Bi-reforming of methane from any source with steam and carbon dioxide exclusively to metgas (CO-2H2) for methanol and hydrocarbon synthesis

Article abstract of DOI:10.1021/ja311796n

A catalyst based on nickel oxide on magnesium oxide (NiO/MgO) thermally activated under hydrogen is effective for the bi-reforming with steam and CO₂ (combined steam and dry reforming) of methane as well as natural gas in a tubular flow reactor at elevated pressures (5-30 atm) and temperatures (800-950 C). By adjusting the CO₂-to-steam ratio in the gas feed, the H₂/CO ratio in the produced syn-gas could be easily adjusted in a single step to the desired value of 2 for methanol and hydrocarbon synthesis.

Full text of DOI:10.1021/ja311796n

Communication
pubs.acs.org/JACS
Bi-reforming of Methane from Any Source with Steam and Carbon
Dioxide Exclusively to Metgas (CO−2H ) for Methanol and
2
Hydrocarbon Synthesis
George A. Olah,* Alain Goeppert, Miklos Czaun, and G. K. Surya Prakash
Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, University Park,
Los Angeles, California 90089-1661, United States
*
S Supporting Information
separation and adjustment steps, which makes the overall
process complex and more expensive.
ABSTRACT: A catalyst based on nickel oxide on
magnesium oxide (NiO/MgO) thermally activated under
hydrogen is effective for the bi-reforming with steam and
Steam reforming CH + H O → CO + 3H
(1)
4
2
2
CO (combined steam and dry reforming) of methane as
ΔH298K = 49.1 kcal·mol−1
2
well as natural gas in a tubular flow reactor at elevated
pressures (5−30 atm) and temperatures (800−950 °C).
Dry reforming
CH + CO → 2CO + 2H (2)
4
2
2
By adjusting the CO -to-steam ratio in the gas feed, the
2
ΔH298K = 59 kcal·mol−
1
H /CO ratio in the produced syn-gas could be easily
2
adjusted in a single step to the desired value of 2 for
methanol and hydrocarbon synthesis.
Partial oxidation CH + 1 O → CO + 2H (3)
4
2
2
2
ΔH298K = −8.6 kcal·mol−
1
ynthesis gas (syn-gas), a variable composition mixture of
We now report the exclusive preparation of a syn-gas mixture
S
hydrogen and carbon monoxide (with some carbon
dioxide), is the basis of Fischer−Tropsch chemistry. Syn-gas
is produced by partial oxidation with steam and oxygen from
of a 2/1 H /CO ratio suitable for methanol synthesis in which
2
dry and steam reforming are combined in a single step, called
4−7
bi-reforming.
In bi-reforming, a specific ratio of methane,
1
virtually any carbon source, including biomass. However,
steam, and CO2 of 3/2/1 produces a gas mixture with
essentially a 2/1 ratio of hydrogen to carbon monoxide, which
was suggested to be called “metgas” to underline its difference
natural (shale) gas and methane are generally the preferred
feedstocks. These are also the source for the large-scale
production of synthetic fuels and chemicals including methanol,
from the widely used syn-gas mixtures of varying H /CO ratio.
2
2
dimethyl ether, and varied hydrocarbons and their products.
This specific 2/1 H /CO gas mixture is for the preparation of
2
Methanol and its derivatives are becoming increasingly
significant fuels and starting materials for varied chemical
products. We have discussed methanol’s potential role and
relevant chemistry that was developed in the framework of the
methanol and subsequently derived hydrocarbon products, with
complete utilization of all the hydrogen (eq 4).
Steam reforming 2CH + 2H O → 2CO + 6H
4
2
2
“
Methanol Economy” in a series of publications, patents, and a
Dry reforming
CH + CO → 2CO + 2H
3
−7
4
2
2
monograph.
The current production of methanol is based
Ni/MgO
on syn-gas following a process first developed by Mittasch et al.
