Al2O3 complex catalyst

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The ReSER-COG process for hydrogen production on a NieCaO/Al2O3 complex catalyst Rong Wu, Su Fang Wu* Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China

article info

abstract

Article history:

The reactive sorption-enhanced reforming process of simulated coke oven gas (ReSER-

Received 20 March 2013

COG) was investigated in a laboratory-scale fixed-bed reactor with NieCaO/Al2O3 complex

Received in revised form

catalyst. Simulated coke oven gases that are free of or contain C2þ hydrocarbons (C2H4,

26 June 2013

C2H6, C3H6, C3H8) have been studied as feed materials of the ReSER process for hydrogen

Accepted 26 June 2013

production. The effects of temperature, steam to methane molar ratio (S/CH4) and carbon

Available online 25 July 2013

space velocity on the characteristics of ReSER-COG were studied. The results showed that the hydrogen concentration reaches up to 95.8% at a reaction temperature of 600  C and a

Keywords:

S/CH4 of 5.8 under normal atmospheric pressure conditions. This reaction temperature

Hydrogen

was approximately 200  C lower than that of the coke oven gas steam reforming (COGSR)

Coke oven gas

processes used for the hydrogen production. The amount of H2 generated by ReSER-COG

Reforming

was approximately 4.4 times more than that produced by the pressure-swing adsorption

Catalyst

(PSA) method per unit volume of COG. The reaction temperature was 50  C lower when

Calcium oxide

simulated COG with C2þ was used, as opposed to when COG without C2þ was used. The complex catalyst has a better resistance of coking during the ReSER-COG process when C2þ gas is present. Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

1.

Introduction

The amount of coke produced in China is above 4.28 billion tons annually, and represented 60% of the total world production in 2011. Accordingly, the annual amount of COG produced is 1800 billion N m3. However, only half of COG is used as fuel, while most of the remaining amount is directly burnt as waste gas. This causes not only wasting of significant energy resources but also serious environmental pollution. Thus, efficient use COG for low-cost hydrogen production has attracted a great deal of attention [1].

Among the many uses of COG, separation of hydrogen from COG using PSA technology is a well-established industrial process. Nevertheless, in addition to the low hydrogen recovery ratio (60%e80%) by PSA [2], this process treats the remaining CH4, CO and C2þ hydrocarbon gases in COG as waste, which remains a major issue. Hence, many researchers have studied chemical processes that make use of the carbon compounds in COG, such as coke oven gas steam reforming (COGSR) reaction and the coke oven gas partial oxidation (COGPOX) reaction. For the COGSR process, Wang et al. [3,4] studied a Ni/Mg(Al) O catalyst that increased the H2 content of COG from 58.3 vol%

* Corresponding author. Tel.: þ86 571 87953138; fax: þ86 571 87953735. E-mail address: [email protected] (S.F. Wu). 0360-3199/$ e see front matter Copyright ª 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijhydene.2013.06.117

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to 77.7 vol% by increasing reaction temperature from 800  C to 875  C under normal atmospheric pressure conditions. However, C2þ hydrocarbons in COG increased carbon deposition on the catalyst to 7.5 wt%. Cheng et al. [5] obtained COG with 71.8 vol% H2 using a Ni/Al2O3eMgO catalyst, but the gas mixture also contained toluene, and the carbon deposition ratio on the catalyst was 10.6 wt%. Although the COGSR process can recover 4 times the amount of hydrogen obtained by the PSA process [3e6] and can even convert tar components in the COG [5,7e10], the elevated temperature required in the reforming reaction leads to high-energy consumption and increases coke deposition on the catalyst. These considerations hindered the application of the COGSR process at industrial scale [3e10]. Previous research indicated that the COGPOX process was more energy efficient than the COGSR process due to its mildly exothermic characteristics [11,12] and that reaction rates were 10 times higher in the COGPOX process than in the COGSR process. However, the COGPOX process was also limited by coke deposition on the catalyst [13e15], and the cost of pure oxygen material input requirement in COGPOX process [16e20] further restricted its application at industrial scale. The ReSER process has been considered more promising because it can produce hydrogen from hydrocarbons more efficiently and achieve better control over CO2 release [21e25]. Cunha A F et al. [24] performed a sorption enhanced steam reforming of ethanol on a Ni/Al2O3 catalyst coupled with a hydrotalcite-based CO2 sorbent and the YH2 =ETOH was 34.8% with respect to 27.1% YH2 =ETOH without sorption enhanced effect. Virginia C M et al. [25] calculated that the thermal efficiency was enhanced with an increase of 81% under the sorption enhanced reaction system for ethanol reforming compared with the conventional process. In our group’s previous studies on the ReSER process of methane with the Ninano-CaO sorption complex catalyst [26e28], the reaction temperature was lowered to 600  C and no carbon deposition on catalyst surface occurred. And only rare CO2 released in the process while H2 contents reached 96 vol%. In this paper, we proposed a new technique to produce hydrogen from COG by ReSER process, which we named the ReSER-COG process. The research examined extensively the effects of reaction temperature, S/CH4 molar ratio and space velocity on hydrogen concentration and on the conversion of COG components. In addition, the study investigated the effect of C2þ hydrocarbons present in simulated COG on hydrogen production (by comparing with experimental results from C2þ-free COG) and examined carbon deposition on catalyst under different experimental conditions.

