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UDC 549.67: 544.47: 542.941.8
USE OF METAL-ZEOLITES AS A CATALYST IN REACTION OF OXIDATIVE DEHYDROGENATION OF NAPHTHENES
A.M.Aliyev, Z.A.Shabanova, A.I.Kerimov, M.F.Bahmanov, F.V.Aliyev, U.M.Najaf-Guliyev
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
[email protected] Received 20.04.2016
Oxidative dehydrogenation of cyclohexane into 1,3-cyclohexadiene and methylcyclohexane into 1-methyl-1,3-cyclohexadiene has been found possible by use of clinoptilolite (CL) {Cu2+ (0.5 mas. %), Zn2+ (0.2 mas. %), Co2+ (0.1 mas. %), Cr3+ (0.1 mas. %)} and CL {Co2+ (0.5 mas. %), Cr3+ (0.25 mas. %)} heterogenic catalysts, prepared by ion-exchange, accordingly. By analyzing experimental data and taking into account bonding energies of exchange cations with dissociative adsorbed oxygen the active centers consisting of components of the catalyst have been grouped and reaction paths have been elucidated. The kinetic model worked out by taking into account these active centers, is presented.
Keywords: cyclohexane, 1,3-cyclohexadiene, methyl cyclohexane, 1-methyl-1,3-cyclohexadiene.
Introduction
Zeolites modified with metal cations have been widely used in practice as a catalyst and they are an object of the intensive investigation in fundamental catalysis. Very important problem is a development of procedures of preparation of modified zeolite catalysts with maximum achieved degree of using the active component. One of the procedures of preparation of this type of catalysts is the modifying of zeolites with metal cations by ion-exchange [1, 2]. Having used this method we synthesized active ultradispersion metal-zeolite catalysts for the reactions of oxidation of lower olefin hydrocarbons into carbonyl compounds, partial oxidation of lower parafin hydrocarbons, oxidative conversion of aliphatic alcohols, oxidative coupling of methane and oxidative dehydrogenation of naphthenic hydrocarbons [3-9]. All these catalysts show high activity and selectivity at relatively lower temperatures. In early published works we have shown that natural clinoptilolite modified with cations Cu2+, Zn2+, Co2+ and Cr3+ by ion-exchange is the active catalyst for reaction of oxidative dehydrogenation of cyclohexane into 1,3-cyclohexadiene [7, 8]. On the basis of experimental kinetic data by using Langmuir-Hin-shelwood rate expression we have established that reaction of oxidative dehydrogenation of cyclohexane proceeds with participation of the dissociative adsorbed oxygen. We have also studied influence of separate components of the
catalyst system on selectivity of the process [7, 8].
The purpose of the present work is to determine a role of the components of the catalytic system in reaction of oxidative dehydrogenation of naphthenic hydrocarbons taking into account the new experimental data on oxidative dehydrogenation of methyl cyclohexane [11] obtained in the laboratory "Catalysis over zeolites" of the Institute of Catalysis and Inorganic Chemistry NAS of Azerbaijan.
Experimental
The catalysts were prepared by the method of ion-exchange using Azerbaijan natural clinop-tilolite (crystallinity, 89.0%) and cations of the different metals [8]. After incorporating of the cations, all of the specimens of the metal-zeolite catalysts were activated by air at temperature, 3500C and space velocity, 2400 h-1 during 30 minutes.
The test of the activity of the prepared metal-zeolite catalysts and a study of the kinetic regularities of the reactions was carried out in a flow apparatus with the quarts tube reactor connected directly to the gas chromatograph. The reactor was placed inside a thermostatic chamber. Small stainless-steel balls of a 0.2 cm diameter were placed before the catalyst bed in order to obtain plug flow conditions. No catalytic activity was shown by these nonporous balls. A fraction of granulated metal-zeolites of about 0.25-0.63 cm of equivalent diameter was used as the catalyst. The analyses of the product of
reactions were performed by gas chromatography (GC), using a column filled with Paropack-T (length, 3 m), helium as the carrier gas, hot wire detector and program control of the temperature (from 50 to 2000C). Runs performed at several feed rates and using granules of catalyst of different sizes showed that external and internal mass transfer effects were negligible under the studied conditions.
Before incorporating the cations, natural clinoptilolite (SiO2/Al2O3=8.68) was treated with 0.5 N HCl solution. Amount of incorporating cations was determined by ion spectral analysis using ICP-MS "Agilent 7700". Purity of using cyclohexane and methyl cyclohexane was 99.5% and 99.0% accordingly. The analyses of the product of the reactions were also performed by gas chromatography using GC "Agilent 7890" with "Agilent 5975" MS and capillary column HP-5MS (length, 30 m).
Results and discussion
The results of a testing of a catalytic activity of the prepared metal-zeolites in the reaction of oxidative dehydrogenation of cyclohexane into 1,3-cyclohexadiene are presented in Table 1. It can be seen from the data of Table 1, natural cli-
noptilolite and its modified form with cations, Zn + (exp. 1, 2) show lower catalytic activity in the reaction. The activity of the speciments of natural clinoptilolite modified with cations; Cr3+,
2+ 9+
Cu and Co is relatively higher than above mentioned ones, particularly in course of aromati-zation of cyclohexane (exp. 3-5), yields of benzene are 15.5%, 12.5 and 9.8% accordingly, and 1,3-cyclohexadiene forms with lower yields. Incorporating of two cations in natural clinoptilolite;
Cu2+, Cr3+ and Co2+, Cr3+ is led to insignificant increasing yields of 1,3-cyclohexadiene in dominating reaction of cyclohexane aromatization (exp. 7, 8). Incorporating in these catalytic system of the third cation, Zn2+ is led to significant increasing in the yields of 1,3-cyclohexadiene and decreasing in the yields of benzene (exp. 12, 13).
