Continuous slurry polymerization volatile removal

Abstract

A process/apparatus is disclosed for continuously separating a liquid medium comprising diluent and unreacted monomers from a polymerization effluent comprising diluent, unreacted monomers and polymer solids, comprising a continuous discharge of the polymerization effluent from a slurry reactor through a discharge valve and transfer conduit into a first intermediate pressure flash tank with a conical bottom defined by substantially straight sides inclined at an angle to that of horizontal equal to or greater than the angle of slide of the slurry/polymer solids and an exit seal chamber of such diameter (d) and length (l) as to maintain a desired volume of concentrated polymer solids/slurry in the exit seal chamber such as to form a pressure seal while continuously discharging a plug flow of concentrated polymer solids/slurry bottom product of said first flash tank from the exit seal chamber through a seal chamber exit reducer with inclined sides defined by substantially straight sides inclined at an angle to that of horizontal equal to or greater than the angle of slide of the polymer solids which remain after removal of about 50 to 100% of the inert diluent therefrom to a second flash tank at a lower pressure.

We claim:  
     
         1 . An apparatus for capturing a higher weight percentage of polymer solids from a circulating slurry in a loop reactor than the weight percentage of solids in the circulating slurry, the circulating slurry being circulated in a direction in the loop reactor comprising: 
 a conduit having a first end, wherein said first end extends for a distance into the loop reactor said conduit having portions defining an opening wherein said opening is positioned relative to the direction of the circulating slurry.    
     
     
         2 . The apparatus of  claim 1  wherein the opening is facing the direction of the circulating slurry.  
     
     
         3 . The apparatus of  claim 1  wherein a portion of the conduit extends outwardly from the loop reactor.  
     
     
         4 . The apparatus of  claim 3  wherein the polymer solids are discharged from the loop reactor through the portion of the conduit extending outwardly from the loop reactor.  
     
     
         5 . The apparatus of  claim 4  wherein the polymer solids are continuously discharged from the loop reactor through the portion of the conduit extending outwardly from the loop reactor.  
     
     
         6 . A process for capturing a higher weight percentage of polymer solids from a circulating slurry in a loop reactor than the weight percentage of polymer solids in the circulating slurry, the circulating slurry being circulated in a direction in the loop reactor comprising the step of: 
 extending for a distance into the loop reactor a conduit having portions defining an opening wherein said opening extends into the circulating slurry.    
     
     
         7 . The process of  claim 6  including the step of positioning the opening in a substantially facing direction to the direction of flow of the circulating slurry.  
     
     
         8 . The process of  claim 6  including the step of extending a portion of conduit outwardly from the loop reactor.  
     
     
         9 . The process of  claim 8  including the step of discharging the polymer solids from the loop reactor through the portion of the conduit extending outwardly from the loop reactor.  
     
     
         10 . The process of  claim 9  including the step of continuously discharging the polymer solids from the loop reactor through the portion of the conduit extending outwardly from the loop reactor.  
     
     
         11 . An apparatus for purging polymer solids from a conduit connected to a loop reactor and in fluid communication with the loop reactor comprising: 
 a sensor;    a first valve in fluid communication with the conduit;    a second valve positioned between a first inert diluent and the conduit, wherein the first inert diluent is in fluid communication with the conduit between the loop reactor and the first valve;    wherein, in response to a signal produced by the sensor, the first valve is closed and the second valve is opened allowing the first inert diluent to enter the conduit in sufficient quantities and under sufficient pressure to purge polymer solids from the conduit.    
     
     
         12 . The apparatus of  claim 11  the sensor is a pressure sensor.  
     
     
         13 . The apparatus of  claim 11  wherein the conduit has a first end, wherein said first end extends for a distance into the loop reactor wherein portions adjacent to the first end define an opening.  
     
     
         14 . The apparatus of  claim 11  further comprising: 
 a third valve positioned between a second inert diluent and the conduit, wherein the second inert diluent is in fluid communication with the conduit between the loop reactor and the first valve;  
 wherein, when the first valve is open and the second valve is closed the third valve is open allowing the second inert diluent to enter the conduit.  
 
