(579g) Elucidation of CO2 Facilitated Transport Mechanisms in Amine-Functionalized Membranes Using Operando Surface Enhanced Raman Spectroscopy

Reactive amines in polymeric facilitated transport membranes facilitate CO₂ transport across the membrane to give rapid and selective CO₂ separation from mixed gas streams such as natural gas and flue gas. However, the fundamental mechanisms by which the amine carriers facilitate CO₂ transport are not well understood. For example, it is not clear whether the amine group catalyzes the transformation of CO₂ into bicarbonate (HCO₃^-) species, which are mobile within the polymer matrix, or if CO₂ hops from one amine group to another as a carbamate (NHCOO^-) species, which is chemically attached to the polymer chain. It is also possible that CO₂ moves across FTMs by some other unknown mechanism.

In this work, we investigate the mechanism of CO₂ facilitated transport across polyvinylamine (PVAm)-based facilitated transport membranes using a new operando surface enhanced Raman spectroscopy (SERS) technique developed in our laboratory. Using this technique, the rate of CO₂ permeation across PVAm can be measured while the CO₂ transport intermediates formed in the membrane (e.g. carbamate, bicarbonate) are detected simultaneously under realistic operating conditions (e.g. flue gas). To enhance the sensitivity to detection of these CO₂ transport intermediates, we incorporated small amounts of plasmonic silver nanoparticles into the PVAm film, which enhanced the Raman signal associated with these CO₂ transport intermediates without compromising the films membrane separation performance. Using this operando SERS technique, we will show that CO₂ moves across PVAm primarily as carbamate species. Further, we observed the well-known carrier saturation phenomenon directly for this first time, to our knowledge.