Catalytic conversion of cellulose to chemicals in ionic liquid

Article abstract of DOI:10.1016/j.carres.2010.10.022

A simple and effective route for the production of 5-hydroxymethyl furfural (HMF) and furfural from microcrystalline cellulose (MCC) has been developed. CoSO₄ in an ionic liquid, 1-(4-sulfonic acid) butyl-3- methylimidazolium hydrogen sulfate (IL-1), was found to be an efficient catalyst for the hydrolysis of cellulose at 150 °C, which led to 84% conversion of MCC after 300 min reaction time. In the presence of a catalytic amount of CoSO₄, the yields of HMF and furfural were up to 24% and 17%, respectively; a small amount of levulinic acid (LA) and reducing sugars (8% and 4%, respectively) were also generated. Dimers of furan compounds were detected as the main by-products through HPLC-MS, and with the help of mass spectrometric analysis, the components of gas products were methane, ethane, CO, CO _2, and H₂. A mechanism for the CoSO₄-IL-1 hydrolysis system was proposed and IL-1 was recycled for the first time, which exhibited favorable catalytic activity over five repeated runs. This catalytic system may be valuable to facilitate energy-efficient and cost-effective conversion of biomass into biofuels and platform chemicals.

Full text of DOI:10.1016/j.carres.2010.10.022

Carbohydrate Research 346 (2011) 58–63
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Catalytic conversion of cellulose to chemicals in ionic liquid
a,b
a
a,
⇑
Furong Tao , Huanling Song , Lingjun Chou
a
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China
Graduate School of Chinese Academy of Sciences, Beijing 100049, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple and effective route for the production of 5-hydroxymethyl furfural (HMF) and furfural from
Received 9 September 2010
Received in revised form 22 October 2010
Accepted 26 October 2010
Available online 31 October 2010
4
microcrystalline cellulose (MCC) has been developed. CoSO in an ionic liquid, 1-(4-sulfonic acid)
butyl-3-methylimidazolium hydrogen sulfate (IL-1), was found to be an efficient catalyst for the hydro-
lysis of cellulose at 150 °C, which led to 84% conversion of MCC after 300 min reaction time. In the pres-
4
ence of a catalytic amount of CoSO , the yields of HMF and furfural were up to 24% and 17%, respectively;
a small amount of levulinic acid (LA) and reducing sugars (8% and 4%, respectively) were also generated.
Dimers of furan compounds were detected as the main by-products through HPLC-MS, and with the help
Keywords:
Microcrystalline cellulose
Hydrolysis
of mass spectrometric analysis, the components of gas products were methane, ethane, CO, CO2, and H
2
. A
mechanism for the CoSO -IL-1 hydrolysis system was proposed and IL-1 was recycled for the first time,
4
Ionic liquids
which exhibited favorable catalytic activity over five repeated runs. This catalytic system may be valuable
to facilitate energy-efficient and cost-effective conversion of biomass into biofuels and platform
chemicals.
CoSO
HMF
Furfural
4
Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved.
1
. Introduction
Raines21 have shown the transformation of lignocellulosic biomass
into furans in a DMA–LiCl system at 140 °C with the yield of HMF
2
2
Prior to the discovery of inexpensive fossil fuels, our society was
up to 48%. Su et al. reported the single-step conversion of cellu-
dependent on plant biomass to meet its energy demands. Renew-
able biomass was to become a source of fuels and chemical prod-
ucts. Cellulose, which is the most abundant biomass, has been the
target of intensive research for conversion and utilization as chem-
lose into HMF using bimetal chlorides (CuCl and CrCl ) dissolved
2
3
in EmimCl; the yield of HMF reached about 55%. We believe some
of these studies on cellulose were inspired by an early report
describing effective conversion of glucose into HMF over metal
1
–4
23
icals.
The conversion of cellulose into materials that dissolve in
chlorides in an ionic liquid.
