Catalytic synthesis of octadiene-1,7 from ethylene and cyclohexene

Article abstract of DOI:10.1016/j.jorganchem.2018.01.059

A new method is proposed for the synthesis of octadiene-1,7 by co-metathesis of ethylene and cyclohexene (ethenolysis). The reaction is carried out in a flow setup at elevated pressures using an original NH₄ReO₄/Al₂O₃ heterogeneous catalyst. At the first stage of the reaction, carbenes are formed as intermediates. The optimal conditions of the co-metathesis process were found. The catalyst developed provides the cyclohexene conversion about 25 wt. %, i.e. close to the thermodynamic limit, at the selectivity to octadiene-1,7 close to 100% (99.9%). The catalyst shows good stability in six cycles including 5-h catalytic runs with intermediate regenerative treatments.

Full text of DOI:10.1016/j.jorganchem.2018.01.059

Journal of Organometallic Chemistry xxx (2018) 1e5
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Catalytic synthesis of octadiene-1,7 from ethylene and cyclohexene
a, b, c, *
, D.B. Furman a
L.M. Kustov
a
N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Leninsky Prospect 47, 119991, Russia
Chemistry Department of Moscow State University, Moscow, Leninskie Gory 1, bldg. 3, 119992 Russia
National University of Science and Technology MISiS, 119071, Leninsky Prospekt 4, Moscow, Russia
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 October 2017
Received in revised form
A new method is proposed for the synthesis of octadiene-1,7 by co-metathesis of ethylene and cyclo-
hexene (ethenolysis). The reaction is carried out in a flow setup at elevated pressures using an original
NH ReO /Al O heterogeneous catalyst. At the first stage of the reaction, carbenes are formed as in-
4 4 2 3
termediates. The optimal conditions of the co-metathesis process were found. The catalyst developed
provides the cyclohexene conversion about 25 wt. %, i.e. close to the thermodynamic limit, at the
selectivity to octadiene-1,7 close to 100% (99.9%). The catalyst shows good stability in six cycles including
29 January 2018
Accepted 30 January 2018
Available online xxx
5-h catalytic runs with intermediate regenerative treatments.
Keywords:
Metathesis
Rhenium
©
2018 Elsevier B.V. All rights reserved.
Ethenolysis
Cyclohexene
Octadiene-1,7
Catalysis
1. Introduction
activation of CdC and CdH bonds. It is practically impossible to
produce -dienes by these methods because the use of rather
a,u
The synthetic routes to alkenes and
olefinic molecules and dienes with a long chain (>C ) are of
4
a
,
u
-alkadienes, in particular,
high reaction temperatures and the presence of acid sites at the
catalyst surface favor migration of the double bonds and poly-
merization as main side processes.
The octene-1 yield in Fischer-Tropsch synthesis is usually not
higher than 1e2% even in the case of most effective catalysts [1,5].
Here the main problems are essentially the same as mentioned
above.
The methods based on the use of homogeneous catalytic sys-
tems for ethene oligomerization, which provide usually high pro-
ductivity and selectivity to terminal olefins with a low molecular
considerable industrial interest because presently there are no
economically viable processes for producing these valuable prod-
ucts. The following sources of octene-1 are used in industrial pro-
cesses: (1) catalytic dehydrogenation of paraffins; (2) Fischer-
Tropsch synthesis on Co or Fe catalysts, (3) oligomerization of
ethene in the presence of metal complex catalysts, all of these
processes being non-selective.
Pyrolysis of oil fractions is of low acceptability for octene-1
production because of the poor yield (~1.5%) [1e3] due to forma-
tion of large amounts of gases and contamination of the target
product with compounds with close boiling points.
4
weight (C ), do not allow the production of individual high-
molecular-weight (>C
4
) terminal olefins in both low-temperature
ꢀ
ꢀ
(ꢁ30-þ20 C, P ¼ 7e40 atm) and high-temperature (>100 C,
P ~ 100 atm) processes. For example, the yield of octene-1 does not
exceed 10e11%. Broad distribution of ethene oligomerization
products in their molecular masses creates additional problems
related to the isolation of the target product - octene-1. At the same
time, the necessity to use Al-organic compounds leads to serious
environmental problems and the need to purify waste water from
aluminum compounds.
