Ternary Systems for Extraction J Calculations J
JULIA& C. SMITH Shawinigan Chemicals Ltd., Shawinigan Falls, Quebec, Canada
The methods of construction, representation, and interpretation of solubility diagrams for ternary liquid systems are described. A list of systems for which complete data on the solubility relationships are available is included. ITHIN the past few years the extraction of liquids with liquids has become of great importance in industrial chemistry, for it often affords a cheap and easy method of recovery and concentration. As a result the triangular solubility diagram, long a plaything of the physical chemist, has come into prominence in the design of extraction equipment. The methods of construction, representation, and interpretation of these diagrams, however, are still not generally known, and the data available on ternary liquid systems are widely scattered through the literature. The methods of designing extraction apparatus and of calculating the efficiency of the extraction were describcd by Sherwood (M), and no mention will be made of them here. All of the methods, however, require a knowledge of the distribution of the third liquid between the two liquid layers, and therefore, the solubility diagram for any given system is of no use for extraction calculations unless the tie lines are included. A great many systems have been studied up to the present, but unfortunately the limiting solubility curve was often all that was determined. In 1910 Bonner (7) made a list of all work done on ternary liquid systems up to that time, and in 1929 the compilers of the International Critical Tables (1’7) did essentially the same thing; but in neither case was any distinction made between the cofnplete diagrams and those giving merely the limiting solubility curve. I n addition, the data available in 1929 were so sketchy and inaccurate that all but four systems are presented graphically, and many of these are given only in part. Since that time a great deal of excellent work has been done, and while a few partial lists of systems are available (2, 8), no complete survey has been attempted. The literature citations a t the end of this paper contain references to all systems which were studied completely a t one temperature a t least. Most of them involve water and two organic liquids, although a few nonaqueous mixtures have been studied, and some systems involving an inorganic substance are included.
Representation of Ternary Systems I n considering systems of three components, it is generally necessary to limit the numbers of variables to three; for although various methods have been suggested ( 2 S ) , the complete representation of more complex systems is difficult, if a t all possible. I n ternary liquid systems the temperature is usually kept constant, and the effect of pressure on the equiIibrium, which is almost negligible, is ignored. The system is then represented a t constant temperature and pressure by plotting the percentages of the three liquids on a triangular diagram of the type described by Gibbs, Schreinemakers, and others (12, 31, SS, 36). 234
The essence of this method of representation is the fact that the sum of the three perpendiculars from any point such as 0 (Figure 1) to the sides of an equilateral triangle is equal to the perpendicular from any apex to the opposite side. The sum of any three such perpendiculars is therefore constant and may be set equal to 100 per cent. For the mixture represented by point 0, then, OX represents the percentage of B present, OY the percentage of A , and 02 the percentage of C. On most triangular graph paper, however, the values of these perpendiculars are not directly indicated, and it is more convenient to measure the coordinates of 0 along lines parallel to the sides of the triangle. Thus A’ represents the percentage of B i n the mixture, M the percentage of C, and I, the percentage of A . When the percentages of three liquids are plotted on such a diagram, provided a t least one pair is only partially miscible, two distinct fields are indicated: an area of homogeneity, where the three liquids are mutually soluble, and one of heterogeneity, in which two liquid layers are formed. The boundary separating the t n o areas is the limiting solubility curve. Any stable mixture represented by a point in the area of heterogeneity exists as tmo phases, each having a composition on the limiting solubility curve. The poiiits representing these conjugate solutions may be joined by a tie line, which must also pass through the point representing the overall composition. The type of diagram most frequently encountered is that resulting vhen two partially miscible liquids are mixed with a third liquid completely miscible with both of them. This gives a diagram similar to that shown in Figure 1. Systems in which the third liquid is completely miscible n ith only one of the other two are soinetinies found, and the result is the type of diagram illustrated by Figure 2. Some mixtures of three liquids, each pair of which is only partially miscible, have been studied, but as yet they are of little importance in extraction processes. The tie lines in the case shown in Figure 1 are not, in general, parallel to the base of the triangle, but slope more and more steeply as the amount of C present in the mixture increases. As this takes place, the two solutions in equilibrium with each other become more and more alike; the ends of the tie lines approach one another, until finally they meet a t point P , a t which the two layers become identical. This point is called the “consolute point” or “plait point”. Owing to the slope of the tie lines P is usually not at the maximum in the limiting curve, hut is displaced to one side or the other. Because of the changing slope of the tie lines, interpolation between them is rather difficult, especially in cases where only a few lines are known. Various methods have been proposed
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INDUSTRIAL AND ENGINEERING CHEMISTRY
