US2904496A - Process for separating wax from oils - Google Patents

Description

2,904,495 Patented Sept. '15, 1959 2,904,496 ROC S E SEPAR IYING WAX FRQM QILS Morton ,G. Bloch, Woodbll fy, Abbott F. Gloucester City, and William H. King, N.J., assignors to Socony corporation of New York No Drawing. Application July 25, 1956 Serial No. 599,902

3 Claims. (Cl. 208-33) Houser, I Woodbury, Mobil Gil Company, Inc., a

This application is a continuation-impart of copending application Serial Number 262,488, filed December 19, 1951, now abandoned.

This invention relates to the separation of wax from oils containing the same, and is more particularly concerned with a process for removing wax from wax-containing hydrocarbon fractions. More specifically, the present invention provides a novel gravity method for removing wax from wax-containing mineral oil.

As is well known to those familiar with the art, mineral oils or hydrocarbon fractions contain, at dewaxing temperatures, particles of solid Accordingly, several processes have been proposed for effecting the removal of the wax particles from the hydrocarbon fractions containing them. In the processes known to the ,art as dein o r e is had t fi t a i n and eennifugation t eifee the mova v The dewaxing processes of the prior art may be classified into three main classes which, for convenience, may be enumerated as follows:

.(1) ilte Pre dew x ng of low-vi osi y wax-containing oils with or v or solvent.

(2) en r fu e d waxing of high-v scosity wax-containing oils diluted with a suitable diluent or'solvent.

(3) S l d waxing of l w .or high-viscosi y waxcontaining oils: v

(A) Employing filtration for separating wax and, 'oil;

E ploy ng ent ug tien fo pa at ng Wax and oil.

Filter press dewaxing of low-viscosity wax-containing oils comprises chilling a wax-containing hydrocarbon fraction having a S.U.V. of about 75-80 seconds at 100 F., to a temperature slightly below that at which the dewaxed hydrocarbon tract-ion should flow and, thereafter, subjecting the thus chilled hydrocarbon fraction to a filter pressing operation to separate, from the hydrocarbon fraction, the wax which has precipitated during the chilling operation. Filter press dewaxing is frequently employed in conjunction with naphtha as a diluent for the stock to be dewaxed, especially when high waxcontent stocks are being processed or when low oilwithout dilution with asuitahle diluent content waxes are desired. However, filter press (lQWfiX- ing is not applicable to the treatment of heavy or residual oils. This is due to the difliculty of filtering oil through the cake formed by the fine crystals of ceresin waxes present in theseheavy oils.

Centrifuge dewaxing comprises passing continuously a chilled solution of residual oil in naphtha through a centrifuge revolving at about 17,000 r.p.rn., separating the oil and wax streams, and, subsequently, removing the naphtha therefrom. Centrifuge dewaxing is generally applicable to the treatment of residual oils but is not generally applicable to the treatment of distillate oils due to .the large crystal structure and the resulting poor flow characteristicsof the parafiin waxes present in low- .viscosity or distillate oils. However, with suitablemodifications, centrifuge dewaxing can be applied to the processing .of distillate oils. Moreover, centrifuge dewaxing has the disadvantage of producing high oil-content .waxes and oils which, on standing, sometimes develop wax :clouds due to ineffectual dewaxing of the waxcontaining residual oil.

' Theavailability of new solvents having given desired characteristics at moderate cost has led to the development of numerous types of solvent dewaxing processes.

'In :general, in these processes, the wax-containing oil is mixed with prescribed amounts of a solvent or diluent and the mixture is chilled to a predetermined temperature. The chilled mixture is then subjected either to a filtering operation or to a centrifuging operation to separate from the oil the wax' which has precipitated during the chilling operation. Finally, the solvent is distilled from the wax and from the dewaxed oil.

The benzol-ketone dewaxing process is typical of the solvent dewaxing processes, and probably, is the most extensively used in the petroleum industry for dewaxing both low and high-viscosity wax-containing oils and for deoiling the waxes thus obtained in rerun processing. In this process, waxy oil or oily wax admixed with a solvent containing about 40 percent methyl-ethyl ketone, 52 percent benzol, and 8 percent toluol, in a proportion of about 1:3, is chilled to the dewaxing or deoiling temperature by exchange with outgoing products and by refrigeration. Oily and waxy materials are separated by employing a rotary drum-type filter and each is subsequent-ly stripped free of solvent. Dewaxing operations are carried out at temperatures of about minus 30 F. to about plus 20 F., while wax deoiling operations are performed at temperatures as high as F. Generally, dewaxing temperatures are about 20 F. lower than the pour point of the finished oil.

