Cooling of pellets from PET solid stating reactor with water

Abstract

Energy savings are realized during the commercial production of polyethylene terephthalate by partially cooling polyethylene terephthalate pellets exiting a solid stating reactor by contact with water, and using the residual heat stored in the pellets to vaporize associated water to form dry pellets.

1 . A process for cooling polyethylene terephthalate pellets exiting a polycondensation solid stating reactor in a polyethylene terephthalate production process, comprising 
 contacting pellets exiting a solid stating reactor with liquid water in an amount sufficient to lower the temperature of said pellets,    removing liquid water from said pellets, and    recovering cooled pellets containing about less than 25 weight percent or less of water.    
   
   
       2 . The process of  claim 1 , wherein said step of contacting is effected by at least one spray of water which contacts said pellets.  
   
   
       3 . The process of  claim 1  wherein said step of contacting comprises directing pellets exiting said solid stating reactor into a moving stream of water.  
   
   
       4 . The process of  claim 1 , wherein following said lowering of the temperature of said pellets, said pellets are introduced into a mechanical dryer.  
   
   
       5 . The process of  claim 4 , wherein said dryer is a paddle dryer or a fluidized bed dryer.  
   
   
       6 . The process of  claim 4 , wherein pellets are separated from at least a portion of water associated with said pellets by mechanical means before entry into said dryer or within said dryer.  
   
   
       7 . The process of  claim 4 , wherein drying is effected without the addition of external heat.  
   
   
       8 . The process of  claim 4 , wherein said dryer is heated by process heat derived from another portion of said PET production process.  
   
   
       9 . The process of  claim 1 , wherein water used in the process is recovered and recirculated to the process.  
   
   
       10 . The process of  claim 9 , wherein prior to contacting pellets in water, water being recirculated to the process is chilled.  
   
   
       11 . The process of  claim 10 , wherein water being recirculated is chilled by means of a heat exchanger.  
   
   
       12 . The process of  claim 1 , further comprising removing liquid water from wet pellets, said wet pellets having a first temperature of from about 50° C. to about 120° C. to provide moist pellets having a first water content of less than 60% by weight, and volatizing water from said moist pellets due to heat retained by said pellets, and recovering pellets having a second temperature lower then said first temperature and a water content lower then said first water content.  
   
   
       13 . The process of  claim 12 , wherein said step of volatizing water takes place in a mechanical dryer in a flow of gas.  
   
   
       14 . The process of  claim 13  wherein said gas is not heated prior to entry into said dryer.  
   
   
       15 . The process of  claim 12 , wherein the water content of pellets following said step of recovering is less then 2% by weight.  
   
   
       16 . The process of  claim 1 , wherein exiting said solid stating reactor are contacted with liquid water in an amount sufficient to lower the temperature of said pellets to a temperature within the range of about 50° C. and 120° C.  
   
   
       17 . The process of  claim 4 , wherein the temperature of the pellets exiting said dryer are 60° C. or less.  
   
   
       18 . The process of  claim 1 , wherein residual heat contained in the pellets exiting a solid stating reactor is used to evaporate water contacting the pellets exiting the solid stating reactor.