tai lieu isolation n-butane

1. IICPT
Inqi Journal of Chcmicel
.rd P.trolcum Enginccritrg
lraqi Chemical Petroleum
Journalof and
Vol.8No.3(September
ISSN:
Engineering
2007)43-48
1997-4884 Univcnity ofBrgbdd
Coll€c of EDtinE iog
Deactivation lsomerization
Studyof Catalysts in Process
to ProduceHigh OctaneGasoline
Khalid A. Sukkar,HayamM. Abrlul-Raheemo Amel Th. Jubern and Jabir Sh.Jurnaly'
ChemicalEngineering - University Technolog,t
Department of - Iraq
' * College Engineering *
- University Al-Nahrain Iraq
Chemical Department
Engineering of of
Abstract
In this study the isomerization desulfuerized
of light lraqi petroleumnaphtha(Al-DuraRefinery)with boilingpoint
range of 37 to 124 oC , 80.5API specificgravity and 68.2 octanenumber has beenirwestigated.Two typesof
catolystswereprepared (P1/HXand Pt/SrX) by impregnationof 0.8 wt%o on l3X-zeolite. The catalyst activity and
Pt
selectivitytowardisomerization, catalyt deactivation
and wereinvestigated.
Theisomerization consisled a vertical tubular stainless
unit of steelreactorof 2 cm internaldiameter, cm external
3
diameter and 68 cm height.Theoperating pressure was atmospheric all experimental
for runs. Theliquidflow of light-
naphtha was A.4 IJh, and the catalystweight was 50 gm, H/H.C ratio usedwas 4 for all experimental runs. The
isomerizationprocess studiedat dfurent tenperatures 250, 270, 275, 300,325, and 350oC , Itwasfound that,
was of
the optimum isomerization is
temperature 270"C
Theisomerizationactivities snd selectivities afunction of timeshowedhigh activity at the beginningof the reaction
os
ord were deactivated rapidly. This indicatesthat the deactivationof PI/HX and Pt/SrX results from the blocking of pore
nouth by the depositedcarbon. Thefollowing deaeliv;ation decreasingorder, PI/HX > Pt/SrX wasfound. On the other
,nnd, PI/HX cotalyst shows higher activity and selectivitythqn that of Pt/SrX.
It waseoncluded that,only an cverage 90 wt% of the carbonatoms
of feed into thereactor(light naphtha)is detected
in theproductstreamduetoformation of cokedeposits which leadsto cqtalystdeactivation. resultsclearlyshowed
The
thot hydrogenis necessary the ltydrogenation olefinsin order to preventoligonerizationreactionthat leadslo
for of
coke formation and catalystdeactivation.
light-napgtha,PIJHX PVSrXcatalysts,
Icywortls; catalyticisomerization, and deactivation.
lnboduction In general,a catalystmay lose its activity or its
selectivity to poisoning,
due fouling,sintering lossof
and
Due to a heightened awareness the environrnental
of activespecies Oneof the mostchallenging
[], tasksin
poblem worldwide,expectations cleanand unleaded
of the designand operation industrialcatalyticprocesses
of
gasoline and world demand for gasoline have been is the prevention,or at least the control, of catalyst
ircreasing.Catzl5'ticisomerization regardedoneof the
is deactivation. Loss of catalyst activity is often
mostimportantprocesses oil refineries
in which produce accompaniedby a loss in selectivity. This leads to
cleanand high octanegasoline. Isomerization convefts n- greater formation of undesired by-products such as
butane, n-pentaneand n-hexaneinto their respective wasteof
carbonoxides,poor utilizationof raw rnaterials,
boparaffinsof substantiallyhigher octanenumber.The energy,and increased pollution [3,4]. Thus, solving
oommon feedstocke isomerization
for process the light
is problems of paramount
deactivation is importance the
for
saight run naphtha, which consists the lighter fraction
of economicand ecologic performance the process
of
cs tc6Lt,2l. industry.Understanding deactivation mechanisms could
Vol.8No.3(September
IJCPE 2007) 43

2. otin,
ultimately lead to the design of inherently stable diameter,3 cm externaldiameter
and 68 cm height
catalysts, considerable
with benefits.Solvine deactivation (reactor volume 214 cm3).The reactor was heated
-of
problems requiresa detailedknowledge th. ,uny uniformlyusingan electrical furnace.Thetemperarure at
causes mechanisms
and involved [6,7,gJ. the reactorcenterof the catalystbed and at different
, On theotherhand,foulingformation regarded of
is one points in reactor and system were determinedby
the most importanttypes of catalystdeictivationin manufacturingan interface system, (Computerized
isomerization process.Generally,the kinetics of a Temperature Measurement System) which has ten
catalyst deactivation a functionof temperature,
is time, calibrated thermocouple sensors K (iron-constantan).