2.

Experimental

2.1.

Reagents and instruments

Nano-CaCO3 (>95% purity, Huzhou Linghua Ltd., China), with a particle size of 70 nm, was used as the nano-CaO-based adsorbent precursor. Ni(NO3)2$6H2O (98% purity, Shanghai Hengxin Chemical Reagent Co., Ltd.) was used as the Ni source.

Table 1 provides the initial mixture composition of the simulated gases for two feed conditions. The desorption gas (DG) feed refers to COG containing C2þ hydrocarbons that are typically components of COG after the PSA separation process; The testing gas (TG) feed indicates the COG without C2þ as control for comparison studies.

2.2. Preparation and characterization of the complex catalyst The NieCaO/Al2O3 complex catalyst was prepared by muddy mixing method, and a similar preparation process was described in our previous work [26]. According to the weight ratio of Ni:CaO:Al2O3 been set as 1:3:3, a certain amount of nano-CaCO3 was dispersed ultrasonically in distilled water to obtain a CaCO3 suspension solution, then mixed with the Aluminum sol and the 0.2 mol/l Ni(NO3)2 solution to make a slurry by fully stirring. The slurry was by spray drying, and calcining at 550  C for 3 h, and sieving to obtain a microsphere NieCaO/Al2O3 complex catalyst with grain size of 40e80 mm, which named as CC-1. The Ni and CaO in CC-1 were presented as NiO and CaCO3 respectively. The crystalline phase of the synthesized complex catalyst was analyzed using an X-ray diffractometer (XRD, D/MAX-RA, Rigaku, Japan) with a copper anode under the following experimental conditions: voltage 40 kV and current 40 mA. The BrunauereEmmereTeller (BET) surface area and the BarretteJoynereHalenda (BJH) desorption average pore diameter of the catalyst were measured using nitrogen physisorption at liquid N2 temperatures with a Micromeritics BELSORP-mini II (BEL Japan, Inc.). The grain size of the catalyst was investigated using transmission electron microscopy (TEM, JEM-1230, JEOL, Japan) with 95% ethanol used as a dispersant and an accelerating voltage of 80 kV. The sorption capacity of the catalyst was measured through thermogravimetric analysis (TGA, Pyris 1, PerkinElmer) using 2 mg of sample.

2.3.

Evaluation of complex catalyst

The carbonation-calcination cyclic test of CC-1 was carried out by TGA. About 3 mg of CC-1 was placed in the platinum basket. The temperature increased from 150  C to 800  C, and maintained for 10 min to make the catalyst decompose completely. Then the carbonationecalcination cycles were going on. Temperatures for the carbonation and calcinations reactions were set at 600  C and 800  C. Both reaction times are 10 min. The reactive gas flow rate was 50 ml/min with a CO2 concentration of 20% (N2 balance) during the carbonation stage and the gas flow rate was kept unchanged in calcination stage with N2 only.

