From lignocellulosic biomass to renewable cycloalkanes for jet fuels

Article abstract of DOI:10.1039/c5gc01583a

A novel pathway was investigated to produce jet fuel range cycloalkanes from intact biomass. The consecutive processes for converting lignocellulosic biomass into jet fuel range cycloalkanes principally involved the use of the well-promoted ZSM-5 in the process of catalytic microwave-induced pyrolysis and RANEY nickel catalysts in the hydrogen saving process. Up to 24.68% carbon yield of the desired C₈-C₁₆ aromatics was achieved by catalytic microwave pyrolysis at 500 °C. We observed that solvents could assist in the hydrogenation reaction of naphthalene; and the optimum result for maximizing the carbon selectivity (99.9%) of decalin was obtained from the reaction conducted in the n-heptane medium. The recovery of organics could reach ～94 wt% after the extraction process. These aromatics in the n-heptane medium were eventually hydrogenated into jet fuel range cycloalkanes. Various factors were analyzed to determine the optimal result under mild conditions. An increased catalyst loading, reaction temperature, and prolonged time could enhance the hydrogenation reactions to improve the selectivity of jet fuel range cycloalkanes. Three types of hydrogenation catalysts (NP Ni, RANEY Ni 4200, home-made RANEY Ni) were chosen to evaluate the catalytic performance. The results indicated that the home-made RANEY nickel is the optimal catalyst to obtain the highest selectivity (84.59%) towards jet fuel range cycloalkanes. These cycloalkanes obtained can be directly used as additives to synthesize the desired jet fuels by blending with other hydrocarbons. Hence integration of catalytic processes and conversion of lignocellulosic biomass paved a new avenue for the development of green bio-jet fuels over inexpensive catalysts under mild conditions.

Full text of DOI:10.1039/c5gc01583a

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From lignocellulosic biomass to renewable
cycloalkanes for jet fuels†
Cite this: DOI: 10.1039/c5gc01583a
Xuesong Zhang, Hanwu Lei,* Lei Zhu, Joan Wu and Shulin Chen
A novel pathway was investigated to produce jet fuel range cycloalkanes from intact biomass. The con-
secutive processes for converting lignocellulosic biomass into jet fuel range cycloalkanes principally
involved the use of the well-promoted ZSM-5 in the process of catalytic microwave-induced pyrolysis
and RANEY® nickel catalysts in the hydrogen saving process. Up to 24.68% carbon yield of the desired
8
C –C16 aromatics was achieved by catalytic microwave pyrolysis at 500 °C. We observed that solvents
could assist in the hydrogenation reaction of naphthalene; and the optimum result for maximizing the
carbon selectivity (99.9%) of decalin was obtained from the reaction conducted in the n-heptane
medium. The recovery of organics could reach ∼94 wt% after the extraction process. These aromatics in
the n-heptane medium were eventually hydrogenated into jet fuel range cycloalkanes. Various factors
were analyzed to determine the optimal result under mild conditions. An increased catalyst loading, reac-
tion temperature, and prolonged time could enhance the hydrogenation reactions to improve the selecti-
vity of jet fuel range cycloalkanes. Three types of hydrogenation catalysts (NP Ni, RANEY® Ni 4200,
home-made RANEY® Ni) were chosen to evaluate the catalytic performance. The results indicated that
the home-made RANEY® nickel is the optimal catalyst to obtain the highest selectivity (84.59%) towards
jet fuel range cycloalkanes. These cycloalkanes obtained can be directly used as additives to synthesize
the desired jet fuels by blending with other hydrocarbons. Hence integration of catalytic processes and
conversion of lignocellulosic biomass paved a new avenue for the development of green bio-jet fuels
over inexpensive catalysts under mild conditions.
Received 12th July 2015,
Accepted 12th August 2015
DOI: 10.1039/c5gc01583a
www.rsc.org/greenchem
susceptible to pyrolytic cracking, resulting in coking in a jet
engine, increasing deposition and fouling of fuel control units
1
. Introduction
Growing concerns about global climate change and rapidly and injectors, and increasing operating costs due to the
8
,9
diminishing fossil-based petroleum reserves have spurred increased maintenance.
On the other hand, the thermal
immense interest in the utilization of renewable resources for stability of a jet fuel can be greatly enhanced by utilizing
developing new generation (hydrocarbon) biofuels, with a par- liquids rich in cycloalkanes because cycloalkanes are compact
1
,2
ticular focus on green aviation fuels. The development of molecules with robust ring strain and contribute to a more
alternative aviation fuels has received more attention in order dense jet fuel and burn cleanly with high heats of combustion
to reduce the dependence on fossil resources. Lignocellulosic and low freezing points, compared with straight-chain
biomass is a ubiquitous and sustainable source of carbon that alkanes and branched-chain alkanes with lower densities
displays promising potential in the manufacture of hydro- (∼0.76–0.78 g mL− ).
1
8,10
However, commercial petroleum fuels
normally do not have very high cycloalkane contents and it is
The commercial aviation fuels designed for use in aircrafts difficult to concentrate the cycloalkanes on a commercial
3
,4
carbon transportation fuels and versatile chemicals.
1
1
are jet fuels, which are exclusively derived from petroleum scale. To fulfill the demand for increasing the density and
5
refining. The current jet fuels originated from fossil resources volumetric heating, it is imperative that cycloalkanes are syn-
6
,7
7
are rich in straight-chain alkanes. It was found that both thesized and added into jet fuels (e.g. Jet A and JP-8). There-
straight-chain alkanes and branched-chain alkanes are highly fore, most efforts to produce jet fuels have focused on
increasing the cycloalkane content, for example JP-5 navy fuel
1
2
contains 52.8% cycloalkanes.
To produce renewable drop-in fuels for aviation, Dumesic’s
have discovered a new route by
aldol condensation of furfural and acetone to synthesize the
Bioproducts, Sciences and Engineering Laboratory, Department of Biological Systems
Engineering, Washington State University, Richland, WA 99354-1671, USA.
E-mail: hlei@wsu.edu; Fax: +1 509 372 7690; Tel: +1 509 372 7628
13,14
6,15
group
and Huber et al.
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
c5gc01583a
long carbon chain intermediates of C –C . The hydrodeoxy-
8
15
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3
1
genation process was introduced stepwise to obtain the formation of organic compounds. Moreover, RANEY®-type
branched alkanes with high thermal stability and energy nickel is utilized in other widespread fields for fine chemical
2
2
density, which could be used as drop-in fuels for aviation. In manufacturing owing to its good catalytic performance. In
general, most studies emphasized on manufacturing jet fuel addition to catalyzing liquid products, costly hydrogen derived
range (C –C ) straight-chain alkanes and/or branched-chain from aqueous-phase reforming could also be obtained over a
8
16
alkanes from the lignocellulose-derived platform compounds, tin-promoted RANEY®-nickel catalyst as reported by Huber
3
2
which cannot meet the specification of cycloalkanes in jet and his colleagues. It was found that water molecules can be
16–18
fuels.
In addition, these multiple processes necessitate easily fixed to the RANEY® nickel surface by oxygen bonding,
expensive reactants and noble metal catalysts, resulting in thereby inhibiting the adsorption of organic substrates on the
3
3
infeasible commercialization in biorefineries compared with metallic surface. Hence the removal of water in bio-oils is an
commercial formulations based on petroleum derived jet fuels. essential step to enhance the catalytic performance in the
In addition, fast pyrolysis has also received special reco- hydrogen saving process. Some solvents (e.g. ethyl acetate) can
gnition and it is one of the viable options to convert ligno- be used to extract the organic mixture from pyrolysis oils.
1
9,20
cellulosic biomass to pyrolysis oil.
