Applied Energy 109 (2013) 79–93

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Applied Energy

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Progress in catalytic naphtha reforming process: A review

0306-2619/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.apenergy.2013.03.080

⇑ Corresponding author at: Department of Chemical Engineering, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz 71345, Iran. Tel.:2303071; fax: +98 711 6287294.

E-mail addresses: rahimpor@shirazu.ac.ir, mrahimpour@ucdavis.edu (M.R. Rahimpour).

Mohammad Reza Rahimpour a,b,⇑, Mitra Jafari a, Davood Iranshahi a

a Department of Chemical Engineering, School of Chemical and Petroleum Engineering, Shiraz University, Shiraz 71345, Iranb Department of Chemical Engineering and Materials Science, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, United States

a r t i c l e i n f o a b s t r a c t

Article history:Received 12 July 2012Received in revised form 12 March 2013Accepted 28 March 2013Available online 25 April 2013

Keywords:Catalytic naphtha reformingCatalystKinetic modelDeactivation modelReactor configuration

Catalytic naphtha reforming process is a vital process for refineries due to the production of high-octanecomponents, which is intensely demanded in our modern life. The significance of this industrial processinduced researchers to investigate different aspects of catalytic naphtha reforming process intensively.Some of the investigators try to improve this process by representing more effective catalysts, while oth-ers try to elucidate its kinetic and deactivation mechanisms and design more efficient reactor setups. Theamount of these established papers is so much that may confuse some of the researchers who want tofind collective information about catalytic naphtha reforming process. In the present paper, the publishedstudies from 1949 until now are categorized into three main groups including finding suitable catalyst,revealing appropriate kinetic and deactivation model, and suggesting efficient reactor configurationand mode of operation. These studies are reviewed separately, and a suitable reference is provided forthose who want to have access to generalized information about catalytic naphtha reforming process.Finally, various suggestions for revamping the catalytic naphtha reforming process have been proposedas a guideline for further investigations.

� 2013 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802. Catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

2.1. Bimetallic catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 802.2. Trimetallic catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

3. Reaction model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

3.1. Kinetic model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 823.2. Catalyst deactivation model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

4. Reactor configurations and process classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

4.1. Suggested reactor configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

4.1.1. Axial-flow tubular reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854.1.2. Radial-flow tubular reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874.1.3. Radial-flow spherical reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 874.1.4. Axial-flow spherical reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

4.2. Process classification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

4.2.1. Semi-regenerative catalytic reformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 884.2.2. Cyclic catalytic reformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 884.2.3. Continuous catalyst regeneration reformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

5. Suggestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 906. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

+98 711

80 M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93

1. Introduction

Although burning any fossil fuel contributes to environmentalproblems due to carbon dioxide and other gas emissions, they arethe main energy source in our world [1–5]. In order to protect envi-ronment, various legislations are passed including increase in oc-tane number. One of the key processes in the petroleum refiningand petrochemical industries is catalytic naphtha reforming, whichis used extensively to convert low-octane hydrocarbons of naphthato more valuable high-octane gasoline components without chang-ing the boiling point range [6,7]. Naphtha is a fraction of petroleum,typically constitutes 15–30% of crude oil, by weight, and boils be-tween 30 �C and 200 �C. This complex mixture consists of hydrocar-bon molecules with 5–12 carbon atoms, mainly including paraffins,olefins, naphthenes, and aromatics. Other components such as sul-fur, nitrogen, oxygen, water, salt, and a number of metal containingconstituents such as vanadium, nickel, and sodium are also exist [8].

In addition, the produced reformate in catalytic naphthareforming process includes valuable aromatics such as benzene,toluene, and xylenes (BTX) that are very important petrochemicalmaterials. Hydrogen is a valuable byproduct of catalytic naphthareforming process, which in most refineries is used for hydrocrack-ing, hydrotreating, and other hydrogen-consuming processes. Italso should be mentioned that according to the problems inducedby the energy crisis and global warming, hydrogen has the poten-tial to revolutionize transportation and, possibly, our entire energysystem [9,10].

Many researchers have investigated different aspect of the cat-alytic naphtha reforming process. These studies mainly focused onthree important issues:

1. Inventing and investigating new catalysts with better selec-tivity, stability, and performance, as well as lowerdeactivation.

2. Studying the nature of the catalytic naphtha reforming reac-tion and revealing suitable kinetic and deactivation models.

3. Suggesting reactor configurations and mode of operationswith higher yield and better operational conditions.

The moiety of these categories in accomplished studies from1949 until now is shown in Fig. 1.

In addition, the total number of existing literature and the per-centage of the aforementioned classes in different years are shownin Fig. 2a and b, respectively, in order to show the distribution ofthe publications thorough time.

2. Catalyst

Naphtha reforming catalyst is a bifunctional catalyst consists ofa metal function, mainly platinum, and an acid function, usuallychloride alumina. The metal function catalyzes the hydrogenation

catalyst49%

kinetic and deactivation

modeling27%

reactor configuration24%

Fig. 1. The percentage of the accomplished studie

and dehydrogenation reactions and the acid function promotethe isomerization and cyclization reactions [11–13]. In order toachieve an optimum performance of the naphtha reforming cata-lyst, adequate balance between these functions is needed [14].

Improving the stability and selectivity of the catalyst as well asreducing catalyst deactivation is a vital issue for enhancing the effi-ciency and yield of the process. This practice could be achieved bymodification of both acid and metal function.

Addition of components to the acid function, such as chloride,changes the strength and amount of support acid sites. Higher acidstrengths increase the acid-catalyzed coking and cracking rates[15]. Although an excessive amount of chlorine would increasethe hydrocracking reactions, carbon deposits would also increase[14].

Modification of metal function could be achieved by adding sec-ondary or ternary metal component to Pt, which is summarizedhere.

