(40%wt Pt), strontium chloride, ammonium chloride were obtained from Fluka AG. The properties and chemical analysis of light-naphtha are tabulated in Tables ...
IICPT Inqi Journal of Chcmicel .rd P.trolcum Enginccritrg
andPetroleum Engineering lraqiJournalof Chemical 2007)43-48 Vol.8No.3(September ISSN:1997-4884
Univcnity ofBrgbdd Coll€c of EDtinE iog
in lsomerization Process Studyof CatalystsDeactivation to ProduceHigh OctaneGasoline Amel Th. Jubernand Jabir Sh.Jurnaly' Khalid A. Sukkar,HayamM. Abrlul-Raheemo - University - Iraq of Technolog,t Engineering Department Chemical ' * Iraq * of Al-Nahrain DepartmentCollegeof EngineeringUniversity Engineering Chemical
Abstract light lraqi petroleumnaphtha(Al-DuraRefinery)with boilingpoint In this study the isomerizationof desulfuerized 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%oPt on l3X-zeolite. The catalyst activity and selectivitytowardisomerization, and catalyt deactivationwereinvestigated. Theisomerizationunit consisledof a vertical tubular stainlesssteelreactorof 2 cm internaldiameter,3 cm external runs. Theliquidflow of lightdiameterand 68 cm height.Theoperatingpressurewas atmospheric for all experimental naphtha was A.4 IJh, and the catalystweight was 50 gm, H/H.C ratio usedwas 4 for all experimentalruns. The isomerizationprocess wasstudiedat dfurent tenperaturesof 250, 270, 275, 300,325, and 350oC , Itwasfound that, the optimumisomerizationtemperatureis 270"C Theisomerizationactivities snd selectivitiesos afunction of timeshowedhigh activity at the beginningof the reaction ord were deactivatedrapidly. This indicatesthat the deactivationof PI/HX and Pt/SrX resultsfrom the blocking of pore nouth by the depositedcarbon. Thefollowing deaeliv;ationdecreasingorder, PI/HX > Pt/SrX wasfound. On the other ,nnd, PI/HX cotalyst showshigher activity and selectivitythqn that of Pt/SrX. It waseoncludedthat,only an cverageof 90 wt% of the carbonatomsfeed into thereactor(light naphtha)is detected in theproductstreamduetoformation of cokedepositswhich leadsto cqtalystdeactivation.Theresultsclearlyshowed thot hydrogenis necessary for the ltydrogenationof olefinsin order to preventoligonerizationreactionthat leadslo cokeformation and catalystdeactivation. andPVSrXcatalysts,deactivation. Icywortls; catalyticisomerization,light-napgtha,PIJHX
lnboduction Due to a heightenedawarenessof the environrnental poblem worldwide,expectations of cleanand unleaded gasoline and world demand for gasoline have been ircreasing.Catzl5'ticisomerizationis regardedoneof the in oil refinerieswhich produce mostimportantprocesses gasoline. Isomerizationconveftsncleanand high octane butane, n-pentaneand n-hexaneinto their respective boparaffinsof substantiallyhigher octanenumber.The oommonfeedstockefor isomerizationprocessis the light saight run naphtha,which consistsof the lighter fraction
cs tc6Lt,2l.
