One-step degradation of cellulose to 5-hydroxymethylfurfural in ionic liquid under mild conditions

Article abstract of DOI:10.1016/j.carbpol.2014.10.062

One-step conversion of cellulose to HMF (5-hydroxymethylfurfural) has been achieved by using metal chlorides (CrCl₃, CuCl₂, SnCl₄, WCl₆) in [BMIM]Cl. The effects of temperature, reaction time, amount of catalysts, and the purity of [BMIM]Cl on the performance have been studied and discussed in detail. More than 63% yield of HMF and 80% yield of TRS (total reducing sugar) were obtained in [BMIM]Cl with CrCl₃ at 120°C under atmospheric pressure. Filter paper and cotton were also used as a source for cellulose degradation to HMF, but only a moderate yield of HMF was obtained (40% for filter paper and 12% for cotton). The reutilization of this system was examined and the reaction mechanism was also discussed.

Full text of DOI:10.1016/j.carbpol.2014.10.062

Carbohydrate Polymers 117 (2015) 694–700
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
One-step degradation of cellulose to 5-hydroxymethylfurfural in ionic
liquid under mild conditions
a
b
a
a
a,∗
a,∗
Lilong Zhou , Yiming He , Zhanwei Ma , Runjuan Liang , Tinghua Wu , Ying Wu
a
Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Institute of Physical Chemistry, Zhejiang Normal University, Jinhua 321004,
PR China
Department of Materials Physics, Zhejiang Normal University, Jinhua 321004, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
One-step conversion of cellulose to HMF (5-hydroxymethylfurfural) has been achieved by using metal
chlorides (CrCl3, CuCl2, SnCl4, WCl6) in [BMIM]Cl. The effects of temperature, reaction time, amount of
catalysts, and the purity of [BMIM]Cl on the performance have been studied and discussed in detail. More
than 63% yield of HMF and 80% yield of TRS (total reducing sugar) were obtained in [BMIM]Cl with CrCl3
Received 22 November 2012
Received in revised form 7 May 2014
Accepted 23 October 2014
Available online 7 November 2014
◦
at 120 C under atmospheric pressure. Filter paper and cotton were also used as a source for cellulose
degradation to HMF, but only a moderate yield of HMF was obtained (40% for filter paper and 12% for
cotton). The reutilization of this system was examined and the reaction mechanism was also discussed.
Keywords:
Cellulose
©
2014 Elsevier Ltd. All rights reserved.
5
-Hydroxymethylfurfural
Ionic liquid
CrCl3
1
. Introduction
It becomes more and more important to prepare chemical
building blocks from renewable resources which allow fossil fuel-
based platform chemicals to be replaced since the price of oil has
risen significantly. HMF (5-hydroxymethylfurfural) is an attractive
chemical among these new chemical building blocks (Roman-
Leshkov, Chheda, & Dumesic, 2006; Zhao, Holladay, Brown, &
Zhang, 2007), since it contains several functional groups which
can be used for synthesis of drug, functional polymers, biomass
fuel (like 2,5-dimethylfuran), and other useful chemicals (Rosatella,
Simeonov, Fradea, & Afonso, 2011).
Cellulose, the most abundant biomass in the world, has attracted
a lot of attention in recent years and is an important renewable
resource (Ragauskas et al., 2006). It will play an important role in
the chemical industries of the future. However, its high degree of
crystalline maintained partly by hydrogen bonds between different
cellulose molecules make it insoluble in water or traditional organic
solvents (Henriksson, Berglund, Isaksson, Lindstroem, & Nishino,
2
008). As known, heterogeneous degradation of cellulose is an
inefficient and energy-consuming process. If the degradation of
cellulose can be processed under homogeneous condition, the reac-
tion efficiency could be improved considerably. Compared to other
solvents, ionic liquids have many advantages, including negligible
vapor pressure, good solubility, a wide electrochemical window,
flame retardant properties, and have been applied in many fields
Much research has been done to produce HMF from fruc-
tose (Zakrzewska, Bogel-Łukasik, & Bogel-Łukasik, 2011). However,
fructose is not available in sufficient quantity to satisfy the demands
of the chemical industry. Another monosaccharide, glucose, is
abundant in nature and is also the monomer of some plentiful
nature polymers such as cellulose. But its molecule structure makes
it hard to be converted to HMF in high yields. A breakthrough has
been made by Zhao et al. (2007) who showed that glucose could be
converted to HMF by chromium chlorides to give yields of about
70% in ionic liquid. Two years later, Hu, Zhang, Song, Zhou, and Han
(2009) reported the degradation of glucose to HMF by SnCl4 with
yield of 60%. However, SnCl4 can be easily hydrolyzed to Sn(OH)4
and HCl. These studies suggest it is possible to produce of HMF from
cellulose.
