After the pretreatment reaction, the mixture was transferred to
settling tank to settle overnight, and then two phases was
occurred. The upper phase consists of the alcohol–water–acid mixture
and the other phase mainly consists of the esterified fatty
acids and initial triglyceride-animal fat (Canoira et al., 2008). The
upper phase was separated from the other phase. As known, when
the FFAs react with alcohol to form esters, water is also formed in
the products. Therefore, it is necessary to separate the water from
the pretreated material since it will inhibit further reaction.
Although methanol–water–acid catalyst phase was removed by
settling, the ester–oil mixture was subjected to a heating under
vacuum to remove any remaining water or methanol. To collect
the waste water and methanol, two stage drying process was performed
manually. First, the ester–oil mixture was subjected to a
heating at 65–70 C to remove any remaining methanol for
20–30 min (the valve of waste methanol tank was open). Then it
was heated to 105 C and kept at this temperature for 30 min to
remove any remaining water (the valve of waste water tank was
open). The recovered alcohol and water were controlled via the
sight glass as seen in Fig. 1. After drying process, the FFA level of
the feedstock was measured and recorded. Two steps pretreatment
reaction was performed for chicken fat because the FFA level could
not be decreased below 1% by the first pretreatment