Patent ID: 7332549
Filing Date: 2008-02-19
Classification: C08F,Y10S

Abstract:
1. Process for the polymerisation or copolymerisation in the gas phase of ethylene by bringing the said ethylene into contact, under polymerization or copolymerisation conditions in a reactor in which the start-up bed is fluidised and/or agitated with mechanical stirring, with a catalyst system, which process comprises a pre start-up operation wherein, prior to the introduction of the catalytic system in the reactor, said process comprises the following steps 1. determining the density d and melt index MI of the polyethylene powder to be produced at start-up, 2. heating the start-up bed by controlling the temperature inside the reactor such that a. the temperature is maintained at least 0.5° C. below the sintering temperature of the start-up bed, and b. the temperature is maintained at a value equal to or higher than the one corresponding to a RTSE value of 4.4 for the d and MI values of the polyethylene powder to be produced, wherein the polymer grade to be produced at started requires a heating temperature of at least 95° C., according to its corresponding 4.2 RTSE value in the tables.