- Email: [email protected]
Improved hydrogen production from dry reforming reaction using a catalytic packed-bed membrane reactor with Ni-based catalyst and dense PdAgCu alloy membrane
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Improved hydrogen production from dry reforming reaction using a catalytic packed-bed membrane reactor with Ni-based catalyst and dense PdAgCu alloy membrane Sarocha Sumrunronnasak a, Supawan Tantayanon b,*, Somchai Kiatgamolchai c, Thitinat Sukonket d a Graduate Program of Petrochemistry and Polymer Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand b Green Chemistry Research Laboratory, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand c Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand d Occupational Health and Safety Science Program, Faculty of Science and Technology, Suan Dusit Rajabhat University, 295 Nakhon Ratchasima Rd. Disit District, Bangkok, 10300, Thailand
article info
abstract
Article history:
A catalytic Pd76Ag19Cu5 alloy membrane reactor packed with 5% Ni/Ce0.6Zr0.4O2 catalyst
Received 3 September 2015
was adopted in this study to investigate hydrogen production performance from the dry
Received in revised form
reforming reaction of methane and carbon dioxide. The 1:1 CH4/CO2 feed was introduced to
30 October 2015
the reactor with 60 mg of the catalyst at a flow rate of 20 ml/min at 550 C. The effluent gas
Accepted 30 October 2015
compositions were examined using an online gas chromatographer (GC). Compared to a
Available online 8 January 2016
conventional reactor without the membrane, the CH4 and CO2 conversions were significantly increased by 3.5-fold and 1.5-fold, respectively. Correspondingly, the overall H2 yield
Keywords:
was greatly improved from about 10e35%. Additionally, the hydrogen selectivity increased
PdAgCu alloy membrane
from 47 to 53%. It is theorized that the in-situ partial hydrogen withdrawal by the mem-
Hydrogen production
brane mainly caused the dry reforming reaction equilibrium to shift forward and created a
Dry reforming
hydrogen-deprived environment unfavorable for the competing reversible water-gas shift
Catalytic membrane reactor
reaction to take place.
Ni-based catalyst
Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Introduction The demand for hydrogen as a clean energy source, a feedstock, or as an intermediate and specialty chemical is
expected to grow rapidly in coming years. The main challenges lie in finding hydrogen sources and economically efficient enrichment processes in order to achieve high purity hydrogen suitable for usages [1e4]. An alternative approach of producing hydrogen is via useful reaction pathways such as
* Corresponding author. E-mail address: [email protected] (S. Tantayanon). http://dx.doi.org/10.1016/j.ijhydene.2015.10.129 0360-3199/Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
2622
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
the dry reforming reaction between CH4 and CO2 facilitated by various metal-based catalysts [5,6]. Carbon dioxide reforming of methane produces synthesis gas with hydrogen to carbon monoxide ratio desirable for many industrial synthesis processes. This reaction also has very important environmental implications since both methane and carbon dioxide contribute to the greenhouse effect [4,7]. The dry reforming of methane (DRM) produces an equimolar synthesis gas (syngas) e which is a mixture of hydrogen (H2) and carbon monoxide (CO) e from carbon dioxide and methane (CH4). In fact, the main reactions involved in this process are as follows [8,9]: 1
DH 298 K ¼ þ247:4 kJ mol
CH4 þCO2 /2CO þ 2H2
(1)
Materials and methods
DH 298 K
CO2 þH2 /CO þ H2 O ðreverse water gas shiftÞ; 1
¼ þ41:2 kJ mol
(2) DH 298
CO2 þ4H2 /CH4 þ2H2 O ðmethanationÞ;
K
1
¼ 165:0 kJ mol
(3)
However, another two undesired reactions occur, producing carbon deposition: CH4 /2H2 þ C DH 298 2CO/CO2 þ C DH 298
K
K
1
¼ þ75:0 kJ mol
(4)
1
¼ 173:0 kJ mol
CO þ H2 /H2 O þ C DH 298
K
CO2 þ2H2 /H2 O þ C DH 298
¼ 131:0 kJ mol K
(5) 1
¼ 173:0 kJ mol
1
In this study, a packed-bed membrane reactor consisting of a Ni-based catalyst and dense PdAgCu alloy membrane was set up to study its hydrogen production performance from the dry reforming reactions between CH4 and CO2. The main goal of this study is to gain better understanding of the factors affecting the reaction and separation performance such as the CH4/CO2 feed ratio, feed flow rate, temperature, and catalyst mass. Additionally, it is interesting to investigate the effect of possible in-situ hydrogen membrane separation taking place during the ongoing reactions that could result in improved hydrogen production.
(6) (7)
As reported in many studies, palladium-based alloy membranes have shown to be effective in hydrogen separation because of their excellent performance in terms of hydrogen permeability and selectivity [10e16]. In particular, dense PdAgCu alloy membranes have been widely used for such applications since the membranes can deliver high hydrogen purity and capacity under a harsh environment in the separation process [15,17e19]. Additionally, the membrane reactor has been extensively studied for the dry reforming of methane using different membrane types such as self-standing PdAg alloys, Pd-ceramic composite, silica/ mullite membrane, Pd film supported on porous stainless steel, and SiO2/alumina membrane [1,8,20e22]. Generally, CH4 conversion can be greatly improved by removing the hydrogen formed with a stable and highly selective dense Pd alloy membrane [23,24]. Through such means, higher conversions have been reported than those corresponding to the thermodynamic equilibrium of a conventional packed-bed reactor operating at the same experimental conditions as the membrane reactor. For an optimal membrane reactor to be developed for hydrogen production, two key requisites must be fulfilled: (i) the development of a well-performing catalyst, and (ii) the use of a stable, highly selective, high H2 permeance membrane [21,25]. The 5% Ni/Ce0.6Zr0.4O2 prepared by the surfactant approach was used since it has shown to be a good catalyst for the CO2 reforming of CH4 with stable activity [26,27]. PdAgCu alloy was selected due to its proven stability at high temperature (550 C) as required by the highly endothermic DRM reaction.
Reaction system The dry reforming reaction of methane was carried out in a packed-bed reactor coupled with palladium alloy membrane. The 5% Ni/Ce0.6Zr0.4O2 catalyst of 0.35 mm grain size was prepared by the surfactant-assisted templating method. The detailed procedure has been described by Sukonket et al. [26,27]. A dense Pd76Ag19Cu5 alloy membrane 15 nm thick supported on a porous stainless steel (316 PSS) disk with a hydrogen permeability of 7.7 109 mol/m.s.Pa0.5 at 350 C was used. The reactor was packed with the well-mixed catalyst and 3.0 g of 0.4 mm quartz sand. The reactant feed was vertically passed through the packed-bed of 5% Ni/Ce0.6Zr0.4O2 and membrane sequentially. The reactor was placed vertically inside a programmable furnace to control the desired temperature. Prior to the reaction, the catalyst was readily reduced by atmospherically purging the 10 mol% hydrogen balanced in nitrogen into the reactor at 710 C with a flow rate of 30 ml/min for 3 h. To the study the reaction unit performance, the dry reforming reaction was carried out in various conditions as follows: a total feed flow rate of 10e50 ml/min, argon purge (for the permeate side of the membrane) at 10 ml/min, CH4/ CO2 molar feed ratios in the range of 3/1e1/3, catalyst mass in the range of 10e80 mg, reaction temperature in the range of 450e550 C, and reaction pressure at 250 kPa. The reaction was monitored by an online GC using an analytical column series of the Porapack Q for the higher molecule (CH4 and CO2) and a molecular sieve (13X) for the smaller molecule (CO and H2) separations in which a thermal conductive detector (TCD) was in place for temperature measurement. Argon gas was used as a carrier gas with a pressure of 50 kPa for the entire experiment. The temperature of the inlet, oven, and detector were 100 C, 35e150 C and 120 C, respectively. The permeated gas composition was analyzed by comparing the area under the peaks with those of the standards from the calibration curve. All of the gases were regulated through pre-calibrated mass (gas) flow controllers with digital readout units. The assembled catalytic membrane reactor and the experimental schematic diagram for the dry reforming reaction system are presented in Figs. 1 and 2, respectively.
Membrane preparation Porous stainless steel disks (316L PSS) of circular shape 0.39 cm in diameter, 1 mm thickness, and an average pore size
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
Fig. 1 e Outline of an assembled catalytic membrane reactor.
2623
at room temperature. The plating and washing steps were repeated 4 times to ensure dense coating [28]. Then, Ag and Cu were sequentially deposited on the Pd layer by the electroplating (EP) technique using a silver bar as an anode (10% AgNO3), and copper bar (25% CuSO4), respectively. A distance of 2.0 cm was maintained between the working and reference anode in a 50 ml plating solution at room temperature. The Ag plating was carried out for a 10 s period with a 1.2 V potential applied followed by the Cu plating for 90 s with a 2.0 V potential applied. The PdeAgeCu membrane was thoroughly washed with 0.01 M HCl, DI water, and ethanol, respectively. The membrane was then annealed at a temperature of 550 C for 80 h in an argon atmosphere. The composition analysis of the prepared alloy membranes was examined using a scanning electron microscope (SEM), JEOL model JSM-5800LV equipped with energy dispersive X-ray diffraction (EDX). From the cross-section SEM-EDX line scan and elemental mapping results, the alloy membrane showed homogeneous element distribution with an average content of 76% Pd, 19% Ag, and 5% Cu, respectively. The average membrane thickness obtained from SEM analysis was 15.55 ± 0.23 mm.