Table 1 e Components content of simulated COG (vol%). Name

H2

CH4

N2

CO CO2 C2H4 C2H6 C3H6 C3H8

DG TG

17.6 23.7

41.9 42.9

17.7 12.3 16.5 12.6

4.3 4.3

3.7 0

1.4 0

0.8 0

0.3 0

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Worn-out catalyst was analyzed for carbon deposition using TGA. The catalyst sample was maintained in N2 at 150  C for 1 h to remove the moisture then heated up from 150  C to 800  C at a heating rate of 15  C min1 to calcine the CaCO3 completely. The Ca was presented as CaCO3 in catalyst sample. Finally, the catalyst was combusted in O2 for 30 min. The process of hydrogen production by ReSER-COG includes the following possible consecutive/parallel reactions, as shown in Table 2. Hydrogen production by ReSER-COG process was evaluated with an experimental setup using the sequence shown in Fig. 1. A laboratory-scale fixed-bed reactor, made of a stainless steel tube with a size of F500 mm  15 mm, was used to carry out the reactions in the ReSER process. Additionally, 5 g of complex catalyst CC-1 were loaded into the constanttemperature zone of the reactor tube. DG or TG streams, provided by appropriate gas mixture cylinders, were mixed with steam, preheated and fed to the reactor. The reaction and regeneration temperature could be automatically detected and controlled by a programmable temperature controller for the furnace. The catalyst was regenerated at 800  C by flowing N2 gas over it, and then, it was reduced at 600  C by a stream of H2 that had been diluted in N2. The composition of the gas mixture produced by the reforming reaction was analyzed by an on-line gas chromatograph. Because COG with C2þ contains different hydrocarbons, conversion Xn was defined by Eq. (1), where n represents CH4, CO or C2H4, Fin n (ml/min) is the inlet flowrate of component n (ml/min) is the outlet flowrate of component n. and Fout n Xn ð%Þ ¼

out Fin n -Fn  100% ðn ¼ CH4 ; CO; C2 H4 .Þ Fin n

(1)

H2 concentration CH2 was defined by Eq. (2) with nitrogen subtracted, where CH2 -D and CN2 -D are the effluent concentrations of H2 and N2detected by GC, respectively. CH2 ¼

CH2 -D  100% 1-CN2 -D

(2)

Hydrogen yield yH2 was defined by Eq. (3), where yH2 is the hydrogen yield, fH2 is the flowrate of hydrogen containing product gas (ml/min) and fCOG is the flowrate of COG as feed (ml/min). yH2 ¼

fH2  100% fCOG

(3)

The catalyst carbon deposition ratio rC was defined by Eq. (4), where Wb (mg) is the catalyst weight before combustion and Wa (mg) is the catalyst weight after combustion.

Table 2 e Reactions resulting in hydrogen production using ReSER-COG. CH4 þ 2H2 O#CO2 þ 4H2 C2 H6 þ 4H2 O#2CO2 þ 7H2 C2 H4 þ 4H2 O#2CO2 þ 6H2 C3 H8 þ 6H2 O#3CO2 þ 10H2 C3 H6 þ 6H2 O#3CO2 þ 9H2 CO þ H2 O#CO2 þ H2 CaO þ CO2 #CaCO3

DH298 DH298 DH298 DH298 DH298 DH298 DH298

¼ ¼ ¼ ¼ ¼ ¼ ¼

165.1 kJ/mol 266 kJ/mol 128.3 kJ/mol 376 kJ/mol 250.4 kJ/mol 41.1 kJ/mol 178.8 kJ/mol

(1) (2) (3) (4) (5) (6) (7)

Fig. 1 e Diagram of the ReSER process used for hydrogen production.

rC ¼

Wb -Wa  100% Wb

(4)

The S/CH4 ratio is the molar ratio of steam to CH4 component in COG, which is different from the S/C ratio, which presents steam to total carbon components including CH4, CO, C2þ. The space velocity (h1) was calculated based on the COG volume flowing over a certain amount of catalyst, per unit time.

3.

Results and discussions

3.1.

Catalyst characterization

Properties of the catalyst CC-1 are listed in Table 3. The specific surface area and pore volume are 42.7 m2 g1 and 0.13 cm3 g1, respectively. The average pore size is 8.4 nm. The adsorption capacity of CC-1 measured by TGA was 3.1 molCO2 kg1 catalyst. The analytical results of the XRD test are shown in Fig. 2. CC-1 was found to contain NiO, Ca(OH)2 and CaCO3 crystals. No metallic Ni phase was present in the catalyst before the reduction. And no Al2O3 diffraction peak was found in the XRD data, indicating that the Al2O3 support was non-crystalline in structure. The fresh catalyst CC-1 TEM image was shown in Fig. 3. The NiO crystal with a size of 5e20 nm, and the nano-CaCO3 crystal with a size of 50e100 nm in a cubic shapes were observed.

