Hydrolysis of cellulose into glucose over carbons sulfonated at elevated temperatures

Article abstract of DOI:10.1039/c0cc02014a

The hydrolysis of cellulose over sulfonated carbons was promoted greatly by elevating the sulfonation temperature. With 250 °C-sulfonated CMK-3 as a catalyst, the cellulose was selectively hydrolyzed into glucose with the glucose yield as high as 74.5%, which is the highest level reported so far on solid acid catalysts.

Full text of DOI:10.1039/c0cc02014a

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Hydrolysis of cellulose into glucose over carbons sulfonated at elevated
temperaturesw
Jifeng Pang,ab Aiqin Wang, Mingyuan Zheng and Tao Zhang*
a
a
a
Received 22nd June 2010, Accepted 22nd July 2010
DOI: 10.1039/c0cc02014a
The hydrolysis of cellulose over sulfonated carbons was promoted
greatly by elevating the sulfonation temperature. With 250 1C-
sulfonated CMK-3 as a catalyst, the cellulose was selectively
hydrolyzed into glucose with the glucose yield as high as 74.5%,
which is the highest level reported so far on solid acid catalysts.
the surface acidity and hydrophilicity/hydrophobicity may be
tuned to best facilitate the hydrolysis of cellulose. Nevertheless,
the sulfonation conditions have rarely been optimized towards
the hydrolysis of cellulose. Herein we report that by elevating
the sulfonation temperature of the active carbon (AC) from
1
50 1C to 250 1C, the glucose yield in the hydrolysis of cellulose
Stimulated by the ever increasing energy crisis and environ-
mental concerns, utilization of renewable resources for the
production of energy and chemicals has attracted more and
more attention. Cellulose, the most abundant source of bio-
mass and non-digestible by humans, is being considered as a
was remarkably enhanced from 7% to 61%. Moreover, when
250 1C-sulfonated CMK-3 (an ordered mesoporous carbon)
was used as the catalyst, a glucose yield was attained as high as
74.5%. To our knowledge, this is the highest glucose yield
obtained to date over a solid acid catalyst.
1
promising alternative to fossil resources. Cellulose is a water-
The sulfonation of the carbon materials was carried out under
nitrogen atmosphere at 150–300 1C for 24 h, using 15 mL
concentrated sulfuric acid per gram of carbon. Before the sulfona-
tion, some carbons were pretreated with nitric acid. The samples
are designated with functional groups followed by sulfonation
insoluble saccharide polymer composed of glucose monomers
linked by b-1,4 glycosidic bonds. Since glucose can be efficiently
converted into fuels and various value-added chemicals
with the commercially available fermentation or chemical
2
processes, the selective hydrolysis of cellulose into glucose
temperature; for example, AC-N-SO H-250 represents the sample
3
represents a key technology in the utilization of cellulose.
The conventional processes for the hydrolysis of cellulose
treated with nitric acid and subsequently sulfonated at 250 1C.
Table 1 lists the acid densities, specific surface areas, and adsorbed
water amount of the sulfonated carbons. It should be pointed out
that the acid densities determined by the titration method are
3
involve the use of mineral acids. The corrosion and waste
disposal problems, however, significantly lower the attraction
of liquid acid-catalyzed hydrolysis. In order to minimize the
environmental impact, new green approaches have been
3
3–5 times larger than those determined by the NH -adsorption
method. Nevertheless, both the methods show the same trend for
samples sulfonated at different conditions. For clarity, we here use
the titration-determined acid densities to discuss the influence of
sulfonation temperatures. The non-treated AC had an acid density
4
developed, such as the use of cellulase enzymes, hydrolysis
5
in sub- or super-critical water, ionic liquid promoted dissolution
6
and hydrolysis of cellulose, hydrogenolysis into polyols
,7
8–12
13–17
as well as hydrolysis into glucose by solid catalysts.
À1
2
À1
Among
of 0.15 mmol g and a specific surface area of 703 m g . After
sulfonation treatment, the acid density had a large increase.