Relatively high yields, of 1,3-cyclohexa-diene is achieved on the catalytic systems containing cations Cu2+, Cr3+, Co2+ and Zn2+ (exp. 19, 20). Natural clinoptilolite modified with cations; Fe, Mn, Sn, Mo and Ni shows relatively low catalytic activity in reaction of oxidative dehydrogenation of cyclohexane into 1,3-cyclohexadiene (exp. № 9-11, 16-18).
№ Catalyst Conversion of C5H12, X, % Selectivity, S, % Yield, A, %
C6H10 C6H8 C6H6 C6H10OH C5H10O CO2
1 CL 14.8 6.1 10.8 0.9 1.7 0.3 0.8 0.3
2 CL Zn (0.2 )* 14.3 2.8 0.7 0.4 0.3 12.1 - 0.8
3 CLCr (0.1) 49.3 9.5 8.8 4.7 15.5 7.9 10.5 1.9
4 CLCu (0.5) 49.7 5.8 3.6 2.9 12.5 10.5 17.7 2.5
5 CLCo (0.1) 41.6 9.4 6.9 3.9 9.8 6.5 10.6 3.9
6 CLZnNi (0.2:01) 18.2 2.7 0.8 0.5 0.9 14.8* - 1.2
7 CLCuCr (0.5:0.1) 39.3 13.9 0.9 5.5 9.8 7.9 8.6 6.6
8 CLCoCr (0.1:0.1) 44.1 18.6 5.4 8.2 9.9 10.8 5.5 4.1
9 CLCuSn (05:0.1) 34.1 9.6 2.2 3.3 1.3 6.1 15.3 5.9
10 CLCuMn (05:0.1) 33.9 12.1 3.8 4.1 7.5 - 13.8 4.7
11 CLCuFe (0.5:0.25) 14.6 54.1 0.6 7.9 1.7 3.7 - 0.7
12 CLZnCoCr (0.2:0.1:0.1) 39.2 30.3 4.8 12.5 4.9 8.5 2.2 6.3
13 CLZnCuCr (0.2:0.5:0.1) 35.5 21.8 0.5 8.4 4.5 6.7 7.9 7.5
14 CLCuCoCr (0.5:0.1:0.1) 47.9 21.5 4.5 10.3 6.4 11.5 8.4 6.8
15 CLCuZnCo (0.5:0.2:0.1) 45.6 25.8 16.7 11.8 2.1 7.2 6.5 1.3
16 CLCoMnCu (0.1:0.5:0.5) 16.3 41.7 3.5 6.8 1.3 - 3.8 0.9
17 CLCoMnCr (0.1:0.5:0.5) 43.1 20.6 11.3 8.9 16.7 - 4.9 1.3
18 CLCoMoCr (0.1:0.5:0.1) 41.4 7.97 7.8 3.3 2.9 13.7 9.3 4.4
19 CLCuZnCoCr (0.5:0.2:0.1:0.1) 35.8 65.1 - 23.3 0.5 7.1 - 4.9
20 CLCuZnCoCr (2:2:1.0:0.5) 54.4 29.7 2.5 16.2 3.9 16.9 13.5 1.4
* - the figures in brackets indicate the containing exchange cations in mas.%
Table 1. The results of the test of activity of modified natural clinoptilolite (CL) catalyst in reaction of oxidative dehydrogenation of cyclohexane (7=380°C, V=2000 h-1, C6H12:O2:N2=1:1:5.3)
From the data of Table 1, it has been concluded that the natural clinoptilolite containing Cu2+ - 0.5 mas. %, Zn2+ - 0.2 mas. %, Co2+ - 0.1 mas. % and Cr3+ - 0.1 mas. % is the active catalyst for reaction of oxidative dehydrogena-tion of cyclohexane into 1,3-cyclohexadiene.
The results of the experimental investigation on a selection of the catalyst for reaction of oxidative dehydrogenation of methyl cyclohexane into 1-methyl-1,3-cyclohexadiene are presented in Table 2. It can be seen from data in Table 2 that natural clinoptilolite modified with cations Zn , Cu2+, Cr3+, Fe2+ and Ni2+ shows relatively low catalytic activity in reaction of oxidative dehydro-genation of methyl cyclohexane into 1-methyl-1,3-cyclohexadiene (exp. 1-6). The natural cli-noptilolite modified with cations
Co and Cr3+
shows relatively high catalytic activity in this reaction (exp. 11-15). Incorporating in composition of these catalytic systems of cation Zn2+ decreases their catalytic activity in the reaction (exp. 16, 17). Natural clinoptilolite containing cations Cu2+, Zn2+, Co2+ and Cr3+ has relatively low catalytic activity in the reaction as compared with the clinoptilolite containing cations Co2+ and Cr3+ (exp. 14, 18). Analysis of the data given in Table 2 shows that the clinoptilolite
containing cations
Co2+ - 0.5 and Cr - 0.25 mas.% is the active catalyst for reaction oxida-tive dehydrogenation of methyl cyclohexane into 1 -methyl- 1,3-cyclohexadiene.
