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 degrees 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.