2.1.1. Characteristics of waste cooking oil
The quality of oil is expressed in terms of the physico-chemical
properties such as acid value, and saponification value. The saponification
value of waste cooking oil (WCO) was 215.2 (mg KOH/g).
The acid value of waste cooking oil was found to be
1.25 mg KOH/g. Its density at 26 C is 0.97 g/cm3. It has been
reported that transesterification would not occur if free fatty acid
(FFA) content in the oil were above 3 wt.% [31]. Since FFA content
of the waste cooking oil is higher than 3 wt.%, i.e. 6 wt.%, thus, one
step transesterification is not suitable. Therefore, a two-step transesterification
process (acid esterification followed by alkali transesterification)
was employed to remove high free fatty acid (FFA)
content and to improve the biodiesel yield.