US3177263A - Concentration of selected aromatic hydrocarbons by extractive evaporation with ammonia - Google Patents

Description

A nl 6, 1965 A. w. FRANCIS 3,177,263

CONCENTRATION OF SELECTED AROMATIC HYDROCARBONS BY EXTRACTIVE EVAPORATION WITH AMMONIA Filed Aug. 11, 1960 3 Sheets-Sheet l Qua 5 3E500 aEzm 5533800 B mm a. Q Eoo m 33:83:02

mm @m hm \llll m o W 302mm w ur on 2:32. mm 222305 =E= oo 2:03am mm o zum cozootxm m N 1 o o 3023. 2:321 wm w 25m INVENTOR Alfred W. Froncls April 6, 1965 A. w. FRANCIS 3,177,263

CONCENTRATION OF SELECTED AROMATIC HYDROCARBONS BY EXTRACTIVE EVAPORATION WITH AMMONIA Filed Aug. 11. 1960 3 Sheets-Sheet, 2

Toluene Toluene Ammonlo TMP Ammonia TMP Fl 6.2 Fl 6.3

Toluene Q0376 94% Ammonia TMP ATM 5% 0.0356

ATM

2.3,4-Trimethylpen'rone :E ,R 0.0l46 C Toluene l l l 1 0.0077 v I Toluene Weigh'fj, Solvenr Free Basis 2,3,4-Tri- M m ethylpenlone Fl G.- 5

JNVENTOR. Alfred W. Francis ZMLW ATTORNEY.

3 Sheets-Sheet 3 A. W. FRANCIS CONCENTRATION OF SELECTED AROMATIC HYDROCARBONS BY EXTRACTIVE EVAPORATION WITH AMMONIA April 6,

Filed Aug. 11, 1960 o oEE woo mBw 06 n M n N 8 9. 8 on 3 on 8 Q 52 m m m W M d g mm m m V E h S Y :oEmBEEE uWQ w B 3 m 9 w m. M w mm 962 23y row a a -2o |o oEE 3 39 058mm w 0 E mmd o United States Patent CQNCENTRATIQN 0F SELECTED AROMATIC HY- DROCARBUNS BY EXTRACTIVE EVAPQRATION WITH AMMONIA Alfred W. Francis, Woodbury, NJL, assignor to Socony Mobil Oil Company, Inc, a corporation of New York Filed Aug. 11, 1960, Ser. No. 48,923 7 Claims. (Cl. 26(i6'74) This invention relates to the separation of aromatic hydrocarbons boiling at temperatures higher than 212 F. from a mixture of aromatic and nonaromatic hydrocarbons boiling at substantially the same boiling point. The invention is particularly directed to a process of solvent extraction to obtain susbtantially pure aromatic hydrocarbons boiling at temperatures higher than 212 F. from mixtures of aromatic and nonaromatic hydrocarbons using ammonia as the extraction solvent.

The need for obtaining quite pure streams of aromatic hydrocarbons has long been recognized in petroleum refining. These aromatic hydrocarbons are useful intermediates in the manufacture of petroleum chemicals as well as products in other branches of chemistry. The pure aromatic hydrocarbons are sold in quantity as solvents and make useful blending stocks in the manufacture of automotive fuel. Many of the most desired aromatic hydrocarbons are found in conjunction with nonaromatic hydrocarbons which boil at substantially the same boiling point. The separation of the aromatic hydrocarbon from the similarly boiling nonaromatic hydrocarbon is expensive. For example, it is desired to obtain toluene which boils at 1'l0.6 C. from parafiinic or naphthenic hydrocarbons boiling at 100 to 120 C. with which the toluene is frequently found commingled. A typical 'paraifin is 2,3,4-trimethylpentane which boils at 113.5 C. There is a growing demand for toluene in purified form for which the impure toluene is not acceptable.

