Effects of temperature and anion species on CO 2 permeability and CO 2/N 2 separation coefficient through ionic liquid membranes

Abstract

The permeability of carbon dioxide (CO 2) through imidazolium-based ionic liquid membranes was measured by a sweep gas method. Six species of ionic liquids were studied in this work as follows: [emim][BF 4], [bmim][BF 4], [bmim][PF 6], [bmim][Tf 2N], [bmim][OTf], and [bmim][dca]. The ionic liquids were supported with a polyvinylidene fluoride porous membrane. The measurements were performed at T = (303.15 to 343.15) K. The partial pressure difference between feed and permeate sides was 0.121 MPa. The permeability of the CO 2 increases with temperature for the all ionic liquid species. Base on solution diffusion theory, it can be explained that the diffusion coefficient of CO 2 in an ionic liquid affects the temperature dependence more strongly than the solubility coefficient. The greatest permeability was obtained with the [bmim][Tf 2N] membrane. The membrane of [bmim][PF 6] presents the lowest permeability. The separation coefficient between CO 2 and N 2 through the ionic liquid membranes was also investigated at the volume fraction of CO 2 at feed side 0.10. The separation coefficient decreases with the increase of temperature for the all ionic liquid species. The membrane of [emim][BF 4] and [bmim][BF 4] gives the highest separation coefficient at constant temperature. The lowest separation coefficient was obtained from [bmim][Tf 2N] membrane which presents the highest permeability of CO 2.