type
pressure and the concentrations of different Theinterface programmed is andrun by a computer (p4).
substances l0].
[9, The reactoris fittsd with accurate meansfor controlof
The principal differences between the various pressure, and liquid flow rates. The experiments
gas
industrial processes isomerization
of relate thecatalyst were conducted atmospheric
to at pressure.Feedmixtures
used; this will in turn affectthe feedpretreatment steps of hydrogenand hydrocarbon were preheated reactor
to
and spent catalyst characterization. The two principal temperature beforeentering bed.
the
typesof catalystidentifiedin the industry areiplatinum
on zeolite,which operates temperatures
at above2OO oC,
and platinum chloride on alumina, which operates at
temperatures below200 oCIll, l2]. Themainadvantage
of zeolites overplatinum chlorinated
on alumina.atalyJtt
is that they have a much betterresistance againstfeed
impurities such as water, which obviates need for
the
expensive drying facilities.Moreover,in zeolitebased
processesit is unnecessary to continuouslyadd
chlorinating agents, remove hydrogen chloride from
effluent steams and take precautions againstcorrosion.
Manyauthon haveinvestigated catalyst
the deactivation
phenomenon over PVA|2O3 catalystusingn-pentane, n-
hexane,and n-heptane a feedstock isomerization
as for
reaction 13,l4].
[ll,
In order to designand optimize catalysts, detailed
a
undentanding of the reaction mechanism,kinetic,
deactivation and catalyst properties is of primary
interesl The combination between catalystperformance
and understanding catalystdeactivation will enable
of
the designof a new catalystwith reduceddeactivation
and increased acrivity and selectivity for desired
products. Therefore, present
the work aimsto:
- providea substantiated Fig.(1)General view of experimental apparatus
knowledge the isomerization
of
reaction based on bifunctional zeolite catalystsby
using light-naphthaas a feed and determiningthe
optimumproc€ss conditions. Materials
- test the performance, deactivationrates and catalyst Two typesof catalysts namedPt/HX and pt/SrX were
stabilityunder optimum process conditions prepared. preparation the catalysts were carried
The of
out by impregnation extrudates x 5) mm of sodium
of (3
Experimental Work typel3X zeolite, SilAl = 2.8 ( Linde Company) with 0.8
wt% platinum.
Catalytic unit Dried and desulfurized Iraqi light petroleum naphtha
The experimental study was carriedout to investigate deliveredby Al-Dura Refinery-Baghdad used as a
was
the catalysts activity, selectivity and catalysts feedstock. Hydrogengas was suppliedfrom Al-Mansour
deactivation rate by building an experimental rig plant (purity is 99.9 %). Various rypes of chemical
specifiedfor isomerization reaction,as shown in Figure compounds wereused.Hexachloroplatonic H2ptCl6acid
(l) whichrepresents general view of experirnental unit. (40%wtPt), strontium chloride, ammonium chloridewere
Figure(2) showsa schematic diagramof a fixed bed obtained from FlukaAG.
