US2063369A - Solvent extraction of wax-bearing oils - Google Patents

Description

1936- s. H. mess ET AL 2,063,369

SOLVENT EXTRACTION OF WAX BEARING OILS Filed Feb. 23, 1932.

JSZOWQ 44 lhl ,5 )7 dew 025m deparazfor 15663026 JZZZZ irk/772 BY James 772. Pa ge,J&

Patented Dec. 8, 1936 UNITED STATES PATENT orrlcs Sterling H. Diggs and James M. Page, Jr., Casper, Wyo., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application February 23, 1932, Serial No. 594,612

9 Claims. (01. 19c 17) This invention relates to a system for extracting undesirable components from an oil-wax mixture and it pertains more particularly to the separation of naphthenic from paraflinic constituents in a mixed base petroleum lubricating oil stock.

A recent innovation in the petroleum art has been the separation of paraflinic from naphthenic components by means of certain selective solvents. One solvent which has proven to be of outstanding superiority is dichlorethyl ether- ClCH2CH2OCH2CH2Clwhich has a boiling point of about 352 F. (175 C.), a freezing point of about -61 F. (-51.7 C.) and a specific gravity at 20 C. of about 1.22. In carrying out the extraction it is the usual practice to mix the oil and solvent at a temperature above the melting point of the paraffin which it may contain. When such a mixture of wax-bearing oil and dichlorethyl ether is cooled, a large amount of wax is thrown out of solution in the form of a buttery mass which is diflicult to handle and which interferes with the separation of'parafiln oils from the dichlorethyl ether solution. The object of our invention is to provide a system and a process which will avoid this dimculty and which will thereby facilitate the rapid separation of paraffin oil from solvent solutions. In our preferred example we will describe the invention as applied to a dichlorethyl ether extraction, but it should be understood that any suitable solvent may be employed, providing its miscibility temperature is within the desired range.

A further object is to reduce the sulfur content, increase the viscosity index, and decrease the sludge-forming tendency of lubricating oil.

A further object is to provide an improved means for separating the wax from lubricating oil. Other objects will be apparent as the detailed description of our invention proceeds.

In practicing our invention we remove the bulk of the wax in the liquid state so that it cannot separate out in the later steps of the extraction process. We have discovered that when solvents of the class described, such as dichlorethyl ether, are mixed with a wax-bearing oil at a temperatureabove the melting point of the wax and sufficiently high to give a homogeneous solution of oil and solvent, the first oil to separate on cooling will contain the largest proportion of the wax. By avoiding cooling below the solidification point of the wax bearing oil it may be readily separated while it is still in the liquid state. This may be accomplished by decantation or by the use of a continuous liquid separator. Accordingly, in

practicing our invention we use a solvent which is immiscible with the oil-wax mixture at a temperature above the melting point of wax, and we prefer to remove the wax from the mixture by removing the first and, if desired, successive increments of the liquid which are thrown out of solution on cooling. When practically all of the wax has been removed, the extraction may be carried out at relatively low temperatures, and the two layers may be readily and rapidly separated without serious interi'erence from solidified wax.

The invention will be more clearly understood from the following detailed description of a preferred embodiment, reference being made to the accompanying drawing which forms a part of this specification and which diagrammatically illustrates the same.

The invention will be described as applied to a waxy lubricating oil stock having a Saybolt viscosity of 83 at'210 F., a cold test of 122 F., and a wax content of about 20%. This oil is commonly known as motor base stock and it is preferably a heavy distillate, although it may be a residual oil. When this oil is extracted at 40 F. with one or two volumes of dichlorethyl ether, a large amount of butter-like solid is formed. As a consequence, some of the solution is occluded in the solid and the efliciency of the extraction is seriously impaired.

In accordance with our invention, the waxbearing oil from storage tank I is introduced by.

pipe I l to mixer l2, where it is thoroughly mixed with one and one-half to two or more volumes of dichlorethyl ether from storage tank l3 and pipe I. The mixer may be of any suitable type, and is preferably the so-called orifice mixer which consists of a series of perforated baflies in a cylindrical casing. Since the oil has a cold test of 122 F. it must be passed through the mixer in heated condition and we prefer to maintain-both the oil stock and the dichlorethyl ether at a temperature of about 145-170" F. If a temperature of 165 is obtained, this particular stock will be completely miscible with the solvent so that little mixing will be necessary. 'Altematively, we may save a considerable amount of heat by using the mixer and employing a lower temperature.