3.2.

The sorption capacity of NieCaO/Al2O3 catalyst

Sorption capacity of CO2 is an important property of the sorption complex catalyst in ReSER hydrogen production.

Table 3 e Properties of CC-1 complex catalyst. Catalyst

Ni/CaO/ Al2O3

Composition/ wt% CaO

Ni

40.0

13.6

Surface area [m2 g1]

Pore size (nm)

Pore volume [cm3 g1]

42.7

8.4

0.13

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sorption capacity(mol·kg )

3.0

intensity

CaCO3

CaCO3 NiO

Ca(OH)2

NiO

2.0 1.5 1.0 0.5 0.0

10

20

30

40

CC-1

2.5

-1

CaCO3

50

60

70

80

0

2

4

2-theta

6 8 cycles

10

12

14

16

Fig. 4 e The sorption capacity of CC-1.

Fig. 2 e XRD patterns of catalysts CC-1.

Fig. 4 shows the cyclic sorption capacity of the complex catalyst. As the number of cycles increased, the sorption capacity decreased and maintained 1.2 mol kg1 after 15 cycles.

shows a post-breakthrough region. There is no C2þ detected through the whole ReSER-COG process of DG. This means C2þ are reacted with steam absolutely. It is more reactive than methane at same temperature.

3.3.

3.4.

Effect of ReSER process

From Fig. 5, it can be observed that typical breakthrough curve obtained during the ReSER-COG process of DG. In prebreakthrough region, the H2 concentration is higher than 95 vol% due to in situ CO2 removal by the CaO reaction. The concentrations of CH4, CO and CO2 in the outlet gas mixture are very low in the pre-breakthrough region. This increase in H2 yield can be explained by Le Chatelier’s principle, where the CO2 removal drives the equilibrium limited forwards to produce H2. As the nano CaO was going on reaction with CO2 and was reduced, the breakthrough region occurs. The concentrations of CH4, CO and CO2 increased and H2 concentration decreased in the outlet gas. When all the nano CaO in catalyst has been converted to CaCO3, the reforming reaction reached an equilibrium content of each component, the curve

Effect of temperature on the production of hydrogen

The effect of reaction temperature on hydrogen production was tested at a molar ratio S/CH4 of 5.8 and a space velocity of 1584 h1 at atmospheric pressure. Fig. 6 shows the range of hydrogen concentrations produced by ReSER-COG from DG and TG feeds at different reaction temperatures. The concentration of hydrogen produced from DG increased from 68% to 96% with the reaction temperature increasing from 450  C to 600  C. The concentration of hydrogen produced from DG was higher than that produced from TG at the same reaction temperature. To obtain a concentration of 94% H2 using DG feed, the required reaction temperature was 550  C, which is approximately 50  C lower than that required when using TG.

100

concentrations (%)

80 Prebreakthrough

60

Postbreakthrough H2

40

CO2 CO CH4

20 0

Fig. 3 e TEM image of fresh CC-1 complex catalyst.

Breakthrough

0

5

10

t (min)

15

20

25

Fig. 5 e The concentrations of products varies with time, at atmospheric pressure, 600  C, S/CH4 molar ratio of 5.8 and space velocity of 1584 hL1.

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100

100

conversions (%)

80

60 40 H2(TG)

20 0 440

480

520

560 T(

600

60 CH4(TG)

40

CH4(DG) CO(TG) CO(DG)

20

H2(DG)

0 440

640

480

Fig. 6 e The effect of reaction temperature on H2 production at atmospheric pressure, S/CH4 of 5.8 and space velocity of 1584 hL1.

