Mendeleev Commun., 2020, 30, 195–197
(a)
(b)
C H
(c)
4
4
35
5
0
3
6
2 4
C H
CH
4
8
0
0
70
60
50
40
30
20
C
2
H
6
7
C H
3
6
60
50
40
30
n 2n
ΣC H
30
25
20
2
0
0
0
15
1
10
0
2
4
6
8
10
0
2
4
6
8
10
1.3
2.6
5.1
10.3
–1
–1
–1
V /mmol min
V /mmol min
V /mmol min
Figure 2 Dependences of (a) the propane conversion, (b) the product selectivity and (c) the productivity of propylene and total olefins vs. the flow rate of
reaction mixture in the propane dehydrogenation under supercritical conditions (600°C, C H :CO = 1:4).
3
8
2
4
3
2
0
0
0
process. The analysis of reaction products revealed arise in the
Gas phase
22,23
formation of olefins.
However, there are still no published
Supercritacal conditions
works on the dehydrogenation of propane with CO under super-
2
critical conditions. The aim of this work was to explore this reaction
in the presence of CO on a Cr(3%)/SiO catalyst under supercritical
10
0
2
2
conditions and to compare its performance with the gas-phase
†
reaction.
n 2n
ΣC H
C
3
H
6
When propane was dehydrogenated in the presence of CO in
2
Figure 3 Space-time yields of propylene and the sum of olefins
ethylene + propylene) for the Cr(3%)/SiO catalyst in the propane dehydro-
genation under supercritical conditions vs. gas-phase conditions (600°C,
the gas phase on a Cr(3%)/SiO catalyst, the propane conversion
2
(
2
1
3
reached 67%, and the propylene selectivity was 75% at 600°C.
–1
For the propane dehydrogenation in the presence of CO under
V = 1.3 mmol min , C H :CO = 1:3).
2
3 8 2
supercritical conditions, the dependence ofthepropaneconversion
and products selectivity on the C H :CO ratio at 600°C was
The productivity towards propylene and overall content of
olefins were highest at the C H :CO ratio of 1:4. A further increase
3
8
2
investigated (Figure 1). Upon a decrease in the C H :CO ratio,
3
8
2
3
8
2
the propane conversion reached 33%, the propylene selectivity was
9%, and the H :CO ratio in products increased from 0.5 to 1.
A further increase in the carbon dioxide content did not result in
any additional growth in the propylene selectivity that remained at
in the CO content in the reaction mixture resulted in a decreased
2
3
productivity of propylene and overall olefins [see Figure 1(b)].
At the second step of catalytic investigations, the dependence
of yield of the target reaction product on the flow rate was revealed
2
–1
the level of 38% [see Figure 1(a)]; the H :CO ratio also did not
(Figure 2). When propane was fed at the rate of 1.3 mmol min ,
its conversion reached 70%, while a further increase in the flow
rate diminished the propane conversion. Upon a rise in the
2
rise. This proves the involvement of CO in the direct oxidation
2
of propane to propene (C H + CO = C H + CO + H O) and the
3
8
2
3
6
2
–1
–1
consumption of hydrogen in the reverse water shift reaction (CO2
H = CO + H O), which shifts the equilibrium towards the
reaction mixture feed rate from 1.3 mmol min to 5 mmol min ,
the propylene selectivity was slightly increased and reached
35%; and after a further increase in the reaction mixture feed rate
+
2
2
propane dehydrogenation. Thus, in the CO -assisted process of
2
–
1
propane dehydrogenation, we have obtained, along with propylene,
to 10 mmol min , there was a slight decrease in the propylene
selectivity.
a valuable by-product, the synthesis gas (CO + H ), which is
2
widely used in the chemical industry. Herewith, the variation in
the C H :CO ratio in the initial mixture allows one to tune the
In conclusion, we have performed a comparison of the experi-
mental results of propane dehydrogenation in the presence of carbon
dioxide under the supercritical conditions and in the gas phase
(Figure 3). It was found that the productivity of Cr(3%)/SiO2
catalyst under the supercritical conditions was increased by a
factor of three based on the propylene content and by a factor of
five based on the overall content of olefins (ethylene + propylene)
as compared to the gas-phase conditions.
3
8
2
H :CO ratio in the products. The peculiarity of reaction is an
2
increased ethylene selectivity, which may be due to an occurrence
of the side cracking reaction (C H ® C H + CH ).
3
8
2
4
4
†
Granulated silica gel (SiO , Acros) was used as the support for the prepara-
2
tion of catalyst samples. The pre-crushed silica gel (fraction of 0.25–0.5 mm)
was dried in a drying oven at 100°C for 6 h. The Cr(3%)/SiO catalyst
2
sample was prepared via impregnating the support with a solution of
chromium nitrate in distilled water of the appropriate concentration. The
sample was completely dried at 100°C, and then calcined in air at 500°C
for 4 h.
The work was supported by the Russian Foundation for Basic
Research (grant no. 18-29-24182).
Propane dehydrogenation into propylene in the presence of CO was
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