The use of heterogeneous catalysts for dehydrogenation of al-
kanes, such as supported metal-oxide systems allows one to reach
the yields of alkenes about 12e18% [1,4] under optimal conditions
ꢀ
(
9
5
reaction temperatures about 450e500 C) with a selectivity about
0e92%. However, the content of
a-alkenes is, as a rule, less than
%. An increase in the reaction temperature results in non-selective
Analysis of the most important sources of terminal olefins leads
to two important conclusions. The yield of individual compounds in
all methods of production described above is low. This is the main
*
Corresponding author. N.D. Zelinsky Institute of Organic Chemistry, Russian
Academy of Sciences, Moscow, Leninsky prospect 47, 119991, Russia.
E-mail address: lmk@ioc.ac.ru (L.M. Kustov).
https://doi.org/10.1016/j.jorganchem.2018.01.059
0
022-328X/© 2018 Elsevier B.V. All rights reserved.
Please cite this article in press as: L.M. Kustov, D.B. Furman, Journal of Organometallic Chemistry (2018), https://doi.org/10.1016/
j.jorganchem.2018.01.059

2
L.M. Kustov, D.B. Furman / Journal of Organometallic Chemistry xxx (2018) 1e5
drawback of available methods used to produce terminal olefins. In
particular, the C olefin fraction in the final products is extremely
2.2. Catalysts
8
low and varies from ~1.5 to 10e11%. The further separation of the
target product from multi-component reaction mixtures with close
boiling points considerably decreases the efficiency of these
methods.
The catalysts were prepared by supporting an active component
2 3
precursor (compounds of Re, Mo and W) onto Al O (surface area,
2
S ¼ 196 m /g; microcrystallite size, 0.5e1.0 mm). Alumina carriers
ꢀ
were calcined at 600 C in air for 3 h before supporting the active
The necessity of searching for the new approaches to develop
4 4
phase, then cooled and impregnated with NH ReO ,
efficient methods suitable for transformation of ethene to C
8
olefins
(NH
4
)
6
Mo
7
O
24 ꢄ 4H
2
O or (NH
4
)
4
W
5
O
17 ꢄ 2.5H
2
O aqueous solu-
ꢀ
with a high selectivity and productivity is obvious, since octane-1 is
widely used in the synthesis of diverse elastomers via co-
polymerization with ethylene and propylene.
tions. The thus prepared catalysts were dried at 150 C in air for
24 h and activated under flowing dry air (3 ml/s) with a tempera-
ture ramping from 20 to 540 C for 3 h, kept for 6 h at 540 C in air
ꢀ
ꢀ
The objective of this research is to develop the catalytic method
of synthesis of octadiene-1,7 from commercially available products
such as ethene and cyclohexene. The target product is octene-1
produced by successive hydrogenation of octadiene-1,7, but hy-
drogenation is an easy step and will not be discussed here. The
method proposed to achieve the goal is based on the reaction of
cyclohexene ethenolysis (co-metathesis) with the formation of
octadiene-1,7. The reaction of co-metathesis (ethenolysis) of
ethylene and cyclohexene on metal-containing catalysts is a benign
approach to develop an effective method of direct activation of the
CdC and CdH bonds in hydrocarbon molecules with the purpose
to prepare octadiene-1,7 and finally octene-1. This reaction is
characterized by a 100% atom efficiency, because no side products
are formed.
Currently ethenolysis of olefinic compounds has been studied in
detail in the case of homogeneous catalytic systems [6e12].
Rhenium catalysts, including heterogeneous systems are widely
used for metathesis reactions [13,14]. However, according to [15],
the reaction of co-metathesis of cyclohexene with ethene does not
take place due to the difficulties with cyclohexene ring opening. To
our surprise and to the best of our knowledge, this is the only
publication on the subject, while there are numerous papers on
ring-opening metathesis polymerization of cyclohexene de-
rivatives. The reaction of co-metathesis of cyclohexene and ethene
and cooled with the air flow switched off. The catalyst drying and
activation at 540 C can be done directly in the reactor. The catalysts
prepared and tested are listed in Table 1.
