Dehydration of fructose, sucrose and inulin to 5-hydroxymethylfurfural over yeast-derived carbonaceous microspheres at low temperatures

Article abstract of DOI:10.1039/c8ra10465d

This work prepared carbonaceous microspheres by hydrothermal carbonization of yeast cells followed by sulfonation with concentrated sulphuric acid (98%) at room temperature. The obtained carbonaceous product (CM-SO₃H) had a high acid density (1.80 mmol g^-1). We evaluated CM-SO₃H as a solid catalyst for the dehydration of fructose-based carbohydrates to 5-hydroxymethylfurfural (5-HMF) in the ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]). The effects of the catalyst and substrate loadings as well as the reaction temperature and time on the yield of 5-HMF were investigated. Under the optimum conditions, a 5-HMF yield of up to 83.5% was obtained from fructose with a reaction temperature of 80 °C for 30 min. Furthermore, 44.8% and 59.2% 5-HMF yields were obtained from sucrose (80 °C for 30 min) and inulin (80 °C for 60 min), respectively. CM-SO₃H and [BMIM][Cl] showed high stability and could be recycled between five and eight times without significant loss of catalytic activity. More importantly, the catalytic system could be applied to high substrate concentrations. CM-SO₃H combined with [BMIM][Cl] is a promising system for transforming fructose-based carbohydrates into 5-HMF.

Full text of DOI:10.1039/c8ra10465d

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Dehydration of fructose, sucrose and inulin to 5-
hydroxymethylfurfural over yeast-derived
Cite this: RSC Adv., 2019, 9, 9041
carbonaceous microspheres at low temperatures†
*
Xiaofeng Li, Yi Wang, Xiaomin Xie, Changhong Huang and Sen Yang
This work prepared carbonaceous microspheres by hydrothermal carbonization of yeast cells followed by
sulfonation with concentrated sulphuric acid (98%) at room temperature. The obtained carbonaceous
product (CM-SO3H) had a high acid density (1.80 mmol gꢀ1). We evaluated CM-SO3H as a solid catalyst
for the dehydration of fructose-based carbohydrates to 5-hydroxymethylfurfural (5-HMF) in the ionic
liquid 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]). The effects of the catalyst and substrate
loadings as well as the reaction temperature and time on the yield of 5-HMF were investigated. Under
the optimum conditions, a 5-HMF yield of up to 83.5% was obtained from fructose with a reaction
temperature of 80 ꢁC for 30 min. Furthermore, 44.8% and 59.2% 5-HMF yields were obtained from
sucrose (80 ꢁC for 30 min) and inulin (80 ꢁC for 60 min), respectively. CM-SO3H and [BMIM][Cl] showed
high stability and could be recycled between five and eight times without significant loss of catalytic
activity. More importantly, the catalytic system could be applied to high substrate concentrations. CM-
SO3H combined with [BMIM][Cl] is a promising system for transforming fructose-based carbohydrates
into 5-HMF.
Received 21st December 2018
Accepted 7th March 2019
DOI: 10.1039/c8ra10465d
rsc.li/rsc-advances
exchange resins,17,18 have been considered for the production of
5-HMF. Functionalization of solid catalysts with –SO3H groups
Introduction
is an efficient and readily available means of improving the
reaction rate and selectivity during the dehydration of carbo-
hydrates to 5-HMF.19
Biomass-derived chemicals have attracted interest for their
potential to reduce global dependence upon fossil fuels.1
Among these chemicals, 5-hydroxylmethylfurfan (5-HMF) is one
of the most important platform chemicals, and has been widely
applied in the production of polymers, ne chemicals, phar-
maceuticals, and biofuels.2,3 5-HMF can be generated from the
dehydration of biomass derivatives such as fructose,4,5 glucose,6
sucrose,7 and cellulose.8 The most efficient method is dehy-
dration of fructose catalysed by acid,9 as the conversion of other
feedstocks requires a carbohydrate-to-fructose step.10
Sulphuric acid11 and hydrochloric acid12 are efficient homo-
geneous catalysts for 5-HMF production through carbohydrate
dehydration, but they have several drawbacks. These include
difficulties with the separation and recycling of the catalyst,
corrosion of equipment, and release of toxic waste.13 Hetero-
geneous catalysts can be used as an alternative to homogeneous
catalysts to address these issues, and are more suitable for
industrial applications.14,15 Therefore, a variety of heteroge-
neous catalysts, such as solid superacids16 and acid cation
SO3H-functionalized carbonaceous materials are very
promising solid acid catalysts because they exhibit high stability
and surface modiability.20,21 Recently, several carbonaceous
materials, including mesoporous carbon, mesoporous carbon–
silica composites, carbon nanotubes, biochar, and carbons
prepared by the hydrothermal carbonization of biomass, have
been modied with –SO3H groups and have shown good cata-
lytic performance in the conversion of carbohydrates to 5-
HMF.19,22,23 However, few studies have used hollow carbona-
ceous materials as catalysts for the conversion of carbohydrates
to 5-HMF. Those carbonaceous materials that have been re-
ported are commonly treated with concentrated sulphuric acid
(98%) at high temperatures to introduce –SO3H groups. As an
example, biochar requires sulfonation at 150 C for 12 h,2 and
ꢁ
carbonized lignin24 and cellulose-derived carbonaceous solids25
require sulfonation at 200 ꢁC for 5–12 h. The high temperatures
required for the sulfonation process are a challenge because
they result in harsh operational conditions and can cause
equipment corrosion.22 However, any material that can be
carbonized can be used to prepare SO3H-functionalized carbo-
naceous materials.26 One such material is yeast produced as an
organic waste by-product of the fermentation industry. The cell
walls of yeast primarily consist of a polysaccharide layer
Beijing Key Laboratory of Farmland Soil Pollution Prevention and Remediation,
College of Resources and Environmental Sciences, China Agricultural University,
Beijing 100193, P. R. China. E-mail: syang@cau.edu.cn; Fax: +86-10-62733470; Tel:
+86-10-62733470
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra10465d
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 9041–9048 | 9041

View Article Online
RSC Advances
Paper
constructed from coiled b-1,3-glucan chains, and hollow Ltd. (Linzhou, China). Ultrapure water was used in all experi-
carbonaceous microspheres (CMs) with meso- and microporous ments. All chemicals were used as obtained without further
shells have been prepared by the mild hydrothermal treatment treatment.