Another widely used solvent dewaxing process is the propane dewaxing process. Propane dewaxing difiers from other solvent dewaxing processes in that a'liquefied hydrocarbon is utilized in pressure equipment. Chilling to temperatures about 3040 F. lower than the pour point of the finished oil is effected by self-evaporation of the propane combined, when desirable, with extraneous refrigeration. Filtration is performed with rotary or leaf-type pressure filters. The proportions of solvent to oil are similar to those employed in the benzol-ketone process and the dewaxing or deoiling temperatures vary from about minus 40 F. to about plus 100 F.

Other solvent dewaxing methods such as the Separator- Nobel and Bari-Sol dewaxing processes, utilize centrifuges for separating oil and wax from solvent-diluted wax-containing oils. The former process employs trichloroethylene as the solvent while the latter utilizes a mixture of benzene with ethylene dichloride as the solvent. In general, the dewaxing or deoiling temperatures are about 20 F. lower than the desired pour point of the dewaxed oil. Solvent-to-oil ratios may be as high as 8: 1.

More recently, new processes for dewaxing wax-containing mineral oils have been proposed. In general, in these processes, waxy oil is emulsified in various aqueous and/or non-aqueous media, the emulsion is then chilled, and, subsequently, oil is leached from the emulsion.

It is well known that there are numerous disadvantages associated with current methods of removing wax from mineral oils. These disadvantages may be classified into two main groups, i.e., those of an operating nature and those of an economic nature. Accordingly, any process which substantially eliminates the inherent technological difiiculties and minimizes the operating costs .of the processes of the prior art is manifestly highly defrom a mineral oil-solvent solution by gravity separation.

It is well known in the art that gravity separation of wax from dewaxed oil-solvent solutions occurs at very slow rates, even when utilizing high-gravity solvents. These rates are of such small magnitude as to preclude any commercial application of dewaxing procedures embodying this method of separation. The rates become especially poor, from the standpoint of commercial feasibility, when it is attempted to process distillate oil stocks containing large, interlocking, parafiin wax crystals. It is postulated that the slow rates referred to are attributable to two factors, viz., the nature of the inter face between the wax phase and the liquid phase in the system, and the relatively small difference between the specific gravity of the wax phase and the specific gravity of the liquid phase.

In US. Patent No. 2,645,598, it is disclosed that the affinity between the wax and the oil could be materially reduced through the conjoint use of surface active agents and of non-freezing aqueous solutions. In this patent, there is disclosed and claimed a process for separating wax and oil from mixtures thereof, which comprises dispersing an aqueous solution which is capable of remaining in substantially the liquid state at the dewaxing temperature, in the mixture, in the presence of specified amounts of specified surface active agents, to associate the wax with the aqueous solution and to produce a wax-aqueous solution phase dispersed in the mixture, introducing a gas into the dispersion to produce a wax-bearing froth, and separating the wax-bearing froth from the mixture.

It has now been found that it is possible to avoid the use of a non-freezing aqueous solution and of surface active agents. In accordance with the present invention, the difliculties inherent in the gravity separation methods of the prior art are overcome through the conjoint use of polar solvents such as will be defined in more detail hereinafter, and of a gas. It is envisaged that the conjoint use of these materials accomplishes the following:

(1) Modifies the nature of the interface between the wax phase and the liquid phase in the system; and

(2) Increases the difference between the effective specific gravity of the wax phase and the effective specific gravity of the liquid phase.

Accordingly, it is a broad object of the present invention to provide a process for separating wax particles from mixtures of wax particles and mineral oils. Another object is to provide a gravity separation method for separating wax particles from mixtures of wax particles and mineral oils without the use of conventional operations and equipment. A further object is to effect dewaxing of wax-containing mineral oils which is efficient, economical, and relatively simple. An important object is to afford an accelerated gravity separation process for effecting the separation of wax from mixtures of wax particles and mineral oils. Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description.

Accordingly, and broadly stated, the present invention provides a process for effecting the separation of wax from wax oil mixtures, which comprises adding specified amounts of a specified solvent to a wax-oil mixture, then cooling said mixture to the dewaxing temperature, then introducing a gas into the mixture to produce a Wax-bearing froth, and separating the waxbearing froth from the mixture.

