The oxidative dehydrogenation of 4-vinylcyclohexene in the presence of modified Ga, Pt-pentasils

Article abstract of DOI:10.1134/S0965544110020076

The oxidative dehydrogenation reaction of 4-vinylcyclohexene (4-VCH) in the presence of a pentasil zeolite (TsVM) modified by platinum, gallium, gadolinium, and potassium was investigated. The influence of the nature of the modifiers on the progression of

Full text of DOI:10.1134/S0965544110020076

ISSN 0965ꢀ5441, Petroleum Chemistry, 2010, Vol. 50, No. 2, pp. 124–128. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © Kh.M. Alimardanov, A.A. Alieva, S.I. Abasov, 2010, published in Neftekhimiya, 2010, Vol. 50, No. 2, pp. 120–124.
The Oxidative Dehydrogenation of 4ꢀVinylcyclohexene
in the Presence of Modified Ga, PtꢀPentasils
Kh. M. Alimardanov, A. A. Alieva, and S. I. Abasov
Institute of Petrochemical Processes, National Academy of Sciences of Azerbaijan, Baku, Azerbaijan
eꢀmail: hafizalimardanov@yahoo.com
Received July 6, 2009
Abstract—The oxidative dehydrogenation reaction of 4ꢀvinylcyclohexene (4ꢀVCH) in the presence of a penꢀ
tasil zeolite (TsVM) modified by platinum, gallium, gadolinium, and potassium was investigated. The influꢀ
ence of the nature of the modifiers on the progression of the reaction and the yields of the desired product,
ethylbenzene and styrene, was established. It was found that the conversion of 4ꢀVCH into ethylbenzene and
styrene proceeds along two parallel routes, the oxidative dehydroisomerization and dehydrogenation of the
reactant hydrocarbon. Conditions for the maximal yield of styrene on potassium hydroxide–promoted
Pt,Ga,Gd/HNa ⎯ TsVM were determined.
DOI: 10.1134/S0965544110020076
The dehydrogenation of hydrocarbons in the presꢀ anism of the reaction; to consider the influence of varꢀ
ence of various hydrogen acceptors has been extenꢀ ious parameters and individual components formed in
sively developed in recent years [1–3]. Research in this the reaction on the selective conversion of 4ꢀVCH;
area has focused on the problem of the preparation of and, hence, to find the optimal conditions for the synꢀ
C4 and C5 unsaturated aliphatic hydrocarbons and alkꢀ thesis of the desired product.
enylarenes (styrene and its methyl derivatives). Among
the traditional methods used for the dehydrogenation
of benzene and its derivatives, alkenylated aromatic
compounds are prepared in some cases via the reacꢀ
tion of ethylbenzene hydroperoxide with propylene
followed by the dehydration of the resulting methyl
phenyl carbinol [4, 5] or via the alkylation of toluene
and other alkylꢀ and alkenylbenzenes with С1–С3
monohydric alcohols in the presence of various zeolite
catalysts [6–9]. A commercially more available
and less expensive feedstock is used in the latter
case as compared to the conventional styrene manuꢀ
facture process according to the scheme: toluene
Earlier, we have shown [18] the feasibility of the
simultaneous preparation of ethylbenzene and styrene
by the oxidative dehydrogenation of 4ꢀVCH in the
presence of some rareꢀearth elements and alkali metꢀ
als (potassium) of iron oxide–modified natural cliꢀ
noptilolite or synthetic mordenite.
This work was devoted to the investigation of the
catalytic transformation of 4ꢀVCH in the presence of
pentasil zeolite modified with platinum metal, galꢀ
lium, and gadolinium oxides; the influence of
admixed byproducts of the reaction on the selectivity
of the process was also studied.
benzene
As shown by published data, the styrene synthesis
according to the scheme butadieneꢀ1,3 4ꢀvinylcyꢀ
clohexene styrene is of great practical importance
as well. Its value is due to both the presence of a conꢀ
siderable source of butadieneꢀ1,3 available with the С4
pyrolysis fraction [10, 11] and the ease of its converꢀ
sion into 4ꢀvinylcyclohexene (4ꢀVCH) [12, 13].
