Avila-Neto_H2 Production From Methane Reforming

8/3/2019 Avila-Neto_H2 Production From Methane Reforming

1/11

Hydrogen production from methane reforming: Thermodynamic assessmentand autothermal reactor design

C.N. Avila-Neto, S.C. Dantas, F.A. Silva, T.V. Franco, L.L. Romanielo, C.E. Hori, A.J. Assis*

Federal University of Uberlandia, School of Chemical Engineering, Av. Joao Naves de Avila, 2121 Bl 1K, Campus Santa Monica, CEP 38408-100, Uberlandia, MG, Brazil

a r t i c l e i n f o

Article history:

Received 7 October 2009

Received in revised form

4 December 2009

Accepted 5 December 2009

Available online 12 January 2010

Keywords:

Methane reforming

Hydrogen production

Chemical equilibrium

Modeling and simulation

Process optimization

Scilab software

a b s t r a c t

In this study, a comparative thermodynamic analysis of methane reforming reactions is conducted usingan in-house code. Equilibrium compositions are calculated by two distinct methods: (1) evaluation of

equilibrium constants and (2) Lagrange multipliers. Both methods result in systems of non-linear alge-

braic equations, solved numerically using the Scilab (www.scilab.org ) function fsolve. Effects oftemperature, pressure, steam to carbon ratio (S/C) (steam reforming), CH4/CO2 ratio (dry reforming),oxygen to carbon ratio (O/C) (oxidative reforming) and steam to oxygen to carbon ratio (S/O/C) (auto-

thermal reforming) on the reaction products are evaluated. Comparisons between experimental andsimulated data, published in the literature, are used to validate the simulated results. We also present

and validate a small-scale reactor model for the autothermal reforming of methane (ATR). Using thismodel, the reactor design is performed and key operational parameters are investigated in order to

increase both H2 yield and H2/CO selectivity. The reactor model considers a mass balance equation foreach component, and the set of ordinary differential equations is integrated using the Scilab function

ode. This ATR reactor model is able to describe the influence of temperature on methane conversionprofiles, aiming to maximize hydrogen production. The experimental results and the model presentedgood agreement for methane conversion in all studied temperature range. Through simulated data of

methane conversions, hydrogen yields and H2/CO selectivity, it is observed that the best reaction

temperature to maximize the yield of hydrogen for the ATR reaction is situated between 723 and 773 K.Inside these bounds, 50% of methane is converted into products. Also, the experimental data indicatesthat the Ni catalyst activity is not compromised.

2009 Elsevier B.V. All rights reserved.

1. Introduction

In recent years, hydrogen has been attracting great interest asa clean fuel for combustion engines and fuel cells (Ayabe et al.,

2003). Among all the potential sources of hydrogen, natural gas,which has methane as its main component, has been considereda good option because it is clean, abundant and it can be easilyconverted to hydrogen (Dias and Assaf, 2004). Actually, the main

route to produce hydrogen from methane is catalytic reforming,which includes steam reforming (SRM, Eqs. (1)(3)), dry reforming(DRM, Eq. (4)), oxidative reforming (ORM, Eqs. (5) and (6)) andautothermal reforming (ATR, the coupling of steam and oxidative

reforming) (Rostrup-Nielsen, 2002).

CH4DH2O/COD3H2 DHo298[206kJ=mol (1)

CODH2O/CO2DH2 DHo298[L41kJ=mol (2)

CH4D2H2O/CO2D4H2 DHo298[165kJ=mol (3)

CH4DCO242COD2H2 DHo298[247kJ=mol (4)

CH4D1=2O2/COD2H2 DHo298[L36kJ=mol (5)

CH4D2O24CO2D2H2O DHo298[L803kJ=mol (6)

Steam reforming of methane (Eq. (1)) is the main industrialroute to produce hydrogen and synthesis gas (a mixture ofhydrogen and carbon monoxide) (al-Qahtani, 1997; Pedernera

et al., 2007). This reaction produces a H2/CO ratio equal to three,which is high when compared to other reforming processes. Inorder to decrease the amount of carbon monoxide present in thesynthesis gas, the former is further processed in a watergas shift

reactor where carbon monoxide is converted into hydrogen and* Corresponding author. Fax: 55 (34) 3239 4189.

E-mail addresses: [email protected], [email protected] (A.J. Assis).

Contents lists available at ScienceDirect

Journal of Natural Gas Science and Engineering

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j n g s e

1875-5100/$ see front matter 2009 Elsevier B.V. All rights reserved.

doi:10.1016/j.jngse.2009.12.003

Journal of Natural Gas Science and Engineering 1 (2009) 205215
http://www.scilab.org/mailto:[email protected]:[email protected]:[email protected]://www.sciencedirect.com/science/journal/18755100http://www.elsevier.com/locate/jngsehttp://www.elsevier.com/locate/jngsehttp://www.sciencedirect.com/science/journal/18755100mailto:[email protected]:[email protected]://www.scilab.org/


2/11

carbon dioxide by reaction with steam (Eq. (2)) (Seo et al., 2002). Itis known that both steam reforming of methane and the watergas

shift reaction are sufficient to represent the thermodynamic equi-librium of a steam reforming of methane process. Nevertheless, Xuand Froment (Xu and Froment,1989) demonstrated that the sum of

both reactions (Eq. (3)) is also necessary to describe experimentalkinetic data.

Considerable attention has also been paid to dry reforming ofmethane (Eq. (4)). It has the advantage of consuming both methane

and carbon dioxide, two major undesirable greenhouse gases, andproducing a synthesisgas with a H2/CO ratio near one, whichcan beused for adjusting H2/CO ratio in steam reforming, suitable forFischerTropsch reactions and methanol production (OConnoret al., 2006; Yin et al., 2007). Nevertheless, the employment of CO2to produce synthesis gas augments the risk of carbon formation (al-Qahtani, 1997; Laosiripojana et al., 2005), since the process yieldslarge amounts of CO and H2 is consumed substantially through thereverse of the watergas shift reaction (al-Qahtani, 1997). Dry

reforming of methane may also be processed with gases producedfrom anaerobic decomposition of organic materials, such as biogas,which contains CO2 and CH4 in adequate ratios for this reaction.

This process is of particular interest, since it allows taking advan-

tage on the CO2 as oxidizer for the reaction, and thus, diminishingthe concentration costs of this species (Benito et al., 2007).

The two previous reforming systems (steam and dry reforming)

are extremely endothermic and require high operational temper-atures in order to obtain reasonable equilibrium conversions. Thisleads to high operational costs. Besides, the necessity to operate insuch severe conditions can result on catalyst deactivation by sin-

tering or coke deposition (Eq. (7)).

CH4/CsD2H2 DHo298[74kJ=mol (7)

Therefore, in order to reduce these costs, oxidative reforming ofmethane has been investigated as an alternative. The partial

oxidation of methane (Eq. (5)) is a slightly exothermic reaction that

produces a H2/CO ratio around two, which is more adequate forFischerTropsch synthesis (Corbo and Migliardini, 2007). However,

increasing the amount of oxygen in the feed may lead to totaloxidation of methane (Eq. (6)), which produces CO2 and H2O.

