Cellulose Acetate–Ionic Liquid Blends as Potential Polymers for Efficient CO2 Separation Membranes

Abstract

CO2 capture, applied in CO2 separation from natural gas or in CO2/N2 separation from power plant flue gas streams, is of great importance for technical, economic, and environmental reasons. The latter seems important because CO2, as a greenhouse gas, is considered the main contributor to global warming. Using polymeric membranes for CO2 separation presents several advantages, such as low energy demand, small equipment volume, and the absence of liquid waste. In this study, two ionic liquids (ILs) were used for the preparation of cellulose acetate (CA)–IL blend membranes for potential CO2 capture applications, namely, 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim+][HSO4−]) and choline glycine ([Ch+]Gly−), as they present adequate CO2 dissolution ability. The first IL is commercially available, whereas the latter was synthesized by a novel route. Several composite membranes were prepared through the solvent casting technique and characterized by a variety of methods, including thermogravimetry, calorimetry, FTIR spectroscopy, and X-ray diffraction. The CO2 sorption in the composite membranes was experimentally measured using the mass loss analysis (MLA) technique. The results showed that the ILs strongly interacted with the C=O groups of CA, which exhibited high affinity with CO2. In the case of [Bmim+][HSO4−], a reduction in the available sites that allow strong intermolecular interactions with CO2 resulted in a decrease in CO2 sorption compared to that of pure CA. In the case of [Ch+]Gly−, the reduction was balanced out by the presence of specific groups in the IL, which presented high affinity with CO2. Thus, the CA-[Ch+]Gly− blend membranes exhibited increased CO2 sorption capability, in addition to other advantages such as non-toxicity and low cost.