From the foregoing, it will become apparent to those skilled in the art that the process contemplated herein may be carried out in accordance with several procedures, continuous or batch, all of which, nevertheless, are oncompassed by the broad statement of invention set forth hereinbefore. By way of illustration, a specific embodiment of the present invention may be practiced as follows: A wax-containing residual mineral oil is first mixed with a mixture consisting of 80 percent by volume of a liquid composed of 80 percent by volume of methyl-ethyl ketone and 20 percent by volume of naphtha, as a solvent, in a proportion of, for example, 1:50, respectively. The mixture is chilled, for example, to 0 F. and is then fed into a fractionator into which a gas is introduced by a suitable distributor. The wax is removed in the froth obtained while the dewaxed oil-solvent fraction remains as a residue.

In general, any wax-containing oil is amenable to the process of the present invention. The charge stock may be either a distillate stock or a residual stock or oily waxes obtained therefrom. Wax-bearing mineral oils, brown coal tar oils, shale oils, and synthetically produced oils, any of which may have been previously subjected to a treatment for the purpose of improving their physical and/ or their chemical nature may be mentioned by way of non-limiting examples of materials suitable as charge stocks for the process contemplated herein. There appears to be nothing critical inthe amount of wax present in the wax-containing oils to be treated. Thus, the wax-content of the charge stocks may vary between about 0.1 percent and about 99.9 percent by weight. On the other hand, the amount of wax present in the oil is largely determinative of the fluidity of the charge to the process.

Accordingly, in practicing the invention, it is usually desirable, although not essential, to increase the fluidity of the charge to the process by the addition of an oilmiscible solvent. For this purpose, the oil-solvents of the prior art may be used. Hydrocarbons such as propane, butane, pentane, propene, butenes, pentenes, naphtha, gasoline, benzol and kerosene, and mixtures thereof may be mentioned by way of non-limiting examples. I

On the other hand, and in accordance with the present invention, the desired fluidity may be attained exclusively through the use of the specific solvents contemplated herein. The solvents utilizable for this purpose are methyl-ethyl ketone, ethylene dichloride and trichloroethylene. These solvents may be used as such or as mix tures, viz., 80 percent methyl-ethyl ketone-20 percent naphtha, and ethylene dichloride-trichloroethylene mixtures.

The amounts to be used will depend upon the nature of the charge stock and of the solvent. In general, the amounts will vary between about 0.5:1 and about 50:1 (volume of solvent to volume of charge stock). More specifically, when the charge stock is a residual oil, the amounts will vary between about 20:1 and about 5021 and higher if desired. One the other hand, when the charge stock is a distillate oil, the amounts will vary between about 0.5 :1 and about 5:1 and higher, if desired. Indeed, in any given dewaxing operation, the amounts of specific solvents of the type contemplated herein, may be reduced, provided that sufficient amounts of the oilsolvents, referred to hereinbefore, are utilized to maintain the dewaxed oil in solution at the dewaxing tem perature of the operation.

The test for establishing the amounts of solvent that will be operable, within the range set forth hereinbefore, in the process of the present invention is the bubble machine test [see Engineering and Mining Journal, 137, 291 (1936)] (equipped with a cold stage when testing the solvents in dewaxing operations). In this test, a block of wax of the type to be separated and having at least one relatively fiat surface is immersed in a mixture of oil and solvent in the amounts to be tested and chilled to the dewaxing temperature. An air bubble is placed in a bubble holder and the bubble is then permitted to come into contact with the relatively flat wax surface. If a.

' finite three-phase (from wax through oil-solvent to air bubble) contact angle can be measured, the amount of solvent being tested will be operable in the process of the present invention. Accordingly, the ainounts of solvents operable herein can be defined as those Which 'produce-athree-phase contact angle-in the bubble machin test.

The following data are indicative-of results obtained in the bubble machine test: 1

TABLE I These results indicate that the floatability of paraffin and microerystalline wax are substantitally the same 29 and "26 contact angles, respectively).

The non-floatability of the microcrystalline wax (originating from residual oils) is due to the effect of the residual oil on the contact angle for paraffin wax and 0 for micro- 'cry'stalline wax, where the'oil is residual oil).

TABLE II Efiect of nature of solvent Contact angle, Solvent Dewaxdegrees Solvent composito oil ing N 0. tion (volume per- Charge ratio tempercent) stock (volature, Microume) Parafcrystalfinwax line wax 3--- N aphtha Distillate 4:1 25 0 o1 4--. 99% naphtha-1% d0 4:1 25 0 MEK. 5 95% naptha5% d0 4:1 25 24 MEK. 6... Naphtha -25 0 IVIEKLU- 25 I 31 MEK 0 34 ii. 9 80% MEK'20% do 50:1 0 18 naphtha. 65% MEK 35% do 4:1 0 0 naptha.