Pyrolysis oil is not However, far too little attention has been paid to evaluate the
3
4
suitable for use as a transportation fuel because of its detri- impact of solvents as part of the catalytic system. Unlike the
mental properties, including its much lower energy density organic synthesis literature, in which the influence of solvents
than petroleum fuels, poor thermal and chemical stabilities, has been well-demonstrated and understood, the effect of
2
1,22
and high viscosity.
pyrolysis oil has to be upgraded to eliminate total or partial commonly neglected and/or rarely comprehended.
oxygenates and to reduce the degree of unsaturation prior to advances towards understanding the effect of solvents on the
To circumvent these problems, raw solvents for hydrogenation and hydrogenolysis reactions is
3
5
Thus
2
3
its practical application as transportation fuel. Among the hydrogenation of bio-oils can lay the foundation for valoriza-
upgrading approaches for jet fuels, hydrodeoxygenation (HDO) tion of bio-oils.
7
is deemed to be a promising and effective process. The HDO
According to the aforementioned consideration, the direct
process conditions are rather severe (300–400 °C, 80–300 bar conversion of lignocellulosic biomass into jet fuels by inte-
2
1,22
H
2
pressure).
It is widely known that the oxygen content in grated processes was conducted. Lignocellulosic biomass was
the fast pyrolysis oils was removed through the HDO process firstly converted into jet fuel range (C –C ) aromatics by cata-
8
16
2
in the form of H O. In this regard, a large amount of costly lytic microwave pyrolysis over well-promoted ZSM-5. The
hydrogen was consumed by the dehydration reaction, which organic phase of the bio-oils derived from catalytic microwave
significantly reduces the hydrogenation efficiency. Although pyrolysis was thereafter extracted with the optimum solvent
advanced jet fuels from the HDO process are expected to be after evaluating the solvent influence on the hydrogenation
produced on a biorefinery scale, high capital costs caused by reaction of model compounds. In the final step, the organic
the tolerance to severe conditions and the low selectivity of mixture was hydrogenated into the desired C –C hydro-
8
16
2
4,25
liquid products render these processes uneconomical.
carbons (including cycloalkanes and minor aromatics) which
Accordingly, the production of jet fuels from renewable satisfy basic requirements of conventional jet fuels by using
biomass resources calls for ideal technologies with efficient RANEY® nickel as the catalyst. Since the coupling of three
solid-phase catalysts to make the processes economically feas- main steps (catalytic microwave pyrolysis, liquid–liquid extrac-
ible under mild, environmentally friendly reaction conditions.
tion, and the downstream hydrogen saving process) over
In contrast, the oxygen content of bio-oil can be partially or regular catalysts has not been previously reported on the direct
even completely eliminated by zeolite cracking during fast use of lignocellulosic biomass, this study demonstrates proof-
2
6
pyrolysis of biomass. Carlson et al. have reported that of-principle of a novel consecutive three-step process to
biomass-derived feedstock can be directly converted into aro- produce cycloalkanes for jet fuels.
matics with ZSM-5 as the catalyst in a single catalytic pyrolysis
2
7,28
step.
Lei and his colleagues have focused on the pro-
duction of aromatics through catalytic microwave-induced
2
. Experimental
2
9,30
pyrolysis of biomass-derived feedstock.
selectivity towards aromatic hydrocarbons was obtained,
belonging to jet fuel range (C –C ) aromatics. In this sense, The feedstock used was Douglas fir sawdust pellets (Bear
Up to 92.60%
2.1 Materials
8
16
certain aromatics with low oxygen content tend to hydrogenate Mountain Forest Products Inc., USA) which were approximately
into cycloalkanes together with minor aromatics under low- 7 mm in diameter and 15 mm in length. Proximate and
severity conditions. The hydrogenation process is regarded as elemental analyses of raw Douglas fir sawdust pellets are
a hydrogen saving process, in which hydrogen is converted in described in Table S1.† It was evidenced that pelleted biomass
the form of cycloalkanes rather than water.
could be maximally decomposed into pyrolytic volatile vapors
It is more reasonable to use Ni-based catalysts for hydro- by microwave heating, which could be thereafter catalyzed into
2
9,30
treating bio-oil because of their high activity for hydrogenation targeted products.
2 2 3
Parent ZSM-5 (SiO /Al O mole ratio:
and low cost. RANEY®-type nickel is widely used as a versatile 50) was purchased from Zeolyst International, USA. Methanol
catalyst in such a hydrotreatment process for reductive trans- (99.8%), 2-propanol (99.7%), ethyl acetate (99.5%), benzene
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(99.5%), n-hexane (99%), cyclohexane (99%), toluene (99.7%), 2.3 Catalytic microwave-induced pyrolysis of lignocellulosic
n-heptane (99%), methylcyclohexane (99%), p-xylene (99%), biomass
ethylbenzene (99%), 1H-indene (97%), indane (95%), naphtha-
A Sineo MAS-II batch microwave oven (Shanghai, China) with a
rated microwave power of 1000 W was employed for microwave
lene (99.6%), 1,2,3,4-tetrahydronaphthalene (97%), decahydro-
naphthalene (98%), 1-methylnaphthalene (96%),
-methylnaphthalene (97%), n-dodecane (99%), anthracene
99%), pyrene (98%), and nickel–aluminum alloy powder in
the unactivated form were used as purchased from Alfa Aesar
Ward Hill, MA, USA). 1,2-Dimethylcyclohexane (99%), 1,3-di-
methylcyclohexane (99%), 1,4-dimethylcyclohexane (99%),
ethylcyclohexane (99%), 1,2,4-trimethylbenzene (98%), 1,2,4-
trimethylcyclohexane (97%), propylcyclohexane (99%), hexa-
hydroindan (99%), bicyclohexyl (99%), perhydrofluorene
pyrolysis. The detailed experimental setting was described in
2
(
29,37
our previous studies.
Fig. S1† shows the schematic
diagram of the microwave-assisted pyrolysis system integrated
with the catalysis process. A fixed amount of Douglas fir
sawdust pellets (25 g) for each run was placed in a 500 mL
quartz flask inside the microwave oven. 0.05 g of activated
carbon powder was used as the absorber for the microwave-
assisted pyrolysis. The system was purged with nitrogen at a
(
−1
flow rate of 1000 mL min for 15 min prior to pyrolysis reac-
(
(
97%), tetradecahydroanthracene (99%), and RANEY® Ni 4200
slurry in water) in the activated form were supplied by Sigma-
tion to maintain an oxygen-free environment. The microwave
pyrolysis was conducted at the temperature of 480 °C for
Aldrich Corporation (St Louis, MO, USA).
1
0 min, which could maximize the pyrolytic volatile yield as
2
9,38,39
reported in our previous studies.
The pyrolytic volatile
2
.2 Catalyst preparation
vapors from the flask were passed through a packed bed cata-
lysis reactor which was filled with the catalyst. The customized
packed-bed reactor was constructed from quartz and externally
heated by using a heating tape. A thermocouple was intro-
duced between the reactor and the heating tape to measure
catalytic temperatures. As reported in previous work, the
optimal temperature to maximize the composition of jet fuel
The activity of parent ZSM-5 was improved by subjecting it to
both hydrothermal and calcination treatments. Under gentle
stirring, parent ZSM-5 powder was added into deionized water
(mass ratio = 1) at 60 °C. After addition, the mixture was
stirred continuously for 2 h under these conditions. The slurry
was then dried at 105 °C till constant weight. The above
process was followed by catalyst calcination: hydrothermally
treated ZSM-5 was calcined at 550 °C for 5 h in a muffle
furnace. The catalysts were pelletized and sieved with
29
range aromatics was set at 500 °C. In this regard, the catalytic
temperature was held at 500 °C and the catalyst (7.5 g) to
biomass ratio was kept constant at 0.3. The condensable liquid
was collected as bio-oil. The non-condensable vapors escaped
as gas at the end of the condensers and were collected for ana-
lysis. The catalytic microwave pyrolysis was duplicated two
times in order to obtain abundant bio-oils which were stepwise
mixed together for the hydrogenation process.
2
0–40 mesh. The main characteristics of the catalyst were
3
6
reported in our previous study.
Non-pyrophoric RANEY® nickel (referred to as NP Ni) was
prepared from metallic alloy powders. Under gentle stirring,
Ni–Al alloy powders (2 g) were slowly impregnated with a
1
.2 wt% NaOH aqueous solution (20 mL) at room temperature.
