Available online at Petroleum & Coal 56(3) , 2014

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1 Petroleum & Coal ISSN Avalable onlne at Petroleum & Coal 56( , 014 A COMPARATIVE STUDY OF SERIAL AND PARALLEL FLOWS OF THE SWEEPING GAS IN TUBULAR MEMBRANE REACTOR IN THE PRESENCE OF CATALYST DEACTIVATION FOR CATALYTIC NAPHTHA REFORMING PROCESS H. Nourzadeh, D. Iranshah Chemcal Engneerng Department, Amrkabr Unverst of Technolog, Tehran 15875, Iran Receved Aprl 14, 014, Accepted June 30, 014 Abstract In ths stud, two modes of the sweepng gas flow n a tubular membrane reactor (TMR are taken nto consderaton for cataltc naphtha reformng process. The performance of the parallel confguraton s compared wth the seral one. The effects of the membrane thckness and hdrogen mole fracton n the sweepng gas are nvestgated on the requred compressors pressures and hdrogen and aromatc elds. Set of coupled PDEs are solved b the orthogonal collocaton method. Results show that the parallel confguraton performs better than the seral one from operatng and heat transfer vewponts. TMR wth the parallel flow of the sweepng gas s superor to the seral one owng to the ndependent operaton of reactors. Snce varables n the parallel flow are easer to desgn and control than the seral ones, a parallel flow s recommended for naphtha reformng process. Kewords: Cataltc naphtha reformng; Tubular membrane reactor; and Seres sweepng gas flow modes; Catalst deactvaton. 1. Introducton Cataltc naphtha reformng plas a maor role n the total benefts of all refner complexes. A vast varet of research areas has been focused on ths process to mprove ts operatonal condtons and to acheve more products eld. Bentez et al. [1], Mazzer et al. [ ], Vswanadham et al. [3], Boutzelot et al. [4], Carvalho et al. [5] and Beltramn et al. [6] nvestgated the effect of varous metal bases on the catalst actvt and the reformng eld. Attempts have been made to acheve hgher effcenc of the process, better use of the avalable feedstocks and the processng of alternatve raw materals [1]. Ren et al. [7] nvestgated a seres of naphtha reformng catalsts from dfferent stages of cokng and the regeneraton processes b NMR and chemcal engneerng methods. Man knetc studes have been conducted on the complex naphtha chan reactons n order to predct the reformng compostons more accuratel. Smth [8] was the poneer of ths feld of studes. Ramage et al. [9-10] developed a detaled knetc model based on studes of an ndustral plot plant reactor. Krane et al. [11] recognzed the presence of varous carbon numbers for reformng reactons. Other studes have been done b Wefeng et al. [1], Kmak [13], Boas and Froment [14], Stepovc et al. [15] and Marn et al. [16]. Iranshah et al. [17] studed the cataltc naphtha reformng n the radal flow sphercal reactors to decrease the pressure drop and to ncrease the aromatc producton. Rahmpour [18], Kolesnkov et al. [19] nvestgated the cataltc naphtha reformng n fludzed bed reactors. Mn et al. [0] modeled a four stages cataltc reformng unt wth a radal flow pattern. Optmzaton of operatng condtons n naphtha reformng process has been performed to ncrease the aromatc eld and annual profts [1-6]. The obectve of ths stud s to compare the effect of applng the parallel flow wth the seral flow of the sweepng gas on the TMR performance n naphtha reformng process. In order to model the TMR confguraton, a heterogeneous model s consdered. A catalst deactvaton model s appled to nvestgate the effect of catalst deactvaton on the performance of TMR. Snce the walls of the tubes n TMR are coated b the Pd-Ag membrane laer, the effect of hdrogen permeaton s taken nto consderaton n mass and energ balances. A set of coupled

2 PDEs are solved b the orthogonal collocaton method. The modelng results are compared wth the plant data of the conventonal tubular reactor (. Ths stud demonstrates that TMR wth the parallel flow of the sweepng gas performs better than the seral one n some cases as wll be descrbed further.. Reactons and Knetc scheme A knetc model s consdered based on the Smth's model [8]. Smth assumed some pseudocomponents to smplf the feedstock of cataltc naphtha reformng. Thus, four domnant dealzed reactons can be taken nto consderaton as follows: Dehdrogenaton of naphthenes to aromatcs. Naphthenes (C n H n Aromatcs (C n H n 6 +3H (1 Dehdrocclzaton of paraffns to naphthenes. Naphthenes (C n H n +H Paraffns (C n H n+ ( Hdrocrackng of naphthenes to lower hdrocarbons. Naphthenes(C n H n + n/3h Lghter ends (C 1 C 5 (3 Hdrocrackng of paraffns to lower hdrocarbons. Paraffns (C n H n+ + (n 3/3H Lghter ends (C 1 C 5 (4 The naphtha reformng reactons are lmted b equlbrum; n order to acheve hgh aromatc producton, the should be carred out at a hgh temperature. The rate equatons for these reactons are as follows: k f 1 3 r ( ( ke p 1 n pa p (5 K 1 h e1 r k f ( ( ke p n ph p (6 K p e k r f 3 3 ( pn p (7 t k r f 4 4 ( p p p (8 t where k f and K e are forward rate constant and equlbrum constant, respectvel. The equatons of these constants for the reactons are reported b Rase [7]. E1 kf 9.87 exp(3.1 a 1 1.8T (9 E kf 9.87 exp(35.98 a 1.8T (10 E3 k f k 3 f 4 exp(4.97 a 1.8T ( K e exp( T ( K 9.87 exp( 7.1 e 1.8T (13 where a s the catalst actvt and E s the actvaton energ of related reacton. The actvaton energes depend on the catalst whch s used. The actvaton energes are derved usng the prevous work b Khosravanpour and Rahmpour [8]. The actvaton energes are as follows:e 1 =36350; E =58550; E 3 =

