Polypropylene purification

Claim 1

IN A PROCESS FOR PRODUCING POLYPROPYLENE WHEREIN PROPYLENE IS POLYMERIZED IN THE PRESENCE OF A CATALYTIC AMOUNT OF TITANIUM CHLORIDE ACTIVATED WITH AN ALUMINUM ALKYL POLYMERIZATION CATALYST TO PRODUCE A SUSPENSION OF POLYPROPYLENE IN LIQUID PROPYLENE, THE POLYPROPYLENE IS SEPARATED FROM THE LIQUID PROPYLENE BY FLASHING IN A CYCLONE SEPARATOR TO LEAVE A SUBSTANTIALLY DRY POLYPROPYLENE PRODUCT CONSISTING ESSENTIALLY OF CRYSTALLINE AND ATACTIC PORTIONS, AND THE POLYPROPYLENE PRODUCT IS SUBSEQUENTLY PURIFIED, THE IMPROVEMENT OF OBTAINING A PURIFIED POLYPROPYLENE PRODUCT CONTAINING LESS THAN 10 PARTS PER MILLION OF TITANIUM, LESS THAN 30 PARTS PER MILLION OF ALUMINUM AND LESS THAN 50 PARTS PER MILLION OF CHLORIDE RESIDUES WHICH CONSISTS ESSENTIALLY IN: (A) UPGRADING AND PURIFYING THE POLYPROPYLENE BY EXTRACTING THE SOLUBLE ATACTIC POLYPROPYLENE AND CATATLYST RESIDUES FROM THE POLYPROPYLENE PRODUCT WITH AN AXEOTROPIC MIXTURE OF ISOPRPYL ALCOHOL-HEPTANE CONTAINING APPROXIMATELY FROM 0.1 TO 0.5 WEIGHT PERCENT HC1 BASED ON THE ISOPROPYL ALCOHOLHEPTANE AZEOTROPE BY REFLUXING NEAR THE BOILING POINT SAID POLYPROPYLENE AND AZEOTROPIC MIXTURE, (B) SEPARATING THE PURIFIED POLYPROPYLENE FROM SAID AZEOTROPIC MIXTURE, (C) WASHING SAID POLYPROPYLENE WITH ANHYDROUS, ACIDFREE ISOPROPYL ALCOHOL-HEPTANE, (D) SEPARATING AND RECOVERING THE POLYPROPYLENE FROM THE WASH LIQUOR, (E) PROCESSING SAID AZEOTROPIC MIXTURE TO REMOVE SAID SOLUBLE ATACTIC POLYPROPYLENE, CATALYST RESIDUES AND CHLORIDE RESIDUES, AND (F) RECYCLING THE RESULTING PROCESSED AZEOTROPIC MIXTURE TO SAID EXTRACTION STEP.