Equilibria in the Systems EthanolWater, EthanoLCellosolve, and Cellosolve-Water E. M. BAKER, R. 0. H. HUBBARD,' J. H. HUGUET,Z AND s. s. MICHALOWSICI3 University of Michigan, Ann Arbor, Mich.
The apparatus described here gives satisfactory results and is believed to be an improvement over earlier apparatus. A study of this apparatus in the light of the Rayleigh equation for differential distillation shows that the volume of distillate withdrawn for analysis must be small in comparison with the volume of liquid in the still. This criterion is met by this apparatus. The system Cellosolve-water has a constant-boiling mixture which contains 92.1 mole per cent water. This value is higher than that of 88.3 mole per cent water previously reported (I).
HIS paper presents the results of equilibrium studies between liquid and vapor, a t one atmosphere pressure, of the three systems ethanol-water, ethanol-Cellosolve, and Cellosolve-water. The following paper (page 1263) will present equilibrium data for liquid and vapor at one atmos-
T
phere pressure for the three component system ethanolCellosolve-water. The distillation apparatus used in this study may be regarded as a modification of that of Trimble and Potts (6) or of Carey and Lewis (8, and is shown in Figure 1. I n Figure 1 the still, A , is a 2-liter, three-neck distilling flask with all stoppers tin-foil-covered to prevent attack by alcohol and Cellosolve. B is the column characteristic of the Othmer apparatus and contains the specially constructed still head, C, to remove as distillate any vapors condensed in the upper portion. This still head prevents the return of reflux to the surface of the still liquor, where it might otherwise partially vaporize and give too rich a vapor phase. Thermometer D records the temperature of the vapors; condenser E condenses the vapors and delivers them to the small receiver, F ; any condensate in C also goes through the condenser to F. Except when liquid and vapor samples are being withdrawn for analysis, the condensate in F goes through the three-way cock, G, and the air-cooled condenser, H , and is returned to the still at I. Condenser H prevents the liquid from flashing back into bulb F when it comes into contact with the hot liquid of the bath. 1 2
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Present address, Eastman Kodak Company, Kingsport, Tenn. Present address, Ethyl-du Pont Company, Baton Rouge, La. Present address, National Tube Company, Lorain, Ohio.
Q
L V
FIGURE 1. DIAGRAM OF APPARATUS 1260
OCTOBER, 1939
INDUSTRIAL AND ENGINEERING CHEMISTRY
Thermometer M records the temperature of the liquid in the still, which is heated internally by an electric coil, L, of Chromel C wire hooked in series to a rheostat and then to the 110-volt line. The rheostat can be adjusted to vary the amount of current through the heating coil and thus the rate of boiling. The temperature of the glycerol bath is kept 2-3" C. above the temperature on thermometer M . The bath is agitated by an electric stirrer. The three necks of flask A are
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wound with aluminum foil and then with asbestos rope. Column B is wound with aluminum foil, Chromel A electric heating coil, and then asbestos rope. Thus heat losses by radiation and convection are eliminated from the system being studied; and since no refluxing can take place, the distillate collected in P should be in equilibrium with the large volume of liquid in still A . Container Q is a 5-gallon can which is used to minimize pressure variations in the still. There are four leads to the
INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 31, NO. 10
tank. Through lead R a small volume of compressed air is TABLEI. REFRACTIVE INDICES FOR THE SYSTEMS CELLOSOLVE- introduced to maintain the pressure. Lead S connects to ETHANOL AND CELLOSOLVE-WATER barometer W which indicates the pressure in the tank. Lead Mole % -Refractive IndexMole % YRefraotive IndexZ connects to a piece of U-shaped glass tubing, on the end of Ethanol EthanolWaterEthanol EthanolWateror Water Cellosolve Cellosolve or Water Cellosolve Cellosolve which is an inverted Gooch crucible. The end of the tube can be adjusted to any depth in the glass container, V , which 1.4038 75 1.3773 1.3887 0 1.4034 1.4036 80 1.3744 1.3845 5 1.4023 is kept filled by means of a small stream of water. The air 1.4012 1.3822 