US2685557A - Hydrocarbon wax deoiling - Google Patents

Description

Patented Aug. 3, 1954 HYDRIOCAR'BON WAX DEOILING Willem Johannes Dominicus van Dijck, The Hague, and Willem Martin Mazee, Amsterdam, Netherlands, assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application June 24, 1950, Serial No. 170,250

Claims priority, application Netherlands September 16, 1949 9 Claims. 1

This invention relates to a process for the removal of oil from oil-containing solid paraflin wax and more particularly it relates to an improved process for the removal of oil from an oil-containing paraiiin wax cake obtained in the solvent dewaxing of a mineral oil, and the solvent deoiling of oily parafiin wax mixtures.

It is known to the art that a waxy oil including lubricating oil distillate as well as residual fraction can be dewaxed to produce a relatively oil-free wax by adding thereto a relatively nonviscous liquid solvent which at the dewaxing temperature dissolves the oil and which solvent is also substantially a non-solvent for the wax at the wax separation or dewaxing temperature. Examples of such a solvent are methyl isobutyl ketone, methyl ethyl ketone, a mixture of methyl ethyl ketone, benzene and toluene, a mixture of benzene and sulfur dioxide, propane, etc. The resulting admixture after having dissolved the wax and oil therein at an elevated temperature is then cooled to a temperature at which the wax separates out in a solid state. The precipitated wax is then separated from the solution by various means such as cold settling, centrifugation or filtration. A Wax cake is thereby produced which usually contains a substantial proportion of oil dissolved in the solvent therein. In order to remove the oil from the wax cake it is the practice to wash the cake with a quantity of a washing liquid which is substantially a non-solvent for the wax and a solvent for the oil, such as the solvent used for dewaxing. In practice the washing liquid employed is the same as the dewaxing solvent and gives a filtrate mixture having a viscosity lower than that of the oil alone but greater than the dewaxing solvent employed. A double volume of washing liquid is usually used, calculated on the pore volume (interstitial volume) of the wax cake, in order to produce a substantially oil free wax cake.

Another method of dewaxing a waxy oil to produce a relatively oil-free wax is to chill the waxy oil without the addition of a solvent and/or diluent thereto, to a temperature at which solid wax precipitates therefrom. The precipitated wax is then separated by various means such as cold settling, pressing, centrifugation or filtration and the resulting wax cake is washed with a liquid which is substantially a non-solvent for the wax and a solvent for the oil contained in the Wax cake, usually one of the hereinbefore mentioned solvents, to produce a relatively oilfree wax cake. Here also a relatively large volume of washing liquid is applied to the wax cake in order to produce an oil-free Wax product; a double amount of washing liquid is usually used, calculated on the pore volume (interstitial volume) of the wax cake.

A principal object of the present invention is to provide an improved process of rapidly and efficiently producing by washing an oil-free wax from an oil-containing wax cake. A further object is to provide an improved process for the production of an oil-free parafiin wax from a waxy oil or an oily wax mixture.

Now in accordance with this invention it has been found that these and other objects are achieved by washing an oil-containing wax with a washing liquid which at the washing temperature is more viscous than the the oil-containing liquid which is present in the wax. More particularly, it has been found that in a process of producing an oil-free wax wherein oil-containing wax is washed with a washing liquid which is a solvent for the oil and a non-solvent for the wax, especially effective results are obtained when the washing liquid is between about 1.5 and about 6 times as viscous as the oil-containing liquid in the Wax.

The invention is particularly applicable to the preparation of oil-free wax from wax obtained in the solvent dewaxing of a waxy mineral oil.

