Carbonaceous microspheres prepared by hydrothermal carbonization of glucose for direct use in catalytic dehydration of fructose

Article abstract of DOI:10.1039/c4ra15296d

A carbonaceous microsphere material was prepared by hydrothermal carbonization (HTC) of glucose, and was used directly for the catalytic dehydration of fructose into 5-HMF without any in situ functionalization or post-modification. The prepared material was found to be a good solid acid catalyst for the production of 5-HMF from fructose in ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), where a 5-HMF yield of 88.1% was obtained at 100 °C for 90 min reaction time, which is due to the contribution of the -COOH groups in the catalyst. It is the first time that a HTC material is reported in the efficient catalytic conversion of biomass without any in situ functionalization or post-modification. In addition, the catalytic system was shown to be applicable to higher fructose concentrations up to ca. 10 wt%. The HTC material catalyst exhibited constant activity for five successive reuses. This journal is

Full text of DOI:10.1039/c4ra15296d

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Carbonaceous microspheres prepared by
hydrothermal carbonization of glucose for direct
Cite this: RSC Adv., 2015, 5, 17526
use in catalytic dehydration of fructose†
ab
Nian Liub and Youfen Lianb
*
Xinhua Qi,
A carbonaceous microsphere material was prepared by hydrothermal carbonization (HTC) of glucose, and
was used directly for the catalytic dehydration of fructose into 5-HMF without any in situ functionalization
or post-modification. The prepared material was found to be a good solid acid catalyst for the production of
5-HMF from fructose in ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM][Cl]), where a 5-HMF
yield of 88.1% was obtained at 100 ꢀC for 90 min reaction time, which is due to the contribution of the
–COOH groups in the catalyst. It is the first time that a HTC material is reported in the efficient catalytic
conversion of biomass without any in situ functionalization or post-modification. In addition, the
catalytic system was shown to be applicable to higher fructose concentrations up to ca. 10 wt%. The
HTC material catalyst exhibited constant activity for five successive reuses.
Received 26th November 2014
Accepted 26th January 2015
DOI: 10.1039/c4ra15296d
www.rsc.org/advances
phosphates can be separated and recycled easily, but they suffer
from medium yields.20 Strong acidic cation exchange resins are
efficient for the conversion of fructose to 5-HMF,13,21 however,
1. Introduction
With the gradual depletion of traditional fossil resources, the
search for sustainable and alternative energy sources is of great
importance for a sustainable society.1 As a renewable resource,
abundant biomass resources can be a promising candidate to
supplement our fuel supply and chemical demands, provided
that efficient transformation pathways can be developed.2
Among the possible biomass-derived value-added chemicals, 5-
hydroxymethylfurfural (5-HMF) is one of the versatile interme-
diate products that can be used for the production of a wide
variety of polymers, pharmaceuticals and biofuels.2,3
In the past few years, considerable efforts have been devoted
to the conversion of various biomass derivatives to 5-HMF, in
which the most efficient method is catalyzed dehydration of
fructose in the presence of an acid catalyst. Thus far, many types
of acid catalysts have been used in the reaction, such as mineral
acids,4,5 organic acid, H-form zeolites,6–8 transition metal
ions,9–12 strong acid cation exchange resins,13–15 acidic ionic
liquids,16,17 and sulfonated carbonaceous materials.18,19
Homogenous acids are inexpensive and effective, but they have
serious drawbacks in terms of products separation, solvent
recycling, and equipment corrosion. H-form zeolites and metal
their application are restricted due to their thermal stability.22
Recently, carbonaceous material solid acids have attracted
more and more attentions in catalytic biomass conversion,23–26
since they not only exhibit excellent catalytic activity and recy-
clability, but also can be prepared from biomass itself (sugars,
starch, cellulose or crude biomass). Thus far, almost all of the
carbonaceous solid acid catalysts catalyze the dehydration of
fructose to 5-HMF with –SO3H as functional groups. For
example, Guo et al.18 prepared a lignin-derived carbonaceous
catalyst through the pyrolysis of lignin at 400 ꢀC followed by
sulfonation with H2SO4, and showed that the catalyst exhibited
high activity for fructose dehydration into 5-HMF that a 5-HMF
yield of 84% was obtained in dimethyl sulfoxide and 1-butyl-3-
methyl-imidazolium chloride mixtures at 110 ꢀC for 10 min
reaction time. Kang et al.27 synthesized biomass hydrochar
derived sulfonated catalysts by hydrothermal carbonization of
lignin, cellulose, wood meal and xylose, followed by sulfonation
with H2SO4, and these carbonaceous material catalysts were
used for the production of 5-HMF from inulin with yields of 47–
65% in ionic liquid at 100 ꢀC in 60 min. These sulfonated
carbonaceous materials are commonly prepared in two steps.
