Hydrolysis of cellulose by using catalytic amounts of FeCl2 in Ionic liquids

Article abstract of DOI:10.1002/cssc.201000184

Microcrystalline cellulose (MCC) is hydrolyzed to an appreciable extent (70-%) by using 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate (IL-1) as effective catalyst. Valuable chemicals, such as 5-hydroxymethyl furfural (HMF) and furfural, are obtained in relatively high yields (15-% and 7-%, respectively). Interestingly, the introduction of FeCl₂ as catalyst into IL-1 further enhances the catalytic activity, as proved by the higher conversion of MCC (84-%) and higher yields of HMF and furfural (34-% and 19-%, respectively) under the same experimental conditions, although small amounts of levulinic acid (LA) and total reducing sugars (TRS) were also found. The hydrolysis of MCC scarcely proceeded, or showed a lower efficiency, in the absence of catalyst (4-%) or with Al₂O₃ (7-%), inorganic acids (≤65-%), or several other ionic liquids (≤24-%) as catalyst. Dimers of furan compounds were detected as the main byproducts, as analyzed by HPLC-MS; from the mass spectrometry analysis, the components of the gas-phase products were determined to be methane, ethane, CO, CO₂, and H₂. A mechanism to explain the high activity of FeCl₂ in the IL-1 system is proposed. Recycling of the IL-1 catalyst showed an almost constant activity during five successive trials. The simple and effective catalyst system may prove valuable in facilitating the energy-efficient and cost-effective conversion of biomass into biofuels and platform chemicals. The use of FeCl₂ as catalyst in an ionic liquid, 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate (IL-1), is found to be effective for the hydrolysis of microcrystalline cellulose (MCC). The conversion reaches >84-%, and yields of 5-hydroxymethylfurfural (HMF) and furfural of 34-% and 19-%, respectively, are achieved; small amounts of levulinic acid and total reducing sugars are also generated.

Full text of DOI:10.1002/cssc.201000184

DOI: 10.1002/cssc.201000184
Hydrolysis of Cellulose by Using Catalytic Amounts of
FeCl in Ionic Liquids
2
[a, b]
[a]
[a]
Furong Tao,
Huanling Song, and Lingjun Chou*
Microcrystalline cellulose (MCC) is hydrolyzed to an appreciable
extent (70%) by using 1-(4-sulfonic acid) butyl-3-methylimida-
zolium hydrogen sulfate (IL-1) as effective catalyst. Valuable
chemicals, such as 5-hydroxymethyl furfural (HMF) and furfural,
are obtained in relatively high yields (15% and 7%, respective-
ciency, in the absence of catalyst (4%) or with Al O (7%), inor-
2
3
ganic acids (ꢀ65%), or several other ionic liquids (ꢀ24%) as
catalyst. Dimers of furan compounds were detected as the
main byproducts, as analyzed by HPLC–MS; from the mass
spectrometry analysis, the components of the gas-phase prod-
ucts were determined to be methane, ethane, CO, CO , and H .
ly). Interestingly, the introduction of FeCl as catalyst into IL-1
2
2
2
further enhances the app:ds:catalytic activity, as proved by the
higher conversion of MCC (84%) and higher yields of HMF and
furfural (34% and 19%, respectively) under the same experi-
mental conditions, although small amounts of levulinic acid
A mechanism to explain the high activity of FeCl in the IL-1
2
system is proposed. Recycling of the IL-1 catalyst showed an
almost constant activity during five successive trials. The
simple and effective catalyst system may prove valuable in fa-
cilitating the energy-efficient and cost-effective conversion of
biomass into biofuels and platform chemicals.