It is known that an activity of the zeolite catalysts in different reactions depends on; crystal structure, nature of cations, method preparation and distribution of cations of metals on a surface of zeolite. In our previous work [8], it was shown that the crystal structure of clinop-tilolite is optimum for preparation of the catalyst for reaction of oxidative dehydrogenation of naphthenic hydrocarbons. It is known that a crystal lattice of clinoptilolite consists of three open channels; A, B and C [12]. In Figure 1 it is presented the polyhedron model of clinoptilo-lite, reflecting a fragment of the structure with exchange cations. A and B channels are parallel to axis, C and consist of tencyclic and octocy-clic rings. They cross with the third octocyclic channel parallel to axis, a. Hexagonal planers in structure of clinoptilolite are surrounded with channels A, B and C in which the exchange cations are localized. Planar molecule of cyclohex-ane is hexacyclic which is solidly adsorbed on the hexagonal planers surrounded exchange cations in the structure of clinoptilolite.
Table 2. The results of the test of the activity of modified natural clinoptilolite catalysts in reaction of oxidative de-hydrogenation of methyl cyclohexane (T=3800C, v=2000h-1, C6H11CH3:O2:N2=1:1:5.3)_
№ exp. Catalyst Conversion of C6H11CH3, X,% Selectivity, S, % Yield, A, %
C6H9CH3 C6H7 CH3 C6H5CH3 CO2
1 Zn (0.2)* 7.6 7.9 0.9 0.6 5.2 0.9
2 Cu (0.5) 28.9 1.03 3.8 0.3 8.5 16.3
3 Cr (0.1) 21.4 21.02 5.9 4.5 9.5 1.5
4 Co (0.1) 19.4 19.6 6.2 3.8 7.4 2.0
5 Fe (0.25) 21.4 - 1.5 - 6.7 13.2
6 Ni (0.1) 50.2 - - 40.3 9.9
7 CuFe (0.5:0.25) 34.6 6.4 3.2 2.2 10.3 18.9
8 CuCo (0.5:0.1) 32.5 10.8 5.8 3.5 15.7 7.5
9 CuCr (0.5:0.1) 28.6 7.7 3.9 2.2 19.8 2.7
10 ZnCr (0.2:0.1) 18.8 4.3 1.9 0.8 14.5 1.6
11 CoCr (0.1:0.1) 32.7 30.3 3.6 9.9 13.9 5.3
12 CoCr (0.5:0.1) 37.4 28.9 5.8 10.8 12.3 8.5
13 CoCr (1.0:0.1) 41.1 23.4 5.2 9.6 13.8 12.5
14 CoCr (0.5:0.25) 49.8 28.9 7.2 14.4 15.6 12.6
15 CoCr (0.5:0.5) 53.9 12.1 1.9 6.5 35.7 9.8
16 ZnCoCr (0.2:0.5:0.25) 45.9 23.3 12.5 10.7 10.9 11.8
17 ZnCoCr (0.2:0.5:0.5) 49.4 13.9 13.5 6.9 21.5 7.5
18 CuZnCoCr (0.5:0.2:0.1:0.1) 37.4 22.7 5.3 8.5 9.9 13.7
* - the figures in brackets indicate the containing exchange cations in mas.%
Fig. 1. Polyhedron model of clinoptilolite, reflected fragment of structure with exchange cations.
In clinoptilolite there are four types of places in localization of exchange cations; they are M1 in channel A, M2 in channel B, M3 in C arranged along axis of a near center of the hex-acyclic ring and M4 - place arranged in channel A in center of inversion. Their quantity is not great. M3 is arranged near M1 [13, 14].
A role of components of the catalytic system in the reaction of oxidative dehydrogena-tion of cyclohexane can be explained by analysis of surrounding of the adsorbed molecules of cyclohexane with the exchange cations bonded with dissociative adsorbed oxygen, taking into account their bonding energies which can be found by expression [15]:
qo = ^ (qads + 50°) ,
(1)
where 500 kJ/mole - energy of dissociation of molecule oxygen, qads - heat of adsorption of oxygen on the pure surfaces of the polycrystal specimens of transient metals [16]; qads(Cu) = 478 kJ/mole, qds(Zn)=240 kJ/mole, qds(Co)= 418 kJ/mole, qads(Cr)=753 kJ/mole. Bonding energies of the components of catalyst with oxygen may be calculated by using formula, (1); qo(Cu)=489 kJ/mole, qo(Zn)=370 kJ/g-atom, q0(Co)=459 kJ/g-atom, q0(Cr)=612 kJ/g-atom.
Depending on solidity of these bonds driving force of hydrogen atoms of cyclohexane changes. The most driving force of hydrogen atoms of cyclohexane is displayed by the oxygen atoms bonded with the component of the catalyst, Cr3+.
On the basis of the experimental data presented in Table 1 and with taking regard to the bonding energies of the components of the catalyst with oxygen atom it is possible to group the active centers of components of the catalyst for reaction of oxidative dehydrogenation of cyclo-hexane which are responsible for formation of 1,3-cyclohexadiene, cyclohexene and benzene. Total scheme of oxidative dehydrogenation of cyclohexane on these active centers is presented in Figure 2.
Fig. 2. Schematic representation of the reaction of oxidative dehydrogenation on an active center of modified clinoprilolite catalyst, CL-CuCrCoZn. i -exchange cation, i=1-4; 1 - Cr3+, 2 - Cu2+, 3 -Zn2+, 4 - Co2+.
