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Research Article
Novel SnCl2-H2SO4 Mixed Catalyst System for Fructose Conversion to
5-hydroxymethylfurfural
Ayuk AA, Oguzie EE, Njoku PC and Duru CE*
Department of Chemistry, Federal University of Technology, Owerri, P.M.B.1526, Owerri Imo State, Nigeria
Abstract
The effect of some metal salts in sulphuric acid mixed catalyst systems on the conversion of D-fructose to
5-hydroxymethylfurfural (HMF) have been studied using UV/VIS spectrophotometry. Differential increases in HMF
yield were observed when the metal salts were synergized with 1 M sulphuric acid solution relative to what was
obtained when the acid was used alone. This differential HMF yield increased in the other: ZnCl2<Pb(NO3)2<NiS
O4<MnCl2<CoCl2<CuSO4<HgCl2<FeSO4<SnCl2. The high 101.8% contribution to HMF yield obtained when SnCl2
salt was synergized with sulphuric acid solution was attributed to the strong reducing ability of this salt in protonic
acid solutions. Kinetic studies of the effect of temperature and SnCl2 concentration on rate of HMF production from
fructose, predicts good thermal stability of the SnCl2-H2SO4 mixed catalyst system.
Keywords: Fructose; 5-hydroxymethylfurfural; Tin (II) chloride;
Mixed catalysts; Fructose dehydration
to levulinic and formic acids, or further increase the HMF production
rate to an extent that the earlier side reaction becomes negligible.
Introduction
Experimental
Glucose and fructose are six-carbon sugar molecules which are
potential feedstocks for the production of biofuels that can replace
petroleum fuels [1]. Recent research efforts have focused on their
conversion to 5-hydroxymethylfurfural (HMF) [2,3], the precursor of
the most recent second generation biofuel 2,5 dimethylfuran (DMF).
Current processes in HMF production involve the use of acid catalysts,
and are mainly limited to fructose as the biomass feed [4-7].
Reagents and sample preparation
The major problem associated with the use of protonic acid catalysts
in aqueous solutions for the conversion of fructose to HMF is that the
HMF decomposes in this medium to give levulinic and formic acids [811], with the levulinic acid being particularly difficult to separate from
HMF.
Quantification of HMF in the acid solutions of metal salts was
carried out using JENWAY 6405 UV/VIS Spectrophotometer [16,17].
The instrument was set at a wavelength range of 200-900 nm, and HMF
was detected at a wavelength (λmax) of 285 nm [18].
Some researchers have used other non-aqueous solvent media for
fructose conversion to HMF and yields have been shown to increase
significantly in these systems because of their ability to partition HMF
from water. Dumesic and coworkers demonstrated high yields from
fructose by using the solvent dimethylsulphoxide [12]. Zhao et al.
[13] have been able to catalyze the dehydration of fructose at 80°C to
HMF, by the addition of catalytic amounts of different metal halides in
1-alkyl-3-methylimidazolium chloride as a solvent class. Best yield of
HMF of up to 70% was obtained with chromium trichloride as catalyst.
Sulphuric acid was also used as catalyst in this solvent, giving high
conversion rate for fructose but with low HMF yield. HMF can also
be formed in high yields from fructose in 1- H-3-methylimidazolium
chloride solvent, which also serves as both acidic catalyst and solvent
[14], and also in sub- and supercritical acetone [15].