2.1. Bimetallic catalysts

The first formulation of the naphtha reforming catalyst, whichwas introduced in 1949 by UOP, consisted of monometallic plati-num supported over chloride alumina (Pt/Al2O3–Cl) [16,17]. In or-der to slow down the coking of this kind of catalyst, high hydrogenpressures were used, which are thermodynamically not favorable.The development of bimetallic catalysts permitted this hydrogenexcess to decrease considerably and improved the catalyst effi-ciency of metal [18–22]. Some of the added metals have catalyticproperties on their own (Ir, Rh, Re), while others, such as Sn, Geare catalytically inactive. The addition of second metal to Pt wasstarted in 1968 by adding Re to the metal function [23], which con-tributed to reduction in the catalyst deactivation rate and improve-ment in catalytic properties such as hydrogen uptake andenhancement in aromatic yields [24,25]. In 1969, the effect of addi-tion of Sn to the metal function was examined [26]. Addition of tinprevents coke deposition on the Pt metal particles and support, andalso enhances the selectivity to aromatics and the stability of Pt/Al2O3 [27–31]. Pt–Sn catalysts are regenerate easily, thus theyare used in the systems in which the catalyst is regenerated contin-uously [32,33]. Addition of germanium to monometallic platinum-supported catalysts was studied in 1971 [34]. This practice contrib-utes to improvement in the catalyst selectivity and stability, aswell as enhancement of the thioresistance of platinum at reactionconditions [18]. In 1976, addition of Ir and In were considered[35,36]. Pt–Ir catalysts had a strong hydrogenolytic capacity andsulfiding pretreatments had to be incorporated in the industrialpractice to prevent the dangerous exothermal runaway producedby massive C–C bond cleavage of the feedstock in the early stagesof the reaction [37]. Indium improves the resistance to deactiva-tion by coke formation and enhance the aromatization/cracking

catalyst

kinetic and deactivation modeling

reactor configuration

s of different categories from 1949 until now.

num

ber

of p

ublis

hed

pape

rs

year

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

perc

enta

ge

year

(a)

(b)

Fig. 2. (a) Total number of the published papers in different years, (b) the difference between accomplished studies of different classes through time.

M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93 81

ratio of the reforming reaction and increases the production of gas-oline [38,39].

Secondary metals have different properties. For example, rhe-nium and iridium are active metals for hydrogenolysis reactions,thus Pt–Re/Al2O3 and Pt–Ir/Al2O3 catalysts are usually presulfidedin situ during commercial practice to passivate their initial hyper-activity for exothermic demethylation reactions. In contrast, Pt–Ge/Al2O3 and Pt–Sn/Al2O3 catalysts are not presulfided becausegermanium and tin are inactive metals for naphtha reforming reac-tions. Therefore, Pt–Ge and Pt–Sn catalysts are good candidates foruse in novel low pressure naphtha reforming processes employingcontinuous catalyst regeneration because these catalysts do not re-quire complex activation procedures [40].

The addition of alternative component to the metal function re-sults in different effects such as:

� modifying the electronic state of the metal,� changing the geometry of adjacent Pt atom clusters,� changing the final Pt particle size.

These items affect the hydrogenation and dehydrogenationreaction kinetics and regulate effective size of Pt clusters, whichcontribute to better selectivity, stability, and activity of the catalyst[41–44].

2.2. Trimetallic catalysts

In order to improve the function of catalysts, the third metal hasbeen added to the bimetallic catalyst. According to our knowledge,the first attempt in preparation of three metallic catalysts for naph-tha reforming process was in 1982, in which Ge was added to Pt–Re/Al2O3 catalyst [45].

Ge addition modified the properties of the metal and acid func-tions of the bimetallic catalysts. The modification of the acidity isdue to the deposition of a part of Ge on the support. Ge was alsoadded to Pt–Ir/Al2O3 catalyst. Studies showed that Ge deposits pro-duce a greater modification of the metal function of Pt–Ir–Ge cat-alysts, as compared to Pt–Re–Ge [13]. In both cases a stronginhibition of the dehydrogenating and hydrogenolytic activityupon Ge addition is seen. Ge also modifies the acidity of the parentPt–Re and Pt–Ir catalysts.

The addition of tin to the bimetallic Pt–Ir increases the stabilityof the catalysts and also the selectivity toward toluene. Studiesshowed that the same toluene yield is obtained with Pt–Sn/Al2O3

and Pt–Ir–Sn/Al2O3 catalysts after 65 h of reaction, but less tin isneeded in the case of the trimetallic catalyst [46].

In the case of the trimetallic Pt–Re–Sn catalyst, Sn addition toPt–Re decreases the hydrogenolytic activity and increases boththe isomerization activity and the stability [47]. The best catalyst

82 M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93

is the one with 0.1% Sn. The addition of Sn to Pt–Re catalysts alsodecreases the benzene/i-C7 ratio of reformate, which is an impor-tant issue from an environmental point of view. In addition, usingPt–Re–Sn catalyst in naphtha reforming process would contributeto elimination of complicated sulfiding pretreatments [48].

The application of other trimetallic catalysts such as Pt–Re–Ir/Al2O3 and Pt–Sn-In/Al2O3 in catalytic naphtha reforming processwas also patented, which could be found in respective Refs. [49–51].

Evolution of two and three metallic catalyst for naphtha reform-ing process is presented in Table 1.

The addition of zeolite to the reforming catalyst is also a poten-tial way to improve the catalyst activity and stability and improv-ing reformer performance [53–55].

3. Reaction model

3.1. Kinetic model

Naphtha is a very complex mixture of hydrocarbons. An analy-sis of a typical naphtha feed revealed that more than 300 compo-nents are present in this hydrocarbon mixture [56]. Differentreactions occur between these components, including dehydroge-nation and dehydroisomerization of naphthenes to aromatics,dehydrogenation of paraffins to olefins, dehydrocyclization of par-affins and olefins to aromatics, isomerization or hydroisomeriza-tion to isoparaffins, isomerization of alkylcyclopentanes andsubstituted aromatics and hydrocracking of paraffins and naphth-enes to lower hydrocarbons [57,58]. Considering all of these com-ponents and their corresponding reactions in a kinetic model is acomplex problem [59,60]. Thus, ‘‘lumped’’ models have been pre-sented, in which the large number of chemical components areclassified to smaller set of kinetic lumps. In this regard, the first

Table 1Evolution of two and three metallic catalyst of catalytic naphtha reforming process.

Catalyst Year Investigator Reference

Pt/Al2O3–Cl 1949 Haensel [16,17]Pt–Re/Al2O3–Cl 1968 Kluksdahl [23]Pt–Sn/Al2O3 1969 Raffinage [26]Pt–Ge/Al2O3 1971 McCallister et al. [34]Pt–Ir/Al2O3 1976 Sinfelt [35]Pt–In/Al2O3 1976 Antos [36]Pt–Re–Ge/Al2O3 1982 Antos [45]Pt–Re–Ir/Al2O3 1985 Kresge et al. [49]Pt–Ir–Sn/Al2O3 1993 Baird et al. [52]Pt–Sn–In/Al2O3 2000 Bogdan [50]

Table 2Evolution in number of lumped components and number of reactions considered in cataly

Number of Lumped component Number of reactions

3 431 7828 8122 4035 3626 1526 4824 7117 1721 5120 3118 1717 1527 5238 86

significant attempt to model a reforming system has been madeby Smith in 1959 [61]. His model consists of three basic compo-nents including paraffins, naphthenes, and aromatics (PNA), whichundergo four reactions. In this model, which is probably the sim-plest model, each hydrocarbon class is considered as a single com-ponent with average properties of that class. After his model, otherresearchers presented more complicate models with more compo-nents and reactions. Evolution in number of lumped componentsand number of reactions considered in catalytic naphtha reformingkinetic is presented in Table 2.

