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AssigneeBasell Polyolefine GmbH
InventorsAlexander Koppl, Rainer Karer, Ulrich Nieken
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Process for preparing polyolefins having high molecular weights in the presence of a catalyst comprising an organic transition metal compound in a gas-phase fluidized-bed reactor, where the polyolefins prepared have a melt flow rate at 2.16 kg and 190° C. in accordance with ISO 1133 of less than 4 g/10 min. According to the present invention, a start-up hase during which a polyolefin having an increased melt flow rate of above 4 g/10 min is produced for a transitional period is provided. In this way, trouble-free start-up of the reactor is ensured even in the case of polymer products having a high molecular weight and a melt flow rate below 4 g/10 min and even when using catalysts based on organic transition metal compounds, in particular metallocene catalysts.
A process for preparing polyolefins in a gas-phase fluidized-bed reactor using a catalyst comprising an organic transition metal compound, wherein the polyolefin prepared has a melt flow rate at 2.16 kg and 190° C. in accordance with ISO 1133 of less than 4 g/10 min and a polyolefin having an increased melt flow rate of above 4 g/10 min is produced for a transitional period during a start-up phase.
A process as claimed in either of the preceding claims, wherein the melt flow rate during the start-up phase is initially above 4.5 g/10 min and is continually decreased to the value below 4 g/10 min.
The process as claimed in any of the preceding claims, wherein the temperature is increased by at least 1° C. compared to the temperature in long-term operation, at least prior to the start-up phase.
A process as claimed in any of the preceding claims, wherein the melt flow rate is regulated via the hydrogen concentration in the reactor.
A process as claimed in any of the preceding claims, wherein the polyolefin is a homopolymer or copolymer of ethylene.
A process as claimed in any of the preceding claims, wherein the organic transition metal compound is a metallocene.
A process as claimed in any of the preceding claims, wherein an alkylaluminoxane is used as activating compound.
Dependencies are inferred from the claim text.