US2096950A - Refining mineral oils - Google Patents

Description

REF INING MINERAL OILS Oct. 26, 1937.

Filed Oct. 6, 1932 INVENTOR bcrtECUzZ n ATTORNEY Patented Oct. 26, 1937 REFINING MINERAL OILS Robert .E. Wilson, Chicago, Ill., assignor to Standard Oil Company, Chicago, 111, a corporation of Indiana Application October 8, 1932, Serial No. 636,492

8 Claims. (Cl. 196-13) This invention relates to a process and apparatus for refining mineral oils and it pertains more particularlyto the recovery of solvents used in the extraction of lubricating oils for improv- 5 ing their viscosity indices.'

It has recently been found that the quality of a lubricating oil can be remarkably improved by extracting it with a solvent, such as dichlorethyl ether. Further recent developments have shown 1 that even better results are obtained when the oil is extracted with a mixture oi such solvents with other solvents, particularly ketones such as acetone, esters, and ethers such as isopropyl ether. Thus, an excellent solvent for extraction purposes may consist of equal volumes of acetone and dichlorethyl ether, or from one-half to four volumes of dichlorethyl ether to one volume of acetone. Dichlorethyl ether is an example of what has been called a primary extracting solvent,

90 other examples of which are nitrobenzene, an-

iline, dichlorbenzene, furfural, etc. Likewise, acetone is herein referred to as an example of a secondary solvent, other examples of which are methylethyl ketone, diethyl ketone, methyl ace- 2 tone, etc. By using this combination of solvents, the resulting mixture possesses greater selectivity for naphthenic, naphthenic-like and aromatic portions of mixed base oils than is possessed by the individual solvents. The process of extracting 80 oils with .these mixed solvents forms no part of the present invention, it being described in a copending application filed by Fred F. Diwoky and Arthur B. Brown, Serial 605,814, filed April 18, 1932.

35 The primary solvents have considerably higher boiling points than the secondary solvents, and they are therefore diilicult to recover from the mineral oil extract and raflinate. They are also frequently subject to decomposition at the tem- 40 perature of distillation, particularly at those temperatures required to separate them from the oil.

- Furthermore, they often cannot be distilled with the aid of steam, as they are frequently decomposed by water, particularly the chlorinated compounds. The word primary in this case means higher boiling and not necessarily more chemically active or in larger proportions. Secondary solvents are usually more volatile and water-soluble. The object of my invention is to provide a 50 method and apparatus for recovering both the primary and secondary solvents from the rafilnate and from the oil extract without decomposing or vhydrolyzing the solvents and without incurring appreciable solvent losses.

The conventional process of stripping the rafllnate and the oil extract with steam is objectionable because the steam will cause the hydrolysis of solvents such as dichlorethyl ether, yielding corrosive acid. Furthermore, when steam is used to distil a mixture containing a water soluble v5 component such as acetone, the latter is removed in the condensed water, making it necessary to recover and dry the acetone before reuse. It has been proposed to use natural gas as a stripping means, but here again it has been found that solvents, such as dichlorethyl ether, are slightly polymerized, and it is very difllcult to scrub and/or recover the acetone from the gases. I avoid all of these difilculties by heating the rafilnate or the extract to such a temperature that both of the solvents are substantially vaporized when introduced into a flash chamber or fractionating tower. By suitable rectifying means, such as bubble plates, I knock back all of the oil and I withdraw the primary solvent at a point in the system above the introduction of the heated mix-- ture. The secondary solvent is removed from the top of the fractionating system as a vapor, is condensed, and a part of it is revaporized and introduced at a point below the introduction of the mixture so that it serves as a stripping means to remove the last traces of the primary solvent from the oil.

The invention will be more clearly understood from the detailed description of a preferred embodiment illustrated in the accompanying drawing, which forms a part of this specification and which diagrammatically illustratessmy improved system.

In the following example I have described my invention as used in the extraction of a mixed base Mid-Continent lubricating distillate havin a viscosity of 114 seconds Saybolt at 210 F., a viscosity index of about 56 and a gravity of about 21.6 A. P. r. Iwill describe the use of an extracting liquid consisting of one volume of dichlorethyl ether and one volume of acetone, and I will use two volumes of this liquid to one volume of oil to be extracted. It should be understood, however, that the invention is equally applicable to the extraction of any oil by the use of mixed solvents, that any primary and secondary solvents may be employed as long as they have different boiling points, and that the volumes of the primary and secondary solvents may be varied throughout a wide range.

