Ultrasound-Assisted Dual-Enzyme System for the Preparation of Fatty Acid Ethyl Esters

This study focuses on the preparation of fatty acid ethyl esters (FAEE) in a solvent-free system using high-acid-value waste oil as the raw material. The research involves the addition of two enzymes with different substrate specificities, accompanied by ultrasonic assistance. The investigation explores the impact of enzyme addition (3–7 wt%), enzyme ratio (3:1–1:3), alcohol–oil ratio (5:1–25:1 mmol/g), reaction temperature (30–70 °C), reaction time (30–210 min), and ultrasonic power (0–150 W) on the experimental outcomes. Reaction conditions were optimized by analyzing regression models. The predicted optimal process parameters for FAEE conversion are as follows: enzyme addition of 5.46 wt%, enzyme ratio of 1:2.23, alcohol–oil ratio of 13.79:1 mmol/g, reaction temperature of 60 °C, reaction time of 160 min, and ultrasonic power of 120 W. Under these optimized conditions, three validation experiments were carried out to take the average value, and the conversion rate of FAEE was 93.57 ± 1.17%, which was in good agreement with the predicted value. These results showed that the synergistic effect of the two enzymes accelerated the migration of acyl groups, verified the advantages of the dual enzyme as a catalyst, and provided theoretical support for the preparation of biodiesel by the dual enzyme system.

Graphical Abstract