Bi‐reforming
3CH + 2H O + CO ⎯⎯⎯⎯⎯⎯⎯⎯→
4
2
2
in 1923 and further improved over the years by companies
8
methanol
including BASF and ICI. What is needed, however, for a wider
4
CO + 8H ⎯⎯⎯⎯⎯⎯⎯ ⎯→ 4CH OH (4)
2
3
use of methanol are more efficient and economic ways of
synthesis
preparation.
The feed is purified when needed before being introduced
The synthesis of methanol from syn-gas requires a H /CO
ratio of about 2. The most commonly used reforming
technology for methane, steam reforming, produces a syn-gas
mixture with a H /CO ratio close to 3 (eq 1). This means that
additional steps are needed to adjust the H /CO ratio. Carbon
dioxide reforming of methane, called dry reforming, produces a
syn-gas with a H /CO ratio close to 1 (eq 2), which is too low
and has also to be adjusted. Partial oxidation of methane with
oxygen can produce a H /CO ratio of 2, but is difficult to
control and can lead to local hot spots and associated dangers
of explosions (eq 3). The combination of steam reforming
and partial oxidation (autothermal reforming) as practiced
industrially produces the H /CO ratio of 2 by further
2
3
into the reforming vessel to remove impurities, mainly H S and
2
SO , which would poison the Cu-based catalyst in the
2
subsequent methanol synthesis step. The needed heat for the
bi-reforming process can be provided by any external energy
source (conventional or alternative energy sources including
hydro, solar, wind, etc. as well as atomic energy).
Bi-reforming to produce metgas is also advantageous in the
use of varied natural gas sources even containing significant
2
2
2
9
2
amonuts of CO . Some natural gas as well as biogas sources
2
10
Received: December 3, 2012
Published: December 20, 2012
2
©
2012 American Chemical Society
648
dx.doi.org/10.1021/ja311796n | J. Am. Chem. Soc. 2013, 135, 648−650

Journal of the American Chemical Society
Communication
contain CO concentration up to 50−70%. Bi-reforming can
2
also be used to recycle CO emissions from sources such as flue
2
gases from fossil fuel (coal, petroleum, natural gas, etc.)-
burning power plants, exhaust of cement factories, and varied
industries.
Bi-reforming to metgas is also adaptable for reforming shale
gas. Dry shale gas is essentially methane (>98%). Wet shale gas
also contains ethane, propane (which can be dehydrogenated to
ethylene and propylene), and some higher hydrocarbon
homologues (eq 5).
3
C H
+ (3n − 1)H O + CO →
n
(2n+2)
2
2
(
3n + 1)CO + (6n + 2)H → (3n + 1)CH OH
(5)
2
3
Figure 1. Single pass CH and CO conversion in bi-reforming of
4
2
Metgas can also be obtained from other natural carbon
sources including coalbed methane and methane hydrates as
well as biomass. Recent findings of significant shale gas
methane over 15-NiO-MgO catalyst at 7 atm and 830 °C: 100
−1
mL·min of CH /CO /H O with a molar ratio of 3/1.2/2.4 and
4
2
2
4
−1 −1
GHSV of 6 × 10 mL·h ·g catalyst.
(
methane) deposits considerably increased the overall reserves
of natural gas. Shale gas production is made possible by
horizontal drilling and rock fracking using high-pressure water,
chemical additives, and sand. The environmental consequences
conditions, the catalytic system is able to perform both dry and
steam reforming simultaneously with ease. This indicates that
11
of these techniques are still under debate.
steam and CO reforming on nickel catalyst involve similar
2
1
,13,18,19
Preferentially, bi-reforming is carried out under 5−30 atm of
kinetics.