3 3. Process Descrpton 3.1. Conventonal process ( A smplfed process flow dagram for s depcted n Fg.1. The naphtha feed s mxed wth the reccled gas contanng 60-90% (b mole hdrogen and preheated before enterng the 1 st reactor. Reactors are packed wth catalsts and the chemcal reactons take place on catalsts' surfaces. Snce naphtha reformng s an endothermc process, the outlet stream must be preheated before enterng the followng reactor b nter-stage heaters. In order to stablze the lqud and separate the gaseous product, the effluent from the 3 rd reactor s cooled and drected nto the separators. The lqud product s called reformate whch manl conssts of aromatcs (60 70 mass% of naphtha feed and saturates n the C 5 C 9 carbon range. The equlbrum converson ncreases b ncreasng temperature owng to the endothermc reacton. The mprovement n the octane number of reformate s acheved b lowerng space veloct, rasng the nlet temperature of the reactor at a constant pressure and shftng the reacton to the aromatc producton b hdrogen removal from the reacton sde (e.g. b usng the membrane technolog. The man reactons n the frst reactor are dehdrogenaton and somerzaton, n the second reactor are dehdrogenaton, somerzaton, crackng and dehdrocclzaton and n the thrd one are crackng and dehdrocclzaton [8]. The operatng condtons of are descrbed n Table1. Table 1 Specfcatons of conventonal naphtha reactor, feed, product and catalst of plant for fresh catalst. parameter Numercal Value unt Naphtha feed stock Kg/hr Reformate Kg/hr H /HC mole rato 4.74 LHSV 1.5 hr -1 Mole percent of hdrogen n 69.5 reccle Dameter and length of 1 st reactor 1.5, 6.9 m Dameter and length of nd reactor 1.67, 7.13 m Dameter and length of 3 rd reactor 1.98, 7.89 m Dstllaton fracton of naphtha feed and reformate TBP Naphtha feed ( o C Reformate ( o C IBP % % % % % FBP Tpcal propertes of catalst d p 1. mm Pt 0.3 wt% Re 0.3 wt% s 0 m /g a 0.3 Kg/l B

4 85 R-1 R- R-3 Off Gas R: Reactor F: Furnace S-1: Separator S-: Stablzer S-1 S- Naphtha Feed F-1 F- F-3 Reformate to Storage Compressor Hdrogen Rch Gas Fgure.1 A smple process flow dagram for conventonal cataltc naphtha reformng ( 3.. Tubular Membrane Reactor Setup 3..1 Tubular Membrane reactor wth the seral flow of the sweepng gas Fg. llustrates the process flow dagram for TMR n whch the sweepng gas lnes are seral. In a seral mode, the sweepng gas enters the shell sde of the frst reactor and t s enrched b hdrogen as proceedng along the reactor. Subsequentl, the outlet stream from the shell sde enters the next reactor. As a result, the performance of the reactors n the seral confguraton s dependent to each other. The potental dfference, hdrogen permeaton drvng force, decreases along each reactor. Accordng to the Severt s law, the drvng force (hdrogen permeaton s proportonal to the hdrogen partal pressure dfference between shell and tube sdes of each reactor. The specfcaton of ths membrane reactor extensvel descrbed n the prevous work [8]. C-1 Naphtha Feed F-1 C- Hdrogen Rch Gas F-1 Off Gas C: Compressor R: Reactor F: Furnace S-1: Separator S-: Stablzer R-1 C-3 R- R-3 C-4 C-5 S-1 S- F- F-3 Reformate to Storage Fgure. Schematc dagram of tubular membrane reactor (TMR wth the seral flow of the sweepng gas. 3.. Tubular Membrane reactor wth the parallel flow of the sweepng gas The scheme of the TMR wth parallel sweepng gas lnes s depcted n Fg.3. The basc dea of a "parallel" confguraton s to connect all reactors wth lower hdrogen partal pressure.

5 In a word, lower hdrogen partal pressure s equvalent to hgher hdrogen permeaton rate. Ths leads to the selecton of a thcker and a durable membrane. The onl dfference between the parallel confguraton and the seral one s the sweepng gas dstrbuton lnes. In the parallel flow, the potental s the same along each reactor unlke the seral flow where t decreases as the sweepng gas s flowng along reactors. As seen, branches provde separate paths for the sweepng gas flows. Snce the man current of the sweepng gas s dvded nto separate pathwas, a break n one or more of those pathwas does not nterrupt the flow n the other paths. Consequentl, reactors operate ndependentl. The total amount of hdrogen s equal to the sum of the currents n each branch. In the parallel flow, the sweepng gas molar flow rate n each branch s one thrd of the total amount. Thus, the nlet molar flow rate of the sweepng gas equals 500 kmol/hr. Moreover, the nlet temperature of the sweepng gas s the same for all reactors. The specfcaton of the sweepng gas and the operatng condtons of TMRs are llustrated n Table. Table Specfcatons for sweep gas and permeaton sde n both seres and parallel confguratons. Inlet sweep gas temperature (K Inlet sweep gas pressure (kpa Inlet sweep gas flow (kmole/hr Inlet sweep gas composton (H % Seres sweep gas flow 1 st reactor nd reactor 10 3 rd reactor 145 Sweep gas flow 1 st reactor nd reactor rd reactor Addtonal nformaton m Membrane thckness ( Hdraulc dameter (m C-1 Naphtha Feed 86 Hdrogen Rch Gas C: Compressor R: Reactor F: Furnace S-1: Separator S-: Stablzer C- C-3 C-4 F-4 R-1 F-1 R- R-3 Off Gas S-1 S- F- F-3 Reformate to Storage Fgure 3 Schematc dagram of tubular membrane reactor (TMR wth the parallel flow of the sweepng gas.

