344
J. Chem. Eng. Data 1980, 25,344-346
Indirect Determination of Vapor-Liquid Equilibria by a Small Ebulliometer. Tetrahydrofuran-Alcohol Binary Systems Yoshio Yoshikawa, Akira Takagi, and Masahiro Kato' Department of Industrial Chemistry, Faculty of Engineering, Nihon University, Koriyama, Fukushima, Japan 963
For the four blnary systems of tetrahydrofuran and alcohol (methyl, ethyl, Isopropyl, and n-propyl), bolllng polnts were measured with a small ebulliometer at atmospherlc pressure, and vapor-llquld equlllbrlum relatlons were lndlrectly determined by using the Wllson equatlon. Values of the Wllson parameters were calculated to mlnlmlre the sum of squares of deviations In the bolllng polnts for all data polnts. Vapor-liquid equilibrium relations are required for practical use such as in the design and operation of distillation equipment. It is possible to determine vapor-liquid equilibrium relationships indirectly from boiling-point curves which can be easily and reliably measured, rather than those from the conventional equilibrium measurements (2). In the present investigation, boiling points were measured with a small ebulliometer at atmospheric pressure for the four binary systems of tetrahydrofuran (THF) and alcohol (methyl, ethyl, isopropyl, and n-propyl), and vapor-liquid equilibrium relations were determined from the experimental boiling-point data by using the Wilson equation ( 10). Experimental Section The experimental apparatus for the measurement of boiling points is shown in Figure 1. The cross sections are shown at the right-hand side of the still. I n the small ebulliometer, the 15 cm3 per boiling-point measurement. required amount is It is constructed entirely of borosilicate glass. An electric cartridge heater is inserted into the boiling flask, and a little glass dust is put on the wall of the heat-transfer surface to stabilize the boiling condition. In the still, the boiling vapor-liquid mixture rises through a Cottrell tube and flushes to a thermometer well. Asbestos tapes cover the entire apparatus except the condenser. The boiling points were measured with a mercury thermometer calibrated to fO.l O C in accordance with the standard platinum resistance thermometer. The atmospheric pressures were measured with the Fortin barometer. The solution of desired composition was prepared within l min in a 30-cm3 Erlenmeyer flask with a stopper by mixing each pure substance, which was weighed by use of syringes and an automatic balance. To minimize the change of composition, the prepared solution was immediately used for the experiment. The accuracy of the composition seems to be within f0.0005 mole fraction. The time required for the boiling-point measurement was -5 min after the solution came to a boil. Special grade reagents supplied by the Koso Chemical Co., Ltd., were used without further purification. The physical properties of the reagents used are listed in Table I.
-
The raw data of boiling points t and the experimental atmospheric pressures T * are presented in Table 11. The experimental raw data of boiling points were then corrected to 760 mmHg pressure by using eq 1, where m indicates the coefficient 0021-956818011725-0344$01 .OO/O
t = t'
+ m(760 - T * )
(1)
(dtldP) which is evaluated in the form of eq 2. The values of
m=
+ m2x2
m,x,
(2)
m , and m2 were obtained from eq 3, derived from the Antoine m,=
(-$
=
( t / + CJ2
(2.3033(760SI)
t/ =
B/ A/ - log (760)
- c/
(4)
equation. A, B, and Care Antoine constants as shown in Table 111. In the present work, the maximum, arithmetic mean, and minimum values for the correction were +0.9,+0.6, and +0.3 OC, respectively. The boiling points corrected to 760 mmHg pressure are given in Table I1 and shown in Figure 2. The vapor-liquid equilibrium relations were calculated from the experimental boiling-point data corrected to 760 mmHg pressure. The expressions proposed by Wilson (70) for representing the activity coefficients, y1 and y2,were employed in the present investigation (eq 5 and 6). Assuming that the In y1 = -In ( x ,
+ A l 2 x 2 )+
