2. The alternative fuel should be found to compensate the future fuel demand and reduce
the pollution.
The vegetable oil/animal fat has a high energy density to meet the energy compensation,
but its properties are not favorable for better atomization and so can be converted in to
biodiesel.
Generally four methods are used to produce biodiesel from vegetable oils and animal
fat.
The four methods of biodiesel production are:
Direct use and blending
Transesterification process
Pyrolysis and
Micro emulsion.
3. SOME POINTS ABOUT BIODIESEL
Biodiesel is the mono alkali ester which is derived from the animal fat or vegetable oil.
The carbon will be neutral when biodiesel is used as a fuel, because during the
combustion process, the amount of carbon emission is equal to an animal or plant
absorbed during it whole life time. So the emission will be low in green combustion of
biofuel.
Diesel is the most dominant fuel in the world including the area of transport,
agriculture, and power generation, some industrial applications, etc.
The vegetable oil can be the alternative for diesel and it could be the fuel in the diesel
engine
4. DIRECT USE AND BLENDING
The animal fat or vegetable oil can be used as a fuel in direct injection engines; it has
a good heating value and could give a sufficient power.
To avoid problems, the alternative fuel sources are directly blended with
conventional fossil fuels. This kind of blending will improve the fuel quality, reduces
the fossil fuel consumption.
The bio oil and diesel blends will be in different ratios like 10:1,10:2, 10:3
6. Catalyst is used to increase the speed of the reaction and quality of the outcome product.
The amount and types of catalyst are decided by the amount of free fatty acid present in the feed stock oil.
The higher amount of free fatty acid is unfavorable for biodiesel production which leads to formation of soap and decrease
biodiesel yield efficiency
The reasons are:
presence of water or Free Fatty Acids (FFA) acts as poison for the catalyst.
the price of pure triglyceride does not allow biodiesel to compete with diesel fuel in cost.
Base catalyst transesterification process
In this stage of the process, potassium Hydroxide (KOH), sodium hydroxide (NaOH) and sodium methoxide are used as
catalysts.
Sodium methoxide (CH3NaO) is the most efficient catalyst but it is not economic. Sodium methoxide is sold as a 30 percent
solution in methanol for easier handling. Base catalysts are very sensitive to the presence of water and free fatty acids. The
amount of sodium methoxide required is 0.3 to 0.5 percent of the weight of the oil. A higher amount of catalyst (0.5 to 1.5
percent of the weight of the oil) is required when NaOH or KOH is used. NaOH and KOH also lead to water formation, which
slows the reaction rate and causes soap (metallic salt of a fatty acid) formation
It is a reaction between alcohol and oil with the presence of base catalyst
The reaction temperature (500
C – 600
C) should be maintained in order to get highest biodiesel yield. The reaction temperature
should be below of methanol boiling point (64.7 0C) – to prevent vaporization.
The stirring process (1300 rpm) to be carried throughout the process for dynamic mixing to increase the rate of reaction.
Appxly. one hour is needed to complete the reaction. Biodiesel and glycerol produced should be kept for separation in a
separating stock for 12 hours to 24 hours. The upper layer ----- biodiesel; the lower will be the glycerol (BP of ethanol = 78.37
0C).
7. Acid catalyst esterification process
Some feed stock oil has more than 1% free fatty acid; this free fatty oil cannot be converted into biodiesel. So
the yield of biodiesel from the transesterification process will be very low. In this case the feed stock oil is
subjected to the acid catalyst esterification before the base catalyst transesterification process. Here the free
fatty acid is converted into the ester.
This process also can be used to convert the triglycerides into the biodiesel but it will take more time. So, it is
not preferred.
In this process, the alcohol will reacts with oil using acid catalyst and produces the biodiesel and water.
The water must be removed immediately because it will lead to the formation of soap while in base catalyst
transesterification process. Here phosphoric acid or sulphuric acid is used as a catalyst. The product obtained
from acid catalyst is use to produce biodiesel through the base catalyst transesterification process.
8. III. THERMAL CRACKING (PYROLYSIS)
Thermal cracking is a process to convert the complex structure of hydrocarbons into its simplest structure with or
without catalyst. Due to this process the density and viscosity of oil will reduce. For vegetable oil as an alternative
fuel, these two properties affect the atomization in engine.
Atomization is the process of converting bulk liquid into fine droplets
Fuel treated by this process could be used directly in diesel engine without any modification
Generally alumina, zeolite and redmud are used as a catalyst in thermal cracking process for biodiesel production
The thermal cracking process happens at temperatures between 250O
C and 350O
C.
The thermal cracking biodiesel plant has a reactor with a safety valve, drain pipe, temperature indicator etc.
The oil or animal fat to be converted into biodiesel is placed inside the reactor, then heat is applied to the reactor.
Now the oil or animal fat gets vaporized and reach the condenser through pipe.
The condenser cools the vapor into the liquid
The liquid is collected in to a vessel and is called as biodiesel
9.
10. IV. MICROEMULSION
The micro emulsion is defined as thermodynamically stable, isotropic liquid mixtures of oil,
water and surfactant.
Surfactants are the compounds that lower the surface tension of a liquid, the interfacial
tension between two liquids.
This process will solve the problems in viscosity and some other atomization properties of
oil.
Generally alcohol used to increase the volatile property of oil, and reduce the smoke.
Alkyl nitrate will be the “Cetane number” improver.
The microemulsion process also used to get a good spray property when injected into the
engine by nozzle.
If micro - emulsified diesel used in diesel engine, some problems will arise such as
incomplete combustion, carbon deposit and nozzle failure.
11. Biodiesel's Physical Characteristics
Specific gravity 0.88
Kinematic viscosity at 40°C 4.0 to 6.0
Cetane number 47 to 65
Higher heating value, Btu/gal 127,960
Lower heating value, Btu/gal 119,550
Density, lb/gal at 15.5°C 7.3
Carbon, wt% 77
Hydrogen, wt% 12
Oxygen, by dif. wt% 11
Boiling point, °C 315-350
Flash point, °C 100-170
Sulfur, wt% 0.0 to 0.0015
Cloud point, °C -3 to 15
Pour point, °C -5 to 10
