Enhancement of mass transfer using colloidal liquid aphrons: measurement of mass transfer coefficients in liquid-liquid extraction.

Abstract

Interphase mass transfer of a sparingly soluble solute is often the rate-limiting step in multiphase biocatalytic processes. Colloidal liquid aphrons (CLA) provide very large interfacial areas, and thus could enhance mass transfer in such processes. The aim of this study was to characterize mass transfer properties of CLA dispersions during transfer of heptanoic acid from water to limonene. The interfacial area per unit volume (a), film mass transfer coefficient (K(L)), and volumetric mass transfer coefficient (K(L)a) values were determined in a stirred-tank reactor. These results were used, along with a literature correlation, to estimate the mass transfer coefficient of the surfactant-stabilized shell surrounding the CLA. The very large increase in a provided by the CLA was only partially offset by a slight increase in the mass transfer resistance of the shell. As a result, the range of K(L)a values obtained using CLA was about an order of magnitude greater than that obtained using a conventional dispersion. The concentration of the aqueous-phase surfactant used to form the CLA strongly affected the Sauter mean diameter of the CLA; however, the concentration of the nonpolar-phase surfactant had little effect. These results suggest that CLA have considerable potential for multiphase biocatalytic applications.