1. Introduction
Rapid growth in population coupled with industrial and
technological developments have been leading towards the
depletion of limited fossil fuel resources of the world. Currently,
research is progressively more directed towards exploration of
alternative renewable fuels. Biodiesel, an alternative diesel fuel, is
a promising, non-toxic and eco-friendly clean fuel [1]. It could be
regarded as petroleum-derived diesel substitute with many
advantages including reduction of exhaust emissions,
biodegradability, high flash point, inherent lubricity, and domestic
origin [2].
Biodiesel (fatty acid alkyl ester) is produced by transesterifying
triglycerides, from vegetable oils or animal fats with an excess
alcohol, usually methanol, in the presence of a catalyst, usually a
strong base such as sodium or potassium hydroxide [3]. The
resulting product therefore can contain not only the desired alkyl
ester product but also unreacted material (mono-, di- and
triglycerides), residual alcohol, residual catalyst and soap. Soap
is formed as a by-product and separated from the biodiesel in the
production process, however, traces thereof can be found in the
final biodiesel product [4].
To meet the requirements of biodiesel standards, removal of
soap are especially important. Moreover, soap is especially