Functional Solution Composed of Cu(I) Salt and Ionic Liquids to Separate Propylene from Propane

Abstract

We prepared a new class of functional solutions by dissolving CuCl or CuBr into 1-butyl-3-methylimidazolium bromide ([BMIM]­[Br]) or 1-ethyl-3-methylimidazolium bromide ([EMIM]­[Br]). We determined experimentally the solubility of propylene and propane in such solutions respectively at 1–8 bar and 298–313 K, and investigated the separation of propylene from propylene/propane mixture. The absorption capacity and selectivity for propylene were enhanced with the addition of Cu­(I) salt and were affected by cationic side chain and anionic species following this order [EMIM]­[Br]-CuCl < [EMIM]­[Br]-CuBr < [BMIM]­[Br]-CuCl < [BMIM]­[Br]-CuBr. It was observed that this absorption was a chemical nature through π-interaction between Cu­(I) cation and propylene. In a typical result, the absorption capacity for propylene of [BMIM]­[Br]-CuBr (Cu­(I) cation, 1.5 M) is 0.13 mol/L at 298 K and 1 bar while it is 0.01 mol/L for propane with a selectivity of 13, which is comparable to those absorption systems with more expensive silver salts; the selectivity is high, up to 64.6 for 80 mol % propylene mixture with propane. The effects of temperature and pressure on absorption were investigated. Such systems of Cu­(I) salt and ionic liquids are potential absorption reagents for separation of propylene and propane with competitive cost to silver systems