The untreated wax-bearing distillate from heated storage tank I0 is withdrawn through pipe H and forced by pump I2 to mixer l3. This 011 is preferably at a temperature of about 125-135 F.

so that it will flow freely and so that all of the wax will be in solution. Dichlorethyl ether from storage tanks l4 or I5 is withdrawn through pipe l5, mixed with acetone from storage tanks 11 and I8, and withdrawn through pipe l9,the mixture of acetone and ether being finally passed through pipe 20, pump 2| and heat exchanger 22 to mixer I3. The heat exchanger may be of any desired form, but I prefer to use a steam exchanger and I prefer to heat the mixture to about or F. The solvents are thoroughly and intimately mixed with the oil in mixer l3, which may be in the form of a horizontal tank provided with perforated, transverse baflles. In some cases it may be desirable to have an extended period of contact which may be obtained by using a large mixer or by placing a soaking drum after the mixer.

After the oil has been thoroughly contacted with the mixed solvent, the mixture is passed through cooler 23 and pipe 24 to centrifuge 25, the lighter raffinate fraction of extracted 011 being withdrawn through pipe 26 to storage tank 21, and the ether extract and the heavier fraction, which is called black-oil or ether extract, is withdrawn through pipe 28 to storage tank 29. Chillers 23 should be provided with mechanical stirrers or scrapers because the mixture is preferably cooled to a temperature of about 40 F., and at this temperature the wax is in solid form. If a wax-"free oil is used there will be no necessity for using scrapers. Similarly, if a waxy oil is being extracted it will be necessary to provide heatin coils in the raflin'ate storage tank so that the oil withdrawn therefrom will not clog up the pipes due to solidified wax.

The separation of the extracting liquids from the oil fractions is the same for the rafllnate as for the ether extract, and for the sake of simplicity I will describe only the separation of the mixed solvents or extracting liquids from the raflinate fraction. It should be understood, of course, that the raflinate only contains about 5 to 15% of mixed solvents, and the ether extract contains a very large proportion thereof--the exact percentage depending on the quality of the oil undergoing treatment.

The mixture of oil with mixed solvents is withdrawn from storage tank 2'! by pipe 30 and forced by pump 3| through tube heater or pipe still 32 wherein the mixture is heated to a sufiicient temperature to cause substantial volatilization of all diluents. Under ordinary conditions the outlet temperature may be 400 F., but this temperature will vary with the nature of the mixture and with the pressure in the system. The hot mixture is then introduced by pipe 33 into an intermediate point of fractionating tower 34. Below the point of introduction I provide stripping plates 35 and above the point of introduction I provide fractionating plates 36. I also provide a suitable reflux coil 31 in the top of the tower and I prefer to passall or a part of the feed stock through this coil in order effectively to utilize the heat in the system and to provide reflux for the purpose of fractionation. Relatively pure vapors of the secondary solvent (acetone) are removed from the top of the tower through pipe 38, condensed in coils 39, collected in storage tank 40, and returned through pipes 4i and 42 to acetone storage tanks l1 and I8.

Relatively pure primary solvent liquid (dichlorethyl ether) is withdrawn from one of the plates above the introduction of oil and solvent from the pipe still and is conveyed in pipe 43 through heat exchanger 44 to storage tank 45, from which it is forced by pump 46 through pipes 41 and 48 to storage tanks l4 and I5.

A small amount of the acetone is withdrawn from collector 40 through pipe 49 and forced by pump 50 through heat exchanger 44, coils in pipe still 32 and introduced by pipe 52 into the fractionating tower at a point below stripping plates 35. The acetone is vaporized in exchanger 44 and superheated in the pipe still coils so that when it is introduced at the base of the fractionating tower it effectively strips the last portions of the primary solvent from the finished oil, which is withdrawn from the base of the fractionating tower through pipe 53. Because of the high vapor pressure of the acetone, however, substantially none will remain dissolved in the oil. The amount of acetone which is used as a stripping medium will depend upon the desired degree of stripping and can be readily calculated for any particular system. The temperature to which the acetone is heated is preferably about 5 or 10 hotter than that to which the oil mixture is heated.

As above stated, I prefer to provide reflux in the top of the fractionating tower by means of condenser coils 31. Alternatively I may pump back acetone through pipe 54 to a point above the primary solvent drawofi.

From the above description it will be seen that I have provided an effective method of removing all of the solvent or extracting liquids from the oil without the use of steam and without the introduction of extraneous gases. of the primary solvents have boiling points so high that they could not be completely removed from the oil by simple distillation. The expense of vacuum distillation would be prohibitive. I have found, however, that the secondary or light solvent is practically insoluble in the oil at the elevated temperatures in the recovery system, and I have found that the primary solvent can readily be stripped out of the oil by means of the superheated secondary solvent.

While I have disclosed a process in which the secondary solvent is superheated in extra pipe stills of the furnace, it should be understood that.