After the addition, the temperature was elevated from room
temperature to 80 °C and held for 30 min. An additional 2 mL
2.4 Hydrogenation of model compounds in diverse solvents
of 12 wt% NaOH aqueous solution was added to the slurry and To evaluate the effect of diverse solvents on the hydrogenation
stirred gently at 80 °C for 30 min for further alkali leaching. of model compounds, a closed reaction system with a stirred
Subsequently the sample was washed to neutrality using dis- stainless batch reactor, the 4592 micro stirred reactor (with a
tilled water and stored in water for future catalytic use.
50 mL vessel), and a 4848 reactor controller from Parr Instru-
The home-made RANEY® nickel catalyst was developed ment Company (Moline, IL, USA) was used (see Fig. S2†). In
using a 20 wt% NaOH aqueous solution to remove Al by the our previous study, naphthalene and its derivatives were the
following procedure. 2 g of the above Ni–Al was slowly added most abundant compositions in the bio-oils obtained from
2
9
into 20 mL of NaOH aqueous solution under gentle stirring. catalytic microwave pyrolysis of Douglas fir sawdust pellets;
After the addition, the slurry was stirred continuously at 80 °C thus it is more appropriate to use naphthalene as the model
for 1 h. The excess of sodium hydroxide was finally washed compound for the hydrogenation reaction. Naphthalene (1 g),
with distilled water until nearly neutral pH was reached. The RANEY® Ni 4200 (0.1 g), and solvent (7 g) were placed in the
obtained RANEY® nickel catalyst was stored in water. In order reactor. The solvents used were methanol, 2-propanol, ethyl
to test the catalytic performance of RANEY® nickel manufac- acetate, benzene, n-hexane, cyclohexane, toluene, n-heptane,
tured by the process, RANEY® nickel 4200 (referred to as methylcyclohexane, decalin, and n-dodecane. Then the reactor
RANEY® Ni 4200) purchased in the activated form was used was sealed and vented five times with hydrogen to get rid of
for catalyzing the hydrogenation reaction of bio-oils. RANEY® the air present in the vessel. Hydrogen was subsequently
nickel is notorious for its pyrophoricity, and it may ignite adjusted to reach the set pressure (500 psi). An automatic con-
spontaneously when dried in air. The RANEY® Ni 4200 slurry troller was employed to control the temperature and the revo-
and the home-made RANEY® nickel catalyst were thus dried at lution of the stirrer (300 rpm). The pressure inside the reactor
6
0 °C till constant weight under the atmosphere of nitrogen to was recorded and the reactions proceeded at the set tempera-
avoid contact with air, prior to the subsequent catalytic test.
ture (200 °C) for 2 h. After the experiment was complete, stir-
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ring was stopped and the reactor was rapidly cooled to (Inficon Inc., Santa Clara, CA, USA) system with a thermal conduc-
ambient temperature. Then, the gas was collected for analysis tivity detector (TCD). A standard gas mixture consisting of H , N ,
2
2
and the reactor was depressurized. Consequently the liquid CH
product was filtered to remove the catalyst particles. yield of non-condensable gas. Alkanes and olefins (>C
samples were either not detected or negligible in this research.
4
, CO, CO
2
, C
2
H
4
, C
2
H
6
, and C
3
H
6
was used to calibrate the
4
) in gas
2
.5 Hydrotreatment of bio-oil derived from catalytic
microwave pyrolysis
2.7 Data evaluation
The combined bio-oils evolved from catalytic microwave pyro-
lysis were extracted with the optimal solvent after determining
the effects of all solvents on the hydrogenation process. To
produce the jet fuel range cycloalkanes, a mixture of organics
and the optimum solvent was loaded into the reactor together
with 10 wt% or 20 wt% catalysts (in terms of the reactants).
The reactor was flushed with hydrogen and then tightly closed.
The experiments for each run were performed at 150, 200, or
The coke mass was determined by the difference before and
after the catalytic pyrolysis. The weight of non-condensable gas
was calculated using the following equation:
Gas mass ¼ biomass mass ꢀ liquid mass
ð1Þ
ꢀ char mass ꢀ coke mass
Conversion of naphthalene, the overall carbon yields of the
liquid, gas, and solid products, and the carbon selectivity of a
specific product were calculated based on the following
equations.
2
50 °C under stirring (300 rpm) for the intended time. The
final step conducted was the same as the aforementioned
hydrogenation of model compounds.
moles of naphthalene reacted
Conversion of naphthalene ¼
2
.6 Analytical techniques
moles of naphthalene fed in
Elemental analysis (C, H, N, and O) of Douglas fir sawdust
pellets, liquid samples, char, and coke deposited on the spent
catalysts was conducted using a 2400 Series II CHN/O Elemen-
tal Analyzer (PerkinElmer, USA).
The textural properties of the catalyst were determined by
means of N2 adsorption–desorption analysis (Micromeritics
TriStar II 3020 Automatic Physisorption Analyzer). Fresh
samples were degassed in a vacuum at 300 °C for 1 h. The Bru-
nauer–Emmett–Teller equation was applied to calculate the
ꢁ
100%
ð2Þ
ð3Þ
moles of carbon in a product
moles of carbon fed in
Carbon yield ¼
ꢁ 100%
moles of carbon in a product
moles of carbon in identified products
100%
Carbon selectivity ¼
ꢁ
ð4Þ
o
specific surface area using adsorption data at p/p = 0.05–0.25.
The pore volume was evaluated by using the Barrett–Joyner–
Halenda (BJH) method.
3
3
. Results and discussion
Powder X-ray diffraction (XRD) patterns were recorded on a
Rigaku SmartLab X-ray diffractometer equipped with a Cu Kα
X-ray source operating at 40 kV and 40 mA. The scattering
angle 2θ was varied from 10° to 80°.
.1 Catalytic transformation of lignocellulosic biomass into
–C16 aromatics
To produce jet fuel range cycloalkanes, the transformation of
–C16) aromatics
the samples were measured with a scanning electron micro- is primarily required. The water content of bio-oils obtained
scope (SEM, FEI Quanta 200 F). was close to 20 wt% (based on biomass loading), which was
C
8
The particle size distribution and surface morphology of lignocellulosic biomass into jet fuel range (C
8
The chemical composition of the bio-oils was determined derived from both the moisture of raw biomass and the sub-
by using an Agilent 7890A GC-MS (GC–MS; GC, Agilent 7890A; sequent dehydration reaction during biomass pyrolysis. The
MS, Agilent 5975C) with a DB-5 capillary column. The GC was yield of organics (7.52 g) in the bio-oils accounted for
first programmed to heat to 45 °C for 3 min followed by 15.04 wt%, prior to the extraction process. The overall carbon
−
1
heating to 300 °C at a rate of 10 °C min . The injection yield distribution by catalytic microwave pyrolysis of biomass
sample size was 1 μL. The flow rate of the carrier gas (helium) is shown in Fig. 1(A). It is noteworthy that the char was found
was 0.6 mL min− . The ion source temperature was 230 °C for to be the dominant composition, occupying 37.37%
the mass selective detector. Compounds were identified by (Table S2†). It was also noted that the carbon yield (34.57%) of
comparing the spectral data with those from the NIST Mass non-condensable gas was calculated by difference. The gas was
Spectral library. The area percent of the changed concen- mainly comprised of hydrogen, carbon dioxide, carbon monox-
trations of model compounds obtained from GC/MS results ide, and methane, originating from decarboxylation, decarbo-
1
was utilized to predict the product concentration in bio-oils.
nylation, cracking, and oligomerization reactions. In addition,
The moisture content in the bio-oils was determined by 24.68% carbon yield of aromatics was obtained after mixing all
using a Karl Fischer (KF) compact titrator (V20 Compact Volu- bio-oils obtained from catalytic microwave pyrolysis of Doulas
metric KF Titrator, Mettler-Toledo).
fir sawdust pellets (for details see Table S3†). In contrast, the
The gaseous product was collected in a 1 L Tedlar gas bag and carbon yield (3.38%) of catalyst coke was much lower than
2
7,28,40,41
then analyzed offline by using an INFICON 3000 Micro-GC other studies reported elsewhere.
