Efficient separation of ethylene/ethane by incorporation of silver salts into protic imidazole ionic liquids

Efficient purification of ethylene (C 2 H 4 ) from ethane (C 2 H 6 ) is one of the seven chemical separations which can change the world. Chemical absorption is considered as the most promising method for C 2 H 4 /C 2 H 6 separation. However, the two critical separation properties of absorbent, the solubility and selectivity, are always trade-offs, which are still needed to both promote and balance in the viewpoint of industrial application. Herein, a series of novel silver-containing protic imidazolium ionic liquids (SPILs), with high chemical activity for efficient C 2 H 4 absorption, have been designed and synthesized. The physical properties of the prepared silver-containing ionic liquids (SILs) were first characterized. Then the separation performances of C 2 H 4 /C 2 H 6 by SPILs and silver-containing aprotic ionic liquids (SAILs) were carefully compared. The C 2 H 4 /C 2 H 6 selectivity of SPILs (16.73) was eight times higher than the value of the latter. Then, the C 2 H 4 absorption mechanism was confirmed by density functional theory (DFT) calculations. The charge density of Ag + was greater and the Gibbs free energy (ΔG) of C 2 H 4 absorption was more negative in [Bim] n [Ag(NTf 2 ) n+1 ]. The proposed SPILs, [Bim] 1.5 [Ag(NTf 2 ) 2.5 ], had a high C 2 H 4 /C 2 H 6 selectivity of 41.2 and C 2 H 4 solubility of 1.86 mol C 2 H 4 /mol Ag + , which were the highest value of ionic liquids (ILs) absorption reported so far. The [Bim] 1.5 [Ag(NTf 2 ) 2.5 ] exhibited excellent reversibility after five absorption–desorption cycles. An absorbent designed strategy of SPILs was proposed with enhanced solubility and selectivity for C 2 H 4 /C 2 H 6 separation.