1.0
INTRODUCTION
A
biofuel is a fuel that is produced through contemporary biological processes,
such as agriculture and anaerobic digestion. Some s are produced by geological
processes such as those involved in the formation of fossil fuels. such as coal
and petroleum, from prehistoric biological matter. Biofuels can be derived
direct} from plants, or indirectly from agricultural, commercial, domestic,
and/or industrial Renewable biofuels generally involve contemporary carbon
fixation, such as those ihu; occur in plants or microalgae through*the process
of photosynthesis. Other renewable biofuels are made through the use or
conversion of biomass (referring to recently living organisms, most : flea
referring to plants or plant-derived materials). This biomass can be converted
to convenient energy-containing substances in three different ways: thermal
conversion, chemical conversion, and biochemical conversion. This biomass
conversion can result in fuel in solid, liquid, or gas form. This new biomass
can also be used directly for biofuels. Bioethanol is an alcohol made by
fermentation, mostly from carbohydrate produced in sugar or starch crops such
as corn, sugarcane, or sweet soghum. Cellulosic biomass, derived from non-food
sources, such as trees and grasses, is also being developed as a feedstock for
ethanol production. Ethanol can be used as a fuel for vehicles in its pure
form, but it is usually used as a gasoline additive to increase octane and
improve vehicle emissions. Bioethanol is widely used in the United States and
in Brazil. Current plant design does not provide for converting the lignin
portion of plant raw materials to fuel components by fermentation. Biodiesel
can be used as a fuel for vehicles in its pure form, but it is usually used as
a diesel additive to reduce levels of particulates, carbon monoxide, and
hydrocarbons from diesel-powered vehicles. Biodiesel is produced from oils or
fats using transesterification and is the most common biofuel in Europe.
There
are various social, economic, environmental and technical issues relating to
biofuels production and use, which have been debated in the popular media and
scientific journals. These include: the effect of moderating oil prizes, the
"food vs fuel" debate, poverty reduction potential, carbon emissions
levels, sustainable biofuel production, deforestation and soil erosion, loss of
biodiversity, impact on water resources, rural social exclusion and injustice,
shantytown migration, rural unskilled unemployment, and nitrogen dioxide (N02)
emission.
CHAPTER TWO
2.1 BIOFUEL GENERATIONS
First-generation biofuels
First-generation"
or conventional biofuels are biofuels made from food crops grown on arable
land. With this biofuel production generation, food crops are thus explicitly
growth for fuel production, and not anything else. The sugar, starch, or
vegetable oil obtained from the crops is converted into biodiesel or ethanol,
using transesterification, or yeast fermentation. Second Generation Biofuel
Second generation biofuels are fuels manufactured from various types of
biomass. Biomass is a wide-ranging term meaning any source of organic carbon
that is renewed rapidly as part of the carbon cycle. Biomass is derived from
plant materials, but can also include animal materials. Whereas first
generation biofuels are made from the sugars and vegetable oils found in arable
crops, second generation biofuels are made from lignocellulosic biomass or
woody crops, agricultural residues or waste plant material (from food crops).
This has both advantages and disadvantages. The advantage is that, unlike with
regular food crops, no arable land is used solely for the production of fuel.
The disadvantage is that unlike with regular food crops, it may be rather
difficult to extract the fuel. For instance, a series of physical and chemical
treatments might be required to convert lignocellulosic biomass to liquid fuels
suitable for transportation.
Third-generation biofuels
From
1978 to 1996, the US NREL experimented with using algae as a biofuels source in
the "Aquatic Species Program". A self-published article by Michael
Briggs, at the UNH Biofuels Group, offers estimates for the realistic
replacement of all vehicular fuel with biofuels by using algae that have a
natural oil content greater than 50%, which Briggs suggests can be grown on
algae ponds at wastewater treatment plants. This oil-rich algae can then be
extracted from the system and processed into biofuels, with the dried remainder
further reprocessed to create ethanol. The production of algae to harvest oil
for biofuels has not yet been undertaken on a commercial scale, but feasibility
studies have been conducted to arrive at the above yield estimate. In addition
to its projected high yield, algaculture -unlike crop-based biofuels - does not
entail a decrease in food production, since it requires neither farmland nor
fresh water. Many companies are pursuing algae bioreactors for various
purposes, including scaling up biofuels production to commercial levels. Prof.
Rodrigo E. Teixeira from the University of Alabama in Huntsville demonstrated
the extraction of biofuels lipids from wet algae using a simple and economical
reaction in ionic liquids.
