A new approach for bio-jet fuel generation from palm oil and limonene in the absence of hydrogen

Article abstract of DOI:10.1039/c5cc06601h

The traditional methodology includes a carbon-chain shortening strategy to produce bio-jet fuel from lipids via a two-stage process with hydrogen. Here, we propose a new solution using a carbon-chain filling strategy to convert C₁₀ terpene and lipids to jet fuel ranged hydrocarbons with aromatic hydrocarbon ingredients in the absence of hydrogen.

Full text of DOI:10.1039/c5cc06601h

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A New Approach for Bio-Jet Fuel Generation from Palm Oil and
Limonene in absence of Hydrogen
Received 00th xx 20xx,
Accepted 00th xx 20xx
Jingjing Zhang and Chen Zhao*
DOI: 10.1039/x0xx00000x
www.rsc.org/
The traditional methodology includes carbon-chain shortening
strategy to produce bio-jet fuel from lipids via a two-stage process
with hydrogen. Here, we propose a new solution using a carbon-
chain filling strategy to convert C10 terpene and lipids to jet fuel
ranged hydrocarbons with aromatic hydrocarbons ingredients in
absence of hydrogen.
Carbon
number
6
7
8
9
10
Biologically derived jet fuel can be a key solution to the
challenges faced by the aviation industry.1-3 The traditional
technique to produce bio-jet fuel from the lipid sources uses a
“carbon-chain shortening strategy” (CSS) to reduce lipid
carbon chain (ranging from C14 to C18) to resemble that of
kerosene (ranging from C9 to C18). This technique involves a
two-step process. In the first step hydrodeoxygenation
removes the oxygen atoms in the carbonyl groups to produce
long-chain alkanes,4-10 whereas the second step involves
isomerization and non-selective C-C bond cracking steps to
generate the range of paraffins which are suitable for jet fuel
(C9-C16 hydrocarbons) (Fig. 1a).11-15
11
12
13
14
15
16
17
18
The main problems faced by the CSS approach includes the
consumption of large amounts of high pressurized H2 during
the two-stage process, substantial carbon loss in the cracking
reaction, the need for the addition of extra aromatic
hydrocarbons to the bio-jet fuel (around 25 vol%), and the
necessity for running the two-stage process.16 The
consequences are therefore a low yield of kerosene ingredient
(maximum yield: 50 wt%) and the high price of bio-jet fuel.17
To overcome these disadvantages, we propose a novel
solution which we refer to as “carbon-chain filling strategy”
(CFS). The novelty of our approach relies on the new one-pot
process based on co-activating lipid and monoterpene in the
absence of external H2 to produce bio-jet fuel ranged
hydrocarbons with some fraction of aromatic hydrocarbons
compositions.
A C10 terpene was selected to co-activate lipid conversion in
absence of external H2, because the terpene releases both
aromatic hydrocarbons and H2,18-19 and produces some smaller
C9-C15 alkanes. The formed aromatics and light alkanes can fill
the gap for constructing a C9-C16 kerosene-like jet fuel. The in-
situ generated H2 can be consumed by lipid to produce C14-C18
alkanes via the hydrodeoxygenation route in a one-pot
process. The exothermic hydrogenation and endothermic
dehydrogenation steps are integrated into one process in
order to maximize energy utilization (see Fig. 1b).
Limonene was used as
a selected terpene for the
dehydrogenation reaction carried out at relatively low
temperatures of 200-300 °C, which was the similar range for
lipid hydrodeoxygenation in the liquid phase.20-22 However,
this system is not free from challenges which include
insufficient pressure of the generated hydrogen to
hydrogenate the lipid, and incompatibility of the designed dual
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active sites for dehydrogenation and hydrogenation. In consistent in the consecutive four recycling tests and
addition, the side reactions of limonene condensation may
prevent the target dehydrogenation step on limonene.
demonstrated that the developed PdNi/HZSM-5 catalyst
exhibited high stability in this catalytic system (Fig. S3).