There are two types of active centers for reaction of oxidative dehydrogenation of cyclohexane into 1,3-cyclohexadiene;{M1(1), M2(2), M3(3)} and {M1(1), Mz(4), M3(3)}. Because of the solidity of bonds of cations; Cr3+, Cu2+ and Co2+ with oxygen atoms they have very strongly driving force of hydrogen atoms of cyclohex-ane, forming molecules of 1,3-cyclohexadiene stabilizided with Zn=0 which has relatively lower bonding energy (Figure 3).
By means of analysis of the experimental data and bonding energies of the components of the catalyst with oxygen atoms three types of active centers may be suggested for reaction oxida-tive dehydrogenation cyclohexane into benzene; {M1(1), M2(1), M3(1)}, {M1(2), Mz(2), M3(2)} and { M1(4), M2(4), M3(4)} as well three types of active centers for reaction oxidative dehydrogena-tion of cyclohexane into cyclohexene; {Ml(1), M2(3), M3(3)}, {M(2), M2(3), M3(3)} and {M(4), M2(3), M3(3)}.
Mi(l) = 0^ H
P-M2(2)
MI(1 )=o
О =M2(2)
H H
1 Мз(3)
+ O
2 -2H,O
+ СбН8 +
1
M,(3)
Fig. 3. Schematic representation of formation of 1,3-cyclohexadiene on an active center, {M1(1), M2(2), M3(3)} of modified clinoptilolite catalyst CL-CuCrCoZn.
X, A, %
40 35 30 25 20 15 10 5 0
7
T, s
Fig. 4. Dependence of oxidative dehydrogenation of cyclohexane on the average residence time, т: 1 -conversion of cyclohexane, X, %; 2 - yield of cyclohexene, Ab %; 3 - yield of 1,3-cyclohexadiene,
A2,%; 4 - yield of benzene, C6H12:O2:N2=1:1:5.3.
A3,%; 7=380UC,
It should be noted that an advantage formation of that or the other product of reaction of oxidative dehydrogenation of cyclohexane depends on amount of active centers for corresponding reaction which depends on concentration and sequence of incorporating of cations by ion-exchange. With the purpose of obtaining of 1,3-cyclohexadiene the optimum succession incorporating of cation in clinoptilolite is
Cu2+ (0.5 mas.%) Zn2+ (0.2 mas.%) Co2+ (0.2 mas.%) Cr3+ (0.2 mas.%) CL.
X, A, %
50 40 30 20 10 0
1
1 2
6 7
T, s
Fig. 5. Dependence of oxidative dehydrogenation of methyl cyclohexane on the average residence time, т: 1 - conversion of methyl cyclohexane, X, %; 2 - yield of methyl cyclohexadiene, A2, %; 3 - yield of methyl cyclohexene, Ab %; 4 - yield of toluene, A3, %; T=380°C, C6HnCH3:O2:N2=l:l:5.3.
Experimental data on a study of the kinetic regularities of the considered reactions over the active catalytic system testified to that these reactions don't proceed on a consecutive mechanism.
In Figures 4 and 5 there is presented an influence of average resident time on proceeding of reactions of oxidative dehydrogenation of cyclohexane over CL-CuCrCoZn and methyl cyclohexane over CL-CoCr catalysts accordingly.
2
If the reactions proceed on a consecutive mechanism with formation of end products; benzene and toluene, then cyclohexene, 1,3-cyclohexadiene and methyl cyclohexene, 1-me-thyl-1,3-cyclohexadiene are the intermediate products of the reactions of oxidative dehydro-genation of cyclohexane and metyl cyclohexane accordingly. It can be seen in Figures 4 and 5 the character of curves of dependence of yieds of intermediate and end-products on average resident time not corresponded to consecutive mechanism of proceeding of these reactions.
Thus on the basis of these experimental data it has been concluded that on the surface of the catalyst there are different active centers consisting of their components which are responsible for formation of the products of the reaction that is agreed with above mentioned hypothesis about structure of active centers.
Stage scheme of mechanism of oxidative dehydrogenation of cyclohexane on above mentioned active centers may be presented as follows:
■> 2ZiQ
-> 2Z2O
O2+2Z1 O2+2Z2
(ZiO+Z2O)+C6Hi2 -(ZiO+Z2O)C6Hi2 -
^ (ZiO+Z2O)C6Hi2 >C6H8+2H2O+ZI+Z2
C6Hi2+O2=C6H8+2H2O
1/2
1/2 1 1
The following exspression can be written for rates of the stages:
r1 = k101PO2 , r2 = k202PO2 , r3 = k383PC6H12 ,
T4 = 4 .
In stationary conditions
r=r1=r2=r3=r4,
where 01, 02, 03 and 04 are fractions of catalyst surface; the sites with the ability to adsorb atom oxygen, the sites with two near arranged adsorbed atom oxygen on different exchange cations and the sites with adsorbed moleculles of cyclohexane.
0 4 —
къ 01 P(-4
кл
01 =■
к3 PC6H12
к1 PO
л/07
0 2 =
к 3 PC6H
к 2 Po2
~ л/03 , 01 + 02 +03 +04 = 1
кз pc6h12 л . _к— 3
(
к PC6H12 + 1к3 PC6H12
кг P
O2
к 2 PO2
л/ёТ -1=о.
Assuming
к3 PC6H12
к
— A.
V
к3 PC6H12
+
к1^2 \
к3 PC6H12
к 2 PO2
= 5.
