Measurement of mass transfer coefficients for the evaporation of liquids by reversed-flow gas chromatography

Abstract

Reversed-flow gas chromatography, a new method for studying heterogeneous catalysis and related phenomena, such as diffusion and adsorption, is applied to the simultaneous determination of mass transfer coefficients for the evaporation of pure liquids or liquid mixtures and the diffusion coefficients of vapours from these liquids into the carrier gas. The necessary mathematical equations were derived and used to calculate the above parameters for the pure liquids methanol, ethanol and propan-l-ol, as well as for the mixtures methanol—water, ethanol—water and propan-l-ol—water, evaporating into carrier gas helium. In the case of mixtures, the variation of the mass transfer coefficient for the evaporation of alcohols with their mole fraction, the working temperature and the carrier gas flow-rate was studied. The mass transfer coefficients measured depend not only on the nature of the alcohol and the other component in the mixture, but also on the mole fraction. Moreover, they increase with increasing temperature, but they are independent of the carrier gas flow-rate. The values of diffusion coefficients found are in good agreement with those calculated theoretically.