Synthesis of high-density aviation fuels with methyl benzaldehyde and cyclohexanone

Article abstract of DOI:10.1039/c8gc01628c

A new two-step process was developed for the synthesis of high-density jet fuel range tricyclic alkanes with methyl benzaldehydes and cyclohexanone which can be derived from lignocellulose. In the first step, C₁₄ oxygenates (i.e. 2-(2-methylbenzylidene)cyclohexanone or 2-(4-methylbenzylidene)cyclohexanone) were obtained by the solvent-free aldol condensation of 2-methyl benzaldehyde (or 4-methyl benzaldehyde) and cyclohexanone. Among the investigated catalysts, the EAOAc ionic liquid (a renewable catalyst which was prepared with ethanolamine and acetic acid) exhibited the highest activity and good stability for this reaction. Over it, high carbon yields (～85%) of C₁₄ oxygenates were achieved under mild reaction conditions (353 K, 6 h). In the second step, the C₁₄ oxygenates were selectively converted into 1-methyldodecahydro-1H-fluorene and 3-methyldodecahydro-1H-fluorene by the aqueous phase hydrodeoxygenation (APHDO) over a commercial Pd/C catalyst. According to our measurement, the 1-methyldodecahydro-1H-fluorene and 3-methyldodecahydro-1H-fluorene as obtained have high densities (0.99 g mL^-1 and 0.96 g mL^-1, respectively, at 298 K). As a potential application, they can be used as additives to improve the volumetric heat values of the current bio-jet fuels.

Full text of DOI:10.1039/c8gc01628c

View Article Online
View Journal
Green
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: J. Xu, N. Li, G. Li,
F. Han, A. Wang, Y. cong, X. Wang and T. Zhang, Green Chem., 2018, DOI: 10.1039/C8GC01628C.
This is an Accepted Manuscript, which has been through the
Volume 18 Number
7 7 April 2016 Pages 1821–2242
Royal Society of Chemistry peer review process and has been
accepted for publication.
Green
Chemistry
Accepted Manuscripts are published online shortly after
Cutting-edge research for a greener sustainable future
www.rsc.org/greenchem
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 1463-9262
CRITICAL REVIEW
G. Chatel et al.
Heterogeneous catalytic oxidation for lignin valorization into valuable
chemicals: what results? What limitations? What trends?
rsc.li/green-chem

Please do not adjust margins
Green Chemistry
Page 1 of 8
View Article Online
DOI: 10.1039/C8GC01628C
Journal Name
ARTICLE
Synthesis of high-density aviation fuels with methyl benzaldehyde
and cyclohexanone
Jilei Xu,a Ning Li,*a Guangyi Li,a Fengan Han,a Aiqin Wang,a Yu Cong,a Xiaodong Wang a and Tao
Zhang*a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
A new two-step process was developed for the synthesis of high-density jet fuel range tricyclic alkanes with methyl
benzaldehydes and cyclohexanone which can be derived from lignocellulose. In the first step, C14 oxygenates (i.e. 2-(2-
methylbenzylidene)cyclohexanone or 2-(4-methylbenzylidene)cyclohexanone) were obtained by the solvent-free aldol
condensation of 2-methyl benzaldehyde (or 4-methyl benzaldehyde) and cyclohexanone. Among the investigated catalysts,
EAOAc ionic liquid (a renewable catalyst which was prepared with ethanolamine and acetic acid) exhibited the highest
activity and good stability for this reaction. Over it, high carbon yields (~85%) of C14 oxygenates were acheived under mild
www.rsc.org/
reaction conditions (353 K,
6 h). In the second step, the C14 oxygenates were selectively converted to 1-
methyldodecahydro-1H-fluorene and 3-methyldodecahydro-1H-fluorene by the aqueous phase hydrodeoxygenation
(APHDO) over a commerical Pd/C catalyst. According to our measurement, the 1-methyldodecahydro-1H-fluorene and 3-
methyldodecahydro-1H-fluorene as obtained have high densities (0.99 g mL-1 and 0.96 g mL-1 at 298 K). As a potential
application, they can be used as additives to improve the volumetric heat values of current bio-jet fuels.
