Method and apparatus for high solids slurry polymerization

Abstract

An olefin polymerization process wherein monomer, diluent and catalyst are circulated in a continuous loop reactor and product slurry is recovered by means of a continuous product take off. The continuous product allows operating the reaction at significantly higher solids content in the circulating slurry. In a preferred embodiment, the slurry is heated in a flash line heater and passed to a high pressure flash where a majority of the diluent is separated and thereafter condensed by simple heat exchange, without compression, and thereafter recycled. Also an olefin polymerization process operating at higher reactor solids by virtue of more aggressive circulation.

What is claimed is:  
     
         1 . A method of continuously obtaining polymer product from an olefin polymerization reactor comprising an endless loop of pipe, the method comprising: 
 circulating within the loop a slurry of polymer particles and liquids while maintaining the reactor at a first pressure above 400 psia;    continuously conveying an amount of the polymer particles from the reactor first through a discharge means located below a horizontal midline of a cross-section of the reactor pipe and then through a transfer line; and    receiving the polymer particles at the inlet of a non-cyclonic primary flash vessel having vertical sidewalls and a conical bottom and maintained at a second pressure less than 25 psia, whereupon the particles settle to the bottom of the flash vessel.    
     
     
         2 . The method of  claim 1  in which the reactor is a horizontal loop reactor.  
     
     
         3 . The method of  claim 2  in which the discharge means is located upstream of a reactor-circulating pump in the reactor.  
     
     
         4 . The method of  claim 1  in which the first pressure is above 600 psia.  
     
     
         5 . The method of  claim 2  in which the first pressure is from 635 to 675 psia and the liquids include isobutane and ethylene.  
     
     
         6 . The method of  claim 1  including controlling the flow through the discharge means in response to the pressure of the reactor, and adding fresh olefin feedstock to the reactor at a constant rate.  
     
     
         7 . The method of  claim 6  in which the reactor is a horizontal loop reactor.  
     
     
         8 . The method of  claim 6  in which the reactor is a vertical loop reactor.  
     
     
         9 . The method of  claim 1  in which the particles enter the non-cyclonic primary flash vessel at a tangent to the vertical sidewall in the upper half of the vessel.  
     
     
         10 . The method of  claim 1  further comprising removing a portion of the polymer particles via an outlet at the bottom of the flash vessel while retaining an amount of particles sufficient to maintain a dynamic seal between the inlet and the outlet of the vessel.  
     
     
         11 . The method of  claim 1  in which the reactor is a vertical loop reactor.  
     
     
         12 . The method of  claim 1   1  in which the particles enter the non-cyclonic primary flash vessel at a tangent to the vertical sidewall in the upper half of the vessel.  
     
     
         13 . The method of  claim 11  further comprising removing a portion of the polymer particles via an outlet at the bottom of the flash vessel while retaining an amount of particles sufficient to maintain a dynamic seal between the inlet and the outlet of the vessel.  
     
     
         14 . The method of  claim 13  in which polymer particles are removed while maintaining a level which fills the conical bottom of the vessel.  
     
     
         15 . The method of  claim 11  including the additional step, before the polymer particles enter the primary flash vessel, of receiving the polymer particles at the inlet of an intermediate non-cyclonic flash vessel with an upper section having vertical sidewalls and the inlet being tangential to the sidewall, a conical bottom with an outlet therein, and operated at a third pressure intermediate between the first and second pressures.  
     
     
         16 . The method of  claim 15  in which the first pressure is above 600 psia and the third pressure in the intermediate flash vessel is above 180 psia, and the second pressure in the primary flash vessel is below 25 psia.  
     
     
         17 . A method of continuously obtaining polymer product from an olefin polymerization reactor comprising an endless loop of pipe, the method comprising: 
 circulating within the loop a slurry of polymer particles and liquids while maintaining the reactor at a first pressure above 400 psia;    continuously conveying an amount of the polymer particles from the reactor first through a discharge means located below a horizontal midline of a cross-section of the reactor pipe and then through a transfer line;    receiving the polymer particles at the inlet of a non-cyclonic primary flash vessel having vertical sidewalls and a conical bottom and maintained at a second pressure less than 25 psia, whereupon the particles settle to the bottom of the flash vessel; and    including the additional step, before the polymer particles enter the primary flash vessel, of receiving the polymer particles at the inlet of an intermediate non-cyclonic flash vessel with an upper section having vertical sidewalls and the inlet being tangential to the sidewall, a conical bottom with an outlet therein, and operated at a third pressure intermediate between the first and second pressures.    
     
     
         18 . The method of  claim 17  in which the first pressure is above 600 psia and the third pressure in the intermediate flash vessel is above 180 psia, and the second pressure in the primary flash vessel is below 25 psia.  
     
     
         19 . A method of continuously obtaining polymer product from an olefin polymerization reactor comprising an endless loop of pipe, the method comprising: 
 circulating within the loop a slurry of polymer particles and liquids while maintaining the reactor at a first pressure above 400 psia;    continuously conveying an amount of the polymer particles from the reactor first through a discharge means located below a horizontal midline of a cross-section of the reactor pipe and then through a transfer line;    receiving the polymer particles at the inlet of a non-cyclonic primary flash vessel having vertical sidewalls and a conical bottom and maintained at a second pressure less than 25 psia, whereupon the particles settle to the bottom of the flash vessel;    removing a portion of the polymer particles via an outlet at the bottom of the flash vessel while retaining an amount of particles sufficient to maintain a dynamic seal between the inlet and the outlet of the vessel and maintaining a level which fills the conical bottom of the vessel.    
     
