Nitrosamine Formation in Amine-Based CO^sub 2^ Capture in the Absence of NO^sub 2^: Molecular Modeling and Experimental Validation

A computational chemistry approach was used to elucidate and verify the different nitrosamine formation mechanisms and pathways. These included nitrosamine formation under acid or basic environments in the presence of NO, O^sub 2^, SO^sub 2^ and CO^sub 2^ without NO^sub 2^. The results clearly showed that nitrosamine could be formed without NO^sub 2^ via 2 different types of mechanisms, namely, addition and elimination forming N-N bond before proton transfer and proton transfer before N-N bond formation, respectively. The essence of these mechanisms identified in this work was that two reaction steps were required to complete both reaction mechanisms with different nitrosating agents. Two steps were both necessary neither of which could be neglected, if the nitrosamine formation reaction was to be completed. Computational simulation performed on the reactant, intermediate, transition state, and product for each set of reactions also validated the proposed mechanisms. Experiment also detected nitrosamine from the reaction of diethylamine and NO, SO^sub 2^, O^sub 2^, and CO^sub 2^ in both liquid and gas phase. Thus, NO^sub 2^ is not necessary for nitrosamine formation to occur in the CO^sub 2^ capture system.