Investigation on Protic Ionic Liquids as Physical Solvents for Absorption of NO at Low Pressures

Nitric oxide (NO)
absorption in ionic liquids (ILs) is an interesting
issue, but little attention has been focused on the removal of NO
at low partial pressures. Herein, a series of protic ionic liquids
(PILs) based on polyamines as the cation and hydroxybenzenes as the
anion were prepared for capturing low-concentration NO (0–0.6
bar). Triethylenetetramine phenolate ([TETAH]­[PhO]) showed an excellent
absorption performance, with low viscosity, fast absorption rate,
and high absorption capacity. The experimental solubility data were
fitted by the Krichevsky–Kasarnovsky (K–K) equation,
and the absorption enthalpy (ΔH) of NO in [TETAH]­[PhO]
was thus calculated to be −43.60 kJ/mol. Density functional
theory calculations were further performed to better understand the
interaction of [TETAH]­[PhO] with NO on the molecular level, and the
results suggest that the weak interaction of NO with the PIL was induced
by the presence of H protons. It is believed that this work may provide
a new method for the efficient and reversible absorption of low-concentration
NO.