Vapor-LiquidEquilibria in Binary System Acetaldehyde Dibutyl Acetal-n-Butanol ALBERT Z. CONNER', PHILIP J. ELVING2, AND SAMUEL STEINGISER3 Publicker Industries Inc., Philadelphia, Pa. Vapor-liquid equilibrium data at atmospheric pressure are presented for the binary system acetaldehyde dibutyl acetal-n-butanol. The isopiestic activity coefficients for the components in the system have been calculated. The specific gravity-composition relation for the binary system was determined. The vapor pressure-temperature relation from 0 to 820 mm. of mercury pressure was determined for the acetaldehyde dibutyl acetal.
T
H E use of precision fractional distillation in the separation of mixtures of various compounds is made possible only by an adequate preliminary investigation of the vapor-liquid equilibrium relations of the systems in question. Adequate and correctly extended and interpreted vapor-liquid equilibrium data are essential to intelligent choice and &esign of distillation and extraction equipment. Since many industrial processes depend almost entirely on distillation methods for the isolation and purification of the final products, and the economic recovery of catalysts and reaction carriers, the need for good vapor-liquid equilibrium data, both in production and research, is apparent. During the study of various methods of separation, the vaporliquid equilibrium data were determined for the binary system composed of acetaldehyde dibutyl acetal and n-butanol. The extent and precision of the measurements of these data were governed by the use for which they were intended, which was primarily to assist in the choice and design of fractionation equipment for the separation of binary mixtures of acetaldehyde dibutyl acetal and n-butanol. I n the calculation of the activity coefficients for the evaluation and interpretation of the experimental equilibrium data, it was found that vapor pressure data for acetaldehyde dibutyl acetal were not known. Consequently, the vapor pressure of acetaldehyde dibutyl acetal over a range of temperatures was determined by a dynamic method. EXPERIMENTAL WORK
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Numerous types of equilibrium stills have been proposed for the investigation of the vapor-liquid relation of miscible liquids. Among the more recent are those designed by Gillespie (4), Jones, Schoenborn, and Colburn (9), Langdon and Keyes ( I O ) , and Othmer ( I d ) , and the modifications by York and Holmes (19). The equilibrium still of Othmer has perhaps found the widest application and was chosen ,for use in the equilibrium determinations to be described. This apparatus, with modification, has been employed successfully a t atmospheric pressure, above atmospheric pressure, and under vacuum by numerous recentdnvestigators (1, 3, 6, 6, 7 , id, 14, 15, 16). The details of construction of the apparatus have been previously described (6, id); the still used was that shown in Figure 1 on page 615 of reference 12 and was made by the Emil Greiner Company of New York. The still was used a t atmospheric pressure without modification, except that the body and vapor neck were lagged
* Present address, Hercules Experiment 2
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Station, Wilmington, Del. Present address, Purdue University, Lafayette, I n d . Present address, University of Connecticut, Storrs, Conn.