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Table 1 Effect of various solvents on the hydrogenation reaction of
a
naphthalene
Carbon selectivity
(
C mol%)
Entry
Solvent
Conv. (%)
Tetralin
Decalin
1
2
3
4
5
6
7
8
9
Methanol
22.6
99.9
100
95.2
99.9
99.9
98.9
100
15.1
52.9
77.1
86.1
7.1
13.4
86.8
0.1
7.5
47.0
22.9
9.1
92.8
86.5
12.1
99.9
69.5
99.5
67.4
2-Propanol
Ethyl acetate
Benzene
n-Hexane
Cyclohexane
Toluene
n-Heptane
Methylcyclohexane
Decalin
99.9
100
100
30.4
0.5
32.6
1
1
0
1
n-Dodecane
a
Reaction conditions: naphthalene (0.0078 mol), solvent (7 g),
RANEY®Ni 4200 (0.1 g, 10 wt% with respect to reactant mass), 500 psi
(initial pressure), 200 °C for 2 h.
H
2
Fig. 1 Overall carbon yield distribution (A) and the carbon selectivity of
main aromatics (B) for extracted bio-oils from catalytic microwave pyrol-
ysis of Douglas fir sawdust pellets.
solvent effect on the hydrogenation of naphthalene demon-
strates that the reaction medium could promote the catalytic
The carbon selectivity of main aromatics obtained from transformation. The experiment conducted in methanol
catalytic microwave pyrolysis of Douglas fir sawdust pellets is achieved only 22.6% conversion of naphthalene (entry 1). A
depicted in Fig. 1(B). Generally the typical compositions trace amount of decalin (7.5% toward carbon selectivity) was
belong to the lumps of jet fuel range aromatic hydrocarbons, detected in this solvent. The results imply that RANEY® Ni
including monocyclic and polycyclic aromatic hydrocarbons. 4200 could be poisoned when hydrogenation was conducted in
The carbon selectivity towards xylenes was 12.54%, which was neat methanol, which is identical to the study reported else-
3
5
the dominant share in the liquid organics. Other monocyclic where. Unlike the inhibition effect of methanol, both 2-pro-
aromatic hydrocarbons, e.g. indene (5.06% carbon selectivity) panol and ethyl acetate led to almost full conversion of the
and indane (2.99% carbon selectivity), were also obtained. The substrate. 47.0% carbon selectivity of decalin in 2-propanol
large amount of polycyclic aromatic hydrocarbons including medium was obtained from the hydrogenation reaction of
naphthalene and its derivatives was evolved from oligomeriza- naphthalene, which is remarkably superior to 22.90% carbon
4
2,43
tion reactions of monocyclic aromatic hydrocarbons.
The selectivity conducted in the medium of ethyl acetate. It is well
carbon selectivity of naphthalene and 2-methylnaphthalene established that 2-propanol could serve as the H-donor in the
4
4
was 10.77% and 12.30%, respectively. The results imply that hydrogen transfer during hydrogenation. Hence, 2-propanol
polycyclic aromatic hydrocarbons were the most abundant as the reaction medium could facilitate the hydrogenation
compounds. Other polycyclic aromatic hydrocarbons with reaction of tetralin to decalin.
three rings had low carbon selectivity, the corresponding
Among the solvents of aromatic hydrocarbons (benzene
and toluene), over 95% naphthalene was converted; however
poor conversions were obtained in decalin (9.1% and 12.1%,
respectively). It was probably due to the unsaturated solvents
carbon number of most of which did not exceed C16
.
3
.2 Solvent effects on the hydrogenation of naphthalene
Aiming to ultimately determine the solvent effect on the hydro- which would have first attached to the surface of RANEY® Ni
genation of aromatics-enriched bio-oils evolved from catalytic 4200 and then reacted with the hydrogen absorbed on the
microwave pyrolysis, we first explored the influence of various surface. The competitive reaction resulted in insufficient
solvents on the hydrogenation reaction of a model compound hydrogen and active sites of the catalyst for the hydrogenation
(
naphthalene). Table 1 summarizes the results of hydrogen- reaction of tetralin to decalin. Conducting the reaction in
ation of naphthalene with RANEY® Ni 4200 performed in alkanes (entries 5 and 6, 8–11), however, contributed to very
several solvents under 500 psi H (initial pressure) at 200 °C high to full conversion: n-hexane (99.9%), cyclohexane
2
for 2 h. As for all experiments, only unreacted hydrogen was (99.9%), n-heptane (100%), methylcyclohexane (99.9%),
detected at the end of reactions, implying that the reactions decalin (100%), and n-dodecane (100%). For maximizing the
were not carried out under hydrogen starved conditions. The hydrogenation of naphthalene to decalin, n-heptane showed
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the best conversion (99.9% carbon selectivity), compared with
n-hexane (92.8%), cyclohexane (86.5%), methylcyclohexane
(69.5%), decalin (99.5%), and n-dodecane (67.4%). As n-heptane
does not dissolve in water but display good extraction perform-
35
ance, n-heptane is the desired solvent that should be used for
extracting the aromatics-enriched bio-oils. Moreover n-heptane
2
is an essential compound in JP-4 and Jet A, the hydrogenated
mixture including cycloalkanes and n-heptane can be directly
utilized as jet fuels or drop-in fuels. Meanwhile, pure cycloalk-
anes can be separated with n-heptane through vaporization.
Accordingly, the results revealed that the hydrogenation reaction
heavily depended on the solvents employed; n-heptane was the
optimal solvent, which was then used for extracting aromatics-
enriched bio-oils and hydrogenation reactions.
3
.3 In situ hydrogenation of extracted bio-oils
.3.1 The effect of catalyst loading on the chemical compo-
3
sition of hydrogenated bio-oils. Given the water influence on
the hydrogenation process, the mixed bio-oils from catalytic
microwave pyrolysis were extracted with the optimum solvent.
7
.02 g of liquid organics (∼14 wt%, based on biomass mass)
were extracted using n-heptane (40 g). The loss of organics
0.5 g) in the aqueous phase can be neglected when consider-
(
ing that the recovery of organics could reach ∼94 wt%. Since
the bio-oils produced by catalytic microwave pyrolysis of intact
biomass principally consisted of C –C range aromatics, aro-
matics with 8–16 carbon numbers are considered as precur-
sors of jet fuels. According to the hydrogenation reaction of
the model compound in the medium of n-heptane, naphthal-
ene of 99.9% carbon selectivity was converted into saturated
Fig. 2 Overall product distribution (A) and the carbon selectivity of
partial aromatics (B) with respect to catalyst loading. Reaction con-
ditions: reaction temperature, 200 °C; initial pressure, 500 psi; reaction
time, 2 h.