(LA) and total reducing sugars (TRS) were also found. The hy-
drolysis of MCC scarcely proceeded, or showed a lower effi-
Introduction
The diminishing fossil fuel reserves and global warming effects
have become major concerns, and the search for sustainable
catalyst, however, considering their toxicity and environmental
pollution, in the present paper, we first report our results on
the hydrolysis of microcrystalline cellulose (MCC), which was
catalyzed with 1-(4-sulfonic acid) butyl-3-methylimidazolium
hydrogen sulfate (IL-1) by addition of a catalytic amount of
[
1]
and alternative energy is of critical importance. Recently, vari-
ous biomass resources which can be transformed into fuels,
chemicals, and energy products have been furiously dis-
[
2–8]
cussed.
The focus is on the catalytic conversion of biomass
FeCl under mild conditions. The conversion of MCC is shown
2
from cellulose, which is the most abundant natural polymeric
carbon source in the world. Unfortunately, it is almost impossi-
ble to solubilize cellulose with water and common organic sol-
in Scheme 1.
[
9]
vents because of its special complex structure.
In recent years, extensive research and development pro- Results and Discussion
grams have been initiated worldwide to convert lignocellulosic
Hydrolysis of MCC with various catalysts
biomass into valuable products, such as monosaccharides, eth-
[
10–14]
ylene glycol, ethanol, and 5-HMF.
However, the hydrolysis
Table 1 summarizes the different catalytic performances using
various acidic catalysts on the reaction system. For various
acids as catalysts, the present system was effective on the hy-
drolysis of MCC. The conversion of MCC was only 3.90% when
the reaction was carried out in the absence of the catalyst
(Table 1, entry 1). As the reaction was performed with a catalyt-
of cellulose is usually catalyzed either by enzymes or by inor-
ganic proton-acid catalysts, and none of the known methods
[
15–19]
are yet cost-effective for large-scale applications.
Accord-
ingly, it is essential to design solvents for cellulose and to pro-
pose a system which requires minimal energy.
Pioneer studies indicated that the ionic liquid (IL) 1-butyl-3-
ic amount of FeCl
conversion could be up to 84.42%. The presence of Al O
2 3
2
, using IL-1 as catalyst (Table 1, entry 9), the
methylimidazolium chloride (C mimCl) was a powerful solvent
4
[
20]
for cellulose, and soon later, the solubilizing mechanism of
cellulose in ILs using NMR spectroscopy was also investigated
[
a] Dr. F. Tao, Dr. H. Song, Prof. L. Chou
State Key Laboratory for Oxo Synthesis and Selective Oxidation
Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences
Lanzhou 730000 (PR China)
[
21]
by Robin Rogers et al. Since then, it has attracted much at-
tention and subsequent chemical hydrolysis and hydrogenoly-
[
22]
Fax: (+86)931 4968129
E-mail: ljchou@licp.cas.cn
sis of cellulose in ILs were reported. In particular, the metal
ions in ionic liquid was demonstrated to be an efficient catalyst
[
13,23–25]
[b] Dr. F. Tao
Graduate School of Chinese Academy of Sciences
Beijing 100049 (PR China)
system for the conversion of cellulose into furans.
Therefore, we imagined that metal ions in acidic ILs might
act as an eco-friendly polar catalyst system for the hydrolysis
of cellulose. Earlier researchers mostly used CrCl or CrCl as co-
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201000184.
2
3
1
298
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2010, 3, 1298 – 1303

Hydrolysis of Cellulose
Scheme 1. Schematic illustration of products from microcrystalline cellulose.
