Amine/Carboxylic Acid Ionic Liquid Composite Membranes\nfor CO₂ Separation

Abstract

Alkanolamine\n+ carboxylic acid-based ionic liquids have shown promising\nhigh CO₂ selectivities. Their addition to cellulose acetate\n(CA) and polyvinyl alcohol (PVA) was investigated in the present study.\nThe <i>N</i>-methyl-2-hydroxyethylammonium propionate IL\n[m-2HEA]­[Pr] significantly enhances the CO₂ separation\nperformance of PVA. Scanning electron microscopy, Fourier transform\ninfrared spectroscopy, and nuclear magnetic resonance analyses indicate\nthat the IL–PVA combination produced IL composite membranes\nwith interactions being predominantly physical. Furthermore, the IL\naddition to CA produced porous membranes with apparent low CO₂ separation efficiency. Pure gas permeation experiments indicate\nthat increasing IL concentration of PVA-based membranes promotes higher\ngas permeabilities. The membranes were prepared containing up to 60.3\nwt % of [m-2HEA]­[Pr], which resisted pressure differentials up to\n6 barg. PVA containing 45.5 wt % of IL produced the most promising\nresults, achieving 26 barrer of CO₂ permeability and permselectivities\nof 122 and 213 for CO₂/CH₄ and CO₂/N₂, respectively. This result was compared to promising\nmaterials from the literature and indicated the overall high CO₂/CH₄ and CO₂/N₂ selectivities\nof PVA/[m-2HEA]­[Pr] membranes, which overcome even the 2008 Robeson’s\nupper boundary.