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Catalytic Naphtha Reforming: Revisiting Its Importance in the Modern Refinery*

Catalytic Naphtha Reforming: Revisiting Its Importance in the Modern Refinery*

Journal of Scientific & Industri al Research Vo l. 62, October 2003, pp 963-978

Catalytic Reforming: Revisiting its Importance in the Modern Refinery*

Uday T Turaga':l and Ramnarayanan Ramanathanb

"Bartl esville Techno logy Cent er, ConocoPhillips, Bartl esvill e, O K 74004, USA

The paper reviews catalytic naphtha reforming, a process th at has completed 50 y of ex istence and has improved th e quality of human life globall y. Al so examines in detail are the hi storical background o f rci'o rming, reaction chemi stry. reacti on thermodynamics, process detail s, process variables, commercial processes, and future outl ook. Recent e nvironmental regulations have completely re-drawn the objecti ves of reforming and have even questioned its relevance. Atte mpts are also made to expl ain , in brief, the new challenges faced by reformi ng.

Keywords: Catalyt ic naphtha reforming, Refin ery, Naphtha reforming, Reforming

Introduction components. T hese hi gh- pool The Prize, often referred to components are mainly branched and aromatic as the Nobe l Prize for the profession, has , whi ch are less prone to ignite been awarded eight- times since its inception in 1988: premature ly in internal combustion engin es and thus for the development of the integrated circuit, the reduce " kn ocking" substantially. The naphtha fraction turbojet engine, the FORTRAN computer language, of crude oil , predominantly conta in s a lkanes and the communication sate llite, fibre optics, the creation , which in a catal yti c reformer are of the internet, medical drug de livery, and catalytic "selective ly reformed" to aromatics. an naphtha reforming. In awarding Vladimir Haense l the important byproduct of the process. finds numerous Charles Stark Draper Prize in 1997, the National applications within th e refining industry particularly Academy of Engineering gave deserved recognition for the production of c lean fu e ls. The presence of to catal ytic reforming - a revolutionary reforming in a refining configurati on of the 1980s is depi cted in Fi gure 3. refining process that in an environmentally beni gn way created c lean and abundant transportation fuel Hydroforming, th e process jointly developed by (Figure I), enabled the modern plasti cs industry, and the Standard Oil Company (now Exxon Research and improved standards of living globalli . Figure I Engineering Company), th e Standard Oil Company of shows the quantum jump in oil consumption, Indiana (now American Oil Company), and the MW explained in part because of reforming, while Figure 2 Ke llogg Company in vo lved the catalyti c shows the distribution of the catalysts business of meth ylcyclohexane (present in amongst various sectors and processes in c luding ) to to lu ene: the concept whi ch reforming. Haensel2 invented Platforming; the first eventually led to th e development of catalyti c commercial reforming process li censed by UOP, reforming. The first commerc ial unit of Hydrofonning thereby giving birth to catalytic re forming. went on stream in 1940 at th e Pan Ameri can Refining The process converts Company in Texas C ity, Texas using a fixed-bed petroleum naphtha to hi gh-octane gasoline pool molybdena-alumina catalyst and was carried out at an external hydrogen pressure of about 15 atmos to avoid ' Dedicated to th e memory of Vl adimir Haensel rapid deacti vati on of th e catalyst. ICorresponding author The second W orld War played a significant role Phone: (91 8) 66 1-0 I 13, Fax: (9 18) 662- 1 I 15 E-mai l: Uday.T.Turarga @conocophillips.com in catalyzin g th e techno logical growth of the hDepartment of , The Pennsylvania State Uni versit y, and catalyti c reforming was no Uni versity Park, PA 16802, USA exception. The need for hi gh-octane gasoline ror the 964 J SCI IND RES VOL 62 OCTOBER 2003

Consumption Cons~ption 1990

1.2 ,------E'h'rifi~ti0(Y

0.8 Platfom1ing

0.0 Alkylation

0.4 Continuous Batch ni>tma';00 Distillation 1 0.2

o ~~-.----=F====~~~-----~--~~--~----~--~ 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020

Figu re I - Oil refining birth through 2000'"

Environment 40 HDT+ Hye FCC 25 ~ 40 Refining r- Other 5 \ 40 I Ch,;;OO" Alkylatio n 25 REF + \ (SOM t5

Fi gure 2a - Applications 01 calalysis,6 Fi gurc 2b - Applicali ()!1 s Or in relining'(' allied forces was substantial but the need for particular, and catalytic reforming, in general, are trinitrotoluene (TNT) obtained from was preferred processes in commerc ial use the worldover greater. In those days, TNT was an important, and for producing hi gh-octane gasoline, hydrogen, and perhaps the only explosive whose increasing demand aromatics as petroche mi cal feedstocks. resulted in six more units of the Hydroforming process'. UOP developed and licensed the fixed-bed Chemistry of Catalytic Reforming Platforming process using Pt on halided alu mina The important reactions (Figure 4) wh ich OCellI' 4 catalyst ,5. It was with Platforming and its vastly during catalytic reforming are: (a) Dehydrogenation superior Pt catalyst that the entire business, science of naphthenes (cyclohexanes in particular), to and technology of catalytic reforming achieved iconic aromatics, (b) Dehydroisomerizati on of alkyl­ status in the refining industry. Almost 50 y later, to aromati cs, (c) Dehydrocyclization of P! atformjng as a commercial process of UOP, in to aromatics, (d) Isomerization of n-alkanes to TURAGA et al.: CAT ALYTIC NAPHTHA REFORM ING 965

Refinery fu el Kefiner yGas LPG II Naptha

Hz UG Isomerization l C5+J Crude ~ Distillation t t fractionation Refonning --+I -,.. -. h Gasoli letfuel Di esel HDS Hz ~ ~ T l Alkylation I Heat! ngOil LPG .-- f CC Vacuum --. Heavy Fuel Distillation 0 il

Coke

I Visbreaking

Refinery Fuel Refinery Fuel

Figure 3 - Systematic of a relinery rc i rca 19801 .1(,

PI sit!;!' (s) ---- - 0+ 3H, ~,------~------~~ o Hydroca rbon fe ed ----. RI h + ---+ Initial poisons + H2 (

