February 1950
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
vanillic acid can be obtained only when 4 or more moles of mixed alkali are employed for each mole of vanillin. As in the last series, later evidence has shown that all yields could be raised somewhat by slightly longer reaction times. PROTOCATECHUIC ACID. Two series similar to the last two were made under the protocatechuic acid-yielding conditions described earlier, The data for the two series have been combined in Table V. The first three experiments, employing potassium hydroxide alone, indicated that 5.5 moles of potassium hydroxide per mole of vanillin is about the lowest alkali-vanillin ratio which will give satisfactory results. The data for the next four experiments, employing 50 to 50 mixed alkali, indicated that an alkali-vanillin ratio of 6 to 1 is the lowest ratio which gives good results and a pure product in the oxidation of vanillin to protocatechuic acid with the 50 to 50 caustic mixture.
379
ACKNOWLEDGMENT
This paper represents a portion of the results obtained in the research program sponsored by the Sulphite Pulp Manufacturers’ Research League and conducted for the League by The Institute of Paper Chemistry. Acknowledgment is made by the Institute for permission on the part of the League to publish these results. LITERATURE CITED
(1) Pearl, I. A., J . Am. Chem. Soc., 68, 2180 (1946). (2) Zbid.,71,2331 (1949). (3) Pearl, I. A., and Beyer, D. L., Zbid., in press. (4) Pearl, I. A.,and McCoy, J. F., FoodInds., 17, 1458 (1945). (5) Pearl, I. A,, and McCoy, J. F., J . Am. Chem. Soc., 69, 3071
(1947). RBCEIVED June 20, 1949. Presented before the Division of Organio Chemistry a t the 116th Meeting of the AMERICAN CHEMICAL SOCI~TY Atlantio , City, N. J. This is paper No. X in a series a n “Reactions of Vanillin and Its Derived Compounds.” For paper No I X see reference ( 3 ) .
Salt Effect in Vapor-Liquid Equilibria ETHANOL-WATER SATURATED WITH POTASSIUM NITRATE ROBERT M. RIEDER’ AND A. RALPH THOMPSON University of Pennsylvania, Philadelphia, Pa. Vapor-liquid equilibrium data have been obtained for the system ethanol-water saturated with potassium nitrate at atmospheric pressure. A large increase in the relative volatility was observed at low ethanol concentrations. The effect of the presence of the salt on the activity coefficients of the two liquid components is illustrated and discussed. The possibility is suggested that salts may be added to many mixtures which are to be distilled in order to improve the separation factor.
EQUILIBRIUM DATA FOR AQUEOUS ETHANOL SOLUTIONS
T
HE problem of solvent recovery from a solution containing salts arose as part of a program (fa) to investigate the
I
possibilities of industrial crystallization of inorganic salts by means of organic precipitants such as the common alcohols, To be economically feasible the solvent must be recovered as completely as possible and to estimate the distillation requirements, the vapor-liquid equilibrium data are necessary for the system under consideration. The addition of a solid substance to a system of two liquid components will affect the solubilities and partial vapor pressures of the two liquids. If the salt is very soluble in one liquid component but not in the other, their mutual solubilities are decreased, ( d ) , and the vapor pressure of the liquid in which the salt is soluble will be decreased while that of the other component will not be appreciably affected (14). From the standpoint of distillation, this means that the liquids in a system of this type would be easier t o separate than if the salt were not present. As little has been published on the exact effect of dissolved salts on the vapor-liquid equilibria of common mixtures, it was felt that quantitative data of this nature would be valuable. Solutions saturated with salt were used because it was expected that maximum influence would be exerted and also because solutions obtained for solvent recovery in the precipitation method of 1 Present
18, Pa.
crystallization would be saturated with salt. The system ethanol-water was chosen as the equilibrium data for this system are well known ( I , & 7, 10,1 1 ) ; this system was used in some of the work on crystallization, and accurate density-composition data are available (6,9). Potassium nitrate was used because it le very soluble in water and only slightly soluble in ethanol and because the density of saturated solutions of this salt in aqueous ethanol had been accurately determined (IS).
