Characterization of hollow fiber supported Ionic liquid membranes using microfocus X-ray computed tomography

This work demonstrates the use of X-ray computed tomography scanning to analyze the three dimensional structure of hollow fiber supported ionic liquid membranes (SILMs). In this type of gas separation membrane, the ionic liquid (IL) acts as the gas transport media, and therefore it is important to understand the distribution of ionic liquid within the hollow fiber support. Using the X-ray computed tomography technique, it was possible to obtain high quality three dimensional images in any plane or radial orientation of the membrane. Furthermore, and more importantly, quantitative data was determined for the density distribution and the pore distribution within the hollow fiber, as well as the distribution of pores filled with ionic liquid 1-hexyl-3-methylimidalzolium bis(trifluoromethylsulfonyl)imide ([C6mim][Tf2N]). This data was used to characterize three types of hollow fibers: (a) a dry fiber, (b) a fiber that was fully saturated with ionic liquid, and (c) a fiber that was saturated with IL and subsequently treated to achieve a selective layer with reduced thickness. Scans of the final type of fiber show that ionic liquid was isolated to the mesoporous outer wall region of the fiber cross section, which demonstrates the possibility of obtaining a thin, immobilized ionic liquid selective layer.