Chemistry Reference
In-Depth Information
and fats as feedstock for biodiesel can offer an appealing alternative to achieve
more sustainable biodiesel production worldwide,
45
avoiding the use of virgin
food crops in fuel applications. However, the potential for biodiesel production
from UCO remains limited, as UCO valorisation can only meet less than 30%
of the world's biodiesel demand, with the remaining amounts to be sourced
from other feedstocks.
Waste oils can be effectively converted, via transesterification with methanol
or ethanol, into fatty acid methyl esters (FAME; biodiesel) (Scheme 6.1 and
Scheme 6.2) using a range of catalysts including solid acids and bases. UCO a
much larger free fatty acid (FFA) and water content than those of virgin oils,
both of which are detrimental in FAME production.
46
The most widely
extended biodiesel production process from UCO is the homogeneous base-
catalysed transesterification of glycerides, which requires a pre-treatment of
the FFA with MeOH/H
2
SO
4
(Figure 6.6), followed by the recovery of
FFA/unrefined FAME (FA material) and unreacted methanol.
There are also literature reports on the use of heterogeneous catalysts that
can eciently catalyse the simultaneous esterification of the FFA as well as the
transesterification of the triglycerides present in the waste oils.
47,48
Hetero-
geneous catalysts such as alkaline oxides,
49
supported enzymes and carbon-
aceous materials have also recently received increasing attention due to their
more environmentally sound credentials, compared to their homogeneous
equivalents.
50
The major issues with the utilisation of heterogeneous catalysts
for biodiesel production from UCO are linked to lower conversion rates,
deactivation of active sites due to the presence of FFA and moisture and
reusability issues, which is one of the major drawbacks of the most widely
utilised heterogeneous catalyst for biodiesel production (CaO).
d
n
9
r
3
n
g
|
0
d
y
y
f
n
n
3
.
O
O
H
2
SO
4
(conc.)
+MeOH
+H
2
O
R
OH
R
OMe
R = C-17
FFA
FAME
Scheme 6.1
Esterification reaction for acid pretreatment.
OCOR
OH
O
T = 60-70 °C
OCOR
+ 3 MeOH
+3
OH
Catalytic NaOMe
R
OMe
OCOR
OH
R = C-17
FAME
Scheme 6.2
Transesterification reaction of triglycerides.
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