Vapor-liquid equilibria of two binary systems, benzene-n-hexane and benzene-cyclohexane, were measured at pressures from 4 to 18 atm. The three-constant Redlich-Kister equation was found satisfactory for correlation.
With the benzene-n-hexane system no azeotrope occurred ; with the benzene-cyclohexane system an azeotrope appeared, and the mole fraction of cyclohexane in it diminished with increase in pressure. Lack of correction for fugacity in the vapor phase introduced a maximum error of 4'% in activity coefficients at highest pressure.
Previously published data on these two normal boiling points of the azeotrope and systems have been restricted to measure-n-hexane. ments a t atmospheric pressure and have
Vapor-liquid equilibria and thermodyconflicted as to the occurrence or absence of namic properties of the benzene-cyclohexane an azeotrope in the benzene+-hexane sys-system have been established by Scatchard, tem. Tonoberg and Johnston (11) reported Wood, and Mochel (10) and by Wood and vapor-liquid-equilibria data on the ben-Austin (12), who attribute the highly zene-n-hexane system a t atmospheric pres-irregular behavior of this system to the sure and found no azeotrope, Other investigators ( I T , 5, ' 7, 6) reported the formation of an azeotrope. Griswold and Ludwig (b), in commenting on the data of Tonoberg and Johnston. stated that the azeotrope perhaps escaped detection because of the small temperature difference, 0.1 "C., between the V. N. Kumarkrislina Rao at prrsent is with Caltax (iil Refining (Ltil.) India, Visakhapatnam,