The coupling of steam reforming and partial oxidation ofmethane has as the main advantage the possibility to use the heat

generated in the exothermic reaction as a source of energy for theendothermic reaction (Li et al., 2004; Mukainakano et al., 2007).This process is called autothermal reforming of methane. Since thissystem presents higher energy efficiency and a more satisfactory

H2/CO ratio for H2 production, this reaction can be considered animportant alternative route for hydrogen production (Dias andAssaf, 2004).

Theconversion of methane and the selectivity of the reactions to

hydrogen or synthesis gas depend on the values of several variablessuch as temperature, pressure, and reagents feed ratio, amongothers. In this way, although the thermodynamic equilibrium ofreform reactions is fairly discussed in the literature, there is a lackof

studies that present and compare all reforming reactions in thesame basis. Additionally, the set of linearly independent reactionsthat describe thermodynamically each reforming system, as well asthe conditions in which each reaction occurs is not clearly

described in the literature.Therefore, this workhas three main objectives. The first one is to

conduct a comparative thermodynamic analysis for the methanereforming process and to assess the influence of key operational

variables on chemical equilibrium. The second one is to determinethe linearly independent reactions that describe in a satisfactoryway the composition of the reformate of each reaction system.

Finally, since there is still a limited number of studies in the liter-ature referring to the reactor design and to the optimization of theoperational conditions for the ATR reaction, the last objective is topresent and to validate a reactor model in small scale for this

reaction and to compare the results with the thermodynamicscalculations. In addition, aiming to maximize the production of H2,

the effects of reactor temperature on methane conversions, H2 yieldand selectivity to H2 formation are investigated. Both analyses areconducted using in-house codes developed in the open-sourcesoftware Scilab (INRIA ENPC,). Although we know the existence of

a free and open-source software such as Cantera (Goodwin, 2004)that is a suite of object-oriented software tools for problemsinvolving chemical kinetics, thermodynamics, and/or transportprocesses, we decided to use Scilab due to its much more mature

development status, with matrices as the main data type, and thepossibility to use the present developed codes in further studiesregarding reactor optimization and automatic control in

a straightforward way.

2. Modeling

2.1. Thermodynamic equilibrium

Equilibrium compositions may be calculated by two distinct

methods: (i) Evaluation of Equilibrium Constants (EEC) and (ii)Lagrange Multipliers (LM). As mentioned by (Smith et al., 2000), theequilibrium state has two distinctive characteristics for the giventemperature and pressure: (i) the total Gibbs energy (Gt) is at

a minimum and (ii) its differential should be zero. Each of thesecriteria may serve as a criterion of equilibrium. Thus, we can writean expression for Gt as a function of the extent of the reaction (x)and look for the value of x which minimizes Gt, or we may differ-

entiate the expression, and equal it to zero, and solve for x. Theformer method is employed in the Lagrange multipliers procedurewhile the second methodology leads to the method of equilibriumconstants. The results from these two methods should be ideally

the same if the reaction system is well posed and the correlationsfor specific heat capacities, fugacity coefficients, virial coefficients,etc., are the same in both methods. In this study, while the LMmethod was applied to all reforming systems described in the

previous section, the EEC method was only applied to steam anddry methane reforming. Both methods result in systems of non-linear algebraic equations, solved numerically.

2.1.1. Evaluation of equilibrium constants method (EEC)An independent multi-reaction system is organized and each

reaction is associated with a reaction coordinate (xj) and with anequilibrium constant (Kj). The equilibrium constant for each reac-

tion in gas phase is described by Smith et al. (2000):

Yi

baini P=PonKj (8)The second term of Eq. (8) represents the product of the activ-

ities, bai , of all species in the mixture. The activities supply theconnection between the equilibrium state of interest and the

standard states of the individual species. By definition, the activitiesare related to the fugacities of each species in the mixture, bfi, by:baihbfi=foi (9)

All methane reforming reactions occur in gaseous state andconsequently the fugacity of species i in this type of reactionalsystem is the fugacity of species i in a mixture of gases. Following

Smith et al. (2000), the standard state of a gas is the state of pure

C.N. Avila-Neto et al. / Journal of Natural Gas Science and Engineering 1 (2009) 205215206


3/11

ideal gas in the standard state pressure, Po, of 1 bar. Thus, forreactions occurring in gas phase, as the fugacity of an ideal gas is

equal to its pressure,foi Po for each species i. The fugacity reflects

in its turn the non-idealities of the mixture and it is a function oftemperature, pressure and composition. For species in gas phase,the fugacity is related to the fugacity coefficient of species i in

mixture, bfi, and to the mole fraction of species i, yi, by theexpression:

bfi bfiyiP (10)Therefore, substituting Eqs. (9) and (10) in Eq. (8), one can

obtain an expression to calculate the thermodynamic equilibriumas a function ofTand P by means of the EEC method.

Yi

yibfini

P=Pon

Kj (11)

Equilibrium constants (Kj) are useful to evaluate if a determinedoperational condition (T, P, composition) favors a certain reaction.This evaluation is made through the analysis of the equilibrium

constant of a reaction compared to the constants of the otherreactions considered in the system.

2.1.2. Lagrange multipliers method (LM)

The system compositionin thermodynamic equilibrium can alsobe found by solving N equilibrium equations (Eqs. (12) and (16)),one per molecule, w mass balance equations (Eq. (13)), one per

element, and two restriction equations (Eqs. (14) and (15)), repre-senting the mass balance for the gas phase and the global massbalance, respectively.

DGfi RTlnbfi=foi

X

k

lkaik 0 ; i 1;2;.;N 1 (12)

Xi

niaik Mk ; k 1;2;.;w (13)

Xi

ni nG ; i 1; 2;.;N 1 (14)

Xi

ni nT ; i 1; 2;.;N (15)

Eq. (12) is valid only for species in gaseous state. Hence, it

represents in this work the mass balance for CH 4, H2O, CO, CO2, O2and H2 (however, as will be shown, O2 is not considered in the SRMand DRM systems).

Since the vapor pressure of solid carbon is practically zero for

low temperatures and pressures, it has a tendency to precipitate.Besides, as the pressure effect on the activity coefficient of a solid is

very small, an insignificant error is introduced by the hypothesisthat the fC=f

oC ratio is one. Hence, for solid carbon, Eq. (12) may be

re-written as:

DGof;CS lCS 0 (16)

Calculating the thermodynamic equilibrium with the Lagrange

multipliers method has the advantage of being independent of theexplicit reactions taking place while the equilibrium constantsmethod is very useful to describe the extent of the reactions overthe entire range of operational conditions. Additionally, there are

numerical differences between the two methods. This is because inLagrange multipliers method, lagrangeans have no physicalmeaning. Therefore, it can be very difficult to provide a good guess

for these variables, which can be very important in non-linear

system solving. Equilibrium constants method suffers from diffi-

culties in convergence when the equilibrium constants are quitedifferent from each other. Overall speaking, each method has itsadvantages and disadvantages and these are somehow dependent

on each specific problem considered.

