Efficient ethylene/ethane separation by rare earth metal-containing ionic liquids in N,N-dimethylformamide

Metal-containing ionic liquids (MILs) have been considered as promising solvents for ethylene/ethane (C 2 H 4 /C 2 H 6 ) separation. With multiple 4f and 5d empty electronic orbitals, special electronic configuration and abundant electron energy levels, rare earth elements have potential to be great electron acceptor of C 2 H 4 . Herein, a new strategy of rare earth metal ionic liquids (REMILs), 1-butyl-3-methylimidazolium trifluoromethanesulfonate containing erbium ([Bmim][TFO]/Er(TFO) 3 ) in N, N-dimethylformamide (DMF) was exploited to separate C 2 H 4 /C 2 H 6 for the first time. The complexation between Er 3+ and C 2 H 4 and interactions in absorbents were adopted to achieve fast and selective C 2 H 4 absorption. The physical properties of the absorbents were measured and studied firstly. The addition of 20 wt% DMF in REMILs was optimized with a decrease in viscosity of 6–7 times at 293 K. The absorption parameters, such as Er 3+ concentration, temperature and regeneration of absorbents were also investigated systematically. The results showed that the selectivity of C 2 H 4 /C 2 H 6 was enhanced with increasing Er 3+ concentration. The solubility of C 2 H 4 in [Bmim][TFO]/Er(TFO) 3  + 20 wt% DMF was 0.95 mg/g with C 2 H 4 /C 2 H 6 selectivity of 10 (at 303 K, 0.1 MPa), much higher than that of conventional ILs. The interaction energy (ΔE) of Er 3+ -C 2 H 4 was more negative than Er 3+ -C 2 H 6 through density functional theory (DFT). Furthermore, the rare earth absorbents exhibited excellent reversibility after five cycles. In summary, this work provides a potential method for efficient separating C 2 H 4 /C 2 H 6 via REMILs in DMF solution.