Green Chemistry
Communication
MW-assisted non-catalytic and catalytic tests were per-
formed using a commercially available mono-mode microwave
Acknowledgements
unit (CEM Discover S-class system) comprised of a calibrated H. Gómez-Bernal wishes to acknowledge Consejo Nacional de
external infrared sensor. Temperature control is achieved by a Ciencia y Tecnología (CONACyT) of Mexico for a Postdoctoral
P.I.D. controller by adjusting the MW power (see ESI† for a Grant. The authors also thank CBMM (Companhia Brasileira
typical temperature profile). During every run, the MW reactor de Metalurgia e Mineração) for kindly providing niobium
was set to dynamic mode with an initial MW power of 150 W. phosphate and Dr Robson Monteiro for helpful discussion.
Initial reaction time (t = 0) was taken when the temperature Nicoletta Nassi o di Nasso is also gratefully acknowledged for
set point was reached. Autohydrolysis tests were carried out in providing corn stover.
a 35 mL reactor and catalytic tests in a 10 mL one, both com-
prising a magnetic stirrer. Catalytic recycle tests were per-
formed with prior acetone washings of spent catalysts (see
ESI†). A comparison autohydrolysis test was also performed in
Notes and references
a Parr reactor as explained in ESI.† Reproducibility of repeated
autohydrolysis and catalytic runs resulted within 5%.
1 S. P. S. Chundawat, B. Venkatesh and B. E. Dale, Biotechnol.
Bioeng., 2006, 96, 219.
Products present in the aqueous solutions were quantitat-
ively analyzed by HPLC (Perkin Elmer Flexar) equipped with RI
detector using a PolyporeCA column eluted with 5 mM H2SO4.
The solid fraction obtained from the first autohydrolysis
stage was characterized with Spectrum One FTIR system
(Perkin Elmer, Wellesley, MA) comprised of a universal ATR
(Attenuated Total Reflection) accessory provided with a ZnSe
surface. These spectra were normalized at a peak position near
1510 cm−1 as referenced by Chundawat et al.1
2 S. Dutta, S. De, B. Saha and M. I. Alam, Catal. Sci. Technol.,
2012, 2, 2025.
3 S. Lima, M. M. Antunes, A. Fernandes, M. Pillinger,
M. F. Ribeiro and A. A. Valente, Molecules, 2010, 15, 3863.
4 R. Xing, W. Qi and G. W. Huber, Energy Environ. Sci., 2011,
4, 2193.
5 J. P. Lange, E. van der Heide, J. V. Buijtenen and R. Price,
ChemSusChem, 2012, 5, 150.
6 L. Zhang, H. Yu, P. Wang, H. Dong and X. Peng, Bioresour.
Technol., 2013, 130, 110.
7 Y. C. Lin and G. W. Huber, Energy Environ. Sci., 2009, 2, 68.
8 G. Garrote, H. Dominguez and J. C. Parajó, Holz Roh-
Werkst., 1999, 57, 191.
Conclusions
This work provides a solid basis for a simple and green valori-
zation of the hemicellulosic fraction of corn stover, leaving
9 C. Moreau, R. Durand, D. Peyron, J. Duhamet and
P. Rivalier, Ind. Crops Prod., 1998, 7, 95.
cellulose and lignin readily utilizable for further processing, 10 S. Lima, M. Pillinger and A. A. Valente, Catal. Commun.,
either by thermochemical or other routes. 2008, 9, 2144.
This MW-assisted, two-stage cascade process, using only 11 R. Weingarten, G. A. Tompsett, W. C. Conner Jr. and
corn stover and water in the presence of niobium phosphate
(NbP) as catalyst, leads to good furfural yields.
G. W. Huber, J. Catal., 2011, 279, 174.
12 V. Choudhary, A. B. Pinar, S. I. Sandler, D. G. Vlachos and
R. F. Lobo, ACS Catal., 2011, 1, 1724.
During the first stage of the process, corn stover was hydro-
thermally fractionated to obtain soluble hemicellulosic sugars 13 A. Takagaki, M. Ohara, S. Nishimura and K. Ebitani, Chem.
and a solid residue containing cellulose and lignin. A mild Lett., 2010, 39, 838.
autohydrolysis treatment was selected so as to produce the 14 E. I. Gürbüz, J. M. R. Gallo, D. Martin Alonso,
least sugar degradation products in this stage. A positive effect
of MW dielectric heating on biomass solubilization was
observed during this stage.
S. G. Wettstein, W. Y. Lim and J. A. Dumesic, Angew. Chem.,
Int. Ed., 2013, 52, 1270.
15 R. Bura, R. Chandra and J. Saddler, Biotechnol. Prog., 2009,
25, 315.
In the second step of the process, the obtained hemicellu-
losic sugars (mostly oligomers) were hydrolyzed and dehydrated 16 A. M. Raspolli Galletti, C. Antonetti, V. De Luise, D. Licursi
over NbP to obtain up to 23% furfural yield. This is a very and N. Nassi o Di Nasso, Bioresources, 2012, 7, 1824.
promising result, taking into account the use of whole raw 17 D. Dallinger and C. O. Kappe, Chem. Rev., 2007, 107, 2563.
biomass in pure water and a heterogeneous catalyst.
18 B. Pholjaroen, N. Lia, Z. Wang, A. Wang and T. Zhang,
The activity of NbP in water was also evaluated for xylose
J. Energy Chem., 2013, 22, 826.
dehydration, yielding up to 43% furfural at 160 °C over 19 T. Armaroli, G. Busca, C. Carlini, M. Giuttari,
30 minutes of reaction time. The spent catalyst was re-used in
two more recycling tests, while still obtaining high furfural
yields.
Further studies are in progress for the optimization and
subsequent exploitation of the residual cellulose and lignin
fractions here obtained, which evaluate more severe conditions
for cellulose valorization.
A. M. Raspolli Galletti and G. Sbrana, J. Mol. Catal. A:
Chem., 2000, 151, 233.
20 I. A. L. Bassan, D. R. Nascimento, R. A. S. San Gil,
M. I. Pais da Silva, C. R. Moreira, W. A. Gonzalez, A. C. Faro
Jr., T. Onfroy and E. R. Lachter, Fuel Process. Technol., 2013,
106, 619.
21 S. Okazaki and N. Wada, Catal. Today, 1993, 16, 349.
This journal is © The Royal Society of Chemistry 2014
Green Chem., 2014, 16, 3734–3740 | 3739