PROCESS FOR TREATING POLYOLEFIN PARTICLES OBTAINED BY GAS-PHASE POLYMERIZATION

摘要

Process for treating polyolefin particles obtained by gas-phase polymerization of one or more olefins in the presence of a polymerization catalyst system and a C 3 -C 5 alkane as polymerization diluent in a gas-phase polymerization reactor, the process comprising the steps of
a) discharging the polyolefin particles continuously or discontinuously from the gas-phase polymerization reactor and transferring the particles to a first degassing vessel;
b) contacting therein the polyolefin particles with a gaseous stream comprising at least 85 mol-% of C 3 -C 5 alkane while the polyolefin particles have an average residence time in the first degassing vessel of from 5 minutes to 5 hours;
c) transferring the polyolefin particles to a second degassing vessel;
d) contacting therein the polyolefin particles with a stream comprising nitrogen and steam while the polyolefin particles have an average residence time in the second degassing vessel of from 5 minutes to 2 hours;
e) transferring the polyolefin particles to a third degassing vessel;
f) contacting therein the polyolefin particles with a stream of nitrogen while the polyolefin particles have an average residence time in the third degassing vessel of from 5 minutes to 8 hours,
and processes for preparing polyolefin polymers by gas-phase polymerization of one or more olefins in the presence of a polymerization catalyst system and a C 3 -C 5 alkane as polymerization diluent in a gas-phase polymerization reactor, wherein the obtained polyolefin particles are subjected to such a treating process.