Production of 5-hydroxymethylfurfural from fructose by a thermo-regulated and recyclable Br?nsted acidic ionic liquid catalyst

Article abstract of DOI:10.1039/c5ra08107f

In this work, a thermo-regulated recyclable catalytic system using ionic liquid [HO₂CMMIm]Cl as the catalyst and isopropanol as the solvent has been demonstrated to be effective for the dehydration of fructose to synthesize 5-hydroxymethylfurfural (HMF). The solubility of [HO₂CMMIm]Cl ionic liquid in isopropanol is temperature-dependent, being miscible with isopropanol at a temperature range suitable for fructose dehydration (e.g., above 80 °C) while not soluble at lower temperatures such as room temperature. Temperature-responsive solubilization/precipitation of [HO₂CMMIm]Cl in isopropanol renders the acidic ionic liquid an appealing thermo-regulated phase-switchable catalyst. Furthermore, the effects of various parameters including catalyst loading, fructose concentration, reaction time and temperature on the catalytic performance of fructose dehydration have been studied systematically. Under optimized reaction conditions, up to 91.2 mol% HMF yield could be obtained. Additionally, when the ionic liquid catalyst precipitated out after the reaction, the solvent can be simply decanted and [HO₂CMMIm]Cl could be directly reused for the next run with freshly added solvent and substrate. It was found that [HO₂CMMIm]Cl could be reused at least five times without considerable loss of activity. Furthermore, a kinetic analysis was carried out, indicating the activation energy for the reaction to be 62.1 kJ mol^-1. This catalytic system can be envisioned to find applications in a wide range of acid-catalyzed reactions with facile, thermo-regulated catalyst recovery features.

Full text of DOI:10.1039/c5ra08107f

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Production of 5-hydroxymethylfurfural from
fructose by a thermo-regulated and recyclable
Brønsted acidic ionic liquid catalyst
Cite this: RSC Adv., 2015, 5, 47377
Yubo Ma,†a Shaojun Qing,†b Lei Wang,ac Nurali Islam,a Shuzhe Guan,d Zhixian Gao,b
a
e
a
ad
*
Xamxikamar Mamat, Hongyi Li, Wumanjiang Eli and Tianfu Wang
In this work, a thermo-regulated recyclable catalytic system using ionic liquid [HO2CMMIm]Cl as the
catalyst and isopropanol as the solvent has been demonstrated to be effective for the dehydration of
fructose to synthesize 5-hydroxymethylfurfural (HMF). The solubility of [HO2CMMIm]Cl ionic liquid in
isopropanol is temperature-dependent, being miscible with isopropanol at a temperature range suitable
for fructose dehydration (e.g., above 80 ꢀC) while not soluble at lower temperatures such as room
temperature. Temperature-responsive solubilization/precipitation of [HO2CMMIm]Cl in isopropanol
renders the acidic ionic liquid an appealing thermo-regulated phase-switchable catalyst. Furthermore,
the effects of various parameters including catalyst loading, fructose concentration, reaction time and
temperature on the catalytic performance of fructose dehydration have been studied systematically.
Under optimized reaction conditions, up to 91.2 mol% HMF yield could be obtained. Additionally, when
the ionic liquid catalyst precipitated out after the reaction, the solvent can be simply decanted and
[HO2CMMIm]Cl could be directly reused for the next run with freshly added solvent and substrate. It was
found that [HO2CMMIm]Cl could be reused at least five times without considerable loss of activity.
Furthermore, a kinetic analysis was carried out, indicating the activation energy for the reaction to be
62.1 kJ molÀ1. This catalytic system can be envisioned to find applications in a wide range of acid-
catalyzed reactions with facile, thermo-regulated catalyst recovery features.
Received 2nd May 2015
Accepted 21st May 2015
DOI: 10.1039/c5ra08107f
www.rsc.org/advances
Department of Energy to be one of the top 12 platform chem-
icals. When produced economically, HMF can be envisioned to
1. Introduction
serve as a building block molecule, having the potential to be
derivatized to synthesize furanic-based polyamides, polyesters,
and polyurethanes analogous to petroleum-based terephthalic
acid.1–6
Continuing and accelerating depletion of fossil-derived carbon
resources has increasingly represented a challenge that has to
be dealt with urgently to meet the goal of achieving a sustain-
able development of the society. In this regard, carbohydrates
provide an attractive alternative to fossil resource, since they
account for almost 75% of biomass feedstock in nature.
