The Svstems: Glycol-n-Amyl Alcohol- ater and Glycol-n-Hexyl Alcohol-Water J
G. S. LADDHA AND J. M. SMITH Purdue University, Lufayette, Ind.
st,andard burets. They were then placed in the 20 C. constanttemperature bath for aperiod of one hour. The titration was carried out in several steps, in order t'hat the mixture could be frequently returned to the constant-temperahre bath to ensure maintenance of the 20" C. temperature. The end point was taken when turbidity appeared over the entire solution. Some difficulty was encountered, at first, at' high n-ater concentrations because of the tendency of the solutions to foam upon vigorous agitation. However, by gentle agit'ation over a relat,ivelg long period, a sharp end point and reproducible results could be obtained. Check experiment's viere carried out over the ~rholerange of the solubility curve, and in t'he region of the unusual indentation (see Figures 1 and 2) several tests were made to establish each point. The tie lines were located by preparing rnisturrs of the three components which would give two phases at equilibrium. After vigorous agitation t'he mixtures m r e placed in the constant temperature bath for- a minimum period of one hour. The individual phases were separated and weighed and the composition of each evaluated by solution of the necessary material balance equations. The compositions of the initial mixtures are indicated by circles within the two-phase region in Figures 1 and 2.
Solubility data and equilibrium phase compositions were measured at 20" C. for the following ternary liquid systems : ethylene glycol-waterprimary n-amyl alcohol and ethylene glycol-water-n-hexyl alcohol. The equilibrium results indicate that the ratio of the glycol concentrations in the water and alcohol phases is greater than unity in both cases and highest for the n-hexyl alcohol system. Previously proposed methods of correlating tie-line data are applied to the present results.
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COSXECTIOS with a study of the extraction of ethylene glycol from aqueous solutions, it was found desirable to consider some normal alcohols of medium chain length as solvents. Solubility and equilibrium distribution data are presented in this paper for two such systems: ethylene glycol-n-amyl alcohol (1-pentano1)-water and ethylene glycol-n-hexyl alcohol-water, both a t 20" C. The results are summarized in Tables I and I1 and Figures 1 and 2. PURITY O F MATERIALS
1. ETHYLENE GLYCOL.Carbide and Carbon Chemicals Conipany technical grade glycol was used. It had a boiling range of 192-195.5 C . with the major portion distilling a t 195.5O C., and a density a t 20" C. of 1.113. The corresponding literature values for pure ethylene glycol are 197" C. (6) and 1.115 (6). 2. n-AMyL ALCOHOL.Xallinckrodt Chemical Company reagent grade 1-pentanol was used. Its specified boiling range was 134-138"C., butnearlyalldistilledat 137°C. The density at 20" C. was 0.817. Published values for pure 1-pentanol are 138' C. (4)and 0.817 ( 4 ) . 3. HEXYL ALCOHOL. Carbide and Carbon Chemicals Company technical. grade hexyl alcohol was used. Its measured boiling range was 156.5-157 C., and density at 20 C. was 0.820. Literature values for pure 1-hexanol are 157.2" C. (4)and 0.819 ( 4 ) . 4. W A T E R . D i s t i l l e d water from the laboratory suppty was used.
Figure 1. Solubility Curves and Tie Lines for System: Ethylene Glycol-n-Amyl Alcohol-Water at 20' C.
EXPERIMENTAL PROCEDURE
All measurements w e r e made a t 20" C. The solubility data were determined by titrating known mixtures of the alcohol and glycol, or water and glycol, Jvith the third component until turbidity appeared. The initial mixtures were prepared by combining volumes of each component measured from
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PO
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4c 4
40
50
V 60
70
80
90
N-Amyl Alcohol
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INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1948
Figure 2. Solubility Curves and Tie Lines for System: Ethylene Glycol-n-Hexyl Alcohol-Water a t 20' C.
