Methanol with p-Xylene and water (IUPAC SDS Volume 69)
Evaluator
Adam Skrzecz Institute of Physical Chemistry, Polish Academy of Sciences
Evaluation
A survey of reported compositions along the saturation curve (sat.), compositions of coexisting phases in equilibrium (eq.) for the system methanol-p-xylene-water is given in Table 13.

Saturation curve
The system methanol-p-xylene-water forms a miscibility gap of type 1. Only one binary system, p-xylene-water, is partially miscible. The data for this system were compiled and critically evaluated in a previously published SDS volumes, Ref. 3. The recommended values of mutual solubility of p-xylene-water system at 298.2 K are: x'2=0.9974 and x"2=0.000 31. The data of Leikola, Ref. 1, taken from the handbook of Kafarov,4, were also taken into account during evaluation but are not reported as compilation sheet because they do not contribute further to knowledge of the system. All experimental saturation data are consistent. The data of Letcher et al.2, describe the whole binodal curve. The end points of saturation curve, Ref. 2, were reported to be x2=0.998 and pure water which is inconsistent with recommended values. Data for the water-rich phase in the range of low methanol concentrations, Ref. 2, were reported to be p-xylene free. All these results are within the accuracy of experimental measurements which were stated by the authors to be 0.005 mole fraction. Phase equilibrium data, Ref. 2, were also used to construct the saturation curve with the exception of one point (x1=0.058 x2=0.916) which appears to contain experimental error. Data at 298.2 K, Ref. 2, presenting both phases (organic-rich and water-rich) were fitted by the equation:
x1=1.1424+0.1264 ln(x2)-1.2561x2+0.1108 x22.
The parameters were calculated by the least-squares method and the standard error of estimate was 0.0194. The points on the saturation curve calculated by this equation for the selected concentrations of p-xylene together with the “best” values of Ref. 3 are presented in Table 14.

Phases in equilibrium
Compositions of coexisting phases in equilibrium of the ternary system methanol-p-xylene-water were reported only by Letcher et al.2 The tie lines are consistent with one another and cover the whole area of the miscibility gap. One point for organic-rich phase (x1=0.058, x2=0.916) appears to contain an experimental error. The phase equilibrium data are considered tentative. All experimental saturation points together with experimental tie lines at 298.2 K are presented in Fig. 7 . The plait point of the system at 298.2 K, calculated by Letcher and Siswana,5 was reported to be x1=0.46, x2=0.49.
TABLE 14. Calculated compositions along the saturation curve at 298.2 K
C $T$ ($\pu{K}$) D $x_{1}$ D $x_{2}$
298.2 0.0 3.1 x 10-5
298.2 6.228 x 10-1 2.00 x 10-2
298.2 6.855 x 10-1 4.00 x 10-2
298.2 7.118 x 10-1 6.00 x 10-2
298.2 7.234 x 10-1 8.00 x 10-2
298.2 7.269 x 10-1 1.000 x 10-1
298.2 7.253 x 10-1 1.200 x 10-1
298.2 7.202 x 10-1 1.400 x 10-1
298.2 7.126 x 10-1 1.600 x 10-1
298.2 7.031 x 10-1 1.800 x 10-1
298.2 6.922 x 10-1 2.000 x 10-1
298.2 6.800 x 10-1 2.200 x 10-1
298.2 6.669 x 10-1 2.400 x 10-1
298.2 6.530 x 10-1 2.600 x 10-1
298.2 6.385 x 10-1 2.800 x 10-1
298.2 6.234 x 10-1 3.000 x 10-1
298.2 4.365 x 10-1 5.200 x 10-1
298.2 4.185 x 10-1 5.400 x 10-1
298.2 4.004 x 10-1 5.600 x 10-1
298.2 3.823 x 10-1 5.800 x 10-1
298.2 3.641 x 10-1 6.000 x 10-1
298.2 3.458 x 10-1 6.200 x 10-1
298.2 3.275 x 10-1 6.400 x 10-1
298.2 3.091 x 10-1 6.600 x 10-1
298.2 2.907 x 10-1 6.800 x 10-1
298.2 2.723 x 10-1 7.000 x 10-1
298.2 2.539 x 10-1 7.200 x 10-1
298.2 2.355 x 10-1 7.400 x 10-1
298.2 2.171 x 10-1 7.600 x 10-1
298.2 1.986 x 10-1 7.800 x 10-1
298.2 1.802 x 10-1 8.000 x 10-1
298.2 1.618 x 10-1 8.200 x 10-1

Figure
Solubility graph
Sources:

1 Leikola, E.; Suomen Kemistil B. 13, 13 (1940).
5 Letcher, T. M.; Siswana, P. M.; van der Watt, P.; Radloff, S.; J. Chem. Thermodyn. 21, 1053 (1989).
3 Shaw, D. G.; 'Hydrocarbons with Water and Seawater, Part II: Hydrocarbons C8 to C36' IUPAC Solubility Data Series, 1989, Vol. 38, Pergamon Press.
4 Kafarov, V. V.; ed.; Spravochnik po Rastvorimosti Vol. 2, Troinye, Mnogokomponentnye Sistemy, Kniga II (Izd. Akademii Nauk USSR, Moskva, 1963).
2 Letcher, T. M.; Siswana, P. M.; Fluid Phase Equilib. 74, 203 (1992).