Abstract
The separation of olefins and alkanes is beneficial for resource utilization of oil products, and liquid-liquid extraction is an important method of liquid-phase olefin/alkane separation. This study investigated the feasibility of bimetallic ionic liquids for the extraction of olefin from liquid-phase olefin/alkane mixtures using 1-hexene/n-hexane as a model hydrocarbon mixture. The bimetallic ionic liquids were first synthesized from different metal chlorides (ZnCl(2), SnCl(2), AlCl(3), FeCl(3)) and CuCl with triethylamine hydrochloride. This newly prepared Fe-Cu bimetallic ionic liquid [Et(3)NH]Cl-0.47FeCl(3)-0.8CuCl had a good extraction performance, and the extraction selectivity could reach up to 8.41, which was about 4 times that of the organic solvent such as N-formylmorpholine and γ-butyrolactone used in the industry. The liquid-liquid equilibrium (LLE) of 1-hexene/n-hexane and Fe-Cu bimetallic ionic liquid system was investigated under different extraction temperatures, extraction times, and mass ratios of extractant to feed. Through 5 recycling experiments, the extraction selectivity decreased by less than 2%, and the characteristic peaks of the recovered bimetallic ionic liquids were unchanged by IR analysis, which proved that the bimetallic ionic liquid had excellent reversibility. Furthermore, the mechanism of 1-hexene extraction was investigated by quantum chemistry calculation and Raman spectroscopy, and there was π-complexation between Cu(+) and 1-hexene. Then, the charge density of Cu(+) in bimetallic ionic liquids was larger than that of cuprous-based ionic liquids. The results revealed that the addition of FeCl(3) could activate Cu(+) and weaken the Cu-Cl bond, enhancing the ability of the bimetallic ionic liquid to extract 1-hexene. Therefore, [Et(3)NH]Cl-0.47FeCl(3)-0.8CuCl was a good potential extractant during the efficient extraction of 1-hexene.