(Olivier-Bourbigou, Magna, & Morvan, 2010). Swatloski, Spear,
Holbrey, and Rogers (2002) found that cellulose could be dissolved
in ionic liquids, such as [C mim]Cl, [C mim]Br, [C mim]SCN. This
4
4
4
research laid a foundation for the homogeneous degradation of
cellulose.
Zhang and Zhao (2010) converted cellulose with different poly-
merization degrees and different kinds of lignocellulose (corn stalk,
straw and pine wood) to HMF in yield of 45–60% with CrCl3
Abbreviations: HMF, 5-hydroxymethylfurfural; TRS, total reducing sugar.
∗ Corresponding authors. Tel.: +86 0579 82282234.
E-mail addresses: thwu@zjnu.cn (T. Wu), yingwu@zjnu.cn (Y. Wu).
http://dx.doi.org/10.1016/j.carbpol.2014.10.062
0
144-8617/© 2014 Elsevier Ltd. All rights reserved.

L. Zhou et al. / Carbohydrate Polymers 117 (2015) 694–700
695
under microwave heating in [BMIM]Cl. However, industrialization
of microwave heating still has a long way to go. Moreover, they got
a high yield of furfural while the HMF yield decreased quickly under
microwave heating. Su et al. used a pair of metal chlorides, CuCl2
was added into the solution for a certain time. At different time
intervals, two samples were withdrawn, weighed and quenched
immediately with cold water each time, one for HMF detection
(recorded as M ) and the other for TRS (recorded as M ). Every
1
2
and CrCl , as the catalyst to convert cellulose to HMF at yield of 55%
reaction was repeated 3 times.
2
in [EMIM]Cl (Su et al., 2011). Though CuCl is effective at degrading
2
cellulose, it also has high catalytic activity for poly-reaction of the
products and thereby reduces the yield of target products. In Zhang,
Du, Qian, and Chen’s work (2010), cellulose was firstly hydrolyzed
2.4. Analysis of HMF and TRS
The analysis of HMF and TRS was performed by the method as
reported (Zhou, Liang, Ma, Wu, & Wu, 2013). Samples were dis-
solved in 1500 times samples volume of deionized water, and they
were centrifuged at 4000 r/min for 5 min. The color intensity of
supernatant fluid was measured in a TU-1810 Model spectropho-
tometer which was obtained by Purkinje General Co. Ltd (Beijing,
China) at 284 nm with a slit width of 0.06 mm (De, Dutta, & Saha,
2011; Hu, Sun, & Lin, 2012; Li, Zhao, Wang, Zheng, & Zhang, 2010).
The concentration of HMF was calculated based on a standard curve
obtained with HMF. The yield of HMF was calculated as follows:
cellulose by HCl and H SO4 in [Emim]Cl followed by the addition
2
of CrCl , the yield of HMF was improved and reached a high level
2
8
9% at last. However, mineral acids are corrosive to the equipment
and the conversion of cellulose to HMF in two steps is inconve-
nient. Zhao, Cheng, Li, Tian, and Wang (2011) synthesized a dual
functional catalyst, Cr[(DS)H PW12O40]3, which has both Brønsted
2
and Lewis acidity for conversion of cellulose to HMF in the yield of
◦
5
2.7% in water at 150 C for 2 h. However, this requires a high pres-
sure and relatively high temperature, and a complicated synthesis
process of the catalyst.
