Oxidative dehydrogenation of cyclohexane over modified zeolite catalysts

Article abstract of DOI:10.1134/S0965544116070021

The catalytic activity of modified zeolites in selective oxidative dehydrogenation of cyclohexane has been studied. It has been established that polymetallic zeolite catalyst, namely, CuZnCoCr-clinoptilolite (0.5% Cu²⁺, 0.2% Zn²⁺; 0.1% Co²⁺; 0.1% Cr³⁺) manifests the highest activity in the reaction under consideration. The kinetic scheme of the reaction mechanism has been proposed, and a kinetic model of the process has been developed on the basis of stepwise mechanism schemes. The numerical values of the kinetic parameters are calculated.

Full text of DOI:10.1134/S0965544116070021

ISSN 0965ꢀ5441, Petroleum Chemistry, 2016, Vol. 56, No. 7, pp. 639–645. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © A.M. Aliev, Z.A. Shabanova, U.M. NadzhafꢀKuliev, S.M. Medzhidova, 2016, published in Neftekhimiya, 2016, Vol. 56, No. 4, pp. 407–413.
Oxidative Dehydrogenation of Cyclohexane
over Modified Zeolite Catalysts
A. M. Aliev, Z. A. Shabanova, U. M. NadzhafꢀKuliev, and S. M. Medzhidova
Nagiev Institute of Catalysis and Inorganic Chemistry, National Academy of Sciences of Azerbaijan,
pr. G. Dzhavida 113, Baku, AZ1141 Azerbaijan
eꢀmail: itpcht@itphct.ab.az
Received September 9, 2015
Abstract—The catalytic activity of modified zeolites in selective oxidative dehydrogenation of cyclohexane
has been studied. It has been established that polymetallic zeolite catalyst, namely, CuZnCoCrꢀclinoptilolite
2+
2+
2+
3+
(
0.5% Cu , 0.2% Zn ; 0.1% Co ; 0.1% Cr ) manifests the highest activity in the reaction under considꢀ
eration. The kinetic scheme of the reaction mechanism has been proposed, and a kinetic model of the process
has been developed on the basis of stepwise mechanism schemes. The numerical values of the kinetic paramꢀ
eters are calculated.
Keywords: cyclohexene, oxidative dehydrogenation, heterogeneous catalysis, polymetallic zeolite catalysts
DOI: 10.1134/S0965544116070021
Alicyclic diene hydrocarbons are the starting mateꢀ zeolites (sodalite, chabasite, erionite, mordenite, cliꢀ
rials for the synthesis of different classes of multifuncꢀ noptilolite, and natrolite) feature selectivity in formaꢀ
tional compounds. The functional derivatives of these
compounds owing to the high activity of the multiple
bond are used in the synthesis of polymer and composꢀ
ite materials of special assignment, physiologically
active compounds, as well as chiral synthons for
directed synthesis of the analogs of natural compounds
and pharmaceuticals. One of the promising trends in
the production of cyclic unsaturated hydrocarbons is the
singleꢀstep catalytic transformation of naphthene
hydrocarbons which resources in oils and refining
products are essential enough. The most thoroughly
studied reaction is the catalytic dehydrogenation of
naphthene hydrocarbons in oxygenꢀfree mode [1–3].
It is known that this reaction, being restricted thermoꢀ
dynamically, is accomplished under severe conditions
which lead to aromatization and resinification of an
essential part of hydrocarbon fraction as well as rapid
coking and deactivation of the catalysts in use.
tion of cyclohexene according to the following scheme
C H
6
C H
6
C H
6 6
12
10
CO2
Cyclohexadieneꢀ1,3 was not detected among the
products of cyclohexane oxidation in the case of any
zeolite tested as a catalyst; the data on production of
cyclohexadieneꢀ1,3 by oxidative dehydrogenation of
cyclohexane over zeolite catalysts are absent in the literꢀ
ature.
