Efficient process for conversion of fructose to 5-hydroxymethylfurfural with ionic liquids

Article abstract of DOI:10.1039/b905975j

An efficient process for the dehydration of fructose into 5-hydroxymethylfurfural (5-HMF) in ionic liquid 1-butyl-3-methyl imidazolium chloride ([BMIM][Cl]) by using a sulfonic ion-exchange resin as catalyst was developed. A fructose conversion of 98.6% with a 5-HMF yield of 83.3% was achieved in 10 min reaction time at 80 °C. When the reaction temperature was increased to 120 °C, a 5-HMF yield of 82.2% was obtained in only 1 min for essentially 100% fructose conversion. No large decrease in 5-HMF selectivity occurred for initial fructose concentrations of up to 20 wt.%. Water content of up to 5% in the [BMIM][Cl] had no effect on the fructose conversion rate and 5-HMF yield, but water content higher than 5 wt.% led to lower conversions and yields. The ionic liquid and sulfonic ion-exchange resin could be recycled and exhibited constant activity for 7 successive trials. The proposed process of using an ionic liquid with ion-exchange resin catalyst greatly reduces the reaction time required over previous works for converting fructose to 5-HMF. The Royal Society of Chemistry 2009.

Full text of DOI:10.1039/b905975j

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Qi et al.
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PAPER
www.rsc.org/greenchem | Green Chemistry
Efficient process for conversion of fructose to 5-hydroxymethylfurfural
with ionic liquids†
Xinhua Qi,*a,b Masaru Watanabe,a Taku M. Aidaa and Richard L. Smith, Jr.*a
Received 26th March 2009, Accepted 8th June 2009
First published as an Advance Article on the web 30th June 2009
DOI: 10.1039/b905975j
An efficient process for the dehydration of fructose into 5-hydroxymethylfurfural (5-HMF) in
ionic liquid 1-butyl-3-methyl imidazolium chloride ([BMIM][Cl]) by using a sulfonic ion-exchange
resin as catalyst was developed. A fructose conversion of 98.6% with a 5-HMF yield of 83.3% was
achieved in 10 min reaction time at 80 ◦C. When the reaction temperature was increased to 120 ◦C,
a 5-HMF yield of 82.2% was obtained in only 1 min for essentially 100% fructose conversion. No
large decrease in 5-HMF selectivity occurred for initial fructose concentrations of up to 20 wt.%.
Water content of up to 5% in the [BMIM][Cl] had no effect on the fructose conversion rate and
5-HMF yield, but water content higher than 5 wt.% led to lower conversions and yields. The ionic
liquid and sulfonic ion-exchange resin could be recycled and exhibited constant activity for 7
successive trials. The proposed process of using an ionic liquid with ion-exchange resin catalyst
greatly reduces the reaction time required over previous works for converting fructose to 5-HMF.
metal halides. It was found that chromium (II) chloride is the
1. Introduction
most effective catalyst, leading to the conversion of fructose and
As a valuable biomass-derived intermediate for plastics, phar-
glucose to 5-HMF with a yield of 83% and 70%, respectively
at a temperature of 80 ◦C for a reaction time of 3 h. The
maceuticals, fine chemicals and liquid fuel, the preparation
of 5-hydroxymethylfurfural (5-HMF) through dehydration of
-
CrCl3 anion seems to play a role in proton transfer, facilitating
fructose has received increasing attention.1–14 In the past
the mutarotation of glucose in [EMIM][Cl] as noted by these
few years, water,10,12,15–18 organic solvents3,16,19–21 and organic–
water mixtures2,8,13,22 have been mainly studied with some of
the drawbacks being low 5-HMF selectivities or environmental
authors.6 Hu et al.4 investigated the conversi◦on of fructose to
5-HMF in choline chloride/citric acid at 80 C, and obtained
a 5-HMF yield of 77.8% without in situ extraction and a
problems with solvent recycling. The application of ionic liquids
yield of 91.4% when continuous extraction with ethyl acetate
as green solvents has been proposed,1,4–6,9,23 and several kinds
was used for a 1 h reaction time. Yong et al.1 studied the
of ionic liquids in the presence of an appropriate catalyst have
production of 5-HMF from fructose and glucose in 1-butyl-
been demonstrated to be effective for the conversion of fructose
3-methyl imidazolium chloride ([BMIM][Cl]) using CrCl2 as
to 5-HMF. Thus far, high 5-HMF yields (80–95%) have been
catalyst, and 5-HMF yields of 96% and 81% were achieved
obtained at moderate reaction temperatures of 80 to 100 ◦C, but
at 100 ◦C for 6 h reaction time for fructose and glucose, re-
these required long reaction times on the order of hours and the
use of relatively toxic chromium catalysts.
