Solvent-free synthesis of C10 and C11 branched alkanes from furfural and methyl isobutyl ketone

Article abstract of DOI:10.1002/cssc.201300318

Our best results jet: C₁₀ and C₁₁ branched alkanes, with low freezing points, are synthesized through the aldol condensation of furfural and methyl isobutyl ketone from lignocellulose, which is then followed by hydrodeoxygenation. These jet-fuel-range alkanes are obtained in high overall yields (≈90 %) under solvent-free conditions. Copyright

Full text of DOI:10.1002/cssc.201300318

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DOI: 10.1002/cssc.201300318
Solvent-Free Synthesis of C10 and C11 Branched Alkanes
from Furfural and Methyl Isobutyl Ketone
Jinfan Yang,[a, b] Ning Li,[a] Guangyi Li,[a, b] Wentao Wang,[a] Aiqin Wang,[a] Xiaodong Wang,[a]
Yu Cong,[a] and Tao Zhang*[a]
With the decline of fossil energy sources and the increasing
social concern about the associated environmental problems,
the conversion of biomass to fuel and chemicals has drawn
a lot of attention.[1] Jet fuel is one of the most demanding
liquid fuels. Lignocellulose is the main component of agricul-
tural wastes and forest residues. Pioneered by the works of the
Dumesic group,[2] the synthesis of jet-fuel-range alkanes with
the platform chemicals from lignocellulose has attracted inten-
sive interests in recent years.[3]
the aldol condensation and low-temperature hydrogenation.
Even in the HDO process, water or organic solvent is still
needed; however, this will lead to higher costs and lower
energy efficiencies. 2) Straight alkanes are obtained during the
HDO process; these alkanes have lower octane numbers and
higher freezing points (e.g., the freezing point of n-tridecane is
about 268 K), and cannot be directly used as jet fuel without
hydroisomerization.
Methyl isobutyl ketone (MIBK) is the product of the self-aldol
condensation and selective hydrogenation of acetone.[11] It has
been used as an extracting solvent to increase the selectivity
towards furfural in the dehydration of xylose or its oligo-
mers.[12] From a process integration point of view, it is prefera-
ble if MIBK can be directly used as the carbonyl compound in
the aldol condensation with furfural. Furthermore, the
branched structure of MIBK also renders it a potential feed-
stock for the direct synthesis of branched alkanes. However, to
the best of our knowledge, there is no report on the synthesis
Furfural is an important chemical that has been produced
on an industrial scale through the hydrolysis–dehydration of
hemicellulose obtained from agricultural wastes and forest res-
idues.[4] In the recent work of the Dumesic group[5] and Huber
et al.,[6] C8 and C13 oxygenates were produced through the
aldol condensation of furfural and acetone, which can be pro-
duced by the acetone–n-butanol–ethanol (ABE) fermentation
of lignocellulose.[7] The as-prepared C8 and/or C13 oxygenates
were hydrogenated at low temperatures before undergoing
hydrodeoxygenation (HDO) to
C8–C13 straight alkanes over a Pt-
loaded solid acid catalyst
(Scheme 1a). The aldol conden-
sation can be catalyzed by min-
eral base,[2a,5] organic base,[8] or
solid
base
catalysts.[2a,6b,9]
Recently, it was demonstrated
that the aldol condensation and
low-temperature hydrogenation
(Step 1 and Step 2 in Scheme 1a)
could be performed in one reac-
tor over Pd-loaded solid base
catalysts.[10] However, there are
still two limitations for the ace-
tone–furfural route: 1) the aldol
condensation products are solid;
to obtain better mass transfer,
organic solvents are necessary in
Scheme 1. a) Previous route versus b) the new protocol for the synthesis of jet-fuel-range branched alkanes.
[a] J. Yang, Dr. N. Li, G. Li, Dr. W. Wang, A. Wang, Dr. X. Wang, Dr. Y. Cong,
Prof. T. Zhang
of jet-fuel-range alkanes that uses MIBK as a platform chemical.
Herein, we report the first highly efficient synthesis of C10 and
C11 branched alkanes from the aldol condensation of MIBK and
furfural, followed by the one-step HDO process under solvent-
free conditions (Scheme 1b). These branched alkanes have low
freezing points and can be blended into jet fuel without
hydroisomerization.
State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics
Chinese Academy of Sciences, Dalian 116023 (PR China)
Fax: (+86)41184691570
E-mail: taozhang@dicp.ac.cn
[b] J. Yang, G. Li
Graduate University of Chinese Academy of Sciences
Beijing 10049 (PR China)
The solvent-free aldol condensation of MIBK and furfural
was performed over a series of solid base catalysts. From the
Supporting Information for this article is available on the WWW under
http://dx.doi.org/10.1002/cssc.201300318.
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analysis of HPLC and NMR spectroscopy (see Figures S1 and S2
in the Supporting Information), 1-(furan-2-yl)-5-methylhex-1-
en-3-one (i.e., 1a in Scheme 1) was identified as the main
product. No C16 oxygenate (generated through the aldol con-
densation of one MIBK molecule with two furfural molecules)
was detected in the liquid product. This result was different to
what has been observed in the aldol condensation of furfural
and acetone, and could be explained by the different reactivity