2.1.3. Simulation methodAlmost all methane reforming reactions occur at low pressures.

Consequently, it could be assumed that the fugacity coefficient ofspecies i in mixture, bfi, is one. Nevertheless, since pressure effect isalso studied in this work, this hypothesis is not employed and bfi isestimated by a generalization of the virial equation of state trun-cated at the second virial coefficient Smith et al. (2000). The secondvirial coefficient is calculated by the correlation of Pitzer and Curl

which was modified by Meng et al. (2004).

lnbfi PRT24Bii 12

Xk

Xj

ykyj

2dki dkj

35 (17)

In both methods, the variations of the standard enthalpies andGibbs free energies of formation of the reaction system (DHj eDGj,

respectively) are functions of temperature and must be correctedwith the specific heat capacities of the gases, CP. This is a key

parameter in equilibrium calculation and some effort must be paidin its estimation. The input parameters of the simulator are: molefraction of the reactants, temperature and pressure in the reactorinput and operational temperature and pressure. The solution of

the equations is made through implemented computational codesin the open-source platform for numerical computation Scilab.Numeric calculations are made through the function fsolve,which uses a modification of the Powell hybrid method with

a tolerance of 1010.

2.2. Autothermal reforming of methane reactor modeling

2.2.1. Chemical reaction

In this study, ATR is defined as a combination of total oxidationand steam reforming of methane. In the reactor, several chemicalreactions occur, and their rates are strongly dependent on thereactions conditions. In order to reduce the number of reactions

and to keep the model as simple as possible, only the reactions withsignificant reaction rates were considered. According to the litera-ture Hoang et al. (2006), the reactions that prevail in the kinetics ofautothermal reforming of methane are: steam reforming (Eq. (1))

(RRM,I), watergas shift (Eq. (2)) (RRM,II), the sum of these twoprevious reactions (Eq. (3)) (RRM,III) and total oxidation of methane(Eq. (6)) (RRM,IV), which is much more exothermic than the partialoxidation. Hence, the model takes into account four reactions and

six gas species: methane, oxygen, carbon dioxide, water, carbonmonoxide and hydrogen. Nitrogen is present in the inlet air and it is

considered as an inert, which affects only the gas properties and theequilibrium conversions.

2.2.2. Reaction kinetic modelThere are a large number of kinetic models for steam reforming

and watergas shift reactions in the literature. The model proposed

by Xu and Froment for nickel catalysts is considered to be moregeneral and it has been the most used in the literature Hoang et al.(2006). For methanetotal combustion, the rate equationproposed byTrimm and Lam (1980) was adopted in this work(SeeEqs. (8)(24)).

kj ko

j exp

Ej=RT

(18)

Kadi Kad;o

i

exp DHi=RT (19)

C.N. Avila-Neto et al. / Journal of Natural Gas Science and Engineering 1 (2009) 205215 207


4/11

rRM;I kI=p2;5H2

pCH4pH2O p

3H2

pCO=KeqI

1=U

2 (20)

rRM;II kII=pH2pCOpH2O pH2pCO2=K

eqII

1=U2 (21)

rRM;III kIII=p3;5H2

pCH4p

2H2O p

4H2

pCO2=KeqIII

1=U2 (22)

rRM;IV kIV;apCH4pO2

1 KCCH4pCH4 KCO2

pO2

2

kIV;bpCH4pO2

1 KCCH4pCH4 KCO2

pO2

(23)

U 1 KCOpCO KH2pH2 KCH4pCH4 KH2 OpH2O=pH2 (24)

This kinetic model was developed for supported platinum

catalysts and the corresponding adsorption parameters wereadjusted for nickel. Ni catalyst was assumed to be in the reducedstate, which implies that total combustion and reforming occur in

parallel (Smet et al., 2001). Hence, the rate corresponding to thesteam methane reforming reaction set (RRM,I, RRM,II and RRM,III) andto the total oxidation of methane (RRM,IV) are represented by Eqs.(20)(24). The equilibrium constants are calculated by means of the

equations available in Table 1. To compute the reaction rateconstants, the parameters of Arrhenius equation (Eq. (18)) are alsoavailable in Table 1, and the adsorption constants of Eq. (19), inTable 2.

The rate of consumption/formation of each species in the gasphase is determined by summing up the reaction rates of eachspecies in all reactions, as shown below in Eqs. (5)(30).

rCH4 rRM;I rRM;III rRM;IV (25)

rH2O rRM;I rRM;II 2rR;III 2rRM;IV (26)

rCO rRM;I rRM;II (27)

rCO2 rRM;II rRM;III rRM;IV (28)

rO2 2rRM;IV (29)

rH2 3rRM;I rRM;II 4rRM;III (30)

2.2.3. Reactor model

A one-dimensional model is proposed to represent a fixed bedreactor, with nickel based catalyst, in small scale, operating in

steady state condition. The reactor considered with 4 mm length isoperated with 120 mL/min of inlet flow and 1 cm3 of catalyst

volume. In this condition, it is reasonable to adopt the followingsimplifying assumptions:

i. interfacial mass transfer resistance and intra particle diffu-sion limitations can be neglected;

ii. pressure drop is negligible;iii. the reactor can be considered as isothermal.

With the assumptions adopted previously, the molar flow alongthe axial direction, for each component, Fi (mol/s), can be described

by the following mass balance equation (Halabi et al., 2008):

dFidz

rb SX

j

rij (31)

where i denotes the gas species;j represents the reaction index;zisthe reactor length (0 to L); density of catalyst bed is rb, with a valueof 1.87 106 g/m3; S(m2) is the reactor transversal area and rij arethe reaction rates.

The model is constituted by a set of ordinary differential equa-tions (ODEs), non-linear, of initial value in length. The initialcondition is given by Fi Fi0, and the inlet composition in molar

ratio is 16.7% of CH4,1.7%of O2, 41.6% ofH2O and40%ofN2. The ODEsystem was integrated numerically using the function ode of the

open-source software Scilab.

3. Results and discussion

3.1. Steam reforming of methane (SRM)

According to Seo et al. (2002), the species in thermodynamicequilibrium for steam reforming of methane are CH4, H2O, CO, CO2,H2, C(s) and the radicals H, O, OH, HO2, HCO, CH and CH2. However,

theirs simulations indicate that the concentrations of radicals canbe neglected when compared to the concentrations of otherproducts and thus, they were not considered in this work.