I do not limit myself to these details. I may heat the oil mixture to such high temperature that liquid acetone may be injected in the base of the fractionating tower, the extra heat in the oil being suflicient to vaporize and drive out the acetone. Likewise I may pump acetone vapors from the top of the tower into the base thereof for use as a stripping medium, or I may pump these vapors through a suitable heater and then introduce them into the base of the fractionating tower.

Also, heat economy may be secured by various expedients, such as exchanging the-heat of the finished oil such as by passing the finished oil through exchanger 54 for preheating the OH on its way to the pipe still. The drawing of my system is diagrammatic only and it should be understood that suitable regulating valves, pressure and vacuum valves, collecting tanks, conduits, insulating means, heat exchanger means, stirring means, etc. may be employed wherever such expedients are necessary. I do not limit myself to any of the details hereinabove described except as defined by the following claims, which should be construed as broadly as the prior art will permit.

I claim;

1. The method of removing dichlorethyl ether Practically all and acetone from mineral oil which comprises heating a mixture of these solvents, with Oil to a temperature of about 400 F., introducing the heated mixture at an intermediate point into a rectifying zone, adding liquid acetone at the upper part of said rectifying zone, withdrawing dichlorethyl ether between the point of introduction oi the acetone and the point of introduction of the heated mixture, introducing hot acetone at a point below the point of introduction of the mixture whereby it serves as a stripping medium, and withdrawing finished oil from the base of said fractionation zone.

2. The method of removing dichlorethyl ether and isopropyl ether from mineral oil which comprises heating a mixture of these solvents with oil to a temperature of about 400 F'., introducing the heated mixture at anintermediate point into a rectifying zone, adding liquid isopropyl ether at the upper part of said rectifying zone, withdrawing dichlorethyl ether between the point of introduction of the isopropyl ether and the point of introduction of the heated mixture, introducing hot isopropyl ether at a point below the point of introduction of the mixture whereby it serves as a stripping medium; and withdrawing finished oil from the base of said fractionation zone.

3. The method of removing dichlorethyl ether and ethyl acetate from mineral oil which comprises heating a mixture of these solvents with oil to a temperature of about 400 'F., introducing the heated mixture at an intermediate point into a rectifying zone, adding liquid ethyl acetate at the upper part of said rectifying zone, withdrawing dichlorethyl ether between the point of introduction of the ethyl acetate and the point of introduction of the heated mixture, introducing hot ethyl acetate at a point below the point of introduction of the mixture whereby it serves as a stripping medium, and withdrawing finished oil from the base of said fractionation zone.

4. In a system of the type described, means for extracting mineral oil with a mixture of a high boiling and a low boiling solvent, means for heating the extracted oil contaminated with said solvents to a temperature at which substantially all of said solvents are vaporized, means for rectifying the vapors to effectively fractionate the low boiling and high boiling solvent and to separatethe high boiling solvent from the oil, and means for introducing vaporized low boiling solvent at a low point to contact directly with the high boiling solvent and oil for removing the last traces of high boiling solvent fromthe oil.

5. A method of refining petroleum oil which comprises separating naphthenic from paraflinic constituents of the oil with a solvent mixture in which the solvents have a boiling point lower than that of the oil and at least one solvent has a boiling point lower than any other solvent, separately heating the naphthenic and paramnio fractions to temperatures suilicient to vaporize most of the solvent mixture contained therein, vaporizing the mixed solvents from the heated oil, rectifyingthe vapors to remove oil from the solvents, and introducing a portion of the lower boiling solvent into the non-vaporized oil at a temperature sufficient to produce the complete vaporization of said lower boiling solvent whereby it serves as a stripping gas to remove the last traces of solvent from the oil.

6. An oil refining process which comprises separating parafllnic from naphthenic constituents of a petroleum oil by extracting said oil with a mixture of a high boiling and a low boiling solvent, both of said solvents and the solvent mixture having a boiling point below that of the oil,

separately heating the paraifinic and naphthenic fractions to-a temperature suflicient to cause vaporization of both solvents, separating the vaporized solvents from unvaporized oil contaminated with solvents, rectifying the vaporized solvents to remove oil therefrom, introducing condensed low boiling solvent for use as a reflux liquid in said rectifying step, and introducing a portion of said low boiling solvent into said unvaporized oil at a temperature high enough to cause complete vaporization of said low boiling solvent whereby it serves as a stripping means for removing the remaining high boiling solvent from the unvaporized oil.

'7. Themethod of claim wherein the low boiling solvent is superheated prior to its use as a stripping agent.

8. The method of claim 6 wherein the low boiling solvent is superheated prior to its use as a stripping agent.

ROBERT E. WILSON.

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