3.2.2. Effect of reaction temperature
As shown in Fig. 6, the reaction temperature had a drastic effect on the FAME yield. At 55 °C, the FAME yield was 65.7% after 30 min of reaction. However, the FAME yield increased to 91.3% at 65 °C after 30 min. As deemed in ref. [42], the diffusion resistance between the three-phases of oil–methanol-catalyst would be reduced at higher reaction temperature, which in turn led to improved FAME yield. Nevertheless, the FAME yield decreased to 87.4% at higher reaction temperature of 70 °C, which could be ascribed to larger amount of methanol vaporized in gas phase and the sharply reduced methanol in the liquid phase at higher temperatures above the boiling point of methanol. In addition, too high temperature would increase the risk of saponification. Therefore, the optimum reaction temperature was considered to be 65 °C.