ring strain. In recent years, the synthesis of jet fuel range high-
density cycloalkanes with lignocellulosic platform compounds
has attracted a lot of attention.7, 8, 9
Introduction
Because of the great social concerns about the renewable
energy and sustainable development, the catalytic conversion
of renewable and CO2 neutral biomass to fuels1 and chemicals2
has become a research hotspot. Jet fuel (includes kerosene-
type jet fuel and naphtha-type jet fuel) is a refined petroleum
product used in jet aircraft engines.3 Globally, jet fuels account
for 12% of current used liquid transportation fuels.4 During the
past decade, tremendous efforts have been devoted to the
production of jet fuel range hydrocarbons with the feedstocks
which can be obtained from biomass.5 So far, three routes
(including Fischer-Tropsch process of bio-synthesis gas,
hydroprocesses of bio-derived esters and fatty acids, or
hydrogenation of farenene from the fermentation of sugars)
have been approved by ASTM D7566 for the production of
sustainable aviation fuels with biomass.6 However, the bio-jet
fuels produced by these routes are mainly composed of
straight or branched chain alkanes which have lower density
(0.76 g mL-1 vs. 0.8 g mL-1) or volumetric heat values than
conventional jet fuel (mixture of chain alkanes and cyclic
hydrocarbons). Compared with chain alkanes, cycloalkanes
have higher density or volumetric heat values due to strong
Methyl benzaldehyde is a lignocellulosic platform compound
which can be obtained by the self-terminated cascade
reactions of biomass derived ethanol and acetaldehyde over
calcium hydroxyapatite catalyst.10, 11 As we know, ethanol can
be obtained from the fermentation of cellulose, hemicellulose,
sugar cane, sugar beet, sugar palm, cassava, corn, potatoes or
other sugar plants.12 Acetaldehyde can be obtained by the
selective oxidation or dehydrogenation of ethanol. Likewise,
cyclohexanone can be produced by the selective
hydrogenation of phenol which can be obtained from the Pd/C
catalyzed hydrogenolysis of Kraft lignin in choline-derived ionic
liquids13 or the pyrolysis of lignocellulose.14 It has been found
by Han et al.15 that phenol can be selectively hydrogenated to
cyclohexanone over a dual supported Pd-Lewis acid catalyst. In
this work, it was reported for the first time that jet fuel range
tricyclic alkanes can be selectively produced in ~80% overall
carbon yield by the solvent-free aldol condensation of methyl
benzaldehyde and cyclohexanone, followed by the aqueous
phase hydrodeoxygenation over a commercial Pd/C catalyst.
The strategy for this process was illustrated in Scheme 1.
Compared with the commodity chemicals that are used today
as additives in kerosene-type jet fuels and the biomass-derived
jet fuel rang cycloalkanes which have been reported in some
recent literature,7, 8, 9, 16 the tricyclic alkanes obtained in this
work have higher density or lower freezing points (see Table
S1 in supporting information). These characters are
advantageous in real application.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 2 of 8
View Article Online
DOI: 10.1039/C8GC01628C
Journal Name
ARTICLE
Scheme 1. Strategy for the synthesis of jet fuel range high-density tricyclic alkanes with lignocellulose and other biomasses.
Aldol condensation. The solvent-free aldol condensation of
methyl benzaldehydes and cyclohexanone was carried out in a
35 mL glass batch reactor. The temperature of the reactor was
controlled by a water bath. Typically, 10 mmol 2-methyl
benzaldehyde, 10 mmol cyclohexanone and 1 mmol ionic
liquid were used for each test. After being magnetically stirred
at 353 K for 4 h, the reaction system was quickly cooled down
to room temperature with ice water. Subsequently,
isophorone was added into the system as internal standard.
The mixture was diluted with tetrahydrofuran and analyzed by
Agilent 7890A GC equiped with a flame ionization detector
(FID). The 1A and 2A as obtained were purified from the aldol
condensation products (according to the method described in
supporting information) and used in the subsequent aqueous
phase hydrodeoxygenation tests.
Experimental
Materials. All of the chemicals used in this work were
purchased from Energy Chemicals and were directly used as
their received. The acetic acid based ionic liquids were
synthesized according to the method developed by Guo and
Ying et al..17 Typically, 0.1 mol ethanolamine was put in a
round bottom flask which was immersed in an ice-water bath.
Under violently stirring, 0.1 mol acetic acid was added
dropwise into the ethanolamine by a constant pressure funnel.
By controlling the addition speed, the system temperature was
maintained in the range of 283-288 K. After the completely
introduction of acetic acid, the mixture was stirred for 24 h at
room temperature. The yellowish viscous liquid as obtained
was denoted as EAOAc. For comparison, we also prepared
other acetic acid based ionic liquids (See Scheme 2) by the
same method using corresponding amines and acetic acid.
Aqueous phase hydrodeoxygenation. The aqueous phase
hydrodeoxygenation (APHDO) of 1A and 2A were carried out
in a 100 mL stainless steel batch reactor (Parr Company).
Typically, 1 g purified 1A or 2A, 0.1 g Pd/C catalyst and 35 mL
water were sealed into the reactor. Before the tests, the
reactor was purged with hydrogen for 3 times to remove the
air in it. Subsequently, 6 MPa H2 was charged into the reactor
at room temperature. After being heated to 453 K and
electromagnetically stirred at that temperature for 4 h, the
reaction system was quenched to room temperature with ice
water. 1.0 g tridecane was added into the system as internal
standard. The mixture was extracted by CH2Cl2 (20 mL) for 3
times. The CH2Cl2 phases were combined together and
analyzed by GC-MS and an Agilent 7890A GC equiped with a
Scheme 2. Chemical structures of acetic acid (HOAc) based ionic liquids and
ethanolamine (EA) used in the aldol condensation tests.
