1902
BUDANOV et al.
n
×
103, mol
Our investigation of the phenylhydroxylamine
hydrogenation kinetic was performed using the static
method in a closed system with vigorous stirring of the
liquid phase at the atmosphere pressure of hydrogen.
The experimental conditions allowed us to exclude the
effect of the internal mass transfer on the reaction rate
[7]. During the experiment, the volume of the hydroꢀ
gen absorbed over time was measured volumetrically,
and the concentrations of phenylhydroxylamine and
aniline were controlled via chromatographic analysis.
3
2
1
nA
The analysis was performed using a Shimadzu liqꢀ
uid chromatograph under the following conditions: a
mixture of acetonitrile and water with an acetonitrile
content of 30 vol % was used as carrier, the rate of the
eluent in a column was 0.9 cm3/min, the temperature
of the column thermostat was 30°C, and the waveꢀ
length of the photometric detector was 322 nm. The
elution time of aniline under the given conditions was
310 10 s, while the elution time of phenylhydroxyꢀ
lamine was 700 20 s. The concentrations were calcuꢀ
lated according to the absolute calibration technique,
using chromatograph software. The chromatographic
analysis allows us to determine reliably the current valꢀ
ues of the reaction product concentrations in time
with an degree of accuracy of no less than 3% of the
measured value. The reaction rates were estimated by
the numerical technique using the smoothing spline
interpolation procedure within the corridor of meaꢀ
surement accuracy. The values of the adsorption of
hydrogenating compound during the reaction were
calculated from the conditions of the material balance
of the system, according to the procedure in [8, 9].
nPHА
nH
2
0
40
80
120
160
200
τ
, s
Fig. 2. Kinetic curves of the phenylhydroxylamine hydroꢀ
genation reaction on a skeletal nickel catalyst in an aqueꢀ
ous solution of 2ꢀpropanole at the atmospheric pressure of
hydrogen,
303 K.
х
= 0.192 mole fractions,
g
= 0.5 g,
T
=
2
cat
exp
the concentrations of intermediate azoxyꢀ and
azobenzenes.
In the opinion of the author of [3], the rates of the
catalytic transformations of phenylhydroxylamine and
azoxybenzene have lower values than those of
nitrobenzene hydrogenation. At the same time, it was
shown in [1, 2, 5] that phenylhydroxylamine transꢀ
forms into aniline at high rates. The analysis of the
scheme shown in Fig. 1 allows us to state that it is the
reactivity of phenylhydroxylamine which determines
the amounts of condensation interactions products
and ultimately the selectivity of the reaction of
nitrobenzene hydrogenation. The literature, however,
contains virtually no results from investigations of the
phenylhydroxylamine hydrogenation kinetic or of any
other intermediate products.
RESULTS AND DISCUSSION
The kinetic curves characterizing the changes in
phenylhydroxylamine, aniline, and hydrogen concenꢀ
trations over time in an aqueous solution of 2ꢀproꢀ
panole with an alcohol molar fraction of 0.192, are
shown as an example in Fig. 2. From the presented
data, we can see that the phenylhydroxylamine conꢀ
centration drops sharply over time, and the kinetic
curve for aniline reaches its maximum. A decrease in
the aniline concentration is observed only after full
phenylhydroxylamine conversion. Such changes in
the phenylhydroxylamine and aniline concentrations
during reaction testifies to the competitive nature of
adsorption between the initial compound and the
aniline. The processing of the experimental results
showed that the change in phenylhydroxylamine conꢀ
centrations over time is linearized in coordinates of the
firstꢀorder reaction equation with a high correlation
coefficient, while the amount of hydrogen absorbed
during the reaction is linearized in coordinates of the
zeroꢀorder reaction equation (Fig. 3).
The aim of this study was to investigate the features
of the reaction kinetic of liquidꢀphase hydrogenation
of phenylhydroxylamine on a skeletal nickel catalyst in
2ꢀpropanole aqueous solutions.
EXPERIMENTAL
Skeletal nickel prepared by treating nickel–alumiꢀ
50; mean particle
radius, 4.5 m) with an aqueous solution of sodium
hydroxide according to the procedure in [7], was used
as a catalyst. The active catalyst had a specific surface
of 90 5 m2/g Ni and a porosity of 0.45–0.5. The maxꢀ
imum of the pore distribution along the radius was
num alloy (composition, 50
×
µ
It follows from the obtained data that an increase in
4 nm [7]. Aqueous solutions of 2ꢀpropanole with alcoꢀ the water content of the solvent leads to an increase in
hol concentrations of 0.073, 0.192, and 0.681 mole the initial rate of phenylhydroxylamine hydrogenaꢀ
fractions were used as solvents.
tion, which could be due to an increase in the adsorpꢀ
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 84
No. 11
2010