Nitrosamine Formation in Carbon Capture

Carbon capture using amine scrubbing is an effective way to reduce CO2 emissions, but nitrosamines, a class of carcinogenic compounds, form from nitrogen oxides (NOx) in the process. Kinetic analysis of reactions involving nitrite and ethanol amine (MEA), piperazine (PZ), diethanol amine (DEA), methylethanol amine (MMEA), and methyldiethanol amine (MDEA) determined the reaction rate of each amine under various conditions. The reactions involving MEA, PZ, DEA, and MMEA were first order in nitrite, carbamate species, and hydronium ion. The tertiary amine, MDEA, did not fit the same rate law. A model accurately predicts reaction kinetics for unhindered primary and secondary amines. The rates of reaction revealed that primary amines react approximately 10 times slower than secondary amines under identical reaction conditions. Increased reactivity was noted in secondary amines which have more electron withdrawing groups attached to the amine. Two proposed mechanisms involve protonation of the carbamate species, nucleophilic attack of carbamic acid by nitrite, and formation of bicarbonate and a nitrosamine. The comparative kinetics can be applied to the analysis of the steady state concentration of nitrosamines in carbon capture, can help identify inhibitors for this reaction, and can be applied to the use of blends to mitigate nitrosation.