5–7
water or organic solvents has been tested for pyrolysis,
enolysis,
hydrog-
Cellulose hydrolysis is a key technology for obtaining sugars
from vegetation, such as grasses, agricultural, and wood waste, be-
cause the total reducing sugars (TRS) can be converted into a range
of important industrial chemicals, including ethanol, HMF, furfural,
8
–10
and degradation in supercritical water.11–13 These
non-catalytic processes generally require harsh conditions and are
problematic, for example requiring high temperature and high pres-
sure. As the use of catalysts allows the reaction to be carried out un-
levulinic acid (LA), and starting materials for the production of poly-
1
4–16
24,25
der milder conditions, the catalytic activities of acids
enzymes
or
mers.
Herein, we report our results on hydrolysis of cellulose,
1
7,18
have been investigated but it is still a great challenge
which was catalyzed with 1-(4-sulfonic acid) butyl-3-methylimida-
zolium hydrogen sulfate (IL-1) by the addition of a catalytic amount
today either from an environmental or an efficiency point of view.
Due to the increased interest and demand for industrial applica-
tion, more efficient catalytic systems have been recently devel-
oped; the utilization of metal ions in ionic liquids was
demonstrated efficiently for the conversion of cellulose into
hydroxymethylfurfural (HMF) and furfural. Seri et al19. reported
of CoSO
vapor pressure of the solvents). In comparison with previous stud-
ies, this method depends on non-toxic and inexpensive CoSO
4
at 150 °C for 300 min under two atmospheric pressure (the
4
,
while promising, it has more economic value. The products formed
from microcrystalline cellulose (MCC) are shown in Scheme 1.
3
that LaCl could catalyze the degradation of cellulose into HMF in
20
water at 250 °C in about 19% yield. Zhao and Zhao studied the so-
lid acid and microwave-assisted hydrolysis of cellulose in ionic liq-
uids; the yield of glucose reached 37% within 8 min. Binder and
2
2
. Experimental
.1. Materials
⇑
Corresponding author. Tel.: +86 931 4968066; fax: +86 931 4968129.
E-mail address: ljchou@licp.cas.cn (L. Chou).
Microcrystalline cellulose (extra pure, average particle size
90 lm) was a commercial product from J&K Chemical Company
0
008-6215/$ - see front matter Crown Copyright Ó 2010 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2010.10.022

F. Tao et al. / Carbohydrate Research 346 (2011) 58–63
59
OH
OH
OH
HO
O
CoSO4
IL-1
O
O
O
HO
HO
OH
HO
O
OH
OH
O
OH
n
O
OH
MCC
IL-1 CoSO4
O
H
OH
levulinic acid
O
HO
O
HMF
O
CHO
furfural
Scheme 1. Products from microcrystalline cellulose.
(
>
Beijing, China); 4-methyl-2-pentanone (AR, >90%), furfural (CP,
90%) and acetonitrile (HPLC) were purchased from Tianjin Chem-
ical Reagent Company (Tianjin, China); 1-methyl imidazole (CP,
99%), 1,4-butanesultone (AR, >99%), 1-chlorobutane (CP,
99.5%), 1-bromobutane (CP, >99.5%) were from Alfa Aesar; HMF
of the reactor with distilled water and pure ethanol. The solid res-
idues recovered were dried at 100 °C for 8 h and then weighed to
calculate the yield of liquefaction. After filtration, extraction, and
separation, the phases of organic and aqueous were collected to
characterize the products. All results were replicated at least three
times; the range of experimental errors for the HPLC analysis was
±1% and ±2% for the TRS analysis.
Cellulose conversion was determined by the change of cellulose
weight before and after the reaction. The yield of products was cal-
culated from the equation: yield (%) = (weight of products)/(weight
of cellulose put into the reactor) Â 100%.
>
>
(
>99%) was from Aldrich; and levulinic acid was purchased from
DaoCheng Chemical Company (Hong Kong, China). All other re-
agents and solvents were reagent grade and were used as received.
