Fructose dehydration to 5HMF in a green self-catalysed des composed of N,N-diethylethanolammonium chloride and p-toluenesulfonic acid monohydrate (p-TSA)

Article abstract of DOI:10.1016/j.crci.2015.11.004

Due to the increasing concerns about the availability and accessibility of fossil fuel reserves, and the subsequent effect of using them on climate change, production of green energy has recently become a hot area of interest in the research field. As a renewable energy source, biomass conversion to biofuels has shown a great potential towards green fuel production; particularly fructose conversion to 5-hydroxymethylfurfural (5HMF) as a building block material and source of green fuels and other high value chemicals. Herein, we investigate fructose dehydration to 5-hydroxymethylfurfural (5HMF) as a green fuel precursor, using a green self-catalysed environmentally friendly Deep Eutectic Solvent (DES), composed of inexpensive N,N-diethylethanolammonium chloride as organic salt and p-toluenesulfonic acid monohydrate (p-TSA) as a hydrogen bond donor (HBD) and novel medium for the fructose dehydration reaction. The advantage of using this DES is its ability to act as a solvent and catalyst simultaneously. It has shown to actively catalyse the dehydration reaction of fructose under moderate reaction conditions with a high 5HMF yield of 84.8% at a reaction temperature of 80 °C, reaction time of 1 h, DES mixing ratio of 1:0.5 salt to p-TSA (w/w), and initial fructose ratio of 5.

Full text of DOI:10.1016/j.crci.2015.11.004

C. R. Chimie xxx (2015) 1e7
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Full paper/Memoire
Fructose dehydration to 5HMF in a green self-catalysed DES
composed of N,N-diethylethanolammonium chloride and
p-toluenesulfonic acid monohydrate (p-TSA)
Amhamed Assanosi, Mohamed M. Farah, Joseph Wood, Bushra Al-Duri*
School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Due to the increasing concerns about the availability and accessibility of fossil fuel re-
serves, and the subsequent effect of using them on climate change, production of green
energy has recently become a hot area of interest in the research field. As a renewable
energy source, biomass conversion to biofuels has shown a great potential towards green
fuel production; particularly fructose conversion to 5-hydroxymethylfurfural (5HMF) as a
building block material and source of green fuels and other high value chemicals.
Herein, we investigate fructose dehydration to 5-hydroxymethylfurfural (5HMF) as a green
fuel precursor, using a green self-catalysed environmentally friendly Deep Eutectic Solvent
(DES), composed of inexpensive N,N-diethylethanolammonium chloride as organic salt
and p-toluenesulfonic acid monohydrate (p-TSA) as a hydrogen bond donor (HBD) and
novel medium for the fructose dehydration reaction.
Received 8 May 2015
Accepted 2 November 2015
Available online xxxx
Keywords:
Fructose
5-Hydroxymethylfurfural (5HMF)
Deep Eutectic Solvent (DES)
Dehydration
The advantage of using this DES is its ability to act as a solvent and catalyst simultaneously.
It has shown to actively catalyse the dehydration reaction of fructose under moderate
reaction conditions with a high 5HMF yield of 84.8% at a reaction temperature of 80 ꢀC,
reaction time of 1 h, DES mixing ratio of 1:0.5 salt to p-TSA (w/w), and initial fructose ratio
of 5.
ꢀ
© 2015 Published by Elsevier Masson SAS on behalf of Academie des sciences.
1. Introduction
valuable chemicals, which can be obtained directly from
carbohydrates [6e8].
The growing anxiety about the sharp reduction in fossil
fuel resources and the effect on climate change resulting
from the increasing rates of emissions have led to great
interest in biomass utilisation as a renewable source of
energy and other valuable materials [1,2]. Particularly, the
carbohydrates obtained from lignocellulosic biomass are a
promising and abundant source of green energy, as they are
obtained from non-edible biomass and are relatively
inexpensive [3e5]. The numerous studies conducted in this
field revealed that 5HMF is a very useful multiple source of
chemical building block material of green fuels and
5-Hydroxymethylfurfural (5HMF) is a heterocyclic fur-
anic compound consisting of two functional groups of hy-
droxide and aldehyde in the positions 2 and 5 in the furan
ring. As shown in Fig. 1, 5HMF is produced from biomass
resources through a variety of carbohydrates and it has
useful downstream derivatives in the form of chemicals,
pharmaceuticals, bioplastics and biofuels.
Carbohydrates and particularly fructose were dehy-
drated to 5HMF in different reaction media such as aqueous
systems [10], biphasic systems [9] and ionic liquids [1]. The
use of all previously mentioned systems in biomass uti-
lisation was inhibited by several drawbacks such as low
5HMF yields, solvent-related environmental aspects, high
cost, and the requirement of severe reaction conditions.
* Corresponding author.
E-mail address: b.al-duri@bham.ac.uk (B. Al-Duri).
http://dx.doi.org/10.1016/j.crci.2015.11.004
ꢀ
1631-0748/© 2015 Published by Elsevier Masson SAS on behalf of Academie des sciences.
Please cite this article in press as: A. Assanosi, et al., Fructose dehydration to 5HMF in a green self-catalysed DES composed of
N,N-diethylethanolammonium chloride and p-toluenesulfonic acid monohydrate (p-TSA), Comptes Rendus Chimie (2015),
http://dx.doi.org/10.1016/j.crci.2015.11.004

