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Green Chemistry
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ICP measurements approved the relative Ni content as 8.3 wt
%, what is in agreement with the measurement failure. Also
after reaction, this wt % did not decrease. (SI-T2) 1.5 g of this
catalyst was placed into a 70 mm cartridge with a diameter of
3.0 mm and therefore a volume of 0.424 mL. The crystalline
size of the tungsten carbide was calculated to 21.3 nm, the
one of nickel to 27 nm according to XRD and the Scherrer
equation. The particle size of the nickel was proven to about
35 nm using the SEM (figure 4). The nitrogen sorption of the
Ni@WC material was measured and gave a specific surface
area of 9 m2 g-1.
xylose, is again easily separable at the end. Development of
alternative catalyst supports avoiding the tendency of humin
DOI: 10.1039/C7GC01055A
deposition or the use of tungsten is another task for catalyst
optimization. Furthermore DMF cannot only be used as fuel,
but also upgraded further, e.g. in a Diels Alder reaction to
produce non oxygen containing hydrocarbons as p-xylene. Also
this step could be easily integrated into a cascade flow process
in the future.
Acknowledgements
We acknowledge the Max Planck Society for financial support,
as well as UNICAT, the German Excellence Cluster for Catalysis.
The technical staff at the MPI is thanked for standard analysis.
Substrate preparation
In compliance with the rules of green chemistry, ethanol was
chosen as a solvent (200 ml) for fructose (1.8 g, 0.05 M).
Alcohol as a solvent brings the advantage of a more simplified
analysis in the GC-MS system as well as a more simple
separation of the products by evaporation. To facilitate the
solubility of sugars in alcohol at room temperature, formic acid
(0.5 M) was added in ten times molar excess due to limited
hydrogen bond formation. The solution was stirred until all the
sugar crystals were dissolved. Formic acid also occurs as a side-
product during the formation of levulinic acid and is therefore
anyway present in the reaction and the circulating solvent.
Since the sulfonic acid groups of Amberlyst 15 have very strong
acidic properties, formic acid is believed to just play a minor
role as homogeneous catalyst[24], but certainly helps for a
potential glucose-fructose equilibration.
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Conclusions
In conclusion it was shown that under given mild conditions, a
combination of commercial Amberlyst 15 (110 °C, 30 bar, 0.25
mL min-1) and synthesized Ni@WC (150 °C, 30 bar, 0.25 mL
min-1, hydrogen) in a simple cascade flow reactor provided a
good conversion of fructose with about 85 % yields to DMF (38
%) and ethyllevulinate (47 %) with a total reaction time of 20
min. This simple set-up enables the continuous synthesis of
DMF as well as ethyllevulinate, two platform chemicals which
are easy to separate by distillation. The stability of the
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within 7 h. The currently used polymeric solid acid catalyst for
dehydration is however considered to be the weak point to
work on, as it showed indications for the formation of humins,
pointing to a potential clogging at extended timescales. In
general we presented a highly worthwhile process, using non-
noble metal catalysis in a wet flow chemistry set-up in the
minute scale. All chemicals used are non-toxic and the whole
process can be considered as green.
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Further work is currently expanded in three directions. On the
one hand using saccharide/glucose is meaningful, and the
isomerization of glucose to fructose could be integrated into
the flow set-up. Expansion to lignocellulosic biomass or similar
waste streams can be considered, but wood sugar is
preferentially made in an upstream step. It however can be
used without purification, as 2-methylfuran, the product of
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