Bifunctional Cr3+ modified ion exchange resins as efficient reusable catalysts for the production and isolation of 5-hydroxymethylfurfural from glucose

Article abstract of DOI:10.1039/c6ra22539j

Cr³⁺ modified readily available cation exchange resins were prepared and explored as heterogeneous bifunctional catalysts for the dehydration of glucose to 5-hydroxymethylfurfural (HMF) in tetraethyl ammonium bromide (TEAB)/water as reaction medium. Excellent HMF isolated yields of up to 70% were achieved using simple crystallization of the reaction medium (TEAB) from ethyl acetate/ethanol which allowed the isolation of HMF in high purity. The best identified catalyst (Amberlyst 15/Cr³⁺) exhibited high activity over 4 cycles. The loss of activity was attributed to the decreased number of acidic sites of the catalyst, thus a simple treatment of the catalyst with 10% HCl efficiently restored its activity in the following cycles.

Full text of DOI:10.1039/c6ra22539j

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ARTICLE
3
+
Bifunctional Cr modified ion exchange resins as efficient
reusable catalysts for the production and isolation of 5-
hydroxymethylfurfural from glucose
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
b*
a*
DOI: 10.1039/x0xx00000x
Joao M. J. M. Ravasco, Jaime A. S. Coelho, Svilen P. Simeonov, and Carlos A. M. Afonso
3
+
www.rsc.org/
Cr modified readily available cation exchange resins were prepared and explored as heterogeneous
bifunctional catalysts for dehydration of glucose to 5-hydroxymethylfurfural (HMF) in tetraethyl ammonium
bromide (TEAB)/water as reaction media. Excellent HMF isolated yields of up to 70% were achieved using
simple crystallization of the reaction media (TEAB) from ethyl acetate /ethanol which allowed the isolation of
3
+
HMF in high purity. The best identified catalyst (Amberlyst15/Cr ) exhibited high activity over 4 cycles.
However, the loss of activity was attributed to the decreased acidic sites of the catalyst, thus a simple
treatment of the catalyst with 10% HCl efficiently restored its activity in the followed up cycles.
Some metal salts were reported to effectively promote the
isomerization and dehydration of glucose. Among several metal
Introduction
4
-6
7-10
salts such as metal oxides and phosphates,
chlorides and in
Nowadays the biorefinery is considered the most promising
approach, which gradually may replace current dependence on
fossil resources, which although cheap and easy to obtain lack any
sustainability in comparison with biorefinery. Among other building
blocks derived from renewable resources such as ethanol, glycerol,
lactic acid and furfural, 5-hydroxymethylfurfural (HMF) has been
recognized as a key biorefining building block derived from
carbohydrates, such as cellulose, glucose, inulin, fructose, etc.
Among them, fructose is currently the only carbohydrate that can
be readily dehydrated into HMF, typically in high yield and
particular chromium chlorides proof to be highly effective. Zhang et
14
2
al. reported the first example of CrCl catalysed dehydration of
glucose achieving nearly 70% HMF yield using the ionic liquid 1-
ethyl-3-methylimidazolium chloride at 100°C. After this pioneer
work, many reports emerged describing the use of chromium
11
chlorides as catalysts for glucose dehydration. Yong et al. reported
3
NHC–CrCl /1-butyl-3-methylimidazolium chloride ([bmim]Cl) system
capable of converting glucose into HMF in up to 81% yield. In 2009
12
Zhao et al. described microwave accelerated glucose dehydration
3
catalysed by CrCl in [bmim]Cl, HMF yield as high as 91% was
1
-2
selectivity. However, fructose has a low abundance in nature
resulting in high cost and very importantly is used in the food
sector. In contrast, glucose has much higher abundancy and is
readily available from non-food cellulosic biomass, thus being a
achieved. CrCl /tetraethylammonium chloride system was reported
3
13
by Lin et al. that efficiently catalyse the glucose dehydration and
was achieved an HMF yield of 71.3%.