Fourth-generation biofuels
Similarly
to third-generation biofuels, fourth-generation biofuels are made using
non-arable land. However, unlike third-generation biofuels, they do not require
the destruction of biomass. This class of biofuels includes electrofuels. And
photobiological solar fuels. Some of these fuels are carbon-neutral. The
conversion of crude oil from the plant seeds into useful fuels is called
transesterification
2.2 TYPES OF BIOFUELS
The
following fuels can be produced using first, second, third or fourth-generation
biofuel production procedures. Most of these can even be produced using two or
three of the different biofuel generation procedures.
Ethanol
Biologically
produced alcohols, most commonly ethanol, and less commonly propanol and
butanol, are produced by the action of microorganisms and enzymes through the
fermentation of sugars or starches (easiest), or cellulose (which is more
difficult). Biobutanol (also called biogasoline) is often claimed to provide a
direct replacement for gasoline, because it can be used directly in a gasoline
engine. Ethanol fuel is the most common biofuel worldwide, particularly in
Brazil. Alcohol fuels are produced by fermentation of sugars derived from
wheat, corn, sugar beets, sugar cane, molasses and any sugar or starch from
which alcoholic beverages such as whiskey, can be made (such as potato and fruit
waste, etc.). The ethanol production methods used are enzyme digestion (to
release sugars from stored starches), fermentation of the sugars, distillation
and drying. The distillation process requires significant energy input for heat
(sometimes unsustainable natural gas fossil fuel, but cellulosic biomass such
as bagasse, the waste left after sugar cane is pressed to extract its juice, is
the most common fuel in Brazil, while pellets, wood chips and also waste heat
are more common in Europe) Waste steam fuels ethanol factory -where waste heat
from the factories also is used in the district heating grid.
Ethanol can be used in petrol engines as a
replacement for gasoline; it can be mixed with gasoline to any percentage. Most
existing car petrol engines can run on blends of up to 15% bioethanol with
petroleum/gasoline. Ethanol has a smaller energy density than that of gasoline;
this means it takes more fuel (volume and mass) to produce the same amount of
work. An advantage of ethanol (CH 3C-H 20H) is that it has a higher octane
rating than ethanol-free gasoline available at roadside gas stations, which
allows an increase of an engine's compression ratio for increased thermal
efficiency. In high-altitude (thin air) locations, some states mandate a mix of
gasoline and ethanol as a winter oxidizer to reduce atmospheric pollution
emissions. Ethanol is also used to fuel bioethanol fireplaces. As they do not
require a chimney and are "flueless", bioethanol fires are extremely
useful for newly built homes and apartments without a flue. The downsides to
these fireplaces is that their heat output is slightly less than electric heat
or gas fires, and precautions must be taken to avoid carbon monoxide poisoning.
Corn-to-ethanol and other food stocks has led to the development of cellulosic
ethanol
Ethanol
has roughly one-third lower energy content per unit of volume compared to
gasoline. This is partly counteracted by the better efficiency when using
ethanol (in a long-term test of more than 2.1 million km, the BEST project
found FFV vehicles to be 1-26 % more energy efficient than petrol cars, but the
volumetric consumption increases by approximately 30%, so more fuel stops are
required). With current subsidies, ethanol fuel is slightly cheaper per
distance traveled in the United States.
2.3 BIODIESEL
Biodiesel is the most common biofuel in
Europe. It is produced from oils or fats using transesterification and is a
liquid similar in composition to fossil/mineral diesel. Chemically, it consists
mostly of fatty acid methyl (or ethyl) esters (FAMEs). Feedstocks for biodiesel
include animal fats, vegetable oils, soy, rapeseed, jatropha, mahua, mustard,
flax, sunflower, palm oil, hemp, field pennycress, Pongamia pinnata and algae.
Pure biodiesel (B100, also known as "neat" biodiesel) currently
reduces emissions with up to 60% compared to diesel Second generation B100
Biodiesel can be used in any diesel engine when mixed with mineral diesel. In
some countries, manufacturers cover their diesel engines under warranty for
B100 use, although Volkswagen of Germany, for example, asks drivers to check by
telephone with the VW environmental services department before switching to
B100. B100 may become more viscous at lower temperatures, depending on the
feedstock used. In most cases, biodiesel is compatible with diesel engines from
1994 onwards, which use 'Viton' (by DuPont) synthetic rubber in their
mechanical fuel injection systems. Note however, that no vehicles are certified
for using pure biodiesel before 2014, as there was no emission control protocol
available for biodiesel before this date. Electronically controlled 'common
rail' and 'unit injector' type systems from the late 1990s onwards may only use
biodiesel blended with conventional diesel fuel. These engines have finely
metered and atomized multiple-stage injection systems that are very sensitive
to the viscosity of the fuel. Many current-generation diesel engines are made
so that they can run on B100 without altering the engine itself, although this
depends on the fuel rail design. Since biodiesel is an effective solvent and
cleans residues deposited by mineral diesel, engine filters may need to be
replaced more often, as the biofuel dissolves old deposits in the fuel tank and
pipes. It also effectively cleans the engine combustion chamber of carbon
deposits, helping to maintain efficiency. In many European countries, a 5%
biodiesel blend is widely used and is available at thousands of gas stations.
