US2081720A - Extraction process - Google Patents

Description

May 25,A 1937. w. J. D; vAN DUCK 2,081,720

EXTRACTION PROCES S Filed om. 19, 195s Improved Primary 7 $77.] H92 u H93' Patented May 25, l 1937 UNITED sTATEs wiuem J. n. van Dijck, The Hague, Netherlands, assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application October 19, 1933, Serial No. 694,280 In the Netherlands November 18, 1930 Bussum sin atA 23 claims. (C1. 19t-1a) This invention relates to extraction processes and constitutes an improvement thereof directed to increase the yield and improve the purity of substances or groups of substances which are obtainable by extraction of liquid mixtures containing the same. The'present application is a continuation in part of the application Serial No. 567,970 filed October 9, 1931.

While extraction processes for separating components of liquid mixtures were known for a long time, the degree of separation as represented by the yield and/or purity of the obtained products, was ordinarily considered to be limited by the dissolving capacity and the selectivity-fof thesolvent at the most favorable uniform operating' temperature. As an advancement in the extractingart, the principle of cont-inuous countercurrent operation is now being widely applied.

More recently it was proposed to extract liquid mixtures by means l,of two partially miscible solvents, flowingcountercurrently to and in contact with each other and through the mixture being extracted, whereby the components soluble in the corresponding solvents are separated from the mixture It was also' prcposedxto substitute one of such selective solvents by one of the components previously separated from the mixture.

It is known further to operate the extraction processes so that the extract and raflinate phases are separately removed from an extraction zone or column and chilled. As a result each of theseprimary phases is caused to separate into secondary extract and raffinate phases outside of the extraction zone, and the secondary rainate phase chilled out of the primary extract phase is returned to the zone at a point near the enter-l ing fresh feed and is mixed therewith, while the secondary extract phase, chilled out of the primary raflinate phase, is returned to the main column at a point near the entering fresh solvent; the secondary extract and raiiinate phases not returned tothe column are freed of solvent. The purpose of such chillingis to obtain a better extract and a better rafiinate than those which would be obtained from the extraction zone at a normal or elevated temperature. effect may be produced by chilling either or both ends of an extraction zone or column just beyond the points of entrance of the feed and the solvent. This process is described in the German Patent No. 410,169. The particular featureof the process of this type is that the composition of the secondary extract phase separated from the primary one by cooling will remain constant,

The same,

as it is fixed only by compOsition of the intake, the relative quantity of solvent and the temperature of cooling.

As an' improvement ofthe above outlined extraction processes, -the present invention contemplates among other features a countercurrent washing of the primary extract phase produced in an extraction zone with a secondary railinate phase chilled out of a primary extractl phase obtained in an earlier operation of the process. As a result .of this washing the composition of the ultimate extract phase produced in the process can be conveniently regulated and improved in the manner and to the degree unobtainable in the old processes which did not employ this washing step.

In the description of the process of this linvention the following nomenclature will be employed:

A and B are components of the mixture to be extracted.

'I'he term component" applies to a portion of a mixture to be extracted, which portionis distiiict from other portion or portions of the same mixture in its chemical and/or physical properties, in that it can be either partly or completely The terms solvent or uselective solvent apply to va preferential solvent for B when both components are brought into contact with said solvent; it may have either lower or higher specic gravity than that of the A+B mixture, and may be either partly or totally miscible with B at the extraction temperature.

The term auxiliary solvent applies to either a non-selective solvent or a preferential solvent for A used in conjunction with the selective solvent; preferably it should be only -partly soluble, if at all, in the selective solvent.

The terms primary ramnate phase and primary extract phase apply to the liquid phases (with relatively low and high contents of the solvents respectively) obtainable'a from the extraction zone, or a column.

The term secondary raiiinate phase applies to the rafiinate phase separated from an extract phase by cooling .or by wholly or partially evaporating the solvent from the extract phase and contingently cooling the remainder. Its solvent content is always lower than that of the original extract phase.

lseparated from said'mixture in a more or less pure state by solvent extraction.

, The term secondary extract phase" lapplies to f the extract phase remaining when the secondary rainate phase has been removed from an extract phase e. g. by cooling.

The termsrainate and "extract apply to the solvent-free portions of the respective phases.

