C. M. Wai et al.
bis(trifluoromethane)sulfonimide
LiN(CF SO ) for 24 h at 708C.
[10]
(
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
2 2
)
The reaction residue was extracted
with dichloromethane after the aque-
ous layer was decanted, then dried
under high vacuum for several hours
at 508C. [bmim]Cl was synthesized
with butyl chloride and methyl imida-
zole and extensively recrystallized
from ethyl acetate/acetonitrile at
À208C by using a method from the
[
11]
literature.
Nitric acid, n-tributyl-
phosphate, and uranyl nitrate hexahy-
drate were purchased from Aldrich.
Deionized water was obtained by
using a Millipore water purification
system.
Procedure: The experiments for the
extraction of uranium were per-
formed as follows: Initially, uranium
nitrate (0.02m) was added to an aque-
ous solution of nitric acid (0.1, 1, or
Figure 8. Apparatus for the extraction of [UO
2
A
H
U
G
R
N
U
(NO
3
)
2
A
H
U
T
E
N
N
(TPB)
2
] from the IL to sc-CO
2
. Products were analyzed
3
[
(
m; 3 mL). The IL was prepared with
bmim][Tf N] (70%) and TBP
30%); 30% TBP is equivalent to
either by trapping in hexane for UV/Vis and fluorescence spectroscopy (bypass fiber-optic cell; arrangement
a) or by an in situ spectroscopic method (arrangement b).
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
1
.22m TBP in the IL phase (TBP
À1
density=0.977 gmL ). After shaking
0
.076 cm, and length 20 cm) was used as the pressure restrictor for the
the aqueous solution and the IL together, followed by centrifugation and
phase separation, the top layer contained the aqueous solution and the
bottom layer contained the IL. Aliquots (2 mL) from each phase were
taken and studied by using UV/Vis and fluorescence spectroscopy.
exit CO . Temperatures of the high-pressure cells were controlled by a
2
thermostat oven. The extraction process involved static supercritical fluid
extraction for 30 min followed by a dynamic flush for 2 h. All SFE ex-
periments were performed at 408C and 200 atm. After the extraction, the
Finally, the IL phase with the extracted uranium complex was back-ex-
system was allowed to depressurize slowly at a controlled flow rate of
À1
tracted into a sc-CO
2
phase, monitored by a fiber-optic device coupled to
extraction products
0.2–0.3 mLmin
.
a CCD-array UV/Vis spectrophotometer. The sc-CO
2
Figure 8 shows the high-pressure system for spectroscopic study of the sc-
were trapped in hexane and analyzed by UV/Vis and fluorescence spec-
troscopy and nondestructive neutron activation analysis. A schematic de-
scription of this two step process is shown in Figure 7. After SFE, the IL
residue was also analyzed by UV/Vis and fluorescence spectroscopy and
neutron activation analysis.
CO phase. Two supercritical fluid extraction modes were performed: In
arrangement a), a regular high pressure cell (35.3 mL) was used and the
fiber-optic cell was bypassed; in arrangement b), the fiber-optic cell was
used for in situ spectroscopic monitoring of the absorption spectra in the
2
sc-CO phase.
2
For in situ spectroscopic monitoring, a high-pressure fiber-optic cell
(
volume 13.24 mL) coupled with a CCD array UV/Vis spectrometer was
used, as shown in Figure 8. The large cell (35.3 mL) shown in the figure
was used as a storage cell for the preheating of sc-CO . A Variac (voltage
regulator), a thermal mantle, and a thermocouple (Omega KMTSS-
62U-6) were used to control and monitor the temperature of the cell
outside the oven. The thermocouple was inserted into the sc-CO phase
2
0
2
through a port located near the middle of the fiber-optic cell to give reli-
able temperature measurements of the fluid phase. The IL sample was
placed in a 5 mL glass vial and loaded into the fiber-optic cell. After pre-
heating the cell to 408C, CO was introduced and the pressure of the
2
system was kept constant at 200 atm. When the stirrer was turned on, the
CCD array UV/Vis spectrometer started to record with a time interval of
6
0 s for a total of 120 acquisitions (2 h).
Figure 7. A schematic diagram showing the two-step procedure for the
extraction of uranium.
Instrumentation: A UV/Vis CCD spectrophotometer (Serious 400) from
Spectral Instruments was used for absorption and on-line measurements
in the spectral range of l=200–500 nm. A 1 cm quartz cuvette was used
for all samples. A standard Holmium Oxide cuvette (Avain Technologies)
was used to ensure that the UV/Vis instrument upheld the minimum
transmittance specification and to confirm wavelength accuracy in the
given spectral range.
Supercritical fluid extraction and in situ spectroscopic monitoring: Super-
critical fluid extraction experiments were performed by using a lab-built
high-pressure extraction apparatus. The apparatus includes a CO
high-pressure syringe pump, stainless steel extraction cells, a stirring and
heating plate, a thermocouple, and a collection vial. SFC-grade CO was
2
tank, a
Fluorescence measurements were carried out by using a HORIBA Jobin
Yvon analytical grade Fluoro-Max3 spectrofluorometer with a 150 watt
xenon arc lamp. In all experiments, a fused silica cuvette (Starna) with
2
supplied with a syringe pump (ISCO model 260D, Lincoln, NB, USA).
As indicated in the schematic diagram shown in Figure 8, all the extrac-
tion experiments were performed with a stainless steel high-pressure ex-
traction vessel (35.3 mL) bypassing the fiber-optic cell. At the oven exit,
stainless steel tubing (SS 316, exterior diameter 0.16cm, interior diameter
1
cm path length was set at right angles to the beam. The excitation mon-
ochromator was calibrated for wavelength accuracy by measuring the
xenon lamp and the water Raman peak for the emission monochromator.
To obtain the uranium spectra, the excitation monochromator was set at
4462
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 4458 – 4463