Biodiesel is also an oxygenated fuel, meaning it contains a reduced amount of carbon
and higher hydrogen and oxygen content than fossil diesel. This improves the
combustion of biodiesel and reduces the particulate emissions from unburnt
carbon. However, using pure biodiesel may increase NOx-emissions. Biodiesel is
also safe to handle and transport because it is non-toxic and biodegradable,
and has a high flash point of about 300 °F (148 °C) compared to petroleum
diesel fuel, which has a flash poin 5 °F (52 °C). In the USA, more than 80% of
commercial trucks and city buses run on diesel.
CHAPTER THREE
1 3.1 OTHER BIO ALCOHOLS
Methanol
is currently produced from natural gas, a non-renewable fossil fuel. In the
future it is hoped to be produced from biomass as biomethanol. This is
technically feasible, but the production is currently being postponed for
concerns of Jacob S. Gibbs and Brinsley Coleberd that the economic viability is
still pending. The methanol economy is an alternative to the hydrogen economy,
compared to today's hydrogen production from natural gas.Butanol (C4H90H) is
formed by ABE fermentation (acetone, butanol, ethanol) and experimental
modifications of the process show potentially high net energy gains with
butanol as the only liquid product. Butanol will produce more energy and
allegedly can be burned "straight" in existing gasoline engines
(without modification to the engine or car), and is less corrosive and less
water-soluble than ethanol, and could be distributed via existing
infrastructures. DuPont and BP are working together to help develop butanol. E.
coli strains have also been successfully engineered to produce butanol by
modifying their amino acid metabolism.
Green diesel
Green
diesel is produced through hydrocracking biological oil feedstocks, such as
vegetable oils and animal fats. Hydrocracking is a refinery method that uses
elevated temperatures and pressure in the presence of a catalyst to break down
larger molecules, such as those found in vegetable oils, into shorter
hydrocarbon chains used in diesel engines. It may also be called renewable
diesel, hydrotreated vegetable oil or hydrogen-derived renewable diesel. Green
diesel has the same chemical properties as petroleum-based diesel. It does not
require new engines, pipelines or infrastructure to distribute and use, but has
not been produced at a cost that is competitive with petroleum. Gasoline versions
are also being developed. Green diesel is being developed in Louisiana and
Singapore by ConocoPhillips, Neste Oil, Valero, Dynamic Fuels, and Honeywell
UOP as well as Preem in Gothenburg, Sweden, creating what is known as Evolution
Diesel.
3.2 BIOFUEL GASOLINE
In
2013 UK researchers developed a genetically modified strain of Escherichia coli
(E.Coli), which could transform glucose into biofuel gasoline that does not
need to be blended. Later in 2013 UCLA researchers engineered a new metabolic
pathway to bypass glycolysis and increase the rate of conversion of sugars into
biofuel, while KAIST researchers developed a strain capable of producing
short-chain alkanes, free fair- acids, fatty esters and fatty alcohols through
the fatty acyl (acyl carrier protein (ACP)) to fatty aeii fatty acyl-CoA
pathway in vivo. It is believed that in the future it will be possible to
"tweak" the jer.es to make gasoline from straw or animal manure.
Vegetable Oil
Been
used for this purpose. Used vegetable oil is increasingly being processed into
biodiesel, or (more rarely) cleaned of water and paraculates and then used as a
fuel. As with 100% biodiesel (B100), to ensure the fiel injectors atomize the
vegetable oil in the correct pattern for efficient combustion, vegetable oii
fuel must be heated to reduce its viscosity to that of diesel, either by
electric coils or heat exchariers. This is easier in warm or temperate
climates. MAN B&W Diesel, Wartsila, and Deutz AG. as well as a number of
smaller companies, such as Elsbett, offer engines that are compatible with
straight vegetable oil, without the need for after-market modifications.
