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Catalytic partial oxidation of methane to syngas in a fixed-bed
reactor with an O2-distributor: The axial temperature profile
and species profile study
Shuhong Liua,b, Wenzhao Lia, Yuzhong Wanga, Hengyong Xua,⁎
aDalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, ChinabGraduate University of Chinese Academy of Sciences, Beijing 100049, China
A R T I C L E I N F O A B S T R A C T
Article history:
Received 31 March 2008
Received in revised form 4 June 2008
Accepted 6 June 2008
Catalytic partial oxidation of methane (CPOM) to syngas has been investigated in a fixed-bed
reactor with an O2-distributor (FR-OD). The axial temperature profile and species profile
along the Ni or Rh-based catalyst bed have been measured at different conditions. As the O 2
was distributed radially into the catalyst bed through several rows of holes arranged at the
special zone of the OD, a microenvironment maintaining a low O2 /CH4 ratio (0.10–0.22) was
provided in the catalyst bed. The hotspot phenomena appeared at the entrance of the
catalyst bed have been effectively controlled. A more uniform temperature profile along the
catalyst bed has been given, which is beneficial to the stability of catalyst and the safety of
reactor operation.
© 2008 Elsevier B.V. All rights reserved.
Keywords:
Catalytic partial oxidation
of methane
O2-distributor
Temperature profile
Species profile
1. Introduction
The conversion of methane to syngas will play an important
role in the 21st century for both large-scale GTL plants and
small unit providing H2 for fuel cell [1,2]. In industry, the main
route for syngas production is steam reforming of methane
(SRM),
CH4 þ H2O→COþ 3H2 ΔH-298 ¼ þ206kJ=mol ð1Þ
which is highly efficient but capital intensive because it in-
volves a big exchange of energy between the steam reformer and heat recovery unit [3]. Recently catalytic partial oxidation
of methane (CPOM)
CH4 þ 0:5O2→COþ 2H2 ΔH-298 ¼ −36kJ=mol ð2Þ
has been studied extensively by both academia and industry
[4,5]. CPOM is excelled at consumed energy and products
composition [6]. However, CPOM process has not yet been
used commercially because it involves premixing of CH4 and
O2 which can be flammable or even explosive under elevated
pressure and temperature. Meanwhile the hotspot formation
near the beginning of the catalyst bed due to highly exo-
thermic complete oxidation reaction
CH4 þ 2O2→CO2 þ 2H2O ΔH-298 ¼ −802kJ=mol ð3Þ
may create severe problems of heat management, safety of
system and stability of catalyst [7,8].
Some novel reactor configurations with the idea of manage-
ment safety of the system and hotspot problem have recently
been reported [9–12]. In the counter-current heat-exchangereactor (CHXR) [9], they fed the hydrocarbon and the oxygen
separately and mixed the two feed gas streams until a few
centimeters in front of the catalyst zone through static mixers.
So thedanger of explosionminimized.In thenew ATRproposed
by Institute of Applied Energy of Japan [10], the oxygen was
separated into three shares or more, meanwhile two different
catalysts, one for oxidation and the other for reforming were
packed with alternating layers for three or more cycles. With
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⁎ Corresponding author. Tel./fax: +86 411 84581234.E-mail address: [email protected] (H. Xu).
0378-3820/$ – see front matter © 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.fuproc.2008.06.004
a v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m
w w w . e l s e v i e r . c o m / l o c a t e / f u p r o c
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this design, it was possible to increase the safety of the system.
Topsoe [11] provided an improved CPOM process comprising a
plurality of sequential, separated steps, whereby in each step
only a small fraction of the stoichiometric amount of oxygen
was added and reacted with the hydrocarbon feed gas on a
catalyst bed. It could increase the safety of the system and
decrease the hotspot. The heat integrated wall reactor (HIWAR)
[12] comprised a ceramic tube on the inner and outer surface of which a metal catalyst film was deposited. The combustion
reaction (3) was taking place on the inner catalyst film and the
reforming reaction (1) on the outer one, absorbing simulta-
neously the heat of combustion. Thus, the HIWAR offered the
possibility of reducing the magnitude of hotspot.
In our previous work, an O2-distributor (OD) was adopted in
a fixed-bed reactor. Part of O2 was distributed radially into the
catalyst bed through several rows of holes arranged at the O2
distribution zone of the OD to avoid premixing with CH4.
