Production of COx-free hydrogen by alkali enhanced hydrothermal catalytic reforming of biomass-derived alcohols

Article abstract of DOI:10.1246/cl.2006.216

CO_x-free hydrogen could be produced by hydrothermal catalytic reforming process when Ca(OH)₂ was added into the reaction, and biomass-derived alcohols were used as the reactants. Copyright

Full text of DOI:10.1246/cl.2006.216

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Chemistry Letters Vol.35, No.2 (2006)
Production of CO -free Hydrogen by Alkali Enhanced Hydrothermal Catalytic
x
Reforming of Biomass-derived Alcohols
ꢀ1
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Yunpeng Xu, Zhijian Tian, Guodong Wen, Zhusheng Xu, Wei Qu, and Liwu Lin
Laboratory of Natural Gas Utilization and Applied Catalysis, Dalian Institute of Chemical Physics,
Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, P. R. China
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2
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences,
57 Zhongshan Road, Dalian 116023, P. R. China
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(Received November 4, 2005; CL-051375; E-mail: xuyp@dicp.ac.cn)
COx-free hydrogen could be produced by hydrothermal cat-
alytic reforming process when Ca(OH)2 was added into the reac-
tion, and biomass-derived alcohols were used as the reactants.
forming catalyst for the production of hydrogen. The hydrother-
mal reforming reaction of alcohols was carried at 533 K and au-
togenous pressure with continuous magnetic stirring. The gas
products were analyzed by a Varian 3800 chromatograph with
two detectors of FID and TCD and a mathanizer for conversion
of low molar concentration of COx to methane then detected by
FID. The quantity of gas product was measured by a wet gas
flowmeter after the reaction finished. Reaction performance of
alcohols such as methanol, ethylene glycol, glycerol, mannitol,
and glucose were investigated in the experiments, separately.
Calcium hydroxide (Ca(OH)2) was used for enhancement of
the hydrothermal reforming reaction of alcohols for its abundant
resources. The detailed experiment data was shown in Table 1.
Alkali-enhanced hydrothermal reforming of alcohols keep
Hydrogen fuel cell attracted much interest of the world be-
1
cause it is environmentally clean and high energy conversion
2
efficiency. It is very promising to be used in power generation,
3
especially in electric automobile, in the future. The production
of hydrogen became more and more important for further appli-
cation of hydrogen fuel cell. Current process for hydrogen pro-
duction is mainly based on no-renewable fossil fuel resources
and generated serious environmental pollution concerns at the
same time.4 Furthermore, hydrogen fuel cells are very sensitive
–7
5
12
towards COx impurities. For example, the CO tolerance of pro-
5
most of advantages of aqueous reforming of alcohols: The
ton exchange membrane fuel cells (PEMs) is only ppm level. So
process was conducted under low temperature (around 500 K)
and aqueous phase facilitated the water gas shift (WGS) reac-
tions. Further more, addition of alkali (Ca(OH)2) in the process
could enhance the hydrogen production and suppress the
COx concentration in the gas product. The ideal total reaction
of aqueous reforming of alcohols for hydrogen production is
listed as follows:
the directly produced hydrogen from most current process can
not be used for hydrogen fuel cells. It must be treated by several
additional steps, such as water gas shift and preferential oxida-
5
tion of CO processes etc., to remove COx impurities. So it is
very useful and economical to develop a clean, sustainable,
and one-step COx-free hydrogen production method directly
for hydrogen fuel cells, e.g., PEMs. In the past years, many ef-
CnHxOy þ ð2n ꢁ yÞH2O ! nCO2 þ ð2n ꢁ y þ x=2ÞH2: ð1Þ
This reaction consists of the following two reactions:
8
–11
forts were made for producing clean hydrogen
or developing
1
2
12
renewable ways for production of hydrogen. Here, we report a
simple, clean, and renewable method of alkali enhanced hydro-
thermal reforming of biomass-derived alcohols for production of
COx-free hydrogen. The main product of this process is predom-
inantly hydrogen. Little mount of alkanes was found in hydrogen
product.
CnHxOy þ ðn ꢁ yÞH2O ! nCO þ ðn ꢁ y þ x=2ÞH2; ð2Þ
CO þ H2O ! CO2 þ H2:
ð3Þ
The reaction (2) is reforming process and (3) is water gas
shift (WGS) process. However, in the real catalytic reactions,
other reactions such as mathanation, Fischer–Tropsch etc. will
The hydrothermal reforming of alcohols was conducted in
a homemade batch autoclave reactor. The reactor has 300 mL
volume and can resist up to 220 atm pressures. 5 wt % Pt/AC
1
2
take place. So alkanes and oxygenated hydrocarbons will be
produced beside the main products of hydrogen and CO2.
When Ca(OH)2 was added into the above process, the
(
5 wt % Pt supported on active carbon) catalyst was used as re-
Table 1. Detailed experiment data of alkali enhanced hydrothermal reforming of alcoholsa
Polyols Amount of alcohol/g Amount of H2O/g Amount of Ca(OH)2/g
Glucose 6.0 90.0 15.0
Experiment number
Amount of catalyst/g
Exp.1
Exp.2
Exp.3
Exp.4
Exp.5
Exp.6
Exp.7
Exp.8
Exp.9
1.2
1.0
1.0
1.2
1.2
1.0
1.0
1.0
1.2
Mannitol
Ethylene glycol
Glycerol
6.0
6.0
90.0
90.0
90.0
90.0
90.0
90.0
90.0
90.0
16.0
16.0
24.0
0
10.0
10.0
6.5
Glycerol
Methanol
Methanol
Methanol
Methanol
16.0
8.0
4.0
0
6.0
6.1
6.5
aReaction conditions: temperature, 533 K; pressure, autogenous pressure; reaction time, 4 h.
Copyright Ó 2006 The Chemical Society of Japan