Cyclohexadieneꢀ1,3 is widely used in production of
a range of physiologically active compounds, food
additives (saffron), flowerꢀfruit perfume (Poison
Dior), different polymers and so on [5]. From
this point of view, the synthesis of a highly active and
selective catalyst based on zeolites for selective oxidaꢀ
tive dehydrogenation of cyclohexane into cyclohexaꢀ
The oxidative dehydrogenation of naphthenes,
resulting in alicyclic diene hydrocarbons, refers to
scarcely studied heterogeneous catalytic reactions
which proceed with participation of oxygen. The
application of molecular oxygen as the hydrogen dieneꢀ1,3 is of high theoretical and practical imporꢀ
acceptor allows one to carry out the process under tance.
milder conditions and prevent the aboveꢀmentioned
Herein, we present the results of investigations on
difficulties.
the oxidative dehydrogenation of cyclohexane via
The catalytic properties of zeolite catalysts in oxiꢀ
molecular oxygen aimed at definition of the condiꢀ
dation of cyclohexane were studied in paper [4]. The
tions for selective formation of cyclohexadieneꢀ1,3 in
authors established that faujasites mainly promote the
reactions of deep and oxidative dehydrogenation, the presence of modified zeolite catalysts and investiꢀ
resulting in carbon dioxide and benzene. Small porous gation of reaction kinetics and mechanism.
639

640
ALIEV et al.
–
1
Table 1. Oxidative dehydrogenation of cyclohexane over different starting zeolites (T = 380°C, V = 2000 h , cycloꢀ
hexane : O = 1 : 1)
2
Yield of products, %
Zeolite
X,
%
S
, %
C H
C H
C H
C H OH C H O
CO2
6
10
6
8
6
6
6
11
6
10
NaY
NaX
NaA
20.4
19.2
22.3
16.6
23.5
–
–
–
3.1
2.7
0.9
1.1
1.7
0.3
1.2
2.1
0.7
0.3
–
16.6
13.9
1.1
–
0.9
16.3
12.5
15.8
–
0.5
0.7
0.3
0.8
5.4
7.8
1.2
1.3
4.6
Mordenite
0.7
Clinoptilolite
19.5
0.3
X
is the alcohol conversion; S is the selectivity for cyclohexadieneꢀ1,3.
EXPERIMENTAL
starting zeolites in oxidative dehydrogenation of
cyclohexane was studied. Table 1 shows the results of
investigations for the zeolites which do not contain
metal cations. The results of investigations confirmed
that Naꢀforms of faujasites, internal cavities of which
are available for cyclohexane molecules, are active
only in deep oxidation, and these zeolites practically
do not promote the oxidative dehydrogenation of
cyclohexane into cyclohexene and cyclohexadieneꢀ
The reaction was carried out on a laboratory flow
unit with a quartz reactor over a fixed catalyst bed at
ambient pressure in the temperature range of 280–
3
3
1
90°C, space velocity of the gas mixture of 1000–
–1
000 h , and cyclohexane : O : N molar ratio of
2
2
: (0.24–1) : 5.3. The work was concerned with synꢀ
= 4.2), Na
= 2.0) and natural zeolites clinoptilolite
= 8.68) and mordenite ( = 9.6) from Azerbaijan
thetic zeolites NaY (SiO /Al O =
λ
X
( =
λ
2
2
3
2
.9), NaA (
λ
1
,3 [6, 7]. Probably, this is explained by the strong
(
λ
λ
adsorption of cyclohexane on faujasites. Unlike wide
porous zeolites (NaX, NaY), narrow porous zeolites
deposit modified by different transition metal cations
and mainꢀgroup elements (Zn, Cu, Co, Cr, Mn, Fe,
Mg, Mo, etc.).
that are characterized by small surface area (8.0–
2
2
0.0 m /g) and small pore sizes (4.2–4.9 Å) facilitate
The catalysts were synthesized by the ion exchange
method. Prior to ion exchange, the natural zeolites
were treated with 0.5 N HCl. The amount of elements
introduced into zeolite composition was defined by
ion spectral analysis on an Agilent 7700 ICPꢀMS
spectrometer and composed 0.1–2% of the zeolite
mass. The catalysts with a particle size of 0.25–0.63 mm
and cyclohexane of 99.5% purity were used.
