Composition of Vapors from
Boiling Binary Solutions1 SYSTEMS OF PHENOL WITH BETA- AND GAMMA-PICOLINES AND 2,6 L UTIDINE
-
DONALD F. OTHMER AND SIDNEY A. SAVITT Polytechnic Institwte of Brooklyn, Brooklyn, N. Y .
Vapor-liquid equilibrium data were determined for systems of phenol with 8-picoline, 2,6-lutidine, and y-picoline at constant pressures of 760, 600, 400, and 200 mm. of mercury by methods previously described (1, 4 ) . The r-y diagrams show that in each case a maximum constant boiling mixture was formed at every pressure encountered. The azeotropic composition (mole per cent picoline) always increased slightly with decreasing pressure. The data are correlated with partial pressures, total pressures, and activity coefficients of the respective components to give straight lines on logarithmic plots, to show the mutual consistency of the data. The plot of vapor compositions against total pressures shows deviations of lines from the horizontal; this indicates the changes in partial molal heat of solution of this nonideal mixture, and also that changes in the rota1 pressure on the system produce significant changes in the vapor-liquid equilibrium.
~,~-LUTIDIKE (6). The impure sample was added to a 60% urea-water mixture a t 80" C. Upon cooling, large coarse crystals of the lutidine-urea addition compound were formed. The crystals were separated from the mother liquor, washed, dried, and then heated t o 130" C. where the molten mixture stratified into two layers. The upper layer (2,6-lutidine) was decanted off. Subsequent drying with sodium hydroxide and distillation yielded a product distilling a t 142-143" C. and chemically free of the other picolines, as was shown by later tests. ?-PICOLINE ( 7 ) . The commercially pure sample was distilled with phenol. The maximum constant boiling mixtures of ppicoline and 2,6-lutidine-phenol boiled a t a relative lower temperature and were discarded. The , -picoline-phenol c.b.m. distilling over a t 190-191 'was collected. Solid sodium hydroxide was added to this mixture, and the mixture distilled again. The fracti06 144-145 C. was collected and dried with solid sodium hydroxide to give pure y-picoline. O
ANALYTICAL METHODS
T
HIS work is a study of the more important vapor-liquid equilibrium data a t atmospheric and subatmospheric pressures of the binary systems of the several picolines-B-picoline, +picoline, and 2,6-lutidine [ (CHS)&bHSN, 2,6-dimethylpyridine] -with phenol. Maximum constant boiling mixtures (c.b.m.) have been reported (7) between the respective picolines and phenol; and more complete data were desired t o make clear the entire vapor-liquid phase relations. Systems at several subatmospheric pressures were therefore studied by methods previously described (1). Besides vapor compositions there also follow, from tHese pressure-temperatures-y data, activities, relative volatilities, andequilibriumconstants; these may also be correlated as described by Othmer and Gilmont (6).
Analysis of the binary mixtures was attempted by determination of a physical property. Neither the refractive index nor density proved adaptable, as' did viscosity and freezing point. Chemical analysis was also used by titrating the picoline with hydrochloric acid after removing the phenol from the mixture. A combination of methods was resorted to, since no one method was adequate to analyze the vapor and liquid samples of various mixtures throughout the entire range of compositions. VISCOSITY. An Ostwald viscometer was calibrabed with water a t 60 C. Various synthetic mixtures of picolines and phenol in known ratios were run through the viscometer and times recorded. The time in seconds required by the standard sample to flow through a particular pipet, divided $y the time in seconds for distilled water, was taken as the relative time of the sample. A curve of relative time against mole per cent picoline was plotted (Figure 1)from data in Table I. I n the high phenol region (below 20% picoline) the curve breaks abruptly, rendering the method inapplicable in this range. The freezing point method was used for the region of high phenol content. FREEZING POINT. A sample of 10 cc. vias placed in a test tube enclosed in a larger test tube having a stirrer and a thermometer. The entire apparatus was then submerged in a n ice water bath. (Care was exercised to allow for the supercooling effect of the sample, since the temperature of first crystal formation is below the actual freezing point temperature.) The temperature rose rapidly t o the freezing point and was recorded when constant. The freezing point curves in Figure 1 were drawn from data in Table I1 as freezing point against mole per cent of the picolines. A small weighed sample CHEMICAL ANALYSIS OF PICOLINE. (approximately 0.5 gram) of 7-picoline-phenol was transferred t o a distillation flask by washing out with 50 cc. of distilled water.