Preliminary studies of the effect of metal salts on HMF yield were
carried out using nine salts: NiSO4, CoCl2, CuSO4, ZnCl2, MnCl2, HgCl2,
Pb(NO3)2, SnCl2 and FeSO4. 100 cm3 of 0.1 M D-fructose were prepared
in 1 M solutions of H2SO4 and transferred into a 250 cm3 beakers. 0.01
M weight of each metal salt was weighed and dissolved separately in
each of the fructose solutions. 50 cm3 of each of these solutions was
transferred in triplicates into a series of ampoules. The ampoules were
sealed and arranged on a rack, and were placed in a thermostated waterbath shaker set at 303 K and left for 24 hours. Thereafter, the ampoules
were taken from the water-bath and directly quenched in an ice-bath at
278 K to stop the reaction. The ampoules were opened, and about 3 cm3
The fact still remains that for the production of HMF to be made
commercial for the purpose of biofuel production, the cheap and readily
available solvent, water, should continue to be the solvent of choice. The
use of cheap mineral acids as catalyst, which give quick conversions
of fructose to HMF, with the only problem being side reactions that
lead to HMF degradation remains the best bet for the production of
commercially affordable biofuel. This paper therefore investigates the
use of mixed catalysts in water, comprising sulphuric acid as a baseline catalyst with high fructose – HMF conversion abilities, and soluble
metal salts as possible stabilizers to either inhibit the conversion of HMF
D-fructose, H2SO4 and metal salts used for this work were of
analytical grade, purchased from FINLAB Nigeria PLC Lagos, and
were used without further purification. The sample and reagents were
further prepared with distilled water.
Instrumentation
Procedure
*Corresponding author: Duru CE, Department of Chemistry, Federal
University of Technology, Owerri, P.M.B.1526, Owerri Imo State, Nigeria,
E-mail: [email protected]
Received November 11, 2012; Published November 15, 2012
Citation: Ayuk AA, Oguzie EE, Njoku PC, Duru CE (2012) Novel SnCl2-H2SO4
Mixed Catalyst System for Fructose Conversion to 5-hydroxymethylfurfural. 1:534
doi:10.4172/scientificreports.534
Copyright: © 2012 Ayuk AA, et al. This is an open-access article distributed under
the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original author and
source are credited.
Volume 1 • Issue 11 • 2012
Citation: Ayuk AA, Oguzie EE, Njoku PC, Duru CE (2012) Novel SnCl2-H2SO4 Mixed Catalyst System for Fructose Conversion to 5-hydroxymethylfurfural.
1:534 doi:10.4172/scientificreports.534
Page 2 of 4
of each reaction mixture was extracted and scanned in triplicates for
HMF using a UV/VIS Spectrophotometer.
Rate Studies
The kinetics of the contributions of SnCl2 and FeSO4 to HMF
yield was carried out using 0.1 M fructose in 1 M solution of H2SO4
as blank. 500 cm3 of this solution was prepared, and 50 cm3 samples
were extracted and transferred in a series of eighteen ampoules. The
ampoules and their contents were placed on a rack and immersed in a
thermostated water-bath shaker set at 313 K and left for 10 minutes to
attain thermal equilibrium with the bath. The ampoules were extracted
in threes at 5 minutes intervals, and directly quenched in an ice-bath
at 278 K to stop the reaction. The absorbance of HMF in each of the
solutions was taken. Concentration of 10-4 M and 10-4 M each of SnCl2
and FeSO4 were dissolved in the blank and the procedure was repeated.
The experiments were performed again at 333 K.
Results and Discussions
The absorbances of HMF in the different acid solutions were used
to relate its concentration according to the Beer-Lambert’s Law [19].
figure 1 gives the UV absorbances of HMF in the different acid – metal
salt solutions at the same concentrations, at 303 K.
The results in figure 1 show that HMF can be produced from
sulphuric acid in aqueous solution. This amount however is boosted
by synergizing the HMF production ability of sulphuric acid with
metal salts. The mixtures of metal salts in this system showed different
degrees of increases in HMF yield. Best results were obtained with
FeSO4 and SnCl2 as shown by the absorbance values of HMF at 1.106
and 1.263 respectively. The percentage contributions to HMF yield by
the different metal salts used for this study in sulphuric acid is shown
in figure 2. Highest percentages were obtained at 76.6% and 101.8%
for FeSO4 and SnCl2 respectively. These values suggest that either the
HMF formed in the solutions of these salts are very stable, or the metal
salts create alternative pathways for faster fructose conversion to this
product.
Tin (II) chloride forms a three-coordinate dihydrate, with one
water molecule coordinated on to the tin, and a second water molecule
coordinated onto the first (Figure 3). It is widely used as a strong
reducing agent in acid solutions and forms complexes with ligands
[20,21]. It is also used in the Stephen reduction [22], whereby a nitrile
is reduced to an aldehyde.
