Nitrosamine formation and mitigation in blended amines for CO2 capture

Nitrosamines were synthesized in situ by addition of sodium nitrite to aqueous amine solutions used for CO2 capture. Amine blends containing a high concentration of secondary amine yielded stoichiometric quantities of nitrosamine. At low concentration of secondary amine, nitrosamine yield and rate was a function of secondary amine concentration. The nitrite scavengers, hydroquinone, ascorbate, cystine, and cysteine reduced nitrosamine yield by up to 63%. Thermal decomposition of nitrosamines at 150 °C was first-order in nitrosamine and in the order: N-nitroso-piperazine (MNPZ) in 8 m piperazine (k = 26.8 ± 1.7 s−1 × 10 − 6) > N-nitroso-1-(2-hydroxyethyl)-ethylenediamine(NHEEDA) in 7 m 1-(2-hydroxyethyl)-ethylenediamine > N-HEEDA or N-nitrosodiethanolamine (NDELA) in 7 m monoethanolamine (MEA) > NDELA in 7 m diethanolamine (DEA). Thermal degradation was successfully used to mitigate MNPZ in two lab-scale CO2 capture cycling systems.