Microwave assisted efficient furfural production using nano-sized surface-sulfonated diamond powder

Article abstract of DOI:10.1016/j.catcom.2018.03.020

Sulfonated nano-sized diamond powder (S-DP) was tested in a typical water-CPME (1:3, v/v) biphasic system and heated in a commercial monowave microwave oven to promote the dehydration of D-xylose into furfural as industrial platform molecule. This new heterogeneous catalyst with a propyl linker between the support and the sulfonyl group expressed remarkable sufficient hydrophilicity, affinity for D-xylose and catalytic activity in presence of NaCl. The solid can act as a strong acidic catalyst without detectable exchange between proton exclusively localized on the surface of the catalyst and sodium ion. It was also stable at 200 °C even after severe recycling treatment. The final optimized condition requires 10 wt% of the catalyst for a maximum furfural yield of 76% when the mixture is heated for 50 min in the current biphasic system.

Full text of DOI:10.1016/j.catcom.2018.03.020

Accepted Manuscript
Microwave assisted efficient furfural production using nano-sized
surface-sulfonated diamond powder
Frederic Delbecq, Yukari Takahashi, Takeshi Kondo, Cristobal
Cara Corbas, Encarnacion Ruiz Ramos, Christophe Len
PII:
DOI:
Reference:
S1566-7367(18)30112-2
doi:10.1016/j.catcom.2018.03.020
CATCOM 5361
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
20 December 2017
12 February 2018
15 March 2018
Please cite this article as: Frederic Delbecq, Yukari Takahashi, Takeshi Kondo, Cristobal
Cara Corbas, Encarnacion Ruiz Ramos, Christophe Len , Microwave assisted efficient
furfural production using nano-sized surface-sulfonated diamond powder. The address
for the corresponding author was captured as affiliation for all authors. Please check if
appropriate. Catcom(2018), doi:10.1016/j.catcom.2018.03.020
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ACCEPTED MANUSCRIPT
Microwave assisted efficient furfural production using nano-sized surface-sulfonated diamond
powder
Frederic Delbecqa, Yukari Takahashib, Takeshi Kondob, Cristobal Cara Corbasc,d, Encarnacion Ruiz
Ramosc,d, ChristopheLene,f
a
Ecole Supérieure de Chimie Organique et Minérale, 1 allée du Réseau Jean-Marie Buckmaster,
F-60200 Compiègne, France
b Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of
Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
c Universidad de Jaen, Department of Chemical, Environmental and Materials Engineering, Campus
Las Lagunillas, 23071 Jaén, Spain
d Universidad de Jaen, Center for Advances Studies in Energy and Environment (CEAEMA), 23071
Jaén, Spain
e Sorbonne Universités, Université de Technologie de Compiègne, Centre de Recherche Royallieu,
CS 60 319, F-60203 Compiègne cedex, France
f
PSL Research University, Chimie ParisTech, CNRS, Institut de Recherche de Chimie Paris, 11 rue
Pierre et MarieCurie, F-75231 Paris Cedex 05, France

ACCEPTED MANUSCRIPT
ABSTRACT
Sulfonated nano-sized diamond powder (S-DP) was tested in a typical water-CPME (1:3, v/v) biphasic
system and heated in a commercial monowave microwave oven to promote the dehydration of
D-xylose into furfural as industrial platform molecule. This new heterogeneous catalyst with a propyl
linker between the support and the sulfonyl group expressed remarkable sufficient hydrophilicity,
affinity for D-xylose and catalytic activity in presence of NaCl. The solid can act as a strong acidic
catalyst without detectable exchange between proton exclusively localized on the surface of the
catalyst and sodium ion. It was also stable at 200 °C even after severe recycling treatment. The final
optimized condition requires 10 wt% of the catalyst for a maximum furfural yield of 76% when the
mixture is heated for 50 min in the current biphasicsystem.
Keywords: sulfonated diamond; furfural;microwave;biphasic system