These properties suggest that the high yield of HMF from this salt in
sulphuric acid could be due to the ability of tin (II) chloride molecule to
remove a proton from a hydroxyl group in a fructose molecule, which
can then be hydrolyzed to an aldehyde. The HMF is finally formed by
the removal of two more water molecules from the fructose moiety
by the tin (II) chloride dehydrate. This hypothetical theory therefore
attribute the high HMF yield in the SnCl2–H2SO4 catalyst system to be
as a result of faster rate of HMF production relative to its removal as
levulinic and formic acids. FeSO4 which is also a reducing agent as well
as some of the metal salts used for this study, are very likely to follow a
similar reaction mechanism as that postulated.
D-fructose dehydration kinetics in SnCl2-H2SO4 and FeSO4H2SO4 catalyst systems
The rates of HMF production at 313 K and 333 K in the SnCl2 –
H2SO4 and FeSO4-H2SO4 catalyst systems are shown in figures 4-7.
Catalytic amounts of SnCl2 and FeSO4 in sulphuric acid were used to
study the effect of temperature and catalyst concentration on rate of
conversion of fructose to HMF. In the presence of 10-3 M and 10-4 M
concentrations of SnCl2 and FeSO4 at 313 K, rate of HMF production
increased steadily over time in the SnCl2 system (Figure 6) with best
yield obtained at 10-4 M concentration of the salt. In the FeSO4 system
at this temperature, rate of HMF production at both concentrations of
the salt increased steadily, with the blank solution (acid and fructose
without metal salt), showing the best yield of HMF (Figure 5). This
feature was even more distinct at 333 K. The reduction in the catalytic
ability of FeSO4 to convert fructose to HMF is likely to be due to the
oxidation of Fe2+ to Fe3+ at higher temperatures, which can rapidly
reduce the concentration of the Fe2+ ions which are the catalyst
Figure 3: Structure of tin (II) chloride dehydrate.
Figure 1: Absorbances of HMF in different H2SO4-metal salt solutions.
Figure 2: Percentage contribution to HMF yield by metal salts in the H2SO4metal salt solutions.
Figure 4: Effect of SnCl2 concentrations on HMF yield at 313 K.
Volume 1 • Issue 11 • 2012
Citation: Ayuk AA, Oguzie EE, Njoku PC, Duru CE (2012) Novel SnCl2-H2SO4 Mixed Catalyst System for Fructose Conversion to 5-hydroxymethylfurfural.
1:534 doi:10.4172/scientificreports.534
Page 3 of 4
which makes the reduction action of the salt on the fructose molecule
difficult. This phenomenon would especially be imminent when the salt
concentration is low in the solution. At high SnCl2 concentrations, the
prevalence of its molecules around the fructose molecule could reduce
this effect, leading to higher rates of HMF production. Figure 7 is a clear
indication of the thermal stability of the SnCl2– H2SO4 mixed catalyst
system in the conversion of fructose to HMF.
Conclusion
Figure 5: Effect of SnCl2 concentrations on HMF yield at 333 K.
The results from this study show that HMF production in protonic
acids like sulphuric acid can be enhanced by synergizing its catalytic
ability with those of soluble metal salts. The loss of HMF normally
experienced by the use of protonic acid catalysts can be reduced
appreciably by this synergy especially in the SnCl2–H2SO4 mixed
catalyst system.
Acknowledgement
We are grateful and appreciative of the Chemistry Department of the National
Institute of Science Laboratory Technology Ibadan, Nigeria (NISLT), for their
technical assistance and provision of the laboratory bench for this work.
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Volume 1 • Issue 11 • 2012
Citation: Ayuk AA, Oguzie EE, Njoku PC, Duru CE (2012) Novel SnCl2-H2SO4 Mixed Catalyst System for Fructose Conversion to 5-hydroxymethylfurfural.
1:534 doi:10.4172/scientificreports.534
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