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) is the lowest-emission diesel fuel. Although liquefied
petroleum gas
and hydrogen have cleaner combustion, they are used to fuel much less efficient
petrol engines and are not as widely available.
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.
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.
Biodiesel
is also safe to handle and transport because it is as biodegradable as sugar, one-tenth
as toxic as table salt, and has a high flash point of about 300°F
(148°C) compared to petroleum diesel fuel, which has a flash point of 125°F (52°C).
In
the USA, more than 80% of commercial trucks and city buses run on diesel. The
emerging US biodiesel market is estimated to have grown 200% from 2004 to 2005.
"By the end of 2006 biodiesel production was estimated to increase
fourfold [from 2004] to more than" 1 billion US gallons
(3,800,000 m3).
This
article is about transesterified lipids. For hydrogenated alkane renewable
diesel, see Vegetable
oil refining.
For biomass and organic waste-to-fuel production, see Biomass to liquid. For unmodified
vegetable oil used as motor fuel, see Vegetable
oil fuel.
Space-filling
model of methyl linoleate, or linoleic acid methyl ester, a common methyl ester
produced from soybean or canola oil and methanol
Space-filling
model of ethyl stearate, or stearic acid ethyl ester, an ethyl ester produced
from soybean or canola oil and ethanol
Biodiesel refers to a
vegetable oil- or animal fat-based diesel fuel consisting of
long-chain alkyl (methyl, ethyl, or propyl) esters. Biodiesel is
typically made by chemically reacting lipids (e.g., vegetable oil, animal fat (tallow)) with an alcohol producing fatty acid esters.
Biodiesel
is meant to be used in standard diesel engines and is thus distinct from the
vegetable and waste oils used to fuel converted diesel engines.
Biodiesel can be used alone, or blended with petrodiesel in any proportions.
Biodiesel can also be used as a low carbon alternative to heating oil.
The
technical definition of "biodiesel" as a mono-alkyl ester.
Historical background
Transesterification of a vegetable oil was conducted as early as 1853 by E.
Duffy and J. Patrick,
many years before the first diesel engine
became functional.
Rudolf Diesel's prime model, a single 10 ft (3 m) iron cylinder
with a flywheel at its base, ran on its own power for the first time in Augsburg, Germany, on 10
August 1893 running on nothing but peanut oil.
In remembrance of this event, 10 August has been declared "International Biodiesel Day".
It is often reported that Diesel
designed his engine to run on peanut oil, but this is not the case. Diesel
stated in his published papers, "at the Paris Exhibition in 1900 (Exposition
Universelle) there was shown by the Otto
Company a small Diesel engine, which, at the request of the French government ran on arachide
(earth-nut or pea-nut) oil (see biodiesel), and worked so smoothly that only a
few people were aware of it. The engine was constructed for using mineral oil,
and was then worked on vegetable oil without any alterations being made. The
French Government at the time thought of testing the applicability to power
production of the Arachide, or earth-nut, which grows in considerable
quantities in their African colonies, and can easily be cultivated there." Diesel
himself later conducted related tests and appeared supportive of the idea.
In a 1912 speech Diesel said, "the use of vegetable oils for engine fuels
may seem insignificant today but such oils may become, in the course of time,
as important as petroleum and the coal-tar products
of the present time."
Despite the widespread use of
petroleum-derived diesel fuels, interest in vegetable oils as fuels for
internal combustion engines was reported in several countries during the 1920s
and 1930s and later during World War II.
Belgium, France, Italy, the United Kingdom,
Portugal, Germany,
Brazil, Argentina,
Japan and China were reported to have tested and used vegetable oils as
diesel fuels during this time. Some operational problems were reported due to
the high viscosity of vegetable oils compared to petroleum diesel fuel, which
results in poor atomization of the fuel in the fuel spray and often leads to deposits
and coking of the injectors, combustion chamber and valves. Attempts to
overcome these problems included heating of the vegetable oil, blending it with
petroleum-derived diesel fuel or ethanol, pyrolysis
and cracking of the oils.
Transformation of vegetable
oils for their uses as fuels"
Belgian Patent 422,877. This patent described the alcoholysis (often referred
to as transesterification) of vegetable oils using ethanol (and mentions
methanol) in order to separate the fatty acids from the glycerol by replacing
the glycerol with short linear alcohols. This appears to be the first account
of the production of what is known as "biodiesel" today.
More recently, in 1977, Brazilian
scientist Expedito Parente invented and submitted for patent, the first
industrial process for the production of biodiesel.
This process is classified as biodiesel by international norms, conferring a
"standardized identity and quality. No other proposed biofuel has been
validated by the motor industry
Research into the use of
transesterified sunflower oil, and refining it to diesel fuel standards, was initiated in
South Africa
in 1979. By 1983, the process for producing fuel-quality, engine-tested
biodiesel was completed and published internationally.
With the erectetion of the first biodiesel pilot plant
in November 1987, and the first industrial-scale plant in April 1989 (with a
capacity of 30,000 tons of rapeseed per
annum).
Throughout the 1990s, plants were
opened in many European countries, including the Czech Republic,
Germany and Sweden. France
launched local production of biodiesel fuel (referred to as diester)
from rapeseed oil, which is mixed into regular diesel fuel at a level of 5%,
and into the diesel fuel used by some captive fleets (e.g. public transportation) at a level of 30%. Renault, Peugeot and other
manufacturers have certified truck engines for use with up to that level of
partial biodiesel; experiments with 50% biodiesel are underway. During the same
period, nations in other parts of the world also saw local production of
biodiesel starting up.
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