The analysis of the reactants and reaction products
was carried out on a gas chromatograph, directly conꢀ
nected with the reaction unit, using a 3ꢀm PorapakꢀT
packed column under conditions of linear temperature
programming from 50 to 200°C. The analysis of
the products was performed also on an Agilent 7890
chromatograph with an Agilentꢀ5975 mass detector and a
HPꢀ5 MS column of 30 m in length. Resulting cycloꢀ
hexadieneꢀ1,3 was identified by chromatography
mass–spectrometry, IR and UV–vis spectroscopy.
the selective conversion of cyclohexane to cyclohexꢀ
ene. From Table 1 it follows that among cationic forms
of narrow porous zeolites, the highest yield of cycloꢀ
hexadieneꢀ1,3 is observed over natural clinoptilolite.
The introduction into clinoptilolite composition of
metal cations which are involved in the popular dehyꢀ
drogenation catalysts (Ni, Co, Cr, Zn, Cu, Mn, and
Mo) leads to a change in the activity of these catalysts.
It was established that the effect of these metal cations
is not the same, and individually they manifest relaꢀ
tively low catalytic activity in terms of the yield of
cyclohexadieneꢀ1,3. Thus, under reaction conditions
2
+
explored (Table 2), over the samples modified by Zn
2+
and Ni cations, the oxidative dehydrogenation of
cyclohexane is accompanied by destructive dehydroꢀ
genation, resulting in hexene (entries 1 and 5); over
the samples modified by Cu , Mn , and Sn —the
partial and deep oxidative dehydrogenation, resulting
in cyclohexanone and carbon dioxide (entries 3, 7 and
2+
2+
2+
RESULTS AND DISCUSSION
2+
3+
8
), over the samples modified by Co , Cr , and
2+
The performed investigations allowed us to reveal Mo — the dehydrogenation, partial and deep oxidaꢀ
both specific and commonly known regularities for tion, resulting in benzene, cyclohexanone and carbon
heterogeneous catalytic processes of oxidative dehyꢀ dioxide (entries 2, 4, 10, and 14). As a result of the perꢀ
drogenation of saturated alicyclic hydrocarbons and formed investigations it was established that the highꢀ
select an efficient catalyst for the reaction under study. est yield of cyclohexadieneꢀ1,3 is observed for CuZnꢀ
2+
It was found that the conversion of cyclohexane CoCrꢀclinoptilolite catalyst bearing 0.5% Cu , 0.2%
2+
2+
3+
over the catalysts under study occurs in the following Zn , 0.1% Co ; and 0.1% Cr (entry 15). An
directions: oxidative dehydrogenation, partial and increase in the concentration of these cations in the
deep oxidation. Firstly, the catalytic activity of the composition of the catalyst leads to a reduction in the
PETROLEUM CHEMISTRY Vol. 56
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OXIDATIVE DEHYDROGENATION OF CYCLOHEXANE
641
–
1
Table 2. Oxidative dehydrogenation of cyclohexane over modified natural clinoptilolite (T = 380°C, V = 2000 h ,
C H : O : N = 1 : 1 : 5.3)
6
12
2
2
Yield of products, %
Entry
Zeolite content, wt %
X
%
S %
C H
C H
C H C H OH C H O CO2
6
10
6
8
6
6
6
10
6
10
1
2
3
4
5
6
7
