USRE21556E

USRE21556E - Process fob treating mineral oils

Info

Publication number: USRE21556E
Authority: US
Publication date: 1940-09-10

Description

` sept. 1o, w40.

M. R. FENSKE ET AL PROCESS FOR TREATING MINERAL OILS original Filed New. 9, 195s 2 sheets-sheer 1 mrs# sou/mr COL uM/v COMA/,ww JOL VMM/va 0a t: Sw

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PROCESS OR TREATIG MINERAL OILS Original Filed Nov. 9, 1933 2 Sheets-Sheet 2 llllllllillll/l/llll Re. 21,556v

UNITED sTATEs PATENT OFFICE PROCESS FOB TREATING MINERAL OILS Merrell B.. Fenske, State College, and Wilbert B. McCluer, Bradford, Pa., assignors `to Pennsylvania Petroleum Research Corporation, a corporation of Pennsylvania Original No. 2,064,422, dated December "15, 1936,

Serial No. 697,344, November 9, 1933. Application'for reissue December 14, 1938, Serial No.

This invention pertains to the vseparation of mixtures of materials. It will be described in connection with the extraction and/or fractionation of mineral oils by the use of solvents. However, it is to be understood that it is applicable to the separation of mixtures in general.

In copending application Serial No. 10,932, led March 13, 1935, by Merrell R. Fenske and Wilbert B. McCluer, which has matured into Patent 2,037,318, April 14, 1936, are described a process and apparatus adapted for the extraction and/or fractionation of mineral oils wherein a pluralityy of liquids of diierent densities are flowed relatively to each other by virtue of differences in their densities. The types of apparatus described in said copendingappllcation employ columns wherein at least one liquid phaseis maintained in a widely distributed form by causing said relative movement between said phases to take place in the presence'of a group of attenuated packing members arranged in the zone of contact side by side and longitudinally oi'V the flow of at least one phase; countercurrent flow, the liquids enter the column at vertically spaced points, the feeding points of said liquids being generally arranged in the order of their densities with the heaviest liquid lbeing fed at the top, although this is 'not absolutely essential. `At least one light solution of the liquids is usually taken off from the column at the top thereof and at least one heavy solution of the liquids is usually taken oil' from the column at the bottom thereof.

In a more specific form of vsaid invention, one Vor more of the counter-currently ilowing liquids is maintained in a plurality of separate streams, highly eiiicient contact means are provided and/or special means is provided -for the prevention of channeling of the counter-currently ilowing liquids with or without the setting up of reflux conditions.

The invention herein also pertains to a process y or scrubbing the phases while in the column.

Provision may be also made in certain instances for taking oil a side stream or side streams ofr any or all oi' the separated portions.

Reflux conditions may be set up by reducing the solvent power of the solvent as it flows In practicing said invention with.

through the column. Reduction in solvent power may be accomplished either by lowering the temperature or bythe addition of a second solvent which acts as a precpitant, or by means of `re, moving the solvent for instance by vaporization. If reduction in solvent power is accomplished by lowering the temperature, the temperature change may be gradual throughout the length of the column or it may be caused to change abruptly at one or more points in the column. The temperature may be reduced in the direction of solvent flow to cause reflux of oil or in the direction of oil flow to cause reux of solvent although the former is desired. If reduction in solvent power is accomplished by the addition of a second solvent which acts as a precipitant, this second solvent may be added at one point .or at a multiplicity of points throughout the length of -the column. The addition of the second solvent at a multiplicity of points throughout the length of the column corresponding to successive increasesv in the concentration of the second solvent in the solvent .phase in the direction of solvent ilow is particularly effective. vReduction in solvent power of any solvent within a column results in continual precipitation of dissolved oil and continual solution of undissolved oil which produces a condition analogous to reflux as occurring in distillation that is highly desirable,

The invention herein pertains more particularly to the alternate engagement and disengagement of phasesin a. continuous system to obtain the advantages not only of ordinary continuous countercurrent contact butA also the advantages of batch contact and particularly batch countercurrent contact.

