New arrangement of dynamic permeation method for determination of gas separation ability of ionic liquids

Abstract

A new arrangement of dynamic permeation apparatus was developed for testing gas transport properties of ionic liquids. This arrangement enables to measure not only the transport of pure gases but also that of gas mixtures. Three ionic liquids (ILs), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]), and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf2N]), were selected for testing the new arrangement of dynamic permeation apparatus for determination of separation of binary CO2/CH4 mixture.A compact IL layer with thickness of around 1mm was created on the surface of a dense support layer from polydimethylsiloxane (PDMS). Permeation experiments of binary mixture with the composition close to equimolar (51mol% CO2 and 49mol% CH4) were performed using a semi-open cell under dynamic pressure conditions at 25°C.A constant pressure of binary mixture CO2 and CH4 at the feed side was maintained, while vacuum was set at the permeate side at the beginning of the experiment. After reaching the required values of permeate pressure a valve that separates the permeate volume of the cell and the evacuated volume with a septum was opened for a few seconds and during this time apart of the permeate was siphoned in this evacuated volume. A sample of the permeate was taken off and analyzed by a GC. Separation factor was determined from the comparison of feed and permeate compositions. The transport of pure gases through the selected ILs was also measured. Good agreement between ideal and real separation factor was achieved.