progress in catalytic naphtha reforming process: a review

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: [email protected], [email protected] (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, Iran b 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 2012 Received in revised form 12 March 2013 Accepted 28 March 2013

Keywords:Catalytic naphtha reforming CatalystKinetic model Deactivation model Reactor configuration

Catalytic naphtha reforming process is a vital process for refineries due to the production of high-octane components, which is intensely demanded in our modern life. The significance of this industrial process induced researchers to investigate different aspects of catalytic naphtha reforming process intensively.Some of the investigators try to improve this process by represe nting more effective catalysts, while others try to elucidate its kinetic and deactivation mechanisms and design more efficient reactor setups. The amount of these establishe d 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 publi shed studies 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 separat ely, and a suitable reference is provided for those 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 proposed as a guide line 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 configuratio n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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

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

1. Introductio n

Although burning any fossil fuel contributes to environmental problems due to carbon dioxide and other gas emissions, they are the main energy source in our world [1–5]. In order to protect environment, various legislatio ns are passed including increase inoctane number. One of the key processes in the petroleum refiningand petrochemi cal industries is catalytic naphtha reforming, which is used extensively to convert low-octane hydrocarbons of naphtha to more valuable high-octane gasoline components without changing the boiling point range [6,7]. Naphtha is a fraction of petroleum, typically constitutes 15–30% of crude oil, by weight, and boils between 30 �C and 200 �C. This complex mixture consists ofhydrocarbo n molecules with 5–12 carbon atoms, mainly including paraffins, olefins, naphthenes, and aromatics. Other components such as sulfur, nitrogen, oxygen, water, salt, and a number of metal containing constituents such as vanadium, nickel, and sodium are also exist [8].

In addition, the produced reformat e in catalytic naphtha reforming process includes valuable aromatics such as benzene,toluene, and xylenes (BTX) that are very important petrochemi cal materials. Hydrogen is a valuable byproduct of catalytic naphtha reforming process, which in most refineries is used for hydrocracking, hydrotreating, and other hydrogen -consuming processes. Italso should be mentioned that according to the problems induced by the energy crisis and global warming, hydrogen has the poten- tial to revolutio nize transportation and, possibly, our entire energy system [9,10].

Many researche rs have investiga ted different aspect of the catalytic naphtha reforming process. These studies mainly focused onthree important issues:

1. Inventing and investiga ting new catalysts with better selectivity, stability, and performanc e, as well as lower deactivation.

2. Studying the nature of the catalytic naphtha reforming reaction and revealing suitable kinetic and deactivati on models.

3. Suggesting reactor configurations and mode of operation s with higher yield and better operational conditions.

The moiety of these categories in accomplis hed studies from 1949 until now is shown in Fig. 1.

In addition, the total number of existing literature and the percentage of the aforementione d classes in different years are shown in Fig. 2a and b, respectively , in order to show the distribut ion ofthe publications thorough time.

2. Catalyst

Naphtha reforming catalyst is a bifunctiona l catalyst consists ofa metal function, mainly platinum, and an acid function, usually chloride alumina. The metal function catalyzes the hydrogenati on

catalyst49%

kinetic and deactivation

modeling27%

reactor configuration24%

Fig. 1. The percentage of the accomplished studie

and dehydrogen ation reactions and the acid function promote the isomerization and cyclization reactions [11–13]. In order toachieve an optimum performanc e of the naphtha reforming catalyst, adequate balance between these functions is needed [14].

Improving the stability and selectivity of the catalyst as well asreducing catalyst deactivati on 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 acid strengths increase the acid-catalyzed coking and cracking rates [15]. Although an excessive amount of chlorine would increase the hydrocracki ng reactions , carbon deposits would also increase [14].

Modification of metal function could be achieved by adding secondary or ternary metal component to Pt, which is summarized here.