Further features of the invention reside in the construction, arrangement and combinations of parts and in the steps, sequences, and combinations of ste l, all of which together with further features wiii come more apparentv to persons skilled in the art as the specification proceeds and upon reference to the drawings in which like reference characters have been appended to like parts in the various figures, and in which Figure 1 is a flow sheet illustrating the reflux action,

Figure 2 is a sectional elevation of a further form of the invention,

Figure 3 is a section on line 3 3 of Figure 2, and

Figure 4 is a sectional elevation shown broken and partly in flow sheet form.

The benefits derived from reux may be evidenced as follows: Figure 1 is aschematicsketch lo an extract pump 3, a condenser 4, a solvent pump 5, a hot circulating medium 6, and aA cool circulating medium 1. This figure represents a specific case in which the solvent is heavier than the oil. If, for simplicity, the specific case is assumed in which the column is charged with a single appropriate quantity of oil and illled with solvent which is circulated continually by the arrangement of apparatus as shown in which no products are removed from the system, a condition of total reflux prevails. That is to say, warm fresh solvent continually dissolves oil at the topA of the column and reaches a saturation value;.

the oil which is dissolved is that of poorer (orv better) lubricating value as dened by viscosity index if the solvent is selective as to type of molecule; this dissolved oil is carried along by the solvent on its downward path through the column: since the column is shown as being lagged and hence under adiabatic conditions except for the top and bottom where heat is added and withdrawn respectively, the solventbecomes progressively cooler on its downward path through the column and`accordingly progressively supersaturated with respect to the amount -p of oil initially dissolved and oil is thrown out of solution or precipitated continually during the downward course of the solvent; this oil which is precipitated is of progressively lower quality as more and more oil is precipitated; and this condition produces a quality gradient in the precipitated oil throughout the length of the co1- umn; as soon as the small dropletsv of oil are precipitated they start to rise through the solvent medium in the column since they are lighter than the solvent; lower quality oil in the unvaporizing pure solvent from the spent solvent containing dissolved oiland returning the fresh solvent to the top of the column and recirculating the extract into thelower portion of the column; under these prescribed conditions a steady state exists within the column and a quality gradient of oil is set up and maintained Within the column.

It is evident that in the case in which.the oilY is heavier than the solvent that the system needonly be reversed in `order to rcarry out a similar effect. It is also evident ,that a similar condition can be eiected if the solvent powers of the solvent are decreased by the addition oi!` a. precipitant as previously mentioned. Under any practical operating condition, it is necessary to remove product either intermittently or continuously. The process described above is operable under either condition although the rlatter is preferred. vIn continuous operation, fresh oil is'fed into the column at some one point or at a multi icity of points although it is preferred to feed th oil into a section of the column where the naturally established quality 'gradient is equal to that of the quality of the feed. In this manner, the equilibrium conditions prevailing In the'column are the least degree.

'showing a contacting column I, a vaporlzer 2,

Improved product is removed continuously from the top of the column while segregated product is removed from the vaporizer. A portion of this latter material may or may not be returned to the lower part of the column depending chiefly upon the temperature diierential employed between the top and bottom of the column and the solubility of the oil in the solvent employed.

. For comparative purposes only, the effect of reflux on increasing the efliciency of any given column in separating lower and higher quality materials from a given quality of feed maybe likened to processing and reprocessing the original material in columns where reflux is not employed;` A

The same method of operation and principles apply when the extraction is used to fractionate an oil to produce materials of varying viscosity Y characteristics instead of varying qualityA characteristics. l

Referring now to Figures 2 and 3, at 65 is shown a column adapted for the alternate en"- gagement and disengagement of phases. It will be noted that Acolumn 65 is provided with means for taking off side streams either of oil or of solvent, or of both. Column 65 as shown comprises a plurality of superimposed sections 66, with each adjacent pair of sections 66 being joined by an interposed segregating chamber 61. Any means may be provided for joining the sections 66 and chambers 61 together, such as the flange construction illustrated.

Each section 66 as shown comprises a plurality of tubes 68 which are supported in and project through a pair of spaced plates or headers 68 and 18.

The upwardly projecting ends 1I of the tubes 68 of the upper section 66 project into feeding and segregating chamber 12, the plate 69 of this section forming the bottom of said chamber 12. The inlet 13 for the heavier liquid is preferably below the upper edges 14 of the ends 1l of tubes 68, and edges 14 are preferably in a horizontall plane so as to act as weirs for uniformly feeding the heavy liquid into each of the tubes 68 of the .upper section -66.

