SECOND EDITION, REVISED and EX3eNDED edited by UOP, LLC Des Plaines, Illinois, U.S.A. George J. fintos flbdullah M. fiitani King Fahd University of Petroleum and Minerals Dhahran, Saudi Arabia M A R C E L MARCEL DEKKER, INC. D E K K E R NEW YORK BASEL The rst edition of this book was published as Catalytic Naphtha Reforming: Science andTechnology, edited by George J. Antos, Abdullah M. Aitani, and Jose M. Parera (MarcelDekker, Inc., 1995).Although great care has been taken to provide accurate and current information, neitherthe author(s) nor the publisher, nor anyone else associated with this publication, shall beliable for any loss, damage, or liability directly or indirectly caused or alleged to becaused by this book. 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Halim Hamid and Moharnmad Ashraf Ali ADDITIONAL VOLUMES IN PREPARATION Preface to the Second EditionNearly a decade has passed since the publication of the rst edition of CatalyticNaphtha Reforming. That book was a survey of the technology encompassing therst 45 years of the use of this process in the rening industry. In preparing thesecond edition, perspective on this rening process was again considered. It isstill true that catalytic reforming is the primary process in the renery forproducing high-octane gasoline to be blended into the gasoline pool. As needsfor gasoline have risen, the demands on the reformer have also increased. Whathas changed is that additional drivers have surfaced, which have added to thedemands on the process.The rst of these demands are the new environment-based regulations forfuel quality parameters. In particular, the targeted reduced-sulfur content forgasoline and diesel fuel has had an impact on the catalytic reformer. Althoughsulfur in the gasoline pool does not originate with the reformer, sulfur content ofnaphtha from the uid catalytic cracker does require signicant treatment in orderto continue inclusion in the pool. Most of the schemes to deal with this sulfurinvolve some level of hydrodesulfurization. Hydrogen is required, and thereformer is one of the few units to provide hydrogen in the renery. The resultis an increased demand on the catalytic reformer. Although many of thesehydrotreating schemes attempt to minimize octane loss, any loss will need tobe countered with more output from the octane machinethe reformer. Environ-mental regulations aimed at lowering sulfur in diesel fuel also increase the needfor hydrogen in the renery. Hydrogen demand has increased overall in therenery, and the catalytic reformer is under pressure to produce more hydrogenby an increased severity of operation or by improved selectivity to aromatics.In addition, in the United States, the drive to eliminate the use of MTBE asan oxygenate component in the gasoline pool will impact the reformer situation.Octane barrels are lost when MTBE is replaced by ethanol. The catalytic reformerwill need to replace these lost octane barrels, largely through an increasedseverity of operation or through higher yields of high octane.Over the past decade, reners have been forced to maximize their existingasset utilization. With capital at a premium, reners must deliver more from theunits they already have. These twin pressures from environmental regulations andiiiasset utilization have impacted the catalytic reformer. New technology, in theform of new catalysts or a minimal revamp of process improvements, wasrequired. The catalyst vendors and process licensors have responded to theseneeds, thereby fullling predictions in the rst edition and providing the basis forthis book.For this edition, prominent authors were again invited to either update anexisting chapter or write a new chapter. The layout of the book is logical andsimilar to that of the rst edition. Part I covers the chemistry of naphthareforming, emphasizing basic reforming reactions, metal/acid catalysis, andnaphtha hydrotreatment. Part II is a detailed review of reforming catalysts. Thechapter on catalyst preparation has been extensively enhanced with an in-depthtreatment of platinum impregnation chemistry, a topic that has been extensivelyinvestigated over the past decade. When combined with the updated chapter oncatalyst characterization, this section serves as a reference source for anyoneinvolved in the preparation of or research on platinum-containing catalysts.Included in this section is a completely updated discussion of the commercialreforming catalysts available from vendors today. Two chapters that are moreexperimental have been included on the future direction of catalyst technology inpore structure optimization and zeolite-hybrid catalysts.Part III focuses on catalyst deactivation by coking and regeneration. Addedto this is a discussion on some of the issues that are important to continuousreformer operations involving catalyst movement and continuous regeneration asexperienced by renery personnel. A separate chapter is dedicated to the recoveryof the precious metals from the reforming catalyst.In Part IV, commercial process technology is covered. The licensedprocesses are reviewed in conjunction with chapters on control systems andmodeling for commercial reformer units.Once again it has been our pleasure to work with the contributors of thisbook. They paid much attention to reviewing the literature in the area, and thenskillfully combined it with their own work and insights. It has been an extensiveeffort and has taken time to bring it to completion. We give special thanks to thecontributors and the publisher for their patience. Our intent was to place ourcombined experience and knowledge of the technology of catalytic naphthareforming into one book in order to share it with all those who need thisinformation. We hope that this second edition will be recognized as a valuableresource for those involved in the reforming or related catalysis areas, whether asacademics, graduate students, industrial researchers, chemical engineers, orrenery personnel. Knowledge and the time to gain it are two assets that wehave attempted to help you manage to your advantage with this volume.George J. AntosAbdullah M. Aitaniiv Preface to the Second EditionPreface to the First EditionThe use of catalytic naphtha reforming as a process to produce high-octanegasoline is as important now as it has been for over the 45 years of its commercialuse. The catalytic reformer occupies a key position in a renery, providing highvalue-added reformate for the gasoline pool; hydrogen for feedstock improvementby the hydrogen-consuming hydrotreatment processes; and frequently benzene,toluene, and xylene aromatics for petrochemical uses. The technology has evenfurther impact in the renery complex. The processes of hydrogenation, dehy-drogenation, and isomerization have all beneted from the catalyst, reactor, andfeed treatment technologies invented for catalytic reforming processes. The long-term outlook for the reforming catalyst market remains strong. The conditions ofoperation of catalytic reforming units are harsh and there is an increasing need forreformate. Presently, the catalytic reforming process is currently operated toproduce research octane numbers of 100 and more.Since its introduction, catalytic reforming has been studied extensively inorder to understand the catalytic chemistry of the process. The workhorse for thisprocess is typically a catalyst composed of minor amounts of several components,including platinum supported on an oxide material such as alumina. Thissimplication masks the absolute beauty of the chemistry involved in combiningthese components in just the proper manner to yield a high-performance, modernreforming catalyst. The difculty in mastering this chemistry and of characteriz-ing the catalyst to know what has been wrought is the driving force behind themany industrial and academic studies in reforming catalysis available today.Several questions come to mind. Why are scientists continuing to researchthis area of catalysis? What have all the preceding studies taught us about thesecatalysts, and what remains unknown? Given the numerous studies reported inthe patent literature and in technical journals, it is surprising that a survey aimedat answering these questions summarizing the preceding experiences is notreadily found. All the editors and contributors of this book are experienced inthe study of reforming catalysts, and each one of them would have employed sucha survey in his own research program. This volume provides information notcurrently available from one single literature source. The chapters are written bywell-known authorities in the elds encompassed by catalytic reforming, startingvwith the process chemistry and focusing on the preparation, characterization,evaluation, and operation of the catalyst itself. The unknown aspects of