of these organisms.27,28 Generally, hollow microspheres exhibit
useful characteristics, such as improved mass transport and
Preparation of the catalyst
diffusion, high pile density and good uidity,29,30 and so can be
CMs were synthesized by a modication of the hydrothermal
method described in our previous study.27 Typically, S. cerevisiae
cells (3.0–4.0 g) were pre-washed with acetone and then
dispersed in ultrapure water (40 mL). The mixture was subse-
quently placed in a 50 mL Teon-sealed autoclave and main-
tained at 180 ꢁC for 8 h. The puce-colored solid product was
used as catalysts or catalyst supports. Most importantly, CMs
are composed of both carbonized organic matter (that is,
aromatic carbon) and non-carbonized organic matter (alkyl
carbon), and the surfaces of these materials are covered with
oxygenated functional groups, including carbonyl, carboxy,
hydroxy, ether, and ester moieties.27,28 Therefore, it is easy to
isolated by centrifugation, washed alternately with ultrapure
modify the surfaces of CMs by mild sulfonation. Even so, few
water and ethyl alcohol three times, and oven-dried at 80 ꢁC for
studies have used CMs fabricated from yeast cells as precursors
8 h. This material is referred to herein as the CMs.
for solid acid catalysts.
The CMs (1.0 g) were then dispersed in concentrated sul-
The solvent is crucial in the production of 5-HMF from
phuric acid (20 mL) at room temperature with stirring at
carbohydrates.24 To date, water and highly polar organic
800 rpm. Aer a certain time, the resulting black precipitate was
solvents have been used as reaction solvents.14,31 However, the
removed by ltration and washed with water until the wash
reaction temperatures are generally high (120–180 ꢁC) and high
water was neutral. The sulfonated material obtained in this
energy inputs are required.7,17,25 As an example, the maximum 5-
manner was dried at 75 ꢁC in a vacuum oven overnight. The
CMs sulfonated for 8 h are denoted herein as CM-SO3H.
HMF yield from the dehydration of fructose using sulfonated
biochar as the catalyst and water as the solvent is obtained at
160–180 C.4 With DMSO as the solvent, the transformation of
ꢁ
fructose into 5-HMF is generally performed at 120 ꢁC.9 Ionic Characterization
liquids (ILs) are organic salts that are liquids at room temper-
Field-emission scanning electron microscopy (FE-SEM, SU
ature and can be easily recycled.32,33 According to the literature,
ILs such as [HMIM][Cl], [OMIM][Cl], and [BEMIM][Cl] can play
a positive role in the dehydration of carbohydrates because of
their good solvating powers.4,21,22,34 The dehydration of fructose
in ILs can give a high 5-HMF yield at temperatures as low as
8020, Hitachi, Japan) was used to obtain images of the CMs and
CM-SO3H. Fourier-transform infrared (FTIR) spectra were
acquired over the range of 400–4000 cmꢀ1 (IS 10, Nicolet, USA)
and the C, H, N, O, and S contents of the samples were deter-
mined using an elemental analyser (Flash 2000, Therom, USA).
The surface areas and pore sizes of the CMs and CM-SO3H were
obtained from N2 adsorption/desorption isotherms acquired at
ꢀ196.15 ꢁC with a physisorption analyser (ASAP 2020, Micro-
meritics, USA). The total number of acid sites in the CM-SO3H
was estimated by acid–base titration.5,9 Briey, CM-SO3H (0.10
g) was suspended in 50 mL of aqueous 0.5 M NaCl and stirred
for 24 h. During this time, H+ was liberated into the aqueous
solution by exchange with Na+. The ltrate was subsequently
titrated using a standard NaOH solution (0.01 M).