2.1. Bimetallic catalysts

The first formulation of the naphtha reforming catalyst, which was introduce d in 1949 by UOP, consisted of monometallic platinum supported over chloride alumina (Pt/Al2O3–Cl) [16,17]. In order to slow down the coking of this kind of catalyst, high hydrogen pressure s were used, which are thermodynam ically not favorable.The developmen t of bimetalli c catalysts permitted this hydrogen excess to decrease considerabl y and improved the catalyst effi-ciency of metal [18–22]. Some of the added metals have catalytic propertie s on their own (Ir, Rh, Re), while others, such as Sn, Geare catalytically inactive. The addition of second metal to Pt was started in 1968 by adding Re to the metal function [23], which con- tributed to reduction in the catalyst deactivati on rate and improvement in catalytic properties such as hydrogen uptake and enhancem ent in aromatic yields [24,25]. In 1969, the effect of addition of Sn to the metal function was examined [26]. Addition of tin prevents coke deposition on the Pt metal particles and support, and also enhances the selectivity to aromatic s and the stability of Pt/ Al2O3 [27–31]. Pt–Sn catalysts are regenerate easily, thus they are used in the systems in which the catalyst is regenerated continuously [32,33]. Addition of germanium to monometallic platinum- supported catalysts was studied in 1971 [34]. This practice contributes to improvem ent in the catalyst selectivity and stability, aswell as enhancem ent of the thioresis tance of platinum at reaction condition s [18]. In 1976, addition of Ir and In were considered [35,36]. Pt–Ir catalysts had a strong hydrogenolytic capacity and sulfiding pretreatments had to be incorporate d in the industria lpractice to prevent the dangerous exothermal runaway produced by massive C–C bond cleavage of the feedstock in the early stages of the reaction [37]. Indium improves the resistance to deactivation by coke formatio n and enhance the aromatiz ation/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 gasoline [38,39].

Secondary metals have different properties. For example, rhenium and iridium are active metals for hydrogenolys is 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 demethylat ion reactions. In contrast, Pt–Ge/Al2O3 and Pt–Sn/Al2O3 catalysts are not presulfided because germanium and tin are inactive metals for naphtha reforming reactions. Therefore, Pt–Ge and Pt–Sn catalysts are good candidates for use in novel low pressure naphtha reforming processes employin gcontinuous catalyst regeneration because these catalysts do not re- quire complex activation procedures [40].

The addition of alternativ e component to the metal function results in different effects such as:

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

These items affect the hydrogen ation and dehydrogenati onreaction kinetics and regulate effective size of Pt clusters, which contribute 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 has been added to the bimetalli c catalyst. According to our knowledge,the first attempt in preparation of three metallic catalysts for naphtha 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 functions of the bimetallic catalysts. The modification of the acidity isdue to the deposition of a part of Ge on the support. Ge was also added to Pt–Ir/Al2O3 catalyst. Studies showed that Ge deposits produce a greater modification of the metal function of Pt–Ir–Ge catalysts, as compared to Pt–Re–Ge [13]. In both cases a strong inhibition of the dehydrogen ating and hydrogen olytic activity upon Ge addition is seen. Ge also modifies the acidity of the parent Pt–Re and Pt–Ir catalysts.

The addition of tin to the bimetallic Pt–Ir increases the stability of the catalysts and also the selectivity toward toluene. Studies showed 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 both the isomerization activity and the stability [47]. The best catalyst


is the one with 0.1% Sn. The addition of Sn to Pt–Re catalysts also decreases the benzene/i-C 7 ratio of reformat e, which is an important issue from an environmental point of view. In addition, using Pt–Re–Sn catalyst in naphtha reforming process would contribute to 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 process was also patented, which could be found in respective Refs. [49–51].

Evolution of two and three metallic catalyst for naphtha reforming 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 improving reformer performance [53–55].

3. Reaction model

3.1. Kinetic model

Naphtha is a very complex mixture of hydrocarbo ns. An analysis of a typical naphtha feed revealed that more than 300 components are present in this hydrocarbo n mixture [56]. Different reactions occur between these components, including dehydrogenation and dehydroi somerization of naphthenes to aromatics,dehydrogen ation of paraffins to olefins, dehydrocycliza tion of paraffins and olefins to aromatics, isomerizatio n or hydroisomeriza- tion to isoparaffins, isomerization of alkylcyclopent anes and substituted aromatics and hydrocracking of paraffins and naphthenes to lower hydrocarbo ns [57,58]. Considering all of these components and their correspondi ng reactions in a kinetic model is acomplex problem [59,60]. Thus, ‘‘lumped’’ models have been presented, in which the large number of chemical components are classified 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/Al 2O3–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 made by Smith in 1959 [61]. His model consists of three basic components including paraffins, naphthen es, and aromatics (PNA), which undergo four reactions . In this model, which is probably the sim- plest model, each hydrocarbon class is considered as a single component with average properties of that class. After his model, other researche rs presente d more complicate models with more components and reactions. Evolution in number of lumped components and number of reactions considered in catalytic naphtha reforming kinetic is presented in Table 2.

