Selective ethylene trimerization with a cyclopentadienyl-arene titanatrane catalyst

Article abstract of DOI:10.1007/s11243-012-9607-2

Cyclopentadienyl-arene titanatrane catalysts activated by methylaluminoxane (MAO) cocatalysts were studied for the trimerization of ethylene. The introduction of electron-rich multidentate ligands to the catalysts' active sites resulted in good productivity and selectivity for ethylene trimerization. Various amounts of MAO were tested, and methods of its introduction to the system were varied. It has been shown that pre-alkylation of the catalyst with MAO increases the productivity of ethylene trimerization. The effects of reaction temperature and pressure on 1-hexene productivity and selectivity were also studied. The rate of ethylene conversion was approximately first order with respect to ethylene concentration. 1-Hexene was produced under moderate conditions, allowing energy savings to be gained through lower temperature reactions. Springer Science+Business Media B.V. 2012.

Full text of DOI:10.1007/s11243-012-9607-2

Transition Met Chem (2012) 37:439–444
DOI 10.1007/s11243-012-9607-2
Selective ethylene trimerization with a cyclopentadienyl-arene
titanatrane catalyst
Young-kook Kim
Seungwoong Yoon
•
Jaeyoung Park
Seung Bin Park
•
•
Received: 14 February 2012 / Accepted: 4 April 2012 / Published online: 22 April 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Cyclopentadienyl-arene titanatrane catalysts
activated by methylaluminoxane (MAO) cocatalysts were
studied for the trimerization of ethylene. The introduction
of electron-rich multidentate ligands to the catalysts’ active
sites resulted in good productivity and selectivity for eth-
ylene trimerization. Various amounts of MAO were tested,
and methods of its introduction to the system were varied.
It has been shown that pre-alkylation of the catalyst with
MAO increases the productivity of ethylene trimerization.
The effects of reaction temperature and pressure on
ethylene. It is mainly used as a comonomer for the pro-
duction of linear low-density polyethylene (LLDPE), and
its price has been very high owing to the imbalance of
supply and demand [4].
The selective trimerization of ethylene can mainly be
achieved with chromium Ziegler-type catalysts, consisting
of a combination of Cr(III) salts (usually carboxylates)
with aluminum alkyls in conjunction with a Lewis basic
donor (usually pyrroles or 1,2-diethoxyethane). The only
current industrial process that can produce 1-hexene by
ethylene trimerization is based on this chromium catalyst
[1, 2, 5–8].
1
-hexene productivity and selectivity were also studied.
The rate of ethylene conversion was approximately first
order with respect to ethylene concentration. 1-Hexene was
produced under moderate conditions, allowing energy
savings to be gained through lower temperature reactions.
5
Cyclopentadienyl-arene titanium complexes [g -C H –
5
4
(bridge)–Ar]–TiCl3, activated by methylaluminoxane
(MAO), have been reported by Hessen et al. to form highly
active catalysts for the trimerization of ethylene [4, 9–11].
This discovery has attracted many researchers’ interest in
developing ethylene trimerization catalysts.
Introduction
Efforts to develop catalysts for ethylene trimerization
have largely focused on the modification of the cyclopenta-
dienyl ring by the addition of a pendant group that can
coordinate to the metal center; or the introduction of a bridge
between the metal and the cyclopentadienyl ring [3, 12].
However, there appear to be no other studies of tri-
merization catalysts involving direct electronic modifica-
tion of the catalytically active site by the introduction of
electron-rich multidentate ligands in place of the mono-
The oligomerization of ethylene is one of the most
important issues for the synthesis of linear alpha olefins
(
LAO) in both academia and industry [1, 2]. The selective
oligomerization of ethylene has recently attracted consid-
erable attention, as unwanted olefin products would not be
produced by selective oligomerization [3]. In particular,
1
-hexene can be produced by selective trimerization of
dentate Cl ligands. In this regard, the potentially tetra-
3
Y. Kim Á S. B. Park (&)
3-
dentate trianionic triethoxyamine (N(CH CH O) , TEA),
2
2
3
Department of Chemical and Biomolecular Engineering, Korea
Advanced Institute of Science and Technology, 291 Daehak-ro,
Yuseong-gu, Daejeon 305-701, Korea
which is the fully deprotonated form of triethanolamine, is
potentially suitable for modifying the active site of ethyl-
ene trimerization catalysts.
e-mail: SeungBinPark@kaist.ac.kr
This work reports the synthesis of cyclopentadienyl-arene
titanatrane catalysts for selective ethylene trimerization.