An outlet 16 is shown for chamber 12- for the Withdrawal of light solution.l

The tubes 68 of each of the sections 66 -are illustrated as being provided with feeding means 11.

The feedingsmeans 11 may be of any desired` construction. That shown is more particularly illustrated in Figure A3 as comprising a main feeder tube 83 having a plurality of branches 8l, each branch communicating with the interior of a tube 68. The flow is illustra-ted as be` ing controlled by metering orifices 95 comprising small tubes of equal length anddiameter. V`The purpose Yof adjusting ilow is to introduce the desired amount of liquid into each of the tubes 68 for the preferred conditions of operation.

The upper ends 1| of eachmf the tubes 68 of the lower and of the intermediate sections 66l project up into a segregating chamber 61, and the lower projecting ends 18 of each of the tubes 68 of the upper and intermediate sections 66 project downwardly into a segregating chamber 61.

'I'he upper edges 14 of the ends 1I of tubes `68 in any chamber 61 are also preferably in the same horizontal plane. l'I'he lower edges 80 of the lower ends 18 of each of the tubes 68 of any section 66 are `also preferably in a horizontal plane.

the tubes 88 of any two or more sections are vertically aligned or vertically over-lapped, a cap 8| is preferably interposed between any two aligned or over-lapping tubes 68 to prevent direct ow of liquid from one tube 68 to the next.

Cap 8| may be of the order of a bubble cap employed in bubble cap towers, if desired, particularly if the bubble cap' contacting eifect is desired. Cap 8l if of the bubble cap type should be so positioned with respect to the end 1l as not to cause the liquids to lock. This may require bringing the bottoms of the saw teeth above the plane ofv the edges 14. However, any other type of cap 8| or other means may be provided for the purposes above set forth.

Each chamber 61 as shown communicates with 'a pipe 83 preferably above the plane-of the edges 88 and with a pipe 84 preferably below the plane of the Aedges 14 for purposes which will hereinafter appear. The ends 19 of the lower section 66 project downwardly into feeding and segregating chamber and each end 18 may be provided with an inverted cap 86 if desired. Any of the other ends 19 may also be provided with inverted caps 86. if desired, for instance, to increase the number of bubble cap contacts.

Chamber 85 'is provided with an inlet 81 for the lighter liquid and an outlet 88 for the heavier solution.

Each of the sections 6G is provided with a shell 88 which is joined to the flanges of the particular section. Each shell 88 is provided with openings 90 for the ingress and egress of a heat exchange fluid.

Each of the tubes 68 is illustrated as being packed with a packing 9i which may be of any desired'type. Jack chain for instance is found to be very suitable, although any other type of packing may be employed.

Certain types of packing comprise carding teeth, single turn, double turn. triple turn, or polyturn helixes, open rings, bent carding teeth,

H shaped, S shaped, doublecrossed shaped wire forms, all having dimensions more or less comparable to carding teeth used in the textile industry. v

The packing may be supported in each tube `68 by any suitable means, such as that illlustrated at 92. However when tubes 68 are of small inner diameter, packing materials may not be required.

Tubes B8 may, of course, have a cross section of any desired geometrical configuration but are preferably of suilciently small cross sectional area to avoid serious channeling of the phases through each other. The preferred limiting cross sectional area for each tube 68 will be not only a function of the type of contacting means (if any), but .also of the manner in which the contacting means is arranged in each tube, for instance of the degree of. uniformity of A distribution of packing. Since the tubes may have sides which `are straight or indented or of other surface configuration, the departure of a tube from a straight or continuous form will have its influence. lFor this reason a denite limit in cross sectional area which, if exceeded in size, will no longer demonstrate the substantial increasel in eflciency which we have discovered results from a constriction of cross sectional area, cannot be given, but may be readily determined, for instance by testing theemciency of single tubes of different size after any contacting means 'to be employed yis arranged there- It may be stated as a. general rule that one should proceed with caution after exceeding a cross sectional area equivalent to that of a circular tube in the neighborhood of two or three inches in diameter although with a proper selection of packing or other contacting means and a careful distribution in each tube, it may. be possible that larger cross sectional lareas may be employed while in other cases smaller cross sectional areas may be required.

