Liquid-phase mass transfer in high-pressure systems with a supercritical and a liquid phase

Abstract

Liquid-phase diffusion coefficients and mass-transfer coefficients were measured in binary two-phase systems at high pressures. Both were determined from the rates of absorption of the gaseous component into the liquid. Diffusion coefficients were measured by observing unsteady-state diffusion into a sell) i infinite liquid phase and fitting transient counterdiffusion mass-flow rates to the visually determined change of the position of the interface between the liquid and the supercritical phase. Mass-transfer coefficients in the liquid phase were determined from the absorption rate of the gaseous component into a falling liquid film of known flow and physical properties. Experiments were performed with the binary systems carbon dioxide-oleic acid, carbon dioxide -methyl myristate, and carbon dioxide-methyl palmitate. Liquid-phase diffusion coefficients rise significantly with concentration as viscosity decreases. Temperature also has a strong effect on diffusivities. Experimental mass-transfer coefficients in nearly saturated liquids agree well with calculations for falling films with known properties, whereas far from equilibrium, Marangoni convection greatly enhances mass-transfer rates. Close to the critical point of the binary system at a given temperature, a sharp decline of the mass-transfer coefficient is observed.