Comprehensive study on PVDF-HFP/BMImBF4/AgBF4 membranes for propylene purification

Abstract

In this work, a comprehensive analysis of PVDF-HFP/BMImBF4/AgBF4 facilitated transport membranes for olefin/paraffin separation is presented. Previous works of our research group have reported high flux and propylene selectivity under dry conditions and using synthetic gas mixtures, highlighting the promising potential of these membranes for industrial applications. This work advances in the understanding of the phenomena involved in membrane performance and moves one step forward in the knowledge of the industrial viability of this membrane system. First, the internal interactions between the silver cations and the polymer backbone, the silver salt dissociation and the silver degradation have been studied using FTIR, Raman and XPS spectroscopic techniques. Secondly, the experimental membrane performance during 110 days and working at changing relative humidity conditions in the feed gas has been assessed. Thermogravimetric techniques helped determining the water uptake capability of the facilitated transport membrane. Thirdly, real gas mixtures from a fluid catalytic cracking unit were provided by the industry and used in permeation experiments to check the membrane behavior under industrial-like conditions. The results provide experimental evidence for the previously theorized facilitated transport mechanisms and reveal a major influence of feed gas humidity on membrane performance. On the other hand, the industrial gas mixture produces no deviation from synthetic feed conditions due to trace contaminants. Finally, the carrier deactivation in long-term permeation has been quantified through a mathematical expression.