The gaseous mixture presented near theentranceof thefixed-
bed reactor with an O2-distributor (FR-OD) was kept at a lower
O2 /CH4 ratio than 0.5, whichdecreased thedanger of explosion
often caused by mixing oxygen and methane under higher
temperature and pressure. In the present study, we further
explore the axial temperature profile and species profile along
the Ni or Rh-based catalyst bed in FR-OD during the CPOM
reaction. With the opinions of economy and safety, route
based on air as oxygen source eliminating the cryogenic air
separation plant has been suggested [13]. So air is chosen as
oxygen source in this work. Small addition of water (H2O/CH4
mole ratio=1) was introduced into the feed to prevent carbon
formation, especially in the case of lower O2 /CH4 ratio which
carbon formation becomes thermodynamics favorable.
2. Experimental
The sketch of FR-OD is shown in Fig. 1. The reactor tube is a
stainless steel tube of dimensions 26 mm o.d., 20 mm i.d. and
600 mm length. The OD is made of a stainless steel tube of
dimensions 8 mm o.d.. Thedistancefrom the first row of holes
to the last one on the OD is 30 mm. The whole holes compose
the O2 distribution zone on the OD. The O2 distribution zone is
imbedded in the catalyst bed.
As shownin Fig.1, air can befed intothe catalystbed in two
ways. We define the air injected into the system through the
OD as Air D and the air premixed with CH4 and H2O prior to thereactor as Air M, respectively. We propose that the parameter D
is used in the present study,
D ¼ FAir D
FAir D þ FAir M 100k
in which FAir Dis the flow rate of the air through the OD and
FAir M is the flowrateof the air premixedwith CH4 andH2O prior
to the reactor in ml/min. D value is in the range of 0%–100%.
When D =100%, total air is distributed into the catalyst bed
through whole holes on the OD without premixing with CH4
and H2O. When D =0%, total air enters the catalyst bed
premixing with CH4 and H2O prior to the reactor.
0.76 wt.%Rh/α-Al2O3 catalyst was prepared by impregnation
method, and 2 wt.%La2O3–7.6 wt.%Ni/MgAl2O4–α-Al2O3 catalyst
was prepared by multistep impregnation method. Experiments
wereperformedusing18gofcatalyst(10–16 mesh) atbed depths
of55 mm. The first row ofholes ontheOD werelocatedat 5 mm
of the catalyst bed. The distance from the first row of holes to
the last one on the OD is 30 mm. The last row of holes on the
OD were located at 35 mm of the catalyst bed. The O2 distribu-
tionzonecomposed of the wholeholeson the ODwas located at
5–35 mm of the catalyst bed. The catalyst was reduced under
hydrogen flow at 780 °C for 1 h before testing.
Methane and air were controlled by mass flow controllers.
H2O was injected into catalyst bed by a pulseless pump. The
feed was CH4:air (O2):H2O= 1:2.4 (0.5):1. The GHSV was
13,200 h−1. The reactor was placed inside a furnace. An on-
line gas chromatography (GC) was used for the analysis of
reactants and products. The reactants, i.e. CH4, O2 and N2 were
Fig. 1 – The sketch of FR-OD.
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analyzed in a 5 A molecular sieve column with He as a carrier
gas while the products, such as CO, CO2, unreacted CH4 and N2
were analyzed in a C molecular sieve column with He as a
carrier gas. H2O was condensed and removed in a condenser
located downstream of the reactor before GC analysis.
In order to measure the axial temperature profile of the
catalyst bed, a ϕ3 thermocouple well was placed in the middle
part between the wall of the reactor and the ektexine of theOD. A ϕ1 thermocouple can be moved upwards and down-
wards in it to measure the temperature. A ϕ2 sampling probe
was inserted into the catalyst bed. By moving the sampling
probe we can get the species profile along the catalyst bed.
3. Results and discussions
3.1. Effect of D values on the catalytic activity
When we investigated the effect of D values on the catalytic
activity, two series of experiments have been performed —
one series was performed at the same outlet temperature as
800 °C and the other was performed at the furnace tempera-
ture maintained at 600 °C. Each series experiments have been
performed at 1 atm and 8 atm on both Ni-based catalyst and
Rh-based one. In this paper, only representational data
obtained on the Ni-based catalyst are listed below. Similar
results have also been obtained on the Rh-based catalyst (not
shown in this paper). No carbon was decomposed over the Ni
or Rh-based catalyst during the CPOM reaction activity test for
the presence of water.
