Abstract
•New IL absorbents with Cu+ are prepared for separation of propane and propylene.•Absorption capability and selectivity are determined at 1–7bar and 298–318K.•Separation capability are comparable to expensive ILs-Ag+, and better than pure ILs.•Such absorbents can be regenerated simply without remarkable activity loss.
Ionic liquids (ILs) coupled with Ag+ or Cu+ salts to form a new kind of reactive absorbent have been studied to separate light olefin from paraffin recently. In this work, we prepared two halogen-free alkylimidazolium thiocyanate ILs with cheaper cuprous thiocyanate, i.e., [Bmim]SCN–CuSCN and [Emim]SCN–CuSCN (Bmim, 1-butyl-3-methylimidazolium; Emim, 1-ethyl-3-methylimidazolium) and investigated their absorption capability for propylene, propane and mixture of both at 1–7bar and 298–318K. The effects of operating parameter including cation nature, temperature, pressure, Cu+ concentration and reuse of absorbent were investigated. Propylene shows a chemical absorption while propane does a physical one, and increasing Cu+ concentration effectively improves the absorption capability for propylene and the selectivity of propylene/propane. [Bmim]SCN–CuSCN has higher absorption capability and selectivity for propylene than [Emim]SCN–CuSCN, e.g., [Bmim]SCN–CuSCN-1.5M can absorb 0.12mol of propylene per liter while 0.012mol of propane per liter at 1bar and 298K, with a selectivity of 10, which is comparable to some other ILs-Ag+ salts and better than pure ILs. Such absorbents can be regenerated through temperature and pressure swing without remarkable activity loss. This work shows that alkylimidazolium thiocyanate ILs with Cu+ salts are promising reactive absorbents to separate propylene from propane.