Oxidation of propylene and isobutylene in a reactor with barrier discharge

Article abstract of DOI:10.1007/s11167-005-0188-0

The oxidation of propylene and isobutylene in barrier-discharge plasma in the presence of octane was studied. The possible reaction mechanism was considered.

Full text of DOI:10.1007/s11167-005-0188-0

Russian Journal of Applied Chemistry, Vol. 77, No. 11, 2004, pp. 1904 1906. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11,
2004, pp. 1922 1924.
Original Russian Text Copyright
2004 by Kudryashov, Ryabov, Sirotkina, Shchegoleva.
BRIEF
COMMUNICATIONS
Oxidation of Propylene and Isobutylene in a Reactor
with Barrier Discharge
S. V. Kudryashov, A. Yu. Ryabov, E. E. Sirotkina, and G. S. Shchegoleva
Institute of Petrochemistry, Siberian Division, Russian Academy of Sciences, Tomsk, Russia
Received April 20, 2004
Abstract The oxidation of propylene and isobutylene in barrier-discharge plasma in the presence of octane
was studied. The possible reaction mechanism was considered.
Recently, the interest in organic synthesis in elec-
tric discharges has been increasing. However, devel-
opment of new technologies based on electric dis-
charges is hindered by the lack of a sufficiently large
body of data on the mechanisms and kinetics of con-
version of organic compounds in plasma, which is, as
a rule, caused by the low selectivity of the occurring
reactions, tarring, and deep degradation of organic
molecules.
ucts are dissolved and are thereby removed from the
zone of the barrier discharge. A flow-through gas-
discharge reactor of coaxial design was used. The
experimental setup has been described in detail previ-
ously [1].
The starting parameters of the process were as fol-
lows: flow rate of oxygen, olefin, and octane through
3
1
the reactor 3.0, 0.6, and 6 10 l h , respectively;
temperature of the reactor walls 10 C; atmospheric
pressure; amplitude of voltage pulses 12 kV; pulse
repetition frequency 500 Hz; specific energy of the
We have shown previously that oxidation of hy-
drocarbons belonging to various classes without for-
mation of tars and products of complete oxidation is
possible in a barrier discharge [1]. This is achieved by
effective removal of reaction products from the zone
of the barrier discharge with a hydrocarbon film
formed by condensation of supersaturated vapor of
a hydrocarbon on the cooled reactor walls. For exam-
ple, oxidation of hexane, cyclohexane, and cumene
mainly yields hydroxy and carbonyl compounds:
alcohols, aldehydes, and ketones with the same
number of carbon atoms as that in the starting com-
pound. The product formed in oxidation of cyclo-
hexene is epoxycyclohexane (62 wt %).
1
discharge 1.3 Wh l .
The liquid reaction products were analyzed by gas
chromatography: heat-conductivity detector in the
isothermal mode at 120 C; 1.2-m-long packed column
with an inner diameter of 3 mm; sorbent Porapak-Q;
carrier gas helium.
The conversions and the composition of products
formed in oxidation of PR and IB are listed in the
table. It can be seen that the main reaction products
are the corresponding epoxides. In contrast to the oxi-
dation of cyclohexene, the oxidation of PR and IB is
accompanied by degradation of the olefin molecule to
give methanol and formaldehyde. At the same time,
It was shown in [2] that the selectivity of cyclo-
hexene oxidation can be, in principle, controlled. The
maximum yield of cyclohexene oxide was 72%.
However, products of oxidation of light olefins are of
greater importance for petrochemical synthesis.
no CO, CO , acids, or tarring products were found in
2
the reaction products, which constitutes a fundamental
difference between the results of this study and those
of previous studies of oxidation of light olefins in
electric discharges [3 5].
In this work we studied oxidation of propylene
(PR) and isobutylene (IB) in a reactor with a barrier
discharge.
It should be noted that octane is oxidized simul-
taneously with the olefins. The conversion of octane is
0.5 wt % in both cases. As a result, hydroxy and
carbonyl compounds characteristic of octane oxidation
products are formed [6].
EXPERIMENTAL
PR and IB were oxidized in the presence of octane
to create a hydrocarbon film in which reaction prod-
A possible mechanism of cyclohexene oxidation
1070-4272/04/7711-1904 2004 MAIK Nauka/Interperiodica