The selectivity for CO and H were 100% and
2
pressure and 830-950 °C temperature, producing metgas,
98%, respectively. When the temperature was increased from
830 to 910 °C, the conversion of both methane and CO2
increased. Methane conversion increased about 15% to reach
12
which can be directly used in the methanol synthesis. Most of
9
,13
the reported studies on dry and combinations of dry
steam
and
1
4−17
reforming have been conducted at atmospheric
86% at 910 °C. The H /CO ratio decreased only very slightly
2
pressure and mostly with pure methane. In order to approach
conditions closer to practical applications, we studied bi-
reforming of methane as well as of natural gas at pressures up to
from 1.99 to 1.97. As expected, however, from the
thermodynamics of endothermic reactions, with an increase
in number of moles (Le Chatelier’s principle), the conversion
of methane decreased with increasing pressure (from 71% at 7
6
,7
30 atm. The reactions were conducted in a tubular flow
reactor system built specially for this purpose and suitable to
withstand pressures up to 100 atm and needed temperatures of
atm to about 52% at 28 atm). On the other hand, the H /CO
2
ratio increased slightly from 1.99 to 2.02 when the pressure was
increased from 7 to 28 atm. Doubling the amount of steam and
CO (CH /CO /H O with a molar ratio of 3/2.4/4.8) at 7 atm
800−1000 °C provided by external heating. All the surfaces in
contact with the catalyst and reacting gases at the high
temperatures were made of alumina to avoid any side reactions
or possible deterioration of the reactor materials. Quartz, which
is often used in reforming studies at atmospheric pressure, was
inadequate, leading to coke formation and eventually reactor
clogging. The preferred catalyst used was based on NiO
deposited on magnesium oxide, i.e., NiO/MgO, which was
active and stable over extended continuous durations (320 h),
as are related supported metal oxides. The NiO content in
NiO/MgO can be between 5 and 35%. A gas feed composition
of CH /CO /H O with a molar ratio of 3/1.2/2.4 was typically
2
4
2
2
increased the methane conversion from 71% to 85%. The
experiments were carried out in a single pass mode, but the
unreacted feed gases can be recycled to improve the overall
conversion.
When the gas hourly space velocity (GHSV) was increased
5
−1 −1
10-fold to 6 × 10 mL·min ·g , methane conversion
decreased only by about 2% but remained stable. CO2
conversion also slightly decreased, as did the H /CO ratio to
2
about 1.95−1.97.
The same 15-NiO-MgO catalyst was also tested under the
studied pressures for the bi-reforming of natural gas (composed
of methane containing ethane, propane, butane, and higher
hydrocarbons). No hydrocarbons other than unreacted
methane were detected in the products, indicating that all
higher hydrocarbons had reacted. At 7 atm, again stable CO2
4
2
2
used with nitrogen as an internal reference. Ni deposited on
MgO had been previously shown to be an effective and stable
13
catalyst for dry reforming reaction.
Reforming is frequently affected by coking, involving the
deposition of carbon in the form of soot or coke on the catalyst
(
reducing strongly its activity), as well as parts of the
and CH conversion was observed for the duration of the
experiment (160 h). The conversion of natural gas was about
4
equipment. Carbon may be formed by both CH (natural
4
gas) decomposition and CO disproportionation (Boudouard
reaction). The relative contributions depend on the reaction
conditions and catalyst used. The undesired formation of
carbon is, however, largely prevented by the presence of steam
and short residence times in the flow reactor.
As an example, after activation at 850 °C under hydrogen, a
catalyst composed of 15% NiO on MgO (15-NiO-MgO)
showed a stable activity in a typical bi-reforming reaction at 830
70%, and the H /CO ratio remained stable at around 1.9. This
2
somewhat lower H /CO ratio compared to the reaction with
2
pure methane is consistent with the presence of higher
hydrocarbons having a lower H/C ratio. The H/C ratio will
get closer to 2 as the alkane chain length increases. Whereas
methane has a H/C ratio of 4, ethane, propane, and butane
have a H/C ratio of 3, 2.7, and 2.5, respectively. Keeping the
same ratio of steam and CO to the hydrocarbon feed results in
2
°
C and 7 atm for the duration of continuous experiment up to
a lower H /CO ratio. However, when the amount of steam in
2
3
20 h (Figure 1). The H /CO ratio remained essentially 2 and
the gas feed was increased by 10%, a constant H /CO ratio of 2
2
2
also remained stable over the reaction time. Under the studied
was obtained. The H /CO ratio can therefore be easily
2
6
49
dx.doi.org/10.1021/ja311796n | J. Am. Chem. Soc. 2013, 135, 648−650

Journal of the American Chemical Society
Communication
modulated by adjusting the ratio of steam and CO in the gas
feed.