Poisons (gas lind surface transport ) (e) C- C-C-C-C-C-C - 0 + 4H , C Initial poi sons '--""'New unsaturat es -::;==:::!: I)ol ymcri zed poisons .. R2 I (d) C-C-C-C-C-C-C _ C- C-C-C-C-C slow crac kin ~ slowc!>1

+ H, ~~------,------~ {oj C-C-C-C-C-C-C -~_ C-C-C-C + C-C-C Acid s ites (rate controll ing)

Figure 4a - Catalyt ic reformin g reacti ons' Fi gure 4b - Postul ateu mechani sm for rerorm in g ~ branched alkanes, and (e) or fragmentati on reactions (hydrocracking or hydrogenolys is) yielding partial pressures. The constraint of catalyst products of number lower than that of the deacti vation from coke depositi on, however, does not 6 reactants . all ow operation of reforming units at high The dehydrogenati on of cyclohexanes (a). the temperatures and low hydrogen parti al pressures 7 dehydroisomerization of alkyicyclopentanes (b), and dictated by thermodynamics Paraffin isomeri zati on the dehydrocycli zation of n-alkanes (c), to produce to (d) and hydrocrackin g and aromati cs are strongly endothermic reacti ons and are (e) are exoth ermic reacti ons wi th the latter being facilitated by higher temperatures and lower hydrogen hydrogen consuming. Tables I and 2 :-.ummarize the 966 J SCI I. D RES VOL 62 OCTOBER 2003

thermodynamic and kinetic aspects of the reactions catalytic reforming is no exception " . T he decisive taking place in a commercial reformer. parameter, which established UOP's Platforming process as the most preferred technology for catalytic Mechanistic and Kin etic Features reforming was th e discovery of the Pt on alumina 2 Reforming catalysts are typically metals (Pt/AI 20 ,) catal yst by Haense l supported on an oxide carrier and possess two Chevron' commerci a li zed the Pt-Re/AI20 1 different types of catalyti c activities: an ability to bimetallic catal yst di scovered at th e ir research center, hydrogenate and dehydrogenate hydrocarbons and the c hang in g th e course of catal yti c reforming and th e ability to catal yze rearrangements . The l 2 1 science of reforming catal ysis conc lusi vely. Exxon .1. fo rmer is a pure ly meta l-cata lyzed reaction and does de ve loped and commerc iali zed the Pt-lriAI 20 :; seri es not require acid sites, while the latter is catalyzed by R of bimetallic re forming catal ysts. Both these catalysts acid sites on the support ,9 . Dehydroisomerization and were muc h more active than th e traditional Pt catalyst, isomeri zation require metal sites for or with the Pt-Jr/AI 20 , developed by Exxon displayin g cycloalk ane dehydrogenation to alkenes through a substantially greate r acti vity. The bimetallic catalysts carbocation-like species followed by rearrangement all but complete ly replaced the Pt/AI20 ; catal yst in on acid sites to form the isomeric branched and the 1970s and earl y 1980s. Improved activities of finally yie lding the isomeric branched alkane through th ese bimetallic catal ysts enabled reforming units to on metal sites. The transportation of run for longer durations between regenerations, or for th e intermediates between these active sites occurs a given length of time, allowed lower pressures for through th e gas phase 10 . From the preceding mode l, hi ghe r reformate yie ld s. we observe that the rates for these reactions are limited by the catalytic activity of the acidic sites. Platilllllll on A llIl1lina Therefore, continued increase in the metal content in The amount of Pt dispersed on alumina in reforming catal ysts leads to no appreciable increase in commerc ial reforming catal ysts is 0.3-0.6 wt per ce nt. catalytic activity and, in fact, covers up the acid sites C hl orine is also present in th e amounts of 0.3-1.0 wt · 9 and reduces the overall re formlllg rate. per cent. T hese catalysts are prepared by Reforming Catalysts impregnation of alumina with chl oroplatinic acid followed by calcination in air between 825-875K. Catal ysis has played a critical rol e III the Surface area of th e a lumina usually used is 150-300 evolution of re fining technology (Figure I) and m2/g. The pressure drop and diffusion limitati ons

Table 1- Thermod ynami c data for lypical rcformin g rea c li on ~ x

Reaclion Kpat 500°C. P in allll 6 H" kll mol of hydrocarhon Cyclohexane H + 3H:! 6 x 10 " 220.7 Melhylcyclopenlane H cyclohexane 0. 086 - IS.X II-hexane H benzene + 4H :! 0.78 x 10 5 265.( l1-hexane H2-lllelh ylp enlane 1.1 -5.9 II -hexane H I-hexenc + H:! 0. 037 129.6

Tabl e 2 - Rale behav ior and heal effecls or impmlanl rci'o rming reac li oll s x

ReaCl ion lype Relalive rale Effecl of increase in lO lal pr e~s un; Heal effect Hydrocrackin g Sl owest Increases ra le Qu ile exolh ermi c Dehydrocyc l izat ion Sl ow Small dec rease in rale End ol hermi c Iso meri zali un of paraffi ns Rapid Decreases rale Mil dlyexolherm ic