Titanatrane denotes cyclic titanium ethers of tris(2-
Y. Kim Á J. Park Á S. Yoon
Daedeok Research Institute, Honam Petrochemical Corporation,
2
4-1 Jang-dong, Yuseong-gu, Daejeon 305-726, Korea
123

4
40
Transition Met Chem (2012) 37:439–444
Me Si
3
Catalyst 1
Catalyst 2
Me Si
Me Si
3
3
Ti
N
Ti
N
Ti
O
O
O
O
O
O
O
O
O
N
Catalyst 3
Scheme 1 Ethylene trimerization catalysts
Catalyst 4
Catalyst 5
oxyalkyl)amine [13]. Cyclopentadienyl-arene titanatrane
complexes were synthesized and tested for ethylene trimer-
ization (Scheme 1).
Synthesis
5
5
(g -C
H
CMe Ph)TiCl
2
, [g -(3-SiMe
)C
H
CMe –3,5-Me
2
-
5
4
3
3
5
3
2
5
5
C H ]TiCl , {g -C H C[(CH ) ]Ph}TiCl , [g -(3-SiMe )C -
H C[(CH ) ]Ph}TiCl , and {g -(3-SiMe )C H C[(CH ) ]–
6
3
3
5
4
2 5
3
3
5
5
3
2 5
3
3
5
3
2 5
3,5-Me C H }TiCl were synthesized by a procedure repor-
2 6 3 3
Experimental
ted elsewhere in the literature [4, 9–11].
5
General procedures
Synthesis of (g -C H CMe Ph)Ti(TEA)
5
4
2
5
All manipulations of water- and/or air-sensitive compounds
were performed using standard Schlenk and glove-box
techniques under deoxygenated argon or nitrogen [14]. The
solvents for synthesis, tetrahydrofuran (THF), n-hexane, n-
pentane, diethyl ether, and methylene chloride (CH Cl ),
In 50 ml of toluene, 6 mmol (2.016 g) of (g -
C H CMe Ph)TiCl was dissolved and cooled to -78 °C.
5
4
2
3
Then, 6 mmol of triethanolamine and 18 mmol of trieth-
ylamine were added dropwise to the solution. The mixture
was allowed to warm up to room temperature and stirred
for 12 h. The orange suspension was filtered through a
Celite bed, and the volatiles were removed under vacuum.
The desired orange product in 60 % yield (3.6 mmol,
2
2
were distilled through an activated alumina column and
˚
dried over molecular sieves (5 A, Yakuri Pure Chemical-
sCo) to eliminate moisture [15]. Chloroform-d(CDCl ) and
3
benzene-d6(C6D6) for NMR analysis were acquired from
1.357 g) resulted after stripping with n-hexane.
1
Cambridge Isotope Laboratories and dried over molecular
˚
sieves (5 A, Yakuri Pure ChemicalsCo) [15]. n-Butyllith-
H NMR(400 MHz, CDCl ): d = 6.70–6.48(m, 5H, ArH),
3
4.28(m, 6H, NCH CH O), 3.08(m, 6H, NCH CH O), 1.70
2
2
2
2
1
3
1
ium (2.5 M in n-hexane), phenyllithium (1.8 M solution in
dibutyl ether), 1-bromo-3,5-dimethylbenzene, 6,6-dimeth-
ylfulvene, triethanolamine, triethylamine, 6,6-pentameth-
(s, 6H, C(CH ) ); C{ H} NMR(100 MHz, CDCl ): d =
3
2
3
154.66 (Phipso), 147.63 (Cpipso), 128.54 (o-Ph), 126.67(p-Ph),
125.89 (m-Ph), 123.55 (Cp), 121.81 (Cp), 70.52(NCH2
CH O), 55.45(NCH CH O), 41.00 (CMe Ph), 28.80 (Me);
ylfulvene, trimethylsilyl chloride, TiCl , and magnesium
4
2
2
2
2
sulfate were acquired from Sigma-Aldrich and used as
received. The MAO cocatalyst (10 wt.% aluminum in
toluene) was purchased from Albemarle. Ethylene was
distilled through an alumina column and Cu-supported
oxygen scavenger before use [15].
