Computer‐aided Measurement of Vapour‐Liquid Equilibria in a Dynamic Still at Sub‐Atmospheric Pressures

Abstract

AbstractA compact new dynamic VLE apparatus has been developed capable of rapidly and accurately furnishing data suitable for separation process design. The equipment is computer controlled to fine tolerances of pressure and temperature and can produce either isobaric or much useful isothermal VLE data. The design incorporates a packed equilibrium chamber of the Yerazunis et al. [1] type in a novel arrangement. It is suggested that VLE stills relying only on a Cottrell pump are unlikely to reach true equilibrium regardless of how long the recirculation period, particularly for system of high relative volatility and or high liquid viscosity. To test the performance of the apparatus, isobaric VLE data were measured for the cyclohexane‐ethanol system at 40 kPa, and isothermal VLE data at 313.15K, 323.15 K and 333.15K. The isobaric data were in good agreement with the data of Morachevsky and Zharov [2]. The isothermal VLE data were found to be thermodynamically consistent. Infinite dilution activity coefficients, in good agreement with literature values were found from the isothermal data by the method of Maher and Smith [3]. Reasonably accurate excess enthalpy estimates were also calculated. The VLE data were best correlated with the Wilson [4] equation. An analysis of the temperature‐pressue sensitivity for binary systems defines the precision required in the control of either pressure or temperature and dictates the choice of equipment for a given system.