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with a thick coat of asbestos, and a drying tube was attached to the condensate reservoir vent. Heat was supplied from a micro gas burner, and the vapor temperature was determined by means of an Anschiitz total-immersion thermometer calibrated t o *0.1" c. The method and technique for experimentally determining vapor-liquid equilibria have been described (11, id, IS, 14). Approximately 150 ml. of one component were charged to the still, and mixtures with various successive additions of the other component were allowed to come to constant temperature. Approximately 30 to 40 minutes were required for equilibrium to be established, after which the composition of the liquid and vapor were determined by suitable analysis of samples withdrawn simultaneously from the still and the condensate reservoir. The values thus obtained were plotted, a smooth average curve was drawn, and the values of the vapor composition at even values of the liquid composition were tabulated. Due to the fact that the experimental points were close to the curve, this method of smoothing was justified t o facilitate use of the data. Carlson and Colburn (d), whose work has recently been elaborated upon by Wohl (18), suggested that the thermodynamic consistency of vapor-liquid equilibrium data may be tested both qualitatively and quantitatively by plotting the logarithm of the activity coefficients for each binary system against the mole fraction of the more volatile component in the liquid. Further comparison may be made by comparing these plots with those obtained from the various integrated forms of the Gibbs-Duhem equation-that is, the van Laar, Margules, and ScatchardHamer equations (d). The vapor pressure of pure acetaldehyde dibutyl acetal was determined by use of a modified Ramsay-Young apparatus similar to that described by Reilly and Rae ( 1 7 ) . The major changes effected included the conversion to an all-glass apparatus with standard-taper joints and the substitution of a calibrated, highly sensitive copper-constantan thermocouple for the mercury thermometer. A notable advantage of this apparatus is the use of absorbent cotton as the evaporating surface. This generally results in excellent vaporization, prevents superheating and other effects of hydrostatic head, and ensures that the liquid a t the thermocouple junction is in equilibrium only with its vapor. By using a cathetometer the precision obtained in the pressure readings was *0.5 mm. of mercury, and the temperature readings were determined within *0.lo C. The procedure followed was essentially that outlined by Reilly and Rae (i7). VAPOR-LIQUID EQUILIBRIUM DATA
The system acetaldehyde dibutyl acetal-n-butanol was studied a t an atmospheric pressure of 762 mm. of mercury. Equilibrium samples were analyzed by specific gravity measurements at 25 O C.; values of the specific gravities of known mixtures are presented in Table I. The refractive indices of the two compounds are too close together to permit the analysis of samples by such measurements. Because of the ease with which acetaldehyde dibutyl acetal is hydrolyzed, care had to be taken to preserve essentially anhydrous conditions throughout the determinations. Preparation
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coefficient plot exhibited a high sensitivity to small changes in composition. Although these variations, which lie within the limit of error for the apparatus, would have little effect on theoretical plate estimation or other design calculations, they are sufficient to cause considerable discrepancies to appear in the activity coefficient plots. Consequently, these points have been omitted from the plot. For very accurate work, the data may be extended as suggested by Carlson and Colburn (3) and Wohl (18).
The van Laar and Rfargules equations ( d ) nwe fitted to the experimental data obtained with fair agreement, although neither equation gave a precise fit.
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20
40 WEIGHT %
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I
60
BUTANOL
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80
h
Figure 1. Boiling Point-Composition Diagram for System hcetaldehyde Dibutyl Acetal-n-Butanol at 762 Mni. of Mercury Pressure
of a pure sample of the acetal was accomplished by vacuum distillation over anhydrous potassium hydroxide. The water was removed axeotropically with benzene. The acetal boiled a t 187.8" C. a t 762 mm. of mercury and had the following physical constants: refractive index n2: = 1.4080 and n2,6 = 1.4060, and specific gravity di: = 0.8335 and d:: = 0.8300.
TABLEI.
