 22.

The secondary wax cake is conducted through pipe 62 to a wax receiver 63. From here, it flows through pipe 64, heater $5 and pipe 66 to a secondary wax mix surge tank 51, which is maintained at a temperature of about 140 F.

A two-phase separation occurs in this tank, the bottom layer being water containing a small amount of dissolved solvent, while the upper layer comprises wax dissolved in solvent liquid. Thisupper layer is conducted through pipe 68 and heat exchanger 69 to a distillation column l0, wherein the bulk of the solvent is distilled from. the wax in the substantial absence of steam. The resulting solvent distillate is conducted through pipe H, condenser 12 and pipe '53 which communicates with a pipe 55 for return to the solvent storage tank Her.

The residual liquid is drawn off from the bottom of column 10 through pipe 14 to a stripper 75, wherein the residual solvent is distilled from the wax in the presence of steam. The solventfree wax is discharged through pipe 76, while the wet distillate is removed through pipe 11, condenser 18 and pipe 19 which communicates with pipe 6 l.

The water layer collecting in tank 6'! is drawn oil through pipe 35 to tank 22.

While not shown, provision may be made for conducting dry solvent from tank l2, via pipes 80 and 8! to each of the filters 5 and 58 as wash solvent for washing the filter cakes therein. As indicated, remaining dry solvent is passed through pipe 82 into tank I2a.

By way of specific example; a Mid-Continent residual lubricating oil stock, previously deasphalted and solvent refined is characterized by having an A. P. I. gravity of about 28.7 and a saybolt Universal viscosity of about seconds'at 210 F. 'I'hi's residual-stock, mixedjwithabout i volumes of solvent to 1 volume of stock, is chilled and filtered at minus 15 F. The solvent comprises a mixture containing about 43% by volume of methylethyl ketone and 57% of a benzenoid or aromatic hydrocarbon mixture of benzol and toluol in about equal proportions.

As a result of this primary dewaxing operation, there is obtained a dewaxed oil of minus 5 pour test and amounting to about 66.1% by volume of the feed stock. The slack wax contained in the primary filter cake has a melting point of about 166 F. and amounts to about 33.9% by volume of the feed stock.

The primary filter cake is dissolved in about 6 volumes of solvent liquid per volume of slack wax, the solvent being substantially free from Water and of the same composition as used in the primary filtration. This mixture is cooled to about +55 F. and filtered, obtaining a secondary filter cake.

The solvent-free secondary wax has a melting point of about 176 F. and amounts to about 12.2% of the residual stock charged to the primary filter.

By contrast, when the primary filter cake is redissolved in the same volume of solvent liquid and sufficient water is incorporated to saturate the solvent liquid at the filtering temperature, the yield of product wax of the same melting point is about 10% greater, namely 13.4% of the residual stock charged to the primary filter. Also there is realized a higher rate of filtration.

The method of flow described is particularly adapted to the use of a solvent liquid mixture of a ketone wax antisolvent and an aromatic hydrocarbon oil solvent where the ketone-water azeotrope formed in the steam stripping step is lower boiling than the aromatic hydrocarbon. Other ketone wax antisolvent liquids with which water is partially miscible under the conditions of use comprise acetone, methyl isobutyl ketone,.methyl normal butyl ketone and methyl normal propyl ketone. These are mentioned by way of example and without intending to exclude other solvents that may be used such as other ketones, aldehydes, etc. Also it is contemplated that instead of employing a mixture of solvents as described, a single solvent may be used.