80 C.35 Among the ILs, 1-butyl-3-methylimidazolium chloride
ꢁ
([BMIM][Cl]) is a suitable medium for the production of 5-HMF
from fructose since it can act as both a proton donor and
acceptor.24,36
In this work, we prepared CMs via the hydrothermal treat-
ment of yeast cells, as reported previously.27 SO3H-
functionalized microspheres were subsequently obtained aer
immersion of these CMs in concentrated sulphuric acid (98%)
at room temperature. The catalytic activities of the resulting
catalysts were estimated during the production of 5-HMF from
fructose, sucrose, and inulin.
Catalytic dehydration of carbohydrates to 5-HMF
The dehydration reactions of carbohydrates were performed in
10 mL glass tubes. Typically, a feedstock (0.50 g of fructose,
0.25 g of sucrose, or 0.25 g of inulin) was dissolved in 2.50 g of
Experimental
Materials and reagents
Budding yeast (Saccharomyces cerevisiae) was purchased from [BMIM][Cl] at 60 ꢁC, aer which 50 mg of CM-SO3H was added
the Angel Yeast Co., Ltd. (Yichang, China). Fructose (99%) and rapidly with stirring at 800 rpm. The reactor was then heated to
sucrose (99%) were purchased from the Sigma-Aldrich Co., Ltd. 80 ꢁC in an oil bath. Aer the desired reaction time had elapsed,
(Missouri, USA). Inulin (90%) was purchased from the Yuan Ye the products were extracted into ethyl acetate with stirring at
Biotechnology Co., Ltd. (Shanghai, China) and 5-HMF (99%) room temperature.
was purchased from the Aladdin Chemicals Co., Ltd. (Cal-
In an experiment to test the reusability of the catalyst, the 5-
ifornia, USA). Acetone (99%), ethyl alcohol (99%), ethyl acetate HMF produced aer 30 min of reaction was extracted by 25 mL
(99%), and concentrated sulphuric acid (98%) were obtained ethyl acetate. Aer four such extractions, the remaining [BMIM]
ꢁ
from the Sinopharm Chemical Reagent Co., Ltd. (Shanghai, [Cl] and CM-SO3H were heated at 80 C for 12 h in a vacuum
China). Methanol (HPLC grade) was purchased from the Fisher drying oven to remove water and residual ethyl acetate. The
Chemicals Co., Ltd. (New Jersey, USA). [BMIM][Cl] (99%) was residue was used directly for the next carbohydrate to 5-HMF
purchased from the Linzhou Keneng Materials Technology Co., conversion with fresh feedstock.
9042 | RSC Adv., 2019, 9, 9041–9048
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
indicates that the catalytic activity of [BMIM][Cl] is dependent
Analytical methods
The 1H nuclear magnetic resonance (NMR) spectrum of 5-HMF
on the reaction temperature.34 However, at 80 C, the catalytic
ꢁ
activity of the [BMIM][Cl] was negligible. Adding 50 mg of CMs
gave a 5-HMF yield of approximately 2.1%, and so it was clear
that the CMs exhibited little catalytic activity under the present
conditions. However, a large increase in the catalytic activity
occurred aer the CMs were sulfonated. The yield of 5-HMF
increased to 64.0% with the addition of CMs that were
sulfonated for 0.5 h, suggesting that –SO3H groups served as
active sites on the catalyst.9 A higher 5-HMF yield of 81.0% was
obtained when the sulfonation time was increased to 2 h, and
a slight further increase in the yield was observed following an
ꢁ
was recorded in d4-methanol at 25 C using a 400 MHz NMR
spectrometer (JNM-ECZ, Jeol, Japan). The amount of 5-HMF
obtained from each reaction was analysed directly by HPLC with
a Zorbax SB-C18 column (4.6 mm ꢂ 12.5 mm) and methanol/
water (20 : 80, v/v) as the mobile phase.37 The ow rate ꢁwas 0.7
mL minꢀ1 and the column temperature was kept at 30 C. The
carbohydrate content was determined by HPLC with an Aminex
HPX-87H column (300 mm ꢂ 7.8 mm) in conjunction with
a refractive index detector. The mobile phase was 5 mM H2SO4
at a ow rate of 1.0 mL minꢀ1 and the column temperature was
maintained at 55 ꢁC.38,39 The 5-HMF yield and carbohydrate
conversion were calculated using the following equations.
1
additional increase in sulfonation time to 8 h. H NMR spec-
troscopy (Fig. S1†) conrmed the production of 5-HMF. These
results show that the sulfonation of CMs at room temperature is
an effective approach to preparing highly active catalysts for the
synthesis of 5-HMF from fructose. Furthermore, the sulfonation
time has a remarkable effect on the catalytic activity of the CMs.
We selected the CMs sulfonated for 8 h (CM-SO3H) as the most
active and stable catalyst for all the following experiments.
