A Single‐Molecule Propyne Trap: Highly Efficient Removal of Propyne from Propylene with Anion‐Pillared Ultramicroporous Materials

Abstract

Propyne/propylene (C₃ H₄ /C₃ H₆ ) separation is a critical process for the production of polymer-grade C₃ H₆ . However, optimization of the structure of porous materials for the highly efficient removal of C₃ H₄ from C₃ H₆ remains challenging due to their similar structures and ultralow C₃ H₄ concentration. Here, it is first reported that hybrid ultramicroporous materials with pillared inorganic anions (SiF₆^2- = SIFSIX, NbOF₅^2- = NbOFFIVE) can serve as highly selective C₃ H₄ traps for the removal of trace C₃ H₄ from C₃ H₆ . Especially, it is revealed that the pyrazine-based ultramicroporous material with square grid structure for which the pore shape and functional site disposition can be varied in 0.1-0.5 Å scale to match both the shape and interacting sites of guest molecule is an interesting single-molecule trap for C₃ H₄ molecule. The pyrazine-based single-molecule trap enables extremely high C₃ H₄ uptake under ultralow concentration (2.65 mmol g^-1 at 3000 ppm, one C₃ H₄ per unit cell) and record selectivity over C₃ H₆ at 298 K (>250). The single-molecule binding mode for C₃ H₄ within ultramicroporous material is validated by X-ray diffraction experiments and modeling studies. The breakthrough experiments confirm that anion-pillared ultramicroporous materials set new benchmarks for the removal of ultralow concentration C₃ H₄ (1000 ppm on SIFSIX-3-Ni, and 10 000 ppm on SIFSIX-2-Cu-i) from C₃ H₆ .