Obviously many modifications and variations of the invention as above 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 production of oil-free wax and. dewaxed oil from wax-bearing lubricating oil stock with a dewaxing solvent liquid which exerts a substantially complete solvent action upon oil but substantially no solvent action upon wax constituents of the mixture at dewaxing temperatures of about 0 F. and below, and in which water is at least partially miscible and wherein said wax-bearing lubricating oil and solvent substantially free from water are chilled to said dewaxing temperature and subjected to wax separation to produce dewaxed oil dissolved in solvent and also wax retaining some solvent and a small amount of oil, and said wax is re-dissolved in a further quantity of said solvent and subjected to a secondary separation at a temperature substantially above said dewaxing temperature to produce a secondary oil dissolved in solvent and a secondary wax of low oil content, the steps which comprise incorporating a small amount of water, obtained from a source subsequently referred to, in the mixture of primary wax and solvent prior to said secondary separation, such that the solvent exerts selective action as between wax and saidretained oil at temperatures substantially below normal room temperature but above said dewaxing temperatures, cooling resulting mixture of wax, retained oil, solvent and water to a wax-crystallizing temperature substantially below normalroom temperature, effecting crystallization of wax therefrom, and removing crystallized wax substantially free from oil from the mixture, subjecting the solutions of oil in solvent resulting from said separations to a flash distillation in the substantial absence of steam to produce distillates of dry solvent and distillation residues of oil and retained solvent, subjecting said distillation residues to distillation in the presence of steam to produce distillates of wet solvent, and using said wet distillates to supply water required for said secondary separation.

2. In the production of oil-free wax and de- Waxed oil from wax-bearing lubricating oil stock with a solvent liquid mixture of an oil solvent liquid and a wax anti-solvent liquid which solvent liquid mixture exerts substantially complete solvent action upon oil constituents of said stock but substantially no solvent action upon wax constituents thereof at dewaxing temperatures of about 0 F. and below and in which water is at least partially miscible, the method comprising mixing the feed stock with said solvent liquid mixture, chilling resulting mixture to a dewaxing temperature in the range of about 0 F. and below to form a liquid phase comprising dewaxed oil and a solid phase comprising wax, separating said phases, the separated solid phase containing a small amount of retained oil and a minor portion of said solvent liquid mixture, adding a further quantity of said solvent liquid mixture to said separated solid phase sufiicient to effect solution therein of wax constituents of said solid phase at substantially above normal room temperature, incorporating a small amount of water, obtained from a source subsequently referred to, in the mixture of wax, retained oil and solvent liquids in an amount such that the solvent liquid mixture exerts selective action as between wax and said retained oil constituents at the temperature at which said wax constituents crystallize from the mixture, cooling resulting mixture of wax, retained oil, solvent and water to a wax crystallizing temperature, separating resulting crystallized wax in substantially oil-free form from the cooled mixture, subjecting the solutions of oil in solvent resulting from said separations to a flash distillation in the substantial absence of steam to produce a distillate of dry solvent and distillation residues of oil and retained solvent, subjecting said distillation residues to distillation in the presence of steam to produce distillates of wet solvent, and using said wet distillates to supply water required for said secondary separation.

3. The method according to claim 2 in which the solvent liquid comprises a mixture of a low molecular weight aliphatic ketone and a benzenoid hydrocarbon.

4. The method according to claim 2 in Which the solvent liquid comprises a mixture of methyl ethyl ketone and commercial benzol.

5. The method according to claim 2 in which the secondary separation is effected at a temperature in the range of about +20 to +50 F. and the solvent is saturated with water at the secondary separation temperature.

