INDUSTRIAL A N D ENGINEERING CHEMISTRY
676
Vol. 18, No. 7
Ethylene Glycol' An Evaluation of Available Information on the Physical Properties of This Compound By C. A. Taylor and Wm. H. Rinkenbach PITTSBURGH EXPERIMENT STATION, BUREAUOF MINES, PITTSBURGH, PA.
THYLENE glycol, CH20H. CH20H, the simplest of the polyhydroxy alcohols, has been of theoretical interest for many years; and during the past twenty years it was realized that many industrial possibilities were offered by the physical and chemical properties of the compound and its derivatives. However, the large-scale production of glycol has been economically feasible only during the past five years, and today it is a new and important industrial chemical because of its increasing use as a solvent, "antifreeze" component, and in the manufacture of glycol dinitrate. This last appears certain to become a n important ingredient in dynamites for general and permissible uses. Much miscellaneous, and in some cases contradictory, information concerning glycol is scattered through the literature. A program for the study of glycol dinitrate having been undertaken by this laboratory, it was considered advisable, in view of the growing importance of this new raw material, to collect, compare, and evaluate the information available concerning the physical properties of glycol itself. This paper contains this information and, in some few cases, values obtained by the writers.
E
General Properties
Under ordinary conditions glycol is a colorless liquid that has little or no odor if pure, is less viscous than glycerol, and has a sweet taste resembling that of glycerol. Commercial glycol is apt to have a slightly "hot" or acid taste, but in the pure compound this is absent. Springer2 has shown that when viewed through a long tube, glycol possesses a blue color which is deeper than that of either water or ethyl alcohol. It is by virtue of lacking color, odor, toxicity, and volatility, together with its miscibility and pleasant taste, that the compound is of use in the manufacture of flavoring extracts. Density
W u r t ~who , ~ discovered glycol, reported a density of 1.125 a t 0' C. It is, then, intermediate between that of water and that of glycerol (1.26). Dunstan4 gave 1.1110 at 25'/4' C.; Walden,5 1.1274 at 0'/4' C., 1.098 at 25'/4O C., 1.0919 a t 50"/4' C.; and de ForcrandG reported 1.1297 a t 0" C. Schwers' measured the density a t a number of temperatures ranging from 11' to 136.5' C. He used extreme care and on plotting his values found they gave a perfectly straight line except for the lower temperatures. From these data he was able to interpolate and extrapolate values at 5-degree intervals from 0' to 197.5" C. He showed that volumes calculated from these values checked well with those actually determined by de Heen.* Since then Riiber, Sorenson, and Thorkelsong have reported a value of 1.113068 a t 20'/4' C. for carefully purified ma1
Received May 6, 1926. Published with approval of the Director,
U. S. Bureau of Minw. 9 Rec. trau. chim., 27, 110 (1908). * A n n . chinr., O S , 400 (1859). 4 Z.physik. Chem., 81, 732 (1905). 8 Ibid., 66, 219 (1906). 4 C o a p t . rend., U P , 569 (1901). 7 Rec. traa. c h i a . , 18, 42 (1909). 3 Mem. cour. aced. 109. Belg.. 1884. 0 Ber., OBB, 964 (1925).
terial, and the present writers have obtained another of 1.11757 at 15.6'/15.6' C. by the use of the pycnometer. Where necessary, values given above were calculated to the basis of 2'/4' C. and all were plotted on a large scale. Inspection showed that the curve over the lower temperature range could he justifiably redrawn so as to miss Schwer's value for 11' C., include his value a t 17.9" C. and those of Riiber, Sorenson, and Thorkelson and of ourselves, and give a more nearly straight line over this range. Values read from this curve from 0' to 25' C. and those given by Schwers for the upper range follow. The value so obtained for 0' C. is 1.1270 as compared with 1.1257 calculated and 1.1260 determined by Schwers. Temperature
c.
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0
Specific gravity xo/40
c.
