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Environ Sci Technol. 2013 Apr 2;47(7):3528-34. doi: 10.1021/es304640f. Epub 2013 Mar 15.

Kinetics of N-nitrosopiperazine formation from nitrite and piperazine in CO2 capture.

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Luminant Carbon Management Program, Department of Chemical Engineering, The University of Texas at Austin, 200 E Dean Keeton St Stop C0400, Austin, Texas 78712-1589, United States.


Piperazine (PZ) is an efficient amine for carbon capture systems, but it can form N-nitrosopiperazine (MNPZ), a carcinogen, from nitrogen oxides (NO(x)) in flue gas from coal or natural gas combustion. The reaction of nitrite with PZ was studied in 0.1 to 5 mol/dm(3) PZ with 0.001 to 0.8 mol CO2/mol PZ at 50 to 135 °C. The reaction forming MNPZ is first order in nitrite, piperazine carbamate species, and hydronium ion. The activation energy is 84 ± 2 kJ/mol with a rate constant of 8.5 × 10(3) ± 1.4 × 10(3) dm(6) mol(-2) s(-1) at 100 °C. The proposed mechanism involves protonation of the carbamate species, nucleophilic attack of the carbamic acid, and formation of bicarbonate and MNPZ. These kinetics and mechanism will be useful in identifying inhibitors and other strategies to reduce nitrosamine accumulation in CO2 capture by scrubbing with PZ or other amines.

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