INDUSTRIAL A S D ENGINEERING CHEMISTRY
608
The high dilution ratio of ethylene dichloride indicates the economy of this product in lacquers and thinners. Use in Cellulose Acetate Lacquers
The solvent mixture required in cellulose acetate lacquer depends largely upon the type of acetate used. Completely acetylated cellulose (44.8 per cent acetyl) is relatively insoluble in all ordinary solvents and is therefore unsuited for use in lacquers. The solubility increases rapidly with a decrease in acetyl content, and a cellulose acetate containing 35.5 per cent acetyl is generally considered to be too soluble for ordinary lacquer work as it is completely dissolved by a mixture of water and acetone. Cellulose acetates containing from 38 to 42 per cent acetyl are generally used in lacquers and may be obtained in a wide range of viscosities. The type that has practically the same viscosity as ordinary ‘/*-second nitrocellulose may be used in formulating a lacquer with a high percentage of solids. The solubility data of this type of cellulose acetate in various solvent mixtures are used as an example of solubility in general and to ,-hom the possibilities of solvent formulation. With the exception that solvent mixtures for cellulose acetate lacquers must contain a higher percentage of active solvents than a mixture for a nitrocellulose lacquer to obtain a Satisfactory film, the same methods are followed in their formulation. The choice of solvents naturally depends upon the drying time desired and the demand nil1 undoubtedly be, as it has been in the case of nitrocellulose lacquers, for a rapid drying lacquer that will be applicable in industrial finishing. One of the simplest cellulose acetate solvents of the rapiddrying type is a mixture containing 70 per cent ethylene dichloride and 30 per cent denatured alcohol by volume. This
-
Vol. 22, Xo. 6
mixture has a dilution ratio of 0.4 with toluene, which may be considered a practical margin of safety. By using this mixture as the basic solvent, the drying time may be retarded by the addition of a medium-boiling solvent and a medium-boiling diluent to produce better flow out of the lacquer. Solvents such as 1,4-dioxan and methyl Cellosolve may be used in considerable quantity without materially increasing the drying time, while the high-boiling solvents, such as diacetone alcohol, Cellosolve acetate, and butyl Cellosolve, when used in smaller amounts, have their greatest use in raising the blush resistance of the lacquer. Several type formulas that have been used in cellulose acetate lacquers are shown in Table T’. Table V-Cellulose Formulas 1 2 3 Ethylene dichloride 70 70 70 Toluene Denatured alcohol PO 20 20 Ethyl acetate Solvatone Methyl Cellosolve 10 1,4-Dioxan Diacetone alcohol Cellosolve acetate Ethyl lactate 10 Butyl Cellosolre 10
Acetate Lacquers 4 5 6 7 60 50 50 70 10 15 IO
10
30
8 70
13
PO 13
15 15
9 40 20 10
10 60
30
10
20
15
10
10
5
The solubility data of cellulose nitrate and cellulose acetate tvith the more common solvents and diluents with ethylene dichloride are shown on the triangular coordinate charts. These data indicate the value and economy of this product in the formulation of lacquers. Literature Cited (1) G. S. Pub. Health Service, Pub. Health Rept. 46, N o . 5 (January 31, 1930).
Use of Azeotropic Data for Calculating General Properties of Binary Systems’ Clyve Allen CHEMIC.4L
LABORATORY, UNIVERSITY O F CALIFORNIA, BERKELEY, CALIF.
H E rapidly growing lists of binary constant-boiling mixtures now available, in addition to furnishing the data for which they were primarily intended, may readily be made in many cases to yield much more information; partial pressures and related properties may be estimated for the entire range of composition. Through the relations indicated in this paper a practical method is offered for gaining information concerning the many systems which deviate considerably from Raoult’s law a t finite concentrations, yet not sufficiently to form two liquid phases. For this purpose the equations ( 2 , 3, 4 )
T
RT In ( a l / N I ) = bNZ2 R T In (a,/NJ = ( b
+ cNz3 + d N Z 44- . . . .
(1)
+ 3 / 2 c + 2 d ) N 1 * - ( c + 8/d).N.I.3.+ dN14+ (2)
are eminently suitable. In these equations the a’s are the activities and the N’s the mol fractions of the components, R is the gas constant, T the absolute temperature, and b, c, d, etc., are empirically determined quantities constant a t a given temperature and pressure with respect to composition. 1
Received March 21, 1930.