The Pd/C catalyst used in the aqueous phase
hydrodeoxygenation process is commercial available.
According to the information from supplier, the Pd content in
the catalyst is 5% by weight (denoted as 5 wt.%).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 2
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 3 of 8
View Article Online
DOI: 10.1039/C8GC01628C
Journal Name
ARTICLE
with cellulose by a two-step process. Taking into consideration
of the high activity and renewability of EAOAc ionic liquid, we
believe that it can be considered as a promising catalyst in
future application.
FID. The densities and freezing points of cycloalkane products
were determined by a DMA 4500M digital densitometer and a
PFA-70Xi freezing point analyzer, respectively.
From Figure 1, we can see that the chemical structures of
ionic liquids have evident influence on its activity in the aldol
condensation of 2-methyl benzaldehyde and cyclohexanone.
For example, the activity of EAOAc is evidently higher that of
EOAc under the same reaction conditions. This result means
that the presence of hydroxyl group is favorable for the aldol
condensation, which can be explained by the hydrogen bond
between the catalyst and reactants. The activity of ionic liquid
catalysts which have only one hydroxyl group decrease in the
order of EAOAc > 3-PAOAc > 4-BAOAc. This result indicates
that the closer interaction of hydroxyl group and amino group
is beneficial for the aldol condensation. Finally, we also studied
the effect of hydroxyethyl group number on the activity of
catalyst. From Figure 1, we can see that DEAOAc which has
two hydroxyethyl groups has lower activity than that of EAOAc.
This can be rationalized by steric effect.
Results and discussion
Aldol condensation. In this work, a series of acetic acid based
ionic liquids were found to be effective catalysts for the
solvent-free aldol condensation of 2-methyl benzaldehyde and
cyclohexanone. From the analysis of GC and NMR spectra (see
Figures S1-S3 in supporting information), both 2-(2-
methylbenzylidene)cyclohexanone (i.e. 1A in Scheme 3) and 2-
(2-methylbenzyl)-6-(2-methylbenzylidene)cyclohexanone (i.e.
1B in Scheme 3) were identified in the product. According to
Scheme 3, 1A and 1B were generated from the aldol
condensation of one cyclohexanone molecule with one or two
2-methyl benzaldehyde molecule(s). As the potential
applications, the 1A and 1B as obtained can be used as
precursors for the production of jet fuel and lubricant range
cycloalkanes, respectively.
2-Methyl benzaldehyde conversion (%)
60
Carbon yield of 1A (%)
Carbon yield of 1B (%)
50
Scheme 3. Reaction pathways for the generation of 1A and 1B from the
aldol condensation of 2-methyl benzaldehyde and cyclohexanone.
40
30
20
10
0
Conversion of 2-methyl benzaldehyde (%)
Carbon yield of 1A (%)
Carbon yield of 1B (%)
70
60
50
40
30
20
10
0
c
c
A
A
A
E
O
O
A
H
E
Figure 2. Conversions of 2-methyl benzaldehyde and the carbon yields of 1A or
1B over EAOAc, EA and HOAc catalysts. Reaction conditions: 10 mmol 2-methyl
benzaldehyde, 10 mmol cyclohexanone, 1 mmol ionic liquid; 333 K, 4 h.
To get deeper insight into the excellent performance of the
EAOAc ionic liquid catalyst, we also studied the activity of
ethanolamine (EA) and acetic acid (HOAc) under the same
reaction conditions. From Figure 2, it is noticed that
ethanolamine can also catalyze the aldol condensation of 2-
methyl benzaldehyde and cyclohexanone. However, its activity
is evidently lower than that of EAOAc. In contrast, the acetic
acid is inactive under the investigated conditions. The 2-methyl
benzaldehyde conversion and the carbon yields of 1A or 1B
over the EAOAc ionic liquid are evidently higher than the sums
of those over ethanolamine and acetic acid. Based on this
result, we think that there is some synergetic effect between
ethanolamine and acetic acid in the aldol condensation of 2-
Figure 1. Conversions of 2-methyl benzaldehyde and the carbon yields of
1A or 1B over ionic liquid catalysts. Reaction conditions: 10 mmol 2-methyl
benzaldehyde, 10 mmol cyclohexanone, 1 mmol ionic liquid; 333 K, 4 h.
Among the investigated catalysts, EAOAc ionic liquid catalyst
which was prepared with ethanolamine and acetic acid
exhibited the highest activity for the solvent-free aldol
condensation of 2-methyl benzaldehyde and cyclohexanone
(see Figure 1). Over it, high 2-methyl benzaldehyde conversion
(62.5%) and good carbon yields (38.5% and 16.2%) of 1A and
1B were achieved under mild conditions (333 K, 4 h). As we
know, acetic acid can be obtained as by-product from the
furfural production by the acid catalyzed hydrolysis-
dehydration of hemicellulose.18 In the recent work of our
group,19 it was also found that ethanolamine can be produced
methyl benzaldehyde and cyclohexanone. According to the
literature about similar reaction system,17,
20
the reaction
mechanism for the aldol condensation of 2-methyl
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 4 of 8
View Article Online
DOI: 10.1039/C8GC01628C
ARTICLE
Journal Name
benzaldehyde and cyclohexanone was proposed in Scheme 4.
