Biofuels are one of the main substitutes for fossil fuel with benefits
such as sustainability, eco-friendly and decent compliance. In the last ten
years, biofuels development has been led by the government guidelines and
regulations. Laws and policies have been conducted by many countries across the
world to ensure biofuels are being sustainably developed. Many biofuel related
projects commercialized with the support of governments. Furthermore, this
report aims to classify the most sustainable options for producing biofuels. It
also shows a comparison of several options based on energy return on energy
invested (EROEI), water and land required for the production as well as their effects
on universal climate change.
Biofuels are currently a provieder of over 1.5% of the overall transportation
fuels around the world. Also, under 2% is the percentage taken by corps grown
for biomass feedstock of the arable land world widely. The United states has
currently overcome Brazil by becoming the largest producer and consumer of
biofuels. Europe is remaining above China as the third largest producer,
although consumption has dramatically decreased recently due to change of
policies in number of European countries. The following figure shows the global
trends in biofuels production by region.
1st and 2nd
overview of biofuels policies and industrialization in the major biofuel
Renewable and Sustainable Energy Reviews, Volume 50, October
2015, Pages 991-1003
Yujie Su, Peidong Zhang, Yuqing Su
Generations of Biofuels
Liquid biofuels are becoming competitive
with petroleum fuels in terms of costs. That is due to the increase in oil costs,
this has also led to a sudden interest in
research and production of biofuels across the globe. Biodiesel,
Bioethanol and Biogas are the most commonly used types of the 1st
generation which are obtained largely from oils, seeds and lignocelluloses
produced by vegetables. Biodiesel can be used as an alternative of diesel while bioethanol is used in terms of
petrol. The main biodiesel feedstock are plant oils such as rapeseed, soybean,
sunflower, palm and some other inedible oils like Mahua, Neem, Karanja,
Jatropha, animal fats such as beef tallow. Consumed cooking oil is also being reproduced
as biodiesel by undergoing refining processes. Biodiesel contains no petroleum,
however, it can be combined at the desired ratio with Number two diesel fuel
for the purpose of being consumed by
diesel engines with slight or no adaptation. The transesterification process is
used to produced Fuel grade biodiesels. On the other hand, bioethanol is
produced commonly from the fermentation of many feedstock, for instance,
sugarcane, corn, maize, wheat as well as potatoes. Moreover, biogas is produced
by cleaning and purifying the raw gases produced by organic wastes of animals
in order to produce a reliable methane-rich fuel.
1st generation ethanol technologies
As mentioned, the main feedstock used to produce ethanol are
sucrose as well as starch. For ethanol production using sucrose, a mechanical
equipment is used to press the juices from the cooked sugarcane or sugar beet
corps followed by fractionation. The next step is that yeast cells are used to
absorb the sucrose and ferment the hexoses. The final step is that the ethanol
is recovered by distillation. For starch, the starch crops are hydrolysed into
glucose prior to the conversion of the carbohydrates by yeast cells into
ethanol. The next step includes milling the grains of wheat, corn or barley before
undergoing liquefaction as well as fractionation processes. Also, acidic or
enzymatic hydrolysis occurs prior to fermentation of the resulting hexoses.
This route ensures high efficiency of the production, however, it uses more
energy which results of more CO2 emissions into the air which varies depending
on the energy sources used. On the other hand, the route that uses sucrose
consumes less energy which means less CO2 emissions.
1st and 2nd biofuel gen
generation biodiesel technologies
Biodiesel is produced using the
transesterification method. The process aims to extract oil from oleaginous
plants and convert vegetable oil into fuel which can be consumed by the engines
directly. The direct vegetable oils could be used just as a fuel in the
modified engines. The transesterification uses enzymatic catalyzers or acids,
alkaline and ethanol or methanol and produces glycerin and fatty acids as a
residue. The process is summarised in the following
the alcohol with the catalyst, usually a strong base, for instance, NaOH or KOH
and wait for the reaction.
begins after The combined alcohol and catalyst are reacted with the fatty acid.
is then formed and should be separated from the biodiesel.
should be detached and recycled from the glycerol and biodiesel.
added to both the biodiesel and glycerol in order to separate them.
is evaporated out of the biodiesel and acid is added to the glycerol in order
to deliver neutralized glycerol.