In the solvent dewaxing of mineral oil, afterv precipitation and separation of the wax, a wax cake is obtained usually containing a considerable amount of oil dissolved in the solvent present therein. It is normal practice in order to produce an oil-free wax therefrom to remove the oil from the wax cake by washing the wax cake with an additional amount of the same solvent employed in the solvent dewaxing step. Accordingly, if methyl isobutyl ketone were employed as the dewaxing solvent, methyl isobutyl ketone would also be used asthe washing liquid. In accordance with the present invention, however, it has been found to be advantageous to employ as the washing liquid a solvent which differs from the solvent employed in the dewaxing step and which is more viscous at the washing temperature than the first used dewaxing solvent, preferably having a viscosity which is between about 1.5 and 6 times the viscosity of the oilcontaining liquid present in the wax to be washed.

When applying this method in practice since the washing liquid as well as the dewaxing solvent is desirably recovered and recycled after use, it is advantageous to select a washing liquid which can easily be separated from the oil and from the dewaxing solvent. For example, it is preferable that the boiling point of the washin liquid difier suficiently from the boiling points of the oil and of the dewaxing solvent so that these materials may be readily separated from each other by distillation. Washing liquids which possess suitable boiling points (the choice of which depends upon the viscosity of the oilcontaining liquid in the wax cake in accordance with the invention) for the method of the invention comprise liquid aromatic amines such as methyl aniline, ethyl aniline, diethyl aniline; certain aliphatic alcohols such as propyl alcohol, iso-propyl alcohol, n-butyl alcohol; cyclic alcohols such as cyclohexanol; certain halogenated hydrocarbons such as tetrachloroethane, etc. Moreover, it is pointed out that the process of the invention is particularly adapted to those washing operations of the type wherein the liquid to be removed from the solid (Wax) is displaced by a washing liquid, e. g., filter cake washing or washing carried out in a centrifuge, rather than a dilution type washing, e. g., preparation of a wax-washing liquid slurry and followed by filtration.

The process of the invention and the advantages to be obtained therefrom will be further elucidated with reference to the following examples of the invention.

EXAMPLE I One volume of a Tandjoeng mineral oil distillate fraction having a boiling point range 430- 437 C. at atm. pressure containing about 60% by weight parafin wax was mixed with five (5) volumes of methyl isobutyl ketone and the resulting mixture was cooled to C. The paraffin wax which separated therefrom as a solid was removed by filtration and had a melting point of 64 C., and a refractive index of 70 C. of 1.4348 (D line). The filtrate obtained consisted of oil dissolved in methyl isobutyl ketone and had a viscosity of 0.9 centipoise at 10 C., the dewaxing and filtering temperature.

Wax cake obtained in the above manner was washed at a temperature of 10 C. with the following various washing liquids, cyclohexanol (viscosity 124 cps. at 10 C.) n-butanol (viscosity 4.8 cps. at 10 0.), tetrachloro-ethane (viscosity 1.4 cps. at 10 C.) and methyl isobutyl ketone viscosity 0.83 cp. at 10 0.).

The amount of oil remaining in the wax cake was determined after each washing for the varying volumes of washing liquid (expressed as per cent of pore volume of the wax cake) and for the various washing liquids employed. The experiments were carried out employing three diilerent amounts of washing liquid, namely, 94%, 100% and 120% by volume of the pore volume. The results obtained are presented in Table I.

Table I SOLVENT WASHING 0F OILY WAX CAKE Volume Percent of Washing Liquid Washing Liquid C-yclo-liexauol (124 cps.) percent oll n-butanol (4.8 cps.) do tetrachloro-ethaue (1.4 cps.) .do methyl isobutyl ketone (0.83 cp.) cdo.

The above results demonstrate that by using a washing liquid which, according to the invention, is more viscous than the oil-containing liquid present in the wax cake (viscosity 0.9 cp. at 10 C.) the oil present in the wax cake is removed much more satisfactorily and considerably less washing liquid is required (depending upon the viscosity of the washing liquid) than if the dewaxing solvent, itself (methyl isobutyl ketone), which has a lower viscosity than the oil-containing liquid in the wax cake, was employed as the washing liquid. Furthermore, the above results demonstrate that the greater the viscosity of the washing liquid over the oil-containing liquid present in the wax cake, the more thoroughly and efficiently the washing (oil removal) is accomplished and a smaller quantity of washing liquid is required to give an oil-free wax. As a practical consideration, however, the viscosity of the washing liquid should not be too great otherwise the rate of filtration would be too low. For this reason it is preferred that the viscosity of the washing liquid should be between about 1.5 and about 6 times greater than the viscosity of the oil-containing liquid in the wax cake.

