INDUSTRIAL A N D ENGINEERING CHEMISTRY
lune 19sO
TABLE I. EQUILIBRIA AND PHASE BOUNDARY DATA* (COnClzlded) Charge Component A B C
Phase I Component A B C - A
Phase I1 Component B C
System 21. Component A 70% Methanol 307 Water. Component B, Hexadscane. Componeni C, p-tert-Butyldhenof Temperature 35' C. 50.0 50.0 0.0 1.4 98.6 0.0 100.0 00 0 0
!;:
A
tj:;
:::
47.8 35.6 16.6 43.8 31.6 24.6 35 6 27.0 37.4 23 31 45.0 The liquid-solid region of
i:; !::: :;$
:;:: g:: l$:i
74.7 0.4 24.9 63.6 1.7 34.7 48.8 3.7 47 5 o.o 91.0 31.6 ll.l 57 a this system was not studied for this work. 1.0 0.5
0.0
96.8 94.0 91.9
2.2
5.5 8.1
System 22. Component A 70% Methanol 30% Water. Component B, Methylnaphthalene. Component C. Hexahcane. Temperature 35' C. 60.0 50.0 0.0 2.4 97.6 0.0 98.9 1.1 0.0 47.6 48.6 3.9 1.7 90.9 7.4 99.0 1.0 0.0 16.1 69.2 14.7 1.4 81.3 17.3 99.1 0.9 0.0
ii;: i::; 40.9 45.1 49.6
15,7
50.0
o.o
6.8
2.2
44.2 48.1 48.2 50.0
i:: !::! it:; ii:: 8;;
8::
1.4 1.4 1.4 1.4
0.3 0.1
0.0
o.o
o.o
26.2 11.3 4.0
72.4 87.a 94.6 g8.6
99.7 99.9 100.0
0.0
0.0
0.0
System 23. Component A, 90% Methanol, 10% Water. Component B, Methylnaphthalene. Component C, Hexadeoane. Tempersture 3 6 O C. 50.0 50.0 0.0 7.0 93.0 0.0 76.5 23.5 0.0 42.0 66.0 2.0 6.4 89.9 3.7 77.4 23.1 0.8 0.2 81.3 18.6 5.0 84.6 10.5 9.0 81.0 10.0
!:$ :! :!:: t:: ii:! ::$ !89.9 : #: it;: !19.7 40.3 2.5 28.8 68.7 8.1 2.0
40.0 63.6
47.6 41.5 60.0
12.1 5.9 1.5 0.0
35.4 46.6 67.0 50.0
2.5 2.0 2.0 2.0
21.9 9.2 2.5 0.0
75.6 88.8
95.6 98.0
95.2 96.9 99.2 99.5
8.7 1.9 0.1 0.0
1.1 1.2 0.7
The data presented show that solvent compositions near 70% methanol by weight present a satisfactory compromise between solvent power and selectivity for separating tar acids from hydrocarbons. Richer solvents tend to dissolve more of the hydrocarbons and leaner solvents less of the tar acids. Unfortunately, a single solvent of the alcohol-water type does tiot effect the separation of hydrocarbon-free tar acids. To achieve this end it is necessary to reextract the primary extract with a second solvent of the type represented by the paraffin hydrocarbons. A suitable solvent of this type may be selected togiveaspreadbetween theboilingpoint of the aromatic hydrocarbons extracted and the solvent, sufficient to permit the separation of solvent and hydrocarbon by distillation. An anticipated development is the increased solubility of the less phenolic tar acids in the aromatic hydrocarbon. This may be observed most clearly by comparing systems 10, 14, 16, and 17 at 35" C. (Figures 10, 14, 16, and 17). These systems were similar in all respects except the species of the phenolic component. The paraffinic hydrocarbon systems did not show this same effect (see system 18,19, and 20,Figures 18,19, and 20). Some of the methanol from the solvent preferentially dissolves in the hydrocarbon-rich phaae of all systems. Thus the composition of the solvent remaining in the solvent-rich phase is shifted from the nominal composition in the direction of a higher percentage of water. This change in composition is slight and In all oases was sukh as to increase the efficiency of the separation of taracidsfrom hydrocarbons.
0.1
* All data are in weight per oent.