Many solvents have been proposed for extraction of aromatic hydrocarbons from mixtures of aromatic and nonaromatic hydrocarbons of similar boiling point. Liquid ammonia is a highly selective, cheap, non-corrm sive solvent, operable at moderate pressures and easily separated from the products. However, like other proposed solvents, ammonia has two serious disadvantages. Ammonia is not only miscible in all proportion-s with most aromatic hydrocarbons, but it is also partly miscible with many nonaromatic hydrocarbons. Using pure liquid ammonia as a solvent, it is impossible to obtain more than about 90% toluene by extraction alone except at exceedingly low temperatures, which are uneconomical. A mix--- ture of 80% toluene, 20% 2,3,4-trimethylpentane (or other parafiin) is miscible with liquid ammonia in all proportions at 25 C. or higher.

It has been proposed in US. Patent No. 2,396,299 to monia with water, ethylene glycol or one of many other liquids to diminish its, solvent power.

number of plates or theoretical stages of extraction re,- quired. This results in decreased throughput and therefore greater expense.

The second major difiicultly encountered inusing liquid ammonia as an extraction solvent is caused by the fact" The proposed solution has the disadvantage of decreasmgsubstantially the selectivity of the solvent, and of so increasing the provide a higher purity of aromatic hydrocarbons when using liquid ammonia as a solvent by diluting the am carbon. And yet when mixed with even small quantities of ordinary diluents, and with hydrocarbon mixtures possessing a reasonable content of aromatic hydrocarbons, the solvent density may become equal to or higher than that of the rafiinate. It therefore becomes difficult to design a flow diagram free from the risk that the two liquid phases may become inverted. This is illustrated in FIGURE 6 attached hereto wherein the specific gravity at 60 F. is plotted against the weight percentage of ammonia in mixtures with water. Ethylene glycol-ammonia mixtures would give similar curves. Densities of n-heptane, benzene, 2,3,4-trimethylpentane, and toluene, typical components in the hydrocarbon system, have been located on the curve.

I have discovered that substantially pure aromatic hydrocarbons boiling'at a temperature higher than 212 F. can be obtained from a mixture with similarly boiling nonaromatic hydrocarbons by first using substantially pure liquid ammonia as an extraction solvent in an extraction processand then conducting evaporation of the solvent from the extract without reflux under conditions which remove the ammonia and the small amount of non-aromatic hydrocarbons carried over with extract. Substantially all of the aromatic hydrocarbon in the mixture is left behind as a liquid. The solvent ammonia and the carried-over hydrocarbons are returned to the extraction zone after the gaseous ammonia has been converted to a liquid. The latter purification feature has been called extractive evaporation since the impurity, consisting of the nonaromatic hydrocarbons, is extracted from the extract by the evaporation of the solvent, leaving substantially pure aromatic hydrocarbons.

The object of invention is to provide a process for separating aromatic hydrocarbons boiling at a temperature higher than 212 F. from nonaromatic hydrocarbons boiling at substantially the same boiling point.

A further object of this invention is to provide a simplified process for using the solvent power of ammonia to separate aromatic hydrocarbons boiling at a temperature higher than 212 from nonaromatic hydrocarbons boiling at substantially the same boiling point.

A further object of this invention is to provide a highly efficient continuous process for separating aromatic hydrocarbons boiling at a temperature higher than. 212 F. from nonaromatic hydrocarbons boiling at substantially the same boiling point using ammonia under moderate temperature levels and mildly advanced pressure as the concentrating medium in a combination extraction and evaporation process.

These and other objects of the invention will be more fully disclosed in the following detailed discussion of the invention, which is to be read in conjunction with the attached figures.

FIGURE 1 shows diagrammatically a complete process for using liquid ammonia to concentrate aromatic hydrocarbons from a mixture of aromatic and nonaromatic hydrocarbons in accordance with the invention.

FIGURE 2 shows a ternary diagram for toluene and 2,3,4-trimethylpentane with ammonia as a solvent mes dium at, a temperature of 25 C.

FIGURE 3 shows a ternary diagram for toluene and 2,3,4-trimethylpentane with ammonia as a solvent medium at a temperature of 0 C.

FIGURE 4 shows a ternary diagram for toluene and 2,3,4-trimethylpentane with a mixture or" 94% ammonia and 6% water being used as the solvent medium at a tem perature of 25 C.