Fig. 1a presents the yield of all species that constitute the

reformate product of steam reforming in chemical equilibrium as

a function of temperature with a pressure of 1 atm and a steam tocarbon ratio (S/C) of 2. At 373 K, CH4 does not react and the speciesin chemical equilibrium are only CH4 and H2O in the proportion

that they were fed to the system. As the temperature is incre-mented, the first reaction to occur is methane decomposition(RSRM,III), generating C(s) and H2. The other two linearly indepen-

dent reactions, steam reforming of methane (RSRM,I) and watergasshift (RSRM,II), start to occur around 600 K (Fig. 1b). It can be seenthat a maximum is formed for reaction RSRM,III approximately at823 K. This is the temperature in which the highest deposition of

coke occurs, with a value around 0.7 mol. Above this temperature,while CH4 decomposition fades rapidly, steam reforming ofmethane and watergas shift reactions start to prevail. There isa maximum of CO2 formation (0.22 mol) around 973 K. However, as

the reaction RSRM,II decreases smoothly as the temperature attends

Table 1

Equilibrium constants and Arrhenius kinetic parameters for ATR.

Reaction, j Equilibrium

constant, Keqj

koj (mol1 kgcat x s

1) Ej (m3 bar1

mol1)

I KeqI exp26;830

T 30:114

(bar2)

1.17 1015(bar0.5) 2.401

II KeqII KeqI K

eqIII (bar

2) 2.83 1014 (bar0.5) 2.439

III KeqIII exp4400

T 4:036 5.43 105 (bar1) 0.6713

IV,a 8.11 105 (bar2) 0.8600IV,b 6.82 105 (bar2) 0.8600

Data taken from the work of Halabi et al. (2008).

Table 2

Vant Hoff parameters for adsorption of different species for ATR.

Kad;oi (bar1) DHi(m

3

bar1 mol1)KC;oi (bar

1) DHC;oi (m3

bar1 mol1)

CH4 6.65 104 0.38280

CO 8.23 105 0.70650

H2 6.12 109 0.82900

H2O 1.77 105 (bar) 0.88680

CH4 (C) 1.26 101

0.27300O2 (C) 7.78 107 0.92800

C Combustion. Data taken from the work of Halabi et al. (2008).



5/11

its maximum value (1273 K), CO2 yield decreases only 0.08 molfrom 973 to 1273 K. On the other hand, H2 yield is proportional toCH4 conversion, and it grows very fast in the temperature interval

studied. From 1123 to 1273 K, H2 yield practically does not vary andit attends a value of 3.11 mol per mole of CH4 in the feed.Furthermore, H2/CO selectivity has a value of 3.8 at theseconditions.

To verify if the equilibrium results obtained by simulation arerepresentative, kinetic and equilibrium CH4 conversion data are

compared in Fig. 2. In this figure, two types of equilibrium curvescan be observed: while the first one (with C(s)) was obtained by

considering the formation of solid carbon in the equilibriumproducts, the second one (without C(s)) was obtained without thisconsideration. From the equilibrium curves and experimentalpoints, it is clearly observed that CH4 conversion increases when

carbon is deposited. Although Schadel et al. (2009) did not conducttests to verify coke deposition, one can suppose that, since theconversion points did not trespass de equilibrium barrier without

C(s), coke has not been deposited in a large scale. The same is not

true for the data obtained by Rakass et al.(2006). The authors noted

the presence of extensive coke deposits for all samples that havebeen exposed to the methane-rich fuel mixtures at temperaturesfrom 50 to 70050 C. Consequently and as expected, the experi-mental points are comprised between the two equilibrium curves.

In the absence of water, since CH4 is the only species in thesystem, it can only be decomposed in H2 and C(s). As shown in Fig.3,it is possible to convert almost 100% of CH 4 at the temperature of1273 K and S/C 0 in 2 mol of H2 and 1 mol of C(s). Since reactions

RSRM,I and RSRM,III produce more H2 than RSRM,II, adding any amountof water to the system always enhances the production of H 2 anddiminishes coke deposition. At the conditions mentioned above,the feed of 3 mol of H2O per mole of CH4 enables the production of

3.25 mol of H2 with a H2/CO selectivity equal to 4.4 and no cokedeposition. On the other hand, CO2 production is increased,attending a value of 0.25 mol at 1273 K (Fig. 3).

At the temperature of 1273 K, the pressure effect on H2 yield is

negligible (see Fig. 4). It can be seen in the figure that, fortemperatures lower than 1123 K, increasing the pressure tends to

decrease H2 yield. Furthermore, this effect is more acute in theinterval between 373 and 873 K. The fact is that the reaction occurs

with an augmentation in the volume and thus, increasing thepressure shifts the equilibrium towards the reactants. As anexample, raising the pressure from 0.1 to 1 atm, decreases H2 yieldfrom 1.74 to 0.58 mol.

Table A.1 shows a comparison between simulated results andliterature data for the SRM reaction system Lutz et al. (2003)employed the software CHEMKIN with the program for chemicalequilibrium calculations Stanjan, with S/C 2 and P 10 atm. The

mean relative error between the results of this work (LM method)and those of Lutz et al. (2003) is 11.8%. Seo et al. (2002) used the

0.8

1.6

2.4

3.2

4.0

0

20

40

60

80

100

CH

4conversion(%)

Yield(mol)

CH4

COCO

2

H2

C(s)

H2O

a

373 523 673 823 973 1123 1 2730.0

0.2

0.4

0.6

0.8

b

Reactioncoordinate(mol)

Temperature (K)

0.0

RSRM,III

RSRM,I

RSRM,II

Fig. 1. SRM equilibrium results as a function of temperature. (a) Products yield.

(b) Reaction coordinates. (P 1 atm, S/C 2).

373 523 673 823 973 1123 12730

20

40

60

80

100

Without C(s)

With C(s)

CH

4conversion(%)

Temperature (K)

Fig. 2. CH4 conversion for SRM. (.) Thermodynamic equilibrium; (-) Unsupported Ni

powder catalysts (Rakass et al. (2006)); (D) Rh-based monolithic honeycomb catalyst

(Schadel et al. (2009)). ( P

1 atm, S/C

2).

0.0 0.5 1.0 1.5 2.0 2.5 3.00.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

CO2

COC(s)

H2

H2O

Yield(mol)

Steam to carbon ratio (mol/mol)

Fig. 3. SRM equilibrium yields as a function of S/C. (T 1273 K, P 1 atm).

373 523 673 823 973 1123 12730.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.1 atm

1 atm

2 atm

3 atm

4 atm

5 atm

Yield(mol)

Temperature (K)

Fig. 4. H2 yield for SRM at various pressures as a function of temperature. (S/C

2).



6/11

software Aspen Plus with S/C 1 and P 1 bar. This time, the

mean relative error reached a value of 128.9%. Nevertheless, withthe purpose to analyze whether coke deposition influences or notthe results significantly, the same analyses were conducted dis-carding the presence of coke in the products. Comparing the results

of this work with those of Lutz et al. (2003), the errors were 4.2%(LM method) and 3.8% (EEC method), whereas for the results ofSeoet al. (2002), the errors reached 30.5% (LM method) and 30.6% (EEC

method). In this way, it can be supposed that neither of the authorsconsidered the formation of coke in the products. As both studiespresented their results by graphs, it was necessary to use the(Software ScanIt) to obtain the data.

