SOLUBILITY DATA AT 20" AND 35" C. THOMAS E. SMITH AND ROBERT F. BOSSER C'. S. Industrial Chemic&, Znc., Baltimore 3, iMd. PURIFICAlION OF I\lATERIALS
T h e binodal curve and tie lines were established for the system n-propyl alcohol-n-propyl acetate-water at 20" and 35' C. Changing the temperature has little effect on the limiting solubility curve, hut appreciably changes the dopes of the tie lines.
The n-propyl alcohol and the n-propyl acetate used vlere purified by fractional distillation. Data on these compounds are conlpiled in Table 1.
T
HE modified Fischer-Tropsch process, as developed for use in this country, is a ready source of straight-chain aliphatic
TABLE 1.
alcohols and acids. A commercially important ester t o be manufactured from these synthetic raw materials is n-propyl acetate. The data presented in this article represent new inforniation on the properties of this compound.
PROPERTIES O F %-PROPYL 1 h C O H O L AND %-PROPYL dCET.4TE
n-Propyl hlcol1ol
$ ~ ~ ~ ~ ; , ~ 0.08 ~ ~ ~ & ~99.2-99.8 0.02 0.006 0.053
Free acid (as acetic), g./100 ml.
ny
1 38625
A.8.T.M. boilingrange, O C.
96 8-97.6
1.38506
...
Literature values 1.3880 t o 1.3854. b Literature value 1.3847.
APPARATUS
a
A survey of the literature revealed the need for a convenient zpparatus for the determination of solubility data a t temperatures above or below room temperature. The constant temperature separator shown in Figure 1 was d e s i g n e d to fill this need and was used to c l e t e r m i n e t h e data 6-24/40 P X)lNT presented in t h i s B-PMM.T STOPCOCK paper. SEALED TO 45 MRI. This apparatus consists of a separatory f u n n e l entirely surrounded by a jacket t h r o u g h which I S passed a fluid a t a constant t e m p e r a t u r e . T h i s fluid m a y be either a liquid or a vapor. A liquid must be forced through by g r a v i t y o r a pump, whereas a vapor is simply distilled through, condensed in a reflux c o n d e n s e r , and returned to the pot via the inside wall of the jacket. The temperature of the i'apor is fixed by picking a liquid with a norrnal boiling point of the temperature d e s i r e d or b y changing t h e pressure in the annular s p a c e u n t i l t h e des i r e d temperature is obtained. As the unit is m a d e e n t i r e l y of borosilicate g l a s s , i t m a y be u s e d w i t h corrosive materials.
n-Propyl Acetate
Sone
ANALYTICAL PROCEDURE
Both wat'er and ester analyses i w r e run on all water and oil layersat,2O0and35"C. Ester analyses were made in the conventional manner by saponifying the samples in an excess of approximately 1 N alcoholic potassium hydroxide and back-titrating t,he unrcact,ed alkali with 0.5 -4; sulfuric acid in the presence of phenolphthalein indicator. Water determinations were made in the following manner: Tw-enty-five milliliters of dry methanol were pipetted into a small-mouthed 8-ounce bottle and tihated to the end point with Karl Fischer reagent (3). The sample was weighed in a 2.5-ml. ampoule and put int'o t,he rubber-stoppered bottle containing the methanol. Aft,er the ampoule had been broken by shaking t,he bott'le, the sample was titrated v i t h Karl Fischer reagent.
JACKET. C-BOTTOM MUST BE TILTED TO ALLOW COMPLETE ORAINAGE.
DETERRIIKATION OF PHASE DIAGRAMS
The constant t,emperature separator described was used t o determine the binodal curve and tie lines at both 20' and 36' C. The temperature of the experimental mixtures was cont'rolled a t 20" C. by pumping water from a eonstant, temperature bath through the annular space in the separator. At 35" C., temperature control was achieved b y distilling a mixture of ethyl ether and ethyl alcohol vapors through the annular space. (A trace of sodium hydroxide Fas added to the flask to prevent the formation of explosive peroxides. ) The procedure for determining a tie line was as follows:
A
A heterogeneous ternary mixture was made up directly in the constant temperature separator, using calibrat'ed burets and correcting for the variation of the volumes with changes in room temperature. As a much larger sample is needed t o determine the ester content of the water layer than for any of the other three analyses, the three components were mixed in such proportions as to give approximately two thirds water layer and one third oil layer. after sufficient' agitation to bring the layers t o equilibrium (usually about 1 hour), the mixture was allowed to separate until each layer, when tested visually Rith a beam of
omo CENTIMETERS
F i g w e 1. Constant Tempera-
ture Separator 896
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
May 1950
0.1'C. THERMOMETER
.c
TO BATH
FROM CONSTA TEMPERATURE -b
Figure 2. Apparatus for Determining Tie Line Data at 20' C.
g 11
&FLASK CONTAINING
-
_ I
light, appeared perfectly clear. This separation required from 1 to 16 hours, the time increasing as the plait point was approached. The oil layer was then sampled with a pipet, care being taken to prevent the tip from touching the walls of the separator or the interface. The water layer was sampled by opening the stopcock and letting the liquid run through the sampler directly into ampoules. After a run was completed, the apparatus was taken apart, washed thoroughly with soap and water, rinsed with acetone, and dried by vacuum. Figure 2 shows the apparatus used for the 20" C. determinations.
ETHER
SODIUM HYDROXIDF E T H Y L ALCOHOL
Figure 3. Apparatus for Determining Coordinates of Binodal Curve at 35" C.