Na phlhene i~omer i zati on Rapid Decreases ra le Mildl yexolh ermi c

Para ff i n dehydroge nation Qu ile ra pi d Decreases c o n ve r ~ i o n End olhermi c Naphthene dehydrogenalion Very rapid Decreases conversi on Very endolherm ic TURAGA et al.: CATALYTIC NAPHTHA REFORMI NG 967 determine the shape of the reforming catalysts and the -Iridium Catalysts preferred shapes are usually pellets. or extruda.tes. Platinum-iridium bimetallic clusters are Di spersion of the metal on the alumma support IS . a prepared by impregnating the alumina support with an critical parameter for reforming, as for any catalytiC aqueous solution of c hl oroplatinic and chloroiridic process, and is defined as the ratio of the amount of acid s 15. After the impregnated support is dried and exposed metal on the surface to the total amount of calcined at mild conditions. it is exposed to flowing metal in the catalyst. Chemisorption studies have hydrogen to reduce Pt and lr. The catal yst contains shown that freshly prepared Pt/AI 20 , reforming comparable amounts of Pt and Ir with a total metal catalysts are characterized by extre mely high Pt content of 0.5-1.0 wt per cent. The metal dispersion is dispersion. Hydrogen chemisorption, extended X-ray close to one, implying that almost all Pt and Ir atoms absorption fine structure (EXAFS) and anomalous in th e catalyst are on the surface. Interaction between X-ray scattering studies have also confirmed high Pt Pt and Ir has been studied extensive ly but conclusive dispersion which exists in an amorphous state, results on the type of interaction, if at aiL are still achi eves microcrystallinity on reduction with e lu sive' . Iridium unde rgoes oxidative agglomeration hydrogen. Other studies, e.g., 195Pt NMR, have also to form clusters of Ir02 at hi gh te mperatures and so reached si mi lar conclusions'. Pt-Ir bimetallic catalysts are calcined at temperatures Acidic Properties of the Alumina much lower th an those used for Pt on alumina catalysts and logically th e regenerati on procedures for Catalytic reforming as a process stimulated these catalysts are different. tremendous interest in the role of the support in the science of catalysis and led to some very seminal Platinum-Tin Catalysts 14 studies. Alumina, known to be amphoteric, has a lot These catalysts were introduced in catalytic of hydroxyl groups on its surface which are the prime reforming units by UOP with th eir Continuous source for Br(llnsted (protonic) acidity and responsible Catalytic Reforming (CCR) process. The combined Pt for hydrocarbon rearrangement reactions. The and Sn content of these catalysts is less than 0.8 wt presence of chlorine (fluorine, in the early 1950s) in per cent. These catal ysts are prepared using chlorided reforming catalysts is thought to impart acidity in precursors and are reduced above 673 K. The Pt-Sn alumina by interacting with the surface hydroxyl catalysts are th e focus of intense research because of groups, although fundamental studies and two issues: th e oxidati on numbe rs of Sn after understandino- on this particular aspect of reforming b . 6 exposure of th e catalysts to hydrogen and the extent to catalysts are still not comprehensive . l5 which bimetallic entities of Pt and Sn are present . Platinum- Catalysts UOP introduced these with the Continuous Catalytic Reformer (CCR) because of the tendency of Pt­ These alumina supported bimetallic catal ysts Sn/AI20 , to deactivate rapidl y. generally contain an amount of rhenium comparable to the amount of Pt (often 0.3 wt per cent each). These PlatinumlKL Zeolite Cawlvsts cataly sts are prepared differently from other All commercial catalysts are limited by low bimetallic catalysts and organometallic precursors as selecti vity of the aromati zation of Cr, and C alkanes dirhenium decacarbonyl, Re2(CO)1O are used to 7 relative to that of hi gher carbon numbe r alkanes in impregnate Pt supported on alumina. Fundamental the naphtha boiling range. The yie ld of these studies invo l ving characterization techniques as catalysts for convertin g C(, alkanes to benzene is chemisorption, EXAFS and X-ray absorpti on have shown that rhenium exists in the reduced form and is typically only about 10 per ce nt as against 60 per cent for methylcyclopentane and 90 per cent for extremely sensitive to poisoning by sulphur and less l6 sensitive to coke deactivation compared to Pt. It is cyclohexane . It has been suggested that thi s may be believed that Pt and rhenium are extensively due to the acidic chlorided alumina support. A coordinated to each other in bimetallic clusters, while catal yst in which KL zeol ite is used as a support for their individual coordination to oxygen in the alumina platinum has a s ignificant advantage over framework is small. These studies indicate that the conve ntional refNming catal ysts. The KL zeolite has composition and concentrati on of these clusters vary narrow (0.71 nm) un idirectional channe ls and is not WI' de I y 15 . acidic. The Pt in the c hannels had di spe rs ion almost 968 J SCI IND RES VOL 62 OCTOBER 20m

equa I to one 17- 19 . TI le p Iattnum' cata I yzes aroma- dehydrogenated intermediates generated by the