Consequently, recent years have witnessed an extensive
research effort aiming to develop technologies that have the
potential to be implemented in order to convert carbohydrates
to useful chemical intermediates economically and practically.
One such carbohydrate-based model molecule is 5-hydrox-
ymethylfurfural (HMF), which has been proposed by US
HMF can be synthesized from C6 carbohydrates (glucose and
fructose) via a triple dehydration reaction, generally catalyzed
by acids.7 Extensive research efforts have studied the production
of HMF using fructose as feedstock, with excellent HMF yields
being reported.8–10 A variety of solvent have been exploited to
carry out this dehydration reaction, namely water,11 organic
solvents
(e.g.,
DMSO),12–14
organic/aqueous
binary
mixtures,11,15,16 ionic liquids.17–26 A multitude of catalyst systems
have been developed for this reaction,10,27–32such as homoge-
neous mineral acids including H2SO4, HCl, H3PO4, and oxalic
acid,4,5,33,34 or heterogeneous solid acids H-form zeolites,35–37
strong acid cation exchange resins,21,38,39 and most recently,
acidic ionic liquids.12,13,24,27,40–43 Because of its unique and
tunable properties, strategies utilizing ionic liquids (ILs) as
solvent or using acidic ionic liquids as catalysts for sugar
dehydration to produce HMF have grown rapidly. For example,
Bao et al. reported that both the Lewis acidic and Brønsted
acidic ionic liquids could effectively catalyze the dehydration of
aXinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences,
40-1 South Beijing Road, Urumqi, 830011, China. E-mail: tianfuwang@ms.xjb.ac.cn;
Fax: +86 9917880514; Tel: +86 9917880514
bInstitute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001, China
cDepartment of Chemistry and Chemical Engineering, Xinjiang University, Urumqi,
830011, China
dXinjiang Institute of Engineering, Urumqi, 830011, China
eXinjiang Products Supervision & Inspection Institute of Technology, Urumqi, 830011,
China
† These authors contributed equally.
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fructose under microwave irradiation, obtaining good HMF features for carbohydrate dehydration reaction is yet to be
yields.40 In addition, systems consisting of IL, 1-H-3-methyl reported.
imidazolium chloride and choline chloride/citric acid as cata-
Herein, we report selective dehydration of fructose to HMF
lysts, could lead to good HMF yields.24,27 Tong et al. reported using a [HO2CMMIm]Cl/isopropanol system, shown in Scheme
that a 72.3% HMF yield (87.2% selectivity) using fructose as 2. In addition to its facile thermo-regulated recyclability,
ꢀ
feedstock can be obtained for 2 h at 90 C in the presence of [HO2CMMIm]Cl also showed high activity for fructose dehy-
Brønsted-acidic ionic liquid [NMP]+[CH3SO3]À catalyst in dration reaction, producing HMF at a yield of 91.2% under
DMSO,12 later the same group reported a 74.8% HMF yield optimized reaction conditions. It is desirable to take advantage
achieved over protic ionic liquid catalyst [NMM]+[CH3SO3]À of the convenient catalyst recyclability of the present catalytic
using an N,N-dimethylformamide–lithium bromide (DMF–LiBr) system to avoid extra separation processing step in practice.
mixed solvent system.13 Liu et al. reported that a 95.7% HMF
yield could be obtained with fructose as the feedstock, using
2. Experimental section
2.1 Materials
[CMIm]Cl as the catalyst in DMSO.42 Although good results
using ionic liquid for fructose dehydration have been obtained,
development of efficient catalytic systems with superior cata-
lytic performance and recyclability is still high desirable.
1-Carboxymethyl-3-methylimidazolium chloride, [HO2-
CMMIm]Cl (Scheme 1) is an acidic ionic liquid with a carboxylic
acid group tethered to the core of the imidazolium ring, which
could be envisioned to be effective in converting fructose to
HMF. In general, [HO2CMMIm]Cl is in the solid form with a
melting temperature of 190 ꢀC. In order to test the catalytic
activity of [HO2CMMIm]Cl for fructose dehydration, screening
experiments of [HO2CMMIm]Cl in various commonly used
organic solvent for fructose dehydration were rst carried out.