3.2. Dry reforming of methane (DRM)

The thermodynamic equilibrium analysis of dry reforming ofmethane is carried out considering the same species as in the case

of steam reforming of methane. Fig. 5a presents the yield of allspecies that constitute the reformate product of DRM in chemicalequilibrium as a function of temperature with a pressure of 1 atmand a carbon dioxide to methane ratio (CO2/CH4) of 1. Fig. 5b shows

the reaction coordinates of the linearly independent reactions that

represent the chemical equilibrium at the conditions mentionedabove. At the temperature of 373 K, 87.5% of CH 4 is converted byreactions RDRM,I and RDRM,III (Eqs. (4) and (7), respectively) in equal

amounts of H2O and C(s). As the temperature is increased, theprevious reactions fade gradually and the reverse of the watergasshift reaction (reaction RDRM,II) starts to raise. At about 973 K, the

reverse of the watergas shift reaction shifts its direction towardsthe formation of CO2 and H2. At 1273 K, reaction RDRM,II is the mainresponsible for the production of H2, and the reformate is consti-tuted of 0.15 mol of H2O, 1.67 mol of CO, 1.84 mol of H2 and

0.24 mol of C(s). Therefore, H2/CO selectivity at these conditionsattends the value of 1.1, that is, 2.7 less then in the steam reformingsystem.

As it can be seen by the experimental data taken from the work

of Donazzi et al. (2008), the points at lower temperatures appear

much below the equilibrium barrier calculated consideringformation of solid carbon (Fig. 6). This is probably due to the fact

that, at the conditions employed to estimate the DRM equilibrium,the catalysts tested by the authors are not selective to coke.However, if formation of solid carbon is not considered in theequilibrium equations, since the formation of CO is not propitiated

at lower temperatures and CH4 cannot decompose, CH4 does notreact by means of reaction RDRM,I, and the equilibrium conversioncurve appears little above the experimental points. As for theexperimental results of Khalesi et al. (2008), all points appear

between the two equilibrium curves, suggesting the formation ofcoke in the surface of the catalysts. Moreover, the authors indicatethat the Ca-based perovskites deposit less coke than the Sr-basedperovskites. One could suggest that, the closer the experimental

points are to the equilibrium curve calculated with formation ofsolid carbon, more susceptible the catalyst would be to cokedeposition. Indeed, analyzing Fig. 6, experimental data related to

the Sr-based catalyst are closer to the equilibrium curve calculatedwith formation of coke.

The effect of CO2/CH4 ratio in the feed for a temperature of1273 K and pressureof 1 atm is shown in Fig. 7. The maximum yieldof H2 is achieved when no CO2 is fed to the system, that is, for the

condition in which only methane decomposition occurs. However,raising the CH4/CO2 feed ratio from 0 to 1 diminishes H2 yield inonly 0.16 mol (or 8%). In doing so, while carbon deposition

decreases from 1 to about 0.23 mol (or 77%), CO production isaffected in an opposite way, augmenting its value from 0 to almost

373 523 673 823 973 1123 12730.0

0.4

0.8

1.2

1.6

2.0

75

80

85

90

95

100

HC

4

)%(noisrevnoc

Temperature (K)

)lom(dleiY

CH4

CO

CO2

H2

C(s)

H2O

373 523 673 823 973 1123 1 273-1.0

-0.6

-0.2

0.2

0.6

1.0

1.4

1.8b

RDMR,II

RDMR,III

)lom(etanidroocnoitcaeR

Temperature (K)

RDMR,I

0.0

RDRM,IIIRDRM,I

RDRM,II

a

Fig. 5. DRM equilibrium results as a function of temperature. (a) Products yield.

(b) Reaction coordinates. (P 1 atm, CO2/CH4 feed ratio 1).

373 523 673 823 973 1123 12730

20

40

60

80

100

Without C(s)

With C(s)

CH

4conversion(%)

Temperature (K)

Fig. 6. CH4 conversion for DRM. (.) Equilibrium; (-) 4% Rh/a-Al2O3 (Donazzi et al.,

2008); (,) Ca0.2La0.8Ni0.3Al0.7O2.9 and (D) Sr0.8La0.2Ni0.3Al0.7O2.6 (Khalesi et al. (2008).

(P 1 atm, CO2/CH4 feed ratio 1).

0.0 0.5 1.0 1.5 2.0 2.5 3.00.0

0.5

1.0

1.5

2.0

2.5

3.0

C(s)

COH

2

CO2

H2

O

Yield(mol)

CO2/CH

4feed ratio (mol/mol)

Fig. 7. DRM equilibrium yields as a function of CO2/CH4 feed ratio. (T 1273 K,

P

1 atm).



7/11

1.7 mol (or 170%). Furthermore, while 100% of CH4 is converted, CO2conversion goes up to 90%.

Concerning the pressure effect (Fig. 8), it seems to affect the

yield of H2 in the same way than in steam reforming. At the

temperature of 1273 K, pressure is almost negligible, but its effectis more acute in the interval from 523 to 1123 K. As in SRM, theDRM reaction system also occurs with an augmentation in the

volume.Table A.2 shows the validation of the simulated results of this

work by comparison with CH4 equilibrium conversion data ofAkpan et al. (2007). The mean relative error between the results of

this work (LM method) and those ofAkpan et al. (2007) is 6.32%. Asimulation considering the formation of coke was not included forthis reaction, but it does not differ a lot from the results attained inthe steam reforming equilibrium calculations.

3.3. Oxidative reforming of methane (ORM)

For the oxidative reforming system, the following species wereconsidered: CH4, H2O, CO, CO2, H2, O2 and C(s). Despite Zhu et al.(2001) consider the formation of others hydrocarbons such as C2H6,C2H4, C2H2, CH3OH, HCHO and HCOOH, the authors obtaineda small yield for these species (


8/11

to stipulate the relationship between the yield of H2 and the oxygen

to carbon ratio. Fig. 11 shows this relationship for a temperature of1273 K and pressure of 1 atm. As expected, CH4 decompositionoccurs at the beginning of the abscissa axis, generating H 2 and C(s).Partial oxidation attends its highest occurrence at O/C 0.5,

producing 0.8 mol of CO and 1.9 mol of H 2. For higher O/C ratios,CH4 decomposition almost stops and steam reforming decreasesproportionally to the augmentation in O/C. Therefore, H 2 is mainlyproduced from dry reforming. At O/C 2, total oxidation dominates

and generates 1 mol of CO2 and 2 mol of H2O.As to the pressure effect, the results for the H2 yield and coke

deposition for O/C 0.5 can be seen in Fig.12a,b, respectively. Thecurves of ORM resemble the curves of SRM. Increasing the pressure

tends to decrease the yield of H2. However, the pressure effect ismore pronounced in the interval from 373 to 873 K. Coke deposi-tion is directly proportional to the pressure, but as the yield of H2,the effect is more acute for intermediate temperatures. At 673 K,

while for 0.1 atm 1 mol of coke is deposited, for 5 atm the depo-sition attends only 0.3 mol.

