The effect of methanol-to-oil molar ratio on the transesterification was also investigated.
As illustrated in Fig. 6, the biodiesel yield increased gradually until the maximum values were acquired with the methanol-to-oil molar ratio increasing from 3:1 to 15:1.
The maximum biodiesel yield for the CaO, 30% RHA800-800 catalyst was, respectively, 93.2% and 91.5%. Correspondingly, the optimum methanol-to-oil molar ratios were 6:1 and 9:1, respectively.
Further increase in the methanol-to-oil molar ratio beyond its optimum value would decrease the biodiesel yield.
This was primarily owing to the following aspect: the excessive methanol made it difficult to separate the biodiesel with
glycerol.