Published on the web November 3, 2012
1453
Supercritical Water Gasification of Organosolv Lignin
over a Graphite-supported Ruthenium Metal Catalyst
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Masayuki Shirai,* Norihito Hiyoshi, Yuka Murakami, Mitsumasa Osada, Osamu Sato, and Aritomo Yamaguchi
Research Center for Compact Chemical System, National Institute of Advanced Industrial Science and Technology (AIST),
-2-1 Nigatake, Miyagino, Sendai, Miyagi 983-8551
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Department of Chemical Engineering, Ichinoseki National College of Technology,
Takanashi, Hagisho, Ichinoseki, Iwate 021-8511
(
Received July 18, 2012; CL-120763; E-mail: m.shirai@aist.go.jp)
A graphite-supported ruthenium metal catalyst was highly
active for catalytic gasification of organosolv lignin in super-
critical water at 673 K because of the easy accessibility of the
reaction intermediates to ruthenium metal sites on the graphite
surface, compared to a charcoal-supported ruthenium metal
catalyst.
(a)
(b)
Gasification using supported metal catalysts is one of the
methods for utilization of woody biomass. However, it requires
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0
n
0
m
nm
20nm nm
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high temperatures of over 1000 K, because lignin, which is one
of the main components of woody biomass, is difficult to
pyrolyze. In addition, drying processes, which require a great
deal of energy, are needed prior to the gasification. In contrast,
gasification over supported metal catalysts in supercritical water
has several advantages. For example, it proceeds at a low
Figure 1. TEM images of (a) Ru/G and (b) Ru/C.
Ru/G and Ru/C were almost the same. Nitrogen adsorption
measurements showed that the surface areas of Ru/G and Ru/C
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¹1
were 268 and 1100 m g , and the pore volumes were 0.44
3
¹1
and 1.0 cm g , respectively. A t-method micropore analysis
showed that the micropore volumes of Ru/G and Ru/C were
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temperature, i.e., 673 K, and it requires no drying processes. We
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have reported that a commercially available charcoal-supported
ruthenium catalyst with a 5 wt % ruthenium metal loading was
0.031 and 0.19 cm g , respectively. Lignin (organosolv lignin
powder) and 4-propylphenol were purchased from Aldrich and
Wako Chemicals, respectively, and used without further purifi-
cation. The gasification reaction was carried out in a SUS 316
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active for the gasification of lignin in supercritical water.
Charcoal has a large surface area because of its micropores
and is a stable support in supercritical water. However, it is
probable that some of the metal particles are buried deep within
the micropores and do not work as catalysts. Because ruthenium
is noble and expensive, the development of active supported
catalysts having low ruthenium loadings is favorable. Graphite
powders with high surface areas and few micropores could be
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tube reactor (inner volume 6.0 cm ). The catalyst, lignin or
4-propylphenol, and water were loaded into the reactor, and the
reactor was purged with argon gas. The reactor was heated up to
673 K using a sand bath, and kept at the reaction temperature of
673 K for a given reaction time. After the reaction, the reactor
was cooled to ambient temperature using a water bath.
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good supports for highly dispersed metal particles. In order to
The volumes of gaseous products were measured using a
calibrated syringe and these products were analyzed by gas
chromatography (Shimadzu, GC-8A) using a Shincarbon ST
column and a thermal conductivity detector. The gas yield based
on carbon and the gaseous composition are defined as follows:
develop highly active catalysts that work in supercritical water,
we studied the gasification profiles of lignin and 4-propylphenol,
which is a model constituent of lignin, over a graphite-supported
ruthenium metal catalyst (Ru/G) and compared them to gas-
ification profiles over a charcoal-supported ruthenium catalyst
gas yield based on carbon ðC%Þ
(
Ru/C).
Ru/G and Ru/C were prepared by an impregnation method,
using an aqueous solution of ruthenium(III) nitrosyl nitrate
STREM Chemicals, 1.5% ruthenium(III) nitrosyl nitrate solu-
¼
=
ðmol of carbon atoms in gaseous productÞ
ðmol of carbon atoms in loaded organosolv lignin
(
or 4-propylphenolÞ ꢀ 100
gaseous composition ð%Þ
ð1Þ
ð2Þ
tion) and high-surface-area graphite (TCI HSAG300) and
charcoal (Wako Chemicals), respectively, followed by treatment
in a flow of hydrogen at 573 K for 2 h. The ruthenium metal
loadings for both catalysts were 1.5 wt %. Carbon monoxide
adsorption measurements showed that the ruthenium metal
dispersion values of Ru/G and Ru/C were 0.48 and 0.58,
respectively. Transmission electron microscope (TEM) images
showed that the average ruthenium metal particle sizes in Ru/G
and Ru/C were 1.7 and 1.8 nm, respectively (Figure 1). The
carbon monoxide adsorption and TEM analysis results showed
that the dispersions and sizes of the ruthenium metal particles of
¼
ðmol of gas productÞ=ðsum of mol of gas productsÞ
ꢀ 100
Catalytic gasification of organosolv lignin proceeded well,
and complete gasification could be observed after 180 min over
Ru/G in water at 673 K (Figure 2a). Methane, carbon dioxide,
and hydrogen were the main gaseous products, and a small
amount of C2 gases such as ethane was obtained. At the
beginning of the gasification, the gaseous compositions of
methane, carbon dioxide, and hydrogen were 45%, 40%, and
Chem. Lett. 2012, 41, 14531455
© 2012 The Chemical Society of Japan
Shirai, Masayuki