address, Eastern Regional Research Laboratory, Philadelphia
The vapor-liquid equilibrium data for the binary ethanol-water system have been very thoroughly investigated by several experlmenters. Carey and Lewis (1, 10) used an Othmer-type still (7); Cornell and Montonna (a)used differential-type distillation; Jones, Schoenborn, and Colburn (6) used a new still of their own design; and Rieder and Thompson ( I 1 ) used a Gillespie still (3). On the whole, the data of these investigators show good agree ment. All the stills mentioned incorporate various features of design to minimize refluxing and fractionation of the vapor sample or entrainment of the boiler liquid into the vapor. The Othmer-type still was chosen for these experiments because it proved most satisfactory for handling ethanol-water solutions saturated with salt. EQUIPMENT AND EXPERIMENTAL TECHNIQUE
The equilibrium still used for these experiments was a slightly modified Othmer-type (7,8), heated by an electric radiant heater placed underneath. The walls of the still were kept at or above the boiling temperature by Nichrome wire embedded in lagging on the walls and on the straight section above the still pot. The modifications consisted of a smaller condensate chamber and a 10-mm. bore, heated sampling stopcock set about 35 mm. above the bottom of the still pot.
380
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
,
I
1
_-A
20 40 60 80 100 MOLE % ETHANOL IN LlOUlD (SALT-FREE BASIS)
WT. % ETHANOL IN LIQUID (SALT-FREE BASIS)
1. Vapor-Liquid Equilibrium Data for Ethanol-Water S a t u r a t e d with Potassium Nitrate at Atmospheric
Figure 2. Vapor-Liquid Equilibrium Data for Ethanol-Water S a t u r a t e d with Potassium Nitrate a t Atmospheric
Figure
Pressure Experimental data, weight
I
Vol. 42, No. 2
Pressure Smoothed data, mole
7 0
The still was charged by pouring in a concentrated solution of salt in water, boiling off the excess water, and adding alcohol to attain the desired composition. A t all times during the runs there were excess crystals in the still. The runs were allowed to continue until the temperature of the exit vapor was constant for a t least 30 minutes. By making several runs for much longer periods of time, it was found that equilibrium was attained in 1.5 hours so most of the runs were made for 2 hours' total duration. The two samples, one from the still pot and one from the condensate trap, were taken simultaneously into chilled, stoppered Erlenmeyer flasks. Immediately after these samples were taken, a still pot sample was drawn off into a chilled, tared, weighing bottle for determination of the percentage of salt. The samples for vapor and liquid composition n-ere analyzed a t room tern perature by measuring the density with calibrated Gay-Lussac bottles. A11 densities were calculated for pure aqueous ethanol solutions a t 20" C. and the percentage of alcohol \!as determined from the tables of the Bureau of Standards (6,Q). The xveight % alcohol present in the saturated salt solutions \vas calculated on a salt-free basis by graphical interpolation of density isotherms given for this system by Thompson and Vener (13).
heated a t 110" C. for a t least 2 hours. Blank tests on this evitporation procedure with a weighed amount of salt dissolved in water at room temperature showed an accuracy of 0.2 mg. Boiling temperatures for the ternary system saturated ith potassium nitrate were determined by placing synthetic solutions in a separate apparatus consisting of a three-necked flask, of 2liter capacity, fitted with a reflux condenser and calibrated thermometer. DATA FOK S4LT-SATURATED SYSTEM
The primary data obtained were boiling temperatures, weight
7' alcohol on a salt-free basis in both vapor and liquid, and percentage of salt in the solution saturated with potassium nitrate at the boiling point. VALUES TABLE I. EXPERIYEXTAL S'.4POR-EIQUID EQUILIBRIUM FOR SOLUTIOKS OF ETHAXOL-TVATERS~ T U R A T E D WITH
s,wt. 07 RUE
KO.
