Oils with high content of free fatty acid (FFA) can be treated by acid
esterification where an alcohol reacts with the given oil in the presence of acid catalyst.
The investigated parameters include methanol to oil ratio, temperature and amount of
catalyst. The optimum conditions for acid esterification which could reduce FFA content in
the feedstock to less than 1.88% (acid value 3.76 mg KOH/g waste cooking oil) were
50 °C, 20% methanol to oil ratio (by volume) and 0.4 vol.% H2SO4 after 5 h. However, oil
with an acid value of more than 1 mg KOH/g oil cannot meet the alkaline catalyzed
transesterification conditions. Under the conditions of NaOH concentration 0.5 N, excess
alkali 15%, 60 °C, 40 min, the FFA removal rate for deacidification reached 77.11%
(acid value 0.86 mg KOH/g esterified oil). The acid value of deacidification product
was reduced below 0.86 mg KOH/g esterified oil, thus meeting the base-catalyzed
trans-esterification conditions.