Effects of Catalysts, Inhibitors, and Contaminants on Piperazine Oxidation

Abstract

The oxidation of aqueous piperazine (PZ) was studied using the HTOR bench-scale degradation apparatus. The HTOR emulates PCCC conditions of absorption/stripping by cycling solvent between a low-temperature oxidation reactor sparged with air and CO2 and an oil bath up to 150°C. PZ oxidation is caused by two similar pathways: the reaction between the solvent and dissolved molecular oxygen carried over from absorber conditions into the heated stripper conditions; and the reaction with dissolved ferrous iron, which can cycle between ferric and ferrous states during the absorption/stripping process to further oxidize the amine. Using a free radical scavenger (Inhibitor A) or nitrogen sparging before the solvent is heated to stripper conditions inhibits the direct oxidation of PZ due to dissolved oxygen, but does not prevent oxidation due to cycling of ferrous iron. In addition to iron, copper is a strong PZ oxidation catalyst. Chromium, nickel, and manganese do not affect the oxidation of PZ in the absence of iron. The solubility of ferrous iron in PZ is strongly correlated with the accumulation of degradation products, indicating that as the solvent degrades a synergistic effect will occur between the rate of dissolved iron accumulation and the oxidation of the solvent.