US 2666796 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
Jan. 19,A 1954 E. @GRIN Em. 2,666,796
REFINING OF TAR ACID OIL Filed sept. 12. 195o 2 sheets-sheet 1 le AouEous #Mg/#fizzl- METHANOL j `|8 soLuTloN :4 5a /I e el l IO TAR `5o AclD 'z Z Q O I O'L 9 24\ zt p i t(- I 4s 'l -J o d u '-J z E Q y 0 v l2 u z o z 3 z o l O Il: C D 2 E 60 z s2 D O 0 n NEUTRAL ou. Y 24 f T A R 1 Q A c los n T f,
`2g y 58` i A FIG.
- INVENTORS ,20 EvERl-:TT GoRlN AND 1 MARE, B. NEuwoRTH NAPHTHA @lL- da ATTORNEY Jan. 19, 1954 E. GORIN ETAL 2,666,796
REFINING OF TAR ACID OIL Filed Sept. 12, 1950 l2 Sheets-Sheet 2 NAPHTHA NAPHTHA ExTRAcT i ExTRAcT TAR ACID TAR ACID NAPHTHA NAPHTHA AouEous AQuEous FIG 2 METHANol. METHANol. ExTRAcT 'ExTRAcT NVENTORS l EVERETT GORIN AND MARTBIQI( .B. NEUWORTH DW/Me ATTORNEY Patented Jan. 19, i954 REFINING F TAR ACID OIL Everett Goria and Martin B. Neuworth, Pittsburgh, Pa., assignors to Pittsburgh Consolidation Coal Company, Pittsburgh, Pa., a corporation of Pennsylvania Application September 12, 1950, Serial No. 184,474
13 claims. (o1. 26o- 627) This invention relates to the art of refining tar acid oil, and more particularly, to the separation and recovery of valuable tar acids from tar acid oil. f
our copending application Serial Number 110,932, now abandoned, filed August 18, 1949, and assigned to the assignee of the present invention.
Primarily, this invention is directed to the recovery of tar acids from the tar produced in the low temperaturer carbonization of coal but the method of the invention is applicable tothe tars produced in W, medium and high temperature carboniz'ation operations on coals, lignite,
oil shale, ytar sands and similar bituminous materials, as Well as to petroleum fractions containing tar acids from the tar acid'salt solution. This caustic processhas the virtue o recovering tar acids quantitatively in high purity but has an inherent disadvantage in consumed in the process. tains only-'a small fraction of tar acids as is the This Aapplication is a continuation-in-part of that ythe reagents are Where the tar con-A case' with tars resulting from high temperature coal carbonization,' this disadvantage ordinarily can be disregarded.`
In contrast to high temperature tars, the tars produced in the low temperature carbonization of coal or in coal hydrogenation processes contain considerable quantities of tar acids. For example, the distillate fractions of the tar obtained from the low temperature carbonization of Pittsburgh Seam coal containslO to 60 weight per cent of tar acids, Ll0 to 60 Weight per cent of neutralv oils and 0 to, 5 Weight per centoftar bases, the exact "composition being Vdependent uponthe method byA which the coal is carbonized andthe particular coal employed. Ffor such tars, a tar acid recovery process is `required Ywhichis less expensive and morev efficient than those now available.
It is, therefore, theobject of the present invention to provide a'methodfor continuously recovering tar acids from tarV acid oil.
A further object of vthis invention is to provide a method for recoveringftar acids from tar acid oil by solvent extraction in a single continuous extraction column. Another object of this invention is to provide a method for continuously separating tar acid oil into tWo -fractionsof which one is substantially extraction column inoperable.
2 pure'tar acids and the other substantially of ,tar acids.
