RESULTS AND DISCUSSION 4.1. Trans-esterification of WCO with methanol
4.1.1. Effect of the variation in quantity of alcohol (methanol) upon the yield of bio-diesel.
The methanol-to-oil ratio is one of the important factors that affect the conversion of triglyceride to Fatty acid methyl esters (FAME) i.e. the yield of Bio-diesel. In Trans-esterification, three moles of methanol are required for each mole of triglyceride, but in practice, a higher molar ratio is required in order to drive the reaction towards completion and produce more FAME as products. The work of Centikaya and Karaosmanoglu , for example, labels trans-esterification as insufficient, at the ratios of methanol/waste cooking oils below 5:1. Furthermore, the methanol/waste cooking oil ratio is also associated with operating parameters such as the type of catalyst used and the quality of waste cooking oils. The optimum ratio of methanol/used frying oils was, for instance, 4.8 in the presence of Sodium Hydroxide ; while, in the presence of acidic catalysts, it could be up to 250 .
The following table shows the effect of methanol to waste cooking oil ratio on the conversion of bio-diesel at a temperature of 30°C in the presence of 0.35g NaOH.
Table: Effect of methanol/WCO ratio on the conversion of Bio-diesel at a temperature of 30 °C and 0.35 g of NaOH.
Weight of oil (g)
Volume of methanol (ml)
Weight of catalyst (g)
Weight of biodiesel (g), produced
Yield of biodiesel (%)
The conversion reached a value of approximately 72% in the time of 2 hours at 20 ml of methanol. Increasing the quantity of methanol from 20ml to 60ml and repeating the procedure, showed the increment in the conversion of about 19-20%.
A further increase in the quantity of methanol caused a reduction in the conversion. It was 84% for the 80ml of methanol. The reduction could be because the excess of methanol could interfere with the separation of ester product and by-products by increasing solubility of glycerol. Consequently, part of the diluted glycerol remained in the ester phase, leading to foam formation and therefore apparent lost ester product. In addition, the excess of methanol could also drive the combination of ester product and glycerol into mono-glycerides . This indicated that the optimum quantity of methanol for 100g of this WCO in presence of 0.35g of NaOH was around 60ml, giving a biodiesel yield of approximately 91–92% after 2 hours. The optimum quantity in this study was in accordance with that obtained from other investigators .
In this optimum case the ester layer was isolated, yellowish and transparent while it was translucent for the other cases and was slow in settling process. This indicated that there was a certain amount of un-reacted glycerides diluted in the ester phase at the ratios below and above this optimum quantity
4.1.2. Effect of concentration of catalyst
The concentration of alkali catalyst is strongly dependent on the type of oils used.
This conclusion is drawn by reviewing the work of other investigators. For example, according to the work of Felizardo et al. the optimum concentration of sodium hydroxide was 0.6 wt%. This value was much lower than the finding of Georgogianni et al. . The results from the work of Leung et al.  showed that the optimum value of NaOH concentration for neat Canola oil and used frying/cooking oil was 1.0 wt% and 1.1 wt%, respectively.
Considering data from literature reviews, the concentration of NaOH was tested in a range of 0.25g-0.55g. The following table shows the effect of concentration of NaOH on the conversion, taking 60ml methanol and 100g of WCO at temperature 30°C. Increasing NaOH concentration from 0.25g to 0.35g increased the conversion. It was 80% and 92% at 0.25g NaOH and 0.35g NaOH, respectively during 120 min. However, the conversion reduced to 75% in the