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Linköping University | Department of Physics, Chemistry and Biology Bachelor thesis, 16 hp | Biology programme: Physics, Chemistry and Biology
Spring term 2017 | LITH-IFM-x-EX--17/3368-SE
The Future of Advanced Bio-Jet
Fuel
Amanda Blochel
Examinator, Urban Friberg, IFM Biologi, Linköpings universitet
Tutor, Johan Edqvist, IFM Biologi, Linköpings universitet
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Keyword: advanced bio-jet fuel, aviation industry, HEFA-SPK, jet fuel, TF-SPK
Sammanfattning Abstract
The aviation industry is growing rapidly and the carbon dioxide emissions from the industry are
following in the same manner. Biofuels made from edible feedstock have had an impact on
lowering the emissions but at the same time an impact on increasing food prices. There are a few
alternative fuels on the market today (TF-SPK, HEFA-SPK) which work in a blend with the
petroleum based fuels, reducing the emissions from the aircrafts. Biofuels from next generation
biomass, also called advanced biomass, such as algae and lignin, seem likely to be a good
substitute for the first generation biofuels. The advanced biofuels are relatively costly to produce.
This is due to the many steps in the production process, which restricts the usage of these sorts of
fuels in the aviation industry. There are some problems associated with a jet fuel produced from
100% biomass. This is because the jet fuel produced from biomass differs from the jet fuels used
today, making it unsafe to use in modern day airplane engines. That is why it is important to find
an alternative jet fuel based on biomass that has the same characteristics as the conventional jet
fuel, to be able to use the same transportation and engines that are in use today. Otherwise the high
cost of advanced bio-jet fuels will make them unusable.
Titel
Title: The Future of Advanced Bio-Jet Fuel
Författare
Author: Amanda Blochel
Table of contents
1 Abstract ................................................................................................... 1
2 Background ............................................................................................. 1
3 Material and Methods ............................................................................. 3
4 Types of Jet Fuel ..................................................................................... 3
5 Alternative Jet Fuels ............................................................................... 6
5.1 Fischer-Tropsch Synthetic Paraffinic Kerosenes (FT-SPK) ............ 6
5.2 Biomass-Derived Synthetic Paraffinic Kerosenes (HEFA-SPK) .... 8
5.3 Alcohol to Jet Synthetic Paraffinic Kerosene (ATJ-SPK) ............... 9
5.4 Blending With Petroleum Based Fuels............................................. 9
6 Feedstock .............................................................................................. 10
6.1 Algae ............................................................................................... 10
6.2 Lignin .............................................................................................. 13
6.2.1 Fungi ......................................................................................... 15
6.3 Camelina ......................................................................................... 16
6.4 Rapeseed ......................................................................................... 17
6.5 Jatropha ........................................................................................... 17
6.6 Switchgrass ..................................................................................... 18
7 Costs ...................................................................................................... 18
7.1 Flights Powered by Bio-Jet Fuel .................................................... 19
8 Discussion ............................................................................................. 20
8.1 Social and Ethical Aspects ............................................................. 21
9 Acknowledgment .................................................................................. 22
10 References .......................................................................................... 23
1
1 Abstract
The aviation industry is growing rapidly and the carbon dioxide emissions
from the industry are following in the same manner. Biofuels made from
edible feedstock have had an impact on lowering the emissions but at the
same time an impact on increasing food prices. There are a few alternative
fuels on the market today (TF-SPK, HEFA-SPK) which work in a blend
with the petroleum based fuels, reducing the emissions from the aircrafts.
Biofuels from next generation biomass, also called advanced biomass, such
as algae and lignin, seem likely to be a good substitute for the first
generation biofuels. The advanced biofuels are relatively costly to produce.
This is due to the many steps in the production process, which restricts the
usage of these sorts of fuels in the aviation industry. There are some
problems associated with a jet fuel produced from 100% biomass. This is
because the jet fuel produced from biomass differs from the jet fuels used
today, making it unsafe to use in modern day airplane engines. That is why
it is important to find an alternative jet fuel based on biomass that has the
same characteristics as the conventional jet fuel, to be able to use the same
transportation and engines that are in use today. Otherwise the high cost of
advanced bio-jet fuels will make them unusable.
2 Background
The avian industry has grown rapidly and the use of jet fuel has followed in
the same manner of growth, leading to a great negative impact on the
greenhouse gas effect (Jiménes-Díaz et al., 2017). Two percent of the
global man made carbon dioxide emissions are from aviation emissions
(Air Transportation Action Group, 2012). However, due to the current
rapid growth within the aviation industry the carbon dioxide emissions are
predicted to have a similar rapid increase leading to increases of
greenhouse gases in the atmosphere (Air Transportation Action Group,
2012). Boeing released a market research outlook in 2016 where they
predicted a growth in passenger traffic by 4.8 % within the next 20 years
(Boeing, 2016). Due to the great impact on the climate the aviation industry
has set up a few targets and one of them is to decrease the carbon dioxide
emission by 50% by 2050 (Air transportation Action Group, 2012). The
most commonly used aviation fuel in, at least, commercial aviation fuels
are jet fuels, and today most of those jet fuels are petroleum based
(Hileman and Stratton, 2014; Liu et al., 2013). Petroleum is a type of crude
2
oil which consists of a mixture of hydrocarbons (Hileman and Stratton,
2014; Liu et al., 2013).
There are fuels which do not produce as high amount of carbon dioxide
emissions (Gronenberg et al., 2013; Liew et al., 2016). Hileman and
Stratton (2014) managed to show that it is possible to significantly lower
the total amount of carbon dioxide emissions from transportation fuels by
switching to a different type of fuel (Hileman and Stratton, 2014). These
types of fuels are based on different types of biomass which are produced
through photosynthesis (Hileman and Stratton, 2014). The released carbon
dioxide from using these types of fuels will thus have a net combustion of
zero (Hileman and Stratton, 2014). These types of fuels are called biofuels
and are normally produced by different types of biomass such as rapeseed
oil or bio-waste (Gronenberg et al., 2013; Liew et al., 2016). It is the
economic and environmental sustainability, energy supply diversity and
competition for energy resources that are the main driving forces for the
development of the different types of biofuels (Hileman and Stratton,
2014).
