US3105809A - Method of solvent dewaxing - Google Patents

Description

R. M. BUTLER ETA].

METHOD OF SOLVENT DEWAXING Oct. 1, 1963 5 Sheets-Sheet. 1

Filed March 14, 1958 mmmQZ Ioxm 320224 Roger M. Butler David M. MocLeod John L. Tiedje Inventors By WM 72% Attorney United States Patent 3,105,809 METHOD OF SOLVENT DEWAXING Roger M. Butler, David M. MacLeod, and John L. Tiedje, Samia, Ontario, Canada, assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Mar. 14, 1958, Ser. No. 721,415

3 Claims. (Cl. 20831) 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 and methyl isobutyl ketone. The specific composition of the solvent depends upon the nature of the particular oil to be treated; the solvent may contain from to 90% of methyl isobutyl ketone.

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 MEK dewaxing process. Commercial MEK dewaxing processes simply require the addition of a suitable quantity of the MEK solvent to the oil to be dewaxed so 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 filtration. While, as indicated, the MEK process has been in commercial use for a great many years, certain deficiencies of this process have become apparent.

In general, three properties are of major importance in determining the suitability of a dewaxing solvent. These are:

(1) The miscibility temperature of the oil and the solvent. This determinesthe lowest temperature at which the solvent is useful.

(2) The solubility of wax in the solvent. This in turn determines the difference between the filtering temperature and the pour point.

(3) The oil filter rate. the filters required.

The comparison of solvents must be made with the heaviest stock which is to be processed, since this will have the highest miscibility temperature with any particular solvent. In Table I thereis set forth the effect of chemical composition of certain normal aliphatic ketones as dewaxing solvents. A heavy stock, namely a 180/190 SUS at 210 F. distillate from Leduc crude, phenol treated to 90 V1. is used in this series.

TABLE I Efiect of Chemical Composition of Normal Aliphatic Ketones on Suitability as Dewaxing Solvents 3 Minimum solid point obtainable at reasonable yield. 4 For solvent to oil dilution ratio of 2.

This determines the size of' 0 From the above table it is evident that as the molecular weight of the solvent increases, the miscibility temperature and the filter rate decrease, while the wax solubility increases. The most desirable solvent from such a series is the one in which the oil is just soluble enough for the liquid to exist as a single phase at the temperature required to give the desired solid point. This solvent will give the best filter rate and the highest filtering temperature. Since 18 F. is a satisfactory temperature for the solid point of the dewaxed heavy stock, methyl propyl ketone is the most satisfactory solvent, shown in Table I.

Methyl propyl ketone has superior filtering temperatures and filter rates to the commercial methyl ethyl ketone-toluene mixture referred to above for a given minimum solid point. Itis, however, very expensive and is available in limited supplies. Alternate solvents, such as diethyl ketone, may be used but this cheaper solvent is somewhat inferior.

It is the principal purpose of the present invention, therefore, to set forth a solvent composition for dewaxing, lubricating oils, and wax-containing oils generally, with a solvent composition of high effectiveness and efficiency which is readily available and which is substantially cheaper than methyl propyl ketone.

Other and further advantages and objects of the present invention will be made more clear hereinafter.

In accordance with the present invention, it has been found that a mixture of 40 to 20 parts of methyl ethyl ketone and 60 to parts of methyl isobutyl ketone is an excellent dewaxing solvent and has substantially the same properties as pure methyl n-propyl ketone.

The use of the dewaxing solvent can be shown by the attached figures. In FIGURE 1, numeral 1 denotes a storage tank whereby waxy oil is maintained at a temperature above its solidification point. The storage tank for fresh ketone is denoted 2. Oil is pumped from storage by means of pump 3, while ketone is pumped from storage by means of pump 4, and the streams are combined at 5 in the desired proportions. The mixture of oil .and solvent is passed through a steam heat exchanger 6 to ensure complete solubility of the waxy oil and solvent.

The mixture then passes through a water-cooled heat exchanger 7 where it is cooled to just above the temperature at which solid wax appears. The mixture is then further cooled in a scraped surface exchanger 8 which utilizes filtrate as a cooling medium, and finally chilled by ammonia. Further solvent, which is chilled by ammonia in the heat exchanger 10, may be added as secondary dilution at 11. The finally chilled and diluted mixture is fed into the filter feed surge tank 12.

