INDUSTRIAL AND ENGINEERING CHEMISTRY
66
a sled or skate slides on ice. Polar explorers have observed that sledges are pulled with considerable difficulty during the coldest polar weather, because the frictional heat and pressure are insufficient to melt the ice under the runner. An observable greater die pull is registered when the w i r e drawing machine is started after it has been idle for some time when using a wax lubricant. The coefficient of friction with a solid lubricant that meets the conditions outlined above depends largely, it is believed, ilm of lubricant rather on the viscosity and thickness of the f than on the chemical nature of the lubricant or surfaces. Points of asperity a t which conditions of boundary lubrication do exist probably account for not obtaining lower frictional coefficients. The lack of exact parallelism between the re-
Vol. 27, No. 1
sults for copper and stainless steel is believed to be due mainly to differences in adhesion of the lubricant for the metal, to the influence of the temperature attained a t the interface, and to specific effects a t points of asperity. LITERATURE CITED W. B., a n d Doubleday, I., Proc. ROY.SOC.(London)
(1) Hardy, 101A, 487 (1922). (2) Lewis, K. B., Wire & Wire Products,8, 197, 234, 266, 331 (1933). (3) National Metals Handbook, 1933. (4) Williams, R. C., J. Phys. Chem., 36,3108 (1932). RECEIVED September 21, 1934. Presented before the Division of Colloid Chemistry at the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 t o 14, 1934.
Glycol-Water Mixtures Vapor Pressure-Boiling Point-Composition Relations H. M. TRIMBLE AND WALTER POTTS, Oklahoma Agricultural and Mechanical College, Stillwater, Okla.
T
HE vapor p r e s s u r e s of The pressure-boiling point-composition relarefractometer which was calitions f o r glycol-water have been inbrated with solutions of glycol the components of glycolwater solutions are of imand water of accurately known vestigated from 0 to 100 per cent glycol and u p to portance, since these solutions composition by weight. The find m a n y applications. The aPProximateb' aimosPheric Pressure* The boilrefractometer was held a t 25" ing point-pressure relations f o r t w i o u s comC . by running water t h r o u g h only i n f o r m a t i o n along this positions are given in lhe f o r m of the Young its chambers from a large therline in the literature seems to be equation, the constants varying wilh the cornmostat* in the form Of a curve g i v e n by Lawrie ( 3 ) . T h i s r e l a t e s Corrections to be applied to position. the thermometer had been dethe boiling Doints of the s o h - . - These mixiures obey Raoult's law fairly closely. termined by comparing it with tions t o t h e p e r c e n t a g e by a s t a n d a r d thermometer calivolume of glycol in the liquid and vapor phases, presumably for atmoqpheric pressure. It was brated by the Bureau of Standards. Corrections were made believed worth while to extend the data t o include the whole for the emergent stem. range of pressures from 0 to 1 atmosphere. Boiling in the still was promoted by introducing boiling tubes of glass. There was no bumping, even a t the lower APPARATUS AND METHOD pressures, and the readings of the thermometer showed no I n this work at the higher temperatures, a form of the irregular variations. It is believed that superheating was small or absent. At the start of a run the temperature rose, Othmer still (4), modified as shown in Figure 1, was used: The still was made from a Kjeldahl flask, and heating was because of preferential loss of water from the boiling liquid. carried out by means of a Cenco electric heater with a 1.25-inch When distillate began to run back from the collecting cham(3.1Scm.) opening in the Transite top instead of by an immersed ber, the temperature fell slightly but soon became constant. coil. Tubes sealed into the bulb of the flask served, respectively, t