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termine their suitability for large-scale oprrn tion and ta obtain
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(3) Kelley, E. C., Wall, M. E., and Willaman, J. J., FeedSttcf.9, 15 (26), 18 (1943).
dat,a on the cost of the various stepR.
(4)
Kuhn, R., and Broakmann, H., 2. phyaik. Chm., 206, 41 (1932).
ACKNOWLEWMENT
(6) Morgal, P. W., Petering. H. G., and Miller, E. J., IND. ENG. CHEM.,33, 1298 (1941). (6) Petering, H. G., Morgal, P. W., and Miller, E. J., ZbU.. 32, 1407
The authors wish to acknowledge the wsistance of Raymond T. Merrow, Samuel Krulick, and Reba Baum in various phases of this research.
(7) Petering, H. G., Wolman. W., and Hibbard, R. P., IND. ENG
LITERATURE
CITED
(1) Holmes, H. N., and Leicester, H. M., J . Am. CAm. Soo., 54, 716 (1932). (2) Kelley, E. G., and Wall, M. E., Ann. Rept. Vegetable Chowera Aiaoc. Am.. 1942, 62.
(1940).
CHEM.,ANAL.ED., 12, 148 (1940). (8)Rose,W.G., Freeman, A. F., and McKinney, R. S., IND.ENQ CREM.,34, 612 (1942). (9) Schertz, F. M., Zbid., 30, 1073 (1938). (10) Strain, H. H., J . BWZ. Chcm., 105, 623 (1934). (11) Wall, M. E., and Kelley, E. G., IND. ENQ.CHSM.,ANAL.ED.. 15, 18 (1943). (12) Willsttitter, R. M., and Stoll, A., "Investigations on Chlorophyll", tr. by Schertz and Mer;. Lancaater, Pa., Science Prem Printing Go., 1928.
Composition of Vapors from Boiling Binary Solutions WATER-ACETIC ACID SYSTEM AT ATMOSPHERIC AND SUBATMOSPHERIC PRESSURES ROGER GILMONT AND DONALD F.' OTHMER Polytechnic Institute, Brooklyn, N. Y.
D
UHLNC: a study of the correlation between vapor-liquid equilibria and partial heats of solution, the vapor-liquid equilibria for the system water-acetic acid were determined at pressures of 760, 500,250, and 125 mm. of mercury. The method adopted for experimentally determining the vaporliquid equilibria has been described (7,9,10).The temperature and pressure are directlyobserved, whereas the composition of
the liquid and vapor states in squilibriuin are determined bj suitable analysis of samples of the liquid withdrawn from the still and distillate trap, respectively. The correlation of these data have already been discussed (11). The details of the equilibrium still were given in another paper (9); the heating arrangement is shown in Figure 3 of that paper. The coil was wrapped around the larger of the reflux heating tubes between layers of asbestos cloth and was rated at 500 watts (considerably € more than needed). Power input was controlled TO A V l f f A T M by a Variac transformer. The arrangement of the apparatus is showu in Figure 1, as prepared for use at subatmospheric pressures. For work at atmospheric pressure, the constant-pressure device was replaced by a small mercury manometer having a slope of about 1 to 10 with the horizontal, and open to the atmosphere. The pressure on the system was then maintained at 760 mm. by adding air to or venting air from the reservoir through cock E. The column of the still wae lagged with many layers of cloth. Cock A served to expel noncondensable gases; cocks B and C' allowed liquid and condensste samples to be withdrawn; and the three-way cock D, v e n t i q to the atmosphere, served to isolate the still from the reservoir while samples were being withdrawn. The 12-liter flask, used as a reservoir, maintained steady conditions by absorbing Figure 1. Arrangement of Apparatus for Subatmospheric Pressure fluctuations of pressure. Both absorption tube8 For use at rtmmphericprsuure the apparatus to the rigbt of ntopeootr E and of tbe contained soda lime and calcium chloride t,n -rvoir w u replaced w i t h a nimple inelined-tuhe manometer.
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The vapor-liquid equilibria and boiling points were determined for the binary system water-acetic acid at the constant pressures of 760, 500, 250, and 125 mm. of mercury by the method previously described (9). The experimental data are presented in graphs and tables, including one for smoothed data obtained from the graphs. A comparison with other data in the literature is given for boiling points and vapor compositions at atmospheric and subatmospheric pressures.