Fromthe surge tank the mixture is conducted to a filter 13, preferably of the conventional rotary type. Chilled solvent is applied as wash at 14 to the wax cake on the filter. The liquid filtered through the cake flows to the filtrate receiver drum 15. The wax cake is discharged at 16 in the usual manner by a doctor knife, and is pumped, still cold, by pump 17 to a second deoiling filter 18. Before entering this filter the wax cake may be diluted with chilled fresh solvent at 19. Chilled fresh solvent is applied as wash to the wax cake on the deoiling filter at 20. The filtrate is pumped to the filtrate receiver drum 15. The wax cake is pumped by pump 21 through a steam heat exchanger 22, which melts the cake, and then into a surge drum 23. It is then ready to be processed inthe solvent recovery section.

The wax and solvent are pumped by pump 24 from the wax surge drum 23 to a distillation tower 25, where most of the solvent, which has a much lower boiling point than the wax or oil, is distilled overhead at 26. The overhead solvent is condensed in condenser 27 and pumped by pump 28 to the fresh solvent tank 2. The bottoms from the tower consist of wax which contains a small percentage of solvent and are fed into a wax stripper tower 29, where steam is injected. By this means the wax is freed from solvent and wax is removed from the bottom of the tower. Steam and solvent are distilled overhead and are condensed at 39 and sent to the solvent settling drum 31.

Solvent is similarly separated from the filtrate, which is pumped by pump 32 from the filtrate receiver through the scraped surface exchanger 8, where the filtrate acts as the cooling medium, into the distillation tower 33. The solvent distilled overhead at 34 from this tower is condensed at 27 and pumped to the fresh solvent tank 2. The oil and ketone from the bottom of the tower are fed to a steam distillation tower 35. The wet solvent overhead goes to the solvent settling drum 31, while solvent-free dewaxed oil is drawn oiT the bottom of the tower.

The solvent settling drum contains the water and solvent distilled from the two previously described steam strippers. The liquids settle into a heav, water-rich phase saturated with solvent and a light, solvent-rich phase which is saturated with water. The Water-rich phase is drawn oil from the bottom of the drum and steam distilled in a packed distillation tower 36. The overhead, 37, from this tower consists of water and solvent which are condensed at 38 and returned to the settling drum, where they separate into water-rich and solvent-rich phases. Pure water is drawn from the bottom of tower 36 and run to the sewer.

The upper layer from the settling drum 31 is distilled in a distillation tower 39 (dehydrator). The overhead, 46, consists of water and solvent and is condensed and returned to the settling drum 31, while water-free solvent is drawn off from the bottom of the tower and pumped FIGURE 2 shows the way in which solvent is recovered when using water saturated solvent. The chilling and filtering sections are exactly the same as in FIG- URE l.

The filtrate, which is almost water-free, flows to a distillation tower 33. The overhead from tower 33 leaves at 34, is condensed in the water-cooled exchanger 27. This overhead is also almost dry and is used as secondary dilution and wash for the filters. Dry solvent is desirable for these uses so that ice does not form in the solvent chillers. If wet solvent were used it might be necessary to use scraped surface chillers for the solvent as well as for the waxy slurry. The bottoms from tower 33 ilow to the steam distillation tower 35, where wet solvent is obtained overhead and dewaxed oil is removed at the bottom. The overhead is condensed (30), and flows to the solvent settling drum 31.

The wax and solvent in the surge drum 23 after the filters contain Water. They are fed to the solvent settling drum 31, where a water-rich lower layer, and an upper layer consisting of a wax and solvent mixture which is water saturated, are formed.

The aqueous lower phase goes to a steam stripper 36, where the solvent is distilled overhead at 37 accompanied with some water, and returned to the settling drum while essentially pure water is discarded to the sewer from the tower bottom.

The upper phase from the solvent settling drum first goes to the distillation tower 25. The overhead from this tower is removed at 26, and contains about 1 or 2 percent of water, i.e. it is less than saturated but still wet. This wet solvent is condensed, 43, and sent to the solvent tank 2, where it is stored for use as primary dilution. The bottoms from tower 25 go to the steam stripper 29,

to the fresh solvent tank 2. where solvent-free wax is obtained at the bottom and wet In order to prevent build-up of water from various solvent is distilled overhead. This wet solvent is consources in the fresh solvent, some solvent is continuously densed at 30 and is sent to the solvent settling drum. withdrawn at 41 and sent to the solvent dehydrator at 42. Table II compares the properties of various ketone It may be seen that essentially dry ketone is used solvents for dewaxing waxy distillates. These data show throughout the dewaxing process. This method of septhat the mixture of the present invention gives substanarating water from the solvent is possible when the vapor tially the best overall performance and is essentially obtained when a mixture of water and solvent is boiled equivalent in physical properties to methyl n-propyl kewill separate into two liquid phases when condensed. It tone, long considered to be the best available material. is particularly applicable to ketones such as methyl n- The mixture of the present invention, however, is far propyl ketone, diethyl ketone and methyl isobutyl ketone 45 cheaper and more readily available.