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1. Introduction
Furfural is a furanic compound obtained from dehydration of pentoses such as D-xylose and
L-arabinose. Both pentoses are all monomers sub-units obtained from the hydrolysis of hemicellulose
or xylan, or any biopolymers rich in xylose. Furfural is overall recognized as a top-value material
source of fuel additives and usually it could become a key -compound for the production of furfuryl
alcohol after reduction of its aldehyde function [1]. It is also known as the precursor of maleic acid
through successive decarbonylation and ring opening oxidation [2]. Furfural is often employed as
starting material for the catalytic transformation into organic solvents such as tetrahydromethylfuran
(MeTHF) or tetrahydrofuran (THF) [3]. Under conventional heating, furfural is produced at
temperature ranging from 170 to 180 °C, always in acidic conditions. Usually, strong mineral acids
such as HCl [4, 5], H2SO4 [6] or H3PO4 [7] were put to good use to perform the dehydration of D-xylose
in solewater.
However, industrially the distillation of this liquid product was necessary to isolate the material
from the crude mixture with enough purity. In addition to the problems of corrosion, safety and
handling, it seems difficult to avoid the associated large waste streams and the yield reduction caused
by the formation of by-products derived from cross-polymerization between furfural and D-xylose, or
from direct resinification of furfural itself, especially in a aqueous monophasic system. These
reactions lead to the generation of insoluble carbonaceous black solid called humin. For preventing of
all above reported concerns, conversion of D-xylose into furfural in a liquid biphasic system in a
presence of NaCl or not with various acid catalysts has been reported [8,9]. Indeed, in a
water-cyclopenthyl methyl ether (CPME) biphasic system with Nafion NR50 as commercial sulfonated
perfluorinated resin [10], novel bio-based sulfonated sporopollenin [11] and a biobased sulfonated
carbon-based material (ex Micanthus) [12] have successively demonstrated their potential for
producing furfural under microwave heating at temperatures around 190 °C giving best furfural yields
found between 60 and 70%. In order to have more economic variation in function of the price of the
starting material, substitution of D-xylose to alginic acid extracted form a variety of microalgae has
been described. In the presence of CuCl2 as catalyst in a mixture of DMSO and -butyrolactone,
furfural was obtained in competitive yield [13]. Whatever the starting material used, the presence of
NaCl permitted to increase the productivity of furfural. NaCl induces a salt-out effect promoting the
transfer of the furfural into the organic layer where the furanic compound was not subjected to
degradation. When stored in a non water miscible organic layer, the furfural is notin contact with any
acidic species, this kind of system is ableto reduce the formation of all solubleand insolublehumin.
As a new catalyst, modified nanoscalled diamond powder by means of 1,3-propanesultone
displays sulfonyl groups covalently bound on its surface (Fig. 1). This material was initially tested for
production of ethylacetate from ethanol and acetic acid. It was also compared to Nafion NR50.
Despite its lower surface acidity, it expressed good activity for esterification in atmospheric condition
and conventional heating [14]. Besides in the literature, there are only a few examples of nanosized
modified carbon based materials employed for the dehydration of D-xylose [15-17]. In this study,

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sulfonated diamond powder (S-DP) with a propyl chain between the support and the sulfonic acid was
tested for producing furfural starting from D-xylose in a typical water-CPME biphasic system under
microwave heating by varying one by one the substrate to catalyst ra tio, temperature, residence time,
the salt-out effect and the xylose loading. Some attempts to regenerate the catalyst were also
realized after one cycle.
Fig. 1. Schematic structure of the sulfonated diamond powder [14].
2. Experimental
2.1. Material and methods
Furfural (99% maximum) and D-xylose were purchased from Acros Organics. Cyclopentyl methyl
ether was supplied by Sigma Aldrich. NaCl and other reagents were used without further purification.
S-DP was synthesized by the procedure as reported in a previous paper [14]. A simple titration
revealed that S-DP displayed 0.072 mmol g-1 of acid which is quite inferior to the value expressed by
Nafion NR 50 which displays a capacity of 0.8 mmol of H+ g-1. Besides, the Zeta-potential of a 0.0125
wt% S-DP aqueous dispersion was measured (result not shown here), and the value varied from - 35
to - 40 mV in a pH range from 3.5 to 11. This result confirmed the polarity of the S-DP surface. The
water used in all experiments was a MilliporeMilli-Q grade.
2.2. General procedure for the synthesis of furfural
In a typical experiment, 0.15 g (1.0 mmol) of D-xylose, 10 wt% of S-DP were introduced in a 10
mL vial closed with a septum, followed by addition of water or brine of different concentrations (1 mL)
and CPME (3 mL). Biphasic batch reactions were carried out by way of microwave heating apparatus
(Anton Paar Monowave 300) and stirred under magnetic stirring (600 rpm) for a desired period of
time. The temperature in the reaction vessel was measured by means of an IR sensor and the vial was
pressurized due to the normal vapor pressure of the solution at defined reaction temperature. At the
end of the reaction, each sample was diluted with acetonitrile to obtain 100 mL of a diluted
monophasic solution which was filtered prior HPLC analysis through a syringe filter (PTFE, 0.45 m,
VWR).
2.3. Product analysis

