Enhancement of Biodiesel Production from High-Acid-Value Waste Cooking Oil via a Microwave Reactor Using a Homogeneous Alkaline Catalyst

Abstract

In this study, low quality oils (waste cooking oils) with high acid value (4.81 mg KOH/g) were utilized as the feedstocks for a transesterification reaction enhanced by additional microwave power and the use of an NaOH catalyst. The kinetics of the transesterification reaction under different reaction times and temperatures was studied. It was found that in the microwave-assisted transesterification reaction, the optimum conditions under a microwave power of 600 W were as follows: an NaOH catalyst of 0.8 wt %, a 12:1 molar ratio of methanol to oil, a reaction time of 2 min, and a reaction temperature of 65 °C. The conversion of waste cooking oil into biodiesel reached 98.2% after this short reaction time. This result conformed to 96.5% of the standard value of Taiwan CNS 15072. In addition, with increases in the reaction temperature from 55 to 65 °C, the reaction rate constant increased from 0.635 to 2.396 min−1, and the activation energy required for the transesterification reaction was 123.14 kJ/mole.