TABLE II Comparison of Dewaxing Solvents Relative Temp. Minimum Solvent Composition Filter Difieren- Solid Price Avail- General Comment Rate tial, F. Point iii/gal. ability of 011, F.

Methyl n-propyl kctonc 100 0 l8 3. 20 Fair Best but very expensive. methyl i-butyl ketone; 30% methyl 100 1 19 0. Good Equivalent to best but ethyl ketone. cheaper. 56% methyl ethyl ketone;44% toluene 75 12 18 0. 53 Good Poor filter rate. Low

filtering temperature. Methyl n-butylketone 72 8 -10 Poor Po0rfilterrate,lowfiltcring temperature. High price. Methyl i-butylkctone 72 5 5 0.94 Poor filter rate, low

filtering temperature. 70% diethylketone; 30% methyl ethylkctonc 120 -l 33 1.49 Poor Good filter rate, poor minimum solid point, expensive, limited availability.

1 Filter rates obtained with different solventshave been compared by taking the filter rate of methyl n propyl kctonc as a standard, and equal to 2 The temperature differential is the number of degrees Fahrenheit that the filtering temperature is above the pour point of the dewaxed oil.

which form azeotropes with water, and whose solubility for water at ambient temperatures is less than the amount of water contained in the azeotrope.

if it is desired to use water saturated solvent, then during the filtering process almost all the water will be precipitated as ice at the low temperatures normally used and the wax cake will contain appreciable amounts of Water, while the filtrate will be essentially water-free.

An important advantage of the mixed solvent dewaxing technique of the present invention is the possibility of varying the'proportion of the solvents in accordance with the type of base stock being dewaxed. This is particularly beneficial in solvent mixtures containing the relatively cheap MEK because lighter oils which have miscibility requirements less difiicult to meet can be processed with an MEK-MiBK containing a higher proportion of MEK.

This leads to higher filter rates because of the lower viscosity of M EK, and higher filtering temperatures can be employed to obtain-oils of the same pour point due to the lower wax solubility of V In Tables 'III and IV are presented data showing theadvantages of using optimum mixtures of MiB-K and MEK for a varied group of feed stocks. These data also show that these mixtures are far superior to conventional mixtures of MEK and toluene. In the tables below, the MCT 60 and MCT 30 stocks are Mid-Continent type motor oil base stocks corresponding to an SAE 60 and an SAE 30 designation, respectively. Barosa 56 and 801-; vent 100 Neutral are northern Louisiana stocks of 106- 107 V1. having a viscosity at 210 of S6 S.S.U. and a viscosity at 100 of 100 S.S.U., respectively.

Table -III shows that inthe case of MCI 60 oil, the mixture of 70% MiBK-30% MEK is better than 80% of MiBK:MEK was essentially equivalent to the normally used, best mixture of MEK and toluene. However,

when the optimum mixture of MiBK and MEK contain- I ing 25 MiB'K and 75 MEK was used, the same advantages were again found for the MiBKzMEJK mixture.

In general, the less viscous the oil, the greater the pro portion of MEK present in the solvent mixture. Thus, when an MST or an 5 oil is dewaxed, which oils have SSU viscosities at 210 of 38r to 45, the solvent may consist of 75 to 90% MEK and 10 to 25% MiB-K. MCT'SO oil has a viscosity of 67 SSU at 210.