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Each reaction sample was analyzed using a Shimadzu prominence HPLC. Unreacted D-xylose was
detected with a low temperature evaporative light scattering detector (ELSD-LTII) and products were
detected with a UV-vis detector (SPD-M20A) at a wavelength of 275 nm. The column used was a
Grace C18 column (250 x 4.6 mm; 5 m). The mobile phase was MeOH-water (9:1, v/v) solution
flowing at rate of 0.5 mL min-1. The column oven was set at 40 °C. Regularly, the calibration curve was
checked out in order to avoid eventual experimental errors associated with all measurements
reported below.
D-Xylose conversion (X), furfural yield (Yi) and furfural selectivity (Yi) wer e calculated using the
following equations :
(
)
(
)
(퐼푛푖푡푖푎푙 푥푦푙표푠푒 푎푚표푢푛푡 푚표푙 − 퐹푖푛푎푙 푥푦푙표푠푒 푎푚표푢푛푡 푚표푙 )
푋 =
푥 100
퐼푛푖푡푖푎푙 푥푦푙표푠푒 푎푚표푢푛푡 (푚표푙)
퐹푖푛푎푙 푓푢푟푓푢푟푎푙 푎푚표푢푛푡 (푚표푙)
푌푖 =
푥 100
퐼푛푖푡푖푎푙 푥푦푙표푠푒 푎푚표푢푛푡 (푚표푙)
퐹푢푟푓푢푟푎푙 푦푖푒푙푑
푆푖 =
푥 100
퐶표푛푣푒푟푠푖표푛 표푓푥푦푙표푠푒
3. Results and discussion
3.1. Nature of the catalyst
Furfural has got a hydrophobic nature and could potentially expressed affinity to the surface of
the catalyst when this one is hydrophobic such as Nafion NR50. This phenomenon could explain the
degradation occurring during the process and the progressive deposit of humin on the surface
reducing the accessibility of the sulfonyl groups for the D-xylose. S-DP has been chosen for this study
for its hydrophilic nature compared with Nafion. S-DP displays carbonyl, hydroxyl and remaining
epoxide groups proven by FT-IR spectra [14] which could prevent furfural adsorption.
3.2. Substrate to catalyst ratio for the production of furfural
The starting point of all experiments was taken from optimized conditions reported in our
previous published papers [8-13]. In an aqueous biphasic system involving CPME as the extraction
solvent, the best production of furfural was obtained in a H2O-CPME (1:3, v/v) volume ratio, especially
when the catalyst is a heterogeneous one [10,12]. By varying the catalyst loading from 10 to 40 wt%
(Fig. 2) at 190 °C for 1 hour under microwave irradiation, the maximum of D-xylose conversion was
observed in the presence of 30 wt% of catalyst. Interestingly, by using less amount of catalyst (20
wt%), a moderate furfural selectivity of 45% was obtained. However, if the catalyst content was
multiplied by two, no real enhancement of the yield was observed and a decision was taken to save
the catalyst (20 wt%) to produce furfural.

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Fig. 2. Effect of catalyst loading on dehydration of D-xylose to furfural. Reaction conditions: D-xylose
(150 mg), water (1 mL), CPME (3 mL), 190 °C, 60 min, MW.
3.3. Effect of reaction temperature and the amount of catalyst for the production of furfural
Impact of the temperature was measured in a range from 130 to 200 °C (Fig. 3). In our hands,
higher temperature than 200 °C cannot be evaluated due to the detected overpressure generated in
the microwave oven. For temperatures inferior to 170 °C, low conversion of D-xylose was observed.
On the other hand, for all temperatures superior to 180 °C, the furfural yield started to increase until
it reached a maximum value of 58% at 200 °C. The maximum of selectivity was observed at 180 °C but
only half of xylose initial amount was consumed after one hour. At 200 °C, further reduction of the
catalyst (10 wt% vs 20 wt%) gave surprisingly similar selectivity in furfural (58% vs 60%). In our
conditions (200 °C, 60 min under microwave activation) dehydration of D-xylose did not require so
much S-DP catalyst (10 wt%).
Fig. 3. Effect of reaction temperature on dehydration of D-xylose to furfural. Reaction conditions:
D-xylose(150 mg), S-DP 20 wt%, water (1 mL), CPME (3 mL), 60 min, MW.