Lansalot-Matras et al.23 studied the acid-catalyzed dehy-
spectively. Those authors considered that NHC/CrClx (NHC =
N-heterocyclic carbene) complexes played the key role in glucose
dehydration in [BMIM][Cl]. Additionally, in the CrCl2/EMIM
dration of fructose in 1-butyl-3-methyl imidazolium tetraflu-
system, a NHC/Cr complex could be formed under the reaction
oroborate ([BMIM][BF4]) and 1-butyl-3-methyl imidazolium
conditions and therefore serves as a catalyst.1
hexafluorophosphate ([BMIM][PF6]) with dimethyl sulfoxide
In this work, we developed an efficient catalytic process for
R
(DMSO) as co-solvent in the presence of Amberlystꢀ 15 sulfonic
the conversion of fructose into 5-HMF, in which the ionic liquid,
ion-exchange resin as catalyst to obtain a high 5-HMF yield of
1-butyl-3-methyl imidazolium chloride ([BMIM][Cl]), was used
◦
87% at 80 C for 32 h reaction time. Zhao et al.6 studied the
as solvent with a strong acidic ion exchange resin as catalyst.
catalytic conversion of fructose and glucose into 5-HMF in an
With the given catalytic process and fructose as the starti◦ng
ionic liquid solvent (1-ethyl-3-methylimidazolium chloride) with
material, a 5-HMF yield of 85.9% could be achieved at 80 C
for a reaction time of 10 minutes. The ionic liquid and catalyst
aResearch Center of Supercritical Fluid Technology, Tohoku University,
6-6-11 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan.
E-mail: qixinhua@scf.che.tohoku.ac.jp, smith@scf.che.tohoku.ac.jp;
Fax: +81 022-795-5864
could be recycled and the catalyst exhibited constant activity
over 7 cycles of evaluation.
bKey Laboratory of Pollution Processes and Environmental Criteria
(Ministry of Education), College of Environmental Science and
Engineering, Nankai University, Tianjin, 300071, China
2. Experimental
2.1 Materials and experimental methods
† Electronic supplementary information (ESI) available: Arrhenius plot
for the dehydration of fructose in [BMIM]Cl (Fig. S1). See DOI:
10.1039/b905975j
Fructose (purity: 99%), 5-hydroxymethylfurfural, H2SO4, HCl,
H3PO4, acetic acid, CuCl2, and PdCl2 were purchased from
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©

Wako Pure Chemical Company, 1-butyl-3-methyl imidazolium
R
chloride ([BMIM][Cl], purum grade, purity: 98%), Amberlystꢀ
R
15 ion exchange resin and Dowexꢀ 50WX8 resin were purchased
from Sigma-Aldrich Company, all of them were used without
further purification.
In a typical reaction, 0.100 g of fructose (0.556 mmol) was
R
dissolved in 1 g of [BMIM][Cl] firstly, and 0.05 g Amberlystꢀ
15 ion exchange resin catalyst was added. The reaction mixture
was heated to 80 ◦C and kept for 10 min in the water bath. The
experiments that used reaction temperatures above 100 ◦C were
conducted with microwave heating. After reaction, each sample
was diluted with 10 g of ultra pure water before analysis. For the
recycling of ionic liquid and catalyst, 5-HMF was extracted out
from the mixture 5 times with 8 ml of ethyl acetate after 0.5 g of
water was added. After extraction, the ionic liquid was heated
at 60 ◦C for 24 h in a vacuum oven to remove water and residual
ethyl acetate. The ionic liquid was then used directly for the next
run by adding fructose.