In general,a catalystmay lose its activity or its fouling,sinteringand lossof selectivitydueto poisoning, activespecies[], One of the mostchallengingtasksin the designand operationof industrialcatalyticprocesses is the prevention,or at least the control, of catalyst deactivation. Loss of catalyst activity is often accompaniedby a loss in selectivity. This leads to greater formation of undesired by-products such as carbonoxides,poor utilizationof raw rnaterials,wasteof energy,and increasedpollution [3,4]. Thus, solving deactivationproblemsis of paramountimportancefor the economicand ecologic performanceof the process could industry.Understanding deactivationmechanisms
2007) IJCPEVol.8No.3(September
43
otin, ultimately lead to the design of inherently stable diameter,3 cm externaldiameter and 68 cm height catalysts, with considerable benefits.Solvine -ofdeactivation (reactor volume 214 cm3).The reactor was heated problemsrequiresa detailedknowledge th. ,uny uniformlyusingan electricalfurnace.Thetemperarure at causes andmechanisms involved[6,7,gJ. the reactorcenterof the catalystbed and at different points in reactor and system were determinedby oneof , On theotherhand,foulingformationis regarded the most importanttypes of catalystdeictivationin manufacturingan interface system, (Computerized isomerizationprocess.Generally,the kinetics of a TemperatureMeasurementSystem) which has ten catalystdeactivationis a functionof temperature, time, calibrated thermocouple sensors typeK (iron-constantan). pressure and the concentrations of different Theinterfaceis programmed andrun by a computer(p4). substances [9, l0]. The reactoris fittsd with accuratemeansfor controlof The principal differences between the various pressure,gas and liquid flow rates. The experiments industrialprocesses of isomerization relateto thecatalyst were conductedat atmospheric pressure. Feedmixtures used;this will in turn affectthe feedpretreatment steps of hydrogenand hydrocarbonwere preheatedto reactor and spent catalyst characterization.The two principal temperature beforeenteringthe bed. typesof catalystidentified in the industry areiplatinum on zeolite,which operatesat temperatures above2OOoC, and platinum chloride on alumina, which operatesat temperatures below200 oCIll, l2]. Themainadvantage of zeolitesoverplatinumon chlorinated alumina.atalyJtt is that they have a much betterresistance againstfeed impuritiessuch as water, which obviatesthe need for expensivedrying facilities.Moreover,in zeolitebased processesit is unnecessaryto continuouslyadd chlorinating agents, remove hydrogen chloride from effluent steams and take precautionsagainstcorrosion. Manyauthon haveinvestigated the catalystdeactivation phenomenon over PVA|2O3catalystusingn-pentane,nhexane,and n-heptaneas a feedstockfor isomerization reaction [ll, 13,l4]. In order to designand optimize catalysts,a detailed undentanding of the reaction mechanism,kinetic, deactivation and catalyst properties is of primary interesl The combinationbetweencatalystperformance and understandingof catalystdeactivation will enable the designof a new catalystwith reduceddeactivation and increased acrivity and selectivity for desired products.Therefore,the presentwork aimsto: Fig.(1)Generalview of experimental - providea substantiated apparatus knowledgeof the isomerization reaction based on bifunctional zeolite catalystsby using light-naphthaas a feed and determiningthe Materials optimumproc€ssconditions. - test the performance,deactivationrates and catalyst Two typesof catalystsnamedPt/HX and pt/SrX were stabilityunderoptimumprocess conditions prepared.The preparationof the catalysts were carried out by impregnationof extrudates(3 x 5) mm of sodium ExperimentalWork typel3X zeolite,SilAl = 2.8 ( Linde Company)with 0.8 wt% platinum. Catalytic unit Dried and desulfurized Iraqi light petroleumnaphtha delivered by Al-Dura Refinery-Baghdad The experimentalstudy was carriedout to investigate was used as a the catalysts activity, selectivity and catalysts feedstock.Hydrogengas was suppliedfrom Al-Mansour plant (purity is 99.9 %). Various rypes of chemical deactivation rate by building an experimental rig compounds wereused.Hexachloroplatonic specifiedfor isomerizationreaction,as shown in Figure acid H2ptCl6 (40%wt Pt), strontiumchloride,ammoniumchloridewere (l) whichrepresents generalview of experirnental unit. obtainedfrom FlukaAG. Figure(2) showsa schematicdiagramof a fixed bed The properties flow-typeapparatus.The isomerizationunit consistsof a and chemicalanalysisof light-naphtha verticaltubular stainlesssteelreactorof 2 cm internal are tabulatedin Tables(l) and (2) respectively. On the otherhand,accordingto G.C, analysisshownin Table
