Desalination 144 (2002) 67–72 Presented at the International Congress on Membranes and Membrane Processes (ICOM), Toulouse, France, July 7–12, 2002. 0011-9164/02/$– See front matter © 2002 Elsevier Science B.V. All rights reserved *Corresponding author. Molecular modelling of polyimide membranes for gas separation Matthias Heuchel* a , Dieter Hofmann b GKSS Research Center, Institute of Chemistry, Kantstrasse 55, D-14513 Teltow, Germany a Tel. +49 (3328)352-465; b Tel. +49 (3328) 352-247; Fax: +49(0)3328/352-452; emails: matthias.heuchel@gkss.de, dieter.hofmann@gkss.de Received 1 February 2002; accepted 15 February 2002 Abstract Well-equilibrated molecular packing models have been produced for seven different polyimides. For all packings the transport properties (solubility and diffusion coefficient) have been calculated for nitrogen, oxygen and carbon dioxide using the Gusev-Suter method. Comparison with experimental data allowed to validate the quality of the model structures. A significant improvement to former results could be assessed for the predicted selectivity values. Keywords: Polyimide; Gas transport; Simulation; Solubility; Diffusion; Selectivity 1. Introduction Polyimides (PIs) have attracted much attention over the past years as material for gas separation membranes [1–3]. Particular PIs synthesized from 2,2'-bis(3,4-dicarboxy-phenyl) hexafluoropropane dianhydride (6FDA) show surprisingly high gas selectivities for gas pairs as O 2 /N 2 and CO 2 /CH 4 . Combined with high inherent chemical and thermal stability as well as mechanical strength, these PIs have been identified as promising materials for applications, such as the recovery of H 2 from industrial gas mixtures of CO 2 , N 2 or CH 4 , the purification of natural gas and the enrichment of either O 2 or N 2 from air. One stimulus for the extensive research was the observed tradeoff relationship between gas permeability and permselectivity. Over the last 2 decades, intensive investigations have been per- formed to study the structure property relation- ships of polyimides by systematically changing the diamine or dianhydride moieties [4–6]. Analysis of this immense experimental material allowed