6. In the production of oil-free wax and dewaxed oil from wax-bearing lubricating oil stock with a solvent liquid mixture of an oil solvent liquid and a wax anti-solvent liquid which solvent liquid mixture exerts substantially complete solvent action upon oil constituents of said 7 stock but substantially no solvent action upon wax constituents thereof at dewaxing temperatures of about 0 F. and below and in which water is at least partially miscible, the method comprising mixing the feed stock with said solvent liquid mixture, chilling resulting mixture to a dewaxing temperature in the range about 0 F. and below to form a liquid phase comprisin de- Waxed oil and a solid phase comprising Wax, separating said phases, the separated solid phase containing a small amount of retained oil and a minor portion of said solvent liquid mixture, adding a further quantity of said solvent liquid mixture to said separated solid phase sufiicient to efiect solution therein of wax constituents of said solid phase at substantially above normal room temperature, incorporating a small amount of water, obtained from a source subsequently referred to, in the mixture of wax, retained oil and solvent liquids in an amount such that the solvent liquid mixture exerts selective action as between wax and said retained oil constituents at the temperature at which said wax constituents crystallize from the mixture, cooling resulting mixture of wax, retained oil, solvent and water to a wax crystallizing temperature, separating resulting crystallized wax in substantially oil-free form from the cooled mixture, subjecting at least one of said solutions of oil in solvent resulting from said separations to flash distillation in the substantial absence of steam to produce a distillate of dry solvent and a distillation residue of oil and retained solvent, subjecting resulting distillation residue to distillation in the presence of steam to produce wet solvent distillate, and using said last mentioned distillate to supply water required for said secondary separation.

7. The method according to claim 6 in which the solvent liquid comprises a mixture of a low molecular weight aliphatic ketone and a benzenoid hydrocarbon.

8. The method according to claim 6 in which the solvent liquid comprises a mixture of methyl ethyl ketone and commercial benzol.

9. The method according to claim 6 in which the secondary separation is eiiected at a temperature in the range'of about +20 to +50 F. and the solvent is saturated with water at the secondary separation temperature.

WILLIAM PROVINE GEE.

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

UNITED STATES PATENTS Number Name Date 2,106,234 Bray .Jan. 25, 1938 2,229,659 Carr Jan. 28, 1941 2,244,407 Smisloff June 3, 1941 2,274,373 Lyman Feb. 24, 1942 2,411,492 Wingrove Nov. 19, 1946 2,446,514 Stewart-ct a1. Aug. 3, 1948 2,486,014 Evans Oct. 25, 1949

Claims (1)

1. IN THE PRODUCTION OF OIL-FREE WAX AND DEWAXED OIL FROM WAX-BEARING LUBRICATING OIL STOCK WITH A DEWAXING SOLVENT LIQUID WHICH EXERTS A SUBSTANTIALLY COMPLETE SOLVENT ACTION UPON OIL BUT SUBSTANTIALLY NO SOLVENT ACTION UPON WAX CONSTITUENTS OF THE MIXTURE AT DEWAXING TEMPERATURES OF ABOUT 0* F. AND BELOW, AND IN WHICH WATER IS AT LEAST PARTIALLY MISCIBLE AND WHEREIN SAID WAX-BEARING LUBRICATING OIL AND SOLVENT SUBSTANTIALLY FREE FROM WATER ARE CHILLED TO SAID DEWAXING TEMPERATURE AND SUBJECTED TO WAX SEPARATION TO PRODUCE DEWAXED OIL DISSOLVED IN SOLVENT AND ALSO WAX RETAINING SOME SOLVENT AND A SMALL AMOUNT OF OIL, AND SAID WAX IS RE-DISSOLVED IN A FURTHER QUANTITY OF SAID SOLVENT AND SUBJECTED TO A SECONDARY SEPARATION AT A TEMPERATURE SUBSTANTIALLY ABOVE SAID DEWAXING TEMPERATURE SUBPRODUCE A SECONDARY OIL DISSOLVED IN SOLVENT AND A SECONDARY WAX OF LOW OIL CONTENT, THE STEPS WHICH COMPRISE INCORPORATING A SMALL AMOUNT OF WATER, OBTAINED FROM A SOURCE SUBSEQUENTLY REFERRED TO, IN THE MIXTURE OF PRIMARY WAX AND SOLVENT PRIOR TO SAID SECONDARY SEPARATION, SUCH THAT THE SOLVENT EXERTS SELECTIVE ACTION AS BETWEEN WAX AND SAID RETAINED OIL AT TEMPERATURES SUBSTANTIALLY BELOW NORMAL ROOM TEMPERATURE BUT ABOVE SAID DEWAXING TEMPERATURES, COOLING RE-

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