2
A. Assanosi et al. / C. R. Chimie xxx (2015) 1e7
Fig. 1. Production of 5HMF from biomass resources and its useful derivatives [9].
The production of 5HMF from carbohydrate started
Lately, a new kind of self-catalysed green solvents
namely Deep Eutectic Solvents (DESs) were explored by
Abbott [15].
A DES is a mixture formed by mixing quaternary
ammonium salts with hydrogen bond donors such as am-
ides, amines, alcohols or carboxylic acids [16].
The first DES form was made of a mixture of choline
chloride as organic salt and urea as the hydrogen bond
donor (HBD) [17].
The principle of DES mixture is an ionic interaction
between the hydrogen bond donor and the organic salt.
This reduces the electrostatic forces between the anions
and the cations, which lead to a decrease in the freezing
point of the mixture [18].
DESs are considered as a type of conventional ionic
liquids. In addition, they share many properties like low
volatility, non-flammable, high thermal stability and non-
toxicity. They are cheaper than conventional ionic liquids,
easy to prepare, biodegradable, non-reactive with water,
have low melting point and high viscosity and no further
purification is needed [19].
Therefore DESs were involved in a wide range of ap-
plications; in addition to their use as alternatives to ionic
liquids, they were used in enzymatic catalysis, molecular
purifications, electrochemistry and bio catalysis processes
[20].
Previous studies reported the use of DES in fructose
dehydration to 5HMF. Liu et al. have reported a 72% yield of
5HMF from fructose dehydration in a DES composed of CO2
and choline chloride at 120 ꢀC [21]. Fructose dehydrated in
different Deep Eutectic Solvents (DES) such as ChCl/oxalic
acid, ChCl/malonic acid and ChCl/citric acid, involving ethyl
acetate as an extraction solvent. The highest 5HMF selec-
tivity obtained was 83.3% with a conversion of 91.9% when
a DES composed of ChCl/citric acid was used at 80 ꢀC and
1 h of reaction time. Also, it was found in this study that the
early in the 19th century by employing aqueous systems.
Different mineral and organic acids were screened in car-
bohydrate dehydration to 5HMF. In recent screening for
different mineral acids; the best 5HMF yield reported was
65.3% when phosphoric acid was used as a catalyst for
fructose dehydration to 5HMF in subcritical water [11]. The
use of aqueous systems in carbohydrate dehydration was
limited by different challenges such as severe reaction
conditions, and 5HMF rehydration to levulinic and formic
acids caused by the presence of water as a solvent [12].
To overcome these drawbacks, great interest was shown
in the use of biphasic systems in order to eliminate the
rehydration of 5HMF by continuous extraction from the
aqueous phase. Different organic solvents were combined
with aqueous systems for this purpose. Roman Leshkov
used a biphasic system to dehydrate fructose to 5HMF in an
aqueous system catalysed by HCl, involving a mixture of
MIBK and 2-butanol as an organic phase for continuous
extraction; 80% yield of 5HMF was obtained [6]. The
development of this system was limited by the disadvan-
tages of some organic solvents, such as the ecological effect
and the high boiling point of some solvents made the
serration of 5HMF energy intensive, in addition to the high
cost of organic solvents.
Ionic liquids were also involved in carbohydrate dehy-
dration to 5HMF using a variety of catalysts. Fructose
dehydration in [Bmim]Cl, catalysed by ion exchange resins
resulted in a 5HMF yield of 86.2% obtained at 75 ꢀC and
20 min [13]. Sucrose dehydrated to 5HMF in [Emim]Br, and
catalysed by using an amino acid, achieved a 5HMF yield of
76% [14]. Even though these examples explain that dehy-
dration of carbohydrates by ionic liquids could be achieved
at mild reaction temperatures in high yields of 5HMF, the
high cost of ionic liquids is still a challenge in developing
their use in carbohydrate dehydration chemistry.
Please cite this article in press as: A. Assanosi, et al., Fructose dehydration to 5HMF in a green self-catalysed DES composed of
N,N-diethylethanolammonium chloride and p-toluenesulfonic acid monohydrate (p-TSA), Comptes Rendus Chimie (2015),
http://dx.doi.org/10.1016/j.crci.2015.11.004

