Heat management in ethylene oligomerization

Abstract

The oligomerization of ethylene using a chromium catalyst having a heteroatomic ligand may be used to provide oligomerization products that are selective towards hexene and/or octene. However, such processes also typically produce some polymer as an undesirable by product. The present invention is directed towards improvements in the selective oligomerization of ethylene.

1 . A solution process for the oligomerization of ethylene, said process comprising contacting ethylene with:
 a) oligomerization catalyst;   b) an activator; and   c) a solvent for said catalyst,   said process being conducted under oligomerization conditions in an oligomerization reactor system, characterized in that said process is conducted with process equipment that includes:   1) a first heat exchanger that is used to provide heat to said process; and   2) a second heat exchanger that is used to remove heat from said oligomerization reactor system.   
     
     
         2 . The process of  claim 1  wherein:
 a) said catalyst consists essentially of a source of chromium that is soluble in said solvent and a bridged diphosphine ligand; and 
 b) said activator consists essentially of an aluminoxane. 
 
     
     
         3 . The process of  claim 1  wherein said oligomerization reactor system comprises at least one liquid full continuously stirred tank reactor. 
     
     
         4 . The process of  claim 1  wherein said oligomerization reactor system comprises a continuously stirred tank reactor and a tubular reactor, with the further provisos that:
 a) said continuously stirred tank reactor is upstream of said tubular reactor; 
 b) said tubular reactor is fed a combination of
 i) first product from said continuously stirred tank reactor; and 
 ii) fresh feed comprising ethylene and solvent, with the additional proviso that said fresh feed is colder than said first product. 
 
 
     
     
         5 . The process of  claim 4 , further characterized in that first product is initially cooled in a heat exchanger prior to being fed to said tubular reactor. 
     
     
         6 . The process of  claim 1  wherein said oligomerization reactor system comprises two continuously stirred tank reactors in series, with the further proviso that:
 a) an upstream continuously stirred tank reactor having a first reactor volume produces a first oligomerization product; and 
 b) said first oligomerization product and fresh feed comprising ethylene and solvent are fed to a downstream continuously stirred tank reactor having a second reactor volume that is greater than said first reactor volume. 
 
     
     
         7 . The process of  claim 3  wherein each of said at least one continuously stirred tank reactor is characterized by having an agitator shaft seal that contains a fluid channel contained therein that permits fluid flushing of said agitation shaft. 
     
     
         8 . The process according to  claim 1 , further characterized in that a portion of said ethylene is dissolved in solvent in a solution absorber that is external to said reactor system, with the further proviso that said solution absorber is equipped with a third heat exchanger for removal of heat of absorbtion. 
     
     
         9 . The process according to  claim 1 , wherein
 1) said oligomerization catalyst comprises:
 1.1) a source of chromium that is soluble in said solvent; and 
 1.2) a ligand defined by the formula (R 1 )(R 2 )—P 1 -bridge-P 2 (R 3 )(R 4 ) wherein R 1 , R 2 , R 3  and R 4  are independently selected from the group consisting of hydrocarbyl and heterohydrocarbyl and the bridge is a divalent moiety that is bonded to both phosphorus atoms. 
   2) said activator comprises an aluminoxane;   3) said oligomerization conditions comprises a temperature of from 10 to 100° C. and a pressure of from 5 to 100 atmospheres.   
     
     
         10 . The process according to  claim 9  wherein said bridge is —N(R 5 )— wherein R 5  is selected from the group consisting of hydrogen, alkyl, substituted alkyl, aryl, substituted aryl, aryloxy, substituted aryloxy, halogen, alkoxycarbonyl, carbonyloxy, alkoxy, aminocarbonyl, carbonylamino, dialkylamino, silyl groups or derivatives thereof and an aryl group substituted with any of these substituents.