silyl chromate S-2 catalysts pre-reduced by three Al-alkyl cocatalysts in a specially
designed gas phase high-speed stirred-autoclave reactor [109]. The catalyst was
pre-activated by TEA, TiBA, or DEAE before the gas phase ethylene polymerization during the catalyst preparation step. As shown in Fig. 12, the gas phase
ethylene homopolymerization kinetic curves over the TEA- or TiBA-modified
S-2 catalysts belonged to type a (Fig. 10a), which is a hybrid type of kinetics
composed of two basic types of typical kinetic curve: one type with fast activation
followed by fast decay and the other type with slow activation followed by slow
decay. Such type of polymerization kinetics might not be suitable for application in
large-scale gas phase olefin polymerization processes because reactor fouling and
agglomeration can easily occur. In the case of the DEAE-modified S-2 catalyst, the
gas phase ethylene homopolymerization kinetic curve is type b (Fig. 10b), which is
a simple type of polymerization kinetics with slow activation followed by slow
decay. Although the polymerization activity for the DEAE-modified S-2 catalyst is
slightly lower than the TEA- or TiBA-modified catalysts, its polymerization kinetics would be of benefit for the heat transfer within the gas phase polymerization
fluidized bed reactor [111]. The differences in the structure and in the reducing and
alkylation capabilities of AlR 3 (TEA and TiBA) and AlR 2 OR (DEAE) cocatalysts
might be responsible for their totally different ethylene polymerization kinetics, but
the mechanism is still not known and awaits further exploration.
3.2 Activation by Al-alkyl Cocatalyst During Polymerization
The Al-alkyl cocatalyst could also be introduced during the polymerization stage,
with simultaneous interaction of catalyst with Al–alkyl cocatalyst and monomer
within the polymerization reactor. Ethylene homopolymerization using Phillips
catalyst PC600 calcined at 600
C followed by activation with TEA cocatalyst
Fig. 12 Kinetic curves of
ethylene polymerization of
S-2 catalysts modified with
various cocatalysts before
gas phase polymerization.
Polymerization conditions:
catalyst amount, 200 mg;
polymerization temperature,
92
C; ethylene pressure,
1.2 MPa
158
R. Cheng et al.
designed gas phase high-speed stirred-autoclave reactor [109]. The catalyst was
pre-activated by TEA, TiBA, or DEAE before the gas phase ethylene polymerization during the catalyst preparation step. As shown in Fig. 12, the gas phase
ethylene homopolymerization kinetic curves over the TEA- or TiBA-modified
S-2 catalysts belonged to type a (Fig. 10a), which is a hybrid type of kinetics
composed of two basic types of typical kinetic curve: one type with fast activation
followed by fast decay and the other type with slow activation followed by slow
decay. Such type of polymerization kinetics might not be suitable for application in
large-scale gas phase olefin polymerization processes because reactor fouling and
agglomeration can easily occur. In the case of the DEAE-modified S-2 catalyst, the
gas phase ethylene homopolymerization kinetic curve is type b (Fig. 10b), which is
a simple type of polymerization kinetics with slow activation followed by slow
decay. Although the polymerization activity for the DEAE-modified S-2 catalyst is
slightly lower than the TEA- or TiBA-modified catalysts, its polymerization kinetics would be of benefit for the heat transfer within the gas phase polymerization
fluidized bed reactor [111]. The differences in the structure and in the reducing and
alkylation capabilities of AlR 3 (TEA and TiBA) and AlR 2 OR (DEAE) cocatalysts
might be responsible for their totally different ethylene polymerization kinetics, but
the mechanism is still not known and awaits further exploration.
3.2 Activation by Al-alkyl Cocatalyst During Polymerization
The Al-alkyl cocatalyst could also be introduced during the polymerization stage,
with simultaneous interaction of catalyst with Al–alkyl cocatalyst and monomer
within the polymerization reactor. Ethylene homopolymerization using Phillips
catalyst PC600 calcined at 600
C followed by activation with TEA cocatalyst
Fig. 12 Kinetic curves of
ethylene polymerization of
S-2 catalysts modified with
various cocatalysts before
gas phase polymerization.
Polymerization conditions:
catalyst amount, 200 mg;
polymerization temperature,
92
C; ethylene pressure,
1.2 MPa
158
R. Cheng et al.