According to Table 1, similar conversion of CH4 and
selectivity of CO have been obtained under the same outlet
temperature as 800 °C whether D =80% or D =0%. As can be
seen in Table 2, when the furnace temperature was main-
tained at 600 °C, a little higher outlet temperature was
obtained in the case of D =80%, and the conversion of CH4
and selectivity of CO increase accordingly.
Both data shown in Tables 1 and 2 agreed with thermo-
dynamic predictions based on the catalyst bed exit tempera-
tures. It should be noted that the compositions of product are
still determined by the catalyst bed exit temperature, in spite
of changing the ways of air feeding by using the OD.
3.2. Effect of D values on the axial temperature profile
along the catalyst bed
The axial temperature profiles of the Rh or Ni-based catalyst
bed with various D values when furnace temperature was
maintained at 600 °C are shown in Fig. 2.
When D =0%, the mixture of total air, CH4 and H2O were
premixed, preheated to 600 °C and delivered to the region in
which the catalyst was sited. An obvious temperature rise
caused by the oxidation reaction of CH4 was observed at the
very entrance (within 1 mm) of both the Rh-based and the Ni-
based catalyst. Maximum temperature 764 °C and 811 °C were
detected over the Rh and Ni-based catalyst, respectively.
Within 1–15 mm of the catalyst bed, the temperatures of the
Ni-based catalyst descended more rapidly than that of the Rh-
based one, which could be ascribed to more endothermic
Table 1 – The effect of D values on the catalyticperformance at outlet temperature 800 °C
D Conv. CH4
(%)Sel. CO
(%)Per cent of product (%)
H2 N2 CO CH4 CO2 H2O
80% 90.45 66.33 35.23 33.16 10.48 1.67 5 .32 13.95
0% 90.30 66.14 35.54 33.18 10.43 1.69 5.34 13.82
Reaction conditions: Ni-based cat., W cat.=18 g, Hcat.=55 mm,
GHSV=13,200 h−1
, CH4:air:H2O=1:2.4:1, 8 atm.
Table 2 – The effect of D values on the catalyticperformance as furnace temperature was maintained at 600 °C
D T out(°C)
Conv.CH4
(%)
Sel.CO(%)
Per cent of product (%)
H2 N2 CO CH4 CO2 H2O
80% 644 85.30 51.08 35.25 33.89 7.77 2.62 7.44 13.02
0% 630 84.77 48.84 35.33 33.96 7.40 2.72 7.75 12.85
Reaction conditions: Ni-based cat., W cat.=18 g, Hcat.=55 mm,
GHSV=13,200 h−1, CH4:air:H2O=1:2.4:1, P =1 atm.
Fig. 2 – Axial temperature profile along the catalyst bed at
various D values. W cat.=18 g, Hcat.=55 mm, CH4 :air:
H2O= 1:2.4:1, GHSV= 13,200 h−1, P =1 atm, T furnace=600 °C.
(a) Ni-based catalyst; (b) Rh-based catalyst; ( □ ) D=100%; ( )
D=80%; ( ) D =60%; ( ) D=40%; ( ) D=20%; ( ■ ) D=0%.
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steam reforming reaction (1) of the remaining unreacted CH4
on the Ni-based catalyst than that on the Rh-based one.
When D =100%,for theNi-basedcatalyst, it is observed that
the inlet temperature decreased to 700 °C. The temperatures
within 5–35 mm of the catalyst bed (i.e. the location of the O 2
distribution zone) were maintained at much higher values
resulted from the exothermic oxidation reactions (2) and (3),
which are quite different with a sharp decrease of tempera-turescaused by the endothermic reformingreactions (1) in the
case of D =0%. In the region of 35–55 mm of the catalyst bed
(i.e. away from the O2 distribution zone), as the O2 has been
completely exhausted, there occurred only the endothermic
reforming reactions (1) which resulted in a further decreasing
of the bed temperature. A similar temperature profile could be
found over the Rh-based catalyst when D =100%.
When 0%bDb100%, the inlet temperature of the catalyst
decreased with increasing of D value, the temperatures within
5–35 mm of the catalyst bed increased with increasing of D
value. When D =60% and 80%, more uniform temperature
profiles have been obtained. That is to say, by using the OD,
hotspot often appeared at the beginning of the catalyst bed
has been controlled effectively.
3.3. O2 profile along the catalyst bed
It is hard to detect the O2 existence along the catalyst bed
during the test period, because once entered the catalyst bed,
oxygen can be exhausted rapidly. It is lucky that the oxygen
source used in this paper is air, so we can deduce the mole
number of distributed O2 by measuring the mole number of
distributed and unreactive N2.
