PRODUCTION OF ULTRA LOW SULFUR DIESEL: SIMULATION AND SOFTWARE DEVELOPMENT

Transcription

1 Peet trool lleeuum & Cooaal ll IISSN Avalable onlne at Petroleum & Coal 49 (), 48-59, 7 PRODUCTION OF UTRA OW SUFUR DIESE: SIMUATION AND SOFTWARE DEVEOPMENT Saed Shokr *, Mahd Ahmad Marvast, MortezaTajeran Research Insttute of Petroleum Industry (RIPI), Tehran , IRAN, Emal: [email protected] Receved December 7, 6, accepted June, 7 Abstract One of the recent challenges n the petroleum refneres s the reducton of sulfur content of gas ol to the new lower lmts. The specfcaton for the sulfur content of gas ol has been reduced from 5 ppm to 5 ppm n 5. At present, the necessty of even deeper desulfurzaton s beng dscussed n Europe and the Unted States. The smulators are useful tools to manage hydrodesulfurzaton operaton and to mprove the proftablty of the process. In ths regard, software was developed to smulate Hydrodesulfurzaton process (HDS) n trckle bed reactors. The smulaton was based on HYSYS envronment, n whch the HDS reactor model results (based on Fortran codes) were mplemented n t through HYSYS Customzaton Capablty.The multphase reactor was smulated wth a one-dmensonal heterogeneous model. The reactor model was valdated wth the plot data. By the use of smulaton results, the effects of some pertnent operatng parameters such as reactor temperature and pressure and H /ol rato n gas ol feed on the performance capablty of the HDS plant were nvestgated. Based on these results the optmum operatng condtons were determned. The smulaton results have been used to estmate the optmum operatng condtons for the HDS plot plant to be operated n RIPI. ey words: Smulaton; Multphase Reactors; Heterogeneous Models; as ol; Hydrodesulfurzaton. INTRODUCTION. The presence of sulphur compounds n crude ol and heavy fractons s an undesrable ssue. Sulfur compounds are one of the most mportant mpurtes n varous petroleum fractons that cause many problems. For example, n the case of fuels they cause envronmental polluton, and n the refnng and petrochemcal ndustres they poson catalysts. It can lead to corrosvty n ols and lubrcants and posonous emssons such as SO and H S when the fuel s burned. Several processes have been proposed to deal wth the problem of removng these compounds. Hydrodesulfurzaton technque s very effectve n sulfur removal from fuel ol, where the molecules that contan sulfur lose that atom by hydrogenaton reactons. The sulfur contanng components are converted to H S and Hydrocarbons n presence of Hydrogen on sold catalyst. Hydrodesulfurzaton process s mostly carred out n trckle bed reactors. There have been reported many works on hydrodesulfurzaton. Song [] revewed both catalyst and process of desulfurzaton of fuels. orsten and Hoffman [] made a model for desulfurzaton of vacuum gas ol n a trckle bed reactor.the smulaton results showed good agreement wth expermental data over a wde range of temperature, pressure, space velocty and gas /ol rato. They used angmur Hnshelwood knetcs for rate equatons. Yamada and oto [3] compared counter - current and co-current operatons for hydrodesulfurzaton. [4] Chowdhyry et al. expanded orsten s models and appled t to desulfurzaton and dearomatzaton of the desel ol. Inert partcles were put on the catalyst to transfer hydrogen from gas to lqud. Dearomatzaton reacton and gas lqud mass transfer n non-actve zone were added to orsten s model. Smulaton results of desulfurzaton and dearomatzaton agreed wth the expermental data.