Fig. 1 Conversion of fructose to 5-HMF in [BMIM][Cl] in the presence
of catalysts. Conditions: fructose 0.05 g, [BMIM][Cl] 1 g, 80 ◦C, 10 min
reaction time, catalyst loading 18 mol% based on sugar, 0.05 g for
AmberlystꢀR 15 ion exchange resin and DowexꢀR 50WX8 resin.
2.2 Analyses
For analysis of solutions, a high performance liquid chromato-
graph equipped with a refractive index detector (HPLC-RI, SH
1011 column) was employed. The column oven temperature was
other hand, H2SO4, CuCl2 and the ion-exchange resins had
very high catalytic activity for the conversion of fructose to
◦
R
5-HMF. Under the experimental conditions, Amberlystꢀ 15
60 C, and mobile phase was a 0.5 mM sulfuric acid aqueous
solution that had a flow rate of 1 ml/min.
resin gave a 99.6% fructose conversion and 83.3% 5-HMF yield
at 80 ◦C for 10 min reaction time. Since results were most
R
favorable for Amberlystꢀ 15 resin, this catalyst was chosen to
2.3 Yield and selectivity definitions
study in detail.
The fructose conversion (mol%), the 5-HMF yield (mol%) and
selectivity (mol%) were evaluated on a carbon basis as shown
below:
3.2 Effect of catalyst dosage on fructose conversion and
5-HMF yield
Fructose conversion (mol%):
Fig. 2 shows the effect of the catalyst dosage on fructose
conversion and 5-HMF yield. The amount of resin used was
0.02, 0.04, 0.08 and 0.1 g respectively. In the absence of catalyst,
at a reaction temperature of 80 ◦C, no fructose conversion was
observed for a reaction time of 20 min (not shown). In the
presence of catalyst (0.02 g), formation of 5-HMF occurred.
When the catalyst dosage increased from 0.02 to 0.04 g, the
5-HMF yield remarkably increased at 80 ◦C for a reaction
Fructoseconcentration in product
X = (1−
)×100%
Fructoseconcentration in theloaded sample
(1)
5-HMF yield (mol%):
Molesof carbon in 5-HMF
Molesof carbon in theloaded asfructose
Y =
×100%
(2)
(3)
5-HMF selectivity (mol%):
Yield of 5-HMF
Fructoseconversion
S =
3. Results and discussion
3.1 Fructose conversion in [BMIM+]Cl- treated with catalysts
[BMIM][Cl] is one of the most common ionic liquids, which
is used broadly as the starting material for the production of
other ionic liquids. We studied the conversion of fructose to 5-
HMF in [BMIM][Cl] with catalysts at 80 ◦C for 10 min. The
catalysts included mineral acids (H2SO4, HCl, H3PO4), organic
acids (acetic acid), Lewis acids (CuCl2, PdCl2) and solid acid
R
R
ion-exchange resins (Dowexꢀ 50WX8 and Amberlystꢀ 15). As
shown in Fig. 1, it can be seen that H3PO4 and acetic acid
exhibited little or no catalytic activity under the experimental
conditions, whereas HCl and PdCl2 had weak activity. On the
Fig. 2 Effect of catalyst dosage on fructose and 5-HMF yield
(AmberlystꢀR 15 ion exchange resin, fructose 0.05 g, [BMIM][Cl] 1 g,
80 ◦C, reaction time 5 min).
1328 | Green Chem., 2009, 11, 1327–1331
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◦
Table 1 Effect of reaction temperature on the conversion of fructose to
5-HMF (conditions: 0.05 g fructose, 1 g [BMIM][Cl], 0.05 g Amberlyst
resin)
temperature was 70 C, the fructose conversion was 52.9% for
a 5-HMF yield of 49.2% for 5 min reaction time. The 5-HMF
yield increased fro◦m 49.2% to 83.5% when conditions changed
◦
from 70 C to 90 C for a 5 min reaction time. For a reaction
Reaction
Reaction Fructose
5-HMF 5-HMF
temperature (◦C) time (min) conversion (%) yielda (%) selectivity (%)
◦
temperature of 120 C, a 5-HMF yield of 82.2% was obtained
for 1 min.