(11) Kerr, R. A. Science 2010, 328, 1624.
12) Methanol Production and Use; Cheng, W.-H., Kung, H. H., Eds.;
Marcel Dekker: New York, 1994.
2
(
The activated NiO/MgO catalyst was thus shown to be
equally active for the bi-reforming of pure methane and natural
gas or other sources. The conversion of methane as well as
carbon dioxide was constant for extended periods of time in the
pressurized (5−30 atm) flow reactor at temperatures of 800−
(13) Bradford, M. C. J.; Vannice, M. A. Catal. Rev.-Sci. Eng. 1999, 41,
1
.
(14) Roh, H.-S.; Koo, K. Y.; Jeong, J. H.; Seo, Y. T.; Seo, D. J.; Seo,
Y.-S.; Yoon, W. L.; Park, S. B. Catal. Lett. 2007, 117, 85.
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(
9
50 °C. The reaction of CH /natural gas and CO conversion
4
2
2008, 125, 283.
decreased with increasing pressure. This effect can, however, be
in part countered by increasing the amount of steam and CO2
in the gas feed and increasing the reaction temperature. The
(16) Koo, K. Y.; Roh, H.-S.; Jung, U. H.; Yoon, W. L. Catal. Lett.
2009, 130, 217.
(17) Koo, K. Y.; Roh, H.-S.; Seo, Y. T.; Seo, D. J.; Yoon, W. L.; Park,
S. B. Int. J. Hydrogen Energ. 2008, 33, 2036.
H /CO ratio can be successfully and easily adjusted to the
2
(
(
(
18) Wei, J.; Iglesia, E. J. Catal. 2004, 224, 370.
19) Rostrup-Nielsen, J. R.; Bak Hansen, J.-H. J. Catal. 1993, 144, 38.
20) Olah, G. A.; Doggweiler, H.; Felberg, J. D.; Frohlich, S.; Grdina,
desired value of 2 ideal for methanol synthesis by adjusting the
CO to steam ratio in the gas feed.
2
In conclusion, the reported bi-reforming effectively converts
methane and its natural sources (natural or shale gas, coal-bed
M. J.; Karpeles, R.; Keumi, T.; Inaba, S.-I.; Ip, W. M.; Lammertsma, K.;
Salem, G.; Tabor, D. C. J. Am. Chem. Soc. 1984, 106, 2143.
methane, methane hydrates) to metgas, a 2/1 H /CO mixture
2
directly applicable for subsequent well-studied methanol
synthesis with high selectivity. A typical single pass conversion
at 7 atm is about 70−75%, which can be increased to 80−85%
by adjusting the feed gas composition. Unreacted feed gases can
be readily recycled. The efficient conversion of methane and its
varied sources to methanol via metgas can also be utilized for
subsequent synthesis of varied hydrocarbons and their products
12
through zeolite-based chemistry or over various bi-functional
20
acidic−basic catalytic routes giving alkenes (mainly ethylene
and propylene) and their derived products, replacing petroleum
oil as the source material.
ASSOCIATED CONTENT
Supporting Information
Experimental details and procedures. This material is available
free of charge via the Internet at http://pubs.acs.org.
■
*
S
AUTHOR INFORMATION
Corresponding Author
olah@usc.edu
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Support of our work by the Loker Hydrocarbon Research
Institute and the United States Department of Energy is
gratefully acknowledged.
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dx.doi.org/10.1021/ja311796n | J. Am. Chem. Soc. 2013, 135, 648−650