US2740746A - Methyl-ethyl ketone dewaxing process - Google Patents

Description

April 3, 1956 o. s. PoKoRNY ETAL 2,740,746

METHYL-ETHYL KETONE DEWAXING PROCESS Filed May l5, 1952 SEDAQAT l MG @RUM f f (2O [l 2i .1 ,Qll'gtvcgffv VAPOR, LIME \1\ @N fu' 1- 'n Y f (omnausEm.

` f WATER. 1Q" l OUTLET 5cm EMT l u E e) WASH F'l LTlzATE cam/EMT STORAGE i2) ML TANK, i5 """.`;'k, KNIFE y t d 25 r2`7- ".5 ,f1/'I' 1 l pEuT WASH LQUD wAx ii 50u/EMT l SLUMY i8" Y LNE l f HEAT l Y 50W M Exd HAM@ El 10 6 J E TV TEAM A Ll E Tua y1' 5T T 95 R 50u/EMT 'Fraai 6 FILTRATE 3L-VENT Qt-HLLESL c WAEHED WAx AnLE vd; fTorzAc-,E TAM. TAMLL States 2,740,746 METHYL-ETHYL KE'I'ONE DEWAXING PROCESS This invention concerns the dewaxing of petroleum oil fractions and in particular the dewaxing of lubricating oil. In accordance with this invention a particular ketone type solvent is employed as a dewaxing agent in a manner to substantially improve the character of the dewaxing operation. The solvent to be employed constitutes a mixture of a methyl-ethyl ketone type solvent with about 60 to 75 of diethyl ketone.

The present application is related to Serial No. 217,976 (now U. S. Patent No. 2,688,587, granted September 7, 1954), tiled March 28, 1951, for Oldrich S. Pokorny and George A. Speer. This application disclosed and claimed that particular portions of diethyl ketone when incorporated in a dewaxing solvent containing a normal propyl group had the eect of an anti-solvent for water. In some manner, 20 to 60% of diethyl ketone serves to minimize harmful etects of water contamination of the aliphatic ketone solvent containing a normal propyl group. The present invention is based on the discovery that the antisolvent powers of diethyl ketone towards water can also be appreciated when employing a methyl-ethyl ketone type solvent, provided about 60 to 75% of the diethyl ketone is employed. The anti-solvent powers of the diethyl ketone then serve to improve the basic characteristics of the methyl-ethyl ketone dewaxing operation so as to decrease sensitivity to water contamination, to increase iilter rates, to decrease oil contamination of the resulting Wax, and to permit attaining an oil of a low solid point at a higher operational temperature.

Since about 1930 one of the commercial processes for recovering Wax from petroleum oils has been the ketone dewaxing process. While other ketones may be employed in this process, it has been the general practice to employ methyl-ethyl ketone (in admixture with aromatics), as the solvent, so that the process has generally been known as the methyl-ethyl ketone, or MBK dewaxing process. Commercial MEK dewaxing processes simply require the addition of a suitable quantity of the MEK solvent to the oil to be dewaxedso as to permit complete solution of all wax present in the oil when the mixture is heated. After the wax has been dissolved, upon cooling down the mixture of oil and ketone, ,the wax is precipitated and is removed from the oil by tiltration. While, as indicated, the MEK process has been in commercial use for a great many years, certain deticiencies of this process have become apparent. For example, it has been found that with certain types of oil stocks, extremely poor iilter rates are obtained, presumably due to the formation of wax crystals which are diicult to separate from the oil. A concomitant of this difficulty is that the oil content of the wax is generally at a level which is undesirably high, which in turn results in poor yields of dewaxed oil. Consequently, it is the principal object of this invention to materially improve the ilter rates, to improve dewaxed oil yields, and to decrease the oil content of the wax obtained in the ketone dewaxing process. For example, it has been found that due to minor portions of water contaminating the dewaxing solvent, poor iilter rates are obtained and it becomes diiiicult to obtain oil of a desirably low pour point. Water contamination as ordinarily encountered in commercial operation furthermore results in a wax of a relatively high oil content and relatively poor yields of dewaxed oil. Consequently,

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it is the principal object of this invention to overcome these disadvantages of the methyl-ethyl ketone dewaxing process.

