US2258279A - Process for extraction - Google Patents

Description

Get. 7, 1941. A. v. cAsELLl :TAL 2,258,279

l PROCESS FOR EXTRAGTION y Filed Jan. 12, 1940 Cooling Coil Causlc Alkali lnvenror's: Alber-l' V. Caselli Alan Quixo Dg their Alfort-leg:

Peienredtoee 7, umv

i UNITED f STATE mais PROCESS EXTB'ACTION Alhertv. (knelt. mso-nf of Delaware admon San Francisco,

and Alan-C. Nixon, teshellnevelopment Galihaeorporathn v sppuesuesnnsarnz, 1940, serial No. :13,566 s cuius..` (ol. iss-sz) 'me invention rentes te e meenemen in me process of transferring of components from their solutions in one phase to another phase which is substantially immiscible in the first phase, and more particularly deals with an arrangement of the flows of the two phases so as to improve the" efficiency of extraction.-

It is the purpose of this invention to conduct the flow of the liquid containing extractable material and the` extracting solution so as to attain maximumv emciency. i e

In our improved method of extraction, the solution phase containing material to be extracted is divided in a manner to produce at least two solution fractions, one of which contains portions of components of said material relatively easy-to remove and one or more of which contains com ponents more difficult to remove.

As a result of the distribution in the various fractions of the components of the material to be transferred, the ease of transferring the material to the other phase is different for each 'A fraction. The "ease of transference as herein defined depends upon the initial and final concentrations of the componentv or components in the fraction aswell as upon their respective extraction coefficients. y

The extraction coemcient of a given component is defined as the concentration of the solute in the extracting solvent divided by the concentration of the same solute in the solution phase at equilibrium; and the ease of transference may be measured by the inverse volume ratio of extracting solvent to solution which is required to reduce under a standard set of conditions the concentration of transferable material in the solutionto a more solvent is required toereachthis level andl hence the ease of transference decreases with increase in starting concentration.

In carrying out the process, the several frac-l tions are subjected to extraction preferably in' countercurrent, in the following manner:

treated first fraction with other treated or untreated fractions of greater ease of transference. By this procedure the rst fraction is treated with a higher ratio of solvent to solution than the mixture. For example, assuming that extraction be carried out in an extraction tower in which the solvent is introduced near one end; assuming further that the solution to be extracted be divided into two fractions as described before, then` n wm be eeen that by this method er sow the fraction containing the components having the lowest ea 'of transference is extracted with a A first fraction-containing the componentsof lowest ease of transference is treated separately with a certain volume of extracting solvent. The

same volume of the same solvent was used prehigher solvent ratio than the other fraction which is treated in combination with the nrst extracted fraction only. If more than two fractions are produced, the other, fractions may be introduced at points between the two end 'fractions in the order of their relative ease of transference.

The effect of this method is that for a given over-al1 ratio of selective solvent to solution containing extractable components, the fraction .containingthe most dimcultly removable components receives treatment with a much larger quantity of extracting solution per unit volume than the fractions containing the components easier to remove. As a result, the content eof removable components in the solution phase can be lowered to a level far below thatl which could be achieved by conventional treatment under otherwise similar conditions with the same over-all ratio of selective solvent lto solution containing the same extractable components. g

. This method shows improvement over the conventional countercurrent extraction primarily, when upon fractionation a marked change in the ease of transference of thecomponents in each of the fractions is effected, and more particularly when components of widely different coefficients ,of extraction are accumulated in different fractions, preferably the fraction containing the components of lowest coeiilcient of extraction being as small as possible.v

- According to the process, this small fraction is viously to extract a mixture of the resulting 'treated with a relatively high ratio of solvent Likewise ii the solution contains components l of approximately equal extraction coecients it is advantageous to accumulate at least somesoi them in one fraction and simultaneously to produce a second fraction containing a lower concentration of vthese components. The components inthe nrst fraction on account of the higher concentration have the lower ease oi transferenceand this fraction should be treated with a greater solvent to solution ratio than the second fraction.v

The main advantage of the extraction as car ried out according to this invention is an increase in over-all extraction emciency mairlngit possible to obtain a given result with a much lower ratio of solvent to total solution than has heretofore been possible.

