Patent ID: 8202951
Filing Date: 2012-06-19
Classification: C08F

Abstract:
1. Process for producing a multimodal polyethylene in at least two reactors connected in series, in which 20-80 wt % of a first polymer is made in suspension in a first reactor and 80-20 wt % of a second polymer is made in suspension in a second reactor in the presence of the first polymer, and a stream or slurry containing the resulting polymer is withdrawn from the second reactor and transferred to a flash tank operating at a pressure and temperature such that at least 50mol % of the liquid component of the slurry, or the non-polymer component of the stream entering the flash tank, is withdrawn from the flash tank as a vapour, wherein the concentration in the stream or slurry entering the flash tank of components having a molecular weight below 50 g/mol, C lights (mol %), satisfies the equation C lights <7+0.07(40−T c )+4.4(P c −0.8)−7(C H2 /C Et ) where T c and P c are respectively the temperature (in ° C.) and pressure (MPa g) at the location where the vapour withdrawn from the flash tank is condensed, and C H2 and C Et are the molar concentrations in the flash tank of hydrogen and ethylene respectively.