Troger's Base-Based Microporous Polyimide Membranes for High-Performance Gas Separation

It is a great challenge for polyimide to increase its permeability and at the same time to maintain its high selectivity. In this work, Troger's Base (TB)-based polyimides through polymerizing Troger's Base diamines with two kinds of anhydrides were successfully synthesized to enhance the permeability of polyimides for gas separation. The TB-polyirnide membranes exhibited greatly improved gas separation performance for H-2/CH4, H-2/N-2, He/CH4, and CO2/CH4 gas pairs, among which the separation performance of 6-FDA-based TB-polyimides approaches or slightly exceeds the 2008 Robeson upper bound. Our results revealed that the TB unit with rigid and in-built amine structure plays an important role for increasing the permeability of polyimides and simultaneously maintaining high selectivity. In addition, the TB-based polyimide membranes exhibited extremely high solubility selectivity for the CO2/N-2 gas pair up to 62.7 due to a strong affinity between CO2 and nitrogen atoms of tertiary amine in TB.