Biodiesel contributes to environmental protection in that it is
biodegradable, renewable, non-toxic, reduces sulphur oxides
emission, reduces carbon monoxide emission, and reduces the
global warming problems [1]. About 95% of world biodiesel
production is derived from edible oils [2]. Consumption of edible
oil in biodiesel production has led to the price of edible oil and
biodiesel to increase to levels 1.5–2 fold higher than diesel fuel [3].
For this reason, non-edible waste cooking oils become more
attractive and promising alternate raw material for biodiesel
production. Waste cooking oil is categorised as a non-edible oil.
Waste cooking oil is considerably cheaper—five times average
lower than refined cooking oil. Utilising waste cooking oil in
biodiesel production is a clean technology solution offering
solutions for both disposal [4] and health problems, e.g. feeding
mixture for domestic animal [5], reusing and recycling [6].
Methanol with a short carbon chain is the most commonly used
in esterification and transesterification due to its easy in separation
process, lower cost and higher nucleophilicity compared to ethanol
having long carbon chain [7]. In terms of alkali catalyst in
transesterification, potassium hydroxide (KOH) resulted in 96%
conversion [8] compared to sodium hydroxide (NaOH) of only
76.9% conversion [9] with waste oil to methanol molar ratio of
1:3 in the presence of 1% alkali catalyst at 50 C within 60 min
reaction time. Shahid et al. [10] also claimed that separation of
biodiesel and glycerol was easier when KOH was used as catalyst
compared to NaOH.