In 1959, Krane et al. [74] investiga ted the presence of various hydrocarbo ns in the whole naphtha. This model consists of a reaction network of twenty different components, containing hydrocarbons from C6 to C10. He also recognized the difference between paraffins, naphthenes , and aromatic s within each carbon number group. Henningsen and Bundgaa rd-Nielson [75] refinedKrane’s model in 1970. He also reported the frequenc y factors and activation energy values of different reforming reactions ofC8 naphtha, and revealed that a linear relation exist between catalyst activity and reactor inlet temperature. In 1972, Kmak [76] usedLangmuir –Hinshelwood kinetics to describe the catalytic naphtha reactions for the first time. He also studied reforming over a wide range of operating conditions using pure components, mixtures and naphtha feed and developed a detailed model in 1973 [77].In 1980, Zhorov et al. [78] considered C5, C6 lumps of naphtha and direct formation of aromatics from paraffins. Marin et al.[79] modified Kmak’s model in 1983. They used Hougen-Wats on- type rate equations and suggested a kinetic model containing hydrocarbo ns with C5 to C10 carbon numbers. Ramage et al.[80,81] studied the nature of catalytic naphtha reforming reaction and presented detailed complete model considering C6–C8 lumpsof naphthenes, paraffins and aromatic s in 1980 and 1987. They described different reactive particular raw materials in his model and considered the deactivation of the catalysts due to the coke formation, which modified the process kinetics. Although, they published a detailed kinetic model based on extensive studies of an industria lpilot-plant reactor, only short range of hydrocarbons of C6–C8 wereconsidered in their model. In 1989 Bommanna and Saraf [82] re-ported the approximat e values of activation energies according tothe plant data. Ancheyta-Juarez and Villafuerte-Ma cias [58] con-sidered the reactions in terms of isomers of the same nature (par-affins, naphthen es and aromatics) and develope d a new kinetic model in 2000. In 2003, Rahimpour et al. [72] considered C6–C9

hydrocarbo ns to simulate catalytic naphtha reformer. Klein et al.[83,84] built and customiz ed reforming reaction network using the 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 naphtha reforming reaction.


Kinetic Model Editor (KME) which presents an end-to-end solution to the kinetic modeling process, including automated feedstock modeling, reaction network construction, kinetic rate estimation,model programm ing, process system configurations, model cust- omizations, compilati ons, model execution and results analysis.In 2009, Boyas and Froment considered the equilibriums of hydrogenation and dehydrogenati ons in their model [85]. Stijepovic et al.[56] recommended a semi-em pirical kinetic model for catalytic reforming and considered the most important reactions of the catalytic 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 these studies 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 may not be able to represent the desired situation, nevertheless, choos- ing a complex model is not profitable because huge amount ofexperimental informat ion is needed to determine the model parameters, which is a time- and money-cons uming task. Thus, asuitable model is that one which despite simplicity is able to predict the situation properly.

3.2. Catalyst deactivat ion model

The yield of catalytic naphtha reforming process depends strongly on the catalyst propertie s. During operation, the catalyst undergoes physiochemical changes, which contribute to decrease in the activity for aromatic production.

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

� Poisoning due to chemisorp tion 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 the catalyst.

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 been demonstrat ed that the main fraction of the coke is deposited over acid sites [89,90]. Prediction of coke formation is a very complex task because this phenomenon depends on various parameters such as operating condition s, oil feed composition, and catalyst properties [91].

Operating conditions strongly affect the coke formatio n. This parameter mainly includes the partial pressure of hydrogen and hydrocarbon, time on stream, gas–oil feed flow, and the reaction temperature . The influence of these factors on coke formation in the commercial process has been described by several authors.

Bishara et al. [92] investigated the effect of operating conditions on catalyst deactivation as well as the yield and quality of reformate for naphtha reforming over an industrial bimetallic reforming catalyst. In their study, the aromatics yield showed a maximum inthe pressure range 7–10 bar, while the carbon depositio n decreased 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 not show any pronounced effect on reformate or aromatic s yield, however, lower H2/HC ratios (e.g.: 3.6) gave decreased aromatic s and increased carbon.