8
16
decalin. It is well known that decalin is the most abundant pletely hydrogenated into hydro-cyclic alcohols under the con-
4
5
cycloalkane in jet fuels. These conditions set a standard for ditions of sufficient catalyst loading. The amount of aromatic
designing the following hydrogenation reaction of extracted hydrocarbons decreased as the catalyst loading was increased,
bio-oils, thus the ratio of the reactant to the solvent was set at implying that more active sites were offered for catalyzing the
1
: 7. In this respect, an additional solvent (9.14 g) was added aromatic intermediates to hydro-aromatic hydrocarbons or
into the extracted bio-oils, maintaining the ratio at 1 : 7. Sub- cycloalkanes. Other oxygenated aromatics showed slight vari-
sequently, the extracted bio-oils (C
–C16 aromatics) were hydro- ations influenced by catalyst loading, varying from 7.50 to
8
genated by using several variables under low-severity conditions. 5.77%. These results indicate that hydrogenated reactions were
The product distribution is summarized as a function of remarkably impacted by the catalyst loading.
catalyst loading (10 wt% and 20 wt% with respect to reactant
The effect of catalyst loading on the carbon selectivity of
mass) in Fig. 2(A). It was observed that cycloalkanes as a sig- partial cycloalkanes is explained in Fig. 2(B). Catalyst loading
nificant composition of jet fuels were in the range of 32.22 to did not have a vital influence on the carbon selectivity of
5
8.90% based on the GC/MS peak area, depending on the monocyclic cycloalkanes. These results indicate that monocyc-
alteration of catalyst loadings. More than half of the aromatic lic aromatic hydrocarbons tend to hydrogenate into mono-
intermediates were converted into jet fuel range cycloalkanes cyclic alkanes even in the presence of low catalyst loading. Two
using 20 wt% RANEY® Ni 4200, whose amount in hydro- aromatic rings of naphthalenes were coplanar and one aro-
genated bio-oils was equal to that in JP-5. Unsaturated hydro- matic ring was readily hydrogenated into a saturated ring;
carbons (hydro-aromatic hydrocarbons and cycloolefins) however the aromatic ring and cyclic alkane ring of tetralin
3
1
partially hydrogenated in the process accounted for were no longer coplanar after hydrogenation. The other aro-
6.81–11.01% and 9.04–10.31%, respectively. The variation of matic ring was thus directed away from the catalyst surface,
3
hydro-aromatic hydrocarbons (e.g. tetralin) was significantly preventing the reduction. If more adequate catalysts were pro-
impacted by the catalyst loading. Adequate catalyst loading vided, the other aromatic ring could also be hydrogenated at
could impel the hydro-aromatic hydrocarbons to be hydro- the spare active sites. It is obvious that the carbon selectivity of
genated into cycloalkanes. Catalyst loading also had a crucial both hexahydroindan (C H16) and decalin (C10H18) increased
9
influence on the selectivity of hydro-cyclic alcohols, occupying when more RANEY® Ni 4200 catalyst was added into the
from 4.74 to 11.74%, which suggests that phenols were com- reactor. In addition, the carbon selectivity of bicyclohexyl
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4
6
(C
12
H
22), perhydrofluorene (C13
H22), and tetradecahydro- through hydrogenolysis reactions. It was found that the
anthracene (C H ) gradually increased as more catalysts were amount of hydrocyclic alcohols was much lower at 250 °C than
1
4
24
employed. These results reveal that more catalyst loading, which that at 200 °C. It can also be seen that the amount of other oxy-
means that more active sites were offered on the RANEY® Ni genated aromatics was also declined to 4.71% at 250 °C. In the
4
200 surface, gave rise to more hydrogenated reactions.
gas fraction, the total amount (less than 1 vol%) of small
3
.3.2 The effect of reaction temperature on the chemical hydrocarbons (such as methane, ethane, propane) was also
composition of hydrogenated bio-oils. Based on the previous detected at 250 °C, which could be produced by hydrocracking
result, a catalyst loading of 20 wt% was feasible for the follow- of larger hydrocarbons. These results suggest that hydrogeno-
ing experiments. In order to further understand chemical reac- lysis and hydrocracking except for hydrogenation reactions
tions in the process and obtain more insight into could take place at high reaction temperatures.
hydrogenated bio-oils, the chemical compounds of hydrogen-
The reaction temperature also had a significant influence
ated bio-oils are elucidated as a function of reaction tempera- on the carbon selectivity of specific cycloalkanes. It is note-
ture in Table 2. It can be seen that the reaction temperature worthy that monocyclic alkanes significantly increased as the
had a significant effect on the in situ hydrogenation reactions. reaction temperature increased, especially from 200 to 250 °C.
The amount of total cycloalkanes progressively increased with Meanwhile, ethylcyclohexane (C H16) dramatically increased
8
the increasing reaction temperatures. It was noticed that from 0.95 to 3.90%, which suggests that high reaction temp-
cycloalkanes were in the range from 47.43% at 150 °C to eratures improved hydrocracking reactions of polycyclic
6
3.34% as the reaction temperature increased to 250 °C, imply- alkanes after being hydrogenated. The carbon selectivity of
ing that a high reaction temperature favored the hydrogenation hexahydroindan was slightly influenced by the changed reaction
reactions. Furthermore, there is a minor selectivity for cyclo- temperature when it was set in the range of 200–250 °C. It
olefins, generally decreased from 9.48 to 5.20% alongside the showed that all indane and indene in the extracted bio-oils were
increment of reaction temperature. Therefore, an elevated completely hydrogenated into hexahydroindan under these con-
temperature could enhance the hydrogenation reaction of ditions. Likewise, there was a small upward trend for decalin
olefins into cycloalkanes. Hydroaromatic hydrocarbons and carbon selectivity, which gradually increased from 12.67 to
aromatic hydrocarbons experienced declined tendencies 15.63%. The carbon selectivity of other polycyclic alkanes
(20.76–11.07% and 8.32 to 2.20%, respectively) as the reaction showed a steady increment, which implies that the hydrogen-
temperature went up to 200 °C, whereas the two compositions ated reactions of polycyclic aromatic intermediates could also
displayed an increased trend as the reaction temperature be facilitated by increasing the reaction temperature.
increased from 200 °C to 250 °C. This is because the elevated
3.3.3 The effect of reaction time on the chemical compo-
reaction temperature possibly favored the scission of the sition of hydrogenated bio-oils. Apart from catalyst loading
hydroxyl group from phenyl to form aromatic hydrocarbons and reaction temperature, reaction time was another crucial
factor that influenced product distribution and cycloalkanes’
carbon selectivity as shown in Table 3. In particular, the
Table 2 Product distribution and partial cycloalkanes’ carbon selecti- product distribution prominently shifted towards the cyclo-
a
vity as a function of reaction temperature
alkanes (39.62–71.92%) with increasing reaction time,
suggesting that hydrogenation reactions were enhanced
because of the longer reaction duration. The amount of cyclo-
olefins appeared to increase slightly to 11.15% at a prolonged
reaction time (3 h). The total amount of hydro-aromatic hydro-
carbons distantly declined, ranging from 29.24 to 0.51%. Like-
Temperature (°C)
1
50
200
250
Overall selectivity (% in area)
Cycloalkanes
Cycloolefins
Hydro-aromatic hydrocarbons
Hydro-cyclic alcohols
Aromatic hydrocarbons
Other oxygenated aromatics
47.43
9.48
20.76
8.34
8.32
5.67
58.90
10.31
11.07
11.74
2.20
63.34
5.20 wise, the selectivity of aromatic hydrocarbons experienced a
16.09
3.78
6.88
downward trend from 9.67 to 1.82%. The prolonged reaction
time could give rise to ring reduction of aromatic hydrocar-
4.71 bons, which resulted in the decrease of aromatic hydrocarbons
to form hydro-aromatic hydrocarbons. Owing to the more time
provided for the reaction, the production of cycloalkanes was
1.80 likely facilitated by means of hydrogenating the related hydro-
cyclic aromatic hydrocarbons. It was noted that the total
amount of hydrocyclic alcohols was significantly impacted by
1.71 the prolonged reaction time especially going from 1 to 2 h.
5.77
Cycloalkanes’ selectivity (C mol%)
1
1
1
,4-Dimethylcyclohexane
,3-Dimethylcyclohexane
,2-Dimethylcyclohexane
1.06
1.23
—
1.18
—
1.35
0.53
0.95
0.29
0.79
10.84
15.13
0.71
1.13
2.90
0.40
3.90
0.35
Ethylcyclohexane
,2,4-Trimethylcyclohexane
0.87
0.23
0.68
9.43
12.67
0.67
1.04
2.01
1
Propylcyclohexane
Hexahydroindan
Decalin
Bicyclohexyl
Perhydrofluorene
Tetradecahydroanthracene
10.66
15.63
1.14
—
The carbon selectivity for mono-cyclic alkanes increased,
especially for ethylcyclohexane (0.87–3.04%), as the reaction
time was elevated, whilst the carbon selectivity for hexa-
hydroindan and decalin decreased for the period of 2–3 h. Aro-
matic intermediates have already been converted into the
corresponding cycloalkanes in 2 h. The prolonged time (3 h)
2.49
a
Reaction conditions: initial pressure, 500 psi; RANEY® Ni 4200,
0 wt% with respect to reactant mass; reaction time, 2 h.
