Removal of catalyst residues from solid polymer slurries by multistage countercurrent extraction

Claim 1

IN A CONTINUOUS POLYMERIZATION PROCESS WHEREIN A MONOMER IS SUBJECTED TO POLYMERISATION IN THE PRESENCE OF A ZIEGLER POLYMERIZATION CATALYST, ADAPTABLE FOR THE LOW-PRESSURE POLYMERIZATION OF ETHYLENE, AND A LIQUID HYDROCARBON SLURRYING MEDIUM FOR THE POLYMER IN AT LEAST A SUFFICIENT AMOUNT TO MAKE A POLYMER LAYER WHICH IS NOT TOO VISCOUS FOR EXTRACTION, A SLURRY OF SOLID POLYMER PARTICLES IS PRODUCED IN SAID MEDIUM AND SAID POLYMER PARTICLES ARE THEREAFTER RECOVERED FROM SAID MEDIUM, THE IMPROVEMENT FOR REMOVING RESIDUES OF SAID ZIEGLER CATALYST FROM SAID POLYMER WHEREIN SAID SLURRY IS SUBJECTED TO CONTINUOUS COUNTERCURRENT MULTISTAGE SOLVENT EXTRACTION BY MEANS OF A LIQUID HYDROXYL-GROUP-CONTAINING SOLVENT FOR SAID RESIDUES, SAID SOLVENT UNDER EXTRACTION CONDITIONS BEING NOT MORE THAN PARTIALLY MISCIBLE WITH SAID SLURRYING MEDIUM AND NOT BEING CAPABLE OF EXTRACTING SAID POLYMER FROM SAID MEDIUM, AND WITHDRAWING SEPERATE PHASES OF POLYMER SLURRIED IN SAID MEDIUM AND RESIDUES OF SAID CATALYST IN SAID SOLVENT.