Supported ionic liquid membranes (SILMs) prepared with inorganic supports are more stable under high temperatures and differential pressures for gas separation than those based on organic membranes. In this study, a hot coating method was used to modify commercial alpha-Al2O3 tubular substrates to prepare high-quality membrane supports. Following impregnation of an ionic liquid (IL; [BMIM][BF4] or [BMIM][Ac]) into the supports over a short time, the as-prepared SILMs were used for separation of N-2 and CO2. The effects of preparation parameters, including impregnation time (0-1800 s) and impregnation temperature (18-59 degrees C) on SILM performance and IL loading were systematically investigated to gain a better understanding of the SILM preparation process. The optimum impregnation time was determined by considering both the permeance and the selectivity. Further, a high temperature was found to be beneficial for the preparation process because the viscosity of ILs is usually low at higher temperatures. However, when the viscosities of the two ILs ([BMIM][BF4] and [BMIM] [Ac]) were maintained at the same value by controlling the impregnation temperature, the qualities of the as-prepared SILMs were different, which may be due to the different surface tensions of these ILs.