Figoli et al. [93] studied the influence of total pressure and hydrogen : hydrocarbo n ratio on coke formation over naphthareforming catalyst. According to the obtained results, they concluded that the decreasing of the total pressure and of the hydrogen to naphtha ratio produces the increment of the coke formatio n over Pt/Al 2O3. Critical values below which there is agreat increment of the amount of coke and its degree of polymerization exist.

Barbier [94] reported that decrease in pressure induces an increase in toxicity for the metallic activity, measured by the benzene hydrogen ation reaction, due to the increase in metal coking.The increase in operating pressure contributes to less coke deposition 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 catalysts can be operated at lower pressure than the monometall ic tohave the same rate of deactivation. He also showed that the change of the coking temperature does not alter the nature and location ofcoke on a Pt/A1 2O3 catalyst. The small influence of temperature isreflected in low activation energy of coking, which is typical of areaction controlle d by diffusion and migration of the coke precursors from the metal to the support. The time of operation at severe condition s produces an increase in the amount of coke on the

Table 3Some of the presented catalyst deactivation models in catalytic naphtha reform ing 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 dCK dt 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 = 7.71 P�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 PACP P2

H2us

expð�aCÞLiu et al. [169,170]


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

In naphtha reforming, as in other hydrocarbo n processes, the characterist ics of the feedstock strongly influence the catalyst performanc e. Heavier cuts are cheaper but produce more coke,making selection of the optimum cut points a compromise. Oil feed composition, especially the relative quantities and structure of alkanes, alkenes, naphthenes, aromatics, heterocycles, etc., aswell as the presence of impurities (metals, especially Ni) should be considered in the deactivation model of the naphtha reforming catalysts.

Figoli et al. [95] investigated the influence of mean boiling point BP and composition of the feedstock on naphtha reforming catalyst activity and stability. They found that cuts of very low or very high BP 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 molecula r weight, and the main reforming reaction was the aromatic s dealkylation to products oflower octane number.

Bishara et al. [92] studied the effect of feed composition on catalyst deactivation by using several naphtha blends having a wide variation in the paraffin, naphthene and aromatics content. They concluded that at any reforming severity, yields of reformate and aromatics are higher and coke deposition is lower for a naphthene-rich naphtha.

The coke rate also depends widely on the catalyst propertie sincluding the number, type and accessibility of the catalyst active centers, which depend in turn on other more elementar y variables,such as composition, preparation, as well as internal structure and pore size.

Barbier [96] reported that the deposited coke on the metal isless dehydrogen ated than the deposited coke on the support.According to his results, for platinum catalysts small metallic particles are less sensitive to coke formation than larger particles. Inaddition, the amount of coke deposited on the metallic function of a bifunctiona l catalyst always corresponds to a small fraction of the amount of coke accumulate d on the whole of the catalyst.

Mazzieri et al. [97] studied the deactivation by coke deposition and sintering and the regeneration of the metal function of Pt–Re–Sn/Al2O3–Cl and Pt–Re-Ge/Al2O3–Cl catalysts. They found that the Pt–Re–Sn catalysts were more stable than the Pt–Re-Ge ones. This was 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 effect improves the selectivity of the catalyst and increased its resistance to deactivati on. The formation of bulk Pt–Ge, Pt–Sn and Pt–Ir–Gealloys contribute to the overall rate of deactivation of these systems. Both Pt–Ir and Pt–Re are highly resistant to deactivati on.Metallic Ir and Re provided sites for the hydrogenation/hy drogen- olysis of coke fragments and therefore reduced the rate of deactivation of these catalysts.

Quantitative correlations are develope d for these observati ons by different researchers. Some of these relations are summari zed in Table 3.

4. Reactor configurations and process classification

Naphtha reforming unit is one of the main units of petroleum refining that is used extensively to convert paraffins and naphthenes to aromatics. Because of the industrial importance of this process, researche rs have studied the design aspect widely to findappropriate configurations to enhance the production of the desired products. Various types of reactor and different mode of operation have been suggested which are summari zed here.