Ni-based catalyst preparation
Fig. 2 e Experimental schematic diagram for the dry reforming reaction in the catalytic membrane reactor.
of 0.2 mm, were used as a substrate. Prior to the plating process, PSS disks were ultrasonically cleaned in an alkaline solution of Na3PO4.12H2O (45 g/l), Na2CO3 (65 g/l), NaOH (45 g/l) and 4 ml/l detergent, at 60 C for 1 h. Then, the prewashed disks were washed thoroughly three times with deionized water until the rinsing water was pH 7. After that, the disks were immersed in isopropanol and dried at 120 C for 3 h. The cleaned stainless steel was oxidized in a high temperature furnace at 600 C for 6 h (with a heating rate of 5 C/min) in air. In order to activate the surface, the substrates were sensitized by immersing sequentially in 1 g/l of SnCl2 (pH 1), DI water and 0.1 g/l of PdCl2 (pH 1), and rinsing with 0.01 M HCl and DI water repeatedly several times until their color changed into dark gray to ensure a sufficient Pd coating on the surface. Firstly, deposition of palladium by electroless plating (ELP) was performed in a solution consisting of 4.0 g/l of Pd(NH3)4Cl2.H2O, 198 ml/l of 28% NH4OH, 40.1 g/l of Na2EDTA, and 5.6e7.6 ml/l of 1 M N2H4.H2O. The activated substrate was immersed in the solution (pH 11) at a constant temperature of 60 C for 90 min. It was then washed with warm deionized water and left to dry
Ce0.6Zr0.4O2 mixed oxide support was synthesized by the surfactant-assisted templating method. The metal nitrite solution was prepared by dissolving Ce(NO3)3.6H2O (25.6 g/l) and Zr(NO3)2.H2O (9.1 g/l) precursor salts in deionized water. The surfactant solution was also prepared in which cetyltrimethylammonium bromide (CTAB; 98% purity, Sigma) was dissolved in DI water at 60 C. The metal nitrate solution was then added into the surfactant solution to obtain a mixed solution with the molar ratio of [CTAB]/[Ce þ Zr] of 0.5. Aqueous ammonia (25 vol.%) was gradually added under vigorous stirring until the precipitation of a gelatinous yellowebrown colloidal slurry was complete (pH 11.8). The slurry was stirred for 60 min in a glass reactor, subsequently transferred into Pyrex glass bottles, sealed and aged hydrothermally in autogenously pressure conditions for 5 days at 90 C. After the aging had finished, the bottles were cooled and the precipitate was filtered out and washed repeatedly with warm DI water. The resulting cakes were dried at 120 C overnight and finally calcined at 650 C for 3 h in a furnace. Wet impregnation of 5 wt% Ni was carried out by immersing 14 g of the catalyst support into 128 ml of the prepared 0.1 M Ni(NO3)2 solution. The mixture was subjected to slow heating under constant stirring in a hot water bath to remove excess water. The obtained dried powder was then calcined at 650 C for 3 h. The BrunauereEmmetteTeller (BET) surface area (SA), pore volume (PV), and average pore diameter (PD) for the synthesized catalyst was evaluated by the N2 physisorption technique. The N2 isotherm of the catalyst was classified as typical mesoporous material in the type IV category and exhibited hysteresis between the adsorption and desorption branch of the N2 isotherm. The presence of impregnated NiO phase on the support obtained by the surfactant-assisted method implied that the catalyst maintains a certain order of mesoporosity. The surface area, pore volume, and average pore diameter measurements of the catalyst were 106.03 m2/g, 0.2563 cm3/g, and 96.70 A, respectively. Accordingly, the XRD
2624
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
pattern of the 5% Ni/CeZrO2 catalyst showed a single phase cubic fluorite structure.
CH 450 C CO 450 C
100
CH 500 C 90
Equations used for calculations of conversion, selectivity and yield
% CH4 conversion ¼ ðCH4 Þin ðCH4 Þout ðCH4 Þin 100
(8)
% CO2 conversion ¼ ðCO2 Þin ðCO2 Þout ðCO2 Þin 100
(9)
% H2 yield ¼ ðH2 Þout ðCH4 Þin 100 0:5 % CO yield ¼ ðCOÞout
ðCH4 Þin þ ðCO2 Þout 100
% H2 selectivity ¼ ðH2 Þout
CH 550 C CO 550 C
70 60 50 40 30 20 10
(10)
0 0
(11)
2 ðCH4 Þin ðCH4 Þout 100 (12)
% H2 recovery ¼ ðH2 Þpermeate
CH4 and CO2 conversion, %
The conversions of CH4 and CO2, yield and selectivity of H2 are as follows:
CO 500 C
80
.h i ðH2 Þpermeate þ ðH2 Þretentate 100
50
100
150
200
250
reaction time, min
Fig. 3 e Illustration of CH4 and CO2 conversions of the dry reforming reaction with 1:1 M ratio feed at a flow rate of 30 ml/min, with 40 mg 5% Ni/Ce0.6Zr0.4O2 as the catalyst at 450 C, 500 C, and 550 C.
(13)
Catalyst performance study on the conventional catalytic reactor Investigation of the proper operation condition: optimum temperature, flow rate, feed ratio (CH4/CO2), and catalyst mass for applying to the membrane reactor was performed using a packed-bed reactor. From the dry reforming reactions, CH4 and CO2 will react with each other to yield the desired hydrogen (H2) and other by-products under certain conditions. The extent of the reaction can be pronounced by the presence of the nickel-based catalysts [22,27,29]. Fig. 3 shows the methane (CH4) and carbon dioxide (CO2) conversions from the dry reforming reactions at various reaction temperatures, using 40 mg of the 5% Ni/Ce0.6Zr0.4O2 catalyst filled in the packed-bed reactor with a volume of 3.39 ml. It clearly shows that the synthesized catalyst could facilitate the reactions, resulting in the consumption of CH4 and CO2 raw material feeds. From the graph, the CH4 and CO2 conversions increased as the temperature increased. The reactions occurred almost instantly upon the feed entering the reactor and reached a steady state very quickly. The CO2 conversion values were higher than those of the methane since CO2 was also consumed by the competing reaction with the generated hydrogen. Similarly, Gallucci et al. reported that CO2 conversion always differs from CH4 conversion, since CO2 and CH4 are involved in several secondary reactions which occur during the dry reforming reaction [8]. The conversions of both CH4 and CO2 were relatively constant after a period of reaction time approximately greater than 1 hour and were sustained over a length of 4 h observation time, indicating the capacity and stability of the catalyst to promote the reactions. Fig. 4 illustrates the effect of temperature on the dry reforming reactions with and without the 5% Ni/Ce0.6Zr0.4O2
CH (without catalyst) CO (without catalyst) CH (with catalyst 40 mg)
100
CO (with catalyst 40 mg)
90 80
CH4 and CO2 conversion, %
Results and discussion
catalyst in which CH4 and CO2 (1:1 M ratio) was fed to the reactor at a pressure of 250 kPa. The percent conversions of both CH4 and CO2 typically increased at higher temperatures. Without the presence of the catalyst, the reactions possibly occurred at very high temperatures. In this case, the methane may have reacted with the carbon dioxide at a temperature of 700 C or more. Because the dry reforming reaction is a highly endothermic process, it requires severe operating temperatures (800e1000 C) to reach high conversion levels [30]. However, the reactions appeared to occur more easily at much lower temperatures (roughly over 350 C) when the catalyst was introduced to the reaction system. It is worth noting that the window of operating temperature suitable for the in-situ hydrogen separation with the PdAgCu membrane could not be
70 60 50 40 30 20 10 0 300
400
500
600
700
800
900
o
reaction temperature, C
Fig. 4 e Steady state reaction conversions of CH4 and CO2 for dry reforming reactions with and without the 5% Ni/ Ce0.6Zr0.4O2 catalyst at various temperatures.
2625
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
50
45 40
CH4 and CO2 conversions, %mol
average yield H2 and CO, %mol
CO 40
H2
30
20
10
0 300
350
400
450
500
550
600
650
700
35 30
CO2
25 20 15 10 5
CH4
0 100
750
200
300
400
500
600
GSHV, hrs
o
reaction temperature, C
Fig. 5 e H2 and CO yields at different reaction temperatures. higher than 550 C to avoid the undesired intermetallic diffusion of the stainless steel substrate that could lead to poor membrane performance [28,31]. Fig. 5 shows the hydrogen (H2) and carbon monoxide (CO) yields as a function of temperature. With increasing temperature, both H2 and CO yields rose as expected. However, the hydrogen yield appeared to be lower than that of the carbon monoxide since the hydrogen was also consumed in the side reaction with the unreacted carbon dioxide. Fig. 6 presents the hydrogen selectivity of the reactions as a function of temperature. More desired hydrogen product could be obtained at higher reaction temperature, suggesting that the temperature should be raised to the upper limit when the application of the membrane was coupled with the reactor to perform in-situ hydrogen separation. Increasing the gaseous feed flow rate resulted in the reduction of both CH4 and CO2 conversion since the residence
700
800
900
-1
Fig. 7 e CH4 and CO2 conversions for the conventional reactor: effect of the increasing feed flow rate on the CH4 and CO2 conversions of the reaction system at 550 C with a CH4/CO2 molar feed ratio of 1:1 and the catalyst amount of 40 mg.
time that allows the reactions to take place inside the reactor was decreased as the feed gas hourly space velocity (GHSV) was raised, as clearly shown in Fig. 7. Additionally, the CH4/CO2 feed ratios were found to have some effect on the extent of reactions. Fig. 8 shows the plot of CH4 and CO2 conversions at various CH4/CO2 feed ratios. The graph shows that the use of CO2-rich feed could result in higher consumption of both CH4 and CO2 in the reaction system. To understand this phenomenon more clearly, the H2 and CO reaction product yields were also investigated, as shown in Fig. 9. Increasing the amount of CO2 in the feed to shift, the ratio of CH4/CO2 gave rise to both H2 and CO yields that reached the maximum values of 10% and 20%, respectively; however, the yields showed a decline for richer CO2 mixed feeds. Since the
100
40
o
at 550 C with the catalyst amount of 40 mg
CH4 and CO2 conversions, %mol
H2 selectivity, %mol
90 30
20
10
0 300
350
400
450
500
550
600
650
700
750
o
Temperature, C
80 70 60 50 40
CO2 CH4
30 20 10 0 3/1
Fig. 6 e H2 selectivity for the conventional reactor: effect of the increasing reaction temperature on hydrogen selectivity of the reaction system from 350 to 700 C with a CH4/CO2 molar feed ratio of 1:1 at 30 ml/min and the catalyst amount of 40 mg.