In 1959, Krane et al. [74] investigated the presence of varioushydrocarbons in the whole naphtha. This model consists of a reac-tion network of twenty different components, containing hydro-carbons from C6 to C10. He also recognized the differencebetween paraffins, naphthenes, and aromatics within each carbonnumber group. Henningsen and Bundgaard-Nielson [75] refinedKrane’s model in 1970. He also reported the frequency factorsand activation energy values of different reforming reactions ofC8 naphtha, and revealed that a linear relation exist between cata-lyst activity and reactor inlet temperature. In 1972, Kmak [76] usedLangmuir–Hinshelwood kinetics to describe the catalytic naphthareactions for the first time. He also studied reforming over a widerange of operating conditions using pure components, mixturesand naphtha feed and developed a detailed model in 1973 [77].In 1980, Zhorov et al. [78] considered C5, C6 lumps of naphthaand direct formation of aromatics from paraffins. Marin et al.[79] modified Kmak’s model in 1983. They used Hougen-Watson-type rate equations and suggested a kinetic model containinghydrocarbons with C5 to C10 carbon numbers. Ramage et al.[80,81] studied the nature of catalytic naphtha reforming reactionand presented detailed complete model considering C6–C8 lumpsof naphthenes, paraffins and aromatics in 1980 and 1987. They de-scribed different reactive particular raw materials in his model andconsidered the deactivation of the catalysts due to the coke forma-tion, which modified the process kinetics. Although, they publisheda detailed kinetic model based on extensive studies of an industrialpilot-plant reactor, only short range of hydrocarbons of C6–C8 wereconsidered in their model. In 1989 Bommanna and Saraf [82] re-ported the approximate values of activation energies according tothe plant data. Ancheyta-Juarez and Villafuerte-Macias [58] con-sidered the reactions in terms of isomers of the same nature (par-affins, naphthenes and aromatics) and developed a new kineticmodel in 2000. In 2003, Rahimpour et al. [72] considered C6–C9

hydrocarbons to simulate catalytic naphtha reformer. Klein et al.[83,84] built and customized reforming reaction network usingthe Kinetic Model Editor (KME) software in 2008. They also en-hanced the Kinetic Modeler’s Toolbox (KMT) and developed the

tic naphtha reforming kinetic.

Year Investigator Reference

1959 Smith [61]1980 Jenkins et al. [62]1987 Froment [63]1994 Saxena et al. [70]1997 Taskar et al. [64]1997 Vathi et al. [69]1997 Padmavathi et al. [73]2000 Ancheyta et al. [58]2004 Hu et al. [65]2004 Hu et al. [168]2006 Weifeng et al. [67]2006 Weifeng et al. [66]2009 Arani et al. [68]2010 Hongjun et al. [71]2012 Wang et al. [166]

Smith (1959) [61]

Hu et al. (2004) [65]

Hongjun et al. (2010) [71]

Fig. 3. Examples of some reaction networks presented for catalytic naphthareforming reaction.

M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93 83

Kinetic Model Editor (KME) which presents an end-to-end solutionto the kinetic modeling process, including automated feedstockmodeling, reaction network construction, kinetic rate estimation,model programming, process system configurations, model cust-omizations, compilations, model execution and results analysis.In 2009, Boyas and Froment considered the equilibriums of hydro-genation and dehydrogenations in their model [85]. Stijepovic et al.[56] recommended a semi-empirical kinetic model for catalyticreforming and considered the most important reactions of the cat-alytic reforming process in their kinetic model in 2009. In 2010,Hongjun et al. [71] suggested a lumped kinetic model with 27lumps in order to predict aromatic compositions in more detail.In 2011, Rodríguez and Ancheyta [57] modified Krane’s model,and proposed a model in which the simplicity of the lumping-based models is combined with the complexity of the most ad-vanced model. The presented reaction networks of some of thesestudies are illustrated in Fig. 3.

Many other attempts are also done in this field that can befound in the respective references.

It should be noticed that a simple model with few lumps maynot be able to represent the desired situation, nevertheless, choos-ing a complex model is not profitable because huge amount ofexperimental information is needed to determine the modelparameters, which is a time- and money-consuming task. Thus, asuitable model is that one which despite simplicity is able to pre-dict the situation properly.

3.2. Catalyst deactivation model

The yield of catalytic naphtha reforming process dependsstrongly on the catalyst properties. During operation, the catalystundergoes physiochemical changes, which contribute to decreasein the activity for aromatic production.

The causes of the catalyst deactivation can be categorized intofour main groups [86,87]:

� Poisoning due to chemisorption of some impurity (such asheavy metals).� Erosion and breakage.� Hydrothermal aging, that is, loss of surface area (metallic area

and support area).� Coke deposition.

The first three reasons are irreversible while the fourth isreversible and the coke deposit could be removed from thecatalyst.

In the catalytic naphtha reforming process, coke formation isthe most important cause of the catalyst deactivation [88].Although coke is formed in both acid and metal sites, it has beendemonstrated that the main fraction of the coke is deposited overacid sites [89,90]. Prediction of coke formation is a very complextask because this phenomenon depends on various parameterssuch as operating conditions, oil feed composition, and catalystproperties [91].

Operating conditions strongly affect the coke formation. Thisparameter mainly includes the partial pressure of hydrogenand hydrocarbon, time on stream, gas–oil feed flow, and thereaction temperature. The influence of these factors on coke for-mation in the commercial process has been described by severalauthors.

Bishara et al. [92] investigated the effect of operating conditionson catalyst deactivation as well as the yield and quality of refor-mate for naphtha reforming over an industrial bimetallic reformingcatalyst. In their study, the aromatics yield showed a maximum inthe pressure range 7–10 bar, while the carbon deposition de-creased with increasing pressure. Increase in temperature led to

an increase in the yield of aromatics at the expense of reformates.Hydrogen: hydrocarbon ratios (H2/HC) in the range 7–12.7 did notshow any pronounced effect on reformate or aromatics yield, how-ever, lower H2/HC ratios (e.g.: 3.6) gave decreased aromatics andincreased carbon.