1.12700 1.12362 1.12015 1.11665 1.11320. 1.10970 1.10601 1.10246 1.09883 1.09513 1.09137 1.08757 1.08363 1.07975
Temperature O
c.
70.0 75.0 80.0 85.0 90.0 95.0 100.0 105.0 110.0 115.0 120.0 125.0 130.0 135.0
Specific gravity x0/40 c. 1.07585 1.07198 1.06803 1.06408 1.06013 1.05618 1.05223 1.04828 1.04433 1.04038 1.03643 1.03248 1.02853 1.02458
Temperature
c.
140.0 145.0 150.0 155.0 160.0 165.0 170.0 175.0 180.0 185.0 190.0 195.0 197.5
Specific gravity x0/40 c. 1.02063 1.01668 1.01273 1.00483 1.00878
1.00088 0.99693 0.98298 0.98903 0.98508 0.98113 0.97718 0.97520
Melting Point
A number of investigators have reported values for this point, de Bouchardat'O stated that glycol solidifies a t from -13' to -25" C. and melts a t -11.5" C. Ladenburg and Krugel,I1 using a thermocouple checked against a hydrogen thermometer, obtained a value of - 17.4' C.; and until lately this value has been accepted as correct although de Forcrande two years later confumed de Rouchardat's value without giving any experimental data or methods. Very recently Parks and Kelley,le using electrical methods of heating and temperature measurement, recorded a value of - 12.3' C. (260.8" K.) for this point. This divergence in the results of careful investigators is not a t all surprising in view of the tendency of glycol and related compounds to supercool. Bouchardat's values for freezing evidence this, and de Forcrand remarks upon it. Recently the writers found13 a similar difference between the apparent freeaing and melting points and tendency to supercool and form a glass in studying the properties of a derivative, .glyool diacetate. It is probable, then, that the true melting point of glycol is intermediate between -17.4' and -11.9' C. Vapor Pressure
I n comparison with those of the common solvents, the vapor pressure of glycol a t a given temperature is quite low. Louguinine,14 by the dynamic method, found that at near atmospheric pressure a variation of 1 mm. in pressure changed Bull. soc. chim., 43, 613 (1885);Comfit. rend., 100, 452 (1885). Ber., 32, IS21 (1899). 12 J . A m . Chem. Soc., 47, 2089 (1925). IaIbid., 48, 1306 (1926). 14 Ann. chim., 13, 289 (1898).
10
11
INDUSTRIAL AND ENGINEERING CHEiMISTRY
July, 1926
the boiling point by 0.048" C. He gave no readings or other experimental data. The only values found in the literature were those given by de Forcrand,ls which are as follows: Temperature
c.
122.5 136.7 140.8
Vapor pressure Mm. Hg 44 83 101
Temperature
Vapor pressure Mm. Hg 357.3 544.3
c.
173.2 186.5
I n addition. the writers have determined the values in the following table. The material used was prepared by fractionating 99 per cent glycol under a pressure of 40 mm. and at a temperature of 120' C. The middle portion, consisting of 60 per cent of the original volume, was retained and carefully kept from contact with air. The apparatus and method used in determining vapor pressures were identical with those used for the same purpose in studying glycol diacetate,'3 with one exception. It was found that glycol had an even greater tendency than its diacetate to superheat, bump, and so give uncertain vapor-temperature readings. ilccordingly, it was found necessary to allow dry air to be slowly drawn through the heated liquid in order to overcome this. The presence of a 20-liter reservoir in the chain made the effect of this on the pressure readings imperceptible, but the results cannot be considered as entirely accurate. Values were determined over the range 103' to 195" C. These were then plotted on a large scale. a smooth, average curve was drawn, and the following valura were read off at regular intervals: Temperature O
c.
105 110 115 120 125 130 135 140 145 I50
Vapor pressure Mm. Hg 27 30 34 42 53
Temperature
68
84 103 125 152
Vapor pressure Mm. H g
c.