2/1
1/1
1/2
1/3
Feed ratio, CH4/CO2
Fig. 8 e CH4 and CO2 conversions for the conventional reactor: effect of the CH4/CO2 feed ratio on the CH4 and CO2 conversions at the reaction time of 180 min.
2626
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
average yield H2 and CO, %mol
30
o
at 550 C with the catalyst amount of 40 mg
20
CO 10
H2 0 3/1
2/1
1/1
1/2
1/3
feed ratio, CH4/CO2
Fig. 9 e H2 and CO reaction product yields at different feed ratios: effect of the increasing feed ratio CH4/CO2 from 3/1 to 1/3 ml/min catalyst amount 40 mg, reaction temperature 550 C.
main dry reforming reaction of methane is reversible, introducing excess amounts of the reactants could drive the reaction forward resulting in more hydrogen being generated. However, the produced H2 could also react with the unreacted CO2 in the reversible water-gas shift side reaction. Therefore, higher CO2 consumption compared to that of CH4 in terms of the conversion was typically observed. The maximum H2 and CO yields were obtained when using equimolar CH4/CO2 (1:1) mixed feed. Considering the stoichiometry of the dry reforming reaction, 1 mol of CH4 requires 1 mol of CO2 to react with each other [8]. In conclusion, shifting the CH4/CO2 ratio to 1:1 or vice versa resulted in an increase in reaction product yields. Fig. 10 shows the effect of the amount of catalyst usage on the CH4 and CO2 conversions. The amount of catalyst used
basically had effect on the extent of the reaction to some degree. Generally, increasing mass usage will increase the reaction conversions. The H2 and CO reaction yields appear to be proportional to the amount of the catalyst used as well, as shown in Fig. 11. Since the catalyst plays an important role in the dissociative adsorption of methane which is the rate-determining step of the reaction, the high mass of catalyst deployed will provide an active surface that facilitates the reaction. It is of note that the reactants have to be transported from the feed stream to the active sites, so adding too many of the relatively small particles of the catalyst can dramatically change the characteristics and flow pattern inside the packed-bed reactor and this will affect the mass transport efficiency of the system. Ideally, an optimum catalyst amount is required to achieve the highest possible conversions or yields without the reactor performance significantly suffering such as through a rapid increase in pressure drop or the throughput capacity drop at the operated conditions.
Catalytic membrane reactor performance study In order to evaluate the performance of the Pd alloy membrane reactor, methane and carbon dioxide conversion using conventional packed-bed reactor and a palladium alloy membrane reactor were compared. The reaction performance was carried out in the packed-bed reactor filled with 60 mg 5% Ni/Ce0.6Zr0.4O2 catalyst coupled with a dense Pd76Ag19Cu5 alloy membrane in which 20 ml/min of the 1:1 CH4/CO2 mixed feed was fed into the reactor at 550 C. Fig. 12 (a) and (b) show the reactant conversions (CH4 and CO2) and reaction product yields (H2 and CO) versus the reaction time, respectively. With the presence of the membrane, it was clearly demonstrated that both CH4 and CO2 conversions were significantly increased when compared to the system without the membrane operated at the same conditions. Methane conversion was clearly increased by approximately two-fold.
30
100
28 26 24
80
H2 and CO yields, %mol
CH4 and CO2 conversions, %mol
90
70 60 50 40
CO2
30
CH4
20
22 20
CO
18 16 14 12
H2
10 8 6 4
10
2
0
0 0
10
20
30
40
50
60
70
80
90
catalyst amount, mg
Fig. 10 e CH4 and CO2 conversions for the conventional reactor: effect of the increasing catalyst mass from 10 to 80 mg. CH4/CO2 molar feed ratio 1:1, feed flow rate 20 ml/ min, reaction temperature 550 C.
0
10
20
30
40
50
60
70
80
90
catalyst amount, mg
Fig. 11 e H2 and CO yields at different catalyst amounts: effect of the increasing catalyst amount from 10 to 80 mg. CH4/CO2 molar feed ratio 1:1, feed flow rate 20 ml/min, reaction temperature 550 C.
2627
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
CH /CO ratio 1:1, feed flow rate 20 ml/min,
CH4 and CO2 conversions, %mol
90
(a)
o
90
CO packed-bed reactor
80
CH membrane reactor
80
CH4/CO2 ratio 1:1, feed flow rate 20 ml/min,
100
reaction temperature 550 C, catalyst amount 60 mg CH packed-bed reactor
CO membrane reactor 70 60 50
CH4 conversion, %
100
reaction temperature 550 C, catalyst amount 60 mg
70 60 50 40
40
30 30
20
20
10
10
0
0 20
40
60
80
100
120
140
160
180
32.5
200
33.0
33.5
reaction time, min
CH /CO ratio 1:1, feed flow rate 20 ml/min,
100
reaction temperature 550 C, catalyst amount 60 mg
(b)
34.5
Fig. 13 e Correlation between the methane conversion and H2 recovery.
H packed-bed reactor
CH /CO ratio 1:1, feed flow rate 20 ml/min,
80
CO packed-bed reactor H membrane reactor
2.0
70
CO membrane reactor
1.8
60
1.6
50
1.4
40
1.2
H /CO
H and CO yield, %mol
90
34.0
H2 yield, %
30 20 10
reaction temperature 550 C, catalyst amount 60 mg Packed-bed reactor Membrane reactor
1.0 0.8 0.6
0
0.4 20
40
60
80
100
120
140
160
180
200
0.2
reaction time, (min)
Accordingly, the CO2 conversion shifted from about 50%e60%. As previously discussed, more CO2 was consumed than CH4 in the conventional packed bed reactor due to the extent of the water-gas shift side reaction. For membrane reactor, it is clearly seen in Fig 12a that the CH4 conversion was observed as being greater than that of the CO2. In this case, hydrogen was constantly withdrawn from the reactor by permeation through the dense PdAgCu alloy membrane which helps shifting the dry reforming reaction in a forward direction resulting in improved hydrogen yield. Since methane is the only source of H atoms contributing to the H2 generation, methane consumption in the main dry reforming reaction could basically influence hydrogen formation. In the membrane system, the hydrogen yield was drastically improved by almost 3.5-fold; correspondingly, the CO by-product yield was also increased by 50%. From Fig 13, the hydrogen yield was increased with increasing methane conversion. Fig. 14 illustrates the H2/CO ratio at various reaction times of the system with and without a membrane. The H2/CO ratio shifted towards 1:1 in the case of using the membrane. When
0.0 20
40
60
80
100
120
140
160
180
200
reaction time, min
Fig. 14 e H2/CO ratios versus reaction time of the pack-bed reactor (C) and the membrane reactor (-).
CH /CO ratio 1:1, feed flow rate 20 ml/min,
2.0
reaction temperature 550 C, catalyst amount 60 mg
1.8
CH /CO packed-bed reactor 1.6
CH /CO conversion ratio
Fig. 12 e Comparison of packed-bed reactor (C) and membrane reactor (-), (a) CH4 and CO2 conversions, and (b) H2 and CO yields.
CH /CO membrane reactor
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 20
40
60
80
100
120
140
160
180
200
reaction time, min
Fig. 15 e Effluent CH4/CO2 molar ratio versus reaction time of the pack-bed reactor (C), and the membrane reactor (-).
2628
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
CH /CO ratio 1:1, feed flow rate 20 ml/min,
100
reaction temperature 550 C, catalyst amount 60 mg 90
Packed-bed reactor Membrane reactor
80
H Selectivity, %mol
70 60 50 40 30 20 10 0 20
40
60
80
100
120
140
160
180
200
reaction time, min
Fig. 16 e H2 selectivity versus reaction time of the pack-bed reactor (C), and the membrane reactor (-).
40 35
%H2 recovery
30 25 20 15 10
equilibrium of the dry reforming reaction was forced to shift forward so that more products could be obtained when the H2 was drawn out of the reactor by the membrane. Additionally, the unreacted CH4 and CO2 molar ratio of the effluent of the membrane reactor was shifted from about 0.6 towards 1.0 which was close to that of the feed entering the reactor (1:1), as illustrated in Fig. 15. The result could imply that the CH4 and CO2 were basically consumed in the reactions in a stoichiometric manner. The CO2 was possibly less involved in the side water-gas shift reaction due to the lack of a hydrogen presence resulting from in-situ membrane separation as previously discussed. In conclusion, the presence of the membrane seemed to minimize the effect of other undesired competing or chain reactions involved in the system. As clearly seen in Fig. 16, the overall hydrogen selectivity improved by 10% (from 48 to 53%). In terms of permeation capacity, the H2 recovery was measured as the in-situ reactionseparation was undergoing, as seen in Fig. 17. The recovery of hydrogen was found to be around 30 percent. It is worth noting that the membrane reactor has a one-pass flow through configuration. The H2 recovery from the unit was reasonably acceptable; nevertheless, the overall H2 production beneficial from the membrane application was significantly improved. As shown in Table 1, the DRM reaction performance results obtained from this study were in good agreement with other studies. However, it is of note that all system configurations are not the same. Various reactor designs with different types of membranes and catalysts were used in each previous study.