2
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Table 3 Product distribution and partial cycloalkanes’ carbon selecti-
vity on the basis of the reaction time
Table 4 Product distribution and partial cycloalkanes’ carbon selecti-
vity in the presence of various catalysts
a
a
Reaction time (h)
Catalyst categories
1
2
3
RANEY®
Ni 4200
Home-made
RANEY® Ni
NP Ni
Overall selectivity (% in area)
Cycloalkanes
Cycloolefins
Hydro-aromatic hydrocarbons
Hydrocyclic alcohols
Aromatic hydrocarbons
Other oxygenated aromatics
39.62
9.27
29.24
5.22
9.67
6.98
58.90
10.31
11.07
11.74
2.20
71.92 Overall selectivity (% in area)
11.15 Cycloalkanes
0.51 Cycloolefins
10.06 Hydro-aromatic hydrocarbons
1.82 Hydrocyclic alcohols
4.55 Aromatic hydrocarbons
Other oxygenated aromatics
59.51
8.94
12.33
9.93
3.09
6.20
58.90
10.31
11.07
11.74
2.20
84.59
2.83
0.60
6.84
0.99
4.15
5.77
5.77
Cycloalkanes’ selectivity (C mol%)
1,4-Dimethylcyclohexane
1,3-Dimethylcyclohexane
1,2-Dimethylcyclohexane
1.02
1.11
0.23
0.87
0.34
0.76
5.02
14.15
0.64
0.67
2.22
1.18
—
—
Cycloalkanes’ selectivity (C mol%)
1.47 1,4-Dimethylcyclohexane
—
1.18
—
—
0.53
0.95
0.29
0.79
10.84
15.13
0.71
1.13
2.90
—
1,3-Dimethylcyclohexane
3.04 1,2-Dimethylcyclohexane
1.00 Ethylcyclohexane
0.94 1,2,4-Trimethylcyclohexane
10.26 Propylcyclohexane
14.51 Hexahydroindan
0.77 Decalin
3.80
0.36
0.99
0.39
1.09
11.05
14.29
0.69
0.64
2.47
4.10
0.66
4.18
1.37
1.65
8.09
16.69
1.13
1.04
3.12
Ethylcyclohexane
,2,4-Trimethylcyclohexane
0.53
0.95
0.29
0.79
10.84
15.13
0.71
1.13
2.90
1
Propylcyclohexane
Hexahydroindan
Decalin
Bicyclohexyl
Perhydrofluorene
Tetradecahydroanthracene
0.77 Bicyclohexyl
3.23 Perhydrofluorene
Tetradecahydroanthracene
a
Reaction conditions: initial pressure, 500 psi; RANEY® Ni 4200,
0 wt% with respect to reactant mass; reaction temperature, 200 °C.
a
2
Reaction conditions: initial pressure, 500 psi; catalyst, 20 wt% with
respect to reactant mass; reaction temperature, 200 °C; reaction time, 2 h.
could allow the cycloalkanes to be hydrocracked and oligomer- detected when using home-made RANEY® Ni, suggesting that
ized, forming monocyclic alkanes or derivatives. For the gas aromatic intermediates were thoroughly hydrogenated into
resulting from the reaction of 3 h, a trace volume of hydrocar- cycloalkanes. As such, the content of hydrocyclic alcohols had
bons was found, suggesting that the hydrocracking and oligo- the same tendency as hydroaromatic hydrocarbons and aro-
merization reactions have taken place in the process. In matic hydrocarbons, which indicates that partial hydrocyclic
contrast, polycyclic aromatic hydrocarbons with three rings are alcohols could be converted into cycloalkanes via the scission
very difficult to be hydrogenated due to their structures. of the hydroxyl group. There was the lowest amount of other
Prolonging the reaction time to 3 h could make these poly- oxygenated aromatics in the hydrogenated bio-oils using
cyclic aromatic intermediates totally hydrogenated, thereby home-made RANEY® Ni as the catalyst, implying that hydroge-
improving the carbon selectivity of polycyclic alkanes. Where- nolysis reactions also took place in the process. Small hydro-
fore these results indicate that prolonging the reaction time carbons detected in the gas revealed that these hydrocarbons
can principally enhance the hydrogenation reactions; hydro- with a small volume were from the hydrocracking and hydroge-
cracking and oligomerization reactions may also occur jointly nolysis of larger hydrocarbons.
in the process after 2 h reaction time.
It was found that the carbon selectivities of both dimethyl-
3
.3.4 The effect of catalyst selection on the chemical com- cyclohexane and ethylcyclohexane were the maximum in the
position of hydrogenated bio-oils. The chemical composition presence of home-made RANEY® Ni. Other monocyclic
of hydrogenated bio-oils in the presence of various catalysts alkanes such as propylcyclohexane and trimethylcyclohexane
(
NP Ni, RANEY® Ni 4200, and home-made RANEY® Ni) is have also shown the largest carbon selectivity. Therefore
depicted in Table 4. Compared with the overall product distri- home-made RANEY® Ni was the optimal catalyst for the pro-
bution over RANEY® Ni 4200 in the purchased form, the result duction of monocyclic alkanes. Of the catalysts, home-made
over NP Ni was similar under the same conditions; while the RANEY® Ni displayed the lowest carbon selectivity for hexa-
result for producing cycloalkanes in the presence of home- hydroindan. These results indicate that hexahydroindan
made RANEY nickel was more superior to the others. It was formed was possibly hydrocracked over the catalyst, thereby
observed that 84.59% selectivity towards cycloalkanes was forming more monocyclic alkanes. Unlike hexahydroindan,
achieved, which was even better than the result using RANEY® the carbon selectivities for decalin, bicyclohexyl, and tetradeca-
Ni 4200 when the reaction time was 3 h. The total amount hydroanthracene were all the highest when using the home-
(
less than 5%) of cycloolefins was acquired in the presence of made RANEY® Ni as the catalyst. These outcomes imply that
home-made RANEY® Ni, whose amount meets the specifica- employing home-made RANEY® Ni as the catalyst could
tions of commercial jet fuels. Small amounts of hydro- improve the overall selectivity of cycloalkanes, and obtain the
aromatic hydrocarbons and aromatic hydrocarbons were highest carbon selectivity for monocyclic alkanes.
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Table 5 Textural properties of the Ni–Al alloy, NP Ni, RANEY® Ni 4200 3.4 Catalyst characterization
a
and home-made RANEY® Ni catalysts
During alkali leaching, Al in the Ni–Al alloy powder was
reacted with a NaOH solution. In this respect, it is expected
that RANEY® Ni is primarily comprised of metallic nickel.
When the Al/NaOH stoichiometry is more than 1, insoluble
S
(
BET
V
pore
S
pore
d
pore
(nm)
m g−1)
2
(cm g−1)
3
(m g−1)
2
Ni–Al alloy
NP Ni
RANEY® Ni 4200
Home-made RANEY® Ni
0.35
0
0
0
Al(OH)
water.
3
7
was also formed by the reaction between Al and the
Therefore NP-Ni produced with an insufficient
157.7
38.1
52.4
0.048
0.112
0.034
38.2
43.0
35.8
5.0
10.4
3.8
4
amount of NaOH is regarded as a Ni–Al(OH)
3
catalyst.
a
S
BET: BET surface area; Vpore: pore volume; Spore: pore surface area; However, there is also a small amount of residual hydrated
pore: average pore size.
d
alumina absorbed in the spongy structure of RANEY® Ni, as
4
7
illuminated by Zhu et al. The textural properties of NP-Ni,
RANEY® Ni 4200 and home-made RANEY® Ni, compared with
the parent Ni–Al alloy powder, are illustrated in Table 5. The
BET surface area, pore volume, and pore surface area of all
catalysts were significantly improved by the alkali treatments.