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protect the mercury from acid or water vapor. Two mercury traps prevented any mercury from being lost if sudden surges took place; the water trap prevented any water from the aspirator 85 from being sucked into the system if sudden changes in 3 water pressure took place. Three-way cock E was used for u rapidly evacuating the system to approximately the correct so 2 pressure before suction was permitted by way of the pressure 0 regulator, which maintained the pressure a t any desired value. a E, Cock F of the constant-pressure regulator (4) enables the correct amount of mercury to be added to the manometer to ob75 tain the arbitrarily chosen pressure. CHARGING STILL.The still was charged with about 200 cc. of pure acetic acid, and the boiling point was determined ttt 70 each pressure. By adding the correct amount of distilled water and draining the corresponding amount of solution after each run, about ten evenly spaced values of weight per cent water for the liquid composition were obtained for each pressure. CORRECTPRESSURE.The system was closed off from the 0 25 50 75 100 atmosphere by turning cock D so as to connect the still with the W e i g h t % H20 reservoir. With cock A opened, the system was evacuated Figure 2. Phase Equilibria of Acetic Acidthrough cock E with the pressure regulator by-passed. When Water System the desired pressure was nearly reached, cock E was turned Upper line at:eaah pressure im for vapor and lower so that all aspirated gas would have to pass through the line ii for liquid, both plotted a@mt temperature. regulator which had been previously set a t the desired pressure. With the system at the corTABLE I. VAPORLLIQUID EQUILIBRIAOBSERVATIONS (IN WEIGHTPERCENT WATER)^ rect pressure, the liquid was C P = 500 Mm.PP 760 Mm.-P 250 Mm.-P 126 Mm.brought to a steady boil by regT'C. % z %u T'C. %Z %u T'C. %x % y TOC. % z %Y ulating the heat input by means 0 0 0 0 85.5 67.8 118.4 0 0 of the transformer. When all non3.9 0.45 1.15 7.1 117.6 80.42 8.3 84.25 4.6 77.33 10.6 17.5 61.53 10.7 17.0 8.9 15.6 109.1 condensable gases appeared to have 29.8 21.4 75.86 16.5 25.5 59.83 105.6 17.3 28.1 been bled through valve A , it was 75.12 20.8 30.7 58.61 36.6 44.2 103.0 32.85 47.0 53.8 45.7 47.4 62.4 73,76 58.10 44.6 101.6 34.2 closed. 101.2 65.75 68.5 73.09 45.0 56.0 57.58 60.1 66.2 72.51 61.0 68.2 57.28 71.3 75.6 100.9 63.6 74.5 EQUILIBRIUM.Boiling was al72.23 70.8 76.1 56.92 82.2 85.4 100.59 74.3 81.7 lowed to proceed until equilibrium 100.37 84.0 88.6 71.87 83.9 87.6 56.68 90.2 92.5 100.12 95.4 96.8 56.57 94.8 96.3 71.63 95.7 93.8 was reached at the desired pressure, 100 100 100.00 100 56.4 100 71.6 100 100 as indicated by a constant reading 5 z liquid; y = vapor. of the thermometer. The average time to come to a steady state DATAOF VAPOR-LIQUID EQUILIBRIA FOR SYSTEM WATER-ACETIC ACID" TABLE 11. SMOOTRED was usually about 20 minutes, Vapoi -Liquid760 mm. 500 mm. 250 mm. 125 mm. although at least 40 minutes were z.1 w: TOC. yi w: T'C. DI W; To C. VI W; To C. UI W; allowed. The temperature of the 115.7 10.1 3.2s 103.0 10.1 3.2s .83.3 10.2s 3.80 65.9 10.2~ 3.30 5 1.5, system in equilibrium was taken 101.81S.O 6.1s 82.3 17.7 6.0s 65.0 17.6 6.0 10 3.2 114.3 18.1 6.2 63.624.3 8.8 80.124.5 8.9 99.625.0 9.1 15 5.0 111.925.5 9.3 when the manometer reading drifted 62.7 30.8 11.7 98.0 32.3 12.4 78.8 31.4 12.0 110.3 32.7 12.6 20 7.0 to the exact value at which the 61.4 42.1 17.8 77.1 43.4 18.6 95.5 44.2 19.1 107.8 44.7 19.4 11.3 30 pressure was previously chosen. 