A. Assanosi et al. / C. R. Chimie xxx (2015) 1e7
3
use of an extraction solvent promoted the 5HMF yield by
3. Results and discussion
9% compared to the run conducted in a monophasic system
(without adding ethyl acetate) [22]. Later, the same author
reported that inulin was converted to 5HMF using two DES
systems composed of ChCl/oxalic acid and ChCl/citric acid
in a biphasic system composed of ethyl acetate, and a 5HMF
yield of 64 and 55% was obtained from the above
mentioned systems, respectively [23]. Zhao used Nano size
Ly3-xHxPW as an acid-base hetero-poly-acid (HPA), to ca-
talyse fructose dehydration to 5HMF in a DES mixture
composed of ChCl and fructose, and a 5HMF yield of 92.3%
was obtained with a fructose conversion of 93.3% at 110 ꢀC
and 1 min [24]. Recently, the authors have reported fruc-
tose dehydration to 5HMF by using a facile acidic choline
chloride with p-TSA as a green DES. A 5HMF yield of 90.7%
was obtained [25].
This work investigates the fructose dehydration by
using a novel self-catalysed green DES mixture composed
of N,N-diethyl ethanol ammonium chloride as organic salt
and p-toluene sulfonic acid monohydrate (p-TSA) as a
hydrogen bond donor (HBD). The examined DES was found
to be an efficient, cheap, environmentally friendly and
renewable catalytic mixture. An 84.8% yield of 5HMF was
obtained.
3.1. The effect of feed ratio
The initial ratio of fructose has a great effect on the
5HMF yield and selectivity. As shown in Fig. 5, the 5HMF
yield and selectivity gradually decreased by increasing the
initial fructose ratio. This could be attributed to the rehy-
dration of the produced 5HMF, caused by the presence of
water generated from the fructose dehydration reaction.
This could be controlled by implementing an efficient
separation technique to remove the produced 5HMF from
the reaction mixture such as using a bed of silica. The
highest yield of 5HMF obtained was 70.5% at a feed ratio of
2.5, with a selectivity of 76.7%. When the feed ratio
increased from 5 to 20, the 5HMF yield decreased from
66.4% to 45% with a 5HMF selectivity of 67.9% and 48.4%,
respectively.
Further increase in the feed ratio led to a further
decrease in the 5HMF yield and selectivity. The lowest
5HMF yield obtained was 21.7% with a selectivity of 22.1% at
a feed ratio of 100. As the 5HMF yield was unstable at an
initial fructose ratio of 2.5, due to the possibly insufficient
mass of fructose, the ratio of 5 was selected for optimising
the process.
2. Experimental
At this point it is worth mentioning that the sample
colour changed to dark brown upon increasing the initial
fructose ratio, which could indicate the occurrence of side
reactions possibly producing humins and polymers.
Humins are dark brown solid compounds that appear as a
by-product in sugar dehydration reactions. As shown in
Fig. 4, this occurs as a result of 5HMF condensation by the
water produced from the reaction, which subsequently led
to a reduction in the 5HMF yield.
2.1. Materials
p-Toluenesulfonic
acid
monohydrate
(p-TSA)
(CH3$C6H4$SO3H$H2O) 98.5%, calcium hydroxide Ca(OH)2
96% and fructose (C6H12O6) 99% were ordered from
Sigma Aldrich. N,N-diethylethanolammonium chloride
(C6H16ClNO), 98% and HPLC grade water were from VWR.
All materials were used with no further purification.
3.2. The effect of reaction temperature
2.2. DES mixture preparations
As shown in Fig. 6, the effect of reaction temperature on
fructose dehydration reactions using a DES mixture of N,N-
diethylethanolammonium chloride and p-toluene sulfonic
acid monohydrate (p-TSA) was investigated. The following
reaction conditions were used: a DES mixing ratio of 1:1,
reaction time of 1 h, feed ratio of 5% and reaction temper-
ature range of 50 ꢀC to 110 ꢀC. Investigation of the effect of
reaction temperature with a range of 50 ꢀC to 90 ꢀC
revealed that there was no significant change in the 5HMF
yield. It varied from 59.8% to 62.8%, while the 5HMF
selectivity decreased from 86.2% at 50 ꢀC to 68.9% at 80 ꢀC.
This could be attributed to the humin formation due to the
occurrence of side reactions as a result of the thermal
degradation of 5HMF and fructose. A further decrease in the
5HMF yield and selectivity is shown; when the reaction
temperature was increased to 100 ꢀC and 110 ꢀC; the yield
The DES mixture consisted of N,N-diethylethano-lam-
monium chloride and p-toluenesulfonic acid monohydrate
(p-TSA); both materials were dried prior to use at 70 ꢀC
under vacuum for 2 h. Afterwards both materials were
mixed together at different molar ratios in a 50 mL stainless
steel cylindrical vessel then stirred by using a magnetic
stirrer at 300 rpm and heated at 80 ꢀC by using an oil bath
for 30 min. A colourless mixture was produced as shown in
Fig. 2. A similar DES was used in free fatty acid treatment
and synthesis of biodiesel [26]
2.3. Fructose dehydration reaction procedure
Fructose dehydration reactions were carried out in a
50 mL stainless steel vessel, using an oil bath as a heating
source and by stirring using a magnetic stirrer at 300 rpm
for 1 h at 80 ꢀC. At the end of the reaction, a brown mixture
was produced as illustrated in Fig. 3. In terms of eliminating
the occurrence of side reactions, at the end of the reaction,
the produced mixture was quenched in an ice bath to be
cooled down rapidly. Afterwards the mixture was diluted in
10 mL of HPLC grade water, then filtered and bottled for
HPLC analysis.
ꢀ
of 5HMF decreased to 53.9% at 100 C with a selectivity of
57.3%.
The lowest yield of 5HMF obtained was 40% at 110 ꢀC,
with a selectivity of 41.4%. Also, it was noticed that the
sample colour was changed to dark brown by increasing
the reaction temperature. As it is illustrated in fig, this may
be attributed to the thermal degradation of 5HMF to
humins upon increasing the reaction temperature. On the
Please cite this article in press as: A. Assanosi, et al., Fructose dehydration to 5HMF in a green self-catalysed DES composed of
N,N-diethylethanolammonium chloride and p-toluenesulfonic acid monohydrate (p-TSA), Comptes Rendus Chimie (2015),
http://dx.doi.org/10.1016/j.crci.2015.11.004

