Foaming of aqueous piperazine and monoethanolamine for CO2 capture

The cause of foaming in aqueous amines used for CO2 absorption was investigated in this study. The effect on foaming of amine concentration and various additives, including electrolytes, liquid hydrocarbon, and degradation products, was measured by a standard method. Both aqueous piperazine (PZ) with 0.3 mole CO2/mole alkalinity (α) and 7 m monoethanolamine (MEA, α = 0.4)) were studied. Formaldehyde at 270 mM substantially increases foaming in PZ. PZ foamed after 163 h of oxidative degradation, but this effect was greatly mitigated with an oxidation inhibitor. Silicone antifoam of 1 ppm reduced the foaminess by 20 times. The tendency of 8 m PZ to foam was increased by 40% with the addition of iron (II) up to a concentration of 1.5 mM, but dissolved iron had no significant effect on 7 m MEA. The tendency to foam and foam stability of 8 m PZ solutions was only slightly affected by 1 mM iron (III), 0.1% heptane in water, 5 mM of copper sulfate, or 100 mM of an oxidation inhibitor.