Water
10
20
30
40
SOLUBILITY DATA
The solubility curves for n-amyl alcohol (Figure 1) and nhexyl alcohol (Figure 2) are similar in form. Both show the unusual indentation in the alcohol-rich phase, although the effect is not so pronounced in the case of the higher alcohol. The maximum glycol content in a two-phase system with nhexyl alcohol is 76 weight %, while with n-amyl alcohol the figure is about 64 weight yo. The higher value for hexyl alcohol would be expected from its lower solubility in water. TIE-LINE DATA
The compositions of the water and alcohol phases in equilibrium are shown by the tie lines in Figures 1 and 2, and also in Figure 3 where the weight fractions of glycol in the two phases are plotted on ordinary coordinate paper. Both alcohols are
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shown to be poor extractive solvents for removing glycol from aqueous solutions. On the other hand, water would be an excellent solvent for extracting glycol from either alcohol. The distribution coefficient (ratio of glycol in the water phase to that in the alcohol phase) varies from about 3 to 8 for n-amyl alcohol and is even higher for n-hexyl alcohol, as indicated in Figure 3. The curves in Figure 3 have been extrapolated (dotted) to indicate their general trend in approaching the plait point which must fall on the 45' diagonal line-Le., the composition of the two phases in equilibrium must be identical a t that point. I n the case of n-amyl alcohol, this point would probably correspond to a glycol content of near 60% and for n-hexyl near 70%. The higher percentage of glycol in the case of n-hexyl alcohol is in agreement with the experimental results showing a higher distribution coefficient for that alcohol as indicated in Figure 3. , The plait point does not necessarily coincide with the point of maximum glycol concentration on the solubility curve. It has been suggested (2) that 0 distribution curves such as those shown in Figure 3 can be transN-Hexyl formed into straight lines by 90 Alcohol plotting the logarithm of the concentration of the solute in each phase rather than the concentration itself. This method has been found to be satisfactory for many systems (8, 8) as long as the plait point is not approached. The data presented in this paper are correlated in the low glycol concentration range by this method, but show a definite curvature as the plait point is approached. That this method of correlation would apply to the plait point only in special instances is evident from Figure 4, in which are shown the results for the systems studied here and also the data of Treybal, Weber, and Daley (7) on acetone-water1,1,2-trichloroethanewhich extends closer to the plait point. Hand (6) found that distribution data such as that shown in Figure 3 would give a straight-line relationship when plotted as X G I X W versus xh/xff, where XG and xw are the weight fractions of 0.7
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TABLEI. SYSTEMETHYLENE GLYCOL+-AMYL ALCOHOLWATERAT 20" C. Glycol 0.0 4.5 9.0 13.3 17.6 25.6 29.3 32.9 39.9 45.8 52.0
Solubility Data, Weight Per Cent n-Amyl n-Amyl alcohol Water Glycol alcohol 8.9 58.8 14.7 9.1 62.2 10.9 9.7 64.3 7.1 11.0 0.0 1.5 12.0 19.8 1.5 14.6 29.5 1.8 39.3 16.0 1.8 17.3 2.4 48.8 20.2 2.7 58.3 23.4 5.1 61.7 25.5 ... ...
Water 26.5 26.9 28.6 98.5 78.7 68.7 58.9 48.8 39.0 33.2
...
Tie-Line Data Alcohol-Phase Composition, Weight yo Water-Phase Composition, Weight% n-Amyl n-Amyl Glycol Water alcohol Glycol Water alcohol 1.9 9,0 89.1 16.4 82.1 1.5 3.7 9.3 87.0 24.1 74.2 1.7 5.8 9.5 84.7 32.1 66.1 1.8 8.1 9.7 82.2 40.3 57.7. 2.0 9.6 10.1 80.3 44.9 52.8 2.3 14.3 11.1 74.6 51.9 45.5 2.6 18.0 12.1 69.9 58.1 38.5 3.4
Weight FfactIon Glycol in AlcDhol Phase
Figure 3.
Distribution of Glycol between Water and Alcohol Phases
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INDUSTRIAL AND ENGINEERING CHEMISTRY Weight Fraction Acetone in
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Phose
Weight *IsWoter i n Woter Phose
Figure 6.