catalystchemistry and fundamental studies attempting to provide an understanding arealso presented. Some attempt is made to predict the future for this catalysttechnology, a task made complicated by the conicting demand for moretransportation fuels and petrochemicals, and the resolution to reduce the pollutionresulting from their use.It has been our pleasure to work with the contributors involved in this book.Their effort in combining their own research with the recent literature in the eldof catalytic naphtha reforming is highly appreciated. This effort would not havebeen possible without their willingness to share valuable knowledge andexperience. Moreover, we express our gratitude for their responsiveness todeadlines and review comments.The editors hope that veteran industrial researchers will recognize thisvolume as an important resource and that novice researchers in the eld ofreforming and related catalystsindustrial chemists assigned to their rst majorcatalysis project, graduate students embarking on the study of catalysis, andchemical engineers in the renery responsible for full-scale commercial catalyticreformingwill nd this a valuable reference volume and tool for their futureendeavors in this exciting area.George J. AntosAbdullah M. AitaniJose M. Pareravi Preface to the First EditionContentsPreface to the Second Edition iiiPreface to the First Edition vContributors ixPart I: Naphtha Reforming Chemistry1. Compositional Analysis of Naphtha and Reformate 1Rune Prestvik, Kjell Moljord, Knut Grande,and Anders Holmen2. Basic Reactions of Reforming on Metal Catalysts 35Zolta n Paa l3. Chemistry of Bifunctional MetalAcid Catalysis 75Jose M. Parera and Nora S. F goli4. Naphtha Hydrotreatment 105Syed Ahmed AliPart II: Reforming Catalysts5. Preparation of Reforming Catalysts 141J. R. Regalbuto and George J. Antos6. Characterization of Naphtha-Reforming Catalysts 199Burtron H. Davis and George J. Antos7. Optimization of Catalyst Pore Structureby Kinetics and Diffusion Analysis 275Jerzy Szczygie8. The New Generation of Commercial CatalyticNaphtha-Reforming Catalysts 335George J. Antos, Mark D. Moser, and Mark P. LapinskiviiPart III: Catalyst Deactivation and Regeneration9. Naphtha Reforming Over Zeolite-Hybrid-TypeCatalysts 353Grigore Pop10. Deactivation by Coking 391Octavio Novaro, Cheng-Lie Li, and Jin-An Wang11. Catalyst Regeneration and Continuous Reforming Issues 433Patricia K. Doolin, David J. Zalewski,and Soni O. OyekanPart IV: Technology and Applications12. Precious Metals Recovery from Spent ReformingCatalysts 459Horst Meyer and Matthias Grehl13. Licensed Reforming Processes 477Abdullah M. Aitani14. Control Systems for Commercial Reformers 497Lee Turpin15. Modeling Catalytic Naphtha Reforming: TemperatureProle Selection and Benzene Reduction 551Rafael Larraz and Raimundo ArveloIndex 595viii ContentsContributorsAbdullah M. Aitani King Fahd University of Petroleum and Minerals, Dhah-ran, Saudi ArabiaSyed Ahmed Ali King Fahd University of Petroleum and Minerals, Dhahran,Saudi ArabiaGeorge J. Antos UOP, LLC, Des Plaines, Illinois, U.S.A.Raimundo Arvelo University of La Laguna, Laguna, SpainBurtron H. Davis University of Kentucky, Lexington, Kentucky, U.S.A.Patricia K. Doolin Marathon Ashland Petroleum, LLC, Catlettsburg, Kentucky,U.S.A.Nora S. F goli Instituto de Investigaciones en Catalisis y Petroqu mica(INCAPE), Santa Fe, ArgentinaKnut Grande STATOIL Research Centre, Trondheim, NorwayMatthias Grehl W.C. Heraeus GmbH & Co., Hanau, GermanyAnders Holmen Norwegian University of Science and Technology, Trondheim,NorwayMark P. Lapinski UOP, LLC, Des Plaines, Illinois, U.S.A.Rafael Larraz* University of La Laguna, Laguna, SpainCheng-Lie Li{National University of Mexico, Mexico City, MexicoHorst Meyer W.C. Heraeus GmbH & Co., Hanau, GermanyKjell Moljord STATOIL Research Centre, Trondheim, NorwayMark D. Moser UOP, LLC, Des Plaines, Illinois, U.S.A.*Current afliation: CEPSA, Madrid, Spain{Current afliation: East China University of Science and Technology, Shanghai, ChinaixOctavio Novaro National University of Mexico, Mexico City, MexicoSoni O. Oyekan Marathon Ashland Petroleum, LLC, Catlettsburg, Kentucky,U.S.A.Zoltan Paa l Hungarian Academy of Sciences, Budapest, HungaryJose M. Parera Instituto de Investigaciones en Cata lisis y Petroqu mica(INCAPE), Santa Fe, ArgentinaGrigore Pop S.C. Zecasin S.A., Bucharest, RomaniaRune Prestvik SINTEF Applied Chemistry, Trondheim, NorwayJ. R. Regalbuto University of Illinois at Chicago, Chicago, Illinois, U.S.A.Jerzy Szczygie Wroclaw University of Technology, Wroclaw, PolandLee Turpin Aspen Technology Inc., Bothell, Washington, U.S.A.Jin-An Wang National Polytechnic Institute, Mexico City, MexicoDavid J. Zalewski Marathon Ashland Petroleum, LLC, Catlettsburg, Kentucky,U.S.A.x Contributors1Compositional Analysis ofNaphtha and ReformateRune PrestvikSINTEF Applied ChemistryTrondheim, NorwayKjell Moljord and Knut GrandeSTATOIL Research CentreTrondheim, NorwayAnders HolmenNorwegian University of Science and TechnologyTrondheim, Norway1 INTRODUCTIONNaphtha is transformed into reformate by catalytic reforming. This processinvolves the reconstruction of low-octane hydrocarbons in the naphtha into morevaluable high-octane gasoline components without changing the boiling pointrange. Naphtha and reformate are complex mixtures of parafns, naphthenes, andaromatics in the C5C12 range. Naphthas from catalytic or thermal cracking alsocontain olens. Naphthas of different origin contain small amounts of additionalcompounds containing elements such as sulfur and nitrogen. These elementsaffect the performance of the bifunctional noble metal catalyst used in catalyticreforming and must be removed to low levels prior to entering the reformer unit.The composition of hydrocarbons and the concentration of additional elementsdetermine the quality as reforming feedstock or as a gasoline blendingcomponent.This chapter describes the chemistry of naphtha and reformate. It includesthe origin from crude oil, the overall composition, and key parameters with1respect to processing ability and product quality. Finally, analytical methodsavailable for performing a complete compositional analysis and parameterdetection are described.2 THE NAPHTHA FRACTION2.1 Origin from Crude Oil Distillation and ProcessingHydrocarbons are the major constituents of crude oil, or petroleum, and accountfor up to 97% of the total mass.[1]These are parafnic, naphthenic, or aromaticstructures ranging from light gaseous molecules (C1C4 alkanes) to heavy waxesor asphaltenic matter. The rest are organic compounds of sulfur, nitrogen, andoxygen, as well as water, salt, andanumber of metal containingconstituents suchasvanadium, nickel, and sodium. Although elemental concentrations of carbon andhydrogen vary only slightly within narrowlimits, typically 8287 wt %Cand 1014 wt % H, the individual concentrations of the different compounds that deter-mine the physical properties are highly variable and depend on the crude oil origin.Full-range naphtha is the fraction of the crude oil boiling between 308Cand 2008C, and constitutes typically 1530% by weight of the crude oil. Thisincludes hydrocarbons ranging from C5 to C12, some sulfur, and small amounts ofnitrogen. Metal containing compounds are usually not present. The naphthaobtained directly from the atmospheric crude distillation column is termedstraight run (SR). However, naphtha is also produced during processing ofheavier parts of the crude oil (e.g., catalytic cracker naphtha, visbreaker naphtha,coker naphtha). As opposed to the straight-run streams, these naphthas alsocontain olenic hydrocarbons. Light naphtha is the fraction boiling from 308C to908C, containing the C5 and C6 hydrocarbons. Heavy naphtha is the fractionboiling from 908C to 2008C. The term medium naphtha is sometimes used forthe fraction of this heavy cut that boils below 1508C and includes mostly C7C9hydrocarbons. Table 1 illustrates how naphtha fractions can range from highlyTable 1 Composition of Medium Naphtha Cuts from Different Crude Oils[2]Oil eldParafns(wt %)Naphthenes(wt %)Aromatics(wt %)Sulfur(wt ppm)Nitrogen(wt ppm)Troll(Norway)13.9 75.2 10.8 20 ,1Norne(Norway)27.7 34.8 37.5 10 ,1Heidrun(Norway)35.4 51.2 13.5 10 ,1Lufeng(China)69.5 27.5 2.9 ,10 12 Prestvik et al.parafnic to highly naphthenic and from low in sulfur to high in sulfur, dependingon the crude oil.Hydrotreated (desulfurized) medium naphtha is the favored feedstock forcatalytic reforming, although full-range stocks are sometimes processed ifbenzene is a desired product. The light naphtha is preferentially upgraded byisomerization whilst the heaviest part of the naphtha is often included in the lightgas oil fraction (jet fuel/diesel). Figure 1 gives an example of a processingscheme for renery gasoline production with