There are two different types of biofuels, first generation biofuels and next
generation biofuels, also called advanced biofuels (Gronenberg et al 2013).
The first generation biofuels are normally produced from edible feedstock
such as rapeseed, corn or sugarcane (Daroch et al., 2013; Fairley, 2011).
This method of creating biofuels from edible feedstock has, however, been
shown to have impacts on the increasing food prices (Daroch et al., 2013;
Fairley, 2011). When producing ethanol or biodiesel, it is normally done on
first generation biofuels (Schubert, 2006). Some of the complications with
first generation biofuels are: food price issues, land and water usages and
pollution (Air Transportation Action Group, 2012). The advanced biofuels
are however based on unpalatable feedstock such as lignocelloluse, which
is the woody parts of plants (Daroch et al., 2013; Schubert, 2006). The
lignocellulose has an abundant source of energy and lignocellulose is
everywhere, trees, cornhusks or wheat straw are just a few places where
lignocellulose can be found (Schubert, 2006). Biofuels made from
feedstock such as lignocellulose have been shown to provide several
benefits to society (Balan, 2014). Biofuels from lignocellulose are
renewable and sustainable, they have also been shown to reduce air
pollution as there would be less burning of the biomass (Balan, 2014). The
main problem with producing advanced biofuel is that it requires high
investment costs, due to the complexity of the conversion of the different
biomasses, and they are more expensive than first generation biofuels
(Fairley, 2011; He and Zhang, 2011; Wingren et al., 2008).
3
Jet fuels based on biological sources would lower the carbon dioxide
emission and the advanced biofuels would be an ideal solution, due to the
complication that lies with first generation biofuels (Air Transportation
Action Group, 2012). However, jet fuels have not completely been
replaced by bio-jet fuels, due to the fact that jet fuels differ from the
traditional transportation engine fuels (Cheng and Brewer, 2017; Kallio et
al., 2014).
3 Material and Methods
This thesis is a literature study. The literature was found through searches
through Linköping’s university’s library search page, Scopus, and google
scholar. Search words such as jet fuel, bio-jet fuel, advanced biofuel,
lignin, and algae were used.
4 Types of Jet Fuel
Jet fuels consists of a mixture of hydrocarbons which includes; paraffins,
branched alkanes, cycloalkanes and aromatics (Corporan et al., 2011;
Dagaut and Cathonnet, 2006; Jiménes-Díaz et al., 2017; Vukadinovic et al.,
2013). It is the different ratio of these hydrocarbons that make up the
different jet fuel types (Corporan et al., 2011; Dagaut and Cathonnet, 2006;
Jiménes-Díaz et al., 2017; Vukadinovic et al., 2013). The hydrocarbon
number range should be within the range of C8-C16; this specific range is
needed to give jet fuel its high yield and low freezing point (Kinder and
Rahmes, 2009; Verma et al., 2011). For the jet fuel to be able to work in
the engine several requirements need to be met, which can be found in
Table 1 (Corporan et al., 2011; Verma et al., 2011).
4
Table 1. The importance of the different characteristics of jet fuel (Hileman and Stratton, 2014; Cheng and Brewer, 2017)
Characteristics Importance
High energy per unit volume (also
known as high energy density)
Simplifies long range flights
High energy per unit mass (also
known as high specific energy)
Improves fuel effectiveness and
decreases the takeoff weight
High flash point. This indicates the
temperature which the fuel
produces vapor that can ignite
Guarantees safe maneuver of the
fuel
Low freezing and vapor point This is important for safe flights at
the high altitudes where the planes
are operating
High thermal stability Prevents fuel blockage
Suitable lubricity Ensures that the fuel pumps
function properly
Suitable aromatic content Prevents seal swell within the fuel
system, important for the avoidance
of fuel leaks
One of these requirements is that the fuel heat of combustion should be
higher than 42.8 MJ kg-1 and viscosity should be lower than 8.0 mm2 s-1.
Another important requirement of the characteristics of the jet fuel is the
hydrogen to carbon ratio, this ratio has an impact on the specific heat of the
fuel at a constant volume and pressure (Bester and Yates, 2009). In Table 2
the different characteristics of three different types of jet fuels are
presented, Jet A (used in commercial flights in North America), Jet A-1
(used in commercial flights in Europe) and JP-8 (a type of fuel used in
military airplanes) (Bi et al., 2015; Corporan et el., 2011; Elmoraghy and
Farag, 2012; Lobo et al., 2011).
5
Table 2. Some of the different types of jet fuels and their characteristics (Bi et al., 2015; Elmoraghy and Farag, 2012; Lobo et al., 2011).
Specifications Jet A Jet A-1 JP-8
Heat of combustion (MJ/kg) 43.3 43.3 43.0
Freezing point (°C) -40 -47 -49
Kinetic viscosity at – 20 °C
(mm2/s)
5.78 4.27 4.10
Hydrogen content (wt.%) 13.6 13.7 13.7
Total oxygen (wt.%) 0 0 -
Total sulfur (wt.%) <0.3 <0.3 0.064
H/C (mol ratio) 1.92 1.92 1.92
Sulfur, nitrogen, and oxygen are all components that can affect the jet fuels
performance in a negative way (Hileman and Stratton, 2014; Kinder and
Rahms, 2009). These impurities, as well as different types of metals, should
be kept to a minimal (Kinder and Rahms, 2009). Aromatic and sulfur
content in jet fuels impact air quality negatively (Hileman and Stratton,
2014). If a change of the fuel composition, which would reduce the
aromatic and sulfur content in jet fuel can be made then it would give the
aviation industry a less negative impact on the air quality (Hileman and
Stratton, 2014).