2
.2. Preparation of IL-1
As illustrated in Scheme 2, 16.4 g (0.2 mol) 1-methyl imidazole
and 27.28 g (0.2 mol) 1,4-butanesultone were mixed in a flask
250 mL) and stirred for 17 h at 42–45 °C. The white solid was
2.4. TRS analysis
(
recovered, ground, washed repeatedly with small portions of ether,
filtered, and dried under vacuum for 4 h at room temperature. An
equimolar amount of white solid was added to 98% H SO and
2 4
the mixture was stirred at 80 °C for 6 h. The obtained viscous liquid
was washed with ether three times and dried in vacuum to form
the ionic liquid, 1-(4-sulfonic acid) butyl-3-methylimidazolium
The yield of the total reducing sugars (TRS) was analyzed by the
2
9
phenol–sulfuric acid method. A mixture containing 0.1 mL reac-
tion sample, 0.9 mL deionized water, 1 mL 5% phenol (freshly dis-
tilled), and 5 mL 98% concentrated sulfuric acid was prepared.
The analysis was performed on HP8453 UV–vis spectrophotometer
at about 490 nm with a slit width of 0.06 mm. The concentration of
TRS was calculated based on the standard curve obtained with
glucose.
hydrogen sulfate (IL-1).26 1H NMR (400 MHz, D
2
2
O): d 1.53 (m,
H), 1.80 (m, 2H), 2.72 (t, 2H), 3.67 (s, 3H), 4.02 (t, 2H), 7.24 (d,
H), 8.47 (s, 1H); ESI-MS: m/z (+)218.6, m/z (À)96.3. Other ionic
mimBF mimPF mimBr, mimCl,
, were synthesized according to the method reported
2
liquids, such as
mimH PO
by Dupont et al.
C
4
4
,
C
4
6
,
C
4
C
4
2.5. Furfural, HMF and levulinic acid analysis
C
4
2
4
2
7
The liquid products HMF, furfural, and levulinic acid were ana-
lyzed by HPLC on a Waters Alliance 2695 series equipped with
Waters 2996 PDA Detector and an Intersil ODS-EP C18 reversed-
2
.3. Typical procedure for microcrystalline cellulose hydrolysis
in IL-1
phase column (250 Â 4.6 mm, 5
lm). During this process, the col-
umn temperature remained constant at 30 °C, while the mobile
phase applied was water–acetonitrile (15:85, v/v) at a flow rate
of 0.5 mL/min, with UV detection at 280 nm for HMF and furfural,
250 nm for levulinic acid, and the volume for each injection was
Experiments were carried out in a stainless steel autoclave with
glass liner tube (100 mL). The reactor was loaded with 0.5 g MCC,
.0 g catalysts, 1 mL of 0.2 M CoSO aq, and 8 mL 4-methyl-2-
2
4
2
8
pentanone (MIBK). The reactor was then placed into an electrical
heating jacket and it took about 20 min to reach 150 °C. After the
appointed reaction time was reached, the reactor was removed
from the electrical heating jacket and quickly quenched in a cool
water bath at atmospheric temperature and pressure. The liquid
and solid fractions were collected by repeatedly washing the inside
10 lL. The concentration of HMF, furfural, and levulinic acid was
calculated based on the standard curve obtained with standard
substances.
2.6. Dimers of furan compounds analysis
The dimers of furan compounds (liquids) were analyzed by LC-
MSD on an Agilent 1100 series LC-MSD Trap VL Equipped with Agi-
lent 1100 Detector and a ZORBAX Eclipse Plus C18 reversed-phase
O
O
O
SO3
S
N
N
N
N
N
N
N
N
column (150 Â 4.6 mm, 5
lm). During this process, the column
temperature remained constant at 25 °C, while the mobile phase
applied was water–acetonitrile (50:50, v/v) at the flow rate of
SO3
2
H SO
SO3H
30,31
4
1
.0 mL/min, with UV detection at 250 nm
and the volume for
2
L. The dry gas was N at the flow of 5 L/
each injection was 5
l
HSO4
min and the dry temperature was 350 °C. In the analysis of mass
Scheme 2. Schematic illustration of IL-1 preparation.
spectra, the ionizing gas was He.