6 4. Reactor model The man structure of the model s ntated b the prevous work whch carred out b Khosravanpour and Rahmpour [8]. The new approach gven b ths stud reles on some modfcatons whch are consdered to mprove the model capablt. The mass and energ balance equatons (for both shell and tube sdes together wth the pressure drop correlatons [9] and a catalst deactvaton model [30] are presented n Table 3. The notatons are presented n the nomenclature n Appen C. Table 3 Mass & Energ balances for tubular membrane reactor. Flud phase (Tube sde C ( u C D a r m z e ( B z z 1 4J H C 1,,..., n 1,,..., m D t T 4 Tube J H keff ( ( u ( ( ( z Cp TTube Tref Cp TShell TTube z z D m 4 ( U ( T T Shell tube a H r B ( C p( T T Tube ref D t 1 Sold phase (Tube sde s kc s ( 0 a C C r (1 s hs ( T T ( H r 0 a (10 (11 (13 Flud phase (Shell sde C ( uzc 4JH C D e ( 1,,..., n 1,,..., m z z D t T 4 Shell J H keff ( ( u ( ( ( z Cp TShell Tref Cp TShell TTube z z D 4 ( U ( T T Shell tube ( C p( T T Shell ref D t Hdrogen permeaton rate exp( EH Q 0 tube Tube J H RT ( P H P H [Abo-Ghander et al.] H H Q molm s pa, E 15.7kmol Boundar & ntal condtons z 0: C C, T T ( z L: C T 0, 0 z z t 0; C ss ss C, T T, T ss T ; a 1; Ergun equaton (Pressure drop dp 150 (1 Q 1.75 (1 Q dz d A d A s s 3 3 s p c s p c (14 (15 (16 (18 (19 (0 87

7 88 Catalst deactvaton da K dt Ed exp( R 1 1 ( a T T 7 d R R 770, d , d T K E mol K h (1 The followng assumptons are made for both shell and tube sdes n the mathematcal modelng of TMR: ( One dmensonal plug flow s assumed. ( Radal dspersons of heat and mass are neglected. ( The gas s supposed to be deal. A set of auxlar correlatons whch are used n the modelng are presented n Appen B. 5. Numercal Soluton A set of coupled PDEs ncludng energ and mass balances as well as ODE and algebrac equatons of the sstem are solved b the orthogonal collocaton method (Appen A. The deactvaton model s an ODE. The auxlar correlatons, knetcs and thermodnamcs of the reacton sstems consttute a set of algebrac equatons. More detals concernng ths subect was presented b Iranshah et al. [17]. 6. Model valdaton 6.1. Unstead state model valdaton Model valdaton s carred out b a comparson between the modelng results of TMR and the hstorcal process data. The predcted results of producton rate, the correspondng observed data and the resdual errors are presented n Table 4. As seen, the model performs well under ndustral condtons and there exsts a good agreement between the dalobserved plant data and the modelng results. Bolng pont ranges are determned b Dstllaton Petro Test D86 [31]. Table 4 Unstead state model valdaton. Tme (da Naphta feed (ton/hr Plant (kmol/hr Tubular (kmol/hr Dev % (Tubular- Plant Stead state model valdaton In order to verf the effcenc of the stead state model, the modelng results are compared wth observed plant data of. Table 5 llustrates the plant data and the predcted mole fractons of components n the output of the sstem. Model results show a good agreement

8 H /HC molar rato (kmole/hr wth the plant data. Analses of components (paraffn, naphthene and aromatc are performed b PONA Test n Stan Hop Seta apparatus. The aromatc s tested especall b ASTM 159 equvalent to UOP 73 method [31]. Table 5 Comparson between model predcton and plant data for fresh catalst Reactor number Inlet temperature (K Inlet pressure (kpa Catalst dstrbuton (wt % Input feedstock (mole % Paraffn Naphthene Aromatc 14.7 Reactor number Outlet temperature (K Aromatc n reformate (mole % Plant plant Seres Results and Dscusson The H /HC versus the dmensonless mass of catalst for and TMRs s depcted n Fg.4. Ths rato s one of the restrcted parameters n the controllng unt of the naphtha reformng process. It s adusted accordng to the nlet amount of feed to the frst reactor. In ndustr, t s recommended to mantan the H /HC n the range of 4-6 [31]. If the H /HC becomes lower than 4, the catalsts wll be subected to cokng and a rapd deactvaton. It mposes a huge burden on catalsts and eopardzes the catalst lfe. On the other hand, hgh ratos decrease the aromatc producton because the frst equlbrum reacton shfts to the reactants sde whch leads to aromatc consumptons. In TMRs, the membrane laer enables to mantan H /HC at approxmatel the nlet amount of 4.73 b the help of the permeaton pressures. Unlke membrane reactors where t mantans approxmatel constant, H /HC ncreases graduall n. The related permeaton pressures are mentoned n Table Seres Mass of catalst (Dmensonless Fgure 4 The H /HC molar rato along and TMRs. The temperature profle of TMR wth seral flow of the sweepng gas (for shell and tube sdes along three reactors s depcted n Fg.5 (a. The tube sde temperature decreases abruptl n the 1 st reactor due to the endothermc reacton n the tube sde. Also, the sweepng gas temperature decreases due to the convectve heat transfer wth the tube sde (reacton sde.