Renewable and Sustainable Energy Reviews 73 (2017) 205–214
generation biogas technologies
It is claimed that biogas production process has higher efficiency
in terms of energy gain amongst the technologies of converting biomass to
fuels, the reason is that an aerobic
digestion can utilise carbohydrate, protein and fat in the feedstock to produce
biogas .Furthermore, the energy invested for an aerobic digestion technology
was found significantly high compared to other thermo-chemical and biological conversion
procedures, this includes the production of ethanol from cellulose. An aerobic
digestion is a process that includes the degradation of biomass by bacteria as
well as methanogenic organisms in the absence of oxygen. The process also
involves aerobic digesters to transform some of the resulted products by the degradation
into carbon dioxide and methane. Anaerobic digestion consists of four groups of
chemical reactions. The reactions are as follows: hydrolysis, acidogenesis,
acetogenesis and methanogenesis. However, since amino and fatty acids are
produced by hydrolysis, it is believed that acidogenesis occurs as a part of
the hydrolysis group. Hydrolysis occurs where proteins, fats and carbohydrates
are separated into smaller molecules, for instance: amino acids, fatty acids
and simple sugars. On the other hand, methanogens use some of the hydrolysis
products in the anaerobic digestion process. These products are then
transformed in acetogenesis before they are made available as nutrients for the
methanogenic organisms. Energy is generated byThe organisms using their
nutrients while converting them to methane. Also, while organisms are absorbing
the nutrients in the biomass, the formation of the acetate ion occurs. The
acetogens are fermentative bacteria which produce an acidic atmosphere, ammonium
salts, carbon dioxide as well as hydrogen in the digestive environment.
Methanogenesis is the final reaction of an
aerobic digestion which produces methane from the final product with the
support of some products from hydrolysis.
Technologies and developments of third generation biofuel
2nd Generation of biofuels
Unlike first generation,
second generation is more sustainable in terms of biomass used, which means
less CO2 emissions are formed during the production process. This generation is
fully dependent on affordable and abundant inedible resources produced by vegetation.
However, although the second generation production is more sustainable and has
less effects on environment it still lacks cost efficiency, that’s due some
issues surrounding the production process. Plant biomass are abundant and
underutilised biological resources which can be used efficiently in the fuel
productions. As it is most basic, electricity and heat can be generated by the
burning process of plant biomass. However, plant biomass can also be an
effective source for many types of biofuel productions. moreover, efforts to
produce biofuels using wood shaving and straw as a sugar feed stock are being
attempted . However, biofuel produced based on agricultural feedstock could
only fulfill a proportion of the growing demand for liquid fuels.
2nd generation technologies
The second generation biofuel production processes are relied on
cellulose hydrolysis followed by sugar fermentation. The biological matters can
be very useful for production of syngas (synthesis gas) by gasification
process. This syngas can be converted into liquid biofuels with the help of
several catalytic processes. In addition, the anaerobic digestion process is
used to produce methane and natural gas. The process includes digestion of
agriculture waste or crops.
Compared to the first generation,
the second generation feedstock are treated differently, for instance,
lignocellulose feedstock, which requires a number of processing steps before
being fermented into ethanol as in first generation. The technologies used in
the processing of biofuels second generation are as following:
The first technology is gasification,
This method has been used broadly in fossil fuels processing. Second generation
gasification tools have been considerably improved to suit the variances in
biomass stock. Wood, black and brown liquor as well as other feedstock are used
in this process. Throughout the gasification process, carbon-based resources
are transformed to carbon monoxide, hydrogen, in addition to carbon dioxide.
This process is unlike combustion in that oxygen is limited. The resulted gas
is known as synthesis gas or syngas which is used to generate heat as well as
Similarly to gasification, fossil
fuels have been produced using this process for years. Moreover, wood, a number
of energy crops as well as an inert gas such as halogen are used throughout the
process with no oxygen involved. The fuel is usually transformed into two
products which are tars and char.
The third reaction is known as torrefaction,
which is comparable to pyrolysis, however, no high temperatures are required in
this reaction. The procedure tends to produce improved fuels for additional use
in gasification or combustion. Torrefaction is often used to convert biomass
feedstock into an easy to transport and store form.
unique or genetically modified
bacteria is used in the fermentation process to deal with second generation’s
feedstock such as landfill gas and municipal waste.
3rd generation of biofuels
The current production process from algae
is classified as third generation of biofuels. Algae can produce oil which can
be further refined to diesel and some products of gasoline easily. The main
disadvantage of this process is that the biofuel produced by the third
generation have less stability than the previous two processes.
One of the most efficient methods to
produce microalgal biofuel is
through transesterification of the algal
oils to produce biodiesel. Biodiesel production includes mixing triglycerides,
methanol, and catalyst (may be alkali such as potassium hydroxide or acid) in a
controlled reaction chamber in order to stimulate transesterification. The
primary product is positioned in an extractor to remove the glycerine from the
product. While the extra methanol is recovered from the methyl esters through
evaporation. The final biodiesel is washed with water, pH neutralised, and then
The remaining biomass from the production
microalgal biomass residues (LMBRs), has
high concentrations of carbohydrates
and proteins. Therefore, LMBRs are potential
substrates for dark
fermentation to produce hydrogen, that serves
an important role in the sustainable growth of microalgal biodiesel production.
Alternatively, the production of methane using
the anaerobic digestion
of microalgal biomass remains of the
biodiesel production process
can meet some energy necessities of the process
of converting primary biomass to fuel. Otherwise, the remaining biomass would
be considered as waste with its disposal cost increasing the total costs for
biodiesel production from microalgae. Thus, the energy extraction from the
residual biomass can be used as a method to maximise the microalgal energy
production, and reduce the total process expenses as well as wastes. It has
also been suggested that the
non-lipid portion of the algal biomass may
be an alternative for electricity generation.