In accordance with our invention, we have discovered that tar acids can be efficiently recovered from tar acid oils by contacting tar acid oil with aqueous methanol and a lov/ boiling parainic naphtha fraction in a continuous, countercurrent, center feed extraction column; provided certain free critical limitations hereinafter set forth are observed. Y
In our new process, tar acids are dissolved selectively in the aqueous methanol Whileneutral oils are dissolved selectively in the naphtha. The use of aqueous vmethanol solution alone as a solvent for the recovery of tar acids is known, but such extractions are unsatisfactory because the neutral oils of the tar also are soluble to a limited extent in methanolv with the result that the tar acids recovered are contaminated with neutral oils. Paraiinic naphtha alone is virtually useless to effect separation of the tar acids. Nevertheless, when aqueous methanol and para'inic naphtha are employed in combination according tothe present invention, high purity tar acids can be recovered from tar acid oils in high yields.
Specifically, a tar acid oil fraction preferably boiling within the range 160 to 300 C; is fed into the-central portion of a continuous, countercurv rent, double solvent, center feed extraction column. Aqueous methanol solution is fed into the top of sa1d column and a low boiling, essentially paramnic naphtha fraction is fed into the bottom.
of saidV column. 'Ihe aqueous methanol passes downwardly through the column dissolving sub` tha will have removed substantially all of the' small portion of dissolved neutral oil therefrom.
The tar acids then may be readily recovered from the methanol-in high purity by distillation; y and slmilarly, the neutral oil may be recovered from the naphtha solution.
In the above process, it is necessary to employ aqueous methanol solution containing from to` '75.per cent by weight ofniethanol. In concentrations below 55 Weight-per cent, the methanol solution forms three phases which render' the Above Aweight per cent concentrations, the methanol solution develops an affinity for neutral oils so that the resulting tar lacids in the methanol extract" are contaminated by the presence of neutral oils.
- in general, for aqueous methanol solvent conta;ning 55 to 75 per cent of methanol by weight,
the recovery of tar acids increases and the purity of the recovered tar acids decreases with higher methanol concentrations.
The plf'oy f this? ir'ii'f'vention? isf further.' criti-A cally cond i'o'hed by the" characteristics of the naphtha solvent. It must be essentially paranig in character. `Such solvents may be obtainecr from the distillation of parainic petroleum stocks. its boiling range should be 0 to l but preferably 60 to 100 C., ordsi pl the subsequentl separation ofM `aplitha the naphtha extract by distillation; And finally; the naphtha density should be less than 0.80 and preferably less than 0.75 to insure? suicientqg'rairs: ity difference betWeenthe two phases inthe ex@ traction column to electa ready separation of the phases. The hexanecut of paranic naphthacoiflfnnes2 all these critical properties and accordingly is preferred as the solvent ini thisr in`r ven'tiorr'.y
process of this hiventin` may' be practiced with1 ethrl naphtha' or aqueous methanol as the continuous phasefthe phase contacting por-tion of?y the extraction column, butthe former-ispre-- ferrdi becausezof. the greater: eilici'ency of separa-'1 tion andircoivery of the taraci'ds.`
The distinguishing features of each type of op; erati'orrvvillabe described later. in thetspeci'cation. However, it should be. pointedf out here that thev system employing aqueousv methanol asf thecon-y tinuousfphaselwas fully. described in. our cepending". application above referred to. Subsequent to th'. filing. of that application, it was discoveredthati theuse of naplrnsha-A as the continuousphase yields-even bett-er, results and for-that reason, the present'. application was prepared to. more: fully. describe ourinvention. Y
a better understanding of our-invention, its objects and advantages, referenceshould behad tothe accompanying drawings-Lof which:
Figure. 1 is aA diagrammatic illustration of4 ap-nl parat-us adaptedV tothe practice of theV` preferred embodiment of Athis invention;
Eigure `2 isla sectional drawing-.of an extraction column in `which one modification of theL present` invention is practiced Figure 3A is asectional drawingofcan extraction column.` which` another` modification of the. present; nvention ispracticed;
' Referring toEig-ure, 1-, tar acid oilzispumpedv from,4 a, storage taule` I0 continuously,throi-ig-l-iV a pipe 'ne lizeintoa continuous countercurrentdou--. sie', Solvent. center feed. extraction column I4'. The extraction .cglumrrimayfbe of; anyv convenient, deisnanableof providing asuicent numberlof theorem ,1. extracting. Staesto keffect ,the desired separation orv` tar .acids from ,thevr tarV acid oil. A cenieriteralracred; .teurer` may, beiused, for exampigaswll as a pierced plate column, a but bli lateolilrm Qn a Column contaminada :of qmescene and turbulenee, Theiter'irnined by the purity and extentof tar-acid re;-i
' 1,1 s iii hfge `Singe.:the-lOvS/festb011-. lngctar vacid,,phenol, boilsjat 13275 G., theminixriunfboilingpoint-:ofthe feed need not begless thanfl Cfin order to assure recoveryof s ubsttiallly all vflow boiling acidsl contained in the.
