US2147579A - Dewaxing wax-bearing mineral oil - Google Patents

Description

Patented Feh. 14, 1939 PATENT OFFICE DEwAx ING WAX-BEARING 01L Edwin C. Knowles Beacon, N. Y., assignor to The Texas Company,- tlon of Delaware New York, N. Y., a corpora- No Drawing. Application September 20, 19:5,

' Serial No. 41,395

3 Claims.

This invention relatesto the separation of wax from mineral oil.

The invention contemplates a. process of dewaxing wax-bearing mineral oil containing either a naturally-occurring or an added wax crystal modifying substance wherein the oil is mixed with a dewaxing solvent liquid and the mixtureof oil and solvent then heated to an elevated tempera-.

ture substantially above the minimum temperain complete solution in the solvent. Thereafter, the heated mixture is chilled to precipitate the wax constituents which are subsequently removed.

The invention has reference to dewaxing with a solvent containing an aliphatic ether and particularly a solvent composed of a mixture of an aliphatic ketone and an aliphatic ether. Such mixture may comprise an aliphatic ketone containing up to about, 5 carbon atoms and an allphatic ether containing up to about 8 carbon atoms.

Aliphatic ketones suitable as a component of the dewaxing solvent mixture of my invention may comprise acetone, methyl ethyl ketone, methyl propyl ketone and diethyl ketone. The aliphatic ethers may comprise ethyl ether, isopropyl ether, methyl butyl ether, isobutyl ether, normal dibutyl ether and amyl ether.

The invention is particularly adapted to dewaxing relatively viscous oils having a Saybolt Universal viscosity above 80 seconds at 210 F., as, for example,.an oil of around 90 or 100 seconds at 210 F. containing naturally-occurring asphaltic and resinous constituents which ap-- parently modify the crystal form of the wax, as

will be more fully explained below. The inven-.-

tion involves dewaxing oil of this character under conditibns such that these naturally occurringconstituents apparently assist crystallization of the wax in a more readily separable and filterable. form.

The invention is also applicable to dewaxing less viscous oils to which wax crystal modifying material has been added. Relatively low viscosity oils, and especially low viscosity distillate oils, are deficient in-the naturally occurring modifying material above referred to, and, therefore, it is advantageous to add a modifying material to these oils and dewax them by-the process. Such added materials maycomprise montan rial tothe more viscous oils may also result in further improvement when dewaxed by my process. Such added material may comprise montan wax, aluminum stearate, and the modifying material obtained by condensation of chlorinated paraflin wax and naphthalene. These materials are added usually in small amount, such as about 0.1% to 1.0% of the wax-bearing oil.

In my copending application, Serial No. 41,393

filed September'20, 1935, for Dewaxing mineral oil, I have broadly disclosed an improved process of dewaxing oil of the above type in which the oil is mixed with a dewaxing solvent, and the resulting mixture heated to a temperature of around 15 to 50 F. above the minimum temperature at which the wax and oil appear to be completely dissolved in the solvent, and thereafter chilling the heated mixture in order to precipitate the wax in a form which is very readily filterable from the cold mixture.

The present invention relates to a process in which wax-bearing oil is mixed with a solvent consisting of a mixture of an aliphatic ether and ketone and the resulting mixture is subjected to heating to a temperature of from 15 to 50 F. above the minimum temperature at which'the wax-bearing oil appears to be completely soluble in the ketone solvent liquid mixture. Following this heating the mixture is chilled to precipitate the wax, and the precipitated wax removed by filtration.

As described in my copending application, Serial No. 41,393, I have found that the wax precipitated from the cold mixture of wax-bearing oil and solvent which has been previously subjected to heating to elevated temperature prior to chilling is much more readily separated from the cold mixture, and as a consequence, the wax may be filtered from the chilled mixture at rates ten or twelve times greater than where the mixture is not subjected to the preliminary heating step of my invention.

The resulting filter cake of wax is less voluminous and, in addition, an increased yield of dewaxed oil is obtained.

As therein explained, it is thought, in the case of viscous oils, that certain of the naturally occurring asphaltic and resinous hydrocarbon constituents constitute wax crystal modifying substances. where the mixture of oil and solvent is not heated to a sumcientlyelevated temperature, these constituents are present in the mixture as a colloidal solution. In this form, they possibly form films on the small plate-type parafiin crystals formed during preliminary precipitation of the wax from the solution, and these films inhibit the normal transformation of the plate-typewax crystals into the more easily fllterable type of crystal.

By heating to temperatures of 15 to 50 F. above the minimum temperature of apparent complete solution of the wax-bearing oil in the solvent, these colloidal or low solubility substances are apparently completely dissolved in the solvent. It is believed that upon chilling the heated solution, they precipitate therefrom substantially co-extensively with the wax in the former nuclear particles which actually assist crystallization of the wax in a more readily separable and filterable form. In the case of relatively less viscous oils to which wax crystal modifying substances have been added, it is believed that, as in the case of the naturally-occurring wax crystal modifying material, these added substances are probably also precipitated from the previously heated solution in a form in which they act as nuclear particles serving to modify wax crystallization.