5
Conclusion
0 20
40
60
80
100
120
140
160
180
200
reaction time, min Fig. 17 e H2 recovery versus reaction time of the membrane reactor.
coupled with the membrane, the in-situ reaction and separation of the hydrogen product could take place simultaneously. The H2 formed by the main reaction between CH4 and CO2 was selectively removed through the membrane at all times as the reaction proceeded. Therefore, there was a lower amount of H2 left to react with the unreacted CO2 in the competing reversible water-gas shift reaction. Furthermore, the
The packed-bed membrane reactor containing the 5% Ni/ Ce0.6Zr0.4O2 catalyst and coupled with the dense Pd76Ag19Cu5 alloy membrane was demonstrated to enhance the hydrogen production from the dry reforming reactions of CH4 and CO2. The overall reactant CH4 and CO2 conversions were significantly increased resulting in better reaction performance in terms of H2 yield and selectivity. With the membrane installed, this allowed the in-situ partial hydrogen to be withdrawn from the reactor during the reactions taking place. It is believed that the equilibrium of the system was perturbed by shifting the dry reforming reaction forward. Additionally, the partial hydrogen removal was shown to affect the reaction
Table 1 e Comparison of methane conversion in the membrane reactor (MR) and packed bed reactor (PBR) from the dry reforming of methane. Membrane
Catalyst type
Pd-based
Pd/Al2O3
Porous PdeAg
Ni/Al2O3
Dense PdeAg
Pt/Al2O3
Dense PdeAg Dense PdAgCu
Pt/CeZrO2/Al2O3 Ni/CeZrO2
T ( C)
%XCH4 ;MR
%XCH4 ;PBR
%X ratio (MR/PBR)
550 600 400 450 400 450 550 550
37.5 48.6 2.1 8.4 7.9 17.8 85 65.2
17.2 40.9 5.6 17.4 5.6 17.4 25 33.5
2.2 1.2 0.4 0.5 1.4 1.0 3.4 1.9
Ref. [32] [8] [33] [21] This work
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
system by minimizing the side reaction effects through the creation of a hydrogen-deprived environment inside the reactor. This conceptual type of reactor could lead to its better design in hydrogen production and purification from the dry reforming reaction between CH4 and CO2. In summary, appropriate downstream H2 separation and purification by well-designed PdAgCu alloy membrane units capable of unreacted CH4 and CO2 recovery and recycled back into the reaction system could make the overall process more feasible and economically achievable so as to attract further development on the high-scale industry level.
Acknowledgments This work was financially supported by the 90th Anniversary of Chulalongkorn University Fund (Ratchadaphiseksomphot Endowment Fund) No.20-1-2556, National Research Council of Thailand (NRCT) No.82619, and the Program of Petrochemistry and Polymer Science, Chulalongkorn University.
references
[1] Bosko ML, Mu´nera JF, Lombardo EA, Cornaglia LM. Dry reforming of methane in membrane reactors using Pd and PdeAg composite membranes on a NaA zeolite modified porous stainless steel support. J Membr Sci 2010;364:17e26. [2] Sanz R, Calles JA, Alique D, Furones L. H2 production via water gas shift in a composite Pd membrane reactor prepared by the pore-plating method. Int J Hydrogen Energy 2014;39:4739e48. n ~ ez S, Marı´n P. [3] Sanz R, Calles JA, Alique D, Furones L, Ordo Hydrogen production in a pore-plated Pd-membrane reactor: experimental analysis and model validation for the water gas shift reaction. Int J Hydrogen Energy 2015;40:3472e84. [4] Abasaeed AE, Al-Fatesh AS, Naeem MA, Ibrahim AA, Fakeeha AH. Catalytic performance of CeO2 and ZrO2 supported Co catalysts for hydrogen production via dry reforming of methane. Int J Hydrogen Energy 2015;40(21):6818e26. [5] Usman M, Wan Daud WMA, Abbas HF. Dry reforming of methane: influence of process parameters e a review. Renew Sustain Energy Rev 2015;45:710e44. [6] Naeem MA, Al-Fatesh AS, Khan WU, Abasaeed AE, Fakeeha AH. Syngas production from dry reforming of methane over nano Ni polyol catalysts. Int J Chem Eng Appl 2013:315e20. [7] Wang S, Lu G, Millar GJ. Carbon dioxide reforming of methane to produce synthesis gas over metal-supported catalysts: state of the art. Energy Fuels 1996;10:896e904. [8] Gallucci F, Tosti S, Basile A. PdeAg tubular membrane reactors for methane dry reforming: a reactive method for CO2 consumption and H2 production. J Membr Sci 2008;317:96e105. [9] Basile Angelo, et al., editors. Membrane reactors for energy applications and basic chemical production. Elsevier; 2015. p. 99e144. [10] Yun S, Ted Oyama S. Correlations in palladium membranes for hydrogen separation: a review. J Membr Sci 2011;375:28e45.
2629
[11] Braun F, Tarditi AM, Miller JB, Cornaglia LM. Pd-based binary and ternary alloy membranes: morphological and permselective characterization in the presence of H2S. J Membr Sci 2014;450:299e307. [12] Burkhanov GS, Gorina NB, Kolchugina NB, Roshan NR, Slovetsky DI, Chistov EM. Palladium-based alloy membranes for separation of high purity hydrogen from hydrogen-containing gas mixtures. Platin Met Rev 2011;55:3e12. [13] Hatlevik Ø, Gade SK, Keeling MK, Thoen PM, Davidson AP, Way JD. Palladium and palladium alloy membranes for hydrogen separation and production: history, fabrication strategies, and current performance. Sep Purif Technol 2010;73:59e64. [14] Dolan MD. Non-Pd BCC alloy membranes for industrial hydrogen separation. J Membr Sci 2010;362:12e28. [15] Ling C, Semidey-Flecha L, Sholl DS. First-principles screening of PdCuAg ternary alloys as H2 purification membranes. J Membr Sci 2011;371:189e96. [16] Peters TA, Kaleta T, Stange M, Bredesen R. Development of thin binary and ternary Pd-based alloy membranes for use in hydrogen production. J Membr Sci 2011;383:124e34. [17] Tarditi AM, Braun F, Cornaglia LM. Novel PdAgCu ternary alloy: hydrogen permeation and surface properties. Appl Surf Sci 2011;257:6626e35. [18] Zhao L, Goldbach A, Bao C, Xu H. Structural and permeation kinetic correlations in PdCuAg membranes. ACS Appl Mater Interfaces 2014;6:22408e16. [19] Nayebossadri S, Speight J, Book D. Effects of low Ag additions on the hydrogen permeability of PdeCueAg hydrogen separation membranes. J Membr Sci 2014;451:216e25. [20] Garcı´a-Garcı´a FR, Soria MA, Mateos-Pedrero C, GuerreroRuiz A, Rodrı´guez-Ramos I, Li K. Dry reforming of methane using Pd-based membrane reactors fabricated from different substrates. J Membr Sci 2013;435:218e25. [21] Silva FA, Hori CE, da Silva AM, Mattos LV, Mu´nera J, Cornaglia L, et al. Hydrogen production through CO2 reforming of CH4 over Pt/CeZrO2/Al2O3 catalysts using a PdeAg membrane reactor. Catal Today 2012;193:64e73. [22] Gallucci F, Fernandez E, Corengia P, van Sint Annaland M. Recent advances on membranes and membrane reactors for hydrogen production. Chem Eng Sci 2013;92:40e66. [23] Kyriakides A-S, Rodrı´guez-Garcı´a L, Voutetakis S, Ipsakis D, Seferlis P, Papadopoulou S. Enhancement of pure hydrogen production through the use of a membrane reactor. Int J Hydrogen Energy 2014;39:4749e60. [24] Brunetti A, Caravella A, Fernandez E, Pacheco Tanaka DA, Gallucci F, Drioli E, et al. Syngas upgrading in a membrane reactor with thin Pd-alloy supported membrane. Int J Hydrogen Energy 2015;40:10883e93. [25] Mardilovich PP, She Y, Ma YH, Rei MH. Defect-free palladium membranes on porous stainless-steel support. AICHE J 1998;44:310e22. [26] Khan A, Sukonket T, Saha B, Idem R. Catalytic activity of various 5 wt % Ni/Ce0.5Zr0.33M0.17O2d catalysts for the CO2 reforming of CH4 in the presence and absence of steam. Energy Fuels 2012;26:365e79. [27] Sukonket T, Khan A, Saha B, Ibrahim H, Tantayanon S, Kumar P, et al. Influence of the catalyst preparation method, surfactant amount, and steam on CO2 reforming of CH4 over 5Ni/Ce0.6Zr0.4O2 catalysts. Energy Fuels 2011;25:864e77. [28] Samingprai S, Tantayanon S, Ma YH. Chromium oxide intermetallic diffusion barrier for palladium membrane supported on porous stainless steel. J Membr Sci 2010;347:8e16.
2630
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
[29] Hwang K-R, Lee C-B, Ryi S-K, Park J-S. Hydrogen production and carbon dioxide enrichment using a catalytic membrane reactor with Ni metal catalyst and Pd-based membrane. Int J Hydrogen Energy 2012;37:6626e34. [30] Soria MA, Mateos-Pedrero C, Guerrero-Ruiz A, Rodrı´guezRamos I. Thermodynamic and experimental study of combined dry and steam reforming of methane on Ru/ ZrO2eLa2O3 catalyst at low temperature. Int J Hydrogen Energy 2011;36:15212e20.
[31] Chotirach M, Tantayanon S, Tungasmita S, Kriausakul K. Zrbased intermetallic diffusion barriers for stainless steel supported palladium membranes. J Membr Sci 2012;405e406:92e103. [32] Galuszka J, Pandey RN, Ahmed S. Methane conversion to syngas in a palladium membrane reactor. Catal Today 1998;46:83e9. [33] Kikuchi E. Palladium/ceramic membranes for selective hydrogen permeation and their application to membrane reactor. Catal Today 1995;25:333e7.
