Purification of octafluoropropane from hexafluoropropylene/octafluoropropane mixtures with a metal–organic framework exhibiting high productivity

Abstract

Octafluoropropane (C₃F₈) electronic specialty gas is widely used in the process of etching and cleaning in the semiconductor manufacturing industry. Removal of hexafluoropropylene (C₃F₆) impurities from C₃F₆/C₃F₈ mixtures is therefore highly important but a formidable challenge since C₃F₆ and C₃F₈ possess similar physicochemical properties and molecular sizes. Herein, we present a cobalt metal–organic framework (MOF) (termed as JXNU-21) constructed using 3-chloroisonicotinic ligands, featuring dangling 3-chloroisonicotinic ligands in the one-dimensional channels. Due to the rotation flexibility of the aromatic rings of the dangling 3-chloroisonicotinate ligands with uncoordinated nitrogen sites, step-wise adsorption isotherms for the large-sized C₃F₈ were observed for JXNU-21. The high adsorption selectivity of 15.6 for the C₃F₆/C₃F₈ (10 : 90) mixture and high C₃F₆ storage density (5.8 mmol g⁻¹) under ambient conditions endow JXNU-21 with high potential for C₃F₆/C₃F₈ separation. Results of breakthrough experiments show that high-purity (99.999%) C₃F₈ gas can be achieved from a C₃F₆/C₃F₈ (10 : 90) mixture in one step. Moreover, a benchmark C₃F₈ productivity of 173.8 cm³ g⁻¹ was obtained from the breakthrough experiments under ambient conditions, outperforming all other reported porous materials.