Renewable and Sustainable Energy Reviews
Fermentation is the
process of obtaining gases and ethanol from sugar along with yeast catalyst. The
fermentation process is widely used bioethanol production by sugar as well as
starch crops as in the first and the second generations. Fermentation method is
also applicable by third generation’s microalgae. Microalgae contain large
amounts of starch, that can be transformed into sugar. The production processes
can be presented as follows:
starch is extracted from the microalgae cells
with the support of an enzyme or mechanical machine.
when the microalgae cells start degrading,
saccharomycess cerevisiae is added into the microalgae feedstock for
fermentation which leads to the production of ethanol and carbon dioxide.
EIOER enegy investment over energy return
The energy invested
over the energy returned for biofuels from larger to lower is as follows:
Sugar Cane Ethanol
has the largest EROEI which is from 8.3:1 to 10.2:1
Cellulosic Ethanol with EROEI of 4:1
Corn Biodiesel which
has EROEI of 3:1
Corn Ethanol with EROEI
Compared to other
sources of energy, biofuels have larger EIOER than some of them such as
hydrogen that has an EROEI of 0.5:1. However, other sources have a slightly
larger EIOER, for instance: Coal and natural gas with EROEI of up to 10:1each,
and Oil Conventional EROEI that is currently estimated average 25:1, however it
One of the main
issues surrounding the production of biofuels is their requirement for great
quantities of land. In fact, biofuels require more land than petroleum fuels.
According to McDonald, biofuels will
require approximately 100 to 200 times more land per unit of area than fossil
fuels by 2030. This means energy demands and food resources cannot be met at
the same time. This issue can be solved by growing inedible plants to be used
as feedstock such as in the second generation of biofuels. Moreover, producing
energy dense feedstock as in the biofuels third generation can help reduce the
quantity of land required by biofuel productions, that is due to not competing for
land or clean water with agriculture or forestry. In fact, non-arable land and
water are suitable for third generation feedstock, for instance, they can be
located in the desert where large quantities of carbon dioxide are produced.
Both, first and
second generation feedstock growing as well as their production require water.
This means large amounts of water are required to produce fuel from biological
feedstock. Therefore, biofuel productions need to decrease the water usage in
order to remain sustainable. The limits in pure water supplies and the
population growth which leads to higher energy demands are the main challenges
facing the sustainability of biofuel production. On the other hand, some second
generation biofuels such as, cellulose feedstock which use small amounts of
water, however, they can only be obtained on small scale which is not enough
for meeting the current fuel demands.
biofuels are no better, the level of water used in the feedstock growing and
the production of Algae biofuels is not sustainable, for instance, around 123
billion liters of water are required to produce 5% of transportation fuel in
the United states.
Biofuel impacts on
Hundreds of analysis
have been performed over the last 20 years regarding the CO2 emissions from the
life cycle of biofuels. The analysis state that first generation biofuels require
fertilizer which produces more N2O, while less fertilizer is used by second
generation, which means less N2O is produced. Also, the second generation
production use non fossil materials hence they do not emit fossil CO2, this
means that their CO2 emissions are lower than first generation as well as
petroleum fuels. The main two impacts of biofuel production on climate change
are the biogeophysical impacts and the nitrogen cycle impacts.
the change in land
use can lead to changes in the physical parameters of the vegetation as well as
evapotranspiration rates. These changes can cause direct effects on the
energy’s absorption and disposition at the surface of the earth, which affects
the regional as well as the local temperatures. Furthermore, the changes affect
the hydrologic cycle as well as climate change in many ways, for instance, via
cloud formation and the forcing of water evaporation using direct radiations
which affect the carbon sequestration and the growth of the vegetation.
The nitrogen cycle
produced by fuels fertilizer or the combustion, can affect sides of the universal
nitrogen cycle, that has a wide variety of environmental impacts, including coastal
and lakes eutrophication, fertilisation of global ecosystems, water and land
acidification, biodiversity changes, respiratory disease in humans, crops can
be damaged by the ozone, and it can also cause changes to global climate.
productions of the first generation are slightly larger than the second
generation although the second generation uses inedible and less expensive
feedstock. however, more industrial developments are being built around the
second generation. Moreover, the third generation is the least developed
amongst the three generations due to being in the early stages of scale up and
commercialization, though, it offers the same advantages as the first and the
second generations. Furthermore, the third generation can produce larger yields
/ acre than other biofuels. In general, biofuels require larger quantities of
land as well as huge amounts of water to remain operative. In fact, they use
more land and water than other fuels which technically makes them not sustainable.
Overall, biofuels must do more efforts in terms of their sustainability based
on feedstock options, water, land use as well as their effects on climate
change in order to be able to compete with other energy sources.