flow-typeapparatus. isomerization consists a
The unit of The properties chemical
and analysis light-naphtha
of
vertical tubular stainless steelreactor 2 cm internal
of are tabulated Tables(l) and (2) respectively. the
in On
otherhand,according G.C, analysis
to shownin Table
44 IJCPE
Vol.B
No.3(September
2007)

3. Khalid A. Suk*ar et oI
bt
d 1-lI eteringburette
tr 3-Dosiug putry
I
3-Liquid meter
flon
U
d J- I iddelralt'e
tr 5- IIJ flon'meter
t 6-5AlloletularSiete
j- Onewa.vtalve
f
8-II iringsettisr
t
3
9-feed preheatiug zone
I 10- Temperamre controls)-stem
1I- Pressure toutt'olsf$em
12- Smiuless reattor
steel
13- eatiug
II fiu'uace
1.1- Tbermocouples
15-Co uterizetl
mp iuterfares.Ystem
16-P4conp ilter
l?- Cooliug sl'srem
18-Gas ChronatograPhY
Fig. (2) Schematic of apparatus'
diagram the experimental
(2), the main components the light-naphthafeed are
of analysis light-Iraqipetroleum
Table(2) Chemical of
n-hexane (35.70 and - 40'8 volYo naphtha
n-pentane and
reipectively) which indicates that, the catalytic ComDosition wl%o
process' n-Pentane 35.70
isomerization suchfeed may be a dominant
for 40.80
n-Hexane
Therefore,such processcan be used to improve the MethvlCvcloPentane l l l3
octanenumberwhen optimum operatingconditionsare Bertzene 1,40
applied. Cvclohexane 2.82
n-HeDtane 3.15
leum n-Octane 1.88
Table( I ) TheproPerlies I
of t-l i
t.54
Property Data Toluene
t{ 604 0.665 1.22
80.5 Total 99.64
API
Distillation
I,B.P, 3? oc Modification 13X-Zeolite'
of
5 Vol.7o distilled 42'C
l0 Vol.o/odistilled 48"C NaX
In orderto modify the NaX zeolitespecification,
20 Vol.%distilled 52'c zeolite were exchangedwith two type of cations
30 Vot.%distilled 560C
40 Vol.% distilled 60.oc (Ammonium and Strontium). The Na+ ions were
50 Vol.%distilled 550C ixchanged for NH4+ ions to obtain the HX by ion
60 Vol,%distilled 68"C exchangingthe original NaX zeolite with (3 N )
70 Vol.% distilled 760c
g20c u*rotiiurn chloride-solution [4]' Thus ?8'75gm of
80 Vol.%distilled
90 Vol.o/odistilled 86'C ammonium chloride in 500m1 distillate water was
95Yol.%distilled 920C contacted with 50gmof NaX zeolitewith stirringfor I hr
124'C oC . Then,the exchangingprocess continued 4
for
E.B.P. at 50 oC.'The exchange
TotaldistiUate 96 Vol.% temperature
laboratory of25
daysat
Totalrecovery Residue 0.7 Yol.o/o
["oss J.3 ol.Yo reiult shows % of exchanging ofNa* by Sr-'
82 rate
68.2 On other hand,SrX form zeolite was prepared ion
by
SulfurContent < 3 ppm(Desulfurized) exchangingthe original NaX zeolite with (3 N )
KinematicViscosity 5.4x10'' m'ls strontium chloride solution [5, 6]' Thus 80gn of
at 25oC
IJCPEVol.8No.3(SePtember
2007) 45

4. Study of catalysts dea9lry!!!9n in isomerizationprocess Io produce high octane gasoline
strontium chloride in 500m1 distillate water were aromatizationand cracking selectiviqr are low, while
contacted with 50gm of NaX zeolite with stirr.ing l hr
for isomerization light-naphtha relativelyhigh. So that,asrhe
of is
at 50oC. Then, the exchanging processcontinued 4for reaction temperature increases above 300 oC the
days at laboratory temperatureof 25 oC with 85% of hydrocracking aromatization
and reactions accelerated
are and
exchanging rate of Na* by Sr*. isomerizationactivity and selectivity startedby,decreasing.
Then, the exchangedsamples(HX and SrX) were Therefore, according to Figure (4) the optimum reaction
.l10 oC
filtered, washedand dried at for l0 hours.The temperature isomerizationis at 270 oC for such type of
for
preparedsample was washedwith deionizedwater to be catalystsand feed composition. the other hand,Figure(3)
On
free of chloride ions, and drying procedureswere indicates that, the PI/HX catalystshows higher selectiviry
repeated twice. The obtained zeoliteswere calcined air
in toward isomen than that of Pr/SrX.This is amribured high
to
at 5000C for 6 hoursto obtainthe HX and SrX forms. surfaceareaand the eflect of cationfvne that forms the final
catalyst.
