3.1. FAME biodiesel
Fatty-Acid Methyl Esters or FAME is obtained from vegetable
oil or animal fats (bio-lipids) which have been transesterified
with an alcohol. The transesterification process is simply
described as the chemical breaking of fatty acids contained in
vegetable oils using alcohol to form alcohol esters and glycerol
targeting to lowering the viscosity and volatility of vegetable
oil. Although ethanol is the preferred alcohol for transesterification
due to its renewable biomass origin and lower toxicity level
methanol is most commonly used due to its price competitiveness
compared with other common alcohols such as ethanol
and isopropanol. This leads to the predominance of fatty acid
methyl esters (FAME)
FAME can be produced from many types of oils, the most
common being rapeseed oil (rapeseed methyl ester, RME) in
Europe and soybean oil (Soya methyl ester, SME) in the USA. In
the transesterification processes catalysts such as sodium or
potassium hydroxide are employed to convert vegetable oil and
methanol into FAME. Moreover, during transesterification undesirable
by-products (glycerine and water) are also formed. Byproducts
must be removed from the final product along with
methanol traces. FAME can be used in diesel engines where the
manufacturer approves such use but it is more often used as a mix
with conventional diesel
FAME biodiesel quality was standardized via international
standard methods such as ASTM and EN. In Europe, biodiesel
blended in diesel is mandatory in many countries and thus
available at many service stations. The world biodiesel production
output was estimated to be 11 million metric tonnes in the year
of 2008, which reached 20 million metric tonnes in 2010.
The main factor determining the current cost of biodiesel
production is the feedstock cost which can be as high as 88% of
the total production cost However, total production cost can
be greatly reduced by lowering the cost of feedstock with the use
of more economical alternatives such as waste fats or oils, which
however lower the FAME quality characteristics.
According to Table 1 FAME biodiesel has very good fuel
properties as a diesel substitute. Thus, the results show that
biodiesel can be used in a wide variety of applications. The
heating value of FAME biodiesel ranges between 37 and 40 MJ/
kg which meets the diesel standards. FAME biodiesel has density
ranging between 0.85–0.9 g/ml which also meets the diesel–
biodiesel international standards. Moreover, the sulphur content
of FAME biodiesel is very low. Furthermore, it has a good cetane
number (45–73), which indicates good auto-ignition quality. The
flash point of FAME biodiesel varies from 96 to 188 1C while it
presents a satisfactory CFPP (min 13 1C). It has very high water
content which shortens the life of fuel filters and affects negatively
the corrosion. Viscosity of FAME is also high, that provides
insufficient lubrication to diesel engines .