It is known that in the chromium catalysed dehydration of glucose
to HMF, the solvent plays a key role and high conversion and
selectivity are usually achieved using ionic liquids as reaction media,
3
highly desirable feedstock. However, due to its resistance to
dehydration and formal carbonyl isomerization, the development of
catalytic systems and processes that could efficiently convert
glucose into HMF is more demanding being still an open topic. It is
known that generally the conversion of glucose to HMF is a two-
step process where first the glucose is isomerized to fructose and
the last undergoes subsequent dehydration to form HMF. The
isomerization step is typically enzymatic, base or metal salt
catalysed, while dehydration is an acid catalysed process. In the
recent years a considerable number of bifunctional catalysts have
been reported allowing this one pot transformation.
14
which was explained by Hensen et al. in which the presence of
highly concentrated and mobile chloride anions from the ionic
liquid that promote various (de)protonation reactions important for
the glucose isomerization (Scheme 1).
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Journal Name
OH
O
OH
HO
HO
OH
O
HO
HO
OH
OH OH
H
H
OH
HO
H O
-H+
+H+
HO
CrCl
-H
2
Cl
Results and Discussion
HO
HO
OH
+
O
Cr
-
2-
HO HO
O
Cr
-
HO
O
Cr Cl
Cl
HO
Cl Cr
Cl
HO
Cl
OH
OH
O
Cl Cr
Cl
Cl
Cl Cl
Cl Cl
It is known that acidic in-exchange resins are successfully applied
Glucose
Cl
3
+ 22,23
for adsorptive removal of Cr .
In this study we were interested
OH
OH
if using this property could be prepared efficient catalysts for
glucose dehydration. A series of such catalysts was obtained by
OH OH
OH
H
HO
HO
OH
HO
H
O
Cl
HO
HO
OH
+
H
+
O
Cr
-
H
H
OOH
O
HO
HO
Cl
- CrCl2
OH
3+
O
Cr Cl
Cl Cl
Cl
Cl
OH
O
OH
-
Cl Cr
Cl
adsorption of Cr over ion exchange resins in MeOH solutions. The
Cr
Cl
Fructose
Cl Cr
Cl
Cl
prepared catalysts were characterized by ICP-AES analyses and the
Cr loading was calculated in w/w %. Amberlyst 15, Amberlyst 36
and Amberlyt 120 exhibit similar results 4.16%, 4.86% and 4.70%
2
+
Scheme 1. Proposed mechanism of the Cr promoted glucose- respectively. As it was expected the highest Cr loading of 5.24% was
fructose isomerization in ionic liquids.
1
4
observed for Amberlite IRC748I being a chelating resin, while only
.41% loading was achieved with IRC 86 (Figure 1). The catalytic
2
However, the problematic downstream separation of HMF from conversion of glucose to HMF was performed using the already
high-boiling organic solvents or ionic liquids and the toxicity and optimized in our previous work TEAB/water (10% w/w) reaction
19
pollution of chromium in the environment are major drawbacks. media. As expected, due to the higher dehydration resistance of
Several attempts to overcome these drawbacks were described. glucose compared to fructose, longer reaction times and higher
1
5
Yang et al. reported recyclable SO H/CrCl bifunctional polymeric catalyst loading were required. However, even after 60 min
3
3
3
+
2
ionic liquids for carbohydrates dehydration to HMF in H O:DMSO/ reaction time at 100°C, using Amberlyst 15/Cr 100% (w/w,
MIBK:n-BuOH biphasic systems. Up to near 49% HMF yield was glucose/catalyst) loading only 34% yield was achieved.
achieved, nevertheless the recyclability of these catalysts in case of Nevertheless, our previous observations about the importance of
16
glucose was not described. Zhang et al. achieved 43.2% HMF yield small amounts of water (10-15%) in the reaction media to achieve
from glucose using heterogeneous chromium-exchanged zirconium clean conversion were confirmed and outstanding purity of 99%
phosphate catalyst in [bmim]Cl. However, this result was obtained was obtained. In the following experiments the effect of
only after 12h reaction time and no catalyst recycling reactions temperature was studied by rising in 10°C steps. The highest HMF
1
7
3+
were reported. More recently Jiang et al. reported Cr modified yield of 70% with outstanding purity of 98% was achieved at 120°C.