The catalytic activity of the CM-SO3H during the dehydration
of glucose, the least reactive substrate, was also assessed.40 A 5-
HMF yield of 10.2% was obtained at 120 ꢁC aer 2 h. The low 5-
HMF yield from glucose may be explained by the lack of Lewis
acid sites on CM-SO3H, because 5-HMF synthesis from glucose
involves isomerization catalysed by a Lewis acid and dehydra-
tion catalysed by a Brønsted acid.41
5-HMF produced ðmolÞ
5-HMF yield ð%Þ ¼
Conversion ð%Þ ¼
ꢂ 100% (1)
ꢂ 100% (2)
initial carbohydrate ðmolÞ
carbohydrate consumed ðgÞ
initial carbohydrate ðgÞ
Each experiment was repeated at least three times with
similar results, and all the reported reaction data are averages.
Results and discussion
Catalyst screening
We prepared all solid acid catalysts under the same conditions,
except that the sulfonation time was varied from 0 to 8 h. The
hydrothermal carbonization was carried out at 180 C for 8 h
Characterization of the CM-SO3H catalyst
ꢁ
SEM images of the CMs and CM-SO3H are presented in Fig. 2.
The obtained CMs were in the form of microspheres with
diameters in the 2.0–3.0 mm range, which was consistent with
our previous results.27 Aer sulfonation, the microsphere
structure was well preserved but the diameter decreased to 1.0–
and the sulfonation was conducted at room temperature in
concentrated sulphuric acid. The catalytic activities of the
samples were investigated based on the dehydration of fructose,
which was found to be the most reactive substrate (Fig. 1).
We carried out a preliminary experiment in the absence of
a catalyst in [BMIM][Cl] at 80 ꢁC for 30 min, but no 5-HMF was
obtained. It should be noted that, at 120 ꢁC, [BMIM][Cl] can act
as both solvent and catalyst during fructose dehydration.24 This
2.0 mm. The surface area of the CM-SO3H was 12.5 m2 gꢀ1
which was slightly higher than that of the CMs (10.5 m2 gꢀ1
,
)
(Table 1). The CMs pore size was 15.5 nm, whereas that of the
CM-SO3H was 16.6 nm. From these results, it was clear that the
CMs were etched by the concentrated sulphuric acid.
Fig. 3 shows the FTIR spectra of the CMs and CM-SO3H. A
new band appearing at 1169 cmꢀ1 in the FTIR spectrum of the
CM-SO3H was ascribed to the O]S]O stretching vibration of
–SO3H groups,42 and this conrmed that –SO3H groups were
successfully incorporated into the CMs during the sulfonation
process.38,43,44 The band at 3431 cmꢀ1 indicated the presence of
Fig. 1 The effect of sulfonation time on the 5-HMF yield from fruc-
tose. Reaction conditions: fructose (0.50 g), catalyst (50 mg), [BMIM]
[Cl] (2.50 g), reaction temperature (80 ꢁC), and reaction time (30 min). Fig. 2 SEM images of CMs (a) and CM-SO3H (b).
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 9041–9048 | 9043

View Article Online
RSC Advances
Paper
Table 1 Acid density (AD), BET surface area (SA), pore size (W), elemental composition, and atomic ratio data for the CMs and CM-SO3Ha
Elemental compositions (wt%)
Atomic ratio
O/C ratio
Sample
AD (mmol gꢀ1
)
SA (m2 gꢀ1
)
W (nm)
C
H
O
N
S
(O + N)/C ratio
CMs
CM-SO3H
0.20
1.80
10.5
12.5
15.5
16.6
60.06
56.27
5.33
5.76
26.68
28.33
4.69
4.62
0.20
4.02
0.33
0.38
0.40
0.45
a
O/C: atomic ratio of oxygen to carbon. (O + N)/C: atomic ratio of the sum of nitrogen and oxygen to carbon.
of the CM-SO3H increased, conrming an increase in the
number of polar functional groups on the surface.27
Because the acid strength of a solid catalyst is a key param-
eter for the dehydration of carbohydrates,19,46 we characterized
the acidities of the samples by titration.5 The acid density was
also greatly increased, from 0.20 mmol gꢀ1 for the CMs to
1.80 mmol gꢀ1 for CM-SO3H (Table 1). Therefore, it is clear that
the enhanced catalytic activity of the CM-SO3H may be attrib-
uted to its high acid density.
The results from our preliminary experiment inspired us to
investigate the synthesis of 5-HMF from fructose and fructose-
based carbohydrates (fructose, sucrose, and inulin) over the
CM-SO3H catalyst in [BMIM][Cl].
Fig. 3 FTIR spectra of the CMs and CM-SO3H.
Effect of the reaction temperature and time on 5-HMF yields
We explored the effects of the reaction temperature and time on
the fructose, sucrose, and inulin dehydrations catalysed by CM-
SO3H in [BMIM][Cl] (Fig. 4). All experiments were carried out
with 50 mg of CM-SO3H and 2.50 g of [BMIM][Cl]. The masses of
fructose, sucrose, and inulin were 0.50 g, 0.25 g and 0.25 g,
respectively. The reaction temperature played an important role
in determining the 5-HMF yield. When the conversion of fruc-
tose was carried out at 70 ꢁC, the 5-HMF yield increased to
a maximum of 80.7% at 60 min and then reached a plateau.