Vegetable
oil can also be used in many older diesel engines that do not use common rail
or unit injection electronic diesel injection systems. Due to the design of the
combustion chambers in indirect injection engines, these are the best engines
for use with vegetable oil. This system allows the relatively larger oil
molecules more time to bum. Some older engines, especially Mercedes, are driven
experimentally by enthusiasts without any conversion, a handful of drivers have
experienced limited success with earlier pre-"Pumpe Duse" VW TDI
engines and other similar engines with direct injection. Several companies,
such as Elsbett or Wolf, have developed professional conversion kits and
successfully installed hundreds of them over the last decades. Oils and fats
can be hydrogenated to give a diesel substitute. The resulting product is a
straight-chain hydrocarbon with a high cetane number, low in aromatics and
sulfur and does not contain oxygen. Hydrogenated oils can be blended with
diesel in all proportions. They have several advantages over biodiesel,
including good performance at low temperatures, no storage stability problems
and no susceptibility to microbial attack. Bioethers (also referred to as fuel
ethers or oxygenated fuels) are cost-effective compounds that act as octane
rating enhancers."Bioethers are produced by the reaction of reactive
iso-olefms, such as iso-butylene, with bioethanol."Bioethers are created
by wheat or sugar beet. They also enhance engine performance, whilst
significantly reducing engine wear and toxic exhaust emissions. Though
bioethers are likely to replace petroethers in the UK, it is highly unlikely
they will become a fuel in and of itself due to the low energy density. Greatly
reducing the amount of ground-level ozone emissions, they contribute to air
quality. When it comes to transportation fuel there are six ether additives:
dimethyl ether (DME), diethyl ether (DEE), methyl teritiary-butyl ether (MTBE),
ethyl ter-butyl ether (ETBE), ter-amyl methyl ether (TAME), and ter-amyl ethyl
ether (TAEE).
The
European Fuel Oxygenates Association (EFOA) credits methyl Ttertiary-butyl
ether (MTBE) and ethyl ter-butyl ether (ETBE) as the most commonly used ethers
in fuel to replace lead. Ethers were introduced in Europe in the 1970s to
replace the highly toxic compound. Although Europeans still use bio-ether
additives, the US no longer has an oxygenate requirement therefore bio-ethers
are no longer used as the main fuel additive.
3.3 BIOGAS
Biogas
is methane produced by the process of anaerobic digestion of organic material
by anaerobes. It can be produced either from biodegradable waste materials or
by the use of energy crops fed into anaerobic digesters to supplement gas
yields. The solid byproduct, digestate, can be used as a biofuel or a
fertilizer. Biogas can be recovered from mechanical biological treatment waste
processing systems. Landfill gas, a less clean form of biogas, is produced in
landfills through naturally occurring anaerobic digestion. If it escapes into
the atmosphere, it is a potential greenhouse gas. Farmers can produce biogas
from manure from their cattle by using anaerobic digesters.
Syngas
Syngas,
a mixture of carbon monoxide, hydrogen and other hydrocarbons, is produced by
partial combustion of biomass, that is, combustion with an amount of oxygen
that is not sufficient to convert the biomass completely to carbon dioxide and
water. Before partial combustion, the biomass is dried, and sometimes
pyrolysed. The resulting gas mixture, syngas, is more efficient than direct
combustion of the original biofuel; more of the energy contained in the fuel is
extracted. Syngas may be burned directly in internal combustion engines,
turbines or high-temperature fuel cells. The wood gas generator, a wood-fueled
gasification reactor, can be connected to an internal combustion engine. Syngas
can be used to produce methanol, DME and hydrogen, or converted via the
Fischer-Tropsch process to produce a diesel substitute, or a mixture of
alcohols that can be blended into gasoline. Gasification normally relies on
temperatures greater than 700 °C. Lower-temperature gasification is desirable
when co-producing biochar, but results in syngas polluted with tar.
Solid Biomass Fuels
Examples
include wood, sawdust, grass trimmings, domestic refuse, charcoal, agricultural
waste, nonfood energy crops, and dried manure. When solid biomass is already in
a suitable form (such as firewood), it can burn directly in a stove or furnace
to provide heat or raise steam. When solid biomass is in an inconvenient form
(such as sawdust, wood chips, grass, urban waste wood, agricultural residues),
the typical process is to densify the biomass. This process includes grinding
the raw biomass to an appropriate particulate size (known as hogfuel), which,
depending on the densification type, can be from 1 to 3 cm (0.4 to 1.2 in),
which is then concentrated into a fuel product. The current processes produce
wood pellets, cubes, or pucks. The pellet process is most common in Europe, and
is typically a pure wood product. The other types of densification are larger
in size compared to a pellet and are compatible with a broad range of input
feedstocks. The resulting densified fuel is easier to transport and feed into
thermal generation systems, such as boilers.