2 Saed Shokr et al./petroleum & Coal 49() 48-6 (7) 49 Thophenc components are known to be the most refractory organc sulfur-contanng components. Rgorous knetcs for the hydrodesulfurzaton (HDS) of thophene and benzothophene has already been derved [5,6]. For dbenzothophene, hydrodesulfurzaton rate equatons have been reported by Broderc and ates [7] and by Edvnsson and Irandoust [8]. Broderc and ates [7] neglected the hydrogenaton of bphenyl nto cyclohexylbenzene, whle Edvnsson and Irandoust [8] dd not determne the nfluence of H S concentraton on the reacton rates. Recently knetc modelng of hydrodesulfurzaton of ol fracton was ntroduced by Froment et al. [9]. Ther work was proceeded by developng rate equatons for all reactons n the network for the hydrodesulfurzatn of dbenzothophene on the commercal CoMo/Al O 3 catalyst by Vanrysselberghe and Froment []. In the present study, a smulaton method for hydrodesulfurzaton of gas ol n trckle bed reactors s presented. The mass balances are descrbed by a reactor model that s based on the two-flm theory [] and the rate of chemcal reactons of Hougen Watson type [] s beng used. The proposed model s valdated by the plot data. Based on the reactor model, a hydrodesulfurzaton process s beng smulated. In addton, a parametrc senstvty analyss on the process performance beng put forward n order to estmate the optmum operatng condtons for the HDS reactor and process.. FORMUATION OF MATHEMATICA MODE Hydrodesulfurzaton of ol fractons s carred out n a multphase reactor. There are three phases n reactor: Fxed bed of porous catalyst partcles, a hydrogen gas phase and a lqud phase. Operaton of trckle-bed reactors s marked by the smultaneous presence of two phases, a gaseous and a lqud one, flowng over and through a thrd catalyst sold phase; both streams are co current down flow []. Orgns of S n desel depend crtcally on how t s formulated from the refnery fractons. Sulphur compounds n the lghtest products are usually the easest and cheapest to treat.the operatng condtons for desulfurzaton of heavy fractons depend crucally on the chemcal nature of the sulphur speces present Fg (). Removng S from hgher molecular weght dbenzothophenes (DBT) especally those wth sde chans n hnderng postons are some of the most dffcult desulfurzaton tasks to acheve. Among thophenc compounds n petroleum fractons, dbenzothophene (DBT) and ts dervatves are the least reactve sulfur-contanng consttuents, and are; therefore, the key components n determnng hydrotreatng process knetcs [3]. The present study knetc modelng and smulaton of gas ol HDS reactor has been carred out for dbenzothophene (DBT) as the most sever resstng component aganst HDS. In ths work the gas phase assumes to be a mxture of hydrogen (H ) and hydrogen sulfde (H S) and lqud phase conssts of gas ol, contanng sulfurc compounds of dbenzothophene (DBT). HDS reactor Smulaton s performed on cobalt molybdenum over alumna support (CoMo/ Al O 3 ) catalyst. as phase s contnuous phase and lqud phase s dspersed, where ts stream on the catalyst partcles s shaped to lamnar form []. easy Relatve reacton rate dffcult most dffcult Fg ()- Impact of sulphur speces on desulphurzaton [4]