to simplify such interpolation. Hand (15) describes a method of changing the units of the diagram so that the plait point is a t the maximum in the limiting solubility curve, and all of the tie lines are thus parallel to the base of the triangle. I n many cases the tie lines when extended come to a point focus (37, S9), but this is not always the case (S). Sometimes the extended tie lines appear to be tangent to a curve (%?),but the exact nature of this curve is not known. A method of representing tie lines by a single line is described in International Critical Tables (17). Straight lines are drawn through the ends of the tie lines parallel to the sides of the triangle, and the locus of their intersection is plotted. This requires the use of a second triangle inverted below the first but makes possible the determination of the plait point by interpolation. A similar method is described by Sherwood (S5), in which one line is drawn parallel to the side, and the other to the base, of the triangle. This eliminates the need for the lower triangle but makes the graphical determination of the plait point difficult. Each of these methods permits easy interpolation, but as the loci are somewhat curved, they require that a t least a few tie lines be accurately known. If the percentage of A in the A-rich layer is plotted against the percentage of B in the B-rich layer, the resulting graph is strongly flexed, but by the use of an arbitrary scale this can be made into a straight line (8). An easier method, however, is to plot the ratio of these two quantities against the percentage of B in the B-rich layer on arithmetical graph paper (S). This also gives a straight line. These methods are best in cases where only a few scattered data are known, since they require the knowledge of only two accurately determined tie lines. The tie lines almost always increase progressively in slope as the amount of the third component is increased, but two systems have been found in which the tie lines change in direction. Miller and McPherson first reported such a condition for the system ethyl alcohol-ethyl ether-water (24); later workers have confirmed their results (16, 18). The system benzene-pyridine-water also exhibits such anomalous behavior (51),which was explained on the basis of compound formation analogous to that in the system lead-zinc-tin described by Wright (53). It is the opinion of other investigators, however, that the anomalies are caused by inaccuracies in the available data (8) or by impurities in the materials used. Bailey (4) showed that the presence of relatively small amounts of impurity may have a profound effect on the equilibrium. As stated before, the diagrams are usually presented for a fixed temperature and pressure. As the temperature is changed, the relations also change, but so far no satisfactory method has been devised for representing them without resorting to space diagrams. I n general, the area of heterogeneity decreases in size as the temperature is raised; the plait point approaches the base of t h e triangle a n d finally reaches it a t C what is called the *‘triple critical point”. Not all systems show this phenomenon, however. I n some cases a small change in temperature has a large effect on the equilibrium (48), b u t in others it B may have almost FIGURE 1 none (SO).
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Construction The commonest method of constructing a solubility diagram is by the “synthetic” method described by Taylor (.do). Known mixtures of two of the liquids are titrated with the third until the limiting solubility curve is reached, as indicated by either the appearance or disappearance of turbidity. Some convenient property-density (61), surface tension, viscosity (bo), refractive index (42, 48)-of the resulting mixture is then determined. The property must be one which varies significantly over the range of compositions. The tie lines are then fixed by making up known mixtures in the region of two liquid layers, and analyzing the conjugate solutions by means of the property previously studied. The mutual solubilities of the two partially miscible liquids in the absence of the third component may also be determined by the synthetic or cloud point method. The titration of mixtures in a constant-temperature bath presents some mechanical problems, for it is hard to provide sufficient agitation and yet permit the end point to be seen. Some ingenious methods have been devised to overcome this difficulty, but many investigators have merely removed the mixture from the bath when examining it for turbidity. The error so introduced is very small in many cases, particularly when the determination is made a t about room temperature, but in some cases it may be quite large. Some uncertainty exists concerning the best method of determining the limiting solubility curve. Some workers (90) believe that it is more accurate to titrate away from turbidity; others have found that the appearance of turbidity gives a sharper end point (6). The methods are probably about equally good, depending somewhat on the specific system involved. I n addition, it is generally possible to back-titrate if the end point is passed, and Hand (15) claims to have eliminated all uncertainty by this means. When one of the components may be easily and accurately determined in the presence of the other two, it is possible to analyze the conjugate layers directly for this component. Once the limiting solubility curve is known, the percentage of one component in each layer is sufficient to define the tie line completely. Even the percentage of one component in one layer is enough to fix the tie line, provided the over-all composition of the mixture is also known. A straight line is drawn through the experimentally determined point on the limiting solubility curve and the point representing the overall composition, and is extrapolated until it intersects the other branch of the limiting curve. The intersection represents the composition of the other layer. Two methods have been suggested for the determination of tie lines without making direct analyses. One of them is based on the relative volumes of the two layers (24); the other depends on the relative weights of the conjugate solutions (10). These methods considerably simplify the experiC mental work and permit the determination of tie lines in systems where it would be difficult by any other means, but they make the subsequent calculations rather tedious. They also depend to a great extent on A the accurate construction and readFIQURE2 ing of the limit-
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Vol. 34, No. 2
TABLE I. TERNARY SYSTEMS WITH WATERAS ONE COMPONENT Components Acetic acidBenzene Benzene Benzene Chloroform Chloroform Epichlorohydrin Toluene AcetoneBromobenzene Chloroform Chloroform Furfural Phenol KOH NaOH AnilineFormic acid Propionic acid BenzeneAcetic acid Acetic acid Acetic acid Ethanol Ethanol Ethanol Ethanol Ethanol Ethanol Pyridine IsobutanolHBr HC1
HI
Temp., C.