The mixture at about 145-170" F. is then introduced by pipe I 5 into settling or separator tank I6. 11' the mixture is already at a temperature of about 145 F. there is no necessity for heating or cooling the mixture in the settling tank. Therefore, this tank may act as a continuous liquid separator. On the other hand, if the incoming mixture is at a temperature of about 165-470 F. we must cool the liquid by means of suitable coils ii. A slow, even stirring is desirable in the cooling tank; this may be accomplished by the use of centrifugal motion as hereinafter described, or it may be effected by suitable paddles or stirring means. Dichlorethyl ether is completely miscible with this stock at 165 1"., and when the temperature is reduced to 145 1". about 50% of the stock separates from the solution. The material separating at this temperature is largely liquid wax and it constitutes about 75% of the wax in the stock. As 145 1'. is well above the melting point of the oilwax mixture, it remains in the liquid phase, and it is a simple matter to remove it through pipe I! while the dichlorethyl ether solution is being withdrawn from the base of the separator through pipe l9.

We next cool the solution in cooler 20 to a temperature of about l25-l30 F. and introduce it through pipe 2i into the second wax separation chamber 22. This chamber is also provided with coils 23 for supplying heating or cooling fluids, if desired. In separating chamber 22 another 25% of the wax is separated from the solution together with sufllcient oil which maintains it in the liquid state at a temperature even below the melting point of the wax.

If the solution were initially cooledto 130 F. the separated layer of an oil would have a strong tendency to solidify because of the large proportion of wax in the mixture and the higher average melting point thereof. Separation would be made diflicult and the efllciency of extraction would be lowered. .(In accordance with our invention, however, we use a solvent which is immiscible with the wax at a temperature above its melting point and we remove the wax in increments so that nearly all of it may be removed as a liquid.)

The wax and oil are discharged from the top of the second wax separator chamber through pipe 24 and the solvent is withdrawn from the base of the chamber through pipe 25. The solvent is then cooled in cooler 28 to a temperature of about 30-40 F. and introduced by pipe 21 into the separation chamber 28. At this low temperature practically all of the parafiinic components of the oil are thrown out of solution and practically all of the undesirable naphthenic constituents remain dissolved in the dichiorethyl ether. The temperature may be regulated by passing heating or cooling fluids through coils 29, the paraillnic components are withdrawn from the top of the extraction chamber through pipe 30 and the solvent with its naphthenic content is withdrawn through pipe 3|.

If desired, the liquid wax from pipe It may be withdrawn through pipe 32 to a/suitable system for removing the oil from the wax. Likewise, the mixture from pipe 24 may be discharged through pipe 33 and the parafiln oil from pipe 30 may be discharged through pipe 34. On the other hand, we may combine these three fractions by header 35 and introduce them all into still 86 for driving out traces of solvent, this solvent being conducted through pipe 31 and condenser 38 to storage chamber II. Oil from the base of the still is withdrawn through pipe 40 to a suitable dewaxing systems The solvent from extraction chamber 28 is introduced by pipe 3| into still H, the naphthenic components being discharged through pipe 42 and the solvent being expelled through pipe 43 and condenser 44 back to the storage tank It.

The lubricating oil obtained from the dewaxed parafiln components is characterized by an extremely high viscosity index. In other words, the change in viscosity with temperature is approximately the same as the change of viscosity of natural paramn type oils which are rated as having a viscosity index of 100. The oils are characterized by a low sulfur content and they are also found to be remarkably resistant to sludge formation.

While we have described in detail a preferred embodiment of our invention it should be understood that we do not limit ourselves to any of the details herein set forth. The settling chambers or continuous liquid separators are shown diagrammatically, and it is understood that any conventional equipment may be used for this purpose. Centrifugal separators are particularly useful and we contemplate the use of centrifugal action obtained by introducing the mixtures tangentially at the center of a vertical cylindrical tank, withdrawing the heavy dichlorethyl ether solution at the periphery of the base and withdrawing the lighter oil in the center of the top. The rotation of the liquids will accelerate the separation thereof.

Dichlorethyl ether is illustrative of a large class of selective solvents which we may use for the separation of wax-containing parafilnic oils from the naphthenic 011 components by our process. Other examples are phenol, ethylene chlorohydrin, glycerol monohydrin, furfural, aniline, 2-4 dinitrochlorobenzene, butyl carbinol, phenylmethanol, etc. Acetone, nitrobenzene, chloroacetone, glycol acetate (cellosolve), 2 methyl propanol, and a large number of other solvents may be used on stocks which have a sufiiciently low pour point. The essential feature of the invention is that the wax (or oil-wax mixture) should be in liquid form at a temperature at which it is immiscible with the solvent.

