Transport mechanisms and modelling in liquid membrane contactors

This paper discusses the use of liquid membrane contactors for extraction of fermentation and pharmaceutical products using different types of carriers. It intends to emphasise the importance of understanding the transport mechanisms involved in liquid membrane extraction with different carriers and also to discuss relevant aspects of the mathematical modelling involved in these extraction processes. Using the extraction of organic acids, namely amino acids, as a case study it is shown how the supramolecular organisation of the extractant determines the solute transport mechanisms involved. Additionally, the resolution of racemic mixtures using chiral carriers is also discussed. The modelling work analyses two different aspects of extraction using membrane contactors with microporous membranes: (i) the importance of using a correct description of solute partition between the feed and the extractant phase (use of a variable partition description versus constant partition); (ii) the correct development of mass transfer correlations in hollow fibre contactors. For the development of mass transfer correlations the calculation method proposed by Wilson has been universally used. Given the currently available mathematical tools, that enable the analytical manipulation of equations and fittings with complex expressions, a new calculation methodology is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.