52.1 24.4 60.5 75.9 53.5 25.6 26.6 93.8 54.9 105.8 55.5 27.1 40 16.6 Two check readings, 10 minutes 59.7 60.7 31.5 62.3 33.0 34.9 74.9 35.6 92.5 64.2 64.9 104.4 22.9 50 apart, were used as a criterion for 59.0 68.8 39.7 74.0 70.3 41.4 91.5 72.8 44.3 103.2 73.7 45.4 30.9 80 58.3 76.7 49.4 73.3 78.1 51.3 90.7 80.7 55.3 102.2 81.3 56.4 41.0 70 concluding the run. 57.7 84.0 61.2 72.7 85.0 62.9 89.9 87.3 67.2 54.3 101.3 87.5 67.6 80 After equilibrium conditions were 68.4 57.5 87.8 72.4 88.5 68.8 89.6 90.2 73.6 101.1 90.4 73.9 62.8 85 57.2 91.8 77.0 72.2 92.3 78.2 89.2 93.3 80.7 100.8 93.4 80.9 verified by the check reading of the 73.0 90 temperature, heating was stopped; 56.81 96.0 87.9 71.82 96.3 88.6 89.00 96.7 89.6 100.3, 96.6 89.3 9S . 85.0 56.6% 98.2 94.0 71.60 98.2, 94.3 88.88 98.3 94.5 100.1, 98.2s 94.3 97.5 91.9 the still (but not the reservoir) was 56.50 99.20 97.68 88.77 99.3s 97.8s 71.61 99.32 97.77 99 96.7s 100.0a 99.28 97.67 opened to the atmosphere through a o mole % in Liquid; y mole % in vapor; w weight % in liquid; w' weight 7% in vapor: aubioript 1 water. cock D. 100
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WITHDRAWAL OF SAMPLES. Samples of the liquid in the still and in the reservoir were withdrawn into previously weighed flasks, each containing 25 00. of approximately 0.2 N barium hydroxide and 2 drops of phenolphthalein, just to remove the pink coloration. The flasks were immediatelystop pered and weighed. For the first set of runs, two mmples were withdrawn from both the still and condewate trap as a check on the method, which was found to be more accurate and convenient than any other attempted. The titrating buret was so arranged that solution could be added directly without any contact with the air. The solution was stsndardised against certified potassium acid tartrate obtained from the National Bureau of Standards. From the titers, the compositions of the vapor and liquid in equilibrium at the given pressure and mcagured temperatures were obtained. CALIBRATIONS AND SMOOTHING OF DATA
The 0.1" C. thermometer for subatmospheric runs was cahbrated by the National Bureau of Standards for total immersion; a stem correction
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F i g u r e 3. Vapor Composition u s . Liquid Composit i o n for Acetic Acid-Water System 0
0
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was
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applied in the manner* The *' thermometer for atmospheric runs was calibmted against the 0.1' thermometer for total immersion, and a stem correction was applied. A magnification glass was that tenths and bunto read the thermometers dredths were estimated on 1" and 0.1' thermometers, respectively. The tkmperature and pressure measurements were calibrated by taking the boiling points of distilled water at several pressures. for vapor the The pressure reading was by comparison with the barometer reading, The amcement between the and true boiling points was excellent; betweenthe range 65" to 850 c., the deviation was less than 0.2". With increasing temperatures the boiling point read too high and was in error by 0.7" at 100" C. Titration showed the reagent-grade acetic acid to contain 99.8% acid by weight; the bulk of the remaining constituents wereassumed to be water as the total amount of other con-
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stituents according to analysis was less than 0.01% by weight. The water used in the experiments was freshly prepared distilled water. The first set of runs a t 760 nun. (Table I) employed the 1" C. thermometer; a second set of runs on dilute acid solutions used the 0.1' thermometer and was performed after subatmospheric data were obtained. I n the first set two samples each of the liquid and vapor compositions were analyzed to check the method of analysis. I n most cases the check was within 0.1% weight concentration and never exceeded 0.2%. The accuracy of the titrations tend to increase as the concentration of acid is diminished, mainly because the size of sample necessarily increases for the 8ame volume of standard solution and also because the loss by evaporation of acid is reduced. A graph of phase equilibria against temperature is given in Figure 2, and of vapor against liquid composition, in Figure 3. From these graphs the data were smoothed as in Table 11. COMPARISON