100
In the blank test with limonene in presence of N2, limonene
was very stable with a conversion lower than 4% at 280 °C.
Subsequently, we selected a variety of Pd-based catalysts
including Pd/C (activated carbon), Pd/ASA (amorphous silica
alumina), Pd/SiO2, Pd/Al2O3, Pd/Zeolite HBEA, Pd/Zeolite HY
(SiO2/Al2O3 ratio: 9-12), Pd/Zeolite HY (SiO2/Al2O3 ratio: 30-60)
and Pd/Zeolite HZSM-5 (SiO2/Al2O3 ratio: 197) to catalyze
limonene dehydroaromatization at 280 °C in the presence of
N2 (Fig. 2a, Electronic Supplementary Information Table S1).
The results showed that Pd center seemed responsible for
p-cymene
2 h pressure
18
a.
80
17
60
16
40
15
20
14
0
1
2
3
4
5
6
7
8
9
1: None 2. Pd/C 3: Pd/ASA 4: Pd/SiO 5: Pd/Al O
2
2 3
achieving
a
p-cymene yield of 60-80 wt.%, with
6: Pd/Hβ 7: Pd/HY(9) 8: Pd/HY(30) 9: Pd/HZSMꢀ5
dehydroaromatization rates of 616-634 mmol∙g-1∙h-1.
Consistent with the kinetic curves of limonene conversion (Fig.
S1), it was observed that limonene isomerization started as the
first step, and the subsequent dehydrogenation reaction
produced p-cymene and H2. The in-situ release of H2 from
limonene over Pd/HZSM-5 achieved 18 bar pressure during the
reaction with a dehydrogenation rate of 634 mmol∙g-1∙h-1. As
the higher pressure would be more favorable for
hydrogenation of the feedstock of stearic acid or other lipids,
and thus, Pd/HZSM-5 was selected as the catalyst for further
investigation.
100
80
60
40
20
0
pꢀcymene
C17
b.
C18
None PdNi PdCo PdCu PdFe PdZn PdRu PdRh PdAu
( HZSMꢀ5 as support for these bimetallic catalysts )
The single Pd/HZSM-5 catalyst showed a poor performance
towards stearic acid hydrodeoxygenation in limonene with a
conversion rate of 14% at 280 °C with N2, so the second metal
was incorporated in order to improve the desired activity. The
addition of Co, Cu, Fe, Zn, and Rh aided with the second Pd
center by the co-impregnation method was shown to be
inactive for stearic acid hydrodeoxygenation in limonene at
identical conditions (Fig. 2b, Table S2). By adding the Ru site to
Pd, the bimetallic RuPd/HZSM-5 catalyzed around 50%
hydrocarbon yield (mainly C17 and C18) from stearic acid in
limonene at 280 °C with N2. It was surprising that the addition
of Ni sharply increased the C17/C18 hydrocarbons to nearly
100% from stearic acid conversion while maintaining a 70% p-
cymene yield from limonene conversion, making a good use
from simultaneous dehydrogenation of limonene over Pd, H∙
transfer from Pd to Ni, and hydrodeoxygenation of stearic acid
over Ni in a one-pot process.
100
80
60
40
20
0
100
80
60
40
20
0
c.
Limonene Conv.
Partial Hydrogenation
Full Hydrogenation
Dehydroaromatization
Isomerization
0
30
60
90
120
Time ( min. )
100
80
60
40
20
0
100
80
60
40
20
0
d.
Conv.
