1
1
While hemicellulose derived from softwood has a degree of
hydrolysis gave ca. 12% glucose yield after 24 h. Therefore,
to confirm that under the reaction conditions employed in
this study cellulose and lignin undergo hydrolysis/degradation,
experiments were carried out with cellulose (Aldrich) and lignin
polymerization (DP) of ca. 100, hemicellulose derived from
25
hardwood typically has a DP of ca. 200. However, we
observed almost same results (ca. 40% yield) under our reaction
conditions (see Fig. S3†).
◦
(Aldrich) as substrates at 170 C for 2.5 h. However, HPLC
It is known that plants require several nutrients (K, Ca, Mg
etc.) for their growth and survival, so it was decided to carry
out ICP analysis of the recovered reaction mixture and spent
catalysts. ICP analysis of the spent catalyst showed the presence
of 7.3 ppm Na and 6.4 ppm K, while the fresh catalyst had
and GC peaks from cellulose- and lignin-derived products
(glucose, 5-(hydroxymethyl)furfural, aromatic compounds etc.)
were not observed. This clearly indicates that under the reaction
conditions employed in this study, the hemicellulose in the
bagasse is being converted selectively.
1
ppm Na and no K. ICP analysis of the reaction mixture
In summary, we have reported a one-pot conversion of
hemicellulose into chemicals by solid acid catalysis. These
catalysts are easily separable and reusable, and thus avoid
waste generation. This study provides a way to convert both
hemicellulose and cellulose together using newer catalysts by
tuning the reaction conditions. For example, if a catalyst such
as Pt/zeolite were synthesized, then the solid acid part of this
catalyst could convert just the hemicellulose into sugars and
showed the presence of 110 ppm Na and 39 ppm K. These
results indicate that the hemicellulose might be the source of
Na and K, the first possibility being that the Na and K are
from the plants themselves. The second possibility is that during
the separation of hemicellulose from cellulose and lignin by the
Kraft process, alkaline solutions are used, resulting in Na and K
getting trapped in the hemicellulose. It is interesting to note that
even though Na and K are present in the catalyst and reaction
mixture, the catalyst was active, since there is a possibility that
2
◦
furfural under the conditions employed in this study (<170 C,
N
2
) while cellulose and lignin will remain intact. Furthermore,
+
◦
Na and K can replace H .
by increasing the reaction temperature to 190 C and replacing
To probe this aspect further, we carried out a TPD-NH
3
study.
N
2
with H
2
, one could selectively convert cellulose to sugar
6
This revealed that the fresh catalyst had total acid content of
alcohols, as reported in earlier work. In this way, in a multi-
step one-pot reaction, it might be possible to selectively convert
hemicellulose and cellulose into soluble products by tuning the
reaction conditions. Work is therefore in progress on catalyst
characterization, improvement of the yields, and the preparation
of new solid acid catalysts.
-
1
-1
0
.55 mmol g , which decreased after reaction to 0.19 mmol g ,
+
indicating that Na and K have replaced H . Based on the
ICP analysis results for spent catalyst, the presence of Na and
K should decrease the acid amount in the spent catalyst by
-
1
-1
0
.33 mmol g . This implies that 0.22 mmol g of acid should
remain in the spent catalyst. This value is in good correlation
-
1
with the amount of acid (0.19 mmol g ) obtained from the
TPD-NH study. XRD characterizations performed on the spent
and fresh catalysts proves that the catalyst morphology remains
intact after the reaction (see Fig. S2†).
Although zeolites are the most active catalysts, diffusion
limitation might be affecting utilization of all the active sites
present in the zeolites. The pore diameter of HUSY (Si/Al =
Acknowledgements
3
The authors thank Dr D. Srinivas and Dr Tambe for discussion
and LC–MS analysis.
Notes and references
1
5) is 0.74 nm, but as the hemicellulose molecule has a length
of several hundred nm, entry into the zeolite channels might
not be possible. It is postulated that hemicellulose hydrolyzes
on the external acid sites, and that once dimers and trimers
are formed these can enter the zeolite pores and interact with
internal acid sites (present inside the pores of zeolites) to
yield monomer sugars, xylose and arabinose. These monomeric
sugars might then undergo dehydrocyclization to give furfural
on these internal sites. The other solid acid catalysts might show
lower activity due to their instability in water, and also because
of their irregular structure (except Al-incorporated mesoporous
silicas). Further studies on the catalyst characterization and
mechanistic aspect of this reaction are ongoing, to establish
if there is a relation between catalytic activity and catalyst
morphology.
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G. Centi and R. A. van Santen, Catalysis for renewables: from
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◦
cellulose, hemicellulose and lignin) at 170 C using HUSY
(
Si/Al = 15) indicates that 45% xylose + arabinose yield and 9%
furfural yield can be obtained after 2.5 h. The total product yield
of 54% is calculated based on 0.18 g hemicellulose being present
in bagasse (for details of the calculations, see ESI†). It was
earlier reported that with zeolite as the catalyst, cellulose (Fluka)
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M. Hara, J. Phys. Chem. C, 2009, 113, 3181.
1
5 Y. Kim, R. Hendrickson, N. Mosier and M. R. Landisch, Energy
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