Freezing Points, Densities, and Refractive Indexes of the System Glycerol-Ethylene Glycol-Water JOHN A. SPANGLER AND EARL C. H. DAVIES, West Virginia University, Morgantown, W. Va.
TABLEI. FREEZING POINTS OF AQUEOUS ETHYLENEGLYCOL SOLUTIONS (' C.) 7'
by
Wefght of Ethylene Glycol
10 20 30 40 50
Curme and Young (3) -2.5 -7.7 -13.9 -23.3 -33.9
Bureau of Olsen Conrad, Standards Brunjea, 'and Hill, and (6) Olsen (IO) Ballman (2) -2.9 -3.3 -3.6 -9.7 -7.8 -8.3 -17.6 -13.5 -14.4 -26.0 -22.1 -22.6 -37.0 -35.4 -34.6
Present Work -3.71 -8.45 -14.91 -24.05 -36.11
reduced pressure of 40 mm. A fractionating column 45 cm. (18 inches) in length, packed with 7.5-cm. (3-inch) lengths of glass tubing, was used; and all connections were made with groundglass joints. Only the constant-boiling middle portion of the distillate was retained, and the purified product showed at I I , I l\\l 25" C. an absolute density of 1.1101 and a refractive index of 6. 9.74 9 0.26 1.4300. -56 7. 0.00 100.00 I The glycerol used was Baker's analyzed, c. P. material. It was purified (from water) by double distillation a t a reduced pressure of 3 mm. Only 20-cm. (8-inch) fractionating column was used in order to prevent decomposition by superheating. FIGURE 1. FREEZING TEMPERATURES FOR BLENDS OF GLYCBumping was effectively eliminated in both these distillations EROL-ETHYLENE GLYCOL IN WATER by filling the distilling flask to the level of the liquid with coarsefiber Pyrex brand glass wool, and using a large distilling flask (3 liters) heated uniformly by an oil bath. The purified glycerol INCE glycerol and ethylene glycol are both used exshowed at 25' C. an absolute density of 1.2580 and a refractive tensively in the automobile antifreeze industry, the index of 1.4720. Comparison with the density tables given in freezing points of aqueous mixtures of these compounds should the International Critical Tables (6)and the Bosart and Snoddy tables ( 1 ) showed this glycerol to be 100 per cent pure. The be of interest, The following material gives the freezing glycerol and ethylene glycol were points of mixtures of these kept in 2-liter Erlenmeyer flasks, three comoounds. and an easv equipped with soda-lime tubes and and exact' methoh of analysfs siphon tubes. The liquid was forced WATER out through the siphon tube by of any mixture of them. means of dried air and was thus exposed to undried air for only a Preparation of Solutions very short time. Ethylene glycol-glycerol mixtures The ethylene glycol was furwere prepared by weighing to the nished by the Carbide and Carclosest milligram varying amounts bon Chemicals Corporation and of glycerol (10 to 126 grams) from was purified by distillation a t a
1
I I 1 I
S
GLYCEROL
ETHYLENE GLYCOL FIGURE 2. FREEZING POINT ISOTHERMS 96
ANALYTICAL EDITION
February 15, 1943
91
of solid carbon dioxide and ethyl alcohol, separated from the freezing point tube containing the liquid by means of a Dewar flask. For the lower freezing points this Dewar flask was replaced by an ordinary freezing point tube, thus furnishing an air jacket. Both cooling and heating curves were run, and three check determinations were made on both the freezing point and the melting point. The exact freezing points and melting points were obtained by extrapolation in the manner explained by Mair, Glasgow, and Rossini (9). The freezing point values differed from the melting point values by 0.02" to 0.05", the latter figure applying to the lower freezing points.
Freezing Point Data Tables I and I1 compare the values obtained in the present work with the freezing points obtained by other investigators for aqueous solutions of ethylene glycol and aqueous solutions of glycerol. The values obtained in the present work are in good agreement with the average of the values FIGURE3. REFRACTIVE INDEXES AT 25" C. FOR BLENDS OF GLYCEROLobtained by the other investigators. The values ETHYLENE GLYCOLIN WATER for the low& temperatures s f o d d be much more accurate than the values obtained by the other investigators, because visual observation does not enter into the determination of the freezing point TABLE 11. FREEZIKG POINTSOF AQUEOUS GLYCEROL with the apparatus used in the present work. The inSOLUTIONB ( " C.) creased accuracy due to this independence from visual obOlsen, servation is due to the fact t h a t mixtures of ethylene glycol Bureau of Brunjes, Feldman % by Weight of Lane Standards and and Present and glycerol with water get extremely viscous at low temGlycerol 10
20 30 35 40 46 50 55 60
(8) -1.6 -4.8 -9.5 -12.2 -15.4 -18.8 -23.0 -28.2 -34.7
(6) -1.7 -4.8 -9.4 -12.3 -15.6 -19.4 -25.8
Olsen (IO) -2.3 -5.5 -9.8 -12.4 -15.7 -18.6 -23.8
Dahlstrom (4) -1.9 -5.4 -9.7
..