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Improved hydrogen production from dry reforming reaction using a catalytic packed-bed membrane reactor with Ni-based catalyst and dense PdAgCu alloy membrane Sarocha Sumrunronnasak a, Supawan Tantayanon b,*, Somchai Kiatgamolchai c, Thitinat Sukonket d a Graduate Program of Petrochemistry and Polymer Science, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand b Green Chemistry Research Laboratory, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand c Department of Physics, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand d Occupational Health and Safety Science Program, Faculty of Science and Technology, Suan Dusit Rajabhat University, 295 Nakhon Ratchasima Rd. Disit District, Bangkok, 10300, Thailand
article info
abstract
Article history:
A catalytic Pd76Ag19Cu5 alloy membrane reactor packed with 5% Ni/Ce0.6Zr0.4O2 catalyst
Received 3 September 2015
was adopted in this study to investigate hydrogen production performance from the dry
Received in revised form
reforming reaction of methane and carbon dioxide. The 1:1 CH4/CO2 feed was introduced to
30 October 2015
the reactor with 60 mg of the catalyst at a flow rate of 20 ml/min at 550 C. The effluent gas
Accepted 30 October 2015
compositions were examined using an online gas chromatographer (GC). Compared to a
Available online 8 January 2016
conventional reactor without the membrane, the CH4 and CO2 conversions were significantly increased by 3.5-fold and 1.5-fold, respectively. Correspondingly, the overall H2 yield
Keywords:
was greatly improved from about 10e35%. Additionally, the hydrogen selectivity increased
PdAgCu alloy membrane
from 47 to 53%. It is theorized that the in-situ partial hydrogen withdrawal by the mem-
Hydrogen production
brane mainly caused the dry reforming reaction equilibrium to shift forward and created a
Dry reforming
hydrogen-deprived environment unfavorable for the competing reversible water-gas shift
Catalytic membrane reactor
reaction to take place.
Ni-based catalyst
Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Introduction The demand for hydrogen as a clean energy source, a feedstock, or as an intermediate and specialty chemical is
expected to grow rapidly in coming years. The main challenges lie in finding hydrogen sources and economically efficient enrichment processes in order to achieve high purity hydrogen suitable for usages [1e4]. An alternative approach of producing hydrogen is via useful reaction pathways such as
* Corresponding author. E-mail address: [email protected] (S. Tantayanon). http://dx.doi.org/10.1016/j.ijhydene.2015.10.129 0360-3199/Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
2622
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
the dry reforming reaction between CH4 and CO2 facilitated by various metal-based catalysts [5,6]. Carbon dioxide reforming of methane produces synthesis gas with hydrogen to carbon monoxide ratio desirable for many industrial synthesis processes. This reaction also has very important environmental implications since both methane and carbon dioxide contribute to the greenhouse effect [4,7]. The dry reforming of methane (DRM) produces an equimolar synthesis gas (syngas) e which is a mixture of hydrogen (H2) and carbon monoxide (CO) e from carbon dioxide and methane (CH4). In fact, the main reactions involved in this process are as follows [8,9]: 1
DH 298 K ¼ þ247:4 kJ mol
CH4 þCO2 /2CO þ 2H2
(1)
Materials and methods
DH 298 K
CO2 þH2 /CO þ H2 O ðreverse water gas shiftÞ; 1
¼ þ41:2 kJ mol
(2) DH 298
CO2 þ4H2 /CH4 þ2H2 O ðmethanationÞ;
K
1
¼ 165:0 kJ mol
(3)
However, another two undesired reactions occur, producing carbon deposition: CH4 /2H2 þ C DH 298 2CO/CO2 þ C DH 298
K
K
1
¼ þ75:0 kJ mol
(4)
1
¼ 173:0 kJ mol
CO þ H2 /H2 O þ C DH 298
K
CO2 þ2H2 /H2 O þ C DH 298
¼ 131:0 kJ mol K
(5) 1
¼ 173:0 kJ mol
1
In this study, a packed-bed membrane reactor consisting of a Ni-based catalyst and dense PdAgCu alloy membrane was set up to study its hydrogen production performance from the dry reforming reactions between CH4 and CO2. The main goal of this study is to gain better understanding of the factors affecting the reaction and separation performance such as the CH4/CO2 feed ratio, feed flow rate, temperature, and catalyst mass. Additionally, it is interesting to investigate the effect of possible in-situ hydrogen membrane separation taking place during the ongoing reactions that could result in improved hydrogen production.
(6) (7)
As reported in many studies, palladium-based alloy membranes have shown to be effective in hydrogen separation because of their excellent performance in terms of hydrogen permeability and selectivity [10e16]. In particular, dense PdAgCu alloy membranes have been widely used for such applications since the membranes can deliver high hydrogen purity and capacity under a harsh environment in the separation process [15,17e19]. Additionally, the membrane reactor has been extensively studied for the dry reforming of methane using different membrane types such as self-standing PdAg alloys, Pd-ceramic composite, silica/ mullite membrane, Pd film supported on porous stainless steel, and SiO2/alumina membrane [1,8,20e22]. Generally, CH4 conversion can be greatly improved by removing the hydrogen formed with a stable and highly selective dense Pd alloy membrane [23,24]. Through such means, higher conversions have been reported than those corresponding to the thermodynamic equilibrium of a conventional packed-bed reactor operating at the same experimental conditions as the membrane reactor. For an optimal membrane reactor to be developed for hydrogen production, two key requisites must be fulfilled: (i) the development of a well-performing catalyst, and (ii) the use of a stable, highly selective, high H2 permeance membrane [21,25]. The 5% Ni/Ce0.6Zr0.4O2 prepared by the surfactant approach was used since it has shown to be a good catalyst for the CO2 reforming of CH4 with stable activity [26,27]. PdAgCu alloy was selected due to its proven stability at high temperature (550 C) as required by the highly endothermic DRM reaction.
Reaction system The dry reforming reaction of methane was carried out in a packed-bed reactor coupled with palladium alloy membrane. The 5% Ni/Ce0.6Zr0.4O2 catalyst of 0.35 mm grain size was prepared by the surfactant-assisted templating method. The detailed procedure has been described by Sukonket et al. [26,27]. A dense Pd76Ag19Cu5 alloy membrane 15 nm thick supported on a porous stainless steel (316 PSS) disk with a hydrogen permeability of 7.7 109 mol/m.s.Pa0.5 at 350 C was used. The reactor was packed with the well-mixed catalyst and 3.0 g of 0.4 mm quartz sand. The reactant feed was vertically passed through the packed-bed of 5% Ni/Ce0.6Zr0.4O2 and membrane sequentially. The reactor was placed vertically inside a programmable furnace to control the desired temperature. Prior to the reaction, the catalyst was readily reduced by atmospherically purging the 10 mol% hydrogen balanced in nitrogen into the reactor at 710 C with a flow rate of 30 ml/min for 3 h. To the study the reaction unit performance, the dry reforming reaction was carried out in various conditions as follows: a total feed flow rate of 10e50 ml/min, argon purge (for the permeate side of the membrane) at 10 ml/min, CH4/ CO2 molar feed ratios in the range of 3/1e1/3, catalyst mass in the range of 10e80 mg, reaction temperature in the range of 450e550 C, and reaction pressure at 250 kPa. The reaction was monitored by an online GC using an analytical column series of the Porapack Q for the higher molecule (CH4 and CO2) and a molecular sieve (13X) for the smaller molecule (CO and H2) separations in which a thermal conductive detector (TCD) was in place for temperature measurement. Argon gas was used as a carrier gas with a pressure of 50 kPa for the entire experiment. The temperature of the inlet, oven, and detector were 100 C, 35e150 C and 120 C, respectively. The permeated gas composition was analyzed by comparing the area under the peaks with those of the standards from the calibration curve. All of the gases were regulated through pre-calibrated mass (gas) flow controllers with digital readout units. The assembled catalytic membrane reactor and the experimental schematic diagram for the dry reforming reaction system are presented in Figs. 1 and 2, respectively.
Membrane preparation Porous stainless steel disks (316L PSS) of circular shape 0.39 cm in diameter, 1 mm thickness, and an average pore size
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
Fig. 1 e Outline of an assembled catalytic membrane reactor.
2623
at room temperature. The plating and washing steps were repeated 4 times to ensure dense coating [28]. Then, Ag and Cu were sequentially deposited on the Pd layer by the electroplating (EP) technique using a silver bar as an anode (10% AgNO3), and copper bar (25% CuSO4), respectively. A distance of 2.0 cm was maintained between the working and reference anode in a 50 ml plating solution at room temperature. The Ag plating was carried out for a 10 s period with a 1.2 V potential applied followed by the Cu plating for 90 s with a 2.0 V potential applied. The PdeAgeCu membrane was thoroughly washed with 0.01 M HCl, DI water, and ethanol, respectively. The membrane was then annealed at a temperature of 550 C for 80 h in an argon atmosphere. The composition analysis of the prepared alloy membranes was examined using a scanning electron microscope (SEM), JEOL model JSM-5800LV equipped with energy dispersive X-ray diffraction (EDX). From the cross-section SEM-EDX line scan and elemental mapping results, the alloy membrane showed homogeneous element distribution with an average content of 76% Pd, 19% Ag, and 5% Cu, respectively. The average membrane thickness obtained from SEM analysis was 15.55 ± 0.23 mm.