Throughout this disclosure, the solvent to be employed will be referred to as a ketone, or specifically as methylethyl ketone. However, it is to be understood that any ketone containing from 3 to 6 carbon atoms may be employed. Again, it is to be understood that the solvent consisting primarily of a ketone of this class may also include up to 50%, or more commonly, from 25 to 50% of an aromatic compound or compounds employed to favorably supplement the solvent action of the ketone. Benzene and toluene are examples of aromatic constituents which may and often are included with the lower molceular weight ketones such as methyl-ethyl ketone `to provide the dewaxing solvent.

In'employing ketone type solvents of the nature described, the oil to be dewaxed is diluted with the solvent and is then heated to a suicient temperature to dissolve all wax present in the oil. On cooling the oil-solvent-wax solution by use of heat exchanging, chilling surfaces, the wax is precipitated from the solution and may be recovered. The use of chilling surfaces or the external chilling of the solution is a characteristic of the ketone dewaxing process.

In accordance with this invention, it has been found that the solvent properties of a methyl-ethyl ketone type dewaxing solvent may be advantageously atiected by incorporation of about 60 to 75% of diethyl ketone. The resulting solvent composition consisting of this mixture of diethyl ketone and methyl-ethyl ketone is particularly desirable as regards the sensitivity of the solvent mixture for water contamination during the dewaxing operation.

In the conduct of commercial scale dewaxing of lubricating oils it is impractical to completely exclude all water. Thus, for example, the dewaxing solvents employed generally contain small percentages of water, usualy between 0.2 to 0.5 volume percent, which may be due to steam distillation employed in the inishing of these solvents. Again, the lubricating oil fraction to be dewaxed ordinarily is contaminated with a low percentage of water. Finally, water inevitably finds its Way into the dewaxing apparatus and feed stream through accidental contamination. The principal sources of this Water contamination are:

1.` Water emulsion in the waxy feed stocks caused by sweating in the storage tanks, leakage of steam used in heating coils employed to prevent crystallization of waxes, etc.

2. Recovery of the last traces of the dewaxing solvent from dewaxed oil or wax by steam stripping and re-usng this solvent in the dewaxing step.

The amount of water contamination which is ordinarily encountered is generally sutlicient to increase the Water content by 0.1 to 0.3 volume percent per day of dewaxing plant operation.

The presence of contaminating water, even in quantities as low as 1% or less, exerts several undesirable functions. First and most important, the presence of water raises the miscibility temperature of the dewaxing solvent and oil. This effect is so marked that the miscibility temperature of oil and methyl-ethyl ketone, for example, is raised 29 F. by the presence of 1% water. The result is that higher dewaxing temperatures would have to be employed to avoid contamination of the wax with oil precipitated from the solvent as a result of the presence of water.

In addition to this factor of adversely changing the miscibility temperature, or as a result of this factor, the filter rates which may be maintained are seriously affected by water. This is presumably due to blinding of the ilter cloths by the oil which is precipitated out when the immiscibility point is reached. The eiiect of water contamination on dewaxing plant operation is shown by the following summary of data obtained when using a mixture of methyl normal propyl ketone with methyl normal butyl ketone as a dewaxing solvent:

to use a continuous type of rotary filter. This consists of a drum 13, the cylindrical surface of which is covered with the filter cloth. The drum is mounted in a casing 14 on an axle, of Vwhich only the end 15 is shown.