155 160 165 1 70 175 180 185 190 195 197.2
708 760
These values check fairly well with those of de Forcrand. Boiling Point
A number of values for the boiling point of glycol have been published. WUrt23 reported 197' to 197.5' C. a t 764.5 mm. Louguinine14 found that varying the pressure by 1 mm. changed the boiling point 0.048' C. and so corrected Wiirtds value to 197.03' C. a t 760 mm. He also reported an experimentally determined value of 197.37' C. a t normal pressure. De ForcrandI5 plotted and extrapolated his rather scanty vapor pressure data to give a boiling point of 197.0' C. a t 760 mm. As shown above, the writers similarly derive a 760 mm. value of 197.2' C. Specific Heat De Heen* reported a mean specific he& of 0.632 from 17' to 96' C.; de Forcrand,6 0.6268 from 13" to 139' C . , 0.5848 from 13' to 59.6' C., 0.5365 from -22.8' to 0' C.; Louguinine,la 0.6808 from 20' to 195' C.; and Schwerst7 0.565 from 20' to 24' C. and 0.591 from 33.5' to 36.5' C. Lately Parks and Kelley12 have determined specific heat values for glycol, using electrical methods of heating and temperature measurement. They give values at certain temperatures. Temperature
c.
-184.6 -183.9 -182.4 -182.2 -165.2 -118.5
CRYSTALLINE GLYCOLTemSpecific perature heat c. 0.103 -79.7 0.163 -77.9 0.165 -76.2 0.166 -74.6 0.186 -63.4 0.236 -59.0 -45.8
Compf. rend., 132, 688 (1901). 18 A n n . chim., 26, 234 (1902).
16
Specific heat 0.277 0.279 0.282 0.283 0.301 0.309 0.334
-LIQVID GLYCOLTemperature Specific heat 0 c. -11.0 0.537 9.8 0.538 2.6 0.552 5.2 0.556 15.0 0.571 20.0 0.575
-
677
When the values of Parks and Kelley are plotted, it is found that those for crystalline glycol form an irregular curve, while those for liquid glycol give a straight line. On plotting the results of the other investigators by mean temperatures over the ranges given for mean specific heat values, it is found that these approximate a straight line of the same slope as and representing a deviation of about -2 per cent from that given by the data of Parks and Kelley. The straight line given by the values of Parks and Kelley can be expressed by the equation H s P = 0.00125t
+ 0.55
where t is expressed in degrees Centigrade. From this we can calculate the following values : Temperature C. -10.0 0.0 20.0 40.0 60.0 80.0
Specific heat of liquid glycol 0.538 0.550 0,575 0.600 0.625 0.650
Temperature O
C
100.0 120.0 140.0 160.0 180.0 195.0
Specific heat of liquid glycol 0.675 0.700 0.725 0.750 0.775 0.794
Heat of Fusion
De Forcrand,6 after assuming a value for the specific heat of solid glycol, reported an average value of 2.66 kg. calories per mol (42.9 calories per gram) as the heat of fusion of glycol. Parks and Kelley12obtained values of 44.68 and 44.84 calories per gram. I n view of the manner in which these determinations were made, the average of these-44.76 calories per gram-should be accepted. This value and those given for specific heats by these same investigators are expressed in 15' C. calories. Parkst7 has previously obtained a value of 25.76 calories per gram for ethyl alcohol. Bertholetls has determined 42.5 calories per gram for glycerol. Latent Heat of Vaporization
LouguinineI4 reported a value of 194.49 calories per gram, but later16 gave 190.90 calories per gram as being more probably correct. De Forcrandls used his vapor pressure data to calculate values by means of the Clapeyron equation. H e obtained
c. 130.6 160
S
188.4
Calories/gram 235.5 228.2 210.3
These values show an approach to that found by Louguinine Ptt the boiling point. Heat of Combustion
Louguininelg reported a heat of combustion value of 283,293 calories per gram molecule under ordinary pressure for glycol and a corresponding value of 392,455 calories for glycerol. Stohmann and Langbein,20after careful work, gave 281,700 calories under constant pressure or 281,400 calories a t constant volume. Parks and Kelley,12 for purposes of calculation, have corrected the value for constant pressure and use the figure 282,200 calories per gram mol. Heat of Formation
Stohmann and Langbein,20 using their heat of combustion data, calculated a molecular heat of formatiw value for glycol of - 113,300 calories under constant pressure. Parks and Kelley12 calculate -111,100 calories per gram mol a t constant pressure and a free energy value of -82,500 calories per gram mol. 1'