In a number of studies devoted to the dehydrogenaꢀ
tion of 4ꢀVCH, high yields of ethylbenzene and only
traces of styrene have been obtained [14, 15]. At the
same time, some processes for the oxidative dehydroꢀ
genation of 4ꢀVCH into styrene have been patented
[16, 17].
ethylbenzene
styrene.
EXPERIMENTAL
The reactant hydrocarbon 4ꢀvinylcyclohexene was
prepared by the dimerization of butadieneꢀ1,3 and the
sharp rectification of the dimer fraction. The following
hydrocarbons were also used in the work: ethylbenꢀ
zene, styrene, ethylcyclohexane, vinylcyclohexane,
and ethylcyclohexene isomers whose purity was deterꢀ
mined by GLC. The physicochemical characteristics
of the aforementioned hydrocarbons were in good
agreement with the published data [19].
The metalꢀcontaining pentasil samples were preꢀ
pared from the HNa−TsVM zeolite (manufactured by
VNIINP) having the ZSMꢀ5 structure (SiO2/Al2O3 =
30) according to the following procedures:
However, the nonsystematic and controversial
character of the investigations in this area does not
(1) joint impregnation of the zeolite matrix with an
make it possible to reveal the general trends and mechꢀ aqueous solution of a mixture of gallium nitrate, gadꢀ
124

THE OXIDATIVE DEHYDROGENATION OF 4ꢀVINYLCYCLOHEXENE
125
olinium nitrate, and ammonium hexachloroplatinate in the oxidation mode. They are characterized by the
followed by their thermal decomposition at 450– most optimal combination of oxidation–reduction
500°С;
and acid–base properties.
(2) successive impregnation of HNaꢀTsVM in indiꢀ
vidual solutions of the relevant salts followed by their
The highest activity in the dehydrogenation of
4ꢀVCH is displayed by the Pt,Ga,Gd/HNaꢀTsVM and
Ga,Gd/HNaꢀTsVM samples prepared according to
procedures 1 and 2, which are characterized by a
higher dispersion of the modifying additives and a
higher stability.
thermal treatment at 500–550
°С
after impregnation
with each individual solution [20];
(3) cation exchange of Na+ ions for Меn ions at
pH 5–6.5 according to the procedure [21]; or
(4) mechanical mixing of gallium oxide, gadolinꢀ
ium oxide, and ammonium hexachloroplatinate with
HNaꢀTsVM.
+
Both the level and selectivity of the 4ꢀVCH converꢀ
sion depend largely on their preparation procedure,
the ratio between the concentrations of the modifiers,
and the reaction temperature (Tables 1, 2). As can be
seen from Table 1, quite high yields of ethylbenzene
and styrene are reached in the presence of the sample
containing 3.0 wt % Ga2O3, 2.0 wt % Gd2O3, and
0.5 wt % Pt. The products obtained in this sample
contain, along with ethylbenzene and styrene, some
amount of the 4ꢀVCH isomerization and disproporꢀ
tionation products whose yield decreases with increasꢀ
ing the temperature (Table 2). These data suggest that
the catalyst surface is modified by the formed comꢀ
pounds and condensation products.
Before use, the catalysts granulated by alumina
hydrogel taken in the amount of 30 wt % (particle size,
0.5–1.5 mm) were activated during 2–3 h at 500°С in
an air flow. The experiments were carried out in a
fusedꢀsilica flow reactor with a fixed catalyst bed in the
temperature range from 250 to 520
0.1 MPa. The products were analyzed by GLC on a
2.4 m 6ꢀmm column packed with 10 wt % SEꢀ30 silꢀ
icone elastomer–coated Chromosorb W (Tcol
140 C, vap = 180 C) or 5 wt % bisꢀ(2ꢀcyanoethyl)sulꢀ
fideꢀcoated Chromaton NꢀAWꢀHNDS (Tcol = 80 C,
vap = 170 C) using nitrogen as the carrier gas.