4.1. Suggested reactor configuration

Various reactor configurations with different advantageous and disadvantag eous have been proposed. These configurations could be categorized accordin g 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 compone nts in the feedstock and the product of 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


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

Numerou s research efforts have been focused on improving the efficiency and operating conditions of these reactor configurations.These efforts mainly include using membrane to remove hydrogen from reaction media, suggesting reactors with lower pressure drop,and using coupled reactor to reduce the capital and operational cost.

Membrane reactor is a combination of chemical reactor and membrane and is used in reaction systems in which removing reaction products from reaction media or adding of reactants along the reactor is beneficial [107–109]. This effective configuration has various advantag es such as increasing reaction rate, reducing byproduct formatio n, requiring lower energy, and relatively safe operating [110,111]. According to thermodynam ic equilibrium , ifthe reactants were removed from the product gases, chemical reactants would shift to products. Considering this fact, researche rs designed Pd based membrane reactors in catalytic naphtha reforming to remove hydrogen from reacting gases.

Presentin g configurations with lower pressure drop also attracts much attention because it has significant effects on the yield and the operational condition s of the process. This parameter plays an important role in the gas-phase reactions , because the concen- tration of reactants and consequentl y the reaction rates and con- versions are affected by change in the total pressure.

Making exothermic and endothermi c reactions proceeding simultaneou sly in one reactor is an interesting idea to use the thermal energy of the exothermic reaction as the heat source of the endothermi c reaction [112,113]. The efficient coupling of exothermic and endothermi c reactions contributes to saving energy and conseque ntly reducing the capital and operational cost that ishighly demanded in our recent world [114–116].

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

4.1.1. Axial-flow tubular reactor A schemati c process diagram of axial-flow tubular fixed-bed

reactor setup for catalytic naphtha reforming reaction is shown in 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 stream containing 60–90 mol% hydrogen. This mixture is heated, at firstby exchange with effluent from the last reactor and then by heat exchange r. The inlet temperature of the beds is mostly adjusted between 750 and 790 K, and operating pressure is about 3.5 MPa.

Naphtha reforming is an endothermi c reaction and contributes to temperature drop in the reactors. Thus, catalytic naphtha reformers are designed with multiple reactors and with heaters between the reactors to maintain reactor temperature at desired levels. The effluent from the last reactor is cooled and entered the separato r, in which hydrogen and some of the light hydrocarbo nsseparate 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 separato rmostly comprised of desired reformat e product but light gases are also exist. Therefore, this liquid is sent to a stabilizer. Refor- mate of the bottom of the stabilizer is sent to storage for gasoline blending . The estimated volume percent of different components in the feedstock and the product of the catalytic naphtha reforming unit are presente d in Table 4.

Membrane concept can be assisted in the axial-flow tubular reactors for selective separation of hydrogen that results in better performanc e and higher yield [119]. The fixed-bed membrane reactor 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 reactor with axial-flow of sweeping gas.


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

The disadvantag es of fixed-bed reactors are poor heat transfer and low catalyst particle effectiveness factors. Catalyst particles have severe diffusional limitatio ns due to their size and smaller particle sizes are infeasible in fixed-bed systems because of pressure drop considerations [120].

Using a fluidized bed reactor is a promising way to overcome the catalyst particle size limitations of fixed-bed reactor. Fluidized bed membrane reactor is a multifunctional reactor that combines the advantages of a membrane and a fluidized bed reactor. This configuration has main advantages such as isothermal operation,arrangement of the membrane package and flexibility in membrane 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 gradients due to the excellent heat transfer characteristics of fluidization[122,123]. In this configuration, the mass and heat transfer occur simultaneou sly between both sides and product yield improves because of hydrogen permeation that is due to hydrogen partial pressure gradient. In order to fluidize the catalyst bed, the reacting gas is entered into the bottom of the fluidized-bed in a co-current flow

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

In a novel thermally coupled reactor, the naphtha reforming,which is an endothermi c reaction, was coupled with hydrogen a-tion of nitrobenzen e to aniline to use its generated heat as a heat source [125,126]. Co-current mode of operation for coupled reactors 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.


highly efficient recuperative reactors. Catalytic reforming takes place in the shell side whereas the exothermic hydrogenati on ofnitrobenzen e to aniline, which provides the heat for reforming process, occurs in the tube side.

