High selectivity production of propylene from 2-butene: Non-degenerate pathways to convert symmetric olefins via olefin metathesis

Article abstract of DOI:10.1039/c2cc30172e

The first example of propylene production from 2-butene in promising yield is described by reacting trans-2-butene over tungsten hydrides precursor W-H/Al₂O₃ at 150 °C and different pressures in a continuous flow reactor. The tungsten carbene-hydride active site operates as a "bi-functional catalyst" through the disfavoured 2-butene isomerisation on W-hydride and 2-butenes/1-butene cross-metathesis on W-carbene.

Full text of DOI:10.1039/c2cc30172e

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COMMUNICATION
High selectivity production of propylene from 2-butene: non-degenerate
pathways to convert symmetric olefins via olefin metathesisw
a
a
a
b
Etienne Mazoyer, Kai C. Szeto, Jean-Marie Basset,z* Christopher P. Nicholas* and
a
Mostafa Taoufik*
Received 9th January 2012, Accepted 7th February 2012
DOI: 10.1039/c2cc30172e
The first example of propylene production from 2-butene in promising
higher than 95%. This reaction is catalyzed by tungsten
tris-hydrides supported on g-alumina, which proceeds as a
yield is described by reacting trans-2-butene over tungsten hydrides
7
–9
precursor W–H/Al
2
O
3
at 150 8C and different pressures in a
‘‘tri-functional single site’’ catalyst.
However, the former
continuous flow reactor. The tungsten carbene-hydride active
site operates as a ‘‘bi-functional catalyst’’ through the disfavoured
system suffers from catalyst deactivation, leading to low yield
8
of propylene. Recently, we described another way to produce
2
-butene isomerisation on W-hydride and 2-butenes/1-butene
propylene from 1-butene. The mechanism of this reaction proceeds
firstly by the thermodynamically favourable isomerisation of
cross-metathesis on W-carbene.
1
-butene to 2-butenes followed by cross-metathesis between
1
1-butene and the newly formed 2-butenes.
0
Propylene supply has been a concern in the recent years.
Classically, propylene is derived as a side product of petroleum
A tungsten carbene-hydride W(H) (Q CHR) has been postulated
as the active site during the ethylene to propylene reaction, in which
the tungsten-hydride performs dimerisation–isomerisation, and the
1
cracking processes. However, increased demand of polypropylene
and propylene oxide is driving the development of on-purpose
2
,3
8
methods for production of propylene like olefin metathesis. The
tungsten-carbene moiety is responsible for the olefin metathesis.
4–6
cross metathesis reaction between ethylene and 2-butenes to
form propylene is an alternative method currently undergoing
significant industrial development.
Herein, we report an efficient heterogeneous catalytic system
to produce propylene from trans-2-butene according to
Scheme 1, a feed which classically gives degenerate products in
olefin metathesis. This reaction is catalysed by a ‘‘bifunctional
single site’’ catalyst that proceeds in two steps: (i) trans-2-butene
double bond migration to 1-butene by a tungsten hydride moiety,
and (ii) cross-metathesis between 1-butene and 2-butenes on the
tungsten carbene site to finally form propylene.
Olefin metathesis opens up new industrial processes for the
production of important olefins in the field of petrochemicals.
In particular, the production of propylene via olefin metathesis
reaction from 2-butenes feedstock (major isomer and available
from steam cracker or refinery based C4 streams) has received
1
1
7
considerable attention. The direct conversion of 2-butenes is
a new scientific challenge for producing a wide variety of more
valuable products such as propylene. As for all symmetrical
olefins, the reaction of 2-butenes with typical olefin metathesis
catalysts always leads, to the best of our knowledge, to
The precursor, tungsten hydride (WH /Al O3-(500)), was
3
2
1
3
obtained by grafting of W(RCC(CH ) )(CH C(CH ) ) ,
3
3
2
3 3 3
2
ꢀ1
on g-alumina(500) (Johnson Matthey, 200 m
g
) followed
by treatment under H at 150 1C (see ESIw). Catalytic performance
2
of trans-2-butene conversion was carried out in a continuous
1
2
degenerate products. It is essential to develop a simple
catalytic system capable of driving non-degenerate pathways
to convert 2-butene to propylene in high yield.
flow reactor (P = 1 bar or 20 bar, T = 150 1C, flow rate =
20 mL min or VHSV = 5200 h ). The reaction undergoes a
C4H8
ꢀ1
ꢀ1
ꢀ
1
ꢀ1
steep maximal conversion rate of 4.9 molC4H8 molW min
at the start of reaction before reaching a pseudo plateau of
Recently, we discovered a new and efficient catalytic reaction
which transforms ethylene directly to propylene with a selectivity
ꢀ
1
ꢀ1
2.2 molC4H8 molW
min , yielding an overall turnover
number, TON, of 14 500 after 90 h (Fig. 1a). In contrast to
the results obtained in the direct transformation of ethylene to
a
Universite´ Lyon 1, Institut de Chimie Lyon, CPE Lyon CNRS,
UMR 5265 C2P2, LCOMS, 43 Bd du 11 Novembre 1918,
69616 Villeurbanne Cedex, France. E-mail: taoufik@cpe.fr;
Fax: +33 472431795; Tel: +33 472431798
Exploratory Catalysis Research, UOP LLC, a Honeywell Company,
25 East Algonquin Road, Des Plaines, IL 60017, USA.
E-mail: Christopher.Nicholas@uop.com; Fax: +1 8473911274;
Tel: +1 8473911261
8
propylene (TON = 300 after 20 h), the conversion profile in
the beginning is quite linear with a deactivation rate of
ꢀ1
b
0.12% h (Fig. 1a). After this period, the conversion converged
3 2
at 15%. WH /Al O3-(500) is known as an efficient classical olefin
8
metathesis catalyst, but it presents a surprisingly high activity in
w Electronic supplementary information (ESI) available: Additional
reaction schemes, conversion and selectivity curves for the experiments
carried out at 20 bar and mixtures of 1-butene and trans-2-butene as
feed. See DOI: 10.1039/c2cc30172e
z Current address: KCC, King Abdullah University of Science and
Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia.
Scheme 1 Reaction occurring during the conversion of 2-butene.
Chem. Commun., 2012, 48, 3611–3613 3611
This journal is c The Royal Society of Chemistry 2012