1 Methyl-ethyl ketone.

The data in Table II indicate that solvents, such as naphtha, are inoperable in the process of the present invention whereas solvents of the type contemplated herein are (note tests Nos. 3, 6, 7 and 8). The data also indicate that the solvents contemplated herein must be present in suflicient concentration to be eliective (note tests Nos. 4, 5 and 9). Finally, a sufficient amount of solvent must be used to maintain the dewaxed oil in solution (note tests Nos. 8, 9 and 10), the amount being appreciably higher in the case of residual oils.

In practicing the process of the present invention, in order to ensure that the wax-oil-solvent mixture constitutes a homogeneous liquid phase at the beginning of the treatment, it is ordinarily preferred to initially heat the mixture to temperatures varying between about 100 F. and "about 200 F. The temperature to be utilized to produce optimum results will depend upon the nature of the stock undergoing treatment. The dewaxing temperatures applicable herein are those of the prior art, i.e., between about 40 F. and about 100 F. It must be recognized, of course, that the dewaxing temperature applicable in any particular instance will de- .pend upon the nature'of the system, -i.e., the solvent uti lized, the type of charge stock, etc.

The rate at which the temperature of the mixture is lowered to dewaxing temperature (the chilling rate) ,is not a critical factor, although, as it will be appreciated by those skilled in the art, an important factor. The chilling rate, as is well known, is determinative of the size of the wax crystals that precipitate out during the chilling operation. For general purposes, it has been found that an average chilling rate varying between about 10 F. per hour and about 500 F. per hour is conducive to optimum results. In general, the higher chilling rates are preferred when processing distillate stocks while the lower chilling rates are employed preferably when treating residual stocks.

Any gas or any substance which is capable of rem-aining in the gaseous state during operation may be employed herein. Obviously, the gas so utilized should, preferably, be substantially insoluble in the components of the system and, also, should be chemically inert with respect to the other components of the system. Air, helium and carbon dioxide may be mentioned as nonlimiting examples of gases utilizable in the process. These gases may be introduced into the system in any suitable manner, as is well known in the art.

It is important to the operation of this inventionthat the gas introduction occur after the wax-oil solvent mixture'has been chilled to the dewaxing temperature. At-

tempts to utilize the gas to chill the mixture in addition to forming the wax-bearing froth have proved unsuclowing Table III. In run 8A the gas was used to both chill and froth While in run 9 the gas was only supplied after chilling, in accordance with this invention.

TABLE III Run 8A 9 Temperature, F.: N z inlet 50 50 0il-solvent Inlet 55 0 Final 0 0 Run length, hrs.:

At dewaxing temp 2% 2 Total 3 A 2% Recovery, weight percent 84 Yield, dewaxed oil, weight percent 71 70 Pour point, F.:

Dewaxed oil 35 20 Wax 7O 75 It will be noted that the process of this invention (run 9) produces a dewaxed oil 15 F. lower in pour point than that of the other process. In addition, it is less time consuming. To procure the data for Table III a west Texas waxy distillate of 65 F. pour point was; dewaxed, using as a solvent methyl-ethyl ketone diluted in equal quantity with toluol. The solvent to oil ratio was four to one and nitrogen was used as the frothforming gas. In addition to the other noted disadvantages, the use of gas to both chill and froth (run 8A) resulted in high gas consumption and losses of large quantities of solvent through evaporation.

As a further example of the operation of this inven* tion a waxy distillate oil stock having a Saybolt Universal viscosity of 36.35 seconds at 210 F. and a pour point of 90 F. was first mixed with a solvent consisting of 65 percent by volume of ethylene dichloride and 35 percent by volume of trichloroethylene, in the proportion of 1:6. The mixture was heated to a temperature of F. and then chilled to 0 F. After chilling the mixture was aerated by agitation and the wax-bearing froth produced collected. The dewaxed oil had a pour point of 20 F.

It is apparent that the present invention provides an efficient, economical and relatively simple process for effecting gravity separation of wax from wax-containing oils. It will be appreciated by those skilled in the art that the present invention may be embodied in other specific 'forms without departing from the spirit or essential attributes thereof. Accordingly, it must be clearly understood that the present embodiments are considered in all respects illustrative and not restrictive, reference being had to the appended claims rather than the foregoing description to indicate the scope of the invention.