Table l Charge Stock Filter Rate, US Percent Extracted: Percent Dewax- Dilu- Wash GaL/sq. ftJhr. Pour Dry Percent Mid- Water ing tion, Solvent, ASTM Wax Qll Continent in Temp., V. V. V./V. o F 1n in Distillate Solvent F. Feed Feed Waxy Dewaxed Feed Wax SAE Grade Feed O Stock 0.2 26 2.8 1. 8 5. 8 5. 1 +25 11. 6 11.0 0. 15 18 2. 8 2.0 4. 5 3. 9 +20` 12. 5 8.5 0. 2 20 2. 9 2. 2 4. 7 4. 1 +15 10. 8 6. 5 0. 8 19 2. 3 1. 9 4. 3 4. 0 +15 4. 5 23 1. 1 20 2. 5 1. 9 3.9 3. 6 +15 4. 5 2S 1. 18 3. 5 1. 9 3. 7 3. 2 +15 7. O 71 1. 0 24 3.6 2. 3 3. 4 1. 9 +20 6.5 88 0. 2 24 3. 4 2. 3 2. 8 2. 5 i-20 9. 6 23 0. 29 3. 3 2. 6 3.1 2. 7 +25 10. 6 13 v`The above data bring out the disadvantages of waterV contamination in dewaxingLresulting in large losses of oilinto the wax cake and inability to reduce the oil content of the wax even after re-pulping of the wax cake followed by a secondary de-oiling step. The wax finishing operation thus becomes more expensive if not, for practical purposes, impossible. Again, the effect of dewaxing under conditions'of incipient immiscibility resulted in a loss of approximately 10% in dev/axing plant throughput incurred largely due lto the more rapid blinding of the filters, necessitating more frequent hot washing of the filter cloth. The oil content of the stripped wax also increased from 8 to 11% to between 16 and 28%.

In accordance with this invention, these disadvantages, brought about by contamination of the dewaxing Voperation with water, may be substantially avoided by including about 60 to 75% of diethyl ketone in the methylethyl ketone dewaxing solvent. The dewaxing solvent thus consists of any one or a mixture of C3 to Cs aliphatic ketones together with about 60 to 75% of diethyl ketone. This solvent mixture may incorporateV up to Vabout 50% of an aromatic compound or compounds to supplement the solvent action of the ketones. A par'- ticularly preferred dewaxing solvent composition for use in this invention is composed of about 23.8% of methylethyl ketone, 5.1% of benzene. 5.1% of toluene and 60% of diethyl ketone. y

The manner in which the dewaxing-s'olvent composition. of this invention is to be employed may be under stood by reference to the accompanyingdrawing illusrtrating a diagrammatical flow plan of a suitable dewaxing operation.

The operation of a continuous filter is well known, and it need vonly besaid that the drum is continually rotated at a low speed, usually of the order of 21/2 minutes per revolution. The liquid ywax slurry is introduced at the bottom of the casing and filtration occurs on about 15 to 40% of the circumference of the filter drum. The filtrate passes through theY cloth and finds its way out through one end of the axle 15, which is of course in the form of a pipe. A pipe 16 connected to the end of the axle conducts the filtrate to a storage tank 17. From the storage tank the filtrate is passedY to a steam still 18 Vfrom which the solvent together withV steam passes overhead through vapor line 19 to a condenser 20. The solvent separates from the condensed steam in a separator drum 21. Water is discarded by pipe 22 and solvent passes by pipe 23 and a pump 24 to the tank 5 for re-use.

As indicated above, about 15 to 40% of the circum` ference of the drum is continually in use for filtration, being directly submerged in the wax-solution mixture. During this period, wax cake is formed which can be described as having a spongy structure, due to the inter locking of Wax crystals, in which the volume of voids filled with the solution is about 6 to l0 times as great as is the volume of the crystalline paraffin wax which isdeposited on the filter blanket. This wax cake continuously moves into the sector (about 40 to 55% of the circumference) in which it is .continuously Washed with VReferring to the drawing, numeral 1 designates al 'storf oil by means of pipe 4 from solvent tank 5 through line 6. g In general this is' done to put the process in operation, but after the conditions have been settled to a steady state, the bulk of the fresh solvent isnot added directly to the oil but is supplied for washing'filter cake l as will be disclosed below, and the washings from the filter, called cycle solvent are added to the oil to be dewaxed through pipe 4, as indicated. Y

The oil-solvent mixture isthen blended in the desired proportion, disclosed below, and is passed to heat exchangers S and 9, then through a chiller 10.V In the chiller the temperature is reduced to such a'poi'nt thatrthe waxy content of the mixture is solidified and the dewaxed oil after removal of wax would be uid at the desired pour temperature. Pipe 11 conducts this mixture of liquid constituents and solid particles of wax to a filter shown generally at 12. The filter may, of course, be an ordinary plate and frame type, but it is preferred fresh pre-cooled solvent. The pre-cooled solvent which is used as a washing liquor is drawn directly from tank 5. by a pump 2S and enters the filter casing at the top where it is distributed into 4 to 6 spray or drip pipes which distribute the wash solvent uniformly over the wax cake surface.

