Dissolved Oxygen Depletion Catalyzed by Amino Acids in Piperazine

Dissolved oxygen (DO) drives the oxidative degradation of amine solvents in CO₂ capture. Ferric iron catalyzes DO consumption in 5 m piperazine (PZ). Amino acids, major degradation products, influence Fe³⁺'s activity by enhancing its solubility and availability, amplifying catalytic effects. Fe³⁺ catalyzed DO consumption with a half-order dependency, exhibiting a reaction order breakpoint at 0.05 mM Fe³⁺, beyond which excess Fe³⁺ likely formed inactive clusters. Amino acids increased the catalytic effect of Fe³⁺ up to a plateau concentration, after which additional Fe³⁺ became inactive. At lower Fe³⁺ concentrations (0.025 mM), some amino acids, such as nitrilotriacetic acid (NTA), sequestered Fe³⁺, reducing its catalytic potential, while others enhanced its activity. Amino acids were ranked by their ability to increase the rate constant for DO consumption in 5 m PZ with 1 mM Fe³⁺: 1 mM ethylenediaminetetraacetic acid (EDTA) > 20 mM 1,2-di(piperazin-1-yl)ethan-1-one (PZAAPZ⁺) > 15 mM nitrilotriacetic acid (NTA) > 15 mM N-(2-aminoethyl)glycine (AEG⁺) > 15 mM ethylenediaminediacetic acid (EDDA) > 15 mM glycine (GLY) > 15 mM iminodiacetic acid (IDA).