Multi-reactor slurry polymerization processes with high ethylene purity

Abstract

A slurry polymerization process for the preparation of polyethylene in a reactor cascade of two or more polymerization reactors comprising the steps of feeding to a polymerization reactor amounts of ethylene, of a Ziegler catalyst, of fresh aluminum alkyl and of a diluent; feeding the slurry product withdrawn from the polymerization reactor to a second polymerization reactor; and feeding additional amounts of ethylene and of diluent wherein the ethylene is first passed through an ethylene purification unit, which reduces at least the concentration of carbon monoxide, carbon dioxide, oxygen, acetylene and water contained in the ethylene, before it is fed to the two or more polymerization reactors of the reactor cascade.

Description

technical field [0001] The present disclosure relates to a process for the polymerization of ethylene. More specifically, the present disclosure relates to a multi-reactor slurry polymerization process using high purity ethylene to produce multimodal polyethylene. Background technique [0002] The use of polyethylene-containing products is well known. Polyethylene can be produced using various processes. In the ethylene slurry polymerization process, a diluent such as hexane is used to dissolve ethylene monomer, comonomer and hydrogen, and the monomer is polymerized with a catalyst. After polymerization, the polymer product formed exists as a slurry suspended in a liquid medium. In a typical multi-reactor cascade process (for example, as shown in WO 2012 / 028591 A1, US Patent No. 6,204,345 B1 and WO2005 / 077992 A1), monomer, hydrogen, catalyst and diluent are fed To the first of the three reactors, the polymer particles contained in the diluent and unreacted monomer form a...

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Problems solved by technology

This can lead to changes in the yield of the reactor and the characteristics of the product

The requirements are even more stringent where multiple slurry reactors are operated in series, where the active catalyst within the polyethylene product flows between the reactors and ethylene is fed to each reactor, the individual polymerization reactors Variations in the amount of aluminum alkyls available in can lead to changes in the properties of the final polyethylene composition, however, fluctuations in the impurity levels of the feed stream can complicate adjustments

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