We claim:

1. A process for separating wax and oil from a wax-oil mixture, which comprises adding a solvent selected from the group consisting of methyl-ethyl ketone, ethylene ldi" chloride and trichloroethylene, to said wax-oil mixture, in an amount falling Within the range varying between about 0.5 volume and about 50 volumes per volume of oil and suificient to produce a finite three-phase contact angle in the bubble machine test, to produce a solventwax-oil mixture, said Wax-oil mixture and said solvent being the sole non-gaseous materials present in the process; cooling said solvent-Wax-oil mixture to the deWaxing temperature to precipitate Wax; subsequently introducing a gas into said solvent-wax-oil mixture to produce a wax-bearing froth; and separating said wax-bearing froth from said solvent-wax-oil mixture.

2. A process for separating wax and oil from a waxdistillate oil mixture, which comprises adding a solvent selected from the group consisting of methyl-ethyl ketone, ethylene dichloride and trichloroethylene, to said Waxdistillate oil mixture, in an amount falling within the range varying between about 0.5 and about 5 volumes per volume of oil, to produce a solvent-wax-distillate oil mixture, said wax-distillate oil mixture and said solvent being the sole non-gaseous materials present in the process; cooling said solvent-wax-distillate oil mixture to the dewaxing temperature to precipitate wax; subsequently introducing air into said solvent-wax-distillate oil mixture to produce a wax-bearing froth; and separating said Wax-bearing froth from said solvent-wax-distillate oil mixture.

3. A process for separating wax and oil from a waxresidual oil mixture, which comprises adding a solvent selected from the group consisting of methyl-ethyl ketone, ethylene dichloride and trichloroethylene, to said waxresidual oil mixture, in an amount falling within the range varying between about 20 and about 50 volumes per volume of oil, to produce a sol'vent-wax-residual oil mixture, said wax-residual oil mixture and said solvent being the sole non-gaseous materials present in the process; cooling said solvent-wax-residual oil mixture to the dewaxing temperature to precipitate wax; subsequently introducing air into said solvent-wax-residual oil mixture to produce a wax-bearing froth; and separating said waxbearing froth iirom said solvent-wax-residual oil mixture;

References Cited in the file of this patent UNITED STATES PATENTS 1,277,935 Hussey Sept. 3, 1918 2,314,994 Lawson et a1 Mar. 30, 1943 2,719,817 Doorn Oct. 4, 1955 2,721,829 Mondria Oct. 25, 1955 FOREIGN PATENTS 244,564 Germany Mar. 11, 1912 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,904,496 September 15, 1959 Morton G. Bloch et al It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 53, for "One" read On column 5, lines 45 to 50, inclusive, Table II, sixth column thereof, under the heading "Paraffin Wax", the numerals should read as shown below instead of as in the patent:

O O 4 O 30 Signed and sealed this 29th day of March 1960 (SEAL) Attest:

KARL H AXLINT. ROBERT C, WATSON Attesting Officer I Commissioner of Patents

Claims (1)

1. A PROCESS FOR SEPARATING WAX AND OIL FROM WAX-OIL MIXTURE, WHICH COMPRISES ADDING A SOLVENT SELECTED FROM THE GROUP CONSISTING OF METHYL-ETHYL KETONE, ETHYLENE DICHLORIDE AND TRICHLOROETHYLENE, TO SAID WAX-OIL MIXTURE, IN AN AMOUNT FALLING WITHIN THE RANGE VARYING BETWEEN ABOUT 0.5 VOLUME AND ABOUT 5/ VOLUMES PER VOLUME OF OIL AND SUFFICIENT TO PRODUCE A FINITE THREE-PHASE CONTACT ANGLE IN THE BUBBLE MACHINE TEST, TO PRODUCE A SOLVENTWAX-OIL MIXTURE, SAID WAX-OIL MIXTURE AND SAID SOLVENT BEING THE SOLE NON GASEOUS MATERIALS PRESENT IN THE PROCESS; COOLING SAID SOLVENT-WAX-OIL MIXTURE TO THE DEWAXING TEMPERATURE TO PRECIPITATE WAX; SUBSEQUENTLY INTRODUCING A GAS INTO SAID SOLVENT-WAX-OIL MIXTURE NTO PRODUCE A WAX-BEARING FROTH; AND SEPARATING SAID WAX-BEARING FROTH FROM SAID SOLVENT-WAX-OIL MIXTURE.