Firstly, EAOAc ionic liquid reacts with cyclohexanone and
generates a corresponding imide ion. Subsequently, the acetic
acid molecule is released from EAOAc to form an enamine
structure. The enamine structure is unstable. Therefore, it can
attack the carbonyl group of 2-methyl benzaldehyde which is
activated by hydroxyl group on enamine structure through
hydrogen-bond. By this way, a new C-C bond and a new ionic
compound are formed. This compound will decompose to
ionic liquid EAOAc and 1C. Finally, 1C is dehydrated into 1A
which is more stable due to its conjugated chemical structure.
Analogously, we can also obtain 1B by the further reaction of
1A with another 2-methyl benzaldehyde molecule.
100
80
60
40
20
0
Conversion of 2-methyl benzaldehyde (%)
Carbon yield of 1A (%)
Carbon yield of 1B (%)
1
2
3
4
5
Initial cyclohexanone/2-methyl benzaldehyde molar ratio
Figure 4. Conversions of 2-methyl benzaldehyde and the carbon yields of 1A or
1B over EAOAc ionic liquid catalyst. Reaction conditions: 10 mmol 2-methyl
benzaldehyde, 1 mmol EAOAc ionic liquid; 353 K, 4 h.
Conversion of 2-methyl benzaldehyde (%)
Carbon yield of 1A (%)
100
Carbon yield of 1B (%)
80
60
40
20
0
Scheme 4. Reaction mechanism for the generation of 1A from the aldol
condensation of 2-methyl benzaldehyde and cyclohexanone.
The effects of reaction conditions (such as reaction
temperature, initial cyclohexanone/2-methyl benzaldehyde
molar ratio in the feedstock, reaction time and catalyst dosage)
on the catalytic performance of EAOAc ionic liquid were
investigated (see Figures 3-6). Under the optimum reaction
conditions (353 K, 6 h, 2 mmol EAOAc ionic liquid catalyst, at
an initial cyclohexanone/2-methyl benzaldehyde molar ratio of
3:1), up to 85% carbon yield of 1A was achieved.
2
4
6
Reaction time (h)
Figure 5. Conversions of 2-methyl benzaldehyde and the carbon yields of 1A or
1B over EAOAc ionic liquid catalyst. Reaction conditions: 10 mmol 2-methyl
benzaldehyde, 30 mmol cyclohexanone, 1 mmol EAOAc ionic liquid; 353 K.
100
Conversion of 2-methyl benzaldehyde (%)
Conversion of 2-methyl benzaldehyde (%)
Carbon yield of 1A (%)
Carbon yield of 1A (%)
Carbon yield of 1B (%)
Carbon yield of 1B (%)
100
80
60
40
20
0
80
60
40
20
0
343
333
353
1
1.5
Dosage of catalyst (mmol)
2
3
0.5
Reaction temperature (K)
Figure 3. Conversions of 2-methyl benzaldehyde and the carbon yields of 1A or
1B over EAOAc ionic liquid catalyst. Reaction conditions: 10 mmol 2-methyl
benzaldehyde, 10 mmol cyclohexanone, 1 mmol EAOAc ionic liquid; 4 h.
Figure 6. Conversions of 2-methyl benzaldehyde and the carbon yields of 1A or
1B over EAOAc ionic liquid catalyst. Reaction conditions: 10 mmol 2-methyl
benzaldehyde, 30 mmol cyclohexanone; 353 K, 6 h.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 5 of 8
View Article Online
DOI: 10.1039/C8GC01628C
Journal Name
ARTICLE
For real application, we also checked the reusability of the
To further check its stability, we also compared the NMR
EAOAc ionic liquid. From Figure 7, we can see that there is an spectra of the fresh, used and regenerated EAOAc ionic liquids.
evident decrease in the activity of catalyst after being used in From the results illustrated in the Figures S4-S6 in supporting
the solvent-free aldol condensation of 2-methyl benzaldehyde information, no evident change in the chemical structure of
and cyclohexanone. Such a phenomenon is normal for aldol EAOAc ionic liquid was observed, indicating that this catalyst is
condensation and can be explained by the negative effect of fairly stable under the reaction (or regeneration) conditions.
water which was generated during the reaction.21 To solve this
In the recent work of Flaherty et al. about the self-
problem, we dried the used EAOAc ionic liquid under vacuum terminated cascade condensation of ethanol and acetaldehyde
condition. It was found that the activity of this catalyst can be to 2-methyl benzaldehyde, 4-methyl benzaldehyde was also
recovered to its initial level by such a treatment.