8
9
Zn (0.2)
14.3
49.3
49.7
41.6
18.2
39.3
34.1
33.9
14.6
44.1
16.3
43.1
45.6
41.4
2.8
9.5
0.7
0.4
4.7
2.9
3.9
0.5
5.5
3.3
4.1
0.3
15.5
12.5
9.8
0.9
9.8
1.3
7.5
1.7
12.1*
7.9
–
0.8
1.9
2.5
3.9
1.2
6.6
5.9
4.7
0.7
4.1
0.9
1.3
1.3
4.4
4.9
1.4
Cr (0.1%)
8.8
3.6
6.9
0.8
0.9
2.2
3.8
0.6
5.4
3.5
11.3
16.7
7.8
–
10.5
17.7
10.6
–
Cu (0.5%)
5.8
10.5
6.5
Co (0.1)
9.4
ZnNi (0.2 : 01)
CuCr (0.5 : 0.1)
CuSn (05 : 0.1)
CuMn (05 : 0.1)
CuFe (0.5 : 0.25)
CoCr (0.1 : 0.1)
CoMnCu (0.1 : 0.5 : 0.5)
CoMnCr (0.1 : 0.5 : 0.5)
CuZnCo (0.5 : 0.2 : 0.1)
CoMoCr (0.1 : 0.5 : 0.1)
2.7
14.8*
7.9
13.9
9.6
8.6
15.3
13.8
–
6.1
12.1
54.1
18.6
41.7
20.6
25.8
7.97
65.1
29.7
–
7.9
8.2
6.8
8.9
11.8
3.3
23.3
16.2
3.7
1
1
1
1
1
1
1
0
1
2
3
4
5
6
9.9
1.3
16.7
2.1
10.8
–
5.5
3.8
4.9
6.5
9.3
–
–
7.2
2.9
0.5
3.9
13.7
7.1
CuZnCoCr (0.5 : 0.2 : 0.1 : 0.1) 35.8
CuZnCoCr (2 : 2 : 1.0 : 0.5) 54.4
2.5
16.9
13.5
*
Hexene yield.
yield of cyclohexadieneꢀ1,3 and an increase in the ments showed that the change in linear velocity of the
yield of the product of partial oxidation (entry 16, see starting mixture does not affect essentially the main
Table 2).
process parameters (yield of cyclohexadieneꢀ1,3 comꢀ
poses 23.1–23.4%, selectivity towards cyclohexadiꢀ
eneꢀ1.3 is 65–65.2 %).
Hence, the performed investigations showed a posꢀ
sibility to convert cyclohexane to cyclohexadieneꢀ1,3
via variation of the structure and composition of zeoꢀ
lites. The optimal composition of cations introduced
Based on the performed investigations, it can be
concluded that the external and internal diffusion facꢀ
tors do not affect the process rate; and the reaction of
oxidative dehydrogenation of cyclohexane over the
2+
2+
into clinoptilolite (Cu —0.5%; Zn —0.2%;
2+
3+
Co —0.1%; Cr —0.1%) and optimal reaction conꢀ
–1
ditions were determined (
T 380°C, Vо 2000 h , catalyst under study proceeds in the kinetic region, in
C H : O : N = 1 : 1 : 5.3), at which 23.3% yield of which all the diffusion steps are essentially faster than
6
12
2
2
cyclohexadieneꢀ1,3 is achieved at 35.8% conversion of chemical reactions composing the mechanism of this
cyclohexane.
reaction. The results of investigations on the effect of
partial pressures of the reagents on the reaction course
are presented in Figs. 1 and 2.
The kinetic experiments were carried out on a
flowing unit at ambient pressure in the temperature
range from 320 to 380°C, volume velocity of 500–
–1
3
0
000 h , partial pressure of the reagents: PC6H12
.05–0.14 atm; PO2 = 0.07–0.25 atm.
=
Table 3. Effect of the catalyst particle sizes on the reaction
–
1
course at C
and = 380°C
H
12 : O
: N
molar ratio of 1 : 1 : 5.3, V
= 2000 h ,
6
2
2
o
T
To define the range of reaction proceeding, a series
of experiments were carried out at different sizes of the
catalyst grains (from 0.25 to 2 mm) and different linear
rates of the starting materials. The results of investigaꢀ
tions on the effect of the catalyst particle sizes on the
reaction course are presented in Table 3.