4
A. Assanosi et al. / C. R. Chimie xxx (2015) 1e7
Fig. 2. The DES mixture.
Fig. 3. Fructose dehydration reaction in DES.
Fig. 4. Fructose dehydration reaction pathway.
other hand, fructose conversion increased with the reaction
temperature ranging from 69.4% at 50 ꢀC to 96.3% at 110 ꢀC.
A reaction temperature of 80 ꢀC was chosen as the opti-
mum reaction temperature.
3.3. The effect of reaction time
The influence of reaction time on the 5HMF yield and
selectivity, as well as the fructose conversion, was studied
Please cite this article in press as: A. Assanosi, et al., Fructose dehydration to 5HMF in a green self-catalysed DES composed of
N,N-diethylethanolammonium chloride and p-toluenesulfonic acid monohydrate (p-TSA), Comptes Rendus Chimie (2015),
http://dx.doi.org/10.1016/j.crci.2015.11.004

A. Assanosi et al. / C. R. Chimie xxx (2015) 1e7
5
Fig. 5. The effect of the feed ratio at a reaction time of 1 h, reaction temperature of 80 ꢀC, and DES mixing ratio 1:1 (w/w).
Fig. 6. The effect of reaction temperature at the reaction time of 1 h, feed ratio of 5 (w/w) and DES mixing ratio 1:1 (w/w).
over the time range from 5 to 120 min. The study was
carried out at 80 ꢀC, at an initial fructose ratio of 5 and a 1:1
DES mixing ratio.
3.4. The effect of DES mixing ratio
The DES mixing ratio is a key variable for the production
of 5HMF by this reaction. As the acid p-TSA is the active side
in the DES, the acid ratio was changed every time, while the
salt molar ratio was fixed at 1.
As expected, Fig. 7 reveals that the reaction time had a
positive effect on the 5HMF yield and selectivity. The 5HMF
yield varied from 58.8% to 66.5%, while the 5HMF selec-
tivity was changing in a range from 62.1% to 78.4%. This
may be attributed to the side reactions like rehydration of
5HMF as illustrated in Fig. 4, also the slight fluctuation in
the 5HMF yield and selectivity as well as the fructose
conversion increase over the time could be a sign of for-
ward and back ward reactions. The fructose conversion was
also effected by the reaction time as it was varying from
78.8% to 97.3.
Due to the notable effect of the reaction time on the
fructose dehydration reaction, and the highest 5HMF yield
obtained was 66.5% at a reaction time of 60 min, it was
chosen as an optimum time in order to be comparable with
a previous study carried out by using a different DES
mixture composed of p-TSA and Choline chloride [25] with
1 h as the reaction time.
In this work different mixing molar ratios were inves-
tigated. They are 1:0.5, 1:1, 1:1.5 and 1:2 of N,N-dieth-
ylethanolammonium chloride to p-toluenesulfonic acid
monohydrate (p-TSA). The DES mixing molar ratio had a
significant effect on the 5HMF yield and selectivity.
As shown in Fig. 8, both the 5HMF yield and selectivity
are sharply decreased upon increasing the p-TSA acid molar
ratio. At a mixing molar ratio of 1:0.5 the highest 5HMF yield
of 84.8% was obtained with a 5HMF selectivity of 88.6%. As
