Nanoporous ceramic supported ionic liquid membranes for CO2 and SO2 removal from flue gas

- Supported ionic liquid membranes were developed by physical infiltration of ionic liquids within porous ceramic substrates.
- The separation efficiency of the developed membranes regarding CO2/N2 and CO2/SO2/N2 gas mixtures was evaluated.
- The effect of the operation conditions on the gas permeation properties and separation performance was investigated.
- The nature of the counter-anion showed substantial impact on the CO2 and SO2 permeation properties.
- The issue of how the presence of low partial pressures of SO2 affect CO2 permeation rates was studied.

In this work supported ionic liquid membranes (SILMs) were developed via physical imbibition of 1-alkyl-3-methylimidazolium-based ionic liquids incorporating either the tricyanomethanide ([TCM]−) or the trifluoromethanesulfonate ([TfO]−) anion, into tubular composite ceramic substrates bearing a mesoporous separation layer. The developed SILMs were evaluated with respect to their efficiency for removal of CO2 and SO2 gases from mixtures simulating dry flue gas. In this context, the effect of temperature, feed composition and trans-membrane pressure gradient on CO2/N2 and SO2/CO2 separation performance was studied. For all SILMs, the highest CO2/N2 selectivity values (up to 47.6) were exhibited at ambient temperature unlike to CO2 permeance that was favored by elevation of temperature. The SO2 permeances varied over the range of 3-9.6·10−8 mol m2 s−1 Pa−1 being much higher than those determined for CO2 at comparable conditions whereas the permeances of the two gases exhibited opposite temperature dependence. The SO2/CO2 selectivity reached up to 30.7 even though it was markedly reduced with rising temperature and applied pressure gradient, in qualitative accordance to the behavior of CO2/N2 selectivity. Besides physical interaction, the embedded ionic liquid incorporating [TfO]− anions showed also weak chemical interaction with absorbed SO2, the contribution of the which resulted in enhanced SO2 permeation rates as compared to the ones through the embedded tricyanomethanide-based ionic liquids.