| CPC C08F 6/003 (2013.01) [C08F 2/001 (2013.01); C08F 2/01 (2013.01); C08F 6/005 (2013.01)] | 20 Claims |
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1. Process for producing a propylene copolymer in at least three reaction stages connected in series, comprising the steps of:
a) pre-polymerizing a polymerization catalyst by introducing propylene and the polymerization catalyst into a pre-polymerization stage to produce a pre-polymerized polymerization catalyst;
b) withdrawing the pre-polymerized polymerization catalyst from the pre-polymerization stage and passing it to a first reaction stage;
c) polymerizing propylene by introducing propylene and ethylene into the first reaction stage to produce a first reaction mixture comprising a first propylene copolymer, unreacted propylene and unreacted ethylene;
d) withdrawing a first product stream comprising the first reaction mixture from the first reaction stage and passing at least a part of it to a second reaction stage;
e) continuing the polymerization in the second reaction stage in the presence of the first propylene copolymer to produce a second reaction mixture comprising a propylene polymer mixture of the first propylene copolymer and a second propylene copolymer, unreacted propylene, and unreacted ethylene;
f) withdrawing a second product stream comprising the second reaction mixture from the second reaction stage and passing at least a part of it to a separation unit and separating the second product stream into a first overhead stream and a first bottom product stream, the first overhead stream comprising unreacted propylene, unreacted ethylene, as well as oligomers, and the first bottom product comprising solid particles of the propylene polymer mixture;
g) recovering the propylene polymer mixture from the first bottom product stream;
h) condensing at least a part of the first overhead stream;
i) passing at least a part of the first overhead stream to a distillation column and separating the at least a part of the first overhead stream into a second overhead stream and a second bottom product stream, the second overhead stream comprising unreacted propylene, and unreacted ethylene;
j) withdrawing the second overhead stream and the second bottom product stream from the distillation column; and
k) condensing at least a part of the second overhead stream, thereby producing a condensed second overhead stream;
wherein the process further comprises the steps of
l) splitting the condensed second overhead stream into a distillation reflux stream, a first recycle stream and a second recycle stream, and returning the distillation reflux stream into the top of the distillation column, passing the first recycle stream to the second reaction stage and passing the second recycle stream to a stripping column; and
m) withdrawing a third overhead stream comprising unreacted ethylene, and a third bottom product stream comprising unreacted propylene from the stripping column, and passing the third overhead stream to the distillation column and passing at least a part of the third bottom stream to a propylene feed vessel, to the pre-polymerisation stage, to the first reaction stage, or to a combination thereof.
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