original/ tar.v onthecther hand, since thehighestboilingxylenol boils. at.225i C,., the upper boil-2 iris'` point of. the` tar. acid oil feedneed not eir- 4 ceed 230 C. when recovery of only the low boiL ing tar acids is desired. Nevertheless, if it is desiredtoregbyer invfadditicn certain higher alkyl phenols; dihyd'ric'L phenols'` and bicyclic phenols present in the tar, the upper boiling point of the t'etr fraction need not exceed 300 C. to include the valuablehigher molecular Weight acids in the tar, nor should* the upper boiling point exceed 300 C., be of the accompanying increased viscosity "o int fractions.
l" solution is fed continuously methanol storage tank i6 through-pipeline t8; into the top of the extraction column i4. Naphtha is fed continuously from the naphtha storage tank 20 through a pipeune 22 into the base of tile extraction column la.
Sineeltliel density off the aqueous methanol solution exceeds the density ofA the, naphtha, they aqueous methanol solutiondescends through the column and dissolves tar acids while the lighter ria'phtha` passes countercurrently upward through the' column and dissolves neutral oils contained in theta-r acid oilfeed. Column throughput andy contact time are dependentk uponl the4 column de sign. We'z foundthat surprisingly, there are no ernulsiii'cation problems. 1
Fori every volume of tarA acidoil feed, from 0.5 tol- 5.0LvolumesV of.' aqueous methanol and from 0.5 toL 5101 volumes. of; nafphtha` should be employed, whenever both highv tar acidrecovery and high tar acid; puri-ty. are desiredi and are, therefore, preferred; Moreover, for thesame consideration', they ratio-off aqueous .methanol to naphtha should be. controlled: according toi, the solvent which is employed as thev continuous; phasei as will be` pointed out. y l
ltl maypbev desirable; to add aVA portion of thev naphthaA solventntotlfietar;y acid o il feed, especiallytvhenl a high end pointfihigh viscosity) tar fractionisbeing treated. When such technique'4 isy employed,l the; naphthagso added should be` considered;v assolventfor the purpose of determining solyent-'to-feedi and solvent-to-solvent ratios.
be heatedor cooledi Vihiletl-ier methqdof thepresent invention is relatively independent of the temperature at operate;.themextractioncolumn LWithin the range of; 60.10,. 1;20,-E. yncreased viscosity of tar acid oil at temperatures below` this rangeihtroduces.y column; o pyeratiin.L diculties, WhleQtlo'e y increasing;l solubility of neutral oils in the aqueous methanol;K solvent; at higher, temperatures decreases. thayeld ar1c1;1 rit'y`- of the recovered tar acids. If necessary, the extraction column may i 4 any convenient manner. Aqueous metharield lxtract, containing purified recover-edtai;- acids, is. Withdrawn. continuously froinfthe extraction column; I4 through a pipeline.2 4;.a nd fedlinto a3 distillationcolufrin 26 for the separation; offthemethanolsolvent from the water,y and purified tar-acidsbothof which leave the still as betten@1 through `pipeline 2S and pass, into, a-phaseseparation .tank 30. Since the. solubility oi tar acids in Water decreases with reductionin temperatura a-cooler 3.2 may be placed inline ,28pm-.- coolthe'wjater and tar acids passing through line 278,* andthereby to. decreasev the' proportion.;offresi-dualjtar acids in the aqueousr` layer in phase separator 30. Purified tar acids; being virtually immiscible inwater, separate from the aqueous layer in ,phase separator 3|);` andt are withdrawn either continuously or intermittently.- as`h product' through pipeline 34, Thev aqueous phase .from the phaseseparator` 30 is withdrawn through pipeline 36 and sent to the aqueous methanol storage tank IB for recirculation.