Yield
of cyclohexadiꢀ
eneꢀ1,3, %
Catalyst particle
Selectivity for
cyclohexadieneꢀ1,3, %
size, mm
0
.25–0.40
.40–0.63
23.1
23.2
23.3
23.4
23.3
65.1
65.2
65.1
65.2
65.1
0
The linear velocity was varied by changing the catꢀ
3
0.63–1.25
1.25–1.60
1.60–2.00
alyst volume (1.0, 1.5, 2.0, 2.5 cm ), retaining the conꢀ
–1
stant volume velocity (2000 h ) at C H : O : N
6
12
2
2
molar ratio of 1 : 1 : 5.3 and
T = 380°C. The experiꢀ
PETROLEUM CHEMISTRY Vol. 56
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642
ALIEV et al.
temperature rise from 320 to 380°C affords a continuꢀ
ous increase in the yield of cyclohexadieneꢀ1,3, and at
80°C the latter reaches 23.3%, therewith, upon furꢀ
As can be seen from Fig. 1, an increase in PO2 from
.07 to 0.17 atm leads to an increase in the yield of
cyclohexadieneꢀ1,3 from 5.9 to 13.1%, which is
explained by an increase in the concentration of surꢀ
0
3
ther temperature increase (380–390°C), it almost
does not change (23.3–23.7%). Over the whole temꢀ
perature range explored, an increase in the yield of
benzene is associated with the high reactivity of cycloꢀ
hexene and cyclohexadieneꢀ1,3 which rapidly convert
to benzene. This evidences that here is realized a
sequential scheme of formation of benzene from
cyclohexane. An increase in the temperature also
affords an increase in the yield of cyclohexanol and
face oxygen, and upon further increase of PO2 to
0
.25 atm almsot does not change (13.3%). In the
whole range with the increased oxygen partial presꢀ
sure, the yields of cyclohexene, benzene, carbon dioxꢀ
ide, and cyclohexanol and cyclohexane conversion
increase.
As can be seen from Fig. 2, as the cyclohexane parꢀ
tial pressure PC6H12 increases from 0.05 to 0.12 atm, the CO2. This is connected with the fact that, at high temꢀ
yield of cyclohexadieneꢀ1,3 increases to 11.7 %. Subꢀ peratures, the deep oxidation of cyclohexene and
sequent increase of PC6H12 from 0.12 to 0.14 atm leads cyclohexadieneꢀ1,3 occurs and the rate of cyclohexene
hydration also increases.
to an essential reduction in the yield of cyclohexadiꢀ
eneꢀ1,3; therewith, the yield of cyclohexene also
increases, while the yield of benzene reduces. This
implies the realization of a sequential scheme of formaꢀ
tion of benzene from cyclohexane.
The aboveꢀmentioned results allow us to conclude
that the optimal partial pressures of the reagents, at
which the highest yield of cyclohexadieneꢀ1,3 is
–1
As the space velocity increases from 500 to 3000 h ,
the yields of benzene, carbon dioxide, and cyclohexanol
and conversion of cyclohexane reduce, which is associꢀ
ated with a reduction in the contact time (Fig. 4), while
an increase in the yield of cyclohexene and cyclohexadiꢀ
eneꢀ1,3 is connected with the fact that a reduction in the
contact time hampers the preoxidative dehydrogenation
of these products into benzene, deep oxidation into CO
and hydration into cyclohexanol.
achieved, are as follows: PC6H12 = 0.12 atm and PO2
.14 atm.
The effect of temperature and volume velocity on
the reaction course was studied at optimal PC6H12 and
=
0
Based on the experimental data, the following
kinetic scheme for reaction of oxidative dehydrogenaꢀ
PO2 , and the results of these investigations are preꢀ tion of cyclohexane over metal zeolite catalyst CuZnꢀ
sented in Figs. 3 and 4. From Fig. 3 it follows that a CoCrꢀclinoptilolite is suggested
C H OH
6
11
k6
+H O
2
k1
k2
k
3
C H
6
C H +1/2O
6
C H + 1/2O
6
C H + 1/2O
2
–H O
2
6
12
2
–H O
2
10
2
–H O
2
6
8
.
(1)
k7
+O2
k4
+O
2
+
O2
k5
CO2
Let us assume that cyclohexene is formed by interacꢀ the Langmuir–Hinshelwood mechanism, the kinetic
tion of adsorbed cyclohexane molecules with dissociaꢀ equation of this reaction will have the following form
tively adsorbed oxygen molecules. Then, according to
k K P K P
1
1
1
2
2
(
2)
r1 =
.
