US1714133A - Dewaxing of oil - Google Patents

Description

May 21,v 1929. E. B. PHILLIPS ET AL DEWAXING OF OIL Original Filed Feb. 19, 1924 ATTORNEY Patented May 2l, 1929..A

UNITED STATES PATENT OFFICE.

ERNEST IB. PHILLIPS, 0F EAST CHICAGO, INDIANA, AND JAMES G. STAFFORD, 0F CHI- CAGO, ILLINOIS, ASSIGNORS T0 SINCLAIR RIEJE'INIII'G` COMPANY, OF CHICAGO, ILLI- N OIS, A CORPORATION OF MAINE.

DEWAXINGv OF OIL.

Original application filed February 19, 1924, Serial No. 693,770. Divided and this application led November 28, 1924.

This invention relates to improvements in the dewaxing of oils, and particularly to the separating of wax from lubricating oils. The

invention relates particularly to an improved method and apparatus for Adewaxing oils. This application is a division of an application filed February 19, 1924, Serial -No. 693,770. Y

One of the troublesome groups of compounds in crude oils are the paraffin waxes.

l:These bodies belong to the saturated or parafiin series of hydrocarbons and vary in character from low melting point amorphous bodies to high melting point crystalline bodies. Of themselves, these'waxes possess very little lubricating value. In Vthe pure state and at temperatures well above their melting points they have many of the properties of kerosene, particularly as regards speciiic gravity and internal friction or viscosity- Further objection to these bodies is found in their tendency to become semi-fluid or solid at 10W temperatures. Oils intended for use in fluid condition at low temperatures must be cleared of Atheir dissolved waxes, else free movement of the lubricating medium over moving parts of machinery will be lost.

From the beginning of the oil industry refiners have been striving to improve commercial methods for removal of wax from their products. Two principal methods of accomplishing this end have reached the stage of practically universal application: 1st-separation by cold pressing; QHd-separation by cold settling.

A brief outline of refinery practice on straight paraffin base crudes will show the essentials of the two lnethods. This type of crude is distinguished by the fact that simple distillation with steam at atmospheric pressure will produce a residue of high quality. Such residues are called steam refined cylindcrstocks and find use as internal lubricants for steam engines. Since the refiner is concerned with obtaining these residues in as' good condition as possible, the whole system of distillation is directed to this end. Temperature of stills, rate of distillation and steam supply are carefully regulated so as to prevent injury to the residue. The. ordinary break-up of crude into fractions is as follows: l-crude naphtha; 2--kerosene stock; 3-300 burning oil stock; 4-gas oil; 5-Wax Serial No. 752,507.

distillate; -residue-steam refined stock. The first four fractions listed contain little or no Wax and therefore may be disregarded.

During the time the wax distillate is being collected every effort is made to drive over as much wax from the residue as possible. Such practice makes for rough separation of waxes originally present in the crude into two groups. Wax distillate will contain a preponderance of crystalline waxes and the residue will hold waxes in amorphous form. The two principal methods for wax removal owe their development to the unlike character of these two stocks.

l/Vaxes present in the wax distillate fraction from crude oil do not lend themselves to separation by cold pressing because of contamination with amorphous wax from the original still residue. To further change these waxes a secondary distillation is resorted to. Under the infiuence of high temperature and scant steam supply many of the amorphous wax bodies are converted into crystalline, yor high-melting point bodies. In refineries this operation is termed cracking wax distillate. The distillate obtained is divided into fractions,-the principal one of which is paraffinc distiliate The residue remaining in the still is a Viscous dark-colored liquidvwhich contains a large part of' the impurities originally in the wax distillate, asphaltic bodies, free carbon and resinous decomposition products. I