The difference in the H2 concentration obtained from the two feeds decreased with increasing reaction temperature. At 600  C, H2 concentration reached 96% when using either DG or TG. This result is possibly due to the C2þ carrying out ReSER reaction more easily than CH4. At a lower reaction temperature, the conversion of CH4 is lower than that of C2þ, resulting in more H2 produced by DG than by TG. The reasonable explanation follows from bond energy theory, the longer the CeC chain, the lower the CeH bond energy, thus the CeH bond breaks more easily. Therefore, C2þ hydrocarbons reacted more efficiently at the catalyst surface than CH4. Hence, C2þ has faster reaction kinetics and higher reactivity than CH4. In addition, Ni was able to sorption the CeC band but not the CeH band [29]. As the experimental results demonstrated, when using DG to produce H2, the reaction temperature could be lowered appropriately for energy conservation. Fig. 7 shows the variation with reaction temperature in CH4 and CO conversion in DG and TG during ReSER-COG process. CH4 conversion increased with reaction temperature, while presence or absence of C2þ in the feed stream appears to have no significant influence on CH4 conversion. As the reaction temperature increased from 450  C to 600  C, CO conversion from DG and TG decreased from 100% to 62.5% and 80%, respectively, mostly likely due to the exothermic water gas shift reaction. CO conversion from DG is lower than that from TG at the same reaction temperature. The increase in CO content can be attributed to the C2þ reforming reaction occurring when DG was used. This trend became more obvious at higher reaction temperatures, which increased the C2þ reforming conversion, thus lowering the CO conversion. The highest sorption enhanced reforming results was obtained at 600  C of hydrogen production with CH4 by ReSER process [30]. Because of the nano CaCO3 will start to decompose and release the CO2 after the temperature of 600  C. And the concentration of CO2 will affect the equilibrium of reforming reaction and caused the lower H2 concentration, so the optimum reaction temperature is 600  C.

520

560 T(

)

600

640

)

Fig. 7 e The effect of reaction temperature on conversions of CH4 and CO in the ReSER process at atmospheric pressure, S/CH4 molar ratio of 5.8 and space velocity of 1584 hL1.

Fig. 8 shows how the C2þ conversion in the DG changed when the reaction temperature was varied. The C2þ converted completely at reaction temperatures higher than 500  C, which demonstrated that C2þ hydrocarbons have lower conversion temperature than CH4. The reaction temperature at which C2þ converted 100% in the ReSER process was 100  C lower than that used in the SR process, which is approximately 600  C [31]. As the reaction temperature went down to 500  C, C2H6 did not convert completely but C2H4, C3H6 and C3H8 did. This means alkenes perform ReSER reaction more easily than alkanes. One possible explanation is that the unsaturated C]C bond is adsorbed more easily on the catalyst surface [32]. Additionally, the energy of the s bond in the C]C bond is slightly lower than that of the CeC s bond of alkanes; thus, the bond can be broken more easily [33]. The order of activity for the hydrocarbons in the DG was as follows: C3H8 ¼ C3H6 ¼ C2H4 > C2H6 > CH4.

100 80 conversions (%)

concentrations (%)

80

60 C2H4

40

C2H6 C3H6

20 0 440

C3H8

480

520

560 T(

600

640

)

Fig. 8 e Relations between temperature and C2D conversions in DG at atmospheric pressure, S/CH4 molar ratio of 5.8 and space velocity of 1584 hL1.

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60 CH4(TG)

40

CH4(DG) CO(TG) CO(DG)

20

Effect of S/CH4 on hydrogen production

In the steam reformation of CH4, the S/CH4 ratio had a great influence on catalytic activity. Generally, the steam reforming of CH4 was performed with the S/CH4 ratio in the range of 1.9e9.0. An S/CH4 ratio of less than 1.4 leads to coke formation at atmospheric pressure [34e36]. Fig. 9 illustrates the effect of the S/CH4 ratio, varying from 2.2 to 5.8, on the H2 production from DG and TG. The H2 concentrations produced by DG and TG increased from 82.3% to 96% and from 87.9% to 96%, respectively, upon increasing S/CH4 ratio from 2.2 to 5.8. The H2 concentration produced by TG is slightly higher than that produced by DG. Fig. 10 shows the effect of the S/CH4 ratio on conversion of CH4 and CO in DG and TG. The conversions of CH4 and CO in TG are both higher than those in DG at the same S/CH4 ratio. The highest conversions of CH4 in TG and DG are 95.8% and 92%, respectively. The C2þ in the DG converted completely when the S/CH4 ratio varied over the range from 2.2 to 5.8, further confirming that C2þ hydrocarbons undergo steam reforming more easily than CH4 under the same reaction conditions [29,31,37]. Considering that the C2þ hydrocarbons reacted prior to the CH4 in the DG during the steam reforming process and that each reaction exhausts stoichiometrically equivalent amounts of water (per carbon atom basis), then the actual S/ CH4 ratio of CH4 reaction was reduced, which affected the conversions of CH4 and CO. The lower the S/CH4 ratio was, the

100

0

2

3

4 S/CH4

5

more obviously the influence became. Correspondingly, when the S/CH4 ratio increased to 5.8, the difference was eliminated.

