Pressure-Swing Absorption and Desorption Behaviors of Ammonia in Fluorocomplex Salts

Ammonia (NH3) plays an indispensable role as a fertilizer and energy carrier in modern society. NH3 synthesis under mild conditions requires selective separation because of the low partial pressure of the NH3 obtained from the reactor. Herein, the fluorocomplex salt enables the absorption and desorption of NH3 by the pressure–swing method (100 ⇄ 500 kPa). Absorption and desorption behaviors of NH3 in four kinds of fluorocomplex salts such as tetrafluoroborate (NaBF4 and KBF4) and hexafluorophosphate (NaPF6 and KPF6) were investigated at a temperature of 300 K. Excellent NH3 separation ability was observed in NaBF4 and KPF6, and the capacity and collection ratio were 48.0 mmol·g–1 and 98% (NaBF4), as 25.9 mmol·g–1 and 100% (KPF6), respectively. Crystallographic structural analysis revealed that the crystal lattice of the fluorocomplex salt was slightly expanded by NH3 absorption and restored by NH3 desorption, confirming that the fluorocomplex salts were stable toward NH3 absorption/desorption.