the mixing ratio increased to 1:1; the 5HMF yield decreased
down to 66.4%, with a 5HMF selectivity of 67.9%. When the
mixing ratio was further increased to 1:1.5, a lower 5HMF
yield of 45% was obtained with a 5HMF selectivity of 49.2%.
The lowest 5HMF yield obtained was 21.1% with a lower
5HMF selectivity of 23% at a mixing ratio of 1:2.
Please cite this article in press as: A. Assanosi, et al., Fructose dehydration to 5HMF in a green self-catalysed DES composed of
N,N-diethylethanolammonium chloride and p-toluenesulfonic acid monohydrate (p-TSA), Comptes Rendus Chimie (2015),
http://dx.doi.org/10.1016/j.crci.2015.11.004

6
A. Assanosi et al. / C. R. Chimie xxx (2015) 1e7
Fig. 7. The effect of reaction time at a reaction temperature of 80 ꢀC, DES mixing ratio 1:1 (w/w) and feed ratio of 5 (w/w).
The severe reduction in the 5HMF yield and selectivity
The analytical method procedure used was 100% HPLC
grade water as the mobile phase, at a flow rate of 0.5 mL per
minute, column oven temperature of 75 ꢀC, injection vol-
ume of 20 mL and total time of 40 min. The fructose and
5HMF peaks appeared at 16 and 35 min, respectively.
can be attributed to the activation of side reactions caused
by the acidic reaction medium as a result of increasing the
acid content in the DES mixture. A previous study using
different DES mixtures showed different trends of the
effect on the fructose dehydration reaction [18]. This may
be referred to the composition of the DES itself. The
fructose conversion was varying between 88.6% and
97.8%.
5. Mathematical equations
The used equations are as follows:
mass of fructose
1. Initial feed mass ratio ¼
DES mass
4. Analysis
acid moles
2. Mixing molar ratio of DES ¼
ꢀ
ꢁ
salt moles
converted moles of fructose
initial fructose moles
Both the reactants fructose and final product 5HMF
were analysed by using a HPLC 1100 Agilent Series, using a
refractive index detector and Rezex RCM-monosaccharide
column with dimensions (300 ꢁ 7.8 mm). The column
was ordered from Phenomenex.
3. Fructose conversion¼
ꢁ 100
ꢀ
ꢁ
producted moles of 5HMF
4. 5HMF yield % ¼
ꢁ 100
initial fructose moles
ꢀ
ꢁ
producted moles of 5HMF
fructose converted moles
5. 5HMF selectivity % ¼
ꢁ 100
Fig. 8. The effect of DES mixing ratio at a feed ratio of 5 (w/w), reaction temperature of 80 ꢀC, and reaction time of 1 h.
Please cite this article in press as: A. Assanosi, et al., Fructose dehydration to 5HMF in a green self-catalysed DES composed of
N,N-diethylethanolammonium chloride and p-toluenesulfonic acid monohydrate (p-TSA), Comptes Rendus Chimie (2015),
http://dx.doi.org/10.1016/j.crci.2015.11.004

A. Assanosi et al. / C. R. Chimie xxx (2015) 1e7
7
6. Conclusion
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Please cite this article in press as: A. Assanosi, et al., Fructose dehydration to 5HMF in a green self-catalysed DES composed of
N,N-diethylethanolammonium chloride and p-toluenesulfonic acid monohydrate (p-TSA), Comptes Rendus Chimie (2015),
http://dx.doi.org/10.1016/j.crci.2015.11.004