When the reaction temperature was increased to 80 or 90 ꢁC, the
reaction rate increased in the initial stages of the reaction. The
maximum 5-HMF yields were obtained at 30 min (83.5%) and
20 min (75.6%) with reaction temperatures of 80 ꢁC and 90 ꢁC,
respectively. The 5-HMF yields then decreased slightly with
–OH groups22,44 on the surfaces of both the CMs and CM-SO3H.
Bands at 2928 and 2853 cmꢀ1 were attributed to –CH2 and –CH
stretching vibrations,19,27 and the intensities of these bands
decreased dramatically aer sulfonation of the CMs, indicating
that these surface functional groups were removed. This could
have been caused by the sulphuric acid, which is a strong
oxidizer.
The elemental compositions of the CMs and CM-SO3H are
shown in Table 1. These results are in good agreement with the
FTIR spectra. Following sulfonation, the sulphur percentage
greatly increased, from 0.20% in the CMs to 4.02% in the CM-
SO3H, which also conrmed the existence of –SO3H groups in
the CM-SO3H.45 In addition, the C and O contents of the CMs
were decreased aer sulfonation. The polarity index, [(O + N)/C],
ꢁ
ꢁ
further increases in the reaction time at 80 C and 90 C.
Fig. 4 Effect of the reaction temperature on the yield of 5-HMF from fructose (a), sucrose (b), and inulin (c). Reaction conditions: catalyst (50
mg), [BMIM][Cl] (2.50 g), fructose (0.50 g), sucrose (0.25 g), and inulin (0.25 g).
9044 | RSC Adv., 2019, 9, 9041–9048
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
Fig. 5 Effect of catalyst loading on the yield of 5-HMF from fructose (a), sucrose (b), and inulin (c). Reaction conditions: [BMIM][Cl] (2.50 g),
fructose (0.50 g), sucrose (0.25 g), inulin (0.25 g), and reaction temperature (80 ꢁC).
The same tendency was observed for sucrose and inulin (30 min for fructose and sucrose, and 60 min for inulin) are
dehydration. At 70 ꢁC, the 5-HMF yields were low and increased required to achieve the maximum 5-HMF yield.
continuously with the reaction time. In contrast, at higher
temperatures (80 and 90 ꢁC), the 5-HMF yields initially
Effect of catalyst and substrate loadings on the 5-HMF yield
increased with the reaction time and then slightly decreased
with further increases in the reaction time. The maximum 5-
HMF yields from sucrose and inulin were 44.8% (80 ꢁC, 30 min)
and 59.2% (80 ꢁC, 60 min), respectively.
The effect of catalyst loading (25–75 mg) together with that of
the reaction time was evaluated at 80 ꢁC in 2.50 g of [BMIM][Cl].
The masses of fructose, sucrose, and inulin were 0.50 g, 0.25 g,
and 0.25 g, respectively. A higher 5-HMF yield was obtained
from each of the substrates in a shorter reaction time when the
mass of catalyst was increased from 25 to 50 mg (Fig. 5). As an
example, the yields of 5-HMF from fructose and sucrose steadily
increased from 49.6% to 57.6% and from 20.2% to 31.1% aer
10 min, respectively. In the case of inulin, the 5-HMF yield
steadily increased from 18.2% to 42.2% aer 30 min. The
increase in the 5-HMF yield with increases in the catalyst
loading may be attributed to an increase in the number of active
sites and their availability.19,47 However, the maximum yields of
5-HMF from the three substrates were obtained with a catalyst
loading of 50 mg, while the 5-HMF yield decreased when the
catalyst loading was increased to 75 mg. These results suggest
that degradation of the 5-HMF is also catalysed by active acid
sites.19,48
The decrease in the 5-HMF yield at higher temperatures
suggests that the 5-HMF was consumed by humins.13,44 The
formation of humins is inevitable in the acid-catalysed dehy-
dration of carbohydrates because water is produced, and the
generation of humins can be simply determined by the obser-
vation of a brown colour in the reaction mixture.22,38 To support
this, we indirectly observed the colour of the reaction mixture by
assessing the ethyl acetate extract (Fig. S2†). Direct observation
of the reaction mixture was not possible because the catalyst
was black and obscured the colour of the solution. The ethyl
ꢁ
acetate extract of the reaction mixture for the reaction at 70 C
for 5 min was colourless. However, when the reaction temper-
ature was increased to 80 or 90 ꢁC, the solution turned very pale
yellow or light yellow, respectively. As the reaction time
increased, the extract became darker (Fig. S2b†).
These results show that higher reaction temperatures both
improve the conversion of fructose to 5-HMF and accelerate the
formation of humins and therefore the consumption of 5-
HMF.22,44 Thus, an appropriate temperature (80 ꢁC) and time
High substrate loadings are essential to improving the
economy of 5-HMF production.17 We investigated the effect of
the initial substrate concentration on the production of 5-HMF
in reactions catalysed by CM-SO3H in [BMIM][Cl] (Fig. 6). The 5-
Fig. 6 Effect of the substrate loading on the yield of 5-HMF from fructose (a), sucrose (b), and inulin (c). Reaction conditions: catalyst (50 mg),
[BMIM][Cl] (2.50 g), and reaction temperature (80 ꢁC).