70
80
90
3
5
10
20
3
5
7
10
1
3
5
7
2
3
0.33
0.5
1
10.2
52.9
93.4
98.6
31.9
90.7
97.3
98.6
52.2
91.5
98.7
99.4
93.0
98.1
77.6
96.5
99.3
9.9
49.2
81.3
83.1
31.6
79.3
82.0
83.3
47.1
79.0
83.5
83.2
79.2
81.6
66.8
81.2
82.2
97.2
93.0
87.0
84.3
99.1
87.4
84.3
84.5
90.4
86.3
84.6
83.7
85.2
83.2
86.1
84.1
82.8
Many works reported a reaction order of one for the dehydra-
tion of fructose to 5-HMF.2,3,13,14 According to this, the kinetic
analysis of the dehydration of fructose in ILs was performed.
Plots of ln(1 - X) (X is fructose conversion) versus reaction
time (t) were made to obtain first order kinetic constants. With
those constants, an Arrhenius plot was generated as shown in
the ESI (Fig. S1†) and an activation energy of 65.2 kJ/mol
was determined. The value of this work was lower than that
of previous values (ca. 100 kJ/mol) reported in the literature,
which may be attributed to the reaction occurring in organic
solvents.2,13 The analysis shows that the activation energy of
fructose dehydration to 5-HMF is lower in ionic liquids than in
organic solvents.
100
120
Also, for comparison, results that other authors have achieved
with ionic liquids for fructose conversion to 5-HMF are summa-
rized in Table 2. The results of this work show that the present
process is more efficient than previous works as evident from the
shorter reaction times. The efficiency of fructose dehydration
mainly depends on the reaction media and catalyst employed.
Compared with organic solvents such as DMSO, ionic liquids
as solvents could effectively increase the reaction rate,9 and it
has been reported that there is an obvious relationship between
activity and catalyst acidity in the reaction, and that high catalyst
acidity leads to high reaction activity.5 The higher acidity of the
strong sulfonic ion-exchange resin over that of the other catalysts
such as CrCl2 and citric acid should probably be responsible for
its higher catalytic activity in this work.
a Byproduct yields: glucose ꢀ2%, levulinic acid ꢀ1%, formic acid ꢀ2%.
time of 5 min, from 25.5% to 81.6%. However, when the
amount of resin was increased from 0.04 to 0.1 g, there was
little change in fructose conversion and 5-HMF yield. As the
fructose conversion and 5-HMF yield did not change with
further catalyst dosage over 0.04 g, this implies that there are
sufficient catalytic sites (ca. 0.2 mmol sulfonic acid sites for
0.04 g resin) available for the substrate fructose (0.278 mmol)
in the system at the experimental conditions.
3.3 Effect of reaction temperature
Table 1 shows the effect of reaction temperature on fructose
conversion. The use of ionic liquid as solvent in the acid catalytic
dehydration of fructose significantly reduced the temperature
required for the reaction compared with aqueous or organic
solvents.2,3,8,13 The fructose conversion was 98.6% for a 5-HMF
yield of 83.3% at 80 ◦C for 10 min reaction time. In our previous
work, the fructose conversion and 5-HMF yield were 95.1% and
73.4%, respectively, at 150 ◦C for 15 min in 70:30 (w/w) acetone–
water mixture in the presence of resin as catalyst.2 Compared
with that work, the reaction temperature could be reduced from
150 ◦C to 80 ◦C for a similar fructose conversion but at shorter
reaction times (Table 1).
3.4 Effect of reaction time
As listed in Table 1, almost all of the fructose was converted
into 5-HMF, and the 5-HMF selectivity was as high as 95%
at the beginning of the reaction. The selectivity decreased as
the reaction proceeded, and went below 85% as the fructose
conversion reached about 99.5%. As the reaction proceeded, the
color of the solution changed to deep brown, which is evidence
for the decomposition of the formed 5-HMF.
