Thermal Degradation of Aqueous Piperazine for CO2 Capture: 2. Product Types and Generation Rates
2012
Freeman, Stephanie Anne | Rochelle, Gary Thomas
The generation of degradation products at 135 to 175 °C was investigated for concentrated, aqueous piperazine (PZ) loaded with CO₂. From 135 to 175 °C, N-formylpiperazine, ammonium, N-(2-aminoethyl)piperazine, and 2-imidazolidone were found to be the most abundant products. These species accounted for 63% of nitrogen and 49% of carbon lost as PZ and CO₂ during degradation. Thermal degradation of PZ is believed to be initiated by the nucleophilic attack of PZ at the α-carbon to a protonated amino function on H⁺PZ to create a ring opened PZ structure. H⁺PZ was found to be the active and likely initiating species required for the initial reactions of thermal degradation. Further SN2 substitution reactions can produce a variety of products. CO₂ is not required for thermal degradation to proceed but is reduced to create formate or formyl amides, reacts with amines to form stable ureas, and dictates the overall product mix. The mechanism for CO₂ reduction to formate or formyl amides is not clear but indicates the severity of thermal degradation conditions.
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