6
0
F. Tao et al. / Carbohydrate Research 346 (2011) 58–63
In addition, the gas fraction was analyzed by mass spectrometry
Inficon, Transpector 2). Molecular weight distributions of liquid
(
phase products were measured through gel-permeation chroma-
tography (Waters 2695 GPC).
2
.7. FT-IR analysis
After the catalyzed hydrolysis reaction was completed, the or-
ganic phase was separated to carry out vacuum distillation, the dis-
tillated components (25–27 °C) were collected and submitted for
FT-IR analysis. All the FT-IR spectra were collected on an FT-IR
À1
spectrometer (Nicolet Nexus 870) with a resolution of 4 cm
À1
and 64 scans in the region of 4000–400 cm
.
3
3
. Results and discussion
.1. Hydrolysis of MCC with different ionic liquids
To obtain efficient ionic liquids (ILs) catalysts for the hydrolysis
Figure 1. The FT-IR spectra of (a) sample catalyzed with C
4
mimCl; (b) sample
of MCC, the catalytic activities of different ILs were tested. 4-
Methyl-2-pentanone (MIBK) was used as phase modifier to contin-
uously extract the products from aqueous phase. As shown in Ta-
catalyzed with IL-1 (0.5 g MCC; 2.0 g ILs; 1 mL 0.2 M CoSO
4
; 8 mL MIBK; T = 150 °C;
t = 300 min; P = 2 atm).
ble 1, the conversion of MCC in C
4 4 4 6
mimBF , C mimPF , and
C
4
mimBr (Entries 2–4) were lower than the one in the absence of
the basic framework of sugars. For sample (b), except for the hy-
droxyl group stretching vibrational bands, the band at 1715 cm
ILs (Entry 1), which were in accordance with the research results
À1
of Rogers and co-workers.2 Specially, the conversion of MCC in
is assigned to C@O stretching vibrational band; the absorbance at
IL-1 (84%, Entry 7) was much higher than the one in C
4
mimCl
À1
1
635 cm is C@C stretching vibrational bands. Additionally, the
(
9%) and C mimH PO (19%), which further indicated that the acid-
4
2
4
À1
peaks at 978, 1165, and 1259 cm prove the existence of furan
ring. Based on the results of FT-IR spectra, the hydrolysis prod-
ucts of MCC catalyzed by C mimCl are mainly the total reducing
ity of solution was an important aspect to the hydrolysis of MCC.
IL-1 in the reaction system was thought to have double functions,
not only it can dissolve the MCC like other ionic liquids but also its
acidity can weaken the glycosidic bonds through and then promote
the hydrolysis of MCC effectively. Additionally, in the absence of
3
2
4
sugars but the furan compounds were also detected as the hydro-
lysis production of MCC which was catalyzed with IL-1.
4
CoSO (Table 1, Entry 8), the conversion of MCC was 70%, and the
yield of HMF and furfural decreased by 8% and 10%, respectively.
Based on the results above, we considered that there was a syner-
3
.3. The effects of different cobalt salts on the hydrolysis of MCC
To better understand the CoSO catalysis, the influence of other
4
4
gistic interaction between IL-1 and CoSO , which can promote the
cobalt salts on the reaction was also studied. As shown in Figure 2,
the addition of cobalt salts was favorable for the conversion of
hydrolysis of MCC efficiently.
MCC, and the catalysis of CoSO
able, which demonstrated the coordination of IL-1 (see below).