Element Analysis: Calcd for C H NO Ti: C 63.67, H 7.21,
20 27 3
N 3.71. Found: C 63.57, H 7.13, N 3.67.
5
Synthesis of [g -(3-SiMe )C H CMe –3,5-
3
5
3
2
Me C H ]Ti(TEA)
2 6 3
NMR spectra were recorded on a Bruker Avance 400
Spectrometer at 25 °C. Chemical shifts (d) are reported for
CDCl (7.24 ppm) and C D (7.16 ppm).
In 50 ml of toluene, 6 mmol (2.616 g) of [g5-(3-
SiMe )C H CMe –3,5-Me C H ]TiCl was dissolved and
3
6
6
3
5
3
2
2
6
3
3
1
23

Transition Met Chem (2012) 37:439–444
441
cooled to -78 °C. Then, 6 mmol of triethanolamine and
vacuum. The desired ivory-colored product in 60 % yield
1
8 mmol of triethylamine were added dropwise to the
(1.164 mmol, 0.569 g) resulted after stripping with n-
hexane.
solution. The mixture was allowed to warm up to room
temperature and stirred for 12 h. The orange suspension
was filtered through a Celite bed and the volatiles were
removed under vacuum. The desired ivory-colored product
in 35 % yield (2.1 mmol, 1.002 g) resulted after stripping
1
H NMR(400 MHz, CDCl ): d 7.44(d, 2H, ArH), 7.24(d,
3
2H, ArH), 7.08(t, 1H, ArH), 6.29(s, 1H, Cp), 6.17(s, 2H, Cp),
4.14(m, 6H, NCH CH O), 2.82(m, 6H, NCH CH O), 2.71(d,
1H, -(CH ) ), 2.57(d, 1H, –(CH ) ), 2.06(m, 2H, –(CH ) ),
2
2
2
2
2
5
2 5
2 5
13
1
with n-hexane.
1
1.53(br, 3H, –(CH ) ), 1.4(m, 3H, –(CH ) );); C{ H}
2 5 2 5
H NMR (400 MHz, CDCl ): d = 6.87(s, 2H, Ar–o),
NMR(100 MHz, CDCl ): d = 146.04, 139.58(Cp and Cpipso),
3
3
6
.77(s, 1H, Ar–p), 6.35–6.37(q, 3H, Cp), 4.26–4.3 (q, 6H,
NCH CH O), 2.26–2.96(t, 6H, NCH CH O), 2.27 (s, 6H,
128.37, 128.31, 125.01(Ar), 121.64, 120.38, 119.8(Cp),
70.58(NCH CH O), 55.52(NCH CH O), 46.07(C[(CH ) ]),
2
2
2
2
2
2
2
2
2 5
ArCH ), 1.7 (s, 6H, C(CH ) ) 0.18(s, 9H, Si(CH ) );
3 2
37.05, 36.87(a–CH ), 26.9(c–CH ), 23.08(b–CH ), -0.087
(Si(CH ) ); Element Analysis: Calcd for C H NO SiTi: C
3 3 26 39 3
3
3 3
2
2
2
1
3
1
C{ H} NMR(100 MHz, CDCl ): d = 152.14, 138.82,
3
1
1
5
2
36.95(Ar and Cp Cipso), 128.14, 127.01, 124.48, 122.63,
63.79, H 8.03, N 2.86. Found: C 63.71, H 7.95, N 2.81.
20.25(Ar CH and Cp CH), 70.73(NCH CH O),
2
2
5
5.73(NCH CH O),
2
40.12(C(CH3)2),
29.78,
Synthesis of {g -(3-SiMe )C H C[(CH ) ]–3,5-
2
3
5
3
2 5
9.54(C(CH ) ), 21.71(ArCH ), -0.149(Si(CH ) ); Ele-
3
Me C H }Ti(TEA)
2 6 3
2
3
3 3
ment Analysis: Calcd for C H NO SiTi: C 62.88, H 8.23,
2
5
39
3
5
N 2.93. Found: C 62.76, H 8.25, N 2.96.