tizatio n of C 6 and C 7 alkanes with hi gh selectivity. metallic fun cti on (Figure 4b). Since the KL zeolite is not acidic, competing Coke depositi on occurs throughout commercial reacti ons of isomerization and hydrocracking are operation on both the acid and meta l sites with the strongly suppressed and thus the of rate of deposition be in g hi gher at the beginning. It is a lkanes proceeds unhinde red . T his catalyst, howe ver, believed that the initial rapid coke formation occurs suffers from extre me sensitivity to sulphur mainly on th e metal functi on. Reforming typicall y pOi sonlllg . contain 0.3 wt per cent Pt which is enough to result in enough steady-state activity to produce all the olefins Deacti va tion. and Regeneration that can be isomeri zed or cycli zed o n th e ac id Most catalysts, whether operated commerc ially functi on. The initial fa st coking of th e metal sites until or in a laboratory, eventually deacti vate. Deactivation a pseudo steady state of th e me tal function is reached is very important in commercial operation because it is call ed a lineout peri od . At longer time operations. influences the choice of the operational conditions the acid function is more deacti vated by th e slow coke and fixes the cycle length between regeneration and deposition. the total I ife of the catalyst. Among the processes of Commerc ia l naphtha reforming catal ysts petroleum refining and the industries, typicall y control the main reaction:.; name ly the catalyti c reforming of naphtha has one of the more isomeri zati on and de hydrocycli zati o n of C6-C9 complicated deactivation phenomena because the paraffins, through th e acid functionality. However, if catalyst presents nearly all the kn own causes of th e meta lli c component is less acti ve or th e working deacti vation. pressure is very low, th e metal may become the The processing of hydrocarbons is generall y controlling fun cti on of th e main reformi ng reacti ons. accompanied by the formation of carbonaceous The length of th e run is also important. If th e run deposits on the catal yst surface. The phenomenon is takes place onl y during th e lineout peri d , it could be referred to as coking and depends on catalyst concluded that the meta l function controls th e catalyst composi tion, operational conditions, and feed deactivation. Thus, results obtained under certain composition . Coke is formed on acid catalysts conditions cannot be ex trapolated to other conditions. (cracking or isomerization of hydrocarbons), metallic The heart of the naphtha reforming process is catalysts ( , hydrogenation, the catalyst and most of the process improvements or de hydrogenation), and bifunctional metal-acid have re lated to catal yst life and stability. Catalyst catal ysts (naphtha reforming, paraffin isomeri zation, regeneration in c ludes several steps such as or hydrocracking). In the case of naphtha reforming, e liminatio n of coke by controlled burning, coke formation is the most rapid cause of oxychl orinatioll to re vive th e metal and ac id deactivation. Reforming catalysts a lso deactivate functionalities, reducti on with hydrogen, and, finally because of poisoning by sulphur and activation by sulphating. With respect to catal yst compounds, sintering (decrease of metallic area), regenerati on, th ere are two models to interpret th e decrease of chloride concentration, and heavy metal coke-burning phenomenon: (i) A homogeneous depositi on. model, when c he mi cal reaction is the controlling steps Bifunctional catalysts coke from accumulation of th e process. In thi s case the gaseous reactants of carbon containing species on the metal and the diffuse through the solid phase reacting in a ll the H support On metallic sites, two mode ls expl ain coke partic le vo lume and ( ii ) A shrinking core mode l that fo rmation. The first mode l involves a series of proposes the ex istence of a non-reacting nuc leus fragmentation and successive de hydrogenation whose size decreases with time surrounded by a reactions forming carbon atoms, which may combine cOlllp lete ly burnt she ll. to form more graphitic and toxic coke deposits. T he second mechani sm suggests that th e routes of coke To increase th e stability of reforming catal ysts, depositi on are based on polymerization reacti ons with some researchers ha ve evalu ateJ dea lulllinatecl ZSM- the formation of different types of carbonaceous 12, zeolite ~ , and thei r composites with yAhO, for the deposits on the meta l surface. Coke formation on acid reforming of industrial naphtha. They found that sites is assumed to ari se from polymeri zation of dealuminated ZSM- 12 de monstrates unique time-on- TURAGA el al.: CATALYTIC NAPHTHA REFORMING 969 stream stability for the reaction investigated. This hi gher aromatic conversi on, hi gh reformate yields, behavior is a combined result of the acidity and pore more efficient catalyst regeneration, longer catalyst stmcture of the zeolite which do not favour coke life and surface stability, and lower pressures and less formation. Zeolites with channel intersections slightly hydrogen recycle. larger than the zeolite aperture do not favor coke Commercially, reformers are typi call y operated formation . The results demonstrated that the to produce a product of constant Research Octane composite catalysts produce more gasoline-range Number (RON). Operating conditions of a reformer hydrocarbons and show much better time-on-stream are usually described in terms of severity. As catalyst behaviour than conventional yAI 20 , catalysts. deactivation in creases, severit y IS in creased to compensate for loss of catalyst activity thereby The Reforming Process maintaining product RON. Commercial reformers are Catalytic reforming has evolved rapidly during designed to process both virgin and cracked the past five decades to emerge as one of the most at 5-30 atmos and 700-800K. Pressure is achieved by advanced processes available to the refining industry the of hydrogen, which is 50-80 per with several commercial licensors (Table 3). The cent of the total pressure. Hydrogen pressure differences characterizing these processes are: decreases catalyst deacti vation and excessive (i) Nature of the catalysts used, (ii ) Catalyst aromatization. A hi gh RO reformate yield requires regeneration procedures, and (iii) Equipment lower pressures and more stable catal ysts. Industri al conformation and process configuration. Catalytic catalytic reformers involve three sections: feedstock reforming processes are modified depending upon pretreatment, reaction secti on, and product separati on process and product configurations which include and stabilizer units.

Table 3 - Li sl of reformin g li ce nsors" Supplier Catalyst description Ac tivc metal Acreon catalyst comp any AR 403. AR 405: aromati cs producti on Pt + promoter Procatalyze CR20 I: continu ous regeneration Pt/S n E20 I-E I 000: gaso line/aromati cs r rod uction Pt or Pt /Re RG seri es: low to hi gh pressure app li cati ons 1"1. Pt /Rc. Ptl Re+ promoter

Pt/l I' + promoter

Criterion catalysts company PH F 4,5: gasoline or BTX p~odu c tion Proprci lary PRH F seri es: gasoline or BTX prod uction Kx 120-190 seri es for gasoli ne and I3TX

In dian Petrochemical Corporation IR C 100 I, 1002 : aromati cs and gaso lin c app li cntions PI. Pt/Rc Limited In stituto Mexieana del Petroteo MP-RNA-I , 2: gasoline/BTX Pt/Rc IMP-R A-4: for co nt inuous proccsses Pt /Sn

UOP R-30 series: continuous regenerati on Prop reil:lry R-SO seri es: hi gh severity semi -rcgeneration Pt/R e R-60 scrics: hi gher stabi lity Pt /Re R-72 seri es: hi gher severity semi-regcncrati on Prop rcit ary R -132, 134 seri es: co ntinuous regcncrat ion Proprcitnry

Kataleuna Gm bH 8815/03, 05 : mono metalli cs [all scries 1'0 1' gasolinclBTX I PI

88 19/B: bime ~ all ie Pt/Rc 8823: bimetallI C Pt /Re 8842: co ntinuous rege ncr:lIi Oil Pt /Sn 970 J SCI IND RES VOL 62 OCTOBER 20m