Although MCC conversion was reduced to 20% when Co(NO
4 2 4 2
, Co (SO )3, and CoCl was remark-
3
C
.2. The FT-IR spectra of hydrolysis products catalyzed with
mimCl and IL-1
4
3 2
)
was used as the cocatalyst, the yield of HMF also improved
Figure 1 shows the FT-IR spectra of the hydrolysis products of
MCC catalyzed by C mimCl (a) and IL-1 (b), respectively. The two
4
spectra are obviously different in vibrational bands. For sample
À1
(
a) the absorbance around 3346 and 3122 cm is associated with
the hydroxyl group stretching vibrational bands and those around
À1
2
901 and 1368 cm are characteristic of methyl, methylene, and
methine C–O–C stretching vibrational bands. Collectively, these
data suggest clearly that the spectrum of sample (a) represents
Table 1
Hydrolysis of MCC with various ionic liquids (0.5 g MCC; 2.0 g ILs; 1 mL 0.2 M CoSO
mL MIBK; T = 150 °C; t = 300 min; P = 2 atm)
4
;
8
Entry Ionic liquids Yield (%)
Sugars HMF Furfural Levulinic acid
Conv. (%)
1
2
3
4
5
6
7
8
Blank
3.38
0.14
0.12
0.43
3.68
2.30
4
0.89
2.26
1.77
1.78
1.13
4.17
24
0.24
1.28
1.12
0.71
0.97
2.86
17
0
6.93
5.73
4.42
4.94
9
19
84
70
C
4
C
4
C
4
C
4
C
4
mimBF
4
0.71
0.36
0.57
0.62
3.34
8
mimPF
mimBr
mimCl
6
mimH
2
PO
4
IL-1
IL-1
a
10
15
7.45
2.56
Figure 2. The effect of different cobalt salts on the hydrolysis of MCC (0.5 g MCC;
a
The reaction was performed with 1 ml H
2
4
O not 0.2 M CoSO .
2.0 g IL-1; 1 mL 0.2 M cobalt salts; 8 mL MIBK; T = 150 °C; t = 300 min; P = 2 atm).

F. Tao et al. / Carbohydrate Research 346 (2011) 58–63
61
somewhat. We considered that the decreasing conversion may be
because nitrate anion should be unfavorable for the reaction. Usu-
À
ally, NO3 cannot directly form stable coordination compounds as
a single ligand, so that the formation of metal nitrate complex is
difficult relative to other cobalt salts.
3
.4. The influence of reaction conditions on the hydrolysis of
MCC
The effect of the experimental conditions was also investigated;
Figures 3 and 4 summarize the influence of reaction time and tem-
perature. As the figures show, both reaction temperature and time
had a large effect on the yields of main products. When the time
changed from 60 to 600 min at 150 °C (Fig. 3), the conversion of
MCC increased from 19% to 86%, the TRS yield decreased, but the
yields of HMF, furfural, and levulinic acid increased correspond-
ingly. In a parallel manner, when the temperature changed from
9
0 to 210 °C for 300 min reaction time (Fig. 4), the tendency of
temperature curve was similar to Figure 3, the yields of HMF and
furfural first increased then decreased. Simultaneously, the conver-
sion of MCC changed from 14% to 86%. These results are consistent
with the hydrolysis MCC (Scheme 1), so the optimum reaction con-
ditions were carried out at 150 °C for 300 min. Compared with pre-
vious work, which also investigated cellulose conversion with IL-
based systems, the temperature we used was a little higher; how-
ever, we studied the single-step conversion of cellulose into HMF
Figure 4. Temperature course of the products during the hydrolysis of MCC (0.5 g
MCC; 2.0 g IL-1; 1 mL 0.2 M CoSO ; 8 mL MIBK; t = 300 min; P = 2 atm).
4
1
5
3.5. Analysis of by-products
In addition, we obtained some important by-products. Through
gel-permeation chromatography analysis (GPC), the molecular
weight distribution of the hydrolysis products was below 2000.
Through LC-MSD, the protonated molecules m/z 410.4 and 354.4
were detected in addition to the main products, HMF, and furfural.