(
CHMF × M1 × 1500)
In this work, cellulose was directly converted to HMF in a high
YHMF = ꢀ
ꢀ
ꢁꢁ
Mcellulose × 0.778 × M /M
yield (more than 60%) with CrCl in [BMIM]Cl without a cosolvent at
1
0
3
relatively low temperature under atmospheric pressure. The effects
including reaction temperature, time, catalyst amount, the purity
of ionic liquid, and polymerization degree of cellulose, were studied
and discussed. The reaction mechanism was also suggested.
where CHMF is the concentration of HMF, M is the mass of the
reaction solution, Mcellulose is the mass of cellulose in the reaction,
0
and M is the mass of sample withdrawn from the reaction mixture.
1
0
.778 is a color intensity correction factor for different volumes of
sample.
HMF was also confirmed by high-performance liquid chro-
matography (HPLC) (It was purchased from Waters (China) Co. Ltd
Shanghai). Waters 2487 dual ꢀ absorbance detector, Waters Binary
2
. Experimental
2.1. Material and methods
(
HPLC pump) with a C18AQ column which was purchased from
Guangzhou Research & Creativity Biotechnology Ltd (Guangzhou,
China) and used a 8:2 v/v methanol: water gradient at a flow rate of
Microcrystalline
cellulose
(MCC,
DP:
215–245),
N-
methylimidazole (AR), 1-chlorobutane (CP) and CrCl ·6H O (≥99%)
3
2
were supplied by Sinopharm Chemical Reagent Co. Ltd (Shanghai,
1
ml/min and a column temperature of 293 K using a UV detector.
Total reducing sugar was detected by DNS method. The sam-
◦
China). Microcrystalline cellulose was dried in blast oven at 100 C
for 1 h before use. CuCl ·2H O (≥99%) was obtained from Guangfu
2
2
ples were taken periodically, and diluted with 150 times samples
volume of deionized water. 1 ml DNS regent was added, then
heated for 20 min in boiling water, and cooled with cold water. The
color intensity of the mixture was measured in a TU-1810 Model
spectrophotometer at 498 nm. The concentration of total reduc-
ing sugars was calculated based on a standard curve obtained with
glucose. The yield of TRS was calculated as follows:
Fine Chemical Research Institute (Tianjin, China). Ionic Liquid
[
BMIM]Cl was prepared according to the reported procedures (Tao,
Song, & Chou, 2011). All other chemicals were purchased from
local suppliers and used without further purification.
2
.2. Preparation of [BMIM]Cl
N-methylimidazole was added into a three-necked round bot-
(CTRS × M2 × 1500)
YTRS = ꢀ
ꢀ
ꢁꢁ
◦
tom flask, and heated to 80 C under stirring. 1-chlorobutane was
added into the flask drop wise by using a tap funnel at the molar
ratio of 1:1.1 and condensed reflux at the same time. After all of
the 1-chlorobutane was added into the flask. Then the mixture was
kept heating and stirring for 48 h. When the reaction was finished,
it was cooled to room temperature and washed by double mix-
ture volume of ethyl acetate for three times. Then double mixture
volume of ethyl acetate, half mixture volume of acetonitrile and a
little crystal of [BMIM]Cl were added to get pure [BMIM]Cl crys-
Mcellulose × 1.11 × M /M
2
0
2.5. FT-IR analysis
The residue was separated and dried for FT-IR analysis. All the
FT-IR spectra were collected on an FT-IR spectrometer (Nicolet
−
1
NEXUS670) with a resolution of 4 cm and 32 scans in the region
−
1
of 4000–400 cm
.
1
tal. HNMR spectra of [BMIM]Cl was recorded on Brucker Advance
4
(
00 MHz spectrometer which was purchased from Brucker Co. Ltd
Switzerland).
BMIM]Cl: 1H NMR (400 MHz, D O): ı0.95–1.00(t, 3H),
3. Results and discussion
[
3.1. Selection of catalysts
2
1
1
.34–1.46(m, 2H), 1.87–1.97(m, 2H), 4.15(s, 3H), 7.51 (s, 1H), 7.61(s,
H), 10.83(s, 1H).
