US2478472A - Solvent dewaxing - Google Patents

Description

Patented Aug. 9, 1949 SOLVENT DEWAXING Roy 'r. Edwards, Hollis, and Robert B. Killingsworth, Douglaston, N. Y., assignors to Socony Vacuum Oil Company, Incorporated, acorporation of New York No Drawing. Application November 22, 1947,

Serial No. 787,622 I 6 Claims. (Cl. 196-18) This invention relates to a method for separating waxy oils into dissimilar constituents of wax and oil. More particularly, the present invention is concerned with an improvement for separating waxy constituents from wax-bearing petroleum oils with the aid of a selective solvent.

It is well known in the art that waxy constituents can be separated from mineral oils by various methods, all of which have in common the feature of cooling the wax-containing oil to relatively low temperatures to solidify the waxy constituents and thereafter filtering, centrifuging, or otherwise physically separating the wax from the oilwax slurry. It is also known in the art that the separation of the wax from wax-bearing oils can be facilitated and diluent materials. Those methods in which the diluent used is one tending to exert a preferential solvent action for oil over waxy material at low temperatures are commonly known as solvent de-; waxing methods. One widely used version of this method makes use of a mixture of an oil solvent such as benzol or toluol and a wax anti-solvent such as a ketone, for example, acetone or methyl ethyl ketone. Other selective solvents which have been used commercially for facilitating the separation of wax and oil include light naphthas, propane, pentane, hexane, and the like, as well as various acetates, alcohols, andchlorinated hydrocarbons. The chlorinated solvents, although well known for their selectivity in separating wax from oil, have not been widely accepted by the refining industry because of high cost and relative instability. The latter undesirable property leads to the formation of hydrochloric acid which, in turn, gives rise to a problem of corrosion.

-A dewaxing process wherein any of the aforementioned solvents are employed usually requires a temperature of the order of F. or lower to obtain an efiicient separation of waxy constituents from the oil. Other difliculties in the processes heretofore employed include changes in the accelerated by utilizing various ing the solvent-waxy oil mixture, which heretofore has been a necessary procedural step in dewaxing operations, is hence eliminated by practice of the present invention.

It has been found that fluorinated aromatic hydrocarbons boiling within the approximate range of 150 F. to 450 F. have an unusually high solvent power for oil with a comparatively low solvent action for wax. Various fluorinated aliphatic hydrocarbons, such as dichlorodifiuoromethane and the like, have this property to a limited extent, but they do not accomplish the desirable results obtained with the use of fluorinated aromatic hydrocarbons boiling in the above defined range and, being extremely volatile, they are not adaptable for use at ambient temperature.

One of the major factors influencing the suitability and adaptability of a material for use as a dewaxing or deoiling solvent is its relative solubility for the waxy constituents and for the oily constituents. The ideal solvent is one which will show a relatively low solubility for the waxy constituents, will exhibit a relatively high solubility for the oily fractions, and will also remain completely miscible with the oily constituents at the temperatures employed for dewaxing. Complete ratio of the constituents of the solvent mixture when the dewaxing operation is carried out in two or more stages.

In accordance with the present invention, there has now been discovered a solvent which may be employed in separating waxy constituents from wax-bearing oils without necessitating refrigeration of the solvent-waxy oil mixture. It has been found that dewaxing operations can be effectively carried out at substantially ambient temperature to provide an excellent separation between wax and oil. The time and expense involved in coolmiscibility between the solvent and the oily constituents is necessary in order to secure a satisfactory separation of the wax crystals from the dewaxing solution.

In addition to having an unusually high solvent power for oil and a comparatively low solvent action for wax, the solvents of this invention have the desirable property of permitting an effective separation of wax and oil to take place at substantially room temperature. This unexpected property thus provides a dewaxing or deoiling procedure wherein the cooling step, heretofore essential with the use of conventional solvents, may be eliminated. Since refrigeration is a rather costly operation, the discovery of a solvent which will precipitate ,wax from oil at ambient temperature provides a separating medium of considerabl value.

Representative of the fluorinated aromatic hydrocarbons which are contemplated for use as solvents in the present process for separating wax and oil are benzotrifiuoride, xylene hexafiuoride, fiuorobenzene, fluorotoluene, fiuoroxylene, fiuoronaphthalene, and mixtures of two or more of the foregoing. The list of above mentioned compounds isnot to be construed as limiting since other fiuorinated aromatics boiling in the range of F. to 450 F. may also be used. However,

under usual operating conditions, preference is accorded fluorinated aromatic hydrocarbons with fluorine present in a saturated aliphatic side chain attached to the aromatic nucleus. Benzotrifluoride and mixtures thereof are particularly preferred since this compound is extremely effective in bringing about a separation of oil and wax at ambient temperature. A blend of benzotrifluoride and xylene hexafluoride has, as will tures. Thus, they may be employed in the treatmerit of fatty oils and acids such as those derived from vegetable and animal sources.