9 Shell sde temperature (K Tube sde temperature (K Temperature n seres mode (K Temperature n parallel mode (K In the nd reactor, heat transfers from the tube sde to the shell sde whch causes a maxmum n the shell sde temperature. Nevertheless, ths s not exactl what we look for. The temperature n the shell sde decreases n the rest of the nd reactor length. As Fg.5 (a shows, the heat transfer alwas takes place from the tube sde to the shell sde of the 3 rd reactor. Ths s mproper for the nd and the 3 rd reactors n the seral flow. The same atttude as the seral confguraton s consdered for analzng and understandng the thermal behavor of the parallel flow (Fg.5 (b. The nlet temperature of the sweepng gas to the three reactors s kept at 777 K n the parallel flow. As a result, the sweepng gas temperature s alwas more than the reacton sde temperature and heat transfers from the shell sde to the tube sde. In ndustr, reactors are nsulated n order to prevent thermal loss. In the parallel flow, the sweepng gas acts as an external protect (secondar nsulaton aganst the events happenng n the reacton sde owng to ts hgher temprature than the seral one. Moreover, f the crcumstances nfluence the reacton sde, changes wll affect the sweepng gas more than the reacton sde. Thus, the reacton sde s mpressed less than the sweepng gas b the varatons. It can be consdered as one of the advantages of the parallel flow n comparson wth the seral one Tube sde Shell sde Tube sde Shell sde Mass of catalst (Dmensonless a Mass of catalst (Dmensonless b Seres Seres Mass of catalst (Dmensonless Mass of catalst (Dmensonless c Fgure.5 Temperature profle of (a shell and tube sdes n a seral flow (b shell and tube sdes n a parallel flow and (c shell sde n seral and parallel flows of TMR (d tube sde along and TMRs. The shell sde temperature along the three reactors for seral and parallel flows s depcted n Fg.5(c. The shell sde temperature n the parallel flow s hgher than the one n the seral flow except for the frst reactor. In the parallel flow, nlet temperatures of three reactors are the same. The shell sde temperature falls abruptl n the frst reactor of the parallel confguraton n comparson wth the one of the seral confguraton due to lower feed flow rate n the parallel flow. Fg.5 (d compares the tube sde temperature along and TMR (for seral and parallel flows. Owng to provdng a heat source b a sweepng gas n the shell sde, the temperatures wll be hgher n the tube sde of TMRs n comparson wth. Ths s n favor of the endothermc reactons n naphtha reformng. The naphtha molar flow rate n the seral flow s d

10 Hdrogen mole fracton n shell sde hgher than the parallel one. Accordng to the relatonshp between the Nusselt number and the Renolds number, the veloct and the heat transfer coeffcent of the seral flow s hgher than the ones n the parallel flow. Thus, the temperature drop n the seral flow s less than the parallel flow. The trend of the tube sde temperature n the nd reactor s smlar to the one n the 1 st reactor. The order of temperature profles for the 3 rd reactor s obvousl llustrated n Fg.5 (a-(b. In the 3 rd reactor, the hghest temperature drop occurs for the seral flow because the sweepng gas temperature s less than the reacton sde temperature. Nevertheless, the temperature drop n the parallel flow s the least. Fg.6 llustrates hdrogen mole fracton n the shell sde of TMRs. In the seral flow of the sweepng gas, hdrogen wth a specfc mole fracton leaves the 1 st reactor and enters serall the nd reactor. The sweepng gas s enrched b hdrogen as t s proceedng along the reactors. Therefore, the hdrogen mole fracton ncreases contnuousl along the three reactors for the seral flow of the sweepng gas. As a result, the drvng force for hdrogen permeaton between shell and tube sdes decreases n the seral flow and hdrogen mole fracton tends to be constant n the 3 rd reactor. On the other hand, the nlet mole fracton of hdrogen equals n the parallel confguraton. In TMR confguraton wth the parallel flow of the sweepng gas, hdrogen permeates through a membrane laer from the reacton sde to the shell sde n three reactors thus, ts mole fracton ncreases n the shell sde of each reactor. Unlke the seral flow, the mole fracton of the sweepng gas s ndependent of each other, thus the reactors operate ndependentl for the parallel flow of the sweepng gas. If there s a techncal defect n the sweepng gas lnes of the seral confguraton, the sweepng gas lnes should be closed n order to hnder ts effect from the subsequent reactors. However, the reactors perform well f the same crcumstance exsts n the parallel confguraton. Ths fgure also shows a sgnfcant dfference n the hdrogen mole fracton n the parallel flow n comparson wth the one n the seral flow. Due to hgher hdrogen molar flow rate n the seral flow than the parallel one (three tmes hgher than the parallel, ts mole fracton does not change consderabl n the 1 st reactor. The hdrogen mole fractons are and n the parallel and seres flow, respectvel Seres Mass of catalst (Dmensonless Fgure.6 Hdrogen mole fracton n the shell sde along TMRs. Fg.7 (a-(b llustrate the reactant consumpton rates along and TMRs. Paraffn molar flow rate for and TMRs s depcted n Fg.7 (a. The paraffn consumpton rate n the 1 st and the nd reactors of TMR confguraton s smlar for the parallel and seral flows. The effectveness of membrane s evdentl demonstrated b comparng the paraffn molar flow rate n and TMRs. Accordng to the Le Chateler's prncple, the second equlbrum reacton shfts