Interestingly, to our surprise, it was found that [HO2CMMIm]Cl
had a temperature-dependent solubility in isopropanol. It is
completely insoluble in isopropanol at the room temperature,
whereas it is miscible in isopropanol when the solution is
heated to temperatures higher than 80 ꢀC. Cooling the solution
down to room temperature resulted in the precipitation of the
ionic liquid out of isopropanol and the solubilization/
precipitation cycle can be performed repeatedly. Inspired by
this observation, we set out to devise a thermo-regulated recy-
clable catalytic system consisting of [HO2CMMIm]Cl as acidic
ionic liquid catalyst and isopropanol as solvent for HMF
production from fructose. To the best of our knowledge, ionic
liquid catalytic system simultaneously having both catalytic
activity and facile, thermo-regulated catalyst recyclability
The ionic liquid (IL) 1-carboxymethyl-3-methylimidazolium
chloride ([HO2CMMIm]Cl) was supplied by Lanzhou Green-
chem ILS, LIPC, CAS (Lanzhou, China). Fructose and iso-
propanol were purchased from Alfa Aesar. HMF standard
sample was purchased from Aldrich sigma. All the materials
were of analytic or higher grad and used as received without
further purication.
2.2 Reaction testing
All the reactions were carried out in 10 ml thick-walled glass
reactors (Alltech). An oil bath was used to heat the reactor
rapidly to the desired reaction temperature, with temperature
and stirring being controlled by an Isotemp digital stirring hot
plate (Fisher Scientic). In a typical experiment, desired
amounts of fructose, desired amounts of [HO2CMMIm]Cl and
3.0 g isopropanol were added to the Alltech reactor. A triangular
stir bar (Fisher Scientic) was also added to allow for adequate
agitation. The reactor was then sealed with PTFE liner covered
caps (Fisher Scientic) and immersed in the oil bath at desired
reaction temperature and stirred at 350 rpm. At specied time,
the reactors were removed from the oil bath and then cooled
rapidly in an ice bath to quench the reaction. For all the reac-
tions, signicant amounts of soluble and insoluble brownish
humins were formed, of which the production rate was difficult
to quantify. The humin formation precluded a closed carbon
balance analysis and thus the only product analyzed was HMF.
Each reaction was repeated at least three times, and the average
yield was reported. In the catalyst recyclability experiment, the
mother liquid was decanted aer the solution was cooled down
and the remaining [HO2CMMIm]Cl solid catalyst was directly
used for the next run by adding fresh fructose and isopropanol.
2.3 Sample analysis
Scheme 1 Molecular structure of [HO2CMMIm]Cl.
Aer each reaction, the liquid sample was ltered and then
analyzed by an HPLC equipped with UV and refractive index
detectors. HPLC analysis was performed using a Shimadzu
LC-20A system equipped with a SPD-20A UV detector at 280 nm
and a refractive index (RI-20A) detector maintained at 333 K.
The samples were analyzed using an Aminex HPX-87H Column
at 333 K with 5 mM H2SO4 at a ow rate of 0.6 ml minÀ1 as the
mobile phase. The amount of HMF was analyzed by HPLC with
a Shimadzu UV-Vis SPD-20A detector at 280.0 nm, and a
Scheme 2 Conversion of fructose into HMF catalyzed by [HO2-
CMMIm]Cl IL in isopropanol.
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InterSustain C18 column at 313 K, with a methanol : 5 mM polymerization and rehydration of HMF44 can also readily take
H2SO4 (8 : 2 v/v) binary solvent as the mobile phase at a ow rate place at high temperature. Based on the results above, the
of 0.7 ml minÀ1. The conversion/selectivity being used in this reaction temperature of 110 ꢀC was used for further reaction
manuscript are dened as below: the conversion of fructose is condition optimization of fructose dehydration.
dened as the moles of fructose reacted divided by the moles of
initial fructose added, the selectivity of HMF is dened as the
moles of HMF produced divided by the moles of fructose reac-
ted, and the yield of HMF is dened as the fructose conversion
multiplied by the HMF selectivity.
3.3 Effect of reaction time
The inuence of reaction time on the conversion of fructose and
the yield of HMF was also examined, and the data are
summarized in Fig. 3. It can be seen that the conversion of
fructose and the HMF yield increased readily with time. At the
reaction time of 3 h, fructose conversion and HMF yield were
ꢁ100% and 90.8% respectively, indicating under studied
condition, full conversion of fructose can be obtained within
3 h. Prolonging the reaction time to 4 h, however, resulted in a
slightly decreased HMF yield of 89% at 100% fructose
conversion.