o The heating was stopped when the temperature had remained hold the thermometer and to introduce liquid and remove samples. constant for 30 minutes to an hour, the still was cut off from The return tube from the condensate collecting chamber was made of 3-mm. tubing to avoid undue mixing of condensate the vacuum train by closing a stopcock; when pressure had been released, samples from the still and the collecting chamwith the solution in the still when boiling was stopped, pre ara tory to takin samples. The addition tube at the top o f the ber were taken and cooled if necessary, and their refractive column was, of course, eliminated. A few runs showed that there indices were determined. By reference to a curve the peris much refluxing in this column, even when it is well lagged with asbestos. To prevent this, a heating coil supplied from the centages of glycol by weight were read. laboratory current was incorporated in the lagging. A thermoVapor pressures a t the lower temperature (25" C . ) for couple with one junction buried in the lagging served to measure glycol-water mixture were studied by one of the authors the temperature. The column was at all times maintained about (Potts). The Walker method as modified by Pearce and 30' C. above the temperature of the boiling liquid. Thus it was assured that all the vapor evolved in boiling passed over to the Snow (5) was used. The current passed to generate the condenser. The thermometer slipped snugly into the long tube electrolytic gas was measured by means of a gas coulomb which held it and was fastened in place by a piece of rubber tubing meter, using alkali of the same concentration as that in the which was wired t o thermometer and tube. Other openings were closed by means of ground-glass sto pers. Thus the liquid electrolyzers, and placed in series with them. Nickel elecand vapors did not come into contact witg anything except glass. trodes were used in both, and efforts were made to maintain As an added precaution against loss of vapors, a condenser was the same conditions in the electrolyzers and in the coulomb sealed to the tube leading to vacuum. The bulb of the ther- meter throughout each experiment. The current passed was mometer dipped directly into the boiling liquid. measured by loss in weight of the coulomb meter. A number The barostat and accompanying apparatus used are de- of tests showed that the current passed, as thus measured, scribed by Daniels, Mathews, and Williams (1). Evacuation was the same as that measured by a copper coulomb meter in series. was accomplished by means of an oil pump. In determining the quantities of glycol and water passing Analyses of the solutions were made by means of an Abbe ~
~
January, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
over with vapors, it was necessary to determine the glycol analytically. This involves oxidizing it in the presence of sulfuric acid, with excess potassium disulfate, and titrating the excess of the oxidizing agent. The ordinary absorbents will not serve under these c o n d i t i o n s ; since they are reactive chemical compounds, t h e y will either react directly with t h e glycol dissolved in it or interfere with its analytical d e t e r mination. A f t e r some experiments i t w a s decided to employ activated silica gel as absorbe n t m a t e r i a l to remove water and glycol from the gas stream. The silica gel s e r v e d t h i s p u r p o s e admirably. The experimental method was as follows: G a s f r o m the e 1e c t r o 1y z e r s was dried by passFIGURE 1. ~ ~ O D I F I E DOTHMERSTILL ing it through sulf u r i c a c i d . It then passed in series through six saturators in the thermostat a t 25" C., containing the solution under experiment. Next in line were three schwartz calcium chloride tubes, containing 6 to 7 grams each of silica gel. This gel had been heated t o about 250' C. for 3 hours to free it of