Atmospheric Oxidation of Piperazine Initiated by ·Cl: Unexpected High Nitrosamine Yield

• DOI: 10.1021/acs.est.8b02510
• Publication Date: 2018-07-31T21:08:52Z
• Authors: Fangfang Ma; Zhezheng Ding; Jonas Elm; Hong-Bin Xie; Qi Yu; Cong Liu; Chao Li; Zhiqiang Fu; Lili Zhang; Jingwen Chen
• Keywords: Kinetics; Nitrosamines; Atmosphere; 13. Climate action; 11. Sustainability; Ethanolamine; Piperazine; 01 natural sciences; 0105 earth and related environmental sciences

Chlorine radicals (·Cl) initiated amine oxidation plays an important role for the formation of carcinogenic nitrosamine in the atmosphere. Piperazine (PZ) is considered as a potential atmospheric pollutant since it is an alternative solvent to monoethanolamine (MEA), a benchmark solvent in a leading CO2 capture technology. Here, we employed quantum chemical methods and kinetics modeling to investigate ·Cl-initiated atmospheric oxidation of PZ, particularly concerning the potential of PZ to form nitrosamine compared to MEA. Results showed that the ·Cl-initiated PZ reaction exclusively leads to N-center radicals (PZ-N) that mainly react with NO to produce nitrosamine in their further reaction with O2/NO. Together with the PZ + ·OH reaction, the PZ-N yield from PZ oxidation is still lower than that of the corresponding MEA reactions. However, the nitrosamine yield of PZ is higher than the reported value for MEA when [NO] is <5 ppb, a concentration commonly encountered in a polluted urban atmosphere. The unexpected high nitrosamine yield from PZ compared to MEA results from a more favorable reaction of N-center radicals with NO compared to O2. These findings show that the yield of N-center radicals cannot directly be used as a metric for the yield of the corresponding carcinogenic nitrosamine.