3 Saed Shokr et al./petroleum & Coal 49() 48-6 (7) 5 The modelng of a fxed bed HDS reactor s presented here. Accordng to the common classfcaton of fxed bed reactor models, one-dmensonal heterogeneous model wth plug flow model for both gas and lqud phases s beng used... Reacton Network The components that take part n catalytc reactons are enumerated as follows: ) H (Hydrogen) 4) C H (Bphenyl, BPH) ) H S (Hydrogen Sulfde) 5) C H 6 (Cyclohexyl benzene, B) 3) C H 8 S (Dbenzothophene, DBT) 6) C H (Bcyclohexyl, B) HDS of DBT nvolves two parallel routes :() hydrogenolyss of the C-S bonds to gve bphenyl and () hydrogenaton of one of the benzenod rngs followed by rapd hydrogenolyss of the C-S bonds to gve cyclohexylbenzene. The general reacton equaton s as follows. ν (Sulfur compounds) + ν (hydrogen) ν 3 (hydrocarbon)+ ν 4 (hydrogen sulfde) The correspondng chemcal reactons are as presented as: DBT + H BPH + HS (σ - Ste) () DBT + 5 H B + HS (τ Ste) () BPH + 3 H B (τ Ste) (3) B + 3 H B (τ Ste) (4) It s generally accepted that there exst two types of adsorpton stes on the surface of the HDS catalyst, one ste on whch DBT and ts products compettvely adsorb and the other ste on whch H adsorbs [6]. Based on recent studes of.f. Froment et al [] the two dfferent types of actve stes nclude: σ -ste for hydrogenolyss and τ - stes for hydrogenaton. The above reactons consttute a network that ts schematcs representaton s shown n Fg () [5]. +H S HHDBT +H S B Fg. Reactons network for HDS of DBT [5]

4 Saed Shokr et al./petroleum & Coal 49() 48-6 (7) 5.. Rate of Reacton: Based on the mechansm proposed by Vanrysselberghe and Froment [], DBT Hydrogenolysed nto BPH and H S on the σ -stes and n parallel DBT Hydrogenated nto THDBT and HHDBT on the τ - stes, followed by hydrogenolyss nto B and H S on the σ -stes. The rate equatons for DBT consumpton on theσ andτ - stes and for BPH, B on τ - stes are wrtten as follows: r r r r DBT, σ DBT, τ BPH, τ B, τ k DBT, σ H, σ DBT, σ = (5) ( + DBT, σ CDBT + H, σ + BPH, σ CBPH + H S, σ S ( + DBT, τ CDBT + H, τ C BPH, τ DBT k DBT, τ H, τ DBT, τ CDBT = (6) 3 + C ) k BPH, τ H, τ BPH, τ CBPH = (7) 3 + C ) ( + DBT, τ CDBT + H, τ ( + DBT, τ CDBT + H, τ BPH, τ kb, τ H, τ B, τ CB = (8) 3 + C ) BPH, τ The reacton rate parameters are presented n table3. C BPH BPH BPH H ) 3 Table3. Reacton rate parameter [] Component k (kmol/kg Index cat hr) (m 3 /kmol) DBT,σ.44336Eexp E 3.363E-exp H,σ BPH,σ H S,σ DBT, τ.86757e6.exp 869 H, τ E-4exp E-8exp E-7exp E-5exp E3exp 5574 BPH, τ exp B, τ.535e.3535e-3.3.reactor Model Equatons The knetc modelng s based on the two flm theory as shown n Fgure 3. Snce no reactons occur n the gas phase, the mass balance equatons for the gaseous compounds (components,) are: u dc. dz C = a ( C ) =, (9) H

5 Saed Shokr et al./petroleum & Coal 49() 48-6 (7) 5 Where H = H RT at Z = C = C =, as qud Sold C C C s as Flm qud Flm T T as Phase qud h Sold Fg.3 Mass transfer model No heat exchange wth the surroundngs of the reactor has to be accounted for, snce hydroprocessng rectors are operated adabatcally. Three energy equatons are consdered, one for each phase. The energy transfer between the gas phase and the lqud phase s made up of a conductve heat flux and convectve contrbuton due to the transport of enthalpy by the nterphase mass transfer.the Energy equaton for gas phase s presented as: dt u ρ CP = h a ( T T ) N acp ( T ), T () dz = at Z = T = T =, Mass -balance equaton for lqud phase s wrtten as: 4 dc s u = N a + ( ε ) ρc vj rj η j =,,...,6 () dz j= Where N C H C = ( ) () at Z = C C = =, For lqud sold heat transfer a convectve transfer term s consdered.the Energy equaton for lqud phase s wrtten as follows: 4 dt s SO u ρ CP = ( ε ) ρcη jrj ( ΔH j ) + ha ( T T ) + NaΔH ( T ) (3) dz = = at Z = T = T =, In ths work a mathematcal model for the effectveness factor calculaton of HDS catalyst has been developed. The effectveness factor for each reacton s calculated from the followng formula: R C s s 3 r rm ( C,... C5, T ) dr η m= (4) 3 s s R r ( C,..., C, T ) c m Where R c s the radus of catalysts. 5 Mass -balance equatons nsde catalyst pellet s descrbed as:

6 Saed Shokr et al./petroleum & Coal 49() 48-6 (7) 53 s NR De C s s ( r ) = ρ r ( C,...,C5,T ),,..., 6 c υ m m = (5) r r r m= B.C: r= R C s l = C = components number (6) r = C s = NR= Number of reacton r The ntegraton n the axal drecton was performed usng a fourth order Runge utta routne wth varable stepsze. The ntrapartcle ntegraton was carred out wth an orthogonal collocaton method. Non-lnear algebrac equatons n catalyst pellets have been solved by orthogonal collocaton method and modfed Powel dogleg numerc methods [7,8]..4. The model parameters The physco - chemcal parameters requred by the model are ntroduced n Table (). Table. Physco chemcal propertes estmaton methods Property Method Property Method Heat transfer coeffcent Chlton Colburn analogy [9] Molecular Dffusvty Tyn-Calus correlaton [9] Henry coeffcent Crtcal specfc volume Raz-Daubert [] correlaton [] Vscosty as-qud mass-transfer [] [9,] coeffcent Heat Capacty [9].5. Man assumptons By formulatng the mass transfer equatons, the followng assumptons are made:. The process s operatng n steady state condton.. Chemcal reactons only take place at the catalyst, and not n the gas or n the lqud phase. 3. Wettng effcency of percent s assumed. 4. There s no temperature dfference nsde the catalyst pores. 5. There s no radal concentraton profle n the reactor 6. The reactor s non- sothermal. 7. Vaporzaton and condensaton of ol do not take place. 3. Model Valdaton In order to valdate the reactor model, the reactor model predctons have been compared wth the data obtaned from the plot plant reported by orsten and Hoffman []. The plot plant characterstcs are shown n Table (). Fg (4) shows the sulfur and H S (n lqud phase) concentraton profles along the reactor length predcted from the model and those from plot data. The results show a good agreement between the model predctons and the plot data. Hydrogen concentraton profles along the reactor length n lqud phase for both the model and plot data are shown n Fg (5). Relatve error of near 4-7% s may be seen between the results obtaned from the plot plant and those predcted the model. Table. Input Data accordng to Plot Plant [] Characterstc Input data Characterstc Input data Pressure, P, MPa Catalyst partcle dameter, (m).3 Temperature, T, C 37 Feed API.7 WHSV, h -.9 MeABP of the feed, o C 45 Reactor dameter (cm) 3 Feed molecular weght 4 Reactor length packed wth.667 Feed densty at 5.6 C, 94.6 catalyst, (m) (kg/m3) Bed vod fracton.5 as flow rate, Qg, (m3/hr).487 Partcle vod fracton.6 qud flow rate, Q, (m3/hr).94 Catalyst partcle densty, (kg/m3) 4