These equations are valid for solutions which obey Raoult’s law in very dilute solution-i. e., Limit (al/N,) = 1 NI +1
Limit ( a z / N z )= 1 Ni +1
(3)
Equation 2 follows from Equation 1 by Duhem’s relation. The thermodynamic significance of these equations and methods for estimating and for calculating the quantities b, c, etc., have been set forth by Hildebrand (2, 3, 4 ) . In applying Equations 1 and 2 to solutions composed of two volatile components, we may without appreciable error replace each of the activities by the equivalent p / p o , where p is the partial pressure of a component and p o its vapor pressure when pure. A number of investigators have shown that the isothermal behavior of a great many systems can be represented quite closely without necessitating powers of N1 and N z higher than the third ( 7 , 8, iO)-i. e., d , etc., may be assumed negligibly small. Moreover, Hildebrand (3) has found that for many systems b, c, etc., vary but little with temperature. Hence, whenever we have the values of the partial pressures a t a given composition and temperature and know the vapor pressures of the pure components a t that temperature, Equations 1 and 2 then enable us to
INDUSTRIAL AA-D ENGIAVEERIAVG CHEMISTRY
June, 1930
calculate b and c and so t'o represent the general behavior of the system. I n general to obtain the above data a measurement of the partial pressures, etc., of the system is necessary. It is the purpose of this paper to call attention to the fact that, owing t'o the special properties of homogeneous constantboiling systems, the customarily recorded data-constant boiling temperature, pressure, and composition-together with the vapor pressures of the pure components, suffice to calculate b and c.
609
temperature, we may estimate them in the usual way by integration of the approximate Clausius-Clapeyron equation d In p/dT = A H / R T 2
under the assumption that the heats of vaporization of the pure components, bH,' and AH2', are constant from the boiling points of the pure components a t pressure K , TI' and Ta', to the constant boiling temperature-i. e.,
.Vole-By "homogeneous" we mean t h a t only one liquid phase is present. T h e critical mixing point and heterogeneous (two liquid phase) systems have received thorough consideration in this connection b y Hildebrand ( 2 , 3, 4) and by Heitler (1).
In homogeneous constant-boiling solutions, as is well known: PiliV1 where
pz/N?, SO PI
NIT,pz = NZT
?r = Pl
+
Sole-For
(4)
+ P,
a boiling solution pi p? = r, t h e total pressure. Assuming Dalton's law for t h e vapor above t h e solution a n d letting primed mol fractions refer t o t h e vapor, P I = Xl'a, $2 = X * ' T . B u t t h e composition 01 a constant-boiling solution is t h e same a s t h e composition of its 1 apor; hence Equations 4 follow.
Hence, neglecting powers of SIand iV2higher than the third, Equations 1 and 2 become
+
R T In (?r/plo) = bN22 ch723 R T In ( x / p ~ O ) = ( b 3/lzc)iV,?- cY13
+
(5)
from which
and employ these values in Equations 6 for estimating b and c. For example, we have (5, ) ' 6 for chloroform AH'/ T o = 21 calories per mol, T o = 334.6' K.; and for acetone .AHo/T' = 22 calories per mol, T o = 329.2' K.; the azeotropic data are T = 337.6' K., L V C ~ C=I , 0.655, x = 1 atmosphere. From Equations 6 and the approximation (Equation 7 ) we then find b/RT = -0.89, c/RT = 0.296, instead of the values in Table I. Table 11-Data for Isothermal Systems. Partial Pressures as Calculated by Modified Duhem-Margules Equation and Observed by Zawidski (10)
PI PI P? Pa 1'1 CALCD.aOBSD.C.4LCD.aOBSD. MoZ Mm. K . fraction M m . ,k'm. M m . Mm. Carbon tetrachloride (1) 308 323.09 0.1758 59.9 5 9 . 7 221 6 2 2 1 . 8 SYSTEM