PURIFICATION O F MATERIALS
None of the several picolines were available in a purity above 95y0; they were purified as follows: @-PICOLINE (8). The impure sample was refluxed with phthalic anhydride and acetic anhydride for 4 hours. The y-picoline and the 2,g-lutidine impurities were converted to pyrophthalones (8), whereas the @-picolinewas not. The solid pyrophthalones were removed by filtration; the filtrate was rendered alkaline by the addition of solid sodium hydroxide and then distilled. The 8-picoline was steam-distilled with water a t 97" C. The distillate was dried with solid sodium hydroxide and again distilled to yield a pure beta fraction at 143-144" C. 1 Previous papers in this series have appeared in 1928, page 743; 1943, page 614; 1944, page 1061; 1945, pages 299 and 895; 1946, page 751; 1947, p. 1175, and in ANALYTICAL EDITION, 1932, page 232.
168
January 1948 1
INDUSTRIAL AND ENGINEERING CHEMISTRY I
1
I
1
I
I VISCOSITY
1
169
I
CURVES
-r
W
m
r P -4
0.0 7
t
2 0.05 tu 0.04 U
0.03
0.02
0.01
Figure 20.
Activity Coefficients of Picolines in Phenol Solutions us. Total Pressures of System at Same Temperatures Figures on lines indicate mole per cent of respective picoline8 in liquid.
Figure 11. Activity Coefficients of Phenol in Picoline Solutions us. Total Pressures of System at Same Temperatares Figures on lines indicate mole per cent of phenol in liquid.
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1948
EQUILIBRIA FOR SYSTEM 0-PICOLINE-PHENOL IN TABLE 111. VAPOR-LIQUID MOLEPERCENT Experimental Data
760 Mm.
TOC.
x
y
99.5 93.0 84.0 78.8 70.3 57.5 45.2 34.0 21.0 11.0 5.0 2
TO
0
C.
181.5 181.6 182.5 185.0 185.5 182,5 173.5 162 5 153.5 148.0 144.0 143.0
5
10 2.0 30 40 50 60 70 80 90 100
TOC.
......... .........
......
...
Smoothed Data To&. y
k 0.0 2.0 5.0 14.0 39.0 63.5 86.5 94.5 98.0 99.0 99.5 100.0
170.5 171.0 173.5 177.0 178.0 174.3 163.7 152.5 143.5 138.7 136.7 135.3
0.0 1.5 3.8 11.3 36.0 63.0 89.0 96.5 98.5 99.5 99.7 100.0
TOC. 157.3 158.0 159.5 163.0 166.3 162.5 153.7 142.0 131.5 124.5 121.5 121.0
VAPOR-LIQUID EQUILIBRIA FOR SYSTEM IN MOLEPERCENT
TABLE IF'.
y
2:
200 Mm.
T'C.
z
Y
110.0 126.5 139.7 143.8 144.1 145.1 146.3 145.0 145.2 143.5
70.5 52.5 45.0 38.5 37.5 34.5 28.6 28.0 26.5 23.0
99.0 93.0 75.6 56.3 55.0 43.0 *21.0 20.6 14.5 8.3
.........
Y 0.0 1.3 2.5 8.3 32.5 62.0 88.5 96.5 99.0 99.5 99.8 100.0
T oC. 137.1 137.7 139.0 145.0 146.2 143.5 131.5 118.5 110.5 105.0 101.0 99.9
600 Mm. y TOC. x
TaC.
z
T'C.
y
.. .. .. .. .. .. .. .. ..
.. .. .. .. .. .. .. .. ..
Y 0.0 1.0 1.0 4.7 26.5 60.0 89.0 97.0 99.0 99.5 99.8 100.0
lines are horizontal, they indicate no change in the vapor composition with a change in is, i t would make no the pressure-that difference a t what pressure this particular liquid mixture was distilled. Correspondingly, in Figures 2, 4, and 6 all of the lines for the different vapor compositions must pass through a common point t o illustrate this same phenomena of oonstanty of vapor composition, irrespective of pressure. If the lines did not intersect in a common point, it would indicate t h a t the corresponding line on Figure 9 could not be straight. Figures 10 and 11 are the logarithmic plots of activity coefficients (6) for the respective constituents of the three picoline-phenol binaries. Straight lines are obtained which show t h a t the data are in excellent agreement among themselves. A rigorous development based on activity coefficients y1 and y~ for the two components may be applied t o the constant boiling mixtures at the several pressures. By definition:
2,6-LUTlDINE-PHENOL
Experimental Data 400 M m .
760 Mm.
TOC.