Therefore, the term relatively small cross sectional area or its equivalent, when Vemployed in this specication and in the claims, is intended to mean a cross section `which is suiciently small to materially increase' the contacting efciency because of the constriction of its area.-

We have obtained highly efficient phase contact without serious channeling in tubes of various cross sectional areas. for instance tubes of circular cross section and of L/4.inch, 1 inch, and of 1.75 inches in diameter.

It is simpler to have tubes 68 of any one setv of substantially the same cross sectional area and packed in a manner to have substantially the same pressure drop. 'I'hus each phase will substantially equally divide between the tubes. Since the result of this ls to maintain substantially the same proportion of solvent phase to oil phase in each tube of the set, it will be obvious that the tubes 68 of the set may be of Adifferent sizes and that the feeding rates may vary according to the difference in perimeters of the tubes and/or adjustments of pressure drop, particularly if substantially the same proportion of phases is maintained in each tube. In other words, the result of having tubes 68 of the same size and of maintaining uniform feeding conditions for each tube is to cause the railinate phase produced by each tube to be substantiallly of the same composition as the railinate phase produced by any other tube; and to cause the extract phase produced by each tube to be of substantially the same composition as the extract phase produced by any other tube. From this it will be obvious that if tubes 68 should vary in size the feeding rates should be adjusted to obtain similar conditions.

'I'he ltubes 68 in any set may be of lany de-l sired number and may be of any desired length.

In choosing such length, consideration will, of course, be given to the number of theoretically perfect batch contacts desired in the particular tubes whether such number be an integer or a fraction.

The column may be operated at any desired pressure. This pressure may be atmospheric, particularly if the solvents are liquid at atmospheric pressure, or elevated, particularly if this is necessary to maintain one or more of the solvents 'in the liquid phase (partially or wholly as desired) while in the column; or reduced, should this be desirable for any reason, for instance to bring a part of the solvent or solvents into the' vapor phase.

In describing the operation of the column 65, it will be assumed that the oil is heavier thanthe solvent. Oil may be fed in through the opening 13 and if so it will rise about the ends 1I of tubes\ 68 of the upper section 66 and if the edges' 1l are in the same horizontal plane, the oil will overflow equally into each tube 68 of the upper section 66.

The undissolved oil flows downwardly into the uppermost chamber 61 and collects therein about the ends 1I of the tubes 68 of the next lower sec` dissolved eventually reachescharnber 85 wherein it segregates from the inowing fresh solvent and is withdrawn at 88.

Fresh solvent will be'fed in through 81 and uniformly up through the tubes 68 of the lower section 66 because of its uniform head at the lower ends of these tubes 68. Caps 86 may be provided over the ends 19 should the bubble'cap contact be desired. Otherwise the caps may be removed and, if desired, ends 19 of lower section 66 may be made flush with the plate 16 thereof.

The solvent upon reaching the lowermost chamber 61 separates from the down-flowing oil and forms a layer about the downwardlyprojecting ends 18 of the tubes 68 of the next higher section 66. Since the edges of the ends 19 are l in a horizontal plane, the up-fiowing solvent will be equally distributed among the tubes 68 oi the latter section 66. Such equal distribution would also take place if the lower edges 80 were Vflush with the plate 18 of the respective section.

The' solvent continues up through the tubes 68 of this section 66 and is redistributed in a like manner in each of the succeeding higher chambers 61,

A counter-current 'flow of voil and solvent is thus brought about with the addition of disengagement of phases and redistribution intermediate the ends of the column.

' This alternate engagement and disengagement of phases combines in one continuous system the advantages of' ordinary continuous countercurrent contact and the advantages of batch contact and particularly batch countercurrent contact.

The redistribution means -provided in each of the chambers 61 permits the taking off of side streams of oil through the openings 84 and/or side streams of solvent through the openings 83.

This construction also makes it possibleV to feed in oil through any of the openings 84 and to feed in solvent through any' of the openings 83. A third liquid such as an oil precipitating liquid previously referred to might also be fed in at any. of the openings 83 or at 'any of the openings 84 instead of through the means 11 more speciiically provided for that purpose.

' If the process is one of solvent extraction, the side streams of oil will have increasing degrees 0i' improvementfrom the top to the bottom of the column and the highest degree of improvement will be obtained in the oil withdrawn at 88.

