A survey of reported compositions along the saturation curve (sat.), compositions of coexisting phases in equilibrium (eq.) and distribution of methanol between phases (distr.) for the system methanol-toluene-water is given in Table 10.
Saturation curve
The system methanol-toluene-water forms a miscibility gap of type 1. Only
one binary system, toluene-water, is partially miscible. Data for this system
were compiled and critically evaluated in a previously published SDS volume.4
The recommended values of mutual solubility of toluene-water system at 298.2
K are: x'2 = 0.9972 and x"2 = 0.000104. This critical
evaluation is based on the original papers with the exception of data of Leikola,2
which were taken from the handbook of Kafarov5; this data set was also taken
into account during evaluation but is not reported as a compilation sheet because
it does not contribute further to knowledge of the system. The end points of
saturation curve3 were reported to be x2 = 0.999 and pure water which is inconsistent
with recommended values but within the accuracy of experimental measurements
(0.001 mole fraction) stated by the authors. The experimental saturation data
reported in Refs. 1 and 3 at 298.2 K show similar behavior of the system with
differences in the most difficult to measure region, close to the plait point.
In this region, 0.15<x2<0.6, Mason and Washburn1 reported a slightly
larger miscibility gap (about 0.04 mole fraction of water) than did Letcher
and Siswana.3 Leikola,2 at 293.2 K, presents a smaller solubility gap than Ref.
1, but a little larger than Ref. 3. It seems, that results of Letcher and Siswana3
at 298 K are the most reasonable. Therefore only data of Ref. 3 presenting saturation
and equilibrium data were used to derive the equation:
x1=1.0652+0.1260 ln(x2)–1.1183 x2+0.0591 x22.
The parameters were calculated by the least-squares method and the standard error of estimate was 0.0070. The equation is valid in the region of 0.02<x2<0.94. Selected points on the saturation curve, calculated by this equation together with the “best” values of Ref. 4 are presented in Table 11 and as solid line in Figure 5 . The water-rich branch of saturation curve contains only a small amount of toluene (x2<0.0001) and toluene was not detected in either study. These experimental points are not described by any model. The maximum methanol
concentration observed on the saturation curve at 298 K was x1 = 0.68 ± 0.01.
Phases in equilibrium
Compositions of coexisting phases in equilibrium of the ternary system methanol-toluene-water were reported only in Ref. 3. The tie lines are consistent with one another. They are considered tentative. Experimental tie lines together with all experimental saturation points at 298.2 K are presented in Figure 5 . The calculated plait point of the system at 293.2 K, Ref. 3, was x1 = 0.43 and x2 = 0.50.