FIGURE 5 a plot of partial pressures of the hydrocarbon components in a mixture of toluene and 2,3,4- trimethylpentaue against weight percentage on a solventfree basis.

FIGURE 6 is a plot of specific gravity of mixtures of ammonia and Water at 60 F. against the weight percentage of ammonia in mixtures with water.

facilitate flow of products.

on refrigerating costs.

Referring now to FIGURE 1, a method of operating the process will be described indetail. An elongated extraction column 1 is operated at a convenient temperature, such as 15 C., and a convenient pressure, such as 100 p.s.i.g. The pressure in the; extractor is normally autogenous, that is, nearly equal to the vapor pressure of ammonia at the operating pressure. However, sincethe extractor is usually liquid full, the pressure may be slightly higher, or even considerably higher if it will A temperature of about 30 C. may be used in the extraction stage with corresponding the case of toluene. The larger amount of nonaromatic impurity to be removed by extractive evaporation means cost for heat. On the other hand, it wouldeconomize The optimum temperature is determined on economicgrounds. The feed is a mixture of aromatic and-nonaromatic hydrocarbons which, for purposes of illustration, may be a mixture of tolueneand 2,3,4-trimethylpentane.

means of the compression pump .3. The compressed feed is introduced'into the extraction column 1 through ,the

conduit 4 whichterminates generally near the midpoint of the column. The feed comprises 16 parts by weight toluene and 37 parts by Weight 2,3,4-trimethylpentane. .Makeup ammonia is added to the extraction column 1 through the conduit 5 which terminates near the midpoint of the column 1. The extraction column is operated at C. and 100 p.s.i.g. having any desired number of extraction plates, such as enough to provide maximum conparticular feed charged. The extract is taken from the top of the column through the conduit 6 and in this illustrative example contains 300 parts by weight of ammonia,

,16 parts toluene and 2-parts 2,3,4-trimethylpentane.

The extract is put under additional pressurein the com- .pression pump 7 and introduced into the extract evap pressure of 170 p.s.i.-g. or more, but this produces. lower 7 concentrations of aromatic hydrocarbons, about 70% in a greater relative recirculation of ammonia, involving The feed is passed through con-, duit 2, and put under extraction column pressure by .centration ofaromatics in, the extract depending upon the i orator 8 through the conduit 9 which'terminates near the midpoint of theextract evaporator 8. Heat is supplied to the extract evaporator 8 by means of the heating coil 10. The temperature in the extract evaporator is maintained at C. and the pressure in the extract evaporator is maintained at 380 p.'s.i.g. Under these conditions the liquid ammonia converts to a vapor and is withdrawn, from the top of the evaporator 8 through the conduit 11. A suitable temperature range for the extractevaporator is found to be about 60 'C; Substantially all the 2,3,4-

trimethylpentane leaves with the ammonia and in addi tion a small amount of toluene leaves with the ammonia. The stream 11 comprises, therefore, 300 parts ammonia, 2 parts 2,3,4-trimethylpentane and 1 part'toluene. The

remaining 15 parts of pure toluene are, removed from the bottom of the extract'evaporator. V

In the extract evaporation stage improvement in separation car: be obtained by diluting the extract with a solvent such as water. The'water flows with the toluene from the bottom of the evaporator through the conduit 12 into a separating chamber 13. The valve 14 in the conduit 12 is used to reduce the pressure to substantially atmospheric pressure and the water-toluenemixture forms .two layers in the separating chamber 13. The toluene is withdrawn 7 from the top-layer through the conduit 15 as a substantially pure aromatic hydrocarbon. Water is withdrawn from the bottom of the separating chamber 13 tl1rough the conduit 16, and put under a pressure of 380 p.s.i.g.

.in the compression pump 17. The water under pressure is reintroduced into the extract evaporator through the conduit 18.

.The ammonia with diluents 2,3,4-trimethylpentane and toluene in conduit 11 is'cooled and liquefied in heat exchanger 19 and depressured to extractionzone pressure by means of the pressure releasevalve 203* The liquid ammonia is reintroduced into the extract column near the midpoint. Only sufficient makeup ammonia need be added through theconduit 5 to make up for losses in the system.