Firstly, a solid carbon material was prepared from the sugars,
cellulose or crude biomass by pyrolysis or hydrothermal
carbonization. Then, the obtained carbon material is treated
with excess amount of concentrated and/or fuming sulfuric acid
to introduce –SO3H groups. This preparation method for the
biomass-derived sulfonated carbon materials suffers from some
problems such as toxic gases release and harsh operation
conditions, and does not meet the principles of green
aAgro-Environmental Protection Institute, The Ministry of Agriculture, Tianjin 300191,
China. E-mail: qixinhua@nankai.edu.cn; Fax: +86-22-2350-8807; Tel: +86-22-2350-
8807
bTianjin Biomass Solid Waste Reclamation Technology and Engineering Center,
College of Environmental Science and Engineering, Nankai University, Tianjin
300071, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra15296d
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chemistry.28,29 Thus, more environmentally benign carbona- room temperature. The resulting crude product was recovered
ceous solid acid catalysts are need for the sustainable biomass by centrifugation and washed repeatedly with ethanol and water
utilization.
for ten times, and oven-dried at 80 ꢀC for 12 h. A carbon
Hydrothermal carbonization (HTC) of biomass is a prom- material yield of 28.3% was achieved from 25 g of glucose.
ising method to synthesize carbonaceous materials that have
potential applications in the elds such as material, adsorption
2.3 Typical experimental procedure for 5-HMF production
from fructose
and energy storage.30 To enhance their performance in catalytic,
adsorption or energetic applications, in situ functionalization or
In a typical reaction, 0.05 g of fructose was pre-dissolved in 1 g
post-modication is generally required to introduce functional
of [BMIM][Cl] in a 10 ml quartz tube reactor with a sealing plug,
groups or expand their porosity and surface area.31,32 In this
then 0.05 g catalyst was added. The reaction mixture was heated
to 100 ꢀC and maintained for a given reaction time in an oil
bath. Aer the desired reaction time elapsed, the reactor was
cooled to room temperature with cold water bath within 1 min
and 0.5 g of water was added to the mixture to promote the
transport of 5-HMF from the ionic liquid phase to the ethyl
acetate phase in the following extraction step. The product 5-
HMF was effectively extracted from the reaction mixture with
work, a carbonaceous microspheres material bearing –COOH
and phenolic –OH groups was prepared by hydrothermal
carbonization of glucose. The as-prepared carbonaceous
microspheres was used directly without any in situ functional-
ization or post-modication and were shown to be efficient for
the catalytic dehydration of fructose to 5-HMF. To our knowl-
edge, it is the rst time that the carbon material prepared from
the carbonization of carbohydrates or lignocellulosic biomass is
ethyl acetate (10 ml  6), since [BMIM][Cl] and fructose were
reported in the efficient catalytic conversion of biomass without
any in situ functionalization or post-modication, indicating
insoluble in ethyl acetate and 5-HMF was the sole product in the
ethyl acetate phase, as presented by Hu et al.33 and Yong et al.34
that the conventional two-step synthesis procedures of hydro-
The product 5-HMF was measured with a Cary-50 Model spec-
thermal carbonization and sulfonation commonly reported in
trophotometer (Varian Inc.) at 284 nm using standard curve
the literature to be unnecessary.
method.
2. Experimental section
2.1 Materials
2.4 Catalyst characterization
The catalysts were characterized by SEM, elemental analysis, FT-
Fructose and glucose (99%) were obtained from Guangfu ne
chemicals research institute (Tianjin) and were used as
received. 5-Hydroxymethylfurfural (98%) was purchased from
the Acros Organics Company (Geel). Ionic liquid 1-butyl-3-
methyl imidazolium chloride ([BMIM][Cl], 99%) was received
from Henan Lihua pharmaceutical Co., Ltd. (Xinxiang).
IR and Boehm Titration. The morphology/size of the samples
was visualized by SEM using a JEOL JSM-6700 instrument.
Elemental analysis was carried out using Elementar Vario EL
cube (Germany). FT-IR spectrum was recorded over the range
from 400 to 4000 cmÀ1 at a resolution of 4 cmÀ1 with a MAGNA-
560 apparatus with DTGS detector (NICOLET), aer the catalyst
was thoroughly mixed with KBr powder and compressed into
pellet. The acidity distributions of the carbonaceous material
was measured by the Boehm Titration method.35
2.2 Preparation of carbonaceous microspheres material
The carbonaceous microspheres material was prepared by
incomplete carbonization of glucose, as depicted below. Typi-
cally, 25 g of glucose was dissolved in 50 ml of water, and the
obtained glucose aqueous solution was loaded into a Teon-
3. Results and discussion
3.1 Characterization of the carbonaceous material
lined, stainless steel autoclave (100 ml volume). Then, it was
ꢀ
heated to 180 C for 10 h under self-generated pressure in the Fig. 1 shows SEM images of the carbonaceous material obtained
closed system. Aerwards, the autoclave was cooled down to by hydrothermal carbonization of glucose at 180 ꢀC for 10 h. It
Fig. 1 SEM images of carbonaceous microspheres material prepared by hydrothermal carbonization of glucose at 180 ꢀC for 10 h.
