Dr. Ajay Singh Lodhi
College of Agriculture, Balaghat
Jawahar Lal Krishi Vishwa Vidyalaya, Jabalpur (M.P.)
A biofuel is a fuel that is produced through contemporary
biological processes, such as agriculture and anaerobic
digestion, rather than a fuel produced by geological
processes such as those involved in the formation of fossil
fuels, such as coal and petroleum, from prehistoric
Biofuels can be derived directly from plants (i.e. energy
crops), or indirectly from agricultural, commercial,
domestic, and/or industrial wastes.
Renewable biofuels generally involve contemporary carbon
fixation, such as those that 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 often referring to plants or plant-derived
3. “Biofuels” are transportation fuels like ethanol and
biodiesel that are made from biomass materials. These
fuels are usually blended with petroleum fuels namely
with gasoline (petrol) and diesel fuel, but they can also
be used on their own. Ethanol and biodiesel are also
cleaner burning fuels, producing fewer air pollutants.
Ethanol is a alcohol fuel made from the sugars found in
grains such as corn, sorghum, and wheat, as well as
potato skins, rice, sugarcane, sugar beets and yard
clippings by fermentation.
Bio-diesel fuel can be made from renewable vegetable
oils, animal fats or recycled cooking oils by trans
4. THE FOLLOWING ARE SOME OF THE CHARACTERS
FOR THE EFFICIENT BIO-DIESEL
Viscosity represents flow characteristics and the tendency
of fluids to deform with stress. Viscosity affects injector
lubrication and fuel atomization.
Fuels with low viscosity may not provide sufficient
lubrication for the precision fit of fuel injection pumps,
resulting in leakage or increased wear. Fuel atomization is
also affected by fuel viscosity.
Diesel fuels with high viscosity tend to form larger droplets
on injection which can cause poor combustion, increased
exhaust smoke and emissions.
It’s the weight per unit volume. Oils that are denser contain
more energy. For example, petrol and diesel fuels give
comparable energy by weight, but diesel is denser and
hence gives more energy per litre.
Biodiesel is generally denser than diesel fuel with sample
values ranging between 877 kg/m3 to 884 kg/m3 compared
with diesel at 835 kg/m3. Thus, density of the final product
depends mostly on the feedstock used.
Heat of combustion: Heating Value or Heat of Combustion,
is the amount of heating energy released by the
combustion of a unit value of fuels. One of the most
important determinants of heating value is moisture
content. Liquid biofuels however have bulk densities
comparable to those for fossil fuels.
6. Melt point or Pour point Melt or pour point:
It refers to the temperature at which the oil in solid form
starts to melt or pour. In case where the temperatures fall
below the melt point, the entire fuel system including all
fuel lines and fuel tank will need to be heated.
The temperature at which an oil starts to solidify is known
as the cloud point. While operating an engine at
temperatures below an oil’s cloud point, heating will be
necessary in order to avoid waxing of the fuel.
7. Flash point (FP) :
The flash point temperature of diesel fuel is the minimum
temperature at which the fuel will ignite (flash) on
application of an ignition source. Flash point varies
inversely with the fuel’s volatility. Minimum flash point
temperatures are required for proper safety and handling of
diesel fuel. The flash point determines the flammability of
the material. Neat biodiesel has a flash point (150°C) well
above the flash point of petroleum based diesel fuel
The total acid number is an indication of the presence of
free fatty acids formed due to oil degradation and
combustion. It can also result from improper manufacturing,
through remaining catalyst or excessive neutralization.
8. Iodine value:
It is an index of the number of double bonds in biodiesel,
and therefore is a parameter that quantifies the degree of
unsaturation of biodiesel. It is reported in terms of the
grams of iodine that will react with 100 grams of a fat or oil
under specified condition. It is a value of the amount of
iodine, measured in grams, absorbed by 100 grams of
given oil. It is commonly used as a measure of the
chemical stability properties of different biodiesel fuels
against such oxidation.
This indicates the tendency of fuel to form carbon deposits
in an engine. An important indicator of the quality of
biodiesel is the carbon residue, which corresponds to the
content of glycerides, free fatty acids, soaps, polymers and
9. Aniline point/Cetane number (CN):
It is a relative measure of the interval between the
beginning of injection and auto-ignition of the fuel. The
higher the cetane number, the shorter the delay interval
and the greater its combustibility. Fuels with low Cetane
Numbers will result in difficult starting, noise and exhaust
In general, diesel engines will operate better on fuels with
Cetane Numbers above 50. Cetane number is usually
measured directly using a test engine. Cetane tests
provide information on the ignition quality of a diesel fuel.
Diesel fuel usually has a cetane rating between 45 and 50
while vegetable oil is 35 to 45. Biodiesel is usually have in
between 50 to 60.
Biodiesel ages more quickly than petroleum diesel fuel due
to the chemical structure of fatty acids and methyl esters
present in biodiesel. Typically there are fourteen types of
fatty acid methyl ester in the biodiesel.
