Ethylene oligomerization in the presence of catalyst systems based on mixed-ligand β-diketonatozirconium chlorides

Article abstract of DOI:10.1134/S0965544106050069

The results of study of ethylene oligomerization in the presence of complex catalysts based on mixed-ligand β-diketonatozirconium chlorides are presented. The influence of the composition of a zirconium compound, the electron affinity of β-diketonate ligands, component ratio of the catalytic system, temperature of the process, solvent nature, and other factors on the catalyst activity and molecular-mass distribution of the product of ethylene oligomerization was studied. Nauka/Interperiodica 2006.

Full text of DOI:10.1134/S0965544106050069

ISSN 0965-5441, Petroleum Chemistry, 2006, Vol. 46, No. 5, pp. 338–342. Pleiades Publishing, Inc., 2006.
Original Russian Text © A.A. Khanmetov, A.G. Azizov, A.G. Piraliev, 2006, published in Neftekhimiya, 2006, Vol. 46, No. 5, pp. 366–370.
Ethylene Oligomerization in the Presence of Catalyst Systems
Based on Mixed-Ligand b-Diketonatozirconium Chlorides
A. A. Khanmetov, A. G. Azizov, and A. G. Piraliev
Mamedaliev Institute of Petrochemical Processes, National Academy of Sciences of Azerbaijan, Baku, Azerbaijan
e-mail: ipcp2005@rambler.ru
Received February 14, 2006
Abstract—The results of study of ethylene oligomerization in the presence of complex catalysts based on
mixed-ligand β-diketonatozirconium chlorides are presented. The influence of the composition of a zirconium
compound, the electron affinity of β-diketonate ligands, component ratio of the catalytic system, temperature
of the process, solvent nature, and other factors on the catalyst activity and molecular-mass distribution of the
product of ethylene oligomerization was studied.
DOI: 10.1134/S0965544106050069
Despite a wealth of studies on ethylene oligomeriza- ity and MMD of ethylene oligomers was studied in the
tion in the presence of complex metalloorganic cata- presence of different zirconium diketonate complexes
lysts, data in the literature on the influence of the com- such as acetylacetonate, benzoylacetonate, and diben-
position of mixed-ligand coordination compounds of zoylmethane, as well as complexes with different con-
transition metals and donor–acceptor properties of tents of diketonate and chloride ligand. The influence of
ligands on the catalyst activity and the molecular-mass strong electron-withdrawing substituents in the diketo-
distribution (MMD) of ethylene oligomerization prod- nate ligand on the catalyst activity and the composition
uct are scarce [1, 2].
of ethylene oligomerization products was also studied.
It was found that catalyst systems based on mixed-
ligand β-diketonatozirconium chlorides exhibit a
higher activity in ethylene oligomerization than the cat-
alysts based on tetradiketonates. The reaction condi-
tions and the main results of ethylene oligomerization
in the presence of diketonatozirconium chloride com-
plexes are given in Table 1.
The obtained data indicate that a change of the com-
position of a diketonatozirconium compound has a sig-
nificant effect on the catalyst activity and the composi-
tion of ethylene oligomerization products. The activity
of the catalyst system based on Zr(acac)3Cl in ethylene
oligomerization at 50°ë, a zirconium to aluminum
molar ratio of 1 : 40, and an ethylene pressure in the
reaction medium of 40 atm was 3179.8 g of oligo-
mers/(g(Zr) h), which is two times that of the catalyst
based on zirconium tetraacetylacetonate Zr(acac)4
(1425.4 g(product)/(g(Zr) h)). Under the same condi-
tions, the activity of the catalytic system Zr(DBM)3Cl +
(C2H5)2AlCl reached 5482.5 g(product)/(g(Zr) h).
In this work, we have shown that mixed-ligand
β-diketonatozirconium chlorides in the presence of
alkylaluminum chlorides as activators are effective cat-
alysts for ethylene oligomerization [3–6].
EXPERIMENTAL
Mixed-ligand β-diketonatozirconium chlorides
were synthesized as described in [7, 8].