1
2 3 4 5 6 7 8 9 10 11 12 13 14
15 16
'
WT. % ETHANOL IN LIQUID (SALT-FREE BASIS)
Figure 3. Solubility of Potassium Nitrate Ethanol-Water Solutions at Their Boiling P o i n t s
in
The bottle containing the sample for percentage of solids was immediately capped and weighed to determine the amount of sample to be evaporated. By working rapidly to avoid evaporation loss, weights were reproducible within 1 mg. The sample was evaporated at 50' C. to prevent splattering, and when almost dry it was
70
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
32 33 34 35 36 37
Duration, Hours 2 2 2 2 2 2 2 2 2 2 2 2 2 1.26 1.75 2 2 2 2 2.25 15.5 2.25 2 2 2 2 2 2
2 2 2 2 2 2 2.5 2 2
Y , Wt. ,yo EtOH i n Vapor 82.6 83.0 83.7 83.2 83.4 84.0 82.7 95.9 87.4 84.8 85,l 85.0 87.1 87.1 88.6 90.6 92.7 93.8 94.8 66.3 77.6 95.7 97.2 97.7 93.8 94.5 96.0 95,s 96.5 49.3 96.8 79.8 23.2 50.9 64.7 81.7 82.6
E~OH i; (Salt-Free Liquid Basis) 48.4 52.0 56.1 58.9 63.5 65.8 45.9 96.3 82.3 73.3 7Z.6 76.3 81.0 82.1 85.7 88.7 91.7 93.4 94.2 2.8 8.1 95.6 97.2 97.8 93.3 94.4 94.7 95.1 95.6 0.9 96.9 12.0 0.8 1.6 2.7 15.3 24.4
wt. yo
KNOa at Saturation at Boiling Point 24.2 24.2 16.8 14.2 10.8 9.3
27.0
2.5 1.6 5.0
3.8 3.0 1.2
i.6 I
.u
0.7 0.4
0.5 0.5 64.9 54.8 0.3 0.2
0.3
0.4
0.5 0.4 0.4
0.3 70.9 0.3
55.5
71.8 69.5 67.7 52.4 48.2
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1950
381
TABLE11. SMOOTHED VAPOR-LIQUID EQUILIBRIUM DATAAND RELATIVEVOLATILITIESFOR ETHANOLWATER SATURATED WITH POTASSIUM NITRATE
x, Wt. % EtOH
MOLE FRACTION ETHANOL
-
Figure 4. Temperature Composition Diagram for Ethanol-Water Saturated with Potassium Nitrate at Atmospheric Pressure Dashed line represents curve for ethanol-water
s
The experimental data for vapor-liquid equilibrium, given in Table I, were plotted on rectangular coordinates and gave a smooth curve as shown in Figure 1. The corresponding curve for the binary ethanol-water system, determined by the authors in the same Othmer still, is shown as a dashed line for comparison. Smoothed values of the compositions in weight yo,X and Y , were taken from these curves and the compositions in mole % were calculated as given in Table I1 and plotted in Figure 2. The solubility of potassium nitrate in ethanol-water solutions a t their boiling points is presented in Figure 3. The boiling points of the ethanol-water solutions as determined separately are given in Table 111. The boiling point-composition diagrams for the ternary system saturated with potassium nitrate (solid line) and for the binary ethanol-water system (dashed line) are presented in Figure 4. The relative volatility or separation factor, a, was calculated from the well known equation: (1
2 / .~ xn = __ XA
'
yB
where z and y are the mole fractions of the given component in the liquid and vapor, respectively. These values are plotted in Figure 5 with similar data for the ethanol-water system shown as the dashed line. SALT EFFECT
From the plots of the percentage of alcohol in vapor and liquid phases (Figures 1 and 2), it is obvious that the addition of salt, which is soluble in one but not in the other component, increases the difference in concentration of the liquid components between the two phases, This is as would be expected from the kinetic theory: by this concept the addition of salt should lower the
in Liquid (Salt-Free) 0.0 0.5 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 12.0 14.0 16.0 18.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0 70.0 75.0 77.5 80.0 82.5 85.0 87.5 90.0 92.0 94.0 96.0 98.0 99.0 99.5 100.0
Y Wt. '7 E t O H i," Vapor
0.0
18.0 37.0 61.0 66.5 70.2 72.7 74.6 76.2 77.4 78.2 78.8 79.8 80.8 81.6 82.3 82.6 82.6 82.6 82.6 82.6 82.6 82.8 83.2 83.5 83.8 84.3 85.0 85.6 88.3 87.3 88.5 89.9 91.5 93.0 94.5 95.9 97.6 98.7 99.2 100.0
x Mole %
EtOH.in Liquid (Salt-Free) 0.0 0.2 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.3 3.7 4.2 5.1 6.0 6.9 7.9 8.9 11.5 14.3 17.4 20.7 24.2 28.1 32.3 36.9 42.1 47.8 54 0 57.3 61.1 64.8 68.8 73.2 77.9 81.7 85.8 90.3 93.0 97.5 99.0 100.0
v, Mole % E t O H in Vapor 0.0 7.9 16.7 38.0 43.7 47.9 51.0 53.5 55.7 57.2 58.4 59.3 60.6 62.2 63.3 64.5 65.0 65.0 65.0 65.0 65.0 65.0 65.3 66.0 66.5 66.9 67.8 68.8 70.0 71.1 73.0 74.4 77.7 80.8 83.8 87.2 90.1 94.2 96.8 98.2 100.0
Relative Volatility, U
42:7 57.3 76.0 63.9 56.5 51.0 46.8 42.0 39.2 36.5 33.2 28.6 25.8 23.3 21.2 19.0 14.3 11.1
8.8
7.2 5.8 4.8 4.1 3.4 2.8 2.3 1.9 1.7 1.6 1.5 1.32 1.27 1.20 1.16 1.13 0.98 0.85 0.78 0.55
...