The paraffine distillate fraction carries a considerable percentage of wax which has been so changed in form that it will crystallize when chilled. 'By cooling pai-affine distillate to the proper temperature it is converted into a semi-solid mass which, when cold pressed under high pressure, will give up its oil content as pressed oil and leave the Wax content as slackwax on the blankets of the press. Without further separation of wax the pressed oil at once becomes stock 'from which all parafiine-base engine oils are made. Slack wax after appropriate treatment, is sweated for required melting point, filtered through 'fullers earth at elevated temperatures and eaked or barrelled for market. The steam-refined cylinder stock fromv the original crude distillation-while a. market product-commands only a low price. Small amounts of asphaltic material, free carbon and inorganic impurities prohibit its use in high-class lubrication work. To satisfy the demand for these high-class products the petroleum refineipis required to further process his steam refined stocks to obtain stock is filtered to color, the end product will solidify at +8()o F. or +90o F.

The\`finished stocks must therefore be dewaxed in order to have them fluid at moderately low temperatures. If naphtha solutions of filtered cylinder oils are gradually cooled, a temperature will be reached at which a large portion of the wax is no longer soluble. If such a chilled solution is allowed to stand for a period (usually about four days) the suspended wax will settle and a clear, cold solution of stock in naphtha can be drawn from the cold settling tanks.

This settled stock mixture. after removal of naphtha and straining through fullers y earth to remove the last traces of impurities,

yields the bright cylinder stocks of commerce. Since these are the highest grade products manufactured every effort is made to obtain maximum yields. The settlings from the chilling tanks contain all of the separated wax and in addition a considerable quantity of high-grade cylinder oil. When the settlings are cleared of naphtha they produce crude petrolatum stock from which all grades of petrolatum are made.

The present tedious method of chilling type stock mixtures is used because wax will not settle bv gravity if the chilling step is hurried. Observation of type stock mixtures while cooling shows that a nucleus of wax first forms to whichstrings of amorphous wax attach themselves. It the cooling starts in the upper portion of atank convection currents are set up which drag down the slightly denser wax and leave a clear layer of oil and naphtha at the top. Aftera a number of days the suspended wax will be found in a more or less concentrated laver at thel bottom of the tank while the. bulk of the charge is a bright. clear solution of cylinder oil in naphtha. Under these conditions heavy investment in plant equipment is re.- ouired. relatively high operating cost for refrigeration is involved. large'volumes of oil are tied up in the process and maximum yields of high-class cylinder stocks cannot he obtained.

Attempts have been made to overcome the faults of the old cold settling method by causing separation of precipitated wax in cold type stock mixtures by means of high speed eentrifuges. On account of the fact,

however, that the density of the suspended wax is so nearly that of the mother liquor, a separating medium in liquid form of considerably greater density than the original solution must be used. At temperatures ordi- .narily met with-+2() to 0 F.-th is liquid must have a low freezing point. Calcium chloride brine is generally used for the purpose. This practice, however, introduces complications which in a large measure offset the advantages. Injury to the cylinder stock in the dewaxed mixture is quite likely to result from contamination with the brine. Centrifuge machines are very costly and are capable of handling only small volumesper hour. After the brine and its accompanying wax has been separated, the whole mass must be warmed to release the wax and the recovered brine must again be chilled before a new cycle of operations can begin.

The present invention provides an improved method and apparatus for the'separation of wax from cold type stock mixtures. or from crude petrolatum stock produced by present dewaxing methods. or from other fractions from which separation of wax is desired: and the invention enables slow settling by gravity of the chilled tvpe stock mixtures to be replaced by a rapid settling operation. or it enables an increased amount of valuable lubricating oil to be recovered from the crude petrolatum stock obtained by present cold settling methods. while other oils can be similarly dewaxed in a rapid and advantageous manner.