WITH OTHER DATA
TOTAL PRESSUREAND BOILING POINTS.For the comparison of boiling points as a function of pressure and composition, the log of total pressure was plotted in Figure 4 against the log of vapor pressure at constant liquid composition, as previously described (8). Included are data from two other sources. The data of Keyes (6) show deviations since the experimenter w&8 essentially concerned with vapor composition rather than temperature measurement; the data of Kahlbaum and Konowalow (6)are in better agreement. The latter investiused the shtiie method of determining total pressure at a given temperature which gives larger errors at decreased pressures. VAPOR-LIQUID EQUILIBRIA AT ATMOSPHERIC PRESSURE. A large plot was made Of (y--2) qgainst (Figure 5, to 'Ompare the experimental values of this investigation with those from available literature (1, d , 8, 7, l d - l 6 ) . The difference plot emphasizes small variations. Wherever possible, the original observations Of the investigator were chosen rather than smoothed data. Another article (11) has discussed the correlation of these data by means of heats of solution and by means of several new methods of plotting developed for handling these p-t-x-y data.
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ACKNOWLEDGMENT
‘C.
li
1000 900
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Thanks are due A. J. Marsh and E. H. Krehbiel for supplying laboratory facilities and assistance at the McKinley Technical High School, Washington, D. C., where the experimental work WIW done.
600
rmE 500
L1TERATURE;CITED
E
e
Y / V
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Vapor
Figure 4.
Pressure
Water
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Total Vapor Pressure of Acetic Acid-Water
Mixturea
v8. Vapor Pressure of Water on Logarithmic Coordinates
n a t a of
Kahlbaum and Konowalow and of Kayem wmpared at 25, SO. and 15 yo weight water.
(1) Bergatram, quoted by Hausbrand in “Prinoiples and Practice of Industrial Distillation”, 4 t h ed., p. 238 (1925). (2) Blacher, Ibid., pp. 238-42. (3) Cornell, L. W., and Montonna, R. E., IND. ENQ.CHEM.,25, 1331 (1933). (4) Gilmont, R., and Othmer, D. F., IND. ENQ. CHEM.,ANAL.ED., 15, 641 (1943). (5) Kahlbaum and Konowalow, International Critical Tables. Vol. 111. D. 308 (1928). (6) Keyes, D. B., IND. ENQ.CE&,. 25,669(1933). (7) Othmer, D. F.,Ibid., 20, 743-6 (1928). (8) Ibicl., 32, 841 (1940). (9) Ibid., 35, 614 (1943). (10) Othmer, D. F.,IND. ENQ.CHEM..ANAL.ED., 4, 232 (1932). (11) Othmer, D. F., and Gilmont, R., IND.ENG. CHEM.,36, 858 (1944). (12) Pascal, Dupuy, Ero, and Garnier, BuU. em. chim., 29, 9 (1921). (13) Povarnin, G.,and Markov, V., Intarnatiod Critical Tables, Vol. 111, p. 310 (1928). (14) Raylei&, phil, M ~ ~ [SI . ; 4, 521-37 (1902). (15) Sorrel, E., Compt. rend., 122, 946 (1896). (16) York, R.,Jr., and Holmes, R. C.. IND. ENQ. CHEM..34, 346 (1942).
iNVE STI G A T 0 R S oThis Investigation oOthrner A York 8 Holmes v C o r n e l l B Montonna o Bergsirom e Rayleigh rn Blocher A Povarnin a Markov Pascal, Dupuy,B. Gornier e Sorrel
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Figure 5.
Difference in Vapor and Liquid Compositions ( i n Mole I’er C e n t ) of Acetic Acid-Water S y s t e m Mole Per C e n t Water in Liquid
20
30
40 50 60 X MOL % H e 0
70
80
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