Freezing Points of the System Ethylene Glycol-Methanol-Water u'
J
FRANK H. CONRAD, E. F. HILL, AND E. A. BALLMAK
HAT an antifreeze of suwas used in the preparation of Missouri School of Mines and Metallurgy, Rolla, Mo. all solutions. perior qualities might be Ethylene glycol is very hydrodeveloped b y m i x i n g scopic. T o determine if an a pre methanol and ethylene glycol, ciable amount of water wouyd be Two of the most widely used antifreeze two of the most widely used absorbed during weighing, the rate materials at the present time are methanol of water absorption was deterantifreeze materials, seems mined in air on an "average day". and ethylene glycol. The possibility of apparent. The use of methanol This was found to be 0.0004 gram would lower the cost and the producing an "optimum" antifreeze from per hour for the equipment used and was considered negligible. glycol would lower the volaa mixture of the two with qualities superior tility of the methanol. Both to either alone makes the quantitative Freezing Point methanol and glycol produce determination of the physical properties Determination only small increases in viscosity of this system over the temperature range ( 8 ) when added to water and The apparatus used in this work hence permit nearly normal radiwas similar to that of Feldman and to which antifreeze mixtures are subjected Dahlstrom ( 4 ) but was simplified. ator circulation and heat transfer. important. This paper presents results of The test tube containing the soluIt was with this idea in mind tion to be investigated was cooled, the freezing point determinations of this that we undertook the present the stopper was removed, and a ternary system as a function of the comwork of the determination of stirrer (copper wire) and a toluene thermometer (smallest graduation position. t h e f r e e z i n g p o i n t s of t h e 0.5 C.) were inserted. The freezternary mixtures of methanol, ing mixture consisted of solid carglycol, and water. bon dioxide and methanol or ethyl ether, depending upon the temperature desired. Two toluene Mixtures of various common antifreeze materials have been thermometers were used, and both were calibrated with the previously proposed, Feldman and Dahlstrom (4) suggested following highly purified substances: water (0 C.), Eastman's the use Of methanok1ycerol mktures and determined the carbon tetrachloride ( -23.00 c.),chlorobenzene ( -45.20 c.), freezing points of the ternary system glycerol-methanoland mercury (-38.9" C.). The solution was stirred until it had reached a temperature approximately 5 " C. below the point water. Aldrich and Querfeld (1) determined the freezing and of crystal formation. The test tube was removed from the bath, boiling points of the system ethanol-methanol-water. inserted in a slightly precooled larger tube, and allowed to warm with constant stirring until the last of the crystals disappeared. Preparation of Solutions The temperature of the solution at the point of crystal disappearance Was recorded as the freezing point. Owing to freeThe methanol and ethylene glycol used were products of the dom supercooling, this has ~ been shown ~to be more ~ Carbide and Carbon Chemicals c ~ The methanol ~ ~ fromand ~ ~ point accurate reproducible than the point of crystal appearance was purified by distillation in a fifteen-plate glass fractionation column, and that portion was collected which distilled in a boiling least two readings were made on all ternary solutions, and range of k0.1' C. at the correct boiling point for the prevailing on approximately one fourth of the entire number two or three pressure The following physical were determined. additional readings were taken by another operator. Duplicate