03 =х2, = x, Ax2+Bx-1 =0,
we'el receive
x — ■
- В + л/5 z + 4 A
2 A
03 = x2 =•
- В + л/ В 2 + 4 A
2 A
Then, the equation of rate of the
formation 1,3-cyclohexadiene appears as
r — r1 и — ко Pc и C6H8 3 C6H12
- В + л/ в 2 + 4 A
2 A
(1)
r rC6H8 k3 PC6H12 '
k3 PC6HU + |k3PC6H12
k,P,
i1 O2
k о P.-, 2 O2 y
k 3 PC6Hi2
+
+ ■
3 PC6Hi^ k 3 PC6Hi2 k1 PO2 V k2 PO2
+ 4
k 3 PC6Hi2
k 3 PC6Hi2
(2)
Stage scheme of mechanism of oxidative dehydrogenation of cyclohexane into benzene on the above-mentioned active centers may be presented as
2
2
к
4
2
2
к
4
к
4
2
O2+2Z3
O2+2Z4
O2+2Z5
2Z3O
2Z4O
-»2Z5O
k
(Z3Ü+Z4O+Z5O)+C6H12-> (Z3O+Z4O+Z5O)C6H
(Z3O+Z4O+Z5O)C6Hj2 C6H6+3H2O+Z3+Z4+Z5
1/2 1/2
1/2 1 1
С,н,:+1т0:=0,а+3н20
Expressions for rates of stages:
n — ь e 2 p
5^5* O9
n = ь e2 p
O9
Vn — kn e 2 P(
7KJ7± O9
r8 = k808PC6H12, r9 = k909,
e5 +e6 +e7 +e8 +e9 = 1,
where e5, e6, e7, e8 and 09 are fractions of catalyst surface; the sites with the ability to adsorb atom oxygen, the sites with three near arranged by adsorbed atom oxygen on different exchange cations and the sites with adsorbed molecules of cyclohexane.
In stationary conditions
Г=Г5=Г6=Г7=Г8=Г9,
л _ k P(C6H12 Q , ö e 9 —-T-e8 e 5 —
k 9
ko P TT 8 C6H12
k5 PO2
e 6 —
k 6 PO2
1
P(C6H12 ^Jq k 7 PO2
ax +bx-1=0,
x — ■
- b + 4b z + 4a
2a
л 2 I - b + 4b2 + 4a e — x —
2a
Then equation of rate of formation benzene will appear as
Г — Vp и — ko Pf тт
- b + 4b
+ V b + 4a 2a
v — Гр ц — koP-i и C6H6 8 C6H12
kP
8 C6H12
k5PO2
k P k P
8 C6H12 , 8 C6H12
i k7Pa2
k6 PO2
kP
8 C6H12
k8 PC6H12
I k5Pa2
k8PC6H12
k6PO2
k8PC6H12
k7 PO2
+4-
kP
^ C6H12 k
kP
8 C6H12 k9
. (3)
Stage scheme of mechanizm of oxidative dehydrogenation of cyclohexane into cyclo-hexene may be presented as
k8 PC6H12 ka
11
k8 PC6H12
k5 PO2
+
k8 PC6H12
k6 PO2
+
+ .
k8 PC6H12
k7 PO2
л/ё8 -1 — 0.
Assuming
k p
1 C6H12
ko
— a
k p
rtoi Л TT 8 C6H12
k5 PO2
+
k P
îVQ JL и 8 C6H12
e8=x2, Vë8
we'll obtain
k 6 PO2
— x,
+
k P
rtûi Л TT 8 C6H12
k 7 PO2
O2+2Z6 2Z6Ü Z6O+C6H12 Z6Ü C6H12 Z6O C6H12 in» C6H10 +H2O +Z6
СбН12+17О2=С6Н10+Н2О
Expressions for rates of stages
1/2 1 1
Гт — k\neinPn„ , Г, — kie,iP^
n — k1 ?e1
'10 O2 , '11 - k11"11 -rc6h12, '9 - k12"12 '
= b , In stationary conditions
'='10='11='12,
where 610, 011 and 012 are fractions of catalyst surface; sites with the ability adsorb atom
2
2
+
+
2
2
2
+
+
+
2
oxygen, sites with atom oxygen and sites adrorbed molecules of cyclohexane
010 +011 +012 - 1>
л _ kn Рс6н12 Q ö 012 --й-011' 01O -
k
12
k11 РСбН12 '011
k10 PO2
k11 РСбН!2
011 +011 +
42
k11 РС
СбН12
k10 PO2
л/07 -1 - 0.
k P
k11 РСбН!2
k]
Assuming
+1 - с,
12 - X,
k11 РСбН12
k10 PO2
- d, 011=x
we'll obtaine cx +dX-1=0,
x-■
d +
+ 4c
2c
л 2 I - d Wd2 + 4c 011 - x -
r - r,
СбН10
- k11 РС
- d +
yfd2
+ 4c
СбН12
2c
r - ГСбНю - к11РС,
бН12
к11РСбН12
k10 PO2
k1 1p
- +
11J СбН12 k12
+1
+
2
( k P >
11 СбН12_|_2
k
12
(4)
2c
Then equation of formation rate of cyclohexene appears as
The results of experimental investigation of kinetic regularities of the reaction of oxidative dehydrogenation of cyclohexane over metal-zeolite catalyst CL-CuCrCoZn are given in Table 3. Kinetic tests were performed in the range of temperature, 320-3800C, at space velocity of 500-3000 h-1, partial pressure of reagents, Pc H =0.05-0.14 atm, PQ =0.07-
0.25 atm.