catalytic reforming.2.2 Naphtha CompositionHydrocarbonsParafns or alkanes are saturated aliphatic hydrocarbons with the generalformula CnH2n2. They are either straight-chain (n-parafns) or branched struc-tures (i-parafns). The boiling point increases by about 25308C for each carbonFigure 1 Example of a processing scheme for renery gasoline production withcatalytic reforming.Compositional Analysis of Naphtha and Reformate 3atom in the molecule, and the boiling point of an n-parafn is always higher thanthat of the i-parafn with the same carbon number. The density increases withincreasing carbon number as well. Olens or alkenes are unsaturated aliphatichydrocarbons. Like the parafns, they are either straight chains or branchedstructures, but contain one or more double bonds. Monoolens have the generalformula CnH2n. Naphthenes or cycloalkanes are saturated cyclic hydrocarbonsthat contain at least one ring structure. The general formula for mononaphthenesis CnH2n. The most abundant naphthenes in petroleum have a ring of either ve orsix carbon atoms. The rings can have parafnic side chains attached to them. Theboiling point and the density is higher than for any parafn with the same numberof carbon atoms. Aromatics have the general formula CnH2n26and contain one ormore polyunsaturated rings (conjugated double bonds). These benzene rings canhave parafnic side chains or be coupled with other naphthenic or aromatic rings.The boiling points and the densities of these polyunsaturated compounds arehigher than that of both parafns and naphthenes with the same carbon number.The reactivity of the unsaturated bonds make the C6, C7, and C8 aromatics or BTX(benzene, toluene, xylenes) important building blocks for the petrochemicalindustry. Aromatics have high octane numbers.The composition of a given naphtha depends on the type of crude oil, theboiling range of the naphtha, and whether it is obtained directly from crude oildistillation or produced by catalytic or thermal cracking of heavier oil fractions.A typical straight-run medium naphtha contains 4070 wt % parafns, 2050 wt % naphthenes, 520 wt % aromatics, and only 02 wt % olens. Naphthaproduced by uid catalytic cracking (FCC), coking, or visbreaking may contain3050 wt % olens. Table 2 shows the hydrocarbon composition for differentnaphtha streams originating from a given crude.In general, the parafnicity decreases when the boiling point of the naphthaincreases (Fig. 2). At the same time the complexity grows because the number ofpossible isomers increases exponentially with the carbon number. The number ofdetectable individual compounds in naphthas ranges typically from 100300 forstraight-run medium naphthas to beyond 500 for full-range stocks containingcracked material (additional olens). In Table 3 the concentration of individualcompounds detected in a medium straight-run naphtha is listed. Components liken-heptane, n-octane, methylcyclohexane, toluene, ethylbenzene, and xylenes areusually present in signicant concentrations, whereas a number of C7C9parafn and naphthene isomers are usually present in much smaller amounts.Heteroatomic Organic Compounds, Water, and MetallicConstituentsSulfur is an important heteroatomic constituent in petroleum. The concentrationis highly dependent on the type of crude oil and may range from virtually zero to4 Prestvik et al.Table2TypicalCompositionsandCharacteristicsofReneryNaphthaStreamsOriginatingfromtheSameCrudeOilStreamParafns(wt%)Olens(wt%)Naphth.(wt%)Aromatics(wt%)Density(g/ml)IBPFBP(8C)Crude(wt%)LightSR554050.664C5903.2MediumSR3150190.771901508.6HeavySR3044260.7971501804.7FCC342311320.752C522020LightVB64102510.667C590HeavyVB46301680.75090150SR,straight-run;FCC,uidcatalyticcracker;VB,visbreaker;IBP,initialboilingpoint;FBP,nalboilingpoint.Compositional Analysis of Naphtha and Reformate 5more than 5% by weight. The sulfur tends to be more concentrated in the heavyend of the crude oil, which means that only ppm levels of sulfur are found instraight-run naphtha fractions. Still, even small concentrations are of greatimportance when it comes to processing the feedstock or using it directly as fuel.Sulfur poisons the noble-metal catalyst used in reforming and also promotesformation of undesirable SOx during combustion. Cracker and coker naphthasoriginating from heavier oil fractions often contain much more sulfur, up to a fewthousand ppm. Sulfur is removed from naphtha by hydrotreating, which meansconversion to H2S over a hydrotreating catalyst under hydrogen pressure.Hydrotreating is described more extensively in Chapter 4. The types of sulfurcompounds found in crude oil are many: mercaptans, suldes, disuldes, cyclicsuldes, alkylthiophenes, benzothiophenes, sulfates, traces of sulfuric acid, andsulfur oxides. In the naphtha boiling range thiophenes, noncyclic mercaptans andsuldes are the major groups. Identied sulfur compounds in naphtha are shownin Figure 3.Organic nitrogen is present in even smaller concentrations than sulfur inthe crude oil (,1.0 wt %) and mostly in the higher boiling point fractions. Thecompounds are usually classied as basic or nonbasic. Basic compounds areFigure 2 Hydrocarbon composition as a function of boiling point upon distillation of aNorth Sea crude.6 Prestvik et al.Table3HydrocarbonCompositionainaStraight-RunNaphthafromNorthSeaCrude,IdentiedbyGCCompoundWt%CompoundWt%CompoundWt%CompoundWt%2,4-Dm-Pentane0.018c-1,4-Dm-CyC60.914C9naphthene160.7841-Me-2-Et-Benz0.2253,3-Dm-Pentane0.078n-Octane5.263C9naphthene180.1523-Et-Octane0.0942-Me-Hexane2.287iPr-CyC50.065C9naphthene200.269C10naphthene100.0142,3-Dm-Pentane1.140C8naphthene60.074C9naphthene220.013C10naphthene110.0301,1-Dm-CyC50.716c-2-Octane0.066C9naphthene230.039C10parafn80.0403-Me-Hexane3.216c-1,2-Et-Me-CyC50.154C9naphthene240.0793-Me-Nonane0.073c-1,3-Dm-CyC51.7422,2-Dm-Heptane0.089C9naphthene260.052C10parafn90.021t-1,3-Dm-CyC51.650c-1,2-Dm-CyC60.279C9naphthene290.0361,2,4-Tm-Benz0.281t-1,2-Dm-CyC53.3282,2,3-Tm-Hexane0.106C9naphthene310.070C10naphthene140.067C7Olen70.0172,4-Dm-Heptane0.276n-Nonane2.226C10naphthene150.081n-Heptane7.8854,4-Dm-Heptane0.035C9naphthene320.062i-But-CyC60.010Me-CyC617.38Et-CyC63.052C9naphthene330.046C10naphthene160.0121,1,3-Tm-CyC50.8662-Me-4-Et-Hexane0.038iPr-Benzene0.205C10naphthene170.0132,2-Dm-Hexane0.1052,6-Dm-Heptane0.719C9olen130.342C10naphthene180.013Et-CyC51.0561,1,3-Tm-CyC60.918C9naphthene350.206i-But-Benzene0.0372,2,3-Tm-Pentane0.4091,1,4-Tm-CyC60.136iPr-CyC60.009s-But-Benzene0.0552,4-Dm-Hexane0.5952,5-Dm-Heptane0.3942,2-Dm-Octane0.067n-Decane0.258ct-124-Tm-CyC50.9903,5-Dm-Heptane0.205C10parafn10.109C10naphthene200.0133,3-Dm-Hexane0.137C9naphthene30.179C10parafn20.0151,2,3-Tm-Benz0.079tc-123-Tm-Pentane1.051C9naphthene40.078C9naphthene360.0531,3-Me-iPr-Benz0.0872,3,4-Tm-Pentane0.162Ethylbenzene1.265n-Pr-CyC60.5191,4-Me-iPr-Benz0.132Toluene6.765C9naphthene50.226C10parafn30.090C10naphthene220.1191,1,2-Tm-CyC50.308tt-1,2,4-Tm-CyC60.472n-But-CyC50.096Indane0.0702,3-Dm-Hexane0.452C9naphthene70.050C10naphthene20.074C10naphthene240.0162-Me-3-Et-Pentane0.180C9naphthene80.031C10naphthene30.020C10naphthene250.0302-Me-Heptane2.741m-Xylene3.039C10naphthene40.041C11parafn20.040(Tablecontinues)Compositional Analysis of Naphtha and Reformate 7Table3ContinuedCompoundWt%CompoundWt%CompoundWt%CompoundWt%4-Me-Heptane0.888p-Xylene0.9273,3-Dm-Octane0.250n-But-CyC60.0363,4-Dm-Hexane0.1232,3-Dm-Heptane0.860C10parafn40.059C10naphthene300.011C8naphthene10.064C9naphthene90.048n-Pr-Benzene0.2781,3-De-Benzene0.012C8naphthene20.0653,3-Dm-Heptane0.090C10naphthene50.0651,3-Me-nPr-Benz0.026c-1,3-Dm-CyC62.9044-Et-Heptane0.1052,6-Dm-Octane0.1451,4-Me-nPr-Benz0.0093-Me-Heptane1.6994-Me-Octane0.433C10naphthene70.039n-But-Benzene0.0123-Et-Hexane1.6642-Me-Octane0.5701-Me-3-Et-Benz0.38313-Dm-5Et-Benz0.0091,1-Dm-CyC60.454C9naphthene110.1241-Me-4-Et-Benz0.150C10naphthene310.014t-13-Et-Me-CyC50.3743-Et-Heptane0.157C10naphthene90.0631,2-Me-nPr-Benz0.015c13-Et-Me-CyC50.4133-Me-Octane0.5711,3,5-Tm-Benz0.16614-Dm-2Et-Benz0.015t-12-Et-Me-CyC50.733C9naphthene110.050C10parafn50.07612-Dm-4Et-Benz0.0131-Me-1-Et-CyC50.107o-Xylene1.260C10parafn60.042n-Undecane0.018t-1,2-Dm-CyC61.649C9naphthene120.061C10parafn70.030cc-123-Tm-CyC50.023C9naphthene140.0234-Me-Nonane0.025aStructuresnotfullyidentiedarenumberedaccordingtotypeofcompoundandcarbonnumber.8 Prestvik et al.pyridine, piperidine, or indoline derivatives whereas the nonbasic are pyrrolederivatives. Straight-run naphtha fractions usually contain sub-ppm concen-trations of nitrogen, whereas cracker and coker naphthas may contain typically10100 ppm by weight. Nitrogen is poisonous to the reforming catalyst as itadsorbs strongly on its acidic sites. Common N-containing components in thenaphtha boiling range are shown in Figure 4.Oxygen-containing organic compounds are normally present only in theheavy fractions of the crude. These are phenols, furanes, carboxylic acids, oresters. The different acids account for the petroleums acidity. High acidity cancause serious corrosion problems in the renery. Little or no organic oxygen isfound in the naphtha fractions.Water is normally present in crude oil to some extent, partly dissolved inthe oil and possibly as a separate water phase. Naphtha fractions will to someextent dissolve moisture during handling and storage. Water has a high heat ofFigure 3 Identied sulfur compounds in naphtha.Figure 4 Identied nitrogen compounds in straight-run naphtha.Compositional Analysis of Naphtha and Reformate 9vaporization compared to petroleum and complicates distillation.