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 9041–9048 | 9045

View Article Online
RSC Advances
Paper
Table 2 Overview of carbohydrate conversion to 5-HMF in different ionic liquidsa
t
Yield
(%)
Car.
Catalyst
Ionic liquid
Ccar. (wt%)
T (ꢁC)
(min)
Con. (%)
Ref.
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
Fructose
Sucrose
Sucrose
Inulin
CM-SO3H
CSS
SBA-15-SO3H
LCC
[BMIM][Cl]
[BMIM][Cl]
[BMIM][Cl]
[BMIM][Cl]/DMSO
[BMIM][Cl]
[BMIM][HSO4]
[BMIM][Br]
[BMIM][Cl]
[BMIM][HSO4]
[BMIM][Cl]
[BMIM][HSO4]
[AMIM][Cl]
20
1
10
10
1
10
10
10
10
10
10
5
80
80
30
10
60
10
90
90
90
30
180
60
83.5
83
98.1
n.m.
ꢃ100
98
n.m.
n.m.
>95.7
99.9
n.m.
99.6
n.m.
n.m.
n.m.
—
44
24
38
22
50
51
—
50
—
50
52
53
120
110
100
120
120
80
120
80
120
100
80
ꢃ81
84
HTC
88.1
88
92.8
44.8
80
59.2
88
65
H3BO3–SiO2
KL zeolite
CM-SO3H
H3BO3–SiO2
CM-SO3H
H3BO3–SiO2
D265-SO3H
Amberlyst-15
Inulin
Inulin
Inulin
300
60
65
[BMIM][HSO4]/[BMIM][Cl]
2.5
82
a
Ccar. ¼ concentration of carbohydrate, T ¼ reaction temperature (ꢁC), t ¼ reaction time (min), n.m. ¼ not mentioned, Car. ¼ carbohydrate, Con. ¼
conversion, Ref. ¼ reference.
HMF yield decreased gradually as the fructose mass increased carbohydrate–[BMIM][Cl] reaction system, we conducted recy-
in the initial stages of the reaction. The highest 5-HMF yields cling experiments at 80 ꢁC according to an established
were 86.5%, 83.5%, and 72.1% with 0.25, 0.50, and 0.75 g of method.44,49 Aer each reaction, the 5-HMF was recovered from
fructose, respectively. With sucrose and inulin, the 5-HMF the reaction mixture by extraction into ethyl acetate (4 ꢂ 25
yields increased slightly as the mass of substrate was increased mL). Subsequently, the [BMIM][Cl] that contained the CM-SO3H
from 0.10 to 0.25 g. However, a further increase in the substrate was dried in a vacuum oven at 80 ꢁC for 12 h and reused directly
mass to 0.50 g led to a decreased 5-HMF yield. The highest 5- in the next reaction under the same conditions.
HMF yields were 42.6%, 44.8%, and 37.7% with 0.10, 0.25, and
The yield of 5-HMF from fructose was almost unchanged
0.50 g of sucrose, respectively. Using 0.10, 0.25, and 0.50 g of aer eight cycles of the reaction with [BMIM][Cl] and the cata-
inulin, the highest 5-HMF yields were 58.0%, 59.2%, and 53.5%, lyst (Fig. 7). The recycled catalyst and [BMIM][Cl] were evidently
respectively.
stable during the conversion of fructose to 5-HMF, indicating
We compared the data for our catalyst with representative that the –SO3H groups were tightly bonded to the CM-SO3H. The
literature data regarding 5-HMF production from various yields of 5-HMF from sucrose and inulin decreased slightly,
heterogeneous catalysts in ILs (Table 2). CM-SO3H compares from 44.8% to 31.0% and from 59.2% to 46.9%, respectively,
favourably with other solid catalysts in terms of the substrate aer ve successive cycles of catalyst reuse. This slight decrease
concentration and reaction temperature when [BMIM][Cl] is in yield is possibly attributable to the generation of glucose
used as the reaction solvent.
during the hydration of sucrose and inulin (based on HPLC
results that are not included herein). This glucose was not
removed from the reaction system and thus could have
combined with the 5-HMF to promote polymerization to form
humins which, in turn, would lower the HMF yield. Moreover,
some portion of the humins likely deposited on the catalyst and
Catalyst recycling
Stability is a key factor for practical applications of solid cata-
lysts. To investigate the reusability of CM-SO3H in the
Fig. 7 Reusability of CM-SO3H for fructose (a), sucrose (b), and inulin (c) conversion to 5-HMF. Reaction conditions: fructose (0.50 g), sucrose
(0.25 g), or inulin (0.25 g); CM-SO3H (50 mg); [BMIM][Cl] (2.50 g); temperature (80 ꢁC); and reaction time (30 min).
