Ethane recovery process and alkylation process with ethane recovery

Abstract

Processes and systems for the production of ethylbenzene using a dilute ethylene feed and subsequent recovery of ethane in the alkylation vent gas.

What is claimed: 
     
         1 . A process for the production of ethylbenzene, comprising:
 introducing benzene and an ethylene feed into an alkylation reaction zone in the presence of an alkylation catalyst to produce an alkylation effluent containing ethylbenzene and an alkylation overhead stream;   separating the alkylation overhead stream into a liquid portion containing benzene and a vapor portion containing unconverted ethylene, methane, and ethane;   absorbing the unconverted ethylene and the ethane in the vapor portion of the first alkylation overhead stream via contact with a lean oil containing benzene and alkylbenzene in an absorption zone to produce a rich oil stream containing the ethylene and the ethane and a vapor stream comprising the methane;   introducing the rich oil stream into a second alkylation reaction zone containing a second alkylation catalyst to produce a first aromatic lean oil stream; and,   fractionating the first aromatic lean oil stream in a deethanizer to produce a deethanizer overhead vapor stream containing the ethane and a liquid bottoms stream containing the lean oil.   
     
     
         2 . The process of  claim 1 , further comprising operating the absorption zone at conditions of temperature and pressure to absorb essentially all of the ethylene and ethane into the rich oil stream. 
     
     
         3 . The process of  claim 1 , further comprising:
 contacting the deethanizer overhead vapor stream with a first portion of a second absorbent comprising poly-ethylated benzene in a first scrubber to absorb benzene in the deethanizer overhead vapor stream and to produce a first scrubber bottoms stream and a first scrubber overhead stream comprising ethane; and   contacting the vapor stream comprising the methane with a second portion of the second absorbent in a second scrubber to absorb benzene present in the vapor stream and to produce a second scrubber bottoms stream and a second scrubber overhead stream comprising methane.   
     
     
         4 . The process of  claim 3 , further comprising:
 introducing the first scrubber bottoms steam and the second scrubber bottoms stream to a transalkylation reaction zone;   contacting the poly-ethylated benzene with benzene in the presence of a transalkylation catalyst to convert at least a portion of the poly-ethylated benzene and benzene to ethylbenzene.   
     
     
         5 . The process of  claim 1 , wherein the deethanizer overhead vapor stream consists essentially of ethane and includes essentially no ethylene, methane, and hydrogen. 
     
     
         6 . The process of  claim 1 , wherein the absorption zone comprises a reboiled absorber column, and wherein the absorbing comprises operating the reboiled absorber column at a bottoms temperature in the range from about 150° C. to about 220° C. and an overhead pressure in the range from about 200 psig to about 500 psig. 
     
     
         7 . The process of  claim 6 , further comprising introducing the lean oil proximate an upper end of the reboiled absorber column at a temperature in the range from about −20° C. to about 50° C. 
     
     
         8 . The process of  claim 6 , wherein the reboiled absorber column comprises multiple reboilers configured to sequentially extract heat from the liquid bottoms stream from the deethanizer. 
     
     
         9 . The process of  claim 1 , further comprising contacting the liquid bottoms stream in indirect heat exchange with the alkylation effluent. 
     
     
         10 . The process of  claim 1 , further comprising contacting the liquid bottoms stream in indirect heat exchange with the rich oil stream. 
     
     
         11 . A system for the recovery of ethylene from a dilute ethylene stream, comprising:
 a reboiled absorber column for contacting a stream comprising methane, ethane, and ethylene with an absorbent-reactant, producing a rich oil stream comprising the absorbent-reactant, ethylene, and ethane, and a vapor stream comprising methane;   a reaction zone for reacting the ethylene and the absorbent-reactant, producing an effluent comprising ethane and a reaction product;   a stripper for stripping the effluent to produce a lean oil bottoms stream and an overhead vapor stream comprising ethane;   a first scrubber for contacting the overhead vapor stream with a first portion of a second absorbent-reactant to absorb unreacted ethylene or absorbent-reactant in the overhead vapor stream and to produce a first scrubber bottoms stream comprising the second absorbent-reactant and a first scrubber overhead stream comprising ethane;   a second scrubber for contacting the vapor stream comprising methane with a second portion of the second absorbent-reactant to absorb ethane, ethylene, and/or absorbent-reactant present in the vapor stream and to produce a second scrubber bottoms stream comprising the second absorbent-reactant and a second scrubber overhead stream comprising methane.   
     
     
         12 . The system of  claim 11 , further comprising one or more heat exchangers to cool the absorbent-reactant upstream of the reboiled absorber column to a temperature in the range from about −20° C. to about 50° C. 
     
     
         13 . The system of  claim 11 , further comprising:
 one or more heat exchangers for reboiling the reboiled absorber column at a bottoms temperature in the range from about 150° C. to about 220° C.; and   one or more heat exchangers for operating the stripper at a bottoms temperature in the range from about 200° C. to about 280° C.   
     
     
         14 . The system of  claim 13 , wherein the reboiled absorber column comprises multiple reboilers configured to sequentially extract heat from the lean oil bottoms stream from the stripper. 
     
     
         15 . The system of  claim 14 , wherein the multiple reboilers comprise one or more side reboilers. 
     
     
         16 . The system of  claim 13 , further comprising one or more stripper side reboilers for extracting heat from the lean oil bottoms stream from the stripper. 
     
     
         17 . The system of  claim 13 , further comprising one or more heat exchangers for contacting the lean oil bottoms stream in indirect heat exchange with the reaction zone effluent and/or the rich oil bottoms stream. 
     
     
         18 . A system for the alkylation of benzene, comprising:
 an alkylation reaction zone for reacting benzene with an ethylene feed in the presence of an alkylation catalyst to produce an alkylation effluent containing ethylbenzene and an alkylation overhead stream;   a separation zone for separating the alkylation overhead stream into a liquid portion containing benzene and a vapor portion containing unconverted ethylene, methane, and ethane;   an absorption zone for absorbing the unconverted olefin and the ethane in the vapor portion of the first alkylation overhead stream via contact with a lean oil containing benzene and alkylbenzene to produce a rich oil stream containing the ethylene and the ethane and a vapor stream comprising the methane;   a second alkylation reaction zone for reacting benzene and ethylene in the rich oil stream to produce a first aromatic lean oil stream; and,   a deethanizer for fractionating the first aromatic lean oil stream to produce a deethanizer overhead vapor stream containing the ethane and a liquid bottoms stream containing the lean oil.   
     
     
         19 . The system of  claim 18 , further comprising a control system configured to operate the absorption zone at conditions of lean oil flow, temperature, and pressure to absorb essentially all of the ethylene and ethane into the rich oil stream. 
     
     
         20 . The system of  claim 18 , further comprising:
 a first scrubber for contacting the deethanizer overhead vapor stream with a first portion of a second absorbent comprising poly-ethylated benzene to absorb benzene in the deethanizer overhead vapor stream and to produce a first scrubber bottoms stream and a first scrubber overhead stream comprising ethane; and   a second scrubber for contacting the vapor stream comprising the methane with a second portion of the second absorbent to absorb benzene present in the vapor stream and to produce a second scrubber bottoms stream and a second scrubber overhead stream comprising methane.