Alkanolamine-based dual functional ionic liquids with multidentate cation coordination and pyrazolide anion for highly efficient CO2 capture at relatively high temperature

Six dual functional ionic liquids (DFILs) with metal chelate cation and pyrazolide anion were synthesized by reacting alkanolamine with pyrazole sodium salt, and characterized by 1H NMR, 13C NMR, FT-IR, and ESI-MS spectra. Thermal decomposition temperature and viscosity were determined. The behavior of CO2 absorption for these DFILs was evaluated at T = 353.2 K. Absorption mechanism and the influence of temperature and N2 on the CO2 absorption were investigated. The results show that the CO2 capacity of the DFILs consisting of alkanolamine with pyrazole sodium in a molar ratio of 2:1 is larger than that of the DFILs in a molar ratio of 1:1. The CO2 absorption mechanism obtained from FT-IR and 13C NMR spectra indicates that CO2 could react with a quasi-aza-crown ether cation and pyrazolide anion simultaneously, resulting in improved capacity of CO2 absorption. According to the saturated CO2 absorption capacity at 333.2-363.2 K and van't Hoff's equation, the enthalpy of CO2 absorption for three DFILs is derived. Furthermore, the DFILs were carried out for five cycles with no obvious loss in the absorption capacity of CO2, indicating that these DFILs may be good candidates for efficient CO2 capture at relatively high temperature.