Similar distribution states of O2 and O2 /CH4 ratio along the
catalyst bed have been obtained over both the Ni-based
catalyst and the Rh-based one. Namely the distribution states
of O2 and O2 /CH4 ratio along the catalyst bed are independence
of the types of the catalysts used in the test when the
arrangement of holes on the OD, the O2 velocity and the
reaction pressure are fixed. Only the data gained over the Ni-
based catalyst were listed in Table 3.
The O2 distribution zone is located in 5–35 mm of catalyst
bed from inlet. As can be seen from Table 3, when D =80% —
the 80% of O2 was divided into approximately 4 equivalent
shares (the data in italic) from 4 rows of holes on the OD to
enter the catalyst bed. Meanwhile, the O2 /CH4 ratios along the
catalyst bed were kept at low values of 0.1–0.22. Usually, the
carbon decomposition is thermodynamics favorable under the
circumstances of such a lower O2 /CH4 ratio. It should benoticed that due to the CH4 feed gas mixed with some water
(H2O/CH4 molar ratio=1) in this work, as a result, no carbon
deposition was observed over either catalyst (Ni or Rh-based
catalyst) or around the hole on the O2-distributor after
catalytic performance test, while plenty of carbon was formed
over the Ni-based catalyst if the water was absent in the feed.
3.4. Axial species profiles when D = 0%
Axial species profiles along the Ni or Rh-based catalyst bed
when D = 0% are shown in Fig. 3.
From Fig. 3, when D = 0%, all of the O2 and 75% of CH4 were
converted, 70% of H2 and CO product were generated, no
Table 3 – Mole number of distributed O2 and O2 /CH4 ratioalong the catalyst beds at D=80% and D= 0%
z (mm)
−1 5 10 25 35 4 5 55
D = 80% O2 (mol) 0.1 0.1 0.13 0.11 0.06 0 0
O2 /CH4 ratio 0.1 0.145 0.224 0.21 0.21 0 0
D = 0% O2 (mol) 0.5 0 0 0 0 0 0
O2 /CH4 ratio 0.5 0 0 0 0 0 0
Reaction conditions: Ni-based cat., W cat.=18 g, Hcat.=55 mm,
GHSV=13,200 h−1
, CH4:air:H2O=1:2.4:1, P =1 atm.
Fig. 3 – Measured axial species profile along the Ni or
Rh-based catalyst bed at D=0% (part 1)a. (solid line): Ni-based
catalyst; (dash line): Rh-based catalyst; (a): O2; (b): CH4 ;
(c): H2O; (d): H2; (e): CO. Reaction conditions: W cat.=18 g, Hcat.=
55 mm, CH4 :air:H2O= 1:2.4:1, GHSV= 13,200 h−1, P =1 atm,
T out =750 °C.
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additional H2O formation was detected within the first 1 mm
of the Rh catalyst bed.
Over the Ni catalyst, only 67% of O2 and 25% of CH4
conversions were detected withinthe first1 mm of thecatalyst
bed. Meanwhile, an additional 0.24 mol H2O was produced
which gave an evidence of the occurrence of complete
oxidation reaction (3). Only 10% of H2 and 20% of CO had
been detected simultaneously. In the following 3–55 mm of the Ni-based catalyst bed, the steam reforming of methane
played an important role — 55% of CH4 was converted and
74% of H2 and 77% of CO had been produced.
Based on the above data, it could be concluded that for the
Rh-based catalyst most of syngas is formed by direct partial
oxidation or extra fast combined combustion-reforming,
while most of syngas has to be formed through a slow steam
reforming reaction on the Ni-based catalyst.
3.5. Axial species profiles when D =80%
Axial species profiles along the Ni-based catalyst bed when
D =80% and D =0% are shown in Fig. 4.We can see from Fig. 4 c, no addition of H2O formation has
been detected at the entrance of the Ni-based catalyst when
D =80%. It seems that the complete oxidation of methane
usually happened at the very entrance of the catalyst when
O2 /CH4 ratio is 0.5 have been hindered triumphantly due to a
low O2 /CH4 ratio (0.1) was provided by using the OD.
In the range of 5–35 mm of the catalyst bed, remained
80% of oxygen was distributed into approximately 4 equal
shares in this zone through the OD and immediately
exhausted (Fig. 4 a). In the same zone, more than 50% of
CH4 converted, about 10% of H2O converted (Fig. 4 b and c),
which means most of methane was reacted with oxygen.