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Fig. 2 Molar selectivity (%) in propylene at 20 h on stream for trans-
-butene conversion on WH /Al 3-(500) at 150 1C at 1 bar and 20 bar.
2
3
2
O
the presence of unfavourable 2-butenes to 1-butene isomerisation
reaction. As described in the case of 1-butene conversion to
1
propylene, the isomerisation of 2-butenes can occur on the
0
1
4,15
W–H bond by the Cossee–Arlman mechanism
followed by
a b-H-elimination. The reaction is equilibrium limited and
disfavours the formation of 1-butene with a 1-butene : 2-butenes
1
6
ratio of 5 : 95 at 150 1C and 1 bar. This equilibrium is displaced
by favourable cross-metathesis between 1-butene and 2-butenes,
and thus drives the selectivity towards propylene.
Fig. 1 (a) Conversion of 2-butene and cumulative TON vs. time on
stream; (b) selectivity vs. time on stream obtained during the 2-butene
We believe that the relatively consistent selectivity to propylene
at low and high pressure is indicative of 2-butenes cross-metathesis
with 1-butene as the rate limiting step in the reaction pathway. As
cross-metathesis is the slow step, probably due to the sterically
unfavorable 1,2-disubstituted metallacyclobutane intermediate
(Scheme 2), the forward and backward butenes isomerization set
up the equilibrium concentration of 1-butene and 2-butene, which
then sets the relative amounts of 1-butene/2-butene cross-metathesis
and 1-butene self-metathesis. Increasing the pressure of the
reaction to 20 bar increases the concentration of 2-butene,
thereby increasing the rate of cross-metathesis while also
favouring the primary cross-metathesis products propylene
and pentenes. We note that analysis is somewhat complicated
by the fact that isomerization of 1-butene back to 2-butenes is
3 2
conversion catalyzed by WH /Al O3-(500) (5.5 wt% W).
conversion of a symmetric olefin such as trans-2-butene, which
1
1
classically only gives degenerate products. This unprecedented
reaction leads to an outstanding and fairly constant selectivity
of 55% to propylene (Fig. 1b), giving a maximum productivity
ꢀ1
ꢀ1
of 50.5 mmolC3H6 gcata
h
after 1 h on stream. Even after
2
0 h on stream, propylene is still the major product with 52.5%
ꢀ
1
ꢀ1
h ). The
selectivity (productivity of 21.3 mmolC3H6 gcata
other products of the reaction are n-pentenes at 36.5%, but only
.5% selectivity to n-hexenes, and 1.5% of ethylene are
9
observed at 20 h on stream (Fig. 1b). The excess of propylene vs.
n-pentenes and the deficit of ethylene vs. hexenes can be explained
by the cross metathesis between 2-butenes and ethylene. Therefore,
as this reaction gives 2 mol of propylene per mole of ethylene
1
0
likely the fastest reaction occurring.
Current data indicate that the concentration of 1-butene in
the feed affects strongly the productivity of propylene. Hence,
we also studied the effect of the proportion of 1-butene from 0%,
33%, 50%, 66% to 100% in 2-trans-butene feed on propylene
(Scheme S1, ESIw), it explains the 16% difference in selectivity to
propylene and 2-pentenes due to the consumption of 8% of
ethylene.
Increasing the pressure to 20 bar while keeping the other
parameters constant shows a beneficial impact on the conversion
rate, which rises from 25% to 35% at the beginning of the curve
production in a continuous flow reactor (P
ꢀ
= 1 bar, T =
ꢀ1
C4H8
1
150 1C, flow rate total = 20 mL min or VHSV = 5200 h ).
(
Fig. S1, ESIw). At 35 h on stream the cumulative TON reaches
0 000 at 20 bar versus 6000 at atmospheric pressure (Fig. S2,
1
10
ESIw). In contrast to what was described for 1-butene conversion,
the drop of selectivity in propylene is small; it remains the major
product, decreasing from 52% to 50%. This change in selectivity is
in favour of pentenes, in which the selectivity slightly increases from
36.5% to 44% (Fig. 2). Increasing the pressure afforded a higher
propylene productivity, as after 2 h on stream at 20 bar, the
ꢀ
1
ꢀ1
and significantly
productivity rate is 64.8 mmolC3H6 gcata
h
ꢀ
1
ꢀ1 10
higher than using 1-butene as feed (50.8 mmolC3H6 gcata
h ).
Furthermore, all linear butene isomers are detected in the
gas phase. The isomeric distribution after 1000 min is 5%
Scheme 2 Catalytic cycle for the conversion of 1-butene on WH3/
Al
1
-butene, 73% trans-2-butene and 22% cis-2-butene, revealing
2 3-(500)
O .
3
612 Chem. Commun., 2012, 48, 3611–3613
This journal is c The Royal Society of Chemistry 2012