I t was decided to define the critical region of the binodal curves by the synthetic method ( 4 ) . Homogeneous mixtures of n-propyl alcohol and water were made up in the constant temperature separator and titrated to turbidity a t 20' and 35" C . with n-propyl acetate. The components were measured with calibrated burets and the volumes corrected for temperature effect. Use of a magnetic agitator (see Figure 3) allowed easy
A-TURBIDITY METHOD
Pr Figure 4. Phase Diagram for System n-Propyl Alcoholn-Propyl Acetate-Water at 20' C.
Figure 5. Phase Diagram for System n-Propyl Alcoholn-Propyl Acetate-Water at 35" C.
898
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 42, No. 5
PrOH TABLE 111. EXPERIXENTAL SOLUBILITY DATA AT 35" C. (Conjugate layers) Oil Layer, Weight % _____ Water Lmyer, Weight yo PrOH PrOAC 1310 PrOH PrOAC HzO 0.0 97.8 2.2 0.0 1.8 98.2 7.9 16.7 26.3 34.3 39.9 42.1
88.4 76.5 63.0 49.5 37.0 25.3
3.7 6.1 8.3 10.7 13.2 16.9
3.7 6.8 10.7 16.2 23.1 32.6
2.0 2.0 2.2 2.2 2.6 3.5
94.3 91.9 89.6 87.1 84.2 79.6
Coordinates for Ri&gLCurve, Weight % PrOH PrO4C Hz0 16.2 20.0 23.9 27.5 30.9 34.1 37.1 39.6 41,l
/
PrOAc Figure 6.
I
I
8
OI0
so
2
H, 0
Comparison of Solubility Data at 20" and 3.5" C.
access to the top'of the separator and supplied sufficient agitation. This method of determining the coordinates of the binodal curves worked well in the region over which it was used. The end point could be titrated to the accuracy of one drop (approximately 0.025 ml.) of n-propyl acetate. An effort was made to check the oil layer sides of the binodal curves by the turbidity method. Mixtures of n-propyl alcohol and n-propyl acetate were titrated with water, but the end point was very indefinite, because the water, having a comparatively high surface tension, did not disperse quickly but formed small globules whi& were slow to dissolve.
3.0 4.7 6.3 8.6 11.1 13.7 16.5 20.0 24.6
80.8 75.3 69.8 63.9 58.0 52.2 46.4 40.4 34.3
(Figure 6 ) reveals that changing the temperature 15' C. has little effect on the binodal curves but changes the slopes of the tie lines considerably. No straight-line method of tie line correlation has been found to fit the above conjugate layer data throughout the entire range of values reported. This deviation from linearity is shown by other systems containing n-propyl alcohol ( 2 , 6). The direction of the slope of the tie lines i n the system n-propyl alcohol-cyclohexane-water ( 5 ) actually changes as the amount of n-propyl alcohol increases. There is indicat'ion that this phenomenon' may occur in the system presented in this paper a t some t,eniperature below 20' C. As the temperature is increased, hoivc.ver, systrrns of this type tend to become more normal ( 8 ) .
PRESENTATION OF RESULTS
The coordinates of the binodal curve and conjugate layers a t 20" C. are given in Table I1 and plotted i n t.he form of a triangular phase diagram in Figure 4. The values obtained a t 35' C. are summarized in Table I11 and presented graphically in Figure
5. The compositions of the ternary mixtures from which the conjugate layers were formed are not plotted on the triangular diagrams. I n each case, however, they fell directly on the tie line, t,hus yielding a weight balance check on the experimental results. Graphical comparison of the data a t 20' and 35" C.
TABLE11. EXPERIMENTAL SOLUBILITY DATAAT 20' C. (Conjugate layers) Water Laser, Weight % Oil Layer, Weight % PrOH PrOAC H20 PrOH PrO.4C Hdl 1.7 0.0 98.3 0.0 2.2 97.8 6.7 9.1 15.3 23.4 26.1 33.5 37.4 40.1 41.4
90.3 87.1 79.5 67.7 63.9 51.1 43.5 35.6 25.6
3.0 3.8
?.3
8.9 10.0
6.8 9.3 10.0
5.2
15.4 19.1
24.3 33 0
D
O
12 I
13.n 15.2 I8
.I
2.3 2.4 2.4 2.3 2.5 2.5 2.6 2.9 3.8
93.4 92.1 90.8 88.4 87.5 85.4
83.9 81.9 77.7
Tie Line Correlation Plot
Figure 7.
A tie line interpolation plot (Figure 7 ) of weight per cent water in the water layer versus Reight per cent n-propyl acetate in the oil layer yields smooth sigmoid curves for both t.he 20' and 35" C. data. ACKROWLEDGMENT
The authors wish to thank B. J. Gaffney and L. 1%'. Bass of U S. Industrial Chemicals, Inc., for their helpful criticism of this paper, and J. J. Velenovskg of this laboratory for his aid in the design of the apparatus. LITERATURE CITED
( 1 ) Beech, D. G., and Glasstone, S., J . Chem. Soc., 1938, 67-73. (2) Pratt, H. R. C., I n d . Chemist, 23, 658-64, 727-33 (1947).
(3) Smith, D. M., Bryant, 'w. M. D., and Mitchell, J., Jr., J . Am. Chem. SOC.,6 1 , 2 4 0 7 - 1 2 (1939). (4) Taylor, S. F., J . P h y s . Chem., 1 , 4 6 1 - 7 3 (1897). (5) Washburn, E. R., e t a l . , J . Ani. Chem. Soc., 64, 1886-8 (1942). R E C ~ I V EOctober D 28. 1949.