Further to explain this invention, a speoic an. .plication will be described in detail; namely the extraction of mercaptans from hydrocarbon oils with aqueous solutions of caustic i.

It is known that mercaptans and other weak organic acids such as alml phenols, thiophenols. etc., can partially he removedirom their solul tions in sour hydrocarbon oils by extracting them with aqueous solutions oi caustic alkali. to proandthe more dimcultly extractable components y are more completely removed.

to ove the mercaptans. solution and the fraction containing the higher `soiling mercaptans, i. e. those ha the lowest ease oi' transference are fed at opposite ends of the system. The fraction containing the lowest boiling meroaptans is introduced at a point in- '.-1ediate between the entrance points of the highest boiling fraction and the aqueous solution. Other intermediate boiling fractions are'lntroduced at ,points between the two end fractions, the order of introduction of these several fractions heing according to the order ot their relative easeoi transference. This may not be necessarily the order or boiling ranges since the eiiect oi the initial concentration of mercaptans and of mercaptan conguration may at times alter this order. As is known, in general, the extraction coemcients of dierent mercaptans with the same number oi' carbon atoms, decrease with increased degree of branching. If desired, the exact order oi ease of transference of the several fractions may be deteined experimentally hy extraction tests under a standardized set oi conduce a spent aqueous solution containing ahsorted organic acids and a treated hydrocarbon oil, and separating the two liquids from one an- A other. The spent aqueous solution may then be regenerated as lay-steam stripping to make it fit for further extractions. v

en sweetening sour hydrocarbon distillates by extraction voi mercapt, itis necary to reduce the mercantan sulfur content ci. the tillate to about .citt as vor by the and Ryland (ind. g. Che. i936, p. i6). To achieve result with a gi n extras :i: medi and given apparatus, it is necessary to auf.; a certain faire' ratio or extracting solution to hydro= i carbon oil which lo can he calculated. ii

the types and amounts ofthe various mercaptans.

in the sour distillate are o.- In general. high boiling mercap :i are more dicult to remove hy extraction than lower boiling ones, because the former are less soluble in the extracting solvent (i. e. the caustic allrali soiutionl than the latter. Therefore where the removal ci high boiling merca t is involvedD a high ratio of selective solvent to organic liquid is u ...als xequired. This in turn necessitates high ste consumption` for regeneration oi the spent aolvent and is responsible for high solvent circulae tion costs.

Our method comps the steps oi mn aratlng the organic liquid containing the more sapiens by fractional distillation 'into atleast tivo fractions, one containing low boiling portions of the mercaptans. the other containing higher boil ing. portions. The distillation method is used mthe resulting fractions. As is known theextrac y' tion coecients for the normal it.; he-

tween hydrocarbon distillates and aqueous line solutions decrease with increase in their hoiling points, and hence fractionall distillation oiiers a simple me for preparing fractions of varyl ing ease oi transference.

The fractions are then treated in a countersystem with an aqueous alli solution mms e; is. n o

ditions. As the several iractionsv ilow counter distillate, is sweetened by extraction or marcaron tous with an aqueous caustic alkali, preferably containing a solutiaer ior the niercantans, such as potessi isohuate. e sour distiliate en= ters heater i through line 2 from a source not shown. and is iractionaily distilled in trattiene ating col Si to produce three fractions. lit is,

oi' course. understood that any desired nher of fractions may loe produced such as 2, i. o, etc., depending entirely on convenience and/or eco= nomical considerations. These f three fractions are withdrawn from column il through lines d. ii

andan. resmctively, and are condensed `and/or cooled in coo coils i, t d t, actively.

i@ is an extraction col which receives the extracting solution near its top through line ii. into the ttoxn` of extractor it is introduced the cooled heaviest distillate fraction from cooler t thrh line i2.

