Plastic and nonmetallic article shaping or treating: processes – Including step of generating heat by friction
Patent
1987-04-30
1989-04-11
Thurlow, Jeffery
Plastic and nonmetallic article shaping or treating: processes
Including step of generating heat by friction
264 83, 264 85, 264102, 264141, 26421121, 366 75, 425202, 425203, 425205, 425812, 528483, B29C 3502, B29C 4736, B29C 4790, C08J 700
Patent
active
048204633
ABSTRACT:
The invention relates to a process for degassing and pelletizing polyolefin particles produced by a gas phase polymerization. The polyolefin particles are submitted to a primary degassing, preferably at the outlet of a reactor for catalytic polymerization in the gas phase. Then the polyolefin particles are subjected to a secondary degassing step comprising agitating the particles by a mechanical stirrer and converting the mechanical energy therefrom into heat such that the temperature of the particles is brought to between 80.degree. and 120.degree. C. which is close to minimum sintering temperature Ts so that the polyolefin particles are substantially freed from the gases accompanying them. The heated degassed polyolefin particles are then pelletized in an extruder of a pelleting unit. Optionally, during the secondary degassing step an inert gas such as nitrogen is circulated to facilitate evacuation of gases from the particles, and/or gas containing oxygen and/or water vapor is circulated to inactivate any catalyst in the particles. Furthermore, during the secondary degassing step the polyolefin particles heated by the conversion of mechanical energy may attain a temperature between Ts-5.degree. C. and Ts+5.degree. C., preferably between Ts-2.degree. C. and Ts+2.degree. C. The polyolefin particles can be polyethylene or copolymers of ethylene and of higher alpha-olefins having 3 to 12 carbon atoms.
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BP Chemicals Limited
Tentoni Leo B.
Thurlow Jeffery
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