Vol. 28, No. 7 (2016)
Development of Heterogeneous Ni-Ni Complex/HPA-RNi Catalyst for Hydrogenation of Benzene 1451
Calculation of activation energy: From the above, the
reaction is of zero order in terms of benzene concentration and
first order in terms of hydrogen pressure. Thus, rate constants
of the reaction at 393, 423, 443 and 473 K, and 2.8 MPa of
pressure were calculated. Using these rate constants, activation
energy of the reaction is determined according to the procedure
described below.
TABLE-1
COMPARISON OF CONVERSION OF BENZENE (X ) USING
FRESH AND SPENT CATALYST (USED FOR 100 h) AT T =
A
4
23 K AND P = 2.8 MPa WITH Ni-Ni COMPLEX HPA-RNi
CATALYST IN BENZENE HYDROGENATION
Conversion (X , %)
A
Time (min)
10
Spent catalyst
(after 100 h of usage)
With fresh catalyst
Arrhenius relation (given in eqn. 8) was used for the
calculation of activation energy of the reaction.
0.0675
0.1367
0.1963
0.2429
0.2859
0.3398
0.3844
0.4772
0.5834
0.6824
0.7767
0.8595
0.1045
0.1616
0.2331
0.2883
0.3347
0.4272
0.5277
0.6367
0.6869
0.7421
0.7732
0.8429
3
6
9
0
0
0
−
Ea
RT
(10)
k = k ×e
0
120
where k
0
is the Arrhenius constant, E
a
is the activation energy
150
180
of the reaction and R is the gas constant.
On taking logarithm:
2
3
40
00
Ea
360
log(k) = log(k ) −
(11)
0
4
4
20
80
RT
i.e. slope of the graph of log (k) vs. 1/T gives the activation
energy and intercept gives the Arrhenius constant.
analysis and various bond lengths and bond angles are reported.
The SEM micrograph of the final heterogeneous catalyst has
shown the presence of the complex in the form of well grown
tiny crystallites on the surface of the support (HPA-RNi). The
catalytic activity of the as prepared catalyst was checked by
carrying out the liquid phase hydrogenation of benzene, in
the temperature range of 393-473 K and in the pressure range
of 2.8 to 3.5 MPa. The experiments were carried out in a semi
batch reactor with continuous supply of hydrogen over 8 h of
reaction time. The catalyst is highly active for the hydrogenation
and very specific to cyclohexane formation. Maximum amount
of conversion obtained is 98 % at a temperature of 473 K and
From the slope of the plot (Fig. 5), activation energy (E )
of the reaction is determined as 35.64 KJ/mol, which is in
good agreement with the values (37.7 KJ/mol [15], 35.4 KJ/mol
a
[
30]) reported in the literature. This implies that the increase
in the rate constant is mostly because of the increase in the
value of k in eqn. 10.
0
-9
-8
-7
-6
-5
-4
2
.8 MPa and at 423 K and 3.45 MPa hydrogen pressure. The
-3
-
2
order of the reaction is nearly zero in terms of benzene concen-
tration and in the range of 0.9 to 1.3 in terms of hydrogen
pressure. Activation energy of the reaction is found to be 35.64
KJ/mol, which is equal to that reported in literature. We have
also showed that the catalyst is highly stable by carrying out
the hydrogenation of benzene with the spent catalyst used for
about 100 h.
-
0
1
.0019 0.0020 0.0021 0.0022 0.0023 0.0024 0.0025 0.0026
1
/T [1/K]
Fig. 5. Arrhenius plot for liquid phase benzene hydrogenation
Study of the stability of the catalyst: In order to find out
whether there is any leaching of the complex from the support
that can result in the deactivation of the catalyst; we carried
out the reaction at 423 K and 2.8 MPa hydrogen pressure
with the spent catalyst, which was used for about 100 h. The
variation in the conversion of benzene with time in the first
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9