FREEZING POINTS OF THE TERNARY SYSTEM
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GLYCEROLMETHANOLWATER HARRY B. FELDMAN AND WALTER G.DAHLSTROM, JR. Worcester Polytechnic Institute, Worcester, Mass.
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pared the relative efficiencies of each for antifreeze purposes. Olsen, Brunjes, and Olsen (7) determined the freezing and flow points of the above solutions as well as those of aqueous FIGURE 1. FREEZING P O I K T S OF AQUEOUSGLYCEROL-METHAmethanol solutions. The only recorded investigation of a SOL SOLCTIOSS ternary system which may be used as an antifreeze agent is that of ethanol-methanol-water made by Aldrich and Querfeld (f) who determined the freezing and boiling points of this system. T PRESEKT the most commonly used agents in the form of aqueous solutions for Preparation of Solutions antifreeze purposes are methanol, deThe methanol used was a product of Commercial Solvents natured alcohol, ethylene glycol (Prestone) , and glycerol. In Corporation. After distillation on a steam bath and collection recent years, owing to the development of the synthetic process of the fraction boiling at 64.6" C., it contained 0.1 per cent for producing methanol and the consequent reduction in price water as determined from its index of refraction, using sodium and increase in purity, its use for this purpose is becoming light and an Abbe refractometer (1.3306 at 15" C.). From more and more common in spite of the fact that at the the data given in the International Critical Tables (5) this concentrations ordinarily necessary for adequate protection 3olution contained over 99.9 per cent methanol. The glycerol methanol is more volatile than ethylene glycol or glycerol. mas prepared from a c. P. product by distilling under vacuum This fact, therefore, necessitates more or less constant inand retaining the middle portion of the distillate. This spection of antifreeze solutions containing methanol in order product gave an index of refraction of 1.4740 at 25" C., that volatilized methanol may be replaced. corresponding to a glycerol concentration of 99.4 per cent (6). Glycerol, althongh comparatively nonvolatile, possesses a Freshfy distiiled relatively high molecular weight. When used in the form of water was used an aqueous solution for antifreeze purposes, larger quantities in the preparaof this material must be used, therefore, for a given freezing The possibility of using tion of all aquepoint depression than of the other antifreeze agents. Jloreaqueous solutions of glycerol ous solutions. over, a more serious difficulty is its effect of increasing The glyceroltremendously the viscosity of aqueous solutions, this factor plus methanol as antifreeze methanol binary becoming important a t low temperatures and high concentraagents with qualities s o l u t i o n s were tions. Methanol, on the other hand, possesses a relatively superior to s o l u t i o n s of prepared by low molecular weight and, in comparison with glycerol, either alone makes t h e weighing to milliproduces a relatively small increase in viscosity when added quantitative determination grams into a to water (4). 100-cc. weighing These facts indicate that an aqueous solution containing of the physical properties of bottle an approboth glycerol and methanol would combine the advantages this system over the tempriate a m o u n t of each agent to a certain extent and minimize the disadvanperature range to which of one c o m p o tageous properties. Thus, glycerol would decrease the antifreeze mixtures are subnent, adding to volatility of methanol since its concentration for a given ject important. This paper it the approxifreezing point depression would be decreased, and methanol mate amount of would decrease the viscosity increase caused by glycerol. presents the results of the the other comPrevious determinations of freezing point-composition determinations of the freezponent, and relations of systems adapted to antifreeze purposes have, for ing points of this ternary weighing again. the most part, been confined to binary systems. Curme and system as a function of the G r o u n d - gla 6s Young ( 2 ) determined the freezing points of aqueous glycerol, composition. s t o p p e r s mere denatured alcohol, and ethylene glycol solutions and comGLYCEROL-
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NO\-ER.IBER, 1936
INDUSTRIAL -4ND ENGINEERING CHEMISTRY
then inserted into the bottles and the contents niixed by shaking.
Determination of Freezing Points The apparatus used in this work was similar to t h a t used by Aldrich and Querfeld (1) but' was very much simplified : The freezing mixture consisted of solid carbon dioxide and ether contained in a 400-cc. Pyrex beaker. An 8-inch (20.3-cni.) Pyrex test t'ube contained the mixture investigated, and this tube was sealed by a two-hole rubber stopper; through one hole passed a glass stirrer and through the other a toluene thermometer. This thermometer was standardized to the freezing points of the following highly purified substances: water (0" C.), aniline (-6.4' C.), carbon tetrachloride (-23.0" C.), chlorobenzene (-45.2' C.). The following method was used in determining the freezing points; Skau and Saxton (8) showed that it is more accurate than the conventional Beckmann method. I t consists in determining the temperature a t which the last portion of crystals disappears on heating. The freezing point temperature determined in this manner will be somewhat higher than the temperature at which ice crystals begin to deposit in an automobile cooling system because of the tendency to supercool. However, the exact degree of supercooling cannot be determined and the temperature obtained in the above manner affords a safety factor when the data are used in preparing antifreeze solutions. An exact amount of water was weighed into the 8-inch test, tube, and a given amount of the glycerol-methanol solution was added from a weighing buret. The tube containing the solution was immersed in the freezing mixture and the solution stirred until a temperature approximately 5' C. above the freezing point was reached. The tube was placed in a larger tube, and both tubes were immersed in the freezing bath until the temperature of the solution had fallen about 3" below that at which crystals first appeared. The tubes mere removed from the freezing bath, and the temperature was allowed to rise with constant stirring. The freezing point mas taken as the temperature at which the final crystals disappeared. Difficulty was experienced in stirring the solutions of high glycerol content at the lowest temperatures because of the high viscosity of the solutions under these conditions. The procedure was repeated five times for each solution. .4t temperatures down t o -30" C. no two of the five successive determinations differed by more than 0.2" C.; at temperatures below -30" C. t,he maximum deviation of any two det,erminations was 0.4" C.
