ENHANCEMENT OF GAS TO WATER MASS-TRANSFER RATES BY A DISPERSED ORGANIC-PHASE

Experimental data are presented on the enhancement of oxygen mass tran sfer into an aqueous sulphite solution in a stirred cell, due to the p resence of a dispersed liquid octene phase. The observed enhancement f actors can be described with a new mass transfer theory, called the Fi lm Variable Hold-up (FVH) model. This model is based on the film theor y and explains the influence of hold-up, droplet diameter and permeabi lity 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 greater than or equal to alpha delta, according to a distribution F unction with parameter values alpha = d(43)/delta and beta = 0.3, wher e d(43) is the volumetric mean diameter of the dispersed droplets, del ta is the mass transfer film thickness, and beta is a geometrical fact or. Surprisingly, also the experimental data of Bruining et al. (1986) for oxygen mass transfer enhancement due to hexadecane droplets and t he 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 m ay indicate that this dispersed phase distribution is similar for diff erent organic droplets dispersed in water, at least if these systems a re characterized by a negative spreading coefficient. The recent obser vation of Wilkinson et al. (1991), that the reaction rate of the uncat alyzed sulphite oxidation increases with decreasing values of the pH, initially adjusted by adding H2SO4, was confirmed.