Session 6

LCST-type Phase Separation of Phosphonium-based Ionic Liquid-Water Mixed Solutions

Toshiyuki Takamuku
on  Wed, 09:25 for  20min
M. Kawano, K. Sadakane, H. Iwase, M. Matsugami, T. Takamuku
1. Graduate School of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502, Japan
2. Faculty of Life and Medical Sciences, Doshisha University, 1-3 Tatara Miyakodani,
Kyotanabe, Kyoto 610-0394, Japan
3. Comprehensive Research Organization for Science and Society (CROSS), 162-1 Shirakata,
Tokai, Ibaraki 319-1106, Japan
4. Faculty of Liberal Arts, National Institute of Technology (KOSEN), Kumamoto College, 2659-2 Suya, Koshi, Kumamoto 861-1102, Japan
5. Faculty of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502, Japan
takamut@cc.saga-u.ac.jp

Abstract

Various ionic liquids (ILs) are miscible with not only polar molecular liquids (MLs) like ethanol, but also nonpolar MLs such as benzene, despite electrolytes. However, ILML mixed solutions often separate into IL-rich and ML-rich phases with varying temperature. Such phase separation of ILML mixed solutions has been applied to a homogeneous liquidliquid extraction for proteins [1]. For imidazolium-based ILs mixed solutions with several MLs, upper critical solution temperature (UCST)-type phase separation occurs with lowering temperature. In contrast, lower critical solution temperature (LCST)-type phase separation of phosphonium-based ILwater mixed solutions takes place with rising temperature. Microscopic interactions among IL’s cation and anion and ML decide the types of phase separation. For application of phase separation of ILML mixed solutions with changing temperature to extraction, the mechanism of phase separation should be understood at a molecular level.

In this investigation, we aimed at clarifying the mechanism of LCST-type phase separation for tetrabutylphosphonium trifluoroacetate ([P4444][CF3COO])water mixed solutions at both microscopic and mesoscopic scales. Figure 1 shows phase diagram for the solutions. NMR and IR spectroscopic techniques were used to observe the change in microscopic interactions with increasing temperature. Furthermore, the microscopic interactions were simulated by molecular dynamics (MD) calculations. Small-angle neutron scattering (SANS) method was applied to observe the enhancement of concentration fluctuation in the mixed solutions with increasing temperature at the mesoscopic scale. The present results on LCST-type phase separation of [P4444][CF3COO]water solutions were compared with those on UCST-type phase separation of 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([CNmim][TFSA], N represents the alkyl chain length) mixed solutions with 1,4-dioxane and formamide previously investigated [2-4].

Figure 1 Phase diagrams of [P4444][CF3COO]H2O and D2O. The dashed line gives 298 K.

Figure 1 Phase diagrams of [P4444][CF3COO]H2O and D2O. The dashed line gives 298 K.

References

[1] Y. Deguchi, N. Nakamura, and H. Ohno, Sep. Purif. Technol., 251, 117286 (2020).

[2] M. Kawano, K. Sadakane, H. Iwase, M. Matsugami, B. A. Marekha, A. Iddrissi, and T. Takamuku, Phys. Chem. Chem. Phys., 22, 5332 (2020).

[3] M. Kawano, K. Sadakane, H. Iwase, M. Matsugami, B. A. Marekha, A. Iddrissi, and T. Takamuku, Phys. Chem. Chem. Phys., 23, 24449 (2021).

[4] M. Kawano, A. Tashiro, Y. Imamura, M. Yamada, K. Sadakane, H. Iwase, M. Matsugami, B. A. Marekha, A. Iddrissi, and T. Takamuku, Phys. Chem. Chem. Phys., 24, 13698 (2022).