Sulfonated polymer impregnated carbon composite as a solid acid catalyst for the selective synthesis of furfural from xylose

Article abstract of DOI:10.1016/j.tetlet.2015.01.116

A sulfonated polymer impregnated carbon composite solid acid catalyst was prepared by the pyrolysis of a polymer matrix impregnated with glucose followed by its sulfonation and used for the dehydration of xylose to furfural. The developed catalyst exhibited excellent activity and provided almost quantitative conversion of xylose with the selective synthesis of furfural. After completion of the reaction, the catalyst was easily recovered and reused for several runs without noticeable loss in its activity and selectivity.

Full text of DOI:10.1016/j.tetlet.2015.01.116

Accepted Manuscript
Sulfonated polymer impregnated carbon composite as a solid acid catalyst for
the selective synthesis of furfural from xylose
Praveen K. Khatri, Neha Karanwal, Savita Kaul, Suman L. Jain
PII:
S0040-4039(15)00154-9
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.01.116
TETL 45786
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
9 November 2014
18 January 2015
19 January 2015
Please cite this article as: Khatri, P.K., Karanwal, N., Kaul, S., Jain, S.L., Sulfonated polymer impregnated carbon
composite as a solid acid catalyst for the selective synthesis of furfural from xylose, Tetrahedron Letters (2015),
doi: http://dx.doi.org/10.1016/j.tetlet.2015.01.116
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Graphical Abstract
Sulfonated polymer impregnated carbon
composite as a solid acid catalyst for the
selective synthesis of furfural from xylose
Leave this area blank for abstract info.
Praveen K. Khatri, Neha Karanwal, Savita Kaul and Suman L. Jain
O
150oC, DMSO
O
O
HO
HO
H
P-C-SO3H
OH
OH
Furfural
D-Xylose
>98 % conv
>99 % selectivity

1
Tetrahedron Letters
journal homepage: www.els evier.com
Sulfonated polymer impregnated carbon composite as a solid acid catalyst for the
selective synthesis of furfural from xylose
Praveen K. Khatri,a Neha Karanwal,b Savita Kaulb and Suman L. Jaina*
aChemical Sciences Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun-248005 (India)
bBiofuel Division, CSIR-Indian Institute of Petroleum, Dehradun-248005 (India)
ARTICLE INFO
ABSTRACT
Article history:
Received
A sulfonated polymer impregnated carbon composite solid acid catalyst was prepared by the
pyrolysis of a polymer matrix impregnated with glucose followed by its sulfonation and used for
the dehydration of xylose to furfural. The developed catalyst exhibited excellent activity and
provided almost quantitative conversion of xylose with the selective synthesis of furfural. After
completion of the reaction, the catalyst was easily recovered and reused for several runs without
noticeable loss in its activity and selectivity.
Received in revised form
Accepted
Available online
Keywords:
2009 Elsevier Ltd. All rights reserved.
Solid acid
Biomass conversion
Xylose
Dehydration
Heterogeneous catalyst
Conversion of biomass through green chemical routes is of
great industrial importance as biomass is considered to be most
widely available inexpensive renewable resource that can be used
as a raw material for the production of biofuel and value-added
organic products. In this regard, acid catalyzed dehydration of
biomass derived pentose sugars (mainly D-xylose) to furfural is a
process of tremendous research interest in current scenario due to
the wider industrial applications of furfural.2 Furfural is an
excellent organic solvent for refinement of lubricants and
separation of butadiene from butene mixture in synthetic rubber
fabrication. In addition it also serve as a promising solvent for
many organic materials, such as resins, polymers and also used as
a building block for synthesis of various valuable chemicals such
as furfuryl alcohol, furan, pharmaceutical, agrochemicals and
THF.3-5
pyrophosphate25 have been reported for this transformation. The
merits of solid acid catalysts lie in their higher activity,
selectivity, and ease of separation from the reaction products.
Furthermore, they are considered as super acids due to the higher
acid strength which is possibly similar to or greater than the
acidity exhibited by strong mineral acids, such as concentrated
sulfuric acid. However, most of the existing catalytic systems
suffer from the drawbacks such as high activation barrier for
xylose dehydration, high reaction temperature, longer residence
period in aqueous media and limited recyclability. Recently, Yu
and coworkers26 reported the synthesis of magnetic porous
carbonaceous solid acid catalyst derived from biomass waste for
the dehydration of xylose to furfural with excellent conversion.
However poor selectivity and longer reaction time (5h) limited
the scope of this investigation. In another report Luong et al
demonstrated the applicability of graphene, graphene oxide,
sulfonated graphene, sulfonated graphene oxide as solid acid
catalyst for dehydration of xylose to furfural in aqueous media
but it is associated with high operating temperature and relatively
lower yield, making the process unfavorable.27
The conventional approach for dehydration of xylose to
furfural involves the use of highly corrosive and toxic acids such
as concentrated sulfuric acid, hydrochloric acid etc as catalyst
and higher reaction temperatures.6-7 Under these conditions, the
selectivity of furfural does not exceed 70 %, unless is
continuously extracted with supercritical fluids. Furthermore, the
process can also promote a number of secondary reactions which
affects the overall selectivity of the desired product.
Subsequently a number of efforts have been made to develop cost
effective, environmentally benign and selective catalytic
processes for the conversion of xylose to furfural. In this regard,
Recently low cost sulfonated carbon catalysts (C–SO3H)
derived from the incomplete carbonization of simple sugars such
as glucose has come out to be a new class of catalysts exhibiting
superior activities than several sulfonated acid catalysts, for
example silica supported Nafion, sulfonated zirconia etc for acid
catalyzed reactions.28-29 However, added stability is another
appealing aspect of sulfonated carbon materials in addition to
low cost. In this regard, Goodwin et al30 reported sulfonated
carbon composite solid acid prepared by the pyrolysis of a
polymer matrix impregnated with glucose followed by
sulfonation as catalyst for the biodiesel synthesis. The title
different
heteropolyacids12
solid acid catalysts including zeolites8-11
,
and sulfonic acid functionalized
mesoporous/microporous materials,13-17 transition metal oxides
and titanates,18-20 MCM-41-supported niobium-oxide,21 ion
exchange polymer resins like Nafion and amberlyst,22-24 vanadyl

