Separation of propylene and propane by functional mixture of imidazolintum chloride ionic liquid - Organic solvent - Cuprous salt

To lower viscosity and possible negative effect on mass/heat transfer in industrial operation, we prepared a new absorption system to separate propylene from propane, i.e., ionic liquids (ILs)-organic solvent-cuprous salt. The absorption system is constructed by IL of 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]); organic solvent of pyridine, N,N-dimethylformamide (DMF) or N-methyl-2-pyrrolidone (NMP); cuprous chloride (CuCl). We experimentally measured the absorption capability and selectivity of such a new system for pure propylene, propane or their mixture at 1-7 bar and 298-318 K. We investigated different factors such as temperature, pressure, species of organic solvent, Cu+ concentration and regeneration and recycling of absorbents. The addition of organic solvent significantly lowers the viscosity of absorption system (approximately one order of magnitude lower). Organic solvent interestingly enhances the absorption capability for propylene while suppresses the absorption selectivity slightly. Species of solvent has a huge effect on separation performance. [Bmim][Cl]-pyridine-CuCl gives the best separation performance, e.g., in the absorption of a mixture of 50 mol% propylene and 50 mol% propane, the solubility of propylene in [Bmim][Cl]-pyridine-CuCl-2M (mass ratio of [Bmim][Cl]:pyridine, 10:1) is 0.064 mol/L at 298 K/2 bar while that of propane is 0.0105 mol/L with absorption selectivity of 6.1, which is comparable to some other ILs-Ag+ or ILs-Cu+ absorption systems. Such an absorption system can be regenerated through temperature and pressure swing and recycled without remarkable activity loss. Therefore, this new system is a good potential absorbent for separating propylene and propane.