From vthe foregoing it will be seen that-this lform of theinvention may be'operated with or without producing reiiux.F

' adding a precipitating liquid, or both and/or sol- -vent-oil solution may be withdrawn at any desired point, concentrated to precipitate oil, which with or without the solvent remaining in the liquid phase, may be returned to the column.

The latter is illustratedin Figure 4.

It will, of course, be undertsood that a, temperature gradient through the column may also be maintained by feeding the solvent at a higher temperature than the feeding' temperature of the oil, or by feeding the oil at a higher temperature than the feeding temperature of the solvent.

The former will cause precipitation of oil from solvent and the latter precipitation of solvent from oil.

In describing the operation with reflux it will be assumed that the lower section 66 is employed solely for the purposes of effecting solution between the oil and solvent (although precipitation with a corresponding degree of reflux and rectification in this section might take place if desired) The up-ilowing solvent 4when it reaches the lowermost chamber 61 will have a certain amount of oil dissolved therein. If this solvent as itp'ass'es up through the tubes 68 of the next higher section 66 is brought to a, supersaturated condition either by reduction of temperature, by the addition of a third liquid, and/or by vaporization of solvent, the excess oil will be precipitated and will flow downwardly into the lowermost chamber 61 and will be fed back into the tubes 68 of the lowermost section 66, whereupon va portion'will be redissolved', and carried back up for repetition of the cycle, therebycausing rectification in the manner previously described. Aside stream might be taken off at the opening 84 of the lowermost chamber 61, or at the opening 83 thereof, or

both as desired.

When the solvent reaches the next higher chamber v61, i t is redistributed and-flows up into the next higher section 66 in which further precipitation might take place causing a. reflux of oil back into this chamber 61 and into the tubes 68 below. One or more side streams might be taken o ff from the latter chamber 61 the same as from the previous chamber 61. This process may be repeated as many .ti es as desired as the solvent proceeds up throug the column 65 since any number of sections 66 may be employed. The solvent eventually reaches chamber 12 in which it may have a final vcontact with the inilowing fresh oil if desired by providing caps 84 of the order of bubble caps over the upper ends of tubes 68 of the upper section 66. The solvent flows out through opening 16.

In the above description the fresh oil came in contact with the refluxe'd oil Aand of coursedesired construction, for instance, that of any of the towers disclosed herein. The point of feed of the side streams may be governed by any of the considerations herein. v

It should be particularly notedthat the column 65 is not only particularly useful in effecting contact between a plurality 'of liquids but is also equally useful for effecting contact between a liquid and a vapor or a plurality of vapors. It is, therefore, suitably adapted to distillation or fractionation. In this event,l ends 19 of tubes 68 may be flush with their respective plates 10 particularly if sidestreams of vapor are not desired and caps 86 may be removed. Caps 8| and '84 might or might not be employed as desired. Such an arrangementwill also operate for solvent treatment purposes since ends 18 are primarlly for assisting the disengagement of phases and obtaining side streams.

. Many variations in constructional form may be resorted to. For instance, that portion/of each tube `68 which falls between plates 69 and 10 of any section might .be dispensed with, in which case the plates 69 and 10 of each section 'might remain in place or might be made integral.

Openings S0 would be plugged. The space between plates 69 and 10 of each section 66 might remain empty 1or it might be partially or completely filled Awith any suitable packing. vAny suitable means might be provided to support the packing, such as the plate 10 or a perforated plate in place of plate 10 or if plate 10 were removed the packing might rest upon the next lower plate 69. In this event, additional jackets might be provided in each section for heat exchange purposes and the third liquid .might still be fed in through the tubes 11 when desired.

' When the oilis lighter than the solvent, the oil may be fed in through 01 and withdrawn through opening 16. Solvent may be fed in through '13 and withdrawn at 68. Side streams of y solvent may bewithdrawn through the openings 84, and side streams of oil may be withdrawn through the openings 83. In this event, the upper section 66 would probably be used exclusively for solution purposes, although notnecessarily.

If it is not desired to have the fresh oil flow n through the rei'luxed oil, the fresh oil might be is illustrated a vaporizer which is connected to` the column 65 in a manner so as to reduce the concentration of solvent in the column or, in other words, to reduce the solvent. power of the solvent Yin the direction of solvent flow.