Table 1. Hydrolysis of MCC with various acidic catalysts: 0.5 g MCC, 1.0 g
2
catalysts, 0.2m FeCl (1 mL), MIBK (8 mL), T=1508C, t=300 min, P=
101325 Pa.
Entry Catalysts
Yield [%]
Conv. [%]
HMF Furfural Levulinic acid TRS
[
a]
1
2
3
4
5
6
7
8
9
1
None
None
0
0
0
0
0
2.97
5.91
5.62
6.14
3.75
0
0
0
2.42
2.47
1.97
3.90
4.32
7.05
Al
HCl
HNO
2
O
3
2.58
14.41
11.75
9.51
16.37
10.89
33.81 18.61
9.08
15.43
[
[
[
[
b]
b]
b]
b]
8.03
4.21
3.02
7.76
2.46
5.93
5.39
2.56
26.25 62.34
21.37 51.28
17.98 49.65
25.36 65.24
1.58 23.68
8.35 84.42
17.62 53.17
10.24 70.00
3
H
H
3
PO
4
2
SO
4
C
4
mimH
IL-1
SO
IL-1
2 4
PO
[
c]
0
H
2
4
4.81
7.45
[
c]
11
[
a] The reaction was performed in the absence of catalyst. [b] The reac-
tion was performed with 0.2m inorganic acids. [c] The reaction was per-
formed with 1 mL H O (not FeCl ).
Figure 1. The hydrolysis results for MCC in different ionic liquids: MCC
0.5 g), ionic liquids (1.0 g), 0.2m FeCl (1 mL), MIBK (8 mL), T=1508C,
t=300 min, P=101325 Pa.
2
2
(
2
(Table 1, entry 3), having both acidic and basic character, result-
ing with the results in the absence of FeCl (Table 1, entry 11),
2
ed in a conversion of 7.05%. The reactions which were cata-
lyzed by a protonic acid (Table 1, entries 4–7) were also effec-
tive with the conversions ranging from 49-65%, and the main
products were the total reducing sugars (TRS). Collectively, the
results above suggested that the strong acidity of a solution
was an important aspect in promoting the hydrolysis of MCC.
Different ionic liquids as catalysts were also investigated,
which are shown in Figure 1. The conversions of MCC in
C mimBF , C mimPF , and C mimBr were slightly lower than
the conversion of MCC increased by 14% in the presence of
FeCl , and correspondingly, the yields of HMF and furfural
2
went up to 33.8% and 18.6%, respectively. When the reaction
was performed with FeCl2 in the absence of IL-1 (Table 1,
entry 2), the conversion was only 4.32%, thus, we suggested
that ILs-1 and FeCl have synergistic and coordination interac-
2
tions, which can facilitate the hydrolysis of MCC.
4
4
4
6
4
Effect of iron salts on the hydrolysis of MCC
the one without ionic liquids; these results are in agreement
[
20]
with the research results of Rogers et al. It was also shown
that the conversion of MCC in IL-1 (84%) was much higher
than in C mimCl (8%) and C mimH PO (24%), which further il-
Knowing the promoting effect of FeCl , other iron salts were
2
investigated. As shown in Table 2, the existence of iron salts
can improve the hydrolysis of MCC. Compared with other iron
salts, the promoting effects of FeSO and FeCl were remark-
4
4
2
4
luminated the importance of the solution acidity. The functions
of IL-1 in the reaction were considered to be two-fold. It can
dissolve MCC comparable to other ionic liquids, but also its
acidity can promote the hydrolysis of MCC effectively. Compar-
4
2
3
+
2+
able. In the presence of Fe or Fe , the yields of HMF and
furfural were also improved. The reason for the promotional ef-
3
+
2+
fects of the iron salts may be due to the Fe or Fe coordi-
ChemSusChem 2010, 3, 1298 – 1303
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
1299

L. Chou et al.
Table 2. Hydrolysis of MCC with various iron salts: MCC (0.5 g), IL-1
1.0 g), 0.2m iron salts (1 mL), MIBK (8 mL), T=1508C, t=300 min, P=
01325 Pa.
(
1
Iron salts
Yields [%]
Levulinic acid
Conv. [%]
HMF
Furfural
TRS
none
15.43
33.81
30.15
31.73
28.45
21.96
7.45
18.61
16.48
17.09
17.75
7.38
2.56
5.93
5.47
6.02
4.88
3.26
10.24
8.35
7.14
7.83
7.74
5.36
70.00
84.42
84.18
84.14
80.28
57.60
FeCl
FeCl
2
3
FeSO
Fe (SO
Fe(NO
4
2
4 3
)
3 3
)
3
+
2+
nation interaction; in addition, Fe or Fe could play an im-
portant role in the selective dehydration of glucose, which im-
proved the yields of HMF and furfural. Based on the decreasing
Figure 3. Effect of the reaction time: MCC (0.5 g), IL-1 (1.0 g), 0.2m FeCl
(1 mL), MIBK (8 mL), T=1508C, P=101325 Pa.