1217
LITERATURE CITED
SOC.Testing Materials, Standard D 268-48, "Sampling and Testing Lacquer Solvents and Diluenta," Sections 9 through 15. (2) Brancher, A. V.,Hunter, T. O.,and Nash, A. W., J . Phys. C h m . , (1) Am.
INTERPRETATION OF THE DATA
The investigation of the ternary and quaternary systems revealed that these systems do not behave in the same manner as the system acetic acid-acetone-chloroform-water used by Brancher et al. (2) in developing their correlation for tie lines in quaternary systems containing one immiscible binary pair. More system have to be studied before it can be whether the correlation suggested in general and these systems form the exception or the correlation is applicable only to the system for which it was developed.
44, 683 (1940).
Aww.
48# 394 (1935)s
(3)
Fischeri
(4)
Kemp, L. C., Hamilton, G. B., and Groaa, H. H., IND. ENG.
(5)
Postlewaite, J. P., and Bondy, H. F., BZOS-Trip 2153, British Intelligence Objectives Sub-committee, Target C30/472 and
Chem*i
CRBM.,40, 220 (1948).
C30/4729.
(6) Ruderman, 1. W., IND. ENQ.CREM.,ANAL. ED.,18, 753 (1946). (7) Rutzler, J. E., Jr., and Bauman, R. G., Abstractsof Papers, 113th Meeting of AM. CHEM.SOC., Chicago, Ill., pp, 86-0, 87-0, 1948. RmcmxVlD January 14,1950.
Toluene Extraction from Petroleum with Water Solutions G . B, ARNOLD AND c. A, COGHLA" Beacon Laboratories, The Texas Company, Beacon, N . Y
?-
Batch equilibrium data are presented on the recovery of toluene from the toluene concentrate from hydroformed naphtha by liquid-liquid extraction with a water solution of 20% ammonia at 274' and 232" C. and a water solution of 25% ethylene glycol at 302' and 274' C. From these data process calculationsare made assuming a threecomponent system of toluene, naphtha, and solvent, and the results are compared with similar calculations on the extraction of toluene with water at 274" and 302" C.
* Present addreas, The Texaa Company, Port Arthur, Tex.
I
T BECAME evident during the early stages of World War I1 that in order to supply toluene for normal deknands and possible needs of the military, considerable expansion of the facilities for the production of toluene was needed. Furthermore, it waa well known that toluene was present in many natural and re formed petroleum stocks. These facts logically led to an investigation of methods of separating toluene from petroleum stocka by a number of procedures, which included liquid-liquid extrac-• tion with selective solvents. A study of the recovery of toluene from a toluene concentrate, prepared from hydroformed naphtha, by liquid-liquid extraction with water at high temperatures has been described (I). This
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1218
Vol. 42, No.
6
Figure 1. Batch Extraction Equipment
paper presents a continuation of the study of the recovery of toluene and is concerned with the use of water solutions as selective solvents in the recovery of toluene by liquid-liquid extraction. Selective solvents for the extraction of toluene from hydrocarbon mixtures fall into two general groups: solvents that are completely miscible and solvents that are only partially miscible with toluene. The recovery of high purity toluene is usually not practical in liquid-liquid extraction employing solvents of the first group, because the toluene content of the extracted material is limited to the maximum toluene content of a stock which forms two phases with the solvent, unless dual solvent or other special techniques are used. However, with solvents of the second group which show an “open” phase diagram, it is theoretically possible to prepare an extract of high toluene content by employing extract recycle, similar to reflux in distillation. Water is only partially miscible with toluene and falls in the
second group of solvents ( 1 ) . As a selective solvent for toluene, it has several favorable and several unfavorable characteristics. It is a very inexpensive solvent, the toluene may be recovered from the solvent by cooling, and toluene of 98.0 volume % purity may be prepared by liquid-liquid extraction with extract recycle. However, because of the low solvent power of water for toluene and the high vapor pressure of water at 302’ C., high solvent dosages and high imposed pressures are required to effect liquldliquid extraction employing water as the solvent. Increasing the solvent power of water by addition of a material of greater solvent power for toluene and yet retaining the desirable solvent properties of water would probably lower the solvent dosages and/or the temperature of extraction. Ammonia ( 8 ) and ethylene glycol (6)are known to be completely miscible with toluene above room temperature. This paper presents equilibrium data and an analysis of those data on the extraction of toluene with water solutions of ammonia and ethylene glycol a t elevated temperatures.
