Chemistry Reference
In-Depth Information
tAbLe 8.8
Ionization Potential (IP) Values of some
Diluents
Diluent
IP (eV)
References
Propane
11.5
300
iso
-Butane
11.4
300
Cyclobutane
11.0
300
Hexane
10.43
90
n
-Heptane
9.83
301
Dodecane
79, 90
10 ± 0.2
n
-Dodecane
9.40
301
Cyclohexane
10.3
90
Cyclohexane
9.82
301
Cyclohexane
9.24
90
Benzene
9.24
90, 300
Toluene
8.82
90
Toluene
8.78
300
Methanol
10.96
300
Dimethyl ether
10.04
300
Tetrachloromethane
11.47
301
Tetrachloromethane
11.5
79
Radiolysis of HNO
3
generates different radicals (
305
), but at high acidity, HNO
3
can also act as a hydroxyl radical scavenger (
306
). Moreover, postirradiation effects
have been observed (variation of the concentration of radicals, for example) (
305
).
In spite of the complexity of the solutions, some authors have managed to iden-
tify the main degradation routes in the presence of HNO
3
: the radiolysis of TBP
proceeded by the preferential loss of a radical H
•
from C-H bonds (
21, 50
), followed
by O-C, C-C, or O-P bond cleavages (
21
). The four primary radicals (presented in
Figure 8.17) interact with species present in the medium, and the classical further
reactions are dimerization, coupling with dodecane, and reaction with O
2
to give the
related hydroxy-TBPs, which can undergo further oxidation or form nitrates (
21
).
The low amount of TBP-dimers (0.3%) and lower homologues has been explained by
the involvement of TBP fission prior to dimer formation (
22
).
8.4.4 e
f f e C t
of f
i
n H i b i t of r S
o n
tbP d
e g r a d a t i To n
To limit the radiolytic degradation of extractants, the influences of free-radical
inhibitors have been measured. The addition of dimethoxybenzaldehydes (DMBA),
particularly 3,5- and 3,4-DMBA, to the PUREX solvent could improve its stability
and decrease its contamination (
307
). DMBA has a double effect, including a protec-
tive effect for the excited molecules of TBP (because of its low ionization potential),
and the aldehyde radiolysis products could react with the HDBP present and there-
fore inhibit its complexing properties.