Feedstock Pretreatment from the process itsel f) and heated to the desired The prime obj ecti ve of feedstock pretreatment is temperature before it enters the first reactor. removal of permanent catalyst poisons such as Temperature profiles are an import;}l1t consideration arseni c, lead, and copper and to reduce temporary in reactor design (Table 5) . The overall reforming catalyst poisons such as, sulphur, oxygen, and reactions are endoth ermic and isothe rmal operati on, nitrogen to lower levels (Table 4). Naphtha although desirable, is impractical on a commerc ial hydrotreatment in volves vapor-phase reaction with scale. To overcome thi s difficulty, the reactors are hydrogen over a sul phur-resistant catalyst such as, separated into several ad iabatic zones operating at 7SSK with heaters in between stages to supply Co-Mo/AI20 1 fo ll owed by cooling, phase separation, and efficient stripping of all H1S and NH, out of necessary heat of reacti on, th ereby hold in g the overall treated naphtha. Water is al so removed as it s presence seri es of reactors at a constant tempe rature. leads to acidic modification of alumina. C hl orine, at a Reactor syste ms are selected depending on predetermined level in the catalyst, is necessary to reforming unit confi gurati ons. Initi a ll y, ax ial influence and generate desired alumina acidity but downfl ow reactor syste ms were used as th ey were chl orine in the feed leads to selecti vity shifts in the cheape r but the huge pressure drops created by them catalyst, and frequentl y, excessive hydrocrackin g. led to the usage of radial down fl ow reactors in fixed­ C hl orine is thus washed away from the feed UStng bed syste ms . Presentl y, many refo rming units use a water or alcoho l. combinati on of both types of reactors. The reacti on te mperature in the first reactor decreases rapidl y due Th e Reforming Reactor to the dehydrogenati on o/" cycloakanes to aromatics, The reacti on section of a conventional reformer wh ich consumes heat. T he efflu ent fro m th e first consists of multi-bed reactors in seri es with pre- and reactor is th en heated and fed to th e second reactor re-heaters between the reactors. Desired product RON where it un dergoes de hyd roisomeri zati on of requires at least three or four reactors. The feedstock, cyclopentanes at a s lower rate th an in th e first reactor. naphtha, is mi xed with hydrogen (usually recycled The second reactor ope rates with a te mperature drop of 29S-30SK. The last stage reactor in vo lves Table 4 - Naphtha Pretreatment Indieators24 hydrocracking and hydrogenolys is, wh ic h is exothermi c leading to s li ght temperature c hanges. T he S S; 10 ppm or 5 ppm at hig h N S; J ppm severity first reactor is th e smallest in size fol lowed by the second, while the third and fourth are very large H20 S; 4 ppm Pb ... As ... Cu < 20 ppb reactors refl ecting th e time taken by the reactions

Table 5 - Typi cal operatin g co nditi ons for a three- reactor system"'

Rea ctor I Reactor 2 Re,lCtor 1

Inl et temperature. K 775 775 775

Ex it temperature, K 706 844 76')

Temperature drop. K 69 3 1 Ii

Octane number 65.5 79.5 SlO.O

Octane- number in crease 27.0 14.0 10. 5

Principal reactions Dehydrogenat ion, Dehydrogenat ion. J-I ydrocracking. Dehydro iso meri zati on Dehydroiso meri za t ion , J-Iydmcrack in g, De hyu n.cyc l iza ti on Dehyclro cycliza ti on

LHSV, If I per reactor 5.5 2.4 1.7

Per ce nt of total catalyst 15 35 50 charge TURAGA el af.: CATALYTIC NAPHTHA REFORMING 971 taking pl ace in each of these reactors. The catalyst beds are regenerated at low pressure of about 8 atmos loaded in the first reactor is only 10-20 per cent of the with air as the source of oxygen. The catalyst total catalyst charge. Temperature profile (/'.,.7) along inventory can be regenerated 5-10- times before its the reactors is another important parameter and is activity falls below the economic minimum, when it is indicative of the type of reactions occurring in each replaced. As catalytic activity decreases, aromatic reactor. yield and hydrogen purity also drops because of increased hydrocracking. Product Separation and Stabilization The advent of bi- and multi-metallic catalysts Effluents from the reactors are cooled and allowed the operation of semi-regenerative units at separated into gaseous and liquid products. The 14-17 atmos for the same cycle lengths compared to gaseous products consist of 60-90 mol per cent hi gher pressures of ~o atmos using PI. Semi­ hydrogen and the rest CIA hydrocarbons. The liquid regenerati ve reformers are generally built with three product, known as the reformate, consists of C).IO to four catalyst beds in series (Figure 5). The fourth hydrocarbons with aromatics in the range of 60-70 wt reactor is usuall y added to some units to all ow an per cent. The crude reformate is purified in a increase in either severity or throughput while stabilizer where volatile and light hydrocarbons are maintaining th e same cycle length. Catalyst amount removed, using a single-column operation under increases with th e cycle length. The product RON sufficient pressure to permit condensation of reflux achievable through this is usually 85- 100, depending from the overhead vapor. Part or most of the on optimized feedstock quality, gasoline qualities and overheads are removed as vapor. quantities, and operating conditions required to Process Class!fication achieve a specified cycle length. Most li censors have semi-regenerative design opti ons (Table ~). Catalytic reforming processes are classified, based on the mode and frequency of catalyst Cyclic (Fully Regenerative) Prucess regeneration, into three types: (a) Semi-regenerative, The !:yclic process, typ icall y uses a train of five (b) Cyclic (Fully regenerative), and (c) Continuous to six fixed catalyst beds, similar to the semi­ Regenerative (Moving bed) process. There are more regenerative process, with one additional swing than 800 commercial (Table 6) installations of the reactor, which is a spare reactor used to substitute any catalytic reforming processes worldwide with a total of the regular reactors in th e train while th e regular 22 24 capacity of 9.5 million barrels/d . . rector is being regenerated (Figure 6). This enables Semi-regenerative Process only one reactor to be taken off-stream while the whole process and reformate yie ld s continue The semi-regenerative catalytic reforming unaffected. Catalyst regeneration takes place at longer process is characterized by continuous operation over intervals as compared to th e semi-regenerative long periods with decreasing catalyst activity and process. The cycli c reformer operates at low pressure, increasing reforming severity to maintain conversion wide-range boiling feed and low hydrogen to to a specific RON. The semi-regenerative process is hydrocarbon ratio. the conventional reforming process, which operates continuously for more then I y. Eventually the The cycl ic process produces re formate of RON reformers are shut down periodically and the catalyst 100-\ 04 but also leads to extensi ve cokin g due to low

Table 6 - Regional distribution of catalytic reformers by process design in I <)<)3 ~.j