' In the washing cycle about 25 to 35% of the solution retained in the voids of the wax cake can be displaced by the wash solvent without changing the concentration of the oil in the filtrate. The filtrate from the Washing cycle is therefore split into two fractions. The first fraction, amounting to between 25 to 35% of the total solution in the wax cake, can easily be displaced, which is Videntical in composition to the main bulk of the filtrate obtained during the -submergence or filtration cycle, and is passed to the filtrate tank. The second fraction which has a substantially lowery concentration of oil than themainrbulk of the filtrate, lis `generally Ycalled cycle solvent and is used forV diluting the incoming waxy charge.- It will bc understood thaty some admixture of the filtrate and of the washing liquor is unavoidable in the commercial Vtype 'rotary lters even though the'axle of the filtering drum indicated by the filtrate passing out of the axle at one end, while the wash liquor or cycle solvent is removed from the opposite end.

The wash liquor ows through a pipe 27 to the heat exchangers 9 and 8, and then passes through a pipe 7 and is mixed with the original waxy feed passed through the pipe 4. As stated before, fresh solvent is not commonly used for diluting the waxy stock but is supplied chiey for washing the wax cake only.

However, when rotary filters operate at filter speeds of the order of 2 minutes per revolution, the hydraulics of the filter design necessitate the adjustment of the slide valve which makes it inevitable that an increased volume of wash liquor or cycle solvent is included in the filtrate. The volume of cycle solvent available is then insuicient for maintaining the desired dilution and when this occurs, the difference must be made up by the fresh solvent from a solvent tank 5. The basic principle which governs the filter operation is to regulate the separation of the filtrate and cycle solvent (wash liquor) so that not more than to 20% of the dewaxed oil is recycled in the dewaxing plant with the solvent used for diluting the waxy feed stock.

The total filtering cycle, i. e. time required for filtration,

l washing, drying and blowing or removing the wax cake,

is not materially lengthened by using a relatively large quantity of solvent for washing the wax cake, as the filtering rate of the fresh solvent towards the end of the wash cycle becomes very high. By applying all or most of the fresh solvent as wash solvent, it is possible however, to produce a wax having very low oil content, while the yield of dewaxed oil is close to the theoretical yield. That is, with an overall dilution of 2.0 to 3.0 parts of solvent to 1.0 part of waxy stock, it is possible to obtain a greater yield of dewaxed oil.

The washed wax cake is carried over into a removal zone, in which the cake is scraped from the filter blanket by means of a suitable doctor knife, and then slides into a trouh fitted with a screw conveyor. It is collected at 28.

The wax cake removed from the filter contains about 6 parts by volume of solvent per unit volume of parain wax. While the solvent to wax ratio can be somewhat reduced by a more prolonged drying on the lter, this would result in a lower throughput. If desirable, a larger reduction can be effected by repulping the Wax cake by means of a centrifugal pump or a mixer and conveying the wax slurry to another rotary filter similar to those used for the dewaxing operation. If desirable, the wax slurry is heated to between 60 and 95 F. before filtration to permit de-oiling at elevated temperatures. The removal of low melting point waxes in the de-oiling step materially aids the sweating operation or facilitates the manufacture of micro crystalline waxes from heavy lubricating oil distillates and residual oils. The solution thus removed might be recycled back as dilution, while the wax cake is collected and sent to the solvent recovery plant.

It will be understood that the dewaxing operation, that is, the mechanical separation of the wax from solution, may be accomplished by other means than by filtration. While filtration is perhaps the most advantageous mechanical means to separate the precipitated wax from the solution, centrifuges may also be employed. This method is, however, inefficient and much less desirable than the previously described removal of wax by continuous filtration.

As indicated, the dewaxing solvent to be employed comprises a mixture of diethyl ketone with methyl-ethyl ketone or other Ca to Cs aliphatic ketones. Benzene, toluene or other aromatics may be included in minor portions. The quantity of solvent to be used per volume of waxy oil will vary considerably depending upon the viscosity of the oil, the wax content, and the desirability of preparing commercial grades of wax from the wax cake formed on the filter. In general, it is possible to use less solvent with the lighter distillates than with the heavier oils. The total amount of solvent used, including that for washing, may be as low as one volume of solvent per volume of waxy oil. With heavier oils, or if it is desirable to produce wax -substantially free of oil, it is preferable to use from 21/2 to 3 volumes of solvent per volume of oil. It is rare that more than 31/2 volumes of solvent are required, although even larger amounts than this may be advantageous when the wax content of the oil substantially exceeds 15 to 20%, chiey to increase the uidity of the wax slurry charged to the continuous filter-s.