Ethylene oligomerization in the presence of cata-
lysts based on the synthesized mixed-ligand β-diketo-
natozirconium chloride complexes was carried out in a
stainless steel reactor 0.2 l in volume equipped with a
magnetic stirrer and a pressure gauge. The temperature
in the reactor was controlled by circulating a thermo-
stated oil through the reactor jacket. The catalyst com-
ponents were loaded into the reactor using the Schlenk
technique: for this purpose, the cleaned and inert gas-
purged reactor was evacuated for 1–2 h at 70–80°ë.
Solutions of a zirconium compound and alkylalumi-
num chloride were fed to the reactor from a Schlenk
vessel. Ethylene oligomerization was carried out for
0.5–1 h. The ethylene oligomerization products were
analyzed by GLC and IR spectroscopy.
The activity and selectivity of the catalytic systems
based on β-diketonatozirconium chlorides in ethylene
oligomerization strongly depends on the electron-with-
drawing properties of β-diketonate ligands present in
the zirconium coordination sphere.
Figure 1 depicts the rate curves of ethylene con-
sumption in the presence of catalytic systems based on
RESULTS AND DISCUSSION
The influence of the composition of mixed-ligand β-diketonate chlorides and tetradiketonates of zirco-
β-diketonatozirconium chlorides on the catalyst activ- nium of different compositions.
338

ETHYLENE OLIGOMERIZATION IN THE PRESENCE
339
Table 1. Influence of the composition of β-diketonatozirconium chloride complexes and the process conditions on the cata-
lyst activity and the MMD of ethylene oligomers (solvent, toluene; activator, (C2H5)2AlCl; ethylene pressure, 40 atm; time,
30 min; [Zr] = 2 mmol/l)
Catalyst
activity,
g(product)
----------------------------
g(Zr) h
Oligomer composition, wt %
C10 C12 C14 C16
44.1 26.0 14.86 7.61 4.1
Composition
of zirconium
compound*
Al : Zr ra- Temper-
tio, (mol) ature, °C
C4
C6
C8
C18
C20+
Zr(acac)4
40 : 1
40 : 1
50
50
1425.4
3179.8
2.16 0.83 0.31 0.03
Zr (acac)3Cl
50.20 26.34 17.63 3.6
42.34 24.56 16.81 10.3
1.32 0.56 0.23 0.11
Traces
Zr(acac)2Cl2
Zr(dbm)3Cl
Zr(dbm)4
40 : 1
40 : 1
80 : 1
80 : 1
80 : 1
80 : 1
80 : 1
50
50
50
50
50
40
40
2302.6
5482.5
5268.1
7675.4
5816.6
3015.3
3491.5
3.3
0.92 0.54 0.2 Traces
65.46 16.36 13.1
64.78 15.25 11.36 4.13 2.2
74.3 13.0 9.24 2.28 0.47 0.38 0.15 0.1
66.94 15.74 10.35 3.78 1.8 0.71 0.27 0.14
3.08 1.38 0.34 0.16 0.18
–
–
–
–
–
–
1.27 0.62 0.3
Zr(dbm)3Cl
Zr(dbm)2Cl2
Zr(acac)3Cl
Zr(bzac)3Cl
60.4 18.2 15.0
68.2 16.7 10.4
3.4
3.0
1.8
1.1
0.6
0.4
0.4
0.2
0.15 0.1
* acac is acetylacetone, bzac is benzoylacetone, dbm is dibenzoylmethane.
The activity of the catalytic system and the compo- tem from 3486.4 to 11419.1 g(product)/(g(Zr) h). The
sition of ethylene oligomerization product depends on
the composition of the diketonate group. When acetyl-
acetone in the acetylacetonate complex is replaced by
benzoylacetone or dibenzoylmethane, the activity of
the catalyst system, as well as the yield of the dimer
fraction, butene-1, increases (Fig. 2).
substitution of fluoride atoms for all six hydrogen
atoms in the acetylacetonate ligand increases the cata-
lyst activity to 14312.2 g(product)/(g(Zr) h).
