.2. Current techniques available in converting WEO into biodiesel
Despite the changes in WEO chemical and physical properties
as compared to fresh edible oil, both of the oil feedstocks can still
be converted to biodiesel using similar method; that is via
catalytic reaction using alkali catalyst, acid catalyst and enzyme or
via non-catalytic reaction in supercritical transesterification
reaction. Nevertheless, the high content of FFAs and water in
WEO has caused alkaline-catalyzed transesterification reaction
less efficient. A more suitable method would be via non-catalytic
supercritical reaction or the two-step transesterification method
that consists of acid-catalyzed reaction followed by alkalicatalyzed reaction. Table 6 summarizes the recently introduced
transesterification techniques to convert WEO into biodiesel as
reported in the literature.