index (Abbb) 1.3306 n'D1,density o,7920 dzu, and boiling determinations by the same operator in all cases agreed within point 64,6 i: o.lo G, at 760 mm. values for pure 0.2" C. down to -30.0' C., and to within 0.3"C. for different methanol are: Refractive index 1.3304 n'D1, density 0.7917 d:O, operators and thermometers. BelOR, - 3 0 , 0 ~ C. the maximum and boiling oint 64.6" C. a t 760 mm. pressure. deviation between readings was 0.5" C. in all cases. The glycofwas purified by distilling under a pressure of 40 mm. and retaining the middle fraction. Dry air was drawn into the distilling flask through a capillary tube to prevent superheating Freezing Point Data and bumping. The product showed a refractive index of 1.4304 n y , a density of 1.1103 dz5, and a freezing point of -13.5" C. Freezing point data were obtained on aqueous solutions of Values in the literature for these three constants of glycol vary ethylene glycol, methanol, and glycol-methanol blends; the considerably, but for comparison the following values are quoted : latter contained 12.1, 21.4, 29.8, 40.2, 49.6, 58.0, 65.0, and Refractiveindex nv 1.4314 (5) to 1.43178 ( f i ) , density d:5 1.1110 78.1 per cent glycol by weight, respectively. The freezing ( 3 ) to 1.1097 ( 8 ) , and freezing point -13.2" C. (5). Methanol-glycol binary mixtures were prepared by weighing to the closest milligram varying amounts of glycol (15 t o 120 grams) from a weighTABLE I. FREEZIXG POIXTS OF AQUEOUSSOLUTIONS ing buret. The approximate weight of methanol was then added in a similar manner to give Soh-Methanol Freesing Point, - ~ l ~ ~ ~ l Freezing PointAldrich Feldman tions differing by approximately 10 per cent inOlsen, Curme % Brunjes, and Present by I. C. T. and and Present crements. total of ten was mixed prepared. These stockAsolutions were"blends" thoroughly by nelght Olsen ( I f ) , Young work, wveight (7). Querfeld Dahlstrom work,
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shaking and allowed to stand in sealed glassstoppered bottles until used. The ternary solutions were prepared by weighing appropriate amounts of the bends directly into an &inch (20.3-cm.) test tube. The desired amount of water was added from a calibrated buret. These were then closed, mixed, and allowed to stand until the freezing points were determined. Freshly distilled water
glycol 10 20 30 36 40 60 60 100
O
-
C.
3.3 7.8 -13.5 -17.1 -22.1 -35.4 -46
...
542
($1,
-
O
C.
2.5 - 7.7 -13.9 -18.6 -23.3 -33.9 -46.4 -11.6
O
-
C.
3.6 8.3 -14.4 -18.2 -22.6 -34.6 -49.3 -13.5
methanol 10 20 25 30 35 40 50
C. 6.6 -15.4 -20.8 -26.4 -32.6 -39.5 -55.6
-
c.
(I), ' C. (41, 6.0 6.3 -14.2 -15.2 -19.0 -20.7 -24.7 -26.5 -30.5 -33.1 -37.5 -39.8
-
-
...
...
O
-
c.
6.8 -15.3 -20.7 -26.3 -33.0 -39.7 -54.9
~
APRIL, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
point data on each series of aqueous solutions were then plotted as ordinates against the per cent by weight of blend in the solution as abscissas, and smooth curves were drawn through the points. By drawing a horizontal line across these curves (Figure 1) a t any desired freezing point, it was possible to read the amounts of each blend required to give a desired freezing point. From these readings and the composition of the glycol-methanol blends it was possible to calculate the composition of the ternary mixtures giving equal freezing points. This information was then plotted as “isothermal” curves on triangular coordinate paper and is shown in Figure 2 for intervals of 10” C. -60 ~
I
543
on warming. Thus, their results mere not entirely free from the effects of supercooling, although the deviation from the results in the present work is in the wrong direction t o be explained on this basis.