*
400 M m . . z Y 124.0 79.0 99.6 128.9 72.2 99.0 151.3 51.5 91.5 161.5 41.0 65.6 166.1 33.0 42.2 166.4 26.0 21.0 165.0 24.0 18.8 161.3 16.5 4.5 159.2 10.0 2.3
600 M m . Y TOC. z 141.0 75.2 98.5 156.1 56.5 95.0 157.5 55.7 94.5 163.8 50.0 89.5 167.5 47.3 84.7 170.7 44.8 78.0 176.9 34.5 48.2 178.0 28.0 30.0 177.8 23.5 17.3 175.4 17.5 8.3
173
200 M m . z ' y 99.5 98.5 96.0 90.0 73.2 56.0 43.4 29.7 23.0 14.0 2.5
. . . . . . ...
if the ratio is desired
Yl=e*&*3 7 2
P;
P2
21
but at a c.b.m. XI = y~and 22 = y ~ or ,
?=E!! 51
Yr
Furthermore
Smoothed Data
T oC.
X
u
TOC.
TOC.
y
y
TOC.
U
0.0
0.0 1.5 5.0 16.0 37.0 56.5 74.0 92.0 97.0 98.5 * 99.8 100.0
0 5 10 20 30 40 50 60 70 80 90 100
0.0 0.3 1.0 4.8 23.0 52.0 78.5 94.5 98.2 98.7 99.5 100.0
1.2 3.8 13.0 34.0 56.0 77.0 93.0 97.0 98.5 99.8 100.0
TABLE V. VAPOR-LIQUID EQUILIBRIA FOR SYSTEM~-PICOLINE-PKENOL Experimental D a t a
T"C.
m
400 Mm.
600 Mm.
760 Mm. y
T'C.
x
T'C.
y
z
200 Mm. Y
T'C.
x
y
......... Smoothed Data 5
T QC.
y
TOG.
y
TaC.
0 5 10 20 30 40 50 60 70 80 90 100
181.5 182 0 183.5 186.8 190.0 187.0 179.0 167.5 156 5 150 3 146 2 144.8
0.0 1.0 3.0 80 25.5 59.5 80.0 93.0 98.0 98.5 99.5 100.0
170.5 171.0 173.2 177.0 181.2 178.5 170 0 158 5 147.5 140.0 136.5 136.0
0.0 0.5 2.1 6.5 23.5 59.0 82.5 93.0 96.5 98.9 99.8 100.0
157.3 158.0 160.0 164.0 167.5 165.0 156.5 146.5 137.0 129.5 123.5 122.6
y 0.0 0.2 1.2 4.2 20.7 57.0 83.0 92.5 96.5 98.5 99.8 100.0
TQC.
Y
137.1 137.4 139.2 143.0 147.0 144.5 134.5 122.0 111.5 106.5 103.5 101.5
0.0 0.1 0.5 2.0 16.7 55.0 84.5 94.5 98.0 99.2 99.8 100.0
z20140
I50
160
170
180
190
20
TEMPERATURE~C.
Figure 12. Mole Fraction of More VolatiIe Component in Azeotrope vs. Temperature e at Various Pressures
174
INDUSTRIAL AND ENGINEERING CHEMISTRY
which is a general relEition for activity coefficients and partial pressures a t any constant boiling point (either maximum or minimum). To check the data against this relation, the values of the last two columns of Table VI1 were calculated. These values of the ratios of the activity coefficients and of the normal vapor pressures of the pure individual components check fairly closely when consideration is given to the tremenddus leverage of this met,hod of comparison. The experimental data were correlat'ed according to the following equation of Kirejew ( 3 ) :
TABLE VII. CONSTANT BOILINGMIXTURES P .%, g. %$
P,", Pi, Mm. Hg Mm. Hg
1z
t:i
2;:'
;:87
i:; ::::!;::
RT - [lnP - z1In p ; 22x1
- x? I n p z ]
92
xi L; L," P P," P; R k
0.235 0.265 0.305 0.325
860 700 510 270
190.5 181.7 168.5 147.5
464 465 442 421
760 600 400 200
0.315 0.325 0.335 0.350
+Picoline-Phenol 950 2150 0.320 780 1750 0.310 540 1300 0,290 800 0.250 300
1980 0.370 0,940 1659 *0.330 0.830 1190 0.335 0.760 750 0.270 0.690
0.394 0,398 0.441 0.391
0,434 0.421 0.428 0,365
0 , 8 0 0 0.400 0.441 0.730 0.425 0,445 0 . 7 0 0 0.414 0.415 0.640 0.391 0,375
(2)
mole fraction of more volatile component in c.b.m. mole fraction of less volatile component in c.b.m. = molal latent heat of vaporization. of component 1 = molal latent heat of vaporization of component 2 = total pressure of c.b.m. a t T oK. = vapor pressure of component 1a t 2'" K. = vapor pressure of component 2 a t T o K. = gas constant = 1.987 calories per degree per mole = constant for each system
Equation 1 was derived thermodynamically with the assumption that the plot of free energy of mixing against concentration gives symmetrical curves and vas shown to be valid in every case to which it was applied. The values of k and of dxz/dT are always positive for a minimum c.b.m. and negative for a maximum c.b.m. Table VI1 gives the calculated values of dx2/T from the data of Table VI. A11 values are negative and show that the concentration of the picoline in the c.b.m. will increase with decreasing temperature and pressure.