Preparation PVHX
of andPt/SrXcatalysts
Table (3) Characterization
dataofprepared catalysts.
The exchangedzeolires(HX and SrX) were loaded
with Pt at concentrations 0.8 wt % by impregnation Characteri;atron Pt/HX Pt/SrX
of
process riith aqueous Source Prepared Preparcd
solutionof hexachloroplatonic acid
($t%o)
Platinumcontent 0.8wt% 0.8wt%
H2PIC16 The prepared
. solutionwas added dropwiseto
t h e z e o l i r e i i h m i x i n g f o r 4 h o u r sa t 2 5 ' C . T h e m i x t u r e Area(m'lg)
Surface 340 325
u
ChlorineContent(wt7o) 0.25 0 .r 8
was then left at room temperaturefor 24 hours, it was (si/Ai) 2.8 2.8
stined interme,liately during this time. The mixture was
then slo*lr eraporatedto drynessover a period of 8
Catalystdeactivation definedas a phenomenon which
is in
hours ar rsmperarure of 75oC. The resultingcatalysts
the sffuctureand stateof the catalystchange,leadingto the
u'ere driec in air ar I l0'C for an additional 12 hours.
loss of active sites on the catalyst'ssuface thus causing a
Then. the sanples riere calcinedin air at 500oCfor l0
decrease catalyst
in performance,Therefore,eachcatalystwas
hours lincreaslrg ro that temperaturewith a rate of
subjected an aging period.After a pretreatrnent 350 "C in
to at
0.5"C mir I ar: i'rnaili reducedat 350oCin flowing H2
flowing hydrogen the catalyst was submitted to l0 hr of
fcrr-l rtrurs ,1. 5,. Then. the samples are referred as to standard reaction conditions (T=270 oC and atmospheric
P t H X a n dP : S : X c a t a l , s t s .
pressure).The catalytic activity, expressed in terms of
percentage iso-butanes,
iso-pentanes iso-hexanes
and yield, is
Procedure plonedas a functionof onsffeam time as shown in Figure(4).
B e t o r et : e e r p e r i r n e n t sh e c a t a l y s w a s d r i e d a t l l 0
t, t Both catalyss showedgood stability,however,the activity of
'C in ii:rc:e; Pt/HX fell rapidly and it was even lower after l0 hr than that
Jlsruicr one hour and then reduced 350 at
"C in hl crLrser florv for three hours. The operating of Pt/SrX. The fast catalystdeactivation that was notedafter
pressure ',r:;e he,,j constant I bar for all experimental
at few hours of reaction time can be attributed to a high
runs. Th: ii.:.riJ t-lo* of light-naphtha was 0.4 Llhr , hydrogenation-dehydrogenationcapacity of platinum
and rhe Brnrrr.rnr of catalyst was 50 gm. A according the conclusions
to submitted the work of Tomp
by
hrdrogerhrC:o;arbon molar ratio used was 4 for all et al. Il l] andJorgeet al. u2l. Also,Figure(4) indicates thar,
experimerui i-u:rs. The isomerization process carriedout both catalysts loseapproximately35% of their initial activity.
a t a r a n i e r . f : 3 n F e i a t J r ev a r i e d e f w e e n 2 5 0 , 2 7 5 , 3 0 0 ,
s b
Ji). ano _.-'(_'-L 80
The feec a:c :he effluent reactor were analyzed in a
gas chromatogiaph(Shimadzu GC-2014) FID using
coiumn ( S.G.E., length=25 mm, l.D.= 0.22
capillar_r 70
mm, film=0.iun: t and usingN2 as a carriergas. I
U)
Results
and Discussion 60
N
Table (3) shous the rnain characterizes prepared
of
catalysts (PtlHX and Pr Sr.. Ir is clearrhat,Pr/HXcaralyst
fU
showsa total surfaceareagieaterthanthat of Pt'SrX.