ꢀ
2.3. Catalytic equipment and testing
A flow-type catalytic setup with a plug-flow reactor was used
for testing. The unit includes the following parts: metal cylinders
with gases, Ar, N and ethene, a high pressure reductor, a fine-
2
3
regulation dosing valve, a glass cylinder (300 cm volume) for
drying gases with calcined (550 C) NaX zeolite, manometers, a
ꢀ
high-pressure pump for liquid supply, two high-pressure
(3e10 mPa) gate valves (upstream), a glass or stainless still verti-
cal cylindrical reactor with the volume 30 ml, a separator for col-
lecting the liquid products, a gas flow meter, a gas-liquid
chromatograph, and a loop for taking samples for analysis.
This catalytic unit provided the simultaneous supply into the
reactor of gases (through purification columns) and a cyclohexene
solution in n-hexane with the help of fine dosing valves. In this
case, the liquid was instantaneously supplied onto the catalyst and
did not plug the ethene supply line. The catalytic unit allowed us to
carry out the experiments under the following conditions: catalyst
3
volume, 0.5e10 cm ; ethylene gas flow rate, Vethene ¼ 0.5e5 nml/
sec; liquid flow rate, 1e12 ml/h; P ¼ 0.1e10 mPa; temperature,
2 3
has been carried out in Refs. [15,16] using a Mo-Co/Al O catalyst
under conditions of a batch reactor. No other data on this reaction
were found in the literature.
ꢀ
5
0e600 C. The ethene pressure constancy in the reactor was
ensured with the help of both the high-pressure reductor and the
regulating gate valve at the inlet to keep the pressure under the
critical value and the high-pressure gate valve at the outlet of the
unit (back-pressure valve).
The catalysts were activated or regenerated first in a separated
unit, which provided the treatment in dry air at a fixed tempera-
ture. The activated catalyst was purged at the reaction temperature
The metathesis reaction usually should proceed at a low tem-
ꢀ
perature (20e100 C) as many other metathesis reactions, i.e., un-
der mild conditions of metal-complex catalysis. These conditions
are favorable for the occurrence of the main reaction but are not
favorable for the side processes (double bond migration, polymer-
ization or destruction) related to the transformation of the starting
compounds and target products. The information about this reac-
tion is scarce and some data are given in only one patent [16].
2
with Ar or N in the catalytic reactor, after that dry ethene or an Ar-
ethene mixture was supplied at a fixed pressure. Then a cyclo-
hexene solution was fed and the flow rate at the outlet was
adjusted. The first sample of the reaction products was taken in
2
. Experimental
15 min after the cyclohexene solution had been fed.
2
.1. Chemicals and materials
The following chemicals and materials were used:
Gases:
Table 1
Catalysts used for co-metathesis of ethylene and cyclohexene.
No.
Catalyst composition
(NH ) Mo O /Al O
[Me], wt. % (mol. %)
3
1
2
3
4
5
6
7
8
9
10
3.4 (3.5)
6.0 (3.5)
6.0 (3.5)
0.5 (0.3)
1.0 (0.8)
2.0 (1.2)
3.0 (1.8)
4.0 (2.3)
4
4
6
4
7
24
2
3
(
(
(
a) ethene (C
b) argon (Ar - 99.993 vol %, O
c) nitrogen (N - 99.9 vol %, O
, CO - 0.0005 vol %).
Liquids:
a) n-hexane, purity ꢂ99.8%, n
2
H
4
- 99.5 vol %, O
2
< 0.0001 vol %, H
< 0.0007 vol %);
2
< 0.005 vol %, H O < 0.0009 vol
2
O mg/m );
(NH
)
W
5
O
17/Al
2
O
3
2
NH
NH
NH
NH
NH
NH
NH
4
4
4
4
4
4
4
ReO
ReO
ReO
ReO
ReO
ReO
ReO
4
4
4
4
4
4
4
/Al
/Al
/Al
/Al
/Al
/Al
/Al
2
2
2
2
2
2
2
O
O
O
O
O
O
O
3
3
3
3
3
3
3
3
2
2
%
2
2
O
(
D
¼ 1.38, H O ꢃ 0.01%;
2
2
O
(
b) cyclohexene, purity 99.5%, n
Materials:
a) NH ReO
b) (NH
c) (NH
D
¼ 1.446.