obtained as a by-product.10 To increase the carbon economy of
this route, we also explored the applicability of EAOAc ionic
liquid to the solvent-free aldol condensation of 4-methyl
benzaldehyde and cyclohexanone. According to the analysis of
NMR and GC (see Figures S7-S9 in supporting information), 2-
Conversion of 2-methyl benzaldehyde (%)
100
80
60
40
20
0
Carbon yield of 1A (%)
Carbon yield of 1B (%)
(4-methylbenzylidene)cyclohexanone
and
2,6-bis(4-
methylbenzylidene)cyclohexanone (i.e. 2A and 2B in Scheme 5)
were obtained from the aldol condensation of cyclohexanone
and 4-methyl benzaldehyde. Under the same reaction
conditions, the methyl benzaldehyde conversions and the
carbon yields of C14 oxygenates (i.e. 1A or 2A) or C22
oxygenates (i.e. 1B or 2B) are very close to each other (see
Figure 8), which means that the position of methyl group have
no evidently effect on the reactivity of methyl benzaldehyde.
As the final aim of this work, we also explored the synthesis
of jet fuel range cycloalkanes by the aqueous phase
hydrodeoxygenation (APHDO) of 1A which was purified from
the aldol condensation product according to the method
described in supporting information. It was found that 1A can
be selectively converted to 1-methyldodecahydro-1H-fluorene
(i.e. 1D in Scheme 6) over the Pd/C catalyst. High carbon yield
(92.5%) of 1D was achieved after the reaction was carried out
at 453 K for 4 h. Besides 1D, small amount of 1E (carbon yield:
0.3%) was also identified in the HDO products. According to
our measurements, the polycycloalkanes as obtained (i.e. a
mixture of 1D and 1E) have high density (0.99 g mL-1 at 298 K)
Fresh
Used
Regenerated
Figure 7. Conversions of 2-methyl benzaldehyde and the carbon yields of 1A or
1B over EAOAc ionic liquid catalyst. Reaction conditions: 10 mmol 2-methyl
benzaldehyde, 30 mmol cyclohexanone, 1 mmol EAOAc ionic liquid; 353 K, 4 h.
Scheme 5. Reaction pathways for the generation of 2A and 2B from the
aldol condensation of 4-methyl benzaldehyde and cyclohexanone.
and
a low freezing point (251 K). Compared with the
Conversion of methyl benzaldehyde (%)
120
perhydrofluorene which has been claimed to be the highest
density bio-jet fuel by Zou et al.,9 this fuel has higher density
(0.99 g mL-1 vs. 0.96 g mL-1) and evidently lower freezing point
(251 K vs. 330 K). These characters are advantageous in real
application.
Carbon yield of C14 oxygenate (%)
Carbon yield of C22 oxygenate (%)
100
80
60
40
20
0
2-Methyl benzaldehyde 4-Methyl benzaldehyde
Figure 8. Conversions of methyl benzaldehyde and the carbon yields of C14 (i.e.
1A and 2A) and C22 (i.e. 1B and 2B) oxygenates over EAOAc ionic liquid catalyst.
Reaction conditions: 10 mmol methyl benzaldehyde, 30 mmol cyclohexanone, 2
mmol EAOAc ionic liquid; 353 K, 6 h.
Scheme 6. Reaction pathways for the generation of polycycloalkanes from the
APHDO of 1A and 2A over the Pd/C catalyst.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 6 of 8
View Article Online
DOI: 10.1039/C8GC01628C
ARTICLE
Journal Name
Analogously, we studied the APHDO of 2A over the Pd/C
catalyst. Under the same reaction conditions as we used for
the APHDO of 1A high carbon yield (82.3%) of 3-
,
methyldodecahydro-1H-fluorene (i.e. 2D in Scheme 6) and
small amount of 1-(cyclohexylmethyl)-4-methylcyclohexane
(carbon yield: 1.1%) were achieved. The density and freezing
point of the polycycloalkane mixture were measured as 0.96 g
mL-1 (at 298 K) and 270
K (also lower than that of
perhydrofluorene), respectively. Compared with the 2-methyl
benzaldehyde route, the 4-methyl benzaldehyde route has
disadvantages at two aspects: 1) Lower feedstock availability.
In the previous work of Flaherty et al.,10 the carbon yields of 4-
methyl benzaldehyde are evidently lower than those of 2-
methyl benzaldehyde, which makes 4-methyl benzaldehyde
less available than 2-methyl benzaldehyde. 2) Lower density
and higher freezing point of final product. However, it is
feasible to produce 1D and 2D simultaneously and save the
energy for the separation of 2-methyl benzaldehyde and 4-
methyl benzaldehyde from the self-terminated cascade
reactions of ethanol and acetaldehyde.
Scheme 7. Reaction mechanism for the generation of different products from the
APHDO of 1A over the Pd/C catalyst.