The individual proportion of presence of these esters in the
fuel affects the final properties of biodiesel. Poor oxidation
stability can cause fuel thickening, formation of gums and
sediments which in turn can cause filter clogging and
Biodiesel and biodiesel blends are much more thermally
stable than diesel. Biodiesel and its blends should not be
stored in a storage tank or vehicle tank more than 6
months. Depending upon the storage temperature and
other conditions suggest the use of appropriate
11. Ash Percentage:
Ash is a measure of the amount of metals contained in the fuel.
High concentrations of these materials can cause injector tip
plugging, combustion deposits and injection system wear. The
ash content is important for the heating value, as heating value
decreases with increasing ash content.
Ash content for bio-fuels is typically lower than for most coals,
and sulphur content is much lower than for many fossil fuels.
Sulfur percentage :
The percentage by weight, of sulfur in the fuel sulfur content is
limited by law to very small percentages for diesel fuel used in
on-road applications. First use vegetable oil and animal fat
based biodiesel has less than 15 ppm sulphur. Many
researchers claim that pure biodiesel is essentially sulphur free
and therefore biodiesel is an ultra-low sulphur fuel.
India is one of the largest petroleum consuming/ importing
country, import about 70% of its demand.
Some vegetable oils, edible as well as a non-edible, can be
used (after some chemical processing) in pure form or
blended with petroleum diesel as fuel in diesel engine
biogas, non-toxic, 100% less SO2, emission with no
Bio-diesel is an eco-friendly, alternative diesel fuel
prepared from domestic renewable resources, i.e.
vegetable oil (edible or non-edible oil) and animal fats.
These natural oils and fats are made-up mainly
triglycerides. These are in similarly to petroleum derived
diesel and are called “Bio-diesel”.
Bio-diesel is a recycled fuel and chemically free fatty acid
Why Biodiesel ?
13. BIODIESEL PRODUCTION
Biodiesel is a liquid biofuel obtained by chemical
processes from vegetable oils or animal fats and an
alcohol that can be used in diesel engines, alone or
blended with diesel oil.
ASTM International (originally known as the American
Society for Testing and Materials) defines biodiesel as a
mixture of long-chain mono-alkylic esters from fatty acids
obtained from renewable resources, to be used in diesel
Blends with diesel fuel are indicated as ‘‘Bx’’, where ‘‘x’’ is
the percentage of biodiesel in the blend. For instance,
‘‘B5’’ indicates a blend with 5% biodiesel and 95% diesel
fuel; in consequence, B100 indicates pure biodiesel.
14. FEEDSTOCKS USED IN BIODIESEL PRODUCTION
The primary raw materials used in the production of biodiesel
are vegetable oils, animal fats, and recycled greases.
These materials contain triglycerides, free fatty acids, and other
contaminants depending on the degree of pre-treatment they
have received prior to delivery.
Since biodiesel is a mono-alkyl fatty acid ester, the primary
alcohol used to form the ester is the other major feedstock.
Most processes for making biodiesel use a catalyst to initiate
the esterification reaction. The catalyst is required because the
alcohol is sparingly soluble in the oil phase. The catalyst
promotes an increase in solubility to allow the reaction to
proceed at a reasonable rate.
The most common catalysts used are strong mineral bases
such as sodium hydroxide and potassium hydroxide. After the
reaction, the base catalyst must be neutralized with a strong
15. Typical proportions for the chemicals used to make
Reactants •Fat or oil (e.g. 100 kg soybean oil)
•Primary alcohol (e.g. 10 kg methanol)
Catalyst •Mineral base (e.g. 0.3 kg sodium
Neutralizer •Mineral acid (e.g. 0.25 kg sulfuric
16. ADVANTAGES OF THE USE OF BIODIESEL
Renewable fuel, obtained from vegetable oils or animal
Low toxicity, in comparison with diesel fuel.
Degrades more rapidly than diesel fuel, minimizing the
environmental consequences of biofuel spills.
Lower emissions of contaminants: carbon monoxide,
particulate matter, polycyclic aromatic hydrocarbons,
Lower health risk, due to reduced emissions of
No sulfur dioxide (SO2) emissions.
Higher flash point.
17. May be blended with diesel fuel at any proportion; both
fuels may be mixed during the fuel supply to vehicles.
Excellent properties as a lubricant.
It is the only alternative fuel that can be used in a
conventional diesel engine, without modifications.
Used cooking oils and fat residues from meat processing
may be used as raw materials.
18. DISADVANTAGES OF THE USE OF BIODIESEL
Slightly higher fuel consumption due to the lower calorific value of
Slightly higher nitrous oxide (NOx) emissions than diesel fuel.
Higher freezing point than diesel fuel. This may be inconvenient in
It is less stable than diesel fuel, and therefore long-term storage
(more than six months) of biodiesel is not recommended.
May degrade plastic and natural rubber gaskets and hoses when
used in pure form, in which case replacement with Teflon
components is recommended.
