Ff

AK

a

ARR1AA

KBHAMA

1

ttssA[camfs

pmsfcolri

0h

Catalysis Today 210 (2013) 19– 25

Contents lists available at SciVerse ScienceDirect

Catalysis Today

jou rn al hom epage: www.elsev ier .com/ locate /ca t tod

ull-scale autothermal reforming for transport applications: The effect of dieseluel quality

ngélica V. González ∗, Lars J. PetterssonTH Royal Institute of Technology, Department of Chemical Engineering and Technology, SE-100 44 Stockholm, Sweden

r t i c l e i n f o

rticle history:eceived 27 July 2012eceived in revised form4 November 2012ccepted 15 November 2012vailable online 23 January 2013

a b s t r a c t

This study evaluates the feasibility of H2 production through a fuel flexible reformer, at realistic operatingconditions for electricity supply by FC-APUs in the transport sector. The fuel flexibility is evaluated bycomparison of autothermal reforming performance with biodiesel (RME), Fischer–Tropsch, low-sulfurdiesel (MK1) and European standard diesel (DIN 590). ATR experiments with two monolithic catalysts,Rh1.0Pt1.0Ce10La10/Al2O3 (CAT 1) and Rh1.0Pt1.0Mg4.0Y5.0/CeO2–ZrO2 (CAT 2), sequentially placed in theaxial direction of the reformer length were used for full-scale tests. The O /C ratio was varied from 0.3

eywords:iodieselydrogenutothermal reformingultifuel study

2

to 0.5 and the H2O/C ratio varied from 2 to 3.5, reaching temperatures in the interval of 700–800 ◦C. Thehydrogen production and fuel conversion showed an upward trend from RME < DIN 590 < MK1 < FT withmaximum 42 vol.% H2 and 99% fuel conversion for FT diesel.

© 2012 Elsevier B.V. All rights reserved.

PU

. Introduction

Reduction of pollutant emissions and fuel consumption in theransport sector are major concerns, which have led innovationoward usage of alternative fuels and integration of technologiesuch as fuel cell auxiliary power units (FC-APUs) for electricityupply. This is the case for heavy-duty trucks in which on-board FC-PUs can provide the extra electricity needed during idling mode

1–3]. Engine idling is both fuel inefficient as well as a significantontributor of exhaust emissions. Replacing the engine idling with

small APU is today considered by the automotive industry as theost viable alternative for reducing idle pollutant emissions and

uel consumption, while providing the end-user significant fuelavings.

Several fuel cell technologies can be used in APU, the low tem-erature proton exchange membrane fuel cell (PEMFC) being theost used for transport applications due to its high power den-

ity, and low operating temperature. These properties are relevantor rapid cold start, and compactness for space restrictions in vehi-le applications [4]. The hydrogen needed for the FC is producednboard the truck in a catalytic fuel processor, thus overcoming

imitations such as hydrogen storage and transport [5]. The fueleformer operates through diesel autothermal reforming (ATR),n which steam and fuel are fed simultaneously to a catalytic

∗ Corresponding author. Tel.: +46 08 790 9150.E-mail address: avga@kth.se (A.V. González).

920-5861/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.cattod.2012.11.009

reactor. ATR can be understood as a combination of endothermicsteam reforming (SR), and of partial oxidation (POX) [4]. After thefuel reformer CO clean-up units are needed, since PEMFC has lowtolerance to CO and sulfur.

Diesel is the most used feedstock for hydrogen generation intransport applications, due to its high energy density and existingfuel infrastructure. Nevertheless, concerns on limited oil resourcesand reduction of CO2 emissions have raised interest in renewableand alternative fuels. Therefore, fuel flexibility is relevant for com-mercialization and assessment of emerging fuels and technologiessuch as FC-APU.

Petro-diesel, due to its complex composition and sulfur con-tent in commercial diesel represents challenges for understandingof reaction mechanisms and catalyst durability of autothermalreforming [6]. The multiple main and side reactions that occursimultaneously during this process make it very difficult to eluci-date general mechanisms [7,8]. Extensive analysis has been madefor ATR studies with simulated diesel [5,9,10]; they have suggestedreaction mechanisms, evaluated heat and mass transfer effects, aswell as the influence of different operating parameters in the prod-uct composition and reformer efficiency. Most of these studies havebeen performed in fixed-bed reactors at bench scale [11].

Efforts have been made to evaluate fuel processors in the kWrange for PEMFC in order to evaluate the feasibility of the system

at real operating conditions. The research group at the ArgonneNational Laboratory (ANL) has extensively investigated the systemfor several surrogated and commercial fuels [12–14]. Their researchdemonstrated the efficiency of the system, and presents a better

20 A.V. González, L.J. Pettersson / Catalysis Today 210 (2013) 19– 25

Table 1Diesel fuel properties [1,31–33].