8.0 (4.7)
10.0 (5.9)
7.3 (7.8) - Mo; 2.4 (4.0) Co
4
NH ReO /Al O
4
2
a
(
(
(
4
4
, chemically pure
Mo O; reagent pure
24 ꢄ 4H
17 ꢄ 2.5H O, reagent pure.
11
4
(NH )
6 7 3 2 2 3
Mo O24-Co(NO ) /Al O
a
4
)
)
6
4
7
O
2
Catalyst No. 11 was prepared according to the patent [16] and tested for com-
4
W
5
O
2
parison in the flow setup (although it was tested in a batch reactor in the patent).
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L.M. Kustov, D.B. Furman / Journal of Organometallic Chemistry xxx (2018) 1e5
3
The analysis of liquid and gas products was performed with a
BIOCHROM chromatograph using a 3 m ꢄ 3 mm column filled with
cellite-545 as a stationary phase and 8% SE-30 as a mobile phase.
The standard analysis was carried out at 100 C. The liquid sample
was taken from the separator and a loop was used for taking
samples downstream for analysis.
equilibrium constant at the standard temperature 298.15 K will be
equal to 0.002. This value corresponds to the degree of cyclohexene
conversion of 7.4% at Pethene ¼ 40 atm. The influence of the pres-
sures of both cyclohexene and octadiene-1,7 vapors was ignored
because the sum of the partial pressures of these compounds at this
temperature was considerably lower than 1 atm.
ꢀ
The gas-liquid chromatographic analysis shows the presence of
a single product in the reaction mixture at the reactor outlet
The thermodynamic functions at 313 K were estimated using
the known data on heat capacities for ethene and cyclohexene and
the calculated heat capacity for octadiene-1,7 in order to estimate
changes in the conversion degree with a temperature increase. It
was suggested in this case that the heat capacity and the evapo-
ration heat within this temperature interval are constant. It was
shown that a temperature increase at the same ethene pressure
results in a decrease in the equilibrium constant to 0.06 and in the
yield to 6.0%. It was also found that at 40 ꢃ P ꢃ 100 atm, the tem-
(
99.9 wt. %). Three independent methods of identification were
used: (1) introduction of octadiene-1,7 into the reaction mixture;
2) chromato-mass-spectrometry (it was shown by this method
(
1
13
that the product is octadiene-1,7); (3) H and C NMR spectra of
the reaction products.
The reaction products contain, in addition to octadiene-1,7, trace
amounts (<0.1%) of an unknown compound, presumably a dimer.
The main product was identified by gas-liquid chromatography of
the mixture formed in the course of cyclohexene ethenolysis using
the temperature-programmed regime of the chromatographic
ꢀ
perature increase from ~10 to 50 C leads to a decrease in the yield
of octadiene-1,7 by ~11%, and the variation of the total pressure
within the chosen interval results in a growth of the cyclohexene
conversion by 4e5 times (from ~3.5% at 20 atm to ~18% at 100 atm).
Taking into account that the thermodynamic functions for
octadiene-1,7 were calculated using the Benson rule [19], a possible
fluctuation from the experimental value of the cyclohexene con-
version could be ±30%.
ꢀ
analysis (temperature rise, 5 /min; temperature interval,
ꢀ
1
00e300 C).
1
Identification of the main reaction product: Н NMR (СDCl3,
ppm): 5.7e5.95 (m, ¼ СН-); 4.9e5.1 (t, ¼ СН -); 2.0e2.2 (d, -СН
at СН ¼ СН ); 1.4e1.5 (m, -СН -); the integral intensity ratio 1: 2: 2:
, respectively. С NMR (СDCl3,
, ppm): 138.601 (¼СН-); 114.079
¼СН -); 33.502 (-СН - at СН ¼ СН
С NMR spectral data also unambiguously confirm the structure
formed in the ethenolysis of cyclohexene as 1,7-octadiene.
d,
2
2
-
2
2
13
2
d
1
(
2
2
2
); 28.258 (-СН
2
-). The Н and
3.2. Catalytic data on cyclohexene ethenolysis
1
3
Cyclohexene noticeably reacted with ethylene in the presence of
ꢀ
rhenium-containing catalysts supported on Al
2
O
3
at 15e20 С to
3
. Results and discussion
form virtually a single reaction product (>99.9 wt %). The com-
pound formed was identified as 1,7-octadiene, as described in
Experimental part.