The term improved or better extract applies to an extract with a comparatively greater concentration of B.

The term improved or better raffinate applies to a raffinate with a comparatively greater concentration of A.

'Ihe term improved or better extract phase applies to an extract phase containing an improved extract.

The term improved or better raffinate phase applies to aranate phase containing an improved raflinate.

The'term extraction column applies to a single extraction column or a series of intercontion of the extraction column between the entrance of the selective solvent and that of the mixture being extracted.

The term washing zone applies to a zone having a substantial length through which the primary extract phase is to 110W under conditions of this invention. The washing zone is adjacent and below the feed when a relatively heavy solvent is used, and above the feed when a relatively light solvent is used. The feed is introduced between the extraction and washing zones.

It is an object of this invention to provide an extraction process whereby the composition and /or yield of a secondary extract may be improved at will without resorting to the employment of a chilling process only as would` be necessary for producing an analogous, improved extract by old methods using one solvent.

Briey, the inventionresidesin the discovery that when a stream of the primary extract phase is allowedto flow down from the feed level, as it would be, for example, in the case of employing a relatively heavy solvent, through a washing zone of a substantial length, at the end of which zone for example this stream. is chilled, to a. suitable temperature, so that a, secondary railinate'phase and a secondaryI extract phase are formed, this secondary rafnate phase, which is thus richer in B than a raffinate phase in equilibrium with the primary extract phase at the elevated temperature, being allowed to rise through and mix (contact) over a substantial length with the descending stream of the primary extract phase within said washing zone and below and away from the incoming feed, then, as a result of this contacting, the compositions of both these phases change, so that an improved primary extract phase would reach the chilled part of the zone and following this an improved secondary extract phase will separate from the chilled mixture. 'I'he new secondary raiiinate phase to be returned to the washing zone, which will be in equilibrium with the improved secondary extract, will bevstill richer in B, and will enrich still more the descending stream-o1" the gradually improving -primary extract phase with the component B.

The rising cold secondary raflinate phase formed upon chilling the primary extract phase will meet a stream of the primary extract which comes from a hotter region. The result will be a change in temperature of both phases, which will cause anexchange of components between ythe two phases, as at'the changed temperature the solubility relations have changed also.

It may be, however, that the temperature of the descending stream is so high, that when the two phases in question meet at a certain point of the washing zone, owing to the exchange of heat the temperature of the mixture becomes so high that a complete miscibility of the two phases present at the point under-discussion occurs. If however two phases cannot exist next to each other, no washing can be carried out.

been found that this feature will prevent complete miscibility of the two phases at any point of the washing zone.

This temperature gradient may be created by cooling down the primary extract phase so far that the secondary raiiinate phase formeithere.- by is so cool that when it rises its temperature vis graduallychanged by contact with the downcoming warm stream of the primary extract phase, andthe temperature Within the washing zone is caused to be so low thatv there never occurs a complete dissolution of the phases.

As, however, the cooling of the primary extract phasealso causes a certain amount of secondary raiiinate to be formed, it is evident that these two magnitudes, i. e. the amount of the secondary It is therefore advantageous to control the temperature throughout the washing zone at the place Where this has to be done e. g. by outward means, such as cooling jackets, so that it is not necessary to rely upon the effect created by the cooled secondary rainate alone.

From the above it is observed that by the continuous chilling of the primary extract phase at the end of the washing zone and by continuously returning the secondary raffinate phase to said zone to rise through and contact with the primary extract phase, thereby taking care that as far as possible a gradual change in temperature is maintained throughout the washing zone, the

composition of the secondary extract phase will be improved, so that by regulating the amounts of the feed (A+B) and the solvent, while mainasimilar view of the column adapted for carr,v ing out the extraction process hereafter speciiicallyv described.

Fig. 1 of the drawing represents a vertical extraction column provided with pipeconnections I, 2,- 3 and 4, for introducing the feed and the solvent, and forwithdrawing `the raiiinate and extract phases, respectively. The extraction column ,communicates with a cooler 5 through the pipes 4 and 5, the latter being provided with a pump, if necessary, for conducting a liquid from the top of4 the cooler to a point of the column,

maintain the contents of the cooler at a tempera- I ture below that of thebottom part of the column.

