CO₂ as a Separation Switch for Ionic Liquid/Organic Mixtures

Abstract

A novel technique to separate ionic liquids from organic compounds is introduced which uses carbon dioxide to induce the formation of an ionic liquid-rich phase and an organic-rich liquid phase in mixtures of methanol and 3-butyl-1-methyl-imidazolium hexafluorophosphate ([C4mim][PF6]). If the temperature is above the critical temperature of CO2 then the methanol-rich phase can become completely miscible with the CO2-rich phase, and this new phase is completely ionic liquid-free. Since CO2 is nonpolar, it is not equipped to solvate ions. As the CO2 dissolves in the methanol/[C4mim][PF6] mixture, the solvent power of the CO2-expanded liquid is significantly reduced, inducing the formation of the second liquid phase that is rich in ionic liquid. This presents a new way to recover products from ionic liquid mixtures and purify organic phases that have been contaminated with ionic liquid. Moreover, these results have important implications for reactions done in CO2/ionic liquid biphasic mixtures.

Molecular dynamics simulation studies of CO2 – [bmim][PF6] solutions: Effect of CO2 concentration

“…[23][24][25][26][27][28][29][30][31][32] scCO 2 has been used for extraction of products from RTILs. [33][34][35][36] The interaction between the solute and the solvent in the mixture can impart new properties which the individual components may not possess. 37 Although CO 2 is remarkably soluble in imidazolium based ionic liquids, 33,[38][39][40][41][42][43] ionic liquids such as [bmim][PF 6 ] do not dissolve much in CO 2 .…”

Influence of water on the carbon dioxide absorption by 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide

“…Liquid-liquid extraction is also not desirable if the process aims to decrease environmental impact by decreasing the use of organic solvents. To avoid these problems, carbon dioxide, generally at high pressures, can be added to induce liquid-liquid phase separation in the mixture [10,11].…”

The Application of Ionic Liquids in Dissolution and Separation of Lignocellulose

“…Therefore, development of new efficient solvents is the first step for the transformation and utilization of lignocellulose. As novel green solvents, ionic liquids (ILs) have many attractive properties, including negligible vapor pressure, non-flammability, thermal stability and recyclability, and have been used in organic synthesis, electrochemistry, catalysis, extraction and among others (Qian et al, 2005;Dupont et al, 2002;Scurto et al, 2002;Kubo et al, 2002). In 2002, Rogers and co-workers (Swatloski et al, 2002) found that some hydrophilic ILs are effective solvents for the dissolution of cellulose.…”