Properties Unit FT MK1 DIN 590 RME

Density at 15 ◦C kg/m3 798 813 844 880Viscosity at 40 ◦C mm2/s 2.56 2.1 3.14 4.25Boiling point at 1 bar ◦C 338–350 180–290 250–350 315–350Cetane number – 74 51 51 52Flash point ◦C 97 68 70 120LHV per mass MJ/kg 44 43 43 38Water content mg/kg 39 50 40 400Aromatics v/v% 0.5 4.5 4.6 6Sulfur content mg/kg 0 0–5 7.9 1

urac

be[bcmtgorthaat

rlM3at

mHataatFtlfti

flclBcmlew

C mass fraction wt.% 85

H mass fraction wt.% 15

O mass fraction wt.% –

nderstanding of the process mechanisms and principles. Theo-etical simulations of ATR for renewable fuels such as biodieselnd diesel surrogates have given insights of thermal equilibriumonditions and reformer efficiency [15,16].

Simultaneous to fuel reformer design, reforming catalysts haveeen developed, noble metal based catalysts being the most used,.g. Rh, Pt, due to their high coke resistance and high H2 yield10,17–19]. The influence of structural and electronic interactionsetween promoters and supports is well known for improving theatalytic activity. Particularly, intrinsic catalytic activity of certainaterials such as Gd2O3, CeO2, ZrO2, MgO and mixed oxides for par-

icular reaction conditions have been studied, especially for exhaustas after-treatment. This is due to their ability to store and releasexygen, known as oxygen storage capacity (OSC), which enhancesedox interactions with noble metals, promoting oxidation reac-ions [20–22]. The alumina supports have been widely used for itsigh surface area and thermal stability. Delta and gamma aluminare the most used for reforming catalysts due to their high surfacerea (100–150 m2/g). The stability of the phases has been reportedo improve with additions of CeO2 and La2O3 [23–25].

In earlier catalytic activity studies in a bench scale monolithiceactor, ATR experiments were performed for bimetallic RhPt cata-ysts supported over �-Al2O3, SiO2, TiO2, and CeO2–ZrO2 for diesel

K1 (sulfur < 10 ppm). Results showed 96% fuel conversion and8 vol.% H2 in the product gas for the CeO2–ZrO2 supported catalyst,nd the catalyst characterization elucidated the key role played byhe support in the catalyst activity improvement [24].

As described above, advances in diesel reforming have beenade, and many studies have been focused on petro-diesel.owever, fossil fuels are constantly subjected to availability fluctu-tions, implying boosted fuel prices. Therefore, attention is drawno find energy sources independent from fossil fuels. The cat-lytic conversion of biofuels and biomass has been presented as

promising alternative for fuel and electricity supply. Studies onhe use of fuels such as rapeseed methyl ester (RME) and syntheticischer–Tropsch diesel reveal that alternative fuels may contributeo reduce exhaust emissions in combustion engines, due to theirow sulfur and aromatic content [26–28]. Even though attentionor FC-APU for the transport sector has been growing, experimen-al evaluation on the use of alternative fuels under real conditionsn this application is limited.

The contribution of the current study is centered on the fuelexibility and the catalyst performance at realistic operatingonditions for autothermal reforming of RME, Fischer–Tropsch,ow-sulfur diesel (MK1) and European standard diesel (DIN 590).esides, according to Rostrup-Nielsen and Højlund-Nielsen [29]atalyst activity from process simulation at bench scale reactors

ight not only give inaccurate information regarding mass transfer

imitations and catalyst deactivation, but also temperature gradi-nts could be different since the bench reactor often is isothermalhereas full-scale reactors operate almost adiabatically. Hence,

87 86 78.513 13.5 10.8

– – 10.5

verification of the catalyst activity results from preliminary benchscale test with Al2O3 and CeO2–ZrO2-supported bimetallic preciousmetals (Rh, Pt) in full-scale tests were performed in the presentstudy.During the ATR experiments the O2/C ratio was varied from0.3 to 0.5 and the H2O/C ratio varied from 2 to 3.5, reaching temper-atures in the interval of 700–800 ◦C. Partial oxidation is believed totake place at the beginning of the catalyst bed, followed by steamreforming in the later part of the bed. Therefore, bimetallic RhPtcatalysts supported on stabilized Al2O3 for partial oxidation andsupported on CeO2–ZrO2 promoted with MgO and Y2O3 for steamreforming, have been used, respectively.

2. Experimental

2.1. Diesel qualities

ATR experiments were carried out for four diesel qualities. Theirproperties are shown in Table 1. Fischer–Tropsch diesel (FT, EcoparAB) presents properties such as high cetane number, low aromatic,and low sulfur content, which significantly reduce formation ofNOx, PM and catalyst deactivation by sulfur poisoning. In fact,research on FT diesel usage in transport applications has shown bet-ter combustion performance and lower hazardous emissions thancommercial diesels [28,30,26].

