The Structure of Adsorbed Species on Immobilized Amines in CO2 Capture: An in Situ IR Study

Abstract

The nature and structure of adsorbed CO 2 on immobilized amine sorbent in the presence and absence of H 2 O vapor have been studied by in situ infrared spectroscopy. CO 2 adsorbed on the primary amine as ammonium carbamate and on the secondary amine as carbamic acid. Adsorbed H 2 O mainly on secondary amine enhanced CO 2 capture capacity by increasing accessibility of amine sites and promoting the formation of carbamic acid. The binding strength of the adsorbed species increased in the order: carbamic acid < adsorbed H 2 O < paired carbamic acid; ammonium carbamate < ammonium chloride. Flowing argon over the amine sorbent at 50 °C removed weakly adsorbed H 2 O and carbamic acid from the secondary amine sites. Raising temperature is required to completely regenerate sorbent by removing strongly adsorbed ammonium carbamate from the primary amine sites and paired carbamic acid. The results of this study clarify the role of H 2 O vapor in amine-sorbents for CO 2 capture and provide a molecular basis for the design of the sorbents and operation of amine-based CO 2 capture processes.