To figure out the reaction pathway for the generation of 1D
from the APHDO of 1A, we investigated the effect of reaction
time on 1A conversion and the carbon yields of different
products. From Figure 9, we can see that the APHDO of 1A is a
fast reaction. During the heating process (0.5 h) from room
temperature to 453 K (or reaction temperature), 1A was
completely converted. 2-(2-Methylbenzyl)cyclohexanone, 2-(2-
methylbenzyl)cyclohexanol (i.e. 1F and 1G in Scheme 7) and 1D
were obtained as the products. With the extension of reaction
time, the carbon yields of 1F and 1G decreased. In contrast,
the carbon yield of 1D increased. Meanwhile, small amount of
1E appeared in the product. The reaction finished after 1 h.
With the further increment of reaction time to 4 h, no evident
change was observed. Based on the results we observed in this
work and some recent literature about similar reaction
systems,7, 9 the reaction mechanism for the APHDO of 1A to 1D
was proposed in Scheme 7.
Conclusions
The solvent-free aldol condensation of methyl benzaldehyde
and
cyclohexanone, followed by aqueous phase
hydrodeoxygenation was found to be an effective method for
the synthesis of jet fuel range high-density tricycloalkanes.
Among the investigated catalysts, EAOAc ionic liquid exhibited
the highest activity and good stability for the solvent-free aldol
condensation of methyl benzaldehyde and cyclohexanone. The
excellent performance of EAOAc ionic liquid can be explained
by its special chemical structure and/or the synergetic effect of
ethanolamine and acetic acid. Under the optimized reaction
conditions, high carbon yields (~85%) of C14 oxygenates can be
obtained from the solvent-free aldol condensation 2-methyl
benzaldehyde (or 4-methyl benzaldehyde) and cyclohexanone.
By the aqueous phase hydrodeoxygenation over a commercial
Pd/C catalyst, the C14 oxygenates as obtained can be
selectively converted to tricycloalkanes which have high
density (
≥
0.96 g mL-1). As a potential application, these
tricycloalkanes can be used as additive to improve the
volumetric heats value of current bio-jet fuels.
100
80
Conversion of 1A (%)
Carbon yield of 1F (%)
Carbon yield of 1G (%)
Conflicts of interest
60
Carbon yield of 1D (%)
Carbon yield of 1E (%)
There are no conflicts to declare.
40
Acknowledgements
20
0
This work was supported by the National Natural Science
Foundation of China (no. 21603221; 21690082; 21776273), the
Strategic Priority Research Program of the Chinese Academy of
Sciences (XDB17020100), the National Key Projects for
Fundamental Research and Development of China
0
60
120
180
240
Reaction time (min)
Figure 9. Conversion of 1A and the carbon yields of different products over the (2016YFA0202801),
Dalian
Science
Foundation
for
commercial Pd/C catalyst as the functional of reaction time. Reaction conditions:
Distinguished Young Scholars (no. 2015R005), Department of
453 K, 6 MPa H2; 1 g 1A, 35 mL H2O, 0.1 g Pd/C.
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Green Chemistry
Page 7 of 8
View Article Online
DOI: 10.1039/C8GC01628C
Journal Name
ARTICLE
Gordon, F.D. Toste and A.T. Bell, Angew. Chem., Int. Ed., 2015,
54, 4673-4677.
IATA Guidance Material for Sustainable Aviation Fuel
Management ISBN 978-92-9252-774-7 © 2015 International
Air Transport Association. All rights reserved. Montreal—
Geneva.
C. Zhao, D.M. Camaioni and J.A. Lercher, J. Catal., 2012, 288,
92-103; Z. Zhao, H. Shi, C. Wan, M.Y. Hu, Y. Liu, D. Mei, D.M.
Camaioni, J.Z. Hu and J.A. Lercher, J. Am. Chem. Soc., 2017,
139, 9178-9185.
J. Yang, N. Li, G. Li, W. Wang, A. Wang, X. Wang, Y. Cong and T.
Zhang, Chem. Commun. (Cambridge, U. K.), 2014, 50, 2572-
2574; X. Zhang, Q. Deng, P. Han, J. Xu, L. Pan, L. Wang and J.-J.
Zou, AIChE J., 2017, 63, 680-688; J. Xie, X. Zhang, L. Pan, G.
Nie, X.-T.-F. E, Q. Liu, P. Wang, Y. Li and J.-J. Zou, Chem.
Commun. (Cambridge, U. K.), 2017, 53, 10303-10305; F. Chen,
N. Li, X. Yang, L. Li, G. Li, S. Li, W. Wang, Y. Hu, A. Wang, Y.
Cong, X. Wang and T. Zhang, ACS Sustainable Chem. Eng.,
2016, 4, 6160-6166; X. Sheng, G. Li, W. Wang, Y. Cong, X.
Wang, G.W. Huber, N. Li, A. Wang and T. Zhang, AIChE J.,
2016, 62, 2754-2761; T.V. Bui, T. Sooknoi and D.E. Resasco,
ChemSusChem, 2017, 10, 1631-1639; Y. Jing, Q. Xia, J. Xie, X.