To validate the simulations, the results were compared with theequilibrium composition data reported by Zhu et al. (2001) (see

Table A.3). However, since the authors did not consider cokedeposition, another program was constructed to generate theresults discarding the presence of C(s), so it was possible to comparedata of the same nature. Thus, the average relative error between

the results of this work(LM method withoutcoke) and thoseofZhuet al. (2001) is 28.7%.

3.4. Autothermal reforming of methane (ATR)

Ayabe et al. (2003) analyzed the activity of 10% Ni/Al2O3 catalystfor ATR reaction as a function of temperature (light-off curve). The

authors observed that there is a large difference in methaneconversions (i) when the reaction begins at low temperatures andthe temperature is increased gradually, compared to the inverse

procedure, (ii) starting the reaction at higher temperatures andgradually reducing it. The results show a strong hysteresis ofconversion behavior in relation to temperature.

Fig. 13 presents a comparison among simulated, experimentaland thermodynamic methane conversions at the reactor exit (or in

z L), with initial conditions given in Section 2.2.3. The experi-mental data for the chemical equilibrium shown in the figure arewith respect to the cooling process and are in line with the simu-lated ones. However, it appears that, at lower temperatures, the

reactor model, based on kinetic expressions, tend to follow theheating process (not shown), where the conversion is much lowerwhen compared to the cooling process. It is also possible to observein Fig. 13 that high methane conversions are favored at higher

temperatures.

The composition profiles of ATR in chemical equilibrium (notconsidering coke deposition) and calculated by the reactor modelare shown in Fig. 14a (light-off curve) for the same conditions

mentioned previously. At lower temperatures, less than 10% of CH4is converted by total oxidation, forming CO2 and H2O. Steamreforming and watergas shift increases in the same degree when

augmenting the temperature until 850 K. At higher temperatures,CO2 mole fraction starts to decrease as a result of the reduction ofthe second reaction. When attending 1273 K, steam reformingoccurs isolated and generates CO and H2. If coke deposition is

considered, it attends a maximum of 1.5 mol at about 750 K andstarts to decrease rapidly as the temperature is incremented.However, when compared to the oxidative reforming system, theamount of coke deposited at 1273 K is lower (see Figs. 9a and 14b).

This is because feeding water to the system tends to shift the

0.0 0.5 1.0 1.5 2.00.0

0.5

1.0

1.5

2.0

CO2

COC(s)

H2

H2O

Yield(mol)

Oxygen to carbon ratio (mol/mol)

Fig. 11. ORM equilibrium yields as a function of O/C. ( T 1273 K, P 1 atm).

0.5

1.0

1.5

2.0a

0.1 atm

1 atm

2 atm

3 atm

4 atm

5 atm

H2yield(mol)

373 523 673 823 973 1123 12730.0

0.2

0.4

0.6

0.8

b 0.1 atm1 atm

2 atm

3 atm

4 atm

5 atm

Cokedeposition(mol)

Temperature (K)

0.0

Fig.12. H2 yield for ORM at various pressures as a function of temperature. (O/C

0.5).

473 573 673 773 873 973 10730

20

40

60

80

100

Without C(s)

With C(s)

CH4conversion(%)

Temperature (K)

Reactor Model

Equilibrium

Experimental

Fig.13. CH4 conversions for ATR as a function of temperature. Experimental data were

obtained by Ayabe et al. (2003) during the heating process of ATR over a Ni/Al 2O3catalyst. (Reaction conditions: CH4, 16.7%; O2, 1.7%; H2O, 41.6%; N2 (balance); S/C 2.5;

SV 7200 h1).



9/11

consumption of methane towards the steam reforming of methanereaction. Besides, the introduction of an inert (in this case N 2)

decreases the consumption of methane by the methane decom-position reaction.

In Fig. 14 for some species the results based on the reactor

model for ATR (solid lines) are slightly above chemical equilibrium(dotted lines), at low and at high temperatures. This can beexplained by the fact that the reactor model whose kineticexpressions were taken from Trimm and Lam (1980) had itsconstants adjusted for temperatures between 773 K and 873 K. In

our analysis, we have broadened this range interval in order tohave a better understanding of each species behavior alongtemperature.

Through the results of methane conversion and composition

profiles, it is possible to establish that, for a maximum in H2production, associated with smaller operational costs, the bestreaction conditions situate between 723 and 773 K. At thesetemperatures, it is possible to obtain a high yield of H2, an

elevated H2/CO selectivity and a methane conversion around 50%.

Besides, the catalyst properties are maintained with smallerchances of sintering. In addition, these conditions have theadvantage of smaller energy costs, because the reaction temper-

ature is low. Nevertheless, as demonstrated in Fig. 14b, one shouldpay attention to coke deposition, since it is thermodynamicallypropitiated at the temperature interval mentioned above.

Accordingly to Fig. 12b, increasing the system pressure or theoxygen to carbon ratio could be a reasonable way to avoid thisreaction.

The validation of the equilibrium data is performed by

comparison with the data reported by Ayabe et al. (2003), in thesame operational conditions (Table A.4). The authors provide ingraphics the conversion of CH4 and H2/(CO CO2) selectivity withfour different types of feed. The average relative error was found to

be less than 1%, not considering formation of coke in the

simulations. Thus, it can be assumed that the authors did notconsider coke deposition.

3.5. Methane reforming: an overview

For all practical purposes, especially considering industrial

production of hydrogen through methane reforming, the best

criterion of process optimization is to minimize the energy used perkilogram of hydrogen produced. The cost of the energy used will bedirectly affected by process temperature and pressure. The shown

results (e.g., Figs. 4, 8, and 12) are for the same temperature range(3731273 K) and the patterns of H2 yield are similar for all reformsalong this temperature range. It canbe seen also that highyields areobtained at pressures around 1 atm. Therefore, the effect of high or

low pressure costs can be neglected as a first approximation. Basedon that, the ratio energy/(H2 produced), can be minimized throughthe maximization of H2 yield (mol) since the energy used will beapproximately the same for equal temperatures. Summarizing,

maximizing H2 yield can be used as a first approximate criterion tocompare all methane reforming. Based on that, it can be seen thatsteam methane reforming process presents the best results

concerning hydrogen production, since it yields around 3 mol,compared to 1.75 mol in DRM and ORM.