7 Saed Shokr et al./petroleum & Coal 49() 48-6 (7) 54 Concentraton E-5 mol/cm3 4 3,5 3,5,5,5 HYDRODESUFURIZATION sulfur con.(the model) Sulfur con.[] HS q(the model) HS lq[],,4,6,8 Reactor ength(m) Fg.4. Sulfur & H S concentraton profle Concentraton(kmol/m3) 7,4E- 7,E- 6,6E- 6,E- 5,8E- 5,4E- HYDRODESUFURIZATION H lqud Con.(the model) H lq Con.[] 5,E-,,4,6,8 Reactor length (m) Fg.5. H concentraton profle 4. SIMUATIONS AND DISCUSSION: The gas ol hydrotreater processes straght-run atmospherc and vacuum gas ols from the crude unt and cracked atmospherc and vacuum gas ols from the hydrocracker fractonator and delayed cokng unts. As a result of hydrotreatng, the sulphur compounds are converted to hydrogen sulphde. The feed system ncludes two ndependent gas feed module and lqud feed module. The gas ol stream enterng the unt, pre-heated and mxed wth hot hydrogen-rch recycle gas stream (The hydrogen system may be once-through or recycle). Ths mxture s passed through a fxed bed reactor (trckle-bed), where hydrogenaton of the contamnants occurs. The hgh-pressure hydrogen-rch gas contacts an aqueous amne soluton, whch absorbs hydrogen sulphde. After purgng a porton to mantan hydrogen purty, the remander of the hydrogen-rch gas, along wth make-up hydrogen, s recycled to the reacton vessel for reuse. The ammona produced n the reacton vessel wll be dssolved n the process water, whch s removed as sour water. The lqud hydrocarbon products from the separaton stage are routed to a fractonaton secton for removal of any dssolved gases and fractonaton nto naphtha/jet and gas ol. The sour gases are sent to the hydrogen recovery unt for further ntrogen and aromatcs reducton. The gas ol s sent to storage for eventual blendng nto the synthetc crude ol. A smplfed process flowsheet for a standalone hydrotreatng confguraton s shown n fg (6). asol Hydrotreatng Reactor Fg.6. Shematcs of hydrodesulfurzaton process The Research Insttute of Petroleum Industry (RIPI) has been beng nvolved n HDS technology development for some years. In ths regard and n order to get more realstc data and beng more famlar wth the challenges of HDS plant operaton n the plot scale, a plot plant has been desgned and s beng constructed n the RIPI. The plot plant smulaton was done usng HYSYS software. The separate Fortran codes wrtten for the reactor smulaton were lnked to the Hysys envronment usng the HYSYS Customzaton tool. The vsual basc program nterface was used to lnk Fortran and HYSYS envronment as shown n Fg (7). In Fg (8) the PFD of the process smulated by HYSYS s shown. The smulaton results up to the reactor nput data that are calculated by HYSYS, go to the reactor model codes (fortran

8 Saed Shokr et al./petroleum & Coal 49() 48-6 (7) 55 codes) to calculate the reactor output results.the reactor output results from the fortran codes are transferred to HYSYS va vsual Basc envronment. Hysys agan calculates the results for the entre smulaton up to the end of process, n whch low sulfur desel s produced. The gas ol feed data, reactor specfcatons and treated gas ol product characterstcs are tabulated n Table (3). S e n d o f o u t p u t n f o r m a t o n t o h y s y s HYSYS Send of output nformaton Transfer of nput nformaton to vsual basc VISUA BASIC Transfer of nput nformaton to FORTRAN FORTRAN aton h hhhhhh output ormatonn Transfer of output nformaton to hysys Transfer of output nformaton to VB Fg. 7. Informaton flow dagram of the smulaton software Fg. 8. PFD of Process smulated by HYSYS. The reactor model results are mplemented nteractvely to the smulaton envronment Table 3. The smulaton nput data and results Specfcaton Value Specfcaton Value Feed: Reactor: Total sulphur, %wt., Reactor dameter, m.3 Specfc gravty@6f,85 Reactor length, m. IBP, o C 3 Temperature, o C 37 5 vol.