2
(
1 + K
P
+ K
P
2
+ K
P
3
+ K P + K P + K P
)
4 4 5 5 6 2
1
1
2
3
Cyclohexadieneꢀ1,3 is formed upon interaction of adsorbed oxygen molecules. The kinetic equation that
adsorbed cyclohexene molecules with dissociatively corresponds to this mechanism is as follows
k K P K P
2
3
3
2
2
r2 =
.
(3)
2
(
1 + K
P
+ K
P
2
+ K
P
3
+ K P + K P + K P
)
4 4 5 5 6 2
1
1
2
3
PETROLEUM CHEMISTRY Vol. 56
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OXIDATIVE DEHYDROGENATION OF CYCLOHEXANE
643
A, X, %
A,
%
A,
X,
%
A,
%
5
45
0
5
4
4
3
3
2
2
1
1
0
5
0
5
0
5
0
5
0
5
0
10
9
8
7
6
5
4
3
2
1
14
12
10
8
1
40
35
30
1
2
2
3
25
20
15
10
5
0
6
4
4
3
4
5
6
5
6
2
0
0.15
0
0.03
0.05
0.07
0.09
0.11
0.13
0
.05
0.10
0.15
PO2
0.20
0.25
P
C H
6
12
Fig. 1. Dependence (
and the yields ( ) of the products (
carbon dioxide, ( ) cyclohexadiene, (
cyclohexene on the partial pressure of oxygen at
1
) of the cyclohexane conversion (
) cyclohexanol, (
) benzene, and (
X
)
Fig. 2. Dependences (
1
) of the cyclohexane conversion of
) of the products ( ) cyclohexadiene,
) carbon dioxide, ( ) benzene, and
) cyclohexene on the partial pressure of cyclohexane at
A
4
2
5
3
6
)
)
(
(
(
X
) and the yields (
A
2
3
6
) cyclohexanol, (
4
5
Ò
=
40°C, = 0.12.
= 2000 h–1, and
V
= 360°C,
= 2000 h–1, and PO2 = 0.14.
V
3
P
T
C H
6
12
The formation of CO proceeds upon interaction following kinetic equation corresponds to this mechaꢀ
2
nism
of adsorbed cyclohexene and oxygen molecules. The
k K P K P
7
3
3
6
2
r3 =
.
(4)
2
(
1 + K
P
+ K
P
2
+ K
P
3
+ K
P
4
+ K
P
5
+ K
P
2
)
1
1
2
3
4
5
6
The reaction of formation of cyclohexanol proꢀ water molecule from the gas phase. The kinetic equaꢀ
ceeds between adsorbed molecule of cyclohexene and tion that corresponds to this mechanism is as follows
k K P P
6
3
3
6
r4 =
.
(5)
(
1 + K
P
+ K
P
2
+ K P + K P + K P + K P
)
3 3 4 4 5 5 6 2
1
1
2
According to the kinetic scheme (1), the total rate cyclohexadieneꢀ1,3 and oxygen and formation of
of formation of cyclohexene can be presented in the benzene upon interaction of adsorbed molecules of
following form
cyclohexadieneꢀ1,3 with dissociatively adsorbed
rC6H10 = r − r − r − r .
(6) oxygen molecules. Based on this mechanism, the
1
2
3
4
following equations for the rates of formation of
The deep oxidation of cyclohexadieneꢀ1,3
occurs upon interaction of adsorbed molecules of CO
and C
H
can be written
2
6
6
k K P K P
5
4
4
6
2
r5 =
,
(7)
(8)
2
(
1 + K
1
P
1
+ K
2
P
2
+ K
3
P
3
+ K
4
P
4
+ K
+ K
5
P
5
+ K
+ K
6
P
2
)
)
k K P K P
3
4
4
2
2
r6 =
.
2
(
1 + K
P
+ K
P
+ K
P
+ K
P
4
P
5
P
2
1
1
2
2
3
3
4
5
6
Accoridng to kinetic scheme (1), the equations of
total rate of formation of cyclohexadieneꢀ1,3 and benꢀ
zene have the following form
rC6H8 = r − r − r ,
(9)
2
5
6
rC6H6 = r6.