After dissolution of the Al component, the BET surface area of
the home-made RANEY® Ni dramatically increased from 0.35
2
−1
to 52.4 m
g , which is higher than that of purchased
2
−1
RANEY® Ni 4200 (38.1 m
g
) and other RANEY® Ni cata-
4
8
lysts.
The decent BET surface area of the home-made
RANEY® Ni assisted the adsorption of hydrogen on the
surface of the catalyst for the hydrogenation reaction. The cata-
lytic activity of NP-Ni was probably inhibited by the large
amount of hydrated alumina adsorbed in the structure,
although the NP-Ni has the highest BET surface area. Besides
Fig. 3 The XRD patterns of the Ni–Al alloy powder, NP-Ni, RANEY® Ni
200, and home-made RANEY® Ni.
4
Fig. 4 SEM images of the Ni–Al alloy powder (A), NP-Ni (B), RANEY® Ni 4200 (C), and home-made RANEY® Ni (D).
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3
−1
2
−1
0
.034 cm g of pore volume and 35.8 m g of pore surface
The SEM images of Ni–Al alloy powder, NP-Ni, RANEY® Ni
area for the home-made RANEY® Ni were also generated. The 4200 and the home-made RANEY® Ni are shown in Fig. 4. The
average pore size of the home-made RANEY® Ni is 3.8 nm. morphological differences between Ni–Al alloy powder and the
The suitable average size is close to the monocyclic aromatics other three catalysts are readily visible from Fig. 4 (A)–(D). It
diameter, thus monocyclic aromatics are prone to adsorption was observed that both RANEY® Ni 4200 and the home-made
4
9
in the pores.
RANEY® Ni are constituted of the typical fractured and angular
5
1
Fig. 3 outlines the XRD patterns of the Ni–Al alloy, NP Ni, particles, which are in line with other reports, while Ni–Al
RANEY® Ni 4200 and home-made RANEY® Ni. The XRD pat- alloy powder shows the intact metallic structure. The small
terns of the Ni–Al alloy indicate that it consists of two kinds of particles of home-made RANEY® Ni are more dispersive in com-
3 2 3
Ni Al and Ni Al domains. After dissolving the Al component parison with RANEY® Ni 4200, confirming a higher BET
in a 20 wt% NaOH solution, the diffractions with respect to surface. For NP Ni, it is composed of nickel angular particles
47
metallic Ni were observed suggesting the amorphous nature of and irregularly oriented aluminum crystal-like particles.
both RANEY® Ni 4200 and home-made RANEY® Ni. They
mainly displayed the diagnostic (111), (200), and (220) diffrac-
3
.5 Reaction pathway for the conversion of lignocellulosic
5
0
biomass into jet fuel range cycloalkanes
was formed These observations are the key points to propose the reaction
and identified according to the peaks assignable to gibbsite pathway for the conversion of lignocellulosic biomass into jet
and bayerite.
fuel range cycloalkanes. Based on the quantified product dis-
tions of fcc Ni at a 2θ of 44.5, 51.8, and 76.3°, respectively.
With regard to NP Ni, the large content of Al(OH)
3
Fig. 5 Proposed reaction pathways for the conversion of lignocellulosic biomass into jet fuel range cycloalkanes.
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tribution in this study, and the related results from direct formed in the form of cycloalkanes, rather than water. The
microwave pyrolysis of woody biomass and catalytic microwave home-made RANEY® nickel is the optimum catalyst to obtain
36,38
pyrolysis of cellulose,
the overall reaction network (includ- the highest selectivity of jet fuel range cycloalkanes. It is more
ing catalytic microwave pyrolysis and the hydrogen saving likely that these high-yield cycloalkanes mixed with minor aro-
process) is summarized and shown in Fig. 5. In the primary matics and cycloolefins can potentially be used as additives in
route from lignocellulosic biomass to jet fuel range cyclo- jet fuels. From this perspective, these integrated processes by
alkanes, cellulose underwent a series of dehydration, decar- using inexpensive catalysts and intact biomass under the mild
boxylation, and decarbonylation to form furan compounds conditions deliver a novel and feasible route, specifically tar-
3
6,52
during catalytic pyrolysis.
These furans then went through geting jet fuel range cycloalkanes. Future efforts will be
decarbonylation, aromatization, and oligomerization reactions directed towards improving the carbon yield of aromatics
inside the pores of well-promoted ZSM-5 to form aromatic obtained from catalytic microwave pyrolysis and implementing
hydrocarbons. Likewise, we observed that hemicellulose was an economic analysis in a biorefinery based on the integral
3
8
decomposed into furan compounds, which was identical to process.
3
6
the result using cellulose as the feedstock. These furan com-
pounds also diffused into the well-promoted ZSM-5 pores,
which underwent dehydration, decarboxylation, decarbonyla-
tion, and oligomerization reactions to generate aromatic
Acknowledgements
hydrocarbons. Monomeric phenolic compounds were primar- This study was supported partially by the Joint Center for Aero-
ily generated from decomposition of lignin in lignocellulosic space and Technology Innovation (JCATI), The Agriculture and
biomass, which were thereafter catalyzed into aromatic hydro- Food Research Initiative of National Institute of Food and
carbons through a series of dehydration, cracking, and oligo- Agriculture, United States Department of Agriculture (Award
2
8,52
merization reactions.
Number: 2015-67021-22911; Grant Number: 2015-11888712)
Single or multiple aromatic rings were transformed into and the Chinese Scholarship Council. We are grateful to
single or multiple alkane rings by hydrogenation reactions in Dr Aftab Ahamed for helping us in performing GCMS
the presence of RANEY nickel catalysts. As a result, the measurements and Dr Valerie Lynch-Holm from Franceschi
achieved aromatic hydrocarbons in the jet fuel range could be Microscopy & Imaging Center (FMIC), Washington State
converted into jet fuel range cycloalkanes by the hydrogen University for SEM training.
saving process under very mild conditions. A trace volume of
small hydrocarbons was also produced by hydrocracking reac-
tions. The cycloalkanes (together with minor aromatics and
cycloolefins) can be used as additives to prepare the desired jet
Notes and references
fuels by blending with other hydrocarbons. The cycloalkanes
produced in the hydrogen saving process can be further
upgraded through the hydrocracking and hydroisomerization
1 E. L. Kunkes, D. A. Simonetti, R. M. West, J. C. Serrano-
Ruiz, C. A. Gärtner and J. A. Dumesic, Science, 2008, 322,
417–421.
2 Q. Yan, F. Yu, J. Liu, J. Street, J. Gao, Z. Cai and J. Zhang,
Bioresour. Technol., 2013, 127, 281–290.
5
3,54
processes to from both straight and branched alkanes.
The
straight and branched alkanes blend with cycloalkanes accord-
ing to the proportions, which can produce different commer-
cial and military jet fuels.
3 Y. Wang, T. He, K. Liu, J. Wu and Y. Fang, Bioresour.
Technol., 2012, 108, 280–284.
4
S. Liu, Q. Zhu, Q. Guan, L. He and W. Li, Bioresour.
Technol., 2015, 183, 93–100.
5
G. Liu, B. Yan and G. Chen, Renewable Sustainable Energy
Rev., 2013, 25, 59–70.
4
. Conclusions
This study demonstrated that the integrated processes are
potentially profound approaches when targeting the pro-
duction of jet fuel range cycloalkanes from lignocellulosic
biomass. The integral processes detailed here were illustrated
to deliver up to 84.59% selectivity for jet fuel range cyclo-
alkanes obtained from intact biomass under very mild con-
ditions. In the first step, the overall carbon yield of jet fuel
range aromatics from catalytic microwave pyrolysis was
6 R. Xing, A. V. Subrahmanyam, H. Olcay, W. Qi, G. P. van
Walsum, H. Pendse and G. W. Huber, Green Chem., 2010,
12, 1933–1946.
7 G. W. Huber, S. Iborra and A. Corma, Chem. Rev., 2006,
106, 4044–4098.
