The Future of Advanced Bio-Jet Fuel - liu.diva-portal.org1112383/FULLTEXT01.pdf · advanced bio-jet fuel, aviation industry, HEFA-SPK, jet fuel, TF-SPK ... greenhouse gas effect (Jiménes-Díaz

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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