Vapor-Liquid Equilibria IN THE TERNARY SYSTEM BENZENE-CY CLOHEXANE-NITROMETHANE AND THE THREE BINARIES H. I. WECK AND HERSCHEL HUNT D e p a r t m e n t of C h e m i s t r y , Purdue University, L a f a y e t t e , Ind.
THE
secaration of the components of a liquid mixture by fractional distillation is of significant import,ance both icdustrially and in the laboratory, and the design of distilling apIaratus fcr the separation of a particular mixture is necessarily based on the vapor-liquid compositions existing a t equilibrium. The addition of a third component to a binary liquid mixture to effect an otherwise impossible separation by the method of fractional distillation due to azeotrope formation is becoming more important industrially. Separation of liquid mixtures by distillation is made possible by the fact, that a t equilibrium in most, systems the liquid and vapor differ in composition. Certain liquid'mixtures forni azeotropes or constant boiling mixtures. This type of mixture will give a vapor of composition identical with that of the liquid a t equilibrium, making i t impossible to separate the components by distillation. Vapor-liquid equilibria of binary systems are usually represcnted graphically by plotting vapor compositions against liquid compositions. This met'hod may be employed to represent the vapor-liquid equilibria of a ternary system graphically, if the concentration of one of the constituents is kept constant while ihe other tKo are varied. BENZENE
Solubility Curve for Ternary System BenzeneCyclohexane Nitromethane Figure 2.
-
Tie lines and lines of constant refractive index and density at 2S' C. 20
80
PERCENT
Figure 1.
NITROMETHANE
Equilibrium Diagram of NitromethaneCyclohexane
The object of this research was to determine the vapor-liquid equilibiia for the binary systems benzene-cyclohexane, benzenenitromethane, and nitromethane-cyclohexane. and for the ternary system benzene-cyclohexane-nitromethane. Because nitromethane and cyclohexane are not completely miscible, their phase diagram is treated separately in Figure 1. In his work on binary mixtures Othmer developed an equilibrium apparatus which was also found effective for use with ternary systems (9). This apparatus consisted of a flask, above which a a s a specially designed still head to prevent refluxing, and a vapor condenser leading to a distillate receiver, from which the distillate could be returned continuously to the still or a sample of the distillate could be drawn off for analvsiq. Equilibrium was established over a period of time between the liquid in the flask and the distillate retallied
2521
2522
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 12
TABLE I. SOLUBILITY CURVEAT 25" C. FOR R E ~ Z E S I C CYCLOHEXAXE-XITROMICTHAXE Cyclohexane, Wt. % 97.80 91.63 84.98 76.40 67.08 57.64 45.61 39.13 35.01 30.97 23.56 18.32 13.06 8.87 7.51 7.08 5.10
Benzene, W t . 70
Sitromethane.
0.00 5.09 10.46 17.03 22.66 27.19 29.86 29.74 27.19 28.63 26.72 23.87 18.91 11.40 7.73 6.12 0.00
2.20 3.29 4.50 G.57 9 . 67 15.17 24.52
Wt. yo
31.1Y
37.81 40.41 49,73 57.81 0 8 . OH 79.72 84.76 80.83 94.90
TABLE11. TIE LISE DATA FOR B E ~ Z E S F ~ - C Y C L O € I E X . ~ N E KITRolTETHAXE WEIGHT % 'A IN T H E LlOLJID
Figure 3. Vapor-Liquid Equilibria i n Binary Systems Benzene-Cyclohexane and Benzene-Nitromethane
Cpdilie, Langdon, and Keges reported the effect of added coniponent,s on the relative volatility of the binary system benzene-cyclohexane ( 1 2 ) . Their results indicated that the addition of nitromethane to the binary mixture benzene-cyclohexane gave as high as threefold increase in the relative volatility of the naphthene relative t o the aromatic component. Complete equilibrium dat,a were not report'ed. This investigation is similar t o the work of Fowler and Hunt, who studied the ternary system, nitromethane-propanol-lmter (3). T h e system nitromethane-henztnen-heptane has been studied by Francis (4). EXPERIMESTA L WORK