%, o C 49 Pressure, kpa 75 vol.% 59 Catalyst partcle densty, kg/m3 4 3 vol.%, o C 8 Catalyst partcle dameter, m.3 5 vol.%, o C 3 WHSV, h vol.%, o C 3 Feed API.7 9 vol.%, o C 354 Product: 95 vol.%, o C 366 Total sulfur, wt ppm 47 FBP, o C 378 Temperature, o C 35 MeABP, o C 96.8 Pressure, kpa 3 Feed rate, bbl/day

9 Saed Shokr et al./petroleum & Coal 49() 48-6 (7) 56 H make up: Temperature, o C 77 Pressure, bar 58 Composton, % mol. H -75, 4-5 H/Ol, scf/bbl 5. PARAMETRIC SENSITIVITY ANAYSIS Based on the HDS plot plant smulaton, parametrc senstvty analyss has been carred out. In ths study, the effects of reactor temperature and pressure and H /ol rato of untreated gas ol on the sulfur concentraton of hydrogenated products have been consdered. The concentraton profles of DBT, BPH, B and B along the reactor length are shown n Fgures (9). It s seen that B s the man product of DBT hydrogenaton.the concentratons of BPH and B products are too low respect to B. The effect of reactor temperature on hydrodesulfurzaton was studed at the temperature range of 34-4 o C and results are presented n Fg (). As t can be seen, at constant pressure and H /ol rato, the product sulfur content decreases as the temperature ncreases. The decrease of sulfur concentraton s rapd up to about 36 o C. Beyond ths temperature the decreases s very slow. Concentraton(kmol/m3),4,3,, HYDRODESUFURIZATION DBT PPH B B,,4,6,8, Reactor length(m) Concentraton(kmol/m3),9,8,7,6,5,4,3,, HYDRODESUFURIZATION B BPH,,4,6,8, Reactor length(m) Fgure 9. Concentraton Profles along Reactor ength. The reactor condtons are presented n Table Hydrodesulfurzaton REACTOR TEMPERATURE Sul.Con (C) Concentraton.(wt.ppm) Hydrodesulfurzaton sulfur Con Pressure P(atm) Fgure. Effect of reactor temperature on sulfur, concentraton n the treated gas ol. The nput characterstcs of the smulaton are presented n table 3. Fgure. Effects of reactor pressure on sulfur Concentraton n the treated gas ol. The nput characterstcs of the smulaton are presented n table 3 Effects of pressure on sulfur concentraton are presented n Fg (). It can be seen that the sulfur concentraton decreases wth ncreasng pressure. Ths nfluence can be reversed above atm. Ths phenomena may be nterpreted as follows: by ncreasng pressure to atm, the rate of reactons ncrease and so the sulfur concentraton n the product decreases. Above atm, the pressure rsng has another effect domnatng over reacton rate ncrease: the vscosty of the ol ncreases wth ncreasng pressure, resultng n decrease n dffusvty and hence mass-transfer