Second order mass spectra analysis was performed to determine
their structure; the fragmentation patterns revealed that the prod-
ucts were furan dimers. The gas products produced during hydro-
lysis of MCC at 150 °C for 300 min were also analyzed using mass
spectrometry: propane, propylene, butane, and isobutane were not
detected; the components of the gas products were methane, eth-
in the absence of H
2 4
SO .
33,34
Based on previous reports,
water is generally thought to
have a negative effect on the dehydration of sugars to HMF. Our re-
sults also confirmed this point. As shown in Table 2 (Entries 1–4),
when the ratio of V (MIBK) to V (CoSO ) was 8:1, the conversion of
4
MCC reaches 84%, which was much higher than the results of the
reaction at the ratio of 8:4 (51%) and 8:3 (61%). Correspondingly,
the yields of HMF and furfural were the highest as the ratio was
8
:1, reaching 24% and 17%, respectively. Moreover, we studied
the effect of IL-1 dosage on the reaction, which is shown in Table 2
Entries 5–8). As the increase of the dosage of IL-1, the conversion
(
2
ane, CO, CO2, and H .
of MCC and the yields of products also increased. When the dosage
was 3.0 g, the MCC conversion was up to 88% but the reaction gen-
erated an odor substance (not soluble, black, viscous and fluffy), so
considering the cost of the experiment, we chose the dosage of IL-1
was 2.0 g.
3.6. Mechanism of MCC hydrolyze to HMF in Co-IL system
In most cases, the glycosidic bonds in cellulose are weakened by
Brønsted acid attack. A Lewis acid can also weaken the glycosidic
bonds through binding with a glycosidic oxygen atom in a similar
manner to protic acid, leading to the dehydration of polysaccharide
to produce monosaccharides. We propose a mechanism (Fig. 5) in
(
2nÀ2)À
which CoSO
manner to LnCl
complexes would promote rapid conversion of the
glucose into the b-anomers through hydrogen bonding between
4
in IL-1 forms complexes [Co(SO
as reported by Rogers and co-workers. These
-anomers of
4
)
n
]
in a similar
35
3
a
2À
oxygen atom in SO4
and the hydroxyl groups. Then the ring
aldoses would reverse to the open-chain form, combining with
the cobalt 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 effect of acidic solu-
tion, the HMF was combined with water to generate levulinic acid
or losed formaldehyde to produce furfural. To confirm the pro-
posed mechanism, we contrast the dehydration of glucose with
or without CoSO
that compared with the reaction in the absence of CoSO
tion of a catalytic amount of CoSO resulted in the yields of HMF
4
under the same conditions. The results suggested
4
, the addi-
4
and furfural being increased by 20% and 3%, respectively. Undoubt-
edly, this demonstrates the important role of cobalt on the dehy-
dration step, which proved the mechanism. Also, to support the
HMF degradation pathway, we performed the reaction using
HMF as substrate under the conditions of Entry 7 of Table 1. The
results suggested that the conversion of HMF reached 58%, the
Figure 3. Time course of the products during the hydrolysis of MCC (0.5 g MCC;
2
4
.0 g IL-1; 1 mL 0.2 M CoSO ; 8 mL MIBK; T = 150 °C; P = 2 atm).