Associated with Fig. 4 d and e, more than 50% of H2 and CO
have been gradually produced along the Ni-based catalyst
bed. Products reached thermodynamic equilibrium value at
the outlet of the reactor.
4. Conclusions
The following conclusions can be derived from the results of
the present study:
(1) The thermodynamics equilibrium of CPOM reaction sys-
tem is notchanged whether or notchangingthe ways of
air feeding by using the O2-distributor.
(2) Due to the O2 /CH4 ratio that was kept at lower values
(0.10–0.22) along the catalyst bed, the hotspot often ap-
pearedat theNi catalyst duringthe CPOM reaction could
be controlled by using the O2-distributor.
(3) Combining the measurements of temperature profile
and species profile, we can speculate that the reaction
path of the CPOM reaction might have some changes at
lower O2 /CH4 ratio when using the O2-distributor.
Acknowledgement
Financial support by the National Basic Research Program of
China, No.2005cb221401.
R E F E R E N C E S
[1] D.J. Wilhelm, D.R. Simbeck, A.D. Karp, R.L. Dickenson, Syngasproduction for gas-to-liquids applications: technologies,issues and outlook, Fuel Processing Technology 71 (2001)139–148.
[2] Vincenzo Recupero, Lidia Pino, Raffaele Di Leonardo,Massimo Lagana, Gaetano Maggio, Hydrogen generator, viacatalytic partial oxidation of methane for fuel cells, Journal of Power Sources 71 (1998) 208–214.
Fig. 4 – Measured axial species profile along the Ni-based
catalyst bed at D=80% and D=0% (part 1)a. (solid line): D=0%;
(dash line): D=80%; (a): O2; (b): CH4 ; (c): H2O; (d): H2; (e): CO.
Reaction conditions: W cat.=18 g, Hcat.=55 mm, CH4 :air:
H2O =1:2.4:1, GHSV= 13,200 h−1, P =1 atm, T out =750 °C.
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[3] Ib Dybkjær, Tubular reforming and autothermal reforming of natural gas – an overview of available processes, FuelProcessing Technology 42 (1995) 85–107.
[4] A.T. Ashcroft, A.K. Cheetham, J.S. Foord, M.L.H. Green, C.P.Grey, A.J. Murrell, P.D.F. Vernon, Selective oxidation of methane to synthesis gas using transition metal catalysts,Nature 344 (1990) 319–321.
[5] S.S. Bharadwaj, L.D. Schmidt, Catalytic partial oxidation of
natural gas to syngas, Fuel Processing Technology 42 (1995)109–127.
[6] M.A. Pena, J.P. Gomez, J.L.G. Fierro, New catalytic routes for syngas and hydrogen production, Applied Catalysis A:General 144 (1996) 7–57.
[7] Shi qing, Wang Ming-bo, Yin Zhi-guo, Gong Li-qian, Zhang Ji-yan, Liu Ji, Sun Li-ju, Deng Lei, Advances on hotspot problemsof catalyst bed in methane partial oxidation to syngas,Science & Technology in Chemical Industry 13 (4)(2005)60–64.
[8] Qing Miao, Guoxing Xiong, Shishan Sheng, Wei Cui, Ling Xu,Xiexian Guo, Partial oxidation of methane to syngas over
nickel-based catalysts modified by alkali metal oxide and rareearth metal oxide, Applied Catalysis A: General 154 (1997)17–27.
[9] U. Friedle, G. Veser, A counter-current heat-exchange reactor for high temperature partial oxidation reactions I.Experiments, Chemical Engineering Science 54 (1999)1325–1332.
[10] Gerald Ondrey (Ed.), Autothermal reformer promises to lower
investment costs for making syngas, Chemical Engineering,vol. 110(3), 2003, p. 17.
[11] Primdahl Ivar Ivarsen, Process and apparatus for catalyticpartial oxidation of a hydrocarbon, EP 0842894 (A1) (1997) 11.7.
[12] Athina Piga, Xenophon E. Verykios, An advanced reactor configuration for the partial oxidation of methane tosynthesis gas, Catalysis Today 60 (2000) 63–71.
[13] Meilin Jia, Wenzhao Li, Hengyong Xu, Shoufu Hou, Qingjie Ge,An integrated air-POM syngas/dimethyl ether process fromnatural gas, Applied Catalysis A: General 233 (2002) 7–12.
1350 F U E L P R O C E S S I N G T E C H N O L O G Y 8 9 ( 2 0 0 8 ) 1 3 4 5 – 1 3 5 0