[3]Water alsoresults in catalyst deactivation by neutralizing the acidic sites of the reformingcatalyst.The heaviest oil fractions rich in resins and asphaltenes contain metalliccompounds. These are usually organometallic complexes in the form ofporphyrins with Ni2 or vanadium oxide (1) cations. These compounds are notfound in the naphtha boiling range. However, other metallic constituents, such asiron (dust or scale or organometallic compounds) from pipeline corrosion orsilicon compounds (siloxanes) originating from antifoam chemicals, might causeproblems in catalytic reforming. Iron dust can cause pressure drop problemswhereas the silicon compounds adsorb onto and deactivate the reformingcatalyst.3 EFFECT OF NAPHTHA COMPOSITION ON PROCESSPERFORMANCE AND PRODUCT QUALITY IN CATALYTICREFORMINGThe hydrocarbon composition, the naphtha boiling range, and the concentrationof impurities affect the quality of the reformate product. The same feedstockcharacteristics also inuence the reforming process, including the performanceand lifetime of the catalyst. In order to understand these relationships it is usefulrst to dene some quality requirements of the product (gasoline specications,octane ratings) and to describe briey the reactions involved in the catalyticreforming process.3.1 Gasoline Quality RequirementsThe purpose of catalytic reforming is primarily to increase the octane number ofthe naphtha feedstock to a level that makes the reformate product suitable as agasoline blend stock. The octane number represents the ability of a gasoline toresist knocking during combustion of the air gasoline mixture in the enginecylinder. European gasoline today must have research octane number (RON)ratings of 9598. Such high octane numbers allow compression ratios needed foroptimal fuel economy of present gasoline engines.Gasoline must have a number of other properties in order to functionproperly and to avoid damage to the environment. Olens have a tendency toform gums by polymerization and oxidation of olens, and can foul the engine. Inorder to avoid emission of volatile light hydrocarbons, the vapor pressure (oftenmeasured as Reid vapor pressure, RVP) must be limited. Certain compounds,such as benzene, are classied as carcinogenic and represent a health hazard.Tetraalkyllead has long been used as an octane booster, but will accumulate in10 Prestvik et al.nature, and is today strictly regulated and largely eliminated. Combustion ofcarbon leads to CO2 (global warming problem) and poisonous CO. Combustionof sulfur and nitrogen (from air) leads to production of SOx and NOx that causeacid rain pollution. The volatile organic compounds produced during combustionof heavy aromatics are toxic in nature and are involved also in the photochemicalreaction with NOx to form ground-level ozone (smog). Exhaust catalysts havereduced emissions of NOx to some extent, but present catalysts are sensitive tosulfur. Stringent regulations on the sulfur level of gasoline are therefore beingdeveloped. The present gasoline specications (Table 4) set upper limits for theallowable concentrations of sulfur, benzene, olens, and aromatics. Somecountries have tax incentives for 50 or 10 ppm sulfur.3.2 The Octane NumberIn practice two octane ratings are measured, the research octane number (RON)and the motor octane number (MON), which differ in test procedure used. RONrepresents the engine performance at low speed whereas MON is representativefor high-speed driving. By denition, the octane number of n-heptane is zero andthe octane number of isooctane (2,2,4-trimethylpentane) is 100. The octanenumber for a gasoline is dened as the volume percent of isooctane in blendingwith n-heptane that equals the knocking performance of the gasoline being tested.Some gasoline components have octane numbers exceeding 100 and have to becharacterized by use of mixtures. A common mixture contains 20% of the actualcompound and 80% of an n-heptane/isooctane (40 : 60) mixture. A hypotheticalblending octane number is then obtained by extrapolating from 20% to 100%concentration. The blending octane number is specic for the mixture and usuallydifferent from the octane number of the pure component, as seen for a range ofdifferent hydrocarbons with octane numbers less than 100 in Table 5.Table 4 Present Gasoline Specications for the United States, Europe, and Japan[46]Max values USA EU JapanRVP (kPa) 60 78Sulfur (wppm) 50 150a100Oxygen (wppm) 2.2 2.7 Benzene (vol %) 1.0 1 Aromatics (vol %) 35 45 Olens (vol %) 15 18 Lead (g/L) 0.005 a50 wppm from 2005.Compositional Analysis of Naphtha and Reformate 11Table5PureandBlendingaResearchOctaneNumbersofHydrocarbons[7]HydrocarbonRONpureRONblendingHydrocarbonRONpureRONblendingParafnsNaphthenesn-Butane94.0113Cyclopentane.100141Isobutane.100122Cyclohexane83.0110n-Pentane61.862Methylcyclopentane91.31072-Methylbutane92.3100Methylcyclohexane74.8104n-Hexane24.819t-1,3-Dimethylcyclopentane80.6902-MethylPentane73.4821,1,3-Trimethylcyclopentane87.7942,2-Dimethylbutane91.889Ethylcyclohexane45.643n-Heptane0.00Isobutylcyclohexane33.7383-Methylhexane5256Aromatics2,3-DimethylPentane91.188Benzene982,2,3-Trimethylbutane.100112Toluene.100124n-Octane,0218Ethylbenzene.1001243,3-Dimethylhexane75.572o-Xylene1202,2,4-TrimethylPentane100.0100m-Xylene.100145n-Nonane,0218p-Xylene.1001462,2,3,3-TetramethylPentane.100122n-Propylbenzene.100127n-Decane,0241Isopropylbenzene.100132Olens1-Methyl-3-ethylbenzene.1001621-Hexene76.4961,3,5-Trimethylbenzene.1001701-Heptene54.565n-Butylbenzene.1001142-Methyl-2-hexene90.41291-Methyl-3-isopropylbenzene1542,3-Dimethyl-1-pentene99.31391,2,3,4-Tetramethylbenzene.100146aObtainedusinga20%hydrocarbon80%60:40mixtureofisooctaneandn-heptane.12 Prestvik et al.Table 5 shows that aromatics generally have much higher octane numbersthan naphthenes, olens, and parafns and are therefore desired reformatehydrocarbon components. The octane number of the aromatics (except forbenzene) is always above 100. Straight-chain parafns have very low octanenumbers (RON , 0 for n-octane and n-nonane), but the octane number increasesmarkedly with the degree of branching (RON . 100 for 2,2,3-trimethylbutane).Light olens and naphthenes generally have higher RON than the parafns, but asfor the n-parafns the octane number declines as the number of carbon atomsincreases. This decline is much less pronounced for the isoparafns. Consideringthe boiling range of gasoline (C5C12 hydrocarbons) and the above comparison,visualized in Figure 5, an increase in the octane number of the reformate can bestbe obtained by transformation of naphthenes into aromatics and of linearparafns into branched parafns or aromatics. These transformations are the keyreactions of the catalytic reforming process.3.3 Catalytic Reforming ProcessCatalytic reforming is carried out at elevated temperature (4505208C) andmoderate pressure (430 bar). By use of a proper catalyst in three or fourserial reactors and in the presence of hydrogen (H2/oil equal to 46 mol/Figure 5 Octane numbers vs. boiling point for hydrocarbon families.