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Several gasoline-ethanol-water multicomponent systems at temperatures of 283.15, 293.15, and 313.15 K were studied, to obtain water tolerances and ethanol concentrations at equilibrium in the upper gasoline-rich phase. The lower aqueous phase was not studied, because of its very small volume. The ethanol and water concentrations were determined by a chromatographic method, using the external standard method for quantification, whereas no other gasoline component was determined. Moreover, the influence of the gasoline volume in the tank was simulated and studied in the laboratory. From experimental results, we conclude that the ethanol concentration decreases as the tank becomes more empty, whereas it is only slightly affected by the temperature within the studied temperature range. A similar behavior was observed for the water tolerance, when the water volume inside the tank corresponds to 0.5 vol % of water. In addition, the loss of ethanol that is drawn into the aqueous phase diminishes dramatically when the water volume in the tank diminishes, and the loss of ethanol becomes negligible when this volume corresponds to e0.05 vol % of water.

Tie-line data for the water, ethanol, and cyclohexane [{w 1 H 2 O + w 2 C 2 H 5 OH + (1 À w 1 À w 2 )C 6 H 12 }] ternary system, where w is the mass fraction, was investigated at T ¼ 303:15 K. A quaternary system containing these three compounds and benzene {w 1 C 2 H 5 OH + w 2 C 6 H 6 + w 3 C 6 H 12 + (1 À w 1 À w 2 À w 3 )H 2 O} was also studied at the same temperature, while data on its other two partially miscible ternary systems were taken from the literature [the fourth {w 1 C 2 H 5 OH + w 2 C 6 H 6 + (1 À w 1 À w 2 )C 6 H 12 } is not partially miscible]. From our experimental results we conclude that this quaternary system presents a very small water tolerance and that phase separation could produce a considerable loss of C 2 H 5 OH drawn into the aqueous phase. On the other hand, the results also show that the aqueous phase generally contains a higher concentration of C 6 H 6 than of C 6 H 12 . A comparison with other similar quaternary systems investigated in our laboratory was also made. The ternary experimental results were correlated with the UNIQUAC equation, and predicted with the UNIFAC group contribution method. As previously, the equilibrium data of the three ternary systems (including those taken from the literature) were used to determine interaction parameters for the UNIQUAC equation. These parameters were then averaged in order to predict equilibrium data of this quaternary system. The UNIFAC method was also used with the same purpose. The UNIQUAC equation appears to be more accurate than the UNIFAC method for this ternary system. However, this last model is slightly better for the quaternary system, as can be seen from the values of both residuals.