The temperature at the bottom oi this extraction ma 'is controlled by w1 coil 2t. at

*a point intermediate between the points of enu .trance of the t lution vand the heaviest rush lines it and it ed iisht and middle iractions from con i "i and t. r ctively, the light traction.v i: @foi at a point above that oi entrancey o middle fraction.

iractions are intr the condensed d .as the three fractions now upward throughcoin' it they are united, and the resulting mixture or tres te erges at the top i one or several of the .ira

e tres if.. solution ws doward through ...a-ma. i0, and as it meets a rxr.. ,ma stream of organic liquid. the ratio oi auueous solution to organic liquid is incre in the direction oithe now ci the extracting solution. The vspent aqueous solution.. laden with mercaptides. leaves col The aqueous alkali carbon distillate to jumnln through une It and is heated 1n heater 4li to be steam stripped in stripping column il,

preferably in lthe manner `described in the YabroE-White Patent No'. 2,152,724; Steam for stripping may be introduced through line Il, and mercaptans together with spent stripping steam emerge through line 20. Regenerated treating Y solution returns to the top of column III throughV line il.

' In a further modification ofthe above sweetening process applicable to sour gasoline distillatos free from HzS which contain organic acids much stronger than mercaptans such as naphthenic acids, thiophenols, alkyl phenols, etc., the distillate may be fractionated to produce one or several heavy fractions containing'substantially all of these strong acids, and lighter fractions for example having end boiling points below 175 C. and preferably below 150 C. substantially free of them. The heavy fractions may be pretreated i with an alkaline solution under conditions to preremove at least those acids which are too strong to be expelled from the caustic alkali solution by steam stripping, thus preventing regeneration-of the solution. This pretreatment is so conducted that few mercaptans are removed. Undersuch conditions, a minimum amount of non-regenerative caustic alkali is consumed.

Thus a heavy fraction may proceed from cooler y 9 through line2i and be treated with aqueous caustic alkali solution, preferably `fliree from solutiaer, from line 22. Distillate and aqueous solutions proceedto settling tank 2l. Spent caustic alkali is withdrawn through line 24 while pretreated distillate freed from the strong acids but still containing a large port-'ou of mercaptans passes through lines 25 and i2 to extraction tower- I0.

The heavy fraction may be further fractionated in a manner not shown into two or more cuts before or after the alkali pretreatment and t the fractions so produced may' then be introduced into extraction column Il in the order vof the ease of transference of the mercaptans contained in them.

Acids, which would neutralize the extracting solution and render it non-regenerative by steam stripping if allowed to enter the regenerative cycle are those having dissociation constants greaterthan about 104. Even acids having dissocia. tion constants of about l1such as many of thealkyl phenols, may only incompletely be removable by steam stripping from their alkali metal salts in strongly alkaline solutions.

Some cracked gasolines contain acetic acid which boils at 118C. In the treatment of such gasolines, the fraction containing the acetic acid should also be given the caustic pretreatment, as described. i

The preremoval of relatively strong acids from fractions containing them is particularly important in the case of sweetening cracked sour Sasolines by extraction of the mercapftans in steamregenerative systems as the or.; described above. Cracked gasolines` usually contain considerable amounts of alkyl phenols, which tend to build-up in the circulating caustic alkali solution to a certain equilibrium concentration', which then remains more or less constant. This equilibrium concentration depends primarily on the concentration of the alkyl phenols in the ingoing hydrotneated, the ratio of feed to treating solution, e nature and concentration of the caustic alkali in the aqueous solution and the amount of steam used in the stripping. .As-

suming and conditions to 'be constant, then with a given extracting solution, the only remaining variable'is the concen' tration of the alkyl phenols in the feed. Now, alkyl phenolates are good solutizers for mercaptans. and from this point of view, their` presence in the extracting solution is quite desirable. However, if alkyl phenolates are allowed to accumulate above a certain concentration, the viscosity of the aqueous solution is raised to an extent so as to cause severe emulsion and carryover difficulties in the extraction operation'. It

has been found that for general usefulness, the

-viscosity of the extracting solution should notbe greater than about 37-38 centistokes at the temperature of the extraction. v

In order to prevent accumulation of alkyl phenol'ates 'in the extracting solution in quantif ties which cause the viscosity of this solution to 2oexceed the danger limit, it is often necessary materially to reduce the alkyl phenol content of the distillate feed. The maximum permissible amount of alkyl phenols in the feed depends on the variables `enumerated above, and can be determined experimentally for any given set of heavy gasoline fraction prior to its entry into the extraction system, or coolers couldbe incorporated into the particular part of the extraction system itself.