(10)
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6
44
ALIEV et al.
X,
A,
X,
%
A,
%
A,
%
10
9
8
7
6
5
4
3
A,
%
45
4
3
3
2
2
1
1
0
5
0
5
0
5
0
5
1
1
4
2
0
40
35
30
25
1
2
1
1
8
6
4
2
0
2
20
3
4
1
5
0
5
3
4
5
6
1
2
1
0
0
500 1000 1500 2000 2500 3000
–1
V
, h
5
6
Fig. 4. Dependences of (
1
) the cyclohexane conversion of
) of the products ( ) cyclohexadiene,
) carbon dioxide, ( ) cyclohexene, and
) benzene on space velocity at a C 12 : O : N molar
= 380°C.
0
3
(
(
(
X
) and the yields (
A
4
2
5
H
10
330
350
, °C
370
390
3) cyclohexanol, (
T
6
6
2
2
ratio of 1 : 1 : 5.3 and
T
Fig. 3 Dependences of (
1
) the cyclohexane conversion of
) of the products ( ) cyclohexadiene,
) carbon dioxide, ( ) benzene, and
) cyclohexene on the reaction temperature at a C H
(
(
(
X) and the yields (
A
2
3
6
) cyclohexanol, (
4
5
C H + 8.5O = 6CO + 5H O,
6 10 2 2 2
:
12
6
= 2000 h–1
V .
C H + 8O = 6CO + 4H O,
6
8
2
2
2
O : N molar ratio of 1 : 1 : 5.3 and
2
2
C H + H O = C H OH.
6
10
2
6
11
Using these equations, the yields of the products
Taking into account the formation of carbon
and stating molar amounts of the reactants, let us
determine the molar rates in flow for cyclohexane,
cyclohexene, cyclohexadieneꢀ1,3, benzene, carbon
dioxide, cyclohexanol, oxygen and water, respectively,
by the following equations
dioxide upon interaction of adsorbed cyclohexane
and oxygen molecules according to the kinetic
equation
k K P K P
(11)
4
1
1
6
2
r7 =
2
0
C H
0
C H
0
C H
0
C H
⎫
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
(
1 + K
P
+ K
P
2
+ K
P
3
+ K
P
4
+ K
P
5
+ K
P
2
)
n
= n
− A n
(
+ A2n
+ A3n
1
1
2
3
4
5
6
C H
6
12
6
12
1
6
12
6
12
6
12
0
0
+
A4n
+ A5n
100
)
C6H12
C6H12
and kinetic scheme (1), the equation of total rate of
formation of carbon dioxide can be presented as
0
nC6H10 = A1n
100
100
100
100
C6H12
rCO2 = r + r + r
5
(12)
0
7
3
nC6H8 = A2n
nC6H6 = A3n
C6H12
The equation of total rate of formation of cyclohexꢀ
anol has the following form
0
C6H12
⎪
⎬.
0
rC6H11OH = r4
,
(13)
nCO2 = 6 A4n
(14)
C6H12
where Ki is the adsorption equilibrium constant
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎪
⎭
0
nC6H11OH = A5n
C6H12
100
Qi
0
i
(
(
RT
)
0
O2
K = K e
,
.