UM BOILINGMIXTURESOF TABLE VI. ~ I A X I MCONSTANT PICOLINES A N D PHENOL Max. B. P., T o C. 187.0 178.0 167.0 146.0
;:;;;;;;%; ;:J;; ::;;;
1;:
760 600 400 200
= =
Pressure, Mm. 760 600 400 200
p;,p,"
:::::;:::;
459 452 438 417
= temperature, K.
Component with Phenol &picoline
y?,y,
;!$:
186.0 179.0 164.5 143.5
TABLEVIII.
T
71
2,6-Lutidine-Phenol
\
where'k =
yz
P-Picoline-Phenol
;;i izy i::
,.
'li
Vol. 40, No. 1
Component in Azeotrope,
Mole % 25.2 26.7 28.5 31.5
T o C.
CALCULATED VALUESOF CONSTANT BOILING hfIXTURES BY KIREJEW'S EQUATIOX
T o K.
P,
Mm. Hg
xz
AT, Cal /AIole X 103
dzz/dT, Theoretical
187 178 167 146
460 451 440 419
p-Picoline-Phenol 760 0.252 600 0 267 400 0.285 200 0 315
- 800 - 760 - 880 - 1070
-0.0006 -0 0004 -0 0005 -0 0004
186.0 179.0 164.5 143.5
459 452 438 417
2,6-Lutidine-Phenol 760 0.235 600 0,265 0 305 400 200 0.325
-
-0,0006
190.5 181.7 168.5 147.5
464 455 442 421
7-Picoline-Phenol 760 0.315 600 '0.325 400 0.338 200 0.350
- 955 - 958 - 1034 - 1160
780 795 880 970
-0.0005 0,0004 -0,0003
-
-0,0003 -0.0003
- 0.0003
- 0,0003
an effect for the variation of the composition of the c.b.m. with pressure opposite from that expected. When Kirejew's equation is considered instead of the rule of thumb, it is apparent that t h e additional term-that is, 2 xl - l/T-may well have a much greater absolute value and thus control the sign of the expression of this variation of composition with temperature as a vr-hole. Figure 12 is a plot of the mole fraction of the picoline (the more volatile .compound) in the azeotrope against the temperature. These curves always slope downward; hence the value of t h e derivative function d x l / d T is always negative, as confirmed by the algebra of Kirejew's equation. ACKNOWLEDGMENT
-4ppreciation is expressed to George Riethof and Roger Gilmont for their help and suggestions and to the Pittsburgh Coke & Chemical Company for sponsoring this project. -,-picoline
760 600
190.5 181.7 168.5 147.5
400
200
31.5 32.5 33.5 35.0
LITERATURE CITED (1)
Gilmont, R., and Othmer, D. F., IND. ENG.CHEM., 36, 1061 (1944).
Hewitt, "Synthetic Coloring Matters," London, England, Longmans, Green and Co., 1922. (3) Kirejew, V. A,, ActaPhysicochim. (U.R.S.S.), 14, No. 3 (1941). (4) Othmer, D. F., IND.ENG.CHmz., 35, 614 (1943). (6) Othmer, D. F., and Gilmont, R., Ibid., 36,858 (1944) (6) Riethof, G., U. S. Patent 2,295,606 (Sept. 15, 1942). (2)
A rule of thumb sometimes quoted is that a reduction in the operating pressure or boiling temperature for many binary mixtures forming maximum constant boiling mixtures gives an increase in the concentration a t the c.b.m. of the component having the higher heat of vaporization (phenol in this case). This expression parallels the value of Ly L;/2kT in Equation 1; but in the present three systems the value of the latent heat of each of the picolines is only very slightly less than that of the phenol. I n other words, the difference is extrerr,ely small, although it indicates
-.
I
(7) Ibid., 2,383,016 (Aug. 21, 1945). (8) Riethof, G., Richards, S.G., Savitt, S. A., and Othmer, D. F., ' I N D . E N G . CHEM., AXAL. ED.,18, 458 (1946). RECEIVED July 30, 1946. Presented before the Division of Industrial and Engineering Chemistry a t the 110th Meeting of the AMERICANCHEWCAL SOCIETY, Chicago, Ill.