In 50 ml of toluene, 1.22 mmol (0.581 g) of {g -(3-
SiMe )C H C[(CH ) ]–3,5-Me C H }TiCl was dissolved
3
5
3
2 5
2
6
3
3
Synthesis of {g5-C H C[(CH ) ]Ph}Ti(TEA)
and cooled to -78 °C. Then, 6 mmol of triethanolamine
and 18 mmol of triethylamine were added dropwise to the
solution. The mixture was allowed to warm up to room
temperature and stirred for 12 h. The orange suspension
was filtered through a Celite bed and the volatiles were
removed under vacuum. The desired ivory-colored product
in 60 % yield (0.732 mmol, 0.379 g) resulted after strip-
5
4
2 5
5
In 50 ml of toluene, 1.92 mmol (0.722 g) of {g -
C H C[(CH ) ]Ph}TiCl was dissolved and cooled to
5
4
2 5
3
-
78 °C. Then, 6 mmol of triethanolamine and 18 mmol of
triethylamine were added dropwise to the solution. The
mixture was allowed to warm up to room temperature and
stirred for 12 h. The orange suspension was filtered
through a Celite bed and the volatiles were removed under
vacuum. The desired orange product in 60 % yield
ping with n-hexane.
1
H NMR(400 MHz, CDCl ): d 7.42(s, 2H, ArH), 6.92(s,
3
1H, ArH), 6.5(s, 1H, Cp), 6.39(s, 1H, Cp), 6.35(s, 1H, Cp),
4.38(m, 6H, NCH CH O), 3.24(m, 6H, NCH CH O),
2.85(d, 1H, –(CH ) ), 2.77(d, 1H, –(CH ) ), 2.46(s, 6H,
(
1.152 mmol, 0.481 g) resulted after stripping with n-
hexane.
2
2
2
2
2
5
2 5
1
H NMR(400 MHz, CDCl ): d 7.45(d, 2H, ArH),
2Me), 2.42(t, 1H, –(CH ) ), 2.16(t, 1H, –(CH ) ), 1.72(br,
2 5 2 5
3
7
.26(d, 2H, ArH), 7.15(m, 1H, ArH), 6.18(s, 2H, Cp),
.09(s, 2H, Cp), 4.17(m, 6H, NCH CH O), 2.85(m, 6H,
3H, –(CH ) ), 1.48(br, 3H, –(CH ) ), 0.25(s, 9H, SiMe );
2 5 2 5 3
1
3
1
6
C{ H} NMR(100 MHz, CDCl ): d = 146.24, 139.6(Cp
2
2
3
NCH CH O), 2.65(d, 2H, -(CH ) ), 2.02(t, 2H, –(CH ) ),
2
and Cpipso), 128.38, 128.32, 125.03(Ar), 121.66, 120.39,
2
2 5
2 5
1
13
1
.56(b, 3H, –(CH ) ), 1.39(m, 3H, –(CH ) );); C{ H}
2 5 2 5
119.8(Cp), 70.6(NCH CH O), 55.57(NCH CH O), 46.09
2
2
2
2
NMR(100 MHz, CDCl ): d = 156.0, 142.1 (Ph and Cp
(C[(CH ) ]), 37.08, 36.89(a–CH ), 27.3(c–CH ), 23.08
3
2 5
2
2
Cipso), 129.2 (Ph o–CH), 127.9 (Ph m–CH), 126.8 (Ph p–
CH), 123.2, 120.9 (Cp CH), 70.55(NCH CH O), 55.35
(b–CH ),), 21.65(ArCH ), -0.085(Si(CH ) ); Element
Analysis: Calcd for C H NO SiTi: C 64.97, H 8.37, N
28 43 3
2
3
3 3
2
2
(
NCH CH O), 45.1 (C[(CH ) ]), 35.8 (a–CH ), 26.1 (c-CH ),
2.71. Found: C 64.92, H 8.25, N 2.78.
2
2
2 5
2
2
2
2.4 (b–CH ); Element Analysis: Calcd for C H NO Ti: C
2
23 31
3
6
6.19, H 7.49, N 3.76. Found: C 66.11, H 7.41, N 3.68.