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Fig. 2 FT-IR spectrum of the obtained carbonaceous material from
hydrothermal carbonization of glucose at 180 ꢀC for 10 h.
Fig. 3 Catalytic dehydration of fructose into 5-HMF by the prepared
carbon microspheres material in [BMIM][Cl] (reaction conditions: 0.01
g of fructose, 1 g of [BMIM][Cl], 100 ꢀC).
can be seen that the obtained carbonaceous material consisted
mainly of aggregates of interconnected uniform carbon spheres
with diameter of about 1.5 mm, which closely corresponds with
the results reported by Sun et al.36
1-butyl-3-methyl imidazolium chloride ([BMIM][Cl]). The cata-
lytic conversion of fructose into 5-HMF by different amount of
catalyst was examined (Fig. 3). In the absence of the carbon
material, only about 10% of 5-HMF yield was obtained at 100 ꢀC
for 240 min. When 0.01 g of carbon material was added, the
5-HMF yield was remarkably increased to 79.9% for 120 min
reaction time, demonstrating that the prepared carbon micro-
sphere material is a highly active catalyst for the dehydration of
fructose into 5-HMF. Although the employed carbon material
catalyst was prepared from the hydrothermal carbonization of
glucose without any in situ or post functionalization, it shows to
be efficient for the 5-HMF production from fructose, which
should be ascribed to the –COOH groups in the catalyst. A
representative carboxylic acid, acetic acid was used for the
catalytic dehydration of fructose to 5-HMF in the system
(Fig. S1†), illustrating the good catalytic activity of –COOH
groups for the reaction. Aer the added catalyst dosage was
increased to 0.03 g and 0.05 g, 5-HMF yield was improved to
80.4% and 88.1%, respectively, in 90 min reaction time.
However, when the catalyst dosage was further increased to
0.1 g, the 5-HMF yield decreased to 78.2% in 90 min reaction
time, which may be resulted from the excess acid-active sites
that facilitate not only the dehydration of fructose to 5-HMF but
also the degradation of the formed 5-HMF into other products
such as humins.40,41 In addition, the prepared carbon material
FT-IR spectrum of the prepared carbon microspheres mate-
rial is shown in Fig. 2. The band at ca. 3430 cmÀ1 can be
assigned to O–H stretching vibration of adsorbed water mole-
cules and surface hydroxyl groups including phenolic
groups.36,37 The band at 2922 cmÀ1 corresponds to the stretch-
ing vibrations of aliphatic C–H and is evidence of aliphaÀti1c
structures.38 The absorption bands at ca. 1702 and 1618 cm
,
are attributed to COOÀ and C]C stretching vibrations,
respectively, demonstrating the existence of a large number of
carboxylic groups in the prepared carbon material.38,39
The elemental compositions (C, H and O) of the prepared
carbon microspheres material are listed in Table 1, indicating it
has a composition of CH0.92O0.34. The acidity distributions of
the material were analyzed by the Boehm method and are also
listed in Table 1, indicating a carboxylic groups concentration of
2.17 mmol gÀ1, which verify the strong adsorption band at 1702
cmÀ1 for –COOH in the FT-IR spectrum in Fig. 2.
3.2 Catalytic dehydration of fructose into 5-HMF by the
prepared carbonaceous microspheres material
The prepared carbon microspheres material was tried to cata-
lyze the dehydration of fructose into 5-HMF in an ionic liquid
Table 1 Elemental composition and acidity distributions of the prepared carbonaceous material by hydrothermal carbonization of glucose from
the Boehm titration
Elemental composition
Acidity distributions
Total acid sitesa
Carboxylic groupsb
Phenolic groupsc
Lactonic groupsd
C (%)
H (%)
5.04
O (%)
29.6
(mmol gÀ1
)
(mmol gÀ1
)
(mmol gÀ1
)
(mmol gÀ1
)
65.3
3.50
2.17
1.33
0.33
a
Obtained by titration with NaOH. b Obtained by subtracting concentration of sulfonic groups from titration results with NaHCO3. c Obtained by
d
subtracting titration results using Na2CO3 from calculated values of NaOH. Obtained by subtracting titration results using NaHCO3 from
calculated values of Na2CO3.