25 25, 35 20, 25 18 20, 25 10 25 0 25 0 25 56.5 0 0 0, 20 0,20
25 25,35 20,25
25 25, 50 20 20, 25 25 25 25
25 25 25
n-Butanolmethanol 0, 15, 30 tert-Butanol-ethyl acetate 0, 20 CSaacetio anhydride 0, 18 Carbon tetrachlorideEthanol 0 0 Methanol 0 n-Propanol
Citation
Components ChloroformAcetic acid Acetic acid Acetone Acetone Ethanol Methanol EthanolIsoamyl alcohol Isoamvl bromide Isoam>l ether Benzaldehyde Benzene Benzene Benzene Benzene Benzene Benzyl acetate Benzyl alcohol Benzyl ethyl ether Bromobenzene Bromotoluene Isobutanol Isobutyl hromide CClr Chloroform Cyclohexane Cyclohexane Cyclohexane Cyclohexene Ethyl acetate Ethyl acetate Ethyl butyrate Ethyl ether Ethyl ether Ethyl ether Ethyl ether Ethyl propionate Ethylene chloride Ethylidene chloride Hexane Hexane Mesitylene Methylaniline
Temp., O C.
20iZ5 25 0
8
Citation
15) (17
rid
15.5,28
(17)
25
(17)
25
(48)
: 8;;
ing solubility curve, and are therefore somewhat subject to error. The plait point is most easily determined by graphical interpolation, using the method described in International Critical Tables (17). Some mathematical methods have been devised (SO),but they are probably not generally applicable. Exactly what determines the equilibrium between the three liquids is not known, although several exhaustive mathematical studies of ternary liquid systems have been made (11, 37). It has been proposed that the nature of the limiting solubility curve depends on the ability of the third component to ionize the other two liquids (82). The ratio of the amounts of the third liquid in the two layers is never constant over the whole range of compositions but varies as the total amount of the third component increases. While no general mathematical relations are known to apply to this variation, some empirical equations for the tie lines have been found to hold true in a large number of cases (8, 87). Woodman (60) describes an interesting method of calculating partition coefficients by considering the third liquid as an ordinary solute distributed between the two layers. Even the coefficients which he obtained by this means, however, vary from constancy by as much as 12 per cent.
List of Available Systems The following is a fairly complete list of systems which have been studied up to the present time. I n all cases both the limiting solubility curve and the tie lines are given, although the data available in International Critical Tables (17) are often incomplete. Table I deals with aqueous mixtures only;
Components Ethanol- (Cont'd) Nitrobenzene p-Kitrotoluene Phenetole Pinene Propyl bromide Toluene Toluene Toluene ?n X y 1en e a-Xylene p-Xylene Ethyl acetatetert-Butanol Ethanol Furfural Methanol Isopropanol n-Propanol Ethyl etherEthanol Ethanol Ethanol Ethanol Triethylamine
-
FurfuralAcetone Isoamyl acetate Ethyl acetate Hydrobromic acidIsoamyl alcohol Isobutanol Hydrochloric acidIsoamyl alcohol Isobutanol Cyclohexanone Phenol Hydriodic acidIsoamyl alcohol Isobutanol
T:mp., C.