absorbed volatile materials, a1lowed to cool somewhat, and put into the Schwartz tubes while still quite hot. The whole of the saturating and absorbing train was immersed in the water of a thermostat at 25" C. The tubes were weighed filled with air and were then connected to the train by means of heavy pressure tubing. All connections were shellacked. The ground-glass stoppers of the Schwartz tubes were lubricated with Lubriseal. After a run the Schwartz tube8 were filled with dried air that was slowly drawn though them to displace electrolytic gas, cleaned, dried, and weighed. Determinations of glycol were made as follows: The tubes were opened by removing their stopcocks, and all Lubriseal was carefully removed. The silica gel with its absorbed material was discharged into small beakers. An excess of potassium di-
i
61
chromate solution and then 25 cc. of 35 per cent sulfuric acid were added. The samples were digested at 70" to 80' C. for 12 hours. It proved difficult to wash out all the dichromate from the silica gel, so the samples were transferred to Gooch crucibles, which were placed in Soxhlet extractors; the gel was then extracted with water for 2 to 2.5 hours. This removed all of the dichromate. The samples were made up to 250 cc., and aliquot portions taken. These were titrated electrometrically with ferrous ammonium sulfate solution. Blanks were run upon the silica gel in every case, and small corrections were made. Silica gel has proved to be a most valuable absorbent for this work. Its effectiveness may be seen from the fact that, in absorbing quantities of vapors as high as 0.7 gram or more, the second of the Schwartz tubes never showed a gain larger than 0.0015 gram. The third Schwartz tube never showed any gain. Silica gel might well be used as absorbent in many cases. such as this. where the ordinary absorbents may prove undesirable. During each run the barometer was read a t f r e q u e n t regular intervals, and the grand average of all r e a d ings mas taken as the pressure prev a i l i n g over the time of the experiment. During the e x p e r i m e n t s the barometer varied from the mean by not more than 1 or 2 mm. The barometric r e a d i n g s w e r e u s e d in the calculation of the FIGURE2. BOILING POINTSOF v o l u m e s of g a s GLYCOL-WATER MIXTURES passed during each Upper curves: vapor composition us. boiling point r u n a n d of t h e Lower curveB: liquid Composition us. boiling p r e s s u r e of t h e point m i x e d vapors of water and-glycol. In the later case it was assumed that the vapors obeyed the perfect gas law.
THEDATA The data as secured by the method of Othmer are presented in Table I. Under each of the pressures are given, in column 2, the boiling point of the solution whose composition
RESULTSWITH OTHMERSTILL TABLEI. EXPERIMENTAL 747
. k T
B. P. 0
c.
99.6 103.7 110.5 112.0 120.6 125.0 127.9 133.0 136.5 140.8 151.2 168.6 171.6 182.6 196.6 196.7
... . . . . ... , . . ,.
. ... ...
h1M.-
Glyco! in liquid
Glycol in vapor
T"
%
0:0 27.3 59.8 61.3 73.7 81.3 83.6 87.0 88.0 90.1 94.2 97.4 97.9 98.7 99.9 100.0
0.0 0.3 2.0 2.8 6.8 10.6 12.8 17.0 20.1 24.0 38.0 61.2 66.0 81.0 99.0 100.0
I"
-AT B.P.
c. 93.7 96.0 97.0 98.6 100.3 102.2 104.7 109.6 113.1 117.5 121.4 126.0 132.1 141.9 151.4 160.2 167.1 172.7 190.0
...
603 MM, Glycol Glyco! in liquid in vapor
% 0.0 14.0 26.13 37.7 45.!3 53.4 613 71.3 77.1 81.2 84.4 88.0
90.8 93.6 95.!3 97.7 98.0 98.9 100.0
% 0.0 0.3 0.8
1.2 1.7 2.8 3.8 6.0 7.2 10.7 13.2 17.0 23.1 34.0 46.8 59.6 67.7 76.2 100.0
AT 430 MM.
7
I
B. P.
c. 85.0 85.7 86.0 86.8 88.6 90.1 91.8 96.5 100.2 104.8 116.9 120.4 129.2 137.6 142.2 146.7 155.5 162.3 167.4 179.5
Glyco! in liquid
Glycol in vapor
%
%
0.0 12.9 16.3 25.6 33.7 43.6 52.7 63.1 71.4 78.1 87.9 90.0 92.5 95.8 96.7 97.6 98.6 99.8 99.9 100.0
0.0 0.1 0.2 0.2 0.7 1.2 1.5 2.9 4.8 7.6 17.1 21.0 31.0 42.8 49.1 56.0 66.4 76.6 83.6 100.0
--AT
228 h l ~ , -
B. P. O
c.
