Enhancement of gas to water mass transfer rates by a dispersed organic phase

Abstract

Experimental data are presented on the enhancement of oxygen mass transfer into an aqueous sulphite solution in a stirred cell, due to the presence of a dispersed liquid octene phase. The observed enhancement factors can be described with a new mass transfer theory, called the Film Variable Hold-up (FVH) model. This model is based on the film theory and explains the influence of hold-up, droplet diameter and permeability of the organic phase, on the obtained enhancement. It is assumed that the dispersed phase hold-up gradually increases from zero at x = 0 (the gas-liquid interface) towards a constant average bulk value for x ≥ αδ, according to a distribution function with parameter values α = d 43 δ and β = 0.3, where d 43 is the volumetric mean diameter of the dispersed droplets, δ is the mass transfer film thickness, and β is a geometrical factor. Surprisingly, also the experimental data of Bruining et al. (1986) for oxygen mass transfer enhancement due to hexadecane droplets and the data of Littel (1991) for carbon dioxide mass transfer enhancement due to toluene droplets can be reasonably well described, assuming the same dispersed hold-up distribution in the mass transfer film. This may indicate that this dispersed phase distribution is similar for different organic droplets dispersed in water, at least if these systems are characterized by a negative spreading coefficient. The recent observation of Wilkinson et al. (1991), that the reaction rate of the uncatalyzed sulphite oxidation increases with decreasing values of the pH, initially adjusted by adding H 2SO 4, was confirmed.