°C at a pressure of
×
=
°
T
°
°
T
°
It is known that the formation of coke deposits durꢀ
ing the catalytic conversion of hydrocarbons over
modified forms of TsVM is mediated mainly by their
strong acid sites responsible for the hydrogenꢀatom
redistribution and arene dealkylation reactions [21].
Therefore, the blocking of these sites by condensation
products leads to a decrease in the yield of benzene
and toluene, however, the yield of ethylbenzene and
styrene remains almost at the previous level.
RESULTS AND DISCUSSION
The NaꢀTsVM zeolite at 300–500 С displays
almost no activity in the dehydrogenation of 4ꢀVCH.
The partial substitution of Na+ cations for NH4+ and
the subsequent highꢀtemperature treatment of the
resulting samples at 500–550°C lead to the formation
°
of active centers responsible for the isomerization of
the initial hydrocarbon. The isomerization of 4ꢀVCH
in the presence of HNaꢀTsVM in the temperature
To determine the influence of the individual comꢀ
ponents of the reaction mixture on the catalyst activity
and selectivity for styrene, the transformation of
binary mixtures of 4ꢀVCH with some hydrocarbons
which are contained in the liquid reaction products
has been studied (Figs. 1a–1d). It has been found that
the introduction of an additional amount of styrene
into the reaction zone increases the amount of ethylꢀ
benzene in the products. It is likely that the dehydroꢀ
genation of 4ꢀVCH over the given temperature range is
accompanied by the coupled hydrogenation process,
and ethylbenzene in all of the experiments is formed
with higher yields as compared to styrene. The presꢀ
ence of some amount of ethylꢀ and vinylcyclohexane
in the products of the conversion of 4ꢀVCH per se in
range of 250–350°С results in the migration of the
multiple bond from the vinyl group to the cyclohexene
moiety in order to form a conjugated diene system.
The products of 4ꢀVCH disproportionation and dehyꢀ
drogenation on this catalyst are detected only at higher
temperatures (400–450°С). Although the yield of the
products is insignificant, the maximal amount of aroꢀ
matic hydrocarbons (15.7% of ethylcyclohexene) is
contained in the products of the reaction run at 450°C
over the HNaꢀTsVM with a degree of Na+ exchange of
75 wt %. The use of oxygen as an oxidant (4ꢀVCH :
О2 = 1 : 0.2) has almost no effect on the isomerization
and dehydrogenation activity of HNaꢀTsVM.
the temperature range of 350–400°С (Table 2) proꢀ
The introduction of platinum and the Ga and Gd vides indirect evidence for this assumption. Therefore,
cations into HNaꢀTsVM leads to a dramatic increase 4ꢀVCH adsorbed on the surface can partially act as a
in the catalyst activity towards dehydrogenation. It is hydrogen acceptor (along with the nucleophilic oxyꢀ
known that Gaꢀ and PtGaꢀpentasils exhibit high gen of the catalyst surface) in the dehydrogenation
activity in the dehydrogenation and aromatization of process. The addition of ethylꢀ and vinylcyclohexane
С2–С4 saturated hydrocarbons [22–26] and in the into the starting 4ꢀVCH at 485°С contributes mainly to
dehydroalkylation of naphthenes [27]. The results of an increase in the yield of the dehydrodealkylation
our investigations have shown that the ternary system products—benzene and toluene; however, the yield of
Pt,Ga,Gd/HNaꢀTsVM with various contents of the ethylbenzene and styrene on a converted 4ꢀVCH basis
active components display a particularly high activity remains almost unchanged.
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126
ALIMARDANOV et al.
