Benchmark C2H2/CO2 and CO2/C2H2 Separation by Two Closely Related Hybrid Ultramicroporous Materials

The removal of CO2 impurities from C2H2-containing gas mixtures is an important step in purifying C2H2, a feedstock chemical used in the production of several commodity chemicals. However, that C2H2 and CO2 exhibit similar size and physicochemical properties makes their separation by physisorption extremely difficult. In this work, we detail how two hybrid ultramicroporous materials (HUMs)—known variant SIFSIX-3-Ni and variant TIFSIX-2-Cu-i—exhibit exceptional CO2/C2H2 and C2H2/CO2 selectivity, respectively. SIFSIX-3-Ni sets a benchmark for CO2/C2H2 selectivity at low partial pressures, whereas TIFSIX-2-Cu-i ranks among the best porous materials in the context of C2H2/CO2 selectivity. The performance of these HUMs was confirmed by real-time dynamic breakthrough experiments. To our knowledge, such yin-yang inversion of selectivity in closely related compounds is unprecedented. We attribute this to the distinct sorbate binding sites in SIFSIX-3-Ni and TIFSIX-2-Cu-i, as revealed by modeling studies.