The manner in which vaporizer |02 is illustrated as being connected to column 65 is more particularly adapted for cases in which the solvent is lighter than the oil, since the inlet to the vaporizer |02 is connected to chamber 61 'adjaf centits top, thatV is, at a point within the solvent-oil solution layer in chamber 61.

In the event that the solvent is heavier than the oil, it is merely necessaryto connect the inlet to the vaporizer ata lower point in chamber 61, for instance, adjacent its bottom, for in such cases the solvent-oil solution layer will be on the bottom.

After the solvent-oil solution has been concentrated in vaporizer |02 either with or without precipitation of dissolved oil, the liquidor liquids may be returned to the chamber 61, or, after separation, either liquid may be so returned as de'- slred.

As illustrated, both the saturated solvent-oil l solution and the precipitate are so returned. In

thiscase. the precipitate will be refluxed down through the column and .the saturated solventoil somtion will continue on up through the column.\

column at the same point as the fresh solvent, or at any point above or below the solvent feed point.

Any other means may be provided for reducing the concentration of the solvent as it flows through the column.

From the foregoing it will be seen that the precipitation of dissolved oil from the solvent for reflux purposes need not necessarily take place within lthe column itself. This also applies when precipitation of dissolved oil for reflux purposes lseffected by a reduction in temperature f the solvent-oil solution, and/or by the addition of a precipitant to the solvent-oil solution. For instance', the vaporizer |02 might be substituted by any suitable receptacle in which the solventanyone or'more of the foregoing precipitation methods might be used.

While the arrangement` shown in Figure 4 is illustrated at a point intermediate the length of column 65, it is to be understood that it may be placed at any desired point including the top or bottom (depending on the relative density of the solvent) of the column and that it may be connected to the column in any desired manner for the purposes herein set forth.

It is also to be understood that any number oi such precipitation means may be employed along the column.

While in the solvent extraction and/or fractionation processes herein described the solvent and the materials to be treated have been more particularly referred to as being in the liquid phase. it is to be-understood that one or more of such substances might be wholly or partially in the vapor or solid phase without departing from the spirit of the invention.

It is also to be understood that the invention may be adapted to many other types oi' operation, for instance, to one in which a counterflow of solvents is obtained with the introduction of oil yat an intermediate point or with the introduction of different solvents along the line of oil flow or along the line of solvent flow. Reference is made to copending application Serial No. 699,050 iiled November 21, 1933, which has matured into issued Patent 2,037,319, April 14, 1936.

The solvents may comprise a single compound l or a plurality of compounds. When a plurality 0f compounds are employed, they may be miscible or partially miscible. A plurality of nonmiscible solvents might also be employed.

While the invention has been particularly described in connection with the treatment of mineral oils, it may also be applied to the treatment of materials in general, whether or not the more valuable, the less valuable, or an equally valuable material is separated from the. treatment.

'I'he term solvent in its broader phases includes any compound or compounds, whetherin the vapor,vliquid and/or solid phase, and regardless of its influence upon the material under treatment.

The relative densities of solvents and/or mineral oils may be obtained upon reference 4to any standard handbook or'by actual measurement.\

While a couhtercurrent flow -of the liquids through the column has been particularly rematerial under ferred to, a certain efect may be obtained even though the liquids pass through the column in the same direction.

Particular forms of apparatus have`been described for the purposes of illustration. It is to be strictly understood that wide departures may be made from the forms shown in the drawings, such as by changes, omissions, additions, substitutions, and/or modifications, without departing from the spirit of the invention. 'I'he claims, therefore, are intended to be limited only as required by the prior art. a

We claim:

1. In a process for treating a mineral oil with a solvent, the steps of continuously flowing said oil and solvent counter-currently through a contacting column, causing the oil and solvent phases to assume layer formations at a plurality of spaced points intermediate the ends of said column, and removing a part of said oil phase through at least one side stream, and separately subjecting said side stream to solvent treatment for stripping purposes.

2. In a process for the treatment of a mineral oil with a solvent by counter-currently flowing said oil and solvent through a column and wherein a part of the dissolved oil is precipitated and `caused to reflux through said column, the steps of precipitating oil from said solvent in a plurality of phase contacting paths of relatively small cross sectional area, causing the precipitate phase in each path to flow counter-currently to the solvent phase in said path, and causing the solvent and precipitate phases to form at least one layer formation intermediate the ends of the column.

