Photodegradation in natural waters of nitrosamines and nitramines derived from CO₂ capture plant operation

Amine solvents used in post combustion CO₂ capture (PCCC) plants react with NO_x, forming carcinogenic nitrosamine and nitramine compounds. These can be emitted to the atmosphere, undergoing deposition to aquatic and terrestrial environments. In the current study, the hydrolytic and photolytic degradation of nine nitramines and nitrosamines identified as possible degradation products of 2-monoethanolamine and piperazine solvents are studied. Nitrosamines and nitramines are generally resistant to hydrolysis, although nitrosopiperazine and piperazine nitramine both undergo up to 50 % degradation at 50 °C and pH 7, but not at lower temperatures or other pH values. Owing to absorbance at ~340 nm, the nitrosamines degrade rapidly in aqueous solution when exposed to sunlight (half-lives in the range 6-11 minutes), whilst nitramines are photolytically stable. Light screening by natural organic matter (1-100 mg/L) lead to an ~3-fold decrease in nitrosodiethanolamine (NDELA; 1 mg/L) degradation rate. A theoretical study indicates environmentally relevant concentrations of NDELA may be persistent due to competition with NOM for photons. The main photodegradation products are identified for each nitrosamine, and degradation mechanisms suggested.