�� �
Dehydrogenation of ethane over gallium oxide in the presence of carbon
dioxide
Kiyoharu Nakagawa,a,b Masato Okamura, Naoki Ikenaga, Toshimitsu Suzuki*a,b† and Tetsuhiko Kobayashic
a
a
a
Department of Chemical Engineering, Faculty of Engineering, and
High Technology Research Center, Kansai University, Suita, Osaka, 564-8680, Japan
Osaka National Research Institute, AIST, MITI, Ikeda, Osaka 563-8577, Japan
b
c
Gallium oxide is found to be an effective catalyst for the
dehydrogenation of ethane to ethene in the presence of
carbon dioxide at 650 °C, giving 18.6% ethene yield with a
selectivity of 94.5%.
20
15
Ethene is predominantly produced by steam cracking of
naphtha, ethane or liquid petroleum gas at high temperatures at
short residence time.
In order to reduce energy consumption of ethene production,
oxidative dehydrogenation of ethane is proposed [eqn. (1)].
1
0
5
0
C
2
H
6
+ 1/2O
2
? C
2
H
4
+ H
2
O
(1)
The reaction becomes exothermic and thermodynamically
could be possible at relatively low temperatures. However, it is
necessary to remove heat from the reaction and to avoid over
2
oxidation to CO to give high selectivity towards ethene.
Recently, a great variety of catalysts have been developed and
tested for this reaction.1 In the oxidative dehydrogenation of
propane, Burch and Crabb4 pointed out that thermal non-
catalytic oxidative cracking of propane proceeded to give
propene in the same yield as compared to catalyzed runs which
were operated about 50 °C lower than that of non-catalyzed
runs. This suggests that catalyzed oxidative dehydrogenation of
lower alkanes is not highly superior to thermal oxidative
pyrolysis.
–3
Fig. 1 Dehydrogenation of C
2 6 2
H in the presence of CO . Catalyst 200 mg;
2
1
21
temperature: 650 °C; C :CO = 5:25 ml min ; SV = 9000 h ml
H
2 6
2
Recently, several attempts have been made to use carbon
2
1
(
g cat)
.
5
dioxide as an oxidant for coupling of methane, dehydrogena-
6
7
tion of ethylbenzene or propane. However, the role of CO
2
in
these reactions is still not clear. In addition, the effects of CO
on the conversion and yield of the product are not significant.
Here, we study the dehydrogenation of ethane to ethene over
2
(18.6%) amongst the various metal oxide catalysts. However,
little work has dealt with Ga O catalyst in the dehydrogenation
2
3
of propane.8
several metal oxide catalysts, and we have found that CO
2
2 3 2 3 2 5
Table 1 lists ethene yields on Ga O , Cr O , and V O
markedly promoted dehydrogenation of ethane over Ga
catalyst.
2
O
3
catalysts in the presence and absence of CO . The activity of the
2
Ga O catalyst in the presence of CO was twice that in the
2
3
2
The catalysts used were commercially available MgO, Al
SiO , CaO, TiO , V , Cr , Mn , Fe , ZnO, Ga
, ZrO , Nb , MoO , In , SnO , La , CeO , Ta
and Tl . The reaction was carried out with a fixed-bed flow
type quartz reactor (i.d. 10 3 350 mm) at atmospheric pressure.
2
O
3
,
,
2 2 6
absence of CO . Dehydrogenation of C H in the presence of
CO over Ga O catalyst produced mainly C H , CO, H and
2 2 3 2 4 2
H O. The yield of ethene with the Cr O catalyst in the presence
2 2 3
2
2
2
O
5
2
O
2
3
O
3
O
4
3
O
2
4
2
O
3
Y
2
O
3
2
2
O
5
3
3
2
O
3
2
2
O
5
O
2 3
of CO was slightly higher as compared to the run in Ar. The
2
promoting effect of CO in the dehydrogenation of C H on
2
3 8
2
1
5
Using 200 mg of a catalyst, 5 ml min of C
2
H
6
and 25 ml
2 3 2
Cr O /SiO has been reported, but the increase in the propene
21
min of CO
2
were introduced. The runs were conducted for 30
yield was only 2.6% at 550 °C. On the other hand, the effect of
min and products were analyzed by gas chromatography.
Fig. 1 shows ethene yields on the various metal oxide
catalysts. Thermal dehydrogenation occurred to give only 2.3%
of ethene yield. Equilibrium conversion of ethane to ethene is
Table 1 Dehydrogenation of ethane in the presence of carbon dioxidea
Surface Conv. Yield
Selectivity (%)
ca. 50% at 650 °C at a C
CaO, SiO , Ta , Al , SnO
any catalytic activity while CeO
2
H
6
–Ar (or CO
, MoO , and Tl
, Nb , Fe
2
) ratio of 1:5. MgO,
area/
m g
(%)
(%)
2
21
2
2
O
5
O
2 3
2
3
O
2 3
did not show
, and ZrO
Catalyst
C
2
H
6
C
2
H
4
C
2
H
4
CH
4
3 8
C H
2
2
O
5
3
O
4
2
Ga
Ga
2
2
O
O
3
(CO
(Ar)
2
)
9.8
9.8
2.8
2.8
3.5
3.5
19.6
9.6
12.1
10.4
9.8
18.6
9.0
11.4
10.2
9.5
95.0
94.0
93.8
97.6
97.1
91.7
3.8
5.0
5.8
1.8
2.9
7.4
1.0
0.7
0.4
0.6
—
exhibited only slight catalytic activity. The order of the activity
of oxides at the reaction temperature of 650 °C was as follows:
3
Cr
Cr
2
O
O
3
(CO
(Ar)
2
)
Ga
>
2
O
3
2
O
3
2 5 2 3 4 2 3
O > TiO > Mn O > In O > ZnO
2
3
La
2
V
V
2
O
5
(CO
2
)
were > 85% in the dehydrogenation of ethane in the presence of
CO . As expected, Cr and V exhibited high activities.
These catalysts are known to be active catalysts for dehydroge-
nation of alkanes. Ga afforded the highest yield of ethene
2
O
5
(Ar)
12.5
11.5
0.9
2
2
O
3
2 5
O
a
Reaction conditions: 650 °C, SV = 9000 h21 ml (g cat)21. Composition
2
1
O
2 3
of the feed gas; C
H
2 6
:CO
2
(Ar) = 5:25 ml min
.
Chem. Commun., 1998
1025