PROCESS FOR THE PRODUCTION OF HIGH MOLECULAR WEIGHT POLYESTER

摘要

PROCESS FOR THE PRODUCTION OF HIGH MOLECULAR WEIGHT POLYESTER A process for the continuous production of high molecular weight polyethylene terephthalate wherein the crystallized prepolymer having an intrinsic viscosity of at least .3 is dried, preheated and polymerized in a single moving bed reaction zone. The method is characterized by an inert gas atmosphere and a reaction zone with a temperature gradiant ranging from about 170.degree.C. at the uppermost portion and a higher temperature of about 225.degree.C. at the lowermost portion. The present invention is an improved process over the conventional one. As in the conventional process, the prepolymer is placed in a feed hopper after which the prepolymer is heated and crystallized in a conventional crystallizer, but leaves the crystallizer at a higher temperature of about 170.degree.C. to about 180.degree.C. The crystallized polyester then enters the moving bed reaction zone through the top and moves downward slowly by a gravitational force. A stream of hot gas enters the reaction zone through the bottom at a constant temperature slightly higher than in the conventional process, 225.degree. as opposed to 220.degree.C. The polyester will leave the bottom of the zone at a temperature slightly lower than the nitrogen inlet temperature, at or about 220.degree.C, The hot oil in the jacket of the reaction zone supplies heat to the prepolymer through the wall of the moving bed reaction zone. The polymer is then discharged into a product cooler wherein the temperature of the polymer is lowered to about 65.degree.C. The inert gas can optionally be recycled by using a conventional clean up system. The recycled gas can then be fed into a heater before entering a blower mechanism whereupon the gas then enters the drier reactor. Preferably the recycled gas can enter the blower before entering the heater whereupon the recycled gas enters the drier reactor.