Renewable transportation fuels which are used for ground transportation
such as biodiesel and ethanol cannot be used in aviation fuel (Air
Transportation Action Group, 2012; Hileman and Stratton, 2014). Biodiesel
used for ground transportation will freeze at the high altitudes, and ethanol
does not meet the requirements of the energy density which is needed (Air
Transportation Action Group, 2012; Hileman and Stratton, 2014).
In the jet engines, soot particles must be kept to a minimum as soot can be
harmful for the mechanical compartments of the engine (Dagaut, 2005).
Soot can lead to carbon deposits and radiant heat loss which can lead to hot
spots combustor wall temperatures that are too high (Dagaut, 2005). The
engines soot emissions will also have an effect on the radar detection of
military jets making them more visible (Dagaut, 2005). Fuels with high
aromatic contents produce more soot and this is why the amount of
aromatics must be limited in jet fuel (Dagaut, 2005). However, a low
amount of aromatics could lead to seal swell which would lead to fuel leaks
in the airplane systems, thus aromatics are still needed to be a component
of jet fuel (Corporan et al., 2011; Hileman and Stratton, 2014; Liu et al.,
2013). Alkyn-benzens, which are types of aromatics, with a low molecular
6
weight are desirable because they cause less soot combustion than other
types of aromatics (Cheng and Brewer, 2017). The aromatic content of the
jet fuel also has an influence on the hydrogen to carbon ratio (Bester and
Yates, 2009).
5 Alternative Jet Fuels
There are several different types of renewable jet fuel alternatives at use in
the market at the moment: Fischer-Tropsch synthetic paraffinic kerosenes
(TF-SPK), biomass-derived synthetic paraffinic kerosenes (Bio-SPK) are
the most common (Corporan et al., 2011; Jiménes-Díaz et al., 2017;
Pearlson et al., 2013; Yao et al., 2017). However, there are renewable jet
fuels techniques that are up and coming and has been tested for use in jet
engines, the technique is called alcohol to Jet Synthetic Paraffinic Kerosene
(ATJ-SPK) (Jiménes-Díaz et al., 2017).
To produce jet fuel from biomass, high temperatures are required for the
hydroisomeration and the hydrocracking (Verma et al., 2011). This is
typically used when producing 8C-15C hydrocarbons (Verma et al., 2011).
Hydroisomeration and hydrocracking is used when longer hydrocarbons
need to be shortened (Bauer et al., 2014; Kallio et al., 2014). The
hydroisomeration is used when producing the branched alkanes which are
important for lowering the boiling point and freeze point (Jiménes-Díaz et
al., 2017; Moser, 2010).
5.1 Fischer-Tropsch Synthetic Paraffinic Kerosenes (FT-SPK)
Fischer-Tropsch synthetic paraffinic kerosenes (FT-SPK) is a method that
uses lignocellosic biomass to produce bio-jet fuels (Liu et al., 2013; Bi et
al., 2015). In this process the biomass is transformed into bio-syngas
which then goes through a Fischer-Tropsch synthetic (FT) process and gets
transformed into biofuels (Corporan et al., 2011; Liu et al., 2013; Bi et al.,
2015). In FT-SPK the biomass must go through gasification which turns
the biomass into bio-syngas (Corporan et al., 2011; Bi et al., 2015).
Gasification is a process which reacts pyrolysis products with either air or
steam to transform bio-syngas (Liu et al., 2013). Pyrolysis products are
products which are produced in the absence of oxygen by direct thermal
decomposition of the biomass (Liu et al., 2013). Bio-syngas consists of
hydrogen gas and carbon monoxide which are converted into hydrocarbons
through the FT process (Liu et al., 2013).
7
The FT process is a chemical process which uses a catalyst to react carbon
monoxide and hydrogen to make paraffins (Bi et al., 2015; Hileman and
Stratton, 2014; Kinder and Rahms, 2009; Kumabe et al., 2010; Moses,
2008; Yan et al., 2013; Corporan et al., 2011). The first step of the FT
process is hydrodeoxygenation; this is done to remove oxygen which is
removed as water (Jiménes-Díaz et al., 2017; Perlson et al., 2013). The
deoxygenated products will be separated by distillation and the heavier
molecules have to be hydrocracked; this is because the normal length of the
hydrocarbons you get from hydrodeoxygenation is C17-C18 (Jiménes-Díaz
et al., 2017). Hydrocracking these components will make them within the
desired length for jet fuel (Jiménes-Díaz et al., 2017). Next selective
hydroisomeration and catalytic cracking are performed on the sample,
followed by an addition of cooling water to cool the samples (Perlson et al.,
2013). The different products are then separated into the different fuel
types, the gas is recovered and hydrogen is produced (Perlson et al., 2013).
The hydrogen can then be reused in the hydrodeoxydation step (Perlson et
al., 2013). For the final step the products are stored and blended (Perlson et
al., 2013). Figure 1 is a simplified picture of the different FT process
stages.
Figure 1. The different stages of the FT production, going from left to right. Within the rectangles are the main FT production with hydrodeoxygenation, isomeration and catalytic cracking, and separation, which then leads to the different types of fuel (Perlson et al., 2013).
This technique is approved for use in commercial jet fuels (Bi et al., 2015;
Hileman and Stratton, 2014; Kinder and Rahms, 2009; Kumabe et al.,
2010; Moses, 2008; Yan et al., 2013). FT-SPK contains a large amounts of
paraffins (hence the name) and the neat combination of the paraffins has
shown that these fuels produce a lower amount of soot than petroleum
8
based jet fuel. When comparing with JP-8 which is a type of military fuel
(Corporan et el., 2011).
