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Refinery Approach of Bio−oils Derived from Fast Pyrolysis of Lignin to Jet
Fuel Range Hydrocarbons: Reaction Network Development for Catalytic
Conversion of Cyclohexanone
Majid Saidi
1
, Alireza Jahangiri
Faculty of Engineering and Technology, Shahrekord University, Shahrekord, Iran
Abstract
This study demonstrated that the bio−oil derived from fast pyrolysis of lignin was excellent
candidate to be converted into the jet and diesel fuel range hydrocarbons by catalytic upgrading
process. This research addresses specifically the kinetic and mechanism of cyclohexanone
conversion using sulfided CoMo/ γ−Al
2
O
3
catalyst in a fixed−bed flow reactor. The main routes
of cyclohexanone upgrading included hydrodeoxygenations (HDO), dehydrogenation,
hydrogenation and coupling. The selectivity−conversion analyses at different operating condition
indicate that benzene, cyclohexene, phenol, and 2−cyclohexen−1−one formed as primary
products and the other main products, 2−methylphenol, cyclohexylbenzene, biphenyl,
2−phenylphenol, 2−cyclohexylcyclohexan−1−one, 2−cyclohexylidenecyclohexane−1−one and
2−cyclohexylphenol appeared as non−primary products. An approximate reaction network and a
first order kinetic model are developed to determine kinetic parameters. Kinetic investigations
indicate that among the various reactions on sulfided CoMo/Al
2
O
3
, HDO is
characterized by
the highest rate and that selectivities for oxygen removal are favored by operation at higher
temperatures and pressures.
The apparent activation energy for the HDO
reaction that leads to
benzene formation is approximately
35.6
kJ/mol; coupling is the reaction class characterized by the
1
Corresponding Author: Majid Saidi, m.saidi@eng.sku.ac.ir, majidsaidi65@gmail.com
© 2017. This manuscript version is made available under the Elsevier user license
http://www.elsevier.com/open-access/userlicense/1.0/
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highest apparent activation energy.
The pseudo−first−order rate constants for formation of the
main products of cyclohexanone conversion decrease in the following order: benzene >
2−cyclohexylidenecyclohexane−1−one > cyclohexylbenzene > 2−cyclohexen−1−one >
2−phenylphenol > phenol > cyclohexene > 2−cyclohexylphenol > 2−methylphenol >
2−cyclohexylcyclohexan−1−one > biphenyl.
Keywords: Bio−oil; Lignin; Cyclohexanone; Catalytic Upgrading; Hydrodeoxygenation.
1. Introduction
In recent years, due to increasing demand for diesel and jet fuel and growing awareness of
important environmental issues, there is an immense interest in developing new generation
hydrocarbon biofuels, with a particular focus on green aviation biofuels
(Alonso et al., 2010;
Czernik and Bridgwater, 2004; Hosseinzadeh et al., 2015; Naik et al., 2014; Rahimpour et al.,
2016; Saidi et al., 2016; Saidi et al., 2014b; Shemfe et al., 2016; Wang et al., 2015)
. Depend on
the type of feedstock, several promising technology such as gasification, Fischer–Tropsch
synthesis (FTS), hydro−processing technologies, including hydro−treating, deoxygenation,
isomerization/hydrocracking and catalytic hydro−thermolysis that convert biomass−based
materials into jet fuel substitutes are available at commercial scale or research and development
stage (Bezergianni et al., 2009; Mohan et al., 2006; Saidi et al., 2014b). In FTS technology as a
developed and commercialized route to transform lignocellulose biomass into jet fuel
hydrocarbons range (particularly alkanes), bio−syngas produces via biomass gasification and
subsequently cleaning and conditioning of crude syngas will be performed
(Liu et al., 2013; Yan
et al., 2013). High pressure FT synthesis and upgrading of crude fuels for jet fuel applications is
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the final step. Based on international standards for certifying aviation fuel such as American
Society for Testing and Materials (ASTM D1655), the most important specifications required to
reach bio−jet−fuels are acceptable viscosity, heating value, electrical conductivity, freeze point
temperature, flash point, aromatics content, acidity and mercaptan concentration. Typically the
jet fuels are comprised of paraffins, naphthenes and aromatics (Branca et al., 2003; Czernik and
Bridgwater, 2004; Oasmaa and Czernik, 1999). Nonetheless, in the well−developed
hydrotreating technologies such as FTS, it is hard to attain acceptable compositions of cyclic
paraffins and aromatics jet fuels.
Lignin as a main underutilized constituent of lignocellulosic biomass is highly aromatic, with a
polymeric structure characterized by ether linkages and hydroxy and methoxy groups and it has
been proven to potentially produce biofuels with aromatic structure by various strategies
(Saidi
et al., 2015a; Saidi et al., 2015b; Zakzeski et al., 2010). Fast pyrolysis of biomass, a process that
is relatively well developed, is one of the viable processes to convert lignocellulosic biomass to
bio−oils
(Akhtar and Amin, 2011; Wang et al., 2012). In fast pyrolysis, lignin is heated in the
absence of air to temperatures between about 650 and 800 K and it will be converted
substantially into compounds such as phenol, anisole, guaiacol, cresol, syringol, etc. Products of
the conversion of these compounds with H
2
include cyclohexanone, and only little research has
been done to investigate the catalytic reactions of this compound with H
2
(Nimmanwudipong et
al., 2011a; Runnebaum et al., 2012).
