Studies in Distillation Liquid-Vapor Equilibria of Ethyl Alcohol-Wat er Mixtures J. S. CAREYAND W. K. LEWIS Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Mass.
ATew and accurate data on the vapor-liquid equilibria of ethyl alcohol and water mixtures, determined at one atmosphere by the method of Othmer, are presented. N THE course of an experimental investigation of the plate efficiencies obtained in the rectification of various binary mixtures, it was desired to include runs on ethyl alcohol-water, The calculation of plate efficiencies from experimental data by any of the methods which have been proposed requires accurate liquid-vapor equilibria. data for the mixture undergoing rectification. While ethyl alcohol is one of the first materials to have been concentrated industrially by rectification, a comparison of the several sets of ethyl alcohol-water liquid-vapor equilibria data available in the literature revealed serious disagreements. Therefore, it was considered advisable to obtain another set of experimental determinations, using especial care in the selection of a method and the technic of application.
I
prevented liquid, formed by any slight condensation in this portion, from falling back into the still. To permit observation of any initial refluxing, the vapor was taken off by a tube set into the stillhead and projecting to a point level with the peep sights as shown. When drops of liquid no longer collected on this tip, refluxing was safely assumed to be absent. Another peep sight in the upper part of the receiver permitted observation of the distillation rate. The major dimensions of the apparatus are indicated in Figure 1.
The only source of error in this apparatus which may be serious is the possibility that the cold reflux returning to the still might flash-vaporize to a certain degree before it has had an opportunity to mix completely with the body of liquid in the still (6). The vapor thus evolved would be richer in alcohol than that corresponding to equilibrium with the body of liquid in the still. Effort was made to avoid this source of METHODUSED error by returning the reflux to the bottom of the still. Its After surveying the various methods for determining low temperature delays its vaporization sufficiently so that experimentally the x-y relation, it was decided to adopt the the ebullition of the main body of the liquid should mix the system involving continuous recycling of distillate to the two perfectly. The only additional precaution would be to equilibrium still. Thus, when steady conditions have been use mechanical stirring, but this was considered unnecessary. A high grade of c. r. 95 per cent reagent ethyl alcohol was established, the composition of the distillate returning to the used in these-determinations. Bestill is the same as the composifore use, it was redistilled through tion of the vapor leaving the still. a short Hempel column, the first T h e e s s e n t i a l principles of this and last 10 per cent portions being method were apparently discovered rejected. Application of the usual by Carveth ( 2 ) . However, Carq u a l i t a t i v e t e s t s , as given by veth depended upon boiling temMurray ( 7 ) , showed all ordinary p e r a t u r e s of liquid and vapor impurities to be absent. samples to determine the composiI n making a run, ft charge of aptions. Yamaguchi (IS), Samishima proximately 315 cc. of ethyl alco( I I ) , and Othmer (9) employed hol-water mixture was introduced Carveth’s principle with different into the still. The pressure-regua r r a n g e m e n t s of apparatus and lating device was then connected m a d e p r o v i s i o n s for analysis of to the vent pipe and so adjusted s a m p l e s of liquid and vapor by that the pressure in the still was methods-other than those used by 760 mm. of mercury. After coolCarveth. ing water