3+
ion exchange resins to effectively promote glucose dehydration in Using Amberlyst 15 without Cr under these conditions the HMF
Bmim]Cl ionic liquid. D001-cc resin modified with CrCl exhibited yield was only 24%. Further increase of the temperature to 130°C
[
3
the best performance and up to 70% HMF yield have been was not beneficial and decreased yield of 55% was observed
achieved. The catalyst was recycled over 6 cycles and decreasing probably due to the unstable nature of HMF at high temperatures
yields were observed after each cycle. Nevertheless, probably due (Figure 2). Using lower catalyst loading of 50% (w/w) resulted in a
to the difficulties associated with the HMF isolation from the ionic lower yield of 59%, thus 100% (w/w) was established as optimal for
liquid only yields determined by HPLC were reported.
the further experiments.
Nonetheless, beside all the achievements reported so far, the
development of a glucose dehydration process that will allow both
easy isolation of HMF from the reaction media and recyclability of
the catalysts from both economic and environmental point of view,
this issue is still an open topic. Previously, we reported that
tetraethyl ammonium bromide (TEAB)/water is an efficient reaction
media for fructose dehydration, which allowed quantitative HMF
isolation via simple TEAB crystallization and subsequent recycling of
1
8,19
both TEAB and organic solvents.
optimized conditions for fructose, we were able to achieve only
5% HMF yield from glucose using CrCl3 as catalysts under
Nevertheless, under the
3
homogeneous conditions. Later, we demonstrated that TEAB/water
reaction media proof to be highly efficient for two-step integrated
chemo-enzymatic production of HMF from glucose. Using this
2
0
approach 87% isolated HMF yield from glucose were achieved,
which to the best of our knowledge still remains among the highest
reported yields as stated in a recent review.
21
Figure 1. ICP-AES Cr quantification.
However, constructing an efficient and recyclable one-pot process
for glucose transformation to HMF using the already proven
TEAB/water reaction media is still challenging. Here in, a series of
cheap and readily available acidic cation exchange resins modified
3
+
with Cr were prepared and used as bifunctional heterogeneous
catalysts in one pot glucose dehydration in TEAB/water reaction
media. The previously developed crystallization method for HMF
isolation was used allowing both quantitative isolation of HMF from
the reaction media and reuse of the catalyst.
2
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3
+
Figure 2. Glucose dehydration under diferent temperatures. Figure 4. Glucose dehydration using diferent Cr modified cation
3
+
Reaction conditions: Amberlyst 15/Cr (0.7g), glucose (0.7g,), water exhange resins. Reaction conditions: Catalyst (0.7g), glucose (0.7g,),
0.7mL), TEAB (7g), 60 min.
water (0.7mL), TEAB (7g), 120°C, 60 min.
(
3
+
Amberlyst 15/Cr was selected as the best catalyst to study its
Further optimization of the reaction time was performed. However, reusability under optimized conditions. Minimal mechanical
prolonged reaction times of 75 min and 120 min resulted in lower destruction of the catalysts was observed over the full set of cycles,
yields of 68% and 64% and purity of 91% and 92% respectively when the stirring was precisely controlled to not overcome 600
(
Figure 3).