1
2
2
>
2
Table 3. The results of kinetic runs
Partial pressure of reagents, atm Space velocity, V, h-1 Temperature, T, 0С ^^ereion, X, % Yields of products of reaction, A, %
P РСбН12 PO2 СбН10 СбН8 СбНб СбН10°Н Ш2
0.12 0.07 2000 320 22.2 4.б 2.1 1.4 0.7 0.1
0.12 0.07 2000 340 10.9 2.7 5.9 1.8 0.3 0.2
0.12 0.07 2000 380 19.б 1.б 12.2 2.8 1.4 1.б
0.12 0.14 2000 340 23.2 4.3 11.7 4.3 1.1 1.8
0.12 0.25 2000 340 31.8 5.2 13.3 б.9 3.2 3.2
0.12 0.09 2000 380 28.б 1.8 17.1 4.1 2.5 3.1
0.05 0.18 2000 380 47.5 1б.5 1.2 0.5 5.4 2.9
0.12 0.25 2000 380 44.8 2.8 23.3 7.2 4.4 7.1
0.05 0.14 2000 340 27.1 0.8 4.1 б.5 б.8 8.9
0.10 0.14 2000 340 24.б 3.4 9.9 5.3 2.5 3.5
0.12 0.14 2000 340 23.2 4.3 11.7 4.3 1.1 1.8
0.14 0.07 2000 3б0 15.б 2.3 9.б 2.2 0.8 0.7
0.25 0.17 2000 3б0 38.8 3.8 20.2 7.5 2.9 4.4
0.3 0.25 2000 3б0 47.б 4.5 21.5 10.б 5.4 5.б
0.12 0.14 500 380 47.5 0.2 12.2 13.7 10.5 10.9
0.12 0.14 1000 380 4б.4 1.9 21.1 8.2 7.1 8.1
0.12 0.14 2500 320 12.5 5.8 4.1 1.2 0.5 0.9
0.12 0.14 3000 340 20.9 5.7 12.4 1.5 0.б 0.7
0.12 0.14 3000 3б0 31.7 4.9 19.8 3.3 1.5 2.2
Assuming that carbon dioxide is formed as a result of interaction of adsorbed molecules; cyclohexane, cyclohexene and 1,3-cyclohexa-diene with adsorbed molecules of oxygen and formation of cyclohexanol proceeds at interaction of adsorbed molecules of cyclohexene with adsorbed molecules of water it can be written the following kinetic equations corresponding to these mechanisms
i
to,
rCO, =
_k1K1 P1K6P2_
1+KiPi +JK2P+K3P3 + K4P4 + K5P5 + K6?2 J2
k14K3 P3K6P2
rCO2
(1+K1P1 +Jk2P2 + K3P3 + K4P4 + K5P5 + KP J2 ' k15K4 P4K6P2
(1 + K1P1 +i
1
r
rC6HnOH
+J K2P2 + K3P3 + K4P4 + K5P5 + K6P2
_k16K3 P3P6_
(1 + K1P1 ^VK2PT + K3P3 + K 4P4 + K5P5 + K P2 )
r
(5)
(6)
(7)
, (8)
Thus we can suppose the following kinetic scheme of proceeding of reaction of oxidative dehydrogenation of cyclohexane over above mentioned metal-zeolite catalyst:
rC6H10 - rC6H10 rCO2 r<16HnOH,
r<C6H8 r<C6H8 r<CO2
r
C6H6 - rC6H6 ,
_ 1 2
rnrt„ — rnr\„ + rnr\„ + ri
'CO
'CO
CO 9
COn
r C6H11OH— rC6H11OH .
(9)
(10) (11) (12) (13)
Equations (9)-(13) make up the kinetic model of the considered reaction.
Similar investigation was carried out for reaction of oxidative dehydrogenation of methyl cyclohexane into 1-methyl-1,3-cyclo-hexadiene. On the basis of experimental data kinetic scheme of the reaction has been established.
£11
C6H11-CH3
C6H9—CH3
+ -°2' - H2O
C6H7—CH3
+-o2, - 2h2o
+ -O2, - 3H2O
O
»C6H7-CH3 5 H O
■>7CO2
o
O
2,
-H
t
C6H1
£16.
k11 ^ ^<H2O ^ C6H10 '
XeHnOH
+ ~°2' - H2O
C6H8
+ -o2, - 2h2o
C6H6
+ -O2, - 3H2O
<-13
■»6CO2
1
The kinetic model of the reaction is form
'C7H12 — £11PC
c7h,
k11PC
C7H14 k10 PO2
k11PC
- +
k
+1
12
+
k11PC
k
12
3
3
k
3
k
8
k
3
k
3
2
k
8
2
+ 9O2, - 6H2O
>
2
r,
1 = kPr
C7H10
3 C7H14
k P
k31 C7H14
k1 PO2
+
k P
k31 C7H14
k2 1 O2
k P
k 31 C7H14 k
^C7H10 rC7H10 rC°2 ,
■ + rC7H8 = rC7H8 :
rCO2 = rCO2 + rCO2 + rCO2
k P
k 31 C7H14
ki P
+
O2
£ p
k 31 C7H14
+ ■
k 21O2 y
+ 4
£ P
k 31 C7H14
k P
k 31 C7H14 k
rCyH8 = VcyH^ <
/
\
k8PC7H1, VcyHM k8PC7H14
8 C7H14 kn
tt /ko-^P TT |koP-< U
I 8 C7H14 + 8 C7H14 + I 8 C7H14
k5PO
k6PO
k7PO
+ 4-
kP
8 C7H14 k0
kP
8 C7H14 k0
faK P1K6 P2
co,
'co,
(1+K1P1 +K3P3 + K4P4+K5P5 + K6P2 f
_k14 k3 p3 k6 p2_
(1+kjpj +jep+k3 p3 + k4p4 + k5 p5 + k 6 p2):
3 _k15 k 4 p4 k 6 p2_
r =-
CO2 (1+K1P1 +JKP+k3p3 + k4p4 + k5p5 + k6p2 )2
rC7H12 rC7H12 rCO2
(14)
(16) (17)
Equations (14)-(17) present the kinetic model of the reaction of oxidative dehydro-genation of methyl cyclohexane over CL-CoCr catalyst. Here Ki - the adsorption equi-
Qi
librium constants ( Kt = K° • eRT ), kt - the
reaction rate constants (k = k° • e RT ), P,
E RT
partial pressure of i-component (Pi
Z »
P)
The results of investigation of kinetic regularities of the reaction are given in Table 4.
