Ag functionalized Carbon Molecular Sieves membranes for separating O2 and N2

Abstract

ABSTRACTIn the last two decades substantial progress has been made in the preparation of Carbon Molecular Sieve (CMS) membranes for gas separation. Today, researchers actively study precursor materials and pyrolysis routes to fully explore the merits of CMS membranes. Successful separation of permanent gas mixtures in which the gaseous components posses only little to no affinity to adsorb onto the internal CMS surface relies highly on the exact tailoring of microsieving regions. Preparation of CMS structures, which are highly permselective towards one of such mixture components, is especially cumbersome if the molecular sizes differ only slightly (e.g. O2/N2).To facilitate the separation of O2 and N2 we have chosen to functionalize the carbon matrix. By introducing nano-sized (40 nm) metallic Ag-clusters, the affinity of the membrane matrix for O2 significantly increases. We have added a silver containing salt, AgNO3, to a solution of BMTA-TDI/MDI co-polyimide (P84, Lenzing) in NMP in the absence of light to obtain homogeneous flat film polymeric precursors. These precursors were pyrolysed, reducing Ag+ to Ag, at different temperatures (350, 500, 600, 700, and 800 °C) in a N2 atmosphere and characterized using Scanning Electron Microscopy, Atomic Force Microscopy, and gas permeation. Thermo Gravimetrical Analysis was used to follow the pyrolysis in detail. From this we observed an increase of the ideal separation factor of 1.6. Moreover, we observed an increase of the permeability to a maximum of 240 %.