69.5 72.4 73.3 74.3 75.0 76.2 77.6 79.3 81.6 85.0 87.8 88.9 90.6 92.8 95.5 98.8 103.0 107.1 114.3 122.1 125.7 133.4 155.1 160.6
Glyco! in liquid % 0.0 23.1 31.9 38.0 43.1 49.7 55.4 61.1 67.4 73.2 77.5 79.2 81.6 83.7 85.5 88.1 90.0 91.4 94.2 95.2 96.6 97.7 99.8 100.0
Glycol in vapor % 0.0 0.4 0.6 1.0 1.1 1.4 1.8 2.1 2.7 4.2 5.7 6.8 7.3 9.1 11.0 13.7 17.1 21.2 29.4 40.2 44.8 57.3 91.2 100.0
INDUSTRIAL AND ENGIKEERING CHEMISTRY
68
Vol. 27, No. 1
TABLE 11. COMPOSITION-BOILING POINTRELATIONS FROM SMOOTHED CURVES = 228 M M . Glycol in liquid 9% . _ Molefractmn
--PRESSURE
GLYCOL IN LIQUID B. P. % C. .. Mole fraction 0 10 20 30 40 50 60 70 80 90 95 97 9s 99 100
... ...
..
69.5 70.6 71.5 72.7 74.0 76.1 78.9 83.1 89.6 103.1 118.4 128.0 134.7 145.0 160.7
0.0 0.03 0.07 0.11 0.17 0.23 0.31 0.40 0.54 0.73 0.85 0.90 0.93 0.97 1.00
-PRESSURE = 430 M M . 7 B. P. Glycol in liquid (7. % M o l e fraction
--PRESSURE
86.0 85.4 86.3 87.4 89.0 91.1 94.1 99.0 106.1 120.0 135.0 145.7 152.6 163.0 179.3
93.7 94.3 95.7 97.1 99.0 101.3 104.2 108.7 115.4 130.2 145.8 156.0 163.4 173.4 190.0
... ... ...
012 0.3 0.7 1.0 2.0 3.4 6.6 17.3 33.4 48.8 59.0 75.4 100.0
0.002 0.003 0.010 0 020 0.06 0.13 0.22 0.30 0.47 1.00
..
6:2 0.3 0.7 1.2 2.3 4.6 9.0 20.7 38.8 53.6 63.2 77.6 100.0
is given in column 1, and the percentage of glycol in the corresponding vapor phase is given in column 3. The data secured with the Othmer still are represented in the curves of Figure 2. From these data a graph was plotted on a large scale and the values a t suitable intervals were read. These are given in Table 11. The results found by Potts at 25" C. and the rounded values obtained from them are presented in Table 111. In the calculations it has been assumed that the vapors obey the perfect gas law. TABLE 111. RESULTSBY METHODOF PEARCEAND SNOW, AND VALUESOBTAINED FROM THEM GLYCOL GLYCOL IN
IN
LIQUID VAPOR % %
TOTAL
CALCD. PRESSURE
GLYCOL GLYCOL
RESULTS A T 26'
0 15 35 50
0 0.42 0.91 1.21
23.8 21.4 18.4 17.4
0 10 20 30 40 50 60 70
0 0.1 0.3 0.5 0.8 1.1 1.7 3.8
23.8 22.8 21.7 20.4 18.9 17.1 15.1 12.7
IN
IN
%
%
LIQUID VAPOR
TOTAL
CALCD.
PRFJSSURE
C.