Ni-based catalyst preparation
Fig. 2 e Experimental schematic diagram for the dry reforming reaction in the catalytic membrane reactor.
of 0.2 mm, were used as a substrate. Prior to the plating process, PSS disks were ultrasonically cleaned in an alkaline solution of Na3PO4.12H2O (45 g/l), Na2CO3 (65 g/l), NaOH (45 g/l) and 4 ml/l detergent, at 60 C for 1 h. Then, the prewashed disks were washed thoroughly three times with deionized water until the rinsing water was pH 7. After that, the disks were immersed in isopropanol and dried at 120 C for 3 h. The cleaned stainless steel was oxidized in a high temperature furnace at 600 C for 6 h (with a heating rate of 5 C/min) in air. In order to activate the surface, the substrates were sensitized by immersing sequentially in 1 g/l of SnCl2 (pH 1), DI water and 0.1 g/l of PdCl2 (pH 1), and rinsing with 0.01 M HCl and DI water repeatedly several times until their color changed into dark gray to ensure a sufficient Pd coating on the surface. Firstly, deposition of palladium by electroless plating (ELP) was performed in a solution consisting of 4.0 g/l of Pd(NH3)4Cl2.H2O, 198 ml/l of 28% NH4OH, 40.1 g/l of Na2EDTA, and 5.6e7.6 ml/l of 1 M N2H4.H2O. The activated substrate was immersed in the solution (pH 11) at a constant temperature of 60 C for 90 min. It was then washed with warm deionized water and left to dry
Ce0.6Zr0.4O2 mixed oxide support was synthesized by the surfactant-assisted templating method. The metal nitrite solution was prepared by dissolving Ce(NO3)3.6H2O (25.6 g/l) and Zr(NO3)2.H2O (9.1 g/l) precursor salts in deionized water. The surfactant solution was also prepared in which cetyltrimethylammonium bromide (CTAB; 98% purity, Sigma) was dissolved in DI water at 60 C. The metal nitrate solution was then added into the surfactant solution to obtain a mixed solution with the molar ratio of [CTAB]/[Ce þ Zr] of 0.5. Aqueous ammonia (25 vol.%) was gradually added under vigorous stirring until the precipitation of a gelatinous yellowebrown colloidal slurry was complete (pH 11.8). The slurry was stirred for 60 min in a glass reactor, subsequently transferred into Pyrex glass bottles, sealed and aged hydrothermally in autogenously pressure conditions for 5 days at 90 C. After the aging had finished, the bottles were cooled and the precipitate was filtered out and washed repeatedly with warm DI water. The resulting cakes were dried at 120 C overnight and finally calcined at 650 C for 3 h in a furnace. Wet impregnation of 5 wt% Ni was carried out by immersing 14 g of the catalyst support into 128 ml of the prepared 0.1 M Ni(NO3)2 solution. The mixture was subjected to slow heating under constant stirring in a hot water bath to remove excess water. The obtained dried powder was then calcined at 650 C for 3 h. The BrunauereEmmetteTeller (BET) surface area (SA), pore volume (PV), and average pore diameter (PD) for the synthesized catalyst was evaluated by the N2 physisorption technique. The N2 isotherm of the catalyst was classified as typical mesoporous material in the type IV category and exhibited hysteresis between the adsorption and desorption branch of the N2 isotherm. The presence of impregnated NiO phase on the support obtained by the surfactant-assisted method implied that the catalyst maintains a certain order of mesoporosity. The surface area, pore volume, and average pore diameter measurements of the catalyst were 106.03 m2/g, 0.2563 cm3/g, and 96.70 A, respectively. Accordingly, the XRD
2624
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
pattern of the 5% Ni/CeZrO2 catalyst showed a single phase cubic fluorite structure.
CH 450 C CO 450 C
100
CH 500 C 90
Equations used for calculations of conversion, selectivity and yield
% CH4 conversion ¼ ðCH4 Þin ðCH4 Þout ðCH4 Þin 100
(8)
% CO2 conversion ¼ ðCO2 Þin ðCO2 Þout ðCO2 Þin 100
(9)
% H2 yield ¼ ðH2 Þout ðCH4 Þin 100 0:5 % CO yield ¼ ðCOÞout
ðCH4 Þin þ ðCO2 Þout 100
% H2 selectivity ¼ ðH2 Þout
CH 550 C CO 550 C
70 60 50 40 30 20 10
(10)
0 0
(11)
2 ðCH4 Þin ðCH4 Þout 100 (12)
% H2 recovery ¼ ðH2 Þpermeate
CH4 and CO2 conversion, %
The conversions of CH4 and CO2, yield and selectivity of H2 are as follows:
CO 500 C
80
.h i ðH2 Þpermeate þ ðH2 Þretentate 100
50
100
150
200
250
reaction time, min
Fig. 3 e Illustration of CH4 and CO2 conversions of the dry reforming reaction with 1:1 M ratio feed at a flow rate of 30 ml/min, with 40 mg 5% Ni/Ce0.6Zr0.4O2 as the catalyst at 450 C, 500 C, and 550 C.
(13)
Catalyst performance study on the conventional catalytic reactor Investigation of the proper operation condition: optimum temperature, flow rate, feed ratio (CH4/CO2), and catalyst mass for applying to the membrane reactor was performed using a packed-bed reactor. From the dry reforming reactions, CH4 and CO2 will react with each other to yield the desired hydrogen (H2) and other by-products under certain conditions. The extent of the reaction can be pronounced by the presence of the nickel-based catalysts [22,27,29]. Fig. 3 shows the methane (CH4) and carbon dioxide (CO2) conversions from the dry reforming reactions at various reaction temperatures, using 40 mg of the 5% Ni/Ce0.6Zr0.4O2 catalyst filled in the packed-bed reactor with a volume of 3.39 ml. It clearly shows that the synthesized catalyst could facilitate the reactions, resulting in the consumption of CH4 and CO2 raw material feeds. From the graph, the CH4 and CO2 conversions increased as the temperature increased. The reactions occurred almost instantly upon the feed entering the reactor and reached a steady state very quickly. The CO2 conversion values were higher than those of the methane since CO2 was also consumed by the competing reaction with the generated hydrogen. Similarly, Gallucci et al. reported that CO2 conversion always differs from CH4 conversion, since CO2 and CH4 are involved in several secondary reactions which occur during the dry reforming reaction [8]. The conversions of both CH4 and CO2 were relatively constant after a period of reaction time approximately greater than 1 hour and were sustained over a length of 4 h observation time, indicating the capacity and stability of the catalyst to promote the reactions. Fig. 4 illustrates the effect of temperature on the dry reforming reactions with and without the 5% Ni/Ce0.6Zr0.4O2
CH (without catalyst) CO (without catalyst) CH (with catalyst 40 mg)
100
CO (with catalyst 40 mg)
90 80
CH4 and CO2 conversion, %
Results and discussion
catalyst in which CH4 and CO2 (1:1 M ratio) was fed to the reactor at a pressure of 250 kPa. The percent conversions of both CH4 and CO2 typically increased at higher temperatures. Without the presence of the catalyst, the reactions possibly occurred at very high temperatures. In this case, the methane may have reacted with the carbon dioxide at a temperature of 700 C or more. Because the dry reforming reaction is a highly endothermic process, it requires severe operating temperatures (800e1000 C) to reach high conversion levels [30]. However, the reactions appeared to occur more easily at much lower temperatures (roughly over 350 C) when the catalyst was introduced to the reaction system. It is worth noting that the window of operating temperature suitable for the in-situ hydrogen separation with the PdAgCu membrane could not be
70 60 50 40 30 20 10 0 300
400
500
600
700
800
900
o
reaction temperature, C
Fig. 4 e Steady state reaction conversions of CH4 and CO2 for dry reforming reactions with and without the 5% Ni/ Ce0.6Zr0.4O2 catalyst at various temperatures.
2625
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
50
45 40
CH4 and CO2 conversions, %mol
average yield H2 and CO, %mol
CO 40
H2
30
20
10
0 300
350
400
450
500
550
600
650
700
35 30
CO2
25 20 15 10 5
CH4
0 100
750
200
300
400
500
600
GSHV, hrs
o
reaction temperature, C
Fig. 5 e H2 and CO yields at different reaction temperatures. higher than 550 C to avoid the undesired intermetallic diffusion of the stainless steel substrate that could lead to poor membrane performance [28,31]. Fig. 5 shows the hydrogen (H2) and carbon monoxide (CO) yields as a function of temperature. With increasing temperature, both H2 and CO yields rose as expected. However, the hydrogen yield appeared to be lower than that of the carbon monoxide since the hydrogen was also consumed in the side reaction with the unreacted carbon dioxide. Fig. 6 presents the hydrogen selectivity of the reactions as a function of temperature. More desired hydrogen product could be obtained at higher reaction temperature, suggesting that the temperature should be raised to the upper limit when the application of the membrane was coupled with the reactor to perform in-situ hydrogen separation. Increasing the gaseous feed flow rate resulted in the reduction of both CH4 and CO2 conversion since the residence
700
800
900
-1
Fig. 7 e CH4 and CO2 conversions for the conventional reactor: effect of the increasing feed flow rate on the CH4 and CO2 conversions of the reaction system at 550 C with a CH4/CO2 molar feed ratio of 1:1 and the catalyst amount of 40 mg.
time that allows the reactions to take place inside the reactor was decreased as the feed gas hourly space velocity (GHSV) was raised, as clearly shown in Fig. 7. Additionally, the CH4/CO2 feed ratios were found to have some effect on the extent of reactions. Fig. 8 shows the plot of CH4 and CO2 conversions at various CH4/CO2 feed ratios. The graph shows that the use of CO2-rich feed could result in higher consumption of both CH4 and CO2 in the reaction system. To understand this phenomenon more clearly, the H2 and CO reaction product yields were also investigated, as shown in Fig. 9. Increasing the amount of CO2 in the feed to shift, the ratio of CH4/CO2 gave rise to both H2 and CO yields that reached the maximum values of 10% and 20%, respectively; however, the yields showed a decline for richer CO2 mixed feeds. Since the
100
40
o
at 550 C with the catalyst amount of 40 mg
CH4 and CO2 conversions, %mol
H2 selectivity, %mol
90 30
20
10
0 300
350
400
450
500
550
600
650
700
750
o
Temperature, C
80 70 60 50 40
CO2 CH4
30 20 10 0 3/1
Fig. 6 e H2 selectivity for the conventional reactor: effect of the increasing reaction temperature on hydrogen selectivity of the reaction system from 350 to 700 C with a CH4/CO2 molar feed ratio of 1:1 at 30 ml/min and the catalyst amount of 40 mg.