There are three pathways for the decomposition of 5-HMF
in acid catalyzed dehydration of fructose,24,25 as depicted in
Scheme 1. The first pathway is the rehydration of 5-HMF
into levulinic acid and formic acid; the second pathway is
The reaction temperature had a large effect on both the
fructose conversion and 5-HMF yield. When the reaction
Table 2 Comparison of fructose conversion efficiencies in different ionic liquids
Solvents
Catalyst
Reaction temperature (◦C)
Reaction time
Fructose conversion (%)
5-HMF yield (%)
Ref.
[EMIM][Cl]
DESa
CrCl2
Citric acid
80
80
3 h
1 h
—
83
6
4
4
1
93.2
94.2
—
77.8
86.8b
96
[BMIM][Cl]
[BMIM][Cl]
NHC-CrCl2
AmberlystꢀR
15 resin
100
80
6 h
10 min
98.6
83.3
This work
100
3 min
98.1
81.6
This work
a Deep eutectic solvent. b With ethyl acetate in situ extraction.
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Scheme 1 5-Hydroxymethylfurfural formation from fructose and
5-HMF decomposition pathways.
the self-polymerization between 5-HMF molecules; and the
third pathway is the cross-polymerization between 5-HMF and
fructose.7,14,24 In non-aqueous systems 5-HMF rehydration can
be suppressed, and in this work, the levulinic acid yield was
always lower than 1.0% since there was only a limited amount of
water in the system that results from the dehydration of fructose
and from any impurities in [BMIM][Cl]. Thus, it is unlikely
that the rehydration pathway causes the 5-HMF selectivities to
decrease.
Self- or cross-polymerization reactions of 5-HMF can occur
and lead to brown soluble polymers and insoluble humins.14
We◦tested the self-polymerization of 5-HMF in the system at
80 C by adding 0.05 g of 5-HMF and 0.05 g resin into 1 g of
[BMIM][Cl] in the absence of fructose. After a reaction time of
20 min, 99.6% of 5-HMF could be recovered, indicating that the
self-polymerization between 5-HMF molecules did not occur in
the system, and that the 5-HMF was stable at the experimental
conditions in the absence of fructose.
Fig. 3 Effect of substrate loading on 5-HMF yield from fructose (80 ◦C,
[BMIM][Cl] 1 g, resin 0.05 g, 10 min).
by about 5%. Additional increases in the fructose/[BMIM][Cl]
weight ratio did not lead to significant lowering of the 5-HMF
selectivity, which is similar to the trends noted by Yong et al.
for the conversion of fructose in [BMIM][Cl] with NHC/CrCl2
(NHC = N-heterocyclic carbene) complexes as catalysts.1 It
can be seen that ionic liquids other than aqueous or aqueous
mixtures can inhibit the formation of humins in fructose
conversions.
3.6 Effect of water content in [BMIM+]Cl- on
fructose conversion
The byproducts that could be analyzed with HPLC in this
work were glucose, levulinic acid and formic acid; the yields
were below 2%, 1% and 2%, respectively. The color of the reacted
solutions was brown, and the brown color remained even after
yellow 5-HMF was extracted from the mixture with ethyl acetate.
The brown products appearing in acid catalyzed dehydration
of fructose are thought to be soluble polymers and humins,
and at present these soluble polymers have not been able to be
quantified.14,24 In this work, the decrease in 5-HMF selectivity
with reaction time is supposed to be due to the polymerization
between 5-HMF and fructose to form humins, which consume
the initial fructose and form 5-HMF, and hence reduce the
5-HMF selectivity.
Water is generally thought to has a negative effect on the
dehydration of fructose to 5-HMF.2,4 Since [BMIM][Cl] is a
hydroscopic ionic liquid, the influence of water content in
[BMIM][Cl] on fructose dehydration was studied. As shown
in Fig. 4, when the water content in [BMIM][Cl] was below
5 wt.%, it had little effect on the fructose conversion and 5-HMF
yield. However, as water content increased to above 5 wt.%, the
fructose conversion and 5-HMF yield decreased significantly.