Anhydrous methanol passes overhead from distillation tower 28 through pipeline 38 to a reux condenser 40. Condensed anhydrous methanolv leaves the reflux condenser'40 and passes through pipeline 42 to the aqueous methanol storage tank I8 for recirculation. A portion of the condensed methanol may be returned through pipeline 44 to the top of distillation column 2S as reux.
It should be pointed out that in the preparation of the aqueous methanol solution in the storage tank I6, caution should beexercised if the solution is prepared and its composition regulatedV by Aspeciiic gravity measurement. The recirculated methanol is saturated with naphtha and this fact must be considered in determining the specific gravity required to'produce a solultion containing 55 to 75 weight per cent methanol. Fresh methanol may be added to the aqueous methanol storage tank I8 from pipeline 43 to make up the necessary 55 to 75 weight per cent methanol solution.
Naphtha wi-th dissolved neutral oil leaves the top of the extraction column |4 through pipeline 48 and passes to a distillation column 50 where the naphtha is separated from theneutral oil. Naphtha passes overhead from the still 50 through pipeline 52 and reiiux condenser 54. A portion of the condensed naphtha may be circulated through pipeline 58 as reux for the distillation column 50.. yThe remainder of the naphtha is returned to the naphtha storage tank 20 through pipeline 58 for recirculation. Neutral oil leaves the still 50 as the bottom -product through pipeline 60. A cooler 62 may be inserted in the exit pipeline 60 to cool the neutral oil product.
Now referring to .Figure 2, the use or naphtha as the continuous phase will be discussed. Tar acid oil is fed through a pipeline 68 into the phase contacting zone 68 of an extraction column 10, suitable for the ex-traction operation of the present invention. `Paralinic naphtha is fed to column through pipeline 'I2 and distributor 'I4 located between the phase contacting zone 68 and the bottom of the extraction'column 10; aqueous methanol enters the column l0 through pipeline 'land distributor 18. Naphtha extract is withdrawn overhead through pipeline 80; methanol extract leaves the column ythrough pipeline V82. p y
The interface 84,. between thenaphtha and methanol phases is maintained at a point between thenaphtha distributor 74 and the bottom ofthe extraction column 10 by regulatingthe rate of extract Withdrawal through pipelines 80 and 82. Thus naphtha constitutes the continuous phase in the extract in column '|0'above the interface84.
Aqueous methanol, in the form of tiny globules, descends as a dispersed phase through the naphtha. In the upper portion of the contacting vzone 88 (above-the feed point of the tar yacid oil). the aqueous methanol selectively dissolves tar acids Iand a small amount of neutral oil. As these methanol lglobules descend further, they `contact and areA dispersed in naphtha containing ,progressively decreasing amounts ofvdissolved neutral oil. Ultimately the'A dispersed 'methanol ,globulesLcontact ,fresh,1. practicallytneutral oil .free naphtha in a phase separation zone 588,'v disaee, te
e. posed below' the phasefcontacting z'ne 68. These contacts between naphtha and dispersed aqueous methanol extract globules vseem to strip the small amount of neutral oil from the globules and to transfer the stripped neutral oil to the naphtha phase, in which the neutral oil solubility is large as compared with the solubility of neutral oil in aqueous methanol. The phases separateI at the Abottom of the column 10 and the purified tar acids, dissolved in aqueous methanol, collect in the methanol phase zone 88 from which the extract is recovered. When naphtha is employed asthev continuous phase, it is neces-l sary in order to obtain high yields of a high purity product to regulate the solvent ratio so that the volume of aqueous methanol is from 0.25 to 4 0`times the volume of naphtha.