rpm. High catalytic activity and repetitive yield of close to 70% was
observed over the first 3 cycles, while low decrease of the yield to
5
9% was observed over the fourth cycle. However, the yield rapidly
3
+
decreases to only 25% in the fifth cycle. The leaching of the Cr in
the reaction mixture was followed by ICP analysis. The leaching
over the first cycle was determined to be 16%. However, over the
second cycle it dramatically decrease to only 1.5%, which can be
3
+
attributed to the fact that non-absorbed Cr was not sufficiently
removed during the catalyst pretreatment. The overall leaching
over the following cycles 3-5 was determined to be 5% and average
of 1.7% per cycle. We assumed that the loss of catalytic activity can
be derived to the decrease of the acid sites of the catalysts since as
we already observed that on one hand only small amounts of Cr are
sufficient to promote the first step of the reaction, and on the other
3
+
hand the determined Cr leaching was minimal, thus after the fifth
Figure 3. Glucose dehydration under diferent reaction times. cycle the catalysts was regenerated using simple treatment with
3
+
Reaction conditions: Amberlyst 15/Cr (0.7g), glucose (0.7g,), water 10% aq. HCl. The use of the regenerated catalyst resulted in 50%
(
0.7mL), TEAB (7g), 120°C.
yield in the sixth cycle which decreased to 35% in the eight cycle.
It’s worthy to be mentioned that restoring the catalytic activity
using 10% aq. HCl was used as a proof of concept and no
optimizations were performed, thus suggesting that full recovering
of the catalytic activity may be possible upon further optimization
(Figure 5).
With the optimized conditions in hands for Amberlyst 15, we
3
+
studied the catalytic activity of the other Cr modified Amberlyst
6, Amberlyst IRC86, Amberlite IRC748I and Amberlyt 120 resins
Figure 4). No direct correlation between Cr loadings and observed
3
(
3
+
yields have been noticed. Surprisingly the two Cr modified ion
exchange resins with the highest Cr loadings Amberlyt 120/Cr
(
3
+
3
+
4.70%) and Amberlite IRC748I/Cr (5.24%) provided very low
yields of only 10% and 27% respectively. Similar yield of 62% as for
3
+
3+ .
Amberlyst 15/Cr was achieved with Amberlyst 36/Cr . Amberlyst
3
+
IRC86/Cr which exhibited the lowest Cr loading of only 2.41%
provided almost identical yield of 68%, thus leading to the idea that
very low amounts of Cr are sufficiently catalysing glucose to
fructose isomerization. However, considering the all process a good
balance between Cr loading and acidity of the catalyst is important.
It is worthy to be mentioned that although considerable variation of
the yields was observed for different resins, the HMF was isolated
in high purities of above 98% in all cases (Figure 4).
Figure 5. Recycling experiments. Reaction conditions: Amberlyst
3
+
1
5/Cr (0.7g), glucose (0.7g,), water (0.7mL), TEAB (7g), 120°C, 60
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th
3+
min. After 5 cycle, the Amberlyst 15/Cr was treated with 10% aq. ethyl acetate (200 mL), stirred for 20 minutes and filtered off over a
HCl.
pad of silica (10g) to yield HMF as brownish liquid, which solidifies
in freezer (-12°C). The product purity was analyzed by HPLC and 1H
NMR.
Experimental
Recycling experiments and catalyst reactivation
The recycling experiments were performed using the described
general procedure, the recovered from the reaction Amberlyst
General
3
+
All chemicals and solvents were purchased from Sigma-Aldrich, Alfa
Aesar and Merck and used as received, unless otherwise noted.
Et4NBr Sigma Aldrich 14023-1kg (water content 1 % w/w),
Amberlyst 15 hydrogen form wet Sigma Aldrich 216399, Amberlyst
1
5/Cr catalyst was directly used in the next cycle upon drying
under vacuum for 1h (0.1 mbar).
3
+
The Amberlyst 15/Cr catalyst isolated from the 5th cycle was
reactivated using the following procedure, the catalyst and 14 mL of
36 Sigma Aldrich 436712, Amberlite IR120 hydrogen form hydrogen
1
0% HCl were charged into 50 mL round-bottomed flask and stirred
form Sigma Aldrich 10322, Amberlite IRC86 hydrogen form Sigma
Aldrich 06455, Amberlite IRC748I Sigma Aldrich 13296-U SUPELCO,
D(+)-Glucose anhydrous Merck Art. 8337. HPLC analysis were
performed using Dionex P680 pump, Dionex UVD 340S diode array
detector, detection at 275 nm, manual injector with 20μl loop,
column HICHROM C18, 250x4.6mm, Rt (HMF) = 9.5 min or Kromasil
at room temperature for 1h. The catalyst was filtered, washed with
absolute ethanol (15 mL) and dried under vacuum (0.1 mbar, 1 h)
prior used in the following cycles without further treatment.