10 Saed Shokr et al./petroleum & Coal 49() 48-6 (7) 57 coeffcent. Ths means that below atm, the reactons are the rate-lmtng step but above that, the dffuson would be the rate-lmtng step n HDS reactons. Effect of H /ol rato on sulfur concentraton n the hydrogenated products s gven n Fg (). It s observed that by ncreasng H /ol rato to 55.7, the sulfur concentraton decreases, but t ncreases agan by ncreasng H /ol rato. It means that the optmum H /ol rato for use n HDS plot plant would be about Ths trend s lke that happened for pressure and could be descrbed lke that. Hydrodesulfurzaton Sulfur Content/ppm ,68 5,4 55,7 6,3 65,8 H/OI RATIO[STD_m3/hr]/[STD_m3/hr] 7,65 Fgure. Effect of H/ol rato on sulfur concentraton n the treated gas ol. The nput characterstcs of the smulaton are presented n table 3 6. CONCUSION Deep hydrodesulfurzaton of gas ol n the trckle bed reactor was smulated usng one dmensonal heterogeneous reactor model. Snce hydrodesulfurzaton s strongly lmted by hydrogen sulfde the chemcal reacton rate s expressed by Hougen Watson rate equaton []. Also as among thophenc compounds n petroleum fractons, dbenzothophene (DBT) s the least reactve sulfur-contanng consttuents, t was selected as the key component n determnng hydrotreatng process knetcs. The present study consst of two sectons: - Smulatng HDS trckle bed reactor. For ths purpose, the sutable reacton rate (Hougen Watson rate of reactons type) and mathematcal model (one dmensonal Heterogeneous model for the reactor, the two flm theory for knetc modelng) was selected and solved. The reactor model results were valdated wth the plot plant data reported n lterature. - Smulaton of HDS process. Followng RIPI s experence n HDS, an HDS plot plant has been desgned and s beng constructed n the RIPI. The plot was smulated by HYSYS n ths study and the HDS reactor model results were mplemented n t through HYSYS customzaton tool. The operatng condtons of the process smulaton were consdered lke those of plot plant. Based on the smulaton, a parametrc senstvty analyss has been carred out. A better performance of the system s acheved by applyng a feed wth an H /ol rato of Increasng the reactor temperature has a major effect on sulfur concentraton n treated gas ol. Increasng reactor pressure up to atm, decreases the sulfur concentraton to mnmum. Notaton a as -lqud nterfacal area per unt reactor volume, (m / m 3 r ) C Molar concentraton of n gas bulk, (mol 3 / m 3 ) C = Molar concentraton of n lqud bulk, (mol / m 3 l ) C Specfc heat, (J / kg o ) s C Component concentraton on the catalyst surface FBP Fnal bolng pont, o C h lqud-gas heat transfer coeffcent, (W / m k) H' Henry s law coeffcent, (J / mol) ΔH Sol Heat of soluton, (J / mol) ΔH Heat of reacton, (J / mol) IBP Intal bolng pont, o C

11 Saed Shokr et al./petroleum & Coal 49() 48-6 (7) 58 Overall mass transfer coeffcent n gas lqud nterface, (m 3 /m.s) MeABP Mean average bolng pont of the feed, o C N Rate of transfer of from the gas bulk to the lqud bulk, (mol/m s) NC Number of Component gas constant, (kj kmol - - ) r j rate of reacton j per unt catalyst mass for heterogeneous reacton,(mol/ g cat.s ) T u Absolute temperature, ( o ) Superfcal gas velocty, (m 3 / m r s) u Superfcal lqud velocty, (m 3 / m r S) WHSV Weght hourly space velocty, (h - ) reek Symbols Subscrpts σ hydrogenolyss ste B bcyclohexyl ε nternal catalyst pore BPH bphenyl ε catalyst bed vod fracton, (m 3 / m 3 P) B cyclohexylbenzene η j effectveness factor of reacton j DBT dbenzothophene ρ gas densty, (kg / m 3 ) H atomc hydrogen ρ C catalyst densty, (kg cat m 3 P) H molecular hydrogen υ j j component from stochometry H S hydrogen sulfde coeffcent matrx τ hydrogenaton ste σ Wth respect to the hydrogenolyss functon τ Wth respect to the hydrogenaton functon Superscrpts g gas l lqud s sold References [] Song