2
conversion of MCC in the presence of Fe(NO ) , the nitrate
3
3
À
anion is most likely unfavorable to the reaction. Typically, NO3
cannot directly be used as a single ligand to form stable coor-
dination compounds, therefore we concluded that the forma-
tion of metal nitrate complex was difficult relative to the
others. However, the selectivity of HMF and furfural was also
improved in the presence of Fe(NO ) , which confirmed the
decreased. These results were in accordance with the hydroly-
sis path of MCC; the hydrolysis of glucose was more complete.
We considered that there were two pathways for the decom-
position of HMF in the hydrolysis of MCC which was catalyzed
by IL-1, as depicted in Scheme 1. One is the rehydration of
HMF into levulinic acid and formic acid and the other is the
loss of formaldehyde in HMF to furfural.
3
3
3
+
promoting effect of Fe
.
Influence of reaction conditions on the hydrolysis of MCC
We also investigated the influence of water content on the
reaction. As shown in Figure 4, when VMIBK: VFeCl2 was 8:1, we
obtained the optimum results; the yields of HMF and furfural
reached 33.87% and 18.61%, respectively. As the water con-
tent increased, the selectivity of the products decreased, in ac-
Figures 2 and 3 show the effects of reaction temperature and
time on MCC hydrolysis. As the figures show, the reaction tem-
perature and time had large effects on both the MCC conver-
sion and product selectivity. The MCC conversion was 84.48%,
the HMF and furfural yields were 33.87% and 18.61%, respec-
tively, at 1508C for 300 min reaction time. The HMF yield in-
creased from 6.58% to 33.87% when conditions changed from
[26–27]
cordance with the previous reports,
which indicated that
water has a negative effect on the dehydration of sugars to
HMF. The effect of the IL-1 dosage on MCC hydrolysis is shown
in Figure S1 (see the Supporting Information); the amounts of
IL-1 used were 0.5 g, 1.0 g, 2.0 g, 3.0 g. In the absence of the
catalyst, at a reaction temperature of 1508C, the MCC conver-
sion was only 4.32% for a reaction time of 300 min (Table 1,
60 min to 300 min for 1508C reaction temperature, and the
time curve shows a similar pattern. As the reaction tempera-
ture was increased and the reaction time was prolonged, the
yield of levulinic acid increased, but in contrast, the TRS yields
Figure 2. Effect of the reaction temperature: MCC (0.5 g), IL-1 (1.0 g), 0.2m
FeCl (1 mL), MIBK (8 mL), t=300 min, P=101325 Pa.
2
Figure 4. Influence of water content on the hydrolysis of MCC: MCC (0.5 g),
IL-1 (1.0 g), MIBK (8 mL), T=1508C, t=300 min, P=101325 Pa.
1
300
www.chemsuschem.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2010, 3, 1298 – 1303

Hydrolysis of Cellulose
[
29]
entry 2). In the presence of IL-1 (0.5 g), the yield of HMF was
up to 20%. When the IL-1 dosage increased from 0.5 g to
as reported by Rogers et al.
We suggested that [FeCl2-
2nÀ
(SO ) ] anion played a role in proton transfer, facilitating mu-
4
n
1
2
.0 g, the HMF and furfural yields remarkably increased from
0% and 14% to 34% and 19%, respectively. However, when
tarotation of glucose in IL-1. These complexes would promote
rapid conversion of the a-anomers of glucose to the b-anom-
ers through hydrogen bonding between the chloride anions or
the amount of IL-1 was increased from 1.0 g to 3.0 g, there
was little change in the HMF and furfural yields, which implied
that there were sufficient catalytic active sites available for the
substrate MCC in the system under the experimental condi-
tions.