1.4034 82 1.3732 15 lo 1.4000 1.4032 84 1.3718 1.3793 from the tank flows through lead Z and out under the Gooch 20 1.3987 1.4029 86 1.3705 1.3758 crucible. By raising or lowering this outlet, the pressure in 1.3720 1.4026 88 1.3692 25 1.3973 the tank can be lowered or raised. The other lead, T,con1.3676 1.4022 90 1.3677 30 1.3958 1.4017 92 1.3662 1.3626 35 1.3943 nects to bulb F so that the distillation pressure can be main1.4012 94 1.3648 1.3568 40 1.3926 1.3500 1.4005 96 1.3632 tained at 760 mm. with a variation in pressure of less than 1 45 1.3908 mm. 50 1.3889 1.3996 98 1.3615 1.3413 55 1.3869 1.3983 100 1.3599 1.3315 The still was run for 20 minutes after the temperature of 1.3967 60 1.3847 1.3946 65 1.3824 the liquid became constant before samples were withdrawn. 1.3920 70 1.3799 While the liquid sample was drawn off through cooler K , the vapor condensate sample was collected in reservoir F and then withdrawn. Inasmuch as the atmospheric pressure was generally below 760 mm., this operation presented no difficulties. TABLE 11. EQUILIBRIUM DATAAT 760 Man. PRESSURE The ethanol, water, and Cellosolve used in these studies Ethanol-Water Ethanol-Cellosolve Water-Cellosolve-' were laboratory reagents, carefully redistilled. The CelloMole Q Mole % Mole % Mole ' 9 Mole % Mole "(0 Mole "(0 Mole yo ethanof ethanol ethanol ethanol water in water in water In water in solve is ethylglycol monoethyl ether (CH~.OH.CHz.O.CzH,), in liquid in vapor in liquid in vapor liquid vapor liquid vapor molecular weight 90.08, boiling point 135" * 0.7"C. 66.4 99.9 99.3 97.4 99.9 85.5 78.6 75.0 65.2 99.3 97.2 94.9 99.3 85.3 76.6 The only reason for studying the system ethanol-water was 72.2 92.1 64.3 98.5 96.3 98.9 85.0 74.2 68.1 to test the accuracy of the technique. It was found that 60.0 88.6 98.0 95.5 98.5 83.9 72.0 65.2 58.2 95.0 85.0 97.0 97.7 83.3 70.7 61.7 heating coil L was essential, because without it vessel A had 55.9 80.8 96.3 94.3 96.5 82.9 68.9 57.5 54.1 77.4 95.5 93.9 96.1 81.9 to be heated so strongly by raising the temperature of the 65.2 49.7 52.8 73.9 94.5 93.3 95.1 81.4 64.3 46.1 bath that superheating and uneven boiling of the liquid oc46.4 93.5 92.8 94.3 68.5 78.6 62.4 42.1 63.5 39.4 92.5 92.3 93.1 74.8 61.3 38.9 curred, with the result that the vapors were not in equilibrium 37.0 56.9 91.5 91.9 90.7 73.2 60.2 36.3 33.0 with the liquid, 49.4 90.7 91.6 88.5 71.2 58.9 33.7 43.1 26.0 89.5 91.1 84.8 65.4 59.1 31.2 The solutions of ethanol-water were analyzed by means of 20.1 88.6 35.9 90.8 80.4 60.5 57.3 28.6 18.0 87.5 28.8 90.8 77.6 58.8 56.2 26.8 specific gravity (4) with a 5-cc. pycnometer which permitted 13.5 86.0 90.1 25.8 72.8 54.1 55.5 24.5 the use of small samples. The solutions of ethanol-cello11.6 80.3 20.6 88.7 67.7 51.2 52.7 20.8 9.0 78.3 16.4 88.1 57.8 47.7 53.1 19.8 solve and of Cellosolve-water were analyzed by taking the 6.4 76.6 15.6 87.8 57.7 44.6 51.6 16.6 4.2 68.7 10.8 80.0 41.6 38.0 50.6 15.6 index of refraction in an Abbe refractometer, thermostatically 32.1 7.5 1.8 68.0 85.8 28.8 45.8 11.0 held a t 30" C. It was necessary to determine the refrac4.3 22.4 42.0 8.8 tive index of solutions of known composition. These data' for the systems Cellosolve-ethanol and Cellosolve-water are given in Table I. Equilibrium data for the system ethanol-water are given in Table I1 and Figure 2. On Figure 2 are also plotted the data of Carey and Lewis (2), Cornell and Montonna (S), Young and Fortey ( 7 ) )and Wade and Merriman (6). Figure 2 shows that although one determination is obviously in error, in general the agreement with the best previous work is good. Hence, the apparatus and technique were regarded as satisfactory, and the study of the other systems was begun. Equilibrium data for the system ethanol-Cellosolve are given in Table I1 and Figure 3, and for the system Cellosolve-water in Table I1 and Figure 4. 7 -
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Literature Cited (1) Carbide and Carbon Chemicals Corp., technical papers on products of the corporation. (2) Carey, J. S., and Lewis, W. K., IND.ENG. CHEM..24. 882 (1932). (3) Cornell, 'L.'W., and Montonna, R. E., Ibid., 25, 1331 (1933). (4) Natl. Bureau of Standards, Circ. 19, 1924. (5) Trimble, H.M., and Potts, W., IND.ENQ. CHEM.,27, 66 (1935). (6) Wade, J., and Merriman, R. W., J. Chem. SOC., 99,997 (1911). (7) Young, S.,and Fortey, E. C., Ibid., 81, 717 (1902).