Table 1. Influence of the mass ratio of modifiers supported on 0.75 HNaꢀTsVM on the yield of 4ꢀVCH oxidative dehydrogenaꢀ
tion products (T = 470°C, V4ꢀVCH = 1 h–1, 4ꢀVCH : O2 molar ratio = 1 : 0.3)
+
Men , wt %
Yield, %
of gas
Yield
Yield
of ethylbenzene, % of styrene, %
of liquid
products
Ga3+
Gd3+
Pt
of coke
1.0
1.0
2.0
2.0
3.0
3.0
3.0
3.0
0.5
0.5
0.5
0.5
0.5
1.0
2.0
2.0
–
92.3
93.0
90.5
90.4
91.1
91.6
93.8
92.4
5.6
5.0
7.0
7.5
7.1
6.2
4.7
5.8
2.1
2.0
2.5
2.1
1.8
2.2
1.5
1.8
10.8
26.4
31.8
35.2
37.9
38.6
40.2
32.5
2.5
4.2
0.3
0.3
0.5
0.5
0.5
0.5
–
12.4
15.1
17.5
17.8
19.6
14.0
Table 2. Influence of the temperature and space velocity on the composition and yield of 4ꢀVCH oxidative dehydrogenation
products (catalyst 3% Ga2O3, 2% Gd2O3, 0.5% Pt/0.75 HNaꢀTsVM)
Liquid products, wt %
Yield
Yield
V
4ꢀVCH
,
T, °C
of ethylbenꢀ of styrene,
zene, %
C6–C8
cycloalꢀ
kanes
benzene,
4ꢀVCH toluene,
xylenes =
h–1
ethylcycloꢀ ethylidenecyꢀ
ethylbenꢀ
zene
%
styrene
hexene
*
clohexene**
370
400
450
470
485
500
520
485
485
485
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.5
2.0
3.0
3.6
2.1
1.0
0.8
–
4.2
3.8
5.1
5.4
2.1
1.0
2.1
2.5
2.0
1.6
14.5
15.6
16.1
13.4
7.2
49.5
40.1
21.8
10.9
9.2
3.0
6.1
5.7
5.8
5.0
3.9
7.7
6.4
3.8
3.9
20.0
23.3
37.3
42.8
52.1
54.8
48.9
52.8
31.1
23.0
5.2
9.0
18.0
20.8
32.5
40.2
44.8
45.7
40.2
45.0
27.4
20.6
4.6
8.0
13.0
20.9
24.4
29.6
26.2
27.9
13.7
10.7
11.3
19.6
21.0
24.7
27.4
23.8
12.1
9.3
–
4.4
6.3
–
4.8
10.3
7.5
–
2.9
–
13.6
16.1
35.8
44.7
–
Notes: * Together with vinylcyclohexane.
** Together with ethylcyclohexadiene isomers.
It is known that the hydrogenation of hydrocarbons proceeds only as the double bond migration and leads
to ethylcyclohexadiene or ethylidenecyclohexene isoꢀ
mers, which are readily dehydrogenated into ethylꢀ
benzene.
in the presence of solid catalysts involves nucleophilic
surface oxygen (base sites), whereas the isomerization
(or disproportionation) occurs on Lewis and Broenꢀ
sted acid sites [28]. The isomerization of 4ꢀVCH in the
The comparison of the data of Table 2 shows that
one of the main factors affecting the yield of ethylbenꢀ
presence of the acid sites of Pt,Ga,Gd/HNa−TsVM, as
in the case of the unmodified HNaꢀzeolite catalyst, zene and styrene, along with the acid–base and oxidaꢀ
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THE OXIDATIVE DEHYDROGENATION OF 4ꢀVINYLCYCLOHEXENE
(а) (b)
127
120
110
100
90
70
60
50
40
30
20
10
45
40
35
30
25
20
15
10
5
95
90
85
80
75
70
65
60
55
6
1
6
8
4
8
4
80
5
7
70
3
2
5
3
60
7
2
1
0
1 : 1
2 : 1 3 : 1 4 : 1 5 : 1
0
1 : 1
2 : 1
3 1
4 : 1
5 : 1
4ꢀVCH : ECH molar ratio
4ꢀVCH : EB molar ratio
(c)
(d)
60
50
40
30
20
10
110
100
90
50
40
30
20
10
100
90
80
70
60
6
6
8
8
80
7
7
2
4
70
4
5
2
1
60
3
3
1
5
0
1 : 1
2 : 1 3 : 1 4 : 1 5 : 1
0
1 : 1
2 : 1
3 : 1
4 : 1
5 : 1
4ꢀVCH : ECHE molar ratio
4ꢀVCH: VCHA molar ratio
Fig. 1. Catalytic transformation of a binary mixture of 4ꢀvinylcyclohexene (4ꢀVCH) with (a) ethylcyclohexane (ECH), (b) ethꢀ
ylbenzene (EB), (c) ethylcyclohexene (ECHE), and (d) vinylcyclohexane (VCHA) in the presence of Pt,Ga,Gd/HNa TsVM:
) C C cycloalkanes; ( ) vinylcyclohexane and ethylcyclohexene isomers; ( ) ethylidenecyclohexene and ethylcyclohexadiꢀ
) benzene, toluene, and xylene isomers; ( ) ethylbenzene; ( ) styrene; and ( ) the conversion of 4ꢀVCH.