Figoli et al. [93] studied the influence of total pressure andhydrogen: hydrocarbon ratio on coke formation over naphtha-reforming catalyst. According to the obtained results, they con-cluded that the decreasing of the total pressure and of the hydro-gen to naphtha ratio produces the increment of the cokeformation over Pt/Al2O3. Critical values below which there is agreat increment of the amount of coke and its degree of polymer-ization exist.

Barbier [94] reported that decrease in pressure induces an in-crease in toxicity for the metallic activity, measured by the ben-zene hydrogenation reaction, due to the increase in metal coking.The increase in operating pressure contributes to less coke deposi-tion on the metal function and higher stability, which is similar tothe effect of addition of Re or Ir to Pt. This is why the bimetallic cat-alysts can be operated at lower pressure than the monometallic tohave the same rate of deactivation. He also showed that the changeof the coking temperature does not alter the nature and location ofcoke on a Pt/A12O3 catalyst. The small influence of temperature isreflected in low activation energy of coking, which is typical of areaction controlled by diffusion and migration of the coke precur-sors from the metal to the support. The time of operation at severeconditions produces an increase in the amount of coke on the

Table 3Some of the presented catalyst deactivation models in catalytic naphtha reforming reaction.

Deactivation model Researcher Reference

%C = 4.99 � 106 e�8955/T P�0.94WHSV�1.28(H2:naphtha)�1.33 Figoli et al. [104]

rcðtÞ ¼ dCKdt ¼ kc � expð�Ec=WAIT=RÞ � Aa

r � Pbh � ðTFEL=T0Þc � v � expð�a � CKÞ Hu et al. [106]

dadt ¼ �Kd exp � Ed

R1T � 1

TR

� �� �a7 Rahimpour [102]

rcoke ¼ A:P�1H2� P0:75

feed � coke�1 � expð�37;000=RTÞ Mieville [100]

%C = k � P�0.7 Barbier [94]%C ¼ 12:67� 0:248BP þ 0:001244BP2 Figoli et al. [95]cC = k � t1/n Barbier [96]Carbon on catalyst, Wt% = 104.7 (H/HCmol ratio)�1.68 Bishara et al. [92]dC=dt ¼ ðkppp þ kApAÞpn1

H2Cn2 aC Schroder et al. [99]

%C = 7.71P�0.96 Figoli et al. [93]dC=dt ¼ rc

�expð�aCÞ Vathi et al. [69]

Ccat ¼ kC

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffitCCn

rcexp �Ecf

RT1

� �rHovd et al. [103]

Coke ¼ gðZ1; . . . ; ZnÞðC=OÞnðWHSVÞn�1eDEC=RTrx Sadeghbeigi [101]

%C ¼ 0:30P1:54P þ 0:01P1:86

N þ 0:85P2:84A þ 0:97� 10�16BP7:56 Figoli et al. [95]

ra ¼ daadt ¼ 5:0� 106e�32;000=RT aaC0:5

ACPTailleur et al. [105]

rm ¼ damdt ¼ 1:2� 104e�25;000=RT amC0:5

ACP1þ0:000809PH2

rcðzi; tjÞ ¼ dCdt ¼

PJk¼1ajkCðzi; tkÞ Pauw et al. [160]

Cðzi; tÞ ¼ 1aD;C

ln 1þ eaD;C Cðzp ;sÞ�1s

� �t

h i

� dadt ¼

kD bA C2A

1þbA CAþbE CE

a�aS1�aS

Ostrovskii [165]

dCdw ¼

Ae�E=RT PACPP2

H2us

expð�aCÞLiu et al. [169,170]

84 M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93

support similar to the increase produced by a decrease in the spacevelocity and the hydrogen-to-naphtha ratio at constant pressure.

In naphtha reforming, as in other hydrocarbon processes, thecharacteristics of the feedstock strongly influence the catalystperformance. Heavier cuts are cheaper but produce more coke,making selection of the optimum cut points a compromise. Oilfeed composition, especially the relative quantities and structureof alkanes, alkenes, naphthenes, aromatics, heterocycles, etc., aswell as the presence of impurities (metals, especially Ni) shouldbe considered in the deactivation model of the naphtha reformingcatalysts.

Figoli et al. [95] investigated the influence of mean boiling pointBP and composition of the feedstock on naphtha reforming catalystactivity and stability. They found that cuts of very low or very highBP produced higher coke depositions and catalyst deactivations.When cuts of very high BP were used, only a very low increase inthe octane number occurred during reforming. Such cuts had ahigh content of aromatics of high molecular weight, and the mainreforming reaction was the aromatics dealkylation to products oflower octane number.

Bishara et al. [92] studied the effect of feed composition on cat-alyst deactivation by using several naphtha blends having a widevariation in the paraffin, naphthene and aromatics content. Theyconcluded that at any reforming severity, yields of reformate andaromatics are higher and coke deposition is lower for a naph-thene-rich naphtha.

The coke rate also depends widely on the catalyst propertiesincluding the number, type and accessibility of the catalyst activecenters, which depend in turn on other more elementary variables,such as composition, preparation, as well as internal structure andpore size.

Barbier [96] reported that the deposited coke on the metal isless dehydrogenated than the deposited coke on the support.According to his results, for platinum catalysts small metallic par-ticles are less sensitive to coke formation than larger particles. Inaddition, the amount of coke deposited on the metallic functionof a bifunctional catalyst always corresponds to a small fractionof the amount of coke accumulated on the whole of the catalyst.

Mazzieri et al. [97] studied the deactivation by coke depositionand sintering and the regeneration of the metal function of Pt–Re–Sn/Al2O3–Cl and Pt–Re-Ge/Al2O3–Cl catalysts. They found that thePt–Re–Sn catalysts were more stable than the Pt–Re-Ge ones. Thiswas due to the lower amount of coke deposited on the surface ofPt–Re–Sn.

Macleod et al. [98] compared the deactivation of a number ofbi- and multi-metallic reforming catalysts including Pt–Re, Pt–Ir,Pt–Sn, Pt–Ge and Pt–Ir–Ge. Addition of Ge (or Sn) to Pt, Ir or Pt–Ir catalysts dilutes the active metal surface. This geometric effectimproves the selectivity of the catalyst and increased its resistanceto deactivation. The formation of bulk Pt–Ge, Pt–Sn and Pt–Ir–Gealloys contribute to the overall rate of deactivation of these sys-tems. Both Pt–Ir and Pt–Re are highly resistant to deactivation.Metallic Ir and Re provided sites for the hydrogenation/hydrogen-olysis of coke fragments and therefore reduced the rate of deacti-vation of these catalysts.

Quantitative correlations are developed for these observationsby different researchers. Some of these relations are summarizedin Table 3.