The ltration rate in continuous rotary filters with these solvents will also vary with the viscosity of the oil, but even in the case of very viscous residual oils and cylinder stocks it is possible to obtain filter rates in excess of 3.5 gallons of waxy oil per square foot of lter area. The separation between oil and wax is remarkably sharp, and while in most cases the pour point of the oil from the filtrate is the same as the dewaxing temperature, it is found that it is even possible to obtain pour points from l0 to 15 F. below the dewaxing temperature.

In considering the desirability of employing diethyl ketone in the solvent compositions described, the following data is significant. f The effect of water on the solubility of a typical lubricating oil fraction employing a variety of dewaxing solvents was determined. In these experiments the lubri eating oil fraction selected was a Mid-Continent SAE- lubricating oil. This oil was diluted with three parts of different solvents having the compositions indicated in the following table. solvent-oil mixtures was determined for the anhydrous solvent compositions and for .5%, 1%, 1/2%, and 2% water contamination. The data is tabulated in the following table:

Table Il Composition of Dewaxnig Solvent Mlseibility Temp. ln F. After Adding- Percent Methyx- Percent Percent gigi@ 0% 0.5% 1% 1.5% 2.0% Ethyl Benzene Toluene Ketone Water Water Water Water Water Ketono 90 l0 39 53 67 8l 94 75 25 27 42 57 70 83 60 40 15 31 46 60 73 60 -2 l5 31 46 49 25 75 1 15 l 7 18 85 26 40 54 68 82 70 ll 27 27 27 2 63 l0 9 25 25 25 52. 5 25 7 16 16 16 5 42 40 -l +2 +2 +2 l 51 40 2l 35 48 23.8 -5 5 -6 -6 1 The methyl-ethyl ketone-aromatics portion consists of 85% methyl-ethyl ketone, 7.5% benzene, 7.5% toluene.

2 The methyl-ethyl ketone-aromatlcs portion consists o! 70% methyl-ethyl ketone, 16% benzene. 16% toluene.

The miscibility tempera-ture of theV As indicated in the preceding table, employing anhydrous methyl-ethyl ketone, the Mid-Continent lubricating oil employed could not be reduced to a pour point substantially below about 46 F. without encounteringV conditions of immiscibility. Furthermore, when pure methyl-ethyl ketone was contaminated with the quantities of water shown in the table, the anti-solvent action of the water resulted in an even poorer solvent power. Thus, for example, with 1% of water in methyl-ethyl ketone, the miscibility temperature of the oil solvent mixture was 75 F. However, when 60% of diethyl ketone is added to methyl-ethyl ketone, the miscibility temperature of this solvent mixture and the lubricating oil employed was sharply dropped. Thus, for this solvent composition, 0.5% of water may be tolerated while permitting attaining a miscibility temperature of only 15 F. An even greater improvement is attained by employing 75 of diethyl ketone. Y

A substantially anhydrous mixture of 85% methylethyl ketone, 71/2% benzene, and 71/2% toluene is required to dewax the lubricating oil distillate at 26 F. to provide an oil having a solid point of about 26 F. However, by incorporating substantial portions of diethyl ketone, the data again shows that substantially greater (to 0.7%) water contamination of the solvent may be tolerated when dewaxing at the same temperature for the same solidil'lcation point.

When a mixture of 70% methyl-ethyl ketone, 15% benzene, and 15% toluene is used in dewaxing Mid- Continent SAE-30 grade distillate to a solid point of 0 or F., the solvent must be substantially anhydrous or conditions of oil-solvent immiscibility will be encountered. However, when about 40% diethyl ketone is added to this solvent, 2% or more water can be tolerated, and conditions of oil-solvent immiscibility will Ynot be experienced.