Moreover, the higher the sulfonation temperature, the higher the
acid density of the sulfonated carbon. For example, the AC
others, the solid catalysts present the advantages of catalyst
recovery, less or even no corrosion, and milder reaction condi-
tions. Various solid acids have been investigated in the hydrolysis
1
3,14
of cellulose, including sulfonated carbon materials,
ion-
3
sulfonated at 300 1C (AC-SO H-300) showed an acid density of
15
16
exchange resins, heteropolyacids, and layered transition-metal
À1
2.19 mmol g , which was 15-fold that of the untreated AC.
Meanwhile, the specific surface areas of the samples were slightly
increased when the sulfonation temperature was raised from
150 to 250 1C, but they decreased rapidly with increasing the
temperature further. It is interesting to note that the pretreatment
with nitric acid prior to the sulfonation led to an additional
increase in the acid density because treating the AC with nitric
acid alone also introduced some acidic functional groups such as
–OH and/or –COOH. On the other hand, the densities of func-
17
oxide. A significant challenge associated with the application
of solid acids is their much lower efficiency than the mineral
liquid acids. Actually, the highest yield of glucose derived from
hydrolysis of cellulose over various solid acids was reported to be
1
3
only about 40%, which is far less than that on mineral acids.
Therefore, it is desirable to develop a highly active and recyclable
solid acid catalyst for the hydrolysis of cellulose.
Compared with resin-type or oxide-type solid acids, sulfonated
carbons are more robust in hot water besides having preferable
textural properties. By sulfonation in appropriate conditions,
tional group –SO
of S, were significantly lower than the acid densities. Moreover, it
was found that the AC-N-SO H-250 possessed the highest density
of –SO H groups, whereas a higher temperature (>250 1C) caused
H, which were determined by elemental analysis
3
3
a
3
State Key Laboratory of Catalysis, Dalian Institute of Chemical
the decomposition of sulfonate. Besides the acid density, we
also investigated the hydrophilicity of the carbon materials. As
shown in Table 1, the adsorbed water amount increased with
the sulfonation temperature, indicating the hydrophilicity of the
carbon materials is improved by elevating the sulfonation
temperature.
Physics, Chinese Academy of Sciences, Dalian 116023, P. R. China.
E-mail: taozhang@dicp.ac.cn; Fax: +86-411-84691570;
Tel: +86-411-84379015
Graduate School of Chinese Academy of Sciences, Beijing 100049,
P. R. China
b
w Electronic supplementary information (ESI) available: Experimental
details. See DOI: 10.1039/c0cc02014a
This journal is c The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 6935–6937 6935

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a
Table 1 The surface properties of AC sulfonated at different temperatures and their catalytic activities for hydrolysis of cellulose
b
H /
c
Acid density /
mmol g
d
Acid density /
mmol g
e
g
h
–
mmol g
SO
3
S
BET
m g
/
Adsorbed
water /%
Y
C (%)
Glu
Conv
C (%)
À1
À1
À1
2
À1
f
Catalyst
AC
AC-NO
—
0.15
1.49
0.80
1.03
1.58
2.03
2.19
2.15
2.18
2.23
2.38
2.39
0.05
0.36
0.22
0.42
0.47
0.59
0.54
0.37
0.43
0.50
0.70
0.78
703
762
709
728
945
462
278
723
741
762
362
30
8.8
0
9.7
7.1
10.0
31.5
25.1
43.4
70.4
66.6
63.1
42.1
64.3
74.3
66.3
68.6
3
0.02
0.19
0.24
0.24
0.23
0.20
0.12
0.34
0.44
0.27
0.27
10.7
13.8
15.4
17.9
18.3
19.6
14.1
15.4
19.6
20.8
21.3
AC-SO
AC-SO
AC-SO
AC-SO
AC-SO
3
H-150
H-200
H-250
H-280
H-300
3
3
3
3
17.9
61.0
56.0
36.7
19.0
56.1
62.6
58.4
54.2
AC-N-SO
AC-N-SO
AC-N-SO
AC-N-SO
AC-N-SO
3
3
3
3
3
H-150
H-200
H-250
H-280
H-300
a
b
The hydrolysis reaction was conducted at 150 1C for 24 h, with 0.27 g of cellulose, 0.3 g of catalyst and 27 mL water in a 50 mL autoclave. The
c
d
density of –SO
by an NH -adsorption method. Specific surface area was measured by N
BET) method. The amount of adsorbed water was measured with a static adsorption method.