vapor pressure of the component in which it is soluble because of the interference effect of the salt molecules a t the interface between the liquid and vapor phases. Also, it follows that relative volatility should increase greatly with addition of salt, and this was proved by the experimental results as illustrated in Figure 5. With the system ethanol-water saturated with potassium nitrate, little effect is noticed on the equilibrium curve above 90% alcohol on the weight basis, since potassium nitrate is so slightly soluble in mixtures of high alcohol concentration. Also, for the same reason, no change in the azeotropic point was observed with this system, although with other systems, change of this point or breaking of the azeotrope might be expected, 8 s is encountered in the case of the isopropyl alcohol-water-ammonium nitrate system (19). I n the course of the experimental work with these saturated solutions a t the boiling point, it was noticed in the region from approximately 20 to 50 weight % ethanol that if the boiling were
TABLE
111. BOILINGPOINTS O F ETYANOLWATER SOLUTIONS SATURATED WITH KNOa
x,Wt. % EtOH,
Temp., O
c.
118.2 96.2 84.0 82.0. 80.4 80.4 80.6 80.6 80.6 80.2 80.0 79.2 78.6 78.2 78.3
in Li uid (Salt-)ree
Basis) 0 5 10 15 20 25
30 40 50
60
70 80 90 95 100
x, Mole % Y Wt To EtOH in Vapor 0 72.7 78.8 81.2 82.6 82.6 82.6 82.6 82.8 83.5 84.3 86.3 91.5 95.2 100.0
EtOH. in Liquid (Salt-Free Basis) 0 2.0 4.2 6.4 8.9 11.5 14.3 20.7 28.1 36.9 47.8 61.1 77.9 88.0
100.0
Y, Mole '70
EtOH in Vapor 0 51.0 59.3 62.7 65.0 65.0 65.0 65.0 65.5 66.5 67.8 71.1 80.8 88.6
100.0
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
allowed to subside, two liquid phaves were clearly evident. Figures 1 and 2 show that the equilibrium curve is horizontal in this range, exhibiting the phenomenon shown by all partially miscible systems. Equipment was not available for determining the eolubility relations in the two liquid phases separately, so the system was kept thoroughly mixed during the boiling and sampling for the several points in this region by slightly increasing the heat Input to the still pot to ensure rapid evolution of vapor.