3.1. Thermodynamic calculations
Under the examined conditions specifying the procedure of
catalyst preparation, active surface formation, and testing experi-
ment, the activity and selectivity of catalysts based on different
metals (Re, Mo, and V) in the ethenolysis of cyclohexene were quite
different (Table 3). An alumina-based rhenium catalyst was found
to be most efficient. Alumina-based tungsten- and molybdenum-
containing catalysts as well as an alumina-based molybdenum
catalyst modified with cobalt according to [16] were found to be
incapable of performing cyclohexene ethenolysis under the chosen
conditions (Table 3, nos. 1, 2, 4).
Thermodynamic calculations were performed on the basis of
the following reaction scheme:
The scheme proposed in Ref. [17] was used for the calculation of
the equilibrium in approximation of an ideal gas and an ideal so-
lution. Necessary thermodynamic data for cyclohexene and ethene
were borrowed from Ref. [18]. The thermodynamic functions for
octadiene-1,7 in the gas phase were calculated using the Benson
additive rule [19]. The comparison of the calculated results with the
experimental thermodynamic functions for C eC dienes showed a
4 7
reasonable correlation. The data for octadiene-1,7 at 298 K are
given in Table 2.
Based on the data presented in Table 3, the reaction of co-
metathesis of cyclohexene with ethylene on a series of NH
Al catalysts was examined in more detail. The experiments were
performed with both pure ethylene and Ar: С gas mixtures;
4 4
ReO /
2 3
O
2 4
Н
thus, the effect of higher pressures (up to 100 atm) on the efficiency
of the reaction can be examined.
The standard thermodynamic functions for octadiene-1,7
necessary for the calculation of the equilibrium reaction constant
for reaction (1) were obtained using the assumption about a phase
equilibrium. NIST tables [18] were used for the calculation of the
thermodynamic functions of cyclohexene. The octadiene-1,7
evaporation entropy change was assumed to be equal to 79.5 J/
mol x K on the basis of the literature data for some dienes. The
evaporation enthalpy change was estimated using the Truton rule:
it was found to be equal to 30.9 kJ/mol assuming that octadiene-1,7
is a non-associated liquid. If we use these values, the reaction
Table 3
Efficiency of cyclohexene ethenolysis on catalysts containing different metals
(
Conditions: cyclohexene: ethylene ¼ 1: 6, Ar: С
Н
2 4
¼ 0.45: 0.55; ethylene gas flow
3
rate ¼ 1.0 ml/s; LHSV(cyclohexene) ¼ 3.0 ml/h; catalyst loading, 5 cm ).
a
ꢀ
Т, Сb
Catalyst composition
[
М
] ,
Yield, wt %
Octa- Other
diene-
mol. %
products
1,7 (>C9)
(
(
NH
NH
4
)
)
6
Mo
7
O
24/Al
17/Al
/Al
Mo
2
O
3
3.5
3.5
3.5
30
32
0.23
0.3
0.05
0.9
4
4
5
W O
2
O
3
NH
4
ReO
4
2
O
3
18
120
11.3
0.9
0.01
0.05
c
(NH
4
)
6
7
O
24-С
о
(NO
3
2
) /Al
2
O
3
7.8Мо
-
Table 2
С
о
Thermodynamic parameters of octadiene-1,7.
a
b
c
[
М
] is the metal concentration.
Optimum reaction temperature under flow conditions.
The catalyst composition and the preparation procedure are described in
C0
70.12
, J/mol x K
S0, J/mol x K
452.71
D
H0
42.47
, kJ/mol
p
f
1
Ref. [16].
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4
L.M. Kustov, D.B. Furman / Journal of Organometallic Chemistry xxx (2018) 1e5
Fig. 1. Time dependences of the octadiene-1,7 yield. Pressures of the gas mixture (Ar:
ꢀ
C
2
H
4
¼ 25: 75) are 60 (1) and 40 atm (2). Reaction conditions: 17 C, cyclohexene: n-
ꢁ
1
hexane ¼ 2.3: 1, LHSV ¼ 3 h , gas flow rate 1 nmL/sec.