Both models, (9)-(13) and (14)-(17) have been subjected to statistical analysis on the basis of the data of Tables 3 and 4 separately. The objective function was
(x )=Z
N C A - A \
exp cal
A
exp
where X - signifies the set of parameters of the considered model. The kinetic parameters obtained for the two models are presented in Table 5. According to these results, the models satisfactorily describe the experimental data of the reactions.
Thus, the kinetic method supports an existence on the surface of the metal-zeolite catalysts for reaction of oxidative dehydro-genation of cyclohexane into 1,3-cyclohexa-diene and methyl cyclohexane into 1-methyl-1,3-cyclohexadiene the different active centers consisted of above mentioned group of exchange cations which responsible for formation of the products of reactions.
2
2
2
>
n
+
2
2
2
2
+
2
2
A3EPEAH#^AHCKHH XHMHHECKHH ^YPHAH № 3 2016
Table 4. The result of kinetic runs
Partial pressure of reagents, atm Space velocity, V, h-1 Temperature, T, 0C Conversion, X, % Yields of products of reaction, A, %
PC7Hi4 PO2 C6H9CH3 C6H7CH3 C6H5CH3 CO2
0.11 0.04 2000 340 11.4 4.2 2.2 3.8 0.06
0.11 0.09 2000 340 36.3 4.4 4.5 5.9 0.2
0.11 0.14 2000 340 44.8 4.5 6.9 7.2 0.4
0.11 0.14 2000 360 49.9 6.02 9.9 10.4 0.6
0.11 0.20 2000 360 22.6 5.9 13.6 11.8 1.1
0.17 0.14 2000 320 35.1 4.5 4.8 4.8 0.2
0.25 0.14 2000 320 48.4 4.5 3.7 3.6 0.1
0.17 0.14 2000 360 30.8 8.0 10.8 7.8 4.2
0.25 0.14 2000 360 27.4 8.7 8.5 6.9 3.3
0.17 0.14 2000 380 43.2 9.1 15.5 10.3 8.2
0.25 0.14 2000 380 39.1 9.9 12.8 10.2 6.2
0.11 0.14 2500 340 21.2 4.4 6.5 7.0 3.3
0.11 0.14 2500 380 46.6 7.2 15.7 12.2 11.5
0.11 0.14 3000 360 31.7 10.1 11.3 6.1 4.2
0.11 0.14 3000 380 43.7 12.0 15.9 9.6 6.2
Table 5. The kinetic parameters of the kinetic models
For kinetic model of reaction of oxidative dehydrogenation of cyclohexane For kinetic model of reaction of oxidative dehydrogenation of methyl cyclohexane
ln kf (ln k0 ) E, (Q,), kcal/mole ln k0 (ln K ) E, (0,), kcal/mole
ln k 0 15.71 E1 8.30 ln k 0 40.93 E1 7.84
ln k 0 4.56 E2 11.0 ln k 0 7.06 E 2 14.62
ln k30 -0.16 E3 10.99 ln k 30 11.44 E3 2.25
ln k 0 -2.63 E4 6.73 ln k 0 26.20 E 4 4.17
ln kf 7.10 E5 4.46 ln k 0 11.70 E5 15.00
ln k60 11.9 E6 6.06 ln k60 27.97 E6 11.07
ln k 0 29.72 E7 7.67 ln k70 8.63 E7 14.74
ln k80 3.93 E8 4.00 ln k80 24.41 e8 2.37
ln k9° -2.39 E9 3.99 ln k9° 5.81 e9 14.54
ln C 12.44 E10 8.39 ln kfe 9.43 E10 13.04
ln k0 16.37 E11 4.00 ln k^ 5.70 E11 13.09
ln k°2 6.94 E12 7.37 ln 4 16.16 E12 10.18
ln £0 20.86 E13 35.15 ln k^ 22.0 E13 32.15
ln k04 -10.51 E14 39.79 ln k^ -9.2 E14 35.49
ln k° 41.52 E15 21.55 ln k°5 42.5 E15 20.09
ln k106 23.17 E16 17.82 - - - -
ln K ° 23.16 Q1 2.49 ln K ° 20.1 01 2.00
ln K 0 1.02 02 11.00 ln K 20 0.99 02 10.12
ln K3° 8.75 03 8.57 ln K3° 7.81 03 7.85
ln K 40 6.84 04 11.00 ln K 40 7.04 04 9.81
ln K 0 25.48 05 3.19 ln k 0 26.11 05 2.72
ln K 60 3.027 06 2.49 ln K 60 3.24 06 1.99
References
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2. Миначев Х.М., Исаков Я.И. Металлсодержащие цеолиты в катализе. М.: Наука, 1976. 111 с.