3. In a process for the treatment of a mineral oil with a solvent by` counter-currently flowing said oil and solvent through a column and wherein a part of the dissolved oil is precipitated and caused to reflux through said column, the steps of' precipitating oil from said solvent in a plurality of phase contacting paths, of relatively .small cross sectionall area, causing the precipitate phase in each'path'to flow counter-currently tothe solvent phase in said path, controlling the precipitation in each path so that the ratio of precipitate phase to solvent phase in said paths will be substantially the same, and causing the solvent and precipitate phases to i'orm at least one layer formation intermediatethe ends ofthe column. r i

4. In a process for treating a mineral oil with a solvent, the steps of flowing said oll and solvent counter-currently, and Aserially through a phase contacting paths to set up reflux conditions, and causing the precipitate thus produced to 4form at least one layer formation intermediate said sets offphase contacting paths.

6. A' process for treating a mineral oil with a solvent comprisi-ng owing said oil andsolve'nt countercurrently through atleast one set of phase contacting paths of relatively small cross sectional area, flowing the solution of oil in solvent through at least one additional set of phase Ycontacting paths of relatively small cross sectional area, precipitating oil from solution in said solvent in at least one of said second mentioned sets of phase contacting paths, owing said preitate to form at least one layer before returning to said first mentioned set of phase contacting paths.

'7. In a process for countercurrently extracting a mineral oil with a solvent wherein extract and rafllnate portions are formed. the steps of owing the solution of oil in solvent through a series of countercurrent phase contacting units containing at least two adjacent sections, preparing a solution of o il in solvent in one section to constitute an extract phase, precipitating a phase containing oil from the solution of oil in solventin a second section adjacent the first section, refluxing at least a part of said precipitated oil` phase through at least a part of said second section and into said first section, withdrawing a part of the precipitate formed in said second section and separately extracting it to form other extract and railinate phases.

8. The process in claim 7 wherein the point of withdrawal of the precipitate from the series of rich in solvent, precipitating a phase containing comprises the withdrawal from the system of at i least a part of the disengaged phase rich in solvent and the addition thereto of a precipitating solvent,`separating the resulting oil phase and solvent phase, returning to the system at a point near the point of withdrawal at least part of one of the phases.

11. In a countercurrent extraction for treating in an extraction system a petroleum oil with a selective 'solvent where the two phases are disengaged at at least one intermediate point, the withdrawal from the system of at least a part of the disengaged phase rich in solvent at said intermediate point, evaporation of part of the solvent therefrom t precipitate oil, and reintroduction .into the system of at least a part of the oil at a point near the point of solvent phase withdrawal.

12. A process for countercurrently extracting mineral oil with a selective solvent comprising owing the oil and solvent in a countercurrent path through a series of phase-contacting units under conditions to secure phase-separation, disengaging the countercurrently flowing phases at at least one intermediate point in ysaid countercurrent path, precipitating a phase containing oil from the solution of oil in solvent at at least yone point between the ends of said series of phasecontacting units, withdrawing at least a part of the oilfthe steps of countercurrently flowing said oil and said solvent in a countercurrent path, fractional'ly precipitating dissolved oil from said solvent-at a plurality of points in said countercurrent path by the addition of a precipitating solvent to the extract phase and causing the precipitated phase to flow countercurrently to the solvent phase.

15. A process for countercurr'ently extracting oil with a selective solvent comprising flowing the .oil and solvent in a countercurrent path under conditions to secure phase separation, disengaging a. phase at at least one intermediate point in the countercurrent pathfsegregating and removing at least part ofthe disengaged phase through at least one side stream, separately and concurrently subjecting said side stream to further extraction to form an intermediate product of the process.

16. A process oil with a selective solvent comprising owlng the oil and solvent in a countercurrent contacting path through a series of phase contacting units under conditions to produce separate phases embracing an extract phase, precipitating oil out o f said extract phase in said countercurrent contacting path by adding thereto a precipitating solvent soluble in the extract phase, andilowing at least a part of the precipitate countercurrently to the extract phase.

MERRELL R. FENSKE.

for countercurrently extractingy WIIBERT B. MCCLUER.. 20