Fig. 3. The dependence of the yield of octadiene-1,7 on Re/Al
Re content in cyclohexene ethenolysis (Ar: C
2
O
3
catalysts versus the
ꢀ
2
H
4
¼ 45: 65). Reaction conditions: 17 C,
Ptotal ¼ 50 atm,
P
ethene ¼ 27.5 atm, cyclohexene: n-hexane ¼ 1: 1, cyclohexene:
Fig. 1 shows typical time dependences for the 1,7-octadiene
formation in the course of 5-h experiments on cyclohexene ethe-
nolysis. We found that the target product yields are reasonably
close to the thermodynamic values at ꢂ99.9% selectivity and these
ꢁ1
ethene ¼ 1: 5, LHSV ¼ 3 h , gas flow rate 1 nmL/sec.
at higher pressures and higher Re concentrations. As can be seen in
Fig. 3, the 1,7-octadiene yield can be increased to 12.3 wt. % at
[Re] ¼ 8e10 wt. % when the rhenium loading approaches the
monolayer surface coverage.
2 4
yields can be attained even with the use of С Н and Ar gas
mixtures.
The results on the effect of the reaction temperature, which
were obtained with low-percentage rhenium catalysts in an
ethylene atmosphere (Fig. 2) are consistent with the calculated data
only in part: no monotonous decrease in the cyclohexene conver-
It is quite possible that, in addition to the reaction thermody-
namics, other factors, for example, the decay of active sites at
ꢀ
Тꢂ50 С, are responsible for the decrease in the cyclohexene con-
ꢀ
ꢀ
sion was observed with increasing temperature from 10 to 40 С.
version as the temperature increased from 40 to 50 С.
ꢀ
The curves of 1,7-octadiene formation exhibit maxima at ~40 С and
When the reaction was performed on high-percentage rhenium
catalysts in an ethylene atmosphere, the 1,7-octadiene yields
approached 16 wt. % with the retention of a high selectivity as the
pressure was increased to 40 atm (Fig. 4).
ꢀ
the yield decreases as the reaction temperature approaches 50 С.
However, even though the target product yields are close to the
thermodynamic equilibrium values, the cyclohexene conversion at
Рtotal ¼ 40 atm and РС2Н4 ¼ 27.5 atm is significantly lower than that
The partial pressure of ethylene demonstrated a crucial effect on
the cyclohexene conversion. Even at [Re] ¼ 6.0 wt. % (Fig. 5), the
yield of the target product increased by a factor of ~1.6 as compared
with catalysts with the Re content 8e10% (Fig. 4) when the ethylene
pressure was raised from 40 to 60 atm. Thus, even at ~60 atm, an
Fig. 2. The temperature effect on cyclohexene ethenolysis for low-percentage Re-
containing catalysts: (1) 0.5 wt. % Re, (2) 1 wt. % Re, (3) 2 wt. % Re. Reaction conditions:
Fig. 4. The influence of the Re concentration on the efficiency of Re/Al
2
O
3
catalysts in
ꢀ
Ptotal ¼ 40 atm,
P
ethene ¼ 33 atm, cyclohexene: n-hexane ¼ 3: 2, cyclohexene:
cyclohexene ethenolysis. Reaction conditions: 20 C, Pethene ¼ 40 atm, cyclohexene: n-
ꢁ
1
ꢁ1
ethene ¼ 1: 10, LHSV ¼ 3 h , gas flow rate 1 nmL/sec.
hexane ¼ 3: 2, cyclohexene: ethene ¼ 1: 10, LHSV ¼ 3 h , gas flow rate 1 nmL/sec.
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L.M. Kustov, D.B. Furman / Journal of Organometallic Chemistry xxx (2018) 1e5
5
containing a Re¼CH
. Conclusions
Thus, the efficient method of synthesis of octadiene-1,7 by
2
fragment represent active sites of the catalyst.
4
cyclohexene ethenolysis (co-metathesis) on a regenerable hetero-
geneous catalyst under flow conditions was found. Based on ther-
modynamic calculations, the theoretically possible conversions of
cyclohexene into 1,7-octadiene by ethenolysis at different tem-
peratures and pressures were close to 20 wt.%.