TABLE I Extractive evaporation of aromatic-nonaromatic mixtures with liquid ammonia Toluene (110.8")2,2,5 Trimethylhexanc (124.1")

I Solvent Percent Aromatic Run Diluent Percent Temp, Ratio,

0. g /NHa/g harge Charge Product Water 3. 5 60 7 89. 2 92. 3 0- k 6.7 I 60 7 89.2 92.5

p-Xylene (l38.4)n-0ctane (125.7)

Toluene (110.63)2,3,4-Trimethylpentane (113.5)

2 Water 4.0 00 as 88.8 02.

3 do 4.0 6.0 93., 9s.

Toluene (110.63)3-Methylheptane (119.0

4 00 as 89.0 01.3 5 Water 4.0 00 5.0 V 89.0 412.1

o-Xylene (144.41)-n-Nonane (150.72)

, R '66 8.2 89.0 90.2 a Water. 7 3.7 66 7.8 89.0 90.2

pentane. in the compression pump 22 and introduced into the -rafiinate evaporator 23 through the conduit 24 which terminates near the midpoint of the raliinate evaporator. Heat is supplied to the rafiinate evaporator by means of The raffinate is taken from the bottom'of the extraction column 1 through the conduit 21 and in this illustrative example contains 3 parts ammonia and 35 parts trimethyl- The rafiinate is put under additional pressure the heating coil 25., The temperature in the rafiinate .evaporator is maintained at 40 C. and the pressure in the raflinate evaporator is maintained at 130 p.s.i.g. Under these conditions the ammonia converts to a gas through the conduit and depressured to substantially atmospheric pressure by means of the pressure release valve 28 located in the conduit 27. The recycle ammonia is 'cooledby the heat exchanger 29 located in conduit 26 and depressured by means of valve 30 to 120 p.s.i.g.

Under these conditions the ammonia converts to a liquid and is returned to the extraction column 1.

I T able I, shown hereinabove, presents 12 extractive evaporations of nonaromatics from aromatics boiling at a temperature higher than 212 F., the aromatics and nonaromatics having boiling points so close that separation by distillation is not practical. The charge in these runs is toluene or xylene mixed with a similarly boiling parafiin such as could be produced in a simple extraction with pure ammonia (88 to 89% toluene or xylene). The

richer charges in runs 3 and to. 12 is such as could be produced by extractive evaporation. Thus, the purity of final product can be raised as high as desired merely by providing a sufiicient relative amount of ammonia in the evaporation stage. q

It is noted that in the evaporation stage pure ammonia is somewhat less efficient than ammonia diluted with water.' It is, therefore, advantageous to dilute the extract in the evaporation stage with a limited amount of a suitable solvent such aswater. This should not carry over into the extraction stage, however, since this would reduce the selectivity of the liquid ammonia. It would also introduce difficulties due to equal densities of the layers in extraction. The diluent for ammonia in the evaporator could be water, ethanolamine, ethylene glycol or any other substance miscible but not reacting with ammonia and not miscible with toluene. The low cost of ble enrichment in the evaporation.

The extraordinary success of this invention in providing substanially pure aromaic hydrocarbons boiling above 212 F. from closely boiling mixture of aromatic and nonaromatic hydrocarbons is due to a secondary selection during recovery of the aromatic hydrocarbon from the extract. It is called extractive evaporation and is distinct in principle from extractive distillation. Under controlled conditions it is very effective in purifying aromatic hydrocarbons. Further purification of a given hydrocarbon after solvent extraction with liquid ammonia, for example, toluene in the toluene-2,3,4 trimethylpentane-ammonia system, can be achieved by distillation of the extract layer. As the ammonia is distilled off, relatively more 2,3,4-trimethylpentane than toluene goes with the ammonia. This leaves a relatively purer toluene in the undistilled material. By recycling more ammonia greater purity of the aromatic hydrocarbon is obtained up to a substantially pure aromatic hydrocarbon product.