The temperatures given in the preferred example are illustrative only and it will vary, of course, with other oil stocks and other selective solvents. For Mid-Continent lubricating oils the temperature for the first separation will probably be about to 1".

The layer insoluble at the high temperature may contain some dichlorethyl ether, which will, of course, be separated out at lower temperatures.

We have found that the oil from the layer insoluble at high temperatures is often materially better than the oil from the later separations. For instance, oil from the -145 insoluble lay.- er has a viscosity index of 86.2, while oil from the top layer at 40 F. has a viscosity index of only 75.3 in tests made on oil from a Casper crude.

We claim:-

l. The method of removing wax from oil which comprises adding dichlorethyl ether to an onwax mixture, and separating the soluble naphthenic portions from the insoluble waxy portions of the mixture at a temperature above the melting point of the oil-wax mixture.

2. The method of obtaining maximum yields of high viscosity index oils from a mixture of paraillnic and naphthenic components in a waxbearing lubricating oil stock, which comprises intimately mixing said stock with a solvent of the class which consists of dichlorethyl ether, phenol, furfural, aniline and nitrobenzene at a temperature above the pour point of the waxbearing stock, efl'ecting phase separation at a high temperature at which wax is separable as a liquid, removing the high viscosity index oil and wax which is insoluble in the solvent from said solvent solution at said high temperature, subsequently cooling said solvent solution and efiecting a phase separation of the remaining lubricating oil stock and solvent at a substantially lower temperature whereby substantially all of the desirable paraflinic components are separated from the solvent, removing the low temperature solvent solution from the insoluble oil layer, and separately recovering the solvent from the solution and from said insoluble oil fractions.

3. The method of removing wax from an oilwax mixture which comprises diluting said mixture with a preferential oil solvent, intimately contacting said solvent with said mixture at a temperature above the melting point of the mixture, separating the undissolved waxy part of the mixture from the solution at a temperature above the melting point of the mixture, cooling the mixture to cause a further separation of the paraflinic liquids from the solution, and separating said liquids therefrom.

4. The method of refining a lubricating oilwax mixture which comprises adding dichlorethyl ether to said mixture, intimately mixing the same at a temperature at which all of the wax is in liquid state, separating the solution from the undissolved liquids at a temperature above the pour point of said undissolved liquids, cooling the solution to separate paraflinic components from the naphthenic components of the oil, and separating the paraffinic components from the solution.

5. The combination of claim 4, which includes the further step of separating liquid wax and oil from the solution at an intermediate temperature.

6. The method of refining a petroleum oil which contains wax, parafllnic and naphthenic components, which comprises admixing said oil with dichlorethyl ether at a temperature near that at which the mixture is completely miscible, intimately mixing said oil and dichlorethyl ether at said temperature, cooling said mixture to etfect the separation of an oil phase containing liquid wax and paraflinic components and an ether phase containing naphthenic components, removing the oil phase from the naphthenicdichlorethyl ether phase, cooling the latter phase to a lower temperature to effect further phase separation, and removing the further separated parafllnic oil from the solution of naphthenic components in the separated dichlorethyl ether.

7. The method of fractionating a wax-bearing petroleum oil into fractions grading from paraffinic to naphthenic, which comprises mixing said oil with dichlorethyl ether at a temperature near that at which the oil is miscible with the dichlorethyl ether and above the pour point of the waxing oil, cooling the mixture in stages, separating wax as a liquid after the first cooling stage and separating paraflinic from naphthenic fractions after the subsequent cooling stages.

8. The method of refining a mixed base waxbearing mineral lubricating oil, which comprises admixing it with dichlorethyl ether at a temperature of about 145-170" F., separating the undissolved liquid from the solution at a temperature of about 145 F. whereby a large proportion of wax is removed from the solution in the liquid state, cooling the solution to about 130 F. and removing a further amount of waxy oil from the solution at said temperature, cooling the solution to about 30-40 F., and separating the solution from the undissolved oil at said temperature, the solution containing the naphthenic components and the undissolved oil containing the paraillnic components of the oil.

9. The method of making a lubricating oil from a petroleum oil containing paraflinic components, naphthenic components and wax, which comprises mixing said oil with at least an equal volume of dichlorethyl ether, heating the mixture to a temperature of at least 125 F., cooling the mixture to a temperature of about 30 F. to cause separation of parafllnic from naphthenic components, removing the parafllnic components from the naphthenic components, and removing wax .from the parafllnic components.

STERLING H. DIGGS. JAMES M. PAGE, JR.

Images