MOLE
ETHANOL IN Liauic ( S A L T - F R E E BASIS)
Figure 5. Relative Volatilities for Ethanol-Water Saturated with Potassium Nitrate at Atmospheric Pressure Dashed line represents curve for ethanol-water
I t is interesting to note the effect which the presence of the salt In the liquid phase has on the activity coefficients of the ethanol and the water. These values were calculated for the two liquids In the ternary system by using the vapor prewures at the boiling points of the solution saturated with Dotassium nitrate. For a given component, A , the activity coefficient is calculated from:
where P = total pressure; P A = vapor pressure of component A ; V A = mole fraction of component A in the vapor; and X A = mole fraction of component A in the liquid. 2C
Vol. 42, No. 2
The activity coefficients for ethanol and water in the ternary system are plotted against salt-free 1iqai.I composition in Figure 6. On this same graph are shown the activity coefficients fro the two components in the binary ethanol-water system using the data of Rieder and Thompson ( 1 1 ) . It can be seen in Figure 6 that the activity coefficient of the water is decreased over the entire range by the presence of the salt while that of the ethanol is increased. This is as ~5ouldhe expected as the salt has a marked solubility in water and a very low solubility in ethanol which would tend to increase the escaping tendency of the alcohol and decrease that of the water. The attraction of the salt molecules for those of water is so great that there is a negative deviation from Raoult’s law (activity coefficient less than unity) shown at liquid compositions lower than about 27 mole % ethanol. h-egative deviations from Raoult’s law are frequently encountered in the case of electrolytes. There is no observable break in the curve at either of the boundaries of the region where two liquid phases occur. These experiments show that recovery of ethanol from a crystallization process is feasible. Because of the increase in separation by the addition of potassium nitrate, the distillation columns necessary for this solvent recovery could consist of fewer plates than are required for an ordinary ethanol-water fractionation. This, of course, would lower the initial investment for equipment. The increase in relative volatility for this system is so large that it suggests the possibility of adding salts of this type to man) mixtures which are to be distilled, to cut down the number of plates necessary for any required separation. When the salt added is more soluble in the low boiling component, there would be no tendency for salt to build up on the plates of the column if the feed were added between the still pot and condenser. The concentration of the less volatile component increases as the lower end of the column is approached and, therefore, the solution would become less saturated with salt as it progressed down the column. Excess salt could be added directly to the still pot to obtain the greatest possible separation in the boiler itself. To recover the bottoms, the solvent could be evaporated from the salt, collected, and the salt re-used for addition to the feed. Investigations are being continued on other systems to determine the practicability of this method and to note the effect of the presence of various ions.
10
LITERATURE CITED S
6
P I= 2
w
4
2 uUw .. 0
* e t
z
e 0 4
1.c .0.8
9.6
I
I
I
I
I
i
0.2 0.4 0.6 0.8 1.0 M O L E FRACTION E T H A N O L IN S A L T - F R E E LIQUID
Yigure 6. Activity Coefficients for EthanolWater Saturated with Potassium Nitrate at Atmospheric Pressure Dashed Lines represent curves for ethanol-water
(1) Carey, J . Y., and Lewis, IT. K., IND.ENC.CHEM.,24,882 (lY3a). and Montonna, R. E., Ibid., 25, 1331-5 (1933). (2) Cornell, L. W., (3) Gillespie, D. T. C., IND.ENG.CHEM.,ANAL.ED., 18, 575-7 (1946). (4) Glasstone, S., “Textbook of Physical Chemistry,” 2nd ed., Neu York, D. Van Nostrand Co., 1946. (5) Jones, C. A.. Schoenborn, E. M., and Colburn, A. P., IND.ENG CHEM.,35, 688-72 (1943). (6) Osborne, K . S., McKelvy, E. C., and Hearce, €1. W., Nail. RUT. Standards Bull. 9, 327 (1913). (7) Othmer, D. F., IND. ENC.CHEM.,20, 743 (1928). ( 8 ) Ibid., 35,614 (1943). (9) Perry, J. H., “Chemical Engineers’ Handbook,” 2nd e d . . pv 441--2. S e w York, McGraw-Hill Book Co., 1941. (10) Ibid., p. 1364. (11) Rieder, R . M., and Thorrlpeoli, .\. R., IND.ENG. CHEM.,41, 2905 (1949). (12) Thompson, A. R., and Molstad, hl. C., Ibid.,37, 1244-8 (1946). (13) Thompson, A. R., and Vener, R. E., Ibid.,40, 478-81 (1948). (14) Walker, Lewis, MeAdama, and Gilliland, “Principles of Chemical Engineering,” 3rd ed., New York, McGraw-Hill Book Go.. 1937. RECEIVED March 1, 1949. Presenwd at the Miniature Meeting of the Philadelphia Section of the A M E R I C A N CHEMICAL S O C I E T Y , January 22. 1948.
