Environmental Engineering Reference
In-Depth Information
non-toxic, contains no sulfur, and releases fewer emissions during combustion
[57]. Biodiesel is often referred to as fatty acid methyl esters (FAME) and can be
produced from a number of different raw materials including palm oil, soybean
oil, rapeseed oil, sunflower oil, and several other vegetable oils via a straightfor-
ward process of chemical modification known as transesterification.
One negative aspect of biodiesel is that its quality may change during storage
due to oxidative and hydrolytic reactions. Another important limitation relates to
the availability of raw materials for biodiesel production. One of the most com-
mon kinds of biodiesel is made from rapeseed oil, rapeseed methyl ester (RME).
RME has the advantage of being renewable (unlike fossil diesel), non-toxic, and
less flammable than many other fuels such as ethanol. RME has the same cetane
number, viscosity, and density as diesel but contains no aromatic compounds and
is biologically degradable, causing only minor soil contamination if spilled.
Up to 3 tons of rapeseed can be produced from 1 ha of land. The main fatty
acids in rapeseed oil are oleic acid, linoleic acid, and linolenic acid. The oil is
pressed from the plant and, after some purification, allowed to react with metha-
nol in the presence of potassium hydroxide as a catalyst to produce fatty acid
methyl esters, as shown in Figure 7.6.
The transesterification reaction generates two byproducts. One is glycerol,
which can be used in the cosmetics industry or as a raw material for producing
other industrial chemicals such as 1,3-propanol or 1,2-propane-diol (propylene
glycol). The other is a protein-rich cake that is left over after pressing the oil from
the seeds, and can be used as animal feed [58]. RME can be blended with diesel
to produce a mixed fuel, and can be handled using existing diesel distribution
systems without modification.
H
O
H
C
O
C
R
1
O
H
H
CH
2
O
C
R
1
O
H
O
H
COH
KOH
+
H
C
COH
OH
CHO
C
R
2
+
CH
3
OH
H
C
O
C
R
2
H
H
O
H
CH
2
O
C
R
3
H
O
H
C
O
C
R
3
H
Triglyceride esters
Methanol
Methyl esters
Glycerol
Figure 7.6
Transesterification of triglycerides to methyl esters and glycerol. R1, R2, and R3 are
the alkyl chains of various fatty acids found in rapeseed oil, for example, oleic acid.
