Styrene process Luyben Chemical engineering

1. ProcessDescription
Ethylbenzene feedof purity0.99 mol % ( impuritybeingBenzene)isfedintothe processatambient
conditions,thatisP=1atm and T=25 degrees Celsius.
A splittertakesinLowpressure steamandsplitsitbetweenfurnace 1and the mixerassociatedwith
the ethyl benzene feed.
The Ethylene feedismixedwithlowpressure steamat1 atm comingfromthe splitterandmore
Ethyl benzene comingfromthe Ethyl benzene recycle streamfromdistillationcolumnnumber2.
Steamisreportedto lowerthe pressure of Ethyl benzene byvirtue of beingadiluent,andsince the
reactionthat converts Ethyl benzene tostyrene andhydrogenisreversible,the forwardreactionis
favoured. Thismixedfeedisthen chargedintothe processthroughtwocountercurrentheat
exchangernetworksinordertoheatup the streamto approach a reactor inletTemperatureof ca
600 degrees Celsius(Luyben2011a).The reactors are adiabatic. Afterthe secondheatexchangerthe
mixedfeedstream entersamixer,uponwhich itisagainmixedwithsteamfromFurnace 2 whichis
operatingat900K. A lotof steamischarged intothe processbecause the highheatcapacityof water
preventsatemperature swingthatcomesaboutbecause the reactionisendothermic.Steamalso
removes coke fromthe promotedironcatalyst( DesignBrief).
From thismixer,the temperature of the Ethyl benzene streamisnow 603 degrees Celsius andso,
the streamentersthroughthe firstreactor,exits,thenentersathirdheatexchanger, whichheatsup
the streamagain because the reactionisanendothermic.Fromthe thirdheatexchangerthe product
streamfrom the firstreactornow entersreactor2 at a temperature of 597 degrees Celsius. The
Temperature issetat approximately600 degrees Celsiusbecause the reactionisendothermic.
HigherTemperaturesare avoidedbecausetheyleadtothe propagationof side reactions. The
productstream fromreactor 2 is sentthroughheatexchangernumber2 andthenintoheat
exchangernumber1in orderto heatup the incomingfeedstream. Fromthe heatexchanger1the
productstream fromreactor 2 now goesto the condenserwhichcoolsdownthe streamtothe
required40 degrees Celsius.
Thereafter,the streamgoesintoadecantor ( 1atm & 40 degrees Celsius),whichconsistsof alight
gas splitterwhichtakeslightgasesoverheadand awater organicphase inthe bottomstream, that
goesintothe water- organicsplitter. Splitfactorsforthe lightgas splitterwere obtainedfrom
(Luyben2011) were [0.013893 0.009568 0.103303 0.034065 0.999367 1 0.966976 0.359118] for
[EB S B T H E CO2 W] respectively (Luyben2011a). For the water- organicsplitterpure wateris
removedviathe bottomstreamandeverythingelsewith5mol% watergoesoverheadtothe first
distillationcolumn. The water- organicsplitter,whichisalsoapart of the decantor,haspure water
leavinginthe bottomsstreamandthe organic phase leavingoverhead.
The overheadforthisfirstcolumn withsplitsfactors[11 1 1 1 1 1 0 1 0.001123] for [T B C0 C02 E H
M S W EB] respectivelyhastoluene ,benzene andlightgases.The bottomsstreamgetsintothe
seconddistillationcolumn [0.00332 0.998 0.74] for [SB T] respectively (Luyben2011a),whichhas
the overheadasan Ethyl benzene recycle andbottomstreamincludingthe productstyrene. An
orderof volatilityandboilingpointswheretakingintoconsiderationfordistillationcolumns
The purityof the Styrene is99.5% witha mass flow rate of 200 117ton/year.