EXAMPLE II Experiments similar to those described in Example I but at a dewaxing temperature of l0 C. were carried out upon a Concepcion mineral oil distillate fraction having a wide boiling point range, a specific gravity of 0.879, a viscosity at 70 C. of 3.9 degrees Engler and containing about 20% by weight paraffin wax. The parafiin wax which separated therefrom as a solid was removed by filtration. The filtrate obtained consisted of oil dissolved in methyl isobutyl ketone and had a viscosity of 2.3 cps. at l0 C., the dewaxing and filtering temperature.

Wax cake obtained in the above manner was washed at a temperature of -l0 C. with the following various washing liquids: n-butanol (viscosity 8.4 cps. at 10 C.) and methyl isobutyl ketone (viscosity 1.1 cps. at l0 C.). The percentage oil remaining in the wax cake was determined after each washing for each solvent. The results are presented in Table II.

Table II n-butanol (8.4 cps.) percent 0il methyl isobutyl ketoue (1.1 cps.) do.

The washing liquid employed according to the invention may consist of a mixture of liquids, e. g. a mixture of the dewaxing solvent and a viscosity-enhancing liquid such as a glycol.

When using e. g. methyl ethyl ketone as the dewaxing solvent (viscosity 0.5 cp. at 0 C.) the addition of 20% ethylene glycol raises the viscosity to 1.5 cps. at 0 C. and the addition of 40% ethylene glycol to 3.5 cps. at 0 C. The liquid mixtures thus obtained may be used as washing liquid.

When a mixture of liquids is used as the washing liquid the mixture should of course be a solvent for the oil and substantially a non-solvent for the wax.

The washing liquid may to advantage be substantially saturated with wax in order to prevent its dissolving wax from the cake to be washed.

If a substantial amount of wax would be dissolved from the cake, the larger pores, through which proportionally the greater part of the solvent will pass, would be still more enlarged and the inhomogeneity of the liquid flow would aggravate.

We claim as our invention:

1. The process of producing a substantially oil-free wax from a wax-containing mineral oil which comprises: forming a solution of said mineral oil with a first liquid consisting essentially of a ketone dewaxing solvent; cooling said solution to a temperature sufl'icient to precipitate solid wax; separating therefrom solid wax containing an oil-containing liquid comprising said first liquid dewaxing solvent together with oil dissolved therein; washing said separated solid wax with a second liquid characterized by having an absolute viscosity at the temperature of contacting at least 1.5 times greater than the absolute viscosity of said oil-containing liquid and further characterized by being a solvent for oil and substantially a non-solvent for wax at the temperature of contacting, the washing being eifected under conditions to prevent the dissolving of substantial amounts of solid wax in said second liquid, and recovering a solid wax substantially free of said oil-containing liquid.

2. The process according to claim 1 wherein the second liquid has an absolute viscosity between about 1.5 and about 6 times greater than the absolute viscosity of the oil-containing liquid.

3. The process according to claim 1 wherein the second liquid consists essentially of an alcohol.

4. The process according to claim 3 wherein the second liquid is a mixture of a ketone and ethylene glycol.

5. The process according to claim 3 wherein the second liquid has an absolute viscosity between about 1.5 and about 6 times greater than the absolute viscosity of the oil-containing liquid.

6. The process of producing a substantially oil-free wax from a Wax-containing mineral oil which comprises: forming a solution of said mineral oil with methyl isobutyl ketone; cooling said solution to a temperature sufiicient to precipitate solid wax; separating therefrom solid wax containing an oil-containing liquid comprising methyl isobutyl ketone together with oil dissolved therein; washing said separated solid wax with n-butanol and recovering a solid wax substantially free of said oil-containing liquid.