3.6.

Effect of space velocity on the hydrogen production

The relation between space velocity and the conversion of reactants indicates the activity of the catalyst. Fig. 11 shows the relations between space velocity and both the conversion of CH4 and concentration of H2. The H2 concentration decreased from 96.8% to 94.2% upon increasing space velocity from 1188 h1 to 2376 h1, but remained higher than 90%. The C2þ converted completely when space velocity values ranged within the interval normally used in the ReSER process, further demonstrating that C2þ hydrocarbons are reformed more easily than CH4 under the same reaction conditions. The H2 concentration and CH4 conversion of TG also decreased with increasing space velocity. The H2 concentration and CH4 conversion of TG are slightly higher than those of DG and, as the space velocity increased from 1188 h1 to 2376 h1, the CH4 conversion gap between TG and DG decreased from 5.1% to

100

98 H2 concentrations(%)

60 40 H2(TG)

20 0

H2(DG)

2

3

S/CH4

4

5

Fig. 9 e The effect of S/CH4 ratio on H2 production at atmospheric pressure, 600  C, and space velocity of 1584 hL1.

6

6

Fig. 10 e The effect of S/CH4 ratio on conversions of CH4 and CO at atmospheric pressure, 600  C, and space velocity of 1584 hL1.

100

80 concentrations (%)

80

80

96 60 94 H2(DG) H2(TG) 20

CH4(DG) CH4(TG)

0 1000

1250

1500

1750

2000

2250

40 20

CH4 conversions(%)

3.5.

100

conversions (%)

According to the experimental results, at 600  C, the H2 yield of 2.0 Nm3 H2/Nm3 COG in the ReSER-COG process was 4.4 times greater than in the PSA process, approximately 0.45 Nm3 H2/Nm3 COG [2]. This indicates that the ReSER-COG process amplified the H2 yield per unit volume of COG to a great extent. Moreover, conducting the ReSER-COG process at a reaction temperature of 600  C reduced the energy consumed when compared with the COGSR and COGPOX processes, which required at least 800  C [4,13].

0 2500

-1

space velocity (h ) Fig. 11 e The effect of space velocity on the H2 production reaction, atmospheric pressure, 600  C, S/CH4 5.8.

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0.7%. These results suggest that the C2þ hydrocarbons in the feedstock impeded CH4 conversion in the ReSER-COG process.

3.7.

Coking is an important factor affecting the stability of the catalyst [38]. The ReSER-COG process was carried out over fresh CC-1 catalyst at atmospheric pressure, an S/CH4 ratio of 4.3 and a temperature of 600  C for 10 h, and the carbon deposition result measured by TGA. The carbon deposition ratio of the used complex catalyst is as low as 0.09%, showing excellent coke resistance performance in ReSER-COG process. Three possible reasons for the enhanced resistance are as follows: the higher S/CH4 ratio of 4.3 promotes the steam reforming process [33e35], the lower reaction temperature of 600  C prevents hydrocarbon cracking, which leads to carbon deposition [39], and alkaline earth oxide CaO present in the catalyst enhanced its coke resistance [40].

4.

[9]

Performance of catalyst coke resistance [10]

[11]

[12]

[13]

[14]

Conclusions

The ReSER-COG process lowered the required reaction temperature by 200  C when compared to the COGSR or COGPOX processes. The process also achieved 95.8 vol% H2 at 600  C, which is higher than the 78 vol% obtained by the COGSR or COGPOX processes. H2 yield per unit volume was 4.4 times that achieved by the PSA process. The C2þ hydrocarbons influence CH4 conversion but lower the ReSER-COG reaction temperature. There was no carbon deposited on the complex catalyst surface during the ReSER-COG process even when C2þ hydrocarbons were present in the simulated COG.