Liu, Y. Guo, J.-j. Zou and Y. Wang, ACS Catal., 2018, 3280-3285.
G. Nie, X. Zhang, P. Han, J. Xie, L. Pan, L. Wang and J.-J. Zou,
Chem. Eng. Sci., 2017, 158, 64-69; G. Nie, X. Zhang, L. Pan, P.
Han, J. Xie, Z. Li, J. Xie and J.-J. Zou, Chem. Eng. Sci., 2017, 173,
91-97.
Science and Technology of Liaoning Province (under contract
of 2015020086-101). Dr. Xu appreciates the Postdoctoral
Science Foundation of China (2015M580235) and the
dedicated grant for methanol conversion from DICP for
funding this work.
6
7
8
Notes and references
1
G.W. Huber, S. Iborra and A. Corma, Chem. Rev. (Washington,
DC, U. S.), 2006, 106, 4044-4098; N. Yan, Y. Yuan, R. Dykeman,
Y. Kou and P.J. Dyson, Angew. Chem., Int. Ed., 2010, 49, 5549-
5553; T.D. Matson, K. Barta, A.V. Iretskii and P.C. Ford, J. Am.
Chem. Soc., 2011, 133, 14090-14097; X.Y. Wang and R. Rinaldi,
Energy Environ. Sci., 2012, 5, 8244-8260; X. Wang and R.
Rinaldi, Angew. Chem., Int. Ed., 2013, 52, 11499-11503; P. Sun,
G. Gao, Z. Zhao, C. Xia and F. Li, ACS Catal., 2014, 4, 4136-
4142; Y. Yang, G. Gao, X. Zhang and F. Li, ACS Catal., 2014, 4,
1419-1425; K. Barta and P.C. Ford, Acc. Chem. Res., 2014, 47,
1503-1512; H. Xu, K. Wang, H. Zhang, L. Hao, J. Xu and Z. Liu,
Catal. Sci. Technol., 2014, 4, 2658-2663; H. Xu, B. Yu, H. Zhang,
Y. Zhao, Z. Yang, J. Xu, B. Han and Z. Liu, Chem. Commun.
(Cambridge, U. K.), 2015, 51, 12212-12215; Q. Xia, Z. Chen, Y.
Shao, X. Gong, H. Wang, X. Liu, S.F. Parker, X. Han, S. Yang and
Y. Wang, Nat. Commun., 2016, 7, 11162.
9
2
M.J. Climent, A. Corma and S. Iborra, Green Chem., 2011, 13,
520-540; M. Besson, P. Gallezot and C. Pinel, Chem. Rev.
(Washington, DC, U. S.), 2014, 114, 1827-1870; Y. Roman-
Leshkov, C.J. Barrett, Z.Y. Liu and J.A. Dumesic, Nature, 2007,
447, 982-985; G. Yong, Y. Zhang and J.Y. Ying, Angew. Chem.,
Int. Ed., 2008, 47, 9345-9348; F. de Clippel, M. Dusselier, R.
Van Rompaey, P. Vanelderen, J. Dijkmans, E. Makshina, L.
Giebeler, S. Oswald, G.V. Baron, J.F.M. Denayer, P.P.
Pescarmona, P.A. Jacobs and B.F. Sels, J. Am. Chem. Soc.,
2012, 134, 10089-10101; T. Prasomsri, M. Shetty, K.
Murugappan and Y. Roman-Leshkov, Energy Environ. Sci.,
2014, 7, 2660-2669; F. Liu, M. Audemar, K. De Oliveira Vigier,
J.-M. Clacens, F. De Campo and F. Jerome, Green Chem., 2014,
16, 4110-4114; Z. Zhao, J. Arentz, L.A. Pretzer, P.
Limpornpipat, J.M. Clomburg, R. Gonzalez, N.M. Schweitzer, T.
Wu, J.T. Miller and M.S. Wong, Chem. Sci., 2014, 5, 3715-3728;
S. Van den Bosch, W. Schutyser, R. Vanholme, T. Driessen, S.F.
Koelewijn, T. Renders, B. De Meester, W.J.J. Huijgen, W.
Dehaen, C.M. Courtin, B. Lagrain, W. Boerjan and B.F. Sels,
Energy Environ. Sci., 2015, 8, 1748-1763; L. Chen, J. Zhao, S.
Pradhan, B.E. Brinson, G.E. Scuseria, Z.C. Zhang and M.S.
Wong, Green Chem., 2016, 18, 5438-5447; Y. Wang, S. De and
N. Yan, Chem. Commun. (Cambridge, U. K.), 2016, 52, 6210-
6224; G. Yi, S.P. Teong and Y. Zhang, Green Chem., 2016, 18,
979-983.
10
11
12
T. Moteki, A.T. Rowley and D.W. Flaherty, ACS Catal., 2016, 6,
7278-7282.
T. Moteki, A.T. Rowley, D.T. Bregante and D.W. Flaherty,
ChemCatChem, 2017, 9, 1921-1929.
