(571b) Elucidating the Role of Water in Amine-Facilitated CO2 Transport Via Operando Transmission FTIR Spectroscopy

Amine-functionalized polymeric membranes selectively facilitate transport of CO₂ over other gases to separate CO₂ from mixed streams with high permeance and selectivity. Water vapor in the feed gas enhances CO₂ permeation across amine-functionalized facilitated transport membranes (FTMs), but how exactly water influences the CO₂ transport mechanism is not clear.

In this talk, I will describe a new operando transmission FTIR spectroscopy tool that we developed to probe CO₂ transport mechanisms of amine-based FTMs under realistic operating conditions, including in the presence of water vapor. This work describes the design of this tool and demonstrates its functionality through investigating the mechanism of CO₂ transport across polyvinylamine (PVAm), a primary amine FTM commonly used for CO₂ separations. We show that CO₂ permeation across PVAm is enhanced in the presence of water due to the conversion of CO₂ to a reactive intermediate, which is most likely carbamate species based on the infrared band positions. Our results suggest that water catalyzes the formation of carbamate by a three-step mechanism: (1) water protonates PVAm resulting in a hydroxide species, (2) CO₂ reacts with the protonated PVAm to form a zwitterion, and (3) the zwitterion is deprotonated by the hydroxide species produced during the PVAm protonation. This new operando transmission FTIR spectroscopy methodology can be applied to a range of membrane systems (e.g., secondary and tertiary amines) to probe transport mechanisms.