Citation
0
0 0 0 0
20 20,25 25 0, 50 0 0
0, 20 0,20 25 0, 20 0,20 0, 20
25 0,25
(16)
25 0 25 ($4) 0, '12.4, 30.5 25 25 25
25 25 25 25 25 12 25 25
Temp., CitaComponents ' C. tion hlethanolIsoamyl alcohol 28 Bromobenzene 0 %-Butanol 0, 15, 30 cc14 0 Chloroform 0 Cyclohexane 25 Cyclohexene 25 Ethyl acetate 0, 20 Ethyl bromide 0 Toluene 25 NitrobenzeneEthanol 0 22 Hi804 PhenolAcetone 56.5 HC1 12 NaOH KOH Traethylamine -2, 67,75 7, 10, Is0 IO anoi8ycEhexane Ethyl acetate Toluene n-PropanolIsoamyl alcohol Bromotoluene CClr Ethyl acetate Propionic acidAniline o-Toluidine TolueneAcetic acid Ethanol Ethanol Ethanol Methanol Isopropanol
15,35 0,20 25 26 0 0 0, 20
0. 30 0, 20
25 20
20,25
26 25 25
at the top of each column is the second component, and below are the third components of the various systems. I n cases where both the second and third components are fairly common, the system has been listed under each of them (e. g., water-acetic acid-benzene and water-benzene-acetic acid); in other cases the system is given under the more common of the last two components (e. g., water-acelone-bromobenzene). Table I1 is a list of systems which do not include water as one component.
TABLE 11. SONAQUEOUS TERNARY SYSTEMS Component Acetone-glycolBenzene Bromobenzene Chlorobenaene Nitrobenzene Toluene Xylene
Temp.,
C.
Citation
27 25 23 22 27 25
Aniline-n-heptane-methylcyclohexane Ethanol-benzene-glycerol
25 25
83
Literature Cited (1) Angelesou, E., BUZZ.SOC. chim. Roomanie, 10, 160 (1929). (2) Baohman, I., IND.ENQ.CHIM.,ANAL.ED.,12, 38 (1940). (3) Bachman, I., J. Phys. Chem., 44,446 (1940). (4) R.J ~* sOc*l 19231 2579. (6) Beach, D. G., and Glasstone, S., Zbid., 1938, 67. 16,380 (1924). ~ ~C. D,,~ i ~ , (7) Bonner, mi. D., J . Phys. Chem., 14,738 (1910).
cHEM.,
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INDUSTRIAL AND ENGINEERING CHEMISTRY
(8) Brancker, A. V., Hunter, T. G., and Nash, A. W., IND. ENO. CHEM.,Ax.4~.ED., 12, 35 (1940). (9) Coull, J., and Hope, H. B.,J . Phgis. Chem., 39,967(1936). (10) Evans, T.W., IND. ENO.CHEM.,ANAL.ED., 6,408(1934). (11) Evans, T.W.,J . Chem. Education, 14,408 (1937). (12) Gibbs, J. W., Trans. Conn. Acad., 3, 176 (1876). (13) Gibby, C. W.,J . Chem. SOC.,1932,1540. (14) Zbid., 1934,9. (15) Hand, D.B.,J. Phys. Chem., 34, 1961 (1930). (16) Horiba, S.,Mem. Coll. Ew. Kyoto I m p . Univ., 3, 63 (1911). (17) International Critical Tables, Vol. 111,pp. 398 et seq., New York, McGraw-Hill Book Co., 1929. (18) Kono, M., J. Chem. SOC. Japan, 44,406(1923). (19) Lloyd, B. A., Thompson, 8. O., and Ferguson, J. B., Can. J . Research, 15B,98 (1937). (20) McDonald, H.J., J. Am. C h m . SOC.,62,3183 (1940). (21) Mason, L. S.,and Washburn, E. R., Ibid., 59,2076 (1937). (22) Mertslin, R. V., and Zhuravlev, E. F., J . Gen. C h m . (U.9. S. R.), 8, 635 (1938). (23) Meurs, G.J. van, 2.physik. Chem., 91,313(1916). (24) Miller, W.L., and McPherson, R. H., J . Phys. Chem., 12, 706 (1908). (25) Mochalov, I., Bull. inst. recherches biol. Perm, 11, 25 (1937). (26) Mochalov, I., J . Gen. C h m . (U. 9. S . R.)8,529(1938). (27) Mueller’ Pugs’ey* I.* and Ferguson’ J’ ” phys* Chem., 35, 1313 (1931). (28) Perel’man, F.,Bull. acad. sci. U . R. S. S., 1936, 379. (29) Pound, J. R.,and Wilson, A. M., J . Phys. Chem., 39,709 (1935). (30) Reburn! W.T.9 and Shearer, w*N.1 J * Am. Chem*SOC.9 5511774 (1933). (31) Roozeboom, H. E. W., 2. physik. Chem., 15,984 (1894).