was circulating through T h e O t h m e r a p p a r a t u s was the condenser jacket, heat was apselected because of its simplicity. plied to the bottom of the still by Since prevention of partial conmeans of a Bunsen burner, and the densation is imperative if e q u i hot gas jacket was brought up to librium data are to be secured, a temperature. heat jacket was added. The apDistillation was carried on at a paratus is illustrated in Figure 1, rate of from 10 to 15 cc. of conand was designed by E. R. Smoley densate per minute. Calculation of this laboratory. FIGURE1. EQUILIBRIUM STILL shows that the superficial vapor This apparatus consisted of a still, velocitv in the still never exceeded c o n d e n s e r and receiver-all constructed of copper with brazed seams and joints. From the 4.6 cm. per second, which obviatid any possibility of entrainbottom of the receiver, provided with a pressure vent, the ment. Usually 15 minutes served to bring the gas jacket and condensate returned to the bottom of the still through an inlagging up to the temperature a t which refluxing ceased. verted U-tube. The body of the still WBS lagged thoroughly. Runs were continued for a t least half an hour after refluxing Hot gases from the circular gas burner flowed upward through the stopped, and vapor temperature had ceased to change. This annular space between the lagging and the external galvanizediron shell. The special construction of the stillhead (Figure 1) insured that the contents of the receiver were completely ,\
882
I N D U S T R I A L A N D E N G I X E E R I N G C H E R.I I S T R Y
August, 1932
changed a t least six times and that a steady state had been reached. At the conclusion of the run, the burner was withdrawn from the still and samples of liquid from the still and the receiver immediately withdrawn into stoppered test tubes, immersed in ice baths and vented through air condensers. The cooling of the samples was rapid so that no loss from flashing occurred. The compositions of the liquids were determined from measurements of specific gravities, using carefully calibrated 50-cc. pycnometers of the type provided with thermometers set into ground-glass stoppers. The pycnometer thermometers were calibrated against a standard thermometer. The compositions, corresponding to the observed specific gravities, were obtained from the specific gravity tables of the Bureau of Standards ( I ) . The data and results of these determinations are given in Table I.
883
boiling temperatures of ethyl alcohol-water mixtures be desired, the data of Koyes and Warfel (8) may be used. Experimental technic prevented refluxing or entrainment and the pressure was regulated to 760 mm. * 0.2 mm. mercury.
OF LIQUID ASD VAPORCOMPOSITIOXS, TABLE I. EQUILIBRIUM ETHYLALCOHOL-WATER MIXTURES
SP. OR. LISKID
S.4rPLE,
RL-S f/4’ 10 14 9 13 8 12 7 6 2 5 11 1 4 3
c.
0.98934 0.97250 0.96598 0.95856 0.94678 0.92588 0.91914 0.90148 0.88343 0.86144 0.85867 0.84769 0.83236 0.82186
TEMP. LIQ- EtOH UID
SAMPLE
IS
LIOLE FRACTION
EtOH IS
LIQ-
LIQ-
UID
UID
c.
Wt. %
22.10 -1.65 21.40 21.45 20.70 21.85 20.45 20.15 21.80 20.25 20.85 22.45 20.60 20.65
4.72 16.57 21.47 26.53 33.74 43.80 47.42 55.43 62.68 72.51 73.45 77.44 84.23 58.31
0.0190 0.0721 0.0966 0.1238 0.1661 0.2337 0.2608 0.3273 0.3965 0.5079 0.5198 0.5732 0.6763 0.7472
SP. GR. VAPOR TEMP SAM- VAPOREtOH SAMIX tE’b. PLE VAPOR O c. W f .% 0.94471 2 2 . 0 6 3 4 . 3 6 0.88507 2 1 . 8 5 6 1 . 9 5 0.87449 2 1 . 6 5 6 6 . 5 3 0.86764 21.65 69.42 0.86092 2 0 . 6 5 7 2 . 5 9 0.85309 2 2 . 0 0 7 5 . 3 4 0.85191 2 0 . 5 5 7 6 . 3 4 0.84808 20.05 78.11 0.84149 21.85 80.14 0.83582 20.20 83.00 0.83448 21.10 83.22 0.82958 2 2 . 4 5 8 4 . 7 0 0.82316 2 0 . 6 0 8 7 . 8 3 0.71703 20.65 90.14
MOLE FRACTION
EtOH IN
VAPOR 0.1700 0.3891 0.4375 0.4704 0.5089 0.5445 0.5580 0.5826 0.6122 0.6564 0.6599 0.6841 0.7385 0.7815