5.2 Biomass-Derived Synthetic Paraffinic Kerosenes (HEFA-SPK)
Biomass-derived synthetic paraffinic kerosenes (HEFA-SPK) are produced
from vegetable oils and fats from animals (Perlson et al., 2013). These oils
and fats are transformed into fuels which have the same characteristics as
the petroleum based fuels (Perlson et al., 2013). Plants such as algae,
jatropha, rapseed and camelina can be used as biomass base for HEFA-
SPK (Rahmes et al., 2009). HEFA-SPK is hydroprocessed esters and fatty
acids (Baena-Zambrana et al., 2013; Schroecker et al., 2011). This
technology is commonly referred to as oil-to-jet (Jiménes-Díaz et al.,
2017).
The FT-SPK process and the HEFA-SPK method are similar processes
they both go through the FT process (Baena-Zambrana et al., 2013; Kinder
and Rahmes, 2009). The main differences in the two different processes are
that no gasification is needed for the production of HEFA-SPK (Hileman
and Stratton, 2014). Instead the HEFA-SPK derives jet fuels from the
biomass oils which are produced into paraffin wax (Hileman and Stratton,
2014; Baena-Zambrana et al., 2013). Due to that both the FT-SPK and
HEFA-SPK go through the FT process the final products are extremely
similar in components (Baena-Zambrana et al., 2013).
Test flights with HEFA-SPK produced jet fuels showed a decreased fuel
flow which did not impact the flight due to an increase in energy density
per unit mass, this indicates that a flight powered by a HEFA-SPK blend
could last longer with the use of less fuel (Kinder and Rahmes, 2009). The
test flights did not show anything different than normal flights, showing
that a HEFA-SPK blend could be used in commercial flights (Kinder and
Rahmes, 2009).
9
5.3 Alcohol to Jet Synthetic Paraffinic Kerosene (ATJ-SPK)
Alcohol to Jet Synthetic Paraffinic Kerosene (ATJ-SPK) is the process
where alcohol is transformed into jet fuel (Yao et al., 2017). This jet fuel is
produced from biomass which has a high sugar content, is starchy and
lignocellulosic (Yao et al., 2017). The sugars from these biomasses are
fermented into ethanol or other alcohols and it is these alcohols that can be
transformed into jet fuel (Yao et al., 2017). The conversion into jet fuel is
done by upgrading the short chain alcohols and the long chained fatty
alcohols (Jiménes-Díaz et al., 2017).
This process can be used to transform ethanol, n-butanol or iso-butanol into
jet fuel (Wang and Tao, 2016). The ATJ process has three main steps;
alcohol dehydration, oligomerization, and hydrogenation (Wang and Tao,
2016; Yao et al., 2017).
Dehydration is needed to produce alkanes which then is oligomerized
(Wang and Tao, 2016). The oligomerization is done to produce heavier
alkanes from the alkanes produced from the dehydration (Wang and Tao,
2016). Hydrogenation is needed to get these heavier alkanes into the
hydrocarbon range which is needed for jet fuel (Bi et al., 2015; Wang and
Tao, 2016). The hydrogenation reduces the number of double bonds (Bi et
al., 2015, Prak et al., 2015).
Test flights were done successfully with ATJ jet fuel in 2012 and in March,
2016 the ATJ production was approved for up to a 30 % blend with
petroleum based jet fuels and can be used in commercial flights (EcoSeed,
2012; Yao et al., 2017).
5.4 Blending With Petroleum Based Fuels
The renewable jet fuels in Sections 5.1, 5.2, 5.3 all contain mostly n-and
iso-paraffins, and have nearly no aromatics or cycloalkanes within the
range required for jet fuel (Corporan et al., 2011; Dupain et al., 2005;
Robota et al., 2013). Due to the lack of aromatics and cycloalkanes bio-jet
fuel needs to be blended with petroleum based jet fuels, for the biofuels to
be allowed to be used as aviation fuels (Hileman and Stratton, 2014; Lobo
et al., 2011). These 50/50 blends still contain less aromatics in the fuel
blend which reduces the aviation industries impact on the air quality
(Bester and Yates, 2009; Hileman and Stratton, 2014; Huber et al., 2006).
10
The renewable biomass derived jet fuels are nearly sulfur free, so a blend
with petroleum based fuels gives a reduced sulfur content (Hileman and
Stratton, 2014; Huber et al., 2006).
Both aromatics and cycloalkanes are important components in jet fuel;
aromatics should be around 10-15% of the fuel and cycloalkanes are the
second most abundant component after paraffins (Vulkadinovic et al.,
2013). Alkyl-benzens with a low molecular weight is desirable in
renewable jet fuels because they cause less soot combustion than other
aromatics (Cheng and Brewer, 2017).
The jet fuel has not completely been replaced by bio-jet fuels because jet
fuels differ from the traditional engine fuels (Cheng and Brewer, 2017;
Kallio et al., 2014). It is however the lack of aromatic and cycloalkane
hydrocarbons in bio-jet fuel that is the main problem (Cheng and Brewer,
2017; Hileman and Stratton, 2014). In order to make a 100% bio-jet fuel, a
biosource must be found where you are able to synthesize aromatics and
cycloalkanes fuel compounds (Cheng and Brewer, 2017). Theoretically
these components can come from cellulosic biomass which would give a
fully synthetical jet fuel (Hileman and Stratton, 2014).
6 Feedstock
6.1 Algae
Oil from algae is one of the oils that can be used in the BIO- SPK process
(Elmoraghy and Farag, 2012; Hussain and Naryan, 2017; Kallio et al.,
2014; Robota et al., 2013; Savage, 2011; Su et al., 2017). Algae are a
photosynthesizing organism needing carbon dioxide, water and sunlight to
be able to grow (Savage, 2011). Algae can grow in polluted water, water
which is not suitable for drinking or for use in agriculture (Kinder and
Rahms, 2009). The algae can be grown in closed or open ponds in salt or in
brackish water (Hussain and Naryan, 2017). Algae has a high growth rate
and can be harvested for oil which can then be processed into biofuel
(Huber et al., 2006; Kinder and Rahms, 2009).