C17
In terms of the kinetics of the chemical conversion process,
Fig. 2c and Fig. 2d present the respective kinetics curves of the
two feedstock. Limonene followed initial isomerization and
partial hydrogenation pathway and finally underwent
dehydroaromatization to produce p-cymene, reaching an
initial dehydrogenation rate of 204 mmol∙g-1∙h-1. On the other
hand, firstly stearic acid was esterified with fatty alcohol
(formed by hydrogenation of stearic acid) as a primary product
with a rate of 5.3 mmol∙g-1∙h-1, then was subjected to the
sequential C-O bond cleavage and finally the decarbonylation
of the ester led to final long-chain alkanes formation (Table S3,
Fig. S2). The durability of PdNi/HZSM-5 catalyst was evaluated
by stearic acid conversion in limonene at 280 °C in the
presence of N2 at 0.8 MPa for 2 h. The obtained activity (100%
conversion after 2 h) and selectivity (100% after 2 h) were
C18
Ester
0
30
60
90
120
Time ( min. )
2 | Chem.Commun., 2015, 00, 1-3
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determined from TEM image (Fig. 4a). High-resolution TEM
image (Fig. 4b) showed the lattice fringes of fcc Ni (200), Ni
(111) and Pd (111), indicating that PdNi nanoparticles were
composed of single- crystallinity or twin-crystallinity particles.
The SEM-mapping and STEM-EDX spectra of PdNi/HZSM-5
both demonstrated that the bimetallic dispersive Ni and Pd
nanoparticles were embedded in an alloy-like structure (Fig.
4c). The SEM-EDX analysis indicated that the surface of such
catalyst contained 1.11 atom% Pd and 3.93 atom% Ni (Figs. 4d-
4e), confirming that the formed bimetallic PdNi nanoparticles
(Pd0.20Ni0.80) basically agreed with the nominal composition
(Pd0.22Ni0.78). The XRD patterns (Fig. 4f) indicated a mixture of
fcc Ni (200), fcc Ni (111), and fcc Pd (111) phase was in the
form of PdNi nanoparticles, consistent with the information
from HRTEM results. The acid sites as probed by IR spectra of
adsorbed pyridine (Fig. 4g) showed that PdNi/HZSM-5 had 92
mmol∙g-1 Brönsted acid site and 208 mmol∙g-1 Lewis acid site
(Table S4).
Figure 3. The influence of pore structures of (a) PdNi/HZSM-5, (b) PdNi/HBEA, (c)
PdNi/ASA for changing products from co-activation of limonene and stearic acid in
a one-pot process in absence of H2.
Another interesting observation was that the pore
properties of the supports greatly influenced the product
distributions. Three typical acidic supports of zeolite HZSM-5,
zeolite HBEA, and amorphous silica alumina (ASA) were chosen
to construct respective PdNi based catalysts. The latter two
samples poorly catalyzed stearic acid conversions at low
alkane yields (1% and 0%, respectively) in limonene (Fig. 3, Fig.
S4), and also they highly promoted side-reactions of limonene
condensations. Brönsted acid sites (BAS) of HZSM-5 and HBEA
were located in the 10-ring and 12-ring pores, while BAS of the
ASA support was situated on the external surface of open
pores. The calculated diameter for the limonene condensation
product was around 5.8 Å (see Fig. S5), while the pore sizes of
HBEA and HZSM-5 are 6.6-7.7 Å and 5.1-5.6 Å, respectively.
Therefore, the unconfined pores in ASA and large pores in
HBEA both help to form limonene condensation products,
whereas the proper pore size and the suitable acidity of HZSM-
5 ensure the occurrence of the targeted coupled reactions of
Figure 5. Proposed mechanism for co-activation of palm oil and limonene on
the surface of PdNi/HZSM-5 with internal hydrogen transfer.
limonene
dehydroaromatization
and
stearic
acid
hydrodeoxygenation within an integrated process.
The data suggest that the dispersed Pd and Ni nanoparticles
loaded on the PdNi/HZSM-5 catalyst may play a beneficial role
for in-situ produced H∙ transfer on the surface of PdNi alloy,
and the proper pore size of HZSM-5 support (5.1-5.6 Å)
prevents the side-reaction (limonene condensation product,
diameter: 5.8 Å) from occurring (Fig. 5).