3.1.1. Degradation of cellulose in [BMIM]Cl by different chlorides
In this study, CrCl , SnCl , CuCl , and WCl , which have been
3
4
2
6
2
.3. Typical procedure for microcrystalline cellulose hydrolysis in
reported as good catalysts for dehydration of glucose to HMF,
were used for the degradation of cellulose (Guan, Cao, Guo, & Mu,
[BMIM]Cl
2
011; Hu et al., 2009; Su et al., 2011; Zhao et al., 2007). As seen
0
.1 g MCC was added into 2.0 g [BMIM]Cl in a round-bottom flask
in Fig. 1, CrCl3 exhibited good catalytic performance for degrada-
tion of cellulose to HMF. Furthermore, HMF was stable in [BMIM]Cl
◦
and the mixture was heated to 100 C. After the mixture became
clear which means all of MCC was dissolved into [BMIM]Cl, the tem-
perature was increased to the target temperature and the catalyst
with CrCl , which may relate with the ability of CrCl3 to recover
3
HMF (Zhao et al., 2007). Cellulose was degraded fast in [BMIM]Cl

6
96
L. Zhou et al. / Carbohydrate Polymers 117 (2015) 694–700
◦
Fig. 1. Degradation of cellulose to HMF with different metal chlorides. (Cellulose 0.1 g, [BMIM]Cl 2.0 g, metal chlorides 0.05 g, reacted at 120 C)
with WCl6 or CrCl –CuCl . However, compared to CrCl both TRS
degradation of cellulose, which is probably because SnCl4 is easily
hydrolyzed into Sn(OH)4 in the reaction.
2
2
3
and HMF yields declined quickly. HMF displays its stability in
BMIM]Cl with CrCl . Meanwhile, there were a lot of black pre-
[
3
cipitates formed. The FT-IR spectra (Fig. 2) show that the black
3
.1.2. Degradation of cellulose in [BMIM]Cl by different
precipitates were different from those obtained with CrCl . The
3
chromium salts
residue from cellulose catalyzed by CuCl2 and WCl6 shows differ-
ent IR absorption peaks from cellulose, indicating it is obviously
−
The effect of Cl in CrCl3 was investigated by using differ-
ent chromium salts with different anions as catalysts. The results
−
1
not cellulose. The absorption peaks at 1571 and 1458 cm , 979
(Fig. 3) show that only CrCl has a good ability in degradation of cel-
3
−
1
and 815 cm can be ascribed to the vibration of carboxylic group
and C C which are not present in cellulose. Other absorption peaks
which belong to cellulose are weakened or disappear. The left-
overs of cellulose catalyzed by CuCl2 and WCl6 have almost the
same absorption peaks as the residue formed by cellobiose which
is commonly called as humin, probably polymerized from the cel-
lulose hydrolysis products (Zhang et al., 2010). The results show
that both CuCl2 and WCl6 have good ability to degrade cellulose,
but degradation products are unstable with these two catalysts.
While the leftover is mainly cellulose from the degradation by CrCl3.
Additionally, WCl6 is more expensive than CrCl3 and is prone to
be hydrolyzed in air. SnCl4 showed a poor performance for the
−
lulose to HMF. It indicates that the Cl in CrCl3 plays an important
−
3+
role in this reaction. First, Cl takes part in coordination of Cr with
-1,4-glycosidic bonds in depolymerization of cellulose to glucose.
␤
2−
−
3+
SO and NO3 also can coordinate with Cr in the reaction (Tao
et al., 2011). However, their larger radius than Cl makes them hard
to coordinate with Cr and attack ␤-1,4-glycosidic bonds between
two glucopyranosyl units. Thus compared to CrCl , the TRS yields
for Cr(NO ) and Cr (SO ) were lower. Also, since NO is smaller
than SO4 , HMF and TRS yield catalyzed by Cr(NO ) are higher than
those of Cr (SO ) . As suggested by Zhao et al. (2007) Cl may also
takes part in the coordination of Cr with glucose to convert glu-
cose to fructose which is the most important step in conversion of
4
−
3+
3
−
3
3
2
4
3
3
2−
3
3
−
2
4 3
3+
Fig. 2. TheFT-IRspectraofhydrolysisleftovercatalyzedwith[BMIM]Clanddifferent
chromium salts.
Fig. 3. Degradation of cellulose to HMF with CrCl3 at different temperature. (Cellu-
lose 0.1 g, [BMIM]Cl 2.0 g, CrCl3 0.05 g.)

