Dynamic Pressure Control in Double Loop Reactor

Abstract

The present invention discloses a slurry loop reactor comprising at least two loop reactors connected in series and wherein the line connecting the two loops is subject to a dynamic pressure difference.

1 - 7 . (canceled) 
     
     
         8 . A method for controlling pressure in a double loop reactor comprising:
 operating a first loop reactor of the double loop reactor at a first initial pressure;   operating a second loop reactor of the double loop reactor at a second initial pressure, wherein the first loop reactor and the second loop reactor are connected in series via a line adapted for transferring polymer from the first loop reactor to the second loop reactor, and wherein the line is subject to a dynamic pressure difference;   linking a set point pressure value of the second loop reactor to a process pressure value of the first loop reactor; and   discharging polymer from the second loop reactor each time a pressure in the second loop reactor equals the set point pressure value, wherein the set point pressure value is equal to the process pressure value minus the dynamic pressure difference.   
     
     
         9 . The method of  claim 8 , wherein when polymer is discharged from the first loop reactor the process pressure value of the first loop reactor drops below the first initial pressure, and wherein pressure in the second loop reactor directly increases while maintaining the dynamic pressure difference. 
     
     
         10 . The method of  claim 9 , wherein the polymer is discharged from the first loop reactor and the second loop reactor by dumping legs of the first loop reactor and the second loop reactor. 
     
     
         11 . The method of  claim 8 , wherein the process pressure value of the first loop reactor increases after the polymer is discharged from the second loop reactor. 
     
     
         12 . The method of  claim 8 , wherein the set point pressure value is between 0 and 5 bars. 
     
     
         13 . The method of  claim 8 , wherein the set point pressure value is between 0.5 and 5 bars. 
     
     
         14 . The method of  claim 8 , wherein pressure in the second loop reactor is controlled in real time by pressure variations in the first loop reactor. 
     
     
         15 . The method of  claim 14 , wherein pressure in the second loop reactor is controlled in cascade by pressure in the first loop reactor through a differential pressure measurement. 
     
     
         16 . The method of  claim 8 , wherein a predetermined pressure difference is maintained between the first loop reactor and the second loop reactor. 
     
     
         17 . The method of  claim 16 , wherein the predetermined pressure difference is not more than 5 bars. 
     
     
         18 . The method of  claim 16 , wherein the predetermined pressure difference is from 0.5 bars to 2 bars. 
     
     
         19 . The method of  claim 16 , wherein the predetermined pressure difference is from 1.5 bars to 2 bars. 
     
     
         20 . The method of  claim 8 , further comprising setting a minimum time between discharges of polymer from the second loop reactor. 
     
     
         21 . The method of  claim 8 , further comprising:
 introducing an olefin monomer into the first loop reactor;   contacting the olefin monomer with a first catalyst system within the first loop reactor to form a first polyolefin;   withdrawing the first polyolefin from the first loop reactor;   transferring the first polyolefin from the first loop reactor to the second loop reactor via the line;   contacting the first polyolefin with a second catalyst system within the second loop reactor to form a second polyolefin; and   withdrawing the second polyolefin from the second loop reactor.   
     
     
         22 . The method of  claim 21 , wherein the second polyolefin is a bimodal polymer, and wherein the first catalyst system and the second catalyst system are both metallocene catalyst systems. 
     
     
         23 . The method of  claim 8 , further comprising collecting growing polymer exiting the first loop reactor by continuous discharge or settling legs. 
     
     
         24 . The method of  claim 8 , wherein the first loop reactor and the second loop reactor are linked by a by-pass line and an alternate route, and wherein the by-pass line collects growing polymer exiting the first loop reactor at exit points and sends the growing polymer to an entry point in the second loop reactor. 
     
     
         25 . The method of  claim 24 , wherein a velocity in the by-pass line is larger than 3 m/s. 
     
     
         26 . The method of  claim 8 , wherein the first loop reactor operates in batch operation. 
     
     
         27 . The method of  claim 26 , wherein the second loop reactor operates in continuous operation.