6
2
F. Tao et al. / Carbohydrate Research 346 (2011) 58–63
Table 2
2
Effect of V (MIBK): V (H O) and m (IL-1) on the hydrolysis of MCC (0.5 g MCC; 8 mL MIBK; T = 150 °C; t = 300 min; P = 2 atm)
Entry
V (MIBK)/V (CoSO
4
)
m (IL-1)/g
Yield (wt %)
Furfural
Conv. (%)
Sugars
HMF
Levulinic acid
1
2
3
4
5
6
7
8
8:1
2.0
4
24
17
8
84
67
61
51
63
73
84
88
8:2
8:3
8:4
8:1
4.60
5.92
7.41
9.73
6.05
4
18.00
14.87
10.62
11.56
14.63
24
13.64
12.23
7.58
10.81
12.62
17
4.08
2.96
1.35
4.05
6.08
8
0.5
1.0
2.0
3.0
2.98
25.04
19.48
9.86
(2n-2)-
OH
OH
O
Co(SO4)n-1
O
O
Co(SO4)n](2n-2)-
[
O
HO
HO
HO
HO
S
O
OH
OH
O
O
OH
α or β
H
(2n-2)-
OH
H
OH
O
O
O
_
[Co(SO4)n](2n-2)-
O
O
HO
HO
HO
HO
β or α
S
O
OH
OH O
OH
Co(SO4)n-1
O
O
S
O
O
O
S
O
OH OH OH
O
Co
Co(SO4)2]2-
[
OH OH HO
O
O
OH
OH OH
H
OH OH
H
_
Co(SO4)2]2-
[
OH
OHO
_
O
3
H2O
HO
OH
HO
O
IL-1
HMF
OH
_
+
2H2O
OH
HCHO
IL-1
IL-1
O
O
HCOOH
O
+
O
Levulinic acid
Furfural
Figure 5. Putative mechanism of CoSO
4
promoted conversion of glucose into the main products.
yields of furfural and levulinic acid were up to 32% and 9%, respec-
tively. Therefore, we considered that there were two pathways for
the decomposition of HMF in the hydrolysis of MCC which was cat-
alyzed by IL-1. As depicted in Scheme 1, one pathway is the rehy-
dration of HMF into levulinic acid and formic acid; the other is the
loss of formaldehyde in HMF to furfural.
moved, and then the catalyst was recycled. As seen in Figure 6,
although a decrease of the conversion from 84% to 73% was ob-
served in the second run, a slight decrease in activity was observed
in the subsequent four recycling. An average MCC conversion of
about 67% was obtained. Also, the yields of HMF, furfural, and lev-
ulinic acid have only slight loss over five repeated runs, about 18%,
1
2%, and 6% could be obtained, respectively. It is possible that the
3
.7. Recycling of IL-1 catalysts
decrease of activity in the second run may be attributed to the non-
complete extraction of small by-product from the liquid-phase,
which inhibited the conversion of MCC and the further dehydra-
tion of glucose. To support this point, we measured FT-IR spectra
of the synthesized IL-1 and the recovered IL-1 (not shown). The
main differences between two spectra were that in the spectrum
of the recovered IL-1, there were obvious vibrational bands that
In the principles of green engineering, catalyst recycling is al-
ways important in metal-catalyzed liquid-phase reactions. There-
fore, the reusability of CoSO and IL-1 catalysts was tested. After
the reaction, IL-1 was separated by extraction of the products with
diethyl ether and water, then solvent MIBK and water were re-
4

F. Tao et al. / Carbohydrate Research 346 (2011) 58–63
63
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4
1
347.
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We have stressed that functional acidic ionic liquid was an
2
effective catalyst for the hydrolysis of microcrystalline cellulose.
By comparing different ionic liquids, we showed that IL-1 has a
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5%, were realized under mild conditions with catalytic amount
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4
2
pounds was confirmed further, the yields of HMF and furfural
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sic bottlenecks of biomass hydrolysis by dispersing the cellulose
1
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into ILs and thus makes glycosidic linkages more accessible to H
2
001, 917, 95–103.
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3
3
3
in the reaction system. A detailed reaction mechanism involved
in the coordination of IL-1 and CoSO and the reusability of ionic
4
liquids are still subjects of future study.
9
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Acknowledgment
3
5. Hines, C. C.; Cordes, D. B.; Griffin, S. T.; Watts, S. I.; Cocalia, V. A.; Rogers, R. D.
New J. Chem. 2008, 32, 872–877.
We gratefully acknowledge the financial support of the State
Key Laboratory for Oxo Synthesis and Selective Oxidation of China.