Ethylene trimerization with MAO as cocatalyst
5
Synthesis of [g -(3-SiMe )C H C[(CH ) ]Ph}Ti(TEA)
The trimerization of ethylene was carried out in a 2L
autoclave equipped with an agitator after pre-heating at
120 °C and cooling to the required temperature. A volume
of 500 ml of toluene and MAO was injected into the
reactor under nitrogen atmosphere and pressurized with
ethylene to the required pressure. After equilibrating for
20 min, the catalyst solution with toluene (including MAO
in some cases) was injected into the reactor. The reaction
pressure was kept constant with an ethylene feed during the
3
5
3
2 5
5
In 50 ml of toluene, 1.94 mmol (0.869 g) of [g -(3-
SiMe )C H C[(CH ) ]Ph}TiCl was dissolved and cooled
3
5
3
2 5
3
to -78 °C. Then, 6 mmol of triethanolamine and 18 mmol
of triethylamine were added dropwise to the solution. The
mixture was allowed to warm up to room temperature and
stirred for 12 h. The orange suspension was filtered
through a Celite bed and the volatiles were removed under
123

4
42
Transition Met Chem (2012) 37:439–444
trimerization reaction. After the run time, the reactor was
depressurized and ethanol was injected to deactivate the
catalyst and the MAO. The reaction products consisted of
three fractions: 1-hexene (trimers of ethylene), 1-decene
and 2 and catalysts 3 and 4. The SiMe -substituted cata-
3
lysts showed slightly improved activity and selectivity over
the non-substituted catalysts.
Each catalyst produced 1–2 wt.% polyethylene byproducts
with molecular weights in the range of 400,000–
600,000 g/mol. Polyethylene from catalysts 1 and 2 had lower
Tm (127–128 °C) than that from catalysts 3, 4, and 5 (130–
131 °C). Catalysts 1 and 2 produced more 1-hexene that was
used as a co-monomer, which lowered the Tm.
(
(
cotrimers of ethylene and 1-hexene), and polyethylene
1–2 wt. %). The liquid fraction of the product was col-
lected and filtered for GC analysis using cyclooctane as
internal standard. Integration of cyclooctane, 1-hexene, and
1
-decene peaks in the GC gives the amount of 1-hexene
and 1-decene. After the polymer was separated from the
liquid mixture, it was stirred in acidic ethanol for 10 min,
repeatedly rinsed with ethanol, and dried under vacuum.
Effects of MAO
Some attention has been paid to the role of MAO in the
catalysts with Ti–O bonds [16–18]. When the catalyst is
activated using MAO, the cocatalyst can induce Ti–O
bonds to open up a site for insertion. It is reported that the
cleavage of the third arm of the ligand by MAO can make
way for monomer incorporation. So MAO was used as a
cocatalyst in the present catalysis system. In the absence of
MAO, there was no activity with these catalysts.
As shown in Table 2, it is clear that the increase in the
amount of MAO has improved the productivity and
selectivity of ethylene to 1-hexene. However, using too
much MAO will make the process uneconomic due to its
high price.
Results and discussion
Effects of triethoxyamine ligands
The effects of replacing the Cl ligands with triethoxy-
3
amine ligands in the trimerization catalyst were tested by
studying catalysts 1–5 with cyclopentadienyl-arene tita-
nium chloride catalysts 6–10. In this paper, productivity is
defined as the amount of 1-hexene with 1 mmol of catalyst
an hour, and selectivity is the 1-hexene portion of all the
reaction products. From the results in Table 1, the intro-
duction of the triethoxyamine ligands to the active sites had
a beneficial influence on the productivity of the 1-hexene,
but had little influence on the selectivity. The potentially
tetradentate electron-rich trianionic triethoxyamine may be
important in selective ethylene trimerization.
Pre-alkylation of the catalyst prior to its addition to the
reactor was tested by feeding half the MAO to the reactor
and stirring it for 5 min; the other half was contacted with
the catalyst for 1 min before being added to the reactor.
Pre-alkylation of the catalyst increased the productivity of
ethylene trimerization (Table 3).
Of the catalysts with triethoxyamine ligands, catalysts 1
and 2 showed the best productivity and selectivity. They both
contained CMe -bridges between the cyclopentadienyl and
2
Effects of reaction temperature and pressure
arene moieties; catalysts 3, 4, and 5 had C(CH ) -bridges. The
2
5
CMe -bridge likely provided stronger arene coordination in
2
The effects of reaction temperature on productivity and
selectivity are shown in Table 4. The catalyst was less acti-
vated at 5 °C and below, which reduced productivity. The
catalyst suffered from high deactivation rates at 25 °C and
the cationic active sites than C(CH ) -bridges.
2
5
The effects of substituents on the catalysts’ cyclopen-
tadienyl moieties were probed by comparison of catalysts 1
Table 1 Ethylene trimerization
a
with catalysts/MAO system
Catalyst
Cat. amount
lmol)
MAO amount
(e.q.)
Temp.