3
H groups was measured by ICP-AES. The acid density was determined by a titration method. The acid density was determined
e
3
2
adsorption at À196 1C according to the Brunauer–Emmett–Teller
f
g
(
Y
Glu was the carbon-based yield of
h
glucose. Conv. was the carbon-based conversion of cellulose determined by analysis of total organic carbon (TOC) of the liquid product.
The above samples obtained at different sulfonation tempera-
tures were investigated for hydrolysis of cellulose. Prior to the
catalytic reaction, the cellulose was pretreated by ball-milling
for 48 h in order to decrease the crystallinity (Fig. S1), as
hydrolysis of cellulose into saccharides; but the glucose yield
1
3
was very low (4%). Onda et al. also used a sulfonated carbon
for hydrolysis of cellulose, and they obtained a much higher
yield of glucose (40.5%) than Suganuma et al. In comparison
1
3–17
reported in the literature.
The hydrolysis reaction was
with the results reported in the literature, the AC-N-SO H-250
3
conducted at 150 1C for 24 h, with 0.27 g of cellulose, 0.3 g of
catalyst and 27 mL water in a 50 mL autoclave. The conversion
of cellulose was determined by measuring the soluble carbon
content in the liquid product using a TOC (total organic
carbon) analyzer, while the glucose yield was calculated by
the ratio of carbon amount in glucose product (determined by
HPLC) to that in cellulose (determined by a CHNS analyzer).
Table 1 shows the conversions of cellulose and the yields of
glucose produced over different sulfonated carbons. The non-
treated AC was poorly active for degradation of cellulose; only
catalyst we report here gave a significantly increased glucose
yield attributed to a higher sulfonation temperature used.
The kinetic study for cellulose conversion over the
3
AC-N-SO H-250 catalyst revealed that the cellulose was
hydrolyzed fast and selectively into glucose at the initial stage
(from 0 to 4 h), followed by a slow hydrolysis process until
20 h (Fig. S2). However, even on prolonging the reaction time
to 48 h, the cellulose could not be fully hydrolyzed. Meanwhile,
the decomposition of glucose took place on extending the
reaction time longer than 24 h. This result may imply that the
degradation of cellulose follows an inhomogeneous process from
the most easily attacked part to the part most difficult to attack.
1
0% of cellulose was depolymerized and no glucose was
detected in the product. In contrast, over sulfonated carbons,
both the conversion of cellulose and the production of glucose
were enhanced. Moreover, they were strongly dependent on
the sulfonation temperature. When the sulfonation tempera-
ture of AC was increased from 150 to 250 1C, the glucose yield
was increased from 7.1% to 61.0% and the cellulose conversion
was increased from 25.1% to 70.4%. However, further eleva-
tion of the sulfonation temperature brought about a decrease
in both the cellulose conversion and glucose yield, although
the sulfonated carbons have a higher acid density in this case.
It was found that the trend of cellulose conversion and glucose
yield was in good agreement with the density of sulfonate
groups, indicating that the acid sites associated with the
3
Taking the AC-N-SO H-250 catalyst as an example, we then
investigated the recovery and reusability of the sulfonated carbons.
As shown in Fig. S3, the catalyst presented excellent stability and
reusability; the glucose yield still reached 59% over the fourth-
recycled catalyst and the cellulose conversion remained the same
as that over fresh catalyst. The analysis of the reused catalyst after
the fourth recycling test revealed that neither the sulfonate groups
nor the acid densities were lost during the repetitive reactions
(Table S1). Further experiment by putting the fresh cellulose into
the filtrate solution after the first run revealed that the glucose yield
did not increase after the reaction at 150 1C for 24 h; instead, it had
a decrease of about 10% due to the degradation of glucose. These
results provide strong evidence that the hydrolysis reaction takes
place solely on the solid catalyst surface.
