Experimental Investigation on Thermophysical Properties of Ammonium-Based Protic Ionic Liquids and Their Potential Ability towards CO 2 Capture

• Published in: Molecules (Basel, Switzerland) Switzerland), 2022-01, Vol.27 (3)
• Main Authors: Zailani, Nur Hidayah Zulaikha Othman, Yunus, Normawati M, Ab Rahim, Asyraf Hanim, Bustam, Mohamad Azmi
• Format: Article
• Language: English
• ISSN: 1420-3049

Ionic liquids, which are extensively known as low-melting-point salts, have received significant attention as the promising solvent for CO capture. This work presents the synthesis, thermophysical properties and the CO absorption of a series of ammonium cations coupled with carboxylate anions producing ammonium-based protic ionic liquids (PILs), namely 2-ethylhexylammonium pentanoate ([EHA][C5]), 2-ethylhexylammonium hexanoate ([EHA][C6]), 2-ethylhexylammonium heptanoate ([EHA][C7]), bis-(2-ethylhexyl)ammonium pentanoate ([BEHA][C5]), bis-(2-ethylhexyl)ammonium hexanoate ([BEHA][C6]) and bis-(2-ethylhexyl)ammonium heptanoate ([BEHA][C7]). The chemical structures of the PILs were confirmed by using Nuclear Magnetic Resonance (NMR) spectroscopy while the density ( ) and the dynamic viscosity ( ) of the PILs were determined and analyzed in a range from 293.15K up to 363.15K. The refractive index ( ) was also measured at T = (293.15 to 333.15) K. Thermal analyses conducted via a thermogravimetric analyzer (TGA) and differential scanning calorimeter (DSC) indicated that all PILs have the thermal decomposition temperature, T of greater than 416K and the presence of glass transition, T was detected in each PIL. The CO absorption of the PILs was studied up to 29 bar at 298.15 K and the experimental results showed that [BEHA][C7] had the highest CO absorption with 0.78 mol at 29 bar. The CO absorption values increase in the order of [C5] < [C6] < [C7] anion regardless of the nature of the cation.