Zhao et al. added water or organic solvents such as glycerol to
3.5 Effect of initial fructose concentration
In acid catalytic dehydration of fructose, initial fructose con-
centration has a large effect on 5-HMF yield and selectivity. As
discussed above, 5-HMF can combine with fructose, and cross-
polymerize to form humins.14 In aqueous systems including
aqueous mixture systems, losses due to humin formation can
be as high as 35% for 18 wt.% fructose solution, although this
value decreases to 20% for 4.5 wt.% fructose solutions.14
The effect of initial fructose concentration on fructose con-
version and 5-HMF selectivity in [BMIM][Cl] is illustrated in
Fig. 3. When the fructose/[BMIM][Cl] weight ratio increased
from 0.01 to 0.05, the 5-HMF selectivity changed slightly
from 86% to 85.2%. As the fructose/[BMIM][Cl] weight ratio
increased from 0.05 to 0.1, the 5-HMF selectivity decreased
Fig. 4 Influence of water content in [BMIM][Cl] on fructose conversion
(80 ◦C, 0.01 g fructose, 1 g [BMIM][Cl], 0.05 g resin, 10 min).
1330 | Green Chem., 2009, 11, 1327–1331
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©

[EMIM][Cl] and proposed that lowering the dielectric constant
ofthereaction mediawould resultin the loss of catalyticactivity.6
had little effect on the fructose conversion rate and 5-HMF
yield, but water content above 5% caused a significant decrease
in the fructose conversions and 5-HMF yields. The ionic liquid
[BMIM][Cl] and resin could be recycled without loss of activity
after the product 5-HMF was separated with ethyl acetate.
Although the process developed is efficient for the conversion
of fructose to 5-HMF, further work is required to improve the
5-HMF yields.
3.7 Recycling of [BMIM][Cl] and catalyst
In the principles of green engineering,26,27 recycling of both
solvent and catalyst is essential so these were examined. Exper-
◦
iments were conducted at 80 C for a reaction time of 10 min.
The product 5-HMF was separated from the solvent mixture
after reaction by extracting 5 times with 8 ml of ethyl acetate
after 0.5 g of water was added, similar to other procedures
in the literature.1,4 [BMIM][Cl] and fructose were found to be
insoluble in ethyl acetate and 5-HMF was the sole product in
the ethyl acetate phase similar to that noted by Hu et al.4 We
examined the amount of 5-HMF in ethyl acetate that represents
the total amount of 5-HMF obtained after separation. The
reaction mixture after extraction was heated at 60 ◦C for 24 hours
in a vacuum oven to remove water and residual ethyl acetate.
It was then used directly in the next run by adding an equal
amount of fructose. It can be seen in Fig. 5 that the recycled
reaction ionic liquid and catalyst gave comparable amounts of
5-HMF showing that the catalyst retained a very high activity
for the conversion of fructose into 5-HMF. The 5-HMF yield in
the recycled system was even higher in some cases than that in
the system with the fresh ionic liquid and resin, which might be
due to the retention of some 5-HMF and unreacted fructose in
the previous cycle.
Acknowledgements
The authors gratefully acknowledge financial support by the
National Natural Science Foundation of China (NSFC, No.
20806041) and the Japan Society for the Promotion of Science
(JSPS).
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4. Conclusions
Catalytic dehydration of fructose to 5-HMF using a strong acid
cation exchange resin as catalyst in ionic liquid [BMIM][Cl] was
investigated. The process we developed was shown to be efficient,
and a fructose conversion of 98.6% with 83.3% of 5-HMF yield
was obtained at 80 ◦C for a relatively short reaction time of
10 min. When the reaction temperature increased to 120 ◦C,
99.3% of fructose conversion with 82.2% of 5-HMF yield was
achieved at a reaction time of 1 min. Initial concentrations of up
to 20 wt.% of fructose in the system did not lead to a lowering
in 5-HMF selectivity. Water content below 5% in [BMIM][Cl]
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