11 Aromatc molar flow rate (kmole/hr Lght ends molar flow rate n tube sde (kmole/hr Paraffn molar flow rate (kmole/hr Naphthen molar flow rate (kmole/hr back to the reactant sde due to the hdrogen removal from the reacton sde. As a result, more paraffn s consumed n TMRs n comparson wth. The dfference between the paraffn consumpton rate n seral and parallel flows becomes more evdent n the 3 rd reactor. It can be ustfed b temperature profles of the 3 rd reactor (see Fg.5 (d. The naphthene consumpton rate s equal n the begnnng lengths of the frst reactor of and TMRs. Owng to hgh reacton rates, the effect of membrane n shftng the reactons can be gnored (see Fg.7 (b for the 1 st reactor. The flow rate arrangement at the outlet of the frst reactor mples that how the reacton temperature can affect the naphthene consumpton Seres Seres Mass of catalst (Dmensonless Mass of catalst (Dmensonless Fgure.7 (a Paraffn molar flow rate and (b Naphtha molar flow rate along and TMRs. Fg.8 (a demonstrates the capablt of usng membrane to ncrease the aromatc producton n refneres. The aromatc producton for the seral flow s more consderable than the parallel one n the 1 st and the nd reactors. In the 3 rd reactor, the aromatc producton rate for the parallel flow s hgher than the seral flow due to hgher temperature of the 3 rd reactor. These occurrences are ustfed b the reacton sde temperatures (see Fg.5 (d. Consderng the small graph n Fg.8 (a shows that the ncrease n the aromatc eld n the parallel flow s approxmatel 1kmol/hr more than the one n the seral flow whch becomes a consderable amount per ear. The lght ends molar flow rate s presented n Fg.8 (b Seres Seres Mass of catalst (Dmensonless Mass of catalst (Dmensonless Fgure.8 (a Aromatc molar flow rate and (b Lght ends molar flow rate along and TMRs. The total hdrogen producton rate has the same trend as the aromatc producton rate shown n Fg.9 (a. It s worth mentonng that the total hdrogen s produced ust because of the reacton (no reccle added. The hdrogen molar flow rate ncreases n the tube sde of (Fg.9 (b. However, t decreases n the tube sde of TMRs owng to the hdrogen permeaton through the membrane laer to the shell sde. A peak n the hdrogen molar flow profle of TMR shows that the hdrogen producton rate s hgher than the hdrogen permeaton rate through the membrane laer n the 1 st and the nd reactors. Furthermore, no dfference s observed between the hdrogen molar flow rates n TMRs due to a hgh hdrogen producton rate.

12 Total molar flow rate n tube sde (kmole/hr Molecualr weght of gas phase n tube sde (kg/kmole Total hdrogen producton (kmole/hr Hdrogen molar flow rate n tube sde (kmole/hr Seres Seres Mass of catalst (Dmensonless Mass of catalst (Dmensonless Fgure.9 (a The total hdrogen producton n and TMRs (hdrogen n the permeaton sde plus the hdrogen content of tube sde and (b the hdrogen molar flow rate n the tube sde along the reactor length for and TMRs. As prevousl mentoned, some modfcatons are consdered to mprove the modelng results. Thus, the total molar flow rate, molecular weght, heat capact, vscost, denst and, etc. are consdered to be varable. Fg.10 (a-(b llustrate how the total molar flow rate and molecular weght change along the reactors. The average molecular weght of the gas phase ncreases n TMRs due to the hdrogen removal from the reacton sde. The mnmum ponts n the graph of the molecular weght (Fg.10 (b are proportonal to the maxmums n Fg.10 (a Seres Seres Mass of catalst (Dmensonless Mass of catalst (Dmensonless Fgure.10 (a Total molar flow rate n the tube sde of and TMRs (b the average molecular weght of the gas phase n the tube sde of and TMRs versus the mass of catalst. The pressure profle along and TMRs s depcted n Fg.11. The pressure drop for both flows n TMRs s lower than. Snce hdrogen permeates through the membrane laer to the shell sde, the total molar flow rate decreases n the reacton sde. Accordngl, the veloct and related vscose loss (pressure drop are lower than the one n owng to lower molar flow rate. The effect of hdrogen mole fracton n the sweepng gas on the products eld and the requred pressures of permeaton sde (to have a desred H /HC are nvestgated n the followng fgures. Frstl, ts effect on the requred pressures of the sweepng gas n three reactors s nvestgated and two case studes (I, II are taken nto consderaton n ths regard. If the hdrogen mole fracton decreases, the compressor pressure should be ncreased to mantan H /HC above The effect of hdrogen mole fracton n the sweepng gas on the requred pressure of the sweepng gas s nvestgated for two case studes n Fg. 1(a-(c. In case I (δ 1 =δ =δ 3 =10µm, b ncreasng the hdrogen mole fracton n the sweepng gas, the requred pressure of the sweepng gas decreases n three reactors. As membranes' thcknesses ncrease as case II (δ 1 =30µm, δ =50 µm, δ 3 =70 µm the requred pressures of

13 Requred pressure for sweep gas n thrd reactor Requred pressure for sweep gas n frst reactor Requred pressure for sweep gas n second reactor Pressure (kmole/hr the sweepng gas do not change consderabl for all three reactors. Thus, thcker membranes are excellent choces aganst the ncreasng pressure n the permeaton sdes Seres Mass of catalst (Dmensonless Fgure.11 Pressure profle along and TMRs , 1 =10 m, =10 m, 3 =10 m, 1 =30 m, =50 m, 3 =70 m Seres, 1 =10 m, =10 m, 3 =10 m 1000 Seres, 1 =30 m, =50 m, 3 =70 m, 1 =10 m, =10 m, 3 =10 m 500, 1 =30 m, =50 m, 3 =70 m Hdrogen mole fracton n sweep gas Seres, 1 =10 m, =10 m, 3 =10 m Seres, 1 =30 m, =50 m, 3 =70 m Hdrogen mole fracton n sweep gas Seres, 1 =10 m, =10 m, 3 =10 m Seres, 1 =30 m, =50 m, 3 =70 m, 1 =10 m, =10 m, 3 =10 m, 1 =30 m, =50 m, 3 =70 m Hdrogen mole fracton n sweep gas Fgure.1 Requred pressure for the sweepng gas n (a the frst reactor (b the second reactor (c the thrd reactor versus the hdrogen mole fracton n the sweepng gas n TMRs for two case studes (I, II. Secondl, the effect of hdrogen mole fracton n the sweepng gas on the aromatc and hdrogen productons s nvestgated for two case studes n Fg.13 (a-(b. The aromatc and hdrogen elds for the parallel confguraton are hgher than the seral one (see Fg.13 (a-(b. The effect of ncreasng the membrane thckness on the aromatc eld s slght. If case stud II (δ 1 =30µm, δ =50 µm, δ 3 =70 µm s appled, the requred compressor pressures decrease drastcall, whle no consderable changes are observed n the aromatc and

