Environmental Engineering Reference
In-Depth Information
Soybean
Jatropha
Canola
Camelina
Castor
Palm oil
Heat
Ve getable oil
Alkali
catalyst
(e.g., KOH)
Fatty acid
methyl esters
+
+
Methanol
Glycerol
or
Biodiesel
Used cooking oil
RCOO
CH
2
CH
2
OH
catalyst
RCOO
CH
+
3 R OH
3 RCOOR
+
CHOH
RCOO
CH
2
CH
2
OH
FIGure 3.2 (see color insert)
The biodiesel production process. (Modified from Sustainable Green
Technologies, sgth2.com/bio-diesel_faq)
3.5.1.1 catalytic transesterfication
Base-catalyzed reactions involve sodium hydroxide or potassium hydroxide, with potassium
hydroxide being preferred because of the fast reaction rates, cheap catalyst, and less corrosive reac-
tion. One disadvantage of using a base catalyst is its reaction with free fatty acids to form soaps,
producing alkaline water that requires energy-intensive waste treatment. Although acid catalyst
transesterification using sulfuric acid and/or phosphoric acid can handle larger amounts of free
fatty acids and water, its disadvantages are a longer reaction time and require higher temperatures
(>100°C) (Demirbas 2008; Nag 2008; Andrade et al. 2011).
Enzymatic transesterification can be used instead of chemical catalysts for several reasons. The
enzymes are generally more selective, allow for easier glycerol removal, convert free fatty acids,
perform at lower temperatures, and have increased reusability of the catalyst. Lipases are derived
from microbes or fungi. According to Al-Zuhair (2007), although the general lipase used is from
Candida antarctica
B, the
Pseudomonas fluorescens
lipase had the better enzymatic activity. Other
factors such as water content, type of alcohol used, type of lipase, and temperature all affect the
usefulness of the lipase in biodiesel production.
3.5.1.2 noncatalytic transesterfication
Noncatalytic methods are supercritical methanol and BIOX. Supercritical methanol has a simpler
procedure and shorter reaction time than catalytic methods as well as being environmentally
