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14.08.12 KB. Accepted version uploaded, ok to add to Spiral, embargo period elapsed. RS

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An investigation was carried out on the effect of process parameters involved in Pre‐Dispersed Solvent Extraction (PDSE) on the stability and interactions in dilute dispersions of Colloidal Liquid Aphrons (CLAs). The aim of this work was to derive empirically‐based engineering relationships that could be used in the design of PDSE processes. For this investigation, CLAs were formulated with an Aliquat 336/n‐octanol/Softanol 120 solvent phase, and a Synperonic A20 aqueous phase. These CLAs were intended for use in the reactive pre‐dispersed solvent extraction of polar solutes such as phenylalanine. Light scattering measurements over a range of continuous aqueous and CLA phase conditions were used as a method of obtaining a measure of the rate of disappearance of CLAs from dispersion (a measure of stability), and a comparison of stability under different conditions. Two forms of CLA interaction occurring by independent mechanisms were identified – CLA break‐up, and CLA flocculation. Break‐up was found to be a first order process, allowing CLA stability to be characterised by a first order half‐life (typical half‐life 15–40 min). This was proposed to occur on collision of CLAs with sufficient energy to overcome the stabilising forces provided by the surfactants at the interfaces of the CLAs. It was shown that flocculation occurred at high ionic strengths (>0.1 M NaCl), and that it was not part of the break‐up mechanism. An apparent size dependent CLA half‐life was proposed to be due to smaller particles having a lower collision energy on average. The data suggested that the resistance to CLA break‐up was not charge repulsion, but derived from an interaction between molecules of one of the surfactants making up the aqueous ‘shell’ of the CLAs (Synperonic A20). Finally, the basis for a semi‐empirical design equation for prediction of CLA half‐life developed from the Arrhenius equation was proposed. © 1999 Society of Chemical Industry