2À
oxygen atom in SO4 and the hydroxyl groups.
The ring aldoses could then reverse to a straight-chain form,
combining with the iron complex to form an enolate structure.
Enolate formation would enable conversion of the aldoses into
ketoses, followed by dehydration to produce HMF. Then with
the help of an acidic solution, the HMF was combined with
water to generate levulinic acid or lost formaldehyde to pro-
For the conversion of MCC, the FTIR spectra of the solid resi-
dues and hydrolysis products catalyzed by IL-1 are shown in
Figure 5a and b, respectively. It is obviously different from (a)
2
À
duce furfural. To confirm the coordination of SO4 in the hy-
drolysis system, the hydrolysis of glucose in 0.2m H SO was
2
4
carried out. The results showed that in the H SO4 catalyst
2
system, by adding a catalytic amount of FeCl , the yields of
2
HMF and furfural increased by 7% and 2% (Table 1, entry 7
and entry 10), which confirmed that the coordination effect of
2À
SO4 and FeCl promoted the hydrolysis of glucose.
2
Moreover, because all the ionic species may be detected by
electron spray ionization mass spectrometry (ESI–MS) analysis,
the interaction between IL-1 and FeCl was also studied by
2
ESI–MS. As shown in Figure S2 (see the Supporting Informa-
tion), the ESI–MS gave rise to complicated spectra both in pos-
itive and negative ion modes. Under the ESI negative ion
-
mode, a proton-removing quasi-molecular ion [M’ÀH] from
IL-1 was formed, an adduct ion from the complex (M=IL-
1
+FeCl ) was [M+Cl]-(m/z 478.7), and there were several other
2
peaks
in
the
ESI–MS
spectrum:
[HSO ]-(m/z 97.1),
4
Figure 5. The FTIR spectra of a) solid residues catalyzed with IL-1; b) hydroly-
[
[
M+Cl+H SO ]-(m/z 576.7), [M+Cl+2H SO ]-(m/z 674.7), and
2
4
2
4
sis products catalyzed with IL-1: MCC (0.5 g), IL-1 (1.0 g), 0.2m FeCl
MIBK (8 mL), T=1508C, t=300 min, P=101325 Pa.
2
(1 mL),
M+Cl+NaÀH+2H SO ]-(m/z 794.6). The ion peak (m/z 280.0)
2
4
was the background and the existence of H SO was due to
2
4
the inadequate purification of IL-1. The results above con-
firmed the rationality of the mechanism.
and (b) in some spectral bands. The absorbances at around
À1
À1
3
346 cm and 3122 cm are associated with the hydroxyl
In addition, small amounts of important byproducts were
obtained. Through gel-permeation chromatography (GPC)
analysis, the molecular weight distributions of the hydrolysis
products for MCC were found to be below 2000 Da. Dimers of
furan compounds were detected by LC–MSD and second order
mass spectra analysis. The gas products were also analyzed
using mass spectrometry; methane, ethane, CO, CO , and H
À1
group stretching vibrational bands. Around 2901 cm and
À1
1
368 cm are methyl, methylene, and methyne stretching vi-
À1
À1
brational bands. The absorbance at 1370 cm , 1282 cm , and
À1
1
165 cm are the characteristic bands of CÀOÀC stretching vi-
brational bands. Collectively, these data suggested that both
spectra shared the framework of sugars. However, spectrum
2
2
À1
(
b) shows additional bands. The band at 1714 cm was as-
were detected for the hydrolysis of MCC at 1508C for 300 min
signed to C=O stretching vibrational bands; the absorbance at
reaction.