14 Aromatc producton (kmole/hr Total hdrogen producton (kmole/hr hdrogen producton rates (compare Fg.1 and 13. The same trend s observed for total hdrogen producton n Fg.13 (b Seres, 1 =10 m, =10 m, 3 =10 m Seres, 1 =30 m, =50 m, 3 =70 m, 1 =10 m, =10 m, 3 =10 m, 1 =30 m, =50 m, 3 =70 m Seres, 1 =10 m, =10 m, 3 =10 m Seres, 1 =30 m, =50 m, 3 =70 m, 1 =10 m, =10 m, 3 =10 m , 1 =30 m, =50 m, 3 =70 m Hdrogen mole fracton n sweep gas Hdrogen mole fracton n sweep gas Fgure.13 (a Aromatc producton (b total hdrogen producton versus the hdrogen mole fracton n the sweepng gas n TMRs for two case studes (I, II. 8. Concluson TMR wth parallel and seral flows of the sweepng gas s modeled and compared wth the plant data of. Results show that TMR wth the parallel confguraton s superor to the seral one. Snce three reactors n TMR operate ndependentl for the parallel flow of the sweepng gas, parallel confguraton can be advantageous f a defect happens for one of the reactors. Moreover, the sweepng gas acts as a secondar nsulaton. As a novel dea, the effect of hdrogen mole fracton n the sweepng gas and membrane thckness on the products eld and the requred pressures of compressors are nvestgated for two case studes. Results show that b choosng thcker membranes (.e., case stud II the requred compressors pressures decrease remarkabl whle the aromatc and hdrogen producton rates do not change consderabl. The optmzaton of the membrane thcknesses can be as a future work owng to obtanng better results n the case stud II. Appen C. Nomenclature Parameter Dmenson Descrpton a [-] catalst actvt A [kmol h -1 ] moles of aromatc formed A c [m ] cross-secton of reactor c p [kj kmol -1 K -1 ] specfc heat c t [kmol m -3 ] molar concentraton E d [J mol -1 ] actvaton energ of catalst E [kj kmol -1 ] actvaton energ for reacton E p [kj mol -1 ] actvaton energ of permeablt FBP [ C] fnal bolng pnt F t [kmol h -1 ] total molar flow rate h f [W m - K -1 ] Heat transfer coeffcent HC [kmol h -1 ] Hdrocarbon H [kmol h -1 ] Hdrogen H [kj kmol -1 ] heat of reacton IBP [ C] ntal bolng pnt k [W m -1 s -1 ] thermal conductvt k c [m h -1 ] mass transfer coeffcent for component k f1 [kmol h -1 kgcat -1 MPa 1 ] forward rate constant for reacton (1 k f [kmol h -1 kgcat -1 MPa ] forward rate constant for reacton ( k f3 [kmol h -1 kgcat -1 ] forward rate constant for reactons (3 k f4 [kmol h -1 kgcat -1 ] forward rate constant for reactons (4 K e1 [MPa 3 ] equlbrum constant K e [MPa 1 ] equlbrum constant L [m] length of reactor m [-] number f data sets used m c [kg] mass of catalst

15 96 MR [-] membrane reactor M [kg kmol -1 ] molecular weght of component M w [kg kmol -1 ] average molecular weght of the feedstock n [-] average carbon number for naphtha N A [kmol h -1 ] molar flow rate of aromatc N [kmol h -1 ] molar flow rate of component NPBR [-] normal packed bed reactor p [kmol h -1 ] moles of paraffn formed P [kpa] partal pressure of component P t [kpa] total pressure r [kmol kgcat -1 h -1 ] rate of reacton for reacton R [kj kmol -1 K -1 ] gas constant RON [-] research octane number R [m] nner radus of palladum laer R o [m] outer radus of palladum laer s a [m kg -1 ] specfc surface area of catalst pellet t [h] Tme T [ K] temperature of gas phase TBP [ C] true bolng pont T s [K] temperature of sold phase T R [K] reference temperature x [m] reactor length [-] mole fracton for component n gas phase s [-] mole fracton for component on sold phase v c [cm 3 kmol -1 ] crtcal volume Greek letters [-] shape factor of pellet [-] vod fracton of catalst bed b [kg m -1 s -1 ] vscost of gas phase v [-] Stochometrc coeffcent of component n reacton b [kg m -3 ] denst of catalst bed g [kg m -3 ] denst of gas phase Subscrpts a [-] Aromatc cal [-] Calculated h [-] Hdrogen lh [-] lght hdrocarbon n [-] Naphthene out [-] Outlet p [-] Paraffn References [1] V.M. Bentez, C.R. Vera, M.C. Range, J.C. Yor, J.M. Grau, C.L. Peck, Modfcaton of Multmetallc Naphtha-Reformng Catalsts b Indum Addton, Ind. Eng. Chem. Res. 48, (009. [] V.A. Mazzer, C.L. Peck, C.R. Vera, J.C. Yor, J.M. Grau, Effect of Ge content on the metal and acd propertes of Pt-Re-Ge/Al O 3 -Cl catalsts for naphtha reformng, Appl. Catal. A, 353, (009. [3] N. Vswanadham, R. Kamble, A. Sharma, M. Kumar, A.K. Saxena, Effect of Re on product elds and deactvaton patterns of naphtha reformng catalst, J. Mol. Catal. A: Chem. 8, (008. [4] M. Boutzelot, V.M. Bentez, V.A. Mazzer, C. Especel, F. Epron, C.R. Vera, C.L. Peck, P. Marecot, Effect of the method of addton of Ge on the cataltc propertes of Pt Re/Al O 3 and Pt Ir/Al O 3 naphtha reformng catalsts, Catal. Commun. 7, (006.