Weight Fraction Glycol in Water Phase
Figure 4.
Log Plot of Solute Distribution
Correlation of Tie-Line Data
glycol and 1%-ater,respectively, in the water phase and d x : , are the weight fractions of glycol and alcohol in the alcohol phase. Figure 5 shows the data of Table I and I1 plotted in this manner. Straight-line correlations are obtained over the range of concentrations investigated. Bachman (1) suggested that tie-line data could be correlated on a rectangular coordinate plot of weight per cent nonconsolute A in the A-rich phase versua the ratio of the weight per cent nonconsolute -4in the A-rich phase and the weight per cent nonconsolute B in the B-rich phase. This has been done in Figure 6 with good results where the weight per cent of r a t e r in the v-ater phase is plotted versus the ratio of the weight per cent of water in the m,ter phase and the weight per cent of alcohol in the alcohol phase. The advantage of the correlations illustrated in Figures 5 and 6 is, of course, that complete tie-line information can be obtained from the minimum experiniental data required to determine the straight line. NOMENCLATURE
n-eight fract,ion of ZTJI = xeight. fract,ion of = weight fraction of N . ~ = !;-eight, fraction of ZG
=
ZC
glycol in tBheivater phase water in the wat,er phase glycol in the alcohol phase alcohol in the alcohol phase
LITERATURE CITED
Figure 5. Correlation of Tie-Line Data
TABLE11. SYSTEM ETHYLENE GLYCOL-WHEXYL ALCOHOLWATERAT 20 ’ C. Solubility D a t a , Weight Per Cent n-Hexyl n-Hexyl alcohol Kate1 Glycol alcohol Water 99.6 0.5 5.7 0.0 94.3 89.5 10.0 0.5 6.5 74.8 79.6 1 9 . 9 0 . 5 7.4 64.8 69.5 29.9 0.6 7.7 61.5 59.6 3 9 . 7 0 . 7 8.4 55.0 49.6 49.6 0.8 10.0 45.0 39.6 1 . 0 5 9 . 4 1 1 . 4 35.4 29.4 68.5 14.0 2.1 26.0 19.2 7 6 . 5 1 6 , 2 4 . 3 17.0 ... ... 17 .O ... 8.3 Tie-Line D a t a ’ Water-Phase Composition, Weight% Alcohol-Phase Composition, Weight % n-Hexyl n-Hexyl Glycol Water alcohol Glycol Water alcohol 78.4 0.5 21.1 5.8 91.7 2.5 69.9 0.6 29.5 5.8 91.2 3.0 59.3 0.7 6.9 90,5 40.0 3.6 Glycol 0.0 18.7 27.8 30.8 36.6 45.0 53.1 60.0 67.8 74.7
Bachman, Irvin, IXD. ENG.CHEM.,ANAL.ED.,12, 38 (1940). Campbell, J. A , , IND. ESG.CHEM.,36, 1158 (1944). Coleman, J. M.,and Swenson, 0. J., Ibid., 38, 834 (1946). Durrans, T. H., “Solvents,” London. Chapman and Hall, 1944. Hand, D. B., J . Phys. Chem., 34, 1961 (1930). “Handbook bf Chemistry and Physics,” 26th ed., Akron, Ohio, Chemical Rubber Publishing Co.. 1942. (7) Treybal, R. E., Weber, L. D., and Daley, J. F., ISD.EXG.CHCU., 38,817 (1946).
(1) (2) (3) (4) (5) (6)
RECEIVED April 2 , 1947. Presented before the Dn-ision of Industiial and Engineering Chemistiy a t the 111th Meeting of t h e A V E R I C A N CHIXICAL SOCIETY, Atlantic City, S. J.
Vapor Pressure of Pure SubstancesCorrection I n the table of corrections on page 1684 of the December 1947 issue, the reference associated with cymene, CloHla,should have been Gibbons and eo-workers, J . Am. Chem. Soc., 68, 1130-1 (1946). DASIELR. STULL Dom CHEXICAL Co MIDLASD,MICH.