Barrett's 1' boiling range, thiophene-free benzene was used in t,hk work. The desired fraction having a refractive index of 1.5012 a t 20" =t0.1" C. and a specific gravity a t 2 O o / 4 O of 0.8784 was obtained by crystallization and dried over Drierite. The nitromethane used was Commercial Solvents technical grade, rect,ified in a still having approximately 12 theoretical plates. The fraction employed in this work had a refractive index of 1.3818 at 20" & 0.1" and a specific gravity a t 20"/4" of 1.1352. Phillips technical grade cyclohexane was used. X product of desired purity having a refractive index of 1.4262 a t 20" i 0.1" and a specific gravity a t 2Oo/4O of 0.7774 was obtained by cryst>allization. Refractive index and density measurements were chosen as rapid and accurate methods for the analysis of equilibrium inixtures. Refractive index nieasurements TTere employed for the analysis of all binaries and a combination of refractive index and density measurements was employed for t,he analysis of the teynarks. Check experiments show the compositions t,o be accurate t,o zk0.3yo and the t,emperatures to &0.0l0. The literature yielded no information concerning the mutual solubilities of cyclohexane and nitromethane. The solubility of nitromethane in cyclohexane was found to be 2.2Y0 by weight nnd the solubility of cyclohexane in nitromethane was found t o he f1.17~ by weight a t 25' zt 0.05" C . The mixture boils a t 69.5' C. and a t t,he t,ernary point it contains 26.5y0nitromethane. T h e end points of the horizontal line in Figure 1 are 91.5y0 nitronitromethane (measured a t 25' C.). methane and 13,8y0 n a t a for the ternary solubility curve of benzene-cj-clohexanenitromethane also were lacking. T h e mutual solubilities of these constituents were determined at 25' zk 0.05' C. (Table I). Several tie lines for the tprnary system were determined a t 25' i 0.05' C. (Table 11).
Nitromethane, Wt.
yo
Cyclohexane,
13enaene, \Ti.
Wt. %
cc
t-pper layer Lower layer
13.5 70.8
2(i. 2
17 5
60.3 12.0
Upper layer Lower layer
6.8 78.9
18.2 12,o
75 0
Top layer Lower layer
4.7 89.3
11.1 4.4
84.2 (i .3
9.1
Figure 2 sliom a triangular plot of the t,ernary system, hen-
zene-cyclohexane-nitromethane,in which line3 of constant refractive index and constant density are plotted. c~irveand tie lines are also indicated.
The solubility
An apparatus similar t o the one employed by Schumacher and Hunt was constructed (IO). A manostat pressure control was used t o maint,ain the system a t a pressure of approximately i 6 0 i 0.9 mm. A modified Gwietoslawski ebulliometer of 20-ml. capacity was employed to measure the boiling point of water. The manostat water head was adjusted until the calibrated Beckman thermometer in the ebullionieter t,hermometer well gave a reading corresponding t,o 100.00" c.
Checks of the apparatus, on several mixtures of ethyl alcoholwater indicated that equilibrium between the distillate retained in the take-off receiver and the residual liquid in the still pot mas established after 30 to 40 minutes. DISCUSSIOR OF RESULTS
Complete vapor-liquid equilibrium data were obtained for the binaries, benzene-cyclohexane and benzene-nitromethane. Data for these systems are given in Tables I11 and IT' and Figure 3. Equilibrium data for both binaries give smooth curves, as indicated in Figure 3. Check points at, 59.5, 92.4, a,nd 92.6 weight yo benzene in the liquid for the benzene-cyclohexane curve indicate gnod reprodurihilitg of results.
DATAFOR B ~ S Z E ~ ~ - C Y C I , O I I ~ Z X A S E TARLE 111. EQUILIBRIUM Benzene, W t . Liquid
Vapor
Temi,.,
c.
D e c e m b e r 1954
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE IV.
2523
EQUILIBRIUM D A T AFOR BEXZEXE-KITR~METHANE
--
Beneene, Wt %-Liquid Vapor 90.0 80.0 69.6 59.3 49.3 38.7 28.6 18.0 8.2
TABLE
V,
T p P C
89.1 82.8 77 .a 73.0 08.7
90.45 90.70 94.40 95.30 96.27 98.70 9!>.3 101.2 108.3
68.2 58.0 47.8 30.0
I'IQUILIBRIUX
n.4TA
I
FOR B E X Z E X E - C Y C L O H E X A X E
I~ITROMETHANE
-
Liquid, W t . % ~. Vapor. W t . To l-itroBenCycloNitroBenCyclomethane zene hexane m e t h a n e Bene hexane
W E I G H T % CYCLOHEX4NE IN T H E LIQUID
1-it r omethane
G.P., Plotted, C. W t . yo
11.0 10.7 10.6 10.4 10.4 10.2
78.0 70.0 60.6 51.1 41.2 30.8
11.0 19.3 28.8 38.5 48.4 59.0
9.7 10.0 13.0 14.0 15 2 13.8
78.0 68.0 32.6 43.6 34.5 27.1
12.3 22.0 34.0 42.4 50.3 59.1
78.0 77.1 75.9 74.9 74.7 71.0
10.4
20.2 20.3 20.5 20.0 19.9
70.7 61.0 50.5 38.1 25.8
9.1 18.7 29.0 41.9 51.3
22 2 22.6 18.8 1g.e 12.5
A7 2 54.2 42.5 38.4 25.3
10.6 23.2 38.7 41.9 61.9
77.8 76.8 75.2 74.2 73.1
211.2
29.3 30.9 30.9 30.7
83.5 50 3 40.2 30.0
7.2 18.8 28.9 39.3
21.1 21.3 21.9 23.8
60 2 46.0 34.7 25.4
18.7 32.7 43.4 50.8
77 9 76.7 75.2 71.6
30.8
Cyclohexane Equilibria i n Ternary System a t Constant Weight Per Cent Nitromethane i n Liquid
Figure 4.