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These results highlight the importance of the dual functionality
of the supported tungsten carbene-hydride W(H) (Q CHR) active
site in the direct conversion of 2-trans-butene into propylene. A
catalytic cycle that involves all these reactions, i.e. isomerisation
of 2-butenes to 1-butene (cycle A), 1-butene/2-butenes cross
metathesis (cycle B), can be proposed (Scheme 2).
1
7
A classical process for producing propylene using olefin
metathesis comprises three separate steps: (i) dimerising
ethylene to 1-butene; (ii) isomerising 1-butene to 2-butenes;
and (iii) cross-metathesis of 2-butenes by ethylene. The present
reaction produces propylene directly in one single step via a
non-degenerate pathway from 2-butenes that has important
1
8
scientific, economical and technical advantages.
In summary, the WH /Al O system is the best unprece-
Fig. 3 Selectivity at 20 h on stream for 1-butene/2-butene metathesis
catalyzed by WH /Al 3-(500) (5.5 wt% W) at 150 1C vs. 1-butene
molar percentage in the 2-butene feed.
3
2 3-(500)
3
2
O
dented single-site catalyst precursor for the direct transformation
of trans-2-butene to propylene, regarding either activity or
selectivity; it operates as a ‘‘bi-functional single active site’’
tungsten carbene-hydride catalyst, opening up the non-degenerate
pathway via 2-butene isomerisation to 1-butene and 2-butenes/
1-butene cross-metathesis. This example simultaneously provides
a novel process to utilise 2-butene feedstock to produce propylene
in promising productivity.
Notes and references
1
2
3
4
5
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6 S. M. Pillai, G. L. Tembe and M. Ravindranathan, Appl. Catal., A,
1992, 81, 273–278.
2
1
3 2
-butene metathesis catalyzed by WH /Al O3-(500) (5.5 wt% W) at
7
E. Le Roux, M. Taoufik, C. Coperet, A. de Mallmann, J. Thivolle-
Cazat, J. M. Basset, B. M. Maunders and G. J. Sunley, Angew.
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50 1C vs. 1-butene molar percentage in the 2-butene feed.
For each ratio 2-butene/1-butene, the conversion profile is
8
9
M. Taoufik, E. Le Roux, J. Thivolle-Cazat and J. M. Basset,
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´
J. M. Basset, C. Coperet, D. Soulivong, M. Taoufik and
very similar, with a maximum conversion for the experiment
where the feed is only composed of 1-butene. It is also notable
that this experiment shows the fastest deactivation rate. After
J. Thivolle-Cazat, Acc. Chem. Res., 2010, 43, 323–334.
1
1
1
0 E. Mazoyer, K. C. Szeto, S. Norsic, A. Garron, J. M. Basset,
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2
3
0 h on stream, the 50% mixture gives a conversion rate with
ꢀ1
ꢀ1
.8 molC4H8 mol
W
min (Fig. S3, ESIw). As expected, the
7
84–790.
selectivity in propylene is slightly better when 1-butene is a
minor component of the feed. It decreases when the molar
percentage of 1-butene increases, raising the selectivity in
hexenes and ethylene, produced by self-metathesis of 1-butene.
Operating with 33% of 1-butene in the feed gives the best
selectivity in propylene with 55% at the steady state (Fig. 3).
At 20 h on stream the productivity rates span from 26.9
2 W. H. Meyer, M. M. D. Radebe, D. W. Serfontein, U. Ramdhani,
M. du Toit and C. P. Nicolaides, Appl. Catal., A, 2008, 340,
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1
3 D. N. Clark and R. R. Schrock, J. Am. Chem. Soc., 1978, 100,
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4 E. J. Arlman and P. Cossee, J. Catal., 1964, 3, 99–104.
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ꢀ1
ꢀ1
to 36.0 mmolC3H6 gcata
is reached with a 1 : 1 ratio of 1-butene to trans-2-butene
Fig. 4).
h
. The maximum productivity
1
1
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(
This journal is c The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 3611–3613 3613