16 97 [5] L.S. Carvalho, C.L. Peck, M.C. Rangel, N.S. Fıgol, C.R. Vera, J.M. Parera, Trmetallc naphtha reformng catalsts II. Propertes of the acd functon and nfluence of the order of addton of the metallc precursors on Pt-Re-Sn/_-Al O 3 - Cl, Appl. Catal. A, 69, (004. [6] J. Beltramn, A. Tanksale, Improved performance of naphtha reformng process b the use of metal zeolte composte catalsts, Proceedngs of 4 th Internatonal FEZA Conference, 008. [7] X.H. Ren, M. Bertmer, S. Stapf, D.E. Demco, B. Blümch, C. Kern, A. Jess, Deactvaton and regeneraton of a naphtha reformng catalst, Appl. Catal. A, 8, 39 5 (00. [8] R.B. Smth, Knetc analss of naphtha reformng wth platnum catalst, Chem. Eng. Prog. 55(6, (1959. [9] M.P. Ramage, K.P. Grazan, F.J. Krambeck, 6 Development of mobl's knetc reformng model, Chem. Eng. Sc. 35, (1980. [10] M.P. Ramage, K.R. Grazan, PH. Schpper, F.J. Krambeck, B.C. Cho, A revew of Mobl's Industral Process Modelng Phlosoph, Adv. Chem. Eng. 13, (1987. [11] H.G. Krane, A.B. Groh, B.L. Schuhnan, J.H. Snfeh, Reactons n Cataltc Reformng of Naphthas, Paper presented n ffth World Petroleum Congress (1960. [1] H. Wefeng, S. Honge, H. Yongou, C. Jan, Lumped knetcs model and ts onlne applcaton to commercal cataltc naphtha reformng process, J. Chem. Ind. Eng. 57(7 (006. [13] W.S. Kmak, A Knetc Smulaton Model of the Powerformmg Process, AIChE Natonal Meetng (197. [14] R.S. Boas, G.F. Froment, Fundamental Knetc Modelng of Cataltc Reformer, Ind. Eng. Chem. Res. 48, (009. [15] M.Z. Stepovc, A.V. Ostoc, I. Mlenkovc, P. Lnke, Development of a Knetc Model for Cataltc Reformng of Naphtha and Parameter Estmaton Usng Industral Plant Data, Energ & Fuels 3, (009. [16] G.B. Marn, G.F. Froment, J.J. Lerou, W. De Backer, Smulaton of a Cataltc Naphtha Reformng Unt, W. Eur. Fed. Chem. Eng. (7, 1 7 (1983. [17] D. Iranshah, M.R. Rahmpour, A. Asgar, A novel dnamc radal-flow, sphercalbed reactor concept for naphtha reformng n the presence of catalst deactvaton, Int. J. Hdrogen Energ 35, (010. [18] M.R. Rahmpour, Enhancement of hdrogen producton n a novel fludzed-bed membrane reactor for naphtha reformng, Int. J. Hdrogen Energ 34, (009. [19] I.M. Kolesnkov, V.I. Zuber, N.A. Svarovskaa, S.I. Kolesnkov, Reformng of naphtha cut n a fludzed bed of catalss, Chem. Technol. Fuels Ols, Vol. 44, No. 3, (008. [0] L.K. Mn, G.H. Yan, P.S. We, A stud on naphtha cataltc reformng reactor smulaton and analss, Journal of Zheang Unverst Scence, 004. [1] M.R. Rahmpour, D. Iranshah, A.M. Bahmanpour, Dnamc optmzaton of a mult-stage sphercal, radal flow reactor for the naphtha reformng process n the presence of catalst deactvaton usng dfferental evoluton (DE method, Int.. Hdrogen Energ 35, (010. [] H. Wefeng, S. Honge, M. Shengng, C. Jan, Multobectve Optmzaton of the Industral Naphtha Cataltc Reformng Process, Chn. J. Chem. Eng. 15(1, (007. [3] H. Wefeng, S. Honge, U. Yongou, C. Jan, Modelng, Smulaton and Optmzaton of a Whole Industral Cataltc Naphtha Reformng Process on Aspen Plus Platform, Chn. J. Chem. Eng. 14(5, (006. [4] J. L, Y. Tan, L. Lao, Modelng and Optmzaton of a Sem-regeneratve Cataltc Naphtha Reformer, Proceedngs of the 005 IEEE Conference on Control Applcatons. [5] U.M. Taskar, Modelng and optmzaton of a cataltc naphtha reformer, Doctor of phlosoph thess, 1996.

17 98 [6] T. Ld, S. Skogestad, Data reconclaton and optmal operaton of a cataltc naphtha reformer, J. Process Control 18, (008. [7] H.F. Rase, Chemcal Reactor Desgn for Process Plants, vol., John Wle & Sons, Inc., [8] A. Khosravanpour Mostafazadeh, M.R. Rahmpour, A membrane cataltc bed concept for naphtha reformng n the presence of catalst deactvaton, Chem. Eng. Process. 48, (009. [9] H.S. Fogler, Elements of Chemcal Reacton Engneerng, second ed., Prentce-Hall Englewood Clffs NJ, 199. [30] M.R. Rahmpour, S. Esmal, G.N.A. Bagher, Knetc and deactvaton model for ndustral cataltc naphtha reformng, Iran. J. Sc. Technol. Trans B Tech 7, (003. [31] Operatng Data of Cataltc Reformer Unt, Domestc Refner, 005. [3] R.G. Rce, D. Do, Appled mathematcs and modelng for chemcal engneers, John Wle & Sons, New York, [33] R.H. Perr, D.W. Green, J.O. Malone, Perr s chemcal engneers handbook, seventh ed., McGraw-Hll, [34] D.T. Jr, H. Kramers, Mass transfer from spheres n varous regular packng to a flowng flud, Chem. Eng. Sc. 8, 71 (1958. [35] C.R. Wlke, Estmaton of lqud dffuson coeffcents, Chem.Eng.Prog. 45(3, 18 4 (1949. [36] R.C. Red, T.K. Sherwood, J. Prausntz, The Propertes of Gases and Lquds, thrd ed., McGraw-Hll, New York, [37] J.M. Smth, Chemcal engneerng knetcs, McGraw-Hll, New York, Correspondng author. (D. Iranshah, Tel.: ; fax: , E-mal address: ranshah@aut.ac.r

