Experimental and thermodynamic analysis of NH3 absorption in dual-functionalized pyridinium-based ionic liquids

Abstract

A novel type of dual-functionalized pyridinium-based ionic liquids (ILs) with acidic protons and hydroxyl groups, were designed and synthesized for ammonia (NH3) absorption. The NH3 absorption isotherms in dual-functionalized pyridinium-based ILs at temperatures from 303.15 to 343.15 K and pressures up to 600 kPa were computed using gas-liquid equilibrium method. It revealed that 4-pyridinemethanol bis(trifluoromethane)sulfonamide [4-MeOHPy][NTf2] showed the maximum NH3 solubility of 3.43 mol NH3/mol IL at 313.15 K and atmospheric pressure, surpassing any nonmetallic ILs previously reported. Furthermore, the characteristics of isotherms under low pressures behaved an obvious chemical reaction between ILs and NH3, and all experimental solubilities were regulated by a reaction equilibrium thermodynamic model (RETM). The thermodynamic properties were further obtained to better understand the NH3 absorption process. The results indicated that this model endorses the 1:1 (NH3-IL) mole ratio of chemical reaction mechanism and the reaction enthalpy is main driving force of NH3 absorption in ILs.