.In operating the apparatus of the present invention. there is added to the solution or oil to be dewaxed. a finely divided gathering material or separating medium which has no effect upon the solution or oil but which will serve to gather the suspended wax so as to permit of filter press operations for separation of the wax from the solution or oil. In the case of naphtha-oil solutions. for example. the addition of a small amount of powdered diatomaceous earth ofthe type of commercial fullers earth to the type stock mixture, either before orafter chilling. will provide a. large number of individual mineral particles serving as nuclei about which the amorphous wvax can gather. `l'nder such conditions the cooling step can be hurried as much as possible and when wax precipitation is complete a normal filter-press operation will cause physical separation of the mineralwax and clear naphtha-oil solution. Instead of extending the cooling step over a period as is the casein the gravity separation method. type stock mixtures carrying 1% by weight of the earth can be chilled while being gently agitated in accordance with the improved method of the invention. and filter pressed without elevation of temperature to etiect a rapid separation of amorphous wax.

`The clear filtrate from the press when iso cleared of naphtha and strained through fullers earth yields type bright cylinder stock. The Wax content of the press cake can be recovered if the cake is thrown in boiling water. Wax in melted state rises to the surface and can be withdrawn while'the fuller-s earth settles to the bottom. After freeing of water and drying in a rotary kiln, the fullcrs earth is ready for re-use in the original wax separation step.

By proceeding in the manner above described, the tedious gravity settling operation for separating the wax from the type stock mixture can be eliminated and a rapid separation of the wax effected. The addition of the earth to a super-cooled solution of wax in oil and naphtha apparently induces a rapid crystal growth of wax crystals upon the particles of the earth as nuclei. If the mixture is relatively quiescent, the crystals will tend to be larger, while if the mixture is agitated, the tendency is for smaller crystals to form. In any event, however, a greatly increased rapidity of the wax separation is effected.

The invention will be further described in conlmetion with the accompanying drawing, which illustrates, in a somewhat conventional and diagrammatic manner, an apparatus embodying the invention and adapted for the practice of the improved method of the invention; but it is intended and will be understood that the illustration is diagrammatic and illustrative, and that the invention is not limited thereto.

In the accompanying drawing the apparatus is shown partly in vertical section and partly in elevation. The tank l is provided with a conical shaped bottom and is heavily insulated. The tank 1 is equipped with coils 2 for cooling, for example, with cold brine, and with a mechanical stirrer 3 for agitating the contents of the tank. An inlet 4 is provided for the oil to be dewaxed, for example, t-he type stock mixture, which is pumped in to charge the tank 1. A finely divided gathering or separating' medium, such as powdered diatomaceous earth, is stored in the bin 5, and is fed into the tank 1 as required. The charge can be chilled to the proper tcmperature and mild agitation can be kept up or maintained by the mechanical stirrer 3. When the charge is chilled to the proper temperature, rapid separation of the wax takes place. Thel batch is then transferred, without loss of refrigeration by the pump 6 and line 7 to the pressure filter shown conventionally at 8, where the physical separation ofthe clear oil-naphtha solution and the suspended mineral-wax takes place. The clear, cold filtrate goes forward by the line 9 to the dewaxed oil storage tank 10. The original press cake after washing with fresh cold naphtha, is dumped from the press into the hopper 11, and is fed into the hot water tank 12. Here the wax portion of the cake is melted and rises to the surface and is withdrawn through line 13 to the wax tank 14. The washings from the filter press go forward with the dewaxed oil through the line 9 to the storage tank 10. The powdered mineral released from the press cake in tank 12 settles to the bottom and is drawn off on to the screen 15. After' draining, it is fed to the rotary dryer 16, and finally returned to the bin 5 for further use in the process.

.lt will tlms be seen that the apparatus comprises a refrigerating tank with means for supplying thereto the oil to be dewaxed, and the gathering or separating medium, together with a stirrer for agitating the charge during its treatment in a refrigerated state with the gathering medium, together with a filter press for separating the refrigerated charge into the dewaxed oil and the wax cake. Provision is also made for melting the Wax and separating the wax from the gathering or filtering medium, and for separating the filtering medium and drying it for further use in the process.