[7,8]Compositional Analysis of Naphtha and Reformate 13mol), naphthenes are transformed into aromatics by dehydrogenation andstraight-chain parafns into branched parafns by isomerization. Parafns alsoundergo dehydrocyclization to form aromatics. Other important reactions arehydrogenolysis and hydrocracking (carboncarbon bond scissions), which resultin low molecular weight parafns, and coke formation that will eventuallydeactivate the catalyst. Figure 6 shows the major reforming reactions.The hydrogen produced in catalytic reforming has become increasinglyvaluable since it is used in hydroprocessing units for removal of sulfur andnitrogen as well as for hydrocracking. The formation of aromatics fromnaphthenes is a very rapid endothermic reaction. It is thermodynamically favoredby high temperature and low pressure, as illustrated by the equilibrium betweentoluene and the C7 naphthenes (Fig. 7). Olens are readily hydrogenated and atequilibrium only small concentrations can exist with the hydrogen partialpressures normally used in reforming. The isomerization of parafns is also rapidand mostly thermodynamically controlled. The dehydrocyclization of parafns isa much slower reaction and kinetically controlled. Hydrocracking rates increasewith the pressure and lower the reformate yield. Coking, which is the main causefor catalyst deactivation, is very slow but increases rapidly at low hydrogenpressure and high temperature. In order to optimize the hydrogen and aromaticsformation, and to avoid severe yield loss due to hydrocracking, the choice is tooperate at a high temperature and at the lowest possible hydrogen pressure,although the latter always is a trade-off with catalyst stability.The catalyst is bifunctional in the sense that it contains both a metallicfunction (platinum) that catalyzes dehydrogenation reactions and an acidicFigure 6 Major reactions in catalytic reforming of naphtha.14 Prestvik et al.function (chlorided alumina) that catalyzes isomerization reactions. Platinum,which is usually used with a second metal, needs to be highly dispersed on theacidic carrier in order to maintain high activity and selectivity throughout acommercial cycle. In units designed for periodic regeneration of the catalyst(semiregenerative reforming), a cycle typically lasts 12 years. Most new unitsare designed with continuous catalyst regeneration implying that each catalystparticle has a cycle time of typically 68 days between regenerations. Twocatalyst formulations prevail commercially: Pt-Re/Al2O3 and Pt-Sn/Al2O3. Theformer is the most stable and is preferred in semiregenerative units, whereas thelatter has the highest selectivity at low pressure and is the best choice incontinuous reforming units. These catalysts are sensitive to sulfur which adsorbsFigure 7 Effect of temperature and pressure on the concentration of toluene inthermodynamic equilibrium with H2 and C7 naphthenes.[9]Compositional Analysis of Naphtha and Reformate 15(reversibly) on the platinum crystallites. Sulfur can be removed by hydro-treatment of the naphtha feedstock. The water content must also be kept low toavoid leaching of chloride and thus loss of acid strength. Metallic poisons arerelatively rare, but iron from plant corrosion and silicon originating fromantifoam chemicals can affect catalyst activity.Effect of Naphtha Hydrocarbon CompositionThe distribution of parafns (P), olens (O), naphthenes (N), and aromatics (A) inthe naphtha determines the richness of the feedstock. A high concentration ofaromatics automatically means that the octane level is quite high. The naphthenesare transformed into aromatics with high selectivity and a high octane is thereforeeasily achieved. A parafnic (or parafnicolenic) feedstock will have a lowoctane number. Severe reaction conditions are required to reach a specied RONlevel, and the yield loss and coke laydown will be signicant. The richness of anaphtha is therefore usually rated by its N A or N 2A value. Figure 8illustrates how the reforming reactor temperature decreases and the liquid yieldof reformate increases when the feedstock N A values increase.Figure 8 Reactor temperature and reformate yield as a function of naphtha N A(naphthenes aromatics) value. Reaction conditions: 100 RON, P 30 bar,WHSV 2.0 h1, and H2/HC 4.5.16 Prestvik et al.The hydrocarbon composition in the naphtha does not affect the reformatecomposition much. The reformate consists mainly of parafnic and aromatichydrocarbons since the large part of the naphthenes is consumed in the reaction.There is a near-linear relationship between the RON value and the concentrationof aromatics (Fig. 9). Thus, regardless of feedstock composition, when operatingwith a constant RON level in the product, the aromatic and parafnconcentrations are usually xed within narrow limits. However, as shown inFigure 9, the RONaromatics relationship changes somewhat with reactionpressure. At elevated pressures the concentration of high-octane cracked products(C5 and C6 isoparafns) increases, and subsequently less aromatics are requiredto reach a specied RON in the product.Effect of Naphtha Boiling RangeThe boiling range of the naphtha feedstock is a key factor in catalytic reforming.The initial and nal boiling points (IBPs and FBPs) and the boiling pointdistribution not only determine the carbon number distribution of the product butFigure 9 RON as a function of aromatics concentration from a number of pilotexperiments using a range of different naphthas and variable reaction conditions.Compositional Analysis of Naphtha and Reformate 17greatly affect reaction conditions, and thus reformate yields, as well as the rate ofcatalyst deactivation.Although the carbon number distribution in the feedstock and in thereformate product are strongly related, the boiling points increase somewhatduring reaction due to aromatics formation. As an illustration, the FBP typicallyincreases by 208C at low to intermediate reaction pressures (,20 bar). Theincrease in FBP from feedstock to product is slightly smaller at higher pressuresbecause the heaviest components undergo additional hydrocracking. Based onboiling points of individual hydrocarbons in naphtha, Figure 10 shows the boilingrange for each carbon number group. Although azeotropic phenomena amongvarious compounds exist, it is still possible by distillation to separate thefeedstock fairly well according to carbon number. Above 1008C the overlap inboiling range between the groups is signicant and separation becomesincreasingly difcult.The choice of naphtha boiling range depends on the intended use of thereformate product. When catalytic reforming is used mainly for benzene, toluene,and xylenes (BTX) production, a C6C8 cut (IBPFBP 601408C), rich in C6, isusually employed. For high-octane gasoline production, especially when thereformate constitutes a major part of the gasoline pool, a C7C9 cut (IBPFBP901608) is the preferred choice. The C6 hydrocarbons may be removed to avoidthe benzene in the naphtha and to avoid further benzene formation from the C6naphthenes. The benzene yield from cyclohexane and methylcyclohexane(primary production) is signicant, as illustrated in Figure 11. These reactions arecontrolled by thermodynamics and favored by low pressure. Benzene is alsoformed by dealkylation of heavier aromatics (secondary production). Thisreaction is kinetically controlled and favored by high temperature and low spacevelocity (Fig. 12).The benzene selectivity from substituted aromatics increases with thelength of the side chain (n-butylbenzene . n-propylbenzene) and with the degreeFigure 10 Boiling range of naphtha hydrocarbons grouped by carbon number.[8]18 Prestvik et al.Figure 11 Benzene selectivity (percentage of the components feed concentration foundas wt % benzene yield) vs. pressure in semiregenerative reforming with PtRe catalyst.RON 101.Figure 12 Benzene in reformate as a function of reaction temperature and spacevelocity using a feedstock with 0.23 wt % C6 hydrocarbons.Compositional Analysis of Naphtha and Reformate 19of sidechain branching (i-propylbenzene . n-propylbenzene). Toluene has arelatively low selectivity to dealkylation. However, considering the very highconcentrations in the reformate, the contribution from toluene and also frommethylyclohexane (which forms toluene) to the secondary benzene production issignicant.The heavy end containing C10 hydrocarbons is the least favorable withregard to processing, particularly in semiregenerative units, due to highdeactivation rates. Figure 13 shows how the relative deactivation rate increaseswith the naphtha FBP. This effect is not related to the reaction temperature but tothe amount of coke precursor in the feed.[10]Alkyl-substituted C10 aromatics(and polycyclics) have been identied as strong coke precursors. For continuousreforming units, heavy stocks can be processed if the coke burning capacity issufcient. The cutpoint in the light end of the naphtha also affects the deactivationrate. When the IBP is increased the naphtha becomes richer and the same octanenumber can be achieved at lower reaction temperatures.The legislative requirements for sulfur removal from gasoline and dieselhave increased hydrogen use in the reneries; hence, reners are looking for waysto maximize their hydrogen yields. The optimal feedstock to a reformer withrespect to hydrogen yield is a C6C9 cut that contains the highest naphtheneconcentrations. No hydrogen can be produced from the C5 fraction and littlehydrogen is produced from the C10 hydrocarbons, which are highly susceptibleto hydrocracking. The highest yields of hydrogen are obtained at low pressuresand high temperatures when the conversion of naphthenes and parafns intoFigure 13 The deactivation rate (measured as the temperature rise needed to maintain102.4 RON relative to a base naphtha) as a function of nal boiling point (FBP).