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

Abstract

• Six protic ionic liquids (PILs) with multiple sites for NH 3 were prepared. • Ethanolamine thiocyanate demonstrates efficient and reversible absorption for NH 3 . • Ethanolamine thiocyanate possesses absorption high up to 0.296 g NH 3 per g PIL. • The absorption behavior was systematically investigated. • The ideal selectivity of NH 3 /CO 2 was as high as 365. Development of high-efficient absorbents for ammonia (NH 3 ) 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 NH 3 uptake to avoid many problems troubling the traditional NH 3 capture technology. In this study, six protic ethanolamine-based ILs (PILs) were synthesized for efficient and reversible NH 3 uptake, with the initial idea of constructing multiple binding sites to enhance the absorption ability for NH 3 . The physical properties and NH 3 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 NH 3 /g PILs at 100.0 and 4.5 kPa NH 3 pressure, respectively. Such absorption ability was higher than all the reported absorbents related with ILs. 1 H NMR spectroscopy illustrated that the outstanding absorption ability was originated from multiple hydrogen-bonding interactions between acidic proton, hydroxyl group and thiocyanate with NH 3 . The absorption enthalpy of −35.5 kJ/mol was further calculated according to the absorption capacity at low NH 3 pressure under corresponding temperatures. In short, present PILs exhibited attractive absorption ability, excellent recyclability, low absorption enthalpy, and competitive selectivity of NH 3 /CO 2 . Present work can provide instructive idea for designing PILs in NH 3 recovery and separation application.