J. A m . Chcm. Soc., 47, 338 (1925).
18 Ann. 19 (0
chim., 18, 386 (1879). I b i d . , 20, 558 (1880). J . prakt. Chem.. 45, 305 (3892).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
678
Heat Conductivity
H e a t of Dilution
When glycol and water are mixed, heat is evolved. De Forcrand'6 studied the contraction of such mixtures and concluded that a hydrate having the composition CzHd(0H)z.2H20 and a heat of formation of 0.60 calorie was formed. Schwers7 also studied the effect of mixing varying proportions of glycol and water, and found that the maximum effect is obtained by mixing 37 per cent glycol and 63 per cent by weight. This he took to indicate the formation of a hydrate of composition CZHd(0H)z.6H20. A consideration of the temperature-concentration equilibrium diagram for the glycol-water system to be given later and of the hygroscopic properties of glycol show that de Forcrand's conclusion as to the composition of the molecular compound formed is correct; and that Schwers found the point of maximum exothermic effect a t another concentration can be ascribed to the molecular compound having a positive heat of solution. That ethylene glycol is very hygroscopic is well known. De Forcrand compared16 it with sulfuric acid and absolute ethyl alcohol in this respect and stated that 100 parts by weight took up about 30 parts in 1 week and 60 parts in 2 weeks. This last concentration approximates the compound C Z H ~ ( O H ) ~ . ~and H ~appears O to be the limit.
-
Riiber, Sorenson, and Thorkelsons also determined the molecular refractivity of glycol, using the sodium D line. They gave M a and ML values of 24.03 and 14.49, respectively, which at a temperature of 20" C. and a density of 1.113068 20"/4" C. correspond to values of 1.4311 and 1.4331, viscosity
Glycol is more viscous than water and less so than glycerol. Dunstan4 determined its 7 value as 0.1733 a t 25" C. Jonesz3 found a similar 7 value of 10.96 for glycerol a t 18.28" C. More recently Pribram and HandIz4studied the specific viscosities of glycol and gave 350 and 300 a t 55" and 60' C., respectively. Solubility and I n f l a m m a b i l i t y Glycol is miscible in all proportions with water, glycerol, ethyl, methyl, and amyl alcohols, acetone, glacial acetic acid, pyridine, and furfuraldehyde. It is not miscible with benzene, toluene, xylene, chlorobenzene, chloroform, carbon tetrachloride, carbon bisulfide, or ether. Knorrz6 states that 100 parts of ether dissolve 1.1 parts of glycol. Glycol is noninflammable. Animal Metabolism
G e r m i c i d a l Value
Fuller2?also found that as a preservative against bacterial, yeast, or mold growth, glycol shows a close approach to ethyl alcohol and is superior to glycerol.
Refractive I n d e x
EykmaqZ2using the a and P hydrogen lines and the A (atmosphere), determined the refractive indices of glycol a t different temperatures and gave:
Phil. Mag..'S'I, 451 (1894). Monatsh. Chem., 2 , 643 (1881). 26 Ber., 30, 909 (1897). *e J . B i d . Chem., 3, 57 (1907). 27 THIS JOURNAL, 16, 624 (1924).
