A novel method to determine the transport parameters of individual gas mixture components in polymers of intrinsic microporosity

The present paper discusses a novel method for the continuous in-line measurement of the gas permeation through polymeric membranes, using a mass spectrometric gas analyser to determine the permeability and diffusion coefficients of the individual components in gas mixtures. Since slightly more than a decade, polymers of intrinsic microporosity (PIMs) are receiving a increasing attention from the scientific community for their potential use as novel high performance membrane materials. Transport of gases and vapours in dense polymeric membranes takes place according to the well-known solution-diffusion mechanism but transport of CO? and its mixtures in PIMs may show highly unusual behaviour. Reasons for the unusual transport properties may be the strong dual mode sorption behaviour or the interaction of the gases with the polymer matrix. In order to fully exploit these novel polymers as successful membrane materials, it is necessary to acquire a better understanding of their basic transport properties. The simplest method to determine the permeability, diffusion and, indirectly, the solubility coefficient of gases in dense polymeric membranes is the so-called time lag method. This measures the transient of the permeate pressure increase in a fixed-volume variable pressure setup. Unfortunately, this method is only suitable for pure gases. The aim of the present work is therefore to study the transient behaviour of gas mixtures, using a mass-spectrometric in-line gas analyser with high sampling rate to follow the permeate gas composition as a function of time in PIMs and other polymers. This allows the determination of the individual permeability and diffusion coefficients of each of the gas species in the mixture under different experimental conditions. By comparison with pure gases, it is also possible to identify positive or negative coupling effects. Acknowledgements: This research received funding from the EU's Seventh Framework Program, Grant Agreement 608490, project M4CO2.