Chemistry Letters Vol.35, No.2 (2006)
217
Table 2. Composition of gas products of reactions
Composition of gas products/mol %
Experiment
number
Polyols
H2
CO2
CO
CH4 C H C H
6
2
3
8
Exp.1
Exp.2
Exp.3
Glucose 81.9 0.0008
0.01
16.2 0.0
1.4
1.5
Mannitol 76.8
Ethylene
0.0
0.4
0.0001 18.2 3.6
glycol 98.8
0.01
0.0
0.7
0.2
0.0
0.2
0.7
0.0
0.0
Exp.4
Exp.5a
Exp.6
Exp.9a
Glycerol 82.9 0.0006
Glycerol 56.7 32.0
16.4 0.6
0.2
8.6
1.8
0.0
0.0
Methanol 99.9 0.001 0.00005 0.1
Methanol 79.9 19.2 0.1 0.7
aWithout addition of Ca(OH)2.
Figure 1. The composition of gas product as a function of
Ca(OH)2 quantity added into the reactions.
following reaction may take place:
alcohol reactant (L/g (alcohol)). The data shows that hydrogen
quantity produced from real reactions is lower than theoretical
calculation for all alcohols with the presence of Ca(OH)2. The
hydrogen production volume decreases in the order of ethylene
glycol > methanol > glycerol > mannitol. It is worthy to no-
tice that 1.7 liters hydrogen is produced per gram of ethylene
glycol, which is slightly lower than the theoretical result 1.8
L/g (alcohol). When Ca(OH)2 is absent, the reaction results
of methanol and glycerol show that the hydrogen volume
produced from the reactions decreased from 1.5 L/g (alcohol)
and 0.7 L/g (alcohol) to 1.1 L/g (alcohol) and 0.39 L/g
Ca(OH)2 þ CO2 ! CaCO3 þ H2O:
ð4Þ
The above reaction will push reactions (2) and (3) to move
towards right hand, so the productions of CO2 and H2 were
enhanced and the production of CO was suppressed theoretical-
ly. It was proved correct by the following reaction data of the
experiments.
Table 2 shows the predominant gas products distributions.
Other products such as alkanes and oxygenated hydrocarbons
are ignored for their negligible amounts. From Table 2, we
can see that the molar concentration of COx was very low in
the gas products of all alcohols with the presence of Ca(OH)2.
However, the results were different with the different alcohols
reactants. When mannitol acted as reactant, no CO2 was detected
in the gas product. Similarly, CO was not found in the gas prod-
uct when glycerol was the reactant. The molar concentrations of
COx in the gas products were relatively higher when glucose and
ethylene glycol were used as reactants. In addition, when the re-
actants were glucose, mannitol, and glycerol, the molar concen-
tration of methane was 16.2, 18.2, and 16.4%, respectively. The
methane molar concentrations were relatively lower (<1%)
when ethylene glycol and methanol were used as reactants.
In general, the molar concentration of hydrogen in the gas
product decreases in the order of methanol > ethylene glycol >
glycerol > glucose > mannitol. The molar concentration of