4. Reactor configurations and process classification

Naphtha reforming unit is one of the main units of petroleumrefining that is used extensively to convert paraffins and naphth-enes to aromatics. Because of the industrial importance of this pro-cess, researchers have studied the design aspect widely to findappropriate configurations to enhance the production of the de-sired products. Various types of reactor and different mode of oper-ation have been suggested which are summarized here.

4.1. Suggested reactor configuration

Various reactor configurations with different advantageous anddisadvantageous have been proposed. These configurations couldbe categorized according to the shape of the reactor and the en-trance flow pattern of the feedstock as follow:

Fee

dto

the

firs

tre

act

or

T=775K

Furnace

T=777K

R-2

R-3

Valve

Flash drum

Stabilizer

P-30

Reboiler

Vapor

Reformate

Condenser

Reflux drum

LPG

Off gasT=777K

R-1

Fresh naphtha feed

Recycled hydrogenHydrogen

Fig. 4. Schematic diagram of axial-flow tubular fixed-bed reactor.

Table 4Estimated volume percent of different components in the feedstock and the productof the catalytic naphtha reforming unit.

Component Feed (vol%) Product (vol%)

Normal paraffins 40–50 20–35Iso-paraffins 2–5 10–15Olefins 0–2 0Naphthenes 30–40 5–10Aromatics 5–10 45–60Hydrogen 0 2

M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93 85

� Axial-flow tubular reactor.� Radial-flow tubular reactor.� Axial-flow spherical reactor.� Radial-flow spherical reactor.

Numerous research efforts have been focused on improving theefficiency and operating conditions of these reactor configurations.These efforts mainly include using membrane to remove hydrogenfrom reaction media, suggesting reactors with lower pressure drop,and using coupled reactor to reduce the capital and operationalcost.

Membrane reactor is a combination of chemical reactor andmembrane and is used in reaction systems in which removingreaction products from reaction media or adding of reactants alongthe reactor is beneficial [107–109]. This effective configuration hasvarious advantages such as increasing reaction rate, reducing byproduct formation, requiring lower energy, and relatively safeoperating [110,111]. According to thermodynamic equilibrium, ifthe reactants were removed from the product gases, chemical reac-tants would shift to products. Considering this fact, researchers de-signed Pd based membrane reactors in catalytic naphtha reformingto remove hydrogen from reacting gases.

Presenting configurations with lower pressure drop also at-tracts much attention because it has significant effects on the yieldand the operational conditions of the process. This parameter playsan important role in the gas-phase reactions, because the concen-tration of reactants and consequently the reaction rates and con-versions are affected by change in the total pressure.

Making exothermic and endothermic reactions proceedingsimultaneously in one reactor is an interesting idea to use the ther-mal energy of the exothermic reaction as the heat source of theendothermic reaction [112,113]. The efficient coupling of exother-mic and endothermic reactions contributes to saving energy andconsequently reducing the capital and operational cost that ishighly demanded in our recent world [114–116].

The aforementioned issues could be considered in the design ofthe reactor of naphtha reforming process in different manners.

4.1.1. Axial-flow tubular reactorA schematic process diagram of axial-flow tubular fixed-bed

reactor setup for catalytic naphtha reforming reaction is shownin Fig. 4 [117,118]. The core of this process is consists of three orfour fixed-bed adiabatically operated reactors in series.

The naphtha feedstock is combined with a recycle gas streamcontaining 60–90 mol% hydrogen. This mixture is heated, at firstby exchange with effluent from the last reactor and then by heatexchanger. The inlet temperature of the beds is mostly adjustedbetween 750 and 790 K, and operating pressure is about 3.5 MPa.

Naphtha reforming is an endothermic reaction and contributesto temperature drop in the reactors. Thus, catalytic naphthareformers are designed with multiple reactors and with heaters be-tween the reactors to maintain reactor temperature at desired lev-els. The effluent from the last reactor is cooled and entered theseparator, in which hydrogen and some of the light hydrocarbonsseparate from each other. The flashed vapor is passed to a com-pressor and then combined with the naphtha charge with H2/HCratio in the range of 4–6. The obtained liquid from separatormostly comprised of desired reformate product but light gasesare also exist. Therefore, this liquid is sent to a stabilizer. Refor-mate of the bottom of the stabilizer is sent to storage for gasolineblending. The estimated volume percent of different componentsin the feedstock and the product of the catalytic naphtha reformingunit are presented in Table 4.

Membrane concept can be assisted in the axial-flow tubularreactors for selective separation of hydrogen that results in betterperformance and higher yield [119]. The fixed-bed membranereactor is made up of two concentric pipes. The inner pipe is filled

H2

NaphthaFeedstock

Products

carrierhydrogen gas

carrierhydrogen gas

Fig. 5. Schematic diagram of fluidized bed membrane reactor.

NitrobenzeneFeed

NaphthaFeed

Catalyst of Endothermic Side

Catalyst of Exothermic Side

Fig. 6. Schematic diagram of coupled reactor in co-current mode of operation.

Products

Naphthafeed

Fig. 7. Schematic diagram of radial-flow tubular packed-bed reactor.

Pd-AgMembrane

PerforatedScreen

CatalystParticle

Inlet NaphthaFeed

Axial Flow of Sweep Gas

PermeatedHydrogen

Radial naphthafeed

Axial sweepgas

Membrane layerCenter pipe

Catalyst particle

Fig. 8. Schematic diagram of radial-flow tubular membrane packed-bed reactorwith axial-flow of sweeping gas.

86 M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93

with catalyst in which catalytic reaction occurred, and hydrogenflows through the shell side. The inner tube supports a dense filmof Pd–Ag and the outer one is the non-permeable shell. Hydrogenpermeates along the reactor in order to control amount of hydro-gen for better operation and efficiency.

The disadvantages of fixed-bed reactors are poor heat transferand low catalyst particle effectiveness factors. Catalyst particleshave severe diffusional limitations due to their size and smallerparticle sizes are infeasible in fixed-bed systems because of pres-sure drop considerations [120].

Using a fluidized bed reactor is a promising way to overcomethe catalyst particle size limitations of fixed-bed reactor. Fluidizedbed membrane reactor is a multifunctional reactor that combinesthe advantages of a membrane and a fluidized bed reactor. Thisconfiguration has main advantages such as isothermal operation,arrangement of the membrane package and flexibility in mem-brane and heat transfer surface, and negligible pressure drop [121].

The benefits of this concept over conventional fixed bed config-uration are the absence of radial and axial temperature gradientsdue to the excellent heat transfer characteristics of fluidization[122,123]. In this configuration, the mass and heat transfer occursimultaneously between both sides and product yield improves be-cause of hydrogen permeation that is due to hydrogen partial pres-sure gradient. In order to fluidize the catalyst bed, the reacting gasis entered into the bottom of the fluidized-bed in a co-current flow

mode with the carrier hydrogen gas in shell. A schematic diagramof this configuration is shown in Fig. 5 [124].