-37.2
-35.5
..
-15.6 -23.6
..
Work -1.99 -5.21 -9.92 -12.65 -15.93 -19.90 -24.55 -30.40 -37.90
a weighing buret. Ethylene glycol was then added in a similar manner to give solutions having approximate ratios of glycol to glycerol of 9 to 1, 7.5 to 2.5, 5 to 5, 2.5 to 7.5, and 1 to 9. Quantities of these blends were then weighed into groundglass stoppered Erlenmeyer flasks and definite weights of water added from a standard, calibrated buret to make solutions containing approximately 10, 30, 50, 70, and 90 per cent of each blend. For the freezing point curves, it was necessary to weigh out tmyo more Sam les for each blend at approximately 60 per cent b i n d in order to establish the eutectic point.
TABLE 111. FREEZIKG POINTSOF ETHYLENE GLYCOL-GLYCEROL BLEXDSIN AQUEOUS SOLUTIONS Blend Ethylene glycol Glycerol % b y weight 100.00 0.00 90.26 9.74 71.40 28.60 51.13 48.87 25.03 74.97 11.28 88.72 0.00 100.00
Freezing Points for the Following % b y Weight Blend in Aqueous Solution 10 20 30 40 50 C. O C. O C. C. C. -3.71 -8.45 -14.91 -24.05 -36.11 -3.54 -23.46 -35.35 -8.26 -14.57 -3.24 -22.21 -33.59 -7.71 -13.83 -30.71 -2.99 -7.10 -12.80 -20.50 -2.81 -6.64 -11.72 -18.59 -28.05 -2.57 -6.18 -10.88 -17.20 -26.09 -1.99 -5.21 -24.55 -15.93 -9.92
of T o t a l 60 C.
... -49:84 -46.12 -43.29 -40.45 -37.90
Freezing Point Determination The freezing point apparatus used in this work consisted essentially of a 2OO-junction, copperconstantan thermocouple (one hundred junctions a t each end), one end immersed in an ice bath and the other end in the solution, the freezing point of which was being determined. Provision for attaining equilibrium a t each end was made by a pro riate means of stirring, and the voltage deveropei was measured by means of a Leeds & Northrup Type K potentiometer and a Leeds & Northrup Type C galvanometer. The use of a thermocouple containing this number of junctions permitted an accuracy well within the limits of errors of the calibration values, using equipment generally available in most chemical laboratories. The thermocouple was calibrated by means of the following highly purified substances: water (0" C.), aniline (-5.98" + C.), carbon tetrachloride (-22.85' C.), chlorobenzene (-45.20' C.), and chloroform (-63.45" C.); The accuracy of these values vary from +0.04 a t . 0" to +O.O6O a t -65.0" C. The liquids being studied were cooled by the use of a bath
PER CENT WATER (BY WEIGHT)
FIGURE 4. DENSITIESAT 25" C. FOR BLENDS OF GLYCEROL-ETHYLENE GLYCOL IN WATER
98
INDUSTRIAL AND ENGINEERING CHEMISTRY
peratures and tend to trap air bubbles during stirring; this causes the solution to take on a milky appearance, making it very difficult to determine whether any crystals are present or not. Figure 1 shows the curves obtained by plotting the freezing point against the per cent of total blend in aqueous solution. From these curves, values were taken for plotting isothermal curves on a triangular coordinate for every 5" as shown in Figure 2. Table 111 lists the freezing points for compositions covering practically the whole range investigated. These data were obtained from the freezing pointcomposition curves.
Vol. 15, No. 2
WATER
Density and Refractive Index Data The refractive indexes and absolute densities (all weighings reduced to vacuum and water of maximum density taken as unity) were determined a t 25" C. using an Abbe refractometer and Leach pycnometers. Figures 3 and 4 show the curves obtained by plotting, respectively, the refractive index and densityagainst the per cent of total blend in
ETHYLENE GLYCOL I"IGVRE5 . COXSTAXT REFRACTIVE IKDEXCURVES AT 25" C.
WATER
GLY CERO L
aqueous solution. From these curves, values were taken for plotting the constant refractive index and the constant density curves on the triangular coordinates shown in Figures 5 and 6. Tables IV and V list the refractive indexes and densities for compositions covering the whole range of this system. These data were obtained from the refractive index-composition and the density-composition curves. Figure 7 shows both the constant density curves and the constant refractive index curves. These curves intersect each other a t an angle of approximately 30". This makes it possible to determine accurately the amount of glycerol and ethylene glycol in an aqueous solution by merely obtaining the density and refractive index for that solution. The point of intersection of the density and refractive index curves for that solution gives the composition immediately. This method of analysis is more convenient, easy, and exact than any chemical means hitherto developed, and should be of great value in determining the ethylene glycol -1.11 content (as an impurity) in glycerol, for the hygroscopic ETHYLENE DENSITY nature of both of these subGLYCOL stances makes it a ternary FIGCRE 6. COKSTAKT DENSITY CURVESAT 25' C. system.