references

[1] Bermu´dez JM, Arenillas A, Luque R, Mene´ndez J Angel. An overview of novel technologies to valorize coke oven gas surplus. Fuel Process Technol 2013;110:150e9. [2] Li YL. Preparation of ultra high pure hydrogen. Low Temp Spec Gas 1996;14(3):38e40. [3] Cheng HW, Yue BH, Wang XG, Lu XG, Ding WZ. Hydrogen production from simulated hot coke oven gas by catalytic reforming over Ni/Mg(Al)O catalysts. J Nat Gas Chem 2009;18:225e31. [4] Yang ZB, Zhang YY, Wang XG, Zhang YW, Lu XG, Ding WZ. Steam reforming of coke oven gas for hydrogen production over a NiO/MgO solid solution catalyst. Energy Fuels 2010;24:785e8. [5] Cheng HW, Lu XG, Ding WZ. Steam reforming of simulated coke oven gas over Ni/Al2O3eMgO catalysts for syngas production. Adv Mater Res 2011;152e153:817e20. [6] Chen WH, Lin MR, Yu AB, Du SW, Leu TS. Hydrogen production from steam reforming of coke oven gas and its utility for indirect reduction of iron oxides in blast furnace. Int J Hydrogen Energy 2012;37:11748e58. [7] Yu F, Yue BH, Wang XG, Geng SH, Lu XG, Ding WZ. Hydrocracking of tar components from hot coke oven gas over a Ni/CeeZrO2/g-Al2O3 catalyst at atmospheric pressure. Chin J Catal 2009;30(7):690e6. [8] Yue BH, Wang XG, Ai XP, Yang J, Li L, Lu XG, et al. Catalytic reforming of model tar compounds from hot coke oven gas

[15]

[16]

[17]

[18]

[19]

[20]

[21] [22] [23]

[24]

[25]

with low steam/carbon ratio over Ni/MgOeAl2O3 catalysts. Fuel Process Technol 2010;91:1098e104. Sarıoglan A. Tar removal on dolomite and steam reforming catalyst: benzene, toluene and xylene reforming. Int J Hydrogen Energy 2012;37:8133e42. Cheng HW, Lu XG, Ding WZ, Zhong QD. Catalytic reforming of model tar compounds from hot coke oven gas over Pd promoted Ni/Mg(Al)O catalysts. Adv Mater Res 2011;197e198:711e4. Onozaki M, Watanabe K, Hashimoto T, Saegusa H, Katayama Y. Hydrogen production by the partial oxidation and steam reforming of tar from hot coke oven gas. Fuel 2006;85:143e9. Guo JZ, Hou ZY, Gao J, Zheng XM. Production of syngas via partial oxidation and CO2 reforming of coke oven gas over a Ni catalyst. Energy Fuels 2008;22:1444e8. Cheng HW, Lu XG, Liu Xu, Zhang YW, Ding WZ. Partial oxidation of simulated hot coke oven gas to syngas over RueNi/Mg(Al)O catalyst in a ceramic membrane reactor. J Nat Gas Chem 2009;18:467e73. Yang ZB, Zhang YY, Ding WZ, Zhang YW, Shen PJ, Zhou YD, et al. Hydrogen production from coke oven gas over LiNi/g-A12O3 catalyst modified by rare earth metal oxide in a membrane reactor. J Nat Gas Chem 2009;18:407e14. Cheng HW, Lu XG, Zhang YW, Ding WZ. Hydrogen production by reforming of simulated hot coke oven gas over nickel catalysts promoted with lanthanum and cerium in a membrane reactor. Energy Fuels 2009;23:3119e25. Liu XT, Zhao HL, Yang JY, Li Y, Chen T, Lu XG, et al. Lattice characteristics, structure stability and oxygen permeability of BaFe1xYxO3d ceramic membranes. J Membr Sci 2011;383:235e40. Zhen Q, Yun Q, Wang HJ, Ding C, Ding WZ, Lu XG. Investigation of chemical stability and oxygen permeability of perovskite-type Ba0.5Sr0.5Co0.8Fe0.2O3d and BaCo0.7Fe0.2Nb0.1O3d ceramic membranes. Solid State Ionics 2011;189:50e5. Xu NS, Zhao HL, Shen YN, Chen T, Ding WZ, Lu XG, et al. Structure, electrical conductivity and oxygen permeability of Ba0.6Sr0.4Co1xTixO3d ceramic membranes. Sep Purif Technol 2012;89:16e21. Chen T, Zhao HL, Xie ZX, Feng LC, Lu XG, Ding WZ, et al. Electrical conductivity and oxygen permeability of Ce0.8Sm0.2O2dPrBaCo2O5þd dual-phase composites. Int J Hydrogen Energy 2012;37:5277e85. Geng Z, Ding WZ, Wang HH, Wu CZ, Shen PJ, Meng XY, et al. Influence of barium dissolution on microstructure and oxygen permeation performance of Ba1.0Co0.7Fe0.2Nb0.1O3d membrane in aqueous medium. J Membr Sci 2012;403e404:140e5. Hufton JR, Mayorga S, Sircar S. Sorption-enhanced reaction process for hydrogen production. AIChE J 1999;45:248e56. Ding Y, Alpay E. Adsorption-enhanced steam-methane reforming. Chem Eng Sci 2000;55:3929e40. Seval G, Timur D. Sorption-enhanced reforming of ethanol over Ni- and Co-incorporated MCM-41 type catalysts. Ind Eng Chem Res 2012;51:8796e805. Cunha AF, Wu YJ, Diaz Alvarado FA, Santos JC, Vaidya PD, Rodrigues AE. Steam reforming of ethanol on a Ni/Al2O3 catalyst coupled with a hydrotalcite-like sorbent on a multilayer pattern for CO2 uptake. Can J Chem Eng 2012;90:1514e26. Virginia CM, Miguel EB, Miguel MZ, Jesu’s SG, Alejandro LO. Absorption enhanced reforming of light alcohols (methanol and ethanol) for the production of hydrogen: thermodynamic modeling. Int J Hydrogen Energy 2012;37:1e15.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 8 ( 2 0 1 3 ) 1 1 8 1 8 e1 1 8 2 5