**
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(32) Saal, N. J., and Van Dyck, W. J. D., T o d d Petroleum Congr., London, 198.9, PTOC.,2, 352. (33) Schreinemakers, F. A. H., 2.physik. Chem., 11, 76 (1893). (34) Schreinemakers, F. A. H., and Bos,J. L. M. van der H. van den, Ibid., 79,551 (1912). (35) Sherwood, T. K., “Absorption and Extraction”, 1st ed., New York, McGraw-Hill Book Co., 1937. (36) Stokes, G., Proc. Roy. SOC.(London), 49,174 (1891). (37) Tarasenkov, D. N., and Paulsen, I. A,, Acta Phisicochem. U . E . S. S., 11, 75 (1939). (38) Tarasenkov, D. N., and Paulsen, I. A,, J . Gen. Chem. (U. S. 8. R.), 7,2143 (1937). (39) Ibid., 8,76 (1938). (40) Taylor, S. F.,J . Phys. Chsm., 1,461 (1897). (41) Trimble, H. M.,and Frazer, G. E., IND.ENQ.CHE)M.,21, 1063 (1929). (42) Varteressian, K.A.,and Fenske, M. R., Ibid., 28, 928 (1936). (43) Ibid.9 291 270 (1937)* (44)Vold, R. D., and Washburn, E. R., J . Am. Chem. SOC., 54,4217 (1932).
~~~~~~; ~ .
~ : , a ~ ~ ~ ~ n ~ ~ ~ ~ : , E a
61, 1694 (1939). (47) Washburn, E. R., Graham, C. L., Arnold, G. B., and Transue, L. F.,Ibid., 62,1454 (1940). (48) Washburn, E. R.,Hnizda, V., and Vold, R. D., Zbid., 53, 3237 (1931). (49) Washburn, E. R., and Spencer, H. C., Ibid., 56, 361 (1934). (50) Woodman, R.M., Chem. N ~140,~1 (1930). ~ , (61) Woodman, R. M., and Corbet, A. S., J . Chem. SOC.,1925,2461. (62) Wright, C. R. A., Proc. Roy. SOC.(London), 49,174 (1891). (53) Zbid., 50,372 (1892).
DRYING OILS AND RESINS Alkali-Induced Isomerization of Drying Oils and Fatty Acids’ THEODORE F. BRADLEY AND DAVID RICHARDSON American Cyanamid Company, Stamford, Conn.
The isomerizing action of alkali metal hydroxides on unconjugated fatty acids and oils is reviewed, and data are presented which show that the isomerizations proceed in water as well as in alcohols, provided the temperatures are sufficiently high. A commercially feasible process is described which has enabled the formation of from 30 to 50 per cent of conjugated acids from soybean and linseed oils. Such acids have been found to be useful for the production of improved drying oils and resins.
1 This paper is the tenth in the series on “Drying Oils and Resins”. Others appeared in 1937, 1938, 1939, 1940, and 1941.
H E recognized benefits of conjugated unsaturation in drying oils and the continued shortage and high price level of conjugated oils have focused the attention of chemists and industrialists alike upon ways and means of providing adequate supplies a t more reasonable cost. It is not desired to review the numerous attempts which have been made to solve this problem or to detail many of the advances which have been effected within the past few years and which appear to offer so much promise. Attention is therefore directed solely to certain means of converting some of our domestic drying oils such as those of linseed, cottonseed, corn, soybean, and the fish oils into conjugated isomers of enhanced value. It has been recognized in biochemical circles since 1933, at least, that during the saponification of drying and semidrying oils with caustic alkalies in alcoholic solvents the unsaturated linkages tended to undergo a permanent shift of position. This became evidenced by a substantial increase of absorption in certain regions of the ultraviolet spectrum (3, 6, 7, IO). Edisbury, Morton, and Lovern (6) considered this to be due to cyclization. Moore (IO),on the other hand, attributed the increased absorption to the formation of conjugated isomers and reported the isolation of an eleostearic acid isomer from
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