Sugar-based natural deep eutectic solvents as potential absorbents for NH3 capture at elevated temperatures and reduced pressures

Abstract

Exploring biocompatible and biodegradable materials for application in chemical processes is an important task of green chemistry. In this work, deep eutectic solvents (DESs) composed of natural compounds−choline chloride (ChCl) and sugars−were proposed as NH3 absorbents for the first time. The capture of NH3 from industrial tail gas is of great significance, to control air pollution and recycle N resources. The physiochemical properties of DESs were characterized, and the NH3 capture performance was examined systematically. Due to the presence of abundant hydroxyl groups that enable strong hydrogen-bond interaction with NH3 in DESs, the absorption of NH3 displays non-ideal behavior, and the NH3 capacities show small decrease as temperatures increase. Thus, ChCl+sugar DESs exhibit the ability to effectively capture NH3 from dilute sources at elevated temperatures (e.g., 1.745 mol/kg at 343.2 K and 14.0 kPa), which is very important for practical application. The mechanism of NH3 absorption was validated by spectroscopic characterizations and quantum chemistry calculations. Moreover, the absorption of NH3 in ChCl+sugar DESs also show excellent selectivities over other components in industrial tail gas (e.g., N2, H2 and CO2), as well as good reversibility.