L. Zhou et al. / Carbohydrate Polymers 117 (2015) 694–700
697
◦
Fig. 4. Conversion of cellulose to HMF with different amount of CrCl3. (Cellulose 0.1 g, [BMIM]Cl 2.0 g, reacted at 120 C)
2
−
−
−
glucose to HMF. SO and NO3 may play the same role as Cl (Tao
3.2.2. Amount of catalyst
4
et al., 2011), thus the selectivity of HMF on Cr(NO ) and Cr (SO )
Increasing catalyst amount can accelerate the reaction rate
(Fig. 5). However, it showed a different trend to the production
yield. Increasing CrCl3·6H2O from 0.01 g to 0.03 g, all products
yields were improved. When more than 0.03 g catalyst was loaded,
the product yields decreased. The reason may be that too much
catalyst leads to some side reactions. Considering the loss of the
catalyst during the extraction step, 0.05 g catalyst was chosen for
the reaction.
3
3
2
4 3
catalysts is also high, more than 80%. The anions of chromium salts
may mainly influence the depolymerization of cellulose to glucose
by their size, but they have little effect on the dehydration of glucose
to HMF.
3.2. Effects of reaction conditions
3
.2.1. Reaction temperature
Temperature is an important factor in this reaction. As temper-
3.2.3. Reaction time
Figs. 1, 3–6 show the effect of reaction time on the yield of
ature increases, both the yield and reaction rate increases (Fig. 4).
◦
◦
HMF and TRS yield. Prolonging the reaction time can improve prod-
ucts yield. However, after reaching the maximal yield, HMF yield
From 90 C to 140 C, HMF yield and TRS yield were increased about
0% and 15%, respectively. The reaction rate was also accelerated.
1
◦
◦
declined slightly (10% at 140 C and 3% at 130 C in 4 h). It indicates
It can be attributed to the reduced the viscosity of this reaction
system which will accelerate the mass transfer rate and facilitated
cellulose chain degradation. Although the reaction rate increased
◦
that HMF is relatively stable in this reaction system (<130 C). After
a long period of reaction, HMF was converted to other chemicals
such as furan dimers. Compared to the process using microwave
heating (Zhang & Zhao, 2010), less furfural was generated (less than
with temperature, the production of HMF was reduced (by about
◦
1
0% within 4 h) if the temperature was too high (≥130 C). The rea-
5
%) in this work. Oil bath is more favorable for producing HMF.
son may be that HMF is unstable at high temperature and is much
easier to be polymerized into by-products like furan dimer, humin
than at low temperature (Tao et al., 2011). Therefore, 120 C was
◦
There is no obviously decrease in HMF yield in 4 h at 120 C. So
it’s convenient to use the traditional equipments with traditional
heating to produce HMF in the future.
◦
chosen as the optimal reaction temperature.
◦
Fig. 5. Degradation of cellulose of different degrees with CrCl3. (Cellulose 0.1 g, [BMIM]Cl 2.0 g, CrCl3 0.05 g, reacted at 120 C)

6
98
L. Zhou et al. / Carbohydrate Polymers 117 (2015) 694–700
◦
Fig. 6. Conversion of cellulose to HMF with different chromic salts (Cellulose 0.1 g, [BMIM]Cl 2.0 g, chromic salt 0.05 g, reacted at 120 C).
3
.2.4. Influence of polymerization degree
This catalysis system was explored to reduce the degrees poly-
and formic acid. However, in these experiments, the conversion of
cellulose declined a lot with high water content (lower than 55%).
The other reason is that water can reduce the solubility of cel-
lulose in [BMIM]Cl. When water content is more than 1 wt%,
the solubility of cellulose in [BMIM]Cl drops clearly (Nishiyama,
Sugiyama, Chanzy, & Langan, 2003; Swatloski et al., 2002). Hydro-
gen bonds formed by [BMIM]Cl with hydroxyl groups on the
cellulose is positive to the breakage of ␤-1,4-glycosidic bonds
(Heinze, Schwikal, & Barthel, 2005). But water can form hydro-
gen bonds with hydroxyl groups on the cellulose more easily than
[BMIM]Cl, which could reduce the solubility of cellulose [BMIM]Cl
(Pinkert, Marsh, Pang, & Staiger, 2009). To confirm this, CrCl3
was added before cellulose was dissolved into [BMIM]Cl. Then
the reaction rate slowed down and the products yield reduced a
little.