Commercial Swedish Environmental class 1 (MK1) is the mostused diesel fuel in Sweden, and therefore tests with this fuel wereperformed. MK1 was tested previously in our research group andwas included in this study to verify the catalyst activity acquiredfrom previous bench-scale experiments with the catalyst composi-tion used herein [24,34]. European Standard diesel (DIN 590, ST1),presents a somewhat similar composition with MK1 diesel; how-ever, it has relatively higher sulfur content and higher viscosity.

Biodiesel is produced from a vegetable oil and is therefore arenewable fuel. Rapeseed methyl ester (RME) is being consideredas an alternative substitutive fuel for fossil fuels. RME is becom-ing implemented in different applications in the transport sector,due to the decrease of HC and CO2 emissions in internal combus-tion engines [31]. The oxygen content in RME enhances oxidationreactions, which may compensate for its low energy content andsubsequent higher fuel consumption [35,36]. Therefore, in thisstudy RME has been preliminarily evaluated in terms of reformingfeasibility and its product gas composition.

2.2. Reactor system and reaction conditions

The experimental equipment used in this study and its detaileddescription is reported elsewhere [1]. Briefly, autothermal reform-

ing takes place in a stainless steel tubular reformer with an innerdiameter of 84 mm and a length of 400 mm. Initially, an air–steammixture is preheated up to 300 ◦C and is further preheated in ajacket around the first monolith. Next, fuel is injected into the

Catalysis Today 210 (2013) 19– 25 21

astaf

cs(otc

app

2

awCt(tIaH

ftCrmtwcs

H

�

3

3

oadsfirdfee

gpo

A.V. González, L.J. Pettersson /

ir–steam mixture in the reformer, at 50 ◦C, with a stainless steelpray nozzle (0.58 mm orifice diameter, Mistjet®, STEINEN). Afterhe initial mixing zone, reactants flowed through a zirconia-treatedlumina foam to provide additional mixing and to avoid that liquiduel reached the catalytic monolith.

Two catalytic monoliths were used. The first monolith wasoated with a washcoat of Rh1.0Pt1.0Ce10La10/Al2O3 (CAT 1) and theecond monolith was coated with Rh1.0Pt1.0Mg4.0Y5.0/CeO2–ZrO2CAT 2). They were sequentially placed along the axial directionf the reformer. The same catalyst composition and location inhe reformer was used for all fuels. The catalyst preparation andharacterization is documented in previous studies [24].

Fuels were evaluated within a range of O2/C ratio of 0.3–0.49nd H2O/C ratio of 2–3, as is shown in Table 2. Measurement of theroduct gas composition was made after 30 min on stream, whenseudo-equilibrium conditions were reached.

.3. Collection and analysis of data

Concentrations of dry reformate (H2, N2, O2, CO, and CO2) werenalyzed using a gas chromatograph (GC) Varian CP-3800 equippedith a thermal conductivity detector (TCD). The wet reformate (CO,O2, H2O, C1–C3 paraffins, C2–C3 olefins, C6H6, and diesel) was con-inuously analyzed using a Fourier transform infrared spectrometerFTIR), MKS MultigasTM 2030 HS. The FTIR diesel response fac-or was configured, designed and provided by the company MKSnstruments. Additional to GC analysis, the hydrogen produced waslso measured by an electron pulse ionization mass spectrometer-SENSE (EIMS) to reassure the obtained data.

The fuel conversion (Xfuel) was defined as the amount of dieseled with respect to the amount of diesel detected by the FTIR inhe wet reformate and divided by the amount of diesel fed. TheO2/(CO2 + CO) product ratio was used to evaluate CO2 selectivityelative to CO. Hydrogen yield (H2 yield), Eq. (1), is defined as theoles of hydrogen in the product gas obtained, divided per the

heoretical yield, which is the moles of H2 contained in the fuel andater. Theoretical calculations were performed assuming that all

arbon reacts to CO2. The reformer efficiency (�Ref) was defined ashown in Eq. (2).

2 yield (%) = molH2 formedtheoreticalH2 yield

× 100 (1)

Ref = FH2 · LHVH2

FFuel · LHVFuel× 100 (2)

. Results and discussion

.1. Temperature profiles

Fig. 1 shows temperature profiles during the resulting optimalperating conditions for each fuel used in this study. Temperaturesre measured at 14 positions in the reformer axial direction; theetailed configuration of the thermocouples is reported in earliertudies [1]. Preliminary experiments, with changes in H2O/C ratiorom 2 to 3 and O2/C ratio from 0.3 to 0.49, show general trendsn temperature profiles. Firstly, the temperatures rise with O2/Catio increments and a constant H2O/C ratio. Second, temperatureecreases with H2O/C ratio increments, showing temperature dif-erences from 10 to 15 ◦C. The temperature differences are to a greatxtent dependent on oxidants in the system and due to reactionnthalpies [37].