ki is the rate constant of reactions
i
nO2 = n
E
RT
−
0
1
2
0
C H
1
0
0
C H
)
k = k e
−
A1n
+ A n
+ 8.5A4n
100
)
i
i
2
C H
(
6
12
6
12
6
12
2
The stoichiometric equations of the gross mechaꢀ
nism of formation of the reaction products can be preꢀ
sented as follows
n
2
H O
0
C H
0
0
0
=
(A1n
+ A2n
+ A3n
+ 5A4n
6 12
C H
100
)
6
12
C H
12
6
C H
6
12
1
2
C H + O = C H + H O,
6
12
2
6
10
2
Let us express the partial pressures of the reagents
by the following equation
1
2
C H + O = C H + H O,
6
10
2
6
8
2
ni
Pi =
P. P1, P2, P3, P4, P5, P6 are partial presꢀ
1
2
n
i
∑
sures of cyclohexane, oxygen, cyclohexene, cycloꢀ
hexadieneꢀ1,3, benzene and water, respectively. A1 A2
C H + O = C H + H O,
6
8
2
6
6
2
C H + 9O = 6CO + 6H O,
,
,
6
12
2
2
2
PETROLEUM CHEMISTRY Vol. 56
No. 7
2016

OXIDATIVE DEHYDROGENATION OF CYCLOHEXANE
645
Table 4. Numerical values of the constants of kinetic model
0
and adsorption heats (Qi is carried out by flexible tolꢀ
)
erance and Powell’s methods using a Poisk program
system [8], where the objective function has the folꢀ
lowing form
0
0
ln ki (ln Ki )
Ei
(
Qi
)
, kcal/mol
25.25
0
m
n
2
3
5
3
2
4
2
1
2
4.18
exp
ji
calc
E1
ln k1
⎛ A − Aji
⎜
⎞
⎟
⎠
F = min
∑∑
j=1 i=1
exp
0
Aji
1.77
2.24
0.86
1.52
3.17
0.51
3.16
31.94
10.01
35.15
21.55
17.82
39.79
2.49
⎝
E2
ln k2
are experimental and calculated values of the yields of
the th component in the th experiment, is the
is the number of comꢀ
0
E3
i
j
m
ln k3
number of experiments, and
ponents.
n
0
E4
ln k4
The numerical values of the constants of kinetic
model are listed in Table 4. The calculations showed
that the relative accuracy of the experimental and calꢀ
culated data did not exceed 10–15%.
Based on the performed investigations and their
discussion, it can be concluded that the suggested
kinetic model in the studied range of parameter variaꢀ
tion describes sufficiently the mechanism of reaction
and can be used in the development of mathematical
model of the process.
0
E5
ln k5
0
E6
ln k6
0
E7
Q1
ln k7
0
ln K1
0
1
8
6
.02
.75
.84
11.00
8.57
Q2
ln K2
REFERENCES
0
Q3
ln K3
1
2
. V. D. Yagodovskii, Z. V. Pskhu, N. Yu. Isaeva, et al.,
Russ. J. Phys. Chem. A 83, 732 (2009).
. E. K. Bruce, A. B. David, and A. C. Emily, J. Mol.
Catal. A 131, 39 (1998).
0
11.00
3.19
Q4
ln K4
0
2
5.48
Q5
ln K5
3. B. B. Rajesh, K. Nobuko, and I. Masaru, J. Catal. Lett.
05, P. 83 (2005).
4. D. B. Tagiev and Kh. M. Minachev, Usp. Khim.
935 (1981).
1
0
3
.027
Q6
2.49
ln K6
50,
1
5
6
7
8
. V. A. Mironov, A. D. Fedorovich, and A. A. Akhrem,
Usp. Khim. 52, 104 (1983).
. Kh. M. Minachev, D. B. Tagiev, Z. G. Zul’fugarov, and
V. V. Kharlamov, Kinet. Katal. 20, 399 (1979).
A3, A4, A5 are the yields of cyclohexene, cyclohexadiꢀ
eneꢀ1,3, benzene, carbon dioxide, and cyclohexanol,
respectively.
Equations (6), (9), (10), (12), (13), and (14) comꢀ
pose the kinetic model of this process. The developed
kinetic model of the reaction was subjected to the staꢀ
tistical analysis based on the kinetic data. The calculaꢀ
tions of preexponential factors of the reaction conꢀ
. C. Brendan and A. K. Mark, J. Catal. Lett., No. 4, 223
(1990).
. T. N. Shakhtakhtinskii, M. F. Bakhmanov, and
G. N. Kelbaliev, Computerized Methods for Optimization
of Chemical Engineering Processes (Elm, Baku, 1985)
[in Russian].
0
i
0
i
0
stants ln k ln K , values of activation energies (Ei
(
)
)
Translated by K. Aleksanyan
PETROLEUM CHEMISTRY Vol. 56
No. 7
2016