21 24
Physik. 2.. 12, 417 (1911). Rec. Irav. chim., 14, 185 (1895). ~~~~
REFRACTIVE INDEX FRACTIVITY, Mol. (COR.TO VACUUM) (n 1)VM O C. DP vol. HE H, A H8 H m A 19.3 1.1134 55.68 1.4&28 1.43098 1.42209 24.i1 24.60 23.50 138.8 1.0230 60.61 1.40063 1.39406 1.38606 24.28 23.88 23.40
When taken into the animal system, glycol is oxidized. Dakin found26 that a marked oxaluria is the result of glycol administration but that this is not appreciable when glycol is injected subcutaneously into rabbits. Fullerz7was unable to detect pathological symptoms when glycol was administered in moderate doses to rabbits.
Hygroscopicity
22
~-
MnI.ECI:L.AR RE.__.._ ~~
The only measurement of this value for glycol is that of Goldschmidt,21 who found that the heat conductivity of glycol measured in c. g. s. units (A) and multiplied by lo7 is 6350 a t 0" C. as compared with similarly derived values of 15,000 for water and 4455 for ethyl alcohol at 0" C. and 7251 for glycerol a t 10" C.
21
VOl. 18, xo. 7
~
Dust Respirators Tested by Bureau of Mines A study of various types of respirators as safeguards against injurious dusts encountered in mining and many other industries has been conducted by chemists of the Pittsburgh Experiment Station of the Bureau of Mines. Many industrial dust respirators, and many fab,rics and filtering materials, including cheesecloth, canton flannel, bleached and unbleached muslin, filter paper, and absorbent cotton, were tested. The filtering efficiencies of the respirators were determined by passing air containing either tobacco smoke or suspended silica dust in minute particles through the respirator at varying rates. A small stream of the air that escaped from the respirator was viewed in a beam of light in a dark box. An equal stream of the unfiltered air was viewed alongside the first stream, and the unfiltered stream was diluted with measured portions of pure air until the two streams reflected light of equal intensity. In this way a measure of the filtering efficiency of the respirators was obtained. While the laboratory study has shown t h a t most dust respirators are not highly efficient in removing tobacco smoke from air, it has been found t h a t a filter which removes 50 per cent of tobacco smoke from air flowing at the rate of 85 liters per minute is very efficient in restraining ordinary industrial dusts, also smokes from burning wood or carbonaceous material, such as those encountered by city firemen. Hence, 50 per cent efficiency against the tobacco smoke by the laboratory tests has been adopted by the Bureau of Mines as a standard requirement, together with others, for approval of respirators or gas masks to afford protection from smoke or dust. To-
bacco smoke was used in the experiments for the reason that, being extremely difficult to arrest, i t subjected the respirators t o a severe test. As the laboratory tests performed on the dust respirators were severe, the low efficiencies do not indicate the general efficiencies of these respirators under all industrial conditions. Many of the industrial dusts are less difficult to restrain, and the over-all efficiency of the respirators in actual service is correspondingly higher. The tests thus show that as a rule the respirators are very beneficial in removing such injurious dust from inspired air. The discomfort caused by respirators covering the face, the heat engendered thereby, irritation of the skin at contact with the respirators, poor fit which allows leakage in some instances, or leakage a t valves, and resistance t o flow of the air breathed, are the most serious disadvantages of respirators. Resistances of industrial dust respirators were 0.25 inch t o 1.5 inches of water t o air flowing at 85 liters per minute. The flat felt filter had a resistance of 2.25 inches and the gas-mask canister 3.6 inches. While the use of respirators should be encouraged among workers in dusty industries, the Bureau of Mines' tests show t h a t respirators cannot be considered a final safeguard. Further details regarding these tests are contained in Serial 2745, "Tests and Characteristics of Dust Respirators," by S . H. Katz, G. W. Smith, and E. G. Meiter, copies of which may be obtained from the Bureau of Miner, Department of Commerce, Washington, D. C.