8 L. M. Balster, E. Corporan, M. J. DeWitt, J. T. Edwards,
J. S. Ervin, J. L. Graham, S.-Y. Lee, S. Pal, D. K. Phelps,
L. R. Rudnick, R. J. Santoro, H. H. Schobert, L. M. Shafer,
R. C. Striebich, Z. J. West, G. R. Wilson, R. Woodward and
S. Zabarnick, Fuel Process. Technol., 2008, 89, 364–378.
9 S. P. Bagley and M. J. Wornat, Energy Fuels, 2013, 27, 1321–
1330.
2
4.68%. The bio-oils were extracted with n-heptane and the
recovery of organics could reach ∼94 wt%. These aromatics in
n-heptane medium were hydrogenated into jet fuel range
cycloalkanes. Compared with the conventional HDO process in
the presence of a noble catalyst, this process is a hydrogen 10 G. Li, N. Li, X. Wang, X. Sheng, S. Li, A. Wang, Y. Cong,
saving process, resulting in the costly hydrogen being trans-
X. Wang and T. Zhang, Energy Fuels, 2014, 28, 5112–5118.
This journal is © The Royal Society of Chemistry 2015
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Green Chemistry
11 B. Demirel, W. H. Wiser, A. G. Oblad, W. Zmierczak and 33 S. Zinovyev, A. Shelepchikov and P. Tundo, Appl. Catal., B,
J. Shabtai, Fuel, 1998, 77, 301–311. 2007, 72, 289–298.
12 D. E. Keil, D. A. Warren, M. J. Jenny, J. G. EuDaly, J. Smythe 34 U. K. Singh and M. A. Vannice, Appl. Catal., A, 2001, 213,
and M. M. Peden-Adams, Toxicol. Sci., 2003, 76, 347–356. 1–24.
13 G. W. Huber, J. N. Chheda, C. J. Barrett and J. A. Dumesic, 35 X. Wang and R. Rinaldi, ChemSusChem, 2012, 5, 1455–
Science, 2005, 308, 1446–1450. 1466.
14 R. M. West, Z. Y. Liu, M. Peter and J. A. Dumesic, Chem- 36 X. Zhang, H. Lei, L. Wang, L. Zhu, Y. Wei, Y. Liu,
SusChem, 2008, 1, 417–424. G. Yadavalli and D. Yan, Green Chem., 2015, 17, 4029–4036.
15 H. Olcay, A. V. Subrahmanyam, R. Xing, J. Lajoie, 37 X. Zhang, H. Lei, G. Yadavalli, L. Zhu, Y. Wei and Y. Liu,
J. A. Dumesic and G. W. Huber, Energy Environ. Sci., 2013,
, 205–216.
6 G. Li, N. Li, J. Yang, L. Li, A. Wang, X. Wang, Y. Cong and
Fuel, 2015, 144, 33–42.
6
38 S. Ren, H. Lei, L. Wang, Q. Bu, S. Chen, J. Wu, J. Julson and
R. Ruan, J. Anal. Appl. Pyrolysis, 2012, 94, 163–169.
39 S. Ren, H. Lei, L. Wang, Q. Bu, S. Chen, J. Wu, J. Julson and
R. Ruan, Bioresour. Technol., 2013, 135, 659–664.
40 H. Zhang, Y.-T. Cheng, T. P. Vispute, R. Xiao and
G. W. Huber, Energy Environ. Sci., 2011, 4, 2297–2307.
41 Y. Zhao, T. Pan, Y. Zuo, Q. X. Guo and Y. Fu, Bioresour.
Technol., 2013, 147, 37–42.
42 T. R. Carlson, J. Jae, Y.-C. Lin, G. A. Tompsett and
G. W. Huber, J. Catal., 2010, 270, 110–124.
43 Y.-T. Cheng and G. W. Huber, Green Chem., 2012, 14, 3114–
3125.
1
1
1
1
2
2
2
T. Zhang, Green Chem., 2014, 16, 594–599.
7 J. Yang, N. Li, G. Li, W. Wang, A. Wang, X. Wang, Y. Cong
and T. Zhang, Chem. Commun., 2014, 50, 2572–2574.
8 X. Sheng, N. Li, G. Li, W. Wang, J. Yang, Y. Cong, A. Wang,
X. Wang and T. Zhang, Sci. Rep., 2015, 5, 9565.
9 V. K. Venkatakrishnan, W. N. Delgass, F. H. Ribeiro and
R. Agrawal, Green Chem., 2015, 17, 178–183.
0 T. Mochizuki, S.-Y. Chen, M. Toba and Y. Yoshimura, Appl.
Catal., B, 2014, 146, 237–243.
1 P. M. Mortensen, J. D. Grunwaldt, P. A. Jensen, K. G. Knudsen
and A. D. Jensen, Appl. Catal., A, 2011, 407, 1–19.
44 F. Alonso, P. Riente and M. Yus, Acc. Chem. Res., 2011, 44,
379–391.
2 X. Wang and R. Rinaldi, Energy Environ. Sci., 2012, 5, 8244–
8
260.
45 Y. Zhang, P. Bi, J. Wang, P. Jiang, X. Wu, H. Xue, J. Liu,
X. Zhou and Q. Li, Appl. Energy, 2015, 150, 128–137.
2
2
3 D. C. Elliott, Energy Fuels, 2007, 21, 1792–1815.
4 G. Fogassy, N. Thegarid, Y. Schuurman and C. Mirodatos, 46 J. Xin, P. Zhang, M. P. Wolcott, X. Zhang and J. Zhang, Bior-
Energy Environ. Sci., 2011, 4, 5068–5076. esour. Technol., 2014, 155, 422–426.
5 A. Sanna, T. P. Vispute and G. W. Huber, Appl. Catal., B, 47 L.-J. Zhu, P.-J. Guo, X.-W. Chu, S.-R. Yan, M.-H. Qiao,
2
2
2
2
2
3
2
015, 165, 446–456.
K.-N. Fan, X.-X. Zhang and B.-N. Zong, Green Chem., 2008,
10, 1323–1330.
48 T. Wang, K. Li, Q. Liu, Q. Zhang, S. Qiu, J. Long, L. Chen,
L. Ma and Q. Zhang, Appl. Energy, 2014, 136, 775–780.
49 M. A. d. Hollander, M. Wissink, M. Makkee and
J. A. Moulijn, Appl. Catal., A, 2002, 85–102.
6 F. Li, Y. Yuan, Z. Huang, B. Chen and F. Wang, Appl. Catal.,
B, 2015, 165, 547–554.
7 T. R. Carlson, T. P. Vispute and G. W. Huber, Chem-
SusChem, 2008, 1, 397–400.
8 T. R. Carlson, Y.-T. Cheng, J. Jae and G. W. Huber, Energy
Environ. Sci., 2011, 4, 145–161.
50 Y. Xiang, L. Ma, C. Lu, Q. Zhang and X. Li, Green Chem.,
2008, 10, 939–943.
9 L. Wang, H. Lei, J. Lee, S. Chen, J. Tang and B. Ahring, RSC
Adv., 2013, 3, 14609–14615.
0 Q. Bu, H. Lei, S. Ren, L. Wang, J. Holladay, Q. Zhang,
51 H. Hu, M. Qiao, S. Wang, K. Fan, H. Li, B. Zong and
X. Zhang, J. Catal., 2004, 221, 612–618.
J. Tang and R. Ruan, Bioresour. Technol., 2011, 102, 7004– 52 K. Wang, K. H. Kim and R. C. Brown, Green Chem., 2014,
007. 16, 727–735.
1 B. H. Gross, R. C. Mebane* and D. L. Armstrong, Appl. 53 M. Santikunaporn, W. E. Alvarez and D. E. Resasco, Appl.
Catal., A, 2001, 219, 281–289. Catal., A, 2007, 325, 175–187.
2 G. W. Huber, J. W. Shabaker and J. A. Dumesic, Science, 54 H. Shi, O. Y. Gutiérrez, G. L. Haller, D. Mei, R. Rousseau
003, 300, 2075–2077. and J. A. Lercher, J. Catal., 2013, 297, 70–78.
7
3
3
2
Green Chem.
This journal is © The Royal Society of Chemistry 2015