Region Per cent of Reformers Semi-regenerative Cyclic Conti nll olls \

United States 57 13 14 16 Europe 66 II 17 6 Japan 70 10 15 5 a Other includes non-regenerative and moving bed systems 972 J SCI IND RES VOL 62 OCTOBER 2003

Light ends to Recovery

Reactors

Heater

Stabilizer

Reformate

Figure 5 - Semi-regenerative reformers"

Fresh Feed

Recycle Gas Compressor

Flash Drum

Product H2

Product to Stabilizer D u Reactor Heater Figure 6 - Cyclic regenerati ve reformers" TURAGA el al.: CATALYTIC NAPHTHA REFORMING 973 pressure and high-octane severity. Using lower changes in unit operating conditions are carried out by pressures enables production of a higher C 5+ changes in operating parameters (Table 7 and 8). The reformate yield and hydrogen. The process suffers variables, which affect performance of the catalyst from the drawbacks that the reactor sizes should all be and change the yield and quality of reformate are the same to enable switching and also that the reactors feedstock properties, reacti on temperature, space alternate between a reducing atmosphere during velocity, reacti on pressure, and hydrogen-to­ normal operation and an oxidizing atmosphere during hydrocarbon mole ratio. regeneration. Feedstock Properties Continuous Regenerative (Moving Bed) Process Boiling range of th e feed is an important UOP in the late I 960s made another advance in parameter whi ch can be contro ll ed and the max imum the technology of catalytic reforming by introducing ASTM end point of 478K is specifi ed for reformer the Continuous Catalytic Reformer (CCR) which reactor charge. This is because hyd rocarbons boiling produces hi gh octane reformate and high-purity above 478K are known to form polycyclic aromatics hydrogen on a continuous basis, using small amounts and thus coke. As a rul e, a change in temperature by of a highly active catalyst. The process has the best of 13K in feed ASTM end point costs about 35 per cent the cyclic reforming process while at the same time of catalyst life between ASTM end point ranges of avoiding its drawbacks. In this process, small 463-491 K for the feed. Straight run naphthas are the 25 quantities of catalyst are continuously withdrawn major feedstocks for reformers . from an operating rector, transported to a regeneration Feedstocks with appreciable content of unit, regenerated and then returned to the reactor unsaturated hydrocarbons arisin g from thermally system. The most common design involves stacking cracked, catalytically cracked, coker and pyrolysis of all reactors on top of one another with the last naphtha must all be hydrotreated before reforming to reactor set beside the stacked reactors. The reactor prevent undue hydrogen consumption and excessive system has a common catalyst bed that moves as a catal yst deacti vation . In add iti on to havi ng sulphur column of particles from the top to bottom of the and nitrogen. th ese stocks also contain substantial reactor. Operating pressures are in the range of 3.5- 17 olefins and diolefins, which are undesirable in atmos to produce a reformate of RON 95-108 reformer feed for several reasons. The most important (Figure 7). side r eaction in a reformer is hydrogenation of olefins causing excessive hydrogen consumption. In additi on, Operating Parameters this undesired side reacti on markedly reduces the Catalytic reformers are designed for flexibility reformate RON. More importantl y, olefin s tend to in operation and product configuration for which polymeri ze and form coke on catalyst surfaces.

REFORMATE FEED [Naptha] Parrafins : 24 wi % Parrafins : 63 wt % Oxygenates: 1 wt % Nitrogenates: 23 wt % Aromatics: 75 wt % Aromatics: 14 wt % ... CCR REFORMER Distill Range: 60 - 170 0 C Distill Range: 85 - 160 ° C P = 4 -7 Bar T=495-515 °C Typical RON: 45 C I-C4 : 8 wt %

Reformate : 88 wt %

Figure 7 - Mass balance for continuous catalyti c reforming" 974 J SCI IND RES VOL 62 OCTOBER 2003

Table 7 - Yield-octane relationship, reforming C(, 633K naphtha, constant teJllp era tur e2~

Pressure (atmo s) Co+ yield (vol. , per cent) Octane C5+ (R+O)" 7 90 92 7 83 99 14 87 92 14 80 99 17 82 92 17 76 99 34 88 92 " Research octane number in the absence of tetraeth yl lead.

Table 8 - Influence of feed properti es and product distribution 2~

H2 H2 Cs+ Delta Reactor

Increase purity a yield yield temp. temp.

Feed property

API +

Paraffin s + Naphthenes + + + +

Aromatics + 0 Initi al

Final boiling point 0(-) + + + + Process variable

Separator pressure + 0 + () ()

Separator temperature 0 () 0 Reactor press ure

Reformate RON C + + + a +, In crease; -, Decrease; 0, No effect

Reaction Temperature Reaction te mperatures are chosen to balance Reformers are generally designed as a series of inc reased catalyst activity (max imu m in th e range reactors, which lead to changes in catalyst bed 733-798K) with inc reased deactivation rate (occurring temperatures as feed flows through them. It is thus in the te mperature range 755-773K). Low-pressure common practice to measure either the Weighted­ processes are operated at s li ghtl y hi gher temperatures A verage reactor Inlet Temperature (WAIT) or the to optimi ze conve rsion\ to hi gh-RON products. Weighted-A verage Bed Temperature (W ABT). WAIT Catalytic reforming results in in creased reformate is the sum of the inlet temperature to each reactor RON with reactor temperature and as a rul e for the multiplied by the weight per cent of total catalyst in RON range of 90-95, WAIT shou ld increase by 2- 26 each reactor. Similarly, WABT is the sum of the 3K1RON increase For a RON range of 95-100, average of the inl et and outlet temperatures of each WAIT increase should correspond to 3-4K1RON reactor multiplied by the weight per cent of the increase. Each feedstock, however, has its own catalyst in the reactor. In day-to-day operations, it is temperature-octane relationship and there is no widely always easier to operate WAIT than W ABT. accepted correlation to account for all feedstock- TURAGA e/ af.: CATALYTIC NAPHTHA REFORMING 975