It is understood that use of pumps, heaters,`

heat exchangers, coolers, condensers wherever necessary vis within the skill of the designer for such equipment.

Suitable amounts of extracting solution are normally about 5 to 160 volume percent-oi the organic liquid feed, although amounts outside '.oi these limits may be employed, if desired.

While the foregoing process has been described .is as applying particularly to the removal of 4weak organic acids having dissociation constants below lil-5 such as mercaptans, alkyl phenols etc., from hydrocarbon oils, it shall be understood that its usefulness is not limited thereto. y.ll'or example,

it may be applicable to the extraction of lubricating oil.

For example, for the solvent extraction of California lubricating oil with furfural in ay twelve stage countercurrent extraction system, three sr, distillate cuts were produced having viscosity inreach the required viscosity index decreases in the order of increasing algebraic viscosity inw dexes. The fractions so separated are then extracted in accordance with our invention, thel ,n fraction of viscosity index -58 being introduced into stage 1 of the countercurrent extractor and flowing through all the stages of the countercurrent extractor. The optimum point of en-l treating conditions. No denite figure for this The temperature of extraction in column It is v dexes of58, -45 and -38 respectively. 'I'he l' y degree of extraction required for each cut to 4 assente trance can be f'fr-rr- :fr for or o nydrom each oi the remaining fractions. us the iracin `which the l groups have 2 to 3 carbon tions or viscosity index of -45 and B may ad.. atoms; allrali metal, and preferably potassium 5, and 7 and 8 respectively and owthrough the carbon atoms. 0r 0f "1- 0 0l' hydrOXy fatty acids remaining stages in combination with the other having from 4i to 6 carbon atoms. 0r 0f phenyl fractions in countercurrent to the urfural. acetic or hydroxy or 1f.- phenyl acetic acids,

Further our process may also be used in procor of alml phenols; or mixtures of the above. esses such as the sep r tion of thiophenols from Particularly useful are potum isobutyrate or alkyl phenol mixtures Where extraction is accoml0 mixtures of isobutyrate 'and alkyl plished with weak inorganic bases; or in the phenolates.

separation `of nitrogen bases from petroleum oils Our inventionis further illustrated by the exby extraction with aqueous solutions of relativeamples below: ly strong substantially oil insoluble acids such 'y Example I as sulfuric, hydrochloric, formic, acetic, etc., l5 A polymer nphth Smcmmmity 696g hun acids. t. 1m 1r f The material to be extracted may be contained wegmtg as gggnsnt of 100% by in any is under A portion of the Doek, naphtha, was fraccondtions and for the duration oi the treattionauy distilled in ma plate distillationcoh ment and substantially insoluble in and chemn@ l to yield two fmcons: & 10W boiling im@ ically inert to the extracting solvent. en non having an end bo u point of mue C com extracting weak organic acids `with caustic alkali prisms 80% by vox of the total naphtha and hydrocarbon oils already mentioned, such as petroleum distillates, coal tar distillates, hydrogeng5 glheTnoramggrcygs ated aromatic hydrocarbons, butanes, nentanes,l 1 in the polymer ngphth and `remm hexanes, benzene, toluenes, Xylen. etc.) chloma 6% of the mercapmm EN, rising the most rinated hydrocarbons as carbon tetrachloride, dmcmly emmcmble merc@ were concem ethylene dichloride, cnlcrpropane, etc.; basic mated m the higher boum imm organic liquids M quimums' @muted pyridms a@ The poler naphtha'was extracted with an Wag? mmm@ L E" l es etc' aqueous solutizer solution ha the following e preferred method for producing` several compitmn. 6N potum hydroxide 155N fractions conta. v f' extractable material of difpotmum is'obutyr o gsN potassium alkyl ferent ease of tr erence is distillation` Howphenolate. The extraction was carried out in a ever,other r may be applicable, Such @s 35 sin stage counterent treater at 70 E'.

iractionalprecipitan,iractional solvent extrac- Four examinons were Wmme@ En two of tion or any process, fi mi or chemical which the r o permits segregati of dierent fractions con- ,porftf @ge ggh; fsrgtg mmm@ femme mmm-m1 of werent se the conventional countercurrent way. The volof transference. d@