The fact t h a t the equilibrium curves for both binaries cross the 45" line indicates t h a t they form azeotropee. T h e azeotrope for benzene-cyclohexane appeals a t a point corresponding t o 55 weight yo in t h e liquid, in good agreement with the figure of 55 v-eight yo benzene reported b y Lecat ( 7 ) . T h e azeotrope for benzene-nitromethane appears a t 87.3 weight yo of benzene in the liquid. A series of runs was made in the one-phase region, in which the amount of nitromethane in the liquid was held constant a t approximately 10, 20, and 30% b y weight. These data are given in Table V and plotted in Figure 4. T h e slight variations in the nitromethane content are not great enough t o vitiate any general trends t h a t the curves may indicate. Although these data are inadequate to show the existence of any ternary azeotropes or t o indicate a possible complete separation of the constituents, several generalizations can be derived. T h e curves indicate t h a t the improvement of the cyclohexane content in the vapor over the cyclohexane content in the liquid a t 30yo cyclohexane and 07, nitromethane is approximately 3.5'?&. With the addition of 10% nitromethane and the same cyclohexane content in t h e liquid, t h e improvement of the amount of cyclohexane in the vapor is 6.1%; a t 20 a n d 3Oy0 nitromethane t h e improvements are 10 and 13.3oJo, respectively. T h e latter is ai-. most a fourfold increase in cyclohexane content of the vapor, as compared t o the increase obtained in the absence of nitromethane. It seems reasonable t o postulate t h a t curves for a nitro-
met'hanc content greater t h a n 30% would follov the same general pattern and improve the volatility of the cyclohexane to a greater degree. This trend cannot be carried beyond the homogeneous system-Le., when the liquid mixture contains lees than 30Yo henzene over most composit,ions the system is no longer homogeneous (see Pigure 2 ) . LITERATURE CITED
(1) E-aker, E. M., and associates, IND. Exo. CHESC.,31, 1260-2 (1939). (2)
Colburn, A. P., Schoenborn, E. hl., and Shilling, D a v i d , I h i d . ,
35, 1250-4 (1943). (3) Fowler, A . R., and Hunt, H . , Ibid.,33, 90-5 (1941). (4) Francis, A. W., J. Phys. Chem., 5 6 , 512 (1952). (5) Jones, C. A . , Schoenborn, E. &I., and Colburn, A . P., IND. ENG.CHEM.,35, GB6-72 (1943). (6) Langdon, W. &I., and Keyes, D. B., Ibid., 34, 938-42 (1942). (7) Lecat, hl.,2. a7soq7. Chcns., 186,119-40 (1930). (8) Marschner, R. F., and Cropper, W. P., ISD. ENG.CrrEar., 38, 262-8- (1946) \----/. (9) Othmer, D. F., I b i d . , 20, 743 (1928).
(10) Sohumacher, J. E., and Hunt, H., Ibid., 34, 701-4 (1942). (11) Stage, H . , and Baunigarten, I. S., Oel u. R o h l e , 40, 126-31 (1944).
(12) Updike, 0 . L., Jr., Langdon, W. &I., and Keyes, D. B., 2'rans. Ana. Inst. Chem. Engrs., 41, 717-36 (1945). RECEIVED for review J a n u a i y 21, 1954. ACCEPTED J u l y 24, 1954 Abstract of a thesis submitted by H. I. Week to t h e faculty of P u r d u e University in partial iulfillnient of t h e requirements ior t h e degree of master of science.
