Hexafluoroethane purification via molecular sieving in a molecule-trap metal-organic framework

Purification of hexafluoroethane (C2F6) from ternary mixtures containing hydrofluorocarbons (C2H2F4 and C2HF5) using conventional routes is energy-intensive. Here, we report C2F6 purification through shape-selective molecular sieving in a molecular-trap metal-organic framework enabled by isoreticular pore-geometry tuning. Starting from PCP-FDCA, we constructed BUT-313 by a minimal O-to-S substitution in the dicarboxylate linker. This single-atom edit transforms the original rectangular channel into an hourglass-like bottlenecked pore with a narrowed constriction of 4.2 Å. As a result, BUT-313 strongly suppresses the uptake of the more symmetric C2F6 while still adsorbing the anisotropic fluorocarbons C2H2F4 and C2HF5. At 298 K and 100 kPa, BUT-313 exhibits the highest uptake ratios of 7.7 for C2H2F4/C2F6 and 6.0 for C2HF5/C2F6, together with a record-high C2H2F4/C2F6 selectivity of 487.0. In ternary breakthrough experiments, BUT-313 delivers >99.98% C2F6 with a productivity of 184.5 L/kg, while retaining its performance over multiple cycles and after scale-up to the 10 g level. By replacing oxygen with sulfur in a MOF linker, researchers reshaped rectangular pores into hourglass bottlenecks, switching separation from thermodynamic to geometry-driven sieving. BUT-313 achieves C2H2F4/C2F6 selectivity of 487.0 and purifies >99.98% C2F6 from ternary mixtures, with stable performance after 10-g scale-up and cycling.