It will be understood that not only the tank 1, but all lines carrying cold oil, will be heavily insulated, and that the hot water tanks will be placed at some distance from the filter press. Also heat interchange devices (not shown) may be utilized. such. for example, as heat interchangers for passing t-he fresh incoming type stock mixture in heat inter-changing relation with'the dewaxed oil, so as to utilize refrigeration of the dewaxed oil for precooling the oil to be dewaxed. The fresh incoming oil to be dewaxed may be passed, for example, through coils in the dewaxed oil storage.

When the type stock mixture is directly treated, in the apparatus of the present invention. the old gravit-y method of cold settling is eliminated, and a radical change in refinery practice is accordingly effected. Where, however. the refinery already has a plant for the old gravity method of cold settling, this apparatus may be employed in conjunction with the apparatus of the present invention; for examplenormal refinery products obtained by routine cold settling miei-ations by the old .gravity met-hed can be further treated in the apparatus of the present invention in accordance with the improved process of the invention. The end products of the old gravity method, so far as wax is concerned, consists of crude ipetroiatum stock having melting points between 100 and 12()o F. Such stock can advantageously be treated by the present invention for the recovery of additional lubricating oil, and wax of a higher melting point, therefrom.

It will thus be seen that the present invention enables a materially increased amount of commercial grade cylinder oil to be obtained from the low-priced petrolatum stock in which it is now contained. The present invention, accordingly, enables such lowpriced petrolatum stock to be further treated for the production of a further amount of lubricating oil therefrom, together with Wax of materially increased melting point.

In refineries which are not provided with the equipment for present day cold settling methods, or Where such equipment is to be replaced by the apparatus of the present invention, the various oils or solutions nonT subjected to the old cold settling method can be subjected to treatment in the apparatus of the present invention. The naphthasolutions of type stock mixture or of type colored cylinder stocks may thus be treated While avoiding heavy investment in cold settling tanks and refrigerating capacity.

The present invention, accordingly, permits radical change in refinery practice and in refinery equipment and greatly simplifies both.

I claim 1. An apparatus for dewaxing oils, comprising an insulated tank having refrigerating and agitating means therein, means for supplying oil to be dewaxed and means -for supplying a nely divided solid material to said tank, a filter` press with a connection for charging the mixture from the tank to the filter press, said filter press being adapted for filtering Wax and finely divided solid material from the oil under pressure, means for se arating the wax from the finely divided so id material, a dryer adapted to receive the finely divided solid material from the said separating means and means for returning dried finely divided solid lnatrial from said dryer to the insulated tank.

2. An apparatus for dewaxing oils, comprising an insulated tank having refrigerating and agitating means therein, means for supplying oil to be dewaxed and means for supplying a finely divided solid material to said tank, a filter press With a connection for charging the mixture from the tank to the filter press, said filter press being adapted for filtering Wax and finely divided solid material from the oil under pressure, a melting tank adapted to receive the Wax and finely divided solid material from the filter press and perlnit the separation of the Wax from the finely divided solid material, a dryer adapted to receive the finely divided solid material separated from the Wax in the melting tank and means for returning dried finely divided solid material from said dryer t0 the insulated tank.

3. An improved method of dewaxing oils, comprising intimately admixing a small amount of finely divided solid material with the oil to be dewaxed and simultaneously agitating and chilling the mixture, and subsequently subjecting the chilled mixture to a filter pressing operation. 4

4. An improved method of recovering Wax from Wax-containing oils, comprising inti'- mately admixing a small amount of finely divided solid material with the Wax-containing oil and simultaneously agitating and chilling the mixture, subjecting the chilled mixture to a filter pressing operation to separate Waxfree oil from the finely divided solid material and adherent Wax, thereafterheating the separated Wax mixture and removing the nely divided solid material from the melted Wax.

In testimony whereof We aix our signatures. u

ERNEST B. PHILLIPS. JAMES G. STAFFORD.

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