In practice, the length f the extraction zone of the column, i. e. its upper part, or the number of mixing and settling stages in the extraction zone, is so selected as to insure the desired composition of the raiiinate phase at the top Aof the column, while the feed A+B is introduced at or near the level of the column where the rafilnate phase which is rising through the column and is undergoing extraction contains a raffinate of substan-l tially the same composition as the feed. The lower part between pipes l and 5 must be of a substantial length in order to provide for proper countercurrent contact between secondary railinate phase and primary extract phase and to cause the composition of the secondary ramnate to approach the ycomposition of the feed, and below pipe 5 for 'settling out -of the improved primary extract phase to be withdrawn into the cooler 5.- y

In-the operation of this, extraction apparatus, when the feed and the solvent are supplied to the column through their respective pipe connections,

v two streams of phases are formed within the extraction zone of the column. The raiiinate phase is collected at the top and withdrawn through the pipe 3, while the extract phase, i. e. the phase with greaterl solvent content, settles down and tends to collect below the feed pipe I. 'I'his extract phase is withdrawn from the column through the pipe 4 into thecooler 5, where itis chilled and caused to separate into secondary ramnate and secondary extract phases; these are allowed to settle out and are withdrawn from the cooler throughpipes 6 and 1, respectively.

The secondary raffinate phase is returned to the column through the pipe 6 and contacted 'with the descending primary extract phase, with the result that an improved primary extract phase is withdrawn through the pipe 4. `A further improved secondary extract phase is separated in the cooler and withdrawn therefrom. As the operation'l is continued, the process of improving the composition of the secondary extract phaseprogresses, tending to reach certain limits fixed by the operating and solubility conditions within the system, with the result that an extract rich in B and poor in or often even substantially free of A can be obtained. It may be found desirable especially in case of some solvents, in order to increase the efficiency of separating the mixture A+B into its components to regulate the temperature gradient from the top to the bottom of the column, that the upper part thereof would be operated at relatively elevated temperatures, while the lower part would be cooled to relatively low temperatures (when a relatively heavy solvent is used; viceversa in case of a light solvent)v all the temperatures being determined by solubility characteristics of the components and the solvent and their relative proportions at each level within the entire column. If desired, the processmay be modified analogous to the manner of operation of the lower section of the column..

y The ultimate extract phase. as well as the ramnate -phasefrom the top of theextraction column, after being withdrawn from the extraction process, are separately treated to separate the extracty and the raflinate, respectively, fro'm the solvent.

An essential feature of the process illustrated by Fig. 1 is the reintroduction of the secondary rallnate phase through the pipe 6 into the main column at a point so remote from the feed pipe l that 4this secondary rainate phase upon being introduced into the column and owing to the fact that a' temperature gradient is maintained, would so change its compositionwhile rising to the level of the feed, that its solvent-'free portion at that level would approach as nearly as vpossible the composition of the feed. The extract phase separating near and below the level of the pipe 6 will then be an improvedy primaryv extract phase, formed principally not by lowering of the temperature at that part of the column, ,but as a result of the countercurrent washing of the primary extract phasewith the secondary rafnate phase. It follows then, that the distance between the entrance of the feed and that of the secondary rainate phase, i. e. the washing zone', should be of an appreciable length, which is to be referred to as an effective length or distance This length may be different for different solvents and mixtures to'be extracted and is a function of 'various properties such as their gravities, viscosities and solubility characteristics at extraction temperatures. Similar conditions should prevail in the lower washing zone of the cooler 5 when the cooler 5' is used, as described.

To point out more clearly the difference between thenew process and such old methods as the ones described in the German patent, it will be noted that in accordancefwiththat old method the secondary raffinate phase should be returned byv means of pipe l5 (broken line of Fig. 1) near thellevel of the pipe I. I Such method, while pro- .ducing a secondary extract phase of a better composition than the primary extract phase, will not operate in such ,a manner as progressively to improve said composition, but would produce a proved by providing an additional cooling means 9 intermediate the feed and the entrance of the secondary raihnate phase. l

' From the foregoing explanation it would follow that the step-wise process of Fig. 1 can be carried out in the manner illustrated vby Fig. 2, which represents an' extraction column provided with pipe connections l, 2, 3 and 1 for introducing the mixture tobe extracted and a solvent and withdrawing the railina'te and extract phases', respectively. A coolingmeans, such as a cooling coil 8, is provided at the lower section of the column, forming a chilling zone ,and a washing zone of an effective length. Cooling means 9 and l0 may bei' provided along the washing zone in order to maintain a gradual temperature drop from the level of the feed towards the chilling zone. A settling l zone, insulated by means I4, if desired, 'may be provided at the bottom of the column.