of two a-carbon atoms in a MIBK molecule.
Conversion of the furfural and the yield of 1a over different
solid base catalysts are shown in Figure 1. The hydrotalcite,
Figure 2. CO2-TPD of the different solid base catalysts (the experimental
detail for the CO2-TPD tests is provided in the Supporting Information).
were observed, indicating that these materials contain stronger
basicity. Combining the results from the activity tests and CO2-
TPD, we believe that the aldol condensation of furfural and
MIBK occurred on the strong base sites, which could have
been the reason for the improved catalytic performance of
hydrotalcite and CaO.
According to our tests, as-prepared 1a existed as a red-
brown liquid, even at 253 K; this rendered it suitable for the
direct HDO process. The liquid state of 1a could be explained
by the branched structure of MIBK, which could lead to
a lower freezing point of the aldol condensation product by in-
corporating the branched structure. This is very advantageous
in practical applications because: 1) the cost of organic sol-
vents and the energy consumption from the evaporation of
solvents can both be reduced, 2) the low-temperature hydro-
genation and HDO can be integrated into one-step process,
which will also improve the energy efficiency.
Figure 1. Conversion of furfural (white bar) and the carbon yield of 1a
(black bar) over different solid base catalysts. The reaction was performed
with 2.0 g furfural, 4.17 g MIBK (furfural/MIBK molar ratio=1:2), and 0.4 g
catalyst at 403 K for 8 h in a batch reactor.
with a Mg/Al atom ratio of 5:1, and CaO exhibited the best
catalytic performances. For example, by using CaO as the cata-
lyst, a 1a yield of up to 95% could be achieved at 403 K after
8 h reaction time. The sequence of the activities of the differ-
ent catalysts followed the order hydrotalciteꢀCaO>
KF/Al2O3 >MgO–ZrO2 >MgO. Under the same reaction condi-
tions, a high furfural conversion (89%) and a high 1a yield
(86%) could also be obtained over the CaO catalyst when the
molar ratio of MIBK/furfural was equal to one. This result fur-
ther proved that the reaction could be performed under sol-
vent-free conditions. To investigate the intrinsic reason for the
different catalytic performances, we characterized the catalysts
by using CO2-temperature-programmed desorption (CO2-TPD).
According to Figure 2, the CO2-TPD curves of both MgO and
MgO-ZrO2 exhibited broad peaks
The direct HDO of 1a was performed under solvent-free
conditions. According to the analysis of the gas-phase and
liquid-phase products by using GC-MS, 1a was fully converted
into hydrocarbons and CO2 over carbon-loaded Pt, Pd, and Ir
catalysts at 643 K and 6 MPa H2. According to Figure 3, the
carbon yields for jet-fuel-range alkanes over the Pt, Pd, and Ir
catalysts were around 90%. The jet-fuel-range alkanes ob-
tained in this work were composed of 2-methyl-decane and
2-methyl-nonane. Both of which are branched alkanes and
have low freezing points (223.5 and 198.3 K, respectively).
Therefore, they could be directly blended with conventional
jet fuels without hydroisomerization. The obtained molar ratio
of 2-methyl-decane/2-methyl-nonane decreased for the cata-
from 363 to 723 K, which could
be assigned as the weak base
sites. For KF/Al2O3, a peak at
786 K was be observed; this
peak could be attributed to the
CO2 desorbed from the medium
base sites. Over the hydrotalcite
and CaO, CO2 desorption peaks
at higher temperatures (>865 K) Scheme 2. Reaction pathway for decarbonylation during the HDO of 1a.
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the routes proposed in previous reports, this new protocol has
many advantages because it is solvent free, involves fewer
steps, and directly produces branched alkanes without hydro-
isomerization. This work opens a new general strategy for the
direct synthesis of jet-fuel-range branched alkanes with MIBK
as a platform chemical. Further work regarding the utilization
of MIBK in the synthesis of renewable jet-fuel-range branched
alkanes with lower freezing points and higher molecular
weights are ongoing in our laboratory.
Acknowledgements
This work was supported by the Natural Science Foundation of
China (No. 21106143), 100 talent project of Dalian Institute of
Chemical Physics (DICP).
Keywords: aldol reaction · alkanes · hydrodeoxygenation · jet
fuel · lignocellulose
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Received: April 9, 2013
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J. Yang, N. Li, G. Li, W. Wang, A. Wang,
X. Wang, Y. Cong, T. Zhang*
&& – &&
Solvent-Free Synthesis of C10 and C11
Branched Alkanes from Furfural and
Methyl Isobutyl Ketone
Our best results jet: C10 and C11
branched alkanes, with low freezing
points, are synthesized through the
aldol condensation of furfural and
methyl isobutyl ketone from lingo-
cellulose, which is then followed by hy-
drodeoxygenation. These jet-fuel-range
alkanes are obtained in high overall
yields (ꢀ90%) under solvent-free
conditions.
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemSusChem 0000, 00, 1 – 4
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5
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These are not the final page numbers!