18 99 Appen A. Orthogonal Collocaton method Jacob Polnomals (, The Jacob functon, J N ( x respect to the weghtng functon x (1 x power seres as follow: N (, N J N ( x ( 1 N, 0 x, s a polnomal of degree N that s, orthogonal wth. The Jacob polnomal of degree N has the The doman of x s n the range [0, 1]. The evaluaton of coeffcents s done b usng the followng recurrence formula N, N, 1 N 1 N. Startng wth N, 1 0 (A 1 (A (A 3 N, are constant coeffcents, and and are parameters characterzng the polnomals. Lagrange Interpolaton Polnomals For a gven set of data ponts ( x1, 1, ( x,,, ( xn, N and ( xn 1, N 1 an nterpolaton formula passng through all ( N 1 ponts s an N th degree polnomal. A sutable nterpolaton polnomal for the orthogonal collocaton method s Lagrange nterpolaton polnomal, whch passes through nteror collocaton ponts, roots of Jacob polnomals, and t s expressed as N ( x where N 1 1 defned as l ( x l ( x N s the N th degree polnomal, ( x x N 1 1 ( x x Furthermore, 0 l ( x 1 s the value of at the pont The frst and second dervatve at the nterpolaton ponts are: N 1 d ( ( N x dl x 1 N 1 d ( N ( x d l x 1 For 1,..., N, N 1. (A 4 x, and l ( x s (A 5 (A 6 (A 7 (A 8 The frst dervatve vector, composed of (N+1 frst dervatves at the (N+1 nterpolaton ponts s: d ( x d ( x ( x ' N 1 N N N N N 1 T N [,,...,, ] ( x Smlarl, the second dervatve vector s defned as d d (A 9

19 d d '' N 1 N N N N N 1 T N [,,...,, ] ( x ( x d ( x The functon vector s defned as values of at (N+1 collocaton ponts as [,,,...,, ] 1 3 N N1 T d ( x (A 10 (A 11 B means of these defntons of vectors and dervatve vectors, the frst and second dervatve vectors can be wrtten n terms of the functon vector usng matrx notaton ' A. '' B. Where the matrces A and B are defned as dl ( x A a ;, 1,,..., N, N 1 d l ( x B b ;, 1,,..., N, N 1 (A 1 (A 13 (A 14 The matrces A and B are (N+1, N+1 square matrces. Once the (N+1 nterpolaton ponts, are completel known, and thus are chosen, then all the Lagrangan buldng blocks, l ( x the matrces A and B are also known [3]. Appen B. Auxlar Correlatons B.1 Gas phase vscost Vscost of reactants and products s obtaned from the followng formula: 1 1T C T 3 C C C T 4 (B 1 where s the vscost n Pa.s and T s the temperature n K. Vscostes are at 1atm [33]. The constants of equaton B-1 are presented n Table B.1. Table B.1 Constant of Eq (B-1 for reactant and product. Component C1 C C3 C4 CnHn CnHn CnHn H L.E B..Gas phase Heat capact Heat Capact of reactants and products at Constant Pressure s obtaned from the followng formula: C p C where 1 C C3 T C snh( T 3 C 4 C5 T C cosh( T 5 c s n J/(kmol K and T s n K [33]. p (B To complete the smulaton, extra correlatons should be added to the model. In the case of heterogeneous model, because of transfer phenomena, the correlatons for estmaton of heat and mass transfer between two phases should be consdered. It s because of the concentraton and heat gradent between bulk of the gas phase and the flm of gas on the catalst surface, whch caused b the resstance of the flm laer. The constants of equaton B- are presented n Table B.. 300

20 301 Table B. Constant of Eq (B- for reactant and product. Component C C 10-5 C C C5 CnHn CnHn CnHn L.E B.3. Mass transfer correlatons To flow through a packed bed, the correlaton s gven b the followng equaton [34] : k c D d m p where 1 1 u 1 (1 p D m d s partcle dameter (m, (B 4 b s vod fracton of packed bed, s shape factor of pellet, u s superfcal veloct through packed bed (m/s, s vscost of gas flud phase (kg/m s and s flud denst (kg/m3. Dffusvt of component n the gas mxture s gven b [35]. D m (1 ( D (B 5 The bnar dffusvtes are calculated usng the Fuller Schetter Gddns equaton whch s reported b Red et al. [36]. In the followng Fuller Schetter Gddns correlaton, v c, M are the crtcal volume and molecular weght of component whch are reported n. D 10 7 T 3/ P ( v t (1/ M 3/ c 1/ M 3/ vc B.4. Heat transfer correlaton 1 (B 6 The heat transfer coeffcent between the gas phase and sold phase s obtaned b the followng correlaton [37] : h f c p c p K / ud b p (B 7 where n the above equaton, u s superfcal veloct of gas and the other parameters are those of bulk gas phase, d s the equvalent catalst dameter, K s thermal conductvt of p gas,, are denst and vscost of gas, respectvel and ε s vod fracton of catalst bed. Molecular weghts and crtcal volumes of the components and other specfcatons of feed at nlet condtons are presented n Table B.3. Table B.3 Molecular weghts and crtcal volumes of the components and other specfcatons of feed at nlet condtons. Parameter Value Dmenson Parameter Value Dmenson M wm 1.8 g/mol vca m 3 /kmol g 1.37 kg/m 3 vch m 3 /kmol c pg 88.3 kj/kmol k v cl. e 0.14 m 3 /kmol cp M wn g/mol K w/m k M wp g/mol vcp m 3 /kmol M wa g/mol vcn m 3 /kmol