The temperature range in the mixing zone for all fuels was ran-ing from 330 to 460 ◦C. This, compared with the temperature of thereheated air–steam mixture (300 ◦C), means that a certain degreef oxidation reactions take place, therefore consuming part of the

Fig. 1. Temperature profile for H2O/C ∼ 2.5 and O2/C in the interval 0.42–0.48according to the fuel used (Table 2).

fuel and producing heat. As a consequence, partial oxidation reac-tions take place in the mixing zone once the fuel is in contact withthe air–steam mixture.

FT diesel, in particular, shows temperatures in the mixing zoneranging from 320 ◦C to 420 ◦C, where according to the low temper-ature combustion mechanism suggested by Spadaccini et al. [38],cool flame reactions may take place. It has also been reported thatsuch behavior may to a higher extent occur during the reformingof straight chain hydrocarbons [2].

MK1 and DIN 590 showed similar trends, with temperatures inthe range of 417–460 ◦C, following the general trends previouslydescribed. RME, due to its complex composition, higher density,and viscosity, presented significant poor mixing and evaporationconditions, leading to a light-off delay compared with MK1 anddiesel EN 590. At 310 ◦C hot spots were formed, as a result of thepoor mixing conditions. After each experiment a reactor inspectionwas made to check the state of the nozzle, catalyst and the reactorwalls. In the case of RME, polymerization of biodiesel on the nozzleand on the walls of the mixing zone was observed as a sign of liquidhydrocarbons not being evaporated properly. Similar observationshave been reported in other studies [2].

Temperature increment is observed (500–600 ◦C) for all fuels,downstream the zirconia-treated alumina foam. This may be theconsequence of process such as better mixing of the reactant gases,in a lower extent for RME. Besides, Creaser et al. [39] reported thatthis increase in temperature may also be ascribed to back radiationfrom the front of the first monolith, where the maximum tempera-ture is achieved due to the exothermic partial oxidation. In addition,at these temperatures partial oxidation can occur. However, it is dif-ficult to predict in which extent these causes influence temperatureincrements.

At the inlet of the first monolith, temperatures from 650 to770 ◦C were recorded as shown in Fig. 1. The high temperaturesare the result of the exothermic partial oxidation mainly occur-ring at the front of the first monolith, CAT 1. These temperatureswere measured at the center of one monolith channel and there-fore they correspond to gas phase temperatures. The temperaturefurther decreases from 650–770 ◦C to 640–736 ◦C at the outlet ofCAT 1, as a consequence of heat losses and promotion of endother-mic reactions such as steam reforming and the reverse water-gasshift reaction (WGS) by lower oxygen concentration. This results ina decreasing temperature gradient through CAT 2.

3.2. Selecting experimental conditions

Reforming experiments were carried out with variations of O2/Cand H2O/C ratios in each fuel, as is shown in Table 2.

22 A.V. González, L.J. Pettersson / Catalysis Today 210 (2013) 19– 25

Table 2Experimental conditions.

Fuel Fuel feed (g/min) Feed O2:C Feed H2O:C GHSV(103 h−1)a �b

FT diesel 19.2 0.34–0.45 2.0–3.0 8.8–12.4 0.23–0.32MK1 19 0.38–0.49 2.0–3.0 9.2–12.9 0.25–0.33DIN 590 20 0.39–0.47 2.0–3.0 9.7–13.7 0.26–0.32RME 23 0.33–0.49 2.5 9.4–11.3 0.15–0.25

a GHSV – gas hour space velocity.b � – air/fuel equivalence ratio.

620 64 0 66 0 68 0 70 0 72 0 74 0

0

5

10

15

20

25

30

35

40

45

T ( ºC)

Pro

du

ct (V

ol%

, H

2O

fre

e)

H2

CO2

CO

CH4

0,34 0,38 0,42 0,45

O /C

10 10,5 10,9 11,3

GHSV (103 h -1

)

3

pitdHow4aKm

600 62 0 64 0 66 0 68 0 70 0 72 0 74 0 76 0 78 0

20

30

40

50

60

70

80

90

100

XF

ue

l(%)

T ( C)

FT

MK1

DIN 590

RME

º

2

Fig. 2. FT reformate composition at H2O/C 2.5.