Ethylene consumption, l
90
5
The yield of the dimer fraction, butene-1, in the
presence of the catalyst system based on Zr(acac)3Cl
was 50% in terms of ethylene converted, whereas the
yield of butene-1 reaches 65.4 wt % of converted ethyl-
ene in the presence of the catalytic system based on
Zr(dbm)3Cl.
80
4
70
3
60
The composition of ethylene oligomerization prod-
ucts in the presence of the catalytic systems based on β-
diketonatozirconium chlorides has the Schultz–Flory
pattern. The products of ethylene oligomerization con-
tain mainly ë4–ë10 oligomers whose yield reaches 92–
98 wt % of ethylene converted. The amount of linear α-
olefins in the oligomers was 98–99%. The butene frac-
tion contains 99.5–100% of butene-1. The chromato-
gram of the ë6–ë18 oligomer fraction obtained over the
system Zr(dbm)3Cl + (C2H5)2AlCl is depicted in Fig. 3.
As follows from the chromatogram, ë6–ë18 oligomers
have a high purity concerning linear α-olefins. This
conclusion is also supported by the IR spectrum of the
ë6–ë18 oligomer fraction.
2
50
1
40
30
20
10
0
5
10
15
20
25
30
Time, min
An increase in the electron-withdrawing power of
diketonate groups increases the activity of the catalytic
system and the amount of the ethylene dimer butene-1
in oligomerization products. As follows from the data
presented in Table 2, the substitution of fluoride atoms
for three methyl hydrogens in triacetylacetonatozirco-
nium chloride increases the activity of the catalyst sys-
Fig. 1. Ethylene consumption rate curves during oligomer-
ization in the presence of ZrA Cl + (C H ) AlCl catalytic
systems: (1) acetylacetone, (2) benzoylacetone, (3) diben-
zoylmethane, (4) trifluoroacetylacetone, and (5) hexafluo-
3
2 5 2
roacetylacetone; 70°ë, PC H = 40 atm; Al : Zr = 80 : 1;
2
4
[ZrA Cl] = 2 mmol/l; the solvent is toluene.
3
PETROLEUM CHEMISTRY Vol. 46 No. 5 2006

340
Oligomer yield, wt %
KHANMETOV et al.
C6
90
80
70
60
50
40
C8
C10
30
20
10
0
1
C12
2
C14
3
C16
C18
C4
C6
C8
C10
C12
C14
Fig. 3. Chromatogram of ë –ë α-olefins produced during
6
18
Fig.2. Influence of the composition of the diketonate ligand
on the MMD of ethylene oligomerization product in the
presence of ZrA Cl + (C H ) AlCl catalytic systems: (1)
ethylene oligomerization in the presence of Zr(dbm) Cl +
3
(C H ) AlCl at 70°ë, P
= 40 atm, [Zr(dbm) Cl] =
3
2
5 2
C2H4
3
2 5 2
acetylacetone, (2) benzoylacetone, and (3) dibenzoyl-
methane; 70°ë, PC H = 40 atm; Al : Zr = 80 : 1;
2 mmol/l, and a time of 30 min in toluene as a solvent.
2
4
[ZrA Cl] = 2 mmol/l; solvent, toluene; time, 30 min.
3
metal compound that are necessary for the creation of
an active metal complex catalyst for ethylene oligomer-
ization.
When the cocatalyst contains chlorine derivatives of
alkylaluminum, such as (ë2ç5)2AlCl, (ë2ç5)3Äl2Cl3,
or ë2ç5AlCl2, the active catalyst is formed beginning
from a ratio of Al : Zr = 10 : 1, and its activity increases
with an increase of this ratio to Al : Zr = 80 : 1 (Fig. 4).
The composition of the alkylaluminum chloride
component of the catalyst has a strong effect on the
activity of the catalyst and the MMD of ethylene oligo-
mers (Table 3). In the presence of (ë2ç5)3Al as an acti-
vator, an active oligomerization catalyst is not formed
at any ratio of Al : Zr in the range 10–100 : 1 and above.