Extractive evaporation isbased on the recognized principle that in a system of two or more phases in equilibrium the partial pressure of any component is the same for each phase, regardless of its concentration in that phase.

Thus, in a two-liquid phase system of ammonia, toluene and 2,3,4-trimethylpentane at 25 C., as shown on the ternary diagram FIGURE 2, the lower hydrocarbon layer R, is 11% ammonia, 24% toluene (20.5 mol percent and 2,3,4-trimethylpentane by weight (41.2 mol percent).

It has by Raoults law .412 .0356 (vapor pressure of 2,3,-

4-trimethylpentane at 25 .C.) or 0.0146 atmosphere pressure compared with only .205 X037 6 or .0077 atmosphese pressure for toluene, in spite ofthe higher vapor pressure of pure toluene at 25 C., .0376 atmosphere pressure. -The partial pressures are respectively the same from the ammonia-rich layer E, even though it contains only 3.0% 2,3,4-trimethylpentane by weight. law is not applicable to this extract layerbecause it is far from an ideal mixture.

. Evaporation of ammonia (partial pressure about 10 atmospheres) from this layer takes with it most of this 2,3,4-trimethylpentane in preference to the normally a higher temperature, 60 C. is recommended for'the' evaporation after separation of the phases at a lower temperature, so as to diminish the amount of ammonia required to carry over the nonaromatic hydrocarbon. At

this higher temperature the corresponding pressures. are as follows:

Atmospheres Ammonia I 25 Toluene: p

Pure 0185 Partial 0.038

2,3,4-trimethylpentane:

Pure "0.174 Partial 0.072

again thepartial pressure of the parafiinis nearly twice as great as that of the toluene from the extract as we'll as from'the rafiinate. At the suggested higher temperature, 60 C., the ammonia vaporpressure has increased only 2.5 fold while those of the hydrocarbons have increased five fold as compared with 25 C. Thus only half as much ammonia is required to carry over the hydrocarbon mixture.

Extractive evaporation is illustrated ongFlGURE 5, showing the partial pressures Ofthe hydrocarboncom-p-onents plotted against weight percentage on a solvent-free basis. The pressures are constant over the range of the two-phase composition, and the pressures curve in the single phase regions to the pressure of the pure components. As ammonia is evaporated from the extract (dashed line EC in FIGURE 2) it will be noted that the composition is no longer on the binodal curve, and so no longer in equilibrium with R. The excess vapor pressure of 2,3,4-trimethylpentane over toluene decreases. At point C (FIGURES 2 and 5) they are equal. is still obtained since the 2,3,4-trimethylpentane in the residue is substantially lower than in the feed. However, enrichment can be continued at a higher level by diluting the ammonia (in the evaporator, but not in the original extractor) so that in eliect point E in FIGURE 5 is moved to the left toward pure toluene (solvent-free basis). The composition of the evaporating liquid remains closer to the binodal curves as shown in FIGURE 4. However, excessive dilution of the ammonia is ineiiective because the new tie lines slope steeply up to the right indicating poor selectivity. The hydrocarbon layer is not much richer in 2,3,4-trimethy-lpentane than the ex- Raoults Enrichment tract. Dilution 'with'water should b'e' maintained within the range to 1 0% by weight,1the -optimum being for 'water about 4% to 6%. 'Other factors which aitect eifi:

ciency of extr'active evaporation are temperature and the concentration of total hydrocarbons: in the ammonia. The pressure under which the extractive evaporation oc- V curs has also been found to be a factor in the efiiciency "of separation with improved results being obtained at the higher pressures. Ingeneral, the pressures in both evaporators will be autogenous, that is, substantially equal to the vapor pressure .of liquid ammonia at the operating temperature' Higher temperatures permit higher concentrationssince less ammonia is required to evaporate "the 2,3,4-trimethylpentane.

Improved results are obtained by increasingthe proportion of ammonia thereby decreasing theconcentration of total hydrocarbons in the ammonia. The disadvantage of the use of an excessive amount of ammonia is the problem of recycling, pressurvolume of ammonia.