OXIDATION OF PROPYLENE AND ISOBUTYLENE IN A REACTOR
1905
was suggested in [2]. In this mechanism, the reaction
products are formed by two pathways. The first of
them yields cyclohexene oxide, cyclohexanone, and
cyclopentylmethanal, and the second, cyclohexenone,
cyclohexenol, and bicyclohexenyl.
Conversions X and composition of products formed in
oxidation of PR and IB*
Selectiv-
ity, wt %
Olefin
X, wt %
Oxidation products
No unsaturated oxygen-containing compounds were
found in oxidation products of PR and IB, which sug-
gests that the reaction predominantly goes by the first
pathway involving activation of oxygen molecules by
electron impact. This can be attributed to the higher
dissociation energies of PR and IB molecules, com-
pared with those of cyclohexene and oxygen mole-
cules [7].
Propylene
1.56
Propylene oxide
Acetone
Acetaldehyde
Methanol
Water + formaldehyde
Isobutylene oxide
2-Methylpropanal
Acetone
43.3
30.9
10.2
3.4
12.2
43.8
23.9
19.2
4.6
Isobutyl-
ene
6.74
Methanol
Water + formaldehyde
By analogy with the previously suggested mechan-
ism of cyclohexene oxidation, the possible mechanism
of PR oxidation can be represented as
8.5
* Conversion obtained in a single pass of the starting mixture
through the reactor at a time of contact with the discharge
zone equal to 10.5 s.
k
.
1
H2 C=CHCH 3 + O(3 P)
H2 C
H2 C
CHCH3
,
O
generation of atomic oxygen in mixtures of oxygen
with PR and IB will be the same, because their mole-
cules have close cross sections of electron energy
scattering. Therefore, the composition of the gas mix-
tures has no effect on the average electron energies.
Hence, expression (1) can be written as
CHCH3
O
k
2
.
H2 C
CHCH3
H3C C CH3
O
O
O
O
CH3
C
,
C
H
, CH OH,
H2 O.
3
H
H
k1/k1" = X1/X2,
(3)
Acetaldehyde, formaldehyde, methanol, and water
are formed by decomposition of a hot molecule of
propylene oxide, with the resulting fragments sub-
sequently involved in radical reactions. In the case of
cyclohexene oxidation, the hot molecule of olefin
oxide does not decompose [1, 2].
where k and k" are the rate constants of interaction of
1
1
atomic oxygen with PR and IB, respectively. The
results of calculation by expression (3) are given
below:
1
k1
2.2 1012 cm3 mol 1 s
2.2 1013 cm3 mol 1 s
=
= 0.183 [8],
The validity of the suggested mechanism of PR and
IB oxidation can be verified by simple calculations.
For the oxidation of olefins, which occurs in a reactor
with a steady flow mode, the following expression is
valid:
1
k1"
X1/X2 = 1.56/6.74 = 0.231.
It can be seen that the calculation results reason-
ably agree with the experiment. The calculation error
is 20.9%.
w1/w2 = X1/X2,
(1)
where w , w , X , and X are the oxidation rates and
conversions of PR and IB, respectively.
1
2
1
2
CONCLUSION
Oxidation of propylene and isobutylene by oxygen
in the plasma of a barrier discharge allows synthesis
of oxides of light olefins without formation of tars or
complete oxidation.
In terms of the oxidation mechanism suggested, the
following expression can be written for the oxidation
rate of PR:
w1 = d[C3H5]/d = k1[O(3P)][C3H6].
(2)
REFERENCES
A similar expression can be written for w .
2
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RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 77 No. 11 2004

1906
KUDRYASHOV et al.
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