The operation of the process of this type is dif- .drawing the separated phases.

ferent from'the process as shown in Fig. 1 only in that the washing of the descending extract phase below the feed is gradual throughout the washing zone of an effective length, i. e. is not step-wise as shown in Fig. 1, while the principle involved and the result are the same, that is the ultimate extract phase withdrawn through pipe 'l is much better than the extract phase, which it would be possible to obtain by withdrawing the extract phase immediately below the feed and chilling it to the same temperature as is had near the coil 8, even if the secondary rafllnate phase in this case would be returned to the column near the feed level. v

It was also found that the eiliciency ofv separating components A and B from their mixture by extraction with a solvent can be increased, if the oil content of the downward streamV of the extract phase within the column is maintained substantially constant. To accomplish this, heating means Il, i2 and I3 may be provided to maintain a gradually decreasing temperature within the extraction zone in the direc.

restricted to the use of preferential solvents heavier than the mixture to be separated, as the preferential solvent may have a lower specie gravity than the mixture to be extracted, in which case the extract phase of the mixture is caused also to pass `through regions of gradually and effectively lowering temperature, so that thelowest temperature. prevails at the part of the extraction zone near the point where the extract phase is being collected and withdrawn, (top of the extraction column, for example) while a relatively higher temperature is maintained at the part of the zone, near which the raffinate phase is removed (bottom of the extraction column, for example). v -e The process may be further explained by the following example illustrated by Fig. 3 diagrammatically representing in cross-section another formh of the extraction apparatus -which was used inI carrying out the extraction hereafter described. The extraction column was provided near one end with a solvent inlet pipe 2 and with an oil feed pipe l near the middle of the column.` Ateach end -of the column draw off pipe connections 3 and 4 were provided for with- One of these pipe connections, namely, theextract phase draw off line, was connected to a cooler 5, provided with a coil 8 and pipe connections 6 and 1. The cold secondary ramnate phase produced by cooling was withdrawn from the bottom' of the cooler 5 through the ypipe connection 6 and was then returned to the' extraction column entering the column near the end from which the extract phase .was being withdrawn.

The continuousprocess, as carried out in this apparatus consisted of introducing a stream of lubricating oil to be extracted into'the column through the pipe I and feeding. at the same time @d/0 alcohol through the-pipe 2. Due to the lower specific gravity of the alcohol as compared to that vof the oil, and due` to .the fact that the oil and the alcohol are not miscible i phase.

with each other, but form, on being contacted beyond certain known proportion limits, two phases, such phases were formed and withdrawn at the respective ends of the column. The ramnate phase descended through the extraction zone towards the incoming alcohol and was withdrawn through the pipe 3, while the extract phase was withdrawn at the top to the cooler 5, where it was chilled. The separated secondary ralnate phase was withdrawn by means of pipe 1 and the raffinate phase was returned to the column by the pipe 6. The temperatures within the column were maintained as follows: 120 C. at the top, 140 C. near the entrance of the lubricating oil and 150 C. at the bottom of the column. A highly -naphthenic extract was obtained. 'I'he described process was carried under Y superatmospheric pressure in order to eliminate the formation of vapors.

dIt is obvious that the above extraction could be carried out by eliminating the cooler and providing, instead a chilling zone near the top of the column, by placing a cooling means in that part of the column, thereby forming a phase by withdrawing the primary extract phase from the column at the end of its travel through the washing zone. There are several methods of producing from this liquid the secondary ramnate phase necessary to carry out the countercurrept washing process throughout the washing of the process of the invention.