SPECIFIC GR.4VITIES O F ACET.4LDEHYDE DIBUTYL L4CETAL-n-BUTANOL ~ I I X T U R E S n-Butanol, wt. % 0 20 40 60 80 100 n-Butanol, mole 0 37.0 61.0 77.9 90.4 100 Sp. gr. d i g 0.8300 0.8263 0.8223 0 8178 0.8130 0.8081
The tendency of dibutyl acetal t o decompose upon heating in the presence of water or acids created experimental difficulty. Figure 2. Vapor-Liquid Equilibrium Diagram for SysIt was found that the prolonged reflux of dibutyl acetal in the tem Acetaldehyde Dibutyl Acetal-n-Butanol at 762 Mm. Othmer apparatus caused the boiling point to drop and fluctuate of Mercury Pressure widely; this indicated decomposition. This effect was reduced to a minimum by the use of highly purified samples, the addition of a drying tube to the condensate reservoir vent, the reduction TABLE11. VAPOR-LIQUID EQCILIBRIUM DATA FOR SYSTEM of equilibrium time to a minimum, and the expedient of starting ACETALDEHYDE DIBUTYL k!ETAL-?n-BUTASOL AT 762 kIM. from the n-butanol side of the equilibrium diagram. Despite Temp., n-Butanol in Liquid Phase n-Butanol in Vapor Phase these precautions slight temperature variations were noted a t e. Teight % Mole % ' Weight % Mole % high concentration of acetal, but their effect on the equilibrium 0.0 0.0 0.0 0.0 187.8 values obtained seems to have been small. 0.2 0.5 12.3 24.7 176.5 1.8 24.6 0.8 43.5 168.1 n-Butanol was purified by distillation through a 4-foot Stedman 4.6 35.3 56.1 2.0 160.0 7.9 52.5 72.3 3.5 fractionating column a t a reflux ratio of 20:l. The fraction 148.0 12.3 24.7 73.3 86.5 133.0 boiling a t 117.8"C. a t 760 mm. of mercury was taken. The 31 .O 51.4 83.9 92.4 125.5 46.7 6 7 . 2 9 0 . 0 9 5.5 122.2 n-butanol boiled a t 117.9" C. a t 762 mm. and had the following 83.0 94.2 97.4 67.4 120.5 92.3 97.1 98.7 83.8 ohvsical constants: refractive index n2:- = 1.3990, 119.0 100.0 100.0 100.0 100.0 117.9 and specific gravity d: = 0.8081. The experimental results obtained are presented TABLE 111. SMOOTHED DATAFOR SYSTEM ACETALDEHYDE DIBUTYL ACETAL- . in Table I1 and shown graphically in Figure 1; TL-BUTANOL AT 762 MM. the corresponding vapor-liquid equilibrium diagram +Butanol in n-.Butanol i n Activity is shown in Figure 2. The smoothed data for the Liquid Phase Vapor Phase Coefficient systema nd the apparent isopiestic activity coeffiTemp C," Weight % Mole % Weight % Mole % %-Butanol Acetal cients for each component were calculated and are 1.00 0.0 0.0 0.0 0.0 187.8 44.0 ... 25.0 2.4 1.0 167.5 recorded in Table 111. The plot of the logarithm ... 59.7 38.8 4.6 2.0 157.5 .... .. ... 77.3 59.0 11.0 5.0 143.4 of these coefficients against the mole fraction of ... ... 84.6 70.0 20.7 10.0 135.1 the more volatile component in the liquid (Figure 1.05 89.4 1.61 78.4 37.0 20.0 129.0 1.10 1.37 92.2 83.6 50.2 30.0 125.8 3) shows the data to be satisfactorily consistent. 1.11 94.2 1.23 87.7 61.0 40.0 123.5 1.11 1.15 95.8 90.7 70.2 50.0 An examination of the activity coefficient plot in 122.0 1.17 1.11 96.9 93.0 60.0 77.9 120.8 Figure 3 revealed an interesting point. Through1.29 1.06 97.7 94.7 84.6 70.0 119.9 i.as 1.03 98.5 96.5 90.4 80.0 119.2 out the main portions of the curves the data were 1.61 1.00 99.2 98.2 95.5 90.0 118.5 ... 100.0 1.00 100.0 100.0 obviously consistent, but where steep slopes were 100.0 117.9 encountered in the equilibrium diagram the activity .
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r 4t
I BUTANOL IN LIQUID
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Figure 3. Activity Coefficient-Composition Diagram for System Acetaldehyde Dibutyl Acetal-n-Butanol at 762 Mm. of Mercury Pressure A.
B.
Activity coefficieqt curve for acetaldehyde dibutyl acetal Activity coefficient curve for n-butanol
Figure 4. Vapor Pressure-Temperature Relation for Acetaldehyde Dibutyl Acetal
VAPORPRESSUREDATA
The vapor pressure-temperature relation, for acetaldehyde dibutyl acetal was determined in the modified Ramsay-Young apparatus previously described. The data are given in Table IV, and a plot of the logarithm of the pressure against the reciprocal of the absolute temperature is shown in Figure 4. For the purpose of convenient approximations an equation for the vapor pressure-temperature relation for acetaldehyde dibutyl acetal was derived from the approximate form of the ClausiusClapeyron equation. Neglecting the volume of the liquid with respect to that of the vapor, assuming ideality of the vapor and assuming the latent heat to be constant over a small temperature range, the equation beomes:
where L = latent heat of vaporization, calories per mole R = gas law,constant, calories per degree per mole p = pressure, mm. of mercury T = absolute temperature, O K.
