GB879142A - Improvements in or relating to the purification of low-pressure polyolefins - Google Patents

Abstract

<PICT:0879142/III/1> <PICT:0879142/III/2> A Ziegler-polymerization slurry of polyolefin, in a light petroleum distillate containing also components of a Ziegler-type catalyst is removed, continuously or intermittently, from reactor 3 and fed through a line 4 to one end of an elongated vessel 5 fitted with a rotatable screw 6 for moving the polymer through the vessel towards an outlet pipe 7. Ethanol or a mixture of ethanol and a light petroleum distillate is fed to the line 4 through a line 9. The vessel 5 with heat-transfer jacket 20 has partitions 10 fixed to a removable top-part 11 of the vessel 5, disposed vertically in spaced apart relationship so that their lower ends 10a fit loosely round the screw 6, and so form compartments 12 each opening out at the bottom, i.e. in the region of the screw 6, into a longitudinal polymer-treating zone 51 formed by the lower part of the vessel 5 which houses the screw 6. Each compartment 12 is connected to a header 14 loading a condenser 16 from which condensate is returned to the exit end of the vessel 5, valved lines 18 and 19 being provided to enable the condensate to be returned either to the exit and adjacent the outlet pipe 7 or to a point further along the vessel 5. The polyolefin slurry removed, at the end of the treatment, via line 7 is conveniently centrifuged to remove supernatant solvent and the resulting solvent-wet polymer then passed to a steam-stripping stage for further treatment e.g. as described in Specification 801,554 and thereafter processed in a devolatilising extruder to give a purified polymer. Specifications 798,912, 799,392, 799,823, 801,031, 810,023, 819,867 and 820,263 also are referred to.