TABLEI. TOLUENE CONCENTRATE EMPLOYED IN EQUILIBRIUM STUDIES
Gravity A. P. 1. Aniline boint: C. Bromine addition No. C.F.R.M. octane No. Benzene volume Toluene‘ volume Xylenea’ volume Total a;omatios, volume % A.S.T.M. ditillation, O C.
$
Hydroformed Naphtha 49.8 15.0 4 76.9 1.4
7.8 12,2 43 39 66 82 131 179 199
208
Toluene Concentrate from Hydroformed Naphtha 49.4
5
..
4i:2
4i:2 100 102 102 106 108
111
117
EXPERIMENTAL WORK
A study of the toluene content of naturally occurring and reformed naphthas ( 1 )indicated that, although toluene was present in almost all naphthas, the most attractive source for large scale recovery was hydroformed naphtha. This material, prepared by dehydrogenation of naphthas over suitable catalysts (5), may be fractionated to produce a toluene concentrate of from 50 to 60 volume % toluene. Because that concentrate appeared to have the greater practical significance, the equilibrium data were obtained on the toluene concentrate from the product of a commercial hydroformer. The full range naphtha was fractionated to obtain a crude concentrate distilling between 88’ and 121” C., which was refractionated into small cuts. Fractions containing toluene as the only aromatic hydrocarbon were combined to form a toluene concentrate. Pertinent tests on the hydroformed naphtha and the toluene concentrate therefrom
INDUSTRIAL A N D ENGINEERING CHEMISTRY
lune 1950
ir
,'
1219
The batch extraction system shown in Figure 1 consisted of a
pressure a t the end of the settling period. This procedure re~ sampling per!od. gwo vented mixing of the phases d . the samples were taken for analysis: $1) the center portion of the solvent-rich phase and (2) the center portion'of the hydrocarbonrich phase. The remainder of the contents of the bomb was collected to check the material balance about each batch extraction, which usually was better than 98% of the materials charged. The samples of the solvenbrich phase and the hydrocarbon-rich phase were cooled to 15.6' C. to se arate the solvent therem and the volume er cent solvent was fetermined b direct observation. The l!ydrocarbon portion of each sampfe was separated and analyzed for toluene. (Analyses for toluene were conducted by a procedure involving the aniline point which is to be published in the near future.) For convenience, all measurements were made a t 15.6' C., or corrected to that temperature with a maximum reading error of 1%.
excess of 5000 unds per square inch) and facilities for charging and removin contents of the bomb,by positive displacement. Wood's m e t i was used as the positive displacing medium because, at the time this work was carried out, mercury was not readily available. However, additional eqm ment W&B necessar2 to maintain the Wood's metal well above t i e melting point (74 C.). The batch extractions were carried out by first evacuating the bomb and then charging with the desired amount of solvent and toluene Concentrate by means of the high pressure charge pumps. This procedure ermtted the bomb to be charged a t temperatures above the toiling points of the solvent and toluene concentrate a t atmospheric pressure without loas. After charging, the union on the bottom of the bomb was broken and the contents of the bomb were aeitated by rotatin the bombabout the center supporta. While being agitated, thetomb was heated to a temperature slightly above the desired extraction temperature. By approaching the extraction temperature from the higher temperature it was possible to obtain e uilibrium very quickly. After agitation for 60 minutes the bomt was stopped in B vertical position and the contents were permitted to settle for 45 minutes. (These times were demonstrated as more than adequate for good rmxlnf and settling.) During the settling period the line from the Wood s metal reservoir and the line to the water-cooled condenser were connected to the bottom and to of the bomb, rea ectively. After the settlin period was compite the contents opthe bomb were displaced by forcing Wood's metal reheated to bomb temperature, into the bottom of the bomb. &e contents of the bomb weraremoved through a valve in the top, which was adjusted for a withdrawal rate to maintain the pressure within the bomb at equal to or up to 100 pounds per square inch gage higher than the
