Synergistic Effect of Silver-Based Ionic Liquid for Ethylene/Ethane Separation

Abstract

Separation of ethylene (C2H4) and ethane (C2H6) is one of the most significant processes in the petrochemical industry. In terms of industrial application, silver nitrate aqueous solution is the most widely used absorbent, but the activity of Ag+ and the absorption of C2H4 are not optimistic. Thus, it is urgent to explore new technologies for efficient separation of C2H4 and C2H6. In this work, several silver-based ionic liquid (Ag-IL) solutions are prepared with ionic liquids (ILs), silver salts, and ethylene glycol (EG). Pure and mixed gas absorption experiments were conducted to explore the effects of various anions and cations of ILs, the molar ratio of IL to silver salt, the EG proportion on absorption performance, and recycling of absorbents. Due to the synergy between ILs, EG, and Ag+, the absorption of C2H4 in [Emim][BF4]/AgBF4/EG (2:1:0.1) is up to 101.75 mg/g (2.17 mol C2H4/mol Ag+), which is the highest value of IL absorbents reported so far, and the highest selectivity is 37.8. Furthermore, the cyclic stability kept constant after five cycles of absorption–desorption. The interaction mechanism of Ag-ILs was studied by NMR and FTIR spectroscopies. ILs and EG synergistically weaken the electrostatic effect between the anion and cation of AgBF4 and increase the amount of active silver to enhance the absorption of C2H4. These task-specific Ag-ILs are expected to be a new medium with commercial potential for C2H4/C2H6 separation.