Oxygenate Conversion to Olefins with Dimerization and Metathesis

Abstract

A processing scheme and system for enhanced light olefin production, particularly for increased relative yield of propylene, involves oxygenate conversion to olefins and subsequent oxygenate conversion effluent stream treatment including dimerization of ethylene to butene and metathesis of butenes and/or hexenes with ethylene. The processing scheme and system may further involve isomerization of at least a portion of 1-butene to 2-butene to produce additional propylene.

1 . A process for producing light olefins from an oxygenate-containing feedstock, the process comprising:
 contacting the oxygenate-containing feedstock in an oxygenate conversion reactor with an oxygenate conversion catalyst and at reaction conditions effective to convert the oxygenate-containing feedstock to an oxygenate conversion effluent stream comprising light olefins and C 4 +hydrocarbons, wherein the light olefins comprise ethylene and the C 4 +hydrocarbons comprise a quantity of butenes;   treating the oxygenate effluent stream in a separation zone and forming a first process stream comprising at least a portion of the ethylene from the oxygenate conversion effluent stream;   dimerizing at least a portion of the ethylene from the first process stream in a dimerization zone maintained with an ethylene to butene ratio from 1:1 to 5:1 to produce a dimerized stream comprising a quantity of butenes;   contacting at least a portion of quantity of butenes from the dimerized stream with ethylene in a metathesis zone at effective conditions to produce a metathesis effluent stream comprising propylene; and   recovering propylene from the metathesis effluent stream.   
   
   
       2 . The process of  claim 1  wherein the oxygenate-containing feedstock is selected from methanol, ethanol, dimethyl ether, diethyl ether, and combinations thereof. 
   
   
       3 . The process of  claim 1  wherein the treating step additionally forms a second process stream comprising at least a portion of the butenes including a quantity of 1-butenes from the oxygenate conversion effluent stream and wherein at least a portion of butenes from the second process stream is contacted with ethylene in the metathesis zone to produce propylene. 
   
   
       4 . The process of  claim 3  additionally comprising:
 isomerizing at least a portion of the quantity of 1-butenes from the second process stream in an isomerization zone to produce an isomerized stream comprising a quantity of 2-butenes; and   contacting at least a portion of the quantity of 2-butenes from the isomerized stream with ethylene in the metathesis zone to produce propylene.   
   
   
       5 . The process of  claim 1  wherein the metathesis effluent stream additionally comprises a quantity of ethylene and a quantity of butenes and wherein the metathesis effluent stream is separated in a fractionation zone to form a propylene product stream, an ethylene recycle stream and a butenes recycle stream. 
   
   
       6 . The process of  claim 5  additionally comprising:
 introducing at least a portion of the ethylene recycle stream into the dimerization zone to produce an additional quantity of butenes; and   treating the butenes recycle stream by one of introducing at least a portion of the butenes recycle stream into the metathesis zone to produce an additional quantity of propylene or introducing at least a portion of the butenes recycle stream to an isomerization zone to produce an additional quantity of 2-butenes.   
   
   
       7 . The process of  claim 1  wherein the dimerized stream additionally comprises a quantity of 1-butenes and wherein at least a portion of the quantity of 1-butenes from the dimerized stream are isomerized in an isomerization zone to produce an isomerized stream comprising a quantity of 2-butenes. 
   
   
       8 . The process of  claim 7  additionally comprising:
 contacting at least a portion of the 2-butenes from the isomerized stream with ethylene in the metathesis zone to produce propylene.   
   
   
       9 . The process of  claim 1  additionally comprising:
 introducing a portion of the ethylene from the first process stream into the metathesis zone.