This failure is obviously due to the inability of
When (ë2ç5)AlCl2 is used as a cocatalyst, the
(ë2ç5)3Al to form the bridging bonds with a transition formed complex exhibits the maximum activity; the
Table 2. Influence of the composition of β-diketonatozirconium chloride complexes on the catalyst activity and the MMD
of ethylene oligomers (Al : Zr ratio, 80 : 1; reaction temperature, 70°C; solvent, toluene, 50 ml; ethylene pressure, 40 atm;
time, 30 min; [Zr] = 2 mmol/l)
Ethylene oligomers composition, wt %
Catalyst activi-
Compositionofzirconium
complex
g(product)
----------------------------
ty,
g(Zr) h
C4
C6
C8
C10
C12
C14
C16
C18
C20+
Zr(AcAc)3Cl
Zr(BAa)3Cl
Zr(DBM)3Cl
Zr(trifacac)3Cl
Zr(trifbzac)4
Zr(hfacac)4
3486.6
6011.9
52.65 26.78 14.51
61.47 19.84 12.46
3.73
3.67
2.33
2.84
2.44
3.17
1.33
1.5
0.5
0.22
0.33
0.24
0.16
0.12
0.12
0.1
Traces
0.47
0.31
0.38
0.28
0.28
0.08
0.008
0.08
0.06
0.06
–
–
–
–
–
8524.6
72.61 14.08
9.57
9.84
9.4
0.59
0.71
0.56
0.47
11419.1
12661.4
14311.2
70.5
73.6
71.4
15.15
13.46
14.54 10.32
PETROLEUM CHEMISTRY Vol. 46 No. 5 2006

ETHYLENE OLIGOMERIZATION IN THE PRESENCE
341
Table 3. Influence of the alkylaluminum chloride composition and aluminum to zirconium molar ratio on the catalyst activ-
ity and the MMD of ethylene oligomers in the presence of Zr(dbm)3Cl + (C2H5)nAlCl3 – n catalytic system (solvent, toluene;
PC H = 40 atm; time, 30 min)
2
4
Catalyst activi-
Oligomer composition, wt %
C8 C10 C12 C14 C16
Al : Zr ra- Temper-
g(product)
(C2H5)nAlCl3 – n
----------------------------
tio (mol) ature, °C ty,
C4
C6
C18
C20+
g(Zr) h
(C2H5)3Al
50 : 1
20 : 1
40 : 1
60 : 1
80 : 1
100 : 1
80 : 1
30 : 1
20 : 1
70
50
50
50
50
50
70
70
70
Catalyst is inactive
59.31 18.0 13.52 4.67
65.46 16.36 13.1 3.08
69.37 13.9 11.58 3.6
(C2H5)2AlCl
(C2H5)2AlCl
(C2H5)2AlCl
(C2H5)2AlCl
(C2H5)2AlCl
(C2H5)2AlCl
(C2H5)2Al2Cl3
C2H5AlCl2
4385.5
5482.5
6359.6
7675.4
6688.6
10087.7
3714.6
1072.3
2.12 0.77 0.31 0.12 Traces
1.38 0.34 0.16 0.08 Traces
0.83 0.46 0.15 0.09
0.47 0.38 0.15 0.1
–
–
74.31 13.01 8.3
2.28
78.44 10.58 8.31 1.67
71.13 11.82 10.32 4.26
0.4
0.34 0.16 0.08
–
1.54 0.53 0.18 0.11
0.06
–
92.17 6.84 0.90 0.09 Traces
–
–
–
Mixture of ethylene oligomers with product of solvent alky-
lation with ethylene oligomers
main reaction product is a mixture of α-olefins with
internal olefins and the products of the solvent alkyla-
tion with ethylene oligomers. Zirconium β-diketonate
chlorides also form an active complex with
(ë2ç5)3Al2Cl3. In this case, the product contains the
dimer fraction in an amount of up to 92% of ethylene
converted.
It is known that the central metal atom in organome-
tallic complexes of transition metals bears partial posi-
tive charge owing to electron delocalization onto the
ligands. Depending on the electron-donating or electron-
withdrawing ability of the ligands, the positive charge on
the metal is either increased or decreased [9, 10].