60 75 90 100
1.64 5.62 13.78 100.00
15.1 11.5 5.8 0.28
8.6 13.8
9.8 5.7 3.0 1.7 1.2 0.6 0.26
SMOOTIIEDVALCES
80 90 95 97 98 99 100
100: 0
The vapor pressure curve for ethylene glycol has been determined by de Forcrand (2) and by Taylor and Rinkenbach (6). The two sets of data are not in good agreement, but the data of Taylor and Rinkenbach appear preferable. They are fairly well expressed by the Young equation: log10 p = A
+ B-T
The present authors' data for solutions containing glycol a t the various concentrations can also be fairly well expressed by this equation. For the data of Table 11 the foilowing equations have been deduced : At 0 % glycol, loglo p 10%
20 7% 30 %
40% 50 % 60% 70 % 80 % 90 % 95% 97%
8 7120 - 2178/T = 8 7000 = 8 6900 = 8 6800 = 8 6700 =
8 6690
-
= 8 6640 = 8 6680 = 8 6730 =
8 7000 -
= 8 8000 = 8 9000 -
2182/T 2185/T 2188/T 2190/T 2201/T 2220/T 2250/T 2293/T 2386/T 2528/T 2632/T 2694/T
8 9500 = 9 0250 - 2800/T 99% = 9 1580 - 2952/T 100% where p = pressure, mm. of mercury T = abs. temp. A , B = constants 98%
...
. . . . ... ...
0.002 0.004 0.012 0.028 0.072 0.16 0.26 0.34 0.50 1.00
B. P. O C.
= 603 MM.-
Glycol in liquid % Mole fraction
- - P R E S ~ U R E = 747 hfM.-B. P. Glycol in liquid C. % Mole fraction
0:1 0.2 0.2
1.2 2.3 4.7 9.4 21.3 39.7 53.2 63.7 78.2 100.0
0.002 0.004 0.013 0.030 0.076 0.16 0.25 0.34 0.51 1.00
108.0 111.2 116.7 124.1 138.7 154.0 164.3 171.3 162.0 196.7
0. I 1.2 2.3 4.9 9.7 22.2 41.3 ~. 55.7 65,3 79.6 ILOO 0
0.002 0.004 0.013 0.031 0.080 0.17
0.27
0.36 0.53 1.00
The results are presented in the form of equation&rather than as curve8 because of their greater exactness. Attempts have been made to fit the data with an equation such as that of Kirchoff-Rankine, but the experimental accuracy hitherto attained in the measurements makes its use possible only in the case of water. Constants for this equation may be found which hold over small portions of the pressure range for the various solutions, but none has been found which would hold over more than a part of it. Taken for the range covered by the determinations, boiling points as calculated from the above equations agree with those found with an average error of 1.1' C. For all points involved, the equations hold well for the higher pressures and leas well a t 25" C. where the total pressures are not as accurately known. As will be seen from Table 11, the percentage of glycol in the vapor coming off from a boiling mixture with water increases slightly with the pressure a t which it is distilled. Similarly, it may be shown that the ratio of glycol in vapor to glycol in solution, although it shows a marked increase with increasing percentage glycol in the solution, varies but little with the pressure. Partial pressures of the components may be calculated from the mole fractions of each in the vapors as found. These partial pressures a t any given temperature, when plotted against mole fraction, prove t o lie nearly on straight lines. When the sums of the partial pressures are plotted against mole fractions of either component, nearly straight lines result; and the total pressures so calculated agree fairly closely with the total pressures as calculated from the equations for the temperature chosen. Thus mixtures of glycol and water obey Raoult's law rather closely. The departures from the law are in the sense of negative deviations up to about 120" C. Above this temperature the departure from Raoult's law is positive.
L~TERATURE CITED (1) Daniels, Mathews, and Williams, "Experimental Physical Chemistry," p. 301, New York, McGraw-Hill Book Co., 1929. (2) Forcrand, de, Compt. rend., 132, 688 (1901). (3) Lawrie, "Glycerol and the Glycols," p. 378, New York, Chemical Catalog C o . , 1928. (4) Othmer, IND. ESG. CHEM.,Anal. E d . , 4, 232-4 (1932). (5) Pearce and Snow, J . Phus. Chem., 31, 231-48 (1927). (6) Taylor and Rinkenbach, IKD.EEG.CHEX.,18, 676 (1926). RECEIVED October 22, 1934. Presented before the Division of Physical and Inorganic Chemistry a t the Twelfth Midwest Regional Meeting of the American Chemical Soriety, Kaneas City, &lo., M a y 3 t o 5, 1934.