High costs in producing algae is the main limitation for the usage of algae
oil (Huber et al., 2006). The high costs include carbon dioxide costs, the
large area it needs to be able to grow, and the many steps of the algae to oil
process (Hileman and Stratton, 2014; Huber et al., 2006; Patil, 2008)
11
The cost has been estimated to be about 200 dollars per metric ton which is
higher than the cost of the biomass lignocellulose, which has been
estimated to about 40 dollars per metric ton (Huber et al., 2006). Algae
needs concentrated carbon dioxide to grow via photosynthesis, and the
amount of carbon dioxide is estimated to be one fourth of the cost of the
production of algae (Hileman and Stratton, 2014; Huber et al., 2006). To
produce 1 kg of algae biomass you would need 1.6-1.8 kg of carbon
dioxide (6.2 kg CO2/kg biodiesel) (Elmoraghy and Farag, 2012; Patil,
2008). However, the cost can be lowered by using waste carbon dioxide
from fossil fuel plants, it would be an advantage for the big scale algae
productions to get their carbon dioxide contribution from nearby powering
plants (Elmoraghy and Farag, 2012; Huber et al., 2006). About 400 tons of
carbon dioxide is produced from an average 500 MW power plant
(Elmoraghy and Farag, 2012).
Another way of decreasing the cost of production of algae would be to
develop a low-cost harvesting process (Huber et al., 2006). Two other key
nutrients which are needed for growing algae are phosphorus and nitrogen,
if there is a lack of these two nutrients it will slow down the growth of the
algae (Elmoraghy and Farag, 2012). Yet another way in bringing down the
cost of the algae production is if the algae grow directly in water where
high amounts of phosphorus and nitrogen are found naturally (Elmoraghy
and Farag, 2012).
Due to the algae being dependent on photosynthesis, where direct sunlight
is needed, they cannot be grown on top of each other (Savage, 2011). If the
layer of algae is greater than a few centimeters thick the sunlight will not
reach the algae in the lower layer and these algae will die (Savage, 2011).
To be able to grow a high number of algae for the production of biofuel a
large area of open surface of water is needed which is another problem
when producing fuels based on algae oil (Savage, 2011).
The algae used in making biofuel are single cell algae that produce
proteins, lipids and carbohydrates from carbon dioxide, hydrogen and
nitrogen (Savage, 2011). The extraction of their oil is done by breaking the
cells open and this oil can then be converted into hydrocarbon-based fuel
(Savage 2011).
The high water content (80-90 % of the content is from water) means that
the algae needs to be pretreated to reduce the content of water (Elmoraghy
and Farag, 2012; Patil, 2008). These pretreatments are harvesting and
dewatering (Elmoraghy and Farag, 2012; Patil, 2008). Some of the
harvesting methods are centrifugation and drying the algae into large dry
12
flakes (Elmoraghy and Farag, 2012; Patil 2008). However, another
possibility is using direct hydrothermal liquefaction; this method is able to
directly convert the wet biomass into fuels without the steps of reducing the
water content (Aresta et al., 2005; Minowa et al., 1995; Patil, 2008).
Biomass liquefaction is the process where the oxygen content of the
biomass is removed and this can be done to some biomass including algae
(Aresta et al., 2005; Minowa et al., 1995; Patil, 2008). The removal of the
oxygen will give a higher heating value which leads to more hydrocarbon
like contents of the product (Patil, 2008). Figure 2 shows a simplified
version of the algae oil based jet fuel production process.
The oils generated from this process have a viscosity which is ten or even
more times greater than the viscosity of jet fuel (Elmoraghy and Farag,
2012). The high viscosity unfortunately leads to the filters in modern day
airplane engines clogging up causing excessive damage to the engine
(Elmoraghy and Farag, 2012). However, there is a way to reduce the
viscosity of the algae oils through transesterification (Elmoraghy and
Farag, 2012).
Figure 2. The different stages of the algae oil based bio-jet fuel production, going from left to right. Within the rectangles are the main production steps where growth and harvesting, oil extraction, transesterification and blending (Elmoraghy and Farag, 2012).
The biomass from the algae that is left after the oil extraction can be used
as a protein source for cattle and can even be fermented into alcohol
(Elmoraghy and Farag, 2012; Patil, 2008).
Even though the production of biodiesel from algae is water costly this
method leaves a smaller water footprint than other types of biodiesel
13
production feedstock, see Table 3 (Elmoraghy and Farag, 2012). The water
footprint is a measurement of how much fresh water that is needed to
produce the biomass which we use, the water footprint can also measure
how much water is used to produce other goods we use such as clothing or
the food we eat (Hoekstra et al., 2011). The water footprint can be
significantly decreased if the method of growing algae in wastewater or
seawater is perfected (Elmoraghy and Farag, 2012; Kinder and Rahms,
2009). There are a lot of investments worldwide in the production of algae
(Su et al., 2017). These investments seem to be mainly focused on the
process of making the production of algae cheaper and in finding the best
suitable species of algae which produces the highest yield of oil (Su et al.,
2017). Table 3. The amount of water used, in liters, in production of 4 l biodiesel from three types of different plant oils; soybean, canola and algae (Elmoraghy and Farag, 2012).
Types of feedstock Water mount in liters
Soybean 59052
Canola 21993
Algae 1136-3784
6.2 Lignin
Lignocellulose is composed of cellulose, hemicellulose and lignin (Zaldivar
et al., 2001). Lignin is a biomass which is rich in aromatic benzene rings
and could theoretically be used in bio-jet fuels (Cheng and Brewer, 2017).