SO
3
H functional groups act as the active sites for the selective
hydrolysis of cellulose into glucose. For the AC-N-SO
3
H
series catalysts, the activity and selectivity were even higher,
attributed to the further increased densities of sulfonate groups
Apart from the sulfonation conditions, the carbon sources and
the carbonization procedures may also affect, even dominate the
functional groups on the carbon surface, which will then influence
the catalytic activity. As shown in Fig. 1, the six sulfonated
3
in comparison with the AC-SO H series catalysts. Among
the AC-based catalysts, the best result was achieved on the
18
AC-N-SO H-250 catalyst which gave the glucose yield of
3
carbons behaved remarkably differently in the hydrolysis of
cellulose, following the order of ACB o MWCNT o
Cell-Carbon o CSAC o Resin-Carbon o CMK-3 in terms
of glucose yield. Especially interesting, the sulfonated CMK-3,
6
2.6% and the cellulose conversion of 74.3%. Previously,
1
Suganuma et al. reported a carbon material bearing SO H,
4
3
COOH, and OH groups which exhibited a high efficiency for
6
936 Chem. Commun., 2010, 46, 6935–6937
This journal is c The Royal Society of Chemistry 2010

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the hydrolysis of cellulose is strongly dependent on the
sulfonation temperature of the carbon materials; 250 1C-
sulfonation was proved to generate a high acid density and
meanwhile did not cause a severe decrease in the specific
surface area. In addition, the carbon source also has a great
impact on the acid density of the sulfonated carbons.
The correlation between the acid density and the catalytic
performance established here will guide the design of new solid
acids for a variety of acid-catalyzed reactions.
Support from the Natural Science Foundation of China
(
NSFC Nos. 20773124, 20903089) and from the 973 Program
of China (2009CB226102) are gratefully acknowledged
Fig. 1 Hydrolysis of cellulose over different carbons sulfonated at
50 1C. The yield of water soluble by-products was calculated from the
difference between the conversion of cellulose and the yield of glucose
according to ref. 13.
2
Notes and references
1 R. Rinaldi and F. Schu
H. Li, W. Wanga and J. F. Deng, J. Catal., 2000, 191, 257;
X. Liang, C. J. Liu and P. Y. Kuai, Green Chem., 2008, 10,
1318; T. Stahlberg, M. G. Sørensen and A. Riisager, Green Chem.,
¨
th, Energy Environ. Sci., 2009, 2, 610.
2
a type of ordered mesoporous material, gave a conversion of
cellulose of 94.4% and a glucose yield of 74.5%, which almost
˚
1
3
2010, 12, 321; M. S. Holm, S. Saravanamurugan and E. Taarning,
Science, 2010, 328, 602; W. Yang and A. Sen, ChemSusChem,
doubles that reported by Onda et al. This is also the highest
glucose yield achieved on solid acids to date. Correlating with the
acid densities of the samples in Table 2, one can find that the
catalytic performance is well consistent with the acid densities of
the carbon materials except for the Cell-Carbon (cellulose-derived
2
010, 3, 597.
3 L. T. Fan, M. M. Gharpuray and Y. H. Lee, Cellulose Hydrolysis,
Springer, Berlin, 1987; M. A. Harmer, A. Fan, A. Liauwa and
R. K. Kumarc, Chem. Commun., 2009, 6610.
4
Y. P. Zhang, M. E. Himmel and J. R. Mielenz, Biotechnol. Adv.,
006, 24, 452.
carbon). Although possessing
a high acid density, the
2
Cell-Carbon has a very low specific surface area which signifi-
cantly decreases the available active sites for the hydrolysis of
cellulose. On the other hand, the sulfonated CMK-3 has a high
5 M. Sasaki, Z. Fang, Y. Fukushima, T. Adschiri and K. Arai, Ind.
Eng. Chem. Res., 2000, 39, 2883; Y. Zhao, W. J. Lu, H. T. Wang
and D. Li, Environ. Sci. Technol., 2009, 43, 1565.
