Polymerization of ethylene under high pressure

Claim 1

IN A PROCESS FOR THE PRODUCTION OF HIGH MOLECULAR WEIGHT POLYETHYLENE HAVING A DENSITY BETWEEN 0.91 AND 0.94 IN WHICH ETHYLENE IS POLYMERIZED IN A TUBULAR REACTOR AT A TEMPERATURE BETWEEN 150% AND 300%C. AND A PRESSURE BETWEEN 1,500 AND 3,000 ATMOSPHERES AND IN WHICH THERE IS USED A CHAIN TRANSFER AGENT SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, ALKANOLS AND CYCLOALKANOLS WITH 1 TO 10 CARBON ATOMS, STRAIGHT-CHAIN AND BRANCHED ALIPHATIC CYCLOALIPHATIC AND AROMATIC HYDROCARBONS CONTAINING 1 TO 8 CARBON ATOMS AND ALIPHATIC CARBONYL COMPOUNDS CONTAINING 1 TO 4 CARBON ATOMS, THE IMPROVEMENT WHICH COMPRISES HEATING THE REACTION MIXTURE TO 168% TO 174%C. IN A FIRST ZONE OF THE TUBULAR REACTOR THROUGH THE REACTOR WALL WITH A HEATING MEDIUM WHOSE TEMPERATURE IS FROM 2% TO 10% HIGHER THAN SAID TEMPERATURE OF THE REACTION MIXTURE AT THE END OF THE HEATING ZONE OF SAID TUBULAR REACTOR AND THEN IMMEDIATELY WITHDRAWING HEAT FROM THE REACTION MIXTURE IN THE FOLLOWING ZONE THROUGH THE RECTORWALL BY MEANS OF A COOLANT WHOSE TEMPERATURE LIES BETWEEN 100% AND 170% C., IN SUCH A MANNER THAT THE TEMPERATURE OF SAID REACTION MIXTURE DOES NOT FALL BELOW 168%C.