The NH ReO /Al O catalyst containing about 6 wt. % Re was
4 4 2 3
found to be an optimum catalytic system for cyclohexene
ethenolysis.
The reaction can be performed in ethylene or Ar þ С
2 4
Н gas
mixtures in the temperature, Re concentration, and pressure ranges
ꢀ
1
5e50 С, 0.5e10 wt. %, and 20e60 atm, respectively. The effects of
the total gas mixture pressure and the partial pressure of ethylene,
the gas temperature and composition, and the Re concentration on
the efficiency of the NH ReO /Al O catalysts were examined.
4 4 2 3
The optimal conditions for the production of 1,7-octadiene at
high selectivity (99,9%) and cyclohexene conversion (up to 25 wt. %)
by heterogeneous catalysis under flow conditions were developed
for the first time. The process developed has no analogs in the
literature. The catalyst virtually retained its efficiency in six 5-h
regeneration cycles.
Fig. 5. The influence of the ethene partial pressure on the octadiene-1,7 yield in
ꢀ
cyclohexene ethenolysis on the 6 wt. % Re/Al
2
O
3
catalyst. Reaction conditions: 18 C,
ꢁ
1
Ptotal ¼ 60 atm, cyclohexene: n-hexane ¼ 3: 2, LHSV ¼ 3 h , gas flow rate 1 nmL/sec,
cyclohexene: ethene ratios are indicated in the figure.
Table 4
Efficiency of alumina-based rhenium-containing catalysts ([Re] ¼ 6 wt. %) in the
reaction of co-metathesis of cyclohexene with ethylene in different regeneration
runs.
Run numbera
P, atm
total partial
[cyclo-С
wt. %
Yield, wt. %
Octadiene-
Other pro-
6 6
] in n-С ,
Acknowledgement
(
C2H4)
1
,7 ducts
The research was supported by Russian Science Foundation
(grant no. 14-50-00126) in the part related to catalyst preparation
and testing and to the Ministry of Education and Science of the
Russian Federation in the framework of the Increase of Competi-
tiveness Program of NUST « MISiS» (No. К2-2017-011) in the part
related to the thermodynamic calculations.
1
2
3
6
60
70
60
60
45.0
52.5
45.0
45.0
58
72
72
58
12.9
20.1
16.7
12.8
<0.1
<0.1
<0.1
<0.1
ꢀ
Experimental conditions: Т ¼ 16e18 С, liquid flow rate V ¼ 3 ml/h; gas flow rate
V
g
¼ 1 ml/s (STP).
a
Regeneration was performed every 5 h of catalyst operation.
References
[
[
[
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increase in the partial pressure of ethylene makes it possible to
approach a thermodynamic yield of 1,7-octadiene (~25 wt %) with
the retention of the high selectivity (Fig. 5). This pressure effect is
consistent with the thermodynamics of gas-liquid reactions: the
solubility of ethylene increases with increasing pressure.
The possibility of almost complete regeneration of the alumina-
based rhenium-containing catalytic system without activity and
selectivity losses (Table 4) at least in six regeneration cycles is an
important property of this system.
In conclusion, an important note should be made. The catalysts
tested were white after thermal pretreatment in air. In the course of
the catalytic process, the system became yellow with time. After
rather long operation, the system became dark gray and rapidly
turned white in air.
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[
[
[
[
[
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[
6
[
(
These catalyst color changes, low-temperature conditions of the
cyclohexene ethenolysis, and high selectivity at conversions close
to thermodynamic equilibrium suggest that a Re metal complex is
the active site of the catalyst.
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It is likely that the formation of this complex at the support
surface started at the contact of ethylene and Re compounds
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[
17] Yu M. Zhorov, Thermodynamics of Chemical Processes, Khimiya, Moscow,
985, p. 91.
18] NIST http:/webbook.nist/gov/cgi.
1
formed upon calcination of NH
4 4 2 3
ReO /Al O and finished at the
[
supply of cyclohexene to the catalyst surface. These carbene species
[19] S.V. Benson, Thermochemical Kinetics, Mir, Moscow, 1971.
Please cite this article in press as: L.M. Kustov, D.B. Furman, Journal of Organometallic Chemistry (2018), https://doi.org/10.1016/
j.jorganchem.2018.01.059