A5 previously mentioned, our method is pme unie ranas of the solutizer solution to polymer ticularly nseiul in coeotion with` the extracother tw@ xtrmom C ma D the fmcnons tion of ammi? Wem mmc acids such as obtained in the above fractional distillation were mercaptfre 'with the aid or aqueous caustic mm Mmmm www@ smut treated in accordance with invention. The

substances ch are readily soluble in the A aqueous soluon of caustic alkali, are good solto the wat ation Stage and the low boiling vents for the weak organic acids, are substangro in between the third 8nd o stages in C l. the second and third tially luble in the organic water insoluble @il t v liquid. are inert to the action of strong caustic s agg@ in m D 5 the er boiling mph' alkali erm atthe elted temperatures oi t tm '95s Hamed i" m the wat few Ses' stripping, and hm@ 0mm temperatures sub, and me combined fractions were treated to- ,stantially above t of water. 'Among the most `@um in th utizer soluusefui sont for weer organic acids, the rs1.1 es tion n stesse e to i in counter lowing may ha at.; primary, Sewndary and current the fractions and spent solution was tertiary am or irony lf-1.1.1; in which "wir t: l. e ted naphtha the ami v nave 2 to 3 carlton atoms; was rvithwn from e l '1s-z stage.. glycols, :um and diao, dinony evi tveremiollotvsz` Conatercarreat of the two fractions of nommer nonnina Vollriemrrotio lof 60u- Neer er non to nephew Mm? t, Run ve'xruy'aptibgri vgtnm 'ser we mam om. enr "n ma?? all bltnaxio-a 'A uns o ilouventional.. gndom g gj! gag 0.2 2. 2 D Mom a. `1.o 0.2 z 3g vantageously be introduced between stages 4 and salts of fatty acids having preferably from to 5 such organic liquids are. for example, (aside from ab he? bo l fraction of @out 20% by WL naphtha lwere 0.2 d 0.4i respectively. In the YS for the W'k 45 ratio of solut solution to total naplitha trasl It will be noted, particularly when comparing runs B, C and D. that better results may be obtained by the method of this invention with only half `of that volume ratioI of extracting solvent to solution which is required in regular countercurrent extraction. This results in a decrease of about 50% in theamount of steam required `for regeneration of the spent solutizer solution.

Esample II A West Texas straight run gasoline, specic gravity .7369, having a mercaptan sulfur content of 0.0388% by` weight, was treated with fthe aqueous solutizer solution and in the countercurrent extractor of Example I.

The extraction was carried out at 85 F. using a solutizer solution to total gasoline ratio of 0.75.

' A portion of the gasoline was fractionally distilled to produce `two fractions: a low boilingu fraction having an end boiling point of 152 C. being about 70% by volume of the totalgasoline and a higher boiling fraction of about 30% by volume. The low boiling fraction contained withdrawing it therefrom, introducing into said' zone at diiIerent points in the. direction of flow of said aqueous solution said fractions in the order of their decreasing ease of transference, flow` ing said fractions through at least partiof said zone in countercurrent to said'aqueous solution combining at least some ofl said fractions within said zone, and withdrawing' them.'

2. In the process of separating mercaptans and relatively strong organic acids having dissociation constants greater than lil-9 from a hydrocarbon distillate containing same by extraction with 56% of the total mercaptan sulfur and the higher boiling fraction contained 44% of the mercaptan sulfur. i

Tworextractions` E and F were performed. In run E the unfractionated` portion was extracted in the conventional countercurrent way. In run F the' fractionated'portion was treated according to the split extraction method of this invention. In the last run, the higher boiling fraction was separately extracted in stages 1 to 3. The low boiling fraction was introduced betweenl stages 3 and 4. and the combined fractions were extracted together in the remaining stages. The solutizer solution was passed through stages 6 to 1 in countercurrent to the fractions and spent solution was withdrawn from stage 1. The treated gasoline was withdrawn from the sixth stage. Results were as follows:

an aqueous solution of alkali metal hydroxide in a regenerative system which comprises extracting in an extraction system said distillate with said aqueous solution to produce a spent solution containing mercaptides, regenerating said spent solution by steam stripping and recirculating the regenerated solution for further extractions, the improvement comprising i'ractionating said hydrocarbon distillate to produce atleast two fractions containing mercaptans of different ease of transference, at least one fraction being substantially free of and the remaining fractions having accumulated in them said'strong organic acids having dissociation constants greater than 109, pretreating only the latter fractions to remove strong acids and to produce pretreated fractions having retained a substantial portion of 'the mercaptan's, flowing said aqueous lution through an extraction zone, introducing into said zone at dierent points in the'direction of flow oi said aqueous solution said pretreated fractions and the fraction originally free from said-strong acids in the order of the decreasing ease of transference 'of the mercaptans which they contain, iiowing said fractions through said zone in countercurrent to the iiow of said solvent, combining said fractions within said zone, and separately withdrawing the resulting solvent and combined iractions.

Countercurrent extraction of the two fractions o] West Texas straight nm gasoline Vollrraze ratio 1of Y so u r so u- Number of tion to gasoline lfggfnf stages for Total percent ,Run Type o! separate numweight in extraction extraction ber of For sep am treated k gahcetvy stages rata etrc' Overgasoline on o oheavym blendX104 tion E Conventional.-- None 6 0.75 9 3) F Mo ed 3 6 2.7 0.75 3. l)

. produce at least two fractions containing portions ofsaid acids. which portions have different degrees of ease of transference toward said aqueous solution of alkali metal hydroxide, flow# ing said solvent through an extraction zone and 3. In the process of separating mercaptans and relatively strong organic acids having dissociation constants greater thanl 10-9 from a gasoline distillate containing same by extraction with an aqueous solutionv of alkali metal hydroxide in a regenerative system which comprises extracting in an extraction system said distillate with said aqueous solution to produce a spent solution containing mercaptides, regenerating said spent'solution by steam stripping and recirculatingthe rev generated solution for further extractions, the Y improvement comprising fractionally distilling said hydrocarbon distillate to produce twoffractions, a low boiling fraction having an end boiling point below C. being substantially free of said strong organic acids, and a smaller high boiling fraction boiling above about 175 C. containing substantially all said strong organic acids having dissociation constants greater than 104,

substantial pretreating the erboiling fraction with aqueous caustic t i ,i to remove strong acids and to produce a pretreated fraction having retained a portion oi the mercapt, iowing said aqueous solution I1 -f 1 h an ention mue, and withdrawing it therefrom, introducing the smaller hizh bo fraction into one end of said extraction zone near the point of withdrawal of the aqueous solution, introducing the low boiling fraction at a point intermediate between the entrance of the aqueous solution and the higher i boiling fraction, owing both fractions in countercurrent to the flow oi vsaid aqueous solution, combining said fractions wi said zone, and withdra the resulting combined fractions.

4. The process of claim i in which the organic acids have dissociation constants of less-than 10-5'.

5. In the process oi separating mercap contained m a dmesrnmuiststy eta ing with an if; solution oi an i metal hydroxide, the impro n i s ally distilling said nydroc on dis illate to duce at least two fractions conta i. i portions oi said'mercaptans, said portions having dierent degrees of ease oitraerence tod said asesora said aqueous solution said fractions in the order of their decreasing ease Ioi' transference oi the mercaptans which they contain, flowing said iractions through said zone countercurrent to the ow of d solvent, comb said fractions within said zone, and separately withdrawing the resulting solvent and combined fractions.

6. In the process of separating mercaptans contained in a hydrocarbon distillate by extracting with an aqueous solution of an alkali metal hydroxide, the improvement comprising fractionally distilling said hydrocarbon distillate to produce two fractions of dierent volumes, a large low boiling and a smaller her boiling fraction, owing said aqueous solution through an extraction zone, and with it therefrom. introducing the smaller fraction into one end of said-extraction zone near the point oi withdrawal of the aqueous solution, introducing the low boiling fraction at a point intermediate between the ence of the aqueous solution and the higher ous solution, o` said aqueous solution.

through an extraction none, introdu a into unid zone at larent points in the direction oi w of i i :l t fraction, flowing 'Both iractions in coun= tercurrent to the now' oi d aqueous solution, combining said wi said zone and withdrawing the resulting combined fractions.

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