Deep eutectic solvents with N–H hydrogen bond network structure for highly efficient ammonia capture

Abstract

The separation and recovery of ammonia (NH3) has been of long concern, since NH3 is not only a hazardous substance in the environment but also a critical chemical raw material. The current study developed and synthesized a series of deep eutectic solvents (DESs) using dual combinations of 1,2,3-triazole (Tri) with 1,2,4-triazle (TrZ), Imidazole (ImZ) or 1H-pyrazole (PyZ) for the absorption of ammonia. The results indicate that this kind of DESs possess satisfactory physical features, high capacities for NH3 absorption, and good selectivities of NH3/CO2, NH3/O2 and NH3/N2. At temperature of 298.15 K, TrZ + Tri (1:2) has a high absorption capacity up to 0.241gNH3·gDES−1 at 102.4 kPa, while PyZ + Tri (1:2) also shows satisfactory NH3 solubility of 0.230 gNH3·gDES−1 at 101.3 kPa, which are much greater than those of ionic liquids and DESs reported previously. TrZ + Tri (1:2) is tested to be highly reversible during ten cycles of absorption–desorption. The dissolution thermodynamic parameters of NH3 in these three DESs are calculated using a RETM equation, and the absorption mechanism is further analyzed and discussed using spectroscopic characterizations. It is especially noteworthy that quantum chemistry calculations are also used to study the interactions between NH3 and the DESs from an atomic level perspective. It is believed that the DESs developed in this study have their own potentials as absorbents for the highly efficient capture of NH3.