As described in section 4, alkyn-benzens with a low molecular weight are
desirable because they cause less soot combustion than other types of
aromatics (Cheng and Brewer, 2017). The fact that they are able to be
produced from lignin makes lignin into a desirable jet fuel base (Cheng and
Brewer, 2017). However, there are some challenges with using lignin as a
base in a bio-jet fuel due to the complexity of the feedstock (Wu et al.,
2017). It is believed that lignin derived biofuel cannot be utilized directly
as transportation fuel, because it has a high oxygen content, acidity and is
instable, and has a high viscosity (Wu et al., 2017). However, there has
been a different approach on deriving jet fuel from lignin and it showed
that it is possible to derive C8-C15 hydrocarbons and aromatics, two
important components in jet fuel, meaning that lignin meets the same
requirements as current day jet fuel (Bi et al., 2015).
The transformation from biomass into the hydrocarbons needed for jet fuel
is done in three steps (Bi et al., 2015). First the lignin has to be cracked to
14
become low-carbon aromatic monomers, this is done by a catalytic
cracking of the lignin (Bi et al., 2015). The catalytic cracking of the lignin
is done at high temperatures, however a temperature over 500 °C leads to a
second cracking which is not favorable for the production of the
hydrocarbons, because the range would be too low for jet fuel (Bi et al.,
2015). In the second step the aromatic monomers has to be alkylated; this is
done to produce C8-C15 aromatics (Bi et al., 2015). This step can be
completed at low temperatures, it can even be done in room temperature,
20 °C (Bi et al., 2015). However, the process seems to favor a slightly
higher temperature to produce the aromatics in the desirable length, there
are indications that 60 °C is the best temperature for this process (Bi et al.,
2015). The final step is done to produce C8-C15 hydrocarbons which are
needed in jet fuel, and is done by hydrogenation of the C8-C15 aromatics
(Bi et al., 2015). This step is temperature dependent, it has been shown that
when hydrogenating C8-C15 aromatics at 90 °C the conversion of the
aromatics was only about 20% (Bi et al., 2015). However, when increasing
the temperature to 180 °C it also improved the hydrogenation efficiency (Bi
et al., 2015). When preforming the last step at this temperature nearly all of
the C8-C15 aromatics had been converted to the desired cyclic alkanes (Bi
et al., 2015).
As shown in Table 4 the two lignin derived products, aromatic biofuel and
cyclic alkane biofuel, meet the specifications of the other jet fuels shown in
Table 2. The findings indicate that from lignin the C8-C15 aromatics and
cyclic alkanes can be reached in the range of jet fuel (Bi et al., 2015).
15
Table 4. Table over Bi et al., work and the specifications of the two different fuels produced; Aromatic biofuel (ABF) and cyclic alkane biofuel (CBAF) (Bi et al., 2015). Some components are undetected, meaning that no trace of these components were found (Bi et al., 2015).
Specifications ABF CABF
Heat of combustion (MJ/kg) 42.5 ± 1.0 45.9 ± 0.8
Freezing point (°C) ≤ 70 ≤ 70
Kinetic viscosity at -20 °C
(mm2/s)
6.22 ± 0.28 7.46 ± 0.31
Hydrogen content (wt.%) 10.4 ± 0.5 14.2 ± 0.7
Total oxygen (wt.%) 0.096 ± 0.007 undetected
Total sulfur (wt.%) undetected undetected
H/C (mol ratio) 1.40 ± 0.07 1.98 ± 0.11
6.2.1 Fungi
As mentioned in section 6.2 the biomass from lignocellulose is attractive as
a renewable fuel source (Cheng and Brewer, 2017; Wu et al., 2017) This is
mainly due to the large availability of the biomass, the low cost of the
production of lignin and the aromatic compounds of the biomass (Cheng
and Brewer, 2017; Wu et al., 2017). However, there is a problem with the
availability of a low-cost way to produce jet fuels from a lignin base, due to
the complexity of the biomass (Wu et al., 2017).
Wu and his colleagues did an experiment in 2017 to look at four
endophytes and their consolidated bioprocessing potential (CBP), these
characteristics have the potential to convert lignocellulosic biomass to
biofuels (Wu et al., 2017). All the endophytes are rich in
carbohydrateactive enzymes, fungal oxidative lignin enzymes and terpene
synthases; this was found through a genomic analysis (Wu et al., 2017).
They found monoterpenes and sesquiterpenes, they are similar to the
hydrocarbons found in petroleum base jet fuels (Edwards et al., 2010;
Harvey et al., 2010; Wu et al., 2017) The monoterpenes and sesquiterpenes
contains close to zero oxygen content and they have high density which
makes them important compounds, indicating that this type of chemical
compound could work in drop in fuels for aviation fuel (Wu et al., 2017).
Drop in fuels means that there is no need for any new equipment, the new
fuel can be used in the systems used today (Air Transportation Action
Group, 2012). After cellulase activity assays they found that the
endophytes have the ability to breakdown the lignocellulosic feedstock
directly because the endophytes secrete cellulase (Wu et al., 2017). By
16
being able to breakdown the feedstock directly, less steps are needed
making the whole process cheaper and making it more plausible for usage
(Wu et al., 2017).
6.3 Camelina
The interest in growing camelina is from the need of oilseed crops for the
transportation industry which do not have a food use (Shonnard et al.,
2010). Camelina is a plant which its oil can be used in BIO-SPK process
(Moser, 2010; Shonnard et al., 2010). Camelina growth season is 85-100
days which is a short season (Moser, 2010; Shonnard et al., 2010). It is a
plant that is well adapted to different sort of stress such us cold and drought
(Moser, 2010; Shonnard et al., 2010). It can germinate at low temperatures
and is frost tolerant which makes it a crop that can grow during winter
seasons (Moser, 2010; Shonnard et al., 2010). However, it has a lower
tolerance for rain than other oilseed crops (Moser, 2010; Shonnard et al.,
2010).
The camelina crops are grown in the same area as wheat (Moser, 2010;
Shonnard et al., 2010). This might indicate that the growing of camelina
will deprive growth area for wheat (Moser, 2010; Shonnard et al., 2010).