Freezing Point Data Freezing point data were obtained on aqueous solutions of glycerol, methanol, and glycerol-methanol blends: the labter contained 10.7, 18.8, 30.2, 39.5, 50.5, 60.9, 69.7, 79.6, and 87.8 per cent glycerol by weight, respectively. The freezing point data on each series of aqueous solutions were then plotted as ordinates against the per cent by weight of each methanol-glycerol blend as abscissas, and smooth curves were drawn through the points. From the eleven curves secured in this manner, the corresponding number of compositions possessing the same freezing points could be determined by drawing a line from the desired freezing point parallel to the composition axis and noting the points where this line intersected each of the curves. I n this way data were secured from which "isothermal" curves-i. e., curves representing compositions possessing the same freezing points--could be drawn on triangular coordinates. A comparison is made in Table I of data on aqueous methanol and aqueous glycerol solutions obtained here with data of previous workers. The freezing points of glycerol solutions obtained in the present work are in all cases higher than those of Olsen, Brunjes, and Olsen, no doubt, because of the difference in the experimental methods. I n the work of the latter, who designated the freezing point as the temperature a t which crystals appeared, supercooling was inevitable. This is particularly noticeable in the comparison of the result on methanol where the freezing points for solut'ions of the same composition differ b y more than 2" C. at the higher concentrations. How-
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ever, while the freezing points determined by the present method are definite constants, those determined by noting the temperature of appearance of crystals are not as exact because of the possibility of different degrees of supercooling of the same solution under different conditions. It seems preferable, therefore, t o determine the maximum temperature a t which crystal formation will result. T.4BLE
I. FREEZING POIXTS
OF
AQCEOCSSOLUTIONS
Methanol Freezing Points -Methanol Freezing Points-. Olsen Aldrich % , b y Olsen, %,by weight Brunjes, Present weight Brunjes, and Present glyc- and Olsen ;ark, metha- I . C. T. and Oisen QuerLeld work, erol (71, C. C. no1 i s ) , C. (71, C. ( I ) , C. C. 10 - 2.3 - 1.9 10 - 6 . 3 - 6 . 8 - 6.0 6.3 20 - 5.5 - 5.4 20 -14.2 -15.3 -16.2 -15.2 25 -20.7 -21,2 9.8 - 9.7 30 -19.0 -20.7 40 -15.7 -15.6 30 -26.6 -28.0 -24.7 -26.5 50 -32.5 -23.8 -23.6 .35 -35.2 -30.5 -33.1 -39.5 60 -37.2 -35.5 -42.0 40 -37.5 -39.8
-
-
Although the results of the determination on methanol solutions agree reasonably well with those in the International Critical Tables, they are about midway b e k e e n those determined by Olsen, Brunjes, and Olsen and by Aldrich and Querfeld. The deviation from the results of the former has already been explained, but there seems t o be no reasonable explanation why the freezing points obtained by Aldrich and Querfeld should be higher than those of the present work. I t is significant that there are differences of over 4" C. in some of the freezing points reported b y Olsen, Brunjes, and Olsen, on the one hand, and Aldrich and Querfeld on the other. This divergence of results shows clearly the dependence of observed freezing points upon the method of determination. Table I1 lists freezing points for compositions covering practically the whole range investigated. These data were secured from the freezing point-composition curves. TABLE11. FREEZING POINTS OF GLYCEROL-METHANOL-WATER SOLUTIONS Methanol in Blend
yo by
weight
0 12.2 20.4 30.3 39.1 49.6 60.5 69.8 81.2 89.3
100.0
-Total 10% O
c.
-1.9 -2.5 -3.2 -3.2 -4.2 -4.2
-?.?
-a.o
-6.0 -6.2 -6,3
Blend in Aqueous Soln., % by Weight:20% 30% 40% 50%
c.
-
5.4 6.5 7.7 8.5 -10.0 -10.2 -12.1 -12.5 -13.8 -14.2 -15.2
c.
-
9.7 -11.5 -13.5 -15.5 -17.5 -18.2 -20.5 -21.0 -23.5 -24.5 -26.5
of2
-15.6 -18.8 -21.5 -23.9 -26.5 -29.2 -32.5 -33.7 -36.2 -37.8 -39.8
c.
-23.6 -28.8 -32.7 -35.5 -39.2 -42.8 -46.7 -47.5 -50.0 -51.5 -53.2
On Figure 1 are plotted isothermal freezing point curves on triangular coordinates for intervals of 10" C. Through thc use of these curves the various compositions corresponding to a desired freezing point may be obtained. The determination of t h e boiling points, composition of the vapor, and flow point's will be a subject of future investigation.
Literature Cited (1) -4ldrich and Querfeld, IND.ESG. CHEM.,23, 708 (1931). (2) Curme and Young, Ibid., 17, 1117 (1925). (3) International Critical Tables, 1-01. IV, p. 262, New York, McGraw-Hill Book Co., 1925. (4) I b i d . , Vol. T', p. 22. (5) Ibid.,Vol. VII, p. 66. (6) Ibid., Vol. VII, p. 68. (7) Olsen, Brunjes, and Olsen, IND.ENG.CHEM.,22, 1315 (1930). (8) Skau and Saxton, J . Phys. Chem., 37, 183 (1933). REcEIvEn Augwt 8, 1936. The experimental portion of this work is taken from the thesis submitted by Walter G. Dahlstrom, Jr., in 1936 in partial fulfillment of the requirements for the degree of bachelor of science in cheniist r y at Worrester Polytechiiic Institute.
