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

The extraction of 2-nitrotoluene from electrolyte solutions containing diff erent ionic species was studied in a lab-scale membrane mass exchanger by m easuring partitioning between electrolyte and aqueous solutions, and organi c flux under different hydrodynamic conditions and for different ion concen trations. Salts were found to affect both the overall mass transfer coeffic ient 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-serie s model based on an activity gradient driving force. The model allows the p rediction of organic flux in saline-membrane-aqueous systems provided that saline-aqueous partition coefficients, and mass transfer coefficients in aq ueous-membrane-aqueous systems, are known. Since these parameters can be ea sily and independently measured or estimated from available correlations, t he model provides a useful methodology for engineered design of multicompon ent membrane extraction process where at least one of the phases constitute s a non-ideal solution. (C) 1999 Elsevier Science B.V. All rights reserved.