| Emulsion liquid membranes (also referred to as multiple emulsions) have a wide variety of applications, especially in separation processes. They can be used in the removal, recovery, and purification of many organic and inorganic compounds from dilute solutions of industrial interest. One serious problem associated with the ELMs (emulsion liquid membranes) is their tendency to undergo swelling and break-up during the separation process. For example, the globules of water-in-oil-in-water (W/O/W) ELM swell due to transfer of water from the external aqueous phase to the internal water droplets.; In this work, osmotic and isotonic swelling behaviors of W/O/W emulsion globules were studied. Osmotic water transport was induced by the concentration difference of the solute between the two sides of the oil membrane. Water molecules from one side permeated through the oil membrane by surfactant facilitation, resulting in swelling of the aqueous phase on the other side. The effects of surfactant concentration, structural configuration of emulsion globules, pH and salt on the swelling behavior were examined. The experimental results shed new light on the mechanism of osmotic water transport. Isotonic swelling behavior of W/O/W emulsion globules under agitation condition was studied in detail. The key factors affecting the isotonic swelling behavior, such as surfactant concentration, pH and salts, and mixing conditions, were investigated. The underlying mechanisms of isotonic water transport are discussed and developed. It is concluded that when sorbitan monooleate (EMSORB 2500) is used as the surfactant in oil membrane phase, isotonic swelling is controlled by surfactant diffusion to the interface. |
