Environmental Engineering Reference
In-Depth Information
O
O
CH
3
O
CR
1
CH
2
OCR
1
O
CH
2
OH
O
(Catalyst)
CH
OC
R
2
+
3 CH
3
OH
CH
3
+
CH
OH
O
C
R
2
O
CH
2
OH
O
CH
2
O
C
R
3
CH
3
O
C
R
3
Triglyceride
Methnol
Mixture of fatty esters
Glycerin
FIGure 14.4
Transesterification of vegetable oil.
O
O
O
O
Catalyst
R'
+ 3R'OH
R
O
O
R
O
OH
+
R
R
O
Step [1]
O
O
O
O
R
R
Alcohol
DAG
TAG
Catalyst
Step [2]
TAG = triacylglycerol
DAG = diacylglycerol
O
MAG = monoacylglycerol
R'
MAG
HO
OH
+
R
O
R' = -CH
3
(normally)
O
O
O
R
R'
= biodiesel
R
O
Catalyst
Step [3]
O
R'
Glycerol
HO
OH
+
R
O
OH
FIGure 14.5
Common steps in transesterification process. (From Moser, B.R.,
In Vitro Cell Dev Biol—
Plant,
2009. doi: 10.1007/s11627-009-9204-z.)
The transesterification process is given various names such as alcoholysis, methanolysis, ethano-
lysis, etc. depending upon the type of alcohol used for the reaction (Romano 1982; Clark et al. 1984;
Freedman et al. 1984; Schwab et al. 1987; Peterson et al. 1992; Ma and Hanna 1999; Srivastava and
Prasad 2000). Among the alcohols that can be used in the transesterification process are metha-
nol, ethanol, propanol, butanol, or amyl alcohol. Methanol and ethanol are used most frequently,
especially methanol because of its low cost and its physical and chemical advantages. Being polar
and the shortest chain alcohol, methanol can quickly react with triglycerides. Among the catalysts,
alkali-catalyzed transesterification using potassium hydroxide (KOH)/sodium hydroxide (NaOH)
or their corresponding alkoxides was found to be used most often because they are much faster,
more efficient, and less corrosive (Freedman et al. 1984; Ma and Hanna 1999; Azam et al. 2005;
Leung and Guo 2006; Marchetti et al. 2007).
14.4.3 B
iodiESEl
c
haractErization
In addition to mono-alkyl esters, glycerol, alcohol, catalyst, FFAs, and tri-, di-, and monoglycerides
comprise the final output of the biodiesel production process. These contaminants can lead to severe
operational and environmental problems. Therefore, the quality control of biodiesel is highly essential
