| Summary: | A molecular modeling study was carried out on linear polyethyleneimine (LPEI) to determine the CO 2 capturing process taking into account structural changes of the material at various amounts of H 2 O. Until now, CO 2 capture by LPEI was described as a combination of carbamic and carbonic acid formation. It was found that humidification below the melting point of LPEI leads to the formation of an LPEI/0.5H 2 O type of phase. Such a type of phase leads to CO 2 capture exclusively via carbonic acid formation, stabilized by secondary amines via ammonium bicarbonate and H-bridged amine carbonic acid complexes. Both the strong physisorption CO 2 complex and the low activation barrier for carbonic acid formation contribute to the overall process. Only in the absence of H 2 O, carbamic acid formation is possible. Thus, under CO 2 capturing process conditions, carbonic acid formation seems to be the only option as H 2 O will be present in flue gas.
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