Bearing in mind that the secondary rafiinate phase must be co-existent with the primary extract phase at the point where this secondary raflin'ate phase is introduced into the washing zone and atv the temperature prevailing there. it may be that the primary extract phase withdrawn from the column only consists of a saturated solution of the pure component B in the selective solvent. In order to make sure that this solution always contains only B it must be continuously in equilibrium with a phase containing only B and no A. It may contain some solvent, but this is not necessary, for a liquid consisting practically entirely of Bl can be in equilibrium with a saturated solution of B in th solvent. y i

In order to prepare such an equilibrium solution it is therefore possibleY to evaporate partly or wholly the solvent from the primary extract phase of the above assumed character, and to use a part of this solution as secondary extract Attention may be drawn to the fact that when the whole` of the solvent is evaporated there is no difference in composition between the secondary extract and the secondary raflinate phase.

The method of partially or wholly evaporating the solvent from the primary extract withdrawn from the column and using a part of the liquid 'obtained as vsecondary raflinate phase, is also applicable when no pure component B is made Vas extract.

to be subsequently cooled to a suitable temperav ture, so that it separates into a secondary rainate and an extract phase, and the cooled secondary taining a gradual temperature drop within the rannate phase, i. e. tnt with .the low solvent mixture of the two iiowing phases in the direccontent, to be returned to the washing zone of the column at an eilective distance from the feed.

the above methods is co-existent with the primary extract phase at the temperature at which it is introduced, it will act as a washing agent vsus amylacetate and others.

when at another level it is contacted at a higher temperature with the primary extract phase, travelling countercurrently.

Comparing the processwith that in which a y liquid mixture is extracted with-two non-misciblev solvents flowing in countercurrent to each other, it may be said that whereas in the iirst process two phases created by two solvents travelling present process it is not necessary that two solvents travel throughout the whole column, it being only necessary to maintain two phases.

One of these phases comprises the preferential solvent laden with components, whereas the se'cond phase ilowing in countercurrent thereto conf tains no auxiliary solvent flowing through the whole column and is not laden with `components but has a changing composition, a temperature gradient being necessary to prevent this second phase from disappearing as phase in a certain part of the column.

It goes without saying that a process as described in the present specification can be repeated several times both with the secondary extract and the railinate obtained with the combined extraction and washing processes. Each of the products of this first combined -process is then extracted and washed separately with a solvent, either the same as that used inl the ilrst combined process or another solvent. i necessary to carry out all these processes at the same temperature or within the same temperature range.

Such a process is specially recommendable when the initial product consists of various series of products, the members of which possess properties which are mutually not widely divergent. The rst extracting-agent can then, for example, be used to separate the groups -of homologues, whereas with a more selectively acting and often much more expensive extracting-agent the op-. eration is continued with a smaller quantity of initial product, whlchpresents the advantage of smaller quantities being required of the second auxiliary liquid.

'I'he method of this invention may be applied to extractions of different kindsof liquids,.such as hydrocarbon oils, e. g., mineral oils and their distillates, tars or to the extraction oifatty acids such as acetic acilgfromtheir aqueous solutions with various selective solvents, such as .liquid SO2, furfural, isopropyl alcohol, aniline, nitrobenzene, chlorex, phenols, organic nitriles and thiocyanates, ketones, aldehydes, esters such as It may also be used in two-solvent extractions, wherein one of the solvents is a selective solvent, while the other is an auxiliary solvent; in this case the operation of the method, as described for a-single-solvent extraction, would be the same as if only the selective solvent were used.

I claim as my invention:

1. In a countercurrentA process for extracting a liquid mixture of hydrocarbons wherein a raffinate phase-flows in contact with and countercurrently to an.A extract phase thestep of mains If the secondary ramnate phase `formed byv yent and the mixture into the apparatus, separately withdrawing said phases therefrom, re-

It -is not.

- tus and the mixt washed extract phase to separate from it la. solute 15,

phase, and using vthe separated vsolute-phase as Vthe washing liquid.

3. In an extraction process carried out by means of an extraction apparatus having'extraction and washing .zones andprovided with means for introducing a solvent and a mixture to be extracted, and means for withdrawing the ultimate rainate and extract phases produced by the process,A the steps of introducingthesolmoving the solvent from the withdrawn extract phase, returning a part ofthe extract into theA apparatus at an eective ldistance from the entrance of the mixture and subjecting the liquids owing through the washing zone to a thermal treatment to create a gradual temperature drop in the direction of ilow of the extract phase.