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3.4. Effect of reaction time for the production of furfural
In the following step, it was important to determine the shorter residence time to get higher
yield of furfural with the maximum of conversion. The previous conditions (D-xylose (150 mg), S-DP 10
wt%, water (1 mL), CPME (3 mL), 200 °C, MW) were applied with variation of the time of the reaction.
Furfural yields increased with the reaction time till 50 min to obtain 54% yield and a selectivity of 60%
(Fig. 4).
Fig. 4. Effect of reaction time on dehydration of D-xylose to furfural. Reaction conditions: D-xylose
(150 mg), S-DP 10 wt%, water (1 mL), CPME (3 mL), 200 °C, MW.
3.5. Salt-out effect of NaCl for the production of furfural
Early in the process, an excess of NaCl (1.5 mmol) was already added in an experiment involving
20 wt% of S-DP in presence of D-xylose (150 mg, 1 mmol). The resulted mixture was heated at 190 °C
for 60 min and the furfural yield reached a value of 63% which is higher than that obtain without the
presence of NaCl. In order to understand the mechanism of the reaction, a simple experience was
carried out. After addition of the salt, the acid catalyst was filtered and pH of the recovered filtrate
was unchanged. It was noteworthy that with Nafion NR50 in presence of an excess of NaCl, the resin
pellets were able to release a great part of their protons in the reaction medium [10]. This result
proved a clear difference between Nafion and sulfonated diamond powder.
Using the optimized conditions (D-xylose (150 mg), S-DP 10 wt%, water (1 mL), CPME (3 mL),
200 °C, 50 min, MW) with an added amount of NaCl (1.5 mmol), 85% conversion with 75% selectivity
to furfural was observed. Then, the impact of NaCl concentration was also monitored (Fig. 5). Under
1.5 mM of NaCl, the furfural yield remained almost constant (60%). However, with higher NaCl
concentration (2.0 mM), quantitative conversion and 76% yield were obtained with the current
improved optimized conditions.

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Fig. 5. Effect of salt-out study on dehydration of D-xylose to furfural. Reaction conditions: D-xylose
(150 mg), S-DP 10 wt%, water (1 mL), CPME (3 mL), 200 °C, 50 min, MW.
3.6. Effect of xylose loading
Using the best furfural dehydration conditions without addition of NaCl, the catalytic activity of
S-DP has been evaluated in samples of increasing concentration and viscosity (Table 1). In a viscous
slurry (3 M), the furfural yields have fallen dramatically (40%) and a large amount of black insoluble
humin was formed. This phenomenon could be connected to the growing difficulty for extracting the
formed furfural by CPME when it was trapped in the sugar based slurry. Thus, furfural is obviously
more easily subjected to the typical cross-polymerization with the neighbouring D-xylose molecules
strongly adsorbed on the surface of S-DP. It should be interesting to notice that furfural yield was
higher with diluted solution of D-xylose (66% vs 54%) even in absence of NaCl but the volumetric
productivity was lower (0.037 mmol s-1 L-1 vs 0.045 mmol s-1 L-1). Even if the furfural yield decrease
(from 54% to 34%) with the increase of the D-xylose concentration the volumetric productivity
increase(from 0.045 mmol s-1 L-1 to 0.113 mmol s-1 L-1).
Table 1 Effect of D-xyloseloading on dehydration of D-xyloseto furfural.
Entry
Xylose(M)
0.7
Yield (%)
66
Conversion (%)
Selectivity (%) Productivity (mmol s-1 L-1)
1
2
3
4
5
100
86
66
63
62
56
60
0.037
0.045
0.083
0.100
0.113
1.0
54
2.0
50
80
3.0
40
72
4.0
34
56
a Reaction conditions: D-xylose, S-DP 10 wt%, water (1 mL), CPME (3 mL), 200 °C, 50 min, MW.
3.7. Used catalyst treatment and recycling for reusability
After carried out the reaction, the sulfonated diamond powder as black insoluble material was
recovered from the liquid by filtration. Then, the solid was immersed in aqueous hydrogen peroxide
solution, recovered by filtration, washed with water and dried. The resulted brown powder was

