Oxidative degradation of Piperazine (PZ) in aqueous KOH/K2CO3 solutions

Abstract

KOH and K₂CO₃ aqueous solutions have demonstrated potential for CO₂ absorption processes due to their low toxicity, non-volatility of the capture agent and resistance to degradation. However, their absorption kinetics are typically slower than those of primary and secondary amines, and therefore promotors may be needed to allow competitive absorption rates and thus absorber heights. Here, we selected piperazine (PZ) as a promoter and investigated its oxidative degradation when blended with KOH or K₂CO₃. The changes in PZ concentration were analyzed by gas chromatography–mass spectrometry (GC–MS), while the degradation products were analyzed by GC–MS and anion chromatography. The results showed that PZ oxidative degradation followed the order KOH/PZ > PZ > K₂CO₃/PZ indicating that KOH enhanced PZ oxidation while K₂CO₃ inhibited PZ oxidation. Therefore, KOH/PZ may still be a promising solvent with appropriate CO₂ loading as the CO₂ protects the PZ from hydroxyl and oxygen radical attacks. The degradation products are similar across the blends and identified as Ethylenediamine (EDA), 2-oxopiperazine (OPZ), Formylpiperazine (FPZ), formate, acetate and oxalate, with formate being the most abundant product for all blends. Furthermore, the PZ first-order rate constants for all solutions were provided, and the oxidation degradation pathway of PZ-based solutions was proposed.