[10]20 Prestvik et al.aromatics is high. The temperature must, however, be kept below a point whenhydrocracking becomes important, which would lower the yield of both hydrogenand reformate. The octane number during maximized hydrogen production istypically in the order of 102105 RON, and it follows that the deactivation rateis high.Effect of Naphtha Sulfur ContentReforming catalysts are sensitive to sulfur impurities in the naphtha feedstock.The surface platinum atoms of the catalyst convert the sulfur compounds intoH2S molecules that readily adsorb onto the surface metal atoms. The poisonedplatinum atoms are no longer active and the temperature must be increased tomaintain RON (i.e., produce aromatics by dehydrogenation). Reformate yielddecreases somewhat due to the temperature rise but not as much as normallyobserved. This is due to the reduced methane production by the metal-catalyzedhydrogenolysis reaction. However, the rate of deactivation increases according tothe temperature increase. The adsorption of sulfur is strong but reversible. Agiven sulfur concentration in the feedstock results in a specic sulfur coverage.However, if the sulfur is removed from the naphtha, the activity will eventuallyreturn to very near the initial level as shown in Figure 14.Figure 14 Effect of sulfur upset on RON level at T 5008C, P 16 bar,WHSV 2.0 h1, and H2/HC 4.3.Compositional Analysis of Naphtha and Reformate 214 ANALYSIS METHODSThe high complexity of naphtha and reformate fractions requires advancedtechniques to obtain a complete compositional analysis and to determine thechemical and physical parameters needed for the rener. Many differentapproaches exist, and the choice of analytical method depends on the neededresolution, the analysis time, and the cost. For industrial products that must meetdened specications, reners are required to follow standardized analysisprocedures. The American Society for Testing and Materials (ASTM) is oneof several recognized organizations for standardization. This chapter willconcentrate on the most common methods for determining hydrocarboncomposition, distillation range, octane numbers, and sulfur/nitrogen contents.Examples of both ASTM and nonstandardized methods are included.4.1 Hydrocarbon CompositionThe most powerful and widely used technique for analysis of hydrocarbons innaphthas or reformates is gas chromatography (GC). This is a separation methodin which the sample is injected into a carrier gas stream, usually helium, andbrought through a dedicated capillary column allowing transport of the differentmolecules at different rates (Fig. 15). The samples may be gaseous or liquid.Vaporized sampling is usually preferred for on-line product testing in researchlaboratories. An adjustable split injector can strongly reduce the sample amountand thereby avoid column overloading and subsequent separation problems.Nonpolar, cross-linked methylsiloxane columns__________give elution times close to the order of increasing boiling point. The columnshave diameters of 0.10.5 mm and the length ranges from a few meters up to100 m. A ame ionization detector creates and detects a signal proportional to theconcentration of each hydrocarbon as the components exit the column. It operatesby collecting (by an electrode) the ions of the ame produced during combustionof the hydrocarbon. The detector response is approximately proportional to theweight of carbon present,[11]which greatly simplies quantitative analysis.The rate of hydrocarbon transport through the column is dependent on thecarrier gas velocity, adjusted for the injector pressure and the oven temperature.The lightest hydrocarbons (methane and ethane) are transported very quicklythrough the column and separation requires low temperature (ambient). On the22 Prestvik et al.other hand, the heaviest aromatics need a temperature of 2008C or more in ordernot to adsorb strongly at the column front. Thus, an advanced temperatureprogram and column pressure selection is required to optimize separation andtime consumption of a GC analysis. The column material and length, the detectortemperature, the carrier gas type, and the split ow rate also affect the separation.Gas chromatography is not an identication method. In order to identify thelarge number of peaks in the chromatogram, the system must be calibrated. Thiscan best be obtained by coupling a mass spectrometer to the column exit of anidentical chromatographic setup (gas chromatographymass spectrometry, GC-MS). Most of the resolved peaks are identied from MS spectra libraries. Theequipment is costly and such an analysis is time consuming, but a good peaklibrary for the GC user is obtained given that the column separation is good. Inpractice, the heavy region of the chromatogram is never fully resolved,Figure 15 Schematic illustration of gas chromatography (GC) with gas/liquidsampling, split injection, and ame ionization detection (FID).Compositional Analysis of Naphtha and Reformate 23especially when additional peaks created by the presence of olens exist, as is thecase for naphthas from catalytic cracking.ASTM D5134 is a GC method for PONA analysis in naphthas andreformates (C5C12). The method, described in Table 6, is limited to straight-runnaphthas, reformates, and alkylates because the olen content is limited to 2%and all components eluting after n-nonane (BP . 150.88C) are collected as onepeak. The analysis time is 122 min. Table 7 describes an even more time-consuming method that applies a longer column, a lower initial temperature, anda more complex temperature program designed to separate most C1C12hydrocarbons in naphthas and reformates. A chromatogram with identied peaksobtained using this method on a reformate sample is shown in Figure 16.Detection of most individual compounds is important for the understanding of thechemistry involved in catalytic reforming. As an example, a precise feedstockand product hydrocarbon analysis makes it possible by mass balance to calculatethe amount of hydrogen produced by the reforming reactions. The data can also,based on simple models, be used to calculate density, vapor pressure, carbon andhydrogen content, and octane numbers. For the process engineer it is oftensufcient to know the PONA group concentrations in order to verify thefeedstock or product qualities, and the least time-consuming GC methods arechosen. Specialized methods for more precise analysis of single compounds areavailable.Table 6 Analysis of C5C12 PONA Hydrocarbons According to ASTM D5134Column 50 m cross-linked methylsiloxaneTemp. program 358C (30 min) !2008C, 28C/min (20 min)Carrier gas Helium, 215 kPaInjector Split, 200 ml/min; T 2008CDetector FID; T 2508CSample size 0.1 ml (liquid)Table 7 Comprhensive Laboratory Analysis for C1C12 PONA HydrocarbonsColumn 100 m cross-linked methylsiloxaneTemp. program 308C (30 min) !508C, 18C/min (10 min) !1408C,28C/min (0 min) !2508C, 108C/min, (30 min)Carrier gas Helium, 300 kPaInjector Split, 800 ml/min; T 2508CDetector FID; T 2808CSample size 0.2 ml (liquid)24 Prestvik et al.Figure 16 Chromatogram of reformate (liquid sample) using the GC method listed inTable 7. Page 1 of 2.Compositional Analysis of Naphtha and Reformate 25Figure 16 Continued.26 Prestvik et al.4.2 Distillation RangeKnowledge about the boiling point distribution of gasolines is most frequentlyobtained by distillation according to ASTM D86. A batch distillation isconducted at atmospheric pressure and the resulting curve shows the temperatureas a function of percent volume distilled. Automated instruments perform themeasurement. Figure 17 shows an ASTM D86 distillation curve and tabulatedvalues for a reformate sample.Another way of analyzing the boiling range characteristics is to simulatethe distillation by use of GC. By using an inert column stationary phase, thecomponents elute in order of their boiling points. The ASTM D3710 method isspecialized for gasoline fractions and gives the result within 15 min.4.3 Sulfur and Nitrogen AnalysisThe fact that only small concentrations of sulfur and nitrogen poison reformingcatalysts calls for highly accurate analysis methods, capable of measuring downto sub-ppm levels. Non-hydrotreated naphthas from thermal or catalytic crackingFigure 17 Results for an ASTM D86 distillation of a reformate sample.Compositional Analysis of Naphtha and Reformate 27processes may reach percent levels of sulfur and 100 ppm levels of nitrogen.Thus, versatile analysis methods covering sulfur and nitrogen from ppb up topercent levels are needed. A large number of methods and instrument types areavailable as shown in Table 8. Most analysis techniques are based on initialcombustion of sulfur into SO2 or SO3 and of nitrogen into NO or NO2. Theamount of these oxides can then be measured by techniques such asmicrocoulometry (sulfur), UV uorescence (sulfur), chemiluminescence(nitrogen), and electrochemical detection (nitrogen). Nonoxidative techniquesfor sulfur analysis include hydrogenolysis, X-ray uorescence, and, nally, GCwith sulfur-selective detection methods such as atomic emission detection(AED), sulfur chemiluminescence detection (SCD), and ame photometricdetection (FPD). The GC technique not only measures total sulfur but may alsodetect and distinguish among different sulfur compounds in the sample.Sulfur and nitrogen analyzers have improved in recent years when it comesto detection limits. Pyrochemiluminescent nitrogen and pyrouorescent sulfurtechnology are such examples and can be combined in one instrument and usedon the same sample injection simultaneously. The principal reactions for themeasurement of sulfur by pyrouorescence are shown in Figure 18. Moderninstruments give total nitrogen determinations from low ppb to 20 wt % and totalsulfur determinations from low ppb up to 40 wt %. The analysis takes only a fewminutes.For research laboratories studying the chemistry of sulfur and its reactions,as in hydrotreatment, the available GC methods are most appealing. By extensiveprecalibration of such a system it is possible to identify the different sulfurstructures present in the sample. Figure 19 shows a chromatogram from analysisof a cracker naphtha using AED. Integration of all peaks in the chromatogramTable 8 Sulfur and Nitrogen Analysis MethodsTarget Technique ASTM Range (wppm)aN OC/chemiluminescence D4629 0.3100N OC/electrochemical detection D6366 0.05100S OC/microcoulometry D3120 3100S OC/UV uorescence D5453 18000S Hydrogenolysis D4045 0.0210S X-ray uorescence D4294 .1000S GC/selective sulfur detector D5623 0.1100baAnalytical range suggested by ASTM method.bConcentration range of each individual sulfur compound.OC, oxidative combustion.28 Prestvik et al.yields the total sulfur concentration. Very good comparisons have been measuredbetween total sulfur analysis by GC/AED and sulfur analysis by pyrouores-cence.[12]The new SCD instruments[13]have extremely high sensitivity and arethe choice for low-sulfur samples.[14]Figure 18 Schematic illustration of total sulfur analysis by pyrouorescence method.Figure 19 GC/AED chromatogram showing the sulfur distribution in full-rangecatalytic cracker naphtha.Compositional Analysis of Naphtha and Reformate 294.4 Octane Number DeterminationOctane ratings are measured directly using a single-cylinder reference motor(CFR engine).[15]The compression ratio and the fuel/air ratio are adjustable andthe engine is solidly built to withstand knocking without damage. The basicprocedure is to increase the compression ratio of the engine until a standardknocking intensity is indicated by a pressure detector in the combustionchamber.[15]The critical compression ratio is recorded and compared with twobinary heptaneisooctane mixtures of neighboring composition. The fuel/airratio is adapted in each case to obtain maximum knocking intensity; it is usuallybetween 1.05 and 1.10. The octane number is calculated by linear interpolation,assuming the primary reference mixture has similar behavior as the fuel beingtested. The distinctions between the two procedures of RON and MONmeasurement concern essentially the engine speed, temperature of admission,and spark advance as indicated in Table 9. The RON and MON methods simulatethe engine performance when driving at low and high speed, respectively.An alternative method for determination of the octane number of a gasolineis by means of calculation, using the hydrocarbon composition from GC analysisas input data. It is not a straightforward task to develop such a model becauseblending of different individual hydrocarbons does not result in an engineknocking performance as expected from the octane numbers of the individualcomponents. Advanced models, both linear and nonlinear and based on a numberof naphthas or reformates with variable compositions and cut points, have beenput forward.An approach to calculate the octane number based only on the totalaromatics content is possible.[16]However, the RONaromatics relationship isnot accurate and changes signicantly with reaction pressure as shown earlier inthis chapter (Fig. 9). Walsh and coworkers[17]developed a linear RONcalculationmodel based on GCanalysis with capillary columns. Agrouping technique is usedTable 9 Test Conditions for RON and MON Determination in CFR Engines[15]Operating parametersRON methodASTM D2699MON methodASTM D2700Engine speed (rpm) 600 90Ignition advance (degrees before top dead center) 13 14 to 26aInlet air temperature (8C) 48 Fuel mixture temperature (8C) 149Fuel/air ratio b baVariable with the compression ratio.bAdapted in each case to obtain maximum knocking intensity.30 Prestvik et al.to produce a manageable number of pseudocompounds. Thirty-one groups weredened by the order of elution in the GC chromatogram and given a regressioncoefcient (br) for calculation of RON after the simple equationRON (brWr), where Wr is the weight fraction of group r. Durand andcoworkers[18]have demonstrated the versatility of this RON model using 60different gasoline samples that were analyzed by GC and rated by ASTM enginetests. The difference in RON values turns out to be less than 1 RON unit in mostcases. The dened model groups with regression coefcients are listed in Table 10.Table 10 Group Denition and Regression Coefcients of Linear RON ModelDeveloped by Walsh and Coworkers[17]Groupno. Group denition by GC elution timesRegressioncoefcient1 Components eluting before n-butane 103.92 n-Butane 88.13 Components eluting between n-butane and isopentane 144.34 Isopentane 84.05 Components eluting between isopentane and n-pentane 198.26 n-Pentane 67.97 Components eluting between n-pentane and 2-methylpentane 95.28 2- and 3-Methylpentane and components eluting between these 86.69 Components eluting between 3-methylpentane and n-hexane 95.910 n-Hexane 20.911 Components eluting between n-hexane and benzene 94.912 Benzene 105.213 Components eluting between benzene and 2-methylhexane 113.614 2- and 3-Methylhexane and components eluting between these 80.015 Components eluting between 3-methylhexane and n-heptane 97.816 n-Heptane 247.817 Components eluting between n-heptane and toluene 62.318 Toluene 113.919 Components eluting between toluene and 2-methylheptane 115.120 2- and 3-Methylheptane and components eluting between these 81.721 Components eluting between 3-methylheptane and n-octane 109.722 n-Octane 10.523 Components eluting between n-octane and ethylbenzene 96.124 Ethylbenzene 122.625 Components eluting between ethylbenzene and p-xylene 45.426 p-xylene m-xylene 102.027 Components eluting between m-xylene and o-xylene 73.328 o-Xylene 123.629 Components eluting after o-xylene up to and including n-nonane 35.030 Components eluting between n-nonane and n-decane 112.031 n-Decane and components eluting after n-decane 85.6Compositional Analysis of Naphtha and Reformate 31Complex, nonlinear models in which the deviation from ideality (asexpressed by the regression coefcients) of each component or component groupis set as a function of the concentrations of the different hydrocarbon families canreduce the error of calculation to less than 0.5 RON unit. Such models will beespecially useful for more complex gasolines in which the concentration ofnonreformate material (alkylates, isomerates, cracker naphtha, polymerate,alcohols, and ethers) is high.A fast and simple alternative to the previously described methods foroctane number determination was proposed by BP[19]and involves the use ofinfrared (IR) spectroscopy. The near-IR region of the spectrum (wavelength:8002500 nm) contains many bands that result from overtones and combinationsof carbonhydrogen stretching vibrations, which are particularly useful foranalyzing gasoline (Fig. 20). The variations in IR spectra can be coupled to arange of gasoline properties including RON and MON numbers. Automated andcomputerized instruments offer fast (1 min) analysis and have the possibility ofFigure 20 Near-IR absorbance spectra of two different gasolines.32 Prestvik et al.on-site sampling. The error of calculation is not signicantly higher than for thecompositionoctane models derived from GC analysis.REFERENCES1. Speight, J.G. The Chemistry and Technology of Petroleum, 3rd Ed.; ChemicalIndustries Vol. 3; Marcel Dekker: New York, 1999.2. http://www.statoil.com (Products and Services/Crude Oil and Condensate).3. Parera, J.M.; Figoli, N.S. In Catalytic Naphtha Reforming, 1st Ed.; ChemicalIndustries Vol. 61; Marcel Dekker: New York, 1995.4. Martino, G. Catalysis for oil rening and petrochemistry: recent developments andfuture trends. In Studies in Surface Science and Catalysis; Corma, A., Melo, F.V.,Mendioroz, S., Fierro, J.L.G., Eds.; Proceedings of the 12th ICC, Granada, Spain,July 914, 2000; Vol. 130A; Elsevier: Amsterdam, 2000; 83103.5. Hartman, E.L.; Hanson, D.W.; Weber, B. Hydrocarbon Proc. 1998, 77.6. http://www.paj.gr.jp/html/english/index.html (Petroleum Association of Japan,Annual Review 1999).7. American Institute Research Project 45, 16th annual report, 1954.8. Weast, Ed. Handbook of Chemistry and Physics, 58th ed.; CRC Press: Boca Raton,1978.9. Gjervan, T.; Prestvik, R.; Holmen, A. In Basic Principles of Applied Catalysis;Baerns, M., Ed.; in press.10. Moljord, K.; Grande, K.; Tanem, I.; Holmen, A. In Deactivation and Testing ofHydrocarbon-Processing Catalysts; OConnor, P., Takatsuka, T., Woolery, G.L.,Eds.; ACS Symposium Series No. 634, 1995; 268282.11. Dietz, W.A. J. Gas Chromatogr. 