The aqueous-aqueous extraction of organic compounds through thin film composite (TFC) membranes is investigated using a mathematical model describing the mass transfer across the membrane and hydrodynamic boundary layers at both membranes sides. The model accounts for organic diffusion and convection due to water flux, and enables the characterisation of water and organic counter transport encountered in saline-TFC membrane-aqueous extractive processes. The reliability of the model is tested using experimental data on rate of extraction of toluene from aqueous solutions of NaCl into water. The model is then used to predict the effect of ionic strength, thermodynamic properties (e.g. organic salting-out coefficient) and membrane morphology on the rate of organic extraction. The analysis shows that the retarding effect of countercurrent water transport on organic extraction can be severe for organic compounds with low salting-out coefficients (e.g. phenolic compounds) or for salts with strong influence on water activity (e.g. AlCl3). The model predictions provide the guidelines for choosing the membrane geometry and morphology which minimise this effect and maximise the rate of extraction of a given organic from a given saline solution. (C) 2002 Elsevier Science Ltd. All rights reserved.
Countercurrent transport of organic and water molecules through thin film composite membranes in aqueous-aqueous extractive membrane processes. Part II: theoretical analysis
NICOLELLA, CRISTIANO;
2002-01-01
Abstract
The aqueous-aqueous extraction of organic compounds through thin film composite (TFC) membranes is investigated using a mathematical model describing the mass transfer across the membrane and hydrodynamic boundary layers at both membranes sides. The model accounts for organic diffusion and convection due to water flux, and enables the characterisation of water and organic counter transport encountered in saline-TFC membrane-aqueous extractive processes. The reliability of the model is tested using experimental data on rate of extraction of toluene from aqueous solutions of NaCl into water. The model is then used to predict the effect of ionic strength, thermodynamic properties (e.g. organic salting-out coefficient) and membrane morphology on the rate of organic extraction. The analysis shows that the retarding effect of countercurrent water transport on organic extraction can be severe for organic compounds with low salting-out coefficients (e.g. phenolic compounds) or for salts with strong influence on water activity (e.g. AlCl3). The model predictions provide the guidelines for choosing the membrane geometry and morphology which minimise this effect and maximise the rate of extraction of a given organic from a given saline solution. (C) 2002 Elsevier Science Ltd. All rights reserved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