It can be seen from these data that there is an op- TABLE HI Advantages Obtained by Use of Optimum Mixture of M iBK and MEK Filter Liquids: V Filtering Pour Point Rate 1 Solids Feedstock Solvent Composition 'lemperaof Dewaxed USG/S Ratio in ture, F. on, F. Ft Cake 70 MiBK, 30 MEK 17 18 7. 9 8. 9 80 LiiBK, MEK l6 l8 7. 6 9. 1 55 MEK, 44 Toluene, 1% Water.. 5 l8 6. 4 8. 7 7O MiBK, 30 IVIEK 28 7. 2 8. 4 35 MiBK, 65 IVIEK 25 26 10. 8 6. 9

Conditions: Filter leaf experiments, 10 MOT 60 dilution 4.0:1, MCT dilution vacuum, filtered for 60 seconds and dried for 30 seconds, no washing. 3.0:1; chilled 6 F./minute.

1 Calculated for a 2% minute per revolution filter speed, for waxy oil charge.

Comparison of MEK'B/HBK TABLE IV M ixtures With MEK:T0luene Mixtures Conditions: 24" Vacuum, chilled 3 F. per minute. Filtering cycle 2 minutes/revolution, 60 seconds filtering, 5 seconds drying, 25 seconds Washing, 10 seconds drying.

MiBK-20% MEK because a better filter rate, higher filtering temperature for the same pour point dewaxed oil, and a drier cake are obtained. A drier cake results in a higher yield of dewaxed oil to be obtained. The 70:30 mixture is the optimum, because higher percentages of MEK would give miscibility difficulties when dewaxing to obtain MCT 60 oil of 18 F. pour point. The 70:30 mixture is also seen to be better than a typical mixture of MEK and toluene in filter rate and filtering temperature.

V The figures given for MCT 30 oil confirm the'above conclusions. Since this is a lighter oil, a higherpercentage of MEK can be'used, and the optimum mixture consists of approximately MiBK and 65% MEK.

Compared with the 70:30 mixture of MiBKzMEK, the optimum mixture gives a higher filter rate, lower pour point for the same dewaxing temperature, and a drier 7 in the presence of water in the recovered solvent.

As indicated previously, the removal of this water from the solvent is important because even small percentages of Water may cause corrosion and also reduce the eifectiveness of the solvent by lowering the solubility of oil in the solvent. Furthermore, wateralso causes foaming during the stripping of oil and wax.

Methyl ethyl lretone and water have widely different boiling points, of 175.3 F. and 212 F. respectively, but they cannot be separated by simple distillation because they form an azeotrope of lower boiling point than either component. This makes it difficult to dehydrate solvents including by the conventional dehydration process involving a dehydrator tower and a decanter because the MEK azeotrope which distil'ls over is a homogeneous one and does not split into two liquid layers on condensation and cooling. This fact has discouraged the use of solvent mixtures containing MEK in dewaxing.

However, although MEK saturated with water does not evolve a vapor which will split into two phases on condensation, in accordance with the present invention only a small quantity of .MiBK has to be present in the boiling, water-saturated ketone for a two phase condensate to be formed. This is shown by the vapor-liquid equilibrium diagram shown in FIGURE 3.

For example, a mixture containing about 70 mole percent MiBK and 30 mol percent MEK could dissolve about 19 mole percent water. This saturated mixture is shown in FIGURE 3 as Point A, which has a composition of 13.3% water, 26% MEK and 60.7% MiBK. Point A is situated just inside the single phase region.

When the mixture represented by point A is boiled the vapors evolved have the approximate composition represented by point B, i.e. 44.8% water, 31.9% MEK and 23.3% MiBK. Point B is within the two phase region for liquid mixtures and the distillation product would form two liquid phases when condensed.

When pure MEK or almost pure MEK has to be dehydrated, this can be done by circulating MiBK as a solvent within the dehydrating system.

In FlGURE 4 is shown schematically a method for dehydration of a mixture of MEK and water using MiBK as a solvent. Wet ketone, if it is in two phases, is passed into the system through line 52 to decanter 54. If the wet feed, however, consists only of one phase, it is passed into the system through line 66 into dehydrator '70. The flow of streams in FIGURE 4 is indicated and it is evident that in accordance with the schematic process described, a substantially anhydrous MEK product may be recovered through line 82.

When substantial quantities of MiBK are present in the solvent, as for example in the 70:30 MiBK-MEK mixture previously discussed, it is not necessary to circulate extra MiBK as in FIGURE 4 and a dehydrating system similar to that shown in FIGURE 1 can be used.

Experimental results obtained in a continuous unit of this design are given in Table V. These results clearly show the high extent of dehydration that may be obtained by this process.