The minimum temperature at which the waxbearing oil appears, on visual inspection, to be completely soluble in the dewaxing solvent, or in homogeneous admixture therewith, depends upon the nature of the oil as well as upon the solvent. In the case of a selective dewaxing solvent of the character of a mixture of about 30% acetone and 70% benzol, for example, the minimum temperature of apparent complete solution of wax-bearing oil in the solvent may range from around 90 to 125 F., the minimum temperature for relatively viscous oils being in the upper portion of this temperature range.

As disclosed in the above-mentioned application, Serial No. 41,393, heating such a solution to temperatures around 160 to 170 F. causes a very great improvement in yield and reduction in the volume of the wax cake. As there shown, the maximum efiect is realized at temperatures above 150 F.

I have found that a solvent composed of a mixture of an aliphatic ketone having up to 5 carbon atoms and an aliphatic ether having up to about 8 carbon atoms is very responsive to the application of the procedure of my invention.

Such a mixture containing around 30% ketone also exerts apparent complete solution on waxbearing lubricating oil fractions at a temperature not in excess of 125 F. when a mixture of such solvent and wax-bearing oil of the type referred to above is heated to temperatures in the range of about 140 to 175 F., then chilled to precipitate the wax, the precipitated wax constituents may be filtered from the cold mixture at rates as high as 60 gallons of wax-free oil per square foot of filtering surface per hour, such rates being even greater than in the case of using a solvent consisting of a mixture of methyl ethyl ketone and benzol by the same procedure. As in the case of a mixture of ketone and benzol, the maadmum effect is realized at temperatures above 150 F. and at temperatures of around 175 F.

The resulting filter cake is compact, relatively dry and composed of crystalline wax which is to be contrasted with the rather bulky and mushy type of cake obtained when not employing the specified preliminary heating step. The volume of the wax cake may be decreased by around 35% while the paraflin wax content of the slack wax may be increased by around 7% or 8%. In addition to these improvements, the yield of waxfree oil without subjecting the filter cake to solvent washing is also very greatly increased.

I have found that these improvements are reali'zed to a very marked extent in the case of dewaxing with a solvent composed of a mixture of aliphatic ethers and ketones such as a mixture of methyl ethyl ketone and isopropyl ether, or mixtures of methyl ethyl ketone and normal dibutyl ether, for example.

The increase in filtration rate when dewaxing with methyl ethyl ketone in the presence of the foregoing aliphatic ethers as auxiliary s0lvents,in accordance with the procedure of my invention, is even greater than when dewaxing with methyl ethyl ketone in the presence of benzol as the auxiliary solvent.

A novel feature of the invention resides in the fact that the solvent mixture may comprise a relatively larger proportion of the ketone than is ordinarily the case when using other auxiliary solvents. Increasing the proportion of ketone is accompanied by increased filter rates. Thus, by the practice of my invention, solvent mixtures consisting of 50 to about 60% of methyl ethyl ketone may be satisfactorily employed while obtaining exceptionally high filter rates, high yields of wax free oil, high paraflin wax content of the slack wax and a very dry, compact wax cake which discharges readily from the filter surface. The effect of variation in the solvent composition of the dewaxing solvent mixture upon the filtration rate may be illustrated by reference to the following data in which a viscous wax bearing lubricating oil distillate, derived from Mid- Continent crude and previously extracted with furfural to remove the low viscosity index constituents, was dewaxed. The tests on this particular lubricating distillate were as follows:

Gravity, A. P. I 26.9 Viscosity Saybolt Universal at 160 F seconds 282. Viscosity Saybolt Universal at 210 F do 112 Carbon residue ..per cent" .32 Pour test degrees Fahrenheit 120 Filter rate 2g Percent ethyl z g g Gals. persq. ft. of ketone filtering surface per hr.

In the following experiments the same distillate Filter rate Percent Percent methyl normal ethyl dibutyl Gals. r sq. it. of ketone ether iilte ng surface per hr.

In each of the foregoing instances the filter rate in gallons of wax free oil per square foot per hour,

was calculated on the basis of the time required to filter .2 gallons of wax free oil per square foot of area. In no instance, was the filter cake sub jected to washing with the solvent to remove retained oil.

In the case of the methyl ethyl ketone-isopropyl ether runs, it will be observed that the filter rate was very greatly increased, namely from 32 to 73 gallons by increasing the methyl ethyl ke tone composition of the solvent from 40 to Likewise, in the case of dewaxing with the methyl ethyl ketone-normal dibutyl mixture, the filtration rate was increased from 6.5 to by increasing the methyl ethyl ketone content of the 'mixture from 40 to In each case a high yield of dewaxed oil with low pour test was obtained.