6
R. P. Swatloski, S. K. Spear, J. D. Holbrey and R. D. Rogers,
J. Am. Chem. Soc., 2002, 124, 4974.
2
À1
acid density and a reasonably large surface area (412 m g ),
both of which are required for the hydrolysis of cellulose into
glucose. In addition, the mesoporous structure also facilitates the
transportation of large molecules (such as glucose, cellobiose,
cellotriose) in comparison with microporous carbons. The
advantages of mesoporous carbons as the catalyst supports have
recently been demonstrated in hydrogenolysis of cellulose as well
7
C. Li and Z. K. Zhao, Adv. Synth. Catal., 2007, 349, 1847;
A. S. Amarasekara and O. S. Owereh, Ind. Eng. Chem. Res.,
2
009, 48, 10152.
8
9
A. Fukuoka and P. L. Dhepe, Angew. Chem., Int. Ed., 2006, 45,
5161.
C. Luo, S. Wang and H. C. Liu, Angew. Chem., Int. Ed., 2007, 46,
7636.
1
0 N. Ji, T. Zhang, M. Y. Zheng, A. Q. Wang, H. Wang, X. D. Wang
and J. G. Chen, Angew. Chem., Int. Ed., 2008, 47, 8510.
12,19
as hydrolysis of cellulose.
In summary, we have developed a highly active and selective
solid acid catalyst for the hydrolysis of cellulose into glucose.
The best result was obtained by using 250 1C-sulfonated
CMK-3 as the catalyst, with the cellulose conversion of
11 M. Y. Zheng, A. Q. Wang, N. Ji, J. F. Pang, X. D. Wang and
T. Zhang, ChemSusChem, 2010, 3, 63.
1
2 Y. H. Zhang, A. Q. Wang and T. Zhang, Chem. Commun., 2010,
6, 862.
4
13 A. Onda, T. Ochi and K. Yanagisawa, Green Chem., 2008, 10, 1033;
A. Onda, T. Ochi and K. Yanagisawa, Top. Catal., 2009, 52, 801.
9
4.4% and glucose yield of 74.5% which is the highest value
1
4 M. Toda, A. Takagaki, M. Okamura, J. N. Kondo, S. Hayashi,
K. Domen and M. Hara, Nature, 2005, 438, 178; S. Suganuma,
K. Nakajima, M. Kitano, D. Yamaguchi, H. Kato, S. Hayashi and
M. Hara, J. Am. Chem. Soc., 2008, 130, 12787; Y. Y. Wu,
Z. H. Fu, D. L. Yin, Q. Xu, F. L. Liu, C. L. Lu and L. Q. Mao,
Green Chem., 2010, 12, 696.
obtained so far on solid acids. The acid density required for
Table 2 The surface properties of different carbons sulfonated
at 250 1C
Acid
density
mmol g
Acid
density
mmol g
15 R. Rinaldi, R. Palkovits and F. Schu
2008, 47, 8047.
16 K. Shimizu, H. Furukawa, N. Kobayashi, Y. Itaya and
¨
th, Angew. Chem., Int. Ed.,
a
H /
b/
c/
–SO
mmol g
3
BET
S /
2
À1
À1
À1
À1
m g
Cat.
A. Satsuma, Green Chem., 2009, 11, 1627.
7 A. Takagaki, C. Tagusagawa and K. Domen, Chem. Commun.,
008, 5363.
8 ACB refers to acetylene carbon black, MWCNT refers to multiwall
carbon nanotube, Cell-Carbon was prepared by pyrolysis of
cellulose at 400 1C according to ref. 14, Resin-Carbon was
prepared by pyrolysis of resin at 800 1C, and CSAC refers to
coconut shell active carbon. For preparation details see supporting
information.
ACB
0.02
0.02
0.63
2.01
0.28
0.33
0.24
0.26
2.39
3.96
2.08
1.10
0.07
0.05
0.88
1.22
0.45
0.28
89
96
412
6
834
981
1
1
MWCNT
CMK-3
Cell-Carbon
Resin-Carbon
CSAC
2
d
a
b
3
The content of –SO H was measured by ICP-AES. Acid density
c
was determined by a titration method. Acid density was measured by
d
19 H. Kobayashi, T. Komanoya, K. Hara and A. Fukuoka,
ChemSusChem, 2010, 3, 440.
3
NH -adsorption. Cell-Carbon was sulfonated at 200 1C.
This journal is c The Royal Society of Chemistry 2010
Chem. Commun., 2010, 46, 6935–6937 6937