In a novel thermally coupled reactor, the naphtha reforming,which is an endothermic reaction, was coupled with hydrogena-tion of nitrobenzene to aniline to use its generated heat as a heatsource [125,126]. Co-current mode of operation for coupled reac-tors is presented in Fig. 6. In this setup, the first two reactors inthe packed-bed configuration have been substituted with the

Fig. 10. Schematic diagram of axial-flow spherical packed-bed reactor.

M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93 87

highly efficient recuperative reactors. Catalytic reforming takesplace in the shell side whereas the exothermic hydrogenation ofnitrobenzene to aniline, which provides the heat for reforming pro-cess, occurs in the tube side.

Catalytic naphtha reforming has also been coupled with hydro-dealkylation of toluene in a fixed bed reactor [127].

As mentioned, fluidized bed reactors have been used widely inthe chemical and petroleum industries because of their numerousadvantages. Coupling of the naphtha reforming and hydrogenationreaction of nitrobenzene to aniline is also investigated in a fluid-ized bed reactor [128].

4.1.2. Radial-flow tubular reactorRadial-flow reactors have been used widely for different reac-

tion systems due to various advantages such lower pressure dropand higher yield [129–131]. Radial-flow pattern has also been usedin a tubular fixed bed reactor for naphtha reforming process [132].As shown in Fig. 7 this reactor consists of three concentric tubes.The reaction takes place in the middle tube, which is packed bycatalyst. The outer annulus is filled by the naphtha feed, which isdistributed uniformly over the packed bed, while the inner annulusis used as a collector to collect the products. It should be noticedthat the flow in the outer and inner annulus is in axial direction,but the flow pattern in the bed of catalytic particle is radial.

Membrane concept can also be assisted in the radial-flow tubu-lar reactors to improve the performance of the catalytic naphthareforming process. In this reactor configuration, the naphtha feedflows radially while the sweeping gas could flow in radial or axialdirection [117,133,134]. Fig. 8 shows the radial-flow tubular mem-brane reactor in which the naphtha feed flows radially through thepacked bed, whereas the sweeping gas flows axially in the gaps(shell side).

4.1.3. Radial-flow spherical reactorSpherical reactor configuration has been investigated widely as

a suitable alternative to conventional tubular reactors [135–138].This reactor setup has various advantageous respects to packedbed reactor such as lower pressure drop, smaller catalytic pelletswith higher effectiveness factor, and lower required material thick-ness [139]. This reactor configuration has been used in naphthareforming process in both axial-flow and radial-flow mode.

A schematic diagram of the radial-flow spherical packed-bedreactor is shown in Fig. 9 [140,141]. This configuration consists

Fig. 9. Schematic diagram of radial-flow spherical packed-bed reactor.

of two concentric sphere. The catalyst is charged in the space be-tween these spheres. The feed gas enters the reactor and flowsfrom the outside through the catalyst bed into the inner sphere.The radial-flow in the spherical reactor offers a larger meancross-sectional area and reduced distance of travel for flow com-pared to traditional vertical columns.

4.1.4. Axial-flow spherical reactorRadial-flow spherical reactor encounter challenges such as dif-

ficulty in applying membrane concept and problems in feed distri-bution [142]. These drawbacks are revamped in axial-flowspherical packed bed reactor.

In the Axial-flow spherical packed-bed reactor, catalysts areplaced between two perforated screens. As depicted in Fig. 10[143], the naphtha feed enters the top of the reactor and flowssteadily to the bottom of the reactor. Achieving a uniform flow dis-tribution through the catalytic bed is important because the flow ismainly occurring in an axial direction. Two screens are placed inupper and lower parts of the reactor to hold the catalyst and actas a mechanical support.

Membrane technology can be easily used in axial-flow sphericalreactor. The main difference between this setup and the previousone is that the inner sphere is coated by a hydrogen perm–selectivemembrane layer. Hydrogen permeates through the Pd–Ag mem-brane layer to the shell side and the sweeping gas carries the per-meated hydrogen. Thus, According to the Le Chatelier’s Principle,the reaction shiftes toward the product side, and higher productyields are achieved [144,145].

4.2. Process classification

Catalytic naphtha reforming units are usually categorizedaccording to the catalyst regeneration procedure. These procedurescould be categorized in three main groups:

1. Semi-regenerative catalytic reformer (SRR).2. Cyclic catalytic reformer.3. Continuous catalyst regeneration reformer (CCR).

Worldwide, the semi-regenerative scheme dominates reform-ing capacity at about 60% of total capacity followed by continuousregenerative at 28% and cyclic at 12% [146].

88 M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93

4.2.1. Semi-regenerative catalytic reformerThe most commonly used type of the catalytic reforming unit is

SRR. This process is characterized by continuous operation overlong periods, with decreasing catalyst activity due to coke deposi-tion. By decreasing the activity of the catalyst, the yield of aromat-ics and the purity of the byproduct hydrogen decrease. In order tomaintain the conversion nearly constant, the reactor temperatureis raised as catalyst activity decline. When the reactors reachend-of-cycle levels, the reformer is shut down to regenerate thecatalyst in situ. Different criteria may be used to determine theend-of-cycle levels such as the reactor metallurgy temperaturelimit, prescribed weighted average inlet temperature (WAIT) in-crease, specified amount of C5+ yield decline, specified amount ofhydrogen decline, and refinery and reformer economics. To maxi-mize the length of time (cycle) between regenerations, these earlyunits were operated at high pressures because high reactor pres-sure minimizes deactivation by coking. The shutdown of this unitoccurs approximately once each 6–24 months. Research octanenumber (RON) that can be achieved in this process is usually inthe range of 85–100, depending on an optimization between feed-stock quality, gasoline qualities, and quantities required as well asthe operating conditions required to achieve a certain planned cy-cle length.

The Pt–Re catalyst is usually used in SRR units because it toler-ates high coke levels and regenerates easily. These catalysts enablea lower pressure and higher severity operation.

Semi-regenerative reformers are generally built with three tofour catalyst beds in series. The fourth reactor could be added toallow an increase in either severity or throughput while maintain-ing the same cycle length. A schematic diagram of SRR unit isshown in Fig. 4, and all of the aforementioned reactor configura-tions have been proposed for this process.