3. Results & discussion
3.1 Rationale
As shown in Fig. 1, a thermo-regulated catalytic system
comprising of [HO2CMMIm]Cl and isopropanol is designed for
fructose dehydration reaction. At low temperature, fructose and
[HO2CMMIm]Cl are not soluble in isopropanol. Increasing the
temperature resulted in the solubilization of fructose and
[HO2CMMIm]Cl, while at the same time, the acid functionality
on [HO2CMMIm]Cl can catalyze fructose dehydration to
produce HMF. When the reaction is complete, isopropanol
solution was cooled down, precipitating out the [HO2CMMIm]
Cl catalyst, which can be recycled and used for the subsequent
reactions. It can be speculated that because of the reversible
solubilization/precipitation of [HO2CMMIm]Cl in a thermo-
regulated manner, the catalytic system can be recycled for
multiple times.
3.4 Effect of catalyst loading
In order to determine the optimal amount of [HO2CMMIm]Cl
catalyst, the effect of catalyst loading on fructose conversion
3.2 Effect of reaction temperature
The effect of reaction temperature on the dehydration of fruc-
tose to HMF in isopropanol with [HO2CMMIm]Cl as the catalyst
(reaction time of 3 h) was examined, and the results are shown
in Fig. 2. When the temperature increased from 80 ꢀC to 110 ꢀC,
both fructose conversion and HMF yield increased gradually,
reaching 100% and 90.8%, respectively at 110 ꢀC. HMF yield
decreased to 71% when the reaction temperature was further
increased to 120 ꢀC although at 100% fructose conversion. It is
concluded that the dehydration of fructose was accelerated by
increasing the reaction temperature while an optimized
temperature would be preferred since side reactions, such as
Fig. 2 Effect of reaction temperature on the catalytic conversion of
fructose to HMF. Experimental conditions: 0.1 g [HO2CMMIm]Cl, 0.1 g
fructose, 3.0 g isopropanol, reaction time of 3 h.
Fig. 1 Designing principle of thermo-regulated recyclable catalytic system.
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Fig. 5 Effect of substrate loading on fructose dehydration. Experi-
mental conditions: 3 g isopropanol, 0.1 g [HO2CMMIm]Cl, reaction
temperature of 110 ꢀC, reaction time of 30 minutes.
Fig. 3 Effect of reaction time on fructose dehydration reaction.
Experimental conditions: 0.1 g [HO2CMMIm]Cl, 0.1 g fructose, 3.0 g
isopropanol, reaction temperature of 110 ꢀC.
110 ꢀC and reaction time of 30 minutes. As shown in Fig. 5,
HMF yield decreased from 91.2% to 74.3% with the amount of
fructose increasing from 50 mg to 150 mg. This may arise from
increased concentration of fructose in isopropanol, which likely
favored side reactions such as polymerization and rehydration
producing humins as the main by-product.45,46
3.6 Catalyst separation and reusability
In contrast to previously reported studies47,48 where the mother
liquor aer each reaction can be used multiple times for sugar
dehydration, the current thermo-regulated catalyst recovery
strategy provided the advantage of a more straightforward and
Fig. 4 Effect of catalyst loading on fructose dehydration. Experimental
conditions: 3 g isopropanol, 0.1 g fructose, reaction temperature of easy catalyst recycling method. As depicted in Fig. 1, catalyst in
110 ꢀC, reaction time of 30 minutes.
this study can be separated from the reaction medium by simply
cooling down the solution. Indeed, as shown in Fig. 6, before
the reaction, both fructose and [HO2CMMIm]Cl catalyst were
and HMF yield was examined. Varying amount of catalyst was
insoluble in solvent (Fig. 6a), whereas fructose and
added to the solution containing 0.1 g fructose and the reaction
[HO2CMMIm]Cl were completely dissolved in the solution
was carried out under 110 ꢀC with a reaction time of 30 minutes,
giving the results summarized in Fig. 4. As shown in the gure,
ꢀ
(Fig. 6b) when the solution was heated above 80 C. When the
reaction was complete, the solution was cooled down to room
fructose conversion correlated positively with catalyst loading,
temperature, thereby precipitating [HO2CMMIm]Cl out from
meaning a higher catalyst loading can result in higher fructose
the solvent for subsequent reaction runs (Fig. 6c). The
conversion rate. However, as catalyst loading increased from
successful thermo-regulated catalyst separation allowed for easy
60 mg to 100 mg, HMF yield also increased, reaching 83.4%
with 0.1 g [HO2CMMIm]Cl catalyst. An extra increase of catalyst
loading, however, slightly decreased HMF yield, namely 79.2%
catalyst recovery and reuse of [HO2CMMIm]Cl.
