Direct air capture of CO₂ with an amine resin: A molecular modeling study of the deactivation mechanism by CO₂

Since 2012, Lewatit R VP OC 1065 was reported as a promising material for direct air capture of CO₂. However, deactivation at a high pressure of CO₂ at 120 °C was reported with detrimental effects on its application. In this study, using density functional theory calculations, a quantitative description of the deactivation mechanism in the presence of CO₂ is presented. Deactivation by CO₂ follows a three-step mechanism. The first step in deactivation of the resin is self-catalyzed formation of a carbamic acid from an amine group and CO₂. The second step is decomposition of a carbamic acid to an isocyanate as the rate-determining step with an activation barrier of 144.4 kJ/mol. The third step is the H₂O-catalyzed addition of a benzyl amino group to the isocyanate, yielding an urea species, responsible for deactivation. However, the process can be made reversible by optimizing H₂O and CO₂ concentration and temperature. The identified deactivation mechanism quantitatively explains the differences between experimental CO₂ sorption data and the earlier reported dual site Langmuir model. ©