Polymerization-induced self-assembly amino acid ionic liquid/poly(ethylene oxide) thin-film composite membranes for CO2 separation

Abstract

It is well known that crosslinking poly(ethylene oxide) (PEO) membranes exhibit high CO₂/N₂ solubility selectivity, and are suitable for separating CO₂ from flue gas. However, the high CO₂/N₂ selectivity is temperature sensitive and decreases rapidly with increasing temperature. To overcome this deficiency, imidazolium-based amino acid ionic liquids (AAILs) are introduced into the PEO membranes. A series of (AAILs-PEO)/PAN thin-film composite (TFC) membranes were prepared by a polymerization-induced self-assembly process. Due to the hydrogen and Coulomb interactions between the imidazolium ring of AAILs and the ether groups of PEO monomers, the morphology of the selective layer changed from micellar to granular upon the introduction of the AAILs into the PEO membranes, while the chain-segment flexibility and interspacing of the PEO are also changed. Compared with the original PEO/PAN TFC membrane, the (AAILs-PEO)/PAN TFC membranes show much higher CO₂/N₂ selectivity, which increases from ∼41 to ∼ 74. In addition, the AAILs show strong hydrophilicity, which leads to a significant increase in CO₂/N₂ selectivity under the wet-gas feed, reaching ∼105. Compared with the original PEO/PAN TFC membranes with CO₂/N₂ selectivity of ∼10 at 70 °C, the (AAILs-PEO)/PAN TFC membranes show the selectivity of ∼30, coupled with CO₂ permeance of ∼1300 GPU at 70 °C. Under the 40: 60 mixtures of CO₂: N₂, which is a common lime kiln exhaust gas, by using the (AAILs-PEO)/PAN TFC membrane, the CO₂ concentration on the downstream side can reach over 90 % at 20 °C and over 70 % at 70 °C, respectively, under a pressure ratio of 5.