Extraction with liquid ammonia is most selective when it is used anhydrous or pure. That is, the tie lines have a minimum adverse slope under such conditions, as shown on FIGURESZ and 3, ascompared With FIGURE 1'5 4. It is essential, in this process, that the extraction be conducted With substantially pure ammonia to provide the maximum selectivity during extraction, and it is preferred that during the extractive evaporation-of the extract. a

"suitable diluent beJadded to theextraot up to the amount providing tion.

improved efficiency in the extractive evapora- The invention has been amply illustrated in the detailed discussion of the invention. These examples are given only to illustrate the invention and are notintended as 1 limitations. The only limitations intended are found in the attached claims.

I claim:

1..A process for separating a mixture of (l) aromatic hydrocarbonsihaving a boiling point higher than 212 F. and (2) nonaromatic hydrocarbonsboiling atsubst'antially the same temperature which comprises contacting said mixture of aromatic and n'on'ar'omatic'.hydrocarbons with liquid ammonia containing substantially no diluent inan V 3 withdrawing gaseous ammonia, and along with the ammonia substantially all of the nonaromatic hydrocarbons and a portion of the aromatic hydrocarbonsfrorn said extract evaporation zone with substantially nocondensation and substantially no reflux, withdrawing separately substantially pure aromatic hydrocarbons. fromsaid extract evaporation zone, reducing thepressure of the gaseous ammonia andhydrocarbons withdrawn from said extract evaporation zone to the pressure of the extraction zone, returning the ammonia and hydrocarbons; contained therein in liquid form to the extraction zone, withdrawing from saidextraction zone a raffinate comprising non aromatic hydrocarbons and liquid ammonia, substantialing and depressuring, heating and cooling such a large Water.

1y increasingthe pressure of the rafiinate and introducing the raffinate into a raflinatc evaporation zoneat the elevated pressure, adding sulfic'ient heat to the raftinate oration zone to the-temperature of the extraction zone,

drawingammonia from saidraffinate evaporation zone, cooling the ammonia Withdrawn from said raifinate evaporation zone to the temperature of the extraction zone, reducing thepressure of'the ammonia-to the pressure of the extraction zone, returning the ammonia in liquid form to the extraction zone, and, separately Withdrawing n0n-' aromatic hydrocarbons from said vraifinate evaporation zone.

i 2. Claim 1 further characterized in that a diluent is introduced into said extract evaporation zone, the diluent is removed with the substantially pure aromatic hydrocarbon, separated from said substantially pure aromatic hydrocarbons and returned to' said extract evaporation 3. Claim 2 further'fcharacterized in that the diluent is 4. Claim 1 further characterized in that the extraction temperature is from 0 C. to +30 v C., and the pressure is at least autogenous.

5. Claim 1 further characterized in that-the aromatic hydrocarbon is toluene. V g f I 6.- Claim 1 further characterizedin' that the-aromatic hydrocarbon is xylene. i i i 7. Claim 3 further characterized. in that the dilnent is add-ed tothe separated extract in an amount to provide a extraction zone at an extraction temperature and at leastautogenous pressure, withdrawing from said extraction zone an extractcomprising the aromatic hydrocarbons,

amomnia and a small portion of the nonaromatic hydrocarbons, substantially increasing the pressure of the extract and introducing the extract into an extract evaporation zone at the elevated pressure, adding suificient heat to the extract evaporation zone to raise the temperature of said extract: to a temperature higher than that of said extraction zone and to convert the ammonia to a gas,

concentration up to 10 percent in theextract evaporation 10/59 Fenske et a1. 260- 674 7 ALPHoNso ,D. SULLIVAN,- Primary Examiner.