15
85
I 6
?+
70
0
5
10
15
2 0 25
3 0 35 4 0 4 5 5 0 55 6 0 6 5 7 0 75 ETHYLENE GLYCOL-
25
FIGURE2. FREEZING POINTSOF AQUEOUSETHYLENE GLYCOL-METHANOL SOLUTIONS Table I1 lists the freezing points for compositions covering practically the whole range investigated. These data were obtained from the freezing point-composition curves and were used in calculating the points plotted in Figure 2. TABLE11. FREEZIKG POINTSOF ETHYLESE GLYCOL-METHANOL BLENDS IN AQUEOUS SOLUTIONS -BlendEthylene
POINTSOF AQUEOUSBLENDSOLUTIONS FIGURE1. FREEZING
A comparison is made in Table I of data obtained on aqueous ethylene glycol and aqueous methanol solutions with data of previous workers. The freezing points of the ethylene glycol solutions obtained in the present work are in some cases higher and in some cases lower than those reported by Curme and Young ( 2 ) . These workers designated the freezing point as the temperature a t which crystals first appeared, and in this method supercooling is inevitable although not always of equal amount. No mention is made in their work of the purification or the degree of purity of the glycol. Results in the work of Curme and Young were presented in graphical form as a plot of freezing point us. per cent by volume of glycol. The values shown for their work in Table I were obtained by converting values read from the curve to per cent by weight using the specific gravity of glycol a t 20’ C. Olsen, Brunjes, and Olsen (11) used Prestone for their investigation, and therefore their results are not exactly comparable to the present work. The results for aqueous methanol solutions are in good agreement with those given in the International Critical Tables (7) and with those of Feldman and Dahlstrom (4). The latter also designated the temperature of crystal disappearance as the freezing point. Aldrich and Querfeld (1) took the freezing point t o be the average of the temperatures of crystal appearance on cooling and of crystal disappearance
glycol Methanol % b y weight 100.0 0 78.1 21.9 65.0 35.0 58.0 42.0 49.6 50.4 40.2 59.8 29.8 70.2 21.4 78.6 12.1 87.9 0 100.0
F. P.. with Following 7 0 by W !. of Total Blend In Aqueous Solution: 10
20
30
40
50
8.3 9.6 -10.2 -10.8 -11.7 -12.2 -12.9 -13.8 -14.8 -15.3
-14.4 -16.1 -17.7 -18.9 -20.1 -21.0 -22.0 -23.6 -23.0 -26.3
-22.6 -25.4 -28.0 -29.4 -31.1 -32.3 -33.6 -35.4 -37.9 -39.7
-34.6 -37.9 -41.6 -44.1 -46.5 -47.7 -49.6 -52.0 -54.0 -54.9
c.
C. -3.6 -4.2 -4.8 -5.0 -5.5 -5.7 -5.9 -6.3 -6.5 -6.8
-
-
c.
c.
c.
It is knoxn that the freezing point curve of aqueous glycol solutions in the region of 60 per cent glycol starts to rise toward the freezing point of pure glycol (IO). For this reason the -50” C. line in Figure 2 is drawn with a dotted line in the lower right-hand corner. -4freezing point of -49.4” C. was obtained for an aqueous solution containing 60.09 per cent glycol by weight. The determination of the boiliiig points and composition of the vapor will be the subject of a future investigation. Literature Cited (1) Aldrich and Querfeld, IXD. ENG.CHEM.,23, 708 (1931). (2) Curme and Young, Zbid., 17, 1117 (1925). (3) Dunstan, 2. physik. Chem., 51, 732 (1905). (4) Feldman and Dahlstrom, IND. ENQ.CHEM.,28, 1316 (1936). (5) Gallaugher and Hibbert, J . A m . Chem. SOC.,58, 813 (1936). (6) Heilbron, “Dictionary of Organic Compounds”, Vol. 11, p. 31, New York, Oxford Univ. Press, 1936. (7) International Critical Tables, Vol. IV, p. 262, New York, McGraw-Hill Book Co., 1928. (8) Zbid., Vol. V, p. 22. (9) Lawrie, “Glycerol and the Glycols”. p. 368, New Tolk,Chemical Catalog Co., 1928. (10) I b i d . , p. 378. (11) Olsen, Brunjes, and Olsen, ISD.EKG.CHEM.,22, 1313 (1930). (12) Skau and Saxton, J . P h y s . Chem.. 37, 183 (1933).