44
IJCPEVol.BNo.3(September 2007)
Khalid A. Suk*ar et oI
bt d tr
burette 1-lI etering putry 3-Dosiug 3-Liquidflonmeter J- I iddelralt'e 5- IIJ flon'meter 6-5AlloletularSiete j- Onewa.vtalve 8-II iringsettisr zone 9-feedpreheatiug s)-stem control 10-Temperamre sf$em toutt'ol 1I- Pressure reattor steel 12-Smiuless e fiu'uac 13-II eatiug Tbermocouples 1.115-Computerizetliuterfares.Ystem 16-P4conpilter sl'srem l?- Cooliug ChronatograPhY 18-Gas
I
U d tr
t f t 3 I
apparatus' Fig. (2) Schematicdiagramof the experimental (2), the main componentsof the light-naphthafeed are n-pentane and n-hexane (35.70 and - 40'8 volYo reipectively) which indicates that, the catalytic isomerizationfor suchfeed may be a dominantprocess' Therefore,such processcan be used to improve the octanenumberwhen optimum operatingconditionsare applied. Table( I ) TheproPerliesof I
t-l
i
t{ 604
API Distillation I,B.P, 5 Vol.7odistilled distilled l0 Vol.o/o 20 Vol.%distilled 30 Vot.%distilled 40 Vol.% distilled 50 Vol.%distilled 60 Vol,%distilled 70 Vol.% distilled 80 Vol.%distilled distilled 90 Vol.o/o 95Yol.%distilled E.B.P. TotaldistiUate TotalrecoveryResidue ["oss SulfurContent KinematicViscosity at 25oC
leum Data
Property
0.665 80.5
Table(2) Chemicalanalysisof light-Iraqipetroleum naphtha ComDosition n-Pentane n-Hexane MethvlCvcloPentane Bertzene Cvclohexane n-HeDtane n-Octane Toluene Total
3? oc 42'C 48"C
wl%o
35.70 40.80 l l l3
1,40 2.82 3.15 1.88
t.54 1.22 99.64
of 13X-Zeolite' Modification
52'c
560C 60.oc 550C 68"C 760c g20c 86'C 920C 124'C 96 Vol.% 0.7 Yol.o/o J.3 \ol.Yo 68.2 < 3 ppm(Desulfurized) 5.4x10'' m'ls
In orderto modify the NaX zeolitespecification,NaX zeolite were exchangedwith two type of cations (Ammonium and Strontium). The Na+ ions were ixchanged for NH4+ ions to obtain the HX by ion exchangingthe original NaX zeolite with (3 N ) u*rotiiurn chloride-solution [4]' Thus ?8'75gm of ammonium chloride in 500m1 distillate water was contactedwith 50gmof NaX zeolitewith stirringfor I hr oC . Then,the exchangingprocesscontinuedfor 4 at 50 oC.'The exchange daysat laboratorytemperatureof25 rateofNa* by Sr-' reiult shows82 % of exchanging On other hand,SrX form zeolite was preparedby ion exchangingthe original NaX zeolite with (3 N ) strontium chloride solution [5, 6]' Thus 80gn of
2007) IJCPEVol.8No.3(SePtember
45
Study of catalysts dea9lry!!!9n in isomerizationprocess Io produce high octane gasoline
strontium chloride in 500m1 distillate water were contactedwith 50gm of NaX zeolite with stirr.ingfor l hr at 50oC. Then, the exchangingprocesscontinuedfor 4 days at laboratory temperatureof 25 oC with 85% of exchangingrate of Na* by Sr*. Then, the exchangedsamples(HX and SrX) were .l10 oC filtered, washedand dried at for l0 hours.The preparedsample was washedwith deionizedwater to be free of chloride ions, and drying procedureswere repeatedtwice. The obtainedzeoliteswere calcinedin air at 5000C for 6 hoursto obtainthe HX and SrX forms.
aromatizationand cracking selectiviqr are low, while isomerizationof light-naphthais relativelyhigh. So that,asrhe reaction temperature increases above 300 oC the hydrocrackingand aromatizationreactionsareaccelerated and isomerizationactivity and selectivity startedby,decreasing. Therefore, according to Figure (4) the optimum reaction temperaturefor isomerizationis at 270 oC for such type of catalystsand feed composition.On the other hand,Figure(3) indicatesthat, the PI/HX catalystshows higher selectiviry toward isomen than that of Pr/SrX.This is amriburedto high surfaceareaand the eflect of cationfvne that forms the final catalyst.
