Modified polyethyleneimine as additive for enhanced direct air capture via membrane contactors

This paper reports the preparation and characterization of asymmetric membranes for direct air capture (DAC) in polysulfone membrane contactors. In the previous studies it was found that blending the polysulfone with modified Lupasol G20 improved the polysulfone membrane performance; however, the hydrophobicity and stability of the additive require improvement for the application in gas/liquid system. In order to achieve this objective, in the current study, Lupasol G20 was grafted with phenyl isocyanate via urea linkages in a solvent-free and eco-friendly method. Membranes with different amount of the additive were prepared by phase inversion and characterized by several techniques in terms of morphology, porosity, wettability, and stability in aqueous KOH solution. Finally, CO2 solubility and mass transfer coefficient were determined and correlated with membranes' performance in the direct air capture device. In general, it was found that the presence of the additive greatly improved the characteristics of the membranes in terms of CO2 capture efficiency and robustness, outperforming the results obtained previously. The best results for were obtained with 5% additive content reaching 0.18 [mol/m2s].