.2.1. Diesel reforming of Fischer–Tropsch dieselFig. 2 shows the product gas composition as function of tem-

erature after CAT 2 at H2O/C ∼ 2.5. A general decreasing trendn hydrogen is shown with gradual temperature increments, dueo more oxidation reactions taking place and consuming H2 pro-uced and therefore fuel conversion increases, as shown in Fig. 3.owever, the lower concentration values may also be the causef dilution effects with higher feed flow, since the O2/C ratioas raised up to 0.45. Maximum hydrogen concentration of

3 vol.% and a fuel conversion of 93% were achieved for O2/C ∼ 0.38nd H2O/C ∼ 2.5. In previous full-scale experiments for FT diesel,aratzas et al. [40] showed that the catalyst composition in bothonoliths, Rh1.0Pt1.0Ce10La10/Al2O3 resulted in 32.8% H2 and 51%

600 620 640 660 680 700 720 740 760 780

0

20

40

60

80

100

CO

2 s

ele

ctivity (

%)

T ( C)

FT

MK1

DIN 590

RME

º

A

Fig. 4. CO2 selectivity (A) and hydr

Fig. 3. Fuel conversion for H2/C 2.5.

of CO2 selectivity via ATR at O2/C ∼ 0.39–0.40 and H2O/C ∼ 2.5.Given that the same reactor set-up, as the one presented inthis study, was used to perform the experiments; the cause forhigher values for fuel conversion and hydrogen production in thisstudy suggests that different reaction conditions and catalyst com-position in the second monolith, Rh1.0Pt1.0Mg4.0Y5.0/CeO2–ZrO2,significantly increases the H2 production.

In fact, characterization studies with this catalyst compositionelucidate the key role played by the redox properties of the supportat reaction conditions, improving the active metal reducibility onthe catalyst surface. Moreover, the WGS reaction is enhanced byCeO2–ZrO2 mixed oxides increasing the hydrogen production [24].CO and CO2 concentrations show stable values as the temperaturerises, shown in Fig. 2. Nevertheless, fuel properties and the high H/C

ratio of Fischer–Tropsch diesel also influence selectivity toward H2in the reformate gas. This is due to the low C C energy bond in aparaffinic hydrocarbon such as FT diesel [41]. This made reforming

600 620 640 660 680 700 720 740 760 780 800

0

10

20

30

40

50

60

70

80

H2 Y

ield

(%

)

T ( C)

FT

MK1

DIN 590

RME

º

B

ogen yield (B) for H2O/C 2.5.

A.V. González, L.J. Pettersson / Catalysis Today 210 (2013) 19– 25 23

Table 3Optimal reaction conditions.

Fuel Flow rate (g/min) O2:C (mol:mol) H2O:C (mol:mol) �a GHSV [103 h−1]b Xfuel (%) H:C

FT 19 0.42 2.5 0.28 10.85 97 2.03MK1 19.7 0.48 2.5 0.33 11.67 98.5 1.86DIN EN 590 20 0.47 2.5 0.32 11.85 92 1.93RME 23 0.45 2.5 0.26 10.98 88 1.88

otp

3

cu0aavtatfhSe

fsremh[p

680 700 720 740 760 780

0

10

20

30

40

H2

CO2

CO

CH4

Pro

duct

(Vol%

, H

2O

fre

e)

T ( C)

0,39 0,43 0,47

11 11,5 11,9

GHSV (103 h

-1)

º

a � – air/fuel equivalence ratio.b GHSV – gas hour space velocity.

f hydrocarbons easier and therefore more H2 is yielded at loweremperatures (Fig. 4 B). This was also noted in the temperaturerofiles, shown in Fig. 1.

.2.2. Diesel reforming of low sulfur diesel (MK1)Full-scale experiments with the new catalyst composition and

onfiguration are presented in this section. Fig. 5 shows the prod-ct gas distribution at H2O/C ∼ 2.5 for values of O2/C from 0.38 to.48. The highest hydrogen concentration, 35.3 vol.%, was obtainedt O2/C ∼ 0.44, with a fuel conversion of 97.5%. At low temper-tures the hydrogen concentration in the product gas has littleariation, unlike FT diesel. However, at 730 ◦C the H2 concentra-ion slightly decreases, while stable concentrations for CO and CO2re seen. These trends could be attributed to the reverse WGS reac-ion promoted at high temperatures [37]. Fig. 3 shows augments ofuel conversion with temperature. This was expected, since heavyydrocarbons are further converted to short-chain hydrocarbons.imilar observations were reported by I. Kang et al. [41] in ATRxperiments of different aromatic structures in a fixed-bed reactor.

In addition to the presented results, experiments were per-ormed with variations of H2O/C ratio, not included in this paper,howing that CO decreases while the CO2 increases with H2O/Catio increments, as more steam is introduced to the systemndothermic reactions are favored. Other studies are in agree-

ent with the above described [42]. The reforming of MK1

as been extensively studied previously in our research group1,24,39,43], and MK1 has been added to this study for comparisonurposes.

640 66 0 68 0 70 0 72 0 74 0

0

5

10

15

20

25

30

35

H2

CO2

CO

CH4

Pro

du

ct (V

ol%

, H

2O

fre

e)

T ( C)

0,38 0,41 0,44 0,48

O2/C

10,5 10,8 11,3 11,7

GHSV (103 h

-1)

º

Fig. 5. MK1 reformate composition at H2O/C ∼ 2.5.

O2/C

Fig. 6. DIN 590 reformate composition at H2O/C ratio 2.5.