2
Tetrahedron
catalyst exhibited higher acid site density, better esterification
found to be 2.44 and 1.28 mmol H+/g, respectively. This is most
likely due to the freely distribution of polycyclic aromatic
hydrocarbons along to the resin framework are much more even
which lead to the greater availability of active sites for
sulfonation, resulted in the higher sulfonic acid density of P-C-
SO3H as compared to the of C-SO3H.30
activity of both small and large free fatty acids (acetic acid and
palmitic acid), and superior reusability than the previously
reported carbon-based catalyst prepared by sulfonating pyrolyzed
sugar. Inspired with these results, we thought it would be
worthwhile to explore the potential of such catalysts in the area
of biomass conversion to value added chemicals. Accordingly,
herein we report an efficient sulfonated polymer impregnated
carbon composite solid acid catalyst for the dehydration of
xylose to furfural selectively in good to excellent yield under
comparatively milder reaction conditions.
Table 1: Properties of the sulfonated catalysts
BET surface
area (m2/g)
SO3H(mmol/g) by
elemental S analysis
Catalyst
<1 (<1)*
<1(<1)*
2.44 (2.42)*
1.28 (0.66)*
P-C-SO3H
C-SO3H
Synthesis and characterization of the catalyst
During the present study, the targeted sulfonated polymer
impregnated carbon composite (P–C–SO3H) was synthesized via
sulfonation of a composite material formed through incomplete
carbonization of hydrolyzed glucose supported in a polymer
matrix based on a copolymer of styrene and chloromethylstyrene
i.e. Merrifield resin (Scheme 1).31 For the comparative study, the
corresponding sulfonated carbon catalyst (C-SO3H) was also
synthesized via incomplete carbonization of glucose.32
*values in parenthesis are of composites of ref. 30
The surface properties and acid densities of the synthesized
composite P-C-SO3H were found to be comparable with the
existing literature.30 However the synthesized C-SO3H displayed
almost twofold excess acid density as compared to the value
reported by Goodwin etal.30
Thermal stability of the synthesized carbon-based catalysts
was determined by thermal gravimetric analysis (TGA). The both
catalysts showed almost similar decomposition pattern when
heated in air (Fig. S3). An initial weight loss was due to water
desorption as the temperature increased from room temperature
OH
OH
Incomplete carbonization
H2SO4
H
O
H
H
H
-H2O
H
OH
OH
OH
C-SO3
H
o
o
D-Glucose
to 100 C. Furthermore in the temperature range of 150–500 C,
the TGA pattern of P–C–SO3H showed a plateau indicating a
much slower rate of weight loss than C-SO3H. Finally a rapid
Polycyclic
aromatic
hydrocarbons
SO3H+
H2SO4/H2O
Impregnation
o
weight loss was occurred in the temperature range 550 to 650 C
when negligible mass was left at this temperature.
Incomplete
carbonization
H2SO4
Swellling
-H2O
P-C-SO3H
Catalytic activity
Merrifield's peptide resin
The catalytic activity of the synthesized catalysts P-C-SO3H
and C-SO3H was checked for the dehydration of xylose to
furfural at 150 C using DMSO as reaction media.33 Among the
o
Scheme 1: Synthesis of P-C-SO3H and C-SO3H catalysts
two catalysts studied sulfonated polymer impregnated carbon
