Production of ultra highly pure H and higher hydrocarbons from
2
methane in one step at mild temperatures and development of the
catalyst under non-equilibrium reaction conditions
Linsheng Wang,*ab Kazuhisa Murata, Abdelhamid Sayari, Bernard Grandjean and
Megumu Inaba
a
b
b
a
a
National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 5, Tsukuba,
Ibaraki 305, Japan. E-mail: linsheng.wang@aist.go.jp
b
Department of Chemical Engineering, Laval University, Quebec City, Canada
Received (in Cambridge, UK) 28th June 2001, Accepted 21st August 2001
First published as an Advance Article on the web 19th September 2001
Ultra highly pure hydrogen and more valuable hydro-
carbons are produced directly from methane in one step
beyond the thermodynamic equilibrium conversion by in-
tegration of the dehydrogenation reaction and hydrogen
separation with a Pd–Ag based membrane reactor at mild
temperatures, and a highly active catalyst is developed
under the non-equilibrium reaction conditions.
Both as an alternative process for production of hydrogen and as
a promising method for the production of higher hydrocarbons
from natural gas, the dehydrogenation and aromatization
reactions of methane on Mo/HZSM-5 and Re/HZSM-5 has
attracted increasing attention since 1993. However, the max-
imum aromatics yield has been reported to be only 7–8% at 973
K on the catalysts by different research groups1–9 and it seems
Fig. 1 Schematic illustration of the membrane reactor.
that this is the thermodynamic equilibrium conversion at this
temperature. In addition, the equilibrium reaction conditions
make it difficult to develop more active catalysts. In the present
communication, direct methane conversion into hydrogen and
higher hydrocarbons beyond the thermodynamic equilibrium
limit becomes possible by integration of the methane dehydro-
equilibrium can be disturbed, leading to much higher conver-
sions than the equilibrium conversion for methane dehydroge-
nation into aromatics, achieved by continuous separation of
hydrogen from the product by hydrogen permeation through the
membrane.
2
genation reaction and H separation with a Pd membrane
reactor, and a highly active catalyst has been developed for the
production of pure hydrogen and higher hydrocarbons under
non-equilibrium reaction conditions.
A high methane conversion of 7.5% is attained on Re/HZSM-
2
1
21
5 at 858 K when the methane SV is 120 ml h
g
at a low
temperature of 858 K. This is ca. twice as high as the methane
The catalysts Re/HZSM-5 and Mo/HZSM-5 were prepared
equilibrium conversion at the same temperature. At the same
by impregnating NH
4
ZSM-5 with NH
4
ReO
4
and
2
time, ultra highly purely H is produced because of the 100%
(
NH Mo 24·4H
4
)
6
7
O
2
O aqueous solution, respectively, followed
selectivity of the membrane for hydrogen permeation and the
pure hydrogen can be directly used in a fuel cell. Fig. 2 shows
the activity profile of Re/HZSM-5 catalyst with time on stream
by drying at 383 K for 4 h and calcination at 773 K for 4 h. The
sample was finally pressed, crushed and sorted into 20–40
meshes. Catalytic tests were carried out in a fixed bed
continuous-flow Pd–Ag based membrane reactor (5/8 inch
diameter 3 10 inch height). The membrane reactor contains
2
when H was separated by selective permeation. The enhanced
Table 1 Effect of hydrogen permeation on methane conversion into
aromatics and C on Re/HZSM-5 at 858 K
four membrane tubes (1/8 inch diameter 3 7 inch height). H
2
2
was continuously separated from the product by permeation
through the membrane tubes and removed by a vacuum pump.
A schematic diagram of the membrane reactor is shown in Fig.
Selectivity (%)
SV/ml
h
H
2
Conversion
2
1
g21 separation (%)
C
2
C
6
H
6
C
7
H
8
10 8
C H
1. The results for methane conversion on Re/HZSM-5 at a low
temperature of 858 K and different methane space velocity (SV)
values are listed in Table 1. Both hydrogen and higher
hydrocarbons are produced from methane dehydrogenation on
the catalyst even at such a low temperature. The major
hydrocarbon products for methane dehydrogenation include
1
1
20
80
No
Yes
No
Yes
No
Yes
No
Yes
No
Yes
No
2.5
7.5
2.4
5.9
2.6
4.9
2.6
4.2
2.4
3.5
2.4
3.3
9.6
3.2
5.4
4.1
6.2
5.5
6.9
6.4
8.8
8.3
11.3
8.2
56.0
53.3
70.8
64.4
69.2
65.3
69.2
66.7
70.8
71.4
62.5
63.6
2.4
3.5
2.9
4.4
3.1
4.3
3.8
4.8
4.6
5.4
4.2
5.5
32.0
40.0
20.8
27.1
23.1
24.5
19.2
21.4
16.7
14.6
22.1
22.4
240
benzene, naphthalene, toluene and C
is not separated from the dehydrogenation product by H
permeation through the membrane, the maximum methane
conversion into aromatics and C on Re/HZSM-5 is ca.
.4–2.6% at 858 K (Table 1). The methane conversion changes
little even for a wide methane SV range of 120–1440 ml
2
products. When hydrogen
3
7
60
20
2
2
2
1
440
Yes
2
1 21
h
g
. Therefore, under thermodynamic equilibrium reaction
conditions, the yield of aromatics and C is only ca. 2.4–2.6%
at 858 K. Of most significance is that this thermodynamic
Pressure = 100 kPa; the permeability of H
5%.
2
through the membrane is ca.
2
7
1952
Chem. Commun., 2001, 1952–1953
This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b105703k