Benzene Carbon disulfide (1)
a t the constant-boiling temperature and composition of the solution. We have calculated b and c for several constant-boiling solutions (Table I) and, under the assumption that these quantities 1-ary but little with temperature, we have calculated from Equations 1 and 2 the partial pressures a t several concentrations, and in Table I1 compared them with those observed by Zawidski ( I O ) . Table I-Data for Several Constant-Boiling Solutions and Resulting Constants for Modified Duhem-Margules Equation 15, 9, 1 0 ) COMPONEUTS T .. X, r Po b R2' c,RT ,1.101
' K . fraction M m . J l m . Carbon tetrachloride (1) 323 09 0.9165 308.43 308 Benzene 0.0835 268 1
0 . 2 1 1 -0
0758 4747
Carbon disulfide (1) hlethylal
310 35 0 . 4 6 0.54
760
555 636
1.336 -0
Carbon disulfide (1) Acetone
312.35 0.61 0.39
760
597 407.5
1 . 6 i t l -0.184
Chloroform (11 Acetone
337 6 0 655 760 0 345
995 4
Ethyl iodide (1) Ethyl acetate
323 09 0 765 0 235
353 5 280 3
364 3
851 1 - 1
lh
fi0
268
T
0.3953 1 2 9 . 4 128.7 165.3 1 6 5 . 8 0.7652 238.2 238.5 6 8 . 9 68.3
513.4 308 17 0.3480 2 7 7 . 6 2 7 8 . 5 4 2 1 . 8 4 1 8 . 3 0.6060 373.0 380.9 3 2 4 . 2 314.6 0.8573 452 7 4 6 2 . 2 1 7 9 . 6 1 7 2 . 5
RIethylal
587.7
Carbon disulfide (1)
513.4 308.17 0.2038 275,O 277.9 290.3 287.0 0.4953 379.7 403.6 250.0 2 4 2 . 4 344 1 0.8280 445.3 464.9 1 7 1 . 2 180.2
Acetone Chloroform (1)
293.1 308.17 0.2630 50.9 5 0 . 4 246.9 2 4 0 . 8 0.4934 114.0 111.6 152.0 143.9 0 . 6 6 2 2 1 7 2 . 2 169.9 86.0 7 9 . 1
Acetone
344.1
Ethyl iodide (1)
353.1 323.09 0 . 1 9 4 6 9 1 . 2 8 9 . 0 2 2 8 . 7 2 3 0 . 5 0 4488 186.9 183.2 164.7 1 6 7 . 5 280.4 0.8253 2 9 6 . 6 2 9 6 . 2 67.0 6 7 . 3
Ethyl acetate
h-ote t h a t the errors in the calculated partial pressures are in m o d instances compensating. so t h a t t h e total vapor pressure would he given even more closely.
At 308.17 ' K. we have from Zawidski's measureinelits 293.1 mm.; ~ ' ( C E , ) , C O = 344.1 mm. Putting these values in Equations 1 and 2, we obtain, for SCHC,, = 0.4934, ~ C H C I , = 117.5 mm., ~ ( c H , ) , c o = 149 mm. Comparison with Table I1 shows that the error introduced by the approximations (Equations 7 ) is appreciable. ~ O C H C I ~=
Acknowledgment
0 654
0 590 -0
1922
The systems tabulated were selected as examples of solutions obeying Equations 3. Zawidski tested the validity of equations similar to (1) arid (2)-containing no term accounting for temperature variation, however-for the isothermal systems studied. Although our calculated b's and c's are not equal to those of Zawidski, it should be noted that they are substantially equivalent in describing the partial pressures. I n addition to calculating partial pressures a t temperatures not far removed from the constant boiling temperature, we can of course obtain many other properties of systems (3,3 , d ) . When pIo and p20 are not known at the constant boiling
The writer wishes to express his thanks to Joel H. Hildebrand and to T. Dale Stewart, of the Chemistry Department of the University of California, for their suggestions regarding this paper. Literature Cited Heitler, . i n n . Physik, 4, SO, 630 (1926). Hildebrand. "Solubility," p. 44, Chemical Catalog. 1924. Hildebrand, Proc. Xall. A c a d . S c i . , 13, 267 (1927). Hildebrand, J. A m . Chem. Sac., 51, 66 (1929). International Critical Tables, Vol. 111, pp. 215, 318, hIcGrdw-Hill. 1928. I b i d . , Val. V, p. 136 (1929). hlargules, S i f z b . d k a d . TViss. Wien, 104, 1243 (1895). Porter, Trans. Faraday Soc., 16, 336 (1921). Rosanoff, Bacon, and Schultze, J. .am.C h e m S o c . . 36, 1833 (1914). Zawidski, Z . p h y s i k . C h o n . , 35, 129 (1933).
