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Vapor-liquid equilibria at elevated temperatures and pressures Whittle, Donald James

Abstract

A modified version of an apparatus by Sage and Lacey for phase equilibrium measurements at elevated temperatures and pressures has been designed and built. Assembly and detail drawings of the apparatus, and a detailed description for its use have been included. The vapor pressure of methanol has been measured at temperatures from 100°C to 225°C, and the vapor pressures of benzene and of toluene have been measured at temperatures from 125°C. to 250°C. Good agreement with literature values was found for the vapor pressures of each of these materials. Vapor-liquid equilibrium composition and pressure data have been measured for the benzene-toluene system at 200°C and compared to values reported for this system by v. Huhn and by Griswold, Andres, and Klein . Activity coefficients calculated for the liquid phase from the experimental data show that the liquid mixture forms a Lewis and Randall perfect solution. Isothermal vapor-liquid equilibrium composition and pressure data for the methanol-toluene system have been measured at 25-degree intervals from 125°C. to 250°C. An azeotrope was found for the system at temperatures of 125°, 150°, and 175°C, and it was estimated that this azeotrope disappears at 193.4°C. Activity coefficients have been calculated from the experimental data using several approximate methods, and tested for thermodynamic consistency using the test proposed by Redlich and Kister . Coefficients calculated using the method proposed by Black were the only ones which showed good thermodynamic consistency when tested in this way, and these have been correlated with a Redlich and Kister four-constant equation. The failure of activity coefficients calculated by approximate methods other than Black's to show good thermodynamic consistency indicates that the solution theories on which these methods are based are invalid for a non-ideal system of the type studied.

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