Foaming Dependence on the Interface Affinities of Surfactant-like Molecules

We have explored the relationship between physical properties and foaming behavior of 30 wt % aqueous monoethanolamine (MEA) solutions with three different surfactant-like additives. The additives included one commercial surfactant, cetyltrimethylammonium bromide (CTAB), and two CO₂ capture catalysts that behave as weak surfactants. The physical properties of interest were the additives' affinity for the liquid-vapor interface and the viscosity, surface tension, and surface elasticity of the solutions. The physical properties were explored using molecular dynamics simulations as well as experiments. The additives' affinity for the liquid-vapor interface played a key role in the foaming behavior by affecting the interfacial properties (surface tension and surface elasticity) of the aqueous MEA solutions. The solution containing CTAB showed the largest surface tension depression and the largest surface elasticity and resulted in the largest amount of foaming. The two catalyst solutions had almost similar surface tensions but differed in their elasticity. The catalyst solution with higher surface elasticity showed more foaming due to higher foam stability.