Method of multistage gas phase polymerization, apparatus...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in two or more physically distinct zones

Reexamination Certificate

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C526S068000, C526S088000, C526S348200, C526S348500, C526S348600, C526S201000

Reexamination Certificate

active

06407184

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method of multistage gas phase polymerization using at least two fluid bed reactors in series, wherein the amount of subcomponents mixed in the polymer powder is reduced when polymer powder produced in an upstream arranged fluid bed reactor is taken up and introduced into a downstream arranged fluid bed reactor.
Furthermore, the present invention relates to a device for reducing the entrainment of subcomponents in the polymer powder as required in the implementation of the above method and relates to an apparatus of multistage gas phase polymerization including this device.
BACKGROUND OF THE INVENTION
In the production of, for example, an ethylene/&agr;-olefin copolymer, it is common practice to employ a gas phase polymerization method in which a gas phase polymerization of a mixture comprising ethylene and an &agr;-olefin is carried out in a fluid bed reactor in the presence of a titanium based solid catalyst.
In the above polymer production, the use of a single fluid bed reactor results in the formation of a polymer whose properties necessarily fall in certain limited ranges. However, products of complex properties are increasingly desired in accordance with the diversification of market demands. Therefore, polymers of the same species but with varied properties, namely differing in molecular weight, purity and physical properties, have been produced by the employment of the method of preparing polymers with varied properties with the use of a plurality of fluid bed reactors connected to each other.
With respect to this method, a method of multistage gas phase polymerization, for example, a method using a two-stage gas phase polymerization apparatus comprising first fluid bed reactor
111
, and continuously connected thereto, second fluid bed reactor
121
as shown in
FIG. 3
is now widely employed.
Specifically, solid catalyst A is fed through supply line
115
into first fluid bed reactor
111
. Simultaneously, a feed gas mixture consisting of, for example, ethylene and an &agr;-olefin is fed through supply line
112
into the first fluid bed reactor
111
at its bottom with the use of blower
113
.
Hydrogen gas as a reaction inhibitor is premixed with the feed gas mixture in order to suppress the excess advance of the polymerization reaction. The molecular weight of the polymer produced by the first fluid bed reactor
111
as the first-stage polymerizer can be limited by appropriately terminating the polymerization reaction by the premixed hydrogen gas.
The fed gaseous olefin is passed through dispersion grid
117
containing, for example, a porous plate, which is arranged in the vicinity of the bottom of the first fluid bed reactor
111
, and forms fluid bed
118
and maintains the fluid bed
118
in fluid form. Polymerization reaction is carried out in the fluid bed
118
.
The thus produced polymer powder (particles) is continuously taken up, delivered into carrying line
125
by means of rotary valve
135
provided on take-up line
130
, and fed through the carrying line
125
into second fluid bed reactor
121
.
Unreacted feed gas having passed through the fluid bed
118
has its flow rate reduced in slowdown zone
119
provided in an upper part of the first fluid bed reactor
111
and discharged outside the first fluid bed reactor
111
through a gas outlet provided at the top of the first fluid bed reactor
111
.
The unreacted feed gas having been discharged from the first fluid bed reactor
111
is passed through circulating line
116
, is cooled by means of heat exchanger (cooler)
114
and joins the supply line
112
. Thus, once more, the unreacted feed gas is continuously fed into the fluid bed
118
formed in the first fluid bed reactor
111
with the use of the blower
113
.
On the other hand, the polymer powder taken up through the take-up line
130
from the first fluid bed reactor
111
is fed through the carrying line
125
into the second fluid bed reactor
121
. Simultaneously, different feed gas mixture from that of the first reactor
111
is supplied through supply line
122
and through the carrying line
125
into the second fluid bed reactor
121
with the use of blower
123
. Thus, fluid bed
128
is formed by the polymer powder, olefin gas and solid catalyst contained in the polymer powder in the second fluid bed reactor
121
, and polymerization reaction is carried out in the fluid bed
128
. Copolymer produced by the second fluid bed reactor
121
is continuously taken up through line
126
.
The carrying line
125
is branched from the supply line
122
, and a remote end of the carrying line
125
is connected to an upper part of the second fluid bed reactor
121
. The olefin containing gas fed from the supply line
122
has its pressure increased by pressure increasing means such as centrifugal blower
141
and entrains the polymer powder taken up from the first fluid bed reactor
111
so that the polymer powder is carried and introduced into the second fluid bed reactor
121
.
Although the above described the two-stage fluid bed reactor, namely the construction consisting of the first fluid bed reactor
111
and, continuously connected thereto, the second fluid bed reactor
121
, use can also be made of a multistage fluid bed reactor consisting of a greater number of fluid bed reactors continuously connected to one another.
When a plurality of properties are imparted to the obtained polymer in the above multistage gas phase polymerization method, a feed gas mixture of desired composition is polymerized in an upstream fluid bed reactor, for example, the first fluid bed reactor
111
, and the thus obtained polymer powder is taken up through the line
130
and fed into a downstream fluid fed reactor, for example, the second fluid bed reactor
121
so that the polymer powder is further polymerized.
In the second fluid bed reactor
121
, the polymerization is generally performed with the use of a feed gas mixture of composition different from that of the upstream in the content of &agr;-olefin gas and hydrogen gas.
However, this method has a drawback in that, while desired property can be imparted to the polymer in the first-stage polymerization reaction, desired property cannot be imparted to the upstream obtained polymer in the downstream performed polymerization reaction.
The inventors have conducted extensive and intensive investigations of the cause thereof. As a result, they have found that desired property can be imparted to the polymer in the downstream polymerization as well by reducing the amount of &agr;-olefin and hydrogen gas (subcomponents) introduced together with the polymer powder to thereby regulate the composition of downstream supplied feed gas mixture during the transfer of the polymer powder from the upstream fluid bed reactor into the downstream fluid bed reactor. The present invention has been completed on the basis of this finding.
OBJECT OF THE INVENTION
Under these circumstances, it is an object of the present invention to provide a method of multistage gas phase polymerization in which, when the polymer powder taken up from an upstream fluid bed reactor is carried while being entrained by a feed gas for a downstream fluid bed reactor so that the polymer powder is introduced into the downstream fluid bed reactor, hydrogen gas and comonomers which inhibit the polymerization reaction in the downstream fluid bed reactor and which render regulation of desired polymer properties difficult are removed from the polymer powder.
It is another object of the present invention to provide a device for removing subcomponents such as hydrogen gas and comonomers from the polymer powder taken up from an upstream fluid bed reactor before the introduction thereof into a downstream fluid bed reactor to thereby lower the subcomponent content of the polymer powder in a multistage gas phase polymerization apparatus. It is a further object of the present invention to provide an apparatus of multistage gas phase polymerization including this device.
SUMMARY OF THE INVENTION
The present i

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