However, the growing grounds can be rotated which would indicate that
every other or every third year camelina can be grown (Moser, 2010;
Shonnard et al., 2010). Having the ground rotated has shown to benefit the
wheat crop (Moser, 2010; Shonnard et al., 2010). The moisture of the soil
will increase which would increase the crop yields the next year (Shonnard
et al., 2010). Not growing the same crops every year and breaking the crop
cycle will reduce pest problems and the crops will be less accessible to
diseases (Shonnard et al., 2010). The camelina has shallow roots which
make them drought resistant and these shallow roots would keep the
nutrients in the soil at the same quantitive as before the camelina season
(Shonnard et al., 2010). The fact that growing camelina favors other crops,
from the rotation of the soil, it will not be any loss in food producing land
(Shonnard et al., 2010).
In the U.S. it is suggested that more than five million acres can potentially
grow camelina which will not have a negative impact on the food supply
(Shonnard et al., 2010). This amount of growing area could produce 800
17
million gallons of oil each year for the usage in biofuel. (Shonnard et al.,
2010)
BIO-SPK fuel from rotation crops has been estimated at a cost of $3.70 per
gallon which is only 60 cents more than commercially used jet fuels used
today (Reimer and Zheng, 2016). The U.S. Air Force has done a few test
flights on a blend of camelina based jet and JP-8 jet fuel. These test flights
where all successful not showing any complications (Moser, 2010).
6.4 Rapeseed
Rape is a plant that produce oil, the plant has small dark seeds and these
seeds has an oil content of 40-50 % (Bernesson, 2004). The rapeseed oil is
an oil that can be used in the BIO-SPK process. One acre of rape produces
ten times less oil than one acre of algae (Naumienko and Rarata, 2010).
However, the biomass from rape which is left after the oil extraction can be
a protein source for cattle (Arvidsson et al., 2011).
During the spring of 2017, SAAB conducted a series of test flights with
their Gripen (SAAB, 2017). The fuel powering the plane was CHCJ-5
which is a 100% bio-jet fuel made from rapeseed oil (SAAB, 2017). The
test went without any complications showing that it is possible for a one
engine plane to be driven by alternative fuel (SAAB, 2017). Being able to
power a flight from 100% renewable fuel takes away the dependents of
importing different kinds of fuel (SAAB, 2017). The rapeseed oil based
fuel can be produced and used in the same country which will save the
transportation costs and might also be important in the future for defense
purposes (SAAB, 2017).
6.5 Jatropha
Jatropha is an oil seed bearing plant which is grown in subtropical and
tropical countries (Zhang et al., 2013; meyer). The plant has a rapid
growth, high oil content and drought tolerance (Zhang et al., 2013).
The oil rich fruit from the Jatropha plant can be used as a base in BIO-SPK
(Zhang et al., 2013; Arvidsson et al., 2011; Rahmes et al., 2009). To reduce
the water content of the fruit they are placed in sunlight (Arvidsson et al.,
18
2011). However, the biomass left from the oil extraction can not be used as
protein sources for cattle due to that it is toxic to animals (Meyer et al.,
2012; Arvidsson et al., 2011). Due to that the Jatropha is toxic, humans
have not been growing the plant for that long which indicates the plant has
not been fully explored (Meyer et al., 2012).
6.6 Switchgrass
Switchgrass is a type of grass which does not need a lot of water, fertilizers
and land to be able to grow (Payan et al., 2014). It is the lignin in this
biomass which can be fermented into alcohol and then transformed into
bio-jet fuel (Payan et al., 2014).
If a flight powered from jet fuel made from switchgrass the carbon dioxide
emissions would be lowered to about 63% compared with petroleum based
flights (Payan et al., 2014). A flight powered by a 50/50 blend of
switchgrass based and petroleum based fuel the carbon dioxide emissions
would be lowered to about 13% (Payan et al., 2014).
7 Costs
Even if bio-jet fuels have the ability to lower emissions of greenhouse
gases it will not be used by airlines if there is no financial gain (Air
Transportation Action Group, 2012; Hileman and Stratton, 2014). Biofuels
for aviation use currently are very rare and comparatively expensive, it is
theorized that with a higher amount of bio-jet fuel products coming onto
the market the prices of biofuels for aviation will most probably decrease
(Air Transportation Action Group, 2012). For the aviation industry to
realistically be willing to use bio-jet fuels the costs will have to meet the
costs of the fossil based fuel used today (Air Transportation Action Group,
2012). The cost of traditional jet fuel will become more expensive over
time, due to tax costs of carbon dioxide emission (Air Transportation
Action Group, 2012). It is supposed that the cost of carbon dioxide
emission will double the cost of fossil fuel by the year 2050 (Air
Transportation Action Group, 2012).
To be able to keep the cost as low as possible renewable jet fuel must be
close to identical to jet fuel that is already used in plane engines (Air
19
Transportation Action Group, 2012). If this requirement is met it will mean
that no new engines or planes would be needed and designing a new fuel
delivery system will not be necessary (Air Transportation Action Group,
2012). Basically, no extra requirements for any airports would be needed
(Air Transportation Action Group, 2012). The renewable fuels also have a
large production potential meaning that this type of fuel will be able to
compete with the petroleum based fuels that are used today (Hileman and
Stratton, 2014). However, a lot of water is needed for the production of
petroleum, water that could be used for producing edible feedstock
(Hileman and Stratton, 2014). This is however also a problem when
creating fuel from biomass (Hileman and Stratton, 2014). The production
of biomass based fuels requires a lot of water when producing the biomass
(Air Transportation Action Group, 2012). That is why, when producing a
biomass based fuel for the aviation industry, the focus is finding a base
which has a low impact on feedstock and water usage (Air Transportation
Action Group, 2012).