It dissolves the deposits of sediments and other contaminants from
diesel fuel in storage tanks and fuel lines, which then are flushed
away by the biofuel into the engine, where they can cause
problems in the valves and injection systems. In consequence, the
cleaning of tanks prior to filling with biodiesel is recommended.
It must be noted that these disadvantages are significantly
reduced when biodiesel is used in blends with diesel fuel.
19. Fats and Oils:
Choice of the fats or oils to be used in producing biodiesel
is both a process chemistry decision and an economic
With respect to process chemistry, the greatest difference
among the choices of fats and oils is the amount of free
fatty acids that are associated with the triglycerides. Other
contaminants, such as color and odor bodies can reduce
the value of the glycerin produced, and reduce the public
acceptance of the fuel if the color and odor persist in the
Most vegetable oils have a low percentage of associated
free fatty acids. Crude vegetable oils contain some free
fatty acids and phospholipids. The phospholipids are
removed in a “degumming” step and the free fatty acids
are removed in a “refining” step. Oil can be purchased as
crude, degummed, or refined. The selection of the type of
oil affects the production technology that is required.
20. The options for the triglyceride choice are many. Among the
vegetable oils sources are soybean, canola, palm, and
rape. Animal fats are products of rendering operations.
They include beef tallow, lard, poultry fat, and fish oils.
Yellow greases can be mixtures of vegetable and animal
There are other less desirable, but also less expensive
triglyceride sources such as brown grease and soap stock.
The free fatty acid content affects the type of biodiesel
process used, and the yield of fuel from that process. The
other contaminants present can affect the extent of
feedstock preparation necessary to use a given reaction
The most commonly used primary alcohol used in biodiesel
production is methanol, although other alcohols, such as
ethanol, isopropanol, and butyl, can be used. A key quality factor
for the primary alcohol is the water content. Water interferes with
transesterification reactions and can result in poor yields and
high levels of soap, free fatty acids, and triglycerides in the final
fuel. Unfortunately, all the lower alcohols are hygroscopic and
are capable of absorbing water from the air.
Many alcohols have been used to make biodiesel. As long as the
product esters meet ASTM 6751, it does not make any chemical
difference which alcohol is used in the process. Other issues
such as cost of the alcohol, the amount of alcohol needed for the
reaction, the ease of recovering and recycling the alcohol, fuel
tax credits, and global warming issues influence the choice of
alcohol. Some alcohols also require slight technical modifications
to the production process such as higher operating
temperatures, longer or slower mixing times, or lower mixing
22. Catalysts and Neutralizers:
Catalysts may either be base, acid, or enzyme materials.
The most commonly used catalyst materials for converting
triglycerides to biodiesel are sodium hydroxide, potassium
hydroxide, and sodium methoxide.
Most base catalyst systems use vegetable oils as a
feedstock. If the vegetable oil is crude, it contains small
amounts (<2%) of free fatty acids that will form soaps that
will end up in the crude glycerin. Refined feedstocks, such
as refined soybeen oil can also be used with base
The base catalysts are highly hygroscopic and they form
chemical water when dissolved in the alcohol reactant.
They also absorb water from the air during storage. If too
much water has been adsorbed the catalyst will perform
poorly and the biodiesel may not meet the total glycerin
23. Although acid catalysts can be used for transesterification
they are generally considered to be too slow for industrial
Acid catalysts are more commonly used for the
esterification of free fatty acids. Acid catalysts include
sulfuric acid and phosphoric acid.
Solid calcium carbonate is used as an acid catalyst in one
experimental homogeneous catalyst process. The acid
catalyst is mixed with methanol and then this mixture is
added to the free fatty acids or a feedstock that contains
high levels of free fatty acids. The free fatty acids convert
into biodiesel. The acids will need neutralization when this
process is complete, but this can be done as base catalyst
is added to convert any remaining triglycerides.
24. There is continuing interest in using lipases as enzymatic
catalysts for the production of alkyl fatty acid esters. Some
enzymes work on the triglyceride, converting them to
methyl esters; and some work on the fatty acids. The
commercial use of enzymes is currently limited to countries
like Japan, where energy costs are high, or for the
production of specialty chemicals from specific types of
fatty acids. The commercial use of enzymes is limited
because costs are high, the rate of reaction is slow, and
yields to methyl esters are typically less than the 99.7%
required for fuel-grade biodiesel. Enzymes are being
considered for fatty acid conversion to biodiesel as a pre-
treatment step, but this system is not commercial at this
25. Neutralizers are used to remove the base or acid catalyst
from the product biodiesel and glycerol. If you are using a
base catalyst, the neutralizer is typically an acid, and visa
versa. If the biodiesel is being washed, the neutralizer
can be added to the wash water. While hydrochloric acid
is a common choice to neutralize base catalysts, as
mentioned earlier, if phosphoric acid is used, the resulting
salt has value as a chemical fertilizer.