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washed further time with acetone to be finally exposed to a 10% HCl aqueous solution before being
dried again. After this conventional treatment the resulted colored solid was re-injected in a fresh
reaction medium and the reaction was performed in the optimized condition in presence of NaCl .
Unfortunately after the first recycling a drop of the furfural yield (51%). Modification of both the
sulfonated diamond powder or its treatment is in preparation.
3.8. Effect of the nature f the sulfonated catalysts for the furfural synthesis
Few sulfonated catalysts such as silica materials, carbonaceaous derivatives were reported in
literature for the production of furfural. Unfortunately, in water silica materials as MCM-41-SO3H and
SBA-15-SO3H lose their activity due to poisoning of acidic site during the process and their instability.
In contrast, sulfonated carbonaceous materials have shown effective solid acid catalytic activities and
stabilities for high temperature production of furfural in water. Most important, the sulfonated
carbonaceous catalysts have the sulfonic acid function directly bonded onto the aromatic cores of the
support. It is important to note that SDP is the first sulfonated carbonaceous catalyst having a propyl
linker between the support and the SO3H group used for the production of furfural. This linker with a
propyl chain should added flexibility of the catalyst.
All things being equal, only reports concerning D-xylose as starting material and sulfonated
graphene, graphene oxide, graphitic carbon nitride, biochar and biobased material as sulfonated
carbonaceous materials have to be taken into account (Table 2). Except our excellent result obtained
with sulfonated graphitic carbon nitride in term of yield, D-xylose loading and temperature, our new
promising results clearly showed that SDP is a potent catalyst for the dehydration of biomass. Similar
selectivities at same temperature (190-200°C) were obtained. Moreover, in our hands D-xylose
loading was more than 3 times higher than this using graphene derivatives.
Table 2 Recent exemples of dehydration of D-xylose to furfural in water using sulfonated
carbonaceous materials.
Entry Xylose
(M)
Catalyst
Temperature
(°C)
Time Yield Conversion Selectivity
Ref
(min)
35
(%)
55
(%)
86
(%)
64
1
2
3
0.20
0.20
1.00
Sulfonated
graphene (2
wt%)
200
[17]
Sulfonated
graphene
oxide (2 wt%)
Sulfonated
biochar (10
wt%)
200
190
35
60
62
60
83
75
60
[17]
[12]
100

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4
3.0
Sulfonated
graphitic
carbon
100
30
96
100
96
18
nitride (8
wt%)
5
6
1.00
0.70
Sulfonated
Sporopolenin
(10 wt%)
Sulfonated
Diamond
Powder (10
wt%)
190
200
40
50
69
66
100
100
69
66
[11]
this
paper
4. Conclusion
S-DP demonstrated strong acid capacity and stability to produce furanic dehydration products in
good yields. The method used a mixture of S-DP and NaCl in a water-CPME biphasic system at 200 °C
under microwave activation for 50 min. The association between S-DP and NaCl generated a
synergetic effect in term of yield (76%). In relation to its hardness and its intrinsic hydrophilicity, it
appeared us interesting to develop in the near future, a microwave or conventionally heated
continuous flow system incorporating S-DP in a hard cartridge to produce rapidly solketal from
glycerol or other furanic compounds of interest such as 5-hydroxymethyl furfural (HMF) or isosorbide.
Acknowledgements
The authors greatfully acknowledge the financial support from the European COST Action
FP1306 (´Valorisation of Lignocellulosic Biomass Side Streams for Sustainable Production of Chemicals,
Materials & Fuels Using Low Environmental Impact Technologies´) and the financial support from the
corresponding partner host institutions: Tokyo University of Science (Japan), Universidad de Jaen
(Spain), Universitéde Technologie de Compiègne (France) and Chimie ParisTech (France).

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Graphical abstract

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Highlights



Microwave activation for the dehydration of xylose to furfural.
Water-CPME as biphasic systems to limit the production of humin.
Sulfonated Diamond Powder (S-DP) as efficient acid catalyst system for the synthesis of
furfural.


Use of waste from diamond industry
The reusability of the catalyst was efficient.