4.2.2. Cyclic catalytic reformerIn the cyclic catalytic reformer unit, an extra spare or swing

reactor is exist, which, as well as other reactors, can be individuallyisolated. Thus, each reactor can be undergoing in situ regeneration

Fig. 11. Schematic process diagram of continuous catalyst regeneration refo

while the other reactors are in operation. In this way, only onereactor at a time has to be taken out of operation for regeneration,while the reforming process continues in operation. In this process,low operational pressure, wide boiling range feed, and low hydro-gen-to-feed ratio may be used, which contributes to high deactiva-tion rate of the catalyst. Thus, catalyst in individual reactors couldbecome exhausted in time intervals of from less than a week to amonth. The research octane number in this process is in the rangeof 100–104.

Low operational pressure and less variation of the overallcatalyst activity, conversion, and hydrogen purity with time re-spect to the semi-regenerative process are the main advanta-geous of the cyclic process. A drawback of this process is thatall reactors alternate frequently between a reducing atmosphereduring normal operation and an oxidizing atmosphere duringregeneration. This switching policy needs a complex processlayout with high safety precautions and requires that all thereactors be of the same maximal size to make switches be-tween them possible.

However, the cyclic catalytic reformer units are not very com-mon, and rarely are used for naphtha reforming process.

4.2.3. Continuous catalyst regeneration reformerCCR is the most modern type of the catalytic reformers. The

continuous process represents a step change in reforming technol-ogy compared to semi-regenerative and cyclic processes. In thisunit the catalyst regenerates continuously in a special regeneratorand adds to the operating reactors. The advantages of CCR processagainst traditional methods are [147–150]:

– Production of higher octane reformate even working with alow feed quality.

– Long time working of the process for hydrogen demand.– Using catalyst with less stability but higher selectivity and

yield.– Lower required recycle ratio and the lower operational pres-

sure with high yield of hydrogen.

rmer (CCR) (in which reactors are placed separately behind each other).

Naphtha feed

Spent Catalyst

Reformate to storage

Hydrogen Rich Gas

Com

bine

d Fe

ed E

xcha

nger

CC

R R

egen

erat

or

RegeneratedCatalyst

Off Gas

Sepa

rato

r

stab

ilize

r

Fig. 12. Schematic process diagram of continuous catalyst regeneration reformer (CCR) (in which reactors are stacked on top of one other).

Naphtha Feed

Products

Catalyst out

Catalyst in

Fig. 13. Schematic diagram of axial-flow tubular rector in CCR process. Naphthafeedstock

Spentcatalyst

Spentcatalyst

Freshcatalyst

Freshcatalyst

product product

Fig. 14. Schematic diagram of radial-flow tubular rector in CCR process.

M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93 89

This process could be designed in different manners. Reactorsmay be placed separately behind each other or stacked on top ofone other, as shown in Figs. 11 and 12, respectively.

The catalyst moves from the bottom of one reactor to the top ofthe next reactor. The regenerated catalyst is added to the first reac-tor and the spent catalyst is withdrawn from the last reactor andtransported back to the regenerator. The design reformate octanenumber in this process is in the 95–108 range.

The used catalyst in CCR process is mainly of the platinum/tinalumina type because addition of tin enhances the selectivity toaromatics, stability, and regeneration ability of Pt/Al2O3 [32–36].It should mentioned that in CCR unit, catalyst regenerates contin-uously, thus, selectivity to aromatics of the catalyst is more

important than its resistance to deactivation, while in SRR unit, de-spite the ability to increase the yield of the process, catalyst shouldbe able to tolerates high coke levels.

It should be mentioned that only axial- and radial-flow tubularrector have been suggested for this type of reforming unit whichare presented in Figs. 13 and 14, respectively [151,152].

Finally, some of the published modeling of the catalytic naphthareforming unit is presented in Table 5. The possibility of comparingthe operational conditions such as temperature and pressure indifferent mode of operations as well as the catalyst, the reactorconfiguration, and the kinetic model is prepared via this table.

Table 5Some of the published modeling of the catalytic naphtha reforming units.

Mode ofoperation

Reactor configuration Number ofreactors

Reactionmodel

Catalyst Temperature Pressure Author Reference

SRR Radial-flow tubular reactor 4 Smith Pt–Re/Al2O3 468–521 �C 1.408–1.730 MPa

Liang et al. [153]

SRR Axial-flow thermally coupled membranetubular reactor

3 Smith Pt–Re/Al2O3 775–777 K 3.4–3.7 MPa Pourazadi et al. [154]

SRR Axial-flow fluidized bed membrane tubularreactor

3 Smith Pt–Re/Al2O3 775–777 K 3.4–3.7 MPa Rahimpour [124]

SRR Axial-flow tubular reactor 1 – Pt/Si–Al2O3 847–904 K 200–600 psig Barker et al. [173]SRR Axial-flow tubular reactor 4 – Pt–Re/g/

Al2O3480–510 �C 1.5–3 MPa Muktar et al. [174]

SRR Axial-flow fixed bed tubular reactor 3 Padmavathi Pt–Re/Al2O3 773 K 3.7 MPa Behin et al. [155]SRR Axial-flow thermally coupled fluidized-bed

tubular reactor3 Smith Pt–Re/Al2O3 775–777 K 3.4–3.7 MPa Pourazadi et al. [171]

SRR Axial-flow tubular reactor 3 Smith Pt–Re/Al2O3 775–777 K 3.4–3.7 MPa Fathi et al. [172]SRR Axial-flow tubular reactor 1 Schroder Pt–Re/cAl2O3 753–773 K 1.0–1.5 MPa Schroder et al. [99]SRR Axial-flow fixed bed tubular reactor 3 Ancheyta Pt–Re 510 K 10.5 kg/cm2 Ancheyta et al. [156]SRR Radial-flow tubular reactor 3 Smith Pt–Re/Al2O3 775–777 K 3.4–3.7 MPa Rahimpour et.al [142]SRR Axial-flow fixed bed tubular reactor 3 Tailleur PtReCl/Al2O3 740–780 K 3.8 MPa Tailleur et al. [105]SRR Axial-flow thermally coupled reactor 3 Smith Pt–Re/Al2O3 775–777 K 3.4–3.7 MPa Meidanshahi

et al.[127]

SRR Axial-flow tubular reactor 4 – Pt–Re/Al2O3 479 �C 13 kg/cm2 Otal et al. [157]SRR Axial-flow fixed bed tubular reactor 3 Taskar – 750–790 K 2–3 MPa Taskar et al. [64]SRR Radial-flow membrane tubular reactor 3 Smith Pt–Re/Al2O3 775–777 K 3.4–3.7 MPa Iranshahi et.al [117]SRR Axial-flow tubular reactor 3 – Pt/Al2O3–Cl 485–520 �C 30 kg/cm2 Sad et al. [176]SRR Axial-flow membrane tubular reactor 3 Smith Pt–Re/Al2O3 775–777 K 3.4–3.7 MPa Khosravanipour

et.al[119]