ANALYTICAL EDITION
February 15, 1943
99
TABLE IV. REFRACTIVE INDEXES OF ETHYLENE GLYCOL-GLYCEROL BLENDSIN Blend Ethylene glycol Glycerol by w e b h t 100.00 0.00
r0
SOLUTIONS AT 25" C.
,---- Refractive Indexes for t h e Following % b y Weight of T o t a l Blend in Aqueous Solution10 20 30 40 50 60 70 80 90
1,3723 1.3736 1.3757 1 .3786 1.3809 1.3826 1.3838 0.00 Refractive indexes for glycerol taken from Iyer a n d Usher (7).
90.26 71 40 48.87 25.03 11.28
AQUEOUS
1.3517 1,3522 1.3533 1.3547 1.3558 1,3563 1.3569
9.74 28.60 51.13 74.97 88.72 100.00"
1,3621 1.3628 1.3643 1.3666 1,3683 1.3693 1.3701
1.3828 1.3843 1.3871 1.3904 1.3939 1.3960 1,3977
1.3927 1.3946 1.3981 1.4026 1.4073 1.4100 1.4123
1.4025 1.4045 1.4092 1.4147 1.4209 1.4243 1.4273
1.4118 1.4148 1.4202 1,4269 1.4343 1.4388 1,4427
1.4210 1.4243 1.4311 1.4393 1.4482 1 ,4529 1.4568
O F ETHYLENE GLYCOL-GLYCEROL BLESDSI N L4QUEOUSSOLUTIONS AT 25 TABLE v. DENSITIES
Blend Ethylene glycol Glycerol % by weight 100.00 0.00
10
20
30
40
9.74 28.60 51.13 74.97 88.72 100.00"
FIGURE 7.
CONSTANT
50
1,0619 1.0682 1.0791 1.0929 1.1078 1.1165 1.1238
60
1,0733 1,0813 1,0952 1,1110 1,1302 1.1411 1.1511
DESSITYAND REFRACTIVE hDEX
Literature Cited (1) Bosart, L. W., and Snoddy, A . O., IND.ENQ.CHEM.,1% 506-10 (1927). (2) Conrad, F. H., Hill, E. F., and Ballman, E. A., Ibid., 32, 542-3 (1940). (3) Curme, G. O., Jr., and Young, C. O., Ibid., 17, 1117 (1925). (4) . . Feldman. H. B.. and Dahlstrom, W. G., Ibid.. 28, 1316-22 (1936). (5) IND. ENG.CHEM.,NEWSED., 4, 1 (Jan. 20, 1926).
70
1,0848 1.0937 1.1100 1.1289 1.1527 1.1666 1.1784
80
90
1.0946 1.1061 1.1239 1.1478 1.1755 1.1918 1,2055
CURVES .%T 25"
1,4300 1,4343 1.4420 1.4516 1,4624 1.4670 1.4722
c.
Densities for t h e Following % by Weight of T o t a l Blend in Aqueous Solution
1,0367 1,0495 1.0097 1,0231 1.0405 1.0544 1.0111 1,0259 1,0631 1,0300 1.0469 1.0128 1,0738 1,0349 1.0541 1.0150 1.0629 1.0857 1.0172 1,0406 1,0674 1.0921 1,0193 1,0438 1.0207 1,0453 1.0707 1.0971 Densities for glycerol taken from Bosart a n d Snoddy tablee (I).
90.26 71.40 48.87 25.03 11.28 0.00 a
7
100
1.1032 1.1157 1.1379 1.1670 1.1976 1.2161 1.2320
100
1.1101 1.1250 1.1521 1.1832 1.21h7 1.2399 1.2580
c.
International Critical Tables, Vol. 3, p. 121 (1928). Iyer, M.P. I. V., and Usher, F. L., J . Chem. Soc., 127,841 (1925). Lane, L. B., IND.ENG.CHEM.,17, 924 (1925). Mair, B. J., Glasgow, R. G., Jr., and Rossini, F. D., J . Research N a t l . Bur. Standards, 26, 591-620 (1941). (10) Olsen, J. C., Brunjes, A. S., and Olsen, J . W., IND. ENQ.CHEM., 22, 1315-17 (1930). (6) (7) (8) (9)
PRESENTED before t h e Division of Physical a n d Inorganio Chemistry a t the 104th Meeting of t h e AMERICAN CABMICAL SOCIETY, Buffalo, N. Y .