These filtration rates as well as the yield of wax free oil are even greater than when dewaxing under the same conditions with a solvent mixture consisting of 40% methyl ethyl ketone and 60% benzol. Thus, when using this latter solvent mixture, a yield of around 71% of oil dewaxed to about the same pour test was obtained with a filter rate around 23 to 25 gallons of wax free oil per square foot of filter area per hour as compared with the rates around 60 gallons reported above. The filter rates obtaining in the case of the methyl ethyl ketone-benzol solvent mixture are, of course, 10 or 12 times greater than obtained with the same solvent mixture where the mixture of oil and solvent is not subjected to the heating step of my invention prior to chilling.

While in the foregoing specific examples four parts of the solvent mixture to one part of wax bearing oil were used, it is contemplated that other proportions may also be employed. For example, from one to six parts of solvent liquid mixture to one part of oil may be used. Usually, satisfactory results are obtained when employing around three to four parts of the solvent mixture to one part of oil. I have found that by employing about three parts of a mixture of equal parts of methyl ethyl ketone and isopropyl ether to one part of oil substantially the same results are obtained as when using four parts of solvent mixture consisting of 30% acetone and benzol to one part of oil, or when using four parts of a mixture consisting of 40% methyl ethyl ketone and 60% benzol to one part of oil.

A dewaxing solvent mixture composed of an aliphatic ketone and an aliphatic ether as above described may therefore permit using a relatively smaller quantity of solvent in the dewaxing system.

In the practice of my invention, it is also desirable from the standpoint of realizing the maximum benefit from the preliminary heating step, to avoid subjecting the mixture of wax bearing oil and solvent to excessive agitation during chilling. Mechanical stirring and particularly excessive mechanical stirring deforms the crystal structure of the wax rendering it more diflicult to filter. For that reason I prefer to subject the mixture of oil and solvent to relatively mild agitation during the chilling step. I have found that this agitation is best effected by bubbling gas through the chilling mixture at a relatively low rate so as to subject it to agitation suflicient merely to effect uniform chilling. I have found that by employing gaseous agitation instead of mechanical stirring the rate of filtration of the chilled mixture is still further increased.

The gas employed may be nitrogen, carbon dioxide, flue gas or a volatile petroleum hydrocarbon. It is preferable to precool the gas to substantially the dewaxing temperature prior to bringing into contact with the mixture of oil and solvent. Furthermore, it is advantageous to saturate the chilled gas with the dewaxing solvent prior to introduction to the chilling vessel so as to avoid having the gas remove any solvent from the chilling mixture.

The invention is adapted to the dewaxing of either viscous distillate or residual wax bearing stocks, containing small amounts of asphaltic and resinous material which renders them diillcult to dewax by normal dewaxlng procedures. As already stated, it is also applicable to dewaxing lubricating oil stocks containing added wax crystal modifiers.

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

I claim:-

1. The method of dewaxing wax-bearing mineral lubricating oil which comprises mixing the oil containing wax crystal modifying material with a solvent composed of a mixture of an aliphatic ether containing up to eight carbon atoms and an aliphatic ketone containing up to about five carbon atoms such that the wax and oil appear to be completely dissolved in the solvent mixture at a temperature not in excess'of about F. and such that upon chilling a mixture of the oil and solvent to precipitate wax, and removing the wax so precipitated, the resulting dewaxed oil, after removal of the solvent, will have a pour test corresponding substantially to the temperature at which the wax was removed heating the mixture of oil and solvent to a temperature substantially above F. such that upon chilling to about 0 F. and filtering, the rate'of filtration is substantially greater than that obtained, and a wax cake is secured having a bulk not more than two-thirds the bulk secured, by heating only to about 125 F., chilling the mixture to about 0 F. and below, and filtering out the wax thus precipitated.

2. The method according to claim 1 in which the mixture of wax-bearing oil and solvent is heated to a temperature of about F.

3. The method of dewaxing wax-bearing oil to produce lubricating oil having a pour test of 0 F. and below which comprises dissolving the waxbearing oil in a solvent composed of a. mixture of an aliphatic ether containing up to eight carbon atoms and methyl ethyl ketone, theketone being in excess of 40% by volume of the solvent mixture such that the solvent mixture has substantially complete selective action as between wax and oil at 0 F. and below and such that when the mixture of wax-bearing oil and solvent is heated to an elevated temperature and then chilled to preclpitate the solid hydrocarbons, the solid hydrocarbons so precipitated can be filtered from the cold mixture at a rate two or more times as rapid as from a cold mixture in which the ketone comprises not over 40% by volume of the solvent mixture, heating the mixture to a temperature of about 175 F., chilling the mixture to precipitate the solid hydrocarbons, and filtering the cold mixture to remove the solid hydrocarbons thereby producing lubricating oil which, after removal of the solvent, will have a pour test of around 0 F.

and below.

. EDWIN C. KNOWLES.