Desorption process in room temperature ionic liquid based-mixtures under vacuum

Hiroshi Abe a, Tomohiro Mori a, Ryo Abematsu a, Yukihiro Yoshimura b, Naohiro Hatano b, Yusuke Imai a, Hiroaki Kishimura a

aDepartment of Materials Science and Engineering, National Defense Academy, Yokosuka, Kanagawa 239-8686, Japan
bDepartment of Applied Chemistry, National Defense Academy, Yokosuka, Kanagawa 239-8686, Japan

Journal of Molecular Liquids 167 (2012) 40-46.

Abstract
A desorption process of room temperature ionic liquids (RTILs) based-mixtures is examined by monitoring the mass transfer and temperature under vacuum. Cations of RTILs are N, N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium, [DEME], 1-ethyl-3-methylimidazolium, [C2mim], and 1-butyl-3-methylimidazolium, [C4mim]. Anions are tetrafluoroborate, [BF4], and bis(trifluoromethanesulfonyl)imide, [TFSI]. Additives for mixtures are H2O, D2O, CH3OH, C2H5OH, n-C3H7OH, i-C3H7OH, (CH3)2CO and C6H6. At the early stage of the desorption process under vacuum, transparent [DEME][TFSI]. and [C2mim][TFSI]-i-C3H7OH turned to be white homogeneously. Then, accompanying with drastic changes in the mass and temperature curves at the late stage, the mixtures become transparent again. At low-pressure, critical scattering as a precursor phenomenon of phase separation appeared only in [DEME][TFSI]- and [C2mim][TFSI]-i-C3H7OH. At room temperature and ambient pressure, different Raman spectra of a [TFSI] anion in [DEME][TFSI]-n-C3H7OH and -i-C3H7OH were observed in propanol-rich region. Therefore, the mixing states are drastically changed by respective propanol isomers.

Fig. 1
Schematic drawing of vacuum pumping system.


Fig. 2
Time dependences of (a) mass and (b) temperature in pure n-C3H7OH and i-C3H7OH. Dotted and solid lines indicate the n-C3H7OH and i-C3H7OH, respectively. Pressure in i-C3H7OH is expressed in the inset of Fig. 2(a). Each yellow region reveals pressure jump as a non-equilibrium state. Due to the pressure jump, it takes relaxation time, tR, from ambient pressure to low-pressure.
Fig. 3.
Normalized evaporation time, τe, for pure liquids against the boiling point, Tb.
Fig. 4.
Time dependences of (a) mass and (b) temperature in [DEME][TFSI]-i-C3H7OH. tR is the relaxation time from ambient pressure to low-pressure. Region I (tR<t<t1) and II (t2<t<td) were determined by the visual observations. Pictures by a digital camera are inserted in the figure. The initial concentration, x(t0), is 98.4 mol%.
Fig. 5.
Time dependences of (a) mass and (b) temperature in [DEME][TFSI]-n-C3H7OH. The initial concentration, x(t0), is 98.8 mol%.
Fig. 6.
Liquid.liquid phase diagram at ambient pressure. Closed blue and red circles represent [DEME][TFSI]-n-C3H7OH and -i-C3H7OH, respectively.
Fig. 7.
Raman spectra of [DEME][TFSI]-n-C3H7OH and -i-C3H7OH. The red solid lines are contributions from C1 anion conformers. The C2 ones are expressed by the blue solid lines. Arrows in the i-C3H7OH mixtures indicate the bulk i-C3H7OH band.
Fig. 8.
Schematic liquid.liquid equilibrium diagram of [DEME][TFSI]-i-C3H7OH. Gray parts reveal the region of a precursor phenomenon of phase separation.
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Last Modified: May 1, 2012