Chemistry Reference
In-Depth Information
range 25-180
◦
C. Volumetric methods (AVD, Microdroplet and others) were used at
25-90
◦
C and atmospheric pressure, while the calorimetric (thermographic) method
(see Fig. 10.4) was employed at temperatures exceeding 100
◦
C and elevated pres-
sures (1.5-4.0 MPa) according to the “nonvolatility” requirement (see Eq. 10.8a).
To identify the effect of the reaction vessel material on the h/c H
2
O
2
decomposi-
tion, a number of experiments involving several materials at various
F
/
V
ratios were
carried out (
F
is the area of the vessel's inner surface,
V
is its volume). For vessels
made of molybdenum glass, opaque quartz and (to a lesser degree) pyrex glass, the
F
/
V
ratio was found to significantly influence the h/c H
2
O
2
decomposition rate. In
contrast, in the cases of Teflon and optical grade quartz, the decomposition rate was
close to its minimum value, and a 3-4-fold change in the
F
/
V
ratio did not affect it.
Thus, under these conditions the liquid phase decomposition of h/c H
2
O
2
occurs as
a homogeneous process, while the contribution of heterogeneous decomposition on
the vessel walls is negligible (Fig. 11.8).
The thermograms obtained were analyzed using the method developed in [15].
A typical thermogram obtained in the experiments aimed at determining the
thermal effect of the reaction,
Q
, is given in Fig. 11.5. The experimental value of
Q
= 2
.
75
0
.
13 kJ g
−
1
was found to be close to that calculated from thermochemical
data (
Q
= 2
.
88 kJ g
−
1
).
The initial and final H
2
O
2
concentrations were determined with a minimum accu-
racy of 0.3% from the refraction index data obtained using a precision reflectometer
IPF-23 (by using tables [8]).
The decomposition of h/c H
2
O
2
was found (from thermogram data) to be a first-
order reaction (
n
= 0
.
9-1.0). Data corresponding to a temperature of 140
◦
Care
presented in Fig. 11.6 as an example.
Due to the fact that the isothermal decomposition reaction without self-
acceleration exhibited rather long periods of quasi-stationary character (see for ex-
ample Fig. 11.7), most of the thermographic experiments were performed according
to the following simple scheme. The liquid with initial concentration
c
0
was kept at
a constant temperature
T
0
up to the point that the quasi-stationary mode, charac-
terized by a constant (maximum) warm-up
±
T
st
, began. Then the experiment was
terminated, the liquid was cooled and the final concentration
c
fin
was measured. The
final conversion degree,
Δ
η
fin
, was calculated from the value of
c
fin
. The correctness
Fig. 11.5
Typical
thermogram obtained for
decomposition of h/c H
2
O
2
at
P
∞
= 1
.
6MPa,
T
0
= 149
.
5
◦
C,
η
fin
= 0
.
9,
α
S
/
V
ρ
=
min
10
−
3
Jg
−
1
s
−
l
deg
−
1
8
.
3
×