3. Алиев А.М., Микаилов Р.З., Гасанов Э.А., Агаева Р.Ю. Гетерогенизация каталитической системы PdCl2/CuCl2 для синтеза МЭК из бутиленов // Азерб. хим. журн. 2004. № 1. С. 10-14.
4. Shakhtakhtinsky T.N., Aliyev A.M., Kuliyev A.R., Kasamansky V.P. Selection of Palladium and Copper Containing Zeolite Catalyst for Oxidation of Ethylene. In the proceedings of the 6th American-Soviet symposium on chemical catalysis. USA. New Jersey, June. 1979. P. 143.
5. Шахтахтинский Т.Н., Алиев А.М., Кулиев А.Р., Меджидова С.М., Матиев К.И., Мурадов М.Х., Касум-заде А.Ю. Подбор активного катализатора и кинетика реакции парциального окисления изо-амилового спирта // Кинетика и катализ. 1996. Т. 37. № 2. С. 286-293.
6. Алиханова З.А., Алиев А.М., Сарыджанов А.А., Бахманов М.Ф. Кинетика окислительного дегидрирования изобутилового спирта на биметаллцео-литном катализаторе CuPdNaY // Изв. Вуюв. Химия и хим. технология. 2009. № 11. С. 106-110.
7. Aliyev A.M., Shabanova Z.A., Aliyev F.V. Oxidative dehydrogenation of hydrocarbons and the partial oxidation of aliphatic alcohols on modified zeolites // European Applied Sciences. 2015. № 5. P. 67-79.
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литных катализаторах // Нефтепереработка и нефтехимия. 2013. № 5. C. 27-31.
9. Алиев А.М., Шабанова З.А., Наджаф-Кулиев У.М. Исследование кинетических закономерностей реакции окислительного дегидрирования циклогексана на модифицированном клиноптилолите // Хим. пром-сть. 2014. № 3. С. 109-112.
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15. Armbruster Th. Dehydration mechanism of clinoptilolite and heulandite; single-crystal X-ray study of Na-poor, Ca-, K-, Mg-rich clinoptilolite at 100 K // Am. Maner. 1993. V. 78. P. 260-264.
16. Jhonson M., O'Connor D., Barnes P. Cation exchange, Dehydration, and Calculation in Clinoptilolite: in Situ X-ray Diffraction and Computer Modeling // J. Phys. Chem. 2003. V. B107. P. 942-951.
NAFTENLORÍN OKSÍDLO§DÍRÍCÍ DEHÍDROGENLO§MO REAKSÍYALARINDA
METAL-SEOLÍTLORÍN TOTBÍQÍ
A.M.Oliyev, Z.A.§abanova, A.LKarimov, M.F.Bahmanov, F.V.Oliyev, Ü.M.Nacaf-Quluyev
ion mübadila üsulu ils sintez olunmu§ klinoptilolit (KL) {Cu2+ (0.5 küt.%), Zn2+ (0.2 küt.%), Со2+ (0.1 küt.%), Cr3+ (0.1 küt.%)} va KL {Co2+ (0.5 küt.%), Cr3+ (0.25 küt.%)} katalizatorlarimn uygun olaraq tsikloheksanin 1,3-tsikloheksadiem va metiltsikloheksanin 1-metil-1,3-tsikloheksadiena oksidla§dirici dehidrogenla§ma reaksiyalarinda tatbiqinin mümkünlüyü müayyan olunmu§dur. Tacrübi malumatlarin tahlili va dissosiativ adsorbsiya olunmu§ oksigen ila mübadila kationlarin rabita enerjilarini nazara almaqla katalizatorun komponentlarindan ibarat aktiv markazlar qrupla§dmlmi¡j va reaksiya yollari aydinla¡jdinlmi¡jdir. Bu aktiv markazlarin nazara alinmasi ila i§lanib hazirlanmi§ kinetik model taqdim olunmu§dur.
Agar sözlar: tsikloheksan, 1,3-tsikloheksadien, metiltsikloheksan, 1-metil-1,3-tsikloheksadien.
ИСПОЛЬЗОВАНИЕ МЕТАЛЛ-ЦЕОЛИТОВ В КАЧЕСТВЕ КАТАЛИЗАТОРОВ В РЕАКЦИЯХ ОКИСЛИТЕЛЬНОГО ДЕГИДРИРОВАНИЯ НАФТЕНОВ
А.М.Алиев, З.А.Шабанова, А.И.Керимов, М.Ф.Бахманов, Ф.В.Алиев, У.М.Наджаф-Кулиев
Установлена возможность использования гетерогенных катализаторов: клиноптилолит (Кл) {Cu2+ (0.5 мас.%), Zn2+ (0.2 мас.%), Со2+ (0.1 мас.%), Cr3+ (0.1 мас.%)} и Кл. {Co2+ (0.5 мас.%), Cr3+ (0.25 мас.%)}, полученных методом ионного обмена в реакции окислительного дегидрирования циклогексана в 1,3-циклогексадиен и ме-тилциклогексана в 1-метил-1,3-циклогексадиен соответственно. На основе анализа экспериментальных данных и с учетом энергий связи обменных катионов с диссоциативно адсорбированным кислородом были сгруппированы активные центры, состоящие из компонентов катализатора, и выяснены реакционные пути. Представлены кинетические модели, разработанные с учетом этих активных центров.
Ключевые слова: циклогексан, 1,3-циклогексадиен, метилциклогексан, 1-метил-1,3-циклогексадиен.