2/1
1/1
1/2
1/3
Feed ratio, CH4/CO2
Fig. 8 e CH4 and CO2 conversions for the conventional reactor: effect of the CH4/CO2 feed ratio on the CH4 and CO2 conversions at the reaction time of 180 min.
2626
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
average yield H2 and CO, %mol
30
o
at 550 C with the catalyst amount of 40 mg
20
CO 10
H2 0 3/1
2/1
1/1
1/2
1/3
feed ratio, CH4/CO2
Fig. 9 e H2 and CO reaction product yields at different feed ratios: effect of the increasing feed ratio CH4/CO2 from 3/1 to 1/3 ml/min catalyst amount 40 mg, reaction temperature 550 C.
main dry reforming reaction of methane is reversible, introducing excess amounts of the reactants could drive the reaction forward resulting in more hydrogen being generated. However, the produced H2 could also react with the unreacted CO2 in the reversible water-gas shift side reaction. Therefore, higher CO2 consumption compared to that of CH4 in terms of the conversion was typically observed. The maximum H2 and CO yields were obtained when using equimolar CH4/CO2 (1:1) mixed feed. Considering the stoichiometry of the dry reforming reaction, 1 mol of CH4 requires 1 mol of CO2 to react with each other [8]. In conclusion, shifting the CH4/CO2 ratio to 1:1 or vice versa resulted in an increase in reaction product yields. Fig. 10 shows the effect of the amount of catalyst usage on the CH4 and CO2 conversions. The amount of catalyst used
basically had effect on the extent of the reaction to some degree. Generally, increasing mass usage will increase the reaction conversions. The H2 and CO reaction yields appear to be proportional to the amount of the catalyst used as well, as shown in Fig. 11. Since the catalyst plays an important role in the dissociative adsorption of methane which is the rate-determining step of the reaction, the high mass of catalyst deployed will provide an active surface that facilitates the reaction. It is of note that the reactants have to be transported from the feed stream to the active sites, so adding too many of the relatively small particles of the catalyst can dramatically change the characteristics and flow pattern inside the packed-bed reactor and this will affect the mass transport efficiency of the system. Ideally, an optimum catalyst amount is required to achieve the highest possible conversions or yields without the reactor performance significantly suffering such as through a rapid increase in pressure drop or the throughput capacity drop at the operated conditions.
Catalytic membrane reactor performance study In order to evaluate the performance of the Pd alloy membrane reactor, methane and carbon dioxide conversion using conventional packed-bed reactor and a palladium alloy membrane reactor were compared. The reaction performance was carried out in the packed-bed reactor filled with 60 mg 5% Ni/Ce0.6Zr0.4O2 catalyst coupled with a dense Pd76Ag19Cu5 alloy membrane in which 20 ml/min of the 1:1 CH4/CO2 mixed feed was fed into the reactor at 550 C. Fig. 12 (a) and (b) show the reactant conversions (CH4 and CO2) and reaction product yields (H2 and CO) versus the reaction time, respectively. With the presence of the membrane, it was clearly demonstrated that both CH4 and CO2 conversions were significantly increased when compared to the system without the membrane operated at the same conditions. Methane conversion was clearly increased by approximately two-fold.
30
100
28 26 24
80
H2 and CO yields, %mol
CH4 and CO2 conversions, %mol
90
70 60 50 40
CO2
30
CH4
20
22 20
CO
18 16 14 12
H2
10 8 6 4
10
2
0
0 0
10
20
30
40
50
60
70
80
90
catalyst amount, mg
Fig. 10 e CH4 and CO2 conversions for the conventional reactor: effect of the increasing catalyst mass from 10 to 80 mg. CH4/CO2 molar feed ratio 1:1, feed flow rate 20 ml/ min, reaction temperature 550 C.
0
10
20
30
40
50
60
70
80
90
catalyst amount, mg
Fig. 11 e H2 and CO yields at different catalyst amounts: effect of the increasing catalyst amount from 10 to 80 mg. CH4/CO2 molar feed ratio 1:1, feed flow rate 20 ml/min, reaction temperature 550 C.
2627
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
CH /CO ratio 1:1, feed flow rate 20 ml/min,
CH4 and CO2 conversions, %mol
90
(a)
o
90
CO packed-bed reactor
80
CH membrane reactor
80
CH4/CO2 ratio 1:1, feed flow rate 20 ml/min,
100
reaction temperature 550 C, catalyst amount 60 mg CH packed-bed reactor
CO membrane reactor 70 60 50
CH4 conversion, %
100
reaction temperature 550 C, catalyst amount 60 mg
70 60 50 40
40
30 30
20
20
10
10
0
0 20
40
60
80
100
120
140
160
180
32.5
200
33.0
33.5
reaction time, min
CH /CO ratio 1:1, feed flow rate 20 ml/min,
100
reaction temperature 550 C, catalyst amount 60 mg
(b)
34.5
Fig. 13 e Correlation between the methane conversion and H2 recovery.
H packed-bed reactor
CH /CO ratio 1:1, feed flow rate 20 ml/min,
80
CO packed-bed reactor H membrane reactor
2.0
70
CO membrane reactor
1.8
60
1.6
50
1.4
40
1.2
H /CO
H and CO yield, %mol
90
34.0
H2 yield, %
30 20 10
reaction temperature 550 C, catalyst amount 60 mg Packed-bed reactor Membrane reactor
1.0 0.8 0.6
0
0.4 20
40
60
80
100
120
140
160
180
200
0.2
reaction time, (min)
Accordingly, the CO2 conversion shifted from about 50%e60%. As previously discussed, more CO2 was consumed than CH4 in the conventional packed bed reactor due to the extent of the water-gas shift side reaction. For membrane reactor, it is clearly seen in Fig 12a that the CH4 conversion was observed as being greater than that of the CO2. In this case, hydrogen was constantly withdrawn from the reactor by permeation through the dense PdAgCu alloy membrane which helps shifting the dry reforming reaction in a forward direction resulting in improved hydrogen yield. Since methane is the only source of H atoms contributing to the H2 generation, methane consumption in the main dry reforming reaction could basically influence hydrogen formation. In the membrane system, the hydrogen yield was drastically improved by almost 3.5-fold; correspondingly, the CO by-product yield was also increased by 50%. From Fig 13, the hydrogen yield was increased with increasing methane conversion. Fig. 14 illustrates the H2/CO ratio at various reaction times of the system with and without a membrane. The H2/CO ratio shifted towards 1:1 in the case of using the membrane. When
0.0 20
40
60
80
100
120
140
160
180
200
reaction time, min
Fig. 14 e H2/CO ratios versus reaction time of the pack-bed reactor (C) and the membrane reactor (-).
CH /CO ratio 1:1, feed flow rate 20 ml/min,
2.0
reaction temperature 550 C, catalyst amount 60 mg
1.8
CH /CO packed-bed reactor 1.6
CH /CO conversion ratio
Fig. 12 e Comparison of packed-bed reactor (C) and membrane reactor (-), (a) CH4 and CO2 conversions, and (b) H2 and CO yields.
CH /CO membrane reactor
1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 20
40
60
80
100
120
140
160
180
200
reaction time, min
Fig. 15 e Effluent CH4/CO2 molar ratio versus reaction time of the pack-bed reactor (C), and the membrane reactor (-).
2628
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
CH /CO ratio 1:1, feed flow rate 20 ml/min,
100
reaction temperature 550 C, catalyst amount 60 mg 90
Packed-bed reactor Membrane reactor
80
H Selectivity, %mol
70 60 50 40 30 20 10 0 20
40
60
80
100
120
140
160
180
200
reaction time, min
Fig. 16 e H2 selectivity versus reaction time of the pack-bed reactor (C), and the membrane reactor (-).
40 35
%H2 recovery
30 25 20 15 10
equilibrium of the dry reforming reaction was forced to shift forward so that more products could be obtained when the H2 was drawn out of the reactor by the membrane. Additionally, the unreacted CH4 and CO2 molar ratio of the effluent of the membrane reactor was shifted from about 0.6 towards 1.0 which was close to that of the feed entering the reactor (1:1), as illustrated in Fig. 15. The result could imply that the CH4 and CO2 were basically consumed in the reactions in a stoichiometric manner. The CO2 was possibly less involved in the side water-gas shift reaction due to the lack of a hydrogen presence resulting from in-situ membrane separation as previously discussed. In conclusion, the presence of the membrane seemed to minimize the effect of other undesired competing or chain reactions involved in the system. As clearly seen in Fig. 16, the overall hydrogen selectivity improved by 10% (from 48 to 53%). In terms of permeation capacity, the H2 recovery was measured as the in-situ reactionseparation was undergoing, as seen in Fig. 17. The recovery of hydrogen was found to be around 30 percent. It is worth noting that the membrane reactor has a one-pass flow through configuration. The H2 recovery from the unit was reasonably acceptable; nevertheless, the overall H2 production beneficial from the membrane application was significantly improved. As shown in Table 1, the DRM reaction performance results obtained from this study were in good agreement with other studies. However, it is of note that all system configurations are not the same. Various reactor designs with different types of membranes and catalysts were used in each previous study.