Sawdust,
bark and chips are already used for decades for fuel in industrial processes;
examples include the pulp and paper industry and the sugar cane industry.
Boilers in the range of 500,000 lb/hr of steam, and larger, are in routine
operation, using grate, spreader stoker, suspension burning and fluid bed
combustion. Utilities generate power, typically in the range of 5 to 50 MW,
using locally available fuel. Other industries have also installed wood waste
fueled boilers and dryers in areas with low-cost fuel.
One
of the advantages of solid biomass fuel is that it is often a byproduct,
residue or waste-product of other processes, such as farming, animal husbandry
and forestry. In theory, this means fuel and food production do not compete for
resources, although this is not always the case. A problem with the combustion
of solid biomass fuels is that it emits considerable amounts of pollutants,
such as particulates and polycyclic aromatic hydrocarbons. Even modern pellet
boilers generate much more pollutants than oil or natural gas boilers. Pellets
made from agricultural residues are usually worse than wood pellets, producing
much larger emissions of dioxins and chlorophenols.
CHAPTER FOUR
4.1 CONCLUSION
Biofuels
in the aviation sector worldwide is really taking off. As airlines come under
increasing pressure to reduce their carbon footprint, biofuels are an obvious
solution. Leading airlines are making strategic alliances with researchers and
fuel producers in order to secure their future supplies. Drop-in biofuels have
the exact molecular structure as mineral vehicle fuels and so can be generally
be used as direct replacements for mineral fuels. Renewable diesel is a drop-in
biofuel and can be used as a 100% replacement fuel.
Bio-Based
lubricants or Bio-Lubes are becoming of increasing interest to both major
producers of conventional lubricants, but also to the consumers and purchasers
of the finished products. Their greater bio-degradability, lesser toxicity,
non-bio-accumulative nature and good physical properties (e.g., high flash
point, low volatility, good lubricity (due to molecular polarity), high
viscosity index (VI)) are all creating a market pull for bio-based base oils.
Until recently, only a few bio-based base oils have been available (e.g.,
polyacetal glycerols [PAGs], esters, etc.), and these were generally only Group
IV base oils - which only have about a 1 percent market share of the
approximately 40 million ton global market. Now, bio-lubes are becoming more
available and are able to meet standards of Group III oils and above opening up
a much larger market potential. Additionally, selected bio-lubes are already
commercially available in some cases, leading to a lower perception of risk. Ethanol
and biodiesel are the major biofuels in production as of 2011. Gasoline engines
can use low-level ethanol blends, and modified engines can use higher-level
blends. Any unmodified diesel engine can use biodiesel, which can also be mixed
in any proportion with regular diesel (see References 1). The U.S.
Environmental Protection Agency investigates the impacts of biofuel use on
emissions and the environment.
Several
passenger vehicles come with a flex-fuel option that allows them to run on
ethanol/gasoline blends from 0 percent to 85 percent ethanol. Even normal
gasoline vehicles can operate on a 10 percent ethanol blend with no problems.
Diesel cars and trucks can run on biodiesel, though older models may need to
have their fuel lines and gaskets replaced with modern synthetic materials,
since biodiesel is a solvent . Some diesel owners have also modified their
vehicles to run on straight vegetable oil.
Recent
testing has shown the viability of biofuel use in the aviation industry, and
use of biofuels to power aircraft is expected to increase substantially in the
next decade. Because current biofiuel production relies heavily on crops that
also function as food or livestock feed, emphasis is on . developing new
sources that don't cause deforestation and compete with food production. A
plant called camelina .. part of the mustard family .. shows early promise.
A
large percentage of off-road equipment — such as vehicles used in agriculture,
mining, forestry construction, and power and heat production — use diesel fuel,
making this equipment suitable diesel use. Diesel for off-road applications has
different standards than diesel for vehicle use, including higher sulfur
content that can lead to environmentally damaging sulfur dioxide emissions.
Because biodiesel has low sulfur content, off-road biodiesel use can reduce
emission levels while lowering the consumption of nonrenewable resources.
Small
engines, like those found in lawn mowers and chainsaws, can use ethanol blends
up to 10 percent without problems. The harrier 10 using higher blends, up to 20
percent, has more to do with manufacturers' warranties f-an limitations of the
technology. Testing indicates that 20 percent ethanol blends do not harm
gasoline engines, but as of 2011, manufacturers have not shown the willingness
to alter warranty guidelines.
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