In .the following Table I are tabulated results iroma number of runs in which the continuous so1vent=phase wasV naphtha. A one-inch diameter, eight-feet long, center feed, countercurrent extraction column was employed and contained in its contacting zone 29 settling stages alternately disposed with 28 agitation stages. The feed stock to the extraction column was a` tar acid oill having a boiling range of 160 to 230 C. The tar acid oil was obtained by fractional distillation of the liquid product from the low temperature carbonization of Pittsburgh Seam coal. The solvent naphtha was a hexane cut of naphth-a boiling inthe range 67 to 72 C. The column was operated at a temperature of 25 C.l
TABLE I Naphtha continuous phase Run number 1 2 3 4 5 8 Feed (mL/mim):
Tar Acid Oil. 3. 5 10 4 5 5 5 70% MeOH 4.8 10 .6 15 2 5 3 5 Naphtha 7.2 30 12 15 l5 15 Tar acid oil fejedcompol siton (weight percent):
Tar acids (160-230 C. 55. 2 55. 0 4.45.7 54. 2 54. 2 54. 2 Neutral oil 44.0 44.2 50.9 45.2 45.2 45.2 Tar bases i.. 0. 8 0. 8 3. 4 0. 6 0. 6 0. 6
Methanol extract (gms. v
perv gm. tar acid oil feed): f
50. 7 40.0 51.2 .47. 2 0.3 0.3 0. 3 0.2 0. 2 0.0 v0.3 1.1 0.3 0.2 0.0 c V109. 7' 164 103 102 75. 2 Naphtha extract (gms.
per 100 gm. Ytar. acidi o feed:
Neutral oil 45. 2 42.9 52.5 44.7 43. 1 45. 1 2.3 3.3 4.8 y8.1 55.2 0.4 1.9 0.4 0.3 0.8 197. 5 203 191 198 211 cent tar acids in extract.v 97. 5 95. 9 92. 9 91. 2 85. 3 0. 55 Purity: weight percent pure tar acids in extract. 98.3 9S. 8 96. 5V 99. 0 99. 3 100. 0
l 60 percent methanol.
- 2 55 percent methanol.
$20 percent methanol.
4 160-300 C. fraction of tar acid oil.
. For a description of those systems lin vwhich aqueous methanol constitutes the continuous solvent phase, reference should be had to Figure 3, in which tar acid oil is fed through pipeline 98 to the phase-contactingzone 98 of an extraction column- |00, suitable furthe extraction operation ofthisjinvention. Parafnic naphtha islfed tothe column |00 through pipeline |02 aridi distributor |04; aqueous methanol enters the ,columnil |00v through pipeline |08l and distribi'1tor--|08,4 -located between the phase contacting zone 98 and the .top. .|09. o'f-the `extraction column |00. Naphtha extractis withdrawn utes, we have explained the principle, preferred construction, and mode of operation of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.
1. A process for separating tar acids from a tar acid oil fraction which comprises the steps of feeding said tar acid oil to a vertical extraction zone at a point located between the ends thereof, feeding an aqueous methanol solution containing 55 to 75 weight per cent methanoland the balance water to the top of said extraction zone, feeding a second solvent consisting of a parafflnic naphtha'fraction boiling within the range of 60 to 130 C. and having a density of less than 0.8 to the bottom of said extraction zone,
passing said aqueous methanol solution and said naphtha fraction through said vertical extraction zone in countercurrent relation, and recovering aqueous methanol extract containing tar acids from the bottom of said verticalextraction zone.
2. VThe process of claim 1 in which the naphtha fraction is the continuous phase in said vertical extraction zone.
3. The process of claim l in which the aqueous methanol solution is the continuous phase in said vertical extraction zone.