     
     
         15 . A process for purging polymer solids from a conduit connected to a loop reactor and in fluid communication with the loop reactor comprising the steps of: 
 closing a first valve in response to a first signal from a first sensor, wherein the first valve is connected to and in fluid communication with the conduit;    opening a second valve in response to a second signal from a second sensor, wherein the second valve is fluid communication between a first inert diluent and the conduit, and wherein the first inert diluent is in fluid communication with the conduit between the loop reactor and the first valve;    flowing sufficient quantities of the first inert diluent under sufficient pressure into the conduit to purge polymer solids from the conduit.    
     
     
         16 . The process of  claim 15  wherein the first and second sensors are the same.  
     
     
         17 . The process of  claim 15  wherein the first and second signals are the same.  
     
     
         18 . An apparatus for returning fines to a polymerization slurry in a loop reactor comprising, 
 a discharge valve for discharging a portion of the polymerization slurry from the loop reactor into a first transfer conduit;    the first transfer conduit communicating said polymerization slurry therein into a first flash tank, the first flash tank converting a portion of the polymerization slurry into a first fluid, the first fluid comprising a diluent and the fines;    a second transfer conduit communicating the first fluid therein to a first cyclone, the first cyclone converting a portion of the first fluid into a second fluid comprising the diluent and the fines;    a third transfer conduit communicating the second fluid into a heat exchanger, the heat exchanger converting the second fluid into a liquid comprising the diluent and the fines; and    a fourth transfer conduit communicating the liquid to the polymerization slurry in the loop reactor.    
     
     
         19 . The apparatus of  claim 18  further comprising a first transfer conduit heater for heat exchange between the first transfer conduit heater and the polymerization slurry.  
     
     
         20 . A process for returning fines to a polymerization slurry in a loop reactor comprising the steps of: 
 discharging a portion of the polymerization slurry from the loop reactor;    communicating the discharge polymerization slurry into a first flash tank;    converting in the flash tank a portion of the polymerization slurry into a first fluid, the first fluid comprising a diluent and the fines;    communicating the first fluid from the first flash tank to a first cyclone;    converting in the cyclone a portion of the first fluid into a second fluid comprising the diluent and the fines;    communicating the second fluid into a heat exchanger;    converting in the heat exchanger the second fluid into a liquid comprising the diluent and the fines; and    returning the liquid to the polymerization slurry in the loop reactor.    
     
     
         21 . A process for producing polymer from a polymerization slurry in a loop reactor operating at a space time yield greater than 2.8 lbs/hr-gal which comprises the steps of: 
 forming the polymer in the polymerization slurry, wherein the polymerization slurry comprises a liquid medium and solids;    discharging the polymerization slurry through a discharge valve into a first transfer conduit, the polymerization slurry after discharge referred to as a polymerization effluent;    heating the polymerization effluent in said first transfer conduit to a temperature below the fusion temperature of the polymer;    communicating said polymerization effluent through said first transfer conduit to a first flash tank wherein the pressure in said first flash tank and the temperature of said heated polymerization effluent are such as to produce a vapor from about 50% to about 100% of the liquid medium;    condensing the vapor obtained in the first flash step by heat exchange;    discharging from said first flash tank polymer solids to a second flash tank through a seal chamber of sufficient dimension such as to maintain a volume of polymer solids in the said seal chamber sufficient to maintain a pressure seal;    communicating the polymer solids to a second flash tank;    exposing the polymer solids to a pressure reduction from a higher pressure in the first flash tank to a lower pressure in said second flash; and    discharging the polymer solids from said second flash tank.    
     
     
         22 . The process of  claim 21  have a weight percent of the solids in the polymerization slurry greater than 47.  
     
     
         23 . The process of  claim 21  wherein the loop reactor is operating at a total circulating pumping head/reactor length is greater than 0.15 ft/ft.  
     
     
         24 . The process of  claim 21  wherein the loop reactor is operating with a recirculating pumping head greater than or equal to 200 ft.  
     
     
         25 . The process of  claim 21  wherein the polymerization slurry is circulated within the loop reactor by multiple pumps and wherein the volume is greater than 20,000 gallons.  
     
     
         26 . The process of  claim 21  wherein the loop reactor has more than eight vertical legs.  
     
     
         27 . The process of  claim 21  wherein heat exchange in the condensing step is accomplished with a heat exchanger equipped with a temperature controlled heat transfer medium.