The lignin−derived bio−oils are unable for use directly as a
fuel because of detrimental properties compared to petroleum fuels, such as much lower energy
density, poor thermal and chemical stabilities, high viscosity and oxygen content. To meet the
requirements of the conventional transportation fuels, lignin−derived bio−oils have to be
upgraded to eliminate total or partial oxygenates and unsaturated degree prior to its practical
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application as valuable fuel
(Alonso et al., 2010; Nimmanwudipong et al., 2011b; Runnebaum et
al., 2011)
. Among the upgrading approaches for jet fuels, hydrodeoxygenation (HDO) is
introduced as a promising process to remove the oxygen content under high temperature and
pressure of hydrogen in the presence of a catalyst.
Bio−oils derived from fast pyrolysis of lignin are excellent feedstock for production of
renewable diesel and jet fuel. Cyclohexanone as an intermediate lignin−derived bio−oil can be
directly converted into aromatics in the range of jet fuel hydrocarbons in a catalytic HDO step
and consequently these aromatics with low oxygen content can be hydrogenated into cyclic
paraffins and olefins.
Numerous researches have presented detailed studies of a wide variety of catalysts and processes
for HDO of lignin−derived bio−oils to valuable fuels include metals, metal sulfides, metal
phosphides, metal carbides, and metal nitrides on various supports
(Badawi et al., 2011;
González–Borja and Resasco, 2011; Li et al., 2011; Saidi et al., 2016; Saidi et al., 2015b; Saidi et
al., 2014b; Sankaranarayanan et al.; Zhu et al., 2011)
. Although noble metals such as platinum
offer high activities for HDO reactions and hydrogenation of aromatic rings, they are expensive.
In a related study, the catalytic transformation of cyclohexanone catalyzed by Pt/HZSM−5 in the
presence of H
2
has been investigated by Alvarez et al. (Alvarez et al., 1994) who detected
formation of families of products such as cyclic and bicyclic hydrocarbons, tricyclic ketones,
cyclohexenylcyclohexanone, cyclohexylcyclohexanone, and phenylcyclohexanone. Also Silva et
al. (Silva et al., 2000) reported that cyclohexanone was converted into cyclohexylcyclohexanone
via successive steps of Aldol condensation, dehydration, and hydrogenation on a bifunctional
Pd/HFAU catalyst. In another work, Nimmanwudipong et al.
(Nimmanwudipong et al., 2011a)
and Saidi et al. (Saidi et al., 2014a) provided a reaction network for catalytic conversion of
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cyclohexanone by Pt/γ–Al
2
O
3
in the presence of H
2
and observed that the main reaction classes
are hydrogenation, dehydrogenation, HDO, dehydration, isomerization, alkylation, and
condensation. In the upgrading process of lignin–derived bio–oils, there is a competition between
HDO and hydrogenation of aromatic rings. Metals involving iron, cobalt, nickel, platinum,
palladium, ruthenium, rhodium and iridium show activity for these reactions. Maier et al. (Maier
et al., 1981) and Shin and Keane (Shin and Keane, 2000) investigated the catalytic upgrading of
cyclohexanone by supported nickel, finding cyclohexanol, phenol, benzene, cyclohexene, and
cyclohexane as the major products. Also Prasomsri et al.
(Prasomsri et al., 2014) experiments
revealed that over MoO
3
catalyst, cyclohexanone conversion proceeds by a deoxygenation
pathway leading to the formation of cyclohexene, which is converted to benzene. They
concluded that the molybdenum−containing catalyst is selective for C–O bond cleavage at low
H
2
partial pressures (Prasomsri et al., 2014).
Metal sulfide catalysts are another important catalyst type which are widely used in
hydroprocessing of lignin–derived bio–oils. These include supported catalysts that incorporate
cobalt and molybdenum or nickel and molybdenum. Durand et al.
(Durand et al., 1984) used
sulfided NiO−MoO
3
/γ−A1
2
O
3
catalyst for the HDO of a group of alcohols and ketones such as
cyclohexanone. They reported that the initial step is hydrogenation of the ketone to the alcohol,
which rate is limiting. The second step is transformation of alcohols into olefins by dehydration
that is subsequently converted by hydrogenation or hydrogenolysis. Olivas et al. (Olivas et al.,
2001) used unsupported Ni–W sulfide catalysts for hydrogenation of cyclohexanone and inferred
that these binary sulfides are more active than the single sulfides. In similar research, Lin et al.
(Lin et al., 2011) concluded that demethylation, demethoxylation, and deoxygenation reactions