SRR Radial-flow tubular fixed bed reactor 3 Mohaddecy Pt–Re/Al2O3 497–515 �C 0.31 MPa Mohaddecy [158]SRR Axial-flow tubular reactor 3 Arani Pt–Re/Al2O3 931 K 2.6–2.9 Mpa Arani et al. [68]SRR Axial-flow fixed bed tubular reactor 1 – Pt–Re/Al2O3 540 �C 6–10 bar Ren et al. [88]SRR Combination of spherical and membrane

tubular reactors3 Smith Pt–Re/Al2O3 775–777 K 3.4–3.7 MPa Rahimpour et al. [159]

SRR Axial-flow tubular reactor 3 Hu Pt–Re/Al2O3 766 K 206 psia Hu et al. [168]SRR Axial-flow tubular reactor 3 – Pt–Re/Al2O3 511.0–

515.2 �C29 bar Adzamic et al. [175]

SRR Radial-flow spherical packed bed reactor 3 Smith Pt–Re/Al2O3 775–777 K 3.4–3.7 MPa Iranshahi et.al [141]SRR Axial-flow tubular reactor 1 – Pt/c-Al2O3 388–436 �C 1.54–

2.76 atm abs.Pauw et al. [160]

SRR Axial-flow spherical membrane reactor 3 Smith Pt–Re/Al2O3 775–777 K 3.4–3.7 MPa Iranshahi et.al [161]SRR Axial-flow tubular packed bed reactor 1 – Pt–Sn/Al2O3 515 �C 8 bar Margitfalvi et al. [162]CCR Fully thermally coupled distillation column 2 – Pt–Sn/Al2O3 84–170 �C �0.17 MPa Lee et al. [163]CCR Radial-flow tubular reactor 4 Hu Pt–Sn/Al2O3 520 �C 0.35 MPa Hu et al. [106]CCR Stacked radial-flow reactor 4 Hongjun Pt–Sn/A12O3 412–505 �C �1 Mpa Hongjun et al. [71]CCR Radial-flow tubular reactor 3 Stijepovic Pt–Sn/A12O3 733 K 0.35 Mpa Stijepovic et al. [151]CCR Stacked axial-flow reactor 4 Weifeng Pt–Sn/A12O3 515–528 �C 0.5 MPa Weifeng et al. [66]CCR Stacked radial-flow reactor 4 Gyngazova Pt–Sn/Al2O3 520 �C 0.7 Mpa Gyngazova et al. [152]CCR Axial-flow tubular reactor 4 Smith Pt–Sn/Al2O3 790 K 10.3 bar Lid et al. [164]CCR Axial-flow tubular reactor 3 Padmavathi Pt–Sn/Al2O3 519 �C 0.54 MPa Mahdavian et al. [148]CCR Axial-flow tubular reactor 4 Smith Pt–Sn/Al2O3 503 �C 23.5–28.5 bar Askari et al. [167]CCR Axial-flow tubular reactor 1 – Pt–Sn/Al2O3 515 �C 8 bar Margitfalvi et al. [162]CCR Circulating fluidized bed membrane

reformer1 – Pt–Re/Al2O3 823 K 1013 kPa Chen et al. [86]

CCR Axial-flow tubular reactor 4 Wang Pt–Sn/Al2O3 516 �C 0.5 MPa Wang et al. [166]

90 M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93

5. Suggestions

Although many investigators have been studied different as-pects of catalytic naphtha reforming process and huge amount ofpapers have been published about this issue, more researches areneeded to characterize the nature of the reaction and revampingthe yield of this process. As a guideline for further investigations,various suggestions have been proposed here.

1. Various kinetic models with different number of lumpedcomponents and reactions have been proposed for catalyticnaphtha reforming reaction. Although considering simplemodels may reduce the accuracy of the modeling, consid-ering a very complex model may have no considerableeffect on the final results. Thus a comparative study isneeded to find out the proper and optimize number ofthe lumped components and reactions.

2. More experimental efforts are needed to assess the pro-posed kinetic model and the results of the reactor modeling.

3. In most of the studies, the reactors are modeled in one-dimensional direction (only axial direction has been consid-ered) while considering other directions (such as radialdirection) may have considerable effect on the obtainedresults. It is suggested to compare the differences betweenone-dimensional and two-dimensional modeling in orderto specify the proper assumptions of the modeling.

4. Most of the presented reactor models are homogeneousmodels, while catalytic naphtha reforming reaction is a het-erogeneous process inherently. It is better to study this pro-cess as a heterogeneous reaction in future studies andinvestigate the differences between these two models.

5. Fewer studies are accomplished on modeling of CCR unitcompared to SRR. Due to the superior features of this unit,more studies are needed to assess this mode of operation.

M.R. Rahimpour et al. / Applied Energy 109 (2013) 79–93 91

Investigating the application of various reactor configura-tions such as membrane reactors and thermally coupledreactors in CCR unit is a novel idea.

6. Conclusion

Catalytic naphtha reforming is one of the backbone processes inrefining industries. This process is used widely for production ofhigh-octane gasoline and aromatic components. Various investiga-tors have been studied different aspects of the naphtha reformingprocess due to the importance of this industrial process.

Finding a suitable catalyst with higher selectivity and stabilityand lower coking and deactivation comprise an extensive part ofthese studies. To achieve this purpose, various components havebeen added to the metal and acid function of the catalyst.Presenting a proper kinetic model with appropriate amount ofcomponents and reactions, and deactivation model involving theaffecting parameters attracts much attention too. Another signifi-cant field study is finding an efficient reactor configuration. Thesuggested reactors are tubular or spherical reactors and thefeedstock may flow in axial or radial direction. Different modesof operations are presented for a catalytic naphtha reforming unitincluding semi-regenerative catalytic reformer (SRR), cyclic cata-lytic reformer, and continuous catalyst regeneration reformer.SRR is the most commonly used type of the catalytic reformingunit, but due to the better performance of CCR, all new units aredesigned based on this technology and old units are revamped tothe continuous process or combination of both.

Aforementioned topics have been investigated widely andmany articles have been published concerning them. Searchingamong these huge papers may be a confusing and time confusingtask for those who want to have collective information aboutnaphtha reforming process. In this paper, the established paperson catalytic naphtha reforming process were reviewed, and the ob-tained results of the impressive studies in this field were presentedin tables. In addition, suggestions are presented as a guideline forfurther investigations.

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