Direct coupling of melt polymerization and solid state processing for pet

Abstract

Strands of molten polyethylene terephthalate (PET) from a PET polycondensation reactor are solidified, pelletized, and cooled only to a temperature in the range of 50° C. to a temperature near the polymer Tg by contact with water. The still hot pellets are conveyed, optionally followed by drying to remove water, to a PET crystallizer. By avoiding cooling the amorphous pellets to room temperature with water and cool air, significant savings of energy are realized.

1 . A process comprising: 
 a) pelletizing a molten polyethylene terephthalate to form amorphous polyethylene terephthalate pellets;    b) transporting the pellets in a stream of water to a dryer to form a stream of dry or moist pellets, wherein the stream of water has a temperature of 50° C. or more; and    c) a crystallization step wherein the stream of dry or moist pellets are crystallized and the stream of dry or moist pellets is introduced into the step of crystallizing at a pellet temperature of 50° C. or more.    
   
   
       2 . The process of  claim 1 , wherein the stream of dry or moist pellets are continuously fed from the dryer to the crystallization step.  
   
   
       3 . The process of  claim 2 , wherein the dryer is a centrifugal dryer.  
   
   
       4 . The process of  claim 3 , wherein said water is separated from the pellets and re-circulated to transport the pellets in said stream of water.  
   
   
       5 . The process of  claim 2 , wherein the stream of dry or moist pellets are continuously fed from the dryer to the crystallization step.  
   
   
       6 . The process of  claim 1 , wherein the stream of dry or moist pellets are dry.  
   
   
       7 . The process of  claim 1 , wherein no external heat is required to maintain the water temperature.  
   
   
       8 . The process of  claim 1 , wherein a portion of the water is separated from the water stream through a dewatering screen.  
   
   
       9 . The process of  claim 1 , wherein the water in the water stream is at a temperature insufficient to cool the temperature of the pellets in the water stream to below the T g  of the pellets.  
   
   
       10 . The process of  claim 1 , wherein water present on the surface of the pellets, if any, after the dryer is evaporated prior to the crystallization step.  
   
   
       11 . The process of  claim 1 , wherein following the crystallization step, the pellets are solid state polymerized.  
   
   
       12 . The process of  claim 1 , wherein the polyethylene terephthalate is a polymer modified with up to 10 mol percent dicarboxylic acids other than terephthalic acid and up to 10 mol percent of diols other than ethylene glycol.  
   
   
       13 . The process of  claim 12 , wherein the diols other than ethylene glycol comprise CHDM.  
   
   
       14 . The process of  claim 12 , wherein the dicaroxylic acids other than terephthalic acid comprise isophthalic acid.