     
         20 . A method of continuously obtaining polymer product from an olefin polymerization reactor comprising an endless loop of pipe, the method comprising: 
 circulating within the loop a slurry of polymer particles and liquids while maintaining the reactor at a first pressure above 400 psia;    continuously conveying an amount of the polymer particles from the reactor first through a discharge means located below a horizontal midline of a cross-section of the reactor pipe and then through a transfer line; and    receiving the polymer particles at the inlet of a non-cyclonic first flash vessel having vertical sidewalls and a conical bottom and maintained at a second pressure less than 25 psia, whereupon the particles settle to the bottom of the first flash vessel.    
     
     
         21 . The method of  claim 20  in which the reactor is a horizontal loop reactor.  
     
     
         22 . The method of  claim 21  in which the discharge means is located upstream of a reactor-circulating pump in the reactor.  
     
     
         23 . The method of  claim 20  in which the first pressure is above 600 psia.  
     
     
         24 . The method of  claim 21  in which the first pressure is between 635 to 675 psia and the liquids include isobutane and ethylene.  
     
     
         25 . The method of  claim 21  in which the first pressure is about 650 psia and the liquids include isobutane and ethylene.  
     
     
         26 . The method of  claim 20  including controlling the flow through the discharge means in response to the pressure of the reactor, and adding one or more input streams to the reactor at a constant rate.  
     
     
         27 . The method of  claim 26  in which the reactor is a horizontal loop reactor.  
     
     
         28 . The method of  claim 26  in which the reactor is a vertical loop reactor.  
     
     
         29 . The method of  claim 20  in which the particles enter the non-cyclonic first flash vessel at a tangent to the vertical sidewall in the upper half of the vessel.  
     
     
         30 . The method of  claim 20  further comprising removing a portion of the polymer particles via an outlet at the bottom of the first flash vessel while retaining an amount of particles sufficient to maintain a dynamic seal between the inlet and the outlet of the vessel.  
     
     
         31 . The method of  claim 20  in which the reactor is a vertical loop reactor.  
     
     
         32 . The method of  claim 31  in which the particles enter the non-cyclonic first flash vessel at a tangent to the vertical sidewall in the upper half of the vessel.  
     
     
         33 . The method of  claim 31  further comprising removing a portion of the polymer particles via an outlet at the bottom of the first flash vessel while retaining an amount of particles sufficient to maintain a dynamic seal between the inlet and the outlet of the vessel.  
     
     
         34 . The method of  claim 33  in which polymer particles are removed while maintaining a level which fills the conical bottom of the vessel.  
     
     
         35 . The method of  claim 31  including the additional step, before the polymer particles enter the first flash vessel, of receiving the polymer particles at the inlet of a second non-cyclonic flash vessel with an upper section having vertical sidewalls and the inlet being tangential to the sidewall, a conical bottom with an outlet therein, and operated at a third pressure intermediate between the first and second pressures.  
     
     
         36 . The method of  claim 35  in which the first pressure is above 600 psia and the third pressure in the second flash vessel is above 180 psia, and the second pressure in the first flash vessel is below 25 psia.  
     
     
         37 . A method of continuously obtaining polymer product from an olefin polymerization reactor comprising an endless loop of pipe, the method comprising: 
 circulating within the loop a slurry of polymer particles and liquids while maintaining the reactor at a first pressure above 400 psia;    continuously conveying an amount of the polymer particles from the reactor first through a discharge means located below a horizontal midline of a cross-section of the reactor pipe and then through a transfer line;    receiving the polymer particles at the inlet of a non-cyclonic first flash vessel having vertical sidewalls and a conical bottom and maintained at a second pressure less than 25 psia, whereupon the particles settle to the bottom of the first flash vessel; and    including the additional step, before the polymer particles enter the first flash vessel, of receiving the polymer particles at the inlet of a second non-cyclonic flash vessel with an upper section having vertical sidewalls and the inlet being tangential to the sidewall, a conical bottom with an outlet therein, and operated at a third pressure intermediate between the first and second pressures.    
     
     
         38 . The method of  claim 37  in which the first pressure is above 600 psia and the third pressure in the second flash vessel is above 180 psia, and the second pressure in the first flash vessel is below 25 psia.  
     
     
         39 . A method of continuously obtaining polymer product from an olefin polymerization reactor comprising an endless loop of pipe, the method comprising: 
 circulating within the loop a slurry of polymer particles and liquids while maintaining the reactor at a first pressure above 400 psia;    continuously conveying an amount of the polymer particles from the reactor first through a discharge means located below a horizontal midline of a cross-section of the reactor pipe and then through a transfer line;    receiving the polymer particles at the inlet of a non-cyclonic first flash vessel having vertical sidewalls and a conical bottom and maintained at a second pressure less than 25 psia, whereupon the particles settle to the bottom of the first flash vessel;    removing a portion of the polymer particles via an outlet at the bottom of the first flash vessel while retaining an amount of particles sufficient to maintain a dynamic seal between the inlet and the outlet of the vessel and maintaining a level which fills the conical bottom of the vessel.