À1
1
641 cm was assigned to C=C stretching vibrational bands;
À1
À1
and the absorbance bands at 973 cm , 1165 cm , and
Recycling of IL-1 for the hydrolysis of MCC
À1
[28]
1208 cm proved the existence of a furan ring. Based on
the results of the FTIR spectra, with our present hydrolysis
system, it was confirmed the existence of furan compounds
and the complicated distribution of hydrolysis products, which
were catalyzed by IL-1.
Catalyst recycling is always important in metal-catalyzed liquid-
phase reactions. In our hydrolysis system, the FeCl and IL-1
2
catalysts can be reused directly after extraction of products
with diethyl ether and water, then pouring out the solvent
MIBK and water. Figure 6 shows the recycling of FeCl and IL-1
2
over five runs. It can be seen from Figure 6 that although a de-
crease of the conversion from 84% to 77% was observed in
the second run, no further obvious decrease in activity was ob-
served in the subsequent runs, that is to say, a stable MCC con-
version of about 74% could be obtained. In addition, the
yields of HMF, furfural, and levulinic acid had only slight loss
Mechanism of cellulose and glucose transformation to HMF
and furfural
To explain the results of the reactions in the presence of FeCl2,
we proposed a mechanism (Scheme 2) in which FeCl in IL-1
2
2
nÀ
forms [FeCl (SO ) ]
complexes in a similar manner to LnCl3
2
4 n
ChemSusChem 2010, 3, 1298 – 1303
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
1301

L. Chou et al.
over five repeated runs, about
26%, 14%, and 4% could be ob-
tained, respectively. The de-
crease of activity in the second
run could be attributed to in-
complete extraction of byprod-
uct from the liquid phase, which
may limit the conversion of MCC
and the further hydrolysis of glu-
cose. How to improve the reusa-
bility of the catalysts remains a
problem for a future study.
Conclusions
FeCl2 in IL-1 was demonstrated
to function as a highly active
catalyst system for the direct hy-
drolysis of microcrystalline cellu-
lose. By comparing different
acidic catalysts, we indicated
that acidic ionic liquids have
higher activity than protonic
acid. High conversion, usually
84–85%, was realized under
mild condition with a catalytic
amount of FeCl in the reaction
2
catalyzed by IL-1. We considered
that there was not only a syner-
gistic interaction but also a coor-
dination interaction between IL-
1
and FeCl . Our methods pro-
2
vided a simple and effective cat-
alyst system to facilitate energy-
efficient and cost-effective con-
version of biomass into impor-
tant platform chemicals. Howev-
er, a detailed mechanism in-
2
Scheme 2. Putative mechanism of FeCl promoted conversion of glucose into HMF and furfural.
volved in the coordination of IL-1 and FeCl and the separation
2
and purification of the main products are remaining subjects
of future studies.
Experimental Section
Preparation of IL-1 (Scheme S1, see the Supporting Information): N-
Methyl imidazole (16.4 g, 0.2 mol) and 1,4-butanesultone (27.28 g,
0
1
.2 mol) were mixed in a flask (250 mL) and stirred at 42–458C for
7 h to give a white solid, which was grinded, washed repeatedly
with a small portion of ether, filtrated, and vacuum dried for 4 h at
room temperature. Equimolar white solid was added to 98%
H SO , and the mixture was stirred at 808C for 6 h, then we ob-
2
4
tained the sticky ionic liquid of 1-(4-sulfonic acid) butyl-3-methyl-
1
imidazolium hydrogen sulfate (IL-1). H NMR (400 MHz, D O): d=
2
1
7
.53 (m, 2H), 1.80 (m, 2H), 2.72 (t, 2H), 3.67 (s, 3H), 4.02 (t, 2H),
.24 (d, 2H), 8.47 (s, 1H); ESI–MS: m/z(+) 218.6, m/z(À) 96.3 ppm.