5
Conclusion
0 20
40
60
80
100
120
140
160
180
200
reaction time, min Fig. 17 e H2 recovery versus reaction time of the membrane reactor.
coupled with the membrane, the in-situ reaction and separation of the hydrogen product could take place simultaneously. The H2 formed by the main reaction between CH4 and CO2 was selectively removed through the membrane at all times as the reaction proceeded. Therefore, there was a lower amount of H2 left to react with the unreacted CO2 in the competing reversible water-gas shift reaction. Furthermore, the
The packed-bed membrane reactor containing the 5% Ni/ Ce0.6Zr0.4O2 catalyst and coupled with the dense Pd76Ag19Cu5 alloy membrane was demonstrated to enhance the hydrogen production from the dry reforming reactions of CH4 and CO2. The overall reactant CH4 and CO2 conversions were significantly increased resulting in better reaction performance in terms of H2 yield and selectivity. With the membrane installed, this allowed the in-situ partial hydrogen to be withdrawn from the reactor during the reactions taking place. It is believed that the equilibrium of the system was perturbed by shifting the dry reforming reaction forward. Additionally, the partial hydrogen removal was shown to affect the reaction
Table 1 e Comparison of methane conversion in the membrane reactor (MR) and packed bed reactor (PBR) from the dry reforming of methane. Membrane
Catalyst type
Pd-based
Pd/Al2O3
Porous PdeAg
Ni/Al2O3
Dense PdeAg
Pt/Al2O3
Dense PdeAg Dense PdAgCu
Pt/CeZrO2/Al2O3 Ni/CeZrO2
T ( C)
%XCH4 ;MR
%XCH4 ;PBR
%X ratio (MR/PBR)
550 600 400 450 400 450 550 550
37.5 48.6 2.1 8.4 7.9 17.8 85 65.2
17.2 40.9 5.6 17.4 5.6 17.4 25 33.5
2.2 1.2 0.4 0.5 1.4 1.0 3.4 1.9
Ref. [32] [8] [33] [21] This work
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
system by minimizing the side reaction effects through the creation of a hydrogen-deprived environment inside the reactor. This conceptual type of reactor could lead to its better design in hydrogen production and purification from the dry reforming reaction between CH4 and CO2. In summary, appropriate downstream H2 separation and purification by well-designed PdAgCu alloy membrane units capable of unreacted CH4 and CO2 recovery and recycled back into the reaction system could make the overall process more feasible and economically achievable so as to attract further development on the high-scale industry level.
Acknowledgments This work was financially supported by the 90th Anniversary of Chulalongkorn University Fund (Ratchadaphiseksomphot Endowment Fund) No.20-1-2556, National Research Council of Thailand (NRCT) No.82619, and the Program of Petrochemistry and Polymer Science, Chulalongkorn University.
references
[1] Bosko ML, Mu´nera JF, Lombardo EA, Cornaglia LM. Dry reforming of methane in membrane reactors using Pd and PdeAg composite membranes on a NaA zeolite modified porous stainless steel support. J Membr Sci 2010;364:17e26. [2] Sanz R, Calles JA, Alique D, Furones L. H2 production via water gas shift in a composite Pd membrane reactor prepared by the pore-plating method. Int J Hydrogen Energy 2014;39:4739e48. n ~ ez S, Marı´n P. [3] Sanz R, Calles JA, Alique D, Furones L, Ordo Hydrogen production in a pore-plated Pd-membrane reactor: experimental analysis and model validation for the water gas shift reaction. Int J Hydrogen Energy 2015;40:3472e84. [4] Abasaeed AE, Al-Fatesh AS, Naeem MA, Ibrahim AA, Fakeeha AH. Catalytic performance of CeO2 and ZrO2 supported Co catalysts for hydrogen production via dry reforming of methane. Int J Hydrogen Energy 2015;40(21):6818e26. [5] Usman M, Wan Daud WMA, Abbas HF. Dry reforming of methane: influence of process parameters e a review. Renew Sustain Energy Rev 2015;45:710e44. [6] Naeem MA, Al-Fatesh AS, Khan WU, Abasaeed AE, Fakeeha AH. Syngas production from dry reforming of methane over nano Ni polyol catalysts. Int J Chem Eng Appl 2013:315e20. [7] Wang S, Lu G, Millar GJ. Carbon dioxide reforming of methane to produce synthesis gas over metal-supported catalysts: state of the art. Energy Fuels 1996;10:896e904. [8] Gallucci F, Tosti S, Basile A. PdeAg tubular membrane reactors for methane dry reforming: a reactive method for CO2 consumption and H2 production. J Membr Sci 2008;317:96e105. [9] Basile Angelo, et al., editors. Membrane reactors for energy applications and basic chemical production. Elsevier; 2015. p. 99e144. [10] Yun S, Ted Oyama S. Correlations in palladium membranes for hydrogen separation: a review. J Membr Sci 2011;375:28e45.
2629
[11] Braun F, Tarditi AM, Miller JB, Cornaglia LM. Pd-based binary and ternary alloy membranes: morphological and permselective characterization in the presence of H2S. J Membr Sci 2014;450:299e307. [12] Burkhanov GS, Gorina NB, Kolchugina NB, Roshan NR, Slovetsky DI, Chistov EM. Palladium-based alloy membranes for separation of high purity hydrogen from hydrogen-containing gas mixtures. Platin Met Rev 2011;55:3e12. [13] Hatlevik Ø, Gade SK, Keeling MK, Thoen PM, Davidson AP, Way JD. Palladium and palladium alloy membranes for hydrogen separation and production: history, fabrication strategies, and current performance. Sep Purif Technol 2010;73:59e64. [14] Dolan MD. Non-Pd BCC alloy membranes for industrial hydrogen separation. J Membr Sci 2010;362:12e28. [15] Ling C, Semidey-Flecha L, Sholl DS. First-principles screening of PdCuAg ternary alloys as H2 purification membranes. J Membr Sci 2011;371:189e96. [16] Peters TA, Kaleta T, Stange M, Bredesen R. Development of thin binary and ternary Pd-based alloy membranes for use in hydrogen production. J Membr Sci 2011;383:124e34. [17] Tarditi AM, Braun F, Cornaglia LM. Novel PdAgCu ternary alloy: hydrogen permeation and surface properties. Appl Surf Sci 2011;257:6626e35. [18] Zhao L, Goldbach A, Bao C, Xu H. Structural and permeation kinetic correlations in PdCuAg membranes. ACS Appl Mater Interfaces 2014;6:22408e16. [19] Nayebossadri S, Speight J, Book D. Effects of low Ag additions on the hydrogen permeability of PdeCueAg hydrogen separation membranes. J Membr Sci 2014;451:216e25. [20] Garcı´a-Garcı´a FR, Soria MA, Mateos-Pedrero C, GuerreroRuiz A, Rodrı´guez-Ramos I, Li K. Dry reforming of methane using Pd-based membrane reactors fabricated from different substrates. J Membr Sci 2013;435:218e25. [21] Silva FA, Hori CE, da Silva AM, Mattos LV, Mu´nera J, Cornaglia L, et al. Hydrogen production through CO2 reforming of CH4 over Pt/CeZrO2/Al2O3 catalysts using a PdeAg membrane reactor. Catal Today 2012;193:64e73. [22] Gallucci F, Fernandez E, Corengia P, van Sint Annaland M. Recent advances on membranes and membrane reactors for hydrogen production. Chem Eng Sci 2013;92:40e66. [23] Kyriakides A-S, Rodrı´guez-Garcı´a L, Voutetakis S, Ipsakis D, Seferlis P, Papadopoulou S. Enhancement of pure hydrogen production through the use of a membrane reactor. Int J Hydrogen Energy 2014;39:4749e60. [24] Brunetti A, Caravella A, Fernandez E, Pacheco Tanaka DA, Gallucci F, Drioli E, et al. Syngas upgrading in a membrane reactor with thin Pd-alloy supported membrane. Int J Hydrogen Energy 2015;40:10883e93. [25] Mardilovich PP, She Y, Ma YH, Rei MH. Defect-free palladium membranes on porous stainless-steel support. AICHE J 1998;44:310e22. [26] Khan A, Sukonket T, Saha B, Idem R. Catalytic activity of various 5 wt % Ni/Ce0.5Zr0.33M0.17O2d catalysts for the CO2 reforming of CH4 in the presence and absence of steam. Energy Fuels 2012;26:365e79. [27] Sukonket T, Khan A, Saha B, Ibrahim H, Tantayanon S, Kumar P, et al. Influence of the catalyst preparation method, surfactant amount, and steam on CO2 reforming of CH4 over 5Ni/Ce0.6Zr0.4O2 catalysts. Energy Fuels 2011;25:864e77. [28] Samingprai S, Tantayanon S, Ma YH. Chromium oxide intermetallic diffusion barrier for palladium membrane supported on porous stainless steel. J Membr Sci 2010;347:8e16.
2630
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 4 1 ( 2 0 1 6 ) 2 6 2 1 e2 6 3 0
[29] Hwang K-R, Lee C-B, Ryi S-K, Park J-S. Hydrogen production and carbon dioxide enrichment using a catalytic membrane reactor with Ni metal catalyst and Pd-based membrane. Int J Hydrogen Energy 2012;37:6626e34. [30] Soria MA, Mateos-Pedrero C, Guerrero-Ruiz A, Rodrı´guezRamos I. Thermodynamic and experimental study of combined dry and steam reforming of methane on Ru/ ZrO2eLa2O3 catalyst at low temperature. Int J Hydrogen Energy 2011;36:15212e20.
[31] Chotirach M, Tantayanon S, Tungasmita S, Kriausakul K. Zrbased intermetallic diffusion barriers for stainless steel supported palladium membranes. J Membr Sci 2012;405e406:92e103. [32] Galuszka J, Pandey RN, Ahmed S. Methane conversion to syngas in a palladium membrane reactor. Catal Today 1998;46:83e9. [33] Kikuchi E. Palladium/ceramic membranes for selective hydrogen permeation and their application to membrane reactor. Catal Today 1995;25:333e7.