3.2.3. Diesel reforming of European standard diesel (DIN 590)Reforming experiments with DIN 590 show an increasing hydro-

gen concentration with temperature, unlike the two precedingfuels tested. Maximum hydrogen concentration of 36 vol.% is

620 64 0 66 0 68 0 70 0 72 0 74 0 76 0

0

5

10

15

20

25

30

H2

CO2

CO

CH4

Pro

duct (V

ol%

, H

2O

fre

e)

T( C)

0,35 0,4 0,45 0,49

O2/C

9,8 10,6 10,9 11,8

GHSV (103 h -1

)

º

Fig. 7. RME reformate composition at H2O/C ∼ 2.5.

24 A.V. González, L.J. Pettersson / Catalysis Today 210 (2013) 19– 25

FT MK1 DIN 59 0 RME30

40

50

60

70

80

90

Fuels

FT MK1 DIN 59 0 RME0

10

20

30

40

Pro

duct

s (v

ol %

, H2O

free

)

Pro

duct

s (v

ol %

, H2O

free

)

Fuels

A B

select

d7

tarSaih[aitt(

3

FCiotlwtsfmagcp

vTodwthi[

Fig. 8. Optimal

epicted in Fig. 6, which corresponds to ∼92% fuel conversion at67 ◦C, shown in Fig. 3.

During experiments with DIN 590 was observed that higheremperatures were needed in order to obtain fuel conversionsbove 90%, as seen in Fig. 3. High temperatures were required foreforming reactions in the study of aromatic surrogates in fuels byhekhawat et al. [5]. This is due to the complex aromatic structurend high-molecular weight hydrocarbons, which makes reform-ng more difficult at lower temperatures. Conversion of aromaticydrocarbons is reported to occur at temperatures beyond 750 ◦C42,44]. H2 yield, Fig. 4B, and CO2 selectivity, calculated with GCnalysis data, showed that more hydrogen and CO2 are formedn the reformate gas as the temperature increases. The CO2 selec-ivity, at low temperatures was steadily constant at 50%, but ashe temperature increases from 720 to 767 ◦C, it rises up to 55%Fig. 4A).

.2.4. Diesel reforming of biodiesel (RME)The product gas distribution for RME reforming is shown in

ig. 7. Hydrogen decreases with temperature, however irregularO and CO2 concentration were observed during RME exper-

ments. These instabilities are due to the thermal instabilitiesf the oxygenated compounds of RME [45]. In contrast withhe previous fuels described, the amount of CO and CO2 is, ateast, 30% lower. Maximum hydrogen concentration 31.3 vol.%

as reached at O2/C ∼ 0.35, however, at this operating condi-ion the fuel conversion reached 40%. In general, RME reforminghowed lower conversion (Fig. 3). Further conversion incrementsrom 79% were recorded with subsequent temperature incre-

ents up to a maximum of 89% fuel conversion was reachedt 745 ◦C. This can probably be due to poor mixing conditionsiven by the injection nozzle, which was initially intended forommercial fuel qualities, relatively low fuel flow and at lowressure.

The high viscosity and density of RME made the mixing andaporization of the fuel in the mixing zone even more difficult.herefore, more fuel was needed to produce the same quantityf energy, 23 g/min, listed in Table 2. In fact, Specchia et al. [15]esigned a fuel reformer for biodiesel in which the injection systemas composed by two nozzles to increase the spray and evapora-

ion of the fuel in the mixing zone of the reformer. On the otherand, the fuel inlet can be emulsified with steam prior to injection

n the reactor mixing zone, where it is subsequently mixed with air46,47].

ed parameters.

3.3. Assessing fuel flexibility

From the above analysis, a selection of the most promisingexperimental conditions was extracted to analyze the fuel flexi-bility of the ATR reformer, shown in Table 3. Fuel conversion fallsin the following order FT > MK1 > DIN 590 > RME, which is related tothe higher reforming temperature needed for more complex fuelssuch as MK1 and DIN 590 due to aromatic and branched compounds[5]. The CO and CO2 concentration gradually increases in the prod-uct gas, following the order FT > MK1 > DIN 590 except for RME,described in Table 3. H2 selectivity, CO2 selectivity, and reformingefficiency are depicted in Fig. 8. The reforming efficiency shows amaximum value for FT diesel of 85% and further decline to 68% forMK1 reforming given the lower heating value for MK1 with 1 MJ/kgless than the one for FT diesel. Reformer efficiency remains steadilyconstant for the fossil fuels with the same heating value. How-ever, for RME with significantly lower heating value the reformerefficiency drops up to 43%, shown in Fig. 8A. The hydrogen produc-tion and fuel conversion shows an upward trend from RME < DIN590 < MK1 < FT with maximum 42 vol.% H2 and 99% fuel conversionfor FT diesel (Fig. 8B).