The desirability of using the present class of dewaxing solvents may be seen fromthe following illustrative examples presented in tabular form, in whichx comparison is made between be shown hereinafter, been found to provide an solvents of this invention and the conventionally excellent separation medium. employed blends of benzol and methylethyl The solvents of the present invention may be ketone. The procedure followed in these exemployed in either deoiling operations, wherein a amples was essentially as followsi A wax charge small amount of oil is removed from larger was brought into contact with the desired solvent,

amounts of wax, or in dewaxing operations, the ratio of solvent to petrolatum being about 4 wherein minor proportions of wax-are removed to 1. The mixture was then heated toatemperafrom oil solutions.- They are suitable for use in ture of 125 F. to insure thorough contact beoperations conducted over a wide range of temtween the waxy charge and solvent. The mix-- perature and pressure conditions. In carrying ture was then cooled to the desired filtration temout the separation of wax and oil in accordance perature, precipitating microcrystalline wax, and

with the present invention, the solvent is added the wax was removed by filtration. The wax cake to the waxy oil and the mixture is heated to asformed was washed once with solvent, removed,

sure complete miscibility of all wax and oil fracand the solvent separated from the cake by evapotions with the solvent. The mixture may then ration. The resultsobtained under varying conbe cooled to a temperature between about .30 F. ditions of temperature are set forth below:

, Table 1 Examples. 1 2 a 4 5 aas er eants? assert, a Benzol. Benwl.

Wax charge, gm. 25;

Solvent/Petrolatum Ratio 4:l

Wash Ratio 1:1..

and about 80? F. While theconventional dewaxing temperatures of from about F. to about 30 F. may be used with the solvents of this invention, a particularly desirable feature of the fiuorinated aromatic compounds employed herein is that they also permit an efiective separation of the wax and oil at temperatures of from about 30 F. up to about 80 F., thereby allowing the dewaxing 0r deoiling procedure to be effected at substantially room temperature. The exact temperature chosen will be dependent upon the char-' acter of the crystallized wax to be removed and the pour point desired in the dewaxed oil. The

crystallized wax is removed either by filtration or v by centrifuging, while the solvent is removed from" the dewaxed oil fraction by distillation.

The amount of solventemployed may vary widely and depends upon the particular oily wax mixture being treated, the solvent employed, and

the characteristics desired in theflnal product.

In general, it ispreferred to employ from one to four volumes of solvent per volume of oil being dewaxed.

Undercertain conditions, the solvents of the present inventionmay be employed in conjunction with various other conventional solvents, such as ketones, benzol, petroleum, naphtha, lower boiling hydrocarbons, and the like.

It is also .oontemplated that the solvents of this invention may be used in the dewaxing of various types of mineral oil stocks .or in the deoiling of different types of slack waxes and waxy An examination of the above data clearly in-- methylethyl ketone was employed at a tempera- .ture of 0 F. Approximately the same yields of microcrystalline waxes of equivalent characteristics were obtained in each of these examples. This indicates that the blend of fluorinated aromatic compounds canbe used to give the same re- F tially lower temperatures.

sults at higher temperatures as are obtained with the benzol-methylethyl ketone blend at substantion of the results obtained in Example} compared with those of Example 4 and the results obtained in Example 3 compared with those of Example 5 shows that the solvents or the present invention as compared with the conventional,

benzol-ketone blends give considerably greater yields of wax when the separation process is carried out under the same conditions of temperature.

It is apparent from the above results that the 7 fluorinated aromatic hydrocarbon solvents of this A further examinainvention represent improved media for effecting the separation of wax and oil over a wide range of temperature and are particularly applicable in effecting said separation under ordinary temperature conditions, thereby eliminating the need for carrying out the separation process at low temperatures of the order of E, which has heretofore been essential with the use of conventional solvent blends.

Obviously, many modifications and variations of the invention, as hereinbefore 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.

We claim:

1. A process for separating waxy constituents from an oil containing the same, which comprises admixing the oil with an oil solvent comprising an efiective amount of xylene hexafiuoride.

2. A process for separating waxy material from a mixture of oil and waxy material, which comprises mixing said mixture with a solvent comprising an efiective amount of xylene hexafluoride, maintaining the mixture of feed and solvent at a temperature at which waxy constituents separate from the mixture in solid form while the oil remains substantially completely dissolved in the solvent and removing the solidified constituents therefrom.

3. A process for effecting the separation of a mixture of wax and oil, which includes the step of contacting said mixture with xylene hexafluoride.

4. A process for de-oiling a wax, which com- 35 2,152632 prises contacting an oil-containing wax with an 6 oil solvent containing an effective amount or xylene hexafiuoride.

5. A process for effecting the separation of a mixture of wax and oil, which comprises contacting said mixture with a solvent comprising an effective amount of xylene hexafiuoride, heating the mixture of feed and solvent to a temperature suflicient to dissolve the wax, cooling the resulting mixture to a temperature between about 30 F. and about F., during which time waxy constituents separate from the mixture in solid form while the oil remains substantially completely dissolved in the solvent and thereafter removing solidified constituents from the mixture.

6. A process for de-oiling a wax, which comprises contacting an oil-containing wax with an oil solvent consisting essentially of xylene hexafiuoride, heating the mixture of feed and solvent to a temperature suflicient to dissolve the wax, cooling the resulting mixture to a temperature between about 30 F. and about 80 F., during which time waxy constituents separate from the mixture in solid form while the oil remains dissolved in the solvent and thereafter removing solidified constituents from the mixture.

ROY T. EDWARDS. ROBERT B. KILLINGSWORTI-I.

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

UNITED STATES PATENTS Name Date Terres June 13, 19 9 Number