Amino Acids: Critical Oxidation Products in CO₂ Capture by Aqueous Piperazine

CO2 capture by aqueous piperazine (PZ) or other amines must address the degradation of the amine by reaction with oxygen from the flue gas. Ammonia, ethylenediamine (EDA), formate, and oxopiperazine (OPZ) have previously been quantified as important degradation products of PZ. In this work, a quadrupole time-of-flight mass spectrometer (QTOF-MS) coupled to a high-performance liquid chromatograph (HPLC) detected six amino acids and their lactams and amides with PZ. These six amino acids were identified and quantified using anion chromatography with pulsed amperometric detection (PAD). Samples were hydrolyzed to amides with NaOH to allow analysis of the total amino acids. The hydrolyzed amino acids included aminoethylglycine (AEG), piperazineacetic acid (PZAA), glycine (GLY), and 3-oxopiperazineacetic acid (3OPZA), the lactam of ethylenediaminediacetic acid. The total amino acids in hydrolyzed pilot campaign samples were present at concentrations (140 mmol/kg), which likely enhanced the effective solubility of Fe2+/Fe3+ and increased the rate of PZ oxidation.