[26] Wu SF, Li LB, Zhu YQ, Wang XQ. A micro-sphere catalyst complex with nano CaCO3 precusor for hydrogen production used in ReSER process. Eng Sci 2010;8(1):22e6. [27] Feng HZ, Lan PQ, Wu SF. A study on the stability of a NiOeCaO/Al2O3 complex catalyst by La2O3 modification for hydrogen production. Int J Hydrogen Energy 2012;37:14161e6. [28] Wu SF, Wang LL. Improvement of the stability of a ZrO2modified Ni-nano CaO sorption complex catalyst for ReSER hydrogen production. Int J Hydrogen Energy 2010;35:6518e24. [29] Maillet T. Oxidation of carbon monoxide, propene, propane and methane over a Pd/Al2O3 catalyst. Effect of the chemical state of Pd. Appl Catal B Environ 1997;14:85e95. [30] He J, Wu SF. The characteristics of sorption enhanced steam methane reforming for hydrogen production on a complex catalyst. Chem React Eng Technol 2007;23:470e3. [31] Schadel BT. Steam reforming of methane, ethane, propane, butane, and natural gas over a rhodium-based catalyst. Catal Today 2009;142:42e51. [32] Patrick OG, Barbara LM, Ommen JG, Lefferts L. Comparative study of steam reforming of methane, ethane and hylene on

[33]

[34]

[35]

[36] [37]

[38] [39]

[40]

11825

Pt, Rh and Pd supported on yttrium-stabilized zirconia. Appl Catal A Gen 2007;332:310e7. Petrucci RH, Harwood WS, Herring FG. General chemistry: principles and modern applications. 8th ed. Beijing: High Education Press; 2004. p. 420e2. Yamazaki O, Tomishige K, Fujimoto K. Development of highly stable nickel catalyst for methane-steam reaction under low steam to carbon ratio. Appl Catal A 1996;136:49e56. Jacob T. The mechanism of forming H2O from H2 and O2 over a Pt catalyst via direct oxygen reduction. Fuel Cells 2006;6:159e81. Roh HS, Jun KW, Park SE. Methane-reforming reactions over Ni/CeeZrO2/qeAl2O3 catalysts. Appl Catal A 2003;251:275e83. Benjamin TS. Steam reforming of natural gas on noble-metal based catalysts: predictive modeling. Stud Surf Sci Catal 2007;167:207e12. Trimm DL. Catalysts for the control of coking during steam reforming. Catal Today 1999;49:3e10. Li J, Shao JX, Liu CX, Rao HB, Li ZR, Li XY. Pyrolysis mechanism of hydrocarbon fuels and kinetic modeling. Acta Chim Sinica 2010;68:239e45. Carrero A, Calles JA, Vizcaı´no AJ. Effect of Mg and Ca addition on coke deposition over CueNi/SiO2 catalysts for ethanol steam reforming. Chem Eng J 2010;163:395e402.