4.1In an extraction process carried out by means of an extraction apparatus having extraction and washing zones and provided with means forintroducing a solvent and a mixture to be extracted, and means for withdrawing the ultimate raffinate and extract phases produced by the process, the steps of introducing the apparae into thecolumn, separately withdrawing sai phases therefrom, removing from the withdrawn extract phase a portion ofthe solvent, cooling the remaining portion of the phase, thereby causing its. separation into secondary raiilnate and extract phases, separating the two cooled secondary phases and returnlng the cooledsecondary rainate phase into the 'apparatus at an eiective distance from the enstep of regulating the heat content of the ilowing phases so as to cause a gradual temperature drop inthe direction of ilow of the extract phase.

6. In a. process of fractionating a liquid mixture of components by countercurrently contact-` ing a iow of the mixture with a -ow of a pref-- erential solvent so asgto produce a flow of a solution of soluble components of lthe mixture in the preferential solvent, the step of continuing the flow of said solution after the solvent h as been .contacted with the liquid mixture and subjecting said continued f low to a change in temperanow, of a preferential solvent, the step. of. sube. 75' i jecting the flow of thel solvent after it has taken up a quantity of the liquid mixturev soluble in the-so1vent to a change in temperature over a substantial length of the continued flow of the solvent after the latter has been contacted with the liquid mixture, said change in temperature being provided in such a way that the temperature decreases in the direction of flow of the solvent and recovering a solution of the dissolvedcomponents in the preferential solvent at the end of its continued flow and the undissolved components of the liquid mixture at the end of the now of the liquid mixture. l

8. The process of separating a mixture of liquid components into two components, which comprises introducing a ow-of said mixture into a column at a point between the top and the bottom thereof, contacting said mixture in said column with a countercurrent flow of a preferential liquid solvent and maintaining as far as possible a gradual change in temperature throughout at least a substantial length of that part of the column which is situated past the point of entrance of the mixture of liquid components in the direction of flow of the preferential solvent, the gradual change of temperature being such thatthe'temperature decreases in the direction of flow of the preferential solvent and recovering the less soluble component at a point past the point of entrance of the mixture in the direction ofthe now of said mixture and the morey soluble component dissolved in the preferential solvent at a. point past the point of entrance of said mixture in the direction of flow of the preferential solvent.

9. 'I'he process of claim 23, wherein the mixture to be extractedisintroduced into'the apparatus at a point where the solvent-free portion of the rafiinate phase lhas substantially the same composition as that of the mixture.

. 10. The process of claim 23,.wherein the contents of the apparatus within the Washing zone are in addition progressively cooled throughout said effective distance.

11. The process of claim 23, wherein a gradual temperature gradient is maintained throughout the extraction apparatus whereby the molal quantity of the solvent free,portion of the ex- A tract phase is maintained constant throughout the column.

l2. In an extraction process carried out by means of an extraction apparatus having extraction and washing zones and provided with .means for introducing a solvent and a mixture to be extracted, and means Afor withdrawing the ultimate rainate and extract phases produced by the process, the steps of introducing thel solvent and the mixture into the apparatus, separately withdrawing said phases therefrom, ysubjecting the withdrawn extract phase to cooling, thereby producing a secondary raffinate phase and a new extract phase, separating these two phases and returning the cooled secondary raillnate phase into the apparatus at' an effective distance from the entrance of the mixture.

13. The process of separating a mixture of liquid components into said components, which comprises contacting the mixture of liquid components with a. preferential liquid solvent while the mixture of liquid components and the'preferential solvent are flowing countercurrently with respectI to each other in separate liquid phases in the same generally conned and elongated column of liquid comprising the said preferential solvent and the liquid components to be sepaaccingo rated, and maintaining as far as possible a gradually changing temperature throughout the greater portion of the length of the said column of liquid, which temperature decreases in the direction of flow of the said preferential solvent, thus causing some of the more soluble component to be separated out of the said solvent in the said gradually increasingly cooler environment whereupon the liberated more soluble component dissolves the less soluble component present in and moving out of the preferential solvent and flows countercurrently to the said preferential solvent, causing the more soluble component to be gradually redissolved by the said preferential solvent, and finally recovering the less soluble component and the more soluble component dissolved in the said preferential solvent at opposite ends of the said column of liquid.

