Hierarchically porous polymers containing triphenylamine for enhanced SF6 separation

Abstract

Porous organic polymers (POPs) have a good potential for gas separation applications owing to their large surface area, structural robustness and chemical tunability. Previous studies have demonstrated the utility of POP-based adsorbents for carbon dioxide separation. However, no study has so far reported on the potential of POPs for capturing sulfur hexafluoride (SF6), which is an extremely potent greenhouse gas. Here we demonstrate that the amine-incorporated POPs synthesized through the co-condensation of dichloroxylene (DCX) and triphenylamine (TPA) for application in SF6/N2 separation. Large surface area and pore volume of DCX-based POPs provide the structural framework for high SF6 adsorption. The incorporation of tertiary amines favors the SF6/N2 selectivity without sacrificing the SF6 adsorption at the point of interest (0.1 bar) according to the combined evaluations of the ideal adsorbed solution theory and idealized vacuum swing adsorption. Further analysis revealed that the tertiary amines increase the isosteric heat of adsorption, a measure of affinity between adsorbate and adsorbent. Undertaking a comparative adsorption kinetics study, we also demonstrated that TPA-containing POPs exhibit much faster SF6 uptake than zeolite 13X, a commonly used commercial adsorbent, owing the co-existence of microporosity and mesoporosity that facilitates the diffusion of adsorbate within the adsorbent. Dynamic breakthrough and chromatographic measurements further confirmed the enhanced SF6 adsorption kinetics of TPA-containing POPs. In overall, we attributed the high SF6 separation performance of TPA-containing POPs to their two main characteristics: i) the presence of large micropores (c.a. 1.2 nm) alongside hierarchical mesoporosity, ii) the selectivity provided by amine functionalities.