As seen from the experiment series, ATR for several diesel qual-ities is feasible with high reformer efficiencies for the cases of FTdiesel, MK1 diesel and the European standard diesel. However, RMEremains to be subject of study, since modification to the actualreformer design are needed, for instance the injection system.Thermal instabilities were also observed during RME experiments,presumably due to the thermal instabilities of the oxygenated com-pounds [45].

4. Concluding remarks

The fuel flexibility of the fuel reformer for FC-APUs wasevaluated at real operating conditions. Two monolithic cat-alysts were used, Rh1.0Pt1.0Ce10La10/Al2O3 (CAT 1) andRh1.0Pt1.0Mg4.0Y5.0/CeO2–ZrO2 (CAT 2), sequentially placed inthe axial direction of the reformer length. Excellent results with FTdiesel demonstrate the feasibility of usage of alternative fuels forFC-APU applications. At the same time the fuel flexibility capabilityof the system was validated by using different diesel qualities for

hydrogen production with 70% reformer efficiency.

From ATR experiments, the hydrogen production and fuel con-version show an upward trend from RME < DIN 590 < MK1 < FTreaching 42 vol.% H2 and ∼97% full-conversion for FT diesel. Results

Catal

fohm

dhtaafhp

wacnwlefit

A

oCGs

R

[[

[

[

[

[

[[

[[[

[

[

[

[

[

[

[

[[

[

[

[[[

[[[

[[

[

[[[

[

A.V. González, L.J. Pettersson /

rom MK1 and DIN 590 show a somewhat similar behavior in termsf product distribution and fuel conversion, the MK1 being slightlyigher. RME reached 88% fuel conversion and 25 vol.% H2 whicheans 40% less H2 generated than with FT diesel.The overall results indicate that the hydrogen concentration

eclines with temperature, except for DIN 590 reforming, whereydrogen generation increases at high temperatures. This is dueo the fact that aromatics and branched compounds are reformedt temperatures above 750 ◦C. Both catalysts used had high activitynd selectivity toward H2, confirming the preliminary experimentsrom a bench-scale reformer. The product gas distribution wasighly dependent on the WGS reaction as well as the fuel com-osition and reformer design.

It should be noted that this study has been primarily concernedith the feasibility of renewable diesel usage for hydrogen gener-

tion and therefore limitations of this study are the poor mixingonditions at the mixing zone given by the nozzle used, which wasot prepared for low heating value fuels such as RME. The nozzleas initially intended for commercial fuel qualities, with relative

ow fuel flow and pressure. In order to address limitations on fuelvaporation in the mixing zone further work on biodiesel emulsi-cation prior injection, and a double nozzle location could be usedo increase the inlet mixing.

cknowledgements

The financial support from The Swedish Energy Agency through-ut this project is gratefully acknowledged. We would like to thankorning Inc. for supplying cordierite substrates, Sasol GermanymbH and MEL chemicals for providing alumina and ceria–zirconiaupply, respectively.

eferences

[1] X. Karatzas, M. Nilsson, J. Dawody, B. Lindström, L.J. Pettersson, Chemical Engi-neering Journal 156 (2010) 366.

[2] B. Lindström, J.A.J. Karlsson, P. Ekdunge, L. De Verdier, B. Häggendal, J. Dawody,M. Nilsson, L.J. Pettersson, International Journal of Hydrogen Energy 34 (2009)3367.

[3] S. Golunski, Energy & Environmental Science 3 (2010) 1918.[4] D. Shekhawat, D.A. Berry, J.J. Spivey, in: S. Dushyant, J.J. Spivey, A.B. David (Eds.),

Fuel Cells: Technologies for Fuel Processing, Elsevier, Amsterdam, 2011, p. 1.[5] D. Shekhawat, D.A. Berry, D.J. Haynes, J.J. Spivey, Fuel 88 (2009) 817.[6] R.K. Kaila, A.O.I. Krause, International Journal of Hydrogen Energy 31 (2006)

1934.[7] R.D. Parmar, A. Kundu, C. Thurgood, B.A. Peppley, K. Karan, Fuel 89 (2010) 1212.

[8] M. Pacheco, J. Sira, J. Kopasz, Applied Catalysis A 250 (2003) 161.[9] I.Y. Kang, H.H. Carstensen, A.M. Dean, Journal of Power Sources 196 (2011)

2020.10] M. Ferrandon, T. Krause, Applied Catalysis A 311 (2006) 135.11] T.G. DuBois, S. Nieh, Fuel 90 (2011) 1439.

[

[[

ysis Today 210 (2013) 19– 25 25

12] M. Krumpelt, T.R. Krause, J.D. Carter, J.P. Kopasz, S. Ahmed, Catalysis Today 77(2002) 3.

13] D.J. Liu, T.D. Kaun, H.K. Liao, S. Ahmed, International Journal of Hydrogen Energy29 (2004) 1035.