Other ILs, such as C mimBF , C mimPF , C mimBr, C mimCl, and
Figure 6. Recycling of IL-1 for the hydrolysis of MCC to the main products:
4
4
4
6
4
4
MCC (0.5 g), IL-1 (1.0 g), 0.2m FeCl
t=300 min, P=101325 Pa.
2
(1 mL), MIBK (8 mL), T=1508C,
C mimH PO , were synthesized according to the method reported
4 2 4
by Jairton Dupont.
[30]
1
302
www.chemsuschem.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 2010, 3, 1298 – 1303

Hydrolysis of Cellulose
Typical procedures for microcrystalline cellulose hydrolysis in IL-1:
Experiments were carried out in a stainless steel autoclave with a
glass liner tube (100 mL); the reactor was loaded with MCC (0.5 g),
catalysts (1.0 g), H O (1 mL, 0.2m FeCl ), and 4-methyl-2-Pentanone
[5] G. Yong, Y. Zhang, J. Y. Ying, Angew. Chem. 2008, 120, 9485–9488;
Angew. Chem. Int. Ed. 2008, 47, 9345–9348.
[
6] Wahyudiono, M. Sasaki, M. Goto, Chem. Eng. Process 2008, 47, 1609–
619.
[7] T. Rogalinski, T. Ingram, G. Brunner, J. Supercrit. Fluids 2008, 47, 54–63.
1
2
2
[31]
(
8 mL). The reactor was then placed into an electrical heating
[
[
8] W. Partenheimer, Adv. Synth. Catal. 2009, 351, 456–466.
9] M. E. Himmel, S. Y. Ding, D. K. Johnson, Science 2007, 315, 804–807.
jacket to heat the system to the desired temperature. After the ap-
pointed reaction time reached, the reactor was removed from the
electrical heating jacket and quickly quenched in a cool water
bath. The liquid and solid fractions were collected by repeatedly
washing the inside of the reactor with distilled water and pure eth-
anol. The recovered solid residue was dried at 1008C for 8 h, then
weighed to calculate the yield of liquefaction. After filtration, ex-
traction, and separation, the organic and water phases were col-
lected to characterize the products. All results were replicated at
least three times.
[
10] N. Ji, T. Zhang, M. Y. Zheng, A. Q. Wang, H. Wang, X. D. Wang, J. G.
Chen, Angew. Chem. 2008, 120, 8638–8641; Angew. Chem. Int. Ed. 2008,
47, 8510–8513; Angew. Chem. Int. Ed. 2008, 47, 8510–8513.
[11] C. Li, Q. Wang, Z. K. Zhao, Green Chem. 2008, 10, 177–182.
12] C. Li, Z. K. Zhao, Adv. Synth. Catal. 2007, 349, 1847–1850.
[
[
13] Y. Su, H. M. Brown, X. Huang, Z. C. Zhang, Appl. Catal. A: Gen. 2009, 361,
1
17–142.
14] Y. Romꢂn-Leshkov, J. N. Chheda, J. A. Dumesic, Science 2006, 312, 1933–
937.
[
1
[
[
15] Z. Xu, Q. Wang, Biomass Bioenergy 2007, 31, 162–167.
16] B. E. Dale, C. K. Leong, T. K. Pham, Bioresour. Technol. 2005, 96, 673–686.
After the reaction, the amount of total reducing sugars was deter-
[32]
[17] N. S. Mosier, A. Sarikaya, C. M. Ladisch, M. R. Ladisch, Biotechnol. Prog.
001, 17, 474–480.
mined by a phenol–sulfuric acid method;
other liquid-phase
2
products were analyzed by HPLC (Waters 2695) and LC–MSD (Agi-
[
[
[
18] Y. H. P. Zhang, L. R. Lynd, Anal. Biochem. 2003, 322, 225–232.
19] G. Stephanopoulos, Science 2007, 315, 801–804.
20] R. P. Swatloski, S. K. Spear, J. D. Holbrey, R. D. Rogers, J. Am. Chem. Soc.