It is evident that the extraction of toluene from a toluene concentrate from hydroformed naphtha with water solutions involves a multicomponent charge oil and a two-component solvent. Interpretation of batch equilibrium data employing four or more components in terms effecting the commercial operation of an extraction procem, the number of stages of extraction and solvent dosage required, would be difficult if not impossible. Maloney and Echubert (4), however, have presented an excellent analysis of a three-component system, solvent, extracted component, and r a f i a t e component. Therefore, in order to simplify the analysis of the equilibrium batch extraction data it is assumed in this work that the multicomponent system can be adequately represented as a three-component system consisting of the solvent, toluene, and nonaromatic hydrocarbons or naphtha. Calculations based on this assumption appear to be well within the range of uncertainty which would be employed in using the data in the design of a commercial extraction system. I t may be observed in Table I, that the toluene content of the toluene concentrate used in this work was 41.2 volume %. In order to obtain equilibrium data over the entire range of toluene content, batch extraction experiments were made with raffinates from previous extractions for the low toluene content range and the toluene concentrate was diluted with nitration grade toluene for the high toluene content range. This technique permitted
are found in Table I. Commercially available nitration grade toluene was used in the experiments requiring toluene. The water solutions of ethylene glycol were blended from distilled water and ethylene glycol to yield 25 volume % ethylene glycol solution a t 15.6" C. The water solutions of ammonia were prepared by absorption of synthetic ammonia in distilled water until a specific gravity of 0.926 a t 15.6' C. was attained, which corresponds to a 20 weight % ammonia solution. The equipment and procedure employed to obtain batch extraction data a t elevated temperaturea and pressurea have been described in dgtail(1) and are reviewed only briefly here. 10,OOO ml. stainless steel bomb (maximum working pressure in
-0
20 40 80 80 100 ,UME PER CENT TOLUENE I N HYDROCARBON RICH PHASE, SOLVENT FREE BASIS CURVES
I
2 3
-
20 40 60 80 VOLUME PER CENT TOLUENE, SOLVENT FREE BASIS
I 0
SOLVENT CURVES SOLVENT 4 WATER SOLUTION OF 2 5 $ ETHYLENE GLYCOL AT 2 7 4 ' C. WATER AT 2 7 4 % . WATER SOLUTION OF 2016 AMMONIA AT 232% 5 WATER SOLUTION OF 2 5 % ETHYLENE GLYCOL AT 302.C. WATER AT 302 'C. 8 - WATER SOLUTION OF 20% AMMONIA AT 274OC.
Figure 2.
-
Synteme Involving Toluene, Toluene Concentrate from Hydroformed Naphtha, a n d Water or Water Solutions
INDUSTRIAL AND ENGINEERING CHEMISTRY
1220
Vol. 42, No. 6
in each phase was then calculated from
TABLE 11. LIQUID-LIQUID EQUILIBRIUM DATAFOR SYSTEMTOLUENE-K'APHTBA- a material balance about each experiWATERSOLUTIONOF 25% ETHYLENE GLYCOL AT 302" C. ment. The degree of reproducibility of (Charge stook, toluene concentrate from hydroformed naphtha) Hydrocarbon-Rich Phase Solvent-Rich Phase Volume % a t 15.6O C. Vol. solVolume % a t 15.6O C. Vol. solToluene' vent/vol. Toluene vent/vol. solventhydrcsolvent- hydroNaphtha Toluene Solvent free carbon Naphtha Toluene Solvent free carbon
0
72.9 67.6
9.4 13.9
69.1 41.9 ,.
21.6 35.6 60.0
11.4 17.0 30.0 23.7 27.7 26.8" 46.0 100.0
17.7 18.5 18.0 17.9 21.9 19.3" 22.5 40.0
0.22 0.23
3.2 2.8
1.6 2.3
0.24 0.29 0.67
3.0 2.6
3.7 7.1 18.7
,.
95.2 94.9 92.8 93.7 93.3 93.3O 90.3 81.3
32.6 45.6 59.2 51.6 56.6 55.W 73.5 100.0
19.8 18.6
13.9 9.3 4.3
Average of three batch extractions
TABLE 111. LIQUID-LIQUID EQUILIBRIUM DATAFOR SYSTEMTOLUENE-NAPHTHAWATERSOLUTIONS
(Charge stock, toluene concentrate from hydroformed naphtha) Hydrocarbon-Rich Phase Solvent-Rich Phase Vol. Volume % a t 15.V C. solvent/ Volume % a t 15.6O C. Toluene vol. Toluene solvent hydrosolventNaphthe, Toluene Solvent free carbon Naphtha Toluene Solvent free 25% Ethylene Glycol at 274O C. 79.8 70.1 66.0 44.7
..