1967, 5, 68.12. Steiner, P.; Myrstad, R.; Thorvaldsen, B.; Blekkan, E., in preparation.13. Benner, R.L.; Stedman, D.H. Anal. Chem. 1989, 61, 1268.14. Adlard, E.R. Ed. Chromotography in the rening industry. J. Chromatogr. Lib., Vol.56; Amsterdam, 1995.15. Wauquier, J.-P. Ed. Petroleum Rening 1, Crude Oil, Petroleum Products, ProcessFlowsheets; IFP Publications, Editions Technip: Paris, 1994.16. McCoy, R.D. ISA AID 73442, 187, 1973.17. Anderson, P.C.; Sharkey, J.M.; Walsh, R.P. J. Inst. Petr. 1972, 58 (560), 83.18. Durand, J.P.; Boscher, Y.; Petroff, N. J. Chromatrogr. 1987, 395, 229.19. Descales, B.; Lambert, D.; Martens, A. Determination des nombres doctane RON etMON des essences par la technique proche infrarouge, Revue de lAssociationFrancaise des Techniciens du Petrole, No 349, 1989.Compositional Analysis of Naphtha and Reformate 332Basic Reactions of Reforming onMetal CatalystsZolta n PaalHungarian Academy of Sciences, Budapest, Hungary1 INTRODUCTIONSince the rst industrial application of reforming for fuel upgrading usingsupported Pt catalysts, this large-scale commercial process has proved to be adriving force for research of metal-catalyzed hydrocarbon reactions. Laboratorystudies, which frequently employed conditions vastly different from industrialones, provided a scientic background for catalytic reforming, and theseapparently remote investigations prepared the ground for several industriallyimportant innovations in the past, and will do so in the future, too. This chapterconcentrates on a few points of laboratory-scale studies that might be of valuefor industry.Several catalytic reactions of reforming involve the rearrangement of thehydrocarbon skeleton; hence, they can be termed as skeletal reactions:aromatization, isomerization, C5 cyclization, and hydrogenolysis. The rst threereactions are useful or value enhancing, the last one disadvantageous foroperation of a reforming plant, since products of lower value are produced.This chapter concentrates on metal catalysts and mechanisms of reactionscatalyzed by them. Relevant problems and the numerous hypotheses suggestedfor their solution will be pointed out rather than by presenting ready andapparently nalized theories. Interactions between metallic and support sites willalso be mentioned. The diversity of ideas, methods, approaches, etc., reectstruly the present situation, where the experimental results as a function of severalparameters lack well-established and generally valid interpretations. This is thereason why a relatively high number of references has been included; still, the35literature covered is far from being comprehensive. Most of the basic informationincluded in the rst edition of this book[1]has been retained, although severalrecent references have been added.2 POSSIBLE MECHANISMS OF THE REACTIONSThe chemistry of the industrial reforming process has been extensivelyreviewed.[2]All the valuable information from results obtained in the 1960s and1970s will not be repeated here. Another, more concise review dealing with bothchemistry and industrial aspects was published in 1991.[3]The excellent book byOlah and Molnar[4]summarized all relevant hydrocarbon reactions. Everyreaction important in reforming (aromatization, C5 cyclization, isomerization,and fragmentation) can also proceed with catalysts possessing metallic activityonly. This feature will be stressed in the present chapter. Laboratorymeasurements are often carried out in the temperature range of 500650 Kand pressures up to 1 bar, being much lower than the conditions of industrialreforming. Yet these studies will be useful in understanding underlyingphenomena.Aromatization (or C6 dehydrocyclization) was rst observed by a Russiangroup as the formation of a second aromatic ring from an alkylbenzene onmonofunctional Pt/C catalyst; the same group reported also the formation of anaromatic C6 ring from alkanes.[5]Later they described the metal-catalyzed C5cyclization of alkanes to alkylcyclopentanes.[6]The aromatic ring is very stableunder these conditions but C5 cyclization is reversible: a ring opening of the C5ring to alkanes also takes place.[7]Metal-catalyzed isomerization [8]may occur(1) via the formation and splitting of the C5 ring;[9](2) in the case ofhydrocarbons whose structure does not allow the formation of C5 cyclicintermediate, by a so-called bond shift mechanism.[10,11]The formerisomerization route is often termed as cyclic mechanism.[12]The presentauthor prefers the name C5cyclic mechanism,[13]which will be used throughoutthis chapter, in agreement with de Jongste and Ponec who pointed out[14]thatbond shift may also involve a C3 cyclic intermediate. Hydrogenolysis ofalkanes has also been a well-known and widely studied reaction.[15]The reactionmechanisms of these reactions and their relative importance over variouscatalysts have been comprehensively reviewed.[13,14,1620]Early ideas for aromatization [21]assumed the dehydrogenation of an open-chain hydrocarbon and the subsequent ring closure of the olen directly to give asix-membered ring. Aromatization on carbon-supported metals was interpreted interms of a direct 1,6 ring closure of the alkane molecule without its preliminarydehydrogenation.[5b]Past and present state of the art has been discussed in theexcellent review by Davis.[22]With the appearance of bifunctional catalysts, the36 Paa lconcept of this 1,6 ring closure has fallen temporarily into the background infavor of the two-dimensional mechanism.[2]This described very satisfactorily thereactions observed under industrial conditions. Still, the possibility of the 1,6 ringclosure has again surfaced due to new evidence. The stepwise dehydrogenation ofheptanes to heptenes, heptadienes, and heptatriene followed by cyclization hasbeen shown over oxidic catalysts.[23]This idea was conrmed recently with n-octane aromatization over CrOx clusters or Cr3 ions as the catalyst, stabilized byLa2O3.[24]Another novel catalyst family included Zr, Ti, and Hf oxides on carbonsupport.[25,26]These oxides were claimed to decompose upon pretreatment in Arat 1273 K and were described as nonacidic Zr/C, Hf/C, Ti/C, producingaromatics with selectivities up to 67% from n-hexane[25]and 8092% from n-octane, likely via the triene route.Hexatriene as an intermediate has been shown also on unsupported Ptcatalysts, partly by using 14C radiotracer.[27,28]This triene mechanism has alsobeen regarded as one of the possible reaction pathways over Pt/Al2O3, togetherwith another, direct C6 ring closure.[29]The assumption of dienes and trienes doesnot mean that these intermediates should appear in the gas phase. It is more likelythat a hydrocarbon pool is produced on the catalyst surface upon reactivechemisorption of the reactant(s). As long as sufcient hydrogen is present, all ofthe chemisorbed species are reactive and may undergo dehydrogenation,rehydrogenation, and, if they have reached the stage of surface olens, doublebond or cistrans isomerization may also occur.[13,28]Their desorption is possiblein either stage; hence, hexenes, hexadienes, etc., may appear as intermediates. Thetrue intermediates of aromatization are surface unsaturated species;[30]thoseappearing in the gas phase are the products of surface dehydrogenation anddesorption process. Desorption should be less and less likely with increasingunsaturation of the surface intermediates. The loss of hydrogen produces either cisor trans isomers. The cis isomer of hexatriene is expected to aromatize rapidly, thechance of its desorption being practically zero. The trans isomer, on the otherhand, has to isomerize prior to cyclization and, during this process, it has also aminor chance to desorb to the gas phase.[13,28]It is also a misunderstanding tosuggest that thermal cyclization of triene intermediates would have anynoticeable importance in heterogeneous reactions[30]just because a gas-phasehexatriene molecule would cyclize spontaneously and very rapidly at or aboveabout 400 K.[28]The temperatures in any catalytic reaction exceed this value.The