In this study, the role of ionic liquid 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIM+BF4-) in poly (vinylpyrrolidone) (PVP)/AgCF3SO3/Al(NO3)(3) complex membrane for enhancement of propylene/propane separation performance was investigated. When BMIM+BF4- was incorporated into PVP/AgCF(3)So(3)/Al (NO3)(3) complex membrane, the selectivity of propylene/propane mixture increased from 5 to 9 without diminishment of mixed-gas permeance. Furthermore, the PVP/AgCF3SO3/Al(NO3)(3)/BMIM+BE4- membrane exhibited long-term stability for more than 100 h, indicating that Ag+ ions were highly stabilized. The coordinative interactions of the PVP/AgCF3SO3/Al(NO3)(3)/BMIM+BF4- membrane were characterized and compared with a PVP/AgCF3SO3/Al(NO3)(3) membrane by TGA, FT-IR, XPS, and FT-Raman. As results, FTIR and XPS showed the electrostatic interaction between the BF4- anions and Ag+ ions led to weakening of the interaction between the Ag+ ions and the C=O bond of PVP. FT-Raman showed ion aggregates were easily formed by the interactions between Al3+ and CF3SO3 in the PVP/AgCF3SO3/Al(NO3)(3)/BMIM+BE4- electrolyte membranes. (C) 2016 Elsevier B.V. All rights reserved.