200 22s 2s0 27s 300 325 350
The reaction temperature uences
infl isomerization !'iN
acti
T e m p e r a t u r e( o C )
and selectivity the catalvst a higler ertenl Figure(3)
of to
shows the effect of reaction temper"arure isomerzation
on
selectivitytoward branchedisomers hrdrocarbons. is noted
lt (3)
Fi_s. The influence reaction
of temperature
on
that, at low reaction temperatures ll,<. 2-0. l-5 oC the isomerizationselectivity
46 I J C P E o l . 8N o . 3( S e p t e r n b e r 0 7 )
V 20
l

5. Khalid A. Sukko a aI
show fast catalystdeactivation causedby deposition of
carbonaceous materials (coke)on the catalyst surface and
s 8 0 pores.The major productformedin the beginning the of
reactionwas iso-butane. Higher contents iso-hexane
of
'! were detectedin the course of the deactivationrun.
; 6 0 However,the presence hydrogenin the reactionzone
of
(Hydroisomerization) essential to minimize coke
is
5 5 0
formation 12,13].
[2,
N
Figure(6) showsaromatization selectivity a function
as
4 4 0
of reactiontime. In this figure, Pt/SrX catalystshows
3 3 0 higher aromatizationselectivity than that of PI/HX
This is attributed high concentration active
catalyst. to of
acid sitesin this type of catalysts, which promoted
in
aromatizationreaction take. This conclusion is in
agreement theworkof Donket al. [14].
with
Fig.(a)Deactivation PVHXandPVSrX
of catalysts
Conclusions
90
x In this paper the isomerization light-naphtha
of for
producing of branchedisomershas been investigated.
Normal paraffin isomerization presence hydrogen
in of
8 7 0
€) (hydroisomerization) an equilibrium
is limitedreaction,
E 6 0 in which branched paraffin isomersare favoredby low
ternperatures, Therefore, was concluded
it that, in order
5 5 0 to prevent the undesiredreactions of cracking and
N
aromatization,the isomerization process should be
b 4 0 oC as an optimum operating
carried out at 270
A 3 0 temperature both PI/HX andPt/SrXcatalysts.
for
6 l0 t2 It was concluded that only an average 90% wt of
of
Time(hr) the carbonatomsfeedinto the reactor(light-naphtha) are
detected in the productstream. This loss(- 10%) is due
with agingtime to formation of coke depositswhich lead to catalyst
selectivity
Fig.(5)Loses catalysts
of
deactivation. the otherhand,the resultscleartyshow
On
that hydrogen is necessary for the hydrogenation of
c 25 olefins in order to preventoligomerization reactionthat
leads cokeformation catalyst
to and deactivation.
.: 20 In spite of the presence cske deposits
of poisoningof
t) the metalsites,cokedeposits alsoblock the acidsitesof a
.{)9 l s zeolite.The followingdeactivation decreasing order of
O
catalysts Pt/HX > PVSrXwas found.On the otherhand'
o l 0 PI/HX catalystshowedhigher activity and selectivity
N thanof PVSTX.
Acknowledgment
L ( )
The authors gratefully acknowledgethe financial
supportprovided for this work by Ministry of Higher
Education and Scientific Research/ Scientists and
selectivity a function reaction
as of Deparrment-Baghdad.
Creators
Fig.(6)
Aromatization
time
On the otherhandFigure(5) showsthe isomerization References
selectivity toward paraffin isomers.The isomerization l- Maloncy, J.C.,
M.L., Gora,L., Mcleary, E.E.,Jansen,
selectivitywas reducedfrom 85% to 55o/o PtlHX
for
and Maschmeyeq "Hydroisomerisation Hexane
T. of
catalystand from 74Yo 46Ysfor Pt/SrXunder l0 hours
to within a ReactorComposedof a Tubular Silicalite
of reactiontime. Both catalystsusedin the present
work
Vol.B
IJCPE No.3(SePtember
2007) 47

6. Study of catalysts deactivation in isomerizationprocess to produce high octanegasoline
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IJCPE
Vol.B
No.3(September
2007)