evaporator heater is then turned off, and the mixture is continued
to rotate for an additional hour. After the reaction, the mixture is
poured into a separating funnel to remove the excess methanol,
catalyst and impurities. The surplus methanol, acid and other
impurities form a layer above the rest of the mixture, which is
removed. The bottom layer is used for the second stage of the
alkaline esterification. The acid esterified oil with an acid value
below 2 mg KOH/g is primarily used for further transesterification.
This value must be reduced to 2 mg KOH/g to yield maximum
biodiesel; otherwise, the alkaline catalyst reacts with the free fatty
acids to form soap instead of ester, reducing the biodiesel
production