Effect of ionic liquids on dissociation of copper flake into copper nanoparticles and its application to facilitated olefin transport membranes

Effects of ionic liquids on dissociation of micrometer-sized copper flakes into copper nanoparticles and on facilitated olefin transport were investigated. Three different ionic liquids (ILs) of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM+BF4−), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM+PF6−) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM+BF4−) were employed for facile synthesis of copper nanoparticles and for inducing the partial surface positive charge of the copper nanoparticles for facilitated olefin transport. The positively charged surface was induced by interactions with anion of the ILs as evidenced by FT-Raman spectroscopy. The intensity of the interactions depending upon the ionic liquid resulted in the difference in the size and its distribution of the nanoparticles as confirmed by TEM images and UV–vis spectra. The separation performance of the ionic liquid/Cu metal composite membranes for olefin/paraffin mixtures was in the following order: EMIM+BF4−/Cu < BMIM+PF6−/Cu < BMIM+BF4−/Cu. Surprisingly, the binding energies of the copper atoms in the ionic liquid/Cu metal composites were strongly correlated the separation performance. Consequently, it was concluded that facilitated olefin transport was consistent with the trend of increasing binding energy of copper atoms.