Absorption and desorption behaviours of ammonia on bis(fluorosulfonyl)amide salts investigated using the pressure-swing method

Abstract

The absorption and desorption behaviours of ammonia (NH₃) on bis(fluorosulfonyl)amide (FSA) salts were investigated using the pressure-swing method. The effects of the cation species and temperature of the four types of FSA single salts (Li[FSA], Na[FSA], K[FSA], and Ca[FSA]₂) and (Na, K)[FSA] eutectic melt on the NH₃ absorption behaviour were evaluated. FSA salts exhibited large NH₃ storage capacities and the NH₃ absorption behaviour was affected by the different FSA salt cation species. The NH₃ storage capacity increased with decreasing temperature. Although the alkaline metal FSA salts were liquefied by NH₃ absorption at 300 K, Ca[FSA]₂ remained solid after NH₃ absorption at 300 K. Additionally, K[FSA] absorbed a lower amount of NH₃ than at 300 K and remained in the solid state after NH₃ absorption at 323 K. These results suggest that NH₃ molecules were dissolved in the FSA salts, and eutectic compounds were formed by NH₃ absorption on the FSA salts. After NH₃ absorption, the salts were found to be composed of ammonium (NH₄⁺) cations and amide (NH₂⁻) and imide (NH²⁻) anions.