C.: An Overvew of New Approaches to Deep Desulfurzaton for Ultra-Clean asolne, Desel Fuel and Jet Fuel, Catal. Today, 86, (3) [] orsten Hans, Hoffmann U.: Three Phase Reactor Model for Hydrotreatng n Plot Trckle Bed Reactors AIE. J, 4, No.5, May (996). [3] Yamata H., oto Sh.: Advantages of Counter-Current Operaton for Hydrodesulfurzaton n Trckle bed Reactors, orean J.Chem.Eng. (4), (4) [4] Chowdhury R., Pedernera E. and Remert R.: Trckle Bed Reactor Model For Desulfurzaton and Dearomatzaton of Desel, AIE J., 48,6() [5] Van Parys I.A.; Froment.F.: netcs of Hydrodesulfurzaton on a CoMo/y-Al O 3 Catalyst.. netcs of the Hydrogenolyss of Thophene, Ind Eng.Chem.Prod.Res, Dev.5, 43, (986) [6] Van Parys I.A., Hosten.H., Froment.F.: netcs Of Hydrodesulfurzatonon a CoMo/y- Al O 3 Catalyst.. netcs of the Hydrogenolyss of Benzothophene Ind Eng.Chem.Prod.Res, Dev.5, 437. (986) [7] Broderck D.H.; ates B.C.: Hydrogenolyss and hydrogenaton of Dbenzothophene Catalyzed by Sulfded CoO-MoO 3 / y-al o 3: The Racton netcs, AIE J.7, 663. (98) [8] Edvsson R.; Irandost S.: Hydrodesulfurzaton of Dbenzothophene n a Monolthc Catalyst Reactor. Ind. Eng.Chem.Res, 3,39, (993) [9] Froment. F., Depauw Cuy A., Vanrysselberghe V.: netc Modelng and Reactor Smulaton n Hydrodesulfurzton of Ol Fractons, Ind. Eng. Chem. Res, 33, P (994) [] Vanrysselberghe V., Froment.F.: Hydrodesulfurzaton of Dbenzothophene on a CoMo/Al O 3 Catalyst: Reacton Network and netcs, Ind.Eng.Chem.Res, 3, , (996) [] Avraam Dmtros., Vasalos Iacovos A.: HdPro a Mathematcal Model of Trckle bed Reactors for the Catalytc Hydroprocessng of Ol Feedstocks, Catalyss Today 79-8;75-83;(3) [] Vanrysselberghe V., Froment.F.: netc Modelng of Hydrodesulfurzaton of Ol Fractons: ght Cycle Ol,. Ind, Eng. Chem. Res, 37, 43 44, (998).

12 Saed Shokr et al./petroleum & Coal 49() 48-6 (7) 59 [3] Yao Wang, Zhongchao Sun, Anje Wang, feng Ruan, Mohong u, Jng Ren, Xang,Chu, Yongkang Hu, and Pngjng Yao: netcs of Hydrodesulfurzaton of Dbenzothophene Catalyzed by Sulfded Co-MOo/MCM-4 Ind, Eng. Chem. Res, 43,34-39 (4) [4] Broderck, D.H.; ates,b.c. Hydrogenolyss and Hydrogenaton of Dbenzothophene Catalysed by Sulfded Co-Mo/ Y -Al O 3 : The Reacton netcs.aie J. 7(4),663,( 98) [5] Toshak abo, azuo Akamatsu, Atsush Ishhara, Shujro Otsuk, Masazum odo,qng Zhang, and Wehua Qan: Deep Hydrodesulfurzaton of ght as Ol..netcs and Mechansms of Dbenzothophene Hydrodesulfurzaton, Ind, Eng. Chem. Res,36,546-55,(997) [6] Snghal,.H., Espno, R.., Sobel, J.E., Huff,.A.: Hydrodesulfurzaton of Sulfur Heterocyclc Compounds: netcs of Dbenzothophene, J. Catal. 6, 457, (98) [7] Rce R.., Do D. D.: Appled Mathematcs and Modelng for Chemcal Engneers, John Wlley & Sons, Canada, (995) [8] Fnlayson Bruce A: The Method of Weghted Resduals and Varatonal Prncples, New York, Academc Press, (97). [9] Polng Bruce E., Prausntz John M., O'Connell John P.: The Propertes of ases & quds, 5th edton, () [] API, Techncal Data Book-Petroleum Refnng, Amer. Pet. Inst.(984) [] Ahmad, T.: Hydrocarbon Phase Behavor, ulf Publshng, Houston, (989) [] Perry, R.H. and D. reen, Ed's, Perry s Chemcal Engneer s Handbook, 6 th ed.mcraw- Hll, New York,(984) [3] apas A.A., Budsteanu R., Drakak., Vasalos I.A.: Producton of ow Aromatcs and ow Sulphur Desel n Hydrodesulfurzaton (HDS) Plot Plant Unt: lobal Nest: the Int. J. Vol,No, pp 5-, (999)