2002, 124, 4974–4975.
[21] R. C. Remsing, R. P. Swatloski, R. D. Rogers, G. Moyna, Chem. Commun.
2006, 1271–1273.
22] S. Zhu, Y. Wu, Q. Chen, G. Wu, Green Chem. 2006, 8, 325–327.
23] Z. H. Zhang, Z. K. Zhao, Bioresour. Technol. 2009, 101, 1111–1114.
24] J. B. Binder, R. T. Raines, J. Am. Chem. Soc. 2009, 131, 1979–1985.
25] H. B. Zhao, J. E. Holladay, H. Brown, Z. C. Zhang, Science 2007, 316,
[33,34]
lent 1100).
The gas products were detected by mass spectrom-
etry (Inficon, Transpector 2); FTIR analysis were carried out on Nico-
let Nexus 870 and the ESI–MS analysis were performed on an Agi-
lent 1100 series LC–MSD Trap VL equipped with an Agilent 1100
detector (see the Supporting Information). Cellulose conversion
was determined by the change of cellulose weight before and
after the reaction. The yields of the products were calculated from
the equation: Yield (%)=(weight of products)/(weight of cellulose
put into the reactor)ꢁ100%.
[
[
[
[
1
597–1599.
26] X. H. Qi, M. Watanabe, T. M. Aida, R. L. Smith, Green Chem. 2008, 10,
99–805.
[
[
7
Acknowledgements
27] S. Q. Hu, Z. F. Zhang, Y. X. Zhou, B. X. Han, H. L. Fan, W. J. Li, J. L. Song, Y.
Xie, Green Chem. 2008, 10, 1280–1283.
We gratefully acknowledge the financial support of the State Key
Laboratory for Oxo Synthesis and Selective Oxidation of China,
and Xiaoxue Hu (Lanzhou Institute of Chemical Physics, Chinese
Academy of Sciences) for her help during this study.
[28] L. H. Yao, C. A. Su, L. Q. Qi, C. J. Liu, Y. M. Hu, H. Zhao, Spectrosc. Spectral
Anal. (Beijing, China) 1999, 1, 32–34.
[
29] C. C. Hines, D. B. Cordes, S. T. Griffin, S. I. Watts, V. A. Cocalia, R. D.
Rogers, New J. Chem. 2008, 32, 872–877.
[30] J. Dupont, C. S. Consorti, R. F. Souza, Org. Synthesis 2004, 10, 184–188.
[
31] Y. Romꢂn-Leshkow, J. N. Chheda, J. A. Dumesic, Science 2006, 312,
933–1937.
32] Q. Dong, L. Y. Zheng, J. N. Fang, Chin. Pham. J. 1996, 31, 550–553.
1
Keywords: biomass
· carbohydrates · hydrolysis · ionic
[
liquids · sustainable chemistry
[33] M. J. Nozal, J. L. Bernal, L. Toribio, J. J. Jimꢃnez, M. T. Martin, J. Chroma-
togr. A 2001, 917, 95–103.
[
34] E. Ferrer, A. Alegria, R. Farrꢃ, P. Abellꢂn, F. Romero, J. Chromatogr. A
002, 947, 85–95.
[
[
1] J. Goldemberg, Science 2007, 315, 808–810.
2] M. Stçcker, Angew. Chem. 2008, 120, 9340–9351; Angew. Chem. Int. Ed.
008, 47, 9200–9211.
3] N. Boz, N. Degirmenbasi, D. M. Kalyon, Appl. Catal. B: Environm. 2009,
9, 590–596.
2
2
[
[
8
Received: June 23, 2010
4] A. Effendi, H. Gerhauser, A. V. Bridgwater, Renewable Sustainable Energy
Rev. 2008, 12, 2092–2116.
Revised: August 16, 2010
Published online on October 8, 2010
ChemSusChem 2010, 3, 1298 – 1303
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemsuschem.org
1303