Effect of ionic strength on extraction of hydrophobic organics through silicone rubber membranes

The extraction of 2-nitrotoluene from electrolyte solutions containing different ionic species was studied in a lab-scale membrane mass exchanger by measuring partitioning between electrolyte and aqueous solutions, and organic flux under different hydrodynamic conditions and for different ion concentrations. Salts were found to affect both the overall mass transfer coefficient and the driving force in the transport of the organic compound through a non-porous silicone rubber membrane. Mass transfer of 2-nitrotoluene in a saline-membrane-aqueous system was described using a resistances-in-series model based on an activity gradient driving force. The model allows the prediction of organic flux in saline-membrane-aqueous systems provided that saline-aqueous partition coefficients, and mass transfer coefficients in aqueous-membrane-aqueous systems, are known. Since these parameters can be easily and independently measured or estimated from available correlations, the model provides a useful methodology for engineered design of multicomponent membrane extraction process where at least one of the phases constitutes a non-ideal solution. (C) 1999 Elsevier Science B.V. All rights reserved.