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

As mentioned, fluidized bed reactors have been used widely inthe chemical and petroleum industrie s because of their numerous advantages. Coupling of the naphtha reforming and hydrogenati onreaction of nitrobenzen e to aniline is also investigated in a fluid-ized bed reactor [128].

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

tion systems due to various advantages such lower pressure drop and higher yield [129–131]. Radial-flow pattern has also been used in a tubular fixed bed reactor for naphtha reforming process [132].As shown in Fig. 7 this reactor consists of three concentr ic 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 annulus is used as a collector to collect the products. It should be noticed that 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 tubular reactors to improve the performance of the catalytic naphtha reforming process. In this reactor configuration, the naphtha feed flows radially while the sweeping gas could flow in radial or axial direction [117,133,134]. Fig. 8 shows the radial-flow tubular membrane reactor in which the naphtha feed flows radially through the packed bed, whereas the sweeping gas flows axially in the gaps (shell side).

4.1.3. Radial-flow spherical reactor Spherica l reactor configuration has been investiga ted widely as

a suitable alternative to conventional tubular reactors [135–138].This reactor setup has various advantag eous respects to packed bed reactor such as lower pressure drop, smaller catalytic pellets with higher effectiveness factor, and lower required material thick- ness [139]. This reactor configuration has been used in naphtha reforming process in both axial-flow and radial-flow mode.

A schematic diagram of the radial-flow spherical packed-bed reactor 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 between 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 mean cross-sec tional area and reduced distance of travel for flow compared to traditional vertical columns.

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

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

In the Axial-flow spherical packed-bed reactor, catalysts are placed 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 distribution 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 act as a mechanical support.

Membrane technology can be easily used in axial-flow spherical reactor. The main differenc e between this setup and the previous one is that the inner sphere is coated by a hydrogen perm–selective membran e layer. Hydrogen permeates through the Pd–Ag membrane 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 product yields are achieved [144,145].

4.2. Process classification

Catalytic naphtha reforming units are usually categorized accordin g to the catalyst regeneration procedure. These procedures could be categorized in three main groups:

1. Semi-regen erative catalytic reformer (SRR).2. Cyclic catalytic reformer.3. Continuo us catalyst regeneration reformer (CCR).

Worldwide, the semi-regener ative scheme dominates reforming capacity at about 60% of total capacity followed by continuous regenerati ve at 28% and cyclic at 12% [146].


4.2.1. Semi-regene rative catalytic reformer The most commonl y used type of the catalytic reforming unit is

SRR. This process is characteri zed by continuo us operation over long periods, with decreasing catalyst activity due to coke deposition. By decreasing the activity of the catalyst, the yield of aromatics and the purity of the byproduct hydrogen decrease. In order tomaintain the conversion nearly constant, the reactor temperature is raised as catalyst activity decline. When the reactors reach end-of-cycle levels, the reformer is shut down to regenerate the catalyst in situ. Different criteria may be used to determine the end-of-cycle levels such as the reactor metallurgy temperat ure limit, prescribed weighted average inlet temperat ure (WAIT) increase, 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 early units were operated at high pressures because high reactor pressure minimize s deactivation by coking. The shutdown of this unit occurs approximately once each 6–24 months. Research octane number (RON) that can be achieved in this process is usually inthe range of 85–100, depending on an optimization between feedstock quality, gasoline qualities, and quantities required as well asthe operating conditions required to achieve a certain planned cycle length.

The Pt–Re catalyst is usually used in SRR units because it tolerates high coke levels and regenerates easily. These catalysts enable a lower pressure and higher severity operation.

Semi-regenera tive 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 schemati c diagram of SRR unit isshown in Fig. 4, and all of the aforementione d reactor configura-tions have been proposed for this process.

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

reactor is exist, which, as well as other reactors, can be individually isolated. 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 one reactor 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 hydrogen-to-feed ratio may be used, which contributes to high deactivation rate of the catalyst. Thus, catalyst in individual reactors could become exhausted in time intervals of from less than a week to amonth. The research octane number in this process is in the range of 100–104.

Low operational pressure and less variation of the overall catalyst activity, conversion, and hydrogen purity with time re- spect to the semi-regenerati ve process are the main advantageous of the cyclic process. A drawback of this process is that all reactors alternate frequent ly between a reducing atmosph ere during normal operation and an oxidizing atmosph ere during regenerati on. This switching policy needs a complex process layout with high safety precautio ns and requires that all the reactors be of the same maximal size to make switches between them possible.

