Designing Low-Viscosity Deep Eutectic Solvents with Multiple Weak-Acidic Groups for Ammonia Separation

Developing NH 3 separation technology with high efficiency is very meaningful for the advancement of the NH 3 synthesis process. In this work, a new class of deep eutectic solvents (DESs) were designed by pairing N, N, N ′, N ′-tetramethyl-1,3-propanediamine dihydrochloride ([TMPDA]Cl 2 ) with phenol (PhOH) at the molar ratios of 1:3∼7. [TMPDA]Cl 2 + PhOH DESs have multiple weak-acidic groups and viscosities of as low as 48.1 cP at 298.2 K. They also exhibit excellent performance for the separation of NH 3, showing not only efficient and selective but also reversible absorption of NH 3 . Especially, the solubilities of NH 3 in [TMPDA]Cl 2 + PhOH DESs at low pressures can reach 4.49 mol/kg of NH 3 at 298.2 K and 13.3 kPa, being superior to those of most of the DESs and ILs reported in the literature. The mechanism of NH 3 absorption was further elucidated by quantum chemistry calculations and 1 H NMR spectra. It is validated that the efficient absorption of NH 3 in DESs origins from the strong interaction of multiple weak-acidic groups of DESs with NH 3 .