CO2 Capture with PEI: A Molecular Modeling Study of the Ultimate Oxidation Stability of LPEI and BPEI

Amine resins are frequently studied to capture CO2 from industrial emission sources and air. Polyethylene imine (PEI) is a typical example showing relatively high CO2 uptake and not too energy demanding desorption of CO2. For practical application, its oxidation stability is of great importance. In this DFT study, the ultimate oxidation stability of the two forms of PEI, linear PEI (LPEI) and branched PEI (BPEI), is investigated. First, the oxidation stability order for amines was determined using small amine clusters: primary > secondary > tertiary amines. Using LPEI and BPEI structure-related clusters, it turned out that under optimal conditions, the formation of α-amino hydroperoxide of PEI is the rate-determining step. Optimal conditions are the total absence of initiators like transition-metal ions, NOx, O3, or hydrocarbons and the presence of H2O and CO2. All computational results are in line with experimental results.