Effects of surfactant type and structure on properties of amines for carbon dioxide capture

Abstract

Nonionic and cationic surfactants were tested for potential use as additives in monoethanolamine (MEA) solution to improve the wetting of solid packing materials (steel, stainless steel, or aluminum) by the solution. This is expected to improve the mass transfer of carbon dioxide (CO2) to the amine solution. The surface activities of surfactants were evaluated based on their ability to lower MEA’s surface tension, which is related to spreading and wetting of MEA on packing materials, to maximize the interfacial area for absorbing CO2. Effects of the surfactants on kinematic viscosity, foam ability and foam stability, CO2 equilibrium loading, and the initial CO2 absorption rate – deemed as the key properties of the MEA solution – were also measured. The results revealed that the surfactant could reduce surface tension of the MEA by 14–56%. Such reduction helped lower the contact angle of the MEA on the test materials by 40–55%. The surfactants did not significantly affect kinematic viscosity of MEA solution, but only slightly increased the amine’s viscosity. Neither were CO2 equilibrium loading nor initial CO2 absorption rate by MEA affected by any of the surfactants. A couple of surfactants, specifically a nonionic surfactant with a small hydrophilic head, and a cationic surfactant with a short linear chain, even slightly increased the initial CO2 absorption rate by MEA. However, the concentration of a surfactant in the MEA solution should be kept below 1 CMC to benefit from improved wetting while keeping foaming to a minimum.