Biodiesel is an alternative diesel fuel produced from the transe-
sterification reaction of triglycerides from vegetable oils or fats
with alcohols like methanol and ethanol in the presence of a
homogenous base catalyst like NaOH or KOH. Biodiesel is biode-
gradable, nontoxic, burns with a low sulphur, carbon monoxide
and aromatic-free emission profile, and is environmentally benefi-
cial in terms of, for example, recycling of spent oils and fats
[1–5]
.
Since these can be spent cooking oils rather than food oils, they
can be viewed as renewable biological sources. However, this
makes the biodiesel production sensitive to the oil free fatty acid
(>0.5% (w/w)) and water composition, two components that are
often at significant levels in waste oils and fats. The presence of
water will lead to ester saponification under the alkali conditions,
and free fatty acids will directly react with the alkali catalyst to
form soap and water rather than biodiesel and, in so doing, remove
the catalyst leading to further reduced biodiesel yields. Whilst pre-
treatment by sulphuric acid and mono-alkyl alcohols to catalyze
the conversion of contaminating free fatty acids to biodiesel is pos-
sible, this is slow and requires the removal of the sulphuric acid
prior to initiation of the conventional alkali-catalyzed transesteri-
fication process. This process itself is a water and energy demand