Desalination 193 (2006) 82–89 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved Presented at the International Congress on Membranes and Membrane Processes (ICOM), Seoul, Korea, 21–26 August 2005. *Corresponding author. Modeling gas sorption in amorphous Teflon through the non equilibrium thermodynamics for glassy polymers (NET-GP) approach Maria Grazia De Angelis a *, Ferruccio Doghieri a , Giulio C. Sarti a , Benny D. Freeman b a Dip. di Ing. Chimica, Mineraria e delle Tecnologie Ambientali,Università di Bologna, V.le Risorgimento 2, 40136 Bologna, Italy Tel. +39 (051) 2090410; Fax +39 (051) 6347788; email: grazia.deangelis@guest.ing.unibo.it b Department of Chemical Engineering, University of Texas at Austin, 10100 Burnet Road, Austin, TX, USA Received 25 March 2005; accepted 6 June 2005 Abstract The solubility of C 2 H 6 and C 2 F 6 in two amorphous glassy fluoropolymers, Teflon ® AF1600 and AF2400, has been modeled with the non equilibrium statistical associating fluid (NE-SAFT) and non equilibrium perturbed hard sphere chain (NE-PHSC) theories. Experimental swelling data during sorption are available to obtain a complete prediction of the solubility isotherms at 35°C. The solubility of C 2 F 6 in both fluoropolymers is rather satisfactorily predicted by the models with no adjustable parameters, while that of C 2 H 6 is overestimated, and a correction factor equal to about 0.90 must be applied on the binary energetic interactions estimated with the first approximation mixing rule. This result, combined with what previously obtained with the NE-lattice fluid (NE-LF) model, reveals inadequate representation of the hydrocarbon solubility in fluoropolymers by the geometric mean rule used to estimate the binary energetic interactions. Keywords: Amorphous Teflon; Gas solubility; Glassy polymers; NELF model; Thermodynamic models 1. Introduction Fluoropolymer membranes are eventually being used in gas and vapor separation for their high thermal stability and low solubility in organic solvents, which leads to high plasticization resist- ance to swelling penetrants such as the higher hydrocarbons [1]. The polymers investigated in this work are two random, glassy copolymers of