(°C)
Pressure
(bar)
C
(kgC
6
= productivity
6
C = selectivity
(
6
/mmolTi h)
(wt.%)
b
1
40
40
20
20
20
40
40
20
20
20
1,000
1,000
1,000
1,000
1,000
1,000
1,000
1,000
1,000
1,000
15
15
15
15
15
15
15
15
15
15
7
7
7
7
7
7
7
7
7
7
6.01
6.55
5.33
5.39
4.35
4.52
4.69
3.82
3.48
3.27
90.3
90.4
75.0
86.0
58.8
90.5
89.7
58.1
83.3
74.6
b
2
b
3
b
4
b
5
a
c
6
Reaction conditions: toluene
solvent, 15 min. reaction time
c
7
b
Cyclopentadienyl-arene
titanatrane catalysts
c
8
c
9
c
Cyclopentadienyl-arene
titanium chloride catalysts
c
1
0
1
23

Transition Met Chem (2012) 37:439–444
443
Table 2 Effects of the amount
of MAO
Entry
MAO amount
e.q.)
Temp.
(°C)
Pressure
(bar)
C
(kgC
6
= productivity
C
(wt.%)
6
= selectivity
(
6
/mmolTi.h)
1
500
20
20
20
7
7
7
4.16
5.98
6.36
87.4
90.8
91.3
Reaction conditions: 40 lmol of
Catalyst 1, toluene solvent,
2
3
1,000
2,000
1
5 min. reaction time
a
Table 3 Effects of the method of MAO feeding
Entry
MAO amount (e.q.)
Temp. (°C)
Pressure (bar)
C
6
= productivity (kgC
6
/mmolTi h)
C
6
= selectivity (wt.%)
1
1,500
1,500
20
20
7
7
6.61
7.98
92.8
92.1
b
2
a
Reaction conditions: 40 lmol of Catalyst 2, toluene solvent, 15 min. reaction time
b
Half of the MAO was pre-contacted with catalyst and half of the MAO was fed to the reactor
Table 4 Effect of the reaction
temperature
Entry
MAO amount
e.q.)
Temp.
(°C)
Pressure (bar)
C
6
= productivity
(kgC /mmolTi h)
6
C = selectivity
(
6
(wt.%)
1
2
3
4
5
6
1,000
1,000
1,000
1,000
1,000
2,000
5
10
15
20
25
30
7
7
2.22
5.72
6.55
6.57
3.80
0.55
48.2
84.5
90.4
92
7
7
Reaction conditions: 40 lmol of
Catalyst 2, toluene solvent,
7
77
10
39
1
5 min. reaction time
Table 5 Effect of the reaction pressure
Entry
MAO amount (e.q.)
Temp. (°C)
Pressure (bar)
C
6
= Productivity (kgC
6
/mmolTi h)
6
C = Selectivity (wt.%)
1
2
1,000
1,000
20
20
7
6.57
10.3
92
92.3
10
Reaction conditions: 40 lmol of Catalyst 2, toluene solvent, 15 min. reaction time
above, which significantly reduced 1-hexene productivity and
selectivity. Operation was optimized at 10–20 °C.
Conclusions
As shown in Table 5, the reaction pressure also had a
clear effect on the productivity of 1-hexene, which
increased with increasing pressure. Selectivity was not
greatly affected by pressure changes. The rate of ethylene
conversion by this type of catalyst was approximately first
order relative to ethylene concentration, similar to Hessen
et al.’s catalyst [9].
The selective trimerization of ethylene was investigated
using catalytic systems containing potentially tetradentate
trianionic triethoxyamine. The catalysts showed selective
ethylene trimerization (92.3 wt.%) with good 1-hexene
productivity (10.3 kgC /mmolTi h). Small amounts of
6
polyethylene byproduct were also produced.
Pre-alkylation of the catalyst with MAO increased the
productivity of ethylene trimerization. Ethylene conversion
was approximately first order with respect to ethylene
concentration. 1-Hexene was produced under moderate
reaction conditions that required less energy to maintain
than other systems. Structural analysis of these compounds
is underway.
These results suggest that the reaction’s temperature and
pressure can be optimized for production of 1-hexene,
which was produced by this catalyst system at a moderate
temperature and pressure compared with a conventional
chromium catalyst (100–130 °C and 50–100 bar) [19–21].
Therefore, this catalyst system could afford energy savings.
123

4
44
Transition Met Chem (2012) 37:439–444
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