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

4.2.3. Continuo us catalyst regeneration reformer CCR is the most modern type of the catalytic reformers. The

continuo us process represents a step change in reforming technology compared to semi-regenerati ve and cyclic processes. In this unit the catalyst regenerates continuously in a special regenerator and adds to the operating reactors. The advantag es of CCR process against traditional methods are [147–150]:

– Productio n of higher octane reformate even working with a low 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 pressure

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.


This process could be designed in different manners. Reactors may 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 reactor and the spent catalyst is withdrawn from the last reactor and transported back to the regenerator. The design reformate octane number in this process is in the 95–108 range.

The used catalyst in CCR process is mainly of the platinum/tin alumina type because addition of tin enhances the selectivity toaromatics, stability, and regenerati on ability of Pt/Al 2O3 [32–36].It should mentioned that in CCR unit, catalyst regenerates continuously, thus, selectivity to aromatics of the catalyst is more

important than its resistance to deactivation, while in SRR unit, despite the ability to increase the yield of the process, catalyst should be able to tolerates high coke levels.

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

Finally, some of the published modeling of the catalytic naphtha reforming unit is presente d in Table 5. The possibility of comparing the operational conditions such as temperature and pressure indifferent mode of operations as well as the catalyst, the reactor configuration, 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

Reaction model

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 membrane tubular reactor

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

SRR Axial-flow fluidized bed membrane tubular reactor

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/

Al2O3 480–510 �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 reactor 3 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/cm 2 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/Al 2O3 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/cm 2 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/Al 2O3–Cl 485–520 �C 30 kg/cm 2 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 reactors 3 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 Adz ˇamic ´ 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

reformer 1 – 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]


5. Suggestions

Although many investigator s have been studied different aspects of catalytic naphtha reforming process and huge amount ofpapers have been published about this issue, more researches are needed to characterize the nature of the reaction and revamping the yield of this process. As a guideline for further investigatio ns,various suggestions have been proposed here.

1. Various kinetic models with different number of lumped components and reactions have been proposed for catalytic naphtha reforming reaction. Although considering simple models may reduce the accuracy of the modeling, consideri ng a very complex model may have no considerable effect on the finalresults. Thus a comparative study is needed to find out the proper and optimize number of the lumped components and reactions.

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

3. In most of the studies, the reactors are modeled in one-dimen- sional direction (only axial direction has been considered) while consideri ng other directions (such as radial direction) may have considerabl e effect on the obtained results. It is suggested tocompare the differences between one-dimensi onal and two- dimensio nal modeling in order to specify the proper assump- tions of the modeling.

4. Most of the presented reactor models are homogeneous models,while catalytic naphtha reforming reaction is a heterogeneous process inherently. It is better to study this process as a heterogeneous reaction in future studies and investigate the differences between these two models.

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


Investigating the application of various reactor configurationssuch as membrane reactors and thermally coupled reactors inCCR unit is a novel idea.

6. Conclusion

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

Finding a suitable catalyst with higher selectivity and stability and lower coking and deactivati on comprise an extensive part ofthese studies. To achieve this purpose, various components have been 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 the affecting parameters attracts much attention too. Another signifi-cant field study is finding an efficient reactor configuration. The suggested reactors are tubular or spherical reactors and the feedstock may flow in axial or radial direction. Different modes of operations are presented for a catalytic naphtha reforming unit including semi-regenerati ve catalytic reformer (SRR), cyclic catalytic reformer, and continuous catalyst regeneration reformer.SRR is the most commonl y used type of the catalytic reforming unit, but due to the better performance of CCR, all new units are designed based on this technology and old units are revampe d tothe continuous process or combinati on of both.

Aforemen tioned topics have been investigated widely and many articles have been published concerning them. Searching among these huge papers may be a confusing and time confusing task for those who want to have collective information about naphtha reforming process. In this paper, the established papers on catalytic naphtha reforming process were reviewed, and the obtained results of the impressive studies in this field were presented in tables. In addition, suggestio ns are presented as a guideline for further investigatio ns.

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progress in catalytic naphtha reforming process: a review

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