4. Conclusions

A fairly complete and systematic thermodynamics analysiswas carried out for steam, dry, oxidative and autothermalreforming of methane. The equilibrium data taken from the

literature were compared with the results obtained with theLagranges multipliers method and the equilibrium constantsevaluation method. Although the results shown in this manu-script were already mentioned in other publications, only few of

them analyzed the deposition of coke and defined the operationalrange in which it happens with more probability. In Figs. 13, forexample, we can see clearly that intermediate temperatures andlow steam to carbon ratios in the feed favors the deposition of

carbon particles.The analyses enabled to validate the simulated results of this

work and to verify the best operational conditions for eachmethane reforming reaction. It was shown that the steam

reforming of methane process generates the highest yield for H 2(3.36 mol per mol of CH4 fed) with full CH4 conversion and almost

no coke deposition (0.05 mol). These values were attended witha temperature of 1120 K, atmospheric pressure and a steam tocarbon ratio of 4. We also determined the linearly independent

reactions that describe in a satisfactory way the reformatecomposition of each reaction system. With this analysis, it waspossible to predict in which operational range each reaction

prevails or not over the others.The proposed mathematical model for ATR has shown a good

adjustment to the experimental data of Ayabe et al. (2003),presenting a good agreement for methane conversions and

hydrogen yields over the whole range of temperature studied. Thesimulated data showed that the best reaction temperature tomaximize the yield of hydrogen is comprised between 723 and773 K, where more than 50% of methane is converted into products.

Acknowledgements

This work has been supported by Brazilian funding agencies,CAPES and CNPq (Grant # 475934/2006-7) as well as, Rede Bra-

sileira de Hidrogenio (CTPETRO/FINEP/PETROBRAS)

10

20

30

40

50a

O2

H2

CO2

CO

H2OCH

4Mo

lefraction(%)

473 673 873 1073 12730

10

20

30

40

0.0

0.4

0.8

1.2

1.6

2.0

b

C(s)

H2

CO2

CO

H2O

CH4

Molefraction(%)

Temperature (K)

Cokedeposition(mol)

0

Fig. 14. Composition and coke deposition in chemical equilibrium and calculated by

the reactor model for ATR. (a) Without coke deposition. (b) With coke deposition. ()

Reactor model. (.) Equilibrium. (Reaction conditions: CH4, 16.7%; O2, 1.7%; H2O, 41.6%;

N2 (balance); S/C 2.5; SV 7200 h1).



10/11

Appendix

Table A.1

Comparison between simulated and literature equilibrium data for SRM.

Operational

conditions

Compounds 773 K 873 K 973 K 1073 K 1173 K 1273 K

This wor k Liter . This work Liter . This work Liter . This work Liter. This wo rk Lit er. This wo rk Liter.

LM EEC LM EEC LM EEC LM EEC LM EEC LM EEC

Lutz et al. (2003)

S/C 2

P 10 atm

CH4 0.267 0.260 0.260 0.210 0.202 0.203 0.133 0.126 0.126 0.058 0.054 0.050 0.015 0.013 0.015 0.003 0.003 0.004

H2O 0.537 0.524 0.524 0.434 0.420 0.421 0.322 0.309 0.314 0.230 0.222 0.222 0.185 0.181 0.184 0.175 0.173 0.176

CO 0.002 0. 002 0.004 0.015 0. 016 0. 015 0.055 0.056 0. 061 0.114 0.115 0.115 0.154 0.154 0.153 0. 169 0.168 0.168

CO2 0.037 0.041 0.038 0.059 0.063 0.061 0.065 0.068 0.065 0.051 0.053 0.050 0.036 0.038 0.038 0.029 0.030 0.027

H2 0.157 0.173 0.174 0.282 0.299 0.300 0.425 0.441 0.434 0.547 0.556 0.563 0.610 0.614 0.61 0.624 0.626 0.625

Seo et al. (2002)

S/C 1

P 1 bar

CH4 0.320 0.317 0.194 0.192 0.137 0.079 0.078 0.055 0.027 0.026 0.018 0.009 0.009 0.004 0.004 0.004 0.000

H2O 0.249 0. 245 0.132 0.128 0. 151 0.054 0. 053 0.064 0.019 0.019 0. 018 0.007 0.007 0.004 0. 003 0.003 0. 000

CO 0.019 0.019 0.090 0. 091 0.059 0.185 0.185 0. 155 0.229 0.229 0.224 0.243 0.243 0.242 0.247 0.247 0.246CO2 0.071 0.072 0.062 0.063 0.046 0.025 0.025 0.023 0.007 0.007 0.004 0.002 0.002 0.000 0.001 0.001 0.000

H2 0.341 0.347 0.522 0.526 0.525 0.657 0.659 0.652 0.718 0.719 0.716 0.729 0.739 0.739 0.745 0.745 0.748

Table A.2

Comparison between simulated and literature equilibrium data for DRM.

Operational conditions Conv. (%) 673 K 773 K 873 K 973 K 1073 K

This work Liter. This work Liter. This work Liter. This work Liter. This work Liter.

LM EEC LM EEC LM EEC LM EEC LM EEC

Akpan et al. (2007)

CH4:CO2:N2 2:2:1P 1 atm

CH4 3.96 3.95 3.38 16.02 16.02 15.8 43.01 43.10 45.1 74.43 74.59 77.8 91.24 91.35 93.2

Table A.3

Comparison between simulated and literature equilibrium data for ORM.

Operational conditions Compounds O/C 0.5 O/C 1.0 O/C 1.5

This work Liter. This work Liter. This work Liter.

LM LM LM

Zhu et al. (2001)

T 873 K

P 1 atm

CH4 0.214 0.156 0.060 0.023 0.005 0.000

H2O 0.107 0.078 0.237 0.198 0.409 0.401

CO 0.155 0.200 0.118 0.148 0.062 0.063

CO2 0.107 0.078 0.195 0.175 0.270 0.268

H2 0.417 0.488 0.390 0.456 0.254 0.268

Table A.4

Comparison between simulated and literature equilibrium data for ATR.

Operational conditions Variable 573 K 673 K 773 K 873 K 973 K 1073 K

Ayabe et al. (2003)P 1 atm

This work Liter. This work Liter. This work Liter. This work Liter. This work Liter. This work Liter.

CH4 H2O O2 N2 LM LM LM LM LM LM

1 2.5 0.1 2.4 Conv. CH4 (%) 11.53 11.8 25.38 26.1 49.92 50.1 82.09 81.6 98.13 97.2 99.85 99.7

1 2.5 0.1 2.4 SelectivityH2

CO CO2

2.26 2.27 3.18 3.15 3.44 3.40 3.34 3.32 3.20 3.20 3.13 3.11

1 2.5 0.3 2.2 1.10 1.11 2.22 2.21 2.84 2.83 2.95 2.93 2.88 2.88 2.80 2.791 2.5 0.5 2 0.69 0.67 1.66 1.67 2.38 2.37 2.60 2.58 2.55 2.54 2.47 2.46

1 2.5 1 1.5 0.30 0.32 0.91 0.94 1.55 1.55 1.77 1.77 1.72 1.73 1.65 1.65



11/11

References

al-Qahtani, H.,1997. Effect of ageing on a steam reforming catalyst. Chem. Eng. J. 66,5156.

Akpan, E., Sun, Y., Kumar, P., Ibrahim, H., Aboudheir, A., Idem, R., 2007. Kinetics,experimental and reactor modelling studies of the carbon dioxide reforming ofmethane (CDRM) over a new Ni/CeO2ZrO2 catalyst in a packed bed tubularreactor. Chem. Eng. Sci. 62, 40124024.