Conclusions
100, C18, 250x4.6mm. Rt (HMF) = 11.4 min. Mobile phase gradient
In conclusion, is described a highly efficient approach for the
direct transformation of glucose to HMF that addresses both
isolation and environmental issues related with the use of Cr
from 1:99 to 50:50 for 40 min acetonitrile:water, flow 1 mL/min,
The purity of HMF was determined by comparing the obtained
integration area of HMF with other observed minor peaks.
3
+
3
+
catalysis. Five Cr modified readily available cation exchange
resins were prepared and explored as heterogeneous
bifunctional catalysts for this transformation. Among them
NMR spectra were recorded at room temperature in a Bruker AMX
3
00 using CDCl as solvent.
3
ICP analyses were performed on radial Horiba Jobin-Yvon, Ultima
ICP-AES equipped with Czerny-Turner monochromator and 40.68
MHz RF generator.
3
+
Amberlyst 15/Cr exhibit the best performance and was
successfully recycled over 4 cycles, while significant decrease
of the catalytic activity was observed only in the 5th cycle.
However, the loss of catalytic activity could be overcome by
simple regeneration of the acidic sites of the catalyst. The
already optimized in our previous studies of TEAB/water
reaction media proof to be highly efficient allowing easy HMF
isolation in high purity, thus providing superior alternative to
the commonly used ionic liquids.
Catalysts preparation
All the catalysts were prepared as follows - A pressure glass reactor
tube (Figure S4) (15 mL, Aldrich Z181064) was charged with 3g of
the corresponding resin and 1g CrCl
3 2
*6H O, 10 mL MeOH was
added and the mixture was heated without stirring at 80°C
3
+
overnight. After cooling down the Cr modified resins were filtered
and washed subsequently with 100 mL of water and 100 mL of
MeOH prior dried in open air for 12h.
Acknowledgements
Catalysts characterisation
3
+
To approximately 100 mg of the corresponding Cr ion exchange
resin were added 0.6 mL 35% aq. HCl and 0.2 mL 69% aq. HNO
3
.
The authors acknowledge Fundação para a Ciência e a
Then, the sample was heated 120°C for 180 min. The obtained Tecnologia
homogeneous solution was transferred in 5 mL volumetric flask and UID/DTP/04138/2013), European Research Area Network;
diluted with deionized water. 1 mL of the resulting solution was ERANet LAC (ref. ELAC2014/BEE-0341), and
(FCT) (ref.
SFRH/BPD/109476/2015
and
transferred in 100 mL and diluted with deionized water. The ICP- REDE/1518/REM/2005 (FF-UL) for the mass service.
AES analyses were performed using the following conditions: RF
power 1050 kW, Coolant gas flow rate (Ar) 12 mL/min, Nebulizer
Mira Mist with 3 bar pressure, Sample flow rate 1.0 mL/min, Notes and references
Wavelength 267.716 nm.
1
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General procedure for catalytic dehydration of glucose into HMF
2
A pressure glass reactor tube (Figure S4) (15 mL, Aldrich Z181064)
was charged with the catalyst (0.7 g), glucose (0.7 g, 3.885 mmol),
water (0.7 mL), tetraethylammonium bromide (TEAB) (7 g) and the
resulting mixture was stirred magnetically at 600 rpm using a cross-
shaped magnetic stirrer and heated with a thermostatically
controlled (0.1°C) oil bath at a certain temperature for a specific
time. Upon cooling to room temperature, the mixture was dissolved
in absolute ethanol (20 mL), the catalyst was filtered and washed
with absolute ethanol (20 mL). The solvent was evaporated under
vacuum and the resulting solid was then dissolved in hot absolute
ethanol (3.5 mL). The clear solution was then precipitated with
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