The following examples illustrate the use of these mixtures for dewaxing extracted Mid-Continent SAE-3() distillate diluted with 3 volumes `of the solvent, chilled at a controlled rate and filtered to remove the wax.

the dewaxing temperature. The follow-ing table shows;l thatthe solubility of wax in a solventconsisting of di ethyl ketone alone is about equivalent to that in a conventional MEK solvent consisting of 70% methyl-ethyl ketone, 15% benzene and 15%` toluene, and is slightly greater than the solubility of the wax in a mixture of methyl-ethyl ketone and 60% diethyl ketone. Hence, the use of diethyl ketone in mixture with methyl-ethyl ketone-aromatics dewaxing solvents will not have an ad- What is claimed is: Y

1. Process ofdewaxing mineral oil which comprises diluting the oil with a solvent comprising methyl-ethyl ketone and about Y60 to 7 5% by volume, based on the total solvent, of'diethyl'ketone, therea ter chilling the mixture to a temperature at which wax is caused to precipitate, removing thewax and recovering dewaxed oil from the filtrate.

2. The processdened by'claim l in which the said solvent includes up to about by volume, based on said methyl-ethyl ketone, of an aromatic hydrocarbon chosen from the group consisting of benzene kand toluene.

3. A dewaxingv solvent composition comprising methylethyl ketone in admixture with about 60 to 75% by 40 volume of diethyl ketone based on the total solvent.

Table III Waxy Dist. Filter Rate) Solvent Composition Ig? 't lro Dewx- Dewafl ohnnng Rate ofiu O11 Solidi- Temg iication o p" Point, lirerriienit P t P t Pelrnc'ent F' F e y el'Cll elCeIl l- Ethyl Benzene Toluene ethyl 2 F'Mm' 5 F'Mm' Ketone Ketonc volume percent, Wax cake approximately 15% oil.

2 Methyl-ethyl ketone-benzene-tolucne portion ot these solvents consist oi 70% methylethyl ketone, 15% benzene, 15% toluene.

These examples indicate that, within the limits of experimental error, the addition of diethyl ketone to the mixture of methyl-ethyl ketone and aromatics does not aiect the filter rate obtainable with the methyl-ethyl ketone and aromatics mixture alone.

As illustrated above, it is not possible to dewax Mid- Continent SAE-30 distillate using methyl-ethyl ketone below about F. (assuming the water content of the solvent to be 0.3% which is normally encountered in commercial plants) without experiencing a condition of immiscibility of the oil and solvent. However, when from to 75 volume percent of diethyl ketone is added to the methyl-ethyl ketone, this distillate may be successfully dewaxed at approximately +l0 F. at a higher filter rate than with diethyl ketone alone.

Solidication points of dewaxed oils obtained from the liltrations of the above table are equal to or lower Ythan 4. A dewaxing solvent composition consisting essentially of methyl-ethyl ketone in admixture with about 60 to 75% by volume, based on the total solvent, of diethyl ketone including up to about 50% by volume, based on the methyl-ethyl ketone of a solvent selected from the group consisting of toluene and benzene.

5. A lubricating oil dewaxing process which comprises admixing the oil with a solvent consisting essentially of up to 40% by volume, based on the total solvent, of methyl-ethyl ketone, up to about 50% by volume, based on said methyl-ethyl ketone, of an aromatic hydrocarbon selected from the group consisting of benzene and toluene, and in the range of about V60-75% by volume based on the total solvent of diethyl ketone, thereafter chilling the said oil-solvent mixture to a temperature at which wax is caused to precipitate, removing the wax and recovering dewaxed lubricating oil.

Claims (2)

1. PROCESS OF DEWAXING MINERAL OIL WHICH COMPRISES DILUTING THE OIL WITH A SOLVENT COMPRISNG METHYL-ETHYL KETONE ABOUT 60 TO 75% BY VOLUME, BASED ON THE TOTAL SOLVENT, OF DIETHYL KETONE, THEREAFTER CHILLING THE MIXTURE TO A TEMPERATURE AT WHICH WAX IS CAUSED TO PRECIPITATE, REMOVING THE WAX AND RECOVERING DEWAXED OIL FROM THE FILTRATE.

3. A DEWAXING SOLVENT COMPOSITION COMPRISING METHYLETHYL KETONE IN ADMIXTURE WITH ABOUT 60 TO 75% BY VOLUME OF DIETHYL KETONE BASED ON TEH TOATL SOLVENT.

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