Novel Protic Ionic Liquid Composite Membranes with Fast and Selective Gas Transport Nanochannels for Ethylene/Ethane Separation.

Protic ionic liquids (PILs) were utilized for the fabrication of composite membranes containing silver salt as the CH transport carrier to perform CH/CH separation for the first time. The intrinsic nanostructures of PILs were adopted to construct fast and selective CH transport nanochannels. The investigation of structure-performance relationships of composite membranes suggested that transport nanochannels (polar domains of PILs) could be tuned by the sizes of cations, which greatly manipulated activity of the carrier and determined the separation performances of membranes. The role of different carriers in the facilitated transport was studied, which revealed that the PILs were good solvents for dissolution and activation of the carrier due to their hydrogen bond networks and waterlike properties. The operating conditions of separation process were investigated systemically and optimized, confirming CH/CH selectivity was enhanced with the increase of silver salt concentration, the flow rate of sweep gas, and the feed ratio of CH to CH, as well as the decrease of the transmembrane pressure and operating temperature. Furthermore, the composite membranes exhibited long-term stability and obtained very competitive separation performances compared with other results. In summary, PIL composite membranes, which possess good long-term stability, high CH/CH selectivity, and excellent CH permeability, may have a good perspective in industrial CH/CH separation.