H. Liu, J. Sun, J.-S. Chang and P. Shukla, Critical reviews in
biotechnology, 2018, 1-17; M. Rastogi and S. Shrivastava,
Renew. Sust. Energ. Rev., 2017, 80, 330-340; B.G. Harvey and
H.A. Meylemans, J. Chem. Technol. Biotechnol., 2011, 86, 2-9;
D.M. Alonso, J.Q. Bond and J.A. Dumesic, Green Chem., 2010,
12, 1493-1513.
13
14
F. Liu, Q. Liu, A. Wang and T. Zhang, ACS Sustainable Chem.
Eng., 2016, 4, 3850-3856.
C. Zhao, Y. Kou, A.A. Lemonidou, X.B. Li and J.A. Lercher,
Angew. Chem., Int. Ed., 2009, 48, 3987-3990; C. Zhao and J.A.
Lercher, Angew. Chem., Int. Ed., 2012, 51, 5935-5940.
H. Liu, T. Jiang, B. Han, S. Liang and Y. Zhou, Science, 2009,
326, 1250-1252.
G. Li, N. Li, X. Wang, X. Sheng, S. Li, A. Wang, Y. Cong, X. Wang
and T. Zhang, Energy Fuels, 2014, 28, 5112-5118; J. Yang, S. Li,
N. Li, W. Wang, A. Wang, T. Zhang, Y. Cong, X. Wang and G.W.
Huber, Ind. Eng. Chem. Res., 2015, 54, 11825-11837; Q. Deng,
J. Xu, P. Han, L. Pan, L. Wang, X. Zhang and J.-J. Zou, Fuel
Process. Technol., 2016, 148, 361-366; G. Nie, X. Zhang, L. Pan,
M. Wang and J.-J. Zou, Chem. Eng. Sci., 2018, 180, 64-69.
C. Zhu, T. Shen, D. Liu, J. Wu, Y. Chen, L. Wang, K. Guo, H. Ying
and P. Ouyang, Green Chem., 2016, 18, 2165-2174.
R. Xing, W. Qi and G.W. Huber, Energy Environ. Sci., 2011, 4,
2193-2205.
15
16
3
4
https://www.eia.gov/tools/glossary/?id=petroleum.
U.S. Energy Information Administration, Monthly Energy
Review, April 2017.
17
18
19
20
21
5
G.W. Huber, J.N. Chheda, C.J. Barrett and J.A. Dumesic,
Science, 2005, 308, 1446-1450; J.Q. Bond, D.M. Alonso, D.
Wang, R.M. West and J.A. Dumesic, Science, 2010, 327, 1110-
1114; B.G. Harvey and R.L. Quintana, Energy Environ. Sci.,
2010, 3, 352-357; A. Corma, O. de la Torre, M. Renz and N.
Villandier, Angew. Chem., Int. Ed., 2011, 50, 2375-2378; P.
Anbarasan, Z.C. Baer, S. Sreekumar, E. Gross, J.B. Binder, H.W.
Blanch, D.S. Clark and F.D. Toste, Nature, 2012, 491, 235-239;
M. Mascal, S. Dutta and I. Gandarias, Angew. Chem., Int. Ed.,
2014, 53, 1854-1857; J. Xin, S. Zhang, D. Yan, O. Ayodele, X. Lu
and J. Wang, Green Chem., 2014, 16, 3589-3595; Q.-N. Xia, Q.
Cuan, X.-H. Liu, X.-Q. Gong, G.-Z. Lu and Y.-Q. Wang, Angew.
Chem., Int. Ed., 2014, 53, 9755-9760; S. Sankaranarayanapillai,
S. Sreekumar, J. Gomes, A. Grippo, G.E. Arab, M. Head-
G.F. Liang, A.Q. Wang, L. Li, G. Xu, N. Yan and T. Zhang, Angew.
Chem., Int. Ed., 2017, 56, 3050-3054.
T. Shen, C. Zhu, C. Tang, Z. Cao, L. Wang, K. Guo and H. Ying,
RSC Adv., 2016, 6, 62974-62980.
E.I. Gurbuz, E.L. Kunkes and J.A. Dumesic, Appl. Catal., B, 2010,
94, 134-141.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Green Chemistry
Page 8 of 8
View Article Online
DOI: 10.1039/C8GC01628C
Table of contents entry
Carbon yield > 82%
Density > 0.96 g mL-1
Renewable
ionic liquid catalyst
H2
+
O
Pd
Pd
Pd
Pd
+
Carbon
-
Lignocellulosic
platform molecules
Carbon yield:
~85%
High density
aviation fuel
Synthesis of high-density aviation fuels with methyl benzaldehyde and
cyclohexanone
Jilei Xu, Ning Li,* Guangyi Li, Fengan Han, Aiqin Wang, Yu Cong, Xiaodong Wang and Tao Zhang*
Jet fuel range tricyclic alkanes were first selectively synthesized with methyl benzaldehyde and cyclohexanone which
can be derived from lignocellulose.