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

Propyne/propylene (C3H4/C3H6) separation is a critical process for the production of polymer-grade C3H6. However, optimization of the structure of porous materials for the highly efficient removal of C3H4 from C3H6 remains challenging due to their similar structures and ultralow C3H4 concentration. Here, it is first reported that hybrid ultramicroporous materials with pillared inorganic anions (SiF62- = SIFSIX, NbOF52- = NbOFFIVE) can serve as highly selective C3H4 traps for the removal of trace C3H4 from C3H6. 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 angstrom scale to match both the shape and interacting sites of guest molecule is an interesting single-molecule trap for C3H4 molecule. The pyrazine-based single-molecule trap enables extremely high C3H4 uptake under ultralow concentration (2.65 mmol g(-1) at 3000 ppm, one C3H4 per unit cell) and record selectivity over C3H6 at 298 K (>250). The single-molecule binding mode for C3H4 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 C3H4 (1000 ppm on SIFSIX-3-Ni, and 10 000 ppm on SIFSIX-2-Cu-i) from C3H6.