merization of cellulose (Fig. 6). The results show that with the
polymerization degree increasing, both reaction rate and HMF
yield declined. In early studies (De et al., 2011; Hu et al., 2012;
Su et al., 2011; Tao et al., 2011), cellulose was first depolymer-
ized to glucose, then the glucose was dehydrated to HMF. There
are at least two steps to convert cellulose to HMF. So a long
time is needed to complete this process. Because of long cellu-
lose chain and high crystallinity in cotton and filter paper, longer
time should be needed for their depolymerization to glucose than
MCC. The reason why HMF yield declined may be that cellu-
lose needs to be depolymerized to glucose first before HMF is
obtained. This whole reaction may reach equilibrium and HMF
yield cannot be improved further. Another reason may be that
as the polymerization degree of cellulose increases, it becomes
much harder to dissolve cellulose in [BMIM]Cl. For instance, cot-
ton cannot be dissolved in [BMIM]Cl, but only at swelling state.
The experimental results show that the purity of [BMIM]Cl is
important. When CrCl3 was added to pure [BMIM]Cl, the colorless
transparent solution became purple red. This phenomenon shows
After addition of CrCl , cotton began to break up into pieces and
3
dissolve into [BMIM]Cl. But only low yield of HMF was obtained
for 16 h.
Table 1
Degradation of cellulose to HMF by CrCl3 and [BMIM]Cl with different impurity.
Entry
Impurity
Reaction time
HMF yield (%)
TRS yield (%)
3
.2.5. Effect of water
Water content influences this reaction significantly (Table 1).
1
2
3
4
5
–
20
3
3
3
3
8
75
70
17
70
28
0.05 g CrCl3
0.02 g imidazole
0.03 gH2O
0.13 gH2O
53
11
48
15
◦
[
BMIM]Cl was heated to remove water in vacuum oven at 100 C
for 12 h. Different amount of water was added to [BMIM]Cl to
examine the effect of water. The results show that with water con-
tent increasing, the product yield decreased. It may be attributed
to two reasons. One is that HMF is hydrolyzed to levulinate acid
◦
There was 0.1 g cellulose in 2.0 g [BMIM]Cl reacted at 130 C. 2∼4 were carried out
◦
with 0.1 g cellulose in 2.0 g [BMIM]Cl by 0.05 g CrCl3 at 120 C.

L. Zhou et al. / Carbohydrate Polymers 117 (2015) 694–700
699
Fig. 7. The mechanism of conversion of cellulose to HMF in [BMIM]Cl with CrCl3.
that CrCl3 has coordinated with [BMIM]Cl and high yield of HMF
3.4. Recycling of catalysis system
and TRS were gained. However, if imidazole existed in [BMIM]Cl,
green solution was formed with CrCl3 and low yield of HMF and
thus TRS were obtained (Table 1). Because imidazole is a weak base
and CrCl3 is a Lewis acid, imidazole can coordinate with CrCl3 to
The reusability of the catalysis system was tested. After the
reaction, some de-ionized water was added into the reaction mix-
ture. Then the solid and liquid were separated by centrifugation.
hinder CrCl from attacking ␤-1,4-glycosidic bonds and converting
3
glucose to HMF.
3.3. Degradation mechanism
According to the above results and related literatures, the
mechanism of cellulose degradation to HMF by CrCl3 was pro-
posed (Fig. 7). CrCl3 first attacks ␤-1,4-glycosidic bonds. [BMIM]Cl
forms hydrogen bond with hydroxyl groups of cellulose to help
the breaking of ␤-1,4-glycosidic bands. Then CrCl3 coordinates
with the generated glucose, ␣-glucose is isomerized to ␤-glucose
3+
which is more easily to be dehydrolyzed. Cr interacts with the
hemiacetal portion of glucopyranose and aldehyde group becomes
enol (Zhao et al., 2007). [BMIM]Cl acts as both proton donor
−
(
C2 H) and acceptor (Cl ) in H-bonding interactions with glu-
cose to improve dehydration efficiency at the same time (Guo,
Fang, & Zhou, 2012). Then aldehyde group is converted to a ketone
group and glucose is isomerized to fructose. Three molecules of
water is removed from fructose to form HMF. The degradation
of cellulose to HMF catalyzed by other salts should follow the
similar mechanism. This mechanism still needs further work to
confirm it.