There are some main theories in how a change in the aviation industry can
occur, with lowering of the carbon dioxide emission (Hileman and Stratton,
2014). The first theory of how to change the aviation industry is to increase
the cost in usage of fossil fuels, a strategy which has to be done through
government climate policies (Hileman and Stratton, 2014). The overall
production cost of the production of jet fuel made from biomass must
decrease as well to theoretically be able to use bio-jet fuels in the aviation
industry. (Hileman and Stratton, 2014). However, it looks like the
economics and the policies surrounding petroleum based fuels are going in
the direction where there will be an increase in the price of the usage of
these types of fuels (Hileman and Stratton, 2014).
7.1 Flights Powered by Bio-Jet Fuel
There have been multiple test flights done with different types of bio-jet
fuels (Kinder and Rahmes, 2009; Moser, 2010; Air Transportation Action
Group, 2012; EcoSeed, 2012; SAAB, 2017; Yao et al., 2017). Over 1500
passenger flights have also been flown on bio-jet fuel blends (Air
Transportation Action Group, 2012). From the advances already made from
bio-jet fuels a few targets have been set up (Air Transportation Action
Group, 2012). Two of these targets are: 1.5% improvement of military fuel
efficiency per year until 2020 and to halve the carbon dioxide emissions
from 2005 by 2050 (Transportation Action Group, 2012). Due to the results
20
from all the different flights powered by bio-jet fuel these targets seem to
be reachable (Air Transportation Action Group, 2012).
8 Discussion
The biomass which could be produced for jet fuel could also be used for
ground transportation, energy, and other heat sources (Hileman and
Stratton, 2014). One example is that treated cellulosic biomass could be
used directly in power plants which would produce energy and heat, which
gives a large competition for renewable energy resources (Hileman and
Stratton, 2014). However, energy and heat we can get from different
energy sources such as wind power and solar energy, cannot be used for the
powering of commercial planes (Air Transportation Action Group, 2012).
Since the production of heat and energy can be found at other power
sources, I believe that it is important to use the biomass which can be used
for aviation fuel for that purpose to help with the lowering of the
greenhouse gas emissions from the aviation industry.
The use of advanced biofuels instead of first generation biofuels would
probably lower the usage of edible feedstock. Thus, the aviation industry
will not be depriving the world of the food it needs.
Some genetic modifications to the different biomasses would probably help
with the costly situation that the bio-jet fuels are in today. To genetically
alter all of the different plants used in BIO-SPK to produce more oil would
probably lower the amount of plants needed and the growth area would
become smaller. A different way of lowering the cost of the production of
bio-jet fuel from algae could be to genetically alter the algae to produce
shorter fatty acids. This would eliminate the need for hydrocracking the
longer chains, which would lower the cost of the production.
More knowledge towards the jatropha plant would probably give a better
growth rate. To genetically alter the plant height, earlier maturity, which
would shorten generation times, and to increase resistance towards pests
and diseases would probably give more fruit and a higher oil yield.
I also believe that more investments are needed in trying to understand and
develop the CBP systems in fungi. This will simplify and make the process
of getting jet fuels from lignin easier, quicker and probably cheaper.
To summarize how to get the advanced jet fuels on the market a
simplification of the production should be found, and a minimization of
21
steps of the different processes. This would probably make the process
cheaper which gives the fuels a possibility to compete with the fuels that
are on the market today.
In the future, there is a possibility that there would be a decrease in demand
of sources of high energy density fuels because ground transportation can
be powered by electricity (Air Transportation Action Group, 2012).
Because of the high energy demand for safe transportation for aviation
transport this industry cannot be powered by electricity (Hileman and
Stratton, 2014). This indicates that more time and money will have to be
invested in bio-jet fuels.
Getting 100 % advanced bio-jet fuels on the market might not happen
tomorrow but the knowledge and production of them are improving
quickly. I believe that it can be done, SAAB already showed that it can be
done by using rapeseed oil and test flights using jet fuel from algae oil or
from lignin will probably soon follow.
8.1 Social and Ethical Aspects
The aviation industry has grown rapidly and the carbon dioxide emissions
have grown as well (Jiménes-Díaz et al., 2017). There are no indications
that the aviation industry will stop growing and within the next 20 years the
commercial aviation industry is expected to grow 4.8 % (Boeing, 2016).
The carbon dioxide emissions will probably grow as well in the same
manner. Fuels made from biomass does not have as big of a negative
impact on the emissions of carbon dioxide (Gronenberg et al., 2013; Liew
et al., 2016). The petroleum prices are set to increase as well probably
making air transportation more expensive for their passengers (Hileman
and Stratton, 2014 ). In order to keep the emissions down a new energy
source needs to be found, and the advanced bio-jet fuels are the ideal fuels
to take over from the petroleum based fuels (Air Transportation Action
Group, 2012).
Fuels made from first generation biomass have a negative impact on our
society due to the increasing food prices, high water usage and pollution
(Air Transportation Action Group, 2012; Daroch et al., 2013; Fairley,
2011). Producing bio-jet fuels from nonedible feedstock would keep the
food prices and pollution down, having a less negative impact on our
society (Balan, 2014; Hileman and Stratton, 2014). The overall water usage
22
for the production of advanced biofuels is also smaller than the usage for
first generation biofuels (Elmoraghy and Farag, 2012).
Using food that people around the world can eat for the production of first
generation bio-jet fuels might not be ethically right but using advanced
biofuels will not deprive the people of their food sources. The advanced
bio-jet fuels could also have a positive impact on the military aviation
(Dagaut, 2005). Advanced bio-jet fuels produce less soot emissions,
making the military planes harder to detect on the radar (Dagaut, 2005).
Improving the military might not be ethically correct but I believe that an
overall improvement on the aviation industry, whatever it is, will probably
always also benefit the military industry.
9 Acknowledgment
I would like to thank my supervisor professor Johan Edqvist for supporting
and helping me in my work. I would also like to thank Alexander Blochel
for helping with the structure of this thesis.
23
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