composite (P-C-SO3H) was found to be superior and provided
almost quantitative conversion of xylose with the selective
synthesis of furfural (Table 2, entry 1-2). Based on these results
we have chosen P-C-SO3H as catalyst for further study and
performed a number of experiments in order to identify the
optimized reaction conditions. The results of these experiments
are summarized in Table 2. At first, the dehydration of xylose to
The powder X-ray diffraction of the synthesized P-C-SO3H
catalyst did not show any characteristic peak and exhibited a
broad peak centered at 2θ value of 25o, indicating that the
synthesized material is amorphous in nature (Fig. S1), which is in
well conformity with the existing literature report.30
o
furfural was performed in water at 150 C for 30 min (Table 2,
FT-IR spectra of the synthesized P-C-SO3H and C-SO3H
catalysts are shown in Fig. S2. As shown, the broad absorption
band around 3300 cm-1 in P-C-SO3H was attributed to OH
stretching with two shoulder peaks due to aromatic C-H
stretching and aliphatic C-H stretching. Double headed
absorption band in the region 1630–1780 cm-1 was related to the
C=O group. Much stronger absorption bands around 1000 cm-1
and 630 cm-1 in P-C-SO3H compare to C-SO3H are assigned to
S=O stretching of -SO3H and C-S stretching respectively which
clearly suggested the higher loading of the acid sites in the
polymer impregnated carbon catalyst i.e. P-C-SO3H than C-
SO3H. The poor acidity of carbon (C-SO3H) catalyst was further
proved by a very weak band around at 1200 cm-1 due to the
asymmetric and symmetric stretching of sulfonic acid group,
which is quite stronger in P-C-SO3H.
entry 3). The reaction was found to be very slow and gave
extremely poor conversion of xylose to furfural (>1%). However,
the reaction was found to be increased with time and gave only
marginally improved yield after 3h (Table 2, entry 3-6).
Consequently, a biphasic solvent system such as mixture of water
and toluene (1:3, v/v) was used at 150 oC for 2 h (Table 2, entry
7). The reaction did not occur and unreacted xylose was
recovered at the end of the reaction. Next, the reaction was
carried out using water/ DMSO in different ratios under
otherwise similar reaction conditions (Table 2, entry 8-9). The
reaction was found to be slow and gave maximum 45 %
conversion of xylose to furfural in 2 h when 1:5 ratio of water
and DMSO was used as reaction media (Table 2, entry 9).
Inspired by these findings next we tried the reaction in DMSO at
150 oC. Surprisingly the reaction was found to occur at faster rate
and gave nearly 72 % conversion of xylose with 98 % selectivity
for furfural in 1h (Table 2, entry 10). Based on these
experimental results we have chosen DMSO as the solvent of
choice for further studies. Further we studied the effect of
reaction time by keeping other reaction parameters constant. As
expected the conversion of xylose was found to be increased with
Sulfur contents or sulfonic acid site densities in both P-C-
SO3H and C-SO3H catalysts were estimated by elemental
analysis (Table 1). The acidity of the P-C-SO3H and C-SO3H
calculated from elemental sulfur analysis assuming that all the
sulfur atoms in the catalyst are presented in -SO3H form was

