Traditional Extractants in Nontraditional Solvents: Groups 1 and 2 Extraction by Crown Ethers in Room-Temperature Ionic Liquids

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• 作者：Ann E. Visser ; Richard P. Swatloski ; W. Matthew Reichert ; Scott T. Griffin ; and Robin D. Rogers
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2000
• 出版时间：October 2000
• 年：2000
• 卷：39
• 期：10
• 页码：3596 - 3604
• 全文大小：98K
• 年卷期：v.39,no.10(October 2000)
• ISSN：1520-5045

文摘

The crown ethers 18-crown-6 (18C6), dicyclohexano-18-crown-6 (DCH18C6), and 4,4'-(5')-di-(tert-butylcyclohexano)-18-crown-6 (Dtb18C6) were dissolved in 1-alkyl-3-methylimidazolium hexafluorophosphate ([C_nmim][PF₆], n = 4, 6, 8) room-temperature ionic liquids (RTILs) and studiedfor the extraction of Na⁺, Cs⁺, and Sr²⁺ from aqueous solutions. In the absence of extractant,the distribution ratios for the metal ions indicate a strong preference for the aqueous phase.With the crown ethers as extractants in RTIL-based liquid/liquid separations, the resulting metalion partitioning depends on the hydrophobicity of the crown ether and also on the compositionof the aqueous phase (e.g., concentration of HNO₃ vs Al(NO₃)₃). Aqueous solutions of HCl, Na₃citrate, NaNO₃, and HNO₃ (the latter at low concentrations) decrease the metal ion distributionratios and also decrease the water content of the RTIL phase. High concentrations of HNO₃decompose PF₆^- and increase both the water content and the water solubility of the RTIL phase.Highly hydrated salts such as Al(NO₃)₃ and LiNO₃ salt out both the RTIL ions and the crownethers; thus, when the aqueous phase contains Al(NO₃)₃, the trend more closely resemblestraditional solvent extraction behavior where D_Sr > D_Cs and the most hydrophobic extractingphase produces the highest partitioning. When [C₈mim][PF₆] is used as the extracting phase,the metal ions can be loaded from Al(NO₃)₃ and stripped using water. Dtb18C6 forms 1:1complexes with Cs⁺ and Sr²⁺ and also yields the highest distribution ratios out of the threecrowns examined. In comparison to traditional solvent extraction behavior, the metal ionpartitioning in these systems exhibits exceptional behavior and, in certain instances, suggestsa complicated partitioning mechanism, which necessitates a more thorough understanding ofRTILs as solvents before interpretation of the results.