Ayabe, S., Omoto, H., Utaka, T., Kikuchi, R., Sasaki, K., Teraoka, Y., Eguchi, K., 2003.Catalytic autothermal reforming of methane and propane over supported metalcatalysts. Appl. Catal. A. 241, 261269.

Benito, M., Garca, S., Ferreira-Aparicio, P., Garca Serrano, L., Daza, L., 2007.Development of biogas reforming NiLaAl catalysts for fuel cells. J. PowerSources 169, 177183.

Corbo, P., Migliardini, F., 2007. Hydrogen production by catalytic partial oxidationof methane and propane on Ni and Pt catalysts. Int. J. Hydrogen Energy 32,5566.

Dal Santo, V., Mondelli, C., De Grandi, V., Gallo, A., Recchia, S., Sordelli, L., Psaro, R.,2008. Supported Rh catalysts for methane partial oxidation prepared by OM-CVD of Rh(acac)(CO)2. Appl. Catal. A: Gen. 346, 126133.

Dias, J.A.C., Assaf, J.M., 2004. Autothermal reforming of methane over Ni/gAl2O3catalysts: the enhancement effect of small quantities of noble metals. J. PowerSources 130, 106110.

Donazzi, A., Beretta, A., Groppi, G., Forzatti, P., 2008. Catalytic partial oxidation ofmethane over a 4% Rh/a-Al2O3 catalyst. Part II: role of CO2 reforming. J. Catal.255, 259268.

Goodwin, D., 2004. CANTERA: object-oriented software for reacting flows. Calif.Inst. Technol.. .

Halabi, M.H., Croon, M.H.J.M., Van Der Schaaf, J., Cobden, P.D., Schouten, J.C., 2008.Modeling and analysis of autothermal reforming of methane to hydrogen ina fixed bed reformer. Chem. Eng. J. 137, 568578.

Hoang, D.L., Chan, S.H., Ding, O.L., 2006. Hydrogen production for fuel cells byautothermal reforming of methane over sulfide nickel catalyst on gammaalumina support. J. Power Sources 159, 12481257.

Hong, X., Wang, Y., 2009. Partial oxidation of methane to syngas catalyzed bya nickel nanowire catalyst. J. Nat. Gas Chem. 18, 98103.

INRIA ENPC. Scilab, On-line. .Khalesi, A., Arandiyan, H.R., Parvari, M., 2008. Effects of lanthanum substitution by

strontium and calcium in LaNiAl perovskite oxides in dry reforming ofmethane. Chin. J. Catal. 29 (10), 960968.

Lanza, R., Canu, P., Jars, S.G., 2008. Partial oxidation of methane over PtRubimetallic catalyst for syngas production. Appl. Catal. A. 348, 221228.

Laosiripojana, N., Sutthisripok, W., Assabumrungrat, S., 2005. Synthesis gasproduction from dry reforming of methane over CeO2 doped Ni/Al2O3:

influence of the doping ceria on the resistance toward carbon formation. Chem.Eng. J. 112, 1322.

Li, B., Maruyama, K., Nurunnabi, M., Kunimori, K., Tomishige, K., 2004. Temperatureprofiles of alumina-supported noble metal catalysts in autothermal reformingof methane. Appl. Catal. A. 275, 157172.

Lutz, A.E., Bradshaw, R.W., Keller, J.O.,Witmer,D.E., 2003.Thermodynamic analysisofhydrogen production by steam reforming. Int. J. Hydrogen Energy 28, 159167.

Mattos, L.V., Oliveira, E.R., Resende, P.D., Noronha, F.B., Passos, F.B., 2002. Partialoxidation of methane on Pt/CeZrO2 catalysts. Catal. Today 77, 245256.

Meng, L., Duan, Y.Y., Li, L., 2004. Correlations for second and third virial coefficients

of pure fluids. Fluid Phase Equilibria 226, 109120.Mukainakano, Y., Yoshida, K., Kado, S., Okumura, K., Kunimori, K., Tomishige, K.,

2007. Catalytic performance and characterization of PtNi bimetallic catalystsfor oxidative steam reforming of methane. Chem. Eng. Sci. 63, 48914901.

OConnor, A.M., Schuurman, Y., Ross, J.R.H., Mirodatos, C., 2006. Transient studies ofcarbon dioxide reforming of methane over Pt/ZrO2 and Pt/Al2O3. Catal. Today115, 191198.

Pedernera, M.N., Pina, J., Borio, D.O., 2007. Kinetic evaluation of carbon formation ina membrane reactor for methane reforming. Chem. Eng. J. 134, 138144.

Rakass, S., Oudghiri-Hassani, H., Rowntree, P., Abatzoglou, N., 2006. Steam reformingof methane over unsupported nickel catalysts. J. Power Sources 158, 485496.

Rostrup-Nielsen, J.R., 2002. Syngas in perspective. Catal. Today 71, 243247.Schadel, B.T., Duisberg, M., Deutschmann, O., 2009. Steam reforming of methane,

ethane, propane, butane, and natural gas over a rhodium-based catalyst. Catal.Today 142, 4251.

Seo, Y.-S., Shirley, S.T., Kolaczkowski, S.T., 2002. Evaluation of thermodynamicallyfavourable operating conditions for production of hydrogen in three differentreforming technologies. J. Power Sources 108, 213225.

Smet, C.R.H., Croon, M.H.J.M., Berger, R.J., Marin, G.B., Schouten, J.C., 2001. Design ofadiabatic fixed-bed reactors for the partial oxidation of methane to synthesisgas. Application to production of methanol and hydrogen-for-fuel-cells. Chem.Eng. Sci. 56, 48494861.

Smith, J.M., Van Ness, H.C., Abbott, M.M., 2000. Introduao a termodinamica daengenharia qumica, fifth ed. LTC, Rio de Janeiro.

Software ScanIt. www.amsterchem.com/scanit.html>.Trimm, D.L., Lam, C.W., 1980. The combustion of methane on platinumalumina

fibre catalysts-I: kinetics and mechanism. Chem. Eng. Sci. 35, 14051413.Xu, J., Froment, G.F., 1989. Methane steam reforming, methanation and watergas

shift: I. Intrinsic kinetics. AIChE J. 35, 8896.Yin, L., Wang, S., Lu, H., Ding, J., Mostofi, R., Hao, Z., 2007. Simulation of effect of

catalyst particle cluster on dry methane reforming in circulating fluidized beds.Chem. Eng. J. 131, 123134.

Zhu, J., Zhang, D., King, K.D., 2001. Reforming of CH4 by partial oxidation: ther-modynamic and kinetic analyses. Fuel 80, 899905.

http://www.cantera.org/http://www.scilab.org/http://www.amsterchem.com/scanit.html%3ehttp://www.amsterchem.com/scanit.html%3ehttp://www.scilab.org/http://www.cantera.org/

Documents

Avila-Neto_H2 Production From Methane Reforming