3
time and gave 92 % conversion in 2h (Table 2, entry 11) and
almost quantitative conversion (> 98 %) within 3h (Table 2, entry
1). Temperature was also found to be a key factor in this reaction
and gave best results at 150 C. Further increase in temperature
did not show any appreciable improvement in the results (Table
2, entry 12-13).
Xylose conversion
Furfural Yield
100
80
60
40
20
0
o
Table 2: Dehydration of xylose to furfural under different
reaction conditionsa
O
O
OH
OH
O
P-C-SO3H
HO
150 oC, DMSO
1
2
3
4
5
6
OH
Furfural
>98 % Conv.
100 % Selectivity
Run
D-Xylose
Entr
y
Solvent
Time/
h
Temp/
oC
Conv.
(%)b
Selec
(%)b
Fig. 1: Results of recycling experiments;
In summary, we have demonstrated sulfonated polymer
impregnated carbon composite (P-C-SO3H) as an efficient and
selective solid acid catalyst for the dehydration of xylose to
furfural. The sulfonated polymer impregnated carbon composite
i.e. P-C-SO3H was found to be superior than sulfonated carbon
catalyst (C-SO3H) and afforded almost quantitative conversion of
xylose with the selective synthesis of furfural. The higher
catalytic activity of P-C-SO3H may be due to the more even
distribution of polycyclic aromatic moieties along the resin
network, leading to more available sites for sulfonation which
resulted in greater sulfonic acid density in P-C-SO3H as
compared to in C-SO3H. After completion of the reaction, the
catalyst was easily recovered and reused subsequently for several
runs without significant loss in its activity.
1
DMSO
DMSO
H2O
3.0
3.0
0.5
1.0
2.0
3.0
2.0
150
150
150
150
150
150
150
98
45
1
100
98
95
99
94
92
-
2 c
3
4
H2O
H2O
1
5
1.5
2.5
-
6
H2O
H2O/Toluene
(1:3)
H2O/DMSO
(1:3)
7
8
9
2.0
2.0
150
150
24
45
96
95
H2O/DMSO
(1:5)
10
11
12
13
DMSO
DMSO
DMSO
DMSO
1.0
2.0
3.0
3.0
150
150
120
160
72
92
12
45
97
99.2
96
97.5
aReaction conditions: xylose (0.5 g, 3.33 mmol), solvent ( 25 ml),
b
catalyst (0.1 g.), conversion and selectivity were determined by
Calculations
HPLC;cC-SO3H was used as catalyst.
The organic phase samples were first subjected to GC-MS
analysis to establish the compounds extracted from the reaction
medium; no major products or intermediates other than furfural
were detected. Furfural in the organic phase samples was
quantified via HPLC using C18 column with water (0.05 mmol
H2SO4) as mobile phase at a flow rate of 0.6 mL min-1 and the
column temperature was maintained at 333 K and detector
temperature of 35 °C were used for optimal peak resolution and
detection. Furfural in the organic phase samples was quantified
via HPLC analysis. Xylose conversion, furfural selectivity and
furfural yield were calculated as given below.
The greater catalytic activity of P-C-SO3H as compared to C-
SO3H can be explained on the basis of a flexible polymeric
framework decorated along with a layer of sulfonated polycyclic
aromatic hydrocarbons, which can quickly swell the liquid phase
enabling the reactant xylose to access more active sites as
compared to in C-SO3H catalyst. Furthermore, structure directing
property of polymer matrix or resin is also an additional factor
for the higher stability of P-C-SO3H through interaction between
carbon moieties and the polymer framework.
Last but not the least, recycling ability of the developed P-C-
SO3H was tested by performing a number of recycling
experiments under similar experimental conditions. After
completion of the reaction, the catalyst was recovered by simple
filtration and reused for the dehydration of xylose to furfural
under optimized reaction conditions. The recycling ability of the
catalyst was tested for six subsequent runs (Fig. 1). In these
experiments the conversion of xylose to furfural was as good as
with first run of catalyst. Furthermore, the sulfur content of the
recovered catalyst obtained after six runs was found to be almost
similar to the fresh one. These results established that the
synthesized composite catalyst is highly stable and can be
efficiently recycle for several runs.
Acknowledgments
We are thankful to the Director, IIP for his permission to
publish these results. Biotechnology division is kindly
acknowledged for providing HPLC analysis of the samples. Neha
Karanwal is thankful to CSIR, New Delhi for working as
Technical HR under XII five year project.

4
Tetrahedron
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