9046 | RSC Adv., 2019, 9, 9041–9048
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
reduced the catalytic activity of the CM-SO3H.13,38 As shown in
Fig. S3,† aer ve cycles of the sucrose dehydration reaction,
humins or other organic residues were deposited on the surface
of the CM-SO3H, even aer washing alternately with hot water
and ethanol three times.
8 Y. Zhang, M. Liu, J. Zhao, K. Wang, M. Meng and Y. Yan,
ChemistrySelect, 2018, 3, 5950–5959.
9 J. Wang, Z. Zhang, S. Jin and X. Shen, Fuel, 2017, 192, 102–
107.
10 F. Parveen and S. Upadhyayula, Fuel Process. Technol., 2017,
162, 30–36.
´
11 Y. Roman-Leshkov, J. N. Chheda and J. A. Dumesic, Science,
Conclusions
2006, 312, 1933–1937.
´
´
´˜
12 D. Garces, E. Dıaz and S. Ordonez, Ind. Eng. Chem. Res., 2017,
We prepared SO3H-functionalized CMs (CM-SO3H) by the
hydrothermal carbonization of yeast cells, followed by sulfo-
nation at room temperature. We applied the CM-SO3H to the
synthesis of 5-HMF from fructose-based carbohydrates in
[BMIM][Cl]. The CM-SO3H exhibited excellent catalytic activity
during the conversions of fructose, sucrose, and inulin to 5-
HMF at low reaction temperatures and high substrate concen-
trations. When 0.50 g of fructose was used, a high 5-HMF yield
of 83.5% was obtained in 2.50 g of [BMIM][Cl] aer reaction at
80 C for 30 min. With 0.25 g of sucrose (30 min at 80 C) or
0.25 g of inulin (60 min at 80 ꢁC), the 5-HMF yields were 44.8%
and 59.2%, respectively. More importantly, the CM-SO3H and
[BMIM][Cl] system showed high stability and could be reused
between ve and eight times with minimal loss of catalytic
activity.
56, 5221–5230.
13 A. Deng, Q. Lin, Y. Yan, H. Li, J. Ren, C. Liu and R. Sun,
Bioresour. Technol., 2016, 216, 754–760.
14 M. Ventura, A. Dibenedetto and M. Aresta, Inorg. Chim. Acta,
2018, 470, 11–21.
15 B. Agarwal, K. Kailasam, R. S. Sangwan and S. Elumalai,
Renewable Sustainable Energy Rev., 2018, 82, 2408–2425.
16 H. Mo, X. Chen, X. Liao and T. Zhou, J. Cent. South Univ.,
2017, 24, 1745–1753.
17 C. Antonetti, A. M. R. Galletti, S. Fulignati and D. Licursi,
Catal. Commun., 2017, 97, 146–150.
18 W. Li, T. Zhang, H. Xin, M. Su, L. Ma, H. Jameel, H. Chang
and G. Pei, RSC Adv., 2017, 7, 27682–27688.
19 R. Liu, J. Chen, X. Huang, L. Chen, L. Ma and X. Li, Green
Chem., 2013, 15, 2895–2903.
20 R. Zhong and B. F. Sels, Appl. Catal., B, 2018, 236, 518–545.
21 R. Zhong, F. Yu, W. Schutyser, Y. Liao, F. d. Clippel, L. Peng
and B. F. Sels, Appl. Catal., B, 2017, 206, 74–88.
22 X. Qi, N. Liu and Y. Lian, RSC Adv., 2015, 5, 17526–17531.
23 F. Huang, W. Li, Q. Liu, T. Zhang, S. An, D. Li and X. Zhu,
Fuel Process. Technol., 2018, 181, 294–303.
ꢁ
ꢁ
CM-SO3H is a promising catalyst for the acid-catalysed
conversion of biomass into value-added chemicals. In partic-
ular, in combination with [BMIM][Cl], CM-SO3H transforms
fructose-based carbohydrates into 5-HMF.
Conflicts of interest
24 X. Guo, Q. Cao, Y. Jiang, J. Guan, X. Wang and X. Mu,
Carbohydr. Res., 2012, 351, 35–41.
There are no conicts to declare.
25 X. Du, J. Zhang, Y. Wang and Y. Qu, Catalysts, 2017, 7, 245–
256.
26 K. Nakajima and M. Hara, ACS Catal., 2012, 2, 1296–1304.
27 D. Ni, L. Wang, Y. Sun, Z. Guan, S. Yang and K. Zhou, Angew.
Chem., Int. Ed. Engl., 2010, 49, 4223–4227.
Acknowledgements
The authors are grateful for nancial support provided by the
National Key Research and Development Program (Grant No.
2017YFD0801500).
28 Z. Guan, L. Liu, L. He and S. Yang, J. Hazard. Mater., 2011,
196, 270–277.
29 Z. Wang, D. Cheng, C. Chen and K. Zhou, Carbon, 2018, 136,
54–62.
Notes and references
1 L. Filiciotto, A. M. Balu, J. C. V. d. Waal and R. Luque, Catal. 30 G. Chen, G. Song, W. Zhao, D. Gao, Y. Wei and C. Li, Chem.
