Experimental and theoretical studies on the influence of ionic liquids as additives on ammonia-based CO2 capture

Ammonia-based CO2 capture is a promising alternative to traditional amine-based CO2 capture, but its application is hindered by the nature of high volatility. In this work, we experimentally and theoretically investigated the influence of six ionic liquids, i.e., [EtOHMim][PF6], [EtOHMim][BF4], [EtOHMim]Cl, [Choline][PF6], [Choline][BF4] and [Choline]Cl, as additives on the performance of ammonia-based CO2 capture. The experimental results showed the addition of ionic liquid additives significantly reduced the ammonia loss and, meanwhile, enhanced the CO2 removal efficiency. By comparison, for the additives with the same cation, the CO2 removal efficiency was promoted as the sequence: [PF6]− > [BF4]− > [Cl]−. However, at the condition of the same anion, [Choline]+ exhibited better performance than [EtOHMIM]+ on the inhibition of NH3 loss. Furthermore, quantum calculation from the aspect of intermolecular interaction revealed that the hydrogen bonding between NH3 and cations should be responsible for the NH3 loss reduction, whereas the promotion of CO2 removal efficiency was ascribed to the van der Waals forces combining CO2 and anions. These experimental and theoretical findings provide a potential approach and guidance to effectively promote the performance of ammonia-based CO2 capture and would be promising in further industrial application.