4. The process of claim l in which methanol is separated from the aqueous methanol extract by distillation and recirculated in said extraction zone and that portion of the aqueous methanol extract remaining after removal of the methanol is separately recovered and the naphtha is separated from the naphtha extract by distillation and recirculated in said extraction zone and that portion of the naphtha extract remaining after the removal of the naphtha is separately recovered.
5. The process of claim 4 comprising the additional steps of recovering by phase separation Vthe Water from the water and tar acids which remain after the methanol has been distilled from the aqueous methanol extract, mixing said recovered water with said distilled methanol in such proportions that the resulting solution contains 55 to 75 weight per cent methanol, recirculating said aqueous methanol solution to the extraction zone andseparately recovering the tar acids from said phase separation.` Y
6. A process for separating tar acids from a tar acid oil'fraction which comprises the steps of feeding said tar acid oil to a vertical extraction zone at point located between the ends thereof, feeding an aqueous methanol solution containing 55 to '75 weight per cent methanol and the balance water to the top of said vertical extraction zone, feeding a second solvent consisting of a parailinic naphtha fraction boiling withinrthe range of 60 to 130 C. and having a density less than 0.8 to the bottom of said vertical extraction zone, circulatingsaid aqueous methanol solution downwardly and said naphtha fraction upwardly through said vertical extraction zone in countercurrent relation, regulating the rate of withdrawal of said solvents from said extraction zone so that the naphtha phase is the continuous phase, regulating the feed rate so that at least 0.5 and not more than 5.0 volumes of said aqueous methanol solution and at least 0.5 and not more than 5.0 volumes of said naphtha are fed to said extraction zone for every volume of said tar acid oil fed to said extraction zone, further regulating the feed rates so that the volume of aqueous methanol solution is'at least 0.25 but not more than 4.0 times the volume of naphtha fed to said extraction zone, and separately recovering the aqueous methanol extract and the naphtha extract.
'7. The process of claim 6 in which the tar acid oil is a fraction boiling within the range of 160 to 300 C.
8. The process of claim 6 in which the naphtha solvent is a paraffinic naphtha boiling within the range of 60 to 100 C.
9. The process of claim 6 in which the naphtha solvent is a hexane cut of petroleum naphtha.
10. A process for separating tar acids from a tar acid oil which comprises the steps of feeding said tar acid oil to a vertical extraction zone at a point located between the ends thereof, feeding an aqueous methanol solution containing to 75 weight per cent methanol and the balance water to the top of said vertical extraction zone, feeding a second solvent consisting of a paraflinic naphtha fraction boiling within the range of to C. and having a density less than 0.8 to the bottom of said extraction zone, circulating said aqueous methanol solution downwardly and said naphtha fraction upwardly through said vertical extraction zone in countercurrent relation, regulating the rate of withdrawal of said solvents from said extraction zone so that the aqueous methanol solution is the continuous phase, regulating the feed rate so that at least 0.5 and not more than 5.0 volumes of said aqueous methanol solution and at least 1.0 and not more than 5.0 volumes of said naphtha are fed to said extraction zone for every volume of said tar acid oil fed to said extraction zone, further regulating the feed rates so that the volume of aqueous methanol solution is at least 0.5 but not more than 2.0 times the volume of said naphtha fed to said extraction zone and separately recovering theV aqueous methanol extract and they naphtha extract.
11. The process of claim 10 in which the Vtar acid oil is a fraction boiling within the range of to 300 C.
12. They process of claim 10 in which the rnaphtha solvent is a paraiimic naphtha boiling References Cited in the le of this patent UNITED STATES PATENTS Number f Name Date 1,934,861 Karpati et al Nov. 14, 1933 1,955,023 Roos et al Apr. 17, 1934 2,041,308 Tuttle May 19, 1936 2,298,816 Ambler, Jr Oct. 13, 1942 2,301,270 Gerlicher Nov. 10, 1942 OTHER REFERENCES 191;? Report 46,391, Available to public, Mai7 22,