Fig xA The relationship between the Thiele
Fig. 7 showed the effect of temperature on the conversion rate of oleic acid. The reaction temperature for Beta (50) zeolite increased from 68.0 °C to 83.0 °C at optimum reaction conditions of the molar ratio of oleic BTS 54-505 to ethanol of 1:20, catalyst loading of 0.167 meq/g (oleic acid) and stirring rate of 600 rpm. The conversion rate of oleic acid increased gradually with increasing the temperature, but declined as the temperature approached 83.0 °C. The highest conversion rate of oleic acid (73.6%) was obtained at 78.0 °C (the boiling point of ethanol at atmospheric pressure) within 10.0 h. The possible reason for the decline was oxidation the ethanol vapor filling in the headspace of reactor was not available for the reaction when the temperature exceeded the boiling point of ethanol. Liu et al.  also reported that the alcohol vaporized rapidly and large amount of bubbles formed when the reaction temperature exceeded the boiling point, resulting in a decrease in the conversion rate of FFAs. In conclusion, the optimum reaction temperature was 78.0 °C.