European Bioenergy Research: Aviation Fuel from Vegetable Oils Report

This report investigates the conversion of vegetable oils into aviation fuel, addressing the need for sustainable alternatives to fossil fuels. The study focuses on the hydrothermal conversion process, detailing the four stages involved: hydrolysis, decarboxylation, cracking, and hydrogenation. It emphasizes the importance of catalysts and optimal conditions to enhance the yield and quality of the biofuel. The report highlights the environmental benefits of biofuel, such as reduced greenhouse gas emissions and a cleaner environment, and discusses the potential of algae as a feedstock. It also references various research papers and publications to support the findings and conclusions, advocating for more innovation in the use of vegetable oils, forest, agricultural products and wastes to produce more environmentally friendly energy. The study concludes that this method of biofuel generation is greener, simpler, and more cost-effective, making it a sustainable solution for the aviation industry. The report also provides details on the methodology used, including the use of heated water as a form of catalyst to minimize the formation of gaseous products.

Converting vegetable oils using co2 as a reactant into aviation fuel
European Bioenergy Research Institute (EBRI), Aston University, UK
Introduction
The inexhaustible, clean, and absence of greenhouse gas emissions are properties that
renewable energy sources have over fossil fuels. Fossils are most applied worldwide but are
not sustainable since they emit CO2 gas in the atmosphere leading to accumulation of
greenhouse gases hence climate change. Renewable friendly sources of energy such as
biofuels that are friendly to the environment are needed to be produced and applied to
improve the health of environment and make it habitable to both human, plants and animals.
One way to be rid of the negative impacts these fossil energy sources have is by
electrification. Batteries charged by renewable energy sources such as wind, hydro, solar.
Charging by non-renewable energy sources is also plausible option as the potential harmful
emissions will be away from the dense population areas. However, planes require a lot of
power, batteries are heavy and planes need to fly. Another line of reasoning is the economic
impact, the positive correlation between the fuel quantity and the operating costs of the
aircraft. Complete electric propulsion is still being proposed, nonetheless, a hybrid system is
an approach used today. The energy from the hydrocarbon fuel and power for the aircraft
systems from the batteries (Atkinsglobal.com, 2019).
Biofuels are known as the liquid fuel generated from the biomass of dissimilar forest
materials, agricultural materials and some biodegradable wastes (Yan, 2017). It is extracted
from the vegetable oil algae, bio butanol. Vegetable oil is an upcoming major source of
biofuel generation in the whole world since they have a close energetic content to
hydrocarbon fuels for transport, but the direct use is not acceptable mainly due to the
relatively low viscosity required by the engines (Neuling and Kaltschmitt, 2017).
Transesterification is a chemical process that converts oil into esters in the presence of a
catalyst. This conversion to biodiesel helps to reduce the viscosity of the vegetable oil and
allows use without any modification to conventional engines. Almost 400 oil crops are
potential sources for diesel engines, but aircraft engines require more specific characteristics
as defined by ASTM D1655 in terms of energy density, viscosity, lower heating value, boiling
point.
Algae are also an upcoming source of biofuel generation as they are known to be safe, non-
competitive and grow very fast, but they have a relatively low solid content and require more
pre-treatment steps before oil extraction (SAIFUDDIN et al., 2016).
Therefore, exploring methods for direct production of bio kerosene is necessary. One of
these is fisher –tropsch processes which involve high-temperature gasification of biomass to
produce a syngas which is later converted catalytically to hydrocarbons. The HEFA process is
another, it is more famous and already being commercialized. However, with the discovery of
solutions and solving problems being the sole aim of science and engineering, there goal of
this research will be to find a way to make this process more efficient (Biofuels International,
2019).
Methodology
This proposed research will focus mainly on the hydrothermal conversion of vegetable oils
using into aviation fuel . The yield and quality of product depend on the process conditions
and feedstock. The application of heated water works as a form of catalyst, minimising the
formation of gaseous products from degraded oil because of the lower temperature used
relative to conventional methods. The procedure is carried out in four stages : i) Hydrolysis ii)
Decarboxylation iii) Cracking iv) Hydrogenation.
Hydrolysis reactions can be performed using heat (thermally) as liquid-liquid reactions or as
gas-liquid reactions utilizing superheated steam. Another method involves the use of lipolytic
enzymes at room temperature. Biofuel can be produced via two routes beginning with
vegetable oils or fats. In the first process, the reaction occurs in two stages. The vegetable
oil/fat is first converted into fatty acids through hydrolysis and then the fatty acid is converted
to the fuel via esterification. The second method which is the conventional method involves
transesterification of vegetable oils into biofuel in the presence of alkali-based catalysts
(Demirbas 2008).
Next, decarboxylation. The thermal decarboxylation of fatty acids at moderate temperatures
less than 400 degrees Celsius produces a low yield of hydrocarbons which then means it is
necessary to use a catalyst. Hydrothermal decarboxylation of fatty acids at moderate
temperatures (less than 400 ) gives low yields if no catalyst is used (Heimann, Karthikeyan,℃
& Muthu 2016). This indicates that a catalyst is necessary to drive the reaction and to boost
the yield. Commonly used catalysts are metals such as platinum Pt, nickel Ni and palladium
Pd (Demirbas 2008).
Following this, the large hydrocarbon molecule is broken down into smaller molecules. In
hydrothermal cracking, high temperatures as high as 750 are used (Boyadjian & Lefferts℃
2018). The pressure used is also very high (in the range of 70 atm) (Boyadjian & Lefferts
2018). It is a combined process of both thermal and catalytic cracking. The major steps in
hydrothermal cracking include:
i) Thermal reactions break down the carbon-carbon (C-C) bonds of the alkane into free
reactive radicals.
ii) This is followed by the dissociation of the free radicals.
iii) The free radicals are then converted into hydrocarbon molecules through catalytic
hydrogenation.
The two reactions (thermal and catalytic) occur in parallel and the thermal reaction
dominates at higher reaction temperature range.
Finally, in order to meet the Jet A1 specification, the double bonds in the alkenes must be
saturated (Demirbas 2008). The overall effect of the addition of hydrogen is the elimination of
the double bond in the alkene. Despite the fact that the reaction is exothermic, the activation
energy is quite high and the reaction cannot take place under normal conditions. Therefore, a
catalyst is normally used to lower the activation energy and to speed up the reaction. A
commonly used catalyst is aluminium (iii) oxide 〖 Al 〗 _2 O_3.
Conclusion
This processes of generating biofuel is greener, simpler and cost-effective hence more
sustainable. More innovations should be done on how to use the vegetable oil, forest and
agricultural products and wastes to generate more clean and friendly energy to the
environment. Algae are most preferred since they are not edible and therefore will reduce
the competition of energy generation and food industry. Generation of biofuel maintain
clean, healthy and friendly environment, reduces the levels of diseases caused by burning
fossil fuels, and also ensure sustainability. Biofuel reduced the emission of greenhouse gases
into atmosphere hence reduces global warming and climate change, therefore it will try to
solve the environmental problems and at the same time meet the need of people in terms of
energy production.
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