The Highly Efficient Absorption of CO2 by a Novel DBU Based Ionic Liquid

Abstract

A novel anion-functionalized protic ionic liquid (IL), [DBUH][Triz], has been synthesized from 1,8-diazabicyclo [5.4.0]undec-7-ene (DBU) and 1,2,4-triazole (Triz). Density (ρ) and viscosity (η) of [DBUH][Triz] at different temperatures have been measured and the influence of temperature has been analyzed quantitatively. Then, the applications of [DBUH][Triz] in CO2 absorption have been investigated. It has been detected that this ionic liquid, which was easily prepared, shows excellent reversibility and a high absorption capacity, about 1.5 mol CO2 per 1 mol of IL (about 0.3 g CO2 per 1 g of IL). In addition, the influence of temperature, pressure and moisture on the absorption performance of [DBUH][Triz] has been studied separately, indicating that absorption is promoted by lower temperature and higher CO2 pressure. In addition, the mechanism of chemical absorption at two active sites has been deduced based on quantum-chemical calculations and 13C NMR spectra coupled with IR spectra. Furthermore, the equilibrium constant of chemical absorption (K) was calculated from the CO2 capacity at different temperatures (T) and a good linear relationship between the natural logarithm of the equilibrium constant ln K and 1/T was obtained with R2 of 0.996. From the slope and intercept of the fitted straight line, the molar reaction enthalpy change (ΔrHm) and molar reaction entropy change (ΔrSm) were analyzed, indicating that the capture of CO2 is an exothermic process and the IL–CO2 complex is less ordered than the pure ionic liquid.