DISCUSSIOK OF RESULTS While vapor temperatures were measured in the experimental runs to determine the establishment of constant conditions, they are not reported because in some of the runs the vapor may have been slightly superheated as it passed the thermometer. This in no way affected the equilibrium conditions with respect to the liquid and vapor compositions. Reference to the data shows that the present experimental determinations cover the range in compositions below that of the constant-boiling mixture, as this was the only portion of the curve required in the present work. The experimentally observed values of vapor and liquid composition are plotted as circles in Figure 2, and a smooth curve has been drawn through the points. Apparently the only other dependable direct experimental determinations given in the literature are those of Bergstrom, quoted by Hausbrand ( 6 ) ,and of Rayleigh (IO). Both these sets of data are plotted in Figure 2. It is seen that Bergstrom checks the present determinations closely. Rayleigh’s data agree exceptionally well a t low concentrations of ethyl alcohol, but fall somewhat below the present curve in the middle range. The data of Evans (3,4)have also been plotted on Figure 2 because they are the only ethyl alcohol-water equilibria data given in the International Critical Tables. It will be noted that all of Evans’ points are high, the error in the middle range amounting to 10 to 15 per cent. However, since Evans stated that his technic involved refluxing, there is no reason to expect his data to correspond to the equilibrium in question. The data were plotted with care and interpolated graphically, the results being given in Table 11. I n this table, as well as on Figure 2, the composition of the constant-boiling mixture a t 760 mm. is shown as the average of the values found by Young and Fortey (14) and Wade and Merriam (12). This point was not determined by the writers. Should the
, FIGURE2. ETHYLALCOHOL-WATER EQUILIBRWX DIAGRAM TABLE 11.
COORDINATES OF CURVEDRAWX THROUGH EXPERIMENTAL POINTS, ETHYLALCOHOL-\VATER EQUILIBRIUM DATA MOLEFRACTION EtOH In liquid, z In vapor, 1/ 0.0190 0.0400 0.0600 0.0800 0.1000 0.1200 0.1400
h?oLE FRACTION EtOH In liquid, z In vapor, y
0.1600
MOLE FRACTIOX EtOH In liquid, z In vapor, 0.6200 0.7065 0.7175 0.6400 0.6600 0.7290 0.7410 0.6800 0.7000 0.7525 0.7200 0.7650 n .7775 0.7400 0 . 76OOa 0 . 78OOQ 0.8040’ 0.8O0Oa 0.8175= 0 . 82004 0.83200,8470a 0 . S400a 0.8600O 0 . 8640a 0 . 88OOa 0.8820” 0.8943b 0.8943b
0.1800 0.2000 0.2200 0.2400 0.2600 0.2800 0.3000 Extrapolated. b Average of data of Young and Fortey, and Wade and hlerriam.
LITERATURE CITED Bur. Standards, Circ. 19 (1924). Carveth, J . Phys. Chem., 3, 193 (1899). Evans, J. IND. ENG.CHEM.,8, 261 (1916). Evans, I b i d . , 13, 168 (1921). HausbSyd, “Principles and Practice of Industrial Distillation, translated by E. H. Tripp, Chapman & Hall, 1926.
Lane and Lalone, private communication. Murray, B. L., “Standards and Tests for Reagent and C. P. Chemicals,” 2nd ed., Van Nostrand, 1927. Noyes and Warfel, J. Am. Chem. SOC.,23, 463 (1901). Othmer, 1x11.ENG.CHEM.,20, 743 (1928). Rayleigh, Phil. Mag., 161 4, 521 (1902). Samishima, J. Am. Chem. SOC.,40, 1462 (1918). Wade and Merriam, J . Chem. Soe., 99,997 (1911). Yamaguchi, J . Tokyo Chem. SOC..34, 691 (1913). Young and Fortey, J . Chem. SOC.,81, 717 (1902). RECEIVED March 18, 1932. Presented before the Division of Industrial and Engineering Chemistry at the 83rd Meeting of the American Chemical Society, New Orleans, La., March 28 to April l , 1932. This paper ia an abstract of a portion of a thesis submitted in partial fulfilment of the requirements for the degree of doctor of science in chemical engineering, Massachusetts Institute of Technology. J. S. Carey’s present address is 347 Walnut Ave., Cranford. N . J.