TABLE V Dehydration of Methyl Ethyl Kctont M ethyl I sobutyl Ketone Mixtures in Continuous Laboratory Unit What is claimed is:

1. A lubricating oil dewaxing process which comprises admixing the oil with a solvent consisting essentially of about 90 to 10 parts by volume of methyl ethyl ketone and about 10 to 90 parts by volume of methyl isobutyl ketone, chilling the said oil-solvent mixture to a temperature at which the wax is caused to precipitate, filtering solvent from said precipitated wax, recovering said wax, passing filtrate to a distillation zone, separating overhead a ketone solvent-containing stream, withdrawing from a lower portion of said zone an oil and ketone containing stream, passing said oil and ketone containing stream to a steam distillation zone, recovering overhead a wet ketone stream, withdrawing from a lower portion of said zone a solvent-free dewaxed oil, passing said wet ketone to a settling zone, withdrawing an upper layer rich in ketone from said zone, distilling said layer in a dehydration-distillation zone, recovering overhead a water and ketone containing stream, withdrawing from a lower portion a substantially water free ketone stream, passing said last named stream to a solvent storage zone, and recycling said water containing ketone stream to said settling zone.

2. The process of claim 1 wherein said dewaxing solvent consists essentially of to methyl isobutyl cetone and 40 to 20% methyl ethyl ketone.

3. In the process of treating an oil stock which comprises contacting the oil stock with a solvent consisting essentially of about -10 parts by volume of methyl ethyl ketone and 1090 parts by volume of methyl isobutyl ketone and cooling the mixture to form a precipitate, separating the precipitate from the solvent oil solution, and separating the solvent from the oil wherein the solvent accummulates substantial quantities of water, the improvement which comprises passing said wet solvent ketone to a settling zone, withdrawing an upper layer rich in ketone from said zone, distilling said upper layer in a dehydration distillation zone, recovering overhead a water and ketone-containing stream, withdrawing from a lower portion a substantially water-free ketone stream, and recycling said overhead water-containing ketone stream to said settling zone.

Temperature of Dry FeedF. Decanter temperature80F.

Dehydration column was 1 inch LD. and contained 10 inches of 0.16 Gannon protruded stainless steel packing.

References (Cited in the file of this patent UNITED STATES PATENTS 2,446,514 Stewart et al Aug. 3, 1948 2,603,589 Schaerer July 15, 1952 2,670,318 Halamka et al. Feb. 23, 1954 2,688,587 Pokorny et al. Sept. 7, 1954 2,745,791 Knox May 15, 1956 2,748,056 Backlund et a1. May 29, 1956

Claims (1)

1. A LUBRICATING OIL DEWAXING PROCESS WHICH COMPRISES ADMIXING THE OIL WITH A SOLVENT CONSISTING ESSENTIALLY OF ABOUT 90 TO 10 PARTS BY VOLUME OF METHYL ETHYL KETONE AND ABOUT 10 TO 90 PARTS BY VOLUME OF METHYL ISOBUTYL KETONE, CHILLING THE SAID OIL-SOLVENT MIXTURE TO A TEMPERATURE AT WHICH THE WAX IS CAUSED TO PRECIPITATE, FITLERING SOLVENT FROM SAID PRECIPITATED WAX, RECOVERING SAID WAX, PASSING FILTRATE TO A DISTILLATION ZONE, SEPARATING OVERHEAD A KETONE SOLVENT-CONTAINING STREAM, WITHDRAWING FROM A LOWER PORTION OF SAID ZONE AN OIL AND KETONE CONTAINING STREAM, PASSING SAID OIL AND KETONE CONTAINING STREAM TO A STREAM DISTILLATION ZONE, RECOVERING OVERHEAD A WET KETONE STREAM, WITHDRAWING FROM A LOWER PORTION OF SAID ZONE A SOLVENT-FREE DEWAXED OIL, PASSING SAID WET KETONE TO A SETTLING ZONE, WITHDRAWING AN UPPER LAYER RICH IN KETONE FROM SAID ZONE, DISTILLING SAID LAYER IN A DEHYDRATION-DISTILLATION ZONE, RECOVERING OVERHEAD A WATER AND KETONE CONTAINING STREAM, WITHDRAWING FROM A LOWER PORTION A SUBSTANTIALLY WATER FREE KETONE STREAM, PASSING SAID LAST NAMED STREAM TO A SOLVENT STORAGE ZONE, AND RECYCLING SAID WATER CONTAINING KETONE STREAM TO SAID SETTLING ZONE.

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