" Aitceting Officer UNITED STATES PATENT OFFlCE CERTIFICATE "OF CORRECTION Patent No. 3,177,265 f I April 6, 1965 Alfred W. Franois It is hereby certified that error appears in the above numbered paten't reqiiring correction and that the said, Letters Patent should read as oorrectedbelow. v a i a Y Column 6,' lines 8 an-d 9, for "atmophese" read atmosphei column 8, line 17, beginningwith, "oration zone" strike'out all to, and including "evaporation Zone,";in*linel8, same columr and insert instead evaporation zone tohconvert theammonia tc a gas, withdrawing ammonia from said raffin'ate evaporation zone,

Signed and sealed this 24th day ofJAu'gus t 1965 7 (SEAL) v Attest:

v EDWARD J. BRENNER Commissioner of Patents" ERNEST W. SWIDER

Claims (1)

1. A PROCESS FOR SEPARATING A MIXTURE OF (1) AROMATIC HYDROCARBONS HAVING A BOILING POINT HIGHER THAN 212*F. AND (2) NONAROMATIC HYDROCARBONS BOILING AT SUBSTANTIALLY THE SAME TEMPERATURE WHICH COMPRISES CONTACTING SAID MIXTURE OF AROMATIC AND NONAROMATIC HYDROCARBONS WITH LIQUID AMMNIA CONTAINING SUBSTANTIALLY NO DILUENT IN AN EXTRACTION ZONE AT AN EXTRACTION TEMPERATURE AND AT LEAST AUTOGENOUS PRESSURE, WITHDRAWING FROM SAID EXTRACTION ZONE AN EXTRACT COMPRISING THE AROMATIC HYDROCARBONS, AMOMNIA AND A SMALL PORTION OF THE NONAROMATIC HYDROCARBONS, SUBSTANTIALLY INCREASING THE PRESSURE OF THE EXTRACT AND INTRODUCING THE EXTRACT INTO AN EXTRACT EVAPORATION ZONE AT THE ELEVATED PRESSURE, ADDING SUFFICIENT HEAT TO THE EXTRACT EVAPORATION ZONE TO RAISE THE TEMPERATURE OF SAID EXTRACT TO A TEMPERATURE HIGHER THAN THAT OF SAID EXTRACTION ZONE AND TO CONVERT THE AMMONIA TO A GAS, WITHDRAWING GASEOUS AMMONIA, AND ALONG WITH THE AMMONIA SUBSTANTIALLY ALL OF THE NONAROMATIC HYDROCARBONS AND A PORTION OF THE AROMATIC HYDROCARBONS FROM SAID EXTRACT EVAPORATION ZONE WITH SUBSTANTIALLY NO CONDENSATION AND SUBSTANTIALLY NO REFLUX, WITHDRAWING SEPARATELY SUBSTANTIALLY PURE AROMATIC HYDROCARBONS FROM SAID EXTRACT EVAPORATION ZONE, REDUCING THE PRESSURE OF THE GASEOUS AMMONIA AND HYDROCARBONS WITHDRAWN FROM SAID EXTRACT EVAPORATION ZONE TO THE PRESSURE OF THE EXTRACTION ZONE, RETURNING THE AMMONIA AND HYDROCARBONS CONTAINED THEREIN IN LIQUID FORM TO THE EXTRACTION ZONE, WITHDRAWING FROM SAID EXTRACTION ZONE RAFFINATE COMPRISING NONAROMATIC HYDROCARBONS AND LIQUID AMMONIA, SUBSTANTIALLY INCREASING THE PRESSURE OF THE RAFFINATE AND INTRODUCING THE RAFFINATE INTO A RAFFINATE EVAPORATION ZONE AT THE ELEVATED PRESSURE, ADDING SUFFICIENT HEAT TO THE RAFFINATE EVAPORATION ZONE TO CONVERT THE AMMONIA TO A GAS, WITHDRAWING AMMONIA FROM SAID RAFFINATE EVAPORATION ZONE, COOLING THE AMMONIA WITHDRAWN FROM SAID RAFFINATE EVAPORATION ZONE TO THE TEMPERATURE OF THE EXTRACTION ZONE, REDUCING THE PRESSURE OF THE AMMONIA TO THE PRESSURE OF THE EXTRACTION ZONE, RETURNING THE AMMONIA IN LIQUID FORM TO THE EXTRACTION ZONE, AND SEPARATELY WITHDRAWING NONAROMATIC HYDROCARBONS FROM SAID RAFFINATE EVAPORATION ZONE.

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