1 refinery configuration Introduction

8/19/2019 1 refinery configuration Introduction

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.1 Introduction

• • In this lecture we present a brief overview of the alkylation process.

• In an alkylation process, olens are reacted with isoparans to yield alkylate product.

• The basic purpose of alkylation is to enhance the octane number of the feed stock.

• For instance, octane number of butane alkylate is about 9 ! 9". This is due to the

formation of a hydrocarbon with side chain arran#ement of carbon and hydro#en atoms.

9.2 Reaction Mechanism

• • There are three basic reaction steps to achieve alkylation

• $tep % involvin# &arbonium ion formation' In this reaction, alkene reacts with a proton

(acid catalyst) to produce a proton substituted olen. The proton substituted olen

reacts with isoparan to #enerate a reactive carbonium ion and alkane.

• $tep involvin# carbonium ion intermediate formation' In this reaction, the carbonium

ion formed in step % reacts with the olen to produce an intermediate carbonium ion.


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• $tep * involvin# re#eneration of carbonium ion' In this reaction, the intermediate

carbonium ion reacts with the isoparan to produce alkylate product and carbonium

ion. Thus carbonium ion is a#ain re#enerated to take part in step reactions alon#

with other additional unreacted olen molecules.

9.3 Reaction conditions

• • To avoid olen polymeri+ation, hi#h isobutane to olen ratios are used.

• Typical isobutene to olen ratios are '% to %'%

• -cid catalysts are used. rimarily sulphuric acid (/$01) or /F are used.

• 2ependin# on the acid catalysts choosed the process comple3ity varies. 4e present

both process technolo#ies to indicate the pertinent process comple3ity.

• 5eaction operatin# temperature' %6 7 68& usin# /$01 and ! 168& usin# /F

• 5eaction temperature' 1.1 bar for /$01 and ". bar for /F

• 4hen /$01 is used refri#eration is used.

• 4hen /F is used, refri#eration is not used.

9.4 Sulfuric acid based alkylation process technology !igure 9.1"


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!igure 9.1 Sulphuric #cid #lkylation $nit

• • %austic &ash' The feed mi3ture (olen : &1 compounds) are rst sub;ected

to caustic wash. 2urin# caustic wash, sulphur compounds are removed and spent

caustic is recycled back to the caustic wash. Fresh caustic solution is added to take care

of the loss.

• Refrigeration' The olen feed enters a refri#eration unit to reduce the feedstock

temperature.

• • #lkylation reactor' The reactor is arran#ed as a series of &$T5s with acid fed

in the rst &$T5 and feed supplied to di


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• The alkylator unit therefore will have two phases in due course of reaction namely the

olen : isoparan mi3ture which will be li#hter and the alkylate stream which will be

heavier and will be appearin# as a bottom fraction if allowed to settle.

• $ince e3cess isoparan is used, the isoparan can be easily allowed as a bypass

stream.

• =ventually, the alkylate product from the last reactor will be taken out as a heavy

stream.

• Thus, the alkylation reactor produces two streams. These are (a) isoparan rich

or#anic phase and (b) alkylate rich phase alon# with acid and isobutane phases.

• These streams should be sub;ected to further purication.

• (hase separator' It so happens that the acid enters the or#anic rich stream and will

be sub;ected to phase separation by settlin#. $imilarly, the olen>isoparan mi3ture will

be also separated by #ravity settlin#. Thus the phase separator produces three streams

namely (a) olen : isoparan rich phase (b) acid rich stream (c) alkylate rich stream.

• )le*n + (ara,n processing' The olen : paran stream is rst sub;ected to

compression followed by coolin#. 4hen this stream is sub;ected to throttlin# and phase

separation, then the olen : paran rich stream will be #enerated. The propane rich

stream from this stream is #enerated as another stream in the phase separator.

• (ropane defractionator' The propane rich stream after coolin# is fed to a

fractionator where propane is separated from the olen:isoparan mi3ture. The olen

: isoparan mi3ture is sent back to mi3 with the olen feed.

• %austic &ash for alkylate rich stream' The caustic wash operation ensures to

completely eliminate acid concentration from the alkylate.

• #lkylate fractionation' The alkylate is fed to a distillation column that is supplied

with isobutane feed and alkylate feeds to produce isobutane as a top product and

alkylate : butane mi3ture as a bottom product.

• -ebutanier' The debutani+er separates butane and alkylate usin# the concept of

distillation.


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1. /hy isobutane is fed to the deisobutanier unit in the sulphuric acid 0o&sheet#ns' The isobutane feed consists of n7butane and it should be separated so that thealkylation reactor is fed with only isobutane. ?ow, the issue is to use a separatedistillation column for separatin# isobutane feed into isobutane and butane. This willincur additional costs. Therefore, instead of two separate columns, both separations are

carried out in the same distillation column. 0fcourse, costs will be saved by this conceptin processin#.

2. plain ho& compression and cooling &ill enable the separation of propaneand ole*n+isopara,ns miture

#ns' The separation of propane from isoparans and olens is very dicult due toclose boilin# points of these streams. ?ow, compression is also re@uired so as to avoidrefri#eration system in the condenser of propane. This is also due to the fact that hi#herpressures increasin# boilin# point of the propane and enable the usa#e of coolin# waterin the condenser. 0n the other hand, removin# heat from the system will enableadiabatic Aash conditions which can be e3ploited to separate the propane and

olen:isoparan mi3ture. his entire operation has signi*cant research in the*eld of thermodynamics and mass transfer sub5ects. (robably6 good numberof simulation studies ha7e *nally yielded the 0o&sheet to obtain suchcon*gurations.

3. /hat are the ad7antages of 82S)4 process &hen compared to the 8!process

#ns'

• • -dditonal e@uipment is not need in this process. This is not the case in /F

process where /F recovery or neutrali+ation re@uires additional processes.

• /F can form a to3ic vapour cloud therefore, safety parameters need to be more

e


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• (a) 2rier

(b) 2eAourinator

(c) $afety instrumentation and accessories

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1 refinery configuration Introduction