Direct air capture of CO₂ with an amine resin: A molecular modeling study of the oxidative deactivation mechanism with O₂

Lewatit R VP OC 1065 is a promising material for direct air capture of CO₂. However, it was found that serious oxidative degradation already started from 80 °C. In this DFT study, oxidative degradation is described as a series of well-known reactions in air-oxidation chemistry. Oxidation of the resin starts with the formation of an α-benzyl amino hydroperoxide. Thermal decomposition of the α-benzyl amino hydroperoxide is the second step and leads eventually to the corresponding amide (R(C=O)NH₂) and the half-aminal (RCH(OH)(NH₂). The half-aminal further solvolyzes predominantly to an aldehyde (RCHO). Both the amide and the aldehyde are responsible for the experimentally observed loss of CO₂ capacity as these groups are not able to capture CO₂. The rate-determining step in oxidative degradation is usually the decomposition of the hydroperoxide, but in this case the formation of the α-benzyl amino hydroperoxide cannot be excluded. The apparent contradiction between the results of Hallenbeck et al. and Yu et al. with respect to the oxygen content before and after exposure of the resin to air at high temperature is explained by the difference in H₂O content before and after and oxygen incorporation by amide and aldehyde formation after exposure to air. The loss of nitrogen content on exposure to air at high temperature is explained by the formation of aldehydes.