Ultrasound strengthened biodiesel production from waste cooking oil using modified coal fly ash as catalyst

• Effects of modified CFA/ultrasound on the WCO conversion into biodiesel were investigated.
• The modified CFA catalyst could increase biodiesel yields under ultrasound assisting system.
• The maximum biodiesel yield from waste cooking oil was up to 95.57%.

This paper investigated the effects of modified coal fly ash as catalyst on the waste cooking oil (WCO) conversion into biodiesel under ultrasound strengthened action. Experimental results showed that the modified coal fly ash catalyst could improve biodiesel yields under ultrasound assisting system, and the maximum biodiesel yield from waste cooking oil reached 95.57% under a molar ratio of methanol to WCO of 10.71:1, a 4.97 wt% modified CFA catalyst (based on oil weight), and a 1.41 min reaction time. The reusability of the modified coal fly ash catalyst was well, and the conversion yield was still higher than 90% after the catalyst was used for 8 times repeatedly.