7. The process of producing a substantially oil-free wax from a wax-containing mineral oil which comprises: forming a solution of said mineral oil with methyl isobutyl ketone; cooling said solution to a temperature sufiicient to precipitate solid wax; separating therefrom solid w containing an oil-containing liquid comprising methyl isobutyl ketone together with oil dissolved therein; washing said separated solid wax with tetrachloroethane and recovering a solid wax substantially free of said oil-containing liquid.

8. The process of producing a substantially oil-free Wax from a wax-containing mineral oil which comprises: forming a solution of said mineral oil with methyl isobutyl ketone; cooling said solution to a temperature sufficient to precipitate solid wax; separating therefrom solid wax containing an oil-containing liquid comprising methyl isobutyl ketone together with oil dissolved therein; washing said separated solid wax with cyclohexanol and recovering a solid wax substantially free of said oil-containing liquid.

9. The process of producing a substantially oil-free wax from a wax-containing mineral oil which comprises forming a solution of said mineral oil with a first liquid consisting essentially of a ketone dewaxing solvent; cooling said solution to a temperature sufiicient to precipitate solid wax; separating therefrom solid wax containing an oil-containing liquid comprising said first liquid dewaxing solvent together with oil dissolved therein; washing said separated solid wax with a second liquid substantially saturated with wax, said second liquid being characterized by having an absolute viscosity at the temperature of contacting at least 1.5 times greater than the absolute viscosity of said oil-containing liquid and further characterized by being a solvent for oil and substantially a non-solvent for wax at the temperature of washing, the washing being efiected under conditions to prevent the dissolving of substantial amounts of solid wax in said second liquid, and recovering a solid wax substantially free of said oil-containing liquid.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,848,636 Livingstone Mar. 8, 1932 2,048,513 Page July 21, 1936 2,229,659 Carr Jan. 28, 1941 2,592,490 Thompson Apr. 8, 1952 2,595,468 Kiersted, Jr. et a1. May 6, 1952 OTHER REFERENCES Lange, Handbook of Chemistry, Sixth edition, Sept. 1946, pages 1571-1576. Published by Handbook Publishers Inc., Sandusky, Ohio.

Claims (1)

1. THE PROCESS OF PRODUCING A SUBSTANTIALLY OIL-FREE WAX FROM A WAX-CONTAINING MINERAL OIL WHICH COMPRISES: FORMING A SOLUTION OF SAID MINERAL OIL WITH A FIRST LIQUID CONSISTING ESSENTIALLY OF A KETONE DEWAXING SOLVENT; COOLING SAID SOLUTION TO A TEMPERATURE SUFFICIENT TO PRECIPITATE SOLID WAX; SEPARATING THEREFROM SOLID WAX CONTAINING AN OIL-CONTAINING LIQUID COMPRISING SAID FIRST LIQUID DEWAXING SOLVENT TOGETHER WITH OIL DISSOLVD THEREIN; WASHING SAID SEPARATED SOLID WAX WITH A SECOND LIQUID CHARACTERIZED BY HAVING AN ABSOLUTE VISCOSITY AT THE TEMPERATURE OF CONTACTING AT LEAST 1.5 TIMES GREATER THAN THE ABSOLUTE VISCOSITY OF SAID OIL-CONTAINING LIQUID AND FURTHER CHARACTERIZED BY BEING A SOLVENT FOR OIL AND SUBSTANTIALLY A NON-SOLVENT FOR WAX AT THE TEMPERATURE OF CONTACTING, THE WASHING BEING EFFECTED UNDER CONDITIONS TO PREVENT THE DISSOLVING OF SUBSTANTIAL AMOUNTS OF SOLID WAX IN SAID SECOND LIQUID, AND RECOVERING A SOLID WAX SUBSTANTIALLY FREE OF SAID OIL-CONTAINING LIQUID.