⎯
6⎯
8
(
1
2
3
ene isomers; (
4
) 4ꢀVCH; (
5
6
7
8
tion–reduction properties of the catalyst, is the reacꢀ increases. At the same time, the conversion of 4ꢀVCH
tion temperature. The highest yields of these hydroꢀ
carbons are reached at 470–485 . It should be
pointed out that the yields of ethylbenzene and styrene
at 500 are 45.7 and 24.7%, respectively; however,
the reaction selectivity is considerably less as comꢀ
pared to the data obtained at 470–485
on the catalyst samples promoted with 0.3–1.0 wt %
KOH remains almost at the previous level. Therefore,
these samples catalyze, along with the above transforꢀ
mation, the direct dehydrogenation of 4ꢀVCH into
styrene, omitting the steps of double bond migration
from the vinyl group to the sixꢀmembered ring. Howꢀ
ever, with an increase in the amount of KOH from 1.0
to 2.0 wt %, the conversion of 4ꢀVCH decreases.
°
С
°С
°С.
The predominance of ethylbenzene in the catalysis
product indicates that the reaction proceeds via the
following consecutive steps:
Thus, the transformation of 4ꢀVCH over the above
heterogeneous catalysts proceeds via two parallel
routes. In the presence of Pt,Ga,Gd/HNaꢀTsVM, the
oxidative dehydroisomerization of 4ꢀVCH into ethylꢀ
benzene and styrene prevails with the former product
prevailing (molar ratio 2–2.5 : 1), and the sample proꢀ
moted with potassium hydroxide mainly catalyzes the
dehydrogenation of 4ꢀVCH to form equal amounts of
4ꢀVCH
ethylcyclohexadiene
ethylidenecyclohexene + isomers of
ethylbenzene styrene.
To lower the isomerizing activity of
Pt,Ga,Gd/HNaꢀTsVM, a certain amount (0.3–2.0 wt %)
of potassium hydroxide was additionally introduced
into the catalyst (Fig. 2). As seen from the figure, in
the presence of potassium hydroxide–promoted cataꢀ
lysts, the ethylbenzene : styrene ratio is changed in
favor of the latter; i.e., the selectivity for styrene ethylbenzene and styrene (molar ratio 1–1.2 : 1).
PETROLEUM CHEMISTRY Vol. 50
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128
ALIMARDANOV et al.
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Yield, %
60
G. L. Avrekh, Processing of Liquid Pyrolysis Products
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50
1
12. T. P. Cheung and M. M. Johnson, US Patent
No. 5625101 (1997).
40
1
1
13. R. W. Diesen, K. A. Burdett, R. S. Dixit, et al., US
Patent No. 5329057 (1994).
30
20
10
0
1
2
1
2
2
2
14. C. S. Davis, US Patent No. 5312180(1994).
2
15. G. Ruckelshauss and K. Kosswig, Chem. Zig. 101, 103
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I
II
III
IV
V
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Fig. 2. Dehydrogenation of 4ꢀVCH over Pt,Ga,Gd/HNaꢀ
TsVM ( = 481°C, 4ꢀVCH : O molar ratio = 1 : 0.3) (I)
unpromoted and promoted with (II) 0.3 KOH, (III) 0.75,
(IV) 1.5, and (V) 2 wt % potassium hydroxide: ( ) ethylꢀ
benzene and ( ) styrene.
T
2
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1
2
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