temperature relationships. Also, increased RON Hydrogen-to-Hydrocarbon Ratio reformates have a reduction in yield by about 13 Hydrogen is essential in reforming to avoid volume per cent of the reformer charge. unwanted side reactions and reduce catalyst deactivation. High hydrogen-to-hydrocarbon ratios Space Velocity require hi gh hydrogen recycle rates and increased Space velocity is an important reforming process energy costs. Operating at reduced hydrogen-to­ variable and is a measure of the contact time between hydrocarbon ratios leads to savin gs in terms of energy the reactants and the catalyst. This is expressed as costs and hence th e va lu e chosen is lower bound by either the Liquid Hourly Space Velocity (volume per the desired amount of hydrocracking and the hour of reactor charge per volume of catalyst, LHSV) maxImum acceptable deactivation. Reformers or the Weight Hourly Space Velocity (weight per designed 111 th e 1950s used a hydrogen-to­ hour of reactor charge per weight of catalyst, WHSV). hydrocarbon ratio of 8-10 and a hydrogen partial Modern commercial reformers usually operate in an pressure of 19-35 atmos while modern reformers LHSV range of 1-2/h . At lower LHSV values, contact operate in hydrogen-to-hydrocarbon ratio range of 2-5 time increases, leading to undesired side reactions and and a partial hydrogen pressure of 5-1 I atmos, a increased hydrocracking, reducing reformate yield. change due to hi ghl y active catalysts. This choice, however, represents a compromise Recent Developments between reducing undesired hydrocracking and increase in desired dehydrocyclization. Aromatizati on Catalytic reforming, in additi on to fulfilling its and isomerization, however, are not affected by original obj ecti ve of producin g hi gh octane gasoline changes in space velocity as these reactions are very has also been used for va ri ous appl ications, including fast and approach equilibrium values even at lower producti on of aromatics, liquefied petroleum gas contact times. (LPG), hydrogen, and upgrad in g olefinic feedstocks and raffinates. Almost 75 di fferent reforming catalysts Generally, for a reformate of 90-100 RON, are avail able currently for specific goals, using doubling LHSV requires an increase of 15-20K in specific feedstocks. C

Reaction Pressure OClan.e Boosting Over the past five decades, reformer unit This is a post-reforming process which cracks pressures have dropped substantiall y. Reformers of straight chain paraffins selectively using a metal (Ni ) th e 1950s used a pressure range of 19-35 atmos while impregnated in a small pore zeolite (ZSM-5 or modern reformers operate between 5-1 I atmos. Each Eri onite) at 25 atmos pressure, hydrogen-to­ of the three or four reformer reactors has different hydrocarbon rati o of 7 and temperatures around pressures and an average reactor pressure is preferred. 600K. Commercial li censors of si milar processes Decreased pressures lead to increased aromatics and include ExxonM obil (Mforming) and UOP hydrogen yie lds but also in crease coking and catalys t (Se lectoforming). deactivati on. It has been demonstrated that at 100 RON, there is an increase in the per cent yield of Aromatics Production and Olefinic Feedstock reformate from 79.7 to 83.5 by a reducti on in pressure Upgrading from 21 to 8 atmos. In oth er words, at the 100 RON r Catalyti c reformers wi th these obj ecti ves process level, liquid yield increases or decreases by about 2 very narrow feed cuts in th e range of 333-363K for vo l per cent of chargel 8 atmos change in pressure. At benzene production and 383-4 13 K for toluene and the 90 RON level, the yield difference is about I producti on with th e exact cut points depending liquid vol per cent of charge/8 atmos change in on crude source. Gasoline production requires full 2R 29 pressure . . Similar quantitative correlations have not range naphtha. These refo rmers operate at hi gh yet been reported for hydrogen yield . severity to ma ximi ze aromatics production. Some of 976 J SCI IND RES VOL 62 OCTOBER 2003

Mtlyear

400 -,------i ------11.. 350 1-----_1-----_1-----_1-- _.- -__ - '___.--_ . ---- Reforming

300

250

200

Alkylation 150

..-..- ~ ,/+----- 100 Etherification / ..K- Isomerization • .------+/ 50 _---A- --A ----t-- " .. -0\- - ...... -~ - -A- - "'~_ .._--- e j A- --e---e- --e ______e__--e- . - -- - e -­ O +. ----'==~-~-----~i---_.---_.---_.----~ 1988 1990 1992 1994 1996 1998 2000 2002

