A novel time lag method for the analysis of mixed gas diffusion in polymeric membranes by on-line mass spectrometry: method development and validation
European Union's Seventh Framework Program (FP7/2007-2013) under Grant agreement no. 608490. project M4CO 2 . CNR/FCT Italian/Portuguese Bilateral Project 2015-2016 "Advanced studies of the transport properties and gas separation by polymers of intrinsic microporosity (PIMs) and Ionic Liquid Gel Membranes via novel methods" and the CNR-CAS Bilateral Agreement 2016-2018 "Innovative polymeric membranes for pervaporation and advanced gas and vapour separations". ; A novel method to determine the individual diffusion coefficients of gases in a mixture during their permeation through polymeric membranes is described. The method was developed in two independent laboratories, using rubbery Pebax® and glassy Hyflon® AD60X membrane samples as standards, and validated using the Tröger's base containing Polymer of Intrinsic Microporosity, PIM-EA-TB. Monitoring of the permeate composition in real time by a quadrupole mass spectrometer allowed the analysis of the permeation transient for gas mixtures. Two operation modes, either with a vacuum in the permeate and a direct connection to the mass spectrometer via a heated restriction, or using a sweeping gas and a heated capillary sample inlet, give excellent agreement with the traditional time lag method for single gases. A complete overview of the method development, identification of the critical parameters, instruments calibration, data elaboration and estimation of the experimental accuracy are provided. Validation with PIM-EA-TB, shows that the method can also successfully detect anomalous phenomena, related to pressure and concentration dependency of the transport properties, physical aging or penetrant-induced dilation. Rapid online analysis of the permeate composition makes the method also very suitable for routine mixed gas permeability measurements. ; publishersversion ; published