91.7 80.1 60.6 47.0 27.2
..
70.4 6Z.O 64.2 39.8 22.8
10.2 18.4 31.7 41.3 80.0 3.4 7.2 30.9 44.2 62.8 80.0 8.1 15.0 21.1 36.1 39.2
10.0 11.5 12.3 14.0 20.0
11.3 0.11 20.8 0.13 30.2 0.14 0.16 48.0 100.0 0.25 20% Ammonia a t 3.6 7.7 33.8 48.5 69.8 100.0 20% Ammonia a t 0.27 10.3 19.5 0.30 28.0 0.33 46.8 0.34 0.61 63.3
4.9 6.7 8.5 8.8 10.0 14.0 21.5 23.0 24.7 25.1 38.0
1.1 1.2 1.1 0.9
..
232O C. 1.2 1.4 1.0 0.7 0.4
..
1.0 1.7 2.9 4.6 10.5
97.9 97.1 96.0 94.5 89.5
0.3
0.7
3.2 4.2 5.1 6.1
274O 0. 1.5 3.6 2.8 3.7 4.6 3.9 6.7 2.4 14.3 3.0
95.0 93.5 91.6 90.9 32.7
Vol. solvent/ vol. hydro. carbon
45.9 59.0 72.5 83.6 100.0
46.6 33.5 24.5 17.2 8.5
21.3 32.5 75.5 84.8 98.3 100.0
65.6 49.0 22.8 19.4 17.2 14.4
30.1 43.3 53.6 74.1 82.5
19.0 14.4 10.9 10.0 4.8
the experiments may be observed from the data in Table 11, where three batch extractions of the toluene concentrate from hydroformate with a water solution of 25% ethylene glycol a t 302" C. under the same conditions are tabulated. Similar batch equilibrium data employing as solvents a water solution of 25% ethylene glycol a t 274" C., a water solution of 20% ammonia, a t 232' C., and a water solution of 20% ammonia a t 274' C. are tabulated in Table 111. In Figure 2 the equilibrium data for these systems are plotted along w t h similar data on water taken from the earlier paper ( 1 ). The commercial possibilities of a toluene recovery process involving m y of the systems described herein depends to a large extent on the relation between the number of stages of extraction and the solvent dosage required to effect the desired separation. These factors may be calculated from the equilibrium data following the procedures described by Maloney and Schubert (4). In considering the application of simple counterflow extraction to the recovery of toluene, the maximum toluene content extract would be obtained when an infinite number of stages of extraction and a minimum solvent dosage are employed. Under these conditions the extract phase is in equilibrium with the charge stock. The results of calculations of the limiting conditions of ex-
accurate determinations of the equilibrium curves in both the enriching and stripping zones. A t the conclusion of each batch extraction] data were available by analysis or direct observation for the amount of solvent and toluene concentrate charged to the bomb, the volume per cent eolvent, and volume per cent toluene (solvent-free) in the solvent. rich and hydrocarbon-rich phases. The volume per cent naphtha
RAFFINATE SEPARATOR
RAFFINATE OIL
EXTRACTION
TOWER CHARGE OIL
I
$
--
ASSUMING A 95 5 RECOVERY OF T O l ' L M FROM A TOLUENE CONCENTRATE CONThfl4lNc 40% TOLUENE AS 98.0 VOLUME PER CENT TOLUENE EXTRACT.
3
EXTRACT RECYCLE
I 5 TOTAL
I, CURVE EXTRACT
SOLUTION
-
SOLVENT SEPARATOR
'
-
~
I
EXTRACT TOLUENE
2 3 4
5
Figure 3, Flow for Extract Recycle Extraction
WATER WATER WATER WATER WATER
I
I
I
IO
I5
20
THEORETICAL
fi
STAGES OF EXTRACTION
SOLVENT AT 274'C SOLUTION OF 20 % AMMONIA AT 2 3 2 ' C . AT M 2 ' C . SOLUTION OF 2 5 % ETHYLENE GLYCOL AT 2 7 4 ' C . SOLUTION OF 2 5 % ETHYLENE GLYCOL AT 302.C.
Figure 4. Recovery of Toluene from 40% Toluene Concentrate from Hydroformed Naphtha by Extraction with Water and Water Solutions
INDUSTRIAL A N D ENGINEERING CHEMISTRY
June 1w
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