Figure 8 - Oil ret1ning birth th rough 2000(ref.36) the well-known processes available towards these With these developments, there is a reduced objecti ves include M2Forming (from ExxonMobil) emphasis on the use of benzen o for octane which processes olefinic feedstocks and thermally enhancement and development of cata lysts and cracked naphtha a( low pressures and high technologies wh ic h a lkylate benzene and tolu ene to temperatures, Aroforming (from Salutec, Australia and Co) aromatics would be the new and IFP, France) usi ng a Ga impregnated ZSM-5 cha ll enges for the refining industry_ Existing catalyst to convert LPG and li ght naphtha to reforming catalysts have to be modified or new post­ aromatics (with no hydrogen recycle), and the BP­ reforming processes added or discovered, to meet this UOP Cyclar process, quite similar to Aroforming. The chall enge. This would also lead to reluctance in Cyclar process has had some succesS in the past but processing full range naphtha to avoid benzene has not been very popular of late'o. production. For octane number enhance ment, the thrust shall be on cata lysts and technologies that Beyond Environmen!l:al Regulations isomerize the li ghter C 6 and C 7 paraffins to branched The Clean Air Act Amendments of 1990 isomers with hi ghe r RON. impacted catalytic reforming by laying restrictions on RVP constraints will result in e li minating fuel qua lity to improve emission standard s_ Limits on from gasoline: excess butane being available for benzene to a I volume per cent maximum amd conversion into iso-butane and iso-butylene, which, in reduced Re id Vapor Pressure (RVP) have forced a particular, is an important feedstock for synthesis of complete rethink of the process and is the biggest MTBE. This is particularly important in countries challenge facing reforming. The offset in octane like, India and China, which have to cope up with the number caused by reduction in benzene was to be met Clean Air Act and are sti ll llsing M T BE but face an by the addition of oxygenates such as methyl tert­ acute shortage of iso-butylene as its feedstock. butyl ether (MTBE) which has a RON of 117. This has, however, received a major setback with the Petrochemical capaciti es are on the ri se globall y recent decisions to stop using MTBE as an octalne­ and especia ll y in the Asia-Pacific where the per capita enhancin bcr additive because of its groundwater consumption of petrochemical products is less than polluting potential. European and the US values by an order of T URAGA et al.: CATALYTIC NAPHTHA RE f-a RM ING 977 magmtu. d e'1 1-141. ' 7. C onsl'd' erm g the a b ove scenano. f or 4 Hein emann H, Handbook of' heterogeneous catalysis, edited the petrochemical industry and the product pattern by G Ertl, H Kn tizinger and J Weitkamp (YCH, Weinheim) 1997. in volving LPG' o, it is expected that major reforming 5 Peer R L. Bennett RW & Fe lch D E, UOP Platformi ng units would now be built in the Asia-Pacific'7, which leadin g octane techno logy illlo the 1990' s. Catal Todav, 18 not only require aromati cs, but also huge amounts of ( 1994) 473. LPG. It would be ideal if reformers could produce 6 Sinfelt J H, Billl etallic catall'sts: Discoveries. concepts, and onl y aromati cs and hydrogen but this is an unlikely application.\' (Wil ey, New Yark) 1983. scenario in the near future and so the preferred 7 Bournonvill e Jean-Paul & Franck Jean-Pi erre, Hvdrogen product di stribution would be aromatics and LPG. effects in catalysis, edited by Z Paal and P G Menon, (Marcel Thus, on an overall basis, catalyti c reforming is Dekker. New York) 1988. expected to increase sli ghtl y or pl ateau out (Figure 8) 8 Gates B C, Katzer J R & Schuit G C A. Chemistry of fo r octane enhancement obj ecti ves but has a strong catalytic processes (McGraw Hill. New York) 1979. outlook as far as aromati cs producti on IS 9 Sinklt J H, Bifunclional cal alysis. Ad" Chelll Eng, 5 (1964) concerned,4.37. 37. 10 Weisz P B & Sweglcr E W, Stepwise reacti on on di ffe rent Conclusions catalyti c centers: isomerization o f saturated hydrocarbons, Science, 126 ( 1957) 3 1. Benzene, toluene, and xy lene are critical II Mart ino G, Court y P & Marcilly G , Handbook of feedstocks for the petrochemical industry and we heterogeneolls catalvsis, ed ited by G Ertl. H Kntizinger. and J Weitkamp (YCH, Wein heim) 1997. expect th at they will be avail abl e to a large extent 12 Sinfelt J H, Po lymetalli c cluster compositions useful as from reforming units. We feel th at there will be hyd rocarbon conversion calalysts, US Pm, 3953368, 1976. renewed focus on reforming as a process toward s 13 Sinfe lt J H, Combinati on re forming. US Pat, 379196 1.1974. producti on of aromatics and hydrogen. Catalyti c 14 Bond G C, Hundbook (!f' heterogeneoll s ('a talvsis, edited by reforming is by far the most effecti ve producer of G Ertl. H Kn tizin ger and .J Weit b mf1 (YC H. Wein heim) hydrogen who' s most efficient use is fo r producing 1997. clean fuels in the refinery and thus, hydrogen 15 Bo iti aux J P, Deves J M. Di dill on B & Marcill y C R, consumption is expected to be very strong for quite Catalytic naphtha re{!lIming: Science and technology, ed ited some time in the future. Higher hydrogen producti on by G .J Antos, A M Ait ani and J M Parera (Marcel Dekk er, means operati ons of reformers at lower pressures and New Yo rk ) 1995. many reforming li censors have processes avail able to 16 O ' Conno r C T , HandlJOo k (~f' heierogeneoll,\' calalysis, edited meet thi s requirement. by G Ertl , H Kntizin ger and J Weit kamp (YCH, Weinheim) 1997. Acknowledgements 17 Corma A, Transformalion of hydrocarbons on zeoli te catalysts. Catal Lell , 3 ( 1993) 22. Uday Turaga is grateful to Jingyan Shao, Weilin 18 Derouane E C & Yanderveken D .I. Structu ral recogniti on Wang, Semih Eser, Anil Oroskar, and Mat Mall adi for and preorgani zation in zeoli te calalys is: di rect aromati zation of hexane; on zeolit e-L based catalysts. AIIIII Catal. 45 ( 1988) useful suggesti ons in preparati on of thi s paper. LIS. Ramnarayanan Ramanath an acknowledges M A 19 Larsen G & Hall er G L, Metal-s

26 Prins R, Chemistry and chemical engin eerillg of catalytic 32 Takeda M & Tamura K. Indi a's petroche mical industry, processes, edited by R Prins and G C A Schuit (S ijthoff and Chemtech, (Jul y 1997) 50. Noord hoff, Alpen aan den Rijn) 1980. 33 Morse P M .. Petroc hemi ca ls: Da rk skies and beyond , Chell! 27 Peer R, Bennet R & Bakas S, Oil Gas J, (May 30, 1988). En g News, (March 23. 1998) 17. 34 Oil Gas 1. (October 12, 199X). 28 Rh odes A K, Oil Gas J, (October I I, 1993 ). 35 Magee Joh n & Dolbear Geoffrey, Pelm/elllll (;C//a lvsi.\· in 29 Little 0 M, Calal Reform (Pen well , Tulsa) 1985. nontechnical lc/ll f.( lIage ( PennWell Publishing Company, Tulsa) 19tJ8. 30 Sivasanker S & Ratnasamy P, Catalytic naphtha reforming: Science and technology, edi ted by G J Antos, A M Ait ani 36 Martino G, Comty P & Marci ll y C, Handbook of and J M Parera (Marcel Dekker; New York ) 1995. heterogeneolls ca/alysis. ed it ed hy G En!. H Kn ozi nger and J Weit kamp (YO-I, Weinheim ) I tJtJ7. 3 I Takeda M & Tamura K. China's petrochemi cal industry, 37 Tull o A H, The nex t wave. Ch{'lIl Eng Nell ·s. (June 2, 2003) Cliemtech, (Janu ary 1996) 42. 26.

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