The recyclability of [HO2CMMIm]Cl catalyst was further
examined. The reactions were performed at 110 ꢀC for 30
at 120 mg, indicating that excess catalyst loading might cause
minutes in the presence of [HO2CMMIm]Cl. Aer the reaction,
the side reactions to produce humins or other compounds.45,46
Therefore, 0.1 g [HO2CMMIm]Cl loading (0.1 g fructose) was
the solution was cooled down and the supernatant was trans-
ferred out, leaving [HO2CMMIm]Cl catalyst inside the reactor.
found to be optimal for the reaction under studied reaction
The solid ionic liquid was washed briey with isopropanol and
congurations.
the same amount of isopropanol and fructose were added for
the next run. As shown in Fig. 7, the catalyst could be reused at
3.5 Effect of substrate loading
least ve times without considerable performance in the HMF
The effect of the amount of fructose on the HMF yield was also production, revealing the efficacy of such thermo-regulated
studied with other reaction conditions being as below: the catalyst system using the combination of [HO2CMMIm]Cl and
amount of [HO2CMMIm]Cl of 0.1 g, reaction temperature of isopropanol.
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Table
1
Reaction rate constants (k) of fructose dehydration at
different reaction temperaturesa
Entry
Temperature (ꢀC)
k (minÀ1
)
Correlation coefficient
1
2
3
90
100
110
0.0202
0.0871
0.1480
0.9878
0.9986
0.9945
a
Experimental conditions: reaction time of 3 h, 0.1 g [HO2CMMIm]Cl,
0.1 g fructose and 3 ml isopropanol.
Fig. 8 Arrhenius plot for the dehydration of fructose in isopropanol
over [HO2CMMIm]Cl.
Fig. 6 Physical state of catalyst at different course of reaction: (a)
before the reaction; (b) during the reaction; (c) after the reaction.
Table 2 Kinetic parameters for the dehydration of fructosea
Reaction order, n
1.0
Activation energy, Ea (kJ molÀ1
)
62.1
Pre-exponential factor, A (minÀ1
Correlation coefficient
)
5.7 Â 107
0.9948
a
Experimental conditions: reaction temperature of 110 ꢀC, 0.1 g
[HO2CMMIm]Cl, 0.1 g fructose and 3 ml isopropanol.
previously described methods.13,34,35,50 Plots of ln k versus reac-
tion time (t) were used to obtain rst-order kinetic constants. As
summarized in Table 1, the value of k increases with increasing
temperature, indicating that higher temperature accelerated
fructose dehydration reaction rate. An Arrhenius plot was
obtained, as shown in Fig. 8. Based on these data, the kinetic
parameters for [HO2CMMIm]Cl catalyzed dehydration of fruc-
tose to HMF can be calculated and summarized in Table 2. An
apparent activation energy of 62.1 kJ molÀ1 was obtained for
fructose dehydration.
Fig.
7 Reusability of [HO2CMMIm]Cl for fructose dehydration.
Experimental conditions: 3 g isopropanol, 0.1 g [HO2CMMIm]Cl, 0.1 g
fructose, reaction temperature of 110 ꢀC, reaction time of 30 minutes.
4. Conclusion
3.7 Kinetics studies with fructose as feedstock
In summary, a thermo-regulated recyclable catalytic system
using a combination of [HO2CMMIm]Cl and isopropanol for
the production of HMF from fructose was developed. It has
been demonstrated that fructose and [HO2CMMIm]Cl ionic
liquid were insoluble in isopropanol before the reaction at room
Kuster49 and Vogel34 reported a reaction order of 1 on substrate
for the dehydration of fructose. In accordance with this result, a
kinetic analysis of the dehydration of fructose in isopropanol
over [HO2CMMIm]Cl catalyst was performed according to
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