14] M. Krumpelt, T.R. Krause, J.P. Kopasz, ASME, Fuel Cell Science, Engineering andTechnology, 2003.

15] S. Specchia, F.W.A. Tillemans, P.F.V.D. Oosterkamp, G. Saracco, Journal of PowerSources 145 (2005) 683.

16] I. Kang, J. Bae, Journal of Power Sources 159 (2006) 1283.17] R.K. Kaila, A. Gutierrez, R. Slioor, M. Kemell, M. Leskela, A.O.I. Krause, Applied

Catalysis B 84 (2008) 223.18] M. Ferrandon, A.J. Kropf, T. Krause, Applied Catalysis A 379 (2010) 121.19] A.F. Ghenciu, Current Opinion in Solid State and Materials Science 6 (2002) 389.20] Z.X. Yang, Y.W. Wei, Z.M. Fu, Z.S. Lu, K. Hermansson, Surface Science 602 (2008)

1199.21] H.M. Li, Q.C. Zhu, Y.L. Li, M.C. Gong, Y.D. Chen, J.L. Wang, Y.Q. Chen, Journal of

Rare Earths 28 (2010) 79.22] M. Boaro, C. De Leitenburg, G. Dolcetti, A. Trovarelli, M. Graziani, Topics in

Catalysis 16–17 (2001) 299.23] Z.S. Yuan, C.J. Ni, C.X. Zhang, D.N. Gao, S.D. Wang, Y.M. Xie, A. Okada, Catalysis

Today 146 (2009) 124.24] X. Karatzas, K. Jansson, A.V. González, J. Dawody, L.J. Pettersson, Applied Catal-

ysis B 106 (2011) 476.25] P.K. Cheekatamarla, A.M. Lane, International Journal of Hydrogen Energy 30

(2005) 1277.26] S.S. Gill, A. Tsolakis, K.D. Dearn, J. Rodríguez-Fernández, Progress in Energy and

Combustion Science 37 (2011) 503.27] J. Sadhukhan, K.S. Ng, Industrial & Engineering Chemistry Research 50 (2011)

6794.28] E. Mancaruso, B.M. Vaglieco, Applied Energy 91 (2012) 385.29] J.R. Rostrup-Nielsen, P.E. Højlund Nielsen, in: J. Oudar, H. Wise (Eds.), Deacti-

vation and Poisoning of Catalysts, Marcel Dekker, New York, 1985.30] M. Lindgren, K. Arrhenius, G. Larsson, L. Bäfver, H. Arvidsson, C. Wetterberg,

P.-A. Hansson, L. Rosell, Atmospheric Environment 45 (2011) 5394.31] J. Krahl, G. Knothe, A. Munack, Y. Ruschel, O. Schröder, E. Hallier, G. Westphal,

J. Bünger, Fuel 88 (2009) 1064.32] M. Dzida, P. Prusakiewicz, Fuel 87 (2008) 1941.33] M. Lindgren, G. Larsson, P.A. Hansson, Biosystems Engineering 107 (2010) 123.34] M. Nilsson, X. Karatzas, B. Lindström, L.J. Pettersson, Chemical Engineering

Journal 142 (2008) 309.35] O.M.I. Nwafor, Renewable Energy 29 (2004) 119.36] P. McCarthy, M.G. Rasul, S. Moazzem, Fuel 90 (2011) 2147.37] D. Shekhawat, J.J. Spivey, D.A. Berry, Fuel Cells: Technologies for Fuel Processing,

Elsevier Science & Technology, Amsterdam, The Netherlands, 2011.38] L.J. Spadaccini, J.A. Tevelde, Combustion and Flame 46 (1982) 283.39] D. Creaser, X. Karatzas, B. Lundberg, L.J. Pettersson, J. Dawody, Applied Catalysis

A 404 (2011) 129.40] X. Karatzas, D. Creaser, A. Grant, J. Dawody, L.J. Pettersson, Catalysis Today 164

(2011) 190.41] I. Kang, J. Bae, G. Bae, Journal of Power Sources 163 (2006) 538.42] R.K. Kaila, A. Gutierrez, A.O.I. Krause, Applied Catalysis B 84 (2008) 324.43] X. Karatzas, Rhodium Diesel-reforming Catalysts for Fuel Cell Applications,

Chemical Engineering and Technology, TRITA CHE report 2011:28, KTH RoyalInstitute of Technology, Stockholm, 2011, p. 81.

44] C. Palm, P. Cremer, R. Peters, D. Stolten, Journal of Power Sources 106 (2002)231.

45] E.C. Vagia, A.A. Lemonidou, International Journal of Hydrogen Energy 33 (2008)2489.

46] G. Nahar, K. Kendall, Fuel Processing Technology 92 (2011) 1345.47] G.J. Kraaij, S. Specchia, G. Bollito, L. Mutri, D. Wails, International Journal of

Hydrogen Energy 34 (2009) 4495.