Fig. 8. Recycle of catalysis system for the hydrolysis of microcrystalline cellulose to
the main products.

7
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L. Zhou et al. / Carbohydrate Polymers 117 (2015) 694–700
HMF was extracted by ethyl acetate for 3 times and the remaining
aqueous phase was heated to remove water at 100 C for the next
microwave irradiation in dimethyl sulfoxide–ionic liquid mixtures. Bioresource
Technology, 112, 312–318.
Heinze, T., Schwikal, K., & Barthel, S. (2005). Ionic liquids as reaction medium in
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◦
reaction cycle. As seen in Fig. 8, both HMF and TRS yield increased
in the first four runs, and then decreased for further runs. The rea-
son why products yield increased is that sugars including glucose
and cellobiose which come from the depolymerization of cellulose
cannot be dissolved in ethyl acetate. They continue be dehydrated
to HMF in the next run, resulting in the improved product yield.
HMF and TRS contents were analyzed in the mixture after extrac-
tion. About 2% HMF and 24% TRS were left in mixture. After this
part was deducted from the results, the catalyst was found to keep
same activity at first four runs. There are many shortcomings in
this reuse process, such as water is not easy to remove and low
extraction efficiency. The recycle of the catalysis system still needs
further improvement.
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. Conclusions
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2
4
6
alysts were used to convert cellulose to HMF in one step. CrCl3
484–489.
exhibited the best performance. More than 63% yield of HMF and
Roman-Leshkov, Y., Chheda, J. N., & Dumesic, J. A. (2006). Phase modifiers pro-
mote efficient production of hydroxymethylfurfural from fructose. Science, 312,
1933–1937.
◦
8
0% yield of TRS were obtained at 120 C in 4 h containing 0.1 g
microcrystalline cellulose and 0.05 g CrCl3 in 2.0 g [BMIM]Cl at
atmospheric pressure. However, when filter paper or cotton was
used as the raw material instead of MCC, a low yield of HMF (40%
for filter paper and 12% for cotton) was obtained. Low content of
water in reaction mixture is beneficial for the production of HMF.
In addition, this system can be reused for many times.
Rosatella, A. A., Simeonov, S. P., Fradea, R. F. M., & Afonso, C. A. M. (2011).
5-Hydroxymethylfurfural (HMF) as a building block platform: Biologi-
cal properties, synthesis and synthetic applications. Green Chemistry, 13,
754–793.
Su, Y., Brown, H. M., Li, G., Zhou, X., Amonette, J. E., Fulton, J. L., et al. (2011). Accel-
erated cellulose depolymerization catalyzed by paired metal chlorides in ionic
liquid solvent. Applied Catalysis A: General, 391, 436–442.
Swatloski, R. P., Spear, S. K., Holbrey, J. D., & Rogers, R. D. (2002). Dissolution of cellose
with ionic liquids. Journal of the American Chemical Society, 124, 4974–4975.
Tao, F., Song, H., & Chou, L. (2011). Catalytic conversion of cellulose to chemicals in
ionic liquid. Carbohydrate Research, 346, 58–63.
Zakrzewska, M. E., Bogel-Łukasik, E., & Bogel-Łukasik, R. (2011). Ionic liquid-
mediated formation of 5-hydroxymethylfurfuralsa promising biomass-derived
building block. Chemical Reviews, 111, 397–417.
Zhang, Z., & Zhao, Z. K. (2010). Microwave-assisted conversion of lignocellulosic
biomass into furans in ionic liquid. Bioresource Technology, 101, 1111–1114.
Zhang, Y., Du, H., Qian, X., & Chen, E. Y.-X. (2010). Ionic liquid–water mixtures:
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Acknowledgements
The project was supported by grants from the National Natural
Science Foundation of China (21373188, 21243010), Nature Science
Foundation of Zhejiang Provience (LY12B03001), Open Foundation
of Key Laboratory of Ministry of Education for Advanced Catalysis
Materials (Zhejiang Normal University) (CL201002).
2
410–2417.
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