RELATION FOR TABLE IV. VAPOR PRESSURE-TEMPERATURE ACETALDEHYDEDIBUTYL ACETAL Temp., O
c.
30.4 83.3 101.7 110.8 115.1 125.2 135.0 135.7 141.9 145.3 153.5
Pressure, Mm. Hg. 1.0 19.3 41.8 63.0 76.4 108.3 153.3 159.5 193.9 216.0 270.4
Temp., O
c.
157.2 161.9 167.5 173.0 176.5 178.6 183.6 186.3 188.1 190.9
Pressure,
Mrn. Hg. 309.2 366.5 428.8 500.0 546.5 595.0 663.3 733.3 756.0 820.0
The vapor pressure-temperature relation from 0 to 820 mm. of mercury pressure was determined for the acetaldehyde dibutyl acetal. The specific gravity-composition relation for the acetaldehyde dibutyl acetal-n-butanol system was determined.
On integration this gives LITERATURE CITED
logp=C-*
*
k
R)
(2.3;s
Now if log p be plotted against 1/T and the slope of the resulting line be calculated, it will be approximately equal to L/ (2.303R). Applying this principle to the subject data and solving for the constant C, the equation becomes: log p = (8.232
* 0.005) - 2470T =t5 ~
The vapor pressure data for 72-butanol were obtained from the International Critical Tables (8). SUMMARY
Vapor-liquid equilibrium data a t atmospheric pressure are presented for the system acetaldehyde dibutyl acetal-n-butanol. From these data the isopiestic activity coefficients for the components in the system have been calculated. Boiling pointcomposition, vapor-liquid equilibrium, and activity coefficientcomposition diagrams are presented for this system.
(1) Bloni, R. H., Rtustakas, G. C., Efron, A,, and Reed, D. L., IND. ENG.CHEM., 37,870 (1945). (2) Carlson, H. C., and Colburn, A. P., Ibid., 34, 581 (1942). (3) Fritssche, R. H., and Stockton, D. L., Ibid., 38, 737 (1946). (4) Gillespie, D. T. C.. IND.EXG.CHEM., ANAL.ED.,18, 575 (1946). (5) Gilmont, R., and Othmer, D. F., IND.ENG.CHEM.,36, 1061 (1944). (6) Hafslund, E. R., and Lovell, C. Id., Ibid., 38, 556 (1946). (7) Harrison, J. M., and Berg, L., Ibid., 38, 117 (1946). (8) International Critiral Tables, Vol. 111, p. 219, New York, McGraw-Hill Book Co., 1927. (9) Jones, C. A., Schoenborn, E. M., and Colburn, A. P., TXD. EXG. CHEM..35.666 (1943). (10) Langdon, W’. M., and Keyes, D. B., Ibid., 34, 938 (1942). (11) Othmer, D. F., I b i d . , 20, 743 (1928). (12) Othmer, D. F., Ibid., 35, 614 (1943). (13) Othmer, D. F., IND. ENG.CHEM., AXAL.ED.,4, 232 (1932). (14) Othmer, D. F., and Benenati, R. F., IND. ENG.CHEM.,37, 299 ( 1 945). (15) Othmer, D. F., and Morley, F. R., Ibid., 38, 751 (1946). (16) Othmer, D. F., Shlechter, N., and Koszalka, W., Ibid.. 37, 895 (1945). (17) Reilly, J., and Rae, W. N., “Physico-Chemical Methods,” Vol. 11, pp. 9-10, New York, D. Van Nostrand Co., 1939. (18) Wohl, Kurt, Trans. Am. I n s t . Chem. Engrs., 42, 215 (1946). (19) York, R., and Holmes, R. C., IND.ENG.CHEM., 34, 345 (1942).
RECEIVED February 12, 1947.