Finally, we used this optimized technique for co-activation
of palm oil and limonene in the presence of the PdNi/HZSM-5
catalyst at 280 °C in the absence of H2. The fatty acid
composition of the used palm oil was analyzed by the
transesterification method with methanol, and mainly
composed of saturated C16 fatty acids (36%), and C18 fatty acids
(including 12% saturated and 50% unsaturated components)
(Table S5). The catalysis test quantitatively showed that palm
oil and limonene were converted to a hydrocarbon mixture
ranging from 4 to 18 carbons (including a large fraction of
aromatic hydrocarbons, Fig. S7) after 2 h using the optimized
catalysis system (Fig. 6a, Table S6). Such formed hydrocarbon
mixture was analogical to the compositions and properties of
commercial bio-jet fuel, please refer to GC-MS analysis of
kerosene purchased from SINOPEC as displayed in Fig. S8. A
trace amount of toluene (1.2%) was observed, as formed by
Figure 4. Characterization of the used PdNi/HZSM-5 catalyst by (a) TEM and
(b) HRTEM images, (c) SEM-mapping image, (d) SEM-EDX, (e) STEM-EDX
analysis of bimetallic PdNi nanoparticles. (f) XRD patterns and (g) IR spectra of
adsorbed pyridine towards three samples of HZSM-5, Pd/HZSM-5, and
PdNi/HZSM-5.
We characterized the bimetallic PdNi/HZSM-5 catalyst
(SiO2/Al2O3 ratio of 197). The particle size of this catalyst
prepared by co-impregnating method was 10.1 ± 2.4 nm, as
eliminating 1 mole of C3H8 from p-cymene. In addition, a yield
of 3% limonene condensation products was also produced.
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from lipids, filling the gap for essential ingredients for a perfect
composition of bio-jet fuel.
The major gas-phase component (Fig. 6b) was H2 derived from
limonene dehydrogenation. In addition, trace amounts of CO
and CO2 (formed in decarbonylation and decarboxylation
reactions), CH4 (generated by methanation of CO and CO2 with
The cascade reactions for palm oil and limonene co-
activation at moderate temperature under the inert N2
atmosphere lead to high yields of bio-jet fuel in a simple,
efficient, and green way. By directly boiling the two biomass
feedstock it is possible to solve the high-demand issues for H2,
aromatics and light alkanes for production of the bio-jet fuel in
a highly integrated one-pot process. Future studies would
focus on a more detailed characterization of the properties of
resultant bio-jet fuel and experiments to optimize the process
at an industrial scale.
H2), C3H8 (released by C-C cracking of
p
-cymene), and other
lighter alkanes (C2H6, C2H4,
also detected (Table S6).
i-,
n
- C4H10, and i-, n- C5H12) were
60
alkane
cyclic alkane
ketone
40
a.
20
limonene condensation
hydrocarbons
arene
cyclic olefin
2.5
2.0
1.5
1.0
0.5
0.0
We gratefully acknowledge the financial support from the
Recruitment Program of Global Young Experts in China,
National Natural Science Foundation of China (Grant No.
21573075), and Shanghai Pujiang Program (No. PJ1403500).
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hydrodeoxygenation which also promoted the equilibrium
shift for the hydrogenation-dehydrogenation reaction of
limonene.
In summary, we demonstrate a novel approach for the
conversion of palm oil and limonene to bio-jet fuel ranged
hydrocarbons without the need of hydrogen. Using
a
PdNi/HZSM-5 zeolite catalyst, a monoterpene can release
aromatic hydrocarbons and hydrogen and smaller C9-C15
alkanes at 280 °C. The in-situ generated hydrogen from
terpene
dehydroaromatization
enables
the
hydro-
deoxygenation of lipid to C14-C18 alkanes. We show that lighter
alkanes and aromatic hydrocarbons are produced from
limonene simultaneously with C14-C18 hydrocarbons generated
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