Today, 2018, 302, 2–15.
Eng. J., 2018, 352, 64–70.
2 L. Cao, I. K. M. Yu, S. S. Chen, D. C. W. Tsang, L. Wang, 31 F. Huang, Y. Su, Y. Tao, W. Sun and W. Wang, Fuel, 2018,
X. Xiong, S. Zhang, Y. S. Ok, E. E. Kwon, H. Song and
C. S. Poon, Bioresour. Technol., 2018, 252, 76–82.
3 M. N. Catrinck, E. S. Ribeiro, R. S. Monteiro, R. M. Ribas,
226, 417–422.
32 A. M. d. C. Lopes and R. Bogel-Łukasik, ChemSusChem, 2015,
8, 947–965.
´
˜
M. H. P. Barbosa and R. F. Teolo, Fuel, 2017, 210, 67–74.
33 A. M. d. C. Lopes, K. G. Joao, D. F. Rubik, E. Bogel-Łukasik,
4 X. Xiong, I. K. M. Yu, S. S. Chen, D. C. W. Tsang, L. Cao,
H. Song, E. E. Kwon, Y. S. Ok, S. Zhang and C. S. Poon,
Catal. Today, 2018, 314, 52–61.
5 Y. Dou, S. Zhou, C. Oldani, W. Fang and Q. Cao, Fuel, 2018,
214, 45–54.
L. C. Duarte, J. Andreaus and R. Bogel-Łukasik, Bioresour.
Technol., 2013, 142, 198–208.
34 Q. Cao, X. Guo, S. Yao, J. Guan, X. Wang, X. Mu and
D. Zhang, Carbohydr. Res., 2011, 346, 956–959.
35 H. Liu, Y. Wang, W. Ma, H. Wang, D. Wang, W. Jiang,
M. Zhang, C. Zhou and H. Li, Chem. Pap., 2017, 71, 1541–
1549.
6 H. Zhao, J. E. Holladay, H. Brown and Z. C. Zhang, Science,
2007, 316, 1597–1600.
7 D. Steinbach, A. Kruse, J. Sauer and P. Vetter, Energies, 2018, 36 V. Kempter and B. Kirchner, J. Mol. Struct., 2010, 972, 22–34.
11, 645–660.
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 9041–9048 | 9047

View Article Online
RSC Advances
Paper
37 C. Moreau, A. Finiels and L. Vanoye, J. Mol. Catal. A: Chem., 45 D. Yamaguchi, K. Watanabe and S. Fukumi, Sci. Rep., 2016,
2006, 253, 165–169. 6, 20327–20334.
38 F. Guo, Z. Fang and T. J. Zhou, Bioresour. Technol., 2012, 112, 46 M. Watanabe, Y. Aizawa, T. Iida, R. Nishimura and
313–318. H. Inomata, Appl. Catal., A, 2005, 295, 150–156.
39 A. H. Jadhav, H. Kim and I. T. Hwang, Catal. Commun., 2012, 47 Z. Wang, H. Li, C. Fang, W. Zhao, T. Yang and S. Yang, Energy
21, 96–103. Technol., 2017, 5, 2046–2054.
40 J. N. Chheda, Y. Roman-Leshkov and J. A. Dumesic, Green 48 S. K. R. Patil and C. R. F. Lund, Energy Fuels, 2011, 25, 4745–
Chem., 2007, 9, 342–350. 4755.
41 H. Xin, T. Zhang, W. Li, M. Su, S. Li, Q. Shao and L. Ma, RSC 49 X. Qi, M. Watanabe, T. M. Aida and J. R. L. Smith, Green
Adv., 2017, 7, 41546–41551. Chem., 2009, 11, 1327–1331.
42 P. A. Russo, M. M. Antunes, P. Neves, P. V. Wiper, E. Fazio, 50 M. Walia, U. Sharma, V. K. Agnihotri and B. Singh, RSC Adv.,
´
F. Neri, F. Barreca, L. Mafra, M. Pillinger, N. Pinna and
A. A. Valente, Green Chem., 2014, 16, 4292–4305.
43 Y. Zhang, Y. Shen, Y. Chen, Y. Yan, J. Pan, Q. Xiong, W. Shi
and L. Yu, Chem. Eng. J., 2016, 294, 222–235.
44 X. Qi, H. Guo, L. Li and J. R. L. Smith, ChemSusChem, 2012, 5,
2215–2220.
2014, 4, 14414–14418.
51 Z. Ma, H. Hu, Z. Sun, W. Fang, J. Zhang, L. Yang, Y. Zhang
and L. Wang, ChemSusChem, 2017, 10, 1669–1674.
52 S. Kang, J. Ye, Y. Zhang and J. Chang, RSC Adv., 2013, 3,
7360–7366.
53 X. Qi, M. Watanabe, T. M. Aida and J. R. L. Smith, Green
Chem., 2010, 12, 1855–1860.
9048 | RSC Adv., 2019, 9, 9041–9048
This journal is © The Royal Society of Chemistry 2019