The maximum activity was exhibited by the cata-
lytic systems obtained from β-diketonatozirconium
chlorides and (ë2ç5)2AlCl.
Activity, g(product)/(g(Zr) h)
8000
1
Using (ë2ç5)2AlCl as an activator at 70°ë and a
ratio of Al : Zr = 80 : 1, the activity of the catalyst based
on Zr(dbm)3Cl was 10087.7 g(product)/(g(Zr) h)
(Table 3). As follows from the data in Table 3, the
enhancement of Lewis acidity of alkylaluminum chlo-
ride in the order (ë2ç5)3Al < (ë2ç5)2AlCl <
(ë2ç5)3Al2Cl3 < ë2ç5AlCl2 increases the amount of
the dimer fraction in the composition of ethylene oligo-
mers.
7000
6000
5000
4000
3000
2000
The addition of electron-donating ligands, (ë4ç4S,
(ë5ç11)2é, (ë2ç5)3N, etc.), as well as donor–acceptor
ligands to the Zr(dbm)3Cl + (ë2ç5)3AlCl catalyst sys-
tem strongly decreases the activity of the catalyst. An
increase in the L/Zr ratio to more than 1 : 1 deactivates
the catalyst. The ligand added to the catalyst system
obviously blocks free coordination sites at the transi-
tion metal in the intermediate active center.
1000
2
0
20
1
40
2
60
3
80
100
Al/Zr ratio (mol)
4
5
L/Zr ratio (mol)
The plots of the activity of Zr(dbm)3Cl +
(ë2ç5)2AlCl catalytic system against the Al : Zr and L :
Zr ratios given in Fig. 4 show that an increase in theAl :
Zr ratio to 80 : 1 increases the activity of the catalytic
system. The further growth in this ratio slightly
decreases the catalyst activity.
Fig. 4. Influence of the (1) Al/Zr and (2) L/Zr ratio on the
catalytic activity of the (1) Zr(dbm) Cl + (C H ) AlCl sys-
tem and (2) Zr(dbm) Cl + (C H ) AlCl + C H S system at
Al : Zr = 80 : 1, T = 50°C, and
a solvent.
3
2 5 2
3
2
5 2
4 4
= 40 atm in toluene as
P
C2H4
PETROLEUM CHEMISTRY Vol. 46 No. 5 2006

342
KHANMETOV et al.
From the above data, it follows that the catalyst
The influence of the composition of zirconium com-
activity and the relative amount of the ë4 fraction in the pounds, alkylaluminum chlorides, and donor–acceptor
product increases with an increase in the electron affin- properties of β-diketonate ligands on the catalyst activ-
ity of the diketonate ligand in the following order: ity and molecular-mass distribution of ethylene oligo-
acetylacetone, benzoylacetone, dibenzoylmethane, trif- mers was studied. It was found that the catalyst systems
luoroacetylacetone, tetrafluoroacetylacetone. The based on mixed-ligand β-diketonatozirconium chlo-
obtained results are explained well in terms of the influ- rides exhibit a higher activity in ethylene oligomeriza-
ence of inner- and outer-sphere polarizing factors on tion in comparison with the catalysts based on zirco-
charge distribution at the catalytic centers of the metal nium tetradiketonates. The catalyst activity increases
complex and, hence, on β-elimination.
with an increase in the electron affinity of the β-diketo-
nate ligands and depends on the composition of alkyl-
aluminum chloride and the molar ratio of the catalyst
components.
A stronger π-electron-withdrawing ability of the
benzoyl radical in diketonate complexes, as well as tri-
fluoro- and hexafluoroacetylacetonates in comparison
with the acetylacetonate ligand, favors an increase in
the positive charge on the zirconium ion in the interme-
diate active center and, consequently, a higher fre-
quency of β-ç atom transfer to the metal with the prev-
alent formation of the ethylene dimer butene-1.
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PETROLEUM CHEMISTRY Vol. 46 No. 5 2006