Long-term thermal stabilities of ammonium ionic liquids designed as potential absorbents of ammonia

Abstract

Searching for potential absorbents in working pairs with NH₃, a series of new ammonium ionic liquids related to choline were designed and synthesized. In order to explore their applicability in refrigeration by absorption, their thermal stabilities were studied. For this proposal, a thermogravimetric analyzer, TGA 7 – Perkin-Elmer, was used in dynamic mode from 100 °C to 800 °C at 10 °C min⁻¹ under dry air atmosphere. From the ionic liquids TG curves, the onset temperatures (T_onset) were determined, as well as the loss of mass at these T_onset. Significant decomposition was detected at lower temperatures than T_onset in all cases, meaning that the true ionic liquids stability is lower than that provided by the dynamic TG. Isothermal studies at lower temperatures than T_onset were also carried out to estimate the long-term thermal stabilities at different temperatures.