Protic ionic liquid ethanolamine thiocyanate with multiple sites for highly efficient NH3 uptake and NH3/CO2 separation

Development of high-efficient absorbents for ammonia (NH3) to improve the quality of atmosphere and ecological environment has gained interest among scholars. Ionic liquids (ILs) with unique properties have been reported as potential solvents for NH3 uptake to avoid many problems troubling the traditional NH3 capture technology. In this study, six protic ethanolamine-based ILs (PILs) were synthesized for efficient and reversible NH3 uptake, with the initial idea of constructing multiple binding sites to enhance the absorption ability for NH3. The physical properties and NH3 absorption performance in these PILs were investigated and analysized on the basis of molecular structures. The results demonstrated that the preferred [EtAN][SCN] had suitable viscosity of 78.18 mPa.s and molality capacity up to 0.296 and 0.0802 g NH3/g PILs at 100.0 and 4.5 kPa NH3 pressure, respectively. Such absorption ability was higher than all the reported absorbents related with ILs. 1H NMR spectroscopy illustrated that the outstanding absorption ability was originated from multiple hydrogen-bonding interactions between acidic proton, hydroxyl group and thiocyanate with NH3. The absorption enthalpy of -35.5 kJ/mol was further calculated according to the absorption capacity at low NH3 pressure under corresponding temperatures. In short, present PILs exhibited attractive absorption ability, excellent recyclability, low absorption enthalpy, and competitive selectivity of NH3/CO2. Present work can provide instructive idea for designing PILs in NH3 recovery and separation application.