14. 'I'he process of separating a mixture of liquid components into said components, which comprises contacting the mixtureof liquid components with a preferential liquid solvent while the mixture of liquid components and the preferential solvent are flowing countercurrently with respect to each other in separate liquid phases, the preferential solvent having a greater specific gravity than themixture of liquid components, whereby the said preferential solvent will flow downwardly in the same generally confined and elongated column of liquid comprising the said preferential solvent and the liquid components to be separated, and maintaining as far as possible a gradually changing temperature throughout the greater portion of the length of the said column of liquid, which temperature decreases in the direction of flow ofthe said preferential solvent, thus causing some of the more soluble component to be separated out of the said solvent inthe said gradually increasingly cooler environment, whereupon the` liberated more soluble component dissolves the less soluble component present in and moving out of the preferential solvent and flows countercurrently to the said preferential solvent, causing vthe more soluble component to be gradually redissolved by the said preferential solvent, and

nally recovering the less soluble component and the more soluble component dissolved in the said preferential solvent at opposite ends of the said column of liquid.

15. In the process of extracting a liquid mixture of components in an extraction zone with a selective solvent for one of said components to produce an extract phase and a raflinate phase having different specific gravities, the improvement which comprises the steps of withdrawing the extract phase from the extraction zone, flowing it through a washing zone in countercurrent to a washing liquid subsequently described to produce a phase which hasy alow solvent content and a washed extract phase, maintaining a gradual temperature drop in the washing zone in the direction of flow of the extract phase, the temperature of the extract' phase after it has traversed at least a substantial portion of the length of the Washing zone being low enough to cause a solute phase to separate from it, and using the separated solute phase as the washing liquid.

16. In the process of extracting a liquid mixture of hydrocarbon components in an extraction zone with a selective solvent for one of said components to produce an extract phase and a ranate phase having different specific gravities, the

prises the steps of withdrawing the washed extract phase from the washing zone, chilling it to separate it intoa solvent phase and a solute phase,

- separating said phases, and returning at least a portion of the solute phase to the washing zone as the washing liquid.

18. A process according to claim 2 in which the extract phase is chilled to separate out a solute phase while it is within the washing zone.

19. The process according to claim 2 which comprises the steps of removing at least `some of the solvent from the washed and chilled extract phase and returning a portion of the resulting solvent-poor extract phase to the washing zone as a component of the washing liquid.

20. In the process of extracting a liquid mixture of components in an extraction zone with a selective solvent for one of said components to produce an extract phase and a raffinate phase vhaving different specic gravities, the improvement which comprises the steps of withdrawing the extract phase from the extraction zone, flowing it through a washing zone in countercurrent to a washing liquid subsequently described to vproduce a phase which has a low solvent content and a washed extractphase, maintaining a gradual temperature drop in the washing zone in the direction of ow of the extract phase, withdrawing the washed extract phase from the washing zone, removing at least some of the solvent from the washed extract phase, and returning a portion of the resulting solvent-poor extract phase to the washing zone as the Washing liquid.

21. In the process of extracting a mineral oil with a liquid solvent wherein some of theoil components are more readily soluble than other oil components the step ofvcommingling the oil and the solvent under conditions to form a primary extract phase and a primary raflnate phase, separating the phases, flowing the primary extract phase through a washing zone countercurrently and in contact with a washing liquid subsequently described to produce a phase which has a low solvent content and a washed extract phase, chilling the washed extract phase to separate from it a secondary rafflnate phase and using the separated secondary railnate phase as the washing liquid.

22. The process of claim 23, wherein a gradual temperature gradient is maintained through the extraction apparatus whereby the molal quantity of the solvent-free portion of the extract phase is maintained substantially constant at least within the washing zone.

23. In an extraction process carried out by means of an extraction apparatus having extraction and washing zones and provided with means for introducing a solvent andal mixture to be extracted, and means for withdrawing the ultimate raflinate and extract phases produced within the apparatus, the steps of introducing the solvent'and the mixture into the apparatus, separately withdrawing said phases therefrom and chilling the contents of the apparatus at the remote end of the washingzone at an effective distance from the entrance of the mixture, thereby creating a gradual change in temperature throughout at least the washing zone.

. WILLEM J. D. vAN DIJCK.

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