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was also tried for the reaction in water and dimethyl sulfoxide the humins have not been able to be quantied,22,42 but their
(DMSO) at 150 ꢀC in 90 reaction time, and 5-HMF yield of 10.7% generation and existence could be observed from the brown
and 83.2% could be obtained, respectively, indicating that the color in the reaction mixture, and the brown color remained
catalyst is also efficient in some other solvents.
even aer yellow 5-HMF was extracted from the mixture with
In our previous work, sulfonated carbon materials were ethyl acetate.
prepared by hydrothermal carbonization of glucose or cellulose
followed by sulfonation with H2SO4.19 These catalysts were used
3.4 Effect of initial fructose concentration on the conversion
for the dehydration of fructose into 5-HMF, and a maximum 5-
HMF yield of 83% could be obtained at 80 ꢀC in 10 min reaction
time in [BMIM][Cl].19 Thus, compared with the carbon material
without any in situ or post modication prepared in this work,
the sulfonated carbon material exhibited higher efficiency in
terms of reaction temperature and reaction time, but it gave a
lower maximum 5-HMF yield, which should be ascribed to the
stronger acidity of the –SO3H groups that not only favor the
dehydration of fructose into 5-HMF, but also promote the
decomposition of the formed 5-HMF.19
of fructose into 5-HMF catalyzed by the prepared carbon
microspheres material
In acid catalytic dehydration of carbohydrates, initial loading
substrate concentration normally has a remarkable effect on
5-HMF yield, since higher substrate concentration leads to an
increase in the molecular collisions opportunities between the
formed 5-HMF molecules or the 5-HMF and substrate mole-
cules, and hence promotes the generation of undesirable
humins. The inuence of initial fructose concentration on the
conversion of fructose into 5-HMF catalyzed by the prepared
carbon material in [BMIM][Cl] was studied and the results are
illustrated in Fig. 5. It can be seen from Fig. 5 that the 5-HMF
yields decreased with increasing initial fructose concentration
at the initial stage of the reaction. For example, when 0.01, 0.03,
0.05 and 0.1 g of fructose was used, respectively, the 5-HMF
yield was 57, 53, 41 and 36% at 100 ꢀC for 10 min reaction time,
respectively. However, the maximum 5-HMF yields in all cases
were above 75%, indicating that the prepared carbon micro-
spheres material by the hydrothermal carbonization of glucose
is applicable to higher feedstock concentrations up to ca.
10 wt%.
3.3 Effect of reaction temperature on the conversion of
fructose into 5-HMF
The conversion of fructose catalyzed by the prepared carbon
microspheres material was investigated at different reaction
temperatures (Fig. 4). When the reaction was conducted at
80 ꢀC, a 5-HMF yield of 53.5% was obtained for 30 min reaction
time, and the 5-HMF yield increased to 76.2% by prolonging the
reaction time to 90 min. The 5-HMF yield increased from 77.3%
to 88.1% when the temperature was elevated from 90 ꢀC to
ꢀ
100 C for 90 min reaction time. With further increase of the
reaction temperature to 110 ꢀC, a maximum 5-HMF yield of
83.4% was achieved within 60 min, and then the 5-HMF yield
began to decrease rapidly with increasing reaction time.
Therefore, it seems that higher reaction temperatures not
only favored the conversion of fructose into 5-HMF, but also
promoted the formation of humins that is inevitably generated
in acid-catalyzed processing of carbohydrates by self-
polymerization between 5-HMF molecules or cross-
polymerization between 5-HMF and fructose.22,42,43 At present,
3.5 Recycling of the prepared carbon microspheres material
To examine the activity and stability of the prepared carbon
material by hydrothermal carbonization of glucose for the
conversion of fructose into 5-HMF in ionic liquid system, the
recycle of the carbon material was studied for ve times to study
its stability in each run (Fig. 6). Experiments were conducted in
ꢀ
[BMIM][Cl] at 100 C for 90 min reaction time. Aer reaction,
the product 5-HMF was separated from the reaction mixture by
Fig. 4 Effect of reaction temperature on the conversion of fructose Fig. 5 Effect of fructose loading on the conversion of fructose into 5-
into 5-HMF catalyzed by the prepared carbon microspheres material in HMF catalyzed by the prepared carbon microspheres material in
[BMIM][Cl] (reaction conditions: 0.01 g of fructose, 1 g of [BMIM][Cl], [BMIM][Cl] (reaction conditions: 100 ꢀC, 1 g of [BMIM][Cl], 0.05 g
0.05 g catalyst).
catalyst).
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program of Chinese Academy of Agricultural Sciences (to Xin-
hua Qi) and the Natural Science Foundation of Tianjin (no.
12JCYBJC13000).
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In the present work, a carbonaceous microspheres material
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hydrothermal carbonization of glucose, and was employed
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tion for the catalytic dehydration of fructose into 5-HMF in ionic
liquid. The prepared carbon material was shown to be efficient
for the 5-HMF formation from fructose, and a high 5-HMF yield
of 88.1% could be obtained at 100 ꢀC for 90 min reaction time,
which should be ascribed to the –COOH groups in the catalyst.
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