A survey of reported compositions along the solubility curve and compositions of coexisting phases in equilibrium for the system nitromethane + benzene + heptane is given in Table 1.
Solubility curve
The system nitromethane + benzene + heptane forms a miscibility gap of Type I, Treybal.3 Only one binary pair of components, nitromethane + heptane, is partially miscible. The data for this system were compiled and critically evaluated (Sazonov et al.4). The recommended values of mutual solubility of the binary nitromethane + heptane system at 303.2 K are: x1″ = 0.0515 and x1′ = 0.9838. The solubility of nitromethane in heptane reported in Kimura et al.2 (0.035 mass fraction; 0.056 mole fraction) is rejected as inconsistent with the recommended value, Sazonov et al.4; the solubility of heptane in nitromethane reported (0.027 mass fraction; 0.017 mole fraction) agrees satisfactorily with the recommended value (Sazonov et al.4). Solubility data obtained by the titration method for the ternary system nitromethane + benzene + heptane were reported in Kimura et al.2 Experimental error was not reported in the paper. Solubility data at 303 K (nitromethane-rich and hydrocarbon-rich branches together) are described by an algebraic equation in the form:
x2 = a + b·x3 + c·(x3)2 + d·ln(x3).
The proposed equation gives a smaller standard deviation than any other tested equations. The equation parameters (a, b, c, d) were calculated by the least squares method: a = 0.6230, b = –0.1190, c = –0.5621 and d = 0.1536; standard deviation of calculated and experimental values is 0.0208 (2.08 %). The binodal curve for this system was calculated and compared to solubility data reported in Kimura et al.2 The solubilities calculated by the proposed equation are presented in Table 2 and Fig. 24 .
Liquid-liquid equilibrium (LLE) data
LLE data for the ternary system nitromethane + benzene + heptane were reported in both references. Composition of each phase, Kimura et al.2 was calculated from the index of refraction-composition curve of saturated mixtures prepared at the time of saturation curve measurements. The tie lines at 298 K in mass fraction (Francis1) cover the whole range of the miscibility gap and are nearly parallel to one another and to of the tie line between nitromethane and heptane. Data reported at 298 K and at 303 K, Francis1 and Kimura et al.2 in mole fractions are in agreement. Experimental errors were not reported in the papers. The critical solubility point was reported only in Francis1 in graphical form and determined by compiler to be x1 = 0.515, x2 = 0.282 at 298 K.
All experimental data are considered tentative.