Chemistry Reference
In-Depth Information
Fig. 6.3
Illustration of a
gas-phase process (from
Burdett, by permission of
the American Chemical
Society)
The reactors for the fluidized gas-phase process are simple in design. There are no mechanical
agitators and they rely upon blowers to keep the bed fluidized and well mixed. Catalysts and
cocatalysts are fed directly to the reactor [
25
].
Rieger and coworkers [
26
] investigated gas-phase polymerization of ethylene with supported
a
-diimine nickel catalysts. The reaction of 2,5 and 2,6 and 1,4 dithiane ligands with Ni(acac)
2
and
trityl tetrakis(pentafluorophenyl)borate gave the corresponding Ni(II) complexes in high yields. These
complexes were supported on silica without a chemical tether and were used as catalysts for ethylene
polymerization reactions in the gas phase. Furthermore, ethylene was polymerized with the unsup-
ported 2,5-complexes in homogeneous solution for comparison. The influence of the ligand structure,
hydrogen, and temperature on the polymerization performance was investigated. The supported
catalysts showed moderate to high activities and produced polyethylenes ranging from high-density
polyethylene to linear low-density polyethylene, without further addition of a
a
-olefin comonomer.
[B(C
6
F
5
)
4
]
SiO
2
R
R
R'
R'
N
N
linear
branched PE
low MW
Ni
O
O
R
R