COx in the gas product could be suppressed to almost zero by
addition of Ca(OH)2.
(
alcohol), respectively.
The effects of quantity of Ca(OH)2 on the composition of
gas product was investigated in the experiment, the results
are shown in Figure 1. In this investigation, methanol was used
as the reactant. Figure 1 shows the alkali amount has obvious
effect on the molar concentrations of components in gas product,
especially the COx concentrations. When additive amount of
Ca(OH)2 decreased gradually from 16.0 to 0 g, CO2 molar
concentration increased from ppm level to 19% step by step.
The same as CO2, molar concentration of CO increased from
0
.5 ppm to 0.2%. Moreover, Ca(OH)2 can also hold back the
alkane production from the reforming reactions as shown in
Figure 1.
All in all, by introducing alkali (Ca(OH)2) into hydrother-
mal reforming reactions of alcohols, the COx, especially CO,
in gas product can be suppressed to the utmost and reach several
ppm or lower level. This is a simple one-step process for produc-
tion COx-free hydrogen from renewable resources such as bio-
mass-derived alcohols.
The amounts of hydrogen produced by hydrothermal re-
forming of alcohols are shown in Table 3. The theoretical quan-
tity of hydrogen produced according to reaction (1) is also listed
in Table 3 for comparison. The hydrogen amount is expressed as
volume at standard temperature and pressure (STP) per gram of
References
1
M. Z. Jacobson, W. G. Colella, D. M. Golden, Science 2005, 308,
901.
Table 3. Amounts of hydrogen obtained from reactions and
calculations
1
2
S. M. Haile, D. A. Boysen, C. R. I. Chisholm, R. B. Merle, Nature
2001, 410, 910.
a
STP volume of hydrogen
Experiment
3
4
5
6
7
8
9
N. Demird o¨ ven, J. Deutch, Science 2004, 305, 974.
J. N. Armor, Appl. Catal. 1999, 176, 159.
T. V. Choudhary, D. W. Goodman, Catal. Today 2002, 77, 65.
J. A. Turner, Science 2004, 305, 972.
D. Day, R. J. Evans, J. W. Lee, D. Reicosky, Energy 2005, 30, 2558.
T. Ishihara, Y. Miyashita, H. Iseda, Y. Takita, Chem. Lett. 1995, 93.
K. Otsuka, T. Seino, S. Kobayashi, S. Takenaka, Chem. Lett. 1999,
1179.
Polyols
(L/g(alcohol))
number
Reaction
Calculation
Exp.2
Exp.3
Exp.4
Exp.5b
Exp.6
Exp.9b
Mannitol
Ethylene glycol
Glycerol
0.62
1.7
1.6
1.8
1.7
1.7
2.1
2.1
0.7
Glycerol
0.39
1.5
10
11
12
R. Metkemeijer, P. Achard, Int. J. Hydrogen Energy 1994, 19, 535.
K. Hashimoto, N. Toukai, J. Mol. Catal. 2000, 161, 171.
R. R. Davda, J. W. Shabaker, G. W. Huber, R. D. Cortright, J. A.
Dumesic, Appl. Catal., B 2005, 56, 171.
Methanol
Methanol
1.1
a
b
Standard temperature and pressure. Without addition of Ca(OH)2.
Published on the web (Advance View) January 21, 2006; DOI 10.1246/cl.2006.216