Preparation of PVHXandPt/SrXcatalysts The exchangedzeolires(HX and SrX) were loaded with Pt at concentrations of 0.8 wt % by impregnation processriith aqueoussolutionof hexachloroplatonic acid H2PIC16 . The preparedsolutionwas added dropwiseto t h e z e o l i r eu 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 was then left at room temperaturefor 24 hours, it was stined interme,liately during this time. The mixture was then slo*lr eraporatedto drynessover a period of 8 hours ar rsmperarureof 75oC. The resultingcatalysts u'ere driec in air ar I l0'C for an additional 12 hours. Then. the sanples riere calcinedin air at 500oCfor l0 hours lincreaslrg ro that temperaturewith a rate of 0.5"C mir I ar: i'rnaili reducedat 350oCin flowing H2 fcrr-l rtrurs ,1. 5,. Then. the samplesare referredto as P t H X a n dP : S : X c a t a l \ , s t s .
Procedure B e t o r et : e e r p e r i r n e n t st h, e c a t a l y s w t a s d r i e da t l l 0 'C in ii:rc:e; Jlsruicr one hour and then reducedat 350 "C in hl crLrser florv for three hours. The operating pressure',r:;e he,,j constantat I bar for all experimental runs. Th: ii.:.riJ t-lo* of light-naphtha was 0.4 Llhr , and rhe Brnrrr.rnr of catalyst was 50 gm. A hrdrogerhrC:o;arbon molar ratio used was 4 for all experimerui i-u:rs.The isomerization processcarriedout a t a r a n i e r . f : 3 n F e i a t J r evsa r i e db e f w e e n 2 5 0 , 2 7 5 , 3 0 0 ,
Table (3) Characterization dataofprepared catalysts. Characteri;atron
Source Platinumcontent($t%o)
Surface Area(m'lg) ChlorineContent(wt7o)
(si/Ai)
Pt/HX Prepared 0.8wt% 340
0.25 2.8
Pt/SrX Preparcd
0.8wt% 325
0 .r 8 2.8
Catalystdeactivationis definedas a phenomenonin which the sffuctureand stateof the catalystchange,leadingto the loss of active sites on the catalyst'ssuface thus causing a decreasein catalystperformance,Therefore,eachcatalystwas subjectedto an aging period.After a pretreatrnent at 350 "C in flowing hydrogen the catalyst was submitted to l0 hr of standard reaction conditions (T=270 oC and atmospheric pressure).The catalytic activity, expressed in terms of percentage iso-butanes, iso-pentanes yield, is and iso-hexanes plonedas a functionof onsffeamtime as shown in Figure(4). Both catalyss showedgood stability,however,the activity of Pt/HX fell rapidly and it was even lower after l0 hr than that of Pt/SrX. The fast catalystdeactivationthat was notedafter few hours of reaction time can be attributed to a high hydrogenation-dehydrogenationcapacity of platinum accordingto the conclusionssubmittedby the work of Tomp et al. Il l] andJorgeet al. u2l. Also,Figure(4) indicates thar, both catalystsloseapproximately35% of their initial activity.
Ji). ano _.-'(_'-L
80
The feec a:c :he effluent reactor were analyzed in a gas chromatogiaph(Shimadzu GC-2014) FID using capillar_rcoiumn ( S.G.E., length=25 mm, l.D.= 0.22 mm, film=0.iun: t and usingN2 as a carriergas.
70 I
U)
Resultsand Discussion
60
Table (3) shous the rnain characterizes of prepared catalysts (PtlHX and Pr Sr.\. Ir is clearrhat,Pr/HXcaralyst showsa total surfaceareagieaterthanthat of Pt'SrX. The reactiontemperatureinfluencesisomerization acti!'iN and selectivityof the catalvstto a higler ertenl Figure(3) shows the effect of reaction temper"arure on isomerzation selectivitytoward branchedisomershrdrocarbons. lt is noted that, at low reaction temperatures ll,
