Foam fractionation with reflux

Abstract

This paper shows that the foam drainage characterisation of Stevenson (2006a) provides a useful basis for the modelling of foam fractionation systems with and without reflux following the conceptual approach first proposed by Lemlich (1968a). Furthermore, the paper shows that surfactant transport between the rising and falling streams during foam fractionation with reflux can be characterised by a simple mass transfer coefficient. A set of non-dimensionalized process parameters is proposed and, using these, it is shown that this approach enables the whole operating regime of a foam fractionation device to be mapped out from a small number of relatively simple experiments to measure the surfactant adsorption isotherm, foam drainage characteristics, bubble size and mass transfer coefficient. The validity of this approach was demonstrated experimentally for a foam fractionation system continuously separating cetylpyridinium chloride (CPC) from a solution of constant concentration under total reflux. The dimensionless mass transfer group appeared to be invariant for this system, with a mean value of 3.7, over the studied range of rising gas to liquid flux ratio. It was shown for this case that the operation could be summarised in a small number of simple heuristic rules which gave valuable insight into the design and operation of this foam fractionation system.