Amine/Carboxylic Acid Ionic Liquid Composite Membranes for CO₂ Separation

Abstract

Alkanolamine + carboxylic acid-based ionic liquids have shown promising high CO2 selectivities. Their addition to cellulose acetate (CA) and polyvinyl alcohol (PVA) was investigated in the present study. The N-methyl-2-hydroxyethylammonium propionate IL [m-2HEA][Pr] significantly enhances the CO2 separation performance of PVA. Scanning electron microscopy, Fourier transform infrared spectroscopy, and nuclear magnetic resonance analyses indicate that the IL–PVA combination produced IL composite membranes with interactions being predominantly physical. Furthermore, the IL addition to CA produced porous membranes with apparent low CO2 separation efficiency. Pure gas permeation experiments indicate that increasing IL concentration of PVA-based membranes promotes higher gas permeabilities. The membranes were prepared containing up to 60.3 wt % of [m-2HEA][Pr], which resisted pressure differentials up to 6 barg. PVA containing 45.5 wt % of IL produced the most promising results, achieving 26 barrer of CO2 permeability and permselectivities of 122 and 213 for CO2/CH4 and CO2/N2, respectively. This result was compared to promising materials from the literature and indicated the overall high CO2/CH4 and CO2/N2 selectivities of PVA/[m-2HEA][Pr] membranes, which overcome even the 2008 Robeson's upper boundary.